Study on the electric discharge behaviour of a single contact in EV motor bearings

Electric current discharge in motor bearings is becoming more of a concern with the move toward electric vehicles (EV), since it can damage bearing surfaces and potentially cause premature failures. Electric discharge (ED) tests were carried out utilizing a self-improved ball-on-disc instrument under elastohydrodynamic lubrication (EHL) regime to better understand the nature of electric discharge in EV motor bearings. The experiments prove that the discharge behaviour is related to the lubricant film thickness and the discharges appear at the minimum film thickness area. An electric discharge energy model was developed to describe the relationship between working conditions and the energy of a single discharge. The model was qualitatively verified by comparing the predicted ED damages with the ball-on-disc test results. •The modified ball-on-disc test equipment can mimic the electric discharge that occurred in EV motor bearings.•Discharge behaviour is lubricant film thickness dependent and the discharges appear at the minimum film thickness area.•A model was developed to link working conditions and the energy of a single discharge.•A mitigation measure to avoid/reduce electric erosion is proposed by controlling the lubricant film thickness.