EP2503037A1

EP2503037A1 - A fabric for use in the manufacture of an inflatable air-bag

Info

Publication number: EP2503037A1
Application number: EP11159477A
Authority: EP
Inventors: Altay Kismir; David Stow; Gary Wootton; Hugh Finn; Ralf Koehnen
Original assignee: Autoliv Development AB
Current assignee: Autoliv Development AB
Priority date: 2011-03-23
Filing date: 2011-03-23
Publication date: 2012-09-26
Anticipated expiration: 2031-03-23
Also published as: EP2503038B1; EP2503037B1; EP2503038A1

Abstract

A fabric for use in the manufacture of an inflatable air-bag, the fabric comprising interwoven warp and weft fibres which are arranged substantially perpendicular to one another, the fibres having non-uniform cross-sections to increase friction between the fibres at their intersections.

Description

Description of Invention

THIS INVENTION relates to a fabric for use in the manufacture of an inflatable air-bag, and a method of making the fabric.
Inflatable air-bags, for use in occupant constraint systems in motor vehicles, are conventionally formed from woven fabrics. These fabrics typically comprise two sets of fibres, known as warp and weft fibres, which are interwoven with one another and arranged approximately at right angles to one another. A coating is often applied to such fabrics, and the coating provides the function of decreasing the permeability of the material, and maintaining the fibres in their intended positions.
It is advantageous to reduce the weight of an air-bag as much as possible. This will not only reduce the quantity of material required to construct the air-bag, thereby reducing the cost of the finished item, but will also reduce the weight that must be transported by a vehicle which contains the air-bag.
Focusing on the fabric of an air-bag, there are two principal options for reducing the weight of the air-bag. One is to reduce the weight per unit length of the fibres used to form the fabric (conventionally measured in tex (1 tex = 1 gram per km) or decitex). The other is to reduce the density of fibres per unit area of the fabric (conventionally measured in sett, i.e. threads per cm, counted in as the number of perpendicular threads that are encountered along the length of one of the warp or weft fibres).
If fibres having reduced decitex are used, it is found that the tear and tensile strengths of the fabric are both reduced. This is the case even if the number of threads per unit area is increased to compensate, as each individual thread will break relatively easily.
If the spacing between the fibres is increased, two undesirable effects typically result. The first is that there are larger gaps between the fibres. If the fabric is not coated, then this will increase the permeability of the fabric. If the fabric is covered with a coating, then the coating material will come under greater stress in the larger regions between the fibres when the pressure difference across the fabric is high. Clearly, this leads to an increased risk of rupturing of the coating material.
Secondly, as the sett is reduced, the wrapping angle of each fibre around adjacent fibres is reduced. This reduces the inter-fibre friction, which is fundamental to the formation of the stable fabric. In addition, as stress is applied to the fabric, individual fibres can slide laterally with respect to adjacent fibres, a phenomenon known as combing. For an uncoated fabric, once again this will increase the permeability of the material. For a coated fabric, this combing movement places additional stress on the coating, which will generally lead to micro-ruptures at the elongated interstices.
It is an object of the present invention to provide a fabric for use in the manufacture of an inflatable air-bag which alleviates some or all of the above problems.
Accordingly, one aspect of the present invention provides a fabric for use in the manufacture of an inflatable air-bag, the fabric comprising interwoven warp and weft fibres which are arranged substantially perpendicular to one another, the fibres having non-uniform cross-sections to increase friction between the fibres at their intersections.
Advantageously, at least one of the warp and weft fibres are formed from two or more filaments which are twisted, wound or assembled together.
Preferably, at least one of the warp and weft fibres are coated with a roughening agent, to increase the surface roughness of the fibres.
Another aspect of the present invention provides a fabric for use in the manufacture of an inflatable air-bag, the fabric comprising interwoven warp and weft fibres which are arranged substantially at right angles to one another, wherein each of at least one of the warp and weft fibres are formed from at least two fibre components.
Conveniently, each of at least one set of fibres is formed from one or more filaments which are twisted, wound or assembled together.
Advantageously, the fabric has a cover value below around 55%.
A further aspect of the present invention provides an air-bag formed from a fabric according to any preceding claim.
Another aspect of the present invention provides a method of forming a fabric for use in the manufacture of an inflatable air-bag, the method comprising the steps of: providing two sets of fibres; treating at least one of the sets of fibres so that the fibres have non-uniform cross-sections and thereby increase the coefficient of friction between one of each of the two sets of fibres thereof; and weaving the sets of fibres together to form a fabric, so that the two sets of fibres form warp and weft fibres of the fabric and are arranged substantially at right angles to one another.
Preferably, the at least one set of fibres is coated with a surface roughener to increase the roughness of the surface of the fibres.
Conveniently, the step of treating the fibres comprises increasing the surface texture of the fibres.
Advantageously, the step of treating the fibres comprises forming a substantially continuous surface texture on the fibres.
Preferably, the method comprises the step of exposing the fibres to at least one jet of pressurised gas.
Conveniently, the method comprises the step of eroding at least a part of the surface of the fibres using a corrosive substance.
A further aspect of the present invention provides a method of forming a fabric for use in the manufacture of an inflatable air-bag, comprising the steps of: forming at least one set of fibres from two fibre components comprising two or more filaments which are twisted, wound or assembled together; and interweaving the fibres with further fibres to form a fabric, wherein the fibres and further fibres comprise warp and weft fibres of the fabric and are arranged substantially at right angles to each other.
Another aspect of the present invention provides a method of manufacturing an air-bag, comprising the steps of: forming a fabric in accordance with the above; and manufacturing the air-bag from the fabric.
In order that the present invention may be more readily understood, embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 shows a fabric embodying the present invention; and
Figure 2 shows a fibre which may be used in the manufacture of fabrics embodying the present invention.

Referring to figure 1, a close-up view of warp and weft fibres 1,2 making up a fabric 3 for use in the manufacture of an inflatable air-bag is shown. Each warp fibre 1 passes alternately under and over weft fibres 2 that are encountered along its length. Similarly, each weft fibre 2 passes alternately under and over warp fibres 1 that are encountered along its length.
The warp and weft fibres 1,2 of the fabric 3 are coated with a substance which increases the friction between the warp and weft fibres 1,2. Preferably, the substance does not produce an adhesive force between the fibres 1,2. In the embodiment shown, the coating comprises solid grains which are adhered to the surfaces of the fibres 1,2, producing an effect which is similar to coating the fibres 1,2 with sand.
If forces are exerted on the warp fibres 1 which would tend to cause the warp fibres 1 to slide with respect to the weft fibres 2, the interaction of the grains will provide a strong resistance to this movement. The result will be an increase in the friction between the warp and weft fibres 1,2 at the junctions 4 therebetween, increasing the overall reliability and stability of the fabric 3.
In further embodiments, the fibres are treated so that their surfaces acquire a texture, which may be regular or irregular.
One method of achieving this result is to expose the fibres to one or more jets of pressurised air (a technique known as "air texturing"), which imposes dents, ridges and other features in the surfaces of the fibres.
In an alternative technique, the surfaces of the fibres can be treated with a corrosive substance such as an acid, which will remove parts of the outer surface of the fibre, once again leading to surface features and irregularities. In these embodiments, it may be desirable to use fibres which are heavier than is actually required in the finished article, so that the weight of the fibres is reduced to the required level as part of the fibre surfaces are removed.
If fibres which have been treated in this way are woven to form a fabric as shown in figure 1, the friction between the fibres at their intersections will be significantly increased, as fibres sliding across one another will encounter raised ridges, nodes and projections, which will impede the sliding movement far more than if the fibres simply presented smooth outer surfaces to one another.
In yet further embodiments of the invention, each fibre may be formed from two separate fibre components or filaments. For instance, as shown in figure 2, each fibre 9 may be formed from two or more thinner strands 10, 11, which are wrapped around each other, or interwoven with each other. The strands 10,11 may be formed from the same material, or in alternative embodiments may be formed from different materials.
It will therefore be understood that the term "fibre", when used in this specification, covers individual strands or filaments, as well as arrangements of two or more strands or filaments which are twisted, wound or otherwise assembled together to form a yarn or thread.
It will be understood that forming the fibre 9 from one or more strands 10,11 will increase the surface texture of the fibre 9. If a plurality of such fibres 9 were to be woven into a fabric as shown in figure 1, it will be understood that the fibres 9 would display a high resistance to sliding with respect to one another, as a fibre sliding with respect to a perpendicular fibre will continually encounter ridges which will provide strong resistance to this sliding motion.
It will be understood that all of the above techniques increase the friction between warp and weft fibres where these fibres meet in a woven fabric. This will provide resistance to slippage of the fibres with respect to one another, increasing the stability and reliability of the resulting fabric. If the fabric is uncoated, the permeability of the fabric will remain low when high forces are exerted on the fabric. If the fabric is coated, slippage of the fibres within the coating will be reduced, therefore helping maintain the regular sizes of the interstitial spaces and hence the integrity of the coating under large forces.
The relationship between the amount of material comprising fibres, and the spaces therebetween, per unit area can be calculated, and the result is known as the "cover factor". The cover factor allows fabrics made with different decitex fibres to be compared, and is also a useful way of describing a fabric without specifying a particular decitex value.
In this specification it is stated that fibres are formed or treated to have non-uniform cross-sections. It is appreciated that all fibres, when inspected closely, will have variations in their cross-sections arising from imperfections in the materials from which the fibres are formed, or from the manufacturing process. However, when used in this specification this term refers to deviations from uniformity which are deliberately formed or applied, and are of a magnitude which is over and above those which arise from a standard manufacturing process for fibres of the type which are generally used to weave fabric for vehicle air-bags.
In preferred embodiments of the invention the fabric has a cover value of 55% or lower, and preferably below 54%. These values are lower than those found in conventional air-bag fabrics, but in using techniques described above robust and versatile fabrics having such low cover values are possible.
When used in this specification and claims, the terms "comprises" and "comprising" and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components.
The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims

A fabric for use in the manufacture of an inflatable air-bag, the fabric comprising interwoven warp and weft fibres which are arranged substantially perpendicular to one another, the fibres having non-uniform cross-sections to increase friction between the fibres at their intersections.
A fabric according to claim 1, wherein at least one of the warp and weft fibres are formed from two or more filaments which are twisted, wound or assembled together.
A fabric according to claim 1 or 2, wherein at least one of the warp and weft fibres are coated with a roughening agent, to increase the surface roughness of the fibres.
A fabric for use in the manufacture of an inflatable air-bag, the fabric comprising interwoven warp and weft fibres which are arranged substantially at right angles to one another, wherein each of at least one of the warp and weft fibres are formed from at least two fibre components.
A fabric according to claim 4, wherein each of at least one set of fibres is formed from one or more filaments which are twisted, wound or assembled together.
A fabric according to any preceding claim having a cover value below around 55%.
An air-bag formed from a fabric according to any preceding claim.
A method of forming a fabric for use in the manufacture of an inflatable air-bag, the method comprising the steps of:
providing two sets of fibres;

treating at least one of the sets of fibres so that the fibres have non-uniform cross-sections and thereby increase the coefficient of friction between one of each of the two sets of fibres thereof; and

weaving the sets of fibres together to form a fabric, so that the two sets of fibres form warp and weft fibres of the fabric and are arranged substantially at right angles to one another.
A method according to claim 8, wherein the at least one set of fibres is coated with a surface roughener to increase the roughness of the surface of the fibres.
A method according to claim 8 wherein the step of treating the fibres comprises increasing the surface texture of the fibres.
A method according to claim 10, wherein the step of treating the fibres comprises forming a substantially continuous surface texture on the fibres.
A method according to any one of claims 8 to 11, comprising the step of exposing the fibres to at least one jet of pressurised gas.
A method according to any one of claims 8 to 12, comprising the step of eroding at least a part of the surface of the fibres using a corrosive substance.
A method of forming a fabric for use in the manufacture of an inflatable air-bag, comprising the steps of:
forming at least one set of fibres from two fibre components comprising two or more filaments which are twisted, wound or assembled together; and

interweaving the fibres with further fibres to form a fabric, wherein the fibres and further fibres comprise warp and weft fibres of the fabric and are arranged substantially at right angles to each other.
A method of manufacturing an air-bag, comprising the steps of:
forming a fabric in accordance with any one of claims 8 to 14; and

manufacturing the air-bag from the fabric.