Reduced piston-ring friction translates into better fuel economy and lower CO2 emissions. For this reason, Federal-Mogul is applying its LKZ piston ring technology currently used in diesels to direct-injection gasoline engines.
Company engineers claim the two-piece ring is capable of reducing oil consumption by up to 50% and friction by up to 15%. Matched against comparable conventional rings, the technology brings fuel economy, lower emissions, and extended-oil-life benefits.
“The LKZ ring is so effective in pulling oil away from the combustion chamber and in reducing oil consumption that we are able to improve ring tension and reduce friction," noted Johannes Esser, Director of Engineering, Rings and Liners, at the company's Burscheid, Germany, technical center.
He added that unlike conventional oil rings, the LKZ ring also provides consistently low oil consumption over the life of the engine. It does this by reducing carbon build-up on critical parts of the piston, such as the area immediately above the compression ring.
LKZ rings currently are used extensively in both light and heavy-duty diesel engines. The broadening of the application to gasoline engines—particularly for highly loaded conditions increasingly found in direct injection units—is seeing “strong interest” because of the gains in fuel economy and reduction in CO2 emissions at low cost, explained Rainer Jueckstock, the company’s Senior Vice President, Powertrain Energy.
Typical piston rings apply equal pressure to the cylinder bore on the downstroke, toward the crankcase, and on the upstroke, toward the combustion chamber. Federal-Mogul engineers explain that the LKZ combustion ring combines a stepped surface and taper on its contacting edge to provide a well-defined pressure to the cylinder wall on the downstroke and a significantly lesser effect on the upstroke.
The downstroke pressure more effectively returns the oil that lubricates the cylinder to the oil pan, instead of allowing it to enter the combustion chamber where it may create carbon on the spark plug, or on the cylinder head, and increase oil consumption.
Also new from Federal-Mogul for gasoline engines is a coated piston called EcoTough that is claimed to combine the properties of low wear and low friction in a single application.
Developed at the company's Piston Technology Center in Nürnberg, EcoTough offers potential fuel-consumption reductions up to 0.8% with reduced CO2 emissions, according to Dr. Frank Doernenburg, Director of Technology, Pistons and Pins. It was designed to be compatible with existing and advanced cylinder bore finishes and to be introduced as a running change into volume engine production.
The piston’s coating comprises solid lubricants, including graphite, molybdenum disulphide (MoS2), plus carbon fiber.
For applications needing additional protection, such as one with a rough cylinder honing structure, the EcoTough coated piston offers a greater coating thickness than conventionally coated pistons, noted Dr. Doernenburg.
Designed for high-volume manufacturing, EcoTough is described by the company as being less sensitive to pretreatment process variations, resulting in greater robustness and more consistent performance.