The present invention relates to a metal gasket with a bore ring, in particular a metal cylinder head gasket with a bore ring to be installed between a cylinder head and a cylinder block of an internal combustion engine.
A cylinder head gasket installed between a cylinder head and a cylinder block of an engine is provided with a plurality of cylinder bores, water holes, oil holes, bolt holes and so on. In the engine, since high temperature and high pressure combustion gases are formed in the cylinder bores when the engine is actuated, sealings around the cylinder bores are important. Thus, the bolts for connecting the cylinder head and cylinder block with the gasket therebetween are arranged generally around the cylinder bores.
Also, sealing means, such as beads, are formed around the cylinder bores of the gasket. When the cylinder head and the cylinder block with the gasket therebetween are tightened, the sealing means are compressed to thereby form counter forces thereat, which generate sealing pressures to seal around the cylinder bores.
On the other hand, since the engine has been developed to provide high power and light in weight with small size, combustion gases with high pressures are formed. Thus, it is the tendency that the tightening pressure and the bead counter force are getting stronger.
Also, in the gasket, since the sealing means, such as bead, is exposed to high temperature and high pressure formed in the cylinder bore, there has been a problem that creep relaxation occurs in the bead, resulting in fatigue destruction of the bead.
As stated above, the engine is required to have light weight. Thus, the cylinder head and the cylinder block are formed of relatively light metal, such as aluminum or aluminum alloy. In this respect, since the gasket is formed of relatively hard metal, the gasket does not fit properly with the cylinder head and cylinder block formed of the light metal. Thus, the difference of heat expansion between the gasket and the engine parts, e.g. cylinder head and cylinder block, becomes greater. As a result, the rubbing occurs between the bead and the gasket attaching portions of the cylinder head and the cylinder block. Namely, the cylinder head and the cylinder block formed of relatively light metal are damaged by the expansion and contraction of the bead to thereby reduce the sealing ability around the cylinder bore.
In view of the above problems, U.S. Pat. No. 5,895,054 has been proposed, wherein a thick ring spacer or annular ring is situated in a cylinder bore of a metal plate for the gasket such that the annular ring does not come off or separate from the metal plate easily by press fitting at several portions.
In this gasket, the annular ring is formed accurately, and is assembled with the gasket. Thus, the surface pressure around the cylinder bore can be formed equally to securely seal around the cylinder bore. However, since the annular ring is very thin, it is very difficult to attach the annular ring to the metal plate with a press fitting. Also, since the annular ring is located inside the metal plate and the metal plate does not have a portion laminating with a different metal portion, the metal plate for the gasket does not have a cushioning mechanism with respect to the engine parts, i.e. cylinder head and cylinder block, so that the gasket does not fit so properly or closely with the engine parts. Especially, if a bead portion of the metal plate contacts the engine parts directly, the engine parts are likely to be damaged by the bead to cause gas leakage thereat.
The present invention has been made in view of the above conventional gaskets, and an object of the invention is to provide a metal gasket with a bore ring, which fits smoothly and closely with engine parts to securely seal around a hole to be sealed.
Another object of the invention is to provide a metal gasket with a bore ring as stated above, wherein a bead of the gasket is protected to prevent creep relaxation.
A further object of the invention is to provide a metal gasket with a bore ring as stated above, wherein a surface pressure for sealing can be accurately adjusted.
A still further object of the invention is to provide a metal gasket with a bore ring as stated above, wherein the gasket can be manufactured easily.
Further objects and advantages of the invention will be apparent from the following description of the invention.
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