Patent Publication Number: US-2015061369-A1

Title: Track joint assemblies and thrust rings for same

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Patent Application No. 61/871,491, filed Aug. 29, 2013, which is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to track assemblies and, more particularly, to track joint assemblies for joining links of the track assemblies. 
     BACKGROUND 
     Many earth-working machines, such as, for example, loaders, tractors, and excavators, include tracked undercarriages to facilitate movement of the machines over ground surfaces. Such undercarriages include drive sprockets that rotate track assemblies about one or more idlers or other guiding components to propel the machines over the ground surfaces. Each track assembly includes a pair of parallel chains, each made up of a series of links, joined to each other by pins and/or bushings (the combination of which is sometimes referred to as a cartridge assembly). Due to extreme wear from abrasion and impacts experienced during use, undercarriage maintenance costs often constitute more than one quarter of the total costs associated with operating the earth-working machines. 
       FIG. 1  provides an example of a prior art cartridge assembly  10  for coupling links, which is disclosed by U.S. Patent Application Publication No. 2012/0267947 by Johannsen et al. As shown, cartridge assembly  10  includes a pin  12  accommodated within an inner bushing  14 , which is, in turn, accommodated within an outer bushing  16 . End portions  17   a,    17   b  of inner bushing  14  are surrounded by inserts  19   a,    19   b,  and end portions  21   a,    21   b  of pin  12  are surrounded by collars  23   a ,  23   b.  Pin  12  has a lubricant channel  25 , which serves as a reservoir for lubricant and delivers lubricant to a gap between pin  12  and inner bushing  14 , and to a gap between inner bushing  14  and outer bushing  16 . The lubricant is retained by seals  27   a,    27   b  positioned between outer bushing  16  and inserts  19   a,    19   b,  and by seals  29   a,    29   b  positioned between inserts  19   a,    19   h  and collars  23   a,    23   b.    
     Cartridge assembly  10  may provide certain benefits that are particularly important for some applications. However, it may have certain drawbacks. For example, manufacturing pin  12  to include channel  25  may be complicated and costly. As another example, manufacturing links large enough to accommodate inserts  19   a,    19   b  and collars  23   a,    23   b  (as opposed to just pin  12  and inner bushing  14 ) may require an excessive amount of material. The disclosed embodiments may help solve these problems. 
     SUMMARY 
     One disclosed embodiment relates to a thrust ring for a track joint assembly. The thrust ring may include a generally cylindrical outer surface. The thrust ring may also include a generally cylindrical inner surface including at least one protrusion extending toward a central axis of the thrust ring. 
     Another disclosed embodiment relates to a track joint assembly. The track joint assembly may include a hushing having a generally cylindrical inner bearing surface defining a bore. Additionally, the track joint assembly may include a solid pin positioned at least partially within the bore. The solid pin may have a generally cylindrical outer surface facing the generally cylindrical inner bearing surface of the bushing. The track joint assembly may also include a thrust ring positioned at an axial end of the bushing and at least partially defining a lubricating fluid cavity. 
     A further disclosed embodiment relates to a track joint assembly. The track joint assembly may include a bushing having a generally cylindrical inner bearing surface defining a bore. The track joint assembly may also include a solid pin positioned at least partially within the bore. The solid pin may have a generally cylindrical outer surface facing the generally cylindrical inner bearing surface of the bushing. Additionally, the track joint assembly may include a link secured to the pin. At least one of the inner bearing surface of the bushing or the outer surface of the pin may include at least one recess at least partially defining a lubricating fluid cavity. The link may have an opening adapted to allow lubricating fluid to be added to the lubricating fluid cavity. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view of a prior art cartridge assembly; 
         FIG. 2  is a perspective view of a track assembly according to the present disclosure; 
         FIG. 3  is a cutaway view of a track joint assembly of the track assembly of  FIG. 2 ; 
         FIG. 4  is a cross-section of the track joint assembly of  FIG. 3 ; 
         FIG. 5  is an enlarged view of a portion of  FIG. 4 ; 
         FIG. 6  is another enlarged view of a portion of  FIG. 4 ; 
         FIG. 7  is a perspective view of a thrust ring of the track joint assembly of  FIG. 3 ; 
         FIG. 8  is a side view of the thrust ring of  FIG. 7 ; 
         FIG. 9  is a cross-section of the thrust ring of  FIG. 7 ; 
         FIG. 10  is a cross-section of another track joint assembly according to the present disclosure; and 
         FIG. 11  is a cross-section of yet another track joint assembly according to the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 2  illustrates an exemplary track assembly  100  for a track-type machine. For example, the track-type machine may be a loader, a tractor, an excavator, a tank, or another mobile machine having track-type traction devices. When operated, a drive sprocket of the track-type machine (not shown) may rotate track assembly  100  about one or more idlers or other guiding components (not shown) to facilitate movement of the track-type machine. 
     Track assembly  100  may include a series of links  110   a  joined to each other and to a series of links  110   b  by laterally disposed pins  120 . As shown, links  110   a  and  110   b  may be offset links. That is, they may have inwardly offset ends  140   a,    140   b  and outwardly offset ends  150   a,    150   b . An inwardly offset end  140   a,    140   b  of each link  110   a,    110   b  may be joined to an outwardly offset end  150   a,    150   b  of each adjacent link  110   a,    110   b.  In addition, an inwardly offset end  140   a  of each link  110   a  may be joined to an inwardly offset end  140   b  of an opposing link  110   b,  and an outwardly offset end  150   a  of each link  110   a  may be joined to an outwardly offset end  150   b  of an opposing link  110   b.  It should be understood, however, that links  110   a  and  110   b  need not be offset links. Rather, in some embodiments, links  110   a  and  110   b  may be inner links and outer links. In such embodiments, both ends of each opposing pair of inner links would be sandwiched between ends of opposing outer links, as is known in the art. 
     Referring to  FIGS. 3 and 4 , an individual track joint assembly  155  of track assembly  100  may include two links  110   a  joined to two links  110   b . As shown, inwardly offset ends  140   a,    140   b  of links  110   a,    110   b  may be secured to a joint bushing  157 , which may be at least partially positioned within bushing bores  160   a,    160   b  of offset ends  140   a,    140   b.  Similarly, outwardly offset ends  150   a ,  150   b  of links  110   a,    110   b  may be secured to a pin  120 , which may be at least partially positioned within pin bores  170   a,    170   b  of offset ends  150   a,    150   b.  For example, the securing may be by way of press-fits. Specifically, bushing  157  may be press-fit into bushing bores  160   a,    160   b,  and pin  120  may be press-fit into pin bores  170   a,    170   b.  Alternatively, the securing may be by way of welds, snap rings, or other mechanisms known in the art. 
     As shown, bushing  157  may be positioned coaxially around pin  120 , and may rotate relative to pin  120 , allowing inwardly offset ends  140   a,    140   b  to pivot relative to outwardly offset ends  150   a,    150   b  as track assembly  100  rotates. In order to facilitate such rotation, one or both of bushing  157  and pin  120  may be coated with diamond like carbon or electroless nickel, or may be carburized, nitrided, or polished to reduce friction between bushing  157  and pin  120 . Alternatively or additionally, a lubricating fluid may be situated between bushing  157  and pin  120 . 
     The lubricating fluid may be added through openings  180   a,    180   b  in links  110   a,    110   b,  and may be contained in a lubricating fluid cavity  190  at least partially defined by a generally cylindrical inner surface  200  of inner bushing  157  and a generally cylindrical outer surface  210  of pin  120  facing surface  200 . Unlike the prior art cartridge assembly discussed above, lubricating fluid cavity  190  may not extend into an interior cavity of pin  120 , as pin  120  may be solid. Since pin  120  may not contain lubricating fluid, lubricating fluid cavity  190  may extend into and be at least partially defined by one or more recesses in surface  200  or surface  210 . Alternatively or additionally, lubricating fluid cavity  190  may extend into and be at least partially defined by thrust rings  220   a ,  220   b  positioned at axial ends  230   a,    230   b  of bushing  157 . Thrust rings  220   a,    220   b  may transmit axial load between adjacent links  110   a,    110   b,  and may limit axial load on seal assemblies  240   a ,  240   b,  which may be positioned radially outward of thrust rings  220   a,    220   b  and form hermetic seals between adjacent links  110   a,    110   b  to retain the lubricating fluid in lubricating fluid cavity  190 . 
     Still referring to  FIGS. 3 and 4 , in some embodiments, track joint assembly  155  may also include an outer bushing  250 , which may be positioned coaxially around hushing  157  (making bushing  157  an inner bushing) to engage a drive sprocket (not shown) that rotates track assembly  100 . Outer bushing  250  may rotate relative to inner bushing  157  when it engages the drive sprocket, reducing wear on outer bushing  250  caused by sliding motion between outer bushing  250  and the drive sprocket. Such rotation may be facilitated by coating one or both of outer bushing  250  and inner bushing  157  with diamond like carbon or electroless nickel, or by carburizing, nitriding, or polishing one or both of outer bushing  250  and inner bushing  157  to reduce friction between outer bushing  250  and inner bushing  157 . Alternatively or additionally, lubricating fluid may be situated between outer bushing  250  and inner bushing  157 . This lubricating fluid may be the same as or different from the lubricating fluid situated between inner bushing  157  and pin  120 . 
     The lubricating fluid may be added during assembly of track joint assembly  155 , and may be contained in a lubricating fluid cavity  260  at least partially defined by a generally cylindrical inner surface  270  of outer bushing  250  and a generally cylindrical outer surface  280  of inner bushing  157  facing surface  270 . Lubricating fluid cavity  260  may be isolated from lubricating fluid cavity  190  so that a leak in lubricating fluid cavity  260  does not impact lubricating fluid cavity  190  (and vice versa). Lubricating fluid cavity  260  may extend into and be at least partially defined by one or more recesses in surface  270  or surface  280 . Alternatively or additionally, lubricating fluid cavity  260  may extend into and be at least partially defined by thrust rings  290   a,    290   b,  which may be disposed in bushing bores  160   a,    160   b,  and which may be positioned at axial ends  300   a,    300   b  of outer bushing  250  and coaxially around inner bushing  157 . Thrust rings  290   a,    290   b  may limit axial load on seal assemblies  310   a,    310   b,  which may form hermetic seals between outer bushing  250  and links  110   a,    110   b  to retain the lubricating fluid in lubricating fluid cavity  260 . 
     As shown in  FIG. 5  and discussed above, bushing  157  may be press-fit into bushing bores  160   a,    160   b.  In particular, axial end portions  320   a,    320   b  of bushing  157  may be disposed in and press-fit into outer portions  330   a,    330   b  of bushing bores  160   a,    160   b.  Additionally, axial end-adjacent portions  340   a,    340   b  of bushing  157  may be disposed in and press-fit into central portions  350   a,    350   b  of bushing bores  160   a,    160   b.  Thus, axial end portions  320   a,    320   b  may contact outer portions  330   a,    330   b,  and axial end-adjacent portions  340   a,    340   b  may contact central portions  350   a ,  350   b.  In some embodiments, outer diameters  360   a,    360   b  of end-adjacent portions  340   a,    340   b  may be larger than outer diameters  370   a,    370   b  of end portions  320   a,    320   b . Accordingly, outer portions  330   a,    330   b  may have different diameters than central portions  350   a,    350   b  to account for the differences between diameters  360   a,    360   b  and  370   a,    370   b.  In other embodiments, however, outer diameters  360   a,    360   b  of end-adjacent portions  340   a,    340   b  may be the same as outer diameters  370   a ,  370   b  of end portions  320   a,    320   b,  in which case outer portions  330   a,    330   b  might have the same diameters as central portions  350   a,    350   b.    
     Referring again to  FIG. 5 , inner surface  200  of bushing  157  may include a generally cylindrical inner surface  380  defining a bore  390 . Pin  120  may be positioned at least partially within bore  390  and its motion may thus be constrained by surface  380 . Accordingly, surface  380  may be a bearing surface. As shown, inner surface  380  may include three valley-shaped recesses  400 , each extending into and along a circumference of bushing  157 , and a sum of lengths  410  of recesses  400 , in an axial direction of bushing  157 , may be approximately 27% of a length  420  of surface  380 . It should be understood, however, that inner surface  380  may include a different number of recesses or differently sized recesses. For example, inner surface  380  may include between one and twenty recesses  400 , and the sum of lengths  410  may be between approximately 5% and approximately 75% of length  420 . It is contemplated, however, that, by using a plurality of recesses  400  (as opposed to a single larger recess  400 ), the structural integrity of bushing  157  may be maintained. It should also be understood that inner surface  380  may include differently positioned or shaped recesses. For example, inner surface  380  may include valley-shaped recesses extending along the axial direction of bushing  157 . Alternatively, inner surface  380  may include helical recesses extending along both circumferential and axial directions of bushing  157 . 
     Outer surface  280  of bushing  157  may include a generally cylindrical outer surface  430 , which may constrain motion of outer bushing  250 . Thus, surface  430  may be a bearing surface. As shown, outer surface  430  may include a different number of recesses than inner surface  380 , and its recesses may be offset, in the axial direction of bushing  157 , relative to those of inner surface  380  in order to avoid compromising bushing  157 &#39;s structural integrity. Specifically, outer surface  430  may include four valley-shaped recesses  440 , each extending into and along a circumference of bushing  157 , and a sum of lengths  450  of recesses  440 , in the axial direction of bushing  157 , may be approximately 37% of a length  460  of surface  430 . It should be understood, however, that outer surface  430  may include a different number of recesses or differently sized recesses. For example, outer surface  430  may include between one and twenty recesses  440 , and the sum of lengths  450  may be between approximately 7% and approximately 38% of length  460 . It is contemplated, however, that, by using a plurality of recesses  440  (as opposed to a single larger recess  440 ), the structural integrity of bushing  157  may be maintained. It should also be understood that outer surface  430  may include differently positioned or shaped recesses. For example, outer surface  430  may include valley-shaped recesses extending along the axial direction of bushing  157 . Alternatively, outer surface  430  may include helical recesses extending along both circumferential and axial directions of bushing  157 . In yet another alternative, outer surface  430  may include recesses that are aligned with (as opposed to offset relative to) those of inner surface  380 . 
     As shown in  FIG. 6  and discussed above, thrust ring  220   a  may be positioned at axial end  230   a  of bushing  157 . Thrust ring  220   a  may include a generally cylindrical outer surface  465 , which may support seal assembly  240   a.  In addition, thrust ring  220   a  may include a generally cylindrical inner surface  470 , which may at least partially define lubricating fluid cavity  190 . As shown, an outer diameter  480  of outer surface  465  (and thus thrust ring  220   a ) may be larger than outer diameter  370   a  of axial end portion  320   a  of inner bushing  157 . Specifically, outer diameter  480  may be approximately 1.16 times outer diameter  370   a.  Alternatively, outer diameter  480  may be another size. For example, outer diameter  480  may be between approximately 1.1 and approximately 2.0 times outer diameter  370   a.    
     Thrust ring  220   a &#39;s larger diameter may ensure that seal assembly  240   a  contacts only links  110   a,  not bushing  157 . Specifically, seal assembly  240   a  may contact a sealing portion  485  of link  110   a  at a seal-link interface  490 . As shown, an outer diameter  500  of seal-link interface  490  may be approximately 1.20 times outer diameter  370   a  of axial end portion  320   a  of inner bushing  157 . Alternatively, outer diameter  500  may be another size. For example, outer diameter  500  may be between approximately 1.05 and approximately 2.5 times outer diameter  370   a.    
     Sealing portion  485  may include a sealing surface  505  of inwardly offset end  140   a  of link  110   a  that faces outwardly offset end  150   a  of adjacent link  110   a.  It may be annular and surround axial end  230   a  of axial end portion  320   a,  and may include a different material from other portions of link  110   a,  That is, it may have different material properties from other portions of link  110   a.  The different material may have a different wear resistance than material of the other portions, and may better resist wear and corrosion resulting from sealing portion  485 &#39;s contact with seal assembly  240   a.  For example, the different material may be an electroless nickel coating, a nitride coating, or a carborized coating. In some embodiments, the different material may be a washer  510  attached to link  110   a.  For example, washer  510  may be press-fit into another portion of link  110   a,  welded to the other portion, fastened to the other portion with an adhesive, or held in the other portion by an annular biasing member positioned at an inner diameter or an outer diameter of washer  510 . In other embodiments, the different material may be clad (e.g., laser clad) to the material of the other portion of link  110   a.  Alternatively, the different material may be a laser hardened or a thermal sprayed material. In yet another alternative, the different material may be a thin film coating of for example, chromium nitride, amorphous diamondlike carbon, or tetrahedral amorphous carbon. 
     Referring to  FIGS. 7-9 , thrust ring  220   a  may include axial ends  520 - 1  and  520 - 2  connecting outer surface  465  of thrust ring  220   a  to inner surface  470  of thrust ring  220   a.  As shown, each of axial ends  520 - 1  and  520 - 2  may include two recesses  530 , which may extend from outer surface  465  to inner surface  470  to facilitate lubricating fluid flow between an exterior of thrust ring  220   a  and an interior of thrust ring  220   a.  Alternatively, axial ends  520 - 1  and  520 - 2  may include another number of recesses. For example, in some embodiments, axial end  520 - 1  may include a different number of recesses than axial end  520 - 2 . 
     As shown in  FIGS. 7-9 , inner surface  470  of thrust ring  220   a  may include three protrusions  540 , all extending along a circumference of thrust ring  220   a  and toward a central axis of thrust ring  220   a.  Protrusions  54 ( )may have approximately rectangular cross-sections  545 , and may be offset, in an axial direction of thrust ring  220   a,  from a center of thrust ring  220   a,  as best shown in  FIG. 9 . Some embodiments, however, may include different configurations of protrusions. For example, some embodiments may have only one protrusion, which may or may not extend along an entire circumference of thrust ring  220   a.  Other embodiments may have a plurality of protrusions, but such protrusions may be shaped or positioned differently than protrusions  540 . For example, instead of having approximately rectangular cross-sections, they may have approximately U-shaped or V-shaped protrusions, and they may or may not be offset from the center of thrust ring  220   a.    
       FIG. 10  illustrates another embodiment of a track joint assembly  155 ′ including a different bushing configuration. Instead of having inner bushing  157  and outer bushing  250 , track joint assembly  155 ′ may include only a single bushing  157 ′. Otherwise, track joint assembly  155 ′ may be identical to track joint assembly  155 . 
     Bushing  157 ′ may be similar to bushing  157 . Accordingly, only the ways in which bushing  157 ′ differs from bushing  157  will be described. Bushing  157 ′ may include a middle portion  570 ′ between axial end-adjacent portions  340   a ′,  340   b ′. Thus, middle portion  570 ′ may be separated from axial end portions  320   a ′,  320   b ′ by axial end-adjacent portions  340   a ′,  340   b ′. Middle portion  570 ′ may have an outer diameter  580 ′ that is larger than outer diameters  360   a ′,  360   b ′ of end-adjacent portions  340   a ′,  340   b ′ to maximize the amount of wear that middle portion  570 ′ may sustain as a result of engagement with the drive sprocket. For example, outer diameter  580 ′ may be approximately 1.49 times outer diameters  360   a ′,  360   b ′. It should be understood, however, that outer diameter  580 ′ may be another size. For example, outer diameter  580 ′ may be between approximately 1.2.5 and approximately 2.00 times outer diameters  360   a ′,  360   b ′. In some embodiments, middle portion  570 ′ may be positioned at least partially within inner portions  590   a ′,  590   b ′ of bushing bores  160   a ′,  160   b ′. In other embodiments, middle portion  570 ′ may not be positioned at least partially within inner portions  590   a ′,  590   b′.    
       FIG. 11  illustrates yet another embodiment of track joint assembly  155 ″ including different bushing and link configurations. Like track joint assembly  155 ′, instead of having inner bushing  157  and outer bushing  250 , track joint assembly  155 ″ may include only a single bushing  157 ″. Additionally, instead of having links  110   a,    110   b,  track joint assembly  155 ″ may include links  110   a ″ and  110   b ″. Bushing  157 ″ may be similar to bushing  157 ′, and links  110   a ″,  110   b ″ may be similar to links  110   a ′,  110   b ′ (and thus links  110   a,    110   b ). Links  110   a ″,  110   b ″ may differ from links  110   a ′,  110   b ′ only in that they include bushing bores  160   a ″,  160   b ″ having only two portions (outer portions  330   a ″,  330   b ″ and central portions  350   a ″,  350   b ″) instead of three portions (outer portions  330   a ′,  330   b ′, central portions  350   a ′,  350   b ′, and inner portions  590   a ′,  590   b ′). And bushing  157 ″ may differ from bushing  157 ′ only in that middle portion.  570 ″ may not be positioned at least partially within inner portions of hushing bores  160   a ″,  160   b ″. Otherwise, track joint assembly  155 ″ may be identical to track joint assemblies  155  and  155 ′. 
     The components of track joint assemblies  155 ,  155 ′,  155 ″ may be constructed of various materials. In some embodiments, links  110   a,    110   b,    110   a ′,  110   b ′,  110   a ″,  110   b ″; bushings  157 ,  157 ′,  157 ″; bushings  250 ; thrust rings  220   a,    220   b;  and thrust rings  290   a,    290   b  may be constructed of metal. For example, each of these components may be constructed of a ferrous metal, such as steel or iron. 
     The configuration of track joint assemblies  155 ,  155 ′,  155 ″ is not limited to the configurations discussed above and shown in the drawings. For example, outer surface  210  of pin  120  may include recesses instead of inner surface  200  of bushing  157 . Such recesses may be similar to recesses  440  in outer surface  280  of bushing  157 . As another example, inner surface  270  of outer bushing  250  may include recesses instead of outer surface  280  of bushing  157 . Such recesses may be similar to recesses  400  in inner surface  200  of bushing  157 . 
     INDUSTRIAL APPLICABILITY 
     The disclosed track joint assemblies may be applicable to track-type machines, such as, for example, loaders, tractors, excavators, and tanks, and may facilitate movement of the machines. The disclosed track joint assemblies may have various advantages over prior art track joint assemblies, For example, the disclosed track joint assemblies may be stronger and more durable than prior art track joint assemblies. In addition, manufacturing the disclosed track joint assemblies may cost less than manufacturing prior art track joint assemblies, and may require less material than manufacturing prior art track joint assemblies. Specific advantages of the disclosed track joint assemblies will now be described. 
     Track joint assembly  155  may include direct connections between links  110   a,    110   b  that strengthen and improve the durability of track joint assembly  155 . Specifically, inwardly offset ends  140   a,    140   b  of links  110   a,    110   b  may be directly connected by being secured to bushing  157 . Likewise, outwardly offset ends  150   a,    150   b  of links  110   a,    110   b  may be directly connected by being secured to pin  120 . Such direct connections between links  110   a,    110   b  may strengthen and improve the durability of track joint assembly  155  by reducing its susceptibility to vibrations and impacts. 
     Track joint assembly  155  may be configured to facilitate rotation of bushing  157  relative to pin  120  even when pin  120  is solid (and thus capable of being manufactured without using costly machining, drilling, or casting processes). In particular, the rotation may be facilitated by coating one or both of bushing  157  and pin  120  with diamond like carbon or electroless nickel, or by carburizing, nitriding, or polishing one or both of bushing  157  and pin  120  to reduce friction between bushing  157  and pin  120 . Alternatively or additionally, the rotation may be facilitated by situating a lubricating fluid between bushing  157  and pin  120 . Specifically, the lubricating fluid may be added through openings  180   a,    180   b  in links  110   a,    110   b , and may be contained in lubricating fluid cavity  190 . Since pin  120  is solid, rather than extending into an interior cavity of pin  120 , lubricating fluid cavity  190  may extend into and be at least partially defined by one or more recesses in inner surface  200  of bushing  157  or outer surface  210  of pin  120 . Alternatively or additionally, lubricating fluid cavity  190  may extend into and be at least partially defined by thrust rings  220   a ,  220   b.    
     Track joint assembly  155  may be configured to minimize the total amount of material required to manufacture links  110   a,    110   b.  Such minimization may be achieved by reducing the number of components disposed in bushing bores  160   a,    160   b  of links  110   a,    110   b.  For example, no collar or seal insert needs to be positioned between bushing bore  160   a  and bushing  157 , because the material of sealing portion  485  of link  110   a  may resist wear and corrosion resulting from sealing portion  485 &#39;s contact with seal assembly  240   a.  Thus, inwardly offset ends  140   a  of links  110   a  may be secured directly to bushing  157 , minimizing the number of components disposed in bushing bore  160   a  and thus the size of bushing bore  160   a  and link  110   a.  For example, the diameter of central portion  350   a  of bushing bore  160   a  may be less than 1.49 times the diameter of pin bore  170   a . Additionally, the diameter of central portion  350   a  of bushing bore  160   a  may be less than 0.87 times the outer diameter of outer bushing  250 . 
     Track joint assemblies  155 ,  155 ′ and  155 ″ may be optimized for specific applications but include many interchangeable parts to minimize manufacturing costs. For example, track joint assembly  155  may be optimized for high impact applications in which drive sprockets quickly wear down bushings connecting links  110   a,    110   b,  while track joint assemblies  155 ′ and  155 ″ may be optimized for low impact applications in which bushing wear is not a major concern. As discussed above, however, such optimizations only affect a few parts of track joint assemblies  155 ,  155 ′, and  155 ″. Thus, virtually all of the parts of track joint assemblies  155 ,  155 ′, and  155 ″ are interchangeable. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed track joint assemblies. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed track joint assemblies. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.