GASKET

Abstract: A gasket (10; 30; 40; 50; 70; 80) comprises at least one sheet (12; 52) having at least one hole (14; 54) therethrough which defines a passage through the gasket. The gasket also comprises a sealing member (16; 56) formed from sheet metal, the sealing member being mounted on said sheet. The sealing member comprises a portion which is in the form of a tube (16a; 56a) which extends as a closed loop around the periphery of said hole. The gasket also comprises a compression-limiting stop (20; 60) which is contained within the tube.

Description: GASKET This invention is concerned with a gasket comprising at least one sheet having at least one hole therethrough which defines a passage through the gasket. The gasket may for example be a head gasket for an internal combustion engine, in which case the hole corresponds to the position of a cylinder of the engine. It is common practice to provide a seal around a hole through a sheet gasket by inserting a sheet metal sealing member into the hole. The sheet metal sealing member extends around the hole and has a c-shaped cross-section with the sheet received between the "arms" of the cross- section. When the gasket is clamped in position, the sealing member resiliently resists and forms a seal around the hole. However, if the sealing member is crushed beyond a certain limit, it loses its resilience and cannot function as required. Accordingly, it is common practice to provide such gaskets with a compression-limiting stop to prevent over compression of the sealing member. Such a compression limiting stop can be provided by a folded over edge of a metal sheet of the gasket, or by metal deposited on a surface of the sheet adjacent to the sealing member. However, in both cases the compression-limiting stop is spaced from the sealing member, thereby reducing its effectiveness . It is known in industrial gaskets for sealing, for example, between flanges at the ends of pipes to provide a sealing member in the form of a tube formed into a closed loop so that the shape of the tube gives resiliency when force is applied thereto. The tube extends around a passage and has, in some cases, an external or internal metal annulus associated therewith to provide a compression limiting stop. In one form of industrial gasket proposed in GB 1,437,052, the loop is formed by a helical spring having sheet metal coverings of a c-shaped cross-section. This document discloses that a compression-limiting stop may be contained within the spring. It is an object of the present invention to provide a gasket with an improved sealing member and incorporating a compression-limiting stop. The invention provides a gasket comprising at least one sheet having at least one hole therethrough which defines a passage through the gasket, the gasket also comprising a sealing member formed from sheet metal, the sealing member being mounted on said sheet, characterised in that the sealing member comprises a portion which is in the form of a tube which extends as a closed loop around the periphery of said hole, and the gasket also comprises a compression-limiting stop which is contained within the tube. The sheet of a gasket according to the invention may be a single sheet of plastics material provided with resilient sealing beads on its opposite surfaces. Alternatively, the sheet may be of a multi-layer construction, eg several layers of sheet metal or a metal core with resilient layers on opposite sides thereof. In the case of a multi-layer construction, the sealing member may be mounted on any of said layers. The gasket may be a head gasket of an internal combustion engine; in which case, it will have several openings for cylinders and a sealing member associated with each opening. In some cases, the sealing members for several or all of the openings may be formed from the same piece of sheet metal. In a gasket according to the invention, the sealing member is in the form of a tube giving increased resilience and the compression-limiting stop is positioned at the point where its effectiveness is greatest, ie at the line of sealing. The compression-limiting stop, may be formed as a closed loop within the tube. The stop may be formed from rigid material such as metal, eg steel. Conveniently, the stop is formed from metal wire. Alternatively, however, the stop may be formed from deformable but incompressible material since the compression of the tube will result in such a stop filling the space within the tube entirely so that the material of the stop will resist further compression. The tube may be of substantially circular or ovoid or may be partially circular or ovoid, in transverse cross- section. The compression-limiting stop may be of substantially circular, oval or rectangular transverse cross-section. In circular stops, where d is the diameter of the stop, t is the thickness of the tube wall, h 0 is the outer cross-sectional distance across the tube when uncompressed, and h, is the outer cross-sectional distance across the tube when compressed, the value of d is constrained by the value which would totally fill the cavity of the tube at its compressed thickness. This is given by:- d 2 < h, (2h 0 - h,) + 4t (t - h 0 ) Where the gasket is an automotive gasket, the width d of the stop is typically in the range from 0.8 to 2.5mm, the thickness of the tube wall, t, is typically in the range from 0.15 to 0.3mm. The outer cross-sectional distance across the tube at its widest point when uncompressed h 0 would suitably be from 1.6 to 3.2mm, and when compressed, h, , would typically be in the range from 0.5 to 2.0mm. The following exemplify some of the values for t, h 0 , h, and d for gaskets in the preferred range for automotive use: First Gasket: t = 0.15mm h 0 = 1.6mm h ! = 0.8mm d = 1.0mm Second Gasket: t = 0.20mm h 0 = 2.4mm h ! = 1.2mm d = 1.6mm Third Gasket: t = 0.30mm h 0 = 3.2mm h, = 2.0mm d = 2.3mm Preferably, the sealing member also comprises at least one flange by which the sealing member is mounted on said sheet. For example, the sealing member may comprise one or two flanges which extend radially outwardly of the tube. The flanges may be secured to the sheet of the gasket by being embedded in the sheet of the gasket, eg by the sheet being moulded from plastics material around the flange or flanges. Alternatively, the flange or flanges, may be clipped over an edge of the sheet. The flanges may be secured together to complete the tube, eg by welding or by embedding in plastics material. The invention also provides a method of manufacturing a gasket according to the invention, characterised in that the method comprises carrying out a bending operation on a piece of sheet metal to form said tube around said stop, the stop being positioned on said piece either before or during said bending. In a method according to the invention, said piece of sheet metal may be an annular portion of said sheet surrounding said hole, or a separate annular piece of metal, or a cylindrical tube. Thus, said bending operation may comprise forming an embossed ridge in an annular piece of sheet metal, the ridge extending around the hole through said piece, and bending the portion of the piece bounded by the ridge around the compression-limiting stop so that it contacts the crest of the ridge. The method may further comprise forming a further embossed ridge in said piece of sheet metal, said further ridge extending around said hole nearer thereto than the first-mentioned ridge, said bending operation being carried out so that the crests of the two ridges are brought into contact. Alternatively, where said piece of sheet metal is in the form of a cylindrical tube said bending operation involves bending the ends of the tube outwardly to form the sealing member around the stop. The tube may be completed by a welding operation or another method of securing the areas bent into contact against displacement from their relative positions. There now follows a detailed description, to be read with reference to the accompanying drawings, of six gaskets which are illustrative of the invention and of two methods which are illustrative of the invention in its method aspects. In the drawings: Figures 1 to 6 are cross-sectional views taken through a portion of the first to the sixth illustrative gaskets, respectively; Figures 7a to 7c are cross-sectional views illustrating stages in the first illustrative method; and Figures 8a to 8c are cross-sectional views illustrating stages in the second illustrative method. Figure 1 shows the first illustrative gasket 10 which comprises a sheet 12 formed of plastics material. The sheet 12 has a hole 14 therethrough which defines a passage through the gasket 10. Specifically, the gasket 10 is a head gasket of an internal combustion engine and the hole 14 corresponds to the position of a cylinder of the engine. Figure 1 shows only a portion of the gasket 10 at one edge of the hole 14. It is to be understood that the gasket 10 incorporates a plurality of holes 14 corresponding to the cylinders of the engine and also incorporates other holes corresponding to coolant passages, oil passages, and bolt holes as is usual in a head gasket. Furthermore, the gasket 10 incorporates resilient beads (not shown) which are mounted on the surface of the sheet 12 to provide seals around the other holes through the gasket. The gasket 10 also comprises a sealing member 16 providing a bore seal around the hole 14. The sealing member 16 is formed from sheet metal, specifically steel which is 0.2mm in thickness. The sealing member 16 comprises a portion which is in the form of a tube 16a of circular cross-section. The tube 16a extends as a closed loop around the periphery of the hole 14. The sealing member 16 also comprises two flanges 16b and 16c which are integral with the tube 16a and extend parallel to one another away from the tube 16a in a plane which is coincident with the plane of the sheet 12. The flanges 16b and 16c are welded together at 18. The sealing member 16 is mounted on the sheet 12 by the flanges 16b and 16c being embedded in the edge of the sheet 12 which surrounds the hole 14. The gasket 10 also comprises a compression-limiting stop 20 in the form of a metal wire which forms a closed loop and is contained within the tube 16a. The wire forming the stop is of circular transverse cross-section. Figures 7a to 7c illustrate how the first illustrative gasket 10 may be manufactured by the first illustrative method. The first illustrative method commences with a piece of sheet metal in the form of a cylindrical metal tube 22 as shown in Figure 7a. The method comprises carrying out a bending operation on the tube 22 to form the tube 16a around the stop 20. First, in the first illustrative method, the bottom end portion of the tube 22 is bent outwardly to form the outwardly projecting radial flange 16b which is joined to the undeformed upper portion of the tube 22 by a semi-circular portion 22a which defines an upwardly-opening groove 24 (the portion 22a is destined to form half of the tube 16a) . This bending operation is carried out using, suitable tooling, in successive stages. Next, in the first illustrative method, the stop 20 is positioned in the groove 24 and a further bending operation is carried out on the upper end portion of the tube 22 bending it outwardly to form the outwardly projecting radial flange 16c and a semi-circular portion which cooperates with the portion 22a in forming the tube 16a containing the stop 20. The flanges 16b and 16c are then welded together at 18 to complete the sealing member 16. The welding may be continuous around the tube 16a or may be at intervals. Next, in the first illustrative method, the sealing member 16, and similar sealing members associated with the other cylinder holes of the gasket 10 are assembled in a mould so that they are in the correct relative positions they will occupy in the finished gasket 10. Then, plastics material is injected into the mould so that the material envelopes the flanges 16b and 16c but not the tubes 16a, thereby forming the sheet 12 with the hole 14 having the tube 16a running around its periphery. The second illustrative gasket 30 shown in Figure 2 is similar to the first illustrative gasket 10 except as explained hereinafter and the same reference numerals are used for like parts which are not further described. The sealing member 16 of the gasket 30 has a tube 16a which is of ovoid transverse cross-section, being elongated in a direction normal to the plane of the gasket 30. The transverse cross-sectional shape of the compression- limiting stop 20 of the gasket 30 is also elongated in a direction normal to the plane of the gasket 30. The stop 20 has a generally rectangular cross-sectional shape with curved upper and lower end surfaces. The second illustrative gasket 30 is manufactured by a variation of the first illustrative method in which the shape of the portion 22a and of the portion which completes the tube 16a are half-ovoids. The third illustrative gasket 40 shown in Figure 3 is similar to the first illustrative gasket 10 except as explained hereinafter and the same reference numerals are used for like parts which are not further described. The transverse cross-sectional shape of the compression- limiting stop 20 of the gasket 40 is ovoid being elongated in a direction normal to the plane of the gasket 40. The third illustrative gasket 40 is manufactured by the first illustrative method. The fourth illustrative gasket 50 shown in Figure 4 comprises a sheet 52 formed of plastics material. The sheet 52 has a hole 54 therethrough which defines a passage through the gasket 50. Specifically, the gasket 50 is a head gasket of an internal combustion engine and the hole 54 corresponds to the position of a cylinder of the engine. Figure 4 shows only a portion of the gasket 50 at one edge of the hole 54. The gasket 50 incorporates resilient beads (not shown) which are mounted on the surface of the sheet 52 to provide seals around other holes through the gasket. The gasket 50 also comprises a sealing member 56 formed from sheet metal, specifically steel 0.15mm in thickness. The sealing member 56 comprises a portion in the form of a tube 56a which extends as a closed loop around the periphery of the hole 54. The tube 56a has a transverse cross-section which is defined by a circular arc and by straight portions at opposite ends of the arc, the straight portions meeting at a point 58 where they are welded together to complete the tube 56a. One of the straight portions continues beyond the point 58 in a straight line to form an annular flange 56b projecting radially outwardly of the hole 54. The other straight portion bends away from the flange 56b before bending to form a flange 56c which extends parallel to the flange 56b but is spaced therefrom. The sealing member 56 is mounted on the sheet 52 by the flanges 56b and 56c being clipped over the edge of the sheet 52. The gasket 50 also comprises a compression-limiting stop 60 in the form of a metal wire which forms a closed loop and is contained within the tube 56a. The wire forming the stop is of circular transverse cross-section. The gasket 50 is manufactured by the second illustrative method which is illustrated by Figures 8a to 8c. The second illustrative method commences with an annular piece of sheet metal 62 (not shown in an undeformed state) . The second illustrative method comprises carrying out a bending operation on the piece 62 to form the tube 56a around the stop 60. Said bending operation comprises forming an embossed ridge 64 extending around the hole through the piece 62 (this is shown in Figure 8a) . The ridge 64 is formed in the outer peripheral edge portion of the piece 62 and has a shape corresponding to that of the straight portion of the tube 56a which bends back on itself to form the flange 58c. Next, the portion of the piece 62 which is bounded by the ridge 64 is bent upwardly to form a cylindrical tube 66 (this is shown in Figure 8b) . This results in a partially circular in cross-section groove 68 formed between the tube 66 and the ridge 64. Next, in the second illustrative method, the stop 60 is positioned in the groove 68 and the tube 66 is bent outwardly so that it covers the groove 68 completing the tube 56a, contacts the crest of the ridge 64 (at the point 58) , and forms the lange 56b. The crest of the ridge 64 is then welded to the flange 56b. The fifth illustrative gasket 70 is similar to the fourth illustrative gasket 50 except that both flanges 56b and 56c are formed by portions which bend back on themselves after contacting at the point 58. The fifth illustrative gasket 70 is manufactured by a variation of the second illustrative method in which a second embossed ridge is formed nearer to the centre of the piece 62 than the ridge 64 and the bending operation brings the crests of the two ridges into contact at the point 58. The sixth illustrative gasket 80 shown in Figure 6 is similar to the gasket 70 except that there is no weld at the point 58 and the tubular portion 56a is held together by plastics material of the sheet 52 in which the flanges 56b and 56c are embedded.

Claims: CLAIMS A gasket (10; 30; 40; 50; 70; 80) comprising at least one sheet (12; 52) having at least one hole (14; 54) therethrough which defines a passage through the gasket, the gasket also comprising a sealing member (16; 56) formed from sheet metal, the sealing member being mounted on said sheet, characterised in that the sealing member (16: 56) comprises a portion (16a; 56a) which is in the form of a tube which extends as a closed loop around the periphery of said hole (14; 54) , the gasket also comprises a compression-limiting stop (20; 60) which is contained within the tube. A gasket according to claim 1, characterised in that the stop (20; 60) forms a closed loop within the tube (16a; 56a) . A gasket according to either one of claims 1 and 2, characterised in that the stop (20; 60) is formed from metal wire. A gasket according to any one of claims 1 to 3 , characteerised in that the tube (16a; 56a) is of substantially circular or ovoid transverse cross- section. A gasket according to any one of claims 1 to 4 , characterised in that the stop (20; 60) is of substantially circular, oval or rectangular transverse cross-section. A gasket according to any one of claims 1 to 5, characterised in that the sealing member (16; 56) also comprises at least one flange (16b, 16c; 56b, 56c) by which the sealing member is mounted on said sheet (12; 52) . A method of manufacturing a gasket according to any one of claims 1 to 6, characterised in that the method comprises carrying out a bending operation on a piece of sheet metal (22; 62) to form said tube (16a; 56a) around said stop (20; 60) , the stop being positioned on said piece either before or during said bending. A method according to claim 7, characterised in that said bending operation comprises forming an embossed ridge (64) in an annular piece of sheet metal (62), the ridge extending around the hole through said piece, and bending the portion of the piece bounded by the ridge around the compression-limiting stop (60) so that it contacts the crest of the ridge. A method according to claim 8, characterised in that the method further comprises, forming a further embossed ridge in said piece of sheet metal (62) , said further ridge extending around said hole nearer thereto than the first-mentioned ridge (64) , said bending operation being carried out so that the crests of the two ridges are brought into contact. A method according to claim 7, characterised in that said bending operation is carried out on a cylindrical tube (22) , the ends of which are bent outwardly to form the sealing member (16) around the stop (20) .

Inventors: CUNNINGTON KEITH, PERCIVAL PAUL REUBEN, WRIGHT VINCENT CLIVE, CUNNINGTON, KEITH, PERCIVAL, PAUL, REUBEN, WRIGHT, VINCENT, CLIVE
Applicants: COOPER PAYEN LIMITED, CUNNINGTON KEITH, PERCIVAL PAUL REUBEN, WRIGHT VINCENT CLIVE, CUNNINGTON, KEITH, PERCIVAL, PAUL, REUBEN, WRIGHT, VINCENT, CLIVE
Application year: 1997
Main classification: F16J15
IPC codes: F16J15