Research On Coordinated Control Of Active Front Wheel Steering And Direct Yaw Moment

With the development and extensive use of electronic control technology,More and more control systems are installed on the chassis,and the interference and coupling problems between systems have also emerged.The individual control of each system cannot guarantee the optimal vehicle performance.Therefore,it is necessary to study the integrated control of chassis.Active front wheel steering(AFS)and direct yaw moment(DYC)control can improve the handling stability of the vehicle,the optimum work range of AFS is the linear area where the lateral acceleration and tire cornering are both small,and has little influence on the longitudinal speed of the vehicle and the comfort is good.The control region of DYC is not limited to the linear region of tire,even in the nonlinear region can obtain good control effect,but the longitudinal speed changes and the comfort is poor.Therefore,it is necessary to study the coordinated control of AFS and DYC.The two control systems have complementary advantages to ensure comfort and improve vehicle stability.1.Considering that the chassis control needs to rely on accurate sideslip angle and road adhesion coefficient,and they are not easy to measure directly,this paper studies the use of extended Kalman filter algorithm to establish the parameter estimation algorithm based on the Dugoff tire model,the sideslip angle and road adhesion coefficient are estimated.The joint simulation model of Car Sim and Simulink is used for verification.The results show that the estimation results of the parameter estimation algorithm are accurate and can be used in the subsequent control research.2.Based on the two-degree-of-freedom vehicle model,the ideal yaw rate and the ideal sideslip angle considering the constraint of road adhesion coefficient are calculated.Due to the complexity of the vehicle system,it is difficult to establish an accurate mathematical model.Therefore,the sliding mode variable structure control theory is used to establish the AFS control system and the DYC control system,and the effectiveness of the control strategy is verified by simulation.3.The characteristics of the AFS and DYC control systems are introduced,and the advantages and disadvantages of the two systems are analyzed.The necessity of the coordinated control of AFS and DYC is pointed out.Then,the influence of longitudinal speed,front wheel angle and road adhesion coefficient on stable region is analyzed by using the phase plane method,determining the boundary of stable region for dividing phase plane according to road adhesion coefficient.Based on this boundary,the coordinated control region is divided,and the range of the coordinated region is determined by using the fuzzy logic control method,and based on the variable universe fuzzy control theory,the expansion factor fuzzy control method is added to improve the dynamic performance of coordinated control.Finally,the allocation rule of the coordinated control is formulated,and the multi-condition simulation is carried out by using the joint model,the results show that in terms of improving vehicle operation stability,the coordinated control is better than the single AFS control,and the control effect of coordinated control is close to that of the single DYC control;In terms of comfort,coordinated control has less interference on longitudinal speed,which is better than single DYC control,and coordinated control solves the chattering problem of sliding mode control.So the comprehensive performance of coordinated control is the best.