Metal gasket

Abstract: A metal gasket (21) has an opening (23) for passing a fluid; relatively small through-holes (24) for receiving bolts and a raised portion (25) surrounding the whole circumference of the opening (23). The raised portion (25) has a double-bead (25a; 25b) structure comprising an inner peripheral bead portion (25a) constituted by an intermediate flat portion (28) and a first conically slant portion (29) which connects it with an inner peripheral flat portion (27) and an outer peripheral bead (25b) portion constituted by the intermediate flat portion (28) and a second conically slant portion (31) which connects it with an outer peripheral flat portion (30). The second slant portion (31) is slanted at an angle which is smaller than that of the first slant portion (29).

Description: The present invention relates to a metal gasket which is, for example, disposed between a flange secured to an end of an exhaust pipe and a flange secured to an end of an exhaust purifier or a muffler to join together the exhaust pipe and the exhaust purifier or muffler in such a manner that no gas will leak through the joint of the two members. An exhaust pipe for exhaust gas from an automotive engine is coupled to an exhaust purifier or a muffler which is provided in the intermediate portion of the exhaust pipe system in such a manner that no gas will leak through the joint of the two members by disposing two flanges which are secured to the respective ends of the exhaust pipe and the exhaust purifier or muffler by means, for example, of welding so as to butt against each other with a gasket interposed therebetween and pressing the gasket between the flanges when the flanges are fastened together by means of nuts and bolts. A gasket consisting essentially of asbestos, carbon or the like has heretofore been employed as one which is pressed between a pair of flanges to prevent leakage of gas through the joint, as stated above. However, with the rise in the exhaust gas temperature as a result of the spread of superchargers, there has been a growing tendency to use metal gaskets which are superior in heat resistance and easy to handle. UK patent specification 1289964 shows a metal gasket structure having a raised portion with respective inner and outer conically slanted portions at each edge of the raised portion. SUMMARY OF THE INVENTION It is a primary object of the present invention to enhance the sealing effectiveness of conventional metal gaskets. To this end, the present invention provides a metal gasket formed from a single metal plate or a plurality of stacked metal plates each having an opening for passing a fluid, relatively small through-holes for receiving bolts and a raised portion surrounding the whole circumference of said opening, wherein said raised portion has a double-bead structure comprising an inner peripheral bead portion constituted by an intermediate flat portion and a first conically slant portion which connects it with an inner peripheral flat portion and an outer peripheral bead portion constituted by said intermediate flat portion and a second conically slant portion which connects it with an outer peripheral flat portion characterised in that the second slant portion constituting said outer peripheral bead portion is slanted at an angle which is smaller than that of the first slant portion constituting said inner peripheral bead portion. Further details of the invention are defined in the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS Figs. 1 to 3 show one embodiment of the metal gasket according to the present invention, in which: Fig. 1 is a plan view; Fig. 2 is an enlarged sectional view taken along the line A-A of Fig. 1; and Fig. 3 is an enlarged sectional view taken along the line B-B of Fig. 1. Figs. 4 and 5 show another embodiment of the metal gasket according to the present invention, in which: Fig. 4 is a plan view; and Fig. 5 is an enlarged sectional view taken along the line B-B of Fig. 4. Fig. 6 is a plan view of a conventional metal gasket. Fig. 7 is an enlarged sectional view taken along the line C-C of Fig. 6. Fig. 8 is sectional view corresponding to Fig. 7, which shows another conventional metal gasket. DETAILED DESCRIPTION OF THE INVENTION A typical conventional metal gasket which is clamped between a pair of flanges to join together an exhaust pipe and an exhaust purifier or the like in such a manner that no gas will leak through the joint has theretofore been arranged as shown in Figs. 6 and 7. More specifically, the metal gasket 1 comprises a single metal plate or a plurality (two in the illustrated example) of stacked metal plates 2. Each metal plate 2 has an opening 3 for passing exhaust gas which is formed in the center and two relatively small through-holes 4 for receiving bolts used to fasten together a pair of flanges, the through-holes 4 being formed in opposite end portions, respectively, of the metal plate 2. The metal plates 2 are typically made of a stainless steel. The periphery of the opening 3 in each metal plate 2 is raised to form an annular raised portion 5 which surrounds the whole circumference of the opening 3 so that, when the metal gasket 1 is clamped between a pair of flanges, the periphery of the opening 3 is subjected to a particularly high pressure, thereby achieving reliable and effective airtight sealing of the periphery of the opening 3. It should be noted that in Fig. 7 flanges F which are respectively secured to pipe elements, for example, an exhaust pipe, are schematically shown. The raised portion 5 is, as shown in Fig. 7, comprised of a raised flat portion 8 formed concentrically with the opening 3 and annular slant portion 6 which is contiguous with a flat portion 10 constituting the body of the metal plate 2. In the example shown in Fig. 7, two metal plates 2 with the same configuration are disposed in mirror image relation to each other to form a gasket 1. When the gasket 1 is clamped between a pair of flanges, the slant portions 6 are elastically deformed to thereby increase the level of force with which the peripheries of the openings 3 are pressed against the respective flanges F. In the example shown in Fig. 7, one raised flat portion 8 is provided with one bead portion, that is, one bent portion comprising the flat portion 8 and the slant portion 6, whereas, in the example shown in Fig. 8, two bead portions are provided for one raised portion. Referring now to Fig. 8, a raised portion 15 of a metal plate 12 comprises a raised flat portion, i.e., an intermediate flat portion 18, a first slant portion 19 which connects it with an inner peripheral flat portion 17, and a second slant portion 16 which connects the intermediate flat portion 18 with an outer peripheral flat portion 20. In this example, one flat portion 18 has two bead portions which are respectively formed along the inner and outer peripheries thereof and, therefore, each metal plate 12 is pressed against the corresponding flange with particularly strong force at two portions. Thus, the airtight sealing capability is increased by a kind of labyrinth seal effect. The conventional metal gasket described above suffers, however, form the following disadvantages. If each metal plate of the metal gasket 1 is merely provided with two bead portions which are elastically deformed when the metal gasket 1 is pressed between a pair of flanges so as to achieve reliable and effective airtight sealing by the metal gasket 1, as shown in Fig. 8, the force that is needed to elastically deform the bead portions to a sufficient extent increases unnecessarily and it becomes difficult to tighten the nuts and bolts to join together the two flanges. The present invention aims at solving the above-described disadvantages of the prior art. The present invention will be described below in more detail by way of one embodiment and with reference to the accompanying drawings. Figs. 1 to 3 show one embodiment of the metal gasket according to the present invention, in which: Fig. 1 is a plan view; Fig. 2 is an enlarged sectional view taken along the line A-A of Fig. 1; and Fig. 3 is an enlarged sectional view taken along the line B-B of Fig. 1. A metal gasket 21 comprises two stacked metal plates 22. Each metal plate 22 has a circular opening 23 for passing a fluid, for example, exhaust gas, which is formed in the center and relatively small through-holes 24 for receiving bolts which are formed in opposite end portions, respectively, of the plate 22. The periphery of the opening 23 in each metal plate 22 is raised to form a raised portion 25 which surrounds the whole circumference of the opening 23. The raised portion 25 of each metal plate 22 comprises an inner peripheral bead portion 25a and an outer peripheral bead portion 25b. The inner peripheral bead portion 25a is constituted by an intermediate flat portion 28 and a first conically slant portion 29 which connects it with an inner peripheral flat portion 27. The outer peripheral bead portion 25b is constituted by the intermediate flat portion 28 and a second conically slant portion 31 which connects it with an outer peripheral flat portion 30 and which slants in the opposite directions to the direction in which the first slant portion 29 does. Thus, the metal plate 22 has two elastically deformable portions at the inner and outer peripheries, respectively, of the raised portion 25. In this embodiment, the two metal plates 22 are disposed in mirror image relation to each other so that a hollow structure is defined between the two raised portions 25. The width of the second slant portion 31 that constitutes the outer peripheral bead portion 25b is set so as to be greater than the width of the first slant portion 29 constituting the inner peripheral bead portion 25a, thereby making the angle of inclination of the second slant portion 31 smaller than that of the first slant portion 29 (i,e., α>β), and thus allowing the outer peripheral bead portion 25b to be deformed more easily than the inner peripheral bead portion 25a. The width of the intermediate flat portion 28 that is present between the first and second slant portions 29 and 31 is varied such that the width of those portions (the portions "a" shown in Fig. 1) of the intermediate flat portions 28 which are closer to the bolt receiving through-holes 24 is smaller than the width of the portions (the portions "b" shown in Fig. 1) thereof which are remote from the through-holes 24. Accordingly, the width of those portions of the raised portion 25 which are closer to the bolt receiving through-holes 24 is smaller than the width of the portions thereof which are remote from the through-holes 24. In this regard, the intermediate flat portion 28 is formed such that the inner peripheral edge thereof has a configuration which is similar to that of the opening 23 (i.e., a circular configuration in the illustrated example), while the outer peripheral edge of the intermediate flat portion 28 is in the shape of an ellipse, the minor axis of which extends on an imaginary straight line intersecting the bolt receiving through-holes 24, thereby maximizing the distance between the through-holes 24 and the raised portion 25 in this direction. Figs. 4 and 5 show another embodiment of the metal gasket according to the present invention. The reference characters used in Figs. 4 and 5 correspond to the same reference characters used in Figs 1 to 3 and designate corresponding parts. In the case of this embodiment, the width of the intermediate flat portion 28 is varied such that the width of those portions of the intermediate flat portions 28 which are closer to the bolt receiving through-holes 24 is larger than the width of the portions thereof which are remote from the through-holes 24. Accordingly, the width of those portions of the raised portion 25 which are closer to the bolt receiving through-holes 24 is larger than the width of the portions thereof which are remote from the through-holes 24. The second slant portion 31 that constitutes the outer peripheral bead portion 25b intersects the bolt receiving through-holes 24 and terminates at the through-holes 24. The metal gasket 21 of the present invention arranged as described above is clamped between a pair of flanges, and nuts are screwed onto bolts received through the through-holes 24 and tightened to thereby reduce the distance between the two flanges and thus elastically compress the raised portions 25. Thus, by tightening the nuts and the bolts received through the through-holes 24, the inner and outer peripheral bead portions 25a and 25b that constitute in combination the raised portions 25 are compressed between the pair of flanges. Since the angle of inclination of the second slant portion 31 constituting the outer peripheral bead portion 25b is smaller than that of the first slant portion 29 constituting the inner peripheral bead portion 25a, the level of force which is needed to elastically compress the outer peripheral bead portion 25b is lower than that needed for the inner peripheral bead portion 25a. Accordingly, although the raised portion 25 has a double-bead structure comprising the inner and outer peripheral bead portions 25a and 25b, the raised portion 25 can be satisfactorily deformed without the need for extra force and there is no particular difficulty in tightening the nuts and bolts for joining together the two flanges. When the metal gasket 21 of the present invention is strongly clamped between a pair of fianges as described above, the level of pressure against each flange at the inner peripheral bead portion 25a including the first slant portion 29 having a relatively great angle of inclination is higher than that against the flange at the outer peripheral bead portion 25b including the second slant portion 31 having a relatively small angle of inclination, so that a main part of the airtight sealing effect at the periphery of the opening 23 is given by the inner peripheral bead portion 25a. Accordingly, only a little fluid, for example, exhaust gas, can reach the outer side of the inner peripheral bead portion 25a and the pressure level of the fluid is low. Therefore, if a leakage should occur at the inner peripheral bead portion 25a, the leaking fluid is easily blocked by the outer peripheral bead portion 25b and there is substantially no possibility of the fluid leaking to the outer side of the outer peripheral bead portion 25b. In addition, since the width of those portions of the raised portion 25 which are closer to the bolt receiving through-holes 24 is made smaller than the width of the portions thereof which are remote from the through-holes 24 to thereby maximize the distance between the through-holes 24 and the raised portion 25 in the case of the embodiment shown in Figs. 1 to 3, it is possible to prevent the level of pressure applied to the raised portion 25 from becoming extremely high at particular portions (near the bolt-receiving through-holes 24) when the nuts and bolts are tightened. Thus, it is possible not only to enable the raised portion 25 to be compressed substantially uniformly over the whole circumference thereof but also to eliminate the possibility that the raised portion 25 will become partially yielding during use. In the case of the embodiment shown in Figs. 4 and 5, unlike the embodiment shown in Figs. 1 to 3, the width of those portions of the raised portion 25 which are closer to the bolt receiving through-holes 24 is made larger than the width of the portions thereof which are remote from the through-holes 24, thereby the raised portion 25 being extended to the through-holes 24. However, since the second slant portion 31 that constitutes the outer peripheral bead portion 25b intersects the bolt receiving through-holes 24 and terminates at the through-holes 24, the raised portion around the through-holes 24 can be deformed relatively easily when the bolts and nuts are tightened. Accordingly, the force applied to compress the raised portion 25 is not concentrated excessively around the through-holes 24 but almost uniformly distributed around the entire circumference of the raised portion 25. Although the present invention has been described by way of an example in which the metal gasket comprises two metal plates which are aligned in mirror image relation to each other, it should be noted here that the metal gasket of the present invention may comprise a single metal plate 22 shown in Figs. 2 and 3. In this case, the inner peripheral bead portion 25a comprising the first slant portion 29 and the intermediate flat portion 28 and the outer peripheral bead portion 25b comprising the second slant portion 31 and the intermediate flat portion 28 are strongly pressed against one flange, while a bead portion which comprises the first slant portion 29 and the inner peripheral flat portion 27 and another bead portion which comprises the second slant portion 31 and the outer peripheral flat portion 30 are strongly pressed against the other flange. Thus, two bead portions are provided for each of the two flanges. Although the present invention has been described through specific terms, it should be noted that the described embodiments are not necessarily exclusive and that various changes and modifications may be imparted thereto without departing from the scope of the invention which is limited solely by the appended claims.

Claims: A metal gasket formed from a single metal plate or a plurality of stacked metal plates (22) each having an opening (23) for passing a fluid, relatively small through-holes for receiving bolts and a raised portion (25) surrounding the whole circumference of said opening (23), wherein said raised portion (25) has a double-bead structure comprising an inner peripheral bead portion (25a) constituted by an intermediate flat portion (28) and a first conically slant portion (29) which connects it with an inner peripheral flat portion (27) and an outer peripheral bead portion (25b) constituted by said intermediate flat portion (28) and a second conically slant portion (31) which connects it with an outer peripheral flat portion (30) characterised in that the second slant portion (31) constituting said outer peripheral bead portion (25b) is slanted at an angle which is smaller than that of the first slant portion (29) constituting said inner peripheral bead portion (25a). A metal gasket according to claim 1, wherein the width of said intermediate flat portion (28) that is present between said first and second slant portions (29,31) is varied such that the width of those portions of said intermediate flat portion (28) which are closer to said small through-holes (24) is smaller than the width of the portions thereof which are remote from said through-holes (24). A metal gasket according to claim 1, wherein the width of said intermediate flat portion (28) that is present between said first and second slant portions (29,31) is varied such that the width of those portions of said intermediate flat portion (28) which are closer to said small through-holes (24) is larger than the width of the portions thereof which are remote from said through-holes (24), and said second slant portion (31) intersects said through-holes (24) and terminates at said through-holes.

Inventors: BUSEKI HIROO, KIMURA HIDETOSHI, TAKAHASHI MASAKATSU, BUSEKI, HIROO, KIMURA, HIDETOSHI, TAKAHASHI, MASAKATSU
Applicants: NIPPON REINZ CO LTD, NIPPON REINZ CO.,LTD.
Application year: 1989
Main classification: F16J15
IPC codes: F02F11, F16L23, F16J15