U.S. patent number 3,768,595 [Application Number 05/055,064] was granted by the patent office on 1973-10-30 for lift truck mast.
This patent grant is currently assigned to White Farm Equipment Co.. Invention is credited to Wilfred H. Kelley, Jr..
United States Patent |
3,768,595 |
Kelley, Jr. |
October 30, 1973 |
**Please see images for:
( Certificate of Correction ) ** |
LIFT TRUCK MAST
Abstract
A lift truck mast having extensible uprights received one within
the other. Each upright includes a pair of rail members each of
which has a web and flanges such that the members are I-shaped in
cross section. The rail members are nested together with the web
portion and end flanges of the inner overlapping the web portions
and end flanges to the outer. The web portions of one rail member
carry rollers which ride on the rear end flanges of the adjacent
nested rail member. Each web portion, when viewed in cross section,
provides a straight section of uniform thickness and a tapered
portion gradually increasing in thickness toward the rear end
flange. The rollers are spaced from, but mounted parallel to, the
straight web portions so as to rotatably engage the rear end
flanges and tangentially contact the tapered web portion. Forward
mast bending loads are taken radially by the rollers and side
thrust loads parallel to their axes of rotation for improved
anti-friction properties and longer wear.
Inventors: |
Kelley, Jr.; Wilfred H. (Maple
Plain, MN) |
Assignee: |
White Farm Equipment Co.
(Hopkins, MN)
|
Family
ID: |
21995345 |
Appl.
No.: |
05/055,064 |
Filed: |
July 15, 1970 |
Current U.S.
Class: |
187/229; 187/226;
187/230; 187/410; 414/634 |
Current CPC
Class: |
B66F
9/08 (20130101) |
Current International
Class: |
B66F
9/08 (20060101); B66b 009/20 () |
Field of
Search: |
;187/9 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Blunk; Evon C.
Assistant Examiner: Lane; H. S.
Claims
What is claimed is:
1. An extensible mast having collapsed and extended positions,
comprising:
a first upright,
a second upright slidably received on the first and extensible
longitudinally therefrom,
a load carriage,
load carriage support means reciprocally supporting the load
carriage on the second upright,
a power lift system operably connected to reciprocate the load
carriage and second upright simultaneously at first and second
differential rates of travel,
latch operator means on the load carriage having a raised position
corresponding to a raised position of the load carriage, and
latch means operable for attaching the load carriage support means
to the second upright for travel therewith at the first
differential rate and actuated by said latch operator means at said
raised position to disconnect substantially simultaneously the load
carriage support means from the second upright and attach it to the
load carriage for travel therewith at the second differential rate,
whereby the mast reaches an extended position by employing said
simultaneous differential rates of travel.
2. An extensible mast according to claim 1 wherein:
the load carriage support means includes a third upright,
said third upright being slidably received on the second and
extensible longitudinally therefrom,
other latch means operable for attaching the second upright to the
first during reciprocation of the load carriage between its lowered
and an intermediate raised position, and
other latch operator means on the lift cylinder having a raised
position corresponding to the intermediate raised position of the
load carriage operable to disconnect substantially simultaneously
the second upright from the first and connect it to the lift
cylinder.
3. An extensible mast according to claim 2 wherein said other latch
means comprises
a pair of spaced hook elements facing in opposite directions and
pivoted on the second upright on a common fore and aft extending
axis,
first dog means on the first upright engageable with one of the
hook elements for preventing extension of the mast,
second dog means movable with said lift cylinder engageable with
said other hook element at said intermediate raised position for
attaching the second upright thereto, and
said first and second dog means cooperating during extension or
retraction of the mast to jointly pivot said hook elements, the
first hook element pivoted out of engagement with the first dog
means and the second into engagement with the second dog means
during extension and in the reverse on retraction of the mast.
4. An extensible mast according to claim 3 wherein said latch means
comprises
a pair of spaced hook elements facing in opposite directions
pivoted on said third upright on a common transversely extending
axis,
third dog means on the second upright engageable with one of the
hook elements for preventing extension of the third upright,
fourth dog means on the load carriage engageable with the other
hook element for attaching the third upright to the load carriage
at its highest point of travel in the third upright, and
said third and fourth dog means cooperating during extension or
retraction of the mast to jointly pivot said hook elements, the
first hook element pivoted out of engagement with the third dog
means and the second into engagement with the fourth dog means
during extension and in the reverse upon retraction of the
mast.
5. An extensible mast having collapsed and extended positions,
comprising:
a first upright,
a second upright slidably received in the first and extensible
longitudinally therefrom,
a third upright slidably received in the second and extensible
longitudinally therefrom,
a load carriage,
means reciprocally supporting the load carriage on one of the
uprights, the one upright on the second and the second on the other
upright,
a power lift system operably connected to reciprocate the load
carriage, the second upright, and the other upright including,
extensible lift means, said power lift system being operable to
provide a greater rate of travel for said load carriage than the
rate of extension of said lift means,
an extensible lift means component having a first intermediate
raised position corresponding to a free lift position of the load
carriage adjacent the top of the collapsed mast and a second
intermediate raised position corresponding to the uppermost
position of the load carriage in the one upright,
first latch means mounted on the second upright operable for
attaching it to the other upright during reciprocation of the load
carriage between its lowered and free lift positions,
second latch means mounted on the one upright operable for
attaching it to the second upright during reciprocation of the load
carriage between its lowered and uppermost positions,
said first latch means being actuated at the first intermediate
position of said lift means component to connect substantially
simultaneously the second upright to said lift means component and
disconnect it from the other upright during extension of the mast,
and
said second latch means being actuated by the load carriage at its
uppr most position to connect substantially simultaneously the one
upright to the load carriage and disconnect it from the second
upright whereby during extension of the mast the second upright and
one upright move jointly relative to the other upright between said
first and second intermediate positions of said lift means
component and thereafter the one upright moves differentially at
said greater rate of travel relative to said second upright and the
above sequence being reversed in retraction of the mast.
6. An extensible mast having collapsed and extended positions,
comprising:
a. a first upright;
b. a second upright slidably received in the first and extensible
longitudinally therefrom;
c. a third upright slidably received in the second and extensible
longitudinally therefrom;
d. a load carriage
e. means reciprocally supporting load carriage on the third
upright, the third on the second and the latter on the first;
f. a power lift system operably connected to reciprocate the load
carriage and the second and third uprights including a stationary
lift cylinder, said power lift system being operable to provide a
greater rate of travel for said load carriage than the rate of
extension of said lift cylinder
g. an extensible cylinder component having a first intermediate
raised position corresponding to a free lift position of the load
carriage adjacent the top of the collapsed mast and a second
intermediate raised position corresponding to the uppermost
position of the load carriage in said third upright,
h. first, second and third transverse structural members on said
first, second and third uprights nested one above the other in the
collapsed position of the mast,
i. a first pair of spaced hook elements facing in opposite
directions on opposite sides of and pivotally mounted on said
second structural member on a common fore and aft extending
shaft,
j. each said first hook elements comprising an elongated downwardly
extending hook portion and an offset upper detent portion and at
least one being splined on the end of the shaft,
k. first dog means mounted on said first structural member and
aligned with the detent portion of one of said first hook elements
and being engageable therewith to pivot the hook portion thereof
into locking engagement with the first dog means between the
lowered and free lift positions of the load carriage,
l. second dog means mounted on said cylinder component and aligned
with the detent portion on said other first hook element and being
engageable therewith to pivot the hook portion thereof out of
engagement with said first dog means and substantially
simultaneously pivot said other hook portion into locking
engagement with said second dog means at the free lift position of
the load carriage enabling said second and third uprights to more
jointly relative to the first upright,
m. a second pair of hook elements facing in opposite directions
pivoted on the third transverse structural member on a common
transverse extending axis parallel to said third structural
member,
n. each said second hook elements comprising an elongated,
downwardly extending hook portion and an upper off-set detent
portion,
o. third dog means mounted on said second upright aligned and being
engageable with the detent portion of one of said second hook
elements to pivot the hook portion thereof into locking engagement
with said third dog means between the lowered and uppermost
position of the load carriage, and
p. fourth dog means mounted on the load carriage and aligned with
the detent portion of said other second hook element and being
engageable therewith to pivot the hook portion thereof into locking
engagement with the fourth dog means substantially simultaneously
disengaging said one hook portion at the uppermost position of the
load carriage enabling said second and third uprights to move
differentially relative to each other when lowering the mast from
the extended to the collapsed position.
7. An extensible lift truck mast having collapsed and extended
positions comprising
a first upright,
a second upright slidably received in the first and extensible
longitudinally therefrom,
a third upright slidably received in the second and extensible
longitudinally therefrom,
a load carriage,
means reciprocally supporting the load carriage on the third
upright, the third on the second and the latter on the first,
a power lift system operably connected to reciprocate the load
carriage and the second and third uprights including a stationary
lift cylinder,
an extensible cylinder component having a first intermediate raised
position corresponding to a free lift position of the load carriage
adjacent the top of the collapsed mast and a second intermediate
raised position corresponding to the uppermost position of the load
carriage in the third upright,
first latch means mounted on the second upright operable for
attaching it to the first upright during reciprocation of the load
carriage between its lowered and free lift positions,
second latch means mounted on the third upright operable for
attaching it to the second upright during reciprocation of the load
carriage between its lowered and uppermost positions,
said first latch means being actuated at the first intermediate
position of the cylinder component to simultaneously connect the
second upright to the cylinder component and disconnect it from the
first upright during extension of the mast,
said second latch means being actuated by the load carriage at its
uppermost position to simultaneously connect the third upright to
the load carriage and disconnect it from the second upright during
extension of the mast and the sequence being reversed when
retracting the mast,
each upright comprising parallel, laterally spaced rail members,
which when nested with the adjacent rail members of the other
upright, overlap outer to intermediate and intermediate to inner to
define parallel, longitudinally extending trackways,
each rail member having spaced end flanges separated by a web
portion and offset forwardly toward the load carriage such that the
end flanges of one laterally overlap with the end flanges of the
adjacent rail member and the web portions overlap in a fore and aft
direction between the end flanges,
a pair of rollers mounted on the web portions of the outer rail
members facing inwardly at the upper end of the first upright,
second and third pairs of rollers mounted on the web portions of
the intermediate rail members facing respectively outwardly at one
end and inwardly at the opposite end of the second upright, and
a fourth pair of rollers mounted on the web portions of the inner
rail members facing outwardly at the lower end of the third
upright,
said first and second pairs of rollers situated in common, parallel
trackways and said third and fourth pairs of rollers situated in
common, parallel trackways inwardly of said other trackways,
and
the rear end flanges of each rail member providing transversely
extending trackway portions engageable with the rollers of the
adjacent nested upright and said web portions diverging from the
plane of the adjacent roller and tangentially contacting the
rollers at the peripheral edge thereof whereby any side thrust
loads are taken generally parallel to the axis of the rollers and
forward bending loads of the mast are taken radially by the
rollers.
8. An extensible lift truck mast according to claim 7 wherein each
rail member has a generally I-shaped cross section having spaced
end flanges separated by a central web portion,
said web portion including a straight section of uniform thickness
extending rearwardly from the forward end flange, said pairs of
rollers being mounted on said straight sections and
a tapered section gradually increasing in thickness toward the rear
end flange and tangentially contacting the rollers of the nested
upright adjacent the peripheral outer circumferential edge at an
angle of between 1.degree. and 20.degree..
9. An extensible lift truck mast according to claim 8 wherein the
tangential angle of contact is between 2.degree. and 6.degree..
10. An extensible lift truck mast according to claim 9 wherein the
tangential angle of contact is approximately 3 1/2.degree..
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention pertains generally to the art of elevator mechanisms.
More specifically, the invention relates to a sectional lift truck
mast of the type having nested uprights. Certain aspects of the
invention are directed to a so-called "triplex" mast having three
sections. One section is stationary, a second is extensible from
the first, and a third from the second so that the mast can reach a
greatly-extended height as compared to its collapsed height.
2. Description of the Prior Art
Industrial fork lift trucks normally have a vertically extensible
cargo mast mounted on the forward end of the truck. It is generally
desirable that the collapsed height of the mast be fairly low to
ensure vertical clearance through passageways and access into
boxcars or the like. But on the other hand, the maximum fork height
should be as great as possible to permit stacking cargo to a
considerable height such as in an open yard or warehouse. Thus, the
triple sectional or triplex mast is often desirable since it has
great height, fully extended, yet a low profile in the collapsed
position.
The mast will have a load carriage for lifting the cargo. The load
carriage reciprocates on the inner extensible mast section. The
distance the load carriage can be raised from its fully lowered
position without any extension of the mast occurring, the so-called
free lift height, is another important consideration. This allows a
cargo to be lifted to the uppermost position consistent with
overhead clearance without extending the mast itself, for example,
inside of a boxcar where elevation of the mast to increase the
cargo height would be prohibited.
The typical mast has a power cylinder which cooperates with a chain
lift arrangement for raising the load carriage and sequentially
extending the mast sections. One type of commercially available
cylinder which can be used with a triplex mast has vertically
extensible cylinder rods selectively movable in opposite directions
out of the cylinder. In the collapsed position of the mast and the
fully lowered position of the load carriage, the cylinder rods are
withdrawn and the cylinder is lowered. In raising the load carriage
to its free lift height, a first cylinder rod strokes out to the
extent permitted by the clearance between the top of cylinder and
the mast. Successively the other cylinder rods are extended in
raising the mast. In the process the cylinder is elevated. When the
last cylinder rod has been fully extended, the mast reaches its
maximum overall height and the cylinder has been elevated several
feet, tending to obstruct the operator's vision through the
mast.
Aside from creating an obstruction, another disadvantage is that
the cylinder is not solidly supported on the mast frame. With the
mast in a collapsed position, the lower cylinder rod projects out
slightly preventing the cylinder from resting solidly on the mast
frame. When the mast is elevated, the cylinder rod extends out
raising the cylinder as well as the entire load of the mast.
Obviously there is a degree of instability in supporting the mast
on a small extended cylinder rod to say nothing of supporting a
load of several thousand pounds in an elevated position.
In masts where the power cylinder remains fixed and does not
elevate, usually a cylinder is required which is larger than the
described elevating type. Since this large cylinder is mounted
directly in front of the operator, his view to the front tends to
be obstructed by it and other structure such as the hydraulic lines
and the load chains. Thus, whether the power cylinder is fixed or
movable vertically as with prior art constructions, operators have,
at times, been forced to lean out of the side of the truck to see
around an obstructing cylinder.
Many mast sections have used generally C-shaped channels for
carrying and for engaging rollers. Forward bending loads of the
mast are taken by the rollers traveling on the end flange portions
of the channels and other rollers, to absorb side thrust loads, are
provided. These thrust loads can be considerable when an unbalanced
load is on the fork of the load carriage.
The space consumed by most prior thrust arrangements has limited
the extent to which mast sections can be nested and, therefore,
further contributed to the problems of limited visibility. An
arrangement has been proposed to reduce cost and provide nesting
through the use of I-beams and cocked forward load absorbing
rollers. That is, the axes of the rollers are inclined at a slight
non-perpendicular angle with respect to a path of mast section
elevational travel. The upper roller is cocked in one direction and
lower roller in the opposite direction. Since the rollers are
cocked, portions of the forward bending loads are applied to the
forward load absorbing rollers at all times as axial rather than
radial loads. In addition, the rollers are required to take axial
loads resulting from imbalanced side thrust loads. Roller bearings
which are designed to withstand axial loads as well as radial loads
are more expensive and have shorter lives than those which have
only radial loads applied.
Moreover, in the described prior mast arrangement, the axial
loading component from the forward bending loads is applied in one
direction while the axial component resulting from thrust loads is
taken in the opposite direction. Thus there are axial loadings in
both directions where cocked rollers are used.
Normally, a system of latches is employed to control the relative
movement of mast sections when the mast is extended or collapsed.
For example, at some point during the elevation of the load
carriage, one latch is tripped to release the first extensible mast
section from the outer or stationary section. The extensible
section in turn carries a latch which releases the inner section,
the latter continuing to elevate until it reaches its full
extension.
A variety of latching mechanisms have been proposed in the prior
art, but for one reason or another none has been entirely
satisfactory. Some have sacrificed free lift height. Others have
employed complex latching systems which, aside from the cost,
require an inordinate amount of adjustment and maintenance.
Most prior latching devices have contributed to poor bearing
conditions for in a typical prior triplex mast, the inner mast
section will be fully extended before the latches release the
intermediate mast section permitting it to extend. Thus, the inner
mast section is fully extended upwardly before the intermediate
section is released to commence its upward travel. This means that
the bearings between the inner mast section and the intermediate
mast section are overworked much of the time since many lifts do
not require extension of the intermediate section. In addition
these bearings are under their worst loading conditions when the
inner section is extended before the intermediate section commences
to move. This is because the bearings are moved closer together
which is the worst loading condition. The bearing loads are in the
best condition with the bearings spaced widely apart. In other
words, the loading conditions are a function of the amount of
vertical overlap between mast sections. As a result, the bearings
interposed between the inner and the intermediate mast sections are
excessively loaded and experience excessive wear since there is
relatively little vertical overlap in many of the frequently
encountered lift heights reached by the extended position of the
inner section alone.
SUMMARY OF THE INVENTION
The mast of this invention has a plurality of sections or uprights
nested one within the other and extensible relative to each other.
Each upright includes a pair of rails which, with the rails of the
nested adjacent upright, define parallel, longitudinally extending
trackways. Rollers mounted on each rail of at least one upright are
adapted to roll in the trackways during raising and lowering of the
mast. Each rail is formed, in part, by a transverse portion on
which the rollers ride. A second portion extends from the
transverse portion at an angle diverging from the rollers. The
rollers are in line engagement with the transverse portions and are
spaced from the second portion but for small tangential contact
such that any side thrust loads are accepted essentially parallel
to the roller axes and forward bending loads are taken only
radially. As a consequence, axial loads are applied to the rollers
in one direction only and normally only under imbalanced load
conditions. Accordingly, wear and friction are minimized on both
the rails and rollers.
In the preferred form of triplex mast, the rails have a generally
I-shaped cross section with a central web section and spaced end
flanges. The web section and end flanges of one rail overlap, in a
fore and aft direction, the web section and end flanges of the
other. The rear half of the web section of each rail is tapered
forwardly toward the load at an angle of between 2.degree. and
6.degree. and preferably about 3 1/2.degree., but may range to a
maximum of between 1.degree. and 20.degree.. The front half of the
web section, forwardly of the tapered portion, is of constant
thickness providing a straight surface parallel to the longitudinal
axis of the lift truck.
Rollers at one end of one upright run longitudinally on the rear
end flanges of the rails of the nested upright. Each roller is
laterally spaced from the opposite straight web portion and has a
peripherally curved outer edge which tangentially contacts the
tapered web portion at one point near to the rearward end
flange.
A power cylinder rests on a bed plate of the outer upright and is
stationary except for slight pivotal movement permitted to
accommodate any possible misalignment. The cylinder has vertically
extensible cylinder components which, in cooperation with a chain
wrap, successively raise a load carriage and thereafter
concurrently extend the intermediate and inner uprights. The
sequence is provided for by a series of latches which ensure that
there is maximum overlap between mast sections during extension and
retraction of the mast.
A first latch is pivotally mounted on the intermediate upright on a
fore and aft extending axis. In the mast collapsed position, the
first latch locks the intermediate upright to the outer. The first
latch is unlocked by the extensible cylinder component after it has
stroked out to an intermediate raised position corresponding to the
position of load carriage at the free lift height. The intermediate
upright, and thus the inner which remains locked to it by means of
a second latch, can now be raised by the cylinder component.
A second latch is pivotally mounted on a transversely extending
axis on the inner upright and locks it to the intermediate until
the cylinder component reaches a position corresponding to the
highest point of travel of the load carriage in the inner upright.
The second latch is then actuated unlocking the inner upright. The
latter now becomes attached to the load carriage and strats moving
out of the intermediate.
Each latch has dual, oppositely movable elements which
simultaneously unlock one part and lock it to another while either
raising or lowering the mast. Specifically, each latch comprises a
pair of hook elements pivoted on a common shaft and facing in
opposite directions. When either latch is pivoted in one direction
in raising the mast, one hook element causes the opposite hook
element to unlock and the other to lock and vice versa when
collapsing the mast.
The chain wrap is such that the load carriage travels at twice the
rate of extension of the cylinder components. The arrangement of
the latches provides that the inner upright remains locked and
travels with the intermediate upright for only a short distance.
Thereafter it is unlocked from the intermediate and locked to the
load carriage. The intermediate and inner uprights now commence to
move relative to each other, the inner rising out of the
intermediate at twice the rate of extension of the intermediate
since it is locked to the load carriage. The uprights extend
simultaneously maintaining a maximum overlapped relationship,
inner-to-intermediate-to-outer, which progressively decreases as
the mast extends to its full height. Thus loads are distributed on
the rollers at near optimum conditions for all mast positions.
Another of the advantages of this invention is to provide an
extensible lift truck mast in which the spacing of parts, both in
the collapsed and fully raised positions, is such as to provide a
maximum viewing area through the mast by the operator eliminating
blind spots in the critical areas. This is accomplished, in part,
owing to the closer nesting of the rails providing a wider open
area of visibility through the mast. But more importantly, the top
of the cylinder remains below the line of sight of the operator
eliminating the cylinder blind spot problem of some prior art
masts.
Another important advantage of the invention is that the uprights
are mounted on anti-friction rollers which, owing to the design of
the rails, take any side thrust loads parallel to their rotational
axes and forward bending loads are taken only radially thereby
minimizing wear on the roller assemblies and rails.
A further advantage is the combination of latch mechanisms which
allows the maximum free lift height to be obtained before any
extension of the mast occurs.
It is also a feature of the invention that the load carriage which
travels in the inner upright be mounted on a plurality of sets of
rollers in an arrangement that allows the carriage to be supported
with the bearings in the best loading condition while it is
traveling but yet permits the carriage to be elevated to a maximum
extended height. This is accomplished by extending the load
carriage above the inner upright thereby gaining added height while
statically supporting the carriage on at least two sets of rollers
which remain in the rail trackways.
Another feature of importance is the arrangement of latching
mechanisms where the extensible uprights are simultaneously
extended even for lifts that do not require the fully raised height
of the mast thereby distributing the load on the rollers to
minimize friction and wear.
A still further advantage is realized in the design of the I-shaped
rails which affords maximum strength to weight ratio at lower
tooling costs.
These and other advantages will become apparent by referring to the
following description and drawings wherein:
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a lift truck and mast of the type
incorporating the features of the invention where the mast is in a
collapsed position and the load carriage is raised to the free lift
height;
FIG. 1A is a front elevational view of the truck and mast of FIG. 1
showing the load carriage in the lowered position;
FIG. 2 is a schematic view showing the mast uprights
disassembled;
FIG. 3 is a side elevational view and FIG. 4 a rear perspective
view of the mast shown in its fully-raised or extended
position;
FIG. 5A is a cross sectional view showing the nested relationship
of the rails and rollers;
FIG. 5B is a broken out enlarged sectional view showing the
roller-to-rail engagement;
FIG. 5C is a schematic diagram showing the balanced distribution of
forward bending loads on the rollers;
FIG. 6 is a schematic perspective view showing the chain wrap
arrangement with the power cylinder fully extended;
FIG. 6A is a fragmentary perspective view showing the latch
mechanism employed between the outer upright and cylinder sheave
block for controlling the intermediate upright;
FIG. 6B is a fragmentary view showing the latch mechanism employed
between the intermediate upright and load carriage for controlling
the inner upright; and
FIGS. 7A-7H are schematic views depicting the sequence of latch
operation and mast extension.
DESCRIPTION OF THE PREFERRED EMBODIMENT
As shown in the drawings, the present invention will be described
in connection with a triple sectional mast assembly 10 for an
industrial lift truck 12. The invention contemplates, however,
improvements in mast elevator assemblies generally and should not
be interpreted as being limited to the description herein,
reference being had instead to the appended claims for a
comprehension of the scope of the invention.
In FIG. 1, the mast 10 is shown in its collapsed position and the
load carriage 14 fully raised to its free lift height, i.e., the
maximum elevation achieved by the carriage before any extension of
the mast 10 occurs. A fork 15 extends forwardly from the carriage
14 for carrying loads. With the load carriage 14 fully lowered
(FIG. 1A) the fork 15 is slightly off the ground. The mast is
pivotally mounted at its lower end to the truck frame and by means
of a pair of hydraulic cylinders 16 operated from the truck, may be
tilted a limited extent in a fore and aft direction.
The mast 10 comprises three nested uprights 20, 22, 24. The outer
upright 20 is stationary. The intermediate and inner uprights 22,
24 are vertically extensible to a maximum height as depicted in
FIGS. 3 and 4. The mast is raised and lowered by means of a chain
wrap arrangement, generally indicated at 25 in FIG. 4 and depicted
schematically in FIG. 6, which is driven by a hydraulic power
cylinder C controlled from the truck. The power cylinder C is
permitted limited pivotal movement to accommodate any vertical
misalignment and rests on a bed plate at the bottom of the outer
upright 20. The cylinder includes a first extensible section B
within which telescopes a second extensible section D carrying at
the top a sheave block 28 which is guided on the sides in parallel,
longitudinally extending guideways G (FIG. 4) secured on the rear
of the inner upright 24.
As will be described more in detail hereinafter, a latching
mechanism (FIG. 6A) is actuated as the cylinder strokes out and the
load carriage is raised to its free lift height (FIG. 1). The latch
unlocks the intermediate from the outer upright. The intermediate
upright now becomes attached to the sheave block 28 and commences
to rise out of the outer upright. Almost simultaneously, a second
latching mechanism (FIG. 6B) is actuated as the load carriage
reaches its full height in the inner upright 24. At this point the
inner upright 24 becomes attached to the load carriage and
commences to rise out of the intermediate upright 22. Both the
intermediate and inner uprights continue to move relative to the
outer upright until the full extension of the mast is reached as
shown in FIGS. 3-4.
MAST CONSTRUCTION
Referring to FIG. 2, the outer, intermediate and inner uprights 20,
22, 24 and the load carriage 14 are shown in a diagrammatic
disassembled fashion. As described hereinafter, like parts of
different sub-assemblies will be identified with the same numerals
with a letter character added to identify a separate
sub-assembly.
The uprights 20, 22, 24 each comprise a pair of parallel rails 26a,
26b, 26c. The rails are joined at the rear by a plurality of cross
beams 27a, 27b, 27c. Viewed in cross section, each rail is
generally I-shaped. There is a central web section 30a, 30b, 30c
and spaced end flanges 31a, 31b, 31c and 32a, 32b, 32c. The rails
26a of outer upright 20 are spaced wider apart than the rails 26b
of the intermediate upright 22 which in turn are laterally spaced
wider than the rails 26a of the inner upright 24. When assembled
the uprights roll end-for-end within each other as denoted by the
dotted assembly lines in FIG. 2. The web sections 30a, 30b, 30c
overlap in a fore and aft direction, outer to intermediate and
intermediate to inner as shown in the partial cross sectional view
in FIG. 5A. The rear end flanges 31a, 31b, 31c likewise overlap
laterally as do the front end flanges 32a, 32b, 32c.
A pair of rollers 34 face inwardly adjacent the upper end of the
outer upright 20. The intermediate upright 22 carries two sets of
opposed rollers 36, 38, one set 36 facing outwardly at the lower
end and the other set 38 facing inwardly at the upper end. The
inner upright 24 carries one set of opposed rollers 40 adjacent the
lower end facing outwardly.
The forward end flanges 32a of each rail 26a and the rear end
flanges 31b of each rail 26b have longitudinal cut-outs 42a, 42b.
The cut-outs 42a face inwardly on the upper end of the outer
upright 20 and the cut-outs 42b face outwardly on the lower end of
the intermediate upright 22. Likewise, the forward end flange 32b
of each rail of the intermediate upright and the rear end flange
31c of each rail of the inner upright 24 are cut out respectively
at 44a, 44b. The cut-outs 44a face inwardly at the upper end of the
intermediate upright 22 and the cut-outs 44b face outwardly at the
lower end of the inner upright 24.
The sets of rollers 34, 36, 38, 40 on each upright are mounted on
stub shafts adjacent the upper and lower ends of the uprights
leaving a clearance in the cut-outs 42a, 42b, 44a, 44b sufficient
to receive the rollers of the nested upright. The cut-outs 42a of
the outer upright 20 receives the rollers 36 at the lower end of
the intermediate upright 22 as indicated by the dotted assembly
lines in FIG. 2. Likewise, the cut-outs 44a at the upper end of the
intermediate upright 22 receive the rollers 40 at the lower end of
the inner upright.
When nested together, as shown in FIG. 5A, the inner rails 26c roll
inside the intermediate rails 26b and the intermediate rails in
turn roll inside the outer rails 26a which are stationary. The rear
end flanges 31c overlap and lie inside of the rear end flanges 31b
which in turn overlap and lie inside of the rear end flanges 31a.
The front end flanges 32c overlap and lie outside the front end
flanges 32b which in turn overlap and lie outside the front end
flanges 32a. Each rail when nested with the companion rail forms
parallel longitudinally extending trackways 41, 42 in which the
roller pairs 34, 36, 38, 40 ride in raising and lowering the mast
as will be described in more detail hereinafter.
The load carriage 14 has upper and lower apron members 50 (FIG. 2)
held by vertically parallel members 51. The members 51 carry three
opposed sets of rollers 52, 53, 54. The members 51 are laterally
spaced to cause the rollers to track within rails 26c of the inner
upright 24. A pair of lower side thrust rollers 56 mounted in the
vertical members 51 roll against the inside surfaces of web
sections 30c and take any side thrusts resulting from imbalanced
loads in cooperation with an upper pair of side thrust rollers 58
mounted on the upper apron 50 and which track along the outer edges
of the front end flanges 32c of the inner upright 24. It will be
apparent that when assembled the carriage 14 reciprocates in the
inner upright 24. During travel of the carriage, forward bending
loads on the fork 15 are taken by the upper set of rollers 52
riding against the front end flanges 32c of the rails 26c and by
the lower set of rollers 54 rolling on the rear end flanges 31c. It
will be noted that the bearing loading is advantageously
distributed between the most widely spaced pairs of rollers 52, 54.
Where the carriage is fully raised (FIGS. 3, 4), the upper rollers
52 project above the top of rails 26c. Static loads are now taken
by the roller pairs 53, 54 which remain in the rails 26c. This
arrangement allows for a greater overall fork height than would be
otherwise possible as well as providing for longer bearing life
through better load distribution during carriage travel.
The forward bending loads thus transmitted to the inner upright 24
tend to force the rails 26c forwardly at the top and rearwardly at
the bottom such that the uuper rollers 38 on the intermediate
upright 22 and the lower rollers 40 on the inner upright 24 are
respectively forced into rolling engagement with the rear end
flanges 31c, 31b of the nested rails 26b, 26c. Likewise, the
forward bending loads transmitted to the intermediate upright 22
force the rear end flanges 31b of the intermediate rails forwardly
against the opposed rollers 34 of the outer upright and the lower
rollers 36 of the intermediate rails ride against the rear end
flanges 31a of the outer rails. This interaction of forces between
the rails and rollers is depicted in FIG. 5C and is a factor in the
design which greatly minimizes friction and wear on the rails and
rollers as will be more fully explained.
Referring to FIG. 5A, which is a partial cross sectional view of
the nested uprights, each rail web section 30a, 30b, 30c will be
seen to have a tapered portion 61a, 61b, 61c and a straight portion
62a, 62b, 62c. The stub shafts which carry the rollers 34, 38
project laterally from the straight portions 62a, 62b on
perpendicular axes. The lower rollers 36, 40 project in the
opposite direction from the tapered portions 61b, 61c (FIG. 2) on
axes perpendicular to the central plane of the web sections. While
only the one carriage roller 54 is shown in cross section, each
roller on both the carriage and uprights includes an inner race 64
mounted on the stub shaft and an outer race 65 rotatably carried by
the inner race 64 on balls 66. The upper and lower rail rollers 34,
36, riding in the outer longitudinally extending trackways 41 lie
in a common plane parallel to the plane of upper and lower rollers
38 and 40 in the intermediate trackways 42. The same applies to the
load carriage rollers 52, 56, 54 rolling in the inner rails 26c.
Each of the respective roller planes is parallel to the
longitudinal center plane of the lift truck.
Unlike some prior art arrangements where the rollers are cocked so
as to run more or less in the corners of the rails requiring them
at all times to take axial loadings in one direction thereby
increasing the friction and wear, the present invention
contemplates a completely different solution to the problem of
friction and wear which has plagued such mast structures
heretofore. Referring to FIG. 5B, an enlarged broken out view of
the roller 34 and rail 26b is shown, but each roller 36, 38, 40
will be similarly in rolling engagement with its respective rail.
The load carriage rollers 52, 53, 54 are spaced from the web
sections of rails 26c by the thrust rollers 56, 58. Each roller 34,
36, 38, 40 is spaced from the opposite rail straight portion 62a,
62b, 62c owing to the fact that the tapered web portion 61a, 61b,
61c has a critical angle diverging from the roller. The rollers 34,
36, 38, 40 tangentially contact the tapered web portions at only a
single point 74 on the roller edge 75 (FIG. 5B). It has been found
that the angle of contact X should be from about 2.degree. to
6.degree. and preferably 3 1/2.degree., but may range for a maximum
of from 1.degree. to 20.degree.. For example, if the angle X gets
much beyond 20.degree., then the nested width of the rails is
inordinately increased. This also creates the condition where the
application of axial loads becomes appreciably a factor. On the
other hand, if the angle X is diminished much below 1.degree., the
possibility of contact by the roller faces on the straight web
portions 62a, 62b, 62c increases. Rubbing contact should be reduced
to the smallest possible area to minimize wear on the rails and
rollers. Ideally, the inclination of the tapered portions 61a, 61b,
61c should be such as to produce a diverging angle X preferably of
in the range indicated, 2.degree. to 6.degree. and most
satisfactory about 3 1/2.degree.. In this way, any axial thrust
loads, if not entirely eliminated, are at least minimized when the
rollers are traveling up and down the rails with a balanced loading
on the fork.
If an imbalanced load is lifted, only thrust in one direction is
taken, not in both directions as with prior art cocked rollers, and
this thrust condition is only temporary since any such loads are
due to abnormal loading conditions on the fork which disappear when
the load is spotted. The radius of edge 75 of the roller will
inscribe an arc tangential with the web tapered portion 61a, 61b,
61c and rail end flange 31a, 31b, 31c at 74, 75 providing clearance
in the corner. The rollers have line engagement with the rear end
flanges 31a, 31b, 31c from the point of tangency 76 to the inner
edge 78 of the roller. This means that forward bending loads are
taken radially and uniformly along a line extending between 76 and
78 greatly increasing roller life and providing for smoother mast
operation.
FIG. 5C depicts the interaction of the rollers and rails as
described earlier. The forward bending loads are depicted in FIG.
5C as vectors acting on the rails as indicated by the directional
arrows. The upper carriage rollers 52 act forwardly against front
flange 32c of the inner upright 26c. However, all of the other
roller pairs i.e., the lower carriage rollers 54 and each of the
rail rollers 34, 36, 38, 40 act rearwardly against the rear end
flanges 31a, 31b, 31c of the rails 26a, 26b, 26c. The result is a
balance of forces on the mast which has the effect of providing
smooth, stick-free operation while raising and lowering the
mast.
POWER CYLINDER AND CHAIN LIFT ARRANGEMENT
Referring to FIG. 6, the hydraulic power cylinder C which is of
conventional design, has a cylinder outer housing which is solidly
but pivotally mounted on a bed plate 79 which has a recess R (FIG.
2) adapted to receive the base of the cylinder outer housing. The
cylinder has a first extensible cylinder component B in which
telescopes a second cylinder component D. The components B and D
may be successively extended by the operator. The sheave block 28
at the upper end of the cylinder component D carries at the
opposite ends thereof sheaves 80, 81. The inner upright 24 also
carries adjacent its lower end a sheave block in which are
rotatably mounted sheaves 82, 83. Guideways G (FIG. 4) on the rear
end flanges of the upright 24 guide the cylinder-driven sheave
block 28. Also mounted on the inner upright adjacent the upper end
are a pair of sheaves 84, 85 (FIG. 4) in parallel alignment with
the sheaves 80, 81, 82 83. A pair of chains 86, 87 are each
anchored at the lower end to the bed plate 79 and extend upwardly
over the sheaves 80, 81 thence down and around the sheaves 82, 83
and again upwardly over the sheaves 84, 85 being anchored at the
opposite end to the load carriage 14 at 88, 89. It will be
appreciated that in FIG. 6, as well as in FIGS. 3 and 4, the
cylinder and chain wrap are as they would be with the mast fully
extended. That is to say, with the mast fully extended, the
cylinder components B, D have each stroked out to the maximum
extent and the sheaves 80, 81, 82, 83 are at the closest point of
travel to each other and the load carriage 41 is at its uppermost
position in the inner upright 24. The mechanical movement of the
chain wrap is such that the rate of travel of the load carriage is
twice the rate of extension of cylinder components B, D. This
allows a shorter cylinder to be used so that the sheave block 28
occupies a position below the line of vision of the operator in the
lowered position (FIG. 1A).
LATCH MECHANISM
The invention provides that the extensible mast uprights are locked
and unlocked in a novel sequence utilizing to the maximum extent
possible, the 2-to-1 ratio of the chain wrap to provide better load
distribution. The latching sequence is such as to ensure that there
is always sufficient overlap of the intermediate with the outer
upright and inner with the intermediate upright. This also gives
maximum strength and rigidity to the mast throughout the upward
movement. The present invention provides a novel latch arrangement
achieving all of these advantages without sacrificing a high mast
strength to weight ratio.
1. First Latch Mechanism
Referring again to FIG. 2, it will be ssen that the intermediate
upright 22 has mounted in the upper cross beam 27b a latch 90. The
latch 90 comprises a pair of oppositely-facing hook elements 91, 92
pivotally mounted on a common fore and aft extending shaft 93 in
the longitudinal center plane of the lift truck. As best shown in
FIG. 6A, an arm 94 on the hook element 91 projects laterally from
the shaft 93 and an arm 95 on the hook element 92 projects
laterally in the opposite direction. The hook elements 91, 92 have
identical profiles. The hook element 91 pivots on the rear side of
the cross beam 27b while the hook element 92 pivots on the front
side within a cut-out 96. The hook element 91 is preferably splined
onto shaft 93 and held in place by a pair of lock rings 97, 98.
Hook element 92 is welded on the shaft at the opposite end The
splined mounting means of securing the hook element 91 has been
found to produce a stronger assembly able to better withstand the
forces acting on the latch.
As seen in FIG. 2, the cross beam 27a of the outer upright 20 has a
vertically extending slot 101. Within the slot 101 and projecting
below the cross beam 27a is a first dog 102. A second dog 103 is
mounted on the rear side of the sheave block 28 which is shown
schematically in FIG. 2 traveling within the inner upright 24.
As shown in FIG. 6A, the first and second dogs 102, 103 are
laterally offset so as to be in vertical alignment with the arms
94, 95 Each dog 102, 103 receives a coil spring which yieldably
supports a button 106, 107 engageable with the detent 94, 95. Each
dog is beveled on the lower end so as to make engagement with the
hook element 91, 92. It will be noted that clockwise rotation of
the latch 90 simultaneously locks hook element 91 and unlocks hook
element 92 and vice versa. The button 106 extends against the arm
94 to yieldably hold the hook element 91 extending through the slot
101 in locked engagement with the beveled end of the dog 102.
Similarly, the button 107 yieldably holds the hook element 92
engaged with the dog 103 when the latch is rotated to the
counterclockwise position. When dog 103 moves upwardly with the
sheave block 28 it engages detent 95 rotating the latch 90,
unlocking hook element 91 from dog 102 and locking hook element 92
to dog 103. This will be discussed later in the description of the
operation of the mast as a whole.
2. Second Latch Mechanism
Referring again to FIG. 2, a second latch mechanism 110 is
pivotally mounted on a transversely extending axis adjacent the
upper cross beam 27c of the inner upright 24. Latch 110 pivots in a
fore and aft direction in a plane laterally offset from the
centerline of the mast. As best shown in FIG. 6B, oppositely facing
hook elements 111, 112 are integral with oppositely facing arms
113, 114. The hook element 111 and arm 113 project rearwardly in
alignment with a third dog 116 mounted on the upper cross beam 27b
of the intermediate upright 22. The hook element and arm 112, 114
project forwardly in alignment with a fourth dog 118 carried on
back edge of the right vertical member 51 of the load carriage
14.
Referring to FIG. 6B, it will be seen that the hook element 111
cooperates with the third dog 116 upon rearward movement. The hook
element 112 and arm 114 cooperate with the fourth dog 118 upon
forward pivotal movement. As with the other dogs, the dogs 116, 118
each receive coil springs which yieldably support buttons 122, 123.
The buttons 122, 123 are engageable with the arms 113, 114
respectively and cooperatively pivot the hook elements 111, 112
alternately into locked or unlocked engagement with the dogs 116,
118. The operation is similar to that of latch 90 in that
oppositely facing hook elements simultaneously unlock one part of
the mast while locking it to another part.
MAST OPERATION
FIGS. 7A-7H are diagrammatic sequence views showing the mast
operation. Referring to FIG. 7A, assume that the mast is in the
collapsed position with the upper cross beams 27a, 27b, 27 c shown
nested, one above the other as they would appear if viewing FIG. 1A
from the rear and representing here the uprights 20, 22, 24. The
fork 15 is fully lowered. The operator now causes the first
cylinder component B to be extended. As it strokes out, the sheave
block 28 advances the dog 103 toward the latch 90. The latch 90 at
this moment is rotated to the locked position with hook element 91
and arm 94 in locking engagement with the dog 102 such that the
intermediate upright is locked to the outer. Also at this moment
the second latch 110 is in the position shown in FIG. 7D. That is,
the hook element 111 and detent 113 are in locking engagement with
the dog 116. Thus the inner upright is locked to the intermediate
and the intermediate to the outer.
As the cylinder strokes out only the load carriage is free to move.
As the sheave block 28 moves vertically to a position corresponding
to the free lift height of the load carriage (FIG. 1) it advances
the dog 103 into engagement with the arm 95 pivoting the hook
element 92 into locking engagement with the dog 103. Hook element
simultaneously simultaneously disengages from dog 102. This is the
condition depicted in FIGS. 7B, 7C. At this point, any further
upward movement of the sheave block 28 commences to elevate the
extensible uprights 22, 24. It is important to note that at the
position shown in FIGS. 7B, 7C, the load carriage 14 is already at
its free lift height, i.e., the maximum height of the fork without
any extension of the mast occurring. It may continue to move
upwardly in the inner upright 24 only a few more inches as depicted
in FIG. 7D before the latch 110 is tripped releasing the inner from
the intermediate upright.
At the position of the uprights shown in FIGS. 7E and 7F, the load
carriage 14 will have reached its highest point of travel in the
inner upright and any further elevation of the fork 15 comes about
as a result of the simultaneous extension of the intermediate and
inner uprights rather than movement of the load carriage. As will
be seen in FIGS. 7E, 7F the intermediate and inner uprights are no
longer locked to the outer upright 20 by the latch 90. Instead,
they are locked onto the sheave block 28 and have elevated slightly
above the outer upright 20. The load carriage has now reached the
point in the inner upright 24 where the dog 118 will trip the latch
110 as shown in FIG. 7G. The dog 118 on the carriage engages the
arm 114 pivoting the latch 110 forwardly (counterclockwise as
viewed in FIG. 7G). This disengages the inner from the intermediate
upright and engages the hook element 112 with the dog 118 locking
the inner upright onto the carriage. The inner upright being now
locked to the carriage commences to be pulled upwardly out of the
intermediate upright by the carriage. As will be seen in FIG. 7G,
the upper set of rollers 52 of the carriage have now extended
beyond the top of the rails effectively increasing the lift of the
fork.
Further elevation of the sheave block 28 by the cylinder continues
to raise the intermediate upright 22 at the rate of travel of the
cylinder. Simultaneously the inner upright 24, which rises out of
the intermediate upright as depicted in FIG. 7H at twice the rate
of travel of the intermediate upright, will reach its fully
extended position (FIGS. 3, 4) at the same time as does the
intermediate.
In lowering the mast the sequence of latching just described will
be reversed so that at all times the uprights 20, 22, 24 are
positively locked either to the outer upright 20, the
cylinder-driven sheave block 28 or the load carriage 14.
Various prior art latching arrangements have been employed in a
number of combinations. In one arrangement the inner upright is
first locked to the stationary cylinder housing to guard against
upward movement of the upright with the carriage in the event the
latter should stick or bind. Control of the inner upright is then
transferred by means of another latch to the carriage which
commences to extend the inner upright out of the intermediate. If
the mast is to be fully extended, stop blocks on the lower end of
the inner upright engage stop block at the upper end of the
intermediate which are effective for raising the latter from within
the outer upright as the load carriage continues up. The result is
that the rollers on the inner upright are over worked since the
majority of loads will be spotted at less than full mast
height.
With the invention, from the position shown in FIG. 7G, should the
mast continue extending until reaching the overall raised height as
shown in FIGS. 3 and 4, there will be a uniform decrease in overlap
between the uprights. That is, there is alwyas a relatively equal
overlap between the inner and intermediate and between the
intermediate and outer uprights owing to the chain wrap and
latching sequence. The inner upright 24 moves relative to the
intermediate 22 which in turn moves relative to the outer upright
20 such that at the initially extended position depicted in FIG.
7H, the extent of overlap is in excess of 90 percent as between the
intermediate and outer uprights and in excess of 95 percent, as
between the inner and intermediate uprights. Thus throughout the
elevation or retraction of the mast the loading on the bearings is
maintained in the most favorable conditions owing to the fact that
the extensible uprights are simultaneously being elevated rather
than one followed by the other. This greatly reduces wear and
friction on any given set of rollers since all sets are cooperating
when any load is lifted above free lift height.
Still in other prior art latching arrangements a plurality of latch
elements are arranged in such fashion as to lock the inner to the
intermediate upright but no provision is made to lock the
intermediate to the outer. Theoretically the forces applied on
opposite sides of the load chains should balance and the load
carriage should rise with no tendency to cock or bind in the inner
upright. In practice, however, this is not always the case. In
masts where reliance is placed on the fact that the weight of the
inner upright will prevent the intermediate from moving up
prematurely, a considerable weight is required to keep the
intermediate upright down. Even so, where extreme side thrust loads
occur, it is possible to raise both the inner and intermediate
uprights prematurely. This, of course, cannot occur with the
present invention since during the free lift period the inner
upright is positively locked to the intermediate and the latter in
turn is positively locked to the stationary outer upright.
In the present invention the intermediate upright is supported
during extension directly by the cylinder which in turn rests on
the bed plate of the mast. Thus the intermediate upright always has
solid support which increases the mast stability.
To further increase the wear properties of the rails, the surfaces
providing rolling engagement for the rollers may be hardened, e.g.,
by hardening the zone of the rear end flanges 31a, 31b, 31c in
rolling contact with rollers 34, 36, 38, 40, 51, 53, 54. Or these
surfaces may be provided with a wear strip of harder material than
the rails themselves.
Modifications and changes may be made to the invention as will be
apparent to those skilled in the art to which it pertains which
modifications and changes are to be regarded as reasonable
equivalents thereof and are intended to be covered by the appended
claims except insofar as limited by the prior art.
* * * * *