Abstract:
Flat gasket with a gasket plate comprising at least one sheet metal layer, at least one fluid through-opening to be sealed, and a plurality of screw through-openings, the sheet metal layer having at least one supporting element for receiving pressing forces, and the supporting element being in the form of a bead stamped into the sheet metal layer; in order to improve the durability of the supporting bead while in operation, the bead is designed so as to form with its bead crest, in a plan view of the sheet metal layer, an endless continuous line closed within itself, so that the bead does not have any free bead ends.

Description:
[0001]    The present disclosure relates to the subject matter disclosed in German utility model application number 20 2006 003 678.4 of Mar. 9, 2006, which is incorporated herein by reference in its entirety and for all purposes. 
       BACKGROUND OF THE INVENTION 
       [0002]    The invention relates to an at least substantially metallic flat gasket with a gasket plate comprising at least one sheet metal layer, at least one fluid through-opening to be sealed (in the case of a cylinder head gasket, for example, for the passage of combustion gases or cooling water or lubricating oil), and a plurality of screw through-openings for the passage of screws therethrough for clamping the flat gasket between sealing surfaces of components (for example, the sealing surfaces of a cylinder head and an engine block), the sheet metal layer having at least one supporting element for receiving pressing forces acting on the flat gasket when the flat gasket is installed, and the supporting element comprising at least one bead stamped into the sheet metal layer and having a bead crest forming a continuous line. 
         [0003]    The invention will be explained hereinbelow with reference to cylinder head gaskets, although a flat gasket according to the invention is also suitable for other applications, for example, for a gasket between a cylinder head and an exhaust manifold, or for a so-called flange gasket between flanges of two pipes or other components to be joined to one another by screws. 
         [0004]    In single-layered and multi-layered metallic cylinder head gaskets, sealing around the combustion chamber through-openings of the gasket plate is usually effected by sealing beads stamped into one sheet metal layer or several sheet metal layers. These sealing beads enclose the combustion chamber through-openings and are mostly formed as so-called full beads with a circular arc-shaped or approximately U-shaped cross section. As these sealing beads must have elastic properties in the direction of their height, so as to also fulfill their sealing function during operation of the engine, a sheet metal layer provided with sealing beads is made of spring steel. In order to prevent the sealing beads from becoming excessively flattened when the cylinder head gasket is being installed and during operation of the engine and thereby becoming damaged (as a result of permanent breakages), the sealing beads have associated deformation delimiters (so-called stoppers), which are thickened zones of one or several sheet metal layers. When the cylinder head gasket is installed and the engine is in operation, these stoppers receive some of the pressing forces acting on the cylinder head gasket after the sealing beads have been flattened somewhat elastically owing to these pressing forces. Accordingly, these stoppers are not only deformation delimiters but also supporting elements which are associated with the sealing beads enclosing the combustion chamber through-openings. However, the present invention does not relate to such supporting elements as are associated with combustion chamber sealing beads and enclose combustion chamber through-openings. 
         [0005]    Above all, in single-layered and multi-layered metallic cylinder head gaskets, thickened supporting elements are also used at other places than around cylinder head gasket openings to be sealed, and the present invention relates to such supporting elements. In a multi-cylinder engine, the usual position of the cylinder head screws results in the cylinder head being drawn in the area of its narrow sides, i.e., its longitudinal ends, with a stronger tendency downwards, i.e., in the direction towards the engine block, than in other areas of the cylinder head. Moreover, when the engine is in operation, the high gas pressures prevailing in the combustion chambers cause the cylinder head to arch up between its longitudinal ends (albeit slightly) during operation of the engine. These two effects have already been counteracted by providing the cylinder head gasket in the area of its longitudinal ends with thickened zones which serve as elevated supporting elements for the longitudinal ends of the cylinder head. However, since a multi-cylinder reciprocating piston engine is often more susceptible to deformation in the areas of its longitudinal sides, for example, on account of the inlet and outlet ports, than in other areas, elevated supporting elements have also already been provided at the longitudinal sides of the cylinder head gaskets. 
         [0006]    U.S. Pat. No. 5,427,389-A discloses a multi-layered metallic cylinder head gasket of the kind mentioned at the outset, wherein a sheet metal layer lying inside the approximately rectangular gasket plate is provided in the end areas of this sheet metal layer in the vicinity of the two narrow sides of the gasket plate with supporting elements which are full beads stamped into this sheet metal layer. The following three different embodiments are disclosed for these supporting beads: in the first embodiment, each of the two aforementioned end areas of the sheet metal layer is provided with a straight-lined supporting bead extending in the proximity of the respective narrow side edge of this sheet metal layer and parallel thereto; in the second embodiment, the supporting bead has approximately the shape of a lying U and extends parallel to the adjacent narrow side edge and over a certain distance parallel to the two longitudinal side edges of the sheet metal layer; in the third embodiment, the supporting bead is, in a plan view of the sheet metal layer, of wave-like configuration and extends in the vicinity of the pertinent narrow side edge of the sheet metal layer approximately parallel to this narrow side edge. As has been ascertained by the firm of ElringKlinger AG, all of these supporting beads have the disadvantage that, when the engine is in operation, they exhibit wear phenomena, starting off from the free bead ends, which increase as the operating time increases, and the cause of which has not been able to be fully clarified. It is also to be assumed that the same or similar wear phenomena occur with other flat gaskets of the kind mentioned at the outset whenever the flat gasket is subjected to dynamic stresses, in particular, load variations, when in operation. 
         [0007]    The object underlying the invention was to create a flat gasket of the kind mentioned at the outset, in which the at least one supporting element formed by at least one bead has a longer service life in operation, i.e., is subject either to no wear or to only a significantly lower degree of wear than the supporting beads disclosed by U.S. Pat. No. 5,427,389-A. 
       SUMMARY OF THE INVENTION 
       [0008]    The inventors have, surprisingly, ascertained that the risk of wear can be at least significantly reduced by a simple measure, namely, in accordance with the invention, in that the bead serving to receive pressing forces (not to seal off a medium) is designed such that, in a plan view of the sheet metal layer, it forms with its bead crest an endless continuous line closed within itself, so that the bead does not have any free bead ends. Such a bead designed in accordance with the invention requires no greater manufacturing expenditure whatsoever than the manufacture of the supporting beads disclosed in U.S. Pat. No. 5,427,389-A. 
         [0009]    In conjunction with the basic concept underlying the present invention it is pointed out that the supporting bead according to the invention does not enclose any through-opening of the flat gasket and, consequently, cannot form any sealing bead. Only one exceptional case is conceivable, to which reference will be made hereinbelow. 
         [0010]    In principle, in a plan view of the sheet metal layer provided with the supporting bead according to the invention, the endless continuous line formed by the bead crest of the supporting bead could form, for example, a flat oval, a flat rectangle or the like, but, embodiments are preferred, in which, in a plan view of the sheet metal layer, the bead has, for the most part, a meandering shape. For, larger pressing forces can be received by such a supporting bead, without the risk of the supporting bead being flattened, than by a supporting bead whose bead crest follows a straight-lined or, at any rate, not meandering, course over a major part of its total length. 
         [0011]    In order that the supporting bead according to the invention can receive as large pressing forces as possible without any appreciable risk of deformation, it is recommended that the supporting bead (in a plan view of the sheet metal layer) be designed such that the meander formed by it has a relatively large “packing density”, and, it is, therefore, proposed that the supporting bead be designed such that, in a plan view of the sheet metal layer, the bead has at least substantially straight-lined meander legs joined to one another by bead arcs. This is in contrast to the supporting bead with a wave-like course shown, for example, in FIG. 5 of U.S. Pat. No. 5,427,389-A. With a view to achieving as high a degree of firmness of the supporting element according to the invention as possible, it is advantageous if, in a plan view of the sheet metal layer, at least several meander legs extend approximately parallel to one another, and it is recommended that, in a plan view of the sheet metal layer, at least in the case of several of the meander legs, the spacing between neighboring meander legs be, at the most, as large as and, preferably, at the most approximately half as large as the bead width of the meander legs. In this case, the bead arcs joining the meander legs to one another have a relatively small radius, which, in conjunction with the small width of the bead, results, in a stamping tool with which the meander bead is stamped into the sheet metal layer, in the rib, corresponding to the meander bead to be stamped, of the one half of the stamping tool being very narrow and, in series production, tending to break away at those rib portions associated with the bead arcs to be stamped. Therefore, in a preferred embodiment of the invention, in a plan view of the sheet metal layer, the bead width in the area of the bead arcs is somewhat larger than in the area of the meander legs, so as to avoid an overloading of the said tool rib at its meander arcs. 
         [0012]    In a supporting element according to the invention, formed substantially by a meander bead, free bead ends are easiest avoided by meander legs lying at two supporting element ends remote from one another being joined to one another by an elongate bead section. The ends of the two meander legs to be joined to one another could lie on the same side of the supporting element or on two different sides of the supporting element—in one case the elongate bead section is shorter than in the other case and runs only along the one side of the supporting element, in the other case, the elongate bead section runs along two sides of the supporting element that are adjacent to one another. 
         [0013]    Precisely when, as will generally be the case, a supporting element according to the invention lies in the proximity of a screw through-opening of the flat gasket, it could be conceivable to allow the aforementioned bead section joining two meander legs to one another to partially enclose the adjacent screw through-opening, so that the screw through-opening lies between the “meander bead package” and the said bead section joining two meander legs to one another. Even then, however, a supporting element according to the invention differs basically from such known metallic cylinder head gaskets in which each screw through-opening is surrounded by a bead closed within itself, which, in a plan view of the pertinent sheet metal layer, is circular, oval or of similar shape, because in the case of these known bead structures an essential feature of preferred embodiments of the supporting element according to the invention is not present, namely that the total length of that portion of the supporting bead which lies on one side of a through-opening of the flat gasket is a multiple of (at least, for example, three, four or five times) the remaining length of the supporting bead. 
         [0014]    As will be apparent from the remarks made at the outset on the various positions of supporting elements, a preferred flat gasket according to the invention, designed as a cylinder head gasket for a multi-cylinder engine, is characterized in that in the at least one sheet metal layer provided with several supporting elements, the supporting elements are arranged in at least one of the following areas of the gasket plate having an elongate shape with two narrow sides and two longitudinal sides: in the end areas of the gasket plate in the proximity of the narrow sides of the gasket plate and in the edge areas of the gasket plate in the proximity of the longitudinal sides of the gasket plate. 
         [0015]    If the flat gasket according to the invention is multi-layered, i.e., has at least two sheet metal layers arranged one on the other, it is advantageous for the bead formed in at least one sheet metal layer to project in the direction towards the other sheet metal layer, i.e., not to project at one of the two free main surfaces of the flat gasket—this could cause indentations or frictional wear phenomena on one of the component sealing surfaces between which the flat gasket is clamped. 
         [0016]    Further advantages, features and details of the invention will be apparent from the following description and the appended drawings of a preferred embodiment of a flat gasket according to the invention, a preferred embodiment of a supporting bead according to the invention and a preferred embodiment of a stamping tool for producing this supporting bead. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  shows a plan view of part of a sheet metal layer of a flat gasket according to the invention, designed as a cylinder head gasket, with supporting elements according to the invention shown schematically therein; 
           [0018]      FIG. 2  shows a plan view of the left lower corner of the sheet metal layer shown in  FIG. 1  and the supporting element according to the invention arranged there; 
           [0019]      FIG. 3  shows a section taken along line  3 - 3  in  FIG. 2  and part of the stamping tool used for stamping the supporting element; 
           [0020]      FIG. 4  shows a detail from  FIG. 2  with an enlarged plan view of an area of the supporting element; and 
           [0021]      FIG. 5  shows a section taken along line  5 - 5  in  FIG. 4  and through part of the stamping tool. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    The sheet metal layer, shown partly in  FIG. 1 , of a cylinder head gasket according to the invention will only be described hereinbelow insofar as this is required for an understanding of the invention. 
         [0023]    The sheet metal layer  10  made from sheet spring steel comprises, in the part shown in  FIG. 1 , combustion chamber through-openings  12  and  14 , screw holes  16  and  18  adjacent to the narrow side of the sheet metal layer, and further screw holes  20 , water holes  22  for passage of cooling water and oil holes  24  for passage of engine oil. The screw holes  16 ,  18  and  20  serve for passage of cylinder head screws therethrough, and the non-circular screw hole  18  serves, in addition, for passage of engine oil. For sealing around the combustion chamber through-openings  12 ,  14 , the sheet metal layer  10  is provided in the usual manner with combustion chamber sealing beads  30  with elastic properties in the direction of their height, which are stamped into the sheet metal layer. These are so-called full beads whose cross section thus corresponds approximately to the arc of a circle or a U. This also applies to the following beads stamped into the sheet metal layer  10 : circular beads  32  enclosing the screw holes  16  and  20 , oil sealing beads  34  and  36  and a so-called water bead  38 , which extends as a continuous line closed within itself around the sheet metal layer  10  in the proximity of the periphery of the sheet metal layer  10  and thus serves together with the other beads, when the cylinder head gasket is installed, to seal those spaces which cooling water can enter owing to the water holes  22  when the cylinder head gasket is installed. 
         [0024]    In the illustrated cylinder head gasket according to the invention, the sheet metal layer  10  is provided in the vicinity of the screw holes  16  and  18  with supporting elements  40 ,  42 ,  44  and  46  according to the invention, which serve, when the cylinder head gasket is installed, to support the longitudinal end areas of the cylinder head adjacent to the narrow sides of the cylinder head, more specifically, by the supporting elements forming thickened areas of the sheet metal layer  10 , which are at least substantially compression-proof, i.e., are not deformable in their height (under the pressing forces acting upon the cylinder head gasket when the cylinder head gasket is being installed and while the engine is in operation). 
         [0025]    In preferred embodiments of the invention, as shown in  FIG. 1 , the supporting elements  40 ,  42 ,  44 ,  46  are arranged not only in the proximity of the narrow side of the sheet metal layer  10  but also in the proximity of the screw holes  16 ,  18  adjacent to this narrow side so as to receive part of the pressing forces generated by the two cylinder head screws adjacent to the narrow side of the cylinder head gasket. 
         [0026]    However, a cylinder head gasket according to the invention may also be provided with one or more supporting elements according to the invention at other places. If, for example, the engine block belonging to the illustrated cylinder head gasket has a lesser stiffness at its one longitudinal side owing to cooling water cavities, namely in the area of that longitudinal side to which the water holes  22  are adjacent, when the cylinder head gasket is installed, the sheet metal layer  10  could be provided with one supporting element or with several supporting elements between two or between several of these water holes. 
         [0027]      FIG. 2  shows the supporting element  40 , serving as an example representative of the invention, which is formed by a bead  50  stamped in the sheet metal layer  10 . The supporting element  40  consists substantially of a meander-shaped structure, designated hereinbelow as meander bead  52 , which is formed by the bead  50 . As shown in  FIG. 3 , the bead  50  is a so-called full bead whose crest is designated by  50   a . The ends of the meander bead  52  that are located at the top left and the bottom right of  FIG. 2  are joined by an elongate bead section  54  in such a way that the bead crest  50   a  forms an endless continuous line closed within itself, so that the bead  50  has no free ends. As an alternative to the embodiment shown in  FIG. 2 , the ends of the meander bead  52  could be joined to one another by a bead section extending, in accordance with  FIG. 2 , to the left of and below the meander bead  52 . The meander bead  52  advantageously consists of straight-lined meander legs  52   b  which are joined to one another by bead arcs  52   a . The meander legs  52   b  extend parallel to one another and are so densely “packed”, i.e., have such a small spacing from one another, as is just still producible by a stamping operation. Owing to this high “packing density”, a particularly stiff supporting element is obtained, which is at least substantially stable, i.e., is not deformable in its height by the pressing forces that occur when the cylinder head gasket is being installed and while the engine is in operation. 
         [0028]    Virtually any outer contour (in a plan view of the sheet metal layer  10 ) of the supporting element  40  may be brought about by different lengths of the meander legs  52   b.    
         [0029]      FIG. 3  shows parts of the two halves  60   a  and  60   b  of a pressing tool  60  for stamping the bead  50 , and a cross section through the meander bead  52  and the bead crest  50   a.    
         [0030]      FIG. 4  shows a plan view of part of the meander bead  52  on an enlarged scale, wherein the meander leg  52   b  was interrupted in order to shorten the vertical extent of this figure of the drawings. In an embodiment which is representative of the invention, the thickness of the sheet metal layer  10  ranges from approximately 0.2 to 0.3 mm. The width, designated A in  FIG. 4 , of the meander leg  52   b  then lies in the range of between approximately 0.5 and approximately 0.9 mm. In the embodiment shown in  FIGS. 4 and 5 , the thickness of the sheet metal layer  10  is intended to be 0.2 mm and the width A of the meander legs  52   b  0.56 mm. 
         [0031]    From  FIG. 5 , which shows a section on line  5 - 5  in  FIG. 4  through the sheet metal layer  10  and the pressing tool  60 , in conjunction with  FIG. 4 , the following will be apparent: the, in accordance with  FIG. 5 , lower pressing tool half  60   b  has a rib  70 , the upper pressing tool half  60   a  has a groove  72 , and, in a plan view, not shown, of the pressing tool, the rib  70  and the groove  72  each have a shape corresponding to the shape, shown in  FIG. 2 , of the bead  50 , i.e., over the greatest part of their lengths the rib  70  and the groove  72  have a meander-shaped configuration, however, in that area which serves to stamp the elongate bead section  54  an elongate, for example, approximately straight-lined configuration. 
         [0032]    Owing to the sharp curvature of the arcs  52   a  of the beads, the rib  70  is subjected to high stress in those areas of the pressing tool  60  which serve to stamp the arcs  52   a  of the beads. In order to prevent the rib  70  from wearing rapidly or even breaking away in these heavily stressed areas, the bead width B (see  FIG. 4 ) at the arcs  52   a  of the beads is, in accordance with the invention, somewhat larger than the bead width A in the area of the meander legs  52   b -if dimension A is, for example, 0.56 mm, then dimension B is, for example, 0.66 mm. 
         [0033]    If a flat gasket according to the invention, in particular, a cylinder head gasket, is multi-layered, i.e., if it has at least two sheet metal layers arranged one on the other, it is advantageous for a bead stamped into one of these sheet metal layers and forming a supporting element according to the invention to project in the direction towards the other sheet metal layer in order that the bead crest  50   a  will rest against a sheet metal layer of the flat gasket and—when the gasket is installed—not against one of the sealing surfaces of those components between which the flat gasket is clamped. 
         [0034]    In a modification of the embodiment shown in the drawings and described hereinabove, the supporting elements according to the invention and the beads serving as sealing elements may be provided on different sheet metal layers in a multi-layered flat gasket. Accordingly, a sheet metal layer with sealing beads and another sheet metal layer with supporting elements could be provided. 
         [0035]    According to the definition of the basic concept underlying the present invention, a supporting element according to the invention comprises at least one bead stamped into a sheet metal layer. In a modification of the embodiment shown in the drawings and described hereinabove, a supporting element could also have several beads, for example, two beads, which both have a meander-like configuration over the greatest part of their length with the meander loops of one bead extending into the meander loops of the other bead, so that the two beads run approximately parallel to each other, in particular, everywhere. Furthermore, a supporting element according to the invention could be formed by a bead which with a first bead section forms a first meander-shaped structure and with a second bead section a second meander-shaped structure, with the meander legs of one meander-like structure extending, for example, approximately perpendicularly to the meander legs of the other meander-like structure, and the ends of one meander being joined to the ends of the other meander by further bead sections in such a way that the bead crest of the entire bead forms a continuous line closed within itself. 
         [0036]    It is pointed out again that—as will be apparent from FIG.  2 —a feature of preferred embodiments of the invention is to be seen in that a supporting element according to the invention comprises:
       (a) a plurality of at least approximately straight-lined meander legs joined to one another by approximately semicircular bead arcs, the meander legs extending at least approximately parallel to one another and being spaced from one another at a distance which is smaller than the bead width, so that the meander legs and the meander arcs form a bead package having as high a packing density as possible, and   (b) an elongate bead section which joins ends of two meander legs lying at the edge of the bead package to one another.