Effect of Crankshaft and Crankcase Material Stiffness on Load Distribution in Main Bearings

Abstract

In multi-cylinder diesel engines, hydrodynamic pressure distribution of main bearings has significant effect on the load distribution applied on engine crankcase, therefore, has an effect on the stress distribution and deflection of crankcase. Flexibility of crankshaft and crankcase assembly has significant effect on load distribution in engine main bearings. In this paper, the effect of elastic deformations of both crankshaft and crankcase on the load distribution in the main bearings is studied. Considering deformations of crankcase and crankshaft together with the elasto-hydrodynamic (EHD) analysis of main bearing is vital to obtain the realistic load distribution and accurate main bearing performance. At the beginning, the results of flexible body dynamic analysis of engine crank train with considering EHD joint for main bearings are presented and the main bearing force and moment are compared with rigid body dynamic analysis. Then, the effects of crankshaft and crankcase flexibilities on main bearing force and moment are studied. Several models with different flexibilities and stiffness of crankcase and crankshaft were prepared using Elasto-hydrodynamic simulation of diesel engine main bearings. According to the results, the load distribution on the engine main bearings and consequently the bearing shell deformation are affected by crankcase and crankshaft elasticities. A fast and time-saving method to obtain reasonably accurate results is proposed in the present paper.