GB1576975A

GB1576975A - Sealed track belt arrangement

Info

Publication number: GB1576975A
Application number: GB53754/77A
Authority: GB
Original assignee: Caterpillar Tractor Co
Current assignee: Caterpillar Inc
Priority date: 1977-05-05
Filing date: 1977-12-23
Publication date: 1980-10-15
Also published as: IT7822509A0; CA1075740A; IT1094458B; JPS53138140A; FR2389526A1

Description

(54) SEALED TRACK BELT ARRANGEMENT (71) We, CATERPILLAR TRACTOR CO., a corporation organised and existing under the laws of the State of California, United States of America, of 100 N.E.

Adams Street, Peoria, Illinois 61629, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement: In earthmoving operations it is sometimes desirable to increase the traction of rubbertyred 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 fitted over a pneumatic supporting tyre 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 British Patent Specification No. 1,367,524 for a more complete description of the flexible track belts described above.

As pointed out in U.S. Patent Specification No. 3,899,220 a particular problem exists concerning 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.

This problem occurs because each rectangular shoe's width (as distinct 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 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 shoes 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 inwardly therefrom for approximately four to six inches.

The sealing ribs between adjacent track shoes disclosed in U.S. Patent Specification No. 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 shoes's surface from the belt surface.

According to the present invention, a track assembly for fitting circumferentially around a pneumatic tyre carcass comprises an elastomeric belt of substantially uniform thickness having at least one internal, substantially inextensible reinforcing ply, the belt having formed on its outer peripheral surface a plurality of equally circumferentially spaced track shoe sites; a plurality of elongate keeper members, with each of the track shoe sites having one of the keeper members spanning the width of the belt and centrally disposed relatively to the site; a plurality of track shoes each removably attached to the keeper member at a respective shoe site; and a spaced pair of elastomeric transverse ribs located at each of the sites, one on each circumferential opposite side of the keeper member, and arranged generally parallel to the longitudinal axis of the respective keeper member, the arrangement being such that, in use, with the track shoe tightened and compressed against the belt, raised protrusions of the elastomeric material of the belt are formed which seal against the leading and trailing edges of the track shoe.

The elastomeric ribs, which may be integral with the belt, need not be continuous across the central portion of the belt. Preferably, the ribs are 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. Preferably, resiliency of the rib will cause it to maintain contact with the underside or bottom surface of the track shoe at all times.

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; FIG. 2 is a plan view of part of the track belt shown in FIG. 1, also shown without track shoes; FIG. 3 is a cross section of the track belt taken on the line III - III of FIG. 2; FIG. 4 is an enlarged partially brokenaway side view of the belt shown in FIG. 1; 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 alternative embodiment of the invention wherein each track shoe includes spaced elastomeric ribs bonded thereto.

An arcuate portion of the 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.

Patent Specification No. 3,606,921.

As can be seen in FIGS. 1 and 2, the track belt 10 of the track assembly includes an elastomeric belt 11 which encircles the outer periphery of a tyre carcass 12 which has a flat crown portion to receive the inner periphery 13 of the belt. At least one cylindrical reinforcing ply 14 is centrally located within. the elastomeric belt and is normally composed of a plurality of loops of substantially inextensible reinforcing filaments, such as wire fila ments or equivalent synthetic filaments 15, having less than 5% elongation under the working tension to which they are subjected in the belt structure during operation. The elastomer and reinforcing ply are vulcanized 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 is usually integrally bonded in the belt adjacent to 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, it should be appreciated that these ribs need not be continuous in the central portion of the belt where the underlying carcass supports the inner periphery of the belt more fully, allowing very little articulation and movement between the shoes and the belt.

However, each rib, to be effective, preferably extends 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 tyre, the track shoe site accepting a track shoe 19 having a width of 6.50 inches would have a width A, which is approximately five inches 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 each side.

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 that volume is 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, 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, in this example, 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.

Also, it should be appreciated that the formation of the rib 27 occurs only when the belt is supported by a pneumatic carcass, thus preventing the belt from varying from a cylindrical configuration when the ribs 25 are deformed.

During operation, the resilient ribs 27 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 "stiffness" will also lessen the relative movements between the shoe and its associated site.

An alternate embodiment is shown in FIG.

7 wherein elastomer ribs 25' are bonded directly to the flat bottom surface 21' of a track shoe 19'. It should be appreciated that these ribs are constructed to the same shape, size and 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.

WHAT WE CLAIM IS: 1. A track assembly for fitting circumferentially around a pneumatic tyre carcass, the assembly comprising an elastomeric belt of substantially uniform thickness having at least one internal, substantially inextensible reinforcing ply, the belt having formed on its outer peripheral surface a plurality of equally circumferentially spaced track shoe sites; a plurality of elongate keeper members, with each of the track shoe sites having one of the keeper members spanning the width of the belt and centrally disposed relatively to the site; a plurality of track shoes each removably attached to the keeper member at a respective shoe site; and a spaced pair of elastomeric transverse ribs located at each of the sites, one on each circumferential opposite side of the keeper member, and arranged generally parallel to the longitudinal axis of the respective keeper member, the arrangement being such that, in use, with the track shoe tightened and compressed against the belt, raised protrusions of the elastomeric material of the belt are formed which seal against the leading and trailing edges of the track shoe.

2. A track assembly according to claim 1, wherein each track shoe has a flat bottom surface and a width greater than the width of

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Claims

**WARNING** start of CLMS field may overlap end of DESC **.

of 6.50 inches would have a width A, which is approximately five inches 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 each side.

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 that volume is 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, 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, in this example, 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.

Also, it should be appreciated that the formation of the rib 27 occurs only when the belt is supported by a pneumatic carcass, thus preventing the belt from varying from a cylindrical configuration when the ribs 25 are deformed.

During operation, the resilient ribs 27 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 "stiffness" will also lessen the relative movements between the shoe and its associated site.

An alternate embodiment is shown in FIG.

7 wherein elastomer ribs 25' are bonded directly to the flat bottom surface 21' of a track shoe 19'. It should be appreciated that these ribs are constructed to the same shape, size and 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.

WHAT WE CLAIM IS: 1. A track assembly for fitting circumferentially around a pneumatic tyre carcass, the assembly comprising an elastomeric belt of substantially uniform thickness having at least one internal, substantially inextensible reinforcing ply, the belt having formed on its outer peripheral surface a plurality of equally circumferentially spaced track shoe sites; a plurality of elongate keeper members, with each of the track shoe sites having one of the keeper members spanning the width of the belt and centrally disposed relatively to the site; a plurality of track shoes each removably attached to the keeper member at a respective shoe site; and a spaced pair of elastomeric transverse ribs located at each of the sites, one on each circumferential opposite side of the keeper member, and arranged generally parallel to the longitudinal axis of the respective keeper member, the arrangement being such that, in use, with the track shoe tightened and compressed against the belt, raised protrusions of the elastomeric material of the belt are formed which seal against the leading and trailing edges of the track shoe.
2. A track assembly according to claim 1, wherein each track shoe has a flat bottom surface and a width greater than the width of

its associated track shoe site as herein defined.
3. A track assembly according to claim 2, wherein the flat bottom surface of each track shoe is rectangular and terminates in rounded leading and trailing edges which are parallel with the shoe's longitudinal axis.
4. A track assembly according to claim 3, wherein the radii of the rounded leading and trailing edges are between 0.12 and 1.5 inches.
5. A track assembly according to any one of claims 1 to 4, wherein the elastomeric ribs are integral with the elastomeric belt.
6. A track assembly according to any one of claims 1 to 4, wherein the elastomeric ribs are bonded to the track shoes.
7. A track assembly according to any one of the preceding claims, wherein the elongate ribs have a uniform cross-section with a height of between 0.05 and 0.50 inches and width of between 0.10 and 0.75 inches.
8. A track assembly according to any one of the preceding claims, wherein each track shoe has a grouser on its radially outer surface.
9. A track assembly according to any one of the preceding claims, wherein the means for attaching each track shoe to the track belt includes holes in the ends of the track shoe for receiving bots for cooperating with a keeper member at a track shoe site to attach the shoe.
10. A track assembly according to any one of the preceding claims, wherein each of the keeper members has a width less than the width of each track shoe.
11. A track assembly according to claim 1, substantially as described with reference to any one of the examples illustrated in the accompanying drawings.
12. A track assembly according to any one of the preceding claims when mounted on a pneumatic tyre carcass, the carcass being pressurized sufficiently to maintain the belt in a cylindrical configuration except in the footprint of the combination when it is employed on a vehicle to support it.