Pedal Feel Study Of Integrated Electro-hydraulic Braking System

With the increasing electrification and intelligence of automobiles,customers’ requirements for automobiles have also increased in tandem.Drivers are not only concerned about the performance of the car in terms of dynamics,but also have increasingly stringent requirements for the actual driving experience.Brake pedal feel is the interrelationship between pedal force,pedal displacement and deceleration,and is a comprehensive feel that incorporates several evaluation indicators.In this article,the Integrated Electro-Hydraulic Brake(I-EHB)system is selected as the research object,the main studies are as follows.(1)The power-on wake-up and power-off self-check scheme of the brake-by-wire system is designed.Three types of braking modes,brake-by-wire,backup braking and system degradation braking,are designed to improve the robustness of braking system performance and meet the braking requirements.The target curve of pedal force-pedal displacement is designed,and the parameter design method of pedal feel subsystem is proposed.The component models of pedal feel subsystem and pressure building subsystem are built,the state space equations of the system under the normal braking mode are obtained,and the kinematic characteristics of the I-EHB system are built and analyzed by simulink.The solenoid valve model is linearized and the influence of pressure drop of long brake line and compressibility of brake fluid on the pressure building response is considered.(2)The static tests and dynamic tests of the vehicle in normal and backup braking modes were designed.The analysis of the compression process of the brake master cylinder and simulator under different stages was carried out.By comparing the simulation data with the vehicle test data,the maximum error is within 5%,which verifies the correctness of the model.The effect of different pedal input speeds on the pedal force-pedal displacement relationship curve was investigated,and the variation of and reasons for the pressure and other parameters in it were analyzed.(3)The effects of pedal ratio,valve port size,empty stroke and brake fluid bulk elastic modulus on brake pedal feel were investigated.A steady-state model of the brake fluid bulk modulus of elasticity is derived,and the correctness of the steady-state model in this paper is verified by comparing it with the commonly used steady-state models.The effects of different gas contents on the bulk elastic modulus of brake fluid and brake pedal feel are investigated according to the derived model.(4)The test method and evaluation index of subjective evaluation of brake pedal feel were proposed,and the evaluation method of subjective evaluation was designed.The subjective evaluation and objective evaluation were carried out on vehicles assembled with different brake system sample parts.The limitations of the existing brake pedal feel index evaluation criteria were analyzed,and the concept of pedal force resolution was proposed.The test results were evaluated and analyzed using the optimized objective evaluation criteria,and the consistency of the subjective and objective evaluation of brake pedal feel was verified.