A Hybrid Rotor Design with Reduced Rare Earth Magnets for Traction Motors

This work presents the opportunity to address potential shortages in critical rare earth elements by substituting neodymium-iron-boron (Nd-Fe-B) magnets with ferrite magnets in traction motors, while maintaining comparable performance. Many attempts have been made to reduce critical rare earth permanent magnet materials in traction motors using full/partial substitution of cost-effective ferrite magnets. Such motors generally use different rotor topologies, such as spoke or synchronous reluctance designs. However, such designs with reduced/without rare earth magnets are still far from achieving matched performance with rare earth permanent magnet machines. This work proposes a hybrid rotor multiple magnet (HRMM) design in which both magnetic torque and reluctance torque are simultaneously harnessed by using Nd-Fe-B magnets only at specific appropriate locations and ferrite magnets at other locations. A commercial traction motor (Prius 2010), designed with Nd-Fe-B magnets for maximum power 60 kW and maximum speed 13,500 rpm, is used as the baseline for comparing the HRMM design. The HRMM design shows comparable performance with the commercial design for the given speed range with ~ 50% reduction in critical rare earth elements and at low cost.