[ISMA 20] Characterization of EV/HEV NVH issues using electrical machine tooth FRF

The article extends the use of tooth Frequency Response Functions (FRF) concept for the analysis of electric motor Noise, Vibration and Harshness due to electromagnetic forces (e-NVH) at intermediate design stage or after manufacturing, using both simulation or testing. This technique is complementary to a full e-NVH virtual prototyping fitted with experimental tests. It allows to identify the impact of each individual e-NVH harmonics on the overall vibration or Sound Power Level of the electrical machine. As the physical origin of the main e-NVH harmonic is pointed out, a quick diagnosis is ensured allowing to efficiently identify noise mitigation actions. The principle of the technique consists in first characterizing the structural response of the housing envelope when exciting stator teeth under radial and tangential harmonic loads. This first step can be performed using measurements (by impact hammer) or numerical simulation. Measured tooth FRF can then be converted by computation to a wave FRF to analyze the structural response under rotating Maxwell stress waves of circumferential wavenumber r. Therefore, combined with the amplitude of each magnetic excitation harmonics, these wave FRF can be used to identify the key contributors to the overall vibration and noise radiated by the machine. Additionally, tooth FRF can be used for modal parameter extraction, or to study the effect of asymmetries, eccentricities and uneven airgap by modulating pulsating magnetic forces driving the NVH behavior of e-motors in EV / HEV automotive applications. Besides, tooth FRF can be used to visualize the operational magnetic force waves acting on the stator using Operational Force Shape analysis, similarly to an Operation Deflection Shape analysis. The contribution of the tangential forces to the overall vibration and noise radiated by the machine can then be computed. Longitudinal FRF concept is also introduced to study skewing effects and optimize the skewing pattern combining tests with simulation under Manatee software, specialized on the electromagnetic and vibroacoustic design of electric motors. Finally, the extension of the concept on stator FRF to rotor FRF is discussed. An application case is included through all the sections demonstrating the benefits of the technique based on a Permanent Magnet Synchronous Motor (PMSM).


Measured rotating FRF