Study of effects of damper oil volume lag on Hydrogas Suspension used in Armoured Fighting Vehicle

Studies on Hydrogas suspension systems have invariably modeled the damper element as a simple velocity co-efficient which is a constant in a passive suspension and may be varied for a semi-active suspension. This model is valid for light vehicles where suspension forces are moderate. In the case of heavy Armoured Fighting vehicles, the Hydrogas suspension units are subjected to huge suspension forces, under which the oil in the damper element is likely to undergo compression and the volume loss would result in a lagging effect manifesting as an unexpected deterioration in performance under random road input. In this paper, the state variable model of a passive suspension system with damper oil volume lag is developed. The frequency response characteristics of the models with and without volume lag is discussed. It is shown that the oil volume lag results in a under-damped response. The response of the system to a random ground excitation for different oil volume lag constants is simulated and the tolerable limit is inferred.