Research on the effects of cooling water velocity on temperature rise of the water-cooled motor in electric vehicles

In order to attain the optimal velocity of water-cooled motors cooling water, the relationship between velocity of water-cooled motor's cooling water and motor temperature was derived based on the heat transfer and hydrodynamic theory. Motor temperature decreased more with the increase of velocity, when cooling water was in laminar flow. When in turbulent flow, the cooling effect on the motor was further enhanced, however, with the velocity increasing, motor temperature dropped to heat saturation with increasing cooling water flow. In this paper a model of water-cooled induction motor based on the thermal network was established. The steady-state temperature rise of motor under rated load was obtained and the temperature distribution of the winding and the stator yoke was also calculated when in different velocity of cooling water. Experiments were conducted on an induction motor prototype to measure the temperature of the motor under rated load and in various flow rates of cooling water. The numerical simulation results and experimental results are consistent with the theoretical analysis results, which proves the correctness of theoretical derivation. The study in this paper provides a reference for the water-cooled motor selecting the rational velocity of cooling water.