Patent Application
20050098995
The invention relates to a gas bag for a vehicle occupant restraint system comprising first and second fabric layers superimposed on each other, and at least one tether means defining a spacing between the fabric layers in the inflated condition of the gas bag, which is secured to the first and second fabric layers.
The expansion of a gas bag can be influenced and controlled for example by internal tethers. These tethers are respectively arranged between two fabric layers lying one over another and are sewn to these or woven by a special weaving technique. In each case, the arrangement of the internal tethers requires a considerable manufacturing expenditure. When the tethers are secured to the fabric layers by seams, these seams must be introduced through the inflation port of the gas bag. The weaving of the internal tethers with the superimposed fabric layers requires a special weaving technique which is very costly and complex.
U.S. Pat. No. 6,457,745 B1 therefore suggests to construct the internally arranged tether means by at least one seam constructed with thread slack. The thread slack of the seam forms loops in the folded condition of the gas bag, which are arranged between the fabric layers or on the outer surface of one of the fabric layers. With the expansion of the gas bag, the thread slack is drawn out until the loops are eliminated. The plurality of taut threads inside the gas bag acts like a tether which delimits the expansion of the gas bag in the direction of extent of the threads. The production of interior loops, however, requires the use of spacers in the production of the gas bag, which means an increased manufacturing expenditure.
In a gas bag for head protection, finally, in the entire restraint region, i.e. the region in which striking by a vehicle occupant is to be expected, a sufficient gas thickness is to be available which is as constant as possible. Currently, gas bags for head protection are divided into several restraint chambers by nip seams, i.e. a connection of the fabric layers by means of a simple seam, in order to also ensure a reliable restraining effect with different striking directions of the head onto the gas bag. In so doing, however, the possibility of a striking of the occupant's head onto a nip seam has to be ruled out, because at this point no air cushion is available.
By comparison, the invention provides a gas bag in which also in the region of the nip seams a residual air bag thickness or an air cushion is present in the case of restraint. Therefore, in a simple manner, a sufficient gas bag thickness is provided over the entire restraint region. Furthermore, the gas bag according to the invention can be produced with simple manufacturing techniques.
For this, according to the invention, a gas bag is provided for a vehicle occupant restraint system comprising first and second fabric layers superimposed on each other, and at least one tether means defining a spacing between the first and second fabric layers in the inflated condition of the gas bag and being secured to the first and second fabric layers, which is characterized in that the tether means in the folded state of the gas bag comprises a seam having at least three threads, at least one of the threads being constructed as a tear thread. Such a seam can be constructed without further auxiliary means with a conventional sewing machine.
On inflating of the gas bag, the seam thread constructed as a tear thread breaks and thus makes possible a loosening of the seam formed by the other two threads or the production of a thread slack during the inflation process. The expansion of the gas bag is delimited in direction of extent of these threads. Hence, however, an air cushion can form between the first and second fabric layers in the region of the seam. Therefore, it is possible without greater expenditure to maintain a division of the gas bag into several restraint chambers and through the construction of the nip seams comprising a seam in the described manner to nevertheless provide a residual thickness of the gas bag.
Preferably, the seam is formed by at least two under-threads which are spaced apart from each other, and an upper thread running between the under-threads, the tear thread being one of the under-threads. A particularly simple embodiment makes provision that the under-threads are arranged on the outer side, i.e. the side facing the exterior of the gas bag, of one of the fabric layers, whereas the upper thread is arranged on the outer side of the other fabric layer and runs between the under-threads in a zigzag pattern. This embodiment is therefore similar to a conventional zigzag stitch. The residual gas bag thickness is established here in a simple manner by the spacing of the under-threads or the stitch rows, with which the under-threads are connected to the fabric layer. The seam pattern can be produced on commercially available sewing machines. Therefore, however, the construction of complex seam geometries is also possible without increased manufacturing expenditure.
Preferably the tear thread or the under-threads constructed as a tear thread has a thickness of about 0.1 mm or less. With thicker threads, the danger exists that the tear thread does not tear reliably or damages the gas bag fabric. The remaining threads of the seam are preferably at least about 0.5 mm thick, in order to be able to effectively delimit the expansion of the gas bag.
Further advantages and features of the invention will be apparent from the following description of an embodiment of the invention with reference to the enclosed drawings. In the drawings:
The section of a gas bag 10, shown in
In the embodiment illustrated here, the seam 16 consists of an upper thread 18, and two under-threads 20, 22 arranged at a lateral distance X from each other. The under-threads 20, 22 are arranged on the outer surface of the second or lower fabric layer 14 in
The upper thread 18 and the under-thread 20 are constructed to have a thickness of approximately 0.5 mm or more. The under-thread 22 is formed as a tear thread having a thickness of approximately 0.1 mm or less.
On inflating the gas bag 10, the under-thread 22 tears owing to the rising internal pressure in the gas bag and frees the stitch row formed on the under-thread 22. Thereby, loops form which with the further expansion of the gas bag are drawn through the stitch row formed at the under-thread 20, until the loops are eliminated. This is the case, for instance, when the spacing X of the first and second fabric layers 12, 14 upon inflation of the gas bag approximately equals the spacing X of the under-threads 20, 22 or of the stitch rows formed at these threads in the condition when the gas bag is spread out flat. The spacing between the first and second fabric layers 12, 14 and hence the residual gas bag thickness, can therefore already be controlled in this way in a simple manner by means of the manufacturing process.
The production of the seam 16 can take place by simple sewing methods, for example similar to a conventional zigzag stitch, without additional process steps being necessary, such as for example the introduction of spacers into the gas bag. In the folded condition, the seam 16 lies closely against the outer surface of the fabric layers 12, 14, so that no risk exists of an impairment to function by a tangling of thread slack or loops.
The invention is not restricted to the seam pattern described here. It is conceivable, for example, that the under-threads 20, 22 are arranged on opposite outer surfaces of the first and second fabric layers and/or that the upper thread runs on both outer surfaces of the fabric layers 12, 14.
| Number | Date | Country | Kind |
|---|---|---|---|
| 103 52 666.8 | Nov 2003 | DE | national |
