A Pin-on-Disc Study on the Electrified Sliding Wear of EVs Powertrain Gears

Abstract

In contrast to conventional powertrains from internal combustion engine vehicles (ICEV), the tribological performance of powertrains of electric vehicles (EVs) must be further evaluated by considering new critical operating conditions such as electrical environments. The operation of any type of electric motor produces shaft voltages and currents due to various hardware configurations and factors. Furthermore, the common application of inverters intensifies this problem. It has been reported that the induced shaft voltages and currents can cause premature failure problems in tribological components such as bearings and gears due to accelerated wear and/or fatigue. It is ascribed to effects of electric discharge machining (EDM), also named, sparking wear caused by shaft currents and poor or increasingly diminishing dielectric strength of lubricants. A great effort has been done to study this problem in bearings, but it has not yet been the case for gears. Considering that EVs powertrains can be configurated with an electric motor coupled to a single-speed or multi-speed transmission, it is expected that shaft currents can also affect gears to some extent. The pin-on-disc test has been widely used to study sliding wear of gear materials under comparable or realistic operating conditions. This accelerated test is effective for screening materials, lubricants and operating conditions allowing evaluations of their friction and wear properties. However, it has not been implemented for studying gear materials under electrified environments. Thus, this paper aims to explore the friction coefficient and wear of gear materials under non-electrified and electrified sliding in a pin-on-disc tester applying typical of EVs powertrain shaft currents during sliding. The tests were carried out at two different DC currents under comparable gear dry and lubricated sliding contact conditions. Friction coefficient, wear volumes and morphologies were evaluated and reported in this work.