Pyrotechnic Inflator for an Air Bag

1. Field of the Invention

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.

2. Background of the Prior Art

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.

It is an object of the present invention to provide a new and improved pyrotechnic inflator for air bags and in particular a new and improved pyrotechnic inflator employing a housing formed of rigid, strong, lightweight, porous metal or ceramic material, which also functions as a filter for entrapping impurities from the gas and absorbs heat from the gas as it passes outwardly through the porous housing walls to inflate the air bag.

It is another object of the invention to provide a new and improved air bag inflator of the type described which eliminates the need for a separate filter element.

Still another object of the present invention is to provide a new and improved air bag inflator wherein the housing itself filters and cools the gas as it passes outwardly through the porous housing to fill an air bag.

Yet another object of the invention is to provide a new and improved air bag inflator of the type described having a porous housing or containment structure for containing gas generating material hermetically sealed therein.

Still another object of the present invention is to provide a new and improved air bag inflator having a relatively large area for discharging the flow of gas into the air bag during deployment.

The foregoing and other objects of the present invention are accomplished in a new and improved pyrotechnic inflator for an air bag which employs a housing formed of strong, rigid, lightweight, porous metal or ceramic material for containing gas generating material sealed inside. 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, Del. 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.sub.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 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 "pores per square inch" rating in the range of 10 to 100. 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.

Obviously, many modifications and variations of the present invention are possible in light of the above teachings. Thus, it is to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described above.