Abstract:
A seat frame for a vehicle seat has side frames disposed on both ends of a seat back frame in the width direction, and a bottom member frame for connecting the bottom ends of the side frames which attach to a seat cushion, wherein: each side frame has a side wall which is positioned on the outside in the width direction and which extends in the vertical direction, and a back wall which extends from the side wall towards the inner side in the width direction; and the lower member frame has a first extension portion extending along the width direction, and second extension portions extending from both ends of the first extension portion in the width direction towards the front. The second extension portions are positioned further inward than the side walls in the width direction and overlap with the side walls.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a National Stage Entry application of PCT Application No. PCT/JP2012/072245, filed Aug. 31, 2012. 
     
    
     BACKGROUND 
       [0002]    Disclosed herein a seat frame for a vehicle seat, and more particularly, a seat frame for a vehicle seat including side frames arranged on both right and left ends of a seat back frame, and a connection frame for connecting bottom ends of the side frames with each other. 
         [0003]    In a seat frame for a vehicle seat, side frames are arranged on both ends of a seat back frame constructing a frame of a seat back, and bottom ends of the side frames are usually connected with each other by a connection frame. 
         [0004]    Moreover, among prior-art side frames, there is such a side frame that an upper portion and a lower portion are independent members, and both portions are joined by welding or the like. For this side frame constructed by the two components, the connection frame is provided to connect the members forming the lower portions with each other (for example, refer to Japanese Patent Document No. 2008-201216 A (“the &#39;216 Document”). 
         [0005]    On the other hand, when the welding is used to assemble the seat frame, the number of times of welding decreases as the number of the components of the seat frame decreases, which is preferred in terms of workability of the frame assembly. Therefore, in a vehicle seat according to Japanese Patent Document No. 2012-126245 A (“the &#39;245 Document”), each of side frames arranged at right and left sides is constructed by a single member, and the side frames are connected with each other by welding a lower frame, which is the connection frame, to bottom ends of the respective side frames, thereby connecting the side frames with each other. 
         [0006]    A description is now given of a frame structure of the vehicle seat according to the &#39;245 Document, and the lower frame is constructed by a metal plate member extending as a straight line, and both ends on an extension direction of the lower frame are welded to rear surface flanges extending from rear surface edges of the side frames toward a seat inside. As a result, the side frames are connected with each other by the lower frame, and a rigidity of each of the side frames, particularly, a rigidity of the bottom end of each of the side frames is secured. 
         [0007]    A rigidity of each of the side frames needs to be further increased, and particularly, a rigidity against such a load as to bend the side frame toward the inside of the seat needs to be secured. In other words, if the bottom ends of the side frames are connected by the connection frame to increase the rigidity, the connection frame needs to be attached to secure such a degree of rigidity to suppress the inward bends of the side frames. 
         [0008]    Further, when the connection frame is attached to the side frames, the connection frame needs to be attached to further increase the rigidity while interference with members around attached locations are avoided. 
         [0009]    Moreover, if the connection frame is attached to the side frames by way of welding, welded areas between the connection frame and the side frames need to be set to promote a welding operation. 
         [0010]    Various embodiments of the present invention consider the foregoing problems, and an object of the embodiments is to provide a seat frame for a vehicle seat particularly realizing a structure capable of increasing the rigidity to such a degree as to suppress the inward bends of the side frames in the configuration in which the bottom ends of the side frames are connected by the connection frame. 
         [0011]    Moreover, another object is to provide a seat frame for a vehicle seat realizing a structure capable of further increasing the rigidity while the interference with the members around the attached locations are avoided when the connection frame is attached to the side frames. 
         [0012]    Moreover, still another purpose is to provide a seat frame for a vehicle seat in which welded areas between the connection frame and the side frames are set to promote the welding operation in the structure in which the connection frame is welded to the side frames. 
         [0013]    The above-described problems may be solved by a seat frame for a vehicle seat including side frames arranged on both ends in a widthwise direction of the vehicle seat in a seat back frame provided for a seat back of a vehicle seat, the side frames each comprising a bottom end, and a connection frame for connecting the bottom ends of the side frames, which are attached to a seat cushion of the vehicle seat, with each other, where each of the side frames further includes a side wall arranged outside in the widthwise direction in the side frame, and extending in a top to bottom direction, and a rear wall extending inward from the side wall in the widthwise direction, the connection frame includes first extension portion extending along the widthwise direction, and second extension portions extending forward respectively from both ends in the widthwise direction of the first extension portion, and each of the second extension portions is located inside the side wall in the widthwise direction, and overlaps with the side wall. 
         [0014]    When the connection frame is attached to the respective side frames in the seat frame for the vehicle seat, each of the second extension portions, which is a portion of the connection frame, is arranged inside the side wall of the side frame in such a state that each of the second extension portions overlaps with the side wall. This configuration increases the rigidity of the side walls of the side frames, particularly a rigidity against a load acting in the widthwise direction of the vehicle seat, and the inward bends of the side frames are suppressed. In other words, the rigidity can be increased to such a degree as to suppress the inward bends of the side frames in the above-mentioned seat frame for the vehicle seat. 
         [0015]    Moreover, the above-mentioned seat frame of the vehicle seat preferably includes a reclining mechanism for swinging the seat back with respect to the seat cushion, where the reclining mechanism is attached to an outside surface located outside in the widthwise direction out of side surfaces of the side wall, the second extension portion abuts against an inside surface located on a rear side of the outside surface in the widthwise direction out of the side surfaces of the side wall, and an area of the side wall of which the second extension portion abuts against the inside surface deviates from an area of which the reclining mechanism is attached to the outside surface. 
         [0016]    Welding marks for attaching the reclining mechanism and the like exist on the inside surface of the portion to which the reclining mechanism is attached on the side wall of the side frame, and some recesses and protrusions are thus formed. In the above-mentioned configuration, the connection frame is attached to avoid the portion where the recesses and protrusions are formed by the welding on the inside surface of the side wall of the side frame, and the connection frame can thus be satisfactorily attached. 
         [0017]    Moreover, in the above-mentioned seat frame of the vehicle seat, preferably, the area of the side wall of which the reclining mechanism is attached to the outside surface is a circular area viewed in the widthwise direction, and at least a portion of the second extension portion extends in an arc shape along an outer edge of the circular area. 
         [0018]    The above-mentioned configuration promotes an operation of attaching the connection frame to avoid the portion to which the reclining mechanism is attached on the side wall of each of the side frames. 
         [0019]    Moreover, in the above-mentioned seat frame of the vehicle seat, more preferably, a swing shaft for the swing of the seat back by the reclining mechanism with respect to the seat cushion is provided in such a state as to pass through the side walls in the widthwise direction, and at least a portion of the second extension portion extends in an arc shape to go around from a rear of the swing shaft to a front thereof. 
         [0020]    When the connection frame is attached while avoiding the portion to which the reclining mechanism is attached on the side wall of each of the side frames, the above-mentioned configuration enables the attachment of the connection frame to the side walls of the side frames in such a state that the interference with the swing shaft is avoided when the seat back swings with respect to the seat cushion. 
         [0021]    Moreover, the connection frame extends in the arc shape to go around from the rear of the swing shaft to the front thereof, and the area in which the portion of the side wall of each of the side frames overlaps with the connection frame is thus somewhat longer in the front to back direction. As a result, the portion increased in the rigidity by the attachment of the connection frame out of the side wall of each of the side frames is provided to extend in the front to back direction of the vehicle seat. As a result, the rigidity of the side frame against the load acting in the widthwise direction of the vehicle seat further increases. 
         [0022]    Moreover, in the above-mentioned seat frame of the vehicle seat, further preferably, a side wall side bent portion bending toward the inside in the widthwise direction is formed on a bottom end of the side wall, a second extension portion side bent portion bending toward the inside in the widthwise direction is formed on a bottom end of the second extension portion, and at least a portion of the second extension portion extends so that the second extension portion side bent portion aligns with the side wall side bent portion, and a portion of the second extension portion side bent portion overlaps with the side wall side bent portion. 
         [0023]    In the above-mentioned configuration, a unity of the bottom end of the side wall of each of the side frames and the connection frame is enhanced, resulting in a further increase in the rigidity in the bottom end of the side wall of each of the side frames. 
         [0024]    Moreover, in the above-mentioned seat frame of the vehicle seat, at least a portion of the area of the side wall of which the second extension portion abuts against the inside surface may be located above the area of which the reclining mechanism is attached to the outside surface, and a bent portion bending toward the inside in the widthwise direction is formed on a top end of the second extension portion. 
         [0025]    In the above-mentioned configuration, the connection frame can be attached to avoid the portion to which the reclining mechanism is attached on the side wall of each of the side frames, and the rigidity of the connection frame itself simultaneously increases, which increases the rigidity of the side frames. 
         [0026]    Moreover, in the above-mentioned seat frame of the vehicle seat, preferably, the area of the side wall of which the reclining mechanism is attached to the outside surface is a circular area viewed in the widthwise direction, the area of the side wall of which the second extension portion abuts against the inside surface is an area in a C shape along the outer edge of the circular area viewed in the widthwise direction, and the second extension portion includes an upper portion arranged above the circular area and a lower portion arranged below the circular area. 
         [0027]    In the above-mentioned configuration, while the portion to which the reclining mechanism is attached on the side wall of each of the side frames is avoided, the connection frame can be attached to the side frames to further increase the rigidity. 
         [0028]    Moreover, in the above-mentioned seat frame of the vehicle seat, more preferably, a swing shaft for the swing of the seat back by the reclining mechanism with respect to the seat cushion is provided in such a state as to pass through between the side walls in the widthwise direction, the upper portion and the lower portion are respectively welded to the side wall, a welded area between the upper portion and the side wall extends in a front to back direction of the vehicle seat so that at least a portion of the welded area is located in front of the swing shaft, and a welded area between the lower portion and the side wall extends in the front to back direction so that at least a portion of the welded area is located in the rear of the swing shaft. 
         [0029]    In the above-mentioned configuration, the respective upper portion and lower portion of the second extension portion of the connection frame can be satisfactorily fixed to the side wall of each of the side frames. Further, each of the welded areas extends in the front to back direction of the vehicle seat, a strength against a load acting in the front to back direction can be secured, and the state in which the upper portion and the lower portion of the second extension portion are respectively fixed to the side wall of each of the side frames can be stably maintained. 
         [0030]    Moreover, in the above-mentioned seat frame of the vehicle seat, a bottom end of the first extension portion at a center may be located further up than the bottom ends of the first extension portion at both ends in the widthwise direction in the connection frame provided for the vehicle seat which is a front seat arranged in front of a rear seat. 
         [0031]    The feet of a passenger on the rear seat may enter into a space located below the connection frame of the front seat. If the bottom end at the center in the extension direction is located above the bottom ends of the ends in the extension direction in the first extension portion located above the feet of the passenger out of the connection frame, an interference of the feet of the passenger with the connection frame can be suppressed. 
         [0032]    In the seat frame for the vehicle seat according to an embodiment, each of the second extension portions of the connection frame is arranged inside the side wall of the side frame in such a state that the second extension portion overlaps with the side wall, the rigidity of the side frame against the load acting in the widthwise direction of the vehicle seat thus increases, and the inward bend of the side frame is suppressed. 
         [0033]    In the seat frame for the vehicle seat according to an embodiment, some recesses and protrusions are formed on the inside surface of the portion to which the reclining mechanism is attached on the side wall of the side frame, and the connection frame can be satisfactorily attached by attaching the connection frame to avoid the portion. 
         [0034]    In the seat frame for the vehicle seat according to an embodiment, the operation of attaching the connection frame to avoid the portion to which the reclining mechanism is attached on the side wall of each of the side frames is promoted. 
         [0035]    In the seat frame for the vehicle seat according to an embodiment, the connection frame can be attached to the side walls of the side frames in a state in which the interference with the swing shaft is avoided. Further, the portion increased in the rigidity by the attachment of the connection frame out of the side wall of each of the side frames is provided to extend in the front to back direction of the vehicle seat, and as a result, the rigidity of the side frames against the load acting in the widthwise direction of the vehicle seat further increases. 
         [0036]    In the seat frame for the vehicle seat according to an embodiment, the unity of the bottom end of the side wall of each of the side frames and the connection frame is enhanced, resulting in a further increase in the rigidity in the bottom end of the side wall of each of the side frames. 
         [0037]    In the seat frame for the vehicle seat according to an embodiment, the connection frame can be attached to avoid the portion to which the reclining mechanism is attached on the side wall of each of the side frames, and the rigidity of the connection frame itself simultaneously increases, which increases the rigidity of the side frames. 
         [0038]    In the seat frame for the vehicle seat according to an embodiment, while the portion to which the reclining mechanism is attached on the side wall of each of the side frames is avoided, the connection frame can be attached to the side frames to further increase the rigidity. 
         [0039]    In the seat frame for the vehicle seat according to an embodiment, the connection frame can be satisfactorily fixed to the side wall of each of the side frames, the strength against the load acting in the front to back direction can be secured, and the state in which the connection frame is fixed to the side wall of each of the side frames can be stably maintained. 
         [0040]    In the seat frame for the vehicle seat according to an embodiment, the interference of the feet of the passenger on the rear seat with the connection frame can be suppressed, when the feet of the passenger on the rear seat enter into the space located below the connection frame of the front seat. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0041]      FIG. 1  is a schematic side view showing an exterior of a vehicle seat according to an embodiment of the present invention; 
           [0042]      FIG. 2  is a perspective view showing an entire seat frame of the vehicle seat according to the embodiment of the present invention; 
           [0043]      FIG. 3  is a rear view showing the seat frame of the vehicle seat according to the embodiment of the present invention; 
           [0044]      FIG. 4  is an exploded perspective view of a neighborhood of a side frame out of the seat frame; 
           [0045]      FIG. 5  is a front view showing a positional relationship among the side frame, a connection frame, and a reclining mechanism; 
           [0046]      FIG. 6  is a perspective view showing a connection state between the side frame and the connection frame; 
           [0047]      FIG. 7  is an explanatory side view of welded locations between the side frame and the connection frame; 
           [0048]      FIG. 8  is a cross sectional view showing a structure of the side frame made on a plane and in a direction indicated by A-A in  FIG. 3 ; and 
           [0049]      FIG. 9  is a cross sectional view of the connection frame attached to the side frame made on a plane and in a direction indicated by B-B in  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION 
       [0050]    Hereinafter, a description is given of a seat frame for a vehicle seat according to various embodiments of the present invention referring to  FIGS. 1 to 9 . A height adjustment mechanism  4  and a slide rail mechanism R described later are not shown in  FIG. 2  for the sake of clarity. 
         [0051]    Hereinafter, a front to back direction is a direction matching a travel direction of the vehicle. Moreover, a widthwise direction is a direction along a lateral width of the vehicle, more specifically in a right to left direction, and corresponds to a widthwise direction of the vehicle seat. Moreover, a top to bottom direction is a top to bottom direction of the vehicle seat. A description given of positions and attitudes of respective portions of the seat in a normal state, in other words, a state in which a passenger is seated hereinafter unless otherwise specified. 
         [0052]    First, a description is given of a basic configuration of the vehicle seat and the seat frame (hereinafter referred to as this seat S and this frame F) according to an embodiment of the present invention. 
         [0053]    This seat S is approximately the same in a basic structure as a publicly known vehicle seat, and is used as a front seat arranged in front of a rear seat particularly in this embodiment. This seat S is not limited to the front seat, and the present invention can be applied to a seat frame for a vehicle seat, which is a rear seat. 
         [0054]    More specifically, this seat S includes a seat back S 1 , a seat cushion S 2 , and a headrest S 3  as main components as shown in  FIG. 1 . On the other hand, this frame F constructing a framework of this seat S includes a seat back frame F 1  provided for the seat back S 1 , and a seat cushion frame F 2  provided for the seat cushion S 2  as shown in  FIG. 2 . Moreover, guide stays fs for supporting the headrest S 3  body when pillars S 3   a  extending from a bottom of the headrest S 3  are inserted into them are fixed to a top of the seat back frame F 1 . 
         [0055]    Moreover, most of portions of this frame F are constructed by metal members. The assembled seat back frame F 1  and the seat cushion frame F 2  are constructed to respectively form rectangular frames as shown in  FIG. 2 . 
         [0056]    Then, bottom ends of side frames  11  provided on both ends in the widthwise direction of the seat back frame F 1  are assembled to rear ends of side portion frames  1  provided on both ends in the widthwise direction of the seat cushion frame F 2 . The bottom end of the side frame  11  is assembled through a reclining mechanism  3  shown in  FIG. 4  to the rear end of the side portion frame  1  in this frame F. 
         [0057]    The reclining mechanism  3  is activated by an operation of a passenger on an operation portion, not shown, and is configured to swing the seat back S 1  forward or backward with respect to the seat cushion S 2 . The reclining mechanisms  3  are individually provided for the respective side frames  11  provided as a left-and-right pair, and are attached to bottoms of outside surfaces  12   a  of the respective side frames  11  in this seat S. Moreover, the reclining mechanisms  3  are welded to rear ends of inner wall surfaces of the side portion frames  1  opposite to the sides welded to the side frames  11 . 
         [0058]    A structure of each of the reclining mechanisms  3  is a known mechanism, and includes reclining mechanism bodies  3   a,  and a penetration shaft  3   b  extending in the widthwise direction in such a state as to pass through the reclining mechanism bodies  3   a.  Then, a drive mechanism which is provided in the body, and is not shown, is activated by a rotation of the penetration shaft  3   b.  As a result of the activation of the drive mechanism, a portion joined to the side frame  11  side out of the reclining mechanism  3   a  relatively swings about the penetration shaft  3   b  with respect to a portion on the opposite side thereof, specifically a portion joined to the side portion frame  1  side of the seat cushion frame F 2 . As a result, the side frame  11  relatively swings about the penetration shaft  3   b  with respect to the seat cushion S 2 . In other words, the seat back S 1  swings about the penetration shaft  3   b  with respect to the seat cushion S 2 . 
         [0059]    The penetration shaft  3   b  is a rotational shaft for rotating to drive the reclining mechanisms  3 , and is also a swing shaft when the seat back S 1  swings with respect to the seat cushion S 2  by the reclining mechanisms  3 . The penetration shaft  3   b  is a shaft shared between the reclining mechanism  3  attached to the one side frame  11  and the reclining mechanism  3  attached to the other side frame  11  in this seat S. In other words, the penetration shaft  3   b  passes through the side wall  12  of the one side frame  11 , extends toward the other side frame  11  along the widthwise direction, and further penetrates the side wall  12  of this side frame  11 . 
         [0060]    Then, each of both ends of the penetration shaft  3   b  passes through the corresponding reclining mechanism body  3   a,  and further passes through to the side portion frame  1  of the seat cushion frame F 2  located by the reclining mechanism body  3   a  as shown in  FIG. 5 . In other words, the penetration shaft  3   b  is provided for rotation in such a state as to penetrate through the side walls  12  of the side frames  11  and the side portion frames  1  in the widthwise direction in this seat S. 
         [0061]    The penetration shaft  3   b  may be rotated through an operation portion such as a lever by the passenger, or may be rotated by a power generated by a drive device such as an actuator or the like. 
         [0062]    On the other hand, the slide rail mechanism R for sliding this seat S in the front to back direction with respect to a vehicle body floor is arranged at a position below the seat cushion S 2 . Then, a height adjustment mechanism  4  for adjusting a seat height is provided between the seat cushion S 2  and the slide rail mechanism R in the top to bottom direction in this seat S. This height adjustment mechanism  4  is activated by the passenger operating the operation lever  5  shown in  FIG. 1 . 
         [0063]    Specifically, the height adjustment mechanism  4  uses a drive force generated by the operation on the operation lever  5  to turn turn links  6  for connecting between the seat cushion frame F 2  and the slide rail mechanism R, thereby adjusting the seat height. 
         [0064]    More specifically, a total of four turn links  6  are provided to be located at both ends in the widthwise direction respectively at a front end and a rear end of the seat cushion frame F 2 . One end of each of the turn links  6  is turnably supported by a support portion Rx provided on an upper rail Ru of the slide rail mechanism R to protrude upward. Moreover, the other end of each of the turn links  6  is turnably attached to the side portion frame  1  of the seat cushion frame F 2 . 
         [0065]    On the other hand, a sector gear  7   a  is formed on the rear turn link  6  located on one end side in the widthwise direction out of the turn links  6 , and a pinion gear  7   b  meshes with the sector gear  7   a.  The pinion gear  7   b  is connected to the operation lever  5  through a connection shaft, which is not shown. As a result, when the operation lever  5  is operated, the pinion gear  7   b  rotates integrally with the connection shaft, and a meshing position between the pinion gear  7   b  and the sector gear  7   a  changes. As a result, the turn link  6  on which the sector gear  7   a  is formed turns, and the other turn links  6  turn in a form of following this turn link  6 . As a result, the seat body including the seat cushion S 2  rises and falls, resulting in adjustment of the seat height. 
         [0066]    A detailed description is now given of the seat back frame F 1  out of this frame F. 
         [0067]    The seat back frame F 1  includes the side frames  11  arranged at both ends in the widthwise direction, an upper frame  21  for connecting top ends of the side frames  11  with each other, and a lower member frame  31  serving as a connection frame for connecting the bottom ends of the side frames  11  as shown in  FIGS. 2 and 3 . 
         [0068]    The upper frame  21  is a portion forming a top end of the seat back frame F 1  as shown in  FIGS. 2 and 3 . The upper frame  21  is constructed by a bent portion  22  including both ends bent in a downward U shape to direct downward and an upper member frame  23  bridging between one end and the other end of the bent portion  22 . 
         [0069]    The side frames  11  form both ends of the seat back frame F 1  in the widthwise direction, and are portions extending from the top to bottom direction. Each side frame  11  is bent in an approximately arcuate shape so that a top end thereof is located somewhat in the rear of a bottom end in this seat S as shown in  FIG. 2 . Moreover, each side frame  11  is formed from a single member, and is specifically formed by machining a single metal plate in this seat S. 
         [0070]    A more detailed description is given of the structure of each side frame  11 . The side frames  11  arranged at the both ends in the widthwise direction have left-right symmetry structures, and a description is given of only the structure on the one side frame  11  hereinafter. 
         [0071]    Each side frame  11  includes the side wall  12  located on the outside in the widthwise direction, and a rear wall  13  extending from a rear end of the side wall  12  inward in the widthwise direction as shown in  FIG. 8 . The side wall  12  extends approximately straight in the top to bottom direction, a top end is in such a pointed shape as to narrow upward viewed from the side in the widthwise direction, a center has a gently curved shape, and a bottom has a semi-ellipsoidal shape. 
         [0072]    Multiple holes are formed on the side wall  12 , a hole  12   c  out thereof is formed at the bottom end of the side wall  12 , and the penetration shaft  3   b  for driving the reclining mechanisms  3  is inserted into this hole. Further, one of the remaining holes is a hole for fixing the side frame  11  when the seat back frame F 1  is assembled, particularly when members constructing the seat back frame F 1  are assembled to each other, and a fixing jig, which is not shown, is inserted for the assembly into this hole. 
         [0073]    Moreover, the reclining mechanism  3  is attached to the outside surface  12   a  located on the outside in the widthwise direction out of side surfaces of the side wall  12  as described before. More specifically, the reclining mechanism  3  is attached at a portion located somewhat above the bottom end of the side wall  12  by way of the laser welding in this seat S. When the reclining mechanism  3  is attached to the outside surface  12   a  of the side wall  12  by way of the laser welding, a laser irradiates on the inside surface  12   b  located on the rear side of the outside surface  12   a  in the widthwise direction out of the side surfaces of the side wall  12 . Therefore, recesses and protrusions are formed as welding marks on the inside surface  12   b.    
         [0074]    A portion out of the reclining mechanism  3  joined to the side wall  12  of the side frame  11 , more specifically, a portion of the reclining mechanism body  3   a  opposing the side wall  12  is circular in this seat S. Thus, an area of which the reclining mechanism  3  is attached to the outside surface  12   a  on the side wall  12  of each side frame  11  is a circular area M viewed in the widthwise direction as shown in  FIG. 7  in this seat S. The hole into which the penetration shaft  3   b  is inserted is formed at a center position of the circular area M. 
         [0075]    Moreover, a side wall side flange  14  bent inward in the widthwise direction is formed at a front end of the side wall  12  as shown in  FIGS. 4 and 8 . This side wall side flange  14  corresponds to a side wall side bent portion, and is provided from the top end to the bottom end of the side wall  12  in order to reinforce the side wall  12 . The bottom end of the side wall  12  has a semicircular shape as described before, and the side wall side flange  14  provided at the bottom end of the side wall  12  is formed in the arc shape to go around from the front to the rear along an outer edge of the bottom end of the side wall  12 . 
         [0076]    The rear wall  13  is adjacent to a rear end of the side wall  12  in such a state as to cross the side wall  12 , and an angle between the rear wall  13  and the side wall  12  is approximately 90 degrees in this seat S. In other words, an outside end in the widthwise direction of the rear wall  13  forms a corner of the side frame  11  along with the rear end of the side wall  12 . 
         [0077]    Moreover, a top end of the rear wall  13  is at a position somewhat lower than the top end of the side wall  12 , and a bottom end of the rear wall  13  is somewhat higher than the bottom end of the side wall  12 . Then, a member frame attachment portion  13   a  in an approximately trapezoidal shape larger in an inward extension amount in the widthwise direction than a portion located above this portion is formed at the bottom end of the rear wall  13  as shown in  FIG. 3 . A lower member frame  31  described later is attached to this member frame attachment portion  13   a.    
         [0078]    Further, a rear wall side flange  15  bent forward is formed at an inside end in the widthwise direction of the rear wall  13  as shown in  FIGS. 4 and 8 . The rear wall side flange  15  is formed from the top end to the bottom end of the rear wall  13  in order to reinforce the rear wall  13 , and extends to the top end of the member frame attachment portion  13   a.  Moreover, the rear wall side flange  15  is similarly formed in an arear located below the main frame attachment portion  13   a  out of the rear wall  13 . On the other hand, the flange  15  is not formed on a portion inside the widthwise direction and a portion on a bottom end side out of an outer edge portion of the member frame attachment portion  13   a  in order to avoid interference with the lower member frame  31 . 
         [0079]    The rear wall side flange  15  formed at the bottom end of the rear wall  13  joins at the outside end in the widthwise direction with the side wall side flange  14  formed to go around to the rear at the bottom end of the side wall  12  as shown in  FIG. 4 . As a result, the rigidity of the entire side frame  11  further increases. 
         [0080]    The lower member frame  31  is a member in an approximately U shape viewed from above as shown in  FIGS. 2 and 9 , and is formed by machining a single plate metal member. The lower member frame  31  includes a fist extension portion  32  extending in the widthwise direction, and second extension portions  33  extending forward from both ends in the widthwise direction of the first extension portion  32 . 
         [0081]    The first extension portion  32  is a portion arranged between the side frames  11  in the widthwise direction, and attached to the rear walls  13  of the side frames  11 , particularly the member frame attachment portions  13   a.  Specifically, each of both ends in the extension direction of the first extension portion  32  is attached to the member frame attachment portion  13   a  by way of the laser welding in a state in which teach end is in contact with a front surface of the member frame attachment portion  13   a.    
         [0082]    Moreover, a through hole  32   b  communicating with a hole (not shown) formed on the member frame attachment portion  13   a  when the first extension portion  32  is attached to the member frame attachment portion  13   a  is formed on an extension direction end of the first extension portion  32  as shown in  FIG. 6 . The hole  32   b  is used to fix the lower member frame  31  when the members constructing the seat back frame F 1  are assembled with each other, and a fixing jig, not shown, is inserted into the hole  32   b  during the assembly. 
         [0083]    A detailed description is now given of the shape of the first extension portion  32 , and a bottom end position of the first extension portion  32  at a center in the extension direction is located somewhat above the bottom end position at the ends in the extension directions as appreciated from  FIG. 3 . In other words, the first extension portion  32  has such a shape that the bottom end somewhat rises at the center in the extension direction in this seat S. A use of this seat S as a front seat is promoted by the provision of the first extension portion  32  shaped in this way. 
         [0084]    More clearly, feet of a passenger on the rear seat may enter a space located below the lower member frame  31  of the front seat. If the bottom end at the center in the extension direction is located above the bottom ends at the extension direction ends in the first extension portion  32  out of the lower member frame  31 , an interference of the feet of the passenger with the lower member frame  31  can be suppressed. 
         [0085]    On the other hand, the extension direction ends of the first extension portion  32  are wider in the top to bottom direction than the center in the extension direction, and the rigidity of the lower member frame  31  is secured as a result. 
         [0086]    Moreover, a protrusion portion  32   a  protruding in an arc shape from a front surface (in other words, a portion recessed in an arc shape on a rear surface) is formed at a center in the top to bottom direction of the first extension portion  32  as shown in  FIG. 3 . The protrusion portion  32   a  is a so-called reinforcement bead, and is formed to a relatively long extent along the extension direction of the first extension portion  32 . 
         [0087]    Moreover, a first extension portion upper side flange  34  bent forward is formed at the top end of the first extension portion  32  as shown in  FIGS. 4 and 6 . The first extension portion upper side flange  34  is formed from the one end to the other end in the extension direction of the first extension portion  32  to reinforce the first extension portion  32 . 
         [0088]    Further, the above-described rear wall side flange  15  (particularly an inside end in the widthwise direction of the flange  15 ) formed at the top end of the member frame attachment portion  13   a  abuts against a portion somewhat closer to the center than the end position in the extension direction of the first extension portion  32  out of the first extension portion upper side flange  34  in this seat S as shown in  FIG. 6 . In other words, the lower member frame  31  is attached to the member frame attachment portion  13   a  as if the rear wall side flange  15  and the first extension portion upper side flange  34  continue to each other in this seat S. As a result, integrity between the lower member frame  31  and the side frame  11  is increased, and the rigidity of the neighborhood of a portion to which the lower member frame  31  is attached further increases in the side frame  11 . 
         [0089]    Moreover, a first extension portion lower side flange  35  bent to the front side is formed at the bottom end of the first extension portion  32  from the one end to the other end in the extension direction of the first extension portion  32 . As a result, the rigidity of the lower member frame  31  further increases. 
         [0090]    The second extension portions  33  are adjacent to the both ends in the extension direction of the first extension portion  32  in such a state as to cross the first extension portion  32 , an angle between the first extension portion  32  and the second extension portion  33  is approximately 90 degrees in this seat S. In other words, the rear end of the second extension portion  33 , along with the extension direction end of the first extension portion  32 , forms a corner of the lower frame member  31 . 
         [0091]    Then, the lower member frame  31  is attached to the member frame attachment portion  13   a  so that the corner of the lower member frame  31  overlaps with the corner of the side frame  11  in this seat frame S as shown in  FIG. 6 . In other words, the second extension portion  33  is located inside the side wall  12  of the side frame  11  in the widthwise direction, and overlaps with the side wall  12 . More specifically, the second extension portion  33  is attached to the side wall  12  by way of the laser welding in such a state as to abut against the inside surface  12   b  of the side wall  12 . 
         [0092]    As described above, the second extension portion  33  of the lower member frame  31  is arranged in such a state as to abut against the inside surface  12   b  of the side wall  12  of the side frame  11  in this seat S, the rigidity of the side wall  12  of the side frame  11 , particularly rigidity against the load acting in the widthwise direction increases, and the inward bend of the side frame  11  is suppressed. In other words, the rigidity can be increased to such a degree as to suppress the inward bend of the side frame  11  by arranging the second extension portion  33  inside the side wall  12  of the side frame  11  in the overlapping state. 
         [0093]    A detailed description is now given of a shape of the second extension portion  33 , and the second extension portion  33  is formed into a C shape viewed in the widthwise direction as illustrated in  FIGS. 6 and 7 . In other words, the second extension portion  33  provided for this seat S is punched off at a center into a circular shape. Moreover, a half area in the bottom side of the front end of the second extension portion  33  is cut off in such a state as to continue to the circular punched-off portion. The second extension portion  33  is configured to include an upper portion  36  arranged above the circular punched-off portion and a lower portion  37  arranged below the circular punched-off portion as a result of the punching or cutting. Then, both the upper portion  36  and the lower portion  37  are joined to the side wall  12  by way of the laser welding in such a state as to abut against the inside surface  12   b  of the side wall  12  of the side frame  11 . 
         [0094]    On the other hand, it should be understood that the circular punched-off portion in the second extension portion  33  is not joined to the side wall  12  of the side frame  11 . Then, the reclining mechanism  3  is arranged at a position opposite to the circular punched-off portion in this seat S across the side wall  12 . In other words, the area in which the circular punched-off portion is located in the side wall  12  of the side frame  11  corresponds to an area of the outside surface  12   a  to which the reclining mechanism  3  is attached in this seat S. 
         [0095]    In other words, areas of the inside surface  12   b  against which the upper portion  36  and the lower portion  37  of the second extension portion  33  abut on the side wall  12  of the side frame  11  are deviated from the area of the outside surface  12   a  to which the reclining mechanism  3  is attached in this seat S. In the area of the outside surface to which the reclining mechanism  3  is attached in the side wall  12 , recesses and protrusions are formed as laser welding marks on the inside surface  12   b  thereof. The second extension portion  33  is attached to the inside surface  12   b  of the side wall  12  to avoid the portion on which the recesses and protrusions are formed, and the lower member frame  31  including the second extension portions  33  are thus satisfactorily attached. 
         [0096]    The area of the outside surface  12   a  to which the reclining mechanism  3  is attached is circular viewed in the widthwise direction in the side wall  12  as described before in this seat S. On the other hand, the center of the second extension portion  33  of the lower member frame  31  is punched off in the circular shape to match the circular area M. Then, the second extension portion  33  is joined to the side wall  12  so that an outer edge of the circular area M and an inner edge of the circular punched-off portion in the second extension portion  33  match each other in this seat S 
         [0097]    In other words, the area of which the second extension portion  33  abuts against the inside surface  12   b  is the area in the C shape along the outer edge of the circular area M in the side wall  12  in this seat S. More specifically, a portion located in the lower side of a center in the front to back direction of the upper portion  36  of the second extension portion  33  is cut off in a semicircular shape as shown in  FIGS. 6 and 7 . Then, the second extension portion  33  is attached to the side wall  12  along an edge of the cutout and an upper portion of the outer edge of the circular area M. In other words, the upper portion  36  out of the second extension portion  33  is a portion arranged above the circular area M. 
         [0098]    On the other hand, the lower portion  37  of the second extension portion  33  extends forward in an arc shape as shown in  FIGS. 6 and 7 . Then, the second extension portion  33  is attached to the side wall  12  so that the lower portion  37  aligns with a lower portion of the outer edge of the circular area M. In other words, the lower portion  37  out of the second extension portion  33  is a portion arranged below the circular area M, and extends in the arc shape along the outer edge of the circular area M. 
         [0099]    As described above, the second extension portion  33  is in the C shape along the outer edge of the area M (the area on the side wall  12  of the side frame  11  to which the reclining mechanism  3  is attached) viewed in the widthwise direction in this seat S. Then, the second extension portion  33  is joined to the side wall  12  so that the circular area M and the circular punched-off portion in the second extension portion  33  match each other. Conversely, the circular area M and the circular punched-off portion in the second extension portion  33  only need to align with each other when the second extension portion  33  is joined to the side wall  12 . As a result, the operation of attaching the lower member frame  31  to avoid the portion to which the reclining mechanism  3  is attached on the side wall  12  of each of the side frames  11  is promoted. 
         [0100]    Particularly when the seat back frame F 1  of this seat S is assembled, first, the reclining mechanism  3  is attached to the side wall  12  of each side frame  11  by way of the laser welding, and, then, the lower member frame  31  is attached to the side frames  11 . When the seat back frame F 1  is assembled in this assembly sequence, if the circular area M and the circular punched-off portion in the second extension portion  33  are aligned with each other, the attachment of the lower member frame  31  to avoid the attachment portion of the reclining mechanism  3  in the side wall  12  of the side frame  11  is further promoted. In other words, the configuration of punching the center of the second extension portion  33  in the circular shape to align with the outer edge of the circular area M is more effective when the seat frame F 1  is assembled in the assembly sequence. 
         [0101]    That the lower portion  37  of the second extension portion  33  extends in the arc shape to go around from the rear of the penetration shaft  3   b  to the front of the penetration shaft  3   b  in the state where the second extension portion  33  is joined to the side wall  12  in this seat S. Similarly, the upper portion  36  of the second extension portion  33  extends from the rear of the penetration shaft  3   b  to the front of the penetration shaft  3   b.  This configuration enables the attachment of the lower member frame  31  to the side walls  12  of the side frames  11  while the attachment portions of the reclining mechanism  3  on the side walls  12  of the side frames  11  are avoided, and the interference with the penetration shaft  3   b  is further avoided. Moreover, the portion increased in the rigidity by the attachment of the lower member frame  31  out of the side wall  12  of the side frame  11  extends in the front to the back direction, and the rigidity of the side frame  11  further increases against the load acting in the widthwise direction 
         [0102]    Moreover, the upper portion  36  and the lower portion  37  of the second extension portion  33  are respectively laser-welded to the side wall  12  of the side frame  11  as described before in this seat S. Then, a welded area X 1  between the upper portion  36  and the side wall  12  extends in an arc shape in the front to the rear direction so that a portion of the welded area X 1  locates in front of the penetration shaft  3   b  as shown in  FIG. 7  in this seat S. Similarly, a welded area X 2  between the lower portion  37  and the side wall  12  extends in an arc shape in the front to the rear direction so that a portion of the welded area X 2  is located in the rear of the penetration shaft  3   b.    
         [0103]    As described above, each of the welded areas X 1  and X 2  is an area having a certain length in the front to the back direction in this seat S, and the upper portion  36  and the lower portion  37  of the second extension portion  33  are thus respectively fixed to the side wall  12  of the side frame  11  satisfactorily. Further, each of the welded areas X 1  and X 2  extend in the front to the back direction, and a strength against the load acting in the front to the back direction can be secured. As a result, even if a load in the front to the back direction acts on the side frame  11  and the lower member frame  31 , a detachment in the welded areas X 1  and X 2  can be suppressed, and the joint state between the second extension portions  33  of the lower member frame  31  and the side walls  12  of the side frames  11  can be stably maintained. 
         [0104]    The welded area X 1  between the upper portion  36  and the side wall  12  is the arc area corresponding to approximately ⅓ of the circumference about the penetration shaft  3   b,  and the welded area X 2  between the lower portion  37  and the side wall  12  is an arc area corresponding to approximately ⅙ of the circumference in this seat S. Further, both the welded areas X 1  and X 2  are separated from each other. Both the welded areas X 1  and X 2  do not correspond to the entire circumference about the penetration shaft  3   b,  and are separated from each other in this way. Therefore, when the seat back frame F 1  is assembled, a welding operation can be carried out more easily than a case in which the entire circumference about the penetration shaft  3   b  is continuously laser-welded. 
         [0105]    Flanges bent inward in the widthwise direction are respectively formed on the upper portion  36  and the lower portion  37  of the second extension portion  33  as shown in  FIGS. 4 and 6 . Specifically, a second extension portion top side flange  38  including a top end bent inward in the widthwise direction is formed on the upper portion  36  of the second extension portion  33 . The second extension portion top side flange  38  corresponds to a bent portion, and is formed from a front end to a rear end of the upper portion  36  in order to reinforce the second extension portion  33 . 
         [0106]    The formation of the flange  38  for the reinforcement at the top end of the upper portion  36  of the second extension portion  33  as describe above increases the rigidity of the lower member frame  31  itself, and, as a result, the rigidity of the side frame  11  to which this frame  31  is attached also increases. 
         [0107]    The second extension portion top side flange  38  continues to the first extension portion top side flange  34  formed at the top end of the first extension portion  32  as illustrated in  FIG. 4 . As a result, the rigidity of the entire lower member frame  31  further increases. 
         [0108]    On the other hand, a second extension portion bottom side flange  39  including a bottom end bent inward in the widthwise direction is formed on the lower portion  37  of the second extension portion  33  as shown in  FIGS. 4 and 6 . The second extension portion bottom side flange  39  corresponds to a second extension portion side bent portion, and is formed from a front end to a rear end of the lower portion  37  in order to reinforce the second extension portion  33 . The lower portion  37  extends in the arc shape to go around from the rear side to the front side of the penetration shaft  3   b  as described before, and the second extension portion bottom side flange  39  thus also extends in an arc shape. 
         [0109]    Then, the front end of the second extension portion bottom side flange  39  overlaps with a rear end extending in an arc shape at a bottom end position of the side wall  12  out of the side wall side flange  14  formed on the side wall  12  of the side frame  11  in the state in which the second extension portion  33  is joined to the side wall  12  as shown in  FIG. 6  in this seat S. 
         [0110]    More specifically, the lower portion  37  of the second extension portion  33  extends so that the second extension portion bottom side flange  39  aligns with the side wall side flange  14 , and the front end of the second extension portion bottom side flange  39  overlaps with the rear end of the side wall side flange  14 . In other words, the lower member frame  31  is attached to the side frame  11  as if the second extension portion bottom side flange  39  and the side wall side flange  14  continued to each other in this seat S. As a result, integrity between the lower member frame  31  and the side frame  11 , particularly integrity with the bottom end of the side wall  12  is increased, and the rigidity of the neighborhood of the portion to which the lower member frame  31  is attached further increases in the side frame  11 . 
         [0111]    Further, the second extension portion bottom side flange  39  connects to the first extension portion bottom side flange  35  formed at the bottom end of the first extension portion  32  as shown in  FIG. 4 . As a result, the rigidity of the entire lower member frame  31  further increases. 
         [0112]    A description is given of the configuration example of the seat frame for the vehicle seat according to various embodiments of the present invention, but these are merely examples for promoting the understanding of the present invention, and do not limit the present invention. In other words, it should be understood that the shapes, dimensions, arrangements, and the like described before can be changed or improved without departing from the purpose of the present invention, and equivalents thereof are included. 
         [0113]    Moreover, the second extension portion  33  of the lower member frame  31  abuts against the inside surface  12   b  on the side wall  12  of the side frame  11  in the embodiment. On the other hand, the area of which the reclining mechanism  3  is attached on the outside surface  12   a  is the circular area M viewed in the widthwise direction on the side wall  12 . Then, the area of which the second extension portion  33  abuts against the inside surface  12   b  is the area in the C shape along the outer edge of the circular area M in the side wall  12 . In other words, the second extension portion  33  includes the upper portion  36  arranged above the circular area M and the lower portion  37  arranged below the circular area M. However, the configuration is not limited to this case, and the second extension portion  33  may have such a configuration as to include a portion corresponding to only one of the upper portion  36  and the lower portion  37 . 
         [0114]    Moreover, though the flanges (second extension portion top side flange  38  and the second extension portion bottom side flange  39 ) for the reinforcement are provided respectively for the upper portion  36  and the lower portion  37  according to the embodiment, the configuration is not limited to this example, and a configuration without including the formed flanges for reinforcement may be adopted. 
       REFERENCE NUMERALS 
       [0000]    
       
         S this seat 
         S 1  seat back 
         S 2  seat cushion 
         S 3  headrest 
         S 3   a  pillar 
         F this frame 
         F 1  seat back frame 
         F 2  seat cushion frame 
         fs guide stay 
         R slide rail mechanism 
         Ru upper rail 
         Rx support portion 
         M circular area 
         X 1 , X 2  welded area 
           1  side portion frame 
           3  reclining mechanism
         3   a  reclining mechanism main body     3   b  penetration shaft   
     
           4  height adjustment mechanism 
           5  operation lever 
           6  turn link 
           7   a  sector gear 
           7   b  pinion gear 
           11  side frame 
           12  side wall
         12   a  outside surface     12   b  inside surface     12   c  hole   
     
           13  rear wall
         13   a  member frame attachment portion   
     
           14  side wall side flange 
           15  rear wall side flange 
           21  upper frame 
           22  bent portion 
           23  upper member frame 
           31  lower member frame (connection frame) 
           32  first extension portion
         32   a  protrusion portion     32   b  hole   
     
           33  second extension portion 
           34  first extension portion top side flange 
           35  first extension portion bottom side flange 
           36  upper portion 
           37  lower portion 
           38  second extension portion top side flange 
           39  second extension portion bottom side flange