Vibrational Analysis Method on High-frequency Electric-drive Motor Noise

When a vehicle is cruising, unpleasant noise in the 4 to 5 KHz high-frequency band can be heard at the center of all seats in the vehicle cabin. In order to specify the source of this noise, the correlation between the noise and airborne noise from the outer surface of the transmission was determined, and transfer path analysis was conducted for the interior of the transmission. The results indicated that the source of the noise was the 0th-order breathing mode specific to the drive motor. To make it possible to predict this at the desk, a vibrational analysis method was proposed for drive motors made up of laminated electrical steel sheets and segment-type coils. Material properties data for the electrical steel sheets and coils was employed in the drive motor vibrational analysis model without change. The shapes of the laminated electrical steel sheets and coils were also accurately modeled. The status of minute slippage between the laminated layers and contact between the electrical steel sheets and the coils were also considered in the model. First, the results of an eigenvalue analysis of the laminated electrical steel sheets in isolation were compared with those of an experimental modal analysis. Natural frequencies and eigenmodes matched with a deviation of within 2% up to 6 kHz. Next, a vibrational analysis of an electric drive motor model featuring coils press-fit into the laminated electrical steel sheets was conducted. In order to enable accurate reproduction of twisting stiffness and bending stiffness in the coil model, which featured a rectangular cross-section, equivalent material properties were defined for the finite element model. In addition, penalty contact stiffness was defined for the laminated steel sheets and coils. Comparison of the results of an analysis conducted using the drive motor model with the results of an experimental modal analysis using an electromagnetic shaker showed that the phenomenon of natural frequency peaks exceeding 2 kHz becoming unclear was captured by the simulation. In addition, the eigenmodes up to 5 kHz, in particular the fact that there is a 0th-order breathing mode at 4.2 kHz, were accurately reproduced.