CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a United States National Phase Application of International Application PCT/EP2014/064895 filed Jul. 11, 2014 and claims the benefit of priority under 35 U.S.C. §119 of German Patent Application 10 2013 213 995.0 filed Jul. 17, 2013, the entire contents of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to a backrest structure for a vehicle seat having a planar base sheet and an additional structural component which are connected to each other by means of laser welding using at least one weld seam, and a vehicle seat having at least one such backrest structure. 
       BACKGROUND OF THE INVENTION 
       [0003]    DE 10 2005 005 485 A1 discloses a backrest structure for a backrest of a vehicle seat having at least one base sheet and a backrest frame comprising a left and a right vertically extending lateral top-hat profile-member and an upper and a lower top-hat profile-member which extends in the transverse direction. The top-hat profile-members are welded to the front side of the base sheet. The lateral top-hat profile-members are welded to the top-hat profile-members which extend in the transverse direction. 
         [0004]    DE 10 2006 000 850 B4 discloses a backrest structure having an integrally constructed, substantially peripheral frame. The frame extends at three edge regions of the base sheet and comprises two longitudinal portions which extend in a parallel manner and a transverse portion which connects the longitudinal portions. In order to increase the rigidity, the base sheet has reinforcement beads. In order to fix and secure a cushion, upholstery suspension channels are provided on the outer edge regions of the base sheet. 
         [0005]    DE 10 2010 054 185 A1 discloses a backrest having a frame which is constructed in several portions. The frame comprises two longitudinal struts which extend in a parallel manner along the lateral edge regions of the base sheet. A transverse strut is arranged along the upper edge region. In order to reinforce the base sheet, bead-like channels are impressed. 
         [0006]    DE 10 2005 001 606 B4 discloses a backrest structure having an integrally constructed frame sheet which extends over a large portion of the surface of the base sheet. The frame sheet and the base sheet are connected to each other by means of laser welding. In this instance, a laser beam penetrates the base sheet and the surface of the frame sheet, whereby a weld seam which welds the base sheet to the frame sheet is produced. 
         [0007]    DE 35 15 598 C2 discloses a weld connection of two thin metal sheets which form an inner and an outer sheet, for example, an inner and an outer sheet for doors and/or hatches in motor vehicles, wherein the outer sheet ( 2 ) forms a visually smooth outer face and is flanged in the edge region thereof. The outer sheet is flanged through 180° on the rear face thereof, and the inner sheet is placed with an edge region on the flanged edge of the outer sheet. The connection between this sheet and the flanged edge is carried out by means of a laser beam from the side facing away from the outer face. 
         [0008]    Base sheets having a material thickness of 0.6 mm and more are generally used in the production of backrest structures. The trend in vehicle seat development is toward lightweight construction. Large sheet components, such as base sheets of backrest structures, have a very high weight proportion of the overall backrest. As a result of the large surface areas of the base sheets, a large amount of material is provided, which results in the high weight. Since the surface-areas of the sheet components cannot be reduced, with a predetermined material, for example, sheet steel, only the sheet thickness of the sheets can be reduced in order to save weight. Thus, the sheet thickness of large sheet components has in the past been continuously reduced. Below a sheet thickness of approximately 0.6 mm, however, weldability of the sheets is no longer ensured in a simple manner since too little material is available. As a result of the small material thickness, there is the risk during the welding process that the laser beam may burn a hole in the base sheet, whereby the sheet becomes damaged and is not welded to the frame. Adapters cannot readily be fitted to the thin sheets. The sheets which are becoming increasingly thin additionally involve an increased risk of injury during handling and further processing. 
       SUMMARY OF THE INVENTION 
       [0009]    An object of the invention is to provide a backrest structure for a vehicle seat having a relatively thin base sheet and thereby reduced weight and a vehicle seat having reduced weight. 
         [0010]    A backrest structure of the generic type comprises a planar base sheet and an additional structural component which are connected to each other by means of laser welding using at least one weld seam. The term “planar” is intended in particular to be understood to mean substantially flat. However, individual geometries such as reinforcement beads require a deviation from an absolutely flat shape. The term “weld seam” is also intended to be understood to refer to weld seams whose length substantially corresponds to the width. Consequently, weld seams also include weld spots. 
         [0011]    According to the invention, there is provision in the region of the at least one weld seam for at least one tongue of the base sheet to be bent through 180° and placed on the remaining base sheet, and for the at least one weld seam to connect the bent tongue, the remaining base sheet and the additional structural component to each other. Consequently, the weld seam extends over the bent part-region, the remaining base sheet and the additional structural component. 
         [0012]    As a result of the bending of the at least one tongue of the base sheet, a doubled material thickness of the base sheet is produced locally. As a result of the doubled material thickness, a weld seam can be produced in a simplified manner by means of laser welding. The risk that the laser beam may burn a hole in the base sheet is reduced. Also, any air gap which may remain between the base sheet and the tongue does not influence the laser welding operation or has only an insignificant influence. Consequently, a relatively thin base sheet with reduced weight can be used, whereby the vehicle seat also has a reduced weight. Furthermore, the production costs are reduced and the efficiency is thereby increased. 
         [0013]    According to an advantageous development of the invention, the at least one tongue is bent multiple times through 180° and placed on the remaining base sheet. The material thickness of the base sheet is thereby not only doubled but multiplied. As a result of the multiplied material thickness of the base sheet, a weld seam can be produced in an even more simplified manner by means of laser welding. 
         [0014]    An advantageous saving of weight is achieved when the base sheet has a material thickness of less than 0.5 mm. Preferably, the base sheet has a material thickness between 0.3 mm and 0.5 mm, in a particularly preferred manner of approximately 0.35 mm. This material thickness brings about an advantageous saving of weight and nonetheless enables safe production of a weld seam by means of laser welding. 
         [0015]    According to a preferred embodiment of the invention, the additional structural component is a backrest frame. 
         [0016]    The rigidity of the backrest structure can be increased by a plurality of bent tongues being arranged along an outer contour of the base sheet and being welded to the backrest frame. The spacings between individual tongues may be equidistant. However, the spacings between individual tongues may also be adapted to the loading of the backrest structure. 
         [0017]    According to an advantageous embodiment, the bent tongue is a rectangular tongue which is separated at three sides from the remaining base sheet and which is bent through 180° at the fourth side which is connected to the remaining base sheet and placed on the remaining base sheet. Such a tongue can be produced in a relatively simple manner by means of punching from the base sheet at any location. 
         [0018]    According to another advantageous embodiment, the bent part-region is edge material which is located at the edge of the base sheet and which is in particular tongue-like. The punching operation can thereby be dispensed with and there is locally produced a relatively large securing region which is located at the edge of the base sheet. 
         [0019]    The base sheet may have at least one securing location which is inwardly spaced apart from the outer contour thereof. This may be supplemented by a securing region in the region of the outer contour of the base sheet. It is thus possible, for example, for backrest frames, which are provided as a top-hat profile-member with two securing flanges which extend in a parallel manner, to be secured to the base sheet. Preferably, the securing locations each comprise a passage region and a tongue. 
         [0020]    If the edge material is simply bent through 180°, there is produced a flat edge contour, which does not have a sharp-edged but instead a rounded edge region. The risk of injury when a backrest structure is produced is thereby reduced. 
         [0021]    If the edge material is bent several times, wherein the edge material and the remaining base sheet enclose a geometric shape, a contoured edge contour is produced. The contoured edge contour also reduces the risk of injury since it does not have a sharp-edged, but instead a rounded edge region. In addition, the contoured edge contour increases the rigidity of the base sheet. 
         [0022]    According to an advantageous development of the invention, the backrest frame has an upholstery suspension channel for securing a cushion. It is consequently not necessary to provide an upholstery suspension channel on the base sheet and, consequently, the base sheet does not need to absorb the load resulting from the tension of the cushion and, consequently, a base sheet having a relatively thin material thickness can be used. 
         [0023]    According to another development of the invention, the base sheet additionally has an upholstery suspension region which is preferably integrated in the upholstery suspension channel of the backrest frame in a positive-locking manner. The rigidity of the upholstery suspension channel is thereby increased. 
         [0024]    The rigidity of the upholstery suspension channel is increased even further when the base sheet is doubled in the region of the upholstery suspension region. 
         [0025]    The rigidity of the base sheet can be increased by means of at least one reinforcement bead. Preferably, the base sheet is produced from sheet steel or sheet aluminum. 
         [0026]    According to another preferred embodiment of the invention, the additional structural component is a wire, in particular a Top Tether clip of an Isofix child seat securing system. 
         [0027]    The object is also achieved with a vehicle seat which comprises at least one backrest structure according to the invention. 
         [0028]    The invention is explained in greater detail below with reference to advantageous embodiments illustrated in the figures. However, the invention is not limited to these embodiments. The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]    In the drawings: 
           [0030]      FIG. 1  is a schematic, partially sectioned view of a vehicle seat; 
           [0031]      FIG. 2  is a perspective view of a backrest structure of the vehicle seat according to  FIG. 1  according to a first embodiment; 
           [0032]      FIG. 3  is a view of a base sheet of the backrest structure according to  FIG. 2 ; 
           [0033]      FIG. 4  is an enlarged illustration of the marked part-region of the base sheet according to  FIG. 3 ; 
           [0034]      FIG. 5  is a sectional view taken along the line A-A from  FIG. 4 , wherein a portion of the frame is additionally illustrated; 
           [0035]      FIG. 6  is a view of a backrest structure of the vehicle seat according to  FIG. 1  according to a second embodiment, when viewed in the travel direction; 
           [0036]      FIG. 7  is a sectional view taken along the line B-B from  FIG. 6 ; 
           [0037]      FIG. 8  is a sectional view through a securing region of a base sheet according to a first configuration of the second embodiment; 
           [0038]      FIG. 9  is a sectional view through a securing region of a base sheet according to a second configuration of the second embodiment; 
           [0039]      FIG. 10  is a perspective view of a backrest structure of the vehicle seat according to  FIG. 1  according to a third embodiment with a Top Tether clip; and 
           [0040]      FIG. 11  is a sectional view taken along line C-C from  FIG. 10 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0041]    A vehicle seat  1  for a motor vehicle, in this instance a rear seat, has a seat member  3  and a backrest  4  which is fitted thereto and which can be adjusted in terms of inclination. However, the vehicle seat  1  could also be a front seat. The backrest  4  comprises a backrest frame  40  and a base sheet  30 , which is constructed as a planar object. The backrest frame  40  and the base sheet  30  together form a backrest structure by being welded together, preferably by means of laser welding. 
         [0042]    The base sheet  30  has in this instance a material thickness of approximately 0.35 mm. The base sheet  30  contains in this instance reinforcement ribs and reinforcement beads  31  and is nonetheless intended to be considered to be planar. In this instance, the backrest frame  40  has a material thickness of approximately 1.5 mm. Other material thicknesses of the backrest frame  40  are also conceivable, in particular between 0.8 mm and 4 mm. 
         [0043]    The arrangement of the vehicle seat  1  inside the vehicle and the conventional travel direction thereof define the directional indications used below. In this instance, a direction which is orientated perpendicularly to the ground is referred to below as the vertical direction and a direction perpendicular to the vertical direction and perpendicular to the travel direction is referred to below as the transverse direction. The vertical direction also includes an angular range relative to the direction which is orientated perpendicularly to the ground, in which range the backrest  4  is located in the conventional position for use. 
         [0044]    In the illustration according to  FIG. 1 , the backrest  4  is in the position for use thereof and consequently extends substantially in the vertical direction. The backrest  4  comprises a cushion  8  which rests at the front in the travel direction on the backrest structure, in particular the base sheet  30 , and is covered with a cover which is not illustrated. At the upper end of the backrest  4  in the vertical direction, which end is facing away from the seat member  3 , a headrest  18  which can be adjusted in terms of height and inclination is further arranged. 
         [0045]    According to a first embodiment which is illustrated in  FIG. 2 , the backrest structure comprises a base sheet  30  and a partially peripheral backrest frame  40  which surrounds the base sheet  30  at three sides. 
         [0046]    Close to the edge region thereof, the base sheet  30  has a plurality of securing locations  32 , of which only one is shown in the simplified illustration of  FIG. 3 . Preferably, a plurality of securing locations  32  are arranged with defined spacings with respect to each other along the three sides on which the backrest frame  40  extends. The spacings may be equidistant. 
         [0047]    In  FIG. 4 , one of the said securing locations  32  is illustrated to an enlarged scale. The securing location  32  comprises a substantially rectangular passage region  34 . The passage region  34  is produced by means of a punching from the base sheet  30  with a U-shaped cross-section. In this instance, there is produced a tongue  36  which is separated from the remaining base sheet  30  at three sides and which is connected to the base sheet  30  at the fourth side thereof. The tongue  36  is then bent along the fourth side through approximately 180° and placed on the remaining base sheet  30 . The base sheet  30  is thus folded once at the securing location  32 , whereby the material thickness is doubled. The backrest frame  40  is then positioned and welded at the side of the base sheet  30  opposite the tongue  36 . 
         [0048]    The tongue  36  is rectangular in this instance but in modifications of the embodiment may, for example, also be of trapezoidal, semi-circular or polygonal form. The shape of the associated passage regions is then formed in accordance with the tongue shape. 
         [0049]    The base sheet  30  is connected to the backrest frame  40  by means of laser welding. In this instance, the energy of the laser beam penetrates through the tongue  36  and the remaining base sheet  30  and is introduced into the backrest frame  40 . In this instance, there is produced in the contact locations of the remaining base sheet  30  with the backrest frame  40  a weld seam  50  which extends, on the one hand, into the backrest frame  40  and, on the other hand, through the remaining base sheet  30  into the tongue  36 . 
         [0050]    Such a weld seam  50 , which connects the base sheet  30  to the backrest frame  40  and extends over three material layers, is illustrated in  FIG. 5 . 
         [0051]    In order to secure the cushion  8  to the backrest structure, the backrest frame  40  has an upholstery suspension channel  42 . The upholstery suspension channel  42  surrounds the backrest frame  40  at three sides in this instance. The upholstery suspension channel  42  has, in the same manner as the remaining backrest frame  40 , a material thickness of approximately 1.5 mm in this instance and is consequently constructed in a more rigid and secure manner than if it were a component of the relatively thin base sheet  30 . 
         [0052]    According to a second embodiment, which is illustrated in  FIG. 6 , the backrest structure also comprises a base sheet  30  and a partially peripheral backrest frame  40  which surrounds the base sheet  30  at three sides and which is welded to the base sheet  30 . 
         [0053]    The base sheet  30  has, similarly to in the first embodiment, a plurality of securing locations  32  with passage regions  34  and tongues  36 . In a similar manner to in the first embodiment, the base sheet  30  is connected to the backrest frame  40  at securing locations  32  by means of weld seams  50  which each extend from the tongue  36  through the base sheet  30  into the backrest frame  40 . 
         [0054]    In addition, securing regions  37  are provided at the edge regions of the base sheet  30 . At each securing region  37 , edge material  38  which is located at the edge of the base sheet  30  and which is preferably constructed as tongues is bent through approximately 180° and placed on the remaining base sheet  30 . A tongue of the base sheet  30  is therefore folded once at the securing region  37 , whereby the material thickness is doubled. The backrest frame  40  is then positioned at the side of the base sheet  30  opposite the edge material  38 . 
         [0055]    The base sheet  30  is also connected to the backrest frame  40  at the securing regions  37 , in a similar manner to at the securing locations  32 , by means of weld seams  50  which each extend from the edge material  38  through the base sheet  30  into the backrest frame  40 .  FIG. 7  is a section through the backrest structure with a securing location  32  and a securing region  37 . 
         [0056]    According to a first configuration of the second embodiment, the tongue-like edge material  38 , as illustrated in  FIGS. 7 and 8 , is simply bent through 180° and placed flat on the remaining base sheet  30 . In this instance, simply a relatively flat first edge contour  51 , which can be produced in a relatively simple manner. 
         [0057]    According to a second configuration of the second embodiment, the tongue-like edge material  38 , as illustrated in  FIG. 9 , is bent several times and subsequently placed flat on the remaining base sheet  30 . In this instance, the edge material  38  and the remaining base sheet  30  enclose a geometric shape, in this instance a rectangle. In this instance, there is produced, optionally partially, a contoured second edge contour  52  which increases the rigidity of the base sheet  30 . Preferably, tongue-like edge material  38  is bent at a plurality of locations of each side of the base sheet  30 . 
         [0058]    Both edge contours  51 ,  52  afford the advantage that sharp-edged edge regions of the base sheet  30  are prevented. The risk of injury when the base sheets  30  are processed during the production of backrest frame structures is thereby reduced. 
         [0059]    According to a third embodiment, which is illustrated in  FIGS. 10 and 11 , the backrest structure comprises a base sheet  30  to which a Top Tether clip  20  is secured. In this instance, the Top Tether clip  20  comprises a central portion  22  which has a substantially circular-cylindrical cross-section. At both sides of the central portion  22 , a securing portion  24  which is constructed in a planar manner is provided. 
         [0060]    The Top Tether clip  20  is produced from a rigid, round wire, wherein the securing portions  24  are produced by means of corresponding pressing or rolling of the wire. The Top Tether clip  20  engages over an opening  26  in the base sheet  30 . In this instance, the securing portions  24  are located on a contact region  25  of the base sheet  30  and the central portion  22  bridges the opening  26 . 
         [0061]    The contact regions  25  of the base sheet  30  are produced, in a similar manner to the securing locations  32  and the securing regions  37 , by tongues  28  which are constructed as flaps being bent through approximately 180°, wherein the tongues  28  are placed on the remaining base sheet  30 . The base sheet  30  is therefore also folded once at the contact regions  25 , whereby the material thickness is doubled. The securing portions  24  of the Top Tether clip  20  are then placed on the side of the base sheet  30  opposite the tongues  28 . 
         [0062]    The base sheet  30  is consequently connected to the Top Tether clip  20  at the contact regions  25 , in a similar manner to at the securing locations  32  described or the securing regions  37 , by means of weld seams  50  which each extend from the tongue  28  through the base sheet  30  into the securing portion  24  of the Top Tether clip  20 .  FIG. 11  is a section through the backrest structure with a Top Tether clip  20 . 
         [0063]    The features disclosed in the above description, the claims and the drawings may be significant both individually and in combination for the implementation of the invention in the various embodiments thereof. 
         [0064]    While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.
A backrest structure for a vehicle seat ( 1) includes a flat base sheet ( 30) and another structural part ( 20, 40) which are connected to each other by at least one laser weld seam ( 50) using a laser welding procedure. In a process, at least one tongue ( 28, 36, 38) of the base sheet ( 30) is bent by 180 DEG in the region of the weld seam ( 50) and placed on the remaining base sheet ( 30). The at least one weld seam ( 50) connects the bent tongues ( 28, 36, 38), the remaining base sheet ( 30), and the other structural part ( 20, 40) to one another. A vehicle seat ( 1) is also provided with such a backrest.