| The hydraulically interconnected suspension (HIS), as one of the advancedsuspensions, is able to independently adjust the spring/damping rates for eachsuspension mode. The vehicle, equipped with the HIS, has better ride and handlingperformance than that with the conventional suspension. Hence, This suspension hasthe extensively applied foreground. However, few research study has been carried outto explore the theory and mechanism of the HIS system for the tri-axle straight truck.The nonlinear differential equations developed by the conventional method, which isemployed to model the dynamics equations of the mechanical and hydraulic couplingsystem, can only implicitly describe the relationships between the evaluation indicesand the key physical parameters of the hydraulic system, which make it is difficult toinvestigate the explicit quantitative relationships between the additional characteristicsand the key physical parameters, and also affects the development study of the designmethodologies for the HIS system.Therefore, this dissertation systematically investigates the characteristics of theHIS system, and aims at contributing some useful researches and trials on theoreticalanalysis and computation for the HIS system. The main research works of thisdissertation are as follows:(1) A modeling methodology has been proposed based on the impedance transfermatrix method. It discretizes the fluid circuits according to the fluid components, andthe state vector of the adjacent nodes for each fluid component are related to each otherby the transfer matrix of the fluid component. The relationships between the nodes, inwhich the flow changes continuously, are described with the connectivity matrix,which is obtained by production of every individual component transmission matrix.By applying the continuity equation at the nodes, where the flow fluctuates, theimpedance matrix between the flow and pressure at the boundaries can be obtained.The hydraulic strut forces are incorporated into the equations of motion of themechanical system as externally applied forces, which are obtained by therelationships between the boundary flows/pressures and the motions of the mechanicalsystem. Finally, the equations of motion of the mechanical and hydraulic couplingsystem have been derived. (2) The interconnection arrangements have been developed for the tri-axle straighttruck based on the independent mode of the suspension. Based on the requirements forthe modeling of the mechanical system, a simplified model, which is characterized aspitch mode, for the rear tandem axle bogie suspension of the tri-axle straight truck hasbeen developed and evaluated. According to the research of the synchronous andopposite interconnection arrangements between two double-acting cylinders, therelationships between additional characteristics and the interconnection arrangementsare obtained. Based on the obtained results, three new HIS systems have been proposedto implement control for the independent suspension mode. The impedance matrices ofthese hydraulic systems have been derived based on the impedance transfer matrixmethod.(3) The characteristics and mechanism research has been carried out for the HISsystem based on the independent mode of the suspension. The H2performances of theHIS system for the quarter-car have been obtained. The dimensionless expressions forthe H2performances of the HIS system has been derived and explicitly described interms of the dimensionless parameters. Then the feasible design region for the stiffnessand damping parameters is figured out from the contour plot of the suspensionperformances with respect to the stiffness and damping parameters. The analogousexpression for the conventional suspension and pitch resitant HIS systems is alsoinvestigated in the pitch plane. Furthermore, the conditions for the roll resistant HISsystem to decouple the heave and pitch modes, as well as roll and warp modes, for thebody and wheel stations have been studied based on the additional stiffness/dampingmode matrix. It is theoretically proved that the HIS is able to independently adjust thespring/damping rate. Meanwhile, the quantitative analysis of the key physicalparameters on the additional mode stiffness/damping has been made in this thesis.(4) Based on the equations of motion of the mechanical and hydraulic couplingsystem for the independent mode, the steady vibration characteristics have beenstudied. An identification method is proposed to find out the eigenvalues of thefrequency dependent characteristic matrix. This method is evaluated by comparison ofthe eigenvalues of the frequency independent characteristic matrix, which are obtainedwith the conventional method. Based on the identified eigenvalues and eigenvectors,the impacts of the pitch and roll resistant HIS systems on the natural frequencies, modeshapes and the truck body oscillation centers have been studied using the ‘real’ motionanalysis method based on the complex modal theory. The power spectral density responses of the coupling system under stochastic road excitation are also investigated.(5) A parameter design method is presented to optimize the performances of theHIS system. A parametric study has been carried out to analysis the effects of the keyphysical parameters of hydraulic system on the performances. Based on the results ofthe parametric study, the conflict performance indices are assembled as the objectivefunctions. The optimized parameter sets, which satisfy the requirements from theobjective functions, can be found by employing optimum design based on the discretevariables. And the parameter set corresponding to the better compromisingperformances is chosen from the optimized sets in terms of the dimensionless factors,which are displayed by the radar-type chart.In summary, this dissertation, whose research objective is the hydraulicallyinterconnected suspension, has investigated into the dynamics of this proposedsuspension, which involve in modeling, interconnection arrangements and vibrationmechanism, parameter design and subjective evaluation methods. This dissertationpresents a new modeling approach for the mechanical and hydraulic coupling system,and provided a new resolution to the theoretical investigation for the HIS system. As aresult, this dissertation is with rather good academic merits and practical value. |
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