An effect of electromagnetic force on acoustic noise of axial-gap in-wheel SR motor

Switched Reluctance (SR) motors are the motor that utilize the reluctance torque originated in magnetic saliency between stator and rotor composed of electromagnetic steel sheet and windings without permanent magnet. Because of its robustness and simple structure, SR motors are suited to in-wheel motor. In flat space, an axial-gap structure has advantage compared with conventional radial-gap structure in space factor of motor. An axial-gap in-wheel SR motor was tested for microbus and the bus could be driven. We had successful results on the motor characteristics. However, the motor emits loud acoustic noise directly to the environment. We proposed freewheeling mode as a control method to reduce vibration. Freewheeling mode has some advantages compared with conventional methods, for example, simple system, low cost, no torque reduction and high versatility. And this method improves acoustic noise. This paper discusses characterizing vibration mechanism of axial-gap SR motor and how to reduce acoustic noise with freewheeling mode.