This work deals with the combined investigation of subjective and ecological evaluation of the drive-off dynamics of passenger vehicles. The main focus is on the drive-off procedure in a mild hybrid powertrain. A connection between the subjective driving impression and ecological factors such as fuel consumption and the thermal load in the clutch is established.
In order to investigate the subjective evaluation of the drive-off dynamics, three test subject studies are conducted with the focus on influence factors maximum acceleration, mean jerk, response time, and engine speed changes. In each study, evaluation criteria related to driving dynamics and ride comfort are used. Statistical tests are carried out to identify the evaluation difference thresholds for these influence factors. The evaluation criteria, sportiness, jerkiness, and comfort, which are used in the ecological evaluation to assess the drive-offs, are objectivated by using a logistic regression model based on the maximum acceleration and mean jerk.
The hybrid modeling approach introduced for the ecological evaluation, which combines forward and backward modeling, ensures a precise simulation of the drive-off behavior. This approach also fulfills the requirement to maintain the neutrality of the battery's state of charge in the mild hybrid powertrain and to follow the reference driving cycle with high accuracy. The results show that the fuel consumption benefits of using the electric motor are most significant during drive-offs at low accelerator pedal positions, but this advantage decreases with increasing accelerator pedal positions due to compensatory fuel consumption for battery recharging.
Furthermore, the work underlines the ecological advantages of support by the electric motor in terms of reducing the thermal load in the clutch. It proves to be effective in reducing thermal load during drive-off and sequential gear upshifting when the electric motor operates as a drive. These advantages go beyond the immediate thermal load reduction and contribute to the goals of sustainable and efficient vehicle design.
For the calibration process, it is beneficial to understand the effects of changes in drive-off dynamics on user experience and ecological aspects. The results of this work provide valuable insights for the calibration process to facilitate fine-tuning of the drive-off characteristics taking into account both subjective driving impression and ecological factors
