Study of high frequency noise from electric machines in hybrid and electric vehicles

This study investigates the tonal high frequency noise characteristics which are present within the cabin of an electric vehicle. As the human ear responds differently to different frequencies of sound and this response varies with age, both the level and the frequency are considered. In addition, the amount of annoyance these sounds will cause for the occupants is a function of the tonality and the level of the noise compared to other masking noise sources present. Metrics for tonal noise taking account of these factors are evaluated for a vehicle creep load case and compared to subjective results to determine suitability for the evaluation of electric vehicles. The Stevens VI loudness metric is shown to give a good indication of the total tonal noise present in the cabin of an electric vehicle. The tone-to-noise ratio and prominence ratio are used successfully to compare the level of a tone to the masking noise present, although general prominence limits are shown to be unreliable for evaluation of electric vehicle tones. Finally the noise sources present in the vehicle are reviewed along with factors that must be considered for the diagnosis and mitigation of these different tonal noise sources .