Bondable autoignition foil

Abstract: An autoignition charge for pyrotechnic automotive airbag inflation devices is provided in the form of a foil (10) comprising a film (12) of a synthetic polymer or of a metal, having an adhesive (16) on one surface of the foil and an autoignition material (14) on the opposite surface of the foil. Pieces of foil are readily attached to inflator housings at any suitable location and are secured to the housing by the adhesive on one surface of the foil.

Description: This invention relates to automotive vehicle pyrotechnic airbag inflation devices as disclosed in US-A-5 100 174 and corresponding to the preamble of claim 1. More particularly it relates to the manner in which an autoignition material is provided in such devices. It is applicable to both driver side pyrotechnic airbag inflators and passenger side pyrotechnic airbag inflators. It is known to provide pyrotechnic airbag inflation devices with an autoignition charge, e.g. as described in Adams et al United States Patent 4,561,675 issued December 31, 1985. It is also known to seal each pyrotechnic airbag inflator using foil bonded to the surface of the diffuser in the inflator, e.g. as described in Davis et al United States Patent 4,380,346 issued April 19, 1983. The disclosures in these patents are intended to be incorporated in this specification by this reference as representative of the prior art. In prior art pyrotechnic airbag inflation devices an autoignition charge is often incorporated into a package which is positioned at one end of a passenger side inflator or at a suitable location in a driver side inflator. The purpose of the autoignition package is to ignite the pyrotechnic inflation charge in the event of a fire when the inflator is in storage prior to being installed in a vehicle or during a fire after it is installed in an automobile. As acknowledged in Nakajima et al United States Patent 5,299,828, issued April 5, 1994, heat transfer to the autoignition charge may be delayed if the autoignition package is positioned at a location remote from the fire. In the device shown in that patent the autoignition charge is provided as a coating inside the diffuser. The coating does not cover the ports in the diffuser and hence the contents, and particularly the pyrotechnic inflation charge in the inflator is not sealed from the environment and is exposed to moisture or other constituents in the atmosphere which may adversely affect the performance of the pyrotechnic charge. Furthermore the application of such a coating requires specialized apparatus and complicates the usual operation in which an inflator is assembled. One object of the invention is to provide a pyrotechnic inflator with an improved autoignition means which is easy to install. Another object is to provide an autoignition means which does not require a separate means for retaining it in an inflator. A further object is to provide an autoignition charge in the form of a foil which may also be used to seal the ports in a pyrotechnic inflator. Still another object is to provide an autoignition charge in the form of a bondable autoignition foil which comprises a film carrying an adhesive on one surface of the film and an autoignition composition on the opposite surface of the film. A further object is to simplify the assembly of a pyrotechnic airbag inflator which includes an autoignition charge. In general, known pyrotechnic inflation devices for airbags include an undeployed airbag cushion and means to inflate said cushion. The inflation means includes a pyrotechnic gas-generating material and ignition means for initiating the generation of gas from said pyrotechnic material in order to inflate the airbag cushion. As described in prior art devices the inflation means may also include an autoignition package. The present invention is addressed to an improvement in the autoignition means in such prior art airbag inflation devices. In the devices of the above noted prior art, the autoignition material is in the form of a separate packet, installed in an appropriate space in the inflation device. In the present invention, the autoignition material is incorporated in a bondable foil which may be attached to any convenient surface of an airbag inflator. Preferably it is attached to a surface which would be exposed to the heat of a bonfire if the inflator was subjected to an accidential fire. Most preferably it may be used to seal an internal component of the inflator from the atmosphere, in place of the foil presently used for this purpose thereby eliminating the necessity of separately providing both a package of autoignition material and a sealing foil as described in United States Patent 5,439,250 issued August 8, 1995. The above noted objects are achieved by the subject-matter defined in claims 1 and 5. Further embodiments thereof are part of the dependent claims. In a preferred form of the present invention, the function of the prior art foil covering and the function of the autoignition charge are combined in such a way that the autoignition charge is exposed for heat transfer more effectively than in the prior art devices, and the need for a separate foil covering and a separate autoignition package is entirely eliminated. By combining the function of the autoignition system in the inflator with the function of the foil, the inflator is simplified, the process of assembling the inflator is simplified and the efficiency and reliability of the system is enhanced. In addition, any problems associated with the handling of the autoignition charge materials and the installation of the autoignition system are eliminated. The invention will be better understood from the description which follows taken in conjunction with the drawings in which: Figure 1 is a schematic view of a driver side airbag inflator in which the autoignition foil of the present invention is installed, showing various locations in which the foil may be installed; Figure 2 is a fragmentary sectional view showing the foil of the invention. Figure 3 and 4 are schematic views of passenger side airbag inflators with the bondable autoignition foil of the present invention; and Figure 5 is a section on plane 5-5 of Figure 3; and Figure 6 is a section on plane 6-6 of Figure 4. As shown in Figure 2, the bondable autoignition foil 10 of this invention comprises a thin film 12 of foil having an autoignition composition 14 disposed on one side of the film 12 and a layer of adhesive 16 bonded to the opposite side of film 12. The autoignition material 14 may consist of particles of black powder or other gun powder type materials or nitrocellulose base pyrotechnic dispersed in a binder such as a thermoplastic resin. A layer of separating material (not shown) may be provided on the adhesive so that the foil can be stored in rolls and dispenses for installation into the airbag inflators of Figures 1 and 4 when they are being assembled. Figure 1 is a schematic representation of the housing 20 of a known driver side airbag inflator device, showing various locations at which the foil may be attached, the foil pieces being designated A, B and C. The components of the device such as the pyrotechnic charge, filter screen, diffuser, igniter etc have been omitted as these are conventional and are well known in the art. As shown in Figure 1, a piece of foil A may be disposed at the base of a well 22 adjacent an outer wall 24 of a driver's side inflator housing 20 such as one shown in Adams et al patent noted above. It will be evident that the foil may be attached to any other suitable surface of the inflator, including internal surfaces which may be perforated or ported. Thus in Figure 1 foil 10 may line the bottom of well 22. The adhesive layer 16 secures the foil B to an internal surface 26 of an airbag inflator housing with the foil covering ports 28 in wall 26, through which gas generated from the pyrotechnic charge (not shown) flows toward an airbag cushion in the usual way as described in the above noted Adams patent. The adhesive backed foil C may be installed on the vertical wall 29 of the diffuser annulus within which the pyrotechnic charge is disposed. In Figure 3 the foil A covers the ports 30 in an igniter tube housing 32 in a passenger side inflator. It is also possible to locate pieces of the autoignition foil in more than a single location in the inflator. For example foil could be on both an endwall and on another surface of the inflator housing. In Figure 4, a passenger side inflator housing 40 provided with autoignition foil piece 42 adhered within a recess 44 in an endwall 46 of the inflator housing 40. It will be seen that by the use of an adhesive backed foil to carry the autoignition charge assembly of the inflator is simplified, less space is required and a weight saving may be achieved.

Claims: An automotive airbag inflation device including an autoignition charge, characterised in that the charge is in the form of a bondable autoignition foil (10) comprising a carrier film (12), a layer of an adhesive (16) adhered to a first face of said film and a coating of an autoignition composition (14) on a second face, opposite said first face of said film. An inflation device according to claim 1 in which the bondable foil (10) is adhered to a wall (26, 29) in said airbag inflation device. An inflation device according to claim 2 in which said foil (10) is adhered to an inner face of an outer wall (24) of a housing (20) for said airbag inflation device. An inflation device according to any preceding claim which includes a casing (20) in which there are apertures (28) and said foil (10) is adhered to said casing and is disposed so as to cover said apertures. An autoignition charge (10) for an automotive airbag inflation device, characterised in that said charge comprises a bondable foil (10) in the form of a carrier film (12) with a layer of adhesive (16) on one side of the film and a coating of an autoignition composition (14) on the opposite side. An autoignition charge (10) according to claim 5 wherein said carrier film (12) is a synthetic polymer or metal film. An autoignition charge (10) according to claim 5 or claim 6 wherein said autoignition composition (14) comprises a gunpowder or nitrocellulose-based pyrotechnic material dispersed in a binder.

Inventors: KENDRICK ALAN D, MONK DAVID B, WOODBURY MARK B, KENDRICK, ALAN D., MONK, DAVID B., WOODBURY, MARK B.
Applicants: AUTOLIV ASP INC, AUTOLIV ASP, INC.
Application year: 1997
Main classification: B60R21
IPC codes: B60R21, C06C9, C06B45, F42C19