Design and electromagnetic analysis of oil-cooled structure of new hairpin-winding motors for automobiles

With the development of the high rotational speed and high power density of automotive permanent magnet synchronous motors, the temperature increase of motors is getting higher and higher, and the cooling methods are transitioning from water cooling to oil cooling. At present, the most commonly used oil circuit structure is the stator yoke-oil circuit. However, this design has difficulty achieving effective cooling of the slot winding, which affects the continuous performance of the motor. To solve this problem, this paper proposes a new oil-cooling path based on the motor structure and magnetic circuit principle, and compares it with the yoke-oil path and a combination of the two oil paths. Then simulation calculations are made on the loss, performance and temperature increase of the motor. Finally, a slot-yoke prototype is built to obtain the temperature increase and compares it with the simulation value. It is shown that the notch oil circuit improves the sustained performance of the motor. However, the leakage of the closed slot affects the peak value of the motor, and the sustained torque of motor III is 3.5% higher than that of motor I and 33.0% higher than that of motor II. Finally, the validity of the simulation is verified by the temperature-increase experiments.