FR2888315A1 - PYROTECHNIC GAS GENERATOR FOR MOTOR VEHICLE SAFETY - Google Patents

Abstract

This generator comprises a tubular casing (1) internally divided by a pair of partitions which delimit two combustion chambers located at the ends of the casing (1) and communicating via nozzle orifices with a central plenum (40), which communicates itself with at least one discharge opening (400), the partition (5A) of at least one (30A) of the combustion chambers being provided with a protective member which prevents inadvertent ignition of the pyrotechnic charge ( 3A) that it contains by the combustion gases from the other chamber; this protective member is a thin and frangible plate (7) applied against the partition (5A) of the chamber (30A) and normally closing the orifice (50A), which has zones of lesser resistance, such as grooves, suitable to rupture under the pressure of the combustion gases produced in the chamber (30A) so that the portions (70 ') bordering these zones of least resistance unfold in petals towards the plenum (40), thereby allowing the passage ( F) gases in the latter.Safety equipment for motor vehicles, in particular for inflating an airbag.

Description

The present invention relates to a pyrotechnic gas generator for

to car safety.

  It relates more particularly to a pyrotechnic gas generator comprising a tubular envelope closed at its ends and internally divided by a pair of partitions which delimit two combustion chambers arranged at the ends of the envelope and communicating each, via nozzle orifices, with a central plenum, which itself communicates with at least one gas outlet opening, said discharge opening, the partition of at least one of the combustion chambers being provided with a protective member which prevents inadvertent ignition of the pyrotechnic charge that it contains under the effect of the combustion gases generated in the other chamber.

  The gases escaping from the plenum chamber through the discharge opening may be used in particular to inflate an airbag designed to protect the occupants of a motor vehicle in the event of an accident.

  A device of this type is described for example in document FR 2 760 710, which may be referred to if necessary, because it illustrates the state of the art in the field.

  In this known generator, one of the partitions is provided, on the side of the plenum chamber, with a safety valve (reference 26) which constitutes the aforementioned protective member. It is a one-lobed valve consisting of an annular washer which is secured by a flexible tongue, a central obturator block adapted to be pressed against the central orifice of the partition, which orifice acts as a nozzle .

  A disadvantage encountered with known devices is related to the diversity of the generators, especially in terms of the dimensions and shape of the partition, the number of orifices forming nozzles provided in the latter, their position (centered or eccentric) and their profile (cylindrical, conical, bevelled, etc.) This results in a heterogeneous character of the structure and dimensions of the (or) valve (s) equipping the generator. This valve must be adapted each time to the characteristics of the generator to be equipped. It must also in some cases, particularly if there are several nozzle orifices, be oriented specifically.

  Finally, the effectiveness of such a valve is not always perfect, because its sealing depends on the flexibility of the (or) tab (s) bearing the stud (s) shutter (s) and the good complementarity of pad with the mouth of the nozzle orifice with which it cooperates.

  The present invention aims to solve these difficulties by equipping the gas generator with a standard protective body, robust, reliable, inexpensive, and easy to assemble.

  The pyrotechnic gas generator for automobile safety, which is the subject of the present invention, comprises a tubular envelope internally divided by a pair of partitions which delimit two combustion chambers located at the ends of the envelope and communicating, via orifices forming a nozzle, with a central plenum chamber, which itself communicates with at least one discharge opening, the partition of at least one of the combustion chambers being provided with a protective member which prevents inadvertent ignition of the pyrotechnic charge it contains by the combustion gases from the other chamber.

  According to the invention, this protective member is a thin and frangible plate applied against said partition, normally closing the orifice, this plate having areas of lower mechanical strength capable of breaking under the pressure of the combustion gases produced in said chamber whose partition is provided with the protective member, so that the parts bordering these areas of least resistance unfold in petals towards the plenum, thus allowing the passage of gases in the latter.

  According to other advantageous features, but not limiting, of the invention: the other partition is also provided with a protective member in the form of a thin and frangible plate similar to that associated with said partition; said zones of least resistance are lines of weakening of material; said lines of weakening of material are grooves hollowed out in at least one of the faces of the thin wafer; said thin and frangible plate is a flat disk; said lines of weakening of material are grooves hollowed in the two faces of the disk, so that its mounting is reversible; - said thin and frangible plate is a domed disc in the central part, whose convexity is turned towards the plenum; said material weakening lines are rectilinear grooves arranged diametrically, or substantially diametrically, and they intersect in the central region of the disk; the peripheral edge area of the disc is not slotted; - The generator comprising a cylindrical sleeve-shaped condenser mounted in the plenum chamber, said thin and frangible plate is interposed between the wall against which it is applied and an end of said cylindrical sleeve constituting the condenser; - The wall facing the plenum chamber has a central zone recessed by a counterbore so that -or- the orifice (s) forming nozzle (s) open at a distance from the thin plate and frangible.

  This is interesting especially when dealing with several orifices forming nozzles because the pressurized gases that escape are clustered in the space upstream of the frangible plate (inside the recess) and help to solicit ; the same phenomenon is obtained with a convex shaped plate as mentioned above.

  According to a possible embodiment of the invention, the generator comprises a tubular envelope closed at its ends and internally divided by a pair of partitions, each separating a combustion chamber located at one end of the envelope, which contains a pyrotechnic charge associated with an igniter, a central plenum communicating with at least one discharge opening in the wall of the casing, each partition being traversed by at least one nozzle orifice which allows a controlled passage of the hot gases generated by the combustion of said pyrotechnic charge from the combustion chamber to the plenum chamber, these gases then being able to escape from the plenum chamber, via said discharge opening, in particular for inflating an inflatable airbag, at least one said partitions being provided with a protective member adapted to prevent inadvertent ignition the pyrotechnic charge of the combustion chamber - said second chamber - which is adjacent thereto by the combustion gases discharged at high speed from the other chamber - said first chamber - after they have passed through the central plenum, when the charge of this first chamber has been switched on, this generator being characterized in that said protective member is a thin and frangible plate which is applied against the partition of the second chamber, on the side of the plenum, so as to normally closing the orifice -or the orifices-, this plate having zones of lesser mechanical resistance, such as lines of weakening of material, capable of breaking under the effect of an overpressure generated by the combustion gases produced inside the second chamber when the charge of this second chamber has been lit, so that the parts of the plaquet those bordering said zones of least resistance are deformed, unfolding (forming petals) towards said plenum (without creating debris), while providing an opening facing said orifice -or said nozzle-forming orifices, thereby allowing the passage of hot gases from the second combustion chamber to the plenum.

  Other characteristics and advantages of the invention will appear on reading the following description of a preferred embodiment of the invention. This description is made with reference to the accompanying drawings in which: - Figure 1 is a schematic view, in axial section, of a pyrotechnic gas generator of the same general type as that of the invention, forming part of the state of the technique; - Figures 2 and 3 are perspective views of two protective members constituted by valves, also part of the state of the art; FIGS. 4 and 5 are views similar to those of FIGS. 2 and 3, respectively, showing two protective members in the form of thin, frangible disks in the form of disks, in accordance with the invention; - Figure 6 is a sectional view of the protective member of Figure 4, the cutting plane extending diametrically and perpendicularly to the plane of the wafer, as indicated by the arrows A-A in Figure 4; FIG. 7 is a perspective view showing another embodiment of the protective member, in the form of a domed disk; - Figure 8 is a partial view similar to that of Figure 1, showing the left side of the generator with its combustion chamber equipped with a protective member similar to that of Figure 4; FIG. 9 is a view similar to that of FIG. 8, illustrating the operation of the device during the ignition of the charge present in said combustion chamber; - Figures 10 and 11 are detail views showing two possible arrangements of the protective members of Figures 4 and 7, respectively.

  The pyrotechnic gas generator illustrated in FIG. 1 comprises a cylindrical casing 1, of cylindrical shape, the wall 10 of which is crimped at each of its ends on discoid-shaped rings 11A and 11B, respectively.

  101A and 101B are designated annular bulges, projecting inwardly, which secure the wall 10 on the rings 11A, respectively 11B.

  Similarly, the wall 10 is crimped onto a pair of transverse partitions 5A, 5B mounted within the casing.

  The annular crimping beads 100A, 100B penetrate into a receiving peripheral groove provided for this purpose in the partition 5A, respectively 5B.

  In its central part, each of these partitions is traversed by one or more orifices forming a nozzle.

  In the illustrated embodiment, the partition 5A is pierced by a single central orifice 6A, while the partition 5B has two orifices 50B and 51B slightly eccentric.

  The envelope 1, the rings 12 and 11, and the partitions 5A and 5B are traditionally made of metal with high mechanical and thermal resistance; the casing 1 is nevertheless made of a metal which has a ductility sufficient to allow crimping.

  Each partition 5A, 5B divides the inside of the envelope 1 into two adjoining chambers, one end, called the "combustion chamber" 30A, respectively 30B, and the other, central, called "plenum chamber" "40.

  The generator comprises a pair of igniters 2A, 2B, which are each associated with a pyrotechnic charge 3A, respectively 3B; the igniter 2A and the load 3A are both located in the combustion chamber 30A located on the left of the figure, and will be called conventionally second combustion chamber; the igniter 2B and the load 3B are both located in the combustion chamber 30B located on the right of the figure, and will be called conventionally first combustion chamber.

  In the embodiment shown, the latter has a greater length than the second chamber, and it contains, correlatively, a larger pyrotechnic charge.

  As can be seen in FIG. 1, each load 3A, 3B has the general shape of an annular sleeve of generally cylindrical shape which is fitted inside the wall of the casing 10.

  The igniter 2A, 2B is mounted in the central portion of the ring 1A, respectively 11B. These latter bear on their inner face a central annular skirt 12A, respectively 12B, wherein the igniter is fitted and retained by crimping the free end portion of the skirt.

  Each skirt 12 forms with the ring 11 associated with one and the same piece.

  An annular seal 20A, 20B, seals the igniter 2A, respectively 2B, at the bottom of the annular skirt, against the ring.

  Each igniter 2A, 2B enters the interior space of a load 3A, respectively 3B.

  This is held in place in the associated combustion chamber 30A, 30B by appropriate centering means, not shown, and is immobilized in translation by a grid 13A, respectively 13B, cup-shaped which is interposed between the load 3A or 3B and the partition 5A or 5B.

  These grids 13 do not interfere with the passage of gases.

  Each igniter 2A, 2B is provided with a pair of pins 21A, respectively 21B, which are intended to allow its connection to a source of electric current.

  This igniter, of known type, is an electropyrotechnic initiator. It includes an electrical initiation system and a fragmentable cap containing a pyrotechnic composition.

  In operation, this pyrotechnic composition releases a flame and hot gases which, in turn, lead to the combustion of the charge 3A 30 or 3B.

  The latter is composed for example of solid propellant, capable of generating a large amount of gas, very quickly.

  In each combustion chamber is disposed a thin lidding plate 6A, 6B, which is hermetically applied against a partition 5A, respectively 5B.

  The nozzle orifices 50A of the second combustion chamber 30A and 50B51B of the first combustion chamber 30B open into the central plenum chamber 40, which is therefore common to them.

  Inside the plenum 40 is mounted a condenser, consisting of a sleeve 4 of filter material, permeable to gas.

  Its function is to capture certain particles present in the gas generated by the combustion of the charge 3, by preventing these particles from emerging from the envelope and entering the airbag.

  Opposite the chamber 40 and the condenser 4, the wall 10 of the casing is pierced with at least one radial hole 400, and preferably with several radial holes, regularly distributed angularly.

  In case of shock of the vehicle, a deceleration sensor produces an electrical signal which is converted by at least one of the igniters 2A, 2B into a pyrotechnic signal, causing the combustion of the propellant charge 3A and / or 3B. The propellant generates gases in the combustion chamber 30A and / or 30B, the exhaust of which is controlled by the nozzle orifices.

  This exhaust can be done only when the pressure of the gases generated in a combustion chamber has reached a predetermined threshold value causing the breakdown of the lid 6A or 6B.

  This exhaust is via the plenum 40, through the filter wall of the condenser 4, to the discharge holes 400, inside the airbag.

  With a generator of this type, it is possible to release only a limited volume of gas, and therefore to inflate the protection cushion only partially by initiating only the ignition system of one of the two combustion chambers 30A , 30B.

  It is also possible to fully inflate the cushion by initiating the two ignition systems simultaneously or with a certain offset in time, the offset firing to modulate the inflation rate of the cushion.

  When only the ignition system of the first chamber 30B is initiated, there is a risk that part of the hot gases escaping at high speed and under pressure from this chamber may exit the plenum 40 via the orifice 50A (because it is located axially vis-à-vis the outlet ports 50B-51B) and then, after having slammed the lid 6A, these gases cause the inadvertent firing of the load 3A of the second combustion chamber 30A.

  To overcome this problem, and in accordance with the teachings of FR 2,760,710 already cited, the partition 5A is provided with a protective member which consists of a valve V whose function is to oppose the passage of gases from the chamber of still 40 to the second combustion chamber 30A, however allowing the passage in the opposite direction, when the load 3A is ignited.

  FIG. 2 shows a traditional single-lobe valve V1, adapted to fit on a partition provided with a single nozzle orifice.

  FIG. 3 represents a traditional two-lobe valve V2, adapted to fit on a partition provided with a pair of nozzle orifices.

  There are similar valves provided for partitions having more than two nozzle ports, including three.

  The disadvantages of this type of valve have been set forth in the preamble of this specification.

  According to the invention, the protective member is a thin and frangible wafer.

  Advantageously, it is cut in a metal strip of uniform thickness, for example of the order of 0.6 mm, having good cold forming capabilities while being able to withstand the aggression of hot gases generated in the first chamber of combustion.

  According to the first and second embodiments illustrated in FIGS. 4 and 5, the wafer is a plane disk.

  Its diameter corresponds substantially (with clearance to its setting) to the inside diameter of the wall 10 of the casing 1.

  The disc plate 7 illustrated in Figures 4 and 6 is slotted on only one of its two faces.

  There is provided a pair of rectilinear grooves 70 which can be made by punching or removal of material; they are arranged at right angles, crossing at the center of the disk. They have a length less than the diameter of the disk, so that the peripheral zone of the latter is not slotted.

  The embrittlement of the disk resulting from this grooving should not be too important so that it can withstand properly, without breaking or deforming, the aggression of hot gases generated in the first combustion chamber and present in the plenum .

  On the other hand, it must be sufficient to allow the breaking of the lines of lesser thickness 70, 71, and the deformation of the adjoining parts, when the disc 7 is subjected to the gases generated in the second combustion chamber.

  For 0.6 mm sheet thickness, a groove depth of 0.30 mm and a groove width of 0.35 mm meet these conflicting requirements.

  The sectional shape of the groove, for example in U or V is not of real importance.

  The disc 7 is intended to be mounted in the generator so that its grooved face is turned towards the plenum chamber, towards which the deployment of the broken parts can be done in petals.

  This poses a manufacturing problem, because the washer must be oriented in a defined manner (front side and back side of the other) when it is placed in the generator.

  This constraint slightly strikes the cost of manufacturing, and is a source of error.

  On the other hand, the disk can occupy any angular position with respect to its central point of symmetry, even if it is associated with several nozzle orifices, which is an advantageous advantage compared with traditional lobed valves.

  The disc plate 8 of FIG. 5 is grooved on each of its two faces by grooving similar to that of the first embodiment of FIGS. 4 and 6.

  On one face are cut two straight grooves cross 80-25 81. An identical groove 80'-81 'is made on the opposite face.

  The two crosses are angularly offset by 45 so that the embrittlement of the disc is distributed homogeneously.

  This disc is reversible, and the need for a specific orientation recto / verso is eliminated.

  The wafer 9 of FIG. 7 is a curved disc, except in its peripheral edge zone which is flat.

Its convex face is slotted.

  In the illustrated embodiment, there are five star-shaped grooves 90, 91, 92, 93, and 94 which meet in the center of the disc.

  As will be seen below, with reference in particular to FIG. 11, the plate 9 is particularly adapted to equip a partition having a plurality of nozzle orifices.

  Referring to Figures 8 and 9, we will now explain the operation of a generator equipped with a wafer 7 according to that previously described.

  This is retained inside the casing 1, between the partition 5A and the annular condenser 4. Its slotted face is turned towards the plenum 40.

  The circular plate 7 almost hermetically closes the mouth of the nozzle orifice 50A.

  In the case where the charge contained in the first combustion chamber (not visible in FIGS. 8 and 9) is ignited, the hot gases that it generates and which arrive at high speed in the plenum chamber 40 are blocked by this wafer and therefore can not reach the second combustion chamber 30A.

  In the case where the charge 3A contained in the second combustion chamber 30A is ignited, the hot gases it generates there induce a high pressure which causes the rupture of the wafer 7 along the lines of weakness 70 - 71; the parts 7 'bordering the broken lines are pushed axially by the gases leaving the nozzle orifice 50A (arrow F) and unfold in petals in the plenum chamber 40 as illustrated in FIG. 9.

  There is no debris that could enter the plenum and then the cushion.

  Because before rupture the wafer 7 is impermeable to gases both in one direction and in the other, its presence allows to dispense with the sealing plate 6A, which it also ensures the function.

  Figures 10 and 11 show devices in which the septum 5A is traversed by two nozzle orifices 50A, 51B.

  In this case the partition is provided with lids (not shown in the drawings). The use of two nozzle orifices makes it possible to maintain a constant operating pressure in the combustion chamber regardless of the temperature or the type of combustion of the propellant constituting the charge.

  For example, for a low operating temperature, a single nozzle orifice is uncapped so as to obtain a sufficient operating pressure. Indeed, at low temperature, the propellant burning rate is relatively low.

  On the contrary, at high temperature, the combustion rate is higher, and the two nozzle ports are uncapped to avoid an excessive increase in operating pressure.

  The covers are therefore calibrated differently to snap at different pressure thresholds.

  Whether the two nozzle orifices are uncapped, or only one is, it is necessary that the wafer 7 is broken. Now the decentering of the orifices 50A and 51A with respect to the central axis of the partition 5A causes the hot gases exiting through one or both of these orifices to generate a pressure that is not centered on the plate. 7. This may therefore not work at breakage and deformation under optimal conditions.

  Indeed, because the weakening lines of material 70, 71 intersect at the center of the disc, it is important that the pressure is exerted in this region, more fragile, and that the broken parts then deploy symmetrically to the 'outside.

  This is true in the same way for the plate 8, with both faces grooved.

  In order to allow a central application of the pressure of the gases leaving one or both of the orifices 50A-50B, the partition 5A of the device of FIG. 10 has a countersink 52 formed in its face turned towards the plenum 40.

  Thus is formed between the flat plate 7 and the counterbore 52 a recess which constitutes a small buffer space receiving the gas from the combustion chamber 30A, which allows to distribute the pressure against the entire central portion of the wafer 7 .

  A similar configuration is advantageously achieved with the reversible plate 8.

  The solution adopted on the device of FIG. 11 is of the same principle.

  At the partition 5A is associated a convex plate 9 such as that previously described with reference to FIG. 7.

  Here, however, the face of the partition 5A facing the plenum 40 is flat and not recessed.

  It is the interior space of the concave portion of the wafer 9 which serves as a buffer to distribute the pressure evenly against the curved wall of the wafer, finally to cause the breaking evenly and homogeneously.

  A wafer having lines of weakening of material similar to those just described could also be associated additionally to the partition 5B of the first combustion chamber 30B, within a generator where the firing can be done first, selectively, in one or the other of the two combustion chambers and not only in priority in the first chamber.

  The zones of weakening of material envisaged in the thin and frangible plates are not necessarily lines; a fortiori, these rectilinear lines are not necessarily rectilinear, nor made by punching or removal of material.

  They could be curved or bent, joining in the central region of the plate.

  They could be formed in the molding, especially if the wafer is made of a molded material, possibly synthetic (non-metallic). The wafer could be fixed at its peripheral edge zone to the partition 5, for example by gluing or welding.

Claims (12)

  A pyrotechnic gas generator for automotive safety, comprising a tubular envelope (1) internally divided by a pair of partitions (5A, 5B) which delimit two combustion chambers (30A, 30B) located at the ends of the envelope ( 1) and communicating, via nozzle orifices, with a central plenum (40), which communicates itself with at least one discharge opening (400), the partition (5A) of at least one (30A) combustion chambers being provided with a protective member which prevents inadvertent ignition of the pyrotechnic charge (3A) that it contains by the combustion gases from the other chamber (30B), characterized in that this organ protector is a thin and frangible wafer (7; 8; 9) applied against said partition (5A), by normally closing the orifice (50A), this wafer having areas of lesser mechanical strength capable of breaking under the pressure of boy Wut combustion zone produced in said chamber (30A) whose partition is provided with the protective member, so that the portions (70 ') bordering these zones of least resistance unfold in petals towards the plenum (40), allowing thus the passage (F) of the gases in the latter.   2. Generator according to claim 1, characterized in that the other partition (5B) is also provided with a protective member in the form of a thin and frangible plate (7; 8; 9) similar to that associated with said partition ( 5A).   3. Generator according to claim 1 or 2, characterized in that said areas of least resistance are lines of weakening material.   4. Generator according to claim 3, characterized in that said lines of weakening material are grooves (70-71; 8081, 80'-81 '; 90-91-92-93-94) dug in the at least one of the faces of the thin wafer (7; 8; 9).   5. Generator according to one of claims 1 to 4, characterized in that said thin and frangible plate (7; 8) is a flat disk.   6. Generator according to claims 4 and 5, taken in combination, characterized in that said lines of weakening material are grooves (80-81; 80'-81 ') hollowed in both sides of the disc (8) , so that its mounting is reversible.   7. Generator according to one of claims 1 to 4, characterized in that said thin and frangible plate (9) is a curved disk in the central portion, the convexity is turned towards the plenum (40).   8. Generator according to one of claims 4 to 7, characterized in that said material weakening lines are straight grooves arranged diametrically, or substantially diametrically, and intersecting in the central region of the disc.   9. Generator according to one of claims 5 to 8, characterized in that the peripheral edge area of the disc is not slotted.   10. Generator according to one of claims 1 to 9, which comprises a condenser (4) shaped cylindrical sleeve mounted in the plenum (40), characterized in that said thin and frangible plate (7; 8; 9) is interposed between the partition (5A, 5B) against which it is applied and an end of said cylindrical sleeve constituting the condenser (4).   11. Generator according to one of claims 1 to 8, characterized in that the face of the partition (5A) facing the plenum chamber (40) has a central zone recessed by a countersink (52) so that the or the orifice (s) (50A, 51A) forming a nozzle (s) open at a certain distance from the thin and frangible plate (7, 8).   12. A pyrotechnic gas generator for automobile safety, comprising a tubular envelope (1) closed at its ends and internally divided by a pair of partitions (5A, 5B), each separating a combustion chamber (30A, 30B) located at an end of the envelope (1), which contains a pyrotechnic charge (3A, 3B) associated with an igniter (2A, 2B), a central plenum (40) communicating with at least one discharge opening (400) ) formed in the wall (10) of the casing (1), each septum (5A, 5B) being traversed by at least one orifice (50A, 50B) forming a nozzle which allows a controlled passage of the hot gases generated by the combustion of said pyrotechnic charge (3A, 3B) of the combustion chamber (30A, 30B) to the plenum (40), which gases can then escape from the plenum (40) via said discharge opening (400). ), in particular for inflating a cushion of pr inflatable otection, wherein at least one (5A) of said partitions is provided with a protective member (V) adapted to prevent inadvertent ignition of the pyrotechnic charge (3A) of the combustion chamber (30A) - said second chamber - which is adjacent to it by the combustion gases discharged at high speed from the other chamber (30B) - said first chamber - after they have passed through the central plenum (40), when the load (3B) of this first chamber has been lit, characterized in that said protective member is a thin and frangible plate (7; 8; 9) which is applied against the partition (5A) of the second chamber (30A), on the side of the plenum (40), so as to normally close the orifice -or the orifices (50A), this plate (7; 8; 9) having zones of lesser mechanical strength, such as lines of weakening of material (70-71; 80-81; 80'-81 '; 90-91-92-93-94); liable to rupture as a result of an overpressure generated by the combustion gases produced inside the second chamber (30A) when the charge (3A) of this second chamber has been turned on, so that the parts of the wafer which border said zones of least resistance deform, unfolding towards said plenum (40), while providing an opening facing said orifice -or said orifices- (50A) forming a nozzle, thereby allowing the passage of gases hot from the second combustion chamber (30A) to the plenum (40).