Research On Electro-hydraulic Composite Brake System Of Pure Electric Vehicle Based On Electric Vacuum Booster

With the continuous progress of industrialization,China’s automobile industry has developed rapidly in the past two decades,and the car ownership has also experienced explosive growth.However,behind the huge car ownership,there are serious social problems such as energy exhaustion and environmental pollution.In order to gradually solve this social problem,relevant enterprises and scientific research institutions have carried out a large number of research and development of pure electric vehicles.Short driving range is a pain point that pure electric vehicles can’t get around for a long time.In the process of vehicle driving,the loss energy caused by the driver’s braking operation accounts for a large proportion of the whole driving energy.Therefore,this paper proposes to introduce the motor regenerative braking system to recover the energy consumed due to braking,so as to extend the whole range of the vehicle and improve the economy of the whole vehicle.However,the intervention of motor regenerative braking system will cause impact on the original hydraulic braking system of the vehicle.In order to coordinate and solve this problem,this paper analyzes and studies the characteristics and control strategies of the electro-hydraulic composite braking system.The main research work is as follows:Taking the composite brake system as the research object,this paper analyzes its key structure and working principle,and summarizes the general functional requirements it should have.A composite brake system is designed,which uses a travel simulator mechanism to decouple the brake master cylinder and the brake wheel cylinder.The fore-end brake control device is designed as driver brake demand identification unit,and its working characteristics are studied through the combination of theoretical modeling and experimental testing,and the relationship between driver brake pedal input and demand brake torque is obtained.With the help of AMESim and Simulink,the model of hydraulic control system and the model of motor brake system are built respectively.The logic threshold control strategy is used to control the pressure rise,pressure maintaining and pressure reduction of the hydraulic control system.In the control of motor braking system,two control strategies are adopted,which are regenerative braking current control based on fixed duty cycle and constant current regenerative braking control.With the help of Labcar experimental platform,the target pressure control experiment of hydraulic brake device based on ESP is carried out,which is compared with the simulation results.The validity and rationality of the hydraulic control system model are verified from two indexes of system response time and maximum error.The controller of the motor braking system is developed and designed.The super capacitor,DC contactor,rectifier bridge,reactor and other components are integrated with it and connected with the experimental vehicle for debugging.The motor braking control experiment is carried out,and the effectiveness of the constant current regenerative control is verified from the experimental level.Considering the requirements of braking laws and regulations and the maximum use of motor braking,the boundary conditions of whether rear axle braking force participates in braking are calculated and the control strategy of composite braking force is put forward.The typical braking conditions of different composite braking modes are selected: low speed small intensity braking,medium speed small intensity braking and medium intensity braking.The simulation analysis of these three conditions is carried out respectively.The results show that the driver’s demand braking torque can be satisfied under the designed control strategy and the energy storage device recovers the energy consumed in the braking process.The methods and achievements of this research will provide theoretical basis and technical guidance for the design and development of the electro-hydraulic composite brake system and the control strategy of the electro-hydraulic composite brake of the electric vehicle,which has a broad application prospect.