Patent Publication Number: US-2019186593-A1

Title: Torque fluctuation inhibiting device, torque converter and power transmission device

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims priority to Japanese Patent Application No. 2017-243112, filed Dec. 19, 2017. The contents of that application are herein incorporated by reference in their entirety. 
     BACKGROUND 
     Technical Field 
     The present disclosure relates to a torque fluctuation inhibiting device, in particular, to a torque fluctuation inhibiting device configured to inhibit torque fluctuation. The present disclosure also relates to a torque converter and a power transmission device both including the torque fluctuation inhibiting device. 
     Background Art 
     A clutch device or a torque converter including a damper device is provided, for example, between the engine and the transmission of an automobile. The torque converter is provided with a lock-up device used for mechanically transmitting torque at a predetermined rotational speed or higher in order to reduce fuel consumption. 
     Japanese Patent Unexamined Publication 2017-053467 discloses a lock-up device including a torque fluctuation inhibiting device. The torque fluctuation inhibiting device in Japanese Patent Unexamined Publication 2017-053467 includes an inertia ring, a plurality of centrifugal elements and a plurality of cam mechanisms. The inertia ring can rotate relative to a hub flange to which torque is transmitted, and the centrifugal elements are subject to centrifugal force due to rotation of the hub flange and the inertia ring. The cam mechanism includes a cam formed on a surface of the centrifugal element and a cam follower which makes contact with the cam. 
     With the device in Japanese Patent Unexamined Publication 2017-053467, if torque fluctuation causes displacement in a rotational direction between the hub flange and the inertia ring, the cam mechanism operates as a result of centrifugal force acting on the centrifugal element. In addition, the centrifugal force acting on the centrifugal element is converted to circumferential force which reduces the displacement between the hub flange and the inertia ring. This circumferential force inhibits torque fluctuation. 
     BRIEF SUMMARY 
     With the torque fluctuation inhibiting device in Japanese Patent Unexamined Publication 2017-053467, a plurality of recesses open externally in a radial direction are formed on an outer peripheral portion of the hub flange, and the centrifugal elements are housed in these recesses in a manner that allows the centrifugal elements to move in the radial direction. With this configuration, gaps are formed between both circumferential sides of the centrifugal elements and wall portions of the recesses which oppose the sides of the centrifugal elements. It is structurally difficult to eliminate these gaps. 
     In the torque fluctuation inhibiting device as described above, the gaps formed between the centrifugal elements and the recesses may cause the centrifugal elements to randomly move in the circumferential direction or randomly rotate and change orientation while the device is operating. 
     Here, when the centrifugal elements randomly move or change orientation within the range of the gaps, hysteresis occurs in the torsional characteristics (characteristics indicating the relationship between a relative rotational angle formed between the hub flange and the inertia ring and torque transmitted between the hub flange and the inertia ring) of the torque fluctuation inhibiting device. Hysteresis reduces the effect of inhibiting torque fluctuation (that is, the ability to dampen torque fluctuation). 
     In addition, if the centrifugal elements randomly move or change orientation within the range of the gaps, the profiles of the cams formed in the centrifugal elements also randomly change, and torsional characteristics in terms of design cannot be appropriately obtained. In other words, the above-mentioned gaps cause torsional characteristics to be unstable, that is, the ability to dampen torque fluctuation to be unstable. 
     It is an objective of the present disclosure to provide a torque fluctuation inhibiting device that is capable of stably maintaining torque fluctuation dampening ability. 
     Solution to Problem 
     (1) A torque fluctuation inhibiting device according to one aspect of the present disclosure is a torque fluctuation inhibiting device configured to inhibit torque fluctuation. 
     This torque fluctuation inhibiting device includes a first rotating body, a second rotating body, a centrifugal element, a support portion and a displacement inhibiting mechanism. Torque is input to the first rotating body. The second rotating body is rotatably disposed relative to the first rotating body. The centrifugal element is subject to centrifugal force due to rotation of the first rotating body and is configured to move in a direction different from a direction in which the centrifugal force acts. The support portion is provided to the first rotating body or the second rotating body and is configured to moveably guide the centrifugal element in the direction different from the direction in which the centrifugal force acts on the centrifugal element. The displacement inhibiting mechanism is configured to generate circumferential force which reduces relative displacement of the first rotating body and the second rotating body when the centrifugal element moves in the direction different from the direction in which the centrifugal force acts on the centrifugal element. 
     With this torque fluctuation inhibiting device, the first rotating body and the second rotating body rotate when torque is input to the first rotating body. If the torque input to the first rotating body does not fluctuate, no phase displacement in the rotational direction occurs between the first rotating body and the second rotating body. In contrast, if the input torque fluctuates, because the second rotating body is rotatably disposed relative to the first rotating body, relative displacement (hereinafter sometimes referred to as “rotational phase difference”) in the rotational direction occurs between the first rotating body and the second rotating body according to the degree of torque fluctuation. 
     Here, when the first rotating body and the second rotating body rotate, the centrifugal element is subject to the centrifugal force. The centrifugal force acts on the centrifugal element in the radial direction to move the centrifugal element in the direction different from the direction in which the centrifugal force acts on the centrifugal element. With this configuration, when relative displacement in the rotational direction occurs between the first rotating body and the second rotating body, the displacement inhibiting mechanism generates circumferential force which reduces the relative displacement between the first rotating body and the second rotating body. The displacement inhibiting mechanism inhibits torque fluctuation. 
     Here, the centrifugal force acting on the centrifugal element is used as force for inhibiting torque fluctuation. Because of this, characteristics for inhibiting torque fluctuation fluctuate depending on rotational speed of the rotating body. Further, characteristics for inhibiting torque fluctuation can be appropriately set and torque fluctuation peaks in wider rotational speed ranges can be inhibited based on, for example, the shape of the cam. 
     In addition, the centrifugal force acts on the centrifugal element in the radial direction and the centrifugal element moves in the direction different from the direction in which the centrifugal force acts on the centrifugal element. With this configuration, if the above-described gaps exist, the orientation of the centrifugal element changes relative to the support portion within the range of the gap. Under this state, the centrifugal element moves in the direction different from the direction in which the centrifugal force acts on the centrifugal element. As a result, even if a gap exists between the centrifugal element and the support portion, the centrifugal element moves relative to the support portion under a state in which the orientation of the centrifugal element is maintained relative to the support portion. 
     With this configuration, hysteresis in the torsional characteristics is inhibited, and hence a reduction in torque fluctuation dampening ability can be avoided. In addition, torque fluctuation dampening ability can be stabilized. In other words, with the present torque fluctuation inhibiting device, torque fluctuation dampening ability can be stably maintained. 
     (2) In a torque fluctuation inhibiting device according to another aspect of the present disclosure, the support portion preferably includes a first wall portion extending in the direction different from the direction in which the centrifugal force acts on the centrifugal element, and a second wall portion opposing the first wall portion in a circumferential direction. Here, the centrifugal element is disposed between the first wall portion and the second wall portion. The centrifugal element is movable in the direction different from the direction in which the centrifugal force acts on the centrifugal element along at least one of the first wall portion and the second wall portion. 
     With this configuration, the centrifugal element can be suitably moved in the direction different from the direction in which the centrifugal force acts on the centrifugal element. As a result, torque fluctuation dampening ability can be stably maintained. 
     (3) In a torque fluctuation inhibiting device according to another aspect of the present disclosure, the centrifugal element is preferably subject to turning moment about an axis parallel to a center of rotation of the first rotating body, so as to make contact with the support portion. 
     In this case, turning moment due to the component force of the centrifugal force acts on the centrifugal element by allowing the support portion to guide the centrifugal element as described above. When this happens, the orientation of the centrifugal element changes and the centrifugal element makes contact with the support portion. As a result, the orientation of the centrifugal element can be maintained relative to the support portion and the centrifugal element can be moved along the support portion. In other words, torque fluctuation dampening ability can be stably maintained. 
     (4) In a torque fluctuation inhibiting device according to another aspect of the present disclosure, the centrifugal element preferably includes a first centrifugal element subject to a first turning moment, and a second centrifugal element subject to a second turning moment opposite to the first turning moment. 
     In this case, torsional characteristics resulting from the first centrifugal element and torsional characteristics resulting from the second centrifugal element combine, and hence more suitable torsional characteristics can be realized. In other words, torque fluctuation dampening ability can be stably maintained. 
     (5) In a torque fluctuation inhibiting device according to another aspect of the present disclosure, with a first straight line connecting the center of rotation of the first rotating body and a center of gravity of the centrifugal element as a reference, the centrifugal element disposed on a first rotational direction side and the centrifugal element disposed on a second rotational direction side opposite to the first rotational direction side have substantially the same mass. 
     Even with such a configuration, the centrifugal element is guided to the support portion as described above, to thereby maintain the orientation of the centrifugal element relative to the support portion. With this configuration, torque fluctuation dampening ability can be stably maintained. 
     (6) In a torque fluctuation inhibiting device according to another aspect of the present disclosure, with a first straight line connecting the center of rotation of the first rotating body and a center of gravity of the centrifugal element as a reference, the centrifugal element disposed on a first rotational direction side and the centrifugal element disposed on a second rotational direction side opposite to the first rotational direction side have different masses. 
     With this configuration, the orientation of the centrifugal element can easily be changed and maintained relative to the support portion. As a result, torque fluctuation dampening ability can be stably maintained. 
     (7) In a torque fluctuation inhibiting device according to another aspect of the present disclosure, the torque fluctuation inhibiting device preferably includes a cam mechanism. Here, the cam mechanism is configured to, when relative displacement occurs in a rotational direction between the first rotating body and the second rotating body, convert the centrifugal force into circumferential force in a direction in which the relative displacement reduces. 
     In this case, through use of the cam mechanism, the centrifugal force can be effectively converted into circumferential force in a direction in which relative displacement reduces. In other words, torque fluctuation dampening ability can be stably maintained. 
     (8) In a torque fluctuation inhibiting device according to another aspect of the present disclosure, the cam mechanism includes a cam and a cam follower. The cam is provided in one of the second rotating body and the centrifugal element. The cam follower is provided in the other of the second rotating body and the centrifugal element and is configured to move along the cam. 
     Even with such a configuration, torque fluctuation dampening ability can be stably maintained. 
     (9) In a torque fluctuation inhibiting device according to another aspect of the present disclosure, the direction different from the direction in which the centrifugal force acts on the centrifugal element preferably differs from a direction in which a second straight line extends. The second straight line is a straight line which connects the center of rotation of the first rotating body and a point of contact between the cam and the cam follower under a state subject to the centrifugal force with no relative displacement. 
     With this configuration, the centrifugal element can be favorably moved in the direction different from the direction in which the centrifugal force acts on the centrifugal element. As a result, torque fluctuation dampening ability can be stably maintained. 
     (10) In a torque fluctuation inhibiting device according to another aspect of the present disclosure, an outer peripheral surface of the first rotating body preferably includes a plurality of recesses open externally in a radial direction. The centrifugal element is housed in the recess. The centrifugal element includes a first guide roller rotatably mounted to a first side portion in the circumferential direction, and a second guide roller rotatably mounted to a second side portion in the circumferential direction. The support portion includes a first wall portion in the recess against which the first guide roller abuts, and a second wall portion in the recess against which the second guide roller abuts. 
     With this configuration, in the centrifugal element, the first guide roller makes contact with the first wall portion of the recess and the second guide roller makes contact with the second wall portion of the recess. Therefore, the orientation of the centrifugal element can be maintained relative to the support portion. As a result, torque fluctuation dampening ability can be stably maintained. 
     (11) In a torque fluctuation inhibiting device according to another aspect of the present disclosure, the first guide roller and the second guide roller each preferably include an outer peripheral roller and an inner peripheral roller disposed radially inward of the outer peripheral roller. 
     With this configuration, the centrifugal element can be stably moved along the first and second wall portions of the recess. As a result, torque fluctuation dampening ability can be stably maintained. 
     (12) In a torque fluctuation inhibiting device according to another aspect of the present disclosure, the second rotating body preferably includes a first inertia ring and a second inertia ring sandwiching and opposing the first rotating body, and a pin linking the first inertia ring and the second inertia ring such that the first inertia ring and the second inertia ring are unrotatable relative to each other. Here, the centrifugal element is disposed between the first inertia ring and the second inertia ring in the axial direction at an outer peripheral portion of the first rotating body and on an inner peripheral side of the pin. 
     With this configuration, the cam mechanism can be made simple and compact. 
     (13) A torque fluctuation inhibiting device according to one aspect of the present disclosure is a torque converter disposed between an engine and a transmission. 
     The torque converter includes an input-side rotational body to which torque from an engine is input; an output-side rotational body which outputs torque to the transmission; a damper disposed between the input-side rotational body and a turbine; and the torque fluctuation inhibiting device of any one of items (1) to (12) above. 
     (14) A torque fluctuation inhibiting device according to one aspect of the present disclosure includes a flywheel; a clutch device provided to the second inertial body of the flywheel; and the torque fluctuation inhibiting device of any one of items (1) to (12) above. Here, the flywheel includes a first inertial body which rotates about a rotational axis, a second inertial body which rotates about the rotational axis and rotates relative to the first inertial body, and a damper disposed between the first inertial body and the second inertial body. 
     With the present advancement, the ability to dampen torque fluctuation can be stably maintained in a torque fluctuation inhibiting device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram for illustrating a torque converter according to a first embodiment of the present disclosure. 
         FIG. 2  is a front view for schematically illustrating a hub flange and a cam mechanism shown in  FIG. 1 . 
         FIG. 3  is a partial front view for illustrating the hub flange and a torque fluctuation inhibiting device shown in  FIG. 1 . 
         FIG. 4  is a diagram as seen from the arrow A in  FIG. 2 . 
         FIG. 5  is an external perspective view of the portion shown in  FIG. 2 . 
         FIG. 6A  is a diagram for explaining component force of centrifugal force acting on a first centrifugal element. 
         FIG. 6B  is a diagram for explaining component force of centrifugal force acting on a second centrifugal element. 
         FIG. 7  is a diagram for explaining operation of the cam mechanism. 
         FIG. 8  is a graph for showing torsional characteristics of a first cam mechanism and a second cam mechanism. 
         FIG. 9  is a graph for showing composite torsional characteristics of the first cam mechanism and the second cam mechanism. 
         FIG. 10  is a characteristic diagram for showing the relationship between rotational speed and torque fluctuation. 
         FIG. 11  is a diagram corresponding to  FIG. 2  showing the first embodiment for illustrating a second embodiment of the present disclosure. 
         FIG. 12  is a diagram corresponding to  FIG. 6  showing the first embodiment for illustrating the second embodiment of the present disclosure. 
         FIG. 13  is a diagram corresponding to  FIG. 8  showing the first embodiment for illustrating the second embodiment of the present disclosure. 
         FIG. 14  is a diagram corresponding to  FIG. 9  showing the first embodiment for illustrating the second embodiment of the present disclosure. 
         FIG. 15  is a schematic diagram for illustrating an Application Example 1 of the present disclosure. 
         FIG. 16  is a schematic diagram for illustrating an Application Example 2 of the present disclosure. 
         FIG. 17  is a schematic diagram for illustrating an Application Example 3 of the present disclosure. 
         FIG. 18  is a schematic diagram for illustrating an Application Example 4 of the present disclosure. 
         FIG. 19  is a schematic diagram for illustrating an Application Example 5 of the present disclosure. 
         FIG. 20  is a schematic diagram for illustrating an Application Example 6 of the present disclosure. 
         FIG. 21  is a schematic diagram for illustrating an Application Example 7 of the present disclosure. 
         FIG. 22  is a schematic diagram for illustrating an Application Example 8 of the present disclosure. 
         FIG. 23  is a schematic diagram for illustrating an Application Example 9 of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
       FIG. 1  is a schematic diagram for illustrating a case where a torque fluctuation inhibiting device  14  according to a first embodiment of the present disclosure is mounted to a lock-up device in a torque converter. In  FIG. 1 , the line O-O represents the rotational axis of the torque converter. 
     [Overall Configuration] 
     A torque converter  1  includes a front cover  2 , a torque converter body  3 , a lock-up device  4  and an output hub  5 . Torque from an engine is input to the front cover  2 . The torque converter body  3  includes an impeller  7  connected to the front cover  2 , a turbine  8  and a stator (not shown). The turbine  8  is connected to the output hub  5  and engages with an inner peripheral portion of the output hub  5  because the input axis (not shown) of the transmission is a spline. 
     A center of rotation O is defined in this embodiment. The center of rotation O is the center of rotation of the torque converter  1 . More specifically, the center of rotation O is the center of rotation of each of the front cover  2 , the torque converter body  3 , the lock-up device  4  (for example, an input-side rotational body  11 , a hub flange  12  and the torque fluctuation inhibiting device  14  to be described later) and the output hub  5 . The center of rotation O is sometimes described as the rotational axis of each component. 
     The terms “axial direction”, “radial direction”, “circumferential direction (circumference direction)” and “rotational direction” are defined with the center of rotation O as a reference. “Axial direction” is a direction in which the center of rotation O extends and corresponds to the direction along the center of rotation O. “Radial direction” is a direction separating from the center of rotation O and, for example, corresponds to the radial direction of a circle centered about the center of rotation O. 
     “Circumferential direction (circumference direction)” is a direction about the center of rotation O and, for example, corresponds to the circumferential direction of a circle centered about the center of rotation O. “Rotational direction” substantially corresponds to the “circumferential direction”. “Rotational direction” may be divided into a first rotational direction R 1  and a second rotational direction R 2  opposite to the first rotational direction R 1 . 
     [Lock-Up Device] 
     The lock-up device  4  includes a clutch portion, a piston which operates using hydraulic pressure, and other components. The lock-up device  4  includes a lock-up on state and a lock-up off state. 
     In the lock-up on state, torque input to the front cover  2  is transmitted to the output hub  5  through the lock-up device  4  without passing through the torque converter body  3 . In contrast, in the lock-up off state, the torque input to the front cover  2  is transmitted to the output hub  5  via the torque converter body  3 . 
     As illustrated in  FIG. 1 , the lock-up device  4  includes the input-side rotational body  11 , the hub flange  12  (rotational body), a damper  13  and the torque fluctuation inhibiting device  14 . 
     The input-side rotational body  11  includes a piston which is configured to move in the axial direction. A friction member  16  is fixed to a side surface of the input-side rotational body  11  on the side of the front cover  2 . Torque is transmitted from the front cover  2  to the input-side rotational body  11  when the friction member  16  is pressed against the front cover  2 . This state is the lock-up on state. 
     The hub flange  12  is disposed opposing the input-side rotational body  11  in the axial direction and rotates relative to the input-side rotational body  11 . The hub flange  12  is linked to the output hub  5 . 
     The damper  13  is disposed between the input-side rotational body  11  and the hub flange  12 . The damper  13  has a plurality of torsion springs and elastically connects the input-side rotational body  11  and the hub flange  12  to each other in the rotational direction. The damper  13  allows torque to be transmitted from the input-side rotational body  11  to the hub flange  12  and absorbs/dampens torque fluctuation. 
     [Torque Fluctuation Inhibiting Device] 
       FIGS. 2 to 6B  illustrate the torque fluctuation inhibiting device  14 .  FIG. 2  is a front view for schematically illustrating the hub flange  12  and the torque fluctuation inhibiting device  14 .  FIG. 3  is a diagram for illustrating in detail the torque fluctuation inhibiting device  14  shown in  FIG. 2 .  FIG. 4  is a diagram showing  FIG. 3  from an A direction.  FIG. 5  is an external perspective view of  FIG. 4 .  FIGS. 6A and 6B  are diagrams for illustrating the torque fluctuation inhibiting device  14  shown in  FIG. 2  in an enlarged manner. Note that in  FIGS. 2 to 4  and  FIG. 6 , one inertia ring  20  (inertia ring  20  on the near side) has been removed. 
     As illustrated in  FIG. 2 , the torque fluctuation inhibiting device  14  includes the hub flange  12 , inertia rings  20  as mass bodies, four centrifugal elements  21 , four cam mechanisms  22  (example of displacement inhibiting mechanism) and a plurality of support portions  23 . 
     [Inertia Ring] 
     As illustrated in  FIGS. 2 to 5 , the inertia ring  20  includes a first inertia ring  201  and a second inertia ring  202 . 
     The first and second inertia rings  201  and  202  are plates with a predetermined thickness and are formed into continuous annular shapes. As illustrated in  FIGS. 3 and 5 , the first and second inertia rings  201  and  202  are disposed on both sides of the hub flange  12  in the axial direction with a predetermined gap therebetween. In other words, the hub flange  12  and the first and second inertia rings  201  and  202  are all disposed along the axial direction. 
     The first and second inertia rings  201  and  202  have the same rotational axis as the hub flange  12 . The first and second inertia rings  201  and  202  rotate along with the hub flange  12  and are configured so as to rotate relative to the hub flange  12 . 
     As illustrated in  FIG. 4 , the first and second inertia rings  201  and  202  are formed with holes  201   a  and  202   a  which penetrate the first and second inertia rings  201  and  202  in the axial direction. The first inertia ring  201  and the second inertia ring  202  are fixed using rivets  203  which penetrate the holes  201   a  and  202   a  . Therefore, the first inertia ring  201  is not movable relative to the second inertia ring  202  in any of the axial direction, the radial direction or the rotational direction. 
     [Hub Flange] 
     As illustrated in  FIGS. 1 and 2 , the hub flange  12  is formed into a circular plate. As described above, the inner peripheral portion of the hub flange  12  is connected to the output hub  5 . As illustrated in  FIGS. 3 and 5 , four protrusions  121  with predetermined widths in the circumferential direction are formed on an outer peripheral portion of the hub flange  12 , the protrusions  121  being protruding further than the outer peripheral portion. 
     A recess  122  with a predetermined width is formed at the center of each protrusion  121  in the circumferential direction. Each recess  122  is formed so as to be open radially outward and has a predetermined depth. Each recess  122  has first and second side walls  122   a  and  122   b  which oppose each other in the circumferential direction. The first and second side walls  122   a  and  122   b  guide the centrifugal element  21 . 
     As illustrated in  FIGS. 6A and 6B , the first and second side walls  122   a  and  122   b  extend in directions DS 1  and DS 2  which are different from the direction in which a centrifugal force CF 0  acts on the centrifugal element  21 . For example, the first and second side walls  122   a  are  122   b  are formed parallel to each other and extend in the directions DS 1  and DS 2  which are different from the direction in which a centrifugal force CF 0  acts on the centrifugal element  21 . More specifically, when the hub flange  12  is viewed from the outer side in the axial direction (the recess  122  is viewed from the outer side in the axial direction), the first and second side walls  122   a  and  122   b  are inclined relative to a straight line L connecting the center of rotation O of the hub flange  12  and a center C of the cam mechanism  22  in the circumferential direction. 
     Here, the direction in which the centrifugal force CF 0  acts on the centrifugal element  21  is a direction in which the centrifugal force CF 0  has acted on a center of gravity G 1  or G 2  of the centrifugal element  21 . In other words, the direction in which the centrifugal force CF 0  acts on the centrifugal element  21  is a radial direction in which the centrifugal force CF 0  passes through the center of gravity G 1  or G 2  of the centrifugal element  21 . 
     The direction DS 1  or DS 2  different from the direction in which the centrifugal force CF 0  acts on the centrifugal element  21  corresponds to a direction (guiding direction) in which the first and second side walls  122   a  and  122   b  guide the centrifugal element  21 . In other words, the direction DS 1  or DS 2  different from the direction in which the centrifugal force CF 0  acts on the centrifugal element  21  corresponds to a direction (movement direction) in which the centrifugal element  21  moves. 
     The direction DS 1  or DS 2  different from the direction in which the centrifugal force CF 0  acts on the centrifugal element  21 , for example the direction (guiding direction) in which the first and second wall portions  122   a  and  122   b  extend, intersects with the direction in which the centrifugal force CF 0  acts on the centrifugal element  21  (radial direction in which the centrifugal force CF 0  passes through the center of gravity G 1  or G 2  of the centrifugal element  21 ). More specifically, the absolute value of the inner product of a direction vector of the direction DS 1  or DS 2  different from the direction in which the centrifugal force CF 0  acts on the centrifugal element  21  and a vector of the direction in which the centrifugal force CF 0  acts on the centrifugal element  21  is less than 1. 
     More specifically, as illustrated in  FIG. 2 , each recess  122  includes a first recess  123  and a second recess  124 . The configuration of the first recess  123  and the configuration of the second recess  124  are substantially the same except for the directions in which the first and second side walls  122   a  and  122   b  are formed. 
     As illustrated in  FIG. 6A , when the hub flange  12  is viewed from an external side in the axial direction (when the first recess  123  is viewed from the external side in the axial direction), a first and second side wall  123   a  of the first recess  123  on the first rotational direction R 1  side is inclined with respect to the straight line L so as to approach the straight line L in the radial direction separating from the center of rotation O along the straight line L. In addition, a first and second side wall  123   b  of the first recess  123  on the second rotational direction R 2  side is inclined with respect to the straight line L so as to separate from the straight line L in the radial direction separating from the center of rotation O along the straight line L. 
     On the other hand, as illustrated in  FIG. 6B , when the hub flange  12  is viewed from an external side in the axial direction (when the second recess  124  is viewed from an external side in the axial direction), a first and second side wall  124   a  of the second recess  124  on the second rotational direction R 2  side is inclined with respect to the straight line L so as to approach the straight line L in the radial direction separating from the center of rotation O along the straight line L. In addition, a first and second side wall  124   b  of the second recess  124  on the first rotational direction R 1  side is inclined with respect to the straight line L so as to separate from the straight line L in the radial direction separating from the center of rotation O along the straight line L. 
     [Centrifugal Element and Support Portion] 
     As illustrated in  FIGS. 2 to 6B , the centrifugal element  21  is disposed in the recess  122  of the hub flange  12 . The centrifugal element  21  is movable in the direction DS 1  or DS 2  different from the direction in which the centrifugal force CF 0  acts on the centrifugal element  21  due to the centrifugal force CF 0  generated by the rotation of the hub flange  12 . 
     As illustrated in  FIGS. 3 and 4 , the centrifugal element  21  includes first guide rollers  26   a , second guide rollers  26   b  and pins  27  which rotatably support each guide roller  26   a  and  26   b.    
     The first guide rollers  26   a  and the second guide rollers  26   b  are disposed in grooves  21   a  and  21   b  on either end of the centrifugal element  21 . The guide rollers  26   a  and  26   b  each include an outer peripheral roller and an inner peripheral roller disposed on an inner circumference side of the outer peripheral roller. 
     The first guide roller  26   a  is configured to roll by abutting against the first side wall  122   a  ( 123   a  or  124   a ) of the recess  122 . The second guide roller  26   b  is configured to roll by abutting against the second side wall  122   b  ( 123   b  or  124   b ) on the opposite side of the recess  122 . 
     In this way, the first side wall  122   a  ( 123   a  or  124   a  ) and the second side wall  122   b  ( 123   b  or  124   b ) of the recess  122  function as support portions  23  which moveably support the centrifugal element  21  in the direction DS 1  or DS 2  (see  FIGS. 6A and 6B ) different from the direction in which the centrifugal force CF 0  acts. In other words, it can be interpreted that each support portion  23  includes the first side wall  122   a  ( 123   a  or  124   a ) and the second side wall  122   b  ( 123   b  or  124   b ). 
     The pins  27  penetrate the groove  21   a  or  21   b  in the centrifugal element  21  in the axial direction. Both ends of each pin  27  are fixed to the centrifugal element  21 . 
     As illustrated in  FIG. 2 , the centrifugal element  21  includes two first centrifugal elements  211  and two second centrifugal elements  212 . In the following description, the four centrifugal elements  211  and  212  are sometimes simply referred to as “centrifugal element  21 ”. 
     The two first centrifugal elements  211  are disposed at positions opposing each other in the radial direction, that is, disposed at an 180° interval in the circumferential direction. Similarly, the two second centrifugal elements  212  are disposed at an 180° interval in the circumferential direction. The first centrifugal elements  211  and the second centrifugal elements  212  are disposed at a 90° interval in the circumferential direction. 
     For example, as illustrated in  FIG. 6A , the first centrifugal elements  211  are disposed in the first recess  123  of the hub flange  12 . The centrifugal force CF 0  generated by rotation of the hub flange  12  causes the first centrifugal element  211  to be guided by the first and second side walls  123   a  and  123   b  in the direction DS 1  different from the direction in which the centrifugal force CF 0  acts on the centrifugal element  21 . 
     As illustrated in  FIGS. 3 and 5 , an outer peripheral surface  21   c  of the first centrifugal element  211  has an arc shape recessed toward the inner peripheral side and functions as a cam  31  (described later). As illustrated in  FIG. 4 , the first centrifugal element  211  is formed extending in the circumferential direction and includes the grooves  21   a  and  21   b  at either end in the circumferential direction. The grooves  21   a  and  21   b  each have a width (interval in axial direction) larger than the thickness of the hub flange  12 . The hub flanges  12  are inserted into the grooves  21   a  and  21   b.    
     As illustrated in  FIG. 6B , the second centrifugal element  212  is disposed in the second recess  124  of the hub flange  12 . The centrifugal force CF 0  generated by rotation of the hub flange  12  causes the second centrifugal element  212  to be guided by the first and second side walls  124   a  and  124   b  to the direction DS 2  different from the direction in which the centrifugal force CF 0  acts on the centrifugal element  21 . 
     The configuration of the second centrifugal element  212  is substantially the same as the configuration of the first centrifugal element  211 . Therefore, the configuration of the second centrifugal element  212  is described with reference to  FIGS. 3 to 5  used to describe the configuration of the first centrifugal element  211 . Here, components of the second centrifugal element  212  are denoted by the same reference symbols as those of the first centrifugal element  211 . 
     The outer peripheral surface  21   c  of the second centrifugal element  212  has an arc shape recessed toward the inner peripheral side and functions as the cam  31  (described later). The second centrifugal element  212  is formed so as to extend in the circumferential direction and includes the grooves  21   a  and  21   b  at either end in the circumferential direction. The grooves  21   a  and  21   b  each have a width (interval in the axial direction) larger than the thickness of the hub flange  12 . The hub flanges  12  are inserted into the groove  21   a  and  21   b.    
     As illustrated in  FIGS. 6A and 6B , the center of gravity G 1  and G 2  of the first centrifugal element  211  and the second centrifugal element  212  is disposed on the straight line L which connects the center of gravity G 1  or G 2  to the center C of the cam mechanisms  22  in the circumferential direction. Component force CF 1   b  and CF 2   b  in the centrifugal direction as component force of the centrifugal force CF 0  acts on the cams  31  of each of the first centrifugal element  211  and the second centrifugal element  212  while the first centrifugal element  211  and the second centrifugal element  212  abut against a cam follower  30  (described later). 
     As illustrated in  FIG. 6A , in the first centrifugal element  211 , the centrifugal force CF 0  is formed of radial direction component force CF 1   a  and circumferential direction component force CF 1   b . As illustrated in  FIG. 6B , in the second centrifugal element  212 , the centrifugal force CF 0  is formed of radial direction component force CF 2   a  and circumferential direction component force CF 2   b . The direction of the circumferential direction component force CF 1   b  acting on the first centrifugal element  211  is opposite to the direction of the circumferential direction component force CF 2   b  acting on the second centrifugal element  212 . 
     Here, more specifically, the straight line L is a straight line which connects the center of rotation O and a point of contact C (point of contact when the centrifugal element  21  is subject to the centrifugal force CF 0  and the hub flange  12  and the inertia ring  20  are not rotating relative to each other) between the cam  31  and the cam follower  30 . The point of contact C between the cam  31  and the cam follower  30  corresponds to the above-mentioned center C of the cam mechanism  22  in the circumferential direction. 
     As illustrated in  FIG. 6A , when the above-described component forces CF 1   a  and CF 1   b  act on the first centrifugal element  211 , anticlockwise turning moment CR 1  acts on the first centrifugal element  211  about an axis (axis parallel to the rotational axis of the hub flange  12 ) including the point of contact C between the cam  31  and the cam follower  30 . As a result, the first centrifugal element  211  rotates about the center C of the cam mechanism  22  in the circumferential direction (point of contact C between the cam  31  and the cam follower  30 ) within the range of the gap between the first centrifugal element  211  and the first and second side walls  123   a  and  123   b.    
     As illustrated in  FIG. 6B , when the above-described component forces CF 2   a  and CF 2   b  act on the second centrifugal element  212 , clockwise turning moment CR 2  acts on the second centrifugal element  212  about the axis (axis parallel to the rotational axis of the hub flange  12 ) including the point of contact C between the cam  31  and the cam follower  30 . As a result, the second centrifugal element  212  rotates about the center C of the cam mechanism  22  in the circumferential direction (point of contact C between the cam  31  and the cam follower  30 ) within the range of the gap between the second centrifugal element  212  and the first and second side walls  124   a  and  124   b . The rotational direction of the second centrifugal element  212  is opposite to the rotational direction of the first centrifugal element  211 . 
     In this way, through the first and second centrifugal elements  211  and  212  turning, the first and second centrifugal elements  211  and  212  separately make contact with the first and second side walls  123   a ,  123   b ,  124   a  and  124   b  of the first and second recesses  123  and  124 . In this state, the first and second centrifugal elements  211  and  212  move along the first and second side walls  123   a ,  123   b ,  124   a  and  124   b  of the first and second recesses  123  and  124 . 
     [Cam Mechanism] 
     As illustrated in  FIG. 3 , the cam mechanism  22  is formed of the cylindrical roller  30  serving as a cam follower and the outer peripheral surface  21   c  of the centrifugal element  21  (first centrifugal element  211  and second centrifugal element  212 ) serving as a cam. The roller  30  is fitted into the outer periphery of a body portion of the rivet  203 . In other words, the roller  30  is supported by the rivet  203 . 
     Note that while the roller  30  is preferably rotatably mounted to the rivet  203 , the roller  30  may be unable to rotate. The cam  31  is an arc-shaped surface which the roller  30  abuts against. When the hub flange  12  and the first and second inertia rings  201  and  202  relatively rotate within a predetermined angle range, the roller  30  moves along the cam  31 . 
     Here, the cams  31  (outer peripheral surfaces  21   c ) formed in the first centrifugal element  211  and the second centrifugal element  212  have the same shape. However, as described above, the directions DS 1  and DS 2  in which the first centrifugal element  211  and the second centrifugal element  212  are guided by the first and second recesses  123  and  124  (first and second side walls  123   a ,  123   b ,  124   a  and  124   b ) are different from each other (see  FIGS. 6A and 6B ). 
     Therefore, the cam mechanism  22  including the cam  31  formed in the first centrifugal element  211  and the cam mechanism  22  including the cam  31  formed in the second centrifugal element  212  have different torsional characteristics. When these cam mechanisms  22  need to be distinguished herein, the former is referred to as “first cam mechanism  221 ” and the latter is referred to as “second cam mechanism  222 ”. 
     When contact between the roller  30  and the cam  31  generates a rotational phase difference between the hub flange  12  and the first and second inertia rings  201  and  202 , the centrifugal force CF 0  generated in the centrifugal element  21  (first centrifugal element  211  or second centrifugal element  212 ) is converted to force in a circumferential direction which decreases the rotational phase difference. Details of this are described later. 
     [Operation of Cam Mechanism] 
     Operation of the cam mechanism  22  (inhibition of torque fluctuation) is described with reference to  FIGS. 3 and 7 . Note that, in the following description, the first and second inertia rings  201  and  202  are also simply referred to as “inertia ring  20 ”. 
     When lock-up is on, the torque transmitted to the front cover  2  is transmitted to the hub flange  12  via the input-side rotational body  11  and the damper  13 . 
     If there is no torque fluctuation when torque is transmitted, the hub flange  12  and the inertia ring  20  rotate as illustrated in  FIG. 3 . In this state, the roller  30  of the cam mechanism  22  abuts against a position on the innermost circumference side of the cam  31  (central position in the circumferential direction) and the rotational phase difference between the hub flange  12  and the inertia ring  20  is “0”. 
     As described above, the amount of phase displacement in the rotational direction between the hub flange  12  and the inertia ring  20  is referred to as “rotational phase difference”, but in  FIGS. 3 and 6 , the amount of phase displacement is represented as deviation between center positions in the circumferential direction of the centrifugal  21  (first centrifugal element  211 ) and the cam  31  and the center position of the roller  30 . 
     Here, if there is torque fluctuation when torque is transmitted, as illustrated in  FIG. 7 , a rotational phase difference θ occurs between the hub flange  12  and the inertia ring  20 .  FIG. 7  illustrates a case in which there is a rotational phase difference of +θ1 (for example,) 5° on a +R side. 
     As illustrated in  FIG. 7 , when a rotational phase difference of +θ1 has occurred between the hub flange  12  and the inertia ring  20 , the roller  30  of the cam mechanism  22  relatively moves to the left in  FIG. 7  along the cam  31 . At this time, because the centrifugal force CF 0  acts on the centrifugal element  21 , the reaction force applied from the roller  30  to the cam  31  formed in the centrifugal element  21  has the direction and magnitude of P 0  in  FIG. 7 . This reaction force P 0  generates first component force P 1  in the circumferential direction and second component force P 2  in the direction in which the centrifugal element  21  is moved along an inner peripheral side. 
     Then, the first component force P 1  becomes force which moves the hub flange  12  toward the left in  FIG. 7  via the cam mechanism  22  and the centrifugal element  21 . In other words, force in the direction in which the rotational phase difference between the hub flange  12  and the inertia ring  20  reduces acts on the hub flange  12 . Further, the second component force P 2  causes the centrifugal element  21  to move toward the inner periphery against the centrifugal force CF 0 . 
     Note that, when a rotational phase difference occurs in the opposite direction, the roller  30  relatively moves to the right in  FIG. 7  along the cam  31 . The operation principle in both these cases is the same. Further,  FIG. 7  illustrates a case in which the first centrifugal element  211  is used, but the operation principle is the same for the second centrifugal element  212  even though the directions of the component forces P 1  and P 2  are opposite directions. 
     As described above, when a rotational phase difference occurs between the hub flange  12  and the inertia ring  20  due to torque fluctuation, the hub flange  12  is subject to force (first component force P 1 ) in the direction in which the rotational phase difference between these components reduces due to the centrifugal force CF 0  acting on the centrifugal element  21  (first centrifugal element  211  and second centrifugal element  212 ) and the operation of the cam mechanism  22 . This force inhibits torque fluctuation. 
     The force which inhibits torque fluctuation varies depending on the centrifugal force CF 0 , that is, the rotational speed of the hub flange  12 , and also varies depending on the rotational phase difference and the shape of the cam  31 . Therefore, the characteristics of the torque fluctuation inhibiting device  14  can be set to optimal characteristics according to engine specifications and the like by appropriately setting the shape of the cam  31 . 
     For example, the shape of the cam  31  can be set to a shape with which the first component force P 1  changes to a linear shape according to the rotational phase difference under a state where the same centrifugal force CF 0  acts. In addition, the shape of the cam  31  can be set to a shape with which the first component force P 1  changes to a nonlinear shape according to the rotational phase difference. 
     Here, a small gap for allowing the centrifugal element  21  to move smoothly is secured between the centrifugal element  21  (first centrifugal element  211  and second centrifugal element  212 ) and the first and second side wall  122   a  ( 123   a  and  124   a ) and  122   b  ( 123   b  and  124   b ) of the recess  122  (first recess  123  and second recess  124 ). 
     In contrast, as illustrated in  FIGS. 6A and 6B , when the centrifugal force CF 0  acts on the centrifugal element  21 , turning moments CR 1  and CR 2  in the opposite direction act on the first centrifugal element  211  and the second centrifugal element  212 , respectively. 
     More specifically, as illustrated in  FIG. 6A , because the direction of the centrifugal force CF 0  acting on the first centrifugal element  211  is different from the direction DS 1  in which the first centrifugal element  211  moves, in the first centrifugal element  211 , the above-mentioned component forces CF 1   a  and CF 1   b  are generated in both the direction DS 1  in which the first centrifugal element  211  moves and a direction orthogonal to the direction DS 1 . 
     Then, the anticlockwise turning moment CR 1  acts on the first centrifugal element  211  about the axis (axis parallel to the rotational axis of the hub flange) including the point of contact C between the cam  31  and the cam follower  30 . As a result, the orientation of the first centrifugal element  211  changes, the outer peripheral roller of the first guide roller  26   a  abuts against the first side wall  122   a  of the recess  122  and the inner peripheral roller of the second guide roller  26   b  abuts against the second side wall  122   b  of the recess  122 . 
     As described above, through the turning moment CR 1  acting on the first centrifugal element  211 , the orientation of the first centrifugal element  211  stabilizes relative to the first and second side walls  122   a  ( 123   a ) and  122   b  ( 123   b ) of the recess  122  (first recess  123 ). 
     As illustrated in  FIG. 6B , when the centrifugal force CF 0  acts on the second centrifugal element  212 , turning moment CR 2  in the direction opposite to the first centrifugal element  211  acts on the second centrifugal element  212 . Then, similar to the first centrifugal element  211 , the orientation of the second centrifugal element  212  changes and the first guide roller  26   a  and the second guide roller  26   b  separately abut against the first side wall  122   a  and the second side wall  122   b  of the recess  122 , respectively. As a result, the orientation of the second centrifugal element  212  stabilizes relative to the first and second side walls  122   a  ( 124   a ) and  122   b  ( 124   b ) of the recess  122  (second recess  124 ). 
     [Torsional Characteristics of Torque Fluctuation Inhibiting Device] 
     The torque fluctuation inhibiting device  14  with the above-described configuration has the torsional characteristics illustrated in  FIGS. 8 and 9 . In  FIG. 8 , the characteristic A is a torsional characteristic resulting from the first cam mechanism  221  and the characteristic B is a torsional characteristic resulting from the second cam mechanism  222 . 
     In  FIGS. 8 and 9 , the horizontal axis represents the rotational phase difference between the hub flange  12  and the inertia ring  20  (torsional angle θ of both components). The vertical axis represents a torque T (corresponding to the circumferential direction component force P 1  in  FIG. 7 ) for inhibiting torque fluctuation with the first and second cam mechanisms  221  and  222 . 
     As described above, there is a gap between the first and second centrifugal element  211  or  212  and the recess  122  and the first and second centrifugal element  211  or  212  moves in the direction DS 1  or DS 2  different from the direction in which the centrifugal force CF 0  acts. 
     Because of this, even if there is no rotational phase difference between the hub flange  12  and the inertia ring  20 , the turning moments CR 1  and CR 2  act on the first and second centrifugal elements  211  and  212  and the orientations of the first and second centrifugal elements  211  and  212  incline when the centrifugal force CF 0  acts on the first and second centrifugal elements  211  and  212 . Here, the turning moment CR 1  that acts on the first centrifugal element  211  is generated by the component forces CF 1   a  and CF 1   b  of the centrifugal force CF 0 . The turning moment CR 2  that acts on the second centrifugal element  212  is generated by the component forces CF 2   a  and CF 2   b  of the centrifugal force CF 0 . 
     In other words, because the shape of the cam  31  formed on the outer peripheral surfaces of the first and second centrifugal elements  211  and  212  inclines, initial torque Ti is generated even if the torsional angle θ is “0”. (see  FIG. 8 ). Because the turning moments CR 1  and CR 2  that act on the first centrifugal element  211  and the second centrifugal element  212 , respectively, are opposite to each other, the initial torque Ti with the torsional characteristics A due to the first cam mechanism  221  and the initial torque −Ti with the torsional characteristics B due to the second cam mechanism  222  have opposite polarities. 
     Here, as illustrated in  FIGS. 6A and 8 , if the torsional angle θ in the first centrifugal element  211  increases in a positive direction (R 1  direction) and, for example, the point of contact C between the cam  31  and the cam follower  30  moves from the straight line L toward the R 1  side, torque T for inhibiting torque fluctuation also increases as a result. 
     On the other hand, if the torsional angle θ increases in a negative direction (R 2  direction) and the point of contact C between the cam  31  and the cam follower  30  moves from the straight line L to the R 2  side, the component force CF 1   b  of the centrifugal force CF 0  gradually reduces. 
     When the component force CF 1   b  of the centrifugal force CF 0  becomes zero and the point of contact C between the cam  31  and the cam follower  30  moves further from the straight line L toward the R 2  side, the first centrifugal element  211  rotates in the opposite direction and the orientation of the first centrifugal element  211  changes. At this time, in a section (section θt in  FIG. 8 ) where a rotational phase difference is present, torque does not substantially change. In addition, after the orientation of the first centrifugal element  211  has changed, the torque T for inhibiting torque fluctuation increases as a result of the torsional angle θ increasing in the negative direction. 
     As illustrated in  FIGS. 6B and 8 , the second centrifugal element  212  also undergoes an orientation change similar to that of the first centrifugal element  211 . The turning moment CR 2  acting on the second centrifugal element  212  is opposite to the turning moment CR 1  acting on the first centrifugal element  211 , and hence the section (section θt in  FIG. 8 ) where a rotational phase difference is present is formed on a side opposite to the first centrifugal element  211  from the vertical axis. 
     In  FIG. 8 , the torsional characteristic A of the first cam mechanism  221  and the torsional characteristic B of the second cam mechanism  222  are shown separately. However, in this embodiment, the same number of first cam mechanisms  221  and second cam mechanisms  222  are provided. In addition, the first cam mechanism  221  and the second cam mechanism  222  are arranged symmetrically with respect to the center of rotation O. Further, the first cam mechanism  221  and the second cam mechanism  222  are alternately arranged in the circumferential direction. 
     Therefore, the torsional characteristics A+B of the entire device are, as illustrated in  FIG. 9 , a combination of the torsional characteristic A and the torsional characteristic B in  FIG. 8 . In the characteristics in  FIG. 9 , the initial torque of the first centrifugal element  211  and the second centrifugal element  212  cancel each other out and the initial torque becomes “0”. 
     On positive and negative sides of the torsional characteristics A+B, in the above-mentioned section θt, the inclination of the characteristics A+B, for example, the torque T changes for inhibiting torque fluctuation with the first and second cam mechanisms  221  and  222  against the torsional angle θ between the hub flange  12  and the inertia ring  20 . 
     However, in conventional technology, the orientation of the centrifugal element  21  may constantly fluctuate while the torque fluctuation inhibiting device  14  is operating. In contrast, with the structure according to the present advancement, the orientation of the centrifugal element  21  is stable. As a result, hysteresis in the torsional characteristics of the torque fluctuation inhibiting device  14  can be eliminated. Similarly, because the orientation of the centrifugal element  21  is stable during operation, desired characteristics can be obtained. 
     In this way, because the orientation of the centrifugal element  21  is stable while the centrifugal element  21  operates, hysteresis in the torsional characteristics of the torque fluctuation inhibiting device  14  can be eliminated. Similarly, because the orientation of the centrifugal element  21  is stable during operation, desired characteristics can be obtained. 
     [Examples of Features] 
       FIG. 10  is a diagram for showing an example of torque fluctuation inhibition characteristics. In  FIG. 10 , the horizontal axis represents rotational speed and the vertical axis represents torque fluctuation (rotational speed fluctuation). The characteristic Q 1  represents a case where a device for inhibiting torque fluctuation is not provided, the characteristic Q 2  represents a case where a conventional dynamic damper device that does not have a cam mechanism is provided, and the characteristic Q 3  represents a case where the torque fluctuation inhibiting device  14  according to this embodiment is provided. 
     As is evident from  FIG. 10 , with the device provided with the dynamic damper device that does not have a cam mechanism (characteristic Q 2 ), torque fluctuation can only be inhibited within a specific rotational speed range. In contrast, with the present embodiment including the cam mechanism  22  (characteristic Q 3 ), torque fluctuation can be inhibited within all rotational speed ranges. 
     Second Embodiment 
     In the first embodiment, there is described an example where the centers of gravity G 1  and G 2  of the first centrifugal element  211  and the second centrifugal element  212  are arranged on the straight line L connecting the centers of gravity G 1  and G 2  and the center C of the cam mechanisms  22  in the circumferential direction. As illustrated in  FIGS. 11 and 12 , the second embodiment differs from the first embodiment in that the centers of gravity G 1  and G 2  of the first centrifugal element  211  and the second centrifugal element  212  deviate from the straight line L connecting the centers of gravity G 1  and G 2  and the center C of the cam mechanisms  22  in the circumferential direction. 
     Excluding this difference, the configuration of the second embodiment is substantially the same as that of the first embodiment. Therefore, in the second embodiment, configurations different from the first embodiment are described and descriptions of other configurations are omitted. Any omitted descriptions herein are equivalent to the corresponding descriptions of the first embodiment. 
     The center of gravity G 1  of the first centrifugal element  211  deviates from the straight line L. The center of gravity G 1  of the first centrifugal element  211  is a center of gravity on the second rotational direction R 2  side from the straight line L. With this configuration, the orientation of the first centrifugal element  211  inclines due to the turning moment CR 1  which occurs due to deviation of the center of gravity G 1 . 
     Similar to the first embodiment, the turning moment CR 1  acts on the first centrifugal element  211  about the point of contact C between the cam  31  and the cam follower  30  due to the component forces CF 1   a  and CF 1   b  in the centrifugal force CF 0  acting on the center of gravity G 1  of the first centrifugal element  211 . 
     Here, the first centrifugal element  211  is asymmetrically formed with respect to the straight line L. For example, a notch portion  211   a  is formed in the first centrifugal element  211  and the first centrifugal element  211  is asymmetrically formed with respect to the straight line L. 
     The thickness of the first centrifugal element  211  is substantially constant in the radial direction and the circumferential direction. When the torque fluctuation inhibiting device  14  is viewed externally in the axial direction (when the first centrifugal element  211  is viewed externally in the axial direction), the area of a portion of the first centrifugal element  211  on the R 2  side is larger than the area of a portion of the first centrifugal element  211  on the R 1  side. Due to this, the center of gravity G 1  of the first centrifugal element  211  is disposed at a position which deviates from the circumferential direction center C toward the rotational direction R 2  side. 
     The portion of the first centrifugal element  211  on the R 1  side corresponds to a portion of the first centrifugal element  211  disposed between the straight line L and the first side wall  123   a  on the R 1  side of the recess  122 . The portion of the first centrifugal element  211  on the R 2  side corresponds to a portion of the first centrifugal element  211  disposed between the straight line L and the second side wall  123   b  on the R 2  side of the recess  122 . 
     Note that the portion of the first centrifugal element  211  on the R 1  side may be thicker than the portion of the first centrifugal element  211  on the R 2  side. In this case, the area of the portion of the first centrifugal element  211  on the R 1  side may be the same as the area of the portion of the first centrifugal element  211  on the R 2  side. 
     The second centrifugal element  212  has substantially the same configuration as that of the first centrifugal element  211 , and hence only configurations of the second centrifugal element  212  different from the first centrifugal element  211  are described. 
     The center of gravity G 2  of the second centrifugal element  212  deviates from the straight line L. The center of gravity G 2  of the second centrifugal element  212  has a center of gravity on the first rotational direction R 1  side with respect to the straight line L. With this configuration, the orientation of the second centrifugal element  212  inclines due to the component forces CF 2   a  and CF 2   b  of the centrifugal force CF 0  acting on the center of gravity G 2  of the second centrifugal element  212 . 
     Similar to the first embodiment, the turning moment CR 2  acts on the second centrifugal element  212  about the point of contact C between the cam  31  and the cam follower  30  due to the component forces CF 2   a  and CF 2   b  in the centrifugal force CF 0  acting on the center of gravity G 2  of the second centrifugal element  212 . 
     Here, similar to the first centrifugal element  211 , the second centrifugal element  212  is asymmetrically formed with respect to the straight line L. For example, a notch portion  212   a  is formed in the second centrifugal element  212  and the second centrifugal element  212  is asymmetrically formed with respect to the straight line L. 
     The thickness of the second centrifugal element  212  is substantially constant in the radial direction and the circumferential direction. When the torque fluctuation inhibiting device  14  is viewed externally in the axial direction (when the second centrifugal element  212  is viewed externally in the axial direction), the area of a portion of the second centrifugal element  212  on the R 1  side is larger than the area of a portion of the second centrifugal element  212  on the R 2  side. Due to this, the center of gravity G 2  of the second centrifugal element  212  is disposed at a position which deviates from the circumferential direction center C toward the rotational direction R 1  side. 
     When the first centrifugal element  211  and the second centrifugal element  212  are configured as described above, the torsional characteristics of the torque fluctuation inhibiting device  14  correspond to those shown in  FIGS. 13 and 14 . 
     The characteristic C is a torsional characteristic resulting from the first cam mechanism  221  and the characteristic D is a torsional characteristic resulting from the second cam mechanism  222 . 
     In  FIGS. 13 and 14 , the horizontal axis represents a rotational phase difference between the hub flange  12  and the inertia ring  20  (the torsional angle θ of both components) and the vertical axis represents the torque T for inhibiting torque fluctuation using the first and second cam mechanisms  221  and  222  (corresponding to circumferential direction component force P 1  in  FIG. 7 ). 
     As described above, there is a gap between the first and second centrifugal element  211  or  212  and the recess  122 . In addition, the first and second centrifugal element  211  or  222  moves in the direction DS 1  or DS 2  (see  FIGS. 6A and 6B ) different from the direction in which the centrifugal force CF 0  acts. In addition, the first and second centrifugal element  211  or  222  has a deviated center of gravity G 1  or G 2 . 
     Because of this, if there is no rotational phase difference between the hub flange  12  and the inertia ring  20  when the centrifugal force CF 0  acts on the first and second centrifugal elements  211  and  212 , the orientation of the first centrifugal element  211  and the orientation of the second centrifugal element  212  incline as described above. 
     In this case, because the shape of the cam  31  formed on the outer peripheral surface of the first and second centrifugal elements  211  and  212  inclines, the initial torque Ti is generated even if the torsional angle θ is “0”. 
     Because the turning moments CR 1  and CR 2  that act on the first centrifugal element  211  and the second centrifugal element  212 , respectively, are opposite to each other, the initial torque Ti having the torsional characteristic C resulting from the first cam mechanism  221  and the initial torque −Ti having the torsional characteristic D resulting from the second cam mechanism  222  have opposite directions. 
     Here, for example, if the point of contact C between the cam  31  and the cam follower  30  approaches the center of gravity G 1  of the first centrifugal element  211  toward the R 2  side from the straight line L, the circumferential direction component force which is the component force of the centrifugal force CF 0  gradually reduces if the point of contact C passes over an action line of the centrifugal force CF 0 . Further, if the circumferential direction component force as the component force of the centrifugal force CF 0  becomes zero, the first centrifugal element  211  inclines in the opposite direction. 
     The second centrifugal element  212  also undergoes an orientation change similar to that of the first centrifugal element  211 . The turning moment that acts on the second centrifugal element  212  is opposite to the turning moment that acts on the first centrifugal element  211 , and hence the section (section θt in  FIG. 13 ) where a rotational phase difference is present is formed on a side opposite to the first centrifugal element  211  with respect to the vertical axis. 
     In  FIG. 13 , the torsional characteristic C of the first cam mechanism  221  and the torsional characteristic D of the second cam mechanism  222  are shown separately. However, in this embodiment, the same number of first cam mechanisms  221  and second cam mechanisms  222  are provided. In addition, the first cam mechanism  221  and the second cam mechanism  222  are arranged symmetrically with respect to the center of rotation O. Further, the first cam mechanism  221  and the second cam mechanism  222  are alternately arranged in the circumferential direction. 
     Therefore, as illustrated in  FIG. 14 , the torsional characteristics C+D of the entire device are a combination of the torsional characteristic C and the torsional characteristic D in  FIG. 13 . With the characteristics in  FIG. 14 , the initial torque of the first centrifugal element  211  and the second centrifugal element  212  cancel each other out and the initial torque becomes “0”. 
     Note that, in torsional angle ranges (θe in  FIG. 14 ) on positive and negative sides of the combined torsional characteristics C+D, suitable torsional characteristics can be obtained by operating the first and second cam mechanisms  221  and  222 . 
     In addition, because the first and second centrifugal elements  211  and  212  is moved in the direction DS 1  or DS 2  different from the direction in which the centrifugal force CF 0  acts, the section θt where torque does not fluctuate is not likely to be generated unless the component forces CF 1   b  and CF 2   b  of the centrifugal force CF 0  exist, even if the first and second centrifugal elements  211  and  212  pass through the center of gravity G 1  and G 2  (even if the point of contact C passes over an action line of the centrifugal force CF 0 ). 
     In other words, the section θt is generated after the point of contact C has passed over the action line of the centrifugal force CF 0  and an action line of the component forces CF 1   a  and CF 2   a  of the centrifugal force CF 0 . With this configuration, the suitable torsional angle range θe can be expanded by moving the first and second centrifugal element  211  or  222  in the direction DS 1  or DS 2  different from the direction in which the centrifugal force CF 0  acts. 
     In this way, because the orientation of the centrifugal element  21  is stable while the centrifugal element  21  operates, hysteresis in the torsional characteristics of the torque fluctuation inhibiting device  14  can be eliminated. Similarly, because the orientation of the centrifugal element  21  is stable during operation, desired characteristics can be obtained. 
     Modification Examples 
     Various arrangements can be adopted if applying the above-described torque fluctuation inhibiting device  14  to the torque converter  1  or another power transmission device. Specific examples of applying the torque fluctuation inhibiting device  14  to the torque converter  1  or another power transmission device are described below with reference to schematic diagrams. 
     (A)  FIG. 15  is a diagram for schematically illustrating a torque converter including an input-side rotational body  41 , a hub flange  42  and a damper  43  provided between the two components  41  and  42 . The input-side rotational body  41  includes members such as a front cover, a drive plate and a piston. The hub flange  42  includes a driven plate and a turbine hub. The damper  43  includes a plurality of torsion springs. 
     In the example illustrated in  FIG. 15 , a centrifugal element  48  is provided in any rotating member forming the input-side rotational body  41  and a cam mechanism and support portion  44  which operates using the centrifugal force CF 0  acting on the centrifugal element  48  is provided. The cam mechanism and support portion  44  may have the same configuration as the configuration described in the embodiments above. 
     (B) In the torque converter illustrated in  FIG. 16 , the centrifugal element  48  is provided for any rotating member forming the hub flange  42  and the cam mechanism and support portion  44  which operates using the centrifugal force CF 0  acting on the centrifugal element  48  is provided. The cam mechanism and support portion  44  may have the same configuration as the configuration described in the embodiments above. 
     (C) The torque converter illustrated in  FIG. 17  has the configuration illustrated in  FIGS. 15 and 16 , and also includes a separate damper  45  and an intermediate member  46  provided between the two dampers  43  and  45 . The intermediate member  46  can rotate relative to the input-side rotational body  41  and the hub flange  42  and operates the two dampers  43  and  45  in series. 
     In the example illustrated in  FIG. 17 , the intermediate member  46  is provided with the centrifugal element  48  and the cam mechanism and support portion  44  which operates using the centrifugal force CF 0  acting on the centrifugal element  48  is provided. The cam mechanism and support portion  44  may have the same configuration as the configuration described in the embodiments above. 
     (D) The torque converter illustrated in  FIG. 18  includes a floating member  47 . The floating member  47  is a member used for supporting a torsion spring which forms the damper  43 . The floating member  47  is, for example, formed into an annular shape and is disposed so as to cover the outer periphery and at least one side surface of the torsion spring. 
     The floating member  47  can rotate relative to the input-side rotational body  41  and the hub flange  42  and rotates together with the damper  43  due to friction between the torsion spring in the damper  43 . In other words, the floating member  47  also rotates. 
     In the example illustrated in  FIG. 18 , the floating member  47  is provided with the centrifugal element  48 , and the cam mechanism and support portion  44  which operates using the centrifugal force CF 0  acting on the centrifugal element  48  is provided. The cam mechanism and support portion  44  may have the same configuration as the configuration described in the embodiments above. 
     (E)  FIG. 19  is a schematic diagram for illustrating a power transmission device including a flywheel  50  having two inertial bodies  51  and  52  and a clutch device  54 . In other words, the flywheel  50  is disposed between an engine and the clutch device  54  and includes the first inertial body  51 , the second inertial body  52  disposed so as to rotate relative to the first inertial body  51  and a damper  53  disposed between the two inertial bodies  51  and  52 . Note that the second inertial body  52  includes a clutch cover which forms the clutch device  54 . 
     In the example illustrated in  FIG. 19 , the centrifugal element  48  is provided in any rotating member which forms the second inertial body  52  and the cam mechanism and support portion  44  which operates using the centrifugal force CF 0  acting on the centrifugal element  48  is provided. The cam mechanism and support portion  44  may have the same configuration as the configuration described in the embodiments above. 
     (6)  FIG. 20  shows an example in which, in a power transmission device similar to that in  FIG. 19 , the first inertial body  51  is provided with the centrifugal element  48 . The cam mechanism and support portion  44  which operates using the centrifugal force CF 0  acting on the centrifugal element  48  is also provided. The cam mechanism and support portion  44  may have the same configuration as the configuration described in the embodiments above. 
     (7) The power transmission device illustrated in  FIG. 21  has the configuration illustrated in  FIGS. 19 and 20 , and also includes a separate damper  56  and the intermediate member  57  provided between the two dampers  53  and  56 . The intermediate member  57  can rotate relative to the first inertial body  51  and the second inertial body  52 . 
     In the example illustrated in  FIG. 21 , the intermediate member  57  is provided with the centrifugal element  48 , and the cam mechanism and support portion  44  which operates using the centrifugal force CF 0  acting on the centrifugal element  48  is provided. The cam mechanism and support portion  44  may have the same configuration as the configuration described in the embodiments above. 
     (8)  FIG. 22  is a schematic diagram for illustrating a power transmission device in which one flywheel is provided with a clutch device. The first inertial body  61  in  FIG. 22  includes one flywheel and a clutch cover for the clutch device  62 . In this example, the centrifugal element  48  is provided in any rotating member forming the first inertial body  61  and the cam mechanism and support portion  44  which operates using the centrifugal force CF 0  acting on the centrifugal element  48  is provided. The cam mechanism and support portion  44  may have the same configuration as the configuration described in the embodiments above. 
     (9)  FIG. 23  illustrates an example in which, in the same power transmission device as that in  FIG. 22 , the centrifugal element  48  is disposed on an output side of the clutch device  62 . In addition, the cam mechanism and support portion  44  which operates using the centrifugal force CF 0  acting on the centrifugal element  48  is provided. The cam mechanism and support portion  44  may have the same configuration as the configuration described in the embodiments above. 
     Other Embodiments 
     The present disclosure is not limited to the above-described embodiments and may be altered or improved in various ways without departing from the scope of the present advancement. 
     (a) In the first and second embodiments, there is described an example in which the torque fluctuation inhibiting device  14  is mounted to a lock-up device in a torque converter, but the torque fluctuation inhibiting device  14  may be disposed in any rotating member forming a transmission, or may be disposed in a shaft (propeller shaft or drive shaft) on an output side of a transmission. 
     (b) In the first and second embodiments, there is described an example in which the torque fluctuation inhibiting device  14  is mounted to a lock-up device in a torque converter, but the torque fluctuation inhibiting device  14  may be applied to a conventional power transmission device provided with a known dynamic damper device or a pendulum damper device. 
     (c) In the first and second embodiments, there is described an example in which the centrifugal element  21  is provided in the hub flange  12 , but the centrifugal element  21  may be provided in the inertia ring  20 . 
     (d) In the first and second embodiments, there is described an example in which the first and second guide rollers  26   a  and  26   b  include an outer peripheral roller and an inner peripheral roller, but the guide rollers may be configured of only one roller. Alternatively, one roller may be provided on each side of the centrifugal element  21  in the circumferential direction, one roller may be provided between the inner peripheral surface of the centrifugal element  21  and the bottom surface of the recess, or three rollers may be used to form the guide rollers. 
     (e) In the first and second embodiments, there is described an example in which the first and second guide rollers  26   a  and  26   b  are used. However, for example, roller bearings may be used as the guide rollers. In this case, friction between the centrifugal element or the recess of the hub flange and the outer periphery of the roller bearing can be further reduced. 
     (f) In the first and second embodiments, there is described an example in which each support portion  23  includes the first and second side walls  122   a  and  122   b  and the centrifugal element  21  includes the first and second guide rollers  26   a  and  26   b . Alternatively, the centrifugal element  21  may be formed of a body portion in which each support portion  23  includes the first and second side walls  122   a  and  122   b  and the first and second guide rollers  26   a  and  26   b  and the centrifugal element  21  does not include the first and second guide rollers  26   a  and  26   b . In this case, the body portion of the centrifugal element  21  is guided by making contact with the first and second guide rollers  26   a  and  26   b  provided on the first and second side walls  122   a  and  122   b.    
     (g) In the first and second embodiments, the first and second guide rollers  26   a  and  26   b  are disposed in the support portion  23 , but another member configured to reduce friction, such as resin lace or a resin sheet, may be provided in place of the first and second guide rollers  26   a  and  26   b . In this case, the member configured to reduce friction is pushed against the centrifugal element  21  or the recess  122  of the hub flange  12  by a biasing member. 
     (h) In the first and second embodiments, there is described an example in which the first centrifugal element  211  and the second centrifugal element  212  are used as centrifugal elements  21 , but either a plurality of first centrifugal elements  211  or a plurality of second centrifugal elements  212  may be used. In this case, although initial torque cannot be made “0”, the orientation of the centrifugal element  21  can be stably held and hysteresis in the torsional characteristics of the torque fluctuation inhibiting device  14  can be eliminated. 
     (i) In the second embodiment, there is described an example in which the centrifugal element  21  is asymmetrically formed, but the centrifugal element  21  may have a symmetrical shape provided that the centrifugal element  21  is movable in the direction DS 1  or DS 2  different from the direction in which the centrifugal force CF 0  acts. 
     In this case, for example, the center of gravity G 1  or G 2  of the centrifugal element  21  can be biased by providing the centrifugal element  21  with a weighted portion (not shown) based on the straight line L. In addition, one side of the centrifugal element  21  may be provided with a thick portion that is thicker than other portions and that portion may be the weighted portion. Further, a member (weighted member) made of a material having a larger specific gravity than other portions may be embedded and fixed on one side of the centrifugal element. 
     REFERENCE SYMBOLS LIST 
     
         
           1  Torque converter 
           11  Input-side rotational body 
           12 ,  42  Hub flange (rotating body) 
           122  Recess 
           122   a  First side wall (support portion) 
           122   b  Second side wall (support portion) 
           14  Torque fluctuation inhibiting device 
           20 ,  201 ,  202  Inertia ring (mass body) 
           21 ,  58 ,  65  Centrifugal element 
           211  First centrifugal element 
           212  Second centrifugal element 
           22  Cam mechanism 
           23  Support portion 
           26   a ,  26   b  Guide roller 
           30  Roller (cam follower) 
           31  Cam 
           41  Input-side rotational body 
           43  Damper 
           50  Flywheel 
           51 ,  61  First inertial body 
           52  Second inertial body 
           54 ,  62  Clutch device