Automotive airbags containing eliminators of undesirable gases

Abstract: Material (21), such as catalysts, absorbents and adsorbents, are disposed within an automotive airbag (14) so as to contact airbag inflation gases passing therethrough and remove undesirable gases therefrom.

Description: The present invention is directed to automotive airbags which contain material for removing any undesirable gases produced by combustion of pyrotechnic gas generants. Most present-day automotive airbag inflators use a gas generant based on sodium azide. This material has the advantage of producing, upon combustion, only nitrogen gas. On the other hand, sodium azide has significant toxicity, presenting disposal problems. Accordingly, there has been a desire to replace sodium azide with less toxic gas generant compositions. A number of such gas generant compositions have been described, for example in U.S. Patents Nos. 3,468,730, 5,084,118, and 5,035,757. Unfortunately, most non-azide gas generant compositions include, in addition to nitrogen, oxygen and/or hydrogen and/or carbon. The combustions of such non-azide gas generant compositions produce large volumes of generally non-toxic gases; however, they also tend to produce small, but significant, levels of undesirable gases, such as NH 3 , NO x , CO, and HCN, each of which may be problematic in the range of 25 to 1000 ppm. In order to reduce or eliminate possible health effects, it is desirable to decrease the levels of these gases. When an airbag is deployed, it must rapidly inflate, e.g., in the range of between 30 and 100 milliseconds, and then rapidly deflate. During deflation, the gases are vented into the passenger compartment of a vehicle. The occupants of the vehicle may thus be exposed to these undesirable gases. The generation of trace, but nevertheless significant, levels of undesirable gases is an important factor in why non-azide gas generant compositions have not replaced azide formulations to a greater extent. A typical automotive airbag system consists of an airbag and a pyrotechnic inflator for producing the gases which inflate the airbag. Inflators, are described, for example, in U.S. Patents Nos. 4,943,086, 5,221,109, and 5,241,910. In a typical airbag inflator deployment system, a remote sensor senses the force of a collision. The sensor is electrically connected to a squib in the inflator, and electrically generated heat in the squib ignites a small charge of pyrotechnic material in the squib. The pyrotechnic charge, in turn, produces heat that ignites a larger charge of ignitor composition. The heat from the ignitor composition then sets off a much larger charge of gas generant composition that produces a substantial volume of gas for inflating the airbag. It is also understood that there are variations of this typical system to which the present invention is applicable; for example, hybrid inflators which inflate airbags with a combination of pyrotechnic-generated gases and compressed gases, such as that described in US-A-5,290,060. As undesirable gases are most problematic with non-azide gas generant compositions, the invention is primarily directed to removing undesirable gases produced by non-azide gas generant compositions. Non-azide gas generant compositions to which the invention is primarily directed are those which contain the combinations of N plus O and/or N plus H, giving rise to NO x (especially NO and NO 2 ) and NH 3 combustion products. Such gas generant compositions commonly also contain carbon atoms, further giving rise to CO and HCN combustion products. However, the invention is applicable to inflators using azide as the gas generant material, as well, because pyrotechnics of the squib and/or ignitor material may produce undesirable gases upon combustion. . It has heretofore been proposed to include undesirable gas-removing materials inside the inflator. However, this approach has not proven to be sufficiently effective. It is likely, that the residence time in the inflator itself is so short than any undesirable gas-removing material does not have time to act effectively. In addition, very high temperatures within the inflator may reduce the effectiveness of such material. JP-A-07-117616 discloses an inflator assembly in which material for removing undesirable gases is contained within an annular cage immediately surrounding the outlet holes of the gas generator and secured to an annular flange surrounding the generator. It has now been discovered that undesirable gas-removing materials are effective when disposed within the airbag itself so as to contact gaseous combustion products as the gases flow through the bag. Accordingly, the present invention provides an automotive airbag assembly comprising an inflator and an airbag made from a gas permeable fabric or fabrics through which inflation gases pass to deflate said airbag, characterised in that a gas eliminator for removing undesirable gases from said inflation gases is contained loosely within said airbag and/or being impregnated in loose sheets of fabric disposed within said airbag so as to contact gaseous products as the gases flow through the airbag. The gas-removing material may be a catalyst, an absorbent or an adsorbent. A catalyst is a substance that accelerates or promotes a chemical reaction, in this case, a substance that promotes a reaction that converts undesirable gases to innocuous materials. An adsorbent is a substances that will hold other substances, e.g., undesirable gases, on its surface. An absorbent is a substance which allows molecules, e.g., molecules of undesirable gases, to penetrate its surface and become trapped. Hereinafter, catalysts, absorbents, and adsorbents will be collectively referred to as "gas-eliminators". Mixtures of such gas-eliminators may be desirably employed in the practice of the present invention, the gas-eliminators being selected according to the gas generant composition and the undesirable gases emitted thereby. Some suitable undesirable gas-removing substances include, but are by no means limited to: Sofnox® K - an absorbent for acidic gases, such as NO x and CO, sold by Molecular Products, U.K. Carbon Monoxide Catalyst - catalyzes oxidation of CO with O 2 to produce CO 2 , sold by Molecular Products, U.K. Ammonia Catalyst - reduces levels of ammonia, sold by Molecular Products, U.K. Sofnofil® - an adsorbent for NO x sold by Molecular Products, U.K. The amount of the undesirable gas-eliminator may vary significantly, depending upon the gas generant material in the inflator and the undesirable gases and relative amounts produced thereby, as well as upon the effectiveness of the eliminator(s) in removing the undesirable gases. Thus, on a weight basis, the undesirable gas-eliminator may typically be present anywhere from 1 to 100 wt%, relative to the weight of the gas generant material in the inflator. Even when disposed within the airbag, the gases generated by combustion of the gas generant have a very limited dwell time within the airbag; thus, a significant excess of undesirable gas-eliminator is preferably employed, relative to the amount which would be required to remove undesirable gases from a generally static environment. Preferred embodiments of the drawings will now be described with reference to the accompanying drawings wherein: FIG. 1 is a cut-away (diagrammatic) perspective view of an inflated airbag and associated inflation module, the airbag containing material for removing undesirable gases. FIG. 2 is a plan view of the rear side of an automotive airbag without vents. FIG 3. is a view, similar to FIG 1, in which the material for removing undesirable gases is impregnated into loose sheets disposed within the airbag. FIG 1 illustrates an inflator/airbag assembly 10, with the inflator 12 represented as a cylindrical container and the airbag 14 shown as inflated. The airbag 14 includes a front fabric 16 and a rear fabric 18 sewn together so as to form an substantially enclosed region. In this airbag design, tethers 20 formed of fabric extend internally from between the front and rear of the airbag to help define the configuration of the airbag during inflation, preventing the front fabric 16 from extending too far forward. While the airbag 14 must very rapidly inflate, it must also very rapidly deflate. In fact, the airbag 14 is deflating, even as it inflates. Deflation is most typically through the rear of the bag. In Fig 2 is illustrated a non-vented bag 14. In such an airbag 14, the front fabric 16 is typically treated or woven so as to be substantially gas-impermeable, while the rear fabric 18 is substantially porous and gas-permeable, whereby deflation is through the rear fabric 18. Both fabrics 16, 18 are typically formed of 6/6 nylon; however, the front fabric 16 is typically coated with a material that renders it substantially gas-impermeable or woven so as to be gas-impermeable. (Other designs may allow the use of gas-permeable fabric on the front panel of the airbag.) A ring or throat 22, formed of multiple layers of fabric and defining a rear fabric opening, provides for attachment of the airbag 14 to the inflator 12. In such an airbag 14, the undesirable gas-eliminator, illustrated as particulates 21 in FIG 1, may be merely packed loosely between the front and rear fabric, 16, 18 in powder or granular form. In fact, at the present time, this has proven to be the most effective deployment of gas eliminator. The powder or granules should be sufficiently small so as to provide a large surface area, but preferably are of a size larger than the pores of the porous fabric 16 and/or 18 so as to be retained within the airbag 14. While there is no significant consequence if some of the undesirable gas-eliminator is carried through the fabric 16 and/or 18 by the out-flowing gases, escape of such particulates tends to give the impression of smoke, and is therefore undesirable. Another approach is to impregnate loose sheets of fabric 38, as shown in FIG. 3 disposed within the airbag, (on the order of "dryer sheets" impregnated with fabric softener) with the undesirable gas-eliminator. The invention will now be described in greater detail by way of specific example. Example Twelve airbag/inflator assemblies were prepared, each inflator containing 61 grams of a gas generant formula of 5-aminotetrazole, cupric oxide, strontium nitrate and guanidine nitrate, such as described in U.S. Patent Application 08/207,922 filed 8 March 1994. Three each of the airbags (for triplicate runs) were filled with nothing (control), 30 grams Sofnox®, 30 grams Sofnofil®, and 30 grams Ammonia Catalyst. Undesirable gases, NO, NO 2 , CO, NH 3 , and HCN were measured. Results are in the table. Load is gas generant in grams. Undesirable Gas levels are in parts per million (ppm) by weight. Inflator No. Configuration Load Cond. Temp. NO NO 2 CO NH 3 HCN 1 Baseline module 61 21°C 74.2 13.8 207.0 372.0 10.3 2 Baseline module 61 21°C 84.9 13.8 189.0 348.0 10.9 3 Baseline module 61 21°C 76.6 0.0 161.0 249.0 7.1 Average = 78.6 9.2 185.7 323.0 9.4 StDev = 5.6 8.0 23.2 65.2 2.1 4 SOFNOX absorbent in bag 61 21°C 33.2 0.0 71.9 121.0 1.8 5 SOFNOX absorbent in bag 61 21°C 92.6 0.0 192.0 265.0 5.8 6 SOFNOX absorbent in bag 61 21°C 88.4 0.0 191.0 251.0 6.5 Average = 71.4 0.0 151.6 212.3 4.7 StDev = 33.1 0.0 69.1 79.4 2.6 % Change= -9.1 -100.0 -18.3 -34.3 -9.1 7 SOFNOFIL absorbent in bag 61 21°C 41.0 0.0 185.0 338.0 5.7 8 SOFNOFIL absorbent in bag 61 21°C 62.8 6.9 183.0 342.0 6.7 9 SOFNOFIL absorbent in bag 61 21°C 34.8 2.3 163.0 318.0 3.0 Average = 46.2 3.1 177.0 332.7 5.1 StDev = 14.7 3.5 12.2 12.9 1.9 % Change= -41.2 -66.7 -4.7 3.0 -45.6 10 NH 3 catalyst in bag 61 21°C 78.0 3.6 190.0 223.0 7.5 11 NH 3 catalyst in bag 61 21°C 74.7 1.9 187.0 201.0 6.5 12 NH 3 catalyst in bag 61 21°C 61.3 7.0 195.0 198.0 4.3 Average = 71.3 4.2 190.7 207.3 6.1 StDev = 8.8 2.6 4.0 13.7 1.6 % Change= -9.2 -54.7 2.7 -35.8 -35.2

Claims: An automotive airbag assembly comprising an airbag (14) and an inflator (12) for generating gas to inflate the airbag, said airbag (14) being made from a gas permeable fabric or fabrics (18) through which inflation gases pass to deflate said airbag, characterised in that a gas eliminator (21) for removing undesirable gases from said inflation gases is contained loosely within said airbag and/or impregnated in loose sheets (38) of fabric disposed within said air bag so as to contact gaseous products as the gases flow through the airbag. An airbag assembly according to claim 1 wherein said gas eliminator (21) is selected from catalytic material, adsorbent material, absorbent material, and mixtures thereof. An airbag assembly according to claim 1 or claim 2 wherein said gas eliminator (21) contained within said airbag is present in an amount of between 1 and 100% by weight relative to said gas generant composition in said inflator. An airbag assembly according to any preceding claim wherein said gas generant composition contains both nitrogen and oxygen atoms and/or both nitrogen and hydrogen atoms. An airbag assembly according to claim 4 wherein said gas generant composition further contains carbon atoms. A method of reducing undesirable gases in an automotive airbag/inflator assembly (10), wherein said gas generant composition is burned to produce airbag-inflating gases, including trace amounts of undesirable gases, comprising disposing a gas-eliminator or mixture of gas eliminators (21) loosely within said airbag (14) and/or impregnated in loose sheets (38) of fabric disposed within the airbag so as to contact said airbag-inflating gases and remove undesirable gases therefrom.

Inventors: COX MATTHEW A, JORDAN MICHAEL P, WARD ALAN J, COX, MATTHEW A., JORDAN, MICHAEL P., WARD, ALAN J.
Applicants: AUTOLIV ASP INC, AUTOLIV ASP, INC.
Application year: 1996
Main classification: B60R21
IPC codes: B60R21, B01J35