Abstract:
The invention relates to a gas bag module comprising a gas bag which has, with respect to its inflated sate, a front wall including a middle portion. The middle portion features a depression in an inflated state of the gas bag, by a restraining means being provided which engages the middle portion and at least partly prevents the same from moving in a direction out of the gas bag module. The restraining means is formed such that it is able to release the middle portion after an initial restraint.

Description:
TECHNICAL FIELD  
         [0001]    This invention relates to a gas bag module comprising a gas bag.  
         BACKGROUND OF THE INVENTION  
         [0002]    Gas bag modules with a so-called ring-shaped gas bag are already known from DE 36 30 685 A1. Here, the front wall is that wall of the gas bag which in the inflated state is directed towards the occupant and which the occupant can impact upon. The middle portion usually is the center of the front wall, which middle portion remains firmly attached to the gas bag module in the case of the known gas bag, so that in the inflated state the above-mentioned ring-shaped chamber is formed.  
           [0003]    From DE 199 04 072 A1 there is likewise known a gas bag module with a ring-shaped gas bag, the middle portion of which is prevented from moving towards the occupant by a finnel-shaped part of the module cover. The funnelshaped module cover is intended to define a deployment direction radially and obliquely outwards, so that occupants disposed clearly outside a central seating position (centrally with respect to the vehicle seat as seen in longitudinal direction of the vehicle) also experience a restraint. Even occupants seated too close to the steering wheel can not be contacted by the accelerated middle portion, which normally first gets in contact with the occupant, as the middle portion is permanently restrained. There is at best allowed a minor movement of the module cover out of the module towards the occupant (deployment direction), this movement being so small that the occupant cannot get in contact with the cover. In the known gas bags, this middle portion is not available for restraint, not even in the case of heavy occupants, which are disposed in a central seating position and thus hit the front wall in the region of the depression.  
         BRIEF SUMMARY OF THE INVENTION  
         [0004]    The invention provides a gas bag which restrains heavy and centrally seated occupants even more safely. This is achieved in a gas bag module comprising a gas bag which has, with respect to its inflated state, a front wall including a middle portion. The middle portion features a depression in an inflated state of the gas bag, by a restraining means being provided which engages the middle portion and at least partly prevents the same from moving in a direction directed out of the gas bag module. The restraining means is formed such that it is able to release the middle portion after an initial restraint. In the gas bag module proposed, the middle portion is initially restrained, so that the gas bag first of all radially moves radially and obliquely outwards, which is favorable for OOP (out-of-position) situations. In this phase of the inflation process, the depression is formed. In the further course of the inflation process, however, the restraining means releases the middle portion, so that the same can move towards the occupant and the occupant can contact the middle portion, and thus can be restrained by the same. This release of the middle portion can be effected obligatorily in any case or depending on specific frame conditions, e.g. from a specific internal gas bag pressure onwards or depending on the position of the occupant. For instance, a heavy occupant or an occupant having an average weight would generate a high internal gas bag pressure in the case of a high impact intensity, when the occupant falls into the gas bag, which high internal gas bag pressure then results in the restraining means releasing the middle portion, and the latter can contribute to a restraint. Via position sensors, the seating position of the occupant can, for instance, be determined. If in the case of an impact the occupant is positioned too close to the gas bag module or off-center, the restraining means would possibly not release the middle portion at all, in order to achieve a better restraining effect and minimize the risk of the occupant being hurt by the air bag. The restraining means can, for instance, selectively be destroyed or released during deployment, in order to release the middle portion. This destruction can be effected by the high internal pressure or, for instance, also by the influence of temperature due to the hot compressed gas. In accordance with one embodiment, the restraining means has a limiting strap which is attached to the middle portion. This limiting strap for instance has a tear seam, which is destroyed for releasing the middle portion. The use of a releasable latching connection as restraining means also is an inexpensive design.  
           [0005]    In accordance with another embodiment, the restraining means has a drive for releasing the middle portion. This drive can be actuated by a control, which is coupled to a sensor, depending on the values detected by the sensor.  
           [0006]    In accordance with a less expensive embodiment, the restraining means comprises a loop attached to the inside of the middle portion, and a retaining ring in which the loop is suspended. The loop or the retaining ring are destroyed from a specific physical load onwards. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    [0007]FIG. 1 shows a first embodiment of the gas bag module according to the invention, with the middle portion not yet released,  
         [0008]    [0008]FIG. 2 shows a perspective top view of the gas bag shown in FIG. 1,  
         [0009]    [0009]FIG. 3 shows an enlarged cross-sectional view of the gas bag module in the region of the module housing in accordance with a second embodiment,  
         [0010]    [0010]FIG. 4 shows a third embodiment of the gas bag module according to the invention, with the middle portion not yet released, and  
         [0011]    [0011]FIG. 5 shows a fourth embodiment of the gas bag module according to the invention, with the middle portion not yet released.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0012]    [0012]FIG. 1 represents a gas bag module which is accommodated in the steering wheel of a vehicle. The gas bag module has a gas generator  5  around which a holding member in the form of a diffuser  6  is arranged. Together with the gas generator  5 , the diffuser  6  is in turn arrested at the housing  7  of the gas bag module. Between the diffuser  6  and the outer wall  8  of the housing  7 , an annular space is formed, in which a gas bag  10  is accommodated in the folded state. A covering cap  11  seals the gas bag module in the non-deployed state of the gas bag and is swiveled outwards upon deployment. The gas bag consists of a gas bag wall, which has several portions, inter alia a portion referred to as front wall  12 . The front wall  12  is that part of the gas bag which is facing the occupant in the inflated state of the gas bag. The front wall has a central portion, subsequently referred to as middle portion  13 , which extends inwards towards the diffuser  6 , i.e. is directed into the interior of the gas bag, so that a depression  14  is obtained.  
         [0013]    On the inside, a limiting strap  15  formed into a loop is attached to the middle portion  13 , to be more precise at the lowest point of the middle portion in the inflated state as shown in FIG. 1. The loop is inserted in a retaining ring  16  which is attached to the diffuser  6 .  
         [0014]    In the state shown in FIG. 1, a large part of the gas generated by the gas generator  5  has already flown into the gas bag  10 . The annular portion of the front wall  12 , which is designated with the reference numeral  18 , serves as restraining surface.  
         [0015]    The loop in the form of the limiting strap  15  together with the retaining ring  16  form a restraining means for the middle portion.  
         [0016]    The gas bag module functions as follows. As soon as an accident is detected, the gas generator  5  will make gas to flow out into the diffuser  6 . The gas then arrives into the gas bag  10 , and the same opens the cover  11 , in order to reach the state shown in FIG. 1, in which the restraining means prevents the middle portion from moving in the direction X out of the module. In this context, direction X is that direction which is defined by the longitudinal extension of the depression  14  from the module to the outside. During normal use of the gas bag module, the direction extends from the module to the occupant.  
         [0017]    Especially in the case of occupants disposed out of position, the initial movement of the portion  18  directed obliquely outwards leads to a better restraint and a smaller load by the deploying gas bag. Even in the case of a centrally seated occupant, the chosen construction leads to small loads, as in conventional gas bags the middle portion  13  is accelerated most. Through reaching a predetermined internal gas bag pressure, the restraining means is selectively destroyed, however, so that the middle portion  13  with relation to FIG. 1 can move upwards, i.e. towards the occupant, in order to provide a larger restraining surface. For instance at the end of the inflation process, the internal pressure becomes high enough due to the gas generator  5  still being active, to ensure that the restraining means is selectively destroyed, i.e. in a controlled manner, and the middle portion is released. Moreover, it is also possible to use the internal gas bag pressure for destroying the restraining means, which is produced by the impact of the occupant on the gas bag  10 .  
         [0018]    Upon release of the middle portion  13 , the gas bag receives an outer shape represented in broken lines in the region of the front wall  12 .  
         [0019]    In the embodiment as shown in FIG. 3 it can be seen that the gas flows from the diffuser  6  through openings  21  in a gas bag retaining metal sheet  22  into the gas bag. On its inside, the middle portion  13  has a limiting strap  23  with an opening through which a pin  24  extends as part of a drive  25 . The pin  24  is the extension of a piston rod of a piston-cylinder unit  26 , which can be put in motion by a pyrotechnical propellant charge  27 . If necessary, the pyrotechnical propellant charge  27  is activated by a control  28  which is coupled with a plurality of sensors  29 ,  30 . The sensors  29  are disposed in the passenger compartment and can detect the position of the vehicle occupant to be restrained by the gas bag  10 . The sensors  30  are so-called crash sensors, which detect an accident and the severity of an accident.  
         [0020]    In the embodiment represented in FIG. 3, the restraining means is formed by the drive  25  and the limiting strap  23 .  
         [0021]    In the case of restraint, the gas bag is first of all completely inflated with the middle portion  13  restrained. If the vehicle occupant is too close to the vehicle steering wheel or out of position (i.e. not centrally aligned on his vehicle seat), the drive  25  is not actuated at all and the gas bag retains the ring-shaped geometry.  
         [0022]    However, if a severe accident has happened, for instance, or the occupant has an above-average weight, so that it must be avoided by all means that due to the depression  14  the available restraining surface is too small or the occupant penetrates too much into the gas bag  10  in the region of the depression  14 , the drive  25  is actuated by the control  28 . The gas flowing into the piston-cylinder unit  26  via the pyrotechnical drive  27  leads to the pin  24  being moved to the right, so that the pin  24  releases the limiting strap  23  and thus the middle portion  13  and the same is moved towards the occupant.  
         [0023]    In the embodiment as shown in FIG. 4, a latching connection  31  is provided as restraining means, in that on the inside of the middle portion  13  a textile part  32  with a thickened end  33  is provided, the thickened end protruding through a centric opening in the diffuser  6 . Upon reaching a specific internal pressure, the latching connection is released, so that the middle portion  13  can move towards the occupant.  
         [0024]    Alternatively, a limiting strap attached to the middle portion  13  by means of tear seams could of course also be provided instead of the latching connection  31 . The limiting strap would then permanently be attached directly to the diffuser  6 . By reaching a specific internal pressure, the tear seam would be destroyed and release the middle portion  13 .  
         [0025]    In the embodiment as shown in FIG. 5, the middle portion  13  is connected with a base sheet  63  of the diffuser  6  via two limiting straps  61 . The limiting straps  61  therefore protrude through the diffuser  6  and extend downwards in the vicinity of outflow openings  65  of the gas generator  5 . In the first phase of deployment, the gas bag  10  assumes the shape as shown in FIG. 5, which shape is greatly determined by the restraining means in the form of the limiting straps  61 . At the end of the deployment process, however, the limiting straps  61  are weakened—by the hot gas impinging on them—to such an extent that they tear and the middle portion  13  is released in a controlled manner for movement towards the occupant. In this embodiment, the restraining means is formed by the limiting straps  61 .