Dual Pitch Track Links For Adjustment Of Cushioned Tracks

Abstract

An adjustable track assembly for a cushioned track system comprising a plurality of shoe-bearing links, said track assembly being mounted circumferentially around a resilient spacer means. Some of said links in the track assembly have one pitch length and the others have a second pitch length. By coupling together a selected number of links of each pitch length, a closed track chain of any given circumferential length is obtained. The particular number of links of each length is conveniently determined by use of a nomogram.

Description

BACKGROUND OF THE INVENTION

This invention relates to a new and improved adjustment means for the track assembly of a cushioned track system. More particularly, the invention is directed to a novel combination of links having long and short pitch lengths and to a method for determining the proper number of long and short pitch length links required to produce a track assembly having a particular desired circumferential dimension.

Cushioned track systems for earth-working vehicles generally comprise a track assembly made from a plurality of shoe-bearing links coupled together and mounted for rotation upon a resilient spacer means which in turn is drivingly mounted upon an earth-working vehicle. Such a cushioned track system is shown in U.S. Pat. application, Ser. No. 884,903, filed Dec. 15, 1969, now U.S. Pat. No. 3,601,212, of common assignment with the present invention.

One problem encountered in cushioned track systems is the difficulty in assuring a proper fit between the track assembly and the resilient spacer means embraced thereby. Small incremental adjustments of the track assembly are often necessary because the circumference of the particular resilient spacer means utilized may vary in use. Also, the rated nominal circumferential dimension of large resilient spacers may not be dependable. For example, newly manufactured earth-moving vehicle tires which may be used as spacer means, may be listed at the same nominal size but, in fact, may vary in circumference by as much as three inches or more. To compensate for these variations in circumferential dimension, some means for readily adjusting the size of the track assembly must be provided.

One means for providing the desired track assembly adjustment is described in U.S. Pat. application, Ser. No. 100,852, filed Dec. 23, 1970, entitled "Adjustable Pitch Track Link," of common assignment herewith. This system utilizes link connecting pivot pins which have eccentric cam means formed thereon. By rotatably adjusting the pivot pin cams, one may vary the effective pitch length between any given set of links.

The present invention is principally directed to another system for adjusting the composite length of a cushioned track assembly which couples a plurality of links of two different pitch lengths in various combinations to achieve any desired composite track assembly length. Additionally, the present invention provides a method for determining the proper number of links of each length required for a particular track assembly length.

One of the objects of this invention is to provide a cushioned track adjustment system which utilizes a plurality of track links which have the same nominal pitch length and which can be manufactured from identical forgings.

Another object of this invention is to provide a cushioned track adjustment system which utilizes track links having the same nominal pitch length but which have been machined to have two different actual pitch lengths.

Still another object of this invention is to provide a plurality of track links having pin and bushing bores which have been machined an incremental amount to either side of their nominal centers to provide links having two different actual pitch lengths.

Yet another object of this invention is to provide a method for rapidly determining the number of track links having long and short pitch lengths which are required to produce a given fit with a given spacer means.

Another object is provide means to accurately control the fit of a track assembly in relation to a resilient spacer in a cushioned track.

Other objects and advantages of the present invention will become apparent from the following description and claims.

The accompanying drawing shows, by way of illustration, the preferred embodiments of the present invention and the principles thereof. It is recognized that other embodiments of the invention applying the same or equivalent principles may be used and that structural changes may be made as desired by those skilled in the art without departing from the present invention and the purview of the appended claims.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a side elevational view of a cushioned track system which embodies the track assembly adjustment means of the present invention;

FIG. 2 is an enlarged side elevational view of a portion of the track assembly employed in FIG. 1;

FIG. 3 is a top elevation showing one form of the link means utilized in the cushioned track system shown in FIG. 1;

FIG. 4 is a side elevational view, similar to the one shown in FIG. 2, which shows a modified form of track shoe to be utilized in the present invention;

FIG. 5 is another top elevation, similar to the one shown in FIG. 3, which shows an alternate form of a track link means for use in the present invention; and

FIG. 6 shows a nomogram which may be used to determine the required number of short and long pitch length links required to produce a cushioned track having any given circumferential dimension.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a cushioned track system 10 which is adapted to replace conventional tires, crawler tracks, or the like, which are employed on standard earth-moving vehicles. The cushioned track system comprises an annular resilient spacer means 11 which is circumnavigated by an endless track assembly, a portion of which is shown at 12. The resilient spacer means 11 may comprise an air-inflated rubber tire or an air bag mounted on a conventional rim assembly 13. Other suitable types of resilient spacer means are disclosed in the above-referenced U.S. Pat. application, Ser. No. 884,903.

The endless track assembly 12 comprises a plurality of closely coupled shoes 14 having ground-engaging grousers 14a which shoes are suitably attached to a chain of link members 15 which completely circumnavigates said resilient spacer means 11.

As more clearly shown in FIG. 2, the preferred embodiment of the link chain of the present invention includes a plurality of links 16, 17, and 18 coupled together by means of pins 19 suitably received in bushings 20. Each individual link is provided with bores for mounting a pin and a bushing, respectively, at each opposite end thereof. The ground-engaging track shoes 14 are secured by bolts or other suitable fasteners to the link chain formed by the coupled links.

Initially, each of the links 16, 17, and 18 has the same nominal pitch length because each link is made from an identical forging. That is, the distance between the nominal centers of the pin and bushing bores of each link is the same. However, by properly machining the link bores, links having two different pitch lengths may be obtained.

For the purpose of illustration, link 17 in FIG. 2 will be designated as a link having a long pitch length and link 18 will be designated as a link having a short pitch length. The letter N is used to designate the nominal pitch length of the link. This is the distance which would separate the centers of the pin and bushing bores on either end of the link if said bores were located uniformly on all links. However, it will be noted that the actual centers of the pin and bushing bores of link 17 have been machined a small amount off center with respect to said nominal centers so that the actual distance between the centers of the pin and bushing bores of link 17 is a distance L, which is incrementally greater than the distance N. In a similar manner, the pitch length of the link 18 has been shortened by the same amount. As can be seen, the nominal pitch length is again designated by the letter N, and the pin and bushing bores have been machined off center to the inside of the nominal centers so as to create a shorter actual pitch length S.

Thus, it is seen that, by proper machining, links of different actual pitch length can be created from forgings having the same nominal pitch length. By coupling together a selected number, including zero, of links having short pitch lengths and a selected member, including zero, of links having long pitch lengths, a link chain of any composite length, or when closed, of any circumferential dimension, can be created.

For example, if links 17 and 18 initially have the same nominal pitch length of 8.00 inches, an actual pitch length differential between the long and short links of 0.250 inches may be obtained. This is done by machining both the pin bore and the bushing bore of the link 18 to 0.062 inches off-center to the inside of the nominal length N providing the link with an actual pitch length of 7.875 inches. Conversely, link 17 has its pin bore and bushing bore each machined 0.063 inches to the outside of the nominal length N, giving it a pitch length L of 8.125 inches. This results in a pitch length differential of 0.250 inches between the two links.

It should be noted that this small difference in pitch length between the various links of the track chain is not enough to create interference problems with the shoes 14. Although all of said shoes are of uniform length, ample overlap is provided between the lugs 40, 41 of each shoe to prevent gapping or mating thereof. The modified shoes shown in the embodiment of FIG. 4 are also provided with sufficient lug overlap to avoid any problems when a limited pitch length differential such as 0.250 inches is used. FIG. 4 also shows a modified form of grouser 14b which may be utilized.

FIGS. 3 and 5 show alternate forms of the link chain which may incorporate the present invention. In FIG. 3, a single-link chain is shown. One of these single-link chains would be adopted for disposition on each side of the resilient spacer means shown in FIG. 1. The shoes 14 would extend transversely across the peripheral surface of said spacer means and would connect the respective link chains at fastening points 30 provided in each link. Each link is provided with a pin bore 31 and a bushing bore 32 at opposite ends which may be machined off-center with respect to their nominal centers to provide either a long or short pitch length, as previously described. The links are provided with blade portions 45 to mate with complementing fork portions 46, as shown.

The modification of FIG. 5 shows a double link chain which may be utilized in lieu of the single link chain of FIG. 3. This chain would be disposed in the same position as the single-link chain, and includes pins 42 and bushings 43 for coupling each set of laterally disposed rail members 44.

In accordance with the present invention, a means and method for determining the proper number of short pitch and long pitch links, sections, or the like which must be articulated to produce a track assembly of the desired circumference is provided. With reference to FIG. 6, it is seen that a nomogram of three scales is provided. The first scale, labeled INTERFERENCE FIT, is graduated from 0 to 10 inches. The term "interference fit" is used herein to describe the desired tightness of fit between the track assembly and the spacer means in any particular application. It refers to the difference between the circumference of the resilient spacer means 11 with and without the track assembly mounted thereupon. In other words, if a resilient spacer means has a circumference of 270.0 inches prior to installation of the track assembly and has a circumference of 265.0 inches when the track assembly is mounted, then the interference fit is 5.0 inches, or the difference between the two circumferential dimensions. The scale at the right of the nomogram is graduated in inches and indicates the measured circumference of the resilient spacer means prior to track assembly installation. The scale at the center of the nomogram indicates both the total number of links and the number of links of each pitch length required to make up a track assembly of a given circumferential dimension.

The utility of the nomogram is best illustrated by way of example. For example, assume that the particular spacer used is a 24 .times. 35 earth-mover tire, and the tire has a measured circumference of 258.5 inches when inflated to operating pressure. Assume that an interference fit of 5.0 inches is desired. That is, assume that the tire circumference will be 253.5 inches when the track assembly is mounted thereupon. To determine the correct number of links of each pitch length required in this situation, one would plot the circumference on the scale at the right of the nomogram, i.e., at A, and one would plot the desired interference fit on the scale at the left of the nomogram, i.e., at B. Then, one would draw a line between the plots A and B. Where this line crosses the center line of the center scale can be found an indication of the total number of links as well as the number of links of each length required.

In this particular example, the line crosses the center scale at a point C. It can be seen that this point is within the confines of the area marked 30 on the total number scale. This means that a total number of 30 links will be required to produce a track chain of the desired fit. The particular number of links of each pitch length is found on each of the scales marked LONG and SHORT in the nomogram. It can be seen that the point C lies on the center line at the graduation marked 25, reading upwardly from 0 to 30 on the LONG scale. This means that 25 long pitch links will be required in this particular combination. Also, reading downwardly from the 0 mark on the SHORT scale, it can be seen that the point C is on the fifth graduation. This means that five short pitch links will be required in the given combination.

Thus, it can be seen that the number of short and long pitch length links can be readily determined by drawing a line between the plots on the spacer circumference scale and the interference fit scale, and that a track assembly with almost any desired length, in increments of 0.250 inches, can be assembled to produce any desired interference fit.

While the preferred embodiments of the invention have been illustrated and described, it is understood that these embodiments are capable of variation and modification and are not limited to the precise details set forth, but rather include such variations and modifications as fall within the scope of the appended claims.

Claims

I claim:

1. An adjustable track assembly comprising a plurality of closely coupled, ground-engaging shoes, at least one articulated link assembly having adjacent links closely coupled together and connected to said shoes, said link assembly comprised of substantially identical links having pivot means connecting each pair of adjacent links together for articulated movement about the pivot means axes to define a predetermined pitch length between each pair of adjacent pivot means axes, each link having bore means disposed at opposite ends thereof for receiving said pivot means, the spacing between said oppositely disposed bore means being fixed for each respective link, the spacing between said oppositely disposed bore means for at least one of said links being different from the corresponding spacing for another of said links so that at least one of said defined pitch lengths is different from another of said defined pitch lengths.

2. The adjustable track assembly of claim 1 including an annular resilient spacer means rotatable about the central axis thereof, said spacer means having a peripheral surface and side surfaces, and said track assembly being mounted completely around said spacer means for unitizing said spacer means therewith.

3. The invention of claim 2 wherein one of said articulated link assemblies is adjacent to each said side surface of said resilient spacer means and extends radially inwardly toward said central axis.

4. The invention of claim 3 wherein each of said links has a blade portion formed at one end thereof and a forked portion formed at the opposite end thereof, and the blade portion of one of said links is positioned within and pivotably connected to the forked portion of another of said links by said pivot means.

5. The invention of claim 3 wherein each of said links is formed with a plurality of laterally-spaced members which are connected together by transverse spacer means.

6. The adjustable track assembly of claim 1 wherein each of said links is constructed from forged link members of the same size, and wherein each of said members is provided with pivot means receiving bores in each opposite end thereof.

7. The adjustable track assembly of claim 6 wherein said pivot means comprises pin means and bushing means and wherein said pivot means receiving bores comprise a bushing means receiving bore at one end of each of said link members and a pin means receiving bore at the opposite end of each of said link members.

8. In a cushioned track assembly wherein an adjustable track assembly surrounds an annular resilient spacer means with a predetermined interference fit, the method of adjusting said interference fit which comprises;

a. providing track links having fixed dimensions which define a first predetermined pitch length,

b. providing substantially identical track links having other fixed dimensions which define a second predetermined pitch length,

c. selecting a predetermined number of links of each of said first and second predetermined pitch lengths, and

d. coupling said links having said first and second predetermined pitch lengths together to form a closed, spacer means-surrounding track assembly.

9. In a cushioned track assembly having a resilient spacer means surrounded by a track assembly having links of two different pitch lengths, the method for determining the number of links of each pitch length required for an annular spacer having a given circumferential dimension and a given interference fit which comprises;

a. plotting the circumferential dimension of said resilient spacer means on a first scale provided for that purpose,

b. plotting the desired interference fit on a second scale provided for that purpose,

c. determining the point of intersection between a line drawn from said first plot to said second plot and a third scale, provided adjacent first and second scales, and

d. selecting the number of links of each pitch length from said third scale.

10. An adjustable track assembly comprising a plurality of closely coupled, ground-engaging shoes, at least one articulated link assembly having adjacent links constructed of forged link members of equal size with pivot means receiving bores in each opposite end thereof, said link members being closely coupled together, and connected to said shoes, said link assembly having pivot means comprising pin means and bushing means, said pivot means receiving bores comprising a bushing means receiving bore at one end of each of said link members and a pin means receiving bore at the opposite end of each of said link members, said pivot means connecting each pair of adjacent links together for articulated movement about the pivot means axes to define a predetermined pitch length between each pair of adjacent pivot means axes, and said bores being machined into said equal-sized link members at a first distance apart in links having a first predetermined pitch length and at a second distance apart in links having a second predetermined pitch length.