US3279563A

US3279563A - Ram assembly with floating piston seal

Info

Publication number: US3279563A
Application number: US425776A
Authority: US
Inventors: Mcneeley Daniel James
Original assignee: Otis Elevator Co
Current assignee: Otis Elevator Co
Priority date: 1965-01-15
Filing date: 1965-01-15
Publication date: 1966-10-18
Anticipated expiration: 1983-10-18

Description

Uct. 18, 1966 D. J. MCNEELEY RAM ASSEMBLY WITH FLOATING PISTON SEAL 5 Sheets-Sheet 1 Filed Jan. 15. 1965 H" /ENTOR DANIEL JAMES MCNEELEY BYh m ATTORNEY 5 Sheets-Sheet 2 D. J. MCNEELEY RAM ASSEMBLY WITH FLOATING PISTON SEAL FIG. 9

Oct. 18, 1966 Filed Jan. 15. 1965 FIG. l2

INVENTOR DANIEL JAMES MC NEELEY BY W ATTORNEY He. II

FIG. IO

Oct. 18, 1966 n. J. M NEELEY RAM ASSEMBLY WITH FLOATING PISTON SEAL 5 Sheets-Sheet 5 Filed Jan. 15. 1965 FIG. 70 I INVENTOR DANIEL JAMES MC NEELEY BY m ATTORNEY United States Patent 3,279,563 RAM ASSEMBLY WITH FLOATING PISTON SEAL Daniel James McNeeley, Cleveland, Ohio, assignor to Otis Elevator Company, NewYork, N.Y., a corporation of New Jersey Filed Jan. 15, 1965, Ser. No. 425,776 14 Claims. (Cl. 1879) able along the movable uprights. Typically the first lift operation of the ram assembly raises the load carriage from the floor to the top of the movable uprights while they remain nested in the stationary uprights. The second lift operation raises the movable uprights and the load carriage along with them.

Two lift hydraulic ram assemblies usually comprise several concentric cylinders one of which remains stationary while the others extend relative to each other in a predetermined sequence as fluid under pressure is admitted. In some cases the cylinder of largest diameter remains stationary at the bottom of the mast assembly while the smaller cylinders extend. This arrangement has the disadvantage that a large diameter cylinder is always directly in front of the operator, thereby obstructing his vision. Accordingly, it is usually preferred to have the smallest diameter cylinder remain stationary at the bottom of the stationary uprights while the larger diameter cylinders rise. This arrangement, while improving visibility has heretofore had the disadvantage that when the cylinders are extended, the outside surface of the smallest cylinder is exposed near the ground and subject to damage. Dents, scratches and other abrasions of this surface tend to tear the packing material forming the fluid seal between this surface and the next larger cylinder, leading to oil leaks and the necessity for frequent repair or replacement.

It is a general object of the present invention to provide an improved lift truck.

Another object is to provide a lift truck with an improved two lift hydraulic ram assembly.

Another object is to provide a ram assembly comprising two relatively extensible concentric cylinders which is less susceptible to damage than prior art devices.

Another object is to provide a ram assembly comprising two relatively extensible con-centric cylinders in which abrasion of that portion of the exterior surface of the smaller cylinder which is remote from the larger when extended has little or no detrimental effect.

Another object is to provide a ram assembly including two relatively extensible concentric cylinders in which only a portion of the exterior surface of the smaller cylinder need be formed with a smooth finish.

Another object is to provide a ram assembly affording two lift operations and suitable for use on a lift truck in which the smaller cylinder may be stationarily mounted near the bottom of the truck yet in which the exposure to damage by abrasion is greatly reduced.

Briefly stated, one embodiment of a ram assembly in accordance with the invention comprises small, intermediate and large diameter concentrically dis-posed cylinders. The invention is centered around a floating piston which provides a fluid seal between the small and intermediate cylinders. This piston, which is generally cylindrical in shape, is interposed between the two cylinders but is fastened to neither. The piston includes tWo rings of packing material, one engaging each cylinder, and is slidable on both. With the cylinders collapsed, the piston rests on a stop ring fastened to the outside of the small cylinder approximate-1y midway between its ends. When fluid under pressure is admitted to the chamber between cylinders, the intermediate cylinder extends, sliding along the piston which remains stationary until it is engaged by a flange projecting inwardly from the end of the intermediate cylinder. Thereafter the piston moves with the intermediate cylinder, sliding along the small cylinder. The outer surface of the small cylinder is a sealing surface for only about one half of its length and only this portion need be formed with a smooth finish. The remainder may be rough finished and minor dents, nicks and scratches in this region have no adverse effect.

For a clearer understanding of the invention, reference may be made to the following detailed description and the accompanying drawing, in which:

FIGURE 1 is an elevation view of a lift truck with the mast assembly col-lapsed.

FIGURE 2 is an elevation view of a lift truck with the mast assembly extended.

FIGURE 3 is a cross section view of the mast assembly taken on the line 3-3 of FIGURE 1.

FIGURE 4 is a cross section View of the mast assembly taken on the line 44 of FIGURE 3 showing the mast assembly collapsed and the lift carriage lowered.

FIGURE 5 is a view similar to FIGURE 4 but showing the mast assembly collapsed and the lift carriage raised.

FIGURE 6 is a view similar to FIGURES 4 and 5 but showing the mast assembly fully extended.

FIGURES 7a, 7b and 7c are each a fragmentary cross section view of a portion of the ram assembly only in its collapsed position, taken on the line 77 of FIGURE 4, each figure showing approximately the portion designated in FIGURE 4. These figures, taken together, constitute a complete cross section view of the ram assembly except that the portion between figures comprising cylinder walls only, has been omitted to permit the other parts to be shown to a larger scale.

FIGURE 8 is a fragmentary cross section view taken on line 88 of FIGURE 7b.

FIGURES 9, 10, 11 and 12 are simplified schematic diagrams of the ram assembly, each showing the parts in different relative positions.

Referring first to FIGURES 1 and 2, a lift truck 21 includes a mast assembly comprising a pair of outer, stationary uprights 22 and a pair of inner, movable uprights 23. The outer uprights 22 may be mounted on the front of the truck by any of several well-known arrangements (not shown), preferably in such a way as to allow the mast assembly to be tilted a few degrees to either side of the vertical. A pair of

braces

24 and 25 add rigidity to the outer upright assembly and a brace 26 aids in holding the inner uprights 23 in position. A carriage 27 is mounted for longitudinal movement along the inner uprights 23 and includes a pair of lift forks 28.

As best shown in FIGURE 3, the inner uprights 23 are of channel shape and are arranged to slide longitudinally within the outer uprights 22 which are slightly larger and also of channel shape. The carriage 27 includes a pair of brackets 31 to which are rotatably mounted a pair of rollers 32 which roll along the inner surfaces of the inner uprights 23. An additional pair of rollers (not shown) preferably are provided directly beneath the rollers 32.

As shown in FIGURES 3, 4, 5 and 6 an hydraulic ram assembly comprises an inner hollow cylinder 35, an intermediate hollow cylinder 36, and an outer hollow cylinder 37. These cylinders are arranged concentrically, are movable longitudinally with respect to each other under the influence of fluid under pressure admitted to the interior thereof, and, as will be more fully explained, are provided with fluid seals between adjacent surfaces. The inner cylinder 35 has a length approximately equal to that of the outer uprights 22 and its lower end rests on a cross piece 38 fastened to and extending acros the bottom of the outer uprights 22. The intermediate cylinder 36 partially surrounds the inner cylinder, is of approximately the same length, and has its upper end fastened to a bracket 39 which in turn is fastened to the brace 26 joining the inner uprights 23. The outer cylinder 37 partially surrounds the intermediate cylinder 36-vand is of approximately one half the length thereof. A pair of pulleys or sprockets 41 are rotatably mounted on a bracket 42 fastened to the outer cylinder 37 near the top. A pair of chains 43 pass over the sprockets 41 and are fastened at one end to brackets 44 fastened to the lift carriage 27 and are fastened at the other end to a collar 45 which in turn is fastened to the lower end of the intermediate cylinder 36.

In the absence of fluid pressure, the parts assume the positions shown in FIGURE 4 with the intermediate cylinder 36, the outer cylinder 37, the inner uprights 23 and the load carriage 27 all in their lowermost positions. The cross sectional areas of the cylinders are selected so that when fluid under pressure is admitted to the interiors, the

outer cylinder 37 rises first, raising the load carriage 27 With the parts in the positions shown in FIGURE 6,

the intermediate cylinder 36 and the large outer cylinder 37 are raised high, leaving only the small diameter inner cylinder 35 directly in front of the operator, thus affording maximum visibility in the crucial area directly in front of the truck. However, the entire outer surface of the inner cylinder is exposed and subject to damage. Many prior devices have tolerated this situation for the sake of improved visibility. The difliculty arises because of the necessity for providing a fluid seal between the exterior of the inner cylinder and the interior of the intermediate cylinder. Such a seal usually comprises a stuffing box fastened to the interior of the intermediate cylinder adjacent .to its lower end and including packing material in sliding engagement with the exterior of the inner cylinder. With this arrangement it has been necessary to finish very smoothly the entire outer surface of the inner cylinder because this entire surface has constituted a part of the fluid seal. Dents, nicks and scratches on this surface interfere with the function of the fluid seal, tear the packing material and cause leaks and the necessity for .frequent repairs.

In accordance with the present invention, it is only necssary that the portion 35a above a stop ring 46, which is approximately midway between the ends of the cylinder 35, be smooth finished. The lower portion 35b, below the stop ring 46, is not a sealing surface and may be rough finished. Minor dents and scratches on thissurface have no adverse effect.

Referring now to FIGURES 7a, 7b and 70, which show the ram assembly in more detail, the inner cylinder 35 is open at the top. A split bushing 51 fits into a groove in the exterior surface of the cylinder 35 near the top and serves to guide the intermediate cylinder 36 as it moves up and down. The bushing 51 is formed with one or more longitudinal slots 52 and does not constitute a fluid seal. A pair of ports 53 are formed in the cylinder 35 just below the bushing 51 to allow fluid to flow between the interior and exterior at this point. A stop ring 54 is threaded to the exterior of the cylinder 35 just below the 4. port 53 and is held in place by a retaining ring 55. The previously mentioned stop ring 46 is welded to the exterior of the cylinder 35 approximately midway between its ends. The bottom of the cylinder 35 is closed by a cylinder end 56 welded thereto. The cylinder end 56 is formed with an axial bore 57 which communicateswith a lateral bore 58 the interior of which is threaded to ac commod-ate a fitting (not shown) for a pipe or hose which leads to the usual source of fluid under pressure (not shown). The bottom of the cylinder end 561s formed with an approximately hemispherical recess 59 which may cooperate with a complimentary protuberance on the mounting surface.

The intermediate cylinder 36 is closed at the top by a plunger head 61 welded thereto and which is formed with a generally cylindrical upstanding portion 62 .with external threads to facilitate its attachment to the bracket 39. The plunger head 61 is formed with an axial bore, closed by a bolt 63, which allows air to be bled from the interior.

A generally cylindrical gland 64 is positioned on the exterior of the intermediate cylinder 36 near the middle thereof as shown in FIGURE 7b and is held in place between two retaining rings 65 and 66 which fit into corresponding grooves in the cylinder 36. One or more ports 67 are formed in the cylinder 36 approximately in the plane of the retaining ring 65 and similar ports sucn as the port 68 are formed in the gland 64 opposite the ports 67. The interior surface of the gland 64 is formed with a recess containing an O ring 69 and a back up ring 71 which form a stationary fluid seal between the gland 64 and the cylinder 36. The gland 64 does not occupy all of the space between the

cylinders

36 and 37 but has a generally L-shaped cross section as shown which defines a recess into which is positioned a generally cylindrical gland 72, held in place by a retaining ring 73 seated in a groove in the gland 64. A recess in the gland 64 contains an O ring 74 and a back up ring 75 which'form a stationary fluid seal between the

glands

64 and 72. A recess on the exterior of the gland 72 is filled with packing material 76, such as chevron rings, which forms a sliding fluid seal between the exterior of the gland 72 and the interior surface of the outer cylinder 37. A wiper ring 77 fits into a recess in the exterior surface of the gland 64 and bears against the interior surface of the cylinder 37.i

The previously mentioned collar 45 is threaded onto the lower end of the cylinder. 36 and is, formed with a radially inwardly extendingflange portion 78. The internal diameter of the flange 78 is greater than the external diameter of the previously mentioned stop ring 46 on the cylinder-35.

A generally cylindrical stufling box 81 is welded to the top of the outer cylinder 37 and is formed with a recess containing a bushing 82 on top of which is placed packing material 83 held in place by a packing nut 84 threaded to the stuffing box 81 thereby forming a sliding fluid seal between the

cylinders

36 and 37. A wiper ring 85 is held. in a recess in the nut 84. A radially inwardly extending stop ring 86 is threaded onto the bottom of the cylinder 37 and is held in place by a set screw 87.

The fluid seal between the inner cylinder 35 and the intermediate cylinder 36 is obtained by a floating piston, denoted generally by the reference character 91.. The piston 91 is of generally cylindrical shape to fit between the exterior of the cylinder 35 and the interior of the cylinder 36. The piston 91 includes two

glands

92 and 93 preferably made of a relatively soft metal such as bronze. The upper portion of the gland 92 substantially fillsthe space between the

cylinders

35 and 36 but the lowerportion has the inner surface cut away, leaving a downwardly extending outer portion 94 which with the exterior of the cylinder 35, defines a recess containing a ring of packing material 95. The lower portion of the gland 93 substantially fills the space between the

cylinders

35 and 36 but the upper portion has the outside surface cut away, leaving an upwardly extending inner portion 96, which, with the interior surface of the cylinder 36, defines a recess containing a ring of packing material 97. The

portions

94 and 96 overlap longitudinally, each extending partially into and closing the opposite recess, thus confining the packing material rings 95 and 97. The lower gland 93 is also formed with two additional recesses, one opening toward each of the

cylinders

35 and 36, and containing wiping rings 98 and 99. The two

glands

92 and 93 are held together by two diametrically oppositely positioned keys, one of which, the key 101, is shown in FIGURES 7b and 8. As shown, the key 101 fits into corresponding keyways cut into the

portions

94 and 96 of the

glands

92 and 93 respectively. Another similar key (not shown) is positioned diametrically opposite.

It is apparent that the piston 91, by virtue of the rings of packing

material

95 and 97, provides a fluid seal between the

cylinders

35 and 36. The piston is not fastened to either cylinder but is free to slide or float to various longitudinal positions as determined by forces applied thereto.

The operation of the hydraulic ram assembly can best be understood by referring to the simplified schematic showings of FIGURES 9-12. FIGURE 9 shows the assembly in its collapsed position, corresponding to FIG- URE 4. Fluid under pressure is admitted through the port 58, flows upward through the interior of the cylinder 35, through the ports 53 to the interior of the cylinder 36, and through the ports 67, exerting pressure between the bottom of the stufling box 81 and the top of the gland 72. Because of the difference in cross sectional areas, the outer cylinder 37 starts to rise and continues to the position shown in FIGURE 10, with the stop ring 86 engaging the bottom of the gland 64. This corresponds to the position shown in FIGURE 5.

Continued admission of fluid pressure causes the inter mediate cylinder 36 to rise, raising the outer cylinder 37 along with it. At this time fluid pressure urges the floating piston 91 downward and it remains in engagement with the stop ring 46 until the position shown in FIGURE 11 is reached. At this time flange 78 engages the bottom of the floating piston 91 and the fluid pressure urging the

cylinders

36 and 37 upward overcomes the pressure urging the piston 91 downward and the

cylinders

36 and 37 and the piston 91 rise as a unit until the position shown in FIGURE 12 is reached at which position the top of the piston 91 engages the stop ring 54. This is the fully extended position and corresponds to that shown in FIG- URE 6.

It is apparent that the present invention provides an improved lift truck. The ram assembly is arranged so that the load is raised by raising the larger diameter cylinders, leaving only the small diameter cylinder directly in front of the operator when the load is raised. At the same time the possibility of damage to the ram assembly is reduced because, although the small cylinder is exposed, the lower portion thereof is not a fluid sealing surface and accordingly minor abrasions do no harm. This desirable situation is made possible by the use of a floating piston in the ram assembly, as described.

The embodiment of the invention herein described in cludes a ram assembly comprising two cylinders each of which is extensible relative to a third. It is apparent that many principles of the invention are also applicable to ram assemblies having but two cylinders and to those having more than three cylinders.

Although a specific embodiment of the invention has been described in considerable detail for illustrative purposes, many modifications will occur to those skilled in the art.

It is therefore desired that the protection afforded by Letters Patent be limited only by the true scope of the appended claims.

What is claimed is:

'1. An hydraulic ram assembly, comprising,

first and second cylinders concentrically disposed for relative axial movement with said first cylinder protruding beyond an open end of said second cylinder leaving a radial space between said first cylinder and said end of said second cylinder, and

a floating piston of generally cylindrical shape interposed between and slidably engaging each of said first and second cylinders,

said piston including first and second fluid sealing means, each slidably engaging one of said cylinders.

2. An hydraulic ram mechanism, comprising,

a first cylinder,

a second cylinder having an open end and a closed end and mounted to be concentric with and partially surrounding said first cylinder and to be axially moveable relative thereto,

said cylinders being mounted with said first cylinder protruding axially beyond said open end leaving a radial space between said open end and said first cylinder,

said piston including first and second fluid sealing means, each slidably engaging one of said cylinders, and

means fastened'to said first cylinder for limiting the movement of said piston relative to said first cylinder.

3. An hydraulic ram assembly, comprising,

a first cylinder,

a first annular stop member fastened to the outside of said cylinder adjacent to one end thereof,

a second annular stop member fastened to the outside of said cylinder intermediate the ends thereof,

a second hollow cylinder formed with one closed end one open end and having an inside diameter greater than the outside diameter of said stop members,

said second cylinder being positioned concentric with and partially surrounding said first cylinder with said closed end nearer to said one end of said first cylinder than to the opposite end of said first cylinder,

a floating piston of generally cylindrical shape interposed between said first and second cylinders in the region between said stop members,

said piston including first and second fluid sealing means each slidably engaging one of said cylinders, and

an annular flange fastened to said second cylinder adjacent to said open end and projecting radially inward toward said first cylinder,

said flange having an inside diameter greater than the outside diameter of said stop members.

4. An hydraulic ram assembly, comprising,

a first cylinder,

a second, hollow cylinder having a closed end and an open end mounted concentric with and partially surrounding said first cylinder for axial movement relative thereto,

a floating piston of generally cylindrical shape interposed between said first and second cylinders,

said piston being substantially shorter than either said first or second cylinders and including fluid sealing means engaging both said cylinders, and

means for introducing fluid under pressure to the chamber defined by said first and second cylinders and said piston.

5. An hydraulic ram assembly, comprising,

a first cylinder,

a second annular stop member fastened to the outside of said cylinder approximately midway between the ends thereof,

a second, hollow cylinder formed with one .closed end and one open end and having an inside diameter a firstcylinder, a second hollow cylinder concentric with said first ing portion engaging the interior of said second cylinder and spaced from said first cylinder, thereby defining a first recess,

a first ring of packing material disposed in said first greater than the outside diameter of said stop memrecess,

bers, a second generally cylindrical gland engaging the exsaid second cylinder being disposed concentric with and terior of said first cylinder and the interior of said partially surrounding said first cylinder with. said second cylinder, closed end nearer to said one end of said first cylinsaid second gland being formed with a second axially der than to the opposite end of said first cylinder, 10 extending portion engaging the exterior of said first a floating piston of generally cylindrical shape intercylinder and spaced from said second cylinder, thereposed between said first and second cylinders in the by defining a second recess, and region between said stop members, a second ring of packing material disposed in said secsaid piston being substantially shorter than either said 0nd recess,

first or second cylinders and including first and secsaid glands being relatively positioned so that said first ond fluid sealing means each slidably engaging one portion extends into said second recess and engages of said cylinders, said second ring of packing material and so that said whereby the exterior of said first cylinder, the interior second portion extends into said first recess and enof said second cylinder including said closed end and gages said first ring of packing material. said piston define a chamber, 10. An hydraulic ram assembly, comprising,

an annular flange fastened to said second cylinder adfirst and second concentric cylinders,

jacent to said open end and projecting radially ina first generally cylindrical gland engaging the exterior ward toward said first cylinder, surface of said first cylinder and the interior surface said flange having an inside diameter greater than the of said second cylinder,

outside diameter of said stop members, and said first gland being formed with a first axially extendmeans for admitting fluid under pressure to said chaming portion engaging the interior surface of said secber. 0nd cylinder and spaced from the exterior surface. of

6. A floating piston interposed between two concentric said first cylinder thereby defining a first recess.

cylinders and forming a sliding fluid seal with each, coma first ring of packing material disposed in said. first prising, 3O recess,

a first generally cylindrical gland formed with a cut a second generally cylindrical gland engaging the exaway portion adjacent to one of said cylinders de terior surface of said first cylinder and the interior fining a first recess, surface of said second cylinder,

a first ring of packing material disposed in said first said second gland being formed with a second axially recess, extending portion engaging the exterior surfaceof a second generally cylindrical gland formed with a cut said first cylinder and spaced from the interior suraway portion adjacent to the other of said cylinders face of said second cylinder thereby defining a secdefining a second recess, and 0nd recess,

a second ring of packing material disposed in said rea second ring of packing material disposed in said seccess, 40 0nd recess,

each of said glands having an extending portion adjasaid glands being relatively positioned so that said first cent to its recess and extending into the recess deportion extends into said second recess and engages fined by the other gland to engage the ring of packing said second ring of packing material and so that said material therein. second portion extends into said first recess and en- 7. An hydraulic ram assembly, comprising, gages said first ring of packing material, and

means for fastening said glands together. 11. Apparatus according to claim 10 in which said means includes a key engaging keyways formed in said extending portions of said glands.

12. An hydraulic ram assembly providing two lift operations, comprising,

cylinder,

a first generally cylindrical gland disposed between said cylinders and formed with a cut away portion adjacent to one of said cylinders and defining therewith a first recess,

a first ring of packing material disposed in said first recess, I

a second generally cylindrical gland disposed between said cylinders and formed with a cut away portion adjacent to the other of said cylinders and defining therewith a second recess,

a second ring of packing material disposed in said seca first hollow cylinder of small diameter,

a second hollow cylinder of intermediate diameter having approximately the same length as said first cylinder and being formed with a closed end and an open end,

said second cylinder being disposed concentrically with and partially surrounding said first cylinder, a third hollow cylinder of large diameter and having a 0nd length. substantially less than that of said first and each of said glands having an extending port1on ad- Second Cylinders,

, lacent o Its recess and extending mm h recess said third cylinder being disposed concentrically with fi by i engage the of Pack and partially surrounding said second cylinder mg materla t erein, an means for fastening Said glands together a floating piston of generally cylindrical shape inter 8. Apparatus according to claim 7 in which said last named means includes a key engaging keyways formed in said extending portions of said glands.

9. A floating piston interposed between first and second concentric cylinders and forming a sliding fluid seal with each, comprising,

posed between said first and second cylinders,

said piston being substantially shorter than said third cylinder and including first and second fluid sealing means slidably engaging said first and second cylinders respectively, third fluid sealing means fastened to the exterior of said second cylinder intermediate the ends thereof and slidably engaging the interior of said third cylinder, fourth fluid sealing vmeans fastened to the interior of said third cylinder adjacent to one end, thereof andv slidably engaging the exterior of said second cylinder, and

stop members fastened to said cylinders for limiting the relative movements of said cylinders and said piston,

said first cylinder being formed with ports adjacent that end nearest said closed end of said second cylinder for providing fluid communication between the interior and exterior thereof,

said second cylinder being formed with ports for pro viding fluid communication between the interior and exterior thereof in the region between aid third and fourth fluid sealing means,

whereby when fluid under pressure is admitted to the interior of said first cylinder, the fluid flows through said ports, first moving said third cylinder with respect to said first and second cylinders and then moving said second and third cylinders as a unit with respect to said first cylinder.

13. A lift truck, comprising,

a frame,

a pair of stationary uprights mounted on said frame,

a pair of movable uprights mounted for endwise movement along said stationary uprights,

a load carriage mounted for movement along said movable uprights,

a first hollow cylinder positioned between said uprights with its lower end abutting said stationary uprights,

second and third hollow cylinders concentric with said first cylinder and operatively connected to move said movable uprights and said carriage upon movement with respect to said first cylinder,

fluid sealing means between said second and third cylinders,

a floating piston of generally cylindrical shape positioned between said first and second cylinders and including first and second fluid sealing means slidably engaging said first and second cylinders respectively,

stop means limiting the sliding movement of said piston to the upper portion of said first cylinder,

whereby the lower portion of the exterior of said first cylinder may be formed with a rough finish, and

means for admitting fluid under pressure to the space between said cylinders whereby the carriage and the movable uprights are raised.

14. A lift truck, comprising,

a frame,

apair of stationary uprights mounted .on said frame,

a load carriage mounted for movement along said movable uprights,

an hydraulic ram assembly for raising said carriage and said movable uprights, said ram assembly comprising,

a first hollow cylinder of small diameter having a first end mounted on said stationary uprights,

a first annular stop member fastened to the outside of said first cylinder adjacent to the second end thereof,

a second annular stop member fastenedto the outside of said first cylinder approximately midway between the ends thereof,

a second hollow cylinder of intermediate diameter having approximately the same length as said first cylinder and being formed with an open end and a closed end,

said second cylinder being disposed concentrically with and partially surrounding said first cylinder with said closed end adjacent to said second end of said first cylinder,

said flange having an inside diameter greater than the outside diameter of said stop members,

a floating piston of generally cylindrical shape interposed between said first and second cylinders in the region between said first and second stop members,

said piston including first and second fluid sealing means slidably engaging said first and second cylinders respectively,

whereby the exterior portion of said first cylinder between said first end and said second stop members is not a fluid sealing surface and may be of a rough finish,

a third hollow cylinder having a length substantially less than that of said first and second cylinders and disposed concentrically with and partially surrounding said second cylinder,

means forming fluid seals between said second and third cylinders,

connecting means for raising said carriage upon movement of said third cylinder,

connecting means for raising said movable uprights upon movement of said second cylinder, and

means for introducing fluid under pressure to the spaces between said first and second cylinders and between said second and third cylinders,

whereby said carriage is first raised with respect to said movable uprights after which said movable uprights are raised relative to said stationary uprights.

References Cited by the Examiner UNITED STATES PATENTS SAMUEL F. COLEMAN, Primary Examiner.

Claims

1. A HYDRAULIC RAM ASSEMBLY, COMPRISING FIRST AND SECOND CYLINDERS CONCENTRICALLY DISPOSED FOR RELATIVE AXIAL MOVEMENT WITH SAID FIRST CYLINDER PROTRUDING BEYOND AN OPEN END OF SAID SECOND CYLINDER LEAVING A RADIAL SPACE BETWEEN SAID FIRST CYLINDER AND SAID END OF SAID SECOND CYLINDER, AND A FLOATING PISTON OF GENERALLY CYLINDRICAL SHAPE INTERPOSED BETWEEN AND SLIDABLY ENGAGING EACH OF SAID FIRST AND SECOND CYLINDERS, SAID PISTON INCLUDING FIRST AND SECOND FLUID SEALING MEANS, EACH SLIDABLY ENGAGING ONE OF SAID CYLINDERS.