New piston skirt coatings promise significant reduction in engine friction

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The EcoTough-New Generation skirt coating for gasoline engines reduces friction by up to 15 percent(Credit: Federal-Mogul Powertrain)

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The piston skirt and pin account for about 17 percent of the frictional loss in a combustion engine as they are the most difficult to keep lubricated and have the largest contact surfaces. OE powertrain manufacturer Federal-Mogul has announced two new-generation coatings that are claimed to reduce this friction by up to 15 percent compared to standard coatings.

Engineers have attempted to overcome the friction losses at the skirt and pin by optimizing the geometry of the piston's clearances and, more recently, by utilizing advanced coatings on the cylinder wall and piston skirt. Each advance has meant improvements in engine longevity, fuel economy, and power output. Federal-Mogul Powertrains says that its latest EcoTough coatings for gasoline and diesel engines take this a step further, reducing skirt wear in a gasoline engine by up to 40 percent compared to today's market standard.

The coating is a metal oxide-reinforced resin with embedded solid lubricant particles. It's applied in a thickness of 15 microns to the piston's skirt surface. It delivers up to 15 percent friction reduction compared to standard coatings, Federal-Mogul says, which directly improves base engine efficiency. Validation testing is near completion, leading to the new coatings coming to market.

This micro-section of the EcoTough coating for gasoline engine pistons shows the individual component materials(Credit: Federal-Mogul Powertrain)

The diesel variant of the coating, called EcoTough-D, was developed for both aluminum and steel diesel pistons and can be used in both passenger vehicles and heavy commercial vehicles. Because the structural rigidity of diesel engines and diesel fuel's higher lubricity, this formulation of the coating should deliver greater improvement, according to Federal-Mogul.

The diesel variant is a polymer-based coating reinforced with short carbon fibers with embedded graphite as the solid lubricant. It reduces piston friction by as much as 35 percent compared to conventional coatings and improves wear resistance by up to 30 percent.

Federal-Mogul expects both coatings to be on the market in 2017.

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