Viscosity Effects on the Dynamic Characteristics of an Elastic Engine Bearing

The dynamic behavior of an engine connecting-rod bearing is related to several parameters and in particular to the elasticity of the bearing and the viscosity of the oil. The computation of the bearing characteristics is achieved in the dynamic isothermal regime for a real polar load diagram and for different values of the lubricant viscosity. The assumption of short bearing is made in order to solve the Reynolds equation.

The pressure distribution and the instant elastic distortions are presented at different intervals for different loads of the engine. The trajectory of the shaft center inside the bearing, the variations of the minimum oil film thickness, the friction torque and the oil flow are compared to the classic results for rigid bearings and different values of the oil viscosity (between 2.5 and 8.5 mPa.s). The distorsions reduce the minimum oil film thickness, increase the friction torque and the oil flow under zero feed pressure.

Even in the case of perfectly smooth surfaces, the elastic distortion introduces a new parameter: the calculated minimum viscosity (CMV) which is estimated to be 1.8 mPa.s for the bearing studied.