Patent Publication Number: US-2009218870-A1

Title: Seat reclining apparatus for vehicle

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2008-047883, filed on Feb. 28, 2008, the entire content of which is incorporated herein by reference. 
     FIELD OF THE INVENTION 
     This invention generally relates to a seat reclining apparatus for a vehicle. 
     BACKGROUND 
     A known seat reclining apparatus for a vehicle such as disclosed in JP2005-313833A includes a lower plate (base arm) attached to a lower frame (seat cushion frame) that supports a seat cushion for a vehicle seat, an upper plate (lock plate) rotatably supported by the lower plate, an upper frame (upper arm), and a reclining lock mechanism. The upper frame for supporting a seatback for the vehicle seat is rotatably supported by the lower frame via the upper plate and the lower plate, and is relatively rotatable with respect to the upper plate. The reclining lock mechanism is arranged between the lower plate and the upper plate. The reclining lock mechanism is switched between a rotation state in which the relative rotation of the upper plate with respect to the lower plate is permitted and a restriction state in which the relative rotation of the upper plate with respect to the lower plate is prohibited, upon an adjustment of a rotational position of the upper frame within a seating available range. 
     In order to move the seatback forward in a state where a reclining angle of the seatback (i.e., a reclining angle adjusted position) is kept or stored (i.e., walk-in operation) at a time of ingress and egress to and from a seat in the rear of the seatback (i e., rear seat), the aforementioned seat reclining apparatus includes a reclining memory mechanism. The reclining memory mechanism includes a ratchet plate (ratchet) between the upper plate and the upper frame. The ratchet plate is fixed to the upper plate and is rotatably attached to (specifically, rotatably engageable with) the upper frame. When the engagement of the ratchet plate with the upper frame is released so that the upper frame rotates relative to the ratchet plate while the aforementioned restriction state of the reclining lock mechanism is being maintained, the walk-in operation is able to be performed with the reclining angle adjusted position being stored. 
     However, according to the aforementioned structure, in a case where an improper operation is conducted, i.e., the restriction state of the reclining lock mechanism is cancelled during the walk-in operation, for example, the upper plate and the ratchet plate are both rotatable regardless of the rotational position of the upper frame. Then, the ratchet plate may engage with the upper frame while a rotational angle phase of the upper plate relative to the lower plate at the seat reclining apparatus provided at a right side of the seat in the width direction of the vehicle is being different from that provided at a left side of the seat. When the reclining operation is then performed with the different rotational angle phases between right and left sides, an operational feeling may be extremely inferior. 
     Thus, the seat reclining apparatus disclosed in JP2005-313833A is equipped with operation limiting means (a first pivot restriction lever, a second pivot restriction lever, and a link lever) for prohibiting one of an unlock operation of the reclining lock mechanism and a memory operation of the reclining memory mechanism when the other one of the unlock operation of the reclining lock mechanism and the memory operation of the reclining memory mechanism is performed. 
     However, the aforementioned operation limiting means have a complicated structure, which may lead to a high cost and a restriction of space. In addition, in a case where one of the unlock operation of the reclining lock mechanism and the memory operation of the reclining memory mechanism is forcedly conduced while the other one of the unlock operation of the reclining lock mechanism and the memory operation of the reclining memory mechanism is being performed by the operation limiting means, a malfunction, a deterioration of an operating member, and the like may occur. 
     A need thus exists for a seat reclining apparatus for a vehicle which is not susceptible to the drawback mentioned above. 
     SUMMARY OF THE INVENTION 
     According to an aspect of the present invention, a seat reclining apparatus for a vehicle includes a lower frame supporting a seat cushion of a seat for the vehicle, a lower plate mounted on the lower frame, an upper plate rotatably supported by the lower plate, an upper frame supporting a seatback of the seat for the vehicle and rotatably supported by the lower frame via the upper plate and the lower plate, the upper frame being relatively rotatable with respect to the upper plate, a first lock mechanism arranged between the lower plate and the upper plate, the first lock mechanism permitting and restricting a relative rotation of the upper plate to the lower plate, a second lock mechanism arranged between the upper frame and the upper plate, the second lock mechanism permitting and restricting a relative rotation of the upper frame to the upper plate, and a stopper member rotatably supported by the lower frame and fictionally engageable with the upper plate, the stopper member applying a resistance force to the relative rotation of the upper plate to the lower plate. 
    
    
     
       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  is a side view illustrating a vehicle seat to which a seat reclining apparatus for a vehicle according to an embodiment of the present invention is mounted; 
         FIG. 2  is an exploded perspective view mainly illustrating a lower plate and a gear plate provided at the seat reclining apparatus; 
         FIG. 3  is a cross-sectional view taken along a center portion of the vehicle seat shown in  FIG. 1 ; 
         FIG. 4  is a cross-sectional view taken along the line IV-IV in  FIG. 3  and illustrating a locked state of first and second pawls; 
         FIG. 5  is a cross-sectional view taken along the line V-V in  FIG. 3  and illustrating an unlocked state of the first and second pawls; 
         FIG. 6  is a perspective view of the first pawl shown in  FIGS. 4 and 5 ; 
         FIG. 7  is a perspective view of the second pawl shown in  FIGS. 4 and 5 ; 
         FIG. 8  is an exploded perspective view mainly illustrating a ratchet plate provided at the seat reclining apparatus; 
         FIG. 9  is an explanatory view illustrating an operation of the ratchet plate and a stopper member in a case where a reclining lock mechanism and a reclining memory mechanism are each in a locked state; 
         FIG. 10  is an explanatory view illustrating an operation of the ratchet plate and the stopper member in a case where the reclining lock mechanism and the reclining memory mechanism are each in an unlocked state; 
         FIG. 11  is an explanatory view illustrating an operation of the ratchet plate and the stopper member in a case where the reclining lock mechanism and the reclining memory mechanism are each in the unlocked state and a large load is applied to the ratchet plate; and 
         FIG. 12  is an explanatory view illustrating an operation of the ratchet plate and the stopper member in a case where the reclining lock mechanism is in the locked state while the reclining memory mechanism is in the unlocked state and an extremely large load is applied to the ratchet plate. 
     
    
    
     DETAILED DESCRIPTION 
     An embodiment of a seat reclining apparatus for a vehicle will be explained with reference to the attached drawings. Directions such as top, bottom, front, and rear described hereinbelow or indicated by arrows in the attached drawings correspond to orientations of a vehicle to which the seat reclining apparatus of the present embodiment is mounted. A seat reclining apparatus for a vehicle  10  (hereinafter simply referred to as a seat reclining apparatus  10 ) according to the present embodiment is provided at each side of a vehicle seat in a width direction (i.e., right and left direction). In the following, a structure of one seat reclining apparatus  10  will be explained, however, the other seat reclining apparatus  10  has substantially the same structure. 
     As illustrated in  FIGS. 1 and 2 , the seat reclining apparatus  10  includes a lower frame  1   c , a lower plate  1 , an upper plate  20 , an upper frame  1   d , a reclining lock mechanism  4 , and a reclining memory mechanism  9 . The lower frame  1   c  supports a seat cushion  1   a . The lower plate  1  is attached to the lower frame  1   c . The upper plate  20  is rotatably supported by the lower plate  1 . The upper frame  1   d , which supports a seatback  1   b , is relatively rotatable with respect to the upper plate  20 . The reclining lock mechanism  4  serving as a first lock mechanism permits or restricts a relative rotation of the upper plate  20  with respect to the lower plate  1 . The reclining memory mechanism  9  serving as a second lock mechanism permits or restricts a relative rotation of the upper frame  1   d  with respect to the upper plate  20 . The upper plate  20  includes an internally toothed gear plate  2  that is engageable and disengageable with the reclining lock mechanism  4 , and a ratchet plate  3  that is engageable and disengageable with the reclining memory mechanism  9 . 
     The lower frame  1   c  is provided at each side of the seat cushion  1   a  in the width direction (i.e., the lower frames  1   c  are provided at right and left sides) so as to extend in a longitudinal direction of the vehicle. Each lower frame  1   c  is formed by a press-molding and to which an upper rail  1   e  is connected. The upper rail  1   e  is slidably attached to a lower rail  1   f  fixed to a surface of a vehicle floor. The lower frames  1   c  arranged at right and left sides of the seat cushion  1   a  are connected to each other by means of a rod that extends in the right and left direction (width direction) of the vehicle. 
     The upper frame  1   d  is provided at each side of the seatback  1   b  in the width direction (i.e., the upper frames  1   d  are provided at the right and left sides) so as to extend in a vertical direction of the vehicle when the vehicle seat is in a seating state. The upper frames  1   d  arranged at the right and left sides of the seatback  1   b  are connected to each other by means of a rod that extends in the right and left direction (width direction) of the vehicle. As illustrated in  FIG. 1 , a lower end portion of the upper frame  1   d  is positioned at an inner side in the width direction of a rear end portion of the lower frame  1   c . The lower end portion of the upper frame  1   d  and the rear end portion of the lower frame  1   c  are operatively connected to each other via the lower plate  1 , the gear plate  2 , and the like. The upper frame  1   d  is biased in a direction where the seatback  1   b  is tilted forward by mean of a spring. 
     As illustrated in  FIGS. 2 and 3 , the lower plate  1  having a disc shape is fixed to the lower frame  1   c  by means of welding. The gear plate  2  is fixed to the ratchet plate  3 , which is engageable and disengageable with the reclining memory mechanism  9 , by means of welding. The gear plate  2  is rotatably attached to the lower plate  1  via the reclining lock mechanism  4 . The ratchet plate  3  is rotatably attached to the upper frame  1   d  via the reclining memory mechanism  9 . 
     The lower plate  1  includes a recess portion  11  opening towards and facing the gear plate  2  and molded by half die cutting. The recess portion  11  includes an inner peripheral surface  11   a  centered at a rotational axis C of both of the gear plate  2  and the lower plate  1 . The gear plate  2  includes an outer peripheral surface  21  that makes slidable contact with the inner peripheral surface  11   a  of the lower plate  1 . When the gear plate  2  rotates relative to the lower plate  1 , the outer peripheral surface  21  of the gear plate  2  functions as a shaft while the inner peripheral surface  11   a  of the lower plate  1  functions as a bearing. 
     A folder  5  is arranged to cover outer peripheries of the gear plate  2  and the lower plate  1 . The folder  5  makes contact with the lower plate  1  at a side surface (i.e., inner peripheral surface) and maintains the gear plate  2  and the lower plate  1  to be rotatable with respect to each other. In addition, the folder  5  is processed, being bent to assemble and hold the lower plate  1  on the gear plate  2  in the final process of the assembly of the seat reclining apparatus  10 . 
     The gear plate  2  includes a recess portion  25  molded by half die cutting and opening towards the lower plate  1 . Internal teeth  25   a  are formed at an entire inner periphery of the recess portion  25  centered at the rotational axis C thereof. Another recess portion  26  is concentrically formed at a radially inner side of the recess portion  25  in a stepped manner by half die cutting. Projections  27   a  and  27   c  (see  FIG. 2 ) are formed at a portion of an inner periphery  28  of the recess portion  26 . 
     The reclining lock mechanism  4  is provided between the lower plate  1  and the gear plate  2 . The reclining lock mechanism  4  includes two types of pawls, i.e., one first pawl  50  and two second pawls  60 , arranged at equally spaced angles within a surface perpendicular to the rotational axis C. As illustrated in detail in  FIGS. 6 and 7 , the pawl  50  includes a projection  51  on a surface. Each of the second pawls  60  has the same shape as that of the first pawl  50  and only differs from the first pawl  50  in that the second pawl  60  does not include a projection such as the projection  51 . 
     Each of the pawls  50  and  60  is made by a plate-shaped steel material. The pawl  50  includes a first surface portion  52  and a second surface portion  53  to be connected to each other in a stepped manner. In the same way, the pawl  60  includes a first surface portion  62  and a second surface portion  63  to be connected to each other in a stepped manner. As a whole, each of the pawls  50  and  60  is formed into substantially a rectangular shape. The pawl  50  includes external teeth  54  at an end surface of the first surface portion  52  to be engageable with the internal teeth  25   a  of the gear plate  2 . In the same way, the pawl  60  includes external teeth  64  at an end surface of the first surface portion  62  to be engageable with the internal teeth  25   a  of the gear plate  2 . A back cam surface  55  is formed at an opposite end surface of the external teeth  54  at a stepped portion between the first surface portion  52  and the second surface portion  53 . In addition, a back cam surface  65  is formed is formed at an opposite end surface of the external teeth  64  at a stepped portion between the first surface portion  62  and the second surface portion  63 . Further, an elongated cam hole  56  is formed at the second surface portion  53  so as to penetrate in a thickness direction thereof. In the same way, an elongated cam hole  66  is formed at the second surface portion  63  so as to penetrate in a thickness direction thereof. Both end portions (surfaces) of the pawl  50  in a width direction across the external teeth  54  and perpendicular to the thickness direction are in parallel with each other. In the same way, both end portions (surfaces) of the pawl  60  in a width direction across the external teeth  64  and perpendicular to the thickness direction are in parallel with each other. 
     As illustrated in  FIG. 4 , six recess portions  12  are formed inside of the recess portion  11  of the lower plate  1 . Each of the recess portions  12  is formed by half die cutting to open in a direction opposite from a direction where the recess portion  11  is opening. Six recess portions  12  are grouped into three pairs, each pair being constituted by the recess portions  12  facing each other across one of the pawls  50  and  60 . Three pairs of recess portions  12  are arranged at equally spaced intervals in a circumferential direction of the recess portion  11  relative to the rotational axis C and at equal distances from the rotational axis C. Each of the recess portions  12  includes a guide wall  121  (slide portion) and a cam engagement portion  122  (engagement portion). The guide walls  121  of the recess portions  12  in the same group face in parallel with each other. A width (length) between the facing guide walls  121  is substantially the same as a width of each of the pawls  50  and  60 . Each of the pawls  50  and  60  is slidably movable towards or away from the rotational axis C while being fitted into a space between the facing guide walls  121  and being guided thereby. Since the guide wall  121  and the cam engagement portion  122  are integrally formed at the recess portion  12 , the number of components of the seat reclining apparatus  10  as a whole is reduced to thereby achieve a compact structure. 
     The reclining lock mechanism  4  further includes a cam  40 . The cam  40  includes a cam surface  41  that is arranged to be rotatable about the rotational axis C within the recess portion  25  of the gear plate  2 . Specifically, three cam surfaces  41  are arranged at equally spaced angles relative to the rotational axis C. Each of the cam surfaces  41  includes a pawl pressing portion  411  and an aligning portion  412 . The pawl pressing portion  411  is capable of making contact with each of the back cam surfaces  55  and  65  of the pawls  50  and  60  (see  FIGS. 6 and 7 ). The external teeth  54  and  64  of the pawls  50  and  60 , respectively, are pressed to engage with the internal teeth  25   a  of the gear plate  2  by means of the rotation of the cam  40 . The aligning portion  412  is engageable and disengageable with the cam engagement portion  122  of the recess portion  12 . That is, three aligning portions  412  engage with three cam engagement portions  122 , respectively, at substantially the same time by means of the rotation of the cam  40 . In addition, projection pins  47  are formed at respective portions of a surface of the cam  40  between the respective cam surfaces  41  and the rotational axis C. The projection pins  47  extend to be inserted into the elongated cam holes  56  and  66  of the pawls  50  and  60 , respectively. 
     As illustrated in  FIGS. 2 and 4 , a hinge shaft  70  is inserted into through-holes  13 ,  42 ,  23 , and  3   a  (see  FIG. 8 ) formed at the lower plate  1 , the cam  40 , the gear plate  2 , and the ratchet plate  3 , respectively, so as to support the lower plate  1 , the cam  40 , the gear plate  2 , and the ratchet plate  3  to be rotatable with respect to the hinge shaft  70 . The hinge shaft  70  is arranged on the rotational axis C. Further, a spline portion  71  is provided at a substantially axially center of the hinge shaft  70 . The spline portion  71  includes multiple grooves at an outer periphery thereof that extend axially and opens radially. The through-hole  42  of the cam  40  includes a female spline portion  43  that engages with the spline portion  71  of the hinge shaft  70 . The hinge shaft  70  and the cam  40  are configured to integrally rotate. The spline portion  43  of the cam  40  is formed to be slightly larger than the spline portion  71  of the hinge shaft  70 , thereby forming a clearance between the cam  40  and the hinge shaft  70  in a radial direction. Accordingly, the cam  40  is movable relative to the hinge shaft  70  (i.e., movable around the hinge shaft  70 ) within the recess portion  25  of the gear plate  2  so as to move in directions where the pawl pressing portions  411  are formed. 
     The hinge shaft  70  further includes a serration portion  74  at an outer periphery of one of axial end portions. The serration portion  74  includes multiple tooth grooves extending in an axial direction thereof. A reclining operation handle  75  having a serration portion that engages with the serration portion  74  of the hinge shaft  70  is integrally attached to the serration portion  74  of the hinge shaft  70 . The operation handle  75  is provided at only one of the seat reclining apparatuses  10  at the right and left sides. With the exception of this point, the seat reclining apparatuses  10  provided at the right and left sides have the same structures as each other. 
     As illustrated in  FIG. 3 , the lower plate  1  includes a recess portion  16  concentric with the recess portion  11  and formed at a radially inner side thereof in a stepped manner by half die cutting. A groove is formed at a portion on an inner peripheral surface of the recess portion  16  to extend radially outwardly. The cam  40  includes a boss portion  45  where a groove  46  is formed as illustrated in  FIG. 2 . Then, a spiral spring  49  of which one end engages with the groove formed at the recess portion  16  and of which the other end engages with the groove  46  of the cam  40  is provided in such a manner that a center of the spring  49  substantially matches the rotational axis C. The spring  49  biases the cam  40  to rotate in a counterclockwise direction in  FIG. 4 . As a result, the pawls  50  and  60  move in a radially outward direction (towards the internal teeth  25   a ) from the rotational axis C by means of movements of the projection pins  47  formed at the cam  40  and the elongated cam holes  56  and  66  formed at the pawls  50  and  60 . At the same time, the back cam surfaces  55  and  65  of the pawls  50  and  60  are pressed in the radially outward direction (towards the internal teeth  25   a ) by the pawl pressing portions  411  of the respective cam surfaces  41 . The internal teeth  25   a , and the external teeth  54  and  64  strongly engage with each other accordingly. 
       FIG. 8  is an exploded perspective view illustrating a structure for assembling the ratchet plate  3  and the reclining memory mechanism  9  on each other. As illustrated in  FIGS. 8 and 3 , the ratchet plate  3 , which is formed into a disc shape, includes the through-hole  3   a  at a center. The ratchet plate  3  and the reclining memory mechanism  9  are arranged between two frame members  18  and  19  constituting a portion of the upper frame  1   d . The frame members  18  and  19  are connected to a main frame also constituting the upper frame  1   d . A recess portion  3   b  formed at an inner periphery of the through-hole  3   a  of the ratchet plate  3  engages with a protruding portion  29  formed at the gear plate  2  (see  FIG. 3 ). The ratchet plate  3  and the gear plate  2  are fixed by means of welding. 
     A pawl  93 , a lever  94 , and a cam  95  each serving as a structural member of the reclining memory mechanism  9  are provided between the frame members  18  and  19 . A pin P 1  fixed to both of the frame members  18  and  19  is inserted into a through-hole  93   a  formed at the pawl  93  in such A manner that the pawl  93  is rotatably supported by the pin P 1 . A protruding portion  93   b  formed at the pawl  93  engages with a recess portion  3   c  formed at an outer peripheral surface of the ratchet plate  3 . The recess portion  3   c  serves as an engagement portion and/or external teeth. 
     A pin P 2  fixed to both of the frame members  18  and  19  is inserted into a through-hole  94   a  formed at the lever  94  and a through-hole  95   a  formed at the cam  95 . The lever  94  and the cam  95  are rotatably supported by the pin P 2 . Because a pin  95   b  formed at the cam  95  by stamping is fitted into a hole  94   c  formed at the lever  94 , the cam  95  is non-rotatable with respect to the lever  94 . The cam  95  and the lever  94  integrally rotate. 
     A pin  93   c  formed at the pawl  93  by stamping is slidably inserted into an elongated bore  94   b  having a cloud shape and formed at the lever  94 . The pawl  93  rotates along with the rotation of the lever  94  by means of the elongated bore  94   b  and the pin  93   c . A spring  96  (see  FIG. 9 ) of which one end engages with the lever  94  and of which the other end engages with the frame member  18  of the upper frame  1   d  biases the lever  94  to rotate in the counterclockwise direction in  FIG. 8 . A wire operating together with a walk-in operation handle is connected to an end portion  94   d  of the lever  94 . 
     The recess portion  3   c  engaging with the pawl  93 , an arc surface  3   d  connected to the recess portion  3   c , a projection portion  3   e , and a slide surface  3   f  (a peripheral surface) are formed at the outer peripheral surface of the ratchet plate  3 . The projection portion  3   e  is formed at an opposite side from the arc surface  3   d  relative to the recess portion  3   c  so as to extend outwardly. The slide surface  3   f  is formed into an arc shape between the projection portion  3   e  and the arc surface  3   d . The frame member  19  includes a stopper  19   a  extending towards the frame member  18 . When the ratchet plate  3  rotates in the counterclockwise direction in  FIG. 8 , the protruding portion  3   e  makes contact with the stopper  19   a  to thereby restrict the rotation of the ratchet plate  3 . 
     A stopper member  8  is in contact with the slide surface  3   f  of the ratchet plate  3  in a frictionally engageable manner. The stopper member  8  is pivotally supported by the lower frame  1   c.  The stopper member  8 , which is formed into an elongated lever shape, includes a stepped portion  83  bent in a thickness direction thereof at a substantially center portion. The stopper member  8  also includes a first end  8   a  where a pivot hole  81  serving as a support portion is formed, and a second end  8   b  where a slide portion  82  is formed to frictionally engage with the slide surface  3   f  of the ratchet plate  3 . A pin P 4  is inserted into the pivot hole  81  and a hole  1   j  formed at the lower frame  1   c  to thereby support the stopper member  8  to be rotatable with respect to the lower frame  1   c . A spring  80  is disposed at a side peripheral surface of the pin P 4  that is inserted into the pivot hole  81  of the stopper member  8 . One end  80   a  of the spring  80  engages with the stepped portion  83  of the stopper member  8  while the other end  80   b  engages with an engagement portion  1   k  (see  FIG. 9 ) formed at the lower frame  1   c.    
     A reclining operation, a forward tilting operation, and a walk-in operation performed by the seat reclining apparatus  10  having the aforementioned structure for the vehicle seat will be explained below. The reclining operation is provided for adjusting a rotational position of the seatback  1   b  within a seating available range for an occupant or a passenger. The forward reclining operation and the walk-in operation are provided for bringing the rotational position of the seatback  1   b  forward (i.e., forward tilting position or state) relative to the seating available range so that ingress and egress to and from a seat in the rear of the seatback  1   b  (i.e., rear seat) is easily performed. More specifically, the forward tilting operation is performed when an occupant seated on the seat where the seat reclining apparatus  10  according to the present embodiment is provided operates the operation handle  75 . The walk-in operation is mainly performed when an occupant seated on the rear seat, an operator stepping out of the vehicle, or the like operates an operation lever provided at an upper portion of the seatback  1   b.    
     [Reclining Operation] 
       FIG. 4  illustrates a locked state of the reclining lock mechanism  4 . In the locked state, the pawl pressing portions  411  of the cam  40  and the back cam surfaces  55  and  65  of the pawls  50  and  60  are in contact with each other. The pawls  50  and  60  are pressed by the pawl pressing portions  411  of the cam  40 , so that the external teeth  54  and  64  of the pawls  50  and  60  and the internal teeth  25   a  of the gear plate  2  engage with each other. As a result, the rotation of the gear plate  2  relative to the lower plate  1  is restricted. In such case, because the cam  40  is movable relative to the hinge shaft  70  within the recess portion  25  in a direction where the pawl pressing portions  411  are formed, the cam  40  substantially uniformly presses the three pawls  50  and  60  to thereby obtain the secure locked state of the reclining lock mechanism  4  without looseness. 
     When the operation handle  75  is operated in the aforementioned locked state, the hinge shaft  70  integrally rotates with the cam  40  in the clockwise direction in  FIG. 4  against a biasing force of the spring  49 . Then, the pawl pressing portions  411  of the cam surfaces  41  disengage from the respective back cam surfaces  55  and  65  of the pawls  50  and  60 . At the same time, the pawls  50  and  60  are pulled towards the rotational axis C along the respective guide walls  121  by means of movements of the elongated cam holes  56  and  66  of the pawls  50  and  60 , and the projection pins  47  inserted into the respective cam holes  56  and  66 . As a result, the external teeth  54  and  64  of the pawls  50  and  60  disengage from the internal teeth  25   a . The seatback  1   b  supported by the upper frame  1   d  is movable to a desired position relative to the seat cushion  1   a  supported by the lower frame  1   c  accordingly. At this time, as illustrated in  FIG. 9 , the recess portion  3   c  of the ratchet plate  3  engages with the protruding portion  93   b  of the pawl  93 . Thus, the ratchet plate  3  integrally rotates with the frame members  18  and  19  constituting a portion of the upper frame  1   d , and the gear plate  2 . 
     The three aligning portions  412  of the cam  40  make engagement with the three cam engagement portions  122  at substantially the same time so that the cam  40  is centered by means of the cam engagement portions  122 . Thus, clearances formed between the internal teeth  25   a  and the external teeth  54  and  64  of the respective pawls  50  and  60  are substantially equal to each other. A possible rotational failure between the upper plate  20  and the lower plate  1  or deterioration in operational feeling because of an engagement between the pawls  50 ,  60  and a portion of the upper plate  20  (gear plate  2 ) can be eliminated. 
     [Forward Tilting Operation] 
     In a case where the seatback  1   b  is tilted forward to rotate relative to the seat cushion  1   a  beyond a predetermined angle, i.e., into a forward tilting angle range, while the locked state of the reclining lock mechanism  4  is being released (i.e., the reclining lock mechanism  4  is in an unlocked state), the projection  27   a  formed at the inner periphery of the recess portion  26  of the gear plate  2  rotates in the clockwise direction in  FIG. 4 . The projection  27   a  moves to be positioned between the projection  51  formed at a surface of the pawl  50  and the internal teeth  25   a  as illustrated in  FIG. 5 . When the operation handle  75  is released in such state, the cam  40  presses the pawl  50  in a direction where the pawl  50  engages with the internal teeth  25   a  by means of the biasing force of the spring  49 . However, the movement of the pawl  50  is blocked by the projections  27   a  and  51  in contact with each other, thereby preventing the engagement between the pawl  50  and the internal teeth  25   a . At this time, two pawls  60  are retained at positions where the pawls  60  are prevented from engaging with the internal teeth  25   a  by means of movements of the elongated cam holes  66  and the projection pins  47  inserted thereto, respectively. 
     Accordingly, the seatback  1   b  is able to rotate into the forward tilting angle range without the reclining lock mechanism  4  to be brought to the locked state. The seatback  1   b  greatly rotates forward at once by means of a biasing force of the spring arranged to bias the seatback  1   b  forward relative to the seat cushion  1   a , thereby facilitating ingress and egress to and from the rear seat. At this time, because the ratchet plate  3  is in engagement with the protruding portion  93   b  of the pawl  93 , the ratchet plate  3  integrally rotates with the frame members  18  and  19  constituting a portion of the upper frame  1   d.    
     When the seatback  1   b  is returned from the forward tilting state to a position where an occupant can be seated again by the operation of the operation handle  75  and the operation handle  75  is then released, the pawls  50 ,  60 , and the cam  40  are returned to the respective positions shown in  FIG. 4  to thereby achieve the strong locked state of the reclining lock mechanism  4 . 
     As specifically shown in  FIG. 4 , the three pawls  50  and  60  constituting the reclining lock mechanism  4  are arranged at a radially inner side of the internal teeth  25   a . The internal teeth  25   a  with which the pawls  50  and  60  engage are not divided or separated and are continuously formed. That is, when the projection  27   a  rotates in the counterclockwise direction in  FIG. 4  to be arranged at a position where the pawl  60  is positioned (i.e., the projection  27   a  partially or fully overlaps with the pawl  60  in  FIG. 4 ), all the pawls  50  and  60  are engageable with the internal teeth  25   a  because each of the pawls  60  does not include a projection such as the projection  51  that prevents the pawl  60  from engaging with the internal teeth  25   a . In addition, because the internal teeth  25   a  are formed at the entire inner periphery of the recess portion  25 , the external teeth  54  and  64  of the pawls  50  and  60  are engageable with any portion of the internal teeth  25   a . That is, each of the external teeth  54  and  64  of the pawls  50  and  60  are engageable with the entire internal teeth  25   a . An operational angle range in the rearward of the seatback  1   b  increases accordingly. 
     When the seatback  15  is tilted rearward relative to the seat cushion  1   a  to move behind the seating available range, the projection  27   c  serving as second stopper means formed at the inner periphery of the recess portion  26  of the gear plate  2  rotates in the counterclockwise direction in  FIG. 4  to make contact with the projection  51  serving as first stopper means formed at the surface of the pawl  50 . Consequently, the rotation of the gear plate  2  in the counterclockwise direction is limited. 
     [Walk-In Operation] 
     Next, an operation performed when the seatback  1   b  is forwardly tilted in a state where a reclining angle of the seatback  1   b  (i.e., a reclining angle adjusted position) is stored upon ingress and egress to and from the rear seat in the rear of the seatback  1   b  will be explained below. When the operation lever provided at the upper portion of the seatback  1   b  is operated by an occupant in the rear seat or an operator outside of the vehicle in the locked state shown in  FIG. 4 , the end portion  94   d  of the lever  94  is pulled upward by mean of the wire to thereby rotate the lever  94  in the clockwise direction in  FIG. 8  about the through-hole  94   a  against the biasing force of the spring  96  (see  FIG. 9 ). 
     Then, the pin  93   c  of the pawl  93  is pulled upward by means of an inner peripheral surface of the elongated bore  94   b  of the lever  94  into which the pin  93   c  is inserted, thereby rotating the pawl  93  in the counterclockwise direction in  FIGS. 8 and 9 . The engagement between the recess portion  3   c  of the ratchet plate  3  and the protruding portion  93   b  of the pawl  93  is released, which results in the frame members  18  and  19  constituting a portion of the upper frame  1   d  to be rotatable with respect to the ratchet plate  3 . The seatback  1   b  is movable and rotatable into the forward tilting angle range as in the same way as the forward tilting operation. The seatback  1   b  greatly rotates at once by means of the biasing force of the spring, thereby facilitating ingress and egress to and from the rear seat. 
     At this time, because the three pawls  50  and  60  are each in the locked state, i.e., the pawls  50  and  60  engage with the internal teeth  25   a , the lower plate  1 , the gear plate  2 , and the ratchet plate  3  are non-rotatable with respect to the lower frame  1   c . Accordingly, the seatback  1   b  rotates forward in a state where the rotational angle of the gear plate  2  relative to the lower plate  1 , i.e., the reclining angle adjusted position, is stored. 
     Once the forward rotation of the seatback  1   b  is started and then the protruding portion  93   b  of the pawl  93  disengages from the recess portion  3   c  of the ratchet plate  3 , the protruding portion  93   b  only moves and slides on the arc surface  3   d  of the ratchet plate  3  even if the occupant or the operator releases the operation lever provided at the upper portion of the seatback  1   b . The forward rotation of the seatback  1   b  is still available. The seatback  1   b  greatly rotates at once by means of the biasing force of the spring, thereby facilitating ingress and egress to and from the rear seat. 
     In a case where the seatback  1   b  is pulled rearward from the forward tilting state as mentioned above, the pawl  93  also moves rearward along with the rotation of the frame members  18  and  19 . The protruding portion  93   b  of the pawl  93  slidably moves on the arc surface  3   d  of the ratchet plate  3  accordingly. At this time, the lever  94  and the cam  95  are biased by the spring  96  in the counterclockwise direction in  FIG. 8 . Then, a lower end portion  95   c  of the cam  95  presses an upper end portion  93   d  of the pawl  93 . Accordingly, the pawl  93  is biased in the clockwise direction in  FIG. 8 , thereby pressing the protruding portion  93   b  of the pawl  93  against the arc surface  3   d . When the protruding portion  93   b  that is slidably moving reaches a point where the recess portion  3   c  is formed, the protruding portion  93   b  makes engagement with the recess portion  3   c.    
     [When Improper Operation is Conducted] 
     In a case where an improper operation is conducted, i.e., the operation handle  75  is operated during the walk-in operation and thus the external teeth  54  and  64  of the pawls  50  and  60  disengage from the internal teeth  25   a  of the gear plate  2 , for example, the gear plate  2  and the ratchet plate  3  to which the gear plate  2  is fixed may be rotatable with respect to the lower plate  1  regardless of the rotational position of the seatback  1   b . However, according to the present embodiment, the ratchet plate  3 , which is provided at each side of the vehicle seat in the width direction, frictionally engages with the slide portion  82  of the stopper member  8  via the slide surface  3   f  as illustrated in  FIG. 10 . Thus, the rotation of the gear plate  2 , which is fixed to the ratchet plate  3 , relative to the lower plate  1  is restricted. Even when the gear plate  2  is allowed to relatively rotate with respect to the lower plate  1  by means of the operation of the operation handle  75 , the rotation of the gear plate  2  relative to the lower plate  1  is still restricted by means of a rotational resistance force (resistance force) received by the ratchet plate  3 . As a result, change of a reclining memory angle determined on the basis of the relative position between the gear plate  2  and the lower plate  1  is restrained. In addition, even when a load is applied to the gear plate  2 , change of the reclining memory angle is restrained because the rotation of the gear plate  2  is restricted by the stopper member  8 . 
     Further, as illustrated in  FIG. 11 , in a case where a load is applied in the rearward direction to the seatback  1   b  by a forceful rearward rotation thereof so that a large load exceeding a frictional engagement force generated between the ratchet plate  3  and the stopper member  8  is applied to the ratchet plate  3  in the clockwise direction in  FIG. 11  in a state where an improper operation is conducted, i.e., the operation handle  75  is operated during the walk-in operation and thus the external teeth  54  and  64  of the pawls  50  and  60  disengage from the internal teeth  25   a  of the gear plate  2 , for example, the ratchet plate  3  slightly rotates in the clockwise direction in  FIG. 11 . When the large load is applied to the ratchet plate  3 , the ratchet plate  3  rotates while the slide portion  52  of the stopper member  8  is slidably in contact with the slide surface  3   f . Then, the stopper member  8  makes contact with the projection portion  3   e  continuously formed at the slide surface  3   f . The projection portion  3   e  projects, interrupting the direction of movement of the stopper member  8 . Therefore, at this time, the projection portion  3   e  receives the frictional engagement force larger than that which is received when the stopper member  8  slides on the slide surface  3   f , from the slide portion  82  of the stopper member  8 . As a result, the rotation of the ratchet plate  3  is restricted by means of the large frictional engagement force received at the projection portion  3   e.    
     Then, after the state illustrated in  FIG. 11 , the protruding portion  93   b  of the pawl  93  engages with the recess portion  3   c  of the ratchet plate  3  while the slide portion  82  of the stopper member  8  is in contact with the projection portion  3   e . When a load is further applied by a forceful rearward rotation thereof so that an extremely large load is applied to the ratchet plate  3  in the clockwise direction as illustrated in  FIG. 12  while the reclining lock mechanism  4  is in the locked state, the ratchet plate  3  rotates against a frictional resistance force received from the stopper member  8  at the projection portion  3   e , which pushes away the slide portion  82  of the stopper member  8 . In this case, the frame members  18  and  19  of the upper frame  1   d  are tilted rearward. 
     Accordingly, in a case where the operation handle  75  is operated during the walk-in operation and at that time the ratchet plate  3  rotates by receiving the large load, the protruding portion  93   b  of the pawl  93  and the recess portion  3   c  of the ratchet plate  3  engage with each other to achieve the locked state of the reclining memory mechanism  9  without the operation of the operation lever of the reclining memory mechanism  9 . In this state, the operation handle  75  of the reclining lock mechanism  4  is operated to thereby release the engagement between the internal teeth  25   a  of the gear plate  2  and the external teeth  54  and  64  of the pawls  50  and  60 . Then, the seatback  1   b  is returned to a previous position by the application of a load in a direction (for example, forward direction) opposite from a direction where the load is previously applied to thereby change the memory angle (for example, rearward direction). In such state, the operation handle  75  is released to cause the external teeth  54  and  64  of the pawls  50  and  60  to engage with the internal teeth  25   a  of the gear plate  2 . 
     According to the aforementioned embodiment, the slide portion  82  of the stopper member  8  frictionally engages with the slide surface  3   f  of the ratchet plate  3  integrally fixed to the gear plate  2 . Thus, the gear plate  2  receives a resistance force against the relative rotation with respect to the lower plate  1 . Therefore, even when the rotation of the gear plate  2  relative to the lower plate  1  is permitted by the reclining lock mechanism  4  in a state where the rotations of the frame members  18  and  19  relative to the ratchet plate  3  are permitted by the reclining memory mechanism  9 , the rotation of the gear plate  2  relative to the lower plate  1  is restricted. As a result, the change of the reclining memory angle determined on the basis of the relative position between the gear plate  2  and the lower plate  1  is restrained. In addition, even when a load is applied to the gear plate  2 , the rotation of the ratchet plate  3  is restricted by the stopper member  8 , thereby restraining the change of the reclining memory angle. 
     Further, the spring  80  is disposed around the pivot hole  81  of the stopper member  8  for biasing the stopper member  8  to rotate in a direction where the slide portion  82  makes contact with the ratchet plate  3 . In a case where a large load that exceeds the biasing force of the spring  80  is applied to the ratchet plate  3  and that exceeds the frictional engagement force of the stopper member  8 , the rotation of the ratchet plate  3  is permitted, thereby preventing the large load from being concentrated and applied to the slide portion  82  of the stopper member  8 . The deformation, damage, and the like of the stopper member  8  are avoidable accordingly. The excessive strength of the stopper member  8  is not required. Further, increase of weight, cost, and space of the stopper member  8  for ensuring the strength are not required. 
     When the large load is applied to the ratchet plate  3 , the slide portion  82  of the stopper member  8  slidably moves along the slide surface  3   f . Then, the movement of the slide portion  82  is blocked by the projection portion  3   e  that extends from the slide surface  3   f . Accordingly, the ratchet plate  3  is prevented from excessively rotating to thereby restrain the change of the reclining memory angle. 
     When the seatback  1   b  is tilted rearward in a state where the aforementioned improper operation is conducted, the projection  27   c  of the gear plate  2  makes contact with the projection  51  of the pawl  50 , so that the rotation of the gear plate  2  in the counterclockwise direction is restricted. Accordingly, the upper frame  1   d  is prevented from rotating beyond an engagement point (i.e., predetermined rotational position) between the protruding portion  93   b  of the pawl  93  of the reclining memory mechanism and the recess portion  3   c  of the ratchet plate  3  by means of the contact between the projections  27   c  and  51 . As a result, the protruding portion  93   b  of the pawl  93  is returned to a state to engage with the recess portion  3   c  of the ratchet plate  3 . 
     According to the aforementioned embodiment, the stopper member  8  is formed into the elongated lever shape including the pivot hole  81  at the first end  8   a  and the slide portion  82  at the second end  8   b , the pivot hole  81  being rotatably supported by the lower frame  1   c  and the slide portion  82  being frictionally engageable with the upper plate  20 . The seat reclining apparatus  10  further includes the spring  80  of which one end  80   a  engages with the stopper member  8  and of which the other end  80   b  is supported by the lower frame  1   c , the spring  8  being disposed around the pivot hole  81  and biasing the stopper member  8  to rotate in a direction where the slide portion  82  makes contact with the upper plate  20 . 
     Further, according to the aforementioned embodiment, the upper plate  20  includes the slide surface  3   f  with which the slide portion  82  of the stopper member  8  makes contact and the projection portion  3   e  continuously formed from the slide surface  3   f  to extend therefrom and making contact with an end of the slide portion  82  to restrict the relative rotation of the upper plate  20  to the lower plate  1 . 
     Furthermore, according to the aforementioned embodiment, the upper plate  20  includes the internally toothed gear plate  2  including the internal teeth  25   a  engageable and disengageable with the reclining lock mechanism  4  and the ratchet plate  3  fixed to the internally toothed gear plate  2  and including the recess portion  3   c  engageable and disengageable with the reclining memory mechanism  9 . 
     The angle of the upper plate  20  relative to the lower plate  1  that is adjusted by the reclining lock mechanism  4  (i.e., reclining angle) is stored. When the engagement between the protruding portion  93   b  of the pawl  93  of the reclining memory mechanism  9  and the recess portion  3   c  of the ratchet plate  3  is released, the rotation of the upper frame  1   d  relative to the upper plate  20  is permitted with the reclining memory angle being maintained. Thus, the walk-in operation is achievable with the reclining memory angle being maintained. 
     The ratchet plate  3  includes the slide surface  3   f  and the projection portion  3   e.    
     In a case where the engagement between the protruding portion  93   b  of the pawl  93  of the reclining memory mechanism  9  and the recess portion  3   c  of the ratchet plate  3  is released, and further the reclining lock mechanism  4  is in the unlocked state, the stopper member  8  frictionally engages with the slide surface  3   f  of the ratchet plate  3 , thereby restricting the rotation of the ratchet plate  3 . The ratchet plate  3  is able to restrict the rotation of the gear plate  2  integrally fixed to the ratchet plate  3 , so that a possible change or displacement of the reclining memory angle is restrained. 
     Furthermore, according to the aforementioned embodiment, the stopper member  8  is formed into the elongated lever shape including the pivot hole  81  at the first end  8   a  and the slide portion  82  at the second end  8   b , the pivot hole  81  being rotatably supported by the lower frame  1   c  and the slide portion  82  being frictionally engageable with the upper plate  20 , and the upper plate  20  includes the internally toothed gear plate  2  including the internal teeth  25   a  engageable and disengageable with the reclining lock mechanism  4  and the ratchet plate  3  fixed to the internally-toothed gear plate  2  and including the recess portion  3   c  engageable and disengageable with the reclining memory mechanism  9 . The seat reclining apparatus  10  further includes the spring  80  of which one end  80   a  engages with the stopper member  8  and of which the other end  80   b  is supported by the lower frame  1   c , the spring  80  being disposed around the pivot hole  81  and biasing the stopper member  8  to rotate in a direction where the slide portion  82  makes contact with the upper plate  20  (ratchet plate  3 ). 
     Furthermore, according to the aforementioned embodiment, the upper plate  20  includes the slide surface  3   f  with which the slide portion  82  of the stopper member  8  makes contact and the projection portion  3   e  continuously formed from the slide surface  3   f  to extend therefrom and making contact with an end of the slide portion  82  to restrict the relative rotation of the upper plate  20  to the lower plate  1 , and the ratchet plate  3  includes the slide surface  3   f  and the projection portion  3   e.    
     The principles, preferred embodiment and mode of operation of the present invention have been described in the foregoing specification. However, the invention which 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 which fall within the spirit and scope of the present invention as defined in the claims, be embraced thereby.