Spiral wound gasket for automotive exhaust system

Abstract: The invention discloses a vortex gasket for automotive exhaust system preferably used with a special flange having a conical seal surface. This gasket is formed by spirally overlaying a metal hoop 2 of flat strip, and an inorganic filler 3 of tape form, and annularly spot welding a winding start portion 2a and a winding end portion 2b of the hoop 2. When an external force is applied in the axial direction, slipping occurs between the hoop 2 and the filler 3, and it is telescopically deformed in the axial direction, and the seal surface contact surfaces 1a, 1b at the ends of the gasket are formed in a conical shape.

Description: FIELD OF THE INVENTION The present invention relates to a vortex gasket to be placed between flange faces having conical surfaces, in a flange joint structure of automotive exhaust system. PRIOR ART Generally, in a flange joint structure of automotive exhaust system, a flat grooved flange orthogonal to the tube axial line is tightened, with a vortex gasket placed in the groove, but this flat flange is manufactured separately from the exhaust manifold and others, and welded later, which causes problems in weight and manufacturing cost. RELATED ART Recently, therefore, in the automotive exhaust system, by bulging the tube end or its vicinity, the flange is integrally formed, and it is attempted to reduce the weight of the exhaust system or rationalize in the aspect of manufacturing cost. In such flange (hereinafter called special flange), the seal surface as the crimping surface of the seal member is not a flat surface orthogonal to the tube axial line as in the case of the above flat plate flange, and it forms a conical shape inclined to the tube axial line. Incidentally, a traditional vortex gasket is formed by integrally overlaying spirally a metal hoop of which sectional shape in the width direction is a waveform, and an inorganic filler in a tape form, and therefore it excels in the property of compressibility and recovery and others because of the presence of the metal hoop, and is ideal as the seal between flanges, but, structurally, it cannot be used in the special flange as mentioned above. EP-0 391 069 describes such a gasket. More specifically, this vortex gasket has the overlaid annular layers of hoop and filler engaged with each other in waveform, and is extremely high in the rigidity against deformation in the axial direction, and hence it is not easy to deform the gasket end surface contacting with the flange seal surface (hereinafter called the seal face contact surface) from the flat state orthogonal in the axial direction. Therefore, when placed between the special flanges, the seal face contact surface cannot be deformed in a conical shape corresponding to the flange seal surface, and if attempted to deform by force, abnormal deformation or gaps may be forced against the filler, and anyway favorable seal function cannot be exhibited. Of course, if fabricated and formed preliminarily in a shape corresponding to the seal surface shape, occurrence of such abnormal deformation and gaps cannot be avoided, and favorable seal function cannot be obtained. Considering from these points, the traditional vortex gasket cannot be used by any means in the special flanges having a conical seal surface. As the seal member to be placed between such special flanges, it may be considered to use something that can be easily deformed and formed into a shape corresponding to the seal surface in the seal face contact surface, for example, a graphite material covered with metal mesh and pressed and formed into a desired shape, but such seal member is inferior to the vortex gasket, as a matter of course, in the property of compressibility and recovery and others, and the tightening surface pressure cannot be raised, and it may be broken when removing after use or is higher in cost, and hence it is not practical. SUMMARY OF THE INVENTION It is hence a primary object of the invention to present a vortex gasket maintaining the intrinsic excellent functions of the vortex gasket as the seal between flanges, preferably usable in special flanges having a conical seal surface, and sufficiently applicable to the recent trend of special flanges in the automotive exhaust system. The invention provides a vortex gasket in accordance with claim 1. The object is therefore achieved by spirally and integrally overlaying a metal hoop of a flat strip, and a filler of a slightly broader tape, in a state deformable in the axial direction so that the gasket end face may be a conical shape. Since the hoop and filler are both flat plates straight in the axial direction, by applying an external force in the axial direction, slipping occurs between the two to cause deformation in the axial direction, so that the seal face contact surface at the gasket end face may be formed into a desired conical shape. Therefore, the seal face contact surface may be properly fitted to the flange seal surface having a conical shape, so that it may be preferably used as the seal between special flanges. Other objects, features, aspects and advantages of the present invention will become apparent upon consideration of the following detailed description of the invention when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1A is a sectional view (with the section along line I-I in Fig.2) showing an embodiment of a vortex gasket for automotive exhaust system according to the invention, exhibiting the state before deformation. Fig. 1B is a sectional view showing the state after its deformation. Fig. 2 is a plan view of the same gasket. Fig. 3 is a longitudinal sectional view showing an example of a flange joint structure in an automotive exhaust system using the same gasket. Fig. 4 is a detailed view magnifying essential parts in Fig. 3. Fig. 5 is a sectional view showing an experimental apparatus. Fig. 6 is a graph showing results of experiment. DESCRIPTION OF A PREFERRED EMBODIMENT Referring now to Fig. 1A to Fig. 4, the constitution of the invention is described in detail below according to an embodiment thereof. A vortex gasket 1 of the embodiment is formed, as shown in Fig. 1A and Fig. 2, by spirally overlaying a metal hoop 2 of flat strip, and an inorganic filler 3 of tape form, and spot welding a winding start portion 2a and a winding end portion 2b of the hoop 2 at plural positions. The hoop 2 is made of thin metal sheet such as stainless steel, and the filler 3 is composed of inorganic paper, flexible graphite sheet, mica sheet or the like, having ceramic fibers or glass fibers blended with inorganic powder such as mica and talc. Preferred ceramic fibers are almino-silicate fibers. The materials of the hoop 2 and filler 3 are properly selected depending on the sealing conditions such as properties of the fluid to be sealed. The width a of the filler 3 is set, as shown in Fig. 1B, slightly broader than the width b of the hoop 2 so that the hoop 2 may not be exposed in seal face contact surfaces 1a, 1b at the gasket end faces when it is deformed telescopically depending on the flange shape. If the projection (bulging) of the filler 3 from the hoop 2 is too small, the hoop 2 may contact with the flange seal surface, and the hoop contact portion may form an escape way, or, to the contrary, if the projection of the filler 3 is excessive, the bulging part of the filler 3 may be dropped off due to sealed fluid pressure or high temperature vibration or the like, and anyway favorable seal function cannot be expected. These dimensions a and b must be determined in consideration of such points, and generally it is desired to determine depending on the seal conditions such as the shape of the flange seal surface in a range of 1 < a/b ≦ 1.5. Thus composed vortex gasket can exhibit, as estimated from its structure, the same seal functions as the traditional vortex gasket mentioned at the beginning, and moreover, since the hoop 2 and filler 3 are both flat plates straight in the axial direction, by applying an external force in the axial direction, slipping occurs between 2 and 3, and a telescopic deformation in the axial direction occurs as shown in Fig. 1B, and the seal face contact surfaces 1a, 1b may be formed in an arbitrary conical shape. Therefore, for example as shown in Fig. 3, in a flange joint structure in which flange seal surfaces 6a, 7a are in conical shape, it may function C favorably as the seal between the flanges. That is, the joint structure shown in Fig. 3 is provided in an automotive exhaust system, and with a front end 5a of an upstream exhaust pipe 5 fitted to a downstream exhaust pipe 4, by tightening flanges 6, 7 with a clamp member 8, the both exhaust pipes 4, 5 are connected. One flange 6 is formed in one body by dilating and deforming the pipe end portion of the downstream exhaust pipe 4, and possesses a conical seal surface 6a. The other flange 7 is formed in one body by bulging and deforming the vicinity of the pipe end of the upstream exhaust pipe 5, and possesses a seal surface 7a in the same shape as the seal surface 6a. In such flange structure, when the vortex gasket 1 made in a flat form as shown in Fig. 1A is placed between the seal surfaces 6a and 7a to tighten the flanges 6 and 7, a slipping deformation occurs in the axial direction by the tightening force, and the seal face contact surfaces 1a, 1b are changed into a shape corresponding to the seal surfaces 6a, 7a, and are finally brought entirely into contact with the seal surfaces 6a, 7a (see Fig. 3 and Fig. 4). Thus, since the deformation property and fitting of the seal face contact surfaces 1a, 1b with the seal surfaces 6a, 7a are very high, a favorable seal function on the special flanges 6, 7 is exhibited. Meanwhile, the vortex gasket 1 may be used in the flat state as manufactured as described above, and, if necessary, the seal face contact surfaces 1a, 1b may be preliminarily formed artificially or by a proper press forming machine into a conical shape corresponding to the flange seal surfaces 6a, 7a (for example, as shown in Fig. 4) before use. According to the experiment by the inventor, no particular difference was noted in the compression characteristics and sealing performance by the presence or absence of preliminary forming, but when preliminarily formed pieces were used, the ease of fitting on the seal surfaces 6a, 7a and sealing properties when tightening at low pressure were further enhanced. In this experiment, as shown in Fig. 5, a pressing base 11 was supported on a foundation base 10 so as to be slidable vertically by means of a tubular frame 12, conical surfaces 10a, 11a forming an angle of 45 degrees were provided on the upper and lower confronting surfaces of the both bases 10, 11, and an annular groove 10b having a bottom with a slope of 45 degrees is formed parallel to the conical surface 10a of the foundation base 10 (groove inside diameter d = 43.1 mm, groove outside diameter D = 58.3 mm, groove depth W = 3.5 mm), thereby setting up the test apparatus. The invention pieces 1 ○, 2 ○, 3 ○ and a conventional piece were put in the annular groove 10b, and were pressed by the pressing base 11, and in this state nitrogen gas G of 29 kPa (0.3 kgf/cm 2 ) was supplied into the inner region of the gasket 1 from a penetration route 10c formed in the foundation base 10, and the leak gas to the outer region of the gasket 1 was recovered from a hole 12a of the tubular frame 12, and its volume (leakage) was measured. The invention piece 1 ○ is a vortex gasket forming a hoop made of a 6 mm wide stainless steel (SUS304) flat strip, and a flat filler of a 8 mm width comprising ceramic mixed sheet, in a flat form of 43.8 mm in inside diameter, 54.2 mm in outside diameter, and 8 mm in thickness in the radial direction, the invention piece 2 is a vortex gasket forming the same hoop, and a flat filler of 8 mm wide flexible graphite sheet, in a flat form of 43.8 mm in inside diameter, 54.1 mm in outside diameter, and 8 mm in thickness in the radial direction, the invention piece 3 ○ is a vortex gasket preliminarily forming the vortex gasket of the piece 1 into a 45-degree conical shape at its both end faces (die forming with a forming pressure of 24.5 MPa (250 kgf/cm 2 )), and the conventional piece is a traditional vortex gasket formed in a W-section in the width direction (43.5 mm in inside diameter, 57 mm in outside diameter, and 4.85 mm in thickness in radial direction). The results of experiment are as shown in Fig. 6, and regardless of preliminary forming, the invention pieces 1 ○, 2 ○, 3 ○ exhibited very excellent sealing performances as compared with the conventional piece, and it is also known that the ease of fitting on the seal surfaces and sealing properties in low pressure tightening were further enhanced by preliminary forming. In Fig. 6, ○ refers to the invention piece 1 ○, Δ to the invention piece 2 ○,  to the invention piece 3 ○, and □ to the conventional piece. The tightening surface pressure (or seating stress) in Fig. 6 means the tightening pressure in the direction orthogonal to the conical surfaces 10a, 10b applied to the vortex gasket 1 by the pressing force by the pressing base 11. In the case of preliminary forming, meanwhile, the hoop 2 and the filler 3 may be retained in shape by using adhesive. Therefore, for example, if some impact is given during transportation, the preliminarily formed piece will not be broken apart. However, the adhesive should be properly selected depending on the gasket properties and seal conditions, so as not to impede the deforming property when tightening the flanges and fitting or sealing performance, in particular. The winding conditions (tightness, etc.) of the hoop 2 and filler 3 may be properly set depending on the seal surface shape and presence or absence of preliminary forming, and a further enhancement of sealing performance may be expected depending on the conditions. Obvious changes may be made in the specific embodiment of the invention described herein, such modifications being within the spirit and scope of the invention claimed, and it is indicated that all the details contained herein is intended to be illustrative and not limiting in scope.

Claims: A vortex gasket for automotive exhaust system, being a vortex gasket (1) to be placed between conical flange seal surfaces, formed by spirally overlaying and integrating a metal hoop (2) of a flat strip and a slightly broader filler (3) in a tape form, in a state deformable in the axial direction so that the gasket end faces may be in a conical shape. A vortex gasket for automotive exhaust system according to Claim 1, wherein the winding start portion (2a) and winding end portion (2b) of the hoop (2) are individually spot welded to form an annulus. A vortex gasket for automotive exhaust system according to Claim 1 or 2, wherein the filler width (a) is 1.5 times or less of the hoop width (b). A vortex gasket according to any one of Claims 1 - 3 to be used in a flange joint structure for an automotive exhaust system having a clamp member (8) which fastens together a flange (6) formed by dilating and deforming a pipe end portion of a downstream exhaust pipe (4) and a flange (7) formed by bulging and deforming the vicinity of a pipe end portion of an upstream exhaust pipe (5) with said pipe end portion of said upstream exhaust pipe fitted in said downstream exhaust pipe wherein said gasket is to be placed between opposing conical seal surfaces (6a,7a) of said flanges (6,7) in such a manner that the gasket can be deformed in the axial direction to take a conical shape corresponding to that of said seal surfaces.

Inventors: HOSHIKAWA SHINGO, MIYOSHI TAKESHI, OKADA KEIJI, TAKAOKA MASAHIKO, YAHAGI HIDEO, HOSHIKAWA, SHINGO, MIYOSHI, TAKESHI, OKADA, KEIJI, TAKAOKA, MASAHIKO, YAHAGI, HIDEO, Hoshikawa, Shingo, c/o Nippon Pillar P.Co.,Ltd., Miyoshi, Takeshi, c/o Nippon Pillar P.Co.,Ltd., Okada, Keiji, c/o Nippon Pillar P.Co.,Ltd., Takaoka, Masahiko, c/o Nippon Pillar P.Co.,Ltd., Yahagi, Hideo, c/o Toyota Jidosha K.K.
Applicants: NIPPON PILLAR PACKING, TOYOTA MOTOR CO LTD, NIPPON PILLAR PACKING CO., LTD., TOYOTA JIDOSHA KABUSHIKI KAISHA
Application year: 1993
Main classification: F16J15
IPC codes: F16J15, F01N13