Patent Publication Number: US-2020292008-A1

Title: Torque limiter device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to Japanese Patent Application No. 2019-049048, filed Mar. 15, 2019. The contents of that application are incorporated by reference herein in their entirety. 
     TECHNICAL FIELD 
     The present invention relates to a torque limiter. 
     BACKGROUND ART 
     A hybrid vehicle, in which an engine and an electric motor are used in combination, is provided with a damper device between the engine and a drive unit disposed on an output side in order to inhibit fluctuations in rotation of the engine. Incidentally, this type of vehicle has a large inertia amount on the output side. Because of this, chances are that in engine starting and so forth, a torque fluctuates with a large amplitude and an excessive torque is transmitted to the engine side. 
     In view of this, there has been proposed a damper device including a torque limiter as described in Japan Laid-open Patent Application Publication No. 2012-210937. The torque limiter described in Japan Laid-open Patent Application Publication No. 2012-210937 includes a friction disc, a pressure plate and a cone spring. Moreover, the friction disc is pressed onto a flywheel by the cone spring through the pressure plate interposed between the friction disc and the cone spring. 
     In the torque limiter described in Japan Laid-open Patent Application Publication No. 2012-210937, the friction disc, the pressure plate and the cone spring are disposed in a recessed portion provided in the flywheel. Besides, the cone spring is attached between the pressure plate and another plate fixed to the flywheel, while being compressed therebetween. 
     In order to avoid using the flywheel as a dedicated component in the torque limiter described above, it can be assumed to provide the torque limiter with a cover to be fixed to the flywheel and accommodate components of the torque limiter in the interior of the cover. 
     However, the cover is normally processed as an integral member by stamping. Hence, a part of the cover, processed by drawing to form a tubular portion, is drafted (tapered). Besides, another part of the cover, processed by bending, is inevitably provided with a curved surface portion. The draft and the curved surface portion herein described hinders increase in diameter of the friction disc. Conversely speaking, in attempt to obtain a desired torque capacity, the torque limiter cannot be made compact in size. 
     BRIEF SUMMARY 
     It is an object of the present invention to realize compactness in radial and axial sizes of a torque limiter in which the components thereof are accommodated in the interior of a cover. 
     (1) A torque limiter device according to the present invention is a device for limiting a torque transmitted between a power source-side member and an output-side member. The torque limiter device includes a cover, a friction disc and an urging member. The cover includes a coupling portion, a tubular portion and a support portion. The coupling portion is coupled to the power source-side member. The tubular portion axially extends from the coupling portion. The support portion extends from the tubular portion to an inner peripheral side. The friction disc is accommodated in an inner peripheral space of the tubular portion of the cover, and is pressed toward the power source-side member. The urging member is supported by the support portion of the cover, and urges the friction disc toward the power source-side member. 
     In the torque limiter device, when an excessive torque is inputted from the output-side member, for instance, slippage is caused by a friction disc-related part whereby the excessive torque is prevented from being transmitted to the power source-side member. 
     Here, the friction disc is disposed on the power source side in the interior of the cover, and is pressed onto the power source-side member by the urging member supported by the support portion of the cover. Therefore, the friction disc is accommodated in a relatively large diameter part of the tubular portion of the cover. Moreover, any curved surface portion does not exist in an outer peripheral part of the friction disc. Therefore, increase in outer diameter of the friction disc is enabled. Conversely speaking, when the friction disc is reduced in diameter by that much, a required torque capacity can be obtained. Hence, the torque limiter device can be made compact in radial dimension. 
     Moreover, the urging member is supported by the support portion of the cover, whereby the support portion elastically deforms. However, a resilient force of the support portion against elastic deformation (an elastic force of the support portion) functions as a pressing force for pressing, together with the urging member, the friction disc toward the power source. Therefore, the support portion of the friction disc is enabled to have a relatively small thickness, whereby the torque limiter device can be made compact in axial dimension. 
     Furthermore, the torque limiter device can be easily attached even to a versatile flywheel, i.e., a flywheel without a special shape for attaching a torque limiter thereto. 
     (2) Preferably, the coupling portion, the tubular portion and the support portion of the cover are integrally processed by stamping. 
     (3) Preferably, the torque limiter device further includes a pressure plate that has an annular shape and is disposed axially between the friction disc and the urging member. 
     (4) Preferably, the urging member is a cone spring that is disposed between the pressure plate and the support portion of the cover while being compressed therebetween. 
     (5) Preferably, the support portion includes a protruding portion that has an annular shape and protrudes toward the pressure plate. The cone spring is supported at an outer peripheral end thereof by the protruding portion. 
     (6) Preferably, the torque limiter device further includes a damper plate that has an annular shape and is disposed between the friction disc and the power source-side member. 
     Overall, according to the present invention described above, it is possible to achieve compactness in radial and axial sizes of the torque limiter in which the components thereof are accommodated in the interior of the cover. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a power transmission device including a torque limiter device according to a preferred embodiment of the present invention. 
         FIG. 2  is a view of the torque limiter device extracted from  FIG. 1 . 
         FIG. 3  is a view of a damper device extracted from  FIG. 1 . 
         FIG. 4  is a view of a hysteresis generating mechanism shown in  FIG. 1 . 
         FIG. 5  is a front view of the damper device shown in  FIG. 1 , from which part of members is detached. 
         FIG. 6  is an external view of the hysteresis generating mechanism. 
         FIG. 7  is a chart showing magnitude of vibration attributed to resonance of an intermediate rotor and magnitude of vibration in the present preferred embodiment. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a cross-sectional view of a power transmission device  1  including a damper device according to a preferred embodiment of the present invention.  FIG. 2  is a front view of the power transmission device  1  that part of members is detached therefrom. The power transmission device  1  is installed in, for instance, a hybrid vehicle. The power transmission device  1  includes a torque limiter device  2  and a damper device  3  that power generated in an engine is inputted thereto through the torque limiter device  2 . The engine is disposed on the right side in  FIG. 1 , whereas an electric motor, a transmission and so forth are disposed on the left side in  FIG. 1 . In  FIG. 1 , line O-O indicates a rotational axis. 
     [Torque Limiter Device  2 ] 
     The torque limiter device  2  is coupled to a flywheel  4  to which the power generated in the engine is inputted. Additionally, when an excessive torque is inputted from an output side, for instance, the torque limiter device  2  limits the magnitude of the excessive torque to a predetermined value or less so as not to transmit the excessive torque therethrough to the engine. The torque limiter device  2  includes a cover  10 , a damper plate  11 , a friction disc  12 , a pressure plate  13  and a cone spring  14 . The friction disc  12 , the pressure plate  13  and the cone spring  14  are accommodated in the interior of the cover  10 . 
       FIG. 2  shows an enlarged view of the torque limiter device  2 . The cover  10  includes a coupling portion  10   a , a tubular portion  10   b  and a support portion  10   c . The coupling portion  10   a , the tubular portion  10   b  and the support portion  10   c  are integrally processed by stamping. Therefore, the tubular portion  10   b  is drafted (tapered) by drawing, and thereby slants to the inner peripheral side with separation from the flywheel  4 . Additionally, a curved surface portion  10   d  is provided between the tubular portion  10   b  and the support portion  10   c.    
     The coupling portion  10   a  has an annular shape and is coupled to the flywheel  4  by a plurality of bolts  15 , while the damper plate  11  is interposed therebetween. The tubular portion  10   b  extends from the inner peripheral end of the coupling portion  10   a  to an output side (a side separating from the flywheel  4 ). The support portion  10   c  has an annular shape and extends from the distal end of the tubular portion  10   b  to the inner peripheral side at a predetermined width. The support portion  10   c  is provided with a support protrusion  10   e  in a radially intermediate part thereof. The support protrusion  10   e  has an annular shape and protrudes toward the flywheel  4 . 
     The damper plate  11  has an annular shape and is provided with a plurality of holes  11   a  in the outer peripheral part thereof. The damper plate  11  is fixed together with the cover  10  to a lateral surface of the flywheel  4  by the bolts  15  that penetrate the holes  11   a , respectively. The outer diameter of the damper plate  11  is equal to that of the flywheel  4 , and the inner diameter thereof is less than that of each friction material (to be described) of the friction disc  12 . 
     The friction disc  12  includes a core plate  17  and a pair of friction materials  18 . The core plate  17  has an annular shape and is provided with a plurality of fixation portions  17   a  extending from the inner peripheral end thereof further radially inward. The core plate  17  is coupled to the damper device  3  through the fixation portions  17   a . The pair of friction materials  18 , each having an annular shape, is fixed to the both lateral surfaces of the core plate  17 . 
     The pressure plate  13  has an annular shape, and is disposed in opposition to the damper plate  11  through the friction disc  12 . In other words, the friction disc  12  is interposed and held between the damper plate  11  and the pressure plate  13 . The inner diameter of the pressure plate  13  is less than that of each friction material  18  of the friction disc  12 . 
     The cone spring  14  is disposed between the pressure plate  13  and the support portion  10   c  of the cover  10 , while being compressed therebetween. The cone spring  14  is supported at the outer peripheral part thereof by the support protrusion  10   e  of the support portion  10   c , and makes contact at the inner peripheral end thereof with the pressure plate  13 , whereby the pressure plate  13  is pressed toward the flywheel  4 . 
     When a torque, transmitted between the engine side and the damper device  3  through the torque limiter device  2  configured as described above, exceeds a torque transmission capacity that is set by the torque limiter device  2 , slippage occurs in a friction disc  12 -related part and the torque to be transmitted through the torque limiter device  2  is limited in magnitude. 
     In this torque limiter device  2 , the tubular portion  10   b  of the cover  10  is drafted (tapered) to the inner peripheral side with separation from the flywheel  4 . Therefore, the output-side end of the tubular portion  10   b  has a smaller inner peripheral surface diameter than the flywheel  4 -side end thereof. Additionally, the tubular portion  10   b  is provided with the curved surface portion  10   d  on the output-side end thereof. Because of this, when it is assumed to dispose the friction disc  12  on the support portion  10   c  side, the friction disc  12  cannot be reliably designed to have a large diameter. 
     However, in the present preferred embodiment, the friction disc  12  is disposed on the flywheel  4  side in the interior of the cover  10 . Hence, the friction disc  12  can be designed to have as large a diameter as possible without being affected by the draft of the tubular portion  10   b . Contrarily speaking, the torque limiter device  2  can be made compact in diameter without changing the torque transmission capacity thereof. 
     Additionally, in the present preferred embodiment, the friction disc  12  is disposed to press the flywheel  4  through the damper plate  11 . Now it is assumed, contrarily to the present preferred embodiment, that the friction disc  12  is disposed on the cover  10  side (the support portion  10   c  side) whereas the cone spring  14  is disposed on the flywheel  4  side. In this assumption, elastic deformation occurs in the support portion  10   c  of the cover  10  such that an inner peripheral part thereof is opened outward. As a result, chances are that relevant one of the friction materials  18  of the friction disc  12  does not uniformly make contact with the support portion  10   c , whereby a desired torque capacity cannot be obtained or abnormal abrasion occurs in the relevant friction material  18 . To avoid such troubles, it is required to increase the thickness of a plate member of which the cover  10  is made. 
     However, in the present preferred embodiment, the friction disc  12  is disposed on the flywheel  4  side, whereas the cone spring  14  is disposed on the cover  10  side (the support portion  10   c  side). Hence, deformation is unlikely to occur in a surface with which the friction disc  12  makes contact (i.e., a lateral surface of the damper plate  11 ). Therefore, the entirely of relevant one of the friction materials  18  of the friction disc  12  uniformly makes contact with the damper plate  11 , whereby a stable torque capacity can be obtained. Moreover, abnormal abrasion can be inhibited from occurring in the relevant friction material  18  of the friction disc  12 . 
     Incidentally, likewise in the present preferred embodiment, elastic deformation occurs in the support portion  10   c  of the cover  10 . However, this elastic deformation acts as a force for pressing the friction disc  12  together with an urging force of the cone spring  14 . Because of this, it is possible to reduce the thickness of the plate member of which the cover  10  is made. Consequently, it is possible to realize compactness in axial size of the torque limiter device  2 . 
     Moreover, the torque limiter device  2 , configured as described above, can be easily attached even to a versatile flywheel, i.e., a flywheel without a special shape for attaching a torque limiter. 
     [Damper Device  3 ] 
     The damper device  3  transmits power, inputted thereto from the torque limiter device  2 , to the output side, and attenuates vibration occurring in transmitting the power.  FIG. 3  shows the damper device  3  extracted from  FIG. 1 . The damper device  3  includes an input-side rotor  20 , an output-side rotor  21 , a plurality of torsion springs  22 , an intermediate rotor  23  and a hysteresis generating mechanism  24 . 
     &lt;Input-Side Rotor  20 &gt; 
     The input-side rotor  20  is rotatable about the rotational axis, and includes a first plate  31  and a second plate  32 . 
     The first plate  31  includes a disc portion  31   a , a plurality of first window portions  31   b  for holding the torsion springs  22 , a plurality of bent portions  31   c  and a plurality of fixation portions  31   d  (see  FIG. 4 ). It should be noted that  FIG. 4  shows a cross-section of the damper device  3 , which is taken in a circumferential position different from that in  FIG. 1 . It should be noted that radial positioning of the first plate  31  is made by the inner peripheral surface of the disc portion  31   a  and the outer peripheral surface of a tubular hub (to be described) of the output-side rotor  21 . 
     The first window portions  31   b  are provided in an outer peripheral part of the disc portion  31   a . Each first window portion  31   b  includes a hole and holding portions. The hole is circumferentially elongated and axially penetrates the disc portion  31   a . The holding portions are provided on the inner and outer peripheral edges of the hole so as to hold the torsion spring  22 . The hole is capable of making contact, at the circumferential end surfaces thereof, with the end surfaces of the torsion spring  22 . 
     Each bent portion  31   c , having an L-shaped cross-section, is formed by bending the outer peripheral end of the disc portion  31   a  toward the flywheel  4 . Enhancement in rotational strength of the first plate  31  is realized by bending the outer peripheral end of the disc portion  31   a  in the cross-sectional L shape. 
     As shown in  FIGS. 4 and 5 , each fixation portion  31   d  is formed by bending the distal end of a circumferentially middle part of each bent portion  31   c  further radially inward. It should be noted that  FIG. 5  is a front view of the damper device  3  that part of members is detached therefrom. Additionally, each fixation portion  31   d  is provided with a rivet fixation hole  31   e . It should be noted that a plurality of rivet swaging holes  31   f  are provided in the same positions as the rivet fixation holes  31   e  of the disc portion  31   a.    
     The second plate  32  is disposed in axial opposition to the first plate  31  on the flywheel  4  side of the first plate  31 . The second plate  32 , having a disc shape, includes a plurality of second window portions  32   b . It should be noted that radial positioning of the second plate  32  is made by the inner peripheral surface of the second plate  32  and the outer peripheral surface of the tubular hub (to be described) of the output-side rotor  21 . 
     The second window portions  32   b  are provided in corresponding positions to the first window portions  31   b  of the first plate  31 . Each second window portion  32   b  includes a hole and holding portions. The hole is circumferentially elongated and axially penetrates the second plate  32 . The holding portions are provided on the inner and outer peripheral edges of the hole so as to hold the torsion spring  22 . The hole is capable of making contact, at the circumferential end surfaces thereof, with the end surfaces of the torsion spring  22 . Each second window portion  32   b  holds the torsion spring  22  together with each first window portion  31   b  of the first plate  31 . 
     Additionally, the second plate  32  is provided with a plurality of rivet fixation holes  32   e  in the same positions as the rivet fixation holes  31   e  of the first plate  31 . The first and second plates  31  and  32  are fixed by a plurality of rivets  33 , penetrating the pairs of rivet fixation holes  31   e  and  32   e  of the both plates  31  and  32 , respectively, so as to be immovable in both axial and circumferential directions. It should be noted that the first and second plates  31  and  32  and the friction disc  12  are fixed to each other, while the fixation portions  17   a  of the core plate  17  in the friction disc  12  are inserted in between the fixation portions  31   d  of the first plate  31  and the second plate  32 . 
     &lt;Output-Side Rotor  21 &gt; 
     The output-side rotor  21  is disposed axially between the first plate  31  and the second plate  32 . The output-side rotor  21  is rotatable about the rotational axis, and is rotatable relative to the first and second plates  31  and  32 . The output-side rotor  21  includes a hub  35  and three flanges  36 . 
     The hub  35 , having a tubular shape, is disposed in the center part of the output-side rotor  21 . The hub  35  is provided with a spline hole  35   a  in the inner peripheral part thereof, and the spline hole  35   a  is coupled to a spline provided on an output-side shaft (not shown in the drawings). As described above, the first and second plates  31  and  32  are radially positioned with respect to the hub  35  by the outer peripheral surface of the hub  35  and the inner peripheral surfaces of the first and second plates  31  and  32 . 
     The three flanges  36  are provided to radially extend from the outer peripheral surface of the hub  35  in a radial shape. The three flanges  36  are disposed at equal angular intervals in the circumferential direction. Each flange  36  includes a hysteresis mechanism attaching portion  36   a , a first support portion  36   b  and a second support portion  36   c . The hysteresis mechanism attaching portion  36   a , made in the shape of a flat surface, is provided on the outer peripheral side of the hub  35 . The first support portion  36   b  extends radially outward from the hysteresis mechanism attaching portion  36   a , and has a smaller circumferential width than the hysteresis mechanism attaching portion  36   a . The first support portion  36   b  make contact, at the both circumferential end surfaces thereof, with spring seats  38 . The second support portion  36   c  is formed by circumferentially extending the both ends of the outer peripheral end of the first support portion  36   b . The second support portion  36   c  makes contact, at the inner peripheral surface thereof, with the spring seats  38 . 
     It should be noted that the second support portions  36   c  of the flanges  36  are disposed in the same radial positions as the fixation portions  31   d  of the first plate  31 . Each second support portion  36   c  is provided with a hole  36   d  axially penetrating therethrough. Rivet swaging of the first and second plates  31  and  32  is made through the holes  36   d  and the rivet swaging holes  31   f  of the first plate  31 . 
     &lt;Torsion Springs  22 &gt; 
     The torsion springs  22  are accommodated circumferentially between the plural flanges  36  of the output-side rotor  21  and are held by the first window portions  31   b  of the first plate  31  and the second window portions  32   b  of the second plate  32 . It should be noted that two torsion springs  22  are disposed between adjacent two of the flanges  36 , and the spring seats  38  are disposed on the both end surfaces of each torsion spring  22 . 
     &lt;Intermediate Rotor  23 &gt; 
     The intermediate rotor  23  is rotatable about the rotational axis, and is rotatable relative to the first plate  31 , the second plate  32  and the output-side rotor  21 . The intermediate rotor  23  is a member for causing two torsion springs  22 , disposed between any adjacent two of the flanges  36 , to act in series. The intermediate rotor  23  includes an annular portion  40  and three intermediate flanges  41 . 
     The annular portion  40  is slid and fitted, at the inner peripheral part thereof, onto the outer periphery of the hub  35  of the output-side rotor  21 . In other words, the inner peripheral surface of the annular portion  40  and the outer peripheral surface of the hub  35  make contact with each other, whereby the intermediate rotor  23  is radially positioned with respect to the output-side rotor  21 . The annular portion  40  is disposed in axial alignment with the flanges  36  of the output-side rotor  21  on the flywheel  4  side of the flanges  36 . 
     Each of the three intermediate flanges  41  includes an offset portion  41   a , a friction portion  41   b , a first support portion  41   c , a second support portion  41   d  and a stopper portion  41   e.    
     As shown in  FIGS. 3 and 5 , the offset portion  41   a  is a portion that couples the annular portion  40  and the friction portion  41   b  therethrough. The both lateral surfaces of the friction portion  41   b  are herein disposed in the same axial positions as those of each flange  36  of the output-side rotor  21 . In other words, the flywheel  4 -side lateral surface of the friction portion  41   b  and that of each flange  36  of the output-side rotor  21  are located on one plane. Likewise, the output-side lateral surface of the friction portion  41   b  and that of each flange  36  of the output-side rotor  21  are located on one plane. The offset portion  41   a  couples therethrough the annular portion  40  and the friction portion  41   b  that are disposed in different axial positions. 
     The first support portion  41   c  extends radially outward from the friction portion  41   b , and has a smaller circumferential width than the friction portion  41   b . The first support portion  41   c  makes contact, at the both circumferential end surfaces thereof, with the spring seats  38 . The second support portion  41   d  is formed by circumferentially extending the both ends of the outer peripheral end of the first support portion  41   c . The second support portion  41   d  makes contact, at the inner peripheral surface thereof, with the spring seats  38 . 
     The stopper portion  41   e  is provided on the circumferentially middle part of the outer peripheral surface of the first support portion  41   c , and protrudes radially outward. The stopper portion  41   e  is disposed in the circumferential middle of adjacent two of the bent portions  31   c  of the first plate  31 . Additionally, the circumferential end surfaces of the stopper portion  41   e  are capable of making contact with those of the adjacent two bent portions  31   c , respectively. 
     In other words, the angle of relative rotation between the input-side rotor  20  and the intermediate rotor  23  (furthermore, the output-side rotor  21 ) is limited to fall within a predetermined angular range by each stopper portion  41   e  of the intermediate rotor  23  and the adjacent two bent portions  31   c  of the first plate  31 . 
     [Hysteresis Generating Mechanism  24 ] 
     The hysteresis generating mechanism  24  is disposed radially between the hub  35  of the output-side rotor  21  and the torsion springs  22 . Besides, the hysteresis generating mechanism  24  is disposed axially between the first plate  31  and both the flanges  36  (specifically, the hysteresis mechanism attaching portions  36   a ) of the output-side rotor  21  and the intermediate flanges  41  (specifically, the friction portions  41   b ) of the intermediate rotor  23 , while being disposed axially between the second plate  32  and both the flanges  36  of the output-side rotor  21  and the intermediate flanges  41  of the intermediate rotor  23 . 
     As shown in  FIGS. 4 and 6 , the hysteresis generating mechanism  24  includes two annular disc plates  45 , two friction plates  46  and a cone spring  47 . The two annular disc plates  45  are different from each other only in terms of dimension, and this is true of the two friction plates  46 . Hence, the annular disc plate  45  and the friction plate  46 , which are disposed on the first plate  31  side, will be hereinafter explained. It should be noted that  FIG. 6  shows the output-side rotor  21 , the intermediate rotor  23  and part of the hysteresis generating mechanism  24 , which are extracted from the damper device  3 . 
     The annular disc plate  45 , having an annular shape, makes contact with the lateral surface of the output-side rotor  21  and that of the intermediate rotor  23 . Additionally, the annular disc plate  45  is fixed to the hysteresis mechanism attaching portions  36   a  of the output-side rotor  21 . Therefore, the annular disc plate  45  is non-rotatable relative to the output-side rotor  21 , but is rotatable relative to the intermediate rotor  23 . It should be noted that albeit not herein described in detail, the annular disc plate  45  is provided with a plurality of fixation portions protruding to the inner peripheral side, for instance, and is fixed at the fixation portions to the output-side rotor  21  by rivets or so forth. 
     The friction plate  46 , having an annular shape, makes contact at the flywheel side lateral surface thereof with the annular disc plate  45 , while making contact at the other lateral surface thereof with the first plate  31 . Additionally, the friction plate  46  is provided with a plurality of engaging protrusions  46   a  axially protruding from the first plate  31 -side surface thereof. Moreover, the engaging protrusions  46   a  are engaged with holes  31   g  provided in the first plate  31 . Accordingly, the friction plate  46  is non-rotatable relative to the first plate  31 , but is rotatable relative to the annular disc plate  45 . 
     As described above, the annular disc plate  45  and the friction plate  46 , disposed on the second plate  32  side, are configured similarly to those disposed on the first plate  31  side. However, the cone spring  47  is attached between the second plate  32  and the friction plate  46  disposed on the second plate  32  side, while being compressed therebetween. 
     With the configuration described above, friction resistance (hysteresis torque) is generated between the friction plates  46  and the annular disc plates  45  when the torsion springs  22  are compressed and extended by relative rotation between the input-side rotor  20  and the output-side rotor  21 . Likewise, a hysteresis torque is generated when relative rotation is produced between the output-side rotor  21  and the intermediate rotor  23  by compression and extension of the torsion springs  22 . In other words, the hysteresis generating mechanism  24  includes a hysteresis generating part  24   a  (see  FIG. 4 ) for generating a hysteresis torque between the input-side rotor  20  and the output-side rotor  21  and a hysteresis generating part  24   b  (see  FIG. 3 ) for applying a hysteresis torque to the intermediate rotor  23 . 
     [Action] 
     Power, transmitted from the engine to the flywheel  4 , is inputted to the damper device  3  through the torque limiter device  2 . In the damper device  3 , the power is inputted to the first and second plates  31  and  32  to which the friction disc  12  of the torque limiter device  2  is fixed, and is transmitted to the output-side rotor  21  through the torsion springs  22 . Then, the power is further transmitted from the output-side rotor  21  to the electric motor, the transmission, a power generator and so forth disposed on the output side. 
     Incidentally, in starting the engine, for instance, chances are that an excessive torque is transmitted from the output side to the engine because the output side has a large inertia amount. In such a case, when transmitted to the engine, the torque is limited in magnitude to a predetermined value or less by the torque limiter device  2 . 
     In the damper device  3 , when the power is transmitted to the torsion springs  22  from the first and second plates  31  and  32 , the torsion springs  22  are compressed. Besides, the torsion springs  22  are repeatedly compressed and extended by torque fluctuations. When the torsion springs  22  are compressed and extended, torsion (displacement) is produced between the first and second plates  31  and  32  and the output-side rotor  21 . 
     The hysteresis generating mechanism  24  is actuated by the torsion between the first and second plates  31  and  32  and the output-side rotor  21 , whereby a hysteresis torque is generated. Specifically, relative rotation is produced between the friction plates  46 , fixed to the first and second plates  31  and  32 , and the annular disc plates  45  fixed to the output-side rotor  21 . Hence, friction resistance is generated therebetween. Accordingly, the hysteresis torque is generated between the first and second plates  31  and  32  and the output-side rotor  21 . 
     Moreover, torsion is also produced between the output-side rotor  21  and the intermediate rotor  23  by compression and extension of the torsion springs  22 . Because of this torsion, relative rotation is produced between the annular disc plates  45  fixed to the output-side rotor  21  and the friction portions  41   b  of the intermediate rotor  23 , whereby friction resistance is generated therebetween. Accordingly, a hysteresis torque is generated between the output-side rotor  21  and the intermediate rotor  23 . 
     Chances are that, depending on the rotational speed of the engine, the intermediate rotor  23  greatly vibrates due to resonance. However, in the present preferred embodiment, the intermediate rotor  23  can be inhibited from vibrating with a large amplitude due to resonance by the hysteresis torque generated between the output-side rotor  21  and the intermediate rotor  23 . 
       FIG. 7  shows the magnitude of vibration of the intermediate rotor  23 . In  FIG. 7 , broken line m indicates a condition in which a hysteresis torque is not applied to the intermediate rotor  23 , whereas solid line M indicates a condition in which a hysteresis torque is applied to the intermediate rotor  23 . As is obvious from  FIG. 7 , vibration due to resonance can be inhibited in magnitude by applying a hysteresis torque to the intermediate rotor  23 . 
     It should be noted that when the angle of torsion is increased between the first and second plates  31  and  32  and both the output-side rotor  21  and the intermediate rotor  23 , one end surface of each bent portion  31   c  of the first plate  31  and that of each stopper portion  41   e  of the intermediate rotor  23  make contact with each other. Because of this, the torsion angle between the first and second plates  31  and  32  and both the output-side rotor  21  and the intermediate rotor  23  can be inhibited from reaching a predetermined angle or greater. Therefore, it is possible to avoid a situation that excessive stress acts on the torsion springs  22 . 
     Other Preferred Embodiments 
     The present invention is not limited to the preferred embodiment described above, and a variety of changes or modifications can be made without departing from the scope of the present invention. 
     (a) The configuration of the hysteresis generating mechanism  24  is not limited to that of the aforementioned preferred embodiment. For example, when resonance of the intermediate rotor  23  does not matter, it is not required to make the intermediate rotor  23  and the annular disc plates  45  slide in contact with each other. 
     (b) In the aforementioned preferred embodiment, the hysteresis generating mechanism  24  is provided with the annular disc plates  45  and the friction plates  46 . However, friction plates can be configured to directly make contact with the output-side rotor  21  and the intermediate rotor  23 . 
     REFERENCE SIGNS LIST 
     
         
           2  Torque limiter device 
           10  Cover 
           10   a  Coupling portion 
           10   b  Tubular portion 
           10   c  Support portion 
           10   d  Curved surface portion 
           10   e  Support protrusion 
           11  Damper plate 
           12  Friction disc 
           13  Pressure plate 
           14  Cone spring