Fluid handling – Line condition change responsive valves – With separate connected fluid reactor surface
Reexamination Certificate
2000-02-11
2001-04-24
Hepperle, Stephen M. (Department: 3753)
Fluid handling
Line condition change responsive valves
With separate connected fluid reactor surface
C184S007300, C251S117000
Reexamination Certificate
active
06220281
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field Of The Invention
The invention pertains to a regulator for regulating a medium flow that is supplied to at least one static fluid (e.g., hydrostatic or aerostatic) pocket of a bearing, a nut for threaded spindles or a guidance arrangement.
2. Description Of The Related Art
Regulators of this type for regulating fluid flows are known (DE 3,533,037 C1). In this case, the fluid flow that is influenced by the regulator increases if the pressure in the hydrostatic pocket increases. In hydrostatic bearings, nuts for threaded spindles or guidances which cooperate with regulators of the above-mentioned type, the attainable stiffness and stress of these elements is significantly higher than in alternative systems under comparable technical circumstances. The flow-through quantity Q is proportional to the third power of the gap height or the height h of the gap of the pocket, through which the medium flows. With laminar flow, the condition Q~p×h
3
/&eegr; applies, where &eegr; refers to the dynamic viscosity of the medium or the fluid. This applies similarly to gaseous media. The previously described relation indicates that a change in the height h due to a pressure change in the hydrostatic pocket caused by an increase in the fluid flow or the flow-through quantity Q can be reduced or practically eliminated. Consequently, if a hydrostatic pocket is stressed such that the pressure in this hydrostatic pocket is increased, a change in the gap height and consequently a displacement of the guided or supported parts can be counteracted by increasing the fluid flow that flows into the hydrostatic pocket via the regulator. This results in increased stiffness.
It was determined that known regulators with a variable second flow resistance, e.g., a throttle, that comprises a control element tend to extremely disturbing vibrations under certain operating conditions, in particular, at relatively large fluid flow quantities, fluids with a low viscosity, as they are primarily required for rapidly revolving bearings, as well as at relatively low pressures in the corresponding hydrostatic pocket.
The present invention is based on the objective of developing a regulator for liquid as well as gaseous media which eliminates this disadvantage.
According to the invention, this objective is attained with a regulator that is realized in accordance with the characteristics which include a bypass that is connected to the hydrostatic or aerostatic pocket which is simply referred to as the pocket below, and to the medium supply that supplies the pocket via the regulator by means of a first flow resistance.
The bypass is provided with a third flow resistance. This means that the pocket is supplied with two medium flows, namely a first partial flow that is influenced by a control element of the regulator which acts as a variable second flow resistance, and a second partial flow that is conveyed via the bypass. The second medium flow that flows through the bypass reduces the first medium flow that flows through the variable second flow resistance to a fraction of the value that can be attained without a bypass, in particular, at low pressures in the hydrostatic or aerostatic pocket and at the regulator output. Due to this measure, the relative changes of the partial medium flow caused by the variable sectioned flow resistance are significantly increased during a change of the medium flow caused by the regulator due to different pressures in the hydrostatic or aerostatic pocket, in particular, at low pressures in the hydrostatic or aerostatic pocket. Due to the previously described mathematical correlation which at least approximately applies also to the control element that acts as the variable second flow resistance, the control element carries out greater control movements and consequently affects the medium flow less strongly. Due to the bypass, the control element carries out greater control movements—in particular, at low pressures in the hydrostatic or aerostatic pocket—such that the first partial flow that flows to the pocket is not influenced as directly, i.e., the tendency to vibrate is reduced.
Another embodiment of the regulator has a third flow resistance which is arranged in the bypass and which is designed for or adjusted to a medium flow that approximately corresponds to the medium flow that flows through the regulator if the pressure at the regulator output is equal to zero. Thus, the flow through the variable second flow resistance of the regulator—at the regulator output pressure in this operating mode—also becomes equal to zero or at least very low. In this embodiment, the bypass increases, in particular, the control movements of the control element that acts as the variable second flow resistance within the range of low pressures in the hydrostatic or aerostatic pocket which is particularly susceptible to vibrations, i.e., the tendency of the regulator to vibrate is reduced.
In order to attain other desirable objectives, a regulator is proposed for regulating liquid media. This regulator comprises three pressure chambers that are separated by the control element, wherein a first pressure chamber is connected to a gas volume. The control element is charged with the pressure of the medium supply, with a second pressure that acts in the second pressure chamber via the first flow resistance as well as a third pressure that acts in the third pressure chamber via the variable second flow resistance. Due to the connection between the first pressure chamber and a gas volume, pressure pulsations in the connecting line from the pump to the regulator act, if at all, upon the first pressure chamber only minimally. Due to the compressibility of the gas volume during dynamic pressure changes, the control element is, in particular, able to dynamically yield in the second as well as the first pressure chamber. This measure also reduces the tendency of the regulator to vibrate.
Another embodiment of the regulator is disclosed for use with liquid media. In this case, the gas volume in the first pressure chamber is situated directly adjacent to the control element or only separated from the control element by an elastic sealing element, wherein the gas volume is connected to an additional gas chamber that, for example, is situated on the gas side of a hydraulic accumulator, the fluid side of which is directly connected to the pump that supplies the hydrostatic pocket.
When the pump is switched on, the gas volume in the first pressure chamber and in the additional gas chamber is compressed to the pump pressure. When the pump is switched off, the gas volume in the first pressure chamber and in the additional gas chamber is adjusted to a pressure that lies slightly below the pump pressure, which reduces the heating of the gas which occurs during the compression of the gas when the pump is switched on. A direct connection between the pump and the first pressure chamber is not required in this embodiment of the regulator.
Since the gas volume can be compressed, the control element can easily move in the direction of the gas volume in the first pressure chamber during a pressure shock in the pocket and thus increase the fluid flow to the pocket. Due to the increased mobility, larger control movements are attained, i.e., problems caused by vibrations are prevented.
The aforementioned objective is also attained with a regulator having a first pressure chamber which is filled with a fluid and connected to the medium supply that supplies the hydrostatic pocket via a fourth flow resistance, where the first pressure chamber is so large that the fluid contained therein dampens vibrations of the control element due to its compressibility. Due to this compressibility of the fluid in the first pressure chamber and the fourth flow resistance, vibrations in the first pressure chamber caused by vibrations in the medium supply are at least reduced. In addition, the control element is able to yield dynamically in the second pressure chamber and the first pressure chamber during dynamic pressu
Fitch Even Tabin & Flannery
Hepperle Stephen M.
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