Robust Control Of 4WS Vehicle Based On Steering-by-Wire Technology

With the rapid development of automobile industry technology, the speed of vehicles has been increased continuously, so the handling stability relating to vehicle safety has been attracting more attention. Some related studies have demonstrated that crosswind,which is a familiar type of disturbance, had a major negative impact on the handling stability of high speed vehicles. Four wheel steering(4WS) technique is one of the most effective maneuvering technologies. In this paper, the 4WS control method is adopted in order to improve the crosswind stability of high speed vehicles. The 4WS vehicle with steer-by-wire(SBW) technique is taken as the controlled object, which has more bright prospects. Front wheel active steering and rear wheel active steering are used simultaneously so that a full feedback control strategy can be successfully designed. Base on the strategy of model reference control, feedforward control and feedback control are used to achieve the control objective of tracking both the desired side slip angle and yaw rate.Before making a thorough study on 4WS control problem, it is essential to learn the physical characteristics of 4WS systems and develop reasonable mathematical models.As the design of vehicle models can be simple or complicated, this paper build several vehicle models to meet different research requirements. In the design phase, a two-degreeof-freedom vehicle model is built up. In the controller validation phase, both a threedegree-of-freedom vehicle model and a full vehicle model based on AMESim software are developed, where the former is lower complexity and the latter is high precision. All above work offers a complete modeling platform for simulation. Furthermore, the effect of crosswind on the high speed vehicle is primarily analyzed according to experiment on full vehicle model.Taking anti-interference ability and actuator saturation into consideration, constrained H∞output feedback control is applied to the design of 4WS controller. A sufficient condition for the existence of the H∞output feedback controllers is proposed and proved, and the solution scheme is formulated in terms of linear matrix inequalities(LMIs). The simulation experiment proves that the constrained H∞output feedback control can improve the vehicle handling stability effectively and present strong robustness against external disturbances, while the control inputs of front and rear wheel angles are under the prespecified bounds.For the implementation of control for nonlinear 4WS vehicle, a disturbance observer based control(DOBC) method is employed in 4WS control problem. DOBC is also a robust control method, which can improve the system robustness and cope with the ignored nonlinear dynamics. A full information feedback control method is proposedreferred to the DOBC method,and the theoretical basis of the controller design and the related proofs are given. In order to improve the handling stability of nonlinear 4WS,the feedback control part of the 4WS system is redesigned. The simulation of high speed vehicle under crosswind disturbance shows that, regardless of one side wind or double side wind occurs, the 4WS vehicle based on DOBC method can always maintain vehicle stability and reduce the difficulty of driving.