A preview for vehicle driveability characterization on subsystem level powertrain

The increasing complexity of driving functions at the overall vehicle level results in a corresponding increase in complexity in the validation process. To expedite this process, validating overall vehicle characteristics at the subsystem level is also beneficial. Validating on subsystems is discussed using the example of the characteristic longitudinal vehicle shuffle as an overall vehicle property concerning the powertrain subsystem. The publication aims to demonstrate, through a literature review, the extent to which consideration of driveability-relevant properties already occurs at the physical subsystem level, with a focus on the frequency range of up to 30 Hz. The literature research shows that the considerations concerning driveability at the subsystem level are currently neither state of the art nor scientific, especially about the increasing number of electric vehicles; the level of knowledge is low. In the second step, this theoretical use case will be presented, in which a physical prototype (powertrain) is used to examine superimposed overall vehicle characteristics (longitudinal vehicle oscillation frequency (shuffle frequency)). For this purpose, a Hardware-in-the-Loop (HiL) approach is presented, which consists of a device under test (DUT) and two highly dynamic, permanently excited synchronous machines as load machines. A suitable manoeuvre (Tip-In) is shown, which makes it possible to evaluate the longitudinal vehicle shuffle. The analysis of the results of a coupled vehicle simulation in the HiL shows evident discrepancies in the verification of the demand values. Concerning a Tip-in, deviations of at least 70% can be determined for the speed required by the whole vehicle simulation and the system response (actual speed signal of the load machines) as a result of the step function. The wheel slip calculated from this propagates the error in the calculation of the virtual vehicle’s longitudinal shuffle frequency. Analyzing the results makes it currently impossible to validate the longitudinal vehicle shuffle at the subsystem level. Finally, there is a discussion about what significant changes are needed to achieve the required goal of vehicle driveability characterization at the powertrain level.