US3786902A

US3786902A - Load-lifting mechanism for a lift truck

Info

Publication number: US3786902A
Application number: US00251253A
Authority: US
Inventors: K Ramsey
Original assignee: KNICKERBOCKER Co
Current assignee: OLOFSSON Corp A CORPORATION OF MICHIGAN; KNICKERBOCKER Co
Priority date: 1972-05-08
Filing date: 1972-05-08
Publication date: 1974-01-22
Anticipated expiration: 1991-01-22
Also published as: FR2183884A1; CA993406A; GB1421351A; FR2183884B3; DE2322409A1; GB1421352A

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 loadlifting 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.

Description

United States Patent [191 Ramsey 1 Jan. 22, 1974 LOAD-LIFTING MECHANISM FOR A LIFT TRUCK [75] Inventor: Keith E. Ramsey, Jackson, Mich.

[73] Assignee: The Knickerbocker Company,

Jackson, Mich.

[22] Filed: May 8, 1972 [21] Appl. No.: 251,253

[52] U.S. Cl. 187/9, 212/128 [51] Int. Cl. B66b 9/20, B66c 19/00 [58] Field of Search 187/9; 212/128, 55; 52/121 [56] References Cited UNITED STATES PATENTS 3,338,335 8/1967 MCNceley 187/9 2,987,140 6/1961 Olson 187/9 3,221,840 12/1965 Weinert 187/9 2,502,465 4/1950 Lehmann 187/9 3,051,265 8/1962 Boyajian et al. 187/9 3,269,561 8/1966 Deligt 212/128 Primary Examiner-Robert S. Ward, Jr. Attorney, Agent, or FirmArthur Raisch et al.

[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.

29 Claims, 20 Drawing Figures PATENTED 3,786,902

SHEET 1 [1F 9 PATENTEDJANZZIQH 3.786.902

' sum 2 BF 9 11 5 l f iT gl'l rl PATENTED JAN 2 2 I974 SHEET [1F 9 PATENTED JAN 22 I974 sum 5 or 9 PATENTED JAN 2 2 I974 SHEET 7 [IF 9 PATENTEB JAN 2 2 I974 sum 9 or 9 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: (I) 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; 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 44 of FIG. 3.

FIG. 5 is a horizontal section taken on the line 55 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. l-l4, 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 usualflexible 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 US. 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-schematically in FIGS. l6, l7 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 operators 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, 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, 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 (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, 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 30 by roll pins ward movement by nuts 64b, 64b screwed onto thethreaded 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 ofa 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 distance 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 between 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 into the strut notches during descent of the carriage onto the bar. The upper end of cylinder 74 has a stop (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 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 extended.

The escapement latching arrangement (best seen in FIGS. 6, l0 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 cross brace 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) 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 1 12 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 cooperate 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

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 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:l 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 sec-' tion 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, 1 1 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, and its plate 164, 164' to adjust the elevation of lugs 160, The free end of each

lung

160, 160 is formed into a 270 cylindr ic al pgr tio n 16 having 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

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 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 retained 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, 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, 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.

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 structure. 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 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 from 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 stationary 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 1 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, 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 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 andlor 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 F 1G. 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 threesection 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 relative 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:l 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.

1 claim:

1. An extensible upright multi-stage, load-lifting mast adapted for mounting on a lift truck, said mast comprising first, second and third telescopic mast sections, a carriage mounted on and movable vertically for free lift travel with respect to said third mast section, a ram having cylinder and plunger elements with one of said elements operably connected to said first mast section,

a lifting bracket mounted on the movable vertically with respect to said second mast section between upper and lower stops connected to said second mast section, escapement means operable in the upward load lifting mode to latch said third mast section to said first mast section to restrain upward movement of said third mast section during free lift travel of said carriage on said third mast section and to latch said carriage at the upper limit of its free lift travel to said third mast section and to release said third mast from its latched connection to said first mast section in response to upward extension of said second and third mast sections said escapement means in the load lowering mode of said mast being operable to relatch said third and first mast sections upon return thereof to their fully telescoped condition and to release said latched connection of said carriage to said first mast section, first flexible element means coupled to the other one of said ram elements and operably connected to said first mast section and to said bracket, a lifting bar movable vertically with respect to said first mast section, second flexible element means coupled to said bracket and operably connected to said third mast section and to said lifting bar, means releasably supporting said carriage on said lifting bar during the free lift range of travel of said carriage and bar stop means releasably connecting said lifting bar to said first mast section in response to upward movement of said carriage to the upper limit of its free lift travel and vice versa.

2. The mast as set forth in claim 1 wherein said one ram element comprises a cylinder and said plunger telescopes within said cylinder.

3. The mast as set forth in claim 2 wherein said plunger constitutes the only movable plunger of said ram and said plunger extends from the upper end of said cylinder, said cylinder being fixed at it lower end to said first mast section.

4. The mast as set forth in claim 3 wherein said first mast section is adapted to be directly supported on a lift truck to serve as the lowermost section of said mast and is adapted to be restrained against vertical movement relative to the lift truck.

5. The mast as set forth in claim 1 wherein said mast sections have cooperative roller means providing rolling engagement between said mast sections.

6. The mast as set forth in claim 1 wherein said escapement means comprises latch means movably mounted on said third section adjacent the upper end thereof, a first actuating means mounted on said carriage and a second actuating means mounted on said first mast section adjacent the upper end thereof, and a latch restraining means mounted on said third mast section adjacent said latch means, said latch restraining means having an over-center relationship with said latch means defining first and second stable overcenter positions of said latch means, said latch means being restrained in said first position by interengagement of said second actuator means, said latch means and said latch restraining means, said latch means being maintained in said second position by interengagement of said first actuator means, said latch means and said latch restraining means.

7. The mast as set forth in claim 6 wherein said latch means comprises a plate having convex surfaces at one end converging to an apex and an oblong slot having its longitudinal axis aligned with saidapex, said plate also having side surfaces juxtaposed to said slot with a notch formed in each of said side surfaces,'a retaining pin extending through said slot to capture said plate for loose pivotal motion and limited bodily movement relative to said pin, said restraining means comprising a roller mounted with its axis parallel to said pin and for rolling engagement with said curved surfaces of said plate, said roller being disposed below said pin and aligned therewith in the direction of carriage travel and mast extension, said first and second actuator means each having rounded portions adapted to engage the associated notches and to have limited journalling motion therein.

8. The mast as set forth in claim 7 wherein said second actuator means comprises an equalizer member pivotally mounted on said first mast section for movement about an axis extending perpendicular to carriage travel and mast extension and perpendicular to the lateral dimension of said mast, said equalizer member carrying first and second latch engaging portions at the opposite ends thereof, said latch means comprising a pair of said plates spaced laterally from one another relative to said third mast section, said first latch engaging portion being adapted to engage the associated notch of one of said plates and said second latch engaging portion being adapted to engage the associated notch of the other of said plates.

9. The mast as set forth in claim 1 wherein said lifting bracket comprises a generally U-shaped framework having first and second upright sleeves, first and second guide rods mounted on said second mast section spaced laterally on either side of the longitudinal centerline thereof, said rods extending slidably through said sleeves of said bracket, said bracket having side plates disposed in spaced relation on the opposite sides of said ram, and pulley means rotatably mounted on said bracket, said second flexible element means being trained over said bracket pulley means and extending downwardly therefrom with one end of said second flexible element means being affixed to the lower end of said third mast section and the other end of said second flexible element means being connected to said lifting bar.

10. The mast as set forth in claim 9 wherein said plunger extends upwardly from said cylinder and carries pulley means at the upper end thereof, said first flexible element means being trained over said plunger pulley means and extending downwardly therefrom with one end connected to said cylinder and the other end to said bracket.

11. The mast as set forth in claim 1 wherein said lifting bar comprises a bar extending laterally of said mast adjacent said ram and said second flexible element means comprises a pair of chains, one connected to each of the opposite ends of said bar, said carriage having a pair of laterally spaced upright struts each having a notch for receiving the associated end of said bar therein, said chains extending through said carriage between and adjacent said upright struts to thereby assist in guiding said bar into releasable carriage lifting engagement in the notches of said carriage.

12. The mast as set forth in claim 1 wherein said lifting bar and said bar stop means have cooperative interengaging releasable detent means adapted to yieldably retain said lifting bar against said bar stop means when said mast sections are extended.

13. The mast as set forth in claim 1 wherein said bar stop means is affixed to said ram and oriented relative thereto such that said lifting bar and said second flexible clement means exert a restraining force on said ram in the extended condition of the mast tending to resist tilting forces on said ram.

14. The mast as set forth in claim 13 wherein said second mast section has restraining means interengageable with said ram in the telescoped condition of said mast to thereby support said ram against tilting forces when said lifting bar is disengaged from said bar stop means and is supporting said carriage.

15. The mast as set forth in claim 14 wherein said restraining means comprises hook means secured to said second mast section, and a chain bracket affixed to said ram adapted to releasably engage with said hook means and being connected to said second flexible element means.

16. The mast as set forth in claim 1 further including a fourth mast section telescopically connected with said first mast section and having a subjacent relationship with said first, second and third mast sections in the extended condition of said mast, said ram having a third element movable relative to said first two mentioned ram elements, flexible element means coupled to said third ram element and operable to extend said first mast section relative to said fourth mast section in response to movement of said third ram element to at least one of said first two ram elements.

17. The mast as set forth in claim 1 further including a fourth mast section telescopically connected with said first mast section and having a subjacent relationship with said first, second and third mast sections in the extended condition of said mast, pulley means mounted on said first mast section and third flexible element means trained on said pulley means and connected at one end to said second mast section and at the other end to said fourth mast section whereby relative movement of said second and fourth mast sections moves said first mast section relative to said fourth mast section.

18. An extensible upright multi-stage, loadlifting mast adapted for mounting on a lift truck, said mast comprising a plurality of telescopic mast sections, a carriage mounted on and movable vertically with respect to one of said mast sections, a ram operably connected to said one mast section, a lifting bracket mounted on and movable vertically with respect to said mast between upper and lower stops connected to said mast, flexible element means coupled to said ram and operably connected to said mast and to said bracket, a lifting bar movable vertically with respect to said mast, said flexible element means being coupled to said bracket and operably connected to said mast and to said lifting bar, means releasably supporting said carriage on said lifting bar during travel of said carriage on said one mast section and bar connector means releasably connecting said lifting bar to said ram in response to upward movement of said carriage to a predetermined point in its travel and vice versa.

19. The mast as set forth in claim 18 wherein said lifting bar and said bar connector means have cooperative interengaging releasable detent means adapted to yieldably retain said lifting bar against said bar connector means when said mast sections are extended.

20. The mast as set forth in claim 18 wherein said bar connector means is connected to said ram and oriented relative thereto such that said lifting bar and said flexible element means exert a restraining force on said ram in the extended condition of the mast tending to resist tilting forces on said ram.

21. The mast as set forth in claim 20 wherein another one of said mast sections has restraining means interengageable with said ram in the telescoped condition of said mast to thereby support said ram against tilting forces when said lifting bar is disengaged from said bar connector means and is supporting said carriage.

22. The mast as set forth in claim 21 wherein said restraining means comprises hook means secured to said other mast section, and a chain bracket affixed to said ram adapted to releasably engage with said hook means and being connected to said flexible element means.

23. An extensible upright multi-stage, load-lifting mast adapted for mounting on a lift truck, said mast comprising a plurality of mast sections, a carriage mounted on and movable vertically for travel with respect to one of said mast sections, a ram operably connected to another of said mast sections, a lifting bracket mounted on and movable vertically with respect to said mast between upper and lower stops connected to said mast, escapernent means operable in the upward load lifting mode to latch said one mast section to said other section of said mast to restrain upward movement of said one mast section during travel of said carriage thereon and to latch said carriage to said one mast section and to release said one mast from its latched connection to said other mast section in response to upward extension of said mast, said escapement means in the load lowering mode of said mast being operable to relatch said one and other mast sections upon return thereof to telescoped condition and to release said latched connection of said carriage to said one mast section, flexible elements means coupled to said ram and operably connected to said mast and to said bracket, a lifting bar movable vertically with respect to said mast, said flexible element means being coupled to said bracket and operably connected to said mast and to said lifting bar, means releasably supporting said carriage on said lifting bar during travel of said carriage and bar stop means releasably connecting said lifting bar to said mast in response to latching said carriage to said one mast section and vice versa.

24. The mast as set forth in claim 23 wherein said ram comprises a cylinder and a plunger telescopable within said cylinder.

25. The mast as set forth in claim 24 wherein said plunger extends from the upper end of said cylinder, said cylinder being fixed at its lower end to said one mast section.

26. The mast as set forth in claim 25 wherein said other mast section is adapted to be directly supported on a lift truck to serve as the lowermost section of said mast and is adapted to be restrained against vertical movement relative to the lift truck.

27. In a lift truck mast having relatively movable load-lifting means and escapement means for releasably interconnecting said load-lifting means, the improvement comprising latch means movably mounted for pivotal and bodily movement on a first one of said mast load-lifting means, a first actuating means mounted on a second one of said load lifting means and a second actuating means mounted on a third one of said load lifting means, and a latch restraining means mounted on said first lifting means adjacent said latch means, said latch restraining means having an overcenter relationship with said latch means defining first and second stable over-center positions of said latch means, said latch means being restrained in said first position by interengagement of said second actuator means, said latch means and said latch restraining means, said latch means being maintained in said second position by interengagement of said first actuator means, said latch means and said latch restraining means.

28. The mast as set forth in claim 27 wherein said latch means comprises a plate having convex surfaces at one end converging to an apex and an oblong slot having its longitudinal axis aligned with said apex, said plate also having side surfaces juxtaposed to said slot with a notch formed in each of said side surfaces, a retaining pin extending through said slot to capture said plate for loose pivotal motion and limited bodily movement relative to said pin, said restraining means comprising a roller mounted with its axis parallel to said pin and for rolling engagement with said curved surfaces of said plate, said roller being disposed below said pin and aligned therewith in the direction of carriage travel and mast extension, said first and second actuator means each having rounded portions adapted to engage the associated notches and to have limited journalling motion therein.

29. The mast as set forth in claim 28 wherein said second actuator means comprises an equalizer member pivotally mounted on said third lifting means for movement about an axis extending perpendicular to carriage travel and mast extension and perpendicular to the lateral dimension of said mast, said equalizer member carrying first and second latch engaging portions at the opposite ends thereof, said latch means comprising a pair of said plates spaced laterally from one another relative to said one lifting means, said first latch engaging portion being adapted to engage the associated notch of one of said plates and said second latch engaging portion being adapted to engage the associated notch of the other of said plates.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3, 786, 902 DATED January 22, 1974 |NVENTOR(S) Keith E. Ramsey It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below;

Column 13, line 17, cancel "first" (first occurrence) and insert third- Signed and Scaled this thirtieth Day of Deamber 1975 [SEAL] Arrest:

RUTH C. MASON Arresting Officer C. IAISIIALL DANN Commissioner 01b!!! and Trademark:

Claims

1. An extensible upright multi-stage, load-lifting mast adapted for mounting on a lift truck, said mast comprising first, second and third telescopic mast sections, a carriage mounted on and movable vertically for free lift travel with respect to said third mast section, a ram having cylinder and plunger elements with one of said elements operably connected to said first mast section, a lifting bracket mounted on the movable vertically with respect to said second mast section between upper and lower stops connected to said second mast section, escapement means operable in the upward load lifting mode to latch said third mast section to said first mast section to restrain upward movement of said third mast section during free lift travel of said carriage on said third mast section and to latch said carriage at the upper limit of its free lift travel to said third mast section and to release said third mast from its latched connection to said first mast section in response to upward extension of said second and third mast sections said escapement means in the load lowering mode of said mast being operable to relatch said third and first mast sections upon return thereof to their fully telescoped condition and to release said latched connection of said carriage to said first mast section, first flexible element means coupled to the other one of said ram elements and operably connected to said first mast section and to said bracket, a lifting bar movable vertically with respect to said first mast section, second flexible element means coupled to said bracket and operably connected to said third mast section and to said lifting bar, means releasably supporting said carriage on said lifting bar during the free lift range of travel of said carriage and bar stop means releasably connecting said lifting bar to said first mast section in response to upward movement of said carriage to the upper limit of its free lift travel and vice versa.

6. The mast as set forth in claim 1 wherein said escapement means comprises latch means movably mounted on said third section adjacent the upper end thereof, a first actuating means mounted on said carriage and a second actuating means mounted on said first mast section adjacent the upper end thereof, and a latch restraining means mounted on said third mast section adjacent said latch means, said latch restraining means having an over-center relationship with said latch means defining first and second stable over-center positions of said latch means, said latch means being restrained in said first position by interengagement of said second actuator means, said latch means and said latch restraining means, said latch means being maintained in said second position by interengagement of said first actuator means, said latch means and said latch restraining means.

7. The mast as set forth in claim 6 wherein said latch means comprises a plate having convex surfaces at one end converging to an apex and an oblong slot having its longitudinal axis aligned with said apex, said plate also having side surfaces juxtaposeD to said slot with a notch formed in each of said side surfaces, a retaining pin extending through said slot to capture said plate for loose pivotal motion and limited bodily movement relative to said pin, said restraining means comprising a roller mounted with its axis parallel to said pin and for rolling engagement with said curved surfaces of said plate, said roller being disposed below said pin and aligned therewith in the direction of carriage travel and mast extension, said first and second actuator means each having rounded portions adapted to engage the associated notches and to have limited journalling motion therein.

13. The mast as set forth in claim 1 wherein said bar stop means is affixed to said ram and oriented relative thereto such that said lifting bar and said second flexible element means exert a restraining force on said ram in the extended condition of the mast tending to resist tilting forces on said ram.

23. An extensible upright multi-stage, load-lifting mast adapted for mounting on a lift truck, said mast comprising a plurality of mast sections, a carriage mounted on and movable vertically for travel with respect to one of said mast sections, a ram operably connected to another of said mast sections, a lifting bracket mounted on and movable vertically with respect to said mast between upper and lower stops connected to said mast, escaPement means operable in the upward load lifting mode to latch said one mast section to said other section of said mast to restrain upward movement of said one mast section during travel of said carriage thereon and to latch said carriage to said one mast section and to release said one mast from its latched connection to said other mast section in response to upward extension of said mast, said escapement means in the load lowering mode of said mast being operable to relatch said one and other mast sections upon return thereof to telescoped condition and to release said latched connection of said carriage to said one mast section, flexible elements means coupled to said ram and operably connected to said mast and to said bracket, a lifting bar movable vertically with respect to said mast, said flexible element means being coupled to said bracket and operably connected to said mast and to said lifting bar, means releasably supporting said carriage on said lifting bar during travel of said carriage and bar stop means releasably connecting said lifting bar to said mast in response to latching said carriage to said one mast section and vice versa.

27. In a lift truck mast having relatively movable load-lifting means and escapement means for releasably interconnecting said load-lifting means, the improvement comprising latch means movably mounted for pivotal and bodily movement on a first one of said mast load-lifting means, a first actuating means mounted on a second one of said load lifting means and a second actuating means mounted on a third one of said load lifting means, and a latch restraining means mounted on said first lifting means adjacent said latch means, said latch restraining means having an over-center relationship with said latch means defining first and second stable over-center positions of said latch means, said latch means being restrained in said first position by interengagement of said second actuator means, said latch means and said latch restraining means, said latch means being maintained in said second position by interengagement of said first actuator means, said latch means and said latch restraining means.