Title:
EXTENDED RANGE VALVE SYSTEM
United States Patent 3825033


Abstract:
A valve system is described including a spool valve in which one face of an outboard land is in engagement with a control fluid which urges the spool in one direction in opposition to a biasing force. The other face of the land is in engagement with a fluid at a pressure much less than the pressure of the control fluid. In order to prevent the leakage of control fluid across the land to the return, the land is formed with several grooves around its cylindrical surface at least one of which is always in communication with a recess formed in the valve housing; this recess is connected to a source of fluid at a pressure substantially equal to that of the control fluid, thereby eliminating the tendency of the control fluid to leak across the land.



Inventors:
HAYNER P
Application Number:
05/331913
Publication Date:
07/23/1974
Filing Date:
02/12/1973
Assignee:
SANDERS ASS INC,US
Primary Class:
Other Classes:
137/625.62, 137/625.64
International Classes:
F15B13/043; (IPC1-7): F16K11/07
Field of Search:
137/625
View Patent Images:
US Patent References:
3583443VALVE WITH HIGHLY SENSITIVE ACTUATING MEANSJune 1971Beckett et al.
3477472SERVOCONTROL VALVE AND SYSTEMNovember 1969Mercier
2897792Servo valvesAugust 1959Baltus et al.
2891517Hydraulic press control systems and pilot operated directional control valve thereforJune 1959Towler et al.
2841168Hydraulic control valve apparatusJuly 1958Levetus et al.



Primary Examiner:
Klinksiek, Henry T.
Attorney, Agent or Firm:
Etlinger, Louis Hunter William L.
Claims:
What is claimed is

1. A valve system for controlling the flow of fluid to a load including a main source of fluid under pressure, a fluid return, a housing formed to define a hollow cylinder, a valve spool within said cylinder including a land one face of which is in communication with a control fluid and the other face of which is in communication with said fluid return, means responsive to an input signal for establishing a control pressure in said control fluid, means for exerting a biasing force on said spool urging it in a direction opposite to that in which it is urged by the pressure of said control fluid said housing and spool being formed to define first and second restricted passageways communicating with said main source and with said control fluid respectively and which open simultaneously to said load upon displacement of said spool from a reference position in response to the pressure of said control fluid, characterized in that said land is formed to define an annular groove extending around its cylindrical surface and in that said housing is formed to define a fluid connection from said groove to a source of fluid at a pressure approximately equal to the pressure of said control fluid, whereby the leakage of control fluid across said land is substantially eliminated.

2. A valve system in accordance with claim 1 in which said fluid connection includes an annular recess formed in said housing and in communication with said annular groove.

3. A valve system in accordance with claim 2 in which said source of fluid connected to said annular recess by said fluid connection is said main source.

4. A valve system in accordance with claim 3 in which said biasing force exerted against said spool comprises a fluid having a pressure approximately equal to the pressure of said main source.

5. A valve system in accordance with claim 4 in which said spool includes first and second outboard lands at opposite ends thereof and in which said land and face in communication with said control fluid is the outer face of said first outboard land and in which said biasing force is exerted against the outer face of said second outboard land.

6. A valve system in accordance with claim 5 in which said spool includes an intermediate land and in which said housing is formed to include a fluid connection between said main source and that face of said intermediate land which is nearer to said first outboard land and in which said housing is also formed to define an intermediate recess cooperating with said intermediate land and in communication with said load to define said first passageway.

7. A valve system in accordance with claim 6 which includes a boss formed on the aforesaid face of said intermediate land and extending to the outer surface thereof and which includes a radial passageway one boundary of which is said face of said intermediate land, said spool also being formed to include an axial passageway providing communication between said radial passageway and said one face of said first outboard land, whereby said axial passageway, said radial passageway and said intermediate recess define said second restricted passageway.

Description:
FIELD OF THE INVENTION

This invention relates generally to valves of the kind in which a valve piston or spool is moveable axially within a hollow cylinder and particularly to such valves in which the spool is positioned by a control fluid in engagement with one of the lands of the spool.

BACKGROUND OF THE INVENTION

Spool valves such as those mentioned above are widely used to control the flow of fluid from a source to a useful load. Typically the spool is formed to define a number of lands which cooperate with annular recesses formed in the cylindrical wall so as to determine the magnitude and sense of the flow of fluid from the source to the load in accordance with the axial position of the spool. The position of the spool may be varied by a control fluid in engagement with one face of one of the lands, such as an outboard land, so as to urge the spool in one direction in opposition to a biasing force such as a spring or another fluid. Many such valves have been built and are now operating satisfactorily. But if, as is frequently the case, the face of the land opposite the control fluid is in engagement with a fluid at a substantially lower pressure, the valve is subject to certain limitations. Control fluid tends to leak across the land, through the space between the land and the interior of the cylinder, to the region of lower pressure. Such leakage tends to reduce the pressure of the control fluid to a value below its intended value thereby degrading the performance of the valve. This situation is more serious at high temperatures because the lower viscosity of the fluid increases the leakage.

The consequences of leakage as above described are especially serious in flow control valves of the kind described in U.S. Pat. No. 3,561,488 granted Feb. 9, 1971 to James Otto Byers and entitled "Fluid Flow Control Valve." In such valves the rate of flow of fluid to the useful load is determined by an input signal and is substantially independent of the back pressure exerted by the load. The input signal establishes a flow of control fluid which is led to the space at one end of the hollow cylinder so as to act on the outside face of the outboard land. The pressure of the control fluid displaces the spool to a position at which the rate of flow of control fluid from the end space through a variable control slot to the useful load is just sufficient to make the pressure of the control fluid equal to that of a biasing pressure which is applied to the opposite outboard land and which is substantially equal in pressure to that of the main fluid supply. At low rates of flow, for example at rates of 5% or less of rated flow, leakage across the land may be a significant portion of the total control fluid flow. It has been found that when the temperature is high and extremely low rates of flow are called for, the leakage alone may be sufficient to reduce the pressure of the control fluid in the end space to the biasing pressure with the result that the flow to the load is completely shut off. The practical result is that the reliable range of operation of the valve is limited to flow rates above those at which the leakage is a significant portion of the rate of flow of control fluid.

It is a general object of the present invention to provide an improved valve.

Another object is to provide a fluid flow control valve having an extended range of reliable operation.

SUMMARY OF THE INVENTION

Briefly stated, the outboard land (or lands) in a valve incorporating the present invention is formed with one or more annular grooves extending completely around the outside. A small annular recess is formed in the body of the valve so as to communicate with one or more grooves regardless of the axial position of the land. This recess is connected to a source of fluid having a pressure substantially equal to that of the control fluid. In the case of a flow control valve of the kind discussed briefly above, the connection may be to the main fluid supply because, at equilibrium, the pressure of the control fluid in the end space is substantially equal to the pressure of the main supply. The result is that leakage of control fluid across the outboard land is substantially eliminated and any leakage from the main supply to the return is of no consequence.

BRIEF DESCRIPTION OF THE DRAWING

The single FIGURE of drawing is a schematic cross section view of a valve system incorporating the present invention.

DESCRIPTION OF PREFERRED EMBODIMENT

Referring now to the drawing, the invention is illustrated as applied to a valve system comprising a four way flow control valve having flow control in both directions of operation and having a flapper first stage, although it is apparent that the invention is also applicable to other valve systems. The valve system illustrated comprises a housing 11 formed to define a hollow cylinder 12. The expression "housing" is intended to include a block, sleeve, end caps, manifolds, etc. Within the hollow cylinder is a spool 13 including first and second outboard lands 14 and 15 respectively and first and second intermediate lands 16 and 17, respectively. Each of these lands is of generally right cylindrical shape and has an outer cylindrical surface making a sliding fit with the interior of the hollow cylinder and includes first and second generally planar faces at opposite ends of the cylindrical surface and perpendicular thereto. The overall length of the spool 13 is substantially less than the length of the hollow cylinder thereby defining end spaces 18 and 19.

The interior of the hollow cylinder 12 between the lands 16 and 17 is connected to a main source 21 of fluid under a pressure designated as P2. The portion of the cylinder between the lands 14 and 16 and also the portion between the lands 15 and 17 is connected to the fluid return, or sump, 22. The housing 11 is formed to define two annular recesses 23 and 24 which, in the neutral position of the valve spool shown in the drawing, are just occluded by the lands 16 and 17, respectively. These annular recesses are connected to two controlled ports designated C1 and C2, respectively, which in turn are connected to a useful load device shown schematically as comprising a hydraulic ram 25.

The right hand face of the land 17, as viewed in the drawing, is formed with a small boss 26 which extends to the outer surface. The boss 26 extends circumferentially for only a small portion of the total circumference, on the order of 30° or so, and is formed to define a radial passageway 27 one boundary of which is the face of the land 17 and which passageway terminates in an opening or slot 28 adjacent to the outer cylindrical surface of the land 17. The central portion of the spool 13 is formed to define an axially extending passageway 29 which connects the radial passageway 27 with the end space 18. The axial passageway 29, the radial passageway 27, and the slot 28 define, along with the recess 24, a restricted passageway which is opened to the load when the spool 13 is displaced to the left of the position shown in the drawing. When the spool is so displaced, the usual restricted passageway extending from the source 21 through the interior of the cylinder 12 and across the edge of the land 27 is opened simultaneously to the recess 24 and the load 25. The land 16 has associated therewith a similar boss 31, radial passageway 32, slot 33, and axial passageway 34 communicating with the end space 19.

The first stage of the valve system, illustrated generally by the reference character 41, includes a source 42 of fluid under a pressure designated P1 which pressure is greater than P2. The source 42 is connected through two restrictors 43 and 44 to nozzles 45 and 46, respectively. Fluid from each nozzle acts on a flapper 47 positioned between them, and the surrounding space is connected to the return. An output conductor 48 is connected intermediate the restrictor 43 and the nozzle 45 and a similar output conductor 49 is connected intermediate the restrictor 44 and the nozzle 46. The position of the flapper 47 relative to the nozzles 45 and 46 is controlled by a force motor 51 which in turn is controlled by an input signal applied to input terminals 52 and 53. The output conduits 48 and 49 are connected by fluid connections including conduits 54 and 55 to the end spaces 18 and 19, respectively. In the absence of an input signal, the flapper 47 will be in the central position shown. There will be a drop in pressure across the restrictor 43 and another drop across the nozzle 45 and these drops will be equal respectively, to the pressure drops across the restrictor 44 and the nozzle 46. In this no signal condition, the pressures in conductors 48 and 49 will be equal to each other and somewhat less than the pressure P1 of the source 42. The relative values of the pressure P2 of the source 21 and the pressure P1 of the source 42 are selected so that the pressure P2 is substantially equal to the pressure in the conduits 48 and 49 at the no signal condition. Various methods can be used to accomplish this end such as employing two separate supplies or by making P1 the main supply and obtaining P2 through a pressure reducer or, alternatively, making the pressure P2 that of the main source and employing a pressure booster to obtain the pressure P1. These details are not germane to the present invention, it being sufficient if the pressure P2 is made to be substantially equal to the pressure in the conduits 48 and 49 at the no signal condition.

The device so far described is conventional. In the absence of an input signal, the pressures in conduits 54 and 55 are equal. The spool 13 becomes stabilized in the neutral position shown with the recesses 23 and 24 completely occluded by the lands 16 and 17 and with the slots 28 and 33 blocked by the interior surface of the cylinder 12 so that there is no flow of fluid to the load. Let us assume that an input signal is applied in such a sense as to initially displace the flapper 47 to the right thereby increasing the pressure in the conduits 48 and 54. The fluid in these conduits and in the end space 18 is regarded as the control fluid and the pressure thereof tends to urge the spool 13 to the left. At the same time, the fluid in the conduits 49 and 55 and in the end space 19 undergoes a decrease in pressure and the force exerted by this fluid against the land 15 is regarded as the biasing force. As the pressure in the end space 18 increases, the spool 13 is displaced to the left and control fluid flows through the restricted passageway comprising the axial passageway 29, the radial passageway 27 and the slot 28 to the recess 24 and to the load. This flow increases the pressure drop across the restrictor 43 and also causes a pressure drop to appear across the now partially opened slot 28. The spool 13 is displaced until flow through the slot 28 is sufficient to reduce the pressure in the end space 18 to equal that in the end space 19. This pressure is very nearly equal to P2. At the same time a much larger quantity of fluid flows from the source 21 across the land 27 and into the recess 24 and to the load 25. Since the pressure drop across the land 17 is substantially the same as that across the slot 28, total flow of fluid is proportionally to the flow of control fluid and is independent of the back pressure exerted by the load.

The above discussion assumes that there is no leakage of control fluid from the end space 18 across the land 14 to the return. As far as Applicant is aware, all of the prior art valves have been subject to such a leakage. As a result, some of the control fluid is bled off and causes a pressure drop across the land 14 which reduces the pressure in the end space 18 independently of the flow through the slot 28. As previously mentioned, this condition is especially severe at high temperatures, when the viscosity of the fluid is less, and also more severe when the input signal calls for a very low rate of flow. In such situations, the leakage across the land 14 may be a significant portion of the total flow of control fluid.

The present invention overcomes this difficulty by forming the outboard land 14 with one or more annular grooves 61 extending completely around the outside cylindrical surface of the land. The land 15 is formed with similar grooves 62. The housing 11 is formed to define annular recesses 63 and 64 adjacent to the lands 14 and 15 respectively and of sufficient axial length so that each recess is in communication with one or more of its associated grooves at all times regardless of the axial position of the spool 13. The housing 11 also includes fluid passageways 65, 66 and 67 from the recesses 63 and 64 to the main supply 21. The pressure P2 of the main supply 21 is substantially equal to that in the end spaces 18 and 19 and accordingly there is no tendency for fluid to flow from either of the end spaces 18 or 19 to the corresponding recess 63 or 64 nor is there any tendency for fluid to flow in the reverse direction. Any fluid which flows from either of the recesses 63 or 64 to the return is of no consequence because such flow does not affect the position of the spool 13 and because the quantity is small indeed compared to the capacity of the source 21.

The invention has been illustrated as applied to widely used kind of valve system including a main stage having a four way valve with flow control slots operable in both directions of operation and including a flapper first stage. It is apparent that the invention is also applicable to valve systems with or without the flow control feature in either direction by means of the restricted passageway, as illustrated, and to valves in which flow control is provided in but one direction and is also applicable to systems in which the control fluid and biasing forces are obtained from other sources, such as pumps and springs, provided the valve has a land across which control fluid tends to leak. However, it is believed that the present invention will find its widest application to valves having the flow control feature.

Although a specific embodiment to the invention has been described in considerable detail for illustrative purposes, many modifications will occur to those skilled in the art. It is therefore desired that the protection afforded by Letters Patent be limited only by the true scope of the appended claims.