Abstract:
The invention relates to a gas bag module comprising a gas bag with a gas bag wall which has a front and a rear wall section. A depression is provided which has a mouth and runs in an inflated state of the gas bag from the front wall section to the rear wall section, which depression is formed in that a part of the gas bag wall is prevented from an unimpeded movement away from the module on unfolding of the gas bag. The module further comprises at least one closure piece which is fastened to the gas bag wall such that in the inflated state it moves in front of the mouth of the depression and closes the depression.

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates to a gas bag module.  
         BACKGROUND OF THE INVENTION  
         [0002]    Known gas bag modules comprise a gas bag with a gas bag wall which has a front and a rear wall section, a depression including a mouth and running in the inflated state from the front wall section to the rear wall section. The depression is formed in that a part of the gas bag wall is prevented from an unimpeded movement away from the module on unfolding. Such gas bags are intended to be incorporated in the steering wheel or the instrument panel and to protect the occupant during a frontal impact. The gas bag has an annular chamber which is to be inflated, the inner wall, delimiting the depression, being formed by the depression. The depression extends from the front wall centrally towards the rear, and the lowest point of the depression is formed by a fabric piece which is permanently fastened to the gas bag module and hence on unfolding is not moved towards the occupant. Furthermore, the gas bag usually emerges obliquely outwards from the module owing to the annular shape of the chamber, and only subsequently does the front wall section move in the direction toward the occupant.  
           [0003]    With an occupant sitting centrally and in the presence of a high impact intensity, it must be prevented that the occupant&#39;s head can plunge into the depression.  
         BRIEF SUMMARY OF THE INVENTION  
         [0004]    The invention provides a gas bag module in which the gas bag even with an occupant sitting centrally and with a high impact intensity achieves excellent restraint values. This is achieved in a gas bag module which comprises a gas bag with a gas bag wall which has a front and a rear wall section. A depression is provided which has a mouth and runs in an inflated state of the gas bag from the front wall section to the rear wall section, which depression is formed in that a part of the gas bag wall is prevented from an unimpeded movement away from the module on unfolding of the gas bag. The module further comprises at least one closure piece which is fastened to the gas bag wall such that in the inflated state it moves in front of the mouth of the depression and closes the depression. The mouth of the depression is the transition of the front wall section to the depression, i.e. the inlet thereof. The closure part moves in front of this inlet, so that at the end of the inflation process a closed wall, without accessible depression, is available to restrain the occupant. The depression is not a chamber to be filled by the gas of the gas generator and is not in flow connection with the gas generator.  
           [0005]    According to one embodiment, the closure piece is a fabric piece which is sewn to the gas bag wall.  
           [0006]    This closure piece can be constructed in a band shape, the two ends of the band being able to be fastened to the rear wall section, and the band running across the front wall section. The band is simple to fasten, is flexible and does not represent a projecting part. The displacement of the band takes place by the front and rear wall sections moving relative to each other, without a device, to be actuated separately, being required for the displacement of the band.  
           [0007]    A closure piece constructed in a cross shape, which is fastened by the free ends on the rear wall section, also offers similar advantages. The crossing point then closes the depression. Through the cross-shaped form, a higher stability of the closure piece is produced compared with the embodiment with a band-shaped closure piece.  
           [0008]    Another design makes provision that at least two closure pieces are provided. These closure pieces are preferably connected with each other, the connection allowing a relative movement of both closure pieces with respect to each other. This has the advantage that in the folded state they can be laid around a central holding piece which will be explained in further detail below. In the folded state, the two closure pieces, which preferably overlap each other, safely close the depression and fix each other in their relative position.  
           [0009]    One closure piece may, for example, have at least one leadthrough opening for the other closure piece, the latter extending right through the leadthrough opening and preferably as far as into the depression.  
           [0010]    In this arrangement, a band-shaped prolongation of one closure piece may extend through the leadthrough opening and as far as to a central holding piece to which also the one part of the gas bag wall is fastened that is prevented from an unhindered movement towards outside of said module. The band-shaped prolongation fastened to the holding piece acts as a limiting strap here.  
           [0011]    The, for instance, band-shaped or cross-shaped closure pieces can help also to replace the limiting straps which were usual hitherto, which delimit the movement of the front wall section and are intended to give the gas bag a defined shape. The holding back of the gas bag wall can in fact take place or be supported by the band-shaped or cross-shaped closure piece.  
           [0012]    The gas bag is preferably housed in an annular chamber in the gas bag module which is defined on the inner face by a centrally arranged holding piece. This holding piece serves mostly to prevent a central piece of a covering of the module from moving outwards. The holding piece extends in the folded state of the gas bag inside the depression, with the depression moving along the holding piece on unfolding and leaving the module via an annular outlet opening. The closure piece, in the folded state, is placed around the holding piece and can then move on inflation such that it comes to lie in front of the depression.  
           [0013]    Another embodiment makes provision that the closure piece has an opening through which, in the folded state, the holding piece extends. On unfolding, the opening moves, more precisely the edge of the opening, outwards along the holding piece. On inflation, the displacement of the closure piece then occurs relative to the gas bag wall, so that the opening is situated outside the depression in the fully inflated state. The embodiment with an opening has the advantage that the closure piece can be constructed as a fabric section having a large area and covering the entire front wall section like a second skin. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 shows a longitudinal section through a gas bag module according to the invention with fully inflated gas bag,  
         [0015]    [0015]FIG. 2 shows a top view onto the front wall section of the gas bag in FIG. 1 in fully inflated state according to a first embodiment,  
         [0016]    [0016]FIG. 3 shows a top view onto the front wall section with fully inflated gas bag according to a second embodiment,  
         [0017]    [0017]FIG. 4 shows a top view onto the gas bag module with folded gas bag, without covering,  
         [0018]    [0018]FIG. 5 shows a top view onto the front wall section of the inflated gas bag according to a third embodiment,  
         [0019]    [0019]FIG. 6 shows a longitudinal section through a forth embodiment of a gas bag module according to the invention, with the gas bag fully inflated,  
         [0020]    [0020]FIG. 7 shows a top view onto detail X of the gas bag shown in FIG. 6, and  
         [0021]    [0021]FIG. 8 shows a top view onto the front wall section with fully inflated gas bag according to a fifth embodiment. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]    In FIG. 1 a gas bag module is illustrated, which is housed in the steering wheel of a vehicle. The gas bag module has an accommodation housing  10  which is closed on the front side with a covering  12 . Housed in the module is a gas generator  14 , which is surrounded by a cage-shaped diffusor  16 . Projecting from the end face of the diffusor  16  is a holding piece in the form of a tube  18  which prevents a central piece  20  of the one-piece covering  12  from swinging outwards on opening of the covering  12 , so that the central piece  20  remains. A gas bag  22  in the module has a gas bag wall which consists of several sections, namely a front wall section  24  which faces the occupant in the inflated state, and a rear wall section  26 . The front wall section  24  has a central opening  28 , which forms a mouth of a depression  30 . The depression  30  is produced in that through the holding piece  18  and the central piece  20  a part of the gas bag wall, namely the actual center of the front wall section  24 , is prevented from moving towards the occupant. Through the depression  30 , which is not filled with gas, an annular chamber  32  of the gas bag  22  is produced, which is to be filled with gas.  
         [0023]    Reference  34  designates the sections of the covering  12  which are severed from the central piece  20  on unfolding of the gas bag and swing outwards to free an annular outlet opening  36 .  
         [0024]    In the folded state, the gas bag is housed in the module in an annular space which is delimited radially by the cage  16 , the holding piece  18  and externally by the peripheral wall  38  of the module housing  10 .  
         [0025]    So that the occupant, who bounces against the wall section  24 , can not penetrate into the depression  30 , the gas bag has a closure piece  40  in the form of a fabric strip or a fabric piece covering the entire wall section  24 , which with its ends  42  is sewn externally on the gas bag wall, preferably on the rear wall section  26 .  
         [0026]    The closure piece  40  is illustrated spaced apart from the gas bag wall in FIG. 1 only for clarification. In fact, the closure piece  40  lies with its full surface against the gas bag wall.  
         [0027]    The closure piece  40  must be fastened to the gas bag wall at such sites that in the inflated state, as illustrated, it moves in front of the mouth of the depression  30  and closes it. It is not absolutely necessary for the closure piece  40  to be fastened to the rear wall section  26 ; a fastening on the housing  10  of the module or on the front wall section  24  is also possible. However, the longer the closure piece is, the greater is the maximum displacement between the closure piece  40  and the mouth of the depression  30 .  
         [0028]    However, when the closure piece  40  in the form of a fabric band is fastened on the rear wall section  26  or even on the housing  10  of the module, it can fulfil an additional function, namely that of a conventional limiting strap which is arranged hitherto inside gas bags. As can be seen from FIG. 1, the gas bag of the module according to the invention preferably does not have a limiting strap arranged inside the chamber  32 .  
         [0029]    In FIG. 2 an embodiment of the closure piece  40  is illustrated, this being constructed as a fabric band  50 . The fabric band  50 , as illustrated in FIG. 1, is fastened to the rear wall section  26  and has an opening  52  which in the unfolded state lies outside the opening  28 , i.e. outside the mouth of the depression  30 . In the folded state, however, the opening  52  is constructed concentrically to the opening  28 , so that the holding piece  18  can extend through the opening  52 .  
         [0030]    On unfolding, however, the opening  52  moves along the holding piece  18  and the central piece  20 , in order to leave these. Then, however, the gas bag wall and the fabric band  50  move towards each other, so that the opening  52  travels outwards.  
         [0031]    In the embodiment according to FIG. 3, the fabric band  50  is constructed without the opening  52 . In the folded state it is housed in the annular space between the holding piece  18  and the peripheral wall  38  such that it is placed around the holding piece  18 . On installation, the gas bag  22  can be gathered up laterally, so that the fabric band  50  can be pushed to the side and the depression  30  is freed for the passage of the holding piece  18  (see FIG. 4). On unfolding, however, the fabric band  50  moves and closes the depression  30 , as illustrated in FIG. 1.  
         [0032]    In the embodiment according to FIG. 5, the closure piece is a cross-shaped fabric piece  62 , which closes the depression at its crossing point  64 . In this embodiment, the four ends of the cross, as in FIG. 1, are attached to the rear wall section  26 . Through this embodiment, the closure piece is given a high stability and can likewise serve as a limiting strap.  
         [0033]    The embodiment according to FIGS. 6 and 7 corresponds essentially to those explained above; this is why only the differences will be considered and the already introduced reference numerals are adopted for parts having the same function.  
         [0034]    Instead of one closure piece, there are provided in the embodiment according to FIG. 6 two closure pieces  40 ′,  40 ″ realized as fabric sections. Both closure pieces  40 ′,  40 ″ are attached to the front wall section  24  at a peripheral edge (by means of sewing, gluing, welding or the like). The closure piece  40 ″ extends as far as to the center of the depression  28  and has, in the vicinity of the depression  28 , several leadthrough openings  70  realized as elongated slots. In the region around the leadthrough openings  70 , the fabric is reinforced so as to prevent a tearing out.  
         [0035]    The closure piece  40 ′ extends beyond the center of the depression  28 , partially across the closure piece  40 ″, in order to overlap it. At its right-hand end with respect to FIG. 6, the closure piece  40 ′ has two band-shaped, long prolongations  72  by means of which it extends through the associated leadthrough openings  70  and into the depression  28 . The prolongations  72  finally are attached to the holding piece  18 . The prolongations  72  act as limiting straps, so that a limiting strap within the chamber  32  is no longer necessary. The provision of the several closure pieces results in a symmetric unfolding behavior of the gas bag and a safe closing procedure, because the closure pieces  40 ′,  40 ″ partially overlap, are tensioned and fixed relative to each other. The prolongations  72  may be embodied as a fabric section of the closure piece  40 ′ or as straps attached thereto. The leadthrough openings  70  may be formed by loop-like, separate parts which are fastened to the closure piece  40 ″.  
         [0036]    Moreover, it is possible to use more than two closure pieces  40 ′,  40 ″. It is also possible that each closure piece has both leadthrough openings and prolongations that protrude through leadthrough openings of an adjacent closure piece, i.e. the upper leadthrough opening  70 , with respect to FIG. 7, is provided at the closure piece  40 ″ whereas the lower leadthrough opening  70  is provided at the closure piece  40 ′.  
         [0037]    According to FIG. 8, the closure piece  40  is attached to the front wall section  24  by a U-shaped seam circumscribing the depression. The open side of the “U” allows to displace the closure piece around the holding piece  18  in the folded state of the gas bag.