LEBAUDY, Franck (9 rue Paul Fort, Brest, Brest, F-29200, FR)
COSTECALDE, Laurent (5 allée François Duine, Quimper, Quimper, F-29000, FR)
LEBAUDY, Franck (9 rue Paul Fort, Brest, Brest, F-29200, FR)
| CLAIMS
1. A gas generator for inflating a motor vehicle airbag, the generator comprising a tank (3) of gas under pressure with an orifice (8) that is closed by at least one cap (82), the cap (82) having an inside (82a) facing towards the gas tank (3) and an outside (82b) facing towards an opener device (7, 12) for rupturing the cap (82) on being triggered, in order to release the gas from the tank (3) and exhaust it to the outside via at least one gas diffusion outlet (10), the orifice (8) being distributed as a plurality of gas-passing holes (81), the gas generator being characterized in that: the opener device (7, 12) is electro-pyrotechnic so as to be suitable, on being triggered, for producing a flow of gas directed inside a chamber (7) towards said outside (82b) so as to strike the cap (82) in such a manner that the flow of gas ruptures the cap (82) so as to open the plurality of holes (81) directly.
2. A gas generator according to claim 1, characterized in that the opener device (7, 12) includes, in front of the orifice (8), a device (60) for focusing the flow of gas towards each of the holes (81) of the orifice (8) .
3. A gas generator according to claim 2, characterized in that the focusing device (60) has a single passage (61) facing at least a portion of each hole (81) of the orifice (8) for focusing the flow of gas onto each of the holes (81) of the orifice (8) .
4. A gas generator according to any one of claims 1 to 3, characterized in that said cap (82) is common to the plurality of holes (82) for closing them.
5. A gas generator according to any one of claims 1 to 3, characterized in that said cap is distributed as a plurality of individual caps (82), each closing a respective one of the plurality of holes (81) .
6. A gas generator according to claim 5, characterized in that the caps (82) present identical mechanical strength.
7. A gas generator according to claim 5 or claim 6, characterized in that for the holes (81) having identical cap-supporting sections, the caps (82) are identical in thickness.
8. A gas generator according to any preceding claim, characterized in that the outside (82b) of the cap (82) and the diffusion opening (10) are in communication in order to enable the gas to pass directly from the holes (81) towards said diffusion opening (10).
9. A gas generator according to any one of claims 1 to 8, characterized in that it is of the hybrid type, the opener device (7, 12) having a combustion chamber (7) on the outside (82b) of the cap (82), the combustion chamber containing an electro-pyrotechnic initiator (12) and a distinct pyrotechnic charge for being ignited by the electro-pyrotechnic initiator (12) in order to rupture the cap (82) .
10. A gas generator according to any one of claims 1 to 8, characterized in that it is of the cold gas type, the opener device (7, 12) having an ignition chamber (7) communicating with the outside (82b) of the cap (82) and containing an electro-pyrotechnic initiator (12) containing its own pyrotechnic material for rupturing the cap (82) . |
A GAS GENERATOR FOR INFLATING AN AIRBAG The invention relates to a gas generator for inflating a motor vehicle airbag.
The purpose of such devices is to protect an occupant of the vehicle in the event of a collision by generating gas for inflating the bag in order to damp the impact .
A field of application of the invention lies both with hybrid gas generators that are made up essentially of an initiator system, a pyrotechnic portion, a tank of gas under pressure, and a device for opening the tank, and also with so-called cold gas generators that are made up essentially of an initiator system, a tank of gas under pressure, and a device for opening the tank. Such gas generators have an orifice for releasing the gas that is stored under pressure in the tank. The orifice is provided with a device for hermetically closing the tank, and generally referred to as a cap.
The gas contained in the tank is released by opening the cap. This opening can be performed using various techniques, including amongst the most frequently used:
• using a projectile;
• retracting a mechanical support;
• using the initiator system or the pyrotechnic portion to attack the cap thermally and/or mechanically; and
• propagating a shock wave.
Applications are becoming generalized that require both a large volume of gas because of the large volume of the bag to be inflated, e.g. 25 liters (L) to 80 L for onebox vehicles having three rows of seats, and also a generator operating time that is short, e.g. 15 milliseconds (ms) to 25 ms . In some circumstances there is also a requirement for pressure to be maintained in the bag for several seconds, e.g. in the range 1.5 seconds (s) to 6 s in order to protect the occupant in the event of the vehicle rolling (Roll-Over) .
Car manufacturers are also always searching for savings in vehicle weight and required space, which means that gas generators must be ever more compact, making use of materials that present high levels of mechanical strength and using high gas storage pressures in the tank.
Several solutions exist for satisfying these requirements .
When retaining the gas mixtures that are conventionally used, e.g. based on nitrogen, the following are possible:
• designing generators that contain more gas by increasing their size so as to achieve the desired inflation capacity, and also increasing the size of the orifice in order to reduce operating time. The drawbacks of this solution are firstly that it requires the cap to be reinforced by improving its mechanical properties and/or increasing its thickness, thus making it more difficult to open, and secondly the increase in size goes against the manufacturers' requirements for reducing weight and for miniaturization;
• increasing the temperature of the gas leaving the generator so as to increase inflation capacity and reduce operating time. The drawbacks of this solution are firstly increasing the risk of burning the occupant, and secondly the gas cooling more quickly inside the bag, which means that the pressure cannot be maintained in the event of the vehicle rolling; and
• increasing the storage pressure of the gas in the tank, thus making it possible to have more moles for increasing the inflation capacity and also enabling the tank to be emptied more quickly so as to reduce operating time. The main drawback of this solution is that it requires the cap to be strengthened by increasing its mechanical properties and/or increasing its thickness, thereby making it more difficult to open.
Another solution is to use a light gas, such as helium for example, that makes it possible firstly to store more moles of gas for given mass, and secondly to release the gas more quickly because of the small size of its molecules. The main drawback of this solution is that the gas is more difficult to retain in a conventional bag, thus penalizing maintaining pressure in the event of the vehicle rolling, or else making it necessary to use a bag that is more expensive. The invention seeks to obtain a gas generator that satisfies the requirements for generating a large volume of gas, for a short operating time, for maintaining pressure in the bag over several seconds, and for improving weight, by having gas stored in the tank at high pressure, and a large orifice that is closed by a cap that is easy to open.
To this end, the invention provides a gas generator for inflating a motor vehicle airbag, the generator comprising a tank of gas under pressure with an orifice that is closed by at least one cap, the cap having an inside facing towards the gas tank and an outside facing towards an electro-pyrotechnic opener device for rupturing the cap on being triggered, in order to release the gas from the tank and exhaust it to the outside via at least one gas diffusion outlet, the gas generator being characterized in that: the orifice is distributed as a plurality of gas- passing holes.
According to other characteristics of the invention: • on being triggered, the opener device is suitable for producing a flow of gas, and comprises in front of the orifice a device for focusing the flow of gas towards each of the holes of the orifice;
• the focusing device has a single passage facing at least a portion of each hole of the orifice for focusing the flow of gas onto each of the holes of the orifice;
• said cap is common to the plurality of holes for closing them;
• said cap is distributed as a plurality of individual caps, each closing a respective one of the plurality of holes;
• the caps present identical mechanical strength;
• for the holes having identical cap-supporting sections, the caps are identical in thickness;
• the outside of the cap and the diffusion opening are in communication in order to enable the gas to pass directly from the holes towards said diffusion opening;
• the gas generator is of the hybrid type, the opener device having a combustion chamber on the outside of the cap, the combustion chamber containing an electro- pyrotechnic initiator and a distinct pyrotechnic charge for being ignited by the electro-pyrotechnic initiator in order to rupture the cap; and
• the gas generator is of the cold gas type, the opener device having an ignition chamber communicating with the outside of the cap and containing an electro- pyrotechnic initiator containing its own pyrotechnic material for rupturing the cap.
The invention can be better understood on reading the following description given purely by way of non- limiting example with reference to the accompanying drawings, in which:
• Figure 1 is a diagrammatic longitudinal section showing an embodiment of the invention for a cold gas type gas generator; • Figure 2 is a diagrammatic longitudinal section showing a variant of the Figure 1 generator; and
• Figure 3 is a diagrammatic front view showing two configurations for the multi-hole orifice used in the generator of Figures 1 and 2. In Figures 1 and 2, the gas generator 1 comprises a tubular part 2, e.g. a circularly cylindrical part, having a wall that defines a tank 3 of inert gas. The
tubular body 2 has a first longitudinal end 4 and a second longitudinal end 5 that are spaced apart from each other by the longest dimension of the body 2 along its longitudinal axis 11. At the end 4, there is secured another body 6 that defines a diffusion chamber 7 having an orifice 8 for communication with the tank 3. The outside wall 9 of the body 6 includes one or more diffusion openings 10 for expelling the gas outwards, e.g. into a bag in order to inflate it. These openings 10 may be circularly distributed around the longitudinal axis 11, for example. The openings 10 are wide open and in direct communication via the inside of the body 6 with the orifice 8.
According to the invention, the orifice 8 is subdivided into a plurality of parallel holes 81, each having a flow section for passing gas from the tank 3 towards the diffusion opening (s) 10.
In the embodiments shown in Figures 1 and 2, the holes 81 are closed by a common cap 82 so as to store the gas within the tank 3. In another embodiment that is not shown, each hole 81 is closed by its own cap 82 provided close to its edge. Below, this or these caps) 82 are referred to generically as being the cap 82.
By way of example, the cap 82 is provided on a support section 83 situated beside the tank 3. The part 84 having the holes 81 is either a portion of the wall of the body 6, as shown in Figures 1 and 2, or else it is an additional fitting for supporting the orifice 8.
A device for opening the cap 82 is secured within the body 6 by appropriate means. In Figures 1 and 2, this opening device comprises an electro-pyrotechnic initiator 12 having control electrodes 13, 14 situated at an outside end 15 of the generator 1 so as to be capable of being connected to an external electric circuit. The end 4 is situated between the outside end 15 and the other outside end 5 of the generator.
With a hybrid generator, the body 6 also contains a pyrotechnic charge situated between the orifice 8 and the initiator 12 suitable for being ignited by said initiator 12. The pyrotechnic charge is then placed in a housing closed by another cap (not shown) inside the chamber 7. A filter may also be added inside the chamber 7 in order to prevent combustion residue and debris from this other cap penetrating into the bag.
The cap 82 thus has an inside 82a facing towards the gas tank 3 and an outside 82b facing through the holes 81 towards the opener device 7, 12.
The initiator 12 is ignited by sending an electric control signal to the electrodes 13, 14. The initiated initiator 12 then causes a flow of hot gas and particles to be sent into the chamber 7. The initiator 12, or the pyrotechnic charge if the generator is hybrid, is placed in such a manner that this flow is directed towards the orifice 8 and towards the outside 82b of the cap 82, i.e. longitudinally in the figures. The initiator 12 or the pyrotechnic charge ignited by the initiator is suitable for giving rise to a reaction in the chamber 7 of the body 6 that is sufficient to rupture the cap 82. The cap 82 is ruptured by the flow that strikes it. This attack on the outside 82b of the cap 82 facing towards the chamber 7 leads to a drop in the mechanical properties of the cap 82, which then ruptures under the effect of the gas storage pressure inside the tank 3. The gas contained under pressure in the tank 3 then passes through the holes 81 so as to pass into the body 6 and escape outwards through the diffusion openings 10.
Compared with an orifice having a single hole for passing gas, as in the state of the art, the invention makes it possible to open directly the holes for putting the gas tank into communication with the diffusion openings so as to shorten the response time of the generator - which response time elapses between the instant the signal is sent for causing the initiator to
operate and the instant that gas actually passes at a prescribed flow rate through the diffusion opening -, while also making it possible to increase the overall flow section of the orifice by increasing the number of holes, each of which may have an individual flow section that is smaller, thus making it possible to reduce the thickness of the cap and to increase the gas storage pressure inside the tank. The invention makes it possible to shorten the response time with a structure that is simpler than that of generators in the state of the art. In the state of the art, caps are placed in cascade on different walls of the tank and they have to be ruptured in succession in order to put the tank into communication with the outside diffusion openings located downstream.
When a plurality of individual caps 82 are provided, they can be arranged in terms of thickness and support section, for example, to present identical mechanical strength, so that they are opened simultaneously. For this purpose, the holes 81 and the caps 82 can be identical, for example.
The use of caps 82 or of a single cap 82, that is/are fine and relatively weak, makes it possible to use an opener device for the tank that is simple and inexpensive, and that presents a response time that is very short.
Two, three, four or more holes 81 may be provided, optionally with their associated caps 82. By way of example, these holes can be disposed as shown in Figure 3 which shows an example of three holes 81a of individual flow section greater than the holes in an example having four holes 81b, both examples providing the same total flow section for the resulting orifice 8. These holes 81a, 81b are disposed circularly around the longitudinal axis 11 of the generator.
Figure 2 shows a variant of the Figure 1 generator in which a device 60 is inserted in the body 6 in front
of the orifice 8 for the purpose of focusing the flow generated from the initiator 12. In Figure 2, this focusing device 60 is thus located in the chamber 7 between the initiator 12 and the orifice 8. With a hybrid generator, the focusing device is located between the pyrotechnic charge and the orifice communicating with the tank.
By way of example, the focusing device 60 has a single passage 61 longitudinally facing at least a portion of each hole 81 of the orifice 8 so as to focus the flow onto each of the holes 81. In Figure 3, the passage 61 of the focusing device 60 is located centrally, for example, on the longitudinal axis 11 and it is circular so as to face the major inside portion of the holes 81, 81a, or 81b, i.e. the portion close to the axis 11. Naturally, a plurality of focusing passages 61 could be provided in the device 60, e.g. one focusing passage 61 facing each of the holes 81.
Figure 1 shows the configuration in which the three holes 81a of Figure 3 are used as the orifice 8. Figure 2 shows the configuration in which the four holes 81b of Figure 3 are used as the orifice 8.
In embodiments that are not shown, the cap(s) may be supported by a support device that is damaged by the opener device on being triggered, so that the cap(s) is/are then ruptured.
Naturally, the cap(s) 82 can also be opened by a mechanism, a projectile set into motion by the flow of gas created from the initiator and then striking said cap(s), or else by a shock wave.
The electro-pyrotechnic opener device 7, 12 causes all of the caps to be ruptured through all of the holes. By way of example, a single electro-pyrotechnic opener device 7, 12 can be provided with a single initiator 7.