Abstract:
A roller-chain bushing with a stress-relief opening centrally located along the seam of a rolled or roll-formed bushing has a tapered or relief segment at each bushing end to permit compressive fitting of the bushing ends into a link-plate hole thereby minimizing deformation of the bushing end, which tapered or relief segment is locally deformed or worked at a specific location prior to forming the bushing and the tapered segment is provided in a bushing region diametrically opposite the seam to reduce barreling of the bushing at mating of the bushing with the roller link-plate, and positioning of the tapered region along the chain pitch line at the point of stress concentration during chain assembly reduces the initial wear of the pin and bushing from initial chain loading.

Description:
BACKGROUND OF THE INVENTION 
     The present invention provides a bushing for a chain. More specifically, a roller-chain bushing has a relief zone provided in proximity to each of its edges, which relief zones are in areas to be compressed or compacted at press fitting of the bushing into an aperture of a bushing-link-plate along the pitch-line of the chain. The bushing-edge relief zone allows movement of bushing material to permit greater continuity and a consequent increase of the contact area between the link pin and the bushing, especially at initial contact between these two elements. 
     Roller chain assemblies generally utilize bushing-links and pin links with spaced apart apertures. A generally cylindrical bushing extends through a roller and between parallel bushing-links, which bushing is press fit into the juxtaposed apertures of the respective links. A pin extends through the bushing to secure the parallel link plates, roller and bushing to form a single link. 
     During assembly of the roller chain, the bushing is secured to the bushing link by press fitting it into the apertures of a bushing link. The as-formed bushings are generally a uniform cylinder, however, press fitting a bushing into the bushing-link holes or apertures deforms the cylinder ends. Bushing-end deformation results in deflection of the cylindrical shape, the inner diameter and the outer diameter of the bushing body, which resulted from the movement of material during press-fitting of the bushing ends. In an early effort to acconmmodate this material movement, material was removed from the bushing blank prior to roll-forming the bushing, which provided an opening or void in the bushing body to assimilate displaced material. This void may be considered as a degree of freedom for the central portion of the bushing. Thus, when the bushing cylinder ends are being deformed during the press fitting operation any movement of material along the bushing barrel-body would presumably be absorbed by the centrally positioned opening in the bushing body. 
     U.S. Pat. No. 2,424,087 to Focke et al. considered that smoother and denser surfaces of pitch holes in the side plates along with more tightly fit pins or bushings in those pitch holes provided greater fatigue resistance to the chain against failure by fracture of the side plates. 
     In another case, it had been indicated that press fitting the bushings into the holes induced residual compressive stress in the material surrounding the holes, which promoted increased fatigue resistance of the outer side plates. As a consequence, it was felt that the increased initial stress in the region of the bushing-receiving holes promoted increased fatigue resistance of the inner side plates. Further, U.S. Pat. No. 2,994,186 to Morrow asserted that utilizing a drift pin to cold work the region around the link plate holes both before and after heat treatment further increases the fatigue resistance of the link plates. The redrifting operation was used to produce improved fatigue resistance in the link plates and also to materially aid the extremely tight fits between the bushing and the link plate, which tight fits were considered to enhance the fatigue resistance of the link plates in the assembled chain. 
     Pressing a chain bushing into the pitch-holes of a bushing link compresses the bushing ends and alters the inner and outer diameter of the bushing. This alteration of the cylinder inner diameter is referred to in the industry as bushing collapse or barreling. As the chain operates, the pin bears, or should bear, against the inside wall of the bushing. As a result of the bushing collapse, the initial contact area between the pin and the bushing inner wall is limited to approximately point contact at the ends of the bushing where the inside diameter is at a minimum. The reduction of contact area between the pin and the bushing causes more rapid initial wear and elongation of the chain during operation. 
     Although the strength of the material surrounding the link hole may be enhanced by the mechanical working from the localized deformation experienced at press fitting of the bushing, the deformation of the bushing at its ends does not enhance the wear properties nor the fatigue properties of the chain. Rather, as noted above, the initial contact between the pin and the bushing is limited to a very small contact area within the bushing-link hole from the compression and deformation of the bushing at press fitting of the bushing and link. In one case, large deformation of the bushing-end deformation at press fitting into the bushing link has been avoided by rolling the edges of the unformed bushing blank to provide a tapered, or reduced, cross-sectional region at the bushing ends. The reduced cross-section avoids large compressive loads and bushing deformation during mating of the bushing and bushing link. 
     Changing the total circumference of the ends of the bushings manufactured from strip material requires an added and expensive operation, that is a separate strip rolling operation. The present invention eliminates the separate strip rolling operation by tapering the bushing blank only at its contact area with the pin along the pitch-line of the chain, which greatly reduces the amount of cold working required to achieve the needed taper. The taper may be provided by various methods, such as roll-forming the taper during blanking of the preform into the bushing or by coining, for example. Other exemplary cold working techniques include swaging, stamping or forging. 
     SUMMARY OF THE INVENTION 
     The present invention provides a roller-chain bushing having a stress-relief opening centrally located along the seam of a rolled or roll-formed bushing. A tapered or relief segment at the bushing ends permits compressive fitting of the bushing ends into a link-plate hole minimizing deformation of the bushing end. Particularly, the bushing inner circumference is locally deformed or worked, such as by coining, at a specific location prior to forming the bushing. The unformed bushing blank is deformed, tapered or worked in a region where the formed bushing will provide the worked region at the bushing ends diametrically opposite the seam. Locating the tapered region in this position avoids, reduces or compensates for barreling of the bushing body at mating of the bushing with the roller link-plate. Placing the tapered region along the chain pitch line at the point of stress concentration during assembly of the chain reduces the initial wear of the pin and the bushing from initial chain loading. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     In the figures of the drawing, like reference numerals identify like components, and in the drawing: 
     FIG. 1 illustrates a plan view of an exemplary roller chain section with a cross-sectional portion of the chain links; 
     FIG. 2 shows an elevational view of a segment of the chain in FIG. 1 with a link end noted in cross-section; 
     FIG. 3 is a plan view of a prior art unformed bushing blank with a stress-relief segment provided at opposing edges; 
     FIG. 4 is a formed bushing of the blank in FIG. 3 with the stress-relief segments in facing alignment and centrally located along the seam of the formed bushing; 
     FIG. 5 is a partial cross-sectional view of a chain link along the line  5 — 5  in FIG. 1; 
     FIG. 6 is a plan view of an unformed blank with the deformed or tapered region noted thereon; 
     FIG. 7 is an end-view of the unformed blank of FIG. 6; 
     FIG. 8 is an enlarged view of the noted end of the blank in FIG. 7; 
     FIG. 9 illustrates a pair of formed bushings in phantom outline with the cold-worked regions noted in solid line; 
     FIG. 10 is a chain segment with the formed bushings oriented along the pitch line and press-fit into bushing links to provide greater contact area between the bushing inner surface and the link-pin; and, 
     FIG. 11 is a longitudinal cross-section of a bushing mated into bushing links. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In FIGS. 1 and 2, a segment or section of roller chain  10  is noted in plan and elevational views, respectively, with partial cross-sectional views of pin and link portions. More specifically, roller chain  10  has alternately arranged bushing links and pin links along each side of chain  10 , which has bushing link-plate  12 , pin link-plate  14 , pins  16 , bushings  18  and rollers  20 . Bushing  18  includes stress-relief opening  22  along bushing seam  24 , which opening  22  is noted as a diamond outline in FIGS. 4 and 5. The connected links in FIG. 1 provide gaps  26  for receipt of sprocket teeth (not shown). 
     Each bushing or roller link has a pair of bushing or roller link-plates  12 , which are parallel and laterally spaced along the length of chain  10 . Each link-plate  12  has first pitch-hole or aperture  28  and second pitch-hole or aperture  30  spaced along pitch-line  32  of chain  10 , as noted in FIG.  1 . Bushings  18  extend between parallel bushing link-plates  12  at each set of apertures  28  and  30 , which bushings  18  are tightly received in apertures  28  and  30  at first bushing end  34  and second bushing end  36 . Rollers  20  are positioned on outer surface  21  of each bushing  18 , which rollers  20  bear upon the teeth of a sprocket associated with chain  10 . 
     Pin links have a pair of parallel pin-link plates  14  with first port  40  and second port  42  along pitch line  32 . Rivets or pins  16  extend between first ports  40  and through bushings  18  at each aligned set of apertures  28 ,  30  and ports  40 ,  42 , respectively. 
     Each bushing  18  suffers a measure of deformation along both the length of its body as well as it its ends  34  and  36  when it is tightly fit or press fit into a bushing-link aperture  28  and  30 , as noted in FIGS. 10 and 11. The specific deformation, or amount of deformation, of bushing  18  may vary with the placement of seam  24  and stress-relief opening  22 . However with this deformed configuration, it can be appreciated that positioning of cylindrical link pin  16  through bushing  18  will result in contact between pin  16  and bushing  18  primarily at the mated and constricted position of bushing  18  in bushing-link apertures  28  and  30 . This contact area between pin  16  and bushing  18  can be considered as aligned along pitch line  32  since assembly of chain  10  provides stress-relief openings  22  of each bushing link in a facing position along line  32 . 
     Roller-link chains  10  are generally constructed in the above-noted manner, as known in the art. It is also known that tightly fit bushing ends  34  and  36  deform at mating with bushing apertures  28  and  30 , as shown in the exemplary illustration of FIG.  11 . The deformation of bushing ends  34 ,  36  reduces the internal reference or as-formed diameter  48  of as-formed bushing  18  at bushing ends  34 ,  36 , which diameter  48  is noted in FIGS. 9,  10  and  11 . The consequent barreling effect on bushing  18  from the noted deformation is shown in FIG. 10 on one side of bushing  18 . This internal deformation reduces the contact area between outer surface  50  of pin  16 , which is shown in FIG. 1, and internal surface  52  of bushing  18  from the overall length of bushing inner surface  52  to the proximate bushing surface at apertures  28  and  30 . 
     Earlier efforts at overcoming the barreling effect on bushings  18  provided a generally centrally located opening  22  along formed bushing seam  24 , as shown in FIGS. 4 and 5. The illustrated shape of opening  22  is exemplary and not a limitation, which shape may vary and it may be formed by various methods. However, bushings  18  are commonly formed by rolling a strip  54  of flat stock, which is exemplified in FIG. 3, around a cylindrical mandrel, as known in the art. Strip  54  has clipped triangular areas  60  and  62  at each end of the preformed bushing blank, which areas  60  and  62  are abutted at formation of bushing  18  to form illustrated opening  22  in FIG.  9 . 
     Strip  54  in FIGS. 3 and 6 is indicative of a shape for a preformed blank for the formation of bushing  18 . Strip  54  has first edge  56  and second edge  58 , which edges cooperate at formation around the noted mandrel to define bushing seam  24 . Scalloped or clipped portions  60  and  62  generally centrally located along first edge  56  and second edge  58 , respectively, are juxtaposed at formation of bushing  18  to form opening  22 . Strip  54  includes outlined depression  64  along upper side edge  66  and similar outlined depression  68  along lower side edge  70 , which depressions  64  and  68  are about diametrically opposite bushing seam  24  after formation of bushing  18 . In FIG. 6, the outlined depressions  64  and  68  are shown as rectangular shapes on preform  54 . It is clear that these rectangular shapes are generally centered between first and second edges  56  and  58 . However, the length of each depression  64  and  68  is less than one-half the length of respective top and bottom edges  66  and  70  between first and second ends  56  and  58 . Thus, when preform  54  is formed into bushing  18  depressions  64  and  68  are positioned diametrically opposite seam  24  and they are less than one-half the inner circumference of bushing  18  at an as-formed bushing reference position. 
     In FIG. 7, strip  54  is noted in a side view. An enlarged view of an encircled region of FIG. 7 along upper side edge  66  is shown in FIG.  8 . Gap  74  in FIG. 8 shows the relative slope or depression of taper  64  and  68  from edge  66 , or  70 , where the taper is about three-thousandths inch from the reference surface  72 , which becomes bushing internal surface  52 , to upper side edge  66  of strip  54 . In the illustration, only a taper of depression  64  is shown but taper  68  is similarly formed. 
     The as-formed bushing  18  and, the relationship between seam  24  and tapers  64  and  68  are noted in FIG. 9, which relationship is also shown in the structures of FIGS. 1 and 5. More specifically in FIGS. 1,  2 ,  9  and  10 , opening  22  is noted along seam  24 . In FIG. 9, tapers  64  and  68  are diametrically opposite seam  24  with tapers  64  and  68  upwardly and outwardly sloping from reference surface and internal wall  52  of bushing  18  to bushing ends  34  and  36 . At assembly or press fitting of bushing  18  in FIGS. 10 and 11, particularly with bushing end  34  or  36  pressed into bushing aperture  28  or  30 , the bushing deformation or barreling is noted with one bushing sidewall appearing to bulge outward from the reference position of surface  52 . However, tapers  64  and  68  deflect to deform the bushing region in proximity to bushing ends  34  and  36  to provide tapers  64  and  68  in substantial alignment with inner surface  52  to thus provide a substantially uniform surface to contact pin  16 . In this context, pin  16  bears against continuous surface  52 , as well as reformed tapers  64  and  68 , in bushing passage  78 . The portion of surface  52  in bushing passage  78 , which is diametrically opposed to tapers  64  and  68 , experiences the deformation at assembly previously known and described above. This prior deformation was, at least partially, to be accommodated by opening  22 . 
     Earlier efforts and methods of accommodating the excess deformation of surface  52  in passage  78  required a separate rolling operation to taper or form edges  66  and  70  of blank  54 . Slight deformation, as shown with deformed regions  64  and  68 , of edges  66  and  70 , at the required location, may be provided by various manufacturing techniques such as coining or stamping. This slight deformation provides the requisite deformation at noted edges  66  and  70  for deformation into a nominally reformed or reconfigured internal surface  52 , that is generally aligned along the load-bearing bushing area of pitch line  32 . Deformed regions  64  and  68  can be formed during bushing manufacture by a simple operation, such as coining, stamping, swaging or roll-forming on a mandrel with a detent, which operation can be accommodated without extensive equipment or with a minimal secondary operation. More particularly, deformation of regions  64  and  68  may be integrated into a stamping operation for the forming of bushing blank or preform  54  with little or no added capital and operational expense. Thus, greater initial surface contact is provided between pin  16  and bushing  18  beyond the bushing initial-contact area within bushing-link apertures  28  and  30 . The increase in contact area spreads the initial contact load of the chain across a greater pin area to avoid or reduce chain elongation and to enhance chain longevity. It is also considered that the geometry of deformed regions  64  and  68 , along with the extant bushing structure and the orientation of regions  64  and  68  along chain pitch-line  32  provides added strength to the formed and assembled links and chain. 
     While only specific embodiments of the invention have been described and shown, it is apparent that various alterations and modifications can be made therein. It is, therefore, the intention in the appended claims to cover all such modifications and alterations as may fall within the scope and spirit of the invention.