Nonlinear modeling and experimental characterization of hydraulically interconnected suspension with shim pack and gas-oil emulsion

Abstract

Although hydraulically interconnected suspension (HIS) have been regarded as one of the promising suspension architectures in recent years, it’s application is still limited due to the many simplifying assumptions in the modeling and analyzing. There has been no published detailed analysis of the effects of shim pack deflection and entrapped gas within oil in HIS system to date. In this study, a nonlinear physical model of HIS is presented with an emphasis on the shim pack deflection and gas-oil emulsion properties and their effects on the stiffness and damping performances. The deflection of the shim pack is formulated based on shim pack deflection theory, and a nonlinear correction function (NCF) is proposed to compensate the errors of the analytical model. The finite element analysis (FEA) method is adopted for parameter identification. Also, the formulation of gas-oil emulsion is derived, in which the variations in the mass density and bulk modulus of the emulsion are formulated as a function of the gas volume fraction. The bench tests for the stiffness and damping characteristics are carried out to validate the developed physical model using the measured strut forces. The measured data and the model are analyzed to highlight the effects of gas-oil emulsion on the stiffness and damping characteristics. Furthermore, the effects of the initial gas volume fraction within oil is discussed under different motion-mode excitation. The results show that the entrapped gas volume changes the compressibility of the emulsion and thus cause significantly reduction to damping forces in a highly nonlinear manner but approximately linear increase to spring forces. It also suggests that the gas volume fraction should be controlled within 4%, so as to reduce the unexpected elastic force caused by gas compression.