Research On Vehicle Stability Control Based On Active Rear Wheel Steering Under Extreme Conditions

With the continuous improvement of vehicle speed and the rapid development of automotive electronic control technology,improving vehicle handling stability and high-speed driving safety has become the focus of research.In particular,the vehicle’s handling stability deteriorates sharply under the condition of high-speed lane change on low-adhesion roads.As an effective means to effectively improve vehicle handling stability and active safety,rear wheel active steering is a trend in the development of future automobiles.In particular,long-wheelbase vehicles can reduce the turning radius and increase flexibility by actively steering at the rear wheels.In this paper,the dynamic characteristics of rear wheel active steering tires are analyzed by distributed drive electric vehicles,and the rear wheel active steering control strategy is studied under the condition of low adhesion road surface and high-speed lane change.Firstly,the model and tire model of the vehicle for control are established,and the two-degree-of-freedom linear reference model for rear-wheel active steering vehicles is derived by ignoring the nonlinear factors in the lateral force of the tire,and the control amount of the control system is determined-the rear wheel rotation angle and the additional pendulum torque and control target-the lateral swing angle speed tracks its expected value,inhibits the lateral declination angle of the centroid and minimizes energy consumption;The objective function is selected according to the control objective and the joint simulation of Car Sim and Matlab/Simulink is performed,and the control effect of the vehicle lateral stability controller under the condition of lowattached road double-shift line is analyzed by simulation experiments.Secondly,in order to solve the problem of excessive slip rate of low-attached road tires,a seven-degree-of-freedom vehicle model and Pacejka tire model considering longitudinal slip and lateral lateral movement were established,and the control target suppressed tire slip rate,the pendulum angle speed tracked its expected value,the zero centroid side declination angle and the energy consumption were as small as possible,and a longitudinal lateral controller of the vehicle based on rear wheel active steering was proposed,and the effectiveness of the controller in suppressing the tire slip rate was verified by simulation experiments.Firstly,the model and tire model of the control-oriented vehicle lateral motion are established,the nonlinear factors of the tire are ignored to derive the linear two-degree of freedom reference model for the active rear wheel steering vehicle,and the control quantity of the control system is determined-the rear wheel angle and the additional pendulum torque and control target-the lateral swing angle speed tracks its expected value,suppresses the centroid lateral declination angle and minimizes the energy consumption,and proposes a lateral stability controller based on the rear wheel active steering.The objective function is selected according to the control objective and the joint simulation of Car Sim and Matlab/Simulink is performed,and the control effect of the vehicle lateral stability controller under the condition of low-attached road doubleshift line is analyzed by simulation experiments.Secondly,in order to solve the problem of excessive slip rate of low-attached road tires,a seven-degree-of-freedom vehicle model and a Pacejka tire model considering longitudinal slip and lateral lateral movement were established,and the control target was determined to suppress the tire slip rate,the pendulum angle speed tracked its expected value,the zero centroid side declination angle and the energy consumption as small as possible,and a longitudinal lateral controller of the vehicle based on the active steering of the rear wheel was proposed,and the effectiveness of the controller in suppressing the tire slip rate was verified through simulation experiments.Finally,the characteristics of the rear wheel active steering,additional pendulum torque and simple coordination of the two are analyzed,and the tire side declination angle is used as the switching condition to make the rear wheel active steering and the additional pendulum torque better coordinated;the actual operation of the vehicle is divided into three states: unsaturated lateral force of the rear wheel tire,lateral force to be saturated,and saturated lateral force,and a controller based on rule switching is designed,and the appropriate control amount is selected according to the different state of the vehicle to control its motion state.Under the condition of low attached doubleshift line,the designed rule switching controller was experimentally verified,and the results showed that the controller can better play its steering flexibility characteristics,when the lateral force is not saturated,the rear wheel angle intervention can track the ideal swing angle speed,reach the stable value faster,and help improve the path tracking ability and flexibility of the vehicle at high speed.