Motor Length Reduction of Outer Rotor Type SPM Motor by Magnet Overhang Structure with Three-dimensional Flux Recovery

This paper presents a novel stator structure for outer rotor type surface permanent magnet (SPM) motors. The magnet overhang structure is a technique to increase the magnet flux by utilizing the space at the coil end, and has been widely used in SPM motors. However, because leakage flux is generated in the overhung area, which is longer than the stator core in the axial direction, the effect of torque improvement was limited. In the proposed stator, the magnet flux in the overhang area was picked using the flux recovery structure. Owing to the proposed stator, the leakage flux was reduced, resulting in a reduction in the motor length compared to conventional motors. In this study, numerical verification was conducted using numerical analysis to clarify the superiority of the proposed structure. From the numerical verification, the motor length reduction effect of the magnet overhung was 1.4 times higher than that of the conventional structure.