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Legislation aimed at reducing carbon dioxide emissions is forcing significant changes in passenger car engine hardware and lubricants. Reduced viscosity lubricants can reduce friction levels and are therefore helpful to manufacturers seeking legislative compliance. MAHLE and Shell have worked together to determine the crankshaft, bearing and lubricant combination which minimizes friction with an acceptable level of durability. This paper describes the results of our joint simulation studies. MAHLE Engine Systems have developed in-house simulation packages to predict bearing lubrication performance. SABRE-M is a “routine” simulation tool based on the mobility method [1] curve fitting from the finite bearing theory to simulate the hydrodynamic lubrication in steady-state conditions. Whereas, SABRE-TEHL is a specialized simulation package used for performing Thermo-Elasto-Hydrodynamic Lubrication (TEHL) analysis of bearing systems.

As engine bearings are subjected to higher loading, the oil film thickness in the loading carrying region becomes thinner and thinner. Under the regime of elastohydrodynamic lubrication (EHL), the differences in the elastic deflection of the bearing/journal along axial direction are shown to have significant influence on the bearing performance. The work reported in this paper made use of SABRE-EHL, a predictive tool developed for the study of automotive engine bearings. The influence of axial profile was firstly investigated by the examination of the operating conditions of both the big-end and main bearings of an modern petrol engine. The investigation was then extended to include a sensitivity study, where different types of axial profile were investigated. The impact of these axial profiles on engine bearing performance was then assessed.