Research On Multi-Stage Energy Recovery Control Strategy Based On Integrated Brake-by-Wire System

In recent years,the automotive industry is reforming in the direction of intelligence and electrification,and the ownership of new energy vehicles,especially electric vehicles,is climbing year by year.As the level of automatic driving increases,the traditional vacuum brake booster system can hardly meet the current demand for high-level automatic driving assistance system for new energy vehicles,and the brake-by-wire system has become the mainstream of today’s brake market development.The brake-by-wire system replaces the vacuum booster with the electric motor as the power source,making the new energy vehicles free from the limitation of vacuum source.With the continuous upgrading of the brake-by-wire system,the integrated brake-by-wire system is more integrated and realizes the complete decoupling of brake pedal and wheel cylinder pressure through pedal sensing simulator and electronic control unit,which has faster pressure response speed and can realize the functions of active braking,compound braking and braking energy recovery,which improves driving safety and comfort.Brake energy recovery technology,as one of the important symbols of pure electric vehicles,provides a new idea to achieve the solution of energy consumption and improve the range of electric vehicles.Based on the integrated brake-by-wire system,a reasonable brake energy recovery control strategy can achieve a higher energy recovery rate and improve the range.In this paper,based on the university-enterprise cooperation project "Special software development for motor control capability improvement of an enterprise" and "IBC integrated braking control algorithm development",the research is carried out for the integrated brakeby-wire system and active pressure control algorithm.Based on the integrated brake-by-wire system,we analyze and study the energy recovery control strategy of the vehicle in different braking stages.The main research contents of this paper are as follows:(1)Analysis and modeling of integrated brake-by-wire system configuration.Firstly,we select three mainstream braking system configuration schemes,introduce the overall structure and main components of each configuration scheme,and analyze the working principle of each configuration scheme in different braking modes;then,we compare and analyze the advantages and disadvantages of each configuration scheme with the available resources in the laboratory,determine the configuration scheme of the braking system to be studied in this paper,and carry out the dynamic simulation modeling of the braking system.The dynamic simulation modeling of the braking system mainly includes permanent magnet synchronous motor,reduction drive mechanism and hydraulic system,and the simulation and experimental bench comparison verification of the established model;finally,the dynamics simulation modeling of the drive motor and battery in the energy recovery system.(2)Research on the control strategy of the integrated brake-by-wire system and drive motor.Firstly,the design of active pressure control algorithm is completed based on the integrated brake-by-wire system,mainly including pressure loop control and servo triple closed-loop control,the pressure loop adopts feedforward compensation control based on the hydraulic characteristics of the braking system plus PID feedback control;the servo triple closed-loop control includes current loop,speed loop and position loop to realize the control of the rotor position of the permanent magnet synchronous motor;then,the active pressure control strategy is verified by the test bench.Then,the active pressure control strategy is verified through the test bench;finally,the torque following control of the drive motor is studied and the simulation verification is completed.(3)Research on multi-stage energy recovery control strategy for vehicles.First,the dynamics of the vehicle in the braking process and the force situation of the front and rear wheels when the vehicle is braking on a horizontal road are analyzed to obtain the front and rear wheel braking force distribution range based on the ideal brake braking force distribution curve and the ECE regulation line limit.Then,the three phases of the vehicle are defined and divided into three phases: closing the accelerator pedal,coasting and depressing the brake pedal,and the phase switching strategy of multi-stage energy recovery control is designed based on the current state of the accelerator pedal and brake pedal to determine the current driving phase of the vehicle.Finally,the energy recovery control strategy is designed for different braking stages,mainly including:(a)closing accelerator pedal stage: the electric mechanism power distribution strategy of braking energy recovery in closing accelerator pedal stage based on fuzzy control theory is designed,and the accelerator pedal displacement and accelerator pedal displacement change rate are used as the input of the fuzzy controller to get the weight coefficient of electric mechanism power;(b)coasting stage: according to the vehicle’s speed-vehicle speed in(c)brake pedal stage: considering the basic theory of braking force distribution and the restrictions of ECE regulations on front and wheel braking force distribution,the multi-objective optimized braking force distribution model is established,the control demand is transformed into control objectives and constraints,and the optimal motor power distribution strategy is obtained based on the model Predictive control algorithm to get the optimal motor regenerative braking torque and hydraulic braking torque.(4)System integration simulation and hardware-in-the-loop experimental verification.First,the joint simulation platform is built based on Matlab/Simulink and Car Sim,the vehicle parameters and simulation environment are set up in Car Sim,and the single braking conditions with different braking intensity and three cyclic conditions are selected to verify the joint simulation of multi-stage energy recovery control strategy.The simulation results show that the control algorithm can effectively improve the energy recovery rate and increase the range of electric vehicles.Then,a hardware-in-the-loop experimental platform based on the d SPACE rapid prototyping control tool and the real-time simulator is built based on the integrated wire control dynamic system.Finally,the experimental verification of the multi-stage energy recovery control strategy is completed based on the hardware-in-the-loop experimental platform,and the test results show that the master cylinder pressure control algorithm and the multi-stage braking energy recovery control strategy of the integrated brake-by-wire system have good control effects.