Integrated Control Of AFS And DYC Based On Sliding Mode Variable Structure Control Theory

It is the most important function of the chassis control system to make the vehicle perform acceleration,deceleration and steering according to the driving operation,improving the vehicle's handling stability,driving safety and comfort.Since the 1980 s,with the wide application of electronic control technology in vehicles,various chassis control technologies have become more and more mature,greatly improving the vehicle's motion performance.However,because of the increasing complexity of chassis control,the traditional single-objective control system has been unable to meet the modern multi-control tasks.There are serious coupling phenomena in different directions of vehicle motion control.It is urgent to coordinate and integrate different chassis control technologies and ESP(Electronic Stability Program)is the typical application of chassis integrated control technology.Longitudinal and lateral dynamics of automobiles are directly related to the handling stability and safety of automobiles.It is the focus and hotspot of active safety technology for automobiles at present.AFS(Active Front-wheel Steering)and DYC(Direct Yaw Moment Control)are the main control systems to improve vehicle lateral and longitudinal dynamic performance respectively.They can improve vehicle handling stability and safety,but they also have their own shortcomings.Within the linear range of vehicle,AFS can effectively improve vehicle driving accuracy and stability,while in the limit state of vehicle,tires enter the non-linear zone,DYC plays a significant role.In order to give full play to the advantages of each system,avoid conflicts between systems and achieve the best comprehensive control effect,integrated control of DYC and AFS systems is needed.Firstly,a 7-DOF vehicle model and a non-linear magic tire model are established,and a joint simulation with the dynamics software Carsim is carried out to test the accuracy of the model for future research.In order to facilitate the driver to control the vehicle within daily driving experience,a 2-DOF linear vehicle model is established,and the yaw rate is taken as the ideal value of the control target.And then respectively build the front wheel active steering controller and direct yaw moment controller based on sliding mode variable structure control theory.AFS controller considers the limitation of tire saturation slip angle and the DYC controller is divided into two layers,the upper layer gets the total yaw moment,and the lower layer distributes the braking moment.In order to verify the accuracy of the controller,the simulation experiments of angular step,sinusoidal hysteresis and open road are carried out.It is found that AFS and DYC control systems can effectively improve the stability of vehicle on-line and non-linear driving state compared with the driving effect without control.Finally,in regard of the integrated control of AFS and DYC,a corresponding table of characteristic speed and critical turning angle is established by judging the driving state of the vehicle dividing their respective action areas.In the overlapping part of the functions of AFS and DYC,a proportional function based allocation algorithm is designed to avoid the sudden change of state caused by system switching and ensure the smoothness of system switching.Angular step and sinusoidal hysteresis experiments are carried out to verify the control effect.