Hydraulic Bushing Research Articles

Experimental dynamic flow characterization of hydraulic bushings

The dynamic properties of hydraulic bushings are often modeled in the time and frequency domains with low-order, lumped-parameter models, typically assuming steady developed flow in their fluid passages, whereas in situ flow conditions are unlikely to meet such criteria. Hydraulic bushings exhibit tuned properties emerging from nonlinear interactions involving these flow characteristics, so higher resolution descriptions of the underlying physics are needed under realistic flow conditions. This paper discusses an approach to isolate the fluid passage features in production bushings to enable experimental characterization for steady, oscillatory, and transient flow. More robust models of dynamic responses in the time and frequency domains are expected to result from this more precise determination of each flow path's contribution to the nonlinear system response. An apparatus capable of generating steady and dynamic flow is proposed, and some validation data are given to demonstrate the functionality of the experiment. Some challenges with the approach are considered, including the system's hydraulic compliance and cavitation. The flow testing apparatus is used on an example two-passage production bushing adapted for controlled steady or dynamic flow through one or both flow paths. Finally, some nonlinear flow properties of a typical hydraulic bushing's flow passages are given.

Simulation of dynamic characteristics of suspension hydraulic bushing

The hydraulic bushing is a common vibration isolator, and its dynamic characteristics influence the ride comfort of the vehicle. Aiming at a suspension hydraulic bushing with inertia components, a one-dimensional model of the hydraulic bushing is established based on Amesim. Secondly, a parameter identification method is proposed, and the equivalent piston area of the hydraulic bushing and the diaphragm strain stiffness are identified by this method. Finally, the identified parameters are input into the Amesim model, and the data results are compared with the experimental results after processing with MatLab. The results show that the dynamic characteristic curve of the hydraulic bushing calculated by this method is consistent with the test curve and can well predict the dynamic characteristics of the hydraulic bushing with inertia elements.

Experimental dynamic flow characterization of hydraulic bushings

The dynamic properties of hydraulic bushings are often modeled in the time and frequency domains with low-order, lumped-parameter models, typically assuming steady, developed flow in their fluid passages, whereas in situ flow conditions are unlikely to meet such criteria. Hydraulic bushings exhibit tuned properties emerging from nonlinear interactions involving these flow characteristics, so higher resolution descriptions of the underlying physics are needed under realistic flow conditions. This paper discusses an approach to isolate the fluid passage features in production bushings to enable experimental characterization for steady, oscillatory, and transient flow. More robust models of dynamic responses in the time and frequency domains are expected to result from this more precise determination of each flow path's contribution to the nonlinear system response. An apparatus capable of generating steady and dynamic flow is proposed, and some validation data is given to demonstrate the functionality of the experiment. Some challenges with the approach are considered, including the system's hydraulic compliance and cavitation. The flow testing apparatus is used on an example two-passage production bushing adapted for controlled steady or dynamic flow through one or both flow paths. Finally, some nonlinear flow properties of a typical hydraulic bushing's flow passages are given.

Modeling Method of Dynamic Characteristics of Hydraulic Damping Rubber Isolator

<div class="section abstract"><div class="htmlview paragraph">The dynamic characteristics of hydraulic damping rubber isolators (such as hydraulic bushing and hydraulic mount) are related to excitation amplitude and frequency. Based on the lumped parameter model of hydraulic damping rubber isolator, a unified linear model of complex stiffness is derived and its deficiency is pointed out. Based on the derived linear model, this paper considers the nonlinear damping of inertia channel and the nonlinear stiffness of the upper chamber of the hydraulic damping rubber isolator, so as to establish a new nonlinear model, which can reflect the amplitude and frequency dependence of the dynamic characteristics of the hydraulic damping rubber isolator. Finally, the nonlinear model is used to analyze the dynamic response of hydraulic damping rubber isolator under harmonic excitation and random excitation respectively, and the results are compared with the test results. The results show that the proposed model can characterize the amplitude and frequency dependence of the dynamic characteristics of the hydraulic damping rubber isolator, and can accurately calculate the dynamic response of the hydraulic damping rubber isolator under harmonic excitation and random excitation.</div></div>

Machinability of rectangular bars of nodular cast iron produced by continuous casting

Continuous bars of ductile iron are widely used for parts produced by machining processes, for example, hydraulic manifolds, hydraulic cylinder pistons, bushings, and pump housings. The main reasons for the selection of ductile iron bars are the high strength, stiffness, toughness, wear resistance, cost, and machinability. Concerning this last property, the best machinability is obtained for a ductile iron with a predominantly soft ferritic matrix. The rate of the solid-state transformation of austenite into ferrite, the so called “stable eutectoid reaction,” is dependent on the diffusion distance from the austenite to graphite particles, in other words, on the maximum distance between the graphite particles. If this distance increases, the time for the reaction may not be sufficient, and a “metastable eutectoid reaction” can occur, with the decomposition of austenite into pearlite, a mixture of soft ferrite with iron carbide. This constituent, called pearlite, shows higher hardness than ferrite, and so it must be machined under different conditions compared with a ferrite matrix. Thus, the distance between the graphite particles, measured by the number of graphite particles per unit area, determines the type of ductile iron matrix. The number of graphite particles is governed mainly by the solidification speed. In the continuous casting of bars of ductile iron, there is a variation in the solidification speed from the surface of the bar to the center of the section, decreasing toward the center. This is particularly important in thick sections, where the difference in the solidification speed is significant, leading to a variation in the microstructure from the surface to the center. This variation in the microstructure was the focus of this study, measuring various parameters connected to machinability, such as torque, power consumption, tool life (with tool wear analysis), and surface roughness. The goal was to show that the machining conditions must be changed when machining different positions on the section of a thick continuous ductile iron bar. Lower torque and shorter tool life were obtained when cutting the core in relation to the periphery region. However, in terms of power consumption and surface roughness, there was no statistical difference between the regions evaluated during the milling process. The variability of the machining output parameters is related to the mechanical properties along the cross section of the bars.

Effect of fractionally damped compliance elements on amplitude sensitive dynamic stiffness predictions of a hydraulic bushing

Abstract Hydraulic bushings exhibit significant amplitude dependent behavior which cannot be captured with the linear time-invariant system theory. Accordingly, Fredette et al. (2016) have proposed a nonlinear model, but the amplitude sensitivity has not been adequately described as it is affected by multiple inherent design features. To further improve the predictive capability of nonlinear models, this article extends the prior work by including two key dissipation effects within the (elastomeric) fluid compliance chambers. First, the conventional fluid compliance element is replaced by an equivalent mechanical spring representing the nonlinear elasticity of the pumping chambers. Fractional calculus based and friction-type damping elements are added in parallel to the nonlinear spring elements of pumping chambers. Second, improved quasi-linear models are proposed at four sinusoidal excitation amplitudes, demonstrating amplitude sensitivity in model parameters. Third, new nonlinear models are proposed and numerically simulated, predicting dynamic stiffness magnitudes and loss angles at multiple excitation amplitudes. The sensitivity of dynamic properties to the fractional and frictional damping parameters is qualitatively evaluated. Finally, both quasi-linear and nonlinear models are experimentally validated and are found to be superior to the ones in the literature.

Nonlinear fluid damping models for hydraulic bushing under sinusoidal or transient excitation

Hydraulic bushings are typically characterized in terms of sinusoidal dynamic stiffness at lower frequencies over a range of excitation amplitudes. However, in practice they are also exposed to severe transient loads in conjunction with sinusoidal excitations. Three improved nonlinear, lumped parameter models for hydraulic bushings are developed with the goal of concurrently predicting amplitude-sensitive dynamic responses to both sinusoidal and step-like excitations using a common dynamic model with the same parameters. First, a fluid resistance element is introduced which extends previous formulations by relaxing the assumption of fully developed turbulent flow, and capturing the transition from laminar flow to turbulence. Second, a bleed orifice element between the two compliance chambers is incorporated to simulate leakage observed in laboratory testing. The sensitivity of the dynamic responses to linearized model parameters is used to guide the parameter identification procedure. Measured dynamic stiffness spectra and step-like responses provide experimental validation of the proposed formulations. The new formulations achieve improved predictions of dynamic stiffness or force using exactly the same set of model parameters at several excitation amplitudes in both time and frequency domains.

Design of Hydraulic Bushing and Vehicle Testing for Reducing the Judder Vibration

Generally, judder vibration is a low-frequency vibration phenomenon caused by a braking force imbalance that occurs when a vehicle is lightly decelerated within a range of 0.1 to 0.2g at a speed of 120 to 60 km/h. This comes from the change in the brake disk thickness (DTV), which is mainly caused by the side run-out (SRO) and thermal deformation. The adoption of hydro-bushing in the low arm G bushings of the vehicle front suspension has been done in order to provide great damping in a particular frequency range (<20Hz) in order to prevent this judder vibration from being transmitted to the body. The hydro bushing was formulated using a lumped parameter model. The fluid passage between the two chambers was modelled as a nonlinear element such as an orifice, and its important parameters (resistance, compliance) were measured using a simplified experimental setup. The main design parameters are the ratio of the cross-sectional area of the chamber to the fluid passage, the length of the fluid passage, etc., and their optimal design is such that the loss angle is greater than 45 ° in the target frequency range of 10 to 20 Hz. The hydro bushing designed for reducing the judder vibration was prepared for the actual vehicle application test and applied to the actual vehicle test. In this study, the proposed hydro bushing was applied to the G bushing of the low arm of the front suspension system of the vehicle. The loss angle of the manufactured hydro bushing was measured using acceleration signals before and after passing through the bushing. The actual vehicle test was performed on the noise dynamometer for the performance analysis of the judder vibration reduction.

Harmonic amplitude dependent dynamic stiffness of hydraulic bushings: Alternate nonlinear models and experimental validation

The dynamic stiffness properties of automotive hydraulic bushings exhibit significant amplitude sensitivity which cannot be captured by linear time-invariant models. Quasi-linear and nonlinear models are therefore proposed with focus on the amplitude sensitivity in magnitude and loss angle spectra (up to 50Hz). Since production bushing model parameters are unknown, dynamic stiffness tests and laboratory experiments are utilized to extract model parameters. Nonlinear compliance and resistance elements are incorporated, including their interactions in order to improve amplitude sensitive predictions. New solution approximations for the new nonlinear system equations refine the multi-term harmonic balance term method. Quasi-linear models yield excellent accuracy but cannot predict trends in amplitude sensitivity since they rely on available dynamic stiffness measurements. Nonlinear models containing both nonlinear resistance and compliance elements yield superior predictions to those of prior models (with a single nonlinearity) while also providing more physical insight. Suggestion for further work is briefly mentioned.

Correlative Analysis of Hydraulic Bushing of Suspension Control Arm and Full Vehicle Ride Comfort

To analyze and compare the vehicle performance effects of hydraulic bushings with those of the traditional rubber bushings of double wishbone front suspensions, we test the static and dynamic properties of the hydraulic bushings of control arms. The mechanical model is built in ADAMS and is then used as the basis for establishing the full vehicle model. The random road surface spectra of different levels are built using the harmony superposition method. The ride comfort of the full vehicle with a control arm installed with hydraulic and rubber bushings is simulated on random and bump roads. The frequency spectrum characteristic and root mean square (RMS) of the vertical and longitudinal acceleration of the foot floor and seat rail are calculated via power spectrum estimation, and the handling stability of the full vehicle is then simulated. The effects of the change in hydraulic bushing stiffness on ride comfort are finally analyzed. The following results are obtained. (1) The effects of such change on vehicle handling are relatively small regardless of the type of bushing used. (2) The vehicle shows acceptable ride comfort on level A and level B roads but shows poor ride comfort on bump road when a hydraulic bushing is used. (3) Large hydraulic bushing stiffness increases the vertical acceleration RMS on level A, level B, and bump roads. However, the variety of RMS is extremely small on level D roads, the responses of the vertical and longitudinal acceleration curves are slow, and the time oscillation of the curves is relatively long on bump road.

Dynamic Analysis of Hydraulic Bushings with Measured Nonlinear Compliance Parameters

Dynamic Analysis of Hydraulic Bushings with Measured Nonlinear Compliance Parameters

Nonlinear dynamic properties of hydraulic suspension bushing with emphasis on the flow passage characteristics

Hydraulic bushings, which are often employed in vehicle suspension systems, exhibit significant excitation-dependent properties. However, previous analyses were mainly based on the linear system theory. To overcome this void, nonlinear characteristics of common hydraulic bushing configurations are examined in this article, with focus on the component properties as excited by sinusoidal or step displacements of various amplitudes. First, a nonlinear model for a laboratory prototype with a long passage and a short passage (in parallel) is developed using a lumped-parameter approach. Then the system parameters and nonlinearities are identified using experimental and computational methods, with an emphasis on characterization of the flow passage resistances. Steady-state harmonic and transient step experiments are conducted on the prototype, and the dynamic pressures inside two fluid chambers and the force transmitted to the base are measured. Numerical solution of the nonlinear model shows that the proposed model predicts both steady-state sinusoidal responses and transient responses well for single-passage and dual-passage configurations; significant improvement over a corresponding linear model is observed. Finally, approximate analytical and semi-analytical solutions of the nonlinear model are obtained by using the harmonic balance method.

Frequency domain properties of hydraulic bushing with long and short passages: System identification using theory and experiment

Fluid-filled bushings with tunable stiffness and damping properties are now employed in vehicles to improve ride characteristics and to reduce vibration and noise. Since scientific literature on this topic is sparse, a bushing prototype which can provide various combinations of long and short flow passages is designed and built. Several common fluid-filled bushing configurations are experimentally examined for their dynamic stiffness and pressure spectra. Linear time-invariant models (with lumped fluid elements) are proposed for a hydraulic bushing with two parallel flow passages. Next, a model with only a long capillary tube passage (an inertia track) is examined. Further, peak magnitude and loss angle frequencies are analytically found. Several methods for the identification of bushing parameters (up to 50Hz) are suggested. The linear models are validated by comparing predictions with measured stiffness magnitude and loss angle spectra. Finally, the principal features of a practical device are diagnosed using analytical models and measurements for two excitation amplitudes.

Identification of the Lumped Parameters for Hydraulic Bushing Based on FSI Finite Element Simulation

Radial damping hydraulic bushing is the object of this study, which is widely used as vibration isolator in the vehicle chassis system. The lumped parameter (LP) model for hydro-bushing is usually applied to the dynamic characteristic analyses. Two-way fluid-structure interaction FEA (nonlinear finite element analysis) technique is used to identify the main parameters of the LP model. The method proposed in this paper can ensure high quality and low cost in hydraulic bushing development.

Time domain responses of hydraulic bushing with two flow passages

Abstract Hydraulic bushings are commonly employed in vehicle suspension and body sub-frame systems to control motion, vibration, and structure-borne noise. Since literature on this topic is sparse, a controlled bushing prototype which accommodates a combination of long and short flow passages and flow restriction elements is first designed, constructed and instrumented. Step-up and step-down responses of several typical fluid-filled bushing configurations are measured along with steady harmonic time histories of transmitted force and internal pressures. To analyze the experimental results and gain physical insights into the hydraulic bushing system, lumped system models of bushings with different design features are developed, and analytical expressions of transmitted force and internal pressure responses are derived by using the convolution method. Parametric studies are also conducted to examine the effect of hydraulic element parameters. System parameters are successfully estimated for both harmonic and step responses using theory and measurements, and the dynamic force measurements are analyzed using analytical predictions. Finally, some nonlinearities of the system are also observed, and the fluid resistance of flow passage is found to be the most nonlinear element.

Study of the Lumped Parameter Models and Parameters Identification of Hydraulic Bushing

This article proposes two types of Lumped parameter models for the hydraulic bushing. Digital computation method is used to estimate the system parameters of LP model, provides a new way to reduce development cycle of hydro bushing. Two results of hydro-bushing dynamic behavior using two LP models are compared and analyzed. This article provides more channel to analyze the operation principle of the hydraulic bushing.

Dynamic Stiffness of Hydraulic Bushing with Multiple Internal Configurations

Dynamic Stiffness of Hydraulic Bushing with Multiple Internal Configurations

Transient Response of Hydraulic Bushing with Inertia Track and Orifice-Like Elements

Transient Response of Hydraulic Bushing with Inertia Track and Orifice-Like Elements

Development of an Active Compliance Chamber to Enhance the Performance of Hydraulic Bushings

With the new improvements in the fuel economy engines and to enhance the passenger’s comfort, the topic of active vibration cancellation has received a lot of attention recently by both the automotive industry and researchers. Engine mounts and bushings are the devices used to suppress the transverse and tensional vibrations of engines, respectively. Engine mounts and bushings are primarily designed for the first order vibration of engine. Higher order vibrations, however, are neglected due to their lower amplitudes. Although lots of research has been focused on the improvement of the design and performance of engine mounts, engine bushings has not been addressed well in the literature. This paper focuses on the modeling and design of an active bushing, which addresses the higher order vibrations in engines. Such a bushing has a significant advantage in the ride quality of the newly commercialized variable displacement engine (VDE), where the amplitude of vibration induced by switching is higher than normal engines. For VDEs the higher amplitude of vibration makes the higher orders sensible. Isolation of these vibrations is beyond the capabilities of the passive hydraulic bushings. In this paper the design of a novel active chamber is proposed, which is ultimately utilized to control the fluid pressure inside the bushing. It is evident that the fluid pressure significantly contributes to the dynamic performance of the hydraulic bushing. The active chamber described in this paper utilizes a magnetic actuator, excited by electrical current signal, which is fed to a solenoid coil. The pulses produced by the magnetic actuator are used to adjust the pressure at any specific frequency. This feature enables the active chamber not only to alter the frequency response characteristic of the hydraulic bushing, but also to generate complex pressure frequency responses. A mathematical linear model for the magnetic actuator, and the active bushing assembly, is provided and then verified experimentally. The experimental results confirm that the active hydraulic bushing can well address the sophisticated vibration isolation requirements particular to the VDE systems.

Development of a bushing with an active compliance chamber for variable displacement engines

In this paper a novel active compliance chamber is designed, which can be used to control the dynamic stiffness of a common hydraulic bushing. This chamber offers a simple and cost-effective solution for the variable displacement engine (VDE) isolation problem. A VDE system requires a soft bushing for the half cylinder mode and a regular one for normal engine operations. A magnetic actuator is used to produce mechanical pulses. The linearisation technique is used for simplifying the nonlinear equation of motion. Different current sources are used to feed the magnetic actuator. The pressure inside the chamber follows linearly the current input signal. The phase shift in various current inputs is used in the form of the transfer functions to create the required pressure response pattern in the frequency domain. Since the dynamic stiffness of a conventional hydraulic bushing is a direct function of the pressure inside it, the active compliance chamber can be used to alter the pressure and consequently produce the required dynamic stiffness response. As a result, it can address the engine vibration problem for VDE situation.