Research On The Key Technologies Of Braking System Of Distributed Driven Electric Vehicle

Electric vehicle is an effective solution for the current energy and environmental crises. Distributed driven electric vehicle emerges with the development of motor and battery. Distributed driven electric vehicle has accurate and fast driving/braking torque response, which helps to improve the brake efficiency and stability. Hence distributed driven electric vehicle has vast prospects. It is meaningful to conduct research on the key technologies of braking system of distributed driven electric vehicle.This research is based on the project named "Research on the characteristics and control methods of hybrid braking system of distributed driven electric vehicle" supported by Major State Basic Research Development Program. Based on the distributed driven electric vehicle test platform, researches were carried out on the individual braking force distribution method during braking-in-turn maneuver,coordinated control strategy of regenerative and hydraulic braking system, and lateral stability control method based on model predictive control.A distributed driven electric vehicle test platform was developed. Driving and regenerative braking are realized by four in-wheel motors. Hydraulic braking is realized by a hydraulic brake-by-wire system. Steering is realized by step motors and corresponding mechanical structure. A vehicle control unit based on single chip microcontroller is in charge of the upper control algorithm and the coordinated control of all the subsystems. The test platform can achieve single wheel driving, regenerative braking, hydraulic braking and steering, and has flexible control mode and good extensibility.The individual braking force distribution method was proposed for braking-in-turn maneuver. Taking the load transfer and lateral force demand into consideration, a sequential distribution method is applied which distributes the front-rear braking force prior to inner-outer braking force. For the front-rear braking force distribution, the lateral force demand is firstly met, on this basis the remaining adhesion force is utilized for the longitudinal braking. For the inner-outer braking distribution, a result is reached that the braking force should be distributed proportional to the vertical force with theoptimization target of tire workloads. The proposed braking force distribution method ensures good adhesion utilization on the premise of lateral stability.The coordinated control strategy is proposed for the regenerative and hydraulic braking systems. A coefficient is proposed which indicates the possibility of anti-lock braking control activation during the transient process between general braking and anti-lock braking. It helps to guide the exit of regenerative braking to prevent the fluctuation caused by frequent anti-lock braking control activation and exit. During the anti-lock braking process, the coordinated control method based on adhesion coefficient is proposed to improve the braking comfort, regenerative efficiency and braking safety.On account of the delayed intervention and exit of active yaw moment control, a lateral stability control strategy based on model predictive control is proposed.Reference yaw rate and side-slip angle are designed. The error of predicted values of reference yaw rate and actual yaw rate is regarded as the control target, taking the vehicle dynamics into consideration. This method can predict the vehicle stability variation trend and improve the timeliness of active yaw moment control. Active yaw moment control method based on side-slip angle stability margin is proposed as supplementary control method to improve the vehicle stability in case of large side-slip angle. The controlled wheel selection strategy is proposed based on the flexible control mode of distributed driven electric vehicle. On this basis, an anti-step distribution method for driving/braking force is proposed to prevent step change of intervention torque.