Thermal Simulation of Ball Bearing in Electric Drive Unit: A CFD Study Using Volume of Fluid and Mixed Timescale Coupled Conjugate Heat Transfer Analysis

The drive unit of electric vehicles is a complex system consisting of an electric motor and a gear train, which work together to provide the necessary power for vehicle propulsion. One essential component within this system is the ball bearing, which supports the rotating components such as gears and shafts. This study focuses on the thermal simulation of a ball bearing within the drive unit conducted using the Volume of Fluid (VOF) method coupled with mixed timescale Conjugate Heat Transfer (CHT) in Simerics-MP+ to reduce the computational time while ensuring accuracy in the analysis. The Computational Fluid Dynamics (CFD) approach considers the geometrical details and clearances of the inner race, outer race, cage, and ball within the ball bearing. By accounting for the relative motions between these components, it can accurately model the film formation of the lubricating oil and its impact on heat removal from the bearing. The simulations are conducted at two different shaft speeds of 4000 and 10500 RPM to investigate the varying frictional heat generation and oil inflow rates. The results of the simulation provide valuable insights into the distribution of oil within the ball bearing, the solid temperatures of the bearing components, and the fluid power losses associated with different operating conditions. Notably, the steady-state outer race solid temperatures obtained from the simulations are in good agreement with experimental test data, validating the accuracy of the numerical approaches. Keywords: Electric Vehicle, E-Drive Unit, Ball Bearing, Lubrication, Computational Fluid Dynamics, Multiphase Flow, Volume of Fluid Method, Conjugate Heat Transfer, Simerics-MP+, Thermal analysis