Study On Modal Characteristics Of Automotive Alternator

Alternator electromagnetic noise has affected the passenger’s comfort, it is strictly limited by auto manufacturers. Due to differences in the modal, the peak of alternator electromagnetic noise is inconsistent with the speed variation, resulting in the control of alternator electromagnetic noise becoming complicated. In this paper, modal consistency rule and its affecating factors were studied based on a car alternator with a combination of experimental and simulation method.Through analyzing alternator noise under the no-load and load conditions, electromagnetic noise, manifested as36th order noise, was generated by the structural resonance radiation which was caused by the periodic electromagnetic pulling force in air gap between the rotor and the stator. Compared to the order of noise between the different alternators in same model and the same alternator in different state, it was found that the alternator existed widespread problems of electromagnetic noise inconsistency. Modal consistency was the key factor affecting the consistency of electromagnetic noise through researching on the electromagnetic excitation force and structure vibration characteristics.Based on modal superposition theory, combined with modal test system, the main components of the alternator and the whole body were modal experimented with multiple measurements to eliminate error, coherent estimates to exclude the effect of non-linear system. The modal parameters were obtained using a peak method and the results were certified by MAC.The consistency of the alternator modal was measured with statistical method. Compared standard deviation of the natural frequency of the main parts and the whole body, it was found that the performance of the low-level modal consistency was good, and the consistency of components natural frequency was better than the whole body natural frequency, and the consistency of the stator natural frequency had the best performance. The complexity of the geometry and the difficulty of the production determined the modal consistent quality.The finite element simulation models of the stator were built with laminated model and integral model, it was showed that laminated model needed a long time to calculate, but the accuracy was not significantly improved; when only considering the radial modal, the integral model could satisfy engineering needs well. Under the premise of parts simulation models availability, the simulation modal model of the whole body was built, and its correctness was verified with modal shape and natural frequency obtained from the experiment.The results obtained in this paper established foundation for further study on electromagnetic vibration and noise control, and also provided reference for similar alternators modal research.