Gasket

A gasket which can secure a sufficient sealing capability even for compact, light and less rigid high-performance engines is to be provided. The gasket comprises a metallic base plate and a shim plate stacked around each of combustion chamber holes in the base plate. A base plate bead consisting of a full bead is formed along the circumference of each of the combustion chamber holes. The shim plate is large enough to be arranged opposite a first flat part, a base plate bead formation position A and a second flat part in the base plate. A plurality of strips of auxiliary beads are formed in the part of the shim plate opposite the base plate.

BACKGROUND OF THE INVENTION

The present invention relates to a gasket which, intervening between the joining faces of a cylinder block and a cylinder head, is caused to seal the gap between the joining faces by being fastened with fastening bolts.

Gaskets each having a base plate and a shim plate include ones disclosed in JP2002-5292A (hereinafter referred to as Patent Document 1) and JP2002-31237A (hereinafter referred to as Patent Document 2), for instance.

In the gasket disclosed in Patent Document 1, a base plate bead is disposed around a combustion chamber hole in a base plate, and a shim plate is so arranged opposite the base plate as to cover that base plate bead. That shim plate is large enough to oppose the base plate from the edge of the combustion chamber hole in the base plate to the position of a water hole farther outside then the base plate bead. On the shim plate, only one strip of auxiliary bead is so formed as to come into contact with a flat part of the base plate from the bead toward the combustion chamber and a flat part farther out than the combustion chamber. Intervening between the joining faces of the cylinder block and of the cylinder head, the gasket is intended, even if a gap is caused to arise in any less rigid part by the deformation of the engine or any other cause when fastening bolts are fastened, to prevent gas or cooling water from flowing into the base plate bead side as the auxiliary bead formed on the shim plate follows the deformation.

Also in the gasket disclosed in Patent Document 2, a base plate bead is disposed around a combustion chamber hole in a base plate, and a shim plate is so arranged opposite the base plate as to cover that base plate bead. That shim plate is large enough to oppose the base plate from the edge of the combustion chamber hole in the base plate to the position of a water hole farther outside then the base plate bead. The end part of the shim plate toward the combustion chamber hole is folded back to have a double structure, and an auxiliary bead is formed farther out than the base plate bead. Intervening between the joining faces of the cylinder block and of the cylinder head, the gasket deforms, when the fastening bolts are fastened, the engine as much as the difference in plate thickness in the gasket to make the contact pressure higher on the combustion chamber hole than on the base plate bead.

However, since the engine is not a rigid body, a difference in deformation arises between the fastening bolts. To improve this difference in deformation, the doubled side end part of the combustion chamber in the shim plate where the contact pressure is higher is so formed by forging as to vary in thickness in the circumferential direction, so as to uniformize the contact pressure in the circumferential direction by lowering the contact pressure where it is high and raising the contact pressure where it is low.

As an aspect of the rapid progress of technological innovation in recent years, engines are increasingly reduced in size and weight, and this tends to entail a further decrease in engine rigidity. In the gasket according to Patent Document 1, since the shim plate disposed along with the base plate is thinner than the base plate, the spring force of the auxiliary bead formed on the shim plate is correspondingly weaker. Also, as there is only one strip of auxiliary bead formed closer to the combustion chamber than the base plate bead, the contact pressure generated by that auxiliary bead is also lower. As a result, especially between bolts under low contact pressure, the high combustion pressure may deform the single-strip auxiliary bead of the shim plate to let high-temperature gas pass the auxiliary bead to reach the base plate bead. The present inventors found that this heat could also have long-term adverse effects including gradual deterioration of the base plate bead.

In the gasket disclosed in Patent Document 2 on the other hand, the end part of the shim plate toward the combustion chamber hole is folded back to have a double structure with a view to increasing the contact pressure. At the same time, it is also intended to increase the contact pressure in the vicinities of the combustion chamber and uniformize the pressure in the circumferential direction. Though this proves more or less effective in a stationary state, its application to modern engines, which are further weakened in rigidity and made more susceptible to thermal deformation due to a rise in combustion temperature as a result of reductions in size and weight and enhancement in performance entailing increases in the number of valves and the compression ratio and involving improvement in diluted fuel combustion techniques, all as aspects of the rapid progress of technological innovation in recent years. Especially, the application of such gaskets to engines which are subjected to greater thermal deformation between bores due to repetition of rapid heating from a cold state and then of cooling, even if the technique described in Patent Document 1 is used in combination with that of Patent Document 2, would invite pulsation of cylinder heads caused by the explosive pressure of combustion occurring simultaneously with the thermal deformation. Although the deformation could be absorbed in the vicinities of bolts by the elastic region of the bolts, the compliance with deformation would prove insufficient between bolts and between bores for its absorption, and this could let the gas blow through. These problems have also been identified by the inventors, and they would arise more frequently when such gaskets are applied to engines of a high compression ratio, especially diesel engines.

An object of the present invention, attempted in view of these problems, is to provide a gasket with a sufficient sealing capability even for compact, light, less rigid and powerful engines.

SUMMARY OF THE INVENTION

In order to solve the problems cited above, a gasket according to a first aspect of the invention is provided with a base plate, in which combustion chamber holes are opened and a bead is disposed surrounding each of the combustion chamber holes, and a shim plate thinner than the base plate and stacked around each of the combustion chamber of the base plate, the shim plate opposing the formation position of the base plate bead; a first flat part, which is a flat part of the base plate toward the combustion chamber relative to the base plate bead formation position;, and a second flat part, which is a flat part away from the combustion chamber, wherein two or more strips of auxiliary beads extending along the circumference of each combustion chamber hole are disposed in a position in the shim plate opposing the first flat part.

A gasket according to a second aspect of the invention is a version of the gasket according to the first aspect wherein a second auxiliary bead is disposed in a position opposite the second flat part in the shim plate.

A gasket according to a third aspect of the invention is a version of the gasket according to the first or second aspect wherein the part of the shim plate opposite the first flat part is a thickened part whose thickness is increased by stacking two or more shim plates, and the auxiliary beads are formed on at least one of the shim plates constituting the thickened part.

A gasket according to a fourth aspect of the invention is a version of the gasket according to any of the first through third aspects wherein two base plates of the above-described shape are stacked and the shim plate and a sub-plate for adjusting the plate thickness are inserted between the two base plates; and a bulge or bulges formed by bending and deforming the sub-plate in the direction of thickness are so disposed as to extend along the circumference of each combustion chamber hole in at least one of the positions on the sub-plate in which the first flat part and the second flat part overlap each other.

A gasket according to a fifth aspect of the invention is a version of the gasket according to any of the first through fourth aspects wherein two base plates of the above-described shape are stacked and one shim plate of the above-described shape and a sub-plate for adjusting the plate thickness are inserted between the two base plates; and a level gap is provided by offsetting the part opposite the shim plate in the sub-plate to be concave toward the other side below other parts by ⅓ to ⅔ of the total thickness of the opposite shim plate.

The invention makes it possible to provide a gasket which can secure a sufficient sealing capability even for compact, light and less rigid high-performance engines.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first preferred embodiment of the present invention will be described below with reference to accompanying drawings.

FIG. 1shows a plan of essential parts of a gasket, which is a first preferred embodiment of the present invention, andFIG. 2, a section along line I-I inFIG. 1.

To describe the configuration first, a metal gasket, which is the first preferred embodiment of the invention, comprises a metallic base plate1and a shim plate4, thinner than the base plate1and stacked around each of combustion chamber holes2in the base plate1as shown inFIG. 1andFIG. 2.

In the base plate1, the combustion chamber holes2are opened in positions matching the bores, and a base plate bead3consisting of a full bead is so formed along the circumference of each of those combustion chamber holes2as to surround the combustion chamber hole2. In the outer circumference of the base plate bead3, liquid holes including water holes7and oil holes8and bolt holes6are opened as appropriate, and another bead is formed where sealing is required.

In the following description, a flat part closer to the combustion chamber than the base plate bead3in the base plate1will be referred to as a first flat part B1, and a flat part toward the outer circumference of the base plate bead3, as a second flat part B2. It is desirable for the second flat part B2, which is the flat part between the base plate bead3, liquid holes7and8and the bolt holes6, to be near the base plate bead3.

The shim plate4is formed of an annular sheet having an opening of the same size as the combustion chamber hole2, large enough to be arranged opposite the first flat part B1, a base plate bead formation position A and the second flat part B2in the base plate1. This arrangement creates differences in plate thickness between the surroundings of the combustion chamber hole2and other parts.

Incidentally, though each combustion chamber hole2is provided with a shim plate4, adjoining shim plates4are combined into a single plate by a link4ain this embodiment of the invention to facilitate fitting.

The shim plates4in this embodiment are so arranged as to cover the convex side of the base plate bead3as shown inFIG. 2.

Each of the shim plates4is provided with a plurality of strips (three strips inFIG. 2) of auxiliary beads5a, surrounding the circumference of the combustion chamber hole2, in the part opposite the first flat part B1farther toward the combustion chamber hole2than the base plate bead formation position A in the base plate1. Each auxiliary bead5ais formed by so bending a shim plate4in the direction of thickness as to make the base plate1side convex, and allows elastic deformation in the direction of thickness. The height of these auxiliary beads5ais set to be lower than that of the base plate bead3of the base plate1.

The fastening forces of the bolts here are stronger in the vicinities of the bolt holes and weaker between the bolt holes. In this embodiment, though not shown, the height of the auxiliary beads5ais so varied in the circumferential direction of the combustion chamber holes2as to gradually increase from the vicinities of the bolt holes toward the center of the spaces between each pair of bolt holes.(Actions and Effects)

Next, the actions and effects of the gasket of the above-described configuration will be described.

When the gasket of the above-described configuration is fitted between the joining faces of a cylinder block and a cylinder head and fastened with fastening bolts, the base plate bead3and the auxiliary bead5aare deformed by compression in the direction of thickness in that order. By the time the fastening is completed, the difference in thickness between the thicker part around each combustion chamber hole2where the shim plate4is arranged and other thinner part (the outer edge of the base plate1) causes the contact pressure to concentrate on the surroundings of the combustion chamber hole2. The heaviest load works on the surroundings of the cylinder bore end, where the sealing conditions are the most stringent, to seal the circumference of the combustion chamber hole2.

In this embodiment, as the shim plate4is so stacked as also to oppose the base plate bead3to create a thickness difference from other parts, the maximum load working on the surroundings of the cylinder bore end (the first flat part B1part) is lighter than in a configuration where the shim plate4is arranged only on the combustion chamber hole2side of the base plate bead3to create a thickness difference. At the same time, there arise a sealing pressure attributable to the elastic restitutive force of the base plate bead3under compressive deformation and a sealing pressure due to the elastic restitutive force of the sealing pressure of the auxiliary bead5aformed on the combustion chamber hole2side of the base plate bead3, resulting on primary sealing by the auxiliary bead5aand secondary sealing by the base plate bead3against the high-temperature high-pressure combustion gas.

When the engine starts operating, the temperature rises, the contact pressure is also raised by expansion, and a vibration amplitude is also caused to occur by explosion. The two kinds of beads3and5a, differing in plate thickness, bead width and height, have the effect of compensating for each other's shortcomings.

Then, the two or more strips of auxiliary beads5aformed on the shim plate4come into contact with the first flat part B1closer to the combustion chamber than the base plate bead3and are markedly deformed in the vicinities of bolts on which the contact pressure is higher, while they are deformed in proportion to the contact pressure to form the primary sealing between bores and between bolts where the contact pressure is lower. In this embodiment, since two or more strips of auxiliary beads5aof the shim plate4are formed, though this is primary sealing, there are two seal lines in effect.

Thus, since the shim plate4is thinner than the base plate1, the spring force of each individual auxiliary bead5aformed on the shim plate4is weaker, but in this embodiment the contact pressure generated by the auxiliary beads5aarranged closer to the combustion chamber hole2than the base plate bead3can be increased by providing auxiliary beads5aof two or more strips. The labyrinth effect of the auxiliary beads5aof two more strips can be expected, too. For this reason, even if a high combustion pressure deforms the first strips of the auxiliary beads5aof the shim plate4on the side closer to the combustion chamber hole2and high-temperature gas passes the auxiliary beads5aespecially between bolts on which the contact pressure is weaker, sealing by the auxiliary beads5atoward the outer circumference forbids the high-temperature gas from reaching the base plate bead3. This prevents such troubles as gradual deterioration of the base plate bead3over time by the heat due to contact with high-temperature gas. Modern engines, are weakened in rigidity and made more susceptible to thermal deformation due to a rise in combustion temperature, as a consequence of reductions in size and weight, and enhancement in performance entailing increases in the number of valves and the compression ratio and involving improvement in diluted fuel combustion techniques, all as aspects of the rapid progress of technological innovation in recent years. However, the application of the invention to such engines helps achieve sufficient compliance with deformation between bolts and between bores, and serves to prevent the gas from blow through.

The use of multi-strip auxiliary beads5aresults in a greater pressure borne by the auxiliary beads5a, which enables the auxiliary beads5ato serve as stoppers preventing total bending of the base plate bead3.

The increased pressure applied by the auxiliary beads5aeven between bolts subjected to less fastening pressure causes the auxiliary beads5ato exert elasticity in the direction of urging the base plate bead3upward, and this can serve to prevent the base plate1from vibration.

In this way, the gasket of this embodiment is so structured as to compensate for the reduced rigidity of engines which are significantly smaller, lighter and improved in performance.

A second auxiliary bead5bmay also be disposed in the part opposite the second flat part B2(the part opposite the outer circumference of the base plate bead3) in the shim plate4as shown inFIG. 3.

In this way, as the second auxiliary bead5bis additionally formed on the outside of the base plate bead3, a tertiary sealing effect is created as viewed from the bore side, and when the auxiliary beads5aand5bformed on the shim plate4before and behind the base plate bead3and the base plate bead3formed on the base plate1are fitted to the engine, they work together to form primary, secondary and tertiary seal lines, and perform sealing, each playing its own part in accordance with the rigidity of the engine. For instance, between bolts where the deformation is greater, the base plate bead3which is more greatly deformed first begins to be deformed; as its deformation proceeds, the second auxiliary bead5bof the shim plate4close to bolts is deformed by contact; and then the auxiliary bead5atoward the combustion chamber is deformed, resulting in balancing between the engine rigidity and the spring stress of the gasket when the fastening is completed.

The tertiary sealing by the second auxiliary bead5bcan prevent, with the sealing pressure created by the second auxiliary bead5b, cooling water from infiltrating toward the base plate bead3through the water hole7.

The height of the auxiliary beads5adisposed on the combustion chamber hole2side of the base plate bead3may be set greater than that of the second auxiliary bead5barranged away from the combustion chamber hole2. As the extent of compressive deformation of the auxiliary beads5ain the position away from the bolt fastening position (the lower contact pressure side) can be increased in this way, the sealing pressures of the two kinds of auxiliary beads5aand5bin the radial direction of the combustion chamber hole2can be uniformized.

Also, though the space between the auxiliary beads5aof the shim plate4and the base plate bead3of the base plate1is substantially uniformized in the radial direction in this embodiment, instead the locus of the auxiliary beads5acan be brought closer to the base plate bead3in the vicinities of the bolt holes and away from the base plate bead3between the bolt holes, and the contact pressure can be adjusted to uniformize the sealing pressure in the radial direction.

Further, though the multi-strip auxiliary bead5aopposite the first flat part B1is formed of a full bead in the configuration described above, it need not be a full bead, but auxiliary beads5aof two or more strips may as well be formed by combining stepwise half beads for instance. Depending on the conditions of use, full beads and half beads may be used differentially.

The base plate1need not be only one. For instance, two base plates1may be stacked, with the shim plate4sandwiched between the two base plates1as shown inFIG. 4andFIG. 5. Although the convex sides of the upper and lower base plates1of the base plate beads3are opposed to each other in these examples, their concave sides may as well be opposed to each other. There may also be two or more shim plates4.

Modifications shown inFIG. 6andFIG. 7are respectively cases in which double-strip auxiliary beads5aand second auxiliary beads5bare formed of stepwise half beads and the concave sides of the base plate beads3are opposed to each other.

Next, a second preferred embodiment of the present invention will be described below with reference to accompanying drawings. Similar parts to their counterparts in the first embodiment described above will be denoted by respectively the same reference signs in the following description.(Configuration)

Whereas the basic configuration of the gasket of this embodiment is similar to that of the first embodiment as shown inFIG. 8, the part of the shim plate4opposite the first flat part B1is increased in thickness.

Thus, the part of the shim plate4toward the combustion chamber hole2is made a thickened part4bby stacking two layers of the shim plate4.(Actions and Effects)

This gasket has the following actions and effects in addition to those already described.

Thus, by increasing the thickness of the part of the shim plate closer to the combustion chamber than the base plate bead3, the contact pressure on the first flat part BI is increased. As a result, the pulsation amplitude during engine operation is reduced even further to enable the auxiliary beads5aformed on the shim plate4to comply with the deformation.

Further, by increasing the thickness of the part of the shim plate4opposite the first flat part B1, the total bending of the base plate bead3can be prevented correspondingly.

Although this embodiment is an example in which the multi-strip auxiliary beads5aare formed in the non-folded part of the shim plate4stacked over the first flat part B1, it is also acceptable to dispose multi-strip auxiliary beads5ain the folded part or to dispose two auxiliary beads5aindividually.

Also, the thickened part4bmay as well be formed by joining a plurality of shim plates4by caulking or otherwise.

It is also acceptable to configure two or more strips of stacked auxiliary beads5aby so forming an equivalent of two shim plates4, arranged opposite the first flat part B1, in the direction of thickness as to corrugate together as shown inFIG. 9.

The base plate1here need not be only one. For instance, two base plates1may be stacked, with the shim plate4sandwiched between the two base plates1as shown inFIG. 10andFIG. 11. In these examples the convex sides of the base plate beads3of the upper and lower base plates1are opposed to each other. There may also be two or more shim plates4.

Also, the concave sides of the base plate beads3of the two stacked base plate1may as well be opposed to each other.(Third Embodiment)

Next, a third preferred embodiment of the present invention will be described below with reference to accompanying drawings. Similar parts to their counterparts in the first embodiment described above will be denoted by respectively the same reference signs in the following description.(Configuration)

The gasket of this embodiment has two base plates1, each provided with the base plate bead3, stacked one over the other, with a single shim plate4having the auxiliary beads5ainserted, together with a sub-plate10for thickness adjustment, between the two base plates1as shown inFIG. 12. The sub-plate10is a plate of substantially the same size as the base plate1, and is thicker than the base plate1in this embodiment as it is shown here.

In further detail, the convex sides of the base plate beads3of the upper and lower base plates1are so stacked as to oppose each other. By offsetting the part opposite the shim plate4in the sub-plate10(the range in which the shim plate4comes into contact) by ½ of the total thickness of the shim plate4below other parts, a level gap10ais provided on the combustion chamber hole2side. That level gap10aenables the shim plate4to be mounted in (fitted into) the concave of the level gap10aformed in the upper face of the sub-plate10. The extent of offset here can be set between ⅓ and ⅔. More preferably, it is ½ of the thickness of the shim plate4in the opposing part.

Auxiliary beads5aand5bare formed on the shim plate4as in the foregoing embodiment. Every one of the auxiliary beads5aand5bis a full bead, the auxiliary beads5aare set higher than the auxiliary beads5b. (Actions and Effects)

By inserting the sub-plate10in this way, the gasket can be adjusted to a desired thickness.

Further by providing the level gap10aequal to ½ of thickness of the shim plate4on the sub-plate10, uniform loads can be imposed on the upper and lower the base plates1when fastening the bolts.

Although this embodiment is a case in which the shim plate4is arranged opposite the upper base plate1alone, the shim plate4may as well be disposed between the sub-plate10and the lower base plate1or shim plates4may also be provided both over and underneath the sub-plate10. When shim plates4are to be arranged both over and underneath the sub-plate10, there is no need to dispose the level gap10a. It is also acceptable, though, to facilitate positioning by forming concaves into which the shim plates4are to be fitted in both the upper and lower faces of the sub-plate10.

Or where the part of the shim plate4opposite the first flat part B1is increased in thickness as shown inFIG. 13, a second level gap10acan be provided in the part opposite the thickened part4bto half that additional thickness, namely the thickness of one shim plate4.

Although two level gaps10aare formed according to the thickness of the opposite shim plate4in the configuration shown inFIG. 13, the second level gap10ais not absolutely necessary in the part opposite the thickened part4b. Even in this case, the extent of offset can be kept within ⅓ to ⅔ of the total thickness of the opposite plates. (Fourth Embodiment).

Next, a fourth preferred embodiment of the present invention will be described below with reference to accompanying drawings. Similar parts to their counterparts in the third embodiment described above will be denoted by respectively the same reference signs in the following description.(Configuration)

The gasket of this embodiment is similar in basic structure to that of the above-described third embodiment as shown inFIG. 14, though different in that this embodiment has a bulge11on the sub-plate10.

In this embodiment, the bead-shaped bulge11is so bent and deformed as to protrude in the direction of thickness toward the part overlapping the area where the multi-strip auxiliary beads5aare disposed on the sub-plate10. This bulge11protrudes less than the base plate bead3, extends along the circumference of the combustion chamber hole2and undergoes plastic deformation by a load in the direction of thickness.

In order to make plastic deformation the predominant factor in the deformation of the bulge11by the load in the direction of thickness, the sub-plate10can be fabricated of a relatively soft metal, such as a zinc-plated iron sheet. In terms of hardness index, the sub-plate10can be formed of a material of Hv 200 or less.

This embodiment is similar to the earlier-described third embodiment in other aspects of configuration.(Actions and Effects)

In this embodiment, the load borne by the first flat part B1when the bolts are fastened is made greater by the presence of the multi-strip auxiliary beads5athan where a single-strip auxiliary bead5ais disposed. At the same time, the bulge11of the sub-plate10is subjected to a load according to the imposed load, and undergoes plastic deformation corresponding to the weight of the load. Then, since the load is less between the bolt holes than in the vicinities of the bolt holes when the bolts are fastened, different parts of the bulge11undergo plastic deformation to adjust the height automatically. As a result, while the plastic deformation of the bulge11prevents the contact pressure on the bore circumference from rising too high, the thickness of the gasket in the circumferential direction is automatically increased or decreased according to the load level at the time of fastening is automatically uniformize the contact pressure on the bore circumference in the circumferential direction. For this reason, the contact pressure on the bore circumference in the circumferential direction can be uniformized without having to accurately increase or decrease the height of the auxiliary beads5ain the circumferential direction according to the level of the pre-applied load or even if the height is neither increased nor decreased at all.

Incidentally, the height and width of the bulge11to undergo plastic deformation may as well be varied in the circumferential direction in advance. In this case, the bulge11may be so adjusted as to become higher or narrower between the bolt holes than elsewhere. The higher or the narrower it is, the more rigid will the bulge11become, accordingly the more difficult to be crushed and easier to bear the load.

Though the embodiment as described above is supposed to have only a single strip of the bulge11by way of example, it may have two or more strips. Also, as it is desired to make the gasket thicker between the bolt holes than elsewhere on the bore circumference, the bulge11may be disposed along the combustion chamber hole2only in the parts between bolt holes.

Or, another bulge11extending in the circumferential direction may also be disposed in the part opposite a second auxiliary base plate bead formation position A in the second flat part B2as shown inFIG. 15. In this way, the contact pressure in the circumferential direction in the second auxiliary base plate bead formation position A can be uniformized, enabling the auxiliary beads5ato generate an appropriate contact pressure even between the bolt holes. This would make it more difficult for liquid from the liquid holes to infiltrate from the base plate bead3side, and the useful life of the base plate bead3, namely that of the gasket, to be elongated.

Or as shown inFIG. 16, two or more thickened parts4bmay be formed on the part of the shim plate4opposite the first flat part B1of the base plate1.

Regarding every embodiment of the invention described so far, folding the end part is shown, inFIG. 10for instance, as the way to stack two or more shim plates4in the position opposite the first flat part, the way to stack them is not limited to this. Another shim plate4may be stacked as well, or the sub-plate10may intervene between the stacked shim plates4; nor is it necessary for the stacked shim plates4and4to be linked to each other. Examples of such alternatives are shown inFIG. 17throughFIG. 21. Incidentally,FIGS. 17 through 20show cases in which one of the shim plates4is fixed to the sub-plate10or the base plate1by welding or otherwise. Further, three or more shim plates4may be stacked as stated above.