US3857404A

US3857404A - Hydraulically operated lock valve assembly

Info

Publication number: US3857404A
Application number: US00355473A
Authority: US
Inventors: H Johnson
Original assignee: Caterpillar Tractor Co
Current assignee: Caterpillar Inc
Priority date: 1973-04-30
Filing date: 1973-04-30
Publication date: 1974-12-31
Anticipated expiration: 1991-12-31
Also published as: BR7401841D0; CA1001925A; GB1399446A; BE814439A; JPS501275A; JPS5750987B2

Abstract

A lock valve assembly for controlling a hydraulic jack, said valve assembly having means for metering the fluid flow from the jack cylinder so that initial movement of the jack is gradual, allowing precise adjustments to be made on a work load or implement associated with the jack.

Description

United States Patent 119 Johnson 1451 Dec. 31, 1974 [54] HYDRAULICALLY OPERATED LOCK 3,145,734 8/1964 Lee et a1 1. 91/420 VALVE ASSEMBLY 3,198,088 8/1965 1011115011 61 a1 91/420 3,250,185 5/1966 Tennis et a1. 91/420 en o Howard J Jollet, 3,563,261 2/1971 Griffith et a1. 137/102 x 3,587,399 6/1971 Dike et a1. 91/420 [73] Assgneecaterp'uar Tractor Peon?" 3,648,968 3/1972 Reid et a1. 251/122 x [22] Filed: Apr. 30, 1973 2 App] 355 473 Primary Examiner-William R. Cline Attorney, Agent, or Firm-Phillips, Moore, Weissenberger Lempio & Strabala [52] US. Cl. 137/102, 91/420 [51] Int. Cl. FlSb 15/00 [58] Field of Search 137/102; 251/122, 205; BS RACT 9l/42O; 138/46 A lock valve assembly for controlling a hydraulic jack, I i said valve assembly having means for metering the [56] References C'ted fluid flow from the jack cylinder so that initial move- UNITED STATES PATENTS merit of the jack is gradual, allowing precise adjust- 2,506,008 5/ 1950 Arps 91/420 X ments to be made on a work load or implement associ- 2,691,964 10/1954 Stickney 91/420 ated with the jack. 2,720,755 10/1955 Gardiner 91/420 X 2,959,190 11/1960 Barnes et a1, 91 /420 X 11 Claims, 3 Drawing Figures 1'3 '+2 '18 11 1111;- 1 111 37 +7 113 -1 1 58 51\ 55 bk 5b l 52 52 wy as,

1 2 -111 73 7 17 52 1,5 1,711 a- 56 1,722 21 \PZ3 z-1 Z9 zq 32 I l 1 1Q Z8 PATENTEDBEEBT I914 3,857. 404

HWZHa H HYDRAULICALLY OPERATED LOCK VALVE ASSEMBLY BACKGROUND OF THE INVENTION Many earthmoving machines employ double-acting hydraulic jacks for adjusting machine work implements. The jacks are usually controlled by spool type valves which direct fluid under pressure to either end of the cylinder while simultaneously exhausting fluid from the opposite end. Spool valves are commonly plagued by a tendency to leak, particularly after slight wear has taken place. This leaking around the valve spool causes the hydraulic jack to have a tendency to drift. Although slight drifting is not detrimental to the operation of most earthmoving machines, it can become a problem on grading and finishing machines which require precise blade and/or wheel positioning. To prevent cylinder drifting, a lock valve is commonly employed in the hydraulic circuit between the control valve and the hydraulic cylinder. The lock valve prevents return flow from either end of the cylinder when the control valve is in theneutral position. Such lock valves frequently utilize a pair of conventional ball type check valves which are highly effective in blocking flow from the cylinder. However, there is a problem associated with these check valves, eg. when the ball check is opened, as by a piston responding to fluid pressure, the opening tends to be very abrupt. This makes it difficult to control the fluid flow and results in a tendency to overshoot. If there happens to be a pressure head in the return line, the tendency to overshoot or overrun is increased. This uncontrolled fluid flow makes it very difficult to make the fine adjustments necessary for precise blade or wheel positioning.

Examples of prior art lock valve assemblies ar shown in the following U.S. Pat. Nos.:

2,619,074, issued Nov. 25, 1952 to Court, 3,145,734, issued Aug. 25, 1964 to Lee et al., 3,198,088, issued Aug. 3, 1965 to Johnson et al., 3,272,085, issued Sept. 13, 1966 to Hajma and 3,411,521, issued Nov. 19, 1968 to Johnson. These patents generally show lock valve assemblies having valve elements of the poppet type.

2,886,065, issued May 12, 1959 to Hershman shows a variable one-way restriction valve and 2,691,964, issued Oct. 19, 1954 to Stickney shows a conventional ball type check valve. 2,588,520, issued Mar. 11, 1952 to Halgren et a1. is of interest in showing a ball type check valve including metering means.

SUMMARY OF THE INVENTION It is the primary object of the present invention to provide means for overcoming the above deficiencies of the prior art.

Another object of the present invention is to provide a lock valve for a hydraulic jack.

A further object of the present invention is to provide a lock valve having means for metering the flow of fluid from a hydraulic jack.

Still another object of the present invention is to provide a lock valve having valve checks and means operative to unseat said valve checks, which unseating means provide graduated metering of fluid from the jack cylinder.

A still further object of the present invention is to provide a lock valve in which the means operative to unseat the valve checks are so dampened that the valve is stabilized during high jack loads.

Still a further object of the present invention is to provide a lock valve including one-way choke means in addition to metering means, which choke means cooperate with the metering means to control fluid flow from the hydraulic jack.

In accordance with the present invention, a lock valve assembly for controlling a hydraulic jack is provided with metering means operative during unseating of check valves of the assembly to provide precise control over positioning of the hydraulic jack under various load conditions.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects and advantages of the present invention will become apparent from the following description when read in conjunction with the accompanying drawings wherein:

FIG. 1 is a view in cross section of a lock valve in accordance with the present invention shown in combination with a fluid circuit and hydraulic jack which are illustrated schematically;

FIG. 2 is a section taken generally along lines 11 II of FIG. 1; and

FIG. 3 is an enlarged, detailed view of one of the check valves of FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings and more particularly to FIG. 1, a lock valve embodying the principles of the present invention is generally indicated by the reference numeral 10. The valve is shown in combination with a manually actuatable control valve 11 which directs fluid under pressure to either end of a double acting hydraulic jack 12. This control system may be employed for adjusting the movement of a work load or implement mounted on an earthmoving vehicle.

Pressurized fluid is drawn from a tank 14 by a pump 13 and directed to the manually actuatable control valve 11 through conduit 16. Fluid exhausted from the control valve 11 is returned to the tank 14 by conduit 17. A relief valve 18, connecting conduit 16 to the tank 14, relieves excessive pressure in the hydraulic system. The manually actuatable control valve 11 serves to selectively direct fluid under pressure to conduits 26 and 27 and to opposite ends of the hydraulic jack 12 through

conduits

36 and 37.

Interposed between

conduits

26 and 36 leading to the rod end of the jack l2 and between

conduits

27 and 37 leading to the head end of the jack 12 is the lock valve assembly of the present invention. The assembly, indicated by reference numeral 10, includes a valve housing 19, provided with an elongated cylindrical bore 20 having a first pair of counterbores 21 and 22 disposed at opposite ends thereof. A pair of

ports

23 and 24 connect the bore 20 with the control valve 11 by means of previously mentioned

conduits

26 and 27. Both

conduits

26 and 27 have a fitting screw 28 threadably secured within their respective ports. A choke valve 29 is disposed in each port above the screw 28.

As best seen in FIG. 2, the choke 29 defines an annular disc having a plurality of reliefs 31 and a centrally disposed aperture 32. A pair of

passages

34 and 35 connect counterbores 21 and 22 with the rod and head end of the jack 12 by means of

conduits

36 and 37.

A second cylindrical bore 38 formed in the valve housing 19 substantially parallel with bore 20, communicates at its proximal end with counterbore 21 by means of passage 34 and at its distal end with bore by means of passage 39.

A crossover relief valve mechanism, generally indicated at 41, is disposed in bore 38 and includes an annular member 42 having an end screw 43 threadably secured within the open end of the bore 38. A recess 44 provided in the outer end of the annular member 42 connects the valve 41 with passage 34. An axial passage 46 extending inwardly from the inner end of the annular member 42 communicates with passage 34 by means of radial passages 47. In addition, the relief valve 41 includes a valve element 48 having a conical tip 49 which is normally seated in the open end of the axial passage 46 by a spring 51. The relief valve 41 prevents overpressurization of the rod end of the cylinder due to heavy external loads and operates whenever there is sufficient pressure in passage 34 to unseat valve element 48. When this happens, the valve 41 admits fluid from passage 34 and returns it to bore 20 by means of passage 39.

A plug 52, threadably secured in each of counterbores 21 and 22, has a recess 53 formed in the inner end thereof. A radial vent passage 56, formed in the plug 52 intermediate its ends communicates with the recess 53 and bleeds off residual fluid pressure in the system prior to removal of the plug 52 during disassembly.

A pair of identical check valve assemblies, generally indicated at 57 and 58, are interposed between port 23 and passage 34 leading to the rod end of the jack 12 and between port 24 and passage 35 leading to the head end of the jack 12. The two assemblies, only one of which will be described in detail, are located in bore 20.

Check valve assembly 57 includes an annular member 59 pressed or otherwise sealingly disposed in the end of bore 20. The annular member 59 has a plurality

coaxial bores

61, 62 and 63 with bore 63 extending inwardly from the outer end and terminating in an annular valve seat 64. The outer end of annular member 59 defines a reduced diameter portion 66 having a plural ity of radial passages 67 and vent passages 68 connecting bore 63 with passage 34. The inner end of annular member 59 defines an annular recess 69 which communicates with the control valve 11 by means of port 23 and conduit 26. A plurality of radial passages 71 connect the annular recess 69 with bore 61. It should be noted at this point that the annular recess 69 of check valve assembly 58 communicates with both relief valve 41 and control valve 11. Communication with the relief valve 41 is by means of passage 39. Communication with the control valve is by means of port 24 and conduit 27. The check valve assembly 57 further includes a ball check or element 72 disposed in bore 63 and urged against the valve seat 64 by a compression spring 73. A close fit between the ball check 72 and the bore 63 provides lateral stability to the check valve assembly. The compression spring 73 biasing the ball check 72 is disposed in bore 63 and the recess of plug 52.

A double-ended actuator piston 74, slidably disposed in the bore 20 between the check valve assemblies 57 and 58, forms a pair of variable volume chambers 76 and 77. The piston 74 is provided with a pair of

plungers

78 and 79 projecting from opposite ends thereof.

Each plunger is formed with an enlarged land portion 81 disposed substantially midway between the center of the piston 74 and outer end of the plunger. The enlarged land 81 has a diameter slightly less than the diameter of the bore 61. Whenthe land 81 enters the bore 61 during initial movement of the piston 74, fluid in the chamber 76 of check valve assembly 57 is forced through the clearance space between the land 81 and the bore 61. This serves to dampen or retard the movement of the piston 74 and thus stabilize the opening of the ball check 72 and the movement of the valve metering head 82 through the bore 62.

Both

plungers

78 and 79 terminate in a valve metering head 82 adapted to engage and unseat the valve check in the return line and to meter fluid flow in the line. When the valve check has been unseated, the head 82 so regulates the flow through the return line as to make it proportional to the flow through the input line. The valve head 82, as clearly shown in FIG. 3, includes a land portion 83 and first and second

tapered sections

84 and 86. The land 83 defines the outermost end portion of the valve head 82 and has a diameter slightly less than the diameter of bore 62. These dimensions allow the land 83 to cooperate with the bore 62 and substantially block the flow of fluid through the check valve 57 during the initial unseating of the ball 72. The first and second

tapered sections

84 and 86, disposed between the land 83 and the plunger 78, comprise conical surfaces having increasing angles of metering in the direction of the piston 74. The metering angle of the first tapered section 84 is designated A and the metering angle of the second tapered section 86 is designated B. In the present invention A is 7 and B is 13. Thus the first tapered section 84, having a shallow angle, meters flow in situations where a pressure head exists in the return line due to heavy loads on the jack 12. The second tapered section 86, having a steeper angle which increases the effective area of the orifice, meters flow in situations where the pressure in the return line is minimal.

OPERATION When the main control valve 11 is in the neutral position both check valve assemblies 57 and 58 are closed and fluid flow from either end of the hydraulic jack 12 is prevented. The term neutral position as used herein is defined as the position required to maintain a work load or implement in a fixed location.

To extend the jack, the main control valve 11 is positioned to direct fluid through port 24 and radial passages 71 into bore 61 and volume chamber 77. This initial fluid pressure in the bore 61 and chamber 77 is exerted agaisnt both the actuator piston 74 and the ball check 72 of check valve assembly 58.

As the ball check 72 of the check valve assembly 58 is unseated, the pressure and flow available in port 24 is communicated to the head end of the jack 12 by way of passage 35 and conduit 37. Simultaneously, and in direct proportion to pressure build-up in chamber 77, the actuator piston 74 is moved to the left and the valve head 82 on the plunger 78 engages and unseats the ball check 72 of check valve assembly 57. At the initial unseating of the ball check 72 the land 83 of the valve head is sufficiently positioned within the bore 62 to block fluid flow from the rod end of the cylinder. With the flow blocked, pressure continues to build up in the chamber 77 and cause further leftward movement of the actuator piston 74 until the land 83 passes through the bore 62. At this point, one of the tapered sections commences metering fluid exhausted from the rod end of the cylinder and thereby prevents any sudden uncontrolled flow during the initial unseating of the ball check 72. The rate of metering return flow is proportional to the volume of fluid directed to the input line. During leftward movement of the ball check 72, fluid in the bore 63 is vented into the return line by passage 68 to prevent a hydraulic block. I

Under certain operating conditions the jack 12 may be required to support a load of sufficient weight as to generate high fluid pressure in the return line of the cylinder. For example, if an external load is pulling on the rod, a pressure head, generated in conduit 36 and pas sages 34 will be brought to bear against the ball check 72 of check valve assembly 57. To extend the jack 12 under these conditions, sufficient fluid pressure must be built up in chamber 77 to move the actuator piston 74 to the left and overcome the pressure head holding the ball check 72 closed. When the ball check 72 is sufficiently unseated to permit fluid flow through the valve 57, the first tapered section 84 provides a small area orifice for metering the flow. Since the amount of flow through a given sized orifice increases proportionally with increase in fluid pressure, the first tapered section is effective in maintaining a flow rate proportional to the flow rate on the input side of the cylinder.

If, on the other hand, the jack 12 is lightly loaded and the pressure head in the conduits minimal, the valve head 82 will pass through the bore 62 sufficiently for the second tapered section 86 to meter the fluid flow, or in some cases, sufficiently to provide unrestricted flow.

During fluid input to the cylinder, the flow in the supply line raises the choke 29 disposed in the supply port 24 and permits unrestricted flow through the port 24. Return flow through the exhaust port 23 however, causes the choke 29 disposed in this port 23 to be seated against the fitting screw 28 secured within the port 23. This causes the full flow of exhausted fluid to pass through the central aperture 32 in the choke 29. This restriction in the return line cooperates with the first tapered section 84 to control a heavy load on jack [2 and to prevent cavitation of the jack 12 when the control valve 11 is actuated.

From the above description, it is seen that there is provided a lock valve assembly having means for metering fluid flow to and from a hydraulic cylinder in a manner insuring smooth and controlled functioning of the hydraulic jack.

While the present invention has been described with respect to a single embodiment it is to be understood that changes and alterations may be made in the illustrated embodiment without departing from the spirit and scope of the present invention as defined by the appended claims.

What is claimed is:

l. A lock valve assembly for controlling fluid flow in a hydraulic jack having inlet and outlet means for selectively supplying fluid to either end of the jack cylinder while exhausting fluid from the opposite end comprising:

a valve housing;

a bore formed in said housing;

a first pair of ports in spaced communication with said bore for communicating with a source of pressurized fluid;

a second pair of ports communicating with said bore and opposite ends of the jack cylinder;

first check valve means disposed in said bore between one of said first ports and one of said second ports;

second check valve means disposed in said bore between the other of said first port and the other of said second port;

each of said first and second check valve means including a passage communicating between each of said respective first and second ports, a valve seat surrounding said passage, and a valve element engaging said seat normally for blocking fluid flow from said second pair of ports to said first pair of ports; and

an actuator piston reciprocally disposed in said bore between said first pair of ports and having a pair of plungers extending axially from opposite ends thereof, said plungers terminating in metering head means operative to engage and unseat either check valve element upon endwise movement of the piston, said metering head means being shaped to provide separate metering portions cooperating with said valve passage for regulating fluid flow through the check valves.

2. The lock valve assembly of claim 1 wherein said separate metering portions comprise a plurality of axially separated annular surfaces defining increasing angles of metering with progressively decreasing diameters of said plunger in the direction of the piston.

3. The lock valve assembly of claim 2 wherein one of said surfaces is an annular land, operating at the initial unseating of the valve element to extend into said passage and substantially block fluid flow through the passage of said check valve means.

4. The lock valve assembly of claim 3 wherein said annular land defines the outermost end portion of the metering head means.

5. The lock valve assembly of claim 2 wherein said axially separated surfaces include first and second conical surfaces sloping in the direction of the piston.

6. The lock valve assembly of claim 5 including oneway choke means disposed in the first pair of ports for restricting fluid flow in the return direction from said lock valve.

7. The lock valve assembly of claim 2 including damping means carried by each of said plungers for cooperation with damping means in said bore for damping movement of said piston.

8. The lock valve assembly of claim 7 wherein said damping means comprises an enlarged land disposed substantially midway between the piston and the outer end of the plunger, said land extending into and cooperating with the bore of a sleeve extending from said check valve means.

9. The lock valve assembly of claim 5 wherein the angle of said first conical surface is substantially 7, and the angle of said second conical surface is greater than that of the first.

10. The lock valve of claim 9 wherein the angle of said second conical surface is substantially 13.

11. The lock valve assembly of claim 1 including oneway choke means disposed in said first pair of ports for restricting fluid flow in the return direction from said lock valve.

Claims

1. A lock valve assembly for controlling fluid flow in a hydraulic jack having inlet and outlet means for selectively supplying fluid to either end of the jack cylinder while exhausting fluid from the opposite end comprising: a valve housing; a bore formed in said housing; a first pair of ports in spaced communication with said bore for communicating with a source of pressurized fluid; a second pair of ports communicating with said bore and opposite ends of the jack cylinder; first check valve means disposed in said bore between one of said first ports and one of said second ports; second check valve means disposed in said bore between the other of said first port and the other of said second port; each of said first and second check valve means including a passage communicating between each of said respective first and second ports, a valve seat surrounding said passage, and a valve element engaging said seat normally for blocking fluid flow from said second pair of ports to said first pair of ports; and an actuator piston reciprocally disposed in said bore between said first pair of ports and having a pair of plungers extending axially from opposite ends thereof, said plungers terminating in metering head means operative to engage and unseat either check valve element upon endwise movement of the piston, said metering head means being shaped to provide separate metering portions cooperating with said valve passage for regulating fluid flow through the check valves.

6. The lock valve assembly of claim 5 including one-way choke means disposed in the first pair of ports for restricting fluid flow in the return direction from said lock valve.

9. The lock valve assembly of claim 5 wherein the angle of said first conical surface is substantially 7*, and the angle of said second conical surface is greater than that of the first.

10. The lock valve of claim 9 wherein the angle of said second conical surface is substantially 13*.

11. The lock valve assembly of claim 1 including one-way choke means disposed in said first pair of ports for restricting fluid flow in the return direction from said lock valve.