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.
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.