Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – To produce composite – plural part or multilayered article
Reexamination Certificate
2000-02-04
2001-08-28
Kuhns, Allan R. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
To produce composite, plural part or multilayered article
C029S894100, C264S271100, C264S313000, C264S317000
Reexamination Certificate
active
06280674
ABSTRACT:
The present invention relates to a method of producing a steering wheel with a seamless casing surrounding a wheel skeleton.
BACKGROUND OF THE INVENTION
The majority of the casings of steering wheels with integrated airbag are constructed today in two parts, with a shaped part surrounding the steering wheel skeleton and with a separately produced covering for the airbag installation opening in the hub region of the steering wheel, great efforts being made to match the two parts with each other in their visual appearance and haptic characteristics. Considerable further difficulties result from the fact that the airbag covering must be constructed so as to be able to be torn open and so as to be movable relative to the steering wheel hub about the touch path necessary to actuate the horn.
As a gap between the shaped part surrounding the steering wheel and the airbag covering is regarded as visually disadvantageous, it has already been proposed to produce the shaped part and airbag covering in one piece. Owing to the tear-open- and actuating functions to be taken into account in the region of the airbag coverings, such methods present certain substantially solvable difficulties with regard to manufacturing technique and automatically require a largely new design of the steering wheel construction, because assembly can only take place from the reverse side of the steering wheel and because special precautions have to be taken for the introduction of the airbag module with folded gas bag and gas generator. Rather, one has found a way to divide the steering wheel skeleton into a base part with hub and possibly spoke stumps, which can be equipped with the airbag module and other function parts, before the steering wheel rim with spokes or spoke stumps and covering in a single piece is put in place and connected with the base part.
It is regarded as particularly disadvantageous here that the fastening between the base part and the steering wheel rim is connected with an additional expenditure of material, which goes against the general aim of saving weight in vehicle construction. In addition, it is difficult to match the two components optimally to each other with regard to size. In particular, the folded gas bag is equipped as a shaped part with considerable tolerances, so that the coordination of the covering region is not simple, which—as it has to be able to be torn open—must not have any particular inherent rigidity and therefore requires the folded gas bag as a support. If the gas bag set is too “thin”, the covering is not sufficiently supported; if it is too “thick”, it is buckled upwards. Both are undesirable.
Similar problems occur with regard to the actuating movements which have to be transferred from the exterior over the plastic shaped part constructed in one piece on the steering wheel rim onto the actuating members mounted in the base part. It should be readily clear that the adaptation of a surface produced by casting mold technique to a mounted surface is very costly in terms of manufacturing technique and that the transfer functions can only be carried out with reliable operation when very close tolerances can be maintained in the adaptation.
BRIEF DESCRIPTION OF THE INVENTION
Present invention provides a method of producing a steering wheel that overcomes above-mentioned difficulties, providing a casing with a continuous surface and possibly a foamed core, avoiding any adaptation problems with a justifiable economic expenditure.
According to the invention, a shaped body of a dissolvable material is attached to the central base part of the steering wheel skeleton, thereafter the steering wheel skeleton is placed with the shaped body into a mold, the casing is molded, and then removed from the mold, and the shaped body is dissolved by addition of a solvent, thereby leaving a hollow accommodation space for the airbag module.
Through the use of a shaped body of soluble material, the casing can be produced with a hollow having an accurate fit, into which subsequently the airbag module can be introduced. The airbag module itself, owing to the “soft” surface of the gas bag set, does not come into consideration as a shaped body, because thereby the nominal rupture line necessary in the covering region of the plastic shaped part can not be formed out in a reproducible manner. On the other hand, with the shaped body of soluble material, in connection with the outer form in the casing, a very precisely dimensioned line of small wall thickness can be produced, which has a closely tolerated strength and on inflation of the gas bag tears open reliably and immediately. The production of the covering region is thereby just as simple as with a covering cap produced as a separate component, i.e. nominal tear lines which are able to be stressed sufficiently in normal operation and are able to be torn open easily in an emergency can be realized just as reinforcement inserts and components acting as a hinge. In addition, through the production in one piece, it is of course ensured that the steering wheel and covering region have the same characteristics visually and haptically.
The shaped body preferably consists of an expandable polystyrene. The shaped body can have a covering of an elastomeric plastic foil or of an elastomeric plastic net.
Toluene, xylene or methylene chloride come into consideration as solvents for the shaped body.
Thus, the invention provides a method by which not only can the difficulties which were initially mentioned be overcome, but which rather is also extremely flexible and reliable in operation.
REFERENCES:
patent: 4863771 (1989-09-01), Freeman
patent: 5207964 (1993-05-01), Mauro
patent: 5560264 (1996-10-01), Xolin et al.
patent: 5792302 (1998-08-01), Nakada et al.
patent: 5804121 (1998-09-01), Gallagher
patent: 5921312 (1999-07-01), Carden
patent: 6098286 (2000-08-01), Kreuzer
Kuhns Allan R.
Tarolli, Sundheim, Covell Tummino & Szabo L.L.P.
TRW Automotive Safety Systems GmbH & Co. KG
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