Lubricant Shear Thinning Analysis of Engine Journal Bearings

Abstract

The high shearing stresses encountered in the modern engine bearing lubricant film lead to significant drop in viscosity of multigrade oils and affect the values of film thickness, power loss and oil flow significantly in the engine bearings. The popular mobility method is incapable to incorporate shear thinning, and time-consuming numerical schemes are not readily acceptable in industry. The present study aims to provide an economic (time and effort saving) and reliable dynamic (considering load and speed variation with crank rotation) analysis to study the combined effect of temperature and lubricant shear thinning on the engine bearing performance. The variation in the lubricant viscosity with shear is considered as described by the Cecim-equation. An effective thermal analysis is used to evaluate the operating oil-temperature that determines the low and high shear viscosity, and shear stability parameter. A crankshaft bearing is analyzed and results are presented for various performance parameters such as minimum film thickness, maximum pressure and the friction loss. These results are compared with those obtained by steady state solutions and full scale numerical methods.