The invention relates to a steering wheel of a vehicle according to the preamble of claim 1 , and to an airbag module adapted for being a part of such a steering wheel according to the preamble of claim 12.

Such a steering wheel comprises a steering wheel body and an airbag module being mounted to this steering wheel body, especially in such a way that the airbag module can be pressed down towards the steering wheel body in order to activate the horn of the vehicle (so-called “floating module concept”).

A generic steering wheel is known for example from CN 212604810 A. The airbag module of this steering wheel comprises a housing element with a housing section, an inflator attached to the housing section of the housing element, a cover attached to the housing section via snap-in features, and an airbag cushion being accommodated in an accommodation unit being defined by the housing section and the cover. The housing element has a first mounting feature, a second mounting feature and a resiliently flexible, U-shaped first positioning feature. The mounting features and the position feature all extend from the housing section and are parts of the housing element. The first positioning feature has two lateral legs and a cross-piece connecting the two lateral legs. The steering wheel body has a hub area for receiving the airbag module and comprises a third mounting feature co-operating with the first mounting feature, a fourth mounting feature co-operating with the second mounting feature and a second positioning feature having a lower contact surface co-operating with the cross-piece of the first positioning feature. This means that in the state in which the airbag module is not pressed down, the cross-piece of the first positioning feature and the lower contact surface of the second positioning feature contact one another such that the axial position of the first positioning feature relative to the second positioning feature is defined. During the mounting process of the airbag module to the steering wheel body, the lateral legs of the first positioning feature are resiliently bent away by the second positioning feature and return to their non-bent initial state when the mounting process is finished.

Starting form this prior art it is an object of the invention to improve the reliability of such a steering wheel.

This task is solved by a steering wheel having the features of claim 1 . An airbag module adapted for being a part of such a steering wheel is defined in claim 12.

During the lifetime of a steering wheel as described above, two kinds of “unusual” events regarding the airbag module can occur. The first one is the activation of the inflator leading to a deployment of the airbag cushion. Of course, any unsnapping of the cover from the housing element should of course be prevented when the airbag cushion deploys. The second “unusual” event is a removal of the airbag module from the steering wheel body for maintenance purposes. In this case, a controlled unsnapping of the module without any breakages is needed.

In order to prepare the airbag module for both above-described events, it comprises two additional features, the first one preventing an unsnapping of the cover from the housing section when the airbag cushion deploys and a second one preventing a breakage of the first positioning feature when this positioning feature needs to be deformed during an un-mounting procedure.

An unsnapping of the cover from the housing section can occur because of a pushing force transmitted from the airbag that just starts to deploy to the inside of the roof of the cover, especially before the at least one door of the roof opens, and is prevented by means of a locking plate for locking the snap-in features of the cover. This locking plate prevents any movement of the snap-in features of the cover, once the airbag module is completely assembled. The locking plate usually extends along the outside of a housing floor and is attached to the same after the cover has been snapped to the housing section. Sections of the edge of the locking plate extend to the snap-in features of the cover such that they cannot move radially inward to an extend that would allow an unsnapping from the housing section.

A breakage of the first positioning feature during a disassembly procedure is prevented by a limiting feature in the vicinity of the first positioning feature. This limiting feature allows a movement of the first positioning feature (which is necessary during the assembly as well as during a disassembly), but limits this displacement such that a breakage due to a too large displacement is prevented. This limiting feature preferably extends parallel to the lateral legs of the first positioning feature. The advantage of providing such a limiting feature is the following: When the airbag module is mounted to the steering wheel body, the U-shaped first positioning feature is “automatically” displaced by the second positioning feature of the steering wheel body, such that there is no risk of a too strong displacement. But in case of a disassembly, the first positioning feature must often be displaced (meaning bent) manually and so there is a risk that the first positioning feature is bent too far and breaks. If this happens, usually the whole airbag module must be thrown away. Providing a limiting feature safely prevents that.

In a first preferred embodiment, the limiting feature is in form of at least one protrusion of the locking plate. This makes it especially easy to provide the necessary stability for the limiting feature, since the locking plate is often made of sheet metal. Since the locking plate is usually a stamped and bent part, no additional production step might be necessary (the limiting feature is formed by the bending process which is necessary anyway).

In an alternative embodiment, the limiting feature is in form of at least one protrusion of the housing element. In this case, the locking plate often has a recess or an opening at the position of the limiting feature.

Often it is preferred that the first positioning feature and the second positioning feature serve only for an axial positioning. This means that only the cross-piece of the first positioning feature and a respective contact surface of the second positioning feature are in contact to one another (when the airbag module is not pressed down), whereas the lateral legs are never in contact with the second positioning feature. If in this case a positioning also in the radial plane is desired, it can be preferred that a third positioning feature extends between the lateral legs of the first positioning feature that co-operates with the second positioning feature. This third positioning feature can especially be in form of two posts and the second positioning feature can be in form of a tongue and/ or hook extending between the two posts and having the lower contact surface abutting the cross-piece of the first positioning feature. The posts do not contact this lower contact surface but each post is usually in contact with a lateral surface of the second positioning feature. The posts preferably have a certain flexibility and because of this and because the posts are not connected via a cross-piece (as the lateral legs of the first positioning feature are), it is prevented what high clamping forces between the second positioning feature and the posts of the third positioning feature occur. Such high clamping forces are not desired since they would countervail the axial positioning as well as an easy press-down operation of the module in order to activate the horn. With this arrangement, a good centering of the airbag module onto the steering wheel body is achieved.

As has been mentioned, the first positioning feature, namely the lateral legs of the latter, needs to be resiliently deflected when the airbag module is mounted to the steering wheel body because the cross-piece is pushed away by the second positioning feature during the airbag module insertion. This movement usually takes place in a radial direction. In order to reduce the necessary force, it can be preferred that each of the lateral legs of the first positioning feature has a first thickness at its module-side end and a second thickness at its cross- piece-side end, wherein the first thickness is smaller than the second thickness. Since it is preferred that the tensile strength is substantially constant along the length of each lateral leg (for avoiding any breakage when the inflator is triggered and the airbag deploys), it is further preferred that each lateral leg has a first width at its module-side end and a second width at its cross-piece-side end, wherein the second width is smaller than the first width. “Width” means the extension in a circumferential direction (substantially perpendicular to a radial direction), and “thickness” means the extension in radial direction. Since the tensile strength depends essentially from the cross-sectional area, it is preferred that each of the lateral legs of the first positioning feature has a first cross- sectional area at its module-side end and a second cross-sectional area at its cross-piece-side end, wherein the first cross-sectional area and the second cross-sectional area are substantially equal.

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

Figure 1 : all relevant elements of a first embodiment of an inventive steering wheel in a strongly schematic cross-sectional representation,

Figure 2: a sub-assembly of an airbag module being formed from elements being shown in Figure 1 ,

Figure 3: the complete airbag module in a representation according to Figure 2,

Figure 4: all elements being shown in Figure 1 in a completely assembled state,

Figure 5: the cover of Figure 1 in a bottom view from direction R1 in Figure 1 ,

Figure 6: the housing element shown in Figure 1 in a bottom view from direction R2 in Figure 1 ,

Figure 7: the locking plate shown in Figure 1 in a bottom view from direction R3 in Figure 1 ,

Figure 8: the armature shown in Figure 1 in a plan view from direction R4 in Figure 1 , Figure 9: the first and third positioning feature of the housing element shown in Figure 1 in a side view from direction R5 in Figure 1 ,

Figure 10: a hook of the housing element of Figure 1 in a view from direction R6 in Figure 1 ,

Figure 11 : a complete steering wheel according to a second embodiment of the invention in a detailed perspective view,

Figure 12: the steering wheel of Figure 11 in a plan view from above,

Figure 13: a sectional view taken along plane A-A in Figure 12,

Figure 14: the locking plate of the second embodiment in a perspective view,

Figure 15: a third embodiment of the invention in a representation according to Figure 4,

Figure 16: a detail of the embodiment of Figure 15 but in a more detailed and prospective view,

Figure 17: first and second positioning feature in a further embodiment,

Figure 17a: the first positioning feature of Figure 17 in a side view from direction R7 in Figure 17, but in a schematic representation, and

Figure 18: first and second positioning feature in another embodiment.

In view to Figures 1 to 10 a first embodiment of the invention is described. The representations are strongly schematic such that the relevant features can be seen clearly.

Figure 1 shows elements of an airbag module as well as a part of a steering wheel body, namely an armature. Of course (and as will be seen later), the complete steering wheel body comprises more elements like a rim, spokes and the like, but these elements are not relevant for the invention such that they are not shown in the Figures 1 to 10 of the first embodiment. Further, coil springs acting between the airbag module and the armature 17 are shown in Figure 1. Figures 5 to 10 show details of elements shown in Figure 1 .

The airbag module comprises a cover 20 (Figures 1 and 5), a housing element 30 (Figures 1 and 6), a locking plate 50 (Figures 1 and 7), an airbag cushion 90, and an inflator 95. First, the elements of the airbag module are described:

As has just been mentioned, the cover 20 of the airbag module is shown in Figures 1 and 5. This cover 20 is usually made from a plastic material and comprises a cover sidewall 24 and a roof 22. Snap-in features 26 in form of snap-in hooks 26 extend from the lower edge of the cover sidewall 24 as is generally known in the field of airbag modules.

As has also already been mentioned, the housing element 30 is shown in Figures 1 and 6. This housing element 30 is usually a one-pieced plastic part and comprises a housing section 31 . This housing section 31 and cover 20 form (in the assembled state) an accommodation for the airbag cushion 90. The housing section 31 comprises a housing floor 32 and a housing sidewall 34. The housing floor 32 comprises at least one hole 36 for receiving the snap-in features 26 of the cover such that the cover 20 can be snapped to the housing section 31 .

The housing floor 32 further comprises a hole 37 for the inflator 95, protrusions 39 for the coil springs 60 and holes 38 for attaching the locking plate 50. The housing floor 32 can further comprise attachment means for horn contacts but those are not shown in Figures 1 to 10.

In order to attach the housing element 30 (and thus the whole airbag module) to the steering wheel body (in the embodiment shown the steering wheel armature 17), the housing element 30 of the first embodiment further comprises the following features: Two hooks 40a, 40b serving as first and second mounting features extend from the housing floor 32 (please see Figures 1 , 6 and 10). Those hooks 40 are rather solid and can withstand the forces which can occur when the airbag cushion 90 is deployed by the inflator 95.

Further, a U-shaped first positioning feature 42 extends from the housing section 31 to ensure a correct positioning of the airbag module 10, in particular along the mounting axis of the airbag module on the steering wheel body. This first positioning feature 32 comprises two lateral legs 46 and a cross-piece 44 connecting those lateral legs 46 (please see Figures 1 , 6 and 9). This first positioning feature extends substantially from an edge of the housing floor and is located on a center-line; the two hooks 40a, 40b are usually arranged symmetrically relative to this center-line C.

In the embodiment shown, the housing element 30 further comprises two posts 48 being located between the lateral legs 46 of the first positioning feature 42; those posts 48 form a third positioning feature. The posts 48 extend parallel to each other at a distance D1 (Figure 9). The posts are (as the rest of the housing element) made of a plastic material and since they have free ends, they can to some extend be deformed, especially in the directions indicated by the arrows in Figure 9.

In order to secure the cover 20 once it has been snapped to the housing section 31 , a locking plate 50 is provided (please see Figures 1 and 7). This locking plate 50 preferably is a one-pieced sheet metal part. This locking plate 50 comprises a hole 54 for the inflator, attachment holes 56 for attaching (for example screwing or riveting) the locking plate 50 to the housing floor 32 and holes 58 for the protrusions 39. Further, this locking plate 50 has an embayment 53 at the position of the U-shaped first positioning feature 42 of the housing element 30 and a protrusion 52 being formed of a bent-away section and forming a limiting feature adjacent to the embayment 53. The steering wheel armature 17 (please see Figures 1 and 8) comprises a hole 72 for each hook 40a, 40b and a mounting spring 74 is held at the lower surface of the steering wheel armature such that the hooks 40a, 40b can be snapped to this mounting spring 74 as is generally known in the prior art. A common mounting spring 74 can be provided or a separate mounting spring can be provided for each hook 40a, 40b. According to the definition chosen in this application, the mounting spring forms a part of the third and fourth mounting feature cooperating with the first and second mounting features (the hooks 40a, 40b), and the mounting spring is a part of the steering wheel body. Thus, the first to fourth mounting features participate to the attachment of the airbag module 10 on the steering wheel body. Similar to the housing floor, protrusions 78 for positioning the coil springs are provided at the steering wheel armature 70.

Further, a second positioning feature 76 in form of a hook is provided for the first positioning feature 42 of the housing element 30. This positioning feature 76 comprises a lower contact surface 76a for contacting the cross-piece 44 of the first positioning feature such that an axial positioning (Z-positioning I positioning along the mounting axis of the airbag module 10 or positioning along a steering column axis) is generated. Further, the second positioning feature 76 has lateral surfaces 76b, 76c that are spaced by a distance D2. This distance D2 is equivalent or nearly equivalent to the distance D1 between the two posts of the third positioning feature.

Figure 2 shows a sub-assembly of the airbag module 10. This sub-assembly is comprised of the cover 20, the housing element 30, the airbag cushion 90 and the inflator 95. One can see that the cover 20 is snapped to the housing element 30 (namely the housing floor 32) via the snap-in hooks 26 which extend through the holes 36.

In a subsequent assembly step the locking plate 50 is attached to the housing floor, 32, for example via studs provided on the inflator 95. The outcome of this assembly step is shown in Figure 3 which shows the complete airbag module 10. One can see that the locking plate 50 extends to the inner edges of the snap-in hooks 26 such that they are prevented from unsnapping even if high pushing forces are applied to the cover when the airbag cushion 19 deploys. One can also see from Figure 3 that the protrusion 52 (the limiting feature) is located in the vicinity of the U-shaped first positioning feature 42 but has some distance from this positioning feature 42 such that the positioning can bend inwards (see arrow in Figure 3), but only to some extent.

Figure 4 shows the airbag module of Figure 3 being mounted (namely snapped) to the steering wheel armature 70. During this assembly step, the mounting spring 74 and the U-shaped first positioning feature 42, namely its lateral legs 46, are resiliently deformed. The distance between the U-shaped first positioning feature 42 and the protrusion (limiting feature) 52 of the locking plate allows a deflection of the U-shaped first positioning feature 42 sufficient for this assembly step but hinders the U-shaped positioning feature 42 from being bent more than necessary for this assembly step.

In the completely assembled state, the coils springs are pre-tensioned and the cross-piece 44 of the U-shaped first positioning feature is thus pressed against the lower contact surface 76a of the second positioning feature 76 such that an axial positioning is generated. Further, the second positioning feature 76 is positioned between the posts 48 of the third positioning feature such that a positioning in the circumferential direction is generated.

Figures 11 to 14 show a second embodiment similar to the first embodiment, but in more detailed representations. The difference is that the airbag module 10 of the second embodiment does not show a third positioning feature between the lateral legs of the first positioning feature, such that the second positioning feature 76 of the steering wheel body only interacts with the first positioning feature of the airbag module and the second positioning feature does not contribute to the positioning in the circumferential direction. Besides that, the description of the first embodiment can directly be applied to the second embodiment and like elements are denoted with like reference numbers. Figures 15 and 16 show an embodiment that is also similar to the first embodiment. Here, the difference is that the limiting feature is not a part of the locking plate, but is a part of the housing element 30. In the example embodiment, the limiting feature is in form of two protrusions 49 extending from the housing floor 32 (see Figure 16) and through the embayment of the locking plate 50.

Figures 17 and 18 show alternative designs of the first positioning feature 40. Here, the width (in circumferential direction) of the lateral legs 46 decreases from their module-side end towards the module-far end while their thickness (in radial direction) increases such that the cross-sectional area remains essentially constant. This enhances the flexibility in radial direction without lowering the tensile strength and thus reduces the effort needed to snap-in the airbag module 10 on the steering wheel armature 70 without lowering the force it can withstand when the airbag module is fired. Due to the presence of the limiting feature, the enhanced flexibility does not increase the risk of a breakage. This type of design can be combined with the presence of a third positioning feature if desired.

List of reference numbers

5 steering wheel

10 airbag module

20 cover

22 roof of cover

24 cover sidewall

26 snap-in hooks (snap-in features)

30 housing element

31 housing section

32 housing floor

34 housing sidewall

36 hole for snap-in hooks of cover

37 hole for inflator

38 hole for attaching locking plate

39 protrusion for coil spring

40a first hook (first mounting feature)

40b second hook (second mounting feature)

42 U-shaped first positioning feature

44 cross-piece

46 lateral leg

46a first section (module-side section)

46b intermediate section

46c second section (cross-piece-side section)

48 third positioning feature (post between lateral legs)

49 protrusion from housing element I limiting feature

50 locking plate

52 protrusion (bent-away section/ limiting feature)

53 embayment

54 hole for inflator

56 attachment hole

58 hole for protrusion 39 60 coil spring

70 steering wheel armature (part of steering wheel body)

72 hole for hook (part of third and fourth mounting feature)

74 mounting spring (part of third and fourth mounting feature) 76 second positioning feature

76a lower contact surface

76b, 76c lateral surface

78 protrusion for coil spring

80 spoke (part of steering wheel body) 82 rim (part of steering wheel body)

90 airbag cushion

95 inflator

C center line