Study On Electronic-hydraulic Composite ABS Hierarchical Control And Bench Design Of EWV

Faced with the increasingly severe energy and environmental problems,new energy vehicle emerges as the times requires,It points out the future direction for the automobile industry.Distributed drive electric-wheel vehicle(EWV)has great advantages,such as simple structure,no pollution and energy recovery,which becomes the research focus of domestic and foreign research institutes.More stable and effective braking control system is needed under complex working conditions.EWV uses a new power source,in-wheel motor can drive and brake,which provides convenience for vehicle dynamics control.In terms of braking,EWV inherits the hydraulic braking system of traditional vehicles,at the same time,EWV can use the braking characteristics of motors and realize the recovery of braking energy,to a certain extent,it solve the problem of poor endurance of electric vehicles.In-wheel motor braking has the advantages of fast response and precise control,but the braking force is limited and it cannot meet the braking requirements fully,and there is a risk of motor braking failure,it can’t undertake braking function alone.Hydraulic braking has the advantages of great braking force,but it has some disadvantages such as slow response and low control accuracy.In theory,electro-hydraulic composite braking system can form complementary advantages and achieve ideal control effect.However,the introduction of motor braking undoubtedly increases the complexity of braking system.At present,few studies have coordinated the electro-hydraulic braking and yaw moment control to meet the active safety requirements of vehicle braking under complex conditions.Supported by the key project of Jiangsu Province development competition(BE2017129),the research of electro-hydraulic composite braking control strategy for EWV is carried out,the longitudinal anti-lock and transverse stable coordinated control strategy of electro-hydraulic composite ABS braking is proposed.A multi-functional test bench was designed to provide a test platform for verifying the hierarchical control strategy of electro-hydraulic composite ABS.The specific studies are as follows:(1)According to the new power structure characteristics of EWV,CarSim is selected to build the vehicle model,driver model and tire model,etc.Simulink is used to design different types of motor models and vehicle control models to match various EWV.Finally,a general simulation test platform of CarSim/Simulink is built to complete various complex conditions,which builds the foundation for verifying the control strategy.(2)Based on the analysis of the braking theory and ABS control method of EWV at home and abroad,the control strategy of electro-hydraulic composite ABS is put forward.The total braking moment is determined by using the PID.The total braking moment is allocated to the hydraulic braking and the motor braking.The hydraulic braking provides the basic braking force,while the motor braking is responsible for controlling the wheel slip rate,and the sum meet the braking requirements.Under the requirement of braking anti-lock,the braking efficiency is improved.The validity of the control strategy is verified by the simulation test of high/low attached and docking road.(3)In complex conditions(split road,turning braking,etc.),the braking stability of automobiles is particularly important.According to the characteristics of EV,the parameters of vehicle stability are estimated by using N~thh data fitting algorithm,and the stability of vehicles is judged,and the braking moment of wheels can be coordinated allocated finally.The proposed hierarchical control system of electro-hydraulic composite ABS includes the decision layer of total braking force and yaw moment,the braking force distribution layer with constraints and the coordinated layer.The effectiveness of the control strategy is verified by the simulation test of emergency braking on split road and turning braking.The test results show that the proposed strategy can significantly improve the active safety and stability of vehicle braking under complex conditions.(4)On the basis of theoretical research and simulation verification,as well as the analysis of the functions required by the comprehensive test bench for EWV,the comprehensive test bench for EWV is developed and designed.According to the modular design idea,inertia simulation module,vertical loading module and dynamometer module are designed,the bench can complete vehicle performance test(power performance,economic performance)and driving/braking research(drive anti-skid,EH composite ABS brake,braking energy recovery),etc.The test bench can quickly match different vehicle models,motors and vehicle control models,and reduce the development cycle and cost of initial development of EWV.