Modelling of a semi-active hydropneumatic spring–damper unit

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.