The invention relates to a metallic flat gasket comprising at least two gasket layers through which at least one through-opening extends. Of the gasket layers, one is shortened compared to the others and has a smaller surface area. A bead, which surrounds the through-opening in a self-contained manner, is provided in a relatively extensive gasket layer. The shortened gasket layer is not present in an outer edge region, radially externally adjoining the bead, of the relatively extensive gasket layer. Metallic flat gaskets of this type are used for example as a gasket in the region of internal combustion engines and the exhaust tract thereof, in particular as exhaust gas manifold gaskets or as cylinder head gaskets.

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. There have been proposed, to increase the compression in the region of the bead, cylinder head gaskets 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 â€œshimâ€ . 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 feet of the outer bead and may reach the water jacket. Usually it is a planar layer which serves exclusively to increase the material thickness in the region of the combustion chamber beads. 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.

In recent times use has increasingly been made of engines in whichâ€”in order to save weightâ€”the motor block is made of light metals or metal alloys such as aluminum or aluminum/magnesium. In addition the motor block has been reduced in a skeleton-like manner to the supporting parts, whereas the openingsâ€”for example the cooling water openings in the open-deck enginesâ€”are very large. This design leads to an increase in temperature and reduced rigidity of the upper side of the motor block and requires cylinder head gaskets which, even at a relatively low screwing force, reliably seal the gap between the motor block and cylinder head. Critical in the case of conventional cylinder head gaskets comprising a shim is in this regard, in particular, the fact that in the event of local weak points in the motor block and insufficient component rigidity, improvement with regard to the sealing gap movements and the distribution of compression is then hardly possible. If the compression is set too high, there is the risk that the beads will be subjected to excessive compression, lose their elasticity at high temperature and excessive compression and therefore no longer produce an adequate seal.

There was therefore a need for a metallic flat gasket, in particular a cylinder head gasket, of the type described at the outset that leads to reliable sealing even under the disadvantageous conditions of high temperature and low rigidity of an opposing surface to be sealed. The object of the invention is accordingly to devise a metallic flat gasket of this type.

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

The metallic flat gasket according to the invention has at least two metallic gasket layers. One of the gasket layers is a shortened gasket layer having a smaller surface area than the at least one other gasket layer. At least one through-opening, which is surrounded by a self-contained bead which is provided in one of the relatively extensive gasket layers, extends through the gasket layers. The shortened gasket layer is not present in an outer edge region, which does not comprise this bead, of the relatively extensive gasket layer. In one of the gasket layers, in a region of the gasket in which the shortened gasket layer is present or directly laterally adjoining this region adjacent to the position of the bead and protruding in the direction thereof, at least one structuring is formed into the gasket layer. This structuring consists of a large number of alternating elevations and depressions. In this case, in a first embodiment, the structuring is present only in certain portions in the circumferential direction around the through-opening. In the region of the structuring the overall height of the layer, including the height introduced by the structuring, is greater than the overall height of the layers in the adjacent region in which the shortened gasket layer is present. The shortened layer can in this case project into the structured region, although this is not necessary.

In a second embodiment the height or width of the structuring changes in the circumferential direction around the through-opening, thus forming at this location regions in which, as a result of the correspondingly tall structuring, the overall height of the layer is greater than the overall height of the layers in the adjacent region in which the shortened gasket layer is present.

In a modification of these two embodiments it is possible for the structuring to be introduced in the shortened layer, in such a way that in the cross section thereof a structured higher region, an unstructured low region and a structured higher region succeed one another.

The structuring of the gasket layer produces locally in a portion around the through-opening a region in which the material thickness is greater than it would be without the structuring. This region is expediently arranged in such a way that it is located at the location where, in the opposing surface to be sealed (i.e. for example the motor block or cylinder head surface) a site of reduced component rigidity is located. Similarly in a structuring, the height of which changes over the circumference thereof, the greater height will be used in the regions of reduced component rigidity. The material thickening produced by the structuring ensures that sufficient compression can be achieved in this critical region.

Critical regions of reduced component rigidity are located, in the case of engines, for example in the region between adjacent cylinder bores or else in the region of undercuts in the cylinder head. Accordingly, the structuring according to the invention is preferably arranged in these regions. The critical regions can however also be all remaining regions around a through-opening in a gasket in which (for example owing to the low material thickness, defects in manufacture (for example surface irregularities) or for other reasons) reduced component rigidities or local structural weak points of the component are to be expected in the adjacent opposing surface to be sealed.

The structuring can be present either between the bead and through-opening or on the side of the bead that is remote from the through-opening or else on both sides of the bead. In a preferred embodiment the longitudinal extent of the structuring reaches only in certain portions around the through-opening, but does not surround said through-opening entirely, but is instead limited to the particularly critical regions such as, for example, a web region between adjacent through-openings. The structuringâ€”in general simply for reasons of spaceâ€”is generally smaller in its width extent than in its longitudinal extent. Preferably, it is configured in a strip-like manner and in particular in the form of an annular segment. In the latter case the structuring expediently follows the course of the through-opening or the bead surrounding said through-opening.

In a preferred variation of the invention the structuring is configured in such a way that its alternating elevations and depressions extend linearly. An undulatory structuring of the corresponding region of the gasket layer is formed in this way. Particularly preferably, the elevations and depressions are in this case configured in the form of concentric ring segments. The cross section of the wave crests and wave troughs of the undulatory profiling in a section in the radial direction can in principle also be configured in any desired manner. Preferred shapes have a sinusoidal, trapezoidal or zigzag-shaped cross-sectional profile. Modifications of these shapes, for example with flanks rising at differing degrees of steepness, flattened peaks, etc. are however also conceivable. The cross-sectional shape can be the same for all wave crests and wave troughs or differ for individual wave crests and/or wave troughs. It is also possible to vary the cross-sectional shape in the course of a single wave crest or wave trough. Such structurings with annularly closed elevations and depressions 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 structuring of the present invention. Reference may therefore be made to the content of the aforementioned documents.

In an alternative embodiment the elevations and depressions of the structuring are arranged on at least one set of virtual straight lines extending substantially parallel over the total extent of the structuring. 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, whose priority is claimed in this respect. The elevations and depressions are preferably trapezoidal, triangular, rounded or rectangular in cross section.

The set of straight lines extending substantially parallel are virtual lines. Although these lines continue over the entire surface area of the structuring, 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. The term â€œa set of straight lines extending substantially parallelâ€ refers, in the case of a substantially parallel course of the lines, to a departure from parallelism of at most 5Â° and in particular at most 2Â°.

The elevations and depressions in the compensating region 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 structured region, the elevations of which protrude beyond both surfaces of the gasket layer. The material thickening produced by the structuring therefore affects both surfaces of the gasket layer. In order to make the material thickening in the structured region effective fully for the neighboring gasket layer, the structured region of the structured gasket layer can be for example cranked in the direction of the neighboring gasket layer. Likewise, asymmetrical tool configuration allows the elevations of the structured region to protrude only beyond one surface of the structured gasket layer.

As a whole, the embossed region 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 compression. 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 region. 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.

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.

The structured region 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.

On the whole, it should be noted that the region of the structuring is a region of increased plastic deformation of the gasket layer that has no or only very little elasticity. Accordingly, the structures of the structuring are much smaller (for example compared to conventional elastically deformable beads). Preferably, the height of the structuring is set in such a way that the elevations protrude by from 0.01 to 0.4 mm beyond the gasket layer into which they are introduced. The height depends in this case primarily on whether or not the structuring overlaps the shortened layer. In the former case (overlap) the height is preferably between 0.01 and 0.05 mm, in the latter case between 0.09 and 0.40 mm. The height can be set during the elaboration 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 portions or over the entire structured region. The distance between adjacent parallel elevations is expediently in a range of up to 2.0 mm, preferably up to 1.6 and particularly preferably up to 1.3 mm, in particular up to 0.7 mm. If the elevations do not have any peak point, but rather a flattened peak region, the distance between the center points of these peak regions is measured, in all cases in a plane which is parallel to the plane of the gasket layer.

The structuring in the structured region imparts to the structured 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 structuring is in this case 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 structured region. 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.

The embossing of the structured region allows the structuring to be set variably in a very broad range without the need for additional material. The structuring does notâ€”as stated hereinbeforeâ€”have to be configured uniformly over the entire structured region, but can rather vary over the surface area of the structured region. A topography can therefore be generated in the structured region which facilitates purposeful influencing of the compression of the bead layer and allows adaptation to the opposing surfaces to be sealed and the component rigidities thereof. Expediently, the topography in the structured region is in this case selected in such a way that the sealing gap movement is as uniform as possible.

The structuring can in principle be configured in any desired one of the gasket layers. One possibility is to configure the structuring in the shortened gasket layer. As the shortened gasket layer has only a comparatively short spatial extent, the structuring will generally extend along one or both of the outer edges thereof, whereas the interior is planar in its configuration and serves as a contact region for the bead. Another possibility is for the structuring to be configured in at least one of the relatively extensive gasket layers. It is then located either in a region in which the shortened gasket layer is present or directly laterally adjoining an outer edge of the shortened gasket layer. The term â€œdirectly adjoiningâ€ means in this case that the distance between the edge of the structuring and the outer edge of the shortened gasket layer is no more than 3 mm, preferably no more than 2 mm. As mentioned hereinbefore, the structuring can also be present on both sides of the bead.

If the structuring configured in a relatively extensive gasket layer overlaps the shortened gasket layer, there is produced in the region of the structuring a local thickening, in the region of which the sums of the thicknesses of all gasket layers present therein is greater than the sum of the thicknesses of all gasket layers in a region adjoining the structuring. A thickened region, which can accommodate increased compression and reduce the compression acting on the bead, is in this way formed laterally adjacent to the bead. Purposeful selection of the height of the structuring allows the sealing gap movement to be limited in this case. It is also possible to configure structurings in both the shortened and a relatively extensive gasket layer. The structurings are then preferably arranged in regions which are laterally offset relative to one another.

If, on the other hand, the structuring does not overlap the shortened gasket layer, the structuring must be configured in such a way that the overall thickness in the region of the structuring is greater than in the adjacent region comprising the shortened layer.

In the simplest embodiment the metallic flat gasket according to the invention has in the shortened gasket layer just a single through-opening which is enclosed by a bead. The shortened gasket layer is then predominantly annular and in particular circular. In most 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 relatively extensive gasket layer. In the case of a plurality of through-openings, the shortened gasket layer is preferably configured in a spectacle-like manner, such as is in principle already known in the art for shims (cf. EP 1065417 A2).

If the metallic flat gasket according to the invention has a plurality of through-openings, each surrounded by a bead, and if the region of the lowest force introduction is at the same time located in the region between the through-openings, the structuring will preferably be present in this region of reduced force introduction, i.e. between adjacent through-openings and in particular only at this location. In an arrangement of this type, allowance can be made for the reduced component rigidity in the narrow web region between adjacent through-openings (for example the cylinder bores in a motor block) and a suitable setting of the compression acting on the bead can be ensured at this location. If there is only a very short distance between adjacent through-openings, it is also possible for the beads to merge in the web region between the through-openings to form a single bead portion. In such cases there is no longer any space for a structuring arranged between the feet of the beads which are remote from the through-openings, at least in the central region where the width of the web is most narrow. However, structurings can be arranged in one or both web edge regions which are adjacent to the central region, as here the edges of the through-openings and the beads depart from one another again.

In addition or as an alternative to the arrangement of the structuring in the web region between adjacent through-openings, the arrangement can in principle be present in the regions in which reduced effective force introduction results from the interplay of the screwing force introduced and the local rigidity of the components to be sealed. More than one surface-structured region can also be present around a through-opening.

In a simple configuration the metallic flat gasket according to the invention has, in addition to the shortened gasket layer, just one further relatively extensive gasket layer into which the at least one bead is then introduced. The structuring can be located in either the shortened and/or the relatively extensive gasket layer.

If the metallic flat gasket has, in addition to the shortened gasket layer, more than one relatively extensive gasket layer, the relatively extensive gasket layers can be the same or different in their configuration. For example the bead can be introduced into one, whereas the other has the structuring and if appropriate also a bead for sealing the through-opening. If it has no bead, the layer is for example a layer which is planar apart from the structuring, which is usually referred to as a spacer layer and contains no beads, folds or the like over its entire extent and serves predominantly to set the overall thickness of the composite structure consisting of a plurality of gasket layers. Alternatively, the structuring and bead are located in the same relatively extensive gasket layer.

Preferred is a variation of the flat gasket according to the invention comprising at least three gasket layers in which at least two relatively extensive gasket layers have mutually complementary beads and in particular beads which are arranged in a mirror-inverted manner with respect to one another. In this case the 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 a plurality of relatively extensive gasket layers, these gasket layers are preferably made of the same material in order to obtain the same spring constant for the beads in the 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 andâ€”if the same spring constant is desired for the beads surrounding the through-openingâ€”to set this spring constant by shaping the beads or in another manner known per se.

Irrespective of this, it is in principle possible to vary the shape of the bead in order to change its properties in the circumferential direction and optimally to adapt them to the predetermined conditions. In a manner known per se, preferably at least one of the following properties is in this case changed in the circumferential direction: the cross-sectional shape of the bead, its height and its width. In principle, it is also possible to adapt the bead properties by means of chemical treatment, laser irradiation or heat treatment. In regions of reduced force introduction, the rigidity of the bead can in this case be purposefully increased.

Furthermore it is possibleâ€”especially if the structuring is provided in the shortened layer and if, in the case of a gasket comprising at least two relatively extensive layers with full beads, the bead apices thereof point toward one anotherâ€”to provide a cranking in at least one of the beaded layers between the full bead and the combustion chamber, the height of the cranking being much lessâ€”for example â…“ the heightâ€”than the height of the bead or to incline this portion out of the plane in such a way that it points in the direction of the other extended layer. These measures can bring about an additional preseal with respect to combustion gases.

In the so-called â€œhinterlandâ€ of the flat gasket according to the inventionâ€”i.e., in the outer edge region where the shortened gasket layer and the structuring are not presentâ€”the flat gasket can in principle be configured as is known in the art. In principle, the shortened gasket layer is configured to be only as large as is necessary for the function of the gasket. Its extent is determined mainly by the dimensions of the beads which are present in the same region as the shortened gasket layer or by the dimensions of the water jacket. Generally the shortened gasket layer has a width (e.g. from the combustion chamber) which is not greater than seven times the distance between the feet of the bead in its region. As mentioned hereinbefore, further openings can be present in the â€œhinterlandâ€ of the gasket. 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 introduced into the at least one relatively extensive gasket layer. The elastomer can be applied to the gasket layer on one or both sides or sprayed onto the opening edge. The sealing elements of the â€œhinterlandâ€ can also be configured in a manner known per se as separate regions (what are known as inserts) which are inserted into the gasket layer.

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 into which beads are introduced as sealing elements for through-openings. For the other gasket layers, which have no beads, softer steel, for example construction steel, can be used. High-grade steels or carbon steels can be used in this case. 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. In this case the coatings known per se can be used to improve the microsealing, the sliding friction properties, etc. The coating can be applied after the embossment or precoated, even coil-coated material can be embossed.

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.

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 or the like. The term â€œflat gasketâ€ 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 open-deck engines in which the water openings are open toward the upper side of the motor block. The shortened gasket layer performs the function of a conventional shim. In contrast to the prior art, a gasket according to the invention adapts, on account of the purposeful arrangement of the structuring in regions in which structural weak points or a reduced rigidity of the components to be sealed are present, more effectively to the opposing surfaces to be sealed and ensures more permanent tightness.

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:

FIG. 1 shows in partial figures a-f schematic plan views onto examples of a metallic flat gasket based in each case on the example of a cylinder head gasket;

FIGS. 2 to 18 are schematic partial cross sections of various exemplary embodiments of cylinder head gaskets according to the invention in a region around a combustion chamber opening in the gasket according to FIG. 1, and

FIG. 19 is a schematic partial cross section through a structuring, which is provided with elevations and depressions, of a metallic flat gasket according to the invention.

FIG. 1-a shows a metallic cylinder head gasket 1 in a plan view onto a relatively extensive gasket layer 3 extending substantially over the entire surface of the opposing surfaces to be sealed (i.e. of a motor block and a cylinder head). The relatively extensive gasket layer 3 is for example made of spring steel. Formed therein are various through-openings, namely inside the gasket layer three through-openings 4 which are arranged next to one another and correspond to the combustion chamber openings. Around the combustion chamber openings 4, various further openings 8 are present in the second gasket layer 3 toward the edge 9 of the gasket 1. These correspond to screw openings, whereas oil openings and openings for cooling liquid are not shown in the present figure for the sake of clarity. Such openings can however be configured in accordance with the prior art.

The through-openings 4 are each surrounded by a bead 5 enclosing said through-openings. The course of the beads 5 is in this case specified by two lines which illustrate the position of the bead legs. The cross-sectional shape of the beads 5 may in principle be of any desired shape. In FIGS. 2 to 18 the beads 5 have a trapezoidal cross section. Beads having a rounded cross section can however also be used.

On the side of the bead 5 that faces the combustion chamber 4, a structuring 7 extends at a distance from the bead but reaching up to the edge 40 of the combustion chamber. Whereas the beads, also for reasons of space, are guided through the web region 30 in such a way that in each case only the leg facing the edge 40 of the combustion chamber is continued, whereas the other leg is extended to the corresponding bead leg of the bead of the adjacent combustion chamber, the remaining space is sufficient to guide the structuring 7 with unreduced width through the web region 30, so any structuring 7 annularly encloses a combustion chamber 4.

Details A and B illustrate the course of the structuring 7 in a preferred embodiment along the edge 40 of the combustion chamber opening 4. The partial images show also the structure of the beads 5 comprising two respective bead legs 50, 51 and a bead apex 52 located therebetween (two of the four lines coincide in the overviews). The structuring 7 is configured over its entire course in the form of alternating elevations 31 and depressions 32 extending on virtual lines which are parallel to one another. In the exemplary embodiment shown, these structures 7 take up an approximately circular region extending concentrically with a combustion chamber opening 4. As a result, the direction of extension of the elevations 31 and depressions 32 extends approximately parallel in portions (in proximity to detail A) and in other portions transversely (see detail B) to the edge 40 of the combustion chamber opening 4 or to the bead 5. A large region of transition extends in each case between these aforementioned portions. In the case of an identical cross-sectional configuration, the structuring causes transversely to the bead greater rigidification of the structured regions than the structuring parallel to the bead. The compensation for the differing component rigidities may thus in some cases be achieved without further measures. Furthermore purposeful configuration of the density of the elevations and depressions or other parameters of their cross-sectional structure allows purposeful compensation for the component rigidities to be achieved.

Unlike in FIG. 1-a, in the following exemplary embodiments 1-b to 1-e the bulk of the structuring extends on the side of the bead 5 that is remote from the combustion chamber 4. In the example of FIG. 1-b a structuring 7 has in this case been dispensed with in the web region 30. The structuring 7 has however been widened in entrance regions 34 to the web regions 30.

In comparison to the exemplary embodiment of FIG. 1-b, in that of FIG. 1-c parts of the web region 30â€”in addition to the enlarged entrance region 34â€”are also structured. The structuring is in this case located between the continuous bead legs. The narrowest region of the web does not however have a structuring owing to lack of space.

In the exemplary embodiment according to FIG. 1-d as well, the course of the structuring according to FIG. 1-b is supplemented with a structuring 7 in the web region 30. In this case, however, the structuring extends on the side of the embodied bead that faces the combustion chambers and runs through all of the web region.

Furthermore FIG. 1-e demonstrates that it is not necessary in every application for the structuring 7 to enclose the combustion chambers 4 annularly or in a spectacle-like manner. In this case the entrance regions 34 to the web regions 30 do not have a structuring either. Furthermore the detailed views of FIG. 1-e show that the two sets, which are present in the example, of virtual straight lines, which are arranged substantially orthogonally with respect to one another, can intersect in the regions in which both sets actually form elevations and depressions, as is shown by way of example in region A in detailed view F. Detailed view E shows on the contrary a region of transition in which, starting from a structuring which maps only the parallel lines extending from the bottom left to the top right in elevations and depressions (region C), a turning, similar to a miter, of the elevations and depressions which are actually present takes place, so the elevations and depressions extend continuously on the second set of parallel lines from bottom right to top left (region B). The regions of transition as shown in detailed views E and F are in this case preferably located in the region which is remote from the fastening means openings.

Finally FIG. 1-f shows that there are also applications in which the structuring is restricted to highly limited regions, for example to the actual web region. A peripheral structuring has been dispensed with in this case owing to the conditions in the respective engine. Similarly in the example of FIG. 1-e it would be possible, if the engine conditions called for this, to dispense with the structuring 7 in the region 39 between the broken lines 38 drawn by way of example, if compensation for low component rigidities is necessary only in the region 37 of the longitudinal rims.

The examples of FIGS. 1-a to 1-f, for reasons of clarity, show the structuring in each case in the top gasket layer. As will be demonstrated hereinafter, the structuring can however also be located in a lower gasket layerâ€”which cannot be seen in the plan views according to FIGS. 1-a to 1-f.

As may be seen in the cross sections of FIGS. 2 to 17, all of the gaskets disclosed therein each have two further gasket layers. The gasket layers cannot be seen in the plan view of FIGS. 1-a to 1-e, as they are arranged below the gasket layer 3. The gasket layer 2 arranged immediately below the gasket layer 3 is a shortened gasket layer which is much shorter than the relatively extensive gasket layer 3. The shortened 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 up to seven times the size of the distance between the feet 50 and 51 of the bead 5.

The shortened gasket layer corresponds to a shim and fully exposes the edge region 6 of the second gasket layer 3. Accordingly, the 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 and a further relatively extensive gasket layer 3â€² arranged below the gasket layer 2. 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 shortened 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 by means of the beads 5.

The further gasket layer 3â€² likewise has a surface area corresponding substantially to the extent of the opposing surfaces to be sealed. It is for example oriented in the direction toward the motor block. The gasket layer 3â€² also has beads 5â€² which each surround one of the combustion chamber openings 4. The shape and course of the beads 5â€² correspond fully to those of the beads 5 of the gasket layer 3. The beads 5 and 5â€² are therefore configured mirror-symmetrically with respect to one another and rest against one another, with the exception of the example from FIG. 17, with their bead apices. The material of which the gasket layer 3â€² is made also corresponds to that of the second gasket layer 3. As a result, the beads 5 and 5â€² have the same spring characteristic.

As is indicated by the broken lines in FIG. 2, the gaskets according to the invention can also contain more than three gasket layers. In the example shown two additional cover layers 3â€³ and 3â€²â€³ are present, of which the former corresponds to the gasket layer 3â€² and the latter to the gasket layer 3. The beads 5â€³ and 5â€²â€³ again extend in a mirror-inverted manner with regard to the beads 5 and 5â€², respectively, of the respectively adjacent gasket layer. In the example of FIG. 18 the gasket contains a smooth sheet metal layer 100 containing neither the structuring nor beads. A layer of this type is often configured so as to be thicker than the remaining layers and can serve to adapt the overall height of the gasket to the sealing gap to be sealed.

The exemplary embodiments shown in FIGS. 2 to 17 differ from one another in terms of the arrangement of the structuring 7. In all cases, however, the structuring 7 serves locally to adapt the gasket to regions of the opposing surfaces that are particularly critical for sealing and, in the examples shown, specifically to the surface of the motor block or the cylinder head. The structuring 7 is in each case arranged in such a way that it allows a local increase in compression in the critical region, compared to a situation in which the structuring is not present. This increase in compression is achieved as a result of the fact that, in the corresponding gasket layer, elevations 31 and depressions 32 are provided, based on which the thickness of the gasket layer in the structured region increases relative to the original thickness of the gasket layer (i.e. the thickness prior to structuring). Depending on the embodiment, the surface elevation protrudes beyond just one surface or beyond both surfaces of the gasket layer.

In the variations shown in FIGS. 2 to 5 and also in FIG. 17, the structuring is in each case configured in the shortened gasket layer 2 and protrudes beyond both surfaces thereof. FIGS. 2 and 3 show the arrangement in a region between the bead 5 and combustion chamber opening 4, FIGS. 4 and 17 show the arrangement on the side of the bead 5 that is remote from the combustion chamber opening 4, and FIG. 5 shows the arrangement on both sides of the bead 5. The structuring 7 is located in the edge regions of the gasket layer 2. The central region is planar so as to supply a flat contact region for the beads 5, 5â€².

In the gaskets according to FIGS. 6 to 16 the structuring 7 is present in the relatively extensive gasket layer 3, in FIGS. 9 and 13 to 16 it is additionally present in the further gasket layer 3â€². The structuring 7 is in each case configured in a strip-like manner and follows in its course the course of the adjacent bead. In the gaskets according to FIGS. 6, 8 and 9 the structuring is located between the bead 5 and combustion chamber opening 4, in FIGS. 7, 10 and 16 on the side of the bead that is remote from the combustion chamber opening 4, and in FIGS. 11 to 15 on both sides of the bead 5. Whereas in FIGS. 11 and 12 the two-sided structure is introduced in the same gasket layer (3), in FIGS. 13 and 14 it is present on each side on another gasket layer (3 and 3â€²). In FIG. 15 finally both layers (3 and 3â€²) have structurings 7 on both sides.

In the examples of FIGS. 6, 7, 11 and 14, as on the side remote from the combustion chamber in FIG. 13, the structuring 7 is arranged laterally of the shortened gasket layer 2. There is therefore no overlap between the gasket layer 2, which is completely planar in all of the examples of FIGS. 6 to 12, and the structuring 7 in the compressed state either. The height which is additionally introduced by the structuring 7 into the structured region is in this case greater throughout than the thickness of the shortened gasket layer 2. This ensures that the gasket in all cases has its greatest thickness in the structured region. The height which is introduced relative to the region of the beads 5 and 5â€² therefore corresponds to the height introduced by the structuring into the structured region less the thickness of the shortened gasket layer 2. It is thus possible purposefully to introduce only small cambers by means of the structuring. The structuring therefore brings the bead locally into a secondary loading connection, whereas in the remaining regions it is in a main loading connection.

In FIGS. 8 to 10, 12, 14 to 18, and also in FIG. 13 on the side facing the combustion chamber, the shortened gasket layer 2 has a larger extent than in the figures described hereinbefore, so the structuring 7 and shortened gasket layer 2 overlap. The structuring is less deep than in the previously disclosed examples. The thickness additionally introduced by the structuring 7 in this case is less than the thickness of the shortened gasket layer 2.

If the structuring is provided in the shortened gasket layer 2, this layer will usually be structured only to such an extent that its thickness, including the structuring, is less than twice the initial thickness of the metal sheet. This is clear from the examples of FIGS. 2 to 5.

In the illustrated examples the structuring 7 consists of elevations 31 and depressions 32 which are each arranged in alternation on straight lines. The straight lines are virtual lines extending in parallel arrangement over the entire structured region. These virtual lines intersect in this case also the through-openings 4 and the beads 5 surrounding said through-openings. The elevations and depressions are in this case however present only in the hatched regions. In the preferred embodiment shown in details A and B from FIG. 1-a all elevations are arranged on adjacent parallel lines. It is however also possible to arrange the elevations and depressions on mutually adjacent parallel lines so as to be in each case offset, so the elevations and depressions alternate also in a direction perpendicular to the parallel lines. Overall, this gives rise to a chessboard-like arrangement of the elevations and depressions in the structured region 7.

The height by which the elevations protrude beyond the surface of the gasket layer in the direction of the adjacent bead can be set so as to correspond to the desired compression. In this case it is in principle possible to vary the height of the elevations in the structured region. In this way allowance can be made for the rigidities of the components 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.

As mentioned hereinbefore, the elevations 31 and depressions 32 of the structuring 7 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 embossed 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. 19.

FIG. 19 shows a detail from a region of a gasket layer, in which a structuring 7 is present. Elevations 31 and depressions 32 are embossed into this region. The elevations 31 protrude by a height H beyond the surface 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 D₃₆in the flank region is therefore less than the thickness D₃₁of 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. For demonstration purpose, the extent of the flank tapering is exaggerated in FIG. 19. It is frequently between 10 and 25%, in particular between 13 and 19%. FIG. 19 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.