Research On Feed-forward And Feedback Control Method Of Automobile Handling Stability Under Driving And Steering Condition

The driver's handling inputs(turning the steering wheel or stepping on the accelerator)could be regarded as interfering factors for a stable running car.Using the advantages of feed-forward control in time to control the interfering factors of the driver's inputs.Utilizing the feedback control to achieve the desired goal and eliminate the deviation for the un-measurable disturbance(crosswind or rough road)and the deviation caused by un-precise feed-forward control.This article proposed a kind of vehicle stability control structure of feedforward and feedback based on direct yaw moment control aim at driving and steering condition.The main work of this paper contains as follows.Firstly,this article discussed the limitations of the classical tire slip angle model applied to the study of vehicle global dynamics,and established a unified tire slip angle model which is suitable for the condition of the large slip angles and possibly backwards running of wheel based on tire Magic Formula.Meanwhile,analysed the differences of wheel coordinate systems between Pacejka adopted and ISO,and established the transformation relationship between the two.Secondly,this article studied the influence factors of tire cornering characteristic,especially the factor of driving torque to tire cornering characteristic.The expression of effective cornering stiffness of tires including driving torque has been established.Taking the desired yaw rate as the goal and based on the 2-DOF linear vehicle model,derived the feedforward control law which taking the driving torque and front wheel angle as the control parameters.The feedback controller is designed with feedback information of yaw rate.The feedforward and feedback make up a combined controller.Set up a strategy distribution of braking torque based on the lower control method of differential braking.And then,this article verified the effect of feedforward control which takes the 2-DOF linear vehicle model and 5-DOF nonlinear vehicle model as the control object respectively.The simulation results show that the feedforward control could improve the under-steering characteristics for front-wheel drive,restrain the over-steering for rear-wheel drive obviously and keep the car running steadily.However it can't eliminate the deviations.Combined with proportional feedback control method,compared and analysed the effect of three controllers(feedforward,feedback,feedforward+feedback)for front-wheel drive and rear-wheel drive respectively.The simulation results show that the proposed control structure of feedforward and feedback could make full use of the advantage of small lag and timely action by feedforward.Moreover,it could keep the strength of overcoming kinds of interference and eliminating deviations by feedback.Each of them has made up their own shortcomings and achieved good control effect.Finally,the virtual scenes of vehicle handling and stability experiments are built.The experiments of driver in the loop for rear-wheel drive were carried out.It verified the proposed combined controller could keep the vehicle steady and controllable.Meanwhile,it could reduce the burden of driver's operation and the degree of tension effectively.