Effect of Form Honing on Piston Assembly Friction 2020-01-5055

Beside the main trend technologies such as downsizing, down speeding, external exhaust gas recirculation, and turbocharging in combination with Miller cycles, the optimization of the mechanical efficiency of gasoline engines is an important task in meeting future CO₂ emission targets. Friction in the piston assembly is responsible for up to 45% of the total mechanical loss in a gasoline engine. Therefore, optimizing piston assembly friction is a valuable approach in improving the total efficiency of an internal combustion engine. The form honing process enables new specific shapes of the cylinder liner surface. These shapes, such as a conus or bottle neck, help enlarge the operating clearance between the piston assembly and the cylinder liner, which is one of the main factors influencing piston assembly friction. To evaluate the potential of form honing, with respect to the optimization of frictional loss in the piston assembly, knowledge of the tribological effects occurring during the combustion cycle is of crucial importance. For this reason, tests of several configurations, with and without form honing, are carried out in a so-called floating liner engine. The single cylinder test carrier introduced, which functions according to the floating liner principle, was developed by the Chair of Internal Combustion Engines of the Technical University of Munich. It allows the direct and crank angle-resolved measurement of the piston assembly friction forces. Based on the crank angle-resolved friction force measurements presented, the effects of the crankcase material, piston clearance, and operation mode of piston cooling on the potential benefits of the form honing are discussed in detail.