Research On Lateral And Longitudinal Integrated Control Strategy Of Intelligent Vehicle Trajectory Tracking

With the continuous increase of car ownership,On the one hand,it improves the convenience of people’s daily travel,on the other hand,many problems such as traffic congestion and traffic accidents caused by this have become more obvious.As a key solution to improve traffic safety and travel efficiency,intelligent car has become a hot spot in modern automotive technology research.The accuracy and stability of intelligent car tracking the desired trajectory are the basis of safe and autonomous driving.However,under the single lateral control method,it is difficult for intelligent car to achieve better control results.Therefore,in this thesis,the trajectory tracking problem of intelligent car is researched by using lateral and longitudinal integrated control strategy.The main contents are as follows:The three degrees of freedom dynamics model of the vehicle was established,and the model of the tire was carried out,in other words,the magic tire formula was introduced to analyze the sideshow characteristics of the tire at a small angle,which is convenient to simplify the dynamics equation of the vehicle.Under the same working condition,the Car Sim software was used to imitate and check the vehicle dynamics model,which shows that the dynamics model could reflect the vehicle motion effectively,thus doing a basic job for the model predictive control.Two expected trajectories,curve line and double shift line,were designed as the road scene of trajectory tracking control.In order to solve the problem that a single lateral control may not be able to meet the tracking requirements of intelligent car under different trajectories and speeds,a hybrid lateral control was adopted.With small comprehensive deviation(lateral and directional deviation)as the goal,the critical switching speed is 60km/h under the condition of double-shift trajectory test.When it is lower than 60km/h,pure pursuit control is adopted;when it is higher than60km/h,model predictive control is adopted,that is a lateral hybrid control.Under the flat road surface,a hierarchical longitudinal control model was built in layers.In the upper controller,the desired acceleration is gained by using sliding mode variable structure control.In the lower controller,according to the expected acceleration/braking switch;During acceleration,an accelerated fuzzy PID adaptive control model was established,and the output was the throttle opening.When braking,the appropriate braking pressure was obtained based on the expected acceleration and the vehicle longitudinal dynamics model.The simulation results show that the longitudinal control model can track the expected speed accurately under constant and variable speed conditions.Finally,the lateral hybrid control and longitudinal control were integrated according to the longitudinal speed to form the lateral and longitudinal integrated control.According to the lateral and longitudinal integrated control strategy,the co-simulation closed-loop system of Car Sim and Simulink was built,and the track simulation verification was carried out under the above two desired trajectories.Compared to individual lateral control,the outcomes reflect that the lateral and longitudinal integrated control could raise the accuracy and driving stability of vehicle trajectory tracking.