Numerical prediction of the frictional losses in sliding bearings during start-stop operation
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ISSN 2223-7690 CN 10-1237/TH
RESEARCH ARTICLE
Numerical prediction of the frictional losses in sliding bearings during start–stop operation Florian KÖNIG*, Christopher SOUS, Georg JACOBS Institute for Machine Elements and Systems Engineering, Rheinisch-Westfälische Technische Hochschule Aachen University, Schinkelstraße 10, Aachen 52062, Germany Received: 25 January 2020 / Revised: 15 April 2020 / Accepted: 09 June 2020
© The author(s) 2020. Abstract: With the increased use of automotive engine start–stop systems, the numerical prediction and reduction of frictional losses in sliding bearings during starting and stopping procedures has become an important issue. In engineering practice, numerical simulations of sliding bearings in automotive engines are performed with statistical asperity contact models with empirical values for the necessary surface parameters. The aim of this study is to elucidate the applicability of these approaches for the prediction of friction in sliding bearings subjected to start–stop operation. For this purpose, the friction performance of sliding bearings was investigated in experiments on a test rig and in transient mixed elasto-hydrodynamic simulations in a multi-body simulation environment (mixed-EHL/MBS). In mixed-EHL/MBS, the extended Reynold’s equation with flow factors according to Patir and Cheng has been combined on the one hand with the statistical asperity contact model according to Greenwood and Tripp and on the other hand with the deterministic asperity contact model according to Herbst. The detailed comparison of simulation and experimental results clarifies that the application of statistical asperity contact models with empirical values of the necessary inputs leads to large deviations between experiment and simulation. The actual distribution and position of surface roughness, as used in deterministic contact modelling, is necessary for a reliable prediction of the frictional losses in sliding bearings during start–stop operation. Keywords: sliding bearing; friction; wearing-in; contact model, mixed elasto-hydrodynamic simulation
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Introduction
In the last decade, automotive engine start–stop systems have led to a significant increase of start–stop cycles during the expected engine lifetime [1–4]. Low friction for the desired lifetime is a key requirement for engine bearings [5–7]. In sliding bearings, methods to improve the frictional performance range from improved mechanical design [8] over different lubricant formulation [8, 9] and novel bearing material solutions [1, 2, 10] to modern surface engineering [11–13]. Furthermore, the frictional losses of sliding bearings can be reduced by wear-induced change of the contact
geometry—hereafter referred to as wearing-in—under boundary or mixed-friction conditions [14–17]. In recent years, the frictional losses in sliding bearings in start–stop operation has gained a significant amount of attention. In a fundamental study, Bouyer and Fillon [18] studied the breakaway torque of sliding bearings made from bronze and whi
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