Vibration Analysis of an Electric Wheel Hub Motor at Stationary Operating Points

In the context of environmentally friendliness and challenging pollution limits the electrification of passenger cars becomes more and more important. In this contribution an innovative electrical drive for automobiles is presented and its vibration behavior is analyzed experimentally. In special, the vibrations of an electric wheel hub motor are studied in detail. For this purpose, a laser scanning vibrometer is used. To be able to measure the vibrations at the running engine a derotator is needed additionally to the laser scanning vibrometer. The electric wheel hub motor is investigated on a test bench at different stationary operating points which differ in the rotational speed as well as in the torque that is applied by an electric brake. Analyzing the vibroacoustic behavior of this special electric machine is of utmost importance as its sound radiation is directed straight to the passers-by of the car. The sound radiation of conventional cars drives is normally shielded and attenuated by the vehicle body and for this reason less critical. Moreover, the application of damping materials is more difficult if the engine is placed within a wheel. In the paper at hand different prototype stages of the electric wheel hub motor are presented. The working principle of this special engine is also explained. For the numerical simulations a holistic simulation workflow has been developed which takes into account the electromagnetic field as the most important vibration excitation as well as the structural vibrations coupled with an air volume around the engine to calculate the sound pressure. First, the electromagnetic forces are calculated which are then applied to excite the structural vibrations of the engine. Finally, the calculated surface velocity is used to excite the surrounding air volume under free field conditions to determine the radiated sound pressure level. In all three steps of the holistic methodology, the finite element method (FEM) is used for the numerical simulations. Beside identifying weak points of the engine prototype as well as obtaining a general understanding of such an electrical machine, the experimental data are used to validate a numerical model of the electric wheel hub motor. With the help of both the validated model and the gained experimental experiences the design of the wheel hub motor is improved. However, this contribution focusses on the experimental analysis of the structural vibrations of the running wheel hub motor.