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Journal Article

Development of a Non-Linear Clutch Damper Experiment Exhibiting Transient Dynamics

2015-06-15
2015-01-2189
Many powertrain structural sub-systems are often tested under steady state conditions on a dynamometer or in a full vehicle. This process (while necessary) is costly and time intensive, especially when evaluating the effect of component properties on transient phenomena, such as driveline clunk. This paper proposes a laboratory experiment that provides the following: 1) a bench experiment that demonstrates transient behavior of a non-linear clutch damper under non-rotating conditions, 2) a process to efficiently evaluate multiple non-linear clutch dampers, and 3) generates benchmark time domain data for validation of non-linear driveline simulation codes. The design of this experiment is based on a previous experimental work on clunk. A commercially available non-linear clutch damper is selected and the experiment is sized accordingly. The stiffness and hysteresis properties of the clutch damper are assumed from the measured quasi-static torque curve provided by the manufacturer.
Journal Article

Comparative Assessment of Frequency Dependent Joint Properties Using Direct and Inverse Identification Methods

2015-06-15
2015-01-2229
Elastomeric joints are utilized in many automotive applications, and exhibit frequency and excitation amplitude dependent properties. Current methods commonly identify only the cross-point joint property using displacement excitation at stepped single frequencies. This process is often time consuming and is limited to measuring a single dynamic stiffness term of the joint stiffness matrix. This study focuses on developing tractable laboratory inverse experiments to identify frequency dependent stiffness matrices up to 1000 Hz. Direct measurements are performed on a commercial elastomer test system and an inverse experiment consisting of an elastic beam (with a square cross section) attached to a cylindrical elastomeric joint. Sources of error in the inverse methodology are thoroughly examined and explained through simulation which include ill-conditioning of matrices and the sensitivity to modeling error.
Journal Article

Volumetric and Dynamic Performance Considerations of Elastomeric Components

2015-06-15
2015-01-2227
Elastomeric joints such as mounts and suspension bushings undergo broadband excitation and are often characterized through a cross-point dynamic stiffness measurement; yet, at frequencies above 100 Hz for many elastomeric components, the cross- and driving-point dynamic stiffness results significantly deviate. An illustrative example is developed where two different sized mounts, constructed of the same material and are shaped to achieve the same static stiffness behavior, exhibit drastically different dynamic behavior. Physical insight is provided through the development of a reduced order single-degree-of-freedom model where an internal resonance is explained. Next, a method to extract the parameters for the reduced order model from a detailed finite element bushing model is provided.
Journal Article

Dynamic Analysis of Hydraulic Bushings with Measured Nonlinear Compliance Parameters

2015-06-15
2015-01-2355
Hydraulic bushings with amplitude sensitive and spectrally varying properties are commonly used in automotive suspension. However, scientific investigation of their dynamic properties has been mostly limited to linear system based theory, which cannot capture the significant amplitude dependence exhibited by the devices. This paper extends prior literature by introducing a nonlinear fluid compliance term for reduced-order bushing models. Quasi-linear models developed from step sine tests on an elastomeric test machine can predict amplitude dependence trends, but offer limited insight into the physics of the system. A bench experiment focusing on the compliance parameter isolated from other system properties yields additional understanding and a more precise characterization.
Journal Article

Effect of Local Stiffness Coupling on the Modes of a Subframe-Bushing System

2013-05-13
2013-01-1904
The elastomeric joints (bushings or mounts) in vehicle structural frames are usually described as uncoupled springs (only with diagonal terms) in large scale system models. The off-diagonal terms of an elastomeric joint have been previously ignored as they are often unknown since their properties cannot be measured in a uniaxial elastomer test system. This paper overcomes this deficiency via a scientific study of a laboratory frame that is designed to maintain a high fidelity with real-world vehicle body subframes in terms of natural modes under free boundaries. The steel beam construction of the laboratory frame, with four elastomeric mounts at the corners, permits the development of a highly accurate, yet simple, beam finite element model. This allows for a correlation study between the experiment and model that helps shed light upon the underlying physical phenomenon.
Journal Article

Comparative Assessment of Multi-Axis Bushing Properties Using Resonant and Non-Resonant Methods

2013-05-13
2013-01-1925
Shaped elastomeric joints such as engine mounts or suspension bushings undergo broadband, multi-axis loading; however, in practice, the elastomeric joint properties are often measured at stepped single frequencies (non-resonant test method). This article helps provide insight into multi-axis properties with new benchmark experiments that are designed to permit direct comparison between system resonant and non-resonant identification methods of the dynamic stiffness matrices of elastomeric joints, including multi-axis (non-diagonal) terms. The joints are constructed with combinations of inclined elastomeric cylinders to control non-diagonal terms in the stiffness matrix. The resonant experiment consists of an elastic metal beam end-supported by elastomeric joints coupling the in-plane transverse and longitudinal beam motion.
Technical Paper

Errors Associated with Transfer Path Analysis when Rotations are not Measured

2007-05-15
2007-01-2179
Previously we had found significant errors in the interfacial force results for a source-path-receiver system where only translational motions were measured. This paper examines the sources of those errors by using computational finite and boundary element models. The example case consists of a source structure (with few modes), a receiver (with many modes) and three steel rod paths. We first formulate indirect, yet exact, methods for estimating interfacial forces, by assuming that six-dimensional motions at any location are available though we focus on only the driving points. One- and three-dimensional sub-sets of the proposed formulation are compared with the six-dimensional theory in terms of interfacial force and partial sound pressure spectra.
Technical Paper

Prediction of High Frequency Response Characteristics of Hydraulic Mounts

2005-05-16
2005-01-2410
The major objectives of this study are to identify the source(s) of high frequency resonance(s), suggest a method to effectively estimate mount parameters and propose both linear and nonlinear models capable of predicting the high frequency characteristics. First, a lumped parameter linear model is derived and the resonances controlled by decoupler, fluid column and rubber element are examined. By using a simplified mechanical model, typical parameters are estimated from measured dynamic stiffness data. Estimations correlate well with experiments and provide quantitative evaluation of the physical parameters, some of which (such as the decoupler damping) are otherwise difficult to measure by using conventional experimental techniques. A nonlinear time domain model for a free decoupler mount is proposed to predict both the inertia track and decoupler resonances. Both nonlinear and linear models match well with high frequency measurements.
Technical Paper

Estimation of Dynamic Stiffness Matrix of Welded or Glued Joints Using a Laboratory Fixture

2003-05-05
2003-01-1710
Accurate quantification of welded or adhesive joints in automotive chassis structures is necessary before reliable models can be developed. Such joints undergo shear and rotational deformations, which must be characterized via diagonal stiffness elements and cross-stiffness terms in order to describe static and dynamic problems. In this paper, a frequency domain decomposition technique is employed to extract static stiffness and viscous damping matrices of dimension 2 via analytical, computational or experimental models. Methods are applied to a laboratory fixture and alternate joints are compared.
Technical Paper

Examination of High Frequency Characterization Methods for Mounts

2001-04-30
2001-01-1444
The knowledge of frequency-dependent dynamic stiffnesses of mounts, in axial and flexural motions, is needed to determine the behavior of many automotive sub-systems. Consequently, characterization and modeling of vibration isolators is increasingly becoming more important in mid and high frequency regimes where very few methods are known to exist. This paper critically examines some of the approximate identification methods that have been proposed in the literature. Then we present a new experimental identification method that yields frequency-dependent multi-dimensional dynamic stiffnesses of an isolator. The scope is however limited to a linear time-invariant system and our analysis is restricted to the frequency domain. The new characterization method uses two inertial elements at both ends of an isolator and free boundary conditions are maintained during testing.
Technical Paper

Vibration Power Transmission Through Multi-Dimensional Isolation Paths Over High Frequencies

2001-04-30
2001-01-1452
In many vibration isolation problems, translational motion has been regarded as a major contributor to the energy transmitted from a source to a receiver. However, the rotational components of isolation paths must be incorporated as the frequency range of interest increases. This article focuses on the flexural motion of an elastomeric isolator but the longitudinal motion is also considered. In this study, the isolator is modeled using the Timoshenko beam theory (flexural motion) and the wave equation (longitudinal motion), and linear, time-invariant system assumption is made throughout this study. Two different frequency response characteristics of an elastomeric isolator are predicted by the Timoshenko beam theory and are compared with its subsets. A rigid body is employed for the source and the receiver is modeled using two alternate formulations: an infinite beam and then a finite beam. Power transmission efficiency concept is employed to quantify the isolation achieved.
Technical Paper

Determination of Viscoelastic Core Material Properties Using Sandwich Beam Theory and Modal Experiments

1999-05-17
1999-01-1677
Damping material for automotive structures is often quantified in terms of composite loss factor or damping ratio by using ASTM/SAE beam or modal tests. Simplified expressions have also been used to estimate certain material properties. However, none of these tests provide any information on the properties of viscoelastic core material such as rubber or adhesive in practical structures. To overcome this deficiency, a refined estimation procedure is proposed. A new sandwich beam model has been developed which describes all layers of an arbitrarily applied damping patch. By using both analytical predictions and modal experiments on a cantilever beam, spectrally-varying loss factor and shear modulus of the unknown core are determined.
Technical Paper

Evaluation of Damping Material at Higher Frequencies with Application to Automotive Systems Including Brakes

1995-05-01
951243
Many discrete tonal type noise and vibration problems in automotive systems and other physical structures require passive multi-layer visco-elastic damping treatments in mid to high frequency regimes. To address such issues, experimental modal analysis and dynamic finite element methods are suggested as suitable tools. Results are presented in terms of several test structures (four thin elastic beams, a thick elastic plate and an automotive brake pad) with free-free boundary conditions. Composite modal loss factors are measured and predicted for two different damping insulators consisting of adhesive, steel and coating combinations. Special attention is paid to the elastic deformation modes of test structures and spectral scaling of material properties for the finite element models.
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