Patent Application
20090200754
The invention relates to a flat gasket comprising a gasket plate incorporating a plurality of passage openings for sealing a seal gap bounded by the seal surfaces of machine components (e.g. the seal surfaces of a cylinder head and an engine block), wherein the gasket plate comprises at least one first sheet metal layer which, on at least one side thereof, has at least one elevated portion that is elongate in a plan view of the flat gasket and includes a crest provided for pressing against at least one seal surface of a machine component, and wherein the elevated portion has an elongate base body formed out from the first sheet metal layer, the material of said base body being constituted in such a manner and the cross section thereof being configured in such a manner that the base body is pressure and creep-resistant and is thus not deformable in height in at least a first longitudinal section thereof and preferably over the whole or virtually the whole length of the base body under the maximum load occurring during the installation of the flat gasket as well as during operation of the machine.
Such flat gaskets in the form of cylinder head gaskets are known from DE-103 24 667-A1 as well as from the EP-0 485 693-B1 which is dealt with in this document.
In the following, the invention is discussed on the basis of a cylinder head gasket, although the subject matter of the invention could also be another type of flat gasket, for example, an exhaust manifold gasket.
The cylinder head gasket described in EP-0 485 693-B1 includes a one-piece metallic gasket plate the design of which is based on the following considerations; For the functioning of a cylinder head gasket, the engine block (crank case) and the cylinder head cannot be regarded as absolutely rigid components; rathermore, the tightening of the cylinder head bolts and the changing gas pressures in the combustion chambers lead to flexure of these engine components, i.e. in the long run, this leads to the seal gap that is bounded by the seal surfaces of the engine components and accommodates the cylinder head gasket not retaining the shape of a thin, plane-parallel plate. In addition, the locally different thermal expansions of the engine block and the cylinder head when the engine is in operation (this also occurring in the axial direction of the combustion chambers) and also the locally different component-rigidities of these two engine components at their seal surfaces as well as in the areas bordering on these seal surfaces (due to recesses and cavities in the engine components) have an effect on the topography of the seal surfaces of the engine components bounding the seal gap when the engine is operating. Now the design of the gasket plate of the cylinder head gasket in EP-0 485 693-B1 is based on the basic idea of adapting the shape of the gasket plate of the cylinder head gasket to the topography of the seal surfaces of the engine components in the areas thereof effective for the sealing process such as occur after tightening the cylinder head bolts, i.e. after the mounting of the cylinder head gasket, and the resilient deformations of the components that are necessary for the maintenance of the seal when the engine is in operation are not permitted to occur at or in the cylinder head gasket, but rather, on or in the engine components, the engine block and the cylinder head, so that the gasket plate of the cylinder head gasket can be made of a material which is stable, i.e. not deformable in thickness when tightening the cylinder head bolts and during operation of the engine.
Naturally, this basic concept for the design of a cylinder head gasket does not exclude the gasket plate from being provided with a coating which serves for the e.g. so-called micro sealing process and can adapt to the surface roughness of the seal surfaces of the engine components; such a coating can be of a synthetic material or could be a coating of another material, e.g. it could also consist of a metal.
Now, there are cases wherein cylinder head gaskets are used in which a cylinder head gasket of the type mentioned hereinabove incorporating a gasket plate which can be regarded as rigid does not lead to optimal results; in the case of a reciprocating piston internal combustion engine incorporating a so-called chain case, the latter is frequently formed by a chain case lower part bordering on the engine block and a chain case upper part bordering on the cylinder head, whereby one of the two parts could also be formed on the neighbouring component, the engine block or the cylinder head; the seal gap is then bounded by the engine block, the cylinder head and at least one chain case part. If the cavity of the chain case is also to be totally or partly sealed by the cylinder head gasket, then this also extends over at least a portion of the chain case part that is manufactured as a separate component. It is not rare however, that, as a consequence of manufacturing tolerances, the seal surface of the chain case part that was manufactured as a separate component and which faces the cylinder head gasket is not exactly flush with the adjacent seal surface of the engine block or the cylinder head after the assembly thereof so that the seal gap which is to be sealed by the cylinder head gasket has a step-like widening or narrowing at the joint between the chain case part and the engine block or the cylinder head and can only be sealed with difficulty by means of a cylinder head gasket comprising a rigid gasket plate—if, for example, manufacturing tolerances lead to the seal gap being narrower in the vicinity of the chain case than it is between the engine block and the cylinder head, a cylinder head gasket comprising a rigid gasket plate can lead to the specific surface pressures between the cylinder head gasket and the engine block on the one hand and the cylinder head on the other in the portion of the seal gap located between the engine block and the cylinder head being insufficient, at least in certain places, to produce a reliable sealing effect under all operating conditions. If a cylinder head gasket of the type mentioned hereinabove has a plurality of relatively closely adjacent passage openings which are to be sealed with respect to one another and in relation to the environment by a plurality of approximately strip-like or linear elevated portions of the cylinder head gasket that abut one another or merge into one another, then the system consisting of the cylinder head gasket and the seal surfaces of the engine components can sometimes be statically over-specified in such a region and lead to a deficient sealing effect. In addition, permanent deformations of the engine block seal surface can occur in those regions of the engine block in which the cylinder head bolts engage, and this can likewise lead to problems, in particular, when replacing the cylinder head gasket, when using an exchange seal comprising a rigid gasket plate.
These problems can be eliminated or at least reduced with the cylinder head gasket described in DE-103 24 667-A1, namely, in that in the case of a seal of the type mentioned hereinabove such as is disclosed in DE-103 24 667-A1, the base body or the base bodies also have longitudinal sections which are deformable in height in plastic manner, possibly also, resiliently to a small extent, under the load arising when mounting the seal as well as in operation thereof, be it because the base body is differently dimensioned in such a longitudinal section and/or has a different cross section than in the longitudinal sections that are not deformable in height, or because the base body possesses other material properties in the longitudinal sections that are deformable in height than in the longitudinal sections which are not deformable in height. In consequence, the cylinder head gasket described in DE-103 24 667-A1 can adapt to alterations in the topography of the seal surfaces of the engine components within selected regions, alterations which can occur when tightening the cylinder head bolts, i.e. when mounting the cylinder head gasket, and/or during the first warming of the engine, and also possibly during an initial period of operation of the engine; furthermore, such a cylinder head gasket is, if necessary, in a position to compensate for manufacturing tolerances and adapt to long term alterations of the seal surfaces of the engine components that were caused whilst the engine was in operation, and especially when installing a replacement seal.
From the above discussion of the state of the art, it is apparent that the known cylinder head gaskets described therein can only reliably fulfil their sealing function if the engine components between which such a cylinder head gasket is clamped have an overall component elasticity in the region of the elevated portions of the gasket plate which is such that, despite the locally different thermal expansions and the changing gas pressures in the combustion chambers, the seal surfaces of the engine components are always pressed against the cylinder head gasket with at least the specific surface pressure required for the sealing process when the engine is in operation, namely, against the crests of the elevated portions when the gasket plate is provided with elevated portions serving for the sealing function on both sides thereof, or against the crests of the elevated portions as well as against the surface portions of the gasket plate opposite the elevated portions when said gasket plate is only provided with such elevated portions on one side thereof.
However, it has now been shown that there are operational fields for flat gaskets of the type under discussion wherein the machine parts do not have the requisite component elasticity at every point where this is necessary to achieve reliable sealing with the help of such a flat gasket.
Consequently, the object of the invention is to provide a flat gasket of the type mentioned hereinabove such as is disclosed in particular in DE-103 24 667-A1 which can reliably fulfil its sealing function even if the machine parts, between which the flat gasket is to be clamped, do not have the requisite component elasticity to provide reliable functioning of the machine in those regions or in a part of these regions between which the elevated portion or the elevated portions of the gasket plate lie when the flat gasket is in position.
In accordance with the basic concept of the solution in accordance with the invention, this object is a deviation from the principle of the known, at least substantially pressure resistant, single layered flat gaskets with supporting elevated portions which are not deformable in height or are at most only slightly deformable in height in certain sections and in a substantially plastic manner even during operation of the machine, and it is proposed that the gasket plate of the known flat gaskets be supplemented by at least one second sheet metal layer which has at least one bead that is deformable in height in a springy-resilient manner in the region of an elevated portion or the elevated portions of the first sheet metal layer (as seen in a plan view of the gasket plate), so that the elevated portion and the bead together form a thickness-resilient region of the flat gasket.
In particular in the case of a cylinder head gasket, sliding movements between the flat gasket and the seal surfaces of the machine components (in particular, the engine block and the cylinder head) between which the flat gasket is clamped can arise during operation of the machine, i.e. when the engine is operating, that is to say, relative movements running parallel to the plane defined by the flat gasket which can also lead to wearing of the flat gasket. The characterisation of the base body or the base bodies of the flat gasket in accordance with the invention as not being deformable in height does not therefore exclude the height or the thickness of a base body being decreased by frictional wear during operation of the machine.
Even if the preferred embodiments of the flat gasket in accordance with the invention are those wherein the base body or the base bodies is or are not deformable in height overall under the maximum load arising during installation of the flat gasket and in operation of the machine, a base body of a flat gasket in accordance with the invention can be produced as regards the material and cross section thereof in such a manner as to be deformed in plastic manner in those regions in which the highest specific surface pressures arise when the flat gasket is in position and during operation of the machine, or everywhere to a slight extent even though to different degrees. Consequently, it is to be understood that a base body or a base body section which is at least substantially pressure and creep-resistant and is thus not deformable in height under operational conditions also includes a base body or a base body section the height of which(even overall in some circumstances) decreases slightly under operating conditions due to a plastic deformation, namely, by locally differing amounts on the one hand and at most by 50 μm on the other, but better, by at most 20 μm and advantageously, by a significantly smaller amount, namely, at most 10 μm.
In this connection, it is pointed out that an important feature of the invention is to be seen in the fact that the base body or the base bodies of a flat gasket in accordance with the invention is or are not resiliently deformable in the height thereof at least in areas thereof, but preferably everywhere, under the dynamic loads arising during the operation of the machine. Hereby, one must take into consideration that no metallic article can be regarded as being absolutely rigid, but rather, always exhibits an unavoidable even though minimal resilient deformation behaviour, and possibly also a plastic deformation behaviour; such an inevitable deformation behaviour should not therefore be excluded by the definition of the present invention.
The second sheet metal layer can extend over the whole or over only a part of the gasket plate—in the latter case, a plurality of second sheet metal layers can also be provided with beads which are arranged close to one another (although possibly spaced from each other) above or below the first sheet metal layer. Naturally, if the component elasticity of the machine parts is adequate in some places but is inadequate in other places, then it also suffices to provide such a bead or such beads just for that elevated portion or those elevated portions or that longitudinal section or those longitudinal sections of the base body or the base bodies where the component elasticity of the machine parts is not sufficient.
The type of flat gaskets affected by the present invention could of course comprise a gasket plate in the conventional sense, but equally however, it is also possible to provide a plurality of flat gasket segments on which elevated portions and beads are provided, and to interconnect the seal segments by connecting webs or the like so that a skeleton-like structure ensues.
Even if the previous discussion alluded to the flat gasket in accordance with the invention having elongate elevated portions with a crest that is provided for pressing against at least one seal surface of a machine component, it follows from this formulation that not all the regions of the gasket plate which are pressed when the flat gasket is in position have to have the shape of such elongate elevated portions.
A flat gasket in accordance with the invention may have one or more of the aforementioned base bodies which can be separated from each other or connected to one another in one piece manner.
In preferred embodiments of the flat gasket in accordance with the invention, the elevated portion or elevated portions of the first sheet metal layer and the bead or beads of the second sheet metal layer serve for sealing around one or more passage openings in the gasket plate; however, the elevated portion or elevated portions, possibly together with the bead or beads, can, at least in places, also have the function of pure supporting elements, by virtue of which surface distortions of one of the machine parts or of both machine parts are prevented or at least minimized within certain regions of the latter when the flat gasket is in position, such as can be desirable for example, in the case of a cylinder head for a multi-cylinder engine in the vicinity of the longitudinal ends of the cylinder head.
By virtue of a flat gasket in accordance with the invention, not only can the posed object be achieved, but yet a further advantage can also be obtained: In particular in the case of cylinder head gaskets but frequently also in the case of other flat gaskets such as exhaust manifold gaskets for example, the engine manufacturer specifies a certain breadth (width) for the seal gap that is to be sealed by the flat gasket. Moreover, in the case of metallic flat gaskets, it is often desirable to provide around a passage opening that is to be sealed, a ring-like sealing element surrounding said passage opening, this being effected in that a sheet metal layer is raised around the edge of this passage opening, i.e. a boundary region of the sheet metal layer adjoining the passage opening is folded back on itself in order to produce around the passage opening an increased pressing action between the flat gasket and the seal surfaces of the machine components accommodating said gasket therebetween. Now, however, in the case of a single layer metallic flat gasket such as is described in EP-0 485 693-B1 or DE-103 24 667-A1 for example, a given seal gap width of more than 1.5 mm necessitates the thickness of the sheet metal layer to be so large that a bead produced in this sheet metal layer by a stamping process, a base body in the form of a rectangular bead such as is described and illustrated in DE-103 24 667-A1 for example, must, because of the given installation thickness, have such a height and consequently for technical reasons such a width that the space available in a flat gasket e.g. that between two neighbouring passage openings, for the thus resulting width of bead is not sufficient. Due to the fact that the second sheet metal layer is provided for a flat gasket in accordance with the invention, then even for a relatively large width of the seal gap, a thinner metal sheet can be used for the first sheet metal layer that is provided with the base body or the base bodies than is the case for the known cylinder head gaskets in accordance with EP-0 485 693-B1 and DE-103 24 667-A1, with the consequence that beads of relatively small width can be produced in both sheet metal layers of the flat gaskets in accordance with the invention, namely height resilient beads in the second sheet metal layer and rectangular beads forming base bodies that are at least substantially not deformable in height in the first sheet metal layer. Moreover, the comparatively small sheet thickness of the first sheet metal layer of a flat gasket in accordance with the invention makes it possible to fold back this first sheet metal layer upon itself around a passage opening that is to be sealed for the purposes of forming a sealing element, without this thereby resulting in the total thickness of the flat gasket being too large in this region in the light of the prescribed width for the seal gap.
Since, in a flat gasket in accordance with the invention, all those regions of the first sheet metal layer which are intended to accommodate compressive forces when the flat gasket is in position should not, at least predominantly, be deformable in height, whereas the bead or beads of the second sheet metal layer should be deformable in height in a springy-resilient manner, the embodiments to be recommended are those wherein the sheet thickness of the first sheet metal layer is greater than that of the second sheet metal layer.
For the second sheet metal layer, a metal sheet consisting of a high-strength steel having resilient properties (referred to as a spring steel sheet in the following) is to be preferred, but it is also possible to use another steel sheet for the second sheet metal layer, this only having springy-resilient properties in the beaded region e.g. due to it being subjected to heat treatment by means of a laser.
In order to enable the base body or the base bodies in a flat gasket in accordance with the invention to be produced by a process of forming the first sheet metal layer and for the base body to exhibit the requisite stability, preferred embodiments of the flat gasket in accordance with the invention are characterised in that the first sheet metal layer consists of an easily workable steel which is cold worked in the base body region due to said base body being stamped out from the sheet metal layer.
The bead or the beads of the second sheet metal layer may be a so-called full bead or a so-called half bead, whereby the full bead has a cross section which is approximately in the form of a circular arc whilst the half bead is approximately in the shape of a step or offset having a region running at an angle to the plane of the layer.
In order to enable the load-bearing regions of the flat gasket in accordance with the invention, i.e. those regions which are pressed when the flat gasket is in position, to adapt as much as possible to the seal surfaces of the machine components bounding the seal gap, it is of advantage if the crest of the elevated portion or the crests of the elevated portions has or have a height profile along the elevated portion or along the elevated portions which is formed, prior to the installation of the flat gasket, at least approximately in accord with the topography of the seal gap that is to be sealed by the flat gasket and results when the flat gasket is clamped between the seal surfaces of the machine components.
Above all then, if, in the case of a flat gasket in accordance with the invention, we are concerned with a cylinder head gasket, it is recommendable that the gasket plate be provided with a coating of synthetic material at least in the region of the crest of the at least one elevated portion, whereby said coating is e.g. a coating which is suitable for preventing leakages resulting from the surface roughness of a seal surface of a machine component or the seal surfaces of machine components.
Further features, details and advantages of the invention are apparent from the following description and the accompanying graphical illustration of a plurality of particularly advantageous embodiments of the flat gasket in accordance with the invention; in the drawing:
In the plan view of a cylinder head gasket in accordance with the invention that is illustrated in
This cylinder head gasket has a gasket plate bearing the general reference 10 in which there are formed combustion chamber openings 12, bolt holes 14 for the entry of cylinder head bolts, oil holes 16 for the passage of pressurised oil, an oil hole 18 for the returning oil as well as various water holes 20 for the passage of a cooling agent.
As is apparent from
Skid-like base bodies 30 having an approximately U-shaped cross section are formed out of the first sheet metal layer 22 by means of a stamping process, these bodies forming elongate elevated portions 32 protruding above the actual first sheet metal layer 22 and comprising flat crests 32a which are pressed against a seal surface of the cylinder head or the engine block when the cylinder head gasket is in position. The base bodies 30 comprise grooves 32b opposite the crests 32a.
The material of the first sheet metal layer 22 is cold worked in the course of forming the elevated portions 32 and the process of stamping in the grooves 32b that is inherent thereto, and the cross section of the base bodies 30 is dimensioned in such a way that, by taking into consideration the rigidity of the material of the first sheet metal layer 22, the resulting elevated portions 32 in the region of the base bodies 30 are pressure and creep-resistant and thus not deformable in height over at least the greater part of the length of the base bodies 30 under the maximum pressure load arising during the installation of the cylinder head gasket as well as in operation of the engine.
The second sheet metal layer 24 consists of a spring steel metal sheet and is provided with beads 24a at least in the region of one or more of the base bodies 30, and preferably in the region of all the base bodies 30, these beads being so-called full beads which extend along the base bodies 30 and bridge the grooves 32b therein, whereby the bead feet (by this, one is given to understand the two lateral edges of a bead where they merge into the adjacent flat regions of the sheet metal layer) are supported on the first sheet metal layer 22 on both sides of a groove 32b. The summit of the bead thus faces the crest 32a of the elevated portion 32.
In like manner to the first sheet metal layer 22, the second sheet metal layer 24 can extend over the whole gasket plate 10 and have a bead 24a at every point where the first sheet metal layer 22 is provided with a base body 30 that is formed out therefrom. However, in place of a single second sheet metal layer 24, this could be replaced by a plurality of mutually spaced segments of such a second sheet metal layer which are arranged next to one another on the first sheet metal layer 22 and are either separated from each other or interconnected by webs. Moreover, cases are conceivable in which a bead 24a or a region of a second sheet metal layer is not assigned to all the base bodies 30.
It is to be assumed for
However, in dependence on the materials of the cylinder head and the engine block, it can be advantageous if the beads 24a rest against the seal surface of the cylinder head and the crests 32a against the seal surface of the engine block. This is intended to be the case for the variant illustrated in
Now as can be seen from
In
The same reference symbols as were used in
In the embodiment illustrated in
In the embodiment in accordance with
The embodiment illustrated in
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2005 019 689.6 | Apr 2005 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2006/003805 | 4/25/2006 | WO | 00 | 4/8/2009 |
