Research On Steering Brake Coordinated Control Of Emergency Collision Avoidance System Of Autonomous Vehicle

With the continuous progress of science and technology,autonomous vehicle have gradually appeared in people’s eyes,when encountering sudden obstacles in front of them,autonomous vehicle must have good coping ability like experienced drivers.In the process of development and improvement of intelligent vehicle,emergency collision avoidance is an inevitable dangerous condition in the traffic process in a long time in the future.In the process of emergency collision avoidance of autonomous vehicle,the stability of the vehicle is very likely to occur due to conditions such as low road adhesion and fast speed.Under this kind of automatic driving emergency avoidance condition,The road tracking control of steering control ensures that the autonomous vehicle tracks the target to avoid collision.The stability control of the braking system ensures the vehicle’s driving stability in the case of extreme handling.However,their control objectives are not the same,which may lead to the failure of the emergency collision avoidance process of self-driving vehicles.The current approach does not consider human or autopilot steering intentions when yaw moment systems are involved in stability control.In this paper,considering the influence of driving decision on yaw moment controller in braking system and yaw moment controller on driving decision,a steering braking coordination control method based on Nash game theory is proposed to ensure that when the vehicle is in emergency collision avoidance,automatic steering intention and stability control are simultaneously controlled in the loop.This method makes the system in the process of dynamic evolution,all the participants in the control decisions,not only consider their own interests function,will also consider the interests of the other participants function,can solve the control of the conflict between two,get autopilot steering control and yawing moment of the global optimal control solution of stability control.Firstly,the brake control system is built,including the direct yaw moment control of the upper layer and the pressure closed-loop control of the lower layer.The upper control based on linear quadratic(LQR)is used to calculate the additional yaw moment to stabilize the vehicle,and the brake force distribution logic is used to calculate the brake pressure that should be applied to each wheel.The pressure closed-loop controller controls each solenoid valve in the hydraulic actuator unit,Complete the additional yaw moment required for the upper layer.Then,the upper control strategy and the lower controller of the steering system based on LQR algorithm are built.The upper control can realize the function of tracking the road,and the lower controller can quickly and accurately execute the target steering wheel Angle required by the upper control.Finally,a steering and braking coordinated control strategy based on Nash game is established.The automatic steering system reflects the driver’s intention to track and avoid collisions on the road,and the direct yaw moment control ensures the stability of the vehicle.However,the control objectives of the two control systems are not consistent,which makes it easy for the collision between the avoidance intention and the stability control.The Nash game method used in this paper correctly simulates the interaction between driver decision and controller,and reduces the conflict between steering control system and braking control system.In order to verify the designed control strategy,The control strategy and road model built by MATLAB/Simulink were cosimulated with the vehicle model in CarSim.The two-degree-of-freedom vehicle model combining steering system and braking system is used to obtain the target control law.The speed and adhesion rate in CarSim are set as the limit condition of high speed and low adhesion.The simulation results show that the steering and braking coordination control strategy can ensure the vehicle can track the collision track well and maintain the vehicle’s stability during collision avoidance.In order to verify the corresponding situation of the steering system and the braking system in the real situation,this paper built the hardware in the ring test bench including the steering system and the braking system of autonomous vehicle based on NI-PXI and dSPACE,and achieved the ideal effect.