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Piston ring trends

ringsThe piston rings in an engine serve to act as a seal to prevent the escape of fresh inlet charge and combustion products into the crankcase, and also to prevent an excess of crankcase oil from reaching the combustion chamber. As such they are an important component to consider in engine design. Poorly performing rings can lead to poor engine performance and increased oil consumption.The general trend in piston ring design is towards lighter weight components and fewer of them.

In four-stroke gasoline racing engines, the accepted wisdom is to fit one or two compression rings and an oil control ring, sometimes known as an oil-scraper. It is widely understood that the piston assembly is the source of a large percentage of the frictional losses in a racing engine and that the piston rings account for much of this loss. If it is possible to dispense with one of the compression rings whilst maintaining low blow-by, then this is generally done, thereby gaining an increase in performance and, in these straitened times, a welcome reduction in piston assembly cost, albeit slight.In general, the compression rings in a Formula One engine are steel and may be surface hardened before the application of a surface coating.

Some years ago the trend was to have a coating of another metal such as molybdenum on the outside diameter of the ring, but these have been replaced by the new generation of engineering coatings with which we have become familiar. Titanium nitride has been a common choice of coating for many years, but this has been largely supplanted by the use of DLC coatings in recent times. I have seen other coatings tested on motored rigs which promise even lower friction, but not with sufficient success to be used for serious testing or racing. The general trend in compression rings is to use as thin a ring as possible, with the attendant benefit of lower piston mass.The design of the compression ring is, generally speaking, a thin ring having a width which is several times the height of the ring, and the groove which houses this then needs an appropriate amount of material between it and adjacent features such as valve pockets or to other external surfaces. The piston ring thus has a large influence on the design of the piston which affects the piston mass accordingly. Therefore it is no surprise to learn that some manufacturers have experimented with alternative designs and one of the manufacturers has successfully raced this technology in Formula One in recent years. The company in question has a much narrower ring than we would consider conventional, and the attendant weight saving in the ring and the piston is considerable. These rings are also made from an unconventional material (for piston rings at least) and offer a weight saving which is worthy of consideration. These rings are coated with what we would consider to be conventional ring coating materials and run in bores which are of conventional materials. This technology would be compatible with most existing Formula One engines. Moreover, they have a very unusual approach to the design of the oil control rings which again is in an unconventional material.We can say therefore that, whilst piston rings appear to be simple components, they could provide a lot of scope for further development, thereby offering reduced mass and friction. These are aims that Formula One in particular should embrace if we believe that we need to develop road-relevant technologies to survive.

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