Characterizing the effect of viscosity on friction in the piston assembly of internal combustion engines

Abstract

The friction mean effective pressure (fmep) contribution of piston assemblies running under motored engine conditions in cylinders with plateau or laser honed bores has been investigated. Results have been obtained for engine speeds in the range 400-2000 r/min and temperatures from -20 to around 60°C. The fmep of the piston assembly is observed to depend most directly on oil viscosity evaluated at the temperature of the cylinder wall at mid-stroke position. The variation of fmep with viscosity provides a basis for comparing the effects of surface finish or piston design modifications. Using liners with fine honed bores reduced piston assembly friction by between 3 and 20 per cent relative to results for pistons running in plateau honed bores. Piston assembly friction was reduced by between 5 and 38 per cent through design changes to the pistons.