DLC Coatings in Racing Engines
There are a very wide range of coatings which are employed in motorsport engines nowadays, and Formula One has been at the forefront of this development for many years. The moot point of excessive budgets is the reason that Formula One has been able in many cases to be a guinea-pig for these exciting technologies and, owing to this development coatings such as DLC are now finding widespread use on series production cars. The aim in these production car applications is to decrease friction and thereby increase efficiency and economy - these coatings are proving a useful tool in the drive to meet ever more stringent emissions regulations.
DLC has been widely applied in racing engines to decrease friction and we should list some of the more important applications of this coating here. Possibly the most popular area of application of DLC coatings is the piston pin (wrist pin / gudgeon pin). Many pin manufacturers were early adopters of this coating, and it has been very successful, despite one or two false starts by some coating suppliers. The problem with failure of DLC coatings is that the debris can be extremely hard and abrasive, and in the contact between a hard piston pin and the pin bore in an aluminium piston this can cause serious damage. We should state here that many now think that it is perfectly possible to run a DLC-coated piston pin in a steel connecting rod without the use of a bush.
The next most popular application, and the one that the automotive manufacturers seem to be very keen on, is on valvetrain components. Where engines are used mainly at part throttle, the friction from the valvetrain can be very considerable and the mitigation of frictional losses is seen as a key area of research. In racing the frictional losses are equally important, possibly even more so. I doubt that there is an engine manufacturer in Formula One who does not use DLC coatings on the valvetrain components. Certainly its application to finger followers is one of the reasons that people have been able use the very high contact pressures and velocities which have been common recently. In formulae not using finger followers, the application of DLC to other types of cam followers is now very common, and the gains in reduced friction, especially when the components are new, is easily measurable. A more expensive option, that some manufacturers choose to use, is to coat both the camshaft and the follower. This is supposed to offer further advantages over simply coating the follower alone.
The application of low-friction hard coatings to gears is not new, and it was pioneered in non-automotive applications, specifically helicopter gearboxes, where the extra seconds of component life in an oil-out situation is the main gain rather than the slightly reduced friction. Some people have experimented with coated gears in motorsport, although it is not a popular application.
The application of DLC to crankshafts in Formula One has been tried by several engine manufacturers, although it has not been taken up by all with equal enthusiasm.
One note of caution about DLC coatings for those with no experience who might be tempted to try them – speak to your coating supplier and seek their advice on the correct application, substrate and steps (possibly including other coatings underneath the DLC) to get the best results. Its application to unsuitably prepared parts, unsuitable materials, or correct materials in the wrong condition can lead to poor results and damage.
Written by Wayne Ward.