Abstract:
In a silent chain, frictional losses and noise are reduced, and power transmitting efficiency is improved, by making the inner profile of each guide plate sufficiently high in relation to a link plate tooth of a link plate overlapped by each said guide plate that engagement between a sprocket tooth and said link plate tooth takes place before engagement of the last mentioned sprocket tooth with said guide plate, even when the chain moves laterally. The tensile hardness of the guide plates is sufficiently low in relation to the bending rigidity of the connecting pins of the chain to prevent substantial warping of the guide plates as a result of tension acting on the chain. The back surfaces of the guide plates are configured to avoid contact with a sliding contact surface of a chain guide on which a back surfaces of the link plates of said chain can slide.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority on the basis of Japanese Patent Application No. 2011-193205, filed on Sep. 5, 2011. The disclosure of Japanese Patent Application No. 2011-193205 is incorporated by reference. 
     FIELD OF THE INVENTION 
     This invention relates to a silent chain having guide plates and link plates that engage with sprockets. The silent chain can be used, for example, to transmit power in automobile engines and industrial machinery. 
     BACKGROUND OF THE INVENTION 
     A typical silent chain comprises alternating guide rows and non-guide rows, each comprising a set of link plates. The link plates of the guide rows and the link plates of the non-guide rows are disposed in interleaved relationship. 
     Each guide row is composed of a pair of spaced, opposed, guide plates and a set of intermediate link plates disposed between the guide plates. The intermediate link plates are engageable with sprockets of a transmission. Each of the non-guide rows is composed of a plurality of inner link plates, which are interleaved with the intermediate link plates of the guide rows and also engageable with the sprockets. Pairs of connecting pins are provided for each pair of guide plates. In the silent chain, the guide rows and non-guide rows are connected in articulating relationship by the connecting pins. A typical silent chain is described in U.S. Pat. No. 6,325,735, granted on Dec. 4, 2001. 
     In the operation of a silent chain transmission, the condition of the chain changes in various ways. In particular, the chain tends to move laterally, or “swing” in the direction of its width. This movement is sometimes referred to as “lateral swing.” 
     As shown in  FIGS. 9A and 9B , a silent chain  501  comprises guide rows  502 , each composed of a pair of guide plates  503  and intermediate link plates  504 , non-guide rows  505 , each composed of a plurality of inner link plates  506 , and pairs of connecting pins  507  fixed to the guide plates  503 . 
     When lateral swing occurs, if an inner end face  503   a  of a guide plate  503  is located in the vicinity of an engagement starting point  504   p , at which an inner flank  504   a  of an intermediate link plate  504  starts to engage a sprocket tooth  509 , it is possible for the guide plate  503  to contact the sprocket tooth  509  before the intermediate link plate  504  contacts the sprocket tooth. Furthermore, as shown in  FIGS. 10A and 10B , when a non-guide row  505  starts to engage the driving sprocket  508 , lateral swing can result in contact between an end surface  503   b  of the guide plate  503  and a sprocket tooth  509  before the inner link plate  506  contacts the sprocket tooth. 
     Ordinarily, the sprocket tooth  509  starts to engage the intermediate link plates  504  and the inner link plates  506  without contacting a guide plate  503 . However, if the sprocket tooth  509  contacts the guide plate  503  before it contacts an intermediate or inner link plate, frictional loss and noise are generated due to contact between the guide plate  503  and the sprocket tooth  509 , causing deterioration in the performance of the silent chain. 
     Furthermore, as shown in  FIG. 11 , when tension in the silent chain  501  increases, the inner link plates  506  can bend the connecting pins  507 , which are held by the pair of guide plates  503  one of which is shown in  FIG. 11 . Bending of the connecting pins  507  can occur when the tensile hardness of the guide plate  503  between the pair of connecting pins  507  exceeds the bending rigidity of the connecting pin  507 . 
     Bending of the connecting pins  507  causes the guide plates  503  to warp so that they become convex toward the intermediate link plates  504  in the chain width direction. Due to the warp, an inner link plate  506  contacts an inside surface  503   a  of the guide plate  503 , causing still more frictional loss when a non-guide row  505  turns relative to an adjacent guide row  502  about the centerline of a connecting pin  507  as the intermediate link plates  504  or the inner link plates  506  start to engage a sprocket. 
     As shown in  FIGS. 9A and 9B , if the back surfaces  503   b ,  504   b  and  506   b  of the guide plate  503 , the intermediate link plate  504  and the inner link plate  506  are co-planar, the contact area of the back of the chain with the sliding-contact surface of a chain guide (not shown) increases, resulting in an additional frictional loss. 
     The several frictional losses described above reduce the power-transmitting efficiency silent chain  501 . Accordingly, there is a need for a silent chain having a plate configuration that reduces frictional losses and improves power transmitting efficiency and noise performance. 
     SUMMARY OF THE INVENTION 
     The silent chain according to the invention is a chain elongated along a direction of chain travel and comprises alternating guide rows and non-guide rows, each row comprising a set of link plates. Each of the guide rows is composed of a pair of guide plates in spaced, opposed relationship, and a plurality of intermediate link plates disposed between the guide plates. Each of the non-guide rows is composed of a plurality of inner link plates. The intermediate link plates of each guide row are interleaved with inner link plates of two adjacent non-guide rows. Two spaced connecting pins are connected to the guide plates of each pair of guide plates, and each of the connecting pins articulably connects a guide row with a non-guide row whereby the guide rows and non-guide rows are disposed in alternating relationship forming a chain. 
     The intermediate link plates and the inner link plates are formed with teeth for engagement with the teeth of a sprocket, and the link plates are rotatable about center lines of the connecting pins. 
     A characterizing feature of the invention is the fact that the inner profile of each of the guide plates is sufficiently high in relation to a link plate tooth of a link plate that is overlapped by each said guide plate that the engagement between a sprocket tooth and said link plate tooth takes place before engagement of the last mentioned sprocket tooth with said guide plate can take place even when the silent chain moves laterally. In addition, the tensile hardness of the guide plates is sufficiently low in relation to the bending rigidity of the connecting pins to prevent substantial warping of the guide plates as a result of tension acting on the chain. Moreover the back surface of each guide plate is configured to avoid contact with a sliding contact surface of a chain guide on which a back surface of a link plate of said chain can slide. 
     With this arrangement, even when the silent chain is moved laterally relative to the sprockets, because the engagement starting point of one link plate of the silent chain is at a position where the guide plate does not contact the sprocket tooth before an adjacent link plate starts to engage the sprocket tooth, it is possible to prevent the guide plate from contacting the sprocket teeth until the sprocket teeth start to engage the inner flanks of the link plates. Accordingly, it is possible to achieve the same engagement starting performance when the chain is moved laterally as when the chain is in its normal position. Frictional losses and noise which would otherwise be caused by contact between the guide plate and a sprocket tooth can be avoided and improved power transmitting efficiency can be achieved. 
     In addition, because the tensile hardness of the guide plates is less the bending rigidity of the connecting pins, it is possible to prevent the connecting pins from bending when the chain is under tension, and to prevent the guide plates from warping due to the bending of the connecting pins. Accordingly, it is possible to reduce frictional contact between the guide plates and the adjacent inner link plates, and thereby achieve a still further reduction in frictional loss. 
     A further reduction in frictional losses is achieved by configuring the back surface of the guide plates to avoid contact with the sliding contact surface of a chain guide. 
     Thus the invention achieves reduction of frictional losses in three ways: by avoiding premature contact between a sprocket tooth and a guide plate, by avoiding warping of the guide plates due to chain tension, and by reducing the contact area between the back of the chain and the sliding contact surface of a chain guide. 
     Another aspect of the invention is the formation of the back surfaces of the guide plates so that they have a pair of spaced portions connected by a concave portion. The spaced portions have a back surface height greater than the back surface height of the concave portion, and the back surface heights of the spaced portions are lower than the back surface heights of the intermediate link plates between the guide plates and lower than the back surface height of the inner link plates of the non-guide rows. 
     The concave configuration of the backs of the guide plates reduces the tensile hardness of the guide plate, making it possible to avoid substantial warping of the guide plates as a result of chain tension. In addition avoiding contact between the back surfaces of the guide plates and the chain guide reduces frictional loss. 
     According to still another aspect of the invention, the back surfaces of the link plates have a convex arcuate shape along the direction of travel of the chain. With this arrangement, it becomes possible to reduce the contact area of the back surfaces with the sliding contact surface of a chain guide and thereby achieve a still greater reduction in the overall frictional loss in the operation of a silent chain transmission. 
     In still another aspect of the invention, at least some of the link plates have back surfaces with convex arcuate shapes in section planes transverse to the direction of travel of the chain. Accordingly, it is possible to achieve a still further reduction in the overall frictional loss of a silent chain transmission. 
     In another aspect of the invention, in at least one set of the rows from a set consisting of the guide rows of the chain and a set consisting of the non-guide rows of the chain, at least one link plate has a back surface configured to avoid contact with a sliding-contact surface when said sliding contact surface is in sliding contact with backs of other link plates in the same row. 
     With this arrangement, it is possible to reduce still further the contact area between the chain and the sliding contact surface of a guide, and thereby achieve a still greater reduction in the overall frictional loss in the operation of a silent chain transmission. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a side elevational view of part of a silent chain transmission incorporating a silent chain in accordance with the invention; 
         FIG. 2  is a sectional a part of the silent chain shown in  FIG. 1  on a plane in which the center lines of the connecting pins; 
         FIG. 3A  is a side elevational of a part of the silent chain transmission, showing the engagement of a guide row of the silent chain in  FIG. 1  with a sprocket; 
         FIG. 3B  is an enlargement of a part of the transmission of  FIG. 3A  outlined by a broken line circle in  FIG. 3A ; 
         FIG. 3C  is a sectional view taken on section plane IIIC-IIIC in  FIG. 3B ; 
         FIG. 4A  is a side elevational view of a part of the silent chain transmission, showing the engagement of a non-guide row of the silent chain in  FIG. 1  with a sprocket 
         FIG. 4B  is an enlargement of a part of the transmission of  FIG. 4A  outlined by a broken line circle in  FIG. 4A ; 
         FIG. 5  is a side view showing a part of the silent chain of  FIG. 1  in sliding contact with a chain guide; 
         FIG. 6  is a sectional view taken on section plane VI-VI in  FIG. 5 ; 
         FIG. 7  is a sectional view corresponding to  FIG. 6  but showing a first modification of the invention; 
         FIG. 8  is another sectional view corresponding to  FIG. 6  but showing another modification of the invention; 
         FIG. 9A  is a sectional view showing engagement of a guide row of a conventional chain with a sprocket; 
         FIG. 9B  is an enlarged view of a part of the silent chain transmission shown in  FIG. 9A  outlined by a broken line circle in  FIG. 9A ; 
         FIG. 10A  is a sectional view showing engagement of a non-guide row of a conventional chain with a sprocket; 
         FIG. 10B  is an enlarged view of a part of the silent chain transmission shown in  FIG. 10A  outlined by a broken line circle in  FIG. 10A ; and 
         FIG. 11  is a sectional view of part of a conventional the silent chain as shown in  FIG. 9A , taken on a plane in which the centerline of the connecting pins lie. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As shown in  FIGS. 1 and 2 , a silent chain  100  is incorporated into a silent chain transmission  1 , which comprises a plurality of sprockets with which the chain is engaged, one such sprocket being shown in  FIG. 1 . The transmission also includes, a chain guide  5  ( FIG. 5 ) on which the silent chain slides. 
     The silent chain  100  is composed of a plurality of guide rows  103 , a plurality of non-guide rows  104 , and a plurality of connecting pins  105  that connect the guide rows  103  with the non-guide rows  104  in alternation relationship to form an endless chain. 
     The sprocket mechanism is composed of a plurality of sprockets, i.e., one or more driving sprockets  3  and one or more driven sprocket  2 , each having a plurality of sprocket teeth  4 . 
       FIG. 1  shows a driving sprocket  3  that rotates in a direction R about an axis Ls. 
       FIGS. 5 and 6  shows a chain guide  6  which can be either a tensioner lever that applies tension to the chain, or a stationary chain guide. In either case, the chain guide has a sliding-contact surface  7  on which the back of the traveling silent chain  100  slides 
     As shown in  FIGS. 1 and 2 , the traveling direction is the direction in which the silent chain  100  moves, and the chain width direction (see  FIG. 2 ) is a direction parallel to the centerline Lc of the connecting pins about which a non-guide row  104  bends relative to a guide row  103 . These centerline Lc are parallel to the axis of rotation Ls of the sprocket  3 . The front and back directions are respectively the direction of chain travel and the direction opposite to the direction of chain travel. A side view is a view from a direction in parallel with the centerline Lc and the sprocket axis Ls, and the radial direction is a direction perpendicular the axis Ls of the sprocket  3 . 
     A lateral swing is condition in which the traveling silent chain  100  swings in the chain width direction, and also includes a condition in which the silent chain  100  is slanted in the chain width direction. 
     The silent chain  100  has guide rows  103 , each comprising a pair of guide plates  110  and a number of intermediate link plates  130 . The chain also has non-guide rows  104 , each having a number of inner link plates  150  exceeding by one the number of intermediate link plates in a guide row. Each guide row comprises a pairs of connecting pins  105  each pin being fixed to both of the opposite guide plates  110 . The pins are separated from each other in the direction of chain travel. Each pin connect the intermediate link plates  130  of a guide row with the inner link plates  150  of an adjacent non-guide row in interleaved relationship, allowing both sets of link plates to rotate about the center line Lc of the pin. 
     In  FIGS. 2 and 6 , gaps between the guide plates  110 , the intermediate link plates  130  and the inner link plates  150  and gaps between the connecting pins  150  and pin insertion holes  131  and  151  are exaggerated. 
     A plurality of intermediate link plates  130  is disposed between the pair of guide plates  110  in the chain width direction in each guide row  103 . Each guide plate  110  is provided with pin holding holes  111  at positions separated from each other in the direction of chain travel, i.e., in the front-back direction. 
     The ends of each of the connecting pins  105  are fixed in the holding holes of the guide plates  110  by suitable means such as press-fitting or caulking. 
     The inner link plates  150  in each non-guide row  104  are disposed in interleaved relationship with the intermediate link plates and guide plates of each of two adjacent guide rows. As shown in  FIG. 2 , inner link plates  150 E, located at ends of each non-guide row  104  are disposed next to guide plates  110  in adjacent guide rows. 
     As shown in  FIGS. 3A ,  3 B,  4 A and  4 B, the intermediate link plate  130  and the inner link plate  150  respectively have a pair of link teeth  132  and  133  and  152  and  153  that project radially inward for engagement with sprocket teeth. Teeth  132  and  133  are front and rear link teeth respectively, and teeth  152  and  153  are front and rear link teeth respectively. 
     The respective link teeth  132  and  133  have inner flanks  144  and  145  and outer flanks  146  and  147 , which can contact sprocket teeth  4 . The respective link teeth  152  and  153  likewise have inner flanks  164  and  165  and outer flanks  166  and  167  which can contact sprocket teeth  4 . 
     The pairs of the inner flanks  144  and  145  and  164  and  165  of the respective link plates  130  and  150  are front inner flanks ( 144  and  164 ) and rear inner flanks ( 144  and  155 ), and the pairs of the outer flanks  146  and  147  and  166  and  167  are front outer flanks ( 146  and  166 ) and rear outer flanks ( 147  and  167 ). 
     The intermediate link plates  130  and the inner link plates  150  are provided respectively with pin insertion holes  131  and  151  through which the connecting pins  105  are inserted as shown in  FIG. 2 . 
     Each pair of connecting pins  105  held by a pair of guide plates  110  in a guide row  103  connects a link plate group composed of the intermediate link plates  130  and the inner link plates  150  of two adjacent non-guide rows, allowing the non-guide rows to articulate with respect to the guide rows about connecting pin centerline Lc. Although the connecting pins  105  shown in the drawings are round pins, the connecting pins can be rocker pins, each composed of two elements having mutually engaging cylindrical surfaces that roll on each other. 
     As shown in  FIGS. 3A through 5 , the profiles of the link plates  130  and  150 , comprise inner profile surfaces  142  and  162  on the side where the sprocket teeth  4  are located and outer profile surfaces, i.e., back surfaces,  141  and  161 , located on a side opposite from the inner profile surfaces  142  and  162 . The pin reference plane A passing through the center lines Lc of the pins marks the border between the inner and outer profile surfaces. The side where the sprocket tooth  4  is located is radially inward of the portion  101  of the chain wrapped onto the sprocket  3 , and the side opposite from the inner profile surfaces is outward in the radial direction. The inner profile surfaces  142  and  162  have flanks  144  through  147  ( FIG. 3A) and 164  through  167  ( FIG. 4A ). 
     With reference to  FIGS. 3A and 5 , and as shown in  FIG. 5  in particular, the back surfaces  141  and  161  of the respective link plates  130  and  150  are convex, having arc-shaped intermediate parts  141   a  and  161   a , where the back surface heights H 4  and H 6  are maximum. 
     The back surface heights H 4  and H 6  of the link plates and the back surface height H 2  of the guide plates are distances respectively from the pin reference plane A to the back surfaces of the plates. As shown in  FIG. 6 , the respective back surfaces  141  and  161  that slide on surface  7  of the guide are convex, arc-shaped, surfaces in a section plane orthogonal to the pin reference plane A. The “arc-shaped” surfaces  121  and  141  can be in the form of an arc having a single radius of curvature, a curve composed of a plurality of arcs having different radii of curvature that merge together smoothly, or an approximated arc. 
     As shown in  FIGS. 3A ,  3 B,  4 A and  4 B, when the silent chain  100  travels normally, and the guide row  103  and the non-guide row  104  engage the sprocket teeth  4 , the front inner flanks  144  and  164  of the respective link plates  130  and  150  start to engage a sprocket tooth  4 . The engagement point moves inwardly along the sprocket tooth  4  as the engagement advances, and the engagement points in the respective link plates  130  and  150  shift from the inner flanks  144  and  164  to the outer flanks  146  and  147  and  166  and  167 . When the link plate is fully engaged with the sprocket, both outer flanks  146  and  147  of the intermediate link plates  130  of the guide row contact a sprocket tooth  4  and both outer flanks  166  and  167  of the inner link plates of the non-guide row contact a sprocket tooth, so that the link plates become seated on the sprocket. Therefore, the silent chain  100  is a referred to as an inner flank-engaging, outer flank-seating type chain. 
     The ordinary position of the chain is a position in which the sprocket tooth  4  is located within the span W ( FIG. 2 ) between the guide plates  110  of guide row  103 . Thus neither of the guide plates  110  overlaps the sprocket tooth in the chain width direction. However, when the silent chain  100  swings laterally, a sprocket tooth may not be within the span W between the guide plates  110 . 
     As shown in  FIG. 2 , the respective guide plates  110  have an outer side surface  112  and an inner side surface  113 . As shown in  FIGS. 3A and 4A , the guide plate  110  has an inner profile surface  122  on the side where the sprocket tooth  4  is located and an outer profile surface, i.e., a back surfaces  121 , located on the side opposite from the inner profile surface  122 . The portion  115  which has a maximum dimension in the direction of chain travel, constitutes the border between the inner and outer profile surfaces of the guide plate. 
     The inner profile surface  122  of the guide plate  110  has an inner end surface  123  having a portion located innermost in the radial direction, and a pair of inner side end surfaces  124  and  125  each extending from the inner end surface  123  to a maximum width portion  115 . 
     When seen from the side, the inner end surface  123  intersects the inner flanks  144  and  145  of an intermediate link plate  130  at locations near the ends of surface  123 , and the inner end surface  123  is located radially inward in the radial direction of inner side end surfaces  124  and  125 . The straight inner side end surfaces  124  and  125  are front and rear inner side end surfaces respectively. 
     As shown in  FIG. 3B , the inner end surface  123  is connected to front inner side end surface  124  by an arc-shaped connecting part. The rear inner side end surface  125  is similarly connected to the inner end surface  123  by an arc-shaped connecting part. The respective inner side end surfaces  124  and  125  can otherwise be straight. This shape of the guide plate  110  makes it possible to form the guide plate easily and to enhance its bending rigidity in the chain width direction even when the back surface  121  is concave. Thus the guide plate can be made more rigid and resistant to bending than a guide plate in which the inner profile surface has one or more concave portions. Consequently it is possible to prevent the guide plate  110  from warping due to chain tension acting on the guide plate through a connecting pin as in the case of guide plate  503  in  FIG. 11 . 
     As shown in  FIGS. 5 and 6 , the back surface  121  of the guide plate  110  has an arc-shaped concave portion  121   c  formed so that the back surface has two parts  121   a  and  121   b  where the back surface height H 2  is maximum. Although the back surface heights H 2  of parts  121   a  and  121   b  are the same in the embodiment described, they can be different. The arc-shape concave portion  121   c  has a maximum depth at  121   e  where the back surface height H 2  is minimum. The maximum depth is at a location midway between the locations of the connecting pins  105 . The concave portion  121   c  is located radially inward relative to parts  121   a  and  121   b.    
     The tensile hardness of the guide plate  110  having the concave portion  121   c  formed as described above is lower than that of a guide plate having no concave portion, and selected so that it is to be smaller than the bending rigidity of the connecting pin  105 . Therefore, due to the ductility of the guide plates and the rigidity of the connecting pins, a force exerted by the link plates on the connecting pins due to excessive chain tension tends to stretch the guide plates instead of bend the connecting pins. Consequently, warping of the guide plates as depicted in  FIG. 11  can be suppressed, and frictional loss caused by contact of the inner side surface  113  of the guide plates with the endmost inner link plates of the guide rows can be avoided or at least significantly reduced. 
     As shown in  FIG. 5 , the back surface height H 2  of the back surface  121 , including that of portions  121   a  and  121   b , is less than the back surface heights H 4  and H 6  of the back surfaces  141  and  161  of the respective link plates  130  and  150  within the range where the back surface  121  of the guide plate  110  overlaps the link plates  130  and  150  in the direction of chain travel. 
     Because of its limited back surface height H 2 , the guide plate  110  is prevented from contacting the sliding-contact surface  7  of the guide even when the back surfaces  141  and  161  of the respective link plates  130  and  150  are in sliding contact with guide surface  7  while the chain is in a slanted contact condition. Accordingly a further reduction in frictional loss can be achieved. 
     When the silent chain  100  is driven by the sprocket  3  while in a lateral swinging condition, engagement starting points P 3  and P 5  of the respective front inner flanks  144  and  164  of the intermediate and inner link plates  130  and  150  with the sprocket tooth  4 , are at positions such that the guide plate  110  is prevented from contacting the sprocket tooth  4  before the front inner flanks  144  and  164  of the respective link plates  130  and  150  start to engage the sprocket tooth  4 . Therefore, contact takes place in the same manner as when the silent chain  100  is located at its ordinary position. 
     Therefore, when the intermediate and inner link plates  130  and  150  start to engage the sprocket tooth  4 , the intermediate and inner link plates  130  and  150  always contact the sprocket tooth  4  before the sprocket tooth can contact the guide plate  110 . 
     Specifically, as shown in  FIG. 3B , the guide plate  110  is configured so that, even when the chain is in a laterally swinging condition, neither the inner end surface  123  nor either of the inner side end surfaces  124  and  125  can engage the sprocket tooth  4   a  before the front inner flank surface  144  of the intermediate link plate  130  starts to engage the sprocket tooth  4   a.    
     Therefore, the entire guide plate  110 , including the inner end surface  123 , is located radially outward from the engagement starting point P 3  before the front inner flank surface  144  starts to engage the sprocket  3 . 
     As shown in  FIGS. 3B and 3C , when the guide plate  110  has an overlapping portion  117  that overlaps the sprocket tooth  4  when seen from the side, the inner end surface  123  is configured so that the sprocket tooth  4  is located within the span W ( FIG. 5 ) in the overlapping portion  117  in order to avoid contact between the inner end surface  123  and the sprocket tooth  4   a  before the front inner flank surface  144  starts to engage the sprocket tooth  4   a.    
     In another example, the guide plate  110  can be configured so that no part of the guide plate overlaps the sprocket tooth  4  when seen from the side before the intermediate link plate  130  starts to engage with the sprocket tooth  4 . 
     As shown in  FIGS. 4A and 4B , the guide plate  110  is configured to prevent the inner end surface  123  and the both inner side end surfaces  124  and  125  from contacting the sprocket tooth  4  before the front inner flank surface  164  of the inner link plate  150  starts to engage the sprocket tooth  4  when the chain is in the lateral swinging condition. Here, the entire inner profile surface  122 , including the rear inner side end surface  125 , is located radially outwardly from the engagement starting point P 5  before the front inner flank surface  144  starts to engage the sprocket tooth  4 , and the no part of the guide plate  110  overlaps the sprocket tooth  4 . 
     The guide plate  110  is configured to avoid contact between the inner profile surface  122  of the guide plate  110  and the sprocket tooth  4   b , or so that the guide plate  110  does not overlap the sprocket tooth  4  when seen from the side, throughout the interval from the start of the engagement of the front inner flank surface  144  of the inner link plate  150  with the sprocket tooth  4  until the both outer flanks  146  and  147  of the intermediate link plate  130  located ahead of the inner link plate  150  seat on the sprocket  3  by contact respectively with sprocket tooth  4   c  ahead of the sprocket tooth  4   a  and sprocket tooth  4   b.    
     Accordingly, the rear inner side end surface  125  of the guide plate is configured so that it is prevented from contacting the sprocket tooth  4  or so that the rear inner side end surface  125  does not overlap the sprocket tooth  4  when seen from the side, throughout the interval from the start of engagement of the inner link plate  150  with the sprocket tooth  4  until the intermediate link plate  130  located ahead of the inner link plate  150  seats on the sprocket  3 . 
     The positions of the engagement starting points P 3  and P 5  described above and the configuration of the guide plate  110  with respect to the sprocket tooth  4  described above prevent the guide plate  110  from contacting the sprocket tooth  4  before the intermediate and inner link plates  130  and  150  contact even when the traveling silent chain  100  is operated while in the lateral swing condition. 
     With the configuration described above it is possible, even when the chain is in a laterally swinging condition, to maintain normal engagement wherein the link plates  130  and  150  of the silent chain  100  first contact the sprocket tooth  4  in the same manner in which they contact the sprocket tooth when the silent chain is traveling in its normal position. Because it is possible to prevent the frictional loss and noise otherwise caused by the contact of the guide plate  110  and the sprocket tooth  4 , improve power transmitting efficiency and noise performance can be realized. 
     Because the inner profile surface  122  is located radially outward relative to the engagement starting points P 3  and P 5 , it is possible to downsize the guide plate  110  in the radial direction and to reduce the weight of the guide plate. Furthermore, because the guide plate  110  is configured to prevent the rear inner side end surface  125  of the guide plate  110  from contacting the sprocket tooth  4  from the start of engagement of the inner link plate  150  with the sprocket until the intermediate link plate  130  seats on the sprocket, it is possible to downsize the guide plate  110  still further by reducing its radial dimensions. 
     Because the tensile hardness of the guide plate  110  is smaller than the bending rigidity of the connecting pins  105  it is possible to suppress warping of the guide plates due to bending of the connecting pins. Suppression of bending of the guide plates, in turn reduces the frictional loss caused by excessive frictional contact between the guide plates and adjacent outermost intermediate link plates. 
     A further reduction of frictional loss is realized by configuring the back surfaces  121  of the guide plates so that they are prevented from contacting the sliding contact surface of a chain guide on which the backs of the intermediate and inner link plates slide. 
     The concave configuration of the back surface of the guide plate  110  also reduces the tensile hardness of the guide plate, reducing the tendency of the connecting pins to bend and cause warping of the guide plate as a result of tension on the chain 
     The convex, arc-shaped configurations of the backs  141  and  161  of the respective link plates reduce the contact area between the chain and the sliding-contact surface of the chain guide, further reducing frictional loss. The convex, arc-shaped, configurations of the backs  141  and  161 , while advantageous, are of course optional. Many advantages of the invention can be realized in a chain the link plates of which do not have convex backs. 
     In a modification shown in  FIG. 7 , an inner link plate  150  can be a sliding-contact link plate the back surface  161  of which has an arcuate shape in the direction of chain travel and an arc-shaped transverse section in the direction of the width of the chain. The intermediate link plates  130  in the guide rows, and, optionally, some of the other inner link plates  150  in the non-guide rows, can be configured to avoid contact with the sliding contact surface of a guide. 
     Alternatively, as shown in  FIG. 8 , an intermediate link plate  130  of the guide rows, can a sliding-contact link plate the back surface  141  of which has an arcuate shape in the direction of chain travel and an arc-shaped transverse section in the direction of the width of the chain. The inner link plates  150 , and optionally one or more of the other intermediate link plates  130  can be configured to avoid the contact with the sliding contact surface of a guide. 
     With the arrangements shown in  FIGS. 7 and 8 , the use of non-sliding-contact link plates makes it possible to reduce the contact area between the chain and the sliding contact surface of a chain guide with a resulting reduction in frictional loss. 
     Although the invention is described with reference to a driving sprocket wherein contact between a sprocket tooth and a guide plate before the start of engagement with a link plate tooth is avoided, advantages of the invention can be realized by configuring the chain so that a similar effect is realized at the engagement of the chain with a driven sprocket. Here, if the sprocket is a driven sprocket, the engagement starting points P 3  and P 5  are located on the rear inner flanks  145  and  165 . 
     The silent chain may be of a type other than the inner-flank-engaging and outer-flank-seating type chain, such as an outer-flank-engaging and outer-flank-seating type chain or an inner-flank-engaging and inner-flank-seating type chain. 
     Advantages of the invention can be realized both in an endless silent chain, or in a reciprocating silent chain not formed into an endless loop.