Friction modelling of tribofilm performance in a bench tribometer for automotive engine lubricants

Abstract

Research focusing on the initial stages of the development of an empirical model to predict friction in boundary and mixed lubrication conditions accounting for additive and surface interactions is reported in this article. The regression model was constructed by applying a fractional factorial design statistical approach. The model considers a typical friction modifier, molybdenum dithiocarbamate, in a model automotive engine lubricant also containing zinc dialkyldithiophosphate in a synthetic polyalphaolefin base oil under conditions representative of the cam and follower interface in an automotive engine. Operating temperature, sliding speed, load, initial surface roughness, and the initial lambda ratio were taken as the factors affecting tribological performance. The empirical model predicts friction at 95 per cent confidence level within the specific range of parameters considered in the experiments. Not surprisingly, molybdenum dithiocarbamate is mainly responsible for the reduction of friction of the tribofilm, whereas temperature, sliding speed, and load are the other significant parameters.