|Publication number||US3563137 A|
|Publication date||Feb 16, 1971|
|Filing date||Jun 30, 1969|
|Priority date||Jun 30, 1969|
|Also published as||DE2029826A1|
|Publication number||US 3563137 A, US 3563137A, US-A-3563137, US3563137 A, US3563137A|
|Inventors||Graber Homer R, Mcfarland James W|
|Original Assignee||Cessna Aircraft Co|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (3), Referenced by (33), Classifications (17)|
|External Links: USPTO, USPTO Assignment, Espacenet|
United States Patent  Inventors HomerR.Graber Pretty Prairie; James W. McFarland, Hutchinson, Kans.  Appl. No. 837,605  Filed June 30, 1969  Patented Feb. 16, 1971  Assignee The Cessna Aircraft Company Wichita, Kans.
 HYDRAULIC SELF-LEVELING CONTROL FOR i E k 3,179,120 4/1965 Ericksonetal. 3,251,277 5/1966 Stacey 2l4/77IX 91/414 ABSTRACT: A control system for the selective operation of hydraulic cylinders positioning the boom and bucket of a front end loader. A multiple spool valve is provided with a control spool for the boom and a control spool for the bucket. When the boom is actuated by directing pressure fluid to one end of the boom cylinder, the fluid displaced from the other end of the boom cylinder is selectively directed through a transfer circuit to a flow divider that diverts a. predetermined portion of the displaced fluid to actuate the bucket cylinder and maintain the bucket level when the boom is raised and/or lowered. Additional controls may include a pressure relief valve for the transfer circuit, a check valve downstream of the flow divider preventing reverse flow through the transfer circuit, and a piston responsive to transfer circuit pressure to meter fluid displaced from the bucket cylinder and prevent cavitation in the system.
lli l T a PATENTEDFEBIBIHYI 3.563137 SHEET 1 UF 5 NE UT RAE 76 NEUTRAL INVENTORS HOMER R. GRABER gMES W. MCFARLAND PATENIEU FEB16 I97! 3.563137 SHEET 2 OF 5 FIG. "2
4/, //29 I 52 VA @3 t 7 49 i so 1/ LOWER 8 LEVEL I NEUTRAL 25 INVENTORS HOMER R. GRABER Fl G. 9 JAMES w. McFARLAND V WM AT ORNEY AGFNT PATENTEUFEBIBIBYI 8.563.137
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w. #45 a 55-. Mr v 5-7 x L30 3 'ELQAT 32 36 38 "t INVENTORS FIG. 6 HOMER R. GRABER JAMES W. MCFARLAND flam AGENT NEUTRAL PATENTEDFEB1|97| 3 553 137 SHEET u [1F 5 NEUTRAL 7| r LLL 48 4m 45 x 42b 8 LEVEL ISE l -FLOAT LOWER NEUTRAL INVENTORS HOMER R. GRABER JAMES W. MCFARLAND ATTORNEY GENT FIG. 7
HYDRAULIC SELF-LEVELING CONTROL FOR BOOM AND BUCKET BACKGROUND OF THE INVENTION This invention relates generally to controls for fluid power systems. More particularly, this invention relates to directional fluid control valves that selectively effect automatic leveling of the bucket on a front end loader or similar device, during movement of the boom arm to which the bucket is attached.
It is conventional practice to provide a hydraulic cylinder for manipulating the bucket of a front end loader, and another cylinder for raising and lowering the boom arm. In addition to various mechanical linkages that move the bucket and keep it level while the boom is being raised, hydraulic self-leveling means have also been devised to divert fluid displaced from the boom cylinder and direct it to operate the bucket cylinder so as to keep the bucket level. A serious drawback to these hydraulic systems is the requirement of matching the sizes of the boom and bucket cylinders so that the volume displaced from the boom cylinder will extend the bucket cylinder the precise distance to hold the bucket level as the boom is raised. As a result, a more expensive, unnecessarily large bucket cylinder is included in the hydraulic system. Further, because opposite ends of a hydraulic cylinder have different displacements due to the space taken by the cylinder rod at one end, bucket leveling can be effected in only one direction of boom movement.
It is therefore apparent that a hydraulic bucket leveling system not requiring matched boom and bucket cylinders would provide a more versatile and economic hydraulic control for front end loaders.
SUMMARY OF THE INVENTION To this end, the present invention contemplates a hydraulic control system that directs only the necessary portion of boom displaced fluid to actuate the bucket cylinder, thereby permitting greater leniency in the size and design of the boom and bucket cylinders.
Accordingly, the invention broadly contemplates a control system for selectively actuating a first hydraulic motor by a portion of the fluid displaced from a second hydraulic motor.
Another object of this invention is to provide a control valve assembly and fluid system for actuating the boom and bucket motors of a front end loader whereby the bucket is automatically leveled during both the raising and lowering of the boom.
A more specific objective of this invention is to provide a control valve assembly including separate valves for regulating the boom and the bucket and a flow divider for directing a portion of fluid returning to the boom control valve into the bucket control valve to operate the bucket cylinder.
Another objective of this invention is to provide a control valve assembly characterized by the foregoing objectives wherein manual actuation of the bucket valve overrides the automatic bucket leveling operation For such a control valve assembly, it is another object of this invention to provide a spool-type boom control valve which has a float position connecting both ends of the boom cylinder to low pressure.
A further object of this invention is to provide a bucket leveling control system comprising a bank of spool-type sectional control valves which can be interchangeably assembled.
Other objects and advantages of the present invention are described in, or will become apparent from, the following detailed description and accompanying drawings of the preferred embodiments.
Briefly, one form of the invention comprises a spool-type control valve selectively interconnecting opposite ends of a boom cylinder motor to a source of fluid pressure and drain to maneuver the boom. A similar control valve directs fluid to and from a hydraulic cylinder motor for positioning a bucket attached to the boom. The boom valve has a transfer passage into which displaced fluid from the boom cylinder can be directed upon proper positioning of the boom valve spool. A flow divider in the transfer passage directs a portion of the boom displaced fluid to the bucket control valve and the remainder to drain, Thetransferred fluid flows to one end of the bucket cylinder, with pressure of the transferred fluid actuating a piston to connect the other end of the bucket cylinder with drain, whereby the bucket operates in the desired manner in correlation with boom movement.
BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: FIG. 1 is a partial schematic of the hydraulic controls for a front end loader including longitudinal section views of the 15 control valves, with the bucket valve in neutral and the boom valve in raise-and-level position;
FIG. 2 is a partial transverse section of a stack valve assembly including the control valves shows in FIG. 1;
FIG. 3 is an enlarged section view of the flow divider; FIG. 4 is a section view of the boom valve of FIG. 1 in a raise position;
FIG. 5 is a view similar to FIG. 4 with the boom valve in lowering position;
FIG. 6 is a view similar to FIG. 4 with the boom valve in 25 float position;
FIG. 7 is a partial schematic of another embodiment of the DESCRIPTION, FIG. 1
More particularly, FIG. 1 illustrates a boom arm 10 and bucket 11 as commonly mounted to the frame 12 of a mobile vehicle. Boom 10 is pivotally attached to the vehicle at pivot 40 13 for up-and-down movement, while bucket 11 is mounted to the boom at pivot 14 to facilitate scooping and dumping movements. Pressurization of the head end 17 of boom cylinder 15 causes extension of rod 16 and raises the boom, while pressurization of rod end 18 retracts rod 16 and lowers 45 the boom arm. Pressurizing head end 21 of bucket cylinder 19 extends rod 20 and rotates bucket 11 clockwise about pivot 14 and boom 10, and pressurizing rod end 22 retracts rod 20 to rotate the bucket counterclockwise. The opposite ends of cylinders 15 and 19 are respectively connected to boom control valve 23 and bucket control valve 26 at control ports 24,
and 27, 28.
Body 29 of boom valve 23 has a longitudinal bore 30 in which a cannelured control spool 31 is movable to different positions to selectively interconnect and isolate various passages numbered 32 through 41 communicating with bore 30 at spaced positions. Passages 32 and 41 communicate with a low pressure fluid return reservoir, and port passages 34 and 40 respectively connect with cylinder chambers 18 and 17 60 through ports 24 and 25. Passages 36, 37 and 38 form the central bypass portion of the open center fluid delivery system,
which system also includes pressure fluid delivery passage 42 and the branch passages and 39 connectable with passage 42 across one-way lift check valve 43.
Port passage relief valve 54 is interposed between passages 40 and 41 to protect port passage 40 and boom cylinder chamber 17 from overpressurization by diverting fluid from passage 40 to drain passage 41 in response to excessive pres sure in the port passage. Relief valve 54 is of conventional 70 structure and operation well known to the art and will not be described in detail.
A transfer passage 33 extends in body 29 from bore 30 to parallel blind bore 44 that is intercepted by drain passage 32 and auxiliary outlet passage 46. Flow divider 45, movable 5 within bore 44, is formed as a hollow sleeve having orifice plugs 48 and 49 securely fastened at either end to define a hollow interior communicating with transfer passage 33 through cross bores 47. The flow divider is clearly illustrated in FIG. 3. Orifice holes 50 and 51, normally of different sizes, connect the flow divider interior respectively with drain passage 32 and auxiliary outlet 46 across the flow orificing restrictions 52 and 53 formed between the chamfered ends of flow divider sleeve 45 and the cooperating portions of valve body 29. The proportional type flow divider 45 directs a certain percentage of flow from transfer passage 33 to auxiliary outlet 46, and diverts the remaining flow to drain passage 32.
Referring again to FIG. 1, bucket valve 26 is structurally similar to boom valve 23, having a fluid delivery system comprising bypass passages 36a, 37a, 38a, and pressure delivery passages 35a and 39a. Moving cannelured control spool 72 either direction within bore 71 directs pressure fluid to port passages 73 and 74 from adjacent passages 35a and 39a that connect with passage 42a across lift check valve 430. Passages 32a and 41a, connected with a low pressure reservoir, also communicate with bore 71. Port passage relief valves 75 and 76, similar in structure and function to relief valve 54 of the boom valve, are respectively interposed between the port passages 73, 74 and drain passages 32a, 41a to protect the chambers 21 and 22 of bucket cylinder 19 from overpressurization.
An auxiliary fluid inlet bore 82 and passage 77 in bucket valve 26 directly communicate with the auxiliary outlet passage 46 of boom valve 26 when valves 23 and 26 are assembled, as shown in dotted lines in FIG. 2. Valves 23 and 26 are of the sectional type'that are secured together in side-byside relationship, along with other sectional control valves if desired, to form a conventional stack valve assembly 130. Port plates 131 and 132 fastened at either end of the bank of valves have a pressure port 133 connected with pump 134 and a drain port 135 communicating with a low pressure reservoir to provide common fluid supply and drain systems for valves 23 and 26. As seen, pressure port 133 communicates with passages 36a and 38a of the central bypass system and drain port 135 connects with passages 32, 37 and 41. Since passages 82 and 46 extend transversely through valve bodies 70 and 29, and because of their similarity in structure as shown in FIG. 2, valves 23 and 26 may be interchangeably assembled with boom valve 23 next to inlet port'plate 131 and bucket valve 26 next to outlet port plate 132.
Again in FIG. 1, auxiliary passage 77 in bucket valve 26 communicates with port passage 73 and the head chamber 21 of bucket cylinder 19 across a one-way check valve 78 that opens, as shown, when pressure in passage 77 overcomes passage 73 pressure and the check valve spring bias. Check valve 78 has a poppet 79 spring biased to a closed position wherein it mates against a cooperating seat formed in valve body 70 to prevent fluid flow from passage 73 to passage 77. I-Iydraulically actuated unloading piston 81 in bore 80 is movable from the open position shown wherein passages 74 and 41a communicate across bore 80, leftwardly to a closed position blocking flow through bore 80. Piston 81 is spring biased toward its closed position and opened by pressure in auxiliary passage 77. The spring preload on piston 81 is greater than the spring preload on check valve poppet 79. The various operational modes will now be discussed in detail.
OPERATION, FIG. 1
Neutral Positions Referring to FIG. 2 with both spools 72 and 31 in neutral, fluid entering inlet port 133 openly bypasses to drain port 135 by flowing from passages 36a, 38a through bore 71 to passages 37a, 36 and 38, across bore 30 to passage 37 and port 135. Actuating either spool 72 or 31 away from neutral blocks this bypass flow at bore 71 or 30, so that pressure builds in port 133; passages 42, 42a of FIG. 1, connected with inlet port 133, then deliver the pressure fluid across the lift checks 43, 43a to the valve work ports. Upon subsequent release of the spool, the centering spring assembly 84 or 84a returns it to neutral.
With spool 72 of bucket valve 26 in the neutral position, FIG. 1, both work ports 73, 74 are isolated from adjacent passages to hydraulically lock both cylinder chambers 21, 22 and hold the bucket in position. Similarly, boom 10 is locked in position when spool 31 is in neutral and blocking port passages 34 and 40 from adjacent passages 33, 35 and 39, 41. Spool 31 is illustrated in neutral in FIG. 7.
Bucket Lift To rotate bucket 11 counterclockwise to effect a scooping and lifting action, spool 72 is manually moved leftwardly from neutral. (Such position of spool 72 is shown in FIG. 7) Central bypass flow through passage 37a is blocked at bore 72, and pressure fluid delivered through passage 42a forces open the spring biased poppet 83 of lift check 43a to flow into branch passage 39a and continue through bore 71, port passage 74, port 28 and the rod chamber 22 of cylinder 19.
Rod 20 retracts under hydraulic pressure, and fluid displaced from head chamber 21 returns to port 27 and passage 73 of valve 26, and flows across bore 71 to drain passage 32a.
Bucket Dump Boom Raise-and-Level The raise-and-level operation extends rod 16 to raise boom 10 and proportionally extends rod 20 of bucket cylinder 19 in order to keep bucket 11 in its same position relative to the ground as it was prior to raising boom 10. For example, bucket 11 is placed in a level position before actuating the boom; in subsequently rotating boom 10 30 counterclockwise about pivot 13, bucket 11 must, at the same time, rotate 30 clockwise about pivot 14 to remain in its original level position. To accomplish this correlated, slave operation of cylinder 19, fluid transfer means including passages 33, 46, 82 and 77 are incorporated to deliver fluid to cylinder 19 during boom raising.
The raise-and-level position of spool 31 shown in FIG. 1
blocks flow through the central bypass system and directs pressure fluid from branch passage 39 to port passage 40, port 25 and head chamber 17 of cylinder 15. Boom 10 is driven upwardly and fluid displaced to port 24 from cylinder chamber 18 passes across bore 30 into transfer passage 33 which is blocked from drain passage 32 by spool land 55. Theboom cylinder displaced fluid continues through cross bores 47 to the hollow interior of flow divider 45 wherein a specified portion is directed to auxiliary outlet passage 46 and connecting auxiliary inlet passages 82 and 77. Pressure in passage 77 builds sufficiently to open check valve 78 and move unloading piston 81 rightwardly to the position shown. The regulated fluid flow into passage 77 then continues to head chamber 21 of cylinder 19 to rotate the bucket clockwise, with displaced fluid from rod chamber 22 returning through port 28, passage 74 and bore 80 into drain passage 41a.
In the fluid flow from transfer passage 33 to each of downstream passages 46 and 32, flow divider 45 places two orifices in series, the first orifice 50, 51 being fixed in size to determine the portion of flow delivered to each downstream passage, and the second orifice 52, 53 being variable in size to compensate for the difference in downstream pressures. By shifting within bore 44, flow divider 45 varies the sizes of secondary restrictions 52 and 53 so that pressure between orifices 50 and 52 at the left end balances pressure at the right end between orifices 51 and 53. With orifice 51 larger than orifice 50 for example, the majority of flow from passage 33 passes through larger orifice 51 to passage 46; flow divider 45 moves leftwardly to reduce the size of orifice 52 and build sufficient back pressure between orifices 50 and 52 to balance pressure from passage 46 exerted on the right end of the flow divider. The equal pressures at either end accordingly dictate equal pressure drops across orifices 50 and 51, so that the sizes of these orifices solely determine the rates of flow to passages 46 and 32.
Orifices 50 and 51 are appropriately sized in accordance with the volume capacities of cylinder chambers 18 and 21 to transfer the required fluid from chamber 18 through orifice 51 to chamber 21 to rotate bucket 11 and maintain the original bucket level position as the boom raises. Fluid in excess of that required by chamber 21 passes through orifice 50 to drain passage 32. Additionally, thepresent invention can divert more or less fluid to bucket cylinder chamber 21 by changing the sizes of orifices 50 and 51, to rotate the bucket to a load dumping or a tilted-back position respectively during boom raising. Generally, therefore, bucket 11 is automatically driven from a prescribed initial position to a predetermined end position during the raise stroke of the boom in accordance with the selection of orifice sizes in flow divider 45.
Unloading piston 81 is moved to an open position only when pressure exists in passage 77. Inadvertent drainage of fluid from cylinder chamber 22 and consequent movement of the bucket is prevented when spool 31 is not in raise-and-level position by the interconnection of passage 33 and drain passage 32 through bore 30 to relieve pressure in passage 77 and allow piston 81 to be spring biased to the closed position. Additionally, pressure operated piston 81 prevents cavitation in bucket cylinder chamber 21 during the raise-and-level operation. Whenever rod 20 tends to be pulled outwardly by a heavy load faster than the transferred fluid is flowing into chamber 21 and, accordingly, begins to establish cavitation of chamber 21, pressure in passage 77 drops and piston 81 moves toward its closed position to restrict or completely block flow from chamber 22 to drain. This metering action by piston 21 thus limits the speed of movement of rod 20 to match the rate of flow into chamber 21 and maintains positive pressure in passage 77 and chamber 21.
The automatic positioning of bucket cylinder 19 in the boom raise-and-level position can be selectively overridden by moving bucket spool 72 to a cylinder actuating position. Leftward actuation of spool 72 from neutral connects passage 73 with drain passage 32a and passage 74 with pressurized branch passage 39a. The consequent loss of pressure in passages 73 and 77 allows piston 81 to move leftwardly to isolate pressure carrying passage 74 from drain passage 41a. Bucket 11 rotates counterclockwise, and displaced fluid from chamber 21 exhausts across bore 71 to drain passage 32a. The
boom is capable of continuing to raise in this override condition, with a slight pressure in passage 77 opening check valve 78 (through such pressure does not overcome the stronger spring bias on piston 81) and allowing boom displaced fluid also to exhaust to drain passage 32a. In moving bucket spool 72 rightwardly from neutral, pressure fluid delivered from passage 35a to passage 73 (acting with the transferred fluid from passage 77 if the boom continues to raise) drives bucket 11 clockwise, while passage 74 is connected with drain passage 41a across both bores 71 and 80 for exhausting fluid from cylinder chamber 22. During raise-and-level operation, therefore, bucket 11 can be selectively positioned in the normal manner by actuating spool 72 to override the bucket leveling operation.
Automatic slave positioning of cylinder 19 may also be accomplished by the present system when boom 10 is in a lowering cycle. For example, by reversing the connections of the cylinder chambers with the valve ports so that chambers 17 and 18 respectively connect with ports 24 and 25, and chamber 21 and 22 respectively connect with ports 28 and 27,
the fluid displaced from head chamber 17 of boom cylinder 15 during lowering of boom 10 will now be conducted through the transfer means to rod chamber 22 of cylinder 19 to retract rod 20. In comparison to the raise-and-level operation, this lower-and-level operation requires the orifices of the flow divider to be sized to divert a smaller portion of the fluid from head chamber 17, which has greater displacement than rod chamber 18, into the rod chamber 22 of cylinder 19 which has less displacement than head chamber 21. It can be seen that a hydraulic system for effecting automatic lower-and-level has been heretofore impractical, as cylinder 19 would have to be larger than cylinder 20 so that the total volume of fluid displaced from head chamber 17 and transferred to rod chamber 22 would appropriately move the bucket to keep it level as boom 10 lowers.
Boom Raise Boom 10 can be selectively raised without automatically leveling the bucket by positioning spool 31 slightly rightwardly from the FIG. 1 raise-and-level position to a position as shown in FIG. 4. In this position spool land 55, being narrower than passage 33, affords intercommunication between port passage 34, transfer passage 33'and drain passage 32. Pressure fluid is still delivered from branch passage 39 to port passage 40 to raise the boom; however, displaced ifluid from the boom cylinder flows directly from port 24 and passage 34 through passage 33 and bore 30 to drain passage 32, rather than being transferred to the bucket control valve. The bucket will remain hydraulically locked in position while the boom is so raised since no pressure fluid is transferred to passage 77 of bucket valve 26 (FIG. 1) to open poppet 79 and piston 81.
Boom Lower As shown in FIG. 5, spool 31 is moved to the right of neutral to lower the boom arm. Central passage 37 is again blocked from passages 36 and 38 so that pressure fluid from the valve inlet opens lift check 43 to deliver fluid through branch passage 35 to passage 34 and the rod end of the boom cylinder. Displaced fluid from the opposite cylinder end returns to port 25 of valve 23 and continues through bore 30 to drain passage 41. Passage 33 remains in communication with drain passage 32 and is blocked from passage 34 by land 55 to relieve pressure from the transfer passage means.
Boom Float A float position of spool 31 is incorporated in control valve 23, as illustrated in FIG. 6, wherein both port passages 34 and 40 are connected with drain passages 32, 41 through bore 30. Reduced diametral portions 57 and 58 reestablish the central bypass flow of the open center fluid delivery system through interconnection of passages 36, 37 and .38, which accordingly relieves pressure from passage 42 to close check valve 43. Again, passage 33 is drained through bore 30 to relieve pressure from the transfer passage means and render inoperative the automatic actuation of the bucket.
With both ports 24 and 25 and the opposite ends of the boom cylinder so drained, the boom rod can freely move within the boom cylinder, and the boom is capable of floating over irregular terrain. Maintenance of a low back pressure within drain passages 32 and 41 to which the cylinder chambers are connected in float position, positively prevents formation of cavitation conditions within the boom cylinder chambers during float operation.
In addition to providing a preferred float operation, location of transfer passage 33 intermediate port passage 34 and drain passage 32 circumvents hydraulic lock of the transfer passage means. As described, transfer passage 33 communicates with drain passage 32 in all positions of spool 31 with the exception of the raise-and-level position wherein it connects with port passage 34. Never being hydraulically isolated, the transfer passage means, therefore, are not subject to collection of pressure fluid leakage, and the consequent inadvertent opening of piston 81 and undesired bucket movement is avoided.
FIG. 7 EMBODIMENT As shown by like numerals for like parts, FIG. 7 is similar in construction and operation to the FIG. 1 control system and additionally includes port passage relief valve 59 in boom valve 60, and a flow divider valve section 100 sandwiched between the boom and bucket control valve sections. Bucket control valve section 26 is shown with its spool 72 positioned in a rod retracting position, and spool 31 of the boom valve is in neutral.
Port passage relief valve 59 is interposed between port passage 63 and drain passage 32 of valve body 61 to divert fluid to drain passage 32 and prevent excessive pressure buildup in passage 63. Valve 59 is similar in construction and operation to conventional port passage relief valves 54, 75 and 76. In raise-and-level operation the relief valve 59 protects both interconnected passages 33 and 63, and is preset to a higher pressure setting than is port relief valve 75 of control valve 26 to which transfer passage 33 is interconnected in the raise-and-level operation. This higher relief pressure setting on valve 59 takes into account the pressure drops in the fluid transferring from passage 33 to passage 73 so that pressure in passage 73 can build to the level allowed by relief valve 75. Also, when rod 20 reaches the end of its stroke while spool 31 is in raise-and-level position, relief valve 59 protects passages 33 and 63; relief valve 75 cannot reliably communicate with and protect these passages in such instance because check valve 78 may be locked in a closed position.
Flow divider section 100 is interpbsed between valves 26 and 60 in the valve bank assembly and has transverse through passages 32b, 37b, 41b and 42b properly interconnecting with the boom and bucket valve passages denoted by corresponding numerals. Flow divider 45 in axial bore 102 is located in the transfer passage means in the same manner as in FIG. 1, since: transverse through passage 104 communicates with bore 62 and transfer passage 33 of boom valve 60; the left passage 103 connects with drain passage 32b; and the right passage 105 connects with through passage 106 that leads to auxiliary inlet bore 82 of valve 26. Accordingly, the operation of flow divider 45 and the FIG. 7 system is the same as described with respect to FIG. 1.
DESCRIPTION, FIG. 8
The hydraulic control system of FIG. 8 is capable of selectively automatically positioning the bucket when the boom is both raised and lowered, by diverting a portion of displaced fluid from boom cylinder to bucket cylinder 19. The control system comprises a boom control valve 64, flow divider valve section 107 and bucket valve 85 generally similar in construction to the valve sections of previous embodiments as illustrated by using the same numerals to identify like features.
Control spool 66 of boom valve 64 is movable from neutral to four cylinder actuating positions and has no float position, though such may be incorporated if desired. Body 65 has a second fluid transfer passage 67 intermediate port passage 40 and drain passage 41. A transverse through bore 68 similar to bore 62 communicates with passage 67 and functions to deliver displaced fluid from cylinder chamber 17 to control valve 85 when spool 66 is in lower-and-level position.
Flow divider section 107 between valve sections 64 and 85 in the assembled bank of valve sections functions to deliver a specified portion of fluid from valve 64 to valve 85 as well as provide a free flow return passage to drain for fluid displaced from cylinder 20. In addition to flow divider 45 in bore 102, body 108 includes bore 109 which receives a second, identical flow divider 45a that operates in like manner as flow divider 45 to regulate flow to bucket cylinder chamber 22 during lower-and-level operation. Three passages 111, 112 and 113 intercept bore 109 at spaced locations: passage 111 connects with drain passage 41b; passage 113 communicates with transverse through bore 114 that connects to auxiliary inlet bore 91 of bucket valve 85; and passage 112 extends transversely through body 108 to communicate with bore 68 of valve 64. Also included within body 108 are a flow divider bypass passage I15 extending between bore 114 and passage 112, and a similar bypass passage 117 between bore 106 and passage 104. Check valves schematically illustrated at 116 and 118 are located in passages 115 and 117 to assure that fluid flows from passages 112, 104 to passages 114, 106 respectively via the flow divider orifices 51 and 51a.
Bucket control valve has an elongated plunger piston 87 and spring loaded check valve 88 in place of the unloading piston 81 of the previously described embodiment of the bucket valve. Check valve 88, like check valve 78 in structure and function, has a poppet 89 normally spring biased to a closed position blocking flow between port passage 74 and passage in body 86. Pressure in either of passages 77 to 90 operates directly and through piston 87 to open both check valves 78 and 88. For instance, as shown in FIG. 8, high pressure in passage 77 acts directly on poppet 79 to move it leftwardly to the open position, and forces piston 87 rightwardly to engage and move poppet 89 rightwardly to the open position. With low pressure in both of passages 77 and 90, the spring bias on poppets 79 and 89 move them inwardly to closed positions as piston 87 is not long enough to simultaneously contact both poppets 79, 89.
OPERATION, FIG. 8
The operation of FIG. 8 in the neutral, bucket lift, bucket dump, boom raise and boom lower modes is as described with respect to FIG. 1 and need not again be set forth in detail. Note that land 69 of spool 66, similar to land 55, is not as wide as passage 67 so that selection of the boom lower operation positions land 69 midway in passage 67 to permit interconnection of the three adjacent passages 40, 67 and 41, and thereby direct displaced fluid entering port 25 and passage 40 to drain passage 41. In boom raise-and boom lower, check valves 78 and 88 remain closed as passages 77 and 90 of the bucket valve are drained through boom valve passages 62 and 67 which are respectively communicating with drain passages 32 and 41.
Boom Raise-and-Level Boom spool 66 is illustrated in raise-and-lvel position in FIG. 8. The transfer of a portion of displaced fluid from cylinder chamber 18 to cylinder chamber 21 to effect the raise-and-level operation is the same as described with respect to the previous embodiments, check valve 118 in flow divider section 107 being held closed by pressure in passage 104 to direct the transferring fluid through flow divider 45 to bore 106. However, fluid displaced from bucket cylinder 19 returns through the boom valve to discharge to drain: Pressure in passage 77, having opened check valve 88 by forcing piston 87 rightwardly, allows fluid displaced from chamber 22 to return through passages 74, 90 and 91 to bore 114 of the flow divider section. This return flow bypasses flow divider 45a by opening check valve 116 and continues to conduit 115, passages 112, bore 68, passage 67 and through the bore 30 to drain passage 41 in the boom control valve.
Boom Lower-and-Level By moving spool 66 to the right until land 69 interrupts flow between passages 67 and 41 as shown in FIG. 9, the lowerand-level operation is'selected. Transfer passage 33 is connected with drain passage 32 through the spool bore, and pressure fluid from branch passage 35 is directed to passage 63, port 24 and the boom cylinder rod chamber to retract the boom cylinder. Fluid displaced from the boom cylinder returns to port 25, passage 40 and continues through passage 67 and bore 68 out of valve 64 and into flow divider section 108 (FIG. 8) at passage 112. This transfer fluid flow closes ball check valve 116 and passes to the interior of flow divider 45a to there be divided, with a specified portion directed through orifice 51a to passages 113 and 114 and the remainder diverted through orifice 50a to drain. The transferred fluid in passage 114 continues to passage 90 of bucket valve 85 to open poppet 89 and urge piston 87 leftwardly to engage and open poppet 79. Fluid in passage 90 continues past poppet 89 to port passage 74 and cylinder chamber 22 and retracts bucket cylinder rod 20 in correlation with the boom cylinder rod retraction to keep the bucket level during boom lowering. Exhausted fluid from bucket cylinder chamber 21 returns past open check valve 78 to passage 77, bore 82 and bore 106 of the flow divider section. The return flow bypasses flow divider 45 by opening check valve 118 and continues to passage 104 into valve 64 (FIG. 9) at passage 33 and through the spool bore 30 to drain passage 32.
Selective overriding of the automatic leveling actuation of the bucket cylinder is accomplished upon movement of bucket spool 72 away from neutral. This function is the same in lower-and-level as it is in raise-and-level. Referring to FIG. 8 and the raise-and-level operation, to override and retract rod 20, spool 72 is moved leftwardly from neutral to interconnect passage 390 with port passage 74 and connect drain passage 32a with port passage 73. Pressure fluid introduced into passage 74 passes through opening 92 to the rear of poppet 89 into spring carrying chamber 93 to assist the spring bias of check valve 88 in moving poppet 89 to its closed position.
Pressure in passage 74 and chamber 93 exerts sufficientlygreater force on poppet 89 than pressure in passage 77 exerts on piston 87, and poppet 89 cannot open. The pressure fluid in passage 74 passes onto cylinder bhamber 22 to retract rod 20 and thereby override the raise-and-level operation. Fluid displaced from chamber 21 drains through passage 73, bore 71 to passage 32a. Assuming the boom continues raising at this time, the fluid in passage 77 displaced from cylinder opens check valve 78 to flow to drain passage 32a.
Moving spool 72 rightwardly to extend rod during raiseand-level simply complement the flow of pressure fluid to chamber 21 and draining of fluid from chamber 22.
Overriding during lower-and-level is accomplished in the same manner, and poppet 79, accordingly, has an opening 94 communicating chamber 95 with passage 73 to assure closure of check valve 78 upon introduction of pressure fluid into passage 73 from passage 35a.
Automatic bucket leveling while lowering and raising the boom can be effected without including a flow divider in each path of transferring fluid flow from passages 33 and 67 to the bucket valve. Leveling while raising the boom can instead be accomplished by the prior art method of matching the cylinder sizes so that all fluid displaced from boom cylinder chamber 18 during raising is used by bucket cylinder chamber 21 in extending rod 20, and during boom lowering is effected by the improved method of the present invention. Flow divider 45 is now and it along with bore 102, passages 103, 105 and check valve 118 can be eliminated from flow divider section 107 to leave continuous fluid communication between passage 33 of valve 64 and bore 82 of valve 85 through the flow divider section. The operation in raise-and-level and in lower-and-level is the same as before except all fluid displaced from f the boom cylinder is transferred to the bucket cylinder in raise-and-level, while still only a specific portion of fluid, as controlled by flow divider 45a, is transferred from boom to bucket during lower-and-level. The adaptability of the correlated bucket movement described before is now, of course, available only while the boom is being lowered.
Modifications to the construction and uses of the invention as specifically set forth in the foregoing description will be apparent to those skilled in the art. For instance, the several valve sections depicted in each of the embodiments may be incorporated into a unitary control valve, or a different pressure fluid delivery system may be used tosupply fluid to the bucket and boom control valves, or various forms of flow dividers may be used in place of that shown, or a pair of cylinder actuators may be substituted for either of the single cylinders 15 or 19. Accordingly, the specific embodiments of the invention herein described are to be considered exemplary in nature and not limiting to the scope and spirit of the invention as set forth in the appended claims.
1. A hydraulic system for controlling the related operation of at least a first and second fluid actuated motor, comprising:
a pressure fluid supply, a reservoir, and control valve means communicating with the fluid supply, reservoir and first motor;
fluid transfer means operatively connected to said control valve means and the second motor to accommodate fluid flow therebetween;
a first control element in said control valve means shiftable to a transfer position directing pressure fluid to the first motor to actuate same and directing fluid displaced from the first motor to said transfer means through said control valve means; and
flow divider means interposed in said fluid transfer means for directing a predetermined portion of said displaced fluid to the second motor to actuate same in correlation with actuation of the first motor.
2. The hydraulic system of claim 1 further comprising check valve means located in said fluid transfer means intermediate said flow divider means and the second motor adapted to prevent reverse flow through said transfer means from the second motor to said control valve means.
3. The hydraulic system of claim 1 further comprising second control valve means communicating with the pressure fluid supply, reservoir and the second motor, said secondvalve means having an associated second control element shiftable to direct fluid from the pressure fluid supply to the second motor to actuate same and override actuation of the second motor by said predetermined portion of displaced fluid.
4. The hydraulic system of claim 1 wherein said flow divider 'means communicates with the reservoir through a discharge duct, and directs the remainder of said displaced fluid to said discharge duct and reservoir.
5. The hydraulic system of claim 4 wherein said flow divider means includes a first flow restrictor interposed in the flow path from said fluid transfer means to said discharge duct and a second flow restrictor interposed in the flow path from said fluid transfer means to the second motor, the relative sizes of said restrictions determining said portion of displaced fluid directed to the second motor.
; voir in all positions of said first control element other than said transfer position 8. The hydraulic system of claim 1 wherein said second motor has opposing variable volume fluid chambers and is actuatable upon introduction of said predetermined portion of displaced fluid into one of said chambers, and said fluid transfer means include a hydraulically operable piston controlling communication between the other of said chambers and the reservoir, said piston movable to an open position connecting said other chamber with the reservoir in response to a predetermined pressure in said fluid transfer means.
9. The hydraulic system of claim 8 further comprising a check valve in said fluid transfer means intermediate said flow divider means and said one chamber adapted to prevent reverse flow from said one chamber to said control valve means.
10. A control for a hydraulic power system including a fluid supply, a reservoir, first and second double acting hydraulic motors having movable barriers therein dividing each of said motors into two variable volume chambers, said control comprising:
a hydraulic valve assembly operatively connected to said supply and reservoir for supply and return of hydraulic fluid, said valve assembly including first and second control passages connected to actuate said fist motor by delivering and returning hydraulic fluid therefrom and third and forth passages connected to actuate said second motor by delivering and returning hydraulic fluid therefrom;
a fluid transfer passage adjacent said first passage and communicating with said third passage;
a first control element selectively shiftable to actuate said first motor, having a first position connecting said first passage with said transfer passage and said second passage with said fluid supply whereby fluid discharged from said first motor is delivered to said transfer passage;
a second control element shiftable to actuate said second motor and having a neutral position wherein said transfer passage is in communication with one chamber of said second motor through said third passage and the other chamber is in communication with said froth passage;
a flow divider interposed in said transfer passage communicating with said reservoir, and being adapted to direct a predetermined portion of flow in said transfer passage to said third passage and directing remaining flow to reservoir;
check valve man in said transfer passage intermediate said flow divider and said third passage blocking reverse flow from said third passage to said first passage; and
pressure responsive means communicating with said transfer passage controlling communication between said fourth passage and said reservoir, whereby positioning said first control element in said first position and said second element in said neutral position directs fluid to said first motor to actuate same, directs fluid displaced from said first motor through said transfer passage to said flow divider whereby a predetermined portion of said displaced fluid is directed to said second motor to actuate same in correlation with actuation of the first motor, and whereby pressure in said transfer means actuates said pressure responsive means to permit return of flow from said second motor to said reservoir through said fourth passage.
11. The control of claim further comprising a pressure relief valve adapted to relieve fluid from said transfer passage to limit pressure therein to a predetermined value.
12. The control of claim 10 wherein shifting said second control element away from said neutral position to actuate the second motor overrides actuation of the second motor by said predetermined portion of displaced fluid.
13. A control valve assembly for selectively actuating first and second fluid motors comprising:
a housing having a supply passage for connection with a source of pressure fluid, a fluid discharge passage for connection with a low pressure reservoir, and first and second axial bores intercepted at spaced positions by said supply and discharge passages;
first and second control passages intersecting said first axial bore and connectable with opposite ends of the first motor;
third and fourth control passages intersecting said second axial bore and connectable with opposite end of the second motor;
first and second cannelured control spools respectively disposed in said first and second axial bores, each movable to various positions interconnecting said control passages with the inlet and discharge passages for selective actuation to the first and second motors;
a transfer passage extending from said third control passage to intercept said first bore intermediate and adjacent said first control passage and said discharge passage, said first spool in a first position interconnecting said first control passage with said transfer passage and blocking same from said discharge passage, and in all other positions interconnecting said transfer passage and said discharge passage;
a flow divider comprising a movable body located in the housing in a third axial bore intercepted by said transfer and discharge passages, said body having first and second flow restrictors formed thereon restricting fluid flow from said transfer passage to said third control passage and said discharge passage respectively, whereby a predetermined percentage of flow in said transfer passage is directed through said first restriction to said third control passage and the remainder is directed through said second restriction to said discharge passage;
a spring biased check valve in said transfer passage intermediate said flow divider and said third control passage permitting one-way flow through said transfer means from said first control passage to said third control passage; and
a hydraulically operable piston biased to a closed position and responsive to a predetermined pressure in said transfer passage to move to an open position interconnecting said fourth control passage with said discharge passage at a position spaced from said first and second axial bores.
14. The control valve assembly of claim 13 wherein said housing comprises an assembly of section valves including:
a first sectional valve having disposed therein said first axial bore, said first control spool, said first and second control passages, said third axial bore and said flow divider;
a second sectional valve operatively adjacent said first sectional valve having disposed therein said second axial bore, said second control spool, said third and fourth control passages, said check valve, and said piston;
end plates enclosing said sectional valves provided with inlet and outlet openings respectively in communication with said supply and discharge passages in said assembly; and
wherein said transfer, supply and discharge passages extend substantially transversely through said sectional valves.
15. The control valve assembly of claim 13 further including a pressure relief valve in said housing extending between said first control passage and said discharge passage, adapted to divert fluid from said first control passage to the discharge passage in response to a predetermined pressure in said first control passage to limit pressure therein.
16. The control valve assembly of claim 15 wherein said housing comprises an assembly of section valves including:
a first sectional valve having disposed therein said first axial bore, said first control spool, said first and second control passages, and said pressure relief valve;
a second sectional valve having disposed therein said second axial bore, said second control spool, said third and fourth control passages, said check valve, and said piston;
a third sectional valve interposed between the first and second sectional valves, having disposed therein said third axial bore and said flow divider;
end plates enclosing said sectional valves provided with inlet and outlet openings respectively in communication with said supply and discharge passages in said assembly; and
wherein said transfer, supply and discharge passages extend substantially transversely through said sectional valves.
17. In a hydraulic system including a pump, a reservoir, 21
first double acting motor having fist and second variable volume fluid chambers, a second double acting motor having third and fourth variable volume fluid chambers, a control valve operatively connected with the pump, reservoir and first motor, and a movable control element mounted in said control valve adapted to connect said first motor fluid chambers with the pump and reservoir to actuate the first motor; wherein the improvement comprises:
first fluid transfer means operatively connected with said control valve adapted to interconnect said first and third fluid chambers upon positioning said control element in a first transfer position directing pressure fluid from said pump to said second chamber, whereby displaced fluid from said first chamber flows to said third chamber to actuate the second motor in a first direction;
a flow divider communicating with the reservoir and inter posed in said first fluid transfer means to direct a predetermined portion of fluid flow therein to a said third chamber and divert the remainder of fluid flow in said first fluid transfer means to reservoir; and
discharge means connected with said second motor and the reservoir operative upon movement of said control element to said first transfer position to interconnect said fourth chamber with the reservoir, and operative upon movement of said control element to said second transfer position to interconnnect'said third chamber with the reservoir.
18. The hydraulic system of'claii li 17 further including a second flow divider communicating with the reservoir and interposed in said second fluid transfer means to direct a predetermined portion of fluid flow therein to said fourth chamber and divert the remainder of fluid flow in said second transfer means to reservoir.
19. The hydraulic system of claim 18 wherein said first transfer meansincludes a firstchecli valve located intermediate the first flow divider and said third chamber biased to a closed position blocking flow therebetween and responsive to a predetermined pressure in said first transfer means to move to an open position, and wherein said second transfer means includes a second check valve located intermediate said second flow divider and said fourth chamber biased to a closed position blocking flow therebetween and responsive to a predetermined pressure in said second transfer means to move to an open position.
20. The hydraulic system of claim 19 wherein said control element connects said second transfer means with the reservoir in said first transfer position, and said discharge means include:
a plunger operably engaging said second check valve and adapted to open same in response to said predetermined pressure in said first transfer means;
a bypass passage connected with said second transfer means in parallel with said second flow divider; and
a unidirectional valve in said bypass passage blocking flow therethrough from said control valve to said second motor, whereby in said first transfer position pressure in said first transfer means opens said second check valve to establish a flow path from said fourth passage through said second transfer means and said bypass passage to the reservoir. r 21. In a hydraulic valve assembly including a body having first and second axial bores intersected by a pressure inlet connected to a pump and a fluid outlet connected to a reservoir, first and second control passages intersecting the first axial bore and connected to expanding and contracting chambers of a first double acting motor, third and fourth control passages intersecting the second axial bore and connected to expanding and contracting chambers of a second double acting motor, and first and second spools mounted in said first and second axial bores respectively and shiftable away from neutral to positions directing fluid to and from said control passages to actuate said motors, wherein the improvement comprises:
first and second fluid transfer circuits in said assembly extending from said first axial bore to said third and fourth control passages respectively; a said first spool having transfer positions for actuating both said motors wherein the first spool is adapted to simultaneously connect the inlet with the expanding chamber of the first motor to actuate same one transfer circuit with the contracting chamber of the first motor to transfer fluid displaced therefrom as actuating flow to the expanding chamber of the second motor, and the other transfer circuit with the outlet to transfer to reservoir the return flow displaced from the contracting chamber of the second motor;
a flow divider interposed in each transfer circuit and communicating with the outlet adapted to direct a preselected portion of said transfer actuating flow to said second motor and the remainder to the outlet whereby the second motor is actuated in predetermined correlation with the first motor;
a bypass conduit communicating with each transfer circuit and arranged parallel to said flow dividers to permit said transfer return flow to bypass said flow dividers;
a unidirectional flow valve interposed in each bypass conduit permitting only .said transfer return flow theretlirough; and
a check valve in each transfer circuit located intermediate the second motor and the bypass conduit openable in response to pressure in either of the transfer circuits when said second spool is in neutral, and responsive to a shift of said second spool away from neutral to move to a closed position blocking transmittal of said transfer actuating flow to the second motor.
UNITED STATES 'PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 5 3, 7 Dated Eehruam; 5 91 Inventor(S) Home: E, Qreber et a1 It is certified that error appears in the above-identified patent and that said Letters Patent: are hereby corrected as shown below:
Column 2, line 4, change comma to a period line 15 change "shows" to --sh0wn-. Column 4, line 16, change "72 to --71--. Column 5, line 75, change "chamber" to --chambe Column 8, line 13, change "to" to --or--; line 43, change "lvel" to --level---. Column 9, line 35, change "complemem to --complements--; line 49, between "and during" insert --leveling--; line 51, between "now and" insert --unnecess2 line 57, delete "f"; line 58, change "specific" to --specified Column 11, line 20, change "man" to --mean& line 55, change "end" to --ends--.
Signed and sealed this 2L .th day of August 1971.
EDWARD M.FLETCHER,JR. WILLIAM E. SCHUYLER, JR. Attesting Officer Commissioner of Patents
|Cited Patent||Filing date||Publication date||Applicant||Title|
|US2798626 *||Nov 19, 1953||Jul 9, 1957||Clark Equipment Co||Mechanism for materials handling machines|
|US3179120 *||May 24, 1963||Apr 20, 1965||Koehring Co||Proportional flow divider|
|US3251277 *||Apr 23, 1964||May 17, 1966||Parker Hannifin Corp||Fluid system and valve assembly therefor|
|Citing Patent||Filing date||Publication date||Applicant||Title|
|US3765554 *||Jul 12, 1971||Oct 16, 1973||Maxon Industries||Self-loading truck|
|US3811587 *||Jul 17, 1972||May 21, 1974||Case Co J I||Hydraulic leveling circuit for implement|
|US3827587 *||Jul 31, 1969||Aug 6, 1974||Carrier Corp||Automatic self-leveling forks|
|US3856163 *||Dec 14, 1973||Dec 24, 1974||Case Co J I||Method of using a hydraulic leveling circuit on an implement|
|US3901264 *||Mar 6, 1972||Aug 26, 1975||Gresen Manufacturing Co||Adjustable flow control for hydraulic valves having high pressure main supply and controls fluid flow to cylinder and exhaust ports|
|US3901395 *||Jul 11, 1973||Aug 26, 1975||Case Co J I||Implement stabilization method and apparatus|
|US3987920 *||Jun 23, 1975||Oct 26, 1976||J. I. Case Company||Self-leveling system for material handling implement|
|US4122868 *||Jan 24, 1977||Oct 31, 1978||International Harvester Company||Hydraulic valve assembly having an axial flow force balanced spool|
|US4126083 *||Feb 7, 1977||Nov 21, 1978||Caterpillar Tractor Co.||Attitude control for implement|
|US4354797 *||May 29, 1980||Oct 19, 1982||Hitachi Construction Machinery Co., Ltd.||Front loading hydraulic excavator|
|US4408518 *||Mar 17, 1981||Oct 11, 1983||The Cessna Aircraft Company||Series self-leveling valve|
|US4709618 *||Oct 2, 1985||Dec 1, 1987||The Cessna Aircraft Company||Series self-leveling valve with single spool for unloading and relief|
|US4715767 *||May 14, 1985||Dec 29, 1987||Edelhoff Polytechnik Gmbh & Co.||Motor-driven garbage truck comprising a detachable container|
|US4815357 *||Jul 21, 1987||Mar 28, 1989||Lull Corp.||Adjustable divided flow self-leveling system|
|US4923362 *||Jun 6, 1988||May 8, 1990||Deere & Company||Bucket leveling system with dual fluid supply|
|US5114304 *||Jul 24, 1990||May 19, 1992||Edelhoff Polytechnik Gmbh & Co.||Motor-driven garbage truck comprising a detachable container|
|US5275086 *||Aug 27, 1992||Jan 4, 1994||Unlimited Solutions, Inc.||Fluid actuator with internal pressure relief valve|
|US5447094 *||Feb 7, 1994||Sep 5, 1995||Delta Power Hydraulic Co.||Hydraulic system for bucket self-leveling during raising and lowering of boom|
|US5669282 *||Dec 22, 1995||Sep 23, 1997||Sanyo Kiki Kabushiki Kaisha||Hydraulic circuit for actuating materials handling machine|
|US5919026 *||Jun 2, 1997||Jul 6, 1999||Kann Manufacturing Corporation||Carry can discharge floor|
|US6308612||Sep 24, 1998||Oct 30, 2001||Delta Power Company||Hydraulic leveling control system for a loader type vehicle|
|US6389953||Oct 10, 2000||May 21, 2002||Delta Power Company||Hydraulic leveling control system for a loader type vehicle|
|US7032378 *||May 18, 2004||Apr 25, 2006||Nabco Limited||Flow divider system and valve device of the same|
|US7059237 *||May 18, 2004||Jun 13, 2006||Nabco Limited||Multiple-directional switching valve|
|US7628174 *||May 28, 2004||Dec 8, 2009||Bosch Rexroth Ag||Hydraulic control arrangement|
|US20040231505 *||May 18, 2004||Nov 25, 2004||Nabco Limited||Multiple-directional switching valve|
|US20040250677 *||May 18, 2004||Dec 16, 2004||Nabco Limited||Flow divider system and valve device of the same|
|US20060191582 *||May 28, 2004||Aug 31, 2006||Bosch Rexroth Ag||Hydraulic control arrangement|
|US20090029813 *||Jul 12, 2008||Jan 29, 2009||Luk Lamellen Und Kupplungsbau Beteiligungs Kg||Pressure relief valve for a hydraulic system|
|DE102004019327B4 *||Apr 21, 2004||Dec 7, 2006||Sauer-Danfoss Inc.||Verfahren zur Steuerung eines Schwenkauslegers und Vorrichtung zur Steuerung desselben|
|EP0856612A1 *||Jan 27, 1998||Aug 5, 1998||Eaton Corporation||Dual self level valve|
|EP1300595A3 *||Oct 3, 2002||Jul 20, 2005||Husco International, Inc.||Electronically controlled hydraulic system for lowering a boom in an emergency|
|WO2002029166A1 *||Sep 28, 2001||Apr 11, 2002||Husco International, Inc.||Two-way, self-level valve|
|U.S. Classification||60/472, 414/708, 414/700, 91/520, 137/596, 60/471|
|International Classification||F15B11/16, F15B13/07, E02F3/43, F15B13/00, E02F3/42, F15B11/00, E02F9/22|
|Cooperative Classification||F15B13/07, E02F3/433|
|European Classification||E02F3/43B2H, F15B13/07|