E-Axle用潤滑油下における軸受鋼の転がり摩擦挙動

Abstract

To extend the cruising range of electric vehicles (EV), it is necessary to improve the power consumption rate. By rotating the motor at high speed, it is possible to reduce the size and the weight of E-Axle, which improves the power consumption rate. However, high-speed rotation increases the number of contacts between gear tooth flanks in E-Axle reduction gears. This promotes the fatigue of the bearings and gears. Additionally, the lubricant has been newly developed for E-Axle, will be used instead of existing automatic transmission fluid. However, the effects of E-Axle lubricants on the fatigue of tooth surfaces have not been elucidated. In addition, on the contact surface of gears, sliding and rolling contact cause stress at the same moment. To evaluate the occurrence factors of fatigue in detail, it is necessary to divide the contact types into sliding and rolling contact and investigate the fatigue on contact surfaces. In this study, we focus on occurrence of pitting by only rolling contact to investigate fatigue factors. In this experiment, ball-on-disk type fatigue tests are conducted to evaluate performances of five different E-Axle lubricants for the occurrence of pitting under pure rolling condition. The results showed that pitting was reduced effectively with the lubricant that has the lowest kinematic viscosity. In addition, the pitting rates increase as the increase of kinematic viscosity. Therefore, the kinematic viscosity is considered to influence the occurrence of pitting fatigue.