Abstract:
A silent chain and sprocket assembly is disclosed for use with a chain tensioner that provides driving contact on both sides of the chain and improved system wear, noise and vibration characteristics without adding to the chain&#39;s weight or material costs. The front-side sprockets employ sprocket teeth and engage the front-side silent chain links in conventional fashion. The back-side driven sprockets differ from prior silent chain sprockets in that the sprockets employ small protrusions instead of traditional teeth. The silent chain engages a back-side sprocket protrusion using the geometry of either a single link, or that of two adjacent links, as the chain wraps on the back-side sprocket.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates generally to silent chain and sprocket power transmission systems. In particular, the present invention relates to silent chain and sprocket systems that are capable of transferring power from either side of the silent chain. 
   Silent chain and sprocket power transmission systems are typically used in automotive engine timing system applications. The timing system transfers power from an automotive engine&#39;s crankshaft to the engine&#39;s camshafts, which operate the engine&#39;s intake and exhaust valves. A timing system may also be used to drive other engine accessories. 
   A basic timing system consists of a chain, two or more sprockets, and a tensioner. As its name implies, a tensioner applies a tensioning force to the chain. This tension ensures that the chain cannot slip on the sprockets, and thus change the engine timing. The tensioner of a timing system is important because, unlike many chain and sprocket applications, a slip by the chain of a timing system will change the valve timing which could result in poor performance or even engine damage. 
   Automotive timing systems also differ from other chain and sprocket applications because noise created by timing systems can reach an unacceptable level. Roller chains create a loud impact noise when the roller element of the chain strikes the sprocket root area. Roller chain and sprocket drives for engine timing systems often generate unacceptable levels of noise. Silent chains attempt to duplicate the quieter sliding contact that characterizes gear-tooth engagement. Therefore, many timing systems now use a silent chain and sprocket drive to reduce the amount of noise generated as the chain engages the sprocket. 
   A conventional silent chain is typically formed of interleaved sets of inverted tooth links. Inverted tooth links of traditional silent chains used in timing systems form two teeth on one side of the chain that engage sprockets. A set or row of links is assembled by positioning several links alongside of or adjacent to each other. The links are connected by pivot means, which are usually round pins received in a pair of apertures of each link of the row. Adjacent rows of links are interleaved so that apertures of adjacent rows are aligned to receive a pivot means that joins adjacent rows and allows relative rotation of the rows. The direction from one joined row to the next is the chain direction. Silent chains having teeth on one side of the chain are incapable of driving sprockets on both sides of the chain. An example of a traditional silent chain used in a timing system application can be found in U.S. Pat. No. 4,509,323. 
   Due to the limited engine compartment space available for separate engine accessory drive systems, many automotive timing systems are also used to drive engine accessories, as well as camshafts. Because traditional silent chains are incapable of driving sprockets on both sides of the chain, long and convoluted serpentine arrangements may be required to drive engine accessories. The size and complexity of today&#39;s automotive timing systems can be minimized if sprockets could be driven on both sides of the timing chain. 
   Roller chain and sprocket systems are well suited for driving sprockets on both the front and the back sides of the chain, but as mentioned above, the noise characteristics of roller chain systems make them undesirable for timing system use. Furthermore, existing silent chain designs that are capable of engaging sprockets on both sides of the chain do so by providing links having teeth on both sides of the chain to achieve driving contact between the back-side of the chain and a toothed sprocket. An early example of such a back-drive chain is disclosed by U.S. Pat. No. 1,140,319.  FIG. 1  shows a chain  54  in back-side driving contact with a toothed sprocket  56 . Back-side teeth  58  engage the sprocket  56 . However, when a conventional silent chain incorporating toothed back-side driving links similar to those in  FIG. 1  is used with a back-side chain tensioner, the intermittent contact between the back-side link teeth  58  and the chain tensioner can result in wear and vibration problems. 
   In timing systems having a tensioner, the tops of the teeth on the back side of such a chain make intermittent contact with the shoe face of the tensioner. That intermittent contact causes wear, shortens the service life of the tensioner shoe, and also leads to vibration problems that may cause the chain to stretch as well as increase the system noise level. 
   U.S. Pat. No. 5,967,926 addresses the intermittent contact problem by adding flat-faced links to the back-side of a silent chain. To promote increased sliding contact between the back-side of the chain and a chain tensioner, as shown by  FIG. 2 , non-driving outer links  66  were added to the chain. The flat profile  68  of the back-side of these outer links  66  extends beyond the back-side link teeth  64 . The flat profile  68  on the rear side of the chain facilitates sliding contact with the shoe faces of a tensioner and prevents the back-side teeth  64  from contacting a tensioner shoe face. Of course, these additional links also add to the weight and material costs of the chain. As shown by  FIG. 2 , a back-side driving chain link  60  may have a shallow back-side driving link tooth root  62  that limits engagement of a sprocket by back-side teeth  64 . 
   There is a need for a silent chain and sprocket assembly for use with a chain tensioner that is capable of providing driving contact on both sides of the chain. Furthermore, there is also a need for a silent chain and sprocket assembly for use with a chain tensioner that provides improved system wear and vibration characteristics over current designs without adding to the chain&#39;s weight or material costs. 
   BRIEF SUMMARY OF THE INVENTION 
   It is an object of the present invention to address the above-mentioned problems of the prior art by a low profile geometry for the back-side of silent chain links and a sprocket having low profile protrusions that engage the low profile geometry of the chain. 
   According to the present invention, a silent chain and sprocket assembly is provided that is capable of driving sprockets on either side of the chain and can be used in systems having a conventional chain tensioner. The sprockets that engage the front-side of the chain have a plurality of conventional sprocket teeth disposed about their periphery. The sprocket or sprockets that engage the back-side of the chain have a plurality of small, low profile protrusions disposed about the periphery of the sprocket or sprockets. 
   A silent chain according to the present invention may be comprised of a series of interleaved inner and outer rows of links. The link rows are formed by adjacent inverted tooth links. The outer link rows each have a pair of outer link plates mounted to spaced pin members. The outer link plates have a front-side and a back-side. The front-side of the outer link plates forms two teeth that engage three sprocket teeth of the front-side sprocket in a conventional manner. The back-side of the outer link plates is formed so as to engage the low profile protrusions on the periphery of the back-side sprocket, either alone overlying a single protrusion, or in combination with an adjacent link row extending along adjacent surfaces of adjacent protrusions, as the chain wraps on the back-side sprocket. 
   Each inner link row may include a pair of bushings through which the pins mounted to the outer link plates extend. The inner link rows also have a front-side and a back-side that are adjacent to the front and back-side of the outer link plates. The front-side of the inner row links form two teeth that engage three sprocket teeth of the front-side sprocket in a conventional manner. The back-side of the inner row link is formed so as to engage the low profile protrusions on the periphery of the back-side sprocket, either alone overlying a single protrusion, or in combination with links of an adjacent link row extending along adjacent surfaces of adjacent protrusions, as the chain wraps on the back-side sprocket. 
   The lack of conventional high profile teeth on the back-side of the chain promotes sliding contact of the links with a chain tensioner and diminishes the abrupt impact that is characteristic of conventional chain teeth and tensioner shoe contact. This arrangement results in lower chain noise levels and improved system wear and vibration characteristics while avoiding the need for costly additional chain links to accomplish this sliding contact. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side view of conventional toothed sprockets engaging the front and back sides of a silent chain having double-sided toothed links. 
       FIG. 2  is a side view of a portion of a silent chain having double-sided toothed links and additional links having surfaces that contact and slide on a tensioner. 
       FIG. 3  is a side view of a portion of a sprocket having low profile teeth shown in driving contact with the back-side of a portion of a silent chain according to the present invention. 
       FIG. 4  is a side view of an individual link of the silent chain shown by  FIG. 3 . 
       FIG. 5  is a side view of a portion of a sprocket having low profile teeth engaging a silent chain having links with a flat back-side according to the present invention. 
       FIG. 6  is a side view of an individual link of the silent chain shown by  FIG. 5 . 
       FIG. 7  is a side view of a portion of a sprocket having low profile teeth shown in driving contact with a portion of a silent chain according to the present invention that is comprised of links having a back-side surface that conforms to the periphery of the sprocket along adjacent surfaces of adjacent low profile protrusions. 
       FIG. 8  is a side view of an individual link of the silent chain shown in  FIG. 7 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   A silent chain and sprocket assembly according to the present invention improves upon known silent chain and sprocket assemblies that drive from the back-side of a silent chain. According to the present invention, a chain is provided that has links with a generally smooth back-side surface. The chain engages a sprocket that has low profile protrusions that engage the back-side of the chain links as the chain wraps the periphery of the sprocket. The links of the chain conform to the sprocket protrusions either individually as depicted by  FIGS. 3 and 4 , or in conjunction with adjacent links, as shown in  FIGS. 5 ,  6 ,  7  and  8 . The generally smooth back-side profiles of these links increase the silent chain back-side to tensioner sliding contact, substantially reducing the wear and vibration problems associated with prior silent chains that engage a sprocket at the back-side of the chain without adding the additional weight and material costs of special links as shown by  FIG. 2 . 
   This improvement is realized by an embodiment of the present invention shown by  FIG. 3 . The chain  5  includes silent chain links  10 . The links  10  are arranged adjacent to each other along a chain direction of the chain  5  and are joined by pins  11 . Links  10  may be positioned adjacent to each other in a lateral direction, perpendicular to the chain direction, to form rows of links  10 . 
   As best shown by  FIG. 4 , the links  10  define apertures  13  that are separated along the chain direction. The apertures  13  are located near opposite ends of the link  10  along the chain direction and are sized to accept pins  11 . The links  10  have a concave back-side surface  12 . The surface  12  conforms to low convex protrusions  18  along the periphery of sprocket  16 . The concave surface  12  extends from a location adjacent to one aperture  13  substantially the length of the link  10  along the chain direction to a location adjacent to the other aperture  13 . As the silent chain  5  wraps around the sprocket  16 , each protrusion  18  contacts a link  10 , or links  10  of a single row. As best shown by  FIG. 3 , the back-side link surface  12  of each link  10  overlies and engages a sprocket protrusion  18  to create a driving contact. The protrusions  18  do not engage links  10  that are adjacent along the chain direction to the link  10  that overlies the protrusion  18 . 
   The low profile back-side link surface  12  also improves sliding contact between the link  10  and a tensioner shoe, as compared to the intermittent contact of conventional toothed designs, such as the front-side of the links  10 . Front-side link teeth  14  formed by the links  10  are of a conventional silent chain tooth design. The teeth  14  of each link  10  engage three teeth of a conventionally toothed front-side sprocket, one tooth at each end of the link  10  along the chain direction, and one tooth along the link  10  between the teeth  14 . By contrast, the back-side link surface  12  is formed to engage only one protrusion  18  that extends substantially the length of the link  10  along the chain direction. The low profile of the protrusions  18  and their length to engage one link  10  along substantially its chain direction length permits the surface  12  to have a profile that is smoother than the profile of the front-side of the link  10  along the teeth  14 . 
   A second embodiment of the present invention, as depicted in  FIG. 5 , includes a silent chain  25  having links  22  that are joined by pins  27 . As shown in  FIG. 6 , the links  22  have a back-side link surface  24  that is flat. The silent chain  25  engages a sprocket  28  that has protrusions  30  along its periphery that are formed by flat surfaces  32 . Each surface  32  extends generally along the periphery of the sprocket  28  to meet an adjacent surface  32  and to form, with the adjacent surfaces  32 , a protrusion  30  at each end of the surface  32  along the periphery of the sprocket  28 . The link back-side surface  24  does not overlie a sprocket protrusion  30 , but rather overlies a flat surface  32 . As the links  22  of the silent chain  25  wrap around the sprocket  28 , adjacent links  22  articulate with respect to each other about a pin  27 . Two adjacent links  22  articulate to wrap a low flat sided protrusion  30  of the sprocket  28  to position a back-side surface  24  of adjacent links  22  against the surfaces  32  that form a protrusion  30 . 
   The back-side link surfaces  24  of the adjacent links  22  come into driving contact with the surfaces  32  that form a sprocket protrusion  30 . The link surface  24  is substantially the length of the link  22  along the chain direction of the link  22 . The length of the protrusions  30  along the periphery of the sprocket  28  is substantially the distance between pins  27  that engage a link  22 , and are consequently substantially the length of the link  22  along the chain direction. 
   The flat back-side link surface  24  again will slide along a tensioner, which is an improvement over the intermittent contact of conventional toothed designs. The front-side  26  of the link  22  is again a conventional silent chain tooth design wherein each link  22  quietly meshes with a front-side sprocket by engaging three teeth of the sprocket. 
   In a third embodiment of the present invention, shown in  FIGS. 7 and 8 , links  36  of a chain  37  have a small amount of material removed from the leading edge  40  and trailing edge  42  as compared to a flat back side link surface  24  of a link  22  as shown by  FIG. 6 . In a similar manner as described for the embodiment shown by  FIGS. 5 and 6 , two adjacent links  36  articulate with respect to each other at a pin  34  that joins the two links. The adjacent links  36  wrap around a protrusion  48  of a sprocket  46 . The surfaces  38  of adjacent links  36  form a geometry that conforms to surfaces  47  that form adjacent surfaces of adjacent low protrusions  48  on the sprocket  46 . The surfaces  47  are generally flat between the ends of the surface, and extend outwardly from the sprocket near the ends of the surfaces  47 . As the links of the silent chain  36  wrap around the sprocket  46 , the back-side link geometry  38  of adjacent links  36  comes into driving contact with a sprocket protrusion  48  at the surfaces  47 . The chain  37  engages larger sprocket protrusions  48  than those in the embodiment of  FIGS. 5 and 6 , thereby holding the chain on the sprocket  46  more securely. 
   The relatively flat back-side link geometry  38  again results in improved sliding contact between the link back-side  38  and a tensioner shoe, as compared with the intermittent contact of conventional toothed designs. The front-side  44  of the link  36  is again a conventional silent chain tooth design wherein each link  36  quietly meshes with a front-side sprocket to contact three teeth of the sprocket. 
   In all embodiments, the back-sides of the adjacent links along the chain direction form a generally continuous smooth back surface of a silent chain. The back-side of the chain links either overlie a single low profile protrusion, or extend over a surface that forms adjacent surfaces of adjacent sprocket protrusions. This is in contrast to the conventional teeth on the front-side of the link which are formed to engage three teeth of a conventional sprocket. Because the back-side of the link engages fewer surfaces along the periphery of a sprocket compared to the conventional teeth of the front-side, the surface of the back-side of the link extends a greater distance along the chain direction of the link than do the flanks of the teeth on the front-side of the link that engage conventional sprocket teeth. 
   While the invention has been described with reference to several preferred embodiments, those skilled in the art will understand that various changes may be made and equivalents may be substituted without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular step, structure, or material to the teachings of the invention without departing from its scope. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.