WO2008034807A1

WO2008034807A1 - Pyrotechnic gas generator enclosing a perforated tubular casing

Info

Publication number: WO2008034807A1
Application number: PCT/EP2007/059804
Authority: WO
Inventors: Yvonnig Patton
Original assignee: Autoliv Development Ab
Priority date: 2006-09-20
Filing date: 2007-09-17
Publication date: 2008-03-27
Also published as: JP5009990B2; DE112007002052T5; JP2010503576A; DE112007002052B4; FR2906022B1; CN101516689A; WO2008034807A8; FR2906022A1; CN101516689B

Abstract

The present invention relates to a pyrotechnic gas generator for automobile safety, comprising a closed tubular casing (10) containing: at least one combustion chamber (C) containing a pyrotechnic charge (3) constituted by material in bulk, with combustion thereof being triggered by an initiator associated with the chamber (C); at least one plenum chamber (T) associated with said combustion chamber (C) and communicating therewith via at least one nozzle (130) that receives the gas generated by combustion of the charge (3) and serves to exhaust the gas to the outside via at least one discharge opening (100) formed in said casing (10). It is remarkable in that combustion chamber (C) and plenum chamber (T) are offset longitudinally, said nozzle (130) also extending longitudinally; that the zone (14) of the casing (10) situated in register with said combustion chamber (C) does not have any opening in communication with the outside.

Description

PYROTECHNIC GAS GENERATOR ENCLOSING A PERFORATED

TUBULAR CASING

The present invention relates to a pyrotechnic gas generator for automobile safety.

It is designed especially to inflate a safety bag commonly known in English as "airbag".

Such a generator generally comprises a closed casing, enclosing at least one combustion chamber containing a pyrotechnic charge, whereof the combustion is triggered by an initiator linked to this chamber. It also comprises at least one plenum chamber linked to the combustion chamber, which receives the gases generated by the combustion of the charge and ensures that they escape to the exterior, via at least one discharge opening formed in the casing.

When the pyrotechnic charge is constituted by pastilles and when the L/D ratio of the generator is greater than 1 (L = length of the generator, D diameter), then combustion problems can appear.

In fact, situations arise in which combustion is concentrated at least in one part of the charge. In fact, during ignition of the charge only the pastilles opposite the igniter are ignited correctly. The other pastilles are masked by these first pastilles and are thus not in communication with sufficient gas hot to ignite correctly. Combustion of the first pastilles creates local excess pressure which, during uncapping of the combustion chamber, can crush the rest of the charge or erode it considerably by the passing gas flow.

Breaking pastilles causes an unwanted sharp increase in the surface to be burnt, the consequence of which is a sharp increase in the pressure in the combustion chamber, which perturbs the operation of the generator . Also, erosion of the charge is forced and random, which impairs repeatability of the combustion. To resolve this problem, it is known to utilise combustible charge blocks having a central opening forming a conduit, this opening constituting an evacuation channel for gases, which also maintain perfect regular and continuous combustion. The central opening also constitutes a housing for the initiator.

Using such a charge in the form of a block is delicate when dealing with a tubular generator of highly elongated shape, (large L/D ratio) . In fact, for the same mass of propergol, using a block augments the dimensions of the generator.

Such a generator is especially placed in a vehicle, at the level of the top of a door, so as to inflate an airbag, known as an "airbag curtain", or integrated into a seat for inflating a side airbag.

This problem is all the more difficult to resolve since one uses traditionally in this type of generator, a pyrotechnic charge bulk, that is, a charge made up of a powder of granules or pastilles of pyrotechnic material .

A generator of concentric structure is described in the document US-A-2006/082112. In its centre extends a combustion chamber whereof the wall has openings forming nozzles. In fact, there is an indication that they can be blocked by a metallic film to allow the pressure to reach a certain level and thus facilitate ignition. This wall thus constitutes the limit of the combustion chamber.

The aim of the present invention is to solve the above problem by proposing a generator of the type mentioned earlier, whereof the combustion of the charge is performed perfectly regularly and continuously, without risk of overrating during combustion of the latter. This concerns a pyrotechnic gas generator designed for automobile safety, which comprises a closed tubular casing which encloses:

- at least one combustion chamber containing a pyrotechnic charge made of a bulk material, combustion of which is triggered by an initiator linked to the chamber ;

— at least one plenum chamber linked to said combustion chamber, which communicate with it via at least one nozzle, which receives the gases generated by combustion of the charge and ensures that they escape to the exterior, via at least one discharge opening formed in said casing.

This generator is remarkable in that said combustion and plenum chambers are offset longitudinally, said nozzle also extending longitudinally, that the zone of the casing situated opposite said combustion chamber is deprived of any opening in communication with the exterior, and that this combustion chamber encloses longitudinally a perforated tubular partition, whereof the internal space delimits a volume for receiving and holding said charge, whereas the peripheral space located between this partition and the casing is exempt of charge and constitutes at least one escape corridor for combustion gases in the direction of the plenum chamber. It is understood from the above that the perforated tubular partition has two functions.

In the first instance, it constitutes and delimits a volume for receiving and holding the combustible bulk charge. Yet it delimits also with the casing of the generator which, in this zone, has no communication opening with the exterior, at least one corridor (or drain) for the evacuation of combustion gases in the direction of the plenum chamber. Due to the presence of this corridor, gases circulate freely, maintain combustion and escape via the plenum chamber.

According to other advantageous and non-limiting characteristics of this generator:

- the casing and the partition are coaxial; - the partition has a circular right section;

- the partition has a right section inscribed in a circle and presents a crenellated outline, its portions of greater diameter coming to bear against said casing; - the end of the partition situated beside said nozzle bears against a grid for protecting this nozzle;

- the grid is frustoconical in shape whereof the base bears against a partition in which said nozzle is pierced; - it is provided with at least one cord containing a pyrotechnic charge, with one end opening out to the inside of said plenum chamber.

Other characteristics and advantages of the present invention will emerge from the following detailed description of certain embodiments. This description will be given with reference to the attached diagrams, in which:

Figure 1 is a sectional view, according to a longitudinal median plane, of a first embodiment of a generator according to the invention, Figure 2 is a sectional view, according to the plane 2 - 2 of Figure 1, of this generator,

Figure 3 is a view similar to Figure 1 of an embodiment of the generator called "a cord", and finally Figure 4 is also a sectional view according to a longitudinal median plane of a third embodiment of a generator which comprises several combustion chambers, as well as two cords.

The pyrotechnic gas generator 1 shown in Figure 1 comprises a tubular casing 10 of cylindrical shape, whereof the wall is set at each of its ends on rings of discoid shape 11, respectively 12. Annular pads, not illustrated, and projecting inwards, ensure blocking of the wall on the rings. Similarly, the wall abuts an additional partition

13, also discoid, which extends parallel to the rings

11 and 12.

This partition is traversed by an orifice 130 forming a nozzle, described hereinbelow. In a variant embodiment, not shown, the number of orifices could be greater than one. The casing 10, as well as the rings 11 and 12 and the partition 13, are made of metal with high mechanical and thermal resistance.

The casing 10 however is made of a metal which has sufficient ductility to allow setting. The partition 13 divides the interior of the casing 10 into two chambers offset longitudinally (in the extension of one another) , specifically a combustion chamber C and a plenum chamber T. The above orifice 130 extends also longitudinally, that is, parallel to the major axis of the generator.

The generator comprises an igniter 2 which is linked to a pyrotechnic charge 3. These two elements are both situated in the combustion chamber C, placed to the right of the figure. In a manner known per se, the igniter is mounted in the central part of the ring 11. According to the invention, this igniter is mounted at an end of the combustion chamber, while the partition 13 provided with a nozzle is mounted at the end of the chamber. The charge 3 which is contained in the combustion chamber is a bulk charge, constituted here by propergol pastilles .

A conical grid 4 with openings 40 bears against the partition 13 and prevents propergol pastilles or fragments thereof from rushing into the nozzle 130 and obstructing it at least partially.

The term "grid" is understood to mean any perforated element, whereof the openings allow passage of gases, but the size of which is selected to constitute an obstacle to the passage of the pastilles. Pursuant to the invention, the zone 14 of the casing 10 which is situated opposite the combustion chamber C, has no opening in communication with the exterior .

In addition, this combustion chamber C longitudinally encloses a perforated tubular partition

5 whereof the internal space delimits a volume for receiving and holding the charge, while the peripheral space between this partition 5 and the casing 10 is free of charge and constitutes at least a corridor E for escape of combustion gases in the direction of the plenum chamber.

In the embodiment of the figures, the casing 10 and the partition 5 are coaxial.

The latter is open at its two ends and, to the side of the partition 13, it bears on the grid 4 described previously.

As shown more particularly in Figure 2, the partition 5 has a right section which is inscribed substantially in a circle and presents a crenellated outline, its portions 51 of larger diameter bearing against the casing 10.

Due to this physiognomy, the partition is positioned relative to the casing, without any need to use centring means relative to the latter. The resulting crenellations delimit as many corridors E for the circulation and evacuation of gas in the direction of the plenum chamber T.

In a variant, not shown in the figures, the partition 5 has, at one of its ends, a perforated bottom wall, which bears directly on the partition 13. In other terms, the grid 4 can be omitted. Of course, in an additional embodiment, also not shown, the partition 5 could have a strictly circular right section, which would require having to utilise blocking means (struts) of this partition relative to the casing.

The embodiment shown in Figure 3 has a structure quite similar to the generator of Figure 1. It is however equipped with a cord 6 enclosing an additional pyrotechnic charge, for example in the form of gellified propergol. Such a structure is known per se, especially from document FR-A-2 845 989.

With such a generator, as soon as a quantity of hot gas reaches the plenum chamber, there is combustion of the charge contained in the cord which then escapes via the evacuation orifices 100 and provides extra feed to the airbag linked to the generator, for the purpose of continuing its inflation.

The embodiment of Figure 4 relates to a generator having an initiator 2 placed in an intermediate position and according to an orientation perpendicular to a central combustion chamber C which communicates by means of two partitions 15, with additional combustion chambers Cl and C2 placed opposite one another. These combustion chambers Cl and C2 each further communicate with a plenum chamber Tl and T2 each receiving a cord 6.

In this embodiment, each of the combustion chambers Cl and C2 is provided with a partition 5 such as described above.

Claims

1. A pyrotechnic gas generator for motor vehicle safety, the generator comprising a closed tubular casing (10) containing: at least one combustion chamber (C) containing a pyrotechnic charge (3) constituted by material in bulk, with combustion thereof being triggered by an initiator associated with the chamber (C);

- at least one plenum chamber (T) associated with said combustion chamber (C) and communicating therewith via at least one nozzle (130) that receives the gas generated by combustion of the charge (3) and serves to exhaust the gas to the outside via at least one discharge opening (100) formed in said casing (10); characterised in that:

- said combustion chamber (C) and plenum chamber (T) are offset longitudinally, said nozzle (130) also extending longitudinally; the zone (14) of the casing (10) situated in register with said combustion chamber (C) does not have any opening in communication with the outside;

- and that said combustion chamber (C) contains longitudinally a perforated tubular partition (5) with the inside space thereof defining a volume for receiving and holding said charge (3) , while the peripheral space (E) situated between the partition (5) and the casing (10) has no charge and constitutes at least one passage for exhausting combustion gas towards the plenum chamber (T) .

2. The generator as claimed in Claim 1, characterised in that said casing (10) and partition (5) are coaxial.

3. The generator as claimed in Claim 1 or Claim 2, characterised in that said partition (5) has a circular right section.

4. The generator as claimed in Claim 1 or Claim 2, characterised in that said partition (5) has a right section that is inscribed in a circle and presents a crenellated outline, its portions (51) of greater diameter coming to bear against said casing (10),

5. The generator as claimed in any one of the preceding claims, characterised in that the end of the partition (5) situated beside said nozzle (130) bears against a grid (4) for protecting said nozzle.

6. The generator as claimed in Claim 5, characterised in that said grid (4) is frustoconical in shape with a base that bears against the partition (13) in which said nozzle is pierced.

7. The generator as claimed in any of the preceding claims, characterised in that it is provided with at least one cord (6) containing a pyrotechnic charge, with one end opening out to the inside of said plenum chamber (T) .