Abstract:
A gasket is formed of a gasket body having at least one hole to be sealed, and a sealing space situated around at least a part of the hole. A heat foamable coating is disposed only in the sealing space. The gasket is installed between two members, and then, the gasket is heated to foam the foamable coating in the sealing space. Thus, the foamable coating provides a surface pressure in the sealing space by foaming to securely seal thereat.

Description:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT 
     The present invention relates to a method for sealing two members and a gasket therefor, in particular, to a method of sealing two engine parts, such as a cylinder head and a cylinder block, and a gasket used for sealing the engine parts. 
     In sealing two engine parts, such as a cylinder head and a cylinder block for an internal combustion engine, a gasket is generally installed between the two parts. In order to securely seal around a hole to be sealed, such as cylinder bores, water holes and oil holes, the gasket is provided with sealing means around the hole, such as a bead, flange or turning portion, grommet, combination thereof, and so on. When the gasket is tightened, the sealing means provides a surface pressure to securely seal around the hole. 
     In case the hole to be sealed has an enough space therearound for sealing, though some technical difficulties may be encountered depending on the structure thereof, the hole can be sealed relatively easily by the sealing means. However, if there is no sufficient space around the hole to be sealed, it is difficult to securely seal around the hole. 
     In case the sufficient sealing space is not obtained or additional sealing means is required, a coating layer containing rubber or resin may be formed on a gasket or between plates for the gasket. The coating layer prevents the fluid from flowing on the gasket or between the plates. 
     Also, it has been known that a foaming layer may be coated on an entire surface of a gasket. In this case, after the gasket is assembled and the foaming layer is foamed, the gasket with the foamed layer is installed between the engine parts. Therefore, when the gasket with the foamed layer is installed and tightened between the engine parts, the foamed layer may be compressed excessively to loose compressibility or resilience. Even if the foamed layer has compressibility when the gasket is installed between the engine parts, in case the gasket is used for a long time, the gasket is compressed repeatedly. Accordingly, the compressibility of the foamed layer is lost gradually. 
     The present invention has been made in view of the conventional gasket, and an object of the invention is to provide a gasket with a foamed layer which can provide an adequate surface pressure. 
     Another object of the invention is to provide a gasket with a foamed layer as stated above, wherein the surface pressure is not substantially lost even if it is used for a long time. 
     A further object of the invention is to provide a gasket with a foamed layer as stated above, wherein the gasket can provide a surface pressure even in a limited space. 
     A still further object of the invention is to provide a method for sealing between two members, wherein an adequate surface pressure is formed between the two members and is kept for a long time. 
     A still further object of the invention is to provide a method as stated above, wherein the adequate surface pressure is formed easily without special treatment. 
     Further objects and advantages of the invention will be apparent from the following description of the invention. 
     SUMMARY OF THE INVENTION 
     A gasket of the invention is used for sealing two parts or members, e.g. cylinder head and cylinder block for an internal combustion engine. 
     The gasket is formed of a gasket body for constituting the gasket, which includes at least one hole to be sealed, and a sealing space situated around at least a part of the hole. A heat foamable coating is disposed only in the sealing space. When the gasket is heated to foam the heat foamable coating in the sealing space after the gasket is installed between the two members, the heat foamable coating foams and provides a surface pressure in the sealing space to securely seal thereat. 
     In case the gasket body includes two holes to be sealed, flanges or shims may be formed around the two holes. In this case, the sealing space is established on the gasket body between the flanges or shims. In case the flange is not formed around the hole, a groove may be formed in the metal plate around the hole as the sealing space. 
     In a method for sealing the two members with holes, a gasket is prepared to have at least one hole to be sealed and a sealing space near the hole, and a heat foamable coating is provided only in the space. Then, the gasket with the heat foamable coating is mounted between the two members, and the heat foamable coating on the gasket is heated together with the gasket to foam the heat foamable coating. The heat foamable coating changes to a foamed layer to thereby provide a surface pressure at the sealing space. 
     Preferably, after the gasket is installed between the two members and before the heat foamable coating is heated, the gasket is tightened between the two members. Accordingly, when the foamable coating is foamed, the desired surface pressure or foaming pressure is obtained at the foamed layer. In this case, also, after the foamable coating is foamed, the foamed layer is not substantially compressed. Thus, the foamed layer is not depressed too much to reduce the thickness thereof, so that the reductions of the surface pressure and the thickness of the foamed layer are substantially avoided. Further, since the foamable coating can foam according to the shape of the space, the sealing ability can be increased. 
     In case the gasket is formed for an internal combustion engine, i.e. cylinder head gasket, the heating step may be performed by actuating the engine, such as running test, after the gasket is installed in the engine. In this case, since the heating step can be avoided in preparing the gasket, the gasket can be formed easily. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partial plan view of a metal gasket of a first embodiment of the invention; 
     FIG. 2 is an enlarged sectional view taken along line  2 — 2  in FIG. 1, wherein the gasket is installed in an engine; 
     FIG. 3 is an enlarged sectional view, similar to FIG. 2, for showing the gasket of the first embodiment after a foamable coating is foamed; 
     FIG. 4 is an enlarged sectional view, similar to FIG. 2, for showing a second embodiment of the invention; 
     FIG. 5 is an enlarged sectional view, similar to FIG. 3, for showing the gasket of the second embodiment after the foamable coating is foamed; 
     FIG. 6 is an enlarged sectional view, similar to FIG. 2, for showing a third embodiment of the invention; and 
     FIG. 7 is an enlarged sectional view, similar to FIG. 3, for showing the gasket of the third embodiment after the foamable coating is foamed. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     With reference to FIGS. 1-3, a first embodiment A of a gasket of the invention is explained. The gasket A is a cylinder head gasket to be installed between a cylinder head CH and a cylinder block CB. The gasket A includes a plurality of cylinder bores Hc, water holes Hw, oil holes Ho, bolt holes Hb and so on, as in the conventional gasket. In this embodiment, the sealing structure formed around the cylinder bores Hc is explained. Therefore, the explanations for the structures of the water holes Hw, oil holes Ho and so on are omitted. Any structures known in the art can be utilized. 
     The gasket A is formed of a lower metal plate A 10 , and an upper metal plate All disposed on the lower metal plate A 10 . The lower metal plate A 10  includes a base portion A 10   a , curved portions A 10   b  extending from the base portion A 10   a  to define the cylinder bores Hc, and flanges A 10   c  extending from the curved portions A 10   b  and disposed on the base portion A 10   a . A sealing space A 12  is established between the flanges A 10   c  situated adjacent to each other. 
     The upper plate A 11  is disposed on the base portion A 10   a  without overlapping the flanges A 10   c . In the upper plate A 11 , individual holes for the cylinder bores are not formed, and one hole communicating with the cylinder bores Hc is formed. Namely, in the upper plate A 11 , there is no portion located in the sealing space A 12  on the lower plate A 10 . Thus, the sealing space A 12  is established on the lower plate A 10 , which is surrounded by edges Alla of the upper plate A 11  and the flanges A 10   c.    
     In the gasket A, the sealing space A 12  between the flanges A 10   c  is too narrow to form a sealing device, such as bead. Thus, a sealing member A 13  is formed in the sealing space A 12 . The sealing member A 13  is a foamed coating or layer A 13   b  made from a foamable coating A 13   a.    
     In particular, when the gasket A is formed, the lower metal plate A 10  and the upper metal plate A 11  are assembled to have the sealing space A 12  surrounded by the flanges A 10   c  and the edges A 11   a , in which the foamable coating A 13   a  is coated. The foamable coating A 13   a  may be a diazo type foamable coating or paint, which is available in a market. The foamable coating does not foam at a temperature in assembling the gasket, such as heating the gasket for drying the foamable coating and other coating if applied, and is foamed at a temperature higher than the assembling temperature. 
     In particular, the foamable coating contains a foaming agent, such as azodicarbonamide (decomposition temperature: 200-210° C.); in a paint, such as rubber type paint. Microcapsules with heat expansion type containing hydrocarbon with a low boiling point, such as butane, may be used as the foaming agent. Dissolving temperature of the microcapsules may be selected between 140-200° C. The foaming rate is preferably 3-5 times. 
     The gasket A with the foamable coating A 13   a  is situated between the cylinder head CH and the cylinder block CB, as shown in FIG. 2, and is tightened. Thereafter, the gasket A is heated to foam the foamable coating A 13   a , so that the foamable coating A 13   a  is changed to the foamed layer A 13   b  in the entire space A 12 , as shown in FIG.  3 . The heat for foaming the foamable coating A 13   a  may be obtained in operating the engine with the gasket A as a running test. In this case, no special heating step is actually required. 
     In the invention, after the gasket A is securely tightened between the cylinder head CH and the cylinder block CB by the bolts to provide the required tightening pressure, the foamable coating A 13   a  is foamed. Thus, the surface pressure at the foamed layer A 13   b  is substantially obtained by the foaming pressure. Namely, the foamed layer A 13   b  is not excessively compressed by tightening the bolts, to thereby provide the ideal surface pressure at the sealing space A 12 . Also, since the foamable coating A 13   a  is foamed according to the shape of the sealing space A 12 , the sealing ability is improved. 
     FIGS. 4 and 5 show a second embodiment B of the gasket of the invention. In the gasket B, the basic structure is the same as the gasket A, but the flanges A 10   c  with the curved portions A 10   b  are not formed in a lower plate B 10 . Namely, the lower plate B 10  has the same shape as in the base portion of the lower plate A 10  without the flanges A 10   c  and the curved portions A 10   b . In the gasket B, however, annular shims B 14  are arranged around the cylinder bores Hc instead of the flanges A 10   c . Thus, a sealing space B 12  is defined by the annular shims B 14  and the edges of an upper plate (not shown), similar to the gasket A, and a foamable coating B 13   a  same as the foamable coating A 13   a  is applied in the sealing space B 12 . 
     The gasket B with the foamable coating B 13   a  is installed between the cylinder head CH and the cylinder block CB and is tightened, and then, the engine is heated to foam the foamable coating B 13   a . Thus, the foamable coating B 13   a  is changed to a foamed layer B 13   b  as a sealing member B 13 , as shown in FIG.  5 . The running test of the engine may constitute the heating of the gasket. The gasket B operates as in the gasket A. 
     FIGS. 6 and 7 show a third embodiment C of the gasket of the invention. The gasket C includes cylinder bores Hc, water holes Hw, oil holes Ho, bolt holes Hb and so on, as shown in the gasket A, but the gasket C is formed of one metal plate C 10 . The gasket C includes grooves or depressions C 10   a  around the cylinder bores Hc extending inwardly from upper and lower surfaces thereof, which are formed symmetrically relative to the center of the plate C 10 . The grooves C 10   a  may be formed by a coining process. Foamable coatings C 13   a  same as the foamable coating A 13   a  are coated in the bottom of the grooves C 10   a.    
     The gasket C with the foamable coatings C 13   a  is installed between the cylinder head CH and the cylinder block CB (FIG.  6 ), and is tightened. Then, the engine is heated to foam the foamable coatings C 13   a . Thus, the foamable coatings C 13   a  are changed to foamed layers C 13   b  as sealing members C 13 , as shown in FIG.  7 . In the gasket C, since the grooves C 10   a  are formed around the cylinder bores Hc, the shapes and depths of the grooves C 10   a  may be changed as desired. The gasket C operates as in the gasket A. 
     In the invention, the surface pressure of the foamed layer may be set as desired by selecting the foaming ratio of the foamable coating and the amount of the coating in the grooves. 
     In the above embodiments, the foamed layers are formed around the cylinder bores. However, the foamed layer may be formed around the water hole, oil hole and so on. Further, the invention need not be limited to the gasket for the engine, and may be used for sealing two members other than the engine parts. 
     In the invention, the gasket with the foamable coating is installed between the two members. After the gasket with the foamable coating is tightened between the two members, the gasket is heated. Thus, the suitable surface pressure is obtained by foaming the foamable coating. Since the excess tightening pressure is not applied to the foamed layer, the foamed layer can keep the suitable surface pressure for a long time. Also, since the foamable coating foams according to the shape to be sealed, the sealing ability is improved. 
     While the invention has been explained with reference to the specific embodiments of the invention, the explanation is illustrative and the invention is limited only by the appended claims.