U.S. patent application number 09/495975 was filed with the patent office on 2001-12-27 for airbag inflation gas generation via a dissociating material and the moderation thereof.
Invention is credited to Green, David J., Mendenhall, Ivan V., Moore, Walter A., Rink, Karl K..
Application Number | 20010054461 09/495975 |
Document ID | / |
Family ID | 27555510 |
Filed Date | 2001-12-27 |
United States Patent
Application |
20010054461 |
Kind Code |
A1 |
Rink, Karl K. ; et
al. |
December 27, 2001 |
Airbag inflation gas generation via a dissociating material and the
moderation thereof
Abstract
An inflator apparatus for inflating an inflatable device and a
method are provided wherein a combination of a dissociative gas
source material and at least one unreactive dissociation reaction
modifier is stored at least partially in liquefied form with the
reaction modifier effective to moderate at least one of the
temperature and concentration of the at least one gas source
material upon the dissociation of at least a portion of the at
least one gas source material.
Inventors: |
Rink, Karl K.; (Liberty,
UT) ; Moore, Walter A.; (Parker, CO) ; Green,
David J.; (Brigham City, UT) ; Mendenhall, Ivan
V.; (Providence, UT) |
Correspondence
Address: |
James D Erickson
Autoliv ASP Inc
3350 Airport Road
Ogden
UT
84405
US
|
Family ID: |
27555510 |
Appl. No.: |
09/495975 |
Filed: |
February 2, 2000 |
Current U.S.
Class: |
149/1 |
Current CPC
Class: |
B60R 21/264 20130101;
C06D 5/04 20130101 |
Class at
Publication: |
149/1 |
International
Class: |
C06B 047/00 |
Claims
What is claimed is:
1. In an apparatus for inflating an inflatable device, the
apparatus includes a first chamber having contents which include at
least one gas source material which, upon initiation, undergoes
dissociation to form dissociation products used to inflate the
inflatable device, the improvement comprising: at least one
unreactive dissociation reaction modifier selected from a group
consisting of CO.sub.2, Xe, SF.sub.6 and mixtures thereof stored at
least partially in liquefied form in fluid contact with the at
least one gas source material in the first chamber, the at least
one unreactive dissociation reaction modifier effective to moderate
at least one of the temperature and concentration of the at least
one gas source material in the first chamber upon the dissociation
of at least a portion of the at least one gas source material.
2. The apparatus of claim 1 wherein the at least one gas source
material comprises nitrous oxide.
3. The apparatus of claim 2 wherein the at least one unreactive
dissociation reaction modifier includes CO.sub.2.
4. The apparatus of claim 1 wherein the at least one unreactive
dissociation reaction modifier includes CO.sub.2.
5. The apparatus of claim 4 wherein the first chamber contents
consist essentially of nitrous oxide and CO.sub.2.
6. The apparatus of claim 1 wherein the first chamber contents have
an equivalence ratio of less than 0.25.
7. The apparatus of claim 1 wherein at least one of the at least
one gas source material and the at least one unreactive
dissociation reaction modifier is introduced within the first
chamber in a solid form.
8. The apparatus of claim 7 wherein the solid form comprises at
least one cryogenically-formed solid.
9. The apparatus of claim 8 wherein the at least one
cryogenically-formed solid comprises the at least one gas source
material.
10. The apparatus of claim 9 wherein the at least one gas source
material comprises nitrous oxide.
11. The apparatus of claim 8 wherein the at least one
cryogenically-formed solid comprises the at least one unreactive
dissociation reaction modifier.
12. The apparatus of claim 11 wherein the at least one unreactive
dissociation reaction modifier comprises CO.sub.2.
13. The apparatus of claim 8 wherein the at least one
cryogenically-formed solid comprises a combination of at least the
at least one gas source material and the at least one unreactive
dissociation reaction modifier.
14. The apparatus of claim 8 wherein the at least one
cryogenically-formed solid comprises a combination of at least
nitrous oxide and CO.sub.2.
15. The apparatus of claim 1 wherein the first chamber contents
additionally include a quantity of oxidative material.
16. The apparatus of claim 1 additionally comprising a chamber
opener including an initiator device and an associated supply of
reactant material.
17. The apparatus of claim 16 wherein the reactant material
comprises an additive effective whereby, upon reaction of the
reactant material, NO.sub.x products are present in a reduced
amount as compared to reaction of the same reactant material
without the additive.
18. The apparatus of claim 17 wherein the additive comprises
ammonium sulfate.
19. The apparatus of claim 18 wherein the reactant material
comprises ammonium sulfate in an amount between about 2 and about
20 composition weight percent.
20. A method for inflating an inflatable safety device in a
vehicle, said method comprising: initiating an at least partially
liquefied inflation gas-resulting combination including at least
one gas source material and at least one unreactive dissociation
reaction modifier selected from a group consisting of CO.sub.2, Xe,
SF.sub.6 and mixtures thereof within a first chamber whereby at
least a portion of the at least one gas source material dissociates
to form dissociation products including at least one gaseous
dissociation product and the at least one unreactive dissociation
reaction modifier moderates at least one of the temperature and
concentration of the at least one gas source material in the first
chamber and releasing inflation gas comprising at least a portion
of the at least one gaseous dissociation product and the at least
one unreactive dissociation reaction modifier from the first
chamber to inflate the inflatable safety device.
21. The method of claim 20 wherein the at least one gas source
material comprises nitrous oxide.
22. The method of claim 21 wherein the at least one unreactive
dissociation reaction modifier includes CO.sub.2.
23. The method of claim 20 wherein the at least one unreactive
dissociation reaction modifier includes CO.sub.2.
24. The method of claim 23 wherein the first chamber contents
consist essentially of nitrous oxide and CO.sub.2.
25. The method of claim 20 wherein the first chamber contents have
an equivalence ratio of less than 0.25.
26. The method of claim 20 additionally comprising the step of
introducing at least one of the at least one gas source material
and the at least one unreactive dissociation reaction modifier into
the first chamber in a solid form.
27. The method of claim 26 wherein the solid form of the at least
one of the at least one gas source material and the at least one
unreactive dissociation reaction modifier comprises a
cryogenically-formed solid.
28. The method of claim 27 wherein the at least one
cryogenically-formed solid comprises the at least one gas source
material.
29. The method of claim 28 wherein the at least one gas source
material comprises nitrous oxide.
30. The method of claim 27 wherein the at least one
cryogenically-formed solid comprises the at least one unreactive
dissociation reaction modifier.
31. The method of claim 30 wherein the at least one unreactive
dissociation reaction modifier comprises CO.sub.2.
32. The method of claim 27 wherein the cryogenically-formed solid
comprises a combination of at least the at least one gas source
material and the at least one unreactive dissociation reaction
modifier.
33. The method of claim 27 wherein the cryogenically-formed solid
comprises a combination of at least nitrous oxide and CO.sub.2.
34. The method of claim 20 wherein the first chamber additionally
contains a quantity of oxidative material.
35. The method of claim 20 wherein the initiating of an at least
partially liquefied inflation gas-resulting combination comprises
the step of reacting a quantity of a reactant material comprising a
gas generant material.
36. The method of claim 35 wherein the reactant material
additionally comprises an additive effective whereby, upon reaction
of the reactant material, NO.sub.x products are present in a
reduced amount as compared to reaction of the same reactant
material without the additive.
37. The method of claim 36 wherein the additive comprises ammonium
sulfate.
38. The method of claim 37 wherein the reactant material comprises
ammonium sulfate in an amount between about 2 and about 20
composition weight percent.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The subject matter of this application is related to prior
U.S. patent application Ser. No. 08/935,014 (now Rink et al., U.S.
Pat. No. 5,941,562, issued Aug. 24, 1999) and Ser. No. 08/935,016
(now Rink et al., U.S. Pat. No. 5,884,938, issued Mar. 23, 1999)
each respectively filed on Sep. 22, 1997, and U.S. patent
application Ser. No. 08/632,698, filed on Apr. 15, 1996 (now Rink,
U.S. Pat. No. 5,669,629, issued Sep. 23, 1997). The disclosures of
each these related patent applications is hereby incorporated by
reference herein and made a part hereof, including but not limited
to those portions which specifically appear hereinafter.
BACKGROUND OF THE INVENTION
[0002] This invention relates generally to inflatable restraint
systems and, more particularly, to the generation of inflation gas
used in such systems. More specifically, the invention relates to
inflation gas generation via a dissociating material and the
moderation thereof.
[0003] 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 the event of a collision. In such systems, an 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."
[0004] "Rise rate", i.e., the rate at which the gas output from an
inflator increases pressure, as measured when such gas output is
directed into a closed volume, is a common performance parameter
used in the design, selection and evaluation of inflator devices
for particular vehicular airbag restraint system installations. It
is commonly desired that an inflatable restraint airbag cushion
initially inflate in a relatively gradual manner soon followed by
the passage of inflation gas into the airbag cushion at a
relatively greater or increased pressure rate. An inflator
resulting in such inflation characteristics is commonly referred to
in the field as producing inflation gas in accordance with an "S"
curve.
[0005] 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 both
pyrotechnic inflators and compressed gas inflators. Unfortunately,
each of these types of inflator devices has been subject to certain
disadvantages.
[0006] For example, pyrotechnic inflators generally produce or
derive inflation gas via the combustion of a gas generating
material, i.e., a pyrotechnic. In practice, 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 costs associated therewith. In
addition, the temperature of the gases emitted from such inflator
devices can typically vary between about 500.degree. F.
(260.degree. C.) and 1200.degree. F. (649.degree. C.), dependent
upon numerous interrelated factors including the desired level of
inflator performance, as well as the type and amount of gas
generant material used therein, for example. Consequently, airbag
cushions used in conjunction with such inflator devices are
commonly constructed of or coated with materials which are
resistant to such high temperatures. For example, in order to
resist being burned through as a result of exposure to such high
temperatures, an airbag cushion such as constructed of nylon fabric
can be coated with neoprene or the like temperature resistant
material or include one or more neoprene coated nylon patches or
the like placed at the locations of the airbag cushion at which the
hot gas initially impinges. As will be appreciated, such specially
fabricated or prepared airbag cushions typically are more costly to
manufacture and produce.
[0007] The term "compressed gas inflator" is commonly used to refer
to the various inflators which contain a selected quantity of
compressed gas. For example, one particular type of compressed gas
inflator, commonly referred to as a "stored gas inflator," simply
contains a quantity of a stored compressed gas which is selectively
released to inflate an associated airbag cushion.
[0008] A second type of compressed gas inflator, commonly referred
to as a "hybrid inflator," typically supplies or provides inflation
gas as a result of a combination of stored compressed gas with the
combustion products resulting from the combustion of a gas
generating material, e.g., a pyrotechnic.
[0009] In the past, stored gas inflators have been at a
disadvantage, as compared to pyrotechnic inflators, in terms of
size, weight and/or cost. This is especially significant in view of
the general design direction toward relatively small, lightweight
and economical modem vehicle components and assemblies. In
particular, the need to store a gas within an inflator at
relatively high pressures typically results in the need for
thick-walled pressure vessels that tend to be more bulky, heavy and
costly than otherwise desired.
[0010] 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 disclose and relate to a new type of inflator device,
sometimes called a "fluid fueled inflator." 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 cushion. In one form of fluid fueled inflator, such a 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.
[0011] While such types of inflator devices can successfully
overcome, at least in part, some of the problems associated with
the prior types of inflator devices, there is a continuing need and
demand for further improved apparatus and techniques for inflating
an inflatable device such as an airbag.
[0012] In at least partial response thereto, further efforts have
led to the development of apparatus for and methods of gas
generation which at least in part rely on the decomposition or
dissociation of a selected gas source material for gas generation.
In particular, such developmental efforts have resulted in the
development of an inflator device which is at least in part the
subject of the above-identified patents: Rink, U.S. Pat. No.
5,669,629; Rink et al., U.S. Pat. No. 5,884,938; and Rink et al.,
U.S. Pat. No. 5,941,562. In one form of such newly developed
inflator device, inflation gas is produced or formed, at least in
part, via the decomposition or dissociation of a selected gas
source material, such as in the form of a compressed gas and such
as via the input of heat from an associated heat source supply or
device. Nitrous oxide is a preferred gas source material disclosed
in one or more of these patents. One or more of these patents
disclose that such an apparatus for and method of gas generation
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.
[0013] Nevertheless, there is a continuing need and demand for
still further improved apparatus and techniques for inflating an
inflatable device such as an airbag. In particular, there is an
ongoing need and demand for such apparatus and methods which
desirably favorably reduce one or more apparatus parameters such as
weight, cost, complexity, and size, for example. Further, there is
a continuing need and demand for such an improved apparatus and
associated or corresponding inflation techniques or methods such as
may either or both improve the safety and facilitate the ease of
operation and manufacture.
SUMMARY OF THE INVENTION
[0014] A general object of the invention is to provide an improved
apparatus and corresponding or associated method for inflating an
inflatable device.
[0015] A more specific objective of the invention is to overcome
one or more of the problems described above.
[0016] The general object of the invention can be attained, at
least in part, through an improved apparatus for inflating an
inflatable device and which apparatus includes a first chamber
having contents which include at least one gas source material
which, upon initiation, undergoes dissociation to form dissociation
products used to inflate the inflatable device. More specifically,
the apparatus is improved through the inclusion of at least one
unreactive dissociation reaction modifier selected from a group
consisting of CO.sub.2, Xe, SF.sub.6 and mixtures thereof. Such at
least one unreactive dissociation reaction modifier is stored at
least partially in liquefied form in fluid contact with the at
least one gas source material in the first chamber. In accordance
with a preferred embodiment of the invention, the at least one
unreactive dissociation reaction modifier is effective to moderate
at least one of the temperature and concentration of the at least
one gas source material in the first chamber upon the dissociation
of at least a portion of the at least one gas source material.
[0017] The prior art generally fails to provide an inflation
apparatus and techniques for inflating an inflatable device wherein
one or more apparatus parameters such as weight, cost, complexity,
and size, for example, is reduced or minimized to as great an
extent as may be desired. Further, the prior art generally fails to
provide an inflation apparatus and associated or corresponding
inflation techniques or methods such as improve either or both the
safety and ease of operation and manufacture to as great an extent
as may be desired.
[0018] The invention further comprehends a method for inflating an
inflatable safety device in a vehicle. In accordance with one
preferred embodiment of the invention, such method includes:
[0019] initiating an at least partially liquefied inflation
gas-resulting combination including at least one gas source
material and at least one unreactive dissociation reaction modifier
selected from a group consisting of CO.sub.2, Xe, SF.sub.6 and
mixtures thereof within a first chamber whereby at least a portion
of the at least one gas source material dissociates to form
dissociation products including at least one gaseous dissociation
product and the at least one unreactive dissociation reaction
modifier moderates at least one of the temperature and
concentration of the at least one gas source material in the first
chamber and
[0020] releasing inflation gas comprising at least a portion of the
at least one gaseous dissociation product and the at least one
unreactive dissociation reaction modifier from the first chamber to
inflate the inflatable safety device.
[0021] 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.
[0022] "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.
[0023] An "exothermic thermal dissociation" is a thermal
dissociation which liberates heat.
[0024] "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:
.phi.=(F/O).sub.A/(F/O).sub.S (1)
[0025] (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.2O). 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.)
[0026] 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.
[0027] References herein to a "pyrotechnic" material, refer to a
material which in its simplest form, consists of an oxidizing agent
and a fuel that produce an exothermic, self-sustaining reaction
when heated to the ignition temperature thereof.
[0028] References to the detection or sensing of "occupant
presence" are to be understood to refer to and include detection
and sensing of one or more of the size, weight, and/or positions of
a particular occupant under consideration.
[0029] References to an "adaptive" inflation system and the like
are to be understood to refer to inflatable device inflation
wherein selected inflatable devices are inflated or inflated in a
manner generally dependent on selected operating conditions such as
one or more of ambient temperature, occupant presence, seat belt
usage, seat position of the occupant and rate of deceleration of
the motor vehicle, for example.
[0030] The terms "gas" and "liquid" as used to describe the form of
matter, can be variously defined or described. For this reason a P,
v, T diagram (where P is the pressure, v is the specific volume,
and T is the temperature) provides a convenient means of
considering the form of a substance. As will be understood by those
familiar with thermodynamics, a phase of matter is generally
considered a gas if it can be condensed (i.e., the specific volume
of the material can be reduced) by a reduction of temperature while
maintaining a constant temperature. To the layman, the terms "gas",
"gases" and the like, as used herein, generally refer to a
substance that boils at conditions of atmospheric pressure and at a
temperature between absolute zero, i.e., -459.67.degree. F.
(-273.14.degree. C.), and about 68.degree. F. (20.degree. C.).
Eleven known chemical elements are gases: hydrogen, fluorine,
chlorine, helium, argon, nitrogen, oxygen, krypton, xenon and
radon. Further, many chemical compounds are, by this definition,
gases including: nitric oxide, ammonia, and carbon dioxide, for
example. In addition, one or more of either or both such gaseous
elements or compounds can be combined to form various gaseous
combinations such as air, for example.
[0031] Again, referring to P, v, T diagrams, a phase of matter can
generally be considered a liquid if it can be vaporized by a
reduction in pressure at constant temperature. Alternatively,
however, a liquid may more simply be described to a layman as a
substance (or a mixture of substances) that displays a "free" or
discernable surface. Those skilled in the art will understand that,
for a pure substance, a point exists (called the critical point)
representing the highest temperature and pressure at which a
species can exist in a gas/liquid equilibrium. At higher
temperatures and pressure, the liquid and gas phases cannot be
distinguished from one another because their properties become
equivalent. Accordingly, matter occupying this region is sometimes
called "supercritical" or simply a "fluid".
[0032] Finally, it will be understood by those skilled in the art
that when considering a P, v, T diagram for a mixture of
substances, the definition of the above regions becomes
increasingly complex. While a complete description of an entire
phase diagram for an arbitrary mixture of substances is well beyond
the scope of this discussion, it is to be understood that practice
of the invention is primarily concerned with co-existing mixtures
of liquids and gases.
[0033] In turn, the term "compressed gases" and the like, as used
herein, generally refers to those gaseous materials which are
stored at pressures greater than atmospheric pressure. Compressed
gases are defined (as in The Handbook of Compressed Gases, fourth
edition, Compressed Gas Association, Kluwer Academic Publishers,
Boston, Mass. (1999) ISBN-0-412-78230-8), as either nonliquefied or
liquefied compressed gases. Nonliquefied compressed gases are
generally defined as those gases that do not liquefy at ordinary
ambient temperatures, regardless of the pressure applied.
Typically, nonliquefied compressed gases have low boiling points,
generally less than about -130.degree. F. (-90.degree. C.), at
atmospheric pressure.
[0034] As used herein, the terms "liquefied gas," "compressed
liquefied gas" or the like are to be understood to refer to those
gases that become liquids at temperatures greater than -40.degree.
C. and at pressures up to about 4500 psia (31.20 MPa).
[0035] The term "heat of vaporization" refers to the quantity of
energy required to effect a change in the phase of a substance from
a liquid to a gas. In general, the heat of vaporization of a
material is proportional to the difference in relative volume of
the liquid and gas phases for the material. As will be appreciated,
different liquid materials are characterized by different heat of
vaporization values. In addition, as the heat of vaporization
parameter is commonly expressed in units of energy per unit mass,
the amount of the material in the liquid phase is an important
parameter in determining the required energy input for
liquid-containing inflator devices.
[0036] As described above, the chemical constituent, amount of
liquid and temperature can effect inflator performance. In
particular, since the density of a particular liquid is known or
can be measured, it is possible to relate the fraction of the total
volume of an inflator pressure vessel occupied by the liquid phase,
sometimes referred to herein as the "liquid fill fraction" or, more
simply as the "fill fraction," to the mass of liquid present within
the inflator. In practice, the use of the term fill fraction has
oftentimes proven a more convenient form of measurement or
differentiation of otherwise similar inflator devices.
[0037] 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.
BRIEF DESCRIPTION OF THE DRAWINGS
[0038] FIG. 1 is a partially in section, schematic drawing of an
airbag inflator in accordance with one preferred embodiment of the
invention.
[0039] FIGS. 2-4 are simplified, partially in section, schematic
drawings illustrating sequential operation of an airbag inflator in
accordance with one embodiment of the invention. More
specifically,
[0040] FIG. 2 illustrates the airbag inflator in a normal or a
"static" state.
[0041] FIG. 3 illustrates the airbag inflator shown in FIG. 2 but
now at an intermediate point in operation prior to the discharge of
inflation gas therefrom.
[0042] FIG. 4 illustrates the airbag inflator shown in FIG. 3 at a
later still point in the operation thereof.
[0043] FIG. 5 is a partially in section, schematic drawing of an
airbag inflator in accordance with an alternative preferred
embodiment of the invention.
[0044] FIG. 6 is a graphical depiction of tank pressure as a
function of time performance realized in Examples 1-3.
[0045] FIG. 7 is a graphical depiction of storage chamber pressure
as a function of time performance realized in Examples 1-3.
[0046] FIG. 8 is a graphical depiction of pressure versus
temperature for fluid mixtures in accordance with one embodiment of
the invention and an ideal gas at selected load densities.
DETAILED DESCRIPTION OF THE INVENTION
[0047] The present invention may be embodied in a variety of
different structures. As representative, FIG. 1 illustrates the
present invention as embodied in an apparatus, generally designated
by the reference numeral 10, in accordance with one embodiment of
the invention. Such a gas producing or supplying device can
advantageously be used to effect the inflation of an inflatable
device such as an inflatable vehicle occupant restraint, e.g., an
inflatable airbag cushion, (not shown). As described above, such a
gas producing or supplying device is commonly referred to as an
inflator.
[0048] While the invention is described below with particular
reference to a passenger side airbag inflator apparatus such as can
be used in association with 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 vehicles including, for example, airplanes,
and other types or kinds of airbag inflator apparatus for
automotive vehicles including, for example, driver side and side
impact airbag assemblies but also for the inflation of various
inflatable devices such as may be apparent to those skilled in the
art. With respect to automotive vehicles it will also be
appreciated that due to usual physical differences between
passenger, side impact and driver side airbag module assemblies,
including the typical difference in size with passenger side
airbags generally being much larger than those used in side impact
and driver side assemblies, the invention may have particular
initial utility in passenger side airbag inflator apparatus. In
addition, due to factors such as relatively large volume and
extended stand-up times associated with inflatable devices of or in
the form of inflatable curtains, inflation devices in accordance
with the invention are believed to have particular practicality for
use in conjunction with such inflatable devices, as are known in
the art.
[0049] Returning to FIG. 1, the inflator apparatus 10 includes a
first or storage chamber 12 that is filled and pressurized with
fluid contents, designated by the reference numeral 14, generally
effective to provide a gaseous inflation medium such as may be used
in the inflation of an associated inflatable device. In accordance
with a preferred embodiment of the invention, the fluid contents 14
include at least one gas source material which, upon initiation,
undergoes dissociation to form dissociation products used to
inflate the inflatable device, and at least one unreactive
dissociation reaction modifier, as described in greater detail
below.
[0050] Each of such at least one gas source material and at least
one unreactive dissociation reaction modifier is preferably in the
nature of a compressed gas or a compressed gas mixture. Such
compressed gases can be stored in gaseous, liquid or multi-phase
form (i.e., partially gaseous and partially liquid mixture). As
will be appreciated, the premium on size generally placed on modem
vehicle design, generally results in a preference for smaller sized
airbag inflators. In view thereof and the fact that the densities
for such compressed gas materials are significantly greater when in
a liquid, rather than gaseous form, storage of such compressed gas
materials primarily in a liquid form will typically be
preferred.
[0051] In view of the above, the first chamber 12 is sometimes
referred to herein as a gas/liquid storage chamber or as simply a
storage chamber and, in the case of an inflator operating with a
dissociative material, a "dissociative" chamber.
[0052] As disclosed in the above-identified 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:
[0053] 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);
[0054] hydrazines such as hydrazine (N.sub.2H.sub.4), mixtures of
hydrazine(s) and water, methyl derivatives of hydrazine, as well as
mixtures of such hydrazine materials with inert gas(es);
[0055] peroxides and peroxide derivatives such as methyl hyperoxide
(CH.sub.3OOH) 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
[0056] nitrous oxide (N.sub.2O) and mixtures of nitrous oxide with
inert gas(es), for example.
[0057] Generally, dissociative gas source materials used in the
practice of the invention are preferably:
[0058] a.) non-toxic and non-corrosive both in the pre- and post-
dissociation states;
[0059] 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;
[0060] 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
[0061] 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.
[0062] A currently preferred dissociative gas source material for
use in the practice of the invention is nitrous oxide (N.sub.2O).
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, the dissociation products produced or formed upon the
dissociation of nitrous oxide ideally are nitrogen and oxygen:
2N.sub.2O.dbd.2N.sub.2+O.sub.2 (2)
[0063] 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. As will be
appreciated, such oxygen may then be available for subsequent
reaction such as may result in further or enhanced inflation gas
production or formation.
[0064] It is to be understood that such nitrous oxide can be stored
in a gaseous, liquid or multi-phase form (i.e., partially gaseous
and partially liquid mixture), as may be desired in particular
applications or installations. In view of the above-identified
general preference for smaller sized airbag inflators 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.
[0065] As detailed below, it has been found generally desirable to
limit or otherwise control the concentration of the dissociative
gas source material within the chamber 12 through the inclusion of
at least one unreactive dissociation reaction modifier. Further,
such at least one unreactive dissociation reaction modifier is
preferably stored at least partially in liquefied form in fluid
contact with the at least one gas source material in the chamber
12.
[0066] In practice, it has been found that the rate of dissociation
of a gas source material, such as nitrous oxide, is generally
proportional to the concentration of the gas source material within
a vessel. Consequently, through the inclusion or presence of such
at least one unreactive dissociation reaction modifier with the at
least one gas source material in the chamber 12, the concentration
and thus the pressure generated or resulting in the chamber can be
desirably controlled or limited.
[0067] For example, the presence or inclusion of such a gas source
material at relatively high concentrations (e.g., in excess of
about 80 mole percent or more) can generally result in the
generation of significantly high pressures within the associated
vessel. In practice, pressure vessels required to be able to
withstand such high pressures must generally be made with increased
structural strength, such as by being made with walls of increased
thickness. However, increasing the thickness of such vessel walls
generally undesirably increases the weight of the associated
vessel.
[0068] Further, the inclusion or presence of such a gas source
material at relatively high concentrations can also result in
increased gas exit temperatures from the vessel. As those skilled
in the art will appreciate, various precautions may be desired or
required in or with inflation assemblies and methods which produce
higher temperature gases. For example, gas treatment assemblies
such as cooling screens or the like may need to be included or used
in conjunction therewith. The need for inclusion or presence of
such added features can undesirably impact apparatus parameters
such as cost, weight and size, for example.
[0069] In addition, the inclusion or presence the dissociative gas
source material nitrous oxide at such concentrations can possibly
result in other undesirable consequences such as, for example:
[0070] 1) relatively high emissions of undesirable products of
dissociation, such as either or both nitrogen dioxide (NO.sub.2)
and nitric oxide (NO), for example, and
[0071] 2) liberation of relatively high concentrations of heated
oxygen as a product of dissociation.
[0072] While the desirability storing or containing dissociative
gas source materials such as nitrous oxide at least partially in
liquefied form has been identified above, the liquid fill fraction
of such inflator devices can strongly affect inflator performance.
During inflator operation, the gas source material, e.g., nitrous
oxide, is heated from ambient temperature to the temperature at
which dissociation occurs. As such dissociation is understood to
primarily occur in the gaseous phase, then if the inflator
originally contains such gas source material in a liquid or
partially liquid form, the gas source material must be first
vaporized and then heated to the dessication temperature. As will
be appreciated, the additional heat required to vaporize the liquid
can be quite substantial. Thus, generally speaking, the amount of
heat required to be produced or supplied to the gas source material
can be significantly increased when the gas source material is
stored or contained in a liquid or partially liquid form.
[0073] Those skilled in the art and guided by the teachings herein
provided will appreciate that various unreactive dissociation
reaction modifiers can be used in accordance with the invention.
Preferred reaction modifiers for use in the practice of the
invention are desirably unreactive with the gas source material.
That is, while the reaction modifier desirably influences, i.e.,
slows, the rate of dissociation, the reaction modifier preferably
does not itself participate in the reactions occurring with the
chamber. In particular, preferred reaction modifiers in accordance
with the invention will not degrade or otherwise react when exposed
to anticipated inflator environments.
[0074] A general characteristic of matter in a liquid phase is that
such phase results in or provides a relatively greater density as
compared to the corresponding gaseous phase, at an equivalent
temperature. Thus, through the incorporation of matter in a liquid
phase, the mass of matter held or contained within a given volume
can be advantageously increased. As will be appreciated by those
skilled in the art and guided by the teachings herein provided,
significant size reductions can be realized as a result of the
increase in density afforded by storing or containing materials in
liquid, as compared to gaseous, form. Moreover, through such
utilization of the liquid phase of matter, such an increase in mass
can be realized without necessitating operation at higher (e.g.,
supercritical) pressures and may therefore afford desirable
advantages in inflator design.
[0075] Thus, preferred reaction modifiers for use in the practice
of the invention are desirably conducive to liquefaction at the
temperatures typically associated with airbag inflatable restraint
operation. For example, airbag inflators are typically or usually
designed to provide or result in desired operation over a
temperature range of about -40.degree. C. to about 110.degree. C.
Thus, the incorporation and use of reaction modifiers conducive to
liquefaction at such temperatures is generally preferred.
[0076] In view of the above, preferred reaction modifiers for use
in the practice of the invention can desirably be selected from the
group consisting of CO.sub.2, Xe, SF.sub.6 and mixtures thereof. A
particularly preferred reaction modifier for use in the practice of
the invention is carbon dioxide.
[0077] Those skilled in the art and guided by the teachings herein
provided will appreciate that carbon dioxide provides or exhibits a
number of qualities or characteristics which make such use thereof
particularly attractive, particularly when used in combination with
the dissociative gas source material nitrous oxide.
[0078] First, both carbon dioxide and nitrous oxide can be
relatively easily liquefied. For example, both carbon dioxide and
nitrous oxide can be liquefied at ambient temperature at relatively
low pressures. Since the density of both liquid phase carbon
dioxide and nitrous oxide are significantly greater than the
corresponding gaseous phases, the mass of material storable within
a given volume is significantly greater for the liquid, as compared
to the gaseous form. As a result, corresponding inflator devices of
having a significantly reduced envelope can be used.
[0079] Further, the storage pressure useable with such nitrous
oxide-carbon dioxide mixtures or combinations is relatively low,
when compared to typical inert gas mixtures. For example, a
135-gram load of a 50/50 molar fluid mixture of nitrous
oxide/carbon dioxide can be held in a 14 cubic inch (229.4 cubic
centimeters) volume at about 832 psi (5.74 MPa) at 20.degree. C. At
these conditions, the liquid fill fraction is about 60-65%. In
contrast, the storage of a 90/10 molar mixture of argon and helium
in the same volume (i.e., 229.4 cubic centimeters) and at the same
temperature (i.e., 20.degree. C.) results in a storage pressure of
about 6325 psia (43.61 MPa). Further, the storage of a 135-gram
load of a 20/70/10 molar mixture of nitrous oxide/argon/helium in a
229.4 cubic centimeter volume and at a temperature of 20.degree. C.
results in a storage pressure of about 5468 psia (37.7 MPa). As
will be appreciated, the use of lower storage pressures, such as
realizable with the subject fluid mixtures can advantageously
relieve the structural requirements for the vessel and, as a
result, a lighter weight design can be used.
[0080] Thus, preferred dissociation reaction modifiers, in
accordance with the invention, are generally effective to moderate
at least one of the temperature and concentration of the at least
one gas source material in the first chamber upon the dissociation
of at least a portion of the at least one gas source material. To
that end, it is generally preferred that such dissociation reaction
modifiers be included in the chamber 12 in a sufficient relative
amount such that the concentration of the gas source material,
e.g., nitrous oxide, within the chamber is no more than about 80
mole percent. In practice, the chamber 12 content of the reaction
modifier is preferably in the range of about 20 to about 90 molar
percent, more preferably the chamber 12 content of the reaction
modifier is in the range of about 30 to about 85 molar percent and,
even more preferably, the chamber 12 content of the reaction
modifier is in the range of about 40 to about 80 molar percent.
More particularly, operation within such ranges has been found to
generally result in suitable inflator performance for inflatable
restraint system applications over typical temperature design
specifications.
[0081] Further, the liquid fill fraction for the chamber 12 is
preferably in the range of about 10 to about 95 percent by volume,
more preferably, in the range of about 30 to about 85 percent by
volume and, even more preferably, in the range of about 50 to about
75 percent by volume, where such quoted fill fractions are at an
ambient temperature of 21.degree. C. For example, the use of
liquids in lesser relative amounts can significantly reduce or
minimize any benefits relating to the use of liquid rather than
gaseous forms. Further, the use of liquids in greater relative
amounts can undesirably introduce design difficulties such as
associated with potentially high internal pressures which may
result upon heating and resulting liquid expansion.
[0082] While the chamber 12 need not contain materials other than
at least one gas source material and at least one unreactive
dissociation reaction modifier, as described above (e.g., 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), the chamber may, if desired, additionally contain at
least certain other materials, as described below. For example, an
inert gas such as helium can be included with chamber contents to
facilitate leak checking of the inflator apparatus or, more
specifically, of the dissociative chamber thereof. Alternatively or
in addition, an inert gas, such as argon and helium, for example,
as well as materials such as nitrogen and carbon dioxide, which are
essentially inert under such processing conditions, or various
combinations thereof can be included such as to supplement the gas
produced or formed upon the dissociation of the nitrous oxide. For
example, in accordance with one alternative embodiment of the
invention, the chamber 12 contains about 50 mole percent nitrous
oxide, about 40 mole percent carbon dioxide and about 10 mole
percent helium as a liquid and gas mixture. It is to be understood,
however, that as helium does not generally liquefy under the
conditions here of interest, the inclusion thereof can
detrimentally significantly increase the fluid storage pressures
associated with the resulting assemblies.
[0083] Additionally or alternatively and as disclosed in the
above-identified Rink, U.S. Pat. No. 5,884,938, the chamber 12 may
contain a quantity of at least one radioactive isotope leak trace
material whereby fluid leakage from the chamber can be detected as
disclosed in therein.
[0084] In addition, if desired, the chamber 12 may additionally
contain a quantity of oxygen gas such as in molecular form and such
as may either or both beneficially or desirably supplement such
molecular oxygen as may be formed upon the dissociation of stored
or included nitrous oxide.
[0085] Still further, such a chamber 12 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, particularly useful 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.
[0086] 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.
[0087] The chamber 12 has been identified above in terms of a
storage chamber for the storage of a fluid which includes at least
one gas source material and at least one unreactive dissociation
reaction modifier, as described above. As described in greater
detail below, upon actuation and operation of the inflator 10, the
chamber 12 may also desirably serve to provide a volume within
which communication and heat transfer between combustion products
formed in or by the inflator 12 and the chamber contents may
desirably occur.
[0088] The chamber 12 is defined by an elongated generally
cylindrical sleeve 16, such as desirably in the form of an open
ended seamless tube. The sleeve 16 includes opposite first and
second open ends, 20 and 22, respectively. An assembly, herein
denominated a "diffuser assembly", generally designated by the
reference numeral 24, is formed or appropriately joined or attached
to the sleeve first end 20. A second end closure 26 is formed or
appropriately joined or attached to the sleeve second end 22. For
example and as shown in FIG. 1, the first sleeve end 20 can be
swagged and the diffuser assembly 24 joined thereto such as by
means of an inertial weld 30. Similarly, the second sleeve end 22
can be swagged and the second end closure 26 joined thereto such as
by means of an inertial weld 32.
[0089] The second end closure 26 includes a fill port 34, as is
known in the art, wherethrough materials can be passed into the
chamber 12. After the storage chamber 12 has been filled, the fill
port 34 can be appropriately blocked or plugged, as is known, such
as by a pin or ball 34a. As will be appreciated, such a fill port,
if included in the inflator apparatus, can alternatively be placed
or positioned, as may be desired and understood by those skilled in
the art. Thus, the broader practice of the invention is not
necessarily limited to the inclusion of a fill port or the position
or placement thereof.
[0090] The diffuser assembly 24 is a multi-component assembly such
as may, at least in part, serve as, contain or hold a chamber
opener 35, such as described in greater detail below and such as
actuatable to produce a discharge effective to open the first
chamber 12 by non-mechanical means, i.e., a discharge effective to
open the first chamber 12 without necessitating the use of or
reliance on mechanical opening devices such as projectiles or
piston members, for example. In particular embodiments of the
invention, such a discharge may be or take the form of a shock wave
or other pressure disturbance, a hot product gas or other elevated
temperature discharge or various combinations thereof, for example
and as will be appreciated by those skilled in the art and guided
by the teachings herein provided.
[0091] In accordance with one preferred embodiment of the
invention, the chamber opener 35 may desirably take the form of or
include a heat source such as may serve to initiate dissociation of
the gas source material. As described in greater detail below, a
suitable heat source for use in the practice of the invention may
desirably include a selected initiator device and an associated
supply of reactant material, such as in the form of a gas generant
reactant material. It is to be understood, however, that the
broader practice of the invention is not necessarily limited to the
use of a chamber opener in the form of a heat source let alone the
inclusion of a gas generant reactant material therein.
[0092] More specifically, the diffuser assembly 24 includes a
housing 36 such as in the general form of a hollow tube side wall
40 having open first and second ends, 42 and 44, respectively. The
side wall 40 includes a plurality of exit ports 46, wherethrough
the inflation gas from the inflator 10 and, particularly the
diffuser assembly 24, is properly dispensed into an associated
airbag cushion (not shown). Thus, the diffuser assembly 24 can
serve to facilitate direction and ballistic control of the
inflation fluid from the inflator 10 into the associated inflatable
airbag cushion. As will be appreciated by those skilled in the art,
the number and positioning of placement of the exit ports can be
selected to provide particular inflation performance
characteristics required or desired in or of a particular inflator
installation. In practice, four generally evenly circumferentially
spaced exit ports have been found sufficient to generally provide a
sufficiently even flow control of the inflation medium, from the
inflator into an associated airbag cushion and such as may
facilitate the desired inflation thereof.
[0093] To the housing first end 42, there is fitted or attached,
such as by means of a crimp 50, a first end closure 52. The first
end closure 52 includes an opening 54 therein wherethrough an
initiator device 56 such as forms, at least in part, a portion of
the chamber opener 35, is appropriately attached. Particular
initiator devices for use in the practice of the invention can
include 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 suitable
pyrotechnic charge.
[0094] The diffuser assembly 24 further includes, such as a part of
the chamber opener 35, a generant canister 60. The generant
canister 60 may advantageously be situated adjacent the first end
closure 52 and particularly the initiator device 56, such as to
facilitate the direct communication therewith by the initiator
device 56 upon the actuation thereof. Such a generant canister 60
can desirably be formed of a metal, such as steel, copper, brass,
aluminum or the like, for example. Further, such metal material of
construction may, if desired, include a suitable coating such as to
provide increased corrosion resistance, for example. In accordance
with one preferred embodiment of the invention, a generant canister
formed of steel with a tin coating has been found desirable and
useful.
[0095] Within the generant canister 60 there is housed a charge,
quantity or supply of a selected reactable gas generant material,
such as represented by the solid pyrotechnic gas generant pellets,
generally designated by the reference numeral 62. Gas generant
materials for use in the practice of the invention can suitably
take various forms including wafer, pellet and grain forms, for
example. As described in greater detail below, in accordance with
one preferred embodiment of the invention, the reactable gas
generant material is reacted to form reaction products effective to
rupture the generant canister and, upon heat transfer communication
with the chamber contents 14, result in the expansion of the fluid
such as to form an inflation medium for the inflation of an
associated airbag cushion.
[0096] Various reactable gas generant materials, such as known in
the art, can be used in the practice of the invention. In
particular, those materials which produce a relatively large
proportion of gaseous products and/or combust to produce a solid
slag residual particulate mass which is relatively easily removable
are generally preferred.
[0097] Preferred gas generant materials for use in the practice of
the invention can desirably include or contain a combustible fuel
and oxidizer combination. In accordance with one preferred
embodiment of the invention, the fuel is preferably composed of an
organic compound that is rich in nitrogen and oxygen content as
such fuel materials can desirably reduce the amount of oxidizer
required for combustion thereof. Specific examples of materials
useful as such fuels include but are not limited to: guanidine
nitrate, aminoguanidine nitrate, diamminoguanidine nitrate,
triaminoguanidine nitrate, nitroguanidine, and nitrotriazalone;
tetrazoles, bitetrazoles, and triazoles, and combinations thereof.
In addition, transition metal nitrate, chlorate, or perchlorate
complexes of organic compounds may be used as fuels. It is to be
understood and appreciated that the fuel component of such gas
generant materials may constitute one or more of such fuel
materials, as may be desired for particular applications. In
general, the fuel component will comprise about 10 to about 90
weight percent of the gas generant material formulation.
[0098] Specific examples of preferred oxidizer component materials
for use in the practice of the invention include but are not
limited to one or more of the following materials: ammonium
nitrate, ammonium perchlorate, transition metal ammine nitrates,
chlorates, and perchlorates; alkaline earth metal peroxides,
nitrates, perchlorates, and chlorates; transition metal peroxides,
nitrates, and perchlorates and alkali metal nitrates, chlorates,
and perchlorates. In general, the oxidizer component will comprise
about 20 to about 80 weight percent of the formulation.
[0099] In addition to fuel and oxidizer components such as
described above, gas generant materials for use in the practice of
the invention may desirably contain one or more additives such as
to provide or result in improved processing, enhanced slag
formation and reduced undesirable effluent gas production or
release. Exemplary processing aids include but are not limited to
organic binders, such as PVC, guar gum, polyacrylamide, polyacrylic
acid, polyvinyl alcohol, etc. Preferred pressing processing aids
include but are not limited to mica, calcium stearate, graphite,
molybdenum disulfide, etc. Enhanced slag formation additives
include but are not limited to silica, alumina, titania, zirconia,
clays, and talcs. Additives useful in reducing undesirable effluent
gases include but are not limited to alkali metal salts and alkali
metal salts or transition metal complexes of tetrazoles and related
nitrogen heterocycles. In practice, the content of such additives
in the preferred gas generant formulations used in the practice of
the invention generally does not exceed about 20 weight percent of
the formulation.
[0100] In addition, gas generant compositions used in the practice
of the invention may advantageously be coated with an ignition
compound to increase the ignitability of the formulation, if
desired. Useful ignition compounds typically include or contain a
metal or metal hydride fuel such as boron, magnesium, aluminum,
titanium hydride, or the like and an oxidizer typically an alkaline
earth metal peroxide, nitrate, chlorate or perchlorate or alkali
metal nitrate, chlorate, or perchlorate. In practice, igniter
levels of about 1 to about 5 percent of the finished pyrotechnic
composition on a weight basis have been found useful in particular
embodiments of the invention.
[0101] In accordance with certain preferred embodiments of the
invention, gas generant compositions used in the practice of the
invention desirably provide or result in a sufficiently high burn
rate with requiring the presence or application of an ignition
material coating. For example, burn rate-enhanced high gas yield
non-azide gas generants such as disclosed in prior U.S. patent
application Ser. No. 09/221,910, filed Dec. 28, 1998, whose
disclosure is hereby incorporated herein in its entirety, can
beneficially be used in the practice of the invention.
[0102] Thus, a preferred gas generant material for use in the
practice of the invention desirably contains between about 35 and
about 70 wt % of guanidine nitrate fuel, between about 30 and about
55 wt % copper diamine dinitrate oxidizer, between about 2 and
about 10 wt % silicon dioxide burn rate enhancing and slag
formation additive, and between about 0 and about 25 wt % ammonium
nitrate supplemental oxidizer.
[0103] A specific example of a preferred such gas generant material
for use in the practice of the invention also desirably contains or
includes a sufficient quantity or relative amount of ammonium
sulfate or the like additive effective to result in a gas generant
material which, upon reaction, produces or results in reduced
quantities or relative amounts of undesirable NO.sub.x products,
without significantly increasing the production of undesirable
SO.sub.x products (where x typically equals 1 or 2). Preferred such
gas generant materials desirably include or contain ammonium
sulfate in an amount between about 2 and about 20 composition
weight percent and, more preferably, in an amount up to about 15
composition weight percent, with such gas generant materials
including or containing ammonium sulfate in an amount between about
4 and about 12 composition weight percent being particularly
preferred. As will be appreciated, the presence or inclusion of
ammonium sulfate in greater than preferred or desired relative
amounts may result in reduced performance, such as measured by tank
pressure for the gas output therefrom, as well as possibly greater
than desired production of oxides of sulfur (SO.sub.x). Further,
the presence or inclusion of ammonium sulfate in lesser than
preferred or desired relative amounts may make it difficult to 1)
achieve significant reductions of undesirable NO.sub.x products and
2) ensure that the formulation attains sufficient compositional
uniformity to provide or result in uniform and consistent
results.
[0104] In practice, such ammonium sulfate-containing gas generant
formulations desirably reduce the formation of nitrogen dioxide
(NO.sub.2) from the subject inflator devices with no apparent
corresponding increase in nitric oxide (NO) formation. As those
skilled in the art will appreciate, the specific mechanisms
relating to the formation of NO.sub.x from the reaction of gas
generant materials can be extremely complex, particularly where
such formation occurs in the presence of either or both
hydrocarbons (such as formed by or resulting from guanidine
nitrate) and ammonia (such as formed by or resulting from ammonium
sulfate). At the present time, it is believed that the reduced
formation of NO.sub.2 is at least in part due to the liberation of
ammonia from the ammonium sulfate and, the subsequent reaction of
at least a portion of such ammonia with available nitrogen dioxide.
At the present time, the role of other chemical intermediate
species is unclear.
[0105] Further, formulations such as detailed above but without the
inclusion of additive material such as ammonium sulfate have been
found to generally result in reaction products containing
significantly higher or increased levels or relative amounts of
NO.sub.2. It is theorized that the ammonium group or resulting
constituent or product of ammonium sulfate is effective to tie-up
or otherwise occupy available nitrate groups (NO.sub.3), such as
present in ammonium nitrate but absent in ammonium sulfate. Thus,
the incorporation of an additive such as an ammonium phosphate,
such as (NH.sub.4)HPO, (NH.sub.4) HPO.sub.4, or
(NH.sub.4)H.sub.2PO.sub.4, for example, which also exhibits an
absence of the nitrate group, may produce or result in
substantially the same effect on the level or relative amount of
NO.sub.2 present in resulting reaction products.
[0106] Returning to FIG. 1, while the utilization and inclusion of
such a gas generant canister or housing 60 can facilitate inflator
assembly and handling during processing, it is to be understood
that the broader practice of the invention is not necessarily so
limited. For example, the invention can, if desired, be practiced
using an inflator wherein a selected gas generant material is
directly or otherwise appropriately placed and contained within an
associated diffuser housing.
[0107] The diffuser assembly 24 may, as shown, also include a
combustion screen 64 or the like such as to screen or otherwise
separate and desirably remove larger sized particulate material
such as may form upon reaction of the reactable gas generant
material. If included, such a combustion screen can be contained
within the generant canister 60, as shown. Alternatively, such a
combustion screen can be included within such a diffuser assembly
externally adjacent the gas generant canister or otherwise
downstream of the gas generant material.
[0108] The diffuser assembly 24 further includes, such as
adjacently positioned relative to the generant canister 60, a flow
control element 66. In this illustrated embodiment, the flow
control element 66 includes a base portion 70, a neck portion 72
and forms a fluid flow conduit 73, such as in the form of a nozzle.
In the illustrated embodiment, the flow control element 66 is
secured within the diffuser assembly 24 by means of a crimp 74
formed by the diffuser housing 36 adjacent the flow control element
base portion 70. In particular, the flow control element base
portion 70 forms an indentation 75 along the outer wall 76 thereof.
The indentation 75 is adapted to receive or otherwise cooperate
with the diffuser housing crimp 74 such as to desirably secure the
flow control element 66 within the diffuser assembly 24 in a
non-movable manner.
[0109] In the particularly illustrated embodiment, the fluid flow
conduit 73 is in the form of a nozzle having a discharge end 78
forming or having a discharge opening 79 wherethrough at least a
portion of the discharge from the chamber opener 35, e.g., reaction
products formed upon reaction of the reactable gas generant
material 62 are desirably directed and transmitted into
chamber-opening communication with the first chamber 12 and, in
turn, communication with the expandable fluid 14 contained
therewithin.
[0110] The first chamber 12 is enclosed at the sleeve first end 20
by means of a burst disk 80. As shown in FIG. 1, the housing second
end 44 includes or has formed thereat a rupture disk support collar
82 whereto the burst disk 80 can desirably be sealed around the
perimeter region thereof, generally designated by the reference
numeral 84, such as to desirably provide a leak-free seal for the
expandable fluid 14 normally contained or stored within the chamber
12. The burst disk 80, at a center portion 86 thereof, is desirably
supported at least in part by the flow conduit discharge end
78.
[0111] In practice, the burst disk 80 is typically in the form of a
thin disk such as fabricated or formed of a metal material such as
Inconel 600 or Inconel 625. In practice, such a disk may typically
have a thickness in the range of about 0.005 inch (0.127 mm) to
about 0.010 inch (0.254 mm), for example.
[0112] It is to be understood that a disk support arrangement such
as described above can advantageously result in the use of a burst
disk of reduced thickness as compared to similar arrangements but
wherein the associated disk lacks such support features. As will be
appreciated, the use of a disk of reduced thickness can facilitate
the desired rupture or opening of the disk, as described in greater
detail below.
[0113] Under high pressure proof testing such as pressures in the
range of about 4500 psi (31.0 MPa) to about 6000 psi (41.4 MPa),
the disk 80 deforms against the support provided by the flow
conduit discharge end 78 such as to provide or result in a first
sealing portion 87. Such burst disk deformation desirably results
in the disk 80 seating tightly against the flow conduit discharge
end 78. Such tight seating of the disk 80 against the flow conduit
discharge end 78 has been found to favorably influence the direct
opening of the burst disk 80 such as via the impingement thereon of
the reaction products produced by or resulting from the chamber
opener 56, such upon the reaction of the gas generant material 62
contained within the diffuser assembly 24. In particular, such
tight seating has in practice been found reliably sufficient
whereby the direct physical joining of the burst disk to the flow
conduit discharge end such as by means of an additional weld
joinder is generally not required in order for the assembly to
reliably result in the gas generant reaction products to be
directed into the chamber 12 rather than, for example, flowing
directly out of the diffuser assembly 24 such as via the exit ports
46 without first entering into the chamber 12. The avoidance of the
need for an additional weld joinder at the center portion 86
simplifies and reduces manufacturing costs and can beneficially
affect reliability associated with the manufacture and operation of
the resulting inflator apparatus. It is to be understood, however,
that the burst disk can, if desired, be joined or attached with or
to the nozzle such as by being welded, brazed or bonded thereto,
for example.
[0114] The disk 80 also deforms against the support provided by the
support collar 82 and, as identified above, can be sealed around
the perimeter region of disk such as to provide or result in a
second sealing portion 88.
[0115] It will be appreciated that the burst disk can, if desired,
include a score 89 such as to facilitate the desired opening of the
burst disk. More specifically, the inclusion of such a score can be
helpful in more specifically locating or positioning the site at
which the burst disk 80 will initially open upon the direction of
the gas generant reaction products from the fluid flow conduit 73
thereagainst.
[0116] As will be appreciated, such burst disk scoring can take
various forms such as known in the art. For example, such a burst
disk may include a score in the form of a cross or a circle, such
as may be desired or particularly suited for a specific
installation. Further, such a score may take the form of an
indentation, marking or otherwise reduction in the thickness of the
burst disk at selected area or portion thereof, as is known in the
art.
[0117] If desired and as shown, the diffuser assembly 24 may
additionally include a screen 90 or like device interposed between
the burst disk 80 and the exit ports 46. As will be appreciated,
the inclusion of such a screen or like device may be desired or
helpful in removing undesired particulates and the like from the
inflation gas prior to passage out of the inflator 10, through the
exit ports 46.
[0118] The manner of operation of an inflator apparatus in
accordance with the invention will now be described in greater
detail making reference to FIGS. 2-4. More specifically, FIGS. 2-4
schematically illustrate an inflator apparatus in accordance with
one preferred embodiment of the invention at various selected
points in the operation process thereof. In particular, FIG. 2
illustrates the inflator apparatus 210 in a "static" or what may be
termed its normal state, similar to that shown in FIG. 1. FIG. 3
illustrates the same inflator apparatus (now designated 210') at an
intermediate point in operation subsequent to actuation and prior
to the discharge of inflation gas therefrom. FIG. 4 illustrates the
same inflator apparatus (now designated by the reference numeral
210") at a subsequent or still later point in the operation
thereof.
[0119] The inflator apparatus 210, as shown in FIG. 2, is generally
the same as the inflator apparatus 10 shown in FIG. 1 and described
above. For example, the inflator apparatus 210 includes a first
chamber 212 filled and pressurized with an expandable fluid 214,
such as in the form including an at least partially liquefied
combination of a dissociative gas source material, e.g., nitrous
oxide, and at least one selected unreactive dissociation reaction
modifier, such as carbon dioxide, for example. The inflator
apparatus 210 also includes a diffuser assembly 224 adjacent the
first chamber 212.
[0120] The diffuser assembly 224 includes a housing 236 having
plurality of exit ports 246, a chamber opener 256, such as at least
in part in the form of an initiator device, a quantity or supply of
a selected reactable gas generant material 262, a combustion screen
264, a flow control element 266 such as includes a fluid flow
conduit 273 such as in the form of a nozzle and having a discharge
end 278 forming or having a discharge opening 279 wherethrough
reaction products formed upon reaction of the reactable gas
generant material are desirably directed and transmitted into
communication with the first chamber 212 and a burst disk 280. As
shown, a rupture disk support collar 282 desirably provides support
to a perimeter region 284 of the burst disk 280.
[0121] As described above relative to the embodiment illustrated in
FIG. 1, the burst disk 280, at a center portion 286 thereof, is
desirably supported by the flow conduit discharge end 279. Further,
the burst disk 280 in cooperation with the flow conduit 273 forms a
first sealing portion 287. Also, the disk support collar 282
provides a base to which the burst disk 280 can desirably be sealed
such as to provide a leak-free seal for the expandable fluid
normally contained or stored within the chamber 212. Further, the
burst disk 280 in association with the support collar 282 forms a
second sealing portion 288.
[0122] As will be appreciated, in FIGS. 2-4, certain
simplifications have been made to simplify illustration and
discussion. For example, FIGS. 2-4 do not illustrate the inclusion
of various welds or crimps such as may desirably be utilized in the
joining together of the component parts of the inflator device.
Further, FIGS. 2-4 do not illustrate the inclusion of a gas
generant canister such as described above relative to the inflator
apparatus 10.
[0123] Operation
[0124] Typical operation of the inflator apparatus 210, shown in
FIG. 2, is as follows:
[0125] Upon the sensing of a collision, an electrical signal is
sent to the chamber opener initiator 256. The initiator 256
functions to ignite the gas generant material 262. The gas generant
material 262 reacts, e.g., burns, to produce or form gaseous
reaction products. The gaseous reaction products are passed through
the screen 264, to the flow control element 266 and into the fluid
flow conduit 273.
[0126] The conduit 273 directs the gas generant reaction products
formed by or from the gas generant material 262 at or to the burst
disk 280 resulting, as shown in FIG. 3, in the opening of the
central portion 287 of the burst disk 280 when the pressure against
the burst disk rises to a predetermined level or range. More
specifically, the burst disk central portion 287 such as formed or
positioned adjacent the flow conduit discharge end 278 and the
opening 279 thereat, desirably ruptures or otherwise opens into or
towards the first chamber 212.
[0127] With the rupture or otherwise opening of the diffuser
assembly-supported burst disk central portion 287, the pressure
within the first chamber 212 desirably results to result in initial
opening of the burst disk second sealing portion 288. More
specifically, the edges of the burst disk second sealing portion
288 desirably petal or otherwise open into or towards the diffuser
assembly 224, as shown in FIG. 4.
[0128] With such opening of the burst disk second sealing portion
288, a portion of the quantity of unheated contents 214 is released
from the first chamber 212. In particular, such released fluid is
passed into the diffuser assembly 224 between the flow control
element 266 and the disk support collar 282 and ultimately out the
exits ports 246 into an associated inflatable vehicle occupant
restraint (not shown).
[0129] Simultaneously with such opening of the burst disk second
sealing portion 288, hot product gases produced upon combustion of
the gas generant material 262, flow into the first chamber 212 via
the flow conduit 273. As will be appreciated, the combustion
products entering into the first chamber 212 must overcome the
pressure gradient created by the contents 214 originally contained
within the first chamber 212. Based on the teachings and guidance
herein provided, conduit or nozzle design parameters such as
including the exit area thereof can be selected or determined based
on factors such as anticipated storage conditions within the
chamber 212.
[0130] As described above, the hot gases contact and communicate
with the remaining contents of the first chamber 212 resulting in
the heating of such fluid and the increasing of the temperature of
such fluid. The heated fluid and products formed or associated
therewith are correspondingly passed or communicated with or
through the diffuser assembly 224 and ultimately out the exits
ports 246 into the associated inflatable vehicle occupant
restraint.
[0131] FIG. 5 illustrates an airbag inflator 610 in accordance with
an alternative preferred embodiment of the invention. The inflator
610 is in some respects similar to the inflator 10 described above.
For example, the inflator 610, similar to the inflator 10, includes
a first or storage chamber 612 that is filled and pressurized with
an expandable fluid 614 effective to provide a gaseous inflation
medium.
[0132] As described above and in accordance with a preferred
embodiment of the invention, such fluid contents desirably include
at least one gas source material which, upon initiation, undergoes
dissociation to form dissociation products used to inflate the
inflatable device, and at least one unreactive dissociation
reaction modifier. Further, each of such at least one gas source
material and at least one unreactive dissociation reaction modifier
is preferably in the nature of a compressed gas or a compressed gas
mixture. Such compressed gases can be stored in gaseous, liquid or
multi-phase form (i.e., partially gaseous and partially liquid
mixture). As will be appreciated, the premium on size generally
placed on modem vehicle design, generally results in a preference
for smaller sized airbag inflators. In view thereof and the fact
that the densities for such compressed gas materials are
significantly greater when in a liquid, rather than gaseous form,
storage of such compressed gas materials primarily in a liquid form
is typically preferred.
[0133] The airbag inflator 610 differs from the inflator 10,
described above, in that the chamber 612, rather than being defined
by an elongated cylindrical sleeve having opposite first and second
open ends, is defined by a generally cylindrical closed end bottle
616. As shown, such a chamber bottle 616 includes an open first end
620 and a closed second end 622 and may desirably be formed in a
one piece construction. As will be appreciated, such a construction
desirably may serve to reduce or eliminate the number of welds
needed or used in the construction such as by eliminating the need
for the welding of an end closure such to close one or more ends of
the resulting storage chamber.
[0134] Further, while the invention has been described above with
respect to the use of a fill port or the like to permit the
introduction of materials within the storage chamber of inflator
assemblies of the invention, it is to be understood that the
broader practice of the invention is not so limited. For example,
if desired a fill technique such as disclosed in above-identified
commonly assigned U.S. Pat. No. 5,884,938, may be employed. In
accordance with such fill method, a cryogenically formed solid mass
of a particular desired material is sealed within such a closed end
bottle 616 without the use of a fill port. As a result, the
corresponding chamber need not include a fill port and a
potentially troublesome leak path from the chamber is
eliminated.
[0135] Moreover, the airbag inflator 610 includes a diffuser
assembly 624 of modified form, as described in greater detail
below. More particularly, the diffuser assembly 624, such as
generally described above relative to previously described
embodiments, is formed or appropriately joined or attached to the
bottle first end 620 such as by means of an inertial weld 630. The
diffuser assembly 624, similar to the above-described embodiments,
serve as, contains or holds a chamber opener 635, actuatable to
produce a discharge effective to open the first chamber 612 by
non-mechanical means. The diffuser assembly 624 includes a
cup-shaped housing 636 which includes a side wall 640, an open
first end 642 and a closed second end 644. The side wall 640
includes a plurality of exit ports 646, wherethrough the inflation
gas from the inflator 610 and, particularly the diffuser assembly
624, is properly dispensed into an associated airbag cushion (not
shown).
[0136] A diffuser housing end closure 652 is joined to the housing
first end 642 such as by means of an inertial weld 653. As will be
appreciated, such form or means of end closure joinder may assist
in one or more of the following respects: simplify construction,
reduce weight and reduce the costs associated therewith.
[0137] The diffuser assembly 624 includes, such as a part of the
chamber opener 635, an initiator device 656 and a generant canister
660, such as described above. Within the generant canister 660
there is housed a charge, quantity or supply of a selected
reactable gas generant material 662 such as described above and
such as may be reacted to form reaction products effective to
rupture the generant canister and, upon heat transfer communication
with the expandable fluid, result in the expansion of the fluid
such as to form an inflation medium for the inflation of an
associated airbag cushion.
[0138] The generant canister 660 also contains, includes or has
associated therewith a combustion canister cap 663 such as located
at the downstream end of the gas generant canister 660. The
inclusion of such a combustion canister cap or the like may be
desired in specific embodiments such as to lend structural support
to the gas generant canister 660 such to prevent or avoid rupture
or opening of the generant canister at a location other than
desired. In the illustrated inflator apparatus 610, the combustion
canister cap 663 is enclosed within the gas generant canister 660
and serves as a support or base for the associated combustion
screen 664 also contained within the canister 660.
[0139] The combustion canister cap 663 is desirably formed or
constructed of lightweight, high strength metal or the like such as
commonly employed in inflator constructions. The cap 663 include a
central orifice or opening 663a wherethrough the discharge from the
gas generant canister 660 can be desirably or otherwise properly
directed towards the chamber 612.
[0140] The diffuser assembly 624 also includes a flow control
element 665 of modified design. In particular, the flow control
element 665 is in the general form of an orifice plate formed such
as to close the second end 644 of the diffuser housing 636. The
flow control element 665 forms, includes or otherwise contains a
fluid flow conduit 673, in particular, the fluid flow conduit 673
is formed, at least in part, as an orifice 674. As will be
appreciated, an orifice plate may include such an orifice form
fluid flow conduit variously placed or positioned thereon. In
practice, however, such an orifice form fluid flow conduit
typically may be desirably centrally placed or positioned on the
orifice plate control element 665.
[0141] The orifice plate control element 665 also includes storage
chamber exit ports 677 wherethrough inflation medium from the
storage chamber 612 can be passed into the diffuser assembly 624
for subsequent passage out of the inflator 610 through the ports
646. As will be appreciated, the size, placement and number of
storage chamber exit port 677 can be desirably selected to
desirably and properly control the flow rate of inflation medium
from the inflator apparatus 610.
[0142] As shown, the storage chamber exit ports 677 and the flow
conduit orifice 673 are desirably sealed by means of a burst disk
680 applied onto the storage chamber side of the orifice plate
control element 665.
[0143] The gas generant canister 660, with its associated
underlying combustion canister cap 663, is designed for placement
in directed contact with the orifice plate control element 665 such
as to create or form a seal between the canister 660 and the flow
control element 665 and thereby avoid or prevent combustion
products formed by the reaction of the gas generant to exit from
the inflator 610 through the exit ports 646 without passing through
the orifice 674 and, in turn, into the chamber 612.
[0144] Alternatively, or in addition, a rupturable covering such as
in form of a metal foil, can be applied over the exit ports 646 to
prevent the undesired passage of material therethrough.
[0145] In FIG. 5, the combustion canister cap opening 663a and the
orifice plate control element orifice 674 are shown as having
identical diameters but the broader practice of the invention is
not necessarily so limited. For example, in certain applications it
may be desirable to make the orifice plate control element orifice
of smaller diameter than the combustion canister cap opening so as
to increase the pressure required to rupture the associated burst
disk. In addition, such differential sizing can serve to prevent
the possibility of combustion products formed by the reaction of
the gas generant to exit from the inflator through the exit ports
without passing through the orifice and, in turn, into the
associated storage chamber.
[0146] If desired and as shown, the diffuser assembly 624 can
include filters 681, such as in the form of metal screen, adjacent
to the exit ports 646 to prevent undesired passage of particulate
or burst disk fragments from the inflator 610 into an associated
airbag cushion.
[0147] The use of such a plate form fluid flow control element can
desirably reduce the length of the resulting inflator apparatus and
thus reduce the envelope required for the installation of such a
designed system into a vehicle. Further, the airbag inflator
apparatus 610 includes at least the following specific features or
modifications such as may desirably serve to improve performance,
reduce cost or both:
[0148] 1. closed end bottle construction;
[0149] 2. elimination of fill port;
[0150] 3. welded diffuser housing end closure; and
[0151] 4. modified form flow control element.
[0152] It is to be understood that inflator apparatus in accordance
with the invention can accordingly be provided in various
"adaptive" inflation system forms, such as will be apparent to
those skilled in the art and guided by the teachings herein
provided. With an adaptive inflatable restraint system, one or more
parameters such as the quantity, supply, and rate of supply of
inflation gas, for example, can be selectively and appropriately
varied dependent on one or more selected operating conditions such
as ambient temperature, occupant presence, seat belt usage, seat
position of occupant and rate of deceleration of the motor vehicle,
for example.
[0153] Further, those skilled in the art and guided by the
teachings herein provided, will appreciate that dissociation
reactions, such as involving the dissociation of nitrous oxide and
for the range of pressures here of interest, commonly follow a
unimolecular decomposition reaction mechanism. More specifically,
the rate of conversion of reactants to products for such reactions
is generally determinable using a unimolecular reaction expression
wherein the specific reaction rate coefficient is independent of
pressure. As a result, the rate of conversion of reactants to
products is essentially directly proportional to the reactant
concentration (e.g., nitrous oxide concentration) in the first
order. In contrast, combustion reactions (such as even those
involving combustion of a hydrocarbon with nitrous oxide) are
typically governed by bimolecular reaction mechanisms. Such
bimolecular reaction mechanisms are generally believed to be much
more sensitive to pressure effects and therefore reaction
parameters associated with such reactions, such as gas production
rate, internal pressure, rise rate, etc., are generally much more
difficult to control. Thus, dissociation-based gas supply devices,
such as described herein provide significant practical advantages
as compared to such combustion-based gas supply devices.
[0154] The present invention is described in further detail in
connection with the following examples which either or both
illustrate or simulate various aspects involved in the practice of
the invention. It is to be understood that all changes that come
within the spirit of the invention are desired to be protected and
thus the invention is not to be construed as limited by these
examples.
EXAMPLES
Examples 1-3
[0155] In these examples, three test inflators identical in
structure to the inflator illustrated in FIG. 1 were built. Each of
the test inflators included a generally cylindrical fluid flow
conduit nozzle (item 73 in FIG. 1) having a diameter of 0.323
inches (8.2 mm) and four circular exit ports (item 46 in FIG. 1)
each of which had a diameter of 0.201 inches (5.11 mm). Each of the
test inflators was filled with 140 grams of a mixture consisting of
50% nitrous oxide and 50% carbon dioxide. The internal volume of
the storage chamber in each of the test inflators was about 11.5
in.sup.3 (188.5 cm.sup.3), which resulted in a storage pressure of
about 860 psia (5.93 MPa) at a temperature of 21.degree. C. Each of
the test inflators contained a pyrotechnic generant load of 26.0
grams of roughly cylindrical pellets 0.25 inches.times.0.80 inches
(6.35 mm.times.20.32 mm). Given dissociation of 30% of the stored
nitrous oxide and gas generation from the pyrotechnic source, the
total expected molar output from each of the test inflators was 4.3
gmol.
[0156] Each of the test inflators was tested at one of three
different temperatures of operation, in accordance with TABLE
1.
1 TABLE 1 Example Temperature (.degree. C.) 1 -35 2 21 3 85
[0157] To ensure that each test inflator had achieved uniformity of
temperature, each inflator was conditioned at its particular test
temperature for two hours prior to test operation.
[0158] FIGS. 6 and 7 illustrate the performance realized with the
test inflators of EXAMPLES 1-3. More particularly, FIGS. 6 and 7
are graphical depictions of tank pressure and storage chamber
pressure, each as a function of time subsequent to inflator
actuation, respectively, for the inflators of EXAMPLES 1-3.
[0159] Discussion Of Results
[0160] As detailed below, the rate of pressure increase (rise rate)
as well as the maximum tank and storage chamber pressures were
typical of those observed with typical hybrid inflators. Such
performance was achieved using inflator devices in accordance with
the invention and which inflators: 1) are of significantly reduced
envelope, as compared to such typical hybrid inflators; 2) avoid
the inclusion or reliance on moving parts while maintaining desired
levels of performance (e.g., attain or achieve inflation discharge
in accordance with an "S" curve manner) and 3) are of simpler
design and construction, such as may reduce the cost associated
therewith.
[0161] The rate of pressure increase (rise rate) and the maximum
tank pressure, shown in FIG. 6 for the test inflators of each of
EXAMPLES 1-3, were typical of those inflators required for
passenger applications. As the flow through area of the flow
control element (i.e., the flow through area of the conduit nozzle)
and the size and number of exit ports strongly influence the rise
rate, it appears that the test inflators were properly dimensioned
in these respects.
[0162] The pressures measured within the fluid storage chamber are
shown in FIG. 7. It is interesting to note the dependence of the
initial pressures (at t=0 ms) on ambient temperature. As mentioned
above, given the internal volume and fluid load conditions within
the chamber, the initial pressure at a temperature of 21.degree. C.
is approximately 860 psia (5.93 MPa). However, at a temperature of
85.degree. C., the internal pressure is about 2000 psia (13.79
MPa), while at -35.degree. C., the initial pressure is only about
650 psia (4.48 MPa). As those skilled in the art and guided by the
teachings herein provided, at least in part due to the presence of
liquefied gases, the fluid behavior is highly non-ideal.
[0163] As shown by the sharp increase in the pressure traces shown
in FIG. 7, at a time interval of about three milliseconds following
actuation (i.e., t=3 ms), it appears that the structural integrity
of the nozzle burst disc ("first sealing portion") was exceeded and
hot combustion products began to flow into the fluid storage
chamber. The maximum pressures achieved in the storage chamber were
typical of those observed in typical hybrid inflators. In
particular, such performance was achieved with test inflators
having an internal storage chamber volume of 11.5 in.sup.3 (188.5
cm.sup.3) whereas typical gas filled hybrid inflators would,
dependent on the specific nature of the gases used therein, require
a gas storage volume of about 21 in.sup.3 (344.1 cm.sup.3) to
provide similar pressure performance.
Examples (Ex) 4-7 and Comparative Examples (Ce) 1-4
[0164] In EXAMPLES 4-7, the internal pressure versus temperature
behavior of a 100 cc (6.1 in.sup.3) inflator test fixture
containing a 50/50 molar mixture of nitrous oxide and carbon
dioxide in load densities of 0.539 g/cc, 0.649 g/cc, 0.704 g/cc,
and 0.795 g/cc, respectively, was monitored. The results are
illustrated in FIG. 8.
[0165] Given these load densities, the approximate liquid fill
fractions in these Examples at a temperature of 21.degree. C.
(70.degree. F.) were 60%, 78%, 85% and 100%, respectively.
[0166] From an examination of FIG. 8 it is clear that higher
loading densities may result in a more severe rise rate in pressure
as the temperature is increased. For example, in EX 6, the pressure
began to increase very sharply at a temperature of about 305 K
(32.degree. C.). On the other hand, the steep portion of the
pressure curve in EX 4 occurred at a temperature of about 315 K
(42.degree. C.). One will also observe that the rate of pressure
increase in EX 6 is greater, as compared to the rate of pressure
increase in EX 4. This difference is attributable to more liquid
being initially present in EX 6 as compared to EX 4.
[0167] As shown, as the system temperature increases, the pressure
also increases. However, when the liquid expands such that the
liquid occupies the entire available volume, subsequent increases
in pressure become more dramatic. As will be appreciated, this
effect will be realized sooner (i.e., occur at a lower temperature)
where the initial liquid fill fraction is greater.
[0168] FIG. 8 also illustrates, for COMPARATIVE EXAMPLES 1-4, the
internal pressure versus temperature behavior of a chamber which
contains an ideal gas at the load densities of 0.539 g/cc, 0.649
g/cc, 0.704 g/cc, and 0.795 g/cc, respectively.
[0169] FIG. 8 clearly illustrates the difference in pressure
performance for fluid mixtures in accordance with the invention (EX
4-7) and ideal gas behavior (CE 1-4). For example, for loading
densities generally preferred for automotive vehicle airbag
applications (e.g., loading densities in the range of about 0.50 to
about 0.70 g/cc) at a temperature of about 295 K, the liquefied gas
storage pressure is roughly about 3500 to about 4500 psia (about
24.1 to about 31.7 MPa) lower for the subject fluid mixtures, as
compared to that of ideal gas behavior.
[0170] It is to be understood that the discussion of theory, such
as the discussion of gas generant material inclusion of additive
material effective to result in a gas generant material which, upon
reaction, produces or results in reduces quantities or relative
amounts of undesirable NO.sub.x products, without significantly
increasing the production of undesirable SO.sub.x products (where x
typically equals 1 or 2) and the mechanism by which such additive
works or functions, for example, is included to assist in the
understanding of the subject invention and is in no way limiting to
the invention in its broader application.
[0171] Thus, the invention provides an inflation apparatus and
techniques for inflating an inflatable device wherein one or more
apparatus parameters such as weight, cost, complexity, and size,
for example, can desirably be reduced or minimized to a greater
extent than otherwise or previously possible or realizable while
providing required or desired performance capabilities.
[0172] 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.
[0173] 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.
* * * * *