Nonlinear Modeling and Multi-Dimensional Performance Decoupling of a Novel Dual-Accumulator Hydro-Pneumatic System for Active Suspension

Purpose: With the rapid electrification of vehicles, driving performance, maneuverability, and safety have been significantly enhanced. As a core component governing vehicle system dynamics, active suspensions have attracted increasing attention in intelligent suspension applications owing to their superior performance potential. However, hydro-pneumatic systems, which constitute the core and fundamental configuration of active suspensions, involve multiple actuation components and complex structural configurations. These characteristics inevitably result in strong coupling between the damping and stiffness characteristics, thereby severely hindering performance matching and forward design. Methods: This paper proposes a novel Dual-Accumulator Hydro-Pneumatic System (DAHPS) configuration, in which the base valves, solenoid valves, and accumulators are independently connected to the compression and rebound chambers. Taking the disc valve as the key component, a Deflection-Throttling-Flow (DTF) property model is developed, which includes deflection property, conical gap throttling property, and orifices flow property. Furthermore, a nonlinear dynamic model of the DAHPS incorporating Variable Gas/air-Oil Physical Property (VGOPP) is developed, which can represent the evolution of the physical properties of the mixture fluid during gas/air dissolution, release, and dispersion processes within the oil under continuously varying pressure conditions. On this basis, the coupling mechanisms, influence regularities, and decoupling principles of the damping and stiffness characteristics of the DAHPS are systematically investigated. Results and Conclusion: The proposed DAHPS configuration enables independent regulation of the damping and stiffness characteristics during both compression and rebound strokes. The DTF model and the fluid-structure interaction method exhibit almost identical results and strong agreement with experimental results. For the disc valve deflection property, the deformation exhibits a characteristic “petal-like” shape. At larger radii near the free boundary, the pressure correction factor remains approximately stable at about 0.4. For the conical gap throttling property, the Throttling Loss Compensation Factor (TLCF) is consistently greater than 1 and increases significantly with increasing disc valve deflection. This trend is attributed to the increasing contributions of the contraction and bend throttling effects relative to the along-gap throttling effect at larger valve deflections. Compared with the model assuming Invariable Oil Physical Property (IOPP), the developed DAHPS model incorporating VGOPP exhibits higher accuracy. The maximum and minimum deviations of the DAHPS model with VGOPP (IOPP) are -6.42% (16.36%) and 0.27% (3.25%), respectively. More importantly, the strut force of the DAHPS is governed by the coupled effects of the structural properties of the accumulator and valve system, and the gas/air-oil physical properties. Specifically, the accumulators establish the pressure foundation, whereas the valve systems generate the superimposed pressure, which together contribute to the chamber pressures. Consequently, the DAHPS strut force is determined by the combined effects of the stiffness and damping characteristics. Notably, gas/air in the oil markedly reduces the density, bulk modulus, and viscosity of the mixture fluid, whereas these physical properties increase with increasing chamber pressure. To ensure stable and superior dynamic performance of the DAHPS, the gas/air content must be minimized, and the gas/air volume fraction should be maintained below 4%.