Handling And Stability Control For Articulated Steer Vehicles And Virtual Reality Model Development

As a special kind of off-road heavy vehicle,the articulated steer vehicles(ASV)are widely used in agricultural,construction,forestry and mining sectors for the advantages of high traction and maneuverability.However,due to a series of problems,such as the lack of automatic aligning torque,the driver's field of view changes with the steering,and the self-defects of full hydraulic steering system,resulting in the deteriorate maneuverability,decreased driving stability,which could increase the driver's operating burden and affect the driving safety.In order to solve these problems,this paper is established in building an accurate mathematical model for ASV and realizing the visual reality simulation.Then deeply study the influencing factors for the yaw stability of ASV,and control the ASV's attitude by the steering control and the vehicle body stability control.Considering that current ASV model can not meet all the requirements of accuracy,real-time performance and visual display capacity at the same time,a nonlinear ASV mathematical model coupling with a full-hy draulic steering system are derived and built in MATLAB/Simulink.Field test and multi-body dy namics model by Adams/View software are compared with the established mathematical model,respectively,to verify the correctness of the model at low speed and high speed.Visualized ASV model based on virtual reality is developed,which makes the ASV model equipped with high precision,better visual effect and faster simulation speed.Through connecting the external steering wheel and pedal components,the driver in the loop simulation for ASV is realized.Based on the 2-DOF and 3-DOF model of ASV,the influences of lateral tire stiffness,vehicle centroid position and equivalent torsional stiffness of hydraulic steering system on ASV stability are analyzed.The advantages and disadvantages of the two linear models are discussed,and a reference model for the stability control of ASV is given.The nonlinear correspondence between the steering wheel angle and the articulation angle of ASV is analyzed by field test results.And through the analyzing the simulation result of the nonlinear vehicle model.the causes of steering wheel and articulation angle can not return to the initial place at the same time are find out.The influence factors of the yaw stability of ASV are analyzed,and the reference Map of the stability of ASV is given.As the ASV has a poor maneuverability and the working road condition will generate direct negative influence on the driver's health,a novel path-following control method is proposed by dynamic virtual terrain field(VTF)method.The vehicle speed controller for the purpose of active safety is designed.The cross-sectional function of the virtual terrain field is established,and the direct side angle control and the virtual road roll control are given to eliminate the influence by side angle.The function of VTF is established and divided into primary and dynamic terrain field reference to the parameter variabilities.According to the vehicle dynamics model and the tire forces generated from the vehicle inclination on virtual terrain,the target articulation angle composed of the main angle and compensatory angle is derived.A method for the steering angle control by the combination of fixed transmission ratio and PID feedback control is proposed to solve the problem that the steering wheel and the articulation angle can not return to the initial place at the same time.The path-following controller for ASV is developed in MATLAB/Simulink environment,simulations are carried out on annular road,double-lane change road and snaking road,and the results arc compared with the driver in the loop simulation.The results show that the path-following controller have absolute superiority than the driver control with smaller error and relative smooth steering operation.The validity of the path-following controller is verified.Two kinds of yaw stability control methods are designed to improve the stability of ASV.The first method is filling-oil pressure control by improving the In draulic steering system structure.Simulation results show that the jack-knife and snaking behaviour are eliminated and the appropriate filling-oil pressure for this ASV is confirmed at 1.0 MPa.The second method is by direct yaw moment control(DYC).The expected yaw moment is calculated by feedforward control and LQR based feedback compensatory strategies.The lower level controller distribute the driving force for each wheel aiming at the optimal utilization rate of tires.The anti-slip controller is also designed.Simulations are carried out to verify the effectiveness and robustness of the control algorithms.