EP0548433B1 - Piezoelectric firing device for the activation of an electric igniter with resistance wire - Google Patents

Description

The invention relates to a piezoelectric firing device designed to actuate an electric igniter with a resistant wire of a pyrotechnic assembly.

Such a device can in particular be used on shooting stations of different natures, to ensure the ignition of any pyrotechnic assembly actuated by an electric igniter with low or medium energy resistant wire.

Piezoelectric generators are often used in armament for the firing of active heads (anti-tank, flash, etc.), equipping rockets, missiles or artillery projectiles. In this case, the piezoelectric generator is consumable. It operates under the effect of impact impact on the target and ignites a very low or low energy detonator or igniter of the spark gap or breakdown type. The operating mode of this type of component is as follows. The high voltage produced by the generator creates a spark between two electrodes, which initiates a pyrotechnic composition. The primary component in turn initiates the entire pyrotechnic chain and leads to the operation of the main charge. As illustrated in document US-A-3 106 161, it has also been envisaged to interpose a transformer between the piezoelectric generator and the detonator.

The invention relates to a non-consumable firing device which can be actuated a very large number of times and capable of igniting an electric igniter with a resistant wire of low or medium energy (1.5 to 5 mJ) and operating by effect. Joule. The firing of such an electric igniter with a resistant wire is carried out in a conventional manner by means of linear electromagnetic devices, devices with a rotating generator or devices with cells or batteries.

Linear electromagnetic devices, constituted for example by a coil with plunger core or by a gap rupture system, are based on an abrupt variation of the flux inside a magnetic circuit. They have the advantage of being able to produce a fairly large amount of energy. However, they are quite heavy and relatively expensive, because they often require a cocking lever, in order to allow the delivery, by action on a trigger, the mechanical energy necessary for the activation of the electromagnetic system.

Devices with a rotating generator such as dynamos and alternators have the advantage of being able to produce, in a small space, relatively large energies. However, these devices are relatively complex and expensive, in particular due to the rapid drive mechanism of the generator.

Battery or battery devices can be classified into three categories.

In the first category, a battery is used directly to produce the ignition. Such a device must include a protective resistor to protect against a short circuit of the igniter. This resistance, which is added to the internal resistance of the battery and that of the igniter, means that the intensity supplied by the device can sometimes be insufficient.

In the second category of devices of this type, a battery charges a working capacitor before firing. This device makes it possible to provide the impulse necessary for firing, but its response time determined by the charging time of the capacitor is sometimes too long.

An improvement to battery and capacitor devices consists in adding an electronic signal processing circuit, making it possible to calibrate the latter according to the conditions of use. This improvement, which does not solve the problems mentioned above, also has the drawback of adding electronic circuits to these devices which can be complex and costly.

A major drawback of these battery or battery devices is that they require checking the condition of the batteries before each use and periodically replacing the batteries. In addition, permanently stored energy requires great rigor in the development of security systems.

In document FR-A-2 123 924, it has also been envisaged to ensure the ignition of an electric igniter by means of a transformer whose primary is connected to a piezoelectric element. However, this element is activated by decompression which results in a delay between the production of electric current and its use.

The subject of the invention is precisely a particularly simple piezoelectric firing device which can be reused a very large number of times (a few thousand), capable of being actuated manually and providing an electrical signal of high intensity and of sufficient duration to order a low or medium energy resistant wire igniter with sufficient safety margin.

According to the invention, this result is obtained by means of a piezoelectric firing device for actuating an electric igniter with a resistant wire, comprising a piezoelectric generator capable of supplying electrical energy when it is stressed, and a control mechanism, characterized by the fact that the control mechanism comprises a control member whose actuation has the effect of propelling a mass with a predetermined force against the piezoelectric generator, the device comprising in association a transformer whose primary winding is electrically connected to the piezo generator -electric and a secondary winding of which is capable of being connected to the igniter.

In such a device, manual actuation of the control member triggers the control mechanism which propels the mass against the piezoelectric generator. The perfectly controlled energy of the shock thus produced generates at the output of the piezoelectric generator a high voltage electrical signal (for example, 10 to 15 kV) of very short duration (approximately 200 μs). The transformer transforms this electrical signal into a low voltage signal (approximately 30 V), but having a high intensity (approximately 15 A) sufficient for the actuation of the resistant wire igniter to take place. In addition, this device provides electrical energy, up to about 17 mJ, which has a sufficient safety margin to ensure the ignition of a low or medium energy resistant wire initiator (1.5 mJ at about 5 mJ).

• un corps fixé au générateur piézo-électrique et dans lequel est formé un alésage dont une extrémité débouche en face de ce générateur ;
• un bouton poussoir monté coulissant dans ledit alésage, et constituant l'organe de commande ;
• des moyens pour commander une rotation de ladite masse dans un premier sens jusqu'à une position angulaire prédéterminée lors d'un enfoncement du bouton poussoir ;
• des moyens pour immobiliser la masse en translation dans ledit corps lorsqu'elle n'est pas dans ladite position angulaire prédéterminée ; et
• des moyens élastiques d'actionnement comprimés entre la masse et le bouton poussoir lors d'un enfoncement de ce dernier, de façon à emmagasiner ladite force prédéterminée qui propulse la masse contre le générateur piézo-électrique lorsque ladite masse atteint la position angulaire prédéterminée.

In a preferred embodiment of the invention, the control mechanism comprises:

• a body fixed to the piezoelectric generator and in which a bore is formed, one end of which opens out opposite this generator;
• a push button slidably mounted in said bore, and constituting the control member;
• means for controlling a rotation of said mass in a first direction to a predetermined angular position when the push button is pressed;
• means for immobilizing the mass in translation in said body when it is not in said predetermined angular position; and
• elastic actuation means compressed between the mass and the push button when the latter is pressed, so as to store said predetermined force which propels the mass against the piezoelectric generator when said mass reaches the predetermined angular position.

So that the device can be reused a large number of times without the operator having to intervene, it also includes automatic reset means controlling the return of the control member and the mass to the rest positions as soon as it stops. actuation of the control member.

Advantageously, these automatic resetting means comprise elastic means for returning the push button to its rest position and means for controlling a reverse and a reverse rotation of said mass to its rest position during a retreat of the push button. .

Advantageously, the means for controlling a rotation of the mass, the means for immobilizing the mass in translation in the body and the means for controlling a recoil and a reverse rotation of said mass comprise a radial pin secured to said mass; this pin passes through at least one cutout formed in a tubular part of the push button and which comprises two opposite ramps, and projects into at least one L-shaped groove formed in said bore and the two branches of which are oriented respectively in a circumferential direction and in an axial direction; means are provided to prevent relative rotation between the push button and the body.

The actuating means can then include a compression spring housed in the tubular part of the push button, between the mass and a push button firing button.

Furthermore, the elastic return means may comprise a second compression spring housed in the bore between one end of the push button and the piezoelectric generator.

In the preferred embodiment of the invention, the piezoelectric generator comprises a piezoelectric element prestressed in the direction of movement of said mass between two electrically conductive parts, electrically isolated from each other, a first of these parts constituting a cap capable of being struck by said mass.

• la figure 1 est une vue en coupe longitudinale représentant un dispositif de mise à feu piézo-électrique conforme à l'invention ;
• la figure 2 est une vue en perspective et en coupe représentant à plus grande échelle l'intérieur de l'alésage formé dans le corps du mécanisme de commande et dans lequel sont reçus le bouton poussoir et la masse apte à venir percuter le générateur piézo-électrique ;
• la figure 3 est une vue en coupe longitudinale partielle représentant une partie du mécanisme de commande dans la position qu'il occupe normalement au repos ; et
• la figure 4 est une vue comparable à la figure 3 représentant la même partie du mécanisme de commande dans sa position enfoncée d'actionnement.

A preferred embodiment of the invention will now be described, by way of nonlimiting example, with reference to the appended drawings, in which:

• Figure 1 is a longitudinal sectional view showing a piezoelectric firing device according to the invention;
• Figure 2 is a perspective view in section showing on a larger scale the interior of the bore formed in the body of the control mechanism and in which are received the push button and the mass capable of striking the piezo generator electric;
• Figure 3 is a partial longitudinal sectional view showing part of the control mechanism in the position it normally occupies at rest; and
• Figure 4 is a view comparable to Figure 3 showing the same part of the control mechanism in its depressed actuation position.

As illustrated in FIG. 1, the piezoelectric firing device according to the invention comprises, inside a bore 12 formed in a housing 10, a control mechanism 14, a piezoelectric generator 16 and a transformer 18 mounted end to end and in this order.

The control mechanism 14 comprises a cylindrical body 20 traversed along its axis by a bore 22. A push button 24 is slidably mounted in this bore 22 and protrudes outside through an opening formed in a removable part 10a of the housing 10. The push button 24 mainly consists of a tubular part 26, the end of which is located outside the housing 10 carries a firing button 28, for example by means of a pin 30.

The push button 24 is immobilized in rotation inside the body 20 of the control mechanism 14, for example by a finger 32 which projects radially outside the cylindrical part 26 and enters a longitudinal groove 34 machined in the bore wall 22.

A metallic mass 36, of cylindrical shape, is mounted in the tubular part 26 of the push button 24 so as to be able to move therein in rotation and in translation. This mass 36 is crossed radially by a pin 38 whose ends pass through two cutouts 40, symmetrical with respect to the axis of the push button 24, formed in the tubular part 26 of the push button 24 and penetrate into two grooves 42, symmetrical by relative to the same axis, machined in the wall of bore 22.

As best shown in FIGS. 3 and 4, each of the two cutouts 40 formed in the tubular part 26 of the push button 24 has substantially the shape of a parallelogram, of which two opposite parallel edges 40a and 40b are oriented parallel to the axis common to the bore 22 and the push button 24 and whose two other parallel opposite edges 40c and 40d form ramps. More specifically, the edge 40c is inclined towards the outer end of the push button 24 carrying the firing button 28, from the edge 40a, and the edge 40d is inclined towards the opposite inner end of the push button 24, from the edge 40b. Furthermore, the edge 40b of each of the cutouts 40 is angularly offset in an anticlockwise direction with respect to the edge 40a, looking from the right to the left in the figures.

As illustrated in FIG. 2, each of the two grooves 42 has the shape of an L, one of the branches 42a of which is oriented in an axial direction, that is to say parallel to the axis of the bore 22, and the other branch 42b of which is oriented in a circumferential direction, that is to say located in a radial plane relative to the axis of the bore 22. The branch 42b of each of the grooves 42 in the form L is connected to the branch 42a at the end of the latter facing the removable part 10a of the housing 10, and rotates clockwise looking from right to left in the figures.

Referring to FIG. 1, it can be seen that a compression spring 44 constituting elastic means for actuating the control mechanism 14 is housed in the tubular part 26 of the push button 24, so as to be compressed between the end of this tubular part carrying the firing button 28 and the end opposite the mass 36.

To complete the description of the control mechanism 14, another compression spring 46 constituting elastic return means for the push button 24 and the mass 36, is housed in the bore 22 between the end of the push button 24 located at the inside the body 20 and the piezoelectric generator 16.

Under the action of the return spring 46, the button push-button 24 and the metallic mass 26 normally occupy at rest the positions illustrated in FIG. 1. The push-button 24 then projects as far as possible outside of the removable part 10a of the housing 10. The pin 38 mounted in the mass 36 is then resting in the closest acute angle to the piezoelectric generator 16, formed between the edges 40a and 40d of each of the cutouts 40. In addition, the ends of the pin 40 are located in the circumferential branches 42b of each of the grooves 42 L-shaped, in the ends of these branches 42b furthest from the longitudinal branches 42a.

When an operator depresses the push button 24 by acting on the firing button 28, there does not occur any rotation of the mass 36 as long as the ends of the pin 38 do not reach the obtuse angles formed between the edges 40a and 40c of each of the cutouts 40 (Figure 3). Consequently, the ends of the pins 38 remain locked in the branches 42b of the L-shaped grooves 42 and the mass 36 remains stationary. There is therefore compression of the spring 44.

If the operator continues to press the push button 24, the pin 38 runs along the inclined edges 40c of the cutouts 40, so that the mass 36 rotates in an anti-clockwise direction looking from the right towards the left in the figures. During this rotation, the ends of the pin 38 run through the circumferential branches 42b of the L-shaped grooves 42, gradually approaching the longitudinal branches 42a. The mass 36 is therefore always immobilized in translation in the bore 22 by the cooperation of the ends of the pin 38 with the branches 42b. During this phase of actuation of the device, the compression of the spring 44 continues.

When the pushing of the push button 24 brings the pin 38 near the angles delimited between the edges 40c and 40d of the cutouts 40 (position illustrated in phantom in Figure 4), the ends of the pin 38 arrive opposite the longitudinal branches 42a of grooves 42 in the shape of L. The energy stored by the compression of the spring 44 is then suddenly released and propels the mass 36 towards the piezoelectric generator 16, so that the mass 36 strikes this generator. Since the stress of the spring 44 for which the displacement of the mass 36 towards the piezoelectric generator occurs is determined by construction, the energy transmitted to the piezoelectric generator is known and reproducible.

When the operator releases his action on the firing button 28, the spring 46 recalls the push button 24 towards its rest position illustrated in FIG. 1. From the start of this movement, the pin 38 comes to bear against the inclined edges 40d of the cutouts 40, near the longitudinal edges 40b. However, since the ends of the pin 38 are then located in the axial parts 42a of the L-shaped grooves 42, the mass 36 cannot rotate and therefore moves together with the push button 24 away from the piezo generator electric 16.

Towards the end of this joint movement, the ends of the pin 38 arrive opposite the branches 42b of the grooves 42, so that the mass 36 is driven in rotation in an anti-clockwise direction looking towards the end open exterior of the bore 22 under the effect of the cooperation of the pin 38 with the inclined edges 40d of the cutouts 40. The mass 36 is thus automatically returned to its rest position illustrated in FIG. 1.

Referring again to FIG. 1, it can be seen that the piezoelectric generator 16 comprises a piezoelectric element 48 constituted by a small piezoelectric ceramic bar, the dimensions of which are determined according to the characteristics which are desired. get. This piezoelectric element 48 is arranged along the axis of the bore 12 of the housing 10, in the extension of the bore 22 formed in the body 20 of the control mechanism 14.

The piezoelectric element 48 is surrounded by an insulating element 50 and compressed axially between two electrically conductive parts constituted by a cap 52 and by a positive stud 54.

The support planes between the axial ends of the piezoelectric element 48 and, on the one hand, the cap 52, and, on the other hand, the positive stud 56 have very good geometric correction in order to guarantee good transmission of electrical signals delivered by the generator.

The cap 52 has a disc-shaped part which penetrates into the adjacent end of the bore 22, one face of which is in contact with the piezoelectric element 48 and the face of which faces towards the inside of this bore carries a convex protuberance 52a (FIGS. 3 and 4) which is struck by the mass 36 during actuation of the control mechanism 14. Outside of the bore 22 and around the insulating element 50, this part in the form of disk of the cap 52 is extended by a frustoconical part of small thickness 52b terminated by a tubular end part 52c.

The positive stud 54 has the shape of a disc, one face of which is in contact with the end of the piezoelectric element opposite the cap 52 and the opposite face of which carries in its center a cylindrical piece 54a of electrical connection.

The part of the positive stud 54 adjacent to the piezoelectric element 48 is surrounded by a second insulating element 56 which also partially surrounds the insulating element 50 and the end of which penetrates inside the tubular end part 52c of the cap 52. The insulating material constituting the element 56 is chosen so as to have good mechanical hardness and high dielectric rigidity.

The piezoelectric generator 16 further comprises a metal carcass constituted by a body 58 and by an annular nut 60. The body 58 placed around the insulating element 56, is supported on one face of this element facing the electrical transformer 18 and is in electrical contact with the tubular end part 52c of the cap 52. The annular nut 60 is screwed onto the end of the body 58 facing the control mechanism 14 and it has a part which projects radially towards the inside, so as to be in abutment on the frustoconical part of small thickness 52b of the cap 52.

This arrangement makes it possible to apply to the assembly an axial prestress on the piezoelectric element 48 between the cap 52 and the positive stud 54. This prestress, which can be measured during assembly using the piezoelectric element electric 48 as a force sensor, or by any other means, makes it possible to guarantee the transmission to the piezoelectric element of the energy resulting from the impact of the mass 36 on the cap 52, whatever the temperature in a predetermined operating range (for example between about -50 ° C and + 60 ° C). The particular structure of the cap 52 described above guarantees the maintenance of an acceptable prestress despite the differential expansions that occur in this temperature range.

The nut 60 further comprises, in its part facing the control mechanism 14, a second threaded part capable of being screwed onto an adjacent threaded end of the body 20 of the mechanism 14, in order to allow the assembly of these two parts.

For a given mechanical energy shock, the electrical energy delivered to the igniter is maximum for a given value of the transformation ratio (for example, about 450), which can be determined according to the characteristics of the circuits. A high yield can then be achieved, for example around 8%.

However, one of the advantages of the invention is that the transformation ratio is not critical, the yield remaining close to its maximum value even if the value of the transformation ratio is modified (for example, between approximately 280 and approximately 500 ).

We can thus, to facilitate the realization of the transformer, slightly lower the transformation ratio by reducing the number of turns in the primary. The transformation ratio can even be reduced more markedly if it is desired to lower the cost of the device appreciably, but this is done to the detriment of the yield and, consequently, of the actuator reliability of ignition.

In the embodiment described, the electrical transformer 18 comprises a primary winding which has a large number of turns (for example around 3000) of pre-insulated fine wire and which is connected directly to the piezoelectric generator by two electrical conductors 62 and 64 respectively connected to the body 58 and to the cylindrical part 54a of the positive stud 54. The secondary winding of the transformer 18 on the contrary comprises a small number of turns of wire (of the order of 8) and it is connected to an electric igniter with resistant wire (not shown) external to the device by two electrical conductors 66 running between the wall of the bore 12, the piezoelectric generator 16 and the control mechanism 14.

The primary and secondary windings of the transformer 18 are placed on a ferrite jar 68 supported by a rod 70 arranged coaxially inside the bore 12. The use of a ferrite jar transformer with a core makes it possible to improve the overall efficiency of the device and avoid any risk of overvoltage in the event of a load fault on the transformer secondary. The rod 70 is integral with a skirt 72 which fills the annular space formed between the piezoelectric generator 16, the control mechanism 14 and the bore 12. The end of this skirt 70 is fixed to the body 20 of the control mechanism 14 for example by means of screws 72.

The assembly formed by the electric transformer 18, the piezoelectric generator 16 and the control mechanism 14 thus constitutes a whole which can be fitted into the bore 12 of the housing 10 when the removable part 10a of this case. To this end, the end of the body 20 facing outwards is advantageously provided with a thread which is screwed into a threaded hole formed in this removable part 10a as illustrated in FIG. 1.

In the piezoelectric firing device which has just been described, the pushing by an operator of the push button 24 of the control mechanism 14 has the effect, as described above, of propelling the metallic mass 36 with a predetermined force against the cap 52 of the piezoelectric generator 16. Under the effect of the impact, an electrical signal of high voltage (10 to 15 kV) of very short duration (approximately 200 µs) is generated by the generator piezoelectric 16.

In transformer 18, this electrical signal is transformed into a low voltage signal (around 30 V). A firing pulse whose maximum intensity reaches approximately 15 A and which lasts approximately 0.2 ms can thus be obtained, which makes it possible to control a resistor with a resistant wire having an inherent resistance of approximately 2 ohms, by using all of the piezoelectric energy supplied by the generator 16. Furthermore, the electrical energy at the output of the piezoelectric ignition device according to the invention can reach up to 17 mJ, which ensures in safe actuation of a resistant wire igniter whose operating energy generally varies between 1.5 and 5 mJ.

Given the very high voltage of the signal delivered by the piezoelectric generator, the electrical conductors 62 and 64 connecting the latter to the transformer 18 are coated with an insulating product 74 with high dielectric strength. It is possible, as indicated above, to reduce the number of turns of the primary, which has the effect of reducing the high voltage and facilitating the insulation of the wires.

The piezoelectric firing device according to the invention makes it possible, in a completely original way, to control an electric igniter with a resistant wire in a particularly simple and inexpensive manner, for a very compact size and an extreme reliability guaranteeing the actuation of the device several thousand times without maintenance. In addition, since the energy is only delivered at the time of firing, any problem of energy storage is eliminated, which significantly improves safety. Finally, the ignition pulse is delivered in a particularly short time (less than 1 ms), which constitutes an appreciable advantage compared to existing battery or battery devices.

Of course, the invention is not limited to the embodiment which has just been described by way of example, but covers all its variants. In particular, it will be readily understood that the control mechanism 14 can be modified according to the shape given to the control member (push button, lever, trigger, pedal, etc.) without departing from the scope of the invention. The same is true of the mounting structure of the piezoelectric generator 16, and of the transformation ratio which is not critical, as has been said.

Claims (10)

1. Piezoelectric firing device for actuating a resistive-wire electric igniter, comprising a piezoelectric generator (16) capable of delivering electrical energy when it is subjected to a strain, and a control mechanism (14), characterized in that the control mechanism (14) comprises a control element (24), actuation of which has the effect of propelling a mass (36) with a predetermined force against the piezoelectric generator (16), the device comprising, in association, a transformer (18), a primary winding of which is electrically connected to the piezoelectric generator, and a secondary winding of which is capable of being connected onto the igniter.
2. Device according to Claim 1, characterized in that it comprises automatic rearming means (46) causing the control element (24) and the mass (36) to return into ready positions as soon as actuation of the control element ceases.
3. Device according to either of Claims 1 and 2, characterized in that the control mechanism (14) comprises:

   - a body (20) which is fixed to the piezoelectric generator (16) and in which a bore (22) is formed, one end of which bore opens facing this generator;

   - a push-button (24) which is mounted so as to slide in the said bore and constitutes the control element;

   - means (38, 40c) for causing the said mass (36) to rotate in a first direction as far as a predetermined angular position when the push-button is pressed;

   - means (38, 42b) for blocking the mass in translation in the said body when it is not in the said predetermined angular position; and

   - elastic actuation means (44) which are compressed between the mass and the push-button when the latter is pressed, so as to store the said predetermined force which propels the mass against the piezoelectric generator (16) when the said mass reaches the predetermined angular position.
4. Device according to Claims 2 and 3 in combination, characterized in that the automatic rearming means comprise elastic means (46) for returning the push-button to its ready position and means (38, 40d) for causing recoil and reverse rotation of the said mass to its ready position when the push-button recoils.
5. Device according to Claim 4, characterized in that the means for causing the said mass to rotate, the means for blocking the mass in translation in the body and the means for causing recoil and reverse rotation of the said mass comprise a radial pin (38) securely attached to the said mass; this pin passing through at least one cutout (40) formed in a push-button part (26) that is tubular and includes two opposite ramps (40c, 40d), and projecting into at least one L-shaped groove (42) that is formed in the said bore (22) and the two branches of which are respectively oriented in a circumferential direction and in an axial direction; means (32, 34) being provided to prevent relative rotation between the push-button (24) and the body (20).
6. Device according to Claim 5, characterized in that the elastic actuation means comprise a compression spring (44) housed in the said tubular part of the push-button, between the said mass (36) and a firing button (28) of the push-button.
7. Device according to any one of Claims 4 to 6, characterized in that the elastic return means comprise a second compression spring (46) housed in the said bore (22) between one end of the push-button and the piezoelectric generator.
8. Device according to any one of the preceding claims, characterized in that the piezoelectric generator comprises a piezoelectric element (48) prestressed in the direction of movement of the said mass (36) between two electrically conductive parts (52, 54) that are electrically insulated from each other, a first of the said parts constituting a cap (52) which the said mass can strike.
9. Device according to any one of the preceding claims, characterized in that the control mechanism (14), the piezoelectric generator (16) and the transformer (18) are placed in this order inside a casing (10).
10. Device according to any one of the preceding claims, characterized in that the transformer (18) comprises a ferrite pot (68) with a core.

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