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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.

The engine start-up process introduces speed-dependent transient vibration problems in ground vehicle drivelines as the torsional system passes through the critical speeds during the acceleration process. Accordingly, a numerical study is proposed to gain more insights about this transient vibration issue, and the focus is on nonlinear analysis. First, a new nonlinear model of a multi-staged clutch damper is developed and validated by a transient experiment. Second, a simplified nonlinear torsional oscillator model with the multi-staged clutch damper, representing the low frequency dynamics of a typical vehicle driveline, is developed. The flywheel velocity measured during the typical engine start-up process is utilized as an excitation. The envelope function of the speed-dependent response amplification is estimated via the Hilbert transform technique. Finally, the envelope function is effectively utilized to examine the effect of multi-staged clutch damper properties.

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.

The transient vibration phenomenon in a vehicle powertrain system during the start-up (or shut-down) process is studied with focus on the development and experimental validation of the nonlinear powertrain models. First, a new nonlinear four-degree-of-freedom torsional powertrain model for this transient event, under instantaneous flywheel motion input, is developed and then validated with a vehicle start-up experiment. Second, the interactions between the clutch damper and the transmission transients are established via transient metrics. Third, a single-degree-of-freedom nonlinear model, focusing on the multi-staged clutch damper, is developed and its utility is then verified.

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.

Combined active and passive damping is a recent trend that can be an effective solution to challenging NVH problems, especially for lightweight vehicle components that demand advanced noise and vibration treatments. Compact patches are of particular interest due to their small size and cost, however, improved modeling techniques are needed at the design stage for such methods. This paper presents a refined modeling procedure for side-by-side active and passive damping patches applied to thin, plate-like, powertrain casing structures. As an example, a plate with fixed boundaries is modeled as this is representative of real-life transmission covers which often require damping treatments. The proposed model is then utilized to examine several cases of active and passive patch location, and vibration reduction is determined in terms of insertion loss for each case.

Several mounting system design concepts have been conceptually used to decouple the engine roll mode though limited success is observed in practice. One shortcoming of the existing theories is that they ignore damping in their formulations. To overcome this deficiency, we re-formulate the problem for a non-proportionally damped, linear system while recognizing that significant damping may be possible with passive (such as hydraulic), adaptive or active mounts. Only rigid body modes of power train are considered and chassis is assumed to be rigid. Complex mode method is employed and the torque roll axis (TRA) paradigms are re-examined in terms of mount rate ratios, mount locations and orientation angles. We will show that true TRA decoupling is not possible with non-proportional damping though it is theoretically achieved for a proportionally damped system.

Competing linear, quasi-linear and non-linear hydraulic mount formulations of fixed and free decoupler types are comparatively evaluated for transient responses. First, features of the realistic excitation conditions are addressed. For instance, the mean load itself may vary with time, and several sinusoidal or transient excitations may be simultaneously present. Second, a multi-staged top chamber compliance model is proposed to capture asymmetric transient responses given step-up (-down) excitations. Third, implicit excitations introduced by the decoupler switching mechanism are identified at the odd harmonics of the explicit excitation frequency. Fourth, discontinuous model of bottom chamber compliance is proposed depending on the operating point(s) and/or dynamic loading. Some of the discrepancies observed between prior models and measurements can be explained using new models.

This paper comparatively evaluates measurement-based quasi-linear and true non-linear (mechanical and fluid type) models of hydraulic engine mounts and examines their dynamic effects within the context of a simplified half-vehicle system. A non-linear approximate model is also developed to provide improved insight into the decoupling effects. The proposed model is validated by comparing predictions with those from a “true” non-linear fluid model. When embedded into the vehicle system, hydraulic mount efficiently provides high amplitude-sensitive damping and tunes the engine bounce mode. Proposed model concepts could be effectively utilized to examine linear and non-linear vehicle responses in both time and frequency domains.

Decoupler nonlinearities of the automotive hydraulic engine mount affect its isolation performance and the transmission of structure-borne noise. The kinematic gap nonlinearity of the decoupler is examined in considerable detail in the context of the quarter car model. It is shown that while modeling it with a “softened” nonlinear expression may only moderately affect predicted system behavior at the excitation frequency, it can significantly after it at higher harmonics, changing the predicted level of structure-borne noise transmission. Studies of multi-harmonic motion and vibratory power transmission under sinusoidal and composite excitation conditions confirm that, in fact, use of a decoupler with a “softened” nonlinearity improves performance.

Lower carbon to Hydrogen ratio of CNG makes it a cleaner fuel, due to this CNG is gaining popularity as an Internal Combustion (IC) engine fuel in transport sector. Hydrogen fuel for IC engines is also being considered as a future fuel due to its simple carbonless structure. But several obstacles have to overcome before commercialization of H2 as an IC engine fuel for transport sector. Hydrogen & CNG blends may be considered as an automotive fuel without any major modification in the existing SI engines. The Present work is undertaken to demonstrate the viability of HCNG as an automotive fuel. A passenger car fitted with a 4 cylinder, 1.3 liter, SI engine has been used in the present investigation. A sequential gas injection system has been developed to avoid the risk of back firing. The effect of gas pressure and gas temperature on the duration gas injection has been considered in the control strategy.

Many automotive components and sub-systems require viscoelastic damping treatments to control noise and vibration characteristics. To aid the dynamic design process, new approaches are needed for modeling of partial damping treatments and characterization of the overall dynamic behavior. The analytical component of the design process is illustrated via the transmission casing cover, along with supporting experiments. First, the vibration response of production casing plates is examined, with and without the constrained layer treatment. A modified flat plate is employed along with a generic housing that provides the realistic boundary conditions for subsequent work. A simplified analytical damping model for constrained viscoelastic layer damping is suggested based on assumed modal functions. Using the analytical model, design guidelines in terms of optimal patch shapes and locations are suggested.

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.

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.

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.

A new semi-analytical framework for the study of passive or active engine mounting systems is presented. It recognizes that most practical problems incorporate a nonlinear mount or isolation element and the resulting physical system, consisting of the engine, mount and flexible base, involves many degrees of freedom. Unlike linear systems, sinusoidal excitation produces a periodic response, including super- and sub- harmonics. Two example case systems are employed to illustrate key concepts of the framework. The first numerical example case involves a passive hydraulic engine mount with an inertia track. The second example case is a novel experimental system that has been developed to study active and passive, nonlinear mounting problems. New analytical and experimental results are presented and various nonlinear phenomena are considered. The impact of nonlinearity on vibratory power transmission and active control is also investigated.

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 chief objective of this paper is to study the non-linear behavior of torque converter clutch within the context of an automotive drivetrain. An analytical procedure to determine the pure stick to stick-slip motions is developed based on the linear system analysis. This procedure can efficiently and accurately identify the frequency ranges where linear or non-linear studies are needed. Stick-slip behavior can be clearly observed as a result of the engine torque irregularity and nonlinear friction characteristics. In particular, the effect of the friction disc inertia is studied. Both analytical and numerical results show that this inertia significantly affects the system dynamics. Our predictions compare well with prior measurements on a passive vibration absorber experiment.

New procedures are proposed to estimate the amplitude-sensitive parameters of hydraulic engine mounts that typically exhibit many nonlinearities. The estimation is based on the premise that the analyst has access to limited dynamic stiffness test data (say up to 50 Hz), and the detailed laboratory work required for the nonlinear model development would be minimized. By using an analogous mechanical model, a 3rd/2nd type transfer function is suggested to curve-fit the empirical dynamic stiffness data. Key parameters (such as the inertia-augmented fluid damping and decoupler gap length) are approximated and the effects of some system nonlinearities (such as the vacuum-induced asymmetric chamber compliance) are quantified, leading to a quasi-linear model. For the sake of illustration, transient predictions for a free decoupler mount are made; simulations match well with measurements. Main simplifications and limitations of the method are briefly discussed.

A reduced model is developed for transient analysis of gear rattle in an automatic transmission (AT) powertrain. Linear modal analysis for the reduced order model compares well with a detailed model that includes planetary gear dynamics. Clearance type lash functions are used for the reduced geared coordinates of the automatic transmission and final drive. Impacts within the gear pairs are affected by the engine surging, shaft stiffness, component inertias, engine harmonics, drag torques, braking, viscous damping and vehicle load. The occurrence of these impacts, or clunk, from shuffle and axle oscillations is demonstrated under typical driving conditions.