GB2405620A

GB2405620A - Reinforced dynamic burn vent

Info

Publication number: GB2405620A
Application number: GB0320976A
Authority: GB
Inventors: Ralmund Nebel; Thomas Wienecke; Claudia Sager; David Stow
Original assignee: Autoliv Development AB
Current assignee: Autoliv Development AB
Priority date: 2003-09-08
Filing date: 2003-09-08
Publication date: 2005-03-09
Anticipated expiration: 2023-09-08
Also published as: GB0320976D0; DE102004043616A1; GB2405620B

Abstract

A fabric air bag comprises a dynamic burn vent 4 having a localised region of high permeability fabric 5. The vent has a central portion 7 of low density fabric and an outer portion 6 of higher density fabric. Surrounding the burn vent 4 and central gas generator aperture 2 is a reinforcement 3 which prevents excess tearing when the bag is inflated. A hole is formed in the high permeability fabric due to heat generated by inflation and increases in size as the pressure increases thus increasing the flow rate of gases through the vent.

Description

DESCRIPTION OF INVENTION

"IMPROVEMENTS IN OR RELATING TO AN AIR-BAG" THE PRESENT INVENTION relates to an air-bag, and more particularly relates to an air-bag to provide protection for an occupant of a vehicle in the event that an accident should arise.

It has been proposed to provide air-bags, of various designs, to provide protection for vehicle occupants in the event that an accident should arise.

It is desirable for such an air-bag to become inflated as swiftly as possible after an accident has been sensed. It is also desirable for the air-bag to provide a relatively soft cushioning effect when the air-bag is struck by a vehicle occupant.

Ideally the air-bag should decelerate the vehicle occupant in a manner which is as gentle as possible. However, the air-bag should not be so "soft" that the vehicle occupant can effectively strike right through the air-bag and engage structure of the vehicle on the far side of the airbag.

The designer of an air-bag is faced with conflicting requirements.

Initially the air-bag should be sealed to enable the air-bag to become inflated just as swiftly as possible. However, the air-bag should also be vented so that, when the air-bag is struck by a vehicle occupant, gas within the air-bag may become ejected from the air-bag through the vent, so that the air-bag provides an appropriate "cushioning" effect.

The present invention seeks to provide an improved air-bag.

According to this invention there is provided an air-bag, the air-bag being formed of fabric of a predetermined permeability, the air-bag being provided with at least one vent region in which the fabric of the air-bag is of higher permeability, the vent region being surrounded by a reinforcement.

Preferably, said fabric of a predetermined permeability has a predetermined density, and wherein the or each said vent region comprises fabric of a lower density.

Advantageously, fabric of a predetermined permeability and said the or each vent regions are formed using different weave patterns.

Preferably there are a plurality of vent regions, the plurality of vent regions being located within a single reinforcement.

Conveniently the reinforcement is a reinforcement around a gas generator aperture formed in the air-bag.

Alternatively there are a plurality of vent regions, each vent region being provided with its own reinforcement.

Preferably the or each vent region the fabric has a first area of a predetermined density, and a second area of a lower predetermined density, each of the said densities being lower than the said predetermined density.

In order that the invention may be more readily understood, and so that further features thereof may be appreciated, the invention will now be described, by way of example, with reference to the accompanying drawings in which: FIGURE 1 illustrates part of an air-bag in accordance with the invention, and FIGURE 2 is a sectional view taken on the line II-II of Figure 1.

Referring initially to Figure I part of an air-bag is illustrated. The air bag is formed of fabric 1 of a predetermined permeability and preferably also a predetermined density. A relatively large aperture 2 is formed in the fabric 1 to accommodate a gas generator. An annular reinforcement 3 is provided, applied to the air-bag surrounding the large aperture 2. A plurality of apertures 4 are formed in the annular reinforcement, each aperture 4 exposing a region 5 of the fabric I forming the air-bag.

Each region of fabric 5, as exposed through an aperture 4, is preferably of lower density of weave than the main part of the fabric 1 and forms a vent region in which the fabric has a higher permeability than the main part of the fabric 1. As can be seen more clearly from Figure 2 each region 5, which is of circular form in the illustrated embodiment, has a peripheral outer part 6 having a density of weave which is lower than the density of weave of the main part of the fabric 1, and a central circular part 7 where the density of weave is even lower than the density of weave in the annular region 6.

The density of weave, and hence permeability, may be adjusted by reducing the number of yarns in a unit area, or by reducing the diameter of the yarns. However, the permeability can also be adjusted by varying the weave patterns of different regions of the fabric.

Thus, each aperture 4 exposes an area of fabric having a central region 7 of extremely high permeability, for example defined by a low density of weave and a peripheral region 6 of a slightly lower permeability (higher density of weave), but nevertheless a permeability which is higher than the permeability of weave of the main part of the fabric 1 used to form the air-bag.

1 S On inflation of the air-bag the regions 5 of fabric will be exposed to hot gas under high pressure. During an initial phase of inflation of the air-bag the regions of fabric 5 will maintain their integrity, thus allowing the air-bag to become fully inflated or substantially fully inflated within a relatively short period of time. However, when the elements 5 of fabric are subjected to hot gas under high pressure, the elements of fabric will deteriorate. The yarns forming the fabric may burn, or the fabric, being relatively weak as a consequence of its low density, will rupture. The central part 5 where the weave is a very low density will deteriorate initially and, the outer-most annular part 6, where the density of the fabric is greater will deteriorate if certain conditions exist, that is to say if the annular region 6 is subjected to a sufficient pressure or a sufficient temperature to cause deterioration. When the fabric has deteriorated a vent opening will be created.

Here it is to be noted that with a hybrid gas generator, that is to say a gas generator which includes not only a source of cold compressed gas, but also a pyrotechnic charge, the pressure of gas developed by the gas generator does depend to a large extent upon the ambient temperature. Motor vehicles may operate within a very wide range of ambient temperatures, from many degrees below zero centigrade, to temperatures in excess of 50 C. Although these temperatures are extreme, in many countries, during the course of a single year, vehicles may operate in temperatures which are separated by 50 or 60 C.

If an air-bag is deployed at a high ambient temperature, the pressure inside the air-bag will be much greater than if the air-bag is deployed at a very low temperature. Of course, the performance characteristic of the air-bag will vary in dependence upon the internal pressure, and thus it is desired to provide a self-regulating venting system which will provide a larger vent if the pressure inside the air-bag is high as compared with the vent provided when the pressure inside the air-bag is low.

It is thus to be understood that in the described embodiment of the invention, should the pressure inside the air-bag be moderate, only the central region 7 of the area 5 will deteriorate, providing a vent of a specific area.

However, if the pressure is very high, the outer annular part 6 of the exposed fabric region 5 will deteriorate, thus providing a relatively large vent hole, of a greater area.

It is to be understood that the reinforcement 3, which surrounds the area where the fabric is of low density, will prevent any tears that will generate during the deterioration of the exposed fabric layer from spreading in an undesirable manner.

It is preferred that the air-bag of the invention may be formed using a one-piece weaving technique, although the invention may be used with airbags of a more conventional form.

Whilst the invention has been described with reference to the fact that the reinforcement provided around the gas generator opening 2 is used as the reinforcement for the described vent regions, it is to be understood that each vent region may be provided with its own separate reinforcement. An advantage of using the reinforcement around the gas generator opening is that, in many embodiments, the vent apertures will open into a gas generator housing, meaning that the gas vented from the air-bag may be vented to a position which is not in direct communication with the vehicle cabin, In the present Specification "comprises" means "includes or consists of" and "comprising" means "including or consisting of''.

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

CLAIMS: 1. An air-bag, the air-bag being formed of fabric of a

predetermined permeability, the air-bag being provided with at least one vent region in which the fabric of the air-bag is of higher permeability, the vent region being surrounded by a reinforcement.
2. An air-bag according to Claim 1, wherein said fabric of a predetermined permeability has a predetermined density, and wherein the or each said vent region comprises fabric of a lower density.
3. An air-bag according to Claim 1 or Claim 2, wherein said fabric of a predetermined permeability and said the or each vent regions are formed using different weave patterns.
4. An air-bag according to any preceding Claim, wherein there are a plurality of vent regions, the plurality of vent regions being located within a single reinforcement.
5. An air-bag according to Claim 4, wherein the reinforcement is a reinforcement around a gas generator aperture formed in the air-bag.
6. An air-bag according to any one of Claims 1 to 3, wherein there are a plurality of vent regions, each vent region being provided with its own reinforcement.
7. An air-bag according to any one of the preceding Claims, wherein the or each vent region the fabric has a first area of a predetermined density, and a second area of a lower predetermined density, each of the said densities being lower than the said predetermined density.
8. An air-bag substantially as herein described with reference to and as shown in the accompanying drawings.
9. Any novel feature or combination of features disclosed herein.