Simulation of Oil Flow Behavior in the Air Gap between Rotor and Stator

In an electric vehicle, the electric motor influences a significant proportion of the losses in the powertrain. The requirements for ever higher power and the necessary limitation of the winding temperatures have led to the active cooling of the windings with oil becoming increasingly important. Oil and oil mist inside the motor pose the risk of oil penetrating the gap between rotor and stator, leading to an increase in frictional losses. To address this important topic, a fully coupled CHT (Conjugate Heat Transfer) model was developed and is presented in this paper. Combining the best of two worlds, an efficient VoF (Volume of Fluids) approach with adaptive mesh refinement and a highly de-tailed Lagrangian approach are used considering:

Using this new approach, several engine speeds were analyzed. The simulations were supported by optical measurements using an experimental stator with the real geometry and implemented optical access window.

This paper gives more insight into the measurement and simulation method chosen and the results from both. Depending on the motor speed, a significant amount of oil could be detected in the gap between rotor and stator. The detectable flow conditions vary also with the speed of the motor. For example, a peak in drag torque is visible at lower motor speeds. The investigations confirmed the suitability of the simulation approach and showed a good correlation between simulation and measurement. The method is well suited for predicting and solving future challenges in the development of oil cooling for electric motors.