Effect of base stocks on the automobile engine bearing

The government has required that engine oil viscosity be lowered and that highly refined base stocks be used in engine oils, with the aim of promoting low fuel consumption and developing long-life oils.To improve the reliability of automobile plain bearings by means of engine oils, we have developed a bearing test apparatus that uses a half-metal. Oil can be supplied through the oil supply port in the same way as in actual engines. In this apparatus, variable loads can be applied to the opposite side of the oil supply hole of the bearing by hydraulic pressure that is synchronized with the rotational speed of the shaft. The influence of the base stocks used for engine oils on the contact between the rotating shaft and the bearing metal, and on the bearing rotating torque generated by rotation of the shaft, were investigated.We found that the contact ratio and the bearing rotating torque varied with different types of base stock compositions, even if the base stocks had the same viscometric properties. Therefore, it is necessary to develop countermeasures to avoid adverse effects when lowering engine oil viscosity and using highly refined base stocks.