Experimental dynamic flow characterization of hydraulic bushings

The dynamic properties of hydraulic bushings are often modeled in the time and frequency domains with low-order, lumped-parameter models, typically assuming steady, developed flow in their fluid passages, whereas in situ flow conditions are unlikely to meet such criteria. Hydraulic bushings exhibit tuned properties emerging from nonlinear interactions involving these flow characteristics, so higher resolution descriptions of the underlying physics are needed under realistic flow conditions. This paper discusses an approach to isolate the fluid passage features in production bushings to enable experimental characterization for steady, oscillatory, and transient flow. More robust models of dynamic responses in the time and frequency domains are expected to result from this more precise determination of each flow path's contribution to the nonlinear system response. An apparatus capable of generating steady and dynamic flow is proposed, and some validation data is given to demonstrate the functionality of the experiment. Some challenges with the approach are considered, including the system's hydraulic compliance and cavitation. The flow testing apparatus is used on an example two-passage production bushing adapted for controlled steady or dynamic flow through one or both flow paths. Finally, some nonlinear flow properties of a typical hydraulic bushing's flow passages are given.