Frequency domain properties of hydraulic bushing with long and short passages: System identification using theory and experiment

Fluid-filled bushings with tunable stiffness and damping properties are now employed in vehicles to improve ride characteristics and to reduce vibration and noise. Since scientific literature on this topic is sparse, a bushing prototype which can provide various combinations of long and short flow passages is designed and built. Several common fluid-filled bushing configurations are experimentally examined for their dynamic stiffness and pressure spectra. Linear time-invariant models (with lumped fluid elements) are proposed for a hydraulic bushing with two parallel flow passages. Next, a model with only a long capillary tube passage (an inertia track) is examined. Further, peak magnitude and loss angle frequencies are analytically found. Several methods for the identification of bushing parameters (up to 50 Hz) are suggested. The linear models are validated by comparing predictions with measured stiffness magnitude and loss angle spectra. Finally, the principal features of a practical device are diagnosed using analytical models and measurements for two excitation amplitudes.