U.S. patent application number 10/608979 was filed with the patent office on 2005-01-20 for dual stage inflator for low melting gas generants.
Invention is credited to Curtis, Anthony J., Fitzgerald, Kevin, Kelly, Michael Eugene, Mulville, Michael Felix, Trevillyan, Dennis A..
Application Number | 20050011393 10/608979 |
Document ID | / |
Family ID | 34062301 |
Filed Date | 2005-01-20 |
United States Patent
Application |
20050011393 |
Kind Code |
A1 |
Kelly, Michael Eugene ; et
al. |
January 20, 2005 |
DUAL STAGE INFLATOR FOR LOW MELTING GAS GENERANTS
Abstract
A dual stage invention is designed to autoignite an autoignition
material before a low temperature gas generant melts. Low
temperature gas generants include a high nitrogen content organic
fuel with ammonium nitrate as the oxidizer. The dual stage inflator
has a first gas generant and a second gas generant that are ignited
by separate igniters. The first gas generant and the second gas
generant are insulated from the inflator housing to delay the heat
transfer from the housing to the first gas generant and second gas
generant during a bonfire test, which needs to be passed to receive
Department of Transportation classification. The dual stage
inflator also has an autoignition cartridge for disposing of the
second gas generant by the first gas generant after the first gas
generant burns for a predetermined amount of time.
Inventors: |
Kelly, Michael Eugene;
(Valrico, FL) ; Curtis, Anthony J.; (Palm Harbor,
FL) ; Mulville, Michael Felix; (Bartow, FL) ;
Trevillyan, Dennis A.; (Plant City, FL) ; Fitzgerald,
Kevin; (Mesa, AZ) |
Correspondence
Address: |
KEY SAFETY SYSTEMS, INC.
PATENT DEPARTMENT
5300 ALLEN K BREED HIGHWAY
LAKELAND
FL
33811-1130
US
|
Family ID: |
34062301 |
Appl. No.: |
10/608979 |
Filed: |
June 30, 2003 |
Current U.S.
Class: |
102/430 |
Current CPC
Class: |
B60R 2021/2633 20130101;
B60R 21/2644 20130101; F42B 3/04 20130101; B60R 2021/2648
20130101 |
Class at
Publication: |
102/430 |
International
Class: |
F42B 010/00 |
Claims
1. An inflator comprising: a housing connected on one end by a
first endcap and connected on an opposite end by a second endcap; a
first igniter having ignition material that burns upon actuation of
the first igniter by an electrical signal, the first igniter being
held at the first endcap; a first autoignition material being in
intimate contact with the first igniter whereby the first
autoignition material is ignited from the burning of the ignition
material of the first igniter; a first gas generant for producing
inflation gas for inflating an airbag, the first gas generant being
separated from direct contact with the first endcap, the second
endcap, and the housing; a first enhancer for igniting the first
gas generant, wherein the burning of the first autoignition
material ignites the first enhancer which then ignites the first
pas generant; and a first enhancer retainer for retaining the first
enhancer, the first enhancer retainer being spaced from direct
contact with the first endcap the enhancer retainer comprises an
enhancer recess for holding the first enhancer, a connection
portion and an annular mounting portion arranged substantially
parallel with the first endcap, wherein the connection portion
connects the enhancer recess to the mounting portion, the
connection portion has a plurality of first enhancer retainer holes
for passage of hot gas from first enhancer to the first gas
generant, the plurality of first enhancer retainer holes and the
enhancer recess being spaced from the first endcap and covered by a
first burst foil located between the first enhancer retainer and
the first endcap.
2. (cancelled)
3. (cancelled)
4. (cancelled)
5. The inflator according to claim 1 further comprising a
cylindrical filter encircling the first gas generant and a focuser
for reducing the quantity of first gas generant in contact with an
inner surface of the cylindrical filter.
6. The inflator according to claim 1 further comprising a second
igniter and a second autoignition material, wherein burning of the
second igniter ignites the second autoignition material.
7. The inflator according to claim 6 further comprising a second
enhancer and a second gas generant, wherein the burning of the
second autoignition material ignites the second enhancer, the
burning of the second enhancer ignites the second gas generant.
8. The inflator according to claim 7 further comprising a second
enhancer retainer comprising a tubular portion for receiving the
second enhancer, the second enhancer retainer comprises an annular
securing portion arranged substantially parallel with the second
endcap.
9. The inflator according to claim 8 wherein the second enhancer
retainer comprises an intermediary portion connecting the securing
portion with the tubular portion, wherein the intermediary portion
has a plurality of second enhancer retainer holes for providing a
passageway for the hot gas from the second enhancer to reach the
second gas generant.
10. An inflator comprising: a housing connected on one end by a
first endcap and on an opposite end by a second endcap; a first
enhancer for igniting a first gas generant, the first gas generant
being separated from direct contact with the first endcap, the
second endcap and the housing a second enhancer for igniting a
second gas generant, the second gas generant being separated from
direct contact with the first endcap, the second endcap and the
housing; a second enhancer retainer spaced from direct contact with
the second endcap comprising a tubular portion for receiving the
second enhancer, an annular securing portion arranged substantially
parallel with the second endcap: and an intermediary portion
connecting the securing portion with the tubular portion, wherein
the intermediary portion has a plurality of second enhancer
retainer holes for providing a passageway for the hot gas from the
second enhancer to reach the second gas generant, the second
enhancer retainer holes and the second enhancer retainer being
spaced from the second endcap and covered by a second burst foil
located between the second enhancer retainer and the second endcap:
and, an autoignition cartridge comprising pyrotechnic material that
ignites at a temperature below the combustion temperature of the
first gas generant whereby the burning of the first gas generant
ignites the pyrotechnic material of the autoignition cartridge, the
burning of the pyrotechnic material of the autoignition cartridge
ignites the second enhancer which in turn ignites the second gas
generant.
11. (cancelled)
12. (cancelled)
13. The inflator according to claim 10 wherein the second gas
generant is in closer proximity to the second endcap than the
second enhancer.
14. The inflator according to claim 13 further comprising a divider
for separating the second gas generant and the second enhancer from
the first gas generant, wherein the autoignition cartridge is
situated between the divider on one side and the second enhancer on
the other side.
15. The inflator according to claim 13 wherein further comprising a
diffuser cap with diffuser cap apertures arranged around the
circumference thereof, wherein hot gas from the burning of the
second gas generant pass through the diffuser cap apertures and
then through a filter, wherein the filter also filters hot gas from
the burning of the first gas generant.
16. The inflator according to claim 13 further comprising a spring
for reducing rattling of the first gas generant and for maintaining
a predetermined distance between the diffuser cap and the first gas
generant.
17. An inflator comprising: a housing connected on one end by a
first endcap and on an opposite end by a second endcap; a first
enhancer for igniting a first gas generant; a second enhancer for
igniting a second gas generant; a second enhancer retainer spaced
from direct contact with the second endcap comprising a tubular
portion for receiving the second enhancer, an annular securing
portion arranged substantially parallel with the second endcap; and
an intermediary portion connecting the securing portion with the
tubular portion, wherein the intermediary portion has a plurality
of second enhancer retainer holes for providing a passageway for
the hot gas from the second enhancer to reach the second gas
generant; an autoignition cartridge comprising pyrotechnic material
that ignites at a temperature below the combustion temperature of
the first gas generant whereby the burning of the first gas
generant ignites the pyrotechnic material of the autoignition
cartridge, the burning of the pyrotechnic material of the
autoignition cartridge ignites the second enhancer which in turn
ignites the second gas generant; and an inflator wherein the second
gas generant is in closer proximity to the second endcap than the
second enhancer.
18. The inflator according to claim 17 further comprising a divider
for separating the second gas generant and the second enhancer from
the first gas generant, wherein the autoignition cartridge is
situated between the divider on one side and the second enhancer on
the other side.
19. The inflator according to claim 17 wherein further comprising a
diffuser cap with diffuser cap apertures arranged around the
circumference thereof, wherein hot gas from the burning of the
second gas generant pass through the diffuser cap apertures and
then through a filter, wherein the filter also filters hot gas from
the burning of the first gas generant.
20. The inflator according to claim 17 further comprising a spring
for reducing rattling of the first gas generant and for maintaining
a predetermined distance between the diffuser cap and the first gas
generant.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to an inflator for providing
inflation gas to fill an inflatable restraint cushion, and
particularly relates to a dual stage inflator capable of tailoring
inflation gas output based upon crash severity in addition to size
and/or position of a vehicle occupant.
BACKGROUND OF THE INVENTION
[0002] Inflatable restraint cushions are commonly installed in
motor vehicles to reduce the likelihood of the vehicle occupants
sustaining injuries during vehicle crashes. Inflatable restraint
cushions are commonly known as airbags in the safety restraint
industry. During a vehicle crash, an airbag is rapidly filled with
inflation gas between the vehicle occupant and the interior of the
vehicle. The airbag absorbs the vehicle occupant's kinetic energy
to provide a controlled, reduced deceleration of the vehicle
occupant and to prevent the vehicle occupant from contacting the
hard surfaces of the vehicle interior.
[0003] The source of inflation gas for an airbag is an inflator. An
inflator may provide inflation gas in a number of manners such as
through burning of pyrotechnic material (pyrotechnic inflator),
through releasing stored gas (cold gas inflator), or through some
combination thereof (hybrid inflator). Each of the above mentioned
manners are well known in the art.
[0004] The pyrotechnic inflator typically includes an igniter, an
enhancer (also known as a booster), and a gas generant. During the
car crash, the igniter is fired, which ignites the enhancer, which
in turn ignites the gas generant. The burning of the gas generant
produces gaseous combustion products useful for inflating a vehicle
airbag. Also well known in the art are dual stage pyrotechnic
inflators, which have two combustion chambers. The dual stage
inflators typically have two igniters for igniting gas generant in
each of the two combustion chambers. The advantage of utilizing a
dual stage inflator is its tailorability. There are numerous firing
scenarios for a dual stage inflator such as, the firing of only the
first stage, the firing of the first stage followed by a delayed
firing of the second stage, and the firing of the first stage and
second stage simultaneously.
[0005] The gas generant useful for a pyrotechnic inflator is a
blend of a fuel and an oxidizer. The combustion of the fuel and
oxidizer produces gaseous combustion products. Higher yield gas
generants are desirable for a couple of reasons. First, higher
yield gas generants require less gas generant to produce the same
gas output as lower yield gas generants. Second, higher yield gas
generants produce less solid particles or slag that need to be
filtered. Organic compounds rich in nitrogen are typically selected
for the fuel. Well-known oxidizers useful as oxidizers in gas
generants are strontium nitrate and potassium nitrate. Another
well-known oxidizer, ammonium nitrate, is desirable because the use
of ammonium nitrate increases the gas yield of the gas generant
because metal ions are not present in the oxidizer. Gas generants
having a high nitrogen content organic molecule and ammonium
nitrate have gas yields over 95%. As used herein, ammonium nitrate
gas generant refers to a gas generant that contains a fuel and
ammonium nitrate as the oxidizer.
[0006] The downside of using an ammonium nitrate gas generant is
the low melting temperature of the eutectics or fuel/oxidizer
mixture. The low temperature property of ammonium nitrate gas
generants becomes a serious issue in obtaining shipping
classification from the United States Department of Transportation.
To obtain shipping approval, the inflator needs to maintain
structural integrity or in other words should not fragment when an
autoignition material in the inflator is induced by external
heating (i.e. bonfire test). The autoignition material is a
pyrotechnic mixture that spontaneously combusts or autoignites at a
temperature before the gas generant undergoes a physical or
chemical change such as decomposition, autoignition, or melting.
Thus, in order for the autoignition material to function properly,
the autoignition material needs to spontaneously ignite below a
temperature that results in a chemical or physical change in the
gas generant. Typically, in the industry the autoignition material
needs to spontaneously ignite at a temperature above 130.degree. C.
If the autoignition material ignites after the gas generant
undergoes a physical or chemical change, then the ballistic
properties of the gas generant become unpredictable and the
structural integrity of the inflator may fail.
[0007] As discussed earlier, ammonium nitrate is a highly desirable
oxidizer for gas generants because this oxidizer increases the
conversion rate of the gas generant to gaseous combustion products.
Ammonium nitrate melts at about 169.degree. C., and the addition of
a fuel to the oxidizer may result in a eutectic that has a lower
melting point. If the fuel is nitroguanidine or guanidine nitrate
the resulting eutectic (fuel and oxidizer) has a melting point at
about 135.degree. C. If the fuel is 5-amino tetrazole, then the
eutectic has a melting point as low as 115.degree. C. Thus, a gas
generant having ammonium nitrate and either nitroguanidine or
guanidine nitrate has a melting point extremely close to
130.degree. C., the lower autoignition temperature limit on the
autoignition material. In order for the autoignition material to
effectively deploy the gas generant, the autoignition material
needs to be ignited before the gas generant melts. Accordingly,
there is a desire to design an inflator that overcomes the
potential melting of the ammonium nitrate gas generant before the
ignition of the autoignition material.
SUMMARY OF THE INVENTION
[0008] A dual stage inflator in accordance with the present
invention is designed to ignite an autoigntion material before a
low temperature gas generant melts. The dual stage inflator
contains a first gas generant and a second gas generant that
generates inflation gas during a car crash. The burning of the
first gas generant and the second gas generant produce gaseous
combustion gases that flow out of the inflator into a folded airbag
to inflate the airbag. The first gas generant and the second gas
generant are surrounded by a housing, a first endcap, and a second
endcap. The first endcap is secured to the housing on one end and
the second endcap is secured to the housing on the other end.
[0009] An aspect of the invention is that the first gas generant is
not in direct contact with the first endcap, the second endcap, or
the housing. Moreover, the second gas generant is not in direct
contact with the first endcap, the second endcap, or the
housing.
[0010] Another aspect of the present invention is that the first
autoigntion material is in intimate contact with the first igniter,
and the firing of the first igniter ignites the first autoignition
material. Likewise, the second autoignition material is in intimate
contact with the second igniter, and the firing of the second
igniter ignites the second autoignition material.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] With this summary of the invention, a detailed description
follows with reference being made to the accompanying drawings
which form part of the specification in which like parts are
designated by the same reference numbers and of which:
[0012] FIG. 1 shows a perspective view of the dual stage inflator
in accordance with the present invention.
[0013] FIG. 2 shows a cross section view of the inflator in FIG. 1
along 2-2.
[0014] FIG. 3 shows an exploded view of the dual stage inflator in
accordance with the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0015] An inflator in accordance with the present invention is
represented in FIG. 1. The inflator is a dual stage inflator 10
capable of providing multiple inflation rates for a vehicle airbag.
The inflator 10 has a generally cylindrical shape having an
elongated housing 11 with a first endcap 12 connected on one end of
the housing 11 and a second endcap 13 connected on the other end of
the housing 11. The housing 11 and the endcaps 12, 13 are made from
a metallic material such as steel, low carbon steel, aluminum, a
metal alloy, and the like. The endcaps are connected with the
housing 11 by welding. The housing 11 contains a plurality of exit
ports 14 arranged around the circumference thereof. The inflation
gas is able to exit the inflator 10 via the exit ports 14 and
travel into a folded airbag (not shown) to inflate the folded
airbag. The exit ports 14 are arranged in a manner so that the
inflator 10 is thrust neutral as inflation gas escapes the inflator
10. It is understood that the number and size of the exit ports 14
may vary without departing from the scope of the present invention.
The exit ports 14 are covered by a burst foil tape 70. The burning
of the first gas generant and the second gas generant produce
inflation gas, which increases the internal pressure of the dual
stage inflator 10. After the pressure reaches a predetermined
level, the burst foil tape 70 ruptures creating a passageway for
the infaltion gas to exit the dual stage inflator. It is
contemplated that the burst foil tape 70 for each exit port may
have different thickness so the burst foil tape 70 rupture as
different internal pressures.
[0016] With reference to FIG. 3, the dual stage inflator 10 has two
electrical igniters, a first igniter 20 and a second igniter 24,
mounted on opposite ends of the inflator 10. The first igniter 20
and the second igniter 24 have the same physical components and
operate in the same manner; however, the first igniter 20 might
differ from the second igniter 24 in terms of the amount of
ignition material loaded therein. The first electrical igniter has
a pair of conducting electrodes 23 for mating with an electrical
connector (not shown) of an electrical wire. The wire is a conduit
of electrical signals transmitted from an electronic control unit.
The electronic control unit processes signals from crash sensors
and/or occupant position sensors. The electrodes 23 of the igniter
are isolated from one another to prevent an electrical signal from
flowing directly from one electrode to the other electrode.
Typically, in an electrical igniter, the electrodes 23 are
connected to one another via a bridge wire characterized by having
a high amount of resistance. The bridge wire is embedded in
multiple layers of ignition material. A well-known example of
ignition material utilized in electrical igniters is zirconium
potassium perchlorate. Due to the high amount of resistance
associated with the bridge wire, as current passes along the bridge
wire, heat is generated to ignite the ignition material. As
mentioned earlier, the first igniter 20 is identical to the second
igniter 24 except for the ignition material load. The first igniter
20 is utilized to ignite the first gas generant 42 in the first
combustion chamber 50, while the second igniter 24 is utilized to
ignite the second gas generant 49 in the second combustion chamber
65. In the present invention, the quantity of first gas generant 42
in the first combustion chamber 50 is greater than the quantity of
second gas generant 49 in the second combustion chamber 65, and
hence the ignition material load of the first igniter 20 needs to
greater than the second igniter 24. It is contemplated that the
ignition material loads for the first igniter 20 and the second
igniter 24 may be equal.
[0017] The firing of the first igniter 20 ignites a first
autoignition material 25. Alternatively, the first autoignition
material 25 is also ignited when the first autoignition material 25
is exposed to a temperature equal to or greater than the
autoignition temperature of the autoignition material. The first
autoignition material 25 is a pyrotechnic mixture that upon burning
produces hot combustion gaseous products. The burning of the first
autoignition material 25 ruptures the first burst foil 37 and
initiates the burning of the first enhancer 35. Autoignition
materials are employed in airbag inflators to ensure that the
airbag inflator functions in a safe manner at elevated
temperatures. Melting or distortion of the gas generant can occur
at elevated temperatures resulting in a perturbation of the surface
area of the gas generant. The perturbation of the surface area of a
gas generant can result in uncontrolled or undefined burning. The
uncontrolled burning of the gas generant may lead to abnormally
high internal pressure in the inflator, which may lead to inflator
housing 11 failure. Therefore, autoignition materials are utilized
in inflators to ignite the gas generant before an elevated
temperature affects the ballistic properties of the gas
generant.
[0018] The first autoignition material 25 is contained within a
first cylinder 28 and is in intimate contact with the first igniter
20. The first cylinder 28 is attached to the first igniter 20 by
pressure sensitive adhesive or other suitable means. The first
cylinder 28 has two open ends. One end of the first cylinder 28
faces the first igniter 20 and the other open end faces the first
enhaner. The open end of the first cylinder 28 that faces the first
enhancer 35 has an annular lip to prevent the first autoignition
material 25 from sliding out of the first cylinder 28. A first
igniter holder 21 partially receives the first igniter 20 and the
first cylinder 28; the first igniter holder 21 is secured to the
first endcap 12 by welding, but it is appreciated that other
securing techniques may be employed such as using threads.
[0019] The burning of the autoignition material ignites the first
enhancer 35. The enhancer is spaced apart from the first
autoignition material 25 and is a pyrotechnic material made from a
mixture of a fuel and an oxidizer that rapidly burns at a hot
temperature upon ignition. The first enhancer 35 is responsible for
igniting the first gas generant 42.
[0020] The first enhancer 35 is stored within a recess 38 in the
first enhancer retainer 36. A bottom portion 41 and a circular wall
51 of the first enhancer retainer 36 define the recess 38. The
bottom portion 41 and the circular wall 51 do not contain any
openings or holes. The first enhancer retainer 36 has an annular
mounting portion 39 for securing the first enhancer retainer 36 to
the inflator 10. The annular mounting portion 39 is substantially
parallel with the circular wall of the first enhancer retainer 36
and the inflator housing 11. The first enhancer retainer 36 has a
connecting portion 40 connecting the circular wall 51 to the
annular mounting portion 39. The length of the bottom portion 41 is
greater than twice the length of the connecting portion 40. The
connecting portion 40 has a plurality of first enhancer retainer
holes 48 therethrough; combustion gases from the burning of the
first enhancer 35 flow through the first enhancer retainer holes 48
to reach the first combustion chamber to ignite the first gas
generant. A first burst foil 37 is fixedly attached to the first
enhancer retainer 36 in a manner that covers the recess 38 of the
first enhancer retainer 36 and also covers the side of the
connecting member facing the first igniter 20 including the first
enhaner retainer holes. The first enhancer 35 is held in the recess
38 of the first enhaner retainer, which is covered by the first
burst foil 37.
[0021] The first enhancer retainer 36 is press fit against a
focuser 45, which is press fit against the inflator housing 11. The
focuser 45 tapers inward in the direction toward the second endcap
13. The focuser 45 restricts the area in which the first gas
generant 42 occupies. The first gas generant 42 is present in the
first combustion chamber 50. The first combustion chamber 50 is
defined by the space created by the first enhancer retainer 36, the
focuser 45, a portion of the filter 46, and a spring 47. The spring
47 is employed for anti-abrasion and anti-rattling of the first gas
generant 42. The spring 47 is made from a metallic material and
biases the first gas generant 42 in the direction of the first
endcap 12. The spring 47 is coiled in a spiral shape at the end
towards the second endcap 13 and is coiled in a circular shape at
the end facing the first endcap 12. Due to the circular shape of
the spring 47 at the end facing the first endcap 12, the first gas
generant 42 is prevented from being able to pass into the interior
space of the spiral end of the spring 47. The first gas generant 42
is a pyrotechnic material comprising a fuel and an oxidizer that
upon ignition produce combustion gaseous products for inflating an
airbag.
[0022] The second gas generant 49 is ignited by the actuation of
the second igniter 24. The second igniter 24 is inserted into the
second igniter holder 22, and the second igniter holder 22 is
welded to the second endcap 13. The second autoignition material 26
is contained in the second cylinder 29 and is in intimate contact
with the second igniter 24. The second autoignition material 26 may
be ignited by the actuation of the second igniter 24 or by the
exposure to elevated external temperatures (i.e. bonfire test).
[0023] The burning of the second autoignition material 26 ignites
the second enhancer 57. The second enhancer 57 is retained in the
tubular portion 54 of the second enhancer retainer 53. The second
enhancer retainer 53 has an annular securing portion 56 aligned
parallel with the inflator housing 11, and an intermediary portion
55 coupling the tubular portion 54 to the securing portion 56. The
intermediary portion 55 has a plurality of second enhancer retainer
holes 61 therethrough; combustion gases from the burning of the
second enhancer 57 flow through the second enhancer retainer holes
61 to reach the second combustion chamber 65 to ignite the second
gas generant 49. A second burst foil 66 is attached to the second
enhancer retainer 53 via a pressure sensitive adhesive whereby the
end of the tubular portion 54 closest to the second igniter 24 and
the second enhancer retainer holes 61 are covered. The second
retainer is press fitted against the funnel 52. The funnel 52
tapers inward in the direction of the first endcap 12. The funnel
52 is press fitted against the inflator housing 11. The portion of
the funnel 52 with the greatest radius contacts the inflator
housing 11 while the securing portion 56 of the second enhancer
retainer 53 contacts the funnel 52. The funnel 52 has a curvilinear
shape whereby the portion of the funnel 52 in closer proximity to
the first gas generant 42 has a smaller diameter than the portion
of the funnel 52 press fit against the housing 11. There is no part
of the second enhancer retainer 53 that directly contacts the
inflator housing 11 or the second endcap 13.
[0024] A circular divider 59 and a diffuser cap 68 are arranged
between the first gas generant 42 and the second gas generant 49.
The divider 59 has a plurality of divider holes 58 therethrough,
and the entire open end of the diffuser cap 68 is covered by a
third burst foil 67. The third burst foil 67 is also attached to
the divider 59 on the side of the divider 59 facing the first gas
generant 42. The diffuser cap 68 has a plurality of diffuser cap
apertures 69 therethrough arranged around the circumference
thereof. The diffuser cap 68 has substantially the same diameter
throughout. The open end of the diffuser cap 68 spreads radially
outward for attachment to the funnel 52. The divider 59 and the
diffuser cap 68 are fixedly attached to the funnel 52 via crimping.
The spiral portion of the spring 47 coils around the diffuser cap
68.
[0025] The inflator 10 in accordance with the present invention
includes an autoignition cartridge 27. The autoignition cartridge
27 is designed to be ignited from the heat created from the burning
of the first gas generant 42. The heat is transferred to the
divider 59, which transfers the heat to the autoignition cartridge
27. The autoignition cartridge 27 has pyrotechnic material that
burns before the second gas generant 49 undergoes a physical or
chemical change. The burning of the pyrotechnic material of the
autoignition cartridge 27 ignites the second enhancer 57, which in
turn ignites the second gas generant 49. Accordingly, the second
gas generant 49 may be ignited by multiple mechanisms. First, the
second gas generant 49 may be ignited by the ignition of the
autoignition cartridge 27, which is triggered by the burning of the
first gas generant 42. Second, the second gas generant 49 may be
ignited by the actuation of the second igniter 24 by an electrical
signal. Third, the second gas generant 49 may be ignited by the
ignition of the second autoignition material 26 triggered by the
elevation of the outside temperature of the inflator 10 over a
predetermined temperature. The autoignition cartridge 27 is a
safety feature incorporated in the present invention to ensure
proper disposal of the second gas generant 49 in the inflator 10.
The autoignition cartridge 27 is designed to ignite the second
enhancer 57 before the second gas generant 49 melts, which would
negatively impact its ballistic properties.
[0026] The second combustion chamber 65 is the region of the
inflator 10 enclosed by the second enhancer retainer 53, the funnel
52, and the divider 59. The second gas generant 49 occupies the
space in the second combustion chamber 65. A ceramic piece 60 or
other suitable material may be employed in the second combustion
chamber 65 for anti-abrasion and anti-rattling purposes for the
second gas generant 49.
[0027] In the inflator 10 of the present invention, one filter 46
is included in the inflator 10 to filter 46 and cool the hot gases
produced from the burning of the first gas generant 42 and the
second gas generant 49. The filter 46 extends from the curved
portion of the focuser 45 to the curved portion of the funnel 52 as
seen in FIG. 2. As discussed above, the filter 46 contributes to
defining the first combustion chamber 50, and thus a portion of the
first gas generant 42 contacts the filter 46. The filter 46 has a
generally cylindrical shape. A plenum or air gap exists between the
filter 46 and inner surface of the housing 11 to prevent the filter
46 from clogging the exit ports 14 and to prevent the limited use
of the filter 46 by the inflation gas. By providing an air gap, the
combustion gases produced from the burning of the first gas
generant 42 and the second gas generant 49 pass through the filter
46 into the air gap and subsequently through the exit ports 14.
Moreover, the plenum helps prevent the exit ports 14 from becoming
partially blocked from the filter 46 while inflation gas departs
the inflator 10. The filter 46 has a two-fold purpose; first, to
act as a heat sink and cool the hot combustion gaseous products and
second, to catch slag or solid particles.
[0028] The dual stage inflator 10 in the present invention employs
a first autoignition material 25, a second autoignition material
26, and an autoignition cartridge 27. The first autoignition
material 25 and the second autoignition material 26 may be the same
autoignition composition as the autoignition composition found in
the autoignition cartridge 27. A well-known autoignition
composition in the industry is nitrocellulose, which autoignites at
a temperature about 185.degree. C. This autoignition material is
suitable for many different gas generants; however, nitrocellulose
is generally not suitable for ammonium nitrate gas generants.
Ammonium nitrate gas generants with nitroguanidine or guanidine
nitrate as the fuel have eutectic (fuel and oxidizer) melting point
at about 135.degree. C. In order for the autoignition to ignite
before the ammonium nitrate gas generant melts, an autoignition
composition having a lower autoignition temperature than
nitrocellulose needs to be gas selected. The autoignition
composition for the present invention may be selected from the
autoignition compositions taught in co-assigned patent application
Ser. No. 10/104,359, which is incorporated by reference in its
entirety. The preferred autoignition composition in this referenced
patent application has nitroguanidine, antimony III sulfide, and
silver I nitrate.
[0029] The first enhancer 35 and the second enhancer 57 may be made
from the same pyrotechnic composition. The fuel for the first
enhancer 35 and the second enhancer 57 is a high nitrogen content
organic compound such as a tetrazole, triazole, nitroguanidine,
guanidine nitrate, and the like. The oxidizer for the first
enhancer 35 and the second enhancer 57 may be selected from one of
more of the following: metal oxides, metal nitrates, metal
chlorate, metal perchlorates, ammonium nitrate, and the like. The
purpose of the first enhancer 35 and the second enhancer 57 is to
rapidly ignite the first gas generant 42 and the second gas
generant 49 respectively. The first enhancer 35 and the second
enhancer 57 typically burn at a higher temperature than the first
gas generant 42 and the second gas generant 49.
[0030] In accordance with the present invention, the first gas
generant 42 and the second gas generant 49 is an ammonium nitrate
gas generant. The fuel for the first gas generant 42 and the second
gas generant 49 is selected from a high nitrogen content organic
compound such as a tetrazole, amino tetrazole, triazole,
nitroguanidine and the like. The oxidizer is ammonium nitrate. The
present invention is not limited to only ammonium nitrate gas
generants; other gas generants may be employed having similar
melting properties as ammonium nitrate gas generants.
[0031] The first gas generant 42 and the second gas generant 49 are
separated from direct contact with the first endcap 12, the second
endcap 13, and the housing 11. The first enhancer retainer 36, the
second enhancer retainer 53, the focuser 45, the funnel 52, and the
filter 46 maintain a minimum distance from the first gas generant
42 and the second gas generant 49 with the first endcap 12, the
second endcap 13, and the housing 11. The reason for incorporating
the minimum distance is to delay the heat transfer from the housing
11 and the endcaps to the first and second gas generants 42, 49
during a bonfire test. Typically, in the industry the autoignition
material needs to spontaneously ignite at a temperature above
130.degree. C. Since ammonium nitrate gas generants with
nitroguanidine or guandine nitrate melt at about 135.degree. C.,
which is very similar to the autoignition temperature of the first
and second autoignition materials, the first and second gas
generants 42, 49 need to be insulated or isolated to prevent the
first and second gas generants 42, 49 from melting before the
autoignition of the first and second autoignition materials.
Because of the minimum distance, as the outside temperature of the
inflator 10 rises during a bonfire test, the first and second
autoignition materials ignite before the first gas generant 42 and
the second gas generant 49 melts.
[0032] In all cases it is understood that the above-described
embodiments are merely illustrative of but a few of the many
possible specific embodiments which represent the applications of
the principles of the present invention. Numerous and varied other
arrangements can be readily devised by those skilled in the art
without departing from the spirit and scope of the invention.
* * * * *