EP0830560B1 - Electro-explosive initiator and vehicle safety system comprising such an initiator - Google Patents

Description

The present invention relates to an initiator electropyrotechnic as described by the preamble of claim 1.

This type of device has the function of being ignited by the passage of an electric current greater than one predetermined threshold value, in order to activate a mechanism.

The electropyrotechnic initiators are intended for be integrated into electrotechnical chains. In particular, they are used in security systems for cars or other vehicles, for example for operate an airbag. They are also used for example in missiles.

Such an electropyrotechnic initiator is known from example of document US-A-5,230,287 (basis for the preamble of claim 1). This initiator known electropyrotechnic includes two pins electric current supply inserted in a base, a bridge establishing an electrical connection between the two pins, a pyrotechnic composition stored in a container, an electronic circuit comprising a deposited bridge on a plate, this plate being connected to the pins electric current supply, and the composition pyrotechnic being compacted in the container and combined with the microcomponent under pressure in the container.

The invention also relates to a vehicle security system comprising one or more several initiators.

The initiators used to date consist of usually a device with two pins electric connected by a welded filament constituting a bridge conductor placed in contact with a composition pyrotechnic.

The rudimentary aspect of the connection between pins has the major disadvantage of not offering mastery sufficient firing.

In more sophisticated initiators, the driver bridge is performed on a printed circuit or equivalent support. Greater precision is thus possible.

However, major drawbacks remain. In particular, a weld bead is required at the connection between the driver bridge and the supply pins current. This affects the flatness of the interface of the driver's bridge with the pyrotechnic composition and affects the regularity of the exchanges calorific. The weld bead also requires the use of a deposition technology, consisting of depositing drops or painting of pyrotechnic product, technology little appreciated for mass production.

In addition, these devices have an architecture not intended to receive either a conductive or semiconductor bridge.

Another disadvantage of the initiators usually used is that protection against static discharge is not taken into account. Very serious consequences can result for the user.

Regarding the detection of leaks, we proceed usually by helium injection, then detection by aspiration. This process is long to implement and it is unreliable.

The invention aims to overcome these drawbacks.

The object of the invention is thus an electropyrotechnic initiator allowing to precisely control a firing, able to be integrated to an efficient chain requiring a high rate of reliability.

Another objective of the invention is an initiator capable of receive either a conductive or semiconductor bridge, with identical architectures, the semiconductor bridge ensuring faster heat exchange with the pyrotechnic composition.

It is also an object of the invention to obtain a stable initiator in time.

The subject of the invention is also a protection against electric shock static.

An additional object of the invention is a technology using a compacted form of the pyrotechnic composition, allowing to preserve the integrity of the interface between the bridge and the composition, even after long storage.

Another object of the invention is a initiator with a long lifespan, thanks to hermetic properties.

The invention also relates to a security system for a vehicle comprising such an initiator.

To this end, the invention relates to an initiator electropyrotechnic comprising the characteristics described in claim 1.

According to the invention, this bridge is deposited on a plate, the bridge and the plate being part of an electronic microcomponent, the wafer is connected to the pins and the composition is compacted in the container. The composition and microcomponent are brought together under pressure in the container.

Compared to existing initiators, the pyrotechnic initiator according to the invention offers thus a unique architecture, allowing to integrate both a conductive and a semiconductor bridge. What is more, the initiator can be made from of two electrical and pyrotechnics assembled under pressure, so that maintain the integrity of the interface between the microcomponent and composition. Compaction of the pyrotechnic composition also allows a perfect control of its ignition thanks to the bridge of electronic component.

According to a preferred embodiment of the initiator, the container has hermetic walls, the base is an airtight crossing and the connection walls at the base is also airtight. We avoid thus infiltrations in the composition.

The initiator according to the invention also comprises a housing inside the container, this housing comprising a material saturated with helium, allowing to detect possible leaks.

Instead of a laborious process used usually to detect a possible leak, the initiator according to the invention allows control very simple hermeticity. The material saturated in helium is indeed a real sponge, and any leakage from the case leads to a loss of helium can be easily detected by suction.

In the preferred embodiment, with walls airtight, it makes sense for the container includes an electrically insulating cup and case metal with airtight walls containing this cup.

The container preferably has an area of its thinned or weakened walls, so that a ignition of the pyrotechnic composition has a privileged effect to the law of this area.

Advantageously, the initiator includes a insulating cap which, together with the cup, constitutes a electrically insulating cage protecting the pyrotechnic composition of all attacks resulting in particular from electricity discharges static.

In a first configuration of the initiator, the bridge being conductive consists of a layer resistive of constant thickness.

The resistive layer then advantageously has a rectangular surface, for example square.

A precise determination of the resistance of the component and of a current intensity likely to trigger the initiator is thus obtained.

In a second configuration of the initiator according to the invention, the bridge is semiconductor.

On the other hand, two contact pads are advantageously provided at opposite ends of the plate, these ranges being intended to facilitate soldering of the pins.

This device eliminates any problem posed by weld beads.

The invention also relates to a system for vehicle security comprising at least one electropyrotechnic initiator according to the invention, able to activate a safety mechanism.

The invention will be described in more detail in reference to the drawings, in which:

Figure 1 shows a longitudinal section of an inert subset, comprising elements electric, part of an initiator according to the invention.

Figure 2 shows a longitudinal section a pyrotechnic sub-assembly corresponding to the inert sub-assembly of Figure 1.

Figure 3 shows an assembly of the sub-assemblies respectively inert and pyrotechnic of Figures 1 and 2, constituting the initiator described in as an example.

Figure 4 shows a micro-component electronics used in the Figure initiator 3, along a cross section IV-IV.

Figure 5 shows the bridge of Figure 4 in perspective.

The electropyrotechnic initiator 1 representative of the invention, shown in the Figure 3, is composed of two parts: a first inert sub-assembly 18 comprising elements electric, and a second pyrotechnic sub-assembly 19, containing products used for firing.

The inert sub-assembly 18, shown in the Figure 1 has two electrical pins 7 intended to be connected to an electrical circuit. These two metal pins 7 for supplying current are typically made of iron-nickel FN50. Their diameter is for example 1 mm. Pins 7 are hermetically sealed in an insulating base electrically. This is preferably made of glass, but can also be ceramic or plastic, for example. A cylindrical body 9 surrounds this base 8 to which it is linked hermetically. This metallic body 9 is of preferably made of stainless steel. Base 8 is covered with a cap 10 threaded on the pins 7. This cap 10 is made of a material electrically insulating, and is preferably in plastic. It is typically a polyamide. The cap 10 electrically insulates the body 9 metal of the pyrotechnic part.

An electronic microcomponent 20 is soldered to the pins 7. The cap 10 facilitates the positioning and contributes to the isolation of the pyrotechnic part.

The pyrotechnic sub-assembly 19, visible on Figure 2, includes the pyrotechnic composition 4 initiation. This is a substance sensitive to the heat. It can typically be chosen from lead azide, tetrazene, lead mononitroresorcinates, lead dinitrororcorcates and lead trinitroresorcinates. The last substance is the one chosen in the example.

Pyrotechnic composition 4 is accompanied of a composition 5 reinforcing an effect pyrotechnic. This reinforcing composition is redox type. Its reducer is typically based on zirconium, titanium, hydride titanium or boron. In a preferred embodiment, it contains 50 to 70% potassium perchlorate, 0 to 10% boron, 20 to 40% titanium hydride and 2 to 5% fluorinated binder.

The compositions 4 and 5 are compacted under pressure in an insulating cup 3. This one is from preferably plastic. Composition 5 reinforcing a pyrotechnic effect is compacted towards the bottom 16 of well 3, and the composition pyrotechnic 4 is compacted above. For example, 50 mg of composition 5 are successively compressed, then 30 mg of the pyrotechnic composition 4.

Well 3 containing the composition pyrotechnic 4 and the reinforcing composition pyrotechnic effect 5 is itself contained in a case 2, preferably metallic.

Cup 3 and cap 10 assembled constitute an electrically insulating cage which protects the pyrotechnic composition from all assaults resulting in particular from landfills of static electricity.

Case 2 has a thinned bottom 15, so as to create prior embrittlement. A firing of the pyrotechnic composition 4 has an effect as well privileged in the direction of the bottom 15. The bottom 16 of the bucket 3 also has a reduced thickness.

Between the bottom 16 of the bucket 3 and the bottom 15 of the case 2 is provided with a housing 6. This housing 6 is filled with a material saturated with helium, presenting preferably in the form of a thin washer. This is placed at the bottom 15 of the case 2 before the loading of the bucket 3. This device makes it possible to test easily the hermeticity of initiator 1, using a helium detector.

The inert sub-assembly 18 and the sub-assembly pyrotechnics 19 are assembled in compression 1 around a common axis 13, as shown in Figure 3 to constitute the initiator 1. A the case 2 and the body 9 are joined together by a circular laser weld 12. This weld 12 maintains constant compression and guarantees airtightness. For example, it can guarantee a state of a pyrotechnic charge compressive with a value of 500 bars. The assembly of two subsets 18, 19 can also be made by gluing the case 2 and the body 9.

Pressure assembly of the two sub-assemblies 18, 19 avoids the presence of air between the microcomponent 20 and the pyrotechnic composition 4, which would harm a control of calorific exchanges. The general advantage of this arrangement is that it allows maintain the integrity of the interface between bridge 23 and composition 4, the latter being carried out precisely according to the desired configuration.

On the whole thus elaborated, the cap 10 electrically insulates the pyrotechnic composition 4 of the metallic body 9. The glass base 8 ensures the tightness of the passage between the pins 7 and the metal body 9, it allows also to maintain the compressive state.

The weld 12 prevents infiltration between the case 2 on the one hand, and the body 9 and the bucket 3 on the other hand, thus giving the container compositions 4, 5 excellent hermeticity, it also helps maintain the compressive state.

The electronic microcomponent 20, detailed on Figure 4, preferably includes a plate 11 alumina. For example, it has a length L1 3 mm in a direction from pin 7 to the other, a width L2 equal to 2.54 mm and a thickness of 0.635 mm. On this plate 11, are arranged by a process of photolithography two 22 conductive tracks in gold arranged symmetrically on the side of each of the pins 7. The tracks 22 are separated by an L3 air gap of approximately 100 µm.

A bridge 23 is screen printed on this air gap L3. It can also be photolithographed or deposited under empty. In the example presented, this is a resistance, this being typically achieved by serigraphy using ruthenium-based ink.

The bridge 23, visible in FIGS. 4 and 5, has a length L'1 along the length L1 of the wafer 11, a width L'2 along the width L2 of the wafer 11 and a thickness e. It therefore has an area S equal to L'1 x L'2. Its section is also defined, for example L'2. By calling ρ the resistivity of bridge 23, the resistance R of the latter is given by:

If we keep a constant ratio L'1 / L'2 for the rectangular surface S of the resistive bridge 23, the resistance R is changed simply by making vary the thickness e and the resistivity ρ. In particular, it is possible to choose a surface S square, in which case L'1 equals L'2. In this case resistance R is ρ / e.

The choice of lengths L'1 and L'2 allows to adjust two important values: an intensity of non-functioning I0 and an intensity of operation I1. Intensity I0 defines a threshold of intensity flowing in bridge 23, below which heating of the wafer 11 is not sufficient to initiate a firing of the initiator 1. The operating intensity I1, greater than the intensity I0 of non-operation, defines a threshold beyond which initiator 1 is systematically ignited. Between I0 and I1, the initiation initiation is not guaranteed.

The intensities I0 and Il can be easily adjusted by playing on the surface S: the more the latter is small, the lower the values I0 and I1. The composition of bridge 23 is also involved in their determination.

By choosing wisely characteristics of the resistive bridge 23, dimensional, mechanical and thermal, it is thus possible to precisely adjust the resistance R and the intensities I0 and I1.

In the example chosen, bridge 23 has a surface S square, and the lengths L'1 and L'2 are all two equal to 150 µm. For an automobile, the resistance R is typically around 2 Ω, at 0.15 Ω close.

Contact resumption areas 21 in platinum-gold are also deposited at opposite ends of the plate 11 corresponding to the positioning pins 7. The pads 21 cover these ends over the entire width L2 of the insert 11. These deposits are made on both sides of the wafer 11, as well as on the edges 24 corresponding to the ends concerned. The beaches 21 facilitate soldering of pins 7, similarly so that for electronic components mounted in surface on printed circuits. Pins 7 are thus connected to the wafer 11 according to a widely proven welding process.

The assembly comprising the plate 11, the bridge 23 resistive, the conductive tracks 22, and the contact pads 21 constitutes the microcomponent electronics 20.

In the case of a semiconductor bridge 23, the architecture adopted is exactly the same. Typically, the wafer 11 is then formed of a semiconductor material deposited on a support made of ceramic material.

The use of a semiconductor bridge 23 is particularly advantageous because it allows a very high accuracy in triggering initiator 1. Indeed, it only becomes resistive from a fixed voltage level. When this level is reached, there is a cascade phenomenon starting with a heating of the bridge 23 going from associated with a decrease in its resistance and ending with the discharge of a plasma into the composition 4. A minimum duration of application of current is required to cause ignition.

As heat exchange occurs by conduction for a resistive component 20, they have essentially by convection in the semiconductor case. Although the importance of an interface perfectly controlled between composition 4 and component 20 is smaller, it remains desirable.

During assembly, the inert sub-assemblies 18 and pyrotechnics 19 are assembled under pressure, a pressure of 500 bars for example exerted on the pyrotechnic composition 4. They are then connected by the weld 12, which maintains after release the pressure applied beforehand.

The architecture is independent of the mode of realization of sub-assemblies 18 and 19. This simplifies the manufacture of the two types of initiator on the same site of the subsets 18, 19. This general configuration provides a very high precision of firing.

The tightness of the operational initiator 1 is then checked before installation in a vehicle with a helium detector, to detect possible leaks from material saturated in helium stored in housing 6.

In operation, in the presence of a bridge 23 conductor, a weak current flows by pins 7 connected to an electrical circuit, in component 20. This intensity, which can be null, is insufficient to trigger the initiator 1. It is less than the intensity I0 of no operation of the bridge 23 conductor. A firing of initiator 1 is caused by an increase sensitive to the current flowing in the pins 7 and greater than the operating intensity Il. he there follows a very rapid heating of the bridge 23 conductor, transmitted to the pyrotechnic composition 4 via the wafer 11. An explosion is thus triggered, its effects propagating from privileged way in the direction of the bottom 16 of the bucket 3.

If bridge 23 is semiconductor, the operation is quite similar. An update initiator 1 fire is however caused from more abruptly when a current passing through pins 7 has an intensity exceeding a value of threshold associated with the semiconductor bridge 23 and that its duration of application is sufficient.

Although the 23 bridges presented as are particularly advantageous, other configurations can be envisaged. In in particular, the bridge 23 may consist of a thin layer as a thick layer. he can also have a surface S other than rectangular, and for example have a shape circular or polyhedral.

In addition, despite poorer airtightness than in the example described and a modifying creep the interface between component 20 and the composition pyrotechnic 4, it is possible to carry out the case 2 and the body 9 made of plastic. The presence of the insulating cup 3 is no longer then necessary.

The initiator according to the invention can be used in especially in vehicles to quickly put in action security mechanisms, such as airbags, locks and unlocking doors, or pretensioners seat belts. However, it is also suitable for any other device requiring a trigger fast and well mastered of a mechanism. As example, it can be used in systems offensive or defensive military, and in fire protection systems or floods.

Claims (10)

1. An electro-pyrotechnic initiator (1) comprising:

   two electrical pins (7) for supplying current inserted into a baseplate (8),

   a bridge (23) setting up an electrical connection between the two pins (7),

   a pyrotechnic composition (4) stored in a receptacle (2, 3),

   said bridge (23) being laid down on a wafer (11), the bridge (23) and the wafer (11) forming part of an electronic micro-component (20) and the wafer (11) being connected to the pins (7) and the composition (4) being compacted in the receptacle (2, 3), the composition (4) and the micro-component (20) being linked together under pressure in the receptacle (2,3) characterized in that the initiator (1) comprises a housing (6) inside the receptacle (2, 3), said housing (6) comprising a material saturated with helium, allowing the detection of possible leaks, by aspiration.
2. An electro-pyrotechnic initiator (1) according to claim 1, characterized in that the receptacle has sealed walls, the baseplate 8 is a sealed crossover and the connection between the baseplate (8) and the walls of the receptacle (2, 3) is also sealed.
3. An electro-pyrotechnic initiator (1) according to claim 2, characterized in that the receptacle (2, 3) comprises an electrically insulating cup (3) and a metal case (2) with sealed walls containing said cup (3).
4. An electro-pyrotechnic initiator according to claim 3, characterised in that it comprises an insulating cap (10) which, with the cup (3) makes an electrically insulating cage protecting the pyrotechnic composition from any attacks resulting, in particular, from discharges of static electricity.
5. An electro-pyrotechnic initiator (1) according to any one of the proceeding claims, characterized in that the receptacle (2, 3) has an area (15, 16) weakened in such a way that igniting the pyrotechnic composition (4) has a favoured effect into said area (15, 16).
6. An electro-pyrotechnic initiator (1) according to any one of the preceding claims, characterized in that the bridge (23) being a conductor is constituted by a resistive layer (23) of constant thickness (e).
7. An electro-pyrotechnic initiator (1) according to claim 6, characterized in that the resistive layer has a rectangular surface (S).
8. An electro-pyrotechnic initiator (1) according to any of claims 1 to 5, characterized in that the bridge (23) is a semiconductor.
9. An electro-pyrotechnic initiator (1) according to any one of the preceding claims, characterized in that two contact pads (21) are provided at opposite ends of the wafer (11), said pads (21) being intended to facilitate brazing of the pins (7).
10. A safety system for a vehicle comprising at least one electro-pyrotechnic initiator (1) according to any one of claims 1 to 9, liable of activating a safety mechanism.

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