Abstract:
A silent chain is directed to prevent bending of the connection pin and reducing surface pressure acting on the connection pin while maintaining bendability of the entire chain. The chain includes multiple link plates, each having a pair of teeth and a pair of pinholes. The links are interleaved in the transverse and longitudinal directions and the link plates are connected by connection pins inserted in the pinholes. Connection pin is composed of center pin at the center of pinhole and of a pair of rocker pins on both sides of said center pin. Guide washer is provided to each connection pin. Guide washer has a guide part extending on both sides of the teeth of link plate and a central apertures for fixing of the end of center pin.

Description:
The subject matter of this application relates to the subject matter of application Ser. No. 09/776,342, filed Feb. 2, 2001, entitled “A Silent Chain With A Guide Washer Having A Single Aperture For A Rocker Joint Pin.” 
    
    
     This invention relates to a silent chain and, in particular, to the structure of a guide link washer for a silent chain. 
     BACKGROUND OF THE INVENTION 
     Conventionally, a silent chain is used as a power transmission chain. FIGS. 6 and 7 show an example of a typical silent chain. 
     As shown in the figures, silent chain  100  has a multiple link plate  102  having a pair of teeth  121 . The links are interleaved in the transverse and longitudinal directions. The link plate  102  is pivotably connected by connection pin  103 , composed of a pair of long and short joint pins  131  and rocker pins  132 , which are inserted into pinhole  122  of link plate  102 . Guide link  104  is placed on the outside of outermost link plate  102 . Both ends of joint pin  131  are fixed to pinholes formed in guide link  104 . 
     When the chain runs on a sprocket during its operation, the link plates bend and, at such time, joint pin  131  makes rolling contact with the sliding surface of  132 . 
     Recently, silent chain power transmission has been used under high load conditions and, for this, a silent chain of high wear resistance is required. However, when a conventional silent chain is used under high load, very high contact surface pressure is generated in the contact surfaces of the joint pin and rocker pin due to their convex—convex contact and, as a result, pitting wear occurs in those pins. Therefore, the requirement for high wear resistance cannot be adequately satisfied by the conventional silent chain. 
     The increased radius of curvature of the rolling surface of each pin can decrease contact surface pressure between joint pin and rocker pin, but a larger radius of curvature reduces the bendability of the link plates and that of the entire chain. As a result, it becomes difficult for the chain to be wrapped or wound around a small diameter sprocket. Therefore, increase of radius of curvature of the rolling surface is limited to ensure bendability of the entire chain. 
     In a conventional silent chain, both ends of the joint pin are fixed to a guide link of higher rigidity than link plates in general, so that, when excessive tensile load, such as a prestressing load, is applied to a chain, the shear load from the link plate acts on the center part of the joint pin while stretching of the pitch of the holes in the guide row is suppressed and, as a result, the bending load acts on the joint pin and the center of the joint pin and rocker pin can warp. 
     This invention addresses such a conventional problem and it offers a silent chain that retains the bendability of the entire chain, reduces the surface pressure acting on the connection pin and prevents or minimizes bending of the connection pin. 
     SUMMARY OF THE INVENTION 
     In one embodiment, the connection pin of the chain of the present invention is shown in FIG.  3 . In the figure, link plates  2   a ,  2   b  are mutually bent. Incidentally, the bending angle here is given as α. Connection pin  3  that pivotably supports the said link plates  2   a ,  2   b  is inserted in aperture  22  formed in each of link plates  2   a ,  2   b.    
     Connection pin  3  is composed of center pin  31  placed in the center of pinhole  22  and the opposing pair of rocker pins  32  on both sides of said center pin. Both side faces of center pin  31  are curved convex, and convex curved face  32   a , corresponding to side face  31   a  of the center pin, is formed in rocker pin  32 . 
     For a conventional rocker joint-type silent chain (FIGS.  6  and  7 ), rolling contact with angle α is necessary at the contact between rocker pin  132  and joint pin  131  to produce bending angle α. 
     Whereas in the present invention, rocker pins  32  are placed on both sides of center pin  31 , as shown in FIG.  3 . Therefore, if rolling contact with angle α/2 for each rocker pin  32  is realized, then bending angle α can be realized between adjacent link plates  2   a ,  2   b.    
     Therefore, in the present invention, rolling contact of the rocker pin with one half of the necessary rolling contact angle suffices, so that the radius of curvature of each pin can be increased by that much; thereby, the surface pressure of the contact surface of the pin can be reduced while bendability of the entire chain is kept and wear resistance is improved. 
     Guide washers corresponding to each connection pin are provided to the chain of the invention and the end of the center pin is fixed to the pinhole of the guide washer. Therefore, stretching of the hole pitch of the guide row is not restricted, even if excessive tensile load, such as a prestressing load is added to a chain and the shear load from the link plate acts on the joint pin and no bending load acts on the joint pin, so that bending of the joint pin and rocker pin is prevented. 
     The preferred cross-section of the center pin is shaped like a Japanese drum or general ellipse. That is, a shape with the center of both side faces curved convex outward. 
     Convex opposing faces of the rocker pin are curved concave or convex. The entire length of the rocker pin is equal to or slightly longer than the total width of the laminated link plates and shorter than the distance between opposing guide washers in the chain width direction. 
     That is, in this case, guide washers are placed independently to each connection pin so that even if the entire length of the rocker pin is somewhat longer than the total width of the laminated link plates, it does not interfere with the attachment of the guide washer. In this manner, the length of the rocker pin has a large tolerance for ease of dimension control. 
     Whereas in a conventional silent chain, the guide link has a pair of pinholes on both of its ends (see FIGS. 6 and 7) so that it is preferable to have the entire length of the rocker pin shorter than the total width of the interleaved link plates. In such case, both ends of the rocker pin need not be too deep inside the pinholes of the outermost link plate, so that the entire length of the rocker pin needs to be close to the total width of the link plates. Because of this reason, tolerance on the rocker pin length of a conventional silent chain is tight and its dimensional control is not easy. 
     In the present invention, the entire length of the rocker pin is longer than the total width of the link plates, so that an effective cross-sectional area of the connection pin can be uniform across the total width of the link plates. 
     The guide washer can also have a blade spring portion. In such case, the elastic force of the blade spring acts in the chain width direction and a frictional force is generated between adjacent link plates in the chain width direction for high bending resistance of the chain and reduced chordal vibration of the chain. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a side view of the silent chain of a practical example of this invention. 
     FIG. 2 shows a front view of the silent chain of FIG.  1 . 
     FIG. 3 shows an enlargement of the connection pin of the silent chain of FIG.  1 . 
     FIG. 4 is a partial enlargement of FIG.  1 . 
     FIG. 5 is a modification of the guide washer where (a) is a top view and (b) is a front view. 
     FIG. 6 is a top view of a conventional silent chain. 
     FIG. 7 is a front view of a conventional silent chain. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A practical example of this invention is explained below with the attached figures. 
     FIG. 1 is a side view of the silent chain of a practical example of this invention. FIG. 2 is a front view of the silent chain of FIG.  1 . FIG. 3 is an enlargement of the connection pin of the silent chain of FIG.  1 . FIG. 4 is a partial enlargement of FIG.  1  and FIG. 5 shows a modified guide washer where (a) is a top view and (b) is a front view. 
     As shown in FIGS. 1 and 2, silent chain  1  is composed of multiple link plates  2 , each having a pair of teeth  21  and a pair of pinholes  22 . The links are interleaved in the transverse and longitudinal directions, and connection pin  3  inserted in pinhole  22  of said link plates, which pivotally support said link plates  2 . 
     As is clear in FIG. 3, connection pin  3  is composed of center pin  31  in the center of pinhole  22  and a pair of opposing rocker pins  32  on both sides of the said center pin. Center pin  31  has convex curved side faces  31   a  and is in the shape of a Japanese drum or general ellipse in cross-section. Rocker pin  32  has convex curved face  32   a  that contacts side face  31   a  of center pin  31 . Concave curved face  32   b  is formed opposite to convex curved face  32   a  of rocker pin  32 . Concave curved face  32   b  of one rocker pin  32  contacts convex sheet surface  22   a , formed in pinhole  22  of link plate  2 , and center pin  31  is longer than the rocker pin  32  (see FIG.  1 ). 
     Guide washer  4  is placed outside outermost link plate  2 . Guide washer  4  is provided to each connection pin  3 . As shown in FIG. 2, guide washer  4  has a pair of guide parts  41  that extend on both sides of teeth  21  of link plate  2 . The guide part  41  is provided to keep the silent chain at a set position on the sprocket (not shown). Pinhole  42  is formed at the center of guide washer  4  and the end of center pin  31  is inserted into pinhole  42  and fixed therein by staking, etc. 
     Next, the length of rocker pin  32  is detailed with the aid of FIG.  4 . FIG. 4 is a partial enlargement of FIG.  1  and the gap between the outermost link plate  2  and guide washer  4  is exaggerated for the purpose of explanation. 
     Then the total length of rocker pin  32 , total width of interleaved link plate  2 , maximum length of rocker pin  32  as rocker pin  32  is put in the pinhole of outermost link plate  2  and the distance between the two guide washers  4 ,  4  are given in FIG. 4 as L, W, w′ (≈w) and W, respectively, the relation there is 
     
       
         w′≦L&lt;W, preferably w≦L&lt;W.  
       
     
     Incidentally, w′≈w indicate that w′ is smaller than W and, in this case, as close as w. 
     That is, total length L of rocker pin  32  is equal to or longer than maximum length w′ of rocker pin  32  when rocker pin  32  is inside the pinhole of outermost link plate  2  and, at the same time, it is shorter than the distance W between the two guide washers opposing in the chain width direction. Preferably, total length L of rocker pin  32  is equal to or longer than total width w of laminated link plate  2  and is shorter than distance W between both guide washers  4 ,  4 . 
     Since guide washer  4  is provided independently to each connection pin  3 , attachment of guide washer  4  is not impeded even if the total length L of rocker pin  32  is slightly longer than the total width w of laminated link plate  2 . In this manner, the tolerance on the length of rocker pin  32  is loose for ease of dimensional control. 
     Whereas, in a conventional silent chain, the guide link has a pair of pinholes on both its ends (see FIGS.  6  and  7 ), it is preferable to have the total length L of the rocker pin shorter than total width w of the laminated link plate for unforced attachment of the guide link to both pinholes, even if the length of the rocker pin in one pinhole and that in the other pinhole are different from each other. 
     In such case, both ends of the rocker pin need to be not too deep in the pinhole of the outermost link plate so that the total length of the rocker pin needs to be close to the total width of the link plates. That is, for a conventional silent chain, the relationship w′≦L&lt;w must be met. 
     As shown above, in a conventional silent chain, the tolerance on the length of the rocker pin is tight and dimensional control is difficult because w′ and w are very close to each other. 
     Next, in FIG. 3, showing the details of the connection pin of silent chain  1 , link plates  2   a ,  2   b , placed at a right angle to the paper sheet surface are mutually bent. When the bending angle of the link plates is given as α, bending angle α can be produced for adjacent link plates  2   a ,  2   b  if the rolling contact with α/2 angle is realized by each rocker pin  32  because rocker pins  32  are placed on both sides of each center pin  31 . 
     Whereas, in a conventional rocker joint-type silent chain (FIGS.  6  and  7 ), rolling contact with angle α is necessary at the contact part between rocker pin  132  and joint pin  131  to obtain bending angle α. 
     As shown above, rolling contact of each rocker pin  32  with one half of the necessary rolling contact angle suffices for this practical example, so that the radius of curvature of pins  31 ,  32  can be increased by that much and the surface pressure at the contact of the pin can be reduced while bendability of the entire chain is maintained and wear resistance is improved. 
     In addition, in this case, guide washer  4  is provided to each connection pin  3  and the end of center pin  31  is fixed to pinhole  42  of guide washer  4 . Thereby, stretching of the hole pitch of the guide row is not restricted, even if excessive tensile load such as the prestressing load is added to a chain and the shear load from the link plates  2  acts on joint pin  32  while no bending load acts on joint pin  32 , so that bending of joint pin  32  and rocker pin  31  is prevented. 
     In a conventional silent chain, stretching of pitch due to friction appeared mainly in the link plates of the link row and not in the link plates in the guide row because the joint pin is fixed to the guide link. This has caused an uneven extension of pitch. Whereas in this practical example the guide row and the link row are not different from each other because of the use of the guide washer, the pitch extension is uniform across the entire chain. 
     The above practical example has convex curved seat surface  22   a  formed in pinhole  22  of link plate  2  but the seat surface can be concave curved too. In such case, convex curved faces are formed on both sides of rocker pin  32  and each rocker pin  32  has a Japanese-drum-shaped cross-section similar to that of center pin  31 . 
     The above practical example has a flat-plate-like guide washer, but blade-spring-like guide washer  4 ′, as shown in FIG. 5, can be used also. Incidentally, the same reference numerals as in the said practical example indicate the corresponding parts. 
     Guide washer  4 ′ in FIG. 5 has a pair of near rectangular guide parts  41 ′ and guide washer  4 ′ has blade spring  43 , that extends to both sides and bends up or down, formed in it. In this case, the elastic force of blade spring  43  acts in the chain width direction to add a frictional force to the adjacent link plates and thereby the bending resistance of the chain increases, the chordal vibration of the chain is suppressed and noise due to chordal vibration is reduced. 
     As detailed above, the connection pin of the silent chain of this invention is composed of a center pin in the center of a pinhole and a pair of opposed rocker pins on both sides of the center pin, therefore, rolling contact of the rocker pin with the center pin at one half of the necessary bending angle suffices to produce the necessary bending angle of the chain, so that the radius of curvature of each pin can be increased by that much and, as a result, the surface pressure of the contact area of each pin is reduced and wear resistance is improved. 
     In addition, a guide washer is provided to each connection pin in this invention so that stretching of the hole pitch in the guide row is not restricted, even when excessive tensile load such as a prestressing load is added to the chain, the shear load from the link plates acts on the joint pin and no bending load acts on the joint pin. As a result, bending of the joint pin and rocker pin is prevented.