Metallic Flat Gasket

Abstract

The invention relates to a metallic-flat gasket (1) comprising at least a first and a second gasket layer (2, 3) in which a bead (20) is provided in at least the first gasket layer (2), said bead (20) surrounding in a self-contained manner a through-opening (4) extending through the flat gasket (1). The first gasket layer (2) has a smaller surface area than the second gasket layer (3) and leaves free an edge region (6) adjoining the outer edge (5) of the flat gasket (1). A compensating portion (7) is provided in an edge region (6) of the second gasket layer (3), which compensating portion (7) protrudes at least in the direction of the first gasket layer (2) and has a height which is less than the thickness of the first gasket layer (2). The compensating portion (7) is arranged at least in certain portions along the outer edge (21) of the first gasket layer (2) and consists of a large number of alternating elevations (31) and depressions (32) which are formed in-the second gasket layer (3).

Description

[0001] The invention relates to a metallic flat gasket comprising at least two gasket layers through which at least one through-opening extends. A bead, which surrounds the through-opening in a self-contained manner, is provided in at least one of the gasket layers. Metallic flat gaskets of this type are used for example as a gasket in the region of internal combustion engines and exhaust tracts, in particular as exhaust gas manifold gaskets or as cylinder head gaskets.

[0002] In order to allow the bead reliably to seal the through-opening, it is generally necessary for the bead to be loaded uniformly and with sufficiently high compression. This applies in particular to the sealing of combustion chamber openings in cylinder head gaskets and in this case especially to cylinder head gaskets used in engines with open-deck designs. To increase the compression in the region of the bead, cylinder head gaskets have been proposed in which an additional layer shaped in a spectacle-like manner is present around the combustion chamber opening. This additional layer is often referred to as the "shim". A shim of this type is a layer which is shortened relative to the remaining gasket layers and, viewed from the combustion chamber openings, often reaches only just beyond the edge of the outer feet of the beads and may eventually reach the water jacket. Usually it is a planar layer which serves exclusively to increase the total thickness of the gasket in the region of the beads and contains no sealing elements. Generally gasket designs of this type--especially if they are intended for petrol engines--do not have any deformation limiters (stoppers) for the beads, by means of which there is generated, laterally adjacent to the beads, a material thickening which is intended to prevent complete flattening of the beads during operation. The aim of the shim is therefore a material thickening in the contact region of the beads, which thickening places the beads in a main loading connection and increases the compression in the region of the beads. Examples of cylinder head gaskets comprising a shim are described for example in EP 1065417 A2.

[0003] A drawback of the cylinder head gaskets described hereinbefore is however that their production is comparatively complex and expensive. Thus, the shim must be made separately and generally of a different material from the further gasket layers. The additional part increases the complexity of fitting the gasket. In addition, it is often difficult to adjust the thickness of the gasket. The thickness of the shim is derivable from the increase in compression of the gasket for a specific engine. It is often possible to achieve the required increase in compression at relatively low material thicknesses, for example of between 0.05 and 0.15 mm. At a material thickness of less than 0.1 mm, processing of the shim is however highly complex and difficult, as for example during punching, but also during transportation, warpages occur within the metal sheet.

[0004] There was therefore a need for a metallic flat gasket which is designed simply and from as few parts as possible and in which--even in the case of a low thickening of the gasket in the region of the shim--the compression acting on the beads can be set in a simple manner as desired. The object of the invention is accordingly to disclose a metallic flat gasket of this type.

[0005] This object is achieved by the metallic flat gasket according to claim 1. Preferred developments of the flat gasket are described in the sub-claims.

[0006] The metallic flat gasket according to the invention has at least two metallic gasket layers, namely a first and a second gasket layer. For the purposes of sealing a through-opening extending through the flat gasket, a bead is provided at least in the first gasket layer, said bead surrounding the through-opening in a self-contained manner. The first gasket layer comprising the bead has a smaller surface area than the second gasket layer and leaves free a region adjoining the outer edge of the flat gasket, referred to hereinafter as the edge region. The proportion of the area of this edge region in relation to the total gasket area depends on the individual gasket. The term "edge region" should therefore be understood not exclusively as a narrow edge strip. A compensating portion protruding in the direction of the first gasket layer is present in the second gasket layer in the edge region. The height of this compensating portion is less than the thickness of the first gasket layer. The compensating portion extends at least in certain sections along the outer edge of the first gasket layer and consists of a large number of alternating elevations and depressions which are formed in the second gasket layer.

[0007] In the metallic flat gasket according to the invention a region is formed around the through-opening, at the location where the first and the second gasket layer are present, in which the material thickness of all gasket layers is greater than in the regions which are more remote from the through-opening and in which the first gasket layer is not present. Accordingly, increased compression is generated in the region of the bead which is provided in the first gasket layer. In contrast to the prior art, this takes place however not by the addition of a shim, but rather by the shortening of the first gasket layer which exposes the edge region of the gasket. In this way the increase in compression can be achieved very much more easily than in the prior art and the bead can be placed very easily into the main loading connection.

[0008] The mere measure of the shortening of the first gasket layer would however allow only very crude adjustment of the increase in compression in the region of the bead. The increase in compression would be defined in all cases by the thickness of the first gasket layer and be dependent on the commercially available material thicknesses or would necessitate the expensive production of separate material. As a bead which performs a sealing function is provided in the first gasket layer, the first gasket layer must have a certain minimum material thickness. This minimum thickness is however often too great for adjusting the appropriate compression in the region of the bead. For adjusting a suitable difference in thickness between the edge region of the gasket and the region in which the first gasket layer is present, a compensating portion is therefore provided in the second gasket layer. The height of this compensating portion can purposefully be set in such a way that the material thickening required for the desired compression is reached in the region of the bead surrounding the through-opening. This is carried out by producing the elevations present in the second gasket layer in the compensating portion at a suitable height. The height of the elevations is in the range between zero and the thickness of the first gasket layer, wherein neither of the two limit values is included in the height range. Particularly preferred are thicknesses in the range of from 30 to 80% of the thickness of the first gasket layer. The height of the elevations can be the same or different throughout the compensating portion.

[0009] The metallic flat gasket according to the invention has the advantage over conventional gaskets comprising a shim of a greatly simplified design. The additional shim for increasing the compression in the region of the bead can thus be dispensed with entirely. This firstly simplifies the design of the gasket, saves material and facilitates handling during manufacture. The flat gasket according to the invention has in addition very versatile uses, as the desired compression in the region of the bead can be adjusted in a broad range of ways by suitably adapting the material thicknesses of the gasket layers and the height of the compensating portion. The invention can be applied not only to two-layer gaskets, but rather also to gaskets comprising three or more gasket layers.

[0010] The compensating portion adjoins, radially outside the first gasket layer, the outer edge of the latter. Preferably, the compensating portion in the second gasket layer is arranged at a distance from the outer edge of the first gasket layer. The distance is in this case at least sufficiently large that the compensating portion does not overlap the first gasket layer even in the state of maximum loading of the flat gasket. The compensating portion in the second gasket layer can be configured in such a way that it completely surrounds the shortened first gasket layer, although this is not absolutely necessary. On the contrary, it may also be sufficient if the compensating portion extends only along one or more partial sections of the outer edge of the first gasket layer. These partial sections are preferably distributed as uniformly as possible around the outer edge of the first gasket layer.

[0011] In a preferred variation of the invention, the compensating portion is present in the region around a plurality of openings which are provided in the second gasket layer in the edge region thereof. These openings in the edge region of the second gasket layer may in particular be fastening means openings, including in the case of cylinder head gaskets oil or cooling liquid openings. In this case the compensating portion can be configured in such a way that it continuously surrounds a plurality of these openings. Preferably, the compensating portion is present along at least 35%, preferably at least 50% and in particular at least 70% of the length of the outer edge of the first gasket layer. Alternatively, it is possible wholly or partly to surround each opening with a separate compensating portion. For example, each of the openings can be surrounded by an annular compensating portion or--in the case of an only partial enclosure--by a ring segment. Preferably, the openings surrounded by a separate section of the compensating portion are fastening means openings. If the fastening means openings are surrounded by the compensating portion, the compensating portion can serve simultaneously as a support region and as a sealing element for the fastening means opening. This applies especially if the elevations and depressions are configured in an undulating manner in the form of alternating concentric rings.

[0012] The embodiment of the elevations and depressions in such a way that they form an undulatory structuring is an expedient way of embodying the compensating portion. Particularly preferably, the elevations and depressions are in this case configured in the form of concentric rings or ring segments. Such structurings of the gasket layer are already known as stoppers for beads which seal an opening in a cylinder head gasket, and are conventionally referred to as wave stoppers. Wave stoppers of this type have previously been described in WO 01/96768 A1 and DE 102004011721 A1 in the name of the applicant. This type of structuring and also the type of manufacture can be used in the described manner for the compensating portion of the present invention. Reference may therefore be made to the content of the aforementioned documents.

[0013] In an alternative embodiment the elevations and depressions of the compensating portion are arranged on at least one set of virtual straight lines extending substantially parallel over the total extent of the compensating portion. Preferably, the elevations and depressions alternate in this case transversely to the direction of extension of the lines. A structuring of this type is likewise in principle already known for metallic flat gaskets and has likewise been described by the applicant of the present invention, namely in European patent application 07008321.7. The elevations and depressions are preferably trapezoidal, triangular, rounded or rectangular in cross section.

[0014] The set of straight lines extending substantially parallel are virtual lines. Although these lines continue over the entire surface area of the compensating portion, elevations or depressions do not necessarily also have to be present at each point of these lines. For example, the virtual lines can intersect the region of an opening or a sealing element in which no elevations and depressions are present. In such a case elevation(s) and/or depression(s) extend on a virtual straight line up to the opening or the sealing element, where they are broken off and then continue again on the opposing side on the same straight line. If the compensating portion is divided into a plurality of portions, the set of straight lines extending substantially parallel is in principle drawn over the entire surface area of the compensating portion, whereas the elevations and depressions on these lines are present only in the compensating portions, but not in the gaps thereof. The elevations are in each case separated from one another by depressions. The term "a substantially parallel course of the lines" refers in the present document to a departure from parallelism of at most 5.degree. and in particular at most 2.degree..

[0015] The elevations and depressions in the compensating portion of the flat gasket according to the invention are produced preferably by embossing. If use is in this case made of two complementary embossment forms, the elevations of which are in each case laterally offset relative to the elevations of the other embossment form and engage with the depressions in the opposing form, there results a compensating portion, the elevations of which protrude beyond both surfaces of the second gasket layer. The material thickening produced by the structuring in the compensating portion therefore affects both surfaces of the second gasket layer. In order to make the material thickening in the compensating portion effective fully for the first gasket layer, the compensating portion of the second gasket layer can for example be cranked in the direction of the first gasket layer. Likewise, asymmetrical tool configuration allows the elevations of the compensating portion to protrude only beyond one surface of the second gasket layer.

[0016] As a whole, the compensating portion has in its cross section elevations, depressions and a respective region of transition, also referred to as the flank, between adjacent elevations and depressions. The structures are generated preferably by means of embossing. In this case the material in the region of the flank is reduced relative to the material thickness in the region of the elevations and depressions, thus rigidifying the compensating portion. The material tapering in the flank region is in this case at least 8%, preferably at least 10%, particularly preferably at least 13% and in particular at least 15% relative to the material thickness in the region of the adjacent elevation or depression.

[0017] Although at first sight, the elements of the structure may resemble a bead, they have less resiliency than the latter, which is also due to the tapering. Moreover, their width is smaller than the one of a bead. This can for instance be shown with respect to the thickness of the gasket layer. The ratio between the width of a bead (starting from the point where it raises out of the plane) and the thickness of the unstructured gasket layer is at least 6, preferably at least 7. In contrast, the ratio between a period of the structure is at the most 4, preferably between 2.5 and 3.5.

[0018] The compensating portion can, in addition to the above-mentioned elevations and depressions alternating transversely to the direction of extension of the virtual straight lines, also be configured in such a way that elevations and depressions on mutually adjacent lines are in each case arranged offset relative to one another. Such cases give rise to a chessboard-like structure of elevations and depressions. Preferably, the depressions extend along at least two intersecting sets of virtual straight lines. Particularly preferred is an arrangement on virtual straight lines which intersect at right angles. In principle, it is also possible for the virtual straight lines to intersect not in the structured region, but rather outside; this produces regions having a differing structuring orientation. Also possible are transitions in which a region in which exclusively the first set of virtual straight lines forms elevations and depressions is followed by a region in which a first and a second set of virtual straight lines can be seen as elevations and depressions and which is adjoined by a region in which only the second set of virtual straight lines is embodied in elevations and depressions.

[0019] The structuring in the compensating portion imparts to the second gasket layer at this location a greater thickness than the thickness of the original gasket layer, i.e. of the planar gasket layer prior to the introduction of the structuring. The height of the compensating portion is measured as the distance between two tangential planes each extending parallel to the plane of the non-deformed gasket layer. The distance is therefore measured between the plane of the untreated gasket layer and a plane resting on the elevations protruding beyond this surface of the gasket layer. In this case the height of the elevations does not have to be uniformly high over the entire compensating portion. Depressions are regions which are lower than the elevations, i.e. not necessarily regions which are sunk into the plane of the undeformed gasket layer.

[0020] The embossing of the compensating portion allows thickenings to be adjusted variably in a very broad range without the need for additional material. The thickening does not--as stated hereinbefore--have to be configured uniformly over the entire compensating portion, but can rather vary over the surface area of the compensating portion. A topography can therefore be generated in the compensating portion which facilitates purposeful influencing of the compression of the bead in the first gasket layer and allows adaptation to the opposing surfaces to be sealed and the component rigidities thereof. Preferably, the topography in the compensating portion is selected in such a way that the compression of the bead in the first gasket layer is as uniform as possible. Preferably, the height of the compensating portion is adjusted in such a way that the elevations protrude beyond the second gasket layer by from 0.02 to 0.3 mm and in particular from 0.05 to 0.20 mm. The height can be set during the manufacture of the elevations from the gasket layer or as a result of the fact that the elevations which are generated are planished, after production thereof, in certain sections or over the entire compensating portion.

[0021] As mentioned hereinbefore, further openings can be present in what is known as the "hinterland" of the gasket--i.e. in the outer edge region. In the case of cylinder head gaskets, these are openings for fastening means, oil and cooling liquid. These openings can in each case be sealed, as is conventional in the prior art, using sealing elements. Use may in this case in principle be made of the sealing elements which are conventional in the prior art, i.e. for example elastomer sealing elements and/or beads which are provided in the second gasket layer. The elastomer can be applied to the gasket layer on one or both sides or molded onto the opening edge. The sealing elements of the "hinterland" can also be configured in a manner known per se as separate regions (so-called inserts) which are inserted into the gasket layer. The compensating portion can be configured in such a way that it--as mentioned hereinbefore--acts itself either as the sealing element for a "hinterland" opening or as the support element for a "hinterland" sealing element. In this case a sufficient distance should however be present between the compensating portion and the "hinterland" sealing element (elastomer or bead) in order not to restrict the elastic sealing element. Suitable distances are for example at least 0.1 mm. It can also be beneficial for the compensating portion to maintain a distance from the outer edge of the second gasket layer, for example if a bead or half-bead extends along the outer edge of the second gasket layer. Alternatively, it is however equally possible to guide the compensating portion up to the outer edge of the gasket.

[0022] In order to save as much material as possible, the first gasket layer is advantageously only as large as is absolutely necessary. Usually this means that the first gasket layer is extended only so far as is required for the function of the bead which is introduced into the gasket layer. Preferably, the first gasket layer will therefore end as close as possible to the foot of the bead that is remote from the through-opening. In an open-deck engine, the first gasket layer reaches usually at least up to the outer edge of the sealing jacket and in some cases even projects somewhat into the region of the water jacket.

[0023] In the simplest embodiment, the metallic flat gasket according to the invention has in the first gasket layer just a single through-opening which is enclosed by a bead. The first gasket layer is then just annular and in particular circular. In many cases the metallic flat gasket will however have a plurality of through-openings which are each surrounded by a bead which is provided in the first gasket layer. It is in this case possible, if there is only a short distance between adjacent through-openings, for the beads to merge in the web region between adjacent through-openings to form a single bead portion. In the case of a plurality of through-openings, the first gasket layer is preferably configured in a spectacle-like manner, such as is in principle already known in the art, for example for shims (cf. EP 1065417 A2).

[0024] In a simple configuration, the metallic flat gasket according to the invention has, in addition to the first gasket layer, just one further layer, namely the second gasket layer, in which the compensating portion is provided. In a particularly simple variation, the second gasket layer is a metal sheet which is completely planar--apart from the compensating portion. The alternative possibility, of attaching one or more elastically deformable sealing elements in the second gasket layer for the sealing of openings in the "hinterland" of the gasket, has already been referred to. It is also possible to provide in the second gasket layer an elastically deformable sealing element for sealing the through-opening extending through the first and the second gasket layer. Preferably, this sealing element is a bead which is introduced into the second gasket layer and surrounds the through-opening. Preferably, the bead of the second gasket layer is configured in a similar manner to the bead of the first gasket layer. Both beads can be arranged with their bead apices pointing toward one another or else pointing away from one another. If respective beads for sealing the through-opening are present in the first and the second gasket layer, both gasket layers are preferably made of the same material in order to obtain the same spring constant for the beads in both gasket layers. The use of the same materials for the gasket layers also facilitates manufacture and reduces costs. It is however also possible to use differing materials for both gasket layers and--if the same spring constant is desired for the beads surrounding the through-opening--to adjust this spring constant by shaping the beads or in another manner known per se.

[0025] The flat gasket according to the invention is not limited to two-layer gaskets; on the contrary, one or more further gasket layers can be present. If the second gasket layer is a metal sheet in which merely the compensating portion but no beads are present, the additional gasket layer can be configured as an active metal sheet in which, for sealing the through-opening and optionally also for sealing further openings in the "hinterland" of the gasket layer, beads are provided or elastomer sealing elements are present. Flat gaskets comprising four or more gasket layers can also be manufactured, wherein the additional gasket layers can be pure spacer layers without functional elements and in particular without elastically deformable sealing elements or are active layers with elastically deformable sealing elements. The gasket layers can also contain, as is in principle known in the art, deformation limiters for elastic sealing elements in the form of material thickenings (by folding, upsetting, material application, embossing, etc.), although this is not preferred.

[0026] In addition, individual gasket layers or all of the gasket layers of the flat gasket according to the invention can be coated wholly or partly, on one side or on both sides. The coating may be applied after the embossment or the embossment may be introduced into pre-coated, even coil-coated metal sheet. In this case the coatings known per se can be used to improve the microsealing, the sliding friction properties, etc. The structuring of the compensating portion improves the adhesion of the coating in this region. Also, the structuring of the compensating portion in the second gasket layer allows comparatively high layer thicknesses to be achieved.

[0027] The individual gasket layers of the flat gasket according to the invention can be joined together in a manner conventional in the prior art, for example by riveting, welding (spot-welding, laser-welding, etc.), by clinching, soldering, bonding, clipping-on, etc.

[0028] The metallic flat gasket according to the invention is suitable for a large number of applications, for example as a flange gasket, exhaust gas manifold gasket other gaskets in the exhaust tract of combustion engines, or the like. The term "flat gasket" expressly includes three-dimensionally deformed gaskets of the type deformed from a two-dimensional body, i.e. for example conical gaskets. The flat gasket according to the invention is particularly suitable as a cylinder head gasket, the through-openings corresponding to the combustion chamber openings. A cylinder head gasket of this type is particularly suitable for engines with cylinder liners and in particular for open-deck engines in which the water openings are open on the upper side of the motor block. The bead which is introduced into the first gasket layer is in this case expediently arranged in such a way that its bead apex is located above the cylinder jacket. The cylinder head gasket is preferably configured in such a way that no deformation limiters for the beads surrounding the combustion chamber openings are present. In this form the gasket is particularly suitable for use in petrol engines. There is obtained a very simply constructed gasket which requires neither a shim nor deformation limiters, but in which sufficient compression which is uniform around the combustion chamber openings can nevertheless be achieved. However, variations of the gasket comprising deformation limiters for the combustion chamber beads (on one side or on both sides of the beads) are also possible. In this case the height of the deformation limiters should however be less than the height of the compensating portion, as otherwise the deformation limiters can impair the function of the compensating portion. The deformation limiters can be configured in any manner conventional in the prior art. It is however preferable if they consist--like the compensating portion--of a structuring which is introduced into the gasket layer in the form of alternating elevations and depressions. Expediently, the deformation limiters are generated in the same step as the compensating portion, preferably by embossing.

[0029] The metallic flat gasket according to the invention can be made of the materials previously conventional for metallic flat gaskets and using the standard production tools. Spring steel is expediently used as the material of those gasket layers in which beads are provided as sealing elements for through-openings. For the other gasket layers, which have no beads, softer steel, for example construction steel, can be used. Stainless steels and carbon steels are equally possible. In addition, the use of alloys having high thermal stability, in particular of nickel-enriched steels and equivalents, is also conceivable.

[0030] The invention will be described hereinafter in greater detail with reference to the drawings. The figures are intended exclusively to illustrate preferred exemplary embodiments, without the invention being restricted thereto. In the figures like reference numerals denote like parts. In the figures:

[0031] FIG. 1(a) is a schematic plan view onto a first exemplary embodiment of a metallic flat gasket based on the example of a cylinder head gasket;

[0032] FIG. 1(b) is a schematic cross section along the line G-G in FIG. 1(a);

[0033] FIG. 2 is a schematic plan view onto a further example of a metallic cylinder head gasket including four details;

[0034] FIGS. 3(a) to 3(d) are schematic plan views onto the individual layers of a two-layer cylinder head gasket according to the invention along with plan views onto the opposing surfaces to be sealed, specifically:

[0035] FIG. 3(a) is a schematic plan view onto the motor block surface;

[0036] FIG. 3(b) is a schematic plan view onto the surface of the cylinder head;

[0037] FIG. 3(c) is a schematic plan view onto the second gasket layer of the flat gasket according to the invention; and

[0038] FIG. 3(d) is a schematic plan view onto the first gasket layer of the cylinder head gasket according to the invention;

[0039] FIGS. 4 to 7 show schematically further exemplary embodiments of metallic flat gaskets according to the invention in partial cross sections in a region around a through-opening;

[0040] FIG. 8(a) is a schematic plan view onto a further example of a metallic flat gasket according to the invention based on the example of a flange gasket;

[0041] FIG. 8(b) is a schematic cross section along the line A-A in FIG. 8(a);

[0042] FIGS. 9(a) to 9(f) are various schematic partial cross-sectional views of different embodiments of two-layer metallic flat gaskets in the region between a through-opening and a screw opening;

[0043] FIG. 9(g) a schematic partial cross-sectional view of a two-layer metallic flat gasket in the region between a through-opening and an area in the backland of the gasket; and also

[0044] FIG. 10 is a schematic partial cross section through a compensating portion, provided with elevations and depressions, of a metallic flat gasket according to the invention.

[0045] FIG. 1(a) shows a metallic flat gasket 1 based on the example of a cylinder head gasket in a plan view onto the second gasket layer 3 thereof, which extends substantially over the entire surface of the opposing surfaces to be sealed (i.e. of a motor block and a cylinder head). The second gasket layer 3 is made for example of spring steel. Formed therein are various through-openings, namely inside the gasket layer four through-openings 4 which are arranged next to one another and correspond to the combustion chamber openings. Around the combustion chamber openings 4, further openings 8 are present in the second gasket layer 3 toward the edge 5 of the gasket 1. Specifically, these are screw openings 80, oil openings 81 and openings 82 for cooling liquid, in particular water.

[0046] The through-openings 4 are each surrounded by a bead 30 enclosing said through-openings. The course of the beads 30 is in this case specified by two respective lines which illustrate the position of the feet 301 and 302 of the bead. As may be seen, in the web region 303 between adjacent through-openings 4 the beads 30 merge to form a single bead portion. The cross-sectional shape of the beads 30 may in principle be of any desired shape. As may be seen in FIG. 1(b), in the case shown, the beads 30 have a trapezoidal cross section. Beads having a rounded cross section can however also be used.

[0047] The oil openings 81 in the edge region 6 of the second gasket layer 3 are likewise surrounded by an elastically deformable sealing element 9. This may also be a bead which is introduced into the gasket layer. Alternatively, the sealing element used may be an elastomer lip. For sealing the water openings 82 there is provided in the gasket layer 3 a half-bead 34 which encircles in a self-contained manner the region between the combustion chamber bead and the outer edge 5 of the gasket.

[0048] For sealing the through-openings 4, further beads 20 are present in a first gasket layer 2. The first gasket layer 2 can not be seen in the plan view of FIG. 1(a), as it is arranged below the second gasket layer 3. This may be seen in FIG. 1(b). It may also be seen that the first gasket layer 2 extends much less far than the second gasket layer 3. For these illustrations as for the subsequent ones, it is fundamentally the case that the illustration, also with regard to the upper side or underside of the gasket, is merely schematic by nature. The upper side, which is shown at the top of the present figure, can in a cylinder head gasket be either the side facing the cylinder head or else the side facing the motor block. The same applies to other types of metallic flat gaskets. The first gasket layer 2 is configured in a spectacle-like manner and extends exclusively in the immediate vicinity around the through-openings 4. Its width is in this case only approximately three times as great as the distance between the feet 201 and 202 of the bead 20. The shape and course of the beads 20 correspond fully to those of the beads 30 of the second gasket layer 3. The beads 20 and 30 are therefore configured mirror-symmetrically with respect to one another and rest against one another with their bead apices. The material of which the first gasket layer 2 is made also corresponds to that of the second gasket layer 3. As a result, the beads 20 and 30 have the same spring characteristic.

[0049] The first gasket layer 2 fully exposes the edge region 6 of the second gasket layer 3. Accordingly, the first gasket layer 2 also contains exclusively through-openings 4, but otherwise no further through-openings. In the edge region 6, the flat gasket 1 according to the invention consists exclusively of the second gasket layer 3. On account of this design, a greater material thickness is achieved in the region around the through-openings 4 than in the edge region 6, where the first gasket layer 2 is not present. As a result, the compression in the region around the through-openings 4 increases, thus allowing improved sealing of the combustion chamber openings to be achieved at this location. The beads 20 and 30 are in main loading connection. If no further measures were taken, the difference in the material thicknesses in the region around the combustion chamber openings 4 and in the edge region 6 would correspond to the thickness d of the first gasket layer 2. However, this difference in thickness frequently does not allow the desired increase in compression to be adjusted. The thickening of the material is often greater than is desired and admissible. In order to counteract this excessive material thickening and to be able to adjust the desired compression at will, according to the invention a compensating portion 7 is provided in the edge region 6 of the second gasket layer 3. This compensating portion 7 protrudes by a height H beyond the surface 33 of the second gasket layer 3 in the direction of the first gasket layer 2. The height H is in this case less than the thickness d of the first gasket layer 2, so overall a thickening is maintained in the region around the combustion chamber openings 4. Appropriate selection of the height H of the compensating portion 7 allows the desired increase in compression to be purposefully adjusted in the region around the combustion chamber openings. Specifically, this takes place as a result of the fact that in the compensating portion 7, which is formed from alternating elevations 31 and depressions 32, the elevations 31 are generated at a specific height. For an exemplary thickness of the second gasket layer 3 of 0.2 mm, the height H of the compensating portion 7 is for example from 0.1 to 0.18 mm, in particular 0.15 mm.

[0050] In the example shown the compensating portion 7 consists of a plurality of sections 70 which each surround a screw opening 80. The individual sections 70 of the compensating portion 7 consist of an undulatory structuring of the second gasket layer 3. In the region immediately adjoining the screw openings 80, the elevations 31 and depressions 32 extend in the form of alternating concentric rings. In the regions arranged further away from the screw openings 80, the elevations and depressions are configured merely as concentric ring segments. In the configuration shown of the compensating portion 7, the elevations 31 and depressions 32 of the individual sections 70 can serve at the same time as sealing and support elements for the screw openings 80. The uniform distribution of the screw openings 80, and thus also of the sections 70 of the compensating portion 7, around the combustion chamber openings 4 ensures uniform adjustment of the compression in the region around the combustion chamber openings 4. In addition, the compensating portion 7 maintains a sufficient distance from the edge 21 of the first gasket layer 2, so the compensating portion does not impair the function of the beads of the first gasket layer either. The working of the beads 20 is not disturbed by the compensating portion 7.

[0051] FIG. 2 is a plan view onto a second gasket layer 3 of another exemplary embodiment of a metallic cylinder head gasket. Apart from the configuration of the compensating portion 7, this gasket corresponds entirely to that shown in FIGS. 1(a) and 1(b). The first gasket layer 2 is, again, arranged below the second gasket layer 3 and corresponds to that shown in FIG. 1(b). In the example of FIG. 2 the compensating portion 7 is configured continuously. It substantially continuously surrounds the through-openings 4 at a distance therefrom and is broken off merely in the left-hand bottom corner of the second gasket layer 3. At this location there is, again, a lowered region 35. The compensating portion 7 is present merely in a relatively narrow strip on the second gasket layer 3 and ends before the half-bead 34, from which the compensating portion maintains a distance.

[0052] The elevations of the compensating portion 7 are not configured in the form of concentric rings as described in the preceding figures; instead, the elevations 31 and depressions 32 are in this case for example in the form of elevations and depressions which are arranged alternately on straight lines. These straight lines are virtual lines extending over the entire compensating portion in a parallel arrangement. These virtual lines intersect in this case also the through-openings 4 and the beads 30 surrounding said through-openings. The elevations and depressions are in this case however present only in the hatched regions. Overall, there is thus obtained a linear arrangement of the elevations and depressions in the compensating portion 7, such as is also illustrated in details A and C. In the lowered region 35 the structuring can extend parallel to the direction of extension of the elevations and depressions of the remaining regions or else at an angle thereto. The height by which the elevations protrude beyond the surface 33 of the second gasket layer in the direction of the first gasket layer 2 can, again, be set so as to correspond to the desired compression. In this case it is possible to vary the height of the elevations in the compensating portion. In this way the gasket can be adapted to the rigidities of the components to be sealed and the compression around the through-openings 4 can be made uniform. Obviously, it is likewise possible, should this be desirable, to set a non-uniform distribution of compression in the region around a through-opening 4 or from one through-opening to another through-opening 4. In principle, it is also possible for the structuring to be configured in such a way that, for example, two sets of parallel virtual lines intersect, thus producing, at the same distances, a chessboard pattern of elevations and depressions. This possibility is indicated in details B and D.

[0053] FIGS. 3(a) to 3(d) illustrate the arrangement of a metallic flat gasket according to the invention based on the example of a two-layer cylinder head gasket in the sealing gap between a motor block and a cylinder head. The motor block illustrated in FIG. 3(a) is of an open-deck design. The motor block is made for example of cast iron or an aluminum alloy. The four cylinder bores 4' are surrounded by a water jacket 82'. The water jacket 82' is upwardly open in the plane of the surface B1 to be sealed. Around the water jacket 82', various screw openings 80' and also oil openings 81' are present in the motor block B.

[0054] The cylinder head K pertaining to the motor block B is illustrated in FIG. 3(b). Cylinder bores 4'', screw openings 80'', oil openings 81'' and water openings 82'' are present in the cylinder head K, corresponding to the position of the openings in the motor block B.

[0055] The cylinder head gasket according to the invention is inserted between the motor block and cylinder head. In the example shown the cylinder head gasket is a two-layer cylinder head gasket comprising a first gasket layer 2 (FIG. 3(d)) and a second gasket layer 3. The second gasket layer is shown in FIG. 3(c) and is for example arranged in such a way that the surface of the gasket layer that points away from the viewer comes to rest against the surface K1 of the cylinder head K. The configuration of the second gasket layer 3 corresponds substantially to that in FIG. 2. In addition, the surface of the gasket layer 3 is provided with a coating 11. This coating reaches from the inner edge of the compensating portion 7 beyond the half-bead 34 partly up to the edge 5 of the gasket. It also covers the left-hand narrow-side edge portion of the gasket layer 3. The coating 11 can for example be applied using a screen printing process and is made preferably of plastics material, for example rubbers or fluoropolymers. A coating of this type allows the microsealing and the sliding friction properties of the gasket to be improved. The presence of the compensating portion 7, with its surface area enlarged by the elevations and depressions, allows the coating 11 to be applied at a greater thickness than onto an unstructured region. In addition, the structuring improves the adhesion of the coating 11 on the metallic gasket layer 3. Preferably, the coating 11 is present also on the opposing second surface 33, which cannot be seen in FIG. 3(c), of the gasket layer 3.

[0056] The first gasket layer 2 is configured in a spectacle-like manner and has four combustion chamber openings 4 which are each surrounded by a bead 20, as may be seen from FIG. 3(d). The beads 20 merge in the web region 203 to form a common bead portion, such as was previously described in relation to FIG. 1(a). Apart from the combustion chamber openings 4, the first gasket layer has no further through-openings.

[0057] The first gasket layer 2 is fastened to the second gasket layer 3 even before the cylinder head gasket has been fitted, for example by spot-welding. In this case the first gasket layer 2 is arranged above the second gasket layer 3 in such a way that the through-openings 4 are positioned in each case precisely one above another and the beads 20 and 30 rest against one another with their apices. The cylinder head gasket comprising the first and second gasket layers is subsequently fastened to the motor block B in such a way that the first gasket layer 2 rests on the surface B1 of the motor block. The through-openings 4 in the cylinder head gasket and the cylinder bores 4' are positioned precisely one above another. The first gasket layer 2 rests in this case on the cylinder jackets B2 of the motor block B. The second gasket layer 3, on the other hand, reaches beyond the cooling water opening 82' and covers the surface B1 of the motor block B substantially completely. The inner edge of the compensating portion 7 reaches right up to the outer edge 820' of the water jacket 82'. The assembly is concluded by positioning the cylinder head K above the second gasket layer 3 and is secured to the motor block by means of screws which are guided through the screw openings 80'', 80 and 80'.

[0058] FIGS. 4 to 7 are partial cross sections through further exemplary embodiments of metallic flat gaskets according to the invention. These can be various types of flat gasket, including flange or manifolds gaskets. The cross sections will however be described based on the example of cylinder head gaskets. Shown in each case is a cross section between a combustion chamber opening 4 and an opening 8 in the edge region 6 of the gasket. The opening 8 can for example be a screw opening.

[0059] FIG. 4 is a cross section of a cylinder head gasket similar to that illustrated in FIG. 1b. For sealing the combustion chamber openings 4 there are, again, two beads 20 and 30 which are arranged mirror-symmetrically with respect to one another, have a trapezoidal cross section and the apices of which rest on one another. In the first gasket layer 2 the edge portion adjoining the outer foot of the bead is shortened compared to the first gasket layer of the gasket illustrated in FIG. 1. The compensating portion 7 adjoins at a relatively short distance the outer foot 301 of the bead 30 in the second gasket layer 3. It consists of elevations 31 and depressions 32 arranged in alternation on virtual parallel lines. In the direction of the outer edge of the second gasket layer 3, the compensating portion 7 is adjoined by a half-bead 34 which can serve, as in FIGS. 1 and 2, to seal the water openings. In the example shown neither a sealing element nor a compensating portion is present in the region around the opening 8.

[0060] FIG. 5 shows a further example of a two-layer cylinder head gasket in which merely in the first gasket layer 2 a bead 20 is provided for sealing the combustion chamber opening 4. The second gasket layer 3 is, on the other hand, entirely without beads and planar in the detail shown, apart from the compensating portion 7. However, this does not rule out the possibility that, for sealing the water and oil openings, there are provided in the edge region of the second gasket layer 3 elastically deformable sealing elements which can consist, for example, of elastomer sealing lips applied to the gasket layer or molded onto the edges of the opening.

[0061] FIG. 6 is a cross section through a further example of a two-layer cylinder head gasket. In this case the orientation of the first gasket layer 2 and second gasket layer 3 relative to one another is different from the preceding examples. Firstly the apices of the beads 20 and 30 point away from one another, so in this case the respective feet of the beads come to rest on one another. Also the first gasket layer 2 is arranged above the second gasket layer. Thus, in this case, the first gasket layer 2 is oriented in the direction of the cylinder head K, whereas the second gasket layer 3 rests on an motor block B. A non-compressed state of said components is shown. Apart from the fact that around the opening 8, for example a screw opening, a structuring is present, preferably in the form of rings extending concentrically with one another (cf. FIG. 1) or of elevations and depressions extending parallel to one another, the illustrated gasket in the edge region otherwise does not differ from that of FIG. 4.

[0062] FIG. 7 is a partial cross section through a three-layer cylinder head gasket. The first, shortened gasket layer 2 corresponds basically to that shown in FIG. 4, although it is in this case provided as the gasket layer oriented on top (for example toward the cylinder head). The second gasket layer 3 is in this case a smooth metal sheet, as it contains no beads. A gasket layer of this type without active sealing elements is conventionally referred to as a spacer sheet. However, in contrast to conventional spacer sheets, a compensating portion 7 is provided in the second gasket layer 3 which extends so as to adjoin the outer edge 21 of the first gasket layer. The structuring of the compensating portion 7 can, again, be elevations and depressions arranged on parallel virtual lines.

[0063] FIG. 8 illustrates in partial images 8(a) and 8(b) the application of the solution according to the invention based on the example of a flange gasket with a single through-opening 4 for, for example, exhaust gases or liquids. For fastening to the components to be sealed, the flange gasket 1 according to the invention has two fastening openings 80. The first gasket layer 2 comprising the bead 20 extends over a highly limited, roughly circular region in immediate proximity to the through-opening 4. The compensating portion in the form of a structuring 7 is present in the region of the fastening means openings 80. In the edge region 6 there is only the layer 3 which, again, has a bead 30 which is arranged mirror-symmetrically with respect to the bead 20.

[0064] FIGS. 9(a) to 9(f) are partial cross sections through further exemplary embodiments of two-layer metallic flat gaskets. The cross sections shown can be used also for other types of flat gaskets, but will be described in greater detail for cylinder head gaskets. Shown is the region between a through-opening 4 and an opening 8, in particular a fastening means opening. In the region of the openings 8 the cylinder head gaskets can be configured like those of FIG. 1(a). Portions of the compensating portion 7 are therefore each present around the individual openings 8. The individual gaskets each differ in terms of the configuration of the regions around the through-openings 4. In contrast to the above-described gaskets, the gaskets of FIG. 9 contain respective deformation limiters 12 for the beads 20 and 30, which are intended to prevent complete flattening of the beads during operation. The deformation limiters 12 consist in each case in a structuring which can be configured similarly to, but is less tall than, that of the compensating portion 7. The deformation limiters 12 for the beads 20 and 30 are manufactured preferably by embossing and consist likewise of alternating elevations and depressions in the respective gasket layer 2 or 3. Preferably, the deformation limiters 12 are generated in the same operation as the compensating portion 7.

[0065] In the gasket shown in FIG. 9(a) a deformation limiter 12 is present at the combustion chamber-side edge of the second gasket layer 3. In the gasket according to FIG. 9(b), in addition to the gasket described hereinbefore, a second deformation limiter 12' is arranged on the side of the bead 30 that is remote from the combustion chamber opening 4. In the gasket according to FIG. 9(c) a deformation limiter 12' is provided in the first gasket layer 2 on the combustion chamber side thereof, whereas in the gasket according to FIG. 9(d) a further deformation limiter 12 is additionally present in the first gasket layer on the side of the bead 20 that is remote from the combustion chamber.

[0066] In the gaskets according to FIGS. 9(e) and 9(f) a respective deformation limiter 12 is provided on the side of the beads that is remote from the combustion chamber, in the gasket according to FIG. 9(e) in the second gasket layer 3 and in FIG. 9(f) in the first gasket layer 2.

[0067] FIG. 9(g) demonstrates that the second gasket layer 3 can have not just a bead, but rather also a surface structuring comprising elevations 31' and depressions 32', the structured region being arranged in such a way that it does not overlap the structured region of the first gasket layer 2. As in FIG. 9(d), the latter is structured on both sides of the bead 20. In contrast to the foregoing figures, the figure is not taken between the combustion chamber through opening 4 and a bolt hole 8 but from the combustion chamber through opening 4 to an area in the backland of the gasket layer which is free from bolt holes. As was already the case in FIG. 6, the structuring 7 in the backland is arranged in such a way that it continues on the other side of a half bead 34.

[0068] As mentioned hereinbefore, the elevations 31 and depressions 32 of the compensating portion and, if present, also the deformation limiter 12 are produced preferably by embossing. The embossing step is carried out preferably using an embossing tool having two complementary embossment forms. These embossment forms expediently each have embossment projections which engage with corresponding depressions in the complementary embossment form. Elevations and depressions of one embossment form are therefore arranged offset relative to the elevations and depressions of the complementary embossment form. If the elevations and depressions of the complementary embossment forms are each of similar configuration, this tool constellation results in a particular distribution of material thickness in the region of the machined gasket layer that is structured with the embossment form. This will be illustrated schematically with reference to FIG. 10.

[0069] FIG. 10 shows a detail from a second gasket layer in a compensating portion 7. Elevations 31 and depressions 32 are embossed into this region. The elevations 31 protrude by a height H beyond the surface O of the gasket layer 3. As a result of the embossing, the thickness of the gasket layer 3 in the region of the flanks 36 has been reduced relative to the thickness of the elevations 31 or depressions 32. The thickness D.sub.36 in the flank region is therefore less than the thickness D.sub.31 of the gasket layer 3 in the region of the elevations or depressions. This reshaping of the material and reduction of the material thickness lead to an increase in the rigidity of the structured region. The extent of the flank tapering is exaggerated in FIG. 10. It is frequently between 10 and 25%, in particular between 13 and 19%. FIG. 10 also indicates that a period of the structuring, P, is usually about 2.5 to 3.5 times larger than the original thickness of the gasket layer, H. The ratio P/H in general does not exceed 4.

Claims

1-23. (canceled)

24. A metallic flat gasket comprising at least a first and a second gasket layer, in which a bead is provided at least in the first gasket layer, said bead surrounding in a self-contained manner a through-opening extending through the flat gasket, characterized in that the first gasket layer has a smaller surface area than the second gasket layer and leaves free an edge region adjoining the outer edge of the flat gasket and in that a compensating portion is present in an edge region of the second gasket layer, said compensating portion protruding at least in the direction of the first gasket layer and having a height which is less than the thickness of the first gasket layer, the compensating portion being arranged outside the outer edge of the first gasket layer and running alongside at least a portion of said outer edge, and consisting of a plurality of alternating elevations and depressions which are formed in the second gasket layer.

25. The metallic flat gasket according to claim 24, wherein the compensating portion is present in a region around a plurality of openings which are located in the edge region of the second gasket layer.

26. The metallic flat gasket according to claim 25, wherein the compensating portion continuously surrounds a plurality of openings.

27. The metallic flat gasket according to claim 24, wherein the compensating portion extends along at least 35%, preferably at least 50% and in particular at least 70% of the length of the outer edge of the first gasket layer.

28. The metallic flat gasket according to claim 24, wherein the compensating portion is divided into separate sections which each wholly or partly surround one of the openings.

29. The metallic flat gasket according to claim 28, wherein the opening surrounded by the separate section is a fastening means opening.

30. The metallic flat gasket according to claim 29, wherein at least 2/3, preferably at least 3/4 and particularly preferably all of the fastening means are at least partially surrounded by the separate section.

31. The metallic flat gasket according to claim 24, wherein the height of the compensating portion is in car engines from 0.02 to 0.30 mm, in particular from 0.05 to 0.20 mm, and in commercial vehicle engines from 0.05 to 0.5 mm.

32. The metallic flat gasket according to claim 24, wherein the elevations and depressions are arranged in an undulating manner in the form of alternating concentric rings or ring segments.

33. The metallic flat gasket according to claim 24, wherein the elevations and depressions are arranged on at least one set of virtual straight lines extending substantially parallel over the total extent of the compensating portion.

34. The metallic flat gasket according to claim 33, wherein the depressions extend along at least two intersecting sets of virtual straight lines and in particular along virtual straight lines intersecting at right angles.

35. The metallic flat gasket according to claim 24, wherein the depressions are embossed into the second gasket layer, the thickness (D.sub.36) of the second gasket layer in the flank region preferably being reduced relative to the thickness (D.sub.31) of the second gasket layer in the region of the elevations or depressions.

36. The metallic flat gasket according to claim 24, wherein the compensating portion extends radially outside the sealing elements at a distance therefrom, the distance being preferably at least 0.1 mm.

37. The metallic flat gasket according to 25, wherein at least some of the openings in the edge region are surrounded by sealing elements which are made of elastomer and/or are formed by a bead which is introduced into the second gasket layer and/or consist of undulatory concentric rings.

38. The metallic flat gasket according to claim 24, wherein the compensating portion maintains a distance from the outer edge of the second gasket layer.

39. The metallic flat gasket according to claim 24, wherein the compensating portion reaches up to the outer edge of the second gasket layer.

40. The metallic flat gasket according to claim 24, wherein the compensating portion has at least a first portion which is thickened relative to the first surface of the second gasket layer and a second portion which is thickened relative to the second surface of the second gasket layer.

41. The metallic flat gasket according to claim 24, wherein the first gasket layer is configured in a spectacle-like manner.

42. The metallic flat gasket according to claim 24, wherein a bead surrounding said through-opening is provided in the second gasket layer around each through-opening.

43. The metallic flat gasket according to claim 24, wherein the second gasket layer contains no bead surrounding the at least one through-opening and in particular no beads at all.

44. The metallic flat gasket according to claim 24, comprising at least one further gasket layer, in particular a gasket layer in which a respective bead is provided surrounding each through-opening.

45. The metallic flat gasket according to claim 44, wherein the beads, surrounding a through-opening, of the first and second gasket layers or of the first and further gasket layers are of similar configuration.

46. The metallic flat gasket according to claim 24, namely a gasket in the region of an internal combustion engine or exhaust tract, in particular an exhaust gas manifold gasket or cylinder head gasket, in which the through-openings correspond to combustion gas openings or combustion chamber openings.