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System and component target setting for noise and vibration are important activities within automotive product development. New challenges arise when electric motors are introduced into cars traditionally powered by combustion engines. The emitted noise from an electric traction motor for hybrid electric vehicles is characterized by high frequency tonal components from the dominating magnetic harmonics which can be perceived as annoying. Sound power is frequently used for quantifying the airborne noise from rotating electrical machines. This paper describes the process of determining the radiated sound power from an automobile electric rear axle drive in-situ and its contribution to interior cabin noise for a prominent rotor order. The sound power was calculated by combining the average stator surface vibration velocity together with an estimate of the radiation efficiency.

When it comes to the acoustic properties of electric cars, the powertrain noise differs dramatically compared to traditional vehicles with internal combustion engines. The low frequency firing orders, mechanical and combustion noise are exchanged with a more high frequency whining signature due to electromagnetic forces and gear meshing, lower in level but subject to annoyance. Previous studies have highlighted these differences and also investigated relevant perception criteria in terms of psycho-acoustic metrics. However, investigations of differences between different kinds of electric and hybrid electric cars are still rare. The purpose of this paper was to present the distribution of tonal components in today's hybrid/electric vehicles. More specifically, the number of prominent orders, their maximum levels and frequency separation were analyzed for the most critical driving conditions. The study is based upon measurements made on 13 electrified cars on the market.