Knee airbag

A knee airbag for a motor vehicle is described. This knee airbag extends in its installed state along a longitudinal direction (X) from a rear end to a front end. The airbag skin (5) of the knee airbag exhibits a front section (20) and a rear section (22) and a connecting line for contouring of the airbag is located on the rear section (22). In order to simplify the assembly of the knee airbag, the connecting line mainly extends transverse to the longitudinal direction (X) and shortens the rear section (22) in longitudinal direction.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to PCT Patent Application PCT/EP2008/007978 filed Nov. 7, 2009, and German Patent Application 10 2008 060 858.0 filed Dec. 9, 2008.

TECHNICAL FIELD OF THE INVENTION

The invention relates to a knee airbag for a motor vehicle which in an installed state extends along a longitudinal direction from a rear end to a front end.

BACKGROUND OF THE INVENTION

Knee airbags are becoming increasingly widespread in the automotive industry and have two basic tasks: on the one hand they should prevent the knee-shin-areas of the vehicle occupant to be protected from coming into direct contact with the lower area of the instrument panel in case of an accident. Furthermore, knee airbags should prevent the pelvic area of the occupants from being displaced forwards; this is particularly important in the case of occupants who are not wearing seat belts.

The knee airbag is arranged in a housing which is located in the lower area of the instrument panel. It is often desired to locate this housing as far as possible in the direction of the footwell, therefore in the front area of the instrument panel which faces away from the occupant, or in the transition area between the instrument panel and the footwell. However, as the instrument panel is domed in a convex fashion, the knee airbag also has to follow this domed shape, thus showing a “banana shaped” cross-section. In principal this can be achieved through the attachment of outer tethers, which is, however, often not desired.

Generic patent application DE 10 2007 005 304 A1 therefore suggests providing a longitudinal fold and several further folds arranged within this longitudinal fold in a rear section of the airbag skin, in other words in the section which is turned towards the instrument panel, whereby the further folds are secured by means of seams. These further folds achieve a shortening of the ridge of the first fold. When the rear section is under tensile stress—which is the case when the airbag is filled—it assumes a concave shape because of the shortening, leading to assumption of the desired “banana shape”. A knee airbag manufactured in this way basically functions well. However, a disadvantage is that several folds have to be provided which are positioned relatively precisely in relation to each other, which on the one hand makes it difficult to automate manufacture, and on the other hand generally requires a precise final inspection.

SUMMARY OF THE INVENTION

Starting from this basis, the present invention sets itself the problem of improving a knee airbag of the generic type in such a way that it can be manufactured in a more rational way.

This task is fulfilled by means of a knee airbag having a rear section of the airbag skin that exhibits a connecting line for contouring of the airbag. The airbag skin is connected with itself along this connecting line, so that a fold is created. The connecting line basically extends transverse to the longitudinal direction of the knee airbag, whereby by longitudinal direction a direction is meant which, when the airbag is in installed and expanded state lies in a vertically standing longitudinal vehicle plane. In other words, the connecting line extends basically perpendicular to the longitudinal direction of the vehicle when in installed and expanded state.

As a rule, one single such connecting line is sufficient, which is located in the vicinity of the fixing points of the knee airbag.

In a preferred embodiment, the rear section of the airbag skin exhibits an oblong-shaped opening, which is closed by the connecting line. This has two advantages: on the one hand it is prevented that the inflated airbag is pushed away from the internal structure by the material of the fold, which would counteract the desired effect and in the worst case would compensate it partially. On the other hand, this measure makes it easily possible to provide a tether which connects the rear with the front section of the knee airbag precisely at the position of the connecting line.

In most applications it will be preferable to form the connecting line as a seam, but it is also possible to implement the connecting line in the form of a weld seam or bonded connection.

Further preferred embodiments result from the embodiment described below with reference to the figures.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1shows a pre-cut piece for a knee airbag,FIGS. 2,3and4each show a tether30,34,38, which are sewn together with pre-cut piece10fromFIG. 1to form a knee airbag. The positions of the seams are indicated inFIGS. 1 to 4and designated with the reference numbers40a,42a,44a,46a,48a,50aand52a.

Pre-cut piece10basically exhibits mirror symmetry in relation to fold line25, around which pre-cut piece10is folded during manufacture of the knee airbag. Fold line25separates and divides rear section22from front section20. An edge seam is located along the edge of pre-cut piece10; the position of the edge seam is designated with reference number40a. Following closing of the edge seam, front section20and rear section22are joined directly with one another along their edges, whereby the edges are formed by the edge seam40band the fold line25. When front section20and rear section22are joined together by means of the edge seam, the areas enclosed by the edge seam first lie on top of one another congruently (with exception of the hole12) and flat.

There are the following deviations from the mirror symmetry of front section20and rear section22: rear section22exhibits side ears23, which are bent over and sewn with the edge seam40bwhen the airbag is sewn together, so that they protect the edge seam at the side. Furthermore, rear section22exhibits an ignition connector opening14at its rearmost end, two bolt holes16,16′ and a cut18. A gas generator can be inserted through this cut18and can be connected with the interior structure of the vehicle by means of bolts which extend through bolt holes16,16′. An ignition cable is connected to the gas generator through ignition connector opening14.

Finally, rear section22exhibits an opening12which is formed in an oblong shape, and whose long axis stands parallel to fold line25, in other words perpendicular to the longitudinal direction X of the pre-cut piece. The position46aof the shortening seam extends around the opening12. The shortening seam is at the same time the third tether seam.

The knee airbag is manufactured of the components described above as follows: as a first step tethers30,34,38are sewn along positions52a,48aand44awith the front section30of pre-cut piece10. After this, the pre-cut piece10is folded along fold line25and initially the third tether38is sewn along position50aand then the first tether30is sewn along position42awith rear section22. At this state of manufacture, front and rear sections20,22lie flat and congruently on top of one another, so that edge seam40bis very easy to create. Following creation of edge seam40b, finally opening12is closed by means of the shortening seam and third tether seam46b, whereby the corresponding end area of second tether46ais held between the edges of opening12.

First and third tether30,38are double T-shaped with side cutouts through which gas can flow. The side facing the rear section22of the second tether34is concave and follows the curvature of the oblong opening12.

FIG. 5shows the finished sewn knee airbag. Edge seam40bcan be seen, along with first tether seam42b, the shortening seam and the third tether seam46band the fifth tether seam50b.

FIG. 6is a schematic section along Plane A-A throughFIG. 5. In this view, it can be seen particularly clearly how tethers30,34,38are sewn to the airbag skin5by means of tether seams42b,44b,46b,48b,50b,52b. In particular it can be seen how the rear end of second tether34is held between the edges of opening12by means of the shortening third tether seam46b.FIG. 6also shows a gas guide element60with additional reinforcement layer62, which can be additionally provided. Gas guide element60and reinforcement layer62are not shown in the other figures.

FIG. 7shows the installed situation when the knee airbag is fully inflated. The knee airbag extends from a rear end R to a front end F basically in the direction X. Here the effect can be seen which is caused by shortening seam46b. Because of this shortening third tether seam46b, rear section22is shortened in X direction in comparison with the front section20, which causes the airbag filled with gas to bend away at this location, and therefore comes to rest against a lower area68of the instrument panel with its support surface22a, which is part of rear section22, and follows this lower area of the instrument panel, so that a banana-shaped cross-section results. The impact surface20alies opposite support surface22a.

Alternatively to the embodiment shown, the airbag skin can be assembled of two pre-cut pieces, whereby one pre-cut piece forms the front section and the other pre-cut piece forms the rear section and a completely surrounding edge seam is provided.

The invention is not limited to the illustrated embodiment, but rather includes all means functioning identically within the meaning of the invention. The foregoing description of various embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise embodiments disclosed. Numerous modifications or variations are possible in light of the above teachings. The embodiments discussed were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.