Basic experimental evaluation of three-dimensional air gap structure for torque improvement in electric motors

A reduction in the amount of rare earth magnets used in high-performance motors is required because they are expensive, and their supply is unstable. Therefore, the development of high-performance motors without rare earth magnets is important. Although the torque characteristics of the motor can be improved by shortening the air gap length of the motor, there is a physical limitation on the air gap length. Therefore, a three-dimensional (3-D) air gap structure was proposed for the motor to improve the torque characteristics. In this study, the effect of the 3-D air gap structure is evaluated based on analytical results. In addition, the torque characteristics and the iron loss of the 3-D air gap structure are examined based on experiment. There are two types of experimental models, each with different materials: laminated steel plate and soft magnetic composites (SMC). Additionally, the iron loss of the 3-D air gap structure models for the case using a pulse width modulated (PWM) inverter is examined.