Formula One crankshafts after 2014

Thursday, September 22, 2011

Tags :  crankshafts

crankshaftsThe provisional rules for the 2014 Formula One World Championship engines are now available to view on the FIA website. The change from the current 18,000 rpm 2.4 litre V8s to the 2014 1.6 litre V6 turbocharged engines was not straightforward, and came after a considerable period during which the engine suppliers were working towards supplying four-cylinder engines for 2013.

There are some important changes and restrictions affecting the design of crankshafts for 2014, which go beyond the obvious requirement to deal with two fewer con rods.

There is a requirement to have crankshafts with only three crankpins; there is no option to have either a six-pin crankshaft or one with 'split' or offset pins. Both offset pin cranks and six-pin cranks are commonly found on production six-cylinder engines, particularly ones whose bank angles are 90º (as is the mandated bank angle for the 2014 Formula One engines). The main benefit of this rule would seem to be the prevention of effort and money being expended on investigating alternative crankpin arrangements.

There are two other new crankshaft regulations that would appear to be linked. These are that the crankshaft height is mandated at 90 mm from the bottom of the engine, and that no material with a density greater than 9000 kg per cubic metre can be assembled to the crankshaft.

In the past, much effort was put into the design of Formula One engines that had the lowest possible crankshaft axis height above the bottom of the engine. Not only could the engine thus be positioned lower in the car, but the gearbox input axis was also positioned low down. With an increased stroke and much higher cylinder pressures in the new turbocharged engines, Formula One engine designers would need to increase crankshaft axis height, but with the new rules, they no longer need to design to a minimum.


crankshafts-full

Combined with mandated fixing locations between the engine and gearbox, this allows engines to be swapped season-to-season, giving privateer teams more opportunity to use the most competitive engines. Quite what this does for independent engine suppliers isn't clear, but it probably doesn't encourage them into the sport/business.

Given an easily achieved crankshaft axis height, there is less incentive to use tungsten counterweighting. However, in the search for minimum crankshaft inertia, people would undoubtedly turn to tungsten crankshaft counterweights, as is the case in other, lower-budget series and even some high-end roadcars. As a method of producing a low-inertia crankshaft, tungsten is very effective. Its removal from the rules doesn't stop people working toward low inertia; it simply means the crankshafts inside these engines will be increasingly intricately machined.

Any gears in the timing drive from the crankshaft to the camshafts must be a minimum of 8 mm wide, having previously not been subject to any restriction, and this logically means that the gear on the crankshaft is also a minimum of 8 mm wide.

The rule prohibiting welding between the front and rear main bearings remains, making the use of the 'hollow crankshaft' unlikely in the near future, although novel manufacturing technologies may allow hollow crankshafts without breaking this particular rule.

Fig. 1 - The option of running a 'split-pin' crank, as per this example from a Honda NSX, isn't an option for the 2014 Formula One engines

Written by Wayne Ward

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Comments

Well documented Wayne, I appreciate your article. Can you tell me if these cranks are hollowed out and tungsten filled? Thanks
Honestly, I don't know why any F1 engine designer would opt for an offset crankpin design on a 1.6L V6.  With the short stroke and light weights of this engine's recip components, vibration definitely won't be an issue. And using split pins makes for a much weaker, less stiff, longer and heavier crankshaft.

As for crank counterweights, since there is an engine life requirement, counterweights may be necessary, and even beneficial.  Besides reducing dynamic imbalance, judiciously applied crank counterweights can reduce main bearing loads, minimize crankshaft dynamic stress due to torsional vibration modes, and improve conrod bearing life by reducing crank bending between the main bearings.

The amount of pin boring that can be achieved to lighten a crank is made easier by the 120deg spacing of the V6's 3 pins.  But the overlap of the main and rod journal diameters with a very short stroke crank also makes boring more difficult.
Vince,

F1 crankshafts have had tungsten attached in a number of ways for many years now. There are a number of methods which have been discussed here and in the magazine.
I don't understand how the use of tungsten can lead to less inertia. Less volume sure, but you will still need the same inertia to balance reciprocating and rotating masses.
While the rules limit what can be done with crankshaft materials, there is still some potential scope for improvements.  

One interesting recent development with regards to high performance alloy steels is the computational metallurgical design technique being developed by Questek.  Questek can digitally design steel alloys to achieve specific properties far better than any existing alloys.  Questek has already done this with carburizing gear steels.  I can just imagine an F1 engine supplier with deep pockets funding Questek to design a nitriding crankshaft steel with improved fatigue life.  Based on their track record with carburizing gear steels, a fatigue life improvement of up to 30% might be possible.

Another approach that I would propose for improving the performance of F1 crankshafts would be 3D topological optimization of crankshaft journal surfaces.  Currently, crank journals are ground cylindrically.  My idea would involve first performing a highly detailed FEA modelling of a particular crankshaft and cylinder block structure under operating conditions to characterize their deflected shapes.  Then use that data to 3 dimensionally profile grind the crank journals to ensure that the journal bearing operating oil films were always centered on the bearing, and also that the operating oil film thickness was as close to EHD conditions as possible.  Keeping the journal bearing oil film at/close to EHD conditions is best for efficiency.  With an F1 engine, this might mean an additional 5 to 10 hp.  The only issue would be that a specialized precision NC crank journal grinder would be necessary.  But since the process would have applications for improving production engines, it might be possible to partner with an OEM to offset the cost.  

Anyway, that's my idea.  Anyone is free to use it if you think it's worthwhile.  Just give me credit if it's successful, but forget I even mentioned it if it's a dismal failure.
Thank you Wayne for the response pertaining the tungsten in the crank. I have in my possession a crank out of a 2.65 turbo indycar vehicle, it does have tungsten in the hollowed out counter weights. I tested the slug and proved it was tungsten. Cheers
vince,

High density metals like tungsten are useful as counterweights with crankshafts that have a limited radial swing, like 2.65L Champ Car V8's or 2.4L F1 V8's.  A tungsten dynamic counterweight will have greater polar inertia than an equivalent volume steel counterweight mass, so the tungsten counterweight can have a smaller volume.  Smaller counterweight volume/swing radius is very important for reducing crank windage losses.
I think the profile of crank journals is not the only factor to consider in oil film thickness. Surface preparation is certainly significant. FEA would be useful in optimization of crank journal design from the perspective of balancing structural strength, friction minimization and bearing speed. Cylinder pressure and rev limit changes in 2014 most certainly would require a re-juggling of design parameters.