Experimental and numerical analysis of the seat track vibrations caused by engine starts in a power-split hybrid electric vehicle

An important method for saving energy and reducing the emissions from hybrid electric vehicles is to shorten the working time of the engine, which results in frequent engine starts and stops. The accompanying vibration and noise problems cause the driveability and the ride comfort to deteriorate significantly. In this study, experiments on the vibrations of the driver's seat track are performed and analysed to evaluate quantitatively the vibrations during the engine start. The measurement results show that vibrations in the longitudinal direction are the most severe, whereas vibrations in the lateral direction are the weakest. Based on the test results, a full-vehicle multi-body dynamics model, including the driveline, the powertrain mounts and the suspensions, is developed and verified. Some countermeasures are researched using numerical simulations to reduce the uncomfortable longitudinal vibrations. Optimization analysis demonstrates that the effects of the reduction in the vibrations are limited even by the optimal initial crank angle, the start-up time and the stiffnesses of the torsional damper and the half-shafts. Hence, parameter optimizations cannot completely eliminate the uncomfortable vibrations. Fortunately, as compensation control benefits from the fast response of electric motors in hybrid vehicles, it can play an active role in reducing the longitudinal seat track vibrations and in improving the ride comfort. However, the effect of the compensation controller greatly depends on the accuracy of the torque estimator.