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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.

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.

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.

This article examines the structure-borne noise transfer path measures by using a laboratory experiment with simulated engine and passenger compartments. It is excited by an emulated powertrain unit that is mounted in the engine room through three hard mounts. Indirect estimation methods for dynamic interfacial forces are first compared with direct measurements over the mid frequency regime. Two alternate path analysis issues, with focus on partial pressures in the receiver room, are then examined. This experimental study clearly demonstrates the strengths and limitations of path rank ordering schemes and analysis methods though only the translational motions are considered.