VENT VALVE FOR CYLINDER MOUNTED CHECK VALVE

Technical Field

The present invention pertains to a load lifting system and, in particular, to a system including a hydraulic cylinder, a check valve mounted to said hydraulic cylinder and being responsive to a vent valve for preventing a load carried by said cylinder from moving should a leak occur in a hydraulic line to the cylinder.

Background Art

Hydraulic systems, such as are found in excavators and the like, employ a hydraulic cylinder to raise and lower relatively heavy loads and at times to support such loads in an elevated position. When the cylinder is required to support the load in such an elevated position, it is normally desirable to isolate a relatively high load generated pressure in the load supporting end of the cylinder from the remainderof the system. This is to prevent the downward drifting of the load due to leakage past a valve spool of a conventional control valve normally used in such systems. The load pressure is also normally isolated to prevent the movement of the load in the event of a hydraulic line failure. This isolation can be accomplished by positioning a load check valve in the hydraulic line leading from the control valve to the hydraulic cylinder. Such a load check valve permits the free flow of fluid to the cylinder, but normally prevents

the escape of fluid from the cylinder. The load check valve can be of the type which is vented behind the check valve spool, such that the check valve closes when the hydraulic line from the venting line is blocked. When the venting line is open, hydraulic fluid can flow from the cylinder through the check valve to the control valve. The load check valve can be mounted directly to the hydraulic cylinder elminating the need for a conduit to connect the cylinder to the check valve and thus eliminating the possibility of a break therein.

However, there is also a possibility that a rupture might occur in the hydraulic line which connects the load check valve to the control valve. If such a rupture occurs and if the venting line from the load check valve is not closed, as can occur when the load is being lowered, the load can lower more rapidly until the operator of the hydraulic system realizes that the load is lowering more rapidly and acts to block the vent line, preventing the load from lowering still further.

The present invention is directed to overcoming one or more of the problems as set forth above.

Disclosure of Invention

In a hydraulic system having a hydraulic cylinder, a check valve communicating with said hydraulic cylinder, a hydraulic line communicating

with said check valve, and a vent valve means for selectively allowing said hydraulic cylinder to communicate with said hydraulic line through said check valve, the improvement comprises means for selectively actuating said vent valve means subject to a predetermined pressure condition existing in said hydraulic lines to allow communication between said hydraulic cylinder and said hydraulic line. Accordingly, should there be a rupture in the hydraulic line directing hydraulic fluid from the hydraulic cylinder, the predetermined pressure condition would not exist in the hydraulic line and the operator would not be able to actuate the vent valve means in order to lower the load held in position by the hydraulic cylinder until the predetermined pressure condition was again established in the hydraulic line. Consequently, should the hydraulic line be ruptured, the operator cannot inadvertently or unknowingly initiate load lowering, and in progress lowering ceases.

Brief Description of the Drawings

Fig. 1 shows an overall schematic circuit diagram of an embodiment of a hydraulic load lifting system of the invention which includes a vent valve for actuating a cylinder mounted check valve.

Fig. 2 is a cross-sectional view of the vent valve and the check valve as depicted in Fig. 1.

Fig. 2A is a cross-sectional view of the vent valve and the check valve of Fig. 2 with the spool of the vent valve moved to another position. Fig. 3 is a cross-sectional view of a blocker valve as depicted in Fig. 1.

FIG. 3A is a cross-sectional view of the blocker valve of Fig. 3 with one of the spools thereof moved to another position. Fig. 3B is a view similar to Fig. 3 with the other of the spools moved to another position.

Fig. 4 Is a cross-sectional view of a sequence valve as depicted in Fig. 1.

5est Mode of Carrying Out the Invention

The hydraulic load lifting system of Fig. 1 is designated by the numeral 10 and includes load supporting hydraulic motor means such as hydraulic jacks or cylinders 12 and a control circuit 14 operatively connected to control the extension of such cylinders 12 for raising load 16 and the retraction of cylinders 12 for lowering load 16. The cylinders 12 include a head end 18 and a rod end 20. Control circuit 14 includes a fluid reservoir 22, a main pump 24 connected for drawing fluid from the reservoir 22 and a pilot operated main control valve 26. A pump line 28. connects pump 24 to the main control valve 26. The control valve 26 is selectively positioned

between the depicted neutral or hold position and either of the two other operative positions for raising and lowering load lβ. The control valve 26 communicates with the reservoir 22 by way of a tank line 30. A relief valve 32 selectively controls communication between the pump line 28 and the tank line 30 to limit the maximum pressure in the control circuit between the pump 24 and the control valve 26. The.control valve 26 is further connected to the head end 18 and the rod end 20 of the cylinders 12 by main control lines 34 and 36, respectively. A pair of main control line relief valves 38 and 40 limit the maximum pressure in the control lines 34 and 36 and the control circuit 14 on the cylinder side of control valve 26.

A pair of identical load check valves 46 and 48 communicate with main control line 34 and with each of the head ends 18 of the hydraulic cylinders 12. The purpose of such load check valves 46 and 48, as will be apparent to those skilled in the art and as further described hereinbelow, is to avoid downward drifting of the load 16 due to leakage through the main control valve 26 and to prevent uncontrolled lowering of the load 16 in the event of a line failure. While a schematic drawing in Fig. 1 shows valves 46 and 48 as being somewhat spaced from cylinders 12, they are preferably mounted directly on their respective cylinders or integral therewith to

allevlate the possibility of a line failure between cylinders 12 and the load check valve 46 and 48.

The control circuit 14 is provided with vent valves 50 and 5 which are mounted directly to load check valves 46 and 48 respectively, and actuating means 51 for actuating vent valves 50 and 52 subject to a predetermined pressure condition existing in line 34. Means 51 includes a blocker valve 54 which communicates with and can provide a positive pressure signal to vent valves 50 and 52 by a line 56, and a communication means 59 comprising a one way valve 60 which is integral with a sequence valve 58. Communication means 59 as will be explained below will communicate positive pressure fluid from the blocker valve 54 to line 34 absent a predetermined pressure in line 34. Blocker valve 54 will selectively vent the load check valves 46 and 48, as will be discussed further hereinbelow.

A pilot control system, indicated generally at 62, is provided for selectively and simultaneously controlling the operation of the main control valve 26 and the blocker valve 54. The pilot system includes a pilot pump 64 connected for drawing fluid from the reservoir 22. Pilot pump 64 supplies fluid to the pilot control valve 66 by a pilot pressure line 68. Line 68 is shown dotted as are all the other pilot lines described below. The pilot control

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valve 66 communicates with the reservoir 22 through a pilot line 70. A relief valve 72 is disposed between pilot pressure line 68 and pilot line 70 to maintain the pressure in the pilot system at a predetermined level. The pilot control valve 66 is further communicated with the opposite ends of the main control valve 26 by way of pilot pressure lines 7 and 76 for providing actuation of the main control valve 26 to one of three positions depending on the position of pilot control valve 66, as can be appreciated by one of ordinary skill in the art. Also as can be appreciated, pilot pressure for system 62 can come directly from main pump 24 described below. The pilot pressure line 74 also communicates with pilot pressure line 75 which communicates with blocker valve 54 to communicate pilot fluid thereto when pilot fluid is directed to the main control valve 26 to shift the control valve 26 to the hydraulic cylinder lowering position. A pilot pressure line 78 provides a positive pressure fluid signal from pilot pressure line 68 to blocker valve 54. Blocker valve 54 and vent valves 0 and are further provided in communication by return lines 80 and 81. Return line 80 also communicates with reservoir 22. Additionally, a pilot pressure line 82 communicates pilot fluid from blocker valve 54 to one way valve 60, the significance of which will be discussed hereinbelow.

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In Fig. 2, cross-sectional views of load check valve 46 and vent valve 50 are depicted. It is understood that the following discussion applies equally well to load check valve 48 and vent valve 52. Load check valve 46 includes a valve body 90 which defines a passage 92. Check valve 46 selectively communicates main control line 34 with fluid line 94 which communicates with the head end 18 of the adjacent hydraulic cylinder 12, and additionally communicates main control line 34 with equalizer line 96 which communicates with the other check valve 48. A manually operated load lowering valve 84 (Fig. 1) communicates with line 96. Valve 84 communicates with tank 22 through a return line 86. Accordingly, load 16 can be lowered should, for example, the engine driven pumps 24 and 64 fail, by draining fluid from the head ends 18 of cylinders 12 through valve 84 to reservoir 22. As shown in Fig. 2, a spool 98 is urged by a spring 100 mounted in spring cavity 102 into a position so as to block passage 92. In order to raise load 16 control valve 26 directs hydraulic fluid through line 34 against spool 98, urging said spool 98 into spring cavity 102 against spring 100. With main control valve 26 actuated to a position to lower the load 16, spring chamber 102 of load check valve 46 is vented by vent valve 50 to allow hydraulic fluid to flow from the head end 18 through passage

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92 to main control line 34. This is accomplished as the hydraulic fluid from the head end 18 of the hydraulic cylinder 12 applies force against shoulder 106 of spool 98 urging it into spring cavity 102. If the spring cavity 102 is not vented by vent valve 50, the hydraulic fluid pressure acting against shoulder 106 will be unable to urge spool 98 into spring cavity 102.

The above venting or non-venting of the spring cavity 102 is, as indicated, accomplished by vent valve 50. Vent valve 0 is provided with a signal comprised of pressurized hydraulic fluid through line 56 from blocker valve 54. Vent valve 50 includes a valve body 120 which defines a bore 122. Valve body 120 additionally defines a first transverse bore 124 which communicates with spring chamber 102 of load check valve 46 (Fig. 2). Transverse bore 124 communicates with an annular channel 126 whichin turn communicates with bore 122. Another annular channel 130 is defined by valve body 120. A second transverse bore 132 provides communication between annular channel 130 and return line 80.

Disposed in longitudinal bore 122 is a vent valve spool 134 which is urged into contact with end 136 of valve body 120 by a spring 138 which is disposed in a spring chamber 140 defined between the spool 134 and an opposite end 142 of valve body 120. Spool 134 includes an axial passage 144 which has a restrictive orifice 146 at the

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end thereof located adjacent end 136 of valve body 120 so as to communicate with line 56. Axial passage 144 additionally communicates with spring chamber 140. Further, spool 134 defines a radial bore 148 which communicates with axial passage 144 and with an annular metering recess 150 defined by spool 134. With the spool In the unactuated position as shown in Fig. 2, spring chamber 102 does not communicate with return line 80. When a positive fluid pressure signal is applied to spool 134 through line 5 from blocker valve 54, spool 134 is urged upwardly against spring 138 into a second position (Fig. 2A) . Thus, annular metering recess 150 comes in to fluid communication with annular channel 126 such that spring chamber 102 is vented to line 80. This allows the fluid pressure in the head end of the cylinder to urge spool 98 into spring chamber 102 and provide communication with head end 18 and control line 34 for lowering the load 16. When a fluid signal is provided to line 56 to urge spool 134 into the second position, some of said fluid signal is passed through orifice 146 into axial passage 144, radial bore 148 and to return line 80 in order to keep the vent valve

50, spool 134 and in particular line 56 warmed to the temperature of the oil and thus to prevent the vent valve 50 from becoming sluggish and non- responsive to a signal or lack of signal in line 56 during cold weather operation.

In Fig. 3 a cross-sectional view of blocker valve 5 is depicted. Blocker valve 54 includes a valve body l6θ which defines two parallel spool bores 162 and 164. In a first end 166 of spool bore 164 is provided a plug 168 which defines a passage 170 which provides communication between spool bore 164 and pilot pressure line 75• Additionally, two axial passages 172 and 174 are provided through valve body l6θ and communicate with spool bore 164.

Spool bore 164 defines first, second, third, and fourth annular recesses 176, 178, 180 and 182. Annular recess 17β communicates with axial passage 172 and with an axial passage 184 defined by body 160. The axial passage 184 is additionally provided in communication with spool bore 162. An orifice 186 is provided in axial passage 184 adjacent annular recess 176. Annular recess 178 communicates with an axial passage 188 which is provided in fluid communication with spool bore 162. Third annular recess 180 communicates with axial passage 174. Fourth annular recess 182 is provided in communication with an axial passage 190 defined by body l6θ, which is additionally in fluid communication with spool bore 162.

Disposed in second spool bore 164 is a spool 192 which defines first and second annular metering recesses 194 and 196 and a spring chamber 198 in which is disposed a spring 200.

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T-shaped passage 202 provides communication between spring chamber 198 and annular metering recess 196. With spool 192 in the first (unactuated) position as shown in Fig. 3, annular metering recess 196 provides communication from axial passage 188 to annular recess 178 and annular recess 180 to axial passage 174 and return line 8l. Also, with spool 192 In the first (unactuated) position, axial passage 190 communicates through T-shaped passage 202 to return line 8l.

A pressure signal provided through pressure line 75 actuates spool 192 to the act-uated position as shown in Fig. 3A. With spool 192 so positioned, annular metering recess 194 provides fluid communication between annular recess -I76 and annular recess 178 so that fluid is directed through both axial passage 184 and 188. Communication between annular recess 178 and 180 is blocked by spool 192.

Spool bore 162 defines first, second, third and fourth annular recesses 204, 206, 208 and 210. Annular recess 204 communicates with an axial passage 212 which is provided in communication with pilot pressure line 82.

Further, annular recess 204 communicates with axial passage 184. Second recess 206 is provided In communication with axial passage 188. Third annular recess 208 is provided in fluid communication with an axial passage 214

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which communicates with line 56. Additionally, annular recess 210 communicates with axial passage 190.

In Fig. 3 a spool 216 is depicted disposed in spool bore 162 and provided in the actuated position. Spool 216 includes a first end 218, an annular metering recess 222, a T-shaped passage 224, and a second end 226 which defines a first portion 228 of a spring cavity 230. T- shaped passage 224 is provided in fluid communication with spring cavity 230. A spring 234 is positioned in spring cavity 230. With spool 216 being actuated to the position in Fig. 3 by pilot pressure fluid provided through axial passage 184 and annular recess 204 to the first end 2l8 thereof, annular metering recess 222 provides fluid communication between annular recess 206 and 208 so that axial passage 188 is in fluid communication with line 56. Should the pressure in annular recess 204 not be sufficient to urge spool 216 rightwardly against spring 234, spool 216 assumes an unactuated position as depicted in Fig. 3B wherein spool 216 blocks communication between annular recess 206 and 208 and T-shaped passage 224 provides communication from line 56 and axial passage 214 to spring cavity 230, annular recess 210 and axial passage 190. From axial passage 190 fluid flows to recess 182, spring chamber 198, and T-shaped passage 202. From T-shaped passage 202,

hydraullc fluid is relieved to return line 81 with spool 192 in the unactuated position. Accordingly, signal line 56 can be drained to tank 22 through return line 81 with spool 216 in the unactuated position and spool 192 in the unactuated position.

In Fig. 4 a cross sectional view of sequence valve 58 is depicted with one-way valve 60 incorporated therein. Sequence valve 58 includes a valve body 240 which defines a longitudinal passage 242 with a reduced diameter front portion 244 and a rear portion 245 which defines spring cavity 246. Valve body 240 defines an annular recess 248. Further, valve body 240 defines an axial passage 250 which communicates with annular recess 248. As can be seen in Figs. 1 and 4, sequence valve 58 is disposed in main control line 34 so that main control line 34 communicates with longitudinal passage 242 and axial passage 250.

Valve body 240 also includes an end plug 252 having a relief passage 254 which relieves fluid pressure from spring cavity 246 to tank 22 through a line 256. Disposed in rear portion 245 of longitudinal passage 242 is a spool 260. Spool 260 includes a first end 262 which defines a beveled edge 264. The other end 266 of spool 260 defines a cavity 268 which receives at least a portion of spring 270 which is additionally received in spring cavity 246.

Spring 270 urges spool 260 leftwardly toward first portion 244 of the longitudinal passage 242 with beveled edge 264 resting on the valve body 240 adjacent front portion 244.

Spool 260 defines a shoulder 272. When the fluid pressure in line 34 located between sequence valve 58 and load check valves 46 and 48 acting on shoulder 272 is great enough to overcome spring 270, spool 260 Is urged rightwardly, allowing communication between front portion 244 of longitudinal passage 242 and axial passage 250. As can be seen in Fig. 4, one-way valve 60 provides fluid communication between line 82 and axial passage 250 and the portion of main control line 34 between sequence valve 8 and vented load check valves 46 and 48 when the pressure in axial passage 250 is less than the pressure In pressure line 82.

Industrial Applicability It is to be understood that system 10 can be incorporated in, for example, an excavator and the like. The operation of the above hydraulic load lifting system 10 is as follows .

With the engine of the vehicle running, such that both pumps 24 and 64 are operable, pump 64 provides pressurized pilot fluid to line 78. The pressurized pilot fluid in line 78 urges spool 216 of blocker valve 54 to the actuated position (Fig. 3) such that pressure line 82 is charged. If the portion of main control line 34

between sequence valve 58 and vented load check valves 46 and 48 is fully operable, the pressure therein will be made equal to the pressure in line 82 by means of flow through one-way valve 60 and spool 216 remains in the actuated position. In order to raise load 16, pilot control valve 66 is actuated to actuate main control valve 26 to provide hydraulic fluid through the main control line 34 which urges spool 260 of sequence valve 58 rightwardly, providing communication of fluid to the remainder of line 34 and to load check valve 46 and 48. The pressure in line 34 forces the spool 98 of check valves 46 and 48 to open, allowing hydraulic fluid to flow into the cylinders 12 to raise the load 16.

In order to lower the load 16, the pilot control valve 66 is properly actuated in order to actuate main control valve 26 to allow hydraulic fluid to flow into main control line 36 and from main control line 34 to tank.

Simultaneously, pilot control valve 66 directs a pilot signal through line 75 urging spool 192 rightwardly to the position shown in Fig. 3A. In this position spool 192 allows pilot fluid pressure to flow from pilot pressure line 78 through annular recesses 176 and 178, axial passage 188, and annular recesses 206 and 20δ of spool bore 162 to line 56. Pilot fluid pressure in line 56 urges spools 134 of vent valves

50 and 52 upwardly so that annular metering recess 150 provides fluid communication between annular channels 126 and 130 allowing the spring cavity 102 to drain through return line 80. With the spring cavity 102 relieved of hydraulic pressure, hydraulic pressure placed on shoulder 106 of spool 98 from the head end 18 of the cylinder 12 through line 94 causes said spool 98 to open, providing fluid communication through line 34. The hydraulic fluid pressure in line 34 between said load check valves and sequence valve 58 is applied against shoulder 272 of spool 260, urging said valve 58 open so that the hydraulic fluid can communicate through main control valve 26 to tank 22, allowing load 16 to lower.

Again, It is noted that hydraulic fluid is provided through the orifice 146 and an axial passage 144 of spool 134 when pilot pressure is provided through line 56. This hydraulic fluid also flows through radial bore 148. The pressure drop across orifice 146 provides a force to overcome the bias of spring 138 and moves spool 134 to an open position. This hydraulic fluid keeps the valve 50 at normal operating temperatures even in cold ambient conditions so that valve 50 is responsive to changing conditions in line 56 and is not slowed up by hydraulic fluid that has not been heated to the proper operating temperature. It is noted that spring chamber 140 is in fluid communication

with axial passage 144.

If for some reason the hydraulic pressure in main control line 3 between sequence valve 58 and load check valves 46 and 48, should be reduced or diminished due to, for example a failure in the above-identified portion of main line 34, the hydraulic pressure in axial passage 250 of sequence valve 58 will be lower than that in pressure line 82. Consequently, one-way valve 6θ will open reducing the pressure in pilot pressure line 82 and the pressure in annular recess 204 of spool bore 162 of blocker valve 54. Simultaneously, the spring 234 will urge spool 2l6 leftwardly due to the reduced pressure in annular recess 204 causing spool 216 to block communication between annular recess 206 and annular recess 208 and thus blocking communication between passage 188 and line 56. Further, T-shaped passage 224 will come into communication with line 56 allowing any fluid in line 56 to be drained therefrom through blocker valve 54 and to tank through line 8l. Thus, with spool 216 so positioned the actuation of spool 192 when pilot, pressure is provided through line 75 will be ineffective and will not allow pilot pressure in line 78 to communicate with line 56 to thereby actuate vent valves 50 and 52. Accordingly, should there be a break in a portion of main control line 3 between sequence valve 58 and the load check valves 46 and 48 actuation

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of pilot control valve 66 and thus main control valve 26 and spool 192 will not allow the loads 16 to be lowered as spool 216 in said blocker valve 54 will prevent signal pilot pressure from entering line 56 to actuate vent valves 50 and 52 to vent the spring chambers of load check valves 46 and 48.

It is to be understood that orifice 186 restricts the flow of fluid to recess 204 from line 78 such that if line 3 should rupture, the flow of fluid from line 78 will not maintain sufficient pressure in recess 204 to maintain spool 216 in a rightward position. Spool 216 will immediately move to the leftward position shown in Fig. 3B.

Accordingly, the invention solves the disadvantages of the prior art device as the load 16 is not allowed to lower if there is a rupture in the main control line 34, except as indicated above by operation of manual valve 84. Further, the motor of the vehicle must be operable and running in order to power the pilot pressure system 62 to provide a positive pressure pilot signal to blocker valve 54 and thus to vent valves 0 and 52 in order to allow the load 16 to be lowered.

Other aspects, objects, and advantages of this invention can be obtained from a study of the drawings, the disclosure, and the appended claims.

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