IMPROVEMENTS IN AND RELATING TO AIR BAG RESTRAINT SYSTEMSThe present invention relates to improvements in and relating to air bag restraint systems.
In air bag restraint systems, the air bags are located behind covers, so that upon inflation of the air bag it will burst through the cover and be deployed in front of the occupant of the vehicle. In order to ensure proper deployment of the air bag, the cover must be capable of bursting in a predictable manner. Hitherto, the covers for air bags have been formed from rubber or a similar soft homogeneous material with grooves formed on its inner surface to provide weakened lines along which the cover will split upon inflation of the air bag.
Furthermore, it is undesirable that upon inflation of the bag, parts of the cover will become detached, so that they could possibly cause injuries to the occupants of the vehicle. The grooves are consequently arranged so that when the cover is burst by inflation of the air bag, hinged flaps will be formed which will remain attached to the associated supporting structure of the vehicle.
In more expensive leather trimmed vehicles, it is desirable that the air bag module is also covered by leather. However, the burst characteristics of leather are unpredictable so that correct deployment of the air bag could not be guaranteed.
According to one aspect of the present invention, a cover for an air bag module of an air bag restraint system comprises an inner cover made of a soft homogeneous material, the inner cover being formed with grooves on its outer surface along which the cover will split upon inflation of the air bag and with hinge formations along which portions of the inner cover will hinge after bursting, a leather outer cover being secured to the inner cover, the leather outer cover being split along lines corresponding to the grooves in the inner cover, the split edges of the leather outer cover being turned into the grooves of the inner cover.
With the cover described above, the edges of the leather cover along the burst lines of the inner cover are presplit, so that the unpredictable nature of the leather will not affect deployment of the air bag. Turning the edges of the leather cover into the grooves of the iller cover, will provide a neat appearance.
The leather outer cover is preferably bonded to the inner cover. Stitching may be provided along the slit edges of the leather outer cover to provide a false seam. The inner cover may be made of rubber or plastics material with similar properties.
An embodiment of the invention is now described, by way of example only, with reference to the accompanying drawings, in which:Figure 1 illustrates a sectional side elevation of an air bag module for mounting in the central boss of a vehicle steering wheel, the air bag module having a cover in accordance with the present invention;Figure 2 is a front view of the air bag module illustrated in Figure 1; andFigure 3 is a section along the line III-III of Figure 2.
As illustrated in Figure 1, an air bag module 10 for location in the central boss of a steering wheel comprises a backing plate 11 in the form of a dished pressing. Studs 12 are secured to the backing plate 11 by which the module 10 may be secured to the steering wheel. An inflator 13 is mounted centrally of the backing plate 11 by means of bolts 14. An air bag 15 is secured to the backing plate 11 around the inflator 13 by means of clamping ring 16. The air bag 15 is folded so that it is disposed around the sides and over the top of the inflator 13. An inner cover 20 formed from moulded rubber is secured to the backing plate 11 by means of a plurality of angularly spaced rivets 21 around the periphery of backing plate 11. The cover 20 closes the dished pressing forming the backing plate 11 to enclose the inflator 13 and folded air bag 15.
The cover 20 is formed with grooves 22, 23 and 24 in the form of an "H". The grooves 22, 23 and 24 form weakened lines in the cover 20, so that upon inflation of the air bag 15, the cover 20 will split along the lines of grooves 22, 23 and 24 to form two hinged portions 25 and 26 which will open to permit deployment of the air bag 15. The portions 25 and 26 of the cover 20 are recessed and filled with a layer of foamed padding material 27.
The central portion 28 of the cover 20 may be moulded to form a badge or a separately moulded badge may be secured thereto in suitable manner. The groove 24 will run along only one edge of the central portion 28, so that the badge will remain secured to one of the portions 25 and 26 after inflation of the air bag 15.
A leather trim 30 is bonded to the outer surface of the cover 20. The leather trim 30 is formed from four pieces 31, 32, 33 and 34, the edges of pieces 31, 32, 33 and 34 adjoining along the lines of grooves 22, 23 and 24 and being turned into the grooves 22, 23 and 24 as illustrated in Figure 3.
The splitting of the leather trim 30 into four pieces 31, 32, 33 and 34, the edges of which adjoin along the split lines of the cover 20, will permit the cover 20 to split upon inflation of the air bag 15, the leather trim 30 not affecting the load required to split the cover 20.
Turning of the edges of the pieces 31, 32, 33 and 34 into the grooves 22, 23 and 24 will provide a neat finish to the leather trim 30.
Various modifications may be made without departing from the invention. For example, while in the above embodiment the grooves 22, 23 and 24 define an "H" so that upon splitting two hinge flaps will be provided, other suitable configurations of grooves may be used.
Furthermore, stitching may be provided along the edges of pieces 31, 32, 33 and 34 of the leather trim 30 to provide false seams therealong.