The Experimental Analysis and Parameters Influence Study on Dynamic Characteristics of Radial Hydraulically Damped Bushing
Radial hydraulically damped bushing (RHDB) is widely used as vibration isolator in vehicle chassis system. In this paper, new experimental process and data used to measure and describe dynamic behaviors of a RHDB are presented and discussed. Furthermore, a lumped-parameter (LP) model for calculating dynamic performances of a RHDB with one inertial track is proposed. Finally, influences of lumped-parameters on dynamic performances of a RHDB are carried out using the LP model. It is found that dynamic characteristics of a RHDB are most sensitive to equivalent pumping area of rubber spring, and are significantly influenced by its volume stiffness with high excitation frequencies above 25 Hz. But only the peak values of dynamic stiffness and loss angle are significantly affected by inertial coefficient and linear resistance of inertial track fluid. Introduction Hydraulically damped bushings (HDBs) can decay oscillations induced by dynamic loads of road with excitation of low-frequency and high-amplitude, and effectively decrease vibrations induced by engine with excitation of high-frequency and low-amplitude in radial direction, while conventional rubber bushing cannot satisfy the contradictory requirements for different excitations. Therefore, HDBs are widely used as a new kind of vibration isolators in engine sub-system, vehicle body and vehicle suspension since the late 1990s, which provides a relative optimum solution for stability and riding comfort of vehicles [1-5]. Experimental study is certainly the best method to investigate dynamic performances of HDBs. In the works of Refs. [6, 7], a laboratory device to investigate nonlinear dynamic characteristics of a HDB with a long inertia track and a short one is investigated. Dynamic pressures inside two fluid chambers and forces transmitted to the base of the HDB are measured with single-passage and dual-passage configurations. In order to decrease number of prototypes and tests, and to save considerable time in designing stage, lumped-parameter (LP) models have been implemented to study dynamic properties of HDBs. In LP models, each lumped parameter represents a certain physical meaning, and dynamic characteristics of HDBs can be explicitly described as a function of lumped-parameters. The first LP model of a HDB with one inertia track is presented in Refs. [8, 9], which is used to investigate dynamic performances of a typical conventional bushing filled with internal fluid. Lumped-parameters of the LP model are identified based on experiment data of dynamic characteristics. It is concluded that the predicted resonant frequency of inertia track fluid correlates well with tested results, and the proposed LP model can be used to calculate dynamic performances of HDBs with multiple inertia tracks. However, accuracy of estimated dynamic performances of HDBs is significantly depended on accuracy of lumped-parameters [10, 11]. These parameters are generally obtained based on experiment data or approximate analytic formula [12-18]. Therefore, it is required to find a more efficiently method which can be used directly to calculate these lumped-parameters of a LP model, while nonlinearities of rubber material and hydraulic fluid should be considered. 307 In this works, dynamic behaviors of a RHDB by presenting new experimental process and data are described and discussed, and a LP model of a RHDB with one inertial track used to calculate its dynamic characteristics is proposed. One of the contributions in this paper includes using the least-squares method to identify lumped-parameters of a RHDB’s LP model which include radial dynamic stiffness, radial damping and equivalent piston area of rubber spring, and volumetric stiffness of chambers and resistance of inertial track fluid. Furthermore, estimated dynamic performances of a RHDB are calculated based on a LP model using lumped-parameters identified. Finally, influences of lumped-parameters on dynamic performances of a RHDB are carried. Experiment Analysis of Static and Dynamic Behaviors of a RHDB Static and dynamic behaviors of a RHDB can be evaluated by a MTS 831 servo-controlled hydraulic test rig, which can provide sweep-sine-excitation frequency ranges of 0.01 Hz to 1000 Hz. Fig. 1 illustrates the experimental setup for measuring radial force versus displacement of a RHDB with one inertial track. Excitation displacement is applied to outer sleeve which is connected to a mobile jaw with a movable exciter, while force response can be measured with a force sensor connected to a fixed jaw.