Fluid handling – Line condition change responsive valves – Pilot or servo controlled
Reexamination Certificate
1997-12-31
2001-07-24
Ferensic, Denise L. (Department: 3753)
Fluid handling
Line condition change responsive valves
Pilot or servo controlled
C137S489000
Reexamination Certificate
active
06263909
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a valve assembly for a hydraulic discharge device and including a piston displaceable in a bore of a housing of the discharge device against a biasing force and having an outer surface, which sealingly engages an inner wall of the housing bore and blocks a channel opening into the bore so that the piston functions as a slide valve for this channel.
The valve assembly of this type are used, e.g., for controlling fluid flow from the discharge device to an actuator. The drawback of the valve assembly of this type consists in that a leakage of pressure fluid between the engageable surfaces of the piston and the bore wall exists. Therefore, the discharge device should always provide an additional amount of fluid flow to compensate for this leakage.
Accordingly, an object of the invention is a valve assembly of the above-mentioned type with improved sealing characteristics, which insure a good control stability of the slide valve.
SUMMARY OF THE INVENTION
This and other objects of the invention, which will become apparent thereafter, are achieved by providing a valve assembly of the above-mentioned type further comprising a valve seat which, together with the piston, form a seated valve, so that the piston functions, on one side, as a slide valve, and on the other side, as a seated valve. Such an arrangement insures the reduction of leakage to a minimum, without adversely affecting the control stability of the valve assembly.
Some of the preferred embodiments of the valve assembly according to the invention is characterized in that the piston, the outer surface of which sealingly engages the inner wall of the housing bore, has an outer edge which cooperates with a sealing surface extending at an angle to the inner wall, the sealing surface providing a valve seat for the piston. This arrangement provides very good sealing characteristics and reduces leakage to a minimum. The sealing surface, which may be, preferably, conical forms, in one of the embodiments of the inventive valve assembly, a part of a sealing ring inserted into the housing bore adjacent to a respective end face of the piston. Providing such a sealing ring results in a rather economical production of the valve assembly. Providing such a sealing ring insures an optimal protection against leakage losses.
In another preferred embodiment of the valve assembly according to the invention, the conical sealing surface forms part of a sealing sleeve received in the housing bore and the interior of which communicates with a pressure space of the housing bore which is supplied by pressure fluid through a channel having its mouth intersecting the bore wall in the region of the pressure space.
In yet another preferred embodiment of the invention, the piston has a conical end region the outer surface of which forms with an edge of an annular valve seat a seated valve arrangement. The conical outer surface can be rather easily obtained during manufacturing of the piston because the piston is a rotationally symmetrical part. According to a more preferred variant of this embodiment, the annular valve seat is formed as an extension of a plug which closes the housing bore and forms a discharge throttle. Here, the valve seat is an integral part of the plug which can be secured in the housing bore by being screwed thereinto.
In another variant of this embodiment, an inner surface of the annular valve seat and the outer surface of the conical end portion of the piston form an annular space. The inner surface of the annular valve seat and the outer surface of the conical end portion of the piston can extend parallel to each other or at an angle to each other. By selecting the arrangement of the inner surface of the annular valve seat relative to the outer conical surface of the piston, it is achieved that, upon opening of the seated valve arrangement, the cross-section of the flow opening can be changed. The changing of the flow opening cross-section permits to further vary the flow characteristics of the valve assembly, in addition to varying them in accordance with path-dependent adjustment of the discharge throttle.
By varying the diameter of either or both of the inner surface of the seat and the outer surface of the conical end portion of the piston, a variable cross-section of the annular space therebetween in an axial direction can be obtained. This permits to control, in a simple and advantageous manner, in accordance with the throttle characteristic of the piston, the flow angle at which the oil flows into a channel leading to the region of lower pressure.
In an especially preferred embodiment, the piston serves as a control slide of a flow control valve, with the slide cooperating with the conical sealing surface. The flow control valve, in this case, is characterized, on one hand, by optimal sealing characteristics in the region of the seated valve arrangement, and on the other side, by good control characteristics of the slide which remain practically unchanged. Specifically, the smooth uniform control, which is provided by a slide valve, remains unchanged.
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Gong Yuejin
Kortge Randolf
Lauth Hans Jürgen
Nguyen Van Doan
Nied-Menninger Thomas
Ferensic Denise L.
Kim Joanne Y.
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