Abstract:
A gas bag for a vehicle occupant restraint system comprises an inflation opening, a fabric piece arranged inside the gas bag opposite the inflation opening and forming an outflow opening for compressed gas which flows through the inflation opening into the gas bag, and at least one tether which is likewise arranged inside the gas bag. The tether is arranged such that the compressed gas flowing out through the outflow opening from a volume surrounded by the fabric piece, substantially does not flow against the tether.

Description:
FIELD OF THE INVENTION 
     The invention relates to a gas bag for a vehicle occupant restraint system. 
     BACKGROUND OF THE INVENTION 
     Such gas bag comprises 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 through the inflation opening into the gas bag, and at least one tether 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 selective 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 tether serves to influence the shape and the dimensions of the gas bag in particular in the unfolded state. In addition, by means of the tether also the unfolding behavior of the gas bag can be influenced. However, it is a problem that the tether 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 tether does not have any negative effect on the unfolding behavior of the gas bag, which is given by means of the fabric piece. According to the invention, a gas bag for a vehicle occupant restraint system comprises an inflation opening, a fabric piece arranged inside the gas bag opposite the inflation opening and forming an outflow opening for compressed gas which flows through the inflation opening into the gas bag, and at least one tether which is likewise arranged inside the gas bag. The tether is arranged such that the compressed gas flowing out through the outflow opening from a volume surrounded by the fabric piece, substantially does not flow against the tether. This ensures that the tether 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 delimited by the fabric piece, for example by the opening being covered. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is described herein below 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 tether; 
     FIG. 2 shows in a perspective view the gas bag of FIG. 1 with tether and fabric piece; 
     FIG. 3 shows in a perspective view a gas bag with tether and fabric piece, the tether and the fabric piece being constructed in one piece; 
     FIG. 4 shows in a top view the blank for the tether and the fabric piece of FIG. 3; 
     FIG. 5 shows in a perspective view a gas bag with tether and fabric piece according to a modified embodiment; 
     FIG. 6 shows in a perspective view a gas bag with tether and fabric piece according to a further embodiment; 
     FIG. 7 shows in a perspective view a gas bag with tether and fabric piece according to an additional further embodiment; 
     FIG. 8 shows in a perspective view a gas bag with tether 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 FIG. 1 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 in addition two tethers  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. 
     In addition, FIG. 2 shows a fabric piece  10  inside the gas bag such that it forms a type of pre-chamber into which the compressed gas enters which flows in through the inflation opening. From this pre-chamber, the compressed gas flows through two outflow openings  3  into the gas bag. 
     An essential feature consists in that the tethers are arranged outside the region in which the compressed gas flows from the pre-chamber into the gas bag. In the embodiment of FIGS. 1 and 2, the tethers 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 during the unfolding of the gas bag no danger that the tethers 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 constructionally 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 and the vehicle floor respectively, and only then towards the vehicle occupant. 
     In FIG. 3 a gas bag is shown in which the fabric piece and the tethers are constructed in one piece (see also FIG.  4 ). The tethers are arranged on opposite sides of the fabric piece  10 . Between the tethers 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 tether arranged on the other side. 
     The tethers 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 tethers extends here through the opening  6 . Thus, one tether 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 tethers 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 tethers 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 each, a further embodiment is shown. In contrast to the preceding embodiments, the tethers  4  are not arranged laterally on the fabric piece  10  but rather engage centrally in a region opposite the inflation opening  2  on the fabrice 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 tethers lying against each other are used, the free ends of which are sewn in opposite directions to the fabric piece  10  and to the wall of the gas bag, respectively. 
     In FIG. 8 a variant of the embodiment of FIG. 7 is shown. In this variant, only a single tether  4  is used, which is sewn centrally onto 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 tethers  4 . For better clarity, the tethers are no longer shown. However, it can easily be seen that the tethers, 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, spread out, which can be cut in one piece from a strip of fabric. The fabric piece  10  contains a central section  12  which is provided with four fastening sections  14 . Each fastening section  14  extends along one of the shorter outer edges of the central section  12  starting from a longer outer edge towards the central longitudinal axis, the fastening sections terminating at a distance from the central longitudinal axis. Each fastening section  14  is provided with two openings  15 ,  16 . 
     Adjoining each fastening section  14  a rectangular reinforcement section  18  is arranged. Each reinforcement section  18  is provided with two openings  20 ,  21 . The openings  15 ,  16  arranged in the fastening section  14  lie on a straight line which is perpendicular to the straight line on which the openings  20 ,  21  of the reinforcement section  18  are arranged. 
     Each reinforcement section  18  is connected with the central section  12  by a transition section  22  which adjoins the corresponding shorter outer edge in a region between the central longitudinal axis of the central section  12  and the fastening section  14 . Adjoining each of the shorter outer edges are therefore a fastening section  14 , two transition sections  22  and a further fastening section  14 , the two fastening sections 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 sections  18  are pushed onto the side of the central section  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 section  14  and the opening  20  of the reinforcement section coincides with the opening  15  of the fastening section. For this purpose, the reinforcement sections  18  must be turned through approximately 90° about a point which lies in the region of the connection section  22 , and also must be folded likewise through approximately 90° around an edge which is situated in the region of the connection section  22 . This state is shown in FIG. 10, in fact projected into one plane. If the reinforcement sections  18  are then sewn with the fastening sections  14  and the central section  12 , the approximately trough-shaped form shown in FIG. 11 (shown turned over here) is produced, in which the central section  12  forms the two side walls and the base of the trough. The fastening section  14  form a part of the end faces of the trough, a passage remaining between the fastening sections which lie opposite each other. In FIGS. 10 and 11, seams by means of which the reinforcement sections  18  are connected with the fastening section  14  and the central section  12 , are given the reference number  30 . Seams which only serve to reinforce the outer edge and the openings  15 ,  16 ,  20   21  respectively, 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  let 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 sections  14  are situated in one and the same plane. The part of the central section  12  which previously represented the base of the trough formed by the central section 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 section  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 the pre-chamber, emerges from the pre-chamber through two outlet openings which are formed between the holding frame and one of the longer outer edges of the central section. In this way, the outflow direction of the compressed gas is predefined.