DE4409405C5 - Method for producing an airbag cover - Google Patents

Abstract

Method for producing an airbag cover (2) which has an inner load-bearing molded layer (3) made of hard polymer material and an overlying layer (4) made of soft polymer material and an outer skin (5), comprising the steps: - producing the cover (2 ) and then - cutting a tear line (7) into the cover (2) starting from the molding layer (3), the tear line (7) being cut by means of a laser or ultrasound knife without exerting pressure on the cover (2), the tear line ( 7) completely penetrates the molding layer (3), and wherein the molding layer (3) has a reduced thickness in the region of the tear line (7).

Description

The present invention relates to a cover for an airbag.

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

An airbag can z. B. in the hub of a steering wheel, wherein the hub is provided with a cover which normally protects the airbag.

Alternatively, an airbag may be mounted in a part of the instrument panel, this part of the instrument panel being provided with a cover which normally protects the airbag. In either case, the cover is usually made of a plastic material and provided with one or more tear lines which are lines of mechanical weakness to allow the cover to rupture to form an opening when the air bag 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 often more desirable to have a cover for an airbag made from a laminate whose outer layer is a relatively low density foam and whose inner layer is high density foam or molded thermoplastic material. By using such a laminate, the cover may have the strength provided by the high density foam or rigid thermoplastic material and a relatively soft, cushioning appearance formed by the relatively low density foam. The low density foam 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 to cut a cover from the inside, this cover having an inner layer of thermoplastic or high density foam and an outer layer of low density foam, the low density foam must be placed on the support surface, and when the cover is cut with a blade exerting pressure, the low-density foam is compressed. This leads to difficulties in performing the cutting process in a precise, consistent manner. This method can also provide a permanent mark visible on the outer surface of the cover.

While it may be possible to provide a tear line simply by forming the layer of thermoplastic or high density foam with a line or extended area of relatively thin material, a very large force may be required to begin ripping the tear line because the material has significant strength. Since the material in the region of the tear line would have to be very thin, it can also be difficult to control the molding process so that the material has exactly the desired thickness. It may also be possible to provide a tear line in which the thermoplastic or high density foam defines a true gap across which are spaced transversal ribs that hold the material together. The low density foam can then be molded to the harder layer. However, if this aid is chosen, the low density foam could well pass through the dividing line during the molding process, lifting the harder layer out of the mold so that the final product is not satisfactory.

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 on a Z-shaped step, at the two parts of the Base layer abut and aligned with each other.

The invention is therefore based on the object to provide an improved method for producing a cover for an airbag.

According to the invention, there is provided a method of making an airbag cover having a load-bearing forming layer of relatively hard polymeric material and an overlying layer of relatively soft polymeric material provided with an outer skin, the method comprising the step of forming the cover and subsequent cutting of a tear line into the cover from the inside of the cover, wherein the tear line completely penetrates the mold layer and the cutting is effected by using a cutting technique which does not exert pressure on the cover.

The mold layer is according to the invention designed with a region of reduced thickness in the region in which the tear line is to be cut.

Conveniently, the cut is performed using a laser. An advantage of using a laser is that the material being cut is evaporated by the laser and the resulting cut is free of burrs that would be expected when a mechanical cutting device, such as a die cutter, is used. As a knife or saw was used. Since there is no knife, it is also possible to visually inspect the cut during the cutting process.

Alternatively, the cut is performed using an ultrasonic knife.

Preferably, the mold layer is formed of a thermoplastic material.

Alternatively, the mold layer is formed of a high density foam.

Preferably, the overlying relatively soft polymer layer comprises a layer of low density polymer foam, which may be polyurethane foam.

Preferably, the cut extends partially into the overlying layer.

Conveniently, the cut extends into the overlying layer at a depth of about 1 mm.

Preferably, the overlying layer is at least twice as thick as the mold layer.

Preferably, the cover is initially made by first forming the mold layer and then subsequently molding the overlying layer to the mold layer before finally cutting the tear line.

In order that the invention may be more readily understood and other features thereof appreciated, the invention will now be described by way of example with reference to 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 tear line is provided in a laminate material forming a cover for an airbag without connecting a thin material portion thereto, whereas the lower part of the figure is an embodiment in which an elongated region of thin material (reduced thickness forming layer) is provided in the region of the tear line.

However, the remaining features of the two alternative embodiments are substantially identical, as can be seen readily from the figure.

With reference to the figures, an airbag cover 2 formed from a laminate, the one below as a molding 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 that at least equal and preferably greater than twice the thickness of the mold layer 3 is.

In the 1 shown cover is with a central area 6 provided essentially by 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 upward, as in the figures, the cover is reversed, 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 material or high-density foam material containing the molding 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 adapted to cooperate with means to provide 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 mold 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 mold layer 3 goes. Thus, there is no possibility that parts of the mold 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 which comprises an element to which ultrasonic pulses are delivered adapted to cut the plastic material. These techniques can also provide 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 mold layer 3 provided, which is formed of rigid thermoplastic material or foam of high density, 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 molding layer formed of thermoplastic material 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 mold 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 cutting through the unrestrained thickness of the mold layer 3 (as in 2 shown).

It should be noted that in the cover described the mold layer 3 is preferably formed of a thermoplastic material which is relatively inexpensive, and the overlying layer 4 is made of a foamed material, such. As polyurethane foam, which preferably has a thickness which is twice as thick as the thickness of the mold 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 mold layer 3 is formed and finally the tear or dividing line 7 is cut with one of the techniques described above.

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

LIST OF REFERENCE NUMBERS

1

Symbolic line

2

Airbag cover

3

mold layer

4

overlying layer

5

shell

6

mid-range

7

tear line

8th

wall

9

Area of the cover

10

Area of the cover

11

Part of the material

12

Part of the material

13

recess

14

Through opening

15

room

16

Area of reduced thickness

Claims (9)

Method for producing an airbag cover ( 2 ), which has an inner supporting shaping 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 molding 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 mold layer ( 3 ) completely permeates, and wherein the mold layer ( 3 ) in the area of the tear line ( 7 ) has a reduced thickness. Method according to claim 1, characterized in that the molding layer ( 3 ) is formed of a thermoplastic material. Method according to claim 1, characterized in that the molding layer ( 3 ) is formed from a plastic foam of high density. Method according to one of the preceding claims, characterized in that the overlying layer is formed from a low density polymer foam. Method according to one of the preceding claims, characterized in that the overlying layer ( 4 ) is formed of 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 mold layer ( 3 ). Method according to one of the preceding claims, characterized in that in the production of the cover ( 2 ) first the mold layer ( 3 ) and then subsequently the overlying layer ( 4 ) to the mold layer ( 3 ) is formed.

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