Nonlinear Controller For Electro-Hydraulic Servo Steering System Of Multi-Axle Vehicle

Multi-axle vehicles are widely used in petrochemical,electric power,high-speed rail and wind power because of its strong dynamic performance and high load carrying capacity.With the rapid development of chinese economy,there is a huge demand for multi-axle vehicles.Multi-axle steering system is one of the core systems for multi-axle vehicle and its performance directly determines the handling stability and driving safety of multi-axle vehicle.It has become one of the key technologies to measure the development level of modern large wheeled vehicles.Therefore,the research of high-performance multi-axle vehicle steering system has important practical significance.Electro-hydraulic servo steering(EHSS)is one of the most potential driving and controlling method in multi-axis steering system.It has the advantages of strong driving ability,fast dynamic response and high precision.The precise control of electro-hydraulic system is the key of electro-hydraulic servo steering,and the conventional PID control has some limitations.Therefore,in order to improve the control performance of the multi-axis steering system,the nonlinear robust control of electro-hydraulic servo steering system(EHSSS)is studied based on the nonlinear control theory.Firstly,the mathematical model of EHSSS is established based on the principle of steering system.A nonlinear dynamics model of steering mechanism is built based on the Lagrange equation.And the flow continuity equation of hydraulic control system is established concerning the valve-controlled dual hydraulic-actuator.A simplified model of tire resistance torque is provided based on existing model which can reflect the basic characteristics of the tire resistance torque.Combined with the steering mechanical,hydraulic system and tire resistance torque,an integrated model of single-axis servo steering system is proposed to analyze the influence on the system performance from the aspects of mechanical structure and sensitive parameters.Secondly,the robustness of PID controller is analyzed based on the integrated model of steering system.PID parameters are adjusted with the genetic algorithm and the performance index of ITAE.Robustness of PID controller is studied under the discontinuity and continuity disturbance of tire load.A single input single output(SISO)nonlinear mathematical model is established based on the analysis of steering system kinematics relation and modern control theory,which provides a control oriented model of nonlinear control for EHSSS.Then,the robustness of the integral sliding mode controller is analyzed based on the control oriented model.Sliding mode controller,integral sliding mode controller and integral sliding mode controller with a differentiator are designed with the state space equation of EHSSS.The stability of the system is determined with Lyapunov stability theory and the control performance of each controller is analyzed.At the same time,the effectiveness of integral sliding mode controller is verified and the robustness of these controllers is analyzed under the disturbance of tire resistance torque.Finally,a single axis electro-hydraulic servo steering test system is built to study the control characteristics of the steering system.The electro-hydraulic servo steering test system is built with the MLC controller and the LabVIEW data acquisition system.The reliability of the mathematical model of EHSSS is verified compared with simulation analysis.The influence of the system tracking error is studied under the different proportional gain of PID control strategy,pump pressure and tire load.At the same time,the robustness of PID controller is analyzed.The innovation of this paper is the proposal of new mathematical model of single-axis EHSSS including steering mechanism,valve-controlled dual hydraulic-actuator and tire resistance torque.It is helpful to analysis and control of EHSSS.The integral sliding mode controller of EHSSS is designed with the novel control oriented model.The effective control of EHSSS is realized,which can suppress the load disturbance so as to improve the steering system control precision and robust performance.