GB2257398A

GB2257398A - A cover for a vehicle air bag

Info

Publication number: GB2257398A
Application number: GB9114880A
Authority: GB
Inventors: Martin Lindstrom
Original assignee: Autoliv Development AB
Current assignee: Autoliv Development AB
Priority date: 1991-07-10
Filing date: 1991-07-10
Publication date: 1993-01-13
Also published as: GB9114880D0

Abstract

The cover, which is moulded from a foamed polymer material, has an outer relatively smooth surface and an inner structured surface. The inner surface comprises two primary rectangular areas separated by a break line 2, and each having a first thickness. Each primary area has a plurality of secondary areas 13, 14, all located within the primary area, having a reduced thickness. The construction helps to avoid deformations caused by internal stresses which arise during moulding of the cover. <IMAGE>

Description

DESCRIPTION OF INVENTION "Improvements in or relating to a Cover for an Air-Bag" THE PRESENT INVENTION relates to a cover for an air-bag.

An air-bag is frequently mounted in position in a steering wheel or in part of a dashboard of a motor vehicle, and means are provided to inflate the air-bag when an accident occurs, the air-bag then acting as a "cushion" for a person within the vehicle.

An air-bag is mounted within an appropriate recess formed in the steering wheel or formed in the dashboard, and is provided with a cover. The cover not only provides a pleasing appearance, but also protects the air-bag, so that the air-bag is not damaged. Equally, however, the cover must be such that it does not hinder the air-bag when the air-bag is to be inflated.

It has been proposed previously to provide an airbag cover fabricated from an element moulded of polymer foam, typically polyurethane foam. Such covers have been manufactured of substantially uniform thickness, and the thickness has been selected to provide the required degree of protection. The cover is, however provided with one or more "break" lines, which are lines where the cover is relatively thin. Thus, in the region of these lines, the cover is relatively weak and, in the event that the air-bag inflates, the cover can "break" in the region of these lines, so that the air-bag can inflate readily without the cover impeding inflation of the air-bag in any way.

It has been found, however, that covers of the type described above have suffered from internal stress. It is believed that such internal stress develops as the plastics material forming the cover is cooled during the moulding process. Such stress can cause the cover to distort or become deformed, which is clearly undesirable.

The present invention seeks to provide an improved air-bag cover.

According to one aspect of this invention there is provided a cover for an air-bag, said cover being moulded from a foamed polymer material to defining an outer relatively smooth surface and an inner structured surface, the cover comprising at least one first area having a first thickness and a plurality of second areas, all located within the first area, having a reduced thickness.

Preferably the air-bag cover is provided with lines of reduced thickness comprises break lines, at least one of said lines separating two of said first areas. Preferably each of the second areas has a dimension which is less than half the width of the cover and which may be less than a quarter of the whole width of the cover. The air-bag cover will be made of polyurethane foam and may be reinforced with a fabric insert.

Preferably said first area comprises a plurality of ribs located between the second areas and a region surrounding the second areas. Preferably the ribs intersect, the recesses comprising substantially diamond and substantially triangular shaped recesses.

The air-bag cover may be provided with metal lugs embedded therein, parts of the lugs protruding to provide means to secure the air-bag cover in position.

In order that the invention may be more readily understood, and so that further features thereof may be appreciated, the invention will now be described, by way of example, with reference to the accompanying drawings in which FIGURE 1 is an underneath view of an air-bag in accordance with the invention, with parts effectively cut away to reveal the internal structure of the air-bag cover, FIGURE 2 is a sectional view taken generally on the line A-A, and is thus partly side view and partly sectional view, and FIGURE 3 is a sectional view taken on line B-B of Figure 1.

Referring to the drawings a cover for an air-bag is moulded from an appropriate polymer foam material such as polyurethane foam. The cover comprises a substantially rectangular central part 1, this part being provided with a central axially extending break line 2 where the cover is relatively thin and thus weak so that along this line can break easily. The break line 2 extends into transversely extending break lines 3 provided at each end of the central part of the cover, and again along these break lines the cover is made to be relatively thin, so that the cover will break easily. The cover is divided into two similar sized rectangular areas by the break lines described above.

The cover is provided with side walls 4,5,6 which extend substantially perpendicularly to the central part of the cover. Embedded in the side walls are metal lugs 7, the lugs protruding from the side walls and each presenting an aperture 8 adapted to receive an appropriate fastening means such as a bolt or the like to enable the cover to be mounted in position.

Incorporated within each of the rectangular areas of the cover is a sheet of fabric 9 which provides internal reinforcement within the cover.

The outer surface of the cover 10 is moulded to be relatively smooth, but the inner surface of the cover 11 is moulded with a predetermined structure. The structure is visible most clearly in Figure 1, but the nature of the structure can be fully appreciated by considering the sectional views of Figures 2 and 3.

It will be appreciated that the central part of the cover 1 is divided into two smaller rectangular areas by the break lines 2 and 3 mentioned above. Each of these areas has a peripheral part 12 of a predetermined thickness which surrounds a region provided with a plurality of diamond shaped and triangular recesses 13,14, where the material forming the cover is of a lesser thickness. The recesses are separated by means of inter-crossing ribs 15.

Thus the recesses are all located within the respective rectangular area.

It has been found that the stresses present in a moulded polyurethane foam material are dependent upon the thickness of the material. It is thus believed that the stress is developed during cooling of the material and if the material is thick it only cools slowly, permitting significant stresses to develop. However, in the embodiment of the invention described above, significant portions of the polyurethane foam material have a reduced thickness, thus leading to increased cooling speeds. Even in the region of the ribs 15 and the peripheral region 12 of each of the rectangular parts of the cover, where the thickness of the foam is the same as in the prior art, nevertheless an increased cooling effect is achieved, thus leading to a lower level of stress within the polyurethane foam. Nevertheless, because the ribs have the same thickness as the thickness of the prior art arrangement, it is found that the cover, as described above, has substantially the same strength as in the prior art arrangement. Consequently, the cover is not distorted due to internal stress, but provides substantially the same degree of strength as the prior art arrangement.

It is to be noted that in the embodiment described the recesses 13 and 14 are such that their greatest dimension is less than half of the width of the whole cover and indeed is less than a quarter of the width of the whole cover. Nevertheless, each of the recesses is surrounded by a part of the cover which has a greater thickness than the thickness within the recess.

Claims

CLAIMS:

1. A cover for an air-bag, said cover being moulded from a foamed polymer material to defining an outer relatively smooth surface and an inner structured surface, the cover comprising at least one first area having a first thickness and a plurality of second areas, all located within the first area, having a reduced thickness.

2. An air-bag cover according to Claim 1 provided with lines of reduced thickness comprising break lines, at least one of said lines separating two of said first areas.

3. An air-bag cover according to any one of the preceding Claims wherein each of the second areas has a dimension which is less than half the width of the cover.

4. An air-bag cover according to Claim 3 wherein each of the second areas has a width which is less than a quarter of the whole width of the cover.

5. An air-bag cover according to any one of the preceding Claims made of polyurethane foam.

6. An air-bag cover according to any one of the preceding Claims reinforced with a fabric insert.

7. An air-bag cover according to any one of the preceding Claims wherein the said first area comprises a plurality of ribs located between the second areas, and a region surrounding the second areas.

8. An air-bag cover according to Claim 7 wherein the ribs intersect, the recesses comprising substantially diamond and substantially triangular shaped recesses.

9. An air-bag cover substantially as herein described with reference to and as shown in the accompanying drawings.

9. An air-bag cover according to any one of the preceding Claims provided with metal lugs embedded therein, parts of the lugs protruding to provide means to secure the air-bag cover in position.

10. An air-bag cover substantially as herein described with reference to and as shown in the accompanying drawings.

11. Any novel feature or combination of features disclosed herein.

Amendments to the claims have been filed as follows CLAIMS: 1. A cover for an air-bag, said cover being moulded from a foamed polymer material to define an outer relatively smooth surface and an inner structured surface, the inner surface comprising at least two primary areas each having a first thickness, each primary area being associated with a plurality of secondary areas, all located within the primary area, - the secondary areas having a reduced thickness relative to said first thickness, the two primary areas being separated by a line of reduced thickness comprising a break line.

2. An air-bag cover according to Claim 1 wherein each of the secondary areas has a dimension which is less than half the width of the cover.

3. An air-bag cover according to Claim 2 wherein each of the secondary areas has a width which is less than a quarter of the whole width of the cover.

4. An air-bag cover according to any one of the preceding Claims made of polyurethane foam.

5. An air-bag cover according to any one of the preceding Claims reinforced with a fabric insert.

6. An air-bag cover according to any one of the preceding Claims wherein each primary area comprises a plurality of ribs located between the secondary areas, and a region surrounding the secondary areas.

7. An air-bag cover according to Claim 6 wherein the ribs intersect, the recesses comprising substantially diamond and substantially triangular shaped recesses which comprise the secondary areas.

8. An air-bag cover according to any one of the preceding Claims provided with metal lugs embedded therein, parts of the lugs protruding to provide means to secure the air-bag cover in position.