Contact and wear thermo-elastohydrodynamic model validation for engine bearings

Abstract

Tribological machine components such as engine crankshaft bearings operating at high load or rotational speeds often experience very thin oil films leading to asperity contact between the bearing and crankshaft. When the oil film thickness drops below the peak asperity height there is an increase in contact, wear and asperity power loss leading to worsening severity factors and seizure risk. Key factors influencing the bearing lubrication performance are the surface characteristics of the materials at the contact interface. SABRE-TEHL is a software simulation tool used for performing thermo-elastohydrodynamic analysis of bearing applications. In this current study, the development of a combined contact and wear model is demonstrated. This includes a hard contact model giving a direct surface contact pressure in areas of zero oil film thickness, a surface yield model with yield limits and plastic gradient from measured stress–strain data, an asperity wear model using measured surface roughness data and an asperity contact model based on measured roughness, asperity density and tip radius. Input surface roughness data are measured using a white light interferometry method. The effects of surface characterization in terms of roughness and stiffness properties are demonstrated using simulation results comparing an aluminium bimetal bearing with a polymer coated bearing, showing a significant reduction in asperity friction for the bearing with a polymer coating. Simulation results are compared with experimental test results for a 1.5 l diesel engine, a 2.0 l diesel engine and for a bearing fatigue test rig. Generally good agreement is seen when comparing the wear contours and wear depth on the bearing surface.