Simulation of journal bearing friction in severe mixed lubrication – Validation and effect of surface smoothing due to running-in

Abstract

This paper focuses on the friction behavior of jour- nal bearings operating from hydrodynamic to mixed lubrication regime where severe metal-metal contact occurs. Therefore, friction tests with two different static loads are carried out on the journal bear- ing test-rig from KS Gleitlager. The test results in form of Stribeck curves provide a solid base to proof the isothermal elastohydrodynamic simulation approach. The simulation approach solves the av- eraged Reynolds equation introduced by Patir and Cheng and considers metal-metal contact by using the Greenwood and Tripp contact model. All nec- essary surface parameters are derived from surface scans. No less essential in this approach are the experimentally identified lubricant properties under high pressure and high shear rate. The calculated friction torque matches the mea- surement results within the measurement uncertainty for a wide range of operation conditions. With the validated simulation approach the influence of surface smoothing due to metal-metal contact is discussed. Additionally, the limits of a constant boundary coef- ficient are identified and the effects of flow factors are presented.