A control strategy for a smooth engine start in a power-split hybrid electric vehicle

摘要

Engine start-stop technology is significant in reduction of fuel consumption and exhaust pollution especially for hybrid electric vehicles. On the other hand, however, it also deteriorates drive smoothness and ride comfort. By insight into the power-split hybrid vehicles, the engine is directly connected to the transmission and driving wheels without any clutch in the driveline. Therefore, it is difficult to make a trade-off between the engine start and vehicle drive smoothness at the same time. For alleviation of the longitudinal impacts and jerks, the power-split hybrid driveline is numerically modelled counting for the torsional damper stiffness nonlinearities, planetary gear phase uncertainties and engine torque time-varying properties. Accordingly, a fundamental control strategy is developed to coordinate dynamic torques of the engine and motors from time to time during the engine starts. In fact, the hybrid passenger car undergoes shuffles and jerks due to severe torsional vibrations, most of which are a series of low-order modal resonances of the hybrid driveline. For reducing vibrations stimulated during the period of engine starts, active damping methods are adopted to compensate the engine torque fluctuations. By simulation results for vibration depressions of the hybrid driveline and vehicle, it is shown that the active damping strategy counting for elastic properties of the torsional damper is efficient.