Vehicle Cornering Stability Control

Driver assistance systems depends on reliable vehicle control performance such as yaw sta-bility with active control.The basic idea of the active control system design is to keep the tires working in the linear region that are familiar to the driver and to ensure that the vehicle lateral dynamics stable.However,the reliability of vehicle control performance in terms of handling,stability and comfort depends greatly on the precise estimate of vehicle states such as longitudinal velocity,lateral velocity,and the tire-road friction coefficient.Hence,real-time estimation of ve-hicle states based on the information from some basic low cost vehicular sensors is necessary to achieve a good control performance.In this paper,the following points have been studied:(1)Modeling of the vehicle dynamics:a lateral tire friction model,a vehicle dynamics model,and a wheel dynamics model are established to describe vehicle characteristics during a cornering process.Especially,considering the model complexity and computational precision,assumption such as ignoring the road grade and the bank angle have been made.(2)Design of the vehicle states hierarchical observer:a novel nonlinear observer for the estimation of vehicle velocity together with the tire-road friction coefficient is presented based on a longitudinal tire force estimation approach and a lateral tire friction model.Compared to the state-of-art methods,the proposed observer design provides accurate estimation of the longitudinal velocity,lateral velocity,and the tire-road friction coefficient simultaneously.Particularly,due to the nonlinear and coupling characteristics of the vehicle system,the sum of the lateral forces of the wheel is considered as a whole,which solves the problem that the lateral force of the single wheel can not be directly calculated.Moreover,the stability property of the observer is analyzed using a Lyapunov-based method,the proposed observer system is input-to-state stable.(3)Design of the yaw stability controller:a hierarchical controller is proposed to enhance the yaw stability of four-wheel-independently-actuated vehicles.In particular,the yaw rate tracks a desired trajectory and the sideslip angle is kept small to ensure stability.At the upper-level,an adaptive sliding mode controller is proposed to stabilize the yaw dynamics considering parameter uncertainties due to different driving maneuvers.At the lower-level,an optimal torque allocation strategy with minimal control efforts and equally utilized tire adhesion is designed to allocate the control signals from the upper-level controller,and maintain the tires working in a safe region.Simulation results in different road conditions show the effectiveness of the proposed control ap-proach.