Patent Publication Number: US-2023150411-A1

Title: Seat back

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is based on Japanese Patent Applications No. 2021-187642 filed on Nov. 18, 2021, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a seat back. Specifically, the present disclosure relates to a seat back that supports a back of a seated person. 
     BACKGROUND ART 
     JP-A-2002-142913 discloses a seat back including, on a back thereof, a back board serving as a decorative plate. The above-described seat back includes a pair of upper and lower auxiliary frames that are provided on side frames of a back frame forming an internal skeleton across a seat width direction. The back board is claw-fitted from the rear to each auxiliary frame and attached to the back frame. 
     SUMMARY OF DISCLOSURE 
     In the seat back described in JP-A-2002-142913, a peripheral edge of the above-described back board is fitted to a back pad to be assembled to the back frame. Accordingly, when the occupant puts a finger to an end of the back board, there is a concern that the back pad may be pushed away and the finger may enter an inside of the seat back. Therefore, the present disclosure provides a seat back capable of preventing a finger from entering an inside of a seat from an end of a back board. 
     In order to solve the above-described matters, the seat back according to the present disclosure has the following aspects. 
     According to an aspect of the disclosure, a seat back includes a back board serving as a decorative plate on a rear side of the seat back, a back frame that is configured to support a seated person, a back pad that is disposed at a front side the back frame, is configured to supports the seated person, and has elasticity, an intermediate board that is interposed between a peripheral edge of the back pad and a peripheral edge of the back board, and a back cover that is disposed over the back pad and the intermediate board. 
     According to the above-described configuration, the peripheral edge of the back board is fitted to the intermediate board. Therefore, it is possible to prevent a finger from entering an inside without expanding the fitting portion when the finger is hung. Further, the back cover is placed between the intermediate board and the back pad, so that it is possible to prevent the finger from entering the inside. 
     The seat back according to the present disclosure may be further configured that an end portion of the back cover is disposed between the intermediate board and the back board. 
     According to the above-described configuration, the end of the back cover may be pulled into the back board and fastened with good appearance. 
     The seat back according to the present disclosure may be further configured that the intermediate board includes a pair of intermediate board members that are provided on both outer side portions of the back frame in a seat width direction, the intermediate board members are fixed to side frame portions at both sides of the back frame, and the back board is provided over the pair of intermediate board members, and is fixed to at least one of the back frame or the intermediate board members. 
     According to the above-described configuration, the intermediate boards may prevent a finger from entering the inside from both side edge portions of the back board in the seat width direction. 
     The seat back according to the present disclosure may be further configured that the back board includes a first coupling portion coupled to the back frame with a first coupling force and second coupling portions coupled to the at least one of the back frame or the intermediate board members with a second coupling force smaller than the first coupling force, and when a given load is applied to the back board from a front side of the seat back, the second coupling portions are decoupled from the at least one of the back frame or the intermediate board members while the first coupling portion are coupled to the back frame. 
     According to the above-described configuration, the second coupling portions are decoupled from an engaged state, so that the excessive load from the front of the seat may be released. Further, by providing the second coupling portions, it is possible to easily control a position at which the load on the back board is likely to be released. 
     The seat back according to the present disclosure may be further configured that the first coupling portion is coupled to an upper frame of the back frame, and the second coupling portions are coupled to the intermediate board members at a position lower than a position of the first coupling portion in a horizontal direction of the seat back. 
     According to the above-described configuration, a coupling state of a portion coupled at a position lower than that of the upper frame of the back board is likely to be released. Accordingly, a load applied to a portion where a body pressure of the seated person is high is likely to be released. 
     The seat back according to the present disclosure may be further configured that the first coupling portion includes a clip detachably attached to a clip attachment portion of the back board, the clip is inserted into an insertion hole of the back frame from a rear side of the back frame and is locked by snap fitting on both sides of a peripheral edge of the insertion hole in a direction orthogonal to an insertion direction of the clip, each of the second coupling portions includes a claw protruding from the back board, and each of the claw is inserted into a corresponding one of coupling holes of the intermediate board members from the rear side and is locked by snap fitting on one side of a peripheral edge of the coupling hole in a direction orthogonal to an insertion direction of the claw. 
     According to the above-described configuration, the first coupling portion may be firmly coupled with a simple configuration in which the clip is simply inserted from the rear. Further, the clip is attachable and detachable, so that the back board may be easily removed from the back frame, and maintainability may be improved. 
     The seat back according to the present disclosure may be further configured that the clip attachment portion is opened upward and configured to accept the clip from above. 
     According to the above-described configuration, when an excessive load is applied from the front of the seat, the clip is less likely to come off the back board. Further, even if the back board receives a force lifted from below due to the above-described load, it is possible that the clip attachment portion is less likely to come off from the clip. 
     The seat back according to the present disclosure may be further configured that the intermediate board members extend between the upper frame and a lower frame of the back frame along the side frame, the second coupling portions include an intermediate coupling portion provided below the first coupling portion, and a lower coupling portion provided below the intermediate coupling portion and coupled the intermediate board members with a larger coupling force than a coupling force of the intermediate coupling portion to the intermediate board members, and when a given load is applied to the back board from the front side of the seat back, the intermediate coupling portion is decoupled from at least one of the intermediate board members while the lower coupling portion is coupled to the intermediate board members. 
     According to the above-described configuration, the intermediate coupling portion, to which the body pressure of the seated person is likely to be strongly applied, is more likely to come off. Accordingly, the load applied to the seated person may be more appropriately released. 
     The seat back according to the present disclosure may be further configured that the intermediate coupling portions are provided at a plurality of positions arranged in an upper-lower direction. 
     According to the above-described configuration, an interval between the intermediate coupling portions may be narrowed. Accordingly, it is possible to appropriately couple the back board to a fitting portion with the intermediate board such that a gap is less likely to be formed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a perspective view of a seat back according to a first embodiment; 
         FIG.  2    is a perspective view in which a back cover of the seat back is transparentized; 
         FIG.  3    is a rear view of the seat back; 
         FIG.  4    is an exploded perspective view of a back frame, a side board, and a back board; 
         FIG.  5    is an exploded perspective view of the side board and the back board as viewed from the front; 
         FIG.  6    is an enlarged perspective view of a clip attachment portion in  FIG.  5   ; 
         FIG.  7    is a rear view of the seat back from which the back board is removed; 
         FIG.  8    is a cross-sectional view taken along a line VIII-VIII in  FIG.  3   ; 
         FIG.  9    is a cross-sectional view taken along a line IX-IX in  FIG.  3   ; 
         FIG.  10    is a cross-sectional view taken along a line X-X in  FIG.  3   ; 
         FIG.  11    is a cross-sectional view taken along a line XI-XI in  FIG.  3   ; 
         FIG.  12    is a cross-sectional view taken along a line XII-XII in  FIG.  3   ; and 
         FIG.  13    is an enlarged cross-sectional view of an attachment structure of a clip in  FIG.  12   . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments of the present disclosure will be described with reference to  FIGS.  1  to  13   . In the following description, directions such as front, rear, upper, lower, left, and right indicate directions shown in the drawings. 
     First Embodiment 
     First, a configuration of a seat back  1  according to a first embodiment of the present disclosure will be described. The seat back  1  according to the present embodiment is implemented as a backrest portion of a seat on which an occupant of an automobile sits. As shown in  FIGS.  1  and  2   , the seat back  1  includes a frame-shaped back frame  10  that supports a load of a seated person, a back pad  50  that is assembled to a front portion of the back frame  10 , a back cover  60  that covers the back pad  50  from the front, and a back board  40  that is assembled to a back portion of the back frame  10 . The seat back  1  may elastically support the load of the seated person by the back pad  50 . The back board  40  is a decorative plate formed of resin, and has a concave curved shape recessed forward. The back board  40  extends over both outer side portions of the back frame  10  in a seat width direction. 
     As shown in  FIGS.  2  and  4   , the seat back  1  includes a pair of left and right side boards  30  that are assembled to both left and right side portions of the back frame  10  from the rear, and that are fitted to both left and right end portions of the back board  40  from the front. Each of the side boards  30  is a vertical plate-shaped member elongated in a height direction along a respective one of the side portions of the back frame  10 . Each of the side boards  30  is formed of resin and has a U-shaped cross section that opens forward as viewed from above (see  FIGS.  9  to  11   ). Each of the side boards  30  protrudes outward from a respective one of the side portions of the back frame  10  in the seat width direction. A front surface portion of each of the side boards  30  supports, from the rear, each rear end portion of the back pad  50  covering both side surface portions of the back frame  10  from an outside in the seat width direction. 
     As described above, the front surface portion of each of the side boards  30  abuts against the back pad  50 , and a rear surface portion of each of the side boards  30  is fitted to the back board  40 . That is, each of the side boards  30  is sandwiched between the left and right end portions of the back board  40  and the rear end portions on the left and right of the back pad  50  in a front-rear direction. Then, the back cover  60  is placed over each of the side boards  30  from the front of a seat, and covers the back pad  50  and an abutting portion between the back pad  50  and each of the side boards  30  from the outside. An end of the back cover  60  is pulled into the inside from a gap between each of the side boards  30  and the back cover  60  and is fastened. The back cover  60  prevents a finger from entering the abutting portion between each of the side boards  30  and the back pad  50 . 
     A fitting portion between each of the side boards  30  and the back board  40  is implemented as a fitting portion at which solid objects are fitted to each other. Accordingly, unlike a configuration in which the back board  40  and the back pad  50  are directly fitted to each other, when the finger of the occupant is put on the fitting portion between the back board  40  and each of the side boards  30 , it is possible to prevent the finger from entering the inside of the back board  40  without widening the gap of the above-described fitting portion. Here, the side board  30  corresponds to an “intermediate board” according to the present disclosure. 
     &lt;Back Frame  10 &gt; 
     Hereinafter, a specific configuration of the seat back  1  will be described. The back frame  10  is formed of metal. The back frame  10  includes vertically long plate-shaped side frames  13  that form side skeletons on both the left and right, a horizontally long plate-shaped upper frame  11  that extends between upper portions of the side frames  13 , and a horizontally long plate-shaped lower frame  12  that extends between lower portions of the side frames  13 . Each of the side frames  13  includes a reclining plate  14  connected to a seat cushion (not shown) on both left and right outer sides of a lower portion of the side frame  13 . The upper frame  11  forms an upper skeleton and has a U-shaped cross section that opens rearward in a side view (see  FIG.  12   ). A headrest (not shown) serving as a headrest portion for the seated person is attached to an upper portion of the seat back  1 , and the upper frame  11  includes, on an upper surface thereof, two holders  15  that are arranged in the seat width direction and into which a headrest stay (not shown) is inserted from above (see  FIG.  2   ). 
     &lt;Bracket  20 &gt; 
     As shown in  FIG.  4   , the back frame  10  includes a bracket  20  that is welded over each of the side frames  13  in a manner of covering the U-shaped opening of the upper frame  11  from the rear. The bracket  20  includes a horizontally long plate-shaped covering portion  21  provided behind the upper frame  11 , and welded portions  22  that extend from both left and right ends of the covering portion  21  and that are welded to upper portions of the side frames  13 . The bracket  20  is integrally formed with the back frame  10  by a part of a peripheral edge of each of the welded portions  22  being welded to a respective one of the side frames  13 . 
     The bracket  20  has circular insertion holes  23  formed at two symmetrical positions on the left and right of the covering portion  21 , and rectangular locking holes  24  formed at lower portions of the welded portions  22 . An upper portion of the back board  40  is coupled to the insertion holes  23  by clips C (see  FIGS.  5  and  6   ) to be described later. Each of the insertion holes  23  is formed in a portion that protrudes in a convex shape toward the rear of the covering portion  21 . Accordingly, the clips C are easily inserted into the insertion holes  23 . Upper portions of the side boards  30  are coupled to the locking holes  24  by hooks  31  (see  FIG.  5   ). 
     &lt;Side Board  30 &gt; 
     Basic structures of the side boards  30  are symmetrical to each other. Therefore, hereinafter, the configuration of the side board  30  provided on the left shown in  FIGS.  4 ,  5 , and  7    will be described as a representative of the side boards  30 . As shown in  FIG.  5   , the side board  30  includes a hook  31  protruding forward from an upper region of the front surface portion of the side board  30 , and three claws  32  formed on an inner surface portion of the hook  31 . Each of the claws  32  has a shape extending forward from the above-described inner surface portion and protruding outward in the seat width direction. 
     The hook  31  has a shape extending from the front surface portion of the side board  30  into a substantially J shape in a lateral direction in a side view. The hook  31  is inserted into the locking hole  24  on the left of the bracket  20  from the rear, so that the hook  31  is snap-fitted to the locking hole  24  in a state of being retained in the locking hole  24 . The three claws  32  are arranged at intervals in a height direction from a middle portion to a lower portion of the side board  30  in the height direction. Each of the claws  32  is locked to an inner edge of a rear edge portion that is bent inward of each of the side frames  13  in the seat width direction. As described above, each of the side boards  30  may be appropriately locked to a respective one of the side frames  13  so as not to form a gap over a wide range in the height direction. The side board  30  is assembled to the back frame  10  by the hooks  31  and the claws  32  described above. 
     As shown in  FIG.  4   , the side board  30  includes a fastening portion  33  to which the end of the back cover  60  is fastened to a back surface portion of the side board  30 , and three rectangular coupling holes  34  to which a left end portion of the back board  40  is claw-fitted from the rear. The three coupling holes  34  are arranged at intervals in the height direction from the middle portion to the lower portion of the side board  30  in the height direction. Each of the coupling holes  34  is formed in a portion that protrudes in a convex shape toward the rear of the back board  40 . Accordingly, the back board  40  is easily claw-fitted to the coupling holes  34 . The fastening portion  33  is a concave portion extending along the height direction of the side board  30 , and is opened forward. The fastening portion  33  is formed on an outer side with respect to each of the coupling holes  34  in the seat width direction. 
     As shown in  FIG.  9   , the end of the back cover  60  is placed along an outer surface portion of the side board  30 . The placed end of the back cover  60  is fastened to the back surface portion of the side board  30  by inserting a resin bead edge  61 , which is sewn in a manner of extending in a long shape along a tip of the end of the back cover  60 , into the fastening portion  33 . Accordingly, the end of the back cover  60  is fixed in a state of being pulled into a back surface side of the side board  30 . The fastening portion  33  is covered from the rear by the back board  40  by assembling the back board  40  to each of the side boards  30  from the rear. Accordingly, the end of the back cover  60  is pulled inward from the gap between the side board  30  and the back board  40 . Accordingly, the end of the back cover  60  may be fastened to the fastening portions  33  with good appearance. 
     &lt;Back Board  40 &gt; 
     As shown in  FIG.  5   , the back board  40  includes a clip attachment portion  41  to which the clip C to be inserted into the above-described bracket  20  from the rear is detachably attached, and an intermediate coupling portion  42  and a lower coupling portion  43  that are coupled to the side boards  30 . As shown in  FIG.  5   , two clip attachment portions  41  are arranged at an interval along an upper edge portion of the back board  40  in the left-right direction. As shown in  FIG.  6   , the clip attachment portion  41  has a hollow box shape protruding forward from a front surface portion of the back board  40 . Each of the clip attachment portions  41  includes a round hole-shaped fitting hole  41   a  penetrating at a center of the front face portion of the clip attachment portion  41  in the front-rear direction, an opening  41 c extending from the fitting hole  41   a  in a manner of opening the fitting hole  41   a  upward, and a narrowing portion  41   b  that narrows a hole width of a boundary portion between the fitting hole  41   a  and the opening  41 c in the left-right direction. 
     As shown in  FIGS.  8  and  13   , the clip C includes an iron-shaped insertion portion C 1 , a cylindrical fitting shaft C 2  that is formed at a center of a base end of the insertion portion C 1  and that extends in an axial direction, and a seat surface portion C 3  protruding in a flange shape from an end portion of the fitting shaft C 2 . The fitting shaft C 2  is wider than the narrowing portion  41   b  of the clip attachment portion  41  in a radial direction. As shown in  FIG.  6   , the clip C is assembled such that the fitting shaft C 2  is inserted into the fitting hole  41   a  of the clip attachment portion  41  from above in a state in which the insertion portion C 1  faces forward. Accordingly, the fitting shaft C 2  is fitted into the fitting hole  41   a  while elastically pressing and spreading the narrowing portion  41   b,  and is set in a state in which a peripheral edge of the fitting hole  41   a  is sandwiched between the base end of the insertion portion C 1  and the seat surface portion C 3  in the front-rear direction. 
     As shown in  FIG.  13   , the insertion portion C 1  of the clip C attached to the clip attachment portion  41  is inserted into the insertion hole  23  of the bracket  20  obliquely upward from the rear. Accordingly, as shown in  FIG.  8   , both side portions of the inserted insertion portion C 1  in the left-right direction are snap-fitted to a peripheral edge of the insertion hole  23 . Accordingly, the insertion portion C 1  generates a strong coupling force with respect to the insertion hole  23  and is prevented from coming off. In this way, by simply inserting the clip C into the insertion hole  23  from the rear, the upper portion of the back board  40  is assembled to the bracket  20 . The clip C is attachable to and detachable from the clip attachment portion  41 . Accordingly, even after the clip C has been inserted into the bracket  20 , the back board  40  may be easily removed from the bracket  20  with the clip C left. Accordingly, maintainability of the back board  40  may be improved. Here, the clip C corresponds to a “first coupling portion” according to the present disclosure. 
     As shown in  FIG.  5   , the intermediate coupling portion  42  is a rib-shaped member that is elongated in the height direction and that protrudes forward from the front surface portion of the back board  40 . The two intermediate coupling portions  42  are arranged at an interval in the height direction on the left and right of the back board  40 . Each of the intermediate coupling portions  42  is provided in an intermediate region of the back board  40  in the height direction. Each of the intermediate coupling portions  42  includes an intermediate claw  42   a  protruding inward from an inner surface of the intermediate coupling portion  42  in the seat width direction (see  FIGS.  9  and  10   ). The intermediate coupling portion  42  provided on an upper side is provided at a position that is closer to the upper frame  11  than is the lower frame  12  in the height direction. The intermediate coupling portion  42  provided on a lower side is provided at a position that is closer to the lower frame  12  than is the upper frame  11  in the height direction. 
     As shown in  FIG.  5   , the lower coupling portion  43  is a rib-shaped member that is elongated in the height direction and that protrudes forward from the front surface portion of the back board  40 . The lower coupling portions  43  are provided on the left and right of the back board  40  in a manner of being located below the intermediate coupling portions  42 . Each of the lower coupling portions  43  includes a lower claw  43   a  protruding inward from an inner surface of the lower coupling portion  43  in the seat width direction (see  FIG.  11   ). 
     As shown in  FIG.  4   , the intermediate coupling portions  42  and the lower coupling portions  43  are inserted into and coupled to the coupling holes  34  of the side boards  30  from the rear. As shown in  FIGS.  9  and  10   , the intermediate claw  42   a  of the inserted intermediate coupling portion  42  is locked to an inner edge of the coupling hole  34 . In the intermediate claw  42   a,  a locking surface  42   b  that abuts against a peripheral edge of the coupling hole  34  is inclined in a manner of extending obliquely forward with respect to a locked abutting surface  34   a  of the coupling hole  34 . As shown in  FIGS.  9  and  10   , an angle α between the locking surface  42   b  and the abutting surface  34   a  in the present embodiment is set to an angle of approximately 30 degrees. As shown in  FIG.  11   , the lower claw  43   a  of the inserted lower coupling portion  43  is locked to the inner edge of the coupling hole  34 . The lower claw  43   a  has a configuration in which the locking surface  43   b  abutting against the peripheral edge of the coupling hole  34  faces and abuts against the abutting surface  34   a  of the coupling hole  34  straight in the front-rear direction. 
     The intermediate coupling portions  42  and the lower coupling portions  43  are implemented such that the intermediate claws  42   a  and the lower claws  43   a  are locked only on one side in the direction (the left-right direction) orthogonal to an insertion direction with respect to the corresponding coupling holes  34  of the side board  30 . Accordingly, as compared with the clips C that are locked on both sides of the insertion holes  23  of the bracket  20  in the direction (the left-right direction) orthogonal to the insertion direction, coupling forces of the intermediate coupling portions  42  and the lower coupling portions  43  are small. Further, the intermediate coupling portions  42  are inclined to the locking surface  42   b  of the intermediate claw  42   a,  so that the coupling forces of the intermediate coupling portions  42  are smaller than those of the lower coupling portions  43 . Here, the intermediate coupling portion  42  and the lower coupling portion  43  correspond to a “second coupling portion” according to the present disclosure. 
     According to the above-described configuration, for example, when the seat back  1  receives a strong load from the seated person due to a rear collision of the automobile, the intermediate coupling portions  42  are decoupled from the side boards  30 . Specifically, when the above-described load is applied, an intermediate region of the back board  40  in the height direction receives a relatively high body pressure action from a vicinity of a waist of the seated person. At the intermediate coupling portions  42 , the above-described intermediate region of the back board  40  is coupled to the side boards  30 . Therefore, the load applied to the vicinity of the waist of the seated person may be appropriately released by decoupling the intermediate coupling portions  42 . When a larger load is applied, not only the intermediate coupling portions  42  but also the lower coupling portions  43  are decoupled from the side boards  30 . Accordingly, it is possible to release a load in a wide region from the vicinity of the waist of the seated person to a vicinity of buttocks of the seated person. 
     On the other hand, the clips C having large coupling forces do not come off from the bracket  20  even if the clips C receive the above-described load. Accordingly, the back board  40  is not completely decoupled from the back frame  10 , and there is no concern that the back board  40  falls out rearward. Even if the back board  40  receives a large load toward the rear due to the above-described rear collision, as shown in  FIG.  13   , the fitting holes  41   a  of the clip attachment portions  41  are supported by the insertion portions C 1  and the seat surface portions C 3  in a state of being prevented from coming off in the front-rear direction. Accordingly, it is possible to prevent the coupling of the clip attachment portions  41  and the clips C from being decoupled. 
     Even if the back board  40  receives a large force lifted from below due to the rear collision, the back board  40  is prevented from being decoupled upward from the clips C. Specifically, as shown in  FIG.  6   , the clips C are attached to the clip attachment portions  41  from above. Accordingly, lower edges of the fitting holes  41   a  are pressed against the clips C even if the back board  40  is lifted. Accordingly, it is possible to cause the upper portion of the back board  40  to be less likely to come off due to the above-described lifting force. 
     In summary, the seat back  1  according to the first embodiment has the following configuration. In the following description, reference signs in parentheses correspond to the configurations shown in the above-described embodiment. 
     That is, a seat back ( 1 ) according to the first embodiment includes, on a back thereof, a back board ( 40 ) serving as a decorative plate. The seat back ( 1 ) includes: a back frame ( 10 ) that is configured to support a load of a seated person; a back pad ( 50 ) that is disposed at a front side of the back frame ( 10 ), is configured to support a load of a seated person and has elasticity; an intermediate board ( 30 ) that is interposed at a fitting portion of a peripheral edge between the back pad ( 50 ) and the back board ( 40 ); and a back cover ( 60 ) that is placed over the back pad ( 50 ) and the intermediate board ( 30 ). 
     According to this configuration, the peripheral edge of the back board ( 40 ) is fitted to the intermediate board ( 30 ). Therefore, it is possible to prevent a finger from entering an inside without expanding the fitting portion when the finger is hung. Further, the back cover ( 60 ) is placed between the intermediate board ( 30 ) and the back pad ( 50 ), so that it is possible to prevent the finger from entering the inside. 
     An end of the back cover ( 60 ) is pulled between the intermediate board ( 30 ) and the back board ( 40 ). 
     According to this configuration, the end of the back cover ( 60 ) may be pulled into the back board ( 40 ) and fastened with good appearance. 
     A pair of the intermediate boards ( 30 ) are provided on both outer side portions of the back frame ( 10 ) in a seat width direction, and are fixed to side frames ( 13 ) on both side portions of the back frame ( 10 ). The back board ( 40 ) is disposed over the pair of intermediate boards ( 30 ), and is fixed to the back frame ( 10 ) and/or the pair of intermediate boards ( 30 ). 
     According to this configuration, the intermediate boards ( 30 ) may prevent a finger from entering the inside from both side edge portions of the back board ( 40 ) in the seat width direction. 
     Further, the back board ( 40 ) includes a first coupling portion (C) to be coupled to the back frame ( 10 ) and second coupling portions ( 42 ,  43 ) to be coupled to the back frame ( 10 ) and/or the intermediate boards ( 30 ) with a smaller coupling force than the first coupling portion (C). When an excessive load is applied to the back board ( 40 ) from the front of a seat, the second coupling portions ( 42 ,  43 ) are decoupled from a coupled state before the first coupling portion (C). 
     According to this configuration, the second coupling portions ( 42 ,  43 ) are decoupled from an engaged state, so that the excessive load from the front of the seat may be released. Further, by providing the second coupling portions ( 42 ,  43 ), it is possible to easily control a position at which the load on the back board ( 40 ) is likely to be released. 
     The first coupling portion (C) is coupled to an upper frame ( 11 ) of the back frame ( 10 ), and the second coupling portions ( 42 ,  43 ) are coupled to the pair of intermediate boards ( 30 ) at a position lower than that of the first coupling portion (C). 
     According to this configuration, a coupling state of a portion coupled at a position lower than that of the upper frame ( 11 ) of the back board ( 40 ) is likely to be released. Accordingly, a load applied to a portion where a body pressure of the seated person is high is likely to be released. 
     The first coupling portion (C) is implemented such that a clip (C) detachably attached to a clip attachment portion ( 41 ) of the back board ( 40 ) is inserted into an insertion hole of the back frame ( 10 ) from the rear and is locked by snap fitting on both sides of a peripheral edge of the insertion hole in a direction orthogonal to an insertion direction. The second coupling portions ( 42 ,  43 ) are implemented such that a claw protruding from the back board ( 40 ) is inserted into a coupling hole of the intermediate board ( 30 ) from the rear and is locked by snap fitting only on one side of a peripheral edge of the coupling hole in a direction orthogonal to an insertion direction. 
     According to this configuration, the first coupling portion (C) may be firmly coupled with a simple configuration in which the clip (C) is simply inserted from the rear. Further, the clip (C) is attachable and detachable, so that the back board ( 40 ) may be easily removed from the back frame ( 10 ), and maintainability may be improved. 
     The clip attachment portion ( 41 ) is opened upward so that the clip (C) may be fitted from above. 
     According to this configuration, when an excessive load is applied from the front of the seat, the clip (C) is less likely to come off the back board ( 40 ). Further, even if the back board ( 40 ) receives a force lifted from below due to the above-described load, it is possible that the clip attachment portion ( 41 ) is less likely to come off from the clip (C). 
     The intermediate board ( 30 ) extends between the upper frame ( 11 ) and a lower frame ( 12 ) of the back frame ( 10 ) along the side frame ( 13 ). The second coupling portions ( 42 ,  43 ) include an intermediate coupling portion ( 42 ) provided below the first coupling portion (C), and a lower coupling portion ( 43 ) that is provided below the intermediate coupling portion ( 42 ) and that is coupled with a larger coupling force than the intermediate coupling portion ( 42 ). When an excessive load is applied to the back board ( 40 ) from the front of a seat, the intermediate coupling portion ( 42 ) is decoupled from a coupled state before the lower coupling portion ( 43 ). 
     According to this configuration, the intermediate coupling portion ( 42 ), to which the body pressure of the seated person is likely to be strongly applied, is more likely to come off. Accordingly, the load applied to the seated person may be more appropriately released. 
     The intermediate coupling portions ( 42 ) are provided at a plurality of positions in an upper-lower direction. 
     According to this configuration, an interval between the intermediate coupling portions ( 42 ) may be narrowed. Accordingly, it is possible to appropriately couple the back board ( 40 ) to a fitting portion with the intermediate board ( 30 ) such that a gap is less likely to be formed. 
     Other Embodiments 
     Although the present disclosure has been described using one embodiment, the present disclosure may be implemented in various forms in addition to the above-described embodiment. 
     1. The seat back may also be widely applied to a seat provided for a vehicle other than an automobile such as a railway, or various vehicles such as an aircraft and a ship. 
     2. The intermediate board may be an upper board that covers the upper frame from the rear in addition to the side board that covers the side frame from the rear. Alternatively, the intermediate board may continuously cover the side frame and the upper frame from the rear. Alternatively, the intermediate board may be a single plate member provided continuously over the pair of left and right side frames. In addition to a configuration of the pair of left and right side boards, the side board may be provided on only one side of the left and right. 
     3. The back board may be fixed only to the back frame or may be fixed only to the pair of intermediate boards. The first coupling portion may couple the back board to the back frame with a screw or a bolt, in addition to the clip. The first coupling portion may be coupled to the side frame or the lower frame of the back frame. The first coupling portion may be coupled to the intermediate board. The second coupling portion may be coupled at a position higher than that of the first coupling portion. The second coupling portion may be coupled to the back frame. 
     4. The intermediate coupling portion may be provided at only one position in the upper-lower direction, or may be provided at three or more positions. The intermediate claw of the intermediate coupling portion may be inclined at an angle smaller than 30 degrees with respect to the abutting surface of the coupling hole. Further, as long as the intermediate claw may be locked to the coupling hole, the intermediate claw may be inclined at a larger angle. The lower coupling portions may be provided at a plurality of positions in the upper-lower direction. 
     5. The back cover may be placed over the back board. 
     6. The clip may be attached in a manner of not being attachable to and detachable from the back board. The clip may be attached to the clip attachment portion in the left-right direction or from below.