AU2003100265B4 - Continuous roller path track shoe with overlap - Google Patents

Description

CONTINUOUS ROLLER PATH TRACK SHOE WITH OVERLAP This invention relates to an improved crawler track for a tracked vehicle, and a track shoe for use in the track. In particular, the invention is directed to a dual roller path crawler track which provides "continuous" roller support.

BACKGROUND ART Some items of large mining machinery, such as hydraulic excavators and shovels, are fitted with crawler tracks for locomotion. The individual links of the crawler tracks are known as "shoes". These track shoes, also known as "crawler shoes", are linked together by pivot pins or link pins to form an endless articulated track. Each track is mounted on support rollers at a respective side of the machine, with drive sprockets being provided at either end of the rollers. The rollers roll along the articulated track shoes when the sprockets are driven.

The rollers may have dual, spaced, flat rims, so that each roller travels upon the track shoes along two parallel paths. Such rollers can be referred to as dual rollers, and the track shoes referred to as dual roller path track shoes.

The weight of the machinery is borne by the particular track shoe(s) upon which the rollers bear. As the rollers move from one track shoe to the next, the load is transferred between shoes. In view of the heavy weight being carried, any point loads or concentrated loads must be avoided, as such loads may crack or distort a track shoe, or otherwise cause excessive wear.

There are various known track shoe designs. A pair of known track shoes for a dual roller crawler assembly is shown in Fig. 1. As can be seen in that drawing, the dual roller paths (shown cross-hatched) cross over from one track shoe to the next. The track shoes are designed such that there is a longitudinal split in each roller path. The aim of the longitudinal split is to transfer approximately half of the load initially from one track shoe to the next, followed shortly thereafter by the other half of the load. The load transfers in the two paths occur simultaneously. In theory, the load is split evenly between two shoes on either side of the longitudinal split.

However, it has been found in practice that the longitudinal split in each roller path causes accelerated wear and metal flow in the track shoes. As the machinery may be operating on sloping or undulating ground, or over rocks, and since the wear characteristics of adjacent track shoes are not identical, the high contact pressure applied by a roller on a roller path is not distributed evenly across the longitudinal split. The effect of concentrating the weight on a track shoe on one side only of the longitudinal split, and particularly on the edge portion of the track shoe near the longitudinal split, is to cause premature metal flow or "toe nailing" of the track shoes along the roller path. This in turn causes the track shoes to bind with mating shoes, resulting in cracking and failure of the track shoe.

There are known dual roller path crawler tracks in which the transition between adjacent track shoes in one roller path is offset in the direction of travel from the transition between the same adjacent track shoes in the other roller path. Thus, during a transition in one roller path, the roller is supported across the whole width of the other roller path, and vice versa. In one known crawler track, the dual roller is also supported momentarily on both roller paths for a short distance between the two staggered transitions, known as the "overlap". However, it has been found that in such known track shoes, any overlap is of insignificant or insubstantial length, particularly when compared with the length of the "footprint" of the roller.

Typically, a pair of adjacent track shoes are linked in an articulated manner by a single transverse pin inserted through aligned or registered pin holes in overlapping portions of adjacent track shoes. Due to the staggered roller path transitions, differential forces are applied to the pins along their length, causing bending of the pins. This may lead to failure of the pins, or difficulty in withdrawing the pins for track maintenance.

It is an aim of this invention to provide an improved crawler track and track shoe which overcome or ameliorate the abovedescribed disadvantages, or which at least provide the consumer with a useful choice.

SUMMARY OF THE INVENTION In one broad form, the invention provides an articulated crawler track comprising a plurality of like track shoes linked together in a first (longitudinal) direction to form an endless track, each track shoe having at least one leading lug extending longitudinally on one side of the shoe, at least one trailing rug extending longitudinally on the opposite side of the shoe and spaced from the leading lug in a second (transverse) direction orthogonal to the first direction, at least two longitudinal roller path surfaces on the track shoe each aligned with a respective one of the leading and trailing lugs, wherein the leading lugs of the linked track shoes are longitudinally aligned, and the trailing lugs of the linked track shoes are longitudinally aligned, so that the roller path surfaces thereby form two parallel roller paths for a roller, and wherein the transition between a pair of adjacent track shoes in one roller path is longitudinally offset from the transition between the same pair of adjacent track shoes in the other roller path whereby, in use, the roller is supported across a complete roller path on at least one track shoe, characterised in that the roller path surface aligned with the leading lug of one shoe overlaps in the longitudinal direction with the roller path surface aligned with the trailing lug of an adjacent shoe by at least 10% of the length of a said roller path surface so that the roller is effectively supported on both roller paths between the offset transitions across the adjacent track shoes, and in that each pair of adjacent track shoes are linked together by at least two pins which are aligned and spaced in the transverse direction.

Preferably, the roller path surface aligned with the leading lug of one shoe overlaps with the roller path surface aligned with the trailing lug of an adjacent (preceding) shoe (hereafter referred to as the "roller path overlap") by about 15% of the roller path surface.

Typically, a dual rim roller is used, and there are two roller paths on each track shoe. As the transitions between track shoes in the two paths are staggered, when one rim of the dual roller is making the transition from one track shoe to the next, the other rim of the dual roller will be fully supported on its roller path on one or the other of the track shoes.

The crawler track of this invention has the advantage that, at any particular time, the roller will be supported across the full width of a roller path on at least one track shoe, i.e. the roller will be supported continuously on at least one full roller path.

The "continuous" roller path track shoe of this invention provides smoother roller transition from one track shoe to the next. Moreover, due to the roller path overlap, the roller will be supported on both roller paths for a substantial portion of travel between the staggered transitions across a pair of adjacent track shoes. This results in an even smoother transfer of weight between adjacent track shoes, reduces wear and metal flow commonly associated with known track shoe designs, and allows faster propelling of the machine over ground.

Another advantage of the crawler track of this invention is that adjacent track shoes are linked together by at least two pins which are aligned and spaced in the transverse direction. Preferably, two pins are used. By using spaced multiple shorter pins, the high bending stresses experienced by single link pins are avoided, resulting in less damage to the link pins.

In order that the invention may be more fully understood and put into practice, a preferred embodiment thereof will now be described with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a plan view of a pair of known track shoes.

Fig. 2 is a perspective view from above of a track shoe according to one embodiment of the invention.

Fig. 3 is a perspective view of part of a crawler track formed by a linked series of track shoes of the type shown in Fig. 2.

Fig. 4 is a plan view of the part of the crawler track of Fig. 3.

As shown in Fig. 2, a track shoe 10 comprises a body having a leading lug 11 extending in one direction (the "longitudinal" direction) on one side of the body, and a trailing lug 12 extending longitudinally on the other side of the body. The leading lug 11 and the trailing lug 12 are parallel and spaced apart in a direction (the "transverse" direction) which is orthogonal to the longitudinal direction.

The track shoe 10 also has a leading connection lug 13 extending longitudinally on the leading side of the body, and a trailing connection lug 14 extending longitudinally on the other side of the body. The trailing connection lug 14 is transversely adjacent the leading lug 11, but spaced behind it. The leading connection lug 13 is transversely adjacent the trailing lug 12, but ahead of it.

A second leading connection lug 15 is spaced transversely from the leading lug 11, and a second trailing connection lug 16 is spaced transversely from the trailing lug 12. Pin holes are provided in the leading lugs 11, 13, 15, and are aligned along a transverse axis. Pin holes are also provided in the trailing lugs 12, 14, 16, and are aligned along a second transverse axis.

The track shoe 10 is typically made of cast steel.

A crawler track can be constructed by linking like shoes 10 by pivot pins to form an endless track. A portion of a crawler track 20 formed from a linked series of nested track shoes 10 is illustrated in Figs. 3 and 4. As can be seen in Fig. 3, the crawler track 20 is formed by placing the track shoes side by side in a longitudinal direction. When the track shoes 10 are nested together, the trailing connection lug 14 of one shoe locates between the leading lug 11' and the second leading connection lug 15' of the following shoe Similarly, the leading connection lug 13 of shoe 10 locates between the trailing lug 12 and the second trailing connection lug 16 of the preceding shoe 10. A pin 17 is inserted between aligned pin holes in the second leading connection lug 15, the first trailing connection lug 14 and the leading lug 11, as illustrated in exploded view in Fig. 3. Similarly, a link pin 18 is inserted into aligned pin holes in the second trairing connection lug 16, the first leading connection lug 13 and the trailing lug 12. Bolt and nut assemblies 19 can be used to fix the pins 17, 18 in place on the track shoe.

The link pins 17, 18 serve as pivot pins, enabling the linked track shoes to pivot relative to each other about the pins.

Each pair of adjacent track shoes are therefore connected together by two link pins 17, 18 which are axially aligned, but spaced transversely.

The track shoe 10 is also provided with a pair of roller path surfaces 21, 22, each aligned with a respective one of the leading and trailing lugs 11, 12. The roller path surfaces 21, 22 are formed by flat or slightly curved upper surfaces of the body of the track shoe 10. When the track shoes 10 are linked together to form an articulated crawler track as shown in Figs. 3 and 4, the roller path surfaces aligned with the leading lugs 11 are aligned longitudinally to form a first roller path A. Similarly, the roller path surfaces aligned with the trailing lugs 12 are aligned longitudinally to form a second roller path B.

In use, a dual roller (not shown) has a pair of spaced wheel rims which travel along respective roller paths A, B. (Typically, a machine may have a plurality of such dual rollers which carry the weight of the machine and travel along the roller paths A, As a roller makes a transition between track shoes in the crawler track, the roller transfers its load from one track shoe to the next.

The steps in the load transfer during a transition from one track shoe to the next will now be described with particular reference to Fig. 4.

As shown in Fig. 4, at an initial position I, the dual rim roller will be supported on both roller paths A, B, and the roller load will be borne entirely by the leftmost track shoe 10. At point II, the rim of the dual roller on roller path A will make a transition from the roller path surface 21 on track shoe 10 to the following roller path surface on the next track shoe 10', and will not be supported on path A during that transition. However, during that transition, the roller will still be supported on the full width of the roller path surface 22 on track shoe At point III, the dual rim roller will again be supported on two roller paths, but on different track shoes. Namely, one rim of the roller will be supported on the roller path surface 21' of middle track shoe 10', while the other rim will be supported on the roller path 22 of leftmost track shoe At the point IV, the other rim of the dual rim roller will commence to make its transition in roller path B from the roller path surface on track shoe to the following roller path surface on adjacent track shoe 10'. During this transition, the roller will be supported across the full width of the roller path surface 21 of track shoe At the point V, the dual rim roller will again be supported on both roller paths A, B, namely on roller path surfaces 21 and 22 of middle track shoe 10. This load transfer cycle is repeated for each transition between adjacent track shoes.

It is to be noted that between points III and IV, the dual rim roller will be supported on both roller paths A, B, but on different track shoes 10, as there is an overlap between the roller path surface 21 on the leading lug of track shoe 10 and the roller path surface 22 on the trailing lug of the preceding track shoe 10. This roller path overlap should be at least 10%, and preferably around 15%, of the length of the roller path surface of a roller path on the track shoe. In a typical track shoe, this overlap may be 50mmto 75mm. The roller path overlap ensures that the load is borne on both roller paths, but on different shoes, during the staggered or offset transitions between a pair of shoes.

The track shoe of this invention, and crawler tracks made from such track shoes, have operating advantages over prior art track shoes, including: The load is borne across the full width of a roller path surface on at least one track shoe at all times, thereby providing an effective "continuous path" for the roller; Since the load is borne on the full width of a roller path, the problems associated with the split roller path track shoe of Fig. 1 are avoided.

Between the staggered transitions from one track shoe to the next, the roller is supported on both roller path surfaces, but on different track shoes. This facilitates load transfer, resulting in smoother 8 transitions with less wear.

The track shoes are joined by a pair of short spaced link pins which avoid the high bending stresses experienced by prior art single link pins extending across a major part of the track.

The foregoing describes only one embodiment of the invention, and modifications which are obvious to those skilled in the art may be made thereto without departing from the scope of the invention as defined in the following claims.

Claims (4)

1. An articulated crawler track comprising a plurality of like track shoes linked together in a first (longitudinal) direction to form an endless track, each track shoe having at least one leading lug extending longitudinally on one side of the shoe, at least one trailing lug extending longitudinally on the opposite side of the shoe, and spaced from the leading lug in a second (transverse) direction orthogonal to the first direction, at least two longitudinal roller path surfaces on the track shoe each aligned with a respective one of the leading and trailing lugs, wherein the leading lugs of the linked track shoes are longitudinally aligned, and the trailing lugs of the linked track shoes are longitudinally aligned, so that the roller path surfaces thereby form two parallel roller paths for a roller, and wherein the transition between a pair of adjacent track shoes in one roller path is longitudinally offset from the transition between the same pair of adjacent track shoes in the other roller path whereby, in use, the roller is supported across a complete roller path on at least one track shoe, characterised in that the roller path surface aligned with the leading lug of one shoe overlaps in the longitudinal direction with the roller path surface aligned with the trailing lug of an adjacent shoe by at least 10% of the length of a said roller path surface so that the roller is effectively supported on both roller paths between the offset transitions across the adjacent track shoes, and in that each pair of adjacent track shoes are linked together by at least two pins which are aligned and spaced in the transverse direction.

2. A crawler track as claimed in claim 1, wherein the roller path surface aligned with the leading lug of one shoe overlaps in the longitudinal direction with the roller path surface aligned with the trailing lug of an adjacent preceding shoe by about 15% of the length of a said roller path surface.

3. A crawler track as claimed in claim 1 or 2 wherein there are two roller paths, and wherein each track shoe has a trailing connection lug behind, and offset transversely from, the leading lug, and a leading connection lug ahead of, and offset transversely from, the trailing lug, and wherein the leading lug of each track shoe is pin-jointed to the trailing connection lug of the preceding shoe, and the trailing lug of each track shoe is pin-jointed to the leading connection lug of the following shoe.

4. A crawler track as claimed in any preceding claim wherein the overlap is between 50mm and A track shoe for an articulated crawler track, the track shoe having at least one leading lug extending in a first (longitudinal) direction on one side of the track shoe, at least one trailing lug extending in longitudinally on the other side of the track shoe, and spaced from the leading lug in a second (transverse) direction orthogonal to the first direction, at least two longitudinal roller path surfaces on the track shoe each aligned with a respective one of the leading and trailing lugs, wherein, when like track shoes are linked to form the crawler track, the leading lugs of the linked track shoes are longitudinally aligned, and the trailing lugs of the linked track shoes are longitudinally aligned, so that the roller path surfaces thereby form two parallel roller paths for a roller, and the transition between a pair of adjacent track shoes in one roller path is longitudinally offset from the transition between the same pair of adjacent track shoes in the other roller path whereby, in use, the roller is supported across a complete roller path on at least one track shoe, characterised in that, when like track shoes are linked to form the crawler track, the roller path surface aligned with the leading lug of one shoe overlaps in the longitudinal direction with the roller path surface aligned with the trailing lug of an adjacent shoe by at least 10% of the length of a said roller path surface so that the roller is supported on both roller paths between the offset transitions across the adjacent track shoes, and in that the track shoe is adapted to be linked to an adjacent like track shoe by at least two pins aligned and spaced in the transverse direction.