Research On Electro-hydraulic Combined Braking Control Method For Electric Vehicles Based On Hydraulic Braking Status

With the deteriorating environment and the energy conservation and emission reduction policies,efficient and zero-emission electric vehicles(EV)are more popular.However,the charging facilities are not perfect.The batteries cost and cruising range of electric vehicles have shortcomings.As the key technology in electric vehicles,the electro-hydraulic combined braking system can not only generate partial braking torque,reduce brake pad wear and thermal decay,but also recover part of the braking energy.However,the control problem in electro-hydraulic combined braking method belongs to the multi-objective and multi-constrained optimization problem,which is very complicated.Therefore,the effect of the control method applied in engineering is not satisfactory.This paper focuses on the hydraulic brake system of the vehicle,and carries out the key problems of the electro-hydraulic combined braking system,including regenerative braking efficiency,safety and stability in the braking process,hydraulic brake system response.In order to solve these problems,this paper takes electric vehicle with in-wheel motors as the research object,and designs a layered centralized controller.The upper layer controller adopts model predictive control(MPC)that is good at dealing with multi-objective and multi-constrained problems to coordinate the distribution of braking torque.According to actual conditions,limit the actual braking force distribution curve,the braking torque range of the motor and hydraulic brake system and SOC upper limit constraint;Select the appropriate objective functions to ensure braking demand,safety and regenerative efficiency.The lower layer controller adopts linear pressure control method to implement the instructions of the upper controller.Finally,a electric vehicle model is built in AMESim to verify the effectiveness of the controller.The contents of this paper is as follows:First the electro-hydraulic combined braking system is analyzed and modeled.Introduce the structure of the four-wheeled wheeled electric vehicle as the research object first,then establish the electro-hydraulic combined braking system model and verify its effectiveness.Second considering the braking force distribution and actuators,a layered centralized controller is designed.Integrating motor,batteries and braking safety,an upper logic controller based on MPC is designed.Establish a dynamic model in the upper logic controller for integrated control of braking torque.To meet braking demand,maximum energy recovery and brake comfort,select the tracking error of the expected braking torque,regenerative efficiency and braking torque fluctuation as the objective function.The lower layer controller adopts the linear pressure control,and controls the valves of each wheel cylinder according to the hydraulic braking torque distributed by the upper controller to guarante pressure tracking.Finally,the vehicle model is built in AMESim and AMESim-Simulink co-simulation was carried out.In order to demonstrate the superiority of the linear pressure control method,a lower-layer controller based on the step pressure control is designed.Then test and verify the overall effectiveness and superiority of the control system.