Pyrotechnic inflator for an air bag

Abstract: A pyrotechnic inflator (10) for an air bag includes a housing (12) for containing gas generating material (22) for inflating an air bag. The housing has a wall formed of rigid, porous material and serves both as a filter for entrapping contaminants from the gas that is generated within as the gas passes outward through the wall into the air bag and cools the gas by absorbing heat therefrom. Gas generating material (22) and an ignition train (25, 18, 22) is hermetically sealed in a bag or packet (24), inside the porous housing which serves triple duty as a solid pyrotechnic container, a gas filter and a gas cooler.

Description: The present invention relates to a new and improved pyrotechnic inflator for air bag cushions used in a motor vehicle. In particular, the new inflator employs a housing formed of strong, rigid, lightweight, porous metal or ceramic material for containing gas generating material and which housing itself also functions to filter and cool when the generating material is reacted so that the generated gas flows outwardly through the porous wall material to rapidly inflate an air bag. Presently available pyrotechnic inflators for air bags and the like utilize a container or canister formed of steel or other metal and having a plurality of ports formed in the walls for directing the gas generated within the canister to flow outwardly and inflate an associated air bag. Prior inflators have required a separate filter mounted inside the inflator housing or canister for entrapping contaminants from the gas as it moves outwardly toward the ports to inflate the air bag. EP-A-0587900 discloses a pyrotechnic inflator for an airbag having a porous housing containing gas generant material adapted to be activated by ignition means to rapidly generate gas to pass outwardly through the porous walls of the housing which serve to filter and cool the gas. The porous housing is formed by winding continuous high tensile strength fibre strands or filaments around the outside of a body of gas generant acting as a mandrel. EP-A-0505024 discloses a gas generant body wherein a stack of propellant grains is enclosed in a pyrotechnic layer such as a PTFE film coated with an oxidizable material, which forms part of an ignition system. The present invention consists in a pyrotechnic inflator for an airbag, comprising: a housing for containing gas generating material for inflating an airbag, said housing being formed with a wall of rigid, porous material for filtering and cooling gas from said gas generant passing through said wall to inflate said airbag; gas generant material inserted into the housing thus formed and adapted to be activated to rapidly generate gas to pass outwardly though said wall into said airbag; and ignition means for activating said gas generant material. There can thus be provided an air bag inflator of the type described which eliminates the need for a separate filter element, and wherein the housing itself filters and cools the gas as it passes outwardly through the porous housing to fill an air bag. Gas generating material is preferably enclosed in a hermetically sealed jacket within the housing. The housing is preferably a tubular one formed of strong, rigid, lightweight, porous metal or ceramic material, giving a relatively large area for discharging the flow of gas into the air bag during deployment. The porous structure of the housing wall serves as a filter for entrapping contaminants from the gas as it passes out through the wall to rapidly inflate an associated air bag. The housing wall also functions to cool the hot gases by absorbing heat therefrom and eliminates the requirement or need for a separate filter. For a better understanding of the present invention, reference should be had to the following detailed description taken in conjunction with the drawings, in which: FIG. 1 is a longitudinal cross-sectional view of a new and improved pyrotechnic inflator for an air bag in accordance with the features of the present invention; and FIG. 2 is a transverse cross-sectional view taken substantially along lines 2-2 of FIG. 1. Referring now more particularly to the drawing, therein is illustrated a new and improved pyrotechnic inflator 10 for inflating an air bag safety cushion used in a motor vehicle. The inflator 10 includes an elongated, generally cylindrical housing or canister 12 having an integrally formed circular wall 14 at a closed end thereof and a separate cap or base 16 at an opposite end. Positioned within the housing or canister 12 is a stack of wafer like, annular discs 22 of gas generating material such as sodium azide or other solid material commonly used for generating air bag inflation gas. Surrounding the gas generating wafers 22 there is provided a thin layer of ignition material in the form of a bag or packet 24 formed of a sheet of "Teflon" plastic film having a thin layer of magnesium bonded thereto or other type of metallized plastic sheet material. One type of film is called "Enerfoil" and is manufactured by a company called I.C.I. located in Wilmington, Delaware. The ignition material is formed into a bag or jacket 24 which completely surrounds and encloses the stack of gas generating wafers 22 exteriorly, and also is in coaxial alignment with and extends through center openings 22a provided in the wafers. This bag 24 is closed and sealed in order to prevent moisture ingestion during the lifetime of the inflator 10. Alternatively, along the central longitudinal axis of the housing 12 there is provided a central ignition core 18 of material which acts as an ignitor when the inflator 10 is activated to generate gas for inflating an air bag. The ignition core 18 is contained within a sealed tube or sleeve 20 formed of thin aluminum or magnesium foil, plastic wrapping material such as polyethylene or "Teflon" plastic sheeting in order to prevent moisture ingestion during the lifetime of the inflator 10. The ignition tube 20 also aids in inserting the central core 18 of ignition material into the housing 12 because the material is generally a granular, powdered or particulate type of material such as BKNO 3 . The core of ignition material 18 is in coaxial alignment with and extends through center openings 22a in the stack of wafer-like, annular discs 22 of gas generating material such as sodium azide or other solid materials commonly used for generating air bag inflation gas. The central ignition core 18 and the stack of solid gas generating discs 22 are all contained in the hermetically sealed bag or package 24 formed of thin, aluminum, magnesium or "Teflon" plastic metallized foil to prevent moisture ingestion during the lifetime of the inflator 10. A squib 25 is mounted in a recess at the center of the end cap 16 and when activated by an electrical signal, causes the material in the elongated core 18 and the jacket 24, to rapidly ignite, burning from the cap 16 to the closed end wall 14 of the porous housing 12. As this occurs, the gas generating wafers 22 are ignited and gas is rapidly produced for filling the air bag. This gas flows outwardly through the myriad of pores and tortuous paths provided in the porous body wall of the housing 12. Gas pressures in the range of 13.79 to 17.24 MPa (2000 to 2500 psi) may be generated within the housing. The housing 12 functions as a gas filter for entrapping larger particulates and other contaminants from the hot gases flowing rapidly out to inflate the air bag. This arrangement eliminates the requirement for a separate filter element. A variety of porous materials of suitable strength are available such as porous nickel, iron and aluminum or a reticulate structure initially formed on a base of open-celled carbon or urethane foam on which metal alloys or ceramic materials are coated in a chemical vapor deposition process. After the deposition of the metal, metal alloys or ceramic material on the base, the foam base material itself can be burned out or eliminated in a heating or sintering process leaving a housing 12 which is strong, rigid and porous to accommodate the outflow of hot gases generated from the discs 22. The strong, rigid, porous reticulated structure of the housing 12 can be formed of metal and/or alloys such as aluminum, copper, iron, molybdenum, nickel, zirconium, niobium and tungsten. Alternatively, a porous ceramic structure can be utilized for the housing 12. Materials such as silica carbide, silica dioxide, alumina silicate mixture, mullite and alumina are available and suitable . All of these materials can be readily formed to the desired shape of the housing 12 and the pore sizes can be selected to provide the proper filtration and cooling. For example, the material of the housing 12 may have a rating of 1.55 to 15.5 pores per cm 2 (10 to 100 pores per square inch). This range of porosity offers suitable resistance to gas flow and because the entire wall surface of the housing 12 is available, a large flow cross-section is provided in contrast to a relatively small flow cross-section of the ports in a typical prior art, solid metal wall inflator. The reticulated structure thus formed of metal alloy or ceramic material is strong, light in weight, and able to handle the high momentary pressures involved without fracturing as well as resist corrosion from exterior sources or degradation over a long period of time. Because the gas generating material of the wafers 22 is hermetically sealed within a containing bag 24, long life is assured. Moreover, the containment tube 20 or seal around the inner core 18 of the ignition train provides further protection against moisture and greatly simplifies the overall assembly of all of the ignition train and gas generating materials and insertion thereof into the housing 12. The porous structure of the housing 12 eliminates the requirement for a separate filter element so that other internal walls normally provided may be completely eliminated. The porous housing 12 also provides excellent cooling characteristics by rapidly absorbing heat from the hot gases flowing therethrough. During assembly of the ignitor, a flat section of film 24 is formed around a narrow rod and affixed tightly to the rod. The gas generant wafers 22 are then inserted over the film on the rod to form a stack. The remaining section of the film 24 is then folded back over the stack of wafers 22 and thus itself to extend back along the stack to the top again forming an encapsulating jacket. The jacket thus forms a double wall; one inner wall 24a extending interiorly through the stack of gas generating wafers 22, the other outer wall 24b extending exteriorly around the stack of gas generating wafers. The exteriorly extending wall section 24b is then closed on itself, hermetically sealing the wafers 22 inside. Alternatively during assembly of the ignitor, a packet or bag 24 is formed initially containing a stack of the gas generating wafers 22 and the sealed ignition core 18 is pre-assembled into the jacket 24. The whole packet is then easily inserted into place in the housing 12 from the open end. An end cap 16 containing the igniting squib 25 is next inserted into place to close the open end of the housing 12. A ring of molten metal 28 is introduced into a grooved wall region between the outer edge of the end cap 16 and the adjacent internal surface of the body 12 such as by liquid metal injection. When the molten material 28 solidifies a positive seal and locking engagement between the end cap or base 16 and the porous housing 12 is produced.

Claims: A pyrotechnic inflator (10) for an airbag, comprising: a housing (12) for containing gas generating material for inflating an airbag, said housing being formed with a wall of rigid, porous material for filtering and cooling gas from said gas generant passing through said wall to inflate said airbag; gas generant material (22) inserted into and sealed inside said housing (12) and adapted to be activated to rapidly generate gas to pass outwardly though said wall into said airbag; and ignition means (18, 24, 25) for activating said gas generant material. An airbag inflator according to claim 1, wherein said wall of said housing (12) is formed of a metal alloy having pores and adapted for filtering and entrapping contaminants from said gas and cooling said gas flowing to inflate said airbag. An airbag inflator according to claim 1, wherein said wall of said housing (12) is formed of a porous ceramic material adapted for filtering and entrapping contaminants from said gas and cooling said gas flowing to inflate said airbag. An airbag inflator according to any preceding claim, wherein said gas generant material (22) includes a packet of gas generating pyrotechnic material contained in a hermetically sealed jacket (24) of thin, moisture-impervious, wrapping material. An airbag inflator according to claim 4, wherein said sealed jacket (24) is formed of flexible metal sheeting. An airbag inflator according to claim 5, wherein said flexible metal sheeting comprises a foil of magnesium or aluminium. An airbag inflator according to claim 4, wherein said sealed jacket (24) is formed of resinous plastics film. An airbag inflator according to claim 7, wherein said resinous plastics film is formed of polytetrafluoroethylene resin. An airbag inflator according to any one of claims 4 to 8, wherein said jacket (24) is formed of ignition material and acts as an igniter of said gas generating material. An airbag inflator according to any preceding claim, wherein said gas generant material includes a core (18) of ignitable material inside a packet of gas generating pyrotechnic material (22) contained in a hermetically sealed jacket (24) contained in said housing (12). An airbag inflator according to claim 10, wherein said gas generating pyrotechnic material (22) comprises a plurality of annular elements in a stack mounted on said core (18) of ignitable material. An airbag inflator according to any preceding claim, wherein said housing comprises a unitary hollow, tubular body (12) formed of said porous filtering material and closed at opposite ends. An airbag inflator according to claim 12, wherein filtering material has pores defining a plurality of tortuous paths for filtering and entrapping contaminants from gas flowing from said gas generator outwardly through said paths to inflate an airbag. An inflator according to claim 12 or claim 13, wherein said tubular body (12) is closed at one end by a base (16). An inflator according to claim 14, including an initiator (25) incorporated with said base (16) for activating said gas generant material. An inflator according to claim 14 or claim 15 wherein said tubular body (12) has an integral end wall (14) at an end opposite said base (16). An inflator according to any one of claims 14 to 16 wherein said base (16) is secured to close said one end of said tubular body (12) when said gas generant material (22) is in place; and a ring (28) of liquid metal injected between facing surfaces of said tubular body and said base solidified to secure and seal said base to said housing means at said one end. An inflator according to any one of claims 12 to 17 wherein said gas generant material (22) includes a mass of pyrotechnical material and an ignition train in a hermatically sealed jacket. An inflator according to claim 18 wherein said ignition train includes a core (18) of ignition material hermetically sealed in a bag of moisture impervious film inside said jacket (24). An inflator according to claim 19 wherein said core (18) of ignition material includes an electrical ignition squib (25) at one end for activating said ignition train.

Inventors: HATT WESLEY L, HOCK CHRISTOPHER, RINK LINDA M, HATT, WESLEY L., HOCK, CHRISTOPHER, RINK, LINDA M.
Applicants: AUTOLIV ASP
Application year: 1995
Main classification: B60R21
IPC codes: B60R21, B01D39, B01D46