GAS-PERMEABLE FABRIC

Abstract: A method of producing a gas-permeable fabric comprises weaving a plain or hopsack pattern with missing or interchanged binding points. Preferably, the degree of permeability in certain areas of the fabric is varied by increasing or decreasing the incidence of missing binding points. The fabric is used in an airbag to control the venting of gases through selective permeability while maintaining similar fabric properties in terms of strength and weight.

Description: GAS - PERMEABLE FABRIC This invention relates to a method of producing a gas-permeable fabric, particularly for use in the manufacture of inflatable airbags for the protection of vehicle occupants in the event of a collision. Such airbags are stored in front of the respective occupants of a vehicle and are arranged to be inflated almost instantaneously in the event of a collision and to immediately commence to deflate, so as to temporarily restrain the occupants and thus prevent them from being injured by being thrown against hard internal surfaces within the vehicle. Currently produced airbags tend to be manufactured from fabric coated with a synthetic rubber such as neoprene which makes the fabric impermeable to gases, and the coated fabric is provided with one or more vent holes of different diameters to permit controlled deflation and consequential energy absorption. As inflation is usually effected by pyrotechnic means which generate hot gases and particles, the vent holes are provided in areas of the bag away from the vehicle occupant to allow the gases to escape without causing thermal injuries to the occupant or thermal damage to the fabric. The larger the area of venting through the fabric, the lower the thermal stress and risk of failure of the fabric through heat. The bags may be woven in one piece, or anufactered by sewing or adhering the edges of two pieces of fabric together. New developments with uncoated fabrics aim to facilitate the production of airbags and make them stowable in a smaller space. These developments control the permeability of the bag by means of yarn type, weave construction, weaving density, or a combination of these systems. However, fabrics produced to certain specifications by these systems have different properties which can have a negative effect on airbags manufactured therefrom. The properties adversely affected may be sewability, seam strength, fabric strength, fabric thickness, fabric weight, dimensional stability, and permeability. The object of the present invention is to produce fabrics with the same properties throughout whilst allowing variations in permeability in different areas. According to one aspect of the invention, a method of producing a gas-permeable fabric comprises weaving a plain or hopsack pattern with missing or interchanged binding points. Preferably, the degree of permeability in certain areas of the fabric is varied by increasing or decreasing the incidence of missing binding points. Preferably, also there are no missing binding points in certain areas of the fabric. Preferably not more than one out of five binding points are missing so as to maintain the stability of the fabric. The method may be effected on a jacquard loom. Alternatively, the method may be effected on a shaft loom. According to another aspect of the invention, an airbag is manufactured from fabric produced in accordance with any one of the methods defined in the preceding six paragraphs. A one-piece airbag .nay be manufactured from fabric produced in accordance with any one of said methods by weaving upper and lower webs of fabric simultaneously whilst causing the two webs of fabric to be woven together in selected areas to define a continuous seam of a desired shape. Alternatively, an airbag is manufactured from two separate webs of fabric produced in accordance with any one of said methods by sewing or adhering the edges of the two webs of fabric together to form a continuous joint of a desired shape. In an airbag according to either of the preceding two paragraphs, the degree of permeability of each of the two webs of fabric may be varied. Alternatively, in an airbag according to either of said paragraphs, the degree of permeability in certain areas of one or both of the two webs of fabric is varied. The invention will now be further described, by way of example only, with reference to the accompanying drawings of which :- Figure 1 illustrates diagrammatically a conventional plain weave pattern; Figure 2 illustrates diagrammatically a plain weave pattern with a missing binding point; Figure 3 shows a web of fabric with a shaded egg-shaped area of different permeability; Figure 4 shows a web of fabric with a shaded cross-shaped area of different permeability; and Figure 5 is a similar diagram to Figures 1 and 2 illustrating an alternative weave pattern. Referring now to the drawings, a web of fabric for use in the manufacture of an airbag, and having an area 10 of higher permeability which is circular as shown in Figure 3 or a quadrant of a cicle as shown in Figure 4, is produced by weaving a plain pattern which, at least within the shaded area, has missing binding points as shown in Figure 2. Oval shapes, e.g. egg- shaped, may be employed, as may other shapes such as cross- shaped. The remaining fabric 12 is of lower permeability and may be of ordinary plain weave. The degree of permeability is varied by increasing or decreasing the incidence of missing binding points, but in order to maintain the stability of the fabric not more than one out of five binding points are missing along each waft yarn, and the missing binding points on adjacent weft yarns are staggered. This weaving pattern can be produced on shaft looms or on jacquard looms, and can be based on a plain pattern as described or on a hopsack pattern, with single layer or multi-layer fabric. By way example, the permeability of the plain weave portions 12 may be about 5 1/sq dm/min, while that of the portions 10 may be between 20 and 100 1/sq dm/min dependant upon weave pattern. The circular shapes of figures 3 & 4 are spaced around the centre but are not in the centre. This is especially important for drivers-side airbags since the gas generator is normally placed in the centre. A one-piece airbag is manufactured as previously proposed by weaving upper and lower webs of fabric simultaneously whilst causing the two webs to be woven together in selected areas to define a continuous seam of a desired shape, for example, circular. The degree of permeability of each of the two webs is varied. For example, the web forming that part of the bag which contacts the vehicle occupant when inflated is of plain weave pattern with no missing binding points, to provide minimal permeability, whereas the web forming that part of the bag having a throat hole for connection to a gas generator is of basically plain weave pattern with an area such as that shown shaded in Figure 3 or Figure 4 having missing binding points to provide increased permeability. The size and shape of said area, and the incidence of missing binding points therein up to a maximum of one in five as aforesaid, are controlled to provide the required rate of deflation of the bag. A more conventional construction of an airbag is manufactured from two separate webs of fabric by sewing or adhering the edges of the two webs together to form a continuous joint of a desired shape, for example circular. Again, the degree of permeability of each of the two webs is varied. For example, the web forming that part of the bag which contacts the vehicle occupant when inflated is of basically plain weave pattern with a uniformly low incidence of missing binding points to provide low permeability, whereas the web forming that part of the bag having a throat hole for connection to a gas generator is of basically hopsack weave pattern with the area outside that shown shaded in Figure 3 or Λ Figure 4 having a somewhat higher incidence of missing binding points whilst the shaded area has the recommended maximum ; incidence of one out of five binding points missing. This airbag, by virtue of the permeability of the fabrics employed but not of its two-piece construction, will provide a different rate of deflation than the bag described in the preceding paragraph. Figure 5 shows a plain weave with interchanged binding points. The principle may be applied also to a passenger airbag which is conventionally manufactred using three main pieces of fabric, one of which has a hole or holes cut for venting. in ' • "his case a complete side piece may have a fabric prodv ad with differential permeability and may utilise any shape of venting area, dependant upon the total area required and shape of the bag. The advantages of both the airbags hereinbefore described, and of the invention in general, are that areas of low and high permeability have the same strength and weight, and that the fabric produced can readily be combined with other fabrics to obtain a good seam.

Claims: CLAIMS 1. A method of producing a gas-permeable fabric comprises weaving a plain or hopsack pattern with missing or interchanged binding points. 2. A method as claimed in claim 1 in which the degree of permeability in certain areas of the fabric is varied by increasing or decreasing the incidence of missing binding points. 3. A method as claimed in either of claims 1 or 2 in which there are no missing binding points in certain areas of the fabric. 4. A method as claimed in any of claims l to 3 in which not more than one out of five binding points are missing so as to maintain the stability of the fabric. 5. A method as claimed in any of claims 1 to 4 carried out on a jacquard loom. 6. A method as claimed in any of claims 1 to 4 carried out on a shaft loom. 7. A method as claimed in any preceding claim additionally comprising the steps of making an airbag from the fabric. 8. A method as claimed in claim 7 in which a one-piece airbag is manufactured from the fabric by weaving upper and lower webs of fabric simultaneously whilst causing the two webs of fabric to be woven together in selected areas to define a continuous seam of a desired shape. 9. A method as claimed in claim 7 in which an airbag is manufactured from two separate webs of fabric by sewing or adhering the edges of the two webs of fabric together to form a continuous joint of a desired shape. 10. A method as claimed in either of claims 8 or 9 in which the degree of permeability of each of the two webs of fabric is varied. 11. A method as claimed in either of claims 8 or 9 in which the degree of permeability in certain areas of one or both of the two webs of fabric is varied.

Inventors: GRAHAM RAYMOND, KAVANAGH CHRISTOPHER, PINEDA FRANSESC, VALKENBURG SIMON, GRAHAM, RAYMOND, KAVANAGH, CHRISTOPHER, PINEDA, FRANSESC, VALKENBURG, SIMON
Applicants: AIRBAGS INT LTD, AIRBAGS INTERNATIONAL LIMITED
Application year: 1992
Main classification: B60R21
IPC codes: B60R21, D03D1