Abstract:
A method and apparatus for rebuilding a track chain assembly is disclosed which restores the ability of the pin joint to retain lubricant to its original condition. The method includes disassembling the track chain assembly, reassembling the track chain assembly and sealing the radial surface of the track bushing at a location radially inward or radially outward from the original seal location. The apparatus includes a seal assembly with a seal portion moved either inward or outward from the original seal location.

Description:
TECHNICAL FIELD  
       [0001]     This invention relates generally to track chain assemblies for track-type work machines, and more particularly to a method and apparatus for rebuilding such track assemblies.  
       BACKGROUND  
       [0002]     Track chain assemblies are used to support and propel track-type work machines and are typically constructed from a plurality of articulately coupled link sections, which have a plurality of track shoes bolted thereto. The link sections have a plurality of pivot joints provided by pin and bushing connections. In addition to forming a portion of the pivot joint, the bushing is used as the drive connection of the track chain with the vehicle through engagement with the drive sprocket of the work machine. As a result of the driving engagement of the bushing with the sprocket and the repeated articulation between seals positioned adjacent the end faces of the bushing, at least two points of wear are formed. The first point of wear being the outer diameter of the bushing that engages the sprocket receives a high amount of wear, while the opposite side of the bushing is substantially free of wear. The other point of wear being the axial end faces of the bushings where the seals are pressed against, to retain lubricant. Grooves form on these end faces due to the repeated articulation.  
         [0003]     In order to compensate for the one sided wear and to utilize the wear life available on the opposite, unworn side of the bushing, it has long been common practice to perform an operation, called “turning the bushings”. This term refers to the process of rotating the bushings relative to their respective links so as to expose the opposite, unworn side to the sprocket and to place the worn side away from the sprocket. The oldest and most common method of accomplishing the above bushing turn is through the complete disassembly of the track chain and then the reassembly of the chain with the bushings mounted in a new rotational position relative to their respective links. The process of disassembly causes a complete loss of the lubricant as well as causing the critical seals of the track to be disturbed. Newer methods leave the track assembled and rotate the bushing in place, such as the method disclosed in U.S. Pat. No. 4,554,720 issued on Nov. 16, 1985 and assigned to the owner of the present application. This method substantially reduces the labor involved and does not disturb the critical seals.  
         [0004]     Additionally, it has long been a desire to improve the corrosion and abrasion characteristics of the end faces of track bushings. Many approaches have been developed for treating the track bushings to improve both corrosion and abrasion resistance. One such approach is described in U.S. Pat. No. 6,089,683 issued on Jul. 18, 2000 and assigned to the owner of the present invention. This method uses a laser cladding process to lay an abrasion and corrosion resistant material in a groove positioned in the bushing end face. Another approach is disclosed in U.S. Pat. No. 6,102,408 issued on Aug. 15, 2000 and assigned to the owner of he present application. In this method a corrosion and abrasion resistant ring is resiliently bonded to the bushing end face. Both of the above approaches have shown great improvements in retaining lubricant throughout the life of a track chain.  
         [0005]     The present invention is directed toward overcoming one or more of the problems as set forth above.  
       SUMMARY OF THE INVENTION  
       [0006]     In one aspect of the present invention a method for rebuilding a track assembly is provided. The method includes disassembling a plurality of interconnected link sections of the track assembly; reassembling the plurality of interconnected link sections of the track assembly; sealing a plurality of track bushings at one of a radially inward and a radially outward seal portion away from an original seal location.  
         [0007]     In another aspect of the present invention a rebuilt track assembly is provided. The rebuilt track assembly includes a plurality of interconnected link sections. Each link section has a left hand track link having an outboard end portion and an inboard end portion, a right hand link having an outboard end portion and an inboard end portion, a bushing having an outer peripheral surface, a pair of end faces and a bore concentric with the outer surface. The bushing is positioned in the inboard end portion of the left and right hand links. The rebuilt track assembly also includes a track pin having a first and a second end portion being positioned in the outboard end portion of the left and right hand link sections. The track pin is pivotally positioned in the bore of the bushing. A seal assembly is positioned in a counter bore of the outboard end portion of the left and right hand link section and makes sealing contact with the pair of end faces of the track bushing radially inward or radially outward from the original seal position.  
         [0008]     In yet another aspect of the present invention a seal assembly for use with a rebuilt track assembly is provided. The track assembly includes a plurality of interconnected link sections with each link section including a left hand link, a right hand link, a track pin, and a bushing. The seal assembly includes a seal ring and a load member which are positioned in a counter bore of each of the left and right hand links. The load member is in biasing contact with the seal ring. The seal ring is adapted to contact the bushing at one of a radially inward and a radially outward seal portion away from an original seal position.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  is a fragmentary plan view of an exemplary track assembly (a portion of the track assembly is shown in a cross sectional view, for clarity of description);  
         [0010]      FIG. 2  is an enlarged fragmentary view of the encircled portion of  FIG. 1  and indicated  2 ; and  
         [0011]      FIG. 3  is an enlarged fragmentary view of the encircled portion of  FIG. 2  and indicated  3 . 
     
    
     DETAILED DESCRIPTION  
       [0012]     Referring now to the drawings and specifically to  FIGS. 1 and 2 , a portion of a track assembly  10  is shown. These track assemblies are used in a number of known track-type work machines (not shown) such as excavators, dozers, and the like. The track assembly  10  is constructed from a plurality of articulately coupled link sections  12 . Each link section  12  includes a set of links, one being a left hand link  14  (the right link in  FIG. 1 ) and the other being a right hand link  16  (the left link in  FIG. 1 ), a pin  18 , and a bushing  20 . The pin  18  has a first and a second end portion  17 , 19 . Each of the links  14 , 16  have opposite, laterally offsetting ends, an inboard end  22  and an outboard end  24 . The offset allows the outboard end  24  of the links of one link section  12  to overlap the inboard ends  22  of the next succeeding link section.  
         [0013]     The inboard ends  22  of the links  14 , 16  each have a larger bore  26  for receiving a respective end of the larger diameter bushing  20 . The outboard ends  24  of the links  14 , 16  each have a smaller bore  28  for receiving a respective end of the smaller diameter pin  18 . The ends of the pins  18  and the bushings  20  are secured into their respective bores  28 , 26  by means of a heavy press fit or other suitable means which is sufficiently great to secure and maintain the pins  18 , bushings  20 , and links  14 , 16  of each of the link sections  12  as a rigid, unitary member. The pin  18  of one link section  12  is pivotally received within a bore  30  of the bushing  20  of the adjoining link section  12  for providing a hinge joint  32  between the adjoining link sections  12 .  
         [0014]     The bushings  20  have an outer peripheral surface  34  that, in use, is drivingly engaged by the drive sprocket (not shown) of a track-type work machine (not shown). As the bushings  20  are maintained in a fixed angular relation to their respective link section  12 , the drive sprocket only contacts a portion of the outer peripheral surface  34  of the bushing  20 , causing a wear pattern  36  on one side of the outer peripheral surface  34  of the bushings  20 . The wear pattern  36  is indicated in phantom in  FIG. 1 .  
         [0015]     Referring now to  FIGS. 2 and 3 , each bushing  20  has a pair of end faces  38  (only one end is shown in  FIGS. 2 and 3 ) with a seal assembly  40  in sealing contact therewith. The seal assembly  40  is disposed within a counter bore  42  positioned in the outboard end  24  of each link  14 , 16 . Over time during normal operation a radial groove corresponding to an original seal location  43  is formed in the bushing end face  38 , prior to the bushing turning operation, where the original seal assembly (not shown) makes contact with the bushing end face  38 . The seal assembly  40  has a central axis  44 , which is the pivot axis of adjoining link sections  12  as seen in  FIGS. 1 and 2 . Seal assembly  40  includes a load member  46  and a seal ring  48 .  
         [0016]     The load member  46  includes a body portion  50  made from any of a number of known resilient materials commonly used to manufacture seals such as elastomeric or rubber compounds, but it could be made from any of a number of materials or combinations thereof. The body portion  50  of the resilient load member  46  has a first radial portion  52  and a first linear peripheral portion  54 . The first linear peripheral portion  54  is spaced from and extends generally parallel with the axis  44 . The first radial portion  52  is generally perpendicular with the axis  44 . The resilient load member  46  also includes a second linear peripheral portion  56  and a second radial portion  58 . The second linear peripheral portion  56  is positioned on the opposite side of the body portion  50  and is spaced from first linear peripheral portion  54 . The second radial portion  58  is positioned on the opposite side of the body portion  50  parallel to and spaced from the first radial portion  52 . A first concave surface  60  is positioned between and joins the first radial portion  52  and the first linear peripheral portion  54 . A second concave surface  62  is located on the opposite side of the body portion  50  spaced from the first concave surface  60  and is positioned between and joins the second linear peripheral portion  58  and the second radial portion  56 . The first concave surface  60  generally has a larger radius than the second concave surface  62 . The second radial portion  56  and the first linear peripheral portion  54  contact a sidewall  64  and a bottom  66 , respectively of the counter bore  42  of the inboard end portion  22 .  
         [0017]     Seal ring  48  has a body portion  68 . Body portion  68  has a first leg  70  that extends along the first linear peripheral portion  54  of the resilient load member  46  and a second leg portion  72  that extends along the second radial portion  58 . A seal portion  74  is positioned on the second leg  72  of the seal ring  48  parallel to and spaced from the second radial portion  58  of the resilient load member  46 . Seal portion  74  contacts a radial surface  76  of the bushing end face  38  that is shown as being radially inward from the radial groove  43 . However, it should be understood that the seal portion  74  might be configured to contact the radial surface  76  radially outward from the radial groove  43  and still retain the desired function. The second leg  72  of the seal ring  48  also includes a debris relief portion  78  adjacent to the seal portion  74  and opposed to the radial groove  43 . Debris relief portion  78  is a reduced width in the second leg  72  radially outward from the central axis  44 . In the embodiment shown the seal portion  74  of the seal ring  48  is manufactured from a polycarbonate material and the body portion  68  is manufactured from a polyurethane material. Other suitable materials may be used for the seal portion  74  and the body portion  68  of the seal ring  48  and still retain the functional attributes as described herein.  
       INDUSTRIAL APPLICABILITY  
       [0018]     During normal operation of a track-type work machine at least two locations of wear occur in components of the track assembly  10 . The first wear location occurs on the outer surface  34  of the track bushing  20  at the point where the sprocket makes contact therewith forming the wear pattern  36 . The other location is at the original seal location  43  at the intersection of the bushing end face  38  and the seal ring  48  of the seal assembly  40 . When these wear points reach a predetermined level of wear or the hours of use reach a predetermined limit, based on the specific working environment, the track assembly  10  can be rebuilt.  
         [0019]     The rebuild process for the current track assembly  10  is performed by first disassembling adjoining link sections  12  from one another. This is done by pressing the track pin  18  from the bore  28  from the outboard end  24  of both left and right hand links  14 , 16 . The bushings  20  are then pressed from the bore  26  of the inboard end  22  of the left and right track links  14 , 16 . The original seal assembly (not shown) is then removed from the counter bore  42  of the outboard end  24  of the links  14 , 16  and discarded. A new seal assembly  40  is placed in the counter bore  42 . Each bushing  20  is then turned to expose an unworn side to the sprocket (not shown) and position the wear pattern  36  in a position so as to not make contact with the sprocket. The bushings  20  are then pressed back into the bore  26  of the inboard end  22  of each link  14 , 16 . The adjoining link sections  12  are rejoined by pressing the track pins  18  back through the bore  28  of the outboard end  24  of one link  14 , 16  through the bore  30  of the bushing  20  and into the bore  28  of the other link  14 , 16 .  
         [0020]     The seal assembly  40  makes sealing contact with the radial surface  76  of the pair of end faces  38  of each bushing  20  at a location radially away from the radial groove/original seal location  43 . In the example shown in the  FIGS. 2 and 3 , the position of the seal portion  74  of the seal assembly  40  is radially inward from the groove  43  however it should be understood that radially outward would work as well. With the seal assembly  40  contacting a location away from the original seal location  43 , the sealing effectiveness is brought back to the original condition. That is, not only is the bushing  20  turned so that the sprocket engages an unworn portion of the outer surface  34  but also the sealing effectiveness between the pair of end faces  38  and the seal portion  74  of the seal assembly  40  is restored to the original production condition. Additionally, the debris relief portion  78  of the seal ring  48  allows for material to be alleviated therefrom. Any debris build up is eliminated from the debris relief portion  78  due to the increased area provided between the pair of end faces  38  and the seal assembly  40  during the repeated articulation there between.