Description

The invention relates to an airbag module according to the preamble of claim 1 .

The invention especially relates to driver airbag modules, but can also be applied to other types of airbag modules, especially other types of frontal airbag modules such as passenger airbag modules.

In the prior art airbag modules are known which comprise an airbag cushion having an impact area, a structure (especially a housing) to which this airbag cushion is attached, and a tether inside of the airbag cushion. This tether has a first end being attached to the impact area of the airbag cushion by means of a first connection (usually a seam), and a second end being attached to the structure in a releasable/ de-attachable manner, such that the deployment depth of the airbag cushion can be controlled. In the simplest case, the tether is in form of a single flat strap.

From generic WO 2018 84479 A1 an airbag module is known whose tether “splits”, such that the first end has a plurality of the end sections, each of those being connected to the impact area. A similar concept is described in JP 2009 154655 A1 . By means of this structure, the pulling force of the tether is distributed over a larger area of the impact area.

Starting from this prior art, it is an object of the invention to improve a generic airbag module comprising a tether being attached to the impact area of the airbag cushion.

This task is solved by an airbag module having the features of claim 1 . It turned out that splitting the tether into a plurality of end sections gives an improvement, but there is still a desire of further improvement, especially in view of obtaining a relatively flat impact area and the avoidance of force peaks.

As is generally known, the tether is made from a flat tether element extending from a first extremity forming the first end of the tether to a second extremity forming the second end of the tether. In order to achieve an even force transmission between the tether and the impact area, at least a first section of the tether element extending from the first extremity is rolled to form a rolled section of the tether.

By this measure, the first connection is usually non-linear or curved such that the force transmission is neither point-like, nor linear, but two-dimensional. This leads to the desired even force distribution and a relatively flat impact area, although the tether element from which the tether is made, is a flat piece of material.

The inventive effect is strongest, if the first connection is closed. In this case, the first connection is usually an ellipse, especially a circle. Indeed, in such situation the connection is closed on itself, i.e. it defines at least one closed area.

In order to save material, weight and packing space, it is preferred that the first section of the tether element widens towards the first extremity, especially such that the first section of the tether element has essentially the shape of a circular sector. In this case, the first section of the tether is cone-shaped such the first connection is - as mentioned - ellipse-shaped, for example circular-shaped. This shape leads to an ideal force-distribution.

As described, the second end of the tether is usually connected to a structure, for example a housing, or another area of the airbag cushion. In most cases, it would be a disadvantage if this connection consumes a lot of space and thus it is usually preferred that the tether additionally comprises a non-rolled section extending from the second end to the rolled section. This additionally eases the folding and the guiding of the tether through a hole, for example in the airbag cushion. This non-rolled section of the tether is made from a second section of the tether element extending between the second extremity and the first section of the tether element. This second section preferably has a substantially constant width.

In order to minimize the assembly (sewing) steps, the tether element can be single-pieced, but in order to minimize the area of the waste-parts, it can also be preferred that the first section of the tether element is made from a first cutting, the second section of the tether element is made from a second cutting and first and second cutting are attached to one another to form the tether element.

In order to prevent an uneven gas distribution inside the airbag cushion, it is preferred that the tether element (especially its first section) comprises at least one hole to form a passageway for the inflation gas in the tether.

In order to further improve an even force distribution, it can be preferred that that the two lateral edges of the tether element are connected to one another at least in sections to form a closed generating surface of the rolled section of the tether.

The invention is especially useful for so-called dual-depth airbag modules, meaning that the tether is attached to the structure in such a way that the second end can be released from structure or the tether can be destroyed near the second end, such that at least a main part of the tether is releasable from the structure, or the other area of the airbag cushion, but it needs to be mentioned that other applications of the inventive tether are also conceivable. For example, the second end of the tether can be connected to a structure or the airbag cushion in a permanent way.

In an especially preferred embodiment, an additional tether having a tether distal end extends from the tether and at least one of the tether distal end of the additional tether and the second end of the tether is releaseably/ destroyably connected to the structure such that the impact area of the airbag cushion remains tethered in both deployment depths. The invention will now be described by means of a preferred embodiment in view of the figures. The figures show:

Figure 1 all cuttings, from which an airbag cushion and a tether according to the invention are made,

Figure 2 the cuttings of Figure 1 being sewn together, such that a precursor assembly is formed (in a schematic sectional view),

Figure 3 what is shown in Figure 2 after turning the airbag cushion inside out such that the airbag cushion and the tether are in conditions for being connected to a housing,

Figure 4 the tether shown in Figures 2 and 3 in a perspective view,

Figure 5 the complete airbag module in a representation according to Figure

3 in a state, in which the airbag is deployed to a first deployment depth,

Figure 6 what is shown in Figure 5 after cutting through the tether near its second end, such that a main part of the tether is released from the housing and the airbag cushion is deployed to a second deployment depth,

Figure 7 the tether element of Figure 1 and an additional tether being sewn to the tether element such that a tether assembly precursor is formed,

Figure 8 a second embodiment of the invention using the tether assembly being made from the tether assembly precursor of Figure 7 in a representation according to Figure 5, and

Figure 9 the second embodiment shown in Figure 8 in a second state according to Figure 6. Figure 1 shows all cuttings of an airbag cushion as well as a tether element, which is in form of a one-pieced cutting in this embodiment. All cuttings can be made from a traditional airbag material, especially a woven plastic material.

It is to be noted that of course additional cuttings, such as reinforcement layers, could be provided, as is known in the art. But such additional elements are not shown, since they are not necessary in order to understand the invention.

The airbag cushion is made of three cuttings, namely a front panel 12, which forms the impact area, a side panel 14 and a back panel 16. In the embodiment shown, the front panel 12 and the back panel 16 are both of circular shape and have the same diameter. The difference between those two panels is that the back panel 16 comprises a plurality of holes, namely a central hole 16c, attachment holes 16a around the central hole 16c and a hole 16b for the tether.

The tether element 20 of this embodiment has two sections, namely a first section 25 having the shape of a circular sector and a second section 26 having a substantially rectangular shape and extending from a second extremity 22 of the tether element to the first section 25. The first section 25 widens towards the first extremity 21 (which has the shape of an arc of a circle) of the tether element 20 which is in form of a section of a circle. Starting from the second section 26, lateral edges 25a and 25b of the first section 25 extend to the first extremity 21 of the tether element 20. Holes 28 are provided in the first section 25. In other embodiments, the first extremity 21 might not have the shape of an arc of a circle, but a differently curved shape, for example in form of an arc of a non-circular ellipse, such that the first section would have the shape of a section of an ellipse.

In an assembly step, the tether element 20 is formed to a tether 30 by rolling the first section 25 around the longitudinal direction (X-direction) to form a cone- shaped rolled section 35 of the tether 30, such that the first extremity 21 of the tether element 20 forms a circular shaped first end 31 of the tether 30 (see especially Figure 4). This first end 31 is connected (usually sewn) to the front panel 12 by means of a first connection 51 , which of course also forms a circle. Asymmetric embodiments are conceivable in which the first end 31 and the first connection 51 are not circles, but non-circular ellipses. Although it is not strictly mandatory that the first connection is closed, it is in any case preferred. The second section 26 of the tether element 20 remains un-rolled and forms a non-rolled section 36 of the tether 30.

After this assembly step, the side panel 14 is attached to the front panel 12 by means of a connection (seam) 40 and the back panel 16 is attached to the side panel 14 by means of a connection (seam) 42. The outcome of these assembly steps is shown schematically in Figure 2.

Now, the airbag cushion 10 being comprised of the front panel 12, the side panel 14 and the back panel 16 is turned inside-out and the non-rolled section 36 of the tether 30 is pushed through the hole 16b for the tether in the back panel 16 (Figure 3).

The already mentioned Figure 4 shows again the tether 30 but now in a schematic perspective view. One can see the cone-shape of the rolled section 35 with the circular shape of its first end 31 . In the embodiment shown, the lateral edges 25a and 25b are not connected to each other, but this would also be possible. Of course, they could also overlap, but not being connected to another. In the shown embodiment a slight gap is present between those two lateral edges 25a and 25b. The holes 28 in the tether element 20 are now located in the generating surface of the cone and form passageways 38 for inflation gas.

Figure 5 shows the assembly being comprised of the airbag cushion 10 and the tether 30 being attached to a structural element, namely a housing 60, to form an airbag module. In the state shown in Figure 5 the airbag cushion is deployed after the gas generator 62 of the airbag module has been triggered. One can see that the second end 32 of the tether 30 is attached to an attachment unit 64 of the housing 60 such that the tether 30 is under tension and thus limits the deployment depth (in X-direction) of the airbag cushion 10. This attachment unit 64 comprises a permanent attachment feature 66 and a cutter 68 designed for cutting through the non-rolled section 36 of the tether 30 near the second end 32 of the tether 30, such that a main part of the tether 30 is releasably connected to the housing 60. Of course, other types of a releasable attachment of the tether could be used, for example like described in WO 2014/029 473 A1. In another alternative, the second end 32 of the tether 30 could be released or slided from an anchor point by an actuatable mechanism.

As long as the tether is uncut and connected to the housing, the tether is under tension when the airbag is deployed and thus limits the deployment depth to a first deployment depth. After triggering the cutter 68 (or otherwise disconnecting the tether or its main part from the housing) the tether loses its tension such that a second deployment depth is reached (Figure 6). Since the non-rolled section 36 is single-layered it can easily be cut and slip through a hole in the housing and the hole 16b in the airbag cushion.

As long as the tether is under tension, its whole circular second end transfers force to the impact area (the front panel 12). This leads to the desired even force distribution and to a relatively flat impact surface 12a.

Figure 7 shows a tether assembly precursor of a second embodiment of the invention. This tether assembly precursor is comprised of a tether element 20 as described above and an additional tether 70 which can, for example, be in form of a rope or a strap (a rope is preferred in most cases). A tether side end 71 is attached (for example sewn) to the tether element 20 by means of a tether-tether connection 74 (a seam for example) and the additional tether extends from there to a distal end 72. The tether-tether-connection 74 is preferably located at the second section 26 near the first section 25.

The next assembly steps are as described in connection with the first embodiment with the following exceptions: The second end 32 of the tether 30 is attached (usually sewn) to the airbag cushion 10 by means of a second connection 52. This second connection 52 is preferably close to the central hole 16c where usually at least one re-enforcement layer is provided (not shown) and in an area which al- most does not move during the inflation of the cushion 10. The tether distal end 72 of additional tether 70 is connected to the attachment unit.

The geometry is chosen such that when the cutter 68 is not triggered and the airbag cushion 10 is deployed, the additional tether 70 is under tension but the section of the tether 30 extending between the tether-tether connection 74 and the second connection 52 is not under tension, such that the airbag cushion 10 deploys to a first deployment depth (Figure 8).

After actuating the cutter 68, the additional tether 70 loses its tension and the airbag cushion deploys to its second deployment depth. In contrast to the first embodiment, this second deployment depth is limited by the tether 30 because its second end 32 remains connected to the back panel 16 of the airbag cushion 10 and a basically flat impact surface 12a is provided in both deployment depths (Figure 9).

Like in the first embodiment, the destroyable or de-attachable connection of the additional tether 70 to the housing (structure) could also be obtained via other kinds of releasable attachment means; for example, the tether distal end 72 of the additional tether 70 could be released or slided from an anchor point by an actuatable mechanism. Further, it would generally be possible (even if generally not preferred) to change the role of the additional tether and the non-rolled section of the tether. Finally, it would generally be possible to attach both, the additional tether and the non-rolled section in a releasable way to the structure such that three deployment depths of the airbag cushion could be reached. List of reference signs

10 airbag cushion

12 impact area I front panel

12a impact surface

14 side panel

16 back panel

16a attachment holes

16b hole for tether

20 tether element

21 first extremity

22 second extremity

25 widening first section of tether element (having the shape of a circular sector)

25a first lateral edge of first section

25b second lateral edge of first section

26 second section

28 hole

30 tether

31 first end

32 second end

35 cone-shaped rolled section of tether

36 non-rolled section

38 passageway

40 connection between front panel and side panel

42 connection between back panel and side panel

51 first connection

52 second connection

60 housing

62 gas generator

64 attachment unit

66 permanent attachment feature

68 cutter additional tether section (rope) tether side end of additional tether tether distal end of additional tether connection connecting the additional tether to the tether