Abstract:
A steel laminate gasket of the invention is designed to be installed in an internal combustion engine having at least one hole to be sealed. The gasket comprises first and third plates having beads around the hole, and a second plate situated between the first and third plates. The second plate does not extend adjacent to the hole. When the gasket is assembled, edge portions of the first and third plates directly face against each other, but the second plate terminates at a portion between or outside the beads. The gasket may provide moderate surface pressure at a portion slightly away from the hole to be sealed to prevent deformation of the engine parts. High surface pressure may be formed near the hole to be sealed.

Description:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT 
     The present invention relates to a steel laminate gasket for an internal combustion engine to provide desired surface pressure around a hole to be sealed. 
     An engine for an automobile has been developed to seek high power and light weight. In order to satisfy these demands for the engine, an engine is made of aluminum alloy, to which high temperature and high pressure are applied. 
     Since a steel laminate gasket is made of a plurality steel plates, the steel laminate gasket is strong against high temperature and pressure. Therefore, the steel laminate gasket has been used widely for a recent engine to which high temperature and pressure are applied. 
     A cylinder head of a recent engine is generally made of aluminum alloy. In some cases, a cylinder block is also made of aluminum alloy. In case the cylinder head or cylinder block is made of aluminum alloy, a large amount of tightening pressure can not be applied to tighten the cylinder head and the cylinder block, because the cylinder head or cylinder block may deform by the tightening pressure. 
     Especially, when the gasket includes a wire ring around the cylinder hole, the cylinder head or cylinder block is liable to deform when tightened. Also, in case a large surface pressure is applied around a cylinder hole when the gasket is tightened, the cylinder head or cylinder block may deform around the cylinder hole. 
     As shown in FIGS. 1 and 2, a gasket 10 formed of an upper plate 11 with a bead 11a, a middle plate 12 and a lower plate 13 with a bead 13a is known. When the gasket 10 is tightened, the beads 11a, 13a deform to provide a strong surface pressure around a cylinder hole Hc. Therefore, unless the cylinder head and cylinder block are strong, the cylinder head and cylinder block may deform when tightened. 
     In U.S. Pat. No. 4,898,396, a gasket is formed of three plates, wherein upper and lower plates extend around a cylinder hole and have sealing mechanisms to seal therearound. In this patent, a surface pressure is formed adjacent to the cylinder hole. 
     Accordingly, one object of the present invention is to provide a steel laminate gasket, in which the cylinder head and cylinder block can be tightened at desired surface pressure when the gasket is tightened. 
     Another object of the invention is to provide a steel laminate gasket as stated above, which can provide moderate surface pressure at an area slightly away from the cylinder hole to prevent deformation of the cylinder hole. 
     A further object of the invention is to provide a steel laminate gasket as stated above, which can be easily and economically manufactured. 
     Further objects and advantages of the invention will be apparent from the following description of the invention. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, the gasket is installed in an internal combustion engine having at least one hole to be sealed. Especially, the gasket is useful as a cylinder head gasket to seal around a cylinder hole. 
     The gasket comprises first, second and third plates laminated with each other. The first and third plates include first and third holes, and beads around the holes, respectively. The second plate is situated between the first and third plates and has a second hole larger than the first and third holes. 
     When the gasket is assembled, edge portions of the first and third plates adjacent the first and third holes directly face against each other, and an inner edge of the second plate is located between or outside of the beads of the first and third plates. Namely, the second plate does not extend adjacent to the cylinder hole. 
     Therefore, when the gasket is tightened, the beads of the first and third plates deform and form a plurality of corrugated beads to seal around the cylinder hole. Since the second plate does not overlap the edge portions of the first and third plates, surface pressure formed by the beads of the first and third plates is not so strong. Moderate surface pressure is obtained by the beads of the first and third plates. Especially, large surface pressure is formed at outside portions on the beads of the first and third plates, and moderate surface pressure is formed at inside portions on the beads. 
     Also, since the beads of the first and third plates are situated away from the cylinder hole, surface pressure formed by the beads and applied to an edge portion of the cylinder hole becomes weak. As a result, deformation of the cylinder head and cylinder block is substantially prevented. 
     A pressure forming member may be provided on at least one of the edge portions of the first and third plates to surround the cylinder hole. Surface pressure at the pressure forming member may be made higher or lower than the surface pressure at the beads as desired when the gasket is tightened. Also, surface pressure laterally outside the beads may be between the surface pressure at the beads and the surface pressure at the pressure forming member when the gasket is tightened. 
     The pressure forming member may be a flange integrally formed with the first or third plate. A part of the plate that the flange is formed may be turned or bent and situated over that plate to form the flange. Also, a part of the plate that the flange is formed may be bent to extend through a hole of the other plate that the flange is not formed, and turned to be situated over the edge portion of the other plate. 
     The pressure forming member may be a grommet installed inside the first and third holes, flanges of the grommet being placed outside the edge portions of the first and third plates. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is partial plan view of a conventional steel laminate gasket; 
     FIG. 2 is an enlarged section view taken along line 2--2 in FIG. 1; 
     FIG. 3 is a section view, similar to FIG. 2, of a first embodiment of a steel laminate gasket of the invention; 
     FIGS. 4 and 5 are section views, similar to FIG. 2, of second and third embodiments of the invention; 
     FIG. 6 is an explanatory section view for showing a compressed condition of the gasket as shown in FIG. 5; and 
     FIGS. 7 and 8 are section views, similar to FIG. 2, of fourth and fifth embodiments of the invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to FIG. 3, a first embodiment A of a steel laminate gasket of the present invention is shown. The gasket A includes cylinder holes Hc, water holes Hw, oil holes Ho and bolt holes Hb, as in the conventional gasket shown in FIG. 1. 
     In the gasket A, an area around the cylinder hole Hc is sealed in accordance with the present invention. Areas around the water holes Hw and oil holes Ho may be sealed in any sealing mechanisms. Therefore, sealing mechanisms around the water holes Hw and oil holes Ho are not explained in the present specification. The areas around the water holes Hw and oil holes Ho may be sealed in accordance with the present invention. 
     As shown in FIG. 3, the gasket A comprises an upper plate A20, a middle plate A21 and a lower plate A22. The upper and lower plates A20, A22 are symmetrically arranged relative to the middle plate A21. 
     The upper plate A20 is provided with a hole A20a corresponding to a cylinder hole Hc, an edge portion A20b located around the hole A20a, and a bead A20c located around the edge portion A20b. A base portion A20d extends substantially the entire area of the gasket A. A bottom surface at the edge portion A20b is located slightly lower than a bottom surface at the base portion A20d. 
     A middle plate A21 is situated substantially under the base portion A20d of the upper plate A20. The middle plate A21 includes a hole A21a larger than the cylinder hole Hc. 
     The lower plate A22 is situated under the middle plate A21. The lower plate A22 is provided with a hole A22a corresponding to the hole A20a, an edge portion A22b located around the hole A22a, and a bead A22c located around the edge portion A22b. A base portion A22d extends substantially the entire area of the gasket A. An upper surface at the edge portion A22b is located slightly higher than an upper surface at the base portion A22d. 
     When the gasket A is assembled, the edge portions A20b, A22b abut against each other, and the middle plate A21 is substantially situated between the base portions A20d, A22d. An edge A21b around the hole A21a is situated between the beads A20c, A22c. The edge A21b does not overlap the edge portions A20b, A22b to thereby form a space, i.e. a part of the hole A21a, between the edge A21b and the edge portions A20b, A22b. 
     When the gasket A thus assembled is tightened between a cylinder head and a cylinder block (both not shown), the beads A20c, A22c are compressed and form a plurality of corrugated beads. The corrugated beads are partly located at the space or the hole A21a between the edge A21b and the edge portions A20b, A22b. Also, as the beads A20c, A22c are compressed, the edge portions A20b, A22b slightly move toward the cylinder hole Hc. 
     Therefore, when the gasket A is tightened, high surface pressure is formed on outside portions of the bead A20c, A22c, and low surface pressure is formed on inside portions of the beads A20c, A22c. Accordingly, moderate surface pressure is obtained when the gasket A is tightened. 
     In the gasket A, the thickness at the base portions A20d, A22d with the middle plate A21 is thicker than the thickness at the edge portions A20b, A22b, and the beads A20c, A22c are formed slightly away from the cylinder hole Hc. Therefore, when the gasket A is tightened, surface pressure is not directly applied just outside the cylinder hole Hc. Thus, deformation of the cylinder holes Hc is substantially prevented. 
     In FIG. 3, the gasket A is arranged such that the edge portions A20b, A22b abut against each other when the gasket A is not tightened. However, the edge portions A20b, A22b need not abut against each other when the gasket is assembled, i.e. a space may be formed between the edge portions A20b, A22b, so long as the edge portions A20b, A22b abut against each other when the gasket A is tightened. Even if a space is formed between the edge portions, the gasket A operates as intended. 
     FIG. 4 shows a second embodiment B of the steel laminate gasket of the invention. The gasket B comprises an upper plate B20 with a bead B20c, a middle plate B21 and a lower plate B22 with a bead B22c, as in the gasket A. However, the lower plate B22 further includes a curved portion B22e to define the cylinder hole Hc and a flange B22f situated above the edge portion B20b. Further, a hole B21a of the middle plate B21 is made larger than the hole A21a. 
     The thickness adjacent the cylinder hole Hc, i.e. total thickness of the flange B22f and the edge portions B20b, B22b, is slightly thinner than the thickness outside the beads B20c, B22c, i.e. total thickness of the upper plate B20, middle plate B21 and lower plate B22. 
     Therefore, when the gasket B is tightened, corrugated beads are partly situated inside a hole B21a. Also as the beads B20c, B22c are compressed, the edge portions B20b, B22b with the flange B22f slightly move toward the cylinder hole Hc. Therefore, the beads B20c, B22c do not form high pressure. Namely, the inner portions of the beads B20c, B22c form relatively low surface pressure, and the outside portions thereof form relatively strong surface pressure. In the gasket B, since the flange B22f is formed around the cylinder hole Hc, an area around the cylinder hole Hc is properly sealed. 
     FIGS. 5 and 6 show a third embodiment C of the steel laminate gasket of the invention. The gasket C comprises an upper plate C20 with a bead C20c, a middle plate C21, and a lower plate C22 with a bead C22c, as in the gasket A. However, in the gasket C, the upper plate C20 further includes a curved portion C20e and a flange C20f located above an edge portion C20b. 
     The total thickness adjacent the cylinder hole Hc, i.e. the thickness of the flange C20f, the edge portion C20b and an edge portion C22b, is sightly thinner than the thickness outside the beads C20c, C22c, i.e. the thickness of the upper plate C20, the middle plate C21 and the lower plate C22. 
     As shown in FIG. 6, when the gasket C is compressed between a cylinder head X and a cylinder block Y, the beads C20c, C22c form a plurality of corrugated beads to provide a moderate surface pressure, as in the gasket A. In the gasket C, when the gasket C is tightened, the curved portion C20e is also firmly compressed. Since the curve portion C20e has resiliency, the curved portion provides a surface pressure thereat. Therefore, the gasket C provides surface pressure adjacent the cylinder hole Hc, in addition to the feature as disclosed in the gasket A. 
     FIG. 7 shows a fourth embodiment D of a steel laminate gasket of the invention. The gasket D comprises an upper plate D20 with a bead D20c, a middle plate D21, and a lower plate D22 with a bead D22c, a curved portion D22e and a flange D22f, similar to the gasket B. In the gasket D, however, the thickness of the lower plate D22 is thicker than the other plates. 
     The total thickness adjacent the cylinder hole Hc, i.e. the thickness of the flange D22f, an edge portion D20b and an edge portion D22b, is slightly thicker than the thickness outside the beads D20c, D22c, i.e. the thickness of the upper plate D20, the middle plate D21 and the lower plate D22. 
     Therefore, when the gasket D is tightened, high surface pressure P 1  is formed near the cylinder hole Hc, i.e. at the flange D22f. The surface pressure P 2  formed at the outer halves of the beads D20c, D22c is weaker than the surface pressure P 1  but stronger than the surface pressure P 3  formed at the inner halves of the beads D20c, D22c. In the gasket D, high surface pressure is formed near the cylinder hole Hc. 
     As explained in the gasket D, when the thickness of the plates is changed, the portion where the surface pressure is applied as well as the strength of the surface pressure may be changed. 
     FIG. 8 shows a fifth embodiment E of the steel laminate gasket of the invention. The gasket E comprises an upper plate E20 with a bead E20c, a middle plate E21, and a lower plate E22 with a bead E22c, similar to the gasket A. The gasket E, however, further includes a grommet E23 with a curved portion E23a and flanges E23b, E23c. The flange E23b is located above an edge portion E20b, and the flange E23c is located under an edge portion E22b. 
     In the gasket E, the thickness near the cylinder hole Hc, i.e. the total thickness of the flanges E23b, E23c and the edge portions E20b, E22b, is thinner than the thickness outside the beads E20c, E22c, i.e. the total thickness of the plates E20, E21, E22. 
     Therefore, when the gasket E is tightened, surface pressure P 1  is formed near the cylinder hole Hc. The surface pressure P 1  is lower than surface pressure P 2  formed at outer halves of the beads E20c, E22c, but higher than surface pressure P 3  formed at inner halves of the beads E20c, E22c. 
     As explained in the gasket E, surface pressure near the cylinder hole may be changed by providing a grommet. Also, the amount of the surface pressure near the cylinder hole may be changed by changing the thickness of the grommet. 
     In the present invention, since the middle plate does not extend adjacent to the cylinder hole, seal coatings, which are not strong against high temperature, may be formed on the middle plate. As a result, it is possible to securely seal between plates adjacent a fluid hole, such as water and oil holes. 
     In accordance with the present invention, the beads are formed slightly away from the cylinder hole Hc, and are designed to provide a moderate surface pressure. In the gasket A, no surface pressure is formed adjacent to the cylinder hole Hc. In the gasket B, a small amount of surface pressure is formed adjacent to the cylinder hole, while the gasket C, a moderate amount of surface pressure is formed due to the curved portion near the cylinder hole. In the gasket D, a large amount of surface pressure may be formed near the cylinder hole. Also, surface pressure may be applied near the cylinder hole by a grommet, as shown in the gasket E. 
     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.