Study on the Thermal Characteristics of In-Wheel Motor Drive System Based on Driving Cycles

The driving conditions of vehicles, such as rapid acceleration, lasting downhill and so on, which demand for drive power, are rapidly increasing. For an electric vehicle driven by in-wheel motor (IWM), the IWM needs to provide greater power to maintain the normal operation of the vehicle. At present, the pursuit of high power density for IWM reduces the volume of motor under the same power. But the loss density is increased correspondingly, which will lead to overheating of IWM. In this paper, a 15-kW IWM drive system is taken as the research object. Based on the establishment of the temperature analysis model, instantaneous thermal characteristics of the IWM drive system are analyzed under the long climbing condition with low-speed and rapid acceleration driving cycles. The results show that the temperature of the stator winding and stator core is relatively high under the two driving cycles. The temperature of the stator winding is always in the highest level, and the maximum all appear on the end winding. The highest temperature of the end winding can reach 229.49 °C under the rapid acceleration driving cycles, which significantly exceeds the limitation for the insulation (155 °C) and will seriously affect the normal operation of the IWM and the vehicle. Therefore, in the follow-up design of cooling system, spray cooling with good local cooling effect can be adopted to focus on the cooling for the end winding. This paper can provide theory for the design of the feasibility thermal cooling solution.