Research On Integrated Vehicle Chassis Control With Active Rear Wheel Cambering

The development of automobile intelligence has put forward higher requirements for active safety technology.Especially under extreme working conditions,the vehicle dynamic performance and the driver’s control ability sharply reduce,so how to ensure the safety of the vehicle and the driver has become increasingly important.Active wheel camber control can generate additional lateral force by adjusting wheel camber angle,dynamically optimize tire attachment characteristics,and increase tire peak lateral force,which is an effective way to improve vehicle stability.However,the current research on active wheel camber control mainly focuses on the fixed camber stiffness,without in-depth analysis of the influence of the coupling characteristics of cornering and camber on tire force,affecting the precise control of tire force and vehicle status under extreme working conditions.The introduction of active wheel camber control in the integrated chassis control is beneficial to optimize the utilization efficiency of tire attachment ellipse and improve vehicle stability.Therefore,this paper established a control-oriented nonlinear camber characteristics tire model,and studied the model predictive control method of active rear wheel cambering considering the nonlinear camber characteristics.An integrated chassis stability control strategy with active rear wheel cambering is proposed to improve the vehicle stability under the condition of low-adhesion and high-speed double line change.The main research contents and conclusions of this paper are as follows:1)The establishment of vehicle dynamics model considering nonlinear tire camber characteristics.First of all,the change law of tire nonlinear camber characteristics under combined camber and cornering conditions is studied.Then,a control-oriented nonlinear camber characteristics tire model is established to more accurately describe the tire force under combined camber and cornering conditions,by integrating the coupling characteristics of tire dynamics into the variable camber stiffness,and model verification are carried out.Finally,the 8-DOF vehicle dynamics model and the lateral-longitudinal driver model are established to provide the basis for the active wheel camber control and simulation.2)The active rear wheel camber model predictive control method considering nonlinear tire camber characteristics.Firstly,according to suspension K&C characteristic test,the wheel attitude change rule is studied,and the wheel attitude is corrected.Then,the vehicle prediction model of active rear wheel camber control is established by the control-oriented nonlinear camber characteristics tire model,which introduces the dynamic update of the tire camber stiffness,and an active rear wheel camber model predictive control method considering nonlinear tire camber characteristics is designed.Finally,the simulation results show that the active rear wheel camber control considering nonlinear camber characteristics improves tire force prediction accuracy by dynamically updating the tire camber stiffness under high-speed single lane change condition with the road adhesion coefficient of 0.85 and the vehicle speed of 90km/h,compared with the fixed camber stiffness active rear wheel camber control,thus the total control amount of left and right wheel camber is reduced by8.78%,making the control smoother,and the yaw rate peak error of 8.98% and side slip angle peak error of 7.58% are reduced,improving the steering stability of the vehicle.3)An integrated vehicle chassis stability layered control strategy with active rear wheel cambering.Firstly,the overall architecture of the integrated chassis stability control strategy with active rear wheel cambering is designed.Secondly,the vehicle stability analysis under different working conditions is carried out.According to the modified ω-β phase plane stability region,the normalized stability evaluation index is proposed,and the upper controller weight adaptive adjustment scheme is designed.An upper stability model prediction controller integrating active front wheel steering,active rear wheel cambering and torque vector control is established.Then,a lower torque distribution controller is established to cooperate with vehicle longitudinal speed tracking and lateral stability control,and the lower controller weight adaptive adjustment scheme based on tire working load rate index and wheel slip rate is designed to achieve torque optimization distribution.Finally,the simulation result of the integrated chassis control distributed drive electric vehicle with active rear wheel cambering under the condition of low-adhesion and high-speed double line change with the road adhesion coefficient of 0.5 and the vehicle speed of 90km/h shows that the integrated vehicle chassis control strategy with active rear wheel cambering can dynamically correct wheel attitude,improve tire attachment characteristics and coordinate the distribution of longitudinal and lateral tire force,compared with only active front wheel steering and torque vector integrated control,generating the maximum additional tire lateral force by 27.48% and increasing tire peak lateral force by 12%.The side slip angle peak error of 25.16% and the lateral position tracking peak error of 6.86% are reduced,and the vehicle handling stability is improved.