Effect of articulated frame steering on the transient yaw responses of the vehicle

Abstract

The directional performance characteristics of articulated frame steering vehicles are known to be strongly coupled with the kinematic characteristics and the dynamic characteristics of the steering system. The reported studies on articulated frame steering generally focus on the yaw divergence behaviour or the snaking tendency of the vehicle based on its free-yaw-oscillation response, while neglecting important contributions due to the kinematics and the dynamics of the steering system. This study characterizes both the free-yaw-oscillation response and the transient steering response of an articulated frame steering mining vehicle, considering the kinematics of the steering struts together with the dynamics of the flow volume-regulated steering valve and the actuating system. The validity of the analytical vehicle and steering system model is demonstrated using the measured data acquired for the vehicle. The free-oscillation behaviour of the articulated frame steering is characterized in terms of the yaw-mode natural frequency and the yaw damping ratio. The transient responses of the articulated frame steering are assessed in terms of the steering gain, the rate of articulation and the articulation overshoot. The effects of the variations in the various articulated frame steering parameters on the free response and the transient response are subsequently investigated and discussed so as to seek guidance for the design of the articulated frame steering system. It is shown that a higher bulk modulus of the hydraulic fluid and longer steering-arm lengths yield a higher yaw stiffness of the articulated frame steering system and thereby a higher frequency of the yaw oscillations. Higher leakage flows and higher viscous seal friction cause a higher yaw damping coefficient but decrease the steering gain and the articulation rate of the vehicle.