Patent Publication Number: US-2009233744-A1

Title: Power transmission chain and power transmission device

Description:
TECHNICAL FIELD 
     The present invention relates to a power transmission chain and a power transmission device. 
     BACKGROUND ART 
     Power transmission devices, such as a pulley-type continuously variable transmission (CVT) in an automobile, include a type provided with an endless power transmission chain wound around a pair of pulleys. Such power transmission chains include a type provided with links each having a pair of pin holes and coupling pins that couples these links one to another (see, for example, Patent Documents 1 through 4). 
     Of these references, Patent Document 2 describes a type that includes, as the coupling pins, a center pin disposed at the center inside the pin hole and a pair of locker pins disposed on both the sides of the center pin. 
     In Patent Document 2, both the side surfaces of the center pin are each in the form of a convex curved surface. Also, convex curved surfaces that abut on the corresponding convex curved surfaces of the center pin are provided to the pair of locker pins. Accordingly, when each locker pin comes into rolling contact with the center pin at a predetermined angle at a time, adjacent links are allowed to bend at a bending angle which is double the predetermined angle. 
     Patent Document 1: 
     Japanese Unexamined Patent Publication No. 2001-234983 
     Patent Document 2: 
     Japanese Unexamined Patent Publication No. 2001-234982 
     Patent Document 3: 
     Japanese Unexamined Patent Publication No. 08-312725 
     Patent Document 4: 
     Japanese Unexamined Patent Publication No. 2005-226831 
     DISCLOSURE OF THE INVENTION 
     Problems to be Solved by the Invention 
     Also, power transmission chains in Patent Documents 3 and 4 include plural links each having a front through-hole and a rear through-hole aligned in the chain travel direction and plural pins that couple these links one to another. The plural pins include pins that are press-engaged in one of the front through-hole and the rear through-hole and pins that are loose-fit into the other one of the front through-hole and the rear through-hole. For the power transmission chains described above, there has been a request to further enhance durability. The invention has an object to solve the problems discussed above. 
     Means for Solving the Problems 
     In order to solve the problems discussed above, one of the options would be to enhance the durability of the overall power transmission chain by making the pins larger for the press-engaged portion of the pin and the link to shape a gentler curve (curved surface) so that the durability of the links is enhanced by reducing stress induced on the links resulting from the load applied from the pins. In this case, however, the overall power transmission chain is increased in size. An increase in size of the power transmission chain is not preferable because making more compact devices is a strong request for automobiles or the like in which the pulley-type power transmission device is to be mounted. Accordingly, there has been a need for a power transmission chain to be enhanced in durability without increasing the size thereof. 
     The inventors of the present application achieved the invention on the basis of their finding that making the engagement state of the links and the pins in a most suitable condition can contribute to a reduction of stress induced on the links, which makes it possible to more enhance the durability of the power transmission chain without having to increase the size thereof. 
     A preferred aspect of the invention includes plural link units aligned in a chain travel direction, and plural coupling members that couple the plural link units to be bendable with respect to one another. The link units each include plural link plates aligned in a chain width direction orthogonal to the chain travel direction. Each link plate has through-holes. Each coupling member has a power transmission member inserted into the corresponding through-holes in the corresponding link plates. Each power transmission member has a pair of end portions with respect to an orthogonal direction that is orthogonal to both the chain travel direction and the chain width direction. Each end portion of each power transmission member is received by a receiving portion provided to the corresponding through-hole in the corresponding link plate. At least the one end portion of each power transmission member includes a curved surface portion received by the corresponding receiving portion. The curved surface portion includes an apex portion with respect to the orthogonal direction. A curvature radius of the curved surface portion is increased continuously or step by step as headed toward the apex portion. 
     According to this aspect, the curvature radius of the curved surface portion of the power transmission member is increased as headed toward the apex portion. Accordingly, the apex portion can be made into a more flat shape. Hence, when the receiving portions of the link plate receive load from the corresponding curved surface portions of the power transmission member, it is possible to suppress the occurrence of stress concentration at the peripheral portion of the through-hole in the link plate. Consequently, the durability of the link plate can be enhanced by suppressing fatigue thereof, which can enhance the durability of the power transmission chain markedly. In addition, because stress induced on the link due to insertion of the power transmission member is reduced, it is possible to make the power transmission member thinner with respect to the chain travel direction. Accordingly, a distance in the chain travel direction between the through-holes adjacent to each other in the chain travel direction can be made shorter by reducing the shape of the through-holes in size. Hence, many more power transmission members are pinched at a time by an object to which power is to be transmitted, such as pulleys. It is thus possible to achieve further enhancement of the allowable transmission torque of the power transmission chain. In addition, it is possible to achieve further enhancement of durability by reducing load per power transmission member. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view schematically showing the configuration of a major portion of a chain-type continuously variable transmission as a power transmission device provided with a power transmission chain according to one embodiment of the invention. 
         FIG. 2  is a partial section of a drive pulley (driven pulley) and a chain of  FIG. 1 . 
         FIG. 3  is a section of a major portion of the chain. 
         FIG. 4  is a section taken on line IV-IV of  FIG. 3  and showing a straight region of the chain. 
         FIG. 5  is a side view of a major portion in a bending region of the chain. 
         FIG. 6  is an enlarged section of a first pin. 
         FIG. 7  is an enlarged section of a second pin. 
         FIG. 8  is a side view of a major portion according to another embodiment of the invention. 
         FIG. 9  is a section of a major portion according to still another embodiment of the invention. 
         FIG. 10  is an enlarged view of a second pin of  FIG. 9 . 
         FIG. 11  is a section of a major portion according to still another embodiment of the invention. 
         FIG. 12  is a section of a major portion according to still another embodiment of the invention. 
         FIG. 13  is a partial section of a major portion according to still another embodiment of the invention. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Preferred embodiments of the invention will be described with reference to the accompanying drawings. 
       FIG. 1  is a perspective view schematically showing the configuration of a major portion of a chain-type continuously variable transmission (hereinafter, also referred to simply as the continuously variable transmission) as a power transmission device provided with a power transmission chain according to one embodiment of the invention. Referring to  FIG. 1 , a continuously variable transmission  100  is to be mounted on a vehicle, such as an automobile, and includes a drive pulley  60  made of metal (structural steel or the like) as a first pulley, a driven pulley  70  made of metal (structural steel or the like) as a second pulley, and an endless power transmission chain  1  (hereinafter, also referred to simply as the chain) wound around a pair of these pulleys  60  and  70 . For ease of understanding, the partial section of the chain  1  is shown in  FIG. 1 . 
     While the continuously variable transmission  100  is driven, the chain  1  undergoes transitions alternately between a straight region where it is stretched straight and a bending region as a region wound around either one of the pair of pulleys  60  and  70 , and transmits power between the pair of pulleys  60  and  70 . 
       FIG. 2  is a partial section of the drive pulley  60  (driven pulley  70 ) and the chain  1  of  FIG. 1 . Referring to  FIG. 1  and  FIG. 2 , the drive pulley  60  is attached in a together rotatable manner to an input shaft  61  that is coupled to a vehicle driving source in such a manner that power can be transmitted from the driving source. The drive pulley  60  includes a stationary sheave  62  and a movable sheave  63 . 
     The stationary sheave  62  and the movable sheave  63  have a pair of mutually opposing sheave surfaces  62   a  and  63   a , respectively. Each of the sheave surfaces  62   a  and  63   a  includes an inclined surface in the form of a circular conical surface. A groove is defined between these sheave surfaces  62   a  and  63   a  and the chain  1  is caught tightly and held in this groove. 
     A hydraulic actuator (not shown) to change the groove width is connected to the movable sheave  63 . The groove width can be varied at speed change by moving the movable sheave  63  in the axial direction of the input shaft  61  (right-left direction in  FIG. 2 ). Accordingly, the chain  1  is allowed to move in the radial direction of the input shaft  61  (top-bottom direction in  FIG. 2 ), which makes it possible to change an effective radius of the pulley  60  with respect to the chain  1  (equivalent to a wound radius of the pulley  60 ). 
     In  FIG. 2 , reference characters to denote components of the driven pulley  70  corresponding to the counterparts of the drive pulley  60  are shown in parentheses. As are shown in  FIG. 1  and  FIG. 2 , the driven pulley  70  is attached in a together rotatable manner to an output shaft  71  that is coupled to the drive wheel (not shown) in such a manner that power can be transmitted to the drive wheel. As with the drive pulley  60 , the driven pulley  70  includes a stationary sheave  73  and a movable sheave  72 . As with the drive pulley  60 , the stationary sheave  73  and the movable sheave  72  have a pair of mutually opposing sheave surfaces  73   a  and  72   a , respectively, to define a groove in which the chain  1  is to be caught tightly. 
     As with the movable sheave  63  of the drive pulley  60 , a hydraulic actuator (not shown) is connected to the movable sheave  72  of the driven pulley  70 , so that the groove width is varied at speed change by moving the movable sheave  72 . It is thus possible to change an effective radius of the pulley  70  with respect to the chain  1  (equivalent to a wound radius of the pulley  70 ) by moving the chain  1 . 
       FIG. 3  is a section of a major portion of the chain  1 .  FIG. 4  is a section taken on line IV-IV of  FIG. 3  and showing the straight region of the chain  1 .  FIG. 5  is a side view of a major portion of the bending region of the chain  1 . 
     Hereinafter, the chain  1  will be described in reference to the straight region of the chain  1  when reference is made to  FIG. 4 , and in reference to the bending region of the chain  1  when reference is made to  FIG. 5 . 
     Referring to  FIG. 3  and  FIG. 4 , the chain  1  includes links  2  as plural link plates and plural coupling members  50  that couple these links  2  to be bendable with respect to one another. 
     Hereinafter, a direction along the travel direction of the chain  1  is defined as the chain travel direction X, a direction orthogonal to the chain travel direction X and along the longitudinal direction of the coupling members  50  is defined as the chain width direction W, and a direction orthogonal to both the chain travel direction X and the chain width direction W is defined as the orthogonal direction V. 
     Each link  2  is in the form of a plate, and includes a front end portion  5  and a rear end portion  6  as a pair of end portions aligned from front to rear in the chain travel direction X, and an intermediate portion  7  disposed between the front end portion  5  and the rear end portion  6 . 
     The front end portion  5  and the rear end portion  6  are provided with a front through-hole  9  as a first through-hole and a rear through-hole  10  as a second through-hole, respectively. The intermediate portion  7  has a pillar portion  8  as a partition between the front through-hole  9  and the rear through-hole  10 . The pillar portion  8  has a predetermined thickness in the chain travel direction X. The peripheral portion of each link  2  shapes a smooth curve, which is deemed as a shape that hardly causes stress concentration. 
     First through third link units  51  through  53  are formed using the links  2 . To be more predetermined, the first link unit  51 , the second link unit  52 , and the third link unit  53  each include plural links  2  aligned in the chain width direction W. In each of the first through third link units  51  through  53 , the links  2  in the same link unit are aligned so that all are lined up at the same position in the chain travel direction X. The first through third link units  51  through  53  are disposed along the chain travel direction X. 
     The respective links  2  in the first through third link units  51  through  53  are coupled to the corresponding links  2  in the first through third link units  51  through  53  using the corresponding coupling members  50  in a bendable manner. 
     To be more concrete, the front through-hole  9  in the link  2  of the first link unit  51  and the rear through-hole  10  in the link  2  of the second link unit  52  are aligned in the chain width direction W and correspond to each other. The links  2  in the first and second link units  51  and  52  are coupled so as to be bendable with respect to each other in the chain travel direction X using the coupling member  50  that is inserted through these through-holes  9  and  10 . 
     Likewise, the front through-hole  9  in the link  2  of the second link unit  52  and the rear through-hole  10  in the link  2  of the third link unit  53  are aligned in the chain width direction W and correspond to each other. The links  2  in the second and third link units  52  and  53  are coupled so as to be bendable with respect to each other in the chain travel direction X with the coupling member  50  that is inserted through these through-holes  9  and  10 . 
     In  FIG. 3 , the first through third link units  51  through  53  are shown one for each. However, the first through third link units  51  through  53  are disposed repetitively along the chain travel direction X. The respective links  2  of two link units adjacent to each other in the chain travel direction X are successively coupled to each other with the corresponding coupling members  50  to form the endless chain  1 . 
     Referring to  FIG. 3  and  FIG. 4 , each coupling member  50  includes a first pin  3  as a first power transmission member and a second pin  4  as a second power transmission member, and these first and second pins  3  and  4  make a pair. The first pin  3  comes into rolling and sliding contact with respect to the second pin  4  disposed ahead in the chain travel direction X in association with bending between the links  2 . 
     The term, “rolling and sliding contact”, referred to herein means a contact state including at least one of rolling contact and sliding contact. 
     The first pin  3  is a plate-like member that extends long in the chain width direction W. A peripheral surface  11  of the first pin  3  extends in parallel with the chain width direction W. 
     The peripheral surface  11  is formed as a smooth surface and has a front portion  12  as an opposing portion facing frontward in the chain travel direction X, a rear portion  13  as a back portion facing rearward in the chain travel direction X, and one end portion  14  and the other end portion  15  as a pair of end portions mutually opposing in the orthogonal direction V. 
     Hereinafter, of the orthogonal direction V, a direction heading from the one end portion  14  to the other end portion  15  is referred to as the chain inside direction, and a direction heading from the other end portion  15  to the one end portion  14  is referred to as the chain outside direction. 
     The front portion  12  opposes the second pin  4  as a counterpart of the pair. The front portion  12  includes a main body portion  12   a  that comes into rolling and sliding contact with a rear portion  19  of the second pin  4  described below at a contact portion T (a contact point when viewed from the chain width direction W), and a contact-avoiding portion  12   b  positioned on the side opposite to the chain travel direction X with respect to the main body portion  12   a.    
     The rear portion  13  includes a flat surface, and has a first angle of attack B 1  (for example, 10°) with respect to a plane A orthogonal to the chain travel direction X (a plane orthogonal to the sheet surface of  FIG. 4 ). The rear portion  13  is inclined at 10° with respect to the plane A in a counterclockwise direction in the drawing, and faces the chain inside direction. 
     The one end portion  14  forms the end portion of the peripheral surface  11  of the first pin  3  on the chain outside direction. The one end portion  14  is shaped in a curved surface that curves convexly to the chain outside direction and is formed as a curved surface portion. A generally intermediate portion of the one end portion  14  in the circumferential direction forms an apex portion  20  (apex line, and an apex point in  FIG. 4 ) of the first pin  3  on the chain outside direction (with respect to the orthogonal direction V). 
     The other end portion  15  forms an end portion of the peripheral surface  11  of the first pin  3  on the chain inside direction. The other end portion  15  is shaped in a curved surface that convexly curves to the chain inside direction, and is formed as a curved surface portion. A generally intermediate portion of the other end portion  15  in the circumferential direction forms an apex portion  22  (apex line, and an apex point in  FIG. 4 ) of the first pin  3  on the chain outside direction (with respect to the orthogonal direction V). 
     A pair of end portions  16  of the first pin  3  with respect to the longitudinal direction (chain width direction W) protrude respectively in the chain width direction W from the links  2  disposed at a pair of the end areas in the chain width direction W. A pair of end faces  17  as power transmission portions are respectively provided to the pair of end portions  16 . 
     Referring to  FIG. 2  and  FIG. 5 , the pair of end faces  17  mutually oppose to each other with a plane orthogonal to the chain width direction W in-between, and have a symmetrical shape. These end faces  17  are to come into frictional contact (engagement) with the corresponding sheave surfaces  62   a  and  63   a  or sheave surfaces  72   a  and  73   a  of the pulleys  60  and  70 , respectively. 
     The first pin  3  is pinched between the corresponding sheave surfaces  62   a  and  63   a  or sheave surfaces  72   a  and  73   a . Accordingly, power is transmitted between the first pin  3  and the pulley  60  or  70 . Because the first pin  3  makes a direct contribution to power transmission at the end faces  17 , it is made of a high-strength material with excellent wear resistance, for example, bearing steel (SUJ2 material). 
     Each end face  17  of the first pin  3  is made in a rounded shape. Each end face  17  is provided with a contact region  21 . Of the end faces  17 , the contact regions  21  are allowed to come into contact with the corresponding sheave surfaces  62   a  and  63   a  or sheave surfaces  72   a  and  73   a  of the pulleys  60  and  70 , respectively. 
     The contact region  21  is, for example, of an elliptical shape, and has a contact center point C (equivalent to the center of figure of the contact region  21 ). When viewed from the chain width direction W, the contact center point C coincides with the center of figure of the end face  17 . The position of the contact center point C, however, may be shifted (offset) from the center of figure of the end face  17 . 
     When viewed along the chain width direction W, a major axis D of the contact region  21  has a second angle of attack B 2 . The second angle of attack B 2  is an angle with respect to the plane A orthogonal to the chain travel direction X. It is set, for example, in a range of 5 to 12° (10° in this embodiment). The major axis D travels in the chain travel direction X as headed from the outside of the chain  1  to the inside of the chain  1  in the chain travel direction X. 
     The first and second angles of attack B 1  and B 2  may be made equal to each other or different from each other. In this embodiment, the first and second angles of attack B 1  and B 2  are equal to each other. 
     Referring to  FIG. 3  and  FIG. 4 , the second pin  4  (called also as a strip or an interpiece) is a plate-like member made of the same material as the first pin  3  and extending long in the chain width direction W. 
     The second pin  4  is made shorter than the first pin  3  in the chain width direction W to prevent a pair of end portions thereof in the longitudinal direction (chain width direction W) from coming into contact with the sheave surfaces of the pulleys. The second pin  4  is disposed ahead in the chain travel direction X with respect to the first pin  3  which is the counterpart of the pair. The second pin  4  is made thinner than the first pin  3  with respect to the chain travel direction X. A peripheral surface  18  of the second pin  4  extends in the chain width direction W and is formed as a smooth surface. 
     The chain  1  is a so-called press-fit type chain. To be more concrete, the first pin  3  is loose-fit in the front through-holes  9  in the respective links  2  so as to allow relative movements, whereas they are press-fit in the rear through-holes  10  in the respective plate links  2  so as to inhibit relative movements. Also, the second pin  4  is press-fit in the front through-holes  9  in the respective links  2  so as to inhibit relative movements, whereas they are loose-fit in the rear through-holes  10  in the respective links  2  so as allow relative movements. 
     In other words, the first pin  3  is loose-fit in the front through-holes  9  in the respective links  2 , whereas the second pin  4  making a pair with the first pin  3  is press-fit therein. Also, the first pin  3  is press-fit in the rear through-holes  10  in the respective plate links  2 , whereas the second pin  4  making a pair with the first pin  3  is loose-fit therein. 
     According to the configuration as described above, the main body portion  12   a  of the front portion  12  of the first pin  3  and the rear portion  19  of the second pin  4  as the counterpart of the pair come into rolling and sliding contact with each other on the contact portion T in association with the bending between the respective links  2  adjacent to each other in the chain travel direction X (bending of the chain  1 ). The contact portion T undergoes displacement along predetermined movement locus. 
     The first pin  3  is inserted through the through-holes  9  or  10  in the respective links  2  on the rear side in the chain travel direction X. The second pin  4  is inserted through the through-holes  9  or  10  in the respective links  2  on the front side in the chain travel direction X. 
     The predetermined movement locus of the contact portion T in reference to the first pin  3  generally shapes an involute curved surface. To be more concrete, the sectional shape of the main body portion  12   a  of the front portion  12  of the first pin  3  is in the form of an involute curve. The curvature radius of the involute curve becomes larger as headed to the chain outside direction in case where the start point is a contact portion T 1  which is the contact portion T in the straight region. 
     Alternatively, the predetermined movement locus may be made into a curve other than the involute curve by making the sectional shape of the main body portion  12   a  of the front portion  12  of the first pin  3  into a curve other than the involute curve. Examples of the curve in this case include a curve having one or more curvature radius. 
     The chain  1  has a predetermined alignment pitch P. The alignment pitch P is defined as a pitch between the first pins  3  adjacent to each other with respect to the chain travel direction X in the straight region of the chain  1 . To be more concrete, it is a distance in the chain travel direction X between the contact portion T 1  of the first and second pins  3  and  4  inside the front through-hole  9  in the link  2  and the contact portion T 1  of the first and second pins  3  and  4  inside the rear through-hole  10  in the same link  2  in the straight region. In this embodiment, the alignment pitch P is set, for example, to 8 mm. 
     One of the characteristics of this embodiment is that the one end portion  14  and the other end portion  15  of the first pin  3  each include a portion whose curvature radius is increased step by step as headed to the corresponding apex portion  20  or  22 . 
       FIG. 6  is an enlarged section of the first pin  3 . Referring to  FIG. 6 , the one end portion  14  of the first pin  3  includes a first portion  23  including the apex portion  20  described above, a second portion  24  disposed adjacently to the first portion  23  behind the first portion  23  in the chain travel direction X, and a third portion  25  disposed adjacently to the second portion  24  behind the second portion  24  in the chain travel direction X and continuing to the rear portion  13 . 
     The first portion  23  is a portion that has a curvature radius r 1 max which is the largest in the one end portion  14 . The curvature radius r 1 max is preferably set to a range of 20% to 25% of the alignment pitch P (see  FIG. 4 ). 
     Referring to  FIG. 6  again, the first portion  23  is defined between first and second planes E 1  and E 2 . Each of the first and second planes E 1  and E 2  is a plane including an axis S 1  passing through the curvature center line of the curvature radius r 1 max (first portion  23 ) and extending in the longitudinal direction of the first pin  3 . In  FIG. 6 , the axis S 1  is an axis extending perpendicularly to the sheet surface. 
     The first plane E 1  has a predetermined angle F 0  with respect to a reference plane E 0 . The reference plane E 0  is a plane including the apex portion  20  of the first pin  3  and in parallel with the rear portion  13 . The reference plane E 0  can also be said as a plane including the axis S 1  and in parallel with the rear portion  13 . 
     A first plane E 1  has an angle F 0  (referred to also as the contained angle, including 0°) of 0° to 10° with respect to the reference plane E 0  and thereby inclines to the chain travel direction X side (clockwise direction in the drawing). Accordingly, the first portion  23  includes a portion positioned ahead in the chain travel direction X with respect to the reference plane E 0 . In this embodiment, the angle F 0  is set, for example, to 5°. 
     The second plane E 2  has an angle F 1  (contained angle) of not less than 30° with respect to the first plane E 1  and thereby inclines to the side opposite to the chain travel direction X (counterclockwise direction in the drawing). In this embodiment, the angle F 1  is set, for example, to 30°. 
     A part of the first portion  23  positioned behind in the chain travel direction X with respect to the apex portion  20  is wider than a part positioned ahead in the chain travel direction X with respect to the apex portion  20 . 
     The curvature radius r 1 max of the first portion  23  is set to a range of 55 to 150% of a plate thickness G of the first pin  3  (0.55G≦r 1 max≦1.5G). The term, “the plate thickness G of the first pin  3 ”, referred to herein means the thickness of the first pin  3  with respect to a direction orthogonal to the rear portion  13 . The thickness G is set, for example, to 2.7 mm, where r 1 max is set to a range of 1.485 mm to 4.05 mm (1.485≦r 1 max≦4.05). Within this range, the curvature radius r 1 max of the first portion  23  is set, for example, to 1.6 mm. 
     In addition, the curvature radius r 1 max of the first portion  23  is set, for example, to not less than 125% of the curvature radius r 1 min of the third portion  25  (r 1 max≧1.25r 1 min) which is the smallest curvature radius in the one end portion  14  of the first pin  3 . In this embodiment, the proportion of r 1 max with respect to r 1 min is set, for example, to 130%. The curvature radius r 1 max of the first portion  23  is set, for example, to 1.6 mm and the curvature radius r 1 min of the third portion  25  is set, for example, to 1.23 mm. 
     The second portion  24  continues to the first portion  23  at one end in the circumferential direction and continues to the third portion  25  at the other end. The second portion  24  is defined between the second and third planes E 2  and E 3 . The third plane E 3  is a plane including the axis S 1 . The third plane E 3  has an angle F 2  of, for example, not more than 30° with respect to the second plane E 2  and thereby inclines to the side opposite to the chain travel direction X. 
     A curvature radius r 1 mid of the second portion  24  is set to a value that is large next to the value of the curvature radius r 1 max, and is set, for example, to 1.4 mm. The curvature radius r 1 mid is set smaller than the curvature radius r 1 max of the first portion  23  (r 1 mid&lt;r 1 max). It is preferable that the curvature radius r 1 mid is set to 55% to 80% of the curvature radius r 1 max of the first portion  23 . 
     The third portion  25  is formed as a portion having the smallest curvature radius in the one end portion  14 . The third portion  25  continues to the second portion  24  at one end in the circumferential direction and continues to the rear portion  13  at the other end. The third portion  25  is defined between the third and fourth planes E 3  and E 4 . The fourth plane E 4  is a plane including the axis S 1 . The fourth plane E 4  has an angle F 3  of, for example, not more than 25° with respect to the third plane E 3  and thereby inclines to the side opposite to the chain travel direction X. 
     The curvature radius r 1 min of the third portion  25  is set to a value that is large next to the value of the curvature radius r 1 mid, and as has been described above, it is set, for example, to 1.23 mm. The curvature radius r 1 min is smaller than both the curvature radius r 1 max of the first portion  23  and the curvature radius r 1 mid of the second portion  24  (r 1 min&lt;r 1 mid&lt;r 1 max). It is preferable that the curvature radius r 1 min is set to 20 to 45% of the curvature radius r 1 max. 
     As with the one end portion  14 , the other end portion  15  of the first pin  3  has the first portion  23  and the second portion  24 . The first portion  23  of the other end portion  15  includes the apex portion  22 . 
       FIG. 7  is an enlarged section of the second pin  4 . Referring to  FIG. 7 , the second pin  4  is of a shape having a recessed part on the rear side with respect to the chain travel direction X in the center portion in the orthogonal direction V. The height of the second pin  4  with respect to the orthogonal direction V is set, for example, to 6 mm. 
     The second pin  4  includes a plate-like main body portion  26 , a pair of end portions  27  and  28  with respect to the orthogonal direction V, and a pair of rib portions  29  and  30  provided to a pair of the end portions  27  and  28  respectively. 
     The main body portion  26  of the second pin  4  is formed to have an elongate sectional shape in the orthogonal direction V. A plate thickness I of the main body portion  26  (thickness in the chain travel direction X) is set, for example, to 1.7 mm. 
     The main body portion  26  has a rear portion  19  as an opposing portion facing rearward in the chain travel direction X and opposing the front portion  12  of the first pin  3 , and a front portion  31  facing frontward in the chain travel direction X. The rear portion  19  is formed as a flat surface orthogonal to the chain travel direction X. The front portion  31  is formed as a flat surface generally in parallel with the rear portion  19 . 
     The rib portions  29  and  30  extend, respectively, from the end portions  27  and  28  of the second pin  4  in a direction opposite to the chain travel direction X. The one end portion  27  together with the one rib portion  29  and the other end portion  28  together with the other rib portion  30  are disposed symmetrically with respect to the orthogonal direction V and have the same configuration. Hereinafter, the one end portion  27  and the one rib portion  29  will be described chiefly. 
     The outer peripheral surfaces of the one end portion  27  and the one rib portion  29  are formed as a curved surface portion  32  in a curved shape. A curved surface portion  32   b  in the rib portion  29  is connected to the rear portion  19  at one end in the circumferential direction. When viewed from the chain width direction W, the curved surface portion  32   b  is shaped like a circular arc having a center H 0  and a curvature radius J. The center H 0  is disposed at a position offset rearward in the chain travel direction X with respect to the rear portion  19  of the main body portion  26 . The curvature radius J is set, for example, to about 0.3 mm. 
     The center H 0  may be disposed to be aligned with the rear portion  19  on a straight line, or it may be disposed at a position offset frontward in the chain travel direction X with respect to the rear portion  19 . 
     A curved surface portion  32   a  of the one end portion  27  is connected to the other end of the curved surface  32   b  at one end in the circumferential direction and connected to the front portion  31  of the main body portion  26  at the other end portion in the circumferential direction. 
     One of the characteristics of this embodiment is that the curved surface  32   a  includes a part whose curvature radius is increased step by step as headed toward an apex portion  33  described below. 
     To be more concrete, the curved surface portion  32   a  includes a first portion  34  including the apex portion  33  (apex line, and apex point in the drawing) in the one end portion  27  of the second pin  4  (with respect to the orthogonal direction V), a second portion  35 , and a third portion  36 . These first through third portions  34  through  36  are aligned along the chain travel direction X and each is of a circular arc shape. 
     Curvature radii r 2 max, r 2 mid, and r 2 min of the first portion  34 , the second portion  35 , and the third portion  36 , respectively, are made smaller sequentially step by step. In other words, from the third portion  36  to the first portion  34 , the respective curvature radii r 2 min, r 2 mid, and r 2 max are increased sequentially step by step. 
     The first portion  34  is formed as a portion having the largest curvature radius in the curved surface portion  32   a , and has a center H 1  and the curvature radius r 2 max. The center H 1  is disposed between the rear portion  19  and the front portion  31  of the main body portion  26  with respect to the chain travel direction X. 
     The first portion  34  is defined between first and second planes K 1  and K 2 . Each of the first and second planes K 1  and K 2  includes an axis S 2  passing through the curvature center line of the curvature radius r 2 max (first portion  34 ) and extending in the longitudinal direction of the second pin  4  (in  FIG. 7 , an axis extending perpendicularly to the sheet surface). 
     The first plane K 1  has a predetermined angle L 0  with respect to the reference plane K 0 . The reference plane K 0  is a plane including the apex portion  33  of the second pin  4  and in parallel with the rear portion  19 . The reference plane K 0  can also be said as a plane including the axis S 2  and in parallel with the rear portion  19 . 
     The first plane K 1  has the angle L 0  (also referred to as the contained angle, including 0°) of 0° to 10° with respect to the reference plane K 0  and thereby inclines to the side opposite to the chain travel direction X (counterclockwise direction in the drawing). In this embodiment, the angle L 0  is set, for example, to 5°. The first portion  34  includes a part positioned rearward in the chain travel direction X with respect to the reference plane K 0 . 
     The second plane K 2  has an angle L 1  (contained angle) of not less than 30° with respect to the first plane K 1  and thereby inclines to the chain travel direction X side (clockwise direction in the drawing). In this embodiment, the angle L 1  is set, for example, to 30°. 
     Referring to  FIG. 4  and  FIG. 7 , the curvature radius r 2 max is set to a range of 20% to 25% of the alignment pitch P (in this embodiment, 1.6 mm to 2.0 mm). 
     By setting the curvature radius r 2 max to not less than 20% of the alignment pitch P, the first portion  34  can be made sufficiently flat, which makes it possible to prevent the occurrence of stress concentration at the peripheral portion of the front through-hole  9  in the link  2 . Also, by setting the curvature radius r 2 max to not more than 25% of the alignment pitch P, it is possible to prevent the curvature radius from varying abruptly in the vicinity of a bottom portion  37  of the curved surface portion  32   a . It is thus possible to prevent the occurrence of stress concentration at the peripheral portion of the front through-hole  9  in the link  2 . In this embodiment, the curvature radius r 2 max is set, for example, to 1.8 mm. 
     Referring to  FIG. 7 , it is preferable that the curvature radius r 2 max is set to 55% to 150% of the plate thickness I of the second pin  4  (thickness of the main body portion  26 ). Also, it is preferable that the curvature radius r 2 max is set to not less than 125% of the curvature radius r 2 min of the third portion  36 . 
     The second portion  35  is a portion having a curvature radius that is large next to the curvature radius of the first portion  34  in the curved surface portion  32   a , and has a center H 2  and the curvature radius r 2 mid. The center H 2  is disposed on a straight line M 2  linking one end of the first portion  34  in the circumferential direction and the center H 1  of the first portion  34 . 
     The curvature radius r 2 mid is set to a range of 55% to 80% of the curvature radius r 2 max (in this embodiment, about 1.0 mm to 1.6 mm). 
     By setting the curvature radius r 2 mid to not less than 55% of the curvature radius r 2 max, the second portion  35  can be made sufficiently flat, which makes it possible to prevent the occurrence of stress concentration at the peripheral portion of the front through-hole  9  in the link  2 . Also, by setting the curvature radius r 2 mid to not more than 80% of the curvature radius r 2 max, it is possible to prevent the curvature radius from varying abruptly in the vicinity of the bottom portion  37  of the curved surface portion  32   a . It is thus possible to prevent the occurrence of stress concentration at the peripheral portion of the front through-hole  9  in the link  2 . In this embodiment, the curvature radius r 2 mid is set, for example, to 1.2 mm. 
     The third portion  36  is formed as a portion having a curvature radius that is large next to the curvature radius of the second portion  35  (portion having the smallest curvature radius) in the curved surface portion  32   a , and has a center H 3  and the curvature radius r 2 min. The center H 3  is disposed on a straight line M 3  linking the one end of the second portion  35  in the circumferential direction and the center H 2  of the second portion  35 . 
     The curvature radius r 2 min is set to a range of 20% to 45% of the curvature radius r 2 max (in this embodiment, about 0.3 mm to 0.9 mm). 
     By setting the curvature radius r 2 min to not less than 20% of the curvature radius r 2 max, the third portion  36  can be made sufficiently flat, which makes it possible to prevent the occurrence of stress concentration at the peripheral portion of the front through-hole  9  in the link  2 . Also, by setting the curvature radius r 2 min to not more than 45% of the curvature radius r 2 max, it is possible to prevent the curvature radius from varying abruptly in the vicinity of the bottom portion  37  of the curved surface portion  32   a . It is thus possible to prevent the occurrence of stress concentration at the peripheral portion of the front through-hole  9  in the link  2 . 
     By providing the third portion  36 , it is possible to secure a large area for the front portion  31  of the main body portion  26  of the second pin  4 , which can consequently make an allowable bending angle of the chain  1  larger. Hence, providing the third portion  36  to the curved surface portion  32  is of great significance. In this embodiment, the curvature radius r 2 min is set, for example, to 0.6 mm. 
     Referring to  FIG. 4 , the front through-hole  9  in the link  2  is provided with a pair of receiving portions  38  and  39  that receive the second pin  4  press-fit therein. The pair of receiving portions  38  and  39  are provided on the front end of the front through-hole  9  with respect to the chain travel direction X and mutually oppose in the orthogonal direction V with the second pin  4  in-between. The receiving portions  38  and  39  receive the corresponding curved surface portions  32   a  of the second pin  4  as well as the corresponding curved surface portions  32   b  at least in part. The receiving portions  38  and  39  are pressed against these curved surfaces  32   a  and  32   b.    
     A pushing force to the chain outside direction is applied to the one receiving portion  38  by the second pin  4 . Also, a pushing force to the chain inside direction is applied to the other receiving portion  39  by the second pin  4 . 
     The rear through-hole  10  in the link  2  is provided with a pair of receiving portions  40  and  41  that receive the first pin  3  press-fit therein. The pair of receiving portions  40  and  41  are provided on the rear end of the rear through-hole  10  with respect to the chain travel direction X and mutually oppose in the orthogonal direction V with the first pin  3  in-between. The receiving portions  40  and  41  respectively receive the one end portion  14  and the other end portion  15  of the first pin  3 . The receiving portions  40  and  41  are respectively pressed against the one end portion  14  and the other end portion  15  of the first pin  3 . 
     A pushing force to the chain outside direction is applied to the one receiving portion  40  by the first pin  3 . Also, a pushing force to the chain inside direction is applied to the other receiving portion  41  by the first pin  3 . 
     The first and second pins  3  and  4  press-fit in the corresponding link  2  sandwich the other first and second pins  3  and  4  loosely-fit in this link  2  in the chain travel direction X. 
     The contact-avoiding portion  12   b  of the first pin  3  is to avoid contact with the one rib portion  29  of the second pin  4  on the outside in chain diameter direction. When viewed in the chain width direction W, the contact-avoiding portion  12   b  is provided between the one end portion  14  and the main body portion  12   a  in the peripheral surface  11  of the first pin  3 . The contact-avoiding portion  12   b  includes a concave portion recessed with respect to the main body portion  12   a . Consequently, as is shown in  FIG. 5 , the one rib portion  29  will not come into contact with the first pin  3  even when the chain  1  is bending. 
     Referring to  FIG. 4 , the pillar portion  8  of the link  2  prevents the bending angle of the chain  1  from exceeding a predetermined range. To be more concrete, the pillar portion  8  of the link  2  includes a pair of side portions  42  and  43  mutually opposing in the chain travel direction X. The other side portion  43  forms a part of the periphery of the rear through-hole  10  and is in the form of a mountain that protrudes rearward in the chain travel direction X. 
     The other side portion  43  has a pair of inclined surfaces  44  and  45  extending so as to cross each other. The pair of inclined surfaces  44  and  45  opposes the front portion  31  of the second pin  4  while being spaced part slightly (for example, with a clearance of the order of several tens of micrometers). 
     As has been described, according to this embodiment, it is possible to achieve the functions and effects as follows. That is, the curvature radii of the one end portion  14  and the other end portion  15  of the first pin  3  and the curved surface portion  32   a  of the one end portion  27  and the curved surface portion  32   a  of the other end portion  28  of the second pin  4  are increased as headed for the corresponding apex portions  20 ,  22 ,  33 , and  33 . Accordingly, the apex portions  20 ,  22 ,  33 , and  33  can be made into a flatter shape. 
     Consequently, when the receiving portions  38 ,  39   40 , and  41  of the link  2  receive load, respectively, from the one end portion  14  and the other end portion  15  of the first pin  3  and the curved surface portion  32   a  of the one end portion  27  and the curved surface portion  32   a  of the other end portion  28  of the second pin  4 , it is possible to suppress the occurrence of stress concentration at the peripheral portions of the respective through-holes  9  and  10  in the link  2 . Consequently, the durability of the link  2  can be enhanced by suppressing fatigue thereof, which makes it possible to enhance the durability of the chain  1  markedly. 
     Because stress induced on the link  2  due to press-fit of the corresponding first and second pins  3  and  4  is reduced, it is possible to make the first and second pins  3  and  4  thinner with respect to the chain travel direction X. Hence, by making the respective through-holes  9  and  10  smaller in shape, it is possible to shorten the distance between the pair of side portions  42  and  43  of the pillar portion  8 . 
     Consequently, many more first pins  3  can be meshed with the respective pulleys  60  and  70  at a time. It is thus possible to further enhance allowable transmission torque of the chain  1 . Moreover, it is possible to further enhance the durability by reducing load per first pin  3 . 
     Also, by setting the curvature radii r 1 max and r 2 max of the first portions  23  and  34  of the first and second pins  3  and  4 , respectively, to not less than 55% of the plate thicknesses G and I of the corresponding first and second pins  3  and  4 , respectively, the first portions  23  and  34  can be made sufficiently flat. It is therefore possible to reduce stress induced on the link  2  due to press-fit of the first and second pins  3  and  4  in a reliable manner. 
     In addition, by setting the curvature radii r 1 max and r 2 max of the first portions  23  and  34 , respectively, to not more than 150% of the corresponding plate thicknesses G and I of the first and second pins  3  and  4 , respectively, it is possible to prevent amounts of variance of the curvature radii in the first portions  23  and  34  from becoming excessively large. Consequently, load to be applied on the peripheral portions of the respective through-holes  9  and  10  in the link  2  can be made more uniform. 
     Further, because the curvature radii r 1 max and r 2 max of the first portions  23  and  34 , respectively, are set to not less than 125% of the curvature radii r 1 min and r 2 min of the corresponding third portions  25  and  36 , respectively, it is possible to reduce stress induced on the link  2  due to press-fit of the first and second pins  3  and  4  in a more reliable manner by making the first portions  23  and  34  of the first and second pins  3  and  4 , respectively, sufficiently flat. 
     Also, by providing the first and second angles of attack B 1  and B 2  to the first pin  3 , it is possible to dispose the first pin  3  most suitably to be meshed with the pulleys  60  and  70  more smoothly. 
     Further, by defining the first portions  23  in the one end portion  14  and in the other end portion  15  of the first pin  3  by the first and second planes E 1  and E 2  that have the contained angles of not less than 30°, it is possible to achieve the effect of reducing stress induced on the link  2  in a reliable manner by securing the first portions  23  sufficiently. 
     Also, by defining the first portions  34  in the one end portion  27  and in the other end portion  28  of the second pin  4  by the first and second planes K 1  and K 2  that have the contained angle of not less than 30°, it is possible to achieve the effect of reducing stress induced on the link  2  in a reliable manner by securing the first portions  34  sufficiently. 
     In addition, by providing the pair of rib portions  29  and  30  to the second pin  4 , the rib portions  29  and  30  are received, respectively, by the pair of receiving portions  38  and  39  of the link  2 . 
     Accordingly, it is possible to secure a large contact area of the receiving portions  38  and  39  of the front through-hole  9  in the link  2  with the second pin  4 . Consequently, the durability of the link  2  can be enhanced by sufficiently lowering the plane pressure applied on the link  2  from the second pin  4 . It is therefore possible to secure the practical durability of the chain  1  sufficiently. 
     In addition, the main portion  26  of the second pin  4  can be made thinner with respect to the chain travel direction X while securing the practically sufficient durability, which can in turn reduce the second pin  4  in size. Consequently, because the alignment pitch P of the links  2  can be made shorter, it is possible to suppress chordal actions resulting from the meshing of the first pins  3  with the pulleys  60  and  70 , which can consequently reduce noises. 
     Also, the apex portion  33  of the curved surface portion  32   a  can be made as flat as possible owing to a synergistic effect of providing the rib portions  29  and  30  in an extending manner and increasing the curvature radius of the curved surface  32   a  from the bottom portion  37  toward the apex portion  33 . It is thus possible to make the opposing portions of the curved surface portions  32  of the second pin  4  and the corresponding receiving portions  38  and  39  into a flatter shape. 
     It is thus possible to prevent the occurrence of stress concentration at the respective receiving portions  38  and  39  of the link  2  in a more reliable manner. Consequently, the durability of the link  2  can be enhanced, which can in turn further enhance the practical durability of the chain  1 . In addition, the alignment pitch P of the links  2  can be made shorter by making the main body portion  26  of the second pin  4  thinner in the chain travel direction X. 
     By setting the curvature radii r 2 max of the first portions  34  of the curved surface portions  32   a  of the second pin  4  to not less than 20% of the alignment pitch P, the first portions  34  can be made sufficiently flat. It is thus possible to prevent the occurrence of stress concentration at the corresponding receiving portions  38  and  39  of the link  2 . Also, by setting the curvature radius r 2 max of the first portions  34  to not more than 25% of the alignment pitch P, it is possible to prevent the curvature radius from varying abruptly in the vicinity of the bottom portions  37  of the curved surface portions  32   a . It is thus possible to prevent the occurrence of stress concentration at the corresponding receiving portions  38  and  39  of the link  2 . 
     Further, by setting the curvature radius r 2 mid of the second portions  35  of the second pin  4  to not less than 55% of the curvature radius r 2 max, the second portion  35  can be made sufficiently flat. It is thus possible to prevent the occurrence of stress concentration at the corresponding receiving portions  38  and  39  of the link  2 . Also, by setting the curvature radius r 2 mid to not more than 80% of the curvature radius r 2 max, it is possible to prevent the curvature radius from varying abruptly in the vicinity of the bottom portions  37  of the curved surface portions  32   a . It is thus possible to prevent the occurrence of stress concentration at the corresponding receiving portions  38  and  39  of the link  2 . 
     Also, by setting the curvature radius r 2 min of the third portions  36  of the second pin  4  to not less than 20% of the curvature radius r 2 max, the third portions  36  can be made sufficiently flat. It is thus possible to prevent the occurrence of stress concentration at the corresponding receiving portions  38  and  39  of the link  2 . Also, by setting the curvature radius r 2 min to not more than 45% of the curvature radius r 2 max, it is possible to prevent the curvature radius from varying abruptly in the vicinity of the bottom portions  37  of the curved surface portions  32   a . It is thus possible to prevent the occurrence of stress concentration at the corresponding receiving portions  38  and  39  of the link  2 . 
     Further, by providing the third portions  36 , it is possible to secure a large area for the front portion  31  of the main body portion  26  of the second pin  4 , which can consequently make the allowable bending angle of the chain  1  larger. Hence, providing the third portion  36  in the curved surface portion  32  is of great significance. 
     Further, by providing the contact-avoiding portion  12   b  to the first pin  3 , it is possible to avoid the contact between the first pin  3  and the second pin  4 , which can consequently prevent interference of the bending between the respective links  2 . 
     In addition, the pair of inclined surfaces  44  and  45  is provided to the other side portion  43  of the pillar portion  8 . Accordingly, by allowing the pair of inclined surfaces  44  and  45  to abut on the corresponding second pin  4 , it is possible to restrict the angle range of relative rotation between the links  2  adjacent to each other in the chain travel direction X. Hence, not only is it possible to achieve smooth bending of the chain  1 , but it is also possible to suppress chordal actions while the chain  1  is driven. It is therefore possible to achieve a reduction of noises, enhancement of the transmission efficiency, and a reduction of load applied on the chain  1 . 
     Further, the first pin  3  is loose-fit in the front through-holes  9  in the respective links  2  and the second pin  4  is press-fit therein, while the first pin  3  is press-fit in the rear through-holes  10  in the respective links  2  and the second pin  4  is loose-fit therein. Accordingly, when the end faces  17  of the first pin  3  come into contact with the corresponding sheave surfaces  62   a  and  63  or sheave surfaces  72   a  and  73   a  of the pulley  60  or  70 , respectively, the second pin  4  as the counterpart in a pair undergoes relative movement by coming into rolling and sliding contact with the first pin  3 , which allows the respective links  2  to bend with respect to each other. 
     In this instance, the sliding contact components can be lessened by increasing the mutual rolling contact components between the first and second pins  3  and  4 . Consequently, the end faces  17  of the first pin  3  are allowed to come into contact with the corresponding sheave surfaces  62   a  and  63   a  or sheave surfaces  72   a  and  73   a  while they hardly rotate. It is thus possible to ensure higher transmission efficiency by reducing a frictional loss. 
     Further, when viewed from the chain width direction W, movement locus of the contact portion T in reference to the first pin  3  draw an involute curve. It is thus possible to suppress the occurrence of chordal actions in the chain  1  when the first pins  3  are successively meshed with the pulleys  60  and  70 . Consequently, noises while the chain  1  is driven can be reduced further. 
     In this manner, it is possible to achieve the continuously variable transmission  100  that is compact and excellent in silence, transmission efficiency, and durability while being capable of suppressing vibrations. 
     In this embodiment, the curvature radius of at least one of the one end portion  14  and the other end portion  15  of the first pin  3  and the curved surface portion  32   a  of the one end portion  27  and the curved surface  32   a  of the other end portion  28  of the second pin  4  may be increased continuously. 
     Also, the curvature radii of the curved surface portions  32   b  of the rib portions  29  and  30  of the second pin  4  may be increased continuously as headed from the bottom portion to the apex portions  33 . 
     Also, the second pin  4  may be shaped asymmetrical with respect to the orthogonal direction V. Further, it may be configured in such a manner that each curved surface portion  32   a  is formed of the first and second portions  34  and  35  alone by omitting the third portion  36  of the curved surface portion  32   a.    
     Further, the angles F 0  through F 3  in the first pin  3  may be larger or smaller than the values shown above. The upper limit of the angle F 1  may be, for example, 40°, 50°, 60°, or larger. 
     Further, the proportion of the curvature radius r 1 max of the first portion  23  of the first pin  3  with respect to the plate thickness G of the first pin  3  may be larger or smaller than the value shown above. The proportion of the curvature radius r 1 max of the first portion  23  of the first pin  3  with respect to the curvature radius r 1 min of the third portion  25  may be smaller than the value shown above. 
     Further, many more portions having different curvature radii may be provided to each of the one end portion  14  and the other end portion  15  of the first pin  3  and the curved surface portion  32   a  of the one end portion  27  and the curved surface portions  32   a  of the other end portion  28  of the second pin  4  so as to make the surface smoother. 
     Further, the other end portion  15  of the first pin  3  may be of the same shape as that of the one end portion  14 , or the curved surface portion may be provided to either one of the one end portion  14  and the other end portion  15 . Further, the curved surface portion may be provided to either one of the one end portion  27  and the other end portion  28  of the second pin  4 . 
     Further, the first pin  3  may be loose-fit in the corresponding rear through-holes  10  in the respective links  2 . Further, the second pin  4  may be loose-fit in the corresponding front through-holes  9  in the respective links  2 . Furthermore, the second pin  4  may be meshed with the pulleys  60  and  70 . 
     In addition, the invention may be applied to a so-called block-type power transmission chain in which members having power transmission portions same as the end faces of the first pins are provided in the vicinity of a pair of the end portions of the first pin in the longitudinal direction, respectively. 
     Further, the locations of the front through-hole  9  and the rear through-hole  10  in the link  2  may be changed with each other. Furthermore, a connecting groove (slit) may be provided to the pillar portion  8  of the link  2  to connect the front through hole  9  and the rear through hole  10 . In this case, an amount of elastic deformation (flexibility) of the link  2  can be adjusted with the height of the slit. 
     It should be noted that the invention is not limited to the configuration in which the groove widths of the both drive pulley  60  and the driven pulley  70  are variable, and it may configured in such a manner that the groove width of either one of the pulleys is variable whereas the groove width of the other is fixed. Further, the embodiment in which the groove widths vary continuously (in a stepless manner) is described above. However, the invention may be applied to other power transmission devices in which the groove widths are varied step by step or fixed (invariable). 
       FIG. 8  is a side view of a major portion according to another embodiment of the invention. Hereinafter, differences from the embodiment shown in  FIG. 1  through  FIG. 7  will be chiefly described. Like components are labeled with like reference numerals and descriptions thereof are omitted herein. 
     Referring to  FIG. 8 , this embodiment is characterized in that plural types of first pins are provided and the shape of the contact-avoiding portion differs from one type of the first pins to another. 
     First pins  3  and  3 A are provided as plural types of the first pins  3 . One of the characteristics of this embodiment is that the contact cycles in which the first pins  3  and  3 A successively come into contact with the sheave surfaces of the respective pulleys are randomized. 
     To be more concrete, the loci (predetermined movement loci) of the rolling and sliding contact of the first pins  3  and  3 A at the contact portions T and TA, respectively, are made different from each other, and when viewed from the chain width direction W, the relative positions of the contact portion T 1  and the contact center point C of the first pin  3  and the relative positions of the contact portion T 1 A and the contact center point CA of the first pin  3 A are different from each other. 
     As a configuration that provides different loci to the rolling and sliding contact of the first pins  3  and  3 A at the contact portions T and TA, respectively, the sectional shape of the main body portion  12   a A of the front portion  12 A of the first pin  3 A is made different from the sectional shape of the main body portion  12   a  of the front portion  12  of the first pin  3 . The base circle radius of the involute curve of the section of the main body portion  12   a A of the front portion  12 A is made smaller than the base circle radius of the involute curve of the section of the main body portion  12   a  of the front portion  12 . 
     The contact-avoiding portion  12   b A of the first pin  3 A is shaped in the form of a curved surface that smoothly continues to the main body portion  12   a A. By making the base circle radius of the involute curve of the main body portion  12   a A smaller, the end portion of the main body portion  12   a A on the outside in chain diameter direction is positioned well behind the second pin  4  in the chain travel direction X. It is thus possible to avoid the contact with the one rib portion  29  of the second pin  4  without the need to make the contact-avoiding portion  12   b A in a recessed shaped. 
     A configuration to make the relative positions of the first contact portion T 1  and the contact center point C of the first pin  3  and the relative positions of the contact portion T 1 A and the contact center point CA of the first pin  3 A different from each other when viewed in the chain width direction W is as follows. 
     That is, when viewed in the chain width direction W, the relative positions of the contact portion T 1  and the contact center point C of the first pin  3  in the straight region are spaced apart by Δx 1  with respect to the chain travel direction X and by Δy 1  with respect to the orthogonal direction V. Meanwhile, when viewed in the chain width direction W, the relative positions of the contact portion T 1 A and the contact center point CA of the first pin  3 A in the straight region are spaced apart by Δx 2  with respect to the chain travel direction X and by Δy 2  with respect to the orthogonal direction V. 
     When viewed in the chain width direction W, the relative positions of the contact portion T 1  and the contact center point C of the first pin  3  and the relative positions of the contact portion T 1 A and the contact center point CA of the first pin  3 A are different at least in one of the chain travel direction X and the orthogonal direction V (in this embodiment, in the both directions) (Δx 1 ≠Δx 2  and Δy 1 ≠Δy 2 ). 
     The first pins  3  and the first pins  3 A are aligned randomly in the chain travel direction X. In this case, the phase, “aligned randomly”, means that at least either the first pins  3  or the first pins  3 A are disposed on an irregular basis in the chain travel direction X at least in part. The phrase, “on an irregular basis”, means that at least one of the periodicity and the regularity is absent. 
     According to this embodiment, by providing different shapes to the contact-avoiding portions  12   b  and  12   b A of the first pins  3  and  3 A, respectively, it is possible to discriminate between the first pins  3  and  3 A with ease, which makes it possible to prevent the occurrence of an error when assembling the first pins  3  and  3 A. 
     Also, the occurrence cycles of meshing sounds produced when the first pins  3  and  3 A are successively meshed with the pulleys are randomized to distribute the frequencies of the meshing sounds in a broader range. It is thus possible to further reduce the noises during the driving. 
     In this embodiment, as a configuration to randomize the occurrence cycles of the meshing sounds produced when the first pins  3  and  3 A are successively meshed with the respective pulleys, only the movement loci of the rolling and sliding contact of the first pins  3  and  3 A at the contact portions T and TA, respectively, may be made different from each other. 
     Also, as a configuration to randomize the occurrence cycles of the meshing sounds produced when the first pins  3  and  3 A are successively meshed with the respective pulleys, only the relative positions of the contact portion T 1  and the contact center point C of the first pin  3  and the relative positions of the contact portion T 1 A and the contact center point CA of the first pin  3 A may be made different from each other when viewed from the chain width direction. 
     It should be appreciated that the invention is not limited to the contents of the embodiments described above, and can be modified in various manners within the scope of the appended claims. 
     For example, as are shown in  FIG. 9  and  FIG. 10 , second pins  4 B having no rib portions may be used. Each of one end portion  27 B and the other end portion  28 B of the second pin  4 B includes a curved surface portion  32   a B. These curved surface portions  32   a B are received, respectively, by receiving portions  38  and  39  of the front through-hole  9  in the link  2 . Because the curved surface portion  32   a B of the one end portion  27 B and the curved surface portion  32   a B of the other end portion  28 B are of the same configuration, the curved surface portion  32   a B of the one end portion  27 B will be chiefly described. 
     The one end portion  27 B has an apex portion  33 B on the outside in the chain diameter direction of the second pin  4 B generally at the intermediate portion thereof in the circumferential direction. The curved surface portion  32   a B includes a first portion  34 B including the apex portion  33 B, a second portion  35 B disposed adjacently to the first portion  34 B ahead the first portion  34 B in the chain travel direction X, and a third portion  36 B disposed adjacently to the second portion  35 B ahead the second portion  35 B in the chain travel direction X and continuing to the front portion  31 . 
     The first portion  34 B is formed as a portion having a curvature radius r 2 Bmax which is the largest in the curved surface portion  32   a B. The first portion  34 B is defined between first and second planes KB 1  and KB 2 . Each of the first and second planes KB 1  and KB 2  is a plane including an axis S 2 B passing through the curvature center line of the curvature radius r 2 Bmax (first portion  34 B) and extending in the longitudinal direction of the second pin  4 B (the axis extending perpendicularly to the sheet surface of  FIG. 6 ). 
     The first plane KB 1  has a predetermined angle LB 0  with respect to a reference plane KB 0 . The reference plane KB 0  is a plane including the apex portion  33 B in the first portion  34 B of the second pin  4 B and in parallel with the rear portion  19 . The reference plane KB 0  can also be said as a plane including the axis S 2 B and in parallel with the rear portion  19 . 
     The first plane KB 1  has an angle LB 0  (also referred to as the contained angle, including 0°) of 0 to 10° with respect to the reference plane KB 0  and thereby inclines to the side opposite to the chain travel direction X (counterclockwise direction in the drawing). In this embodiment, the angle LB 0  is set, for example, to 5°. The first portion  34 B includes a portion positioned rearward in the chain travel direction X with respect to the reference plane KB 0 . 
     The second plane KB 2  has an angle LB 1  (contained angle) of not less than 30° with respect to the first plane KB 1  and thereby inclines to the chain travel direction X side (clockwise direction in the drawing). In this embodiment, the angle LB 1  is set, for example, to 30°. 
     The first portion  34 B has a portion present frontward in the chain travel direction X with respect to the apex portion  33 B, which is wider than a portion present rearward in the chain travel direction X with respect to the apex portion  33 B. 
     The curvature radius r 2 Bmax of the first portion  34 B is set to a range of 55 to 150% of the plate thickness IB of the second pin  4 B (0.55IB≦r 2 Bmax≦1.5IB). The thickness IB is set, for example, to 1.7 mm, and accordingly r 2 Bmax is set to a range of 0.935 mm to 2.55 mm (0.935≦r 2 Bmax≦2.55). The curvature radius r 2 Bmax of the first portion  34 B is set, for example, to 1.5 mm. 
     The curvature radius r 2 Bmax of the first portion  34 B is set to not less than 125% of the curvature radius r 2 Bmin of the third portion  36 B whose curvature radius r 2 Bmin is the smallest in the one end portion  27 B of the second pin  4 . In this embodiment, the proportion of the r 2 Bmax with respect to the r 2 Bmin is set, for example, to 150% (r 2 Bmax=1.5r 2 Bmin). The curvature radius r 2 Bmax of the first portion  34 B is set, for example, to 1.5 mm, and the curvature radius r 2 Bmin of the third portion  36 B is set, for example, to 1.0 mm. 
     The second portion  35 B continues to the first portion  34 B at one end in the circumferential direction and continues to the third portion  36 B at the other end. The second portion  35 B is defined between the second and third planes KB 2  and KB 3 . The third plane KB 3  is a plane including the axis S 2 B. The third plane KB 3  has an angle LB 2  of, for example, not more than 30° with respect to the second plane KB 2  and thereby inclines frontward in the chain travel direction X. 
     The curvature radius r 2 Bmid of the second portion  35 B is set, for example, to 1.3 mm and is made smaller than the curvature radius r 2 Bmax of the first portion  34 B (r 2 Bmid&lt;r 2 Bmax). 
     The third portion  36 B is formed as a portion having the smallest curvature radius in the curved surface portion  32   a B. The third portion  36 B continues to the second portion  35 B at one end in the circumferential direction and continues to the front portion  31   b  at the other end. The third portion  36 B is defined between the third and fourth planes KB 3  and KB 4 . The fourth plane KB 4  is a plane including the axis S 2 B. The fourth plane KB 4  has an angle LB 3  of, for example, not more than 25° with respect to the third plane KB 3  and thereby inclines to the chain travel direction X side. 
     As has been described, the curvature radius r 2 Bmin of the third portion  36 B is set, for example, to 1.0 mm, and is made smaller than both the curvature radius r 2 Bmax of the first portion  34 B and the curvature radius r 2 Bmid of the second portion  35 B (r 2 Bmin&lt;r 2 Bmid&lt;r 2 Bmax). 
     Instead of the second pin  4  and the second pin  4 B as described above, a second pin  4 C shown in  FIG. 11  may be used. The second pin  4 C having one end portion  27 C and the other end portion  28 C is configured in such a manner that a rib portion  30 C is provided to the other end portion  28 C alone. 
     Further, a second pin  4 D shown in  FIG. 12  may be used as well. The second pin  4 D having one end portion  27 D and the other end portion  28 D is configured in such a manner that a rib portion  29 D is provided to the one end portion  27 D alone. 
     It should be appreciated that the invention is not limited to the embodiments described above. For example, as is shown in  FIG. 13 , it may be configured in such a manner that single first pins  3  may be used as the coupling members. A front portion  47  of the peripheral portion  46  of a front through-hole  9 E in a link  2 E is of a flat shape orthogonal to the chain travel direction X. The front portion  12  of the first pin  3  loose-fit in the front through-hole  9 E comes into rolling and sliding contact with the front portion  47  of the link  2 E. Receiving portions  40 E and  41 E of a rear through-hole  10 E in the link  2 E receive the one end portion  14  and the other end portion  15  of the first pin  3 , respectively, and thereby fix the first pin  3 E to the link  2 . 
     In this case, the absence of the second pins can shorten the distance (pitch) between the first pins  3  adjacent to each other in the chain travel direction X, which makes it possible to reduce the chain in size. Moreover, load per first pin  3  can be reduced by allowing many more first pins  3  to be meshed with the respective pulleys at a time. It is thus possible to achieve enhancement of allowable transmission torque and enhancement of durability. 
     While the embodiments of the invention have been described in detail, modifications, alterations, and equivalents of the invention readily occur to anyone skilled in the art who understands the contents. The sprit and the scope of the invention, therefore, are limited by the scope of the appended claims and their equivalents. 
     This application corresponds to the Japanese Patent Application No. 2004-338201 filed with the Japanese Patent Office on Nov. 22, 2004, and the Japanese Patent Application No. 2005-301034 filed with the Japanese Patent Office on Oct. 14, 2005, the entire contents of which are incorporated herein by reference.