The effects of alternating current (AC) electrification on the tribological performance of gear materials with internal combustion engine (ICE) and electric vehicle (EV) transmission lubricants

Electric Vehicles (EVs) present a vastly different set of tribological challenges to internal combustion engine (ICE) vehicles. Not only does the high torque production and high rotor speeds experienced in EV motors extenuate existing tribological challenges in the automotive sector; the inherent electrified nature of EV drivetrains is a key challenge. Many forms of stray electric current are prevalent within such systems, which cause the deterioration of key mechanical components through several electrochemical and electromechanical wear mechanisms. In this study, a novel electromechanical apparatus has been implemented to investigate the effects of alternating current (AC) discharge across ball-on-disc unidirectional sliding contacts, lubricated by commercially available transmission fluids. Three lubricants were compared at 80°C under both unelectrified and AC conditions. The three lubricants were used: a group IV poly-α-olefin (PAO 4) synthetic base oil and two commercially available transmission fluids – currently implemented within ICE vehicles and EVs, respectively. The key findings of this study highlight a reduction in friction under electrified conditions, combined with expedited material wear and tribochemical surface modification. The friction behaviour of the ICE transmission lubricant deteriorated over time due to electrification causing fluid property degradation.