Gas generator

Abstract

A disc-shaped pyrotechnic gas generator includes a housing with a plurality of diffusion holes. A pyrotechnic substance is arranged in the housing. A filter is arranged in the housing. A containment member is arranged in the housing between the pyrotechnic substance and the filter. A drainage member is arranged in the housing between the pyrotechnic substance and the containment member. The filter is to provide support to a supported portion of the containment member at a start of operation of the gas generator.

Claims

1. A disc-shaped pyrotechnic gas generator, comprising: a housing including a plurality of diffusion holes; a pyrotechnic substance arranged in the housing; a filter arranged in the housing, the filter having a central void; a containment member arranged in the housing between the pyrotechnic substance and the filter, the containment member configured to rupture by forming at least one petal extending into the central void of the filter; and wherein the containment member is a metal disk radially extending beyond the filter and unitarily formed to include a supported portion axially adjacent the filter and supporting the filter and a non-supported portion axially adjacent the central void of the filter, the non-supported portion configured to rupture to form the at least one petal extending into the central void of the filter, wherein the containment member defines a centering receptacle for centering the filter axially within the housing, and wherein the containment member further includes a radially extending flange axially spaced from the supported portion and interconnected to the supported portion by an axially extending portion, the axially extending portion being radially adjacent to the filter.

2. The gas generator of claim 1, wherein the housing includes a base having an open axial end and a diffuser secured to the base at the open axial end, the diffuser defining the plurality of diffusion holes, the containment member entirely disposed within the base in an axial direction.

3. The gas generator of claim 2, wherein the containment member is directly welded to the diffuser.

4. The gas generator of claim 2, wherein the containment member is connected to the diffuser and the base of the housing at an inertia welding zone.

5. The gas generator of claim 4, wherein an upper axial end of the base and the containment member abut a radially extending portion of the diffuser in the inertia welding zone.

6. A method of assembling the gas generator according to claim 2, wherein the gas generator includes an ignition device, the method comprising: securing the ignition device to the base; loading the pyrotechnic substance by gravity into the base in contact with the ignition device through a base load opening; positioning a drainage member between the pyrotechnic substance and the base load opening; positioning the containment member above the drainage member and in an area of the base load opening; positioning the filter onto the containment member; and welding the diffuser to the base such that the filter is inserted between the containment member and a wall of the diffuser to block the base load opening with the containment member.

7. The gas generator of claim 1, wherein the pyrotechnic substance is a loose load of tablets around an ignition device of the gas generator.

8. The gas generator of claim 1, wherein the containment member is connected to a diffuser and a base of the housing at an inertia welding zone.

9. The gas generator of claim 8, wherein an upper axial end of the base and the containment member abut a radially extending portion of the diffuser in the inertia welding zone.

10. The gas generator according to claim 1, wherein the plurality of diffusion holes form nozzles for controlling combustion of the pyrotechnic substance.

11. The gas generator according to claim 1, wherein a space is established between the filter and the plurality of diffusion holes.

12. The gas generator according to claim 11, wherein the space is established between a downstream surface of the filter and a wall of the housing penetrated by the plurality of diffusion holes and has a thickness in an area of the plurality of diffusion holes of at least 1 mm.

13. The gas generator according to claim 1, further comprising a drainage member arranged in the housing between the pyrotechnic substance and the containment member and an ignition device disposed in the housing and axially spaced from the drainage member.

14. The gas generator according to claim 1, wherein the housing includes a cover and a main body portion, the filter radially extending below the cover and captured between the cover and the containment member.

15. The gas generator according to claim 1, wherein the housing includes a cover and a main body portion, the containment member including an axially extending flange at an outer circumference thereof, the axially extending flange directly opposed in an axial direction by the cover.

16. The gas generator of claim 1, wherein the housing includes: a base on a first axial side of the containment member; and a diffuser on a second, opposite axial side of the containment member, the containment member welded directly to the diffuser in a leak-proof manner, wherein the filter is axially captured between the diffuser and the containment member.

Description

DETAILED DESCRIPTION OF THE DRAWINGS

(1) Other characteristics and advantages of this invention will appear more clearly when reading the following detailed description of two embodiments of the invention provided as examples, which are in no way restrictive, and illustrated by the appended designs, in which:

(2) FIG. 1 presents a cross-section of a first embodiment of a gas generator according to this invention, before its operation;

(3) FIG. 2 presents a cross-section of a second embodiment of a gas generator according to this invention, before its operation;

(4) FIG. 3 presented the gas generator from FIG. 1 after its operation.

DETAILED DESCRIPTION

(5) FIG. 1 presents a gas generator including housing 10 formed from a base 11 inertially welded to a diffuser 12, which includes multiple diffusion holes 13.

(6) Inside the housing 10, pyrotechnic substance 20 is placed around an ignition device 70 consisting of a case 71 containing ignition pyrotechnic substance, overmolding 72, and connection pins 73 to receive an electrical ignition signal. In other words, the ignition device 70 here is an electric pyrotechnic igniter.

(7) Means of immobilization 60 (for example a foam wall) and means of drainage such as a perforated metal sheet 51 are placed in the base 11 above the pyrotechnic substance 20. The means of drainage can also be created from metal mesh or compacted wire and shaped appropriately to mold to the internal diameter of the base 11. The function of the means of drainage is to retain, upstream of the means of filtration 30, the pyrotechnic substance during its combustion. This allows the combustion of the pyrotechnic substance to be controlled during combustion. In fact, movement of the pyrotechnic substance to come into contact with the filter would partially block the filter, which would restrict the flow of gas and result in an increase in pressure in the gas generator. This is not desirable in a generator for front applications with a diameter generally greater than 40 mm. For generators of this diameter, their resistance to pressure requires increases in wall thickness that represent too great a disadvantage for the total mass of the generator.

(8) The pyrotechnic substance 20 is a loose load of propellant tablets, but a single block of propellant can be envisaged.

(9) The means of filtration 30 are arranged in the diffuser 12, and a seal 41 is welded to the diffuser 12 in the same area as the base 11, in inertia welding zone S. As a result, the seal 41 and the inertia welding zone S form means of containment 40 for the pyrotechnic substance 20: this substance is separated or isolated from the diffusion holes 13 in a leak-proof manner, because the seal 41 is a metal disc directly welded onto the diffuser 12.

(10) Typically, the means of filtration 30 are a filter made from perforated sheet metal, wound around itself, or a shaped compacted wire, or a compacted metal mesh. As can be seen in FIG. 1, the means of filtration 30 have a general toric shape, with an internal diameter D1 and an external diameter D2, inserted into a counterbore of the seal 41 so that they are correctly positioned in relation to the latter, thus guaranteeing the final positioning of the means of filtration in relation to the diffuser 12.

(11) During the gas generator's operation, it is therefore necessary for the seal 41 to rupture in order to release the combustion gases from the pyrotechnic substance 20 so that they flow through the means of filtration 30 and are diffused by the diffusion holes 13 before inflating an airbag.

(12) For this purpose, the seal 41 has a portion supported by the means of filtration, and a non-supported portion at the internal diameter D1.

(13) Typically, the seal 41 has a thickness in the non-supported portion within a range from 0.4 to 0.8 mm with for example at least a marked portion notably cross-shaped with a remaining thickness equal to 0.3±0.05 mm. The following mechanical characteristics can be envisaged: breaking strength (Rm) within a range from 300 MPa to 800 MPa, and/or elongation at break (A %) greater than or equal to 16%, and/or an elastic strength (Re) greater than or equal to 420 MPa. A steel of the type S420MC (1.0980) (standard EN 10149-2-1996) can be envisaged.

(14) Consequently, after a phase in which the pyrotechnic substance 20 is ignited by the ignition device 70, the pressure increases in the compartment of the housing 10 containing the pyrotechnic substance 20 and which is closed by the seal 41, until it causes the latter to rupture, in the non-supported portion, as can be seen in FIG. 3.

(15) In fact, FIG. 3 shows that the seal 41 has ruptured, forming petals 42 in the area of diameter D1 of the means of filtration 30. The rupture of the seal 41 is controlled, because the means of filtration 30 force its opening in the area of diameter D1, with the support provided to the supported portion of the seal 41 (the stress upon the seal 41 is directly dependent on the pressure, but also on the value of diameter D1). Diameter D1 also avoids the tear of the petals 42 from spreading.

(16) Furthermore, the rupturing kinematics is determined, with a folding or rolling of the petals 42 around the lower edge of the internal diameter of the means of filtration 30.

(17) The support provided by the means of filtration 30 therefore dictates the value of the unsealing pressure, and the rupturing kinematics, which allows repeatable and reliable ignition, and the absence of loose debris. In fact, the petals 42 remain attached to the seal 41.

(18) The means of filtration 30, sandwiched between the seal 41 and the internal upper surface of the diffuser 12, form a mechanical bridge to provide support to the means of containment (the seal 41) and avoiding requiring a thick metal sheet. Furthermore, during operation, the pressure of the combustion gases continuously pushes the seal 41 against the means of filtration 30 and against the internal upper surface of the diffuser 12, which forces the combustion gases to flow through the means of filtration 30, and not between these means and the diffuser 12 or the seal 41.

(19) Finally, it should be noted that a void is established between the means of filtration 30 and the diffuser 12, in particular in the area of the diffusion holes 13. This arrangement helps ensure that the diffusion holes 13 are never obstructed, even partially, by the means of filtration 30 and that all diffuse an equivalent flow of gas. There is no imbalance in the flow rate, which explains the canceling out of thrust and the lack of movement if the gas generator is ignited alone without being held in place.

(20) Typically, the gas generator according to this invention is used in front safety modules (integrated into a vehicle steering wheel or a dashboard to protect an occupant in the event of a head-on impact). The load of pyrotechnic substance 20 can be in the form of tablets with a diameter of 6.35 mm, and a thickness of between 1.5 mm and 3 mm. The pyrotechnic substance can have a burning rate of approximately 21 mm/s at 20 MPa (and in any case at a pressure lower than 25 MPa). In these conditions, the combustion pressure Pcomb measured in the base 11 is not much higher than the diffusion pressure Pdiff measured in the internal diameter D1 of the filter 30.

(21) This result is obtained thanks to the low height of the load of tablets in comparison to the internal diameter of the base 11 (the combustion gases do not have to flow through a thick bed of tablets), and also thanks to the internal diameter D1 of the filter 30 which allows a significant flow of gas.

(22) The applicant has measured and found that the ratio Pcomb/Pdiff is less than 1.5, at least in the following configurations:

(23) TABLE-US-00001 Example 1 Example 2 Example 3 Height of load Between 23 mm Between 26 mm Between and 28 mm and 30 mm 37 mm and 40 mm Internal diameter 47 ± 1 mm 50 ± 1 mm 57 ± 1 mm of the base 11 Internal diameter 18 ± 2 mm 20 ± 2 mm 24 ± 2 mm of the filter 30 Thickness of the 10 ± 2 mm 12 ± 2 mm 16 ± 2 mm filter 30 Number of 20 to 24 20 30 diffusion holes Ø of the diffusion 1.7 mm 2.2 mm to 2.9 mm holes 2.4 mm Equivalent 45.4 mm.sup.2 to 76 mm.sup.2 to 198 mm.sup.2 diffusion area 54.5 mm.sup.2 90 mm.sup.2

(24) The gas generator according to this invention therefore has a uniform pressure between the base 11 and the inside of the filter 30, which limits the internal forces (as there are minimal pressure differences).

(25) FIG. 2 presents a second implementation of a gas generator according to the invention. In the same manner as for the first implementation, the housing 10 is formed by the base 11 welded to the diffuser 12 through inertia welding. However, the means of containment 40′ here include a seal 43 and a gasket 44 installed in the base 11 to ensure a leak-proof barrier between the diffusion holes 13 and the pyrotechnic substance 20. The seal 43 can be formed from two parts, as presented, glued or welded together or from one single part.

(26) Finally, the means of drainage here include a perforated metal sheet 52 which is thicker than in the first implementation.

(27) In the same manner as for the first embodiment, the means of filtration are sandwiched between the diffuser 12 and the seal 43 to provide support to the latter. Consequently, the non-supported part of the seal 43 can open repeatably in the internal diameter of the means of filtration 30, at a repeatable pressure and repeatable time, without losing any fragments.

(28) The manufacturing process of the generator under the first or second implementation is almost identical: the base 11 fitted with the ignition device 70 with its upper opening (which will be welded to the diffuser 12 at the end of manufacturing) is placed under a device for loading the propellant tablets. As a result, the propellant tablets can be dropped by gravity into the base 11, through the opening of base 11 so as to fill the base 11 with the pyrotechnic substance 20. The loose propellant tablets are therefore arranged around, and possibly over, the ignition device 70.

(29) Once the propellant tablets have been loaded into the base, the means of immobilization 60, the means of drainage and the means of containment may be successively placed into the base in this order. The means of filtration 30 are then positioned onto the means of containment, and the diffuser 12 is then welded.

(30) In the case of the first implementation, the seal 41 is intended to have means of fitting with the base 11 so that it is attached at least when rotating, so that the inertia welding (or friction welding) between the base 11, the diffuser 12 and the seal 41 occurs at the same time.

(31) It is understood that this manufacturing process does not require any prior preparation of the propellant tablets into a subassembly (for example a case containing the tablets) manufactured away from the production line and placed into the base 11. Rather, the loose propellant tablets can be placed directly into the base 11, in contract with the side walls of the latter, and in contact with the ignition device 70. Consequently, the manufacturing process is simple, the gas generator does not include a container specifically for the tablets and its volume is reduced as far as possible because no space has been left between the tablets and the ignition device.

(32) It is understood that various modifications and/or improvements, obvious to a person skilled in the art, may be made to the invention's different embodiments described in this description without going beyond the scope of the invention defined by the appended claims. In particular, reference is made to an ignition device 70 which is an igniter on its own, but it is possible to envisage using a pyrotechnic relay between the igniter and the pyrotechnic substance 20. Furthermore, it should be noted that the means of drainage can be made from metal mesh or from compacted wire, which gives them a function of capturing combustion heat during operation, and maintaining this heat far away from the gas generator's external walls, which can be in contact with plastics, and so these plastics will be less exposed to heat.