Composite gasket

Abstract: A composite gasket is provided which exhibits good vibration isolation, whilst still providing an effective seal. In one example of the composite gasket (10), a central core member comprising a stainless steel plate (1) having a bolt portion (11) and a liquid sealing portion (22) is provided, wherein NBR rubber (2) acting as a first relatively hard elastic member is disposed adjacent to the bolt portion (11), whilst NBR foam rubber (3) acting as a second relatively soft elastic member is disposed adjacent to the liquid sealing portion (22).

Description: The present invention relates to a gasket for, for example, vibration isolation (floating) of various parts around an automobile engine, such as the head cover, intake manifold, gear case and oil pan. In particular, the present invention relates to a composite gasket for isolating transmitted vibration and providing an effective seal to prevent leaks in an automobile engine. In order to provide an effective seal, a gasket should possess the following characteristics:- (1) low torque-down of a bolt portion and the ability to maintain a clamping force over time; (2) good conformability (i.e. a close fit) to the surface to be sealed so as to cater for surface roughness; (3) sufficient robustness to resist mechanical damage owing to movements due to, for example, internal pressure changes and thermal deformation; and (4) resistance to leaking through the sealing material itself. On the other hand, in order to provide effective vibration isolation, a gasket requires the following characteristics:- (1) a low spring constant (soft) so that a resonance frequency can be shifted towards the lower frequency side; and (2) a high loss factor as a viscous elastic body and a high vibration absorbing capacity. Many of the characteristics listed above are incompatible with one another for satisfying both an effective seal and vibration isolation. For an effective seal, conformability and mechanical robustness, including resilience after deterioration, are required, whereas for vibration isolation, a relatively soft material needs to be used. In general, a soft vibration isolating material is easily buckled, which is incompatible with providing a robust and effective seal. Heretofore various gasket materials have been devised in order to satisfy either one of the two sets of requirements. One known gasket is prepared by mixing fiber and other components with a rubber elastic substance and forming the mixture into a sheet. However, the gasket thus obtained is necessarily rather hard in order to improve torque-down and tensile strength of the bolt portion thereof and consequently exhibits relatively poor vibration isolation. By using a gasket obtained by coating a metal plate with a thin rubber layer, which is vulcanized thereafter, not only is the mechanical robustness increased significantly owing to the metal plate, but also a good conformability can be obtained owing to the rubber layer. In addition, the gasket does not suffer unduly from creep, because the rubber layer is relatively thin. Although sealing performance can be improved by subjecting the gasket to a bead process, the gasket still exhibits relatively poor vibration isolation, owing to the relatively thin rubber layer. A gasket in which a metal plate is coated with foam rubber generally has a high sealing property (even if it is not subjected to a bead process), a low spring constant owing to the foam rubber and good vibration isolation. However, a large torque-down in the bolt portion is usually required and such gaskets are easily buckled in use and the environments in which they can be used are, accordingly, limited to low load applications. Gaskets developed primarily for vibration isolation are generally formed so that the vulcanized rubber layer is relatively thick. Accordingly, such gaskets exhibit good vibration isolation and readily conform to the surface to be sealed, for example a flange surface. However, since the gasket can be compressed significantly in use, there is a risk that it may be clamped too much. In this case, vibration isolation may be diminished and the rubber layer may itself be damaged or buckled. Additionally, if and when creep occurs, not only is it possible for the sealing capacity to deteriorate, but the bolt can also fall off. In order to prevent the latter problem, a so-called size limiting mechanism may be used, but this increases fabrication costs. As described above, it is difficult to reconcile the characteristics of sealing and vibration isolation and attempts to do so generally increase fabrication costs and result in gaskets which are difficult to use in practice. An object of the present invention is to provide a composite gasket which addresses the problems associated with the prior art gaskets. The present invention provides an improved gasket material which has good sealing and vibration isolation properties, and for which it is possible to suppress torque-down of a bolt portion, even if it is affected by thermal deterioration over time. In order to achieve the above objects, a composite gasket according to an invention defined by Claim 1 is characterized in that it comprises a central core member having a bolt portion, a liquid sealing portion, etc.; a first elastic member disposed at the bolt portion of the central core member, which is hard, having a small compression deformation; and a second elastic member disposed at the liquid sealing portion apart from the bolt portion, which is soft, having a high fitness, wherein the second elastic member is as thick as or thicker than the first elastic member. A composite gasket according to an invention defined by Claim 2 is characterized in that, in the invention defined by Claim 1, the first elastic member is made of vulcanized rubber; the second elastic member is made of foam rubber; and the central core member is a metal plate; in which the vulcanized rubber and the foam rubber are adhered to the bolt portion and the liquid sealing portion, respectively, on both the surfaces of the metal plate. A composite gasket according to an invention defined by Claim 3 is characterized in that, in the invention defined by Claim 2, a bead is formed along the periphery of the sealing portion in the metal plate acting as the central core member. A composite gasket according to an invention defined by Claim 4 is characterized in that, in the invention defined by Claim 3, the metal plate acting as the central core member is a spring steel plate. A composite gasket according to an invention defined by Claim 5 is characterized in that it comprises a first sheet member, forming a bolt portion, in which sheet member a first elastic member relatively hard having a small elastic deformation is adhered to a first metal plate; and a second sheet member, forming a liquid sealing portion, in which sheet member, a second elastic member, which is soft and has a high fitness, is adhered to a second metal plate, wherein the first and the second sheet member are linked to each other at positions, where functions of the bolt portion and the sealing portion are not obstructed, and the second elastic member is as thick as or thicker than the first elastic member. A composite gasket according to an invention defined by Claim 6 is characterized in that, in the invention defined by Claim 5, the first elastic member is made of vulcanized rubber and the second elastic member is made of foam rubber. A composite gasket according to an invention defined by Claim 7 is characterized in that it comprises a central core member having a bolt portion, a liquid sealing portion, etc.; a first sheet member, in which a first elastic member relatively hard having a small elastic deformation is adhered to a metal plate; and a second sheet member, in which a second elastic member, which is soft and has a high fitness, is adhered to a second metal plate, wherein the first and the second sheet member are superposed on each of both surfaces of the bolt portion and the liquid sealing portion, respectively, of the central core member and the second elastic member is as thick as or thicker than the first elastic member. A composite gasket according to an invention defined by Claim 8 is characterized in that, in the invention defined by Claim 7, the central core member is a metal plate and the first and the second sheet member are adhered to both the surfaces of the metal plate or linked mechanically relatively loosely thereto at positions, where functions of the bolt portion and the sealing portion are not obstructed. A composite gasket according to an invention defined by Claim 9 is characterized in that, in the invention defined by Claim 7, a bead is formed along the periphery of the sealing portion in the metal plate acting as the central core member. A composite gasket according to an invention defined by Claim 10 is characterized in that, in the invention defined by Claim 9, the metal plate acting as the central core member is a spring steel plate. A basic constructional requirement of the composite gaskets according to the inventions is to construct a composite gasket formed in one body suitable for desired uses by using the first elastic member relatively hard having a small compression deformation for the bolt portion in the gasket and the second elastic member, which is soft and has a high fitness, for the liquid sealing portion or the vibration isolating portion in the gasket and by disposing these first and second elastic members combined with each other on a plane. Consequently, in a mode of realization of the composite gaskets according to the present inventions, a metal plate, e.g. a stainless steel plate or a spring steel plate, having the bolt portion, the liquid sealing portion, etc. is used for the central core member and the first and the second elastic member are adhered to the bolt portion and the liquid sealing portion, respectively, in the metal plate. Or the first and the second sheet member are formed by adhering the first and the second elastic member to the first and the second metal plate, respectively, which are disposed on the bolt portion and the liquid sealing portion in the gasket, respectively, and linked to each other at positions where functions thereof are not obstructed. In this case, using a metal plate acting as the central core member, the first and the second sheet member may be superposed thereon. The first and the second sheet member are adhered to both the surfaces of the central core metal plate. They can be joined in one body by using relatively loose joining means such as mechanical caulking, etc. at positions where functions of the bolt portion and the sealing portion are not obstructed. For the composite gasket according to the present invention it is possible to improve the sealing property and to supplement the self holding property of shape by forming a bead along the periphery of the sealing portion in the metal plate acting as the central core member. The basic constructional requirement of the composite gasket according to the present invention consists in the first and the second elastic member and when raw materials are selected for realizing the present invention, any quality and any combination of the selected raw materials may be used, if they are suitable for utilization environment, taking a resistance to environment, etc. into account. For example, for a gasket used in an extremely low load environment, "hardness" of the first hard elastic member is not necessarily so high with respect to a gasket used in a high load environment and it is sufficient, if it is harder than the second soft elastic member used at the same time. When a gasket is used in an immersion environment in oil, gasoline, etc., both the first and the second elastic member should withstand it under required conditions such as temperature, etc. For the reasons described above following raw materials can be cited as those used for the composite gasket according to the present invention. For the first elastic member vulcanized rubbers (NBR, ACM, EPDM, FKM, silicone, etc.) and other macromolecular materials (resins) can be used and it is possible to give them softness for the second elastic member by foaming them. Suitableness thereof can be determined, depending on various properties of matter such as hardness, spring constant, amount of compression deformation, permanent compression stress after the thermal deterioration, etc. Further, recently, raw materials (rubber coated metals), in which metal plates are coated with these elastic materials, which are vulcanized if necessary, are supplied stably, and it is possible to improve the self shape holding property at the same time and to secure stable quality by using them. Thus it can be said that they are efficient means. Metal plates used here are cold rolled steel plates, aluminium plates, stainless steel plates, copper plates, zinc galvanized steel plates, etc., among which suitable plates may be selected, depending on required environments. As a material for the central core member, particularly in case where a bead is formed thereon and bead recovery force is used efficiently, a stainless steel plate is useful. If it is important to satisfy only the self shape holding property, the central core member may be an aluminium plate or a plastic plate. On the other hand, if it is not necessary to take rust into account, a cold rolled steel plate can be used also without any problem. Further, as means for joining these raw materials in one body for constructing a gasket, adhesive is used; nails are raised and the raw materials are caulked; the raw materials are superposed on each other and caulked in one body while being extruded; the raw materials are secured to each other in one body by means of eyelets, rivets or grommets; etc. Any means may be used, if a plurality of raw materials are not separated from each other. However, if appropriate raw materials can be located at predetermined positions where they are required, when the gasket is mounted on a flange, it is not necessary that all the constructional raw materials of a gasket according to the present invention are secured to each other in one body, but they can be secured to each other in one body by any method, depending on requirements at that time. According to the present invention, torque-down at the bolt portion causing worsening the sealing property is suppressed and at the same time it is prevented that different metal plates are brought into contact by disposing the first hard elastic member at the bolt portion, which is useful also to the vibration isolation. Further, by disposing the second soft elastic member at the sealing portion, fitness to the sealing surface and at the same time the resonance frequency can be shifted towards the lower frequency side, which increases the vibration isolation. In addition, by using the central core member, it becomes easier to arrange the first hard elastic material and the second soft elastic material on a plane and it is possible also to achieve a robustness necessary for the self shape holding. Further, by forming a bead on-the central core member, since superficial sealing can be transformed into linear sealing, it is possible to supplement deficiency in the sealing property. For flanges moving specifically violently, by forming a bead on a spring steel plate such as stainless steel plate, etc. acting as the central core member, resiliency of the bead can be increased and it is possible also to increase the following property of the gasket to flange behavior. In addition, it is useful at following points to use a sheet plate, to the two surfaces of which the first hard elastic member and/or the second soft elastic member are previously adhered; (1) that even if the central core member is not necessarily used together, it is possible to increase the self shape holding property; (2) that, since it is possible to arrange the different elastic members separately on both the surfaces of a metal plate, each layer can be made thinner than a single layer of each of the different elastic members and flow accompanied by clamping bolts can be suppressed by adhering them solidly; and (3) that, in case where the central core member is used together, since it is possible to superpose the elastic members, divided further into a plurality of layers, this is useful for increasing the sealing property and the vibration isolation and even at a place where a great thickness is required, adjustment is possible by regulating the thickness of the central core member. The first hard elastic material means an elastic material such as vulcanized rubber, etc. having a high hardness and a high tensile strength as well as a small amount of compression deformation and a small amount of permanent compression stress and it is possible to improve further these characteristics by coating a metal plate therewith. On the other hand, the second soft elastic material means an elastic material such as vulcanized rubber, etc. having a low hardness and a low spring constant, specifically excellent in the fitness and among others foam rubber, etc. has high values of these characteristics. It is possible also to supplement deficiencies in tensile strength, flow, etc. by coating specifically thinly the metal plate therewith. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a plan view of a first embodiment of the present invention; Fig. 2 is an enlarged view showing a part of a cross-sectional construction along an A-A line in Fig. 1; Fig. 3 is a plan view of a second embodiment of the present invention; Fig. 4 is an enlarged view showing a part of a cross-sectional construction along an A-A line in Fig. 3; Fig. 5 is a diagram showing joining means (X) along a B-B line in Fig. 3; Fig. 6 is a cross-sectional view of an example showing a first sheet member in the second embodiment; Fig. 7 is a cross-sectional view of an example showing a second sheet member in the second embodiment; Fig. 8 is a plan view of a third embodiment of the present invention; Fig. 9 is an enlarged view showing a part of a cross-sectional construction along an A-A line in Fig. 8; Fig. 10 is an enlarged view showing a part of a cross-sectional construction along a B-B line in Fig. 8; Fig. 11 is a plan view showing the part X in Fig. 8 in detail; Fig. 12 is an enlarged view showing a part of a cross-sectional construction (caulking shape) along a C-C line in Fig. 11; Fig. 13 is a plan view of a fourth embodiment of the present invention; Fig. 14 is an enlarged view showing a part of a cross-sectional construction along an A-A line in Fig. 13; Fig. 15 is a plan view of a first example for comparison; Fig. 16 is an enlarged view showing a part of a cross-sectional construction along an A-A line in Fig. 15; Fig. 17 is a plan view of a second example for comparison; Fig. 18 is an enlarged view showing a part of a cross-sectional construction along an A-A line in Fig. 17; Fig. 19 is a plan view of a third example for comparison; and Fig. 20 is an enlarged view showing a part of a cross-sectional construction along an A-A line in Fig. 19. DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinbelow several embodiments of the present invention and examples for comparison, with which they are compared, indicated in the figures will be explained. Figs. 1 and 2 show a first embodiment for a composite gasket 10 used in an apparatus around an automobile motor such as an intake manifold according to the present invention. In the figures, reference numeral 1 indicates a central core member, for which a stainless steel plate (SUS301H) having a bolt portion 11 and a liquid sealing portion 12 is used for the purpose of preventing production of rust. 2 is a first hard elastic member, for which an NBR rubber is used, and which is disposed at the place of the bolt portion 11. 3 is a second soft elastic member, for which an NBR rubber, to which foaming agent is added, is used, and which is disposed at the position of the liquid sealing portion 12. For fabricating the composite gasket constructed as described above, for example, raw materials, which are a stainless steel plate 1 acting as the central core member 1, an NBR rubber acting as the first elastic member 2 and an NBR rubber, to which foaming agent is added, acting as the second elastic member 3, are arranged at predetermined positions in a die designed according to the shape of the gasket. That is, the hard NBR rubber is placed at the bolt portion 11 and the NBR rubber to which foaming agent is added, is placed at the sealing portion 22. They are formed by press vulcanization and they are adhered to the stainless steel plate at the same time as vulcanization. Figs. 3, 4 and 5 show a second embodiment of the composite gasket 20 of the present invention, in which 4 is a first sheet member and 5 is a second sheet member. The first sheet member 4 consists in a steel plate coated with vulcanized rubber, in which a cold rolled steel plate 4b is coated with an NBR rubber 4a acting as the first hard elastic member, as indicated in Fig. 6. On the other hand, a second sheet member 5 is fabricated by coating a cold rolled steel plate 4d with an NBR foam rubber 4c acting as the second soft elastic member, as indicated in Fig. 7. The first sheet member 4 is placed on the bolt portion 21, while the second sheet member is put on the liquid sealing portion 22 and they are joined with each other e.g. by means of mechanical caulkings 23 at positions where functions of the bolt portion and the sealing portion are not obstructed, as indicated in Fig. 5. For fabricating the composite gasket 20, after having dissolved NBR rubber mixture, which will form the first hard elastic member, in a solvent, a cold rolled steel plate is coated with a solution thus obtained, which is vulcanized as it is to obtain a first sheet member. On the other hand, foaming agent is added to NBR rubber mixture, which will form the second soft elastic member, and after having dissolved a mixture thus obtained in a solvent, a cold rolled steel plate is coated therewith, which is foamed in a vulcanizing process to obtain a second sheet member. Figs. 8, 9, 10, 11 and 12 show a third embodiment of the composite gasket 30 according to the present invention. Reference numerals 6 and 7 indicate a first and a second sheet member, respectively. The constructions thereof are identical to those indicated in Figs. 6 and 7, respectively, and they are fabricated by the methods described previously. 8 is a central core member, for which e.g. a stainless steel plate is used. The first and the second sheet member 6 and 7 are superposed on each of both surfaces thereof, arranged in predetermined positions, and joined therewith. For joining the first and the second sheet member 6 and 7 with the stainless steel plate acting as the central core portion 8, a method is adopted, by which they are secured mechanically to each other in one body at positions where functions of the bolt portion and the sealing portion are not obstructed after having superposed the formers on the latter. For example, as indicated in Fig. 10, the second sheet member 7 and the central core member 8 are made in one body at positions where the sealing property is not obstructed by means of eyelets 9a. On the other hand, as indicated in Figs. 11 and 12, the first sheet member 6 and the central core member 8 are made in one body at four positions by means of caulking 9b, which is an application of washer technique. Figs. 13 and 14 show a fourth embodiment, in which a bead is formed in the embodiment indicated in Figs. 8 and 9. In the figures, 8a represents the bead formed along the periphery of the sealing portion of the central core member 8. Figs. 15 and 16 show a prior art gasket as a first example for comparison, which consists in a rubber coated steel plate 31, in which a cold rolled steel plate is coated with a solution obtained by dissolving NBR rubber in a solvent, which is vulcanized thereafter, and a bead 31b is formed on the sealing portion 31a. Figs. 17 and 18 show another prior art gasket as a second example for comparison, which consists in a rubber coated steel plate 32, in which a cold rolled steel plate is coated with a solution obtained by dissolving NBR rubber mixture, to which foaming agent is added, in a solvent, which is foamed in a vulcanizing process. Figs. 19 and 20 show still another prior art gasket as a third example for comparison. As indicated in the figures, NBR rubber 36 is formed by press vulcanization on a stainless steel plate (SUS304) 32 worked by a punching process in a gasket shape in a die having the gasket shape so that the NBR rubber 36 is arranged on the sealing portion 34 and the bolt portion 35 of the central core member 33 made of the stainless steel plate 32 and at the same time it is adhered by vulcanization thereto. Several examples of specifications of the first to fourth embodiments of the present invention and the first to third examples for comparison are indicated in detail in TABLE 1. In the table, a sign (*) attached to the thickness of an elastic material indicates the thickness of the elastic material stuck to each surface of the rubber coated steel plate. For this reason, the overall thickness of the rubber coated steel plate is equal to the thickness of the metal plate + (the thickness of the elastic material x 2). Further, since the third example for comparison is for vibration isolation, the elastic material is classified as a soft elastic material for convenience. TABLE 2 shows evaluation results of the first to fourth embodiments of the present invention and the first to third examples for comparison. In the table, it is supposed that in measurements of the sealing pressure the initial clamping torque is 50kgf-cm. Further thermal deterioration characteristics (including buckling) are measured after having left gaskets under a following condition: Atmosphere: oxidation in air Temperature: 130°C Duration: 200 hours According to the evaluation results indicated in TABLE 2, it can be seen that all the examples for comparison have both merits and demerits in characteristics, while all the embodiments indicate good characteristics. In particular, the third embodiment is excellent in the vibration isolation and not bad in the sealing property and the creeping property. In addition, a high sealing property can be expected for the fourth embodiment, in which a bead is formed. Further, according to the present invention, it is preferable that the second soft elastic material is as thick as or suitably thicker than the first hard elastic material. An appropriate thickness at this time is such a thickness that when the second soft elastic material is clamped by means of bolts, a state is realized where it is not completely compressed, but the first hard elastic material plays a role of a stopper so that the second soft elastic material is compressed up to the thickness of the first hard elastic material at that time and that softness of the second soft elastic material suitably remains. This state is efficient also for the sealing property and the vibration isolation. As explained above, by the composite gasket according to the present invention, since the first hard elastic member having a small compression deformation is arranged at a portion which is directly clamped by the bolt portion, while the second soft elastic member is arranged at a portion where the sealing property and the vibration isolation are required, it is possible to suppress decrease in the clamping torque in a creeping environment such as thermal deterioration, etc. In addition, it is possible to define an appropriate amount of compression of the second soft elastic member and further it is possible to avoid contact of different metal pieces not only at the sealing surface but also at the bolt portion. Consequently, according to the present invention, it is possible to realize a gasket, in which high sealing property and vibration isolation (floating) are compatible and torque-down of the bolt portion even under thermal deterioration in a long term is suppressed and in addition which is cheap.

Claims: A composite gasket comprising: a central core portion having a bolt portion and a liquid sealing portion; a first elastic member disposed adjacent to the bolt portion, wherein the first elastic member is relatively hard, having a small compression deformation; and a second elastic member disposed adjacent to the liquid sealing portion, spaced from the bolt portion, wherein the second elastic member is relatively soft, having a high conformability, and wherein the second elastic member is as thick as or thicker than the first elastic member. A composite gasket according to claim 1, wherein the first elastic member is made of vulcanized rubber, the second elastic member is made of foam rubber and the central core member is a metal plate, and wherein the vulcanized rubber and the foam rubber are adhered to the bolt portion and the liquid sealing portion, respectively, on both surfaces of the metal plate. A composite gasket according to claim 2, wherein a bead is formed along the periphery of the sealing portion in the metal plate. A composite gasket according to claim 2 or claim 3, wherein the metal plate is a spring steel plate. A composite gasket comprising: a first sheet member, forming a bolt portion, in which a first relatively hard elastic member having a small elastic deformation is adhered to a first metal plate; and a second sheet member, forming a liquid sealing portion, in which a second relatively soft elastic member, having a high conformability is adhered to a second metal plate, wherein the first and second sheet members are linked to each other at positions where functions of the bolt portion and the sealing portion are not obstructed and the second elastic member is as thick as or thicker than the first elastic member. A composite gasket according to claim 5, wherein the first elastic member is made of vulcanized rubber and the second elastic member is made of foam rubber. A composite gasket comprising: a central core member having a bolt portion and a liquid sealing portion; a first sheet member, in which a first relatively hard elastic member having a small elastic deformation is adhered to a metal plate; and a second sheet member, in which a second relatively soft elastic member having a high conformability is adhered to a second metal plate, wherein the first and the second sheet members are superposed on each of both surfaces of the bolt portion and the liquid sealing portion, respectively, of the central core member and the second elastic member is as thick as or thicker than the first elastic member. A composite gasket according to claim 7, wherein the central core member is a metal plate and the first and second sheet members are adhered to both surfaces of the metal plate or linked mechanically relatively loosely thereto at positions where functions of the bolt portion and the sealing portion are not obstructed. A composite gasket according to claim 8, wherein a bead is formed along the periphery of the sealing portion in the metal plate. A composite gasket according to claim 9, wherein the metal plate is a spring steel plate.

Inventors: NIWA TAKAHIRO, SEARASHI SHIUNICHI, UEDA KATSUNORI, NIWA, TAKAHIRO, SEARASHI, SHIUNICHI, UEDA, KATSUNORI
Applicants: NICHIAS CORP, NICHIAS CORPORATION
Application year: 1997
Main classification: F16J15
IPC codes: F16J15, F02F11