Design And Control Strategy Of Whole Wheel Steering System For Three-axle Emergency Rescue Vehicle

Emergency rescue vehicles need good maneuverability,flexibility and stability.Using multi-axle steering technology can reduce turning radius at low speed and reduce sideslip and torsion at high speed,which can greatly improve the flexibility of vehicles at low speed and the handling stability at high speed.Therefore,the research on multi-axle steering system technology of emergency rescue vehicles has important theoretical significance and practical application value.This paper is based on the National Key R&D Program “ Key Technology Research and Application Demonstration for the High-Mobility Multi-Functional Emergency Rescue Vehicles”(2016YFC0802900).This paper designes the mechanical steering structure and hydraulic steering system of the full-wheel steering system of the three-axle emergency rescue vehicle,studies the control strategy of the full-wheel steering of the three-axle emergency rescue vehicle,and improves the flexibility and handling stability of the vehicle.This paper establishes a linear two-degree-of-freedom model of three-axle steering vehicle,derives the transfer function from front wheel corner to vehicle yaw angular velocity and centroid sideslip angle,analyzes the transient response and steady-state response of a three-axle vehicle and determines the advantages of full-wheel steering for Three-axle vehicles.This paper focuses on the influence of tire nonlinearity on vehicle steering performance,establishes a three-degree-of-freedom nonlinear steering dynamics model of three-axle full-wheel steering vehicle,and simulates and calculates the dynamic characteristic curve of three-axle full-wheel steering vehicle.According to the design requirement of minimum turning radius of emergency rescue vehicle,this papers calculate the maximum steering angle of wheel and steering resistance moment of vehicle during steering.This paper optimizes the basic parameters of steering trapezoidal mechanism,designs the trapezoidal steering mechanism of three-axle steering vehicle,uses ADAMS to analyze the wheel rotation angle and force of the steering mechanism,and uses Workbench software to carry out finite element analysis of the key parts of the trapezoidal steering mechanism.Aiming at the electronically controlled hydraulic steering system of emergency rescue vehicles,this paper firstly determines that the front axle adopts mechanicalsteering and hydraulic power steering system and the middle axle and rear axle adopt electro-hydraulic proportional steering system,which includes median hydraulic cylinder.Then this paper focuses on the static and dynamic design of the electro-hydraulic system of three-axle vehicle and designs and models the steering cylinder and electro-hydraulic servo proportional valve.Finally,this paper does frequency response analysis and AMESim simulation analysis of the electronic hydraulic steering system.This paper establishes a full-wheel steering proportional feed-forward plus fuzzy feed back controller,according to the three-degree-of-freedom non-linear dynamic model of three-axle vehicle.The feed-forward controller is designed by using zero-center-of-mass side-slip angle proportional control.The fuzzy feedback controller is designed about the center-of-mass side-slip angle,yaw angular velocity and the joint control of center-of-mass side-slip angle and yaw angular velocity.The simulation results show that the steady-state yaw angular velocity decreases by 43%and the steady-state sideslip angle decreases by 83% by using the combined fuzzy control,which greatly improves the handling stability of the three-axle full-wheel steering vehicle.