Development of low-torque-ripple motor with high rotational speed to downsize electrical systems

Electrification is progressing across different fields such as automobiles and construction machinery. Motors for electric systems are required to be compact and achieve high power density. In this study, we developed a small motor with rotation speed of 22,000 r/min by reducing stress concentration. Each pole has three magnets in the circumferential direction, and the magnets are arranged in a U-shape. The magnet insert slots are comprised of expanded flux barriers on the inner diameter side and a guide-less structure. The magnet slots reduce stress concentration. Additionally, the rotor has two dents on the outer diameter surface and expanded flux barriers on the outer diameter side. The dents have different shapes between the North (N) and South (S) poles. The structures reduce the torque ripple.