DE4409405B4 - Method for producing an airbag cover - Google Patents

Abstract

A method of making an airbag cover (2) having an inner support layer (3) of hard polymeric material and an overlying layer (4) of soft polymeric material and an outer skin (5), comprising the steps of
- Making the cover (2) and then
Cutting a tear line (7) into the cover (2) starting from the carrier layer (3),
the tear line (7) being cut on the cover (2) by means of a laser or ultrasonic knife without applying pressure,
the tear line (7) completely penetrates the carrier layer (3),
and wherein the carrier layer (3) has a reduced thickness in the region of the tear line (7).

Description

The The present invention relates to a cover for an airbag.

It it has been proposed to provide an airbag in a motor vehicle, wherein the airbag adapted is that he in case of an accident, inflated to provide protection for a driver or a passenger in the motor vehicle.

One Airbag can e.g. be included in the hub of a steering wheel, wherein the hub is provided with a cover which is normally the Airbag protects.

alternative For this purpose, an airbag mounted in a part of the dashboard be, with this part of the dashboard with a cover which normally protects the airbag. In any case, that is Cover usually made of a plastic material and with one or more tear lines representing lines of mechanical weakness to enable that the Cover rips, around an opening to form when the airbag is inflated.

US-A-4,120,516 discloses an airbag cover wherein the cover is formed of a laminate having an outer layer formed of high density polyurethane foam and an inner layer of low density polyurethane foam integral with the outer layer of the laminate. The laminate is cut from the inside to form lines of mechanical weakness or tear lines.

It is common desirable a cover for to have an airbag made of a laminate whose outer layer a foam of relatively low density and its inner layer High density foam or cast thermoplastic material. By using such a laminate, the cover can provide the strength, through the high-density foam or the rigid thermoplastic Material available and have a relatively soft, cushioning appearance by the Foam of relatively low density is formed. The foam is lower Density can, as is known, have an outer skin.

If the cover of US-A-4,120,516 the cut is made through the low density foam and into the relatively high density foam. The high density foam can be carried on a support surface so that pressure can be exerted by the cutting blade without causing problems.

However, if an attempt is made, a cover from the inside to cut, this cover has an inner layer of thermoplastic High density material or foam and an outer layer of low density foam has, must Low density foam will be placed on the support surface, and if the cover is cut with a blade that exerts pressure compressed the low density foam. This leads to difficulties the implementation the cutting process in a precise, consistent manner. This Method can also create a permanent marker on the outer surface of the Cover is visible.

While it possible can be a tear line simply by designing the layer of thermoplastic material or high density foam with a line or a lengthened one Area of relatively thin Material available can make a very big Force to begin to rupture the tear line because the material has significant strength. Since the material in the Area of the tear line very thin could be, can it also be difficult to control the molding process so that the material exactly the desired one Thickness has. It may also be possible be a tear line to create in which the thermoplastic material or the foam high density a true gap defined, over which extend at intervals, transverse ribs, that hold the material together. The low density foam can then to the harder Layer are formed. However, if this resource is chosen, could the Low density foam during go through the dividing line well, the harder layer Lifting out of the mold, so that the final product is not satisfactory is.

The US-A-5,082,310 describes to cut in an airbag cover with a knife on the inside of a notch in a decorative part so that the notch is not visible from the outside. An inner supporting part of the airbag cover is provided with pot-like depressions as predetermined breaking points. The space between the decorative part and the inner supporting part is filled after aligning the predetermined breaking points to each other with a relatively soft foam.

The JP 02-099324 discloses cutting an intermediate layer between a forming member as a base layer and an outer skin by means of a laser beam from the inside of the airbag cover, preventing the cutting of the base layer being transparent. The base layer has as a predetermined breaking point a Z-shaped step on which two parts of the base layer abut each other and are aligned with each other.

Of the The invention is therefore based on the object, an improved method for generating a cover for an airbag available to deliver.

According to the invention is a Method for producing an airbag cover, which is a carrier layer made of relatively hard polymer material and an overlying layer of relative soft polymer material provided with an external hand, provided the method comprising the step of making the cover and subsequent cutting of a tear line in the cover of the inside of the cover comprises, wherein the tear line the backing Completely penetrates and cutting by using a cutting technique is effected, which exerts no pressure on the cover.

The backing is according to the invention with a Area of reduced thickness designed in the area in which the tear line to cut is.

conveniently, the cut is done using a laser. One Advantage of using a laser is that the material, which is cut by the laser is evaporated and the resulting Cut free of burrs that would be expected if a mechanical Cutting device, such as e.g. a knife or a saw used has been. Since there is no knife, it is also possible to cut during the Visually check the cutting process.

alternative this is done by cutting using an ultrasonic knife carried out.

Preferably becomes the carrier layer formed from a thermoplastic material.

alternative this is the carrier layer formed from a foam of high density.

Preferably comprises the overlying, relative soft polymer layer, a layer of a polymer foam lower Density, which can be polyurethane foam.

Preferably The cut extends partially into the overlying layer.

conveniently, the cut extends into the overlying layer in one Depth of about 1 mm.

Preferably is the overlying layer at least twice as thick as the carrier layer.

Preferably the cover will be initial made by first the backing layer shaped and then subsequently the overlying layer to the backing is shaped before finally the tear line is cut.

Around the invention easier to understand to make other features of the same appreciated can, The invention will now be described by way of example with reference to FIG On the accompanying drawings, in which:

1 3 shows a view from below of an airbag cover according to the invention adapted to be mounted in a steering wheel, the upper part of the figure representing an embodiment and the lower part of the figure an alternative embodiment,

2 a view in section along the line II-II in 1 shows, and

3 a view in section along the line III-III in 1 shows.

Referring to the drawings 1 in fact, two alternative embodiments that are very similar to an airbag cover. The figure is represented by a symbolic, horizontally extending line 1 divided in two parts. The upper part of the figure represents an embodiment in which a cut or a tear line is provided in a laminate material constituting a cover for an air bag without connecting a thin material portion thereto, whereas the lower part of the figure is an embodiment in which an extended area of thin material (reduced thickness support layer) is provided in the region of the tear line.

however are the rest Features of the two alternative embodiments substantially identical, as can be seen easily from the figure.

With reference to the figures, an airbag cover 2 formed from a laminate, the one below as a support layer 3 designated inside 3 , which may be formed of thermoplastic or dense foam, and an overlying layer hereinafter 4 designated outer layer 4 which is formed of a low-density foam, preferably polyurethane foam. The overlying layer 4 can with an outer skin 5 be provided, which may be formed with the foamed layer as a whole. The overlying layer 4 has a thickness at least equal to and preferably greater than twice the thickness of the backing layer 3 is.

In the 1 shown cover is with a central area 6 provided essentially from a tear line 7 is surrounded. The area 6 forms the upper part of a portion of the cover, which is a hanging wall 8th has (the wall 8th is in the 2 and 3 as shown extending upwards, since in the figures the cover is turned over, with the outer skin 5 the cover at the bottom of the figure. The lower part of the cover is the in 1 visible part of the cover).

The cover of 1 is with two areas 9 and 10 on opposite sides of the center 6 out over the wall 8th unload, and another area 10 over the wall 8th emanating from the edge, which is the lower edge of the center region 6 forms. These areas 9 and 10 are provided so that the cover can be received in a cooperating steering wheel hub, wherein the areas 9 and 10 aligned with the spokes of the steering wheel. These features are thus design features that relate only to the illustrated, particular embodiment.

It should be noted, however, that in each of the overhanging areas 9 , in the 2 and 3 can be seen, a part 11 . 12 rigid or high density foam material, which is the backing layer 3 forms, is provided, the area 9 to support, and a channel or a recess 13 in the outer skin of the layer 4 is made of low density foam for design purposes. It should also be noted that the side wall 8th with a passage opening 14 which is adapted to cooperate with means to form an airbag and a pyrotechnic propellant for an airbag in the room 15 to be fastened by the center area 6 the cover and the side wall 8th is limited.

The following is the tear line 7 in the region of the cover which is not provided with a thin material area (area of reduced thickness), as in the upper part of the 1 and more specifically in 2 shown, to be considered.

The following is the tear line 7 in the part of the cover which, as shown, is not provided with a region of thin material. As can be seen from the upper part of the 1 and from 2 results is the tear line 7 in this part of the cover to the base of the rising side wall 8th and thus formed from the bottom of the cover toward the top of the cover. The tear line is formed by a cut having a width of about 0.3 mm. The cut extends through the carrier layer 3 formed of thermoplastic material or high density foam and having a thickness of about 2 mm in its layer, and into the layer of low density foam, which typically has a thickness of 5 mm. The cut extends into the low density foam at a depth D which is typically about 1 mm. As the cut extends into the low density foam, it is ensured that the cut is completely through the backing 3 goes. Thus, there is no possibility that parts of the carrier layer 3 on opposite sides of the tear line 7 continue to be held together.

The cut, the tear line 7 forms, results using a cutting technique that exerts no pressure on the cover. Preferably, the cut is created using a laser knife. A laser is used to direct a beam of high light intensity to the area to be cut. The jet vaporizes the plastic material in the area of the cut. The vapor can be removed using a suitable vacuum device. It should be noted that no pressure is applied by cutting the material using a laser knife and thus the overlying layer 4 low density foam is not compressed. Thus, the cut can be carried out extremely accurately. The cut is burr-free and can be optically checked during the cutting process.

It should be noted that alternative means may be used instead of a laser knife which does not apply pressure to the material forming the cover. Thus, the cut can be performed using a hot knife. Such a hot knife may comprise an element which is heated to a temperature such as when combined with the thermoplastic material or high density foam forming the side and subsequently with the material forming the layer 4 formed from low density foam, is brought into contact, the material melts. A hot knife of this type is preferably formed of an element which is electrically heated to the desired temperature. Again, a vacuum device may be used to remove the molten plastic material.

Again Alternatively, an ultrasonic knife may be used an element comprises the ultrasonic pulses are delivered, which are adapted that she cut the plastic material. These techniques can too deliver a burr-free cut.

In the following reference is made to the in 1 shown part, which is provided with a region of thin material, as in 3 shown.

In this embodiment, the cover is with a region of the carrier layer 3 provided, made of rigid thermoplastic material or High density foam is formed, which has a reduced thickness. This area is considered an extended area 16 shown. It can be seen that the area 16 with the position of the tear line 7 coincides and thus at the base of the wall 8th adjoining runs. The area 16 the reduced thickness has a width X, as in 3 shown, which is typically 3 mm. The thickness of the backing layer formed of thermoplastic or high density foam 3 is approximately 2 mm, and in the region of reduced thickness, the thickness is reduced to approximately 0.5 mm. The cut, the tear line 7 is performed in the region of reduced thickness and extends through the rigid support layer 3 from thermoplastic foam or high-density foam and into the layer 4 low-density foam at a depth D that is approximately 1 mm. When cutting through the area 16 reduced thickness consumes less energy than when cutting through the unrestrained thickness of the carrier layer 3 (as in 2 shown).

It should be noted that in the cover described the carrier layer 3 is preferably formed of a thermoplastic material which is relatively inexpensive, and the overlying layer 4 is of a foamed material, such as polyurethane foam, which preferably has a thickness which is twice as thick as the thickness of the carrier layer 3 made of thermoplastic material. The cover thus provides a soft appearance and is relatively inexpensive. The cover can be made by first forming the layer of thermoplastic or high density foam and subsequently the foamed layer 4 to the carrier layer 3 is formed and finally the tear or dividing line 7 is cut with one of the techniques described above.

While the Invention with reference to a cover which is specially adapted to be arranged in a steering wheel has been described The invention may as well be applied to a cover in one Part of a dashboard is integrated, to be applied.

1

symbolic line

2

Airbag cover

3

backing

4

overlying layer

5

shell

6

mid-range

7

tear line

8th

wall

9

Area the cover

10

Area the cover

11

part of the material

12

part of the material

13

recess

14

Through opening

15

room

16

Area reduced thickness

Claims (9)

Method for producing an airbag cover ( 2 ) which has an inner carrier layer ( 3 ) of hard polymer material and an overlying layer ( 4 ) made of soft polymer material and an outer skin ( 5 ), with the steps - Making the cover ( 2 ) and then - cutting a tear line ( 7 ) in the cover ( 2 ) starting from the carrier layer ( 3 ), where the tear line ( 7 ) by means of a laser or ultrasonic knife without applying pressure to the cover ( 2 ), the tear line ( 7 ) the carrier layer ( 3 ) completely penetrates, and wherein the carrier layer ( 3 ) in the area of the tear line ( 7 ) has a reduced thickness. Method according to claim 1, characterized in that the carrier layer ( 3 ) is formed of a thermoplastic material. Method according to claim 1, characterized in that the carrier layer ( 3 ) is formed from a plastic foam of high density. Method according to one of the preceding claims, characterized characterized in that overlying Layer is formed from a polymer foam of low density. Method according to one of the preceding claims, characterized in that the overlying layer ( 4 ) is formed from polyurethane foam. Method according to one of the preceding claims, characterized in that the cut is partly in the overlying layer ( 4 ). Method according to claim 6, characterized in that the cut into the overlying layer ( 4 ) penetrates about 1 mm. Method according to one of the preceding claims, characterized in that the overlying layer ( 4 ) at least twice as thick as the carrier layer ( 3 ). Method according to one of the preceding claims, characterized in that in the Production of the cover ( 2 ) first the carrier layer ( 3 ) and then subsequently the overlying layer ( 4 ) to the carrier layer ( 3 ) is formed.