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.

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.

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.