Torque coordination of clutch, engine and motor during power transition for a hybrid electric bus

Ideal running performance requires that series-parallel hybrid electric vehicles smoothly transite between series and parallel operation modes. Clutches are widely applied to series-parallel hybrid electric vehicles to connect or disconnect powertrain components. Due to discontinuous nonlinear effect of clutch friction characteristics, smooth transition with little frictional dissipation is difficultly achieved. Hence, it is desirable to take friction discontinuity into consideration for improving the mode transition performance of hybrid electric vehicles. In this paper, a model reference adaptive control scheme based on hyperstability theory is developed to coordinate the torques of clutch, engine and motor for a post-transmission configured hybrid electric bus. It is worth emphasizing that the clutch is controlled to engage quickly and smoothly by a small frictional torque, which contributes directly to small jerk and little frictional dissipation. Results of simulations and experiments demonstrate that both vehicle jerk and frictional dissipation are decreased greatly compared to conventional operation. The effectiveness of the proposed adaptive control scheme is validated.