This study is focusing on the distortion phenomenon of the vibrational resonance peak when testing an e-drive assembly via RPM-sweep excitation. As the ramp rate increases, the measured response function deviates more and more from the stationary response. This distortion leads to a reduced peak amplitude, a shift in resonant frequency, changes in response shape and consequently, results in an increased half-power bandwidth, eventuating an increased apparent modal damping. These changes in the response are dependent on the sweeping direction and other physical parameters as well, like oil pressure and -temperature. The phenomenon was investigated earlier for linear systems, but not for operational testing of rotary machines, where the characteristics of the spectrum distortion are governed by different principles and are influenced by many other physical factors. A novel way for handling amplitude distortion of e-drives during transient testing is elaborated, which can be used to optimize RPM-sweep rate and other measurement parameters.

The electrification of the vehicle industry has led to a significant increase in the demand for innovative vibration testing. The RPM-sweep experiments of e-motors and e-drives are considered to be fundamental, as they provide valuable vibration and durability data for further analysis. The aim is to model the behavior of rotating-dynamic systems throughout their life cycles. However, inaccuracies in the definition of measurement and test parameters can result inaccurate transfer functions, ultimately reducing the accuracy and reliability of the test results. This paper focuses on two critical parameters: frequency resolution and RPM-sweep rate. Both of these parameters have a significant impact on the amplitude response of the system and can lead to substantial distortion of the FRFs. In this study, we characterize these distortions and propose a method to ensure that the error introduced by the chosen frequency resolution and RPM-sweep rate remains below a predefined threshold value. In addition to the theoretical derivation, we demonstrate the application of this method using real measurement data. This research aims to address the challenges associated with NVH testing in the context of the electrification of the vehicle industry, providing a valuable contribution to the development of more accurate and reliable testing methodologies.