Patent Publication Number: US-6708810-B2

Title: Damper disk assembly

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a damper disk assembly. More specifically, the present invention relates to a damper disk assembly exhibiting a torque characteristic that has two stages of rigidity. 
     2. Background Information 
     A conventional damper mechanism used in a clutch disk assembly of a vehicle has an input rotary member, an output rotary member, and an elastic coupling member. The input rotary member is designed to be coupled to an input flywheel to transfer torque therefrom to the output rotary member. The output rotary member is coupled to a shaft that extends from a transmission. The elastic coupling member elastically couples the input rotary member and the output rotary member together in the rotational direction. The input rotary member has a clutch disk and a pair of input plates fixed to the inside thereof. The output rotary member has a hub that is coupled to the shaft in such a manner that the two cannot rotate relative to each other. The hub has a boss that is splined to the shaft and a flange that extends radially outward from the boss. The elastic coupling mechanism has a plurality of coil springs. Each coil spring is housed inside a window hole formed in the flange and is also supported by corner windows formed in the pair of input plates. When the pair of input plates and the hub rotate relative to each other, the coil springs are compressed between the input plates and hub in a rotational direction. This compressing or damping function serves to absorb and damp torsional vibrations inputted to the clutch disk assembly. 
     Also known are clutch disk assemblies that use springs of different rigidities to accommodate the various types of vibrations that occur under different traveling conditions. This type of clutch disk assembly achieves a two-stage torsional characteristic. The small coil springs are compressed and a low-rigidity characteristic is obtained when in the region of small twisting angles. Further, the large coil springs are compressed and a high-rigidity characteristic is obtained when in the region of large twisting angles. One known structure for achieving this characteristic is a separated flange type clutch disk assembly in which the flange is independently formed from the hub and the flange and hub are coupled together in the rotational direction by small, low-rigidity coil springs. Also known is an integral type clutch disk assembly in which window holes for large coil springs and window holes for small coil springs are provided in an integral hub flange unit and coil springs are arranged in the window holes. 
     The separated flange type clutch disk assembly can achieve a wide-angle, low-rigidity torsional characteristic. However, since both a hub and a flange are required, the number of parts is greater than in clutch disk assemblies whose flanges are not separated. Thus, separated flange type clutch disk assemblies have a higher cost. 
     In the integral type clutch disk assembly, the twisting angle is determined by the rotational angle between the notches in the hub flange and the stop pins arranged in the notches. Furthermore, since four to six large coil springs are arranged in the rotational direction, the notches cannot be made sufficiently large, i.e., a sufficient twisting angle cannot be secured because of the relatively large number of coil springs. Consequently, a small-angle, high-rigidity torsional characteristic is obtained. 
     In view of the above, there exists a need for a damper disk assembly that overcomes the above mentioned problems in the prior art. This invention addresses this need in the prior art as well as other needs, which will become apparent to those skilled in the art from this disclosure. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a damper disk assembly having a simple structure and a wide twisting-angle torsional characteristic. 
     A damper disk assembly in accordance with a first aspect of the present invention is provided with a hub flange, a pair of first elastic members, a pair of second elastic members, an intermediate rotary member, and a pair of plate members. The hub flange has a boss that can be coupled to a shaft and a flange formed integrally on the outer circumference of the boss. The flange has formed therein a pair of first window holes arranged radially opposite each other and a pair of second window holes arranged radially opposite each other. The two first elastic members are arranged respectively in the pair of first window holes. The two second elastic members have a higher rigidity than the first elastic members and are arranged respectively in the pair of second window holes. The intermediate rotary member couples the first elastic members and the second elastic members together in the rotational direction. The two plate members are arranged on both axially facing sides of the flange and have a support part that supports the second elastic members. 
     This damper disk assembly uses the pair of second elastic members, which are positioned opposite each other in the radial direction, as the springs for transmitting power and absorbing vibrations when the vehicle is traveling. Consequently, the problem of the limited angle between the stop pins and notches is solved and a wide-twisting angle torsional characteristic can be achieved. 
     Meanwhile, the two first elastic members, which are arranged in the first window holes of the flange, are used as the springs for absorbing small torsional vibrations during idling. Since the hub flange is a single unitary member, the number of parts does not increase. 
     A damper disk assembly in accordance with a second aspect of the present invention is a damper disk assembly of the first aspect, wherein the intermediate rotary member has a first member arranged on one axially facing side of the flange and a second member arranged on the opposite axially facing side of the flange. The second member has a protruding part that protrudes toward the first member in the axial direction and engages with the first member such that the two members cannot rotate relative to each other. 
     In this damper disk assembly, the intermediate rotary member, which couples the pair of first elastic members and the pair of second elastic members in the rotational direction, has two members, a first member and a second member. The second member has a protruding part that engages with the first member. Consequently, conventional sub-pins can be omitted and cost can be reduced by reducing the number of parts. 
     These and other objects, features, aspects, and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Referring now to the attached drawings which form a part of this original disclosure: 
     FIG. 1 is a vertical cross-sectional view of a clutch disk assembly in accordance with a preferred embodiment of the present invention; 
     FIG. 2 is an elevational view of the clutch disk assembly with a portion removed for illustrative purposes; 
     FIG. 3 is a vertical cross-sectional view of a hub flange of the clutch disk assembly; 
     FIG. 4 is an elevational view of the hub flange; 
     FIG. 5 is an elevational view of window holes of plates of the clutch disk assembly; 
     FIG. 6 is an elevational view of a second window hole of the hub flange; 
     FIG. 7 is cross-sectional view of a first member of an intermediate rotary member of the clutch disk assembly; 
     FIG. 8 is an elevational view of the first member of the intermediate rotary member; 
     FIG. 9 is cross-sectional view of a second member of the intermediate rotary member; 
     FIG. 10 is elevational view of the second member of the intermediate rotary member; 
     FIG. 11 is an enlarged partial view of FIG. 1; 
     FIG. 12 is an alternate enlarged partial view of FIG. 1; 
     FIG. 13 is an elevational view illustrating the engagement between the first member and the second member of the intermediate rotary body; 
     FIG. 14 is an elevational view illustrating positional relationships between the hub flange and the first member of the intermediate rotary member; 
     FIG. 15 is an elevational view illustrating positional relationships between the hub flange and the second member of the intermediate rotary member; 
     FIG. 16 corresponds to FIG.  15  and serves to illustrate a twisting operation of a damper mechanism of the clutch disk assembly; 
     FIG. 17 corresponds to FIG.  15  and serves to illustrate the twisting operation of the damper mechanism; 
     FIG. 18 is an enlarged elevational view of an end part of a coil spring assembly of the clutch disk assembly; 
     FIG. 19 corresponds to FIG.  18  and serves to illustrate the twisting operation of the damper mechanism; 
     FIG. 20 corresponds to FIG.  18  and serves to illustrate further the twisting operation of the damper mechanism; 
     FIG. 21 is a view of a mechanical circuit diagram illustrating constituent features and a twisting operation of the damper mechanism; 
     FIG. 22 is a view of a mechanical circuit diagram illustrating the constituent features and twisting operation of the damper mechanism; 
     FIG. 23 is a view of a mechanical circuit diagram illustrating the constituent features and twisting operation of the damper mechanism; 
     FIG. 24 is a view of a mechanical circuit diagram illustrating the constituent features and twisting operation of the damper mechanism. 
     FIG. 25 is a view of a torsional characteristic diagram for the damper mechanism; 
     FIG. 26 is an elevational view of a spring seat of the coil spring assembly; 
     FIG. 27 is a rear elevational view of the spring seat; 
     FIG. 28 is a lateral elevational view of the spring seat; and 
     FIG. 29 is a perspective view of the spring seat. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Selected embodiments of the present invention will now be explained with reference to the drawings. It will be apparent to those skilled in the art from this disclosure that the following description of the embodiments of the present invention is provided for illustration only, and not for the purpose of limiting the invention as defined by the appended claims and their equivalents. 
     (1) Constitution 
     FIG. 1 is a cross-sectional view of a clutch disk assembly  1  of a preferred embodiment of the present invention and FIG. 2 is an elevational view of the same. The clutch disk assembly  1  is a power transmission device used in a clutch apparatus of a vehicle and has both a clutch function and a damper function. The clutch function is provided to transmit and interrupt torque by engaging and disengaging with a flywheel (not shown). The damper function is provided so that by using springs or the like torque fluctuations inputted from the flywheel are absorbed and dampened. 
     In FIG. 1, line O—O is the rotational axis of the clutch disk assembly  1 . An engine and a flywheel (both not shown) are disposed to the left in FIG. 1 and a transmission (not shown) is disposed to the right in FIG.  1 . In FIG. 2, arrow R 1  indicates a drive direction or positive rotation direction of the clutch disk assembly  1  and arrow R 2  indicates the opposite direction or negative rotation direction. In the following explanation, the terms “rotational (circumferential) direction,” “axial direction,” and “radial direction” are used to describe the directions of the clutch disk assembly  1 , which serves as a damper mechanism, unless a more specific direction needs to be described. Also, rotational angles and other actual numerical values used in the following explanation are merely used to describe, for example, the relative size of the angles and are not intended to limit the present invention. 
     As seen in FIGS. 1 and 2, the clutch disk assembly  1  chiefly has an input rotary body  2 , an output rotary body  3 , and an elastic coupling part  4  disposed between the input rotary body  2  and the output rotary body  3 . The input rotary body  2  is a member to which torque is inputted from the flywheel (not shown). The input rotary body  2  chiefly has a clutch disk  11 , a clutch plate  12 , and a retaining plate  13 . The clutch disk  11  is the portion that is pressed against and couples with the flywheel (not shown). The clutch disk  11  has a cushioning plate  15  and a pair of friction facings  16  and  17  that are fixed to both axially facing sides of the cushioning plate  15  by rivets  18 . 
     The clutch plate  12  and the retaining plate  13  are both preferably disk-shaped, ring-shaped members made of sheet metal and are disposed at a prescribed distance from each other in the axial direction. The clutch plate  12  is disposed on the engine side and the retaining plate  13  is disposed on the transmission side. A pair of coupling parts  13   a  that are preferably made by drawing and protrude toward the clutch plate  12  are provided on a portion of the retaining plate  13  positioned radially to the outside of coil springs  8  arranged in a hub flange  7 . Each of the coupling parts  13   a  is fixed to the clutch plate  12  by a plurality of rivets  20 . The retaining plate  13  is also provided with wall parts  13   b  that extend in the axial direction between the coupling parts  13   a  and the rest of the retaining plate  13 . The clutch plate  12  and the retaining plate  13  are each formed with a center hole. The hub flange  7  (discussed later) is disposed inside these center holes. 
     A plurality of window parts  25 , arranged in the circumferential direction, is formed in the clutch plate  12  and the retaining plate  13 . More specifically, in each plate  12  and  13 , there are preferably two window parts  25  formed so that they oppose each other in the radial direction. The positions are preferably symmetrical with respect to the center axis O-O. As shown in FIG. 5, each of the window parts  25  of the plate  12  or  13  has a hole that is long in the circumferential direction. In other words, the maximum distance from one end of the window part  25  to the other in the circumferential direction is longer than the maximum distance from one end to the other in the radial direction. The hole of each window part  25  passes through the plate  12  or  13  in the axial direction. Further, a spring support part  27  is formed along the edge of the hole. The spring support part  27  has an outside support part  27   a , an inside support part  27   b , and rotational direction support parts  27   c  and  27   d . The outside support part  27   a  is preferably curved into a shape that lies roughly on a circle that is concentric with the plates  12  and  13  and the inside support part  27   b  extends substantially in a straight line. The rotational support part  27   c  is on the R 1  side of the window part  25  and the rotational support part  27   d  is on the R 2  side. The rotational direction support parts  27   c  and  27   d  extend along straight lines lying roughly on radii of the plates  12  and  13 . The entirety of the outside support part  27   a  and the portions of the rotational direction support parts  27   c  and  27   d  that are farther from the center axis of the clutch disk assembly  1  preferably have raised parts that support the spring seats  42  and  43  in the axial direction. 
     The output rotary body  3  will now be explained. Referring to FIGS. 1 and 3, the output rotary body  3  chiefly has the hub flange  7 . The hub flange  7  is a member that is disposed inside the center holes of the clutch plate  12  and the retaining plate  13 . The hub flange  7  is splined to the transmission input shaft (not shown), which is inserted into the center hole of the hub flange  7 . As shown in FIGS. 3 and 4, the hub flange  7  has a boss  7   a  and a flange  7   b  formed integrally on the outer circumferential surface thereof. The flange  7   b  has the shape of a flat plate but it is preferably not circular. Rather, the flange  7   b  is comparatively elongated in one radial direction. In other words, it has the shape of a circular material that has been cut in a substantially parallel manner on both sides. More preferably, the hub flange  7  has an outline resembling the shape of a bow of bowtie. The distance in a circumferential direction between end faces  7   e  on opposing sides of a second window hole  7   d  preferably increases as the radial distance from the boss  7   a  increases. Further, the end faces  7   e  on the same side of one of the second window holes  7   d  are joined by a curved portion that protrudes in a radial direction opposite the boss  7   a . Preferably, a pair of first window holes  7   c  and a pair of second window holes  7   d  are formed on the flange  7   b . The two first window holes  7   c  are arranged radially opposite each other in the small diameter section (i.e., the portion to the left and right sides of the boss  7   a  in FIG. 4) of the flange  7   b . The coil springs  8  are preferably arranged inside the first window holes  7   c . The two second window holes  7   d  are arranged radially opposite each other in the large diameter section (i.e., the portion above and below the boss  7   a  in FIG. 4) of the flange  7   b . Each window hole  7   d  stretches substantially across the entire width of the large diameter portion and occupies an angle of 80 degrees in the circumferential direction. The two the first window holes  7   c  are preferably out of phase by 90 degrees with respect to the second pair of window holes  7   d.    
     The second window holes  7   d  of the flange  7   b  are formed so as to correspond to the window parts  25  in plates  12  and  13 . As shown in FIGS. 4 and 6, each second window hole  7   d  has an outside support part  35 , an inside support part  31 , and rotational direction support parts  33  and  34 . The rotational direction support part  33  is disposed on the R 1  side and the rotational direction support part  34  is disposed on the R 2  side. The outside support part  35  is curved so as to lie on a circle having its center at the center axis of the clutch disk assembly  1 . The rotational direction support part  33  and the rotational direction support part  34  extend substantially linearly so as to lie roughly on radii extending from the center of the clutch disk assembly  1 . Further, recessed parts  33   a  and  34   a  are formed in the middle section of the rotational direction support parts  33  and  34 , respectively. Each recessed part  33   a ,  34   a  is of a shallow cut-out shape whose depth runs in the circumferential direction of the clutch disk assembly  1 . In other words, each recessed part  33   a  and  34   a  is concave in a circumferential direction in relation to the inside of the second window hole  7   d . More specifically, the recessed part  33   a  occupies an angle of 2 degrees in the circumferential direction, which corresponds to the thickness of a bent claw  52   f  of a plate  52  of an intermediate rotary member  10  (discussed later). The recessed part  34   a  occupies an angle of 3 degrees in the circumferential direction, which is 1 degree larger than the thickness of the bent claw  52   f  and allows the bent claw  52   f  to move 1 degree within the recessed part  34   a.    
     A recessed part  31   a  is formed in the middle section of the inside support part  31 . The recessed part  31   a  is a cut-out portion that is closer to the center of the clutch disk assembly  1  than the rest of the inside support part  31 . In other words, the recessed part  31   a  is generally recessed in a radial direction relative to the inside of the second window hole  7   d . The recessed part  31   a  preferably has two end sections that extend in a radial direction. The end sections are joined by a curved section that is convex relative to the inside of the second window hole  7   d . The curved section preferably does not extend past the inside support part  31  in a radial direction toward the inside of the second window hole  7   d.    
     Referring to FIGS. 2 and 6, the elastic coupling part  4  chiefly has a plurality of coil spring assemblies  9 . There are preferably two coil spring assemblies  9 . Each coil spring assembly  9  is disposed inside a second window hole  7   d  and a window part  25 . Each coil spring assembly  9  has a coil spring  41 , a pair of spring seats  42  and  43  provided on the both ends of the coil spring  1 , and a float body  44 . The cross section of the wire of the coil spring  41  is circular and both ends of the coil spring form closed-end end windings. The center axis of the coil spring  41  is roughly linear. The face part of the end windings has preferably been ground smooth. 
     The spring seats  42  and  43  are preferably made of rigid resin, elastic resin material, or metal. As shown in FIGS. 26 to  29 , the spring seats  42  and  43  have a seat part  46  and a protruding part  47  that is structured to extend inside the coil spring  41  from the seat part  46 . The seat part  46  has a seat surface  46   a  for bearing the end winding face parts of the coil spring  41  and a rear surface  46   b  for being supported by the second window hole  7   d  or the window part  25 . The protruding part  47  has a roughly solid cylindrical shape. The tip face of the protruding part  47  is straight and runs parallel to the axial direction, but in a side elevational view, as seen in FIG. 6, it is slanted such that the portion that is farther from the center axis of the clutch disk assembly  1  is positioned closer to the outside of the second window hole  7   d  in the circumferential direction than is the portion that is closer to the center axis of the clutch disk assembly  1 . 
     As is clear in FIG. 26, the seat surface  46   a  is preferably circular. The seat surface  46   a  has a roughly flat first surface  46   a  and a slanted second surface  46   d  that gradually becomes higher as one moves from one end thereof to the other (the clockwise direction in the elevational view of FIG.  26 . One end of the second surface  46   d  is formed so as to blend uninterruptedly with the first surface  46   c  while the other end forms a step with respect to the first surface  46   c . On this step portion is formed a contact surface  46   e  that faces in the circumferential direction (clockwise in the elevational view). The shape of the seat surface  46   a  matches the shape of the end winding face parts of the coil spring  41 . When the end winding has not been significantly ground, it is acceptable for the seat surface  46   a  to have a curved cross section that matches the cross section of the coil. The tip end part of the coil spring  41  preferably touches against the contact surface  46   e  of the spring seat  42 . 
     Since the spring seat  42  and the spring seat  43  have substantially the same shape, their respective contact surfaces  46   e  face in opposite directions in terms of the circumferential direction of the seat surface when the two the spring seats  42  and  43  are arranged facing each other. 
     As seen in FIG. 27, two recessed parts  46   f , one at each corner, are formed on the radially outward facing side of the rear surface  46   b  of the spring seat  42 . A portion of the outside support part  27   a  of the window part  25  engages with these recessed parts  46   f . As a result, the spring seats  42  and  43  can separate from the circumferentially facing edges of the window parts  25  in the rotational direction (toward the opposite circumferentially facing edge) but, when engaged with the outside support part, they cannot move in the axial direction or radial direction. 
     As seen in FIGS. 6,  18 , and  19 , the spring seats  42  and  43  are also supported by the bent claws  52   f  of the intermediate rotary member  10  (discussed later). More specifically, each rear surface  46   b  touches against the inside circumferentially facing surface of a bent claw  52   f . Consequently, the rear surface  46   b  of each spring seat  42  and  43  is disposed so as to be separated from the rotational support part  33  or  34  of the second window hole  7   d  by a prescribed angle. More specifically, a rotational angular gap of 7 degrees is secured between the rotational support part  33  and the spring seat  42  and a rotational angular gap of 2 degrees is secured between the rotational support part  34  and the spring seat  43 . 
     The entire surface of each circumferentially facing end face of the coil spring  41  touches against the seat surface  46   a  of the seat part  46 . Moreover, the tip end parts of the coil spring  41  touch against the contact surfaces  46   e . Consequently, the coil spring  41  cannot rotate about its own center axis with respect to the pair of the spring seats  42  and  43 . That is, the coil spring  41  cannot rotate in either direction about its center axis because the contact surfaces  46   e  of the pair of the spring seats  42  and  43  face in opposite directions with respect to the winding direction of the coil spring  41 . In this condition, there are preferably seven active windings on the side of the coil spring  41  that is closer to the center axis of the clutch disk assembly  1  and six active windings on the side that is farther from the center axis of the clutch disk mechanism. That is, the number of active windings on the side that is closer to the center axis of the clutch disk mechanism is preferably larger than the number of active windings on the side that is farther from the center axis of the clutch disk mechanism. Furthermore, the coil spring  41  does not rotate with respect to the spring seats  42  and  43  about the spring center axis and the spring seats  42  and  43  do not rotate with respect to the plates  12  and  13  about the spring center axis. Consequently, the coil spring  41  does not move out of position and, thus, the number of active windings on the side that is closer to the center axis of the clutch disk mechanism is always larger than the number of active windings on the side that is farther from the center axis of the clutch disk mechanism. 
     The float body  44  is, for example, a solid-cylindrical member preferably made of elastic resin that is arranged inside the coil spring  41  such that it can move in the rotational direction. The float body  44  serves to generate a large torque or stopper torque by being pinched between the protruding parts  47  of the spring seats  42  and  43  when the coil spring  41  is compressed beyond a certain point. 
     Referring to FIGS. 2 and 4, both rotationally facing end faces  7   e  of the portion of the hub flange  7  where the second window hole  7   d  is formed are of a linear shape and arranged so as to have a rotational gap with respect to the rotationally facing end faces of the wall parts  13   b  of the coupling parts  13   a  of the retaining plate  13 . This rotational gap is the operational angle of the coil springs  8  and coil spring assemblies  9 . Further, the end faces  7   e  of the hub flange  7  and the coupling parts  13   a  constitute a stopper mechanism of the second stage of the torsional characteristic. With this arrangement, the clutch disk assembly  1  can be made more lightweight because it is not necessary to use stopper pins. 
     Next, as seen in FIG. 13, the intermediate rotary member  10  is described. The intermediate rotary member  10  serves to couple the coil springs  8  and coil spring assemblies  9  together in the rotational direction. The intermediate rotary member  10  has a bush  51  and the plate  52 . The bush  51  is an annular member preferably made of a material such as resin, and, as shown in FIG. 11, disposed between the flange  7   b  and an inner circumferential section of the clutch plate  12 . 
     As shown in FIGS. 7 and 8, the bush  51  has a pair of window parts  51   a  in positions corresponding to the first window holes  7   c . The window parts  51   a  are recessed parts formed in the lateral face of the flange  7   b . Further, the portion of the coil springs  8  that face the engine in the axial direction are arranged in the window parts  51   a . Projections  51   b  that extend in the axial direction are formed adjacent to each window part  51   a  on the side thereof that faces radially inward toward the center axis of the clutch disk assembly  1 . Each projection  51   b  has a thin-walled form that is arced in the rotational direction and is positioned within a first window hole  7   c  on the side of the coil spring  8  that faces radially inward toward the center axis of the clutch disk assembly  1 . A pair of first fixing parts  51   c  that extend in the axial direction are formed on the outer edge at positions located radially outward from the window parts  51   a . The first fixing parts  51   c  have a prescribed length in the circumferential direction and a plurality of semicircular projecting parts  51   d  lined up in the circumferential direction formed on the edge thereof. 
     A pair of linear parts  51   e  positioned radially opposite each other is formed on the outer edge of the bush  51  at positions 90 degrees out of phase with the pair of the first fixing parts  51   c . The linear parts  51   e  are relatively long and preferably parallel to each other. Projections  51   f  that protrude outward are formed at both ends of each linear part  51   e . A spring housing space  51   h  is formed by the linear part  51   e  and opposing end faces  51   g  of the projections  51   f . A second fixing part  51   i  that protrudes in the axial direction is formed in the center section of the linear part  51   e . The second fixing part  51   i  extends inside the recessed part  31   a  of the second window hole  7   d . The second fixing part  51   i  has a prescribed width in the direction parallel to the linear part  51   e . The prescribed width of the second fixing part  51   i  is preferably smaller than the length of the linear part  51   e . The second fixing part  51   i  has a wall surface that extends straight in the axial direction on the side facing the spring housing space  51   h . Also, a plurality of semicircular projecting parts  51   j  is formed on the tip of the second fixing part  51   i  so as to extend in the axial direction and line up in the direction parallel to the linear part  51   e.    
     Referring to FIGS. 7 and 11, a surface  51   k  of the bush  51  faces the engine in the axial direction and touches against the lateral face of the clutch plate  12  near the center hole of the clutch plate  12 . A surface  511  of the bush  51  faces the transmission in the axial direction and occupies the innermost portion of the bush. The surface  511  touches against the surface of an innermost section  7   f  of the flange  7   b  that faces the engine in the axial direction. An annular part  51   m  that protrudes toward the engine in the axial direction is provided on the innermost edge of the bush  51 . The annular part  51   m  is sandwiched between the internal surface of the center hole of the clutch plate  12  and the external surface of the boss  7   a . The annular part  51   m  serves to position the plate  12  with respect to the boss  7   a  in the radial direction. As seen in FIG. 8, a straight line joining the centers of the window parts  51   a  is not parallel to the linear part  51   e  but is displaced slightly in the R 1  rotational direction. The straight line is preferably displaced by 2 degrees. 
     As seen in FIG. 11, the plate  52  is an annular member disposed between the flange  7   b  and the retaining plate  13  and made of sheet metal, for example. As shown in FIGS. 9 and 10, the plate  52  is provided with a center hole  52   a . The plate  52  is also provided with a pair of window holes  52   b  that correspond to the window parts  51   a . A plurality of semicircular recessed parts  52   c  is aligned in the rotational direction on the outer edge at positions located radially outward from the window holes  52   b . The projecting parts  51   d  of the bush  51  engage with the recessed parts  52   c.    
     A pair of arc-shaped curved surfaces  52   d  are formed radially opposite each other on the outside edge of the plate  52 . Projecting parts  52   e  that extend outward in the radial direction are formed at both ends of each arc-shaped curved surface  52   d . The bent claws  52   f  that extend in the axial direction are provided on the tips of the projecting parts  52   e  such that they face each other. As shown in FIG. 13, the surface of each bent claw  52   f  that faces circumferentially outward touches against one end face  51   g  of the bush  51 . Furthermore, as seen in FIG. 15, the bent claws  52   f  are formed in correspondence to recessed parts  33   a  and  34   a  of the rotation direction support parts  33  and  34 . The bent claws  52   f  can fit into recessed parts  33   a  and  34   a  from the rotational direction. The rotational angle or thickness occupied by each bent claw  52   f  is preferably 2 degrees. 
     Thus, as seen in FIG. 10, a spring housing space  52   g  is formed by the curved surface  52   d  and a pair of the bent claws  52   f . A plurality of recessed parts  52   h  is formed in the center section of curved surface  52   d . The recessed parts  52   h  are configured to engage with the projecting parts  51   j  of the bush  51 . Since the projecting parts  51   d  and  51   j  respectively engage with the recessed parts  52   c  and  52   h , the bush  51  and the plate  52  rotate as a single unit. 
     As previously mentioned, the bush  51  and the plate  52  abut against each other in the axial direction and engage with each other in the rotational direction so as to form a single integrally-rotating member. As seen in FIGS. 11 and 12, the bush  51  and the plate  52  are configured to couple such that the flange  7   b  is axially disposed therebetween. Since the axial distance between the bush  51  and the plate  52  is larger than thickness of the flange  7   b , both axially facing lateral surfaces of the flange  7   b  are separated from members  51  and  52 , respectively. 
     FIG. 13 shows the relationship between the bush  51  and the plate  52 , which constitute the intermediate rotary member  10 . The window parts  51   a  and window holes  52   b  match each other in terms of position and size and, respectively, serve to support both the circumferentially facing ends and the axially facing outside sections of the coil springs  8 . The spring housing spaces  51   h  and the spring housing spaces  52   g  also roughly match each other. Further, the end faces  51   g  and the bent claws  52   f  are disposed on both circumferentially facing sides of each coil spring assembly  9 . 
     Next, the relationship between the intermediate rotary member  10  and the flange  7   b  is explained using FIGS. 14 and 15. On the R 2  side of each second window hole  7   d , the end face  51   g  is aligned with the rotational direction support part  34 . Therefore, the bent claw  52   f  is separated from the recessed part  34   a  by 3 degrees in the R 1  rotational direction. On the R 1  side of each second window hole  7   d , the end face  51   g  is separated from the rotational support part  33  by 7 degrees in the R 2  direction. Therefore, the bent claw  52   f  is separated from recessed part  33   a  by 7 degrees in the R 2  direction. The rotationally inward facing surface of each bent claw  52   f  touches against the rear surface  46   b  of one of the spring seats  42  and  43 . 
     The intermediate rotary member  10  has two members, i.e., the bush  51  and the plate  52 . Further, the bush  51  has protruding parts ( 51   c ,  51   i ,  51   b ) that engage with the plate  52 . Consequently, conventional sub-pins can be omitted and cost can be reduced because there are fewer parts. 
     Thus constituted as described heretofore and as shown in FIG. 21, the damper mechanism of the clutch disk assembly  1  is arranged so that the low torsional rigidity damper formed by the coil springs  8  and the high torsional rigidity damper formed by the coil spring assemblies  9  of the elastic coupling part  4  operate in series. More specifically, the coil springs  8  elastically couple the hub flange  7  and the intermediate rotary member  10  together in the rotational direction and the coil spring assemblies  9  couple the intermediate rotary member  10  and the plates  12  and  13  together elastically in the rotational direction. The coil springs  8  accomplish a so-called first stage (i.e., a low-rigidity region for absorbing small vibrations during idling) due to their torsional characteristics and the coil springs  41  of the coil spring assembly  9  accomplish a so-called second stage (i.e., a high-rigidity region for damping torsional vibrations during acceleration). 
     As shown in FIGS. 11 and 12, a first friction plate  61  and a first cone spring  62  are arranged between the retaining plate  13  and the innermost section  7   f  of the flange  7   b . The first friction plate  61  touches against the innermost section  7   f  of the flange  7   b  and, as discussed later, rotates integrally with the retaining plate  13 . The first cone spring  62  is compressed axially between the first friction plate  61  and the retaining plate  13  and exerts a force against the first friction plate  61  in the axial direction toward the engine. As a result, the first friction plate  61  is always pressed against the innermost section  7   f  of the flange  7   b . The section just described generates sliding resistance between the hub flange  7  and the retaining plate  13 , and thus, by extension, generates sliding resistance between the input rotary body  2  and the output rotary body  3 . The section just described is hereinafter called “first friction generating mechanism  70 .” 
     A second friction plate  63  and a second cone spring  64  are disposed between the plate  52  and the retaining plate  13 . The second friction plate  63  engages with the first friction plate  61  in such a manner that the two plates cannot rotate relative to each other. Further, the second friction plate  63  also engages with the retaining plate  13  by means of a claw projection  63   a  such that it cannot rotate relative thereto. The second cone spring  64  is compressed axially between the second friction plate  63  and the retaining plate  13  and exerts a force on the second friction plate  63  in the axial direction toward the engine. As a result, the second friction plate  63  is pressed strongly against the plate  52  consequently ensuring that the bush  51  is also pressed strongly against the clutch plate  12 . The section described here, which generates sliding resistance between the intermediate rotary member  10  and plates  12  and  13 , is hereinafter called “second friction generating mechanism  71 .” 
     The sliding section between the surface of the intermediate rotary member  10  and the lateral surface of the innermost section  7   f  of the flange  7   b  is called “friction generating mechanism  69 .” 
     Now the structure is described in further detail. As seen in FIG. 2, the two coil spring assemblies  9  are disposed in two locations that are opposite each other in the radial direction. The reason the number of the coil spring assemblies  9  can be reduced in comparison with conventional damper mechanisms is that the coil springs  41  of the coil spring assemblies  9  do not rotate about their own center axes and, thus, the number of active windings on the side that is closer to the center axis of the clutch disk mechanism can be arranged always to be larger than number of active windings on the side that is farther from the center axis of the clutch disk mechanism. Since the strength and durability of the coil springs  41  are improved, torque capacity of each coil spring can be increased. More specifically, at least one of the two coil spring assemblies  9  can absorb 35% or more (more specifically 35 to 50%) of the twisting torque of the damper mechanism and the two coil spring assemblies  9  can absorb 70% or more (more specifically 70 to 100%) of the twisting torque. Thus, the two coil springs  41  of the present invention provide the same twisting torque and rigidity as, for example, four coil springs in a conventional damper mechanism. Also, since there are only two coil spring assemblies  9 , the layout is simpler and the shapes of the hub flange  7 , etc., are simpler. This means higher yields during the manufacture of each member. The degree of design freedom for the entire clutch disk is also increased. In short, with this structure, the number of coil spring assemblies can be reduced and the structure of the damper mechanism can be simplified while maintaining the same torsional characteristics as conventional damper mechanisms. 
     Additionally, since a large space is formed between the two coil spring assemblies  9  in the circumferential direction, the degree of design freedom for the first-stage the coil springs  8 , which are located circumferentially-between the coil spring assemblies  9 , is improved. More particularly, the two coil springs  8  are positioned midway between the pair of coil springs  9  in the circumferential direction and, thus, are not restricted by the coil springs  9  in the radial direction. For example, the small coil springs  8  can be positioned farther from the center axis of the clutch disk assembly  1  than in the case of conventional damper mechanisms. Alternatively, larger diameter springs can be used then than in conventional damper mechanisms. 
     (2) Operation 
     Next, the twisting operation of the damper mechanism of the clutch disk assembly  1  is explained. As seen in FIGS. 21 and 22, it is assumed that the plates  12  and  13  are twisted in the rotational direction with respect to the hub flange  7  from a free state. In the region of small twisting angles, the coil springs  8 , which have a very low relative rigidity, will be compressed between the hub flange  7  and the intermediate rotary member  10  and a low-rigidity characteristic will be obtained. When this occurs, the intermediate rotary member  10  and the plates  12  and  13  will rotate relative to the hub flange  7  and, consequently, only friction generating mechanism  69  and first friction generating mechanism  70  will operate such that the desired low hysteresis torque is generated. If all members of a stopper mechanism of the first stage touch against each other, then the coil spring assemblies  9  will be compressed between the hub flange  7  and the plates  12  and  13 . When this occurs, the hub flange  7  will rotate relative to the plates  12  and  13  and, as a result, both the first friction mechanism  70  and the second friction mechanism  71  will operate such that the desired high hysteresis torque is generated. 
     The coil springs  41  of the coil spring assemblies  9  are compressed in the rotational direction between rotational direction support parts  33  of the second window holes  7   d  and the bent claws  52   f  of the intermediate rotary member  10  on one end and the rotation direction support parts  27   c  or  27   d  of the window parts  25  on the other. When this occurs, the deflection of each coil spring  41  is larger on the side that is farther from the center axis of the clutch disk assembly  1  than on the side that is closer to the center axis of the clutch disk assembly  1 . However, since the number of windings on the side that is closer to the center axis is larger than number of windings on the side that is farther from the center axis, the difference in the per-winding deflection between the two sides is smaller than in conventional damping mechanisms. That is, the per-winding deflection on the side that is farther from the center axis is larger than per-winding deflection on the side that is closer to the center axis, but the difference between the two is smaller than in conventional damping mechanisms. As a result, it is difficult for there to be a difference in the generated stress between the portion of the coil spring  41  that is closer to the center axis of the clutch disk assembly  1  and the portion that is farther from the center axis of the clutch disk assembly  1 . In other words, there is little difference between the stress generated in the portion of each winding that is farther from the center axis of the clutch disk assembly  1  and the stress generated in the portion of each winding that is closer to the center axis of the clutch disk assembly  1 . As a result, the life of the coil spring  41  is extended. 
     Also, as seen in FIG. 2, the angle occupied by each coil spring  41  in the circumferential direction (i.e., the angle formed by two radii passing from center axis O—O to the ends of the coil spring  41  on the side of the coil spring that is closest to the center axis) is roughly 80 degrees. When the angle occupied in the circumferential direction by the linear coil springs is 60 degrees or larger, the coil springs are larger than in conventional damper mechanisms. Thus, the number of coil springs can be reduced and the structure of the damper mechanism can be simplified while maintaining the same or similar torsional characteristics as conventional damper mechanisms. However, it is best to keep this circumferential angle as small as possible from the standpoint of securing space between the coil springs  41  in the circumferential direction. A good effect can be obtained if the circumferential angle occupied by the coil springs  41  is in the range from 60 to 140 degrees. Furthermore, it is better if the circumferential angle is in the range from 60 to 120 degrees or, still more preferable, in the range from 70 to 100 degrees. 
     Next, the twisting operation of the clutch disk assembly  1  is explained based on FIGS. 14 to  19  (these figures are used to explain the positional relationship between the hub flange  7  and the plate  52 ), FIGS. 20 to  23  (mechanical circuit drawings), and FIG. 24 (torsional characteristic diagram). 
     Assume that, starting from the neutral state shown in FIGS. 14 and 21, the hub flange  7  is rotated in the R 2  rotational direction with respect to the other members. In other words, a positive-side operational state is achieved in which the plates  12  and  13  are twisted in the R 1  direction with respect to the hub flange  7 . When the twisting angle reaches 7 degrees, the clutch disk assembly  1  is in the state shown in FIG.  16 . When this occurs, the bent claw  52   f  on the R 1  side touches against the recessed part  33   a  and, in the elevational view, lies in the same plane with the rotational support part  33 . Therefore, when the twisting angle is 7 degrees or larger (i.e., when in the second stage of the positive side of the torsional characteristic), the intermediate rotary member  10  always rotates integrally with the hub flange  7 . Therefore, in the second friction generating mechanism  71 , the plate  52  and the second friction plate  63  slide against each other and high hysteresis torque is generated. 
     Now assume that, starting from the neutral state shown in FIGS. 14,  18 , and  22 , the hub flange  7  is rotated in the R 1  rotational direction with respect to the other members. In other words, a negative-side operational state is achieved in which the plates  12  and  13  are twisted in the R 2  direction with respect to the hub flange  7 . When the twisting angle reaches 2 degrees, the clutch disk assembly  1  is in the state shown in FIG.  23  and the rotational direction support part  34  of the hub flange  7  touches against the rear surface  46   b  of the spring seat  43 . When this occurs, as shown in FIGS. 17,  19 , and  23 , the bent claw  52   f  on the R 2  side is coplanar with the surface of the rotational direction support part  34  and has a 1-degree gap with respect to the bottom surface of the recessed part  34   a . When the twisting angle increases one more degree, the bent claws  52   f  touch against recessed parts  34   a  and, conversely, a 1-degree gap is secured between the bent claws  52   f  and the rear surface  46   b  of the spring seat  43  of the coil springs  41 . Therefore, if small torsional vibrations within 1 degree in magnitude are inputted while in the state shown in FIG. 24 (second stage, negative side), the torque of the coil springs  41  act on the hub flange  7  but not on the intermediate rotary member  10  and, consequently, the plate  52  and the second friction plate  63  of second friction generating mechanism  71  do not slide against each other. This means that high hysteresis torque is not generated in response to small torsional vibrations when the clutch disk assembly  1  is operating in the second stage region on the negative side of the torsional characteristic. 
     Next, while referring to the torsional characteristic diagram of FIG. 24, the torsional characteristic of the clutch disk assembly  1  is described for specific cases in which different types of vibrations are inputted. 
     During idling, the clutch disk assembly  1  fluctuates repeatedly between first stages of the positive and negative sides of the torsional characteristic in response to the small torsional vibrations. The small torsional vibrations are absorbed by the low rigidity, low hysteresis torque characteristic. 
     When torsional vibrations having a large amplitude—such as longitudinal vibrations of the vehicle—occur, the clutch disk assembly  1  fluctuates repeatedly across the full range of both the positive and negative sides of the torsional characteristic. In such a case, the longitudinal vibrations of the vehicle are quickly damped by high rigidity, high hysteresis torque generated by the second stage on both the positive and negative sides of the torsional characteristic. 
     Next consider a case in which engine combustion fluctuations cause small torsional vibrations to be delivered to the clutch disk assembly  1  when, for example, the vehicle is being decelerated by engine braking. In this case, the intermediate rotary member  10  rotates relative to the hub flange  7  within the 1-degree rotational gap shown in FIGS. 20 and 24 and does not slide against the second friction plate  63 . Consequently, high hysteresis torque is not generated in response to the small vibrations. Even if the coil springs  41  operate within the range of the 1-degree rotational gap indicated in the torsional characteristic diagram, sliding does not occur in the second friction generating mechanism  71  and only low hysteresis torque is obtained. It is preferred that the low hysteresis torque be roughly {fraction (1/10)} the size of the hysteresis torque across the entire torsional characteristic. In this way, the vibrations and noise level associated with engine breaking can be greatly reduced because a rotational gap has been provided on the negative side of the torsional characteristic such that the second friction generating mechanism  71  does not operate within a prescribed angular range. 
     Since a rotational gap that prevents the second friction generating mechanism  71  from operating within a prescribed angular range is not provided on the positive side of the torsional characteristic, there is no degradation of the noise and vibration performance in the vicinity of the resonance rotational speed in such vehicles as front-engine front-drive or FF vehicles, in which the resonance peak often remains in the region of practical engine speeds. 
     In short, the noise and vibration performance for both acceleration and deceleration is improved by securing a rotational gap that prevents the friction mechanism from operating within a prescribed angular range on only one side, i.e., the positive side or negative side, of the torsional characteristic. 
     As described heretofore, the damper mechanism of the present invention achieves an overall preferred torsional characteristic by not only having different torsional rigidities on the positive and negative sides of the torsional characteristic but also providing on only one side of the torsional characteristic a structure that does not allow high hysteresis torque to be generated in response to small torsional vibrations. 
     Second Embodiment 
     A damper disk assembly in accordance with a second embodiment will now be explained. Moreover, the descriptions of the parts of the second embodiment that are identical to the parts of the first embodiment may be omitted for the sake of brevity. 
     The structure used to stop the coil springs from rotating about their own axes with respect to the plate and hub flange is not limited to that used in the previous embodiments. For example, the coil springs can be stopped from rotating about their own axes with respect to said members without using spring seats. Also, even if spring seats are used, the structure used to stop the spring seats from rotating about the spring axes with respect to the plate and hub flange is not limited to that used in the previous embodiments. 
     The end windings of the coil springs may be ground as in the previous embodiment, but it is also acceptable if the end windings are not ground at all. 
     In the previous embodiment, the end parts of the coil springs were close-ended but it is also acceptable to use open-ended coil springs. Also, the number of windings, the winding direction, and the cross sectional shape of the coil springs are not limited to those used in the previous embodiments. 
     The constituent features of the clutch disk assembly are not limited to those of the previous embodiments. 
     The damper disk assembly described in the present application can be used in other power transmission devices in addition to clutch disk assemblies. For example, the present invention can be applied to a flywheel assembly that elastically couples two flywheels together in the rotational direction or to a lockup device for a torque converter. 
     Effects of the Invention 
     The damper disk assembly of the present invention uses a pair of second elastic members arranged in positions opposite each other in the radial direction as the springs for transmitting torque and absorbing vibrations when the vehicle is traveling. Therefore, such problems as the angle restriction that occurs between stop pins and notches are solved and a wide twisting angle torsional characteristic is achieved. 
     Meanwhile, a pair of first elastic members arranged in the first window holes of the flange is used as the spring for absorbing small torsional vibrations during idling. The hub and flange are integrated as a single unit, thus keeping down the number of parts. 
     As used herein, the following directional terms “forward, rearward, above, downward, vertical, horizontal, below, and transverse” as well as any other similar directional terms refer to those directions of a device equipped with the present invention. Accordingly, these terms, as utilized to describe the present invention should be interpreted relative to a device equipped with the present invention. 
     The terms of degree such as “substantially,” “about,” and “approximately” as used herein mean a reasonable amount of deviation of the modified term such that the end result is not significantly changed. These terms should be construed as including a deviation of at least±5% of the modified term if this deviation would not negate the meaning of the word it modifies. 
     This application claims priority to Japanese Patent Application No. 2001-342079. The entire disclosure of Japanese Patent Application No. 2001-342079 is hereby incorporated herein by reference. 
     While only selected embodiments have been chosen to illustrate the present invention, it will be apparent to those skilled in the art from this disclosure that various changes and modifications can be made herein without departing from the scope of the invention as defined in the appended claims. Furthermore, the foregoing description of the embodiments according to the present invention are provided for illustration only, and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.