Yuming Yin

Multi-performance analyses and design optimisation of hydro-pneumatic suspension system for an articulated frame-steered vehicle

ABSTRACT This study investigates the coupled ride and directional performance characteristics of an articulated frame-steered vehicle (AFSV). A three-dimensional multi-body dynamic model of the vehicle is formulated integrating the hydro-mechanical frame steering and hydro-pneumatic suspension (HPS) systems. The model parameters are obtained from field-measured data acquired for an unsuspended AFSV prototype and a validated scaled HPS model. The HPS is implemented only at the front axle, which supports the driver cabin. The main parameters of the HPS, including the piston area, and flow areas of bleed orifices and check valves, are selected through design sensitivity analyses and optimisation, considering ride vibration, and roll- and yaw-plane stability performance measures. These include the frequency-weighted vertical vibration of the front unit, root-mean-square lateral acceleration during the sustained lateral load transfer ratio period prior to absolute rollover of the rear unit, and yaw-mode oscillation frequency following a lateral perturbation of the vehicle. The results suggested that the implementation of the HPS to the front unit alone could help preserve the directional stability limits compared to the unsuspended prototype vehicle and reduce the ride vibration exposure by nearly 30%. The results of sensitivity analyses revealed that the directional stability performance limits are only slightly affected by the HPS parameters. Further reduction in the ride vibration exposure was attained with the optimal design, irrespective of the payload variations. The vehicle operation at relatively higher speeds, however, would yield greater vibration exposure.

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

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.

Design optimization of an articulated frame steering system

The articulated frame-steered vehicles (AFSV) exhibit enhanced maneuverability but reduced yaw stability and greater steering power consumption. Apart from kinematics of the steering system, the dynamics of the actuating system strongly influence the performance of the AFSV, which is generally neglected in the reported studies. In this study, a yaw-plane model of the articulated vehicle coupled with the kinematic and dynamics properties of the steering struts is formulated to identify objective measures of the AFSV under steering inputs. The results suggest that the vehicle yaw oscillation/stability, steering power efficiency and maneuverability can be objectively measured in terms of the strut length, yaw oscillation frequency and damping ratio, steering gain, and steering response rate and overshoot. The layout of steering struts and properties of the steering valve and hydraulic fluid are optimized while employing the weighted-sum method and a combination of pattern search and sequential quadratic programming algorithms. The relative weights of individual performance measures were obtained using the analytic hierarchy process (AHP) model. The solutions of the optimization problem revealed more compact articulated frame steering (AFS) system design with over 20% reduction in strut length and 24% gain in the yaw oscillation frequency. Increasing the fluid bulk modulus resulted in more compact AFS layout and further increase in the yaw oscillation frequency with lower response overshoot. The optimal design based on weighted sum of various performance measures, however, revealed negligible changes in terms of the steering power efficiency.