Research On Control Strategy Of Vehicle Active Collision Avoidance System

With the development of society,people have higher and higher requirements for the safety performance of automobiles.The problem of active safety of automobiles has attracted more and more attention from enterprises and research institutions,and has become a hot research topic in the automotive field.Aiming at the problem of active collision avoidance of intelligent vehicles,this paper takes the intelligent vehicle with the previous steering as the research object,establishes the vehicle model and the four-degree-of-freedom nonlinear dynamic model,and proposes the collision avoidance control strategy based on the collision limit distance to solve the problem of active collision avoidance of vehicles..The main research contents of the thesis are as follows:(1)The throttle opening and the wheel-cylinder pressure during the driving process are calculated by establishing the inverse longitudinal dynamic model of the vehicle.In order to solve the problem of real-time and model accuracy of the model predictive control method,the vehicle dynamics model is simplified,and the vehicle four-degree-of-freedom dynamic model is established as a predictive model to solve the system delay problem and model accuracy problem.(2)In order to maintain a safe distance between the self-vehicle and the preceding vehicle,the road surface adhesion coefficient,the front vehicle acceleration,and the self-vehicle speed are comprehensively considered,and the variable time distance safety distance model is improved to improve the adaptability of the safety distance model.The vehicle's limit braking distance is analyzed for the vehicle in front,the front vehicle at a low speed and the front vehicle emergency braking.In order to solve the problem that the curvature of the lane change track is continuous and the lane change condition is safe during the lane change process,the reference trajectory of the vehicle lane change is obtained by the fifth-order polynomial fitting,and the limit distance of the lane change is obtained.Finally,by analyzing the relationship between the braking limit distance and the lane change limit distance,the control strategy of the vehicle in active collision avoidance is designed,which improves the traffic efficiency of the road and the safety of the vehicle.(3)Design a longitudinal collision avoidance controller and a lane change avoidance controller.The hierarchical control is used to realize the longitudinal control of the vehicle.The upper controller inducts the reasonable expected acceleration by designing the fuzzy controller.The lower controller uses the PID controller to track the desired acceleration.For the parameter tuning problem of the PID controller,the particle swarm optimization algorithm is used.Optimization,the results quickly converge and the tuning parameters are accurate.The design model predictive controller performs vehicle lane change trajectory tracking,linearizes the four-degree-of-freedom nonlinear dynamic model,solves the real-time problem of the algorithm,and adds the constraint condition to make the yaw angle and side of the vehicle during the lane change process.The inclination and lateral displacement are all within the desired range.(4)Based on the CarSim/Simulink co-simulation platform,different initial vehicle speeds and initial distances are set for longitudinal braking collision avoidance and lane avoidance collision verification.The simulation results show that when the vehicle is driving at medium and high speeds outside the braking limit distance range,the fuzzy controller can determine a reasonable expected deceleration according to different working conditions.The lower controller can control the vehicle to achieve stable tracking of the expected deceleration,realize the braking collision avoidance of the vehicle under certain conditions,proving the effectiveness of the longitudinal collision avoidance control strategy and controller.The simulation results of lane change avoidance show that the self-vehicle can realize safe collision avoidance under the condition of smaller car spacing,and stably follow the interfering car with low speed driving in the adjacent lane.The trajectory tracking is accurate and the yaw angular velocity is stable,proving the lane change collision control strategy and controller are effective.