This is a Division of application Ser. No. 07/049,819 filed May 14, 1987, now U.S. Pat. No. 4,861,120. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to an endless track drive system, and methods of making, installing and repairing such a system. Endless track drive systems are used on vehicles such as tractors, bulldozers and tanks. 
     Many efforts have been made to improve endless track drive systems. In Edwards U.S. Pat. No. 4,093,318, issued June 6, 1978 (fully incorporated herein by reference), an endless track drive system is disclosed and claimed which includes a plurality of endless track drive sections, each section having a substantially flat contact surface and sloped surfaces to distribute weight and shed dirt and other foreign objects. Although U.S. Pat. No. 4,093,318 represented a marked improvement in endless track drive systems existing prior to that time, the pivotal means of connecting the endless track drive sections was subject to excessive wear, and the endless track drive system there disclosed continued to be excessively difficult and time-consuming to make, install and repair. It was further found that dirt and foreign objects continued to interfere with proper operation of the endless track drive system, although again not to the extent of track drive systems existing prior thereto. 
     In further recent developmental work, Edwards and his partners/co-inventors Harper and McNew have further improved upon the endless track drive system disclosed in Edwards U.S. Pat. No. 4,093,318. Their U.S. Pat. Nos. 4,569,561 issued Feb. 11, 1986, and 4,616,883 issued Oct. 14, 1986 (both fully incorporated herein by reference), disclose and claim an endless track drive system made up of a number of drive sections interconnected by cable connector sections. As there disclosed, the drive sections have sloping sides with removable rubber wear pads, and the cable connector sections include cables encased in rubber or other similar suitable material. As a result of such features, the endless track drive system disclosed and claimed therein experiences improved flexibility and tensile strength, reduced noise, and reduced maintenance. The detrimental effects of dirt and debris are likewise mitigated. 
     Despite the marked improvement in endless track drive systems resulting from the recent work of Edwards, Harper and McNew, as represented in U.S. Pats. Nos. 4,569,561 and 4,616,883, there remained a need for simplification in the manufacture, installation and repair of even that improved endless track drive system. Furthermore, the industry is always interested in and receptive to mitigating even further the effects of dirt and debris on endless track drive systems because of the resulting operational problems, downtime and increased maintenance. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention has been developed to overcome the foregoing shortcomings of the prior most recent improved endless track drive system, and to provide an endless track drive system which has an improved construction, is simpler, less costly and less time-consuming to manufacture, install and repair, and which is less susceptible to interference by dirt and debris. 
     It is therefore an object of the present invention to provide an endless track drive system with improved construction which is more resistant to contamination by dirt, sand, gravel and other foreign objects. 
     It is yet another object of the present invention to provide an endless track drive system which can be efficiently and economically manufactured. 
     It is still a further object of the present invention to provide an endless track drive system which can be quickly and economically installed on an endless track drive vehicle. 
     It is even yet a further object of the present invention to provide an endless track drive system which can be quickly and economically repaired in situ on an endless track drive vehicle. 
     Thus, in accordance with one aspect of the present invention the shortcomings of existing endless track drive systems are overcome by an endless track drive module comprising a plurality of base portions, at least on connector member, and a polymeric structure extending from said base portions and encasing all but the ends of said at least one connector member, the polymeric structure forming a plurality of drive members equal in number to said plurality of base portions, each said drive member including at least one drive face. 
     In accordance with another aspect of the present invention, the connected member ends of adjacent drive modules are joined by polymeric master links to form an endless track. The master links preferably have upper and lower base portion parts for fastening connector members extending from adjacent drive modules, and drive faces configured similarly to the drive module drive faces. 
     In accordance with yet another aspect of the present invention, the modular endless track drive system includes a drive wheel, the drive wheel preferably having a plurality of drive surfaces shaped to substantially match the shape of drive faces of the drive module drive members and master links. 
     In accordance with still another aspect of the present invention, the drive wheel of the modular endless track drive system further includes a sprocket for engaging with another drive face on each of the drive module drive members and master links thereby further driving the endless track drive system. 
     Still further aspects of the present invention include removable tread members and means for scraping dirt and debris from the modular endless track drive system, and methods of making, installing and repairing the modular endless track drive system in accordance with specified steps. 
     These and other aspects and advantages of the present invention are described in or apparent from the following detailed description of the preferred embodiments. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The preferred embodiments are described with reference to the drawings in which: 
     FIG. 1 is a perspective view of a bulldozer equipped with a modular endless track drive system in accordance with the present invention; 
     FIG. 2 is a perspective view of an endless track drive module in accordance with the present invention; 
     FIG. 3 is a transverse sectional view of the endless track drive module of FIG. 2 taken through one of the drive members thereof; 
     FIG. 4 is a longitudinal sectional view of the endless track drive module of FIG. 2 taken along the line 4--4 of FIG. 3; 
     FIG. 5A is a longitudinal sectional view of a master link in accordance with the present invention; 
     FIG. 5B is a transverse sectional view of the master link of FIG. 5A; 
     FIG. 6 is a plan view of the lower base portion part of the master link of FIG. 5A; 
     FIG. 7A is a longitudinal sectional view of the master link of FIG. 5A linking two adjacent drive modules equipped with removable tread members; 
     FIG. 7B is a longitudinal sectional view of a master link in accordance with another embodiment of the present invention linking two adjacent drive modules and two adjacent modular, cable reinforced removable tread members; 
     FIG. 8 is a perspective view of a master link in accordance with yet a further embodiment of the present invention; 
     FIG. 9 is a sectional view taken through an axle of a drive wheel in accordance with an embodiment of the present invention depicting the modular endless track drive system incorporating a sprocket; 
     FIG. 10 is a side view of the drive wheel and sprocket of FIG. 9; 
     FIG. 11 is a further sectional view of the drive wheel and sprocket of FIG. 9 taken through the drive wheel axle; 
     FIG. 12 is an elevational view of a drive wheel in accordance with yet a further embodiment of the present invention incorporating debris escape holes; 
     FIG. 13A is an elevational view of an endless track drive module in accordance with yet a further embodiment of the present invention; 
     FIG. 13B is an elevational view of an endless track drive module in accordance with still a further embodiment of the present invention; 
     FIG. 14 is an exploded view of a master link base portion, removable backing plate and removable tread usable in the modular endless track drive system of the present invention; 
     FIG. 15 is a sectional view of a bias-ply, fiber reinforced removable tread member usable in the endless track drive system of the present invention; 
     FIG. 16 is a sectional view of the cable reinforced removable tread member of FIG. 7B; 
     FIG. 17 is a perspective view, partially in cross-section, depicting the endless track drive module of FIG. 2 in position on the drive wheel of FIGS. 9-11; and 
     FIG. 18 is a perspective view of a modular removable tread member for use with the endless track drive system of the present invention; 
     FIG. 19 is an exploded view similar to FIG. 14 showing a drive module base portion, removable backing plate and removable tread usable in the modular endless track drive system of the present invention; and 
     FIG. 20 is an elevational view of a scraper tool usable with the modular endless track drive system of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 depicts a modular endless track drive system 2 of the present invention installed on a bulldozer 1. FIG. 1 depicts only one modular endless track drive system, but it will be understood that the typical track vehicle is equipped with at least two such systems. 
     Each modular endless track drive system 2 is made up of a plurality of endless track drive modules 3 which are linked together by connector members 4 (FIG. 2) fastened together by master links 5 in a closed loop to form an endless track. The endless track drive system further includes the necessary drive wheels 6, and any necessary supporting wheels, such as opposite end wheels 7 and idler wheels or rollers 8. The modular endless track is installed so as to pass around the wheels 6, 7 and 8. The idler wheels 8 are irregularly spaced so as not to simultaneously engage like points on the endless track, thereby preventing undue vibrations. Of course, the track vehicle is further equipped with the necessary power source and controls to power the endless track drive system 2 and thereby propel the vehicle over varying terrain as desired. 
     FIGS. 2-4 depict an endless track drive module 3 in accordance with the present invention. Endless track drive module 3 includes a plurality of base portions 9 on top of which is a polymeric structure 10. The base portions 9 are preferably made of steel or other metal, but may be made of some other strong, rigid material. The polymeric structure is preferably molded onto base portions 9, but may be constructed in other ways. The polymeric structure can be formed of any polymeric material which will provide a suitable frictional drive surface with limited operational noise; examples are rubber, polyurethane, or other plastics. As shown in FIGS. 2 and 4, the polymeric structure 10 is formed into a plurality of drive members 11 equal in number to the number of base portions 9. Although FIGS. 2 and 4 depict an endless track drive module with four drive members, the drive module can be formed of any number of drive members. 
     Encased within the polymeric structure 10 is at least one connector member 4, the connector member 4 both reinforcing the endless track drive module 3 and providing the means by which adjacent drive modules can be joined together to form an endless track. The connector members 4 are preferably steel cables, but also may be made of other materials such as nylon or other high strength light weight cord. Although ten connector members are depicted in FIG. 2, it will be appreciated that any desired number of connector members may be utilized. It will further be appreciated that the connector members 4 must be suspended above base portions 9 prior to the forming of polymeric structure 10 onto base portions 9 so that connector members 4 may be substantially encased within the polymeric structure. The ends 4&#39; of the connector members 4 must be left exposed so as to be available for joining adjacent drive modules to form an endless track. 
     As depicted in FIGS. 2 and 3, each drive member 11 includes at least one drive face 12. Each drive member 11 is preferably formed with two lateral frictional drive faces 12 which slope inwardly from the respective base portion 9 toward one another to form substantially an inverted V-shaped transverse cross-section with respect to said base portion. However, drive members 11 may be provided with any suitable type, number and configuration of drive faces. For example, each drive member 11 could be provided with two lateral frictional drive faces which slope outwardly from a central portion of its respective base portion 9, thereby providing drive members 11 with concave V-shaped transverse cross-sections with respect to base portions 9. Other configurations will further be understood from the above disclosure. 
     Drive members 11 may also be provided with vertically extending planar portions 13 below drive faces 12 so that base portions 9 will extend beyond the radial peripheries of wheels 6 and 7 thereby raising the track vehicle 1 higher above the terrain to further protect the structural mechanisms of the track vehicle from dirt and debris. Drive members 11 also may have front and rear edges (lateral drive face side edges) 70, 71 which are inwardly sloped with respect to a longitudinal direction of the endless track drive system so that such edges will lie substantially parallel to one another as they proceed around drive wheel 6 of the track vehicle (see FIG. 9), thereby providing smoother operation, permitting use of a sprocket, and further reducing influx of detrimental dirt and debris. The gaps between adjacent drive members and master links resulting from sloped edges 70 and 71 further permit dirt and debris to escape along straight runs to the endless track. 
     To reduce the mass of drive modules 3, and also reduce consumption of polymeric material and consequent cost, one or more holes 14 optionally may be formed in each drive member. Furthermore, an additional upper drive surface 15 may be formed on each drive member for either frictional drive or sprocket drive by an axle of drive wheel 6 to be described below. Additionally, a support structure 16 may be fastened to each base portion 9 by welding, screws, bolts or other fastening means in order to further reinforce drive members 11, render it easier to mold polymeric structure 10 onto base portions 9, and further secure base portions 9 to polymeric structure 10. An additional support structure 69 may also be provided for suspending cables 4 above base portions 9 and further securing base portions 9 to polymeric structure 10. Support structures 16 and 69 may be in the form of metal straps, or may be made from a rigid plastic material or other suitable rigid substance. Support structure 16 is preferably shaped to conform wiht the desired configuration of drive faces 12, but may be shaped in other configurations to serve its intended purposes. Support stucture 69 likewise may be configured in a number of ways other than as shown. 
     FIGS. 5A-8 depict various embodiments of the master link which is used to join adjacent drive modules in order to form the endless track. As depicted in FIGS. 5A-7A, master link 5 preferably has the same general configuration and construction as each individual drive member 11 of drive module 3, and like elements are identified with like reference numerals. However, the base portion of master link 5 has upper and lower parts 21, 22 which can be fastened together with a threaded bolt or other appropriate fastening means with connector members 4 sandwiched therebetween, thereby joining adjacent drive modules. FIG. 7A depicts master link 5 fastened in place joining two adjacent drive modules 3. 
     Preferably the ends 4&#39; of connector members 4 are provided with retaining members 23 which are crimped onto or otherwise fastened to connector member ends 4&#39;. The upper and lower parts 21, 22 of the base portion of the master link 5 are in this case provided with cooperating recesses 24-27 and channels 28-31 which together are of the same general configuration as cable ends 4&#39; with retaining members 23. Each cable end 4&#39; and retaining member 23 can be provided with their own individual recess and channel as shown in FIG. 5B, or upper and lower base portion parts 21, 22 can be provided with single recesses 24-27 and multiple channels 28-31 as shown in FIG. 6. In either case, recesses 24-27 and channels 28-31 must be sufficient to accommodate the connector members of adjacent drive modules. Although retaining members 23 and recesses 24-27 are depicted in the drawings as being generally spherical, it will be appreciated that other configurations are possible consistent with the above disclosure. 
     FIG. 7B depicts another master link 5&#39; which is adapted to accommodate additional connector members 32. These additional connector members are utilized to reinforce backing plates 18c of removable tread members 17c (see also FIG. 16) and to join adjacent removable tread members 17c. Master link 5&#39; has the same general configuration and construction as master link 5, but includes an intermediate base portion part 33. Intermediate part 33 contains additional recesses 34-37 and channels 38-41 corresponding respectively to recesses 24-27 and channels 28-31 of upper and lower base portion parts 21 and 22. Accordingly, intermediate part 33 has sufficient recesses and channels to accommodate four rows of connector members, two rows of connector members from one drive module and its removable tread member and two rows from an adjacent drive module and its removable tread member. 
     FIG. 8 depicts yet another master link 5&#34; which is different in construction from master link 5. Master link 5&#34; has upper and lower base portion parts 42, 43 which correspond to upper and lower base portion parts 21, 22 of master link 5, with like recesses and channels to accommodate connector members and retaining members from adjacent drive modules. Of course, master link 5&#34; could also be provided with an intermediate base portion part as depicted in FIG. 7B so as to be able to accommodate additional connector members and retaining members from adjacent removable tread members. Master link drive member 5&#34; further includes side walls 44, 45 with similar slope and configuration to drive faces 12 of drive members 11, and removable polymeric drive faces 46, 47 are fastened thereto with countersunk bolts, locator pins and holes, or other known fastening means. An upper drive face 48 is provided corresponding to drive faces 15 of drive members 11 for frictional or sprocket drive to be described below. Drive faces 46, 47 may be rounded at the top to meet drive faces 48 or eliminate the need for drive face 44 altogether, thereby taking on a configuration similar to master links 5 and 5&#39;. 
     As depicted in FIGS. 2, 17 and 19, endless track drive module 3 also preferably includes removable tread members 17, each including a metal backing plate 18 and a rubber tread 20 bonded to a metal supporting plate 19. Rubber tread 20 may include a bias-ply, fiber reinforced layer 68 as shown in FIG. 15. Individual treads and backing plates each preferably have four unthreaded holes 63 and 64, respectively, and are removably fastened to each of the base portions 9 of drive module 3 with suitable bolts or other fastening means received in threaded holes 65 of the base portions. 
     Master links 5 and 5&#34; also preferably are equipped with removable tread members of slightly different configuration. As shown in FIG. 14, each master link tread member 17a includes a metal backing plate 18a and a rubber tread 20a bonded to a metal supporting plate 19a, each preferably having three unthreaded holes 61, 60 and 66, respectively. The metal supporting plate 19a includes two outer holes 66 which are smaller than and concentric with the outer holes 60 in rubber tread 20a, such that the tread and backing plate can be removably fastened to lower master link base portion part 22 with suitable bolts or other fastening means received in two other threaded holes 62 of the lower base portion part. The center holes of tread 20a, supporting plate 19a and backing plate 18a are all large enough that a suitable bolt or other fastening means can be passed therethrough and received in the center threaded hole 62 of lower master link base portion part 22. In this way, tread member 17a can be removed from the master link without completely disconnecting the upper and lower base portion parts of the master link. 
     FIG. 7A depicts another type of removable rubber tread member 17b, including a rubber tread 20b molded with a rubber backing plate 18b. Backing plate 18b dovetails with adjacent tread member backing plates, the ends of adjacent tread member backing plates being fastenable together with bolts or other fastening means into the base portion of a given drive member 11. Backing plates 18b and treads 20b can be bias-ply, fiber reinforced as described above relative to rubber treads 20 and as shown in FIG. 15. 
     FIG. 7B depicts another removable tread member 17c, including a rubber tread 20c molded with a rubber backing plate 18c which is cable reinforced (see also FIG. 16) and equal in length to the length of a given drive module. FIG. 18 depicts yet still another removable rubber tread member 17d with a rubber tread 20d and a dovetailed rubber backing plate 18d similar to FIG. 7A, but having substantially the same length as a given drive module. Of course, metal treads could also be utilized, or metal backing plates could be provided with metal grouser bars. The type of tread and backing plate to be utilized, and the material of the chosen tread and backing plate, whether rubber, metal or other material, are functions of the type of terrain over which the endless track drive vehicle is to be utilized, and are left to operator discretion. 
     FIGS. 10 and 11 depict a drive wheel 6 suitable for use in the endless track drive system in accordance with the present invention. Drive wheel 6 includes first and second side portions 48, 49 connected together by angle portion 50. Each side portion 48, 49 preferably includes interior drive surfaces 51 sloped and shaped to substantially match the angle and shape of drive faces 12 of drive members 11 and master link 5, 5&#39; (drive faces 46, 47 of master link 5&#34; ) for engagement therewith. Axle 50 further preferably includes drive surfaces 52, the number, shape and size of which are determined by the configuration of drive members 11 and master links 5, 5&#39; and 5&#34;, and specifically respective drive faces 15 and 48 thereof which may engage with drive surfaces 52. Although the interior of drive wheel 6 preferably includes drive surfaces 51, 52 as discussed above, axle 50 may be deleted altogether, side portions 48 and 49 then being directly connected to ane another, and drive surfaces 51, 52 may also be eliminated. Furthermore, wheels 7 and 8 of track vehicle 1 may or may not contain interior drive surfaces corresponding to drive surfaces 51 and 52 of drive wheel 6. Drive wheel 6 may also contain holes 55 as shown in FIG. 12 to permit escape of dirt and debris. 
     As depicted in FIGS. 9 and 11, drive wheel 6 may also include a sprocket 53 for further driving the modular endless track drive system. Sprocket 53 includes concave drive surfaces 54 which are configured for engagement with drive surface 15 of drive members 11 and master links 5 and 5&#39;, and drive surface 48 of master link 5&#34;. FIG. 17 depicts a drive member 11 of drive module 3 engaging with interior drive surfaces 51 and sprocket 53 of drive wheeel 6. Of course, the sprocket may take other forms. For example, rounded bars may be added between drive surfaces 51 of drive wheel side portions 48, 49 to interfit between adjacent drive members and master links to provide positive engagement therewith. By way of yet a further example, drive pins may be provided extending from the tops of the drive members and master links for positive engagement with spaced recesses in the drive wheel axle. Other possible sprocket arrangements will be appreciated from the above disclosure. 
     As depicted in FIG. 20, the modular endless track drive system may also be provided with a scraper or sweeper 75 for removing dirt and debris from drive wheel 6 and the various drive faces on the drive modules and master links of the endless track. For example, scraper 75 may include an upwardly directed convex, inverted V-shaped scraper blade 76 and a downwardly directed concave, inverted V-shaped scraper blade 77 supported by a bracket 78 affixed on a supporting surface of the endless track drive vehicle. Thus, scraper 75 can be located so as to clean the drive wheel and endless track simultaneously, thereby preventing dirt and debris from interfering with the operation of the endless track drive system. With the structure shown in FIG. 20, any dirt scraped from drive wheel 6 will fall and be diverted by scraper blade 77 instead of becoming entrapped in the endless track. Of course, scraper 75 may be located at various positions on the endless track drive vehicle, may be provided with scraper blade 76 or 77 alone, and may be of a configuration other than as shown. Additionally, bristles, brushes or other cleaning instruments may be utilized in lieu of scraper blades 76 and 77. 
     The above-described modular endless track drive system is easy and cost-effective to make, install and repair. The base portion 9 of drive modules 3 can be forged, cast or otherwise manufactured to the desired size, and support structures 16 and 69 can be affixed thereto by conventional means. Connector members 4 can then be suspended above a desired plurality of base portions 9, and a suitable polymeric material molded or otherwise applied onto the base portions to encase the connector members and provide a plurality of drive members of desired configuration. The recesses and channels in the upper, lower and intermediate base portion parts of master links 5, 5&#39;, 5&#34; easily can be machined or formed during casting of the master link base portion, and the upper, lower and intermediate parts can be appropriately threaded for receipt of conventional fasteners. The alternative master link 5&#34;, drive wheel 6, and sprocket 53 likewise easily can be manufactured through the use of known manufacturing techniques based upon the above disclosure of those features of the present invention. 
     A necessary plurality of drive modules and master links can then be assembled and laid out on the ground in a linear fashion leaving two disconnected drive module ends, the endless track drive vehicle can be positioned over the modular track, and the modular track then easily can be placed around the drive wheel and supporting wheels of the vehicle and the final master link fastened in place to connect the last two drive modules and form the endless track. If one or more drive modules 3 and/or master links 5, 5&#39;, 5&#34; are broken during operation of the endless track drive vehicle, the modular endless track drive system easily can be repaired by removing and replacing in situ only those drive modules and master links necessary to the repair. 
     In accordance with the above, an improved modular endless track drive system is provided which can be constructed, installed and repaired quickly, easily and cost-effectively, and which provides excellent operability. 
     Obviously, many modifications and variations to the disclosed modular endless track drive system and methods of making, installing and repairing same are possible in light of the above teachings. For example, wider base portions 9&#39;, 9&#34; can be provided as depicted in FIGS. 13A and 13B to provide for vehicles requiring wider modular endless tracks. In such cases, the polymeric endless track drive modules can each be molded in the form of half modules 3&#39; or double modules 3&#34;. Drive modules 3&#39; can be driven by a wider drive wheel or two properly spaced pneumatic driving tires. Drive modules 3&#34; can be driven by two properly spaced drive wheels or four properly spaced pneumatic drive tires. Of course, the described master links, removable tread members and scraper would have to be reconfigured accordingly to coordinate with drive modules 3&#39; and 3&#34;. It is to be further understood that, within the scope of the appended claims, the invention also may be practiced otherwise then as specifically described. For example, the various aspects of the invention may be selected for combination in a number of permutations other then those shown and described. 
     Thus, while only certian embodiments of the invention have been specifically described herein, it will be apparent that numerous modifications may be made thereto without departing from the spirit and scope of the invention.
A modular endless track drive system for use on a track vehicle such as a bulldozer is made up of a number of polymeric drive modules interconnected with polymeric master links. Each drive module includes a plurality of drive members with lateral frictional drive faces for engagement with a drive wheel, each master link having similarly configured drive faces. The drive wheel is provided with drive surfaces shaped to match the shape of the lateral drive faces on the drive modules and master links and/or a sprocket for engaging with additional drive faces on the drive modules and master links. A drive module is made by molding a polymeric multiple drive member structure atop a plurality of base portions, encasing one or more connecting members therein with their ends exposed. The master links are made in a similar fashion, but with upper and lower base portion parts for fastening the drive module connector members therebetween to form an endless track. The system is readily installed by assembling the necessary drive modules and all but one of the master links to form a track with two disconnected ends, laying the assembled track linearly across the ground, positioning a track vehicle thereover, looping the track over the wheels of the track vehicle, and installing the final master link to form the endless track. Repairs to the system are made by simply removing and replacing broken drive modules and master links in situ.