Research On Handling Stability Of A 6×6 All-Wheel Steering Vehicle

Multiaxial vehicles always have longer wheelbase, bigger quality and higher centroid,so they have a larger turning radius and poor mobility when steering with a low-speed, and have poor stability and controllability when the steering speed is high. Therefore, a study on driving stability of multi-axle steering 6 × 6 heavy vehicle is necessary. The article took a 6 × 6 multi-axle steering vehicle as the research object, analyzed and compared the steering stability of the vehicle under different steering modes based on zero sideslip angle proportional control from a practical point of view. The research details as follows.(1) The triaxial all-wheel steering model with linear two degrees of freedom was established, deduced angle control law based on the zero sideslip angle proportional control strategy. The three modes are the former two-axis mechanical steering, while rear wheel does not turn; the former two-axis mechanical steering, while rear wheel steering under ratio control; and the first axis mechanical steering, while two rear steering under ratio control.(2) The time-domain response characteristic simulation studies in MATLAB /Simulink was carried out, analysis the impact and the role of the the vehicle handling stability under at three steering modes of triaxial vehicle comparatively. The affect on the gain of yaw angular velocity with the changes of central axis relative to the vehicle mass center under the same steering mode was studied.(3) According to the information of vehicle’s mass and structure, three axis all-wheel steering model of ADAMS/Car was built. The axis pinion-and-rack gear and back-shaft actuator were added into steering system to make middle and rear wheels steering. By the displacement driving function, rack and actuator can control turning angle’s quantity and direction of all wheels. And that function was defined by the vehicle steering control strategy, changing with vehicle speed. This method takes advantages of combining different steering control strategy to realize the goal of multi-axle steering for vehicle model.(4) The three axis all-wheel steering model was controlled under the strategy of zero sideslip angle proportional control and the steering stability simulation experiment was carried out. The simulation results of different steering modes were analyzed. The results showed that when the vehicle was in the mode with the first axis mechanical steering, while two rear steering under ratio control, it had better steering stability. This steering modecould improve the mobility at low speed and had a better driving stability in high speed.(5) Aiming at the problem that the three axis vehicle’s yaw rate gain decrease obviously at high speed, research on optimal control of AWS vehicle in middle and high speed was implemented. Based on linear 2DOF vehicle dynamic model, used the control strategy that tracking theoretical model with feed forward and state feedback method to control rear wheel angle. Designed AWS linear optimal control system, comparated simulation to the traditional three axis vehicle with proportional control strategy and front wheel steering three axle vehicle in MATLAB/Simulink. The result showed that AWS vehicle with optimal control strategy can ensure the vehicle to achieve the best performance in the middle and high speed, improved the stability of the vehicle and enable the driver to maintain the original steering feeling without increasing driving burthen.