Abstract:
A method for folding an airbag ( 10 ) provides that the airbag ( 10 ) is first folded in a zigzag manner, that a gas generator ( 14 ) and/or an airbag-retaining metal sheet is/are placed In the airbag ( 10 ), whereupon end portions of the airbag extend around the outer circumference of the gas generator ( 14 ) and/or of the airbag-retaining metal sheet toward each other in opposite directions up to a folding zone ( 26 ) from where the end portions are folded over outwards and are laid down in the opposite direction. Also disclosed is a corresponding airbag module.

Description:
RELATED APPLICATIONS 
       [0001]    This application corresponds to PCT/EP2015/001121, filed June 2, 2015, which claims the benefit of German Application No. 10 2014 007 5 834.5, filed Jun. 2, 2014, the subject matter of which are incorporated herein by reference in their entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The invention relates to a method for folding an airbag as well as to an airbag module comprising a gas generator and an airbag in which the gas generator is located. 
         [0003]    The folding of an airbag is an extremely demanding technique, as folding has a significant influence on the later unfolding operation, because the folding itself has to be perfectly reproducible so as to minimize the tolerances in positioning the folds and the airbag and because the folding also has to be carried out in an economical manner. 
         [0004]    In particular for folding steering wheel airbags there are most various variants. For example, DE 101 44 776 C2 describes a method in which the steering wheel airbag is first zigzag folded so that an elongate airbag package is resulting which is then folded over inwards with its ends, namely ahead of the gas generator and consequently in the vicinity of the deployment opening in the airbag module. 
         [0005]    From DE 195 02 744 C1 likewise a method for folding a steering wheel airbag is known in which the airbag is folded into an elongate package by parallel zigzag folding, wherein the gas generator is located in the middle of said package. Each of the two ends of the elongate package is folded in wave shape in opposite directions and then is forced from outside radially in the direction of the gas generator. 
       SUMMARY OF THE INVENTION 
       [0006]    It is the object of the invention to provide an alternative folding behavior which produces an airbag to be accommodated in a very space-saving manner which offers excellent deployment properties and above all can be folded very easily and quickly. 
         [0007]    The method according to the invention provides the following steps of:
       a) folding an airbag in a zigzag manner into an elongate state,   b) inserting a gas generator and/or an airbag-retaining metal sheet into the airbag, with the gas generator and/or the airbag-retaining metal sheet being located in the central third of the longitudinally folded airbag so that two end portions of the airbag are projecting laterally from the gas generator,   c) guiding the end portions of the airbag around the outer circumference of the gas generator and/or of the airbag-retaining metal sheet in opposite circumferential directions and toward each other up to a folding zone in which the end portions of the airbag at least almost contact each other,   d) folding over the end portions of the airbag from the folding zone outwards and guiding the end portions of the airbag in the opposite direction around the outer circumference of the gas generator and/or of the airbag-retaining metal sheet and around the internal part of the airbag end portions lying thereon for forming an external part.       
 
         [0012]    The method according to the invention enables the airbag to be laid very closely against the outer circumference of the gas generator on the outside by means of two large superimposed parts of each end portion of the airbag each extending by almost 180° in the circumferential direction. That is to say, the zigzag-shaped elongate airbag package subsequently is not frequently folded once again but extends in curved shape around the gas generator or the airbag-retaining metal sheet so as to be then folded once outwards instead of inwards as in prior art. Hence also the space along the outer circumference of the gas generator is exploited almost in its entirety as an accommodation space for the airbag package. 
         [0013]    Preferably the external parts of the airbag end portions should be folded over so far that the ends thereof contact each other. This, too, is carried out with respect to preferably exploiting the distance around the airbag. 
         [0014]    Moreover it may be provided to position the gas generator in step b) within the airbag so that transversely to the longitudinal extension of the zigzag-folded airbag folds extend on opposite circumferential sides of the gas generator along the gas generator. In this intermediate state of the folding process the elongate airbag package is quasi divided towards its center info two package portions. Whereas the end portions of the airbag are located at 3 o&#39;clock and at 9 o&#39;clock relative to the centrally arranged gas generator, for example, the splitting package portions extend in the center on the one hand at 6 o&#39;clock and on the other hand at 12 o&#39;clock along the gas generator and/or of the airbag-retaining metal sheet. 
         [0015]    The airbag package itself can be folded, on the one hand, in a more reproducible manner and, on the other hand, in a more space-saving manner, when the airbag is thermally heated and/or compressed for creating the zigzag folding. When the airbag is heated and compressed, a so-called thermofixed pre-folding occurs which results in an elongate concertina-like airbag package that forms an intermediate state of the airbag. 
         [0016]    An embodiment of the invention provides that the gas generator is toroidal and the folds are laid along the outer circumference of the torus. 
         [0017]    In particular, the airbag module in question is a steering wheel module. 
         [0018]    The airbag may be folded and accommodated in a cup-shaped module casing. 
         [0019]    The folded portions of the airbag can extend in a peripheral gap between the outer circumferential wall of the module casing and the outer circumference of the gas generator. 
         [0020]    At least a part, preferably a majority of the end face of the gas generator is covered only by one airbag layer in the deployment direction. This means that, on the end face toward the exiting direction of the airbag, the gas generator is neither completely nor in large part covered by the airbag package. In this central area relatively little resistance is offered to the gas during deployment, which ensures rapid deployment in the central area of the airbag. 
         [0021]    As an option it may be provided that from the internal part of each of the two airbag end portions a folding bead projecting in a jaw-like manner, i.e. a segment of the airbag package, protrudes from the end face of the gas generator. 
         [0022]    According to a preferred embodiment the individual folding heights of the zigzag-folded airbag layers are formed to have different heights. Preferably in this case a further inwardly located fold (to be arranged more closely to the gas generator) is formed having a lower height than a further outwardly located fold (to be arranged more distant from the gas generator). It is preferred that a minimum fold height is designed to be smaller than half the height of the gas generator or of the folded airbag package. Apart from that, it is preferred that a maximum fold height is designed to be larger than half the height of the gas generator or of the folded airbag package, especially approximately or (except a thickness of one to five times the material thickness of the airbag material) exactly as high as the height of the gas generator or of the folded airbag package. Accordingly it is preferred that a minimum fold height of less than 30 mm, preferably than 20 mm is formed. In addition, it is preferred that a maximum fold height of more than 35 mm, preferably more than 50 mm, further preferred more than 70 mm is formed. 
         [0023]    This is beneficial in that the folding can be appropriately adapted to the module environment (interior geometry) so as to permit optimum deployment (so-called cordial deployment), especially in the case of in-and-out-of-position load cases. It is a particular advantage of this embodiment of the folding according to the invention that this deployment technique or characteristic allows renouncing two-stage pyrotechnical airbag gas generators in some applications for the protection in so-called out-of-position situations. 
         [0024]    Another advantage of the folding technique according to the invention is an excellent and rapid deployment characteristic of the airbag between the lower steering wheel rim and the abdomen of the driver which offers a further improvement as compared to random folding. This is especially effective in vehicle situations in which the occupant is seated close to the steering wheel (e.g. the so-called 5% woman). 
         [0025]    Moreover the invention also relates to an airbag module comprising a gas generator and an airbag in which the gas generator is located. The airbag is laid into plural folds extending in parallel to each other so as to form an elongate package in an intermediate state. The gas generator is located in the central third of the elongate package, wherein starting from the central third end portions of the airbag of the package are folded into at least two package layers, hereinafter referred to as parts, wherein the two inner package layers (parts) extend along the outer circumference of the gas generator toward each other up to a folding zone and then, when folded over outwards, extend along the respective inner package layer in the opposite direction. The two end portions of the airbag thus are laid along the outer circumference of the airbag so as to form an internal part The end portions of the airbag then are folded over outwards so as to provide an external part adjacent to the internal part of the package. 
         [0026]    In accordance with a preferred embodiment, individual ones of the folding heights of the zigzag-folded airbag layers are different in height. Preferably there is arranged a further inwardly located fold (to be arranged more closely to the gas generator) having a smaller height than a further outwardly located fold (to be arranged more distant from the gas generator). It is preferred that a minimum fold height is designed to be smaller than half the height of the gas generator or of the folded airbag package. In addition, it is preferred that a maximum fold height is designed to be larger than half the height of the gas generator or of the folded airbag package, especially approximately or (except a thickness of one to five times the material thickness of the airbag material) exactly as high as the height of the gas generator or of the folded airbag package. In this context a minimum fold height is preferred to be lower than 30 mm, preferably lower than 20 mm. In addition, a maximum fold height is preferred to be higher than 35 mm, preferably higher than 50 mm, further preferred higher than 70 mm. 
         [0027]    This is beneficial in that the folding can be appropriately adapted to the module environment (interior geometry) so as to permit optimum deployment (so-called cordial deployment), especially for in-and-out-of-position load cases. It is a particular advantage of this embodiment of the folding according to the invention that this deployment technique or characteristic allows renouncing two-stage pyrotechnical airbag gas generators in some applications for the protection in so-called out-of-position situations. 
         [0028]    Another advantage of the folding according to the invention is an excellent and rapid deployment characteristic of the airbag between the lower steering wheel rim and the abdomen of the driver which offers a further improvement as compared to random folding. This is especially effective in vehicle situations in which the occupant is seated dose to the steering wheel (e.g. the so-called 5% woman). 
         [0029]    The airbag end portions may contact each other in the folding zone and/or at their ends. 
         [0030]    The gas generator is toroidal, for example, and the folds extend along the outer circumference of the gas generator. 
         [0031]    The airbag may include folds in the central third extending along opposite circumferential sides of the gas generator. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0032]    An embodiment of the invention shall be illustrated in the following drawings, in which: 
           [0033]      FIG. 1  shows a first step of the method according to the invention for folding an airbag, 
           [0034]      FIG. 2  shows a second step for folding the airbag according to the invention, 
           [0035]      FIG. 3  shows a third step for folding the airbag according to the invention, 
           [0036]      FIG. 4  shows the airbag folded according to the invention in a fop view, drawn without an airbag module, 
           [0037]      FIG. 5  shows a top view of a further embodiment of an airbag folded according to the invention, and 
           [0038]      FIG. 6  shows a sectional view across an airbag module according to the invention. 
       
    
    
     DESCRIPTION 
       [0039]      FIG. 1  illustrates an airbag  10  in the form of a steering wheel airbag pre-folded in zigzag shape and comprising numerous folds  12  extending in parallel to each other. 
         [0040]    Said folding of the airbag  10  into an elongate airbag package shown in  FIG. 1  is performed, for instance, by a so-called thermofixed pre-folding in which the airbag  10  is compressed into plural Z-shaped folds while simultaneously heat is supplied. A concertina-like structure is resulting. 
         [0041]    The airbag includes a so-called injection mouth, i.e. an opening disposed in its central third related to the elongate package in  FIG. 1 . 
         [0042]    After the folding according to  FIG. 1 , either the gas generator  14 , in this case a toroidal gas generator  14 , and/or a retaining metal sheet for the gas generator  14  is/are inserted through said opening. 
         [0043]    The retaining metal sheet equally takes the shape shown in  FIG. 2  and during the folding process possibly also serves as a placeholder for the space later occupied by the gas generator  14 . After inserting the gas generator  14  or the corresponding retaining metal sheet, the airbag package adopts the structure shown in  FIG. 2  including two end portions  16 ,  18  of the airbag pointing in two opposite directions related to the gas generator  14  or the retaining metal sheet in which the package maintains the shape as shown in  FIG. 1  and including a central portion in which the airbag package splits into two parts  20 ,  22  extending along opposite circumferential sides of the gas generator  14  or of the retaining metal sheet in close contact with the same. 
         [0044]    In a subsequent step the two end portions  16 ,  18  of the airbag are guided, as illustrated in  FIG. 2  by the arrows, in opposite circumferential directions and toward each other around the outer circumference of the gas generator  14  and/or of the retaining metal sheet so that the respective portions extend in close contact with the outer circumference. This guiding around then results in the intermediate state shown in  FIG. 3 . 
         [0045]    The end portions  16 ,  18  extending toward each other then will contact each other or approximately contact each other in a so-called  20  folding zone  26  located at half the peripheral distance between the two end portions  18 ,  18  of the airbag related to  FIG. 3  at approximately 6 o&#39;clock. 
         [0046]    In said folding zone  26  the end portions  16 ,  18  of the airbag are folded over, as shown by the arrow direction in  FIG. 3 , outwardly and in the opposite direction again and in turn are laid against the already existing package from outside. The state shown in  FIG. 4  is resulting. 
         [0047]    Up to the folding zone  26  thus an internal part  28 ,  30  of the respective airbag end portion  16  and, resp.,  18  is resulting. After folding over outwards, respective external parts  32  and, resp.,  34  of the corresponding end portion  16 ,  18  of the airbag are laid along said internal part  28 ,  30 . Optionally the ends  36  and  38 , resp., of the airbag end portions  16  and, resp.,  18  then may contact each other. This is not absolutely necessary, however. 
         [0048]    As can be inferred from  FIG. 4 , the folded part of the airbag  10  extends along the outer circumference of the gas generator  14 . That is to say, it is not laid or folded onto the end face  40  of the gas generator  14  facing the deployment direction (from the plane of projection). This area above the end face  40  remains completely or largely free from the folded package of the airbag  10  so that only one layer of the airbag  10  extends over the end face  40 . 
         [0049]    As regards the drawings, it is mentioned that the folds in practice extend by far more closely to each other, as a matter of course; they are shown at a definite distance from each other in the Figures for graphical and illustrative reasons only. 
         [0050]    In the embodiment according to  FIG. 5  jaw-like folding beads  51  projecting radially inwardly and protruding from a part of the end face  40  of the gas generator are shown. Said folding beads  51  are portions of the internal part  28 ,  30  of the end portions  16  and  18 , resp., of the airbag. As is illustrated in  FIG. 5 , however, the majority of the end face  40  of the gas generator  14  is still covered by one layer only and is not covered by the airbag package. 
         [0051]      FIG. 6  illustrates a section across an airbag module according to the invention in which the airbag  10  presented in the afore-described Figures surrounds the gas generator  14 . Moreover the airbag module includes a module casing  50  having an outer peripheral wall  52 . As is evident from  FIG. 6 , between the outer circumference of the gas generator  14  and the outer peripheral wall  52  a circumferential gap  54  is formed into which the airbag is folded or, resp., in which the folded airbag extends. 
         [0052]    Also, in  FIG. 6  it is especially clearly visible that according to a preferred embodiment shown here the individual folding heights of the zigzag-folded airbag layers are designed to be of different height. (When speaking of the height of the folds, it has to be considered or measured in the direction of a central or symmetry axis of the gas generator  14 , viz. perpendicularly to the end face  40  thereof). Preferably, a further inwardly located fold  28 ,  30  (to be arranged more closely to the gas generator  14 ) is designed to have a smaller height than a further outwardly located fold  32 ,  34  (to be arranged more distant from the gas generator). A minimum fold height is preferred to be designed smaller than half the height (or than ⅔ of the height) of the gas generator or of the folded airbag package. In this way, gas may flow out of the outlet orifices of the gas generator over the heads of the folds to the inside of the portion of the airbag package facing the driver and inflate the airbag in a primary inflating operation more quickly toward the driver, before the deployment toward the side takes place, in addition, it is preferred that a maximum fold height is designed larger than half the height of the gas generator or of the folded airbag package, especially approximately or (except a thickness of one to five times the material thickness of the airbag material) exactly as high as the height of the gas generator or of the folded airbag package. Accordingly, a minimum fold height is preferred to be designed less than 30 mm, preferably less than 20 mm. In addition, a maximum fold height is preferred to be designed higher than 35 mm, preferably higher than 50 mm, further preferred higher than 70 mm. It is especially preferred that the height of the folds increases from the inside to the outside (from the gas generator  14  toward the module edge). In this way the afore-described effect is even increased. 
         [0053]    As a matter of course, this embodiment of the folding increasing toward the outside is or can be configured especially (or only) for the innermost folding packages or folding package portions  20 ,  22  (located closest to the gas generator  14 ) ( FIG. 2, 3 ). In the outer or re-folded portions  16 ,  18  then preferably an alternately decreasing and increasing contour of the folding heights (in V or VV shape) is formed. However, this does not affect the afore-described effect.