Modeling of Hydrogas Unit for Tracked Vehicle Suspension

Abstract

Tracked vehicles equipped with conventional suspension are limited in their ability to achieve high mobility. This limitation is due to the linear characteristics and the consequent poorer ride performance [1-3]. Hydro gas suspension due to their inherent non-linear behavior can provide higher mobility and better ride comfort performance [4]. This paper aims to evaluate the characteristics of hydro-gas suspension system and apply this nonconventional system for the armored fighting carrier BMP-1. To achieve this goal, theoretical and experimental studies were carried out. The theoretical study includes modeling of the hydro gas suspension unit mathematically and validation of the developed model using MATLAB/SIMULINK. The experimental measurements are carried out to validate the results obtained from the model. The force, created inside the hydro gas unit during its action, includes the elastic and damping forces, the variation of such force with displacement and velocity of moving part are recorded (obtained). This variation is used as input parameters in the equation of oscillation of vehicle hull to study its vibration response. The obtained results show that the proposed hydro gas suspension system is more acceptable than the conventional one. Keywords: tracked vehicle suspension, hydrogas suspension system, hedrogas unit. Nomenclature area of orifice, m 2 A o area of floating piston, m 2 A f area of the piston, m 2 A p area of rod, m 2 A r Bulk , s modulus 0f oil, Pa Β discharge coefficient viscous friction coefficient for the piston, Ns/m C d C v viscous friction coefficient for the floating piston, Ns/m Ff mass of floating piston, kg m f mass of piston, kg m p flow rate of oil through the orifices, m 3 /s Q pressure in the lower fluid chamber, pa P 1 pressure in the upper fluid chamber, pa P 2 nitrogen gas pressure in the nitrogen chamber, pa P g initial pressure of nitrogen gas in nitrogen chamber, pa P o volume of lower chamber, m 3 V 1 volume of upper chamber, m 3 V 2 initial volume of nitrogen chamber, m 3 V o volume of nitrogen in nitrogen chamber, m 3 V g displacement of floating piston, m X displacement of the rod, m Z Hydro gas Suspension Unit HSU Paper: ASAT-16-015-HF 1. Introduction As the operating speed of high mobility tracked vehicle increases, the vibration induced by rough road condition also increases and it induces fatigue on crew members and many delicate instruments inside the vehicle. Also, vibration in a gun barrel reduces the shooting accuracy. Excessive vibration in high mobility tracked vehicle limits the maximum vehicle speed and consequently reduces the survivability and operational efficiency in combat situations [5]. Consequently, the vehicle suspension system is needed to operate on different kinds of terrain conditions including on roads and off-roads. The mobility performance of high mobility tracked vehicles is often limited by the operator's endurance to withstand the transmitted shocks and vibrations, and his ability to maintain control. With a continual demand for increased power to weight ratio and higher speeds, the present trend is towards the use of advanced suspension systems such as hydro gas or hydro pneumatic suspension. These tend to be lighter and more compact; can be mounted outside the hull, incorporate integral damping arrangements, and offer load-leveling capabilities due to their non linear progressively stiffening spring characteristics [6]. In this type of suspension, gas is used as a spring medium and hydraulic oil is utilized for force transmitting and dampening out the oscillations. The advantage of employing the hydro gas suspension in a tracked vehicle is not only to isolate the primary vibrations induced into the suspension system but also to offer a better ride comfort through nonlinear springing of the gas chamber. The design principle of hydro-pneumatic unit is as the road wheel rises, the axle arm is lifted and this rotates the crank which moves the piston via the connecting rod, the piston displaces oil through the damper valve and moves the separator piston as illustrated in figure (1). The hydrogas suspension unit contains both hydraulic fluid and compressed gas, usually nitrogen [7], separated by either a floating piston or a flexible diaphragm. The suspension forces are generated by pressure drop acting on the main piston. Damping forces are generated by the flow of hydraulic fluid through constrictions provided by either a damper plate or valve housing, while restoring forces are generated by compression and extension of the gas charge.