CA1319962C - Igniter for electric ignition systems - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

An igniter for electric ignition systems is made up of intergrally formed terminals and heating elements of metal thin film. Therefore, it maintains its stable ignition performance, high dafety, and high reliability over a long period of time even in a severe environment. The heating element is covered with a protective coating film made of an inorganic material to ensure good heat conduction and to maintain the initial performance over a long period of time.

Description

13`~9~2 The present invention relates to an igniter for electric ignition systems used for electric detonators and automotive air bag gas generators.

It is an object of the present invention to provide an igniter for electric ignition systems which maintains its high reliability in a severe environment.

The gist of the present invention resides in an igniter for electric ignition systems which comprises a pair of terminals of metal thin film formed and disposed a certain distance apart on the surface of a thin insulating board and at least one heating element of metal thin film which integrally connects said terminals to each other.

The gist of the present invention resides also in an igniter for electric ignition systems which comprises a pair of terminals of metal thin film formed and disposed a certain distance apart on the surface of a thin insulating board and at least one heating element of metal thin film which integrally connects said terminals to each other, said heating element being covered with a protective coating film of inorganic thin film.

According to the present invention, the terminals and heating elements are integrally made of metal thin film.
This structure permits an electric current to flow through the terminals and heating element certainly and to generate heat in a short time because of the small mass of the heating element.

According to the present invention, the heating element is covered with a protective coating film made of an inorga-nic material to ensure good heat conduction and to maintain the initial performance over a long period of time.

2 13199~2 A preferred embodiment of the present invention will now be described with reference to the accompanying drawings in which:

Fig. 1 is a plan view showing the igniter for electric ignition systems in one example of the present invention;

Fig. 2 is a longitudinal sectional view taken along line II-II in Fig. l;

Fig. 3 is a longitudinal sectional view showing the igniter of the present invention applied to the gas generat-ing system to inflate an air bag;

Fig. 4 is a perspective view showing the plug proper shown in Fig. 3;

Fig. 5 is a plan view showing the heating element as shown in Fig. 3, with the protective coating film formed thereon;

Fig. 6 is a sectional view taken along line VI-VI in Fig. 5;

Fig. 7 is a graph showing the relationship between the thickness of the protective coating film and the ignition time;

Fig. 8 is a perspective view showing a conventional igniter; and Fig. 9 is a longitudinal sectional view showing a conventional igniter applied to an electric detonator.

i3~99~2 The conventional type of igniter for electric ignition systems used for the above-mentioned applications is made up of two lead wires 11, with their ends functioning as a pair of terminals 13, and a heating element 15 disposed between the paired terminals 13, as shown in Figs. 8 and 9. The heating element 15 is a fine platinum wire or nichrome wire having a high electric resistance, and it is bonded and connected to the terminals 13 with solder or electrically conductive adhesive 17. When turned on, this type of igniter for electric ignition systems 18 permits an electric current to flow through the high-resistance heating element 15 via the conductors 11 of the lead wires and the terminals 13, generating heat in the heating element 15 as the result of conversion from electric energy into thermal energy.

The above-mentioned conventional type of igniter for electric ignition systems 18 may be used for an electric detonator (electric ignition system) as shown in Fig. 9, in which the reference numeral 19 denotes two lead wires to supply an electric current. Between the ends of the conduc-tors 11 of the lead wires 19 is disposed the igniter for electric ignition systems 18. Around the igniter for electric ignition systems 18 is disposed the priming charge 21. On the priming charge 21 is disposed the blasting powder 23. The lead wires 19 and the priming charge 21 are surrounded by the insulation resin 25 and 26, respectively, which prevent the priming charge 21 from being ignited by static electricity. When triggered, the electric detonator mentioned above permits an electric current to flow through the lead wires 19 and the igniter for electric ignition systems 18. The electric current generates thermal energy which ignites the priming charge 21 which, in turn, explodes the blasting powder 23.

i3~9~2 In the meantime, as the speed of automobiles increases, the development of the safety air bag is going on for the reduction of shocks to the driver in the event of an accident.
The safety air bag is inflated by a pyrotechnic gas generator.
The igniter 18 for the gas generator is required to have a high reliability so that it never works when the car is in the normal state but generates a gas instantaneously for the reduction of shocks to the driver in the event of an accident.
In the conventional safety air bag, this reliability is achieved by providing the igniter 18 with two or three heat-ing elements 15 arranged in parallel so that ignition takes place certainly even in the case where one of the heating elements 15 is disconnected from the terminal 13.

The conventional igniter 18 mentioned above has a disadvantage that there is no way to confirm that the fine heating element 15 is firmly connected to the terminal 13 of the lead wire 19 because the connection is made with adhesive or solder. It has another disadvantage that there is a possibility that the heating element 15 is disconnected from the terminal 13 while the air bag is left unused for a long period of time in an environment where there are consi-derable temperature changes, vibrations, and shocks. With the heating element disconnected, the igniter does not work.

For the conventional igniter 18 to be highly reliable, it is necessary that the igniter 18 be provided with two or three heating elements arranged in parallel. This creates difficulties of making the fine heating elements uniform in resistance and igniting performance. The present invention was completed to solve the above-mentioned problems.

~3~99~2 4a The invention will be described in more detail with reference to one embodiment illustrated in the drawing.

Fig. 1 is a plan view showing one embodiment of the igniter for electric ignition systems pertaining to the present invention. In Fig. 1, the reference numeral 31 denotes a rectangular thin insulating board, about 0.6 mm thick, made of ceramics. This thin insulating board may be replaced by an insulation layer formed on a glass plate or metal plate.

On the thin insulating board 31 are disposed a pair of terminals 33 at a certain distance apart, and between the paired terminals 33 are disposed two heating elements 35.
The terminals 33 and the heating elements 35 are integrally made of metal thin film.

3 ~ 2 Fig. 2 is a longitudinal secdonal view of the igniter 36 taken along the line II-II in Fig. 1. There are shown the thin insulating board 31 and the terminals 33 and heating elements 3s of nichrome, tantalum nitride, or other metal thin film formed thereon.
Incidentally, thc terminals 33 and headng dements 3s may bc of singlc-layered structurc or muldple-layered structure.
When triggered, the igniter 36 constructed as mentioned above perrnits an electric currcnt to flow through thc terminals 33 and headng elemenss 35, generadng heat in the hcating clemcnts 3s.
Thc ignitcr for electric ignition systems rnendoncd above is produccd in the following manner. At first, thc thin insulating board 31 of cerarnics is endrely coated with metal thin film, 500 to 5000 A thick, by thc sputtering method or vacuum dcposition mcthod. Thc mctal thin film is subjcctcd to photo-etching to rcmovc thc unneccssary part indicatcd by the chain linc in Fig. 2. Thus the terminals 33 and heating dcments 3s of metal thin film are integrally fo~ned as shown in Fig. 1.
Thc ignitcr for clcctric ignition systems 36 constructed as mentioned abovc diffcrs from the convendonal onc in that it is not necessary to bond thc fine headng clcmcnt 15 to thc terminals 13 of lead wires with solder or electrically conductivc adhcsivc as shown in Fig. 8. According to this invention, thc terrninals 33 and heating clcmcnts 35 arc intcgrally formed on thc thin insulating board 31. Thcrcforc, thc hcating clcmcnt 35 y/orks certainly to gencratc heat even in a scvere environment. This lcads to thc rdiability of thc igniter for electric ignition systems 36.

... .

131 99~2 According to thc deposition and etching processes, it is possiblc to form thc terminals 33 and heating elements 35 in an extremely small size, and it is also possible to arrange fine headng elements 35 in paralld. Thus this manufacturing process permits thc casy producdon of the cxtremely small, highly rcliablc ignitcr for dectric ignidon systcms 36.
Fig. 3 is a longitudinal sectional view of thc igniter for clectric ignidon systcms pertaining to the present invention which is applied to thc air bag gas gencrator. The refercncc numeral 41 indicates the lead wirc for an clectric cu~rent.
Thc lcad wirc 41 is made up of the conductor 43, which is a dn-plated soft coppcr wirc, and the covering 44 of crosslinked polyethylene. The end of thc conductor 43 of thc lead wirc 41 is conncctcd to the solderlcss tenninal 47 of oxygen-frcc copper having thc projecdng part 45. Thc solderless terminal 47 and the lead wirc 41 are fixed to the plug proper 49 made of insulating resin such as polyethylene, polyvinyl chloride, and Ryton. The plug propcr 49 is composcd of two split parts as shown in Fig. 4. Thc partSI to hold thc soldcrlcss tcrminal has thc projection 55 for pressing, and thc part S3 to hold the lead wire has thc projection 56 for pressing. Whcn thc two parts of thc plug proper 49 are joined together, thc projection SS prcsses thc projecting pa~t 45 of thc solderless tcrminal 47 in placc and the projection S6 presses thc lead wirc 41 in placc.
To facilitate the joining of the two halves of the plug proper 49, one half is provided with the semicylindrical fitting piecc 57 and the other half, thc holc (not shown) to receive the fitting piecc S7. In addition, to facilitate the joining of the two halves of the plug proper 49 by ultrasonics, each half is provided the V-shaped rib 58 on one side thereof.

1~199~

Thle upper part of the joined plug proper 49 is provided with the fitting cap 59 made of an insulating resin such as polyethylene, polyvinyl chloride, and polyphenylene sulfide. The plug assembly composed of the plug proper 49 and the cap 59 is protected by the plug case 61 made of aluminum, iron, or stainless steel.

At the center 63 of the plug assembly is disposed the a~ove-mcntioned ignitcr 36.
On thc thin insulating board 31 of tbe igniter 36 are integrally formed the terminal 33 and heating element 35 by deposition. The terminal 33 is fixed to the center 63 of the plug assembly by bending the end of the projecting piece 45 of the solderless terminal 47. The end of the proiecting piece 45 is bonded to the terrninal 33 with solder 6~. The igniter 36 is f~y bonded to the center 63 of the plug with an epoxy adhesivc.
The top of the heating element 35 is covered with the protectivc coating fiLnl 67, about 3 llm thick, made of inorganic thin film such as silicon oxide and silicon nitride, as shown in Figs. S and 6. The protective coating film 67 of desired shapc as shown in Fig. 5 is formed by deposition through plasma reaction or the likc and then dry etching with a gas. The protective film 67 controls the ignition time according to its thickness.
Experimental results indicate that the thicker the protective coating 67, the longer the ignition time as shown in Pig. 7.
The upper part of the plug proper 49 is ~Illed with the priming chargc 69 such as tricinate, lead rhodanide and potassium chlorate, diazonitrophenol, and barium styph-nate. In other words, the priming charge 6g is on the protective coating ~llm 67.
The igniter 36 constructed as mentioned above is installed in thc ignition systcm for the air bag gas generator. When triggered, the igniter permits an electric current to flow through the conductor 43 of the lead wire 41, the solderless terminal 47, the terminal 33, and the heating element 35 having a smaller surfacc area. Thc clcctric current generates heat in the heating element 35. The heat ignites the priming charge 13193~2 69 placed on the headng element 35, and the priming charge 69 melts the top of the cap 59 and ignites the blasting powder (not shown). The blasting powder generates a gas to inflate the air bag instantaneously.
The air bag ignidon system constructed as mentioned above has many advantages as follows: The cap S9 fitting to the plug proper 49 keeps the priming charge 69 in the plug proper 49 and prevents spark discharge which is othcrwise induced between the solderless terminal 47 and the plug case 61 by static electricity. The lead wire 41 and the ~olderless terminal 47 are protected from being pulled out or bent, because the lead wire 41 is pressed in place by the pressing projection 56 formed in the lead wire holder 53 and the projecting piece 45 of the solderless terminal 47 is pressed in place by the pressing projecdon 55 formcd in thc solderless tcrminal holder 51. The protectdve coadng film 67 separates the heating element 35 from the priming charge 69, thereby protecting the heating element 3S from corrosion, breakage, and change in resistance which would otherwise occur when the priming charge 69 deteriorates. It is possible to properly change the thickness of the protective coating film 67, the surface area and material of the heating element 35, and the kind of the priming charge 69 according to the desired performance of the igniter 36. This contributes to the high safety and reliability even in a severe environment. The igniter 36 is fixed by bending the end of the projecting piece 45 of the solderless terminal 47 and the projecting piece 45 is fixed to the terminal 33 on the thin insulating board 31 with solder. This connecdng method is easier and certainer than the conventional direct connecting method, and contributes to high safety and reliability even in a severe environment.

131~2 l[n thc above-mentioned example, the lead wire 41 is connected to the ignitcr 36through thc solderless terminal 47. Altematively, the conductor 43 of ~hc lcad wirc 41 may be connected directly to the terminal 33 of the igniter 36 without the soldcrless terminal 47.
It goes without saying that the igniter for electric ignidon systcms pertaining to the present invendon may be used for electric detonators and ~Irearms as well as the gas gencrating system to inflatc an air bag.
Thc ignitcr for electric ignidon systems pertaining to the present invention has the heating element which is narrower than the part adjoining the terminal 33 so that the heating element generates a prescribed amount of heat. Thc number of the heatingelements may be one or two or more according to the object, although it is two in the abovc-mentioned cxamplc. Thc heating element as shown in Fig. 1 is used for the ignition system in which ~hc heating element is not subject to pecling and corrosion, and the heating element as shown in Fig. 5 is used for the ignition system in which the heating element is subject to peeling and corrosion.

As mendoned above, the igniter of thc present invention is made up of intcgrallyfo~ned terminals and heating elcmcnts of metal thin film. Thercforc, it maintains its stable ignitdon perforrnance, high safety, and high reliability ovcr a long period of dmc even in a scvere environmcnt.

Claims (2)

1. An igniter for electric ignition systems, said igniter comprising a pair of terminals of metal thin film formed and disposed a certain distance apart on the surface of a thin insulating board and multiple heating elements of metal thin film which integrally connect said terminals to each other, said heating elements being covered with a protective coating film of inorganic thin film, wherein there are multiple heating elements arranged parallel to each other and perpendicular to the terminals, wherein the igniter, when triggered, permits an electric current to flow through the terminals and through the heating elements, thereby generating heat in the heating elements.

2. An electronic ignition system comprising (a) a pair of conductors, (b) a pair of solderless terminals, each having a projecting part, connected to the conductors, (c) an ignitor connected to the projecting parts of the solderless terminals, (d) a primary charge on top of and in contact with the ignitor, (e) a cap on top of the primary charge, and (f) a plug assembly in contact with the cap and encasing the conductors and solderless terminals, wherein the ignitor comprises a thin insulating board and disposed on the board is a pair of terminals at a certain distance apart and between the terminals are disposed multiple heating elements, wherein on top of the heating elements is a protective coating film or inorganic thin film, wherein the igniter, when triggered, permits an electric current to flow through the conductors, the solderless terminal, the terminals and the heating elements, generating heat and thereby igniting the primary charge which melts the top of the cap.