Research On Torque Coordinated Control Of Braking Mode-switching For A Pure Electric SUV

With the global warming and the determination of the prohibition schedule of traditional fuel vehicles around the world,the research on electric vehicles have become a hot spot at present.All major OEMs,universities and research institutes around the world have invested a lot of scientific research resources,hoping to make breakthroughs in key technologies of electric vehicles.The regenerative braking control of electric vehicle is one of the electronic control technologies of the vehicle,and the electronic control technology is the core technologies of the industrialization of electric vehicle,which is the key and bottleneck to realize the optimization of the performance of the complete vehicle.In this paper,through the formulation of braking force distribution strategy,the establishment of electro-hydraulic composite braking system simulation model,the analysis of dynamic response characteristics of motor and hydraulic braking torque,and the proposal of brake mode-switching coordination control strategy,the problems of the total braking torque fluctuation and the jerk of complete vehicle of a pure electric SUV during mode-switching are solved.The ride comfort of vehicle is improved under the premise of braking safety during mode-switching.The main works are summarized as follows:According to the structural characteristics of the vehicle,the braking characteristics of the motor and the regulations of the braking law,the braking force distribution control strategy of the front and rear axles is formulated,which considers the efficiency optimization and the braking safety comprehensively.The rationality of the distribution of the braking force is verified based on ECE R13 braking regulations.The simulation model of electro-hydraulic braking system was built based on MATLAB/Simulink simulation platform.For the motor braking system,the excitation current and torque current are controlled by double closed-loop PI control,and the motor speed loop is controlled by sliding mode control.A controller combining a PID controller and a fuzzy controller is used to adjust the pressure in the wheel cylinder of the hydraulic braking system to achieve precise control of hydraulic braking torque.According to the change of brake pedal opening,the torque coordinated control strategy for brake mode switching is developed.When brake pedal opening is stable,the fast response of motor braking torque is used to compensate the hydraulic braking torque.When brake pedal opening is unstable,the brake pedal stroke and its change rate are used to reflect the braking intention of driver,and to modify the target hydraulic braking torque based on fuzzy control algorithm according to whether the driver pays more attention to brake safety or ride comfort.At the same time,the rapid response of the motor braking system is used to compensate the insufficient braking torque caused by the slow response of the hydraulic braking system,so as to ensure the ride comfort and stability of the braking during mode-switching.The forward simulation model of a pure electric vehicle was established in MATLAB/Simulink in this study,to verify the effectiveness of the brake force distribution control strategy and the torque coordination control strategy during brake mode-switching.The simulation results show that the braking force distribution strategy can improve the energy recovery efficiency on the premise of ensuring the braking safety.The torque coordination control strategy of this paper not only can modify the motor and hydraulic braking torque according to driver’ braking intention,but also can significantly reduce braking torque fluctuation and the jerk of the complete vehicle,thereby improving ride comfort and safety.