Pressure vessel inflator having a preformed opening feature

An apparatus for inflating an inflatable device, which apparatus includes a pressure vessel having a preformed opening feature and a method of fabricating a corresponding single chamber apparatus for inflating an inflatable device.

BACKGROUND OF THE INVENTION 
This invention relates generally to pressurized fluid-containing 
apparatuses and devices and, more particularly, to such an apparatus or 
device used in the inflation of an inflatable device such as an inflatable 
vehicle occupant restraint airbag cushion used in inflatable restraint 
systems. 
It is well known to protect a vehicle occupant using a cushion or bag, 
e.g., an "airbag cushion," that is inflated or expanded with gas when the 
vehicle encounters sudden deceleration, such as in a collision. In such 
systems, the airbag cushion is normally housed in an uninflated and folded 
condition to minimize space requirements. Upon actuation of the system, 
the cushion begins to be inflated, in a matter of no more than a few 
milliseconds, with gas produced or supplied by a device commonly referred 
to as "an inflator." 
Many types of inflator devices have been disclosed in the art for the 
inflating of one or more inflatable restraint system airbag cushions. 
Prior art inflator devices include compressed stored gas inflators, 
pyrotechnic inflators and hybrid inflators. Unfortunately, each of these 
types of inflator devices has been subject to certain disadvantages such 
as greater than desired weight and space requirements, production of 
undesired or non-preferred combustion products in greater than desired 
amounts, and production or emission of gases at a greater than desired 
temperature, for example. 
In view of these and other related or similar problems and shortcomings of 
prior inflator devices, a new type of inflator, called a "fluid fueled 
inflator," has been developed. Such inflators are the subject of commonly 
assigned Smith et al., U.S. Pat. No. 5,470,104, issued Nov. 28, 1995; 
Rink, U.S. Pat. No. 5,494,312, issued Feb. 27, 1996; and Rink et al., U.S. 
Pat. No. 5,531,473, issued Jul. 2, 1996, the disclosures of which are 
fully incorporated herein by reference. 
Such inflator devices typically utilize a fuel material in the form of a 
fluid, e.g., in the form of a gas, liquid, finely divided solid, or one or 
more combinations thereof, in the formation of an inflation gas for an 
airbag. In one such inflator device, the fluid fuel material is burned to 
produce gas which contacts a quantity of stored pressurized gas to produce 
inflation gas for use in inflating a respective inflatable device. 
While such an inflator can successfully overcome, at least in part, some of 
the problems commonly associated with the above-identified prior types of 
inflator devices, there is a continuing need and demand for further 
improvements in safety, simplicity, effectiveness, economy and reliability 
in the apparatus and techniques used for inflating an inflatable device 
such as an airbag cushion. 
To that end, the above-identified Rink, U.S. Pat. No. 5,669,629 discloses a 
new type of inflator wherein a gas source material undergoes decomposition 
to form decomposition products including at least one gaseous 
decomposition product used to inflate an inflatable device. 
Such an inflator can be helpful in one or more of the following respects: 
reduction or minimization of concerns regarding the handling of content 
materials; production of relatively low temperature, non-harmful inflation 
gases; reduction or minimization of size and space requirements and 
avoidance or minimization of the risks or dangers of the gas producing or 
forming materials undergoing degradation (thermal or otherwise) over time 
as the inflator awaits activation. 
Nevertheless, there is a need and demand for yet still further improvements 
in safety, simplicity, effectiveness, economy and reliability in the 
apparatus and techniques used for inflating an inflatable device such as 
an airbag cushion. 
For example, it is common in prior inflator devices to have one or more 
preformed openings or passages with each such opening or passage normally 
covered or blocked by a device, such as a burst disc or the like, until 
such time as when flow through the opening or passage is desired. As a 
result of the use of a separate covering or blocking device, the number of 
component parts may be greater than desired for optimal handling and 
manufacture and the risks associated with the formation of leak paths from 
an inflator device pressure vessel may be greater than desired. In 
addition, current inflator assembly designs commonly weld such burst discs 
or the like in place. Unfortunately, welding can be a relatively expensive 
manufacturing process. For proper welding, the surface conditions of the 
components to be joined must usually be well controlled in terms of 
geometric tolerances and surface cleanliness. Further, the equipment 
needed or used in such weld processing can be expensive to purchase and 
maintain. Still further, weld processing is typically a source of high 
scrap rates in high volume production programs. 
Consequently, there is a need and a demand for still further reductions in 
the number of inflator component parts such as through the elimination of 
a burst disc or the like and for inflator assemblies which can simplify 
manufacture and avoid or minimize the risks of possibly forming leak paths 
from the pressure vessel. In particular, there is a need and demand for an 
improved inflator apparatus such as may be helpful in either or both 
reducing or simplifying the number or types of component parts and 
manufacturing process steps. Further, there is a need and demand for an 
improved pressurized inflator apparatus which reduces or minimizes the 
possible number of leak paths and thus may result in improved reliability 
and simplified manufacture and production. 
SUMMARY OF THE INVENTION 
A general object of the invention is to provide an improved apparatus for 
inflating an inflatable device such as an inflatable vehicle occupant 
restraint such as used in vehicular inflatable restraint systems. 
A more specific objective of the invention is to overcome one or more of 
the problems described above. 
The general object of the invention can be attained, at least in part, 
through an apparatus for inflating an inflatable device, which apparatus 
includes a unitary pressure vessel wall having, at a selected location, at 
least one preformed pressure vessel opening feature whereat the unitary 
wall preferentially opens upon application of sufficient pressure 
thereagainst. 
The prior art fails to provide an inflator apparatus wherein the number or 
types of component parts and manufacturing process steps have either or 
both been reduced or simplified to as great an extent as may be desired. 
The prior art further fails to provide a pressurized inflator apparatus 
which reduces or minimizes the possible number of leak paths and thus can 
result in further improved reliability and simplified manufacture and 
production. 
The invention further comprehends a side impact inflatable device inflator 
which inflator includes a pressure chamber and an initiator device. The 
pressure chamber is formed at least in part by an elongated, generally 
cylindrical unitary pressure vessel wall. The unitary pressure vessel wall 
includes an open axial end and, at a selected location, at least one 
preformed pressure vessel opening feature whereat the wall preferentially 
opens upon application of sufficient pressure thereagainst. The pressure 
chamber contains contents including a quantity of nitrous oxide which, 
upon actuation, undergoes dissociation to form dissociation products 
including at least one gaseous dissociation product used to inflate the 
side impact inflatable device. The initiator device is fixed to the open 
axial end of the unitary pressure vessel wall. The initiator device is 
actuatable to be in dissociation initiating relationship with at least a 
portion of the quantity of nitrous oxide contained within the pressure 
chamber. 
The invention still further comprehends a method of fabricating a single 
chamber apparatus for inflating an inflatable device. The method includes 
the step of providing an intermediate part which includes a bulkhead and 
which bulkhead contains at least one preformed pressure vessel opening 
feature. The part also includes first and second oppositely disposed 
tubular extensions of respective first and second lengths extending from 
the bulkhead with the first and second tubular extensions each having an 
open end. The method also includes the step of securing an initiator 
device to the open end of the first tubular extension to form a closed 
pressure vessel chamber. The closed pressure vessel chamber contains 
contents including a quantity of at least one gas source material which 
undergoes dissociation to form dissociation products including at least 
one gaseous dissociation product used to inflate the device. The method 
further includes the step of securing a diffuser member to the open end of 
the second tubular extension. 
As used herein, references to "dissociation," "dissociation reactions" and 
the like are to be understood to refer to the dissociation, splitting, 
decomposition or fragmentation of a single molecular species into two or 
more entities. 
"Thermal dissociation" is a dissociation controlled primarily by 
temperature. It will be appreciated that while pressure may, in a complex 
manner, also influence a thermal dissociation such as perhaps by changing 
the threshold temperature required for the dissociation reaction to 
initiate or, for example, at a higher operating pressure change the energy 
which may be required for the dissociation reaction to be completed, such 
dissociation reactions remain primarily temperature controlled. 
An "exothermic thermal dissociation" is a thermal dissociation which 
liberates heat. 
"Equivalence ratio" (.phi.) is an expression commonly used in reference to 
combustion and combustion-related processes. Equivalence ratio is defined 
as the ratio of the actual fuel to oxidant ratio (F/O).sub.A divided by 
the stoichiometric fuel to oxidant ratio (F/O).sub.S : 
EQU .phi.=(F/O).sub.A /(F/O).sub.S (1) 
(A stoichiometric reaction is a unique reaction defined as one in which all 
the reactants are consumed and converted to products in their most stable 
form. For example, in the combustion of a hydrocarbon fuel with oxygen, a 
stoichiometric reaction is one in which the reactants are entirely 
consumed and converted to products entirely constituting carbon dioxide 
(CO.sub.2) and water vapor (H.sub.2 O). Conversely, a reaction involving 
identical reactants is not stoichiometric if any carbon monoxide (CO) is 
present in the products because CO may react with O.sub.2 to form 
CO.sub.2, which is considered a more stable product than CO.) 
For given temperature and pressure conditions, fuel and oxidant mixtures 
are flammable over only a specific range of equivalence ratios. Mixtures 
with an equivalence ratio of less than 0.25 are herein considered 
nonflammable, with the associated reaction being a decomposition reaction 
or, more specifically, a dissociative reaction, as opposed to a combustion 
reaction. 
Other objects and advantages will be apparent to those skilled in the art 
from the following detailed description taken in conjunction with the 
appended claims and drawings.

DETAILED DESCRIPTION OF THE INVENTION 
The present invention may be embodied in a variety of different structures. 
Referring initially to FIG. 1, there is illustrated an airbag inflator 
assembly, generally designated by the reference numeral 10, in accordance 
with one preferred embodiment of the invention and such as may be used to 
inflate an inflatable vehicle occupant restraint, e.g., an inflatable 
airbag cushion, (not shown). As is known and upon proper actuation, such 
inflatable vehicle occupant restraints are typically inflated by a flow of 
an inflation fluid, e.g., gas, from an inflator assembly to restrain 
movement of an occupant of the vehicle. In practice, it is common that the 
inflatable vehicle occupant restraints be designed to inflate into a 
location within the vehicle between the occupant and certain parts of the 
vehicle interior, such as the doors, steering wheel, instrument panel or 
the like, to prevent or avoid the occupant from forcibly striking such 
parts of the vehicle interior. 
While the invention is described hereinafter with particular reference to 
an inflator for side impact airbag assemblies in various automotive 
vehicles including vans, pick-up trucks, and particularly automobiles, it 
is to be understood that the invention also has applicability not only 
with other types or kinds of airbag installations for automotive vehicles 
including driver side and passenger side airbag assemblies, but also with 
other types of vehicles including, for example, airplanes. 
With respect to such automotive vehicles it will be appreciated from the 
following discussion that the invention is perceived to have the most 
particular utility, at least initially, in side impact airbag assemblies 
wherein the rate of gas release from the inflator device into the 
associated airbag cushion is generally not as specifically or finely 
controlled as in driver or passenger side airbag assemblies, for example. 
The inflator assembly 10 comprises a pressure vessel 12 forming a chamber 
14, an initiator device 16 and a diffuser member 20. 
As will be described in greater detail below, the chamber 14 of the 
inflator assembly 10, in accordance with one preferred embodiment of the 
invention, contains a gas source material. As disclosed in 
above-identified Rink, U.S. Pat. No. 5,669,629, there are various gas 
source materials which, under specified conditions, undergo reaction 
variously termed decomposition or dissociation reactions to form products 
including at least one gaseous product such as may be used to inflate an 
associated vehicle occupant restraint. Thus, the chamber 14 is sometimes 
referred to herein as a "dissociation chamber." 
The chamber 14 is defined at least in part by an elongated generally 
cylindrical unitary sleeve 22, having the form of an elongated cylindrical 
wall 23 with first and second ends, 24 and 26, respectively. The sleeve 
first end 24 is closed as the end 24 is joined in sealing relationship 
with the initiator device 16. The sleeve second end 26 is closed by means 
of a bulkhead 30. As shown in FIG. 1 and in accordance with one preferred 
embodiment of the invention, the unitary pressure vessel wall 22 includes, 
as will be described in greater detail below, at least one preformed 
pressure vessel opening feature 32 whereat the unitary pressure vessel 
wall 22 preferentially opens upon application of sufficient pressure 
thereagainst. Specifically, the preformed pressure vessel opening feature 
32 of the inflator assembly 10 is situated along or at the bulkhead 30. 
The diffuser member 20 includes a flange edge portion 36, such as may be 
useful to facilitate attachment or securement thereof in the inflator 
assembly, and a plurality of openings 38 for dispensing inflation gas from 
the inflator assembly 10 into the associated airbag cushion. In accordance 
with one preferred embodiment of the invention and as illustrated in FIG. 
1, the diffuser member 20 is externally joined adjacent to the pressure 
vessel 12 adjacent to the preformed pressure vessel opening feature 32. In 
the illustrated embodiment and as will be described in greater detail 
below, a tubular extension 40 from the bulkhead 30 is roll crimped about 
the diffuser flange edge portion 36 to effect such joinder. As will be 
appreciated by those skilled in the art, the diffuser member can 
alternatively be joined to or attached with or to an inflator assembly in 
accordance with the broader teachings of the subject invention. For 
example, a diffuser member can simply be welded, joined by fasteners or 
otherwise adhered or fixed to the bulkhead, if desired. 
As identified above, the inflator assembly 10 generates inflation gas via a 
decomposing material or, more specifically, a dissociative material. As 
disclosed in Rink, U.S. Pat. No. 5,669,629, a wide variety of gas source 
materials which undergo dissociative or decompositional reactions, 
preferably an exothermic such reaction, to form gaseous products are 
available. Such gas source materials include: 
acetylene(s) and acetylene-based materials such as acetylene and methyl 
acetylene, as well as mixtures of such acetylene(s) and acetylene-based 
materials with inert gas(es); 
hydrazines such as hydrazine (N.sub.2 H.sub.4), mixtures of hydrazine(s) 
and water, methyl derivatives of hydrazine, as well as mixtures of such 
hydrazine materials with inert gas(es); 
peroxides and peroxide derivatives such as methyl hyperoxide (CH.sub.3 OOH) 
and mixtures of methyl hyperoxide and methanol, hydrogen peroxide, alkyl 
hydroperoxides, propionyl and butyryl peroxides, as well as mixtures of 
such peroxides and peroxide derivatives with inert gas(es); and 
nitrous oxide (N.sub.2 O) and mixtures of nitrous oxide with inert gas(es), 
for example. 
Generally, dissociative gas source materials used in the practice of the 
invention are preferably: 
a.) non-toxic and non-corrosive both in the pre- and post- dissociation 
states; 
b.) relatively stable at atmospheric conditions thus permitting and 
facilitating storage in a liquid phase, where a liquid, as compared to a 
gas, permits the storage of a greater amount of material in the same 
volume at a given pressure; 
c.) do not require the presence of catalyst(s) to trigger the dissociation 
reaction, and which catalysts may be difficult to remove or handle; and 
d.) form products of dissociation which do not contain undesirable levels 
of undesirable species, such as carbonaceous material (e.g., soot), 
CO.sub.x, NO.sub.x, NH.sub.3, for example (where x=1 or 2). 
A currently preferred dissociative gas source material for use in the 
practice of the invention is nitrous oxide (N.sub.2 O). Nitrous oxide is 
advantageously generally non-toxic and non-corrosive. Further, nitrous 
oxide, as compared to gases such as air, nitrogen and argon, liquefies 
relatively easily at ambient temperatures. Additionally, nitrous oxide is 
relatively inert up to temperatures of about 200.degree. C. or more. As a 
result, nitrous oxide is desirably relatively safe to handle, thermally 
stable, facilitates storage, and alleviates manufacturing concerns. 
Further, in accordance with the chemical reaction (2) identified below, 
upon the dissociation of nitrous oxide, the dissociation products ideally 
are nitrogen and oxygen: 
EQU 2N.sub.2 O=2N.sub.2 +O.sub.2 (2) 
Thus, not only does such reaction form products which are generally 
non-toxic and non-corrosive but also results in the production or 
formation of molecular oxygen, such as may be desired with certain 
inflator designs. 
It is to be understood that such nitrous oxide gas source material can, for 
example and as desired, be stored in a gaseous, liquid or multi-phase form 
(i.e., partially gaseous and partially liquid mixture). The premium on 
size generally placed on modern vehicle design, however, results in a 
general preference for smaller sized airbag inflators. In view thereof and 
the fact that the density of nitrous oxide is significantly greater when 
in a liquid rather than gaseous form, one preferred embodiment of the 
invention involves storage of nitrous oxide primarily in a liquid form. 
It is also to be understood that while such nitrous oxide dissociative gas 
source material can be contained within the dissociation chamber in a pure 
form (e.g., such that the chamber contents include no more than minor 
levels of other materials, such as air as may be present in the 
dissociative chamber prior to being filled with the dissociative gas 
source material), it may be preferred to include an inert gas therewith. 
For example, an inert gas such as helium can be included with nitrous 
oxide to facilitate leak checking of the inflator apparatus or, more 
specifically, of the dissociation chamber thereof. Alternatively or in 
addition, an inert gas, such as argon and helium, for example, or mixture 
of such inert gases, can be included to supplement the gas produced or 
formed upon the dissociation of the nitrous oxide. 
Additionally or alternatively and as disclosed in the above-identified U.S. 
patent application Ser. No. 08/935,016, the dissociation chamber 14 may 
contain a quantity of at least one radioactive isotope leak trace material 
whereby fluid leakage from the chamber can be detected as disclosed 
therein. 
In addition, the dissociation chamber 14 can, if and as desired, also 
include a sensitizer material to promote or accelerate the rate of such 
dissociative reaction. Various sensitizer materials disclosed and 
identified in above-identified Rink, U.S. Pat. No. 5,669,629. As disclosed 
therein, sensitizer materials are typically hydrogen-bearing materials. 
Such sensitizer materials are generally added to the dissociative gas 
source material in small amounts. Specifically, the sensitizer material is 
preferably added to the dissociative gas source material in an amount 
below the flammability limits for the content mix, such that the contents 
of the dissociative chamber are generally at an equivalence ratio of less 
than 0.25, preferably less than 0.15. At such low relative amounts, the 
chamber contents are essentially non-flammable and thus combustion and the 
formation of combustion products are practically avoided. 
Hydrogen-bearing sensitizer materials useable in the practice of the 
invention are typically gaseous, liquid, solid, or multi-phase 
combinations thereof including hydrogen, hydrocarbons, hydrocarbon 
derivatives and cellulosic materials. Preferred hydrocarbon 
hydrogen-bearing sensitizer materials useable in the practice of the 
invention include paraffins, olefins, cycloparaffins and alcohols. 
Molecular hydrogen (H.sub.2), which does not result in the formation of 
carbon oxides such as carbon monoxide or carbon dioxide, has been found to 
be quite effective as a sensitizer and is an especially preferred 
hydrogen-bearing sensitizer material for use in the practice of the 
invention. 
To minimize possible leak paths, a cryogenic fill technique, such as 
disclosed in the above-identified U.S. patent application Ser. No. 
08/935,016, may be employed. Alternatively, the dissociation chamber may 
include a fill port or other appropriate means to permit the introduction 
of material into the chamber. 
In such an assembly, the initiator device can be of any suitable type of 
initiator means including: bridgewire, spark-discharge, heated or 
exploding wire or foil, through bulkhead (e.g., an initiator which 
discharges through a bulkhead such as in the form of a metal hermetic 
seal), for example, and may, if desired, optionally contain a desired load 
of a pyrotechnic charge. In practice, however, a relatively large heat 
input such as from the initiator, may be helpful in obtaining a more 
thorough initiation of dissociation of various gas source materials, such 
as nitrous oxide (N.sub.2 O). In view thereof, as pyrotechnic 
charge-containing initiators can typically more easily produce such 
relatively large heat inputs from a relatively small sized initiator 
device, the practice of the invention with such initiators can be 
particularly advantageous. 
In operation, such as upon the sensing of a collision, an electrical signal 
is sent to the initiator device 16. The initiator device 16 functions and, 
when it is a pyrotechnic initiator, discharges high temperature combustion 
products into the dissociation chamber 14 and the contents thereof, which 
in a preferred embodiment includes primarily liquid-phase N.sub.2 O. The 
large heat addition results in commencement of the exothermic thermal 
dissociation of the N.sub.2 O wherein N.sub.2 O begins to breakdown into 
smaller molecular fragments. As the N.sub.2 O molecules fragment, the 
associated release of energy results in further heating of the remaining 
chamber contents. Additionally, as the dissociation process proceeds, 
heating of the contents results in conversion of at least some of the 
N.sub.2 O from a liquid to a gaseous phase. Thus, this dissociation 
results in not only both the release of heat and the formation of gaseous 
dissociation products but also an increase in gaseous species due to the 
conversion of N.sub.2 O from a liquid to a gaseous phase. The increase 
both in temperature and the relative amount of gaseous products within the 
dissociation chamber 14 results in a rapid pressure rise within the 
dissociation chamber. 
When the gas pressure within the dissociation chamber 14 exceeds the 
structural capability of the preformed pressure vessel opening feature 32, 
the preformed pressure vessel opening feature 32 ruptures or otherwise 
permits the passage of the inflation gas therethrough from the chamber 14 
into the diffuser member 20 and subsequently through the diffuser openings 
38 and into the associated airbag cushion. 
As will be appreciated, the inclusion of a preformed opening feature (or 
sometimes alternatively referred to as a failure or rupture feature) in 
the wall of the inflator pressure vessel can provide or result in various 
advantages. For example, through the inclusion of such a preformed opening 
feature, the number of component parts required in the assembly can be 
reduced such as by avoiding the need for a preformed opening or passage 
which is normally covered or blocked by a device such as through the use 
of a burst disc or the like until such time as when flow through the 
opening or passage is desired. Further, such reductions in the number of 
components such as through the elimination of a burst disc or the like can 
simplify manufacture and avoid or minimize the risks of possibly forming 
leak paths from the pressure vessel. 
FIG. 2 illustrates an airbag inflator, generally designated by the 
reference numeral 210, in accordance with an alternative embodiment of the 
invention. The airbag inflator 210 is generally similar to the airbag 
inflator 10, described above, and includes a pressure vessel 212 forming a 
chamber 214 that, as with the chamber 14 described above, contains at 
least one gas source material, such as N.sub.2 O, for example. 
The inflator assembly 210 also includes an initiator device 216 and a 
diffuser member 220, having a plurality of openings 238 for dispensing 
inflation gas from the inflator assembly 210 into the associated airbag 
cushion (not shown). 
The chamber 214, similar to the chamber 14 described above, is defined at 
least in part by an elongated generally cylindrical unitary wall sleeve 
222, having the form of an elongated cylindrical wall 223 with first and 
second axial ends, 224 and 226, respectively. The sleeve first end 224 is 
closed as the end 224 is joined in sealing relationship with the initiator 
device 216. The sleeve second end 226 is closed by means of a rounded end 
closure 250. As will be appreciated, the incorporation and use of such a 
rounded end closure can serve to avoid seams or corners that might 
otherwise lessen or reduce the pressure-containing capability of the 
associated pressure vessel 212. 
The inflator unitary pressure vessel wall 222 includes at least one 
preformed pressure vessel opening feature 232, whereat the unitary 
pressure vessel wall 222 preferentially opens upon application of 
sufficient pressure thereagainst. The preformed pressure vessel opening 
feature 232 is situated along the elongated cylindrical wall 223 of the 
sleeve 222. Thus, the preformed pressure vessel opening feature 232 is 
radially disposed relative to the sleeve open axial end 224 whereat the 
initiator device 216 is fixed. 
The diffuser member 220 is externally disposed relative to the unitary 
pressure vessel wall 222 about the at least one preformed pressure vessel 
opening feature 232. 
From the above description and the above-identified embodiments, it is to 
be appreciated that the preformed pressure vessel opening feature of the 
subject inflator assemblies can generally be located where desired along 
the inflator unitary pressure vessel wall provided some other inflator 
assembly component or design aspect does not adversely influence the 
proper operation of the opening feature. For example, one preferred 
location for placement of the preformed pressure vessel opening feature 
is, as shown in FIG. 1, generally directly axially from the associated 
inflator assembly initiator, in the end wall of the pressure vessel. 
Another possibly desirable location is shown relative to the embodiment of 
FIG. 2 wherein the preformed pressure vessel opening feature is placed in 
the side wall of the pressure vessel. 
As will be appreciated, the particular design configuration selected can 
vary dependent on the particular geometric constraints of a particular 
inflatable restraint installation. 
In addition, the preformed pressure vessel opening feature of the subject 
inflator assemblies can generally assume various particular forms. In 
general, the specific geometry of the preformed pressure vessel opening 
feature will be dependent, at least in part, on one or more selected 
factors including, for example: material of construction and strength 
thereof, flow through area required to be provided by the feature, the 
pressure or other performance characteristic value at which the preformed 
pressure vessel opening feature is designed to open, and 
temperature-dependent variations in pressure vessel storage capability. 
As will be appreciated, the opening feature selected for use can be 
uni-directional (e.g., designed to fail or open in only one direction) or 
bi-directional (e.g., designed to fail or open in either direction). 
FIGS. 3(A-E) illustrate fragmentary portions of unitary pressure vessel 
walls 322(a-e), respectively, each having first and second surfaces 
360(a-e) and (362(a-e), respectively. Each fragmentary portions of unitary 
pressure vessel walls 32(a-e) includes a preformed pressure vessel opening 
feature 332(a-e), respectively, in accordance with an alternative 
embodiment of the invention. 
FIGS. 3(A-C) illustrate embodiments wherein the opening or rupture of the 
opening features, 332(a-c), respectively, generally results from a tensile 
failure of the material forming the respective feature, with failure or 
opening of the feature generally occurring in a direction of higher 
pressure to lower pressure. For example, in each of FIGS. 3(A-C), the 
first surface 360(a-c) generally corresponds to the "high" pressure side 
while the second surface 362(a-c) generally corresponds to the "low" 
pressure side, with the respective features 332(a-c) failing or opening in 
the direction from high to low, e.g., in the direction of the arrows 
364(a-c). 
FIG. 4A is a view of the unitary pressure vessel wall fragmentary portion 
322a taken substantially along the line 4A--4A of FIG. 3A. As shown, the 
opening feature 332a has the general shape of form of a cruciform. As will 
be appreciated, the utilization of such a cruciform opening feature 332a 
may better ensure or result in a more controlled or uniform performance of 
the opening feature. 
The desired tensile failure, rupture or otherwise opening of the opening 
features 332(a-c) generally occurs without the undesired formation of 
separate and distinct vessel chamber fragments. As will be described in 
greater detail below, at least certain preferred embodiments of the 
invention utilize such opening features which desirably generally fail, 
rupture or otherwise open without the undesired formation of separate and 
distinct vessel chamber fragments. 
FIGS. 3D and 3E illustrate embodiments wherein the opening or rupture of 
the opening features, 332d and 332e, respectively, is in shear such as may 
result from the application of a sufficient pressure differential between 
the pressure applied against the respective first and second surfaces. In 
such embodiments, the opening features are bi-directional and do not have 
a specifically designated high or low pressure side. 
Those skilled in the art will appreciate that many possible opening feature 
configurations and designs are possible and the invention, in its broader 
application and practice is not specifically limited to those illustrated 
and described herein. 
It will be appreciated that inflator assemblies in accordance with the 
invention need not necessarily include an external diffuser member. More 
specifically, certain inflator applications may not require the gas 
diffusion action provided by or resulting from such incorporation of a 
diffuser. For example, in certain side impact inflatable restraint system 
installations, such as because of the extremely rapid required response, 
the action of a diffuser may neither be required nor desired. 
For example, FIGS. 5A and 5B illustrate one such airbag inflator, generally 
designated by the reference numeral 510. The airbag inflator 510 is 
generally similar to the airbag inflator 210, described above, and 
includes a pressure vessel 512 forming a chamber 514 that, as with the 
chamber 214 described above, contains at least one gas source material 
such as N.sub.2 O, for example. The chamber 514, similar to the chamber 
214 described above, is defined at least in part by an elongated generally 
cylindrical unitary wall sleeve 522, having the form of an elongated 
cylindrical wall 523 with first and second axial ends, 524 and 526, 
respectively. The sleeve first end 524 is closed as the end 524 is joined 
in sealing relationship with an initiator device 516. The sleeve second 
end 526 is closed by means of a rounded end closure 550. 
As with the airbag inflator 210, the airbag inflator 510 includes, situated 
along the elongated cylindrical wall 523 of the sleeve 522, radially 
disposed relative to the sleeve open axial end 524 whereat the initiator 
device 516 is fixed, a preformed pressure vessel opening feature 532, 
whereat the unitary pressure vessel wall 522 preferentially opens upon 
application of sufficient pressure thereagainst. 
The preformed pressure vessel opening feature 532 is in the form of a 
cruciform, similar in nature to the opening feature 332a shown in FIGS. 3A 
and 4A and described above. As identified above, the desired tensile 
failure, rupture or otherwise opening of such an opening feature generally 
occurs without the undesired formation of separate and distinct vessel 
chamber fragments. The avoidance of such fragment formation may be 
particularly desirable in those airbag installations which do not utilize 
a diffuser or the like device either as a part of the inflator or the 
associated housing structure and which diffuser or like device may 
normally also serve to capture, retain or otherwise prevent the passage of 
such fragments from the inflator to other system components, e.g., the 
associated airbag cushion. 
Turning now to FIG. 6, there is illustrated an airbag inflator, generally 
designated by the reference numeral 610, in accordance with another 
alternative embodiment of the invention, and which inflator assembly also 
does not include an external diffuser member. Similar to the 
above-described embodiments, the airbag inflator 610 includes a pressure 
vessel 612 such as contains at least one gas source material, such as 
N.sub.2 O, for example, and an initiator device 616. 
As with the above-described embodiments, the inflator 610 includes an 
elongated generally cylindrical unitary wall sleeve 622, having the form 
of an elongated cylindrical wall 623 with first and second axial ends, 624 
and 626, respectively. The sleeve first end 624 is closed as the end 624 
is joined in sealing relationship with an initiator device 616. The sleeve 
second end 626 is closed by means of a rounded end closure 650. 
As with the above-described embodiments, the inflator unitary pressure 
vessel wall 622 includes at least one preformed pressure vessel opening 
feature 632, situated along the elongated cylindrical wall 623 of the 
sleeve 622, whereat the unitary pressure vessel wall 622 preferentially 
opens upon application of sufficient pressure thereagainst. The preformed 
pressure vessel opening feature 632, however, is an axially extending 
elongated thinned region formed in the cylindrical wall 623. 
One method by which such a preformed pressure vessel opening feature can be 
formed is by heat treating the vessel wall 622 over a selected area, such 
as at a particular desired location. For example, such heat treatment can 
in practice take the form of annealing or tempering the unitary wall 
material at the selected location such as by the direct application of the 
thermal or other output of a flame torch or laser source onto the unitary 
wall material over the selected area. 
It will be appreciated that operation of the inflator 610 will generally be 
similar to the operation of the subject inflators described above. More 
specifically, such as upon the sensing of a collision, an electrical 
signal is sent to the initiator device 616. The initiator device 616 
functions and, when it is a pyrotechnic initiator, discharges high 
temperature combustion products into contact, thermal or otherwise, with 
the gas source material, e.g., N.sub.2 O, stored within the inflator 610. 
As described above, N.sub.2 O begins to breakdown into smaller molecular 
fragments upon thermal dissociation thereof. As the N.sub.2 O molecules 
fragment, the associated release of energy results in further heating of 
the remaining contents within the inflator chamber. Thus, as described 
above, the increase in either or both temperature and the relative amount 
of gaseous products within inflator assembly 610 continues such that when 
the gas pressure exceeds the structural capability of the axially 
extending elongated preformed pressure vessel opening feature 632, the 
preformed pressure vessel opening feature 632 ruptures or otherwise 
permits the passage of the inflation gas therethrough from the inflator 
assembly 610 and into the associated airbag cushion. 
It will further be appreciated that certain inflatable restraint system 
installations may preferably rely on a reaction canister housing, used to 
house or store the system inflator device, to provide necessary or desired 
inflation gas diffusion. As a result, more uniform or standardized 
production of inflator devices may be realized, with desired inflation 
performance variability and inflation gas direction being provided or 
supplied through appropriate design modification of the reaction canister, 
rather than of the inflator device. For example, the above-described 
inflator assemblies 510 and 610 can, if desired, be utilized in an 
inflatable restraint system installation which relies on or utilizes the 
reaction canister housing, used to house or store the system inflator 
device, to provide necessary or desired inflation gas diffusion. 
FIG. 7 illustrates an airbag module assembly, generally designated by the 
reference numeral 770, incorporating the airbag inflator assembly 610, 
described above. In the airbag module assembly 770, the inflator assembly 
610 is normally housed in a reaction canister or module housing 772. The 
reaction canister 772 includes a first storage volume 773 adapted to 
receive, house or contain the inflator assembly 610 (consequently, such 
storage volume is sometimes referred to as an inflator storage volume) and 
a second storage volume 774 adapted to receive, house or contain an 
associated airbag cushion (not shown, with such storage volume 
consequently sometimes referred to as a "cushion storage volume"). 
The airbag module assembly 770 includes a diffuser 776 which generally 
separates the inflator storage volume 773 from the cushion storage volume 
774. The diffuser 776 includes a plurality of openings 778 therethrough 
which place the inflator storage volume 773 in fluid communication with 
the cushion storage volume 774 such that upon operation and release of 
inflation fluid from the inflator 610 such fluid can be passed and 
directed into the cushion storage volume 774 and, more specifically, into 
the associated airbag cushion stored or housed therein. 
In operation, such as upon the sensing of a collision, an electrical signal 
is sent to the initiator device 616. The initiator device 616 functions to 
actuate the inflator assembly 610, resulting in an increase in pressure 
within the inflator assembly 610 with the preformed pressure vessel 
opening feature 632 rupturing or otherwise permitting the release or 
passage of inflation gas from the inflator assembly 610 when the force or 
pressure against the opening feature 632 reaches a preselected value. 
Released inflation gas will then pass through the diffuser openings 778 to 
the airbag cushion stored within the storage volume 774. 
As will be appreciated, one or more of the size, shape, pattern or location 
of the diffuser openings can be appropriately selected such as to provide 
or result in desired inflation gas flow or direction into the associated 
airbag cushion. 
Another aspect of the invention relates to a simplified or improved 
technique to fabricate an inflator apparatus such as described herein. A 
preferred method of fabricating a single chamber apparatus for inflating 
an inflatable device will now be described with particular reference to 
FIGS. 8 and 9. Specifically, a preferred method of fabricating an inflator 
apparatus, such as the inflator assembly 10, shown in FIG. 1 and described 
above, will be described. 
FIG. 8 shows an intermediate part, generally designated by the reference 
numeral 880. The intermediate part 880 includes the bulkhead 30 containing 
the at least one preformed pressure vessel opening feature 32. The 
intermediate part 880 also includes, oppositely disposed from the bulkhead 
30, first and second tubular extensions 882 and 884, respectively, and 
each having an open axial end, 882a and 884a, respectively. 
Such an intermediate part can produced or formed using various techniques. 
One particularly useful processing technique to produce such an 
intermediate part is by applying a dual impact forging process to a single 
solid slug of a parent material such as steel, for example. 
Such as to simplify manufacture and production, it will generally be 
preferred that the tubular extensions 882 and 884, respectively, be formed 
to have the same general diameter as the bulkhead 30. The lengths of the 
tubular extensions 886a and 886b, respectively, can be appropriately 
selected to satisfy the particular requirements or needs of the 
application to which the particular extension is directed. For example, 
the first tubular extension 882 is sized and dimensioned for use in the 
formation of the pressure vessel 12, shown in FIG. 1. More specifically, 
the first tubular extension will desirably be of a length, designated L1, 
such as to provide a volume sufficient containing contents including a 
quantity of at least one gas source material which undergoes dissociation 
to form dissociation products including at least one gaseous dissociation 
product used to inflate the device. The second tubular extension 884 will 
desirably be of a length, designated L2, such as effective for use as the 
tubular extension 40 used to secure the diffuser member 20 in the inflator 
assembly 10, such as shown in FIG. 1. 
As shown in FIG. 9, the initiator device 16 is secured to the first tubular 
extension open end 882a such as by swagging the open end 882a about the 
initiator device 16, followed by welding the initiator device 16 to the 
tubular extension open end 822a. The diffuser member 20 is secured to the 
second tubular extension open end 884a such as by roll crimping the open 
end 884a about the diffuser flange edge portion 36 to effect joinder of 
the diffuser member to the part 880. 
As will be appreciated, such a fabrication technique can provide various 
processing advantages such as permitting the direct attachment of a 
diffuser device to the inflator assembly without requiring the diffuser to 
be welded to the assembly. Thus avoiding a weld process which is generally 
considered an expensive processing technique in high volume production 
environments, such as associated with the mass production of motor 
vehicles. 
While the fabrication technique has been described above with particular 
reference to the fabrication of the inflator assembly 10 shown in FIG. 1, 
it will be appreciated that such technique can, with appropriate 
modification, be used to fabricate or construct other such inflator 
assembly embodiments. 
In view of the above, it will be appreciated that the invention can 
advantageously provide an inflator apparatus wherein the number or types 
of component parts and manufacturing process steps are either or both 
reduced or simplified to an extent not previously readily realized with 
prior inflator designs. Further, the invention can advantageously provide 
a pressurized inflator apparatus which reduces or minimizes the possible 
number of leak paths and thus can result in further improved reliability 
and simplified manufacture and production. 
The invention illustratively disclosed herein suitably may be practiced in 
the absence of any element, part, step, component, or ingredient which is 
not specifically disclosed herein. 
While in the foregoing detailed description this invention has been 
described in relation to certain preferred embodiments thereof, and many 
details have been set forth for purposes of illustration, it will be 
apparent to those skilled in the art that the invention is susceptible to 
additional embodiments and that certain of the details described herein 
can be varied considerably without departing from the basic principles of 
the invention.