Comparison of Cooling Circuit in Electric motors for Automobiles

The cooling system of electric motors plays a critical role in ensuring the performance and reliability of electric vehicles. In this work, three different oil cooling circuit configurations for an Interior Permanent Magnet(IPM)motor were designed and evaluated through CFD simulations. The proposed cases include: (i) coolant flow through a hollow shaft, (ii) cooling channels embedded in both the shaft and rotor laminations, and (iii) an additional cooling channel created by indenting the magnets by 0.5 mm between the shaft and rotor laminations. Considering the anisotropic thermal properties of stator windings, the equivalence of the rotor–airgap region, and the stator water jacket. The thermal-fluid simulations were carried out using the Multiple Reference Frame (MRF) method in ANSYS FLUENT, and an electromagnetic analysis was performed to verify the impact of different cooling structures on motor performance. The results show that among the three designs, the third configuration provides the most efficient cooling effect, significantly reducing winding and rotor temperatures. The proximity of the coolant to the heat source enables a more effective reduction in rotor temperature; nevertheless, the associated complexity of the piping system results in a greater pressure drop. Moreover, due to the inherently low thermal conductivity of the air within the air gap, variations in rotor cooling strategies exert only a negligible influence on the cooling performance of the stator. Moreover, it demonstrates no adverse influence on the electromagnetic characteristics of the motor. This study highlights the importance of optimized cooling design in enhancing the thermal performance of IPM motors for automotive applications.