Steel laminate gasket
CROSS REFERENCE TO RELATED APPLICATION 
     This is a divisional application of Ser. No. 449,216 filed on Dec. 12, 1989 now abandoned, which is, in turn, continuation in part of application Ser. No. 231,303 filed on Aug. 11, 1988, and U.S. Pat. No. 4,898,396. 
    
    
     BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT 
     The present invention relates to a steel laminate gasket for an internal combustion engine to securely seal around cylinder holes and through holes. 
     An internal combustion engine is provided with a plurality of cylinder holes and other holes, such as holes for bolt, water, oil and push rod. When an engine is actuated, high pressure and high temperature are applied to the cylinder holes due to combustion of a fuel, while relatively low pressure and low temperature are applied to the other holes. 
     In order to properly seal between two engine blocks of an engine, a gasket is situated between the two engine blocks, such as a cylinder head and a cylinder block, and is tightened so that areas around the cylinder holes as well as the other holes are securely sealed. However, since the sealing conditions around the cylinder holes and other holes are different as explained above, it is not easy to securely seal around all the holes. 
     It has been known that beads are formed around the cylinder holes and other holes to securely seal around the holes. However, in case the beads are simply formed, sealing can not be perfectly made. Namely, while an engine is actuated, leakage may happen around the cylinder holes and other holes. 
     In some cases, seal rings may be separately attached around holes for water and oil. However, since the seal rings are separately prepared and installed in the gasket, it requires additional cost. Therefore, this method is not practical. 
     Accordingly, an object of the present invention is to provide a steel laminate gasket which can seal properly around all kinds of holes in an engine. 
     Another object of the present invention is to provide a steel laminate gasket as stated above, which can be manufactured easily and economically. 
     Further objects and advantages of the present invention will be apparent from the following description of the invention. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, a steel laminate gasket is installed in an internal combustion engine having at least one cylinder hole and at least one through hole. The gasket basically comprises first, second and third plates. 
     The gasket is provided with first and second means for sealing around the cylinder hole, third means for sealing around the through hole, and sealing layers located at least between the first and second plates and between the second and third plates. The first means is integrally formed with one of the first, second and third plates, and includes a base portion, a curved portion situated around the cylinder hole and a flange. The second means is situated inside the first means around the curved portion. 
     The third means is formed on at least one of the first, second and third plates to securely seal around the through hole when the gasket is tightened. The third means may be a bead. 
     In one embodiment, the first means is formed on the first plate, and the second means is formed on the second plate. The second means may be a bead. 
     On the other hand, the first means may be formed on the second plate, wherein the first and third plates do not extend adjacent to the cylinder hole. The second means may be a wire ring or a bead in the form of a ring. 
     The sealing layers are provided outside the second means relative to the cylinder hole and are made of soft materials to prevent fluid from passing between the plates. Since the sealing layers are not provided adjacent to the cylinder hole, the sealing layers may be made of soft materials which is not strong against heat but effective to fluid. As a result, in the gasket of the present invention, areas around the cylinder holes and areas around the through holes are effectively sealed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partial plan view of a first embodiment of a steel laminate gasket of the present invention; 
     FIG. 2 is an enlarged section view taken along line 2--2 in FIG. 1; 
     FIG. 3 is a perspective view of a middle plate for constituting the gasket of the present invention; and 
     FIGS. 4, 5, 6A, 6B, 7 and 8 are section views, similar to FIG. 2, of second to fifth embodiments of a steel laminate gasket of the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to FIGS. 1-3, a first embodiment A of a steel laminate gasket of the present invention is shown. The gasket A is provided with cylinder holes Hc, bolt holes Hb, water holes Hw, oil holes Ho and push rod holes Hp, as in the conventional gasket. The areas around the water holes Hw, oil holes Ho and push rod holes Hp are sealed in the same manner. For convenience, the cross section of the water hole Hw and cylinder hole Hc is shown in FIG. 2. 
     As shown in FIG. 2, the gasket A comprises an upper plate A10, a lower plate A12 and a middle plate All situated between the upper and lower plates A10, A12. The upper plate A10 includes a hole A13 for the water hole Hw. Also, the upper plate A10 is provided with a curved portion A10a to define the cylinder hole Hc, a flange A1Ob, a base portion A10d facing the flange A1Ob, and a bead A10c around the hole A13. The curved portion A10a seals around the cylinder hole Hc, and the bead A10c seals around the water hole Hw. 
     The middle plate A11 includes a hole A14 for the cylinder hole Hc, and a hole A15 for the water hole Hw. The middle plate A11 is also provided with a bead A11a adjacent the curved portion A1Oa, and coatings A16 covering upper and lower surfaces of the middle plate A11. The coatings A16 are not formed at an area adjacent the cylinder hole Hc, i.e. on and around the bead A11a, as shown in FIG. 3. 
     The coatings A16 are made of soft materials to provide resiliency. Gum, such as NBR gum and silicone gum is preferred, but soft resin may be used. The thickness of the coating A16 is 5-100 micra, preferably 10-50 micra. 
     The lower plate A12 includes a hole A17 for the cylinder hole Hc, and a hole A18 for the water hole Hw. The lower plate A12 is also provided with a bead A12a adjacent the hole A18 to seal around the water hole Hw. An end portion of the lower plate A12 is situated between the flange A10b and the middle plate A11. 
     When the gasket A is situated between two engine blocks (not shown) and is tightened, the bead A11a provides sealing pressure around the cylinder hole Hc, while the beads A10c, A12a provide sealing pressure around the water hole Hw. 
     In the present invention, it is important that the coating is made of a soft material. As a result, the soft material seals properly between the plates to thereby prevent leakage of fluid from the water hole Hw. Also, it is important that the coating is not formed adjacent the cylinder hole Hc. This is because if the coating is exposed to high temperature, creep relaxation of the soft material occurs to cause leakage around the cylinder hole Hc and water hole Hw. 
     Namely, an effective coating material around the water hole Hw is weak against heat. Therefore, the middle plate is not directly exposed to the cylinder hole, and coatings are formed on the middle plate at an area away from the cylinder hole Hc. 
     Generally, small scratches are formed on outer surfaces of an engine block when manufacturing the engine block. In order to fill up the small scratches, coatings which are strong against heat may be formed on outer surfaces of the gasket. Therefore, in the present invention, thin coatings may be formed on the outer surfaces of the upper and lower plates A10, A12, which contact the engine blocks. 
     FIG. 4 shows a second embodiment B of a steel laminate gasket of the invention. The gasket B comprises an upper plate B10 with a curved portion B10a, a flange B10b and a bead B10c, a middle plate B11 with a bead B11a, a lower plate B12 with a bead B12a, and coatings B16 provided on both sides of the middle plate B11, similar to the gasket A. 
     The gasket B is further provided with a surface pressure regulation plate B19 for the bead B11a, which includes a coating B19&#39; similar to the coating A16. In the gasket B, pressure around the cylinder hole Hc is regulated by the plate B19. Also, the coatings are situated between the respective plates, so that liquid does not leak between the plates. An area around the water hole Hw is securely sealed. 
     FIG. 5 shows a third embodiment C of a steel laminate gasket of the present invention. The gasket C comprises an upper plate C10 with a curved portion C10a and a flange C10b, a middle plate C11 with coatings C16, and a lower plate C12 with a bead C12a, similar to the gasket A. However, the middle plate C11 is provided with a curved portion C11a and a flange C11b, instead of the bead A11a in the gasket A. Also, an end portion of the lower plate C12 does not engage the flange C10b. Therefore, the lower plate C12 can regulate surface pressure of the flanges C10b, C11b. 
     In the gasket C, since the curved portion C11a and flange C11b is situated adjacent to the curved portion C10a, when the gasket C is tightened, strong sealing pressure is formed around the cylinder hole Hc. An area around the water hole Hw is securely sealed by the bead C12a. The gasket C is effective when high sealing pressure is required around the cylinder hole Hc. 
     FIG. 6A shows a fourth embodiment D of a steel laminate gasket of the present invention. The gasket D comprises an upper plate D10, a middle plate D11, and a lower plate D12. 
     The upper and lower plates D10, D12 are similar to each other and have substantially the same structure. Namely, the plates D10, D12 have holes D20 larger than the cylinder hole Hc, and holes D21 for the water hole Hw. The upper plate D10 is provided with a coating D16 at a side facing to the middle plate D11, and a coating D22 at an opposite side thereof, while the lower plate D12 is provided with a coating D16&#39; at a side facing to the middle plate D11 and a coating D22&#39; at an opposite side thereof. 
     The coatings D16, D16&#39; are the same as the coating A16, which is soft and effective to seal around the water hole Hw. On the other hand, the coatings D22, D22&#39; are strong against heat for filling up scratches of the engine block. 
     The middle plate D11 is provided with a curved portion D11a situated adjacent to the cylinder hole Hc, a flange D11b, and a bead D11c around a hole D15. A wire ring D23 is provided around the curved portion D11a. 
     In the gasket D, an area around the cylinder hole Hc is sealed by the curved portion D11a and the wire ring D23, while an area around the water hole Hw is sealed by the bead D11c. Since the soft coatings D16, D16&#39; are provided between the plates, water leakage is substantially prevented. Also, since the soft coatings D16, D16&#39; are formed away from the cylinder hole Hc, the soft coatings are not damaged by heat from the cylinder hole Hc. 
     FIG. 6B shows a gasket D&#39; similar to the gasket D. In the gasket D&#39;, a plate D11&#39; does not have a bead around a water hole Hw, but plates D10&#39;, D12&#39; have beads D10c&#39;, D12a&#39;, respectively, around the water hole Hw to seal therearound. The rest of the structure of the gasket D&#39; is the same as the gasket D. 
     FIG. 7 shows a fifth embodiment E of a steel laminate gasket of the present invention. The gasket E comprises an upper plate E10 with coatings E16, E22, a middle plate E11 with a bead E11c,  and a lower plate E12 with coatings E16&#39;, E22&#39;, similar to the gasket D. The middle plate E11 is also provided with a curved portion E11a and a flange E11b similar to the gasket D, but the entire width of the flange E11b is slightly longer than that of the gasket D. 
     In the gasket E, a bead E24 in the form of a ring is situated adjacent to the curved portion E11a. Accordingly, when the gasket E is tightened, an area around the cylinder hole Hc is resiliently sealed by the bead E24 and the curved portion E11a. The gasket E operates as in the gasket D. 
     In accordance with the present invention, the coating material which is weak against heat but effective to seal around fluid holes is provided between plates to be situated away from a cylinder hole. Therefore, areas around the fluid holes can be effectively sealed by even a single bead. Also, an area around the cylinder hole can be effectively sealed. 
     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.