| With such excellent performance as vibration resistance, anti-roll ability, balancingaxle load and adjustable vehicle height, the interconnected hydro-pneumatic suspension isbeing increasingly applied in heavy multi-axle vehicles. However, with all of theexcellence, the multi-branch structure has also brought about some problems. In this paper,analytical research and experiments are performed on multi-branch hydro-pneumaticsuspension on the basis of the university-enterprise cooperation project. With the fractionalorder theory applied to the modeling of hydro-pneumatic suspension, the research isfocused on the stiffness-damping coupling problem and the non-coincidence problem instiffness and damping existing in multi-branch hydro-pneumatic suspension. A testingbench of multi-branch hydro-pneumatic suspension is built to experiment on the theoreticalinference and simulation, building the theoretical and experimental foundation for thedesigning of multi-branch hydro-pneumatic suspension and the controlling of the wholevehicle. This paper is mainly focused on:Models of major components of hydro-pneumatic suspension are built based onknowledge of hydromechanics and ideal gas equation of state. According to the flowingconnection of every component, the simplex and multi-branch hydro-pneumatic suspensionmodels of integral order are built respectively with the validity verified through bench tests.The simplex and multi-branch hydro-pneumatic suspension models of fractional orderbased on the fractional order theory, the feasibility and advantage of which are verifiedthrough the comparison of the bench tests on fractional and integral order models. Theinfluence of change of fractional operator on the system characteristics is analyzed to servethe subsequent non-coincidence problem in stiffness and damping in multi-branchhydro-pneumatic suspension.In view of interconnected hydro-pneumatic suspension, on the basis of the models ofvalves, the input-output relationships among every component model of the interconnectedhydro-pneumatic suspension under various excitation modes are analyzed, and themodeling and simulation are also conducted on single-wheel excitation, in-phase andopposed-phase excitation on front and rear wheels on the same side, in-phase andopposed-phase excitation on left and right wheels on the same axle and excitation on allfour wheels, and then the dynamic characteristics of the interconnected hydro-pneumaticsuspension under all these excitations are analyzed, which provides theoretical basis fordesigning of interconnected hydro-pneumatic suspension.The stiffness-damping coupling problem of multi-branch hydro-pneumatic suspensionis proposed, and then the elastic and damping force expressions of multi-branchhydro-pneumatic suspension are derived. The stiffness-damping coupling characteristics ofmulti-branch hydro-pneumatic suspension are analyzed theoretically, and the couplingmechanism is revealed through simulation. Then the influence of stiffness-domainparameters(pre-charge pressure of accumulator), damping-domain parameters(diameter of throttle) and motion-domain parameters(piston displacement and velocity of cylinder) onthe stiffness-damping coupling characteristics of multi-branch hydro-pneumatic suspension,which provides theoretical foundation for subsequent research on non-coincidence instiffness and damping of multi-branch hydro-pneumatic suspension.The non-coincidence problem in stiffness and damping of multi-branchhydro-pneumatic suspension is proposed. Based on its model built above, the statevariables of multi-branch hydro-pneumatic suspension are compared, which reveals theroot cause of the. Then the influence of stiffness-domain parameters(pre-charge pressure ofaccumulator), damping-domain parameters(diameter of throttle) and motion-domainparameters(piston displacement and velocity of cylinder) on the non-coincidence problemin stiffness and damping of multi-branch hydro-pneumatic suspension, and the influentialfactors are compared and analyzed respectively and quantitively, which is further study ofthe stiffness-damping coupling characteristics of multi-branch hydro-pneumaticsuspension.To meet the need of experiment, a bench test program for multi-branchhydro-pneumatic suspension is designed, in which every component in the system ispurchased or designed and a testing bench for characteristics of multi-branchhydro-pneumatic suspension system is set up. Then the theoretical inference and simulationanalysis of the system model, stiffness-damping coupling characteristics andnon-coincidence in stiffness and damping of multi-branch hydro-pneumatic suspension areverified through the bench test. |
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