Abstract: During the noise test evaluation of a DD Motor for drum type washing machines, a high order rotation frequency noise problem caused by rotor was found. The noise is represented by a high peak near frequency of rotation times the number of stator slots and the interval is about the rotation frequency. Through theoretical analysis and test verification, it is found that the noise problem is mainly related to the shape of inner circle of rotor. In order to quantify the shape characteristics of the inner circle of the rotor, a method to measure the shape of the inner circle of the rotor of DD motor is presented, which can measure the complete shape profile of the rotor. Through theoretical and experimental research, the key technology points of DD motor noise control are defined, which is conducive to the improvement of product competitiveness. Meanwhile, the research results are applicable to all kinds of external rotor brushless DC motors.

Key words: External rotor motor, Drum washing machine, Direct drive motor, Rotor shape, Noise