A Design Approach Considering Axial Asymmetry Position of Rotor to Stator in Permanent Magnet Synchronous Motor for Compact Size

This paper presents a design approach of a permanent magnet synchronous motor to use effectively the space of the housing inside by considering the axial asymmetry position of the rotor to the stator. This approach helps to utilize the motor space effectively, and make compact size and light weight. However, when the rotor and stator are offset from each other in axial direction, the axial attractive force (AAF) is generated, which is able to generate noise and vibration of the motor. To obtain the stability of the motor in this case, the bearing should be properly chosen. To avoid losing the space secured in the axial asymmetric position by a larger bearing than necessary, AAF were calculated and analyzed to select the proper bearing. Firstly, the AAF depending on the axial position of the rotor to the stator is investigated by three-dimensional finite element analysis (3-D FEA). The torque is also calculated under the same condition to verify that the system requirements are met. Then, the bearing type is selected to ensure that the allowable load of the bearing is higher than the value of both AAF and radial force of the motor. Based on the analysis results, the proper axial position of the rotor with respect to the stator is proposed. Finally, the experiment is conducted to validate the accuracy of the analysis result.