Patent Publication Number: US-2010120568-A1

Title: Silent chain with bushings

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority on the basis of Japanese patent application 2008-286804, filed Nov. 7, 2008. The disclosure of Japanese application 2008-286804 is hereby incorporated by reference. 
     FIELD OF THE INVENTION 
     This invention relates to a silent chain with bushings, for use in the transmission of power, for example as a timing chain in an automobile engine, or as a drive chain in industrial machinery. 
     BACKGROUND OF THE INVENTION 
     Silent chains with bushings have been used to transmit power from a driving sprocket to a driven sprocket. A conventional silent chain with bushings is shown in  FIGS. 10 ,  11  and  12 . The silent chain  21  is composed of outer links  25  and inner links  28 . The outer links are composed of guide plates  22  arranged on the outermost sides of the chain in the chain width direction, intermediate plates  23  adjacent the insides of the guide plates, and connecting pines  24 . The inner links  28  are composed of inner plates  26  and bushings  27 . The inner and outer links are in an alternating arrangement in the longitudinal direction of the chain and connected because the connecting pins  24  of the outer links extend through the bushings  27  of the inner links. 
     As shown in  FIG. 11 , each of the guide plates  22 , on the outermost sides of the chain, has a pair of pin holes  22   a , but no sprocket-engaging teeth. As shown in  FIG. 12 , the intermediate plates  23  have pin holes  23   a , and sprocket engaging teeth  23   b . In the outer link  25 , the guide plate  22  and the intermediate plate  23  are in side-by-side relationship, and the ends of the connecting pins  24  are press-fit into the pin holes  22   a  and  23   a  of the guide plates  22  and the intermediate plates  23 , respectively. 
     Each of the inner plates  26  of the inner link  28  has a pair of bushing holes  26   a  and a pair of engagement teeth  26   b , and the both ends of bushings  27  are respectively press-fitted into and secured to a pair of bushing holes  26   a  of the spaced inner plates  26 . That is the bushing  27  are press-fit into bushing holes  26   a  of the inner plates  26 . 
     In the conventional silent chain with bushings, the outer links  25  and the inner links  28  are alternately arranged in the longitudinal direction of the chain and are articulably connected to one another by inserting the connecting pins  24  of the outer links  25  through the bushings  27  of the inner links  28 . The conventional silent chain is described in greater detail in United States Patent Publication 2002/132690. 
     Because guide plates  23  are provided on both sides of the chain, they occupy space in the direction of the width of the chain corresponding to twice the thickness of a guide plate  23 . As a result the overall width W ( FIG. 10 ) of the chain, the space occupied by the chain, and its weight, are all large, and the chain does contribute to the satisfaction of the current demand for size and weight reduction in engines and the like. 
     The length of the portions of the connection pins  24  that protrude from bushings  27  large. Therefore, flexion of the connecting pins is increased as increasing tension loads are applied to the chain. As a result, problems of excessive wear due to uneven contact between the connecting pins  24  and the bushings  27  occurs, and deformation of the guide plates  22  and the intermediate plates  23  can occur as a result of pin flexion. 
     In the inner link  28 , the inner link plates  26  are press-fit onto both ends of the bushing  27 . Significant deformation of the inner surface of the bushing occurs during the press-fitting operation. As a result, contact between the outer circumferential surface of the connecting pin  24  and the inner circumferential surface of the bushing  27  becomes non-uniform and, as a result, increased wear of the outer circumferential surface of the connecting pin  24  and of the inner circumferential surface of the bushing  27  occurs. 
     An object of the invention is to solve the above-described problems by providing a silent chain with bushings in which significant narrowing of width of the chain and significant weight reduction can be achieved, in which flexion of the connecting pins and deformation of the inner surfaces of the bushings during press-fitting can be suppressed, and wear of the connecting pins and of the bushings can be suppressed. 
     SUMMARY OF THE INVENTION 
     The silent chain according to the invention comprises outer and inner links interconnected in alternating relationship. Each outer link comprises outer plates disposed in opposed, spaced relationship to each other on opposite sides of the chain. These outer plates are the outermost in the direction of the width of the chain, have teeth for engaging teeth of a sprocket. The outer plates also have pin holes. Each outer link also comprises connecting pins press-fit into the pin holes of its outer link plates, and connecting the outer plates. Each inner link comprises a center guide plate disposed at a location midway between the sides of the chain in the direction of the width of the chain, a set of inner plates having teeth for engaging the teeth of a sprocket, and bushings. Each connecting pin of an outer link extends through a bushing of an adjacent inner link, thereby connecting the outer and inner links of the chain are in alternating relationship. In each inner link, the center guide plate has a pair of bushing holes into which the bushings of the inner link are respectively press-fit. In each inner link, inner plates of the inner link are disposed adjacent to, and on both sides of, the center guide plate, and in each inner link, each of the inner link plates has a pair of bushing holes into which the bushings of the inner link are press-fit. 
     Because the guide plates of the chain are single, centrally located, guide plates instead of pairs of guide plates on opposite sides of the chain, the chain of the invention can be made narrower and lighter in weight than a conventional silent chain. Furthermore, since the connecting pins can be made shorter than the connecting pins of a conventional silent chain, unbalanced contact between the connecting pins and the bushings can be prevented, and wear due to unbalanced contact between the pins and the bushings can be suppressed. For the same reason, deformation of the pins can be reduced. 
     In addition, since the centers of bushings are press-fit into bushing holes in the central guide plate, less deformation of the inner surfaces of the bushings occurs as the bushings are press-fit into bushing holes of the adjacent inner plates. As a result contact between the outer circumferential surfaces of the connecting pins and the inner circumferential surfaces of the bushings is made more uniform so that wear of the connecting pin and of the bushing is reduced. 
     In an embodiment in which only one inner plate is provided on each side of center guide plate, the chain can be made much narrower than a conventional chain having similar capabilities. However, by providing two inner plates on each side of the center guide plate, the lengths of the bushings can be increased, and the contact area between the connecting pins and the bushings is correspondingly increased so that the wear of the connecting pins and the bushings can be suppressed, and wear elongation of a chain can be suppressed. 
     Furthermore, since the center guide plate is press-fit onto the center of the bushing, if the bushing is press-fit into a bushing hole in each of the two inner link plates on each side of the center guide plate, when the bushing is press-fit into the bushing holes of the pairs of inner plates on both sides of the center guide plate uniformity of the shape of the inner surface of the bushing is promoted, so that wear of the connecting pin and of the bushing can be suppressed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plain view of a part of a silent chain with bushings according to the invention; 
         FIG. 2  is a side elevational view of the part of the silent chain shown in  FIG. 1 ; 
         FIG. 3A  is a front elevational view of an outer plate of the chain; 
         FIG. 3B  is a front elevational view of an inner plate of the chain; 
         FIG. 3C  is a front elevational view of a center guide plate of the chain; 
         FIG. 4  is a front elevational view of an outer link of the chain; 
         FIG. 5A  is a front elevational view of an inner link of the chain; 
         FIG. 5B  is a cross-sectional view of the inner link; 
         FIG. 6  is a cross-sectional view showing the engagement of the silent chain with a sprocket; 
         FIG. 7  is a side elevational view showing the engagement of the silent chain with a sprocket; 
         FIG. 8  is a plan view showing a part of a silent chain with bushings according to a second embodiment of the invention; 
         FIG. 9  is a cross-sectional view showing the engagement of the silent chain of  FIG. 8  with a sprocket; 
         FIG. 10  is a plan view, partly in section, of a part of a conventional silent chain with bushings; 
         FIG. 11  is a side elevational view of the part of the conventional silent chain as shown in  FIG. 10 ; and 
         FIG. 12  is a cross-sectional view showing the engagement of the conventional silent chain with a sprocket. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A silent chain  1  according to the invention is shown in  FIGS. 1 and 2 . An outer link  4  of the chain comprises outer plates  2  arranged on the outermost sides of the chain in the chain width direction and connecting pins  3 . An inner link  8  comprises a center guide plate  5  arranged midway between the sides of the chain, inner plates  6 , and bushings  7 . The outer and inner links are arranged alternately along the longitudinal direction of the chain, and are connected to each other by insertion of the connecting pins  3  through the bushings  7 . The outer link  4  is a non=guide row, and the inner link  8  is a non-guide row. 
     The outer plate  2 , as shown in  FIG. 3A , has a pair of pin holes  2   a  and a pair of sprocket tooth engaging teeth  2   b . The center guide plate  5  of the link  8  is arranged at the center of the chain in the chain width direction and is formed with has a pair of bushing holes  5   a  as shown in  FIG. 3C , but has no sprocket-engaging teeth. The inner plates  6 , as shown in  FIG. 3B , which are provided on both sides of the center guide plate  5 , have a pair of bushing holes  6   a  and a pair of engagement teeth  6   b.    
     As shown in  FIG. 4 , the outer link  4  comprised two outer plates  2  in opposed spaced relationship to each other, and connected by two connecting pins  3  press-fit into and secured to pin holes  2   a  ( FIG. 3A ). The outer plates  2  are arranged on the sides of a non-guide row of the silent chain  1  so that they are the outermost plates of the chain in the chain width direction. The length of a connecting pin  3  of an outer link  4  becomes the width W 1  of the silent chain  1 , as shown in  FIG. 1 . 
     As shown in  FIGS. 5A and 5B , in the inner link  8  bushings  7  are press fit in bushing holes  5   a  of the center guide plate  5  and guide plate  5  centered on bushing  7  so that it is located midway between the ends of the bushing. Inner plates  6  are located on opposite sides of, and adjacent, the center guide plate  5  and bushings  7  are press-fit into holes  6   a  of the inner plates. 
       FIGS. 6 and 7  show THE engagement of silent chain  1  with a sprocket  9 . The sprocket has a concave groove  9   b  formed in the middle of each of its teeth  9   a , midway between the sides of the sprocket. The teeth  2   b  of the outer plates  2  and the teeth  6   b  of the inner plates  6  engage the sprocket teeth  9   a , but the center guide plate  5  enters the concave groove  9   b . It does not engage the tooth faces of the sprocket teeth  9   a  in driving relationship, but instead guides the chain, preventing it from moving laterally out of engagement with the sprocket  9  by engagement with the sidewalls of the groove  9   b.    
     Since the guide plate in each guide row of the chain is only a single central guide plate  5 , the width W 1  of the chain can be narrower than the width of a conventional silent chain with bushings, which has two guide plates in each guide row, by an amount equal to the width of a guide plate. In other words, whereas the conventional silent chain with bushings has a total of six plates in the widthwise direction as shown in  FIG. 10 , the silent chain in embodiment of the invention shown in  FIGS. 1-7  has a total of only five plates in the widthwise direction, as shown in  FIG. 1 . Thus, W 1 &lt;W. As the result the silent chain according to this embodiment of the invention takes up less space, and can be lighter in weight, than a conventional silent chain with bushings. In addition, because the chain according to the invention has one guide plate in the widthwise direction instead of two, and the overall width of the chain is reduced by the thickness of one guide plate, the connecting pins can be shortened by the same amount. Pin flexion resulting from chain tension is therefore suppressed, and wear of the connecting pin  3  and of the bushing  7  due to non-uniform contact between them is also suppressed. In addition, since pin flexion is suppressed, deformation of the outer plates  2  resulting from pin flexion can also be prevented. 
     In the inner link  8 , the bushings  7  are press-fit into the respective bushing holes  5   a  of the central guide plate  5 . When bushings  7  are press-fit into bushing holes  6   b  of the adjacent inner plates  6 , expansion of the outer diameter of the bushing  7  is limited by the center guide plate  5 , and consequently deformation of the inner surface of the bushing  7  is reduced. As a result, the contact between the outer circumferential surface of the connecting pin  3  and the inner circumferential surface of the bushing  7  is more uniform, and wear of the connecting pin  3  and the bushing  7  is accordingly reduced. 
     A second embodiment of the invention is shown in  FIGS. 8 and 9 , in which a silent chain  11  corresponds to silent chain  1  described above, except that double inner plates  6  are provided in place of the single inner plates on both sides of the center guide plate  5 . 
     With two inner plates  6  on each sides of the center guide plate  5 , the length of the bushing  7  can be increased. As a result, the contact area between the connecting pins  3  and the bushings  7  is increased, so that wear elongation of the chain is suppressed. As in the first embodiment, bushings  7  are press-fit into bushing holes in the center guide plate  5 , and into bushing holes  6   a  of at least the inner plates  6  immediately adjacent the center guide plate on both sides thereof. Preferably, the bushings are press fit into both of the inner link plates on each side of the center guide plate. Press-fitting of the bushings into the center guide plate decreases deformation of the inner surface of the bushing when it is press-fit into the inner plates  6 , and consequently wear of the connecting pins  3  and the bushings  7  is suppressed.