Abstract:
A guide link for a back-drive silent chain includes a pair of flat outside surfaces and window holes. The flat outside surfaces are formed on the opposite sides of the center line of the apertures for contacting a chain guide or tensioner arm. The edge portions of the window holes in the vicinity of the apertures are formed of arcuate surfaces equally spaced apart from the edge portions of the apertures.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a back-driving silent chain, and in particular, it relates to a guide link for a back-driving silent chain that has window portions to reduce the stiffness or rigidity of the link. The chain has a plurality of rows of links that are interleaved and connected by a connecting pin inserted in the apertures of each of the link plates. In its preferred embodiment each row comprises multiple link plates, each with a pair of apertures and a pair of teeth on both sides of the aperture or pinhole center line. The link plates have guide links positioned on the outermost side of the link plates. The invention relates to an improvement in the construction of the guide links. 
     Silent chains are used conventionally as power transmission chains for automobiles and motorcycles in transmissions and transfer cases for four-wheel drive vehicles. In general, a silent chain is comprised of multiple link plates, each of which has a pair of teeth. Each link typically includes a pair of apertures. The links are interleaved and are connected by connecting pins placed in the apertures. Guide links are positioned on the outermost side of the link plates and the ends of the connecting pins are press fit into apertures in the guide links. 
     FIGS. 7 and 8 show examples of a conventional low-rigidity or low stiffness guide links. FIG. 7 shows the guide link disclosed in Japanese Utility Model No. 4-52641 (&#39;641) (U.S. Pat. No. 5,176,586). In this case, guide link  100  has pinholes  101 ,  102  and window hole  103 . As is clear from the shape of pinholes  101 ,  102  and lines  1 - 2  of the &#39;641 specification, the silent chain with guide link  100  is the rocker joint-type silent chain that uses a rocker joint composed of a pair of long and short connecting pins and pinholes  101 ,  102  that secure the press-fit end of the longer pin of the rocker joint. Incidentally, single-dot line  110  in the figure indicates the pinhole center line. 
     When the silent chain comprising multiple link plates and guide links such as guide link  100  is operated, tension acts along the entire length of the chain. Tensile force applied through the connecting pins, in the direction to expand the aperture center distance (or pitch), acts on the apertures  101 ,  102  of the guide links and on the apertures of the link plates. Because the rigidities or stiffness of the inner links differs from the stiffness of the guide links, the connecting pins of a conventional silent chain can be deformed or possibly fractured. 
     Therefore, various ideas have been implemented in the past to equalize the elongation of the guide links and inner links caused by the tensile load (tensile rigidity). The tensile load is applied during chain operation or, more commonly, during a preloading or pre-stressing operation after assembly of the chain. 
     FIG. 8 shows the guide link disclosed in Japanese Laid-Open Patent Heisei 4-210144 (&#39;144) (U.S. Pat. No. 5,345,753) and guide link  200  has pinholes  201 ,  202  and slit  203 . As is clear from the shape of pinholes  201 ,  202 , the silent chain with this guide link  100 , too, is a rocker-joint-type silent chain and the end of the longer pin of the rocker joint is press-fit in apertures  201 , 202 . Incidentally, single-dot line  210  in the figure indicates the pinhole center line. 
     For these guide links, the tensile rigidity of the guide link is lowered by formation of a window hole  103 ,  203  or slit. That is, the guide link is made to deform or elongate equally with the link plate against the tensile load, to prevent deformation of the rocker joint. 
     However, the conventional guide links are guide links for the rocker joint, as shown in FIGS. 7 and 8. Material thickness d at the edge of pinholes  101 ,  102  and window hole  103  differs from material thickness d′ at the pinholes  201 ,  202  and slit  203 . Depending on the position of the pinhole, the press-fit between the end of the pin of the rocker joint and pinhole may not be secure. 
     In the example in FIG. 8, although the material thickness d′ at the edges of slit  203 , pinholes  201 ,  202  looks sufficient in the figure, the material thickness can be considerably less locally at the edges of the pinhole and slit as shown in FIG.  7 . If the round pinhole of the guide link  200  is changed to receive a round pin, while a similar slit,  203 , is utilized, decrease of the force that secures the end of the rocker joint pin in the pinhole can occur easily. 
     On the other hand, in the case of the back-driving silent chain, which includes links with pairs of teeth on both sides of the centerline between the apertures, the thickness of the guide link must be sufficient to ensure the contact area between the chain and the shoe of an associated chain tensioner arm. Thus, the rigidity of the guide link is higher than that of the normal guide link. Therefore, a low-rigidity guide is strongly needed, especially for the back-driving silent chain. 
     This invention addresses the above-described situations and its purpose is to offer a back-driving silent chain of low rigidity that does not result in the decrease of the fitting force between the pinhole of the guide link and the connecting pin. 
     SUMMARY OF THE INVENTION 
     In its preferred embodiments, the silent chain or power transmission device of the present invention comprises a silent chain having multiple rows of links. Each of the link rows is comprised of multiple link plates each having a pair of circular apertures formed at both ends thereof and a pair of teeth on each of the opposite sides of the center line extending between the center of the apertures. The link plates are connected with one another by round pins received in the pair of apertures. 
     Guide links are placed on the outer edges of the rows of links of the chain in the transverse direction and the ends of the round pins are press-fit into the apertures of the guide links. Each of the guide links include a pair of flat outside surfaces at the upper and lower edges of the guide links in the vertical direction. The flat outside surfaces are formed on the opposite sides of the center line between the apertures. A chain guide or tensioner arm shoe contacts the flat outside surfaces. The guide links also include window holes with the edge portions of the window holes in the vicinity of the apertures being formed of arcuate surfaces equally spaced apart from the edge portions of the apertures. 
     In another embodiment, the back-driving silent chain of this invention comprises multiple link plates having a pair of circular apertures at both ends thereof and a pair of teeth on the opposite sides of the center line of the apertures. The link plates are connected with one another by round pins received in the apertures. Guide links are press-fit on the outer edges of the rows of plates. The ends of the round pins are press-fit into the apertures of the guide links. Each of the guide links include a pair of flat outside surfaces and a pair of slits formed on the opposite sides of the center line of the apertures. A chain guide or tensioner arm shoe contacts the flat outside surfaces of the guide links. The edge portions of the slits are in the vicinity of the apertures and are formed of arcuate surfaces equally spaced apart from the edge portions of the apertures. 
     In the silent chain of this invention, the end of the round connecting pin is press-fit into a corresponding round pinhole of the guide link. Window holes or slits are formed on both sides of the center line of the pinholes of the guide link. The edge in the vicinity of such a window hole or slit is formed by arcuate surfaces which arc at equal distances from the edge of the pinhole. 
     The contact area between the guide link and chain guide or shoe of the chain tensioner is along the outside edges of the guide link. At the same time, the rigidity of the guide link is reduced and the material thickness at the edges of the window hole or pinhole in the vicinity of the slit can be made uniform. As a result, the fitting force between the pinhole and connecting pin, or the force of the link that holds the pin press-fit in the aperture, is not reduced. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A preferred embodiment of this invention is explained with reference to the attached drawings. In the drawings: 
     FIG. 1 is a perspective view of a portion of the back-driving silent chain of one embodiment of this invention. 
     FIG. 2 is an enlarged front view of the link plate of the silent chain of FIG.  1 . 
     FIG. 3 is an enlarged front view of the guide link of the silent chain of FIG.  1 . 
     FIG. 4 is a second embodiment of the guide link of the present invention. 
     FIG. 5 is a third embodiment of the guide link of the present invention. 
     FIG. 6 is a fourth embodiment of the guide link of the present invention. 
     FIG. 7 is an enlarged front view of a conventional guide link of the prior art. 
     FIG. 8 is an enlarged front view of another conventional guide link of the prior art. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As shown in FIG. 1, multiple link plates  2 , each of which has a pair of teeth  21 ,  21 ′ and a pair of pinholes  22 , are placed in rows and interleaved to form silent chain  1 . Link plates  2  are pivotally connected by inserting round connecting pin  3  in pinhole  22  of the link plate. Guide link  4  is positioned on the outermost side of the row formed by multiple link plate  2 . 
     As shown in FIG. 2, a pair of teeth  21 ,  21 ′ is formed on each of both sides of pinhole center line L of round pinholes  22 . Link plate  2  is symmetric about pinhole center line L. Thereby, silent chain  1  engages with sprocket  10  on the side of teeth  21  (FIG. 1) and the sprocket (not shown) on the side of teeth  21 ′. A pair of teeth  21 ,  21 ′ are formed on both sides of pinhole center line L of link plate  2 . A back-driving silent chain, which drives with teeth on both sides of each link, is composed in this manner. 
     Tooth  21  is composed of inside flank  23  and outside flank  24 . Inside flank  23  is composed of a nearly straight flat surface or a slightly curved surface and outside flank  24  is composed of a nearly straight flat surface  24   a  formed near the tip of tooth  21  and convex surface  24   b  formed in the vicinity of pinhole  22 . 
     Similarly, each tooth  21 ′ is composed of inside flank  23 ′ and outside flank  24 ′. Inside flank  23 ′ is composed of a nearly straight flat surface or a slightly curved surface and outside flank  24 ′ is composed of a nearly straight flat surface  24 ′ a  which is formed near the tip of tooth  21 ′ and a convex surface  24 ′ b  formed in the vicinity of pinhole  22 . The shapes of inside flank  23 ,  23 ′ and outside flank  24 ,  24 ′ are not limited to those shown in FIG.  2 . 
     As shown in FIG. 3, the guide link has a pair of round pinholes  41  of radius r and the end of connecting pin  3  is press-fit in these pinholes  41 . A pair of flat outside surfaces  4   a,    4   b  are formed in guide link  4  on both sides of pinhole center line L. Preferably, guide link  4  is symmetric to pinhole center line L. These outside surfaces  4   a,    4   b  are for contacting an associated chain guide or shoe of a chain tensioner (not shown). 
     A pair of window holes  42 ,  42 ′ are also formed in guide link  4 . These window holes  42 ,  42 ′ are preferably symmetrical about pinhole center line L and substantially triangular in shape. The window holes  42 ,  42 ′ each have a pair of arcuate sides  50   a,    50   b  which in the vicinity of the pinhole is formed by an arcuate surface of radius R around pinhole center O. The equal spacing of the pair of arcuate sides  50   a,    50   b  from a corresponding aperture edge creates a uniform material thickness D, which equals (R−r), between each edge of window holes  42 ,  42 ′ in the vicinity of the pinhole and edge of pinhole  41 . 
     The size of this material thickness is set such that the diameter of the aperture of pinhole  41  of guide link  4  does not expand or increase when the tensile load in the direction of chain pitch acts on the silent chain. Accordingly, the material thickness between the edges of window holes  42 ,  42 ′ and the edge of pinhole  41  can be made uniform in the vicinity of the pinhole. As a result, decrease of the fitting force between pinhole  41  and connecting pin  3  is not reduced or decreased. 
     Window  42  of guide link  4  is primarily for the purpose of the reduction of the rigidity of guide link  4  during engagement of teeth  21  of link plate  2  with the sprocket teeth. Window  42 ′ is primarily for reduction of the rigidity of guide link  4  during engagement of teeth  21 ′ of link plate  2  with the sprocket teeth. However, window  42 ′ and window  42 , respectively and supplementarily contribute to the reduction of rigidity of the guide link  4  when teeth  21  and  21 ′ engage with the sprocket teeth. The window reduces the stiffness of the guide link and thus permits greater elongation of the guide link when the chain is under tension, such as in operation or during a pre-stress operation. Thereby, the rigidity of guide link  4  is reduced. 
     The center of the arc (i.e., center point of the radius that forms the arc) that forms each edge of windows  42 ,  42 ′ in the vicinity of the pinhole need not necessarily coincide with pinhole center O. As long as the material thickness between the edges of window holes  42 ,  42 ′ and the edge of pinhole  41  are substantially uniform, the center of the arc that forms each edge can be on the edge of pinhole  41  or outside of pinhole  41 . Also, each edge of window holes  42 ,  42 ′ can be composed of multiple arcs. 
     The window hole formed in guide link  4  is not limited to that of the above example. An alternate embodiment is shown in FIG.  4 . Incidentally, the same number references in FIG. 4 indicate the same parts as in FIG.  3 . In this case, one window hole  44 , which is symmetrical about pinhole center line L, is formed. The window hole is generally I-shaped having a top side or edge  51 ′ and a bottom side or edge  51  and a left side  52   a  and a right side  52   b.  Each left and right side or edge  52   a,    52   b  of window hole  44  in the vicinity of the pinhole is formed by the arcuate surface with radius R which is concentric with pinhole center O. The equal spacing of the pair of arcuate sides  52   a,    52   b  from a corresponding aperture edge creates a uniform material thickness D, which equals (R−r), between each edge of window hole  44  in the vicinity of the pinhole and edge of pinhole  41 . 
     Thereby, similar to the FIG. 3 embodiment, the rigidity of guide link  4  can be reduced and the material thickness between the edge of window hole  44  and the edge of pinhole  41  can be made uniform in the vicinity of the pinhole, which avoids a reduction in the fitting force between pinhole  41  and connecting pin  3 . In addition to window hole in guide link  4  shown in FIGS. 3 and 4, the invention can include a slit, as shown in the FIGS. 5 and 6, and described below. 
     FIG. 5 shows another embodiment of this invention and, in the figure, the same reference characters as in the above embodiments indicate the same or corresponding parts. In this example, a pair of slits  46 ,  46 ′ extend from the center of outside surfaces  4   a,    4   b  of guide link  4  to the side of link center line L. Slits  46 ,  46 ′ are preferably symmetrical to pinhole center line L. Each of slits  46 ,  46 ′ is substantially triangular in shape with a pair of arcuate sides  50   a,    50   b  in the vicinity of the pinhole. Arcuate sides  50   a,    50   b  are formed by an arcuate surface with radius R which is concentric with pinhole center O. Openings  53 ,  53 ′ in slits  46 ,  46 ′ open to outside surface  4   a,    4   b.  Uniform material thickness D, which equals (R−r), is ensured between the arcuate sides  50 ,  50   b  and the edge of pinhole  41 . Thereby, the rigidity of guide link  4  can be reduced and the material thickness between each edge of slits  46 ,  46 ′ and the edge of pinhole  41  in the vicinity of the pinhole can be made uniform, which avoids a decrease of the fitting force between pinhole  41  and connecting pin  3 . 
     FIG. 6 shows another embodiment of this invention. In this figure, the same reference characters as in the above embodiments indicate the same or corresponding parts. In this example, an arcuate surface with radius R, which equals (r+D), that centers around pinhole center O, is formed around pinhole  41  in each of a left end  5   a  and at right end  5   b  of guide link  4 . Each of the left and right ends  5   a,    5   b  extend beneath outside edges  4   a,    4   b  to form openings  48 ,  48 ′. Each of openings has at least one arcuate surface equally spaced from a corresponding aperature edge. Uniform material thickness D, which equals (R−r), is ensured between the edge of openings  48 ,  48 ′ and the edge of pinhole  41  in the vicinity of the pinhole. Thereby, the rigidity of the guide link  4  can be reduced and the material thickness between the edge of slits  48 ,  48 ′ and the edge of pinhole  41  in the vicinity of the pinhole can be made uniform, which prevents decrease of the fitting force between pinhole  41  and connecting pin  3 . 
     In the examples illustrated in FIGS. 4,  5  and  6 , an example of the coincidence or agreement of the center of the arc that forms the edges of the window hole and slit in the vicinity of the pinhole, with pinhole center O, was shown, but this invention is not limited to those examples. As long as the material thickness between the edges of the link and the edge of the pinhole is substantially uniform, the center of the arc that forms each link edge can be at the edge of the pinhole or the outside of the pinhole. 
     As explained above, in the back-driving silent chain of this invention, window holes or slits are formed on both sides of the pinhole center line of the guide link and the edges of the window holes and slits in the vicinity of the pinhole are formed by arcuate surfaces of equal distance from the edge of the pinhole. Thus, the rigidity of the guide link can be reduced. The material thickness between the edges of the window holes and slits and the edge of the pinhole can be made uniform in the vicinity of the pinhole, which avoids a decrease of the fitting force of the connecting pin into the pinhole.