Abstract:
A dynamic vibration absorbing device for an automobile can be on an output-side member of a torque converter. The dynamic vibration absorbing device includes a rotary member, a mass part, and an elastic member. The rotary member is fixed to the output-side member. The rotary member can be rotated about a rotational center of the output-side member. The mass part includes a first accommodation part. The mass part is for attenuating vibration of the output-side member by rotating about the rotational center relative to the rotary member. The elastic member is held by the first accommodation part. The elastic member elastically couples the rotary member and the mass part in a rotational direction. The elastic member is for generating a hysteresis torque by sliding against the first accommodation part in rotation of the rotary member.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a dynamic vibration absorbing device for an automobile. 
       BACKGROUND ART 
       [0002]    Torque converters are provided with a lock-up device (see PTL 1). In the lock-up device, an inertia member is attached to an output member fixed to a turbine hub, while being rotatable relatively thereto. Additionally, torsion springs are provided as elastic members between the output member and the inertia member. 
         [0003]    Thus, in the lock-up device, the inertia member is coupled to the output member through the torsion springs. Hence, the inertia member and the torsion springs function as a dynamic damper. Fluctuations in rotation transmitted from a turbine to the turbine hub are attenuated by the dynamic damper. 
       CITATION LIST 
     Patent Literature 
       [0004]    PTL 1: Japan Laid-open Patent Application Publication No. 2009-293671 
       SUMMARY OF THE INVENTION 
     Technical Problems 
       [0005]    The well-known dynamic damper attenuates torque fluctuations when a torque of the turbine is outputted to an input shaft through the turbine hub. This type of dynamic damper is often used when the stiffness of a member coupled to the input shaft is high, for instance, when front-wheel drive is employed or so forth. Here, the member coupled to the input shaft is a member that transmits a torque to a transmission. 
         [0006]    On the other hand, when the stiffness of the member coupled to the input shaft is low, for instance, when rear-wheel drive is employed or so forth, it is concerned that resonance of the turbine occurs due to lowness of the stiffness. In this case, a vibration frequency intended to be attenuated by the well-known dynamic damper is different from a resonant frequency of the turbine. Hence, it is difficult for the well-known dynamic damper to attenuate torque fluctuations attributed to resonance of the turbine. 
         [0007]    The present invention has been made in view of the aforementioned drawback. It is an object of the present invention to provide a dynamic vibration absorbing device capable of effectively attenuating torque fluctuations of an output-side member of a torque converter. 
       Solution to Problems 
       [0008]    (1) A dynamic vibration absorbing device for an automobile according to an aspect of the present invention is provided on an output-side member of a torque converter. The present dynamic vibration absorbing device includes a rotary member, a mass part and an elastic member. The rotary member is fixed to the output-side member and is rotated about a rotational center. The mass part includes a first accommodation part. The mass part attenuates torque fluctuations of the output-side member by rotating about the rotational center in relative to the rotary member. The elastic member is held by the first accommodation part. The elastic member elastically couples the rotary member and the mass part in a rotational direction. 
         [0009]    The elastic member generates a hysteresis torque by sliding against the first accommodation part. 
         [0010]    In the present dynamic vibration absorbing device, the rotary member is fixed to the output-side member of the torque converter. Additionally, in rotation of the rotary member, the mass part is moved relatively to the rotary member through the elastic member, whereby torque fluctuations of the output-side member of the torque converter can be directly attenuated. 
         [0011]    Here, torque fluctuations of the output-side member of the torque converter, when attenuated in the present dynamic vibration absorbing device, partially increases in the vicinity of an intended rotational speed targeted by the present dynamic vibration absorbing device. 
         [0012]    However, in the present dynamic vibration absorbing device, when the rotary member is rotated while the elastic member is held by the first accommodation part of the mass part, the elastic member and the first accommodation part of the mass part slide against each other, whereby a hysteresis torque is generated. Thus, in the present dynamic vibration absorbing device, the partially increased toque fluctuations of the output-side member of the torque converter can be attenuated by the hysteresis torque. 
         [0013]    Thus, in the present dynamic vibration absorbing device, principal torque fluctuations of the output-side member of the torque converter can be directly attenuated, and simultaneously, subsidiary torque fluctuations occurring by attenuation of the principal torque fluctuations can be also attenuated. In other words, in the present dynamic vibration absorbing device, torque fluctuations of the output-side member of the torque converter can be effectively reduced. 
         [0014]    (2) A dynamic vibration absorbing device for an automobile according to another aspect of the present invention may be configured as follows. The hysteresis torque is set to be greater than or equal to 2 Nm and less than or equal to 30 Nm. 
         [0015]    In this case, the hysteresis torque is set to be greater than or equal to 2 Nm and less than or equal to 30 Nm. Hence, compared to a well-known dynamic vibration absorbing device, torque fluctuations, subsidiarily occurring in the output-side member of the torque converter, can be effectively attenuated in a high rotational speed range. 
         [0016]    (3) A dynamic vibration absorbing device for an automobile according to yet another aspect of the present invention may be configured as follows. The mass part has a smaller inertia than a turbine of the torque converter. 
         [0017]    In this case, the inertia of the mass part is set to be smaller than that of the turbine of the torque converter. For example, when the inertia of the mass part is increased, it is possible to enhance an attenuation effect on the principal torque fluctuations in the intended rotational speed. On the other hand, it is concerned that the subsidiary torque fluctuations in the vicinity of the intended rotational speed increase with increase in inertia of the mass part. Therefore, it is effective to set the inertia of the mass part to be smaller than that of the turbine in order to attenuate the principal torque fluctuations without, as much as possible, increasing the subsidiary torque fluctuations. In other words, with this configuration, it is possible to inhibit increase in subsidiary torque fluctuations occurring in attenuation of the principal torque fluctuations. 
         [0018]    (4) A dynamic vibration absorbing device for an automobile according to yet another aspect of the present invention may be configured as follows. The rotary member includes a second accommodation part in which the elastic member is capable of being disposed. The mass part is disposed on both sides of the rotary member in an extending direction of the rotational center. 
         [0019]    In this case, the elastic member is held only by the first accommodation part of the mass part on the both sides of the rotary member, while being disposed in the second accommodation part of the rotary member. Accordingly, a hysteresis torque can be stably generated wile the elastic member is reliably held by the first accommodation part of the mass part. 
         [0020]    (5) A dynamic vibration absorbing device for an automobile according to yet another aspect of the present invention may be configured as follows. The first accommodation part includes a flange part. The flange part holds the elastic member and is capable of sliding against the elastic member. 
         [0021]    In this case, a hysteresis torque can be more stably generated while the elastic member is reliably held by the flange part of the first accommodation part of the mass part. 
         [0022]    (6) A dynamic vibration absorbing device for an automobile according to yet another aspect of the present invention may be configured as follows. The second accommodation part of the rotary member includes a contact part with which the elastic member makes contact in the rotational direction. The contact part is formed along a straight line extending from the rotational center in a radial direction. 
         [0023]    In this case, when the mass part is rotated relatively to the rotary member, the elastic member is pressed by the contact part of the second accommodation part of the rotary member while being held by the first accommodation part of the mass part. Accordingly, the elastic member is compressed. Here, the contact part is formed along the straight line extending from the rotational center in the radial direction. Therefore, when pressed by the contact part, the elastic member becomes likely to deflect in a direction separating from the rotational center, and slides against the first accommodation part of the mass part. Accordingly, a hysteresis torque can be more stably generated. 
       Advantageous Effects of Invention 
       [0024]    According to the present invention, torque fluctuations of an output-side member of a torque converter can be effectively reduced in a dynamic vibration absorbing device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]      FIG. 1  is a cross-sectional view of a torque converter including a dynamic damper device according to an exemplary embodiment of the present invention. 
           [0026]      FIG. 2  is an enlarged cross-sectional view of the dynamic damper device in  FIG. 1 . 
           [0027]      FIG. 3  is a front view of the dynamic damper device in  FIG. 1  as seen from an engine side. 
           [0028]      FIG. 4  is a chart for explaining characteristics of the dynamic damper device. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0029]    [Torque Converter] 
         [0030]      FIG. 1  shows a torque converter  1  according to an exemplary embodiment of the present invention. In  FIG. 1 , an engine is disposed on the left side, whereas a transmission is disposed on the right side. Line O-O depicted in  FIG. 1  is a rotational axis (an exemplary rotational center) of the torque converter  1 . 
         [0031]    The torque converter  1  is a device that transmits a torque from the engine to the transmission. The torque converter  1  mainly includes a torque converter body  3 , a lock-up device  5  and a dynamic damper device  7 . 
         [0032]    &lt;Torque Converter Body&gt; 
         [0033]    As shown in  FIG. 1 , the torque converter body  3  includes a front cover  11  into which a power is inputted, an impeller  13 , a turbine  15  (an exemplary output-side member) and a stator  19 . 
         [0034]    The outer peripheral part of the front cover  11  and that of the impeller  13  are welded to each other. A fluid chamber is formed by the front cover  11  and the impeller  13 . 
         [0035]    The turbine  15  is disposed in opposition to the impeller  13  within the fluid chamber. The turbine  15  includes a turbine shell  16 , a plurality of turbine blades  17  fixed to the inside of the turbine shell  16 , and a turbine hub  18  fixed to the inner peripheral part of the turbine shell  16 . 
         [0036]    The turbine hub  18  includes a tubular part  18   a  and a flange part  18   b  extending radially outward from the tubular part  18   a . The inner peripheral part of the turbine shell  16  is fixed to the outer peripheral part of the flange part  18   b  by a rivet(s)  11 . It should be noted that the turbine hub  18  includes a spline hole  18   c  in the inner peripheral part thereof. An input shaft, transmitting a torque to the transmission (not shown in the drawings), is coupled to the spline hole  18   c.    
         [0037]    The stator  19  regulates the flow of hydraulic oil from the turbine  15  to the impeller  13 . The stator  19  is disposed axially between the inner peripheral part of the impeller  13  and that of the turbine  15 . 
         [0038]    &lt;Lock-Up Device&gt; 
         [0039]    The lock-up device  5  is disposed between the front cover  11  and the turbine  15 . The lock-up device  5  includes a piston  21 , a clutch part  31  and a damper mechanism  41 . 
         [0040]    The piston  21  is axially movable. Detailedly, the piston  21  is axially movable by difference between a hydraulic pressure in a space between the piston  21  and the front cover  11  and that in a space between the piston  21  and the damper mechanism  41 . 
         [0041]    The piston  21  includes a body  22  and a pressing part  23 . The body  22  has a substantially annular shape. The body  22  includes a first body  22   a  and a second body  22   b.    
         [0042]    The inner peripheral part of the first body  22   a  is disposed on the outer peripheral part of the turbine hub  18 . The inner peripheral part of the first body  22   a  is supported by the outer peripheral surface of the turbine hub  18  while being axially movable thereon and being rotatable relatively thereto. A seal member is disposed between the inner peripheral part of the first body  22   a  and the outer peripheral surface of the turbine hub  18 . 
         [0043]    The inner peripheral part of the second body  22   b  is supported by the outer peripheral part of the first body  22   a  while being axially movable thereon and being rotatable relatively thereto. A seal member is disposed between the inner peripheral part of the second body  22   b  and the outer peripheral part of the first body  22   a . The outer peripheral end of the second body  22   b  is supported by the inner peripheral part of a fixed part to be described, while being axially movable thereon. A seal member is disposed between the outer peripheral part of the second body  22   b  and the inner peripheral part of the fixed part. 
         [0044]    The pressing part  23  is integrated with the body and axially protrudes therefrom. Detailedly, the pressing part  23  is integrated with the second body  22   b  and axially protrudes therefrom. More detailedly, the pressing part  23  protrudes from the outer peripheral part of the second body  22   b  toward the damper mechanism. 
         [0045]    The clutch part  31  includes a fixed part  32 , a torque transmission part  33 , a plurality of friction members  34  and a positioning member  35 . The fixed part  32  is fixed to the front cover  11 . The torque transmission part  33  is disposed in opposition to the fixed part  32  on the inner peripheral side of the fixed part  32 . 
         [0046]    Each of the plural friction members  34  has a substantially annular shape. The plural friction members  34  are disposed between the fixed part  32  and the torque transmission part  33 . The plural friction members  34  include a plurality of first friction members  34   a  and a plurality of second friction members  34   b . The first friction members  34   a  and the second friction members  34   b  are disposed axially in adjacent to each other. The plural first friction members  34   a  are engaged with the fixed part  32  and are axially movable. The plural second friction members  34   b  are engaged with the torque transmission part  33  and are axially movable. 
         [0047]    The positioning member  35  is a component that positions the friction members  34 . The positioning member  35  has a substantially annular shape. The positioning member  35  is fixed to an axial end (an end on the opposite side of a fixed end) of the fixed part  32 . The plural friction members  34  are disposed axially between the positioning member  35  and the piston  21  (the pressing part  23 ). 
         [0048]    The damper mechanism  41  includes a pair of retaining plates  42  and  43 , an output flange  44 , a plurality of first and second torsion springs  45  and  46  (outer peripheral side torsion springs  45  and inner peripheral side torsion springs  46 ). 
         [0049]    The pair of retaining plates  42  and  43  is a pair of annularly shaped disc members disposed axially in opposition to each other at an interval. The pair of retaining plates  42  and  43  includes a plurality of spring accommodation parts  42   a ,  43   a  in the outer peripheral parts thereof and includes a plurality of spring accommodation parts  42   b ,  43   b  in the inner peripheral parts thereof. 
         [0050]    The outer peripheral parts of the pair of retaining plates  42  and  43  are fixed to each other by a fixation member(s) such as a rivet(s) (not shown in the drawings). The inner peripheral part of one retaining plate  42  more extends to the inner peripheral side than that of the other retaining plate  43 . The inner peripheral part of the one retaining plate  42  is fixed to the clutch part  31 , for instance, the torque transmission part  33  by a fixation member(s) such as a rivet(s)  49 . 
         [0051]    The output flange  44  is disposed axially between the pair of retaining plates  42  and  43 . The output flange  44  includes first and second openings  44   a  and  44   b  for accommodating springs in the outer peripheral part and inner peripheral part thereof. An inner peripheral end  44   c  of the output flange  44  is fixed to the flange part  18   b  of the turbine hub  18  by the rivet(s)  11 . 
         [0052]    The first torsion springs  45  (outer peripheral side torsion springs) are disposed in the outer peripheral side first openings  44 a of the output flange  44 , while being supported by the outer peripheral side spring accommodation parts  42   a  and  43   a  of the pair of retaining plates  42  and  43 . The second torsion springs  46  (inner peripheral side torsion springs) are disposed in the inner peripheral side second openings  44   b  of the output flange  44 , while being supported by the inner peripheral side spring accommodation parts  42   b  and  43   b  of the pair of retaining plates  42  and  43 . 
         [0053]    &lt;Dynamic Damper Device  7 &gt; 
         [0054]    The dynamic damper device  7  attenuates torque fluctuations in a predetermined rotational speed range. Here, the dynamic damper device  7  is set to be capable of attenuating torque fluctuations in a high rotational speed range. 
         [0055]    As shown in  FIG. 2 , the dynamic damper device  7  is attached to the torque converter body  3 , for instance, the turbine shell  16 . The dynamic damper device  7  includes a damper plate  51  (an exemplary rotary member), a pair of inertia rings  57  (an exemplary mass part) and a plurality of third torsion springs  60  (an exemplary elastic member). 
         [0056]    As shown in  FIGS. 2 and 3 , the damper plate  51  is a disc member having a substantially annular shape. The damper plate  51  includes a disc part  52  having an annular shape, a plurality of spring placement parts  53  and a plurality of support protrusions  54 . The inner peripheral end of the disc part  52  is fixed to the turbine shell  16 . For example, as shown in  FIG. 2 , the inner peripheral end of the disc part  52  is fixed to the turbine shell  16  by welding. As shown in  FIG. 3 , the respective plural spring placement parts  53  are integrated with the disc part  52  and protrude radially outward therefrom. The respective spring placement parts  53  are provided at predetermined intervals in the circumferential direction. In other words, recesses  55  are provided, each being interposed between circumferentially adjacent spring placement parts  53 . 
         [0057]    Each spring placement part  53  (an exemplary second accommodation part) includes a third opening  63  for spring placement. Each third torsion spring  60  is disposed in the third opening  63 . The ends of each third torsion spring  60  are contactable to a pair of opening edges  63   a  (a pair of circumferential edges; an exemplary contact part) circumferentially opposed to each other in each third opening  63 . Each of the pair of opening edges  63   a  is formed along a straight line Cl radially extending from a rotational axis of the torque converter  1  (see  FIG. 3 ). Predetermined intervals are produced between a pair of radially opposed wall parts in each third opening  63  and the outer peripheral part of each third torsion spring  60 . 
         [0058]    The plural support protrusions  54  position the inertia rings  57  in the radial direction. Detailedly, the plural support protrusions  54  position one of the pair of inertia rings  57  (a first inertia ring  58  to be described) in the radial direction. The plural support protrusions  54  protrude from the disc part  52  toward the lock-up device  5 . The respective plural support protrusions  54  are integrated with the disc part  52  while being circumferentially aligned at predetermined intervals. 
         [0059]    As shown in  FIGS. 2 and 3 , the pair of inertia rings  57  is coupled to the damper plate  51  through the third torsion springs  60 . In other words, rotation of the pair of inertia rings  57  relative to the damper plate  51  is controlled by the third torsion springs  60 . Resonance of the torque converter  1  is inhibited by this control. 
         [0060]    Here, the inertia of the pair of inertia rings  57  is set to be smaller than that of the turbine  15  of the torque converter  1  in order to effectively attenuate torque fluctuations in the high rotational speed range. For example, the inertia of the pair of inertia rings  57  is set to be one-twentieth of that of the turbine  15  of the torque converter  1 . 
         [0061]    The pair of inertia rings  57  is composed of the first inertia ring  58  and a second inertia ring  59 . The first inertia ring  58  and the second inertia ring  59  are substantially annular members. The first inertia ring  58  and the second inertia ring  59  are rotatable relatively to the damper plate  51 . 
         [0062]    The first inertia ring  58  and the second inertia ring  59  are disposed axially at a predetermined interval. The damper plate  51  is disposed axially between the first inertia ring  58  and the second inertia ring  59 . The first inertia ring  58  and the second inertia ring  59  are axially coupled to each other by fixation members such as rivets  56 . The shafts of the rivets  56  are disposed in recesses  55  of the damper plate  51 , respectively. 
         [0063]    With this configuration, the first inertia ring  58  and the second inertia ring  59  are rotatable relatively to the damper plate  51  in the circumferential direction on the both axial sides of the damper plate  51 , while the first inertia ring  58  is supported by the support protrusions  54  of the damper plate  51 . 
         [0064]    Next, configurations of the first inertia ring  58  and the second inertia ring  59  will be explained. 
         [0065]    The first inertia ring  58  includes a first ring body  65  and first window parts  66  (an exemplary first accommodation part). The first ring body  65  has a substantially annular shape. The first window parts  66  hold the third torsion springs  60 , respectively, and are capable of sliding against the third torsion springs  60 . A hysteresis torque attributed to slide resistance of the first window parts  66  and the third torsion springs  60  is set to be, for instance, in a range of greater than or equal to 2 Nm and less than or equal to 30 Nm. By thus setting the hysteresis torque, secondary torque fluctuations (to be described) can be effectively attenuated when occurring in the high rotational speed range. 
         [0066]    The first window parts  66  are rectangular openings extending in the circumferential direction. Each first window part  66  includes a pair of first flange parts  67  and  68 . For example, the pair of first flange parts  67  and  68  is provided radially in opposition to each other. Additionally, the pair of first flange parts  67  and  68  protrude toward the lock-up device  5 . 
         [0067]    More specifically, one first flange part  67  (an outer peripheral side flange part) includes an outer peripheral side circular-arc flange part  67   a  and outer peripheral side corner flange parts  67   b . The outer peripheral side circular-arc flange part  67   a  circumferentially extends on the radially outer edge in each first window part  66 . The outer peripheral side corner flange parts  67   b  cover the radially outer corners of the circumferentially opposed edges in each first window part  66 . 
         [0068]    The other first flange part  68  (an inner peripheral side flange part) includes an inner peripheral side circular-arc flange part  68   a  and inner peripheral side corner flange parts  68   b . The inner peripheral side circular-arc flange part  68   a  circumferentially extends on the radially inner edge in each first window part  66 . The inner peripheral side corner flange parts  68   b  cover the radially inner corners of the circumferentially opposed edges in each first window part  66 . 
         [0069]    The outer peripheral side corner flange parts  67   b  and the inner peripheral side corner flange parts  68   b  hold the ends of each third torsion spring  60 . The outer peripheral side circular-arc flange part  67   a  and the inner peripheral side circular-arc flange part  68   a  are capable of sliding against each third torsion spring  60 . 
         [0070]    The second inertia ring  59  includes a second ring body  75  and second window parts  76  (an exemplary first accommodation part). The second ring body  75  has a substantially annular shape. The second window parts  76  hold the third torsion springs  60 , respectively, and are capable of sliding against the third torsion springs  60 . 
         [0071]    The second window parts  76  are rectangular openings extending in the circumferential direction. Each second window part  76  includes a pair of second flange parts  77  and  78 . For example, the pair of second flange parts  77  and  78  are provided radially in opposition to each other. Additionally, the pair of second flange parts  77  and  78  protrude toward the turbine  15 . 
         [0072]    Similarly to the pair of first flange parts  67  and  68 , the pair of second flange parts  77  and  78  includes an outer peripheral side circular-arc flange part  67   a , outer peripheral side corner flange parts  67   b , an inner peripheral side circular-arc flange part  68   a  and inner peripheral side corner flange parts  68   b . The outer peripheral side circular-arc flange part  67   a , the outer peripheral side corner flange parts  67   b , the inner peripheral side circular-arc flange part  68   a  and the inner peripheral side corner flange parts  68   b  do not directly appear on the drawing and are therefore indicated by reference numerals within parentheses in  FIG. 3 . 
         [0073]    It should be noted that the configurations of the second flange parts  77  and  78  are the same as those of the first flange parts  67  and  68 , excluding that the pair of second flange parts  77  and  78  protrude toward the turbine  15 . Therefore, detailed explanation of the configurations of the second flange parts  77  and  78  will be herein omitted. The explanation herein omitted conforms to that of the first flange parts  67  and  68 . 
         [0074]    The plural third torsion springs  60  are disposed in the spring placement parts  53  of the damper plate  51 , the first window parts  66  of the first inertia ring  58  and the second window parts  76  of the second inertia ring  59 . 
         [0075]    Detailedly, the both ends of each third torsion spring  60  are contactable to the pair of opening edges  63   a  in each spring placement part  53  of the damper plate  51 . Additionally, the both ends of each third torsion spring  60  are held by each pair of outer peripheral side corner flange parts  67   b , each pair of outer peripheral side corner flange parts  77   b , each pair of inner peripheral side corner flange parts  68   b  and each pair of inner peripheral side corner flange parts  78   b  in the first inertia ring  58  and the second inertia ring  59 , while making contact with these corner edges  67   b ,  77   b ,  68   b  and  78   b . Moreover, the outer peripheral part of each third torsion spring  60  is capable of sliding against the outer peripheral side circular-arc flange parts  67   a  and  77   a  and the inner peripheral side circular-arc flange parts  68   a  and  78   a  in the first inertia ring  58  and the second inertia ring  59 . 
         [0076]    When the first inertia ring  58  and the second inertia ring  59  are rotated relatively to the damper plate  51 , one of the both ends of each third torsion spring  60  described above is compressed by one of the pair of opening edges  63   a  of the damper plate  51 , while being held by the corner edges  67   b ,  77   b ,  68   b  and  78   b  in the first inertia ring  58  and the second inertia ring  59 . In this case, one of the pair of opening edges  63   a  of the damper plate  51  makes contact with the other of the both ends of each third torsion spring  60 . 
         [0077]    [Actions of Torque Converter] 
         [0078]    While the front cover  11  and the impeller  13  are rotated, the hydraulic oil flows from the impeller  13  to the turbine  15 , and a power is transmitted from the impeller  13  to the turbine  15  through the hydraulic oil. The power transmitted to the turbine  15  is transmitted through the turbine hub  18  to the input shaft (not shown in the drawings) for transmitting a torque to the transmission. 
         [0079]    When the rotational speed of the input shaft reaches a given constant speed, the lock-up device  5  is turned on, and a power is mechanically transmitted from the front cover  11  to the turbine hub  18  through the lock-up device  5 . Specifically, the piston  21  is moved toward the transmission by change in hydraulic pressure, and the plural friction members  34  are interposed and held by the piston  21  (the pressing part  23 ) and the positioning member  35  of the clutch part  31 . Accordingly, the power of the front cover  11  is transmitted from the torque transmission part  33  of the clutch part  31  to the pair of retaining plates  42  and  43 . Then, the power is transmitted to the output flange  44  through the pair of retaining plates  42  and  43  and the outer peripheral side and inner peripheral side torsion springs  45  and  46 , and is outputted to the turbine hub  18 . 
         [0080]    [Actions of Dynamic Damper Device] 
         [0081]    The dynamic damper device  7  is attached to the torque converter body  3 , for instance, the turbine shell  16 . Due to this, torque fluctuations of the turbine  15  are inhibited by the dynamic damper device  7 . The dynamic damper device  7  in the present exemplary embodiment will be hereinafter explained in detail. 
         [0082]    For example, when the dynamic damper device  7  is not installed, as shown in  FIG. 4 , there are chances of occurrence of torque fluctuations in the vicinity of a predetermined rotational speed range of the engine, for instance, in the vicinity of a high rotational speed range (1900 rpm) (see characteristic curve E 1 ). The torque fluctuations are considered as being caused by resonance of the turbine  15  attributed to the stiffness of the input shaft, that of a member coupled to the input shaft, and/or so forth. 
         [0083]    On the other hand, when the dynamic damper device  7  is installed, as shown in  FIG. 4 , the torque fluctuations (primary torque fluctuations T 1 ) in the aforementioned high rotational speed range are attenuated by the dynamic damper device  7  (see characteristic curves E 2  to E 4 ). Thus, the present dynamic damper device  7  (e.g., the pair of inertia rings  57  and the plural third torsion springs  60 ) is set to be capable of effectively attenuating the primary torque fluctuations in the aforementioned high rotational speed range. 
         [0084]    Here, in this case, the primary torque fluctuations T 1  (exemplary principal torque fluctuations) at an intended rotational speed targeted by the dynamic damper device  7  can be attenuated, but toque fluctuations in the vicinity of the intended rotational speed, for instance, secondary torque fluctuations T 2  (exemplary subsidiary torque fluctuations) in the vicinity of 1700 rpm and those in the vicinity of 2000 rpm partially increase (see e.g., characteristic curve E 2 ). It should be noted that in  FIG. 4 , for instance, 1900 rpm is assumed as the intended rotational speed. 
         [0085]    However, in the present dynamic damper device  7 , each third torsion spring  60  slides against the first inertia ring  58  (the outer peripheral side circular-arc flange part  67   a  and the inner peripheral side circular-arc flange part  68 a) and the second inertia ring  59  (the outer peripheral side circular-arc flange part  77   a  and the inner peripheral side circular-arc flange part  78   a ), whereby a hysteresis torque (a toque due to slide resistance) occurs. The aforementioned secondary torque fluctuations T 2  are attenuated by the hysteresis torque (characteristic E 3 , characteristic E 4 ). 
         [0086]    Especially, among the secondary torque fluctuations T 2 , torque fluctuations on the low rotational speed side, for instance, those in the vicinity of  1700  rpm, are effectively attenuated. It should be noted that characteristic curve E 2  is obtained when the hysteresis torque is not taken into consideration. On the other hand, the hysteresis torque in characteristic curve E 3  and that in curve characteristic E 4  are set to be, for instance, in a range of greater than or equal to 2 Nm and less than or equal to 30 Nm. Characteristic curve E 3  and curve characteristic E 4  are different in magnitude of hysteresis torque, and the hysteresis torque in characteristic E 3  is smaller than that in characteristic E 4 . 
         [0087]    When the rotational speed of the engine herein increases, the hysteresis torque also increases. Hence, among the secondary torque fluctuations T 2 , toque fluctuations on the high rotational speed side (e.g., torque fluctuations in the vicinity of 2000 rpm) are less affected by the magnitude of hysteresis torque. 
         [0088]    Thus, the present dynamic damper device  7  attenuates the primary torque fluctuations T 1  at the intended rotational speed by the inertia rings  57  and the third torsion springs  60 , and attenuates the secondary torque fluctuations T 2  occurring in attenuation of the primary torque fluctuations T 1  by the hysteresis torque. 
         [0089]    [Features] 
         [0090]    (1) In the present dynamic damper device  7 , the damper plate  51  is fixed to the turbine  15  of the torque converter  1 . Additionally, in rotation of the damper plate  51 , the inertia rings  57  are moved relatively to the damper plate  51  through the third torsion springs  60 , whereby the primary torque fluctuations T 1  of the turbine  15  can be directly attenuated. 
         [0091]    Here, when the primary torque fluctuations T 1  of the turbine  15  are attenuated in the present dynamic damper device  7 , torque fluctuations of the turbine  15  partially increase in the vicinity of the intended rotational speed targeted by the present dynamic damper device  7 . 
         [0092]    However, in the present dynamic damper device  7 , when the damper plate  51  is rotated while each third torsion spring  60  is held by each first window part  66  and each second window part  76  of the inertia rings  57 , each third torsion spring  60  and both each first window part  66  and each second window part  76  of the inertia rings  57  slide against each other, whereby a hysteresis torque is generated. Thus, in the present dynamic damper device  7 , the partially increased secondary torque fluctuations T 2  of the turbine  15  can be also attenuated by the hysteresis torque. 
         [0093]    In the present dynamic damper device  7 , the primary torque fluctuations T 1  of the turbine  15  can be directly attenuated, and simultaneously, the secondary torque fluctuations T 2 , occurring by attenuation of the primary torque fluctuations T 1 , can be also attenuated. In other words, in the present dynamic damper device  7 , torque fluctuations of the turbine  15  of the torque converter  1  can be effectively reduced. 
         [0094]    (2) In the present dynamic damper device  7 , the hysteresis torque is set to be greater than or equal to 2 Nm and less than or equal to 30 Nm. Hence, compared to a well-known type of dynamic damper device  7 , the secondary torque fluctuations T 2 , subsidiarily occurring in the turbine  15  of the torque converter  1 , can be effectively attenuated in a high rotational speed range. 
         [0095]    (3) In the present dynamic damper device  7 , the inertia of the inertia rings  57  is smaller than that of the turbine  15  of the torque converter  1 . For example, when the inertia of the inertia rings  57  is increased, it is possible to enhance an attenuation effect to be exerted on the primary torque fluctuations T 1  in the intended rotational speed. On the other hand, it is concerned that the secondary torque fluctuations T 2  in the vicinity of the intended rotational speed increases with increase in inertia of the inertia rings  57 . Therefore, it is effective to set the inertia of the inertia rings  57  to be smaller than that of the turbine  15  in order to attenuate the primary torque fluctuations T 1  without, as much as possible, increasing the secondary torque fluctuations T 2 . In other words, with this configuration, it is possible to inhibit increase in secondary torque fluctuations T 2  occurring in attenuation of the primary torque fluctuations T 1 . 
         [0096]    (4) In the present dynamic damper device  7 , each third torsion spring  60  is held only by each first window part  66  and each second window part  76  of the inertia rings  57  on the both sides of the damper plate  51 , while being disposed in each spring placement part  53  of the damper plate  51 . Accordingly, a hysteresis torque can be stably generated while each third torsion spring  60  is reliably held by each first window part  66  and each second window part  76  of the inertia rings  57 . 
         [0097]    (5) In the present dynamic damper device  7 , a hysteresis torque can be more stably generated on the outer peripheral side circular-arc flange part  67   a  and the inner peripheral side circular-arc flange part  68   a  of each first window part  66  and each second window part  76  of the inertia rings  57 , while each third torsion spring  60  is reliably held by the outer peripheral side corner flange parts  67   b  and the inner peripheral side corner flange parts  68   b  of each first window part  66  and each second window part  76  of the inertia rings  57 . 
         [0098]    (6) In the present dynamic damper device  7 , when the inertia rings  57  are rotated relatively to the damper plate  51 , each third torsion spring  60  is pressed by the opening edges  63   a  of each spring placement part  53  of the damper plate  51 , while being held by each first window part  66  and each second window part  76  of the inertia rings  57 . Accordingly, each third torsion spring  60  is compressed. Here, each opening edge  63   a  is formed along the straight line C 1  extending from the rotational center in the radial direction. Therefore, each third torsion spring  60 , when pressed by the opening edges  63 a, becomes likely to deflect in a direction separating from the rotational center and slides against each first window part  66  and each second window part  76  of the inertia rings  57 . Accordingly, a hysteresis torque can be more stably generated. 
         [0099]    [Other Exemplary Embodiments] 
         [0100]    The present invention is not limited to the aforementioned exemplary embodiment, and a variety of changes or modifications can be made without departing from the scope of the present invention. 
         [0101]    (A) The aforementioned exemplary embodiment has exemplified the configuration that the lock-up device  5  includes the first torsion springs  45  and the second torsion springs  46 . However, the configuration of the lock-up device  5  is not limited to that of the aforementioned exemplary embodiment, and may be arbitrarily set. 
         [0102]    (B) The aforementioned exemplary embodiment has exemplified the configuration that the clutch part  31  includes the plural friction members  34  (the first friction members  34   a  and the second friction members  34   b ). However, the configuration of the clutch part  31  is not limited to that of the aforementioned exemplary embodiment, and may be arbitrarily set. 
         [0103]    (C) The aforementioned exemplary embodiment has exemplified the configuration that the outer peripheral side circular-arc flange part  67   a  and the inner peripheral side circular-arc flange part  68   a  of the first flange parts  67  and  68  and the second flange parts  77  and  78  have circular-arc shapes. However, the shapes of the first flange parts  67  and  68  and those of the second flange parts  77  and  78  may be arbitrarily set as long as the aforementioned hysteresis torque can be generated by slide between each third torsion spring  60  and both the first flange parts  67  and  68  and the second flange parts  77  and  78 . For example, the shapes of the outer peripheral side circular-arc flange part  67   a  and the inner peripheral side circular-arc flange part  68   a  may be other than the circular-arc shapes. 
         [0104]    (D) The aforementioned exemplary embodiment has exemplified the configuration that each third torsion spring  60  is capable of sliding against both the outer peripheral side circular-arc flange parts  67   a  and  77   a  and the inner peripheral side circular-arc flange parts  68   a  and  78   a . Instead of this, the first flange parts  67  and  68  and the second flange parts  77  and  78  may be configured such that each third torsion spring  60  is capable of sliding against only the outer peripheral side circular-arc flange parts  67   a  and  77   a.    
         [0105]    Additionally or alternatively, the first flange parts  67  and  68  and the second flange parts  77  and  78  may be configured such that each third torsion spring  60  slides against both the outer peripheral side circular-arc flange parts  67   a  and  77   a  and the inner peripheral side circular-arc flange parts  68   a  and  78   a  in a low rotational speed range, whereas each third torsion spring  60  slides against only the outer peripheral side corner flange parts  67   b  and  78   b  in a high rotational speed range. 
       REFERENCE SIGNS LIST 
       [0106]      1  Torque converter 
         [0107]      7  Dynamic damper device 
         [0108]      15  Turbine 
         [0109]      51  Damper plate 
         [0110]      53  Spring placement part 
         [0111]      57  Inertia ring 
         [0112]      60  Third torsion spring 
         [0113]      66  First window part 
         [0114]      76  Second window part 
         [0115]    O Rotational center