Seat back frame for vehicle

A seat back frame for a vehicle for supporting a seat back, includes a first back frame, at which a shoulder belt anchor for supporting one end portion of a seat belt is provided, a second back frame arranged substantially in parallel with the first back frame, and a cross member connecting the first back frame and the second back frame, wherein a protruding portion or a recessed portion is formed at the cross member so as to extend in a longitudinal direction thereof, a first recessed surface portion or a first protruding surface portion is formed at the first back frame and a second recessed surface portion or a second protruding surface portion is formed at the second back frame so that the first back frame and the second back frame are fittedly connected to the protruding portion or the recessed portion of the cross member.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 U.S.C. §119 to Japanese Patent Application 2009-018391, filed on Jan. 29, 2009, and Japanese Patent Application 2009-018450, filed on Jan. 29, 2009, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

This disclosure generally relates to a seat back frame for a vehicle. More specifically, this disclosure pertains to a seat back frame for a vehicle having a first back frame, which includes a shoulder belt anchor for supporting one end portion of a seat belt, and a second back frame, which is arranged so as to be in substantially parallel with the first back frame.

BACKGROUND

Disclosed in JP2005-297960A is a seat cushion frame for a vehicle having a left and right cushion side frames (i.e. first and second back frames). JP2005-297960A states that the left and right cushion side frames are adaptable as left and right back-side frames, respectively. Accordingly, the seat cushion frame for the vehicle according to JP2005-297960 will be explained below with the left and right back-side frames. Each of the left and right back-side frames has a shape, which is obtained by bending both end portions of a plate member in order to form two boxes. Furthermore, a recessed portion is formed between two boxes of each of the left and right back-side frames. The both end portions of the plate member of each of the left and right back-side frames are connected to the main body thereof at which the recessed portion is formed in a state where the end portions of the plate member face each other in order to enhance a strength of the seat back frame for the vehicle.

Disclosed in JP2005-67331A is a seat back frame for a vehicle having right and left back-side frames (first and second back frames), an upper cross member for connecting the right and left back-side frames at upper portions thereof and a lower cross member for connecting the right and left back-side frames at lower portions thereof. Each of the right and left back-side frames is formed in a box shape. Each of the upper cross member and the lower cross member is formed in a tubular shape. The lower cross member is connected to the right and left back-side frames by welding in a state where both end portions of the lower cross member are inserted into holes formed at right and left back-side frames, respectively, in order to ensure a strength at the seat back frame for the vehicle.

Disclosed in DE10048128A1 is a seat back frame for a vehicle having right and left back-side frames, an upper cross member for connecting the right and left side frames at upper portions thereof and a lower cross member for connecting the right and left side frames at lower portions thereof. Each of the right and left back-side frames is obtained by bending both end portions of a plate member into substantially cylinder shapes. Furthermore, the upper cross member is formed in a tubular shape. The lower cross member is formed in a bar shape. The right and left back-side frames are arranged so that plate surfaces thereof face each other. Furthermore, both end portions of each of plural lower cross members are connected to circumferential surfaces of cylindrical-shaped portions of the right and left back-side frames positioned at a back-side in front-rear direction of the vehicle, respectively, in order to ensure a strength at the seat back frame for the vehicle.

Disclosed in DE102004048351A1 is a seat back frame for a vehicle formed as a unit. A portion of the seat back frame for the vehicle disclosed in DE10200404835A1 corresponding to the lower cross member is formed in a substantially flat surface shape in order to ensure a strength at the seat back frame for the vehicle.

Generally, in a case where a shoulder belt anchor for supporting one end portion of a seat belt is provided at an upper portion of the seat back frame for the vehicle, if the vehicle is involved in a crash, the seat belt is pulled forward by a great tensile force because of an inertia generated by an occupant, thereby applying a great load to the shoulder belt anchor. For example, the seat belt is arranged so as cross the passenger's body from the right shoulder to the left waist and then to the right waist. Therefore, in the case where the vehicle is involved in the crash, a diagonally forward left-torsional bending moment is generated at the seat back frame for the vehicle because of the above-mentioned load. A similar situation may occur at a seat for two people used as a back seat for the vehicle.

In a case where the configuration of the back-side frame of the seat back frame for the vehicle disclosed in JP2005-297860A is adapted as a center back-side frame, a compression deformation may occur at the center back-side frame with the recessed portion as a fiducial point when the torsional bending moment acts on the center back-side frame, because two box shaped portions are divided at the recessed portion, to which the end portions thereof are connected. On the other hand, in a case where the configuration of the back-side frame of the seat back frame for the vehicle disclosed in JP2005-67331A is adapted as the center back-side frame, a compression force acts on a front wall portion of the plate shaped member, which is bent to have a box shape and which is arranged at a front portion of the seat in the front-rear direction of the vehicle, because of the torsional bending moment. Therefore, a compression deformation may occur at a connected portion at the front wall portion because of the compression force acting on the front wall portion, at which end portions of both side end portions of the plate-shaped member bent to form a box is overlapped and connected.

According to the seat back frames disclosed in JP2005-297960A and JP2005-67331A, the center back-side frame may be formed to have a curved shape, so that a recessed portion is formed at a rear portion of the seat in order to provide a comportability for the occupants seated on the seat for two, furthermore, in order to simplify the configuration of the center back-frame.

In the case where the plate-shaped member of the center back-side frame having the configuration of the back-side frame disclosed in JP2005-297960A is formed to have a curved shape so that the recessed portion is formed at the rear portion of the seat, a tension acts on the side end portions of the plate-shaped member, which form the box-shaped portion at the rear portion of the seat. Therefore, flatness of the plate-shaped member may be achieved with accuracy, which may result in facilitating a connection between the recessed portion and the both end portions of the plate-shaped member. However, because the side end portions of the plate-shaped member forming the box-shaped portion are compressed when being processed, unevenness or crinkle is likely to generate on surfaces of the side end portions of the plate-shaped portion. Accordingly, the flatness of the side end portions of the plate-shaped member may not be obtained with high accuracy, which may result in causing a difficulty in connecting the end portions of the plate-shaped member with the recessed portion.

The lower cross member of the seat back frame for the vehicle according to JP2005-67331A may have a rigidity against the torsional bending moment because the lower cross member is formed in the tubular shape. However, the lower cross member and the back-side frame are connected in a manner where an outer circumferential surface of the tube-shaped member contacts an inner circumferential surface of a hole formed at the plate-shaped member, in other words, the lower cross member and the back-side frame are connected along a line (i.e. a connected line). Therefore, in a case where a tension is concentrated on the connected portion between the lower cross member and the back-side frame because of the torsional bending moment, a compression deformation may occur at the connected portion.

The lower cross member of the seat back frame for the vehicle according to DE10048128A1 is formed in the bar shape. Therefore, a rigidity of the lower cross member against the torsional bending member may be lower than the lower cross member formed in the tubular shape. However, because plural lower cross members are provided at the seat back frame for the vehicle disclosed in DE10048128A1, a load applied thereto may be dispersed. The back-side frame and each of the lower cross members are connected in a manner where an outer circumferential surface of the bar-shaped portion contacts an outer circumferential surface of the cylindrical member, in other words, the back-side frame and each of the lower cross members are connected along a line (i.e. a connected line). Therefore, in a case where a tension is concentrated on the connected portions between the lower cross members and the back-side frame because of the torsional bending moment, the connected portions may fracture. Furthermore, according to DE10200404835A1, because the seat back frame is formed as the unit, a load applied thereto may be dispersed. However, the portion corresponding to the lower cross member is formed in a substantially flat surface shape. Therefore, if the seat back frame for the vehicle is even slightly deformed, the seat back frame for the vehicle may be suddenly compressingly deformed.

A need thus exists to provide a seat back frame for a vehicle which is not susceptible to the drawback mentioned above.

SUMMARY

According to an aspect of this disclosure, a seat back frame for a vehicle for supporting a seat back, includes a first back frame, at which a shoulder belt anchor for supporting one end portion of a seat belt is provided, a second back frame arranged substantially in parallel with the first back frame, and a cross member arranged so as to connect the first back frame and the second back frame, wherein a protruding portion or a recessed portion is formed at the cross member so as to extend in a longitudinal direction thereof, a first recessed surface portion or a first protruding surface portion is formed at the first back frame so as to be fittedly connected to the protruding portion or the recessed portion of the cross member, and a second recessed surface portion or a second protruding surface portion is formed at the second back frame so as to be fittedly connected to the protruding portion or the recessed portion of the cross member.

DETAILED DESCRIPTION

An embodiment of a seat frame for a vehicle (which will be hereinafter referred to as a seat frame) having a seat back frame for the vehicle (which will be hereinafter referred to as a seat back frame) will be described below in accordance with the attached drawings. In this embodiment, “up (upward)”, “down (downward)”, “right” and “left” correspond to directions in reference to an occupant seated on a seat for the vehicle (which will be hereinafter referred to as a seat). As illustrated inFIG. 1, the seat frame includes a seat cushion frame10for supporting a seat cushion90, a seat back frame20for supporting a seat back91, a recliner30for rotatably connecting the seatback91relative to the seat cushion90and for adjusting a rotational angle of the seat back91, and a shoulder belt anchor27provided at an upper end portion of the seat back frame20. The shoulder belt anchor27includes a joint portion27aand a belt guide portion27b.

A left side back frame21(a second back frame) and a right side back frame22(the second back frame), each of which is formed so that a cross-sectional shape thereof is formed in a substantially bracket shape and is curved to form a recess at a rear portion of the seat, are arranged at left and right portions of the seat back frame20, respectively. Furthermore, a center back frame23(a first back frame) is provided at a substantially intermediate portion of the seat back frame20. The center back frame23is formed in a quadrangle-hollow-column shape and is curved so as to form a recess at the rear side of the seat. An upper end portion of the left side back frame21and an upper end portion of the right side back frame22are connected by means of an upper cross member24. An upper end portion of the center back frame23is connected to an intermediate portion of the upper cross member24by means of the joint portion27a. The joint portion27aalso protects a shoulder belt portion51a. The belt guide portion27bfor guiding reel out and reel in of the shoulder belt portion51ais provided at an upper portion of the joint portion27a. A lower end portion of the left side back frame21, a lower end portion of the center back frame23and a lower end portion of the right side back frame22are connected by means of a lower cross member25(i.e. a cross member).

A left cushion frame11and a right cushion frame12are provided at left and right portions of the seat cushion frame10, respectively. Furthermore, a cushion center-frame13is provided at a substantially intermediate portion of the seat cushion frame10. A bracket, which is made of a thick plate material, is provided at an upper portion of the cushion center-frame13. The recliner30is provided at the right side back frame22, so that the recliner30rotatably connects the seat cushion frame10and the seat back frame20. The recliner30is connected to a recliner17, which is provided at a portion between the center back frame23and the bracket14by means of a connecting shaft18.

A retractor50is provided at the seat back frame20, so that one end portion of a seat belt51, which includes the shoulder belt portion51aand a lap belt portion51b, is reeled in by the retractor50. The other end portion of the seat belt51is fixed at an anchor plate15, which is attached at the cushion center-frame13. The seat belt51is inserted into a tongue plate52, so that the seat belt51engages with the tongue plate51at a substantially intermediate portion of the seat belt51. The tongue plate52is detachably connected to a buckle16, which is attached to the left cushion frame11. Additionally, a portion of the seat belt51from the retractor50to the tongue plate52is referred to as the shoulder belt portion51a. On the other hand, a portion of the seat belt51from the tongue plate52to the anchor plate15is referred to as the lap belt portion51b.

Detailed explanations about the left and right side back frames21and22, the center back frame23and the lower cross member25will be given below with reference toFIGS. 1 to 5. As illustrated inFIGS. 1 and 2, the left side back frame21, whose cross-section is formed in the substantially bracket shape, is arranged so that an opening portion thereof opens towards the right. Furthermore, the left side back frame21is bent to have a curved shape, so that the recess is formed at the rear portion of the seat. Similarly, the right side back frame22, whose is formed in the substantially bracket shape, is arranged so that an opening portion thereof opens towards the left. Furthermore, the right side back frame22is bent to have a curved shape, so that the recess is formed at the rear portion of the seat. The seat back frame20is curved to have the recess at the rear portion of the seat so as to properly support the back of the occupant.

The center back frame23includes a closed section portion23A at an upper portion thereof and an open section portion23B at lower portion thereof. More specifically, a plate-shaped member is formed in the quadrangle-hollow-column shape and is curved to have the recess at the rear portion of the seat, thereby forming the closed section portion23A at the upper portion of the plate-shaped member (i.e. the center back portion23). Furthermore, a plate-shaped member is bent so that a cross-section thereof forms a substantially bracket shape, so that the plate-shaped member (i.e. the center back portion23) is arranged in a manner where an opening portion thereof opens to the left, thereby forming the open section portion23B at the lower portion of the center back portion23. According to the center back portion23having the above-described configuration, the center back portion23ensures a rigidity because of the closed section portion23A. On the other hand, weight of the center back portion23is reduced because of the open section portion23B. Furthermore, a connection between the recliner17and the center back portion23may be facilitated.

The lower cross member25is made of a band-plate shaped member. Furthermore, the lower cross member25includes a protruding portion25aso as to protrude forward in the front-rear direction of the vehicle and so as to extend in a longitudinal direction of the lower cross member25. A left recessed surface portion21a(a second recessed surface portion) is formed at a rear portion of the left side back frame21. A left-end portion of the protruding portion25a(which will be hereinafter referred to as a left-end protruding portion25aa) formed at the lower cross member25is fitted into and connected to the left recessed surface portion21a. Similarly, a right recessed surface portion22a(the second recessed surface portion) is formed at a rear portion of the right side back frame22. A right-end portion of the protruding portion25a(which will be hereinafter referred to as a right-end protruding portion25ab) is fitted into and connected to the right recessed surface portion22a. A center recessed surface portion23a(i.e. a first recessed surface portion) is formed at a rear portion of the open section surface portion23B of the center back frame23. A substantially intermediate portion of the protruding portion25a(which will be hereinafter referred to as an intermediate protruding portion25ac) is fitted into and connected to the center recessed surface portion23a. Accordingly, the open section portion23B of the center back frame23is reinforced by means of the lower cross member25, thereby ensuring the rigidity of the seat back frame20.

As illustrated inFIGS. 3 to 5, the lower cross member25is formed so that a width wc at the intermediate protruding portion25ac, which is connected to the center back frame23, is formed to be the widest, a width wb at the right-end protruding portion25ab, which is connected to the right side back frame22, is formed to be narrower than the width wc, and a width wa at the left-end protruding portion25aa, which is connected to the left side frame21, is formed to be the narrowest. In other words, the lower cross member25is formed so that the width thereof linearly decreases from the intermediate protruding portion25acto the right-end protruding portion25ab, and from the intermediate protruding portion25acto the left-end protruding portion25aa, in other words, from the width wc to the width wb, and from width wc to the width wa.

A size (an area) of a cross-section of the recessed surface portion23aof the center back frame23is formed to be the greatest when comparing to the right recessed surface portion22aof the right side back frame22and the left recessed surface portion21aof the left side back frame21. A size (an area) of a cross-section of the right recessed surface portion22aof the right side back frame22is set to be smaller than the recessed surface portion23aof the center back frame23but to be greater than the left recessed surface portion21aof the left side back frame21. A size (an area) of a cross-section of the left recessed surface portion21aof the left side back frame21is formed to be the smallest. The protruding portion25aof the lower cross member25is formed so that a size (an area) of a cross-section of the intermediate protruding portion25acis formed to be the greatest so as to correspond to the size (the area) of the cross-section of the center recessed surface portion23a, a size (an area) of the right-end protruding portion25abis formed to be smaller than the intermediate protruding portion25acbut to be greater than the left-end protruding portion25aaso as to correspond to the size (the area) of the left recessed surface portion22a, and a size (an area) of the left-end protruding portion25aais formed to be the smallest so as to correspond to the size (the area) of the left recessed surface portion21a.

As illustrated by oblique lines in a detailed diagram of a portion111B inFIG. 3B, the center back frame23and the lower cross member25are connected to each other at a bottom portion of the center recessed surface portion23aand surrounding portions on the one hand and a top portion of the intermediate protruding portion25acand surrounding portions on the other by welding and the like, and at a flat surface portion23bin the vicinity of the center recessed surface portion23aand a flat surface portion25fcin the vicinity of the intermediate protruding portion25acby welding and the like. As illustrated by oblique lines in a detailed diagram of a portion IVB inFIG. 4B, the right side back frame22and the lower cross member25are connected to each other at a bottom portion and the right recessed surface portion22aand surrounding portions on the one hand and a top portion of the right-end protruding portion25aband surrounding portions on the other by means of welding and the like, and at a flat surface portion22bin the vicinity of the right recessed surface portion22aand a flat surface portion25fbin the vicinity of the right-end protruding portion25abby welding and the like. As illustrated by oblique lines in a detailed diagram of a portion VB inFIG. 5B, the left side back frame21and the lower cross member25are connected to each other at a bottom portion of the left recessed surface portion21aand surrounding portions on the one hand and a top portion of the left-end protruding portion25aaand surrounding portions on the other by welding and the like, and at a flat surface portion21bin the vicinity of the left recessed surface portion21aand a flat portion25fcin the vicinity of the left-end protruding portion25aaby welding and the like. Additionally, screw holes may be provided at the lower cross member25, and screws may be provided at the left side back frame21, the right side back frame22and the center back frame23in order to connect the left side back frame21, the right side back frame22and the center back frame23with the lower cross member25, instead of welding.

Accordingly, because the protruding portion25ais formed at the lower cross member25, the cross-section of the lower cross member25is formed to have an uneven shape (protrusions and recesses), the rigidity of the lower cross member25may be enhanced. Furthermore, the left and right side back frames21and22on the one hand and the lower cross member25on the other hand are connected with each other in a manner where the left and right recessed surface portions21aand22acontact the left-end and right-end protruding portions25aaand25ab, respectively (i.e. a surface connection). Similarly, the center back frame23and the lower cross member25are connected to each other in a manner where the center recessed surface portion23acontacts the intermediate protruding portion25ac(i.e. the surface connection). Therefore, connection strength at connected portions between the left and right side back frames21and22on the one hand and the lower cross member25on the other, and between the center back frame23and the lower cross member25may be enhanced.

In a case where the vehicle is involved in a crash, the seat belt51is pulled forward with a great tensile force because of an inertia of the occupant. As a result, a great load is applied to the shoulder belt anchor27, which is provided at the center back frame23, thereby generating a torsional bending moment at the seat back frame20because of the load. However, as described above, because the rigidity of the lower cross member25is enhanced, a compression deformation may be avoided from occurring at the lower cross member25. Furthermore, because the connection strength between the center back frame23, the left side back frame21and the right side back frame22on the one hand and the lower cross member23on the other is enhanced, the compression deformation or a fracture may be avoided from occurring at each connected portion.

The torsional bending moment, which is generated when the vehicle is involved in the crash, tends to become the maximum at the connected portion between the lower cross member24and the center back frame23. Therefore, the compression deformation or the fracture is likely to occur at the connected portion between the lower cross member25and the center back frame23when the vehicle is involved in the crash. Therefore, the connected portion between the lower cross member25and the center back frame23needs to be formed to have a sufficient width to resist against the maximum torsional bending moment. However, if the lower cross member25is formed in a rectangle shape to have the sufficient width to resist against the maximum torsional bending moment, the lower cross member25is likely to be enlarged. However, according to the lower cross member25of the embodiment, the width we at the connected portion between the center back frame23and the lower cross member25is formed to be wider than the width wa at the connected portion between the left side back frame21and the lower cross member25and the width wb at the connected portion between the right side back frame22and the lower cross member25. Furthermore, the lower cross member25is formed so that the width thereof linearly decreases from the connected portion between the center back frame23and the lower cross member25towards the connected portions between the left and right side back frames21and22on the one hand and the lower cross member25on the other hand. Therefore, the lower cross member25ensures a sufficient resistance against the torisonal bending moment, because the connected portion between the center back portion23and the lower cross member25is formed to have the sufficient width to resist against the maximum torsional bending moment, while the widths of the connected portions between the lower cross member25on the one hand and the left and right side back frames21and22are not unnecessarily enlarged. Accordingly, the lower cross member25may be reduced in size and weight.

Furthermore, in general, the intermediate protruding portion25ac, which is fitted into the center recessed surface portion23aof the center back frame23, needs to be formed to have a sufficient size to resist against the maximum bending moment. However, if the left and right protruding portions25acand25abof the lower cross member25, which are fitted into the left and right recessed surface portions21aand22aof the left and right side back frames21and22, respectively, are formed to have the same size as the intermediate protruding portion25ac, the size of the lower cross member25is increased. However, according to the lower cross member25of the embodiment, the cross-section of the intermediate protruding portion25acis formed to be greater than the cross-sections of the left and right recessed surface portions21aand22aof the respective left and right side back frames21and22. Accordingly, even if the cross-section of the intermediate protruding portion25acis formed to have the sufficient size to resist against the maximum torsional bending moment, the sizes of the left and right recessed surface portions21aand22ado not need to be unnecessarily enlarged. Accordingly, the size and the weight of the lower cross member25may be reduced.

The closed section portion23A of the center back frame23will be described in detail below with reference toFIGS. 6 to 8. As illustrated inFIG. 6, the closed section portion23A of the center back frame23is obtained by bending the plate-shaped member by roll-forming or by press-forming, so that the plate-shaped member forms the quadrangle-hollow-column shape while being curved to form the recess at the rear portion of the seat. A portion of the closed section portion23A forming a right side surface thereof is referred to as a first side plate portion23c. A portion of the closed section portion23A forming a seat front surface is referred to as a first wall portion23d. A portion of the closed section portion23A forming a seat rear surface is referred to as a second wall portion23e. A portion of a left side surface of the closed section portion23A forming a surface, which continuously extends from the first wall portion23d, is referred to as a second side plate portion23f. Furthermore, a portion of the left side surface of the closed section portion23A forming a surface, which continuously extends from the second wall portion23e, is referred to as a third side plate portion23g.

As illustrated inFIG. 7, a lower portion of the closed section portion23A of the center back frame23configures a first linear portion23AL. The first liner portion23AL includes a portion of the first wall portion23dpositioned at a front side of the seat and a portion of the second wall portion23epositioned at a rear side of the seat, whose lateral views form substantially linear shapes. An intermediate portion of the closed section portion23A configures a curved portion23AM, which includes a portion of the first wall portion23d, whose lateral view is greatly curved, and a portion of the second wall portion23e, whose lateral view is gently curved. An upper portion of the closed section portion23A configures a second linear portion23AN, which includes a portion of the first wall portion23dand a portion of the second wall portion23e, whose lateral views form substantially linear shapes. The closed section portion23A of the center back frame23is formed so that an area of the cross-sectional shape thereof is the greatest at the a bottom portion of the first linear portion23AL and gradually decreases from the curved portion23AM towards the second linear portion23AN, so that the cross-sectional shape of the closed section portion23A becomes the smallest at an upper portion of the second linear portion23AN.

A forming process of the closed section portion23A of the center back frame23will be described below. Firstly, a plate-shaped member is pressed to have a shape, from which the closed section portion23A of the center back frame23is formable. As illustrated inFIG. 8A, a recessed portion23hin an arc shape is formed at a portion of the center back frame23where a curvature thereof is increased, i.e. at a side end portion corresponding to a portion of the second side plate portion23fat the curved portion23AM. Generally, when one side end portion of the first wall portion23d, which forms the recess at the rear side of the seat, is bent towards the rear side of the seat in order to form the second side plate portion23f, compression is likely to be generated in the vicinity of a side end portion of the second side plate portion23fat the curved portion23AM, which may result in generating an unevenness or a crinkle thereat. However, according to this embodiment, because the recessed portion23hin the arc shape is formed at the side end portion of the second side plate portion23fat the curved portion23AM, the compression generated in the vicinity of the side end portion of the second side plate portion23fmay be reduced, therefore, the unevenness or the crinkle may be avoided from being generated at the second side plate portion23f. As a result, the surface of the second side plate portion23fmay be formed with high accuracy.

As illustrated inFIG. 8A, both end portions of the first side plate portion23c, which configures the right side surface, are bent so as to form the recess at the rear side of the seat, thereby forming the first wall portion23d, which is positioned at the front side of the seat, and the second wall portion23e, which is positioned at the rear side of the seat. In this case, as mentioned above, both end portions of the side end portions of the second side plate portion23fin an up-and-down direction are positioned closer to each other. However, the compression generated in the vicinity of the side end portion of the second side plate portion23fmay be reduced because of the recessed portion23hin the arc shape. Then, as illustrated inFIG. 9A, one side end portion of the first wall portion23dis bent towards rear side of the seat, thereby forming the second side plate portion23f. The second side plate portion23fis further bent until the second side plate portion23fbecomes substantially in parallel with the first side plate portion23c, and one side end portion of the second wall portion23eis bent towards the front side of the seat to form the third side plate portion23g, as illustrated inFIG. 10A. In this case, the both end portions of the side end portion of the second side plate portion23fat the curved portion23AM are positioned further closer to each other. However, the compression generated in the vicinity of the side end portion of the second side plate portion23fmay be reduced because of the recessed portion23hin the arc shape. Accordingly, the unevenness or the crinkle may be avoided from being generated in the vicinity of the side end portion of the second side plate portion23fat the curved portion23AM. As a result, the surface of the second side plate portion23fmay be formed with high accuracy.

In the case where the second side plate portion23fis formed, a curvature radius Rdf formed at a bent portion23dfbetween the first wall portion23dand the second side plate portion23fis set to be greater than a curvature radius Rcd formed at a bent portion23cdbetween the first side plate portion23cand the first wall portion23d, a curvature radius Rce formed at a bent portion23ceformed between the first side plate portion23cand the second wall portion23eand a curvature radius Reg formed at a bent portion23egbetween the second wall portion23eand the third side plate portion23g(see a diagram viewed in a direction H inFIG. 11A). By forming the curvature radius Rdf at the bent portion23dfto be great, an excessive compression may be avoided from being generated in the vicinity of the side end portion of the second side plate portion23f. Accordingly, the unevenness or the crinkle may be avoided from being generated in the vicinity of the side end portion of the second side plate portion23fat the curved portion23AM. As a result, the surface of the second side plate portion23fmay be formed with further high accuracy.

As illustrated inFIG. 11A, the third side plate portion23gis further bent until the third side plate portion23gbecomes substantially in parallel with the first side plate portion23c, so that the third side plate portion23gis overlapped on the second side plate portion23fin a manner where the third side plate portion23gcontacts the second side plate portion23f. In this case, because an accuracy of the surface-forming of the second side plate portion23fis enhanced, an overlapped portion between the second side plate portion23fand the third side plate portion23gis easily and properly connected. Furthermore, because the first side plate portion23fand the third side plate portion23gare closely in contact with each other, the second side plate portion23fand the third side plate portion23gmay be connected by laser welding, which may result in reducing man-hours for forming the center back frame23.

A connected portion23fgbetween the second side plate portion23fand the third side plate portion23gis set so that a distance d between the connected portion23fgand a center point C of the curvature radius formed at the bent portion23dfbetween the first wall portion23dand the second side plate portion23fbecomes as small as possible. In other words, the connected portion23fgis positioned in the vicinity of a corner portion of the center back frame23at a front-left side of the seat. In a case where the connected portion23fgbetween the second side plate portion23fand the third side plate portion23gis positioned in the vicinity of a corner portion of the center back frame23at a rear-left side of the seat, a length of the second side plate portion23ffrom the bent portion23dfneeds to be enlarged. In this case, a further excessive compression is likely to be generated in the vicinity of the side end portion of the second side plate portion23fbecause of bending of the second plate portion23f, an occurrence of the unevenness of the crinkle in the vicinity of the side end portion of the second side plate portion23fat the curved portion23AM may be difficult to avoid. Therefore, in this embodiment, the connected portion23fgbetween the second side plate portion23fand the third side plate portion23gis positioned in the vicinity of the corner portion of the center back frame23at the front-left side of the seat, the occurrence of the unevenness or the crinkle in the vicinity of the side end portion of the second side plate portion23fat the curved portion23AM may become avoidable. In other words, a position of the connected portion23fgbetween the second side plate portion23fand the third side plate portion23gis set at an unevenness and crinkle-occurrence avoiding limited position, and at a position where a surface of the second side plate portion23fand a surface of the third side plate portion23gcontact with each other. Furthermore, as described above, when the vehicle is involved in the crash, the seat belt51is pulled forward with the great tensile force because of the inertia of the occupant, therefore, the great load is applied to the shoulder belt anchor27, which is provided at the center back frame23. As a result of the great load applied to the shoulder belt anchor27, the torsional bending moment is generated at the seat back frame20. In this case, a compression force acts on the first wall portion23dof the center back frame23positioned at the front side of the seat. However, because the connected portion23fgbetween the second side plate portion23fand the third side plate portion23gis located at a position the distance d away from the first wall portion23d, a moment smaller than the moment acting on the first wall portion23dacts on the connected portion23fg. Therefore, an occurrence of the compression deformation at the connected portion23fgmay be avoidable.

The reclining apparatus will be described in detail below with reference toFIGS. 9 and 10. The recliner30is formed in a disc shape. More specifically, the recliner30includes a lower plate31, an upper plate33and a holder34. The lower plate31is attached to the right cushion frame12by welding. The upper plate33is attached to the right side back frame22by welding. The holder34covers outer circumferential surfaces of the lower and upper plates31and33. A recessed portion is formed at the lower plate31by half cutting, so that the lower plate31is arranged to open towards the upper plate33. The upper plate33is fitted into the recessed portion of the lower plate31while allowing an inner circumferential surface of the recessed portion of the lower plate31and the outer circumferential surface of the upper plate33slidably contact with each other. A slidably-contact surface between the lower plate31and the upper plate33serves as an axis and a bearing in a case where the lower plate31and the upper plate33rotate. A recessed portion is formed at the upper plate33by half cutting, so that the upper plate33is arranged to open towards the lower plate31. A gear32, with which a reclining lock mechanism is meshed, is formed along an entire inner circumferential portion of the recessed portion of the upper plate33. A stepped portion33ain a disc shape is formed at an end surface of the upper plate33opposite from a surface at which the recessed portion is formed. A stopper plate35is fitted onto the stepped portion33a. Furthermore, plural column-shaped protruding portions33b(in this embodiment, six protruding portions33b) are formed at the end surface of the upper plate33. The protruding portions33bare fitted into the right side back frame22. The protruding portions33bform a forming pitch circle centering on an axis hole33cof the upper plate33so as to have a predetermined diameter. Furthermore, the protruding portions33bare provided at an end surface of the stepped portion33awhile forming regular angles (in this embodiment, 60 degrees) between the neighboring protruding portions33b. The protruding portions33bare fitted into upper plate holes33d, which are formed in elliptical shapes at the right side back frame22.

An attachment mechanism of the recliner30includes the stopper plate35for controlling an inclined angle of the seat back frame20, a spiral spring36for biasing the seat back frame20towards the front side of the seat, a spring mount37, at which one end portion of the spiral spring36is engaged, and a hook38, at which the other end portion of the spiral spring36is engaged and to which the stopper plate35contacts. The stopper plate35is formed in a ring-plate shape. More specifically, protruding portions35aare formed at an inner circumferential surface of the stopper plate35so as to serve as detent. Furthermore, two protruding portions35baand35bbare formed at circumferential lower portions of the stopper plate35while forming a predetermined angle. Furthermore, the protruding portions35baand35bbare formed so as to be contactable with the hook38. When the protruding portion35bacontacts the hook38, the seat back frame20is inclined to the rear-most position at the seat. On the other hand, when the protruding portion35bbcontacts the hook38, the seat back frame20is inclined to the front-most position at the seat. The stopper plate35is fitted onto the stepped portion33a, which is formed at the end surface of the upper plate33so as to have a shape corresponding to the inner circumferential shape of the stopper plate35, so as not to rotate relative to each other. Additionally, the upper plate33is attached to the right side back frame22in a state where the stopper plate35is fitted onto the upper plate33.

The spring mount37is formed in a half-cylindrical shape. More specifically, the spring mount37includes protruding portions37a, which serve as detents, and an engagement portion37bfor engaging one end portion of the spiral spring36therewith at an end portion of an outer circumferential surface of the spring mount37. The spring mount37is fixed at the right side back frame22by welding and the like in a state where the protruding portions37aare fitted in spaces formed between neighboring protruding portions33bof the upper plate33protruding from the respective upper plate holes33dof the right side back frame22. The engagement portion37bis obtained by being a protruding portion so as to form a clearance relative to the outer circumferential surface of the spring mount37. An inner end portion of the spiral spring36is fitted into the clearance formed between the engagement portion37band the outer circumferential surface of the spring mount37, thereby engaging the spiral spring36with the spring mount37.

The hook38includes an attachment portion38a, which is formed in a rectangular-plate shape and which is attached to the right cushion frame12, a contacting portion38b, which extends from one end portion of the attachment portion38aso as to be contactable with the stopper plate35, and an engagement portion38c, which is formed to protrude from the contacting portion38bin a substantially L-shape so that the other end portion of the spiral spring36is engaged with the engagement portion38c. The attachment portion38ais provided at a position of the hook38so as to be positioned in the vicinity of a lower portion of the recliner30, which is attached to the right cushion frame12, so that the contacting portion38bis contactable only with the protruding portions35baand35bbof the stopper plate35, and so that the contacting portion38band the engagement portion38cdo not interfere other components. Additionally, a cut-out is provided at the lower end portion of the right side back frame22, so that the right side back frame22does not interfere with the contacting portion38bof the hook38. The engagement portion38cis divided into two while forming a clearance therebetween. An outer end portion of the spiral spring36is fitted into and engaged within the clearance of the engagement portion38c.

Accordingly, the recliner30, to which the stopper plate35is fitted, is arranged between the right cushion frame12and the right side back frame22. The spiral spring36and the spring mount37are arranged at the left side relative to the right side back frame22. A hinge shaft39a, at which an operation lever39is fixed, penetrates and is inserted into a shaft hole, which is formed at the right side back frame22, through a shaft hall12hformed at the right cushion frame12and a shaft hall33cformed at the upper plate33. On the other hand, the recliner17, which has a similar configuration as the recliner30, is attached on the center back frame23. The hinge shaft39aof the recliner30is connected to a hinge shaft of the recliner17via the connecting shaft18. When the operation lever39is upwardly rotated, the locked state of the reclining lock mechanisms of the recliner30and the recliner17is cancelled, thereby allowing the seat back91to be reclinable forward and rearward.

Generally, a known seat back frame20does not include a hook for engaging an end portion of a spiral spring therewith at an outer side relative to a recliner. Therefore, the recliner and the like are likely to be enlarged, which may result in increasing size and weight of a seat (see e.g. JP2008-54712). On the other hand, according to the above-descried embodiment, the engagement portion38cof the hook38, to which the end portion of the spiral spring36is engaged, is arranged at an inner side relative to an outer circumferential portion of the recliner30. Therefore, the recliner30and the like may be reduced in size. Accordingly, the size and the weight of the seat may be reduced.

The case where the manual-type reclining apparatus is adapted as the reclining apparatus is described above. In a case where the power-type reclining apparatus is manufactured on the basis of the manual-type reclining apparatus without largely changing the configuration of the seat, the manufacturing costs may be reduced. Therefore, it may be favorable if each component used at the reclining apparatus is formed so as to be commonly used for both of the manual-type reclining apparatus and the power-type reclining apparatus. However, generally, an external gear of an upper ring, which is provided within the power-type recliner, eccentrically moves relative to an internal gear of a gear plate. Therefore, a forming pitch circle of protruding portions of an upper plate of the power-type reclining apparatus needs to be formed so as to be greater than a forming pitch circle of the protruding portions33bof the upper plate33of the manual-type reclining apparatus.

Generally, the upper plate holes are formed at the right back frame so as to correspond to the forming pitch circle of the power-type reclining apparatus or the forming pitch circle of the manual-type reclining apparatus. Therefore, in a case where the components used for the manual-type reclining apparatus are adapted to the power-type reclining apparatus, the right side back frame22needs to be newly formed, which may result in an increase of the manufacturing costs (see e.g. JP1009976A). On the other hand, according to the seat back frame20of the embodiment, plural upper plate holes33d(in this embodiment, six upper plate holes33d) in the elliptical shapes are formed at the right side back frame22in a radial manner centering on the shaft hole33c. Therefore, as illustrated inFIG. 14A, radially inner portions of the respective upper plate holes33din the elliptical shapes are formed to correspond along the forming pitch circle of the protruding portions33bof the manual-type reclining apparatus. Furthermore, as illustrated inFIG. 14B, radially outer portions of the respective upper plate holes33din the elliptical shapes are formed to correspond along a forming pitch circle of protruding portions33bp of the power-type reclining apparatus. Accordingly, the protruding portions33bp of an upper plate33p, which is adapted to the power-type reclining apparatus, may be fitted into the respective upper plate holes33dwithout reforming the right side back frame22.

Accordingly, the right side back frame22is adaptable to both of the manual-type reclining apparatus and the power-type reclining apparatus without newly forming the right side back frame22, which may result in reducing the manufacturing costs. In this case, the right side back frame22and the upper plate33of the manual-type reclining apparatus are connected at a portion pm (a connected portion) connecting the upper plate holes33dof the manual-type reclining apparatus. On the other hand, in the case where the power-type reclining apparatus is adapted to the seat back frame20of this embodiment, the right side back frame22and the upper plate33pare connected at a portion pp (a connected portion) positioned at a radially outer side relative to the upper plate holes33d. The right side back frame22is connected to the upper plate33of the manual-type reclining apparatus at the portion pm by laser welding or arc welding. Similarly, the right side back frame22is connected to the upper plate33pof the power-type reclining apparatus by the laser welding or the arc welding. Accordingly, the connection strength between the upper plate33and the right side back frame22, and between the upper plate33pand the right side back frame22may be ensured.

In this embodiment, the protruding portion25ais formed at the lower cross member25. Furthermore, the left recessed surface portion21aand the right recessed surface portion22a, to which the protruding portion25ais fitted, are formed at the left and right side back frames21and22, respectively. However, the back seat frame of the embodiment may be modified so that a recessed portion is formed at the lower cross member25, a left protruding surface portion (the second protruding surface portion) and a right protruding surface portion (the second protruding surface portion), with which the recessed portion of the lower cross member25engages, are formed at the respective left and right side back frames21and22, and a center protruding surface portion (the first protruding surface portion), with which the recessed portion of the lower cross member25engages, is formed at the center back frame23. Even in this case, advantages and merits similar to the advantages and merits described above are achievable.

According to the seat back frame20of the embodiment, the protruding portion25aor the recessed portion is formed at the lower cross member25so as to extend in the longitudinal direction thereof, the center recessed surface portion23aor the center protruding surface portion is formed at the center back frame23, the left and right recessed surface portions21aand22aor the left and right protruding surface portions are formed at the respective left and right side back frames21and22, so that the protruding portions25aor the recessed portion of the lower cross member25engages with the center recessed surface portion23aor the center protruding surface portion and the left and right recessed surface portions21aand22aor the left and right protruding surface portions. Accordingly, the center back frame23, the left side back frame21and the right side back frame22on the one hand and the lower cross member25on the other hand are connected to each other in a manner where the surfaces of respective center back frame23, the left side back frame21and the right side back frame22contact the surface of the lower cross member25(i.e. the surface contact). Therefore, the connection strength at the connected portions between center back frame23, the left side back frame21and the right side back frame22on the one hand and the lower cross member25on the other hand may be increased. Furthermore, because the cross-section of the lower cross member25is formed in the uneven shape. The rigidity of the lower cross member25may be increased. Accordingly, even in the case where the seat belt51is pulled forward with the great tensile force because of the inertia of the occupant when the vehicle is involved in the crash, so that the great load is applied to the shoulder belt anchor27, which is provided at the center back frame23, and the torsional bending moment is generated at the seat back frame20because of the load, the occurrence of the compression deformation or the fracture at the connected portions between the center back frame23, the left side back frame21and the right side back frame22on the one hand and the lower cross member25on the other hand may be avoidable. As a result, the occurrence of the compression deformation of the lower cross member25may be avoidable.

Furthermore, the lower cross member25in the band-plate shape is formed so that the width we at the connected portion, at which the center back frame23and the lower cross member25are connected, is set to be wider than the widths wa and wb at the connected portions between the lower cross member25on the one hand and the left and the right side back frames21and22on the other hand. The torsional bending moment, which is generated when the vehicle is involved in the crash, is likely to reach the maximum at the connected portion between the lower cross member25and the center back frame23. Hence, the compression deformation or the fracture is likely to be generated at the connected portion when the vehicle is involved in the crash. Therefore, generally, the connected portion between the lower cross member25and the center back frame23needs to be formed to have a sufficient width to resist against the maximum torsional bending moment. However, if the lower cross member is formed in the rectangle shape while having the sufficient width to resist against the maximum torisonal bending moment, the size of the lower cross member is likely to be increased. On the other hand, according to the lower cross member25having the above-described configuration, even if the connected portion of the lower cross member25, at which the lower cross member25and the center back frame23are connected, is formed to have the sufficient width to resist against the maximum torsional bending moment, the widths of the connected portions, at which the lower cross member25contacts the left and right side back frames21and22, do not need to be unnecessarily enlarged. As a result, the size and the weight of the lower cross member25may be reduced.

Furthermore, according to the embodiment, the center back frame23is formed so that the cross-sectional shape of the center recessed surface portion23aor the center protruding surface portion thereof becomes greater than the cross-sectional shapes of the left and right recessed surface portions21aand22aor the left and right protruding surface portions of the respective left and right side back frame21and22. Accordingly, the cross-sectional shape of protruding portion25acor a recessed portion of the protruding portion25a, which is engaged with the center recessed surface portion23aor the center protruding surface portion of the center back frame23, is also formed to be greater than the protruding portions25aaand25abor the recessed portions of the lower cross member25, which are engaged with the left and right recessed surface portions21aand22aor the left and right protruding surface portions of the left and right side back frames21and22, respectively.

The torsional bending moment, which is generated when the vehicle is involved in the crash, becomes the maximum at the connected portion between the center back frame23and the lower cross member25. Therefore, the compression deformation or the fracture is likely to be generated at the connected portion between the center back frame23and the lower cross member25. Hence, generally, the protruding portion25acor the recessed portion of the lower cross member25, which is engaged with the center recessed surface portion23aor the center protruding surface portion of the center back frame23, needs to have a sufficient size to resist against the maximum torsional bending moment. However, if the entire protruding portion25aor the entire recessed portion of the lower cross member25, which are engaged with the left and right recessed surface portions21aand22aor the left and right protruding surface portions of the respective left and right side back frames21and22, is formed to have the same size as the protruding portion25acor the recessed portion of the lower cross member25, the size of the lower cross member25is increased. On the other hand, according to the lower cross member25having the above-described configuration, even if the protruding portion25acor the recessed portion of the lower cross member25, which is engaged with the center recessed surface portion23aor the center protruding surface portion of the center back frame23, is formed to have the sufficient size to resist against the maximum torsional bending moment, the protruding portions25acand25abor the recessed portions, which are engaged with the respective left and right recessed surface portions21aand22aor the left and right protruding surface portions of the respective left and right side back frames21and22, do not need to be unnecessarily enlarged. Therefore, the size and the weight of the lower cross member25may be reduced.

According to the embodiment, the center back frame23includes the closed section portion23A and the open section portion23B. Furthermore, the center recessed surface portion23aor the center protruding portion is formed at the open section portion23B, so that the lower cross member25is connected thereto. According to the center back frame23having the above-described configuration, the rigidity thereof is ensured because of the closed section portion23A, while the weight of the center back frame23is reduced because of the open section portion23B. Furthermore, because the open section portion23B is reinforced by the lower cross member25, the rigidity of the seat back frame20is further enhanced. Additionally, in this embodiment, the case where the seat back frame20is adapted to the seat for two passengers. However, the seat back frame20of the embodiment may be adapted to a seat for one passenger.

Accordingly, both end portions of the first side plate portion23c, which form one side surface, of the center back frame23, which is formed in the hollow rectangular column shape, are bent so as to form the recess at the rear side of the seat, thereby forming the first wall portion23dpositioned at the front side of the seat and the second wall portion23epositioned at the rear side of the seat. One side end portion of the first wall portion23dis bent towards the rear side of the seat so as to be substantially in parallel with the first side plate portion23c, thereby forming the second side plate portion23f. Similarly, one side end portion of the second wall portion23eis bent towards the front side of the seat so as to be substantially in parallel with the first side plate portion23c, thereby forming the third side plate portion23g. The third side plate portion23gis overlapped on the second side plate portion23f, so that the third side plate portion23gcontacts the second side plate portion23f. More specifically, the overlapped portion between the second side plate portion23fand the third side plate portion23gare connected at a portion of the overlapped portion in the vicinity of the bent portion23dfbetween the first wall portion23dand the second side plate portion23f.

In the case where the connected portion23fgbetween the second side plate portion23fand the third side plate portion23gis positioned in the vicinity of the bent portion23egbetween the second wall portion23eand the third side plate portion23g, the length of the second side plate portion23ffrom the bent portion23dfbetween the first wall portion23dand the second side plate portion23fneeds to be increased. However, the excessive compression may be generated in the vicinity of the side end portion of the second side plate portion23fbecause of bending, the occurrence of the unevenness or the crinkle in the vicinity of the side end portion of the second side plate portion23fmay be difficult to avoid. Therefore, in this embodiment, the connected portion23fgbetween the second side plate portion23fand the third side plate portion23gis positioned in the vicinity of the bent portion23dfbetween the first wall portion23dand the second side plate portion23f, so that the occurrence of the unevenness or the crinkle in the vicinity of the side end portion of the second side plate portion23fis avoidable. Furthermore, in the case where the vehicle is involved in the crash and the seat belt51is pulled forward with the great tensile force because of the inertia of the occupant, the great load is applied to the shoulder belt anchor27, which is provided at the center back frame23, so that the torsional bending force is generated at the seat back frame20because of the load applied to the shoulder belt anchor27. As a result, the compression force acts on the first wall portion23dpositioned at the front side of the seat. However, according to the embodiment, because the connected portion23fgbetween the second side plate portion23fand the third side plate portion23gis positioned in the vicinity of the first wall portion23d, a smaller bending moment than the moment acting on the first wall portion23dacts on the connected portion23fg. Accordingly, the occurrence of the compression deformation at the connected portion23fgmay be avoidable.

The recessed portion23his formed at the side end portion of the second side plate portion23fat the portion23AM, at which the curvature of the center back frame23is increased. Generally, in the case where one end portion of the first wall portion23d, at which the recess is formed to as to be positioned at the rear side of the seat, is bent towards the rear side of the seat in order to form the second side plate portion23f, the compression is likely to occur in the vicinity of the side end portion of the second side plate portion23f, which may result in generating the unevenness or the crinkle in the vicinity of the side end portion of the second side plate portion23fat the portion23AM, at which the curvature of the center back frame23is increased. However, according to the embodiment, because the recessed portion23his formed at the side end portion of the second side plate portion23fat the portion23AM, at which the curvature of the center back frame23is increased, the compression in the vicinity of the side end portion of the second side plate portion23fmay be reduced, which may result in avoiding the occurrence of the unevenness or the crinkle at the second side plate portion23f. Accordingly, the surface of the second side plate portion23fmay be formed with high accuracy. Furthermore, the second side plate portion23fand the third side plate portion23gare easily and surely connected at the overlapped portion therebetween.

Furthermore, the bent portion23dfbetween the first wall portion23dand the second side plate portion23fis formed so that the curvature radius Rdf at the bent portion23dfis set to be greater than other curvature radiuses Rcd, Rce and Reg (i.e. the curvature radius Rcd at the bent portion23cdbetween the first side plate portion23cand the first wall portion23d, the curvature radius Rce at the bent portion23cebetween the first side plate portion23cand the second wall portion23eand the curvature radius Reg at the bent portion23egbetween the second wall portion23eand the third side plate portion23g). Accordingly, the compression generated in the vicinity of the side end portion of the second side plate portion23fis reduced, which may further result in avoiding the occurrence of the unevenness or the crinkle in the vicinity of the side end portion of the second side plate portion23f. As a result, the surface of the second side plate portion23fis formed with high accuracy, which may further result in easily and surely connecting the second side plate portion23fand the third side plate portion23gat the overlapped portion therebetween. In the above-described embodiment, the seat back frame20is adapted to the seat for two passengers. However, the seat back frame20may be adapted to a seat for one passenger.

According to the embodiment, the seat back frame20for supporting the seat back91includes the center back frame23, which is formed in a hollow angular column shape and at which the shoulder belt anchor27for supporting one end portion of the seat belt51is provided. Furthermore, the seat back frame20includes the left and right side back frames21and22, which are arranged at the left and right sides relative to the center back frame23so as to be substantially in parallel with each other (i.e. so as to be substantially aligned with each other). The center back frame23includes the first side plate portion23cforming one side surface of the first back frame23, the first wall portion23dand the second wall portion23e, which are formed by bending both end portions of the first side plate portion23fso as to form the recess at the rear side of the seat, so as to be positioned at the rear side and a front side of the seat, respectively, the second side plate portion23f, which is obtained by bending the side end portion of the first wall portion23dtowards the rear side of the seat so as to become substantially in parallel with the first side plate portion23c, and the third side plate portion23g, which is obtained by bending the side end portion of the second wall portion23etowards the front side of the seat so as to become substantially in parallel with the first side plate portion23c. The third side plate portion23gis overlapped on the second side plate portion23fso as to be in contact with each other, and the second side plate portion23fand the third side plate portion23gare connected at the overlapped portion in the vicinity of the bent portion between the first wall portion23dand the second side plate portion23f.

In the case where the connected portion between the second side plate portion23fand the third side plate portion23gis positioned in the vicinity of the bent portion between the second wall portion23eand the third side plate portion23g, the length of the second side plate portion23ffrom the bent portion between the first wall portion23dand the second side plate portion23fneeds to be increased. In this case, the excessive compression may be generated in the vicinity of the side end portion of the second side plate portion23fwhen being bent to from the second side plate portion23f. Therefore, the occurrence of the unevenness or the crinkle in the vicinity of the side end portion of the second side plate portion23fmay be difficult to be avoided. Therefore, in this embodiment, the connected portion between the second side plate portion23fand the third side plate portion23gis positioned in the vicinity of the bent portion between the first wall portion23dand the second side plate portion23f. Accordingly, the occurrence of the unevenness or the crinkle in the vicinity of the side end portion of the second side plate portion23fmay be avoidable. Furthermore, in the case where the vehicle is involved in the crash and the seat belt51is pulled forward with the great tensile force because of the inertia of the occupant, the great load is applied to the shoulder belt anchor27, which is provided at the center back frame23, which may result in generating the torsional bending moment at the seat back frame20because of the load applied to the shoulder belt anchor27. As a result, the compression force acts on the first wall portion23dpositioned at the front side of the seat. However, according to the embodiment, because the connected portion between the second side plate portion23fand the third side plate portion23gis positioned in the vicinity of the first wall portion23d, a smaller bending moment than the moment acting on the first wall portion23dacts on the connected portion. Accordingly, the occurrence of the compression deformation at the bending portion may be avoidable.

According to the embodiment, the recessed portion23his formed at the side end portion of the second side plate portion23fat the portion23AM, at which the curvature of the center back-side frame23is increased. Furthermore, according to the embodiment, the bent portion between the first wall portion23dand the second side plate portion23fis formed so that the curvature radius at the bent portion is set to be greater than the curvature radiuses at other bend portions of the center back frame23.

Generally, in the case where the one side portion of the first wall portion23dis bent towards the rear side of the seat in order to form the second side plate portion23f, the compression is likely to be generated in the vicinity of the side end portion of t second side plate portion23f, which may further result in generating the unevenness or the crinkle in the vicinity of the side end portion of the second side plate portion23fat the portion23AM, at which the curvature of the center back frame23increases. However, according to the embodiment, because the recessed portion23his formed at the side end portion of the second side plate portion23fat the portion23AM, at which the curvature of the center back frame23increases, the compression generated in the vicinity of the second side plate portion23fmay be reduced, which may result in avoiding the occurrence of the unevenness or the crinkle at the second side plate portion23f. As a result, the surface of the second side plate23fmay be formed with high accuracy. Furthermore, the second side plate23fand the third side plate23gmay be easily and surely connected with each other.

Accordingly, the occurrence of the unevenness or the crinkle generated in the vicinity of the side end portion of the second side plate portion23fmay be further avoidable. Accordingly, because the surface of the second side plate23fis formed with high accuracy, the second side plate portion23fand the third side plate portion23gmay be further easily and surely connected with each other.

The lower cross member25includes the protruding portion25aor the recessed portion so as to extend in the longitudinal direction thereof. The center back frame23includes the center recessed surface portion23aor a center protruding surface portion, which is fittedly connected to the protruding portion25aor the recessed portion of the lower cross member25. Furthermore, the left side back frame21and the right side back frame22includes the left recessed surface portion21aand the right recessed surface portion22aor a left protruding surface portion or a right recessed surface portion, respectively, so that the left recessed surface portion21aand the right recessed surface portion22aor a left protruding surface portion or a right recessed surface portion are fittedly connected to the protruding portion25aor the recessed portion of the lower cross member25. Accordingly, the center back frame23, the left side back frame21and the right side back frame22on the one hand and the lower cross member25on the other contact with one another at the surfaces of the center back frame23, the left side back frame21, the right side back frame22and the lower cross member25, therefore, the connection strength at the connected portions (connected surfaces) between the center back frame23, the left side back frame21and the right side back frame22on the one hand and the lower cross member25on the other may be increased. Additionally, because the lower cross member is formed so that the cross-sectional shape thereof is formed to be uneven, the rigidity of the lower cross member may be increased. Therefore, even if the vehicle is involved in the crash and the seat belt51is pulled forward with the great tensile force because of the inertia generated by the occupant, so that the great load is applied to the shoulder belt anchor27and the torsional bending moment is generated at the seat back frame20for the vehicle because of the load applied to the shoulder belt anchor27, the occurrence of the compression deformation or the fracture at the connected portions between the center back frame23, the left side back frame21and the right side back frame22on the one hand and the lower cross member25on the other may be avoided. Furthermore, the occurrence of the compression deformation of the lower cross member25may be avoidable.

According to the embodiment, the lower cross member25is formed in the band-plate shape so that the width of the portion of the lower cross member25connected to the center back frame23is set to be wider than the width of the portions of the lower cross member25connected to the left and right side back frames21and22, respectively.

Accordingly, the lower cross member25in the band-plate shape is formed so that the width of the portion of the lower cross member25connected to the center back frame23is set to be wider than the width of the portions of the lower cross member25connected to the left and right side back frames21and22. The torsional bending moment generated when the vehicle is involved in the crash is likely to become the maximum at the connected portion between the center back frame23and the lower cross member25. Therefore, the compression deformation or the fracture is likely to be generated at the connected portion between the center back frame23and the lower cross member25. Hence, the connected portion between the center back frame23and the lower cross member25needs to have a sufficient width to resist against the maximum torsional bending moment. However, if the lower cross member is formed in the rectangular shape having the sufficient width to resist against the maximum torsional bending moment, the lower cross member25is likely to be enlarged. However, according to the above-described configuration of the lower cross member25, even if the connected portion between the lower cross member25and the center back frame23is formed to have the sufficient width to resist against the maximum torsional bending moment, the connected portions between the lower cross member25on the one hand and the left and right side back frames21and22on the other hand are avoided from unnecessarily being enlarged. Accordingly, the size and the weight of the lower cross member25may be reduced.

According to the embodiment, the center back frame23is formed so that the cross-sectional area of the center recessed portion23aor the first protruding surface portion thereof is set to be greater than the cross-sectional area of the left and right recessed surface portions21aand22aor the left and right protruding surface portion of the left and right side back frames21and22, respectively.

Accordingly, the center recessed surface portion23aor the center protruding surface portion of the center back frame23is formed so that the cross-sectional area thereof is formed to be greater than the cross-sectional area of the left recessed surface portion21aand the right recessed surface portion22aor the left protruding surface portion and the right protruding surface portion of the left side back frame21and the right back frame22, respectively. Accordingly, the lower cross member25is also formed so that the cross-sectional area of a portion of the protruding portion25aor the recessed portion thereof fittedly connected to the center recessed surface portion23aor the center protruding surface portion of the center back frame23is set to be greater than the cross-sectional area of portions of the protruding portion25aor the recessed portion fittedly connected to the respective left recessed surface portion21aand the right recessed surface portion22aor the respective left protruding surface portion and the right protruding surface portion (i.e. the left-end protruding portion25aaand the right-end protruding portion25abor a left-end recessed portion and a right-end recessed portion).

The torsional bending moment generated when the vehicle is involved in the crash becomes the maximum at the connected portion between the center back frame23and the lower cross member25. Therefore, the compression deformation or the fracture is likely to occur at the connected portion between the center back frame23and the lower cross member25. Hence, the portion of the protruding portion25aor the recessed portion of the lower cross member25(i.e. the intermediate protruding portion25acor the intermediate recessed portion) fittedly connected to the center recessed surface portion23aor the center protruding surface portion of the center back frame23needs to have a sufficient size so as to resist against the maximum torsional bending moment. However, if the portions of the protruding portion25aor the recessed portion of the lower cross member25(i.e. the left-end protruding portion25aaand the right-end protruding portion25ebor the left-end recessed portion and the right-end recessed portion of the lower cross member) fittedly connected to the left recessed surface portion21aand the right recessed surface portion22aor the left protruding surface portion and the right protruding surface portion of the left and right side back frames21and22, respectively, are formed to have the same size as the portion of the protruding portion25aor the recessed portion of the lower cross member25(i.e. the intermediate protruding portion25acor the intermediate recessed portion) fittedly connected to the center recessed surface portion23aor the center protruding surface portion of the center back frame23, the size of the lower cross member25is likely to be increased. However, according to the lower cross member25having the above-described configuration, even if the portion of the protruding portion25aor the recessed portion of the lower cross member25(i.e. the intermediate protruding portion25acor the intermediate recessed portion) fittedly connected to the center recessed surface portion23aor the center protruding surface portion of the center back frame23is formed to have the sufficient size to resist against the maximum torsional bending moment, the portions of the protruding portion25aor the recessed portion of the lower cross member25(i.e. the left-end protruding portion25aaand the right-end protruding portion25ebor the left-end recessed portion and the right-end recessed portion of the lower cross member) fittedly connected to the left recessed surface portion21aand the right recessed surface portion22aor the left protruding surface portion and the right protruding surface portion of the left and right side back frames21and22, respectively, do not necessarily be enlarged. Accordingly, the size and the weight of the lower cross member25may be reduced.

According to the embodiment, the center back frame23includes the closed section portion23A and the open section portion23B. The center recessed portion23aor the first protruding surface portion is formed at the open section portion23B of the center back frame23.

Accordingly, the center back frame23includes the closed section portion23A and the open section portion23B, so that the center recessed surface portion23aor the center protruding surface portion of the center back frame23is formed at the open section portion23B, at which the lower cross member is connected. Accordingly, the center back frame23having the above-described configuration ensures the rigidity at the closed section portion23A, while the weight of the center back frame23is reduced because of the open section portion23B. Furthermore, the rigidity of the center back frame23at the open section portion23B is reinforced by the lower cross member.

According to the embodiment, the second back frame includes a pair of left and right side back frames21and22positioned at the left and right portions of the seat back91, respectively. The first back frame includes the center back frame23arranged between the pair of the left and right side back frames21and22. Furthermore, the lower cross member25is arranged so as to connect the pair of the left and right side back frames21and22and the center back frame23.

Accordingly, the seat back frame20for the vehicle according to the embodiment is adaptable to any seat used for, for example, a rear seat, and for any desired number of occupant(s).

According to the embodiment, the center back frame23is formed in the hollow angular column shape. Furthermore, the center back frame23includes the first side plate portion23cforming one side surface of the center back frame23, the first wall portion23dand the second wall portion23e, which are formed by bending the end portions of the first side plate portion23cso as to form the recess at the rear side of a seat, so as to be positioned at the rear side and the front side of the seat, respectively, the second side plate portion23f, which is obtained by bending the side end portion of the first wall portion23dtowards the rear side of the seat so as to become substantially in parallel with the first side plate portion23c, and the third side plate portion23g, which is obtained by bending the side end portion of the second wall portion23etowards the front side of the seat so as to become substantially in parallel with the first side plate portion23c. The third side plate portion23gis overlapped on the second side plate portion23fso as to be in contact with each other. Furthermore, the second side plate portion23fand the third side plate portion23gare connected at the overlapped portion in the vicinity of the bent portion between the first wall portion23dand the second side plate portion23f.

In the case where the connected portion between the second side plate portion23fand the third side plate portion23gis positioned in the vicinity of the bent portion between the second wall portion23eand the third side plate portion23g, the length of the second side plate portion23ffrom the bent portion between the first wall portion23dand the second side plate portion23fneeds to be increased. In this case, the excessive compression may be generated in the vicinity of the side end portion of the second side plate portion23fwhen being bent to from the second side plate portion23f. Therefore, the occurrence of the unevenness or the crinkle in the vicinity of the side end portion of the second side plate portion23fmay be difficult to be avoided. Therefore, in this embodiment, the connected portion between the second side plate portion23fand the third side plate portion23gis positioned in the vicinity of the bent portion between the first wall portion23dand the second side plate portion23f. Accordingly, the occurrence of the unevenness or the crinkle in the vicinity of the side end portion of the second side plate portion23fmay be avoidable. Furthermore, in the case where the vehicle is involved in the crash and the seat belt51is pulled forward with the great tensile force because of the inertia of the occupant, the great load is applied to the shoulder belt anchor27, which is provided at the center back frame23, which may result in generating the torsional bending moment at the seat back frame20because of the load applied to the shoulder belt anchor27. As a result, the compression force acts on the first wall portion23dpositioned at the front side of the seat. However, according to the embodiment, because the connected portion between the second side plate portion23fand the third side plate portion23gis positioned in the vicinity of the first wall portion23d, a smaller bending moment than the moment acting on the first wall portion23dacts on the connected portion. Accordingly, the occurrence of the compression deformation at the bending portion may be avoidable.

According to the embodiment, the recessed portion23his formed at the side end portion of the second side plate portion23fat the portion23AM at which the curvature of the center back frame23increases.

Generally, in the case where the one side portion of the first wall portion23dis bent towards the rear side of the seat in order to form the second side plate portion23f, the compression is likely to be generated in the vicinity of the side end portion of t second side plate portion23f, which may further result in generating the unevenness or the crinkle in the vicinity of the side end portion of the second side plate portion23fat the portion23AM, at which the curvature of the center back frame23increases. However, according to the embodiment, because the recessed portion23his formed at the side end portion of the second side plate portion23fat the portion23AM, at which the curvature of the center back frame23increases, the compression generated in the vicinity of the second side plate portion23fmay be reduced, which may result in avoiding the occurrence of the unevenness or the crinkle at the second side plate portion23f. As a result, the surface of the second side plate23fmay be formed with high accuracy. Furthermore, the second side plate23fand the third side plate23gmay be easily and surely connected with each other.

According to the embodiment, the bent portion between the first wall portion23dand the second side plate portion23fis formed so that the curvature radius at the bent portion is set to be greater than the curvature radiuses of other bent portions at the center back frame23.

Accordingly, the occurrence of the unevenness or the crinkle generated in the vicinity of the side end portion of the second side plate portion23fmay be further avoidable. Accordingly, because the surface of the second side plate23fis formed with high accuracy, the second side plate portion23fand the third side plate portion23gmay be further easily and surely connected with each other.