The Effect of Heat Transfer on Hydro-Pneumatic Springs

Abstract

AbstractHeat build-up is a significant concern for vehicles with a hydro-pneumatic suspension system. Heat build-up arises due to the dissipation of heat from the damper and results in an increase in gas temperature in the hydro-pneumatic spring. Increased gas temperature results in a change in static ride height that may negatively affect the performance of the vehicle. The force-displacement characteristic of hydro-pneumatic springs is best characterized when a real gas approach is incorporated into the energy equation (EE) of the First Law of Thermodynamics. The thermal time constant (TTC) is included in the EE; it influences the rate of heat transfer between the gas and the surroundings. It is postulated that the TTC can be tuned to mitigate heat build-up in the hydro-pneumatic strut, either by introducing damping to the system in the form of a hysteresis loop or by increasing heat transfer to the surroundings. The effect of different TTCs on the gas temperature and hysteresis loop area was investigated. The effects of excitation frequencies and amplitudes were also investigated. The hysteresis loop can indeed introduce significant additional damping to the system, but this is only realized at large excitation amplitudes at low frequencies. The effect of the TTC is almost negligible at high frequency excitation with small amplitudes. In conclusion, the TTC cannot be tuned to mitigate the heat build-up typically associated with hydro-pneumatic suspensions. However, certain special case scenarios where it may indeed be a useful tool to mitigate heat build-up are discussed.KeywordsHydro-pneumatic springRide comfortSuspension modelling