Electro-hydraulic Braking Stability Control Of Distributed Drive Electric Vehicle

With the global attention to energy saving and environmental protection,governments around the world have set off a boom in the development of electric vehicles.Electric vehicles take electric energy as the energy source,with high energy utilization rate and no emission of pollutants,which has become one of the important directions of the development of the automobile industry.EHB system,as a linear control system,USES liquid to transfer power,which can not only produce a large braking torque,but also realize independent regulation of brake fluid pressure of four wheels,but its response speed is slow.As for the distributed drive electric vehicle,with in-wheel motor as the driving unit,the four wheels can drive or brake independently,which has the characteristics of rapid torque response,but can output a small braking torque.The combination of motor braking and mechanical braking can give full play to the advantages of motor braking and mechanical braking and realize compound braking,which can not only improve the stability of vehicle braking,make up for the deficiency of traditional braking methods,but also realize energy recovery.It is very important to carry out the transverse stability control of distributed driven electric vehicle based on EHB system.Accurate physical model is the basis of vehicle dynamics control research.In this paper,AMESim software is used to respectively model the hub drive system,EHB system,15-degree-of-freedom chassis model,tire and road model,aerodynamics model,steering system model,suspension system model and signal measurement module of distributed driven ev.Then,aiming at the problem of easy instability of steering under driving state and braking state respectively,the research on lateral stability control of hybrid braking of distributed driven electric vehicle is carried out.The transverse stability controller is designed in three layers,namely,motion tracking layer,torque distribution layer and torque control layer.The motion tracking layer is divided into reference model and direct yaw moment controller.The reference model obtains the desired side slip angle and yaw rate velocity according to the current state of the vehicle.The direct yaw moment controller calculates the direct yaw moment based on the difference between the expected value and the actual value of the side deflection Angle and yaw velocity of the center of mass.The torque distribution layer distributes the braking torque of the four wheels.The torque distribution layer is divided into torque distribution controller and compound braking decision.The torque distribution controller adopts single-wheel braking or all-wheel braking according to whether the opening of the brake pedal is 0.When the brake pedal opening is 0,according to the steering characteristics and steering direction to determine the need to brake the single wheel.When the brake pedal opening is not 0,the optimization algorithm is used to realize the torque distribution of the whole wheel brake.The coordination strategy of compound braking decides whether to apply motor braking,mechanical braking or compound braking in the current speed,body deceleration,battery soc constraint and motor maximum torque constraint.The torque control layer is the bottom layer of the controller,which controls the torque of the motor and the hydraulic pressure of the wheel cylinder respectively.Through the co-simulation of AMESim and Simulink,the lateral stability control of steering in driving state and steering in braking state were respectively carried out.Finally,simulation results show that the proposed lateral stability controller can ensure the lateral stability of the vehicle under normal driving conditions.Under the condition of steering under braking,not only the lateral force of the tire can be avoided,but also the slip rate of the wheel can be effectively limited.The lateral stability and braking performance of the vehicle under the steering braking condition are guaranteed.