Gas generator for a safety system

Abstract

A gas generator for a safety system, the gas generator comprising: at least one pyrotechnic substance arranged to generate a gas; 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 characterized 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, so as to temporarily block at least one degree of freedom between the first part and the second part, allowing the first part and the second part to be simultaneously friction welded to the third part.

Description

[0001] The present invention relates generally to a gas generator for a safety system, such as an airbag, and more particularly to such a gas generator whose components are assembled by friction welding, such as inertia welding.

[0002] From the prior art, generators assembled according to a welding process are known, and this generator is described in document WO2017103135. This document proposes welding a first component and a second component simultaneously to a third component, the welding zone of the first component and the welding zone of the second component being very close to each other. This proximity of the welding zones can in some cases deteriorate certain properties of the weld in terms of sealing level. Indeed, the welding zones can influence each other or deform the adjacent welded components.

[0003] One aim of the present invention is to remedy the drawbacks of the prior art documents described above, and in particular to propose first of all a gas generator whose welds are improved.

[0004] To this end, a first aspect of the invention relates to a gas generator for a safety system, comprising:

[0005] - at least one pyrotechnic substance arranged to generate a gas,

[0006] - a first component,

[0007] - a second component,

[0008] - a third component,

[0009] - and a fourth component separate from the previous components,

[0010] the first component and the second component being friction welded to the third component,

[0011] characterized in that the fourth component comprises:

[0012] - a first interface for positioning with the first component,

[0013] - a second interface for positioning with the second component so as to temporarily block at least one degree of freedom between the first component and the second component, allowing the simultaneous friction welding of the first component and the second component to the third component.

[0014] The friction welding operation uses the friction between two components which, when a force is applied along a welding axis, rotate relative to each other along the welding axis so as to generate heat at the interface of the two components and assemble them together by melting thereof.

[0015] To this end, in the present application, the second part is reversibly positioned (until the welding operation) relative to the first part via the fourth part. Once this sub-assembly has been formed, it is then welded to the third part by a friction welding operation. Thus, the first part and the second part are simultaneously welded to the third part in the same single welding operation. During the welding operation, a weld bead is generated at the contact zone between the first part and the third part and between the second part and the third part.

[0016] The fourth part makes it possible to improve the positioning of the second part relative to the first part in order to improve the quality of the welds generated during the friction welding operation. Indeed, the fourth part makes it possible to limit or even eliminate the contact between the first part and the second part. This makes it possible to leave space for the weld bead when it is formed.

[0017] By blocking at least one degree of freedom between the first part and the second part, the fourth part blocks at least one translation of the second part relative to the first part, generally along the welding axis of the friction welding operation, by means of the first positioning interface and the second positioning interface. The fourth part can also make it possible to block the rotation of the second part relative to the first part, generally around or along the welding axis of the friction welding operation.

[0018] When the first part, the second part and the fourth part form a sub-assembly before the friction welding operation, at least one degree of freedom is temporarily blocked. Once the friction welding operation is carried out, the welds between the first part and the third part on the one hand and between the second part and the third part on the other hand fix the positioning of the second part relative to the first part.

[0019] The second part is advantageously mounted in the first part.

[0020] Advantageously, the first positioning interface and the second positioning interface are arranged so that the rotational or translational movement of the first part during the friction welding operation is along the second part. In other words, the fourth part makes it possible to avoid any relative rotational and / or translational movement between the first part and the second part. In other words, the second part is carried by the first part via the fourth part.

[0021] Advantageously:

[0022] - the first part comprises a first welding interface,

[0023] - the second part comprises a second welding interface and defines a space between the second welding interface and the first welding interface before the operation of simultaneously friction welding the first part and the second part to the third part.

[0024] The welding interface is the part of the component that is physically affected by the welding operation. Typically, for a friction welding operation, the welding interface is the end of a cylindrical or columnar shaped component and has a predetermined thickness. Guaranteeing a space between the welding interface of the first component and the welding interface of the second component makes it possible to avoid any interference that could occur between the bead generated during the welding of the first welding interface and another bead generated during the welding of the second welding interface. In particular, the contact between the two beads at the beginning of the welding can deteriorate one or the other of the welds, in particular the tightness of the welds. The tightness provided by the friction welding makes it possible to guarantee the storage of the pyrotechnic substance away from water for a long time, for example up to 15 years.

[0025] Advantageously, the space defined between the second welding interface and the first welding interface before the friction welding operation is between the thickness of the second component at the second welding interface and the thickness of the first component at the first welding interface.

[0026] The custom space makes it possible to optimally use the heat emitted during the friction welding operation while guaranteeing the space necessary for the formation of the bead. This is particularly advantageous when the thickness of one of the components at its welding interface is significantly different from the thickness of the other component.

[0027] For example, when the thickness of the second component at the second welding interface is between 33% and 66% of the thickness of the first component at the first welding interface and / or when the thickness of the second component at the second welding interface is between 33% and 66% of the thickness of the third component facing the second welding interface.

[0028] Indeed, in order to guarantee a solid weld, it is necessary to reach a given temperature at the welding zone, using certain welding parameters (rotation speed, force applied during the operation, etc.) to reach said temperature. When there is a difference in thickness between the two welded components, the difficulty lies in heating the thicker component sufficiently without thereby reaching a too high temperature that can deteriorate the thinner component. As claimed, the small space makes it possible to use the heat generated by the friction of the first component on the third component (thickest component) to weld the second (thinnest) component to the third component.

[0029] Typically, a space of between 1 mm and 3 mm can be provided.

[0030] The space is measured between the inside of the first component and the outside of the second component at their respective welding interfaces along a direction perpendicular to the welding axis. In other words, the space corresponds to the difference between the inner radius of the first component at the first welding interface and the outer radius of the second component at the second welding interface.

[0031] Advantageously, the first positioning interface and the second positioning interface are arranged so as to temporarily block the six degrees of freedom between the first part and the second part before the friction welding operation.

[0032] In other words, there is no contact between the first part and the second part before the welding operation. The space between these two parts is free during the formation of the bead of these two parts. This makes it possible to ensure optimal positioning of the second part in order to guarantee a solid weld.

[0033] Advantageously, the first part is a chamber containing pyrotechnic substances, the second part is a cover plate, and the third part is a diffuser.

[0034] This embodiment makes it possible to use a cover plate to close the chamber in a sealed manner, without there being a direct sealing connection between the cover plate and the chamber.

[0035] Advantageously, the fourth part is a grate arranged to hold the pyrotechnic substances during the operation of the gas generator.

[0036] In this embodiment, the fourth part has two functions, namely positioning the second part relative to the first part before and during the welding phase, and holding the pyrotechnic substances during the operation of the generator. The construction of the generator is thus optimized, since the number of parts forming the generator is limited.

[0037] Advantageously, the thickness of the second part at the second welding interface is between 33% and 66% of the thickness of the first part at the first welding interface, before the friction welding operation.

[0038] The invention makes it possible to simultaneously weld two parts of different thicknesses to a third part. This is particularly advantageous when the aim is to close a chamber that must withstand the combustion of pyrotechnic substances using a cover plate that must yield to a predetermined pressure.

[0039] Advantageously, the thickness of the second part at the second welding interface is between 33% and 66% of the thickness of the third part facing the second welding interface.

[0040] Advantageously, the thickness of the second part at the second welding interface is between 0.5 and 1 mm, and the thickness of the first part at the first welding interface is between 1.3 and 3 mm.

[0041] Advantageously, before the friction welding operation, when the first part, the second part and the third part form an assembly, the second welding plane formed by the second welding interface is offset from (or arranged at or below) the first welding plane formed by the first welding interface, so that the second part contacts the third part simultaneously with or preferentially after the first part contacts the third part.

[0042] This makes it possible to limit the risk of buckling of the second welding interface during the friction welding operation.

[0043] Advantageously, the diameter of the external tangent at the second welding interface is the maximum external tangent diameter of the second part.

[0044] According to this embodiment, the second welding interface is less subject to deformation, in particular to forging forces, during the welding operation. Uncontrolled deformation is detrimental because if the welding interface yields during welding, the bead is not formed correctly and the quality of the weld is degraded. In other words, the second welding interface is a wall of a cylindrical part, the first fold of which is a fold towards the axis of revolution of the part. The axis of revolution of the part is combined with the welding axis during the friction welding operation.

[0045] Advantageously, the first interface for positioning the fourth part has a continuous contact surface with the first part.

[0046] The continuous contact surface makes it possible to prevent any welding protrusion, generally incandescent shavings, from being transmitted to the first interface. Such protrusions can ignite the pyrotechnic substance when it is loaded in the first part.

[0047] Advantageously, the first welding interface and the second welding interface have a cylindrical form.

[0048] Cylindrical welding interfaces, in particular cylindrical welding interfaces, are particularly suitable for friction welding.

[0049] Advantageously:

[0050] The first part, the second part and the fourth part are in the form of a bowl having a bottom and lateral surfaces,

[0051] A portion of the outer lateral surface of the fourth part abuts against a portion of the inner lateral surface of the first part and a portion of the outer lateral surface of the second part abuts against a portion of the inner lateral surface of the fourth part.

[0052] In other words, the second part and the fourth part are contained in the first part. In addition, this enables a compact nesting of the first part, the second part and the fourth part.

[0053] Advantageously, the second positioning interface is a convex form complementary to the concave form of the second part.

[0054] These forms enable a good engagement of the second part with the fourth part so as to block any relative rotation of one part with respect to the other.

[0055] Advantageously, the gas generator comprises a fifth part positioned between the second part and the third part, the concave form of the second part being arranged to position the fifth part with respect to the third part.

[0056] The fifth component can be a filter. The second component makes it possible to guarantee the presence of a space between the filter and the third component, in particular when the third component is a diffuser. The gas flow during operation of the generator is optimized.

[0057] Advantageously:

[0058] The second positioning interface is formed by the junction between the lateral surface and the bottom of the fourth component, and

[0059] The concave form of the second component is formed by the junction between the lateral surface and the bottom of the second component.

[0060] When formed in this way, the second component is easier to manufacture, simpler and more robust, since the concave form participates in reinforcing the junction between the lateral surface and the bottom of the second component, in addition to participating in the positioning of the second component. The same applies to the fourth component.

[0061] Advantageously:

[0062] The first positioning interface is a concave form complementary to a convex form of the first component,

[0063] The first positioning interface is formed by the junction between the lateral surface and the bottom of the fourth component, and

[0064] The convex form of the first component is located on the lateral surface of the first component.

[0065] When the fourth component is inside the first component, the convex form of the first component is located on the inner lateral surface of the first component.

[0066] A second aspect of the application relates to a safety module comprising a gas generator according to the first aspect of the application.

[0067] A third aspect of the application relates to a motor vehicle comprising a gas generator according to the first aspect of the application.

[0068] A final aspect of the application relates to a process for manufacturing a gas generator according to the first aspect, the process comprising the following steps:

[0069] - positioning the fourth component on the first component via the first positioning interface,

[0070] - positioning the second component on the fourth component via the second positioning interface,

[0071] - implementing the operation of simultaneously friction welding the first component and the second component to the third component.

[0072] In other words, the manufacturing process proposes to form the sub-assembly by first assembling reversibly (until the friction welding operation) the first part, the second part and the fourth part, then welding the sub-assembly to the third part.

[0073] Advantageously, the welding operation comprises the following steps:

[0074] - holding the first part and the welding tool together,

[0075] The fourth part makes it possible to avoid any relative movement of the second part with respect to the first part via the first and second positioning interfaces.

[0076] “Avoiding any movement” is intended to mean preventing any movement that makes it impossible to obtain a weld that does not meet the standards required for the manufacture of a gas generator in terms of sealing and strength.

[0077] Other characteristics and advantages of the application will become clearer on reading the detailed description that follows, given by way of non-limiting example, and illustrated by the attached drawings in which:

[0078] - Figure 1 A side view of a generator according to the application is shown.

[0079] - Figure 2 An exploded isometric view showing certain parts of the generator from Figure 1 is shown.

[0080] - Figure 3a A cross-sectional view of the generator from Figure 1 along the A-A axis defined in Figure 1 before the friction welding operation is shown.

[0081] - Figure 3b The generator from Figure 3a after the friction welding operation is shown.

[0082] - Figure 4 A cross-sectional view of the generator from Figure 3a along the B-B axis defined in Figure 3a is shown.

[0083] - Figure 5 A cross-sectional view of the generator from Figure 4 along the C-C axis defined in Figure 4 is shown.

[0084] Figure 1A gas generator of the type generally used for frontal protection in the form of an airbag is shown 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 its periphery in order to diffuse the combustion gases from the pyrotechnic substance 6 contained in the gas generator in the airbag not shown.

[0085] The lateral surface of the chamber 1 comprises deformations 14 which are visible from the outside of the generator and are in the form of Figure 3a the component in the form of a convexity 12 visible in the view.

[0086] Figure 2 Three parts of the gas generator not assembled are shown according to an isometric view: the chamber 1, the second part as a cover plate 2 and the third part as a grate 4.

[0087] The chamber 1 and the diffuser 3 are the thickest parts since they must withstand the operating pressure of the generator during the combustion of the pyrotechnic substance. A thickness can be provided extending from 1.3 mm to 3.5 mm.

[0088] The cover plate 2 has weakened 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 this operating pressure, it can be thinner, for example 33% to 66% thinner than the chamber 1 or the diffuser 3. A thickness can be provided extending from 0.3 mm to 1.2 mm.

[0089] The grate 4 comprises a first interface 41 for positioning with the chamber 1 and a second interface 42 for positioning with the cover plate 2. The bowl form of the grate 4 and the cover plate 2 can be clearly seen in this view. The grate 4 comprises a bottom 43 and lateral surfaces 44 while the cover plate 2 comprises a bottom 26 and lateral surfaces 27.

[0090] Figure 3a A cross-sectional view is shown of the generator from Figure 1 along the A-A axis defined in Figure 1 the view. The generator contains a pyrotechnic substance 6 defined so as to produce a gas when ignited by an electric pyrotechnic initiator 7. The initiator 7 is connected to the chamber 1 in a sealed manner by an overmould 8. The gas is cooled by a filter 5 before diffusing into the airbag.

[0091] This view before welding makes it possible to visualize the sub-assembly consisting of the chamber 1 containing the pyrotechnic substance 6 and the grate 4, and which is closed by the cover plate in the position in which it is to be welded to the diffuser 3. For this purpose, the diffuser 3 is rotated around the welding axis S and, during the rotation movement, the sub-assembly is pressed onto the diffuser 3 using a force F.

[0092] To this end, the chamber 1 comprises a first welding interface 11 defining a first welding plane 111, while the cover plate 2 comprises a second welding interface 21 defining a second welding plane 211. The second welding plane 211 is located below the first welding plane, that is to say, the second welding plane 211 is contained within the volume formed by the chamber 1 enclosed by the first welding plane 111. In other words, during the application of the force F during the welding operation, the first welding plane 111 contacts the diffuser 3 before the second welding plane. Typically, the offset is approximately 0.5 mm ± 0.25 mm.

[0093] The first positioning interface 41 makes it possible to position the grate 4 relative to the chamber 1 along a direction perpendicular to the welding axis S and also to position the grate 4 in the chamber 1.

[0094] Figure 3b The generator from Figure 3a after the welding operation is shown. The filter 5 contacts both on the cover plate 2 and on the diffuser 3.

[0095] The cover plate 2 comprises a hollow concave form 24, which makes it possible to position the filter 5 relative to the diffuser 3, in particular to guarantee a radial space between the filter and the inner surface of the diffuser 3 so as to ensure the unobstructed flow of the gas produced by the pyrotechnic substance 6 during the operation of the gas generator.

[0096] A portion of the first welding interface 11 disappears 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 disappears in the form of a second weld bead 23 between the cover plate 2 and the diffuser 3.

[0097] The grate 4 has a lateral surface 44 that is in continuous contact with the inner surface of the first part 1. This limits any risk of welding particles passing through the first positioning interface 41 towards the pyrotechnic substance protrusion.

[0098] Figure 4 The generator from Figure 3a after the welding operation is shown. The filter 5 contacts both on the cover plate 2 and on the diffuser 3. Figure 3a The cross-sectional view of the generator from along the B-B axis defined in

[0099] The first and second positioning interfaces of the grate 4 are more clearly visible.

[0100] The second interface 42 is a convex form positioned on the inner lateral surface of the grate. This convex form is complementary to the concave form 22 formed on the outer lateral wall of the cover plate 2 so as to avoid any rotation of the cover plate 2 relative to the grate 3 about the welding axis S. This embodiment comprises eight first interfaces 42. This number will be adjusted according to the force required for the welding operation.

[0101] Figure 5 A cross-sectional view along the C-C axis defined in Figure 4 shows the generator from Figure 4 . It makes it possible to visualize more clearly the interaction between the second positioning interface 42 and the cover plate 2, in particular at the concave form 22. The second positioning interface 42 makes it possible to position the cover plate 2 in the chamber 1 in a direction perpendicular to the welding axis S and also to position the cover plate 2 along the welding axis S relative to the grate 4. In other words, the second positioning interface 42 acts as an axial stop for the cover plate 2, in particular during the welding operation. Thus, the second welding interface 21 does not yield during the application of the force F during the welding operation, in particular because of the bending of the cover plate 2. In this embodiment, the welding interface is thus supported along the welding axis S over more than 70% of its periphery. This makes it possible to ensure a satisfactory tightness of the weld. A helium leak test can be implemented in order to verify that the weld meets the current tightness specifications for automotive safety, such as the standard USCAR-24 revised for the second time in April 2013. For example, the helium leak rate is less than 1.10 -4 cm 3 . atom -1 .s -1 of the combustion chamber can be considered to be tight (100% helium in the initial combustion chamber).

[0102] The second welding interface 21 is a cylindrical wall of the axis S. The first fold present along the wall is a fold towards the inside of the component, i.e. towards the axis S. Thus, the diameter circumscribed at the second welding interface 21 is the maximum circumscribed diameter of the cover plate 2. This further reduces any risk of bending of the welding interface 21 during the welding operation.

[0103] It will be understood that various modifications and / or improvements to the different embodiments of the application described in the present specification can be made to persons skilled in the art without departing from the scope of the application as defined by the appended claims. In particular, the chamber 1 is mentioned as a first component, the cover plate as a second component and the diffuser 3 as a third component. The application is applicable to all other components of the gas generator that are friction welded.

Claims

1. A gas generator for a safety system, the gas generator comprising: - At least one pyrotechnic material (6), said at least one pyrotechnic material being arranged to produce gas, -First component (1), -Second component (2), -Third component (3), -and a fourth component (4) separate from the previous components, The first component (1) and the second component (2) are friction-welded to the third component (3). The fourth component (4) is characterized in that it comprises: - First positioning interface (41), the first positioning interface is used to position together with the first component (1), - A second positioning interface (42) is used to position itself together with the second component (2) to temporarily block at least one degree of freedom between the first component and the second component, thereby allowing the first component and the second component to be simultaneously friction-welded to the third component (3), and, The fourth component, by means of the first positioning interface and the second positioning interface, prevents the second component from at least translating relative to the first component during the friction welding operation. The first component, the second component, and the fourth component are in the form of a bowl with a bottom and side surfaces, wherein a portion of the outer side surface of the fourth component (4) abuts against a portion of the inner side surface of the first component (1). A portion of the outer surface of the second component (2) abuts against a portion of the inner surface of the fourth component (4), and The first component (1) is a chamber containing the pyrotechnic material (6), the second component (2) is a cover plate, and the third component (3) is a diffuser.

2. The gas generator according to the preceding claims, wherein the first positioning interface (41) and the second positioning interface (42) are arranged such that the rotational or translational motion of the first component (1) during the friction welding operation drives the second component (2).

3. The gas generator according to any one of the preceding claims, wherein: - The first component (1) includes a first welding interface (11), - The second component (2) includes a second welding interface (21), and a space is defined between the second welding interface (21) and the first welding interface (11) prior to the operation of simultaneously friction welding the first component and the second component to the third component (3).

4. The generator according to claim 1, wherein the first positioning interface (41) and the second positioning interface (42) are arranged such that six degrees of freedom between the first component and the second component are temporarily blocked before the friction welding operation.

5. The generator according to claim 1, wherein the fourth component (4) is a grate arranged to hold the pyrotechnic material (6) during operation of the gas generator.

6. The generator according to claim 3, wherein prior to the friction welding operation, the thickness of the second component (2) at the second welding interface (21) is between 33% and 66% of the thickness of the first component (1) at the first welding interface (11).

7. The gas generator according to claim 3, wherein the outer diameter of the second welding interface (21) is the maximum outer diameter of the second component (2).

8. The gas generator according to claim 1, wherein the first positioning interface (41) of the fourth component (4) has a surface in continuous contact with the first component (1).

9. The generator according to claim 3, wherein the first welding interface and the second welding interface have a cylindrical shape.

10. The gas generator according to claim 1, wherein the second positioning interface (42) is formed by the junction between the lateral surface (44) of the fourth component (4) and the bottom (43), and The concave shape (22) of the second component (2) is formed by the joint between the lateral surface (27) and the bottom (26) of the second component (2).

11. A safety module comprising a gas generator according to any one of the preceding claims.

12. A motor vehicle comprising the safety module according to claim 11.

13. A method for manufacturing a generator according to any one of claims 1-10, the method comprising the following operations: - Position the fourth component (4) on the first component (1) via the first positioning interface (41). -The second component (2) is positioned on the fourth component (4) via the second positioning interface (42). - Perform the operation of simultaneously friction welding the first component and the second component to the third component (3).

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