The Research On Electro-hydraulic Servo Steering System Of Multi-axle Vehicle With Controllable Tie Rod

Multi-axle vehicle is widely used in military affairs,electric power,high-speed rail and wind power because of its dynamic behavior and bearing capacity.With the rapid development of Chinese economy,there is a huge demand for multi-axle vehicle.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.And it is one of the key technologies to appraise the level of large wheeled vehicle.Therefore,the research of high-performance multi-axle vehicle steering system has important practical significance.As the traditional trapezoidal steering mechanism belongs to single degree of freedom structure,it cannot achieve full wheel rolling steering,which leads to the wear of tire in large steering angle.Consequently,it will seriously affect the steering characteristic of vehicle and cannot meet the demand of steering in different conditions.Therefore,in this paper,a 2-DOFssteering system with controllable tie rod is proposed,and its system characteristics are analyzed comprehensively.Firstly,based on the geometric relationship of steering trapezoidal structure,the mathematical description of left and right wheel rotation angle is obtained.Comparing the pure rolling steering motion with the traditional steering motion,the reason why the steering trapezoid mechanism can't realize the pure rolling steering is analyzed.Combined with the steering characteristics in different steering modes,the limitation of traditional steering system is further proved.Secondly,the design principle of the variable cell steering trapezoid mechanism and 2-DOFs steering hydraulic system is described in detail.Based on the virtual work principle,the tie rod force analysis is carried out,and the corresponding Simulink model for tie rod force solution is established.It is found that the force of the tie rod is always pulled during the steering process,and is compressed only when the gap between the left and right loads is huge.According to the force law of tie rod,the structure sizes of the tie rod cylinder are optimized.According to the chosen cylinder,the concrete design scheme of the transverse rod cylinder is put forward.Then,a nonlinear dynamics model of steering mechanism is built based on the Lagrange equation.The flow continuity equation of hydraulic control system is established concerning the valve-controlled dual hydraulic-actuator.Based on the mathematical model of mechanical structure and hydraulic system,the Matlab/Simulink model of single-axis 2-DOFs steering system is established,and the influence of key parameters on the system characteristics is analyzed.Finally,based on the principle of 2-DOFs steering system,the AMESim simulation model of steering system is established.Based on the simulation model,the relationships among transverse rod cylinder,the pump source pressure and tire load on electro-hydraulic servo steering system are analyzed.The results of Simulink model and AMESim model are compared to verify the correctness of the mathematical model.The innovation of this paper is that,based on the principle of virtual work,the force law of the tie rod is obtained,which provides a reference for the design of the tie rod.The mathematical model of single-axis 2-DOFs steering hydraulic system including steering mechanism and hydraulic system is proposed.It is helpful to the analyses and control of electro-hydraulic servo steering system.The AMESim simulation model of 2-DOFs steering system is established to explore the characteristics of steering system.In addition,it can provide a reference for the optimization design and model verification of the system.