U.S. patent number 3,695,179 [Application Number 05/092,474] was granted by the patent office on 1972-10-03 for electrically actuable ignitor for passenger restraint system employing an inflatable cushion.
This patent grant is currently assigned to Westinghouse Electric Corporation. Invention is credited to Jacob F. Michael, Nicholas J. Rainone.
United States Patent |
3,695,179 |
Rainone , et al. |
October 3, 1972 |
ELECTRICALLY ACTUABLE IGNITOR FOR PASSENGER RESTRAINT SYSTEM
EMPLOYING AN INFLATABLE CUSHION
Abstract
A reliable and inexpensive ignitor for rapidly "firing" the
combustible gas-producing charge of an inflatable-cushion type
safety apparatus for motor vehicles. The ignitor preferably
comprises a modified AG 1/2 photoflash lamp assembly which has an
open-ended glass tube instead of the sealed glass envelope normally
employed and is devoid of shredded foil. The open end of the tube
is sealed by a plastic diaphragm which ruptures when a
predetermined amount of primer inside the tube is ignited by
passing electric current through a wire filament that is embedded
within the primer.
Inventors: |
Rainone; Nicholas J. (Clifton,
NJ), Michael; Jacob F. (Paramus, NJ) |
Assignee: |
Westinghouse Electric
Corporation (Pittsburgh, PA)
|
Family
ID: |
22233395 |
Appl.
No.: |
05/092,474 |
Filed: |
November 24, 1970 |
Current U.S.
Class: |
102/202.11;
280/741; 280/734; 431/362 |
Current CPC
Class: |
C06B
33/06 (20130101); C06C 9/00 (20130101); F42B
3/198 (20130101); F42B 3/125 (20130101) |
Current International
Class: |
F42B
3/12 (20060101); F42B 3/00 (20060101); F42c
019/12 (); B60k 035/00 () |
Field of
Search: |
;102/7.2R ;180/13AB
;313/53,178 ;431/94,95,98 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Borchelt; Benjamin A.
Assistant Examiner: Doramus; J. V.
Claims
We claim as our invention:
1. An electrically actuable ignitor adapted for use in a passenger
restraint system having an inflatable cushion, said ignitor
comprising;
a rigid hollow body of electrically non-conductive material that is
closed at one end by a diaphragm and has a seal at its opposite end
through which a pair of spaced conductors extend,
a wire filament fastened to the inner ends of said conductors,
and
a primer comprising a quantity of thermally ignitable combustible
material disposed on at least a portion of said filament,
said diaphragm having a wall thickness less than that of said
hollow body and thereby constituting an end closure that ruptures
when said ignitor is actuated.
2. The ignitor according to claim 1 wherein; said rigid hollow body
is composed of frangible vitreous material, and
the walls of said hollow vitreous body are covered by an exterior
layer of plastic that encloses and constitutes a protective sheath
for said vitreous body.
3. The ignitor according to claim 1 wherein said primer comprises a
mixture of a fuel and an oxidizer.
4. The ignitor according to claim 3 wherein said fuel comprises a
powdered incandescible metal and said oxidizer comprises admixed
potassium perchlorate and strontium nitrate.
5. The ignitor according to claim 4 wherein said powdered
incandescible metal is a metal selected from the group consisting
of zirconium, magnesium, and mixtures thereof.
6. The ignitor according to claim 1 wherein;
said rigid hollow body comprises a glass tube,
said seal comprises a press seal formed at the end of said glass
tube,
said conductors comprise a pair of lead-in wires,
said primer encloses the filament and the associated segments of
said lead-in wires but only partly fills the glass tube,
said diaphragm comprises a film of plastic material that is bonded
to the rim of said glass tube, and
a protective coating of plastic covers the outer surfaces of said
plastic diaphragm and glass tube, including the adjacent portions
of the press seal, and thereby constitutes a hermetic enclosure for
the ignitor.
7. The ignitor according to claim 6 wherein;
said filament comprises a fine tungsten wire,
said lead-in wires are joined by a glass bead that is located
between the press seal and the inner ends of said wires, and
said glass tube, lead-in wires, bead and filament comprise an AG
1/2 type photoflash lamp mount assembly.
8. The ignitor according to claim 7 wherein said primer comprises
from about 100 to 115 milligrams of a mixture of potassium
perchlorate, strontium nitrate, a binder, and a powdered
incandescible metal selected from the group consisting of
zirconium, magnesium, and mixtures thereof.
9. The ignitor according to claim 8 wherein;
said protective plastic coating comprises a layer of cellulose
acetate,
said binder comprises nitrocellulose, and
said primer contains stoichiometric amounts of potassium
perchlorate, strontium nitrate and powdered zirconium.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention generally relates to an inflatable-cushion type
safety system for motor vehicles and has particular reference to an
ignitor for triggering such a system by means of an electric
current.
2. Description of the Prior Art
Various safety devices utilizing rapidly inflated bags or cushions
for protecting the passengers of automobiles from injury during a
collision are known and are presently being evaluated. A passive
restraint system of this type employing a flexible dual-chamber
container that is rapidly inflated by a gas mixture is disclosed in
U.S. Pat. No. 3,476,402. A similar apparatus utilizing an
inflatable cushion that is attached to a pressure container which
is opened by detonating an explosive charge and wherein at least a
portion of the cushion is made of porous material is disclosed in
U.S. Pat. No. 3,511,519.
In other systems the bag or cushion is inflated with gases
generated by a charge of fulminating material such as a mass of an
explosively combustible chemical. In order to be practical from
both a functional and cost standpoint, systems of this type require
an ignitor which is not only simple, inexpensive and reliable but
one which will set off the gas-producing charge within the alotted
time -- typically, a few milliseconds.
SUMMARY OF THE INVENTION
The present invention provides an ignitor which meets all of the
foregoing requirements. Briefly, the ignitor comprises a component
that is similar to a miniature electric lamp and can thus be
actuated by a small electric current.
In accordance with a preferred embodiment the ignitor comprises a
modified AG 1/2 photoflash lamp mount and bulb assembly. The
tungsten filament is coated with a large but controlled amount of a
selected thermally ignitable primer material and the sealed bulb is
replaced with a tubular glass sleeve that is closed at one end by
the usual press seal but has its opposite end closed by a
rupturable diaphragm of thin plastic. The ignitor, accordingly, has
the same basic structural features as an AG 1/2 photoflash lamp.
Embryonic ignitor assemblies can thus be efficiently and
economically manufactured on the same high-speed machines used to
make such lamps. The subsequent operations required to deposit the
proper amount of primer on the filament, form the rupturable
plastic diaphragm, etc. can readily be performed by automated
equipment.
The present invention accordingly provides ignitors that can be
mass produced in a manner which drastically reduces their unit cost
and insures the high degree of quality and uniformity necessary to
meet the stringent reliability standards of the safety system in
which they will be used. The ignitors are hermetically sealed and
will thus remain "fresh" and ready for use over long periods of
time. They are also very rugged and will withstand the various
vibrational forces, etc. encountered in the cars and other vehicles
in which they are installed.
BRIEF DESCRIPTION OF THE DRAWING
A better understanding of the invention will be obtained from the
exemplary embodiment shown in the accompanying drawing,
wherein:
FIG. 1 is a schematic elevational view, partly in cross-section, of
an inflatable-cushion type safety apparatus which includes the
electrical ignitor component of the present invention;
FIG. 2 is an enlarged elevational view, partly in section, of the
ignitor component used in the apparatus shown in FIG. 1; and
FIGS. 3-5 are elevational views, mainly in cross-section,
illustrating the various operations required to complete the
ignitor.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In FIG. 1 there is shown a safety system 9 for an automobile or
other vehicle which uses the inflatable cushion or bag concept for
protecting passengers from injury during a crash. The system 9
includes the usual gas generator such as a metal casing or bottle
10 that contains a charge 12 of a pyrotechnic type material that
will ignite in an explosive-like manner and generate a sufficient
quantity of gas to rapidly inflate and deploy a flexible bag 16
secured to the bottle. The gas-producing charge 12 is set off by an
ignitor 18 that is seated in a suitable socket 20 mounted in an
opening in a wall of the bottle 10.
The ignitor 18 is so positioned that hot gases and incandescent
particles ejected from the ignitor will strike the gas-producing
charge 12 and set it off when the ignitor 18 is electrically
energized. The latter is achieved by a pair of conductors 22 that
are connected to a voltage source (the car battery for example)
through a suitable electromechanical sensor, such as an inertia or
pendulum type switch, that instantaneously detects and is activated
by a collision.
The present invention relates to the electrically actuable ignitor
18 which fires the gas-producing charge 12 of the restraint system
9 and this component and the manner in which it is manufactured
will now be described.
As shown in FIG. 2, the ignitor 18 comprises an elongated hollow
body of vitreous material, preferably a glass tube 24 of circular
cross-section as illustrated, that is terminated at one end by a
press seal 26 and has its opposite end closed by a rupturable
membrane or diaphragm 28 that is secured to the lip of the tube.
While various types of diaphragms 28 may be used, in the preferred
embodiment shown it consists of a thin film of a suitable plastic,
such as that marketed by the Dow Chemical Company under the trade
name "Saran." The diaphragm 28 is protected from physical damage
during handling, storage etc. by an overcoating 30 of a suitable
plastic, such as cellulose acetate, that extends around the
exterior side walls of the glass tube 24 and covers the adjacent
portions of the press seal 26 of fused glass. The exterior plastic
coating 30 thus hermetically seals the ignitor 18 and also serves
as a protective sheath which holds the pieces of the shattered
glass tube 24 in place and prevents them from being propelled into
the inflatable bag 16 and possibly causing it to rupture when the
ignitor is actuated.
A pair of spaced conductors such as rigid lead-in wires 32 are
embedded in and extend through the press seal 26. A fine-wire
filament 34 of tungsten or the like is attached to the inner ends
of the lead-in wires 32 and a suitable thermally ignitable primer
36 is disposed on the filament 34. The amount of primer 36 required
to achieve rapid ignition of the gas-producing charge 12 is such
that the primer material completely encloses the filament 34 and
the ends of the attached lead-in wires 32, as illustrated in FIG.
2. The exposed ends of the lead wires 32 engage the contacts of the
socket 20 and thus constitute the terminals of the ignitor 18.
To facilitate manufacture, medial portions of the lead-in wires 32
that are located between the rigid body of primer 36 and the press
seal 26 are joined by a glass bead 38 -- thus providing a unitary
mount that can be readily handled and press sealed into the glass
tube 24. The beaded mount and press seal features of the ignitor 18
are preferably identical with those employed in conventional AG 1/2
photoflash lamps and the ignitors 18 can, accordingly, be
manufactured in embryonic form on the same high-speed machines
presently being used to make such photoflash lamps.
An embryonic ignitor 18' produced by such a machine is shown in the
right-hand portion of FIG. 3. As will be noted, it consists of the
open-ended glass tube 24 one end of which is formed into a press
seal 26 that encloses the end of a beaded mount consisting of the
lead-in wires 32 and conjoined glass bead 38 and tungsten filament
34. The first operation in completing the assembly of the ignitor
consists of dipping the end of the filament mount into a hardenable
slurry or suspension of primer material. This can be achieved by
lowering the embryonic ignitor 18' into a cup 40 (as indicated by
the arrow at the right of FIG. 3) which contains the primer
suspension 41 and fits inside of the glass tube 24. Thus, only the
filament 34 and inner ends of the leads 32 are dipped into the
primer material 41. After the mount has been dipped a sufficient
number of times to deposit the proper amount of primer 36 on the
filament and leads, the ignitor assembly 18' is retracted from the
cup 40, as indicated by the arrow at the left of FIG. 3. Of course,
the deposited primer is dried after each of the dipping
operations.
The next operation consists of closing the open end of the
embryonic ignitor 18' with a rupturable diaphragm, which operation
is shown in the split-view of the ignitor depicted in FIG. 4. As
will be noted, the partly fabricated ignitor 18' as received from
the primer-dipping operation is immersed (with its open end
downward as indicated in the right half of FIG. 4) into a shallow
cup 42 that contains a solution of a suitable hardenable plastic
resin, such as the aforementioned "Saran" plastic. The open end of
the tube 24 is submerged to a depth sufficient to cause a thin film
28 of the plastic to be bonded to the rim of the tube after the
assembly 18' is slowly retracted from the cup 42 and the adhered
plastic has dried and rigidified, as indicated in the left half of
FIG. 4. As will be noted, the cup 42 is larger than the end of the
glass tube 24 to permit free insertion and withdrawal of the
latter.
The final step in the manufacture of the ignitor is shown in the
split-view illustrated in FIG. 5 and consists of dipping the
assembly 18' produced by the previous operations into a vessel 44
that contains a solution of another plastic 45. This step is shown
in the right half of FIG. 5. As will be noted, the vessel 44 is of
sufficient depth and size to permit the entire ignitor assembly 18'
to be immersed in the plastic solution 45 approximately to the end
face of the press seal 26. After the assembly 18' has been
withdrawn from vessel 44 and the adhered plastic has cured to form
a protective coating 30 of substantially uniform thickness, as
shown in the left half of FIG. 5, a completed ignitor 18 of the
type shown in FIG. 2 is provided.
SPECIFIC EXAMPLE
For those wishing to practice the invention, following is a
specific example of the various materials used in making the
ignitor 18 which have given satisfactory results.
When made in the AG 1/2 configuration shown in the drawing, the
completed ignitor had a diameter of approximately 9 millimeters and
a length (from the end face of the press seal 26 to the opposite
end of the ignitor) of approximately 19 millimeters. The primer
composition 41 into which the mount was dipped had the following
formulation:
Primer Composition
Lacquer (2.7% solids mixture of 50 cc nitrocellulose and amyl
acetate) Powdered zirconium 50 grams Finely-divided potassium
perchlorate 29 grams Finely-divided anhydrous strontium 29 grams
nitrate
The nitrocellulose serves as an organic binder which holds the
hardened primer material in place on the end of the mount. In the
above formulation, the potassium perchlorate, strontium nitrate and
powdered zirconium are present in stoichiometric amounts and such
amounts are preferred in order to achieve primer ignition in a
minimum amount of time. From approximately 100 milligrams to 115
milligrams of primer 36 were coated over the filament 34 and inner
ends of the lead wires 32. Tests have shown that 100 milligrams of
the aforesaid primer formulation will ignite within 4 milliseconds
after the ignitor 18 has electrically energized.
The plastic diaphragm 28 was formed by dipping the end of the
embryonic ignitor 18' approximately 2 millimeters into a solution
consisting of 10 cc of methyl ethyl ketone and 2.5 grams of F--310
"Saran" powder (marketed by the Dow Chemical Company). "Saran" is
the trade name for a resin consisting of a copolymer of vinylidene
chloride and vinyl chloride.
The protective plastic coating 30 was formed by dipping the
embryonic ignitor 18' into a solution consisting of 21.9 percent by
weight cellulose acetate in a suitable solvent such as a mixture of
acetone and various alcohols. Such solvents are well known in the
photoflash lamp art.
While zirconium, potassium perchlorate and strontium nitrate have
been specified in the aforementioned formulation, the invention is
not limited to these materials. The primer can, accordingly,
comprise any suitable mixture of an oxidizer and a fuel. The fuel
can comprise any suitable powdered incandescible metal, such as
magnesium or the like, or a mixture of such metals. The primer can
also contain bulk materials (such as iron filings, larger magnesium
particles and glass powder) which will carry the heat from the
ignited primer 36 to the charge 12 of gas-producing material and
thus further minimize the time required to activate the restraint
system 9 and inflate and deploy the bag 16.
* * * * *