Thermal Analysis And Calculation Of In-wheel Motor For Electric Vehicle

Since the growing shortage of energy and environmental problems, green electricvehicle (EV) is getting increasing attention of researchers. The motor system in EV isof the most importance to the whole performance of the vehicle. Among differentmotors applied in EV, in-wheel motor has special advantages. For the in-wheel motor,the drive and reduction gear devices are omitted, thus the underframe structure of EVis simplified, and the driving performance of EV is improved. However, in-wheelmotor of EV requires not only high starting torque and small size, but also high powerdensity, this results in a higher requirements of thermal performance of the motor. Therise of motor’s temperature will affect the output power of the motor, operationalreliability，as well as its service life. At present, most study focus on the temperaturefield in large motors, and relatively less on those of small power motors. Therefore, itis necessary to analyze the temperature field of in-wheel motors used in EV.This research is a sub-subject of the national863project “the next generation ofin-wheel motor driving system”. To acquire more accurate results, the finite-elementmethod (FEM) was used to study the temperature field of the prototype designed inthe project. A2-D model was built, and basic assumptions and boundary conditionswere given. The magnet filed distribution was firstly studied, then the heat source wasanalyzed to get the distribution of the temperature field. According to the heat transfertheory, the heat transfer process between the stator and rotor was dealt equally as thethermal convection. Finally, some factors impact the temperature rise were discussed,such as the slot insulation thickness, transfer coefficient, stator yoke height, etc.To solve the over-heat problem, solutions were proposed in the research. One ofthe solutions is to increase the heat dissipating capacity by increasing height of statoryoke. Another one is to decrease the slot insulation thickness in order to reduce motortemperature rise. The analysis result of the electromagnetic field and temperature fieldof in-wheel motor will help to improve the motor design level and accuracy.