Design of Hybrid Electric Vehicle Braking Control System with Target Wheel Slip Ratio Control

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]. Basis on the analysis and comparison of various type of regenerative braking system, a new combined control strategy for PHEV is presented in this paper. The control strategy adopts a fuzzy logic approach to keep a certain target slip ratio to make a best compromise between hydraulic braking torque and regenerative braking torque acts on the vehicle. A simulation system is built up with an 8 DOFs (Degree-of-Freedom) nonlinear vehicle model and a non-steady non-linear tire model in the environment of Matlab/Simulink. The simulation results show the robustness and effectiveness of the proposed strategy in this paper.