Design and Manufacture of A High-Torque-Density Permanent Magnet Traction Motor For Light-Duty Electric Vehicles

Transportation electrification has greatly altered the way people live, leading to the light-duty vehicles such as electric bicycle, wheelchair and scooter, which brings great convenience to daily travel. The ability of direct drive and large torque for traction motor is the key to fulfill the faster, safer and cheaper vehicles. As for the regular permanent magnet (PM) motor, the improvement of torque density is challenging due to the limited magnetic field energy utilization. In this paper, a high-torque-density PM traction motor is proposed which features the open-slot stator, and spoke-type magnet rotor with dual-axial-flux bridges. The proposed motor obtains high torque density owing to two benefits. On one hand, the open-slot stator creates additional magnetic field harmonic besides fundamental one in regular PM motor. Both field harmonics could engage in electromechanical energy conversion and output torque. On the other hand, the unique design of dual-axial-flux bridges could effectively amplify two field harmonics, facilitating higher magnet field energy utilization within a limited usage of magnet. The analytical and simulation results show that torque density of the proposed motor can reach 30.5Nm/L at 200A/cm electric loading, which almost triples that of the regular PM counterpart. Hence, it is of great significance for the development and promotion of light-duty vehicles and has multiple application prospects.