Nonlinear Control Strategy Of Four-wheel Steering Vehicle Based On Steering-by-wire Technology

Under the influence of the "new four modernizations" of the automotive industry,which includes electrification,intellectualization,networking and sharing,the automotive active safety technology with the participation of modern advanced control theory and technology has attracted more and more attention.Among them,the active four-wheel steering vehicle based on steering-by-wire technology(SBW-4WS),as a comprehensive chassis technology,can effectively improve vehicle handling stability,driving comfort and active safety.It meets the market demand and development direction of the current resource-saving,environmental protection and energy-saving automobile industry,and has good commercial value and development prospects.Firstly,the vehicle handling dynamics is briefly introduced.Through the analysis of vehicle lateral dynamics,it can be seen that the influence of tire nonlinearity on vehicle handling stability and driving safety can not be ignored.After analyzing the influence of different tire models on controller design,the tire map table is introduced to characterize the non-linear characteristics of tires,and the non-linear vehicle model with map is established.The sideslip angle and yaw rate are selected as state variables,and the front and rear wheel angles are the controller outputs.In order to improve the possibility of engineering realization of active four-wheel steering vehicle based on steering-by-wire technology,a nonlinear triple-step method is adopted in the controller design of the SBW-4WS vehicle.The nonlinear triple-step method is a model-based control method extracted from modern automotive engineering.It consists of three parts: steady state control,reference feed-forward control and error feedback control.The nonlinear triple-step method controller avoids the influence of nonlinear factors in the design process by checking the map table,which provides an effective solution for the application of control algorithm and controller design of non-affine systems.The simulation in Carsim proves the effectiveness,anti-interference and robustness of the controller,and proves that the nonlinear triple-step controller can improve the handling stability and active safety of SBW-4WS vehicle.In order to fully exploit the potential of the map table,a data-driven predictive control scheme is proposed,which provides a new solution for the application of non-linear predictive control in fast system.Through the hash technology to storage,lookup and call of the map table,the nonlinear predictive control is transformed into linear predictive control,reducing the burden of online computing.The Particle Swarm Optimization is used to solve the data-driven MPC optimization problem.The simulation results show that the proposed algorithm can effectively reduce the complexity of nonlinear MPC based on the SBW-4WS control requirements.