Patent Publication Number: US-2007096529-A1

Title: Recliner apparatus for vehicle seat

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
      This application is based on and claims priority under 35 U.S.C. § 119 to Japanese Patent Application 2005-315603, filed on Oct. 31, 2005, the entire content of which is incorporated herein by reference.  
     FIELD OF THE INVENTION  
      This invention generally relates to a recliner apparatus for a vehicle seat. More specifically, this invention pertains to a recliner apparatus for a vehicle seat for supporting a seat back to a seat cushion so that an angle between the seat back and the seat cushion can be adjusted.  
     BACKGROUND  
      Generally, a recliner apparatus for a vehicle seat has an advantage that a seat back can be fixed quickly at an arbitrary angle position because the seat back automatically returns by virtue of a return spring. However, problem may occur in that the seat back strongly collides with an occupant as the seat back quickly pulls back, which results in an uncomfortable feeling to the occupant.  
      For overcoming this, for example, as described in JPH7 (1995)-137564A (Patent document 1) or in JPH9 (1997)-252868A (Patent document 2), various kinds of recliner apparatuses for vehicle seats, in which returning speed of a seat back is slow, are suggested. In Patent document 1, for reducing rising speed of a seat back, the seat back is rotated while an end portion of a leaf spring included in a clutch case is elastically deformed in a direction in which a diameter thereof is enlarged to lock a seat back, and in turn while an opposite end of the leaf spring is elastically deformed in a direction in which a diameter thereof is reduced. By repeating this, the seat back tilts forward while appropriate braking is applied. On the other hand, in a recliner apparatus for a vehicle seat according to Patent document 2, for reducing rising speed of a seat back, a coil spring is provided in a drum-shaped cover to bias the seat back in an opposite direction of a return spring provided for rising the seat back. As the seat back rises, because a diameter of the coil spring is enlarged toward an inner wall of the cover, rising speed of the seat back becomes gradually slow by frictional resistance between the coil spring and the cover.  
      In the recliner apparatus for the vehicle seat described in Patent document 1 described above, because lock and rotation is repeated for applying braking to the seat back to reduce the rising speed, the seat back moves awkwardly in an actual operation. Accordingly, an occupant may feel uncomfortable while using the recliner apparatus. Further, an apparatus added for braking the seat back to reduce rising speed functions also in a situation where an occupant conducts a normal adjustment of an angle of the seat back. Accordingly, resistance is applied while the leaf spring is taken along with the seat back even though the diameter thereof is reduced. On the other hand, the seat back is raised while rising torque is smaller than load applied to the recliner apparatus because the seat back does not accelerate while rising. By these reasons, there is a problem that adjustment cannot be performed well.  
      Further, in the recliner apparatus for the vehicle seat described in Patent document 2 described above, for reducing rising speed of the seat back, the diameter of the spring in the cover is enlarged. Accordingly, for reducing a speed of the seat back accelerated from a near full-flat position, sufficient resistance need to be generated (the diameter of the spring need to be sufficiently enlarged) in a normal-use range. However, an inconvenience may occur in that the seat does not rise when an occupant intends to adjust an angle of the seat back in the normal-use range because of the resistance, and adjustment of the seat cannot be performed well.  
      A need thus exists for a recliner apparatus for a vehicle seat, which has a clutch mechanism operated by centrifugal force to reduce operational speed of a seat back. The present invention has been made in view of the above circumstances and provides such a recliner apparatus for a vehicle seat.  
     SUMMARY OF THE INVENTION  
      According to an aspect of the present invention, a recliner apparatus for a vehicle seat having a seat cushion and a seat back includes a first member attached to the seat cushion side, a second member attached to the seat back side and relatively rotatable to the first member, a return spring for biasing the seat back forward or backward relative to the seat cushion and a clutch mechanism provided between the first member and the second member and operated by centrifugal force action concurrent with a rotational operation of the second member for giving rotational resistance to the second member. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The foregoing and additional features and characteristics of the present invention will become more apparent from the following detailed description considered with reference to the accompanying drawings, wherein:  
       FIG. 1  represents a diagram illustrating a seat for a vehicle;  
       FIG. 2  represents a cross-sectional view illustrating a recliner apparatus for a vehicle seat according to a first embodiment of the present invention;  
       FIG. 3  represents a cross-sectional view taken on line III-III of  FIG. 2 ;  
       FIG. 4  represents a cross-sectional view illustrating a variation of  FIG. 3 ;  
       FIG. 5  represents a cross-sectional view illustrating another variation of  FIG. 3 ;  
       FIG. 6  represents a cross-sectional view illustrating a recliner apparatus for a vehicle seat according to a second embodiment of the present invention;  
       FIG. 7  represents a cross-sectional view taken on line VII-VII of  FIG. 6 ; and  
       FIG. 8  represents an enlarged cross-sectional view illustrating a part of  FIG. 7 . 
    
    
     DETAILED DESCRIPTION  
      A first embodiment of the present invention will be explained with reference to drawing figures. As illustrated in  FIGS. 1 and 2 , a recliner apparatus  10  for a vehicle seat  2  for a vehicle  1  includes a seat cushion  11 , a seat back  12  and a reclining adjustment mechanism  13  for adjusting an inclination of the seat back  12  relative to the seat cushion  11  in accordance with occupant&#39;s preference.  
      The reclining adjustment mechanism  13  includes a disk-shaped lower arm  15  and a disk-shaped upper arm  16 . The upper arm  16  is fitted to the lower arm  15  and is rotatable relative to the lower arm  15 . The lower arm  15  is fixed to a seat cushion frame  17  attached to the seat cushion  11  by welding, or the like. The upper arm  16  is fixed to a seat back frame  18  attached to the seat back  12  by welding, or the like.  
      In the meantime, at least one of the lower arm  15  and the seat cushion frame  17  serves as a first member. At least one of the upper arm  16  and the seat back frame  18  serves as a second member.  
      A recessed portion  21  is formed at the lower arm  15  by half die cutting so that the recessed portion  21  opens to the upper arm  16  side. The recessed portion  21  includes an inner peripheral surface  21   a  of which a center is a rotational axis line C of the upper arm  16  and the lower arm  15 . The upper arm  16  is fitted to the lower arm  15  so that an outer peripheral surface  16   a  of the upper arm  16  slides along the inner peripheral surface  21   a  of the lower arm  15 . Sliding surfaces of the lower arm  15  and the upper arm  16  function as a shaft and bearing for mutual rotation. On the other hand, a recessed portion  23  is formed at the upper arm  16  by half die cutting so that the recessed portion  23  opens to the lower arm  15  side. Inner teeth  23   a  are formed at the recessed portion  23  over entire circumference of an inner peripheral portion of which a center is the rotational axis line C.  
      A ring member  25  is fixed by a rivet so that the ring member  25  covers an outer periphery of the lower arm  15 . One side surface of the ring member  25  rotatably supports an outer peripheral portion of the upper arm  16  as if one side surface of the ring member  25  embraces the outer peripheral portion of the upper arm  16 . By this, the lower arm  15  and the upper arm  16  are retained in a state where the lower arm  15  and the upper arm  16  are assembled to be relatively rotatable.  
      A conventional lock mechanism  27  is provided in the recessed portions  21  and  23  of the lower arm  15  and the upper arm  16  for locking the seat back  12  at an adjusted angle position. The lock mechanism  27  mainly includes a pawl including engaging teeth, which engages with/disengages from the inner teeth  23   a  formed at the lower arm  15 , a pawl plate rotated by operation of an operational lever through a rotational axis  28  and a can for engaging/disengaging the pawl with/from the inner teeth  23   a  by rotation of the pawl plate. The lock mechanism  27  is conventional and described in, for example, JP2003-9978A. Accordingly, detailed explanations thereof will be skipped.  
      A plate  30  is attached to the seat cushion frame  17  described above so that the plate  30  faces the seat back frame  18 . A cylindrical case  31  with a bottom is attached to the plate  30  as a unit. The cylindrical case  31  includes an inner peripheral surface  31   a  of which a center is the rotational axis line C. As illustrated in  FIG. 3 , a ring-shaped engaging member  32  is freely rotatably fitted in the cylindrical case  31 . A friction spring  33  is wound and provided between an outer peripheral surface of the engaging member  32  and the inner peripheral surface  31   a  of the cylindrical case  31  along the inner peripheral surface  31   a  of the cylindrical case  31 . One end of the friction spring  33  is bended inwardly in a radial direction and attached to the engaging member  32 . The other end of the friction spring  33  is attached to the cylindrical case  31 .  
      The friction spring  33  is inserted into the cylindrical case  31  in a state where the friction spring  33  is contracted to reduce a diameter thereof. The friction spring  33  normally contact the inner peripheral surface  31   a  of the cylindrical case  31 . Accordingly, in a situation where the engaging member  32  rotates in a direction of an arrow illustrated in  FIG. 3  (a rotational direction of the seat back frame  18  in a situation where the seat back  12  rises forward), the sliding friction resistance of the friction spring  33  exerts braking force.  
      Plural engaging recessed portions  32   a  are formed at an inner periphery of the engaging member  32  at equal angle intervals on a circumference. An engaging end surface  32   a   1 , which is orthogonal to a rotational direction, and an inclined end surface  32   a   2  are formed at both end portions of each engaging recessed portion  32   a  in a rotational direction. The engaging end surface  32   a   1  is located frontward in the direction of the arrow illustrated in  FIG. 3 , and the inclined end surface  32   a   2  is located rearward in the direction of the arrow illustrated in  FIG. 3 .  
      A supporting block  36  is fixed to the seat back frame  18 . The supporting block  36  penetrates the plate  30  and is inserted into the cylindrical case  31 . A supporting pin  37  is screwed to the supporting block  36  in parallel with the rotational axis line C. One end of a swing arm  35  is swingably supported by the supporting pin  37 . The swing arm  35  functions as a weight member, of which an end portion  35   a  swings outwardly in a radial direction by centrifugal force generated concurrently with rotational operation of the seat back  18 . As illustrated in  FIG. 3 , two swing arms  35  are provided in the engaging member  32  on a circumference. A torsion spring  38  is fitted to the supporting pin  37 . One end of the torsion spring  38  is attached to the supporting pin  37 . The other end of the torsion spring  38  is attached to the end portion  35   a  of the swing arm  35 .  
      The swing arm  35  is normally retained in an angle state where the end portion  35   a  of the swing arm  35  is retracted inwardly in a radial direction by biasing force of the torsion spring  38 . In this state, the swing arm  35  does not contact the inner periphery of the engaging member  32 , and the swing arm  35  can freely rotate in the engaging member  32 . Then, in a situation where centrifugal force, which is larger than the biasing force of the torsion spring  38 , is applied to the swing arm  35 , the swing arm  35  is swung so that the end portion  35   a  of the swing arm  35  swings outwardly in a radial direction around the supporting pin  37  as a supporting point.  
      By this, the end portion  35   a  of the swing arm  35  is inserted into the engaging recessed portion  32   a  of the engaging member  32 . Then, at this time, in a situation where the seat back frame  18  is rotating in the direction of the arrow illustrated in  FIG. 3 , the end portion  35   a  of the swing arm  35  engages with the engaging end surface  32   a   1  of the engaging recessed portion  32   a . Thus, the engaging member  32  rotates with the swing arm  35 . However, in a situation where the seat back frame  18  is rotating in an opposite direction of the arrow illustrated in  FIG. 3 , the end portion  35   a  of the swing arm  35  slides along the inclined end surface  32   a   2  of the engaging recessed portion  32   a  and leaves therefrom. Thus, the engaging member  32  does not rotate with the swing arm  35 .  
      Accordingly, in a situation where the seat back frame  18  rotates in the direction of the arrow illustrated in  FIG. 3 , in other words, in a situation where the seat back  12  returns forward, the engaging member  32  rotates in the direction of the arrow with the swing arm  35 . Accordingly, sliding resistance of the friction spring  33  exerts braking force to the engaging member  32  and a member rotating with the engaging member  32  as a unit.  
      A clutch mechanism  39  is configured from above-described cylindrical case  31 , the engaging member  32 , the friction spring  33 , the swing arm  35  and the torsion spring  38 , or the like. The clutch mechanism  39  is operated by centrifugal force generated in a situation where the seat back  12  is raised with great force and functions to reduce rising speed of the seat back  12 .  
      A reference number  41  indicates a return spring, of which one end is attached to a bracket  42  fixed to the seat back frame  18 . The return spring  41  normally exerts biasing force to the seat back frame  18  in a direction in which the seat back  12  reclines forward. Accordingly, in a situation where a lock of the lock mechanism  27  is released by the operation of the operational lever described above, the seat back  12  returns forward by virtue of the biasing force of the return spring  41 .  
      Next, operation of the recliner apparatus  10  for the vehicle seat  2  according to the first embodiment described above will be explained. In a normal-use region (region of an angle range Z 1  illustrated in  FIG. 1 ), in which a tilting angle of the seat back  12  is adjusted in a state where an occupant is seated, because the amount of adjustment of the tilting angle is relatively small, rotational speed of the seat back frame  18  in a situation where the seat back  12  returns forward is low. Accordingly, centrifugal force exerted to the swing arm  35  is small, and the centrifugal force exerted to the swing arm  35  cannot be larger than the biasing force of the torsion spring  38 . As a result, the swing arm  35  is retained in a normal angle state, in which the end portion  35   a  of the swing arm  35  is positioned inwardly in a radial direction by virtue of the biasing force of the torsion spring  38 , and the swing arm  35  does not contact the engaging recessed portion  32   a  of the engaging member  32 .  
      Thus, by the operation for returning the seat back  12  forward by the operational lever, the seat back  12  can quickly return by virtue of the biasing force of the return spring  41 , and angle adjustment of the seat back  12  can be quickly performed.  
      On the other hand, for example, in a situation where the seat back  12  is raised from a full-flat state indicated by a chain double-dashed line in  FIG. 1  with great force, because rotational speed of the seat back frame  18  becomes high, centrifugal force, which is larger than the biasing force of the torsion spring  38 , is exerted to the swing arm  35 . The swing arm  35  is swung around the supporting pin  37  as the supporting point by the centrifugal force action. Then, as indicated by a chain double-dashed line in  FIG. 3 , the end portion  35   a  of the swing arm  35  engages with the engaging end surface  32   a   1  of the engaging recessed portion  32   a  of the engaging member  32 . By this, the engaging member  32  rotates around the rotational axis line C with the swing arm  35 . Thus, the swing arm  35  is operationally connected to the friction spring  33  through the engaging member  32 . Here, sliding resistance of the friction spring  33  is exerted to the engaging member  32 . Therefore, returning speed of the seat back  12  can be reduced by sliding friction of the friction spring  33 . Accordingly, strong collision of the seat back  12 , which is rapidly rotating to a forward-tilting position, with an occupant, can be prevented with reliability.  
      In a situation where the centrifugal force becomes small, the swing arm  35  is swung inwardly in a radial direction by the biasing force of the torsion spring  38 , and the swing arm  35  is disengaged from the engaging member  32 . Accordingly, the seat back  12  can be operated without receiving sliding resistance of the friction spring  33 .  
      In the meantime, in an opposite situation where the seat back  12  is laid with great force, in other words, in a situation where the seat back frame  18  rapidly rotates in an opposite direction of the arrow illustrated in  FIG. 3 , the swing arm  35  is swung by centrifugal force, and the swing arm  35  comes in contact with an inner surface of the engaging member  32 . However, because the swing arm  35  slides along the inclined surface  32   a   2  of the engaging member  32  and leaves therefrom in the rotational direction of the seat back frame  18 , the clutch mechanism  39  is not operated, and the seat back  12  can be operated quickly in a direction in which the seat back  12  is laid. Thus, the clutch  39  has a function as a one-way clutch.  
      According to the first embodiment described above, the clutch mechanism  39  is operated on the basis of magnitude of centrifugal force exerted to the swing arm  35  generated in accordance with rotational speed of the seat back frame  18 . Accordingly, the clutch mechanism  39  is not operated at the time of normal-use by an occupant, and the seat back  12  can return forward without resistance, and an angle adjustment can be performed without uncomfortable feeling.  
      On the other hand, in a situation where the seat back  12  is raised with great force, because the clutch mechanism  39  is operated on the basis of centrifugal force action exerted to the swing arm  35 , sliding resistance between the friction spring  33  and the inner peripheral surface  31   a  of the cylindrical case  31  reduces rising speed of the seat back  12 . By this, strong collision of the seat back  12  with an occupant can be prevented with reliability.  
      In the meantime, appropriate setting of the swing arm  35  or the torsion spring  38 , or the like, which configure the clutch mechanism  39 , can reduce speed of the seat back  12  also in a situation where the seat back  12  rises from the normal-use region by relatively short distance. The recliner apparatus for the vehicle seat is not limited to that the clutch mechanism  39  is not operated in the normal-use region. Further, timing of generating sliding resistance by operation of the clutch mechanism  39  can be appropriately set by, for example, adjusting positions or the number of the engaging end surfaces  32   a   1 .  
      Further, a variation of the first embodiment will be explained. In addition to the engaging member  32  and the swing arm (weight member)  35  described above, another swing arm (weight member), which engages with another engaging member in a situation where the seat back frame  18  rotates in an opposite of the direction described above, can be added to correspond to rapid rotation of the seat back  12  in both forward and backward ways. By this, in a situation where the seat back  12  is pushed backward and laid by hand with great force, or in a situation where an occupant leans back on the seat back  12  by using his/her weight, operational speed of the seat back  12 , which exceeds a predetermined speed or acceleration, can be reduced. Accordingly, an occupant can be prevented from a sudden rearward leaning caused by the seat back  12  being rapidly moved backward.  
       FIGS. 4 and 5  represent diagrams illustrating variations of the clutch mechanism  39 . In the clutch mechanism  39  illustrated in  FIG. 4 , sawtooth inner teeth  32   b  are formed at an inner peripheral surface of the engaging member  32  freely fitted in the cylindrical case  31 , and on the other hand, engaging teeth  35   b , which engage with the inner teeth  32   b  of the engaging member  32  in a situation where the swing arm  35  is swung outwardly in a radial direction by centrifugal force, are formed at the end portion  35   a  of the swing arm  35 . In this variation also, as indicated by a chain double-dashed line illustrated in  FIG. 4 , in a situation where the engaging teeth  35   b  of the swing arm  35  engage with the inner teeth  32   b  of the engaging member  32 , the engaging member  32 , to which one end of the friction spring  33  is attached, starts rotating with the swing arm  35  as a unit, and sliding friction of the friction spring  33  is exerted.  
      Further, in the clutch mechanism  39  illustrated in  FIG. 5 , the engaging member described above is removed, and one-end of the friction spring  33  is extended inwardly in a radial direction so that one end of the friction spring  33  can contact the swing arm  35 . By this, in a situation where the swing arm  35  is swung outwardly in a radius direction by centrifugal force, the end portion  35   a  of the swing arm  35  directly engages with one end of the friction spring  33 , and the swing arm  35  is operationally connected to the friction spring  33 . In the meantime, in  FIG. 5 , for reducing play between the swing arm  35  and one end of the friction spring  33  in a rotational direction, two friction springs  33   a  and  33   b , which respectively engage with the swing arms  35 , provided at two positions on a circumference, are provided. However, the number of the swing arms  35 , or the number of the friction springs  33  can be furthermore increased.  
      In the meantime, in  FIGS. 4 and 5 , identical reference numbers are assigned to configuration members identical to those descried in the first embodiment, and explanations thereof will be skipped.  
      Next, a second embodiment of the present invention will be explained with reference to  FIGS. 6, 7  and  8 . In a recliner apparatus  10  for a vehicle seat  2  according to the second embodiment, a configuration of a clutch mechanism  139 , which is operated in a situation where the seat back  12  is raised with great force, is different from the clutch mechanism  39  in the first embodiment. In the meantime, in  FIG. 6 , illustration of the lock mechanism provided in the recessed portions of the lower arm  15  and the upper arm  16  are omitted.  
      In  FIGS. 6 and 7 , similarly to the first embodiment described above, the lower arm  15  and the upper arm  16  are assembled and relatively rotatably retained by the ring member  25  fixed by a rivet and provided at the outer periphery of the lower arm  15 . A ring-shaped case member  51  is located at an outer periphery of the ring member  25  so that the case member  51  covers the ring member  25 . Movement of the case member  51  relative to the ring member  25  in an axial direction is restricted. A first inner peripheral surface  51   a , which is freely fitted to an outer peripheral surface of the ring member  25  with a clearance therebetween, and a second inner peripheral surface  51   b , which is freely fitted to a stepped outer peripheral surface  16   b  of the upper arm  16  with a clearance therebetween, are formed at the case member  51 .  
      A sliding resistance member  52  made of, for example, a resin ring, is provided between the first inner peripheral surface  51   a  of the case member  51  and the outer peripheral surface of the ring member  25 . The case member  51  can rotate relative to the ring member  25  with sliding resistance exerted by the sliding resistance member  52 . Plural wedge portions  53  are provided at the stepped outer peripheral surface  16   b  of the upper arm  16 , which faces the second inner peripheral surface  51   b  of the case member  51 , to recess on a circumference. As illustrated in  FIG. 8  in detail, a wedge surface  53   a , which is inclined in a rotational direction, is formed at a bottom surface of each wedge portion  53 . By this, depth of each wedge portion  53  gradually increases toward a rotational direction (direction of arrows illustrated in  FIGS. 7 and 8 ) of the upper arm  16  in a situation where the seat back  12  rises forward. A roller bearing  54 , which serves as a weight member, is accommodated in each wedge portion  53  so that the roller bearing  54  can move along the wedge surface  53   a  between a deep position and a shallow position. The roller bearing  54  is pressed toward a rotational direction of the upper arm  16  by biasing force of a coil spring  55 . By this, the roller bearing  54  is normally retained at a position where the roller bearing  54  contacts a deep-side end surface of the wedge portion  53 .  
      In a normal state where the roller bearing  54  is positioned at the deep-side end surface of the wedge portion  53 , there is a clearance between the roller bearing  54  and the second inner peripheral surface  51   b  of the case member  51 . Accordingly, the upper arm  16  can rotate regardless of the case member  51 . However, centrifugal force action in accordance with increase of rotational speed of the upper arm  16  (seat back frame  18 ) moves the roller bearing  54  along the wedge surface  53   a  outwardly in a radial direction against the biasing force of the coil spring  55 . Then, as indicated by a chain double-dashed line illustrated in  FIG. 8 , the roller bearing  54  is caught between the second inner peripheral surface  51   b  of the case member  51  and the wedge surface  53   a  of the wedge portion  53  of the upper arm  16 . As a result, the upper arm  16  and the case member  51  are connected to one another through the roller bearing  54 , and rotation of the upper arm  16  is transmitted to the case member  51  through the roller bearing  54 . By this, the case member  51  and the upper arm  16  start rotating relatively to the ring member  25  with sliding resistance exerted by the sliding resistance member  52 .  
      The clutch mechanism  139  is configured from the case member  51 , the sliding resistance member  52 , the wedge portion  53 , the roller bearing  54 , and the coil spring  55 , or the like, which are described above. The clutch mechanism  139  is operated on the basis of centrifugal force generated in a situation where the seat back  12  is raised with great force. The clutch mechanism  139  functions to reduce rising speed of the seat back  12 .  
      The recliner apparatus  10  for the vehicle seat  2  according to the second embodiment is configured as described above. Accordingly, in the normal-use region (region of the angle range Z 1  illustrated in  FIG. 1 ), in which the tilting angle of the seat back  12  is adjusted in a state where an occupant is seated, because adjusted angle range is relatively small, rotational speed of the upper arm  16  in a situation where the seat back  12  returns forward is low, and centrifugal force exerted to the roller bearing  54  is small. Therefore, the roller bearing  54  is retained at a position where the roller bearing  54  contacts the deep-side end surface of the wedge portion  53  by virtue of the biasing force of the coil spring  55 , and the roller bearing  54  does not contact the second inner peripheral surface  51   b  of the case member  51 .  
      Accordingly, operation for returning the seat back  12  forward by the operational lever can quickly return the seat back  12  by virtue of the biasing force of the return spring  41 , and angle adjustment of the seat back  12  can be quickly performed.  
      On the other hand, in a situation where the seat back  12  is raised with great force, because rotational speed of the upper arm  16  becomes high, centrifugal force also becomes large. This centrifugal force action moves the roller bearing  54  along the wedge surface  53   a  outwardly in a radial direction against the biasing force of the coil spring  55 . As a result, as indicated by the chain double-dashed line illustrated in  FIG. 8 , the roller bearing  54  is caught between the second inner peripheral surface  51   b  of the case member  51  and the wedge surface  53   a  of the wedge portion  53  of the upper arm  16 , and rotation of the upper arm  16  is transmitted to the case member  51  through the roller bearing  54 . Accordingly, the case member  51  rotates with the upper arm  16  as a unit. At this time, sliding resistance exerted to the case member  51  by the sliding resistance member  52  reduces returning speed of the seat back  12 .  
      In the meantime, in a situation where the seat back  12  is laid with great force, in other words, in a situation where the upper arm  16  rapidly rotates in an opposite direction of the arrows illustrated in  FIGS. 7 and 8 , the roller bearing  54  comes in contact with the second inner peripheral surface  51   b  of the case member  51  by centrifugal force. However, in this rotational direction of the upper arm  16 , the roller bearing  54  is not caught between the wedge portion  53  and the case member  51 . Accordingly, the case member  51  does not rotate with the upper arm  16  as a unit. Thus, the clutch mechanism  139  has a function as a one-way clutch, similarly to the clutch mechanism  39  described above.  
      According to the second embodiment described above, similarly to the clutch mechanism  39  described in the first embodiment, the clutch mechanism  139  is operated only in a situation where centrifugal force concurrent with rotational operation of the upper arm  16  (seat back frame  18 ) is large. The clutch mechanism  139  functions to reduce rising speed of the seat back  12 . Further, the recliner apparatus  10  for the vehicle seat  2  can be configured only by locating the clutch mechanism  139  as a unit at an outer peripheral portion of the lower arm  15  in the first embodiment. Accordingly, the cylindrical case  31  in the first embodiment can be removed. Therefore, the clutch mechanism  139  can be located in a small space without restriction from layout, and miniaturization of the recliner apparatus  10  can be possible.  
      Further, a variation of the second embodiment will be explained. In the variation, in addition to the wedge portion  53  described above, a wedge portion opposite to the wedge portion  53  can be added. Then, a roller bearing, which serves as a weight member, can be accommodated in the opposite wedge portion. By this, countermeasure can be anticipated against both forward and backward rapid rotation of the seat back  12 . Accordingly, similar to the description above, an occupant can be inhibited from a sudden rearward leaning caused by the seat back  12  being rapidly moved backward.  
      In the meantime, in the second embodiment, resistance (sliding friction resistance) was exerted to operation of the seat back  12  by the sliding resistance member  52 . However, such a resistance is not limited to sliding friction resistance, but can be exerted by other resistance members, for example, by fluid resistance means, in which shearing resistance of fluid is utilized, or the like.  
      In the embodiments described above, explanations were made with an example, in which the seat back was biased forward by the return spring. However, the present invention can be applied not only to the seat back, but also to, for example, a seat, which is biased backward, as an arrangement means of a rear seat (a means for making the seat change to a tumbled state by raising a seat cushion forward with a seat back laid forward).  
      Further, in the embodiments described above, rotational resistance was exerted by the sliding resistance member  52  made of, for example, a resin ring, provided between the case member  51  and the ring member  25 . However, a rivet ring of the ring member  25 , or the like, which is originally included in a recliner apparatus, may be utilized as a resistance member without separately providing the sliding resistance member, or the like.  
      As described above, the present invention is not limited to the embodiments described above. Variations can be made without departing from the spirit of the present invention described in the scope of the invention.  
      According to a first aspect of the present invention, a recliner apparatus for a vehicle seat having a seat cushion and a seat back includes a first member attached to the seat cushion side, a second member attached to the seat back side and relatively rotatable to the first member, a return spring for biasing the seat back forward or backward relative to the seat cushion and a clutch mechanism provided between the first member and the second member and operated by centrifugal force action concurrent with a rotational operation of the second member for giving rotational resistance to the second member.  
      According to a second aspect of the present invention, in the recliner apparatus for the vehicle seat according to the first aspect, the clutch mechanism includes a friction spring slidable along an inner peripheral surface of a cylindrical case attached to the first member and a weight member accommodated in the cylindrical case and operated by the centrifugal force action concurrent with rotation of the second member and operatively connected to the friction spring.  
      According to a third aspect of the present invention, in the recliner apparatus for the vehicle seat according to the second aspect, the clutch mechanism includes the friction spring slidable along the inner peripheral surface of the cylindrical case, an engaging member rotatably accommodated in the cylindrical case and engaged with one end of the friction spring and the weight member attached to the second member and engaged with the engaging member by the centrifugal force action.  
      According to a fourth aspect of the present invention, in the recliner apparatus for the vehicle seat according to the first aspect, the clutch mechanism includes a case member rotatable relative to the first member, a resistance portion for exerting rotational resistance between the case member and the first member and a weight member accommodated in a wedge portion provided at the second member and engaged with the case member by the centrifugal force action.  
      According to a fifth aspect of the present invention, in the recliner apparatus for the vehicle seat according to any one of the first aspect to the fourth aspect, the clutch mechanism has a one-way clutch function for giving rotational resistance to the second member only in a situation where the clutch mechanism is operated in a direction in which the seat back returns forward.  
      According to the first aspect of the present invention, rotational resistance is given to the second member by the clutch mechanism located between the first member and the second member and operated on the basis of the centrifugal force action concurrent with the rotational operation of the second member. Accordingly, operational speed of the seat back can be reduced only in a situation where the clutch mechanism is operated by the centrifugal force action. Therefore, accidental situation caused by rapid operation of the seat back can be inhibited. Further, at the time of normal use of the seat back, the clutch mechanism is not operated. Therefore, the seat back can be operated without resistance, and angle adjustment can be performed without uncomfortable feeling.  
      According to the second aspect of the present invention, the clutch mechanism includes the friction spring, slidable along the inner peripheral surface of the cylindrical case attached to the first member and the weight member accommodated in the cylindrical case and operated by the centrifugal force action and operationally connected to the friction spring. Accordingly, operation of the weight member by the centrifugal force action can reduce the operational speed of the seat back by sliding friction resistance of the friction spring.  
      According to the third aspect of the present invention, the clutch mechanism includes the friction spring slidable along the inner peripheral surface of the cylindrical case, the engaging member rotatably accommodated in the cylindrical case and engaged with one end of the friction spring and the weight member attached to the second member and engaged with the engaging member by the centrifugal force action. Accordingly, effects similar to the second aspect can be obtained, and the sliding friction resistance of the friction spring can be stably exerted by virtue of the engaging member.  
      According to the fourth aspect of the present invention, the clutch mechanism includes the case member relatively rotatable to the first member, the resistance portion for exerting rotational resistance between the case member and the first member and the weight member accommodated in the wedge portion provided at the second member and engaged with the case member by the centrifugal force action. Accordingly, the clutch mechanism can be provided without restriction from layout, the clutch mechanism can be located in a small space and miniaturization of the recliner apparatus can be possible.  
      According to the fifth aspect of the present invention, the clutch mechanism has a one-way clutch function, which gives rotational resistance to the second member only in a situation where the seat back is operated in a direction in which the seat back returns forward. Accordingly, the operational speed is reduced only in an operation in a direction in which the seat back rises, and exertion of rotational resistance can be prevented in a direction in which the seat back is laid.  
      The principles, preferred embodiment and mode of operation of the present invention, have been described in the foregoing specification. However, the invention that is intended to be protected is not to be construed as limited to the particular embodiments disclosed. Further, the embodiments described herein are to be regarded as illustrative rather than restrictive. Variations and changes may be made by others, and equivalents employed, without departing from the spirit of the present invention. Accordingly, it is expressly intended that all such variations, changes and equivalents that fall within the spirit and scope of the present invention as defined in the claims, be embraced thereby.