Passive hydraulic engine mounts are commonly employed for motion control and vibration isolation in vehicle powertrain systems. Such devices are often tuned in terms of their low frequency resonance and damping ratio (say corresponding to the engine bounce mode) to control noise and vibration and improve the ride comfort, quality, and safety of the vehicle. Mount tuning concepts with one inertia track and one decoupler using the track length or diameter are well understood, but the dynamic response with multiple tracks, orifices, or decouplers is not. To overcome this void in the literature, dynamic tuning concepts of hydraulic engine mounts, with emphasis on multiple (n-) inertia tracks, fixed decoupler-type designs, are analytically and experimentally examined in this thesis.
Since a wide variety of n-inertia track configurations is possible, dynamic stiffness models are developed to explain a family of such configurations, based on linear time-invariant lumped fluid system theory. Furthermore, a new n-track prototype mount concept is designed, built, and tested in a controlled manner, with the capability of varying the type (capillary tube, orifice) and number (n) of inertia tracks, in addition to length and diameter of each. This prototype is used to examine several designs with alternate n-track configurations for improving performance compared to the n = 1 track case. Three narrowband devices are designed and tested to refine existing theory for predicting peak frequency of loss angle, in addition to examining and validating an n = 3 track mount for the first time. Two broadband devices are designed and tested successfully by tuning damping ratios of the mount with orifice-type tracks for the first time. Several n-track mount designs with orifice-type tracks are also proposed, which successfully describe a special broad-tuned design utilizing a controlled ‘leakage’ path flow area for the first time. Lastly, a quasi-linear dynamic stiffness model is developed to study excitation amplitude- and frequency-dependent behavior of equivalent inertia track resistance, which should lead to nonlinear models of n-track devices and improved adaptive or active mounts in future studies. Chief contributions of this work include experimentally validated extensions of prior lumped parameter, linear time-invariant dynamic stiffness models, which are now applicable to predictions for narrow-tuned and/or broad-tuned mounting devices with n greater than or equal to 2.