Comparison of different gas models to calculate the spring force of a hydropneumatic suspension

• A hydropneumatic suspension system is modelled using five approaches.
• Simulation results are compared to laboratory test results on a single suspension unit.
• Simulation results compared to test results for a full vehicle.
• Extremely important to take heat transfer into account for accurate spring modelling.
• Model can accurately predict spring force of a hydropnemautic suspension system.

When developing any simulation model some compromise must be made between computational efficiency and the accuracy of the model. This study compares the performance of three ideal gas (IG) law variations (IG with the energy equation (EE), isothermal and adiabatic), and two real gas approaches (Benedict Webb Rubin (BWR) equation with and without the EE) to model the spring force of a hydropneumatic suspension. These models are compared with experimental data obtained from laboratory tests on a single hydropneumatic suspension unit. Both the BWR and IG models with the EE offer a significant improvement in correlation compared to the models without the EE. The real gas BWR approach offers a small improvement over the IG approach under the test conditions. The best (BWR with EE) and worst (IG isothermal) models are then used to model the spring forces in a full vehicle model of a 4 × 4 Sports Utility vehicle (SUV). The data is again compared with experimental results and the BWR model with the EE correlates significantly better than the IG isothermal model. It is thus concluded that the inclusion of the EE will yield significantly better results and it should only be omitted if the parameters investigated are not sensitive to errors in the spring model.