Load-lifting mechanism for a lift truck

[57] ABSTRACT

A load-lifting mechanism for lift trucks in which an extensible three-stage mast carries a load-lifting carriage and is vertically actuated by a hydraulic ram and associated load-lifting chains. A simple piston and cylinder ram operates to elevate the carriage through a full free lift travel on the upper, inner mast section in the collapsed condition of the mast via a system of two sets of chains and associated lifting bar and lifting bracket. One set of chains is trained over the piston of the ram and coupled at its opposite ends to the lower mast section via the ram cylinder and the lifting bracket which is guided for limited travel on the intermediate mast section. The other set of chains is trained over the lifting bracket and coupled at one end to the inner mast and at its other end to the lifting bar which engages the carriage during free lift thereof and then couples to the stationary outer mast via the ram cylinder during mast extension. A latch system automatically couples the inner and outer mast sections during free lift of the carriage and interconnects the carriage and inner mast section during extension of the mast.

Claims, 20 Drawing Figures

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LOAD-LIFTING MECHANISM FOR A LIFT TRUCK

This invention relates generally to industrial and offthe-road lift trucks, and more specifically to telescopic load-lifting masts adapted to be mounted on such trucks.

An object of the present invention is to provide an improved load-lifting mechanism for industrial and/or off-the-road lift trucks having an extensible load-lifting mast and associated load-lifting chains or other flexible tension elements actuated by a hydraulic ram to lift the load supported on a carriage of the mast, as well as to provide an improved load-lifting and latching system for use in such masts, which results in: (1) an economical and lightweight construction which is efficient and reliable in operation; (2) positive sequencing of the carriage and mast extension through the use of a positive acting escapement; (3) greatly improved visibility for the operator of the truck through the mast during the upper portion of the lift sequence; (4) the vertical reach capability of the usual triple-stage extensible mast while also providing full free lift of the carriage on the upper inner mast section prior to any extension of the mast sections; (5) additional lift height for a given collapsed height of the mast and also increased loadlifting capacity; (6) the accomplishment of the above improved results through only one simple piston and cylinder type ram, thereby enabling improvement in lifting speed, reducing the oil requirements of the ram and providing a constant 4:1 lifting ratio and constant lift speed of the load; (7) the accomplishment of the above improved results without increasing the width of the mast so that the mast is adaptable to mounting on a majority of existing lift trucks without requiring special wide drive axles; and (8) an improved positive acting escapement or latching mechanism which is of rugged, simple and reliable construction.

Other objects, features and advantages of the present invention will become apparent from the following detailed description taken into conjunction with the accompanying drawings wherein:

FIG. 1 is a perspective view of a conventional lift truck equipped with an improved extensible lift mast constructed pursuant to the present invention, the same being illustrated with the mast in collapsed condition and the carriage elevated to the upper limit of its full free lift travel.

FIG. 2 is a perspective view similar to FIG. 1 but with the mast extended to its full height.

FIG. 3 is a perspective view of the mast shown by itself in collapsed condition with the carriage at the lower limit of its full free lift travel, the forks of the carriage being omitted for clarity.

FIG. 4 is a top view of the mast illustrated in FIG. 3 as viewed on the line 4—4 of FIG. 3.

FIG. 5 is a horizontal section taken on the line 5—5 of FIG. 3.

FIG. 6 is a fragmentary rear view of the upper end of the inner mast section as viewed on the line 6—6 of FIG. 5, and illustrating in part the latching mechanism of the invention.

FIG. 7 is a vertical sectional view taken along the line 7—7 of FIG. 5.

FIG. 8 is an exploded perspective view of the outer, lower section of the mast and associated ram, chain and latch parts.

FIG. 9 is an exploded perspective view of the intermediate section of the mast and the associated chain, lifting bracket and guide structure.

FIG. 10 is an exploded perspective view of the inner, upper mast section and associated carriage, lifting bar and latch parts.

FIG. 11 is a fragmentary perspective and partially exploded view of a portion of the carriage structure including a latch actuator and a side guide roller.

FIG. 12 is a fragmentary side elevational view taken partially in section through a portion of the carriage and lifting bar structure.

FIGS. 13,14 and 15 are fragmentary side elevational views taken partially in section on the line 13—13 of FIG. 6 illustrating operation of the escapement latch mechanism, FIG. 13 illustrating the inner mast latched to the outer mast, FIG. 14 illustrating an engagement of the carriage latch actuator with the latch to unlock the inner mast from the outer mast, and FIG. 15 illustrating the carriage latched onto the being carried by the inner mast which in turn has been unlatched from the outer mast.

FIGS. 16, 17 and 18 are schematic diagrammatic views of the mast of FIGS. 1-14, FIG. 16 illustrating the mast in its fully collapsed condition with the carriage at the lower limit of its full free travel, FIG. 17 illustrating the carriage at the upper limit of its full free lift travel with the mast still collapsed, and FIG. 18 illustrating the mast fully extended.

FIGS. 19 and 20 are schematic diagrammatic views of second and third embodiments of extensible masts also constructed in accordance with the present invention.

INTRODUCTION

The principles of the present invention are applicable to load-lifting mechanisms incorporating an extensible framework, commonly termed a “mast,” made up of a plurality of “sections,” preferably three in number as illustrated herein. The lerm “mast section,” as used herein refers to a single stage of the mast usually comprising a rectangular framework made up of a pair of horizontally spaced and vertically extending “rails” suitably interconnected by horizontal cross braces and adapted to telescopically interengage with the rails of another such section of the mast. The term “rails” refers to the vertical side members of a mast section, which may be mill-formed channel, I-beam or other beam sections, and which are commonly used in pairs as the uprights of a mast section. The term “ram” as used herein refers to the hydraulically operated piston and cylinder unit employed to impart vertical movement to the load lifting mechanism and preferably comprises a simple two-part ram made up of a cylinder which constitutes the external lower member of the ram and which remains fixed at its lower end to the lowermost, outer mast section, and a plunger carrying a fluid actuated piston and which telescopes within the cylinder so as to movably extend from the upper end thereof. However, other known multi-part ram constructions may be employed if desired, as will become apparent hereinafter. The term “carriage” refers to the apron which travels vertically on the uppermost, inner mast section and which usually carries forks or other associated cantilever attachments which directly carry the cargo or load to be raised, lowered and/or transported. The term “chain” refers to the usual flexible

3,786,902 load supporting elements which transmit tension loading and operatively interconnect the ram, mast sections and carriage. These elements preferably comprise the well-known link and roller type chains since they operate with a minimum of friction and stretch, but other types of chains, cables, belts or equipment elements may be employed if their “stretch factor” is suitably taken into account.

GENERAL STRUCTURAL ORGANIZATION AND OPERATION OF MAST SECTIONS

Referring in more detail to the accompanying drawings, FIGS. 1 and 2 illustrate an exemplary but preferred load-lifting mechanism constructed in accordance with the present invention which comprises a three-stage or three-section mast 20 having a lifting range of somewhat greater than the usual conventional three-stage mast, or conversely having the same maximum height extension capability with a shorter collapsed height. Referring to FIG. 1, mast 20 is shown in its fully collapsed condition but with its carriage 22 raised to its upper limit of full free lift travel. Mast 20 is shown mounted in a conventional manner on the front axle of the lift truck 24 which may be of a hard tire industrial type as shown or an off-the-road type. Mast 20 may be mounted in a fixed upright position by suitable bracing structure 26 connected to the forward end of the truck, or may be pivotally mounted on the truck axle and connected by suitable tilting rams (not shown) so as to be pivotable fore and aft of the truck in the well-known manner.

As best seen in FIG. 2, mast 20 has three sections, a lower dual rail section 28 provided with suitable attachment structure so as to be demountably supported at or near its lower end on the front end or axle of truck 24, a dual rail intermediate section 30 and a dual rail uppermost inner section 32. Section 30 telescopes within section 28 and section 32 telescopes within section 30. Although conventional sliding rail interengagemnt of the sections may be employed, preferably mast 20 employs a roller guided construction such as that disclosed in more detail in U.S. Pat. No. 3,213,967 issued Oct. 26, 1965 in the name of Russell Hastings, Jr. and Elmer R. Backofen and assigned on its face to Clark Equipment Company of Buchanan, Michigan, which is incorporated herein by reference for brevity. Mast 20 is also equipped with a suitable load-lifting carriage 22 carrying on its upper horizontal rail 23 a pair of detachable forks 24 and 24' and which tracks by means of fore and aft guide rollers 52, 52 and side guide rollers 25 on the rails 36, 36’ of upper section 32. A two-part ram 34 and two sets of lift chains 33, 33' and 35, 35' are also employed in mast 20.

Further details of the structure and operation of mast 20 will become apparent from the following description of the carriage and mast lifting structure as shown in detail in FIGS. 3 through 15, in conjunction with a general explanation of the structural organization and operating principles of the principal components of mast 20 as shown semi-schematicaily in FIGS. 16,17 and 18. In these schematic views, some of the parts are displaced fore and aft out of their true relationsip in order to permit clearer illustration of the chain reeving arrangement. Also, the schematic illustrations of FIGS. 16-18 show only one of those elements which are employed in pairs. Since much of the mast structure is symmetrical, the left-hand (as viewed from the opera tor’s position on the truck) components are generally duplicates of the right-hand components and their reference numerals have been given a prime mark “ ' ” suffix to indicate this relationship.

Referring to FIGS. 16, 17 and 18, as supplemented by reference to other figures as will be indicated, the individual mast sections 28, 30 and 32 of the multistage mast 20 telescope from a collapsed condition (FIG. 16) to a fully extended position (FIG. 18) to give at least the vertical reach of a conventional “three-rail” mast. The innermost mast section 32 as seen in FIGS. 16 and 7 thus becomes the uppermost section in FIG. 18, the intermediate section 30 elevates to remain the middle section and the outermost section 28 remains stationary and hence becomes the lowermost section.

As best seen in FIGS. 2, 8, 9 and 10, each mast section 28,30 and 32 has two vertical parallel rails 40,40'; 38, 38' and 36,36' joined by suitable cross braces 122, 209; 31,69 and 224 and 100,101 and 103 respectively. By way of a preferred example, and as best seen in FIG. 5, rails 36,36' of inner section 32 are I-beam members, as are rails 38,38' of the intermediate section 30. However, rails 40, 40' of the outermost mast section 28 are channel or C-shaped in cross section, although I-beam members may also be used. Preferably, mast 20 is a roller-type mast; i.e., the rails are guided relative to one another by rollers mounted on the rails rather than the rails sliding directly on one another, although the invention is also applicable to the latter type of mast construction. Thus, as shown in FIGS. 4 and 7, rails 40,40' of section 28 have suitable roller stub axles 41,41' near their upper ends which carry rollers 42, 42' respectively which track in the outer groove of the associated rail 38, 38' of the intermediate mast 30. Each of the rails 38,38' has stub axles 43, 43' and 45, 45' carrying inner rollers 44, 44' and outer rollers 46, 46' respectively. The inner rollers are disposed at the upper end of the rails and the outer at the lower end, and respectively track in the outer grooves of the associated rails 36, 36' and in the inner grooves of the associated rails 40, 40' of section 28. Rails 36, 36' of inner section 32 have stub axles 47, 47' respectively carrying rollers 48, 48' near the lower ends of the rails which track in the inner grooves of rails 38, 38'. Load lifting carriage 22 is vertically elevatable on inner mast section 32 and has two upright struts 50, 50' each of which carries an associated pair of upper and lower rollers 52, 54, 52', 54', each pair tracking in the inner groove of the associated rail 36, 36'.

CARRIAGE AND MAST LIFTING STRUCTURE AND OPERATION

Among the principal features of the present invention are the provision of a sliding channel of U-shaped bracket 60 (FIGS. 5, 9 and 16-18) which has a pair of tubular guides 62, 62' respectively slidably receiving guide rods 64, 64'. Rods 64, 64' are attached at their upper ends by apertured blocks 66, 66’ mounted on cantilever arms 140, 140' welded to the rails of intermediate mast 30 and at their lower ends by apertured blocks 68, 68' welded onto a lower cross brace 69 secured to rails 38,38'. Bracket 60 thus can slide up and down on the intermediate mast, with the end limits of travel of bracket 60 determined by blocks 66, 66' and 68, 68' (FIG. 9) which thus serve as stops. As will be evident from FIG. 9, rods 64, 64' are secured against upward movement relative to section 3o by roll pins

3,786 5

64α, 64α' inserted into the lower ends of the rods below blocks 68^68', and the rods are secured against downward movement by nuts 64/?, Mb' screwed onto the threaded upper ends of the rods above blocks 66, 66'.

Another feature is a lifting bar 70 (FIG. 2, 5, 7 and 10) for reversing the lifting relationship of bracket 60 relative to carriage 22 and to the inner mast section 32, and which also serves as an anti-tilt restrainer for rams 34.

A further feature is an escapement mechanism including a latch 72 (FIGS. 13-15) for connecting inner mast section 32 to outer mast section 28 during free lift travel of the carriage (FIG. 13), which intermast connection is released by upward movement of the carriage as it reaches the upper end of rails 36, 36' (FIG. 14) whereupon the carriage becomes latched onto the upper ends of rails 36, 36' (FIG. 15) and then is carried by the latch on rails 36, 36' for the remainder of its upward travel during mast extension.

These features permit the use of a simple two-part hydraulic ram 34, consisting of a single outside cylinder 74 (FIG. 8) and a single plunger 76 contained therein, having a collapsed height less than that of the mast sections (FIGS. 3, 7 and 16) and permit cylinder 74 to be stationarily affixed to rails 40, 40' of lowermost mast section 28. They also enable carriage 22 to be lifted from ground level (FIG. 16) to the upper end of rails 36, 36' while the rails are in their fully collapsed condition (FIGS. 1, 3, 7, 16 and 17), thus providing what is termed in the art “full free lift” action, while retaining or exceeding the full vertical reach capability of prior art three-section masts.

To explain in more detail, plunger 76 carries a pair of chain pulleys or sheaves 80, 80' at its upper end having chains 33, 33' respectively trained thereover (FIGS. 4 and 8). The rear runs (as shown in the schematic diagrams of FIGS. 16-18) of chains 33, 33' are affixed at their lower ends to cylinder 74 via a bracket 82 (FIGS. 8 and 17). Note that lifting bracket 60 is shown out in front of ram 34 in FIGS. 16-18 for clarity, but as seen in FIGS. 3-5 and 9, the guide sleeves 62, 62' of bracket 60 are actually mounted behind the ram, the side plates 61, 61' of bracket 60 extend forwardly with a clearance on opposite side of the ram, and a cross brace 63 of bracket 60 is disposed in front of the ram. The front runs of chain 33, 33' are affixed at their lower ends at 84, 84' (FIGS. 4, 9 and 17-19) to horizontal gussets in the lower front corners of bracket 60. With this reeving arrangement, vertical movement of plunger 76 will raise or lower bracket 60 at a 2:1 dis- ⁵⁰tance multiplying ratio.

Lifting bracket 60 carries a pair of chain sheaves 86, 86' (FIGS. 4, 7, 9 and 17-19) at its upper end over which chains 35, 35' are respectively trained. The rear runs of chains 35, 35' are affixed at their lower ends to brackets 88, 88' respectively mounted on the inner flanges of rails 36,36' at the lower ends thereof (FIGS. 4 and 10). The front runs of chains 35, 35' are affixed at their lower ends to lifting bar 70 (FIG. 10). Lifting bar 70 cam move up and down relative to the rails 40, 40' and is guided in such movement by trapped supporting engagement with carriage 22 during travel thereof in the collapsed condition of mast 20. As best seen in FIGS. 5, 7 and 12, struts 50, 50' of carriage 22 are notched at their lower ends to receive bar 70 therein so that the carriage rests on bar 70 to vertically support the carriage during travel of the carriage be902 tween the positions thereof shown in FIGS. 16 and 17. The proximity of chains 35, 35' to the inner sides of struts 50, 50' assists in guiding bar 70 into the strut notches during descent of the carriage onto the bar. 5 The upper end of cylinder 74 has a stop 90 (FIG. 8) affixed thereto with a vertical central bore 91 (FIG. 4) which receives an upright central spike 71 of bar 70 therethrough, the abutment of bar 70 with stop 90 limiting upward movement of bar 70 when the same 10 reaches the position thereof shown in FIGS. 17 and 18.

Spike 71 has a circumferential groove 71' (FIG. 7) which is engaged by a spring-biased detent ball 93 (FIG. 4) mounted in stop 91 to yieldably retain bar 70 engaged with stop 90 while the mast sections are ex15 tended.

The escapement latching arrangement (best seen in FIGS. 6, 10 and 13-15) consists of a pair of identical automatically actuated escapement mechanisms, one located adjacent each of the rails 36, 36' on an upper 20 cross brace 100 of inner mast 32 which is affixed to the rear sides of rails 36, 36' (FIG. 10). Each escapement (only the reference numerals of the right-hand escapement being used hereinafter, it being understood that the left-hand escapement parts have the prime suffix) ²⁵ consists of a pair of spaced vertical plates 102 and 104 welded to the underside of brace 100, a roller 106 journalled between plates 102 and 104 on an axle pin 108, and a generally triangularly-shaped escapement latch 72. Latch 72 has a central slot 110 loosely receiving a cross bolt 112 which in turn extends through plates 102 and 104 above and parallel to pin 108 to thereby loosely pivotally mount latch 72 between plates 102 and 104. The curved lower side surfaces 114 and 116 of latch 72 are adapted to respectively abut a limit stop 118 on carriage 22 and a limit stop 120 on an upper cross brace 102 of outer mast section 28 in the two extreme overcenter positions of latch 72 (FIGS. 15 and 13 respectively). Latch 72 has two opposed semicircular notches 124 and 126 which respectively coop⁰ erate with latch actuators 128 and 130 which in turn are carried respectively on the upper end of carriage 22 and on the cross brace 122 of mast section 28.

When latch 72 is in the position shown in FIG. 13, the lifting force exerted on inner mast section 32 by chains ⁵ 35, 35' develops via roller 106 an actuator 130 a locking moment acting on latch 72 which maintains it in the over-center position shown in FIG. 13. Hence, inner mast section 32 is securely latched to outer mast section 28 by the escapement to thereby restrain upward movement of the inner mast while carriage 22 is being lifted anywhere between its fully lower position shown in FIG. 16 and its uppermost free-lift position shown in FIG. 17 by chains 35,35' acting through the lifting bar 70. Since inner mast section 32 has been held immobile up to this point by its latched connection to outer mast section 28, carriage 22 will be lifted at a 2:1 ratio relative to upward movement of bracket 60 and hence at a 4:1 ratio relative to upward movement of piston 76.

As actuator 128 travels upwardly from the position thereof shown in FIG. 13, it can clear the shoulder 132 at the entrance to notch 124 due to the tilted orientation of latch 72, and hence actuator 128 will travel past shoulder 132 and then strike the opposite shoulder 134 of notch 124 when the carriage reaches a position just below that shown in FIG. 14 during its ascent. Once actuator 128 engages latch 72 during upward travel of the carriage, the force exerted by actuator 128 upwardly

3,786,902 and clockwise on latch 72 will, due to the greater leverage exerted by actuator 128 on latch 72, cause latch 72 to pivot clockwise and move bodily relative to pin 112, thus causing curved surface 114 to move on roller 106 as the carriage continues its upward motion. Actuator 128 thus overcomes the locking force exerted on latch 72 by roller 106 and actuator 130 so that, as carriage 22 continues its upward movement, actuator 128 will pivot latch 72 clockwise as shown by the progression of FIGS. 13,14 and 15 until the apex 136 of latch surfaces 114 and 116 passes over the mutual centerline of roller 106 and actuator 130, whereupon surface 116 will bear on roller 106, which simultaneously pivots shoulder 138 of latch 72 clear of acutator 130. When this action is completed, carriage 22 becomes latched to inner mast section 32 and thereafter, while the carriage and latch 72 are above actuator 130, the weight of the load carried on the carriage will hold the escapement locked in the condition shown in FIG. 15. At the same time, inner mast section 32 has been unlocked from outer mast section 28 and hence is free to be lifted upwardly. Should excessive pivotal motion of latch 72 tend to occur as a result of transient force reversals or during the latch pivoting transition, the same will be limited by surface 116 abutting stop 120, or surface 114 abutting stop 118 in the other stable condition of the latch.

At the point where carriage 22 reaches the full free lift position thereof shown in FIG. 17 and is latched to section 32, the load-lifting bar 70 will simultaneously strike stop 90 on cylinder 74. This snubs bar 70 against any further upward movement, further lifting of carriage 22 thereafter being performed by inner mast section 32. Also, bracket 60 will concurrently have moved up the full length of its travel relative to intermediate mast section 30 (half the free lift travel of crriage 22) and the upper ends of guide tubes 62, 62' will have struck the stops 66, 66', thereby snubbing further upward movement of bracket 60 relative to intermediate section 30 and causing bracket 60 to exert a lifting load on section 30. Thus, as plunger 76 moves upwardy beyond its position shown in FIG. 17, chains 33, 33' will act through bracket 60 and its abutment with its stops 66, 66' to directly lift the intermediate mast section 30 at a 2:1 ratio relative to plunger travel. As bracket 60 moves up and lifts section 30 with it, the inner upper mast section 32 will be lifted by chains 35, 35' at a 2:1 ratio relative to the movement of bracket 60 and section 30. Hence, inner section 32 will move upwardly at a 4:1 ratio relative to plunger travel, carrying carriage 22 with section 32 at the same rate until the mast is fully extended as shown in FIG. 18. Thus, the movement of carriage 22 from its ground position in FIG. 16 to its fully elevated position in FIG. 18 will occur at constant 4:1 ratio relative to plunger travel to provide smooth ascent and descent of the carriage throughout its vertical travel. During descent of the mast and carriage, the above-described sequence will be reversed but will also occur in a smooth manner at the aforementioned travel ratios.

AUXILIARY FEATURES

The structure of the latch escapement actuator 128 preferably comprises a pair of lugs 160 and 160' (FIGS. 4,11 and 13-15) respectively secured to the associated carriage struts 50, 50' by studs 162, 162', each stud being screwed into a threaded hole on the underside of an associated rearwardly extending plate 164, 164' welded to the associated strut 50, 50'. As shown only in FIG. 15, one or more shims 166, 166' may be inserted between each lug 160, 160' and its plate 164, 164' to adjust the elevation of lugs 160,160L The free end of each lung 160,160' is formed into a 270° cylindrical portion 168having a radius substantially equal to that of the associated latch notch 124,124'.

As best seen in FIG. 8, actuator 130 preferably comprises a rocker plate 170 having a central bore 172 which receives a pivot mounting pin 174 therethrough. Plate 170 is retained against axial motion by a snap ring 176 received in a groove on pin 174, the inner end of pin 174 being welded to the front face of cross brace 122 and to an associated reinforcing gusset 178. A pair of cam follower rollers 180,180' are rotatably secured to the opposite ends of plate 170, these rollers having a radius substantially equal to the associated latch notches 126, 126'. A pair of stop pads 182, 182' are welded to the upper surface of plate 170 and project rearwardly over the upper surface of cross brace 122 with suitable vertical spacing between pads 182, 182' and brace 122 to permit limited pivotal motion of plate 170 about the axis of pin 174. Plate 170 of actuator 130 thus serves as an equalizer arm to insure simultaneous operational engagement of the rollers 180, 180' with their respective latches 72, 72' as the inner mast section 32 is descending through the sequence of FIGS. 15, 14 and 13. The level arm action of actuator 130 also insures equal load distribution between the two latches 72, 72' to provide smooth and simultaneous operation of the latches despite small variances in locational tolerances of the various parts of the escapement latching mechanism.

Preferably, the latch escapement mechanism of mast 20 is provided with a latch orienting detent mechanism as shown in FIGS. 13,14 and 15. This mechanism comprises a pair of detent plungers 184, 184' disposed in associated spring housings 186,186' which are threadably mounted in cross brace 100 with each plunger spring biased to protrude downwardly toward the upper surface 188, 188' in the locked positions of the latches, as shown in FIGS. 13 and 15, but the plungers are not engaged by surfaces 188, 188' until apex 136 of each latch approaches the centerline between its associated roller 106,106' and pin 112,112' as shown in FIG. 14. The spring biased detent thus offers a yieldable resistance to the latch being jarred from one overcenter position to the other. The resistance of the plunger is adjusted so that latches 72,72' will be maintained in the orientation thereof shown in FIG. 13 when mast 20 is being shipped from its point of manufacture to a customer. Hence, when the customer has installed the mast on a lift truck and is ready to first elevate the carriage, latches 72, 72' will be properly synchronized for their normal mode of latching operation as described previously herein. However, the spring resistance of the plungers 184,184' is not sufficient to interfere with the normal operation of the escapement latching mechanism when normal lifting and lowering forces are applied to the mast.

It has been found that there is a tendency for ram 34 to tilt forwardly during operation of the mast, particularly in the collapsed condition of the mast when the carriage is being raised and lowered through its free lift travel. Accordingly, in accordance with another feature of the present invention, mast 20 incorporates anti-tilting ram restraining devices which utilize for the

3,786,902 most part existing lifting and ram structure. As will be best seen in FIG. 8, ram 34, in addition to the parts previously described, has the usual piston rod wiper 190, bushing 192, externally threaded cylinder cap 194, sleeve spacer 196, O-rings 198 and 200 which are re- 5 tained in spaced grooves of piston 152, a wear ring 202, a cylinder packing ring 204 and retaining ring 206 which secures parts 202 and 204 to the lower end of piston 152. The lower end of cylinder 74 is suitably affixed to and supported on the usual saddle bracket 207, 10 the rear flanges of which are bolted to the lower cross brace 209 of lower mast section 28. Also, chain sheave 80' has associated with it a bearing 208 received on an axle pin 210 which is secured to the frustoconical head 212 of plunger 76, together with a thrust washer 214, 15 a retainer 216, mounting screw 218 and sheave lubrication fitting 220. Cap 194 threads into the upper end of cylinder 74 and plunger 76 extends coaxially therethrough and is connected by retaining ring 206 to piston 152. 20

It is to be noted that bar stop 90 is welded to the front edge of the tube flange of cap 194 and chain anchor bracket 82 is welded to the rear edge of this flange. Parts 90 and 82, in addition to their previously described functions, serve as parts of the ram anti-tilting ²⁵structure. When mast 20 is in its fully collapsed condition, a pair of hooks 222, 222' (FIG. 9), which are welded to the front face of intermediate cross brace 224 of the section 30, overlie bracket 82 and have their dependent arm portions respectively received in the 30 spaced notches 226, 226' of bracket 82 (FIG. 8). Thus, hooks 222, 222' grip bracket 82 and restrain ram 34 against forces tending to tilt it forwardly away from mast section 30.

When the intermediate mast section 30 is first lifted to begin telescopic extension of mast 20 as described previously, lifting bar 70 will have seated against stop 90 and will have been releaseably latched thereto by the detent 93 engaging spike 71 as described previously. Hence, as hooks 222 and 222' are lifted out of engagement with bracket 82, the ram will thereafter be restrained against forward tilting by the forces exerted on the upper end of cylinder 74 via bar 70 and its associated lifting chains 35,35'. Although the restraint thus exerted via bar 70 on the ram during extension of the middle and upper sections 30 and 32 of the mast is less positive than that exerted by hooks 222, 222' in the collapsed condition of the mast, nevertheless the restraining force exerted by the chains on bar 70 is greatest when it is most needed (i.e., during initial extension of the mast sections) because the forces tending to tilt the ram are progressively diminished as the mast is extended to its full height. The ram tilting forces are most severe when the mast is in collapsed condition, but under this condition positive restraint is provided by hooks 222, 222' via bracket 82.

ADVANTAGES

In addition to the objects, features and advantages described previously herein, it will now be apparent ⁶from the foregoing description that lift mast 20 of the present invention has the capability of a full free lift three-section mast but requires only one simple twopart ram 34, the cylinder 74 of which remains station- ₆₅ary with the outer mast section 28 and which is automatically restrained against tilting by multi-function structure. The cost of the ram and associated support structure is thus reduced as compared to a ram which travels vertically to actuate the mast and/or compared to three or four part rams. Hydraulic fluid line connections to the ram are also simplified; i.e., the present invention enable a short permanent immovable fluid conduit 142 of conventional construction (FIG. 2) to be connected to the lower end of cylinder 74 to feed the hydrulic fluid to the working chamber of the cylinder from the usual pump and reservoir (not shown) on lift truck 24. The use of a stationary cylinder 74 also permits a single stationary fluid vent line 150 (FIG. 2) to be run from the space in cylinder 74 above the piston 152 back to the fluid reservoir on the truck, rather than venting this space directly to the atmosphere. Thus, problems associated with an atmospheric vent are avoided; i.e., leakage of oil past the piston 152 as the same becomes worn causing oil to leak out onto the exterior of the ram. With vent line 150 connected to the fluid reservoir, this leakage oil will be returned to the system rather than being spilled out of the ram.

In addition to the above advantages, the 4:1 ratio provides ample lifting stroke multiplication and hence the ram can be made shorter than the length of a single mast section. This in turn permits the two sheaves 80, 80' to be mounted close to one another on top of plunger 76 so that chains 33,33' are closely spaced adjacent cylinder 74 of the ram. Hence, there is more open space laterally between chains 33, 33' and the rails of the mast sections to afford better driver visibility through the mast.

Mast 20 requires only two sets of chains 33, 33' and 35, 35' which is no more rigging than used in conventional three-section masts. Moreover, the escapement latch mechanism 72,128,130, although rugged and reliable, is quite simple and does not add significant cost to the mast. The same is true of the lifting bracket 60 and associated guiding structure. The ratio of collapsed to fully extended height of the mast is also maximized by the lifting structure of the present invention due to distance multiplying effect of the particular chain rigging and cooperative lift bracket and lift bar sequence.

SECOND EMBODIMENT

Referring to the schematic illustration of FIG. 19, a second embodiment 300 of an extensible mast is shown in its fully extended condition wherein the mast provides the vertical reach of a four-stage extensible mast. Mast 300 may include substantially all of the components of mast 20 described previously, the reference numerals of such structure of mast 20 being also used in FIG. 19 and the description therof not repeated. The hydraulic ram 340 of mast 300 has an external cylinder 74 and plunger 76 extending upwardly therefrom as in ram 34. However, ram 340 differs from ram 34 in that ram 340 is a conventional three-part ram and hence includes an additional plunger 302 which telescopes within plunger 76 and extends downwardly from the lower end of cylinder 74. One such three-part ram suitable for this purpose is shown in U.S. Pat. No. 2,518,251, issued August 8, 1950 in the name of George F. Quayle. Plunger 302 rotatably carries a pair of spaced chain sheaves 304, 304' at its lower end around which are respectively trained a pair of chains 306, 306', only one sheave and one chain of each pair being shown in FIG. 19. One end of each chain 306, 306' is affixed at 308 to the bracket 310 which mounts

3,786,902 the lower end of cylinder 74 in fixed relation to the lower end of mast section 28. The other end of each chain 306, 306' is secured to a chain anchor bracket 312 which in turn is secured to a fourth dual rail mast section 314. Section 314 is similar in construction to section 28 and has the usual roller guide telescopic engagement therewith so that in the collapsed condition of mast 300 all four mast sections 32, 30, 28 and 314 are nested together with their upper and lower ends respectively flush with one another similar to the collapsed condition of mast 20 shown in FIG. 16. Suitable hydrulic fluid line connections (not shown) are provided between ram 340 and the lift truck on which it is mounted, as will be well understood in the art.

In operation, application of pressure fluid to ram 340 initially causes plunger 76 to extend upwardly from cylinder 74 to provide full free lift travel of carriage 22 on mast section 32 while the mast remains in its telescoped collapsed condition in the same manner as mast 20 described previously. Due to its greater working area and/or lighter load, plunger 76 will continue its upward motion relative to cylinder 74, after carriage 22 is latched to section 32, until it reaches the end of its upward stroke before any extension of the lower plunger 302 takes place. Hence, section 28 remains nested in the lowermost section 314 and sections 30 and 32 will be extended to the height thereof corresponding to the fully extended condition of mast 20 shown in FIG. 18, thereby continuing the elevation of carriage 22 at a 4:1 ratio with respect to the movement of plunger 76 relative to cylinder 74. Once this extended condition has been obtained, further application of pressure fluid to ram 340 will cause plunger 302 to begin to extend from the lower end of cylinder 74 so as to move downwardly relative thereto, or as viewed by a stationary ground observer, causing cylinder 74 to move upwardly relative to plunger 302 while plunger 76 is hydraulically held in its fully extended condition so as to move up with cylinder 74. This action will cause chains 306 to lift section 28 and all the structure supported thereon upwardly at a ratio of 2:1 relative to the travel of plunger 302 with respect to cylinder 74. When plunger 302 reaches its fully extended position as shown in FIG. 19, section 28 will have been elevated a distance somewhat less than the height of the lowermost section 314 and thus carriage 22 likewise will have been raised to a correspondingly higher elevation above that obtained in the fully extended condition of mast 20 shown in FIG. 18. To lower mast 300, the pressure fluid is gradually released in the usual manner, first causing plunger 302 to retract within cylinder 74, followed by retraction of plunger 76. Carriage 22 is thus first lowered at the 2:1 ratio as section 28 returns to its fully telescoped collapsed relationship to section 314 and then carriage 22 is lowered the remainder of the way to ground level at the 4:1 ratio in the same manner as with mast 20.

Mast 300 thus illustrates that the three-section mast 20 can serve as a subassembly for incorporation into a four-section mast to provide increased vertical reach with only a relatively simple three-part ram and one extra set of chains. With this arrangement, the vertical speed of carriage 22 is cut in half when it is being elevated a distance approximately the height of one mast section during the last portion of its upward motion and the first portion of its downward motion, a desirable feature from the standpoint of stability and safety. However, it is to be understood that the ratio of the rel12 ative working areas of plungers 76 and 302 of ram 340 may be varied, if desired, to modify the relative sequencing of plunger 76 and 302 to provide a more uniform speed of ascent and descent of carriage 22, as will be readily understood by those skilled in the art from the foregoing description.

THIRD EMBODIMENT

FIG. 20 is a schematic illustration of third embodiment 400 of an extensible mast also constructed in accordance with the present invention. Mast 400, like mast 300, is a four-stage mast utilizing as a subassembly for its upper three sections the components of mast 20. However, mast 400 bears an even closer resemblance to mast 20 in that it utilizes the same two-part ram 34 as well as the other previously described components of mast 20. Mast 400 also utilizes an outer lowermost fourth section 402 similar to section 314 of mast 300. The only other modifications required to convert mast 20 to a four-stage mast are the addition of a pair of chain sheaves 404, 404' and a set of lift chains 406, 406' (only one of each pair being shown), each chain 406,406' being trained under and around its associated sheave 404, 404'. One end of each chain 406, 406' is secured to a chain anchor bracket 408 affixed to mast section 30 adjacent the lower end thereof and the other end of each chain 406, 406' is secured to a chain anchor bracket 410 affixed to mast section 402 adjacent the upper end thereof.

In operation, mast 400 will raise and lower carriage 22 through the full free lift range of its travel along the innermost mast section 32 prior to any extension of the mast sections in the the same manner ast mast 20, and at a 4:1 ratio relative to the movement of plunger 76 relative to cylinder 74. However, once carriage 22 is latched to section 32 and sections 32 and 30 begin to extend relative to one another and relative to section 28 due to the action described previously in conjunction with mast 20, the movement of section 30 relative to the lowermost section 402 will cause chains 406 to lift section 28 and all of the structure carried thereby at a 2:1 ratio relative to section 402. Accordingly, once mast extension is initiated the speed of ascent of carriage 22 will be at an 8:1 ratio relative to the movement of plunger 76 relative to cylinder 74. In other words, the rate of lift of carriage 22 during mast extension or retraction will be double that occurring during its free lift travel if the rate of ram extension and retraction remains constant. Mast 400 thus is simpler and more economical in construction than mast 300. However, if constant carriage speed is desired, conventional automatic control systems may be added which will monitor the mast extension sequence and control the rate of supply of the hydraulic fluid to the ram so that the rate of ram extension can be correlated with the lifting ratio of the chain reeving such that carriage 22 is elevated throughout its travel from ground position to its full reach at a constant speed, as will be well understood by those skilled in the art.