Seal for a joint or juncture – Seal between fixed parts or static contact against... – Contact seal between parts of internal combustion engine
Reexamination Certificate
1999-02-22
2001-06-26
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
Reexamination Certificate
active
06250644
ABSTRACT:
The present disclosure relates to the subject matter disclosed in German Application No. 198 08 544.3 of Feb. 28, 1998, the entire specification of which is incorporated herein by reference.
The invention relates to a so-called metal-layer cylinder head gasket, the gasket plate of which is formed by at least three layers, namely by two external metal layers (referred to in the following as outer layers) and at least one inner layer arranged between these outer layers. The invention relates, in particular, to cylinder head gaskets of this type for commercial vehicle engines.
The gasket plate of such a cylinder head gasket has one or more combustion chamber apertures as well as one or more fluid apertures for the passage of lubricants and/or coolant and is provided with a combustion gas sealing system around the combustion chamber aperture as well with a fluid sealing system around the fluid aperture. In the case of current metal-layer cylinder head gaskets, the combustion gas sealing system is formed by a full bead (i.e. a bead with an approximately U-shaped cross section) of an inner layer of the gasket plate, this bead surrounding the combustion chamber aperture, by the edge regions of the two outer layers of the gasket plate covering this bead and extending around the combustion chamber aperture as well as by a combustion chamber border; the latter is either a sheet-metal strip, which is approximately C-shaped in cross section, extends around the combustion chamber aperture and engages over the specified edge regions of the outer layers as well as the bead of the inner layer, or a free edge strip of the one outer layer, which extends around the combustion chamber aperture and has been folded through 180° such that it engages over the edge region of the other outer layer surrounding the combustion chamber aperture as well as the bead of the inner layer. In order to form the fluid sealing system the outer layers of the current metal-layer cylinder head gaskets are provided with beads which surround the relevant fluid aperture and are supported, on the one hand, (when the gasket is fitted) against the adjacent sealing surface of the cylinder head or engine block and, on the other hand, against an inner layer of the gasket plate. Beads provided in the outer layers at a distance from the combustion chamber apertures do, however, result in disadvantages:
During operation of the engine, so-called vertical sealing gap movements occur, i.e. the size of the gap between the sealing surface of cylinder head and engine block accommodating the cylinder head gasket is not a constant size during operation of the engine, and these vertical sealing gap movements are all the greater, the greater the distance of the location of the sealing gap under consideration from the cylinder head bolts. This does not, however, apply for the areas of the gasket plate immediately bordering on the combustion chamber apertures since metal-layer cylinder head gaskets are dimensioned in the area of the combustion gas sealing systems such that the greatest, specific surface pressures occur there in any case in order to prevent leakages being able to occur between the cylinder head gasket and the cylinder head or the engine block in these areas during operation of the engine. A bead, which is used in an outer layer of a metal-layer cylinder head gasket for sealing a fluid aperture and is intended to seal in a fluid-tight manner when a gasket is installed (i.e. when this is clamped between cylinder head and engine block) on account of its elastic spring-back resilience capability, does, however, lead to vertical sealing gap movements resulting in horizontal displacement movements between the bead and the cylinder head or the engine block. This also applies for so-called semi-beads (beads with a cross section which is similar to a Z or an S lying on its side) which are preferred for sealing fluid passages in the case of cylinder head gaskets for modern engines since a semi-bead requires less space (measured in the plane of the gasket plate transversely to the longitudinal extension of the bead) than a full bead and often very little space is available between the apertures in these engines. The result of these horizontal displacement movements is channels worn into the sealing surfaces of cylinder head and engine block, even when these engine components do not consist of a light-metal alloy but cast iron. In this connection, it must be borne in mind that the areas of contact between the beads and the sealing surfaces of motor engine and cylinder head, which bring about the sealing effect, have a more or less linear configuration and in these areas of contact relatively high, specific surface pressures exist which lead to appearances of wear and tear on the sealing surfaces of engine block and cylinder head, i.e. to the channels mentioned, when the horizontal displacement movements described above occur. Channels of this type do, however, result not only in the disadvantage that leakages can occur because a stationary state cannot be attained in the specified areas of contact during operation of the engine but also during replacement of the cylinder head gasket the sealing surfaces of cylinder head and engine block must always be machined in order to remove these channels and again provide absolutely flat sealing surfaces.
Unevenness, namely indentations in the sealing surfaces of cylinder head and engine block, which have to be eliminated during replacement of the cylinder head gasket by way of machining the sealing surfaces, also result, however, from the combustion chamber borders, which are C-shaped in cross section, of the known metal-layer cylinder head gaskets described above since, as already mentioned, the specific surface pressures around the combustion chamber apertures of the cylinder head gaskets are particularly great.
The object underlying the invention was to provide a metal-layer cylinder head gasket, with which it is possible to reduce or even eliminate those problems which are caused during use of the known cylinder head gaskets described above due to alterations in the sealing surfaces of engine block and cylinder head, and, where applicable, even in the case of those engines, in which the engine block is provided with liners, the upper end faces of which form parts of the sealing surface of the engine block.
The invention is based on a cylinder head gasket with a gasket plate which has several metal layers placed on top of one another, at least one combustion chamber aperture as well as at least one fluid aperture and is provided with a combustion gas sealing system around the combustion chamber aperture as well as with a fluid sealing system around the fluid aperture, wherein two external metal layers (outer layers) of the gasket plate enclose between them at least one inner metal layer (inner layer) which has a bead which surrounds the fluid aperture and is supported against two adjacent metal layers when the gasket is fitted.
Such a cylinder head gasket is designed in accordance with the invention to accomplish the set object such that
(a) the inner layer is such a spring-steel sheet metal layer that its bead is stressed at least predominantly in the elastic range when the gasket is fitted and thus can compensate for vertical sealing gap movements essentially by way of its spring-back resilience properties;
(b) the bead is a semi-bead forming a closed ring with a cross section similar to a step or approximately Z-shaped (or a cross section similar to an S lying on its side), and
(c) the outer layers are designed over the two entire main surfaces of the gasket plate as smooth and flat sheet metal layers and form these main surfaces.
In the case of an inventive cylinder head gasket, the fluid-tight sealing around a fluid aperture does not take place between the bead of the fluid sealing system and the sealing surface of the cylinder head or engine block but between this bead and the adjacent metal layer of the cylinder head gasket, and the horizontal displacement movements described above also
Biedermann Martin
Diez Armin
Schweizer Peter
Staib Ulrich
Elring Klinger GmbH
Knight Anthony
Schwing Karlena D.
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