Research On Composite Braking Control Strategy Of Electric Vehicle Driven By Wheel Hub Motor

The use of oil-burning vehicles is increasing all over the world,and the problem of oil shortage and environmental pollution is becoming more and more serious.In the face of both pressures,electric cars are increasingly popular.As a new type of drive,hub-driven electric vehicles have great application prospects due to their high transmission efficiency and excellent dynamic performance.The composite braking system can use the hub motor for braking,which can not only reduce the working time of the hydraulic braking system but also improve the braking energy utilization rate and extend the driving distance.Taking the four-wheel hub-driven electric vehicle as the research object,this paper designs the structure scheme and establishes the model of the compound braking system of the four-wheel hub-driven electric vehicle,and establishes the braking force distribution strategy aiming at the braking stability and energy recovery,which improves the braking energy recovery effect on the basis of ensuring the braking stability.The main research contents of this paper include:(1)To design the structure scheme of the composite braking system: firstly,the structure of the commonly used composite braking system is compared and analyzed,and the appropriate structure type is selected;Then the working principle of motor braking is analyzed and the hydraulic braking system of compound braking system is designed;Finally,the motor braking system and hydraulic braking system are arranged on the chassis of the four-wheel hub-driven electric vehicle.(2)Establishment the composite braking system simulation model: the composite braking system model is established according to the structure of the designed four-wheel hub-driven electric vehicle composite braking system,which mainly includes motor model,battery model and hydraulic braking system model.The hydraulic braking system is composed of brake master cylinder,brake wheel cylinder,brake pedal,one-way valve,solenoid switch valve,accumulator and brake pipeline.(3)Establish the composite braking control model and control strategy: establish the braking controller by means of hierarchical control.The upper control target is braking stability,control its slip rate and directional stability,and distribute braking force to each wheel.The lower control target is the braking energy recovery.The proportion of the electric power and hydraulic braking power of each wheel is calculated to maximize the energy recovery.Finally,the control methods of the upper controller and the lower controller are synthetically analyzed,and the braking force distribution strategy of the vehicle is obtained.(4)Conduct simulation analysis on the composite braking system: verify the braking performance of the composite braking system under the conditions of high adhesion road surface,low adhesion road surface,followed-off road surface,low adhesion road surface,high-speed turning braking and common braking cycle.The results show that the compound braking control strategy designed in this paper has an improvement in braking efficiency and energy recovery.(5)Design test to verify the simulation results: design verification test for brake strength identification and hydraulic brake control respectively.The experimental data are obtained by building the corresponding experimental model,and the experimental results are compared with the simulation results to verify the rationality of the simulation results.