Study On Vehicle Active Obstacle Avoidance Path Planning And Tracking Control Based On Safety Distance Model

Safety,energy saving and environmental protection are the three eternal themes of automotive technology development.In recent years,with the continuous high growth of car ownership,the series of problems such as road safety,traffic congestion,energy shortage and environmental pollution have become increasingly serious,which has given birth to the development of intelligent and networked vehicles,making intelligent network Automobile has become the key starting point for the intelligent transportation system and the industry of choice for many important tasks and fields of "Made in China 2025".The active safety technology issues of intelligent networked vehicles mainly include environmental perception,intelligent decision-making and control execution,and the key is the vehicle’s active obstacle avoidance technology.In view of the collision-free obstacle avoidance and driving stability requirements of vehicles on structured roads,this paper studies three aspects: braking or steering active obstacle avoidance strategy,local obstacle avoidance path planning,and path tracking control.The main research contents are as follows:(1)By analyzing the collision avoidance process of vehicles in structured roads,a braking or steering safe distance model is constructed under the collision avoidance condition of the preceding vehicle in the same lane and the collision avoidance condition of the preceding vehicle changing lanes in the adjacent lane.By introducing the prediction time-varying weight coefficient function,the weighted fusion of the CTRA motion model and the polynomial curve model is used as the trajectory prediction model of the vehicle lane change,which can solve the time when the lane changing vehicle enters the driving area of the obstacle avoidance vehicle for the first time,and use the safety distance model to assess the collision risk.The influence of relative vehicle speed and road adhesion coefficient on braking safety distance and steering safety distance is analyzed,and an active obstacle avoidance strategy based on relative vehicle speed is designed,which lays a theoretical foundation for vehicle active obstacle avoidance path planning.(2)Based on traffic rules and vehicle geometry characteristics,the lane potential field in the form of logarithmic function,the static obstacle potential field in the form of power function,the dynamic obstacle potential field in the double ellipse range,and the corresponding three-dimensional environmental potential field are established.The simulation results of the artificial potential field gradient descent method to search for the obstacle avoidance path verify the effectiveness of the designed environmental potential field.The path planning algorithm plans a safe obstacle avoidance path that does not exceed the lane for small static obstacles,and After avoiding obstacles,it can automatically return to the center line of the lane to continue driving,and plan a lanechanging obstacle avoidance path that satisfies the vertical and horizontal safety distance constraints for dynamic obstacles according to different relative vehicle speeds.(3)A three-degree-of-freedom single-track model and a tire model are established.By simplifying the nonlinear vehicle model into a linear model,the linear time-varying prediction equation in the finite prediction time domain is derived,and the path tracking controller is designed based on the principle of model predictive control.In view of the problem of low tracking accuracy and stability under low adhesion road conditions,the linearized front and rear wheel side slip angle constraints are added for improvement.Car Sim and Simulink are used to build a co-simulation platform to simulate the effect of path tracking control.,in the scenarios of different driving speeds,the lateral deviation does not exceed 0.1 m,and the yaw angle deviation does not exceed 0.7°,which verifies that the control algorithm has good speed robustness;Compared with the controller without the tire side-slip angle constraint,the side-slip angle of the controller with the side-slip angle constraint is reduced by 0.1°.In the high-speed and low-adhesion road scene,the controller with the tire side-slip angle constraint is better than the controller without the tire side-slip angle constraint.The maximum lateral deviation of the controller is reduced by 0.3 m,the maximum yaw angle deviation is reduced by 1.2°,and the center of mass slip angle is reduced by 0.7°,which verifies that adding tire slip angle constraints can significantly improve the tracking accuracy and stability under low adhesion road conditions.(4)The driving environment potential field is introduced into the model predictive control framework,the objective function including the road potential field and the obstacle potential field is established,and the lateral acceleration constraint is added to improve the traceability of the planned path under different driving speeds and road conditions,and a hierarchical controller model integrating path planning and control is constructed.In the static and dynamic obstacle scenarios,the simulation experiment of the obstacle avoidance effect of the layered controller is carried out.The simulation results show that the obstacle avoidance vehicle can plan the optimal reference path which can satisfy the obstacle avoidance constraint and the maximum lateral acceleration constraint according to different initial vehicle speeds,and the peak value of lateral acceleration during obstacle avoidance are all less than 0.67μg,which verifies the correctness and availability of the designed control algorithm and path planning algorithm.