Transient Multi-Dimensional Conjugate Heat Transfer (CHT) Simulation of an Oil-Cooled Automotive Electric Motor Operated in a Drive Cycle

<div class="section abstract"><div class="htmlview paragraph">In an electric vehicle, nevertheless, the primary component is the electric motor (e-motor). Understanding the thermal performance of the e-motor is paramount in ensuring the overall efficient functioning of the electric vehicle. Usually, the high-power e-motors are oil-cooled due to relatively high thermal loads. The e-motor thermal response is monitored under extreme conditions like warm-up cycle allowing the vehicle to move in a circular track multiple-times. In this condition, the vehicle undergoes heavy lateral and longitudinal accelerations, the e-motor speed varies and the consequent thermal losses from the rotor and stator components also vary accordingly. Importantly, the cooling oil sloshes rigorously that affects the heat removal capacity of the oil. The advanced capabilities of Computational Fluid Dynamics (CFD) allow to virtually simulate the warm-up cycle and capture the extremely transient thermal response of the e-motor in the given conditions.</div><div class="htmlview paragraph">In the current effort, a general purpose 3-D CFD software, SimericsMP+ from Simerics, Inc. is used for the virtual simulation. A Conjugate Heat Transfer (CHT) model of the e-motor is created with all the important components such as windings, rotor, stator laminate, endrings, gears etc. The multiphase Volume of Fluids (VOF) approach is used to capture the oil flow across the components. A novel CHT approach is devised that allows to simulate the transient fluid-solid coupled simulation for a rotation of the vehicle in the circular track and the later solid alone heat transfer is simulated with a convective heat transfer boundary condition derived from the coupled simulation. The approach proved to be promising in terms of the accuracy of the temperature prediction on the windings compared to the test and the overall simulation time is acceptable to conduct multiple design studies of the e-motor.</div></div>