Tribological failure mechanisms and mitigation strategies for bevel gear differentials in electric vehicles

Abstract

During start-up, rapid acceleration, and energy regeneration (involving alternating forward and reverse rotation), electric vehicle (EV) drivetrains-including reduction gears and differentials-are subjected to higher instantaneous torque loads, significantly increasing the risk of component failures such as wear compared to internal combustion engine vehicles. Investigating wear failures and their mechanisms in differentials under high-load conditions is essential for enhancing the operational safety and stability of EVs. In this study, a durability bench test was conducted on the differential of a specific EV model under differential-speed and torque-bias conditions. The wear behavior of key components was analyzed and characterized. Experimental results revealed typical wear failures such as circumferential furrow, adhesive wear, and plastic deformation on the planetary gear shafts and the inner bores of the planetary gears. Contact behavior analysis indicated that the overturning displacement of the planetary bevel gears under meshing force causes localized contact pressure concentrations at the shaft-bore interfaces, which are likely the main cause of the observed surface wear. Modifying the geometry of the planetary gear bore (i.e., surface modification) was found to be an effective strategy for relieving stress concentrations. An optimal modification amount exists that minimizes contact pressure at the shaft-bore interface without introducing new stress concentration zones. The findings not only elucidated the failure mechanism, but also yielded operative geometric optimization strategies based thereon, thereby providing theoretical underpinnings for anti-wear design and service life enhancement of electric vehicle differentials.