Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BACKGROUND OF THE INVENTION
According to the present invention, in earthmoving
; operations it is sometimes desirable to increase the traction
of rubber-tired work vehicles and/or to increase their
resistance to damage due to the environment, such as sharp
rocks and the like. To achieve these objectives, flexible
belts with track shoes mounted at equally spaced intervals
about their outer periphery have been employed over a pneu-
matic supporting tire carcass. Normally such belts are
formed by placing one or more cylindrical reinforcing plies
in the central portion of an elastomer cylindrical belt
and attaching track shoes thereto by placing a keeper on
the inside periphery of the belt for each track shoe on
the outer periphery and clamping the belt between the
keeper and the underside of its associated track shoe.
Reference is made to this assignee's U.S. Letters Patent
3,773,394 issued to Grawey on November 20, ~973 for a more
complete description of the flexible track belts described
above.
As pointed out in this assignee's U.S. Letters ;
Patent 3,899,220 issued to Grawey et al on August 12, 1975, -
a particular problem exists relative to the ingress of
dirt and other abrasive materials in the area directly
under the track shoe, where such materials can cause rapid `
deterioration of the elastomer portions of the belt and
even damage the reinforcing plies, in more severe situations.
This problem occurs because each rectangular shoe's
width (as distinguished from its transverse length) is
wider than the width of the underlying keeper member
associated with it. As a result, the leading and trailing
portions of each shoe's undersurface, when the shoe passes
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into, through and out of the footprint, can separate
from the outer circular belt surface, allowing foreign
materials to become trapped therebetween. Large sharp
rocks are particularly detrimental, as they can penetrate
the elastomer surface of the belt to the reinforcing plies,
leading to complete belt failure when the reinforcing ply
separates.
Normally, the "fit" of the track shoes to the track
belt is best in the central or middle portion of the belt
where there is the greatest support from the underlying
carcass. Thus, the articulation and/or movement of track
s~oes relative to one another is greatest at the edges of
the belt where there is less underlying support. For this
reason, the problem is the greatest at the edges and in- ~-
wardly therefrom for approximately four to six inches. `
The sealing ribs between adjacent track shoes
disclosed in U.S. Letters Patent 3,899,220 mentioned
above, combined with the flat track shoe mounting site
vulcanized in the outer cylindrical surface of the belt,
are partially effective in reducing this problem, as are
the mating ribs and grooves formed with the underside
surface of the track shoes and belt surface. However,
these features fail to provide increased stiffness in the
portions of the belt between adjacent keepers where the
flexing of the belt occurs, which leads to the separation
of the shoe's surface from the belt surface.
SUMMARY OF THE INVENTION
According to the present invention, there is
provided an improved track shoe for use with track belts
employed around pneumatic tire carcasses comprising a
rectangular track shoe having a flat bottom surface
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terminating in rounded leading and trailing edges which are
parallel with said shoe's longitudinal axis, and means for
attaching said shoe to a track belt by clamping the belt
against said bottom surface so said edges are normal to the
; 5 mid-circumferential plane of said belt, said flat bottom
surface having bonded thereto spaced elongated elastomer
ribs, with at least one such rib mounted parallel and
adjacent to each of said edges.
The elastomeric ribs, which may be integral with
the belt, need not be continuous across the central portion
of the belt, but they should be of a sufficient height to
maintain contact with the underside surface of the track shoe
attached to the site at the maximum flexing angle which can
occur between adjacent track shoes. Alternatively, the ribs
could be bonded to the underside of the track shoes mounted
on the site so they would be in the same location when the -,
shoes are mounted on the site. In either case the raised
elastomeric ribs will be distorted when the track shoe is
attached to its site and the belt is clamped between it and
the keeper member. As an elastomer does not compress, it is
caused to flow, thereby somewhat enhancing the belt ~;
stiffness directly beneath each rib. Resiliency of the rib
will cause it to maintain contact with the underside or
bottom surface of the track shoe at all times.
DRAWINGS
Some examples of a track assembly according to the
invention are illustrated in the accompanying drawings, in
which:
FIG. 1 is a partially broken away side elevation of
the elastomeric track belt of the track assembly without -
track shoes mounted thereon;
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FIG. 2 is a plan view of pa~t of the track belt
shown in FIG. 1, also shown without track shoes;
FIG. 3 is a cross section of the flexible track
belt along line III - III of FIG. 2;
FIG. 4 is an enlarged broken-away portion of the
flexible belt shown in FIG. l;
FIG. 5 is an exploded view of a broken-away portion
of the track belt shown in FIG. 1 with an associated track
shoe for mounting on the track shoe site;
FIG. 6 is the same view as shown in FIG. 5 with the
belt and shoe assembled with one another; and ;~
FIG. 7 is an alternate embodiment of the invention
wherein each track shoe includes spaced elastomer ribs
bonded thereto.
DESCRIPTION OF A PREFERRED EMBODIMENT -
An arcuate portion of the impro~ed track belt 10
is shown in FIG. 1 mounted on a pneumatic support carcass 12.
A suitable supporting carcass is disclosed and described in
U.S. Letters Patent 3,60~,921 issued to Grawey on
September 21, 1971, and commonly assigned with this appli- -
cation.
As can be seen in FIGS. 1 and 2, the improved track
belt 10 includes an elastomer belt 11 which encircles the
outer periphery carcass 12 which has a flat crown portion
2~ to receive the inner periphery 13 of the belt. At least
one cylindrical reinforcing ply 14 is centrally located
within the elastomer belt and is normally composed of a
plurality of loops of inextensible reinforcing filaments,
such as wire filaments or equivalent synthetic filaments 15,
having less than 5% elongation under the working tension to
which they are subjected in the belt structure during
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operation. The elastomer and reinforcing ply are vulcan-
ized as an integral unit.
In FIGS. 4 and 5, the detail of each track shoe site
S and the associated keeper member 16 can be seen. Each
keeper member 16, one shown in cross section in FIG. 3, is
usually integrally bonded to the belt on the inner periphery
13 of the belt so its trough-like structure receives a
substantial portion of the belt thickness. Holes 17 in the
projecting ends 18 of the keeper member are used to attach
a track shoe 19 to the site with a bolt passing through ~-
mating holes 20 in the extending ends of the track shoe.
Tightening the bolts pulls the bottom surface 21 of the
track shoe into its associated site and clamps the belt
between the keeper member and the track shoe as shown in
FIG. 6. Bolts 22 extend through holes 20 and 17 and into
a threaded retaining block 23 to attach the shoe to its
site S.
More particularly, the details of each site S can
best be appreciated by referring to FIGS. 2, 4 and 5.
In FIG. 4, the site is defined as the circumferential outer
surface portion of the flexible belt between the outer edges
24 of ribs 25 having a keeper member 16 located between
the inner edges 26. As can be seen, these ribs 25 run
transversely across the belt parallel with the longitudinal
axis of their adjacent keeper member and have a uniform
cross section. Further, they do not overlap the keeper
member, which has a width less than the width of the
rectangular track shoe 19. While the ribs 25 are shown
~ as extending completely across the surface of the track belt,
-~ 30 it should be appreciated that these ribs need not be con-
tinuous in the central portion of the belt where the
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underlying carcass supports the inner pexiphery of the belt
more fully, allowing very little articulation and movement
between the shoes and the belt. However, each rib, to be
effective, must extend inwardly at least six inches from
each edge of the belt. Thus, the terminology of spaced-apart
parallel ribs does not require that the ribs 25 be continuous,
and it can be appreciated that they can be formed of
several segments.
In a belt for a 76 inch tire, the track shoe site
accepting a track shoe 19 having a width of 6.50 inches
would be a distance A, which is approximately five inches
wide measured between edges 24. The distance B between the
top inner edges of the ribs 25 would be approximately four
inches and the width C across the top of each rib would be
.375 inches. In this size belt, the height D of the rib
above the arcuate surface of the belt is approximately
0.20 inches, and the shoe 19 would extend beyond the site
by .75 inches on both sides.
The height of the ribs can vary between .05 inches
to .50 inches, while the average width can vary from .10
inches to .75 inches. These parameters define a volume of
an elastomer ribbon on the surface belt which will be
deformed when the shoe is clamped thereon and result in
some elastomer "flow". Looking at FIG. 6, it can be
appreciated that volume should be sufficient for this flow
to cause a slightly raised rib 27 to develop contiguous
to the leading and trailing edges of the track shoe 19.
When rib 27 develops, the volume of elastomer will be
sufficient to increase the "stiffness" of the belt directly
beneath the leading and trailing edges, 28 and 29 respectively,
of the track shoe. In reference to the shape of the rib 25,
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it should be appreciated that the preferred shape is shown
in the drawings. It should also be appreciated that it
could have a more irregular shape, so long as the necessary
volume of elastomer is present in the critical area defined
as being from the edges of the belt and inwardly at least
six inches. The necessary volume can be defined as a
regularly shaped rib having the parameters defined above.
As can be seen, the bottom surface 21 of each track
shoe 19 is substantially flat, and it is desirable to round
the leading and trailing edges of the shoe. A half-inch
radius is often satisfactory, and will reduce wear between
the belt and the shoe in the vicinity of rib 27 when it is
formed. It is preferred that radii on the leading and
trailing edges of the track shoes be from .12 inches to
1.5 inches, since when held to within these limits, the
erosion of the belt immediately adjacent and contiguous
thereto can be sharply reduced, sometimes as much as 50%.
Also, it should be appreciated that the formation of
the rib 27 occurs only when the belt is supported by a
pneumatic carcass that prevents the belt from varying from
a cylindrical configuration when the ribs 25 are deformed.
During operations, the resilient ribs 25 will
maintain contact with the bottom surface of the shoe, sealing
out dirt and the like which would otherwise decrease the
belt's service life. Further, the increased belt "stiff-
ness" will also lessen the relative movements between the
shoe and its associated site.
~ An alternate embodiment is shown in FIG. 7 wherein
7 elastomer ribs 25' are bonded directly to the flat bottom
surface 21' of a track shoe l9'. It should be appreciated
; that these ribs are constructed to the same shape, size and
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configuration as described above for those incorporated in
the track belt 10. Also, the track shoe 19' has its leading
and trailing edges rounded to the preferred radii described
above.
As a result, when such ribs 25' are bonded directly
to each track shoe and spaced in the same manner as those
described for the ribs 25 incorporated in the belt, a similar
elastomer "flow" will occur in a belt without elastomer ribs
incorporated in its individual track shoe sites S when each
track shoe 19' is mounted by clamping the belt between the
bottom surface 21' of the track shoe 19' and the associated
keeper member 16. Thus, a similar sealing rib 27 will form -~
at the leading and trailing edges of the shoe 19' when it
is attached as described above. Obviously the ribs 25'
will maintain a seal between the bottom of the shoe and the
contiguous area of the belt, due to their resiliency.
It may be possible to adopt other "shapes" for the
elastomer ribs 25 and 25' that will develop the necessary
elastomer "flow" to cause the raised protrusions 27 at the
leading and trailing edges of the track shoe. When such
protrusions form, the belt is stiffened directly beneath these
protrusions, allowing less articulation between the bottom
of each shoe and the belt surface on which it is mounted
when the shoe passes through the footprint. Obviously this -
lessens the ingress of foreign material between the shoe and
the belt, leading to improved service life.
.
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