Title: Modelling of a semi-active hydropneumatic spring–damper unit

Authors: N.J. Theron, P.S. Els

Addresses: Dynamic Systems Group, Department of Mechanical and Aeronautical Engineering, University of Pretoria, Pretoria 0002, South Africa. ' Dynamic Systems Group, Department of Mechanical and Aeronautical Engineering, University of Pretoria, Pretoria 0002, South Africa

Abstract: The mathematical modelling of a suspension unit is considered. The unit comprises a hydraulic cylinder connecting the vehicle body to the unsprung mass, two nitrogen-filled accumulator springs and two damper ports. The model takes the deflection rate as input and iteratively employs simple fluid dynamics theory to calculate the flow-rates from each accumulator to the cylinder. It calculates the pressure in the accumulators by time-integrating the flow rates to determine the gas volumes and then invoking ideal gas theory. This renders the dynamic force of the unit as output. Model predictions are compared with measurements.

Keywords: semi-active suspension; hydropneumatic spring damper; twin accumulator spring–damper; vehicle dynamics; off-road; mathematical modelling; simulation; model verification; vehicle design; vehicle suspensions; deflection rate; fluid dynamics; ideal gas theory.

DOI: 10.1504/IJVD.2007.014917

International Journal of Vehicle Design, 2007 Vol.45 No.4, pp.501 - 521

Published online: 17 Aug 2007 *

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