Electric traction motors in hybrid electric vehicles (HEV) are new components in the drive train which can introduce additional noise and vibrations. Their noise and vibration characteristics differ significantly from that of combustion engines or gearboxes, in particular due to their tonality and the strong high frequency content. For the structural dynamic analysis of these drives, conventional methods can be applied for measurements and simulations. However, calculation and characterization of the exciting forces during operation require a new approach. This paper studies the force excitation and vibration characteristics of a permanent magnet synchronous motor for an HEV which is placed in the transmission housing. The study is based on acoustic measurements, finite-element simulations and theoretical modeling. The main noise source is the electromagnetically excited radial force acting on the stator of the machine. The force is calculated by finite-element simulation and decomposed into its modal components. The paper explains how the dominating frequencies and excitation mode shapes are determined by the machine geometry and configuration. The influence of the power electronics converter is taken into account. It is shown that a mode 0 excitation dominates in a typical large diameter ring-type machine with a high number of pole pairs. At medium to high speeds, this breathing mode causes a strong whining noise when the dominant speed dependent excitation frequency coincides with the mainly radius dependent structural resonance frequency. Special focus is laid on generalizing the techniques and results to make them applicable to a large range of drive configurations.
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