This paper was produced for the 2019 NAFEMS World Congress in Quebec Canada
This paper deals with motor noise that determines the quality of an electric vehicle (EV) for a customer’s point of view. Generally, it is known that an electric vehicle is superior to traditional vehicle having an internal combustion engine in terms of noise, vibration and harshness (NVH) performance. However, motor noise of an electric vehicle has a pure-tone component of high frequency which induces detrimental subjective noise evaluation. The main source of this motor noise is the electromagnetic force, which is determined early by the rotor and stator design. Therefore, in order to design the motor for robust NVH performance, fast and accurate prediction of NVH characteristics is essential in the early stage of development.
In this paper, a method to correlate analytical models with test results in order to predict the exact level of motor noise is presented. First, the modal test is performed at the component level. This test result is compared to the prediction of the modal analysis from the component-level analytical model to prove out a validity. In this component-level model, the homogeneous modelling technique considering the orthotropic characteristics of the rotor and the stator core composed of laminated structures is applied to improve the prediction of vibration characteristics. Second, modal test and analysis is performed at a sub-assembly level, which is composed by several validated components. In this stage, various modelling techniques are examined such as bolt fastening and shrink-fit for main housing and stator assembly. Finally, assembly level, motor assembly model with verified sub-assembly is constructed, and correlated with test results.
For the motor noise analysis, the analysis of the electromagnetic force is performed for predicting the main excitation source, and the cavity model is additionally prepared for structural – acoustic coupling. After that, the noise analysis is performed with the electromagnetic force as the dynamic excitation. The effectiveness of the motor noise model is verified by comparing to the test results according to the motor operating conditions.