[DESCRIPTION]

[invention Title) METAL GASKET WITH EMBOSSING FOR STOPPER

[Technical Field] The present invention relates, in general, to a metal gasket with embossments acting as a stopper and, more particularly, to a metal gasket, which is used for sealing the junction between the cylinder block and the cylinder head of an internal combustion engine and is provided with embossments on a plate assembly thereof, thus compensating both for a gap formed by a lift-off force generated in the engine and for a strain of an interval between deck surfaces caused by bolting, thereby realizing improved sealing performance of gaskets.

[Background Art] Generally, a gasket is an element, which is placed between the junction surfaces or between the contact surfaces of parts in internal combustion engines, hereinbelow referred to simply as 'engines' or in hydraulic/pneumatic machines, in which a pressurized fluid, such as pressurized liquid or gas, flows, so that the gasket realizes watertightness or airtightness at the junction between the parts, thereby preventing the leakage of fluid from the junction.

Gaskets are preferably used in engines of vehicles .

Described in detail, in the vehicle engines, gaskets are placed between the deck surfaces of a cylinder block and a cylinder head, and between the contact surfaces of the cylinder head and

a cylinder head cover, thus functioning as sealing means for preventing the leakage of high pressure combustion gas from a combustion chamber of a cylinder to the outside. The interior of the combustion chamber is a severe mechanical environment in which the pressure continuously varies during a four-stroke cycle, which comprises repeated compression, expansion, explosion and exhaust strokes.

Particularly, the gas pressure in the cylinder during an explosion stroke is so high as to exceed the locking force of head bolts, which are bolted to both the cylinder head and the cylinder block, and lock them together. Thus, a lift-off force, hereinbelow referred to simply as 'lift-off, is exerted against the cylinder head and pushes the cylinder head upwards while the four-stroke cycle is performed, so that a minute gap may be formed between the gasket and the cylinder head or between the gasket and the cylinder block.

For example, when lift-off is exerted against the cylinder head of a compression-ignition engine, the cylinder head is lifted up from the deck surface of the cylinder block by about lOμm (O.Oluim) ~ 15μm (0.015mm), so that a variable gap may be formed in the junction between the cylinder head and the cylinder block.

In the above .state, the internal gas pressure of the cylinder is about 200 times atmospheric pressure, and thus the gas may leak to the outside of the cylinder through the gap, thus badly influencing the combustion efficiency of the engine.

As described above, the size of the minute gap, which is formed in the junction between the cylinder head and the cylinder block, varies in response to the variation in the load acting in the cylinder while the cycle is performed, so that it is necessary to provide a metal gasket, which has high elasticity and high durability capable of maintaining a desired sealing effect in an engine and preventing the formation of minute gaps between the gasket and the cylinder head or between the gasket and the cylinder block during an explosion stroke. As shown in FIG. 1 and FIG. 2, a conventional metal gasket is placed between the cylinder head and the cylinder block of an engine, and is mounted to the lower surface of either the cylinder head or the cylinder head cover through riveting, and is, thereafter, tightly locked to both the cylinder head and the cylinder block through bolting.

The conventional metal gasket has a laminated structure, comprising a plurality of thin metal plates Ia and Ib, so that the metal gasket may resist high temperatures and high pressures, and has predetermined elasticity and durability. The conventional metal gasket is also provided with lubricant supply holes, coolant supply holes, rivet holes, head bolt holes, and openings 2a and 2b, which correspond to the cylinder bores of an engine .

Here, the laminated plate Ia of FIG. 1 has a folded stopper structure 3. As shown in the enlarged sectional view, taken along the line A-A, a folded stopper 7 is formed on the

lower surface of a subsidiary plate 9 at a location inside a bead 5 by folding the edge of the opening 2a of the subsidiary plate 9. Meanwhile, the metal plate Ib of FIG. 2 has a welded stopper structure 4. As shown in the enlarged sectional view taken along line B-B, an annular stopper 8 is welded to the upper surface of the plate Ib at a location inside a bead β.

The conventional metal gasket, having the above-mentioned construction, executes its primary sealing function for preventing gas leakage using the stoppers 7 and 8, and executes its secondary sealing function for preventing gas leakage using the spring force of the formed beads 5 and 6.

Here, the beads 5 and 6 are formed on respective plates by shaping annular embossments, having waved cross-sections, on the plates at locations around the holes, such as the openings 2a and 2b, the supply holes for lubricant and coolant, and rivet and bolt holes, such that the beads 5 and 6 have elasticity. Thus, when a variable gap is formed between the cylinder block and the cylinder head due to lift-off, the beads 5 and 6 are minutely deformed upwards or downwards due to their elastic restoring forces, thus maintaining a desired effect of sealing the gasket.

Further, as shown by the arc-shaped dotted lines in the drawings, the stoppers 4 support the beads 5 and 6 such that the beads 5 and β are not completely flattened even when the beads 5 and 6 are compressed. Thus, the stoppers 4 reduce the internal stress acting in the contact ends of the beads 5 and

6 .

However, although the conventional metal gasket is provided with the stoppers, when the metal gasket is placed between the cylinder block and the cylinder head and is locked thereto through bolting, the cylinder head is undesirably bent by the bolting, and the gaps at locations around the openings increase, and, further, the gaps become crooked. Particularly, the interval between the deck surfaces of the cylinder head and the cylinder block at locations near the bolted parts is different from the interval between the deck surfaces at interbore locations, at which the parallely arranged cylinder bores meet each other, and which are remote from the bolted parts. Thus, the interval between the deck surfaces becomes waved, so that the combustion gas may leak from the cylinder bores at the interbore locations, at which the waved interval between the deck surfaces forms peaks, or impurities laden in the combustion gas may be accumulated, thus reducing the sealing performance of the metal gasket.

Further, although the stoppers are produced separately from the plate assembly and are, thereafter, added thereto, the stoppers cannot compensate for the minute gaps, which are formed by the lift-off occurring during the operation of an engine .

[Disclosure] [Technical Problem]

Accordingly, the present invention has been made keeping

in mind the above problems occurring in the related art, and an object of the present invention is to provide a metal gasket, which is provided with elastic embossments on a plate assembly to compensate for a difference in the interval between the deck surfaces of the cylinder head and the cylinder block, caused by bolting, wherein the elastic embossments efficiently compensate for the difference in the interval between the deck surfaces of the cylinder head and the cylinder block, thus minimizing the minute displacement while the gasket is produced or assembled and an engine having the gasket is operated without changing the variation in the compression rate of a plurality of beads, so that the beads can be prevented from cracking and gas leakage from the cylinders can be prevented.

[Technical Solution] In order to accomplish the above object, the present invention provides a metal gasket having embossments acting as a stopper, comprising a plate assembly, comprising: an opening formed through the plate assembly at a location corresponding to a cylinder bore; a bead provided in the plate assembly around the opening; and a plurality of bolt holes formed through the plate assembly at locations outside the bead, the plate assembly being installed between junction surfaces of a cylinder head and a cylinder block through bolting, thus sealing the junction between the cylinder head and the cylinder block, wherein the plate assembly further comprises a plurality of embossments, which are provided in the plate assembly

outside the opening at locations between the edge of the opening and the bead, such that the embossments protrude in the same direction as the protruding direction of the bead.

In the metal gasket, the plate assembly preferably has a laminated structure. Described in detail, the plate assembly may comprise an upper plate and a lower plate, the bead may comprise a first bead part formed in the upper plate and convex downwards, and a second bead part formed in the lower plate and convex upwards, and the embossments may comprise a plurality of first embossments formed in the upper plate and a plurality of second embossments formed in the lower plate such that the valley portions and the crest portions of the first and second embossments are in contact with each other.

In the metal gasket, the first and second embossments may be formed such that the heights of the embossments, located near the bolt holes, are lower than the heights of remaining embossments .

More preferably, the heights of the first and second embossments are determined such that, when the height of the embossments, located in areas X at intermediate portions between the bolt holes, is set as H ₁ , the height of the embossments, located in areas Y near the bolt holes, is set as H ₂ , and the height of the embossments, located in areas Z at intermediate portions between openings of the plate assembly, is set as H ₃ , the relationship between the heights of the embossments is set as H ₂ <Hi<H ₃ .

In the metal gasket, each of the first and second embossments may be a conical embossment. Further, the crest portion of each of the first and second embossments may be a flat portion. Further, to realize the high sealing performance of the metal gasket, the first and second embossments may be formed around the edges of the openings of the respective plates to form at least one circle on the respective plates.

Further, the valley portions defined by the first and second embossments may be coated with a coating layer.

[Advantageous Effects]

The metal gasket having embossments acting as a stopper according to the present invention is advantageous in that the embossments, having the same height or having different heights, are provided on a plate assembly of the gasket, which is placed between the cylinder head and the cylinder block, such that the embossments compensate for a difference in the interval between the deck surfaces of the cylinder head and the cylinder block caused by a difference in the strain of the cylinder head due to lift-off, thereby realizing improved sealing performance.

Further, the metal gasket having embossments acting as a stopper according to the present invention is advantageous in that the elasticity of the embossments compensates for a minute gap, which is formed by lift-off occurring during the operation of an engine, thus preventing the leakage of gas to the outside

of the engine .

Further, the metal gasket having embossments acting as a stopper according to the present invention is advantageous in that it comprises a plate assembly, and does not require an additional stopper for compensating for the strain of the cylinder head, and uses the plate assembly comprising laminated plates without having a fixed stopper, thus simplifying the process for producing the gasket and reducing the number of welding processes, thereby minimizing the minute displacement. Further, the metal gasket having embossments acting as a stopper according to the present invention is advantageous in that each of the embossments may be formed as a rectangular cross-sectional shape with a flat crest surface such that the embossment has an increased bearing width D, thus efficiently distributing the load per unit area and reducing the vertical strain of the cylinder head.

Further, the metal gasket having embossments acting as a stopper according to the present invention is advantageous in that the valley portions, defined between the embossments, are coated with a coating layer, thus securing a uniform bearing pressure on the contact surfaces of the cylinder head and the cylinder block and enlarging the contact surface using the coating layer, thereby realizing improved sealing performance of the gasket . Although the preferred embodiments of the metal gasket having embossments acting as a stopper of the present invention

have been described for illustrative purposes with reference to the accompanying drawings, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the present invention.

[Description of Drawings]

FIG. 1 is a view illustrating the construction of a conventional metal gasket in a plan view and in a sectional view; FIG. 2 is a view illustrating the construction of another conventional metal gasket in a plan view and in a sectional view;

FIG. 3 and FIG. 4 are exploded perspective views illustrating the first and second embodiments of the present invention;

FIG. 5 and FIG. 6 are plan views of plate assemblies, which are elements of the embodiments of the present invention shown in FIG. 3 and FIG. 4 ;

FIG. 7 through FIG. 10 are side sectional views and front sectional views illustrating the operational states of the embodiments of the present invention shown in FIG. 3 and FIG. 4;

FIG. 11 is a plan view illustrating a bearing width, which is defined by the contact surface formed by the engagement of first embossments and second embossments of the present invention shown in FIG. 4;

FIG. 12 and FIG. 13 are perspective views illustrating the operational states of the embodiments of the present invention shown in FIG. 3 and FIG. 4;

FIG. 14 and FIG. 15 are exploded perspective views illustrating third and fourth embodiments of the present invention;

FIG. 16 and FIG. 17 are, respectively, a plan view and a circumferential sectional view of a plate assembly, which is an element of the embodiment of the present invention shown in FIG. 15;

FIG. 18 and FIG. 19 are, respectively, a radial sectional view and a circumferential sectional view, which illustrate the operational state of the embodiment of the present invention shown in FIG. 15; FIG. 20 is a perspective view illustrating the operational state of the embodiment of the present invention shown in FIG. 15;

FIG. 21 is a sectional view illustrating the engagement of the embossments of the present invention of FIG. 3 with a coating layer formed on the embossments;

FIG. 22 is a view illustrating a bearing pressure distribution of the embossments of the present invention of FIG. 3, which are not provided with a coating layer,- and

FIG. 23 is a view illustrating the bearing pressure distribution of the embossments of the present invention of FIG. 3, which are provided with a coating layer.

[Best Mode]

Hereinbelow, metal gaskets having embossments acting as stoppers according to the preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings .

FIG. 3 and FIG. 4 are exploded perspective views illustrating first and second embodiments of the present invention, respectively. FIG. 5 and FIG. 6 are plan views of plate assemblies, which are elements of the embodiments of the present invention shown in FIG. 3 and FIG. 4, respectively. FIG. 7 through FIG. 10 are radial sectional views and circumferential sectional views, which illustrate the operational states of the embodiments of the present invention, shown in FIG. 3 and FIG. 4. FIG. 11 is a plan view illustrating a bearing width, which is defined by the contact surface formed by the engagement of first embossments and second embossments of the present invention shown in FIG. 4. FIG. 12 and FIG. 13 are perspective views illustrating the operational states of the embodiments of the present invention shown in FIG. 3 and FIG. 4. FIG. 14 and FIG. 15 are exploded perspective views illustrating third and fourth embodiments of the present invention. FIG. 16 and FIG. 17 are a plan view and a circumferential sectional view of a plate assembly, which is an element of the embodiment of the present invention shown in FIG. 15. FIG. 18 and FIG. 19 are a radial sectional view and a circumferential sectional view, which illustrate the

operational state of the embodiment of the present invention shown in FIG. 15. FIG. 20 is a perspective view illustrating the operational state of the embodiment of the present invention shown in FIG. 15. FIG. 21 is a sectional view illustrating the engagement of the embossments of the present invention of FIG. 3 with a coating layer formed on the embossments. FIG. 22 is a view illustrating a bearing pressure distribution of the embossments of the present invention of FIG. 3, which are not provided with a coating layer. FIG. 23 is a view illustrating a bearing pressure distribution of the embossments of the present invention of FIG. 3, which are provided with a coating layer.

As shown in FIG. 3, FIG. 4, FIG. 14 and FIG. 15, each of the metal gaskets according to the preferred embodiments of the present invention comprises an upper plate 10a and a lower plate 10b, which are shaped as thin plates and have respective openings 11a and lib, which correspond to the cylinder bores of an engine.

An annular bead 12a, 12b, which has a waved cross-section, is integrally formed around each of the holes 11a and lib of the upper and lower plates 10a and 10b at a location spaced apart from the hole 11a or lib by a predetermined distance. The bead 12a, 12b is convex downwards or upwards and has predetermined elasticity. Described in detail, the upper plate 10a is provided with a first bead 12a, which is convex downwards, while the lower

plate 10b is provided with a second bead 12b, which is convex upwards, so that the crests of the first and second beads 12a and 12b are in contact with each other. Thus, when the cylinder head 31 and the cylinder block 30 of the present invention are locked to each other using head bolts, which are fastened through bolt holes 13a and 13b of the cylinder head 31 and the cylinder block 30, the crests of the beads 12a and 12b are compressed together, thus sealing the junction between the cylinder head 31 and the cylinder block 30 at locations around the openings 11a and lib.

The present invention is characterized in that a plurality of embossments 21, 22, 23, 24 is provided in the upper and lower plates 10a and 10b outside the openings 11a and lib at locations between the edge of each of the openings 11a and lib and an associated bead 12a, 12b such that the embossments protrude in the same direction as the protruding direction of the bead 12a, 12b. Described in detail, the embossments are formed in the upper and lower plates 10a and 10b of the plate assembly 10 at locations around the openings 11a and lib such that, as shown in FIG. 5, FIG. 6 and FIG. 16, first embossments 21a, 22a, 23a, 24a are formed in the upper plate 10a and second embossments 21b, 22b, 23b, 24b are formed in the lower plate 10b in the same directions as the protruding directions of the beads 12a and 12b. In the first embodiment of the present invention, the first embossments 21a and the second embossments 21b are formed

as conical shapes, as shown in FIG. 3.

Further, the first embossments 21a of the upper plate 10a and the second embossments 21b of the lower plate 10b are preferably configured such that the valley portions and the crest portions of the first and second embossments 21a and 21b are in contact with each other, as shown in FIG. 8.

When the metal gasket having the above-mentioned construction according to the present invention is placed and fastened between the cylinder head 31 and the cylinder block 30, the first embossments 21a and the second embossments 21b engage with each other and act as a stopper for preventing gas leakage from the cylinder bores and preventing the beads from being fully compressed. Further, when the cylinder head 31 and the cylinder block 30 are locked together through bolting, a difference is generated in the interval S between the deck surfaces of the cylinder head 31 and the cylinder block 30 by a difference in the strain of the cylinder head 31, which is generated between the locations near the bolted parts on which the bolting pressure acts strongly, and the interbore locations and the intermediate locations between the bolted parts, on which the bolting pressure weakly acts. However, in the present invention, the elastic first and second embossments 21a and 21b compensate for the difference in the interval S between the deck surfaces, thus realizing improved sealing performance of the metal gasket .

Meanwhile, in the second ^■ embodiment of the present

invention, as shown in FIG. 4, each of the embossments 22a and 22b is formed as a rectangular cross-sectional shape with a flat crest surface. Described in detail, each of the embossments according to the second embodiment of the present invention is configured as a cubic shape, as shown in FIG. 4.

In the second embodiment, the first embossments 22a, which are formed on the upper plate 10a, and the second embossments 22b, which are formed on the lower plate 10b, are preferably formed such that the valley portions and the crest portions of the first and second embossments 22a and 22b are in contact with each other, as shown in FIG. 10. Thus, when the embossments 22a and 22b are formed on the respective plates 10a and 10b in a circular arrangement, the intervals between neighboring embossments are preferably set as regular intervals such that the first embossments 22a and the second embossments 22b are completely engaged with each other.

In the same manner as that described for the first embodiment of the present invention, when the metal gasket having the above-mentioned construction according to the second embodiment of the present invention is placed and fastened between the cylinder head 31 and the cylinder block 30, the first embossments 22a and the second embossments 22b engage with each other and act as a stopper for preventing gas leakage from the cylinder bores and preventing the beads from being fully compressed. Further, as described above, each of the embossments 22a and 22b is formed as a rectangular cross-

sectional shape with a flat crest surface, so that the contact surfaces of both the first embossments 22a and the second embossments 22b, which are engaged with each other, are increased, thereby realizing improved sealing performance. Further, the embossments 22a and 22b efficiently distribute the load acting on the area, thereby preventing vertical strain, which may be generated in the cylinder head 31 by stress concentration. Thus, the width of the flat crest surface of each of the first embossments 22a and the second embossments 22b is preferably set to be a large width, which can efficiently distribute the stress, although the width of the flat crest surface must be determined in consideration of the formability of the embossments 22a and 22b.

Further, the elastic first and second embossments 22a and 22b according to the second embodiment of the present invention efficiently compensate for the difference in the interval S between the deck surfaces of the cylinder head 31 and the cylinder block 30, which is generated by the difference in the strain of the cylinder head 31, which is generated between the locations near the bolted parts on which the bolting pressure strongly acts and the interbore locations or intermediate locations between the bolted parts, on which the bolting pressure weakly acts, when the cylinder head 31 is locked to the cylinder block 30 through bolting. Thus, the embossments 22a and 22b realize improved sealing performance of the metal gasket .

More preferably, in the first and second embodiments of the present invention, to realize desired sealing performance of the metal gasket, each set of the first embossments 21a, 22a and the second embossments 21b, 22b is preferably arranged around the edge of an opening 11a, lib of an associated plate 10a, 10b in at least one circular arrangement, as shown in FIG. 5 and FIG. 6. The embossments 21a, 22a, 21b, 22b, which are arranged in one or more circular arrangements, realize improved sealing performance, efficiently compensate for the difference in the strain of the cylinder head, and increase the bearing width, thus efficiently distributing the stress.

The operation of the metal gaskets according to the first and second embodiments of the present invention will be described hereinbelow, with reference to FIG. 12 and FIG. 13. FIG. 12 and FIG. 13 are enlarged view showing the metal gaskets of FIG. 3 and FIG. 4, each of which is placed between the cylinder head and the cylinder block. As shown in the drawings, each of the metal gaskets according to the first and second embodiments of the present invention has a laminated structure, in which the upper plate 10a and the lower plate 10b are sequentially layered such that the ridge of the first bead 12a of the upper plate 10a is in contact with the ridge of the second bead 12b of the lower plate 10b.

The metal gasket of the present invention is placed between the cylinder head 31 and the cylinder block 30 and is locked thereto using a locking means, such as bolts, thus

sealing the junction between the cylinder head 31 and the cylinder block 30.

In the above state, the cylinder head 31 is deformed during the bolting process such that the cylinder head 31 is highly deformed at the locations near the bolted parts, on which the bolting pressure strongly acts, so that a camber is formed at the interbore locations or intermediate locations between the bolted parts, on which the bolting pressure weakly acts. Due to the camber, the interval S between the deck surfaces of the cylinder head 31 and the cylinder block 30 is deformed and becomes waved, as shown in FIG. 12 and FIG. 13. To compensate for the waved deformation of the interval between the deck surfaces, the elastic embossments 21a, 22a, 21b and 22b are provided on the upper and lower plates 10a and 10b and engage with each other, thus compensating for the strain on the interval between the deck surfaces .

Particularly, in the second embodiment of the present invention, each of the embossments 22a and 22b is configured as a rectangular cross-sectional shape with a flat crest surface, so that the embossments 22a and 22b, which engage with each other, as shown in FIG. 11, increase the bearing width D of the contact surfaces of the embossments 22a and 22b.

Meanwhile, FIG. 14 and FIG. 15 illustrate a metal gasket according to the third embodiment and the fourth embodiment of the present invention, in which the arrangement and shape of the embossments are altered. In the following description of

the third and fourth embodiments, a description of portions of the construction and function of the metal gasket that are the same as those described for the first and second embodiments of the present invention is deemed unnecessary, and those elements common to the first and second embodiments and the third and fourth embodiments will carry the same reference numerals.

In the third and fourth embodiments of the present invention, the metal gasket comprises a thin upper plate 10a and a thin lower plate 10b, which are provided with respective openings 11a and lib corresponding to the cylinder bores. The upper plate 10a is provided with a first bead 12a, which is convex downwards, while the lower plate 10b is provided with a second bead 12b, which is convex upwards.

Further, the plate assembly further comprises a plurality of embossments 23a, 24a, 23b, 24b, which are provided in the plate assembly outside the opening 11a, lib at locations between the edge of the opening 11a, lib and the bead 12a, 12b, such that the embossments 23a, 24a, 23b, 24b protrude in the same direction as the protruding direction of the bead 12a, 12b. As shown in FIG. 14, in the metal gasket according to the third embodiment of the present invention, the first embossments 23a and the second embossments 23b are configured as conical embossments. Meanwhile, in the fourth embodiment of the present invention, as shown in FIG. 15, the first embossments 24a and the second embossments 24b are configured as a rectangular cross-sectional shape with a flat crest

surface. Described in detail, each of the embossments has a cubic shape .

As described above, the construction and function of the embossments 23a, 24a, 23b and 24b according to the third and fourth embodiments of the present invention remain the same as the embossments 21a, 22a, 21b and 22b of the first and second embodiments of the present invention.

However, unlike the metal gaskets according to the first and second embodiments of the present invention, the metal gaskets according to the third and fourth embodiments of the present invention are characterized in that the embossments 23a, 24a, 23b and 24b, which are arranged around the openings 11a and lib in a circular arrangement, have different heights such that the embossments, which are located adjacent to the bolt holes 13a and 13b, are lower than the other embossments.

Described in detail, as shown in FIG. 14, FIG. 15 and FIG. 17, the heights of the embossments 23a, 24a, 23b and 24b according to the third and fourth embodiments of the present invention are determined such that the relationship between the height H ₁ of the embossments, located within the area X between the bolt holes 13a and 13b, the height H ₂ of the embossments, located within the area Y near the bolt holes 13a and 13b, and the height H ₃ of the embossments, located within the area Z between the openings 11a and lib, are determined as H ₂ <H!<H ₃ . In other words, the embossments located within the area Z between the openings 11a and lib and having the height H ₃ are

configured as higher embossments, the embossments located within the area X between the bolt holes 13a and 13b and having the height H ₁ are configured as middle height embossments, and the embossments located within the area Y near the bolt holes 5 13a and 13b and having the height H ₂ are configured as lower embossments. When "lift-off," which means that the cylinder head is lifted up during an operation of an engine, occurs, the cylinder head is lifted up to a higher height at the interbore locations, corresponding to the areas Z between the openings

10 11a and lib, is lifted up to an intermediate height at the locations corresponding to the area X between the bolt holes 13a and 13b, and is lifted up to a lower height at the locations corresponding to the area Y near the bolt holes 13a and 13b, to which the highest locking force is applied by the

15 bolts. Thus, the interval S between the deck surfaces of the cylinder head 31 and the cylinder block 30 cannot maintain constant, but becomes different between the areas by the difference in the strain of the cylinder head 31. To compensate for the difference in the interval S between the 0 deck surfaces, the embossments are configured as embossments having different heights.

In the above state, to realize reliable sealing performance of the metal gasket, the first embossments 24a and the second embossments 24b are formed around the edges of the 5 openings 11a and lib of the respective plates 10a and 10b to form at least one circle on the respective plates 10a and 10b,

as shown in FIG. 16. Thus, the metal gasket having the embossments 24a and 24b has improved sealing performance, compensates for the difference in the strain of the cylinder head 31, and increases the bearing width, thus efficiently distributing the stress. (The above description of the function of the metal gasket is to be taken with reference to FIG. 16, which illustrates the fourth embodiment of the present invention, and it is understood that the third embodiment of the present invention will provide the same operational function as that of the fourth embodiment.)

Hereinbelow, the operation of the metal gasket according to the fourth embodiment of the present invention will be described with reference to FIG. 20.

FIG. 20 is an enlarged view of the metal gasket according to the present invention of FIG. 15, which is placed between the cylinder head and the cylinder block and is locked thereto. As shown in the drawing, the metal gasket according to the fourth embodiment of the present invention has a laminated structure, in which the upper plate 10a and the lower plate 10b are sequentially layered such that the ridge of the first bead 12a of the upper plate 10a is in contact with the ridge of the second bead 12b of the lower plate 10b.

The metal gasket according to the fourth embodiment of the present invention is placed between the cylinder head 31 and the cylinder block 30 and is locked thereto using a locking means, such as bolts, thus sealing the junction between the

cylinder head 31 and the cylinder block 30.

During the operation of the engine, the cylinder head 31 is deformed by lift-off so that a camber is formed in the cylinder head 31 by the difference in the deformation between the area Z between the openings 11a and lib and the area X between the bolt holes 13a and 13b. Due to the camber, the interval S between the deck surfaces is deformed and becomes waved, as shown in FIG. 20. To compensate for the waved deformation of the interval S between the deck surfaces, the upper and lower plates 10a and 10b of the plate assembly 10 are provided with respective sets of embossments 24a and 24b, which are engaged with each other. Due to elasticity and the difference in the height of the embossments, the strain of the cylinder head 31 around the openings 11a and lib is compensated for.

Further, the embossments 24a and 24b according to the fourth embodiment of the present invention are configured such that they have flat crest surfaces, so that the bearing width of the contact surfaces of the embossments 24a and 24b is increased.

As shown in FIG. 21, the valley portions, defined by the embossments 21a and 21b according ^' to the present invention, may be coated with a coating layer 14. Described in detail, after the embossments 21a and 21b are formed on the respective plates 10a and 10b, the valley portions, defined by the embossments 21a and 21b, are coated with the coating layer 14, made of, for

example, rubber. In the present invention, the coating layer 14 is preferably formed through a screen coating process, which can selectively coat the valley portions of the embossments 21a and 21b with the coating layer. When no coating layer 14 is formed in the valleys of the embossments, surface pressure is generated within the area B corresponding to the crests of the embossments, but no surface pressure is generated within the area A corresponding to the valleys of the embossments, as illustrated in FIG. 22, which shows the state of contact surfaces of a pressure sensing paper relative to an object, such as the cylinder head or the cylinder block. The imbalance in the surface pressure results in a reduction in the sealing performance of the metal gasket in the junction between the cylinder head 31 and the cylinder block 30.

However, when the valleys defined by the embossments according to the present invention are coated with the coating layer 14, surface pressure Pi is generated within the area B corresponding to the crests of the embossments, and surface pressure P ₂ is generated within the area A corresponding to the valleys of the embossments, as illustrated in FIG. 23. Further, additional contact surfaces, formed by the coating layer 14, are added to the respective junction surfaces of the cylinder head 31 and the cylinder block 30, which are in contact with the respective plates 10a and 10b of the plate assembly, thus improving the sealing performance of the gasket.

The above description of the coating layer 14 is to be taken with reference to FIG. 21 through FIG. 23, which illustrate the first embodiment of the present invention, however, it should be understood that the coating layer 14 may be adapted to the second embodiment, the third embodiment and the fourth embodiment of the present invention, without affecting the functioning of the present invention.