Robust Bi-Objective Optimization and Dynamic Modeling of Hydropneumatic Suspension Unit Considering Real Gas Effects

Vehicles are now rapidly transitioning from a conventional torsion bar suspension to an in-arm suspension unit (ISU), reflecting the growing industrial demand for more compact, high-performance systems. Although the ISU system can adapt well to rough terrain, the side forces produced when the piston moves can affect its reliability. Current models built on ideal gas assumptions fail to describe the complex nonlinear behavior of nitrogen under extreme pressure and temperature variations. This study incorporates the Beattie–Bridgeman real-gas equation into a dynamic force-displacement model to overcome this limitation. Furthermore, a bi-objective optimization strategy was devised that simultaneously minimizes the side forces and enhances acceleration stability across diverse environmental conditions. The optimized design based on a metamodel and a hybrid metaheuristic algorithm resulted in an 81.4% reduction in peak lateral forces and a 53.3% improvement in acceleration robustness, which marks a significant increase in suspension system durability. These findings not only advance ISU design methodologies but also offer viable solutions to existing reliability challenges.