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Effects of Entrapped Gas within the Fluid on the Stiffness and Damping Characteristics of a Hydro-Pneumatic Suspension Strut

SAE International Journal of Commercial Vehicles

Concordia University Montreal-Yuming Yin, Subhash Rakheja
IRSST-P-E. Boileau
  • Journal Article
  • 2017-01-0411
Published 2017-03-28 by SAE International in United States
This study is aimed at characterizing the nonlinear stiffness and damping properties of a simple and low cost design of a hydro-pneumatic suspension (HPS) that permits entrapment of gas into the hydraulic fluid. The mixing of gas into the oil yields highly complex variations in the bulk modulus, density and viscosity of the hydraulic fluid, and the effective gas pressure, which are generally neglected. The pseudo-static and dynamic properties of the HPS strut were investigated experimentally and analytically. Laboratory tests were conducted to measure responses in terms of total force and fluid pressures within each chamber under harmonic excitations and nearly steady temperature. The measured data revealed gradual entrapment of gas in the hydraulic fluid until the mean pressure saturated at about 84% of the initial pressure, suggesting considerably reduced effective bulk modulus and density of the hydraulic fluid. An analytical model of the HPS strut was formulated considering polytropic change in the gas state and increased fluid compressibility due to entrapped air. Both the measured data and the model results showed progressively hardening stiffness…
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Analysis of a Flow Volume Regulated Frame Steering System and Experimental Verifications

Concordia University-Yuming Yin, Subhash Rakheja
IRSST Montreal-P. E. Boileau
Published 2015-09-29 by SAE International in United States
The articulated frame steering (AFS) systems are widely implemented in construction, forestry and mining vehicles to achieve enhanced maneuverability and traction performances. The kinematic and dynamic performances of articulated steered vehicles are strongly influenced by properties of the frame steering system. In this paper, a flow volume regulated frame steering system is described and analytically modelled. The analytical model of the steering system is formulated in conjunction with yaw-plane model of a 35 tonnes mining vehicle to investigate steady as well as transient responses of the steering system and the vehicle. A field test program was undertaken to measure responses of the steering system and the vehicle under nearly constant speed turning as well as path-change maneuvers. The validity of the vehicle and the steering system model is demonstrated on the basis of the measured data in terms of steering wheel angle, articulation angle, hydraulic struts pressure, struts displacements and vehicle yaw rate. The results revealed reasonably good agreements between the measured and model responses under the maneuvers considered. The model could thus serve as…
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