Pyrotechnic inflator for an air bag

A pyrotechnic inflator for an air bag includes a housing for containing gas generating material 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 and an ignition train is hermetically sealed in a bag or packet inside the porous housing which serves triple duty as a solid pyrotechnic container, a gas filter and a gas cooler.

BACKGROUND OF THE INVENTION 
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. 
OBJECTS OF THE INVENTION 
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. 
BRIEF SUMMARY OF THE PRESENT INVENTION 
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.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION 
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.