Patent Publication Number: US-10308210-B2

Title: Method of folding an airbag, airbag, airbag module and vehicle safety system

Description:
RELATED APPLICATION 
     The application claims priority from German Application No. 10 2016 007 748.4, filed Jun. 27, 2016, the subject matter of which is incorporated herein by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     The invention relates to a method of folding an airbag, especially for a driver airbag module, comprising a front airbag layer which is connected at least in portions to a rear airbag layer. Apart from that, the invention relates to a folded airbag and an airbag module as well as a vehicle safety system comprising said airbag. 
     Occupant restraint systems for automotive vehicles usually include airbag modules comprising an airbag which in the case of impact is inflated so as to reduce the probability of body parts of a vehicle occupant colliding with a vehicle component. Some of these airbag modules are provided for being fixed in the steering wheel of an automotive vehicle as a driver airbag module. Accordingly, the airbag is arranged in a casing of the airbag module in a folded state, wherein it is especially important that the folded airbag, i.e. the airbag package, occupies a minimum volume. It is further important that in the case of release the airbag can deploy in a spilt second. Hence the development of new folding techniques of airbags aims at folding the airbag to an as small size as possible so as to minimize the storage space required while ensuring unhindered deployment of the airbag. 
     SUMMARY OF THE INVENTION 
     It is the object of the invention to state a method alternative to known methods which enables an airbag to be folded, especially an as small volume as possible of a folded airbag to be produced. Furthermore it is to be ensured by the method that in a case of crash the airbag can treaty deploy and inflate, preferably in a directed manner. It is another object of the invention to provide such folded airbag and an airbag module as well as a vehicle safety system comprising such folded airbag. 
     In accordance with the invention, this object is achieved with respect to the method of folding an airbag by the subject matter of claim  1 , with respect to the folded airbag by claim  4  or  5 , with respect to the airbag module by the subject matter of claim  9  and with respect to the vehicle safety system by the subject matter of claim  10 . 
     The invention is based on the idea to state a method of folding an airbag which is designed especially for a driver airbag module comprising a front airbag layer which is connected at least in portions to a rear airbag layer, the method comprising the following steps of:
         a) flatly spreading the airbag onto a support surface so that the front airbag layer comes to rest on the rear airbag layer,   b) folding at least in portions, especially zigzag folding, each of an upper airbag portion and a lower airbag portion in the direction of a transverse axis of the airbag,   c) furling each of a left-hand lateral airbag portion and a right-hand lateral airbag portion in the direction of a longitudinal axis of the airbag.       

     The advantage of the method according to the invention consists in the fact that a reproducible folding of an airbag can be achieved by method steps that are easy to carry out. Moreover, the invention provides a method in which the airbag can be folded into an especially small volume, as no means such as compressed air have to be introduced to the airbag. In addition, the method enables a directed inflating behavior of the airbag to be obtained. 
     The front airbag layer is the layer of the airbag which in the inflated state faces the vehicle occupant and especially the driver. The rear airbag layer is the airbag layer of the airbag which in the inflated state faces the vehicle components, especially the instrument panel. 
     The front airbag layer is connected, especially stitched and/or welded, at least in portions to the rear airbag layer. 
     In step a) this arrangement of front and rear airbag layers is flatly spread on a support surface. For example a table or a desk may serve as a support surface. The airbag is spread on the support surface so that the front airbag layer comes to rest on the rear airbag layer. The person folding the airbag consequently looks onto the front airbag layer, whereas the rear airbag layer rests on the support surface. 
     When spreading the airbag flatly onto a support surface, care has to be taken that during folding no big forces are applied to seams intended to tear in the inflated state. 
     In step b) there follow folding at least in portions, especially zigzag folding, of each of an upper airbag portion and a lower airbag portion in the direction of a transverse axis of the airbag. The upper airbag portion is the upper airbag portion which is visible in a top view onto the airbag. The lower airbag portion is the lower segment of the airbag visible in a top view onto the airbag. The transverse axis of the airbag extends from the left to the right in a top view, i.e. when the airbag is viewed by the person folding the airbag. 
     In step c) each of a left-hand lateral airbag portion and a right-hand lateral airbag portion is furled in the direction of a longitudinal axis of the airbag. In this context, too, it is applicable that the left-hand lateral airbag portion and the right-hand lateral airbag portion are resulting from a top view onto the airbag, i.e. when the airbag is viewed by a person folding the same. The longitudinal axis of the airbag extends from the top to the bottom in the described top view. 
     The longitudinal axis and the transverse axis are preferably arranged substantially perpendicularly to each other and extend substantially normal to each other. By substantially normal also deviations from a right angle of +/−10° especially of +/−5° especially of +/−2° are to be understood in this context. 
     In a top view onto the airbag, the longitudinal axis extends through a 6 o&#39;clock position and a 12 o&#39;clock position of the airbag. 
     The transverse axis preferably extends through a 3 o&#39;clock position and a 9 o&#39;clock position of the airbag. 
     The given 3, 8, 9 and 12 o&#39;clock positions of the airbag are defined with respect to the orientation of the airbag typically mounted and inflated in the steering wheel and the vehicle, respectively. 
     It is possible that at a/the 12 o&#39;clock position of the airbag and/or extending from the middle to a/the 12 o&#39;clock position of the airbag a gas discharge device is formed. A gas discharge device may consist of vents, as they are called. A so called vent enables gas to escape from the airbag in the inflated state. There are known, for example, so called self-adaptive vents (SAV) and/or flap vents. The airbag folded in accordance with the invention may comprise both a self-adaptive vent and a flap vent. Moreover, it is possible that the airbag comprises seams which tear when a particular stress/load is applied. 
     The airbag to be folded in accordance with the invention may further include a tether device, especially a restraint and/or tether strap, wherein the tether device, especially a restraint and/or a tether strap and/or a tether seam, is positioned so that it extends along the longitudinal axis or substantially in parallel to the longitudinal axis. This prevents strong twisting and/or kinking inside the airbag so that the tether device can work properly also in the inflated state of the airbag folded in accordance with the invention. 
     Prior to step a) an inflator and/or an airbag fixture may be placed, preferably centrally, in a clearance formed by the front airbag layer and the rear airbag layer, in other words, the clearance constitutes the airbag interior. Therein, preferably before the airbag is flatly spread, an inflator preferably having a circular cross-section and/or the airbag fixture have to be placed. The airbag fixture may be, for example, a holder plate including fasteners, especially screws and/or bolts, arranged thereon. Folding, especially zigzag folding, of the upper and/or lower airbag portions as well as furling of the two lateral airbag portions preferably is performed such that the inflator and/or the airbag fixture are not displaced. Of preference, the rear airbag layer includes openings through which the fasteners of the airbag fixture can be guided. 
     When placing the airbag fixture, especially the fasteners of the airbag fixture, it is important to take care that they do not impair a/the tether device during positioning inside the airbag interior and inside the clearance, respectively. 
     It is further possible that an airbag sheath is provided. The airbag sheath is arranged on the rear airbag layer, preferably connected to the rear airbag layer. When carrying out the method, the airbag sheath is located beneath the rear airbag layer. The airbag sheath is preferably located between the support surface and the rear airbag layer. Especially preferred, the airbag sheath is not folded, i.e. neither folded nor furled, when the method of folding an airbag is implemented. The airbag sheath preferably remains flatly on the support surface when implementing the method according to the invention. 
     Especially when carrying out step b), between the upper airbag portion and the lower airbag portion a center strip which is not laid, especially not folded, is formed which extends especially on the transverse axis or in parallel to the transverse axis. That is to say that especially in step b) such non-reversed, especially non-folded center strip is formed such that the inflator and/or the airbag fixture, for example, need not be displaced for folding the inflator. 
     Preferably in step b) for zigzag folding a first airbag portion that corresponds either to the lower and/or to the upper airbag portion and in particular constitutes the upper airbag portion, a first folding blade is aligned substantially in parallel to the transverse axis and placed substantially vertically onto the front airbag layer so that a lateral edge of a/the center strip is formed, wherein subsequently the first airbag portion, especially a 12 o&#39;clock position portion and/or a 6 o&#39;clock position portion of the airbag, especially preferred a 12 o&#39;clock position portion of the airbag, is folded in the direction of the first folding blade so that the front airbag layer is laid over the first folding blade and at least one surface portion of the rear airbag layer is aligned substantially perpendicularly to the support surface. 
     The folding blade is considered to be such aid which is in the form of a ruler. By means of the height of the folding blade, i.e. the blade height, the width of a fold is defined. Preferably the folding blade has such length that the folding blade is longer than the width of the airbag. The width of the airbag is to be understood as the extension along the transverse axis of the airbag. 
     In a further method step which belongs to the step b) preferably a second folding blade is put against the surface portion of the rear airbag layer and subsequently the first airbag portion is laid over the second folding blade so that a first folding portion is formed between the first folding blade and the second folding blade and a first folding bend is formed over the second folding blade and adjacent to the first folding bend a second folding portion is formed. 
     A folding bend is considered to be the connecting point between two folding portions. Starting from the folding bend a fold opening is formed between two folding portions. Such fold opening extends in the state of the method step b) substantially perpendicularly to the support surface. Hence, due to the zigzag folding, a concertina-like folding is resulting which is formed to stand upright on the support surface. 
     In another sub-step of step b) preferably a third folding blade is put against the second folding portion and subsequently the first airbag portion is folded toward the third folding blade so that the front airbag layer is laid over the third folding blade and at least one surface portion of the rear airbag layer is aligned substantially perpendicularly to the support surface and subsequently a fourth folding blade is put against the surface portion of the rear airbag layer and after that the first airbag portion is laid over the fourth folding blade so that beneath the third folding blade a second folding bend is formed and between the third folding blade and the fourth folding blade a third folding portion is formed and above the fourth folding blade a third folding bend is formed and adjacent to the third folding bend a fourth folding portion is formed. 
     Preferably, for carrying out the method step b) plural folding blades are used. They may be inserted in holding fixtures arranged on the side of the airbag so that the individual folding blades need not be held by a person. Alternatively and/or additionally it is imaginable that merely two folding blades are used, with the previously used first folding blade, for example, being used as the third folding blade. The previously used second folding blade, for example, may be used as the fourth folding blade. For this purpose it is required, however, that the already formed folding portions and/or folding bends are caught by means of clips or similar holding fixtures. In other words, the third folding blade may be a third folding blade to be used. 
     Preferably the steps for zigzag folding including at least six folding blades are carried out so many times that at least five folding bends and at least six folding portions are formed. 
     The folding bends may also be referred to as folding edges and folds, respectively, and/or may be configured as folding edges and folds, respectively. Due to a relatively thick airbag material and the two-ply configuration during folding of the airbag, respectively, folding edges are not necessarily recognizable as such. 
     Of preference, prior to carrying out step c), the folding portions of the first airbag portion are turned over in the direction of the transverse axis such that the first folding portion rests on the center strip, wherein preferably the folding blades are additionally removed, in other words, it is provided that prior to carrying out step c) the zigzag folds whose openings extend substantially perpendicularly to the support surface are folded over such that the openings of the zigzag folds extend substantially in parallel to the support surface. For this, the first folding portion rests on the center strip, especially on the non-reversed and, resp., unfolded center strip. The folding blades can be removed prior to turning over the folding portions and/or after turning over the folding portions. 
     Preferably the folding portions and/or the folding bends are held together after turning over in the direction of the transverse axis by means of clips or similar fixing means. 
     In a preferred embodiment of the invention, in step b) for zigzag folding a further, especially a second, airbag portion corresponding either to the lower airbag portion or to the upper airbag portion and preferably being the lower airbag portion, a first folding blade is aligned substantially in parallel to the transverse axis and is placed substantially perpendicularly onto the front airbag layer so that a lateral edge of a/the center strip is formed. After that the second airbag portion, especially a 12 o&#39;clock position portion or a 6 o&#39;clock position portion of the airbag, especially preferred a 6 o&#39;clock position portion of the airbag, is folded in the direction of the first folding blade so that the front airbag layer is laid over the first folding blade and at least one surface portion of the rear airbag layer is aligned substantially perpendicularly to the support surface. During zigzag folding of the second airbag portion, the first folding blade is arranged more distant from the center of the airbag than a/the first folding blade during zigzag folding of a/the first airbag portion. 
     Of preference, during zigzag folding of the second airbag portion a perpendicular is adjusted from the center of the airbag to the first folding blade, the perpendicular amounting to 90 mm-150 mm, especially 100 mm-140 mm, especially 110 mm-130 mm, especially 115 mm-125 mm, especially 120 mm, wherein a broadened center strip portion is formed between the first folding blade and the center of the airbag. 
     In a preferred embodiment of the invention a second folding blade is put against the surface portion of the rear airbag layer and subsequently the second airbag portion is laid over the second folding blade so that between the first folding blade and the second folding blade a first folding portion is formed and above the second folding blade a first folding bend is formed and adjacent to the first folding bend a second folding portion is formed. 
     Moreover, a third folding blade is preferably put against the second folding portion and subsequently the second airbag portion is folded in the direction of the third folding blade so that the front airbag layer is laid over the third folding blade and at least one surface portion of the rear airbag layer is aligned substantially perpendicularly to the support surface. After that, a fourth folding blade is put against the surface portion of the rear airbag layer and then the second airbag portion is laid over the fourth folding blade so that beneath the third folding blade a second folding bend is formed and between the third folding blade and the fourth folding blade a third folding portion is formed and above the fourth folding blade a third folding bend is formed and adjacent to the third folding bend a fourth folding portion is formed. 
     Especially preferred, a first airbag portion, especially the upper airbag portion, and a second airbag portion, especially the tower airbag portion, are folded, and especially zigzag folded, in a different way. In particular in connection with the second airbag portion, a broadened center strip portion is formed. The first airbag portion and the second airbag portion are configured to be especially non-symmetrical to the transverse axis of the airbag. They rather include different foldings and/or folding portions. 
     Before carrying out step c) the folded second airbag portion is laid in the direction of the transverse axis of the airbag such that initially the broadened center strip portion and/or the first folding portion is/are guided in the direction of the transverse axis of the airbag so as to subsequently lay a last, especially fourth, folding portion onto the rear airbag layer of the broadened center strip portion and/or of the first folding portion. In other words, the last folding portion is preferably turned over so that it does not come to rest on the uppermost position of the second airbag portion but is rather covered by another folding portion of the second airbag portion. 
     Preferably, the folding portions of the upper airbag portion and the folding portions of the lower airbag portion are turned over in the direction of the transverse axis such that a/the inflator which is/was placed in a/the clearance formed by the front airbag layer and the rear airbag layer is covered. In other words, both the folding portions of the upper airbag portion and the folding portions of the lower airbag portion are turned over in the direction of the transverse axis, with an inflator and/or an airbag fixture being covered by the upper and lower airbag portions. By covering in this context no direct resting on the inflator is to be understood. Above the inflator especially an upper airbag layer of the center strip is provided. Hence covering is to be understood as covering of the front airbag layer which is arranged in the area of the inflator and/or the airbag fixture. 
     In step b) both the upper airbag portion and the lower airbag portion are folded, especially zigzag folded. It is possible that first the upper airbag portion and then the lower airbag portion is folded. A reverse order is imaginable as well. Immediately before carrying out step c) possibly provided clips and/or fasteners have to be removed. 
     In step c) a left-hand and/or a right-hand lateral airbag portion, especially a 3 o&#39;clock position portion and/or a 9 o&#39;clock position portion of the airbag is furled starting from a lateral edge of the airbag, especially with the aid of a roll blade, in the direction of the longitudinal axis of the airbag, wherein preferably a/the inflator which is/was placed in a/the clearance formed by the front airbag layer and the rear airbag layer is not covered, at least in portions, by the left-hand and/or the right-hand lateral airbag portion. 
     Preferably, first the right-band lateral airbag portion and then the left-hand lateral airbag portion will be furled. An order of proceeding deviating herefrom is possible, too. 
     Furling of the left-hand lateral airbag portion and/or the right-hand lateral airbag portion may be performed by means of a roll blade. This again is a ruler-type element which, starting from a lateral edge of the airbag for furling the left-hand and/or right-hand lateral airbag portion remains inside the furled airbag portion until a final position is reached. 
     In other words, the inflator at least in portions remains free from the left-hand and/or right-hand lateral airbag portion. 
     The right-hand lateral airbag portion and/or the left-hand lateral airbag portion comprise portions of the folded upper airbag portion and of the folded lower airbag portion. 
     After carrying out step c), folding of an airbag sheath can be performed in a step d). For this purpose, the airbag sheath may be put around the folded airbag, for example. 
     The folded airbag may be positioned in a module casing. This is preferably effectuated along with a/the airbag sheath. 
     Within the scope of another aspect, the invention is based on the idea to state an airbag that was folded following an afore-mentioned method according to the invention. There are resulting advantages similar to those explained already in connection with the afore-mentioned method according to the invention. 
     Another independent aspect of the invention relates to a folded airbag, especially for a driver airbag module, comprising a front airbag layer that is connected at least in portions to a rear airbag layer. 
     In accordance with the invention, the folded airbag includes an upper airbag portion, a lower airbag portion, a left-hand lateral airbag portion and a right-hand lateral airbag portion, each of the upper airbag portion and the lower airbag portion being folded, especially zigzag folded, and each of the left-hand lateral airbag portion and the right-hand lateral airbag portion being furled toward the middle of the airbag. Concerning the terms “upper, lower”, “left-hand lateral” and “right-hand lateral”, the foregoing explanations are referred to. 
     Preferably the upper airbag portion or the lower airbag portion is folded, especially zigzag folded, such that a first folding portion of the upper airbag portion or of the lower airbag portion rests on a canter strip of the front airbag layer so that an inflator placed or adapted to be placed in a clearance formed by the front airbag layer and the rear airbag layer is covered at least in portions by the upper airbag portion or the lower airbag portion. In this respect, advantages similar to those stated already in connection with the methods according to the invention are resulting. 
     In a preferred embodiment of the invention, the upper airbag portion or the lower airbag portion is folded, especially zigzag folded in portions, such that a broadened center strip portion rests on a/the center strip so that an/the inflator placed or adapted to be placed in a/the clearance formed by the front airbag layer and the rear airbag layer is covered at least in portions by the upper airbag portion or the lower airbag portion, with a last folding portion, viewed starting from the middle of the airbag, resting on the rear airbag layer of the broadened center strip portion and/or of a first folding portion. 
     It is further possible that an/the inflator placed or adapted to be placed in a/the clearance formed by the front airbag layer and the rear airbag layer is not covered at least in portions, preferably completely, by the left-hand and/or the right-hand lateral airbag portion. In other words, the inflator is free of the left-hand and/or right-hand lateral airbag portion at least in portions, preferably completely. In this context, covering is equally intended to mean that the material of each of the mentioned airbag portions does not rest directly on the inflator but on the front airbag layer formed above the inflator. 
     Another independent aspect of the invention relates to an airbag module, especially for arrangement in a steering wheel, comprising an airbag according to the invention and/or an airbag that was folded following a method according to the invention. The airbag module further comprises an inflator for inflating the airbag. 
     There are resulting advantages similar to those already stated in connection with the method according to the invention for folding an airbag and/or in connection with the airbag folded according to the invention. 
     Another independent aspect of the invention relates to a vehicle safety system, especially a driver airbag module, comprising an airbag folded according to the invention and/or comprising an airbag folded following a method according to the invention and/or comprising an airbag module according to the invention, and wherein at least one sensor unit for detecting data as well as an electronic decision-making unit is provided which is suited, incorporating the data detected by the sensor unit, for defining the presence of a trigger case for the airbag module and/or for transmitting a trigger signal to the airbag module. There are resulting advantages similar to those already stated in connection with the method according to the invention for folding an airbag and/or with the airbag module according to the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Hereinafter the invention shall be illustrated by way of embodiments with reference to the enclosed schematic drawings, in which: 
         FIGS. 1 a  and 1 b    show two different embodiments of airbags spread on a support surface; 
         FIG. 2 to 6   c  show individual steps of the method according to the invention for folding an airbag; and 
         FIG. 7  shows a folded airbag. 
     
    
    
     Hereinafter the same reference numerals ere used for equal and equally acting parts. 
     In  FIG. 1 a    an airbag  10  is shown in a state spread on a support surface  15 . The support surface  15  is the surface of a working table or a desk, for example. 
     The airbag  10  includes a front airbag layer  11  and a rear airbag layer  12 . The rear airbag layer  12  is not visible in the representation as it rests on the support surface  15 . The front airbag layer  11  is visible which is connected, especially stitched and/or welded, at least in portions to the rear airbag layer  12 . When flatly spreading the airbag  10  onto the support surface  15 , care has to be taken that no forces are applied to the seams intended to tear in the inflated state of the airbag  10  during the subsequent method steps. 
     The representation of  FIG. 1  corresponds to the viewing direction of a person folding the airbag  10  lying in front of her/him. A longitudinal axis L and a transverse axis Q are visible. The airbag  10  may be divided into an upper airbag portion  20 , a lower airbag portion  21 , a left-hand lateral airbag portion  30  and a right-hand lateral airbag portion  31 . The given 3, 6, 9 and 12 o&#39;clock positions of the airbag  10  are defined with respect to the orientation of the airbag typically mounted and inflated in the steering wheel and the vehicle, respectively. The longitudinal axis L extends through the 6 o&#39;clock position and through the 12 o&#39;clock position. The transverse axis Q, on the other hand, extends through the 3 o&#39;clock position and the 9 o&#39;clock position of the airbag  10 . The longitudinal axis L and the transverse axis Q are substantially perpendicular to each other. 
     A tether device  13  is indicated which especially comprises at least one restraint and/or at least one tether strap. The tether device  13  is positioned so that it extends in parallel to the longitudinal axis L. 
     In a clearance formed by the front airbag layer  11  and the rear airbag layer  12  an inflator (not shown) is already provided. The latter is preferably centrally placed. The middle M of the airbag  10  is evident by way of a circular seam. When positioning the inflator and an airbag fixture care has to be taken that neither the inflator nor an airbag fixture does impair the tether device  13 . 
     A gas discharge device may be formed at the 12 o&#39;clock position of the airbag  10  and, respectively, extending from the middle M to the 12 o&#39;clock position of the airbag  10 . The gas discharge device may be a so called flap vent, for example. 
     After having spread the airbag  10  flatly on the support surface  15 , in a step b) the upper airbag portion  20  and the lower airbag portion  21  are zigzag folded in the direction of the transverse axis G of the airbag  10 . 
       FIG. 1 b    illustrates another airbag  10  which includes a tether device  13 ′ deviating from the embodiment according to  FIG. 1 a   . The latter merely consists of two straight portions, whereas the tether device  13  of  FIG. 1 a    includes bent portions in the lower segment. 
     The airbag according to  FIG. 1 b    further comprises a gas discharge device, i.e. a so called self-adaptive vent visible on the edge portion  19 . 
     The method steps shown in the following Figures may be carried out both in connection with an airbag  10  according to  FIG. 1 a    and in connection with the airbag  10  shown in  FIG. 1   b.    
     As is illustrated in  FIG. 2 , a first folding blade  40  is aligned substantially in parallel to the transverse axis Q. The first folding blade  40  is put substantially perpendicularly onto the front airbag layer  11 . Hence a lateral edge  60  of a center strip  51  extending in parallel to the transverse axis Q is formed. The center strip  51  is non-reversed, especially non-folded. 
     The first folding blade  40  is a ruler-type aid. The length LK of the first folding blade  40  is longer than the width B of the airbag  10 . The first folding blade  40  may be inserted in holding fixtures  49  arranged on the right and on the left of the airbag  10 . 
     In a further method step, the upper airbag portion  20 , especially the portion of the airbag  10  comprising the 12 o&#39;clock position, is folded in the direction of the first folding blade  40  so that the front airbag layer  11  is laid over the first folding blade  40  and at least one surface portion of the rear airbag layer  12  is aligned substantially perpendicularly to the support surface  15 . 
     In  FIG. 3  the airbag  10  is shown in a viewing direction from the 9 o&#39;clock position. It is evident that the airbag  10  includes an airbag sheath  18 . The latter initially is not folded and rather will stay resting on the support surface  15 . As can be inferred from  FIG. 3 , the folding operation is carried out by a total of six folding blades, i.e. the first folding blade  40 , the second folding blade  41 , the third folding blade  42 , the fourth folding blade  43 , the fifth folding blade  44  and the sixth folding blade  45 . A seventh folding blade  46  is provided to retain the entire upper airbag portion  20  in its folded shape. Above and, resp., beneath the folding blades folding bends are formed (cf.  FIG. 4 b    in this context). Said folding bends interconnect the individual folding portions. The zigzag folding operation in connection with the upper airbag portion  20  is carried out with the lower airbag portion  21  as well. 
       FIG. 4 a    illustrates that both the upper airbag portion  20  and the lower airbag portion  21  are folded, especially zigzag folded, in the direction of the transverse axis Q of the airbag  10 . 
     The lower airbag portion  21  is equally zigzag folded, with the folding operation being carried out by means of five folding blades  40 ′,  41 ′,  42 ′,  43 ′,  44 ′. 
     When zigzag folding the second airbag portion  21 , the first folding blade  40 ′ is arranged to be further distant from the center point MP of the airbag  10  than is the first folding blade  40  when zigzag folding the first airbag portion  20 . 
     A perpendicular LS from the center point MP of the airbag  10  to the first folding blade  40 ′ especially amounting to 120 mm is adjusted, wherein between the first folding blade  40 ′ and the center point MP of the airbag  10  a broadened center strip portion MA is formed. Said broadened center strip portion MA constitutes a broadening of the center strip  51 . 
     In  FIG. 4 b    depicting a sectional view, the upper airbag portion  20  and the lower airbag portion  21  are shown in the folded state. In the clearance  55  formed by the front airbag layer  11  and the rear airbag layer  12  an airbag inflator  60  is placed. Equally, the center strip  51  which is not folded or, resp., is unfolded is visible. The center strip  51  is constituted by the two lateral edges  50  on each of which folding blades stood upright in the previous method steps. The upper airbag portion  20  includes a first folding bend  22 , a second folding bend  23 , a third folding bend  24 , a fourth folding bend  25  and a sixth folding bend  26 . 
     There are equally evident the first folding portion  71 , the second folding portion  72 , the third folding portion  73 , the fourth folding portion  74 , the fifth folding portion  75  as well as the sixth folding portion  76 . The folding portions  71 - 76  are interconnected by the folding bends  22 - 26 . In total five folding bends  22 - 26  as well as six folding portions  71 - 76  are formed by six folding blades  40 - 45 . The openings  77  of the foldings are configured to be perpendicular to the support surface  15  according to the representation of  FIG. 4   b.    
     The lower airbag portion  21 , too, includes three folding bends  22 ′,  23 ′ and  24 ′ as well as the folding portions  71 ′,  72 ′,  73 ′ and  74 ′. Also in this respect it is true that the openings  77  of the folds are configured to be parallel to the support surface  15 . 
     The respective first folding portions  71 ,  71 ′ of the upper airbag portion  20  as well as of the lower airbag portion  21  are subsequently turned over in the direction of the transverse axis Q such that they rest on the center strip  51  and the broadened center strip portion MA, respectively. This is illustrated in detail in  FIGS. 5 a    to  5   c.    
     First ( FIG. 5 a   ) the folded lower airbag portion  21  is laid in the arrow direction in the direction of the transverse axis Q of the airbag  10  so that initially the broadened center strip portion MA and/or the first folding portion  71 ′ is guided in the direction of the transverse axis Q of the airbag  10 , while the center strip portion MA rests on the center strip  51 . The lower airbag portion  21  covers the inflator  60  at least in portions. In other words, the lower airbag portion  21  rests on the portion of the front airbag layer  11  which is configured above the inflator  60 . 
     As is shown in  FIG. 5 b   , the last, especially the fourth, folding portion  74 ′ is turned over so that it comes to rest on the rear airbag layer  12  of the broadened center strip portion MA. Accordingly, the lower airbag portion  21  is turned over so that the first folding portion  71 ′ is configured as the uppermost folding portion of the lower airbag portion  21 . The openings  77  of the foldings are configured to be parallel to the support surface  15  after the method step shown in  FIG. 5 b    at the latest. 
       FIG. 5 c    illustrates a last sub-step of step b) to be carried out prior to step c). The folding portions  71 ,  72 ,  73 ,  74 ,  75 ,  76  of the first airbag portion  20  are turned over in the direction of the transverse axis Q so that the first folding portion  71  rests on the center strip  51 , wherein moreover the folding blades  40 ,  41 ,  42 ,  43 ,  44 ,  45 ,  46  are removed. The openings  77  of the foldings are configured to be in parallel to the support surface  15  after this sub-step. 
       FIG. 6 a    illustrates a sub-step of step c). Accordingly, the right-hand lateral airbag portion  31 , especially the 3 o&#39;clock position portion of the airbag  10 , is furled starting from the lateral edge  14  of the airbag  10  by means of a roll blade  65  especially in the form of a ruler in the direction of the longitudinal axis L of the airbag  10 . 
     It is shown that the right-hand lateral airbag portion  31  is not completely furled. Rather, the inflator  60  is not covered by the right-hand lateral airbag portion  31  at least in portions. In other words, the inflator  60 , especially the portion of the front airbag layer  11  and, resp., the portions of the upper airbag portion  20  as well as of the lower airbag portion  21  arranged above the inflator  60 , remain free from the right-hand lateral airbag portion  31 . 
     As is illustrated in  FIG. 6 b   , also the left-hand lateral airbag portion  30  is furled in the direction of the longitudinal axis L of the airbag  10  as in the manner shown in  FIG. 8 a   . The inflator  60 , especially the portion of the front airbag layer  11  arranged above the inflator  60  and, resp., the portions of the upper airbag portion  20  and of the lower airbag portion  21  arranged above the inflator  60 , at least in portions remain free from the left-hand lateral airbag portion  30 . 
       FIG. 6 c    illustrates the furled state of the left-hand lateral airbag portion  30  and of the right-hand lateral airbag portion  31 . 
       FIG. 7  shows a folded airbag  100 . Each of the upper airbag portion  20  and the lower airbag portion  21  is zigzag folded. The left-hand lateral airbag portion  30  and the right-hand lateral airbag portion  31  are furled toward the middle and, resp., toward the longitudinal axis L of the airbag  10 . The folded airbag  100  is provided within a module casing  110 . The folded airbag  100  requires relatively little space. It is additionally characterized by a directed inflating behavior. 
     LIST OF REFERENCE NUMERALS 
     
         
           10  airbag 
           11  front airbag layer 
           12  rear airbag layer 
           13 ,  13 ′ tether device 
           14  lateral edge 
           15  support surface 
           18  airbag sheath 
           19  edge portion 
           20  upper airbag portion 
           21  lower airbag portion 
           22 ,  22 ′ first folding bend 
           23 ,  23 ′ second folding bend 
           24 ,  24 ′ third folding bend 
           25  fourth folding bend 
           26  fifth folding bend 
           30  left-hand lateral airbag portion 
           31  right-hand lateral airbag portion 
           40 ,  40 ′ first folding blade 
           41 ,  41 ′ second folding blade 
           42 ,  42 ′ third folding blade 
           43 ,  43 ′ fourth folding blade 
           44 ,  44 ′ fifth folding blade 
           45  sixth folding blade 
           46  seventh folding blade 
           49  holding fixture 
           50  lateral edge 
           51  center strip 
           55  clearance 
           60  inflator 
           65  roll blade 
           71 ,  71 ′ first folding portion 
           72 ,  72 ′ second folding portion 
           73 ,  73 ′ third folding portion 
           74 ,  74 ′ fourth folding portion 
           75  fifth folding portion 
           76  sixth folding portion 
           77  opening of folding 
           100  folded airbag 
           110  module casing 
         B width of airbag 
         L longitudinal axis 
         LK length of folding blade 
         LS perpendicular 
         M middle of airbag 
         MA center strip portion 
         MP center point of airbag 
         Q transverse axis