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Besides a conventional powertrain system, a Parallel Hybrid Electric Vehicle (PHEV) employs an Electric Vehicle (EV) powertrain system. And also in most PHEV there are conventional braking system and regenerative braking system working together. In a conventional braking system, typically it includes a frictional drum or a disc braking assemblies selectively which actuated by a hydraulic system. In the regenerative braking system, the electric machine provides a negative torque to the wheels to convert some kinetic energy into electrical energy for recharging the battery. Energy regeneration during braking is important for hybrid electric vehicle to improve its fuel economy and extend its driving range. There come some dynamic changes of braking torque in conventional hydraulic braking system when the regenerative braking system works. [1,2].

During braking, energy regeneration for hybrid electric vehicles (HEV) is an important technique to improve their fuel economy and extend their driving range. Due to the effect of regenerative braking torque added by the electric motor, the control logic of the braking system should be adjusted. This paper presents a control strategy for an HEV braking system, which calculates the optimal target wheel slip ratio based on vehicle dynamic states; a fuzzy logic approach is applied to maintain the optimal target slip ratio so that the best compromise between hydraulic braking torque and regenerative braking torque can be obtained for the vehicle. This control strategy is implemented with an 8-DOF nonlinear vehicle model and a “Magic Formula” tire model; the simulation results show that the proposed strategy is robust and effective.