Investigation of Squeeze Film Damping and Associated Loads

Digital hydraulics have attracted attention towards fast switching valves and the increased focus on reliable fluid power entail that the lifetime of such valves is of great concern. An inherent feature of most valves for digital hydraulics is that of a mechanical end stop. Consequently, the squeeze film damping associated with end stops of switching valves is an interesting topic. This damping effect is perceived as beneficial for high lifetime and low impact sound, as the consequence of lowering the impact velocity at the mechanical end stops. In this paper the squeeze film damping effect is reviewed with a focus on maximum surface stresses. Using the Barus relation for viscosity-pressure dependency and different film geometries, the classical lubrication theory is applied together with the equation of motion, to obtain the gap height motion equation, both for the iso-viscous and piezo-viscous case. In consequence, this enable insights concerning the influence of piezo-viscosity on this damping effect. These models are used to investigate the loads, which the approaching surfaces experiences. Based on Hertzian theory, comparisons of impact loads and the dynamic squeeze loading are performed, whereby the relation between design parameters and the relative severity of these occurrences are analyzed.