Seal for a joint or juncture – Seal between fixed parts or static contact against... – Contact seal between parts of internal combustion engine
Reexamination Certificate
2000-06-15
2002-02-26
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
Reexamination Certificate
active
06349945
ABSTRACT:
BACKGROUND OF INVENTION
The invention relates to cylinder head gaskets, with which at least the one side of the gasket plate, i.e. at least its one main surface, is formed by a sheet-metal layer.
Cylinder head gaskets of this type mainly have a gasket plate which has several sheet steel layers placed one on top of the other, of which one or more consists or consist of spring steel sheet and is or are provided with embossments serving as sealing elements which surround through openings of the gasket plate. The embossments may be so-called full bead embossments which are approximately trough-shaped or U-shaped in cross section or so-called half bead embossments which are approximately step-like or Z-shaped in cross section. If such a bead-like embossment is located on the outer side of the cylinder head gasket, i.e. the bead-like embossment is formed in an outer layer of the gasket plate, in the case of a full bead embossment this abuts against the cylinder head or the engine block either with the convex embossment ridge or with its two so-called embossment feet when the cylinder head gasket is fitted; in the case of a half bead embossment, a, to a certain extent, linear abutment of the embossed metal layer on the cylinder head or engine block likewise results in one of the areas of the metal layer, in which this has been bent to form the half bead embossment.
In the case of cylinder head gaskets, with which the main surfaces of the gasket plate are formed by one or more metal layers, it is customary to coat the metallic main surfaces of the gasket plate partially or completely with a plastic material having elastic properties, in particular, in order to prevent leakages in the area of pores and/or cavities in the surfaces (sealing surfaces) of engine block and cylinder head to be sealed in relation to one another for the purpose of the so-called microsealing. These coatings normally have a layer thickness of 18 to 28 &mgr;m and consist of an elastomeric material, the degree of cross-linking of which is so great that the coating has sufficient elastic properties for the microsealing.
During operation of the engine, the sealing surfaces of cylinder head and engine block adjacent to the cylinder head gasket carry out movement in a direction at right angles to these surfaces, i.e. the width of the so-called sealing gap formed by the specified surfaces alters during operation of the engine not only with respect to time but also spatially (as a result of the component rigidities of cylinder head and engine block which are not the same all over). During these variations in the width of the sealing gap occurring during operation of the engine, the sealing surfaces of cylinder head and engine block may lift away from the cylinder head gasket in certain areas, despite the spring-back resilience properties of the cylinder head gasket, which can lead to leakages in the area of the bead-like embossments despite the coating described above:
Chippings or other machining residues but also dirt particles can be flushed out of an oil or a refrigerant channel of the engine block or cylinder head during operation of the engine and washed onto a surface area of the cylinder head gasket, from which the adjacent sealing surface of the engine block or cylinder head has just lifted away. Machining residues or dirt particles can, however, already reach the bead-like embossment during the fitting of the cylinder head gasket and, irrespective of how and when they reached the bead-like embossment, certainly have such dimensions that they cannot be pressed and embedded completely into the plastic coating of the cylinder head gasket by way of the sealing surface pressure between the cylinder head gasket, on the one hand, and engine block or cylinder head, on the other hand, and consequently leakages result. This applies, in particular, for the area of a bead-like embossment surrounding an oil or refrigerant through opening of the cylinder head gasket since the plastic coating will already be displaced partially or even entirely in the area of the approximately linear sealing zone, in which the coated bead-like embossment is pressed against the cylinder head or engine block, during the fitting of the cylinder head gasket, i.e. during tightening of the cylinder head screws. If, for example, a metal chip reaches this sealing zone between the bead-like embossment and the cylinder head or engine block, a passage results on both sides of the chip which results in leakage.
If the bead-like embossment is a half bead embossment, this projects outwards—proceeding from the through opening to be sealed—, i.e. in the direction towards the cylinder head or the engine block. In the case of a full bead embossment, this can either likewise project outwards or point away from the sealing surface of the cylinder head or engine block with its convex embossment ridge so that the two embossment feet facing this sealing surface each form, when the cylinder head gasket is fitted, an approximately linear, self-contained sealing zone with increased sealing surface pressure. In the last-mentioned case, as well, the problem explained above exists that chippings or other machining residues or dirt particles can reach the embossment feet and result in leakages.
The same problems may, however, also result in the interior of the gasket plate of a cylinder head gasket, the gasket plate of which has several—at least two—metal layers, of which at least one has elastic properties and is provided with a bead-like embossment surrounding the through opening to be sealed since, during operation of the engine, chippings or the like can pass between the metal layers and then onto such an “interior” bead-like embossment because, during operation of the engine, two metal layers of a gasket plate can also be lifted away from one another in certain areas, namely also in the area of an embossment ridge or an embossment foot. It should also be mentioned that such an “interior” bead-like embossment can also be a full bead embossment or a half bead embossment.
SUMMARY OF INVENTION
The object underlying the invention was to prevent the disadvantageous results of such a leakage in cylinder head gaskets of the types described, brought about at a bead-like embossment by a particle contamination.
On the one hand, the invention proceeds on the basis of a cylinder head gasket with a gasket plate which has at least one metal layer with elastic properties, one side of which forms an outer side of the gasket plate, wherein the gasket plate has a through opening as well as a bead-like embossment surrounding the latter and formed in the metal layer, this bead-like embossment forming an approximately linear, self-contained sealing zone with increased sealing surface pressure on the outer side of the gasket plate when the gasket is fitted, and wherein the metal layer has a first coating consisting of a plastic material with elastic properties on the outer side of the gasket plate at least in the area of the sealing zone as well as to both sides of the latter.
To accomplish the object as set, such a cylinder head gasket is designed in accordance with the invention such that the metal layer is coated on the outer side of the gasket plate with a sealing bead closed upon itself, surrounding the through opening and consisting of a plastic material, this sealing bead being arranged on the side of the sealing zone facing away from the through opening as well as at a slight distance from the sealing zone, wherein the ridge or apex of the sealing bead is at a greater distance from the metal layer than the upper side of the first coating of the metal layer.
On the other hand, the invention proceeds on the basis of a cylinder head gasket with a gasket plate which has at least two metal layers, of which at least a first one has elastic properties, wherein the gasket plate has a through opening as well as a bead-like embossment surrounding the latter and formed in the first metal layer, this bead-like embossment abutting against the other metal layer when the gasket is fitted and th
Schenk Peter
Schmucker Frank
Beres John L.
ElringKlinger AG
Knight Anthony
LandOfFree
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