The invention relates to a steering wheel comprising a steering wheel armature and an airbag module according to claim 1 , and to an airbag module adapted for being used as a part of such a steering wheel according to claim 15.

So-called floating module steering wheels are widespread in today’s automotive industry. Such a floating module steering wheel comprises a steering wheel armature (which is a part of the steering wheel body) and an airbag module comprising an airbag cushion and an accommodation for this airbag cushion. For activating the vehicle horn, the whole airbag module can be pressed towards the steering wheel armature (or a part of this armature) against the force of an elastically deformable arrangement (usually a plurality of coil springs). The airbag module usually comprises a housing element being comprised of a plastic material, wherein this housing element comprises a housing section. Further, the airbag module usually comprises a cover being attached to the housing section of the housing element, such that the housing section and the cover form the accommodation for the airbag cushion. An inflator (for example a gas generator) is attached to the housing section, usually to a bottom wall of this housing section.

As has been mentioned, the airbag module can be pressed down against the steering wheel armature in order to activate the vehicle horn. Consequently, at least one coupling arrangement allowing a pressing down of the airbag module towards the steering wheel armature (in the following often only “armature”) needs to be provided.

For example, generic EP 1 348 595 B1 shows a floating cover steering wheel with such a coupling arrangement. This coupling arrangement comprises an armature-side positioning device, a module-side positioning device and a coil spring extending between the armature-side positioning device and the module- side positioning device. This coil spring defines a coil spring axis which extends in the axial direction of the steering wheel (the axial direction of the steering wheel is defined by its rotational axis). The armature-side positioning device as well as the module-side positioning device each comprises a positioning surface having the shape of an inner cylinder wall. The coupling arrangement further comprises a pin extends between the armature-side positioning device and the module-side positioning device, such that a complete positioning in the radial plane is provided at the location of the coupling arrangement. Further, this pin serves for an axial positioning, since it is snapped to a locking spring at its module-side end.

Starting from this prior art, it is an object of the invention to provide a steering wheel of the generic type, whose parts are cost-effective to produce and that can easily be assembled. Additionally, the coupling arrangement should provide a precise positioning in at least one direction in the radial plane, especially in a clearance-free manner. Finally, it should be possible to design the module such that it has a small footprint (because it is a tendency in the automotive industry to design steering wheels in such a way that the airbag modules become smaller and smaller).

This task is solved by a steering wheel having the features of claim 1 . An airbag module adapted for being used as a part of such a steering wheel is defined in claim 15.

According to one aspect of the invention, the module-side positioning device comprises a first positioning protrusion, which is in direct contact to a first positioning surface section of the armature-side positioning device and a separate pin as in the generic EP 1348595 B1 is avoided. Because of this, a free space inside the coil spring is gained and used for a horn switch.

In order to provide a clearance-free guiding, the first positioning surface defines the position of the first positioning protrusion in exactly one direction. The module-side first positioning protrusion is preferably in form of an elongated positioning finger such that it is to some extend elastically deformable. This helps to achieve a clearance-free positioning.

In order to provide a proper positioning of the coil spring, it is preferred that the coupling arrangement further comprises a holding arrangement for this coil spring. So, it is preferred that the armature-side positioning device further comprises an armature-side holding structure for holding the armature-side end of the coil spring and/ or the module-side positioning device comprises a moduleside holding structure for the module-side end of the coil spring. In addition, it can be preferred to have the module-side holding structure distinct from the first positioning protrusion in order not to stiffen the positioning protrusion. Indeed, the first positioning protrusion needs to be sufficiently flexible not to increase the mounting force of the airbag module on the steering wheel or the horn activation force as well as proposing good positioning or centering behaviour.

In order to facilitate the assembly of the airbag module on the steering wheel, only a module-side holding structure for the coil spring is provided, such that the coil spring and the armature-side positioning device are free of a holding arrangement for the coil spring: the armature-side positioning device comprises only one abutting surface (substantially perpendicular to the axial direction) to compress the spring along the horn activation direction (the axial direction) but no other contacting surface in perpendicular directions which could influence the positioning of the airbag module and would make the assembly more complicated.

In case that a module-side holding structure is provided, it can be preferred that this module-side holding structure comprises at least two module-side holding protrusions located outside the module-side end of the coil spring. This can have advantages in view of arranging parts of the horn switch and of the horn circuit at the housing element. In case that an armature-side holding structure is provided, it can be preferred that this armature-side holding structure comprises at least one - especially exactly one - armature-side holding protrusion located inside the armature-side end of the coil spring. This armature-side holding protrusion can additionally serve as an attachment basis for an armature-side horn-contact.

In order to simplify the production, the armature-side positioning device is preferably a one-pieced part of the armature. For the same reason, the positioning protrusion is preferably integrally formed with the housing section. Additionally, tolerances can be reduced by means of these measures.

In order to get a good positioning and centering of the airbag module on the steering wheel, the coupling arrangement is free of any retention feature of the airbag module on the steering along the horn activation axis.

The horn switch can be formed in a conventional manner and can comprise a module-side electrical contact and an armature-side electrical contact, both being located inside the coil spring. In this case it can be preferred that the module further comprises a conductive element, wherein a section of this conductive element is located between the housing section and the module-side electrical contact, such that current can flow between the two contacts when the airbag module is pressed down. Since the housing element is usually made of an electrically insulating plastic material, the module-side contact would be isolated without such a conductive element.

In case that the armature is made of an electrically conductive material (usually a light metal like magnesium), the armature-side electrical contact is preferably in direct contact to the armature.

As an alternative, it would also be possible to provide another type of horn switch, for example in form of a micro push-button or in form of a proximity sensor, on the inside of the coil spring either at the armature-side positioning device or at the module-side positioning device. In order to obtain a positioning in two directions, it can be preferred that the armature-side positing device further comprises a second positioning surface section being orientated substantially perpendicular to the first positioning surface section, and the module-side positioning device further comprises a second positioning protrusion extending towards the armature and abutting the second positioning surface section. Like in the case of the first positioning protrusion, it is preferred that also the second positioning protrusion is to some extend elastically deformable and is thus in form of an elongated positioning finger. A gap or space can be provided between the first positioning protrusion and the second positioning protrusion in order to maintain the flexibility of those protrusions and keep the two positioning protrusions independent one to the other.

In order to obtain a full positioning in one dimension, it can be further preferred that the armature-side positioning device further comprises an additional positioning surface section being orientated substantially parallel to the first positioning surface section, and the module-side positioning device further comprises an additional positioning protrusion extending towards the armature and abutting the additional positioning surface section. Also here, the additional positioning protrusion is preferably an isolated, elongated positioning finger.

Since the steering wheel according to the invention is a floating module steering wheel, each positioning surface slides along its allocated positioning surface section when the airbag module is pressed towards the armature. In order to prevent that one element machines the other (especially that the positioning protrusion machines the positioning surface section indeed, the positioning protrusion can be charged with glass fibers and can erode the armature during horn activation actions and/or vibrations during serial life of the vehicle), it can be preferred that each positioning protrusion comprises a flat or planar contact surface being in contact to its allocated positioning surface section (which is preferably also flat or planar), such that the contact area is large (and especially not line or dotshaped) and thus, erosion limited. In order to provide a full positioning of the airbag module in the radial plane and especially to hinder the module from rotational displacement, it can be preferred that the steering wheel further comprises a second coupling arrangement being mirror-symmetrical to the first coupling arrangement.

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

Figure 1 all relevant parts of a steering wheel according to the invention (all parts except a covering of the steering wheel armature),

Figure 2 a part of the steering wheel armature, namely its base, as well as coil springs and locking springs located at the base of the armature,

Figure 3 a part of the steering wheel shown in Figure 1 in a cross sectional view,

Figure 4 a cross sectional view taken along plane A-A in Figure 3,

Figure 5 a second embodiment of the first coupling arrangement in an exploded representation, and

Figure 6 the first coupling arrangement shown in Figure 5 in an assembled state.

The invention will now be described in detail by means of two embodiments in view of all Figures 1 to 6. Figures 1 to 4 show a first embodiment and Figures 5 and 6 show a second embodiment. Since the embodiments only differ in the position of the holding protrusions 62 (in the first embodiment these protrusions are located inside a coil spring, in the second embodiment they are located outside the coil spring), reference is made to all Figures. As can best be shown from Figure 1 , the steering wheel 5 according to the invention comprises an airbag module 10 and an armature 20. As is generally known in the prior art, the airbag module 10 comprises a housing section 16 and a cover 12 being snapped to this housing section 16, such that the cover 12 and the housing section 16 form an accommodation for an airbag cushion (the airbag cushion itself is now shown in the Figures, but in Figure 3 one can clearly see the accommodation space being formed by the housing section 16 and the cover 12). Further, an inflator (usually in form of a gas generator) is attached to a bottom wall of the housing section 16 in order to inflate the airbag; this inflator is also not shown in the Figures.

The housing section 16 is a part of the housing element 14. This housing element 14 is at least partly made of plastic and usually made in one piece, but it is also possible that plastic features are overmolded on another element, wherein it is possible that this “other element” is also made of plastic. As will be described later in more detail, mounting- and positioning features extend from the housing section 16 of the housing element 14; those mounting and positioning features are also a part of the housing element 14 and especially they are made in one piece with the housing section 16.

The armature 20 is a part of a steering wheel body and usually consists of a light metal as magnesium and comprises a base 20a, to which the just described airbag module 10 is mounted. The armature 10 further comprises at least one spoke 20b and a rim 20c. In the completely manufactured state of the steering wheel 5, sections of this armature 20 (especially the spoke and the rim) are covered by a covering, for example by a foam, wherein the base 20a remains in general mostly uncovered. One can see the fitting 26 for a steering column attachment, such that a rotational axis is defined. This rotational axis further defines the axial direction DA of the steering wheel.

As can best be seen in Figure 2, the base 20a of the armature 20 comprises holes 22 for hooks of the housing element 14 (those hooks are not shown in detail in the Figures, but such hooks are known in the prior art). Retaining springs 24 are provided, such that the hooks can be snapped to the steering wheel body. A retaining spring and a hook form an axial positioning means. An additional axial positioning means can be provided, especially at the 12 o’ clock position (please see reference sign P in Figure 2).

A first coupling arrangement 40 and a second coupling arrangement 40’ are provided. Those coupling arrangements 40, 40’ serve for a positioning of the airbag module 10 relative to the armature 20 (namely the base 20a of the armature 20) and for providing horn switches. Those both coupling elements 40, 40' are symmetrically relative the centerline C of the steering wheel (see for example Figure 2). Since those two coupling arrangements 40, 40' are symmetrical to one another, only the first coupling arrangement 40 is described in view of Figures 2 to 5, especially in view of Figure 5. These coupling arrangements are independent of the axial positioning means.

The first coupling arrangement 40 (and this of course also applies to the second coupling arrangement 40’) comprises a module-side positioning device 60, a module-side contact 68 in form of a rivet, a armature-side positioning device 50, an armature-side contact 58 in form of a rivet, and a coil spring 30. The coil spring axis extends in the axial direction of the steering wheel.

The module-side positioning device 60 is a part of the housing element 14 and thus consists of a plastic material. The armature-side positioning device 50 is a part of the armature 20 (namely the base 20a of the armature 20) and thus consists of metal, usually magnesium. Because the armature 20 consists of a conductive metal, the armature-side contact 58 can directly be riveted to the armature-side positioning device 50; the armature 20 is usually electrically connected to the vehicle ground.

The plastic housing element 14 is usually not conductive and so a conductive element 70 (for example in form of a metal strip) is provided and the module-side contact 68 is an electrical (and thus also mechanical) contact to this conductive element 70, which usually extends along the bottom surface of the housing sec- tion 16. This metal strip 70 is a part of the horn circuit. This horn circuit is closed when the two contacts 58, 68 come in contact to one another. As can best be seen from Figures 4 and 6, the contacts 58, 68 (and thus the horn switch as such) are located inside the coil spring 30.

The armature-side positioning device 50 is formed by a raised portion 51 having substantially the shape of frustum of a regular pyramid with a square base, and a circular structure 52 on top of this raised portion 51 to which the module-side contact (rivet) 58 is attached. In the embodiment shown, the raised portion 51 is at least on three sides surrounded by a groove. Since this raised portion 51 is in form of frustum of a pyramid, it has four lateral surface sections and three of those form positioning surface sections. Those three positioning surface sections are: a first positioning surface section 54, a second positioning surface section 55 being perpendicular to the first positioning surface section 54, and an additional positioning surface section 56 being perpendicular to the second positioning surface section 55 and thus parallel to the first positioning surface section 54. The surface normals of all positioning sections point slightly upwards. If the raised portion was a cuboid, the surface normal of the positioning surface sections would be located in the radial plane and thus perpendicular to the axial direction of the steering wheel and thus to the axis of the coil spring 30. But it turned out that the pyramid-shape with slightly inclined positioning surface sections is preferred because of better positioning results. Providing inclined positioning surface sections is possible because of the flexibility of the positioning protrusions.

The module-side positioning device 60 comprises holding protrusions 62 (in the embodiments shown four holding protrusions) for the coil spring 30. In the embodiment of Figures 1 to 4, the holding protrusions 62 are located inside the coil spring 30, in the embodiment of Figure 5 and 6, the holding protrusions 62 are located outside the coil spring 30 and each of those holding protrusions 62 comprises a groove 62a on the inside such that the coil spring 30 can be snapped to those holding protrusions 62 (namely on the inside of the holding protrusions 62). The module-side positioning device 60 further comprises a first positioning protrusion 64 having a flat first contact surface 64a, a second positioning protrusion 65 having a flat second contact surface 65a and an additional positioning protrusion 66 having a flat additional contact surface 66a. The three positioning protrusions (which could also be denoted as positioning fingers) are not connected to each other (only indirectly via the housing section 16 from which they extend) such that each of the positioning protrusions 64 has a free end on its armatureside end.

The first contact surface 64a is anti-parallel orientated to the first positioning surface section 54, the second contact surface 65a is anti-parallel orientated to the second positioning surface section 55 and the additional contact surface 66a is anti-parallel orientated to the additional positioning surface section 56. The dimensions are chosen such that in the mounted state (Figure 6) the first contact surface 64a contacts the first positioning surface section 54, the second positioning surface 65a contacts the second positioning surface section 55 and the additional positioning surface 66a contacts the additional positioning surface section 56. The positioning protrusions are to some extend resiliently deformable, especially in the direction indicated by the arrows in Figure 6, such that during the assembly of the airbag module on the steering wheel, the positioning protrusions bent to fit with the raised portion 51 of the armature-side positioning device 50 and so position and center the airbag module with respect to the armature. Thus resulted gaps remaining between the airbag module and steering wheel are more regular or constant resulting to an improved fit and finish.

Because all surfaces that contact each other are flat and almost parallel to one another due to the bending of the positioning protrusions, it is avoided that one element machines the other, especially when the airbag module is pressed down in order to activate the horn (or during the vibrations accruing during the functioning of the vehicle) and the contact surfaces 64a to 66a slight along the positioning surface sections 54, 55, 56. One sees that the airbag module is in the radial plane directly positioned at the steering wheel armature (without the need of additional pins or the like) such that the tolerance chain is as short as possible. Further one sees that positioning means, the coil spring and the horn switch are concentrated on a small area such that a small footprint module can be designed. Finally, the positioning is clearance-free.

List of reference numbers

5 Steering wheel

10 airbag module

12 cover

14 housing element

16 housing section

20 armature

20a base of armature

20a spoke of armature

20b rim of armature

22 hole for hooks of the module

24 spring to which hook of the module is snapped

26 fitting for steering column

30 coil spring

40 first coupling arrangement

40’ second coupling arrangement

50 armature-side positioning device

51 raised portion

52 armature-side structure (single protrusion)

54 first positioning surface section

55 second positioning surface section

56 additional positioning surface section

58 armature-side contact (rivet)

60 module-side positioning device

62 holding protrusion of module-side holding structure

62a groove in holding protrusion

64 first positioning protrusion (first positioning finger)

64a contact surface of first positioning protrusion

65 second positioning protrusion (second positioning finger)

65a contact surface of second positioning protrusion

66 additional positioning protrusion (additional positioning finger) 66a contact surface of third positioning protrusion 68 module-side contact (rivet)

70 conductive element (metal strip)

DA axial direction

P position of additional axial positioning means at 12 o’ clock position