Abstract:
The invention relates to a gas bag module comprising a gas bag including a gas bag wall which has a front and a rear wall section and including at least one chamber. The gas bag further comprises an indentation running from the front wall section in an inflated state in a direction toward the rear wall section. The indentation is formed in that a part of the gas bag wall is prevented from an unimpeded movement towards outside of the module on unfolding of the gas bag. The gas bag, in a region of a mouth of the indentation, has a bubble-like inflatable extension in flow connection with the at least one chamber of the gas bag, which extension closes the indentation.

Description:
TECHNICAL FIELD 
     The invention relates to a gas bag module. 
     BACKGROUND OF THE INVENTION 
     Known gas bag modules comprise a gas bag with a gas bag wall which has a front and a rear wall section, an indentation running from the front wall section in the inflated state in the direction toward the rear wall section, which indentation is formed in that a part of the gas bag wall is prevented from an unimpeded movement towards outside of the module on unfolding of the gas bag. Such gas bags are intended to be incorporated in the steering wheel or the instrument panel and to protect the occupant in a frontal impact. The gas bag has an annular chamber which is to be inflated, and the inner wall, delimiting the indentation, is formed by the indentation. The indentation extends from the front wall centrally towards the rear, and the lowest point of the indentation is formed by a fabric piece which is permanently fastened to the gas bag module and hence on unfolding is not moved freely towards the occupant, to prevent him from being held back. 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 towards the occupant. 
     BRIEF SUMMARY OF THE INVENTION 
     With an occupant sitting centrally and with a high impact intensity, it is to be prevented that the occupant&#39;s head can plunge into the indentation. This is achieved by constructional approaches that are differingly complicated. The invention provides a simple, cost-effective solution for this. 
     This is achieved in a gas bag module which comprises a gas bag including at least one chamber as well as including a gas bag wall which has a front and a rear wall section. The gas bag further comprises an indentation running from the front wall section in an inflated state in a direction toward the rear wall section. The indentation is formed in that a part of the gas bag wall is prevented from an unimpeded movement towards outside of the module on unfolding of the gas bag. The gas bag, in a region of a mouth of the indentation, has a bubble-like inflatable extension in flow connection with the at least one chamber of the gas bag, which extension closes the indentation. 
     According to the preferred embodiment, the gas bag according to the invention has an indentation which at least in sections runs obliquely, which indentation is preferably already closed at its mouth and thus prevents the slightest plunging of the occupant&#39;s head into the indentation. The obliquely running wall section makes it possible that, at least in the case of a heavy occupant plunging in the gas bag, the extension is supported by the gas bag wall defining the indentation. If applicable, such supporting is already provided in the fully inflated state of the gas bag, without an occupant acting. The inflatable extension may impart an asymmetric shape to the gas bag, and may compress the mouth laterally from one side and close it. 
     Preferably, the extension moves on inflation radially towards the mouth, in order to close it and to give the indentation an oblique orientation. The oblique orientation, however, is not necessarily to be created by the extension. The oblique orientation can be achieved by a middle axis of the indentation running obliquely with respect to the middle axis of the gas bag or by a part of the gas bag wall defining the indentation extending at least partially obliquely so that the indentation has not a fully cylindrical shape. 
     In the inflated state, the extension preferably projects outwards with respect to the front wall section, which is useful for the stability of the gas bag and also gives the extension, which acts like a closure, a greater stability. 
     The preferred embodiment of the gas bag makes provision that, in relation to the spread-out, non-inflated state of the gas bag, the latter consists of at least four fabric sections lying one over the other and being connected with each other. An upper and a lower fabric piece are provided to form the front and rear wall sections, respectively. In addition, the gas bag has two inner fabric pieces which delimit the indentation. These inner fabric pieces may have an asymmetrical annular shape and a bulge to form the extension. The inner fabric pieces are usually sewn to each other at their outer edges. 
     In one embodiment, provision can be made in addition that all the fabric pieces have a central opening, with the possibility of arranging the openings so as to be concentrical to each other, again in relation to the spread-out, non-inflated state of the gas bag. 
     The inner fabric pieces may have an identical external geometry, which facilitates the sewing of the two fabric pieces on the outer edge. 
     The bulges of the inner fabric pieces preferably have a shape which is similar to a mushroom cap. A ring segment then adjoins the underside of the cap. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a side view of the gas bag module according to the invention, with the gas bag inflated, 
     FIG. 2 shows a top view of the gas bag illustrated in FIG. 1 in the spread-out, non-inflated state, 
     FIG. 3 shows a sectional view through the inflated gas bag along the line III—III in FIG. 2, 
     FIG. 4 shows a sectional view through a gas bag module according to the invention, in the spread-out state and with the fabric layers being slightly pulled apart, 
     FIG. 5 shows a top view of the inflated gas bag of FIG. 4, and 
     FIG. 6 shows a top view of a gas bag that is slightly modified with respect to the one shown in FIG.  4 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIG. 1 a gas bag module is illustrated, which is housed in the steering wheel of a vehicle. The gas bag module has a mounting housing  10  which is closed on the front face with a covering  12 . In the module, a gas generator  14  is housed, which is surrounded by a cage-like 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 covering  12 , in one piece, 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 which forms a mouth  28  of an indentation  30 . The indentation  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. This center is that part of the gas bag wall that is located under the central piece  20  in FIG.  1  and forms the lowermost point of the indentation. Through the indentation  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. As an alternative, the chamber  32  may also be divided into several chambers. 
     Reference numerals  34  designate the sections of the covering  12  which detach themselves from the central piece  20  on unfolding of the gas bag and swing outwards to free an annular outlet opening  36 . 
     In the folded state, the gas bag is housed in the module in an annular space which is delimited radially by the diffusor  16 , the holding piece  18  and externally by the peripheral wall  38  of the module housing  10 . 
     So that the mouth  28  of the indentation  30  is closed as close as possible to the front wall piece  24 , the gas bag has in the region of the mouth  28  a bubble-like inflatable extension  50  being in flow connection with the chamber  32  via an overflow opening  40 , which extension  50  closes the indentation in the inflated state already at the mouth  28 . The overflow opening  40  extends across the entire depth of the indentation  30 , which is not necessarily so, however. The extension presses the entire indentation  30  obliquely outwards, in relation to FIG. 1 to the right, so that the indentation  30  extends from its lowest point beneath the central piece  20  obliquely towards the front wall section  24 . 
     The inflatable extension  50  gives the entire gas bag a highly asymmetrical form and on inflation it pushes from one side radially against the mouth  28 . In the inflated state, the extension  50  projects in addition beyond the front wall section  40 . Within the indentation  30 , the extension rests at least partially at the gas bag wall, in order to provide a support for the extension. 
     The gas bag  22  consists of four fabric layers which in the inflated, unfolded state lie one on the other and are connected with each other. The upper fabric layer forms the front wall section  24 , the lower fabric layer forms the rear wall section  26 , both being connected with each other along their outer periphery at a seam  52 . The upper fabric layer is connected at the edge of its central opening with the edge of the opening of a first inner fabric piece  54  in the form of a ring along a seam  56 . The outer edge of the fabric piece  54  is, in turn, sewn with a second inner fabric piece  58  along the closed peripheral seam  60 , which second fabric piece forms the lower part of the indentation  30 . The fabric pieces  54  and  58  form inner fabric pieces and together define the indentation and the extension  50 . 
     In FIG. 2 the blank of the fabric pieces and also their position after being sewn together can be seen, all the outer edges of all fabric pieces having been projected into the plane of the drawing, for the purpose of illustration. The outer peripheral edge  70  is the peripheral edge that is common to the upper and lower fabric pieces, i.e. of the front and rear wall sections  24 ,  26 . The inner fabric pieces  54 ,  58  have exactly the same external geometry with an outer edge  72 . All the fabric pieces  24 ,  26 ,  54 ,  58  have a central opening  74 , the individual openings being able to be of differing size. They are arranged concentrically to each other and in the unfolded, inflated state lie one over the other, as FIG. 2 shows. 
     The fabric piece  58  can also have several openings which do not have to lie centrally with respect to the openings of the remaining fabric pieces. If, for example, an emblem is fastened on the outer face of the central piece, screw bolts may project from the emblem on the rear face through the central piece and the fabric piece  58 , so that the fastening of the emblem also serves for fastening the fabric piece  58 . When the openings  74  of the fabric pieces  24 ,  26 ,  54 ,  58  do not lie one over the other, the fabric pieces must be moved to folds until they lie one over the other. 
     In order to form the extension  50 , the inner fabric pieces  54 ,  58  have a circular ring section  76  which at a lateral end of the opening  74  continues into a bulge  78 , which has the shape of a mushroom cap, and which in the inflated state defines the extension  50 . The circular ring sections  76  delimit, on inflation, the movement of the wall section  24  towards the occupant. 
     In FIG. 3 it can be seen that the extension  50  in the inflated state rests laterally at sections  80  even on the front wall section  24  and comes to lie on it, because it overlaps the wall section  24 , in order to securely close the indentation  30  in the region of the mouth  28 . 
     The embodiments according to FIGS. 4 to  6  correspond partly to the one describe above, so that parts and sections that are equivalent and have the same function are provided with the same reference numeral, and only the differences will be discussed hereinbelow. 
     The gas bag  22  according to FIG. 4 has inner fabric pieces  54 ,  58 , that are formed in the shape of a ring and that do not form the extension  50 . Rather, the extension  50  is formed by two separate, preferably circular fabric layers  90 ,  92 . Except of one or more places, the fabric layers  90 ,  92  are connected with each other at the peripheral edge  94 . At that place where the fabric layers are not connected with each other, there is/are formed one or more overflow opening(s), so that a flow connection exists that leads to the chamber  32 . For this, the seam  60  is omitted in the region of the overflow opening  40 . The fabric layers  90  and  54  and layers  92  and  58 , respectively, are connected with each other in the region of the overflow opening by means of seams or seam sections  60 ′ and  60 ″. Hence, the overflow opening  40  is situated approximately halfway up of the depth of the indentation  30 , as regards the fully inflated state indicated in broken line. As is also shown in FIG. 5, the overflow opening  40  has a very small cross-sectional area, so that in the fully inflated state there may prevail a pressure in the extension  50  that is somewhat lower than the one in the chamber  32  (depending on the design). In the embodiment according to FIG. 4, the extension  50  has the shape of a separate, small gas bag filling the indentation  30 . This separate, small gas bag is able to rest at obliquely and outwardly running sections  98  of the indentation  30 , which thereby runs also obliquely outwards; to be more precise, it may rest at least in sections at the gas bag wall defining the indentation  30  and be supported preferably radially and/or axially by the chamber  32 , at least during an occupant plunging in. 
     In FIG. 6 there is shown that two overflow openings  40  are provided. 
     In all embodiments, the entire gas bag in the folded state is to be configured so as to extend around the center piece  30 , without directly resting on it from above.