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This study examines clutch-damper subsystem dynamics under transient excitation and validates predictions using a new laboratory experiment (which is the subject of a companion paper). The proposed models include multi-staged stiffness and hysteresis elements as well as spline nonlinearities. Several example cases such as two high (or low) hysteresis clutches in series with a pre-damper are considered. First, detailed multi-degree of freedom nonlinear models are constructed, and their time domain predictions are validated by analogous measurements. Second, key damping sources that affect transient events are identified and appropriate models or parameters are selected or justified. Finally, torque impulses are evaluated using metrics, and their effects on driveline dynamics are quantified. Dynamic interactions between clutch-damper and spline backlash nonlinearities are briefly discussed.

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.

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.

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.

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.

This article studies the effects of tooth surface waviness and sliding friction on the dynamics and radiated structure-borne noise of a spur gear pair. This study is conducted using an improved gear dynamics model while taking into account the sliding frictional contact between meshing teeth. An analytical six-degree-of-freedom (6DOF) linear time varying (LTV) model is developed to predict system responses and bearing forces. The time varying mesh stiffness is calculated using a gear contact mechanics code. A Coulomb friction model is used to calculate the sliding frictional forces. Experimental measurements of partial pressure to acceleration transfer functions are used to calculate the radiated structure-borne noise level. The roles of various time-varying parameters on gear dynamics are analyzed (for a specific example case), and the predictions from the analytical model are compared with prior literature.

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.

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.

A vibration isolator or mount is often modeled by the Voigt model describing uni-axial (longitudinal) motion with frequency-invariant parameters. However, wave effects due to the mass distribution within the isolator are observed as the frequency is increased. Further, flexural stiffness components play an important role, leading to off-axis and coupling effects. Thus, the simplified mount models could lead to erroneous predictions of the dynamic behavior of an overall system such as automotive powertrain or chassis mounting systems. This article compares various approximate isolator models using a multi-dimensional mobility model that is based on the continuous system theory. Harmonic force and moment excitations are separately applied to a rigid body source to investigate the multi-dimensional vibratory behavior. Analysis is however limited to a linear time-invariant system and the mobility synthesis method is utilized to predict the frequency domain behavior.

Structure-borne noise within vehicle structures is often transmitted in a multi-dimensional manner and thus the vibro-acoustic model(s) of automotive powertrain or chassis must incorporate longitudinal and transverse (flexural) motions as well as their couplings. In this article, we employ the continuous system theory to model a typical vibration isolator (say the engine mounting system) and a compliant receiver that could simulate the body structure. The powertrain source is however assumed to be rigid, and both harmonic force and moment excitations are considered. Our analysis is limited to a linear time-invariant system, and the frequency domain based mobility method is utilized to synthesize the overall system. Contributions of both in-plane and flexural motions to structure-borne and radiated noise are incorporated. Two examples are considered to illustrate the methodology.

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.

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.

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.

The automotive NVH research infrastructure at Ohio State includes the Center for Automotive Research, the Acoustics and Dynamics Laboratory, and the Gear Dynamics and Gear Noise Research Laboratory. This paper describes the facilities of these laboratories. Two unique existing facilities, namely the transmission error measurement of gears and a laboratory for the experimental measurement of engine breathing systems, will be emphasized. Also covered are the enhancements that are envisioned through a recent grant from the Ohio Board of Regents.

The sources of gear rattle in automotive transmission and other components are clearance non-linearities, which include backlashes, multi-valued springs, hysteresis, etc. Periodic vibro-impacts are generated because of the single sided or double sided impacts. It is obviously desirable to develop an appropriate computer simulation model which can aid in the control of transient noise and vibration signatures. Such models can also be used to design experiments and to interpret measured data. Several approaches have been attempted in the past, but most common is the digital simulation of the governing differential equations describing the non-linear, torsional dynamics of the drivetrain. Some progress has been made in understanding the basic rattle phenomenon and in developing suitable mathematical models. This article intends to be a status report on the mathematical or computer models including pre- and post-processing considerations.

Performance characteristics of passive, active, and broadband adaptive engine mounts are compared over a wide frequency range up to 250 Hz in the context of a quarter-vehicle heave model. The optimal damping coefficient of a rubber-metal mount is determined using random vibration theory. The small-scale active mount employs proportional-plus-integral control based on linear optimal control theory. The new adaptive hydraulic mount system implements an on-off damping control mode by using engine intake-manifold vacuum and a microprocessor-based solenoid valve controller. Through analytical methods, it is observed that this adaptive mount provides most desirable dynamic performance with regard to the engine-bounce control, shock absorption and vibration isolation performance requirements. Although technical prospects of the proposed adaptive system appear promising, in-situ performance needs to be evaluated.