Leaving ill-informed opinion aside and concentrating on the mechanical and physical aspects of titanium alloys, it is still a strange material. Even though the alloys used for motorsport components are relatively strong, their behaviour when subjected to even modest levels of surface stress is extremely poor. For example, it is impossible to use titanium in almost any application where sliding is involved. Despite its strength when loaded in tension or bending, we cannot use titanium or its alloys for sliding applications unless we take measures to improve the surface through the use of hard engineering coatings such as chromium nitride (CrN), titanium nitride (TiN), diamond-like carbon (DLC) or a metallic coating such as molybdenum.

Titanium also has notably low thermal conductivity, and its ability to insulate components from the effects of heat gives it some applications in engines, where the material is allowed. Titanium, in being viewed (wrongly, in my opinion) as an exotic material, is banned in many governing bodies’ regulations for race engines. It can be used to provide an insulating ‘gasket’ for some applications, and titanium fasteners reduce heat transfer through joints compared to steel and other materials. Even though we might see the fasteners as representing a small cross-sectional area compared to the rest of the joint, the heat transfer can be significant, and measurable reductions in component temperatures can be measured by changing from steel fasteners to titanium.

The combination of thermal conductivity, density and specific heat capacity mean titanium has a very low thermal diffusivity, which is the measure of a material’s ability to conduct heat divided by its ability to store heat. Materials with low thermal diffusivity show high temperature gradients in response to local heating, as the transfer of heat from ‘hotspots’ to cooler areas is poor. The thermal diffusivity of titanium is less than 50% that of steel, and about 10% that of aluminium.

Titanium, while unremarkable in terms of strength and stiffness, has a low ratio of stiffness to strength. In some circumstances, notably in the case of fasteners, this is a very attractive combination. For a given service load on a joint, a reduction in fastener stiffness leads to reduction in cyclic load borne by the fastener. This is why, in highly stressed fasteners such as cylinder head studs or con rod bolts, the shanks are waisted. In some cases, changing from steel fasteners to titanium can also be accompanied by a reduction in the dimensions of the fasteners without a loss of durability.

The density of titanium compared to steel means that, for an equivalent component mass, more titanium can be used. For a component such as a con rod, this represents an opportunity to improve the bending and torsional stiffness. The actual deflection in normal operation may not be a concern, but stiffness has an important influence on vibration and resonance, and the increased stiffness of a titanium component may be significant in this respect.

Written by Wayne Ward

For a given type and displacement of engine, it is a rule of thumb that maximum potential torque is a fixed amount – for example, all 600 cc four-cylinder, four-stroke engines with sufficient attention given to gas-exchange processes and friction will produce the same level of torque. Power depends on the torque and the speed at which it can be achieved. The same applies to electric machines, as the potential maximum torque is fundamentally a function of the electrical design choices and the construction of the motor, and the power depends at what speed this torque can be maintained. As with engines, there is a strong incentive to run an electric motor at high speed.

There are however a number of barriers to running at ever-increasing speeds, although they are very different from those in a reciprocating engine. There are no strong second-order forces and couples as we find in an engine, and fewer causes of excitation to provoke a strong resonant response.

The main enemy is centrifugal force. For a permanent magnet motor, it is not a simple task to keep the magnets in place at very high speed. The motors used on the electric machines in the exhaust heat recovery motors, driven by the exhaust turbine in Formula One, run at speeds up to 100,000 rpm. It is certainly not enough to simply rely on the magnetic forces to keep the magnets in place, and the mechanical strength of magnets leaves much to be desired – even if we were to be able to ‘stick’ them to the rotor, they are unlikely to remain intact.

It is necessary therefore to restrain the magnets radially to prevent both loss and breakage. In low- and medium-speed motors this is sometimes done with glass-fibre reinforced polymers, but for high-speed motors, higher strength composites such as carbon or PBO are used. The limitation is then the strength of the composite sleeve.

It is also important to have high-speed rotors properly balanced to a high degree of accuracy in order to prevent early bearing failures and to minimise the transmission of vibration to adjacent components. When dealing with very high-speed rotors, the machinery for balancing them can be complex.

Another problem can be maintaining the rotor magnets within their operating temperature range. At relatively modest temperatures the magnets can become demagnetised, and this is not a property that returns when temperatures fall to more desirable levels. Some companies resort to liquid or forced-air cooling of rotors in order to keep magnet materials sufficiently cool.

Written by Wayne Ward

Providing a low-friction bearing capable of operating at the very high speeds a turbocharger sees – more than 150,000 rpm – and which can also survive the high temperatures experienced within a turbine housing is no easy task. For many years, the most common solution was a simple bronze-bushed affair, with an oil supply and in some cases a water cooling jacket. In high-performance applications, this approach has given way to more efficient ball bearing systems, which generate less friction and therefore help to increase turbine efficiency, allowing for faster spooling and thus reduced turbo lag.

Ball bearing designs also reduce the amount of oil required to provide adequate lubrication compared to journal bearings, and this lower oil volume reduces the risk of seal leakage. Ball bearings are also more tolerant of marginal lubrication conditions, reducing the possibility of failure.

While such systems are undoubtedly more efficient than a simple bush, there is still a lot of scope for improvement. The answer to achieving greater durability and lower friction has been the introduction of ceramic-based bearing elements, using silicon nitride instead of steel to provide a number of advantages over regular steel bearings and races. Ceramic bearings are generally available in one of two types – pure ceramic, where all the elements of the bearing are made from ceramic material; and hybrid, where ceramic balls or rollers run in steel rings.

The advantages of ceramic bearings are considerable. Ceramic bearing balls can weigh up to 40% less than steel ones, depending on their size and the materials used, and this can reduce centrifugal loading and skidding, allowing hybrid ceramic bearings to operate 20-40% faster than conventional steel bearings. As a result, ceramic and hybrid ceramic bearings have less inertia, and thus in turbo applications can increase response rate over steel bearings. Ceramics also need far less lubrication than steel, further reducing the oil supply requirements over both ball bearing and journal bearing systems.

The thermal characteristics of ceramic balls are also very attractive, as they experience minimal expansion even at very high temperatures. To give an example that quantifies the performance possible with such bearings, one turbo manufacturer worked with its bearings supplier on producing a hybrid ceramic ball bearing turbo unit that saw peak speeds of more than 220,000 rpm, with a shaft temperature in excess of 300 C – conditions far beyond those in which a traditional steel bearing could survive.

From this it is clear that ceramic technology provides the best current solution for high-efficiency turbocharger bearings. There are other potential development avenues when it comes to further reducing friction in turbo applications, but currently they exist only in theory or in very large machinery applications. For example, the use of foil-air or magnetic bearings offers the prospect of almost completely eliminating friction, but a practical application of these technologies in an automotive turbocharger has yet to be realised.

Written by Lawrence Butcher

Much like the engine crankshaft therefore, which can be excited by the forces of combustion and fail catastrophically when the frequency with which it is excited approaches the component’s natural frequency of vibration, the camshaft can also be subjected to such effects. Rarely does this lead to a torsional failure but, if unchecked, the vibration can have disastrous effects on components such as the valve timing or valve spring control.

If we take the case of an inlet camshaft opening and closing a single valve, the forces involved and hence the torques induced look similar to those outlined in Fig. 1. If you have ever tried to turn a camshaft over by hand you will realise that the forces required (and hence the instantaneous torques) can be surprisingly high, but once moving, the effort is considerably less, the force used to compress the valve spring being recovered when it expands a few degrees later. The total energy expended over a complete rotation may be minimal but the instantaneous forces at any one time to accelerate the valve opening can be amazingly high.

Now, if we consider that 140 cam degrees or so later, after the inlet cam closes, the exhaust cam will open, producing a similar set of forces but displaced by the 140º or so down the shaft. Again, the forces may be high but the overall energy input is low. If we then move along to the next cylinder in this engine (let us say it has four cylinders) we will realise that the inlet cam forces are similar to those of cylinder 1 but displaced by 90º (in the case of an engine firing at 1-3-4-2) and likewise the exhaust cam.

Repeating the exercise for cylinders 3 and 4, if we start to sum up all these instantaneous forces algebraically for the full four cylinders, the instantaneous torques produced at each angle around the camshaft could begin to cancel themselves out along the shaft. As a result, the peak torques will fall and the overall energy used to power the camshaft could be comparatively small. How small will depend on the precise timing of the inlet and exhaust cams to each other and the amount of friction in the system.

Clearly the greater the number of cam lobes along the shaft (say in an inline six – or even, god forbid, eight cylinder) the greater this smoothing effect.

In all cases, however, these instantaneous forces or torques will generate a level of vibration in the shaft which, when analysed or split up using a mathematical technique known as a Fourier analysis, will be represented as a large number of sine waves of different amplitude over a wide range of oscillating frequencies.

If the natural frequency of the shaft – or indeed any component in the system – is the same or close to any of these frequencies, and the forcing amplitude is sufficiently large, then unless it is damped in some way the shaft or component will resonate at that frequency, creating far higher loads than usual. This could be detrimental to either the performance of the unit or its durability. In the extreme case, with a hollow camshafts gun-drilled to remove much of the inner core, these forces could fatigue the component, or if the amplitude of vibration was such that it altered the valve events in relation to the piston position, then piston-to-valve contact could occur. 

This issue is not normally a problem with small, low-speed or short engines, but arises in high-speed, multi-cylinder, multi-cam units where the need for weight reduction can be greatest or the search for outright performance paramount.

Fig. 1 - Cam drive torque at 10,000 rpm engine speed

Written by John Coxon

The idea behind them is a very attractive one. For every unit of fuel burnt in the engine, less heat escapes directly to the components next to the combustion chamber, so there is a reduced cooling requirement. This reduction is very attractive to engineers in charge of cooling systems and aerodynamics, as lower heat rejection is associated with smaller coolers, lower cooling air flows and reduced aerodynamic drag. It also means more energy is retained in the combustion chamber, where it can be used for producing extra torque. Good news all round, or so you may think.

There are two problems though that need to be overcome before the coatings become common in race engines. One is the issue of longevity. The aim will be to take maximum advantage of such coatings, and the reduced heat transfer will naturally lead design engineers to redesign components to work at lower temperatures, but if the coating fails and heat transfer is locally increased, it will cause component failure. People who stand to gain the most from the technology also need to be convinced the most of the reliability of the coatings. The coating process also needs to be carried out at a temperature that does not harm the component – especially important for pistons which are very highly stressed but which can stand only relatively modest temperatures before their mechanical properties are degraded.

The other problem is the management of heat and temperature. If volumetric efficiency is to be maintained, so that the amount of air drawn into the engine is not adversely affected by increased component wall temperatures, the coatings’ surfaces need to be able to cool quickly. If the effect of the coating is to increase component surface temperatures such that volumetric efficiency is impaired, the result could be a reduction in performance. To present an overall advantage in terms of performance, any increased fuel conversion efficiency – that is, the ratio of mechanical energy extracted divided by the chemical energy in the fuel – needs to outweigh any loss in volumetric efficiency.

Having worked with a group of engineers who had used low thermal conductivity pistons for extensive trials and found large gains in fuel conversion efficiency, combined with large losses in volumetric efficiency, this can be a real concern. The conductivity of the coating and its thickness need to be managed to give an overall advantage in terms of performance for most racing applications. However, with racing increasingly rewarding fuel efficiency, it might be that thermal barriers which lead to an overall reduction in performance but do this while achieving increased fuel economy may prove useful in certain types of racing, such as categories where a loss of 5% of performance might be tolerated if the car can go one more lap before entering the pits for refuelling.

Written by Wayne Ward

The con rod fastener is by some margin the most highly stressed fastener in the engine, and is almost certainly exceeded in absolute stress levels only by the valve springs. In restraining the mass of the rod and piston assembly at top dead centre on the exhaust stroke, the inertia forces are responsible for the peaks on the cyclic load curve for the con rod bolted joint. How this load is translated into a stress which the rod fastener sees is a function of the design of the rod itself, the design of the bolt and its initial tightening conditions.

The worst scenario is when the initial tightening of the bolt is insufficient to keep the con rod joint loaded during maximum inertia conditions. If the two parts of the rod become separated, leaving only the fasteners to maintain them as an assembly, then the fasteners take all of the inertia load, and they are not designed to do this. Engine failure is guaranteed in this case – it is simply a matter of time.

When the fastener is correctly tightened, the joint will remain loaded, and the extra load experienced by the fastener is much smaller than the earlier scenario. The proportion of the total load to which the fastener is subjected is defined by the internal load coefficient of the joint, and this is a function of the stiffness of the fastener and that of the clamped members.

It is of paramount importance that the fastener is correctly tightened and, in the case of con rod fasteners, that this is very accurately checked by measuring the length of the fastener before and after tightening. The elongation measured in tightening is proportional to the load in the bolt, and this is a very much more accurate way to confirm the load in the bolt compared to other methods such as torque tightening or torque and angle.

For this reason there are features on the end of the rod bolts that make measuring the elongation easier when using a specially adapted micrometer, which is provided with ball-shaped ends instead of the traditional flat measuring tips. These engage with centre drillings in each end of the rod bolt, providing a far more repeatable assessment of length than simply measuring over the ends of the fastener with a standard micrometer. The improvement is something you can assess for yourself if you have both types of micrometer available.

Written by Wayne Ward

Another analytical method of course is to use tried and tested mathematical formulae. The Log Mean Temperature Difference (LMTD) is a popular calculation here, and relies on knowledge of overall heat transfer coefficients, the effective surface area of the radiator, a correction factor (sometimes referred to as an ‘ignorance’ factor) and a parameter called the LMTD of the two fluids in use.

A third method much along the same lines expresses the heat transfer in a different way: the difference in temperature between the air and the radiator wall, the surface area, the local air velocity and the type of radiator typified by its ‘K’ factor. From this we could calculate the heat dissipated – assuming, of course, the ideal condition where there are no leaks and the mass of air flowing is constant. The K factor of a radiator is often developed from tables of similar designs, but what if you don’t know your K factor or if your radiator is not of a traditional size or shape? Obviously you could wait for it to be installed and tested in situ in a vehicle and never know if its poor performance was down to its design or installation. Failing that, you could use some kind of radiator test rig or wind tunnel.

A radiator wind tunnel is fundamentally different from one used to test the aerodynamics of vehicles. The most obvious difference is that radiator rigs will generally have a much higher blockage factor, since all the airflow will be channelled through it. This effectively dictates the type of fan that can be used. In vehicle ‘aerodynamic’ tunnels the blockage factor of the car under test is comparatively low, and the pressure drop across the test section is consequently also very low or non-existent. The type of fan preferred will be that of an axial flow ‘air mover’ situated after the test section to avoid introducing turbulent flow to the vehicle or model. A radiator tunnel, however, filling the whole cross-section of the test item, will have a comparatively large pressure drop across it, and will therefore be more suited to the characteristics of a centrifugal blower, which will need to be placed in front of the test section.

Unfortunately the airflow of such a fan is far from uniform, and any turbulence induced by the rotating blades needs to be corrected and ‘straightened’ out to present laminar flow to the radiator. This is most efficiently achieved by slowing the air down through a diffuser and passing it through some form of ‘flow straightener’. The angle of this diffuser can be quite critical to avoid flow separation and the localised turbulent flow that results. At the same time, space is often at a premium and so a compromise of around a 15-20º taper is often used.   

After the diffuser comes the settling chamber. Designed to dampen out the last dregs of swirl from the airflow and create a uniform laminar flow to present to the radiator core, the settling chamber will include a honeycomb section placed across the path of the air. Usually hexagonal and made from thin aluminium or paper, the diameter-to-width ratio of the individual cells should be such as to straighten out the flow with the minimum of losses to the flow. For a typical radiator size of, say, 40 cm², a minimum number of these cells should be around 5000-6000 (75 x 75) but figures up to 25,000 (150 x 150) or more can be easily justified. Finally, after passing through another and much finer mesh, the air will be accelerated again through a converging section into the working section. 

And of course, once you have your radiator wind tunnel, you will be able to correlate the results from your CFD studies.

Fig. 1 - Radiator wind tunnel schematic

Written by John Coxon

The forces exerted by these rotating masses are proportional to the stroke of the crankshaft and the square of engine speed. As engine speeds have risen, so has the need for crankshaft counterbalancing. Although we see many crankshafts with a pair of counterweights opposite each crankpin, this is not actually necessary, and there are crankshafts with four pins that have four counterweights, and in some cases only two.

There is always some discussion about the proper level of balance to be provided by any crankshaft counterweighting. When engineers refer to a percentage balance factor, this is to do with to the percentage of the reciprocating mass that we aim to balance. A more accurate way to describe it would be 100% of rotating mass and 50% of reciprocating mass – 50% is often the ‘standard’ that people aim for, and this can give a reasonable compromise between crankshaft mass/inertia, peak bearing loads and vibration. However, balance factors of between 20% and 80% are commonly used for various engine architectures, various running speeds and types of use, from light use on the roads to much higher duty cycles in motorsport. Sticking to a favourite value or something that is recommended for a particular brand of engine is often not the best case for engine performance.

Knowing the masses involved, speeds of rotation, cylinder pressures and so on, a good estimate can be made of the bearing loads throughout the engine cycle and at various relevant operating speeds, and if you have been involved in the design of a bespoke race engine then this may be a process you have worked through (unless you have a kind bearing supplier who will do the work on your behalf).

Depending on operating conditions, it might be found that a different balance factor would be a performance advantage, and it is possibly at this stage that the bearing supplier will want to be recompensed for its extra input if you want them to work through all the possible permutations. While the peak bearing load might increase, for example by changing to a lower balance factor, the mean bearing load through the operating cycle in the engine’s operating speed range may fall significantly. By comparing the expected frictional losses for various levels of balance factor, it might be decided to look at a crankshaft with a balance factor of less than 50%.

Like so many other aspects of race engine design, the choice of balance factor is a matter of compromise. In order to run the balance factor that is most advantageous for engine performance, the engine supplier may have to accept lower mileages between engine rebuilds (if the bearings are the limiting factor) or having to use more expensive bearings with a high load rating. 

Written by Wayne Ward

The force transmitted by the vehicle tyre to the ground is limited by a number of factors, but principally by vehicle corner weight and the amount of weight transferred as a result of vehicle dynamics. Tangential to this force at the contact with the ground is the tractive force, which in the static case of a given vehicle-tyre combination is a fixed constant but which will increase as the tyre under power begins to lose traction and begin to slip. Generally referred to as the ‘slip ratio’ – the ratio of the speed of slip to that of the driven wheel – this coefficient increases up to a point, after which it falls away again, as shown in Fig. 1. Highly dependent on the tyre, its temperature and the surface upon which the car is running, this best relative slip speed for a given tyre/surface is somewhere around 10-15%. The role of a vehicle launch system therefore is to assist the driver in maintaining this level of tyre slip without exceeding it and without overspeeding the engine.

Generally included as part of the traction control system on many aftermarket engine management systems, at their simplest level they will need to incorporate a method of determining tyre slip, a sensor in the clutch-actuating mechanism and a method of initiating the system at the start line. Inputs to the algorithm necessary to control this most basic of system are therefore wheel speeds, throttle position, clutch position and engine speed. Tyre slip is readily calculated using wheel speed inputs from a non-driven wheel (usually a front wheel or the average of the two front wheels) and that of the driven wheel or wheels.   

On a command to activate the system (a simple on-off switch) as the clutch is depressed, the driver will then open the throttle until the engine reaches the desired engine launch speed. This will most likely be a ‘soft’ speed limit beyond which the fuel to one or more cylinders would be cut. As a safeguard, at around 250 rpm higher, a ‘hard’ rev limit will be set, beyond which the engine will not go.

Held at this condition in readiness for the start, in the case of a turbocharged engine this could be for a couple of seconds while the boost pressure builds up. Once the engine speed has stabilised (along with the boost pressure if needed), on re-engaging the clutch and with the vehicle beginning to move, the system will cut in until the desired level of slip is created. By now, at full throttle, the system will modulate the fuel to the cylinders until the point where second gear is requested.

At this point it must be noted that with such a simple system there is no control over the clutch or its speed of engagement other than by the driver. It is assumed that for this part of the process the clutch will be either ‘in’ or ‘out’ and that the driver, through skill and/or experience, will be able to operate this without the engine stalling or ‘bogging down’. To have a fully automatic launch control system and therefore the possibility of a two-pedal (brake and throttle) driving layout will need additional sensors, an actuator and a clutch control system controlling engine speed and clutch position at optimum tyre slip.

Launch control systems may be effective and may, it is argued, make the first few seconds of the race marginally safer. However, as a bit of a purist, from the point of view of the sport I do feel it downgrades the skills of the driver.

Fig. 1 - Friction as a function of tyre slip

Fig. 2 - A simple launch control flow chart 

Written by John Coxon

What is not yet so widespread though is the integrated use of the various CAE approaches. When several load cases (such as mechanical and thermal loads) come together, and perhaps fluids are involved as well then things become very complex, and a high level of experience is needed to make full use of CAE.

One of the more complex areas in engine design is the interface between the cylinder head and the crankcase. Granted, we all know we need to keep sufficient clamping load on the cylinder head gasket to secure sealing under all conditions, but what really happens to the cylinder head, crankcase, liners, pistons and so on under varying load conditions – and being able to predict what happens – is a different thing altogether. Trying to predict in which circumstances this interface is most critical requires a structured approach and, as well as skilled CAE engineers, sufficient computational power to get to realistic results.

First though we should clarify what we are trying to achieve. The main goal is to determine the deformations working on the interface, see which stresses will arise because of this and how the interface reacts to the loads under certain operating conditions. These conditions include not only firing (temperature and gas load) but assembly loads such as the interference fit of the valve seats and guides, as well as cylinder head bolt pre-load – and, if applicable, injector clamping loads. All of these will lead to cylinder head gasket deformation and stress.

Some typical load cases can be described which, in certain combinations, will be the most critical load case. Take assembly loads for example. The engine itself is in cold conditions and all components have been assembled with the correct bolt pre-loads and interference fits. This will lead to an initial stress in the components.

Then there is the temperature load, which depends on the temperature of the combustion gases as well as that of fluids such as oil and coolant. Certain deformations and stresses also occur here.

The third case, which is related to some extent to the assembly loads, is the load coming from external system effects – in this case, cylinder head deformation as a result of cyclic injector load transferred through the injector clamp onto the head. With gasoline fuel injectors these loads can be neglected, but with diesel injectors they can play a major role when combined with the other loads.

As a next step, the combined load cases that would lead to the most critical situation should be defined. Something that is often not considered is that one of the most critical operating conditions for the cylinder head gasket to perform its sealing function is when an engine is warming up. Everything is cold, so overall clamping load of the bolts onto the gasket is minimal, and combustion load is trying to lift the head from the gasket.

So, in these CAE simulations the related components are modelled, mostly in a CAD system, after which the components will need to be meshed (the creation of small elements within the components) for further use with CAE simulation tools. Meshing will need some attention, where typically the shape and size of the mesh is based on the engineer’s experience and will be tailored to specific analysis needs (smaller in areas of interest and somewhat bigger in other areas, all to reduce simulation duration).

The distribution of the temperature throughout the components, especially within the cylinder head and top end of the crankcase, then needs to be determined. Together with the heat transfer coefficients of the various materials in use, this will allow the stresses in the components to be simulated, as well as the predicted component and surface temperatures under the chosen – and most critical – running conditions.

When adding in the external system loads, which lead mostly to local stresses in certain areas of the cylinder head – as with high-pressure diesel injection – the overall stress levels can be simulated. The only thing left to do now is to determine the crank angle (position) at which the combined loads are critical. Here, some rather straightforward analysis will provide this type of information rather easily. Then the computational power comes into play, calculating the statuses of the separate elements in the mesh using finite element methodology.

Then, as a last step, post-processing the results allows us to determine which information is relevant. Mostly we would be interested in verifying the design and predicting the lifetime of some of the parts. This includes gasket pressure but also, for example, the liner deformation in order to predict oil consumption. Apart from this, critical temperatures could be subject to attention as well, such as the maximum temperature on the liner and piston top ring, cylinder head flame deck and many other areas.

I hope from this short summary that integrated simulation techniques have come a long way in being able to predict with greater accuracy what is happening inside an engine at critical interfaces. Some things are now becoming possible with hybrid systems, in areas perhaps even more complex than ‘just the internal combustion engine’ – a design we have been studying for more than 100 years now.

Fig. 1 - Cylinder head gasket pressure shown rotated over 360º of cylinder angle

Fig. 2 - FEA result of local gasket pressure used to quantify sealing quality of the cylinder head gasket, in this case sealing of the combustion chamber

Written by Dieter van der Put

Materials have an important effect on exhaust system design, and there are normally four choices here if we are talking about basic materials groups: steel, stainless steels, superalloys and titanium.

Of these, titanium is the easiest to deal with because it is used mainly for applications where the exhaust system is well supported – that is, with multiple supports along the length of the system – and this is generally the case on motorcycles where, as a minimum, systems are supported at the cylinder head and towards the rear of the machine. Full titanium systems are expensive, but are found on road and racing motorcycles. Titanium is relatively strong and light, but can suffer from brittleness when used at high temperature as oxygen diffuses into the surface. Ideally it should be welded in an inert atmosphere to prevent the material forming oxides and nitrides.

Steel, stainless steel and superalloys could all be used in many applications, but there are important differences in properties.

Steel is the cheapest option. It is easily available and is the cheapest of the three. It bends and forms nicely, so is easy to work with, and it requires no special processes for welding. Its weaknesses lie in the lack of strength at temperature and its inherent lack of corrosion resistance. The combination of these leads to systems that can lack durability, and to make up for loss of strength, it is necessary to use greater wall thicknesses than would be possible in other types of material.

Stainless steel is the next step up from steel, and in exchange for improved high-temperature mechanical properties, there are other disadvantages to contend with. Stainless is more costly than steel, and can be harder to form and weld. There are special stainless steels for welding that have elements added to prevent internal corrosion of the welds. Slip joints can become seized together occasionally, as stainless has a strong tendency to gall and fret. Compared to steel, the high-temperature properties of stainless allow systems to be made in thinner wall sections for the same level of durability.

Superalloys are the most expensive materials. They have been developed specifically for high-temperature service, and possess a very desirable combination of strength and corrosion resistance. They are composed of elements that are generally expensive to buy and, owing to their melting points, are also expensive to process. The superalloy sheet or tube material is consequently expensive as well.

Superalloys have to be welded in an inert atmosphere, otherwise the alloy will react with oxygen and nitrogen, detracting from the strength of the weld. Their room-temperature strength and stiffness make them more difficult to form than other types of materials, but they are used where maximum durability or minimum weight is needed. No other type of material has yet come close to being able to match it in these respects. Wall thicknesses of less than 0.4 mm have commonly been used for 10 years or more on car systems that are supported only at the cylinder head.

Written by Wayne Ward

As mentioned before, axial thread interference is occasionally used, mainly as a way to improve the distribution of load between threads, but it has the happy coincidence of introducing some extra friction into the relationship, which is useful when trying to avoid bolts coming undone. This practice is nearly always used for very highly loaded fasteners.

Also mentioned was that radial interference on threads is not common; that is to say, ‘bulk’ interference over the entire length of the thread is not often used. It gives an inconsistent level of additional friction during tightening, which is very unhelpful when trying to achieve a known level of load in a fastener. However, interference fits on a single or small number of threads is used, as this approach gives a constant and repeatable amount of extra friction when tightening. This extra friction can be measured using a torque wrench or electronic device, and can be accounted for in the torque-tension relationship.

Thin-walled metallic nuts are commonly supplied with specially deformed threads that act to give a controlled and constant amount of friction. Originally designed for use in aerospace applications, these are widely used in motorsport. Most people tend to call them K-nuts, and they come in various types. The locking action is achieved by the elliptical deformation, and the most commonly used are the hexagonal K-nuts with a flange, which also exist in a high-temperature silver-plated version. Other types that are riveted to sheet metalwork or composite panels provide thread-locking in applications such as engine intakes.

All-metal locking nuts are a real favourite in aerospace applications, so we also find them used in motorsport. Another popular type of nut, often known as aero nuts or aerotight nuts, have slots cut towards the top of the nut, a couple of threads down from the top, de-stiffening the top part of the nut which is then deformed slightly in the axial direction.

Various suppliers of wire thread inserts market inserts with a single deformed thread to provide a constant amount of friction when installing a fastener. Other than chemical thread-locking methods, deformed wire inserts are the main method of positively locking a standard fastener into a threaded hole, as they have the advantage of providing a constant amount of additional friction to the system. Chemical thread-locking methods are prone to inconsistencies between operators and differences in application, speed of tightening and so on, and here the mechanical wire insert is much more predictable, albeit at a much higher cost.

Locking thread inserts are sometimes installed in nuts that are made of soft materials or those prone to surface damage during tightening: titanium and aluminium nuts are available in this locking configuration. The wire insert in the nut also provides an improved load distribution between threads, leading to a lower stress concentration factor on the male fastener.

Written by Wayne Ward

Now, it has to be said that that the experience of many countries adopting higher rates of ethanol sooner has not apparently been as calamitous as feared. This could be because those countries don’t have as much of a history of running older vehicles as in the UK and US, but when it comes to the safety of our fuel systems and the seals used therein, it pays to be careful.

In 2008, the Minnesota Center for Automotive Research published a series of papers looking at the effect of E20 (20% ethanol in gasoline) on fuel system plastics and elastomers. The study was to compare the effects of E20 with those of E10 and non-oxygenated gasoline (that is, containing no ethanol) fuels by testing to Automotive Industry SAE and ASTMS standards.

In the case of the elastomers, samples were prepared and immersed in the fuels at 55 C for 500 hours, after which changes to their physical properties of volume, weight, tensile strength, elongation at break and hardness were measured. The results of testing acrylic rubber, polychloroprene (Neoprene), nitrile rubber (NBR), nitrile/PVC and fluorelastomers showed that although there was a degree of swelling for all of them when the samples were immersed, there were no significant changes in hardness or tensile strength.

Apparently sponsored by the US Department of Agriculture, however, which was encouraging the growing of wheat corn for the production of ethanol, this report was not considered to be totally independent, so when the Indian government was considering a move from E5 to E10 the work was repeated. Testing four types of elastomer – Neoprene, NBR/PVC, hydrogenated nitrile butadiene rubber (HBNR) and nitrile rubber – representing those commonly found in their markets, and using fuels more typical of those found in India (19% olefin, 28% aromatic), the results were interpreted slightly differently.

Since the weight and volume of the Neoprene samples were far greater it was concluded that, compared to the E5 fuel, Neoprene was totally incompatible with that of the E10. For nitrile and HBNR specimens there was also a significant increase in weight and volume between E5 and E10, which at the same time was accompanied by a loss in hardness and tensile strength. HBNR and nitrile rubbers were therefore also considered to be incompatible with E10. On the other hand, PVC/NBR showed better overall resistance from E5 to E10.

So while in the wet state all the elastomers apart from PVC/NBR exhibited some significant degree of swelling in both E5 and E10 fuels, when dried they all showed signs of some level of leaching – all of which proves that with hundreds of different types of elastomers currently used in engines, many older designs could experience sealing failure with the advent of higher levels of ethanol in fuel.

Fig. 1 - Test results after immersion in the fuel

Written by John Coxon

In the bigger diesel engines, which can tolerate large amounts of excess air, if matched correctly, no further control systems may be necessary. In smaller engines however, particularly spark ignition units, additional controls may have to be introduced. In this latter group therefore, turbocharger controls are a necessity, and fall into two categories – those that protect the turbocharger by limiting its speed, and those that protect the engine by restricting the compressor outlet pressure and hence the engine boost. Transferring all this a typical compressor map the operating envelope is therefore the compressor ‘surge’ line to the left of a typical compressor map, the maximum safe wheel speed to the top,  and the compressor ‘choke’ area to the right.

For reasons of reliability and durability, it is always preferable to restrict turbocharger controls to the cold, engine air intake side of the application, if at all possible.

Perhaps the most obvious control is some form of blow-off valve. This is designed to re-route the compressor outlet air before it enters the intake manifold, and in most applications limits surge forces in the compressor wheel and bearing assembly when the throttle is snapped shut, as in the case of a gear change, for instance. Under such transitory conditions, interruption to the airflow would otherwise result in high-pressure spikes upstream of the throttle. A safety feature perhaps, but any bleed-off of the post-compressor air is wasted work by the turbine applying a back-pressure on the engine to compress the engine intake air in the first place, and therefore inefficient.

For maximum effectiveness and to increase overall engine efficiency, the boost condition is best controlled by limiting the hot, exhaust gas passing through the turbine wheel. The most common of these methods uses a wastegate or bypass valve, and takes its signal to open (limiting the flow of exhaust gas to the turbine), from a pressure tapping located on the compressor or a similar tapping from the exhaust manifold.

More usually these days, this bypass valve is integrated into the turbine housing next to the turbine wheel. These valves must be large enough to flow all of the anticipated bleed-off gas to prevent a phenomenon known as ‘boost creep’, which is the condition when exhaust gas flow completely overwhelms the bypass valve when fully open and the exhaust gas pressure consequently continues to rise in the upstream (exhaust) manifold. Under such conditions the intake manifold pressure will also continue to rise, creating even more exhaust gas and eventually producing dangerously high boost pressures with potentially catastrophic results for the engine.

From an efficiency viewpoint, however, the optimal method of controlling boost pressure is by using a variable geometry turbine. Sometimes also referred to as a variable area turbine nozzle, the most common of these consist of a circular array of pivoted aerofoil blades situated inside the turbine housing where the exhaust gas enters the turbine wheel. Designed to alter the angle of exhaust gas flow to the wheel according to its rotational speed, turbines such as these give much better low-speed torque characteristics as well as shorter spool-up times. As ever though, challenges to be overcome are the extremely hostile environment of high temperature gradients in the area and the corrosive nature of the exhaust gas.

With the increasing emphasis on fuel economy, not only in the auto industry but also the race track, surely it can’t be long until all engines – however small – are fitted with boost-controlled turbochargers.

Fig. 1 - Turbo wastegate valve

Written by John Coxon

With the chemical symbol MoS₂, this black crystalline compound occurs as the mineral molybdenite, the principal ore from which molybdenum metal is extracted. It is commonly used as a solid lubricant, thanks to its low-friction properties, which are similar to those of graphite, as well as its high load-bearing capabilities and the fact that it is relatively unreactive, being unaffected by dilute acids and oxygen. Most usefully when it comes to engine applications, it has good thermal stability, up to 350-400 C in an oxidising environment.

Molybdenum disulphide was first discovered more than 250 years ago, when the lubricating properties of an unknown ore were noted in 1744 by Johann Alexander Cramer. The ore was similar to lead, galena and graphite, and these substances were labelled with the Greek word ‘molybdos’, meaning lead-like. In 1778, a Swedish scientist named Carl Wilhelm Scheele identified molybdenite as the sulphide of a distinct metallic element by heating it to yield a white oxide powder. At his suggestion, Peter Jacob Hjelm, another Swedish scientist, successfully isolated the metal in 1782 and named it molybdenum.

The first use for the material was as a strengthening agent in steel production, a use to which it is still put, but it was not until 1935 that it was used for its lubricating properties. A German engineer, Alfred Sonntag, had designed a huge machine to simulate aircraft vibrations, but it failed due to friction between the moving parts. He tried many lubricants to solve the problem, but none had sufficient load-bearing capability to be effective. However, he came across an 18th century text that mentioned the lubricating properties of molybdenite, and on using it as a lubricant found it to be highly effective. After this discovery, Sonntag developed a method of purifying molybdenite, which contains traces of quartz, into the powdered lubricant that is in use now.

Molybdenum disulphide takes the form of microscopic hexagonal platelets, with several molecules making up each platelet. These platelets are attracted to metal surfaces which, when combined with sliding force between metal parts, results in a thermo-chemical reaction, creating a protective coating of MoS₂ on the parts in question. This coating can withstand pressures of about 500,000 psi, and as such makes MoS₂ an attractive option for use on components where boundary lubrication is an issue, such as the interface between camshafts and tappets.

While the application of MoS₂ as a dry-film lubricant was established in the mid-20th century, using it effectively in oil took longer to perfect. The problem was that the particles would not stay in suspension in oil, leading to the particles forming a sludge that could block oil passageways (while also negating the material’s lubricating benefits). However, once methods were found to prevent this, MoS₂ has proved to be a highly effective anti-wear additive. For example, tests undertaken at the Argonne National Laboratory, in Illinois in 2012* showed that adding MoS₂ nano-particles, 50 nm in size, to a polyalphaolefin base oil showed significant reductions in friction between the piston skirt and cylinder liner on heavy-duty industrial engines. These same benefits can also be realised in transmission oils, where boundary lubrication is far more common.

As with any technology though, the use of molybdenum disulphide as an oil additive is not a silver bullet. For example, it only acts a friction reducer under boundary lubrication conditions; in hydrodynamic and full-film regimes, the particles do not come into play and some studies have even shown that they can actually marginally increase friction. However, provided its limitations are recognised, it can have considerable benefits when used correctly.

* Nicholaos, G., Demas, Elena, V., Timofeeva, Jules L., Routbort, George R. Fenske, “Tribological effects of BN and MOS 2 nanoparticles added to polyalphaolefin oil in piston skirt/cylinder liner tests”, Argonne National Laboratory, 2012

Written by Lawrence Butcher

The piston ring has an inherent amount of radial pressure, which we feel as drag when we insert a piston into a bore, or via the force when we check the fit of the rings in the bore before fitting them to the piston. This is often done when confirming or adjusting ring end gaps. Indeed, the radial pressure or ‘ring tension’ is often expressed as a force needed to bring the ring into a form that will fit in the nominal bore size.

This radial pressure is augmented by gas pressure behind the ring, and it is this component of the ring force that can be increased through detailed design. The technique to improve pressure behind the ring is known as ‘gas porting’ or ‘gas jetting’, and the idea is to use the pressure in the combustion chamber to enhance the pressure behind the ring. This can be done by using a series of small drillings directly from close to the periphery of the piston crown through into the top ring groove. These are usually known as vertical gas jets, although they are not necessarily absolutely vertical.

The second type of gas porting, which is more common, is radial gas porting, also known as horizontal gas porting, side gas porting or lateral gas porting. These features are produced using a milling cutter rather than a drill, especially if they are added to existing pistons. The reason for this is that the radial type of gas jet is not a continuous hole, but is a semicircular cut with its axis intersecting with the top side of the ring groove.

Among the reasons that piston rings may not seal is insufficient side clearance between the ring and the groove – that is, across the width of the piston ring. To avoid ring flutter, small clearances are used, and this can prevent sufficient pressure reaching the back of the piston ring groove.

However, the use of low-tension rings and gas ports is often intentional, being a design feature from the start. Through the use of gas porting, the only time there is sufficient radial force on the ring to seal combustion pressure is when pressure is present – when we need it. At all other times, the ring tension alone forces the ring against the cylinder wall, and this means the average radial force is lower by using a low-tension ring and gas porting than would be achieved using a piston ring of higher tension and no gas porting.

Written by Wayne Ward

There are several benefits to anodising, but we should make an early distinction between hard anodising, which applies a relatively thick oxide surface on aluminium components (hard anodising is not used on titanium), and the decorative version of the surface treatment, which applies a far thinner and more transparent layer. The hard anodising treatment gives a significant increase in hardness of the component’s surface, and a big improvement in wear resistance, to an aluminium component. It can also reduce the coefficient of friction, especially if the anodised surface is sealed with a low-friction polymer such as PTFE. Hard anodising is often used to prevent wear problems in piston ring grooves, for example, and we commonly find it used on aluminium pulleys of both the conventional and polyvee types.

The more decorative version of anodising does not give the same level of wear resistance as the  much thicker hard anodising process: with the oxide layer being far thinner, it has only the substrate to support it, rather than a thick layer of the stiff oxide. However, decorative anodised processes allow dyes to be used, and aluminium components can thus be colour-coded to aid identification or to add a little colour to an engine that perhaps looks otherwise a little dull, although on the grounds of taste some people object to the use of multi-coloured components ‘adorning’ the exterior of an engine. Decorative coatings do provide a degree of corrosion resistance though, which can be an important factor. There is a huge number of applications in engines and transmissions for these thinner processes.

The downside of anodised surface treatments is the loss of fatigue strength that results from their use. This loss can be significant, but depends very much on the exact process used and the alloy being processed. If the area requiring the coating does not have a significant stress concentration, it may be possible to locally mask the ‘danger area’ to avoid compromising its strength. For example, on polyvee pulleys the base of the grooves (which are the area of greatest stress concentration) can be masked by O-rings, while the wear surfaces – namely the tips and flanks of the teeth – are anodised.

To mitigate the deleterious effects of hard anodising on the fatigue strength of aluminium, some success has been found by using shot peening, although when peening is combined with hard anodising, the peening must be done before anodising. The improvement that comes with pre-anodising peening can be dramatic – a 30% decrease in fatigue strength without peening has been turned into a 10% increase in strength compared to an identical component that was neither peened nor anodised.

Reference

Champaigne, J., “Shot Peening Overview”, available at www.shotpeener.com, 2001

Written by Wayne Ward

One area that has long been of interest to cylinder head tuners is the analysis of flow velocities within a port and around the valves. For decades, pitot tubes have been used to take spot pressure readings from inside the ports, and most flow benches come supplied with a port to accept a pitot.

A pitot tube can be used in various ways, either by being placed in a static location to measure flow velocity at that point or moved around like a wand, to try to identify areas of high or stagnant flow. While this makes them a useful tool for obtaining a general idea of flow velocity within the port, however, they have their limitations, the most notable of which is the fact that inserting a pitot tube into a port introduces an obstruction that can interfere with the airflow and skew the accuracy of readings.

This problem has led some head tuners to develop methods of taking pressure measurements from within the ports in such a way that there are no obstructions to the flow. For example, the author has seen one example of a test head where the tuner drilled a series of holes (known as pressure taps) around the valve seating area, with each attached to its own manometer. This allowed pressure readings to be taken without any impact on the flow conditions around the valve as there was no obstruction present.

The data it generated was also interesting, giving a snapshot of how pressures differed around the valve and changed with valve lift. It also allowed for comparative testing between different port designs.

There is one big disadvantage with this approach though, in that the heads that were drilled in this way could not be used for anything other than testing.

This brings us to a second novel approach to assessing differences in flow across the valve. It involves using a specially made valve that incorporates a pressure tap in the valve head. The tube from the pressure tap then runs up the valve stem to a tube that can be connected to the pitot port present on many flow benches.

As the head is run on the flow bench, the pressure at the point on the valve where the pressure tap is located can be recorded, either manually or via a flow bench software package. Once the pressures at that point of the valve have been recorded through the range of valve lifts, the valve can be rotated to record at a different point; adding an indexed collar on the valve stem means this can be done in a repeatable fashion.

The end result is a full pressure map of flow at the valve head throughout the valve’s entire lift range, providing an invaluable insight into a particular design’s flow characteristics.

These two systems just go to show that, although CFD and complex flow visualisation systems are the favoured approach these days for large racing operations, there is still plenty that can be learnt from a good old-fashioned flow bench.

Written by Lawrence Butcher

It is well documented that finishing the working surfaces of gears and their root fillet regions to a very low roughness can result in a considerable increase in surface durability, as well as reducing friction and operating temperatures. Achieving such finishes using traditional methods such as surface grinding and honing is very time-consuming though, and carries considerable risk that the profile of the gear teeth can be irreparably changed. The use of chemically accelerated vibratory finishing methods, generically referred to as superfinishing, can avoid such problems while also resulting in a much smoother surface finish. The average roughness achievable with grinding techniques is about 6.0-12 µin, whereas superfinishing can produce a roughness in the region of 1-3 µin.

Superfinishing is undertaken in vibratory finishing tubs, of the same type that have been used for many years in other abrasive media finishing processes. The media used in these tubs is a high density, non-abrasive ceramic material, with the shape and size of the media selected to match the geometry of the gears being finished. The media does not itself remove any material from the gears, it is only once a reactive agent is introduced into the finishing tub that changes in the surface finish of the gears occur.

The reactive agent produces a stable, soft conversion coating across the asperities of the gear surfaces. As the media in the finishing tub rubs across this coating, the peaks and valleys of the material are gradually smoothed out, until the surface is, to all intents and purposes, free of asperities. The reactive agent is mildly acidic and, depending on the concentration used, stock removal occurs at 0.00005-00040 in/h. This removal is beneficial, allowing gears with an initial surface roughness of around 60 µin to be finished to a final roughness of 3 µin.

Interestingly, a consequence of using hard ceramic media in the process is improved wear resistance in use. Although the material is non-abrasive, it still leaves a micro-textured surface on the material being finished. Testing undertaken by the University of Cardiff, Wales, to look at scuffing performance of test discs treated with ceramic and plastic media respectively showed that the ceramic media-treated parts had a much higher resistance to scuffing than those treated in plastic media. This was surprising, given that the plastic media leaves a smoother surface. It therefore follows that there is an optimum surface roughness that needs to be achieved in order to reap the greatest benefits from the process.

Overall then, superfinishing can improve durability and performance in transmissions compared with traditional ground finishes. As a result, many high-performance transmission manufacturers now use the process to ensure their gears are better able to survive the rigours of competition use.

Written by Lawrence Butcher

Higher-revving engines are a challenge for the valvetrain, and the overhead cam engines used in these smaller engines are much less problematic than their pushrod counterparts. The connection between the cam lobe and the head of the valve is far stiffer, and has fewer components, so controlling the valve at high speed is easier.

Race engines are even more of a challenge. As engineers, we want to open the valves further and for them to open and close very rapidly, and we want our engines to operate at higher speeds than an engine from a typical passenger vehicle. So, where the camshafts in a passenger car are driven by a belt – or by chain on a motorcycle – most bespoke race engines use a geartrain to drive the camshafts. The advantages of gears over belts and chains are increased stiffness and greater accuracy, particularly over extended periods of time. Belts and chains stretch over time; gears do not.

Cam drive gears are made from steel, but their loading is complex as the torque transmitted is far from uniform through the engine’s operating cycle. Despite this, some of the gears in a race engine geartrain can have impressively small face widths (the term given to the width of the gear tooth between the faces of the gear at the pitch circle).

Moving inwards from the ‘working’ portion of the tooth, the root radius needs to be considered. While these radii are usually generated by the action of the gear cutter, some people advocate producing a more optimal form in this area to reduce stress concentrations.

It is common to reduce the width of the gear between the hub and the teeth, but the designer needs to be careful to provide sufficient ‘depth’ of material to support the teeth. The narrowed area, which reduces the mass and inertia of the gear, is often provided with holes and slots to further reduce mass, but if too many holes are used then cracks can develop. There may also be a penalty in terms of oil drag and shear from using holes rather than simply making the web between the hub and rim of the gear thinner.

The number of teeth chosen for the gears is dictated to some extent by the 2:1 speed ratio required between crankshaft and camshafts, but the choice is made so that the same highly loaded teeth are not always in contact with each other. So, we find that prime numbers are often used here.

It is not always possible to find gears that will fit in the allowable space and operate at the exact centre distances required. In such cases, it is necessary to adjust the profile of the gears in a design process called ‘profile shifting’, which allows a gear to operate properly but with a slightly larger or smaller diameter than its tooth size and number of teeth suggest. Profile shifting needs to be done carefully, however, so as not to compromise the strength of one or both gears.

Written by Wayne Ward

Being open-wheeled vehicles, the tyres of a Formula One car play a major role in its aero performance and, as such, understanding their impact here is an important part of optimising the car’s overall aero package. Tyres are dynamic entities though, so their shape and size changes when loaded by the car on track. Along the straights, they will grow in diameter and get narrower; in corners, vertical and horizontal loads will cause them to deform laterally.

To ensure that the impact of this deformation is accounted for in aerodynamic testing – both in CFD and the wind tunnel – requires some clever methodologies. Most Formula One teams keep such testing secrets close to their chest; however Honda has revealed some of the techniques it used during its last stint in the sport.

For scale-model wind tunnel testing, scale rubber tyres are used to replicate the behaviour of their full-scale counterparts. In most wind tunnels though, it is only possible to apply vertical forces to the tyres, and perhaps a small amount of side force by yawing the car on the wind tunnel’s moving belt. To combat this problem, Honda devised various testing methods based on deformation measurements taken from its cars on track. This data could then be fed into its CFD simulations to gauge the impact of this deformation on overall aerodynamic performance.

The actual data for deformation was gathered using a tyre test rig, with the inputs for side loadings derived from load cell measurements of the car’s suspension when on track. The measurement of the deformation was achieved by scanning the tyres as they were on the test rig, and using this information to create 3D models of the tyres. These models could then be fed in to Honda’s CFD simulations. As an example of the level of deformation present, a side loading of 7000 Nm on the tyres’ tread caused a deflection of the side wall of about 20 mm.

The impact of this deformation on the flows around the tyre were considerable. Looking at the front tyres, CFD simulation showed that as the tyre deformed, the separation point of the flow at the base of the tyre sidewall moved backwards. As a result, flow that moved around the tyre when it was not deformed, started to flow under the car, reducing the effectiveness of the underfloor aerodynamics.

With this new-found knowledge, Honda went on to replicate the tyre deformations as accurately as possible in the wind tunnel, using both scale and full-sized vehicles. It was verified, through force measurements and PIV (particle image velocimetry) visualisation, that the changes to the flow in CFD correlated with the real-world effects. It is interesting to note that one method suggested by Honda to more accurately replicate tyre deformation in the wind tunnel involved fitting a roller inside the test wheels that could be used to load the sidewall of the tyre to produce the same deformation as seen on track.

It is more than likely that current teams have various other methodologies for assessing problems such as tyre deformation, no doubt helped by advances in CFD and other simulation methods. However, Honda’s study provides an interesting example of the amount of effort needed to accurately quantify just one area of a Formula One car’s overall aero behaviour.

Written by Lawrence Butcher

The inerter was developed by a Professor Smith, of Cambridge University, England, as a solution to the age-old problem of balancing ride compliance with stiffness. A regular suspension set-up, be it on a car or motorcycle, is based around two components – springs and shock absorbers (dampers). Together these contribute to the car’s ride and handling, but no matter how the system is tuned, there is always a compromise between handling, comfort and grip. Even in racing machines, where comfort is less important, the suspension needs to be set to allow both sensitive handling, which requires a harder suspension, and a good mechanical grip, which requires suspension compliance.

The upshot is that there is oscillation of the suspension as the load on the tyres varies. If these oscillations reach a high enough frequency, the damper and spring package will not be able to react fast enough to damp them out, so tyre contact with the track surface will be reduced.

Prof Smith realised that this poor trade-off between handling, comfort and grip could be better resolved if a third type of component was added to a suspension system to make it more flexible – hence the inerter. Superficially it looks like a conventional shock absorber, with an attachment point at each end. In the case of a Formula One unit, the inerter will be attached to the suspension rocker and the chassis. A plunger slides in and out of the inerter’s main body as the car moves up and down. As this happens, a flywheel mounted on the plunger rotates in proportion to the relative displacement between the attachment points. The result is that the flywheel stores rotational energy as it spins.

In combination with the springs and dampers, the inerter reduces the effect of oscillations in the suspension and tyre, and thus helps the tyre retain a better grip on the track surface. By changing the weighting of the flywheel, the level of ‘inertance’ can be varied, allowing the effect on chassis behaviour to be fine-tuned; the latest systems even allow for the inerter to be completely disengaged in certain circumstances.

One area where inerters are of particular use is on vehicles with large tyre sidewalls, such as those in Formula One. A large sidewall is more prone to uncontrolled deflection at high suspension frequencies, which an inerter can be highly effective at combating, the result being a more consistent tyre contact patch and thus greater mechanical grip.

Speaking at the time the technology came into the public domain, in 2008, Prof Smith was surprised that no-one had thought of the idea before. “I was nervous about talking about the idea at first because it seemed so elementary a concept,” he said. “It was very difficult to believe that nobody had thought of it before, and I presumed that either it had been done already or there was some sort of snag.

“As I discussed the idea with colleagues, however, I began to realise it hadn’t been done and that it was possible to achieve this trade-off to improve vehicle suspension. The next question was whether it could actually be done, and once I had worked out what it should look like, that was a fairly simple matter."

Since these initial developments a decade ago, inerter technology has been refined to the point where it is now an indispensable part of a Formula One car’s chassis package. The technology has also begun to filter down into other series – for example, Porsche’s factory LM P1 is thought to use inerters, while they have also been widely adopted in Pro Stock drag racing, where they have allowed tuners to obtain much more consistent chassis set-ups.

Written by Lawrence Butcher

The vast majority of body panels on a Formula One car are made from different types of carbon composite materials. Optimising these materials to provide the best compromise between weight and stiffness (or, if some degree of aero elasticity is desired, a lack of stiffness) is an integral part of the Formula One design process. In some areas, for example the bodywork that forms the engine cover, advances in composite materials such as the adoption of spread tow fabrics has allowed fewer material plies to be used and thus weight reduced. However, finding savings in other areas, such as the front and rear crash structures, is more complicated.

Front and rear crash structures at the of the car must fulfil a number of tasks, specifically taking the most aerodynamically efficient form possible, while also meeting the stringent crash test requirements laid down by the FIA. In the past, the most common method for creating these structures was to use an aluminium honeycomb structure, housed in a composite shell. Here, the aluminium would provide the bulk of the structure needed to absorb the energy of an impact.

In recent years though, advances in composite simulation technology and lay-up methods has allowed structures to be created that do away with the aluminium honeycomb, relying solely on the composite for energy absorption. Honda for example, while it was still involved in Formula One, was able to make a 15% weight saving by replacing its aluminium-based nose cone with a solely composite item. The nose cone used four composite ‘pillars’ inside the nose, which provided energy absorbance as well as good structural stiffness.  

Engineers face similar challenges when constructing the monocoque. On the one hand, weight needs to be kept to a minimum, but this cannot be at the expense of chassis performance. Again, information released by Honda sheds an interesting light on this balancing act. The team found that local stiffness around the suspension mounting points had a far greater bearing on chassis performance than overall chassis stiffness. With this in mind, reinforcing plies in areas of the chassis that did not carry suspension mounts were removed, with a consequent 20% reduction in overall torsional stiffness. Meanwhile, the areas around the front suspension mounts and the engine-to-chassis interface were reinforced. Track testing showed that this had no adverse impact on vehicle performance, and netted a very useful 6.5% reduction in weight and a lowering of the centre of gravity by 2 mm.

No doubt the current teams use many other ingenious methods to find similar weight savings and performance gains, but this example shows clearly why it is sometimes necessary to reassess theories about chassis construction that are seemingly set in stone, in order to find that elusive extra performance.

Written by Lawrence Butcher

3D printing with polymers has been available for more than 20 years and has been used by Formula One engineers, but if you exclude the fibre-reinforced polymer composites that make up most of a modern racecar, plastics have only limited applications on the car itself.

In general, printed plastic parts have been used predominantly for mock-ups and space claim (the use of a model to represent the overall dimensions of a component, but generally without functionality, to allow other components to be designed and added to the system without interfering with existing parts), wind tunnel models and more recently for tooling in the production of components from composites. The limited structural capabilities and temperature resistance generally restrict the selection of polymers, whether 3D printed or produced via more conventional methods; however, the geometric freedom unlocked by AM and the potential advantages this can deliver make it a technology that will continue to find applications in Formula One.

This is supported by more recent developments in AM which have seen the increasing availability and capability of metallic 3D printing. This opens up a world of opportunities with the ability to rapidly manufacture components in high-performance alloys such as Inconel, a nickel-chromium superalloy, and 6Al4V titanium alloy, both commonly used in machined, cast and fabricated motorsport parts.

These opportunities have not gone unnoticed by the Formula One engineering fraternity, and techniques such as direct laser metal sintering (DLMS) and laser melting are being exploited to deliver a range of benefits that are not solely concerned with reducing weight. In fact, it is often the ability to reduce development times that make these techniques so attractive, although unsurprisingly this can come at a cost.

Some examples of metallic AM components include turbine housings that form part of the current turbo powertrain ERS systems, and at least one team has used DLMS to produce fully functional prototype housings in steel for development and testing. The parts were post-machined, as would be required for a more conventional cast version, but the build resolution and material properties offered by this technology allowed the wall thickness to be reduced by a third, from 3 to 2 mm.

The reduction in lead time and weight is significant, especially when considering the additional patterns and tooling required for casting, but with a price tag of around £20,000 (about $32,000) per housing the metal printing technology is currently still too expensive for the limited ‘production’ required by Formula One teams, even with their budgets.

Other teams have been developing titanium valve bodies for shock absorbers, and by optimising the component geometry for the printing process and understanding the design freedom and limitations, significant returns are possible.

Ongoing r&d into the printing of metallic honeycomb structures may also have some applications in motorsport. The prospect of printing cores for fibre-reinforced composite structures could offer some interesting properties, especially in crushable structures, as the core can be engineered to behave auxetically (exhibiting a negative Poisson’s ratio), potentially increasing its ability to absorb energy. (Poisson’s ratio is the negative ratio of transverse to axial strain. When a material with a positive Poisson’s ratio is compressed in one direction it tends to expand in the other two directions perpendicular to the direction of the applied force. An auxetic material, which has a negative Poisson’s ratio, exhibits the opposite behaviour, and when compressed in one direction become thinner in the perpendicular directions.

Metallic AM parts have generally exhibited properties exceeding those of equivalent cast materials, but which fall short of the performance offered by the alloys in wrought form.  The continual and rapid developments in these technologies are beginning to address this deficit though, as well as improving build resolution and surface finish.

Heat treatments for annealing and stress relief of titanium are delivering improved ductility and fatigue strength, while solution treatment and precipitation hardening (ageing) of Inconel offer improved mechanical properties, making these materials a viable alternative to machining from solid wrought alloys.

As the cost of the raw powdered alloys and machines decrease, and the capability, capacity and availability increase, the use of 3D printed components on Formula One cars will continue to rise. The early compromises regarding material properties and build resolution (wall thicknesses of 150 microns are achievable) are being addressed, offering the potential to take metallic AM technology from its niche applications in prototypes and complex integrated geometry designs to a production alternative for the small batch volumes required in Formula One.

Near-net shape printing with minimal post-machining could offer racing significant advantages in development and production times and ultimate costs, as well as all the potential performance gains that can be achieved once freed from the geometry constraints of conventional manufacturing techniques.

Mechanical properties of wrought materials

Table of AM mechanical properties (Courtesy of Renishaw)

Table of mechanical properties of titanium 6Al-4V-AM (Courtesy of Renishaw)

Written by Dan Fleetcroft

Originally designed for military pilots in the mid-1950s, HUDs expanded into commercial aviation in the 1970s, and the late 1980s saw the first production car with a fully integrated HUD. The technology then found its way into Formula One in the early 1990s with Team Lotus, which used a Frazer Nash system where a tiny projector and half-mirrored glass panel were fitted to the inside of the driver’s helmet in front of one eye. It could display information such as rpm warning lights and gear position, but the drivers did not warm to the system because of safety concerns about having hardware in front of their faces; they also seemed to find the system distracting.

The next and so far last time HUDs featured in Formula One was in the 2003 season, when the BMW Williams F1 team developed a system for Ralph Schumacher, and his third place in Hungary marked the first and only time a HUD has been used in race. Specifically designed for Schumacher’s eyesight, the 6 x 8 mm display was integrated into the chin cup of his helmet, and the system worked by storing messages and images in a dataset that could be called up from the pits and then displayed to him by projecting a ‘transparent’ image through his visor.

The display was high-resolution true colour, based on the active matrix liquid crystal display (AMLCD) technology, a type of flat panel display commonly used in mobile phones and televisions these days. The ‘active matrix’ refers to the thin-film transistors and capacitors in the display of the screen that control each individual pixel, resulting in quicker response times and a clearer picture, as opposed to a ‘passive’ matrix that has to alter a full row of pixels to modify a single pixel, and is therefore slower. The active matrix ensures that the system is brighter, more colourful and capable of dealing with faster moving images, and a unique lens element called a free form prism is used to make the picture sharp.

The display was located in the peripheral vision field of Schumacher’s dominant eye, making it easier for him to see, without having to look at the display directly. This offers an advantage over the current display on the steering wheel because when a driver looks at the steering wheel, the horizon becomes unfocused, whereas when the driver focuses on the track ahead, the display remains in focus. Furthermore, unlike the screen on the steering wheel, which rotates with every steering input, the HUD only moves with the driver’s helmet. It also enables the driver to choose when he wants to receive the information, for example when it is safe or on a straight, unlike with radio communications from the pits.

Regarding recent events at the Japanese GP in Suzuka and the reduced radio rules, HUDs may offer an alternative to the steering wheel display. From a safety point of view, critical information such as track status and yellow zones can could be displayed constantly in the driver’s peripheral vision, which arguably is less distracting. Also, as the HUD display can be slightly larger than the display on the steering wheel, the size of the steering wheel can be reduced, which in essence is what delayed the radio rule change until 2015.

Schumacher’s feedback in 2003 was positive, although the system was banned by the FIA because of the safety implications of having the display mounted inside the helmet. One chief technical officer said that, although they are effective, HUDs will only work in Formula One if the focus point is at infinity, to avoid the driver having to refocus, and if the safety of the system is developed further.

Figs. 1 and 2 - The system developed by BMW Williams in 2003 specifically for Ralph Schumacher’s eyesight. A variety of information was displayed to him, and this may be a way of communicating yellow flagged zones and the car’s status without using radio. However, the safety aspect of having the display so close to a driver’s face remains an issue

Written by Gemma Hatton

If the FIA were to open Formula One to driverless cars next year, what are the chances – disregarding the available development time, hypothetically speaking – that one of the top teams would field a car quicker over either a qualifying lap or a Grand Prix distance than a human-driven car?

Nick Wirth knows a thing or two about unmanned technology having in the past created sophisticated robots as well as Formula One cars. He discounts the possibility of a driverless Formula One car outrunning its manned equivalent in the short term.

By contrast, a Formula One team technical director, who wishes to remain nameless, says, “In my opinion, based purely on experience with closed-loop lap simulation results, there is significant evidence to suggest that a virtual ‘driver model’ can cope with a significantly more ‘unstable’ car compared to reality. The big question though is whether this theoretical increase could be converted into reality.

“Control system recognition and response is the key factor here,” he says. “I think there is enough evidence to suggest that, in theory, a digital controller could function at a higher bandwidth compared to a human being. If this can be achieved then the digital controller should outperform its human counterpart.

“Obviously, both the development resource and the time required to achieve this is significant, but I believe it could eventually be done. Therefore, all the big-budget teams would ultimately be interested in this development thread if it were legal, which it obviously isn't.”

Mike Lancaster is the brains behind one of the top suppliers of control electronics to professional racing, and he says, “The quick answer is that I have little idea, and I suspect that will be the same for most of us. That said, my initial thoughts are that the human driver is a complex creature endowed with a vast array of subtle feedback systems, and controlled ultimately by the most sophisticated parallel processing system that as far as we know exists anywhere. Despite this, the organic brain is very slow, not only to process information in real time but sluggish in machine terms to react appropriately.

“Lined up against the organic computer is a vastly faster albeit single-minded ‘brain’ that knows nothing at all beyond following sequential instructions. Assuming the driverless car was able to drive around each corner alone and unimpeded, and with sufficient and no doubt considerable time to adapt to circumstances, in the end it would be faster than any human in my opinion.

“The analogue is a modern fighter aircraft, which is fundamentally unstable and controlled by computer, without which it could not be flown by a human. Assuming the same budget was applied to racing a land-based vehicle without a driver then the writing is on the wall. All of that said though, I doubt if the current driverless technology for production vehicles is at the level needed to go faster than a human… yet.”

Written by Ian Bamsey

Much of the saving, of course, was in the energy recovered under braking, energy that would have otherwise gone to waste in the form of heat out of the exhaust, but in adopting electric motor/generator technology there is so much more potential for efficiency than many might at first think. Take the turbocharger compressor wheel design for instance, and the potential for efficiency savings in compressing the intake charge.       

Powered by an exhaust gas-driven turbine or the electric motor of the motor/generator unit, the engine intake air is drawn into the centre of a centrifugal compressor wheel and accelerated radially outwards, increasing the kinetic energy of the intake gas. Having left the perimeter of the wheel, the rapidly moving air is slowed down again, or ‘diffused’, so that the kinetic energy is converted into pressure energy – the intake manifold boost pressure. The design and angle of the blades of the compressor wheel, the diffuser and the scroll of the compressor housing all work together to generate the compression characteristics of the system in the form of a compressor ‘map’, examples of which are shown in Fig. 1.  

Essentially a plot of pressure ratio against the mass flow, the left-hand side of the operating envelope is referred to as the ‘surge’ line. At this point the aerodynamic elements of the compressor wheel create reverse flow effects, leading to stress reversals in the compressor blades and a ‘coughing’ type of sound as the airflow stalls. At the other side of the map, towards the right-hand side of the envelope, the limit is one of compression efficiency. Normally taken to be around 60%, at these values excessive heating of the air intake charge takes place, the mass flow drops significantly and the compressor is effectively ‘choked. In between, the map consists of a series of contours connecting points of equal compression efficiency, rather like the height contours on a map, and superimposed on all this are the lines of constant compressor wheel speed.

The operating range, or ‘width’ of the map, is in part a function of the compressor wheel design – the type and the number of blades and their angle of twist. When designed to have a degree of what is called ‘backsweep’, these impeller blades create maps with higher peak compression efficiencies at the expense of being narrower and therefore more difficult to match to engine applications, particularly those used in applications with variable speed and load. In most automotive applications, therefore, the running position of the compressor is governed by the boost pressure which, once achieved, is regulated by the turbine wastegate.

However, if you now throw in the potential to drive the compressor using, say, an electric motor/generator then you now have the opportunity to match the compressor to the peak efficiency point using the electric motor when insufficient exhaust is available or when there is too much gas, to absorb the excess power and feed some of it back into the battery storage system. Either way, the compressor can be redesigned to operate at a more efficient point in its range than would otherwise be the case, producing the minimum heating to the engine intake air and resulting in smaller intercoolers and a more efficient vehicle aerodynamic package.

So not only are the new-for-2014 direct injected engines producing impressive fuel economy, the opportunities available in powering the compressor using an electric motor can make the overall engine vehicle package even more efficient.

Fig. 1 - Typical turbocharger maps: a) conventional wastegated approach; and b) using an electric motor/generator unit to give higher compression efficiency

Written by John Coxon

The reason for this unusual choice was that data obtained during track test had indicated the possibility that normalised downforce levels fell when the vehicle was decelerating. In particular, the team thought it was possible that the normalised downforce was declining because of the development of a boundary layer at the rear wing as the wake from the rear wing overtook the wing section as the car decelerated. The team’s then current simulation methods could not be relied on to accurately predict such subtle transient flows, so they decided to use a full-sized rear wing in a water towing tank. This would allow analysis of the occurrence, or non-occurrence, of flow separation and the changes in loadings as the vehicle was decelerated.

The most important factor in such a test was to account for the differing densities of air and water. The key benefit of such a test is the fact that water’s higher density effectively allows flows to be simulated in slow motion. Roughly speaking, for the same dynamic pressure across the wing, the speed of water flow over the wing element need only be 1/30th of that if it were in air. Provided the differing factors such as viscosity are properly accounted for – the acceleration rate needed to generate representative forces were about 1/1000th of those in air – it is therefore feasible to collect data in a water tank that can be directly related to operation in air.

Given this, it is possible to conduct slow-motion tests in water, and assess transient aerodynamic loads during deceleration – which are challenging to measure when the vehicle is actually running on a race track – to be measured with a high degree of accuracy. During Honda’s specific rear wing assessment programme, deceleration tests from 0.005-0.05 g and fixed-speed tests from 1.02-2.94 m/s (corresponding to 106-307 kph in air) were conducted.

The tank used for the test was 200 m long, 10 m wide and 5 m deep. The rear wing assembly was placed in the tank, inverted and attached to a six-component load cell, 1 m below the surface. To prevent waves forming on the surface of the water that could potentially skew the results, a flat acrylic plate was placed near the water surface.

Honda conducted tests with this system to assess the rear wing flows under deceleration, and was able to conclude that the flow was not reversing over the wing and that the wing was operating as it should at all times. The tests also showed that such methods were a useful additional testing tool, particularly for physically assessing hard-to-measure behaviours such as aero elasticity.

Whether other teams have undertaken such tests is not known, but it raises an interesting question – would such methods fall outside the CFD and wind tunnel limits set by the FIA, therefore providing a valuable extra source of unrestricted aerodynamic data?

Written by Lawrence Butcher

The applications for which these tool steels were developed means there is a range of materials with the ability to resist cracking or loss of strength at moderately elevated temperatures, or steels that can be hardened in air rather than oil or water, and by which method they can minimise distortion. Most tool steels are designed to be resistant to wear from a number of mechanisms – cutting tools need to resist abrasive and adhesive wear under intense sliding conditions with poor lubrication, while mould tools need to resist wear under the action of viscous, hot fluids flowing over their surfaces.

The combination of wear resistance and high fatigue strength, along with a degree of temperature resistance, makes some tools steels attractive candidates for manufacturing race engine components. This is often not a trivial undertaking, as the highly alloyed nature of these steels means the heat treatment processes involved are very specialised. Many tool steels require double and even triple tempering steps in order to gain the full benefit of their enhanced properties, and some steels also incorporate cryogenic treatments to fully transform their structures. The benefits of using the materials therefore needs to be substantial.

Tool steel camshafts are specified where a combination of high stress and endurance is required. Some also make good candidate materials for camshafts coated with DLC, as they do not to soften at the temperatures used during the coating process. As we might expect, tool steels are also sometimes used for cam followers.

Continuing with valvetrains, several suppliers specify tool steels for pushrods used in overhead valve race engines, while others who use tool steel ends fitted to pushrods produced from more conventional steels.

Gears for pump and camshaft drives are sometimes also made from tool steels. Traditionally these gears are made from carburised steels, but the carburising process (also known as case hardening) often has the disadvantage of introducing significant distortion. There is often very little difference in cost between tool steel and carburised gears made in small batches.

Tool steels are sometimes used for piston pins, and again we see that the materials they replace are often those where carburising or nitriding has been used previously.

A number of tool steels are used where high-strength fasteners are used, and con rod bolts are sometimes specified in tool steels such as H13.

Some tool steels, especially powder metallurgy types, can be so highly alloyed that their elastic moduli are significantly increased relative to traditional steels, combined with a reduced density. Several of them show a 10% increase in modulus, and I have seen at least one which has a specific modulus (elastic modulus divided by density) that is 20% higher than a typical steel. Increased stiffness is very attractive to design and development engineers, especially where valvetrain and cranktrain components are concerned.

Written by Wayne Ward

All sorts of schemes were considered, from conventional electric hybrids to flywheels and pneumatic systems. Eventually, everyone opted to run an electric system, although more than one team seriously investigated alternatives.

High-speed flywheels often have high energy densities, but have to run in a vacuum if frictional losses aren’t to be too great. The problem comes in transferring the energy out of the vacuum chamber and to a device such as a constantly variable transmission, which allows the energy to be smoothly deployed for propulsion. There are a few alternatives to this. The two commercially successful options, both initially developed for motorsport, are now both finding a wide range of applications including racing, advanced prototypes for mainstream automotive companies, and notably on public transport.

One solution is a special type of shaft seal, developed by a British company based at the Silverstone race circuit. Although it develops hybrid systems, it might be argued that its ingenious seal is its real treasure. It is simple in principle and allows the vacuum flywheel chamber to suffer very little leakage, so the vacuum is easily maintained with a very small pump that needs to run only rarely.

The second option, which has been used very successfully in endurance racing, is to run the flywheel as an integral part of an electric motor. Energy is stored and recovered electrically, therefore a high-speed rotating shaft does not need to cross the boundary between the vacuum chamber and the outside world.

There are other, less well-developed options that have yet to be successfully deployed in racing. One of these is magnetic gearing, where there is no need for a physical coupling between the shaft in the vacuum chamber and the output shaft, which runs in ambient conditions.

There is one definite advantages to flywheel hybrid systems, whether they are fully mechanical or electro-mechanical, and that is the fact that the storage medium is not a battery. The flywheels used in motor racing and for automotive hybrid development are made from simple materials that are well understood, namely carbon fibre-reinforced polymer composites and steel.

What is more, they are not prey to the various maladies that batteries are known to suffer from, such as finite lifetime, an inability to work over the full charge-discharge range without suffering shortened life or the ‘thermal runaway’ events that sometimes make the news when a lithium-ion battery goes wrong. On the other hand, with electrical systems nobody needs a patent to exploit them, and the technology is well understood by many companies.

Written by Wayne Ward

Although in the past Formula One engines have used rolling element bearings for applications such as the main and rod bearings, in recent times plain journal-type bearings have been the favoured solution. One area that Honda focused on with its bearing developments was the con rod big-end bearings. In physical terms, these were similar in size to those one would expect to find on a mass-production engine of 600 cc or so; however, the loads they experience are substantially greater. According to data from the bearing development programme, Honda showed that a standard production bearing can expect to experience loads in the region of 20 kN vertically and 5 kN horizontally. By contrast, the Formula One rod bearing saw loads of 50 kN and 20 kN respectively.

As engine speeds rose throughout the first decade of the 21st century, and regulations demanded longer service lives from power units, Honda began to find that its existing bearing solutions were not up to the task, and occurrences of bearing damage or failure started to become common. This led the team to investigate new bearing materials and designs. The solution was a move to a silicon-bronze bearing material, instead of the copper-steel bi-metal bearing type it had been using.

The existing bearings were of quite traditional construction, with a steel backing supporting a copper-lead intermediate layer that was topped with a thin coating of an alloy containing lead, copper and silicon. This bearing make-up provided low friction, but could not withstand the high contact pressures of the Formula One application and could not effectively dissipate the high levels of heat built up under running conditions.

The silicon-bronze bearing, however, was constructed without a steel backing, consisting instead simply of a silicon-bronze lining coated with a thin layer of lead-indium. While having marginally lower ‘slideability’ and a lower level of heat dissipation than the pure copper material, it provided a bearing shell that was stronger in all respects than the steel-copper item. Also, the heat transfer rate of the whole bearing assembly was higher than the copper-steel item, as the steel – which has relatively poor thermal conductivity – was removed from the equation. 

The results of using the new material were impressive: its greater strength and heat dissipation characteristics allowed lower-viscosity oil to be used, reducing windage losses. More important, bearing failures became rare, allowing the engines to exceed the regulation-imposed working life of 1500 km. 

Written by Lawrence Butcher

The primary goal of any camshaft though is to assist the opening and subsequent closing of the valves in the shortest space of time, to ensure the greatest flow of air into the engine in the time available. In direct-acting tappet designs the velocity of the valve is limited by the diameter of the rotating follower, while the acceleration is limited by the forces in the system and ultimately the strength of the spring with which to slow the valve down again as it reaches full lift.

At full lift of course the situation changes, and suddenly the issue is likely to be one of Hertzian stress just below the surface on the camshaft nose. For the return journey back to its seat, for many years the profile would have been a simple reflection of the opening phase, but of late, with the widespread availability of cam design software, the complex mathematics involved is no longer an issue. In the distant past, crunching all the data to develop the lift, velocity and accelerations (and possibly even jerk if you were keen) and getting them to match at each node, would simply have little or no time – let alone the will – to design a different closing profile. The tendency therefore was to repeat the opening flank but in reverse.  Ensuring the valve landed gently back onto its seat was, however, often a problem.

But having designed the cam motion as above, the great concern now is to ensure that, with modern compact combustion chambers and large valve lift and diameters valves, the timing is optimally set to give maximum power without valve-to-piston contact. At this point I am reminded of a conversation with a championship-winning engine builder going back to the days before ‘crate’ engines. In those days, even though the series engine regulations were very restrictive, the camshaft timing relative to the crankshaft was still unregulated. Naturally engine builders do what they invariably do and, having experimented with all the normal engine ‘tweaks’, this builder resorted to altering the camshaft timing, particularly that of the intake cam. The engine already had valve-shaped cut-outs in the piston which, under the engine regulations, could not be altered, but testing had revealed that the engine performance clearly increased with advanced camshaft timing. The question was: did it go on climbing into the region where the valve might hit the piston?

Finally, and saying a short prayer as he did so, the builder advanced the cam to the point when it was just about touching the piston at top dead centre and then, with fingers crossed, ran the engine again through another power curve. The fact that the engine survived is a matter of record, and with it too the marginal increase in top-end performance such a tweak produced. Unfortunately this was at the expense of a slight drop in maximum torque at a lower speed and so – both to sleep at night and preserve his customer’s championship lead at the time – the decision was taken to retard the cam back to its former position.

The interesting thing was that, after stripping the engine, a clear mark remained on the top of the piston where the valve had just about been in contact with it – not quite enough to cause mayhem but in reality close enough to remove the carbon from it, leaving a patch of almost clear aluminium.

Now that’s what I call optimal cam timing!

Fig. 1 - Setting valve lash can sometimes be critical

Written by John Coxon

I have had some involvement in motorsport hybrid systems over the past 15 years, some of it on the Panoz Q9, some of it on the KERS systems in Formula One, and some on the early development phases of the current Formula One energy recovery systems. The march of technology has been relentless and impressive, with each iteration showing an increase in performance or a decrease in size; it’s just a shame that those ‘outside the box’ aren’t able to get an appreciation for the dramatic progress which has taken place. As with personal computing, for example, hybrid systems benefit from the miniaturisation and tighter packaging of components.

The problem with the increasingly tight packaging of high-voltage components though comes when we have components working at different voltages getting too close together. The effects of creepage and clearance have been discussed previously in respect of fasteners, but there are other components that absolutely must be metallic if they are to function correctly: one example here might be shields to prevent the effects of electromagnetic interference. In the same way that the ‘Faraday cage’ effect that shields the occupants of a car from lightning, EMC (electro-magnetic compatibility) shielding protects electronics from the effects of interference which might, for instance, be the result of having electronics packaged close to powerful electric motors, where fields are being created and then collapsing rapidly as the motor is used to generate torque or harvest energy.

Plasma and thermal spray processes can be used to help create effective shields. One way to do this is to spray an electrically conducting shield (commonly sheet metal) with an insulating material. The insulation means the shield can then be placed very close to conductors without providing a path to earth or between two other components working at different voltages.

Another approach, which can work out much lighter, is to use an electrical insulator as the substrate for a shield, with the shield being formed by a sprayed coating of a metal – typically something like aluminium, which itself can be over-sprayed with an insulating ceramic or polymer. In order to provide the necessary shielding, very little thickness of aluminium is required, and the substrate can easily be made stiff, especially if it is a moulded composite component. If we try to produce the same effect with a metallic shield, we need to resort to expensive press tooling to form a stiff shape, whereas a simple machined mould for a composite tool can be made pretty quickly these days.

It is possible to incorporate EMC shielding based on thermal/plasma sprayed coatings into composite outer cases rather than using separate shields. Again, a thin metallic coating is sprayed directly onto the casing, and this may or may not be over-sprayed with an insulator.

Written by Wayne Ward

Another four-cylinder motorcycle engine, although not a race engine, also had an unusual number of con rods to control its pistons. The Wooler had a single-throw crankshaft, a single primary con rod and four secondary con rods, although the primary rod was not actually connected directly to the pistons. Whether we consider this engine to have one con rod or five, it is certainly a novel concept. Fig. 1 shows an actual Wooler engine while Fig. 2 is a cutaway drawing of it.

The primary con rod, connected to the crankshaft, actuates a lever, causing the actuation point to move back and forth along an arc. The lever is connected to a further lever to which four secondary rods are attached, which move the pistons back and forth in the bores. The pistons are arranged in pairs above each other, with two opposing banks of cylinders. The engine was arranged with the cylinders on each bank above each other and these cylinders above the crankshaft,  making the engine pretty tall. The images here show the layout of the engine, which is difficult to describe with words alone. The lubrication of the cranktrain would be problematic, as only the crankshaft end of the primary rod is in constant motion – the remaining pivot points would all experience intermittent motion.

The Wooler’s cranktrain is a complex mechanism, and is perhaps not a pretty packaging concept. The connection between crankshaft and pistons is not very stiff, and there are more moving components than are strictly necessary. All of this means we are unlikely to see anything like the 1950s Wooler 500 cc motorcycle return to the roads, and we can be almost certain that we won’t see its like on a racetrack.

However, as an unusual mechanism and use of con rods, it has been worthy of this brief examination. It seems to be a complex solution to a problem that didn't exist: there were a number of four-cylinder motorcycle engines of the same capacity which worked perfectly well with more conventional layouts although, at the time, single- and two-cylinder motorcycles were definitely the norm for road bikes as well as many racing bikes.

Fig. 1 - The Wooler engine, showing the arrangement of the primary and secondary con rods

Fig. 2 - Cutaway drawing of the engine, revealing more details of the packaging of the other components 

Written by Wayne Ward

These days of course we are a lot more enlightened, and the realisation that the position of the radiator and how it is installed – and not just its overall size and thickness – can make a great difference to a vehicle’s overall performance. That means carefully ducting just enough cooling air into and through the radiator core with the minimum of aerodynamic losses, something that few vehicle modifiers or special builders fully understand or manage.

For any given heat exchanger the rate of heat dissipated is proportional to the mean temperature difference between the radiating surface and the airstream, as well as (airstream velocity) ^0.6 and (air volumetric flow rate)^0.8 passing through it. This means that for a given radiator the thermal efficiency and internal drag are both reduced by slowing the velocity of air passing through the core. High-energy air passing into the ducting thereafter needs to be slowed down progressively before it gets to the core. At the core the velocity energy of the incoming air is converted to pressure energy which, having absorbed as much heat energy as it can, needs to be accelerated away back out into the airstream as quickly as possible. A divergent nozzle should be used to minimise any further aerodynamic losses.

In a number of branches of motorsport, however, many competitors choose to dispense with the radiator altogether, thinking that the reduction in aerodynamic drag will result in reduced elapsed times. In hillclimbs for instance, dispensing with the radiator can save valuable weight, but with the engine cooling jacket overheating, by the end of the climb this can cause considerable loss of power, not to say the possibility of the engine running into detonation as the engine coolant temperature climbs.

In drag racing though, competitors often to go to extremes, preferring sometimes to dispense with the water jacket altogether, or some even fill the void caused by the missing coolant with concrete or a thermosetting resin. This, it is said, is designed to stiffen the stock cylinder block and resist the prodigious torques often delivered by such engines. The Top Fuel boys also machine their cylinder heads direct from aluminium billet, omitting any hint of a coolant jacket. Desperate indeed but when you consider that the fuel they use – a mixture of nitromethane and methanol – has such a high latent heat of vaporisation that for short bursts of 6-7 s (the time taken to complete the course) the risk of seizure is minimal. And when engines are routinely rebuilt between runs, such abuse is easily justified in terms of run times.

For more practical sustainable running for the rest of us, however, the radiator installation needs to be carefully thought out.

Fig. 1 - 1965 McLaren M6A radiator exit duct

Written by John Coxon

However, the Norton race bikes were anything but. They were incredibly fast, once the engines ‘picked their feet up’, and I remember watching them reel in the faster-starting opposition at Mallory Park in Leicestershire, England, in the late 1980s. These engines won British Superbike and Formula One championships and an Isle of Man TT race. There was even special dispensation given for the machines to compete in the 500 cc Grand Prix series in 1991 and beyond.

For every supporter, however, there was someone vehemently opposed to the Nortons, saying that their 588 cc capacity was nonsense and that they were actually twice as large. That depends though on how the engine is judged to operate. If it is classed as a two-stroke, then 588 cc is probably correct, as the engine draws in the same amount of air as a 588 cc two-stroke. You see what is coming next – the engine also draws in the same amount of air as an 1176 cc four-stroke, but it is neither, so the debate continues to rage.

In addition to the discussion over capacity, there is some debate among engineers as to the correct name for the Wankel’s crankshaft. Thankfully, as with the conventional crankshaft, engine swept volume – that is, displacement – is directly proportional to the throw of the crankshaft. The shafts, compared to those in a reciprocating engine, use much lower throws; in our usual parlance we might say they have a high degree of overlap.  There is no requirement to provide thrust surfaces on the eccentrics (the equivalent of crankpins) as the thrust of the rotors is taken by the housings. There are not the large inertia forces to cope with that we have in the reciprocating engine, and with a large overlap the stresses on the bearings are modest.

Where more than two rotors are used, the crankshaft/eccentric shaft needs to be built up in stages. Each additional rotor requires an eccentric sleeve extension to be added. There have been a number of three and four-rotor engines used in racing – the Le Mans-winning Mazda 787 for example had a four-rotor engine called the R26B, and the extra rotor sections are keyed to the central section, with one fitted at each end in the case of the four-rotor design. Lubrication of the bearings was a simple matter, with eccentrics and main bearings fed from a large drilling running along the axis of the R26B’s crankshaft.

Rotary engines were always rare in racing. They were fast, but their notorious thirst for fuel meant they needed a fuel tank for many race series. Where air restrictors are used to control output, rotaries require a significantly larger restrictor area in order to be competitive. Mazda found racing success some years ago with a rotary engine, but nobody is now seriously considering rotary racers, despite a short-lived attempt by Norton a few years ago to repeat its one-off rotary TT success.

Fig. 1 - The late Steve Hislop won an Isle of Man TT on a Norton with a twin-rotor engine

Fig. 2 - The displacement of the rotary engine is directly proportional to the ‘throw’ of the crankshaft, but beyond this, engineers fail to agree unanimously on engine capacity. This example is from a two-rotor engine

Written by Wayne Ward

At the time we didn’t fully appreciate the reliability bit, but anyone who owns a classic vehicle from the period will know how thick and heavy many of the wiring looms were. Little did we realise at the time how important the concept of multiplexing would become, and how just about every single vehicle (including race vehicles) made in the 21st century would rely on the technology.

These days of course, more and more electrical/electronic functions are being put into the car, most of which require some form of control and many of which require some form of local intelligence. One of the earliest protocols devised to transfer serial data between systems is known as CAN (Controller Area Network) or more exactly, the CAN bus, and it is still the most popular. Essentially it is a pair of twisted wires replacing up to 100 or more ‘normal’ wires, with control devices connected in a daisy-chain fashion.

Designed to handle short messages up to 8 bytes in length at rates of up to 1 Mbit/s, the protocol uses a method known as Carrier Sense Multiple Access (CSMA) to transmit the data frames, allowing each control unit or node in the system to transmit the data in frames at any time. The data will include a node address to which the message is to be delivered (a sort of mail post or zip code) as well as the message itself. Passed between nodes in turn, if the postcode does not match that of the node then the message is simply ignored and passed on. Should two or more messages be sent at the same time, a collision will be detected and the message with a higher priority indicator will continue, with the one of lower priority repeated later.

Although satisfactory for most powertrain applications, for x-by-wire safety-critical systems –braking and throttle – another and more powerful system is being touted. Known as FlexRay and similar to CAN, this system is faster (up to 10 Mbit/s) and can handle up to 254 bytes of data in a frame. Wired in much the same way as CAN, FlexRay can be configured if desired to support two separate cable paths, giving the opportunity to transmit the same, repeated data to provide safety-critical redundancy in the system or a completely new set of data to increase the overall throughput should better control be desired.

Whereas with CAN frames vary in length, for FlexRay the frames are split into two, with the first portion the same for all. Since these occur at well defined times in the message they can be used to synchronise the execution of the message in the multiple control units at the individual nodes. Referred to as Time Division Multiple Access (TDMA), each frame is assigned a dedicated time slot in the signal, and since no two frames are assigned the same slot in time, collisions between messages are impossible.

Currently more expensive than CAN, FlexRay’s supporters claim that with wider adoption, prices will fall. But as brake-by-wire systems become more integrated, particularly into regenerative hybrid applications, perhaps this technology will be a better option than just CAN.

And for our door application? Well, designed as a low-cost option for applications not requiring the same degree of control, we have LIN – Local Interactive Network. But that’s another story.

Fig. 1 - The fixed-length FlexRay message

Written by John Coxon

Other than these, and mainly for manufacturing and serviceability reasons, the major engine parts are designed as we know them today, with separate components connected using bolts and sealed with one or more gaskets. As these designs became standard practice, the development of gasket materials started. Initially, the loading on the gaskets was rather low because of moderate power output and limited internal pressures, so gasket design was focused on sealing two or three mating components with only small machining defects, porosities and other imperfections. This is why early gaskets consisted of materials that yielded to some extent, enabling them to deform and fill those imperfections.

As engine temperatures and pressures increased though, these gaskets showed significant failure rates, typically leading to blown head gaskets and/or leaking exhaust manifolds. As early adopters of new concepts, Formula One engineers switched to copper or steel ring head gaskets, which showed to be a significant improvement for sealing the combustion chamber. Soon after that, these gaskets were introduced for production cars as well, where additionally, for ease of assembly, they became integrated into cylinder head gaskets.

Later, the head gasket material changed to single-layer steel. This was a major improvement over earlier materials, which often contained asbestos, a now forbidden material. Single-layer steel gaskets provide significant better mechanical strength as well as the ability to cope better with micro-movements of the mating surfaces. With earlier materials these movements could lead to gasket damage and possibly cracks in the gasket material.

As one of the later steps in the development, multi-layer steel (MLS) gaskets were introduced, with so-called ‘beads’ to increase local sealing capability. To get a feel for their dimensions, the bead shapes are typically up to about 0.4 mm high, depending on size and application, where the actual layer thickness is even less (about 0.25 mm). The top and bottom layers are often coated to reduce friction, in case micro-movements occur.

For  exhausts in particular, given their extremely high temperatures, MLS gaskets have vastly improved the sealing capability, although the actual sealing geometry – as in the bead-deformed zones – remains the sensitive area of the gasket due to relaxation of the material under high temperatures.

The basis of an MLS gasket are multiple layers of steel, of which one or more layers have pressed beads, being positioned on top of each other. When the layers are being assembled and the bolts are being torqued, the beads deform, leading to elevated local pressures in the beads, the actual sealing location. These beads will deform partly plastic and partly elastic, meaning they can adapt to temperature and load fluctuations (as long as the fluctuations are not larger than the elastic compression of the bead).

What was occasionally seen however was that the beads were compressed more plastically than intended, reducing the remaining elasticity in the gasket beads, leading to too little reserve against temperature and load fluctuations. To improve this, a so-called ‘stopper’ layer was introduced. The thickness of this layer – which is also the third or middle layer of the MLS gasket – determines the amount of maximum deformation of the beads of the upper and lower layers, leading to better control over the elastic deformation of the beads. This can be controlled by the thickness of this middle layer.

If a further, more local optimisation of the bead deformation needs to be achieved, the stopper or middle layer can also be designed with a certain topography rather than just being flat. For example, it might be desirable that the beads have more elastic deformation between two bolts, giving a lower clamping load with increased bolt spacing.

In general there are no limits to how this stopper or middle layer can be shaped. That means a very homogeneous contact pressure distribution can be achieved, even with flat gaskets and significant bolt spans.

Fig. 1 - Multi-layer steel gasket with stopper element seen between the two outer layers

Written by Dieter van der Put

Many of the national championships and the World Touring Car series are based on cars that are available with a 2.0 litre turbocharged engine. As this is a popular choice for buyers of family cars in Europe, this is a sensible choice. In Australia, for example, their ‘touring car’ is a 5.0 litre naturally aspirated V8, while in Germany, the national motor manufacturers fight it out among themselves with 4.0 litre naturally aspirated V8 engines. In Japan, there have also been cars with V8s, some of which were bespoke V8 race engines based on endurance engines competing at Le Mans. The Vemac from the early 2000s, for example, used a Zytek V8.

The different race series have had very differing demands in terms of exhausts, not only in terms of layout but also such aspects as the physical size and operating temperatures. The turbocharged engines which are used in WTCC and Japanese SuperGT, for example, will run higher exhaust gas temperatures, for example, than those in naturally aspirated engines.

Even where engine regulations are superficially similar, there may be large disparities in engine output and therefore large differences in the effect on exhaust systems. Many touring car series are powered by engines that are limited in terms of power by intake air restrictors or fuel flow meters. Both devices have the same effect – they limit power by limiting engine speed. The Japanese SuperGT championship, which uses a fuel-flow limit, has 2.0 litre turbocharged engines producing around 500 bhp, while the WTCC has an air intake restrictor applied to the same type of engine, but with the resulting power output thought to be around 350 bhp.

The difference in maximum exhaust gas mass flow is proportional to the power output, so there may be noticeable differences in exhaust design in order to maintain performance. In particular, packaging the exhaust so as to avoid flow loss through flow separation from the ‘inside’ of bends in pipes might require different pipe bend centreline radii to be used. Apart from this difference, it wouldn’t be a surprise to find that different primary pipe diameters are used. To improve transient engine response, it is likely that any series using turbocharged engines will probably see teams running some form of thermal insulation on the primary pipes, which may be anything from a ceramic coating to a formed metal enclosure.

Such thermal insulation around the exhaust primary pipes is not necessary for naturally aspirated engines, although some form of exhaust insulation might be required in order to reduce heat transfer to adjacent components or to the driver compartment.

Written by Wayne Ward

It is possible to specify fasteners with a dry threadlock compound applied. In such compounds, an adhesive is encapsulated in a resin binder, typically epoxy. The encapsulated adhesive is not released until sufficient pressure is applied, and this typically happens as the pre-load is developed. The prevailing torque during tightening – that is, the extra torque due to friction – for this type of threadlocker is due simply to the increased drag from the epoxy. Unlike wet threadlockers, there is no torque developed from an unknown and increasing amount of threadlocking compound beginning to cure and set.

These micro-encapsulated adhesive threadlocking systems are available in a variety of specifications, depending on the application and the service temperature, and are applied over a specified number of threads. The recommendation is that they are not re-used, as the holding power on the second and subsequent uses is a function only of the remaining adhesives after the first use. Some compounds are designed to provide a seal in addition to locking the thread.

Mechanical thread locking can take a number of forms, but a convenient starting point is the type which is most similar to the dry threadlocking compounds. It is also possible to specify fasteners that have a number of threads coated with a thin layer or patch of polymer, which acts to put the fastener into slight interference in its hole. There are also options as to the amount of coverage, which will dictate the prevailing torque measured on installation. Nylon is typically used as the locking material.

Continuing with polymeric locking elements, some specialised fasteners are supplied with a polymer bung inserted radially into the thread. As with the previous option of a nylon patch, any prevailing torque is constant after initial compression of the polymer element.

Interference-fit threads, where the male and female components are in radial interference, are not commonly used owing to the unpredictability of the prevailing torque and the possibility of thread damage. Small differences in the amount of interference can make large differences in prevailing torque; however, a degree of axial interference achieved through the use of deliberately mismatched thread pitch is sometimes used on very critical high-strength fasteners. This provides a degree of protection against loosening, and has been shown to improve the distribution of load between the individual threads and to markedly reduce the degree of stress concentration at the first engaged thread.

Written by Wayne Ward

The fixed-jet carburettor works by pulling fuel from a reservoir in response to a pressure signal from the venturi in the engine intake air. The depression thus created causes fuel to flow from the fuel reservoir in the carburettor while at the same time encouraging a small flow of air at atmospheric pressure to mix with the fuel. The fuel is metered through the main jet while the air is controlled through what is generally called the ‘air correction jet’. Somewhere in between, the fuel and air are intermixed to form an emulsion – a fine dispersant of the air inside the fuel. This assists the atomisation of the fuel as it eventually enters the engine airstream.

At times of low fuel demand, the air drawn in is very small and the fuel flow regulated by the main fuel jet will contain little in the way of an emulsion. With the throttle only slightly open, drops of liquid fuel will land on the throttle plate and atomise thereafter into the air. However, with increasing engine speed or load, as the fuel demand increases then the restriction of the main jet causes an increased depression in the air correction circuit, and this air passing through the emulsion tube effectively leans off the mixture: the higher the engine speed or load, the greater this air correction effect. Metering the fuel and the air is one thing, but mixing it and presenting it in a form so it readily mixes with the intake air is quite another. This is the function of the emulsion tube.

The essential points to remember are that the fuel passes around the outside of the emulsion tube at its base while air, coming from the top, comes down the inside of the tube and is extracted through a series of drilled holes of varying sizes and heights to mix with the fuel on the outside. When the engine is stationary, the fuel level will be the same as that in the float chamber, and will come to a level within the emulsion tube. As soon as fuel is demanded, the fuel level will drop in the chamber, uncovering more holes that will allow more air to mix, thus leaning the mixture.

As well as altering the size and height of these holes, it is also possible to alter the diameter and thickness of the emulsion tube in its cavity within the body of the carburettor. This acts as a restriction to the flow of fuel which, when all fashioned together, can tailor the flow of fuel more or less precisely to that required by the engine throughout its operating map. Under wide-open throttle acceleration the emulsion tube plays little part since the overriding effect is that of the main and air correction jet. At part-throttle however, when the quality of the fuel atomisation arguably has to be significantly better, the emulsion tube can be considered more critical. Understanding this and being able to apply it in practice is therefore one of the dying ‘black arts’.

Setting up a fixed-jet carburettor may be a long and often confusing business, but when the vehicle starts and drives smoothly and progressively, the satisfaction is immeasurable.

Fig. 1 - Fuel enters through the main jet at the bottom and flows out of the large holes just above the base. Meanwhile, air comes in through the air correction jet at the top, coming out into the fuel through the small holes midway down

Fig. 2 - Emulsion tube from a fixed-jet Weber DCOE carburettor

Written by John Coxon

Although rare back in 2005, variable geometry intake manifold systems for Formula One engines were relatively simple and generally fell into one of two formats. The first was a two-position device that moved in a straight line up and down inside the intake plenum to give two effectively differing lengths of intake tract. Comparatively simple in its concept, its limitations were always the point at which the switchover was to take place and the speed with which this would happen.

The second system was a development of the first, and consisted of a pair of concentric telescopic tubes running inside one another. In response to a speed signal the tubes either expanded or collapsed to give an infinitely variable length trumpet. Potentially more controllable since instantaneous switching wasn’t the issue, the downside here was that in spraying fuel down the intake ports (engines were port injected in those days), as the engine speed increased and the telescopic tubes collapsed then any fuel attached to the wall of the intake would be scraped off and be drawn into the engine, creating a richer fuel-air mixture than the one mapped; a momentary fall in power could result. With modern engine control systems this could be combatted to a certain extent in software but back then, according to reports, the effect on outright performance was noticeable.

Modern Formula One engines are of course directly injected, so the problem of stray fuel altering the carefully metered fuelling is now non-existent. Freed up from this need though, what might the variable geometry intake manifold of 2015 look like?

Of course we could go back to a development of the first system above from about ten years ago. This would work quite well but might increase the height of the engine installation to ensure that, as the intake runner length increased the proximity of the top of the airbox would not inadvertently restrict the air flow Another way might be to introduce a system of two or even three stages using an arrangement of flap valves inside a compact V6 intake manifold, similar to those used in a number of production vehicles from about 15 years or so ago. With an array of one or two sets of flap valves, two or three different intake runner lengths could be accommodated within the confines of the engine vee.

For my part, I thought I might want to examine a design based on the combination of the two – a simple continuous collapsible tube which in the shape of an arc could be moved by either electrical or hydraulic means. Not of much interest to the roadcar business perhaps, and therefore possibly not strictly roadcar-relevant as Formula One is supposed to be these days, but such a system could minimise the height of the airbox if this was indeed and considered an issue. It might be fanciful, and it might be difficult to make – and perhaps take a bit of development – but isn’t that what Formula One is all about?

The real question though is that with the availability of turbocharging and no restrictions on the level of manifold boost, in terms of outright performance is there any significant advantage to a variable intake system in place of simply more boost?

Fig. 1 - Ideas on variable intake manifolds

Written by John Coxon

As its name suggests, the primary role of the scavenge system is to scavenge oil from the engine and pump it to the oil tank, ready to be pumped back into the engine by the pressure pump. In most dry-sump systems, particularly those that are additions to previously wet-sump engines, one pump body will take care of both pressure and scavenge operations. From a packaging perspective, this can be less than ideal, particularly within the tight confines of a Formula One engine. These engines, whether they be the previous generation of V8s or the new V6s, therefore tend to have separate pumps for scavenge and feed duties.

In the first iterations of Honda’s V10s the system relied on a single-stage scavenge pump. This drew oil from a sump pan that was split into chambers to reduce pumping losses associated with the movement of air and blow-by gases from cylinder to cylinder, caused by the rise and fall of the pistons. In later iterations of the V10, and then the V8, Honda moved to a multiple scavenge pump set-up as this was shown to provide a more efficient solution, scavenging more oil for less power consumption.

In effect this meant that each sump chamber had its own dedicated scavenge pump, which then fed into a common centrifugal oil-air separator before feeding into the oil tank. The layout Honda settled on until the end of its involvement with Formula One featured five scavenge pumps located on the right-hand side of the crankcase and a single oil feed pump on the left-hand side of the front of the motor.

On particular problem the team encountered during the development of the scavenge system was ensuring the consistent presence of oil at the pump inlets. Using the analogy of a straw, if the end of the straw is not completely immersed in liquid then it is almost impossible to suck the liquid up. The same applies to the inlets of the scavenge pumps, which have to be completely immersed in oil to operate.

Initially, Honda’s scavenge pump relied on the volume of oil displaced by the crank and rod rotating to fill the pump inlet. Unfortunately this approach could not guarantee a consistent supply, particularly under cornering where the g-forces were such that they pushed the oil away from the inlet. To combat this, Honda incorporated an oil trap into the inlet of the pump. This took the form of a small cavity just next to the pump inlet that acted as a reservoir that was filled by the oil thrown from the rotating components, ensuring a constant supply regardless of the g-forces.

Interestingly, owing to high operating pressures of 20-40 kPa, Honda also opted for a compression-type pump design rather than a positive-displacement pump for the scavenge system, the reason being the increase in pumping efficiency such a design offered. However, it did mean having to include a pressure relief system in each scavenge. This was because the pumps were specified to transport the light oil-gas mix that the crankcase contained; if they pumped no aerated oil, such as when the engine was initially started, the pressure increase caused by the higher-viscosity fluid could have caused damage.

As with the feed pump system examined last month, the level of development that went into optimising this relatively mundane engine subsystem is impressive, and highlights the level of refinement necessary in engines such as those in Formula One to ensure optimum performance and reliable operation.

Written by Lawrence Butcher

In many instances, piston pins are kept in their intended position with round-wire clips of varying design. Some are free to rotate within their grooves, while others are designed with features that locate in an appropriate hole or slot in the piston. For racing use, round-wire circlips are usually manufactured from a high-strength wire, and these have been covered in another previous article.

However, as usual, there are alternatives, and the Spirolox clip (often referred to as Spiralock clips or Spiral locks) was mentioned in the article on alternatives to round-wire clips, but not discussed. There are two types – single and dual coil. The single coil is essentially a circlip formed from a small, flat bar, rather than round wire. However, the double-coil type is often used for more demanding applications. Compared to a round-wire clip, the beam section of the Spirolox type gives the single-coil clip much greater stiffness, owing to a greater moment of inertia. It is the double-coil type that is normally fitted in order to retain piston pins.

To ease fitting and help take up any axial clearance in the piston, the double coil is strained axially, so that the flat clip is opened up into a helix. This is then carefully fed into the groove, sometimes with a special tool but often only with fingers. Because the clip has been strained plastically, it retains some elasticity and therefore tries to resume its ‘expanded’ form, thus taking up any clearance in the groove. As this design of clip is flat on its outside diameter, it does not work in the same way as a round-wire clip, which centralises itself within its groove, which is also machined with a round cross-section.

It is common to find two of these clips on each side of the piston pin, although this choice is by no means universal. However, if the piston is provided with a groove designed for two clips to be used then two clips should be used in order to prevent excessive axial movement of the piston pin.

Compared to a round-wire circlip, the Spirolox clip has much more abutment area and bears against the end face of the piston pin. It is the combination of size and position of the circlip groove the chamfers that controls the maximum piston pin end-float where a round-wire clip is used, but this doesn’t apply with Spirolox clips, so the chamfers on the pin are solely for ease of fitting. During manufacture, it is much easier to control the length of a pin than to control the distance between gauge diameter on opposite ends of the pin.

Written by Wayne Ward

Although not widely used for this purpose, there are applications where precision pickling produces tight-tolerance final dimensions on components, owing partly to the simultaneous effects of improvement of surface finish (roughness reduction) and removal of burrs from production that would require ‘artisan’ – that is, manual and non-repeatable – intervention. Depending on the acid and the material being treated, pickling can produce a surface with high quality and low roughness. As the acid preferentially attacks and removes material with a high ratio of surface area to volume, it quickly removes undesired features such as burrs as well as peaks in the surface finish of the material.

However, while pickling or etching to a precise final dimension is not widely used, the general principle of using strong acids to remove material as a way of reducing the thickness of sheet materials can be used both on raw materials and finished components, especially fabricated parts. The selective pickling of thin fabricated assemblies can be accomplished by masking critical areas (typically welds) followed by immersion in a bath of acid so that the remaining unmasked areas are ‘eroded’ to the desired thickness.

The amount of time required depends on the alloy, the particular acid used and its strength and temperature. It is therefore necessary to carry out regular tests of the rate of material removal before use. As the cumulative effect of pickling/etching on the acid is to weaken it and reduce the rate of material removal, if these tests are neglected then you may find produce components that are oversize and/or overweight. The advantage of using acid pickling/etching is that materials that are too thin to weld reliably can be specified, so it is possible to fabricate components such as oil tanks and water tanks, for example, that are much lighter by etching down to the desired thickness after welding.

Pickling is also used to remove surface contamination from some components. For example, stainless steel or titanium fabrications can be pickled to remove traces of steel from their surface, which can cause problems in later processing or might provide an initiation site for a corrosion problem. In the same way, some castings are acid-etched to remove the surface layer, which can include some foreign material (casting sand or investment casting mould materials) that might be a fatigue crack initiation site.

This technique is likely to be used on titanium gearbox main-case castings, as found in Formula One for example. Ferrari pioneered the use of titanium for gearbox main cases, although this was as a fabricated assembly rather than a casting. Minardi used cast-titanium main cases from 2000 onwards, and the technique was quickly adopted by other teams.

The rate of material removal varies widely with material type and alloy, so care needs to be taken and sufficient data gathered before using the process. It should also be noted that, because material is preferentially removed where the ratio of surface area to volume is high, sharp external corners are likely to be removed. This may or may not be the desired effect.

Written by Wayne Ward

In ultrasonic testing, high-frequency sound waves are reflected from flaws in predictable ways, producing distinctive echo patterns that can be detected, displayed and recorded. Its ease of use and non-destructive nature of makes it a very useful tool for the quality control of engine and transmission components, particularly cast or fabricated components. In this month’s article we will take a closer look at the details behind it.

Ultrasonic testing relies on the fact that sound waves travelling through a medium will be reflected or transmitted in different ways if the composition of the medium varies. They can therefore be used to identify flaws or voids in materials. Using an ultrasound transducer to generate an ultrasonic sound wave, a wide range of materials can be tested for integrity.

There are two methods of receiving the reflected ultrasound waveform: reflection and attenuation. Using the reflection (or pulse-echo) method, a single transducer performs both the sending and receiving of the pulsed waves, as the process relies on the sound waves that are reflected back from the material being tested. The reflected ultrasound that is received by the transducer from an impervious obstacle such as the back wall of the object or an imperfection within it. These results are then displayed in the form of a signal with an amplitude representing the intensity of the reflection and the distance from the sensor, which is represented by the time difference between sending and receiving. As the transducer passes over a flaw, the signal displayed will change from that produced by homogenous material.

With the attenuation (or through-transmission) mode, a transmitter sends ultrasound through one surface and a separate receiver detects the amount that has reached it on another surface after travelling through the test sample. Imperfections or other conditions in the space between the transmitter and receiver reduce the amount of ultrasound transmitted, thus revealing their presence. This type of testing is used to check large-volume components.

There are several features of ultrasound testing that make it particularly attractive for use in motorsport. As mentioned, it is non-destructive, meaning valuable parts do not need to be chopped up to check their integrity. Ultrasonic testers are also portable, so they can be easily used trackside for checking components, and this portability means they can also be used to examine large assemblies. They can also be used for tasks ranging from checking welds to assessing castings for porosity. Overall, ultrasonic testing is an exceptionally useful technique that can provide an invaluable capability in any race ’shop.

Written by Lawrence Butcher

Materials for gears in general can be divided in two categories: metallic and non-metallic. Unsurprisingly, gears in racing transmissions fall into the first group. Although there is ongoing research into the potential uses of composite materials for gear construction, their application is as yet not truly feasible. The requirements for transmission gear materials are high surface hardness, good core toughness, fatigue strength for tooth bending, rolling contact fatigue resistance, and high density to resist pitting and sub-surface spalling during heavy use. The most common metals used here are wrought surface-hardening and through-hardening carbon steels.

The needs of motorsport and mass-production transmission manufacturers are broadly similar, but the very high loadings and quest for the smallest, lightest gears possible (not to mention greater freedom from cost and complexity constraints) means that the materials used for motorsport gear construction are subtly different from those found in the average high-performance roadcar.  

Surface-hardening steels are hardened to a relatively thin case depth and the various types include carburising, nitriding, and carbonitriding steels. Surface-hardening steels include plain carbon and alloy steels with a carbon content generally not exceeding 0.25% C.

Through-hardening steels can be comparatively shallow hardening or deep hardening, depending on their chemical composition and method of hardening. They include plain carbon and alloy steels with a carbon content ranging from 0.30 to about 0.55%. The mechanical properties can be tailored by varying the quantities of the allying elements and the heat treatment process: for example, the bending and surface hardness can be improved. Another example of such tailoring would be the addition of molybdenum to help reduce rolling contact friction. 

The highest grade of carburising steels tend to be found in motorsport gear applications, although such materials were often initially developed for other industrial sectors such as aerospace. Taking the gears used in a helicopter’s transmission as an example, these need to be exceptionally strong and resistant to fatigue, with the consequences of failure being far more serious than in a racecar. Also, the budgets available for aerospace development dwarf even the biggest racing operations and thus industries such as defence, aerospace and even OEM vehicle manufacturers have the resources to develop new high-performance materials that race teams do not. There are of course exceptions, and several manufacturers of racing gearboxes have commissioned bespoke steel blends to suit their specific applications.

One area in particular where steels used for motorsport and other high-performance applications differ from more run-of-the-mill materials is their ‘cleanliness’. The number and type of inclusions in steel billets destined for use as gears can have a major impact on ultimate fatigue resistance and strength, so the very best steels are smelted in a vacuum, where there is minimal opportunity for contamination of the metal. It is not unusual for very ‘clean’ steels to be vacuum melted up to three times, giving them a very consistent molecular structure but making them anything but cheap!

This is only a brief overview of the materials and requirements that need to be accounted for when specifying gears for use in racing transmissions, but in future articles we will revisit the subject to cover specific areas in greater detail.

Written by Lawrence Butcher

What we need is a material with temperature resistance, high thermal conductivity, thermal expansion which is close to that of the cylinder head and good mechanical properties, especially fatigue resistance. Often, as engineers, we find ourselves ‘painted into a corner’ in one of these areas. We may need higher thermal conductivity but can only find it in a material with lower strength, or we may find another characteristic that we like but find that the thermal expansion coefficient puts the cylinder head at risk due to high stresses. In order to solve another problem, we may need to lower stresses by widening the valve-to-seat contact, which can harm performance.

The traditional materials have been copper alloys, namely different types of bronzes. In recent years, beryllium-copper alloys have become a firm favourite; often we find a mix of two alloys in the same engine with one alloy – usually a high-strength type – specified for the inlet seats, and a different, lower strength but high thermal conductivity alloy used for the exhaust seats.

Sometimes, however, we find that we can’t get the seat material to live for long enough. The long-life engines, which once comprised only endurance racers but nowadays include series such as Formula One and MotoGP, may need a different class of material altogether. Powder-metal valve seats are based on a ‘pre-form’, which consists of a sintered metal (often steel) that is deliberately made porous. This is then infiltrated with an alloy that lends the structure stiffness and thermal conductivity. The infiltration alloy is generally a copper or bronze.

The thermal conductivity of the powder-metal seat material, compared to one of the normal bronze candidates, is compromised owing to the amount of material now displaced by the pre-form (which is of lower conductivity). However, because a significant proportion of its volume consists of a high-strength material, with increased heat resistance, the combined properties of the material mean its strength is markedly increased, as is its resistance to deform gradually at the higher end of the operating temperature range.

Such materials are essentially a type of metal-matrix composite (MMC) but in powder-metal valve seat materials, the reinforcement is in much greater proportion and of much greater size than in a traditional MMC. It is an unusual material in that the strengthening reinforcement and the matrix (if we wish to consider the softer, weaker material as the matrix) are both continuous structures, whereas traditional powder reinforcements in MMCs are designed to be discontinuous and evenly distributed within the matrix.

Written by Wayne Ward

However, because motorsport’s use of MMCs has only ever been a very small niche compared to other markets such as automotive development of brakes, aerospace and defence and so on, the development of MMC materials has not been affected to any great extent by our enforced lack of interest.

Many researchers in the field of MMC development are concentrating on metal-matrix nano-composites, sometimes referred to as MMnC materials. The reinforcement in MMCs can take one of three forms – continuous fibres, whiskers/short fibres or particulates.

The clue to the thrust of MMnC development activities lies in the name. The reinforcement particles in nano-composite materials are very much smaller than has customarily been used, and the results of doing so seem promising. The particulate size is not necessarily in the realm of single-digit nanometres, but the scales are much smaller than the so-called micro-scale composites, and there is certainly some work being done where nano-scale reinforcements are below 10 nanometres in size. However, people working on nano-composites are generally discussing MMCs which have particulate reinforcement that can be several hundred nanometres in size rather than multiple micrometres.

We hear a great deal about the possible applications of carbon nanotubes and how they might bring about a revolution in materials, and there are a lot of researchers working on carbon nanotube-reinforced materials, particularly based on aluminium and titanium matrices. Such materials are often denoted by the letters CNT, so for example you will find a number of technical papers by searching for ‘Al-CNT’. CNT materials look extremely promising, but it remains to be seen whether the much-vaunted step change in materials properties actually happens.

However, much of the research into metal-matrix nano-composites is based on smaller-scale reinforcement using ‘traditional’ MMC fillers such as titanium diboride (TiB₂), aluminium oxide (Al₂O₃) or silicon carbide (SiC), and these too are yielding improvements in mechanical properties such as strength and stiffness.  

There are some processing difficulties in dealing with very fine particulate reinforcements, such as the particulates not being dispersed evenly within the matrix and poor bonding between the matrix and reinforcement. Consequently there is a great deal of research being done on the processing of the materials. One reason that nano-composite materials aren’t more widely available is that the optimum processing methods and associated parameters have not yet been found. There are a number of liquid-state techniques, where the material is processed in its molten state, which show promise, but these often require some expensive secondary processing to achieve optimum properties.

Powder metallurgy methods are perhaps the closest to being perfected for commercial use. Here, the matrix and reinforcement are thoroughly mixed as finely divided powdered solids before being sintered under pressure, and there are commercially (though not widely) available aluminium nano-composites. Such materials have been used for engine components, and they offer distinct advantages for customers, not only in terms of improved properties but in the ease of manufacturing. Where micro-scale aluminium MMCs often required special cutting tools, aluminium nano-composites can be machined conventionally.

Written by Wayne Ward

First there is a motor/generator unit, which is used either as a propulsion motor to augment the engine’s torque or, in the case of purely electric vehicles, to provide all the motive effort. Then there is a battery, or possibly a supercapacitor, which is where the electrical energy is stored. It is possible to connect a motor to a battery without any other components, but this is generally not the case, especially not in automotive propulsion, where we require precise control. The third component, generally called the ‘power electronics’, carries out a number of very important functions.

The battery supplies a voltage and a direct current (dc); the voltage varies depending on a number of factors, as does the current. It is highly likely though that the propulsion motor is a multi-phase alternating current (ac) device, which is not compatible with a dc supply, so one of the important roles of the power electronics is to turn the ac output of the motor/generator unit, when it is acting as a generator, into dc, which can be fed to the battery. When the motor/generator is acting as a motor, the power electronics acts to convert the dc output of the battery to ac, switching it between phases very precisely so that the motor propels the vehicle forward with peak efficiency.

In the Formula One cars of 2014, the electric motors running at the same speed as the turbocharger; the speed at which the switching of current takes place is incredible, and any inaccuracy in its timing can mean a serious loss of power conversion efficiency. Where dc machinery is being run from an ac supply in a workshop, the device responsible for the conversion is referred to as a rectifier, and where an ac device is run from a battery, it is called an inverter. The power electronics combines both of these roles and has to switch very swiftly from one to the other.

Another important job for the power electronics is to supply from the battery an almost constant voltage to a number of other electronic components. This process of converting a high dc voltage to a lower one allows us to dispose of the traditional 12 V battery and run everything electronic on the car from the main propulsion battery. Components that we might need to run include starter motors, electrically powered pumps, lights and injectors, among others.

Written by Wayne Ward

Increased bearing load results in higher bearing surface temperatures which, after all the analysis has been undertaken and the tests completed, results in thinner, less viscous oils having even thinner oil films at the higher temperatures involved. The inevitable conclusion to all this for a fixed flow rate of oil is even smaller journal-to-bearing diametrical clearances.

As these clearances diminish, however, the shape and topological nature of the bearing becomes more important, making them more susceptible to fatigue or failure due to seizure, particularly in the initial stages of running where conformability of the bearing is at its most critical. The trick therefore is to make a bearing with reduced running clearance, which will bed-in quickly to the dynamic requirements of the rotating journal.

Under a (very powerful) magnifying glass the surface of a bearing looks like a series of peaks and valleys. These peaks are often referred to as asperities, and they are the key when it comes to reducing friction. A plain bearing works most efficiently in what engineers refer to as the beginning of the ‘hydrodynamic’ part of the lubrication regime, which is when the relative movement of two surfaces separated by the lubricant generates a pressure to force those surfaces apart. In doing so, the opposing surface asperities are forced to disengage, allowing the surfaces to glide across each other with the minimum of drag.

‘Mixed’ or ‘boundary’ regimes – when these asperities are in partial contact – may occur when the oil flow is reduced, at high oil temperatures or excessive loading, and at these times the bearing is particularly vulnerable to failure. It is therefore at these times during its early life, before the assembly has had time to fully conform, that the risk of failure is at its greatest.

Clearly any plain bearing design therefore needs to have a surface finish that holds the oil and retains it as long as possible. At the same time, the surface must have no barriers to the movement of the oil in the direction of rotation, while effectively discouraging it from escaping out of the sides of the bearing.

Such a surface can be obtained using a method of boring that produces a surface roughness parallel to the movement of the journal with a cross-section such as that shown in Fig. 1. This retains the oil in the grooves, minimising the flow escaping to the side and with the reduced supporting area quickly conforming to the dynamic movement of the system, creating a uniform polished bearing and giving maximum support in the minimum of time. Bearings of this nature may appear to wear quickly after initial start-up, but taken over the life of the power unit they have a lower risk of seizure and greater durability – and, ultimately, a higher loading capacity.

Bearing wear was rarely a problem with older engines, but the use of lower-viscosity oils in more modern units is creating a new set of challenges.

Fig. 1 - Microprofiled bearing

Written by John Coxon

It was much later in life that the word ‘overlap’ in relation to engines was to enter my vocabulary, and funnily enough, and as you might expect, it was to do with camshafts and timing of the engine valves. As a reminder, valve overlap is that period when the exhaust valve is just about to close and the inlet valve has started to open. In our theoretical engine, the exhaust valve would close instantaneously at top dead centre and the inlet would open at the same time. However, the laws of physics prohibit instantaneous movement (and infinite accelerations!) and anyway, having both valves open a certain amount at the same time has advantages.  

First, the delayed closing of the exhaust valve encourages the last remnants of exhaust gas trapped in the clearance volume, where the piston cannot reach, to exit down the exhaust port. And second, the opening of the intake valve before piston top dead centre allows a fresh charge to enter, helping the exhaust gas to flow out of the exhaust port and replacing it with an additional charge to be burned during the following cycle. Provided little or no fresh charge is lost through the exhaust valve, scavenging the cylinder in this way increases the total volume of intake charge and also removes the potential ‘heatsink’ effect, when heat from the following combustion process is used to heat up the trapped exhaust using heat that would otherwise be turned into power. If ever there was a case of a double whammy, this is it.

The amount of overlap shouldn’t be too great though, and it very much depends on the restrictions to the intake and exhaust flow, both upstream and downstream of the cylinder. At a given engine speed, a four-valve chamber for instance will usually require much less overlap than, say, a two-valve head since scavenging in the former is more efficient. On the other hand, a race engine more used to running up to 6000-7000 rpm may well require an overlap much larger than that of a road-based machine. In such cases, a race engine could demand well over 100º of overlap for maximum power, whereas our roadcar is quite happy with 15-25º.

For comparison, a few years on from my garage-floor lesson, the Coventry Climax FWMV V8 of 1965 revving to just over 10,300 rpm at the time used a constant 89º of overlap to produce its maximum power. Three years later, the Cosworth DFV revving to only 9000 rpm used 116º. In road-going cars of course, maximum power isn’t always the only target – also of primary concern is engine idle ‘quality’, the ability to exhibit a stable engine idle speed using minimum fuel and giving minimal exhaust emissions, which is why most modern road engines use variable cam timing systems to alter this overlap when the engine is running.

In this way the manufactures get to have their cake and eat it. The overlap is minimised for best idle quality but increased again as the engine speeds up to give optimum scavenging when maximum performance is demanded.

Things have come a long way from those early side valve days in my life, but the sight of those two valves sticking up at the same time out of the top of the cylinder block alongside the tops of the pistons is still lodged in my memory.

Fig. 1 - The 1965 Formula One Coventry Climax V8 valve timing

Written by John Coxon

A large part of the revolution in economy and efficiency is energy recovery, and most car companies and race teams have chosen the electric hybrid route. Also, electric racing is now with us, with some big names – teams as well as drivers – signed up to Formula E.

High-powered electric motorsport might prove exciting to watch, if not to listen to. However, for engineers there are challenges with moving from designing complex engine parts to assemblies with very few moving parts. Many adjacent components need to be separated by large gaps or electrical insulation. The problem is possibly most acute in the propulsion motors. The individual turns of the coils in the motor windings need to be separated from each other electrically; the same applies to the coils in each phase, and all the windings need to be insulated from the stator ‘iron’ and the motor’s casing.

In motorsport we want everything to be compact, so we try to make the windings small. We pull the windings around relatively sharp corners, and during winding the coils rub hard against each other, so it is very easy for the insulation on the winding wire to become damaged. A lot of electrical winding wire is coated in a polymer, and several layers of insulating coating may be used. There is a compromise here: more insulation is more robust and reliable, but it also increases the size of the bundle of conductors. There may also be additional insulation applied after winding, in the form of transformer varnish or lacquer.

Elsewhere in the stator of the electric motor, it is possible that insulating ceramic or polymer coatings could be applied to other components. The problem with coatings compared to much thicker separate insulating components is that coatings are far more easily damaged, and at the end of winding a motor a minor short can mean that the whole motor is scrap. The skill of the people winding the motor and assembling the stator into the case is as much a factor here as the integrity of the coating in many cases. The designer also needs to consider the lack of damage tolerance in any coating selected, and balance this against his or her desire to make everything as small and light as possible.

Written by Wayne Ward

It was a three-cylinder two-stroke diesel engine with a single crankshaft, six pistons and 12 con rods, plus six rockers that formed part of the cranktrain. Two-stroke diesels are an interesting concept; we don’t see them widely used but they are among the most efficient internal combustion engines. Even the latest energy recovery systems used in Formula One – which have been nothing short of a revolution in fuel efficiency in motorsport – cannot easily compete with a well developed two-stroke diesel. Brake thermal efficiencies in excess of 45% are possible for power units developed for commercial transport, and huge stationary engines can achieve considerably higher figures than this.

In the TS3 engine, each pair of pistons moved towards each other in a cylinder and, compared to the similar concept of opposed pistons used on the Napier Deltic (which used three crankshafts to do the same thing in a much larger package size) the Commer was a very tidy and compact design in terms of packaging. The link at the end of the article shows the engine in section, and if you refer to this or another sectioned drawing of the engine, it will make the process of understanding this unique engine much easier.

The inlet charge for each cylinder was compressed by a pair of pistons. Each piston had a short con rod attached to a very substantial rocker. In turn, the rocker was connected to the crankshaft by a further con rod. The rocker appears not to have had a 1:1 ratio – that is, the piston stroke was larger than the crankshaft stroke. The rocker also had some offset, which was necessary as the pistons in each cylinder clearly needed to be coaxial, but the motion was imparted by separate throws on the crankshaft spaced 180° apart.

So, in the cranktrain, we have a much more complex arrangement than in a normal engine, but this is offset in an opposed piston engine design by the fact that the engine has no cylinder head.

Does this have any relevance to race engine designers? Some years ago, when the possibility of hybrid systems was first being considered in Formula One, and when I was working on Formula One engine development, I took part in a discussion of what we might do if given a set amount of energy to start a race with, and no other restrictions. A turbocharged two-stroke diesel engine was mentioned at the time. If fitted with systems for energy recovery and running at near-constant speed, powering a generator, it might prove to be a  good solution. In terms of packaging, an opposed piston design such as the Commer Double Knocker might well be a good solution.

At the moment though it seems unlikely that this sort of power unit would be used in any kind of motorsport, but for passenger and freight applications a similar concept could prove to be a better solution to the ‘range extender’ engines now being developed for electric vehicles.

For sectioned views of the engine go to: https://www.flickr.com/photos/jeffspiccies/5384257681/

Written by Wayne Ward

In the automotive world the classic air-air intercooler matrix is made from sheet or tube aluminium alloy, which is pre-assembled and hot-dipped in a suitable molten aluminium-silicon brazing solution to bind and seal it. Before this though the matrix has to be cleaned by dipping it into a corrosive flux solution, all trace of which has to be removed afterwards. The corrosive nature of the chemicals involved means this is a hazardous process and subject to many rules and regulations concerning the materials involved. Having made the matrix core, and depending on the application, the end tanks will be fabricated and the whole lot welded together to produce a unit similar to the one shown in Fig. 1.

This manufacturing method therefore makes any form of heat exchanger or intercooler an expensive component which, given its proximity to the front or outer parts of the bodywork, can be easily damaged in the cut and thrust of modern racing. To reduce costs and improve product quality, OE manufacturers tend to make the end tanks these days out of injection-moulded plastics that are then mechanically clamped to the aluminium matrix core and sealed using sheet material sandwiched between the tank and the core.

While minimising costs as far as the technology allows, however, even this process still renders the matrix core susceptible to corrosion and damage as a result of cyclic fatigue. Aluminium alloys have no lower stress limit below which they will operate safely forever, so at some time during use they are bound to crack, with the inevitable loss of engine boost.

Since the end tanks are currently made from plastic injection components, the next stage in intercooler development must surely be to manufacture the matrix core out of similar materials, since most plastics do not corrode and the use of extruded or welded plastics is altogether a less hazardous process. The principal objection to this though would seem to be the relatively poor thermal conductivity of plastics compared with that of aluminium alloys – but not so, according to some reports. Computer simulation has indicated that, in modelling the heat exchange process, the thermal resistance of the thin plastic tubing used compared to that of aluminium was not the major problem one might have reasonably thought. The real issue would appear to be the boundary layer between the bulk air flowing and the tube materials.

By making the heat exchanger core out of extruded polyamide tubing, which could be laser welded together under precise computer control, 100% plastic intercoolers could be manufactured quicker and cheaper without many of the expensive and environmentally hazardous processes that go with current manufacturing methods. In addition, once fully developed, intercoolers will not only be more robust but lighter too.

And I guess there can’t be many areas where engine or vehicle technology is taking its lead from the solar panel industry.

Fig. 1 - Traditionally fabricated aluminium alloy intercooler

Written by John Coxon

The crankshaft itself rotates in bearings in the crankcases, and at very high speeds in some cases. MotoGP engines rev close to 20,000 rpm, while in the mid-2000s Formula One engines were in the same speed range. I have an old 750 cc motorcycle from 25 years ago that will run happily to 14,000 rpm.

Where we have rotating motion, we have centrifugal forces. We often see these as unhelpful in the context of an oil system as we need to run high oil pressures in order to feed oil into the crankshaft oil drillings, fighting the centrifugal forces that are trying to return the oil to whence it arrived. However, it is possible to take advantage of these forces for the good of the oil system and hence the health of the race engine.

Two problems we might suffer from in a race engine as far as the oil system is concerned are aeration and contamination. Excessive amounts of air in the oil can lead to problems with lubrication, and bearings are especially susceptible to damage through oil that contains too much air. Contamination in the form of solid debris is also particularly damaging to bearings, as well as other components. Anywhere that hard, solid particles can enter a narrow sliding contact presents opportunity for damage. For both these situations, we can use centrifugal forces to help us.

The key is to get the main feed of oil onto the crankshaft centreline. This can be achieved when feeding from a gallery into a main bearing, but it is conventionally done with a nose-feed crankshaft, where the main feed of oil is fed into the non-output end of the crankshaft.

In terms of air separation, we have two options. One is very passive and is by the simple expedient of a small oil drilling on the centreline of the crankshaft, passing into the crankcases; the air, which is forced towards the crankshaft axis owing to its very low density, can pass through without dragging very much oil along. The other option is to use a device to take advantage of the difference in angular momentum between the crankshaft and the oil as it is introduced. This is an active air-oil separator, whose function is the same as that of the simple on-centre drilling, but it should be much more effective.

Regarding solid debris, this is again normally much more dense than the oil. If the oil is moving sufficiently slowly axially, it will have time to pick up enough momentum to force the solid debris to the outside of the drilling. By introducing a ‘dam’ at some point along the cavity into which the oil is introduced, the solid debris should be retained there. A scheme working on the same principle was used in some of the Rolls-Royce Merlin engine variants. It must be said though that trying to include the active separation scheme and the debris centrifuge may not be possible in most engines owing to lack of space.

Written by Wayne Ward

Whether they are for automotive or motorsports use, electrical connectors are generally made from copper alloys plated with tin, silver or gold. Consisting of an outer female part that retains a bullet- or spade-shaped inner part under the action of spring loading, the reliability of the contact is controlled by the mechanical properties of the base material and the conductive properties of the surface layer. Should anything interfere with these properties – be it contamination, oxidation, the formation of sulphides or corrosion – then the resistivity of the joint may be impaired to the point where the electrical circuit is unsustainable. Thus, not only is the normal contact force between male and female parts important but so is the type of plating and its thickness.

A large part of what drives the selection and thickness of the coating is eventually down to cost, but in recent times the drive to reduce the amount of lead in all its forms in the manufacturing environment has led to the replacement of traditional tin-lead coatings with pure tin. In common with most other plating surfaces (except silver in some cases – see below) nickel is used as an underplating of 1-1.5 microns in thickness to prevent the copper migrating through from the base material to form a copper-tin compound, which can reduce the ability of the contact to be soldered if required and could induce a level of compressive stress in the tin deposit to form a type of ‘whisker’, which will eventually lead to system failure.

If tin is selected as your coating, the options are bright tin or matt tin. Bright, apparently polished tin has a more pleasant appearance and a lower coefficient of friction of the two, which may be important if the level of force required to press-fit male and female parts together is large. Matt tin on the other hand is easier to plate but softer and therefore less durable should parts need to be routinely dismantled.

A more expensive plating is pure silver. Favoured for its higher current power applications, silver has the highest electrical (and thermal) conductivity of any metal. Because of the high-power applications therefore, forces normal to the connectors when mated together should be very high. For these high values, and when the thickness of the silver is up to 20 microns, no underplating is generally required. Lower power ratings tend to need a nickel underplating, but because of the low thickness of the silver, such connectors are far less durable in  assembly and dismantling. Let’s not forget also that over time silver will tarnish, so this may not be the best option if the working environment is even slightly corrosive.

The best coating material for both electrical contact and durability though is of course gold. When applied using a nickel underplating, gold will supply a stable and low contact resistance throughout the whole operating life of the connection – but at a cost. Almost inert chemically, gold will not form an insulating film between contacts, and because of this the assembly (and disassembly) forces can be comparatively low. As a result, metal-to-metal contact is easily established with low contact forms, and is the reason why the coating is the preferred choice for applications using low voltages or currents.

Tin-, silver- or gold-plated contacts? Just another decision to be made when designing your wiring loom. 

Fig. 1 - Tin-plated contact

Written by John Coxon

When considering coolant jacket height, the mid- or bottom stop liner, which has its mounting surface located low on the liner, gives the design freedom to achieve an open-deck design and therefore to get the coolant highest up and as near as possible to the flame deck. The main aim is to have the top ring in top dead centre, as close to the coolant as possible. With modern pistons, with very little compression height, the top ring is positioned very near to the top deck and therefore the jacket design around the liner is of major importance.

An open-deck solution like the bottom or mid-stop would therefore be preferable. From the point of view of overall length, however, this design is not really preferred.

But what if your engine has a top stop liner? First, you could ask a specialist company to convert your engine block to mid- or bottom stop liners. Make sure you find a company with excellent references though, because this is a very delicate job, and if it’s not done properly it will cost you your engine.

Another option would be to check in detail how your liner has been positioned. Most engines have their liners positioned just under the liner's flange and typically have a tight radial clearance between liner and block. With this design the coolant cannot fully reach the lower side of the flange, leading to decrease in cooling of the top ring.

One solution would be to position the flange on the top diameter (flange outer diameter). This way the diameter of the liner can be decreased just below the flange, which enables coolant entry into this region. Make sure the clamping force between the head and block, which is being transferred through the flange, can still be withstood by the engine block balcony below the flange.

By creating this additional coolant ring below the flange the balcony is obviously reduced, so we need to ensure that the strength remains sufficient. One possibility to achieve the required sealing of the coolant between liner and block would be to include an O-ring groove in the outer diameter of the flange, and install a small O-ring here. This is to ensure proper sealing of the coolant to prevent leakages under the head gasket.

What should this coolant ring look like? For cooling, flow is required, so the ring should be big enough to enable flow. The target should be to achieve a ring of at least 2 mm, depending of course on the pressure drop over the ring. It might therefore be a good thing to connect the ring on one side to the highest possible pressure (directly after the coolant pump) and on the other side to the suction side of the coolant pump. That way the highest pressure drop will be achieved and the ring can be kept as small as possible, limiting the overall length of the engine.

Coming back to the sealing, one might also choose to make use of a line contact between the underside of the liner flange and the block. The benefit here is that no O-ring is needed; the downside though is that this feature might carve itself into the block structure under thermal and combustion loads (leading to micro-movements between liner and block).

If there are still cooling difficulties after these conversions, another option is to drill holes through the flange of the liner to enable flow through (and therefore also just below) the liner flange. This might require additional modifications to the head gasket and cylinder head, but that is not always possible in existing engines.

In the end though, if cooling issues remain in the top end region then it might not have been the best thing to choose that particular engine for the increased performance you had in mind.

Fig. 1 - Cylinder liner concept and alignment/mating surfaces. You can see the difference in coolant height in relation to the piston top end ring

Written by Dieter van der Put

Attracting less attention than the car category but no less competitive is the motorcycle category. The motorcycles have evolved over the years in a number of ways. In the early days, the key criteria for a motorcycle to be successful were reliability, plenty of ground clearance and a big fuel tank. The requirements for ground clearance and a large-capacity fuel tank made the motorcycles quite ponderous initially, and they remained vulnerable to mechanical damage in the event of any accident. As competition grew, speeds increased and it became more important to make the motorcycles tolerant of any day-to-day damage caused during riding as well as minor accidents.

The BMW R80 was often the machine of choice for Dakar rally entrants, the flat-twin engine offering the necessary ground clearance and the basic motorcycle being renowned for reliability. The exhausts on the early motorcycles were particularly vulnerable to damage, with the unprotected primary pipes exiting forward from the cylinder heads and being swept underneath the head before exiting in a low-level silencer. Later variants swept the exhaust upwards, with a high-level silencer being less vulnerable in the case of the rider falling off and when crossing rivers.

Over the years, more manufacturers were drawn to the Dakar, and the basic engine configuration of single- and twin-cylinder engines with front-exiting exhausts meant the first part of the primary pipes were less prone to damage from a collision, but perhaps more likely to being damaged by stones thrown up by the front wheel. Following the example of the later BMW R80 machines, rally raid bikes now all have high-level silencers, although they are sometimes only upswept just before the silencer entry. Having the silencer exit at a high level at least protects the engine from the ingress of water via the exhaust if the machine were to come to a halt in the middle of a river crossing.

What has happened is that the primary pipes are now very carefully shielded from impact damage and are very often not visible for most of their length, particularly where they are routed low along the side of the bike. Metallic as well as carbon composite materials have been used to protect the exhaust system from stone impact damage and from the results of the rider falling off the machine.

In recent years, the trend for motorcycles has been towards smaller-capacity machines that are more agile and easier for the rider to handle. From 2014, only single- and twin-cylinder machines with a maximum capacity of 450 cc are eligible, with the result that the manufacturers who produce 450 cc motocross and enduro bikes have had a sound basis for their rally raid machines. The entry from Yamaha, for example, is a single-cylinder machine, although this has a forward-facing inlet and a rear-facing exhaust. In this case, the primary pipe is much better protected from damage than some rival machines owing to the fact that the rest of the engine acts as a combined stone and bash guard for the pipe.

The exhausts are better supported than on many road and competition bikes too, with extra supports between the cylinder head and the silencer bracket.

Written by Wayne Ward

The best way to ensure that a fastener remains tightly fastened is to understand its behaviour, and to tighten it accurately. The most critical fastener in any reciprocating engine with split con rods are the con rod bolts, and these are rarely equipped with any positive method to prevent loosening. However, con rods are a rare case where we can accurately measure pre-load (indirectly via measurements of bolt extension and a knowledge of the stiffness of the fastener).

For most other applications we do not have this luxury. There are many ways of preventing a fastener from loosening; some are chemical and some are mechanical. The chemical solutions to fastener tightening are based on either wet or dry thread-locking compounds. There are various dry thread-locking compounds, but they aren’t very widely used in comparison with the wet thread-locking chemicals that many of us are probably familiar with. They come in various strengths and levels of temperature resistance. The weakest is specified for fasteners that require routine disassembly, while the strongest types are really only used for applications where the intention is for the fastener never to be removed. The very strong grades also often require heat to weaken them before studs can be removed.

Such thread-locking compounds are basically anaerobic adhesives, which rely on an absence of air in order for them to cure. Their cure time is affected by temperature, and although there are chemical accelerants available to reduce cure times, the final strength of the thread-locking compound is often compromised by their use, although new activators have been developed by some companies that bring the cured strength back to 100% of the ‘unactivated’ strength.

The strength of the bond is also affected by the material to which the compound is applied. When applied to a bare steel substrate, such compounds are often much stronger than when applied to fasteners that have been chromated, for example. The bond gap also has a large effect on the cure time and the final cured strength of the thread-locking compound, with larger gaps showing increased cure times and significantly diminished performance, as measured by the torque required to loosen the fastener.

Experience of using thread-locking compounds in trials where clamp load was measured for a critical application shows it is important to develop a process for the use of the compound, detailing how much is used, where it is applied, how much delay there is before fitting the bolt and how it is tightened. During some trials I organised, the clamp load – particularly with high-strength thread-locking compounds – showed much greater variation for a given torque than for oil-lubricated fasteners. It was clear from the trials that the thread-locker was beginning to cure and to exert some resistance before the joint was fully tight.

Written by Wayne Ward

Let me say here that I consider that the use of specialist racing fuels as being no bad thing. Racing fuels tend to burn so much cleaner, and for those who complain about the increased cost surely this is insignificant compared to all the other costs of competing?

However, for those who because of choice or budget restrictions prefer to use ‘pump’ or service station forecourt fuels, the issue I am about to refer to may make them think again if they continue to use lightweight aluminium fuel tanks.

Although light, aluminium is a highly reactive metal that relies on an oxide layer for protection against its corrosion. This oxide layer occurs naturally, and the low levels of ethanol such as E10 (10% ethanol, 90% gasoline) or the 5% ethanol blend often found in Europe are usually not a problem. The problem occurs principally when the ethanol content in the fuel is increased beyond these levels. The issue, although complex, generally centres on the presence of water in the fuel.

The accepted reason for the corrosion of aluminium in ethanol-blended gasoline fuel is the phase separation theory. According to this, the hydrophilic (water-loving) property of ethanol allows water to be absorbed into the fuel, which helps to divide the single phase ethanol-gasoline mixture into two phases – a water-ethanol mixture and gasoline. Acting as a form of galvanic cell, and helped by the presence of alloying metals in the aluminium, the oxide layer is overcome and erosion/corrosion takes place. 

There are many ways of tackling the problem though. Less susceptible forms of aluminium can be used, but this doesn’t really help anyone with an existing aluminium tank, although the tank can be modified by anodising the internals. Anodising or hard anodising creates a more resilient oxide barrier that tends to be thicker than the normal aluminium oxide surface and better protects the metal underneath.

Other barrier systems can be coated on the inside of the tank, substances such as LLDPE (linear low-density polyethylene) or some kinds of epoxy-based resins similar to those used in glass-reinforced fibre applications. Tanks made from GRP (glass fibre-reinforced plastics) have also sometimes been recommended as an alternative for boats using aluminium tanks, but even these may be suspect at the higher levels of ethanol mentioned, so do your research carefully.

Of course, for anyone with the appropriate budget, some form of foam-filled internal bladder would be the best choice, and this would be my favoured approach. The aluminium tank would need to have access apertures bored into it for the bladder to be inserted, but the extra safety against serious impact damage in the event of an on-track incident must surely be worth it. Not compulsory in many forms of racing – perhaps it should be – but the requirement to replace it every five years irrespective of use might put off many budget racers.

The current discussions in the EU are only proposals, and are vigorously opposed by vehicle manufacturers, and although the fuel developers will introduce some form of anti-corrosion additives, the mandatory introduction of higher levels of ethanol could mean yet another raft of modifications to racers of vintage or classic machinery.

Fig. 1 - Aluminium fuel tank with internal bladder

Written by John Coxon

These days though it’s not so easy to impress people, since opening the bonnet or hood to reveal the engine in all its glory displays only a mass of pipes and actuators. But for those in the know, the equivalent discussion to that of 50 years ago might be one of a single large throttle body against an array of port throttles.

Single large throttle plates are generally used in the original equipment installations of vehicle manufacturers. Comparatively cheap to manufacturer, and easy to set up on the bench away from the vehicle, they tend to be far more than just a throttle plate. With a couple of throttle angle potentiometers and an electric dc motor to open or shut the throttle in response to a signal from the engine’s ECU, these devices are no longer attached directly to the throttle pedal.

Used mainly where the vehicle needs to pass regulatory exhaust gas emission tests or to control the engine torque more precisely during transient conditions, in response to rapid opening (or closing) of the throttle, the response is relatively tardy as the manifold steadily fills up (or empties). Alongside this, the transient airflow has to be modelled so that the fuel demanded can be corrected to avoid rich or lean spikes in the exhaust gas, which could cause exhaust after-treatment issues downstream.

Port throttles on the other hand tend to be far more responsive to the throttle pedal, as the volume of air downstream of the throttle plate is rapidly consumed. This gives the driver a more urgent feel to the car during driving, particularly with the initial pull away from rest. The car may have the same overall power of the single throttle but the transient ‘feel’ of the vehicle is generally much better. The downside tends to be one of poorer control of exhaust emissions, despite the potential to improve fuel economy brought about by the reduced negative work on the piston at part-throttle.

Another advantage of port throttle applications is their ability to tolerate camshafts with a wider inlet and exhaust valve overlap at engine idle speeds. The close proximity of the closed throttle plate acts as a barrier to any residual exhaust gas finding its way back into the inlet port at intake valve opening, which in turn enables the engine to idle less erratically.

Perhaps the biggest advantage of using port throttle systems though is in the ability to design a suitable intake system to maximise outright engine performance. Using a number of simple intake runners (each with a throttle plate close to the intake valve) leading into a common plenum, while the length of the runner can be optimised for maximum performance, the plenum volume can be made as large as the space practically available, removing any performance-limiting design constraints away from the immediate vicinity of the engine and transferring it to the intake of the plenum. In the large single-throttle application, engine performance will inevitably be limited by the distance between the back of the intake valve and the throttle. Too large, and transient engine response will suffer; too small and the engine may suffer from inter-cylinder distribution problems.

But as an enthusiast appreciating the finer points of engine design I just like the throttle system detail under the bonnet.

Fig. 1 - Multi-throttle intake system – something to impress your friends?

Written by John Coxon

Taking as an example the dry-sump system found on Honda’s V8-engined cars in use until the end of 2008, there are in fact two pumps on the engine, one feeding the oil and the other scavenging it from the sump. These pumps had torocoid rotors, with four inner and five outer teeth, which provided excellent volumetric efficiency.

A key design requirement for Honda was that each section of the engine should get the correct volume of oil, at the correct pressure, all the time. Ensuring that this happened was no easy matter, for example the valvetrain needed a high volume of oil at low engine speeds, but the demand did not rise with engine speed. Conversely, the oil supply to the main and big-end bearings, supplied though a centre feed in the crank, needed to rise in pressure as engine speed rose.

One major problem the team faced was a loss of feed pump performance as engine speeds increased (to more than 18,000 rpm eventually), due to suction cavitation in the pump. One potential solution would have been to reduce the pump speed and increase its size, but given the ever-present pressure to reduce mass and packaging size, this was not considered to be a viable option. Instead, Honda identified the root causes of the cavitation.

There were found to be two clear contributing factors. First, an insufficient volume of oil was being drawn into the rotor suction chamber during rotational transfer at high speeds. Second, the oil that was being drawn into the rotor chambers was leaking out because of centrifugal force. To cure the first issue, Honda replaced the thick, single rotors with thinner twin rotors, while the second was addressed by redesigning the suction port, so that as the suction chamber filled with oil, the port closed, preventing leakage.

The modifications were a resounding success. In 2005, Honda’s feed pump was rotating at 12,800 rpm but suffered a considerable decline in pressure at these speeds. With the modifications, which allowed for the basic pump design to be retained, flow rate increased by 30% for no reduction in speed.

Another interesting area of development for Honda was the pump rotor material itself. Initially, these rotors were constructed from sintered aluminium; however, in a bid to reduce rotating weight, and hence overall engine losses, Honda experimented with different materials.

The last generation of engines, used during the 2008 season, featured an inner rotor made from sintered magnesium, with an outer rotor of plastic. Due to the soft nature of these materials – particularly the plastic – the team had to develop a new profile for the rotors, which retained pumping efficiency but reduced surface pressure between the teeth. If the tooth geometry had been left the same as that used for the harder materials, the level of friction between the teeth would have increased, negating any gains from the rotors’ reduced mass.   

This is only a small insight into the level of optimisation that goes into just one component in a Formula One powertrain, but it shows the lengths engineers will go to in order to find performance gains in such series and the interesting paths down which such investigations may lead them. 

Written by Lawrence Butcher

With few exceptions, race engines use piston rings of the conventional gapped type – that is, there is a carefully controlled gap between the ends of the piston rings. A report by Jung and Jin (1) shows that, at one engine speed, the speed and direction of piston ring rotation depends on load, and it is not necessarily the case that both rings rotate.

Their study, although weighted toward the technique used in the measurements, monitored oil consumption and was able to correlate this with the relative positions of the piston ring gaps. It is perhaps unsurprising to find that oil consumption rose to a maximum when the two ring gaps were aligned, and fell to a minimum when the ring gaps were spaced 180° apart. This makes sense, as the flow losses would be greatest when the ring gaps are as far apart as possible, so for a given pressure difference there would be less flow through the gaps in the rings.

The speed of rotation of piston rings has been measured experimentally. Shaw and Nussdorfer (2) examined the phenomenon on a large engine and found that, at 1000 rpm engine speed, the piston rings were “observed to rotate as rapidly as 1 rpm”. Jung and Jin reported in more detail: on the engine they used, at 4000 rpm and 2 bar bmep, the rings rotated at 0.6 rpm in opposite directions to each other, with the second ring initially oscillating between two positions before finally beginning to rotate continuously.

At higher load, the top ring didn’t rotate, and the second ring rotated at speeds from 0.5 to 3 rpm. On the same engine and at lower engine speed, the top ring simply moved to a given angular position and then remained stationary at 2 bar load. With an increase to 4 bar, there was a change in top ring position but still no continuous rotation. The second ring was also observed to be stationary at this speed in some tests, some of which found the ring gaps aligned – the condition where oil consumption is highest.

It is clear that the piston rings in any engine lead a mysterious life where, depending on the load and speed conditions that apply, they might rotate continually, oscillate between certain positions or remain stationary. Oil consumption is found to vary with ring position and, where the rings rotate periodically, the rate of oil consumption is a function of the rotation period of the rings. Other than pinning the piston rings to prevent rotation (which is commonly done in two-stroke engines), there is little we can do to influence ring position or speed of rotation. It is clear that whatever position the rings are in during the engine build will not be maintained during service. 

References

1. Jung, S., and Jin, J., “Monitoring of Rotational Movements of Two Piston Rings in a Cylinder Using Radioisotopes”, Journal of the Korean Nuclear Society; vol 31(4); ISSN 0372-7327, August 1999

2. Shaw, M., and Nussdorfer, T., “A Visual and Photographic Study of Cylinder Lubrication”, NACA Technical Report no 850, 1946

Written by Wayne Ward

There is a multitude of applications for vibratory finishing in engines and transmissions, and the main thing they have in common is that most of the treated components are in some form of sliding or rolling contact with other components. The merits of improved surface finish in such contacts are widely understood: by removing the high spots on any surface through a surface treatment such as vibratory finishing, we reduce friction and increase reliability by giving the oil film a higher margin of safety. Until the oil film is sufficiently developed – as in it becomes thick enough to separate the components – parts of the components are in contact, and friction is a function not only of the partially developed oil film but also of the solid contact, hence the high friction.

With poor lubrication conditions such as this, wear can rapidly cause a component to fail. The smaller the surface finish height, the thinner the oil film can be. So, particularly at start-up or low speeds, the improved surface finish is a real bonus. Components such as gears, cams and cam followers benefit from such treatments. Vibratory finishing is also used sometimes on crankshafts, again improving surface finish on bearing surfaces.

In terms of energy, there are some components where we definitely want a high-energy process capable of removing burrs and taking off sharp edges. For example, the edges of cam lobes and gear teeth are better when the edges are thoroughly de-burred and given a small radius.

However, there are applications in engines where we definitely want to retain sharp edges. On some machined edges on engine poppet valves, the sharp edges on the back of the valve are important, and choosing to put a nice radius on the wrong one of these can bring a measurable performance penalty.

The reason is that some sharp edges are carefully developed features to enhance the energy in the flow over the valve, acting in a similar way to a flow trip. By increasing turbulence in intake valve flows, for example, there are circumstances where the flow through the valve seat is greater because there is a reduced degree of separation. There are specific designs of valves to create these conditions, and if the critical sharp edges are turned into small radii then the valves can represent a step backwards compared to a conventional valve design, rather than giving the intended improvement.

There are some extremely high-energy vibratory finishing processes that are characterised as peening techniques, whose aim is to create significant residual compressive stresses in component surfaces, but the energies involved are far beyond those that can be imparted by conventional vibratory finishing treatments.

Written by Wayne Ward

For example, during the development of its Formula One V8 engines, the Honda team wanted to improve the driveability of its engine through closer control of the air-to-fuel ratio (AFR) entering the combustion chamber. The demands placed on an engine such as those found in the previous generation of Formula One car are considerable, not least the need to be able to move from fully closed throttle to wide-open throttle almost instantly. This requires exact control of the fuel injection events, and if this is not achieved then the AFR – particularly in the immediate vicinity of the spark plug – may end up rich or lean, hindering flame front propagation and impacting driveability.

By measuring in-cylinder pressures, Honda had found that misfires were occurring under certain transient throttle conditions, which it thought was down to an incorrect AFR. Naturally it wanted to find out why these misfires were occurring and take steps to improve the situation. To do so, the team used a micro-Cassegrain sensor incorporated into a spark plug, which was able to measure the chemi-luminescence of different elements in the flame front inside the combustion chamber. By studying the intensity of this luminescence, the rate of flame propagation and the AFR could be established.

To ensure that the sensor system was not interfering with the normal operation of the spark plug, Honda ran sensors in only four of the eight cylinders and compared the variation in combustion pressures between instrumented and non-instrumented cylinders. Also, the micro-Cassegrain sensing elements were placed behind sapphire glass shields to protect them from the extreme heat and pressure in the combustion chamber. By coupling the sensors to a high-speed data acquisition system, the team was able to record data at high resolution, with measurements accurate to within 1º of crank angle at 18,000 rpm.

The results Honda obtained from the measurement system allowed the team to gain considerable insight into the combustion behaviour of individual cylinders. For example, it was found that variations in the design of the air inlet scoop had a considerable impact on the AFR around the plugs in particular cylinders, something that had not been apparent before.

However, it was the results obtained during transient testing that were most revealing. As mentioned, the team had already found that certain cylinders were misfiring, but could not confirm why. The sensor provided the insight needed for this confirmation, and it was found that the AFR around the plugs from cylinder to cylinder varied considerably under transient throttle conditions, from rich to lean, causing the misfires that had been detected.

As with any form of testing, it is often the case that being able to record something that was previously un-recordable leads to more questions than answers. In Honda’s case, it discovered the reason behind its engines’ driveability issues, but finding a solution that would allow sufficiently precise mixture control to combat it was a different matter. However, without the ability to study exactly what was occurring in the cylinders, any solutions the team may have devised would have been mere guesses, as the exact problem it was trying to address would not have been clear to see.

Written by Lawrence Butcher

The impact of such coatings on transmission efficiency and durability can be considerable, netting useful gains in both areas. For the purposes of this article, we will look at the Honda team’s transmission development during its previous foray into Formula One, which ended in 2008.

The main losses found in a transmission relate to the sliding motion of the gear teeth as they rotate. It is well known that DLC coatings have good low-friction characteristics, so coating the gears should help reduce overall losses. When Honda first looked at doing this it realised that existing coatings, used for components such as valvetrain parts, would not have sufficient durability for a transmission because of the high surface pressure loads experienced between gears. To counter this, it therefore set about developing a new coating formulation that could better handle these loads.

There were two key requirements for the coating:

• It must be able to withstand surface pressures of 2.2 GPa for a duration of four races (the then current regulation life of a transmission)
• The application method must allow for a uniform coating over the complex gear tooth shape.

There are some clear differences in requirements between gear and valvetrain coatings. As already mentioned, the surface pressures are higher, but also the lubrication regime differs considerably. In valvetrain applications, the oil film breaks down as valve motion is reversed, which can lead to scuffing. To this end, the coating Honda developed for its valvetrain featured a hard bonding layer under the DLC top coat to prevent scuffing. In a gear train though the oil film does not break down, so Honda decided that the hard coating could be removed, with the development focus being on a top coat composition that had improved wear resistance.

The higher surface pressure led Honda to revise the surface finish on the gears to aid adhesion of the coating film, settling on a roughness of 0.1 Ra combined with enhanced cleaning of the parts to remove contaminants that could potentially compromise the coating. Honda then developed a coating composition to match the requirements of the gears. This consisted of a chromium adhesion layer, on top of which was a layer of metal-impregnated carbon coating, the combined thickness of these layers being 0.6 µm. This was followed by a DLC top coat 1 µm thick, with all the layers being applied using a sputtering process.

The results obtained after coating were impressive. The coating itself, when compared to Honda’s standard DLC as applied to valvetrain parts, showed an improvement in seizing pressure of 40%, as well as a considerable reduction in frictional losses. With the coating applied to all ratios in the box as well as the final drive and bevel gears, overall frictional losses were reduced by 3.3 kW – a very useful gain.

This work shows just how effective the use of coatings can be in increasing transmission efficiency. Better still, with commercial suppliers of such coatings now offering products at ever-decreasing prices, it has even become feasible for teams and constructors outside of the rarefied atmosphere of Formula One to take advantage of such benefits.

Written by Lawrence Butcher

Like me, you may be surprised to learn that some companies have combined the function of these components, the merits of this being lower cost, improved reliability, lower mass and reduced complexity. The component resulting from this unusual marriage, known as a lash lock, is actually, as is the case with any conventional valve lock, a pair of components that allow the locks to engage with a groove cut into the valve stem.

Where the lash cap and valve locks are separate components, the lash cap contacts the top of the valve stem, but in the case of lash locks, this is not always the case. In order to locate properly in the stem groove, the lash cap part of the component must remain clear of the valve in all cases. Allowance therefore needs to be made for the case where the groove is in its most distant position relative to the end of the stem. The load transfer is then not via the top of the valve stem but through the wall of the lash lock.

The result of having a split component is that the top surface of the lash lock is not continuous and flat – there is a cut that crosses it. Thankfully, on the components I have seen pictures of, the cut is not a simple straight line but is in an ‘S’ shape, meaning that the end of any rocker will not come to an abrupt ‘valley’ as it traverses the top of the lash lock. Such a straight cut might have an upsetting influence on valvetrain dynamics if the rocker tip were to ‘drop’, however slightly, into the groove and have to climb out again. If we rely on having a nominally flat top to a conventional lash cap for reasons of lubrication – to sustain an oil film in sliding or rolling motion – the gap in the lash lock’s top surface will adversely affect this.

If these lash locks were used in overhead camshaft (OHC) engines with inverted bucket followers, this would not be a concern. The lash cap, where it is used to change the valve clearances, is a very simple component to change for one of the correct thickness, and certainly for OHC engines this is the way valve clearances are adjusted. However, for a lash lock, the act of changing the component is far more complex, as we have to compress the valve spring as we would when installing or removing the valve locks.

It remains to be seen whether such components take an increasing share of the market from conventional valve locks and lash caps, but at the moment they seem to be a niche offering.

Fig. 1 - A CAD model of a combined lash cap and valve lock

Written by Wayne Ward

The option to couple solvers is not limited to structural solvers. The new set of technical regulations in Formula One has put greater emphasis on cooling, and in turn on understanding heat transfer. This is an area where CFD methodology has been developed extensively by roadcar manufacturers, with engine bay cooling airflow and exhaust modelling simulations now commonplace. Such coupling would also allow Formula One teams to evaluate their cooling package as part of their aero simulations and accurately model the flow of the air escaping from the rear of the car. 

This methodology could also have proved more effective in recent years, with the prominence of exhaust-blown diffusers. Wind tunnel models are rather limited in their ability to mimic how the exhausts truly behave, as it is impossible to put a scale engine in a wind tunnel model that produces the same mass flow and temperatures through the exhaust. Even accounting for the correct temperature of an exhaust, it would have been hard to correctly model the mass flow through it. In reality, an exhaust’s behaviour is linked to what the engine is doing, and what the engine is doing is changing at an alarming rate. 

This again leads to the argument for using transient methods, although it should be noted that a fully transient coupled simulation – where ride heights, yaw, steer and roll trajectories and exhaust parameters are changing – is still beyond the time constraints of a Formula One team. However, a compromise has been developed by at least one automotive OEM. 

This was developed by taking a car around a race track and monitoring the velocity and dynamics of the car together with the exhaust parameters. A filtering process is then applied to identify the most significant velocities and exhaust parameters, and from this a sample of points is taken to simulate 20 or so steady-state RANS simulations. From these results an understanding can be developed of how the car is truly behaving around a circuit. The time needed to complete this analysis is within a working week – a potentially acceptable timeframe in Formula One – although at the moment this approach would take up most of the restricted CPU time available just to analyse a single car configuration. 

Staying with the theme of coupling with a heat transfer solver, brakes obviously get hot and cool down, and it is important to keep a racecar’s brakes within a specific operating temperature range. In recent years, front and rear brake ducts have been an area of aggressive aerodynamic development for teams, but when optimising these ducts for aerodynamic gain it is perhaps easy to overlook their cooling requirements. Coupling the braking system geometry with a heat transfer solver would allow teams to analyse the extent to which they are keeping within operating temperatures, while also analysing the aerodynamic effect of modifying their brake duct design. 

The CPU time penalty incurred by coupling solvers implies though that this is not a methodology that is currently attractive to Formula One teams. Moreover, brake cooling effect is inherently associated with wheel shape, so modelling the rotation of the wheel as accurately as possible via sliding mesh techniques should greatly enhance the accuracy of such simulations. 

Formula One has undoubtedly added to mainstream automotive technologies over the years, with ABS and semi-automatic gearboxes being prime examples, and the modification of the powertrain regulations for 2014 will hopefully once again improve the series’ relevance to roadcar technology. In terms of manufacturing, Formula One also continues to drive the development of new techniques. 

With regard to aerodynamics and CFD, however, Formula One’s relevance to the wider world is arguably diminishing. The 2014 regulations aim to reduce costs, but by linking the wind tunnel usage limit to the CFD usage limit, the FIA is surely overlooking the fact that CFD is cheaper than using a wind tunnel. So, in the context of cost-efficient development, should CFD not be encouraged? 

The phrase in the regulations most damning to the development of CFD methodology is surely the one that states that the CFD limit line will change every three years “to take account of changes to CFD hardware ownership and running costs”. This suggests that the FIA is being naive in its view of the rate of development of both CFD methodology and computational hardware, so Formula One needs to ensure that the rule makers are not prejudiced about the benefits of CFD. 

The fact remains though that some teams are not using their current hardware to its full potential. The hardware is expensive but brain power is free – provided you are employing the right brains!

Written by Sam Wakelam

Traditionally, the usual material for exhaust construction in Formula One is either Inconnel or titanium, both of which provide relatively low weight, mechanical strength and reliability. However, with the weight of the exhausts sitting relatively high in the car, the potential gains from further weight saving are significant. 

Honda therefore developed a carbon-carbon (CC) exhaust system, which saw extensive dyno testing and some limited track use. Regular carbon composites, as used in panel work and chassis structures, use carbon fibres in a resin matrix. It is this matrix that is the limiting factor when it comes to temperature resistance, since although the carbon fibres themselves can withstand exceptionally high temperatures, most resins lose their integrity above 200 C. There have been recent developments in higher temperature resins, but there are none as yet that would survive reliably at the temperatures seen in an exhaust system. 

Honda’s answer was to use a CC material similar to that used for making brake discs and pads. It is a carbon fibre composite that uses carbon as a matrix, in essence a synthetic form of charcoal. While by no means weak, CC structures have nowhere near the mechanical properties of regular composites or metallic materials, so Honda’s development started with a target durability of 25 laps, aiming to use the parts for qualifying only. It began by developing collector and tail parts, but the ultimate goal was a complete set of CC exhaust pipes including the primaries, which if realised could net a weight reduction of 39% over the metal equivalents. 

Despite the challenges of using CC, there were other potential benefits in addition to the weight savings in terms of geometric freedom and packaging. For example, the use of Inconel entails the use of welded fabrication methods, which in turn requires that a certain material thickness be used to ensure weld integrity; it also limits the geometrical complexity of the parts. The CC parts are created in a mould, so such constraints were not a problem, and the result – Honda hoped – would be a lighter and more compact system.

Unsurprisingly, development was not trouble-free, and issues were encountered along the way, for example the integrity of the interface between the CC collector and the still Inconel primaries. CC has a very low coefficient of thermal expansion, and at operating temperatures gaps opened up between the two materials, making it hard for the engine control electronics to maintain a steady air-fuel ratio (which is measured using lambda probes in the primaries). To combat this, Honda developed a gasket material to fill the gaps. 

Additionally, the low resistance to oxidation of the CC material at high temperatures meant that a surface coating had to be developed to prevent this. Ultimately, the team was able to prevent surface oxidisation and maintain structural integrity for up to three hours at 900 C, which was found to equate to 30 laps at racing speed. 

Unfortunately for Honda though, regulation changes removed the possibility of running qualifying-only parts and ultimately the exhausts were never raced. However, the development process proved that the concept was feasible and it would be reasonable to expect that, given the renewed emphasis on weight saving in the new powertrains, such avenues of investigation may well come to the fore again.

Written by Lawrence Butcher

In addition, the 2014 Formula One rubber is notoriously fickle, with many teams saying it is hard to get it into the correct operating temperature widow without unduly impacting its durability. At the 2014 British GP for example, Andy Green, technical director at Force India, explained that while it was possible to get the tyre to the correct temperature through aggressive warming, this led to very rapid degradation, and finding a chassis set-up that could get the tyre up to temperature reasonably quickly without this being an issue was challenging.  

One widely used tyre model in motorsport is Pacejka’s ‘Magic Formula’, which uses data on slip angle, slip ratio, camber and tyre load to calculate tyre force. However, it misses out on one key variable, which in the closely fought world of Formula One has a huge bearing on performance – tyre temperature. Only when the tyre compound is at the correct temperature will it perform optimally. As a result, if the car does not work the tyre hard enough to get it to this temperature, performance will be compromised. Also, changes in tyre temperature due to slow laps behind safety cars need to be accounted for in race strategies, as does the variation in tyre behaviour from one heat cycle to the next. 

Although the spec tyre supplier, Pirelli, provides teams with a tyre model, most chose to develop their own, which allows for far greater flexibility of development. A few years ago, Honda, which withdrew from Formula One in 2009, developed just such an in-house model, by identifying the elements with the greatest effect on the accuracy of calculations for tyre forces. 

Tyre forces are determined chiefly by the structural deformation of the tyre and the friction characteristics between it and the road surface. The friction coefficient of a tyre changes significantly according to environmental conditions and driving conditions, including road surface roughness, dust on the road surface, tyre surface temperature, tyre slip speed, rubber wear and thermal degradation. 

When devising the model, Honda separated characteristics such as structural deformation and heat transfer – which could be modelled on the basis of theoretical concepts and the results of bench tests – from elements such as the friction coefficient, which depend on track conditions, the parameters for which were established using data gathered on track. By accounting for these variables, Honda was thus able to develop a model that gave a far more accurate picture of tyre performance than would be possible with more readily available models. A brief look at some of the aspects of the model gives a good insight into just how complex a task this was. 

For example, the model treated deformation of the tyre contact patch by dividing it into a belt section and a tread rubber section. Belt deformation was approximated by expressing it as a quadratic function in relation to the position of the tyre contact patch in the longitudinal direction. The deformation obtained in this manner was corrected using the tyre side force, self-aligning torque, internal pressure and longitudinal force, all of which needed to be calculated theoretically or derived from on-track data from sensors recording tyre temperate, wheel loads and so on. 

The complete details of such a model are far too complex to go into fully in a single article, but suffice to say, such models are essential in Formula One these days. However, it also has to be remembered that a model is only as accurate as the data fed into it, so for it to be effective a team must also be on top of all the other aspects of vehicle simulation and data recording. 

The benefits of getting it right are considerable, and not only in terms of performance and development efficiency. Simply through observing tyre behaviour phenomena and analysing the mechanisms by which they take place, previously unforeseen avenues of development and performance enhancement can be discovered.

Written by Lawrence Butcher

KERS systems were originally split into mechanical (flywheel) and electrical (battery) types, harvesting energy during braking to be released subsequently for shorts boosts in performance. Flywheel technology works by using braking forces to spin a mass (5 kg) at very high rotational velocities in excess of 60,000 rpm, and to improve efficiency the flywheel is housed within a vacuum. This creates sealing challenges, increasing the complexity of the manufacturing and assembly techniques to produce and build it. 

Modern Formula One engine turbos spin at even higher rates ( about 100,000 rpm) and both these and the flywheels demand incredibly high tolerances of manufacture. Bearing alignment and cooling are critical at these angular velocities, and when combined with high operating temperatures, centripetal acceleration, incredibly tight packaging and light weight there is little to no margin for error. To this end. teams have been specifying a concentricity of 1 micron (0.001 mm) on the turbo shafts to ensure alignment for seals and oil flingers, and reduce radial loading on the bearing and shaft vibration. 

It is also critical that all rotating components are dynamically balanced, with this process having to be repeated at every sub-assembly level. Accuracy of components not only has an impact on assembly but also the speeds at which these systems can operate and therefore their ultimate performance. With reliability so important in Formula One components, quality is paramount, and given the amount of energy in a spinning flywheel or turbine wheel the result of a bearing failure or clash can be catastrophic. 

The teams on this season’s grid run an energy recovery system (ERS), an evolution of the KERS, in combination with the turbocharged V6 engines. The ERS stores energy generated under braking in (lithium) batteries, and works with two motor generator units (MGUs) to convert mechanical and heat energy into electrical energy. 

The first MGU, MGU-Kinetic, uses the car’s kinetic energy to ‘charge’ the batteries, which can then in turn power the MGU-K to drive the car via the crankshaft. The second generator, MGU-Heat, is connected to the turbo and converts heat energy from the exhaust gases into electrical energy, which is again stored in the batteries and can be used to power the car through the MGU-K as well as spooling the turbo to reduce lag. 

For both generators, and the complex system they form, efficiencies and performance are related to the precision of the components and assemblies. However, there are further challenges with the manufacture and assembly of the batteries themselves. 

First there are the United Nations Transport of Dangerous Good regulations that make recommendations for the transportation of lithium batteries. These guidelines are enforced to reduce the risk when shipping these high energy-density cells, which is relevant due to the air freight requirements of Formula One’s international race calendar. This results in the energy storage batteries being housed in Zylon fibre-reinforced epoxy composite cases with integrated busbars (connectors) co-cured into the laminated components. These casings have to pass ballistic tests to ensure they are safe to ship and race. 

The next manufacturing challenge is the intricacy of the battery design. The batteries are made from multiple components in multiple materials with complex features including integrated cooling circuits, which are all critical to performance and safety. Creepage distance requires careful consideration and further complicates the design and subsequent manufacturing; it is not enough to consider the clearance distance between two conductive parts, measured through air. At high voltages a partially conducting path of localised surface deterioration of the insulating material can result in an electrical discharge between conducting components along the surface contours of a non-conducting part, a process known as tracking. This can be minimised by ensuring adequate creepage distance between these parts, but with available packaging space at a premium this is achieved by additional features that increase the creepage distance rather than simply moving conducting components physically further apart. 

Finally there is the battery assembly process. The cells are assembled on bespoke trollies, in environmentally controlled areas usually outside of the main factory. The operators are earthed and wear rubber gloves, and all other engineers authorised into the build area are encouraged to keep their hands in their pockets to avoid the prospect of a hefty electric shock. 

The reason for all these precautions is the potential for a short circuit in an ERS battery initiating a chain reaction through the cells leading to a ‘thermal event’. This reaction is exothermic and uncontrollable, and can generate enough heat to vaporise aluminium. The standard procedure to deal with an unstable battery is to move it, and hence the trolley and external workshop, as far away from buildings and people as quickly as possible! 

All aspects of Formula One push the engineering boundaries in the quest for ultimate performance. ERS and turbo technology may just be pushing manufacturing that bit harder, the prize being additional performance if components can be produced and measured with greater accuracy.  

Written by Dan Fleetcroft

Fundamentally unchanged in its design for decades, the brake pedal is at in essence a simple part, being a pivoting lever with a plate for the driver’s foot and a bearing housing midway up the lever for the bias adjustment mechanism. However, the detail design and construction have evolved massively into optimised, stiff and light brake pedals.

Since the advent of clutch paddles on the steering wheel, all Formula One cars feature just two pedals, and the driver operates the brake exclusively with his left foot. To this end, modern Formula One pedals feature large footplates with flanged sides, as the driver does not need to slip his foot to operate a clutch or ‘heel and toe’. Each driver has a preference for the design of the footplate, which often has a grippy abrasive material applied to its surface.

Driver preference goes even further with the detail design of the pedal and its interaction with the hydraulic elements of the braking system: teams will optimise the dynamics of both the mechanical and hydraulic elements of the brake bias adjustment mechanism. Ideally the driver wants a bias that shifts during braking, which isn’t possible using active control systems, but by designing the bias bar and valves in the system it is possible to get this behaviour. Everything from the fluid properties, orifice sizes, pipe compliances, bias bar mass, inertia and friction characteristics has an effect. Teams will model these variables in modelling software to design the ideal braking set-up for a specific driver.

One team found an issue when one driver applied the brakes at ten times the velocity of the other driver.

Being only some 240 mm tall, with the bias bar just under half that distance from the pivot, a driver pressing 130 kg with his leg under braking puts great stresses on the pedal; the catastrophic effects of a pedal failure do not bear thinking about. Thus the construction of the pedal has evolved over the decades, from fabricated steel pedals, through the use of titanium, machined aluminium and latterly carbon fibre. With such optimised design the weight of the pedal is now 200-300 g.

These days, Formula One teams are still split between carbon pedals and machined aluminium. One contemporary aluminium pedal seen by the author eschews the simply bar design for an almost semicircular arrangement, where the master cylinders attach to this triangulated shape for even greater stiffness.

It’s also now common for the bias adjuster to be mounted to the bulkhead, and the master cylinders directly to the peal. This frees up space in the footwell for the adjuster cable to reach to the bias mechanism.

Fig. 1 - Moulded carbon fibre and fabricated steel Formula One brake pedals 

Written by Craig Scarborough

The function of the CE is to control the ac three-phase power of the Motor Generator Units (MGUs) and the dc power from the battery. Currently Formula One uses two MGUs, one for the kinetic system and one for the heat system, where the kinetic system is an upscaled version of the recent KERS and the heat system is attached to the turbocharger. To control these two systems two separate CEs are used, appropriately termed CUK and CUH.

Inside the CE there are two sides to its operation, a low-voltage side, with logic boards controlling the high-voltage side with switches, and capacitors switching the power between the MGU and the battery.

When harvesting energy, the relevant MGU will send its ac power via three high-current cables to its CE. Inside the control unit’s casing is a series of high-current switches called IGBTs (insulated gate bipolar transistors) that switch the current, which also passes through capacitors. The electronics here convert the current to dc format.

The CE then sends the dc power via two cables to the battery. By inverting this process the CE can also take battery power to spin the MGUs.

This process of converting from ac to dc and back creates heat and therefore losses. Keeping the electronics at their working temperature is critical for reliability, and air cooling alone is not sufficient to manage the heat rejection so this is achieved with a dedicated water cooling circuit, which requires a small pump and radiator mounted in the sidepod. 

Conveniently, the CEs provide the car with its 12-24 V supply for the car’s other electrical systems, so the car does not need an alternator or its own battery.

Where to mount the CEs in the car is decided between the power unit manufacturer and the teams, so installations vary, with the units mounted either with the battery in a recess under the fuel tank or on the sidepods, depending on the team’s philosophy on fuel tank size and its impact on wheelbase length, cooling and sidepod packaging. 

New rules limits team to five complete power units for each season, and from 2015 just four. For practicality purposes the power unit is split into six elements, one of which is the CE for the ERS. Should a team fit a sixth CE then there will be a grid penalty for the driver, with further penalties for further new units being used.

This places great importance on reliability, despite these power units being all-new for the 2014 season. At the season’s halfway point, several drivers had already used four CEs, the CE itself proving to be an unexpectedly unreliable part of the complex new power units. Teams have reported that any failure in the CEs tends to be on the high-current side, not the lower-voltage logic boards. The result of high-voltage spikes tends to be catastrophic on the internal components and render the CE unusable.

Although the reliability of the CEs had improved in the latter part of the first half of the season there will be drivers who suffer penalties as a result of these units. 

Fig. 1 - A typical CE unit with the capacitors and high-current cabling evident 

Written by Craig Scarborough

Back then, and much like 2014 in some respects, one team dominated. In 1988 it was McLaren. Winning all but one of the races that year using a V6-configured engine; there the similarities end though. In 1988, the winning engines (the Honda 1.5 litre RA168E, for thus it was designated) were reputed to deliver something like 504 kW (685 PS) at 12,500 rpm on 2.5 bar boost using a fuel consisting of 84% toluene and 16% normal heptane. Of course, regulation in Formula One was much less restrictive back then, and so long as the fuel used bore some resemblance to road-based or ‘pump’ fuels – in that it had a Research Octane Number (RON) no greater than 102 (the Honda fuel was 101.8) – then all was well. The lack of low boiling point constituents in some fuels, which meant they had to be heated to around 75 C before being injected into the engine, wasn’t seen as an issue, and neither was the reportedly evil-smelling brews of other fuels, but hey, this was the 1980s and Formula One was pushing the boundaries.

In 2014, the engines could appear to the uninitiated to be very similar to those used in 1988. These days we still have V6 engines – this time 1.6 litres – and we now have turbochargers again, a single unit as opposed to most teams using twin units in ’88, but the ‘forecourt’ fuel of 2014 is totally different from that used in 1988. Indeed, even though Article 19 of the technical regulations remains unchanged the fuel used in 2014 will be significantly different from that used in 2013.

In designing a fuel for any engine, fuel technologists will look at many aspects. The heating value, the stoichiometry and even the density of the fuel in some cases will all be considered. But the fuel requirements of a 2.4 litre naturally aspirated V8 revving to 18,000 rpm will be totally different from those of a 1.6 litre turbocharged V6 doing not much more than 12,000 rpm. So from 2013 to 2014, although the fuel regulations did not change so far as the make-up the fuel is concerned, the precise blend of hydrocarbons within it almost certainly will have.

At 18,000 rpm the fuel has about 0.001 s in which to burn from the point of ignition to the opening of the exhaust valve. As it burns progressively across the bore, if the fuel ignites in front of the flame front then detonation will occur. This will cause a sudden increase in local pressure and temperature in the cylinder which, if allowed to continue, will damage the piston. At 18,000 rpm the speed of burn and the motion within the cylinder is such that there is generally insufficient time for this to occur. At this speed, this resistance to detonation (or ‘knock’) governed by the fuel’s octane number is therefore not so important.

However, at 12,000 rpm – the typical top speed of the new V6 engines –the time available for this flame front to move across the bore is now 50% greater, which is a lot more time for any stray pockets of end gas from previous combustion cycles to ignite any fuel-air charge in front of the flame front and cause detonation. At these speeds, and at the increased charge temperatures and pressures in the combustion chamber of a turbocharged engine over that of a naturally aspirated unit, the resistance to detonation of the fuel typified by its octane number is therefore more significant.

So while the 2013 fuels may have been blended more for their rapid speed of burn, in 2014 the emphasis is more likely to be on the resistance of the fuel to detonation. And as each species of hydrocarbon – be it aromatic, olefin, paraffin or naphthene – will have its own speed of burn and blending octane, so the optimum fuel for each engine made up from varying amounts of these will almost certainly vary.

Fig. 1 - Comparative flame speeds of some commonly used aromatic hydrocarbons

Written by John Coxon

A lot can be gleaned simply by looking at the cars as they sit in the pit lane, for example McLaren’s ‘mushroom’ rear wishbones in the 2014 season. But obtaining quantitative data on the competition can be trickier. In the world of production cars, a manufacturer will often buy a competitor’s vehicle to assess the technology it contains, but this is clearly not feasible in Formula One. Teams therefore need to be a little more creative. 

For example, before on-track data was recorded and displayed by the governing body for TV audiences, teams would use audio analysis techniques to ascertain the revs the cars were reaching at various points on the track. This could then be combined with speed data gathered by someone trackside using a speed gun, and factors such as likely gear ratios calculated. 

The widespread availability of handheld thermal imaging equipment, and even the images generated by thermal cameras as part of the current TV coverage, can provide an insight into the way a particular car is using its tyres. For example, by recording the tyre surface temperatures using a camera at a specific part of the track, comparisons can be made between cars. Also, by looking at variations in surface temperature distributions, teams can combine that with other analysis and data gathered from their own on-car sensors to begin to see how the opposition may be working their tyres. 

Image analysis can also provide a considerable volume of information. Using still images, known reference points on the car can be taken, and from these the orientation of other components can be studied. For example, if a known vertical plane can be established at the rear of a car, then the camber of the rears wheels can be estimated, as can the roll attitude of the body. Fig. 1 below shows how this is achieved, though it should be noted that this is a quick Photoshop mock-up, albeit based on a real team’s analysis imagery. 

Taking this a step further, capturing stereoscopic images can help to understand the relationship of one part of  car to another, particularly when it comes to suspension or aerodynamic components. This information can be fed into a CAD package, and from it 3D approximations of components created, revealing useful information such as suspension geometry and relative component sizes. Although it is not known whether any teams have used such devices, compact handheld 3D laser scanners capable of millimetre-accurate measurement are commercially available, and if someone could devise a means of using one in the pit lane without being noticed, no doubt the data gathered would be very revealing. 

Video footage, either captured by the a team trackside or from the readily available TV feeds, is another useful analysis aid. By comparing footage of competitors’ cars taken from a fixed position to their own (for which they have real-world data), factors such as corner entry speed, differing racing lines and braking points can all be ascertained. Teams have even used high-speed cameras trackside to deduce factors such as wheel slip rates, by comparing the difference in rotational angles between front and rear wheels. 

There a undoubtedly many other cunning methods used by teams to get the measure of their opposition, all of which will be fed back into the overall car development programme for assessment. While understanding how a competitor’s car works will not win a team races, it is important intelligence when combined with a thorough and verified understanding of their own car. As Sun Tzu, the 5th century Chinese military strategist, said in his seminal work The Art of War, “If you know the enemy and know yourself, you need not fear the result of a hundred battles. If you know yourself but not the enemy, for every victory gained you will also suffer a defeat. If you know neither the enemy nor yourself, you will succumb in every battle.” 

Fig. 1 - Basic trackside photography can be used to calculate factors such as approximate camber and roll angles (Composite image: Lawrence Butcher)

Written by Lawrence Butcher

The reason that aluminium is so widely used is its combination of properties and its cost. However, people have looked seriously at magnesium in the past as a piston material. While they have found it wanting when compared to aluminium, it is not beyond reason to expect people to look again in the light of new racing regulations and recent developments in engine and manufacturing technologies.

So when aluminium is such a well understood and relatively cheap material, why would people look towards magnesium as a possible replacement? Well, it’s a question of density – at 1800 kg per cubic metre, aluminium is 50% more dense – but the stiffness of magnesium compared to aluminium is pretty much proportional to their densities, (that is, magnesium is about two-thirds of the stiffness of aluminium). With most of the piston’s stiffness being a function of its behaviour in bending, the required increase in section thickness to achieve the same stiffness as aluminium would still leave the magnesium piston much lighter. It is true that the room-temperature strength of good wrought magnesium alloys is lower than typical aluminium piston alloys, but at higher temperatures magnesium stands up to much closer scrutiny. For example, at 250 C the tensile strength of WE43 magnesium is higher than that of 2618, which is a favoured aluminium piston alloy.

With the combination of high-temperature strength, sufficient stiffness and very low density, shouldn’t magnesium be a popular piston material? The most important reason why we don’t use it is its low thermal conductivity – it has around 60% lower thermal conductivity than 2618, which means that without considerable effort put into cooling, the magnesium piston will tend to run much hotter than its aluminium counterpart. This degrades performance, as some of the heat in the piston will be rejected to the incoming fresh charge, raising its temperature and lowering volumetric efficiency in the process, although there ought to be a significant decrease in the heat rejected from the combustion process, so we could expect fuel conversion efficiency to be improved.

Where a set of racing rules rewards increasing power from a given fixed engine capacity, especially with an imposed maximum engine speed, any loss in volumetric efficiency is going to hurt performance. However, where fuel efficiency is at a premium – and this is an important factor in many forms of racing – improved fuel conversion efficiency is to be highly valued. There are types of racing where engine size, engine speed and breathing capacity are free, but the instantaneous fuel flow rate and total fuel load for the race are limited. In these types of racing, where the engine is constricted in terms of performance by an upper fuel flow limit, then fuel conversion efficiency equals performance. With the fashion for regulation that rewards efficiency, the magnesium piston may yet see a new dawn.

Written by Wayne Ward

Is there a real gain to be had from r&d in motorsport? Does it matter outside of the company in question? Well, yes, and people in positions of influence within governments do take notice. The British system of government, like many others, has an upper and lower chamber. The upper chamber (the House of Lords) is now populated by people who, in the main, represent political parties but who are proposed rather than elected. Two such people are Lord Rooker and Lord Astor of Heverbrook, and during a debate on the armed forces in March 2014, Lord Rooker asked a question on the UK’s use of biofuels in defence. In the question, he stated that most of the fuel and materials development in Britain stems from motorsport. In replying on behalf of the government, Lord Astor assured him that the government is working closely with the motorsport industry, and went on to give examples of our good work.

Fuels are an excellent example of how, as an industry or a business, motorsport can make itself relevant to the outside world. We can see that biofuels are going to form an important element of our liquid fuel supply in the future, so we should make rules that encourage motorsport to be early adopters of such fuels. There is no doubt that motorsport can be an extremely cost-effective way to undertake the rapid development of engineering concepts. Developing engines and fuel systems suited to the use of, for example, bio-butanol might be seen by the wider world as something very worthwhile, and technical partnerships might be forged that benefit everyone involved.

As far as the armed forces are concerned though, we aren’t going to be of much use for developing fuels for powering jet fighters, but there still remain myriad uses for piston engines – both small and large – and there is a very important role for companies with a motorsport background. What we should excel at is carrying out development for the wider automotive industry, and it seems that we are now waking up to this fact. We should take a long look at the direction roadcar fuel development is going in and get ahead of the game. If we are late to the party then we are an irrelevance – we have no role in development and derive little benefit from adopting such technologies. If we are the earliest adopters though, and can present multiple options, we assure our financial future far more easily.

Motorsport companies are always looking to do something new, especially if it can give them some advantage, but there needs to be an incentive to invest in development. We need to take a longer-term view of what future passenger car fuel trends are and move in that direction.

Written by Wayne Ward

In Al-Sn-Si bearings the tin content, which can be as much as 40%, acts as the soft component distributed within the aluminium matrix. As a separate phase this produces a diffuse network along the edges of the grain boundaries of the aluminium to give the bearing surface its low frictional properties under boundary lubrication conditions. On the other hand, the high-hardness silicon is distributed across the aluminium matrix and serves to polish the mating journal while retaining the lubricant on the bearing surface to support hydrodynamic lubrication. 

Aluminium-tin-silicon bi-metal bearings consist of two layers bonded onto a steel backing plate. The intermediate layer, which consists of pure aluminium or an aluminium-manganese alloy, is bonded to the steel backing strip, after which the Al-Sn-Si is roll-bonded on top. The actual process might vary from one manufacturer to another, but the intermediate layer is there to help adhesion, stabilising the bonding between the outer layer and the steel shell, and also helps to serve as a cushion should edge loading be applied to the bearing in service.

Once bonded to the steel backing strip, bearings are formed into a semicircular shape and processed to the required bearing size In this state, the bearings are soft compared to copper-lead high-performance derivatives and so some method of hardening has to be introduced in order to improve their resistance to fatigue. The most common method is solid solution treatment, whereby the bearings are heated to 400-550 C and then rapidly cooled. Unfortunately, while this method increases the strength of the outer bearing layer it decreases the bonding strength of the intermediate layer, creating a brittle intermetallic layer next to the steel backing. The formation of this brittle aluminium-iron (Al-Fe) compound, although dependent on temperature, is also a function of the chemical composition of the aluminium alloy next to the steel.

This was an issue in early stages of development but was ultimately resolved by replacing the aluminium or aluminium-manganese intermediate layer by one consisting of aluminium and around 7-8% silicon. Instead of forming FeAl₃, this aluminium-silicon material forms an Al-Fe-Si compound, at a much higher temperature than that used during heat treatment of the outer bearing material. The presence of the silicon would appear to suppress the formation of the brittle FeAl₃ compound, producing a bearing with a much higher resistance to fatigue, but perhaps even more crucially the higher temperatures allowed would prove beneficial in optimising the composition of the outer bearing material to create even greater strength.

Just like the human body, once the problem of fatigue is overcome then the person can go from strength to strength.

Fig. 1 - Aluminium bearings after testing

Written by John Coxon

Using simple theoretical analysis it’s easy to see why. In any sliding element, as soon as the boundary friction has been overcome and the friction drops then, as the relative movement necessary to generate the wedge of oil increases, the resistance to movement (equivalent to friction) actually starts to build up again. In the case of rolling contact where, strictly speaking, there is only line contact across the cam-follower mating surface, the absence of relative movement suggests the absence of friction or its inevitable result, wear.

From the outset though, it must be appreciated that rolling contact components are generally much larger than sliding ones and are therefore likely to be much heavier, in general making them useful only in relatively low-revving larger engines as opposed to the much smaller faster-revving units that use sliding technology.  

Apart from the apparent reduced friction, there are of course other issues. For example, a rolling contact increases the contact stresses where the cam meets the follower. Anyone who understands the theory of Hertzian stresses will realise that the maximum stress in the camshaft will occur just slightly below the surface of the cam, and is a function of the radius of both the follower and the instantaneous radius of the cam at the contact point. The larger the roller, the lower the Hertzian stress, but the larger the roller then the heavier it is likely to be and the more difficult it will be to incorporate it within the engine.

The presence of the roller will also change the valve lift curve, simply as a result of the geometries involved, and while it may be possible to generate more rapid valve opening by using negative-radius cam profiles, this further increases the surface stresses, so even higher quality fatigue properties on the cam material are needed to prevent the formation of surface pitting.

While the analysis may also assume little or no slip between the rolling element and the cam, in reality that may not always be case. Slip is almost unavoidable, as a result of elastic deformation of the parts. This increases the surface area over which these forces are applied, reducing the contact pressure and increasing the likelihood of slippage or skidding. Minimising distortion by using materials with a higher Young’s modulus will increase contact pressure but will also increase the levels of Hertzian stress. As ever in the design process, the solution will inevitably fall somewhere between the two.

Whichever way you look at it, roller followers may sound like a good idea at the outset, but like many good ideas the exploitation of the benefits may be down to the matter of detail design.

Fig. 1 - Cam and roller follower

Written by John Coxon

Metallic coatings of any description have struggled to be newsworthy though, as they are unable to come close to the new engineering coatings in terms of hardness, friction or wear resistance. However, there is a wide range of soft metallic coatings that remain popular and to which the new hard coatings pose no threat. In this article we will look at some uses of these coatings.

Gold plating is something we might associate with cheap jewellery or cutlery that is more for show than use. However, it is used in motor racing, especially in electrical contacts, where its very low strength and stiffness allow it to conform under low loads. Gold-plated components brought into contact with each other quickly deform under light pressure to give large contact areas. This leads to a lower contact resistance and therefore an increase in efficiency. Gold-plated connectors are used for a range of purposes, from electrical power transmission to sensor wiring and earth terminals.

Silver plating, which is again something we might normally associate with jewellery or trinkets, is widely used on fasteners in industry. Such coatings are not the shiny, chemically brightened type used for decorative products but are quite dull, which may or may not disappoint you depending on whether you like your racing powertrains to look like they were made by Harley-Davidson.

Silver-plated fasteners are used widely to prevent seizure, either due to material compatibility problems (stainless bolts installed in stainless tapped holes are a particular problem) or where thread lubricants can’t stand the high temperatures in service. In this latter case, we find silver-plated fasteners used on exhaust manifolds, especially on boosted engines. A number of suppliers offer silver-plated nuts in various styles for this purpose.

The most common use of soft metal plating is on plain bearings. The coatings on bearing shells may consist of one or more extremely soft coatings, commonly based on lead. These very low shear-strength coatings allow the engine to run with little damage during start-up, and they are used in most forms of motorsport for crankshaft main bearings, con rod big-end bearings and sometimes for camshaft bearings. Their combination of coating thickness and softness allows hard particles to become embedded in them, preventing the particles from going any further and causing damage. This ‘embeddability’ can prove crucial in terms of engine durability, preventing critical bearing surfaces from becoming scored.

The cages of rolling element bearings are also often coated with soft metal plating. Copper is widely used for needle roller bearing cages, and silver is also found in this application too. Such bearings are often used to support the gears in cam drives. Silver plating is sometimes found on valve collets as well, helping them to conform to the valve and retainer geometry.

Written by Wayne Ward

If we deal with the first of these, this is solved relatively easily. If we interpose a bearing block between the crankshaft and the rod then we can reduce contact pressures; the block is ‘racetrack shaped’ – that is, a round-ended block – with a cylindrical bore. Both of these contacts are conformal, and the contact between the crankpin and bearing block bore is much as it would be in a conventional con rod, while the contact on the outside of the block is simply two flat surfaces in sliding contact.

It would be relatively easy to assure ourselves via calculation that our bearings can generate a proper oil film. In the case of the block running in the slot, we need to take account of the fact that the bearing block is reciprocating in the slot and comes to a stop when the crankpin is at ±90° relative to top dead centre. Coming to a stop means there is no velocity to generate an oil film, and this could lead to wear. However, with a suitably arranged feed of pressurised oil, it should be possible to preclude any wear problems.

The stiffness of the ‘big end’ of the rod is also a concern, as is its strength. In order to make the big end of the rod stiff enough, a lot of detailed design and analysis would be required, especially if the design was of the type that is split through the big end, as is the case with most four-stroke engines. The bolts would need to be large, as the bending moment would be considerable.

When the inertia loads are at their maximum, the distance from the bolts to the line of action of the applied load is much greater than in a conventional rod. However, this is mitigated to an extent by the fact that there are no secondary inertia forces, owing to the fact that the motion of the piston is simple harmonic motion. Also, because there are no concerns over high secondary forces or high side thrust loads – both of which are associated with short articulating con rods – the Scotch Yoke rod can be made as short as is practical, thereby minimising the reciprocating mass and the inertia forces associated with it.

The concept lends itself best to 180° vee engine architectures, because on such flat engines two pistons and the rod assembly operate on a single axis – that is, there is no bank offset – and some of the mass penalty of a Scotch Yoke mechanism is shared with another cylinder. However, the flat engine is not widely used in motorsport where bespoke engines are concerned. Granted, there are a great many Porsches competing in all kinds of racing, and Subarus have long been a favourite for rallying, but the unique packaging challenges of a flat engine means that the most advantageous engine configuration for the Scotch Yoke would present its own disadvantages in most race vehicles.

Written by Wayne Ward

EPDM is the product preferred for most automotive cooling systems currently. Capable of withstanding temperatures typically in the 110-130 C range, and sometimes up to 150 C, EPDM combines good heat and ozone (weather) resistance with better than adequate protection against oil and other under-bonnet chemicals such as ethylene or propylene glycols. To enhance its performance, especially under partial vacuum (for instance at the entry to the cooling pump), it can be reinforced with aramid braided yarn to increase stiffness, give greater burst strength and yet still maintain a level of flexibility.

Properly designed, hoses made from EPDM generally last for the full lifetime of the vehicle, which is normally reckoned to be up to at least 15 years or 150,000 miles. However, a word of warning: there have been instances where corrosion inhibitors in some organic acid-based coolants– which are designed to protect modern cylinder head/block alloys containing aluminium and/or magnesium – may have leached out certain components of the EPDM, causing corrosion in the narrow passageways of the cylinder head. While we are told that this issue has now been solved, it emphasises the need to use only the approved engine coolant anti-freeze/corrosion inhibitor in any application.  

While EPDM hoses are the most likely to be found on many road transport vehicles, for applications where the requirements are more severe then silicone rubber is making headway. This is a polymerised siloxane or polysiloxane that consists of a chemical backbone of Si-O-Si-O-Si units. Unlike most other polymers, which have a carbonaceous backbone to them, polysiloxanes are inorganic and, unlike their organic counterparts, the bond angles in them are large and the bonds also vary in length. Thus, when the product is injected into the mould and then cured, the system of crosslinking between each chain of molecules gives a far less rigid product than EPDM, and it is this flexibility as well as many other attributes which is courting appeal.

Perhaps the best attribute of silicone elastomers is their incredible resistance to extremes of temperature while still maintaining their useful properties. Silicone elastomers can routinely withstand temperatures as low as -55 C and as high as +170 C, which is more than adequate for most under-bonnet applications. To counter this flexibility if used under partial vacuum – when the hose can collapse – the material can be reinforced with up to five layers of a medium-duty knitted or woven polyester fabric. A liner made of a natural rubber can also sometimes be placed inside to seal off potential leakage paths caused by any exposed fibre.

In applications where hydrocarbon fluids may be present (oil mist in engine induction systems, for example), silicone hose lined with a fluorosilicone is normally used; this prevents the migration of the fluids through the hose wall over time, causing the hose material to swell. In this way the hose will not become brittle and fail. Furthermore, the operating temperatures will be increased to up to 250 C, which makes them ideal for turbo or supercharger/intercooler hoses or on passenger vehicles that are subject to stringent emissions tests.

Above all though, silicone rubber hoses can seriously improve the appearance of your engine bay.

Fig. 1 - Seen in the paddock at the Shelsley Walsh Hillclimb, a black EPDM hose in the cooling circuit, and blue silicone for the supercharger air hose

Written by John Coxon

As with many aspects of powertrain design, it is possible to combine the thinking behind two concepts, and so it is with the visco-elastic damper. We have described the basic concept of an inertia damper where an inertia ring reacts against vibrations via elastic elements, normally either springs or elastomeric elements such as O-rings. Elastomers can act very effectively as dampers, but we have to be aware of the rate at which we are putting energy into any system containing them. Beyond a certain wattage (or BTU per hour for those who prefer imperial units) per unit volume, the elastomer will quickly degrade into something unsuited for further use as a damping element, so the critical rate of heat addition to a volume of elastomer depends on the exact type and grade used.

So, if we want some controllable damping but don’t want to rely on an elastomer to provide it, is there an alternative? Well, if we are willing to accept a degree of extra complexity, the answer is yes. A visco-elastic damper incorporates springs that have very little damping, and a liquid that takes care of the damping. It allows us to have independent control over the behaviour of the elastic elements (springs) and damping which we don’t have in an inertia damper with elastomer elements. A viscous damper has damping in abundance but no springing.

In a visco-elastic damper, when there is vibration present, fluid is forced to travel through small orifices between pairs of chambers, and the motion of the inertia ring relative to the crankshaft is also controlled by springs. It can be likened to a rotary version of a very simple suspension unit (shock absorber) that we might find on our car or motorcycle. Owing to its elastic elements, the visco-elastic damper can be tuned to react to vibrations that occur at certain frequencies, corresponding to those at which we know serious vibrations occur.

The extra complexity in manufacture comes from having to machine precise orifices for metering the damping fluid and to incorporate seals that will prevent the damping fluid from escaping. There is also the matter of having to put the assembly together with the correct amount of fluid in there. It is fortunate therefore that there are companies which supply such complex units.

I don’t know if any race engine suppliers are using such units, owing to their comparative bulk, but they are certainly used for controlling torsional vibrations on crankshafts and camshafts in industrial engines. Don’t read anything significant into the fact that these are fitted to crankshafts to infer the size of the industrial engines which are equipped with viscoelastic dampers; I have seen more than one highly optimised race engine fitted with camshaft dampers.

Written by Wayne Ward

At the simplest level, the main channels on any data logger are likely to be engine speed and throttle angle. To understand how the power unit works in conjunction with the chassis, inputs such as steering and lateral acceleration are also a must. Using these five channels and not having to understand anything else about the engine, a driver can generate more than enough data to improve his driving skills by comparing data lap after lap. Indeed, some kind of chart-overlaying feature is the first stage in any data analysis process, and is the one most commonly used, while a popular add-on feature these days is the ability to synchronise video data files to those logged directly from the engine controller.

As power unit engineers, however, we are much more interested in engine control, so in addition to the above recorded channels we might wish to include a number of pressures (oil, fuel and so on), a smattering of temperatures (coolant, intake air, oil and exhaust gas, say), injector pulse widths, lambda (a function of air-to-fuel ratio) and ignition timing. Logging all these against time for a typical 15-minute club race will generate far more data than many engineers or drivers can ordinarily handle, so some simple way of analysing the data has to be found. Fortunately, even the simplest data logger has a number of ways in which it can assist.

To start with what is generally the default setting, multiple channels can be plotted against the time or distance travelled. This enables the driver or engineer to pinpoint certain events during the lap and read off other parameters happening at the same time.

Many analysis software packages can also generate histograms or sometimes more usefully x-y plots. In the latter case, one channel can be plotted against another to infer whether there is any causal relationship between the two. One example of this is a plot of gallery oil or fuel pressure against the lateral g-force when a slight fall-off in the pressure on right- or left-hand corners could indicate the presence of oil or fuel surge.

A particularly useful feature in many systems is the ‘maths’ channel. By using the data measured on one channel, a new function can be computed to help our understanding. A good example of this, and one that is highly topical in Formula One, is the subject of fuel consumption. By using our knowledge of the pulse width applied to the fuel injector, along with fuel pressure and temperature, we can determine the amount of fuel going into the engine per injection pulse and, summed over a unit of time, the rate of fuel consumption can be calculated. Summed over the whole race, the total fuel consumed can be derived. How accurate this is compared to, say, a fuel flow meter is open to debate, but the whole idea of maths channels increases the flexibility and potential usefulness of any system. 

As powertrains become more complex, the need for data logging and subsequent analysis of the data can only increase.

Fig. 1 - A simple histogram, summarising coolant outlet temperature

Written by John Coxon

Another significant engine component that has a direct relationship with these increased loads is the cylinder head, so let us take a closer look at the consequences for the head, and which design modifications would be needed to overcome them.

In principle, every cylinder head has three major loads working on its structure – assembly (bolt loads), thermal and gas loads. In the previous article we saw that the maximum gas load has risen significantly, given the fact that the peak firing pressure went from 100 bar with the naturally aspirated V8 engines to more than 200 bar with the current turbo engines. Because of this we estimated an increase in bolt size from M11 to M14. The corresponding load on the cylinder head increases as well, and therefore the material thickness under each bolt head will need to be increased.

Since the bore of the engine has fallen from about 98 to 80 mm we already have a little less room for the coolant jacket, and because of the increase in material thickness another couple of millimetres is taken from the coolant jacket.

The other two loads have a direct relationship with each other and need to be balanced. On the one hand, the increase in peak firing pressure would require the flame deck of the cylinder head to be thicker, simply to withstand the bending of the head under these increased gas loads. Unfortunately, a thicker flame deck means the coolant is further away from the combustion temperatures, leading to higher material surface temperatures. And we mustn’t forget the fact that we were facing increased specific power, again a reason for higher flame deck temperature.

The most critical issue here is thermo-mechanical fatigue (TMF), which is damage of the material based on the differential temperature between hot and cold areas in relation to the material’s inability to expand and shrink freely under these conditions. The question now is which of the measures – increasing or decreasing the thickness of the flame deck – will be more important.

In this context the reduction of the bore by about 18 mm is helpful, simply because the increased gas load works on a smaller area. The resulting average load increase will be about 33%, a negative factor.

So what works in our favour then? Since the wall thicknesses of the ports are constrained by the casting process rather than design, there would be no reason to assume that these have decreased with the bore reduction to 80 mm. Therefore the structural function of these ports in the cylinder head (creating a kind of pillar between the flame deck and the upper deck of the head) has increased relatively.

On the other hand, cooling of the cylinder head needs to be improved because of the higher specific power (from about 225 to 300 kW/l). This increase will result in higher temperatures of the area around the exhaust valves and higher strain in the valve bridges between the exhaust and intake valves.

Another factor is the valve orientation, which is such that the exhaust valves are on one side of the engine and opposite to the intake valves. Thermal growth is more difficult to control in the longitudinal direction of the engines because the cylinders are next to each other. The internal material damage will therefore be greater because in this direction the head provides more resistance during expansion under temperature load, putting the highest strain in the intake-to-exhaust valve bridges. This, in combination with the fall-off in aluminium’s material properties under higher temperatures, means that reducing temperature in these areas is key.

Since the valve area is filling almost the entire bore, there are not many areas where the flame deck wall thickness can really be kept at its minimum. Looking at the very few pictures of Formula One cylinder heads that are available, I would estimate a wall thickness of around 8 mm as a minimum.

Not having any design experience specifically with Formula One engines, I am going to make an educated guess at estimating a reduction of up to 30-40 C flame deck temperature per 1 mm wall thickness reduction (getting the coolant closer to the combustion). These levels of temperature reduction will significantly improve resistance to TMF.

This is the main reason for me coming to the conclusion that the maximum effort, going from naturally aspirated V8s to the current turbo engines, must have been in reducing the flame deck wall thickness instead of increasing it due to gas loads, and I think the area between the valves has probably received the most attention.

We should not forget though that achieving these kind of reductions is not only how well one can design these critical areas but, even more important, how they can be produced – the cylinder head core packages must have been more detailed and more accurate than ever before. Hopefully it will soon be possible to write an article that focuses on these production processes.

Fig. 1 - In red is shown the wall thicknesses between coolant and flame deck. As can be seen, there is no real homogeneous wall thickness, given the complex structure of the head (Courtesy of Toyota Motorsport)

Written by Dieter van der Put

Audi needs to remain competitive in the face of new competition, and its latest diesel engine seems to be a match for the gasoline competition, although Porsche is surprisingly quick in its latest foray into the top division at Le Mans.

We last covered diesel exhaust systems specifically in 2010, when the focus was on diesel particulate filters. In that article we explained why such filters were required, how they work, how they affect noise and so on. The press pictures of the latest Audi R18 diesel do not clearly show where a particulate filter might be, but comments by Audi engine chief Ulrich Baretzky about being able to eliminate a second particulate filter seem to point to the fact that Audi still needs to use one to prevent visible smoke.

Why one filter instead of two? There is no magic in this – the R18 engine is based on a V6 block with a wide-angle vee, and the inlet system feeds the heads from the outside of the vee. The exhaust system is therefore in the centre of the vee, and the exhaust manifolds on each bank feed into a single twin-inlet turbocharger. One exit pipe, one particulate filter.

This exhaust system architecture makes sense for an engine with a single turbo, and is possible because of engine rules that are not too restrictive. Formula One, on the other hand, has a single turbo mounted to a V6 engine, and the exhaust routing is far less elegant because the rules mandate that the inlet system is in the centre of the vee and the exhausts on the outside.

From the available ‘spy’ pictures, there does appear to be a ‘racetrack-shaped’ particulate filter housing – that is, a block with round ends – immediately following the turbocharger. There has been speculation that the filter is housed within the single cylindrical exit pipe, but the pictures of the engine from other angles tell the true story.

It would be possible to make such a small-diameter long filter, but that would present too great a restriction to flow and an unacceptable pressure loss that would give reduced efficiency and increased fuel consumption. It is unlikely that there would be significant blockage of the R18’s filter by unburned soot owing to the high exhaust gas temperatures because of the high load.

During extended safety car running this might be a concern, but the carbon should be burned off quickly, either when returning to racing speeds or by using a controlled regeneration cycle that increases exhaust gas temperature in order to achieve the same effect (thanks to Paul Cole for his comments on my previous online article).

The racetrack-shaped filter elements are more expensive than the cylindrical types to manufacture and to house, but these are often used when packaging requirements won’t allow a sufficiently large filter face area with a cylindrical form.

Written by Wayne Ward

One fundamental choice that we need to make is that of threadform. We need to carefully select the correct size of fastener so that it can provide sufficient pre-load and withstand the service loads we expect to subject it to. There is a wide variety of threadforms to choose from; not all threads are designed for use as fasteners, so those such as acme and trapezoidal threads can be discounted instantly. We will generally choose between metric (M) and unified (UN) threadforms, both of which have flank angles of 60°. Unified threads are imperial (inch) sizes and are most widely used in the US, which continues to use the inch as its preferred unit of length.

There are fatigue-resistant versions of both these types of threads, known as J-form threads. For any given thread pitch, these have a more generous root radius on the male thread than the ‘non-J’ equivalent. The increase in root radius increases the fatigue strength of the fastener for two reasons. The first is that the stress concentration is reduced slightly owing to the radius increase, and the second is that the minor thread diameter is also increased. J-form threads are denoted by MJ for metric and UNJ for imperial sizes, and there are only certain combinations of nominal diameter and pitch for which J-form threads are available.

Whitworth threads incorporate a controlled radius on the major diameter of the tap, so that the female threaded component is rendered more resistant to fatigue by having a reduced stress concentration at its major diameter.

The aero thread is a very clever but complex thread system that has never gained widespread acceptance. It incorporates a number of features that make it resistant to fatigue but it is rarely (if ever) used for new designs, and I have never seen an example of this in anything other than a textbook. The male thread is semicircular and relatively shallow. It therefore resists fatigue for the same reasons as the J-form threads but to an even greater extent.

The female thread is cut into a nut or casting, for example, and is of a completely different form to the male thread, being similar in terms of geometry to a common 60° flank angle thread. There is an intermediate member which is a thread insert to be installed into the female component. The thread insert has a 60° flank angle thread on the outside and the semicircular thread on the inside. Thread inserts de-stiffen the female thread, and this is known to improve the distribution of load along the thread. In a conventional metric or unified thread, the first loaded thread takes very much more of the load than any of the other threads, and the use of female components of lower stiffness than the male thread makes the load distribution much more even.

Aero threads are expensive to produce, and the lack of availability of suitable inserts makes them impractical. However, the concept of using thread inserts to improve load distribution (and hence reduce stress concentration factor or improve fatigue strength) is very valid, and suitable thread inserts are available in most metric and imperial thread sizes.

Written by Wayne Ward

But while the science of injector fouling is now well understood, the one thing that can increasingly defeat many a design is its hot fuel handling capability. And if you consider that the role of the fuel in contemporary injector architecture is one of cooling then this would seem to be a major failing.

In most commonly used injectors these days, the fuel arrives via the pump and filter and accumulates in a fuel rail under pressure. In response to the ECU-activated signal energising the solenoid, and thus opening the injector, the fuel flows axially down the injector through a simple strainer and around the solenoid coil, thus cooling it. So long as the fuel continues to flow and is injected into the cylinder, all will be well, but when the fuel stops flowing then any residual heat soak from the engine or the injector solenoid will migrate into the fuel still sitting in the injector.

As the temperature of this fuel rises then fuel vapour will form, causing a phenomenon called vapour lock, making restarting the engine very difficult. With the desire for engine packages to become much smaller, and as engine performance levels increase, this extra heat and the proximity of components such as exhaust-driven compressors will make the issue of vapour lock even more critical. In future therefore, hot fuel handling could be a major issue in low-pressure port injection systems.

Fear not though, all is not lost. One way around the problem is to increase the pressure in the fuel at restart. This should condense the fuel in the injector back into its liquid form and enable the engine to start again as planned – and indeed, most current vehicle systems work this way. Another way though, and one that is highly attractive in liquid-fuelled LPG applications, is to use so-called ‘bottom feed’ injectors.

Here, instead of feeding the fuel into the top of the injector and clamping the injector between cylinder head and the fuel rail, as is normally the case, the fuel intake into the injector is via a series of drilled holes through its side towards the bottom. Flowing through a gallery, perhaps even integrated with the cylinder head, the fuel passes into the injector and is injected out into the cylinder without going anywhere near the controlling solenoids, and any vapour (which is less likely to be formed anyway) can be easily vented and out of harm’s way. This type of system works best when the fuel is re-circulated back to the tank for cooling, and will be essential if using LPG-type fuels that boil at temperatures only slightly greater than ambient at rail pressures of about 8-10 bar.

Bottom-feed injectors were typically used on throttle body systems many years ago, but with the increasing interest in alternative fuels could they be another case of ‘back to the future’?

Fig. 1 - A bottom-feed injector

Written by John Coxon

Engineers have grappled with this problem for many years, and while the currently favoured approach (given a healthy if not quite unlimited budget) would be to use computational fluid dynamics (CFD) and powerful computers, such facilities are rarely available to the average engine tuner or workshop. On the less virtual side of the industry, where funding is often hard to find, the task is downgraded to the physical: that of testing the airflow in the cylinder head. The CFD output of pictures of meshed intake ports and coloured streamlines flowing through the intake port may look ‘sexy’ (if sometimes a little confusing) but believe it or not similar results can be obtained using instrumented equipment measuring local flows on the airflow rig.

The most obvious way is to use a pitot tube inserted into the port. Handheld and used correctly, this can be moved around inside the port to give an idea of the distribution of the air flowing around the valve. However, introducing the tube to measure the velocity of the airflow in this way also has the effect of altering the local airflow around it, so what you think may be happening in the port and around the valve may not actually be the case when the tube is not there.

In the past of course, many engineers have grappled with introducing pressure tappings drilled into the port wall around the outside of the port throat, and while that can give an indication of the static pressure in this zone, it is difficult to do and destroys the cylinder head in the process (in drilling through water jackets an so on). Also, the data generated is relevant only to the static pressures around the wall of the port, as it makes no link with the bulk flow of the air away from the wall. Essentially, all we need is some kind of probe that extends into the critical airstream without altering the flow, and in a sense we already have that in every port – the valve!

By taking the pressure tapping off the seat of the valve and routing back through the valve stem, we can estimate the pressure of the air as it passes the restriction caused by the valve seat. Like the port wall tappings referred to above, since these seat tappings are normal to the direction of airflow then this measurement would be one of static pressure and not include the dynamic element of the flow, but by indexing the valve in a number of positions (different valve lifts and rotational position of the valve, for example) a good idea of how the air flows through the valve seat curtain area is obtained.  

This method may not impress your boss as much as CFD, or produce a pretty picture of how the air flows down and around the port, but in terms of speed and the fact that you will be testing the actual components to be used, the technique has much to recommend itself.

Fig. 1 - Airflow testing at the valve seat

Written by John Coxon

In the early days of racing it was perfectly acceptable to simply vent crankcase pressure directly to the atmosphere. However, given that the gas being vented contains a mixture of unburnt fuel, combustion debris and oil mist from the crankcase, this approach became unacceptable in the post-war era as environmental concerns started to grow.

The simplest solution to containing these by-products is a closed circuit breather system, where the case pressure is vented directly into the engine inlet. Over time, these have evolved into quite complex systems to manage case venting at varying engine loads and speeds. For example, the systems used on modern roadcars will use valves that prevent oil mist being sucked directly from the engine at low speeds when case pressure is low and inlet vacuum high.

While some race engines feature such systems their complexity is not appealing, and neither is the ingestion of oil mist into the inlet charge. Thus, in racing applications, by far the most popular method of controlling oil expelled through any vents is to use a catch tank with either a separate or integral oil separator.

The most basic type of oil separator consists of a simple volume through which the blow-by gases flow. As the gas enters the volume, its velocity slows, allowing oil to drop out of suspension and pool in the bottom of the volume. The oil can then be either fed back into the engine or into a catch tank. Taking the void approach one step further is the use of what is known as a ‘labyrinth’ system of baffles. These force the blow-by gas to slow down by directing it around tight corners, and again the oil drops out of suspension.

More complex are centrifugal-type separators. These cause the gas to spin through a chamber, with the oil droplets separating out and running down the chamber walls. ‘Driven’ centrifuges, where the cylinder is actively rotated, are one option but they are rarely used because of their complexity. Far more common are non-driven centrifuges, where the gas enters a circular chamber at a tangent and is encouraged to flow in a circular motion, creating enough centrifugal force to throw the suspended oil against the chamber walls.

Most catch tanks with integral separators will use either this type of design or a labyrinth-type baffle. Note though that most dry-sump oil tanks also rely on the centrifugal approach to help de-aerate scavenged engine oil. 

The most important design consideration for an oil separator or oil catch is its cross-sectional area. This needs to be large enough to allow for the speed of the blow-by gases entering the device to drop below 1 m/s as they transit the separator/tank to the vent. It is also worth having an inlet angle that is tangential to the wall of the tank, in order to promote a circular motion regardless of whether centrifugal force is destined to be the sole method of oil separation.  

Written by Lawrence Butcher

The role of surface treatments and coatings is important here: if selected correctly, they can significantly increase the durability of the component. If we look at the common example of a steel piston pin, there are a lot of possible surface treatments and coatings. However, we find that racing pins are very often made from a nitriding steel, or other types of steel that respond well to nitriding even if they weren’t ‘designed’ for this purpose.

The nitriding treatment both hardens the surface and puts it into a state of residual compressive stress. The hardening of the surface is an important factor in making the surface resistant to damage, and the compressive residual stress means the pin is much more durable – its fatigue resistance is increased markedly for any given level of service load. The resistance to surface damage is an important part of this fatigue resistance too: as the surface is difficult to damage, there is little risk of a significant stress concentration forming during the piston’s working life.

Coatings are an important consideration as well. As with nitriding, hard low-friction coatings also increase wear resistance and also reduce any tendency for the component to seize in either the con rod or the piston. The most common type of coatings we find on racing piston pins are the diamond-like carbon (DLC) group. If DLC is not properly ‘supported’ by the substrate though, there is a risk that small particles of what is a very hard, sharp and abrasive coating could be introduced into the contact between pin and piston or between pin and rod bore, where they would be likely to cause significant damage.

The effect of strengthening the surface of the component by surface hardening is an effective way to improve the durability of coatings. The hardening process, if properly specified and carried out, prevents the pin surface from yielding. While DLC coatings are very good, however, they are not known for their ability to conform if the substrate deforms plastically.

Nitrided piston pins were very popular before DLC-coated pins started to become commonly used, perhaps 15 years ago, although their superiority over non-hardened pins had been obvious for a long time. With the advent of piston pins with hard coatings that could potentially cause damage if they were to fail, the role of the nitriding is therefore more important than ever.

Written by Wayne Ward

Low-pressure carburising minimises the distorting effect of carburising, which has been one of the main drawbacks with the process. In order to control the properties of the carburised material, it is necessary to quench the component, and it is at this stage where traditional processes can introduce distortion, especially where liquids such as oil are used for the quenching. It is very hard to achieve an even rate of heat removal when an extremely hot component is plunged into cool oil.

One solution is to quench using a gas. Even though the carburising process is low pressure, the pressure of the gas quench can easily be 10 bar or more. In order to improve surface finish, inert gases are used and, in contrast to traditional oil-quenched carburising processes, the parts emerging from a vacuum carburising process followed by an inert gas quench remain bright and shiny in appearance. Typically nitrogen is used as a quench gas, but helium is also finding some use as it offers higher rates of heat removal owing to its lower introduction temperature and high specific heat capacity. Argon is also occasionally used.

If we consider where our carburised part fits in the engine, we might find that we need to fasten it to another component, perhaps even using threaded holes; we may also need to have thin areas of material. The danger with threaded holes is not limited to distortion but also the fact that the whole thread might be completely carburised, rendering it very brittle and prone to failure. In the same way, very thin sections of material might be hardened completely through.

Fortunately though we can indicate to the carburising supplier which areas of the component are to be treated, those that must not and those that are optional, by supplying them with a drawing. The part of the drawing that deals with heat treatments and surface treatments is often the key to success in component design, so it is important to ensure any general notes, instructions on drawing views or attempts to specify which areas are not to be treated are specific and clear.

The areas that are not to be carburised can be mechanically masked, but are most often plated or painted to prevent a carbon-rich case being formed. Copper plating is an effective method of preventing carburising; it’s a process known as ‘stopping off’. Also, copper-bearing paints can be applied either by spraying, brushing or dipping, and a number of the more modern stop-off paints are water-based and so water soluble, so can simply be washed off after use.

Written by Wayne Ward

In simple terms, a CAN bus is a network of individual electronic controllers that communicate using a protocol which automatically gives important signals priority over less urgent ones. As vehicle electrical systems grew in complexity, CAN systems were developed to reduce the amount of wiring needed. This reduction is achieved owing to the fact that each controller needs only two wires to transmit signal data.

For example, if a car’s stability control system featured wheel speed, brake pressure and suspension displacement sensors on each wheel then, without CAN, each of them would need to be hardwired to the stability control ECU. With a CAN system, however, the sensors can input into individual control boxes located either at each corner of the car or, say, one front and one back, which then process the sensor signals and communicate with the main ECU via simple twin wires. In the old system, anything up to 20 individual wires would need to run to the ECU, while with CAN this can be reduced to just four if only two processing boxes are used.

From a data engineering perspective, these systems make it very easy to add or remove functionality from a particular data recording set-up. If properly implemented, CAN will also provide much better system redundancy in the event of components getting damaged.

There are two key ways of going about this with a production car already fitted with a CAN system. The first and easiest option is simply to connect to the factory ECU (if used) through the diagnostics port. With the correct interface and data logger, the information the ECU is receiving from its various sensors can be easily recorded. The alternative is to run a system piggybacked onto the existing wiring, sharing the CAN data signal being sent to the ECU.

“If you are doing a test and you want to add some functionality to the car, the CAN is very useful,” explains Steve Dunlop, an engineering and racecar constructor with the JRM team, which has extensive experience of running both rally cars and track machinery. “One particular area that that comes to mind is when you want to add a wideband lambda sensor instead of the narrowband type usually found in production cars; it is very easy to add it to the CAN stream and integrate it with your existing system. It also means you do not need to cut into the existing wiring looms, and the new additions simply run in parallel with the sensors already present.” 

The benefits of CAN-based vehicle electronics have also seen their growing adoption over the past five years in motorsport-specific engine control systems. For example, the Fiesta R5 rally car features a near-comprehensive CAN-based wiring system, with individual control modules designed specifically for the demands of motorsport sited throughout the car. The result is less cabling in the car, meaning simpler and thus cheaper and lighter wiring, combined with easier maintenance thanks to the improved fault diagnostics capability the CAN system has over a regular wiring loom.

Written by Lawrence Butcher

For example, one electric drag car I have studied features a pair of astoundingly powerful electric motors, pushing out in the region of 700 bhp, which would have more than enough power to propel it down the strip at great speed. However, it also has a planetary geared transmission, which helps make the most efficient use of the car’s motors.

As the owner and builder of the car explains, “The power band of our motors gives us peak horsepower between 2400 and 3400 rpm, so it is a narrow band. What we are able to do with the use of a transmission is go through that peak four times in a run. Our goal, after studying the data we gained from our first car, was to keep the car in that power band for as much of the run as possible.”

The result is blistering acceleration all the way down the track. By using an under-driven ratio for first gear, the car achieves very low 60 ft times, leveraging the instantaneous torque delivery of the motors to the maximum, while the additional three ratios help it reach a speed of more than 150 mph by the end of a run.

Another interesting EV transmission design draws its technology directly from that used in the current generation of MotoGP ‘seamless-shift’ transmissions. It eliminates the dog rings found in a regular sequential transmission, and instead uses ‘bullet rings’ to engage the gears. A gear is selected when one ring is moved until its bullets hook onto drive teeth on the side of that gear. A second bullet ring moves in the same direction, with its bullets filling the gap between the teeth, eliminating any slack between the gears.

Eliminating this slack is what creates seamless upshifts and downshifts. By integrating the dampers inside the gear hubs, the manufacturer claims that the need for a clutch is eliminated – and this, combined with a seamless change of ratio, means the motor’s torque delivery can remain constant.

On a simpler level (although in terms of overall system complexity, far higher), hybrid vehicles that use electric drive motors on one or both axles can also benefit from a transmission. Taking the latest generation of hypercar road-going hybrids and both Porsche’s and Audi’s LMP cars as an example, the use of clutch systems and reduction gears helps increase motor efficiency. For instance, Porsche’s 918 roadcar uses a system of clutches on the front drive motors to disengage them above 146 mph, with the clutches being electronically controlled to provide the function of an active differential.

Meanwhile, other cars use reduction boxes to maximise the already high torque output of their electric motors in order to assist acceleration. This is a logical approach when thinking of an optimised racecar package. The boost provided by an electric motor should be far more beneficial to lap times if it can increase corner exit speed, rather than being used at high speed where the extra power has far less impact.

The age of electric and hybrid racers is still young, but rest assured that the rise of electric motors does not mean the end of multi-speed transmissions.

Written by Lawrence Butcher

When excited at certain frequencies, the spring will vibrate at one of its natural frequencies, and in such situations the stresses in the spring may be far higher than those in which we intend the spring to operate. It is therefore imperative that engine designers consider techniques and methods to reduce the tendency of the spring to operate in this resonant condition, which is often known as spring surge.

The first thing that should be done is to ensure that none of the major harmonics of the cam profile coincide with the natural frequencies of the spring. A cam profile is not a simple sinusoidal wave, and can be analysed to show the strength of a number of harmonics. Basically, the profile is made up of sine waves of frequencies that are integer (whole-number) multiples of the actual frequency of valve opening. The strongest of these are the low-number harmonics, so we need to avoid these if possible.

The exact number that needs to be avoided is not universally accepted, and depends on the experience of the engine designer. I’ve heard of people avoiding as few as the first five harmonics, and others who choose eight or more. This essentially means that the natural frequency of the spring and mass system (the mass being that of the components, the action of which the spring controls) needs to be N times the basic excitation frequency. So, if the engine revs to 18,000 rpm and the cam turns at 9000 rpm, which equates to 150 opening and closing events per second, we need the natural frequency to be at least 150 N. This is the strongest fundamental defence against surge.

Where two or more springs are used to control each valve then we can have them specified and supplied with a light interference fit. It is usual to specify the springs with different natural frequencies so that, if surge should occur, only one spring will resonate at a time. The damping action due to friction between the resonating spring and its partner reduces the damage done by converting some energy to heat and, where space allows, some spring suppliers also supply special dampers that fit between pairs of nested springs.

Progressively wound springs, which have tighter coils at one end, are also effective. As the spring compresses, the most tightly wound spring coils come into contact, changing the  effective number of coils and increasing the spring rate, which is a measure of the spring’s stiffness. The natural frequency of the spring-mass system is proportional to the square root of the spring stiffness, and where the change in stiffness throughout the opening event is large enough, the fact that the excitation no longer coincides with the natural frequency of the spring effectively controls vibration.

Where a single spring is used, beehive or tapered springs are also another way of providing a spring with a changing natural frequency throughout the lift curve, achieving the same effect as a conventional progressively wound spring.

Written by Wayne Ward

The regulations impose a limit on the combined use of CFD and wind tunnel time must fall below a limit line. The natural implication of this is that, for most teams, CFD use is compromised to an extent in favour of wind tunnel time, given that it remains the primary development tool of the teams.

It follows then that one of the most desirable attributes for a CFD simulation is fast turnaround. This has led to a great deal of convergence of methodology between teams to using commercial Reynolds averaged Navier Stokes (RANS) solvers with wall modelling, high under-relaxation factors and high-quality meshes capable of producing steady values of lift and drag within a few hundred iterations.

While this methodology can produce well-correlated results in a timely fashion, however, it does not represent the forefront of development in CFD methodology, and arguably shows that teams are heading towards a stagnation in accuracy improvements. Practicality governs the use of this methodology but the regulations prohibit more accurate and more computationally expensive methodologies. Now let’s examine the possibilities the teams are dissuaded from pursuing.

First, if we discount methods such as direct numerical simulation, large eddy simulation and (to an extent) detached eddy simulation as being impractical – particularly in terms of providing a result within an acceptable timeframe for a Formula One team – then we are still left with main ways of simulating the unsteady flows characterised by a Formula One car: the unsteady RANS and Lattice-Boltzmann methods.

Both provide a wealth of data beyond steady-state RANS solvers, as the ability to look at transient data makes it is easier to visualise how flow structures interact with one another and how vortices generated at the front of the car propagate downstream. Both are available in existing commercial software, the Lattice-Boltzmann method in particular allowing transient data to be obtained at a relatively low computational cost, and because it is inherently transient and has greater numerical stability, it is harder to make the simulation crash. These methods could realistically be used by Formula One teams on a daily basis to drive development; it is primarily the regulations that stop them exploring them further.

Aside from using new methods, teams are equally restricted in trying to maximise the information they can generate in conjunction with their existing RANS solvers. In recent years there has been more emphasis on creating aero-elastic bodywork, which allows teams to set up their car with minimum compromise or (depending on your opinion) completely flout the regulations. Rightly or wrongly, aero-elastic bodywork is an area of interest to Formula One teams, and much of the focus on it has concerned the front wings, specifically flexing the wing to move the ends closer to the floor to further exploit the ground effect or to place the wing into a stall condition to reduce drag.

Aero-elasticity is particularly difficult to model in a wind tunnel: the materials used and the size of the (scale) models are different from the car they mimic, and hence behave differently. Computationally it is possible to model aero-elasticity, although at present it invariably involves coupling a fluid dynamics solver with a structural solver. This presents its own difficulties: scripting is needed to couple the solvers, as is potentially the need to re-mesh the geometry after it has altered shape and skewed some elements. Naturally though, the passing of information between solvers and the need to run longer to achieve convergence for each iteration of geometry change means this is not currently an attractive way for Formula One teams to run their solvers on a daily basis.

It is often said by technical writers that the wheels and tyres account for around a third of the drag on a Formula One car, so modelling the flow interaction with the wheels is seen as crucial to being able to engineer an efficient car. There are currently two main ways of modelling wheel rotation – using a moving reference frame, and using a sliding mesh. The former is the norm for Formula One teams, and relies on assigning a constant speed of rotation to a volume region. The latter is generally out of reach to teams as it invariably requires a transient simulation to be run, although neglecting its use means teams are not modelling the true rotation of the wheel.

Aside from modelling the rotation, another key area teams seek to optimise to improve their correlation is the squash shape of the tyre. Modelling the deformation of the tyre would again involve coupling the simulation with a structural solver, and is hence not possible within the framework of the regulations. So while teams model different trajectories of yaw, steer, roll and ride heights, their accuracy is limited by their grasp of tyre squash.

Next edition’s article on this keyword will continue to examine what the current regulations implicitly prohibit, focusing predominantly on thermal applications. 

Written by Sam Wakelam

The catalyst for this move was a crash experienced by driver Robert Kubica at the 2007 Canadian GP, where the side of the car impacted a solid object at an acute angle. At the time of this crash, the side impact structures used consisted of straight carbon fibre tubes that extended out from the car at a 90º angle. Kubica’s crash showed that, while these existing structures were very effective at absorbing crash energy in a direct side impact, if struck at an angle the tubes were prone to break away, negating their effectiveness.

FIA Institute research consultant Andy Mellor, who led the project to develop a new structure, explained in 2013, “We went back to basics to examine what a side impact structure really needs to do in different types of accident. We used Robert Kubica’s crash in Montreal as a specific reference point since that was a major impact at an acute angle.”

To find a more effective solution, the FIA approached teams and asked them to come up with a new design that was effective regardless of the direction of impact. Three teams came up with designs, which included both improvements to the existing tube-based system and other solutions such as a layer of aluminium honeycomb material bonded to the outside of the monocoque. However, as can be seen in the video below, the honeycomb approach was unsatisfactory, with the material breaking away under certain loadings.

Ultimately, a solution devised by Red Bull Racing was settled on, and this consists of a series of laminated carbon fibre pillars, constructed in such a way as to crush during an impact rather than break off. These pillars essentially disintegrate under impact, in much the same way as a front or rear crash structure, absorbing the energy that would otherwise be transmitted directly into the monocoque.

Unlike the previous crash structures, which were built individually by the teams and had to undergo separate crash tests, the new side impact devices are a spec item. Exactly where they are mounted is still left up to teams, as each monocoque is unique, but the mounting points must be able to withstand horizontal loads of up to 60 kN as well as vertical loads of 35 kN without deforming.

Although the new structures provide a higher degree of safety for the drivers, they also present more headaches for teams’ engineers, as Eric Gandelin, chief designer for the Sauber F1 team, explained before the start of the 2014 season. “The new changes now regulate the design of the structures. This means the dimension of the tube and the laminate is now set and the same for all teams. And these tubes are overall much bigger and result in bulkier sidepods, especially compared to the very slim sidepods we had on the C32.”

Written by Lawrence Butcher

To date, it is thought that Ferrari, Red Bull and Mercedes are all using such a coating. It is also thought that the coating in question is a generally available solvent-based product that contains polymers of silicon. The coating is described as a ‘liquid glass’, which is normally clear, but adding a black pigment aids heat exchange between the wheel and the tyre. While a similar effect could be achieved using paint, the added weight would negate some of the performance benefits, adding 50-100 g per wheel. On the other hand, the coating is said to add only about 5 g to the mass of an individual wheel, presenting a negligible weight penalty. This is because, when applied, it is only a few microns thick (and also has a very high surface hardness of around 9 H).

The coating also has secondary benefits relating to airflow within the rim, as its very smooth and glossy finish reputedly helps reduce turbulence. It is not just smooth coatings that are applied to wheels though, and there are a number of heat-resistant coatings available that can be applied with an extremely smooth finish for the same reasons. Another benefit of the high-gloss finish is that it makes the inside of the wheel rim less susceptible to the build-up of debris picked up as a result of brake wear and from the track surface.

Coatings are not the only trick that some teams have used in an effort to improve the thermal and aerodynamic performance of their wheels. In the past, great effort was put into creating carefully sculpted wheels that steered the air where it was most needed. Those days are long gone now though, and wheel design is tightly regulated. However, this has not stopped some teams working within the regulatory constraints to try to garner every last ounce of performance. For example, observers spotted at the end of the 2013 season that the Mercedes team’s wheels featured a ‘textured’ finish on the inner surfaces, while those of Red Bull sported a dimpled effect.

The purpose of such finishes could be twofold. First, the texture could help to reduce the boundary layer of air on the inside of the wheel rim as it rotates close to the brake cooling drum, thus helping to reduce drag in much the same way as dimples on a golf ball. Second, the finish presents a greater surface areas, which combined with a heat-absorbing coating would further increase heat transfer from the brakes into the tyre carcass.

It is steps such as these that highlight the extent of the detail engineering that goes into a modern Formula One machine, and the fact that for the top teams, no stone goes unturned in the quest for performance.

Written by Lawrence Butcher

The increasing complexity of the modern racecar, from both structural and aerodynamic perspectives, has led to a reliance on simulation software to evaluate and optimise designs. Materials and aerodynamic behaviour can no longer always be predicted confidently without these tools, and they offer engineers a fuller understanding of the physics governing performance.

The recent FIA restrictions on wind tunnel and track testing have further increased the dependence on simulation software, particularly CFD codes, but their use is also now limited by the technical regulations. The consequence is that Formula One engineers need optimisation tools that work faster and smarter to maximise performance in the shortest timescales.

The traditional approach for optimisation using simulation software is to evaluate the design, make geometric modifications based on the results and engineering experience, and then re-run the simulation. This design loop is repeated until the required performance is obtained, and it can be a protracted process, with the need to re-mesh and solve the models for each geometric iteration.

It is also not guaranteed that the changes implemented will produce the desired or anticipated results, with the stress distributions and flow regimes calculated not necessarily being intuitive. This can lead the design in the wrong direction, wasting time and resources on pursuing the ‘wrong’ solution. In addition, to ensure a robust solution is reached, there are many potential variables to consider, which increases the simulation overhead.

There are however some software technologies being developed that may provide an answer to these challenges and accelerate the path to an optimised design. For example, topology optimisation software can be used with FEA solvers to generate conceptual designs for lighter and stiffer structures based on ‘minimum metal’ solutions. Existing designs can be improved using shape-optimising tools that automatically modify a component’s surface geometry to minimise stress and strain, or a combination of parameters, to deliver more reliable and efficient parts. 

Similarly, adjoint solver technology can be combined with CFD codes to optimise aerodynamic performance. In standard CFD methodology, a number of inputs such as the properties of air, ground roughness and angle of attack must be described to define the problem. These inputs are then used to calculate the flow information desired by the engineers – for example, vortex shedding, exhaust gas mixing, brake cooling and so on. Adjoint technology reverses this approach though, and effectively asks how the input variables can be altered to effect a particular change in the output results. For a racecar, geometry represents one of these input parameters, so by exploring how the shape of a front wing, say, must be altered to increase downforce, the adjoint solver – coupled with a tool to automatically ‘morph’ the surface geometry – can deliver an optimised solution after it has evaluated multiple geometric options.

Fig. 1 shows the improved downforce-to-drag ratio achieved using adjoint solver technology to modify the endplate geometry of a simplified Formula One front wing in a straight-ahead position. In reality, on track the car experiences a multitude of conditions, from ride height and speed changes to varying cornering rates, so to give a robust and optimised solution all these permutations need to be considered by the solver. If it is assumed that during a lap the car’s geometry is fixed then the circuit’s characteristics can be condensed into a probability density function (PDF) that is then used as an input into the adjoint solver.

Fig. 2 shows a graphical representation of all steering angles and velocities experienced by the car around a lap of Monza, and characterises the track’s unique identity (for these parameters). This PDF is then used to sample design points for the adjoint solver where steering angle and free-stream velocity are adjusted for each point. A mean value penalty (MVP) distribution is selected such that the downforce-to-drag ratio is significantly shifted for the entire range of defined steering angles and velocities to provide an improved performance over the entire lap, as shown in Fig. 3.

The geometry is automatically morphed in the software, and the blue wing in Fig. 4 shows the optimised design that corresponds to the density function shown in blue in Fig. 3. This wing is optimised for a particular track, not a single condition, and the changes implemented by the adjoint solver would have been difficult to predict in advance.

There are of course some challenges to overcome before topology optimisation and adjoint solvers become mainstream tools in an engineer’s development toolbox. For example, there can be issues with the optimised geometry generated, resulting in designs that are difficult or impractical to manufacture, although these are already being addressed, with parameters such as production costs being used to influence the optimisation process. There is also the challenge of exporting the optimised geometry back into the CAD packages so that it can be engineered for manufacture.

Questions may be asked regarding whether these tools are eroding the skills of the engineer, but ultimately it will be the engineer’s knowledge as to how to define the input parameters and boundary conditions, and their ability to interpret and evaluate the results, which will make these tools valuable.

These optimisation technologies are starting to provide real opportunities for accelerating the development and optimisation of designs, and look set to provide a significant competitive advantage to the Formula One teams that adopt them.

Fig. 1 - Improvements in downforce-to-drag ratio using an adjoint CFD solver on a generic Formula One front-end geometry

Fig. 2 - Derived density function for the Monza track

Fig. 3 - Downforce-to-drag density functions for the baseline geometry (red) and optimisation wing geometries (blue)

Fig. 4 - Blue wing showing the optimised geometry against the baseline design (in red) corresponding to the density function in blue in Fig. 3

(All images courtesy of Ansys UK) 

Written by Dan Fleetcroft