Magnet Shape Design and Verification for SPMSM of EPS System Using Cycloid Curve

A low cogging torque and torque ripple are the most important qualities for electric power steering (EPS) motors. Therefore, various design methods are employed to obtain EPS motors with these qualities. In this study, a novel design method for the pole shape was developed by adopting a cycloid curve to realize the desired qualities of EPS motors without reducing the torque. An evaluation index (δq) was used to design the pole shape of the magnet and to compare the pole shape between the proposed method and the conventional method. The proposed and conventional methods were applied to existing machine designs, and their performances were compared using a finite-element analysis (FEA). The results of the FEA and prototype tests indicated an improved motor performance for the proposed method.