EP0174891B1 - Electric switch triggered by immersion, and pyrotechnical device making use of such a switch - Google Patents

Description

The invention relates on the one hand to an electrical contactor, the closure of which is directly ensured by the aqueous medium in which the contactor is immersed, and on the other hand to a pyrotechnic device, in particular a gas generating device actuating a pyrotechnic system, of which the ignition uses such a contactor. The contactor comprises at least two electrodes placed inside a housing which can be electrically connected by the aqueous medium, these electrodes being connected to an electronic circuit, preferably comprising at least one thyristor, the tripping threshold of which is reached when the aqueous medium connects the two electrodes, and, the pyrotechnic device triggered by immersion comprises such a contactor interposed between an electrical supply and the internal electrical resistance to the sensitive ignition composition of a pyrotechnic system.

Electrical contactors that can be triggered by immersion are known, and for example US-A-3739673 describes a contactor which is used when a pyrotechnic cable cutter is triggered, this contactor being more particularly represented in FIGS. 3 and 4. The contactor described comprises in particular a rigid cup which can move axially relative to the body of the contactor under the effect of pressure and which comprises the movable contact blade which is initially kept away from the fixed blade by means of a partially destructible spacer. Such contactors give full satisfaction in a high pressure range, in particular the pressures generated by an underwater explosion, but even by removing the spacer, they do not allow tripping under low pressure, in particular because of the friction of the seal. sealing placed between the rigid cup and the body of the contactor.

Other electrical contactors that can be triggered by immersion are also known, and for example the patents FR-A-2025679 and FR-A-2025680 describe contactors which are used to trigger a pyrotechnic system for automatically inflating lifejackets. The contactor does not form an independent element but is integrated in the pyrotechnic device whose internal surface of the casing constitutes one of the terminals of the contactor, this casing being pierced with free orifices allowing the penetration and the flow of the aqueous medium of immersion. The other electrical terminal of the contactor is a cylindrical ferrule arranged inside the casing but at a sufficient distance so that humidity and water drops cannot establish a direct contactor between the two terminals. To counter, by condensation of a salty humid air or by exposure to sea spray, a relatively very conductive film will form between the two electrical terminals, and to avoid any untimely tripping, the electronic circuit of such a contactor must have a high trigger threshold, but the conductance of a film of salt water may be higher than the conductance of a body of fresh water partially filling the interior of the housing, and it is practically impossible to adjust the threshold release to present a correct operating reliability in saline atmosphere and in fresh water, moreover the partial filling of the inside of the casing can occur in the case of a heavy rain or worse of a simple wave crest entering contact with the pyrotechnic device, especially if it is not strictly maintained in the vertical position.

The object of the present invention is to obtain the tripping of the contactor only by a total immersion of a few seconds under a few decimetres of water, and this whatever the orientation of the pyrotechnic device and whatever the nature and the conductance of the immersion aqeux medium, any untimely triggering by projection or runoff of fresh or sea water being impossible.

The present invention is characterized in that, on the one hand, the housing of the electrical contactor comprises at least one opening closed by a filter of very low porosity which can only be crossed by the aqueous medium when the latter is in continuous overpressure, the simple contact of the aqueous medium with the filter does not allow this medium to pass through this filter, and in that, on the other hand, the two electrodes are located near the inner surface of the filter.

The porosity to be adopted depends on the material or materials constituting the filter as well as on the structure of this filter which can in particular be made of sintered material or of fibrous material. Filter suppliers do not always have the data to select the filters that may be suitable in the context of the present invention, and this selection itself depends on the permissible overpressure so that the aqueous medium passes through the fluid within the required time, the selection is all the more rigorous as this overpressure is low. Only very low porosity filters can be used, but when the aqueous medium must pass through the filter with an overpressure of less than 10,000 Pa (0.1 bar) in less than 10 seconds, it is desirable to carry out a double permeability test of the filter. The first test consists in placing the filter horizontally under a shower head, located 2 meters above, and the size of the holes and the flow rate correspond to a heavy rainstorm; under these most unfavorable conditions, water must not pass through the filter, even after half an hour of artificial rain. The second test, much simpler and much more repetitive, consists in immersing a transparent container at a given depth in the aqueous medium, the only opening of which is closed by the filter, and to note the time after which the droplets appear on the internal face. of the filter, the detection of this appearance can be facilitated by a very slight partial deposition on this internal face of a color-changing reagent in the presence of water.

Preferably the filter has a porosity of a few micrometers and can only be crossed by the aqueous medium when the latter is at a pressure whose value is at least 1000 Pa (0.01 bar) greater than the pressure value which prevails in the internal chamber of the contactor, this filter comprising at least one layer of sintered material or one layer of fibrous material, in particular polymer fibers, the mixed filters being very suitable.

In order to improve the reliability of the detector, the electrodes are substantially parallel to the interior surface of the filter and the distance between the electrodes is less than 2 millimeters so that a single drop can establish contact, the distance between the electrodes and this surface internal being itself less than 3 or 4 millimeters, the contact being able to be thus established while the drops of the aqueous medium are not yet completely formed on this internal surface and still adhere to this surface.

Advantageously, on the one hand the two electrodes are branched and nested parallel to each other, so that contact can be established in any zone of appearance of drops of the aqueous medium on the interior surface of the filter, and on the other hand the distance between the electrodes and this interior surface is adjustable, in particular by screwing.

A particularly advantageous embodiment consists in that the electrodes belong to the same printed circuit, each electrode can be constituted by a peripheral element in a semicircle, a substantially radial element and a bundle of substantially parallel branches. The electronic circuit can then be directly placed on the face of the printed circuit opposite to the face carrying the electrodes, in particular when this circuit is reduced to a thyristor and a capacitor.

More particularly, the contactor housing is dimensioned so that the ratio (V / S) between the volume of the internal chamber of the contactor and the total opening surface of the housing is less than 6, a wide opening facilitating the penetration of the aqueous immersion medium, which is limited by the back pressure prevailing in the internal chamber since the internal air compresses when the contactor is immersed in an aqueous medium.

A small volume of the internal chamber is sufficient, and a volume of less than 10 cm ³ makes it possible to obtain practically all the triggering pressures between a thousand and a few hundred thousand Pascal (0.01 bar and a few bars), by choosing a thicker and lower porosity filter for the highest pressures, and adapting the distance between the electrodes and the internal face of the filter for the lowest pressures.

The present invention also relates to a pyrotechnic device triggered by immersion, which comprises an electrical supply and a pyrotechnic system, in particular a pyrotechnic mechanism or a gas generator assembly, the sensitive composition of which is ignited by means of an internal electrical resistance, and which is characterized in that the electrical switch triggered by immersion has the technical characteristics mentioned above.

Preferably for this particular application, the contactor housing, on the one hand constitutes the housing of an electric cell, and on the other hand comprises a bore in which the pyrotechnic charge is positioned, this bore extending through an exhaust orifice combustion gases from the pyrotechnic charge to the pyrotechnic system.

Advantageously, the contactor housing consists of two cylindrical elements mounted one inside the other and the electric cell is fixed in the interior element of the housing by an overmolding of insulating material which simultaneously allows the setting and the necessary sealing.

The advantages obtained thanks to this invention consist essentially in that the contactor has substantially the same tripping characteristics whatever the nature of the aqueous medium, fresh water or sea water, since it is the continuous overpressure of this aqueous medium which will allow triggering, such a feature being advantageous in particular for the life jackets of aviators or parachutists whose pyrotechnic inflation devices must be able to be actuated whatever the nature of the aqueous medium. In this application it is also particularly advantageous that the electrical contactor does not trigger the inflation of the life jacket if the paratrooper only lands in a shallow water area, hence the advantage of the invention which only allows tripping if a continuous overpressure equivalent to 50 cm or 1 m of water is reached. The condition for applying a continuous overpressure, even if it is only 5 or 10 seconds, is particularly advantageous, since it makes it possible, for example, either to prevent the life jacket of a sailor from being automatically inflated as soon as a wave crest hits it, or when a device triggered by immersion is activated by heavy rain, regardless of the orientation of the detector and the device.

The contactor according to the invention therefore avoids any untimely tripping while allowing the main tripping conditions which are the value of the excess pressure of the aqueous triggering medium and the duration of application of this excess pressure to be adjusted.

• - la figure 1 est une vue en coupe longitudinale d'un perforateur pyrotechnique équipé d'un contacteur électrique déclenchable par immersion,
• - la figure 2 est une vue en coupe axiale d'un contacteur électrique indépendant déclenchable par immersion,
• - la figure 3 correspond au schéma électrique du perforateur pyrotechnique représenté à la figure 1,
• - la figure 4 est une vue de face partielle du circuit imprimé formant les électrodes des contacteurs représentés aux figures 1 et 2.

In the following, the invention is explained in more detail using a drawing representing two particular embodiments, for which:

• FIG. 1 is a view in longitudinal section of a pyrotechnic perforator equipped with an electrical contactor triggerable by immersion,
• FIG. 2 is a view in axial section of an independent electrical contactor triggered by immersion,
• FIG. 3 corresponds to the electrical diagram of the pyrotechnic perforator shown in FIG. 1,
• FIG. 4 is a partial front view of the printed circuit forming the electrodes of the contactors shown in FIGS. 1 and 2.

FIG. 1, which corresponds to the preferred application of the electrical contactor according to the invention, represents a particular device making it possible to perforate the cover of a reserve of pressurized gas, which is not shown, but which is screwed into the thread (15) of the receiver system (12b) shown in broken lines. The assembly of this FIG. 1 represents a pyrotechnic perforator triggerable by immersion particularly suitable for use with a life jacket which is inflatable automatically in the event of sufficient immersion.

The housing (3) is constituted by a first internal cylindrical element (3a) fitted into a second cylindrical element (3b), these two elements fixed to each other providing an internal chamber (6) which extends transversely under the cover (3c) of the housing. This cover which is glued or welded by friction to the internal element (3a) encloses the filter (5) which comprises two discs of porous material, the external disc being a stainless steel membrane with an average porosity of 15 micrometers, and the inner disc being a felt of compacted polytetrafluoroethylene fibers. The inner element (3a) of the housing is closed by a disc-shaped printed circuit (7) which adheres to the two-component filling resin (8). This resin immobilizes and fixes on the one hand the electronic circuit (4) mounted on the internal face of this printed circuit and on the other hand a cylindrical battery (11) Iithium / Mn02 delivering a voltage of approximately 3.3 V, the wiring between all these active elements being defined in FIG. 3, and the two connection conductors (9a) and (9b) leaving the filling resin (8). These two conductors are connected to an igniter 12a) constituted by an igniter whose pearl of sensitive composition coats the igniting filament (13 - fig. 4), and by gas-generating powder contained in a metallic envelope. The igniter (12a) is housed in the axial bore of the two cylindrical elements (3a) and (3b) of the housing, the three constituent parts of this housing being made of polyamide filled with fiberglass, and the external element ( 3b) of the housing is screwed into the receiving mechanism (12b) which is metallic and which is provided with an exhaust orifice (10) for combustion gases, temporarily closed by a cover. The distance between the upper surface of the printed circuit (7) on which the electrodes are arranged, and the lower surface of the fibrous layer of the filter (5) is 2 mm, and the two components fixed on the lower face of this printed circuit are a thyristor (4a) and a capacitor (4b).

Referring to FIG. 3, the thyristor (4a) behaves like a power switch which can be triggered when a positive voltage is applied to its trigger, even with a very small trigger power, the ignition currents according to the thyristors being of the order of 0.2 to 0.5 mA. The capacitor (4b) has a capacity of 1 nanofarad and the electrodes (1) and (2) of the printed circuit are branched and nested parallel to each other, the resistor (13) corresponding to the internal filament of the pyrotechnic composition sensitive. FIG. 4 specifies the particular arrangement of the electrodes formed on the printed circuit (7) each of these electrodes being constituted by a peripheral element in a semicircle (1a, 2a) a substantially radial element (1b, 2b) and a beam ( 1c, 2c) of parallel branches which are spaced 1 mm apart.

During periods of non-use, the opening of the casing (3) of the pyrotechnic perforator is advantageously protected by a cover (not shown), the porosity of the filter being an important operating condition which implies the cleanliness of this filter. In the operational position, the perforator is in the state shown in Figure 1, its orientation can be absolutely arbitrary. In the event of rain, even heavy, the very low porosity of the filter which is in the example 15 to 30 [tm, for a total thickness of 2 mm, prevents any penetration of water through this filter. In the event of immersion at a depth of 10 cm, the water penetrates only partially and very slowly into the filter and no triggering of the perforator occurs within ten minutes. On the other hand, in the event of immersion at more than 30 cm the triggering occurs, and at a depth of 60 cm, the perforator is triggered within 5 to 10 seconds which corresponds to the time necessary for at least one drop of water forms partially on the internal surface of the filter and touches two contiguous ramifications of the electrodes, this very low conductance contact being sufficient to trigger the thyristor (4a) which then connects the battery (11) to the setting filament (13) fire. The combustion gases from the igniter (12a) then break the cover of the exhaust orifice (10) and propel the beveled axis (16), the tip of which tears open the cover of the reserve of compressed gas secured to the perforator by means of the thread (15), this compressed gas escaping through a network of pipes to a device for use such as an inflatable life jacket.

FIG. 2 is specific to an electrical contactor not integrated in a pyrotechnic device, this independent contactor being very easily adjustable, on the one hand by varying the distance between the internal surface of the filter (25) and the network of electrodes of the circuit printed (27), and on the other hand by means of a set of filters having different porosities staggered between 3 and 50 micrometers. According to an alternative embodiment, the internal chamber (26) could be of variable volume, which would allow an additional adjustment of the depth and of the immersion time to close the electrical contactor, this variable chamber being able to be produced by means of a housing (23) in two parts which would be screwed into each other and which would be provided with an O-ring as waterproofing. According to the example of Figure 2, the housing (23) of the contactor is integral and metallic and comprises, on the one hand a high internal thread in which is mounted the filter support (25), and on the other hand in the lower part an insulating shutter which molds the two pins (30a) and (30b) for connecting the contactor. The electrodes have the same arrangement as that described previously with reference to FIG. 4, but the printed circuit (27) has a cup shape in which the thyristor (4a), the capacitor (4b) and the cables take place. The electrical diagram corresponds to that of FIG. 3, the pins (30a) and (30b) being located on either side of the assembly constituted by the electrical supply (11) and by the user elements (13).

Claims (20)

1. Electric switch triggered by immersion, comprising at least two electrodes (1) and (2) placed inside a casing (3, 23) and adapted to be electrically connected by the aqueous medium in which the switch in immersed, said electrodes being connected to an electronic circuit (4) preferably including at least one thyristor (4a) whose triggering threshold is reached when the aqueous medium connects the two electrodes (1) und (2), characterized in that on the one hand the casing (3) has at least one opening closed by a filter (5, 25) through which the aqueous medium can pass only when it is at a pressure whose value is at least 1000 Pa (0,01 bar) higher than the value of the pressure prevailing in the inside chamber (6, 26) of the switch, and in that on the other hand the distance between the two electrodes (1) or (2) and the inside surface of the filter (5, 25) is less than 3 millimetres.

2. Electric switch according to claim 1, characterized in that the filter (5, 25) has a porosity of a few micrometers.

3. Electric switch according to either of claims 1 or 2, characterized in that the filter (5, 25) has at least one layer of sintered material.

4. Electric switch according to one of the preceding claims, characterized in that the filter (5, 25) has at least one layer of fibrous material.

5. Electric switch according to claim 1, characterized in that the electrodes (1) and (2) are substantially parallel to the inside surface of the filter (5,25).

6. Electric switch according to one of claims 1 or 5, characterized in that the distance between the electrodes (1) and (2) is less than 2 millimetres.

7. Electric switch according to one of claims 5 or 6, characterized in that the electrodes (1) and (2) are branched and imbricated parallel to one another.

8. Electric switch according to claim 5, characterized in that the distance between the electrodes

(1) or (2) and the inside surface of the filter (5, 25) is adjustable.

9. Electric switch according to claim 7, charc- terized in that the electrodes (1) und (2) belong to the same printes circuit (7, 27).

10. Electric switch according to claim 9, characterized in that each electrode (1) and (2) is composed of a semicircular peripheral member (1a, 2a), a substantially radial member (1b, 2b), and a bundle (1c, 2c) of substantially parallel ramifications.

11. Electric switch according to claim 9, characterized in that the electronic circuit (4) is directly disposed on the opposite face of the printes circuit (7) to the face carrying the electrodes (1) and (2).

12. Electric switch according to claim 11, characterized in that the electronic circuit (4) is reduced to a thyristor (4a) and a capacitor (4b).

13. Electric switch according to one of claims 1 or 2, characterized in that the ratio (V/S) between the volume of the inside chamber (6) of the switch and the total opening area of the casing 3 is less than 6.

14. Electric switch according to claim 1, characterized in that the volume of the inside chamber (6) is less than 10cm'.

15. Pyrotechnical device procided with an electric switch triggered by immersion, an electricity supply (11), and a pyrotechnical system (12a, 12b) the sensitive composition of which is fired by means of an internal electric resistor (13), characterized in that the electric switch triggered by immersion is in conformity with one fo the preceding claims.

16. Pyrotechnical device according to claim 15, characterized in that the casing (3) of the switch constitutes the housing of an electric battery (11).

17. Pyrotechnical device according to one of claims 15 or 16, characterized in that the casing (3) of the switch has bore in which the pyrotechnical charge (12a) is positioned, said bore being extended by an outlet aperture for the combustion gases of the pyrotechnical charge leading to the receiver system (12b).

18. Pyrotechnical device according to one of claims 15 to 17, characterized in that the casing (3) of the switch is composed of two cylindrical members (3a) and (3b) mounted one in the other.

19. Pyrotechnical device according to claim 18, characterized in that the electric battery (11) is fixed in the inner member (3a) of the casing by insulating material (14) moulded over it.

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