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When a vehicle is cruising, unpleasant noise in the high-frequency band between 4 kHz and 5 kHz can occasionally be heard at the centers of front seats in the vehicle cabin. To search for the generation source of this noise, a study of the correlation between the cabin noise and airborne noise at the outer surface of the transmission, and an analysis of vibration transfer paths in the interior of the transmission were conducted. The results indicated that the source was the 0th-order breathing mode unique to electric-drive motors. For making it possible to predict this at the desk, vibrational analysis method for an electric-drive motor comprising laminated electrical steel sheets and segmented coils was proposed. Material property data for the electrical steel sheets and the coils was employed unmodified in the electric-drive motor vibrational analysis model. In addition, Laminate electrical steel sheets and the coils were modeled accurately. The analysis model defined the small sliding contact between the layers and also the contact between the electrical steel sheets and the coils taking into consideration. The contact stiffness between the electrical steel sheets and the coils was defined. First, the results of an eigenvalue analysis of the electrical steel sheets in isolation and of an experimental modal analysis were compared. The natural frequencies and eigenmodes in both sets of results corresponded well, with a difference of within 2%, up to 6 kHz. Next, vibrational analysis was conducted using an electric-drive motor model in which the coils were inserted into the laminated electrical steel sheets. the coil model used a rectangular cross-section, and defined equivalent material properties using a finite element analysis model in order to make it possible to accurately reproduce twist stiffness and bending stiffness. A comparison of the results of the analysis conducted using the electric-drive motor model and the experimental modal analysis using an electromagnetic shaker demonstrated the phenomenon of the peaks of natural frequencies exceeding 2 kHz becoming unclear. In addition, eigenmodes up to 5 kHz, in particular the 0th-order mode at 4.2 kHz, were accurately reproduced. Finally, this electric-drive motor was mounted into a transmission case and the modal analysis of structural vibration was conducted. Consequently, the tendency of the vibration level between the simulation and the measurement agreed well.
Mr. Toshihiro Saito, Honda R&D Co., Ltd. Automobile Center, JAPAN