Seal for a joint or juncture – Seal between fixed parts or static contact against... – Contact seal between parts of internal combustion engine
Reexamination Certificate
2001-05-17
2003-03-04
Gall, Lloyd A. (Department: 3676)
Seal for a joint or juncture
Seal between fixed parts or static contact against...
Contact seal between parts of internal combustion engine
C277S591000, C277S592000, C277S594000
Reexamination Certificate
active
06527277
ABSTRACT:
The invention relates to a flat gasket for sealing a sealing gap between sealing surfaces of machine components which can be pressed against the flat gasket which comprises a gasket plate formed by a sheet metal layer.
The sheet metal layer forming the two main surfaces of the gasket plate of such flat gaskets is usually provided with beads at particularly critical places with respect to the sealing function where an increased sealing surface pressure is to be generated between the flat gasket and the sealing surfaces of the machine components which are to be sealed off from one another. However, such beads have proven inadequate at places where the machine component sealing surfaces, between which the flat gasket is clamped, are uneven, for example, have steps, as is the case when with a machine component sealing surface resting against the flat gasket there are several, for example, two, sealing surface areas which are formed by several separate machine components resting against one another in the area of this step, i.e., forming a joint—at such joints manufacturing and/or assembly tolerances can result in a step in the said sealing surface.
This problem typically occurs with flat gaskets in the form of cylinder head gaskets for reciprocating internal combustion engines with an, in particular, multipart chain case which is likewise to be sealed off by the cylinder head gasket, because in this case the two machine component sealing surfaces between which the cylinder head gasket is clamped, are formed, on the one hand, by the cylinder head and a chain case top part, and, on the other hand, by the engine block or crankcase and a chain case bottom part—with such an engine construction there is both a joint between the cylinder head and the chain case top part and a joint between the engine block and the chain case bottom part. However, the top part of the chain case can also be formed by the cylinder head so that there is no separate chain case top part, or the bottom part of the chain case can be formed by the engine block so that there is no separate chain case bottom part. Nevertheless, a joint still results in the bottom or top one of the sealing surfaces between which the cylinder head gasket is clamped.
Several solutions to the above-described problem caused by joints are to be found in the prior art:
EP-A-0 059 777 discloses a single-layer, metallic flat gasket for a multipart gear housing with a housing top part and a housing bottom part, between which the flat gasket is clamped. The housing top part itself is made up of several parts so that joints result in the sealing surface of the housing top part which has to be pressed against the flat gasket, and these can lead to steps in an area of the sealing surface. For this reason, the flat gasket has an elongate, slot-shaped opening, which extends over all these joints when the gasket is installed and into which a strand-shaped, elastomeric sealing element is placed, which projects on both sides above the two main surfaces of the flat gasket and is made as a prefabricated insert.
Solutions to the above-described problem for cylinder head gaskets which also serve to seal off a chain case are also to be found in the prior art:
DE-C-43 37 758 shows a multilayer, metallic cylinder head gasket in which prefabricated elastomeric sealing elements are inserted, more specifically, at places on the cylinder head gasket which each lie over a joint between engine block and chain case. In a first, four-layered embodiment of this cylinder head gasket, each of the sealing elements has an approximately T-shaped cross section with a sealing portion and a head portion which is thickened in relation to the latter and serves to fix the sealing element in the cylinder head gasket. For this purpose, the two center layers have for each sealing element rectangular, window-like openings lying above one another for receiving the head portion of the respective sealing element, while the one cover or outer layer is closed in the area of the sealing elements and the other cover layer has for each sealing element a rectangular, window-like opening through which the sealing portion of the sealing element engages and which is smaller than the openings of the center layers and the cross section of the head portion. In the unpressed state of the cylinder head gasket, the sealing portions of the sealing elements already project to a considerable extent beyond the cover layer provided with the openings. In a second embodiment of this known cylinder head gasket, which has three layers, all three layers have at the locations of the sealing elements rectangular, window-like openings lying above one another, and the openings of the center layer are somewhat larger than the openings of the cover layers, which are of the same size, so that the sealing elements are held securely against displacements between the cover layers with central areas of increased diameter. In this second embodiment, too, the sealing elements already project beyond the one main surface of the gasket in the unpressed state of the cylinder head gasket.
Finally, EP-B-0 701 051 discloses a multilayer, metallic cylinder head gasket which also serves to seal off a chain case. The gasket plate of this cylinder head gasket has a relatively thick center layer and two relatively thin outer layers, which are each provided with a so-called half bead, which extends around the chain case opening as a bead line closed within itself (in contrast to full beads of approximately U-shaped cross section a half bead has a cross section which corresponds to a step or Z pulled more or less flat). Beside each of the two narrow sides of the chain case opening the center layer has a cutout in the form of an elongate, rectangular window, which extends parallel to the adjacent narrow side of the chain case opening, and a prefabricated, strand-shaped, elastomeric sealing element which is inserted with play in the respective window and projects on both sides over the two main surfaces of the center layer (already prior to installation of the cylinder head gasket, i.e., while it is unpressed). One of the outer layers is closed over the sealing elements, i.e., continuously, while the other cover layer has a large, approximately rectangular window which is larger than the chain case opening and exposes the two sealing elements, i.e., in a plan view of the cylinder head gasket, the two sealing elements lie within this window. EP-B-0 701 051 does not explain how with this known cylinder head gasket the two sealing elements are to be prevented from falling out of the gasket during handling thereof. Furthermore, this known cylinder head gasket is only able to partly solve the problem explained at the outset when in the machine component sealing surfaces to be pressed against the cylinder head gasket, there are joints on both sides of the cylinder head gasket because the chain case is comprised of a chain case top part and a chain case bottom part. Moreover, as will be apparent from the following, this known gasket can also lead to problems when on the side of the outer layer provided with the windows there is a chain case part which is inserted from the side during assembly thereof.
When assembling engines with a chain case comprised of a top part and a bottom part, it has already been attempted to solve the problem set forth at the outset by providing the cylinder head gasket on either side of the chain case opening with a relatively small, oval hole which passes through all layers of the multilayer metallic cylinder head gasket and into which an initially viscous sealant is injected in the course of assembly of the engine, which can be cured to an elastomeric material at elevated temperatures, for example, when the engine is first put into operation. It is, however, obvious that such a procedure when assembling the engine in series production is unsatisfactory for several reasons: Today, vehicle manufacturers tend to delegate as many work steps as possible to their suppliers, and in series production it is also difficult,
Elring Klinger AG
Gall Lloyd A.
Peavey Enoch
LandOfFree
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