Abstract:
A gas bag for a vehicle occupant restraint system comprises an inflation opening and a fabric piece arranged in the interior of the gas bag opposite the inflation opening and defining a volume for compressed gas introduced into the gas bag through the inflation opening. The fabric piece forms at least one outflow opening for the compressed gas. The outflow opening defines a gas exit area affected by the compressed gas flowing through the outflow opening, and comprising at least one limiting strap arranged in the interior of the gas bag but outside of the gas exit area.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a gas bag for a vehicle occupant restraint system. 
     Conventional gas bags comprise an inflation opening, a fabric piece which is arranged inside the gas bag opposite the inflation opening and forms an outflow opening for compressed gas which flows into the gas bag through the inflation opening, and at least one limiting strap which is likewise arranged inside the gas bag. 
     The fabric piece serves to deflect in a desired direction the hot compressed gas entering into the interior of the gas bag after a gas generator has been activated. This prevents the hot compressed gas from striking directly onto the wall of the gas bag and damaging it. In addition, through the specific deflection of the compressed gas, the unfolding behavior of the gas bag can be influenced to a large extent. According to the direction of inflow of the compressed gas into the gas bag, for example it can be achieved that the gas bag firstly unfolds in lateral direction, in particular upwards and downwards towards the windscreen and towards the floor of the vehicle, and to the vehicle occupant only towards the end of the unfolding process. 
     The limiting strap serves to influence the shape and the dimensions of the gas bag in particular in the unfolded state. In addition, by means of the limiting strap also the unfolding behavior of the gas bag can be influenced. However, it is a problem that the limiting strap can have a negative effect on the unfolding behavior which is attempted to be maintained by means of the fabric piece. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The invention provides a gas bag in which the limiting strap does not have any negative effect on the unfolding behavior of the gas bag, which is predetermined by means of the fabric piece. According to the invention, a gas bag for a vehicle occupant restraint system comprises an inflation opening and a fabric piece arranged in the interior of the gas bag opposite the inflation opening and defining a volume for compressed gas introduced into the gas bag through the inflation opening. The fabric piece forms at least one outflow opening for the compressed gas. The outflow opening defines a gas exit area affected by the compressed gas flowing through the outflow opening, and comprises at least one limiting strap arranged in the interior of the gas bag but outside of the gas exit area. This ensures that the limiting strap does not lie in front of the outflow opening and thereby does not alter in a disadvantageous manner the outflow speed and the outflow direction of the compressed gas from the volume which is delimited by the fabric piece, for example by the opening being covered. 
     Advantageous embodiments of the invention will be apparent from the sub-claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is described hereinbelow with reference to preferred embodiments which are illustrated in the enclosed drawings, in which: 
     FIG. 1 shows in a perspective view a gas bag with limiting strap; 
     FIG. 2 shows in a perspective view the gas bag of FIG. 1 with limiting strap and fabric piece; 
     FIG. 3 shows in a perspective view a gas bag with limiting strap and fabric piece, the limiting strap and the fabric piece being constructed in one piece; 
     FIG. 4 shows in a top view the blank for the limiting strap and the fabric piece of FIG. 3; 
     FIG. 5 shows in a perspective view a gas bag with limiting strap and fabric piece according to a modified embodiment; 
     FIG. 6 shows in a perspective view a gas bag with limiting strap and fabric piece according to a further embodiment; 
     FIG. 7 shows in a perspective view a gas bag with limiting strap and fabric piece according to an additional further embodiment; 
     FIG. 8 shows in a perspective view a gas bag with limiting strap and fabric piece according to an alternative embodiment; 
     FIG. 9 shows in a top view a blank for a further embodiment of the fabric piece; 
     FIG. 10 shows in a developed illustration the fabric piece of FIG. 11; 
     FIG. 11 shows in a perspective view the fabric piece of FIG. 9 in a sewn, three-dimensional state; 
     FIG. 12 shows in a first side view the fabric piece of FIG. 10 fastened on a holding frame; 
     FIG. 13 shows in a bottom view the holding frame with the fabric piece of FIG. 10 fastened thereon; and 
     FIG. 14 shows in a second side view the fabric piece of FIG. 10 fastened to the holding frame. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In FIGS. 1 and 2 the basic construction of a gas bag according to the invention can be seen. The gas bag  1  has an inflation opening  2  through which compressed gas can be introduced into the interior of the gas bag, in order to unfold the gas bag. 
     Inside the gas bag, a fabric piece  10  is arranged such that it forms a type of pre-chamber into which the compressed gas enters which flows through the inflation opening. From this pre-chamber, the compressed gas flows through two outflow openings  3  into the gas bag. 
     Inside the gas bag in addition two limiting straps  4  are arranged. In this embodiment, these connect the wall region of the gas bag, surrounding the inflation opening, with the region of the wall which faces a vehicle occupant who is to be restrained. 
     An essential feature consists in that the limiting straps are arranged outside the region in which the compressed gas flows into the gas bag from the pre-chamber. In the embodiment of FIGS. 1 and 2, the limiting straps are arranged laterally on the fabric piece  10 , so that they lie in a plane which is perpendicular to the plane in which the central points of the outflow openings  3  lie. Owing to this arrangement, there is also no danger during the unfolding of the gas bag that the limiting straps get in front of the outflow openings  3  and thereby prevent the outflow of the compressed gas from the pre-chamber or have a negative influence thereon. The constructively provided outflow behavior from the pre-chamber is therefore maintained, so that the gas bag unfolds in the desired manner. Provision can be made in particular that the gas bag, owing to the upwardly and downwardly directed outflow openings, firstly unfolds towards the windscreen or towards the vehicle floor and only then towards the vehicle occupant. 
     In FIG. 3 a gas bag is shown in which the fabric piece and the limiting straps are constructed in one piece (see also FIG.  4 ). The limiting straps are arranged on opposite sides of the fabric piece  10 . Between the limiting straps and the fabric piece one reinforcement region each is constructed which is provided with a recess  5 , the dimensions of which correspond to those of the inflation opening  2 . Finally, in the region between a reinforcement region and the fabric piece, an opening  6  is formed which serves for the passage of the limiting strap arranged on the other side. 
     The limiting straps and the fabric piece run in the following manner. The fabric piece is placed in the manner of a ring so that the two reinforcement regions lie one on the other such that the recesses  5  coincide with the inflation opening. One of the limiting straps extends here through the opening  6 . Thus, one limiting strap each protrudes on both sides from the annular fabric piece  10  which forms the pre-chamber. The fabric piece is sewn with the wall region of the gas bag which surrounds the inflation opening, or is connected for example by a holding ring. The free ends of the limiting straps are sewn with the region of the wall of the gas bag which faces a vehicle occupant who is to be restrained. 
     In FIG. 5 a further embodiment is shown. In contrast to the embodiment according to FIG. 3, the limiting straps are not sewn centrally with the region of the wall of the gas bag which faces a vehicle occupant who is to be restrained, but rather laterally in the region of the seam which connects the side pieces of the wall of the gas bag with the central wall piece. 
     In FIGS. 6 and 7, respectively, a further embodiment is shown. In contrast to the preceding embodiments, the limiting straps  4  are not arranged laterally on the fabric piece  10  but rather engage centrally in a region opposite the inflation opening  2  on the fabric piece  10 . The fabric piece of FIG. 6 is sewn with its outer edges to the wall of the gas bag. The fabric piece of FIG. 7 has an annular shape, as is known from FIG.  3 . In both embodiments, two limiting straps lying adjacent to each other are used, the free ends of which are sewn to the fabric piece  10  and, respectively, to the wall of the gas bag, in opposite directions. 
     In FIG. 8 a variant of the embodiment of FIG. 7 is shown. In this variant, only a single limiting strap  4  is used, which is sewn centrally to the fabric piece  10  in a region lying opposite the inflation opening  2 . 
     Hereinbelow, a particular embodiment of a fabric piece  10  is shown, which can be used together with the limiting straps  4 . For better clarity, the limiting straps are no longer shown. However, it can easily be seen that the limiting straps, in an identical manner to that in the preceding embodiments, can be constructed either in one piece with the fabric piece or sewn to the fabric piece. 
     In FIG. 9 the fabric piece  10  is shown in the spread out condition, which fabric piece can be cut in one piece from a strip of fabric. The fabric piece  10  contains a central portion  12  which is provided with four fastening portions  14 . Each fastening portion  14  extends along one of the shorter outer edges of the central portion  12  starting from a longer outer edge towards the central longitudinal axis, the fastening portions terminating at a distance from the central longitudinal axis. Each fastening portion  14  is provided with two openings  15 ,  16 . 
     Adjoining each fastening portion  14  a rectangular reinforcement portion  18  is arranged. Each reinforcement portion  18  is provided with two openings  20 ,  21 . The openings  15 ,  16  arranged in the fastening portion  14  lie on a straight line which is perpendicular to the straight line on which the openings  20 ,  21  of the reinforcement portion  18  are arranged. 
     Each reinforcement portion  18  is connected with the central portion  12  by a transition portion  22  which adjoins the corresponding shorter outer edge in a region between the central longitudinal axis of the central portion  12  and the fastening portion  14 . Adjoining each of the shorter outer edges are therefore a fastening portion  14 , two transition portions  22  and a further fastening portion  14 , the two fastening portions together occupying approximately two thirds of the length of the corresponding shorter outer edge. 
     In FIG. 11 the fabric piece  10  is shown in a three-dimensional state, sewn together. This is obtained starting from the two-dimensional blank, shown in FIG. 9, in the following manner: The reinforcement portions  18  are pushed onto the side of the central portion  12 , which is later to form the inner face of the fabric piece, and are turned such that the opening  21  of the reinforcement piece  18  coincides with the opening  16  of the fastening portion  14  and the opening  20  of the reinforcement portion coincides with the opening  15  of the fastening portion. For this purpose, the reinforcement portions  18  must be turned through approximately 90° about a point which lies in the region of the connection portion  22 , and also must be folded likewise through approximately 90° around an edge which is situated in the region of the connection portion  22 . This state is shown in FIG. 10, in fact projected into a plane. If the reinforcement portions  18  are then sewn with the fastening portions  14  and the central portion  12 , in FIG. 11 the approximately trough-shaped form (shown turned over here) is produced, in which the central portion  12  forms the two side walls and the base of the trough. The fastening portions  14  form a part of the end faces of the trough, a passage remaining between the fastening portions which lie opposite each other. In FIGS. 10 and 11, seams by means of which the reinforcement portions  18  are connected with the fastening portion  14  and the central portion  12 , are given the reference number  30 . Seams which only serve to reinforce the outer edge or the openings  15 ,  16 ,  20 ,  21  are given the reference number  32 . 
     In FIGS. 12 to  14 , the finished, sewn-together fabric piece  12  is shown, which is arranged on a holding frame  40 . The holding frame serves to secure a gas bag to the housing of the gas bag module. Fastening bolts  42  inset in the holding frame  40  serve to do this, which bolts  42  pass through the openings  15 ,  16 ,  20 ,  21 . 
     When the fabric piece  12  is fastened to the holding frame  40 , the fastening portions  14  are situated in one and the same plane. The part of the central portion  12  which previously represented the base of the trough formed by the central portion now extends starting from one end face of the frame in an arc to the other end face. The longer outer edges of the central portion  12  extend approximately in the form of a half ellipse starting from the corresponding longitudinal side of the holding frame. 
     The fabric piece  10  therefore forms a pre-chamber over the holding frame  40 . Compressed gas which flows in through the holding frame  40  into this pre-chamber, emerges from the pre-chamber through two outlet openings which are each formed between the holding frame and one of the longer outer edges of the central portion. In this way, the outflow direction of the compressed gas is provided.