Research On Speed Planning And Motion Control Of Autonomous Vehicles Under Rainfall Conditions Based On CVIS

Vehicle speed planning and motion control are the key technologies to realize autonomous driving.During the driving process,rainfall will directly affect road conditions and traffic conditions,and indirectly affect the stability and safety of vehicle operation.Therefore,speed planning and In-depth research on motion control is of great significance.This paper taken the impact of road friction coefficient changes on vehicle operation stability and steering characteristics under rainfall conditions into account,concentrates on speed planning and motion control of autonomous vehicles based on cooperative vehicle infrastructure system under rainfall conditions.The following research work is carried out in three parts consists of speed planning under rainfall conditions,lateral path following control and longitudinal speed control.Firstly,the traffic environment information requirements of autonomous vehicles running on expressways under rain conditions is analyzed,and a speed planner under rain conditions is designed.Analyzes the traffic environment information requirements to ensure the safe operation of highway autonomous vehicles under rainfall conditions,and establish road water film thickness,road friction coefficient,and interval average vehicle speed calculation models under rainfall conditions based on information requirements.The S-shaped speed curve planning principle is systematically analyzed.The calculation model of road friction coefficient and interval average speed are introduced,and take the interval average speed as the expected speed,a speed planner based on the S-shaped speed curve is designed.In order to realize the accurate follow-up of the reference path,a model predictive lateral path following controller is designed.Firstly,the basic vehicle handling model with two degrees of freedom is adopted,the lateral displacement deviation and the yaw angle deviation are introduced,and the path tracking deviation state equation is established.The road friction coefficient calculation model under rainfall conditions is introduced,and take the maximum front wheel angle which is adjust to the friction coefficient under rainfall conditions and the adhesion ellipse into account.Furthermore,take the maximum front wheel angle as the constraint.Finally,the lateral controller is designed based on the idea of model predictive control rolling optimization,and its effectiveness is verified by simulation.In order to realize the accurate following of the desired speed,a layered longitudinal controller is designed.Firstly,the road friction coefficient calculation model under rainfall conditions is introduced,and the maximum longitudinal acceleration which is suit for the road friction coefficient under the rainfall conditions and the adhesion ellipse is considered.Then use the maximum longitudinal acceleration as the constraint of acceleration,the upper controller is established based on MPC,and the lower controller is established based on Proportional Integral Derivative.Finally,the effectiveness of the controller is validated by simulation.In order to verify the performance of the speed planner and the lateral and longitudinal controller under rainfall conditions,some sections of the Yakang Expressway were selected as experimental sections firstly.Then the road friction coefficient of each section under rainfall conditions are calculated and the speed planning is carried out.Finally,the speed planner,lateral and longitudinal controller are integrated into a comprehensive controller,and the effectiveness of the comprehensive controller is verified through simulation.