US3680713A

US3680713A - Fluid power device

Info

Publication number: US3680713A
Application number: US87998A
Authority: US
Inventors: Robert E Langley
Original assignee: SNORKEL FIRE EQUIPMENT CO
Current assignee: ECONOMY ENGINEERING COMPANY A CORP OF ILLINOIS; American LaFrance LLC; SNORKEL FIRE EQUIPMENT CO
Priority date: 1970-11-09
Filing date: 1970-11-09
Publication date: 1972-08-01
Anticipated expiration: 1989-08-01

Abstract

A fluid power device including wall means defining a cylindrical chamber therewithin and including piston rod means therein having primary and secondary pistons associated therewith, so that upon application of fluid under pressure to one side of both pistons, the piston rod means is moved outwardly during at least a portion of its stroke with a predetermined force greater than the force produced by the application of fluid under pressure to the primary piston alone.

Description

United States Patent Langley 1 Aug. 1, 1972 [s41 FLUID POWER DEVICE [72] Inventor: Robert E. Langley, St. Joseph, Mo.

[73] Assignee: Snorkel Fire Equipment Company [22] Filed: Nov. 9, 1970 [21] Appl. No.: 87,998

[52] US. Cl ..212/35 HC, 212/46 R, 212/59 R, 91/411 R, 92/62 [51] Int. Cl. ..B66c 23/00, B66c 23/54 [58] Field of Search ..92/62; 91/41] R, 170 R; 212/46 R, 46 A, 46 B, 54, 144, 145, 35 HC [56] References Cited UNITED STATES PATENTS 3,149,537 9/1964 Fink ..92/62 3,218,934 11/1965 Daniels ..92/62 3,153,522 10/1964 Piper et a1. ..92/62 3,150,563 9/1964 Carrigan et al. ..92/62 3,410,307 1 1/ 1968 Szereszewski ..91/41 1 3,018,762 1/1962 Korb ..91/170 3,288,036 11/1966 Fisher .,92/62 Primary Examiner-Edgar W. Geoghegan Assistant Examiner-Clemens Schimikowski Attorney-Dressler, Goldsmith, Clement & Gordon [57] ABSTRACT A fluid power device including wall means defining a cylindrical chamber therewithin and including piston rod means therein having primary and secondary pistons associated therewith, so that upon application of fluid under pressure to one side of both pistons, the piston rod means is moved outwardlyduring at least a portion of its stroke with a predetermined force greater than the force produced by the application of fluid under pressure to the primary piston alone.

21 Claims, 5 Drawing Figures SHEET 3 OF 3 P'A'TENTED ms 1 I972 \AQNW wk mum WEB mum -l Nmb mg wmm l FLUID POWER DEVICE BACKGROUND OF THE INVENTION the field of fire-fighting apparatus as a force applying member to move one boom section of a multi-section folding boom relative to another boom section. The

fluid power device of the present invention has particular utility with the fire-fighting apparatus of the type disclosed in Broderson et al. US. Pat. No. 3,066,756 wherein an aerial platform is provided at the end of a pair of articulated boom members. Although the fluid power device of the present invention has particular utility in connection with a multi-section boom of a pumper truck or the like, it will become evident from the following description that the device may be used in any equipment wherein cylinder force decreases with extension of the cylinder. As examples of such different equipment, fluid power devices constructed in accordance with the teachings of the present invention may be used in connection with crane booms where a load line is applied rather than an aerial basket, and in connection with vehicles having dumping bodies, such as earth haulers, and trash trucks.

The apparatus disclosed in the above-mentioned patent includes a boom structure that utilizes hydraulic cylinders for moving the boom between a compact road ready transport position, and one of a plurality of operative positions. The boom includes an inner section that is pivotally mounted upon a rotatable support, and an outer section that is pivotally connected to the end of the inner section.v External conduits are provided for conveying water to a nozzle that is provided at the end of the outer section for delivering water to a fire. A first hydraulic cylinder is connected between the support and the first boom section for pivoting the same to a position that is selected by the operator of the apparatus. A second hydraulic cylinder is connected between the first boom section and the outer boom section for pivoting the outer boom section relative to the inner boom section to a desired working position. In the road travel position, the cylinder for pivoting the second or outer boom section has an extremely small mechanical advantage, and a great deal of force is required to initially pivot the outer .boom relative to the inner boom.

Several methods have been proposed to provide an additional lifting torque to initially pivot the outer boom section relative to the inner boom section from the road travel position, and these methods have included the use of larger pumps to increase fluid pressure to a cylinder, a plurality of cylinders, or larger cylinders and linkage means as shown in the abovementioned Broderson et al. patent. While these methods can produce the desired end result, they are obviously costly and compound maintenance problems in use.

BRIEF SUMMARY OF INVENTION I when necessary, and specifically for providing an additional torque for initially pivoting an outer boom section relative to an inner boom section in fire-fighting apparatushaving a boom comprised of a plurality of foldably connected boom sections. The fluid power device of the present invention provides this result by using a conventionally sized cylinder having more than one tandem arranged pistons therein that are exposed to fluid under pressure for providing a cumulative lifting force during the initial movement of the piston rod means associated with the pistons. e

In one embodiment, a unitary piston rod is provided and the first or primary piston is fixed to the piston rod.

The secondary piston is in the form of a sleeve that is freely slidably received on the piston rod, with the sleeve being engageable with an abutment on the piston rod, so that when a first side of the primary and secondary pistons are exposed to fluid underpressure, the piston rod will be shifted with a force that is equal to the pressure of the fluid times the combined area of each of the pistons. An abutment is provided the cylinder that is engageable with the second piston, so that after a predetermined travel, when the additional force is no longer required, the piston rod will move freely relative to the second piston under the force applied to the first piston. v I I In other embodiments of the invention, a common fluid source is connected to one side of boththeprimary and secondary pistons through a passage means .in one section of a multiple section piston rod means. This latter arrangement simplifies porting and sealing problems, and the casings of these latter embodiments are preferably constructed in a manner so as to enable them to be readily disassembled for replacement of seals, service and the like. Certain embodiments of the invention also preferably include cushioning means adjacent one end of the cylinder for cushioning the impact of the return movement of the piston rod.

In certain embodiments of the. invention, the pistons of both the primary cylinder sectionand the secondary cylinder section are fluid powered in both directions,

i.e., during the extension stroke and during the retraction stroke. The wall means, of. each section of the cylinder are provided with outlet ports which communicate with a hydraulic control valve connected to a source of fluid under pressure and a hydraulic reservoir or tank, so that as the primary and secondary pistons move outwardly fluid that is present within the primary and secondary portions of the chamber will flow to the tank. Stop means is provided for stopping the secondary piston after the moment arm of the cylinder has increased to a point where the combined force of the primary and secondary cylinder portions is no longer required. Since such fluid power devices are primarily loaded in compression in the environment specifically described herein, the secondary piston will not move away from its stop even though it is'more or less free floating within its portion of the chamber.

In a preferred embodiment of the invention a fluid power device is provided that may be used as either a tension or a compression cylinder. In the preferred embodiment, the outlet passage of the secondary portion of the chamber is connected directly to tank, thereby assuring that the secondary piston will remain adjacent its stop regardless of whether tension or compression used as compression cylinders. I

' struction; and forudetails of the structure with truck 10 arenot specifically describedherein, 1 the disclosures'of the above mentioned patent is hereby expressly herein to the extent that they'- at'the rear of truck 1 for rotation abouta vertical axis, anda sectionalized boom assembly 16 is connected to turntable assembly '14. The boom as- 1 sembly 16 includes an inner or lower boom section 18 .pivo'tally at 20 to turntable assembly 14, and

- an outer or upper boom section 22 pivotally connected *at 24fto .the end of inner section 18.'An aerial v v platfonn 23 is connected tothe outer end of boom secr tion 22 in the manner described in the above mensembly on the platform. i i .s

eylinder' withthe piston'of the cylinder I being'returned mama-cred position by the piston 5 rodofth'epriniarycylinderasitreturnstoitsretracted .isamroEscrtnfiioNjoFnrEsEvERAL i 'oriimmm'wmos no; 1. is a elevationallview Ora pumper truck M5118 nf d s e o in Whid! the mp fl d of the'presentinventionisused; Z-is a elevational vview, partially in central section, illustrating-a first embodiment of. the fluid mt i m nos. 34 in views similar to no. 2, and illustrating o r har fi h b i sp y- 1 t H W a I trated-indetaiLthecylinder'includesaprimarysection',

' '29definedinpartbyatubularwallsection3flthatpro V 'vides'a '32 end T Wampum-mo 7 thkinventionis suseepsbie-or embodiment in I r'nany difl'erentforms, thereis shown'in thedrawings andwillhereinbe'describedindetailapreferred'errr' v v.

' 2S 36for reoervingaprvot pin bodi'rnent of' invention and modifications thereof,

, with the understanding that the present disclosure 'm-to be consideredas anexemplification of the-principles of the invention andis not intended to limit the invention to the embodiments, illustrated. The scope of the invention-will be pointed'out in the appended claims, and unless otherwise restricted, the claim should be interpreted to cover fluid power devices that could be used-as both tension and compression cylinders, aswell as fluid power devices .thatare primarily. intended to be f The fluid power device of the present invention is illustrated in iconnectioniwithfire-fighting apparatus 10, such as a pumper. truck of conventional design and conare not with thejfollowing description. As isfw'ell known, pumpertruck" 12 a chassis frame, a water tank and a'storage rack for lengtln of A water pump (not shown) is car.- ried by the truck, and is adapted to be operatively cou- P withawumofvatsrauchasafire hydfanwrflw so ingr'pe'rpendicularly thereto. Flange 60 includes' an opening 62 centrally thereof that provides a clearance like; to increase thepressureof the water delivered by pump'er truck 12.. Suitable "'valvesand gauges areas with the pump to control-and indicate the water. pressure A turntable assembly 14 is tioned patent, and external conduits on the boom sections are connected to; a .water delivery pipe (not shown) of .truck'l2for supplying water to a nozzle aspe p i 'ry ofpiston 44-to provide a seal between .A m hydraulic 18, while a second'hydrauliccylinderassemblyllfl is connectedbetweenboomsections22andl8. Cylinder assembly 28Vcould be connected to, a linkageimeans, suchasshownintheabovementio'nedBrodersonetal;

patent-"if As'is clearifromFlGiLwhen' the boom asernbly, 1,6 is'in the roadtr'avel position illus trated'in broken jlines,the -eifective moment of cylinder 28 .is present invention provides foree'tran'smitted by 28 to upperboom section 22' to the movement thereof out or travel valves are provided for operation of the Referring is illus'I plate'34 is secured in sealed relatirmship to'one' end of tube 32,and end 34 includes a transverse bore with amounting lug on section 18. First means is provided in tube 30 in the form ofa-radial'port38 adjacent closure 34;and is provide'd fad 5mm the other end of tube 30" in the form of a radial Piston rod 42 is forreciprocating movement 'chamberf32; anda'first or primary piston 44 is fixed'on the righthandend (as viewed in FIG. 2) 0f rodIPiston'rod'42. includes a 35 reduced diameter right-hand end portion 46 that pro vides'an facing shoulder 48 against-which pistong44 is The outermost end of piston-rod the inner surface of wall 30, f and a" further annular seal 54 is provided-at the inner I v 7 piston 44andthereduceddiarneterrodportion46.

' The end of chamber32 opposite from-closure34 is sealed by a gland 56 includinga. sleeve having an axially 7 extending portion 58 and an annular flange 60 extend- Annular seals are positioned in recesses in the inner peripheryof. member 64 and are positioned in sealing engagement with rod 42'. A further annular sealing member 72 is positionedin arecess in the outer gagernent with the inner diameter of sleeve portion 58.

A still further annular seal 74is positioned in a recess in the outer diameter of sleeve portion 58 in sealing relatiomhip with the inner periphery of wall 30. Thus, gland 56 provides a fluid tight seal for the end .of chamber 32 opposite from closure 34, which seal allowsthe piston rod 42 to move freely therethrough.

position icylinders26-and'28 areboth connected tea 7 source of fluid on truclr' lL-andcontrol annular recess in-the inner wall of sleeve portion 58.

periphery of member 64 andis positioned'in' sealing en- From the foregoing, it will be understood that when fluid under pressure is admitted into the chamber portion 32a to the right of piston 44 through port 38, the piston rod 42 will be moved to the left in a boom-section unfolding direction with a force that is equal to the pressure of the fluid times'the area of the exposed face of piston 44. Fluid that is present in the chamber portion 32b will be forced outwardly of the chamber through port 40. In a like manner when fluid under pressure is admitted to the chamber portion 32b to the left of piston 44 through port 40, piston rod 42 will be moved to the right in a boom collapsing direction, while the fluid within chamber portion 32a is forced outwardly of port 38.

Cylinder 28 further includes a boost cylinder portion 76 that is defined by a tubular member 78 that is secured, by welding or the like, to a flange 80 that extends outwardly from the sleeve portion 58 of gland 56. A plurality of circumferentially spaced, axially extending external tie rods 82 (one of which is shown) are threaded into lugs that are carried by tubular members 30 and 78 so that the boost section 76 can be readily disconnected from the remainder of the cylinder, when desired.

Tubular member 78 defines a cylindrical member 84 therewithin that is arranged coaxially with chamber 32, and chambers 32 and 84 preferably have the same internal diameter. The right-hand end of chamber 84 is closed by the aforementioned gland 56, and the lefthand end of chamber 84 is sealed by a closure member 86 having an externally threaded portion that is threaded into an internally threaded outer end portion 88 of wall 78. A secondary piston 90 is mounted for reciprocating movement within chamber 84, and piston 90 is defined in part by an axially elongate annular sleeve 92 having piston rod 42 freely slidably received therein. Piston 90 further includes a combined sealing and guiding member 94 that is held against a flange 96 which extends outwardly from sleeve 92 by an annular disc 98 and retaining ring 100 that is seated in a groove adjacent the right-hand end of sleeve 92. Annular seals 102 are seated in recesses in the outer periphery of member 94 and are positioned in sealing engagement with the inner diameter of wall 78.

The left-hand end portion of sleeve 92 extends outwardly of wall 78 through an opening 104 in closure member 86, an annular seal 106 is provided in a recess in the inner periphery of closure member 86 in engagement with the outer diameter of sleeve 92 to prevent fluid leakage through closure member 86. A wiper 107 is also provided in a recess in the inner periphery of closure member 86 outwardly of seal 106. An annular seal 108 is seated in a recess in the inner periphery of sleeve 92 adjacent the outer end thereof and is positioned in sealing engagement with rod 42. A wiper 109 is also seated in a recess in the inner periphery of sleeve 92 outwardly of seal 108. Rod 42 includes an enlarged outer end portion 110 having a transverse bore 112 therethrough for reception of a pivot pin to connect the rod 42 to the outer boom section 22. Enlarged rod portion 110 provides a shoulder 114 that faces rearwardly toward sleeve 92, and which is engaged by sleeve 92 when it moves outwardly of tubular member 78 as will hereinafter be explained.

First passage means is provided in tubular member 78 in the form of a radially extending port 116 that is positioned adjacent the right-hand end of member 78, and second passage means is provided in member 78 in the form of a radially extending port 118 adjacent closure member 86. When fluid under pressure is admitted to the right-hand end 84a of chamber 84 through port 1l6,piston 90 is moved to the left by a force that is equal to the pressure of the fluid times the exposed area of the piston 90. As the piston 90 moves to the left, the fluid that is present in the left-hand end 84b of chamber 84 is forced outwardly thereof through port 1 18. When fluid under pressure is admitted to chamber portion 84b through port 118 piston 90 is moved to the right, and fluid that is present in chamber portion 84a is forced outwardly of port 1 16. v

Conduits

120 and 122 preferably connect

ports

116 and 38, respectively, to a common conduit 124 that is connected to a control valve 126 for simultaneously providing a constant volume of pressurized fluid to the right-hand sides of

pistons

44 and 90. Valve 126 is connected in a suitable hydraulic circuit to a source of fluid under pressure, not shown. Similarly,

conduits

128 and 130 preferably connect ports 118 and 40, respectively, to a common conduit 132 that extends to valve 126. In operation, assuming that the piston rod 42 is in the retracted position illustrated in FIG. 2, with piston rod shoulder 114 bearing against the outwardly extending end of sleeve 92, valve 126 is actuated to simultaneously provide fluid under pressure to the righthand sides of

pistons

44 and 90 through

conduits

124, 122 and 120. Piston rod 42 is initially moved to the left by a force that is equal to the fluid pressure times the combined area of the exposed faces of

pistons

44 and 90. During outward movement of the

pistons

44 and 90, valve 126 places line 132 in communication with tank to minimize the back pressure of the fluid flowing outwardly of ports 40 and 118 through

conduits

128 and 130 to conduit 132..As the boom section 22 begins to pivot relative to boom section 28, the moment arm of cylinder 28 gradually increases, so that the necessity for the combined force of pistons 44 and gradually decreases. When the boom section 22 reaches a position where the force output of the primary cylinder section 29 is adequate for further movement of the boom section, the flange 96 on sleeve 92 moves into engagement with the rearwardly facing surface 134 on closure member 86 that defines a stop preventing further outward movement of piston 90. At this point, further outward movement of piston rod 42 is attributable solely to the pressure of the fluid times the exposed surface area of piston 44; however, this latter movement will be at an increased speed, since the volume of fluid that was formerly flowing to chambers 32 and 84 will now flow entirely into chamber 32 thereby increasing the speed at which the piston rod 42 is extended.

When it is desired to return the

boom sections

18 and 22 to the road-ready position illustrated in broken lines in FIG. 1, cylinder 26 is actuated to pivot boom section 18 downwardly, and valve 126 is manipulated to admit fluid under pressure into the left-hand ends of chambers 32 and 84 through ports 40 and 118, respectively.

Ports

116 and 38 are connected to tank through

lines

120, 124 and 122 and valve 126, and piston rod 42 will move to the right until the shoulder 114 engages the end of sleeve 92 to move the piston 90 along withthe rod 42to the fully retracted position'of FIG. 2.

Each of theembodiments of FIGS. 3, 4 and 5 is similar in many respects to the embodiment of FIG. 2.

, Thedescription of the common elements will not be repeated in the following description of the embodiments power device 228 illustrated therein differs from the fluid power device illustrated in FIG. 2 in that the pri-- mary cylinder section 229 is provided at therod end of the cylinder, while the secondary cylinder section 276 is provided at the head end of the cylinder. In this connection, primary piston 244 is secured to piston rod means 242, and the primary piston is mounted for reciprocating movement within the right-hand portion of chamber 232. This chamberportion is closed at its gland 256; One end of wall portion 278 iswelded to closure member 234, and the opposite end of wall portion 278 makes a threaded connection with a'reduced diameter portion 257 of gland 256. The end portion of sleeve 292 is positioned to engage the end of piston rod 242, so that when fluid under pressure is applied to pistons 242 and 290, the piston rod 242 will be moved to the right, as viewed in FIG. 3, with a force that is equal to the product of the fluid pressure times the combined area of the exposed faces of pistons'244 and 290.

The porting arrangement for the embodiment of FIG. 3 also diflers from the porting arrangement of the embodiment of FIG. 2, and in this connection, a radial port 237 in the closure member 234 at the head end of the cylinder communicates with an axial passage 239 that in turn communicates with secondary chamber portion 284a. A passage 293 extends axially of sleeve I 292, and a further passage 295 extends radially of sleeve 292 beyond gland 256 to establish communication between passage 293 and the primary chamber portion 232a. A further passage 297 is provided adjacent the end of sleeve 292 remote from passage 295,. so that when valve 326 ismanipulated to pressurize port 237, fluid under pressure is applied to secondary piston 290 through passage 239 and to primary piston 244 through

passages

297, 293 and 295. Passage 297 may conveniently be in the form of a slot that is milled into the end of sleeve 292.

The porting of cylinder portions 232b and 284b is also slightly difi'erent than-the porting arrangement in the embodiment of FIG. 2, and in this connection, a radial port 241 is provided in closure member 286,is in radial alignment with port 240 in wall 232, with port 240 communicating with a fitting 243 that is secured to wall 230. A port 319 is provided in gland 256 for 5 receiving and admitting fluid to secondary charnbe portion 284b. A fitting 321 is fixed to gland 256, and

fluid flows from chamber portions 232b and 284b to and from valve 326 through conduits 332a and 332b that are secured to

fittings

243 and 321, respectively.

The end of port 239 remote from chamber portion 2840 is preferably connected to an emergency'bleed down valve (not shown) which enables manual control of the boom by bypassing valve326. 'The emergency bleed down valve arrangement is utilized in the event of a power failure and a subsequent loss of fluid pressure to actuate the cylinder 229. Turning now to the embodiment of cylinder 228 in the specific manner of assembly of the cylinder structure, and in the provision of cushioning means 540 at the rod end of the cylinder. A stop member 541 beyond cushioning means 540 includes an enlarged lip 542 that is seated within a recess in the intemal periphery of wall 430, and stop member 541 is retained in place by closure member A seal 543 is provided in an annular recess in the outer surface of stop member 541, and a further seal 544 is provided within a central opening 545 in the stop member in sliding, sealing engagement with rod 442. Cushioning means 540 functions to absorb the impact of primary piston 444 as it moves into engagement with stop member 541 at the end of its working stroke.

Cushioning means 540 is partially defined by a plurality of axially spaced ports 546, 547 and 548 that extend through wall 429 into a chamber 549 in fitting 443. Ports 547 and 548 are preferably smaller in diameter than port 546. A passage 550 extends generally radially outwardly from chamber 549 and communicates with a passage 551 that extends generally axially of fitting 443. Passage 551 includes a central portion 552 of reduced diameter that forms a valve seat adjacent one side thereof, and a valve member 553 is held against the valve seat by a spring 554. The force of spring 554 can be adjusted by a screw 555 that is threaded into the outer end of passage 551. Valve member 553 includes a small diameter opening 556 therein that receives fluid .from port 440 in the side wall 430 of the cylinder.

As piston 444 begins to move to the right during its working stroke, fluid within chamber portion 432b is forced outwardly of

passages

546, 547, 548 and 440. The fluid flows through fitting 443 to tank through lines 532a and 532b. As piston 444 approaches stop member 541, passages 546, 547 and 548 are covered in sequence. As the passages are progressively covered, the resistance to flow of fluid outwardly of cylinder portion 432b generally increases to thereby slow the movement of piston 444 toward stop member 541. During the latter portion of the stroke of piston 444, after openings 546548 have been covered, the fluid that remains in cylinder portion 432b is forced outwardly of port 440 and passes through the restricted passage 556 in valve member 553 so that a large flow restriction is provided which substantially brakes the movement of piston 444 as it approaches stop member 541. It will be understood that during return movement of piston 444, valve member 553 moves away from the V valve seat provided by reduced diameter portion 552 to allow fluid to flow freely into chamber portion 432b.

FIG. '4, the cylinder 428 illustrated therein differs essentially from The construction of the embodiment of FIG. 4 also facilitates the assembly and disassembly of the cylinder, and provides a more reliable operation by eliminating the threaded connection to the central gland that was utilized in the embodiment of FIG. 3. The gland 456 of the embodiment of FIG. 4 is fixedly connected to the facing ends of walls 430 and 478, as by welding at 560 and 561. The embodiment of FIG. 4 also differs from the previously described embodiments by providing a flange 562 that is secured to the left-hand end portion of wall 478 to provide a removable connection with the end closure member. The end closure member 434a in the embodiment of FIG. 4 is adapted to be pivotally connected to the boom section, and a flange portion 434!) is secured to flange portion 562. Flange portions 434b and 562 include a plurality of aligned internally threaded openings that threadably receive fastener member 563 (one fastener being shown in FIG. 4) to removably mount the end closure member to the wall 478. Flange member 434b includes a reduced diameter portion 564 which is retained in sealing engagement with the inner periphery of wall 478 by an annular sealing member 565 that is mounted in a recess in portion 564.

All of the above-mentioned cylinder embodiments have primary and secondary cylinder sections wherein fluid power is applied to move the primary and secondary pistons to a retracted position, as well as to force the pistons outwardly during a working stroke. The embodiment of FIG. differs from the embodiments of FIGS. 2-4 essentially in that the piston of the secondary cylinder section 676 is fluid powered only in the extension direction, whereas the piston of the primary cylinder section 629 is fluid powered in both directions.

The embodiment of FIG. 5 is essentially identical with the embodiment of FIG. 4, except that port 718 in the secondary cylinder section 676 is connected directly to tank T by line 632b instead of being connected to line 732a, as with the previous embodiment. The embodiments of FIGS. 2-4 are primarily intended to function as compression cylinders, since when acting as a tension cylinder (taking FIG. 4 as an example) wherein fluid under pressure is admitted into chamber portion 432b and 48412 to move thepistons 444 and 490 to the left, the fluid present in chamber 432a is forced into chamber portion 484a through passage 493 so that oppositely directed forces are applied to piston 490. It has been found that under these circumstances, the displacement of the primary cylinder cannot be accurately controlled so that control of the boom is erratio.

The embodiment of FIG. 5 functions satisfactorily as both a compression cylinder and a tension cylinder, since, when the cylinder is loaded in tension and fluid under pressure is admitted into chamber portion 632b,

fluid will flow outwardly from chamber portion 632a into chamber portion 6840 through passage 693, and since there is no pressurized fluid present in chamber portion 684b acting on the opposite face of piston690, the control of the displacement of the cylinder will be accurate and positive.

While all of the above described cylinder embodiments disclose two tandem arranged cylinder sections in a common housing, it should be understood that the present invention is not limited to the provision of two cylinder sections and in fact more than-two cylinder sections can be. utilized, if it is desired to further increase the force output of the cylinder. The scope of the invention will be pointed out in. the appended claims.

What is claimed is;

l. A system for generating additional lifting force for an elongate, cantilever supported boom member comprising a support means; an elongate boom member pivotally connected at one end to said support means for cantilever support of the other end therefrom; and an elongate fluid power device adjacent saidone end, a first end of said fluid power device beingpivotally mounted on said support means and a second end of said fluid power device being pivotally connected to said boom member for pivoting said boom member relative to said support means, said fluid power device comprising: wall means defining a chamber therewithin; sealing means intermediate the ends of said wall means and dividing said chamber into first and second chamber portions; piston rod means mounted for reciprocating movement within said chamber, said piston rod means extending outwardly of said chamber and providing one end of said fluid power device; a primary piston within said first chamber portion and fixed to said piston rod means; passage means for establishing communication between one side of said primary piston and a source of fluid under pressure for moving said piston rod means'in one direction; a secondary piston mounted within said second chamber portion; further passage means for establishing communication between one side of said secondary piston and a source of fluid under pressure for moving said secondary piston in said one direction; and means establishing a driving connection between said secondary piston and said piston rod means, whereby upon movement of said secondary piston in said one direction an additive force is provided for moving said piston: rod means in said one direction to pivot said boom member with respect to said support means.

2. A system as set forth in claim 1 wherein conduit means connects both of said means to a common source of fluid under pressure.

3. A system as set forth in claim 2 in which said wall means includes stop means for engaging said secondary piston after a predetermined amount of movement in said one direction.

4. A system as set forth in claim 3 wherein conduit means is arranged to direct the entire output of said common source through said first mentioned passage means when said secondary piston moves into engagement with said stop means, with a resultant decrease in output force and an increase in the speed of movement of said piston rod means.

5. A system as set forth in claim 4 including valve means for controlling the flow of fluid through said conduit means.

6. A system as set forth in claim 1 in which said further passage means includes a fluid port in said wall means, and wherein said first mentioned passage means includes a passage extending through said secondary piston from said one side thereof and establishing communication with said one side of said primary piston.

7. A system as set forth in claim 1 in which said secondary piston includes a sleeve extending toward with said stop.

. said primary piston, and wherein said means establishing a drivingconnection between said secondary piston and said piston rod means includes a stop on said piston rod means and an abutment on said sleeve engageable 8. A system as set forth in claim 7 in which said sealing means has an opening slidably receiving said sleeve,

and wherein said first mentioned passage means includes a passage extending through said sleeve establishing communication between'said one side of said secondary piston and said one side of said primary piston.

9. A system as set forth in claim 1 in which said first and second chamber portions have the same diameter.

10. A system for generating addi-tional lifting force for an elongate, cantilever supported boom member comprising a support means; an elongate boom member pivotally connected atone end to said support means for cantilever support of the other end therefrom; and an elongate fluid power device adjacent said one end; a first end of said fluid power device being pivotally mounted on said support means and a second end of said fluid power device being pivotally connected to said boom member for pivoting said boom member relative to said support means, said fluid powerdevice comprising: wall means defining a chamber there-within, said wall means including first and second spaced wall sections; sealing means fixedly secured to facing ends of said wall sections and dividing said chamber into a primary portion and a secondary portion; piston rod means mounted for reciprocat-ing movement in the primary portion of said chamber, said piston rod means extending outwardly of said chamber ing with a source of fluid under pressure and with said primary and secondary chamber portions for forcing said abutment into engagement with said stop to apply a given force to saidpistonrod means while fluid pressure is simultaneously applied to said primary piston to provide an additive force to said piston rod means; andclosure means for the ends of said first and second wall sections remote from said intermediate sealing means,

: both of said end closure means being removably connected to its wall section, whereby said piston rod 'means and said primary piston can be readily removed from one end of said chamber while said secondary piston and sleeve can be readily removed from the opposite end of the chamber.

11.. A system as set forth in claim 10 wherein the pressure of the fluid applied to each of said pis-tons is the same.

' 12. A system as setforth in claim 10 wherein said wall sections andchamber portions are axially aligned,

with said chamber portions having the same 'intemal dimension.

13. A system'as set forthin claim -li-wherein said chamber portions and pistons are cylindrically shaped.

l4. A'system as set forth in claim 10 further comprising welds fixedly securing said sealing means to the facing ends of said wall sections. v g

15. A system for generating additional lifting force for an elongate, cantilever supported boom member comprising a support means; an elongate boom member pivotally connected at one end to said support means for canvilever support of the other end therefrom; and an elongate fluid power device adjacent said one end, a first end of said fluid power device being pivotally mounted on said support means and a second end of said fluid power device being pivotally connected to said' boom member for pivoting said boom member relative to said support means, said fluid power device comprising: wall. means defining a chamber therewithin; first and second closure means at opposite ends of said wall means sealing said chamber; sealing means intermediate the length of said wall means dividing said chamberinto a primary portion and a secondary portion; piston rod means mounted for reciprocating movement in said primary chamber portion, said piston rod means extending outwardly of said chamber and providing onefend ofsaid fluid power device; a primary piston fixed to said piston rod means having a first side facing said sealing means and a second side facing said first closure means; a secondary second closure and 'a-second side facing said sealing means; means for establishing a driving connec- 'tion between said secondary piston and said piston rod means; passage means communicating with a source of fluid under pressure and with said primary and secondary chamber" portions for applying 1 fluid. pressure against the first sides of said primary and secondary pistons to move said piston rod means in one direction with a force that is equal to the fluid pressure times the combined working areas of the first sides of 'said primary and secondary pistons; further passage means'adjacent said first closure means and communicating with the primary chamber portion, said further passage means being in selective communication with a source of fluid under-pressure or with tank for selectively applying fluid under pressure against the second side of said primary piston to retract said piston rod means and for allowing fluid to flow to tank when-said piston rod means moves in said one direction; still further passage means adjacent said sealing means and communicating with said secondary chamber portion and directly with tank for allowing fluid to flow to tank when said secondary piston moves in said one direction and isolating said secondary chamber portion from fluid pressure during retraction of said piston rod means; and valve means controlling said passagemeans and said further passage means. 7

16. A system as set forth in claim 15 in which said sealing means includes an opening, and wherein a sleeve is fixed to said secondary piston and is positioned in sliding engagement within said opening, the

' end portion of said sleeve being positioned to'engage said piston rod means to define said means for establishing a driving connection between said secon dary piston and said piston rod means.

. 14 to facing ends of said wall sections.

20. A system in accordance with claim 1, and further comprising a passage continuously establishing communication between the other side of said secondary piston directly with tank both when said secondary piston moves in said one direction and when said secondary piston moves in the other direction.

21. A system in accordance with claim 1 wherein said secondary chamber portion is substantially shorter than said primary chamber portion.

* k l l l UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,680,713 Dated August 1, 1972 Inventor(s) Robert E. Langley It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

0'01. 7, .line 37, "242 and 290" should be 2 m and Col. 8, line 55, "generally" should be gradually --5 Col. 10, line A, insert "passage after "said"; 001. 10, line '50, insert said after "wherein";

"001. 11, line 16, delete the hyphen in "eLddi-tionel";

C01. 11, line 28, delete the hyphen in "therewithin";

Col. ll, line 32, delete the hyphen in "reciprocating 5 Col. 11, line 62, delete the hyphen in "pis-tons'",

Col. 12, line 22, insert and after "means" Signed and sealed this 30th day of January 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents

Claims

1. A system for generating additional lifting force for an elongate, cantilever supported boom member comprising a support means; an elongate boom member pivotally connected at one end to said support means for cantiLever support of the other end therefrom; and an elongate fluid power device adjacent said one end, a first end of said fluid power device being pivotally mounted on said support means and a second end of said fluid power device being pivotally connected to said boom member for pivoting said boom member relative to said support means, said fluid power device comprising: wall means defining a chamber therewithin; sealing means intermediate the ends of said wall means and dividing said chamber into first and second chamber portions; piston rod means mounted for reciprocating movement within said chamber, said piston rod means extending outwardly of said chamber and providing one end of said fluid power device; a primary piston within said first chamber portion and fixed to said piston rod means; passage means for establishing communication between one side of said primary piston and a source of fluid under pressure for moving said piston rod means in one direction; a secondary piston mounted within said second chamber portion; further passage means for establishing communication between one side of said secondary piston and a source of fluid under pressure for moving said secondary piston in said one direction; and means establishing a driving connection between said secondary piston and said piston rod means, whereby upon movement of said secondary piston in said one direction an additive force is provided for moving said piston rod means in said one direction to pivot said boom member with respect to said support means.

7. A system as set forth in claim 1 in which said secondary piston includes a sleeve extending toward said primary piston, and wherein said means establishing a driving connection between said secondary piston and said piston rod means includes a stop on said piston rod means and an abutment on said sleeve engageable with said stop.

8. A system as set forth in claim 7 in which said sealing means has an opening slidably receiving said sleeve, and wherein said first mentioned passage means includes a passage extending through said sleeve establishing communication between said one side of said secondary piston and said one side of said primary piston.

10. A system for generating addi-tional lifting force for an elongate, cantilever supported boom member comprising a support means; an elongate boom member pivotally connected at one end to said support means for cantilever support of the other end therefrom; and an elongate fluid power device adjacent said one end; a first end of said fluid power device being pivotally mounted on said support means and a second end of said fluid power device being pivotally connected to said boom member for pivoting said boom member relative to said support means, said fluid power device comprising: wall means defining a chamber thEre-within, said wall means including first and second spaced wall sections; sealing means fixedly secured to facing ends of said wall sections and dividing said chamber into a primary portion and a secondary portion; piston rod means mounted for reciprocat-ing movement in the primary portion of said chamber, said piston rod means extending outwardly of said chamber and providing one end of said fluid power device; said piston rod means including a primary piston having a first side facing said sealing means, said piston rod means also including a stop facing toward said sealing means; a secondary piston within the secondary portion of the chamber and having a first side; a sleeve connected to said secondary piston and extending through an opening in said sealing means, the end portion of said sleeve defining an abutment engageable with the stop on said piston rod means for establishing a driving connection therebetween; passage means communicating with a source of fluid under pressure and with said primary and secondary chamber portions for forcing said abutment into engagement with said stop to apply a given force to said piston rod means while fluid pressure is simultaneously applied to said primary piston to provide an additive force to said piston rod means; and closure means for the ends of said first and second wall sections remote from said intermediate sealing means, both of said end closure means being removably connected to its wall section, whereby said piston rod means and said primary piston can be readily removed from one end of said chamber while said secondary piston and sleeve can be readily removed from the opposite end of the chamber.

11. A system as set forth in claim 10 wherein the pressure of the fluid applied to each of said pis-tons is the same.

12. A system as set forth in claim 10 wherein said wall sections and chamber portions are axially aligned, with said chamber portions having the same internal dimension.

13. A system as set forth in claim 12 wherein said chamber portions and pistons are cylindrically shaped.

14. A system as set forth in claim 10 further comprising welds fixedly securing said sealing means to the facing ends of said wall sections.

15. A system for generating additional lifting force for an elongate, cantilever supported boom member comprising a support means; an elongate boom member pivotally connected at one end to said support means for canvilever support of the other end therefrom; and an elongate fluid power device adjacent said one end, a first end of said fluid power device being pivotally mounted on said support means and a second end of said fluid power device being pivotally connected to said boom member for pivoting said boom member relative to said support means, said fluid power device comprising: wall means defining a chamber therewithin; first and second closure means at opposite ends of said wall means sealing said chamber; sealing means intermediate the length of said wall means dividing said chamber into a primary portion and a secondary portion; piston rod means mounted for reciprocating movement in said primary chamber portion, said piston rod means extending outwardly of said chamber and providing one end of said fluid power device; a primary piston fixed to said piston rod means having a first side facing said sealing means and a second side facing said first closure means; a secondary piston within the secondary portion of said chamber, said secondary piston including a first side facing said second closure means and a second side facing said sealing means; means for establishing a driving connection between said secondary piston and said piston rod means; passage means communicating with a source of fluid under pressure and with said primary and secondary chamber portions for applying fluid pressure against the first sides of said primary and secondary pistons to move said piston rod means in one direction with a force that is equal to the fluid pressure times the combined working areas of the first sidEs of said primary and secondary pistons; further passage means adjacent said first closure means and communicating with the primary chamber portion, said further passage means being in selective communication with a source of fluid under pressure or with tank for selectively applying fluid under pressure against the second side of said primary piston to retract said piston rod means and for allowing fluid to flow to tank when said piston rod means moves in said one direction; still further passage means adjacent said sealing means and communicating with said secondary chamber portion and directly with tank for allowing fluid to flow to tank when said secondary piston moves in said one direction and isolating said secondary chamber portion from fluid pressure during retraction of said piston rod means; and valve means controlling said passage means and said further passage means.

16. A system as set forth in claim 15 in which said sealing means includes an opening, and wherein a sleeve is fixed to said secondary piston and is positioned in sliding engagement within said opening, the end portion of said sleeve being positioned to engage said piston rod means to define said means for establishing a driving connection between said secondary piston and said piston rod means.

17. A system as set forth in claim 16 wherein said first mentioned passage means is defined in part by a passage in said sleeve that establishes communication between said primary chamber portion and said secondary chamber portion.

18. A system as set forth in claim 15 including means for cushioning said primary piston as it approaches said first closure means.

19. A system as set forth in claim 15 in which said wall means includes first and second spaced wall sections, and wherein said sealing means is fixedly secured to facing ends of said wall sections.