Abstract:
In a vehicle occupant restraint system there is provided a gas bag having a wall ( 12 ) which has portions distributed across its surface area which, with increasing gas bag internal pressure, increase the volume of said gas bag ( 10 ) by a deployment or smoothing action. If the internal pressure in the gas bag rises due to increased power output of the gas generator or in case of high temperatures, a limitation of the increase in pressure is achieved by the increase in volume of the gas bag.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a gas bag for a vehicle occupant restraint system comprising an inflation port and a wall. Such gas bags are inflated, when the vehicle is involved in a collision, within a few milliseconds by the gas provided by an inflator and serve to absorb the impact of the vehicle occupant. 
     It is often a disadvantage with conventional gas bags that they are inadequately adapted to the inflator output. The amount of gas expelled may vary greatly which in extreme situations may result in the gas bag being insufficiently filled or caused to rupture. In addition, such gas bags are typically dimensioned merely for vehicle occupants of average stature and weight. Thus, for example, as compared to the impact of a lightweight occupant, the typical gas bag does not offer additional possibilities for compensating the kinetic energy of a relatively heavy occupant to diminish the rebound of the heavy occupant from the gas bag. 
     From DE-A-20 30 863 there is known a gas bag comprising an inflation port and a wall, in which gas bag the wall comprises portions distributed across its surface area which, with increasing gas bag internal pressure, increase the volume of the gas bag by a deployment or smoothing action. 
     WO-A-9009295 discloses a gas bag in which tethers, made of stronger threads as compared with the remaining gas bag fabric, are interwoven with the gas bag wall at predetermined sites. As the fabric of the gas bag wall is pre-shrinked in contrast to the threads of the tethers, a controlled expanding of the gas bag can be achieved with the tethers. 
     SUMMARY OF THE INVENTION 
     The invention provides a gas bag which better adapts to the load concerned. By individually setting the volume and thus the hardness of the gas bag corresponding to the load, the gas bag may adapt to various crash situations as well as to various power outputs of the gas generator. 
     For this purpose it is made provision according to a first aspect of the invention that in a generic gas bag, as is known from the cited DE-A-20 30 863, the wall comprises folds formed by constrictions of the wall portions. 
     According to a second aspect of the invention the portions of the wall consist of a textile fabric comprising tear threads with loops woven therein. 
     According to a third embodiment the portions of the wall consist of a corrugated material. 
     The design of the gas bag in accordance with the invention results in the advantage that the risk of the gas bag rupturing at extremely high temperatures—and the associated greater expansion of the gas generated by the inflator for inflating the gas bag—is reduced by the possibility of compensating the overpressure by providing an additional volume. As a result of this, the gas bag volume can be diminished so that the gas bag is adequately filled even at extremely low temperatures to offer the occupant protection. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further features and advantages of the invention read from the following description and from the drawing to which reference is made and in which: 
     FIG. 1 a  illustrates a first embodiment of a gas bag; 
     FIG. 1 b  is a schematic side view of a taken-in wall portion in accordance with a first variant; 
     FIG. 2 a  illustrates a second embodiment of a gas bag; 
     FIG. 2 b  is a schematic side view of a taken-in wall portion in accordance with a second variant; 
     FIG. 3 a  illustrates a third embodiment of a gas bag; 
     FIG. 3 b  is a schematic side view of a taken-in wall portion in accordance with a third variant; 
     FIG. 3 c  illustrates a taken-in wall portion the same as in FIG. 3 b  but turned inside out in a first way; 
     FIG. 3 d  illustrates a taken-in wall portion the same as in FIG. 3 b  but turned inside out in a second way; 
     FIG. 4 illustrates a fourth embodiment of a gas bag; 
     FIG. 5 a  illustrates a fifth embodiment of a gas bag; 
     FIG. 5 b  is a schematic side view of a constricted wall portion; 
     FIG. 6 a  illustrates a sixth embodiment of a gas bag; 
     FIG. 6 b  is a schematic side view of a wall portion with loops woven therein; 
     FIG. 7 illustrates a seventh embodiment of a gas bag. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to FIG. 1 a , there is illustrated a plan view of an inflated gas bag in accordance with a first embodiment. The gas bag  10  comprises on the inner side of its part of the wall  12  facing the vehicle occupant several taken-in wall portions  14 . The seams  16 , each of which is oriented radially to the inflation port  18  of the gas bag  10 , are configured as tear seams, designed to tear at a predetermined internal pressure of the gas bag  10 . In the process, it depends on the nature of the impact as to whether or which seams  16  tear. When, for instance, a relatively lightweight occupant impacts the gas bag  10  fewer seams  16  tear than in the case of a likewise severe impact by a heavier occupant. In addition, the location of the impact also determines which of the seams  16  is caused to tear. In addition to this, the gas bag  10  can be adapted to the output of the inflator by seams  16  being caused to tear corresponding to the expansion and thus to the pressure of the gas made available, so that the volume of the gas bag  10  is increased. 
     Referring now to FIG. 1 b  there is illustrated schematically a taken-in wall portion  14  of the gas bag  10  as shown in FIG. 1 a . In this embodiment, as shown in all others described below, the folds of the wall  12 , formed by taking in are directed toward the interior of the gas bag so that the vehicle occupant when diving into the gas bag  10  does not come into contact with the folds; in addition to this the seams  16  may be additionally stitch-locked. The gas bag  10  has an inner wall surface I and an outer wall surface  0 . 
     Referring now to FIG. 2 a  there is illustrated a second embodiment which differs from the first by threads differing in thickness being used alternatingly for the tear seams  16   a ,  16   b . The seams identified  16   a  are formed by thicker threads, featuring a higher tear strength than the thinner threads as used and identified  16   b . As an alternative to the method as illustrated in FIG. 1 b  the wall portions  14  of the gas bag  10  may also be taken in as shown in FIG. 2 b.    
     Referring now to FIG. 3 a  the gas bag  10  comprises tear seams  16   a ,  16   b  oriented in a concentric circle around the inflation port  18 . For the tear seams  16   a ,  16   b  threads the same in thickness or threads alternating thin and thick may be used. A taken-in wall portion  14  of the gas bag  10  as shown in FIG. 3 a  is evident from FIG. 3 b . It is possible to turn the wall portion inside out prior to stitching, FIGS. 3 c  and  3   d  illustrating two such variants, the latter of which shows start and end of the seam being additionally stitch-locked by two stitches  20 . 
     A fourth embodiment of a gas bag  10  is illustrated in FIG.  4 . In this case the seams  16  are distributed to four inner side portions of the part of the wall  12  facing the occupant. In the individual portions the seams  16  run in a straight line and parallel to each other, they being oriented perpendicular to the axes of symmetry  22  and  24 , respectively. Each of the seams  16  of one portion runs perpendicular to that of the adjacent portion. 
     Referring now to FIG. 5 a  there is illustrated a gas bag  10 , the wall  12  of which comprises a plurality of folds. These folds are formed by constricting specific wall portions  14 , as evident from FIG. 5 b , each fold being looped around three times by a thread  26  and subsequently firmly knotted or sewn up. The thread may also be knotted and additionally sewn up. The effect of these constrictions corresponds to that of the tear seams  16  in the embodiments as already described, i.e. the thread  26  or seam tearing when correspondingly stressed, thus releasing the fold. 
     Referring now to FIG. 6 a  the gas bag  10  illustrated therein comprises several wall portions  14  having a special fabric structure as evident from the cross-section in FIG. 6 b . Loops  30  directing toward the interior of the gas bag are woven into the continuous tear threads  28 . In this arrangement the tear threads  28  are thinner than the threads of the loops  30 . When a force acting thereon is high enough to cause the tear threads  28  to tear, the tear-resistant loops  30  are released. With an appropriate overpressure in the interior of the gas bag the fabric is thus not destroyed, the volume of the gas bag  10  instead being increased by defined tearing of the wall portions  14 , analogous to the embodiments as already described. The tear seams  28  may be of differing thickness. 
     Finally, in FIG. 7 there is illustrated a seventh embodiment of a gas bag  10 . In this version the upper and lower side of the wall  12  is formed from a material blank which is corrugated. The filaments of the fabric are not stretched so that they can be expanded by up to approximately 100%. A gas bag  10  woven from such threads remains corrugated when the gas stream ejected from the inflator is relatively light or the impact of the vehicle occupant is relatively light, whilst its surface becomes smooth when the gas ejection is comparatively high or the impact is relatively severe, accompanied by a corresponding increase in volume of the gas bag  10 .