Joint simulation of radiated noise of electric powertrain based on finite element modeling and boundary element method.

Evaluation of the NVH (noise, vibration and harshness) performance of automotive powertrain has been an integral part of the vehicle development process. Although electric vehicles are generally considerably quieter than their counterparts powered by internal combustion engines, some problems about NVH still exist, which are becoming more challenging in terms of the future of vehicle. Firstly, the sound only from dominant engine but not from tire, wind or auxiliaries disappears, which consequently becomes increasingly audible due to the removal of the masking sound of broadband engine. Moreover, the interior noise is characterized by high-frequency noise components which can be subjectively perceived as annoying and unpleasant. Thirdly, as the electric vehicle develops toward the direction of high speed and large torque, electric vehicle vibration and noise problems highlight gradually. The subject of this paper is the numerical and experimental evaluation of the acoustic behavior of an electric powertrain, which is helpful for the electric vehicle in the design stage. For this purpose, a co-simulation method based on finite element modeling (FEM) and boundary element method (BEM) for the acoustic radiation analysis of an electric powertrain under multi-excitations is presented. The vibration and noise characteristics of electric vehicle are quite different from that of internal combustion engine due to different exciting forces. The calculation of the internal excitations of motor-reducer integrated drive system is the foundation of dynamic analysis. The internal dynamic excitations of a certain electric powertrain in rated revolution are calculated by theoretical analysis and numerical simulation method on the basis of gear dynamics and electromagnetism, including the electromagnetic radial force, electromagnetic tangential force and external circuit in the motor, and the time-varying gear meshing stiffness, meshing error and meshing impact in the gear system. The amplitude of the electromagnetic forces is concentrated on the current harmonic frequencies, while the gear meshing force is on the meshing frequencies. On this basis, a structural dynamic model is established based on FEM to carry out the vibration modal analysis and calculate the vibration responses. The analysis shows that the electric motor can be influenced by the reducer, which makes the NVH characteristics of the electric motor are totally different from that without reducer. Then, an acoustic model of the electric powertrain is established based on BEM to calculate the radiated sound pressure with the results of vibration response analysis, in order to find out its effect on the acoustic radiation. From the contour graph of different field points' acoustic pressures, it can be learnt that sound pressure level of radiation noise near motor and reducer is higher than any other places and radiation noise spreads in radial lines. In order to testify the theoretical analysis, an experimental bench is used to test the radiation noise of the electric powertrain in a semi-anechoic chamber. The results derived from both simulation and experiment indicate that the 6th and 12th harmonics of current are the main reasons of making electromagnetic noise, and meanwhile the gear's active meshing frequency as well as its doubling and tripling frequencies contributes to the gear whining. Thus, a template from end to end to predict NVH performance of an electric powertrain has been established. The results can provide a beneficial support for the further study of electric powertrain noise control. [ABSTRACT FROM AUTHOR]