A Simplified Prediction of Gear Currents Propagation in EV Drivetrains Using a Conductive Susceptibility Framework

Stray electrical currents generated in electric motors are a reliability concern in electric vehicle (EV) drivetrains, as they can promote premature tribological failures. Most existing studies focus on bearing currents assuming that bearings are the primary discharge paths to ground during stray current events. However, EV drivetrains combine electric motors with multi-stage gear transmissions, introducing additional lubricated contacts that may contribute to critical failures during operation. The potential involvement of gear contacts in stray current phenomena has received little attention, partly due to the complexity of electrified drivetrains and the insufficient maturity of the topic. This work proposes a simplified predictive methodology toward identifying operating conditions under which gear contacts in EV drivetrains may become susceptible to conduct or discharge stray currents (gear currents). The occurrence and propagation of these currents along the drivetrain can be a potential failure risk since electrically assisted surface degradation may promote accelerated wear and unexpected efficiency loss situations. The study framework combines operating conditions derived from a common driving cycle, elastohydrodynamic lubrication simulations, and a simplified resistive network linking tribological behavior with electrical conduction. It is applied to a two-stage EV drivetrain by considering two different study cases of surface roughness conditions for bearings and gears. The results show that conductive paths are highly dependent on operating conditions and lubrication regimes. Gear meshes exhibited significant conductive susceptibility and frequently participated in dominant current paths under typical roughness values for gears. In contrast, smoother gear surfaces improved lubrication separation and shift current propagation toward bearings.