Patent Application
20110227295
The present invention relates to a two-material composite gasket. More particularly, the present invention relates to a two-material composite gasket that can be effectively used to simultaneously seal three surfaces of members of an automobile engine and the like.
Relatively large-sized gaskets are used for inlet manifolds, filter blankets, cylinder head covers, cam covers, and the like of automobile engines. Such a gasket is configured to seal hermetically a gap between two members, one of which has a groove and the other of which has a flat part, by inserting the gasket in the groove. However, since the depth of the groove is affected by tolerance induced during processing of the groove or assembling, the entire groove does not necessarily have a uniform depth (see Patent Document 1).
In an automobile engine, two members of the engine, i.e., an engine cylinder block and a cylinder head, are hermetically sealed to each other through a cylinder head gasket, and a chain cover is provided to integrate the engine with a power transmission mechanism attached to these members. Since the chain cover is disposed orthogonally across the joint surface of the block and the head, an irregular three-surface simultaneous sealing function is required at the intersection of mating surfaces of these members.
In order to integrate a power transmission mechanism attached to these members with the engine, a chain cover 24 is provided a part to accommodate a gear shift mechanism for transmitting the rotational movement converted by the cylinder head to the outside of the engine. Since the chain cover 24 is disposed orthogonally across the joint surface of the cylinder block 21 and the cylinder head 22, a gasket 26 is required as a sealing member, which is required to have an irregular three-surface simultaneous sealing function, at the intersection of the mating surfaces of these members, that is, a three-point sealing part 25.
As a sealing material capable of reliably sealing a three-surface mating part even when respective thermal expansion amounts of a cylinder head, a cylinder block, and a chain cover are different, Patent Document 2 proposes a sealing material for sealing a three-surface mating part, the sealing material comprising a first sealing piece for sealing a gap between the lower surface of a cylinder head and the upper surface of a cylinder block; a second sealing piece projecting from the rear side of the first sealing piece toward between the front side end of the cylinder head lower surface and the front side end of the cylinder block upper surface, for sealing a gap between the front side end of the cylinder head lower surface and the front side end of the cylinder block upper surface; a first rib for obliquely connecting the upper part of the rear side of the first sealing piece and the upper surface of the second sealing piece; and a second rib for obliquely connecting the lower part of the rear side of the first sealing piece and the lower surface of the second sealing piece. In this proposal, the sealing material is formed of the first sealing piece and the second sealing piece.
Moreover, as a gasket material for sealing the joint part of three members of an engine, i.e., a cylinder block, a cylinder head, and a front cover, Patent Document 3 proposes a gasket structure for use in the joint part of the three members. In the gasket structure, a head gasket is provided between the cylinder block and the cylinder head, and a front cover gasket is provided between the cylinder block and cylinder head, and the front cover at a right angle with respect to the head gasket. The head gasket is positioned slightly recessed from the end surface of the side of the three-member joint part. The three-member joint part of the front cover gasket projects at right angles to form an approximately cross-shaped part, and the contact surface of the approximately cross-shaped part with the head gasket partially projects to form a convex part. In this proposal, it is necessary to specify the position of the mating surface, and airtightness in the three-point sealing part is insufficient because of the variation in the size due to the tolerance of the three members.
The present applicant has previously proposed a gasket that can seal a gap between two members in such a manner that the gasket is inserted in an insertion groove provided in one of the two members, and compressed by the two members. The portion of the gasket on the high-pressure side is formed so as to be more easily compressed than the portion of the gasket on the low-pressure side, and the side surface of the gasket is inclined so that the central portion of the gasket body is bent to project toward the low-pressure side region when the gasket is compressed by the two members (see Patent Document 4).
An embodiment of this proposed invention is a gasket for sealing a gap between two opposing surfaces, one of the surfaces having a concave gap portion, which is to be sealed by the gasket, the gasket having an oblong cross-sectional shape to be seal a gap and having sealing projections on the top end and bottom end thereof. However, as gasket materials, for example, acrylic rubber, nitrile rubber, fluororubber, and other rubber materials having a rubber hardness (Durometer A: JIS K6253) of 40 to 70, or thermoplastic elastomers are singly used.
For example, a joint structure composed of three members, i.e., a cylinder block, a cylinder head, and a chain cover, has a problem that an irregular gap formed in the mating surface cannot be sealed with a gasket alone. At present, silicone-type liquid rubber is used to seal such a gap in the assembling of the joint structure; however, silicone-type liquid rubber is not used as a sealing material that can generate surface pressure, but is merely used as a pad to block the gap portion. Accordingly, a problem of material degradation (permanent set) occurs after long-term use, causing leakage. Particularly, silicone-type liquid rubber is very vulnerable to degradation by new fuels, such as bioethanol. Moreover, the assembly line includes multiple complex processes (e.g., coating-assembling-drying) and has difficulty in manual correction when in-process defects occur. Another problem is that the management of silicone-type liquid rubber itself is difficult.
An object of the present invention is to provide a gasket for sealing a gap between two opposing surfaces, one of the surfaces having a concave gap portion; particularly a gasket having an oblong cross-sectional shape and having sealing projections on the top end and bottom end thereof. The gasket is used to seal the gap portion, and allows three-surface simultaneous sealing of a gap formed by three members, preferably as typified in a joint structure composed of a cylinder block, a cylinder head, and a chain cover of an automobile engine.
The above object of the present invention can be accomplished by a two-material composite gasket for sealing a gap between two opposing surfaces, one of the surfaces having a concave gap portion, which is to be sealed by the gasket, the gasket having an oblong cross-sectional shape and having projections on the top end and bottom end thereof, the gasket including an upper low-hardness elastomer molded part formed of vulcanized rubber having a Shore A hardness of 5 to 35, a lower high-hardness elastomer molded part formed of vulcanized rubber having a Shore A hardness of 45 to 80, and a parting line bonding the low-hardness elastomer molded part and the high-hardness elastomer molded part, the parting line being positioned so that the height of the low-hardness elastomer molded part is 5 to 40% of the height of the entire gasket.
Preferably, the gasket for sealing a gap between two opposing surfaces is an annular gasket, and the center of the top end and the center of the bottom end of the gasket are each provided with projections.
The two-material composite gasket of the present invention has the following effects:
(1) The gasket can be effectively used to seal a gap between two opposing surfaces, one of the surfaces having a concave scratch or groove as a gap portion formed in the mating part of the two surfaces.
(2) Since the entire surface of the gasket is configured to be able to seal three surfaces, the gasket allows three-surface simultaneous sealing without specifying the position of the mating surface.
(3) When the gasket is inserted, the high-hardness elastomer molded part of the lower part of the gasket provides sufficient reaction force, and the upper projection of the low-hardness elastomer molded part of the upper part of the gasket effectively blocks and seals an irregular gap portion formed in the mating surface of three members bonded to each other (e.g., a cylinder block, a cylinder head, and a chain cover of an automobile engine), thus allowing airtight sealing.
(4) The use of the gasket as a sealing material does not require multiple complex processes (coating-assembling-drying), as in the use of silicone-type liquid rubber, and improves the problems in product management that occur when silicone-type liquid rubber is used as a sealing material. Additionally, manual correction when in-process defects occur, and maintenance at the time of vehicle inspection and the like can also be facilitated.
A two-material composite gasket, preferably a two-material composite annular gasket according to the present invention can seal a gap between two opposing surfaces, one of the surfaces having a concave gap portion, which is to be sealed by the gasket. The gasket has an oblong cross-sectional shape and has projections in the center of the top end and the center of the bottom end thereof. The upper part of the gasket is formed of a low-hardness elastomer, and the lower part of the gasket is formed of a high-hardness elastomer. The form of the annular gasket may be a circle, square, or the like, and the gasket may take any form.
Here, the low-hardness elastomer has a Shore A hardness of 5 to 35, preferably 10 to 20, in order to achieve excellent gap-filling properties. The high-hardness elastomer has a Shore A hardness of 40 or more, preferably 45 to 80, because it is a support generating reaction force, and is required to have hardness sufficient for enabling hermetic sealing of an insertion groove, on the other hand. Moreover, the high-hardness elastomer, which is a support generating reaction force, is preferably resistant to permanent set (compression set). The rubber hardness is adjusted by controlling the amount of filler and cross-linking density. For example, the hardness is increased by increasing the amount of filler or cross-linking density. The Shore A hardness was measured according to Type A Durometer of JIS K6253 corresponding to ISO 7619-1.
When the gasket is inserted, the lower high-hardness elastomer molded part provides sufficient reaction force, and the upper projection of the low-hardness elastomer molded part blocks an irregular gap portion formed in the mating surface of three members that are bonded to each other, while increasing surface pressure, thereby performing hermetic sealing. On the other hand, the lower projection enhances the sealing properties of the lower part of the gasket.
The projection in the upper center of the low-hardness elastomer molded part has a curvature. Similarly, the projection in the lower center of the high-hardness elastomer molded part has a curvature. The projections having a curvature achieve high surface pressure, while reducing deformation during compression. In terms of strain relaxation and improvement in gap-filling properties for the three-surface mating member, the curvature is preferably about 0.3 to 0.5.
The cross-sectional area of the upper gasket formed of low-hardness elastomer must be designed to have a size larger than the cross-sectional area of a gap portion formed by three surfaces to be sealed so that it can certainly fill and enter into the gap portion. Moreover, the height of the cross-sectional surface of the lower gasket formed of high-hardness elastomer must be greater than the height of the cross-sectional surface of the low-hardness elastomer molded part of the upper gasket, because it is necessary to achieve sufficient reaction force required for the low-hardness elastomer molded part to enter into the gap portion formed by three surfaces.
Conversely, when the gasket has a uniform cross-sectional area, and the height of the high-hardness elastomer molded part is lower than the height of the low-hardness elastomer molded part, sufficient reaction force cannot be obtained, while buckling is likely to occur. Accordingly, from the viewpoint of the generation of sufficient reaction force and the prevention of buckling, the height of the low-hardness elastomer molded part is preferably about 5 to 40% of the cross-sectional height of the entire two-material composite gasket. When this value is less than about 5%, the low-hardness elastomer can insufficiently enter into the gap portion, failing to perform complete sealing.
Generally, various engine annular gaskets are designed to have an oblong cross-sectional shape with a height of about 5 to 20 mm and a width of about 1.5 to 6 mm. In the two-material composite annular gasket of the present invention, the aspect ratio (width d0/height h0) is set within the range of 0.2 to 0.3. Regarding the width of the cross-section of the gasket, both side surfaces are preferably inclined so that the width becomes gradually narrower toward the lower edge of the lower high-hardness elastic part from the upper low-hardness elastic part. Such structure enhances the reaction force characteristics of the lower high-hardness elastic part, and ensures transfer of the reaction force to the upper low-hardness elastic part, gap-filling properties, and support of the upper low-hardness elastic part.
At the interface between the low-hardness elastomer molded part and the high-hardness elastomer molded part, these parts are bonded to each other in terms of hermetical sealing performance. Although they may be bonded to each other by an adhesive, vulcanization bonding is preferred in terms of molding and peel strength. Moreover, in terms of the peel strength of vulcanized products, the low-hardness elastomer and the high-hardness elastomer are preferably the same type of elastomer having the same crosslinked structure. Specific examples thereof include acrylic rubber, silicone rubber, fluororubber, and other elastomers having excellent oil resistance, heat resistance, cold resistance, and chemical resistance, in terms of the functionality of gaskets for use in the vicinity of an engine. Furthermore, for example, a cured product of a composition comprising (A) an acrylic polymer having at least one alkenyl group capable of undergoing hydrosilylation reaction, (B) a hydrosilyl group-containing compound curing agent, and (C) a hydrosilylation catalyst as essential components can also be used (see Patent Document 5).
In
The parting line bonding the low-hardness elastomer molded part and the high-hardness elastomer molded part is positioned so that the height (h1) of the low-hardness elastomer molded part is about 40% or less, preferably about 5 to 40%, more preferably about 15 to 40%, with respect to the height (10 of the entire gasket, as described above.
Moreover, the parting line is not flat, but is preferably designed so that the upper low-hardness elastomer molded part side has a concave surface, and the lower high-hardness elastomer molded part side has a convex surface, as shown in
The two-material composite annular gasket of the present invention is suitably used for three-surface simultaneous sealing of a gap formed by mating surfaces of three members. More specifically, the gasket is held between two opposing surfaces, i.e., the unsealed surface of two members sealed to each other by a sealing material and the surface of another member, one of the surfaces having a gasket insertion groove, and the other opposite surface having a concave gap portion positioned across the insertion groove. The high-hardness elastomer molded part side of the gasket is inserted in the insertion groove. The low-hardness elastomer molded part side of the gasket is brought into contact with the other opposite surface having the gap portion and deformed, so that the gap portion is hermetically coupled with the low-hardness elastomer molded part.
For example, referring to
In this case, the volume of the low-hardness elastomer molded part must be set larger than the volume of the gap (gap formed by three mating surfaces) to be subjected to three-surface simultaneous sealing.
The following describes the present invention with reference to an Example.
A T-shaped, tapered and annular gasket having the cross-sectional shape shown in
In the embodiment shown in
The gap area was measured when the two-material composite annular gasket (Example) of the present embodiment and a conventional single-material gasket of the same form entirely formed of acrylic rubber having a Shore A hardness of 50 (Comparative Example) were used. The following table shows the obtained results.
The above results demonstrate that the two-material composite annular gasket of the present invention has excellent gap-filling properties for the housing.
Incidentally, the gap area was measured in the following manner.
A putty was previously placed in a rectangular concave groove (a pseudo-gap portion) formed in a metal plate. When the metal plate, including the putty, was pressed to a gasket, the putty was extruded from the groove in a volume corresponding to the volume of the gasket material entering into the gap portion. Part of the putty remaining in the groove was cured as it was. After the putty was cured, a different colored putty was further poured into the groove and cured. The two-colored putties after curing were simultaneously removed from the groove, and cut at a right angle to the groove direction. The cross-sectional surface thereof was photographed, and the photograph was subjected to image processing. Then, the cross-sectional area of the initial putty that had remained in the rectangular part was measured as a gap area.
The two-material composite annular gasket of the present invention can be used, for example, as an engine gasket, as shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-299406 | Nov 2008 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2009/069769 | 11/24/2009 | WO | 00 | 5/23/2011 |
