Land vehicles – Wheeled – Attachment
Reexamination Certificate
2000-11-20
2001-11-20
Dickson, Paul N. (Department: 3618)
Land vehicles
Wheeled
Attachment
C280S732000
Reexamination Certificate
active
06318752
ABSTRACT:
The invention relates to an instrument panel made from thermoplastic material for a motor vehicle, having an invensible cover for an airbag system which as seen from the interior of the motor vehicle, is arranged behind the instrument panel.
BACKGROUND OF THE INVENTION
In the following text, the term “instrument panel” is to be understood as meaning a shell structure which defines the visible side of a vehicle cockpit and generally bears control elements and display instruments. Vehicle cockpits with corresponding instrument panels are described, for example, in DE 34 47 185 A1 and EP 0 515 287 A1. In this prior art, the instrument panels comprise a supporting, dimensionally stable carrier part which, on the visible side, is generally laminated with a decorative plastic film. It is also customary to lay a foam cushion beneath the decorative film of the lamination, over the entire surface or in some areas, in order to achieve a pleasant handle (feel). The carrier parts are manufactured from different materials: rigid foam shells with a foamed-on lamination, injection-molded thermoplastic shells and shaped wood fiber parts are usual.
Since the introduction of the airbag, the instrument panel has had the additional role of covering the passenger airbag in a visually appealing form without limiting its function. There is an increasing demand for the airbag system to be impossible to pick out on the visible side of the instrument panel (so-called “invisible” airbag). For this purpose, the instrument panels have a U-shaped or H-shaped notch on the rear side in the opening area of the airbag, so that the expanding airbag can open one or two flaps. In this arrangement, either the material of the carrier part itself and/or a separately arranged component serves as a “plastic hinge”. By way of example, please refer to DE 36 11 468 A1. The airbag system also includes a guide connection piece for the expanding airbag, the so-called ejection channel, which is usually a separate component which may be prefitted on the instrument panel. Manufacturing instrument panels as a thermoplastic injection molding makes it possible, with simple vehicle equipment, to dispense with lamination of the instrument panels, for example in favor of surface structuring (leather grain effect or the like). However, with unlaminated instrument panels there are difficulties with attaching additional elements, for example with prefitting an ejection channel for the airbag. Only those joining processes which do not form a disruptive presence on the visible side (adhesive bonding, welding) are suitable, thus limiting design and manufacturing options. In addition, a very wide range of requirements are imposed on the material properties of the instrument panel itself, of the ejection channel and the opening area for the invisible airbag. The instrument panel should not become brittle at cold temperatures, but should remain dimensionally stable at elevated interior temperatures; the material must therefore not be excessively flexible, while there are no excessively great demands placed on its tensile strength. On the other hand, the hinge area of the opening flaps of the invisible airbag system should be as flexible as possible, so as to be able to fulfill the appropriate function. The ejection channel should have a high strength and be rigid. The moduli of elasticity, the elongation at break and the tensile strength of said elements of an instrument panel with an invisible airbag are therefore required to differ greatly. In practice, materials which also differ are used, but this has the drawback of making recycling more difficult and more expensive. Furthermore, the lack of uniformity of the materials makes it more difficult to use unlaminated instrument panels, in which joining components using rivets or screws on the visible side is undesirable, even though the manufacture of thermoplastic injection moldings is economically beneficial and leaves a great deal of design freedom.
SUMMARY OF THE INVENTION
Therefore, the invention is based on the object of providing an instrument panel made from a thermoplastic material which makes it easy to fit an invisible airbag and which can be recycled more easily.
This object is achieved by means of the features described hereinafter, including specified advantageous refinements of the instrument panel according to the invention.
By providing a rear-side cross-sectional weakening in the instrument panel, weakening which defines an opening area in the instrument panel for the airbag and completely surrounds the opening area, i.e. a continuous desired breaking location, which does not come into view on the visible side, the opening area of the airbag is thrown off completely, as a cover, when the airbag is actuated. This has two advantages:
The material of the instrument panel does not have to be adapted to properties of a plastic hinge, but rather may be of the rigidity which is required to achieve dimensional stability under hot conditions.
The risk which is present in conventional instrument panels with a U-shaped and H-shaped weakening, that uncontrolled cracks in the instrument panels will start from the ends of the weakened section, is no longer present.
An ejection channel which is prefitted on the instrument panel not only facilitates overall assembly of the instrument panel, but also makes it possible to securely attach the opening area, which can be thrown off as a cover, of the instrument panel for the airbag with the aid of a large-area integral polymer hinge (i.e. a plastic hinge). Prefitting the ejection channel and securing the integral polymer hinge to the “opening cover” of the instrument panel with the aid of large-area welded material ensures an unblemished visible side of the instrument panel, since in both cases the welding takes place on its rear side. The integral polymer hinge does not necessarily have to be attached to the ejection channel exclusively by means of welded material; for example, it may be expedient to use screws and/or rivets as additional securing means; since the ejection channel is arranged on the rear side, there is no effect on the visible side. To achieve a secure welded joint, according to the invention, the instrument panel, ejection channel and integral polymer hinge comprise a thermoplastic of the same polymer base, but differently flexibilized. The uniform polymer base ensures that all the components can be welded together without problems, while the possibility of different degrees of flexibilization by compound formation (chemical combination of materials, copolymer) make it possible to provide the integral polymer hinge with an elongation at break of up to, for example, 300% and thus to reliably prevent the “opening cover” from tearing off. An adapted mineral filling of the thermoplastic matrix makes it possible to produce the required dimensional stability of the instrument panel under hot conditions; in the case of the ejection channel, which is the component which is subject to the highest mechanical loads when the airbag is triggered, a fiber reinforcement provides the increased strength given a low level of flexibilization of the base polymer. A suitable polymer base is, for example, polypropylene, which has an advantageous price to properties ratio; for the copolymer formation for flexibilization purposes, the prior art offers sufficient possible options; one example which may be mentioned is ethylene/polypropylene diene (EPDM). While for the integral polymer hinge it is possible to achieve elongations at break of up to 300% by means of flexibilization, the level of flexibilization of the instrument panel itself is lower; in this case, the flexibilization should be just sufficient to avoid brittle fractures at low temperatures (winter temperatures). For this purpose, the thermoplastic of the instrument panel may contain a mineral filling, for example talc, of 15-20% by weight, in order to ensure dimensional stability under hot conditions. Like the instrument panel, the material of the ejection channel has an equally low leve
Flick Andreas
Grübler Günter
Kunkel Thomas
Warnecke Frank
Dickson Paul N.
Sommer Allibert-Lignotock GmbH
Young & Basile P.C.
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