The compatibility of crankcase lubricant-material combinations in internal combustion engines

Recent advances in engine technology have seen the introduction of new materials and surface coatings leading to an overall reduction in weight and improved durability. However, the lubrication requirements of these materials are not fully understood. In this paper the lubrication of traditional Cr-bearing steel and Al-Si alloy-based components is investigated using two fully formulated lubricants. These two lubricants have the same viscosity grade and phosphorous levels but differing base stock and detergent systems. A pin-on reciprocating plate configuration was used for the tribological experiments and analysis was performed using X-ray Photoelectron Spectroscopy (XPS), Environmental Scanning Electron Microscopy (ESEM) and Energy Dispersive X-ray analysis (EDX). It has been found that in a completely ferrous-based system, fully formulated lubricants are effective in reducing wear and friction and a relatively thick anti-wear film is formed. In partially aluminium systems the fully formulated lubricant is less effective and a thin (and therefore unstable) anti-wear film is formed when a cast iron pin is rubbed on the Al-Si alloy plate. In completely non-ferrous systems the wear film is absent. In this paper the fundamental aspects of the film formation as well as the practical aspects of the results will be discussed.