Vibration Effects of Axial Preload in Ball Bearings of an Electric Drive Unit Using Multi-Body Dynamics Simulation

The vibration characteristics of bearings in the Electric Drive Unit (EDU) of electric vehicles have a direct impact on the overall Noise, Vibration, and Harshness (NVH) performance. Due to the high speed of the drive motor, the importance of reducing shaft system vibrations has grown. Wave Washer (WW) is used to apply axial preload to bearings, thereby mitigating shaft system instability. In this study, the EDU was modeled using the Multi-Body Dynamics (MBD) simulation software ADAMS, and the effect of WW preload on bearing vibration was analyzed. The simulation results revealed that the dominant low-order vibration peak around 400 Hz was reduced by up to 30 dB. Notably, the vibration reduction effect was evident as the preload increased to level A, whereas only marginal improvements were observed beyond this level, indicating a saturation tendency. To provide a physical interpretation of this behavior, a simplified analytical stiffness formulation based on Hertzian contact theory was employed. The results suggest that the observed saturation tendency is associated with both the stabilization of rolling-element contact conditions and the nonlinear relationship between preload and bearing stiffness.