Simulation of Transient Processes in Pneumohydraulic Suspensions Using a Coupled Hydrodynamic and Thermodynamic Model

Abstract

we developed a simulation model and performed a numerical simulation of transient processes in pneumohydraulic devices used in vehicle suspension systems. The model coupled a zerodimensional thermodynamic model of the gas chamber and the piston equation of motion with axisymmetric unsteady Navier–Stokes equations for a viscous incompressible fluid filling the working chambers. We solved the hydrodynamic equations using the finite volume method with an implicit time-stepping scheme and treated the pressure–velocity coupling using an implicit operator-splitting procedure. We validated the model against experimental data and the results of a zero-dimensional model. We then performed a parametric study to assess the effects of the throttle-orifice radius, initial gas-chamber volume, and fluid viscosity and temperature on the transient response to step loading. We found that the throttle-orifice radius is the main damping parameter: small orifices produce an aperiodic response with a short-lived pressure peak similar to a local hydraulic shock, whereas large orifices produce weakly damped oscillations. The initial gas volume determines the effective stiffness of the gas spring and the final piston displacement, while changes in fluid temperature over the operating range alter the device’s stiffness–damping characteristics because of changes in fluid viscosity spanning several orders of magnitude. Based on these results, we formulated practical recommendations for selecting throttle-unit parameters and working fluids for suspension-system design.