GB2124309A

GB2124309A - Cylinder head gasket for combustion engine

Info

Publication number: GB2124309A
Application number: GB08315545A
Authority: GB
Inventors: Hugo Eicher; Werner Klose
Original assignee: Sigri GmbH
Current assignee: Sigri GmbH
Priority date: 1982-06-19
Filing date: 1983-06-07
Publication date: 1984-02-15
Also published as: DE3223003A1; FR2528911B3; GB2124309B; FR2528911A1; GB8315545D0

Abstract

A cylinder head gasket 1 consists of a laminated graphite body 1%, 1_, 1>. The gasket is clad in the region of openings therethrough as a protection against the attack of combustion products. The thickness of the laminated body in these regions is less than the thickness of the unclad parts of the gasket at least by the thickness of the cladding 5. As a result of the stepped thickness of the gasket, the forces acting on the cladding 5 are reduced. <IMAGE>

Description

SPECIFICATION Cylinder head gasket for combustion engine This invention relates to a cylinder head gasket for an internal combustion engine.

Cylinder head gaskets consisting predominantly of asbestos have been subjected to increasing criticism on account of the possible damage they may cause to health. In addition, on technical grounds, these gaskets are not entirely satisfactory, in particular when subject to strong thermal stressing. Hence numerous other materials have been investigated alone or in combination for their suitability for use on manufacture of cylinder head gaskets. Cylinder head gaskets made of graphite foils possess a desirable thermal resistance and are insensitive to change in conditions to which they are subject.

Graphite foils are obtained in general from flakeshaped natural graphite which is reacted with acids acting in oxidising manner to form graphite intercalation compounds. The intercalation compounds are thermally decomposed, whereupon the particles expand to concertina shaped expanded forms and can then be rolled or pressed together without addition of binders to form flexible foils or laminated bodies. By the term laminated bodies is here understood shaped bodies which, on account of the direction in which the expanded particles lie, possess a marked optically recognisable layer structure and correspondingly vectoral properties, such as thermal and electric conductivity and the thermal expansion coefficient, which indicate a large degree of anisotropy (German Patent Specification 1,253,130).

It is additionally known to reinforce mechanically the laminated bodies by means of metal inlays in the form for example of wide mesh webs or thin perforated sheet metal with needle like attachments with a view in particular, to increasing the shearing resistance (German Offenlegungsschrift 25 18 351). Cylinder head gaskets formed of reinforced graphite laminate bodies are provided with a number of openings therethrough which will be aligned, in use, with the cylinder bores of the internal combustion engine and other bores or recesses which serve perhaps for the through passage of cooling or lubricating fluids.When the engine is operated, the openings corresponding with the cylinder bores are subjected in particular to considerable stressing as a result of periodic pressure and temperature cycles and the structural changes caused thereby favour the attach of the eroding, oxygen-containing combustion gases on the laminated bodies. In order to improve the resistance to oxidation of such cylinder head gaskets consisting of graphite laminate bodies, it is known from U.S. Patent Specification 3,841,289 to compress the laminated bodies to a greater density in a region annularly enclosing each cylinder bore than over the rest of the gasket.

One therefore ends up with a cylinder head gasket which possesses in the annular region a greater density than in the remainder of the gasket. On stressing, the overall gasket is compressed to the same thickness, with the annular gasket region being compressed more strongly, for example to almost 100% of the theoretical density. Such cylinder head gaskets are, on account of the greater erosion and oxidation resistance of the denser region, more resistant to working conditions without any need for the bearing pressure on the gasket to be essentially increased.

Cylinder head gaskets with compressed zones in the region of the bores and parts which face other recesses of the combustion engine possess in general sufficient service lives when subject to low and intermediate stressings. When in contact with combustion gases, which possess high oxygen and solids contents, the stability of the gasket is not sufficient. Under these conditions, it has been necessary to use cylinder head gaskets whose surface in the region of the openings is clad with thin metal layers or plates. Examples of such oxidation and erosion resistant ciaddings are galvanised or aluminium-plated steel sheets with a thickness of about 0.15 to 0.25 mm which are applied by the usual flanging methods to the cylinder head gasket. The gasket body is necessarily compressed more strongly in the clad or flanged regions in this procedure, than in the unclad regions of the gasket.The difference amounts, with the usual compression and thickness ratios to about 40 to 50% so that the restoring forces are greater in the clad region almost by about this amount. The stresses frequently cause the formation of cracks in the metallic cladding, which thereby loses its protective function.

According to the present invention, there is provided a cylinder head gasket for use in an internal combustion engine, which is formed from a laminated body made from a plurality of layers of flexible graphite, which comprises several openings intended to be aligned with the cylinder bores and with any other recesses present in the engine and which is provided in the region of said openings with a cladding for protecting the graphite against erosion and burn-off, the laminated body possessing in its clad parts a thickness which is less where the cladding is present than in the unclad part.

With a cylinder head gasket embodying this invention, should the thickness of the sheet metal forming the cladding amount for example to 0.2 mm, the thickness of the laminated body is, in the clad part, less by at ieast this amount than in the free part of the laminated body. It is preferred that laminated bodies are used which possess over the width of the cylinder head gasket a different number of graphite layers, so less layers are present in the clad parts of the laminated body and more layers are present in the unclad part. The laminated bodies with a stepped number of layers are appropriately produced by compression of expanded graphite particles in a die with use of profiled upper and lower punches or by rolling of graphite foils provided with openings or perforations on a core of foils free from openings.

The bulk density and accordingly the degree of compression of the graphite layers is individually determined by the degree of expansion of the graphite particles used in their production and the conditions of use of the gasket, layers with a bulk density of 1.0 to 1.5 g/cm3 being however of special advantage on account of the broad range of uses of the gasket.

This invention is based on the observation that a high degree of compression of the laminated body in the clad parts of the cylinder head gasket, which bound openings in the gasket surfaces lead frequently to tears in this region on account of the large restoration forces and cause harm or even destruction of the cladding. By the reduction of the thickness of the clad parts of the laminated body, these forces are lowered in the critical regions of the cylinder head gasket to a value not affecting the strength of the cladding. As a consequence, the effective life of the gasket increases considerably.

For a better understanding of this invention and to show how the same can be carried into effect, reference will now be made, by way of example only to the accompanying drawings, wherein: Figure 1 is a plan view of a cylinder head gasket, and Figure 2 is a schematic cross-section through the cylinder head gasket of Figure 1.

Referring to the drawings, a laminated body formed of flexible graphite consists of layers 1', 1" and 1"' and possesses openings 2 and 3 therethrough. The openings 2 correspond to the cylinder bores when the cylinder head gasket is in use in an internal combustion engine and the openings 3 correspond in their positioning to recesses of the engine serving for the transport of cooling and lubricating fluids. In a zone 4 annularly surrounding the openings 2 the laminated body 1 consists only of the layer 1" which is clad with the sheet metal 5. The thickness of the layer 1" is less than the doubled thickness of sheet metal 5. In order to increase the mechanical strength of the laminated body 1, it contains a needled metal sheet 6 with points bent up in the form of needles from the plane of the metal sheet.

To produce the cylinder head gasket as illustrated, graphite foils are for example rolled on both sides onto a needled metal sheet whose thickness amounts to 0.15 to 0.25 mm, about 1.8 to 2.0 mm inclusive of the needles, the graphite foils having a thickness of 0.4 to 0.6 mm and a bulk density of about 1.0 g/cm3. In a second operating step, a further graphite foil of the same constitution is rolled on each side, these graphite foils having previously been provided with recesses whose size and distance correspond to the parts of the gasket, which are provided with a cladding. The gaskets and the different openings disposed symmetrically in the gaskets with respect to the recesses are stamped from the laminated body whose bulk density without the inlaid needled sheet metal amounts to 1.3 to 1.5 g/cm3, and these parts of the laminated body are clad in the region of the openings by flanging with metal sheets.

Claims

1. A cylinder head gasket for use in an internal combustion engine, which is formed from a laminated body made from a plurality of layers of flexible graphite which comprises several openings intended to be aligned with the cylinder bores and with any other recesses present in the engine and which is provided in the region of said openings with a cladding for protecting the graphite against erosion and burn-off, the laminated body possessing in its clad parts a thickness which is less where the cladding is present than in the unclad part.

2. A cylinder head gasket as claimed in claim 1, wherein the laminated body is made of flexible graphite reinforced with metal inlays.

3. A cylinder head gasket as claimed in claim 2, wherein the metal inlay is a needled metal sheet.

4. A cylinder head gasket as claimed in any one of the preceding claims, wherein the graphite layers have a bulk density of 1.0 to 1.5 g/cm3.

5. A cylinder head gasket, substantially as hereinbefore described with reference to and as shown in the accompanying drawings.