Research On Intervention Criterion And Coordinated Control Of Active Front Steering And Direct Yaw Moment Based On Estimation Of Tire State

In order to maximize the vehicle’s handling stability and meet people’s requirements for vehicle safety,the vehicle chassis active safety control system has always been the focus of industry research.Active front steering(AFS)and direct yaw moment(DYC)is the most important two systems in the active control safety of vehicle chassis.Both of them control the vehicle chassis through the tire force with coupling relationship.On the one hand,the traditional simple superposition control method of the two systems cannot make full use of the tire force to produce the maximum efficiency,on the other hand,the difference between the scope of action of the two systems and the characteristics of the system makes the two systems conflict with each other.The difference makes the two systems interfere with each other.In the pass research,the influence of tire state and different road adhesion coefficient is not considered.The traditional intervention criterion based on vehicle state is not an optimal method.The intervention intensity of the system increases with the deviation of the state parameters.Based on the "result" factor of vehicle state as the intervention criterion,the intervention may have some lag.Especially in the case of emergency steering,if we can make a complete decision at the beginning of steering input,rather than strengthen the intervention with the deteriorating state of the vehicle,the stability control system will have a faster response.Therefore,in order to fully improve the efficiency and response speed of the active stability control system of the vehicle under the emergency steering condition,this paper studies the intervention criteria and coordination control strategy of AFS and DYC system,and the specific contents are as follows:Firstly,the 7-DOF dynamic model and magic formula nonlinear tire model is established.At the same time,the unscented Kalman filter(UKF)state observer is designed to estimate the road adhesion coefficient and vehicle key parameters,which provides accurate parameters for the coordinated control system.In order to ensure the accuracy of the model,the commercial vehicle dynamics software Carsim is used to verify the vehicle model and state sensor.Based on the analysis of the characteristics of AFS and DYC system,the intervention criteria and coordinated control strategy of AFS and DYC based on the state of tire lateral force and the current front wheel angle are proposed.This paper studies the judgment of tire lateral force linear / nonlinear / saturated state,and puts forward and perfects the method of judging tire lateral force state by critical front wheel angle.The relationship between front wheel angle and yaw rate is used to determine the critical front wheel angle between linear and nonlinear tire.The UKF + PSO method is used to estimate the tire force,and the critical front wheel angle between the nonlinear area and the saturated area of the tire lateral force is obtained.The two critical angles are plotted as a map,and the tire state information is quickly provided through the table lookup method,so as to provide a decision for the stability control system Policy support.The specific intervention criteria are as follows:When the steering angle exceeds the tire’s linear/non-linear critical steering angle,it indicates that the current steering behavior will cause the tire to enter the nonlinear region without reaching the saturation region.At this time,the AFS and DYC system cooperatively control the intervention while ensuring comfort and Stability,when the steering angle exceeds the critical angle between the tire’s nonlinear region and saturation region,it indicates that the tire will enter the saturation region,at this time,the DYC system alone intervenes to provide the most powerful intervention at the beginning of the steering to avoid further loss of control of the vehicle.Then,the tracking weights the stability control system between the yaw rate and the sideslip angle are divided based on the sideslip angle phase plan,and the vehicle speed,road surface adhesion coefficient and steering angle are fully considered.Based on this,the Sliding Mode Controller is designed to calculate the target yaw moment required to maintain the vehicle,and the target yaw moment is distributed to the AFS and DYC systems according to the intervention criteria and coordinated strategy.The additional steering angle and braking force are generated by the two systems and the vehicle completes the stability control.Finally,a fishhook steering experiment and a step steering test are carried out to prove that the proposed intervention criterion and coordinated control method have has good performance and faster response in maintaining vehicle stability.