Vibration analysis of the BLDC axial-gap type motor using fem and its application to understanding noise generation characteristics

Abstract

The axial-gap type motor consists of a rotor (magnets) and a stator (coils). The magnetic force between the rotor and the stator is affected by the geometries and number of magnets and coils. The vibration and noise of the Axial-gap motor are usually generated due to structural resonance of the motor, air inside the motor and the magnetic force between the rotor and the stator. Therefore, an analysis for the vibration and noise of the motor is required. In this paper, the vibration and the noise generation characteristics of the axial-gap type motor are analyzed. Experimental modal analysis was performed to understand the vibration characteristics of the motor. The natural frequencies and mode shapes of the motor were analyzed. The generated noise was measured in an anechoic room. Sound pressure level (SPL) is measured and its dependence on the rotating speeds was analyzed. The vibration and noise of the motor were related to its structural resonance. Finite element analysis was performed to investigate the vibration characteristics of the motor. For acoustic structure interaction analysis, acoustic elements were used inside the motor. For modal verification, the predicted modal characteristics were compared to the measured values. The vibration of the rotor had strong coherence with the external mode shapes measured for motor housing. The rotor is driven by the magnetic force, so the vibration of motor is generated and increase due to the resonance of the motor. From the vibration of the motor housing the noise is generated especially at its resonance frequencies.