The control strategy of optimal brake energy recovery for a parallel hydraulic hybrid vehicle

The purpose of this paper is to develop a control strategy of optimal brake energy recovery for a parallel hydraulic hybrid vehicle, in which the shifting schedule of the torque coupler and the distribution of the braking force are the most important impact factors based on a detailed study of braking characteristics. The two implementable schemes are compared to achieve a better shifting schedule for the torque coupler. An optimal distributive curve and the corresponding models of braking forces are also established, which not only avoids the situation of rear wheels locking earlier than front wheels but also determines the distributive ratio of the braking forces in each case. The simulation models of the vehicle are developed on the basis of the software, Advisor 2002, which is validated by the road tests. The simulation results indicate that 42.7% of the brake energy can be recaptured in the hydraulic hybrid vehicle, whereas 41.6% of the traction energy is wasted in the braking of a conventional vehicle. Therefore, the control strategy of optimal energy recovery is very effective in improving the efficiency of brake energy recovery in the hydraulic hybrid vehicle.