Electric Powertrain NVH

Romax Technology and Hyundai Motor Company co-author paper on Electric Powertrain NVH

Romax Technology are proud to have co-authored a paper with Hyundai Motor Company titled “Robust Development of Electric Powertrain NVH for Compact Electric SUV”. Read the abstract below for a comprehensive summary of the project and visit the SAE website to download the full paper.

Electric vehicles (EV’s) present new challenges to achieving the required noise, vibration & harshness performance (NVH) compared with conventional vehicles. Specifically, high-frequency noise and abnormal noise, previously masked by the internal combustion engine can also cause annoyance in an EV. Electric motor (E-motor) whine noise caused by electromagnetic excitation during E-motor operation is caused by torque ripple and stator local excitation. Under high speed and high load operating conditions, the sound level is low, however high frequency whine noise is a factor that can impair the vehicle level NVH performance. An example of a previously masked abnormal noise is a droning noise that can be caused by manufacturing quality variation of the spline coupling between the rotor shaft of the E-motor and the input shaft of the reducer, it is dominated by multiple higher orders of the E-motor rotation frequency. In this study, the high speed and high load condition whine noise problem was reproduced through electromagnetic and structural analysis, and the countermeasure (E-motor geometry refinements to reduce the excitations and mechanical system transfer path modifications to reduce the vibration response) were defined and the effects investigated. Mechanical system modification to improve NVH performance without increasing the mass is challenging, however E-motor air-gap geometry optimization, such as slot opening modulation and rotor notch modifications achieved significant noise reduction without critical trade-off of other performance. This paper also describes the basic improvement plan proposed through the simulation of the abnormal droning noise behavior. To investigate the abnormal noise problem, a multi-body dynamic model of the system containing the E-motor shaft, gearbox input shaft, spline coupling connecting the two shafts and support bearings was developed. The model was solved in the time-domain using an Ordinary Differential Equation solver to capture any transient phenomena that can potentially lead to droning noise behavior. The main two manufacturing errors (pitch error in the spline coupling and the alignment error between the rotor and the gearbox shafts) that are responsible for the abnormal noise were identified. Through simulation it was shown that the droning noise can be reduced through improved quality control and tolerance design optimization of factors such as axis self-alignment and spline gear tooth quality.

SAE Publication Details: Ha, T., Huh, J., Choi, S., Min, D. et al., “Robust Development of Electric Powertrain NVH for Compact Electric SUV,” SAE Technical Paper 2020-01-1503, 2020.

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