Research On Control Of Electro-hydraulic Composite Braking System For Electric Vehicles

The application of automotive active safety technology in traditional vehicles has been relatively mature,while in distributed drive electric vehicles,the hub motor with rapid response make more excellent active safety technology have a basis for development.Applications in distributed driving EV of motor in emergency braking of energy recovery technology has also been corresponding developed,but non-linear response characteristic of hydraulic braking system and the limited participation of the motor also restricts the ABS system's performance in high speed during emergency braking.Therefore,to study electro-hydraulic composite braking system also is very necessary on the distributed drive electric vehicles.In this paper,vehicle state observer design,control design of a new electro-hydraulic composite braking system and coordination control of lateral and longitudinal stability are discussed.It mainly includes the following contents:1)The vehicle state observers were designed and verified by real vehicle experiments.For the subsequent ABS algorithm design based on slip rate control,a vehicle speed observer based on the combination of kinematics and dynamics was developed,and the results of its operation in the ABS system were corrected by the idea of frequency division.For the subsequent development of the yaw stability control strategy,a state space-based centroid Sideslip Angle observer was developed,and a non-observable solution was proposed for the vehicle traveling in a straight line.It is verified by the simulation and actual vehicle experimental data,the results show the effectiveness of the state observers.2)Explore the influence of the nonlinear characteristics of the hydraulic braking system on the ABS system.Working in the ABS system,the brake pressure change according to certain frequency which is high,and with the braking system of elasticity,damping and the friction lining and the brake fluid in the hydraulic pressure regulator,many uncertain factors such as the viscosity of brake pressure and torque response in saturation,dead zone and hysteresis nonlinearity,lead to delay the response of the brake pressure and brake torque as a result,affectting the braking effect of the ABS system.Through the establishment of the nonlinear model of hydraulic braking system by simulation confirmed that the nonlinear deterioration in the braking effect of the ABS system.3)A new electro-hydraulic composite braking system is proposed based on the method of frequency reconstruction.When the ABS system is working,the brake pressure changes at a certain frequency and the frequency is high.In the braking system,many uncertain factors such as the elasticity,damping and friction of the lining in the brake system and the viscosity of the brake fluid in the hydraulic regulator cause the brake pressure-torque response to saturate,dead zone and hysteresis.The nonlinear characteristics,the brake pressure and the braking torque response delay,etc.,affect the braking effect of the ABS system.The nonlinear model of the hydraulic brake system is established.It is verified by simulation that its nonlinearity will lead to the deterioration of the braking effect of the ABS system.4)Design the yaw stability control algorithm,and complete the coordination control of lateral and longitudinal stability control system.The acutual emergency braking conditions are not limited to linear emergency braking,but more often emergency braking with steering movement.Therefore,in order to demonstrate the performance of the new electro-hydraulic composite brake system in the case of steering emergency braking conditions,it is very important to desigen and verify the lateral stability control system and to study the coordinated control of the lateral and longitudinal stability control system.The DYC controller is designed based on the fuzzy control theory,and further considers the effect of load transfer on the yaw moment to compensate it.On this basis,the coordinated control of the lateral and longitudinal stability control systems is studied,and the new proposed electro-hydraulic composite brake control strategy is applied.The simulation control strategy is verified by high-speed steering emergency braking.