Fundamental evaluation of direct-cooling technology for in-wheel drive system

We are developing a small and lightweight direct-drive system toward the realization of in-wheel electric vehicles (EVs). To increase the power density of the motor, we developed a direct-cooling motor that immersed the core, coils, and magnets in cooling oil and improved cooling efficiency. Moreover, we performed measurements of frictional loss, measurement of pressure drop, and a continuous heat-run test on the test bench. The results demonstrated that direct cooling is effective and continuous operation can be achieved. Additionally, it was found that the coil temperature can be controlled by the flow rate of the cooling oil. In this paper, we report on the concept of direct cooling and the measurement results.