U.S. patent application number 12/906416 was filed with the patent office on 2011-02-10 for gas generating system.
Invention is credited to David M. McCormick.
Application Number | 20110031727 12/906416 |
Document ID | / |
Family ID | 35539975 |
Filed Date | 2011-02-10 |
United States Patent
Application |
20110031727 |
Kind Code |
A1 |
McCormick; David M. |
February 10, 2011 |
Gas Generating System
Abstract
A baffle system is provided including a first end plate having
at least one opening formed therein, and a second end plate having
at least one opening formed therein. At least one baffle element
extends between the first and second end plates. The at least one
baffle element defines a chamber. The at least one first end plate
opening and the at least one second end plate opening are blocked
so as to prevent fluid flow from the chamber to an exterior of the
chamber system through the at least one first end plate opening and
through the at least one second end plate opening. In addition, the
blockage of the end plate openings is such that fluid flow is
enabled into the chamber from the exterior of the chamber through
the at least one first end plate opening and through the at least
one second end plate opening.
Inventors: |
McCormick; David M.; (St.
Clair Shores, MI) |
Correspondence
Address: |
L.C. Begin & Associates, PLLC;510 Highland Avenue
PMB 403
Milford
MI
48381
US
|
Family ID: |
35539975 |
Appl. No.: |
12/906416 |
Filed: |
October 18, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11167849 |
Jun 27, 2005 |
7814838 |
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12906416 |
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60583427 |
Jun 28, 2004 |
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Current U.S.
Class: |
280/742 ; 138/40;
165/181; 280/801.1 |
Current CPC
Class: |
C06D 5/06 20130101; B60R
2021/2633 20130101; B60R 2021/2648 20130101; B60R 21/2644
20130101 |
Class at
Publication: |
280/742 ;
280/801.1; 138/40; 165/181 |
International
Class: |
B60R 21/26 20110101
B60R021/26; B60R 22/00 20060101 B60R022/00; F16L 55/027 20060101
F16L055/027; F28F 1/20 20060101 F28F001/20 |
Claims
1. A baffle system comprising: a first end plate having at least
one opening formed therein; a second end plate having at least one
opening formed therein; at least one baffle element extending
between the first and second end plates, the at least one baffle
element defining a chamber, wherein the at least one first end
plate opening and the at least one second end plate opening are
blocked so as to prevent fluid flow from the chamber to an exterior
of the chamber system through the at least one first end plate
opening and through the at least one second end plate opening, and
so as to enable fluid flow into the chamber through the at least
one first end plate opening and through the at least one second end
plate opening from the exterior of the chamber.
2. The baffle system of claim 1 further comprising a sequence of
baffle elements extending between the first and second end plates,
the sequence of baffle elements including the first baffle element
and at least one additional baffle element, each additional baffle
element in the sequence of baffle elements being spaced outwardly
apart from a preceding baffle element in the sequence of baffle
elements, the first baffle element having an orifice configuration
for enabling fluid communication between the chamber and an
additional baffle element, each additional baffle element in the
sequence of baffle elements having an orifice configuration for
enabling fluid communication between a preceding baffle element and
an exterior of the additional baffle element.
3. The baffle system of claim 2 wherein the first baffle element
orifice configuration is spaced apart a first predetermined
distance from one of the at least one first end plate opening and
the at least one second end plate opening, and the orifice
configuration in each additional baffle element is spaced apart an
additional predetermined distance from the orifice configuration in
the preceding baffle element, a sum of the first predetermined
distance and the additional predetermined distances being
approximately equal to an estimated total length per unit baffle
element area of a flow path of a fluid necessary to cool a fluid
flowing through the baffle system from a first temperature to a
temperature within a predetermined temperature range.
4. A method for producing, in a gas generating system, a gas having
a temperature within a predetermined temperature range, the method
comprising the steps of: estimating a total length of a flow path
of a gas along a given surface area of a predetermined baffle
element material necessary to cool a gas to from a first
temperature to a temperature within the predetermined temperature
range; and providing a baffle system having a total internal gas
flow path length per unit baffle element surface area substantially
equal to the estimated length of gas flow path necessary to cool
the gas to from a temperature in the at least one combustion
chamber to a temperature within the predetermined temperature
range.
5. The method of claim 4, wherein the step of providing a baffle
system comprises providing a baffle system having an orifice
configuration within the baffle system along the internal flow path
for the gas, the baffle system orifice configuration being
configured for reducing a pressure of a gas from a pressure in the
at least one combustion chamber to a pressure within a
predetermined pressure range.
6. The method of claim 4 wherein the step of providing a baffle
system comprises the steps of: providing a sequence of baffle
elements formed from the baffle element material, a first baffle
element of the sequence of baffle elements defining a chamber
having an entrance adapted for receiving therethrough a gas from at
least one combustion chamber upon activation of the gas generating
system, each additional baffle element in the sequence of baffle
elements being spaced outwardly apart from a preceding baffle
element in the sequence of baffle elements; providing an orifice
configuration in the first baffle element for enabling fluid
communication between the chamber and an additional baffle element,
the first baffle element orifice configuration being spaced apart a
first predetermined distance from the chamber entrance; and
providing an orifice configuration in each additional baffle
element in the sequence of baffle elements for enabling fluid
communication between a preceding baffle element and an exterior of
the additional baffle element, the orifice configuration in each
additional baffle element being spaced apart an additional
predetermined distance from the orifice configuration in the
preceding baffle element, a sum of the first predetermined distance
and the additional predetermined distances being approximately
equal to the estimated total length of a flow path of a gas
necessary to cool the gas to a temperature within the predetermined
temperature range.
7. The method of claim 6 wherein the step of providing a baffle
system further comprises the step of specifying an orifice
configuration in at least one of the baffle elements such that the
pressure of a gas flowing through an orifice configuration in a
last baffle element in the sequence of baffle elements is at a
pressure within the predetermined pressure range.
8. The method of claim 7 wherein the step of varying an orifice
configuration in at least one of the baffle elements comprises
varying the sizes of the orifices in at least one of the baffle
elements.
9. The method of claim 7 wherein the step of varying an orifice
configuration in at least one of the baffle elements comprises
varying the number of orifices in at least one of the baffle
elements.
10. The method of claim 6 wherein the step of providing a baffle
system further comprises the step of varying the spacing between
adjacent baffle plates such that the pressure of a gas flowing
through an orifice configuration in the last baffle element in the
sequence of baffle elements is at a pressure within the
predetermined pressure range.
11. A gas generating system comprising a baffle system in
accordance with claim 1.
12. A vehicle occupant protection system comprising a baffle system
in accordance with claim 1.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of, and claims the benefit
of, U.S. application Ser. No. 11/167,849 filed on Jun. 27, 2005,
which claims the benefit of U.S. Provisional Application Ser. No.
60/583,427 filed on Jun. 28, 2004.
BACKGROUND OF THE INVENTION
[0002] The present invention relates generally to gas generating
systems and, more particularly, to filterless gas generating
systems for use in applications such as inflatable occupant
restraint systems in motor vehicles.
[0003] Installation of inflatable occupant protection systems,
generally including airbag systems as standard equipment in all new
vehicles has intensified the search for smaller, lighter and less
expensive protection systems. Accordingly, since the inflation gas
generator used in such protection systems tends to be the heaviest
and most expensive component, there is a need for a lighter and
less expensive gas generating system.
[0004] A typical gas generating system includes cylindrical steel
or aluminum housing having a diameter and length related to the
vehicle application and characteristics of a gas generant
composition contained therein. Inhalation by a vehicle occupant of
particulates generated by gas generant combustion during airbag
activation can be hazardous. Thus, the gas generating system is
generally provided with an internal or external filter comprising
one or more layers of steel screen of varying mesh and wire
diameter. Gas produced upon combustion of the gas generant passes
through the filter before exiting the gas generating system.
Particulate material, or slag, produced during combustion of the
gas generant in a conventional system is substantially removed as
the gas passes through the filter. In addition, heat from
combustion gases is transferred to the material of the filter as
the gases flow through the filter. Thus, as well as filtering
particulates from the gases, the filter acts to cool the combustion
gases prior to dispersal into an associated airbag. However,
inclusion of the filter in the gas generating system increases the
complexity, weight, and expense of the gas generating system. While
various gas generant formulations have been developed in which the
particulates resulting from combustion of the gas generant, are
substantially eliminated or significantly reduced, certain types of
gas generants are still desirable notwithstanding the relatively
high percentage of combustion solids they produce, given favorable
characteristics of these gas generants such as burn rate, sustained
combustion, and repeatability of performance.
[0005] Other ongoing concerns with gas generating systems include
the ability to achieve any one of a variety of ballistic profiles
by varying as few of the physical parameters of the gas generating
system as possible and/or by varying these physical parameters as
economically as possible. Also important are the need to increase
manufacturing efficiency and the need to reduce manufacturing
costs.
SUMMARY OF THE INVENTION
[0006] In one aspect of the embodiments of the present invention, a
baffle system is provided including a first end plate having at
least one opening formed therein, and a second end plate having at
least one opening formed therein. At least one baffle element
extends between the first and second end plates. The at least one
baffle element defines a chamber. The at least one first end plate
opening and the at least one second end plate opening are blocked
so as to prevent fluid flow from the chamber to an exterior of the
chamber system through the at least one first end plate opening and
through the at least one second end plate opening. In addition, the
blockage of the end plate openings is such that fluid flow is
enabled into the chamber from the exterior of the chamber through
the at least one first end plate opening and through the at least
one second end plate opening.
[0007] In another aspect of the embodiments of the present
invention, a method is provided for producing, in a gas generating
system, a gas having a temperature within a predetermined
temperature range. The method includes steps of estimating a total
length of a flow path of a gas along a given surface area of a
predetermined baffle element material necessary to cool a gas to
from a first temperature to a temperature within the predetermined
temperature range; and providing a baffle system having a total
internal gas flow path length per unit baffle element surface area
substantially equal to the estimated length of gas flow path
necessary to cool the gas to from a temperature in the at least one
combustion chamber to a temperature within the predetermined
temperature range.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] In the drawings illustrating embodiments of the present
invention:
[0009] FIG. 1 is a cross-sectional side view of one embodiment of a
gas generating system in accordance with the present invention;
[0010] FIG. 2 is a cross-sectional side view of a first end closure
in accordance with the present invention;
[0011] FIG. 3 is a cross-sectional side view of a second end
closure in accordance with the present invention;
[0012] FIG. 4 is a cross-sectional side view of a first ignition
cup in accordance with the present invention;
[0013] FIG. 5 is a cross-sectional side view of a second ignition
cup in accordance with the present invention;
[0014] FIG. 6 is a cross-sectional side view of a first end plate
in accordance with the present invention;
[0015] FIG. 7 is a cross-sectional side view of a second end plate
in accordance with the present invention;
[0016] FIG. 8 is a cross-sectional side view of a first annular
sleeve in accordance with the present invention;
[0017] FIG. 9 is a cross-sectional side view of a second annular
sleeve in accordance with the present invention;
[0018] FIG. 10 is a cross-sectional side view of a first baffle
plate in accordance with the present invention;
[0019] FIG. 11 is a cross-sectional side view of a second baffle
plate in accordance with the present invention;
[0020] FIG. 12 is a cross-sectional side view of a third baffle
plate in accordance with the present invention;
[0021] FIG. 13 is a cross-sectional side view of a second
embodiment of a gas generating system in accordance with the
present invention;
[0022] FIG. 14 is a cross-sectional side view of a baffle system in
accordance with the present invention;
[0023] FIG. 15 graphically illustrates the preferred ballistic
performance of silicon-coated gas generant compositions as compared
to the same uncoated compositions containing silicone as a binder;
and
[0024] FIG. 16 is a schematic representation of an exemplary
vehicle occupant restraint system incorporating an inflator in
accordance with the present invention.
DETAILED DESCRIPTION
[0025] The present invention broadly comprises a gas generating
system that is fabricated without the wire mesh filter required in
earlier designs for removing particulate materials from a stream of
inflation gas. A baffle system is employed in place of the filter
whereby, upon gas generant combustion, slag is formed within the
buffer system and gases are also cooled therein. Selection of
suitable gas generant compositions capable of combusting to produce
inflation gas without an undue quantity of particulates further
obviates the need for a filter. Obviating the need for a filter
enables the gas generating system to be simpler, lighter, less
expensive, and easier to manufacture. Furthermore, the gas
generating system described herein actually provides cooler output
gases than many known inflators equipped with a typical filter/heat
sink. Although the embodiments of the gas generating system
described herein do not contain a filter, a filter formed by known
or otherwise suitable methods may be included, if desired.
[0026] FIG. 1 shows one embodiment of a gas generating system 10 in
accordance with the present invention. Gas generating system 10
includes a substantially cylindrical housing 12 having a pair of
opposed ends 12a, 12b and a wall 12c extending between the ends to
define a housing interior cavity. Housing 12 is made from a metal
or metal alloy and may be a cast, stamped, drawn, extruded, or
otherwise metal-formed. A first end closure 14 is secured to end
12a of housing 12, and a second end closure 16 is secured to an
opposite end 12b of housing 12 using one or more known methods. In
FIG. 1, ends 12a and 12b of housing 12 are crimped over portions of
first and second end closures 14, 16 to secure the end closures
within the housing. One or more openings 12d are provided in
housing wall 12c to enable fluid communication between an interior
of the housing and an exterior of the housing.
[0027] Referring to FIGS. 1 and 2, first end closure 14 has formed
therealong a peripheral shoulder 14a, a central orifice 14b, and a
peripheral cavity 14c. Peripheral shoulder 14a is formed along a
face 14d of the end closure and is dimensioned so that an end
portion of a wall 22b of an ignition cup 22 (FIG. 4, described in
greater detail below) having a predetermined outer diameter may be
positioned along face 14d to form an interference fit with shoulder
14a, thereby suspending the ignition cup radially inward of housing
wall 14. A first O-ring or seal 18 is positioned in peripheral
cavity 14c to seal the interface between first end closure 14 and
housing wall 12c.
[0028] Referring to FIGS. 1 and 3, second end closure 16 has formed
therealong a peripheral shoulder 16a, a central orifice 16b, and a
peripheral cavity 16c. Peripheral shoulder 16a is formed along a
face 16d of the end closure and is dimensioned so that an end
portion of a wall 24b of an ignition cup 24 (FIG. 5, described in
greater detail below) having a predetermined outer diameter may be
positioned along face 16d to form an interference fit with shoulder
16a, thereby suspending the ignition cup radially inward of housing
wall 12c. A second O-ring or seal 20 is positioned in peripheral
cavity 16c to seal the interface between second end closure 16 and
housing wall 12c. End closures 14, 16 may be stamped, extruded, die
cast, or otherwise metal formed and may be made from carbon steel
or stainless steel, for example.
[0029] Referring to FIGS. 1 and 4, a first ignition cup 22 is
positioned adjacent first end closure 14, and is nested within
housing 12 for a portion of the housing length. Ignition cup 22 has
a base portion 22a and a wall 22b extending from the base portion
to abut first end closure 14 along first end closure shoulder 14a.
Base portion 22a, wall 22b, and first end closure 14 define a
cavity 22d for containing a pyrotechnic compound 26 therein. At
least one ignition gas exit orifice 22c is formed in ignition cup
22 for release of ignition compound combustion products once
ignition compound 26 is ignited. An annular recess 22e is formed in
base portion 22a and is dimensioned so that an end portion of an
annular sleeve 34 (described below) having a predetermined inner
diameter may be positioned within recess 22e to form an
interference fit with base portion 22a. Ignition cup 22 may be
stamped, extruded, die cast, or otherwise metal formed and may be
made from carbon steel or stainless steel, for example.
[0030] In the embodiment shown in FIG. 1, a rupturable, fluid-tight
seal 23 is positioned across ignition orifice 22c to fluidly
isolate cavity 22d from a first combustion chamber 34a (described
below) prior to activation of the gas generating system. Seal 23 is
secured to a face of ignition cup base portion 22a and forms a
fluid-tight barrier between cavity 22d and combustion chamber 34a.
Various disks, foils, films, tapes, etc. may be used to form the
seal.
[0031] Referring to FIGS. 1 and 5, a second ignition cup 24 is
positioned adjacent second end closure 16, and is nested within
housing 12 for a portion of the housing length. Ignition cup 24 has
a base portion 24a and a wall 24b extending from the base portion
to abut second end closure 16 along second end closure shoulder
16a. Base portion 24a, wall 24b, and second end closure 16 define a
cavity 24d for containing a pyrotechnic compound 28 therein. At
least one ignition gas exit orifice 24c is formed in ignition cup
24 for release of ignition compound combustion products once
ignition compound 28 is ignited. An annular recess is formed in
base portion 24a and is dimensioned so that an end portion of an
annular sleeve 36 (described below) having a predetermined inner
diameter may be positioned within recess 54 to form an interference
fit with base portion 24a. Ignition cup 24 may be stamped,
extruded, die cast, or otherwise metal formed and may be made from
carbon steel or stainless steel, for example.
[0032] In the embodiment shown in FIG. 1, a rupturable, fluid-tight
seal 25 is positioned across ignition orifice 24c to fluidly
isolate cavity 24d from a second combustion chamber 36a prior to
activation of the gas generating system. Seal 25 is secured to
either of opposite faces 24f and 24g of ignition cup base portion
24a and forms a fluid-tight barrier between cavity 24d and second
combustion chamber 36a. Various disks, foils, films, tapes, etc.
may be used to form the seal.
[0033] Referring again to FIGS. 1 and 4, a quantity of a
pyrotechnic compound 26 is contained within cavity 22d. In the
embodiment shown in FIGS. 1 and 4, pyrotechnic compound 26 is a
known or suitable ignition or booster compound, whose combustion
ignites another, main gas generant charge 38 positioned in
combustion chamber 34a. In an alternative embodiment, pyrotechnic
compound 26 in cavity 22d comprises the main gas generant charge
for the gas generating system and is formed from a gas generant
composition (for example, a smokeless gas generant composition) as
described in greater detail below. This alternative embodiment may
be used in applications in which a relatively small amount of
inflation gas (and, therefore, a correspondingly smaller amount of
gas generant) is needed. One or more autoignition tablets (not
shown) may be placed in cavity 22d, allowing ignition of
pyrotechnic compound 26 upon external heating in a manner
well-known in the art.
[0034] Referring again to FIGS. 1 and 5, a quantity of a
pyrotechnic compound 28 is contained within cavity 24d. In the
embodiment shown in FIGS. 1 and 5, pyrotechnic compound 28 is a
known or suitable ignition or booster compound, whose combustion
ignites another, main gas generant charge 40 positioned in
combustion chamber 36a. In an alternative embodiment, pyrotechnic
compound 28 in cavity 24d comprises the main gas generant charge
for the gas generating system and is formed from a gas generant
composition (for example, a smokeless gas generant composition) as
described in greater detail below. This alternative embodiment may
be used in applications in which a relatively small amount of
inflation gas (and, therefore, a correspondingly smaller amount of
gas generant) is needed. One or more autoignition tablets (not
shown) may be placed in cavity 24d, allowing ignition of
pyrotechnic compound 28 upon external heating in a manner
well-known in the art.
[0035] Referring again to FIGS. 1 and 2, a first igniter assembly
30 is positioned and secured within first end closure central
orifice 14b so as to enable operative communication between cavity
22d containing ignition compound 26 and an igniter 30a incorporated
into the igniter assembly, for igniting ignition compound 26 upon
activation of the gas generating system.
[0036] Similarly, a second igniter assembly 32 (FIG. 3) is
positioned and secured within second end closure central orifice
16b so as to enable operative communication between cavity 24d
containing ignition compound 28 and an igniter 32a incorporated
into the igniter assembly, for igniting ignition compound 28 upon
activation of the gas generating system. Igniter assemblies 30 and
32 may be secured in respective central orifices 14b and 16b using
any one of several known methods, for example, by welding,
crimping, using an interference fit, or by adhesive application.
Igniter assemblies suitable for the application described herein
may be obtained from any of a variety of known sources, for example
Primex Technologies, Inc. of Redmond, Wash. or Aerospace Propulsion
Products by, of The Netherlands.
[0037] Referring to FIGS. 1 and 8, recess 22e in first ignition cup
22 (FIG. 4) and recess 44a in first baffle end plate 44 (FIG. 6,
described below) are adapted to accommodate end portions of a first
annular sleeve 34 therein. In the embodiment of the gas generating
system shown in FIG. 1, first sleeve 34, in combination with first
igniter cup 22 and first end plate 44 define a first combustion
chamber 34a containing a main gas generant composition 38
(described in greater detail below.) First sleeve 34 is spaced
apart from housing wall 12c to form a first annular gas flow
passage 56 extending along first combustion chamber 34a. Upon
activation of the gas generating system, first combustion chamber
34a fluidly communicates with cavity 22d by way of ignition cup
orifice 22c.
[0038] Referring to FIGS. 1 and 9, recess 24e in second ignition
cup 24 (FIG. 5) and recess 46a in second end plate 46 (FIG. 7,
described below) are adapted to accommodate end portions of a
second annular sleeve 36 therein. In the embodiment of the gas
generating system shown in FIG. 1, second sleeve 36, in combination
with second igniter cup 24 and second baffle end plate 46 define a
second combustion chamber 36a containing a gas generant composition
40 (described in greater detail below.) Sleeve 36 is spaced apart
from housing wall 12c to form a second annular gas flow passage 58
extending along second combustion chamber 36a. Upon activation of
the gas generating system, second combustion chamber 36a fluidly
communicates with cavity 24d by way of ignition cup orifice 24c.
Sleeves 34 and 36 may be formed by extrusion or other suitable
metal forming methods.
[0039] Referring again to FIG. 1, gas generant compositions 38 and
40 are positioned within combustion chambers 34a and 36a,
respectively. Chambers 34a and 36a may contain the same or
different gas generant compositions. In addition, chambers 34a and
36a may contain the same or different amounts of gas generant, and
the chambers may be the same or different sizes.
[0040] In addition, "smokeless" gas generant compositions are
applicable to gas generating systems according to the present
invention, although the present invention is not limited to the use
of smokeless gas generant compositions therein. As used herein, the
term "smokeless" should be generally understood to mean such
propellants as are capable of combustion yielding at least about
90% gaseous products based on a total product mass; and, as a
corollary, no more than about 10% solid products based on a total
product mass. It has been generally found that the use of gas
generant compositions having the combustion characteristics
described in cited patents helps obviate the need for the filters
used in other gas generating system designs.
[0041] Gas generant compositions 38 and 40 positioned in combustion
chambers 34a and 36a may be any known gas generant composition
useful for airbag application and is exemplified by, but not
limited to, compositions and processes described in U.S. Pat. Nos.
5,035,757, 5,872,329, 6,074,502, 6,287,400, 6,306,232 and
6,475,312, 6,210,505, and 6,620,266, each incorporated by reference
herein. Other suitable compositions are set forth in the U.S.
patent application Ser. Nos. 10/407,300 and 60/369,775,
incorporated by reference herein.
[0042] U.S. Pat. No. 5,037,757 discloses azide-free gas generants
including tetrazole compounds such as aminotetrazole, tetrazole,
bitetrazole and metal salts of these compounds, as well as triazole
compounds such as 1,2,4-triazole-5-one or 3-nitro
1,2,4-triazole-5-one and metal salts of these compounds. Certain
metal salts (alkaline earth metals) of these compounds can
function, at least in part, as high temperature slag formers. For
example, the calcium salt of tetrazole or bitetrazole forms, upon
combustion, calcium oxide which would function as a
high-temperature slag former. Magnesium, strontium, barium and
possibly cerium salts would act in similar manner. In combination
with a low-temperature slag former, a filterable slag would be
formed. The alkali metal salts (lithium, sodium, potassium) could
be considered, at least in part, as low-temperature slag formers
since they could yield lower melting silicates or carbonates upon
combustion.
[0043] Oxidizers generally supply all or most of the oxygen present
in the system. In addition, however, they are the preferred method
of including a high-temperature slag former into the reaction
system. The alkaline earth and cerium nitrates are all oxidizers
with high-temperature slag forming potential, although most of
these salts are hygroscopic and are difficult to use effectively.
Strontium and barium nitrates are easy to obtain in the anhydrous
state and are excellent oxidizers. Alkali metal nitrates, chlorates
and perchlorates are other useful oxidizers when combined with a
high-temperature slag former.
[0044] Set in the above context, the pyrotechnic, slag forming gas
generating mixture disclosed in U.S. Pat. No. 5,037,757 comprises
at least one each of the following materials.
[0045] a. A fuel selected from the group of tetrazole compounds
consisting of aminotetrazole, tetrazole, bitetrazole and metal
salts of these compounds as well as triazole compounds and metal
salts of triazole compounds.
[0046] b. An oxygen containing oxidizer compound selected from the
group consisting of alkali metal, alkaline earth metal, lanthanide
and ammonium nitrates and perchlorates or from the group consisting
of alkali metal or alkaline earth metal chlorates or peroxides.
[0047] c. A high temperature slag forming material selected from
the group consisting of alkaline earth metal or transition metal
oxides, hydroxides, carbonates, oxalates, peroxides, nitrates,
chlorates and perchlorates or from the group consisting of alkaline
earth metal salts of tetrazoles, bitetrazoles and triazoles.
[0048] d. A low-temperature slag forming material selected from the
group consisting of silicon dioxide, boric oxide and vanadium
pentoxide or from the group consisting of alkali metal silicates,
borates, carbonates, nitrates, perchlorates or chlorates or from
the group consisting of alkali metal salts of tetrazoles,
bitetrazoles and triazoles or from the group consisting of the
various naturally occurring clays and talcs.
[0049] The fuel may comprise 5-aminotetrazole which is present in a
concentration of about 22 to about 36% by weight, where the oxygen
containing oxidizer compound and high-temperature slag former is
strontium nitrate which is present in a concentration of about 38
to about 62% by weight, and said low-temperature slag former is
silicon dioxide which is present in a concentration of about 2 to
about 18% by weight.
[0050] Alternatively, the fuel and high-temperature slag forming
material may comprise the strontium salt of 5-aminotetrazole which
is present in a concentration of about 30 to about 50% by weight,
where the oxygen containing oxidizer compound is potassium nitrate
which is present in a concentration of about 40 to about 60% by
weight, and the low-temperature slag former is talc which is
present in a concentration of about 2 to about 10% by weight. The
talc may be replaced by clay.
[0051] Another combination comprises the 5-aminotetrazole which is
present in a combination of about 22 to about 36% by weight, where
the oxygen containing oxidizer compound is sodium nitrate which is
present in a concentration of about 30 to about 50% by weight, the
high-temperature slag forming material is magnesium carbonate which
is present in a concentration of about 8 to about 30% by weight,
and the low-temperature slag former is silicon dioxide which is
present in a concentration of about 2 to about 20% by weight.
Magnesium carbonate may be replaced by magnesium hydroxide.
[0052] Yet another combination comprises the potassium salt of
5-aminotetrazole which is present in a concentration of about 2 to
about 30% by weight which serves in part as a fuel and in part as a
low-temperature slag former and wherein 5-aminotetrazole in a
concentration of about 8 to about 40% by weight also serves as a
fuel, and wherein clay in a concentration of about 2 to about 10%
by weight serves in part as the low-temperature slag former and
wherein strontium nitrate in a concentration of about 40 to about
66% by weight serves as both the oxygen containing oxidizer and
high-temperature slag former.
[0053] U.S. Pat. No. 5,872,329 discloses nonazide gas generants for
a vehicle passenger restraint system employing ammonium nitrate as
an oxidizer and potassium nitrate as an ammonium nitrate phase
stabilizer. The fuel, in combination with phase stabilized ammonium
nitrate, is selected from the group consisting of amine salts of
tetrazoles and triazoles having a cationic amine component and an
anionic component. The anionic component comprises a tetrazole or
triazole ring, and an R group substituted on the 5-position of the
tetrazole ring, or two R groups substituted on the 3- and
5-positions of the triazole ring. The R group(s) is selected from
hydrogen and any nitrogen-containing compounds such as amino,
nitro, nitramino, tetrazolyl and triazolyl groups. The cationic
amine component is selected from an amine group including ammonia,
hydrazine, guanidine compounds such as guanidine, aminoguanidine,
diaminoguanidine, triaminoguanidine, dicyandiamide, nitroguanidine,
nitrogen substituted carbonyl compounds such as urea,
carbohydrazide, oxamide, oxamic hydrazide, bis-(carbonamide) amine,
azodicarbonamide, and hydrazodicarbonamide, and amino azoles such
as 3-amino-1,2,4-triazole, 3-amino-5-nitro-1,2,4-triazole,
5-aminotetrazole and 5-nitraminotetrazole. Optional inert additives
such as clay or silica may be used as a binder, slag former,
coolant or processing aid. Optional ignition aids comprised of
nonazide propellants may also be utilized in place of conventional
ignition aids such as BKNO.sub.3. The gas generants are prepared by
dry blending and compaction of the comminuted ingredients.
[0054] Preferred high nitrogen nonazides employed as primary fuels
in gas generant compositions include, in particular, amine salts of
tetrazole and triazole selected from the group including
monoguanidinium salt of 5,5'-Bis-1H-tetrazole (BHT.cndot.1GAD),
diguanidinium salt of 5,5'-Bis-1H-tetrazole (BHT.cndot.2GAD),
monoaminoguanidinium salt of 5,5'-Bis-1H-tetrazole
(BHT.cndot.1AGAD), diaminoguanidinium salt of 5,5'-Bis-1H-tetrazole
(BHT.cndot.2AGAD), monohydrazinium salt of 5,5'-Bis-1H-tetrazole
(BHT.cndot.1HH), dihydrazinium salt of 5,5'-Bis-1H-tetrazole
(BHT.cndot.2HH), monoammonium salt of 5,5'-bis-1H-tetrazole
(BHT.cndot.1NH.sub.3), diammonium salt of 5,5'-bis-1H-tetrazole
(BHT.cndot.2NH.sub.3), mono-3-amino-1,2,4-triazolium salt of
5,5'-bis-1H-tetrazole (BHT.cndot.1ATAZ),
di-3-amino-1,2,4-triazolium salt of 5,5'-bis-1H-tetrazole
(BHT.cndot.2ATAZ), diguanidinium salt of 5,5'-Azobis-1H-tetrazole
(ABHT-2GAD), and monoammonium salt of 5-Nitramino-1H-tetrazole
(NAT-1NH.sub.3). The nonazide fuel generally comprises 15-65%, and
preferably comprises 20-55%, by weight of the total gas generant
composition.
[0055] The foregoing amine salts of tetrazole or triazole are
dry-mixed with phase stabilized ammonium nitrate. The oxidizer is
generally employed in a concentration of about 35 to 85% by weight
of the total gas generant composition. The ammonium nitrate is
stabilized by potassium nitrate, as taught in co-owned U.S. Pat.
No. 5,531,941, entitled, "Process For Preparing Azide-Free Gas
Generant Composition", and granted on Jul. 2, 1996, incorporated
herein by reference. The PSAN comprises 85-90% AN and 10-15% KN and
is formed by any suitable means such as co-crystallization of AN
and KN, so that the solid-solid phase changes occurring in pure
ammonium nitrate (AN) between -40.degree. C. and 107.degree. C. are
prevented. Although KN is preferably used to stabilize pure AN, one
skilled in the art will readily appreciate that other stabilizing
agents may be used in conjunction with AN.
[0056] If a slag former, binder, processing aid, or coolant is
desired, inert components such as clay, diatomaceous earth,
alumina, or silica are provided in a concentration of 0.1-10% of
the gas generant composition, wherein toxic effluents generated
upon combustion are minimized.
[0057] Optional ignition aids, used in conjunction with the present
invention, are selected from nonazide gas generant compositions
comprising a fuel selected from a group including triazole,
tetrazolone, aminotetrazole, tetrazole, or bitetrazole, or others
as described in U.S. Pat. No. 5,139,588 to Poole, the teachings of
which are herein incorporated by reference. Conventional ignition
aids such as BKNO.sub.3 are not required because the tetrazole or
triazole based fuel, when combined with phase stabilized ammonium
nitrate, significantly improves ignitability of the propellant and
also provides a sustained burn rate.
[0058] U.S. Pat. No. 6,074,502 discloses nonazide gas generant
compositions including phase stabilized ammonium nitrate (PSAN),
one or more primary nonazide high-nitrogen fuels, and one or more
secondary nonazide high-nitrogen fuels selected from the group
including azodicarbonamide (ADCA) and hydrazodicarbonamide
(AH).
[0059] One or more primary nonazide high-nitrogen fuels are
selected from a group including tetrazoles and bitetrazoles such as
5-nitrotetrazole and 5,5'-bitetrazole; triazoles and nitrotriazoles
such as nitroaminotriazole and 3-nitro-1,2,4 triazole-5-one;
nitrotetrazoles; and salts of tetrazoles and salts of
triazoles.
[0060] More specifically, salts of tetrazoles include in
particular, amine, amino, and amide nonmetal salts of tetrazole and
triazole selected from the group including monoguanidinium salt of
5,5'-Bis-1H-tetrazole (BHT.cndot.1GAD), diguanidinium salt of
5,5'-Bis-1H-tetrazole (BHT.cndot.2GAD), monoaminoguanidinium salt
of 5,5'-Bis-1H-tetrazole (BHT.cndot.1AGAD), diaminoguanidinium salt
of 5,5'-Bis-1H-tetrazole (BHT.cndot.2AGAD), monohydrazinium salt of
5,5'-Bis-1H-tetrazole (BHT.cndot.1HH), dihydrazinium salt of
5,5'-Bis-1H-tetrazole (BHT.cndot.2HH), monoammonium salt of
5,5'-bis-1H-tetrazole (BHT.cndot.1NH.sub.3), diammonium salt of
5,5'-bis-1H-tetrazole (BHT.cndot.2NH.sub.3),
mono-3-amino-1,2,4-triazolium salt of 5,5'-bis-1H-tetrazole
(BHT.cndot.1ATAZ), di-3-amino-1,2,4-triazolium salt of
5,5'-bis-1H-tetrazole (BHT.cndot.2ATAZ), and diguanidinium salt of
5,5'-Azobis-1H-tetrazole (ABHT.cndot.2GAD).
[0061] Amine salts of triazoles include monoammonium salt of
3-nitro-1,2,4-triazole (NTA.cndot.1NH.sub.3), monoguanidinium salt
of 3-nitro-1,2,4-triazole (NTA.cndot.1GAD), diammonium salt of
dinitrobitriazole (DNBTR.cndot.2NH.sub.3), diguanidinium salt of
dinitrobitriazole (DNBTR.cndot.2GAD), and monoammonium salt of
3,5-dinitro-1,2,4-triazole (DNTR.cndot.1NH.sub.3).
[0062] A preferred gas generant composition results from the
mixture of one or more primary nonazide high-nitrogen fuels
comprising 5%-45%, and more preferably 9%-27% by weight of the gas
generant composition; one or more secondary nonazide high-nitrogen
fuels comprising 1%-35%, and more preferably 1%-15% by weight of
the gas generant composition; and PSAN comprising 55%-85%, and more
preferably 66%-78% by weight of the gas generant composition.
Tetrazoles are more preferred than triazoles due to a higher
nitrogen and lower carbon content thereby resulting in a higher
burning rate and lower carbon monoxide. Salts of tetrazoles are
even more preferred because of superior ignition stability. As
taught by Onishi, U.S. Pat. No. 5,439,251, herein incorporated by
reference, salts of tetrazoles are much less sensitive to friction
and impact thereby enhancing process safety. Nonmetallic salts of
bitetrazoles are more preferred than nonmetallic salts of
tetrazoles due to superior thermal stability. As also taught by
Onishi, nonmetallic salts of bitetrazoles have higher melting
points and higher exothermal peak temperatures thereby resulting in
greater thermal stability when combined with PSAN. The diammonium
salt of bitetrazole is most preferred because it is produced in
large quantities and readily available at a reasonable cost.
[0063] An optional burn rate modifier, from 0-10% by weight in the
gas generant composition, is selected from a group including an
alkali metal, an alkaline earth or a transition metal salt of
tetrazoles or triazoles; an alkali metal or alkaline earth nitrate
or nitrite; TAGN; dicyandiamide, and alkali and alkaline earth
metal salts of dicyandiamide; alkali and alkaline earth
borohydrides; or mixtures thereof. An optional combination slag
former and coolant, in a range of 0 to 10% by weight, is selected
from a group including clay, silica, glass, and alumina, or
mixtures thereof. When combining the optional additives described,
or others known to those skilled in the art, care should be taken
to tailor the additions with respect to acceptable thermal
stability, burn rates, and ballistic properties.
[0064] U.S. Pat. No. 6,287,400 discloses gas generant compositions
containing 5-aminotetrazole nitrate (5-ATN) provided at 25-100% by
weight of the gas generant, depending on the application. 5-ATN is
characterized as an oxygen-rich fuel attributed to the oxygen in
the nitrate group. The use of 5-ATN within a gas generant
composition therefore requires little or no additional oxidizer,
again depending on the application. 5-ATN is more preferably
provided at 30-95% by weight and most preferably provided at 55-85%
by weight of the gas generant composition.
[0065] In certain applications, the oxygen balance must be tailored
to accommodate reduced levels of carbon monoxide (CO) and nitrogen
oxides (NOx) as driven by original equipment manufacturer toxicity
requirements. For example, the gas generated upon combustion of a
gas generant within a vehicle occupant restraint system must
minimize or eliminate production of these toxic gases. Therefore,
when adding an oxidizer to 5-ATN, it is generally understood that
an oxygen balance of about -4.0 to +4.0 is desirable when the gas
generant is used in an airbag inflator. The preferred percentages
of 5-ATN reflect this characteristic.
[0066] One or more oxidizers may be selected from the group
including nonmetal, alkali metal, and alkaline earth metal
nitrates, nitrites, perchlorates, chlorates, and chlorites for
example. Other oxidizers well known in the art may also be used.
These include alkali, alkaline earth, and transitional metal
oxides, for example. Preferred oxidizers include phase stabilized
ammonium nitrate (PSAN), ammonium nitrate, potassium nitrate, and
strontium nitrate. The oxidizer(s) is provided at 5-70% by weight
of the gas generant composition and more preferably at 20-45% by
weight of the oxidizer.
[0067] Standard additives such as binders, slag formers, burn rate
modifiers, and coolants may also be incorporated if desired. Inert
components may be included and are selected from the group
containing clay, silicon, silicates, diatomaceous earth, and oxides
such as glass, silica, alumina, and titania. The silicates include
but are not limited to silicates having layered structures such as
talc and the aluminum silicates of clay and mica; aluminosilicate;
borosilicates; and other silicates such as sodium silicate and
potassium silicate. The inert component is present at about 0.1-20%
by weight, more preferably at about 0.1-8%, and most preferably at
0.1-3%. A most preferred embodiment contains 73.12% 5-ATN and
26.88% PSAN10 (stabilized with 10% potassium nitrate).
[0068] U.S. Pat. No. 5,872,329 discloses nonazide gas generants
including phase stabilized ammonium nitrate (PSAN), nitroguanidine
(NQ), and one or more nonazide high-nitrogen fuels. One or more
high-nitrogen fuels are selected from a group including tetrazoles
such as 5-nitrotetrazole, 5,5'-bitetrazole, triazoles such as
nitroaminotriazole, nitrotriazoles, nitrotetrazoles, salts of
tetrazoles and triazoles, and 3-nitro-1,2,4 triazole-5-one.
[0069] More specifically, salts of tetrazoles include in
particular, amine, amino, and amide salts of tetrazole and triazole
selected from the group including monoguanidinium salt of
5,5'-Bis-1H-tetrazole (BHT.cndot.1GAD), diguanidinium salt of
5,5'-Bis-1H-tetrazole (BHT.cndot.2GAD), monoaminoguanidinium salt
of 5,5'-Bis-1H-tetrazole (BHT.cndot.1AGAD), diaminoguanidinium salt
of 5,5'-Bis-1H-tetrazole (BHT.cndot.2AGAD), monohydrazinium salt of
5,5'-Bis-1H-tetrazole (BHT.cndot.1HH), dihydrazinium salt of
5,5'-Bis-1H-tetrazole (BHT.cndot.2HH), monoammonium salt of
5,5'-bis-1H-tetrazole (BHT.cndot.1NH.sub.3), diammonium salt of
5,5'-bis-1H-tetrazole (BHT.cndot.2NH.sub.3),
mono-3-amino-1,2,4-triazolium salt of 5,5'-bis-1H-tetrazole
(BHT.cndot.1ATAZ), di-3-amino-1,2,4-triazolium salt of
5,5'-bis-1H-tetrazole (BHT.cndot.2ATAZ), and diguanidinium salt of
5,5'-Azobis-1H-tetrazole (ABHT.cndot.2GAD).
[0070] Amine salts of triazoles include monoammonium salt of
3-nitro-1,2,4-triazole (NTA.cndot.1NH.sub.3), monoguanidinium salt
of 3-nitro-1,2,4-triazole (NTA.cndot.1GAD), diammonium salt of
dinitrobitriazole (DNBTR.cndot.2NH.sub.3), diguanidinium salt of
dinitrobitriazole (DNBTR.cndot.2GAD), and monoammonium salt of
3,5-dinitro-1,2,4-triazole (DNTR.cndot.1NH.sub.3).
[0071] A preferred fuel(s) is selected from the group consisting of
amine and other nonmetal salts of tetrazoles and triazoles having a
nitrogen containing cationic component and a tetrazole and/or
triazole anionic component. The anionic component comprises a
tetrazole or triazole ring, and an R group substituted on the
5-position of the tetrazole ring, or two R groups substituted on
the 3- and 5-positions of the triazole ring. The R group(s) is
selected from hydrogen and any nitrogen-containing compounds such
as amino, nitro, nitramino, tetrazolyl and triazolyl groups. The
cationic component is formed from a member of a group including
amines, aminos, and amides including ammonia, hydrazine, guanidine
compounds such as guanidine, aminoguanidine, diaminoguanidine,
triaminoguanidine, dicyandiamide, nitroguanidine, nitrogen
substituted carbonyl compounds such as urea, carbohydrazide,
oxamide, oxamic hydrazide, bis-(carbonamide) amine,
azodicarbonamide, and hydrazodicarbonamide, and, amino azoles such
as 3-amino-1,2,4-triazole, 3-amino-5-nitro-1,2,4-triazole,
5-aminotetrazole and 5-nitraminotetrazole. Optional inert additives
such as clay, alumina, or silica may be used as a binder, slag
former, coolant or processing aid. Optional ignition aids comprised
of nonazide propellants may also be utilized in place of
conventional ignition aids such as BKNO.sub.3.
[0072] Certain disclosed gas generant compositions contain a
hydrated or anhydrous mixture of nitroguanidine, at least one
nonazide high-nitrogen fuels selected from the group consisting of
guanidines, tetrazoles, triazoles, salts of tetrazole, and salts of
triazole, and an oxidizer selected from the group consisting of
phase stabilized ammonium nitrate and ammonium perchlorate. The
nonazide fuels may be further selected from the group consisting of
1-, 3-, and 5-substituted nonmetal salts of triazoles, and 1- and
5-substituted nonmetal salts of tetrazoles wherein the salts
consist of nonmetallic cationic and anionic components, and, the
salts are substituted with hydrogen or a nitrogen-containing
compound.
[0073] A preferred gas generant composition results from the
mixture of gas generant constituents including nitroguanidine,
comprising 1%-30% by weight of the gas generant composition, one or
more amine salts of tetrazoles and/or triazoles, comprising 4%-40%
by weight of the gas generant composition, and PSAN, comprising
40%-85% by weight of the gas generant composition. In the
percentages given, an even more preferred embodiment results from
the mixture of gas generant constituents consisting essentially of
NQ, PSAN, and amine salt(s) of 5,5'-bis-1H-tetrazole. In the
percentages given, a most preferred composition results from the
mixture of gas generant constituents consisting essentially of NQ,
PSAN, and diammonium salt of 5,5'-bis-1H-tetrazole
(BHT.cndot.2NH.sub.3). When combined, the fuel component consisting
of NQ and one or more high nitrogen fuels as described herein,
comprises 15%-60% by weight of the gas generant composition.
[0074] Other nonmetal inorganic oxidizers such as ammonium
perchlorate, or oxidizers that produce minimal solids when combined
and combusted with the fuels listed above, may also be used. The
ratio of oxidizer to fuel is preferably adjusted so that the amount
of oxygen allowed in the equilibrium exhaust gases is less than 3%
by weight, and more preferably less than or equal to 2% by weight.
The oxidizer comprises 40%-85% by weight of the gas generant
composition.
[0075] An optional burn rate modifier, from 0-10% by weight in the
gas generant composition, is selected from a group including an
alkali metal, an alkaline earth or a transition metal salt of
tetrazoles or triazoles; an alkali metal or alkaline earth nitrate
or nitrite; TAGN; dicyandiamide, and alkali and alkaline earth
metal salts of dicyandiamide; alkali and alkaline earth
borohydrides; or mixtures thereof. An optional combination slag
former and coolant, in a range of 0 to 10% by weight, is selected
from a group including clay, silica, glass, and alumina, or
mixtures thereof. When combining the optional additives described,
or others known to those skilled in the art, care should be taken
to tailor the additions with respect to acceptable thermal
stability, burn rates, and ballistic properties.
[0076] U.S. Pat. No. 5,872,329 discloses gas generants including
5-aminotetrazole nitrate (5-ATN) provided at 25-100% by weight of
the gas generant, depending on the application. 5-ATN is
characterized as an oxygen-rich fuel attributed to the oxygen in
the nitrate group. The use of 5-ATN within a gas generant
composition therefore requires little or no additional oxidizer,
again depending on the application. 5-ATN is more preferably
provided at 30-95% by weight and most preferably provided at 55-85%
by weight of the gas generant composition.
[0077] In certain applications, the oxygen balance must be tailored
to accommodate reduced levels of carbon monoxide (CO) and nitrogen
oxides (NOx) as driven by original equipment manufacturer toxicity
requirements. For example, the gas generated upon combustion of a
gas generant within a vehicle occupant restraint system must
minimize or eliminate production of these toxic gases. Therefore,
when adding an oxidizer to 5-ATN, it is generally understood that
an oxygen balance of about -4.0 to +4.0 is desirable when the gas
generant is used in an airbag inflator. The preferred percentages
of 5-ATN reflect this characteristic.
[0078] One or more oxidizers may be selected from the group
including nonmetal, alkali metal, and alkaline earth metal
nitrates, nitrites, perchlorates, chlorates, and chlorites for
example. Other oxidizers well known in the art may also be used.
These include alkali, alkaline earth, and transitional metal
oxides, for example. Preferred oxidizers include phase stabilized
ammonium nitrate (PSAN), ammonium nitrate, potassium nitrate, and
strontium nitrate. The oxidizer(s) is provided at 5-70% by weight
of the gas generant composition and more preferably at 20-45% by
weight of the oxidizer.
[0079] Standard additives such as binders, slag formers, burn rate
modifiers, and coolants may also be incorporated if desired. Inert
components may be included and are selected from the group
containing clay, silicon, silicates, diatomaceous earth, and oxides
such as glass, silica, alumina, and titania. The silicates include
but are not limited to silicates having layered structures such as
talc and the aluminum silicates of clay and mica; aluminosilicate;
borosilicates; and other silicates such as sodium silicate and
potassium silicate. The inert component is present at about 0.1-20%
by weight, more preferably at about 0.1-8%, and most preferably at
0.1-3%. A most preferred embodiment contains 73.12% 5-ATN and
26.88% PSAN10 (ammonium nitrate stabilized with 10% potassium
nitrate).
[0080] U.S. Pat. No. 6,210,505 discloses high nitrogen nonazides
employed as primary fuels in gas generant compositions which
include, in particular, ammonium, amine, amino, and amide nonmetal
salts of tetrazole and triazole selected from the group including
monoguanidinium salt of 5,5'-Bi-1H-tetrazole (BHT.cndot.1GAD),
diguanidinium salt of 5,5'-Bi-1H-tetrazole (BHT.cndot.2GAD),
monoaminoguanidinium salt of 5,5'-Bi-1H-tetrazole
(BHT.cndot.1AGAD), diaminoguanidinium salt of 5,5'-Bi-1H-tetrazole
(BHT.cndot.2AGAD), monohydrazinium salt of 5,5'-Bi-1H-tetrazole
(BHT.cndot.1HH), dihydrazinium salt of 5,5'-Bi-1H-tetrazole
(BHT.cndot.2HH), monoammonium salt of 5,5'-Bi-1H-tetrazole
(BHT.cndot.1NH.sub.3), diammonium salt of 5,5'-Bi-1H-tetrazole
(BHT.cndot.2NH.sub.3), mono-3-amino-1,2,4-triazolium salt of
5,5'-Bi-1H-tetrazole (BHT.cndot.1ATAZ), di-3-amino-1,2,4-triazolium
salt of 5,5'-Bi-1H-tetrazole (BHT.cndot.2ATAZ), diguanidinium salt
of 5,5'-Azobis-1H-tetrazole (ABHT.cndot.2GAD), and monoammonium
salt of 5-Nitramino-1H-tetrazole (NAT-1NH.sub.3). The primary fuel
generally comprises about 13 to 38%, and more preferably about 23
to 28%, by weight of the gas generating composition.
##STR00001##
[0081] A generic nonmetal salt of tetrazole as shown in Formula I
includes a cationic component, Z, and an anionic component
comprising a tetrazole ring and an R group substituted on the
5-position of the tetrazole ring. A generic nonmetal salt of
triazole as shown in Formula II includes a cationic component, Z,
and an anionic component comprising a triazole ring and two R
groups substituted on the 3- and 5-positions of the triazole ring,
wherein R.sub.1 may or may not be structurally synonymous with
R.sub.2 An R component is selected from a group including hydrogen
or any nitrogen-containing compound such as an amino, nitro,
nitramino, or a tetrazolyl or triazolyl group from Formula I or II,
respectively, substituted directly or via amine, diazo, or triazo
groups. The compound Z forms a cation by displacing a hydrogen atom
at the 1-position of either formula, and is selected from an amine
group including ammonia, hydrazine; guanidine compounds such as
guanidine, aminoguanidine, diaminoguanidine, triaminoguanidine, and
nitroguanidine; amides including dicyandiamide, urea,
carbohydrazide, oxamide, oxamic hydrazide, Bi-(carbonamide)amine,
azodicarbonamide, and hydrazodicarbonamide; and substituted azoles
including 3-amino-1,2,4-triazole, 3-amino-5-nitro-1,2,4-triazole,
5-aminotetrazole, 3-nitramino-1,2,4-triazole, and
5-nitraminotetrazole; and azines such as melamine.
[0082] The foregoing nonmetal salts of tetrazole or triazole are
dry-mixed with phase stabilized ammonium nitrate (PSAN). PSAN is
generally employed in a concentration of about 46 to 87%, and more
preferably 56 to 77%, by weight of the total gas generant
composition. The ammonium nitrate is stabilized by potassium
nitrate as taught in co-owned U.S. Pat. No. 5,531,941, entitled,
"Process For Preparing Azide-Free Gas Generant Composition", and
granted on Jul. 2, 1996, incorporated herein by reference. The PSAN
comprises 85-90% AN and 10-15% KN and is formed by any suitable
means such as co-crystallization of AN and KN, so that the
solid-solid phase changes occurring in pure ammonium nitrate (AN)
between -40.degree. C. and 107.degree. C. are prevented. Although
KN is preferably used to stabilize pure AN, one skilled in the art
will readily appreciate that other stabilizing agents may be used
in conjunction with AN.
[0083] The gas generants further contain a metallic oxidizer
selected from alkali metal and alkaline earth metal nitrates and
perchlorates. One of ordinary skill will readily appreciate that
other oxidizers such as metallic oxides, nitrites, chlorates,
peroxides, and hydroxides may also be used. The metallic oxidizer
is present at about 0.1-25%, and more preferably 0.8-15%, by weight
of the gas generating composition.
[0084] The gas generants yet further contain an inert component
selected from the group containing silicates, silicon, diatomaceous
earth, and oxides such as silica, alumina, and titania. The
silicates include but are not limited to silicates having layered
structures such as talc and the aluminum silicates of clay and
mica; aluminosilicate; borosilicates; and other silicates such as
sodium silicate and potassium silicate. The inert component is
present at about 0.1-8%, and more preferably at about 0.1-3%, by
weight of the gas generating composition.
[0085] A preferred embodiment contains 56-77% of PSAN, 23-28% of
diammonium salt of 5,5'-Bi-1H-tetrazole (BHT.cndot.2NH3), 0.8-15%
of strontium nitrate, and 0.1-3% of clay.
[0086] The combination of the metallic oxidizer and the inert
component results in the formation of a mineral containing the
metal from the metallic oxidizer. For example, the combination of
clay, which is primarily aluminum silicate (Al, Si.sub.4O.sub.10)
and quartz (SiO.sub.2) with strontium nitrate (Sr(NO.sub.3).sub.2)
results in a combustion product consisting primarily of strontium
silicates (SrSiO.sub.4 and Sr.sub.3SiO.sub.5). It is believed that
this process aids in sustaining the gas generant combustion at all
pressures and thus prevents inflator "no-fires".
[0087] Burn rates of gas generants containing a nonmetal salt as
defined above, PSAN, an alkaline earth metal oxidizer, and an inert
component are low (around 0.30 ips at 1000 psi), lower than the
industry standard of 0.40 ips at 1000 psi. Thus, these compositions
quite unexpectedly ignite and sustain combustion much more readily
than other gas generants having burn rates below 0.40 ips at 1000
psi, and in some cases, perform better than gas generants having
burn rates greater than 0.40 ips.
[0088] Optional ignition aids, used in conjunction with the present
invention, are selected from nonazide fuels including triazoles,
triazolone, aminotetrazoles, tetrazoles, or bitetrazoles, or others
as described in U.S. Pat. No. 5,139,588 to Poole, the teachings of
which are herein incorporated by reference. Conventional ignition
aids such as BKNO.sub.3 are no longer required because a gas
generant containing a tetrazole or triazole based fuel, phase
stabilized ammonium nitrate, a metallic oxidizer, and an inert
component exhibits improved ignitability of the propellant and also
provides a sustained burn rate with repeatable combustible
performance.
[0089] The manner and order in which the components of the gas
generating composition of the present invention are combined and
compounded is not critical so long as a uniform mixture is obtained
and the compounding is carried out under conditions which do not
cause decomposition of the components employed. For example, the
materials may be wet blended, or dry blended and attrited in a ball
mill or Red Devil type paint shaker and then pelletized by
compression molding. The materials may also be ground separately or
together in a fluid energy mill, sweco vibroenergy mill or bantam
micropulverizer and then blended or further blended in a v-blender
prior to compaction.
[0090] When formulating a composition, the ratio of PSAN to fuel is
adjusted such that the oxygen balance is between -4.0% and +1.0%
O.sub.2 by weight of composition as described above. More
preferably, the ratio of PSAN to fuel is adjusted such that the
composition oxygen balance is between -2.0% and 0.0% O.sub.2 by
weight of composition. It can be appreciated that the relative
amount of PSAN and fuel will depend both on the additive used to
form PSAN as well as the nature of the selected fuel.
[0091] In Tables 1 and 2 below, PSAN is phase-stabilized with 15%
KN of the total oxidizer component in all cases except those marked
by an asterisk. In that case, PSAN is phase-stabilized with 10% KN
of the total oxidizer component.
[0092] In accordance with the present invention, these formulations
will be both thermally and volumetrically stable over a temperature
range of -40.degree. C. to 110.degree. C.; produce large volumes of
non-toxic gases; produce minimal solid particulates; ignite readily
and burn in a repeatable manner; contain no toxic, sensitive, or
explosive starting materials; and, be non-toxic, insensitive, and
non-explosive in final form.
TABLE-US-00001 TABLE 1 Moles Grams of Oxygen Burn Rate Composition
of Gas/ Solids/ Balance at 1000 by Weight 100 g of 100 g of by
Weight psi EX Percent Generant Generant Percent (in/sec) 1 76.43%
PSAN 4.00 5.34 0.0% 0.48 23.57% BHT.cndot.2NH.sub.3 2 75.40% PSAN
4.00 5.27 -1.0% 0.47 24.60% BHT.cndot.2NH.sub.3 3 72.32% PSAN 4.00
5.05 -4.0% 0.54 27.68% BHT.cndot.2NH.sub.3
TABLE-US-00002 TABLE 2 Oxygen Balance Composition Mol Gas/ Grams of
Solids/ in in Weight 100 g of 100 g of Weight EX Percent Generant
Generant Percent 4 73.06% PSAN* 4.10 3.40 -4.0% 26.94%
BHT.cndot.2NH.sub.3 5 76.17% PSAN* 4.10 3.55 -1.0% 23.83%
BHT.cndot.2NH.sub.3 6 78.25% PSAN* 4.10 3.65 +1.0% 21.75%
BHT.cndot.2NH.sub.3 7 73.08% PSAN 3.95 5.11 -4.0% 26.92%
BHT.cndot.1GAD 8 76.08% PSAN 3.95 5.32 -1.0% 23.92% BHT.cndot.1GAD
9 78.08% PSAN 3.95 5.46 +1.0% 21.92% BHT.cndot.1GAD 10 73.53% PSAN
3.95 5.14 -4.0% 26.47% ABHT.cndot.2GAD 11 76.48% PSAN 3.95 5.34
-1.0% 23.52% ABHT.cndot.2GAD 12 78.45% PSAN 3.95 5.48 +1.0% 21.55%
ABHT.cndot.2GAD 13 46.27% PSAN 3.94 3.23 -4.0% 53.73%
NAT.cndot.1NH.sub.3 14 52.26% PSAN 3.94 3.65 -1.0% 47.74%
NAT.cndot.1NH.sub.3 15 56.25% PSAN 3.95 3.93 +1.0% 43.75%
NAT.cndot.1NH.sub.3
[0093] U.S. Pat. No. 6,220,266 discloses improving the combustion
and ballistic properties of a given nonazide gas generant
composition, particularly within a gas generator of an airbag
inflator or within a seatbelt pretensioner, by coating the gas
generant composition with silicone. By coating the outside of the
generant pellets or granules with a curable silicone or silicone
gumstock, an easily ignitable formulation that sustains combustion
is obtained. Exemplary inflators/gas generators include those
described in co-owned U.S. Pat. Nos. 5,628,528, 5,622,380,
5,727,813, and 5,806,888 herein incorporated by reference.
Exemplary pretensioners include those described in U.S. Pat. Nos.
5,397,075 and 5,899,399, herein incorporated by reference.
[0094] The nonazide gas generant compositions contain one or more
fuels, at least one oxidizer, and if desired, other additives well
known in the art. In general, compounds that function primarily as
binders are not required given that the granules, pellets or
tablets are pressure formed. Therefore, elastomeric binders (i.e.
rubber or silicone, and the like) are not combined or mixed into
the gas generant composition, particularly in view of the ballistic
performance of gas generant compositions containing such binders.
See FIG. 15. Other binders not having an elastomeric nature may be
used if desired, however.
[0095] Stated another way, the gas generant compositions do not
include azides as fuels, nor do they contain any azido or azide
groups within any constituent combined therein. The gas generant
compositions contemplated herein contain a nitrogen-containing fuel
selected from the group including tetrazoles, bitetrazoles,
triazoles, triazines, guanidines, nitroguanidines, metal and
nonmetal salts and derivatives of the foregoing fuels, and mixtures
thereof; and, an oxidizer selected from the group including
nonmetal or metal (alkali, alkaline earth, and transitional metals)
nitrates, nitrites, chlorates, chlorites, perchlorates, oxides, and
mixtures thereof. Exemplary fuels include nitroguanidine, guanidine
nitrate, aminoguanidine nitrate, 1H-tetrazole, 5-aminotetrazole,
5-nitrotetrazole, 5,5'-bitetrazole,
diguanidinium-5,5'-azotetrazolate, nitroaminotriazole, and melamine
nitrate; and metal and nonmetal salts of the foregoing fuels.
[0096] U.S. Pat. Nos. 5,035,757, 5,139,588, 5,531,941, 5,756,929,
5,872,329, 6,077,371, and 6,074,502, herein incorporated by
reference, exemplify, but do not limit, suitable gas generant
compositions. In general, any gas generant composition (within any
gas generator or any pretensioner, for example) may be coated with
silicone, thereby resulting in improved ignitability and improved
combustion and ballistic properties. The burn rate is vigorously
sustained throughout combustion of a gas generant composition
coated with silicone.
[0097] Exemplary nitrated fuels employed in "smokeless" gas
generant compositions include nitrourea, 5-aminotetrazole nitrate
(5ATN), dinitrodiaminotriazole, urea nitrate, azodicarbonamide
nitrate, hydrazodicarbonamide nitrate, semicarbazide nitrate, and
carbohydrazide nitrate, biuret nitrate, 3,5-diamino-1,2,4-triazole
nitrate, dicyandiamide nitrate, and 3-amino-1,2,4-triazole nitrate.
Certain fuels may be generically described as containing a nitrated
base fuel such that the end compound will be the base fuel plus
HNO.sub.3 For example, urea nitrate is H.sub.2NCONH.sub.2HNO.sub.3.
It is conceivable that some of the fuels may be dinitrates although
most will be mononitrates.
[0098] One or more "smokeless" fuels may also be selected from the
group including amine salts of tetrazole and triazole including
monoguanidinium salt of 5,5'-Bis-1H-tetrazole (BHT.cndot.1GAD),
bis-(1(2)H-tetrazole-5-yl)-amine (BTA.cndot.2NH.sub.I),
diguanidinium salt of 5,5'-Bis-1H-tetrazole (BHT.cndot.2GAD),
monoaminoguanidinium salt of 5,5'-Bis-1H-tetrazole
(BHT.cndot.1AGAD), iaminoguanidinium salt of 5,5'-Bis-1H-tetrazole
(BHT.cndot.2AGAD), monohydrazinium salt of 5,5'-Bis-1H-tetrazole
(BHT.cndot.1HH), dihydrazinium salt of 5,5'-Bis-1H-tetrazole
(BHT.cndot.2HH), monoammonium salt of 5,5'-bis-1H-tetrazole
(BHT.cndot.1NH.sub.3), diammonium salt of 5,5'-bis-1H-tetrazole
(BHT.cndot.2NH.sub.3), mono-3-amino-1,2,4-triazolium salt of
5,5'-bis-1H-tetrazole (BHT.cndot.1ATAZ),
di-3-amino-1,2,4-triazolium salt of 5,5'-bis-1H-tetrazole
(BHT.cndot.2ATAZ), 5,5'-Azobis-1H-tetrazole (ABHT.cndot.2GAD), and
monoammonium salt of 5-Nitramino-1H-tetrazole
(NAT.cndot.1NH.sub.3). Co-owned U.S. Pat. Nos. 5,872,329,
5,501,823, 5,783,773, and 5,545,272, each incorporated by reference
herein, further elaborate on other "smokeless" gas generants and
the manufacture thereof. Other "smokeless" gas generant
compositions known in the art and as defined herein are also
contemplated.
[0099] The gas generant compositions of the present invention
further contain one or more inorganic oxidizers selected from the
group of nonmetal, alkali metal, and alkaline earth metal nitrates
and nitrites for example. Other oxidizers well known in the art may
also be used. These include oxides or coordination complexes, for
example. Preferred oxidizers include phase stabilized ammonium
nitrate, ammonium nitrate, potassium nitrate, and strontium
nitrate.
[0100] The gas generant composition, absent the silicone coating,
contains 15-95% by weight of fuel and 5-85% by weight of oxidizer.
The gas generant composition more preferably contains 20-85% by
weight of fuel, and 15-80% by weight of oxidizer (not including the
silicone coating). The gas generant constituents are homogeneously
dry or wet blended and then formed into granules (800 .mu.m to 12
mm, and more preferably 0.1 mm to 3 mm, in rough diameter),
pellets, tablets, or other desired shapes by well known methods
such as extrusion or pressure forming methods. The gas generant
composition is then physically coated with 1-50%, and more
preferable 3-20%, by weight (gas generant and the silicone) of a
silicone gumstock or curable silicone polymer. Gas generant
granules, tablets, pellets, or other desired shapes are formed and
then added with an effective amount of silicone to a tumble blender
and blended, preferably for at least two hours.
[0101] The term "silicone" as used herein will be understood in its
generic sense. Hawley describes silicone (organosiloxane) as any of
a large group of siloxane polymers based on a structure consisting
of alternate silicon and oxygen atoms with various organic radicals
attached to the silicon:
##STR00002##
Or, silicone can be more generically represented as shown Formula
2:
##STR00003##
[0102] Note, "n" in the Formulas indicates a multiple of the
polymeric group or portion of the molecule given within the
brackets, to include the organic groups attached to the
silicon.
[0103] Exemplary silicones include those disclosed in U.S. Pat.
Nos. 5,589,662, 5,610,444, and 5,700,532, and, in Technology of
Polymer Compounds and Energetic Materials, Fraunhofer-Institut fur
Chemische Technologie (ICT), 1990, each reference and document
herein incorporated by reference.
[0104] Standard slag formers and coolants may also be incorporated
if desired. Binders are not generally utilized because the gas
generant constituents described herein are homogeneously blended
and then preferably compacted or formed into granules or other
shapes through pressure or other known physical methods. If binders
are used, however, elastomeric, rubber, or silicone binders are not
combined in the present compositions given the poor ballistic
performance shown in FIG. 15.
[0105] Other "smokeless" gas generant compositions containing
5-ATN, or any other nitrated base fuel, are also contemplated. The
base fuels include, but are not limited to, nitrourea,
5-aminotetrazole, diaminotriazole, urea, azodicarbonamide,
hydrazodicarbonamide, semicarbazide, carbohydrazide, biuret,
3,5-diamino-1,2,4-triazole, dicyandiamide, and
3-amino-1,2,4-triazole. Each of these base fuels may be nitrated
and combined with one or more oxidizers. Thus, methods of forming
gas generant compositions containing 5ATN and one or more
oxidizers, as described below but not thereby limited, exemplify
the manufacture of gas generant compositions containing any
nitrated base fuel and one or more oxidizers.
[0106] The constituents of the nitrated gas generant compositions
may all be obtained from suppliers well known in the art. In
general, the base fuel (in this case 5AT) and any oxidizers are
added to excess concentrated nitric acid and stirred until a damp
paste forms. This paste is then formed into granules by either
extrusion or forcing the material through a screen. The wet
granules are then dried.
[0107] The nitric acid can be the standard reagent grade (15.9M,
-70 wt. % HNO.sub.3) or can be less concentrated as long as enough
nitric acid is present to form the mononitrate salt of 5AT. The
nitric acid should be chilled to 0-20.degree. C. before adding the
5AT and oxidizers to ensure that the 5AT does not decompose in the
concentrated slurry. When mixing the 5AT and oxidizers in the
nitric acid medium, the precise mixing equipment used is not
important--it is simply necessary to thoroughly mix all the
components and evaporate the excess nitric acid. As with any
process using acids, the materials of construction must be properly
selected to prevent corrosion. In addition, sufficient ventilation
and treatment of the acid vapor is required for added safety.
[0108] After forming a wet paste as described above, several
methods can be used to form granules. The paste can be placed in a
screw-feed extruder with holes of desired diameter and then chopped
into desired lengths. An oscillating granulator may also be used to
form granules of desired size. The material should be kept wet
through all the processing steps to minimize safety problems. The
final granules can be dried in ambient pressure or under vacuum. It
is most preferred to dry the material at about 30.degree. C. under
a-12 psig vacuum.
[0109] Other suitable compositions are set forth in the U.S. patent
application Ser. Nos. 10/407,300 and 60/369,775, incorporated
herein by reference. Use of a smokeless gas generant composition
allows the gas generating system to operate without the need for a
filter to remove particulate materials from the inflation gas. It
should be appreciated, however, that a filter might be disposed
within or external to the gas generating system described herein if
desired, for example, in applications wherein a non-smokeless gas
generant material is used.
[0110] Referring again to FIG. 1, a baffle system, generally
designated 42, is provided for cooling and removing slag from
combustion products generated by combustion of gas generant
composition 38 in first combustion chamber 34a and gas generant
composition 40 in second combustion chamber 36a. As used here, the
term "baffle" refers to a device that regulates the flow of a
fluid.
[0111] In the embodiment shown in FIG. 1, baffle system 42 is
positioned adjacent both the first and second combustion chambers
so as to enable fluid communication with both first combustion
chamber 34a and second combustion chamber 36a upon activation of
the gas generating system. As seen in FIGS. 1, 6, 7, and 10, in one
embodiment baffle system 42 comprises a first end plate 44, a
second end plate 46, and at least one baffle element 48 positioned
and secured between first and second end plates 44, 46 for
channeling gases flowing through baffle system 42 from first and
second combustion chambers 34a and 36a. In the embodiment shown in
FIG. 1, first combustion chamber 34a is positioned on an opposite
side of baffle system 42 from second combustion chamber 36a.
However, the combustion chambers need not be positioned
diametrically opposite each other. In addition, more than two
combustion chambers may be operatively coupled to baffle system
42.
[0112] Referring to FIGS. 1 and 6, a first perforate end plate 44
is press fit or otherwise secured within housing 12. An annular
recess 44a is formed on a face of end plate 44 along a periphery of
the plate. Recess 44a is dimensioned so that an end portion of
annular sleeve 34 (described above) having a predetermined inner
diameter may be positioned within recess 44a to form an
interference fit with end plate 44.
[0113] First end plate 44 also has at least one annular slot 44b
(and preferably a plurality of annular slots) formed therein for
positioning and securing one or more corresponding annular baffle
elements 48 within baffle system 42.
[0114] At least one orifice 44b is provided in end plate 44 to
enable fluid communication between gas generant combustion chamber
34a and an interior of baffle system 42. In the embodiment shown in
FIGS. 1 and 6, a plurality of orifices 44b is formed in end plate
44. End plate 44 is made from a metal or metal alloy and may be a
cast, stamped, drawn, extruded, or otherwise metal-formed and
finish-machined as necessary.
[0115] A rupturable, fluid-tight seal (not shown) may be positioned
across orifices 44b to fluidly isolate baffle system 42 from first
combustion chamber 34a prior to activation of the gas generating
system. The seal is secured to a face of end plate 44 and forms a
fluid-tight barrier between baffle system 42 and combustion chamber
34a. Various disks, foils, films, tapes, etc. may be used to form
seal 45.
[0116] Referring to FIGS. 1 and 7, a second perforate end plate 46
is press fit or otherwise secured within housing 12. An annular
recess 46a is formed on a face of end plate 46 along a periphery of
the plate. Recess 46a is dimensioned so that an end portion of
annular sleeve 36 (described above) having a predetermined inner
diameter may be positioned within recess 46a to form an
interference fit with end plate 46.
[0117] End plate 46 also has at least one annular slot (and
preferably a plurality of annular slots) formed therein for
positioning and securing a plurality of corresponding annular
baffle elements 48 within baffle system 42.
[0118] At least one orifice 46b is provided in end plate 46 to
enable fluid communication between gas generant combustion chamber
36a and an interior of baffle system 42. In the embodiment shown in
FIGS. 1 and 7, a plurality of orifices 46b is formed in end plate
46. End plate 46 is made from a metal or metal alloy and may be a
cast, stamped, drawn, extruded, or otherwise metal-formed and
finish-machined as necessary.
[0119] In the embodiment shown in FIG. 1, a rupturable, fluid-tight
seal (not shown) may be positioned across orifices 46b to fluidly
isolate baffle system 42 from combustion chamber 36a prior to
activation of the gas generating system. The seal is secured to a
face of end plate 46 and forms a fluid-tight barrier between baffle
system 42 and combustion chamber 36a. Various disks, foils, films,
tapes, etc. may be used to form seal 47.
[0120] Referring to FIGS. 1 and 10, at least a first baffle element
48a is provided for channeling gases flowing through baffle system
42 from first and second combustion chambers 34a and 36a, and for
providing a tortuous flow path for the gases. In the embodiment
shown in FIGS. 1 and 10, first baffle element 48a is in the form of
a relatively thin plate.
[0121] First baffle plate 48a defines a chamber 60 adapted for
receiving therein (through end plate openings 44b) a gas from first
combustion chamber 34a and for receiving therein (through openings
46b) a gas from second combustion chamber 36a upon activation of
the gas generating system.
[0122] First baffle plate 48a also has at least one opening 61
therealong for enabling fluid communication between chamber 60 and
an exterior of the chamber. In the embodiment shown in FIG. 10,
multiple orifices 61 are provided and are arranged to form a first
baffle member orifice configuration, generally designated 61a. In
this embodiment, openings 12d formed in housing wall 12c are is
spaced apart from orifice configuration 61a so as to provide a
tortuous path for flow of a gas between chamber entrance openings
44b and openings 12d in housing wall 12c.
[0123] The embodiment shown in FIG. 13 is identical to the
embodiment shown in FIG. 1 except for the inclusion of additional
baffle plates 48b and 48c. The embodiment shown in FIG. 13 includes
a first baffle plate 48a, a second baffle plate 48b, and a third
baffle plate 48c. Any desired number of baffle plates may be
incorporated into baffle system 42, depending on the requirements
of the baffle system.
[0124] In FIGS. 1 and 11, second baffle plate 48b is positioned
interior of housing wall 12c and exterior of first baffle plate 48a
so as to define a first fluid flow passage 70 extending between
second baffle plate 48b and first baffle plate 48a. Third baffle
plate 48c (FIG. 12) is positioned interior of housing wall 12c and
exterior of second baffle plate 48b so as to define a second fluid
flow passage 72 extending between second baffle plate 48b and third
baffle plate 48c. Second baffle plate 48b has at least one opening
62 formed therealong for enabling fluid communication between first
fluid flow passage 70 and second fluid flow passage 72. In the
embodiment shown in FIG. 11, multiple orifices 62 are provided and
are arranged to form a second baffle member orifice configuration,
generally designated 62a. Third baffle plate 48c (FIG. 12) has at
least one opening 63 formed therealong for enabling fluid
communication between second fluid flow passage 72 and housing wall
12c. In the embodiment shown in FIG. 12, multiple orifices 63 are
provided and are arranged to form a third baffle member orifice
configuration, generally designated 63a.
[0125] In the embodiment shown in FIG. 13, openings 12d in housing
12 are spaced apart from third baffle member orifice configuration
63a (FIG. 12) and third baffle member orifice configuration 63a is
spaced apart from second baffle member orifice configuration 62a
(FIG. 11) so as to provide a tortuous path for flow of a fluid
between at least one of baffle plate chamber entrances 44b, 46b and
housing wall openings 12d.
[0126] In the embodiment shown in FIG. 13, baffle plates 48 are
generally cylindrical. However, one or more of the baffle plates
may have an alternative cross-sectional shape, if so required by a
particular application. In the embodiment shown in FIG. 13, baffle
plates 48 are positioned coaxially within housing. However, baffle
plates 48 need not necessarily be positioned coaxially. Baffle
plates 48 may be formed using any of a variety of known methods,
such as extrusion or roll-forming. Orifice patterns 61a, 62a, and
63a in baffle plates 48 may be formed by punching or piercing.
[0127] Referring to FIG. 1, a fluid flow passage 56 may be formed
interior of housing wall 12c and extending along at least a portion
of first combustion chamber 34a. Fluid flow passage 56 is in fluid
communication with baffle system 42 and with an exterior of the
housing via housing openings 12d.
[0128] Referring again to FIG. 1, an additional fluid flow passage
58 may be formed interior of housing wall 12c and extending along
at least a portion of second combustion chamber 36a. Fluid flow
passage 58 is in fluid communication with baffle system 42 and with
an exterior of the housing via housing openings 12d.
[0129] Operation of the gas generating system will now be discussed
with reference to the Figures. Upon receipt of a signal from a
crash sensor, an electrical activation signal is sent to one (or
both) of igniters 30a and 32a. Either of igniters 30a and 32a may
be activated alone. Alternatively, both of igniters 30a and 32a may
be activated separately, in sequence, or simultaneously. Combustion
products from igniters 30a and 32a expand into associated cavities
22d and 24d, igniting associated booster compounds 26 and 28
positioned in the cavities. Products from the combustion of booster
compounds 26 and 28 proceed out of cavities 22d and 24d through
associated ignition cup orifices 22c and 24c, igniting gas
generants 38 and 40 positioned in associated combustion chambers
34a and 36a.
[0130] Products form combustion of gas generants 38 and 40 proceed
through associated baffle end plate orifices 44b and 46b into
chamber 60 of baffle system 42. From there, the gases exit through
first baffle orifice configuration 61a formed in first baffle
element 48a, proceeding through second baffle orifice configuration
62a formed in second baffle element 48b, then through third baffle
orifice configuration 63a formed in third baffle element 48c. The
gases then exit housing 12 through housing openings 12d. Thus, as
may be seen in FIG. 13, gases produced in combustion chambers 34a
and/or 36a flow alternately along baffle plates 48, during which
the gases are cooled and slag is removed from the gases.
[0131] In alternative embodiments (not shown), housing openings 12d
are positioned along fluid flow passage 56 and/or along fluid flow
passage 58, rather than along the portion of housing 12 occupied by
baffle system 42. In these embodiments, the total length of flow of
the fluid through the gas generating system is increased by
directing the fluid through passages 56 and/or 58 after exiting the
baffle system, thereby providing additional cooling and slag
removal if needed.
[0132] It is believed that the degree of cooling of the gas in the
baffle system is largely dependent upon the total surface area of
the relatively lower-temperature baffle elements over which the gas
flows when transiting the baffle system. It is also believed that
the pressure drop in the gas as it transits the baffle system is
largely dependent upon the size and number of orifices through
which the gas flows in the baffle system, and also on the spacing
between adjacent baffles. Thus, the physical characteristics of
baffle system 42 may be varied to produce a gas exiting the gas
generating system with desired properties (for example, temperature
or pressure.)
[0133] Referring to FIGS. 1-14, in one example, a gas having a
pressure within a predetermined pressure range and a temperature
within a predetermined temperature range may be produced. In a
first step, a total length of a flow path of a gas along a given
surface area of a predetermined baffle element material necessary
to cool a gas to from a temperature in at least one of combustion
chambers 34a and 36a to a temperature within a predetermined
temperature range is estimated. A baffle system is then configured
having a total length of internal flow path for the gas
substantially equal to the estimated length of gas flow path
necessary to cool the gas to within the desired temperature range.
In one embodiment, as described above, a suitable sequence of
baffle elements is formed from the baffle element material. A first
baffle element 48a of the sequence of baffle elements defines a
chamber 60 adapted for receiving therein a gas from one or more of
combustion chambers 34a and 36a upon activation of the gas
generating system. Each additional baffle element 48b, 48c in the
sequence of baffle elements is spaced outwardly apart from a
preceding baffle element in the sequence.
[0134] An overall baffle system orifice configuration (comprising
orifice configurations 61a, 62a, and 63a formed in individual
baffle elements of the baffle system) is incorporated into the
baffle system along the internal flow path for the gas, to enable
fluid communication between the various elements and flow passages
of the baffle system. In one example, when it is desired to cool a
gas emanating from first combustion chamber 34a, an orifice
configuration 61a is provided in the first baffle element 48a for
enabling fluid communication between chamber 60 and second baffle
element 48b spaced outwardly apart from the first baffle element.
First baffle element orifice configuration 61a is spaced apart a
first predetermined distance L1 from an entrance 44b to the first
baffle element chamber 60 from first combustion chamber 34a. In
addition, orifice configurations 62a and 63a are provided in each
additional baffle elements 48b and 48c outside the first baffle
element. Orifice configuration 62a in baffle plate 48b enables
fluid communication between first baffle plate 48a and an exterior
of additional, second baffle plate 48b. Orifice configuration 63a
in baffle plate 48c enables fluid communication between second
baffle plate 48b and an exterior of third baffle plate 48c. The
orifice configuration in each additional baffle element is spaced
apart an additional predetermined distance from the orifice
configuration in the preceding baffle element. Thus, orifice
configuration 62a in baffle plate 48b is spaced apart a
predetermined distance L2 from orifice configuration 61a in baffle
plate 48a. Also, orifice configuration 63a in baffle plate 48c is
spaced apart a predetermined distance L3 from orifice configuration
62a in baffle plate 48b. The baffle elements and their respective
orifice patterns are structured such that a sum of the first
predetermined distance L1 and the additional predetermined
distances L2 and L3 are approximately equal to the estimated total
length of a flow path of a gas necessary to cool the gas to a
temperature within the predetermined temperature range.
[0135] The overall baffle system orifice configuration may also be
adapted for modifying the pressure of a gas transiting the baffle
system, to provide a gas having a pressure within a predetermined
pressure range.
[0136] In one example, an orifice configuration in at least one of
baffle elements 48 is varied such that the pressure of a gas
flowing out of the baffle system through orifice configuration 63a
in last baffle element 48c is at a pressure within the
predetermined pressure range. The orifice configuration in at least
one of baffle elements 48 may be varied, for example, by varying
the sizes of the orifices in the baffle element or elements. The
orifice configuration in at least one of the baffle elements may
also be varied by varying the number of orifices in the baffle
element or elements. In another example, the spacing between
adjacent baffle plates 48a, 48b, 48c is varied to correspondingly
vary the pressure of a gas flowing through orifice configuration
63a in last baffle element 48c such that the outflow pressure is at
a pressure within the predetermined pressure range. When baffle
plate arrangement having appropriate orifice configurations and/or
spacings has been achieved, the baffle system is positioned within
the housing so as to enable fluid communication with the first and
second combustion chamber upon activation of the gas generating
system, as previously described. As described above, determination
of the baffle element dimensions and orifice configurations
suitable for a particular application may be an iterative
process.
[0137] In addition, the baffle system orifice configurations may be
varied to control a flow rate of gas exiting the gas generating
system. For example, reducing the sizes and number of internal
orifices in baffle system 42 acts to restrict the flow of gases
through the baffle system, thereby lengthening time period over
which gases are dispensed from housing 12.
[0138] Increasing the number of nested baffle elements increases
the number of flow passages traversed by the gases flowing from
first baffle chamber 60 to housing openings 12d. Thus, the baffle
surface area along which the gases flow prior to exiting the gas
generating system is increased. It is believed that this results in
an increase in the heat transferred from the gases to the baffle
system and correspondingly reducing the temperature of the gases
exiting the housing. Maximizing the baffle surface area also
provides as large an area as possible for the capture of
particulates from the combustion products.
[0139] Increasing the number of fluid flow passages also increases
the pressure drop experienced by the inflation gases between
chamber 60 and housing openings 12d. To a certain extent, the
pressure drop caused by increasing the number of baffles may be
compensated for by increasing the sizes and/or number of gas flow
openings formed in baffle plates 48, to aid in reducing resistance
to gas flow through the baffle system. Also, the pressure drop may
be reduced by making the spacing between adjacent baffles as large
as possible.
[0140] Alternatively, characteristics of the baffle system may be
controlled such that the pressure of the inflation gas exiting
housing 12 is within a predetermined pressure range. Minimizing the
number of baffle elements in the baffle system will aid in
minimizing the pressure drop in the gas due to passage through the
baffle system. However, minimizing the number of baffle elements
also reduces the ability of the baffle system to cool the
gases.
[0141] It may be seen that by suitable controlling the physical
parameters of the baffle system (for example, the number of baffle
elements, the lengths of the baffle elements, and the sizes and
number of gas flow openings in the baffle elements), gases having a
wide variety of desired characteristics (for example, predetermined
pressure, temperature, dispersal time from the gas generating
system, etc.) may be obtained.
[0142] The gas generating system described herein provides several
advantages over known designs. The properties of the gases
generated may be varied according to design requirements by varying
the number and arrangement of baffle elements and the number and
configuration of orifices within the baffle system.
[0143] In addition, the use of interference fits and other means
for securing together the components of the baffle system and gas
generating system obviate the need for welds in assembly of the gas
generating system.
[0144] In a particular application, the gas generating system
described above is incorporated into an airbag module of a vehicle
occupant protection system. Referring to FIG. 16, any embodiment of
the gas generator described herein may be incorporated into an
airbag system 200. Airbag system 200 includes at least one airbag
202 and a gas generating system 10 as described herein coupled to
the airbag so as to enable fluid communication with an interior of
the airbag. Airbag system 200 may also be in communication with a
known crash event sensor 210 that is in operative communication
with a known crash sensor algorithm (not shown) which signals
actuation of airbag system 200 via, for example, activation of
igniter 68 (not shown in FIG. 16) in the event of a collision.
[0145] Referring again to FIG. 16, an embodiment of the gas
generator or an airbag system including an embodiment of the gas
generator may be incorporated into a broader, more comprehensive
vehicle occupant restraint system 180 including additional elements
such as a safety belt assembly. Safety belt assembly 150 includes a
safety belt housing 152 and a safety belt 160 extending from
housing 152. A safety belt retractor mechanism 154 (for example, a
spring-loaded mechanism) may be coupled to an end portion of the
belt. In addition, a safety belt pretensioner 156 may be coupled to
belt retractor mechanism 154 to actuate the retractor mechanism in
the event of a collision. Typical seat belt retractor mechanisms
which may be used in conjunction with safety belt 100 are described
in U.S. Pat. Nos. 5,743,480, 5,553,803, 5,667,161, 5,451,008,
4,558,832 and 4,597,546, incorporated herein by reference.
Illustrative examples of typical pretensioners with which safety
belt 160 may be combined are described in U.S. Pat. Nos. 6,505,790
and 6,419,177, incorporated herein by reference.
[0146] Safety belt assembly 150 may be in communication with a
known crash event sensor 158 (for example, an inertia sensor or an
accelerometer) that is in operative communication with a known
crash sensor algorithm (not shown) which signals actuation of belt
pretensioner 156 via, for example, activation of a pyrotechnic
igniter (not shown) incorporated into the pretensioner. U.S. Pat.
Nos. 6,505,790 and 6,419,177, previously incorporated herein by
reference, provide illustrative examples of pretensioners actuated
in such a manner.
[0147] It will be appreciated that the various constituents
described above are formed in known manners. For example, the
baffles and various chambers may be molded. stamped or otherwise
metal formed from carbon steel, aluminum, metallic alloys, or
polymeric equivalents.
[0148] It will be understood that the foregoing description of the
present invention is for illustrative purposes only, and that the
various structural and operational features herein disclosed are
susceptible to a number of modifications, none of which departs
from the spirit and scope of the present invention. The preceding
description, therefore, is not meant to limit the scope of the
invention. Rather, the scope of the invention is to be determined
only by the appended claims and their equivalents.
* * * * *