| The development of automobile intelligent technology requires more precise and agile dynamic control,which puts forward higher requirements for tire and vehicle dynamic performance.Active camber control can actively adjust tire lateral force and dynamically optimize tire adhesion by adjusting camber angle,which can improve the vehicle dynamic performance and improve the extreme cornering and emergency obstacle avoidance ability.However,the research on tire camber transient dynamics is still imperfect,which affects the real-time description and control of vehicle transient dynamics with active camber control.In order to solve this problem,this paper has studied the tire transient dynamics under the input of dynamic camber,established the tire dynamic model under combined conditions considering transient camber.The wheel attitude correction is introduced to make the description of the vehicle model more accurate.And an active camber control method considering the transient tire dynamics is proposed to improve the vehicle handling and stability.The main research contents and conclusions of this paper are as follows:1)A tire dynamic model under combined conditions considering transient camber is studied.Firstly,the steady tire model under combined conditions is established.Secondly,the characteristics of the relaxation length under dynamic camber input are studied.The lateral slip caused by dynamic camber is equivalent to that by cornering,and the tire model considering transient camber under combined conditions is established.Then,the transient tire camber test is designed,and the characteristics of camber relaxation length are analyzed.Finally,the effects of camber on the tire performance are analyzed.The results show that when slip angle is 6deg,the lateral force approaches the limit value,and the peak lateral force of tire adhesion ellipse under combined conditions considering camber is increased by 8.6%compared with that under the combined conditions only with cornering and longitudinal slip.The mechanism that camber can increase the peak lateral force is analyzed by brush model.The tire transient lateral force response lags significantly under dynamic camber input,and the higher the input frequency,the more obvious the relaxation effect.Therefore,the influence of tire camber transient dynamics can not be ignored in the study of active camber control.2)The vehicle transient dynamics with active camber control is studied.A linear twoDOF vehicle model with active camber control is established,and the vehicle transient steering response dynamics with active camber control are studied.Then,a nonlinear eightDOF vehicle dynamics model with active camber control considering tire transient dynamics is established,which provides a platform for simulation analysis of active camber control.The effects of tire transient dynamics on vehicle steering response and active camber control on vehicle stability are studied.The research shows that tire transient dynamics will cause vehicle steering response lag and overshoot.Active camber control can ensure the vehicle handling stability and improve steering response in steer step test.3)An active camber control method based on model predictive control considering the transient tire dynamics is studied.Through model predictive control,the dynamic update of tire relaxation length and tire stiffness is introduced into the vehicle dynamics prediction model,and the vehicle prediction model with active camber control considering tire transient dynamics is established,and the active camber control method based on model predictive control considering the transient tire dynamics is designed.The simulation analysis shows that by updating the vehicle state in real-time and compensating for the vehicle transient response lag,active camber control can effectively reduce the overshoot of vehicle response during steer step test and single line change test,and it can improve vehicle steering stability. |
