Land vehicles: bodies and tops – Bodies – Structural detail
Reexamination Certificate
1999-10-21
2002-12-31
Patel, Kiran (Department: 3612)
Land vehicles: bodies and tops
Bodies
Structural detail
C296S214000, C296S210000, C296S901010
Reexamination Certificate
active
06499797
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a sandwich structure for vehicle bodies, in particular for flat areas of a vehicle including which require sufficient rigidity and good thermal and sonic insulation.
In order to achieve sufficient rigidity in the case of prior art construction of a roof (GM 79 29 367 U1), an initially separate semi-finished profile frame, rigid with respect to torsion, must first be prepared and must then be irremovably fastened to the outer skin of the roof along its edges. The foamed on plastic layer covers the semi-finished product profile frame connected irremovably to the skin of the roof. If the skin of the roof consisting of light metal or plastic is to be effectively made rigid with respect to bending, according to the known proposal, at least one profile strut extending transversely to the longitudinal beams of the semi-finished product profile frame must be provided. The prior art construction of such a roof requires a significant expenditure in material and production.
The corresponding description applies to the sandwich structures for the bodies of vehicles known from GB 2 311 966 A. According to this state of the art, an outer shell and an inner shell for the sandwich structure are produced from plastic by means of injection molding, and connected firmly and tightly to one another in a subsequent step by a plastic welding process or by the application of adhesive along their edges. Then the hollow body so formed is filled with plastic and allowed to harden. Alternatively, a filling body can be prepared in advance which is inserted between the outer and the inner shells when they are connected together. For higher rigidity requirements, reinforcing parts of aluminum must be inserted in the cavity between the outer and inner shells provided the outer shell is formed with channels for accommodating such reinforcing parts.
Finally, roofs of composite material are also known (DE 32 02 594 C2) that are composed of an airtight and rain-tight outer skin, a central honeycombed/structural layer with aluminum or cardboard webs or moderately hard foam and fleece structures, a partly rigid, porous inner layer, and a cushion and/or decorative layer, and produced by means of a hot pressing process.
SUMMARY OF THE INVENTION
In general terms, this invention includes a sandwich structure for a vehicle body. The structure has a deep-drawn outer skin and, foamed onto the inner side of the outer skin, a plastic layer which is provided, if necessary, with a textile flat pattern or a decorative plastic film on its upper surface, the outer skin is formed without a frame at its outer edges, and is provided with an encircling canting where the foamed-on plastic layer reaches up to the canting, and in the foamed-on plastic layer a sheathing—not rigid in itself—is provided over the entire flat area of the outer skin by which method the modulus of elasticity of the foamed-on plastic layer is increased.
According to the invention, a sandwich structure for the body of a vehicle is provided without additional expensive profile elements for frames and struts, but which nonetheless, due to the effect of the outer skin and sheathed plastic layer, achieves a rigidity with respect to bending and total rigidity that satisfies all the stability requirements of the sandwich structure for the operational demands of the vehicle. The sheathing is not rigid in itself—set within the plastic layer makes possible an effective sheathing of the plastic layer up to into the edge areas of the outer skin when formed with an encircling canting in a certain way.
Textiles, knitted materials, fleece, grids, mats, and so on such as glass, plastic (for example, polyester or aramide), and/or carbon fibers which are bendable or not rigid in themselves come into consideration as sheathing to the extent that they are adapted to the form of the outer skin into their edge areas, and can be penetrated and encircled by the foamed-on plastic in the closed foaming tool. Preferably, however, fibrous materials are used for the formation of the sheathing that are incorporated into the plastic layer as sections of fiber lengths in uniform distribution but in unordered position.
Particularly good results were achieved by the use of a sheathing of fiberglass materials that are present in longitudinal sections of twisted fiberglass bundles of ca. 4,800 TEX between ca. 12 mm and ca 100 mm in length. The modulus of elasticity of the foamed plastic material, which has a value of ca. 300 N/mm
2
without this sheathing, could be increased to over 1600 N/mm
2
according to claim
4
with the application of a fiberglass sheathing of 25 wt % with respect to the total weight of the sheathed plastic foam.
The fiberglass materials can be used in longitudinal sections of different lengths where particularly good sheathing results have been achieved by the use of two different lengths with a larger percentage on the smaller length, about two thirds of the amount of fiberglass. In the scope of the range of longitudinal sections, however, longitudinal sections of a single length can also be used.
Metallic materials such as steel or aluminum sheets are suitable for the outer skin. However, the use of an outer skin of thermoplastic plastic film, deep-drawn in a vacuum, preferably of a two-layer co-extrusion film, yields a sandwich structure of convincing stability.
The co-extrusion film advantageously includes PMMA for the outer layer as well as a mixture of PC and ASA for the inner layer, and has the layer thickness ratios specified whereby the thickness of the outer layer preferably makes up about 15% of the total thickness of the outer skin. For example, the total thickness of the co-extrusion film is about 1.3 mm of which about 0.2 mm is due to the outer layer.
The use of a plastic also offers the advantage that the plastic in the mass can be prepared in the color desired such that the sandwich structure does not have to be retroactively lacquered. The plastic film can furthermore be given a shining surface by use of a high-gloss, polished, deep-drawn form in the form of a shell or a grained surface by previous calendering during the production of the outer skin.
If the outer skin is formed of a thin aluminum sheet, its thickness can be relatively small because of the sheathed plastic layer, preferably ca. 0.6 mm in the interest of conserving weight. For the outer skin the aluminum alloy 0.4 Si 1.2 is particularly suitable.
With the use of an aluminum sheet as material for the deep-drawn outer skin, the sheet can be lacquered ready-made in the desired color through its hydraulic deep-drawn deformation, and provided with a protective film. In the case of the deep-drawn deformation, the lacquer layer remains undamaged after withdrawal of the protective film. The lacquer structure can be multi-layered to withstand the deformation of the aluminum sheet with tears or other damage.
A covering polyester-based lacquer of about 18 to 23 um in thickness can be applied, which in turn can be covered by a clear lacquer layer of PVDF of 22 um thickness to a primary layer of epoxy resin of about 5 to 7 um in thickness a covering lacquer on the basis of polyester of about 18 to 23 um in thickness. The burning in temperature for a multi-layer lacquer structure of this type is about 240° C. The hydraulic deep-drawn deformation of the ready made lacquered aluminum sheet can be done in several steps, for example in three steps. Deep-drawing rates of 60 mm/s have proven themselves as non-damaging for the lacquer structure.
Canting the outer skin before trimming the edges passes into an encircling flange edge angled outwards such that the sheathed plastic layer is guided on the canting up to the flange edge. The trimming of the edge of the sandwich structure, for example by contour cutting or laser section, removes the encircling, angled off flange edge and the outer area of the canting of the outer skin, as well as the sheathed plastic layer adhering to the areas sloping away near it. A canting edge of the outer skin, important for r
Becher Thomas
Böhm Horst
Grimm Rainer
Carlson & Gaskey & Olds
Meritor Automotive GmbH
Patel Kiran
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