GAS GENERATOR FOR A SAFETY SYSTEM

Abstract

Gas generator for a safety system, comprising: at least one pyrotechnic substance arranged to produce gases; a first part; a second part; a third part; and a fourth part separate from the previous parts, the first part and the second part being friction-welded to the third part. The gas generator is characterised in that the fourth part comprises: a first interface for positioning with the first part, and a second interface for positioning with the second part, such as to temporarily block at least one degree of freedom between the first and second parts in order to allow the first and second parts to be simultaneously friction-welded to the third part.

Claims

1.-15. (canceled)

16. A gas generator for a safety system, comprising: at least one pyrotechnic substance arranged to produce gases, a first part, a second part, a third part, and a fourth part separate from the previous parts, the first part and the second part being friction-welded to the third part, characterized in that the fourth part comprises: a first interface for positioning with the first part, a second interface for positioning with the second part, such as to temporarily block at least one degree of freedom between the first and second parts in order to allow an operation of simultaneous friction welding of the first and second parts to the third part.

17. The gas generator according to the claim 16, wherein the first positioning interface and the second positioning interface are arranged such that a rotational or translational movement of the first part during the friction welding operation carries along the second part.

18. The gas generator according to claim 16, wherein: the first part comprises a first welding interface, the second part comprises a second welding interface, and wherein a space is defined between the second welding interface and the first welding interface before the operation of simultaneous friction welding of the first and second parts to the third part.

19. The generator according to claim 16, wherein the first positioning interface and the second positioning interface are arranged so as to temporarily block six degrees of freedom between the first and the second part before the friction welding operation.

20. The generator according to claim 16, wherein the first part is a chamber containing the pyrotechnic substance, the second part is a cover plate and the third part is a diffuser.

21. The generator according to claim 16, wherein the fourth part is a grate arranged to hold the pyrotechnic substance during operation of the gas generator.

22. The generator according to claim 16, wherein, before the friction welding operation, a thickness of the second part at the second welding interface is between 33% and 66% of a thickness of the first part at the first welding interface.

23. The gas generator according to claim 16, wherein a diameter circumscribed at the second welding interface is the largest circumscribed diameter of the second part.

24. The gas generator according to claim 16, wherein the first interface for positioning the fourth part has a continuous contact surface with the first part.

25. The generator according to claim 16, wherein the first and second welding interfaces have a cylindrical form.

26. The generator according to claim 16, wherein the first, second and fourth parts have bowl forms with a bottom and a lateral surface, wherein a portion of the outer lateral surface of the fourth part bears against a portion of the inner lateral surface of the first part, and wherein a portion of the outer lateral surface of the second part bears against a portion of the inner lateral surface of the fourth part.

27. The gas generator according to claim 25, wherein the second positioning interface is formed by a junction between the lateral surface and the bottom of the fourth part, and wherein the female form of the second part is formed by a junction between the lateral surface and the bottom of the second part.

28. A safety module comprising a gas generator according to claim 16.

29. A motor vehicle comprising a safety module according claim 16.

30. A process for manufacturing a generator according to claim 16, comprising the operations of: positioning the fourth part on the first part via the first positioning interface, positioning the second part on the fourth part via the second positioning interface, carrying out the operation of simultaneous friction welding of the first and second parts to the third part.

Description

[0046] Other features and advantages of the present invention will be seen more clearly from the following detailed description of an embodiment of the invention provided by way of a non-limiting example and illustrated by the appended drawings, wherein:

[0047] FIG. 1 shows a side view of a generator according to the invention.

[0048] FIG. 2 shows an exploded isometric view of certain components of the generator from FIG. 1.

[0049] FIG. 3a shows a sectional view of the generator from FIG. 1, before a friction-welding operation, along the A-A axis defined in FIG. 1.

[0050] FIG. 3b shows the generator from FIG. 3a after the friction-welding operation.

[0051] FIG. 4 shows a sectional view of the generator from FIG. 3a, along the B-B axis defined in FIG. 3a.

[0052] FIG. 5 shows a sectional view of the generator from FIG. 4, along the C-C axis defined in FIG. 4.

[0053] FIG. 1 shows a gas generator for airbag of discoid form, generally used for frontal protection, and comprises a first part forming a chamber 1 which is welded to a third part forming a diffuser 3. The diffuser 3 comprises diffusion holes at the periphery thereof, in order to diffuse, in an airbag which is not shown, combustion gases from a pyrotechnic substance 6 contained in the gas generator.

[0054] The lateral surface of the chamber 1 comprises deformations 14 which are the parts visible from the outside of the generator, of male forms 12 visible in FIG. 3a.

[0055] FIG. 2 shows three components of the unassembled gas generator according to an isometric view: the chamber 1, a second part which is a cover plate 2 and a third part which is a grate 4.

[0056] The chamber 1 and the diffuser 3 are the thickest components, since they have to withstand the operating pressure of the generator, during the combustion of the pyrotechnic substance. It is possible to provide a thickness within a range extending from 1.3 mm to 3.5 mm.

[0057] The cover plate 2 has weak zones 25 which are thinner zones arranged to break at a predetermined pressure during the operation of the generator. Since the cover plate 2 does not have to withstand the operating pressure, it can be thinner, for example between 33 and 66% thinner than the chamber 1 or the diffuser 3. It is possible to provide a thickness within a range extending from 0.3 mm to 1.2 mm.

[0058] The grate 4 comprises a first interface for positioning 41 with the chamber 1 and a second interface for positioning 42 with the cover plate 2. The bowl form of the grate 4 and of the cover plate 2 can be clearly seen in this view. The grate 4 comprises a bottom 43 and a lateral surface 44 while the cover plate 2 comprises a bottom 26 and a lateral surface 27.

[0059] FIG. 3a shows a sectional view of the generator from FIG. 1, before a friction-welding operation, along the A-A axis defined in FIG. 1. The generator comprises a pyrotechnic substance 6 defined so as to produce gas when it is ignited by an electro-pyrotechnic initiator 7. The initiator 7 is connected in a leaktight manner to the chamber 1 by an overmolding 8. Before being diffused into the airbag, the gases are cooled by a filter 5.

[0060] This view before welding makes it possible to visualize the sub-assembly composed of the chamber 1 containing the pyrotechnic substance 6 and the grate 4 and closed by the cover plate 2 which is in the position to be welded to the diffuser 3. For this purpose, the diffuser 3 is caused to rotate about the weld axis S and, during the rotational movement, the sub-assembly is pressed with a force F onto the diffuser 3.

[0061] To this end, the chamber 1 comprises a first welding interface 11 defining a first weld plane 111 while the cover plate 2 comprises a second welding interface 21 defining a second weld plane 211. The second weld plane 211 is located under the first weld plane, that is to say that the second weld plane 211 is contained inside a volume formed by the chamber 1 closed by the first weld plane 111. In other words, during the application of force F during the welding operation, the first weld plane 111 touches the diffuser 3 before the second weld plane. Typically, the offset is approximately 0.5 mm0.25 mm.

[0062] The first positioning interface 41 makes it possible to position the grate 4 relative to the chamber 1 along a direction perpendicular to the weld axis S and also positions the grate 4 in the chamber 1.

[0063] FIG. 3b shows the generator from FIG. 3a after the welding operation. The filter 5 is in contact both on the cover plate 2 and on the diffuser 3.

The cover plate 2 comprises a hollow female form 24 which makes it possible to position the filter 5 relative to the diffuser 3 and in particular to guarantee a radial space between the filter and an inner surface of the diffuser 3 so as to ensure an unrestricted flow of the gases produced by the pyrotechnic substance 6 during the operation of the gas generator.

[0064] A portion of the first welding interface 11 has disappeared in the form of a first weld bead 13 between the chamber 1 and the diffuser 3. A portion of the second welding interface 21 has disappeared in the form of a second weld bead 23 between the cover plate 2 and the diffuser 3.

[0065] The grate 4 has a lateral surface 44 in continuous contact with an inner surface of the first part 1. This limits any risk of projection of weld particles toward the pyrotechnic substance through the first positioning interface 41.

[0066] FIG. 4 shows a sectional view of the generator from FIG. 3a, along the B-B axis defined in FIG. 3a. The first and second positioning interfaces of the grate 4 are more clearly visible.

The first interface 41 is a female form positioned on an outer lateral surface of the grate. Its form is complementary to a male form 12 formed on an inner lateral wall of the chamber 1, so as to avoid any rotation of the grate 4 about the weld axis S relative to the chamber 1. This embodiment comprises four first interfaces 41. This number is to be adjusted depending on the forces required for the welding operation.

[0067] The second interface 42 is a male form positioned on an inner lateral surface of the grate. Its form is complementary to a female form 22 formed on an outer lateral wall of the cover plate 2, so as to avoid any rotation of the cover plate 2 about the weld axis S relative to the grate 3. This embodiment comprises eight first interfaces 42. This number is to be adjusted depending on the forces required for the welding operation.

[0068] FIG. 5 shows a sectional view of the generator from FIG. 4, along the C-C axis defined in FIG. 4. It makes it possible to more clearly visualize the interaction between the second positioning interface 42 and the cover plate 2 in particular at the female form 22. The second positioning interface 42 makes it possible to position the cover plate 2 relative to the grate 4 along a direction perpendicular to the weld axis S and also positions the cover plate 2 in the chamber 1 along the weld axis S. In other words, the second positioning interface 42 serves as an axial stop for the cover plate 2, in particular during the welding operation. Thus, the second welding interface 21 cannot give way, in particular due to bending of the cover plate 2, during the application of force F during the welding operation. In this embodiment, the welding interface is thus supported, along the weld axis S, over more than 70% of its periphery. This makes it possible to ensure satisfactory leaktightness of the weld. It is possible to carry out a helium leak test in order to verify that the weld meets the current leaktightness specifications in automotive safety, such as standard USCAR-24, 2nd revision of April 2013. For example, for an entirely pyrotechnic generator, a combustion chamber with a helium leak rate of less than 1.10.sup.4 cm.sup.3.atm.sup.1.s.sup.1 can be considered to be leaktight (with 100% helium initially in the combustion chamber).

The second welding interface 21 is a circular-cylindrical wall of axis S. The first fold present along the wall is a fold toward the inside of the part, i.e. toward axis S. Thus, a diameter circumscribed at the second welding interface 21 is the largest circumscribed diameter of the cover plate 2. This yet further reduces any risk of bending of the welding interface 21 during the welding operation.

[0069] It will be understood that various modifications and/or improvements obvious to those skilled in the art can be made to the different embodiments of the invention described in the present description, without departing from the scope of the invention as defined by the appended claims. In particular, reference is made to a chamber 1 as first part, a cover plate as second part and a diffuser 3 as third part. The invention can be applied to all other parts of a gas generator that are friction-welded.