Note: Descriptions are shown in the official language in which they were submitted.
2i~061 PATENT
F2984-21-00
FUEL ~ ~ T~N'r FOR FLllID FUELED
AIRBAG I~7FLATOR8
B~7~r.C~7D OF T~E ~ hv~n~ 7
This invention relates generally to inflatable restraint
systems such as are used to provide protection to vehicle
occupants and, more particularly, to inflator devices such as
used in such systems.
It i8 well known to protect a vehicle occupant using a
cushion or bag that is inflated or ~ypAn~ with gas when the
vehicle encounters sudden deceleration, such as in a collision.
Such a cushion or bag is commonly referred to as an "airbag. "
In such systems, the airbag is normally housed in an
uninflated and folded condition to minimize space requirements.
Upon actuation of the system, the airbag is commonly inflated in
a matter of a few mi 11 i ~econds with gas produced or supplied by
a device commonly referred to as "an inflator. "
Many types of inf lator devices have been disclosed in the
lS art for inflating an airbag for use in inflatable restraint
systems . Prior art inf lator devices include compressed stored
gas inf lators, pyrotechnic inf lators and hybrid inf lators .
Unfortunately, each of these types of an inflator device is
subject to certain disadvantages.
For example, stored gas inflators typically require the
storage of a relatively large volume of gas at relatively high
. As a result of such high storage ~Le:s~u~-~s, the walls
of the gas storage chamber are typically relatively thick for
increased strength. The combination of large volume and thick
walls results in a relatively heavy and bulky inf lator design.
With respect to pyrotechnic inflators wherein gas is derived
from a combustible gas generating material, i.e., a pyrotechnic,
such gas generating materials can typically produce various
undesirable combustion products, including various solid
particulate materials. The removal of such solid particulate
material, such as by the incorporation of various filtering
devices within or about the inflator, undesirably increases
inflator design and processing complexity and can increase the
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
21~0~61 Pi~TE~7T
F298~-21-o~
costs associated therewith. In addition, the temperature of the
gaseous emission from such inflator devices can typically vary
between about 500F (260OC) and 1200F (649C), ~ rPnr~ t upon
numerous interrelated factors including the desired level of
5 inflator performance, as well as the type and amount of gas
generant material used therein, for example. Consequently,
airbags used in conjunction with such inflator devices typically
are specifically cu.,~LL~ ed of or coated with a material
resistant to such high temperatures. For example, in order to
10 resist burn-through as a result of exposure to such high
temperatures, an airbag such as constructed of nylon fabric can
be prepared such that the nylon fabric airbag material is coated
with neoprene or one or more neoprene coated nylon patches are
placed at the locations of the airbag at which the hot gas
15 initially impinges. As will be appreciated, such specially
fabricated or prepared airbags typically are more costly to
manufacture and produce.
Hybrid inflators wherein airbag inflating gas results from
a combination of stored ~ ~ssed gas and combustion of a gas
20 generating material, e.g., a pyrotechnic, also typically result
in a gas having a relatively high particulate content.
A new type ûf inflator device which utilizes 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, has
25 been developed. For example, in one such inflator device, the
f luid fuel is burned to produce gas which contacts a quantity of
stored pressurized gas to produce inflation gas for use in
inf lating the respective inf latable device .
While such type of inflator can successfully UV~::L- -, at
30 least in part, some of the problems associated with the
above-identified prior types of inflator devices, i.lyr.,v~ nts
in the design, operation and performance of such inflators as
well as ilU~lU~ s in the hAnlll i n~, storage and transport of
the fuel material are continually sought in the competitive
35 marketplace to increase manufacturing and production freedom and
flr Yihi l Lty without unduly detrimentally impacting the costs
associated with such manufacture and production.
,~ 2lsoa6l
PATE2iT
F298~-21-00
8T~ Y OF ~E INVENTION
A general object of the invention is to provide an improved
fluid fueled inflator and improved fluid fuel cont~ t for
airbag inf lators .
A more specif ic obj ective 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 a particular apparatus for inflating an
inf latable device described herein. The apparatus includes a
10 first chamber wherein at least one fuel in the form of a fluid
is burned to produce combustion products. The apparatus also
includes a fuel cont ~i t assembly which, in a first
, includes a capsule having an outer wall and defining
an onrlos~cl fuel storage volume. The enclosed fuel storage
lS volume is adapted to contain at least a supply of the at least
one fuel in the form of a fluid prior to installation of the
capsule in the apparatus. The capsule is adapted to open at
predetermined operating conditions to be in f luid communication
with the f irst chamber . The apparatus additionally includes an
20 initiator to initiate burning of the at least one fuel in the
f irst chamber .
The invention also comprehends an ~mho~li- l wherein the
fuel cont~i --t assembly includes a closed housing having an
outer wall. The housing is adapted to contain a supply of the
25 at least one fuel in the form of a fluid with the outer wall
impervious to the at least one fuel. The housing is adapted to
open at predetermined operating conditions to be in f luid
iC2tion with the first chamber. The housing also has,
along a second wall, an initiator to initiate burning of the at
30 least one fuel in the first chamber.
The prior art fails to provide an inflator assembly which
utilizes a fuel in the form of a rluid that is burned to produce
inflation gas and which assembly can easily and effectively
~noderate the impact of operation at varying ambient temperature
35 conditions. Further, the prior art fails to provide such an
inflator assembly having as greatly as desired moderation or
control of the rate at which th~ fuel is introduced into the
2~0~61
PA~ENq
F298~-21-00
combustion chamber and, in turn, as greatly as desired moderation
or control of the rate of reaction of such fuel.
The invention further comprehends an inflation apparatus
which includes a closed fuel containment assembly wherein a fuel
in the form of a fluid is stored. The apparatus additionally
includes f irst and second chambers and an initiator .
Specifically, in one ~mho~ir ~, the fuel containment
assembly includes a capsule having an outer wall and defines an
enclosed storage volume. The storage volume is adapted to
contain, prior to installation of the capsule in the apparatus,
contents including at least a supply of at least one fuel in the
form of a fluid. The fuel containment assembly is adapted to
open at predetermined operating conditions.
Upon opening of the fuel contA i - t assembly, the f irst
chamber i8 in fluid communication with at least a portion of the
supply of the at least one fuel from the capsule. In the first
chamber, the at least one fuel is burned to produce combustion
products i n~ i n~ hot combustion gas . The initiator initiates
the burning of at least a portion of the at least one fuel in the
first chamber. The combustion of the at least one fuel increases
the temperature and pres,u ~ within the first chamber. The first
chamber is adapted to open when a predetermined increase in
~r~aSDuL~ within the first chamber is realized, whereby at least
a portion of the hot combustion gas is expelled therefrom.
The second chamber contains a supply of p~es-uLized stored
gas. Upon the opening of the first chamber, the second chamber
is in f luid ~ i ration with the f irst chamber with the hot
combustion gas expelled from the first chamber mixing with the
pressurized stored gas to produce inf lation gas. The second
chamber i8 adapted to open when a predetermined increase in
~L__~u~e within the chamber is realized after the hot combustion
gas PYpel l~cl from the first chamber mixes with the pressurized
stored gas to produce the inflation gas, w~ereby at least a
portion of the inflation gas is expelled from the second chamber
to inflate the device.
In another such inflator apparatus ~mho~ 1, the fuel
cont~ i t assembly i n~lu~ s a closed housing having an outer
~ 21~0061
PAT~NT
F298~-21-00
wall. The assembly and specifically the housing is adapted to
contain contents including a supply of at least one fuel in the
form of a fluid. The outer wall of the housing is impervious to
the at least one fuel and is adapted to open at predetermined
5 operating conditions.
Upon opening of the housing outer wall, the f irst chamber
i5 in fluid ~- lication with the fuel containment assembly.
In the first chamber, at least a portion of the supply of the at
least one fuel is burned to produce combustion products including
lo hot combustion gas. This combustion o~ the at least one fuel is
initiated by the initiator and increases the temperature and
prcsDuL~ within the first chamber. The first chamber is adapted
to open when a predetermined increase in pressure within the
rirst chamber is realized, whereby at least a portion of the hot
15 combustion gas is Pyrpll~d therefrom.
The second chamber contains a supply of pressurized stored
gas. Upon the opening of the first chamber, the first and second
chambers are in fluid ication with each other, with the hot
combustion ga~ PYrPl led from the first chamber mixing with the
20 pressurized stored gas to produce inf lation gas. The second
chamber is adapted to open when a predetermined increase in
y,~DuL~ within the second chamber is realized after the hot
combustion gas ~Yr-~l lPd from the first chamber mixes with the
pressurized stored gas to produce the inflation gas, whereby at
25 least a portion of the inflation gas is expelled from the second
chamber .
The invention still further comprehends a method for
inflating an inflatable safety device in a vehicle using an
inrlation apparatus. The method includes the steps of opening
30 either: a) a closed capsule containing, prior to installation in
the apparatus, at least a supply Or at least one fuel in the form
of a fluid, or b) a closed ruel housing of a fuel cont~i L
assembly, the housing containing at least a supply of at least
one fuel in the form of a rluid prior to the opening. Either
35 such opening results in a release of at least a portion of the
supply of the at least one fuel into a f irst sealed chamber.
The method then p~ eeds with the step of burning the
.
219006i PATENT
F298~-21-00
released portion of the supply of the at least one fuel in the
first sealed chamber to produce combustion products including hot
combustion gas. This step is then followed by, releasing
inf lation gas including at least a portion of the combustion gas
5 from the apparatus to inflate the inflatable safety device.
The invention still further comprehends a method of
manufacturing an apparatus for inflating an inflatable device.
This method includes the step of at least partially f illing a
capsule, having a closed outer wall which defines an enclosed
10 storage volume, with a supply of least one fuel in the form of
a fluid. Thereafter, the fuel-containing capsule is loaded into
an apparatus subcombination. The apparatus subcombination
;nc~ P-~ a first chamber in fluid ~ ication with the
fuel-containing capsule upon opening of the capsule, wherein the
15 at least one fuel is burned to produce combustion products. The
apparatus subcombination additionally includes an initiator to
initiate burning of at least a portion of the supply of the at
least one fuel in the first chamber.
As used herein, references to a chamber or volume as being
20 "free of combustion oxidant" are to be understood to refer to a
chamber or volume sufficiently free of oxidant such that, over
the range of ~S-UL~S and temperatures experienced during the
~torag~ of th~ fluid fuel therein, the amount of heat liberated
by chemical reaction (since the chemical reaction rate is non-
25 zero for all temperatures) is less than the amount of heatdissipated to the ~ju~L~ nlin~s. It will be appreciated that as
the rate of such ~hPm;c:~l reaction (and hence the amount of heat
liberated upon reaction) is ~PrPn~lPnt on the cor,~ .tL~tion of
oxidant as well a~ the temperature, the amount of heat liberated
30 can be m;n;m;7Pd through proper control of the quantity of
oxidant initially present therein.
The term "equivalence ratio" (~) is commonly used in
reference to combustion processes. EquivalenCe ratio is defined
as the ratio of the actual fuel to oxidant ratio (F/O)A divided
35 by the stoichiometric fuel to oxidant ratio (F/o)s:
~ = (F/O)A/ (F/)s
6 ~
PAT~NT
F298~-21-oo
(A stoichiometric reaction is a unique reaction def ined as one
in which all the reactants are ron -~ and converted to products
in their most stable form. For example, in the combustion of a
hydrocarbon fuel with oxygen, a sto;rhi~ ~.ic reaction is one
in which the reactants are entirely cun~, ' and converted to
products entirely constituting carbon dioxide (CO2) and water
vapor (H2O). Conversely, a reaction involving identical
reactants is not stoichiometric if any carbon ~orlo~ide (CO~ is
present in the products because CO may react with 2 to form CO2,
which is considered a more stable product than CO.) In general,
for given temperature and pLeS-UL~ conditions, fuel and oxidant
mixtures are flammable over only a specific range of equivalence
ratios .
other objects and advantages will be apparent to those
skilled in the art from the following detailed description taken
in conjunction with the App ~n~ed claims and drawings.
R~Tl~ D~e~ OF TU~ DRA~IING8
FIG. 1 is a simplified, partially in section schematic
drawing of a fluid fueled inflator in accordance with a first
nt of the invention.
FIG. 2 is a simplified, partially in section fragmentary
schematic drawing of the f luid fueled inf lator of FIG .1 having
a fUQl con ~; t assembly in accordance with one ~ L of
the invention.
FIG. 3 is a simplified sectional schematic drawing of a fuel
con~ assembly in accordance with an alternative embodiment
of the invention.
FIG. 4 is a simplified sectional schematic drawing of a fuel
con~ assembly in accordance with another alternative
~o'i--nt of the invention.
FIG. 5 is a simplified fragmentary perspective view of
alternatively either a housing or a capsule: -nPnt of a fuel
con~ assembly in accordance with one . -ir--~ of the
invention .
FIGS. 6A, 6B, 6C and 6D are simplified fragmentary views o~
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
OO~l
PATENT
F298~-21-oO
alternative score arrangements or forms for alternatively either
a housing or a capsule - ~nPnt of a fuel con~A i - ~ assembly
in accordance with alternative Dlnho~l i - ts of the invention .
FIGS. 7A and 78 are simplified perspective views of a fuel
5 contAi ~ assembly ~ ~ne~t, i.e., either a housing or a
capsule, having a scored dome in accordance with one r~`-Q~ t
of the invention before and after opening, respectively.
FIGS. 8A and 88 are simplified perspective views of a fuel
ContAi ~ assembly housing in accordance with one alnho~i
lo of the invention before and after opening, respectively.
FIGS. 9A, 98 and 9C show the fuel con~ t housing of
FIG. 8A housed within a combustion chamber portion of a f luid
fueled inflator assembly after openinq at various selected
ambient temperature operating conditions.
FIG. 10 is a simplified, partial in section, fragmentary
peIa~e- ~ive view of alternatively either a housing or a capsule
t of a fuel con~A i t assembly in accordance with an
alternative ~nho~ir ~ of the invention.
FIG. 11 is a simplified, partially in section, fragmentary
20 schematic drawing of a fuel containment assembly in accordance
with one Dmhorl i - ~ of the invention wherein a wire screen mesh
is used to at least in part to :.ULLUUnd a fuel capsule.
FIG. 12 is a simplified, partially in section perspective
schematic drawing of a fuel containment assembly in accordance
25 with yet another alternative a~ho~lir t of the invention.
FIG. 13 is a ~implified sectional schematic drawing of the
fuel cont~ t assembly of FIG. 12.
FIG. 14A is a simplif ied perspective view of a fragmentary
portion Or the inner layer of the side wall of the fuel
30 con~Ai t assembly of FIGS. 12 and 13.
FIG. 148 is a simplified fragmentary cross sectional view
~howing an open gas f low orif ice in the inner layer of the side
wall of the fuel contAi L assembly of FIGS. 12 and 13.
FIG. 15 is a simplified, partially in section schematic
35 drawing of a fluid fueled inflator in accordance with an
alternative ~o~ t of the invention.
~190~61
PA$E~rr
F298~-21--oo
FIG. 16 is a simplified schematic drawing Or a fuel
containment assembly c ~ ~n~nt in accordance with one PmhqA j-- L
of the invention.
FIGS. 17A and 17B are simplified and enlarged fragmentary
drawings of alternative arrangements for a section of the fuel
containment assembly -nt shown in FIG. 16.
n~r~TTT~n D~ ON OF T~E .Lh~n~
Referring initially to FIG. 1, there is illustrated a fluid
fueled inflator assembly 10 for inflating a vehicle occupant
restraint, such as an airbag. It will be understood that the
invention described hereinafter has general applicability to
various types or kinds of airbag assemblies including driver
side, passenger side, and side impact airbag assemblies for
automotive vehicles including vans, pick-up trucks, and
aut~
The inflator assembly 10 comprises a ~ ,u~e vessel 12
including a storage chamber 14 that is filled and pressurized
with an inert gas such as argon or nitrogen to a yLe~Su~
typically in the range o~ 2000-5000 psi.
The chamber 14 is def ined by an elongated generally
cylindrical sleeve 16, having a first and a second end, 20 and
22, respectively. The first end 20 is partially closed by means
of an integral qh~ r portion 24. A diffuser assembly 26 is
attached by a circumferential weld 27 in sealing relation to the
sleeve first end 20. A combustion chamber assembly 30 is
attached by a circumferential weld 31 in sealing relation to the
sleeve second end 22.
The diffuser assembly 26 comprises a generally cylindrical
sleeve 32 having a cap portion 34 and a base portion 36 to define
a diffuser chamber 40. Each of the diffuser assembly cap and
base portions, 34 and 36, respectively, include a closed first
end 42a and 42b, respectively, and an open second end 44a and
44b, respectively. The diffuser assembly cap portion 34 in~ q
3S a plurality of openings 46, adjacent the closed cap first end
42a, for dispensing inflation gas from the inflator assembly into
an airbag assembly (not shown). The diffuser assembly base
21~061
PATENT
F298~-21-00
portion 36 additionally includes a plurality of openings 48,
adjacent the closed base first end 42b, for passage of inflation
gas from the storage chamber 14, into the diffuser chamber 40.
The diffuser assembly cap and base portions, 34 and 36,
5 respectively, are aligned with the open second end of each, i.e.,
ends 44a and 44b, respectively, being closed by sealing means,
e.g., by means of a rupture disc 50 abutting thereagainst. The
diffuser assembly rupture disc 50 is joined in sealing relation
with the diffuser assembly cap and base portions, 34 and 36,
10 respectively, by means of a circumferential weld 51 at the
periphery of the disc 50. In the static state, the disc 50
serves to separate the contents of the storage chamber 14 from
the airbag.
The combustion chamber assembly 30 comprises a cap portion
54 and a base portion 56 to define a combustion chamber 60. The
combustion chamber cap portion 54 includes a sleeve 62,
constituting a side wall 64 with a dome 66 joined thereto via a
cap shoulder connecting portion 68. The combustion chamber dome
66 includes an orifice, referred to herein as a gas exit opening
20 70. The gas exit opening 70 is normally closed by sealing means,
e.g, by means of a rupture disc 72 joined in sealing relation
with the combustion chamber dome 66 by means of a circumferential
weld 73 at the periphery of the disc 72.
The combustion chamber dome 66 is generally designed to
25 withstand the internal ~L~S~Ur~S generated upon the combustion
of the flammable mixture, such as described below, within the
combustion chamber 60. In the static state, the disc serves in
maintaining the gas storage chamber 14 in a sealed condition.
The combustion chamber base portion 56 includes a base ring
30 74 with a base cap 76 joined thereto via a base shoulder
connecting portion 78. The base _hol~ld~r connecting portion 78
serves as a convenient means of locating the combustion chamber
base portion 56 relative to the combustion chamber sleeve 62, as
well as providing a location for a circumferential weld 79
35 whereby the combustion chamber assembly base portion 56 is
attached in sealing relation to the combustion chamber cap
portion 54.
g~
PATENT
F298~-21-00
The base cap 76 includes an opening 80 therein, wherethrough
an initiator device 82, such as described in greater detail
below, is attached in sealing relation, such as with a weld,
crimping or other suitable hermetic seal, within the combustion
chamber 60. The initiator device 82 includes a discharge end 84.
A fuel cont~; ~rt assembly 86 in accordance with the invention
and such as described in greater detail below is located within
the combustion chamber 60, adjacent the initiator device
discharge end 84. The fuel cont~; t assembly 86 contains or
holds contents which include a quantity of at least one fuel
material in the form of fluid, as described in greater detail
below .
In operation, such as upon the sensing of a collision, an
electrical signal is sent to the initiator device 82, such as a
conventional pyrotechnic initiator device. Such an initiator
device will upon receipt of an appropriate electrical signal
ignite and emit energy, such as in the f orm of a hot,
particle-laden discharge, into the fuel cont~ t assembly 86.
In turn, the temperature and ~L~aDuL~ of the fuel stored within
the closed volume of the fuel cont ~ t assembly 86 will
increase. Upon the ~y~eetlinq of the structural capability of the
assembly 86, e.g., at predet~rmin~d operating conditions such as
at a sel~cted threshold internal pL~sauL~ or temperature, the
assembly will rupture or otherwise open placing the heated fuel
ln f luid ~ i ~ation with the combustion chamber 60 . In the
combustion chamber 60, the oxidant (such as normally stored
within the combustion chamber 60 outside of the fuel containment
assembly 86 and thus apart from the fuel material or, as
described in greater detail below, stored together with the fuel
material within the fuel containment assembly 86) and the heated
fuel form a fl~ -hl~ mixture which, via initiation by the
initiator 82, ignites and burns at an elevated temperature and
~3DU~: .
The hot gas ~ lu~ed upon the burning of the f lammable
mixture resultsD in a rapid ~e3au~ rise within the combustion
chamber 60. When the gas ~IIBSDU~6 within the combustion chamber
60 exceedDs the D~.u..-u.al ~ ~r~hil ity of the rupture disc 72, the
11
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ .
' ~190~1
PATENT
F298~-21-00
disc ruy~ur-~S or otherwise permits the passage of the hot gas
through the gas exit opening 70 and into the storage chamber 14.
Wherein, the hot combustion gas expelled from the combustion
chamber 60 mixes with the pressurized gas stored within the
separate storage chamber 14 to produce inflation gas for use in
inflating the inflatable restraint device, e.g., an airbag. It
will be appreciated that augmenting the combustion gas with the
stored inert gas produces an inf lation gas having both a lower
temperature and reduced byproduct concentration (e.g., C0, N0x,
H20, etc. ) than the combustion gas alone.
When the gas yLes~u ~ within the storage chamber 14 exceeds
the structural capability of the rupture disc 50, the disc
LUyLuL~s or otherwise permits the passage of the inflation gas
through the diffuser base portion 36 and into the diffuser cap
portion 34 and thus allows this inflation gas to vent through the
opon;n~s 46 into the airbag assembly.
The fluid fuels useable in such an apparatus include a wide
range of gases, vapors, finely divided solids and liquids such
that, when used with one or more suitable oxidants in proper
proportion(s) at selected conditions (either alone or in
conjunction with one or more inert gases) form a flammable
mixture .
Such fluid fuels include hydrogen, as well as
hydrocarbon-based fuels such as hydrocarbon and hydrocarbon
derivative fuels. For example, such hydrocarbon fuels include
tho5e constituting napthenic, olefinic and paraffinic hydrocarbon
groups, particularly C~-C4 paraffinic hydrocarbon fuels.
Suitable fuels that can be used in the practice of the invention
include, for example; gasoline, kerosene, and octane. In
addition, hydrocarbon derivative fuels such as those constituting
various alcohols, ethers, and esters, for example, particularly
those containing four or fewer carbon atoms and, in particular,
alcohol~ such as ethyl and propyl alcohol can advantageously be
used in the practice of the invention.
In general, the finely divided solid fuels useable in the
practlce of the invention must be o~ su~icient energy content
and reactivity to heat the volume of stored gas to inf late the
12
~19~Xl
PATENT
F298~-21-00
inflatable restraint device at the desired rate, without the
inf lator device being of an undesirable large size.
Additionally, the fuel desirably produces no more than acceptable
levels of combustion products, such as C0, N0, HCN, or NH~, for
5 example, which are or become toxic at sufficiently high
concentrations .
The finely divided solid fuel useable in the practice of the
invention can include one or more various powders or dusts such
as those of:
a) carbon~reo~lc materials such as coal and coal products
(e.g., anthracite, bit~minollc, sub-bitll~;nouc, etc.,
such as with various volatile contents), charcoal, oil
shale dust, and coke;
b) cottons, woods, and peat (such as various cellulosic
materials including, for example: cellulose acetate,
methylcellulose, ethylcellulose, and cellulose
nitrate, as well as wood and paper dusts);
c) food feeds (such as flours, starches and grain dusts);
d) plastics, rubbers, and resins (such as epoxies,
polyesters and polyethylenes); and
e) metal and metal alloy materials (e.g., aluminum,
magnesium, titanium, etc., as powders, grits, and/or
shavings, in pure or - ' form).
It is to be understood that such fuel can, if desired, be
25 held in combinations with varying contents of liquid, vapor and
combinations thereof of water.
Further, it will be appreciated that the finely divided
solid fuels useable in the practice of the invention will
typically include solid particles of varying size and shape. In
30 general, however, the particle size of such finely divided solid
fuel will typically vary in a range between about S to 500
microns and preferably in a range of about 10 to 125 microns,
with mean particle sizes in the range of 10 to 40 microns. In
practice, such sized finely divided solid fuels can desirably
35 result in rapid and complete combustion, reducing or even
eliminating the need for filtration of particulate from the
~-u~ ing inflator assembly design.
13
~190~6~
PATENT
F2984-21-00
The use of finely divided solid fuels can result in various
processing advantages. For example, such solid fuels, at least
as compared relative to gaseous or liquid fuels, can simplify
handling requirements and facilitate storage within an
5 appropriate fuel storage chamber. Such facilitation in handling
can, in turn, result in manufacturing cost reductions.
Such f inely divided solid fluid fuels are generally to be
distinguished from pyrotechnic materials typically used in airbag
inflator devices. In general, such prior pyrotechnic materials,
10 even when used in a powdered or similar form, include an oxidant
as a . ~~~nt of the pyrotechnic. In contrast, the finely
divided solid f luid fuels of the invention do not include an
oxidant as a part of the material itself.
It will be appreciated that the fuel material, particularly
15 fuel materials such as liquid hydrocarbons and liquid hydrocarbon
derivatives (e.g., alcohols) may include therewith, in limited
proportions, materials such as water that are normally not
considered to be fuels. This is particularly true for those fuel
materials for which complete water separation is not normally
20 practically r~ i 7~hle. Additionally, the presence of water in
minor amounts, e.g., less than about 10 volS, typically between
about 4-8 vol%, can beneficially reduce the possibility of
undesired autoignition of the inf lator assembly without
significantly affecting the low temperature performance of the
25 assembly.
It is also to be appreciated that various fuel materials
can, if desired, be used mixed together. This is particularly
true for those fuel materials, such as commercial grade butane,
for which complete separation is not normally practically
30 realizable. For example, fuel mixtures which have been used
include: a) a 200 proof alcohol mix containing about 5-10% methyl
alcohol, 0.5-1% methyl isobutyl ketone and the balance
constituting ethyl alcohol and b) an alkane mix containing about
90+9~ (e.g. about 95%) butane, 2-6% (e.g., about 4%) propane and
35 with the balance constituting methane, ethane and other various
trace hydrocarbon species. An example of one such fuel material
is the denatured ethanol, "~N~YPRr~L SOLVENT SPECIAL, P~-4083, 200
14
006~
PAT~NT
F298~-21-00
Proo~l', sold by Union Carbide Chemicals and Plastics Company Inc.
and containing 85.8% ethanol, 13.3% methanol and 0.9% methyl
isobutyl ketone.
Further, such fuels can be used in multi-phase combinations
5 of two or more of the fuels in different states (e.g. gas,
liquid, and solid). For example, the fluid fuel used can
constitute a combination or mixture of a finely divided solid
fuel in a liquid fuel, such as a starch in ethyl alcohol, for
example. Similarly, the fluid fuel can constitute a combination
10 or mixture of a gaseous fuel held in intimate contact with a
liquid fuel. For example, such a gaseous fuel could be held in
contact with the liquid fuel under pressure, similar in fashion
to a carbonated beYerage held in a container.
Oxidants useable in the invention include various
15 oxy~n c.,.-~aining gases including, for example, pure oxygen, air,
diluted air, and oxygen ,: `- i n~d with one or more gas diluents
such as nitrogen, carbon dioxide, and noble gases such as helium,
argon, xenon. In practice, the use of pure oxygen (2~ may be
disadvantageous for a number of reasons including: 1) from a
20 production viewpoint, such use may present hAndl inq difficulties,
2) such use can magnify autoignition difficulties, 3) when
combined with the proper amounts of fuel (stoichiometric or near
stoichiometric, 0.8 ~ ~ ~ 1.2), ex~L~ ~lyhighflametemperatures
can result (Papeci~ly at the elevated ~Les,-ur~s commonly
25 associated with such inflator designs, and 4) at equivalence
ratios Or less than 0 . 8, excess quantities of oxygen and carbon
r ' ~1P can cause concern .
In view thereof, mixtures of argon and oxygen may be
preferred. Argon advantageously is relatively: 1) inert, 2)
30 inPYrQnaiVe, 3) 5are, and 4) easy to handle. The preferred
relative amounts of the ~ ts of such a mixture will in
general be clf~rPn~Pnt on factors such as the inflator, -tLy and
the particular fuels used therein. For example, an oxidant
mixture of 50-65 vol% oxygen with the balance being argon can
35 advantageously be used with ethyl alcohol-based fuel-containing
A~.'' lies.
' ~lgOO~l
PATENT
F2984-21-00
It will also be appreciated that such oxidant mixtures can
be used in conjunction with minor amounts of air, such as may be
initially present in the chamber to be filled with oxidant, prior
to the addition of the oxidant therein.
In one preferred embodiment of the invention, the fuel
material is stored separate and apart from the combustion
oxidant. For example, the fuel is stored within the fuel
cont~ i t assembly while the oxidant is stored outside of the
fuel con~ assembly but within the combustion chamber such
that the fuel and oxidant are in fluid communication only after
the fuel contA i - t assembly has ruptured or otherwise opened.
It is to be appreciated, however, that if desired, the fuel
material and oxidant can be stored in contact with each other.
In one alternative preferred ~mho8ir t, a fuel material and
oxidant can be stored together as a single material such as a
hydroxyl ammonium nitrate-based liquid monopropellant. Such
propellants are ~licclosecl in U.S. Patent 5,060,973, the
disclosure of which is herein incorporated.
A particularly suitable liquid propellant composition
containing both a fuel material and an oxidant material
comprises, by mass, approximately 60% hydroxyl ammonium nitrate
as an oYidi~ r, 20% triethanol ammonium nitrate as a fuel, and
20~ water as a solvent.
It is to be appreciated that with a liquid propellant such
as an aqueous solution of hydroxyl ammonium nitrate and a
nitrated hydrocarbon salt, such as triethanol r~ m nitrate,
the exo~hDrmic~l ly generated gases generally consist of nitrogen,
carbon dioxide and water vapor, all of which are generally
c~nci~ar~ed non-toxic. Furth- ~, the combustion of such a
propellant material generally results in no significant
particulate by-product and thus preferably renders as llnnP, --cc~ry
the post c ~ion f iltering of the products of combustion.
Thus, the invention permits the use of a wide range of fuels
in a variety of ~orms (including gaseous, liquid, and solid, as
well as mixtures thereof, i ncl~ i n~ multi-phase combinations of
two or more fuel materials) and a wide variety of oxidant
species, and also a wide range of relative amounts of fuel and
16
00~1
PATENT
F298~-21-00
oxidant species.
In general, the inflator assemblies of the invention are
preferably operated with equivalence ratios in the range of
0 . 4 S ~ S 1. 6, preferably in the range of 0 . 6 S ~ S 1.1.
As with the gas stored in the storage chamber 14, storage
of gas within the combustion chamber 60 at relatively high
~_ur~s advantageously helps min1m;7e the overall size of the
inflator a~ well as minimi7e ignition delay, thereby resulting
in higher and faster performance by the inflator assembly, as
well as resulting in more complete combustion, such as through
increased temperature and, hence, reaction rates. In addition,
such an inflator assembly minimizes emission of incomplete
products of combustion.
It will be appreciated that the combustion chamber
~uLL~ullding the fuel containment assembly of the invention can
alternatively contain, as desired or needed, one or more gaseous
materials such as air, oxidant or inert gas.
FIG. 2 illustrates a fragmentary portion of a fluid fueled
inflator 110 in accordance with one ~ L of the invention.
The illustrated portion of the fluid fueled inflator 110 includes
an inflator combustion chamber base cap portion 112 with an
opening 114 wherethrough an initiator device 116 is secured or
attached and a fuel containment assembly 120.
ThQ fuel cont~i t assembly 120 includes a housing 122
having an outer wall 124. Such a housing can be fabricated from
various appropriate selected materials including plastic (such
as acetal, chlorinated polyvinyl chloride (CPVC),
polyetheretherketone, propylene, andpolytetrafluoroethylene, for
example), ceramic (such as silicon and alumina-based ceramics,
for example) or, more typically, a metal (such as aluminum or a
low carbon steel, for example).
The housing 122 is closed in that:
1. the housing def ines a closed storage volume 126
wherein, for example, the housing is adapted to
contain a supply of at least one fuel in the for_ of
a ~luid, as described above, and
17
21~61
PATENT
F2984-21-00
2. the outer wall is impervious to the fuel, that is, the
material comprising the outer wall is not normally
significantly changed, affected or physically altered
as a result of contact with or by the fuel.
As described above, in one preferred ~ho~;~~nt, the fuel
is preferably stored free of combustion oxidant. However, such
as also described above, the fuel and oxidant can, if desired,
be stored together therein.
The housing 122 is generally bullet shaped with the outer
wall 124 including a generally cylindrical side portion 130
having an open first or base end 132 proximate to the combustion
chamber base cap portion opening 114 and a second end 134 which
is closed by means of a dome-shaped portion 136.
If desired, and as shown, a selected portion or portions of
the assembly 120 can be pre-weakened, such as by the inclusion
o~ external axial score lines 137a and 137b or otherwise have the
th~rkne~-s of the outer wall 124 selectively reduced. It will be
appreciated that such inclusion of score lines or the like (e.g.,
dimples) to selectively reduce the thickness of the outer wall
124 can facilitate opening of the assembly 120 at specific
predetermined operating conditions ag well as better ensure that
assembly desirably ~ uL ~g or opens at predetermined locations
and preferably avoids forming undesired fragments upon opening.
Further, it will be appreciated that the scores or other
appropriately selected forms of ~JL~ k~-nin-J can be ~-^hine-l
into the wall surface or molded into the surface such as when the
part has been mold fabricated, such as may conveniently be done
when the part is ~abricated from plastic material.
It will al~o be appreciated that while the assembly 120 has
been shown with external score lines (i.e., score lines on the
outer surface 138 of the respective wall 124), if desired, such
score lines or the like can be appropriately alternatively or
complimentarily located, such as along the inner surface 139 of
the outer wall 124, for example.
18
~19~0~1
PATE~IT
F298~-21-Oo
The open base end 132 is partially closed by means of a
housing base 140 and the initiator device 116. It will be
appreciated that the housing ~ase can, if desired, include
features and seals (not shown) such as O-rings, crimps, flanges,
etc. or, alternatively or additionally, a selected means of
interference and press fit to facilitate and secure attachment
or joinder of the initiator device therein.
As will be appreciated relative to this illustrated
, ~_'ir t, a fuel material held in such the storage volume 126
normally directly contacts the housing outer wall 124.
The initiator 116 includes a discharge end 142, wherefrom
upon actuation, initiation products are discharged. If desired,
and as shown, a hermetic seal 144 such as in the form of a disc
of metal can be applied about the initiator discharge end 142 to
prevent the fluid fuel material from directly contacting the
initiator 116. The inclusion of such a seal can assist in
avoiding and preventing undesired deterioration or degradation
of the initiator such as could result from undesired contact of
the initiator by the fuel material as well as better ensure the
avoidance of fuel leakage.
In operation, such as upon receipt of an appropriate
electrical signal by the associated initiator 116, a discharge
of energy such as in the form of a hot, particle-laden discharge
is directed therefrom to the fuel containment assembly 120,
specifically from the discharge end 142, through the seal 144 and
to the fuel material stored within the fuel storage volume 126,
whereupon the temperature and ~L~ Le of the fuel material will
increase. Upon the c-Yre~ling of the structural cAr~hjlity of the
wall 124, the housing 122 will rupture or otherwise open at or
proximate to the scores 137a and 137b, placing the heated fuel
in f luid communication with the combustion chamber and the
oxidant held therein. Thereafter, operation will generally be
similar to that for the above-described: ' ~i t.
FIG. 3 illustrates a fuel containment assembly 150 in
accordance with an alternative ~ -rl_ of the invention. The
fuel con~Ai - L assembly 150, similar to the fuel containment
assembly 120 illustrated in FIG. 2, includes a housing 152 having
19
. ~ 21~8~
PATE~rr
F298~-21-oO
an outer wall 153 which is generally bullet-shaped and includes
a generally cylindrical side outer wall 154 having an open first
or base end 156 and a second end 160 which is closed by means of
a dome-shaped closed end outer wall 162.
As with the above-described inflator assembly llo, the open
first or base end 156 is designed for placement adjacent a
CGLL ~ Ain~ combustion chamber base cap portion opening (not
shown). Specifically, the open first or base end 156 includes
an outwardly curled lip 164 and defines an initiator placement
volume 166 wherein, in a final assembly, an initiator device (not
shown) can be placed.
The fuel containment assembly 150 differs, however, differs
from that in the above-described Pn~hodir---t of FIG. 2 in that the
fuel material is contained within a capsule device 170, rather
being stored in the housing in direct contact with the housing
outer wall.
The capsule 170 can be fabricated from a wide range of
materials such as metal (such as aluminum, carbon steel and
81 ainl~cls steel) or, preferably, plastic material so as to
provide desired strength and resiliency, for example. It is to
be appreciated that while the fuel capsules of the inYention can,
if desired, be fabricated form materials such as ceramic and
glass, such materials of fabrication may at Ieast initially find
limited applicability due to the propensity of such materials,
in operation, to fragment such as a result of brittle fracture.
It is also to be appreciated that the invention, if desired,
can be practiced with c~rs~lP~ fabricated of a material, such as
certain plastics, which is itself, at least in part and in some
cases preferably substantially if not totally, combustible and
therefore c~n~cl~r-ble in the oxidizing environment of the
combustion chamber. A capsule made of such con~llr-hle material
may provide additional energy which can be used in the pro~-~rtion
of inflation gas as well as avoid the need for the provision of
particular capsule features such as particular opening
arrangements or ports.
The capsule 170 includes a closed outer wall 172 which
defines an enclosed storage volume 174 therein adapted to contain
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
e~l
~ATENT
F298~-21-00
at least a supply of at least one fuel material in the form of
a fluid, as described above. Specifically, the closed outer wall
172 includes a generally cylindrical side 176, a domed first end
180 and an initiator adjacent second end 182.
As shown, the capsule 170 is fitted within the housing 152
adjacent the dome-shaped closed end housing outer wall 162.
It is to be understood that as described above, in one
preferred amhoA;r-nt, the fuel is preferably stored free of
combustion oxidant. However, it is also to be appreciated that
the fuel and oxidant can, if desired, be stored together therein,
such as previously described.
In operation, such as upon receipt of an appropriate
electrical signal by the associated initiator device, a discharge
of energy such a~ in the form of a hot, particle-laden discharge
i5 directed therefrom to the fuel containment assembly 150,
specif ically the capsule 170 whereupon the temperature and
pIes:,uL~ of the fuel material held within the enclosed storage
volume 174 will increas~. Upon the PY~-eeA i n~ of the structural
capability of the capsule wall 176, the capsule 170 will rupture
or otherwise open and in turn rupture or otherwise open the
housing outer wall 153, placing the heated fuel in f luid
i-~tion with the combustion chamber and oxidant held
therein. Thereafter, operation will generally be similar to that
described above.
Increased or i ù~.d moderation or control of the rate at
which the fuel is introduced into the combustion chamber and, in
turn, increased or i uv~d moderation or control of the rate of
reaction of such fuel resulting in gas production are significant
benefits resulting from the utilization of a fuel contai --~
assembly in accordance with the invention. Such rate control can
be realized through the appropriate selection of various design
parameters. For example, the sizing and pyrotechnic loading of
the initiator device can be selected to provide the desired
degree o~ ~racturing or opening for a given assembly _ t.
Another design parameter which can be appropriately selected is
the fracturability of the _ --t which can be varied based on
factor~ such as wall 1 hirl~npss~ surface preparation (such as
21
~9~61
PATEN~r
F298~-21-00
through the inclusion of areas of pre-w~k~n; ng such as through
the inclusion of scores or the like, as well as the depth,
location and arrangement of any such areas of pre-we Ik~n; nq) as
well as the material of construction for the . ~n~nt. It will
be appreciated that the selection, amount and fill fraction of
the fuel material are additional design parameters which can be
used to desirably affect assembly performance and
characteristics .
Thus, the fuel~contAi --l. assembly of the invention can be
designed to appropriately tailor the rate at which the fuel
stored therein i9 introduced into the combustion chamber for
reaction and gas production. As a result, such fuel containment
assemblies permit greater flexibility in the designing of the
cuLL~ Ain~ inflators to meet particular processing or
operational needs. For example, by moderating the rate at which
fuel i8 introduced into the combustion chamber, combustion
chamber conditions which would typically be considered too
aggressive or url~-o~rùllable~ such as because of a too rapid an
increase in ~Sa~L-~ within the combustion chamber resulting from
too great a rate of fuel introduction therein, can desirably be
avoided .
FIG. 4 illustrates a fuel contA; t assembly 150' in
accordance with an alternative ~ L of the invention. (As
the fuel con~ assembly 150' is generally similar to the
fuel contli -r~ assembly 150 shown in FIG. 3, like parts are
designated by the addition of an apo~ uul,e, i . e., " "' , to the
reference numeral. )
The fuel con~ assembly 150' includes a housing 152'
and a capsule 170'. As in the abu~ des.,ibed ~mhori;- t, the
capsule 170' includes a closed outer wall 172' which defines an
enclosed storage volume 174' therein. As shown, the capsule 170'
is fitted within the housing 152' adjacent the dome-shaped closed
end housing outer wall 162 ' .
The capsule 170 ', however, is adapted to facilitate
att~. t with and adjacent to an associated initiator device
(not shown). Specifically, the capsule outer wall 172' includes
an initiator adjacent second end 182~ molded to form a profile
22
2190Q6~
PATENT
F298~-21-00
190 adapted to cuLL~ nd to the associated initiator device.
As a fuel assembly cont~inr t device so formed will in practice
desirably position the fuel load generally adjacent the discharge
end of the associated initiator device, such a cont~i t device
5 can beneficially facilitate operation of the inflator.
It will be appreciated that other than for place_ent of the
initiator within the assembly, operation will generally be
similar to that described above for the assembly 150 of FIG. 3.
As described above, the housing of a fuel containment
10 assembly, i~ desired and in accordance with the invention, can
include areas of pre-wP~kpnin~ such as in the form of scores or
the like such as to facilitate opening of the assembly at
specific predetermined operating conditions. It will also be
appreciated that for those assemblies including a capsule device,
15 the outer wall of the capsule can, if desired, include scores or
the like such as to facilitate opening of the capsule. It is
thus to be appreciated that in fuel containment assemblies in
accordance with the invention and which include both a housing
and a capsule:
1. both the capsule and housing can be fabricated to
include areas of pre-wP~kPni n~ such as in the form of
scores or the like,
2. either the capsule or the housing can be fabricated to
include areas of pre-wpAkpn i nq such as in the f orm of
scores or the like, or
3. both the capsule and the housing can be fabricated to
not include areas of pre-wP IkPn i n~ such as in the f orm
of scores or the like.
Further, in those fuel cont:~i L ~&Pmhlies in accordance
30 with the invention which include only one of either a capsule or
a housing ~ ~~ t, such ~ can be fabricated to include
or not include areas of pre-wP~kP~in~ such as in the form of
scores or the like, as desired.
FIG. 5 illustrates a fuel cont ~ assembly nt
35 210, i.e., either a housing or a capsule, in accordance with one
L o~ the invention. Specifically, the ~ -nt 210,
similar to those described above includes a generally bullet
23
2190061
~ ATENT
F298~-21-oO
shaped outer wall 212 having a generally cylindrical side wall
portion 214 with an end 216, closed by means of a dome-shaped
wall portion 220.
The outer side wall 214 differs from those previously
5 described in that it includes non-continuous axial scores which
form an annular ring 221 of non-reduced wall th; rkness in a
region of the ~ -st 210 which is subjected to high stress
when the - ~ has been properly actuated.
Three sets of such nol~ continuous score~ are shown: 222a and
lo 222b, 224a and 224b, and 226a and 2i6b. Specifically, the axial
line of each such score arrangement is interrupted by a
non-scored region, e.g., regions 222c, 224c, and 226c,
respectively. These non-scored regions form a part of the
annular ring 221. It will be appreciated that the inclusion of
such a ring can increase the strength of the ~~-nt S~LUl.il.UL~
such as to strengthen the ~ -nt in case of application of
increased external storage preSauL~s thereagainst.
FIGS. 6A, 6B, 6C and 6D each illustrate a fuel containment
assembly ~ t 240a, 240b, 240c and 240d, i.e., either a
houslng or a capsule, wherein a portion of the outer side wall
242a, 242b, 242c and 242d includes alternative score arrangements
or forms 244a, 244b, 244c and 244d.
More particularly, FIG. 6A illustrates a score arr I , --t
244a comprising a continuous axially extending score line,
similar to that shown in FIG. 2 and described above.
FIG. 6B illustrates a score arrangement 244b comprising a
no~. co~.tinuous axially extending score line, similar to that
shown in FIG. 5 and described above.
FIG. 6C illustrates a score arrangement 244c comprising a
radially extending score line, such as would circumscribe the
- -nt 240c about the outer side wall 242c.
FIG. 6D illustrates a score arrangement 244d comprising a
cylindrical helix axially extending score line about the outer
side wall 242d.
Additionally, while the invention has been described above
relative to possible inclusion of one or more scores, areas of
reduced 1-hi rl~n~q or the like about the outer side wall of one
24
~,
2190061
PATENT
F298~-21-oO
or more fuel containment assembly components (e.g., the housing
and/or capsule), it will be appreciated that scores or the like
can alternatively or additionally be included elsewhere about the
respective fuel containment assembly component, if desired,
5 including about the dome-shaped outer wall portion to facilitate
opening thereat.
FIGS. 7A illustrates a fragmentary portion of a fuel
cont~ assembly component 260, i.e., either a housing or a
capsule, before opening, while FIG. 7B illustrates that same fuel
10 contAi --L assembly --Ant, now designated 260', after
opening .
The ~ ~ 260 includes a domed, generally
hPm;S~FhPrically-shaped outer wall 262, which has been scored in
accordance with one Pmho~ of the invention. Specif ically,
15 the wall 262 includes six (6) score lines or grooves individually
designated 264(a-f~ which generally extend from the top center
266 of the hPmiA-rhpre to the tangency point 270 around the edge
of the hemispherically-shaped outer wall 262. These grooves
264 (a-f) taper, gradually decreasing in depth the further away
20 from the top center 266. It will be appreciated that such a
structure and arrAn~, t can be used when discharge of the fuel
rrom the end of the: -nt is desired. For example, such an
arrA-, t can be sued when due to c -nPnt size limitations,
such as insufficient side wall area, the ~ -nt lacks adequate
25 room for the inclusion of scoring along the side walls.
In operation, such as upon receipt of an appropriate
electrical signal by the associated initiator device, a discharge
of energy such a~ in the form of a hot, particle-laden discharge
i~ directed therefrom to the fuel con~ assembly . .~nt
30 260, whereupon the temperature and yLes-~lL~ of the fuel material
held within the ~r--~ 260 will increase. Upon the PxceP~linj
of the structural capability of the ~ nt outer wall 262, the
wall 262 will open, as shown in FIG. 7B, with the dome-shaped
wall forming petals 272 (a-f) which petal open to place heated
35 fuel in f luid communication with the combustion chamber and
oxidant held therein. Thereafter, operation will generally be
similar to that described above.
219~061
PATENq!
F2ss~-21-oo
FIG. 8A illustrates a fuel containment assembly housing 310
in accordance with one ~mho~lir~~t of the invention before
opening, while FIG. 8s illustrates that same fuel contA1 - t
assembly housing, now designated 310', after opening.
The housing 310 is generally similar to the housing 122
shown in FIG. 2 and described above. More specifically, the
housing 310 i5 generally bullet shaped with an outer wall 312
which includes a generally cylindrical side portion 314 having
an open first or base end 316 such as would be positioned
lo proximate to the combustion chamber base cap portion opening (not
shown) and a second end 320 which is closed by means of a
dome-shaped portion 322.
The housing 310 has been selectively pre-weakened by the
inclusion of six (6) generally equally spaced, axially extending
score lines 324 (e.g., lines whereat the thi r--n-~c5 of the outer
wall 312, specifically the cylindrical side portion 314 thereof,
has been reduced), such as described above. In FIG. 8A, only
three of the score lines 324 are visible and have been designated
324a, 324b and 324c, respectively. As shown, the score lines 324
do not extend into the dome-shaped portion 322, resulting in a
smooth, unscored dome surface 326.
As shown by the fuel containment housing 310' of FIG. 8s,
in operation and upon actuation, the pI~s~uL~ builds up within
the housing results in rupture or opening of the housing along
weakest areas of the outer wall 312, i.e., along the score lines
324 whereat the outer wall is the thinnest. As a result, the
es-u-e build-up which causes the housing to radially swell or
bulge outward is preferably exhausted through score line opPnin~a
330 formed in the outer wall 312 generally along the score lines
324. After opening, the dome-shaped portion 322 remains joined
a~ a part of the housing 310' by means of bands 332 of the side
wall 314, extending between adjacent score line op-~nin7a 330.
In addition to the above-described benef it of increased or
d moderation or control of the rate at which the fuel is
introduced into the combustion chamber, the fuel containment
assembly arr~ J t of the invention can provide benef icial
moderation of the inf luence of ambient temperature on inf lator
26
2190061
PATENT
F298~-21-00
performance. Such moderation of the inf luence of ambient
temperature on inflator performance (also referred to as
"self~ tion") is described below with reference to FIGS.
9A, 9~ and 9C which show the fuel containment housing, shown in
FIG. 8A and described above, herein individually designated 310a,
310b and 310c, respectively, wherein the housing is within a
combustion chamber portion 340 of a fluid fueled inflator
assembly 342, at various selected ambient temperature operating
condition~. It is to be appreciated that the external pressure
load on the fuel cont~i t housing 310 will increase
significantly as the temperature in the combustion chamber rises.
FIG. 9A shows the housing 310a after opening when the
ambient temperature within the combustion chamber is about 21C
and the pL.=S~uLæ. within the combustion chamber is about 1850 psi.
FIG. 9B shows the housing 310b after opening when the
combustion ambient conditions are generally considered to be
"cold", e.g., a temperature of about -40C, whereat the ~resau.
within the combustion chamber is about 1595 psi.
FIG. 9C shows the housing 310c after opening when the
combustion ambient conditions are generally considered to be
"hotn, e.g., a temperature o~ about 90C, whereat the pL~55U~
within the combustion chamber is about 2425 psi.
In each o~ FIGS. 9A, 9B and 9C, the area provided by the
passage score line openings, designated 330a, 330b and 330c,
respectively, varies with the particular conditions of operation.
As shown, at low ambient t~ ~Lu~ ~s, the housing device is
subjected to relatively low external ~es~u.e and is
comparatively easier to open. At a higher ambient temperature,
the device is subject to relatively greater external pressure and
would~ as a result typically be comparatively more difficult to
open. Specifically, at a higher ambient temperature (all other
factors, such as fuel drop size, equivalence ratio, oxygen
C~ ,6~1~t dtion, etc. held constant) th~ ~le..,ur~ within the
35 combustion chamber will be greater and it is hence more difficult
for an initiator of a given strength to fully open the housing.
Thus, as the ambient temperature and hence pressure increases,
27
.
~ 061
PA'rE:NT
F2ss~-2~-oo
the relative amount of passage area provided upon opening of the
housing decrease, resulting in a decrease in the rate fuel
material passes from the housing into the combustion chamber.
Additionally, it is believed that the quality of the degree of
5 atomization is reduced in that the relative size of the fuel
drops ~rud-lced increases. Relatively larger sized drops will
require more time to be heated, vaporized and burned. In view
of the fuel materials of the invention generally being more
reactive at higher temperatures, an inflator assembly having such
10 a fuel con'~i t device can self c -~ate for the effect of
a typical or normally anticipated change in ambient temperature
such as by more quickly releasing fuel when at a lower ambient
tltU~ and, alternatively, more slowly releasing fuel at a
higher ambient temperature.
It is to be appreciated that similar effects can also be
realized when the fuel con~ device is a capsule, such as
described herein.
As a result, inflators utilizing fuel contai ~rt devices
such as described herein can generally desirably experience
significantly reduced variability in performance with changes in
ambient temperature.
While the invention has been described above with reference
to the possible inclusion of score lines or the like in fuel
assembly _ ~ Ls (such as a housing or a capsule) such as to
facilitate assembly opening at specific predet~rrnined operating
condition~, it will be appreciated that, if desired, the
invention can be practiced with the selective inclusion of one
or more ~ hening or stiffening features to prevent, avoid
or make more difficult opening of the assembly or of selected
portions thereof.
For example, FIG. 10 illustrates a fuel assembly ~ ~nt
350, i.e., either a housing or a capsule, with an outer wall 352
having a generally circular cross section and de~ining an inner
volume 354. The ~ ~ 350 includes within the internal
volume 354, adjacent the inner surface 356 of the outer wall 352
a wall support feature 360, shown in the form of a stiffening
circular ring or rib. Such inclusion of a wall support feature
28
~190061
PATENT
F298~-21-oO
can generally serve to increase the external load capacity of the
component 350, such as to prevent buckling of the outer wall when
subjected to increase external storage pressures, without
significantly affecting the internal pressure required to open
the cr-r^,nPnt wall 352.
It will be appreciated that while the support feature has
been shown in the form of a continuous circular ring or rib,
other appropriate f orms or shapes can be used to provide the
desired effect. For example, support features in the form of
non-circular rings as well as nol. co-.tinuous forms, such as only
along specific or particular portions of the outer wall of the
~ -nt can, as desired be utilized. In general, however, as
continuous forms of such support features will generally provide
increased support, such forms will typically be preferred.
It will be appreciated that a support feature such as the
ab~ es-_Libed stiffening ring can typically be formed of the
same material, such as metal plastic or ceramic, used in the
rabrication of the specific assembly _ --^^t but with variation
in I h ~ rl~n--~5, as required .
While the invention has been described above relative to the
use Or a fuel cont~i t assembly housing having an outer side
and dome wall which is solid (i.e., free of openings), it is to
be understood that the invention, at least in its broader
aspect~, is not so limited. For example, when the fuel
cont~ t assembly includes a capsule wherein the fuel i5
stored and a housing which at least in part is in !-uLLoullding
relati~^n~h;r with the capsule, as the housing is not in fluid
communication with the fuel in the at rest state for the
assembly, the housing can include vpeninqq placed or situated as
desired to effect performance.
FIG. 11 illustrates one such fuel containment assembly 370
in accordance with the invention. Specifically, the fuel
contAi -nt assembly 370 includes a capsule 372 generally similar
to that described above in reference to FIG. 4 and a wire screen
mesh housing 374, which serves to appropriately retain the
capsule and should the capsule fracture into separate pieces upon
29
'~190~6~
PAT~T
F298~-21-00
actuation of the fuel containment assembly such a housing can
serve to retain such formed capsule pieces.
The capsule 372 includes an outer wall 376 which defines an
enclosed storage volume 380 therein. The capsule outer wall 376
includes an initiator adjacent second end 382 molded to form a
profile 384 adapted to correspond to the associated initiator
device (not shown).
The housing 374 is made of metal wire screen mesh, for
example, in conjunction with a capsule fabricated of plastic, a
o 10-24 mesh per square inch wire screen can be used and in
conjunction with a capsule fabricated of ceramic, a 24-100 mesh
per square inch wire screen can be used.
In practice, such housings will typically be fabricated from
steel, aluminum or the like metal wire materials. It will also
be appreciated that appropriate alternatives to wire form screen
mean~ can be used. For example, rather than screen means formed
by metal wires, appropriate screen means can be formed from
perforated metal and Pyr~nApd metal, as desired.
FIGS. 12 and 13 illustrate a fuel containment assembly 410
in accordance with yet another alternative P~ho~ 1. of the
invention. The assembly 410 includes a capsule 412 of molded
material, e.g., plastic, adapted for direct at1~ t to a
cLL ~ r~in~ portion of an inflator assembly, for example, the
inf lator combustion chamber base cap portion 112 shown in FIG.
2.
The capsule 412, similar to the capsule 170' described
above, includes an outer wall 414 which defines an enclosed
storagQ volume 416 therein adapted to contain at least a supply
of at least one fuel material in the form of a fluid, as
described above. Specifically, the outer wall 414 includes a
generally cylindrical side 420, a domed first end 422 and an
initiator adjacent second end 424 molded to form a profile 426
adapted to c-,L~e~ d to the associated initiator device (not
shown) .
~lolded into the capsule outer wall 414 is a retainer 430
havinq a first end 431 with an outwardly curled lip 432 and a
second end 433 molded into the capsule outer wall 414, between
~ ~006~
PA~rENI
F298~-21-oo
an inner layer 414a and an outer layer 414b. The retainer 430
extends circumferentially about the inner layer 414a and is
included to facilitate direct attachment of the capsule in an
inf lator assembly .
In practice, such retainers will typically be fabricated of
metal material, e.g., steel or aluminum, with the metal material
stamped and inserted into a mold with, for example, a suitable
plastic capsule material molded there around.
The thickness of the retainer as well as the length the
retainer extends between the inner and outer layers of the
capsule outer wall can be appropriately selected to provide the
desired strength to the assembly.
The assembly 410 includes gas flow orifice passageways 434
along the capsule side wall 420, through the outer layer 414a and
the retainer 430. The enclosed storage volume 416 is normally
blocked from fluid _ ication with these orifices passageways
by means of the inner layer 414a of the capsule outer wall 414.
However, at a desired point in time, e.g., upon proper
flln~tionin~ of the initiator device resulting in a pressure
increase within the enclosed storage volume 416, the orifice
closing portions of the inner layer 414a of the outer wall 414,
hereinafter designated 435, will properly fail and permit
discharge of the capsule contents.
To facilitate opening of such an assembly at specific
predetermined operating conditions, the orifice closing portions
435 of the inner layer 414a can be selectively pre-weakened such
as by the inclusion, along the outer surface 436 of the inner
layer 414a, of areas o~ reduced wall thickness such as by the
scoring o~ at least a portion of the perimeters of the portions
435. These scores are designated 438.
For example, FIG. 14A illustrates a portion 440 of the outer
~urface 436 o~ the capsule side wall inner layer 414a which
ln~ gas flow ori~ices, individually designated 434a and
434b, having CU~L~ ;ng orifice closing portions 435a and
435b. As shown, the perimeters of the orifice closing portions
435a and 435b include areas of reduced thickness, designated 438a
and 438b, respectively. These areas of reduced thickness are
31
. ~ 2~061
PATENT
F298~-21-00
generally in the form of an incomplete circle and outline the
perimeter of the orifice closing portions 435a and 435b. The
circle of reduced thickness is incomplete in that a portion,
designated 446a and 446b, respectively, of the wall layer 414a
5 in the path of the circle is of an unreduced thickness and thus
serves to retain the CULL-_IJ~ ;ng closing portions 435a and 435b
with the balance of the wall layer material upon the opening of
the orifice p~s~geways 434a and 434b, as shown in FIG. 14B for
gas flow orifice passageway 434a.
In operation, such as upon receipt of an appropriate
electrical signal by the associated initiator device, a discharge
of energy such as in the form of a hot, particle-laden discharge
is directed therefrom to the fuel cont~ assembly 410,
specifically the capsule 412, whereupon the temperature and
pressul~ of the fuel material held within the enclosed storage
volume 416 will increase. Upon the P~cee~lin~ of the structural
capability of the capsule wall 414, the capsule 412 will rupture
or otherwise open, placing the heated fuel in fluid communication
with the combustion chamber and oxidant held therein.
Thereafter, operation will generally be similar to that described
above .
FIG. 15 illustrates a fluid fueled inflator assembly 510 in
accordance with an alternative ~mho~ of the invention. The
inflator 510 includes an elongated generally cylindrical
2s sleeve 516, having a first and a second end, 520 and 522,
respectively, and defines a chamber 523, herein referred to as
a combustion chamber.
The first end 520 is partially closed by means of an
integral ~h~ portion 524. A diffuser assembly 526, such as
described above relative to the diffuser assembly 26 of FIG. 1,
i5 attached by a circumferential weld 527 in sealing relation to
the sleeve first end 520. As with the diffuser assembly 26, the
diffuser assembly 526 includes a generally cylindrical sleeve 532
having a cap portion 534 and a base portion 536 to define a
diffuser chamber 540. Each o~ the diffuser assembly cap and base
portions, 534 and 536, respectively, include a closed first end
542a and 542b, respectively, and an open second end 544a and
32
_, . _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
~
PAq~El
F298~-21-Oo
544b, respectively. The diffuser assembly cap portion 534
includes a plurality of openings 546, adjacent the closed cap
first end 542a, for dispensing inflation gas from the inflator
assembly into an airbag assembly (not shown). The diffuser
assembly base portion 536 additionally includes a plurality of
opPnin~q 548, adjacent the closed base first end 542b, for
passage of inflation gas from the chamber 523, into the diffuser
chamber 4 0 .
The diffuser assembly cap and base portions, 534 and 536,
io respectively, are aligned with the open second end of each, i.e.,
ends 544a and 544b, respectively, being closed by sealing means,
e . g., by means of a rupture disc 550 abutting thereagainst. The
diffuser assembly rupture disc 550 is joined in sealing relation
with the di~fuser assembly cap and base portions, 534 and 536,
respectively, by means of a circumferential weld 551 at the
periphery of the disc 550. In the static state, the disc 550
serves to separate the contents of the chamber 523 from the
airbag .
An end base 560 is attached by a circumferential weld 562
in sealing relation to the sleeve second end 522. The end base
560 includes a base cap 564 joined thereto via a base shoulder
connecting portion 566. The base shoulder connecting portion 566
serves as a convenient means o~ locating the end base 560
relative to the sleeve 516, as well as providing a location for
a circum~erential weld 562 whereby the end base 560 is attached
in sealing relation to the sleeve 516.
The end base 560 includes an opening 570 therein,
wheL~hr~u~l~ an initiator device 572 is attached in sealing
relation, such as with a weld, crimping or other suitable
hermetic seal, within the inflator 510. The initiator device 572
i nr~ s a discharge end 574 . A fuel cont~ t assembly 576
in accordance with the invention and such as previously described
herein is located within the chamber 523, adjacent the initiator
device discharg~ end 574. The fuel con1 ai t assembly 576
contains or holds contents which include a quantity of at least
one fuel material in the form of fluid.
33
061
PAT~NT
F298~-21-oo
In operation, such as upon the sensing of a collision, an
electrical signal is sent to the initiator device 572, such as
a conventional pyrotechnic initiator device. Such an initiator
device will upon receipt of an appropriate electrical signal
ignite and emit energy, such as in the form of a hot,
particle-laden discharge, into the ruel containment assembly 576.
In turn, the temperature and pressure o~ the fuel stored
within the fuel cont~ assembly 576 will increase. Upon the
PYrPe~n~ of the structural capability of the a6sembly 576, e.g.,
at predetermined operating conditions, the assembly will rupture
or otherwise open placing the heated fuel in fluid ~ nication
with the chamber 523. In the chamber 523, the heated fuel and
oxidant (such as normally stored apart from the fuel in the
chamber 523 or, as previously described herein, stored together
with the fuel material within the fuel containment assembly 576)
form a flammable mixture which, via initiation by the initiator,
ignites and burns at an elevated temperature and pressure.
The hot gas produced upon the burning of the f lammable
mixture results in a rapid pressure rise within the chamber 523.
When the gas ~Las~uLe within the chamber 523 exceeds the
~-Lu~iLu~al capability of the rupture disc 550, the disc LUIJ~ULeS
or otherwise permits the passage of the hot gas through the
diffuser assembly 526 and out the opPninJ~ 546 into the airbag
assembly .
It will be appreciated that as such an inflator design does
not include a separate storage chamber rOr the storage of a
pL~S~U' ized gas separate from the fuel and/or oxidant, such an
inflator design typically will be _ ~secl of fewer parts as
compared to the above-described inflator design of FIG. 1. Such
reduction in parts and simplified assembly can desirably
facilitate and reduce the costs associated with manufacture and
assembly as well as reduce the weight of the inf lator assembly .
As described above, the pre-wP~Pning of fuel cont~ t
assembly ~ ~nPnts, e.g., either a housing and/or a capsule,
such as by selectively reducing the thickness of the outer wall
of the -t such as by the inclusion of one or more score
lines or the like, can minimize or reduce the amount of pressure
34
_ _ _ _ _ _ _ _
~190~1
PAT~NT
F298~-21-00
or force and in turn the amount of energy required to open such
a ~ ~ ~nt. Further, allowing the ~n-nt to preferentially
open along a predetermined path such as provided by such a score
line results in a more controlled opening and can thus reduce or
minimize the potential for undesired fragmentation of the
~ t upon opening.
However, in addition to opening in a controlled manner (e.g.
without undesired fragmentation) to allow the fuel and combustion
oxidant to properly contact and mix upon initiation, fuel
cont~ as6emblies in accordance with the invention generally
are required to perform additional various functions including
being able to withstand large external pressure lo~ds (e.g., up
to 2000 psi or more) without collapsing or buckling.
It will be appreciated that the pL~ k_ninq of fuel
cont^i !r~ assembly components can detrimentally impact the
external ~as, ~La load capacity of the fuel cont~i ~ assembly
--~. specifically, the inrl~ ^n of score line grooves or
the like which are relatively long and thin, typically can reduce
the strength of the fuel cont ~i ~ assembly ~~ -nt by 50~6
or more, as the bur~l inq ~.a~ (e.g. registance to b'~r~l inq)
of the ~ nt is generally a strong function of the wall
~hirl~nAgg and, particularly, the score groove length and depth.
Alternatively, the utilization of relatively short shallow score
line grooves while having a less detrimental impact on the
external load capacity of the ~ t, generally can more
commonly result in r~ ~tion of the ~ ^nt upon initiation
of the assembly.
In an effort to avoid or overcome at least some of the
abu.~ de~_.ibed complication~ resulting from reducing the
thickness of a ~ t outer wall, one aspect of the invention
has been the dev~l:, t, as described below, of selectively
reducing the, t outer wall thirlrn-~s to multiple depths,
what is referred to hereinafter as "multiple depth" grooves or
score lines.
Turning now to FIG. 16, there is illugtrated a simplified
schematic of a fuel cont~i t assembly ~ ^-t 610, i.e.,
either a housing or a capsule. Specifically, the - --^nt 610,
_ _
. ~ ~19~061
PATENT
F298~-21-oo
similar to those described above, includes an outer wall 612
having a generally cylindrical side wall portion 614 with a first
end portion 616 and a second end portion 618. The cylindrical
side wall portion 614 includes a section, designated 624, which
as detailed below with reference to FIGS. 17A and 173, has been
~L~ n~d~ such as by having the thickness of the outer wall
612, specifically along the cylindrical side wall portion 614,
selectively reduced by the inclusion of one or more axial score
lines .
lo FIGS. 17A and 17s are simplif ied and enlarged fragmentary
drawings illustrating alternative arrA, Ls, designated 630
and 632, respectively, of the cylindrical side wall portion
section 624 of FIG. 16 wherein the th i ~nPC8 of the outer wall
612 has been selectively reduced. Specifically, the arrangement
630 of FIG. 17A illustrates a score line 634 of generally
constant depth, similar to that previously shown in FIG. 2, for
example, and whereat the outer wall 612 has a generally uniform
thirl~n-s,, designated 635, along the length of the score line
634 .
The arrangement 632 of FIG. 17B illustrates a multiple depth
groove or score line 636 in accordance with one _mhoSi- t of the
invention. Specifically, while the outer wall 612 has a general
thickness designated 638, the score line 636 includes a segment
640, in the general center portion of the cylindrical side wall
614, ~orming a relatively short and deep groove. At the score
line segment 640, the outer wall 612 has a thickness designated
642, which is less than the general thickness 638 of the outer
wall 612.
The incc,~uLc.tion of such a short and relatively deep groove
3 0 generally reduces the amount of energy required to open the
t, e.g., a 50 formed ~ --t will generally open at a
lower internal ~Le__l.e.
The score line segment 640 is bordered on both ends by score
line 5~ - t s 646a and 646b whereat the outer wall 612 has a
thickness designated 650. The l h~.~Ln_cs 650 of the outer wall
at score line segments 646a and 646b, while greater than the
outer wall ~hirL-n-ss 642 at the central score line segment 640
36
~igO~61
PATENT
F298~-21-00
is still less than the general thickness 638 of the outer wall
612 .
The inclusion of the bordering score line segments 646a and
646b which, as compared to the score line segment 640, are of
comparatively greater thickness provide a path along which the
opening of the _ ~?nt can propagate thereby resulting in the
---nt opening in a more controlled manner and reduce or
minim;7e the potential for undesired fragmentation of the
-~lt upon opening. Additionally, the thicker bordering
score line segments provide greater stiffness or resistance to
bl~ n~. As a result, the inclusion of such a multiple depth
selectively reduced wall thickness in a fuel containment assembly
~r~! t of the invention minimizes or reduces the amount of
pressure or force and in turn the amount of energy required to
open such _ fnt while still providing sufficient strength to
avoid undesired ,hllr~l ing of the ?~t.
While fuel contAi t assemblies in accordance with the
invention have been described above with reference to assemblies
containing a housing or a capsule fuel contA i t assembly
-- ~, either alone or togelh~r, it will be appreciated that
when one of these ts is used alone without the other,
then the: t used would typically be constructed to be able
to withstand a larger external pressure as compared to those
assemblies i n~ n1 both such ~ ~rts.
For example, a capsule which is used without a fuel
con~?,i t assembly housing (such as, at least in some
circumstances, the capsule 412 shown in FIGS. 12 and 13, for
example) would typically be constructed more robustly, e.g., with
a thicker outer wall, as 2d to a capsule (such as the
capsule 170 shown in FIG. 2) situated within a housing (such as
the housing 152 shown in FIG. 2) which housing would typically
carry at least a portion if not substantially all of the
external p~eSauLé applied to the assembly. It will be
appreciated, however, that in at least some applications
ln~ ludin1 both a housing and a capsule ?rt, it may be
desirable to rely on s~ch an underlying structure as the capsule
to carry at least some of the external ~r eSa~lL ~ load . In such
37
~19V~61
PATENT
F298~-21-00
an instance, the housing wall thickness can be appropriately
reduced or minimized.
As described-above, the fuel cont l i t ~c~ l i es of the
invention are generally designed or adapted to rupture or open
5 at predetermined operating conditions. In general, such fuel
cont~i - t assembly design can represent a ~ ncing of various
factors including the general desire for rapid release of the
stored fuel and the ability of the assembly to withstand higher
or relatively greater external loads.
lo More specifically, as the inflation of automotive airbags
must meet very stringent performance criteria, in practice it
will be appreciated that in certain applications utilizing the
f luid fuel materials of the invention in the fuel containment
assemblies of the invention it may be advantageous and desirable
15 for the fuel containment assembly to open or release the stored
fuel as quickly as reasonably possible. Such quick opening of
the fuel cont~i ~ assembly will permit the rapid release,
vaporization and combustion of the released fuel and may be
particularly desirable for those assemblies containing relatively
20 heavier fuels, e.g., fuel materials of higher molecular weight,
viscosity, surface tension and/or heat of vaporization, for
example .
The external load on the fuel con~;-i t lc~ s of the
invention are generally a result of the elevated p~ ~s~uL ~s
25 normally present in the combustion chamber. In practice, the
fuel con ~i I assemblies of the invention will be designed to
safely withstand a high external load without failure or rupture.
It is also to be appreciated that i vv-~d safety can be
realized through the use of a pre-filled fuel-containing assembly
3 o _ 1 in accu~ance with the invention .
For example, as allowed with at least some of the
above-described: hQr~ 5, the appropriately selected assembly
~ can be filled with fuel at a location remote from the
site of the balance of the inf lator production or assembly.
35 Thus, in one ~ir-- t, a capsule can be appropriately filled
with ruel at a location remote from the location at which the
inflator is a~ iately ~illed to contain a pressurized
38
~9V~61
P~TENT
F298~-21-00
oxidizing gas, for example. As a result, the potential for a
possible fire or explosion from the undesired contact of the fuel
and oxidant can be significantly reduced ir not eliminated. Such
a safety development can be ~reci 1l ly significant in a high
5 assembly rate environment such as associated with the mass
production of vehicular restraint system airbag inf lators .
Additionally, such a fuel-containing co-r~nPnt can be
checked for the undesired leakage of fuel prior to installation
of the: ~ into the inflator housing, with the appropriate
10 rejection of any unacceptable ^-~ts. Then, following
installation of an appropriately checked c - ~, the assembled
inflator can in appropriate situations itself be leak checked.
Such a leak check process can better ensure the quality of
installed inf lator assemblies .
In view of the above, the invention provides an inf lator
assembly which utilizes a fuel in the form of a fluid that is
burned to produce inflation gas and which assembly appropriately
moderates the impact of operation at varying ambient temperature
conditions. Further, the invention provides such an inflator
20 assembly having i ~ d moderation or control of the rate at
which the fuel is ill~.v-l~ced into the combustion chamber and, in
turn, i u~ moderation or control of the rate of reaction of
such ruel.
The invention illustratively disclosed herein suitably may
25 be practiced in the absence of any element, part, step,
~ --t, or ingredient which is not specifically disclosed
herein .
The foregoing detailed description is given for clearness
o~ understanding only, and no -, PcPss~ry limitations are to be
30 understood therefrom, as modirications within the scope of the
invention will be obvious to those skilled in the art.
Consistent therewith, appearances of mean-plus-function clauses
in thQ claims are intended to cover not only structural
equivalents but also equivalent structures. For example,
35 although a nail and a screw may not be considered e~uivalent
l-~LU~;~UJ~3 in that a nail employs a cylindrical surface to secure
parts together, whereas a screw employs a helical surface, in the
39
~190~
PATENT
F298~-21-00
envirOnment of part fastening, a nail and a screw ~ay be
equivalent structures.
