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There is considerable pressure to reduce particulate matters, nitrogen oxides and other toxic substances in the emissions of internal combustion engines. In order to protect particulate filters and de-NOx catalysts in the exhaust gas flow, designers have sought to reduce sulfated ash, phosphorous and sulphur (SAPS) in lubricating oils. Also, the drive to reduce energy consumption has seen the reduction of oil viscosities. This paper examines the way viscosity and volatility influence lubricating oil consumption (LOC).

We have developed a tappet with a cam lobe contacting tip made of a hard sintered material whose base material is cobalt, which adheres less to the steel of camshafts, and which also contains fine particles of tungsten carbide and chrome carbide. We have established a new evaluation method to access wear resistance performance of the tappet. It enables us to measure directly the friction force generated between the cam lobe and tappet and to evaluate anti-scuffing performance with high accuracy because we can clarify the time, load and cam angle at which scuffing occures.