Metal gaskets

Details Metal gaskets Metal gaskets

1999-08-03

2002-01-08

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

59

Reexamination Certificate

active

06336639

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a metal gasket for sealing between confronting surfaces of the cylinder block and the cylinder head in the engine and, more particularly, to the metal gasket composed of carrier plate with beads thereon and a stopper plate with folded constructions thereon.
2. Description of the Prior Art
Conventionally, the metal gaskets have been widely applied to the engines in sealing between a cast-iron cylinder block, which is less in both of wall thickness and weight, and an aluminum cylinder head of less weight and also in sealing between the aluminum-made block and head. In prior metal gaskets of various types, a metal gasket has been well known to those skilled in the art, which includes a stopper plate having folded constructions to help ensure what is referred as “compression stopper function”, which protects a bead carrier plate from a permanent set or flattering out owing to the excessive compressive loading or stress. The exemplary metal gaskets having the compression stopper function are disclosed in Japanese Utility Model Laid-Open Nos. 170053/1985; 118147/1989; 118148/1989; 134761/1989 and Japanese Patent Laid-Open Nos. 255253/1986; 101575/1988 and 15372/1992. Although the folded constructions in the prior metal gaskets disclosed in the above citations have for their objects to achieve the functions or effects of compression stopper as well as air-tight sealing, there has been heretofore disclosed no concept or consideration as to what change happens at a gap in the folded construction during engine operation, or how relationship is present between the degree or effect of the gap and the structure or material of the engines.
Experimental data required for the design of metal gasket have been commonly obtained by measuring the deformation in the cylinder head when the cylinder bores have been repeatedly compressed and decompressed, on the assumption that the cylinder block may be considered an absolute or ideal rigid body and, therefore, only the cylinder head is subject to the deformation due to the engine operation. As an alternative prior art to gain the data for the metal gasket design, the thermal deformation of the cylinder head has been measured, which takes place when the cylinder head is heated up to a high temperature.
Nevertheless, the prior experimental data heretofore prevailed for the design of metal gasket, whether it depends on variation in pressure or in temperature, belongs to the data as to the static deformation and, therefore, fails in measuring the simulation of the phenomenon, which may come into action in the metal gasket, accompanied with the deformation which might occur in the cylinder block when the metal gasket is squeezed interposed between the mating cylinder block and head, the permanent distortion which might exerted on the cylinder block owing to undue thermal stress or fatigue as a result of the engine operation, and the intolerable clearance caused between the gasket and the cylinder block by the distortion in the cylinder block or head. That is to say, any prior experience for the design of the metal gasket has provided no data representing the true behavior on the deformation of the metal gasket, which fairly reflects the operating conditions of the engine. Moreover, the state of the art in metal gaskets has recently progressed in the theoretical analysis technique on an aspect of dynamics of structure in accordance with the finite-element method, whereas there is scarcely any experimental data about the behavior of the metal gasket, which is in compliance with the behavior of the distortion occurring in the cylinder head under the test of actual engine performance. Thus, such prior state of the art in metal gaskets has been quite insufficient to design and produce the metal gaskets rich in reliability.
Referring to
FIG. 19
in which a conventional metal gasket is shown placed between confronting surfaces of a cylinder head
20
and a cylinder block
21
, which are made of either aluminum alloy or thin cast iron, the metal gasket is composed of a pair of carrier plates
22
,
24
having thereon with corrugations, or beads, not shown, and a stopper plate
23
partially folded back so as to have flanges
25
that are made in face-to-face close engagement with any one surface of the major portion of the stopper plate
23
. When squeezing or tightening the metal gasket constructed as described above between the mating surfaces of the cylinder head
20
and the cylinder block
21
, the cylinder block
21
is often rendered deformed at
36
, or at peripheral edges around cylinder bores in the cylinder block
21
, which may results from either the thermal stress or the fatigue owing to the engine operation. This causes the permanent set or permanent strain in the associated carrier plate
24
of the metal gasket, resulting in causing intolerable clearances
36
S between the associated plates of the metal gasket. Thus, the metal gasket is made inferior in sealing performance and, in some cases, damaged by cracks or the like, which may be caused at beads formed on the carrier plates
22
,
24
. It will be noted that the cause of the problem involved in the prior metal gasket is somewhat exaggerated in schematic view of FIG.
19
.
The major sources of the damages occurring in the prior metal gaskets may be considered as follows. In the stopper plate incorporated in the prior metal gasket, in which the folded flanges are made in face-to-face close contact with the major portion of the stopper plate around the entire periphery of the cylinder bores, the folded constructions are designed so as to become relatively higher in strength, so that they remain in substantially horizontal state they have been placed on the deck surface of the cylinder block, even under the thermal stress during the engine operation. Thus, the folded constructions may not help compensate for undue clearances that might happen between the bottom surface of the metal gasket and the mating deck surface around the peripheral edges of the cylinder bores. It would seem most fitting that such undue clearances grow into permanent set or permanent distortion in the bead carrier plates, resulting in the occurrence of intolerable clearances either between any adjoining metal plates or between the cylinder block and its associated bead carrier plate. Moreover, in case where the intolerable clearances occurring in the metal gasket result in increasing excessively the intervals of gaps in the folded constructions of the stopper plate and also the strength of the folded constructions is too inadequate for compensating for the intolerable clearances, a serious problem arises in which the engine operation as in starting the engine causes repeatedly a vicious spiral of premature loss of the gaps, permanent set in fatigue of the beads, reduction in compressive force of the tightening bolts, increase in distortion of the cylinder head and propagation of the permanent set, thus resulting in making it much more difficult to compensate for the changes of the clearances between the cylinder block and the head. This causes cracks at the beads of the carrier plates, which are thus subject to the corrosion at the beads by the gases leaking out of the cracked beads with the result of the failure in sealing performance of the metal gaskets. The problem described just above will become increasingly critical under any situation where the compressive forces of the tightening bolts are considered less or the counter-bores are less in depth.
In a metal gasket a stopper plate is partially folded back to thereby form the folded constructions for providing the compression stopper function, the folded constructions are simply twice as thick as the stopper plate. The folded constructions of twice thicker than the stopper plate itself, in some cases, are too sufficient for the compressive stopper function, instead, may cause sometimes the stress concentration of the compressive surface-to-surface pressure at the areas around the

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