U.S. patent application number 10/143383 was filed with the patent office on 2003-11-13 for airbag inflator with adaptive flow orifice.
Invention is credited to Larsen, Alan R., Roueche, Clark.
Application Number | 20030209894 10/143383 |
Document ID | / |
Family ID | 29400117 |
Filed Date | 2003-11-13 |
United States Patent
Application |
20030209894 |
Kind Code |
A1 |
Larsen, Alan R. ; et
al. |
November 13, 2003 |
AIRBAG INFLATOR WITH ADAPTIVE FLOW ORIFICE
Abstract
An inflator device having a chamber wherein a pressure dependant
gas generant reacts to produce inflation gas and at least one
orifice allowing the gas to pass and inflate an airbag. The at
least one orifice is defined at least in part by a shape memory
alloy having an austenite finishing temperature (T.sub.f). The at
least one orifice has a first fluid flow through area (A.sub.1)
when at a temperature less than T.sub.f and a second fluid flow
through area (A.sub.2) when at a temperature greater than T.sub.f.
The second fluid flow through area (A.sub.2) is less than the first
fluid flow through area (A.sub.1).
Inventors: |
Larsen, Alan R.; (Layton,
UT) ; Roueche, Clark; (Plain City, UT) |
Correspondence
Address: |
James D. Erickson
Autoliv ASP, Inc.
3350 Airport Road
Ogden
UT
84405
US
|
Family ID: |
29400117 |
Appl. No.: |
10/143383 |
Filed: |
May 10, 2002 |
Current U.S.
Class: |
280/736 |
Current CPC
Class: |
B60R 21/2644 20130101;
B60R 2021/26094 20130101 |
Class at
Publication: |
280/736 |
International
Class: |
B60R 021/26 |
Claims
What is claimed is:
1. In an inflator device having at least one orifice wherethrough
inflation gas can pass, an improvement comprising: the at least one
orifice at least in part defined by a shape memory alloy material
having an austenite finishing temperature (T.sub.f), wherein the at
least one orifice defines a first fluid flow through area (A.sub.1)
when at a temperature less than T.sub.f and a second fluid flow
through area (A.sub.2) when at a temperature greater than T.sub.f,
where A.sub.2<A.sub.1.
2. The improvement of claim 1 wherein the inflator device comprises
a plurality of orifices wherethrough inflation gas can pass and
wherein at least several of the plurality of orifices are at least
in part defined by the shape memory alloy material.
3. The improvement of claim 1 wherein the inflator device comprises
a chamber wherein a supply of a combustible gas generant material
is burned to produce the inflation gas.
4. The improvement of claim 3 wherein the combustible gas generant
material has a burn rate which is pressure dependent.
5. The improvement of claim 4 wherein the pressure dependency of
the burn rate of the combustible gas generant material, as
represented by n in the burn rate
expression:r.sub.b=k(P).sup.nwhere, r.sub.b is the burn rate of the
gas generant material, k is a constant, P is the combustion
pressure, and n is the slope of a linear regression line drawn
through a log-log plot of burn rate versus pressure, is at least
about 0.4 at 1000 psi.
6. The improvement of claim 1 wherein the at least one orifice is
additionally at least in part defined by at least one opening
formed in the inflator device and wherein the shape memory alloy
material forms a restrictor disposed adjacent the at least one
opening.
7. The improvement of claim 6 wherein the restrictor comprises an
opening aligned with the at least one orifice.
8. The improvement of claim 7 wherein the restrictor opening has a
first cross sectional area (a.sub.1) when the shape memory alloy
material is at a temperature less than T.sub.f and a second cross
sectional area (a.sub.2) when the shape memory alloy is at a
temperature greater than T.sub.f.
9. The improvement of claim 8 wherein the shape memory alloy
material of the restrictor is punched to form the restrictor
opening having the second cross sectional area (a.sub.2) and
wherein the restrictor opening in the shape memory alloy material
of the restrictor is subsequently extruded to have the first cross
sectional area (a.sub.1).
10. The improvement of claim 1 wherein the shape memory alloy
material has an austenite finishing temperature (T.sub.f) of at
least 90.degree. C.
11. The improvement of claim 10 wherein the shape memory alloy
material comprises an alloy including nickel and titanium.
12. The improvement of claim 1 wherein the shape memory alloy
material comprises a ternary alloy comprising copper, aluminum and
nickel.
13. The improvement of claim 1 wherein the shape memory alloy
material comprises a ternary alloy comprising copper, aluminum and
bromine.
14. The improvement of claim 1 wherein the shape memory alloy
material comprises a ternary alloy comprising iron, manganese and
silicon.
15. The improvement of claim 1 wherein the shape memory alloy
material has an austenite finishing temperature (T.sub.f) of
greater than 107.degree. C.
16. The improvement of claim 1 wherein the at least one orifice
comprises a circular shape.
17. The improvement of claim 1 wherein the at least one orifice is
an orifice wherethrough inflation gas exits the inflator
device.
18. The improvement of claim 1 wherein the at least one orifice is
an orifice internally within the inflator device.
19. An airbag inflator device comprising: a first chamber wherein a
supply of a combustible gas generant material reacts to produce gas
and an orifice assembly in fluid communication with the first
chamber and defining at least one of orifice wherethrough at least
a portion of the produced gas can pass, the orifice assembly
comprising at least one inflator device opening and a restrictor
disposed adjacent the at least one inflator device opening, the
restrictor at least in part defined by a shape memory alloy
material having an austenite finishing temperature (T.sub.f)
whereby the at least one orifice defines a first fluid flow through
area (A.sub.1) when at a temperature less than T.sub.f and a second
fluid flow through area (A.sub.2) when at a temperature greater
than T.sub.f, where A.sub.2<A.sub.1.
20. The airbag inflator device of claim 19 wherein the inflator
device comprises a plurality of orifices wherethrough inflation gas
can pass and wherein at least several of the plurality of orifices
are at least in part defined by the shape memory alloy
material.
21. The airbag inflator device of claim 19 wherein the combustible
gas generant material has a burn rate pressure dependency,
represented by n in the burn rate
expression:r.sub.b=k(P).sup.nwhere, r.sub.b is the burn rate of the
gas generant material, k is a constant, P is the combustion
pressure, and n is the slope of a linear regression line drawn
through a log-log plot of burn rate versus pressure, of at least
about 0.4 at 1000 psi.
22. The airbag inflator device of claim 19 wherein the restrictor
comprises an opening aligned with the at least one orifice.
23. The airbag inflator device of claim 22 wherein the restrictor
opening has a first cross sectional area (a.sub.1) when the shape
memory alloy material is at a temperature less than T.sub.f and a
second cross sectional area (a.sub.2) when the shape memory alloy
is at a temperature greater than T.sub.f.
24. The airbag inflator device of claim 23 wherein the shape memory
alloy material of the restrictor is punched to form the restrictor
opening having the second cross sectional area (a.sub.2) and
wherein the restrictor opening in the shape memory alloy material
of the restrictor is subsequently extruded to have the first cross
sectional area (a.sub.1).
25. The airbag inflator device of claim 19 wherein the shape memory
alloy material has an austenite finishing temperature (T.sub.f) of
at least 90.degree. C.
26. The airbag inflator device of claim 19 wherein the shape memory
alloy material has an austenite finishing temperature (T.sub.f) of
greater than 107.degree. C.
27. The improvement of claim 19 wherein the at least one orifice is
an orifice wherethrough the produced gas exits the inflator
device.
28. The improvement of claim 19 wherein the at least one orifice is
an orifice internally within the inflator device and wherethrough
the produced gas exits the first chamber.
29. A self-regulating inflation gas rate flow inflator device
comprising: a first chamber wherein a supply of a combustible gas
generant material having a burn rate which is pressure dependent is
burned to form a product gas and at least one orifice wherethrough
at least a portion of the product gas can pass, the at least one
orifice at least in part defined by a shape memory alloy material
comprises a ternary alloy comprising copper, aluminum and one of
nickel and bromine, the shape memory alloy having an austenite
finishing temperature (T.sub.f) of at least 90.degree. C., wherein
the at least one orifice defines a first fluid flow through area
(A.sub.1) when at a temperature less than T.sub.f and a second
fluid flow through area (A.sub.2) when at a temperature greater
than T.sub.f, where A.sub.2<A.sub.1.
30. The device of claim 29 wherein the inflator device comprises a
plurality of orifices wherethrough inflation gas can pass and
wherein at least several of the plurality of orifices are at least
in part defined by the shape memory alloy material.
31. The device of claim 29 wherein the pressure dependency of the
burn rate of the combustible gas generant material, as represented
by n in the burn rate expression:r.sub.b=k(P).sup.nwhere, r.sub.b
is the burn rate of the gas generant material, k is a constant, P
is the combustion pressure, and n is the slope of a linear
regression line drawn through a log-log plot of burn rate versus
pressure, is at least about 0.4 at 1000 psi.
32. The device of claim 29 wherein the at least one orifice is
additionally at least in part defined by at least one opening
formed in the inflator device and wherein the shape memory alloy
material forms a restrictor disposed adjacent the at least one
opening.
33. The device of claim 32 wherein the restrictor comprises an
opening aligned with the at least one orifice.
34. The device of claim 33 wherein the restrictor opening has a
first cross sectional area (a.sub.1) when the shape memory alloy
material is at a temperature less than T.sub.f and a second cross
sectional area (a.sub.2) when the shape memory alloy is at a
temperature greater than T.sub.f.
35. The device of claim 34 wherein the shape memory alloy material
of the restrictor is punched to form the restrictor opening having
the second cross sectional area (a.sub.2) and wherein the
restrictor opening in the shape memory alloy material of the
restrictor is subsequently extruded to have the first cross
sectional area (a.sub.1).
36. The improvement of claim 29 wherein the at least one orifice is
an orifice wherethrough inflation gas exits the inflator
device.
37. The improvement of claim 29 wherein the at least one orifice is
an orifice internally within the inflator device.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates generally to inflators such as for
use in inflating inflatable restraint airbag cushions to provide
impact protection to occupants of motor vehicles. More
particularly, the invention relates to inflators which rely
primarily on reaction of a combustible material for the production
of an inflation gas and such as may provide a gas flow orifice for
adaptive inflation gas output.
[0002] It is well known to protect a vehicle occupant using a
cushion or bag, e.g., an "airbag," that is inflated or expanded
with gas when the vehicle encounters sudden deceleration, such as
in the event of a collision. In such systems, the airbag cushion is
normally housed in an uninflated and folded condition to minimize
space requirements. Upon actuation of the system, the cushion
begins being 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."
[0003] Various types of inflator devices have been disclosed in the
art for the inflation of an airbag such as used in inflatable
restraint systems. One type of known inflator device derives
inflation gas from a combustible pyrotechnic gas generating
material which, upon ignition, generates a quantity of gas
sufficient to inflate the airbag.
[0004] In general, the burn rate for a gas generant composition can
be represented by the equation (1), below:
r.sub.b=k(P).sup.n (1)
[0005] where,
1 r.sub.b = burn rate (linear) k = constant P = pressure n =
pressure exponent, where the pressure exponent is the slope of a
linear regression line drawn through a log-log plot of burn rate
versus pressure.
[0006] As will be appreciated, the pressure exponent generally
corresponds to the performance sensitivity of a respective gas
generant material, with lower burn rate pressure exponents
corresponding to gas generant materials which desirably exhibit
corresponding lesser or reduced pressure sensitivity.
[0007] Typical pyrotechnic-based inflator devices commonly include
or incorporate certain component parts including, for example: a
pressure vessel wherein the pyrotechnic gas generating material is
burned; various filter or inflation medium treatment devices to
properly condition the inflation medium prior to passage into the
associated airbag cushion; and a diffuser to assist in the proper
directing of the inflation medium into the associated airbag
cushion.
[0008] To date, sodium azide has been a commonly accepted and used
gas generating material. While the use of sodium azide and certain
other azide-based gas generant materials meets current industry
specifications, guidelines and standards, such use may involve or
raise potential concerns such as involving handling, supply and
disposal of such materials. Further, economic and design
considerations have also resulted in a need and desire for
alternatives to azide-based pyrotechnics and related gas generant
materials. For example, interest in minimizing or at least reducing
overall space requirements for inflatable restraint systems and
particularly such requirements related to the inflator component of
such systems has stimulated a quest for gas generant materials
which provide relatively higher gas yields per unit volume as
compared to typical or usual azide-based gas generants. Still
further, automotive and airbag industry competition has generally
lead to a desire for gas generant compositions which satisfy one or
more conditions such as being composed of or utilizing less costly
ingredients or materials and being amenable to processing via more
efficient or less costly gas generant processing techniques.
[0009] As a result, the development and use of other suitable gas
generant materials has been pursued. Through such efforts, various
azide-free pyrotechnics have been developed for use in such
inflator device applications including at least some which have or
exhibit a relatively high burn rate pressure dependency, e.g., have
a burn rate pressure exponent of 0.4 or more, at 1000 psi.
[0010] Typical pyrotechnic-based inflators involve the reaction of
a gas generant to form an inflation gas which is released from the
inflator device to effect the desired inflation of an associated
airbag cushion. The rate at which inflation gas is produced or
formed in an inflator is typically a significant factor in the rate
at which an associated airbag cushion is inflated. While a rapid or
high inflation rate is generally required in order to achieve
inflation and deployment of an associated airbag cushion in order
to provide desired vehicle occupant protection, efforts have been
directed to reduce the mass flow rate of inflation gases into the
airbag cushion during the initial stages of deployment such as to
minimize or avoid the risk of injury to a vehicle occupant who are
out of the desired traveling position (with such vehicle occupants
often referred to as "out of position occupants").
[0011] Airbag installations providing a slower initial deployment
rate, also referred to as low onset inflation, followed by an
increased deployment rate can have the benefit of providing a more
gradual initial deployment of the associated airbag cushion into
the occupant-containing vehicle compartment yet still achieve
desired full or complete inflation within the desired time frame.
Current low onset inflation is generally best achieved via
two-stage inflator devices. However, two-stage inflators commonly
require two electrical initiators and are generally more expensive
than single stage inflator devices.
[0012] Methods of obtaining low onset inflation via single stage
inflators have generally not provided the desired deployment rate
curve. Such single-stage inflator methods include: inhibiting the
surface of the gas generant such as by coating or otherwise
covering a surface portion or side of a gas generant tablet;
initially cooling the inflation gasses in a heat sink that
saturates quickly, wherein the saturated heat sink will no longer
cool the gasses resulting in an increased pressure; methods for
altering generant grain shape; and other methods that alter the
ignition conditions to provide a non-synchronous ignition of all
gas generant material.
[0013] In view of the above, there is a need and a demand for
improved arrangements and methods for providing low onset inflation
of airbag cushions, particularly with single stage inflator devices
such as employ only a single electrical initiator. Further, there
is a need and a demand for combustible material-based inflator
devices which provide or result in a slower initial rate of
deployment followed by an increase in deployment rate. Further,
there is a need and a demand for such an inflator device which more
freely permits the use of azide-free pyrotechnics, such as those
which have or exhibit a relatively high burn rate pressure
dependency. Still further, there is a need and a demand for such a
low onset inflator device that is less costly to manufacture or
produce. Yet still further, there is a need and a demand for single
stage inflator devices that provide or result in low onset
inflation without requiring the inclusion of complex or costly
control devices or arrangements.
SUMMARY OF THE INVENTION
[0014] A general object of the invention is to provide an improved
inflator and associated or corresponding methods of supplying
inflation gas.
[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 inflator device having at least
one orifice wherethrough inflation gas can pass. In accordance with
one preferred embodiment of the invention, the at least one orifice
is at least in part defined by a shape memory alloy material having
an austenite finishing temperature (T.sub.f), wherein the at least
one orifice defines a first fluid flow through area (A.sub.1) when
at a temperature less than T.sub.f and a second fluid flow through
area (A.sub.2) when at a temperature greater than T.sub.f, where
A.sub.2<A.sub.1.
[0017] As described in greater detail below, shape memory alloys in
accordance with the invention can be initially formed into a first
shape and subsequently deformed or stressed into a second shape
while in a martensite phase. When heated to a temperature where the
shape memory alloy forms the austenite phase, referred to as the
austenite finishing temperature (T.sub.f), the shape memory alloy
generally returns to the prestressed or unmodified martensite
shape.
[0018] In accordance with a preferred practice of the invention,
adaptability in inflator output is achieved through change in cross
sectional area of the orifice such as to result in a change in
combustion pressure. In particular, practice of the invention in
conjunction with a gas generant material, e.g., pyrotechnic, having
a burn rate which is pressure dependant as herein defined, results
in changes in combustion pressure correspondingly changing the burn
rate of the gas generant, thus altering or adapting the inflator
output, e.g., inflation gas mass flow rate. For example, reducing
the inflator orifice area raises the combustion pressure within the
gas production chamber which, in turn, raises the burn rate of the
gas generant material which increases the inflation gas mass flow
rate from the inflator. Correspondingly, increasing the inflator
orifice area reduces the combustion pressure within the gas
production chamber which, in turn, reduces the burn rate of the gas
generant material which decreases the inflation gas mass flow rate
from the inflator. Such performance behavior is opposite to that of
at least certain prior art inflator devices such as certain stored
gas inflators which incorporate an adjustable exit area. In
particular, such prior art inflator devices typically experience a
reduction in inflation gas mass flow rate with a reduction in exit
area and an increase in inflation gas mass flow rate with an
increase in exit area.
[0019] The prior art generally fails to provide inflator devices
with low onset inflation that are of as simple a design and
construction as may be desired. In particular, the prior art fails
to provide such a low onset inflator device which relies largely or
primarily on the reaction of a combustible material, e.g., a
pyrotechnic, especially such as various azide-free pyrotechnics
which have or exhibit a relatively high burn rate pressure
dependency, to form or produce inflation gas. Further, the prior
art generally fails to provide adaptive performance inflatable
restraint assembly combinations which incorporate shape memory
alloy technology to change or alter the internal pressure of the
combustion chamber thereby increasing gas mass flow rate as the gas
generant reacts.
[0020] The invention further comprehends an airbag inflator device
with a first chamber wherein a supply of a combustible gas generant
material reacts to produce gas and an orifice assembly in fluid
communication with the first chamber. The orifice assembly defines
at least one orifice wherethrough at least a portion of the
produced gas can pass. The orifice assembly includes at least one
inflator device opening and a restrictor disposed adjacent the at
least one opening. The restrictor device is at least in part
defined by a shape memory alloy material with an austenite
finishing temperature (T.sub.f). The at least one orifice defines a
first fluid flow through area (A.sub.1) when at a temperature less
than T.sub.f and a second fluid flow through area (A.sub.2) when at
a temperature greater than T.sub.f. The second fluid flow through
area (A.sub.2) is less than the first fluid flow through area
(A.sub.1) allowing for adaptability in inflator output.
[0021] The invention still further comprehends a self-regulating
inflation gas rate flow inflator device with a first chamber for
burning a supply of a combustible gas generant material having a
burn rate which is pressure dependent to form a product gas and at
least one orifice wherethrough at least a portion of the product
gas can pass. The at least one orifice is preferably at least in
part defined by a shape memory alloy material comprising a ternary
alloy including copper, aluminum and one of nickel and bromine. The
shape memory alloy has an austenite finishing temperature (T.sub.f)
of at least 90.degree. C. and the at least one orifice defines a
first fluid flow through area (A.sub.1) when at a temperature less
than T.sub.f and a second fluid flow through area (A.sub.2) when at
a temperature greater than T.sub.f. The second fluid flow through
area (A.sub.2) is less than the first fluid flow through area
(A.sub.1) allowing for adaptability in inflator output.
[0022] As used herein, references to a "shape memory alloy" are to
be understood to refer to metal alloys characterized by the ability
to be quickly restored to a prestressed shape at a predetermined
temperature that causes a change from a martensite phase to an
austenite phase. Shape memory alloys can be formed into a first
shape and then stressed into a second shape while in the martensite
phase. Upon heating the alloy material to the austenite phase, the
alloy is suitably returned to the prestressed martensite shape.
[0023] As used herein, references to "austenite finishing
temperature" generally refer to the temperature at which the
martensite to austenite reaction is completed upon heating.
[0024] As used herein, references to "self-regulating" inflation
gas flow inflator devices are to be understood to generally refer
to those inflator devices which require no external sensors or
other control equipment to adjust the gas flow from the inflator
device to an associated airbag cushion. Correspondingly, the
"self-regulating" function of shape memory alloys in accordance
with a preferred embodiment of the invention is dependant on
predetermined temperatures and therefore desirably requires no
additional sensors or control equipment.
[0025] Further, references herein to a combustible gas generant
material, e.g., a pyrotechnic, having a burn rate which is
"pressure dependent" are to be understood to refer to those
combustible gas generant materials having a relatively high burn
rate pressure dependency. In the context of the invention, such a
relatively high burn rate pressure dependency is generally
signified by a burn rate pressure exponent of at least about 0.4 at
1000 psi, preferably by a burn rate pressure exponent in the range
of about 0.4 to about 0.6, at 1000 psi.
[0026] 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
[0027] FIG. 1 is a simplified, schematic drawing of an inflator in
accordance with one preferred embodiment of the invention, shown
partially in section.
[0028] FIG. 2 is a simplified fragmentary cross-sectional,
schematic drawing of an orifice of an inflator in accordance with
one preferred embodiment of the invention.
[0029] FIG. 3 is a simplified fragmentary cross-sectional,
schematic drawing of an orifice of an inflator in accordance with
one preferred embodiment of the invention.
[0030] FIG. 4 is a simplified, schematic drawing of an inflator in
accordance with another preferred embodiment of the invention,
shown partially in section.
DETAILED DESCRIPTION OF THE INVENTION
[0031] The present invention provides an improved airbag inflator
device having an orifice with a fluid flow through area adaptable
at a predetermined temperature resulting in an increase in gas flow
therethrough and such as to an associated airbag, for example. FIG.
1 illustrates an inflator device, generally designated with the
reference numeral 10, in accordance with one preferred embodiment
of the invention. While FIG. 1 represents a simplified driver side
airbag inflatable restraint system installation, it will be
understood that the invention has general applicability to other
types or kinds of inflatable restraint system installations
including other types or kinds of airbag inflatable restraint
system installations including, for example, passenger side, and
side impact airbag assemblies such as for automotive vehicles
including vans, pick-up trucks, and particularly automobiles. The
inflator device of FIG. 1 is simplified to facilitate illustration
and understanding and does not show various inflator device
internals such as including filters or the like. As will be
appreciated, such inflator device internals are generally well
known in the art and do not generally form limitations on the
broader practice of the invention.
[0032] As shown in FIG. 1, the inflator device 10 has a generally
cylindrical external outline and includes a housing assembly 12
formed of two structural components, i.e., a lower shell or base
portion 14 and an upper shell or diffuser cap portion 16, such as
may be desirably fabricated of steel and appropriately joined or
fastened together such as via application of an appropriate welding
operation. The housing assembly 12 at least in part defines a
chamber 20 (sometimes referred to as a combustion chamber). A
combustible gas generant material, schematically shown and
designated by the reference numeral 24, is located within the
chamber 20 of the inflator device 10. The combustible gas generant
material 24 is ignited by an ignition device, schematically shown
and designated by the reference numeral 26. Upon ignition, the gas
generant material 24 reacts within the chamber 20 to produce an
inflation gas for inflating an associated airbag cushion (not
shown).
[0033] The gas generant material 24 and ignition device 26 are
schematically represented in FIG. 1 to facilitate illustration and
comprehension of the invention. Those skilled in the art and guided
by the teachings herein provided will appreciate that various forms
or types of gas generant materials and ignition devices can
desirably be used in the practice of the invention and the broader
practice of the invention is not necessarily limited to specific
forms or types of gas generant materials and ignition devices.
[0034] According to one embodiment of the invention, at least upon
actuation of the inflator device 10, the contents of the chamber 20
are in fluid communication with at least one and preferably a
plurality of orifice assemblies 30. Each of the orifice assemblies
30 defines at least one orifice 32 through which at least a portion
of the produced gas can pass. As shown and in accordance with one
preferred embodiment of the invention, the inflator device 10
includes a plurality of orifices 32 wherethrough inflation gas can
pass. In this illustrated embodiment, the gas passing through the
orifices exits the inflator device 10 such as to inflate an
associated airbag cushion (not shown). Consequently such orifice
assemblies and orifices are sometimes referred to as "external"
orifice assemblies and "external" orifices, respectively.
[0035] While the invention can desirably be practiced employing
orifices 32 which have a generally circular cross section, those
skilled in the art and guided by the teachings herein will
appreciate that the invention can be practiced employing orifice
assemblies, and orifices, in various numbers, sizes, shapes, and
layouts, as may be desired for particular installations.
[0036] In one embodiment of this invention, the combustible gas
generant material 24 has a burn rate which is pressure dependent.
In general, the burn rate for such gas generant material can be
represented by the equation (1), below:
r.sub.b=k(P).sup.n (1)
[0037] where, r.sub.b is the burn rate of the gas generant
material, k is a constant, P is the combustion pressure, and n is
the pressure exponent, where the pressure exponent is the slope of
a linear regression line drawn through a log-log plot of burn rate
versus pressure.
[0038] While the invention may, if desired, be practiced employing
various gas generant materials, as are known in the art, the
invention has particular perceived utility when used in conjunction
with those gas generant materials, e.g., pyrotechnics, which have
or exhibit a relatively high burn rate pressure dependency, e.g.,
have a burn rate pressure exponent of 0.4 or more, at 1000 psi,
such as described above. Such gas generant materials include
various newly developed azide-free pyrotechnics. The metal ammine
nitrate-containing azide-free gas generant compositions disclosed
in U.S. patent application Ser. No. 09/221,910, filed Dec. 28,
1998, now U.S. Pat. No. 6,103,030, issued Aug. 15, 2000, and whose
disclosure is fully incorporated herein, are examples of one
preferred form of an azide-free gas generant composition having
such a high burn rate pressure dependency for use in the practice
of the invention. As disclosed in that U.S. patent, one
particularly preferred gas generant composition in accordance
therewith includes: between about 35 and about 50 weight % of
guanidine nitrate fuel, between about 30 and about 55 weight %
copper diammine dinitrate oxidizer, between about 2 and about 10
weight % silicon dioxide burn rate enhancing and slag formation
additive, and between about 0 and about 25 weight % ammonium
nitrate supplemental oxidizer. As the burn rate of such pyrotechnic
gas generant materials is a strong function of pressure, higher
combustion pressures can produce or result in higher mass flow
rates of produced or formed gases. Correspondingly, with such
pyrotechnic gas generant materials, lower combustion pressures can
produce or result in lower mass flow rates of produced or formed
gases.
[0039] Those skilled in the art and guided by the teachings herein
provided will appreciate that the incorporation and use of such
high burn rate pressure dependency gas generant materials in the
practice of the invention desirably allows or facilitates a more
controlled or adaptive generation or production of inflation gas.
Controlling the amount of gas generated by the gas generant, in
turn, allows for desired control of the rate of deployment of an
associated airbag cushion. As identified above, inflatable
restraint installations which provide or result in a less rapid or
less aggressive initial deployment followed by an increase in
deployment rate are generally desired or sought such as to better
provide for out of position occupants. The pressure dependency of
the burn rate of the combustible gas generant material, in
accordance with one preferred embodiment of the invention, is at
least about 0.4 at 1000 psi.
[0040] In accordance with a preferred embodiment of the invention,
the orifice 32 of the inflator device 10 is at least in part
defined by a shape memory alloy material. Shape memory alloy
materials employed in the practice of the invention desirably
undergo phase transformations due to particular changes in
temperature. These alloys are generally characterized by memory of
a first configuration imposed upon the alloy while in a martensite
phase at a relatively low temperature. The martensite phase of the
shape memory alloy allows the shape memory alloy material to be
relatively easily deformed into a second shape. Upon heating to a
temperature at which the shape memory alloy undergoes a phase
transformation from the martensite phase to the austenite phase,
the memory effect of the shape memory alloy is manifested by a
return to the undeformed shape of this shape memory alloy in the
martensite phase. This effect is sometimes called "detwinning." The
austenite phase change "resets" the modified martensite lattice
structure to the unmodified martensite shape.
[0041] For example, the shape memory alloy material has an
austenite finishing temperature (T.sub.f). The orifice 32 defines a
first fluid flow through area (A.sub.1) when at a temperature less
than T.sub.f and a second fluid flow through area (A.sub.2) when at
a temperature greater than T.sub.f. The second fluid flow through
area (A.sub.2) is less than the first fluid flow through area
(A.sub.1).
[0042] In one embodiment of this invention, as shown in FIG. 1, the
orifice 32 is at least in part defined by at least one exit opening
40 formed in the inflator device 10 and a restrictor 42. As shown
in FIG. 1, the restrictor 42 can desirably be disposed adjacent an
area of the inside of the inflator device 10. The restrictor 42
comprises an opening 44 in combination with the exit opening 40,
thereby forming the orifice 32. One skilled in the art guided by
the teachings herein provided will appreciate that the number of
exit openings 40 and/or exit openings 40 in combination with
restrictor openings 44 can be selected dependant on the
requirements of the particular inflatable device installation.
[0043] The restrictor opening 44 can be formed in the restrictor 42
by punching the restrictor opening 44 having a second cross
sectional area (a.sub.2). The restrictor opening 44 having the
second cross sectional area (a.sub.2) is formed while the shape
memory alloy of the restrictor 42 is in the martensite phase. In
the martensite phase the restrictor opening 44 can be subsequently
deformed by extrusion to widen the opening 44 to a cross sectional
area (a.sub.1). A heat treatment application may be desired or
necessary to set the extrusion and preserve the memory effect.
[0044] Referring to FIG. 1, extrusion of the restrictor opening 44
results in a restrictor opening collar 46. The restrictor opening
44 maintains the cross sectional area (a.sub.1) when the shape
memory alloy material is at a temperature less than T.sub.f and
when at a temperature greater than T.sub.f, the restrictor opening
44 at least partially closes to an opening having the second cross
sectional area (a.sub.2). At a temperature greater than T.sub.f,
the undeformed martensite phase shape returns, e.g., the extruded
martensite shape returns to the pre-extruded martensite shape. The
shape memory alloy of restrictor opening 44 preferably returns to
the pre-extruded martensite shape having the same cross sectional
area as was originally formed, but it is desired that the
post-extruded restrictor opening 44 at least have a cross sectional
area less than the martensite restrictor opening 44 having the
first cross sectional area (a.sub.1). The shape memory alloy allows
for a self-regulating inflation gas rate flow inflator device in
that the shape memory alloy functions as a result of temperature
and requires no additional outside control to close the orifice
32.
[0045] In FIG. 2 the restrictor opening 44 of the restrictor 42 is
aligned with the exit opening 40 forming the orifice 32. FIG. 2
shows the extruded restrictor opening 44 at a temperature less than
T.sub.f wherein the restrictor opening 44 has the first cross
sectional area (a.sub.1) and orifice 32 has the first fluid flow
through area (A.sub.1). In FIG. 2 the exit opening 40, the first
fluid flow through area (A.sub.1), the restrictor opening 44, and
the first cross sectional area (a.sub.1) are all shown as equal in
diameter, although the restrictor opening 44 and the first cross
sectional area (a.sub.1) can differ in size from the first fluid
flow through area (A.sub.1). Upon sudden vehicle deceleration, the
ignition device 26 ignites the reaction of the gas generant 24, and
gas begins flowing out through the orifice 32, as represented by
the arrows 50 in FIG. 2. As the gas generant reacts the temperature
within the inflator device rises to a temperature greater than
T.sub.f, resulting in the shape memory alloy of the restrictor 42
returning to its original martensite shape.
[0046] FIG. 3 shows the restrictor opening 44 at a temperature
greater than T.sub.f. The extruded restrictor opening 44 has
returned to its pre-extruded shape. The second cross sectional area
(a.sub.2) of the restrictor opening 44 results in the second fluid
flow through area (A.sub.2) of the orifice 32. The smaller second
fluid flow through area (A.sub.2) restricts gas flow and increases
the pressure inside the chamber 20 as the generated gas (as
represented by the arrows 50) has less area to escape. The
increased pressure within the chamber 20 causes the pressure
dependent gas generant 24 to react at an increased rate creating
more gas and thereby increasing the gas mass flow rate out of the
orifice 32 and increasing the rate of inflation of the associated
airbag. The shape memory alloy restrictor allows for an adaptable
airbag inflation rate, with a slower initial rate of inflation
followed by an increased rate of inflation, while still inflating
an airbag within a desired time frame.
[0047] Those skilled in the art and guided by the teachings herein
provided will appreciate that various shape memory alloys such as
known in the art can be used in the practice of this invention. One
such shape memory alloy is an alloy containing nickel and titanium
called nitinol (Nickel Titanium Naval Ordanance Laboratory)
developed by the United States Navy.
[0048] Shape memory alloy materials used in the practice of the
invention desirably have an austenite finishing temperature
(T.sub.f) of at least about 90.degree. C. As will be appreciated, a
general standard applied in the United States for automotive
component parts is a capability to be stable at temperatures of at
least 107.degree. C. Thus, in accordance with certain preferred
embodiments, shape memory alloy materials used in the practice of
the invention desirably have an austenite finishing temperature
(T.sub.f) of greater than about 107.degree. C.
[0049] In addition, shape memory alloys used in the practice of the
invention desirably maintain stability and shape memory
characteristics over extended periods of time (as inflatable
restraint system installations within a particular vehicle may not
be actuated for many years after installation, if at all).
[0050] In view of the above, shape memory alloys such those
comprising a ternary alloy of copper, aluminum and nickel; a
ternary alloy of copper, aluminum and bromine; and a ternary alloy
of iron, manganese and silicon, particularly those of such alloys
having a desired austenite finishing temperature (T.sub.f) of at
least about 90.degree. C. and, for at least certain preferred
embodiments, an austenite finishing temperature (T.sub.f) of
greater than about 107.degree. C., are generally currently
preferred for use in the practice of the invention.
[0051] While the invention has been generally described above
making reference to specific inflator device embodiments wherein
one or more orifices in accordance with the invention are employed
as an external orifice, e.g., an orifice wherethrough gas exits
from an inflator device, it will be appreciated by those skilled in
the art and guided by the teachings herein provided that the
broader practice of the invention is not necessarily so limited.
For example, if desired, inflator devices in accordance with the
invention can advantageously employ orifice or orifice assembly
constructions in accordance with the invention in a location
internal to the inflator device.
[0052] FIG. 4 is a simplified, schematic drawing of an inflator
device assembly, generally designated by the reference numeral 410,
in accordance with another preferred embodiment of the invention.
In FIG. 4, the inflator device assembly 410 is shown partially in
section. The inflator device assembly 410 includes a generally
cylindrical housing 412 having an at least partially open first end
414 and a closed second end 416. The first end 414 is closed with a
base 420, such as of steel. The base 420 includes an opening 422
wherethrough is passed an initiator device 424 such as with an
associated adapter 426. Various initiator devices and adapters such
as known in the art can be used and the broader practice of the
invention is not limited to specific or particular such devices or
elements.
[0053] The housing 412 forms a combustion chamber 430 and a
diffusion chamber 432. The combustion chamber 430 houses or
contains a supply of a combustible gas generant material, such as
described above and not here shown to facilitate illustration. The
diffusion chamber 432 has or includes one or more exit ports 434,
such formed in the housing 412, wherethrough inflation gas can exit
the inflator device 410 and pass directly or indirectly, as is
known in the art, into an associated inflatable element (not
shown). The diffusion chamber 432 also houses or contains a filter
or inflation medium treatment assembly 436, such as known in the
art and such as may be desired to condition or otherwise treat the
inflation medium prior to passage out of the inflator device
assembly 410. Examples of inflation medium treatment assemblies
such as may be suitable for use in the practice of such an
embodiment include filter elements made of knitted or woven metal
wire.
[0054] In the illustrated embodiment, the combustion chamber 430
and the diffusion chamber 432 are generally axially aligned. The
combustion chamber 430 and the diffusion chamber 432 are separated
by a restrictor plate 440 such as includes an orifice 442, such as
formed of or with a shape memory alloy, as described above. The
inflator device assembly 410 may, as shown, also include a support
disk 444, such as made of low carbon steel, and such as may be
interposed between the restrictor plate 440 and the inflation
medium treatment assembly 436. The support disk 444 includes an
opening 446 generally aligned with the restrictor plate orifice
442. In accordance with a preferred embodiment of the invention,
the support disk opening 446 is desirably designed to avoid being a
flow restricting opening, e.g., the cross sectional area of the
support disk opening 446 is desirably at least as great as the
cross sectional area of the shape memory alloy restrictor plate
orifice 442. As will be appreciated, through the assembly inclusion
of such a support disk 444, the restrictor plate 440 can desirably
be supported against the pressure exerted thereagainst such as by
the combustion products gases formed upon reaction of the gas
generant material housed or contained within the combustion chamber
430. In addition, the housing 412 may desirably be crimped, such as
shown at 450, or otherwise shaped or formed such as to assist in
maintaining desired or required orientation or positioning of the
inflator assembly components, e.g., the desired orientation or
positioning of the restrictor plate 440.
[0055] Thus, the inflator assembly 410 is an example of an inflator
device, in accordance with the invention, which includes or
contains an internal gas flow orifice in accordance with the
invention.
[0056] Those skilled in the art and guided by the teachings herein
provided will appreciate that the actuation time for a shape memory
alloy material restrictor or the like orifice defining component
can be desirably altered or tailored via various design parameters
such as including bulk and thickness. Other approaches or
procedures for suitably altering or tailoring the
temperature-dependency of action by such shape memory alloy
components include surface treatments such as anodizing or other
methods to thermally isolate the component composed of the shape
memory alloy material, e.g., the restrictor.
[0057] While the invention has been illustrated and described with
reference to an embodiment wherein the inflator device housing
assembly includes a restrictor made of the shape memory alloy
material, the broader practice of the invention is not necessarily
so limited as those skilled in the art and guided by the teachings
herein provided will appreciate that in accordance with certain
preferred embodiments the invention can, if desired, be practiced
wherein the inflator housing assembly itself is at least in part
composed of the shape memory alloy material.
[0058] 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.
[0059] 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.
* * * * *