Abstract:
The invention relates to a gas bag module comprising a gas bag, an outer contour of the gas bag being defined by a gas bag wall which has a front wall for the impact of an occupant and a depression starting from the front wall. The depression is formed in that during inflation of the gas bag a center portion of the gas bag wall is prevented from freely moving and is restrained. The gas bag has around the depression a ring-shaped chamber to be filled with gas. At least one limiting strap is provided which engages the gas bag wall at a transition from the front wall to the depression, substantially extends alongside the depression and determines a depth of the depression.

Description:
TECHNICAL FIELD  
         [0001]    This invention relates to a gas bag module comprising a gas bag.  
         BACKGROUND OF THE INVENTION  
         [0002]    Known gas bags have a gas bag wall which has a front wall for the impact of an occupant and a depression starting from the front wall, the depression being formed in that a center portion of the gas bag wall is prevented from a free or any movement during inflation and is restrained. The gas bag has around the depression a ring-shaped chamber to be filled with gas. With such ring-shaped gas bags, the center portion is prevented from moving towards the occupant in that it remains attached to the module. Restraint is effected via the ring-shaped front wall around the depression.  
         BRIEF SUMMARY OF THE INVENTION  
         [0003]    The invention provides a gas bag module in which the depression is closed at least partly, preferably completely. This is achieved in a gas bag module which comprises a gas bag, an outer contour of the gas bag being defined by a gas bag wall which has a front wall for the impact of an occupant and a depression starting from the front wall. The depression is formed in that during inflation of the gas bag a center portion of the gas bag wall is prevented from a free or any movement and is restrained. The gas bag has around the depression a ring-shaped chamber to be filled with gas. At least one limiting strap is provided which engages the gas bag wall at a transition from the front wall to the depression, substantially extends alongside the depression and determines, i.e. defines a depth of the depression. While in gas bags known so far, the depression itself determines the depth of the gas bag, a limiting strap is provided close to the depression in the module proposed, which limiting strap limits the depth of the depression. This means that the portion of the gas bag wall bridged by the limiting strap is longer than the limiting strap itself, so that the limiting strap and not the gas bag wall in the region of the depression determines the depth thereof. The region of the gas bag wall which defines the depression will, however, bulge into the depression in the inflated condition, so that the depression has a smaller opening surface than without a corresponding limiting strap with otherwise identical geometries of the gas bag fabric. The term “completely closed” should not define that the depression is closed gas tight. Rather, portions of the gas bag wall are pressed against each other so that small openings having a few square millimeter cross area might remain instead of large openings having some square centimer cross area.  
           [0004]    Preferably, the gas bag wall—in the region where it defines the depression will even bulge to such an extent that portions of the gas bag wall contact each other, preferably opposite portions.  
           [0005]    With the invention it is possible that the portions of the gas bag wall contacting each other will rest against each other such that the depression is substantially closed.  
           [0006]    This closing of the depression is preferably effected close to the transition from the depression to the front wall, which can be achieved by an appropriate adjustment of the length of the limiting strap to the depth of the gas bag wall which forms the depression.  
           [0007]    In accordance with one aspect of the invention, the limiting strap is attached to the front wall or to the region of the gas bag wall that defines the depression.  
           [0008]    This attachment can, for instance, be effected as follows: The front wall and the region of the gas bag wall defining the depression preferably consist of fabric layers sewn to each other. At the seam connecting the fabric layers of the front wall and of the depression, the limiting strap is attached to the gas bag, so that with one seam three parts are connected, namely the fabric layers for the front wall and the depression as well as the limiting strap.  
           [0009]    In accordance with another embodiment, in which front wall and depression likewise consist of various fabric layers, the fabric layer of the front wall has an opening for forming the transition to the depression. At least one fabric tab of the fabric layer of the front wall protruding into the opening is provided for the attachment of the limiting strap. This embodiment can for instance be realized in that a U-shaped slot is punched into the fabric layer of the front wall, the “U” circumscribing the fabric tab.  
           [0010]    In accordance with the preferred embodiment, a plurality of limiting straps are provided, which are attached to the front wall and whose points of attachment to the front wall substantially define a plane in the inflated condition of the gas bag. In the inflated condition, the portion of the gas bag wall provided inwards of the points of attachment either lies in the plane or even protrudes from the plane, namely towards the occupant, i.e. opposite to the depression. This means that the gas bag has no funnel-shaped depression in the region of the transition from the front wall to the depression, but the gas bag rather faces the occupant as a planar, closed surface, where some kind of dome may even protrude from the plane.  
           [0011]    Closing the depression close to the front wall may even be supported by an expedient cut of the fabric layer defining the front wall. It was found out that a circular opening provides such support less than e.g. a C-shaped, slotted, rectangular, triangular or oval opening. Even a cross-shaped opening or a T-shaped or H-shaped, slotted opening suitably supports closing near the front wall. Surprisingly, these various geometries of the opening are not even a hindrance during deployment of the gas bag. During deployment, the opening must be moved through a ring-shaped outlet opening in the module cover along a stationary middle portion to the outside.  
           [0012]    With its end close to the gas bag module, with respect to the inflated condition of the gas bag, the limiting strap is attached to the center portion. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 shows a cross-sectional view of a gas bag module according to the invention, with the gas bag inflated,  
         [0014]    [0014]FIG. 2 shows a cross-sectional view of another embodiment, in which the attachment of the limiting straps is represented in greater detail,  
         [0015]    [0015]FIG. 3 shows a cross-sectional view in accordance with a further embodiment, in which the attachment of the limiting straps is represented in greater detail,  
         [0016]    [0016]FIG. 4 shows a cross-sectional view of the gas bag in accordance with a fourth embodiment with a further variant of the attachment of the limiting straps,  
         [0017]    [0017]FIG. 5 shows a top view of the inflated gas bags as shown in FIGS.  2  to  4 , and  
         [0018]    [0018]FIGS. 6 a  to  6   f  show top views of various embodiments of the gas bag in accordance with the gas bag module according to the invention, with various cuts of the front wall. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]    [0019]FIG. 1 represents a gas bag module which has a gas bag  3 , a gas generator  5  and a module housing  7  with a module cover  9 . The gas generator  5  is surrounded by a pot- or bell-shaped diffuser  10 , which has been put over the gas generator  5  from above and is attached to the module, to be more precise at the module housing  7 .  
         [0020]    The gas bag has a gas bag wall including several regions or portions, for instance a front wall  11  which faces the occupant in the inflated condition and restrains the same, as the occupant impacts onto it. The gas bag wall defines the outer contour of the inflated gas bag. Moreover, a rear wall  12  is provided. In the middle of the gas bag, i.e. in the center, a depression  17  extends from the front wall  11  towards the gas generator  5 . The depression  17  is formed in that a portion of the outer gas bag wall, subsequently referred to as center portion  16 , is prevented from moving out of the module in the case of restraint. As a result, a ring-shaped chamber  18  to be inflated and to be filled with gas is obtained. The depression  17 , however, is not to be inflated.  
         [0021]    The module cover  9  has a middle portion  19  which adjoins the center portion  16  and is permanently attached to the diffuser  10 . For the attachment of this middle portion  19 , a reinforcement sheet is provided inside the middle portion, from which reinforcement sheet threaded bolts protrude, which extend through the center portion  16  and the diffuser  10 , so as to be screwed with nuts from below. As a result, the center portion  16  is positively attached to the diffuser and also frictionally clamped between the middle portion  19  and the diffuser  10 .  
         [0022]    In the folded condition, the gas bag  3  is accommodated in an annular space  20  between the diffuser  10  and an outer wall of the module housing  7 . Moreover, the cover  9  has a ring-shaped cap  21  composed of segments, which cap covers a ring-shaped outlet opening  22  when the gas generator  5  is not yet activated.  
         [0023]    In the interior of the chamber  18 , there are provided two limiting straps  23 ,  24  disposed opposite each other with respect to the depression  17 , which limiting straps extend from the front wall  11  as far as to the center portion  16  and are sewn to the front wall  11  and the center portion  16 . The limiting straps  23 ,  24  are shorter than the length S of the part of the gas bag wall  25  bridged by them, so that in the inflated condition as shown in FIG. 1, the limiting straps  23 ,  24  are tensioned and determine the depth T of the depression and of the gas bag.  
         [0024]    Due to the limiting straps  23 ,  24  extending alongside the depression  17 , the part of the gas bag wall  25  defining the depression  17  can bulge towards the depression  17  to such an extent that portions  26  close to the transition  27  between the front wall  11  and the depression  17  contact each other, so that the depression is substantially completely closed from the outside. As a result, a substantially completely closed restraining surface is provided for the occupant.  
         [0025]    FIGS.  2  to  4  in particular refer to the attachment of the limiting strap to the gas bag wall.  
         [0026]    In the embodiment as shown in FIG. 2, the gas bag consists of four ring-shaped fabric layers. A first fabric layer  30  above all forms the rear wall  12 . A second fabric layer  32  in particular forms the front wall  11 . The fabric layer  32  has a centric opening, which is formed in that an H-shaped slot is cut into the fabric layer  32 . There are obtained two substantially square fabric tabs  34 , which in the inflated condition project towards the gas generator, and to each of which a limiting strap  23 ,  24  is sewn. To the edge of the opening in the fabric layer  32  there is likewise sewn a ring-shaped fabric layer  36 , so that the opening is closed to the outside. The fabric layer  36  forms the upper part of the depression  17 . The outer edge of a fabric layer  38 , which is likewise ring-shaped, is in turn sewn to the inner edge of the fabric layer  36 . The fabric layer  38  extends as far as to below the middle portion  19  and includes the center portion  16 . The lower ends of the limiting straps  23 ,  24  are sewn to the fabric layer  38  in the region of the center portion  16 .  
         [0027]    In the inflated condition, the opening in the fabric layer  32  is closed in that the fabric layer  36  bulges radially to the inside and in part also to the top, so that portions  26  of the fabric layer  36  rest against each other and close the depression  17 , as is shown in FIG. 5. In FIG. 5, the limiting straps  23 ,  24  are also represented in broken lines. The embodiments in accordance with FIGS. 3 and 4 substantially correspond to the embodiment shown in FIG. 2, so that only the differences will be discussed. As shown in FIG. 3, the fabric layer  32  has an oval, rectangular or slotted opening to whose edge the fabric layer  36  is sewn. The limiting straps  23 ,  24  are then attached to the fabric layer  36  at a distance from the surrounding seam  51 . In accordance with this embodiment, there is obtained a relatively small depression  53  in the region of the front wall which for better clarity is represented exaggeratedly deep in FIG. 3. The limiting straps  23 ,  24  extend as far as to below the middle portion  19  and completely overlap each other in this region and are sewn to the fabric layer  38  also below the middle portion.  
         [0028]    In the embodiment as shown in FIG. 3, the limiting straps  23 ,  24  are thus attached to the gas bag wall defining the depression  17 , but still directly at the transition  27  from the front wall  11  to the depression  17 .  
         [0029]    In the embodiment as shown in FIG. 4, not only the fabric portions  32  and  36  are sewn to each other by the surrounding seam  51 , but at the same time the limiting straps  23 ,  24  are sewn to the gas bag wall. In this embodiment, however, the limiting straps  23 ,  24  are integrally connected with each other below the middle portion  19 , i.e. a long strip of fabric is provided, both ends of which form the limiting straps  23 ,  24 . In this embodiment, the depression  17  can be closed almost over the entire depth T, since the gas bag wall can bulge to the inside to such an extent that portions of the gas bag wall rest against each other over a large surface. The ring-shaped front wall  11  is thereby completely closed. The particularity of this feature is that contrary to FIG. 3 no depression  53  is formed, but in the inflated condition of the gas bag the portions  57  of the fabric layer  36  rather lie outside a plane E which is defined by the points of attachment  51  of the limiting straps  23 ,  24  to the front wall  11 . In the region of the portions  57  the gas bag thus bulges to the outside in the direction towards the occupant, opposite to the depression  17 , or it lies in the plane E.  
         [0030]    The illustrated form can also be extended such that, as shown in broken lines, a surrounding bead  59  can be formed. With a view to the front wall  11 , the gas bag presents itself to the occupant as a closed impact surface, and only in the middle folds  60  can be seen, with portions  26  of the gas bag wall, which defines the depression, resting against each other.  
         [0031]    [0031]FIGS. 6 a  to  6   g  represent various blanks of the fabric layer  32 , which forms the front wall  11 , as well as the position of the limiting straps  23 ,  24 . Moreover, in the inflated condition the openings will be much smaller than in the blanks illustrated.  
         [0032]    [0032]FIG. 6 a  represents an H-shaped opening  71 , from which the depression extends to the inside.  
         [0033]    In the embodiment as shown in FIG. 6 b , a T-shaped opening  71  is provided.  
         [0034]    [0034]FIG. 6 c  shows a C-shaped opening  71 , which can also be closed by only one limiting strap  23 , where appropriate.  
         [0035]    In the embodiment as shown in FIG. 6 d , a square opening  71  is provided, and in the embodiment as shown in FIG. 6 e  an oval opening  71 . FIG. 6 f  shows a triangular opening  71  and three limiting straps  23 ,  24 ,  75 , which are arranged at an angle of 120° with respect to each other.