EP2769168B1 - Gas generator provided with a safety device for slow heating - Google Patents

Description

The invention relates to a gas generator, and more particularly to a gas generator comprising a body delimiting at least a portion of a combustion chamber, said part containing a main pyrotechnic charge adapted to generate gases in the combustion chamber. combustion when said charge is initiated in combustion.

The gas generator according to the present invention is particularly adapted to be integrated in a device for ejecting a payload, in particular a beacon or a decoy, or in a jack.

More generally, throughout the present application, the term "device to be actuated" means a device in which can be integrated the gas generator according to the invention.

A gas generator of the aforementioned type, through the initiation of its main pyrotechnic charge, generates in a very short time a large amount of gas inside the combustion chamber. The pressure of the gases inside this chamber can then cause the actuation of the device to be actuated, in particular the displacement of a piston.

During an unexpected rise in temperature, caused for example by a fire, the main pyrotechnic charge of the generator may ignite inadvertently by auto-ignition. It can then react violently, burn abnormally, and even explode, endangering the surrounding people.

In order to prevent this unwanted and uncontrolled operation of the gas generator, it has been considered in the past to incorporate a thermal fuse whose self-ignition temperature was lower than that of the main charge, allowing the firing the main charge before it reaches its autoignition temperature. Such a solution, described in particular in the patent application FR 2,870,234 has several disadvantages. Firstly, the main pyrotechnic charge is always initiated in case of abnormal heating, even when the temperature has not reached its autoignition temperature. Moreover, the device is still effectively triggered, even in case of fire, which can endanger the nearby people and, if necessary, lead to the loss of a payload, the cost of which can be high.

According to another request FR 2 827 376 , the main pyrotechnic charge of a munition is combined with a block of pyrotechnic material forming suitable safety igniter, in case of slow heating, to cause the combustion of the main charge without detonation.

The object of the invention is to provide a gas generator of the aforementioned type which, in the event of abnormal heating, avoids the inadvertent initiation of the main pyrotechnic charge as long as the self-ignition temperature of said charge has not been reduced. has not been reached and prevents the operation of the device to be operated.

This objective is achieved by means of a gas generator comprising a body delimiting at least a portion of a combustion chamber, said part containing a main pyrotechnic charge adapted to generate gases in the combustion chamber when said charge is initiated in combustion, and characterized in that it further comprises a slide located outside said body and defining therewith a second chamber housing a secondary pyrotechnic charge whose self-ignition temperature is lower than that of the pyrotechnic charge main feature, in that a flow passage for the gases out of the combustion chamber is formed in the body, in that the spool closes the gas flow passage when in a first position, and in that, under the effect of gases released by said secondary pyrotechnic charge, the slide is adapted to pass into a second position in which said passage n ' is more closed, allowing the gases contained in the combustion chamber to flow outwards.

During a normal start-up, the gas generator according to the invention operates as follows: Under the effect of one or more pyrotechnic initiator (s), the combustion of the main charge is initiated. Very quickly, gases from combustion are released into the combustion chamber. Under the effect of pressure, these gases operate the device in which the generator is integrated, for example by causing the movement of a piston communicating with the combustion chamber. During normal operation, the load pyrotechnic secondary housed in the second chamber is not initiated. It does not ignite, so no gas is released into the second chamber. In fact, the drawer remains in its first position, in which it closes the flow passage of gases out of the combustion chamber. The gases can not escape the combustion chamber, it rises very quickly in pressure and causes a sudden and effective actuation of the device to operate.

It is recalled that, according to the invention, the self-ignition temperature of the secondary pyrotechnic charge is lower than that of the main pyrotechnic charge.

• Au cours de sa combustion, la charge pyrotechnique secondaire va progressivement libérer des gaz, mettant en pression la deuxième chambre. Sous l'effet de cette pression, le tiroir va passer de sa première position décrite ci-dessus à une seconde position, dans laquelle le passage d'écoulement des gaz hors de la chambre de combustion est ouvert (i.e. n'est plus obturé par le tiroir).

When the gas generator is subjected to an increase in temperature, especially in case of fire, the pyrotechnic material contained in the second chamber, between the drawer and the body, will therefore be initiated first. It then plays a role of thermal fuse or safety organ, as follows:

• During its combustion, the secondary pyrotechnic charge will gradually release gases, putting pressure in the second chamber. Under the effect of this pressure, the spool will move from its first position described above to a second position, in which the flow passage of gases out of the combustion chamber is open (ie is no longer closed by the drawer).

In this position, in case of initiation of the main pyrotechnic charge as a result of the increase in temperature, the gas flow passage prevents the pressure inside the combustion chamber from reaching the threshold of pressure beyond which the device is actuated (for example the pressure threshold beyond which a piston of the device is moved). This ensures that in case of fire, or in all other cases of unexpected heating, the device to be actuated is not started, even when the temperature exceeds the auto-ignition temperature of the pyrotechnic charge main.

Moreover, in the gas generator according to the invention, the secondary pyrotechnic charge, forming a thermal fuse, can be easily replaced. During maintenance operations, the drawer is easily disconnected from the generator body.

According to an exemplary embodiment, the drawer is able to move by sliding in a rectilinear trajectory.

In another example, the drawer could be able to move by pivoting about the axis of the body of the generator.

In one example, the drawer is coaxial with the body.

According to an example, the body comprises at least a first section having a first diameter and a second section of greater diameter located in the extension of the first, a shoulder being defined between the first and the second section, and the drawer comprises a first adapted portion sliding along the second section and a second part extending radially inwards and whose inner radial face is adapted to slide along the first section, the second chamber being defined between the shoulder and the second part of the drawer .

In another example, the gas flow passage comprises a plurality of holes distributed over the entire periphery of the body.

In another example, the drawer has at least one opening adapted to come into communication with the flow passage for the gases when the drawer is in its second position, the gases contained in the combustion chamber can then flow to the outside through said flow passage and said opening.

The opening comprises for example a plurality of holes distributed over the circumference of the drawer and each opening on the outer face and on the internal face of the drawer.

In this case, if the gas flow passage consists of corresponding through-holes formed in the thickness of the generator body, it is necessary, in order to ensure the flow of the gases, to ensure proper alignment of the holes of the slide and of those of the body. To ensure the flow of the gases without a too important accuracy in the relative positioning of the two elements is necessary, it is possible to provide that the opening of the slide comprises a circumferential groove formed on its inner face and at least one hole opening in said groove and on the outer face of said drawer, said groove defining an annular chamber with the body when the drawer is in its first position and being adapted to come into communication with the gas flow passage when the drawer is in its second position. position. According to one variant, the gas flow passage comprises a groove circumferential formed on the outer face of the body and at least one hole opening into said groove and on the inner face of said body, said groove defining an annular chamber with the drawer when it is in its first position and being adapted to come into communication with its opening when the drawer is in its second position. It is also possible that the drawer and the body both comprise circumferential grooves as defined above.

The present invention also relates to a device comprising a gas generator as defined above, wherein the gases emitted by the main pyrotechnic charge of the gas generator when it is initiated in combustion, are adapted to actuate said device. The device is therefore adapted to be actuated under the effect of the pressure generated by the gases delivered by the generator. This device to be actuated may for example comprise a device for ejecting a payload or a jack.

• la figure 1 montre une vue partielle, en coupe axiale, d'un générateur de gaz selon un mode de réalisation de la présente invention, avant échauffement ;
• la figure 2 montre le générateur de gaz de la figure 1, après un échauffement anormal.

Other features and advantages of the invention will become apparent on reading the following description of exemplary embodiments of the invention given by way of illustration and not limitation. This description refers to the attached drawing sheets in which:

• the figure 1 shows a partial view, in axial section, of a gas generator according to one embodiment of the present invention, before heating;
• the figure 2 shows the gas generator of the figure 1 after an abnormal warm-up.

The gas generator 10 as shown in FIG. figure 1 is intended to be integrated with a payload ejection device 22 which will be described in more detail below.

The gas generator 10 comprises a body 12, generally cylindrical with axis A in the example shown, and open at one of its axial ends 12b (hereinafter free end).

The body 12 houses a main pyrotechnic charge 16 and a pyrotechnic initiator 18 to ignite said charge 16.

As illustrated on the figure 1 a plurality of holes 50, the function of which will be described in more detail below, is formed in the body 12.

In the example, the body 12 comprises, from its upstream end 12a towards its free end 12b, a succession of sections 51, 52, 53 of increasing diameter, forming recesses or bearings 54, 55.

On the figure 1 , the body 12 comprises a first section 51 of diameter d1 and axial length L1. Downstream of this first section 51, the body 12 comprises a second section 52 of diameter d2 greater than d1 and of length L2, and downstream of this second section 52, a third section 53 of diameter d3 greater than d2 and of length L3. . A first and a second shoulder 54, 55 are respectively defined between the first and the second section 51, 52 and between the second and the third section 52, 53.

The gas generator 10 comprises, in addition to the aforementioned elements, a slide 60 surrounding the body 12. In the example, the slide 60 is coaxial with the body 12 and able to slide rectilinearly along said body 12, in the direction of axis A.

• Le tiroir 60 présente une forme générale annulaire. Il comprend une première portion 62 s'étendant axialement, apte à coulisser le long d'un tronçon 52 du corps 12 (ici le second tronçon), et une seconde portion 64 s'étendant radialement vers l'intérieur depuis une extrémité de la première portion 62 et faisant face à une portion radiale adjacente du corps 12 (ici le premier épaulement 54) en délimitant avec lui une chambre de sécurité ou deuxième chambre 66.

The body 12 and the slide 60 of the gas generator 10 may, for example, be arranged in the following manner:

• The drawer 60 has a generally annular shape. It comprises a first portion 62 extending axially, slidable along a section 52 of the body 12 (here the second section), and a second portion 64 extending radially inwardly from one end of the first portion 62 and facing an adjacent radial portion of the body 12 (here the first shoulder 54) delimiting with it a security chamber or second chamber 66.

For this, in the example, when the downstream end of the first portion 62 of the slide 60 bears against the second shoulder 55 of the body 12, a minimum spacing is maintained between the first shoulder 54 and the second portion 64 of the drawer 60.

The first portion 62 of the slide 60 has, on its inner face, a circumferential groove 70 defining with the body 12 an annular chamber. It further comprises at least one exhaust hole 72, preferably a plurality of holes 72, extending from this circumferential groove 70 and opening onto the external face of the slide 60.

The security chamber 66 houses a pyrotechnic material 74, forming a secondary pyrotechnic charge, chosen so that its T1 auto-ignition temperature is lower than T2 of the main charge 16 for reasons that will be explained below. Examples of pyrotechnic materials that can be used in the present invention are given in the application FR 2,870,234 .

As indicated above, the gas generator 10 is intended to be mounted on a payload ejection device 22, and more particularly an ejection device 22 of the type illustrated on FIG. figure 1 , comprising a main body 14 housing a piston 30 and a payload 40.

In the example, the gas generator 10 is mounted by its free end 12b, at an axial end of the main body 14, so that the main body 14 of the ejection device 22 and the body 12 of the gas generator are located in the extension of one another.

The connection between the free end of the body 12 of the gas generator 10 and the main body 14 of the ejection device 22 is represented on the figure 1 by the line referenced 21.

Note that, in the present application, unless otherwise specified, a radial direction is a direction perpendicular to the axis A and intersecting this axis A. In addition, an axial direction is a direction parallel to the axis A. The axial adjectives and radial are used with reference to the aforementioned axial and radial directions. Similarly, an axial plane is a plane containing the axis A and a radial plane is a plane perpendicular to this axis.

Furthermore, the upstream and downstream are defined relative to the direction of movement of the piston 30 and the payload 40 along the axis A (from upstream to downstream).

In the example illustrated, the main body 14 is closed, at its upstream end, by a cover 26. At its periphery, the cover 26 is connected directly to the main body 14 by a zone of weakness 24 adapted to break when the pressure applied to it reaches a predetermined sufficient value P1.

When the gas generator 10 is mounted on the device to be actuated, the body 12 of the generator, the main body 14 of the device and the lid 26 define a combustion chamber 20 housing the main pyrotechnic charge 16.

It will be noted that, according to other exemplary embodiments, the lid may be omitted, and the combustion chamber 20 may be delimited directly by the piston 30 of the ejection device.

As indicated above, a series of first holes 50 is formed in the portion of the body 12 defining at least a portion of the combustion chamber 20 along which slides the slide 60 (here the second section 52). These holes 50, which can be distributed over the entire periphery of the body 12, constitute a flow passage allowing the flow of the gases contained in the combustion chamber 20 out of said chamber.

In normal operation, the volume of the safety chamber 66 defined between the slide 60 and the body 12 of the gas generator 10 is minimum. The slide 60 abuts against the second shoulder 55 of the body 12. In this position, the groove 70 does not communicate with the gas flow holes 50 of the body 12 and the slide 60 completely closes these holes 50. The chamber combustion 20 is closed.

When the pyrotechnic initiator 18 ignites the main charge 16, the latter, on burning, releases gases. In the absence of a flow passage 50 for the gases, the pressure inside the combustion chamber 20 increases very rapidly, up to a value P1 for which the zone of weakness 24 breaks and the seal 26 is detached from the body 14. Under the effect of pressure, the piston 30 is suddenly set in motion, ejecting, in its stroke, the payload 40.

In the different case of a progressive rise in temperature and in particular in the event of a fire, the temperature of the gas generator 10 increases progressively until reaching a threshold temperature T1 corresponding to the self-ignition temperature of the pyrotechnic material. As indicated above, this temperature is obviously chosen to be lower than that T2 of the main pyrotechnic charge.

Under the effect of its combustion, the pyrotechnic material 74 emits gases, which increase the pressure inside the security chamber 66.

The pressure of the gases inside the safety chamber 66 then tends to increase the volume of said chamber 66 and, for this purpose, urges the sliding drawer 60 away from the body 12. A stop 58 limits the travel of the drawer 12 to a second limit position illustrated on the figure 2 .

In this position, the groove 70 faces the gas flow holes 50 formed in the body 12 of the actuator 10. Through these flow holes 50, the groove 70 and the exhaust holes 72 formed in the drawer 60, the combustion chamber 20 is in fluid communication with the external environment.

Two cases can then be envisaged: Either the temperature reaches the autoignition temperature T2 of the main charge 16, and in this case the main charge 16 is ignited, releasing gases into the combustion chamber 20. Either the temperature does not reach the auto-ignition temperature T2 of the main charge 16 (for example because the fire is extinguished in time).

In the first case, part of the gas escapes out through the flow passage 50. This flow passage 50 is sized so that the pressure inside the combustion chamber 20 can not reach the value P1, which is the one for which the piston is moved. In this way, in case of fire, the zone of weakness 24 remains intact, the cap 26 remains in place, and the piston 30 is not displaced. People in the vicinity of the actuator 10 are not endangered by the unexpected ejection of the payload 40, and said load 40 is preserved for later use.

In the second case, the main pyrotechnic charge 16 does not light. It remains intact and the device to be operated remains at rest. Only the pyrotechnic material 74 contained in the security chamber 66 has burned and will have to be replaced.

Claims (11)

1. A gas generator (10) comprising:

   a body (12) delimiting at least a part of a combustion chamber (20), said part housing a primary pyrotechnic charge (16) adapted to generate gases in the combustion chamber (20) when said charge is initiated in combustion,

   characterised in that it also comprises a slide valve (60) located outside said body (12) and defining with the latter a second chamber (66) housing a secondary pyrotechnic charge (74) whereof the self-ignition temperature (T1) is less than that (T2) of the primary pyrotechnic charge (16),

   in that a gas flow channel (50) for flowing gas out of the combustion chamber (20) is formed in the body (12),

   in that the slide valve (60) blocks the gas flow channel (50) when it is in a first position, and

   in that, under the effect of gases released by said secondary pyrotechnic charge (74), the slide valve is adapted to move to a second position wherein said channel (50) is no longer blocked, allowing gases contained in the combustion chamber (20) to flow outwards to the exterior.
2. The gas generator according to claim 1, wherein the slide valve (60) is capable of moving by sliding as per a rectilinear trajectory.
3. The gas generator according to claim 1 or 2, wherein the gas flow channel (50) comprises a plurality of holes distributed over the circumference of the body (12).
4. The gas generator according to any one of claims 1 to 3, wherein the slide valve (60) comprises at least one opening (70, 72) adapted to communicate with the flow channel for the gas (50) when the slide valve (60) is in its second position, the gas contained in the combustion chamber then able to flow towards the exterior through said flow channel (50) and said opening (70, 72).
5. The gas generator according to claim 4, wherein the opening (70, 72) comprises a circumferential groove (70) formed on the internal face of the slide valve (60) and at least one hole terminating (72) in said groove (70) and on the external face of said slide valve (60), said groove (70) delimiting an annular chamber with the body (12) when the slide valve (60) is in its first position and being adapted to communicate with the gas flow channel (50) when the slide valve (60) is in its second position.
6. The gas generator according to claim 4 or 5, wherein the gas flow channel (50) comprises a circumferential groove formed on the external face of the body and at least one hole terminating in said groove and on the internal face of said body, said groove delimiting an annular chamber with the slide valve when the latter is in its first position and being adapted to communicate with its opening when the slide valve is in its second position.
7. The gas generator according to any one of claims 1 to 6, wherein the slide valve (60) is coaxial to the body (12).
8. The gas generator according to any one of Claims 1 to 7, wherein the body (12) comprises at least one first section (51) having a first diameter and a second section (52) of greater diameter located in the extension of the first section (51), a shoulder (54) being defined between the first and the second section (51, 52), and wherein the slide valve (60) comprises a first part (62) adapted to slide along the second section (52) and a second part (64) extending radially towards the interior and whereof the internal radial face is adapted to slide along the first section (51), the second chamber (66) being defined between the shoulder (54) and the second part (64) of the slide valve (60).
9. A device to be actuated comprising a gas generator according to any one of claims 1 to 8, wherein the gases emitted by the primary pyrotechnic charge of the gas generator when it is initiated in combustion are adapted to actuate said device.
10. The device to be actuated according to claim 9, comprising a payload ejection device.
11. The device to be actuated according to claim 9, comprising a cylinder.

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