Patent Publication Number: US-2021179212-A1

Title: Track joint assembly for ground-engaging track having track pin with enlarged center section

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to a track joint assembly, and more particularly to a track pin having a center section with an enlarged diameter relative to ends of the track pin. 
     BACKGROUND 
     Various machines used in off-highway environments utilize tracks as ground-engaging propulsion elements, notably, track-type excavators and track-type tractors. Such tracks typically include rotatable track-engaging elements, with each of two tracks at opposite sides of the machine forming endless loops moved about the rotating elements during operation. Two parallel chains of coupled-together links, with bolted-on track shoes, is a typical configuration for each individual track. The demands placed upon such machines and their associated tracks can be quite substantial depending upon operating environment and particular working application. Machine tracks used in so-called production dozing, for example, are typically designed with more or less continuous travel and harsh underfoot conditions of the machine in mind, as the machine will commonly be driven to dig, push, and distribute material nearly continuously during service. Other applications including, for example, excavator applications, often employ tracks designed for softer or otherwise less challenging underfoot conditions and designed for only intermittent driving of the machine since much of excavating work takes place while the machine is stationary. 
     Understanding and addressing wear phenomena in machine tracks has received considerable engineering attention in recent years. The various wear phenomena and wear rates experienced by machine track are typically a result of how the machine is used as noted above, the skill and experience of the operator, and the particular underfoot conditions and substrate materials encountered in the operating environment. Field service life of machine track can vary based upon these and other factors. Since machine track components can be relatively expensive to service and replace, not to mention the negatives of machine downtime, engineering efforts in this field have often centered around reducing and managing wear between and among components. U.S. Pat. No. 4,150,856 to Hakkenburg et al. discloses one known example of a machine track design, including a one-piece track pin. 
     SUMMARY OF THE INVENTION 
     In one aspect, a track joint assembly includes a first track chain and a second track chain each having track links with an outboard link strap having an outboard pin bore, and an inboard link strap having an inboard pin bore. The track joint assembly also includes a track pin defining a longitudinal axis and having a first pin end, a second pin end, and a center section extending from the first pin end to the second pin end and having an outer wear surface. The track joint assembly also includes a first track joint having an outboard link strap in a track link in the first track chain, the first pin end, a first interference-fitted insert within the respective outboard pin bore and supporting the first pin end for rotation, and a first bearing surface extending circumferentially around the longitudinal axis. The first track joint further includes an inboard link strap in a track link in the first track chain, and a first portion of the center section positioned in the respective inboard pin bore. The track joint assembly further includes a second track joint having an outboard link strap in a track link in the second track chain, the second pin end, a second interference-fitted insert within the respective outboard pin bore and supporting the second pin end for rotation, and a second bearing surface extending circumferentially around the longitudinal axis. The second track joint further includes an inboard link strap in a track link in the second track chain, and a second portion of the center section positioned in the respective inboard pin bore. A track guiding space extends between the first track chain and the second track chain. The center section of the track pin has an enlarged diameter, relative to the first pin end and the second pin end, and the outer wear surface is exposed to the track guiding space. 
     In another aspect, a ground-engaging track system includes a track roller frame, and a ground-engaging track having a first track chain and a second track chain, each including track links, and track pins coupling the first track chain and the second track chain together. The track links each include an outboard link strap and an inboard link strap. The track pins each include a first pin end extending through and supported for rotation in an outboard link strap in a track link in the first track chain, a second pin end extending through and supported for rotation in an outboard link strap in a track link in the second track chain, and a center section extending from the first pin end to the second pin end. A track guiding space extends between the first track chain and the second track chain. The center section of each of the track pins includes an enlarged diameter, relative to the first pin end and the second pin end, positioned in part within inboard link straps in each of the first track chain and the second track chain and forming an outer wear surface exposed to the track guiding space. 
     In still another aspect, a track pin for a track joint assembly in a ground-engaging track system includes a solid pin body defining a longitudinal axis extending between a first pin end having a first terminal end surface, a second pin end having a second terminal end surface, and a center section extending between the first pin end and the second pin end. The center section includes a first lead-in chamfer and a second lead-in chamfer formed adjacent to the first pin end and the second pin end for interference-fitting, respectively, a first portion and a second portion of the center section with inboard link straps in the second track chain and the second track chain. The solid pin body has a full axial length, and the first pin end and the second pin end each have a pin end axial length. The center section has an enlarged diameter, relative to the first pin end and the second pin end, and a center section axial length. The enlarged diameter is greater than the pin end axial length. The center section axial length is from 60% to 63% of the full axial length, and from 314% to 318% of the pin end axial length. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagrammatic view, partially open, of a machine having a ground-engaging track system, according to one embodiment; 
         FIG. 2  is a partially sectioned diagrammatic view of a track joint assembly, according to one embodiment; 
         FIG. 3  is a sectioned side diagrammatic view of a track joint assembly, according to one embodiment; 
         FIG. 4  is a sectioned side diagrammatic view of a track joint assembly, according to one embodiment; and 
         FIG. 5  is a sectioned side diagrammatic view of a track pin, according to one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , there is shown a machine  10  according to one embodiment, and including a frame  12 , an operator cab  14  and an implement system  16 . Machine  10  further includes a ground-engaging track system  18  for moving machine  10  about a work area. Machine  10  is shown in the context of an excavator, where cab  14  and implement system  16  can be rotated about ground-engaging track system  18 . Ground-engaging track system  18  includes a first track  20  and a second track  22  positioned at opposite sides of frame  12 . Description and discussion of features and functionality of track  20  and associated components can be understood to refer by way of analogy to track  22 , as the respective tracks will typically be substantially identical. Track system  18  also includes a track roller frame  24  structured to support a plurality of rotatable track engaging elements, including a drive sprocket  26  visible in the illustration of  FIG. 1 , an idler typically positioned at an opposite end of track roller frame  24  from sprocket  26 , track rollers structured to support much of the weight of machine  10  and distributed between the idler and drive sprocket  26 , and carrier rollers supporting track  20  above track roller frame  24 . Track  20  also includes a first track chain  30  and a second track chain  32 , and a plurality of track pins  34  coupling together first track chain  30  and second track chain  32 . In  FIG. 1 , drive sprocket  26  is shown in contact with track pins  34 , and can be rotated to advance track  20  about the various rotatable track-engaging elements in an endless loop to move machine  10  about a work area. A plurality of track shoes  36  may be mounted to first track chain  30  and second track chain  32 , such as by bolting in a generally conventional manner. As will be further apparent from the following description, ground-engaging track system  18  may be uniquely configured for improved resistance to degradation or failure of components and extended service life compared to known systems. 
     Referring also now to  FIG. 2 , ground-engaging track system  18  can include a plurality of track joint assemblies  38 , one of which is shown in partially sectioned view. Track joint assembly  38  includes a first track chain  30  and a second track chain  32  each including track links  40  and  42  having, respectively, an outboard link strap  44  and  46  with an outboard pin bore  48  and  50 . Track links  40  and  42  also include, respectively, an inboard link strap  52  and  54  with an inboard pin bore  56  and  58 . In the illustrated embodiment, track links  40  and  42  are mirror images of one another, and have an offset configuration where outboard link straps  44  and  46  are laterally offset relative to inboard link straps  52  and  54 . 
     Track joint assembly  38  further includes a plurality of track pins  34  each including a solid pin body  35 , and each defining a longitudinal axis  60 . The plurality of track pins  34 , hereinafter referred to in the singular, each include a first pin end  62 , a second pin end  64 , a center section  66  extending from first pin end  62  to second pin end  64  and having an outer wear surface  68  that contacts drive sprocket  26  within sprocket pockets alternating with sprocket teeth. First track chain  30  includes a first track rail  55  and second track chain  32  includes a second track rail  57 . An idler and track rollers (not shown) can ride on track rails  55  and  57  in a generally conventional manner. First pin end  62  includes a first terminal end surface  88  and second pin end  64  includes a second terminal end surface  90 . 
     Track joint assembly  38  further includes a first track joint  70  that includes an outboard link strap  44  in a track link  40  in first track chain  30 , first pin end  62 , a first interference-fitted insert  72  within the respective outboard pin bore  48  supporting first pin end  62  for rotation, and a first bearing surface  74 . First bearing surface  74  extends circumferentially around longitudinal axis  60 , and is located radially between first pin end  62  and outboard link strap  44 . First track joint  70  further includes an inboard link strap  52  in a track link  40  in first track chain  30 , and a first portion  76  of center section  66  positioned in the respective inboard pin bore  56 . Track joint assembly  38  also includes a second track joint  78  including an outboard link strap  46  in a track link  42  in second track chain  32 , second pin end  64 , and a second interference-fitted insert  80  within the respective outboard pin bore  50  and supporting second pin end  64  for rotation. Second track joint  78  also includes a second bearing surface  82  extending circumferentially around longitudinal axis  60 , and positioned radially between second pin end  64  and outboard link strap  46 . Second track joint  78  still further includes an inboard link strap  54  in a track link  42  in second track chain  32 , and a second portion  84  of center section  66  positioned in the respective inboard pin bore  58 . 
     In the illustrated embodiment, first portion  76  and second portion  84  of center section  66  are interference-fitted in the respective inboard pin bores  56  and  58 . Also in the illustrated embodiment, each of first interference-fitted insert  72  and second-interference-fitted insert  74  extends axially through the respective outboard pin bore  48  and  50 . Each of first track joint  70  and second track joint  78  may further include a rotatable bushing  94  and  95  having the respective bearing surfaces  74  and  82  formed thereon. 
     As noted above, first pin end  62  and second pin end  64  are supported for rotation by way of first interference-fitted insert  72  and second interference-fitted insert  80 . Each of first interference-fitted insert  72  and second interference-fitted insert  80  may include an inwardly extending flange portion  96  and  97 , respectively, with rotatable bushings  94  and  95  being trapped axially between center section  66  of track pin  34  and the respective inwardly extending flange portion  96  and  97 . Each of first track joint  70  and second track joint  78  may further include a pin retainer  98  and  99  positioned outboard of and adjacent to the respective inwardly extending flange portion  96  and  97 . Track pin  34  may also have formed therein a first circumferential groove  41  on first pin end  62 , and a second circumferential groove  43  on second pin end  64 . Each of pin retainer  98  and pin retainer  99  may include a snap ring fitted into the corresponding groove  41  and  43  as shown, and contacted by inwardly flange portions  96  and  97 , respectively, to maintain desired relative axial positioning of first pin end  62  and second pin end  64  in outboard link straps  44  and  46 . In alternative embodiments, welded-on plates could be attached to first pin end  62  and  64  in lieu of snap rings within grooves, or some other pin retention strategy could be used. 
     Also in the illustrated embodiment seals, such as lip seals, may be positioned in first track joint  70  and second track joint  78 , including a first seal  91  at an inboard position in track joint  70 , and a second seal  96  at an outboard position. Another seal  93  may be positioned at an inboard position in track joint  78 , and yet another seal  92  positioned at an outboard position in track joint  78 . Bushings  94  and  95  could be self-lubricating bushings or bearings, with no internal lubricant supplied. Each of track joint  70  and track joint  78  could also be grease lubricated. In an excavator implementation the relatively low proportion of tramming time, and other service conditions ordinarily expected, can be consistent with ground-engaging track system  18  being a dry track system, or lubricated by way of self-lubricating or greased bearings. Track system  18  differs from certain other track systems, notably track systems used in many excavators, in that outboard portions of track joints  70  and  78  are rotating pin joint connections, in contrast to other systems where the track pin is interference-fitted with and therefore does not rotate relative to outboard link straps. Also in contrast to certain known track systems and track joint assemblies, no bushing is positioned upon track pin  34  and, instead, contact with sprocket  26  is direct contact between outer wear surface  68  and sprocket  26 . 
     It will be recalled that first portion  76  of center section  66  and second portion  84  of center section  66  may be interference-fitted within inboard link straps  52  and  54 , respectively. Accordingly, inboard link straps  52  and  54  do not rotate in such an implementation relative to pin  34  as track  20  is advanced about the various rotatable track-engaging elements. A track guiding space  86  extends between first track chain  30  and second track chain  32 . Center section  66  of track pin  34  has an enlarged diameter, relative to first pin end  62  and second pin end  64 , and outer wear surface  68  is exposed to track guiding space  86 . It can further be noted that track pin  34  has a stepped profile within each of first track joint  70  and second track joint  78 . In addition to omitting a center bushing, track joint assembly  38 , and other track joint assemblies contemplated herein, differs from certain known designs in that the relatively enlarged diameter of track pin  34  provides sacrificial wear material of track pin  34  itself that can be gradually worn away over the course of a service life of ground-engaging track system  18 . 
     Referring now to  FIG. 3 , there is shown a track joint assembly  138  according to another embodiment, and using certain reference numerals to identify features that may be the same or identical to features described in connection with the preceding embodiment. Track joint assembly  138  includes a first track joint  170  and a second track joint  178  including track chains  130  and  132  with track rails  155  and  157 , respectively. A track guiding space  186  extends between track chains  130  and  132 . A track shoe  36  is shown attached to track chains  130  and  132 . Track joint assembly  138  also includes a track pin  34  having an outer wear surface  68 , with track pin  34  potentially being substantially identical to the track pin discussed in connection with the preceding embodiment. Track joint assembly  138  differs from the preceding embodiment in that rather than a system of interference-fitted inserts and bushings to support opposite ends of track pin  34 , only a single inserted element is provided in each track joint to support track pin  34  for rotation. Track pin  34  can include an outer bearing surface  134  formed directly thereon, and rotatable within an interference-fitted bushing  172 . Another bearing surface  182  is shown at an opposite end of track pin  34 . Track pin  34  may be interference-fitted with inboard track links in track chains  130  and  132  in a manner generally analogous to that of the preceding embodiment. 
     Referring now to  FIG. 4 , there is shown a track joint assembly  238  according to another embodiment and including a first track chain  230  and a second track chain  232 . A first track joint is shown at  270  and a second track joint is shown at  278 . Retention of track pin  234  in an outboard link strap  244  can be generally analogous to the embodiment of  FIG. 2  where a first pin end  262  of track pin  234  is supported for rotation. A second pin end  264  may be analogously configured and supported. Track pin  234  also includes a center section  266  having an enlarged diameter, relative to first pin end  262  and second pin end  264 . A track guiding space  286  extends between track chain  230  and track chain  232 . Reference numeral  246  identifies an inboard link strap in track chain  230 . Rather than being interference-fitted with inboard link straps, track pin  234  and center section  266  may be rotatably supported and track joint assembly  238  may thus include bearing surfaces, one of which is labeled at  277 , rotatably supporting center section  266  within each of the subject inboard link straps. 
     Referring now to  FIG. 5  in particular, track pin  34  may be dimensioned and proportioned in a manner that enables the desired configurations and functionality of first track joint  70  and second track joint  78  in at least certain embodiments. A first lead-in chamfer  100  and a second lead-in chamfer  102  are formed on center section  66  adjacent to first pin end  62  and second pin end  64  for interference-fitting, respectively, first portion  76  and second portion  84  of center section  66  with inboard link straps  52  and  54  in first track chain  30  and second track chain  32 . Track pin  34 , including solid pin body  35 , has a full axial length  400  extending between first terminal end  88  and second terminal end  90 . First pin end  62  and second pin end  64  may each have a pin end axial length  430 , with the pin end axial length  430  being equal on each of first pin end  62  and second pin end  64 . It will also be recalled center section  66  has an enlarged diameter shown via reference numeral  410  in  FIG. 5 . Enlarged diameter  410  is greater than pin end axial length  430 . Center section  66  also has a center section axial length  420 . Center section axial length  420  is from 60% to 63% of full axial length  400 , and from 314% to 318% of pin end axial length  430 . In a refinement, enlarged diameter  410  is 50% to 51% of center section axial length  420 , and 61% of full axial length  400 . Also in the refinement center section axial length  420  is 318% of pin end axial length  430 . A pin end diameter is shown at  440  in  FIG. 5 , and may be approximately equal to pin end axial length  430 . In a further refinement, full axial length  400  is about 200 millimeters, more particularly 207 millimeters. In the further refinement, pin end axial length  430  is about 40 millimeters. In the further refinement, enlarged diameter  410  is about 60 millimeters, and more particularly 63 millimeters. In the further refinement center section axial length  420  is about 130 millimeters, more particularly 127 millimeters. The term “about” is understood herein to mean generally or approximately, for example using conventional rounding such that “about 127 millimeters” means from 126.5 millimeters to 127.4 millimeters, within measurement error. In other instances, the term about could have a different or broader meaning to a person skilled in the art than conventional rounding practices, depending upon context. 
     INDUSTRIAL APPLICABILITY 
     As discussed above, ground-engaging track system  18 , and other track systems contemplated herein, departs from conventional designs in various ways. Track systems are often purpose-built for certain types of machines and/or certain types of working applications. For these and other reasons, track configurations that provide fixed interfaces between certain components, and rotating interfaces between other components, are often not readily adapted to other configurations without potentially affecting the manner and extent of wear or other relationships between or among components. In the present case, ground-engaging track system  18 , and track pin  34  in particular, is configured in a manner that can be expected to be installed and operated in a machine such as an excavator without significant modifications or alterations to the track system, or undesired changes in the expected wear patterns or service life. In other words, ground-engaging track system  18  can be installed to an existing excavator platform quite easily. This is due, at least in part, to the design of track pin  34 , including its dimensions and proportions, which do not alter factors such as pitch or track width as compared to earlier strategies, and does not require a bushing on the track pin, or further additional components. 
     The present description is for illustrative purposes only, and should not be construed to narrow the breadth of the present disclosure in any way. Thus, those skilled in the art will appreciate that various modifications might be made to the presently disclosed embodiments without departing from the full and fair scope and spirit of the present disclosure. Other aspects, features and advantages will be apparent upon an examination of the attached drawings and appended claims. As used herein, the articles “a” and “an” are intended to include one or more items, and may be used interchangeably with “one or more.” Where only one item is intended, the term “one” or similar language is used. Also, as used herein, the terms “has,” “have,” “having,” or the like are intended to be open-ended terms. Further, the phrase “based on” is intended to mean “based, at least in part, on” unless explicitly stated otherwise.