FR2933929A1 - Gas generator for activating airbag of motor vehicle, has storage chambers for storing respective gases or gas mixtures, and igniter activated to cause liberation of gases, their mixtures and their ignition and activation of safety device - Google Patents

Abstract

The generator (1) has a storage chamber (2) for storing gas or reactive gas mixture at specific initial pressure. Another storage chamber (3) stores another gas or reactive gas mixture that reacts with the former gas or gas mixture, at another initial pressure. An igniter (5) is activated to cause simultaneous or quasi-simultaneous rupture of storage caps (21, 31), when pressure at the interior of a cylindrical diffusion chamber (4) is less than a threshold, liberation of the gases, their mixtures and their ignition and activation of a safety device i.e. airbag. The gas or reactive gas mixture in the storage chamber (3) is selected from hydrogen, methane and a mixture of hydrogen or methane with helium, nitrogen, carbon dioxide or argon. The gas or reactive gas mixture in the storage chamber (2) is selected from oxygen, air and a mixture of oxygen or air with helium, nitrogen, carbon dioxide or argon.

Description

The invention relates to a gas generator for an automotive safety device, in particular an airbag also known in the English terminology of "airbag", intended to be inflated by said generator.

These protective cushions are designed to inflate in front of the occupant of the motor vehicle in the event of an accident. However, the cushion should be inflated too quickly or aggressively, which could cause injury to the occupant. For this purpose, it has been proposed to inflate the protection cushion in two stages.

To do this, a device is used to start inflating the cushion by introducing a first small quantity of gas, then to inflate it completely by introducing a second quantity of flammable gas, ignited with an igniter . In order to avoid any unintentional ignition of the flammable gas, it is already known from the state of the art, a gas generator that can separately store a combustible gas in a first chamber and a combustion gas in a second separate chamber the first, the two gases being mixed, introduced into the cushion and ignited only when the generator is activated.

The present invention relates to this type of gas generator. US 6 672 616, GB 2 417 066 and GB 2 416 199 are already known from gas generators comprising two separate gas storage chambers, mounted on a central support block which defines an access passage leading to the protective cushion. An igniter makes it possible to generate a gas, in order to move a mechanical element, such as a piston, present in said central block, from a first position in which it closes the outlet orifices of said storage chambers, to a second position in it no longer blocks these openings and allows the mixing of gases, their ignition and their passage to the protective cushion.

All these generators known in the state of the art have the disadvantage of using a large number of mechanical parts, which makes them more complex and more expensive to build.

In addition, the use of a moving mechanical part, such as a piston poses a potential problem of resistance in time, since the generator must be able to trigger when necessary, even after being inactive for a long period of time .

The object of the invention is therefore to overcome the aforementioned drawbacks. The invention more precisely aims to provide a gas generator for automotive safety device, which comprises two separate chambers, one of which contains a reactive gas and the other a gas capable of reacting with the aforementioned gas, this generator being equipped with a device that permits the simultaneous or almost simultaneous opening of these two chambers, the mixing of the two gases they contain and its ignition with a certain delay with respect to the beginning of the activation of the said safety device and this, without using a moving mechanical part as in the state of the art mentioned above.

For this purpose, the invention relates to a gas generator for an automobile safety device, in particular an inflatable protection cushion intended to be inflated by said generator, this generator comprising a first storage chamber, containing a first gas or a mixture of gases. reagent, stored at an initial pressure P2, a second storage chamber, containing a second gas or gas mixture capable of reacting with the first gas or gas mixture in a redox reaction, stored at an initial pressure P3, a chamber diffusion and an igniter that generates particles and / or hot gases in said diffusion chamber when activated, each storage chamber being provided with at least one orifice, called "drain" which opens into said chamber diffusion and is closed by a seal called "storage" In accordance with the invention, the diffusion chamber contains a third gas or mixture of inert gas or reactive with one of the first two, stored at an initial pressure P4 to support the two storage lids so that they close said drain holes, in that said diffusion chamber is provided with at least one orifice called " "discharge" which defines a passage for the flow of gas towards said automotive safety device and which is closed by a cover, called "discharge", and in that the activation of the igniter causes the rupture of said operculum discharging when the pressure Pdif4 inside said diffusion chamber exceeds a threshold value Psi, the release of the third gas or mixture of gases, then the simultaneous or near-simultaneous rupture of said storage lids when the pressure Pdif4 within said diffusion chamber is below a certain threshold Ps2, the release of the first and second gases, their mixing, their ignition and the activation of said automotive safety device. According to other advantageous and nonlimiting features of the invention, taken alone or in combination: - each storage lid is able to break when subjected to a pressure difference APsto2, APsto3 on both sides of its two opposite faces, whose absolute value is greater than the absolute value of the pressure variation Pdif4 inside the diffusion chamber between the initial pressure P4 and the pressure Pst reached at the moment of activation of the igniter; the initial pressures P2, P3 and P4 respectively prevailing in the first and the second storage chamber and the diffusion chamber are identical; the initial pressure P4 prevailing in the diffusion chamber is lower than the initial pressures P2 and P3 respectively prevailing in the first and the second storage chamber; - The storage caps are broken simultaneously between 0.5 and 5 ms after rupture of the discharge cap has occurred; the first gas or reactive gas mixture is chosen from oxygen, air and one of these two gases, mixed with an inert gas, in that the second gas or reactive gas mixture is chosen from hydrogen, methane and one of these two gases in admixture with an inert gas and in that said inert gas is selected from argon, helium, nitrogen or carbon dioxide; the first and second storage chambers are disposed diametrically opposite each other on either side of the diffusion chamber; the first and second storage chambers are annular and are arranged one above the other and around the cylindrical diffusion chamber; the first and second storage chambers are coaxial, in that one is arranged around the other and in that their drain holes open axially into the diffusion chamber; the igniter is arranged axially in the diffusion chamber; the igniter is arranged radially in the diffusion chamber. Other features and advantages of the invention will appear from the description which will now be made, with reference to the accompanying drawings, which show, by way of indication but not limitation, several possible embodiments. In these drawings: FIG. 1 is a diagram showing a first embodiment of the gas generator according to the invention; FIGS. 2 to 4 are diagrams representing the various stages of operation of the gas generator of FIG. Fig. 5 is a graph showing the evolution of pressure and pressure variations on different constituent parts of the gas generator as a function of time, and Figs. 6 to 8 are diagrams showing respectively a second, a third and a fourth embodiment of the gas generator according to the invention. A first embodiment of the gas generator according to the invention will now be described with reference to FIGS. 1 to 4. In FIG. 1, it can be seen that this generator, referenced 1, comprises two storage chambers. a gas or a mixture of gases, referenced 2 and 3, a diffusion chamber 4 which also contains a gas and an igniter 5. The storage chambers 2 and 3 are arranged on either side of the chamber of diffusion 4. Each storage chamber 2, 3 comprises at least one orifice 20, respectively 30, called drain, which opens into said diffusion chamber 4. These emptying holes 20, 30 are closed respectively by so-called storage lids , referenced 21 and 31. The diffusion chamber 4 further comprises at least one discharge port 40, 25, which defines a passage in the direction of the automotive safety device that the gas generator is intended to activate. The discharge port 40 is closed by a seal 41, called discharge. These different caps are welded to the inside of the wall defining the diffusion chamber 4. In the embodiment shown in FIGS. 1 to 4, the discharge orifice 40 opens into a diffuser 6, This diffuser 6 is itself placed inside the safety device to be actuated, for example inside a protective cushion, not shown in the figures.

In the embodiment shown in FIGS. 1 to 4, the generator has a generally tubular shape, of axis X-X ', the orifices 20, 30 are axial and the orifice 40 is radial. The walls of the various chambers 2, 3, 4 are sufficiently thick to hold the pressure at which the different gases are stored, so that each chamber is sealed with respect to the gases contained in another chamber and to prevent the migration of these gases through the walls. The material used is preferably steel but a composite material could be envisaged.

According to an alternative embodiment, the two chambers 2 and 3 are made separately. Chambers 2 and 3 are generally cylindrical in shape and can be made by cold-forming or any other known prior art. A filling orifice is provided for example at the end of the chambers. The two chambers 2 and 3 are then assembled for example by welding or crimping on the diffusion chamber 4. This chamber 4 is formed of a cylindrical sleeve at the ends of which the two storage chambers 2, 3 are assembled. The igniter 5 is welded to the wall of the diffusion chamber 4, so that its connection pins are accessible from the outside and that its primary pyrotechnic charge can explode inside the diffusion chamber 4, when it is activated, and generate there particles and / or hot gases. In this embodiment, the igniter 5 is radial. The first storage chamber 2 contains a first gas or reactive gas mixture, which is stored therein at an initial pressure P2.

The second storage chamber 3 contains a second gas or gas mixture, able to react with said first gas or gas mixture by a redox type reaction. This second gas or mixture of gases is stored at an initial pressure P3. The first gas or reactive gas mixture is selected from oxygen, air or a mixture of one of these two gases with an inert gas. The second gas or reactive gas mixture is selected from hydrogen, methane and one of these two gases mixed with an inert gas. In the two cases mentioned above, this inert gas is, for example, argon, helium, nitrogen or carbon dioxide. The diffusion chamber 4 contains a third gas or gas mixture, which is stored at an initial pressure P4.

This third gas or mixture of gases is either chemically inert, that is to say that it does not react with any of the two gases or mixtures contained in the first and second storage chambers 2 and 3, or that is capable of reacting chemically with the gas or mixture contained in one of these chambers.

The initial pressure P4 at which this third gas is stored makes it possible to keep the two storage louvers 21, 31 welded opposite the emptying orifices 20, 30 in order to seal them and to keep the storage chambers 2 and 3 watertight. P2, P3 and P4 storage are generally between 20 and 600 bar (20 and 600.105 Pa). The filling of the various chambers 2, 3, 4 is carried out as follows. The ideal solution is to fill these three rooms simultaneously. Filling orifices, not shown in the figures, are provided for this purpose. However, although this solution is industrially feasible, it is very expensive and also requires an important safety device since reactive gases are used on the same workstation. Consequently, another simpler solution to be implemented is to first fill the diffusion chamber 4, then 20 successively the two storage chambers 2 and 3. The operation of the device will now be described in more detail by making Referring to Figures 1 to 4 and 5. In what follows, it is considered that the initial pressures P2, P3 and P4 are identical. In the initial state, represented in FIG. 1, all the covers are in 25 places and the pressures prevailing in the storage chambers 2 and 3, denoted Psto2 and Psto3, respectively, and the pressure prevailing in the diffusion chamber 4, noted Pdif4. are constant. The pressures Psto2, Psto3 and Pdif4 are furthermore equal to P2, P3 and P4, respectively. In FIG. 5, the evolution of the pressures Psto2 and Psto3 during the time t is represented in solid line, while the evolution of Pdif4 is represented in bold lines. On the other hand, it is considered that the pressures Psto2 and Psto3 vary in the same way over time. The situation in the initial state is shown on the left half of Figure 5, to the left of the vertical line A.

The motor vehicle equipped with the generator according to the invention is provided with deceleration sensors which, in the event of an accident, produce an electrical signal transmitted to the igniter 5. When the igniter 5 is activated, as represented in FIG. it generates particles and / or hot gases inside the diffusion chamber 4, which has the effect of causing an increase in the volume and pressure of the third gas contained therein. The vertical line A of FIG. 5 corresponds to the activation of the igniter 5. In this figure, it can be seen that Pdif4 increases up to the vertical line B which represents the moment when the discharge cap 41 breaks. . During the same period, Psto2 and Psto3 remain constant and respectively identical to the initial pressures P2 and P3. It should be noted that the excess pressure temporarily prevailing inside the diffusion chamber 4 (increase of Pdif4) must not cause rupture of the storage lids 21, 31 and that these must be designed accordingly, both with regard to their dimension as the nature of the material constituting them and their mechanical strength. The discharge cap 41 is designed to rupture when the pressure Pdif4 inside the diffusion chamber 4 exceeds a threshold value Psi. With reference to FIG. 3, it can be seen that the rupture of the discharge cap 41 has the effect of causing the release of the third gas or mixture of gases from the diffusion chamber 4, through the orifice of discharge 40, towards the safety device, here the diffuser 6 and the protective cushion 25 not shown. The protective cushion thus begins to inflate. Simultaneously Pdif4 decreases as can be seen in Figure 5. During this time, the Psto2 and Psto3 pressures inside the chambers 2 and 3 remain constant as shown in Figure 5, and up to the vertical line C which represents the rupture point of the storage lids 21, 31. The pressure Pdif4 inside the diffusion chamber 4 continues to decrease until it reaches a value Ps2 beyond which the storage lids 21, 31 are subjected to a pressure difference on both sides of their two opposite faces which is large enough to cause them to rupture. In FIG. 5, the difference between the pressures exerted on each side of the two opposite faces of the storage lid 21, (respectively of the lid 31) is represented in phantom and is noted APsto2, (respectively APsto3), with APsto2 = Psto2 - Pdif4 and APsto3 = Psto3 - Pdif4. As can be seen, the deviations APsto2 and APsto3 are first zero until the line A, as shown on the left part of FIG. 5. Between the lines A and B which correspond to the activation of the igniter 5 and the rupture of the discharge cap 41, pressure differences APsto2 and APsto3 become negative, since Pdif4 becomes greater than the pressures Psto2 and Psto3 which correspond to the initial pressures P2 and P3.

After the rupture of the discharge cap 41, Pdif4 decreases until it becomes identical again to the initial pressure P4. At this moment, the pressure differences APsto2 and APsto3 become zero again. When the emptying of the diffusion chamber 4 continues, the pressure differences APsto2 and APsto3 become positive, until reaching a value Prsto corresponding to the simultaneous or near-simultaneous rupture of the storage caps 21, 31. In other In other words, the covers 21, 31 break when the pressure inside the storage chambers 2, 3 exceeds by a certain value that prevailing in the diffusion chamber 4.

When the two storage lids 21, 31 are broken, the first and second gases or gas mixtures contained in the storage chambers 2 and 3 are mixed inside the diffusion chamber 4. In the presence of the residual hot particles formed during the activation of the igniter 5, the mixture ignites and then escapes via the discharge port 40, towards the safety device, for example the diffuser 6 and the protective cushion. The latter is then completely inflated, having been simply pre-inflated during the previous step. In other words, each storage cap 21, (respectively 31), is capable of breaking when the absolute value of the pressure difference APsto2, (respectively APsto3) is greater than the absolute value of the pressure difference. inside the diffusion chamber 4 between the initial pressure P4 and the pressure Psi reached at the moment of the activation of the igniter 5. Note that according to an alternative embodiment of the invention, the initial pressure P4 prevailing in the diffusion chamber 4 could be lower than the initial pressures P2 and P3 prevailing respectively in the first and second storage chambers 2 and 3. In this case, the opening time of the two lids will be longer. Also preferably, the storage lids 21 and 31 are designed to break simultaneously between 0.5 and 5 ms after the rupture of the discharge cap 41 has occurred. This corresponds to the difference between lines B and C in FIG. 5. FIGS. 6 and 7 illustrate a second variant embodiment of the invention, in which the first and second storage chambers 2 and 3 are coaxial, preferably cylindrical, one being arranged around the other and their discharge openings 20, 30 opening into the diffusion chamber 4. In FIG. 6, these emptying orifices 20, 30 open axially into the diffusion chamber 4 and igniter 5 is disposed radially in this chamber. In FIG. 7, the emptying orifices 20, 30 open axially into the diffusion chamber 4, and the igniter 5 is also axially disposed in the diffusion chamber 4 opposite these orifices. The drain holes 20, 30 arranged in this case side by side can be closed by a single storage cap. In FIG. 7, the diffusion chamber 4 comprises two discharge orifices 40 arranged radially. Finally, FIG. 8 illustrates a third embodiment in which the first and second storage chambers 2 and 3 are annular and are arranged one above the other and around the diffusion chamber 4 of cylindrical shape.

The gas generator which has just been described could also be used in a safety device, such as an active structure type system intended to reinforce the body of the vehicle during an impact, in particular the doors of this vehicle.

Claims (11)

REVENDICATIONS1. Gas generator (1) for an automotive safety device, in particular an inflatable airbag intended to be inflated by said generator, this generator comprising a first storage chamber (2), containing a first gas or reactive gas mixture, stored at an initial pressure (P2), a second storage chamber (3), containing a second gas or gas mixture capable of reacting with the first gas or mixture of gases in a redox reaction, stored at an initial pressure (P3 ), a diffusion chamber (4) and an igniter (5) which generates particles and / or hot gases in said diffusion chamber (4) when activated, each storage chamber (2, 3) being provided with at least one orifice (20, 30), called "emptying" which opens into said diffusion chamber (4) and is closed by a cover (21, 31) called "storage", this generator being characterized in that that the diffusion chamber (4) contains a third second gas or mixture of inert or reactive gas with one of the first two, stored at an initial pressure (P4) for supporting the two storage lids (21, 31) to close off said drain holes (20, 30), in that said diffusion chamber (4) is provided with at least one orifice (40) called "discharge" which defines a passage for the flow of gas towards said automobile safety device and which is closed by a seal (41), called "discharge", and in that the activation of the igniter (5) causes the rupture of said seal (41) when the pressure (Pdif4) inside said chamber diffusion (4) exceeds a threshold value (Psl), the release of the third gas or mixture of gases, then the simultaneous or near-simultaneous rupture of said storage lids (21, 31) when the pressure (Pdif4) within said diffusion chamber (4) is below a certain threshold (Ps2), the release of the first and uxième gas, mixing, ignition and activation of said automotive safety device. 2. Gas generator according to claim 1, characterized in that each storage lid (21, 31) is capable of breaking when subjected to a pressure difference (APsto2, APsto3) on either side of its two opposite faces, whose absolute value is greater than the absolute value of the variation of pressure (Pdif4) inside the diffusion chamber (4) between the initial pressure (P4) and the pressure (Psl) reached at the moment of activation of the igniter (5) .ii 3. Gas generator according to claim 1 or 2, characterized in that the initial pressures (P2, P3 and P4) prevailing respectively in the first and the second storage chamber (2, 3) and the diffusion chamber (4). are the same. 4. Gas generator according to claim 1 or 2, characterized in that the initial pressure (P4) prevailing in the diffusion chamber (4) is lower than the initial pressures (P2, P3) prevailing respectively in the first and second chamber. storage (2, 3). 5. Gas generator according to one of the preceding claims, characterized in that the storage lids (21, 31) break simultaneously between 0.5 and 5 ms after the rupture of the discharge cap (41) is intervened. 6. Gas generator according to one of the preceding claims, characterized in that the first gas or reactive gas mixture is selected from oxygen, air and one of these two gases mixed with an inert gas, in that the second gas or reactive gas mixture is selected from hydrogen, methane and one of these two gases in admixture with an inert gas and in that said inert gas is selected from argon, helium, nitrogen or carbon dioxide. 7. Gas generator according to one of the preceding claims, characterized in that the first and second storage chambers (2, 3) are arranged diametrically opposite on either side of the diffusion chamber (4). . 8. Gas generator according to one of claims 1 to 6, characterized in that the first and second storage chambers (2, 3) are annular and are arranged one above the other and around the diffusion chamber (4) of cylindrical shape. 9. Gas generator according to one of claims 1 to 6, characterized in that the first and second storage chambers (2, 3) are coaxial, in that one is arranged around the other and in their drain holes (20, 30) open axially into the diffusion chamber (4). Generator according to Claim 8, characterized in that the igniter (5) is arranged axially in the diffusion chamber (4). 11. Generator according to claim 8, characterized in that the igniter (5) is arranged radially in the diffusion chamber (4).