Research On Control Strategy Of Electro-hydraulic Composite Brake System Based EHB With Electric Vehicle

The electrification,intelligence and networking of the automobile have promoted the development of the brake system to the X-by-wire and electro-hydraulic composite brake technology.The electro-hydraulic brake system within wire control technology has the advantages of adjustable brake feeling,active pressure building,fast response,precise control of hydraulic pressure,and high recovery rate of brake energy,has been used in the electrohydraulic composite brake system.The main contents of this paper are as follows:This paper introduces,compares and analyzes the development status and key problems of EHB system and electro-hydraulic composite brake system.Several typical electro-hydraulic composite brake systems for different vehicle types are analyzed.The structure characteristics and working principle of each sub module in the electro-hydraulic composite braking system are elaborated.According to its mathematical model,the motor model,the power battery model,the vehicle model,the tire model and the driver model are built in Simulink.From the view of analyzing driver’s brake intention,the fuzzy theory is applied to transform the driver’s brake pedal opening into the driver’s target brake strength.Based on the theoretical analysis of automobile braking force,a series braking force distribution strategy based on EHB system is proposed by referring to the typical electro-hydraulic braking force distribution strategy and the optimal regeneration torque curve of motor.The driver’s brake pedal opening is divided into three stages: the braking empty travel stage,the priority electric braking force stage and the joint action stage of electric and hydraulic braking forces.Output the maximum target motor braking torque according to the brake pedal opening.The proposed electro-hydraulic composite brake force distribution strategy is simulated and analyzed under single brake condition,NEDC condition and ftp75 condition respectively.Under single brake condition,corresponding to small and large driver brake intention,the brake energy recovery rates of 68.59% and 30.08% are obtained respectively.Under NEDC condition,the brake energy recovery rate can reach 20.83%,and under Ftp75 condition,the brake energy recovery rate can reach 22.01%.Under CLTC condition,the brake energy recovery rate can reach 26.30%.The driving range experiment of NEDC was carried out on the hub test-bed,and the driving range of vehicles under the conditions of with brake energy recovery and without brake energy recovery were compared.The conclusion showed that the proposed strategy can increase the driving range of vehicles by 33.33%.Aiming at the problem of brake feeling consistency in electro-hydraulic composite brake system,this paper analyzes the problem from subjective evaluation and objective evaluation of brake pedal feeling,and obtains the subjective evaluation table of brake pedal feeling at low speed and high speed and the upper and lower reference boundary of brake pedal displacement and brake pedal force curve.It provides a theoretical method and technical guidance for evaluating the brake feeling consistency of the electro-hydraulic composite brake system.