Lift truck mast

Abstract

A lift truck mast having extensible uprights received one within the other. Each upright includes a pair of rail members each of which has a web and flanges such that the members are i-shaped in cross section. The rail members are nested together with the web portion and end flanges of the inner overlapping the web portions and end flanges of the outer. The web portions of one rail member carry rollers which ride on the rear end flanges of the adjacent nested rail member. Each web portion, when viewed in cross section, provides a straight section of uniform thickness and a tapered portion gradually increasing in thickness toward the rear end flange. The rollers are spaced from, but mounted parallel to, the straight web portions so as to rotatably engage the rear end flanges and tangentially contact the tapered web portion. Forward mast bending loads are taken radially by the rollers and side thrust loads parallel to their axes of rotation for improved anti-friction properties and longer wear.

Description

This is a division, of application Ser. No. 55,064, filed July 15, 197075 76 providing clearance in the corner, so that the arcuate connecting surface is spaced from the radius edge of the roller. The rollers have line engagement with the rear end flanges 31a, 31b, 31c from the point of tangency 76 to the inner edge 78 of the roller. This means that forward bending loads are taken radially and uniformly along a line extending between 76 and 78 greatly increasing roller life and providing for smoother mast operation.

FIG. 5C depicts the interaction of the rollers and rails as described earlier. The forward bending loads are depicted in FIG. 5C as vectors acting on the rails as indicated by the directional arrows. The upper carriage rollers 52 act forwardly against front flanges 32c of the inner upright 26c. However, all of the other roller pairs, i.e., the lower carriage rollers 54 and each of the rail rollers 34, 36, 38, 40 act rearwardly against the rear end flanges 31a, 31b, 31c of the rails 26a, 26b, 26c. The result is a balance of forces on the mast which has the effect of providing smooth, stick-free operation while raising and lowering the mast.

POWER CYLINDER AND CHAIN LIFT ARRANGEMENT

Referring to FIG. 6, the hydraulic power cylinder C which is of conventional design, has a cylinder outer housing which is solidly but pivotally mounted on a bed plate 79 which has a recess R (FIG. 2) adapted to receive the base of the cylinder outer housing. The cylinder has a first extensible cylinder component B in which telescopes a second cylinder component D. The components B and D may be successively extended by the operator. The sheave block 28 at the upper end of the cylinder component D carries at the opposite ends thereof sheaves 80, 81. The inner upright 24 also carries adjacent its lower end a sheave block in which are rotatably mounted sheaves 82, 83. Guideways G (FIG. 4) on the rear end flanges of the upright 24 guide the cylinder-driven sheave block 28. Also mounted on the inner upright adjacent the upper end are a pair of sheaves 84, 85 (FIG. 4) in parallel alignment with the sheaves 80, 81, 82, 83. A pair of chains 86, 87 are each anchored at the lower end to the bed plate 78 and extend upwardly over the sheaves 80, 81 thence down and around the sheaves 82, 83 and again upwardly over the sheaves 84, 85 being anchored at the opposite end to the load carriage 14 at 88, 89. It will be appreciated that in FIG. 6, as well as in FIGS. 3 and 4, the cylinder and chain wrap are as they would be with the mast fully extended. That is to say, with the mast fully extended, the cylinder components B, D have each stroked out to the maximum extent and the sheaves 80, 81, 82, 83 are at the closest point of travel to each other and the load carriage 14 is at its uppermost position in the inner upright 24. The mechanical movement of the chain wrap is such that the rate of travel of the load carriage is twice the rate of extension of cylinder components B, D. This allows a shorter cylinder to be used so that the sheave block 28 occupies a position below the line of vision of the operator in the lowered position (FIG. 1A).

LATCH MECHANISM

The invention provides that the extensible mast uprights are locked and unlocked in a novel sequence utilizing to the maximum extent possible, the two-to-one ratio of the chain wrap to provide better load distribution. The latching sequence is such as to ensure that there is always sufficient overlap of the intermediate with the outer upright and inner with the intermediate upright. This also gives maximum strength and rigidity to the mast throughout the upward movement. The present invention provides a novel latch arrangement achieving all of these advantages without sacrificing a high mast strength to weight ratio.

1. First Latch Mechanism

Referring again to FIG. 2, it will be seen that the intermediate upright 22 has mounted in the upper cross beam 27b a latch 90. The latch 90 comprises a pair of oppositely-facing hook elements 91, 92 pivotally mounted on a common fore and aft extending shaft 93 in the longitudinal center plane of the lift truck. As best shown in FIG. 6A, an arm 94 on the hook element 91 projects laterally from the shaft 93 and an arm 95 on the hook element 92 projects laterally in the opposite direction. The hook elements 91, 92 have identical profiles. The hook element 91 pivots on the rear side of the cross beam 27b while the hook element 92 pivots on the front side within a cut-out 92. The hook element 91 is preferably splined onto shaft 93 and held in place by a pair of lock rings 97, 98. Hook element 92 is welded on the shaft at the opposite end. The splined mounting means of securing the hook element 91 has been found to produce a stronger assembly able to better withstand the forces acting on the latch.

As seen in FIG. 2, the cross beam 27a of the outer upright 20 has a vertically extending slot 101. Within the slot 101 and projecting below the cross beam 27a is a first dog 102. A second dog 103 is mounted on the rear side of the sheave block 28 which is shown schematically in FIG. 2 traveling within the inner upright 24.

As shown in FIG. 6A, the first and second dogs 102, 103 are laterally offset so as to be in vertical alignment with the arms 94, 95 Each dog 102, 103 receives a coil spring which yieldably supports a button 106, 107 engageable with the detent 94, 95. Each dog is beveled on the lower end so as to make engagement with the hook element 91, 92. It will be noted that clockwise rotation of the latch 90 simultaneously locks hook element 91 and unlocks hook element 92 and vice versa. The button 106 extends against the arm 94 to yieldably hold the hook element 91 extending through the slot 101 in locked engagement with the beveled end of the dog 102. Similarly, the button 107 yieldably holds the hook element 92 engaged with the dog 103 when the latch is rotated to the counterclockwise position. When dog 103 moves upwardly with the sheave block 28 it engages detent 95 rotating the latch 90, unlocking hook element 91 from dog 102 and locking hook element 92 to dog 103. This will be discussed later in the description of the operation of the mast as a whole.

2. Second Latch Mechanism

Referring again to FIG. 2, a second latch mechanism 110 is pivotally mounted on a transversely extending axis adjacent the upper cross beam 27c of the inner upright 24. Latch 110 pivots in a fore and aft direction in a plane laterally offset from the centerline of the mast. As best shown in FIG. 6B, oppositely facing hook elements 111, 112 are integral with oppositely facing arms 113, 114. The hook element 111 and arm 113 project rearwardly in alignment with a third dog 116 mounted on the upper cross beam 27b of the intermediate upright 22. The hook element and arm 112, 114 project forwardly in alignment with a fourth dog 118 carried on back edge of the right vertical member 51 of the load carriage 14.

Referring to FIG. 6B, it will be seen that the hook element 111 cooperates with the third dog 116 upon rearward movement. The hook element 112 and arm 114 cooperate with the fourth dog 118 upon forward pivotal movement. As with the other dogs, the dogs 116, 118 each receive coil springs which yieldably support buttons 122, 123. The buttons 122, 123 are engageable with the arms 113, 114 respectively and cooperatively pivot the hook elements 111, 112 alternately into locked or unlocked engagement with the dogs 116, 118. The operation is similar to that of latch 90 in that oppositely facing hook elements simultaneously unlock one part of the mast while locking it to another part.

MAST OPERATION

FIGS. 7A-7H are diagrammatic sequence views showing the mast operation. Referring to FIG. 7A, assume that the mast is in the collapsed position with the upper cross beams 27a, 27b, 27c shown nested, one above the other, as they would appear if viewing FIG. 1A from the rear and representing here the uprights 20, 22, 24. The fork 15 is fully lowered. The operator now causes the first cylinder component B to be extended. As it strokes out, the sheave block 28 advances the dog 103 toward the latch 90. The latch 90 at this moment is rotated to the locked position with hook element 91 and arm 94 in locking engagement with the dog 102 such that the intermediate upright is locked to the outer. Also at this moment the second latch 110 is in the position shown in FIG. 7D. That is, the hook element 111 and detent 113 are in locking engagement with the dog 116. Thus the inner upright is locked to the intermediate and the intermediate to the outer.

As the cylinder strokes out only the load carriage is free to move. As the sheave block 28 moves vertically to a position corresponding to the free lift height of the load carrier (FIG. 1) it advances the dog 103 into engagement with the arm 95 pivoting the hook element 92 into locking engagement with the dog 103. Hook element 91 simultaneously disengages from dog 102. This is the condition depicted in FIGS. 7B, 7C. At this point, any further upward movement of the sheave block 28 commences to elevate the extensible uprights 22, 24. It is important to note that at the position shown in FIGS. 7B, 7C, the load carriage 14 is already at its free lift height, i.e., the maximum height of the fork without any extension of the mast occurring. It may continue to move upwardly in the inner upright 24 only a few more inches as depicted in FIG. 7D before the latch 110 is tripped releasing the inner from the intermediate upright.

At the position of the uprights shown in FIGS. 7E and 7F, the load carriage 14 will have reached its highest point of travel in the inner upright and any further elevation of the fork 15 comes about as a result of the simultaneous extension of the intermediate and inner uprights rather than movement of the load carriage. As will be seen in FIGS. 7E, 7F the intermediate and inner uprights are no longer locked to the outer upright 20 by the latch 90. Instead, they are locked onto the sheave block 28 and have elevated slightly above the outer upright 20. The load carriage has now reached the point in the inner upright 24 where the dog 118 will trip the latch 110 as shown in FIG. 7G. The dog 118 on the carriage engages the arm 114 pivoting the latch 110 forwardly (counterclockwise as viewed in FIG. 7G). This disengages the inner from the intermediate upright and engages the hook element 112 with the dog 118 locking the inner upright onto the carriage. The inner upright being now locked to the carriage commences to be pulled upwardly out of the intermediate upright by the carriage. As will be seen in FIG. 7G, the upper set of rollers 52 of the carriage have now extended beyond the top of the rails effectively increasing the lift of the fork.

Further elevation of the sheave block 28 by the cylinder continues to raise the intermediate upright 22 at the rate of travel of the cylinder. Simultaneously the inner upright 24, which rises out of the intermediate upright as depicted in FIG. 7H at twice the rate of travel of the intermediate upright, will reach its fully extended position (FIGS. 3, 4) at the same time as does the intermediate.

In lowering the mast the sequence of latching just described will be reversed so that at all times the uprights 20, 22, 24 are positively locked either to the outer upright 20, the cylinder-driven sheave block 28 or the load carriage 14.

Various prior art latching arrangements have been employed in a number of combinations. In one arrangement the inner upright is first locked to the stationary cylinder housing to guard against upward movement of the upright with the carriage in the event the latter should stick or bind. Control of the inner upright is then transferred by means of another latch to the carriage which commences to extend the inner upright out of the intermediate. If the mast is to be fully extended, stop blocks on the lower end of the inner upright engage stop block at the upper end of the intermediate which are effective for raising the latter from within the outer upright as the load carriage continues up. The result is that the rollers on the inner upright are over worked since the majority of loads will be spotted at less than full mast height.

With the invention, from the position shown in FIG. 7G, should the mast continue extending until reaching the overall raised height as shown in FIGS. 3 and 4, there will be a uniform decrease in overlap between the uprights. That is, there is always a relatively equal overlap between the inner and intermediate and between the intermediate and outer uprights owing to the chain wrap and latching sequence. The inner upright 24 moves relative to the intermediate 22 which in turn moves relative to the outer upright 20 such that at the initially extended position depicted in FIG. 7H, the extent of overlap is in excess of 90 percent as between the intermediate and outer uprights and in excess of 95 percent, as between between the inner and intermediate uprights. Thus throughout the elevation or retraction of the mast the loading on the bearings is maintained in the most favorable conditions owing to the fact that the extensible uprights are simultaneously being elevated rather than one followed by the other. This greatly reduces wear and friction on any given set of rollers since all sets are cooperating when any load is lifted above free lift height.

Still in other prior art latching arrangements a plurality of latch elements are arranged in such fashion as to lock the inner to the intermediate upright but no provision is made to lock the intermediate to the outer. Theoretically the forces applied on opposite sides of the load chains should balance and the load carriage should rise with no tendency to cock or bind in the inner uprights. In practice, however, this is not always the case. In masts where reliance is placed on the fact that the weight of the inner upright will prevent the intermediate from moving up prematurely, a considerable weight is required to keep the intermediate upright down. Even so, where extreme side thrust loads occur, it is possible to raise both the inner and intermediate uprights prematurely. This, of course, cannot occur with the present invention since during the free lift period the inner upright is positively locked to the intermediate and the latter in turn is positively locked to the stationary outer upright.

In the present invention the intermediate upright is supported during extension directly by the cylinder which in turn rests on the bed plate of the mast. Thus the intermediate upright always has solid support which increases the mast stability.

To further increase the wear properties of the rails, the surfaces providing rolling engagement for the rollers may be hardened, e.g., by hardening the zone on the rear end flanges 31a, 31b, 31c in rolling contact with rollers 34, 36, 38, 40, 51, 53, 54. Or these surfaces may be provided with a wear strip of harder material than the rails themselves.

Modifications and changes may be made to the invention as will be apparent to those skilled in the art to which it pertains which modifications and changes are to be regarded as reasonable equivalents thereof and are intended to be covered by the appended claims except insofar as limited by the prior art.

Claims

1. A structural member for use in a multi-sectional mast having a stationary and extensible section, one being laterally offset relative to the other and each extending longitudinally parallel to the axis of the mast and said extensible section being longitudinally parallel to the axis of the mast and said extensible section being longitudinally slidable relative to the stationary section forming therewith longitudinally extending trackways, and anti-friction rollers carried on at least one of said sections adapted to roll in said trackways when extending or retracting one section relative to the other, said structural member being adapted to form a portion of said trackways and comprising,

a web portion for defining a longitudinally extending side of said trackways and having a surface inclined to and tangentially contactable by an edge surface of the rollers in said trackways and then diverging, in cross section, on a line from a the point of tangency with said rollers and joining a straight surface at an angle of between 1° and 20° relative thereto, said straight surface extending perpendicularly to the axis of said rollers and said inclined surface and straight surface being laterally spaced from and out of contact with said rollers roller edge surface, so that a clearance is provided between said web portion and said roller except at said point of tangency on the inclined surface thereby minimizing any tendency for axial loading of said rollers.

2. A structural member according to claim 1 wherein said inclined surface diverges at an angle of between 2° and 6°.

3. A structural member according to claim 2 wherein said inclined surface diverges at an angle of approximately 31/2°.

4. A structural member according to claim 1 wherein, viewed in cross section, said member has transversely extending end flanges on said web portion forming a generally i-shaped cross sectional configuration and one portion of one end flange joining said inclined surface of the web portion for providing a rolling surface for said rollers and adapted to transmit radial loads thereto.

5. A structural member according to claim 4 wherein the portion of said end flange for providing rolling engagement with the rollers is hardened during the manufacture of said structural member to a greater extent than the rest of said member.

6. A structural member according to claim 5 wherein said portion of the end flange for providing rolling engagement with the rollers is provided with a wear surface of greater hardness than the remainder of said structural member.

7. A structural member having an i-shaped cross section for use in a multi-sectional mast having fixed and extensible mast sections adapted to nest one within the other defining parallel, longitudinally extending trackways and anit-friction rollers received in said trackways for supporting the extensible mast section for movement relative to the fixed mast section, said structural member comprising

a web having a tapered portion joined by a straight portion, said straight portion extending perpendicularly to the axes of said rollers, and

a pair of end flanges, one being integrally formed with said tapered portion and the other with said straight portion and each extending transversely thereto,

the one end flange formed with the tapered portion adapted to provide a rolling surface for said rollers, and said tapered portion inclined away from said rollers and joining said straight portion at an angle of between 1° and 20° providing a space between the rollers and said straight and tapered portions from a point of tangency on said tapered portion to said other end flange and joined to said one end flange by an arcuate surface, said tapered and straight portions and said arcuate surface each being spaced from each of said rollers except at points of tangency between an edge surface on each one of said rollers and the tapered portion.

8. A structural member according to claim 7 wherein said tapered portion diverges at an angle of between 2° and 6°.

9. A structural member according to claim 8 wherein said tapered portion diverges at an angle of approximately 31/2°.

10. An extensible mast having collapsed and extended positions, comprising:

a. inner and outer mast sections nested inner within the outer and being relatively longitudinally extensible;

b. each of said mast sections including two parallel laterally spaced rail members;

c. said rail members of at least one of said mast sections carrying a plurality of rollers mounted for rotation about parallel axes;

d. each of said rollers defining a peripheral surface and an end surface joined by a curved interconnecting surface;

e. said rail members of said other mast section defining track surfaces engageable with said peripheral surfaces, and defining inclined surfaces adjoining said track surfaces and tangentially contactable with the junctures of said interconnecting and said end surfaces of said rollers to absorb thrust loads; and,

f. said inclined surfaces being spaced from each of said rollers except at the points of tangency with said end interconnecting surfaces so that a clearance is provided between the interconnecting surfaces and corners of said rail members.

11. The mast of claim 10 wherein said track surfaces extend in planes paralleling said axes of said rollers, and said peripheral roller surfaces are cylindrical surfaces concentric about said axes.

12. The mast of claim 10 wherein said end surfaces of said rollers extend in planes perpendicular to the axes of said rollers, and said inclined surfaces are inclined at angles relative to said end surfaces within the range of about 1° to 20°.

13. The mast of claim 12 wherein said angles are within the range of about 2° to 6°.

14. The mast of claim 10 wherein said inclined surfaces are inclined at angles relative to said end surfaces within the range of about 1° to 20°.

15. The mast of claim 14 wherein said angles of inclination are within the range of about 2° to 6°.

16. The mast of claim 15 wherein said angles are about 31/2°.

17. The mast of claim 10 wherein:

a. each of said rail members includes a pair of spaced end flanges connected by a web;

b. said webs and said end flanges of said inner section rail members overlap said webs and said end flanges of said outer section rail members;

c. said track surfaces are formed on said end flanges of said other mast section rail members; and

d. said inclined surfaces are formed on said webs of said other mast section rail members.

18. The mast of claim 17 wherein said points of tangency are located radially inwardly on said end surfaces from said the junctures of said peripheral interconnecting and end surfaces, whereby no contact is made between said inclined and connecting web surfaces and said rollers, at said the junctures of said interconnecting and end surfaces.

19. The extensible mast of claim 17 wherein:

a. said rollers include a first pair of rollers mounted on the webs of the outer section rail members, and a second pair of rollers mounted on the webs of the inner section rail members;

b. each of said rail members has an end flange defining one of said track surfaces; and

c. each of said rail members has a web defining one of said inclined surfaces.

20. The mast of claim 17 wherein each of said webs which define one of said inclined surfaces has, in cross section, a region of substantially uniform thickness extending toward one of the integrally formed end flanges, and a region of increasing thickness extending toward the other integrally formed end flange, said region of increasing thickness defining said one inclined surface.

21. The mast of claim 17 additionally including a load carriage supported on one of said mast sections and including:

a. a pair of parallel, longitudinally extending load carriage support members laterally spaced from and overlapping load carriage trackways defined by the rail members of said one mast section;

b. first, second and third opposed pairs of rollers rotatably carried on said load carriage support members and received in said load carriage trackways for rolling engagement with said one mast section rail members when reciprocating said load carriage;

c. said first pair of rollers mounted above the second pair and the second pair above the third; and,

d. said first and third pairs of rollers primarily taking the dynamic fork loads during reciprocation of the load carriage throughout the length of said load carriage trackways, said first pair of rollers extending out of said load carriage trackways in the fully raised position of said load carriage free of any loading, and said second and third pair of rollers then cooperating in taking the static fork loads whereby bearing loading conditions are improved and the maximum fork height is increased.

22. A lift truck mast according to claim 21 wherein said load carriage support members carry side thrust rollers rotatably mounted on fore and aft extending axes to rotatably engage the webs of said one mast section rail members during reciprocation of the load carriage thereby isolating the other rollers from side thrust loads.

23. An extensible lift truck mast, comprising:

a. inner and outer mast sections nested inner within the outer and being relatively longitudinally extensible;

b. each of said mast sections including laterally spaced rail members;

c. each of said rail members having spaced end flanges connected by a web;

d. said webs and said end flanges of said inner section rail members overlapping said webs and said end flanges of said outer section rail members to define longitudinally extending trackways;

e. said rail members of at least one of said mast sections carrying a plurality of rollers mounted for rotation about parallel axes, said rollers each having a peripheral surface and an end surface joined by a curved interconnecting surface;

f. said rail members of the other of said mast sections having track surfaces defined on its end flanges for engaging said peripheral surfaces of said rollers;

g. said webs of said other section rail members having cross sections of increased thickness near said track surfaces and joined to said track surfaces by a connecting surface, said increased thickness cross sections defining inclined surfaces that extend into tangential contact with the interconnecting surfaces near the junctures of said interconnecting and said end surfaces at angles within the range of about 1° and 20° relative to said end surfaces, and said web connecting surface being spaced from said rollers.

24. The mast of claim 23 wherein said angles are within the range of about 2° and 6°.

25. The mast of claim 24 wherein said angles are about 31/2°.