Description

The invention relates to an airbag module according to the preamble of claim 1 and to a method for manufacturing the same according to claim 13.

The invention relates in the first place to so-called driver airbag modules being designed and intended for being mounted to a steering wheel body of a vehicle steering wheel. For this reason, reference is mainly made to such a driver airbag module, but it needs to be mentioned that the invention could also be applied to other kinds of airbag modules, especially to so-called passenger airbag modules.

A driver airbag module usually comprises a housing and a cover, such that the housing and the cover enclose an accommodation space for an airbag cushion. Further, an inflator is provided and this inflator is usually attached to a bottom wall of the housing. The cover of course comprises a roof spanning over the housing, wherein this roof has a visible outer surface. A section of this roof forms a door which can be opened by the deploying airbag cushion. This door is connected to a surrounding section of the roof by at least one split line and at least one hinge.

In most cases the cover further comprises a sidewall being attached to the housing, often by means of a snapping connection. The cover is usually an injection- molded plastic part.

In order to enhance the optical appearance of the cover (namely its roof) it is known to provide an illuminating arrangement having a light emitting surface forming a section of the outer surface of the roof of the cover.

For example from EP 1 973 767 A1 it is known to provide a light emitting element (which could also be called “light generating element”) outside the accommoda- tion space for the airbag cushion and to direct the light of the light emitting element via a light guide to a center section of the roof which has a light emitting surface. The problem is here that the light guide is usually in the deployment way of the airbag cushion.

US 6 848 706 also shows an airbag module whose roof has a light emitting surface. Here, the illuminating arrangement is completely outside the accommodation space of the airbag cushion, such that this illuminating arrangement does not hinder the deployment of the airbag cushion.

Starting from this prior art it is an object of the invention to further improve a generic airbag module.

This task is solved by an airbag module having the features of claim 1 . A method for manufacturing such an airbag module is defined in claim 13.

The process of forming the accommodation space by the housing and the cover while placing the airbag cushion inside this accommodation space is often relatively rough and special machinery is needed. It turned out that it can be difficult to ensure that the elements of the illuminating arrangement are not damaged during this process. So, according to the invention, the design of the airbag module is such that the airbag module comprises a first sub-assembly comprising the airbag cushion being packed in the accommodation space and the elements enclosing this accommodation space, wherein this sub-assembly can be manufactured before any element of the illuminating arrangement is mounted to it.

In order to achieve this, the cover cannot be formed of a single part (as is common in the prior art), but of at least a first part, a second part, and a third part. The first part can be connected to the housing such that this first part and the housing enclose the accommodation space for the airbag. This first part can comprise a first section of the roof which shows at least one door that can be opened by the deploying airbag cushion. The second part can be located outside the accommodation space and comprises a second section of the roof covering the light emit- ting element. This second section of the roof can be at least in sections spaced from the first section of the roof. Further, the cover can comprise a third part distinct from the first part. This third part can comprise a third section of the roof filling the gap between the first section of the roof and the second section of the roof and can comprise the light emitting surface.

Since the second part of the cover usually needs to have properties different from the properties of the first part and the second part (especially it needs to be transparent or translucent at least in sections), it is often preferred that the first part of the cover, the second part of the cover and the third part of the cover are distinct parts. As an alternative, the third part could be molded to the second part.

In an optically and mechanically preferred geometry, the third section of the roof can be annular-shaped and encircles the first section of the roof, and the second section of the roof can be also annular-shaped and encircles the third section of the roof. In this geometry, the third section of the roof can additionally form a sealing between the first section of the roof and the second section of the roof.

In order to ease the assembly process, it can be preferred that the third part of the cover is in snapping connection to at least one of the first part of the cover or the second part of the cover, preferably to the first part of the cover and to the second part of the cover.

As it has already been mentioned, the third section of the roof can comprise the light emitting surface. For this reason, the third part preferably can be or can comprise a light diffusor. A preferred material for his light diffusor is silicone, especially a silicone having a shore hardness between 30 and 90 Shore A. This further eases the assembly process and provides a tight sealing.

Since the third part is not light generating, the illuminating arrangement usually comprises a light receiving surface for receiving light from the light emitting element. Although it would in principle be possible to feed the light generated by the light emitting element directly into the third part of the cover, it can be for geomet- rical reasons and in order to optimize the light diffusion homogeneity, often preferred that the illuminating arrangement further comprises a distinct light guiding element for guiding light from the light emitting element to the third part of the cover, wherein this light guiding element comprises the light receiving surface. This light guiding element can for example consist of silicone, Poly(methyl methacrylate (PM MA) or Polycarbonate (PC).

As has already been mentioned, the housing, the first part of the cover, and the airbag can be parts of a first sub-assembly. This first sub-assembly can additionally comprise the inflator. The second part of the cover, the third part of the cover, and the light emitting element can be parts of a second sub-assembly being attached to the first sub-assembly. If a light-guiding element is used, this can also be a part of the second sub-assembly.

In a preferred method for manufacturing an airbag module, the assembly of the first sub-assembly can be finished before the second sub-assembly or parts of the second sub-assembly are mounted to the first sub-assembly in order that a damaging a part of the second sub-assembly is avoided. Preferably the whole second sub-assembly can be assembled before to be mounted to the first sub-assembly.

The invention will now be described in detail by means of preferred embodiments in view of the figures. The figures show:

Figure 1 all elements of a first sub-assembly of the described embodiment of the airbag module,

Figure 2 all elements of a second sub-assembly of the described embodiment of the airbag module,

Figure 3 the complete mounted first sub-assembly and the completely mounted second sub-assembly in a state in which the second subassembly is not yet mounted to the first sub-assembly, Figure 4 the completely assembled airbag module (the first sub-assembly of Figure 3 and the second sub-assembly of Figure 3 being mounted to the first sub-assembly),

Figure 5 the detail D of Figure 4 but with the airbag cushion not being shown, and

Figure 6 a perspective view to the airbag module.

A main concept of the invention is that the airbag module comprises two subassemblies, wherein one sub-assembly (the first sub-assembly) comprises all elements which are necessary to form a “traditional” airbag module. The elements of this first sub-assembly are shown in Figure 1 :

A housing 10 and a first part 30 of the cover define an accommodation for an airbag cushion 80 which can be deployed by a gas generator 70. This gas generator 70 is attached to the bottom wall 11 of the housing 10 as is known in the prior art. The space enclosed by the housing 10 and the first part 30 of the cover is also preferred to as the accommodation space for the airbag cushion.

Most of the housing 10 is formed like a traditional housing, meaning that it comprises a housing sidewall 14 and the just mentioned bottom wall 11. A hole 12 for the inflator is provided in the center of the bottom wall 11 . Further, a plurality of holes 13 for hooks of the first part of the cover are provided in a radial outer section of the bottom wall 11 . In the embodiment shown, the gas generator 70 comprises a main body 72 and a mounting flange 74 for attaching the gas generator 70 to the bottom wall 11 .

A mounting section 15 extends from the upper end of the sidewall 14 radially to the outside. Instead of providing an annular mounting section 15 it would also be possible to provide a plurality of mounting sections 15. Like a common cover, the first part 30 of the cover comprises a sidewall 34 and a roof section, namely the first section 31 of a roof. The first section 31 of the roof is substantially flush with the sidewall 34.

Like it is generally known in the prior art, mounting hooks 36 extends from the lower edge of the sidewall 34.

Figure 2 shows all elements of a second sub-assembly of the airbag module. In the embodiment described, this second sub-assembly has the following elements: a second part 40 of the cover and a third part 50 of the cover are provided. In this embodiment the second part 40 of the cover exclusively forms a second section 42 of the roof and the third part 50 of the cover exclusively forms a third section 53 of the roof. For this reason, the terms “second part of the cover” and “second section of the roof” can be used interchangeably and the terms “third part of the cover” and “third section of the roof” can also be used interchangeably.

The second part 40 of the cover is usually an injection-molded part made from an opaque standard airbag module cover material, for example from thermoplastic olefin (TPO) and/or thermoplastic elastomer (TPE) but another material can be used as this second part 40 of the cover is outside the accommodation space receiving the airbag cushion 80.

The third part 50 of the cover (also referred to as diffusor) consists of a translucent, diffusing material which preferably has certain elasticity. According to current knowledge, the preferred material for this third part 50 is silicone.

Both, the second part 40 and the third part 50 are annular-shaped such that the second part 40 forms and outer ring and the third part 50 forms an inner ring. Connecting features are provided such that the third part 50 can be attached to the second part 40, wherein it is preferred that these attachment features work without any glue or similar. In this embodiment this attachment features are a protrusion 43 at the second part 40 and a groove 54 in the third part 50. In an alterna- tive way, the second part 40 can be over molded on to the third part 50 or vice versa.

The third part 50 also has attachment features for attaching the third part 50 to the first part 30 of the cover.

When the airbag module is completely assembled, the upper surface of the third part 50 forms a light emitting surface 53a of the roof of the cover of this airbag module. Since the third part 50 is not light generating, an illuminating subassembly 60 for providing light to the third part 50 is provided. In the embodiment shown this illuminating sub-assembly 60 comprises three elements:

- For generating the light, an electronic unit 65 is provided which comprises an annular-shaped printed circuit board (PCB) 64 and a plurality of lightemitting diodes (LEDs) 66 as light emitting elements (which could also be called light generating elements). The LEDs 66 are mechanically and electrically connected to the PCB 64.

- In order to transport the light generated by the LEDs 66 to the third part 50 of the cover (the diffusor), a light guiding element 68 having a tubular section with a light receiving surface 68a is provided.

- Finally, a mounting element 62 having a flange section 62a and a tube section 62b serves for mounting the electronic unit 65 and the light guiding element 68 to the mounting section 15 of the housing sidewall.

Figure 3 shows the first sub-assembly being comprised of the elements shown in Figure 1 and the second sub-assembly being comprised of the elements shown in Figure 2. It is relevant to note that these two sub-assemblies can be assembled completely independently from one another, such that the first sub-assembly (comprising the first part 30 of the cover, the housing 10, the airbag cushion 80 and gas generator 70) is completely free from any light generating, light guiding or light emitting parts. The first sub-assembly is assembled like a traditional airbag module, such that no further explanation is necessary. Regarding the second sub-assembly: the third part 50 is mounted to the upper ends of the tube section 62b of the mounting element 62 and the light guiding element 68, such that the third part 50 is in contact or in close proximity to the upper end of the light guiding element 68, such that the light entering the light guiding element 68 at the light receiving surface 68a is guided to the third part 50, such that it can be emitted by the light emitting surface 53a. The LEDs 66 are close to the light receiving surface 68a of the light emitting element 68. The second part 40 of the cover is at its upper end attached to the third part 50 of the cover as described above and attached to the flange section 62a of the mounting element 68 at its lower end.

The LEDs 66 are completely enclosed by the second part 40 of the cover and the flange section 62a, such that light generated by the LEDs 66 can leave this enclosure only via the light emitting surface 53a of the third part 50.

Figure 4 shows the completely assembled airbag module after the second subassembly has been mounted to the first sub-assembly. During this final assembly step, the flange section 62a is attached to the mounting section 15 and the third part 50 of the cover is snapped to the first part 30 of the cover.

Figure 5 shows the detail D of Figure 4, but without showing the airbag cushion 80. One can see the light emitting surface 53a, the outer surface of the roof 25a and the second section of the roof 42 are flush and form a single continuous outer visible surface.

Figure 6 shows again the airbag-module and especially its roof 25. One can see the annular structure of the third part 50 and the second part 40. One can especially see that the third part of the cover (third section 53 of the roof) fills and seals the gap between the first section 31 of the roof and the second section 42 of the roof. The light emitting elements (the LEDs 66) are hidden under the second section 42 of the roof, but when they are in their active, light emitting state, at least a fraction of this light is emitted by the light emitting surface 53a.

List of reference numbers

10 housing

11 bottom wall

12 hole for inflator

13 hole for hooks of cover

14 housing sidewall

15 mounting section of housing sidewall

20 cover

25 roof

25a outer surface of roof

30 first part of cover

31 first section of roof

31 a outer surface of first section of roof

34 sidewall of first part of cover

36 mounting hook

40 second part of cover

42 second section of roof

42a outer surface ofsecond section of roof

43 nose

50 third part of cover (diffusor)

53 third section of roof

53a outer surface of third section of roof/ light emitting surface

54 groove

60 illuminating sub-assembly

62 mounting element

62a flange section

62b tube section

63 screw

64 PCB

65 electronic unit

66 LED (light emitting element)

68 light guiding element 68a light receiving surface

70 gas generator

72 main body of gas generator

74 mounting flange 80 airbag cushion