WO1980001940A1

WO1980001940A1 - Balanced spool valve

Info

Publication number: WO1980001940A1
Application number: PCT/US1979/000132
Authority: WO
Original assignee: Mcwilliams O
Priority date: 1979-03-05
Filing date: 1979-03-05
Publication date: 1980-09-18

Abstract

A spool valve (10) has a spool (12 or 112) provided with a relatively narrow land (14 or 114) at a pump to tank valve passage (36-27-26-28-35-34), and longitudinal metering slots (14a & 14b or l14a & 114b) in the land (14 or 114) surface. Pressure across the spool (12 or 112) is balanced by a plurality of shallow recesses (46 or 146) which are evenly circumferentially distributed about the land (14 or 114) surface in spaced relationship to any of the metering slots (14a & 14b or 114a & 114b) and intersecting bores (47 or 147a & 147b) in the land (14 or 114) which provide communication between all the recesses (46 or 146).

Description

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Description

BALANCED SPOOL VALVE

Technical Field

This invention relates to a spool valve which ^• requires balancing of pressure across the spool at a pump to tank valve passage where the spool has a rela¬ tively narrow land provided with longitudinal metering slots in the land surface.

Background Art Many spool valves have a direct pump to tank passage which is fully open when the hydraulic equipment controlled by the valve is idle. When the valve spool is shifted to connect the pump for pressurizing the equipment, a land of the spool valve must close to shut off the pump to tank connection. To eliminate the shock of substantially instantaneous closing of the pump to tank connection, such a land commonly is pro¬ vided with longitudinal metering slots through which liquid flow from the pump to the tank continues on a gradually diminishing basis^* as the valve spool moves to the position that it occupies during full pressuriza- tion of the controlled hydraulic equipment.

The progressive closing of the metering slot results in a steady increase in the velocity of fluid passing through the slots, and^' in some cases this velocity becomes high enough to sweep the hydraulic fluid film from between the surface of the land and the surface of the valve casing bore into which the land moves as it closes the pump to tank passage. < This phenomenon, coupled with the fact that the valve casing bore and the valve spool land are rarely perfectly finished and concentric results in irregular metal to metal contact between the land and - 2 -

the valve bore; and this can produce sticking and valve malfunction when the time comes to return the valve to its original position. Commonly the problem is obviated by providing the land with circumferential grooves which permit pressure to equalize around it, as illustrated in U.S. patents 3,735,780 and 3,857,404.

However, as shown by U.S. patent 3,759,292, some spool valves have a^* narrow land a*t the pump to tank pas¬ sage which must be provided with longitudinal metering slots formed in the land surface. In such a situation, circumferential grooves cannot be used for balancing the pressure across the valve because such grooves would intersect the metering slots.

Disclosure of Invention The present invention is directed to over¬ coming the problems as set forth above.

A spool valve has a spool provided with a rela¬ tively narrow land at a pump to tank valve passage, arid longitudinal metering slots in the land surface. Pres- sure across the spool is balanced by a plurality of shallow recesses which are evenly circumferentially distributed about the land surface in spaced relation¬ ship to any of the metering slots, and intersecting bores^* in the land which provide communication between all the recesses.

A valve spool which has a solid body may be provided with a simple set of radial bores which intersect on the longitudinal axis of the spool.

A spool which has an axial center bore requires a system of balancing bores which extend into the land from each recess along chords of the circle defined by a transverse cross section of the land, with bores extending into the land from adjacent recesses inter-

_* secting to provide continuous communication between all the recesses. - -

Brief Description of Drawings

Fig. 1 is a longitudinal central sectional view of a spool valve which has a spool embodying the invention, with a hydraulic circuit utilizing the valve illustrated diagrammatically;

Fig. 2 is a fragmentary sectional view on an enlarged scale illustrating a spool valve embodying a first form of the invention with the valve land in closed position; Fig. 3 is a transverse sectional view taken substantially as indicated along the line III-I I of Fig. 2 and illustrating only the land; and

Fig. 4 is an end elevational view, partly in section, of a valve spool land embodying a second form of the invention.

Best Mode for Carrying Out the Invention

Referring to Fig. 1, a spool valve, indicated generally at 10, has a casing, indicated generally at 11, and a valve spool, indicated generally at 12. The spool has a stem 13 with spaced lands 14, 15, 16 and 17, and end lands 18 and 19, all of which make smooth sliding fits in a bore 20 which extends from end to end of the casing 11. A spring housing 21 has a spring 22 between sliding guide plates 22a and 22b so that the valve spool 12 has a normal position as illustrated in

Fig. 1. A valve head 23 in a valve control fluid cavity 24, and the end land 19 in a control fluid cavity 25 are selectively subjected to fluid under pressure from respective ports 24a and 25a for the purpose of shifting the valve spool 12 both ways from the position illus¬ trated in Fig. 1.

The valve casing 11 has a series of enlarged cavities 26, 27, 28, 29, 30, 31, 32 and 33, which com¬ municate, variously, with fluid passages 34, 35, 36, 37, 38, 39 and 40 which provide for communication bet iween one another and through the valve to various components - 4 -

of a hydraulic circuit the operation of which is con¬ trolled by the valve 10.

The valve controls operation of a two-way hydraulic cylinder C which is supplied with hydraulic fluid from a sump S by a pump P. In the illustrated position of the valve 10, the spool land 16 blocks communication between the pump and the head end of the cylinder, while the land 17 blocks communication between the pump and the rod end of the cylinder. Fluid from the sump is pumped through the conduit 41, the valve ^•passages 38 and 36, the valve cavity 27, around the portion of the valve stem 13 between the lands 14 and 18, and back to the sump through the valve passage 34 and the conduit 42. When pilot pressure is admitted through the port 24a to shift the valve spool 12 to the left, fluid from the conduit 41 flows through the chamber 31, into the chamber 30, through the valve passage 37 and a con¬ duit 43 to the head end of the cylinder C, while fluid from the rod end passes through a conduit 44, the passage- 39, the valve chamber 32, metering slots 17a in the land 17, the valve chamber 33, the valve passage 40 and a conduit 45 back to the sump.

When pilot fluid is admitted through the port 25a to shift the valve spool 12 to the right, fluid from the pump P which enters the valve cavity 31 passes around the rod into the valve cavity 32 and through the passage 39 and conduit 44 to the rod end of the cylinder, while fluid from the head end of the cylinder is forced out through the conduit 43, the valve passage 37, the chamber 30, metering slots 16a in the land 16, the valve passage 35 and the valve chamber 26 so as to return to the sump through the valve passage 34 and the conduit 42. Pressure for the pilot circuit is provided by a pump PI, and the flow of fluid from the pump PI. to the two ends of the valve 10 is controlled by a manual, pilot valve V.

The land 14, which contains the particular structure of the present invention, is best seen in Figs. 2 and 3 to be provided with metering slots 14a which are directed toward the valve cavity 26 and meter¬ ing slots 14b which are directed toward the valve cavity 28. Accordingly, as the valve is shifted to the left to admit fluid to the head end of the cylinder C, the direct flow of fluid from, the pump P to the sump S through the passages 36 and 34 is cut off by the land 14, and the metering slots 14a cause the cutoff of fluid flow to occur gradually so it is only completely stopped as the right end of the metering slots 14a pass the left-hand margin of the valve cavity 27. During this motion, of course, the land 15 also blocks communication between the passage 36 and the passage 35 through the valve cavity 28. When the valve spool 12 moves to the right from the positon of Fig. 1 to admit fluid to the rod end of the cylinder C, the metering slots 14b cause cutoff of fluid from the passage 36 through the passage 35 to occur gradually as the land 14 moves into the bore 20 between the cavities 27 and 28.

During the above described movement of the land 14 in either direction the gradual closing of fluid flow through the metering slots 14a or 14b causes a progressive acceleration of the fluid passing through the metering slots which tends to sweep away the oil film that normally remains between the surface of the land 14 and the surface of the bore 20, thus leaving a possibility for inadequately lubricated metal to metal contact. Because the bore surfaces and the land sur¬ faces are never completely smooth and completely con¬ centric, the above described loss of lubricant usually occurs differentially about the perimeter of the spool 14 which results in a substantial likelihood that ithe valve spool 12 may stick when the' spring 22 is

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to return it to its normal position. The specific improvement of the present invention eliminates this problem.

As seen in Fig. 3, the valve spool 14 is pro- vided with a plurality of shallow recesses 46 which are evenly circumferentially distributed about the surface of the land 14 and which are also spaced from any of the metering slots 14a and 14b. Extending into the land from each of the recesses 46 is a bore 47 which, in the embodiment of Figs. 2 and 3, extends along a radius of the land; and the four bores 47 meet on the longitudinal axis A of the spool. Hydraulic fluid under pressure is thus equally distributed ..at the four shallow recesses 46, and this pressure is maintained as the spool 14 gradually closes into the bore 20 eithe to the left or to the right as seen in Fig. 1. This creates a balanced pressure condition which tends to keep the spool centered in the bore so as to ameliorate or eliminate the problem of spool sticking heretofore described.

Referring now to the second embodiment of the invention illustrated in Fig. 4, a valve spool, indi¬ cated generally at 112, includes a.stem 113.and a land 114; and there is a longitudinal bore 113a in the valve stem. A spool with such a longitudinal bore may be utilized, for example, in a spool valve which applies a signal pressure from one end, such as the end 24, through the axial bore 113a to a signal port.in the valve spool 18 which moves in and out of registry with a signal passage in the head of the valve casing. Such a valve construction is conventional and is what gives rise to the need for the second embodiment of the inven¬ tion illustrated in Fig. -4. The land 114 is provided with metering slots 114a and 114b, and also with evenly circumferentially distributed shallow recesses 146, all as in the first embodiment of the invention.. Because - 7 -

radial bores, such as the bores 47 of Fig. 3, would intersect the bore 113a on the axis of the spool 112, each of the recesses 146 has two bores 147a and 147b extending into the land 114 at an acute angle to one another and along identical chords of the circle defined by a transverse cross section of the land. A bore 147a from one recess 146 and a bore 147b from the next adjacent recess 146 intersect one another along a radius of the land which bisects radii through the center of the two adjacent recesses 146, so there is continuous communication between all of said recesses. This arrangement of intersecting bores 147a and 147b, together with the evenly circumferentially distributed recesses 146, provides a balanced condition of the valve spool 112.

Industrial Applicability

The structure of the present invention may be used wherever there is a spool valve having a relatively narrow land in a pump to tank passage where there are metering slots occupying enough of the land surface that circumferential pressure equalizing grooves cannot be used because they would intersect the metering slots. Such valves are very commonly used in hydraulic circuits of the type illustrated in Fig. 1 of the drawings; and may, of course, be used in numerous applications other than the pressurizing of a two-way hydraulic cylinder.

The valve need not be of the precise type here shown, which is spring-centered and moved in both direc¬ tions by pilot pressure; but it has little applicability except in valves which are to be used in a circuit where there is direct pump to tank communication which must be gradually closed as a spool valve moves to permit application of fluid pressure to some part of a hydraulic system. 8 -

Other aspects, objects and advantages of this invention can be obtained from a study of the drawings, the disclosure and the appended claims. The foregoing detailed description has been given for clearness of understanding only and no unnecessary limitations should be understood therefrom as modifications will be obvious to those skilled in the art.

Claims

- 9 -Claims

1. In a valve (10) of a type which has a cylindrical valve casing (11) with fluid passages (34-40). therein, and a spool member (12 or 112) which is axially slidable in said valve casing (11) and has

5 a relatively narrow land (14 or 114) at a pump to tank^' valve passage (36-27-26-28-35-34) with longitudinal metering slots (14a & 14b or 114a & 114b) in the surface of the land (14 or 114) , the improvement comprising:

10 a plurality of shallow recesses (46 or 146) which are evenly circumferentially distributed about the land surface and spaced from any of said metering slots (14a & 14b or 114a & 114b); and intersecting bores (47 or 147a & 147b)

15 in said land (14 or 114) providing communication between all of said recesses (46 or 146) .

2. The improvement of claim 1 in which there are four recesses (46 or 146) in the surface of the land (14 or 114).

20 3. The improvement of claim 2 in which there are four radial bores (47) which meet on the longitu¬ dinal axis (A) of the spool (12) .

4. The improvement of claim 2 in which the spool member (112) has an axial passage (113a) , a first

25 bore (147a or 147b) extends into the land (114) from each recess (146) along a chord of the circle defined by a transverse cross section of the land (114) and a second bore (147a or 147b) which extends into the land (114) along a different chord of said circle intersects

30 said first bore (114a or 114b) , whereby there is con¬ tinuous communication between all of said recesses (146) . .10 -

5*. The improvement of claim 4 in which there are two bores (147a & 147b) extending into the land (114) from each recess (146) at an acute angle to one another and along identical chords of the circle defined by a transverse cross section of the land (114) , two of the bores (147a & 147b) from each two circumfer¬ entially adjacent recesses (146) intersecting one another along a radius of the land which bisects radii through the center of said two recesses (146) .

6. The improvement of claim 1 in which there are more than two recesses (46) in the land surface, and bores (47) extending radially into the land from said recesses intersect on thelongitudinal axis (A) of the spool (12) .

7. The improvement, of claim 1 in which the

• spool (112) has an axial passage (113a) , there are more than two recesses (146) in the surface of the land, and a bore (147a or 147b) which extends into the land (114) from each recess (146) along a chord of the circle defined by a transverse cross section of the land (114) intersects a bore (147a or 147b) which extends into the land (114) from the next adjacent recess (146) along a different chord of said circle, whereby there is continuous communication between all of said recesses (146).

8. The improvement of claim 7 in which there are two bores (147a _ 147b) extending into the land (114) from each recess (146) at an acute angle to one another and along identical chords of the circle defined by a transverse cross section of the land (114) , two of the bores (147a & 147b) from each two circumferentially adjacent recesses (146) intersecting one another along a radius of the land which bisects radii through -the center of said two recesses (146) .