Journal Bearing Friction Optimization

Abstract: Engine downsizing, improving fuel efficiency while satisfying the environmental legislations are one of the main driving forces in developing new solutions for passenger cars.Engine main bearings, are journal bearings which support the crankshaft and operate principally in full film lubrication. Defining the optimum design parameters of the bearings which can provide low friction and high durability for automobiles represents a multi-variable problem.Being the supporters of the main shaft driven by the internal combustion engine, main bearings are subjected to strenuous operating conditions. These include high loads and pressures amongst others. The trend in lubricant selection for these components is shifting towards choosing engine oils with lower viscosity to further reduce fuel consumption. Simultaneously with the shift in oil, new solutions for controlling the geometry and the topography on the micro-scale are becoming available. Three main bearing top layers plated on a conventional aluminum alloy containing tin and silicon were selected for the study. The top layers, one bismuth based and two newly developed polymer based, were investigated for their frictional and wear performance.In order to study experimentally the influence of different design parameters on bearing performance a test rig and a methodology was developed. The selected engine main bearings were tested in lubricated condition with two oils having different viscosity. Pre - and post test analysis of the shaft surface roughness was performed using white light interferometry. The wear performance of the bearings was measured both as mass loss and surface topography.The results suggest that the developed test rig can be used to simulate close to running condition testing. The measurement method and set up shows good consistency at a load of 2000 N, but indicates inconsistency in set up at 500 N.It is found that the newly developed engine main bearing top layers have promising frictional and wear performance, providing a reduction in friction by up to 20%.