Seal for a joint or juncture – Seal between fixed parts or static contact against... – Contact seal between parts of internal combustion engine
Reexamination Certificate
1999-12-21
2002-02-05
Knight, Anthony (Department: 3626)
Seal for a joint or juncture
Seal between fixed parts or static contact against...
Contact seal between parts of internal combustion engine
C277S594000, C277S596000
Reexamination Certificate
active
06343795
ABSTRACT:
The invention relates to a flat gasket, in particular, a cylinder head gasket which has a gasket plate with at least one aperture and at least one sheet-metal layer which is provided with a bead surrounding the aperture as well as with a stopper device which prevents any excessive bead deformation and consists at least substantially of an elastomeric material which is arranged in the recess formed by the bead and fills the recess at least over part of its depth.
In the case of flat gaskets, the gasket plate of which is formed by one or several sheet-metal layers placed one on top of the other, beads surrounding apertures in a sheet-metal layer having elastic properties (customarily consisting of spring steel sheet) serve to seal against gases or liquids in that such a bead is pressed resiliently against another sheet-metal layer of the gasket plate or against components which are to be sealed in relation to one another, such as engine block and cylinder head, with the bead ridge, on the one hand, and with the two, so-called bead feet, on the other hand. Particularly in the case of cylinder head gaskets there is the risk that cracks will form in the bead during the course of operation because the width of the sealing gap between engine block and cylinder head to be sealed by the cylinder head gasket alters continuously during operation of the engine and, consequently, such a bead is constantly stressed dynamically; in order to prevent such a bead from deforming to too great an extent, i.e. from being flattened, during installation of the seal and/or during operation, so-called stoppers or stopper devices are allocated to the bead and these consist, for example, of a sheet-metal ring adjacent to the bead and welded onto the beaded sheet-metal layer, the thickness of the sheet metal of this ring being considerably less than the height of the non-deformed, i.e. non-stressed bead — the stopper then prevents any excessive bead deformation and is intended to ensure that the bead is, during operation, always deformed and stressed in the elastic range.
Stopper devices of the type mentioned at the outset are, however, already known in the form of a rubber ring which is inserted into the recess formed by the bead and completely fills this recess (cf.
FIG. 9
of DE-28 49 018-C); as a result of the rubber ring, the degree of bead flattening during the installation of the gasket is intended to be reduced, and polymeric material squeezed out of the bead during the installation of the gasket is intended to improve the microsealing (since rubber is an incompressible material and the bead is unavoidably flattened to some extent during the installation of the gasket, some of the material of the rubber ring will, in any case, be squeezed out of the bead during the installation of the gasket).
A similar stopper device is disclosed in EP-O 866 245-A (cf. in this case, e.g., FIGS. 3, 5, 6 and 8 to 13), wherein the stopper function is undertaken by a rigid or rather stiff ring arranged in the bead and consisting of a resin (annular rigid resin layer) which fills the recess formed by the bead over approximately half its depth.
In the case of cylinder head gaskets, it has, however, been shown that during operation of the engine bead ruptures attributable to a crack formation cannot permanently be prevented even with stopper devices of this type, provided that another, additional stopper device, e.g., in the form of the sheet-metal ring described above is not present—if, however, such an additional stopper device is used, filling of the bead with elastomeric material is superfluous. The cramped space conditions often found in modern engines for cylinder head gaskets make it seem, however, to be often advisable (or even make it imperative) to do without a stopper to be arranged next to the bead.
The object underlying the invention was therefore to improve a flat gasket of the type mentioned at the outset, as known, for example, from DE-28 49 018-C, such that the endurance strength of a bead can be considerably increased in relation to dynamic stresses at right angles to the plane of the gasket plate even when dispensing with an additional, different stopper device, namely also during the occurrence not only of very slight bead deformations (flattenings).
During their efforts to solve this object the inventors have established completely surprisingly that a complete or partial filling of the bead with an elastomeric material is successful when this displays under pressure and at operating temperatures (temperatures at least corresponding, however, to the ambient temperature) flow properties (capability of plastic deformation) which are considerably above those of completely cross-linked polymeric materials. In order to delimit the present invention in practice by means of a measurement of the material properties in relation to the known state of the art, the following definition of the material properties can, in particular, be used:
The elastomeric material should be plastically deformable under pressure at a temperature corresponding at least to the ambient temperature (21° C.) in such a manner that it has at least the following set-down behavior: With a vertical pressure load on a circular pressure-load area of a uniform, flat layer of the elastomeric material having an initial layer thickness of approximately 24 &mgr;m, wherein the pressure-load area has an outer diameter of 65.4 mm and an inner diameter of 64.6 mm and the pressure load is 40 N per mm
2
of the pressure-load area, the layer thickness of the elastomeric material in the pressure-load area at 21° C. after a pressure-load duration of approximately 0.5 hours is at the most only approximately 85%, preferably only approximately 83 to approximately 37%, of the initial layer thickness.
Tests on spring steel sheets, which are provided with a bead and the recess of which formed by the bead was completely filled in one case with an almost completely cross-linked elastomeric material and in the other case with an elastomeric material with a low degree of cross-linking, have surprisingly resulted in the bead being flattened, during a dynamic pressure load, i.e. a pressure loading of the bead with a pressure altering quickly with respect to time, as is the case for a cylinder head gasket during operation of the engine, to more than double the amount without tearing when the elastomeric material with a relatively low degree of cross-linking is used (in comparison with the elastomeric material which is cross-linked almost completely).
Preferably, the bead is a so-called full-bead with a cross-section similar to a flat U.
Elastomeric materials which are preferred for the inventive gasket have, under pressure, such flow properties that the layer thickness of the elastomeric material decreases rapidly with respect to time after pressure is applied and is scarcely reduced further after approximately 0.2 hours. Such preferred, elastomeric materials display, in particular, such a set-down behavior with respect to time that after a pressure-load duration of approximately 1 hour the layer thickness is at the most only approximately 80%, in particular only approximately 80% to approximately 35% of the initial layer thickness.
The invention has a particularly advantageous effect when the elastomeric material does not completely fill the recess of the bead when the bead is not yet compressed but only over such a part of its depth that when the gasket is installed but not yet dynamically pressure-loaded the recess formed by the bead flattened somewhat in accordance with the assembly forces which are always specifically predetermined is completely filled by the elastomeric material.
The elastomeric material can be applied to the beaded sheet-metal layer only in the bead area; embodiments are, however, preferred, with which the elastomeric filling of the bead is part of an at least partial coating of the sheet-metal layer which also extends on both sides of the bead; the sheet-metal layer can, therefore, also be completely coated with the elastomeric material, na
Anhorn Thomas
Baur Matthias
Diez Armin
Schenk Peter
Winkovic Victor
ElringKlinger AG
Knight Anthony
Leydig , Voit & Mayer, Ltd.
Peavey Enoch
LandOfFree
Flat gasket does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Flat gasket, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Flat gasket will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2965766