GB2226371A - Cylinder head gasket - Google Patents

Abstract

A metal gasket comprises perforated metal sheets (11, 13) corrugated around at least one aperture and secured by an intervening layer (15) of adhesive extending across the corrugations. The peaks of the corrugations have elastomer layers (23). The corrugations preferably have a profile providing a hard right-angled junction between the corrugation and the plane sheet, and a relatively shallow intervening arc, causing the corrugation to collapse with a rolling action under compression. In a cylinder head gasket, the cylinder apertures are not provided with corrugations but shims (21) are provided between the gasket sheets around the cylinder apertures. The gaskets have been found to provide exceptionally reliable sealing in adverse circumstances.

Description

CYLINDER HE4D GASKET This invention relates to the operational qua)ty/perforu'ance of meta3Jic seals and in particular to metallic cylinder head gaskets for sealing between the cylinder heads and cylinder brocks of internal combustion engines.

Metal gaskets have been used for many years for sealing purposes, in particular for sealing the cylinder heads of internal combustion engines In a common arrangement, the gasket has apertures corresponding to the cy3inders, oil passages, water passages etc,, and around each of these apertures the metal gasket has a corrugated cross-section. When the gasket is cramped between the cylinder head and cylinder block, the peaks of the corrugations contact the cylinder head and hock surfaces under pressure and the corrugations, during the compression, deform and flow into the mating faces and establish a metal to metal seal.

Numerous forms of corrugation profile have been used, for example arcuate, broad in tilidth and flat topped, and M-shaped (my patent British 1583322) with the corrugation peaks projecting on one face only.

Known metal gaskets have been very successful, but in sortie circumstances have been found to be unabJe to provide satisfactory sealing. With certain layouts of the cylinder and other apertures and of the clamping bolts, there may be insufficient clamping load to make the corrugations flow into the opposed mating faces of the cylinder head and cylinder block to establish a satisfactory seal simultaneously at all of the apertures. It has been found that with certain cylinder head configurations, a seal can be established at the peaks of the corrugations but not at the bases of the corrugations owing to lack of support on the inner edge of the corrugation and dissipation of the load concentration on the outer edge of the corrugation.The fact that there are 2 points of contact of the base of the corrugation means that load in this area is inllnediately halved. This situation is further aggravated because during compression the contact area of the outside base diameter of the corrugation grows much more quickly in area to that of the peak of the corrugation.

In gaskets which do have adequate distribution of the clamping load sealing problems can still arise because of distortion and poor quality machining of mating components.

An object of the present invention is to provide a gasket which overcomes the problems outlined above.

According to one aspect of the invention, a gasket comprises a pair of metal sheets each provided with at least one aperture and with a corrugation extending around the aperture, the corrugations on the two sheets being Inirror images of one another.

according to another aspect of the invention, a metal gasket comprises a pair of Inetal sheets each having at least one cylinder aperture and at least one further aperture, at least one sheet being corrugated around the further aperture or apertures, and a shim being provided between the sheets, around the cylinder aperture or apertures.

Preferably the shim is corrugated, According to a further aspect of the invention, a metal gasket has at least one aperture and a corrugation around a said aperture, which corrugation, in cross-section, consists of an arcuate central region of relatively large radius of curvature, joined to the remainder of the gasket by way of shoulder regions of substantially smaller radius of curvature, Preferably these shoulder regions meet the remainder of the gasket substantially at right angles, and there is a short perpendicular wall region extending from the surface of the gasket to meet the first radiused portion of the corrugation.

According to yet another aspect of the invention, a gasket comprises at last two metal sheets each provided with at least one aperture and at least one sheet being corrugated around a said aperture, the sheets being bonded together hy an intervening layer of adhesive.

The gasket may further comprise a centre plate between the outer metal sheets, likewise bonded by a layer of adhesive, and/or a fire ring around cylinder apertures, which may likewise be bonded by an adhesive.

Preferably, an elastomer is provided at least on the peak or peaks of the corrugation or corrugations.

In a preferred construction, the gasket is provided l,lith at least one shim or other thickening in an edge region. This can reduce or eliminate bowing of the cylinder head when clamped owing to cantilever action of the corrugations at the apertures, leading to the advantage that the clamping pressure is more evenly distributed and in particular an adequate clamping pressure is applied to the corrugations and to the periphery of the cylinder aperture, In a preferred embodiment of the invention, the respective aspects of the invention set out above are provided in combination in a gasket.

A cylinder head gasket according to a preferred embodiment of the invention will be described llith reference to the accompanying drawings, in which; Fig. 1 is a plan view of the gasket.

Fig. 2 is a pJan uiew of a shim used in the gasket of Fig. 1.

Fig, 3 is a cross-section on the line - of Fig. 1, on a larger scale.

Fig. 4 is a cross-section on the line B-B in Fig. 1 showing a corrugated shim.

Fig. S is a cross-section on the line C-C in Fig, 1 showing an edge shim.

Fig. 6 is a cross-section of a corrugation provided around a secondary aperture of the gasket.

Fig. 7 is a cross-section of the completed gasket in the region of a secondary aperture, Fig. 8 is a view corresponding to Fig. 7, after compression of the gasket between a cylinder head and cylinder block, Fig. 9 is a plan view of a singe cylinder gasket.

Fig. 10 is a cross-section on the line 8-8 in Fig. 9.

Fig. 11 is a cross-section on the line 9-9 in Fig. 9.

The gasket illustrated in Figs I to 8 has been designed for use in a high performance four cylinder automobile engine of 998 cc capacity. The dimensions given herein and marked in Fig. 6, in inches, relate to this particular engine.

The gasket has four ovoid apertures 1 corresponding to the cylinders, and a number of secondary apertures corresponding t oil and water passages and bolt holes.

Apertures A are for high pressure oil, R1 for oil drainage, C1, n, F, G for water, C and B are bolt holes.

It was found impossible to seal this engine using conventional metal gaskets. The non-uniform widely spaced placing of the clamping bolts relative to the cylinders and secondary apertures made it impossible to provide adequate clamping pressure around all of the apertures.

The present gasket comprises a pair of metal sheets 11, 13 bonded together, for example by an intervening layer of adhesive 15.

Typically, each sheet has a thickness of 0.010 inches (0.25 iron). This thickness has been found suitable to provide good sealing without leading to unacceptable bowing of the cylinder head when clamped on the gasket.

Around each of the secondary apertures, each sheet is provided with a single corrugation 17 having a flattened arcuate profile as shown in Figs. 6 and 7, projecting from the sheet by 0.025 inches (0.63 mm), The respective corrugations on the two sheets are mirror images, so that when the plates are placed together back to back, the secondary apertures are surrounded by corrugations projecting symmetrically from both upper and lower surfaces of the gasket. The corrugations are formed conventionally by embossing the individual metal sheets before these are assembled together, The illustrated corrugation has been so designed that it requires minimal load to compress it.

The material from which each gasket sheet is made is the finest quality tinned steel, T1 quality which is the softest grade. It is important to use soft high-quality metal.

The cross-sectional profile of the corrugation comprises a shallow arc of relatively large radius e.g 0,026 inches internal (0.660mm), joined to the main flat body of the gasket plate by way of relatively hard squarer corners of reduced radius e.g. 0.010 inches (0.254mm).

These corners or shoulders meet the main flat body of the gasket plate at right angles, and preferably there is a short perpendicular wall region extending between the niain flat body of the plate and the beginning of the radiused corners. The provision of these harder corners provides locally increased strength so that when the corrugation is compressed a rolling effect occurs.

Because of the greater proportional strength in the corners of the corrugation, that is, hoop strength, the base of the corrugation strongly resists any increase in diameter when the corrugation is compressed, and therefore the peak of the corrugation can be deformed only by flowing into the base of the corrugation, as can be seen in Fig. 8. With a conventional corrugation profile, there is a tendency for the base region of the corrugation and adjacent parts of the gasket plate to spread outwards and/or buckle. The rolling effect achieved by the illustrated corrugation results in an extremely small residual aperture within the compressed corrugation as shown in Fig, 8.The corrugations, when fully compressed, retain energy providing a restoring or sealing force, such that if the clamping force where released the height of the corrugation would increase by, for example, 0.001 to O,Q2 inches (0,025 to 0.OStnrn).

The adhesive 15 is applied in such a way that it is present between the corrugations, and therefore, when the corrugations are compressed, their inner surfaces become bonded to one another by the intervening adhesive, so that the bonded surface of the gasket plates is progressively extended as the corrugations are compressed, It has been found, that the two gasket plates become so firmly bonded together that air is trapped in the gap between the corrugations and provides a cushioning effect when the corrugations are compressed, This cushioning effect is additional to the restoring force trapped in the compressed corrugations, and is believed to enhance the ability of the gasket to provide adequate sealing at all of the apertures provided with corrugations even if the clamping load is not uniformly distributed.

Around the cylinder apertures 1, the gasket is not provided with corrugations. Instead, the individual metal sheets 11, 13 are spaced apart and have between them metal shims 21 corresponding in shape and size to the cylinder apertures. Around the cylinder apertures, the metal sheets 11, 13 are provided with embossed steps 19 to provide the spacing between the sheets to accommodate the shims. The shims are for example 0.012 inches thick (0,305 mm).

In the illustrated gasket, a respective single shim is provided for each pair of cylinders, and the respective shims touch at the center of the gasket as can be seen in Fig. 1.

The overall thickness of the gasket adjacent the cylinder apertures is 0.032 inches (0.813 mm). The thickness over the corrugations at the secondary apertures is 0.072 inches (1.83 mm). The gasket is designed to prouide a thickness when compressed of approximately 0.028-0.032 inches (0.71 - 0.81 mm). If greater ouerall thickness is required, a compression plate may be provided between the sheets forming the gaskets. A compression plate is a flat metal plate, of the thickness required to prouide the desired ouerall thickness, cut to exactly the same outline as the gasket, inserted between the two gasket sheets, the whole being bonded together. If a compression plate is used, further shims are provided, so that there is a respective shim on each surface of the compression plate between the plate and the associated corrugated gasket sheet.

The adhesive typically has an initial thickness of 0.002 inches (0.OSmm), decreasing to 0.001 inches (0.05mm) when the gasket is compressed. The adhesive is of such a nature that it does not become rigid in use, and therefore can act as a further means for distributing clamping loads over the gasket, providing some restoring force, and permitting the gasket to flex without cracking the adhesive.

lo provide enhanced sealing at the corrugations, the crests of these are preferably provided with coatings of an elastomer 23, for example a suitable silicone elastomer. These coatings can he applied by screen printing, for example.

The elastomer coating is so placed that when the corrugations are compressed, the elastomer coating not only covers the compressed peaks of the corrugations tiut also has a wedge et'fect on both the inner and outer edges of the flattened corrugation. Xrl compression a corrugation is very rarely if elver completely flattened: there is usually a difference of 0.001 to 0.002 inches (0.025 to 0.05 mm).

Because of the presence of the cylinder hore shims 21 and the edge shims 22 (if provided), which limit l:he nip which car he applied to the gasket, there will he a gap of 0.003 - 0.001 inches (0.075 to 0.1 Ilim) between each face of the gasket and the apposirig face of the cylinder head or cylinder block.

Where the hard contact of the corrugation finishes a small wedge of elastorner occurs to Fill his gap which tapers from 0.001" (0.025 mm) to 0.004" (0.030 mm) in this very localised area. Ihis edge effect further contributes to successful sealing at all of the corrugations The gasket described ensures that a sufficiently high nit loading can be exerted around all of the apertures to erasure satisfactory sealing, with the elastomer providing perfect sealing around the secondary apertures, without depriving the rims of the cylinder apertures of the necessary share of the clamping load required to ensure sealing of- the high pressure cylinder bores. The gasket is so designed, and its thickness at the corrugations and over the shims is so chosen, that there is sufficient clamping pressure ouer the shims to seal the cylinder bores. Only a limited clamping load remains available for compressing the corrugations. The corrugations are designed with a profile which is relatively weak and makes the best use of the available clamping load, but the elastomer layers are highly desirable to ensure complete sealing around all of the secondary apertures prouided with corrugations.

In the illustrated gasket, the ouerall thickness over the corrugations when compressed is typically 0.028 inches (0.71mum) and the thickness ovr the shims is appreciably greater.

It is important to ensure that, when the cylinder head is clamped ouer the gasket, the head is not subjected to bowing due to forces applied in cantilever fashion.

This can impair the evenness of the pressure distribution on the gasket, reducing sealing efficiency, and in particular, bowing can reduce the pressure ouer the cylinder shims.

The described thicknesses of gasket plates and shins and corrugation heights have been selected to reduce these disadvantageous effects.

Ss a further measure, additional shims may be fitted at the outer edges of the gasket, to increase the overall thickness in the edge regions and thereby reduce the cantilever effect arising when the cylinder head and gasket are clamped. These edge shims support~the sides of the cylinder head, in particular the lungitudinal sides, and thereby ensure that the centre line of the cylinder head is not deprived of a proper share of the clamping load.

In the illustrated embodiment, edge shims 22 of U or channel section are fitted around the outer edge of the gasket, as shown in Figure 1 and in cross-section in Fig. 5 They are secured for example by spot welds 24.

These. shims are made of the same metal as the gaskets.

The cylinder shims 21 may be plain, i.. flat. However, to reduce the effect of variations of the clamping load, particularly around the cylinder bores, due to manufacturing variations in the cylinder head and/or block, these shims may have a fine corrugation embossed in then, as shown in cross-section in Figure 4, In the case of a double shim as illustrated in Figure 2, the corrugations of the two bore shims preferably intersect in the regions of the shims between the bores, as shown at 26 for the right hand double shim in Figure 1.

These features provide improved sealing performance and in particular, reduce or eliminate loss of sealing performance due to bowing of the cylinder head and manufacturing variations in the cylinder head and cylinder block.

X method of making the illustrated gasket will now be described, First, the two metal gasket sheets 11, 13, cut or punched from metal sheet or strip, are embossed to provide the corrugations, and the steps 19 for accommodating the shims The respective embossed gasket sheets are mirror images of one another, One sheet is placed on a location jig with the peaks of its corrugations projecting downwards, n layer of adhesive, preferably a contact adhesive, for example 3M Scotch No. 467, is applied to the gasket. The adhesive may for example be applied by dipping, spraying, or roller coating but these processes make it difficult to apply a totally uniform layer of adhesive.Furthermore, it is desirable that the adhesive should extend across the bases of the corrugations so as to bond these to one another when the corrugations are compressed. It has been found that a particularly advantages and' convenient way of applying the adhesive is to provide the adhesive on a paper backing, the backing being cut to a shape corresponding to the gasket, and applying the backed adhesive to the gasket sheet on the jig. The adhesive adheres to the metal gasket sheet, and the paper backing can then be removed from the adhesive, The adhesive extends across the corrugations. The adhesive is cut so that it terminates at the outer edges of the shims. Adhesive is not provided between the shims and the gasket sheets, except that a small amount of adhesive can be expected to ooze into contact with the edges of the shims.The shims are located essentially by the steps embossed in the gasket plates.

The described method of applying the adhesiue provides excellant results and is very simple to use, and is superior to application by roller coating or other methods.

Next, the shims 21 are put in place on their location pins, inside the adhesive layer. Then, the other gasket sheet, with its corrugation peaks projecting upwards, is placed on the jig onto the adtlesive layer, and pressure is applied to the upper gasket plate so that the upper and lower gasket plates, with, the intervening shims, are securely bonded together by the adhesive.

The assembly operation should be carried out under clean conditions and in particular it is important to ensure that no foreign matter is trapped between the gasket sheets, The metal components are preferably degreased before assembly, and if the assembly process is performed manually, the operator should wear cotton or rubber gloves to preuent contamination. These measures not only enhance the quality of the gasket and facilitate the operation of joining the sheets and shims, but also ensure that the surfaces of the peaks of the corrugations are in suitable condition for coating with the elastomer. The elastomer coating can be applied for example by roller coating or silk screening, and may then be cured. One example of a suitable elastomer is Dow Corning 96-083.

It will be understood that if a compression plate is provided to increase the overall thickness of the gasket, the assembly process will include the further steps of placing the compression plate over the shims, placing second shims on the compression plate, and providing an upper layer of adhesive between the compression plate and the upper gasket sheet, The present invention is applicable to a wide range of sealing applications, for example large diesel engines, in which problems similar to those outlined at the beginning can arise.

The form and dimensions of the corrugations will be designed to suit particular applications. The corrugations may, in cross-section, be arcuate, broad and flat, or M-section.

Gaskets embodying the invention can also overcome leakage problems due to distortion and poor quality machining of mating components.

Fig. 7 illustrates a single cylinder Diesel head gasket with a back to back sandwich construction, made generally as described above. In this gasket, the bore is sealed with a surrounding M-section corrugation 33 as shown in Fig. 9, and a single corrugation 31 as shown in Fig, 8 is provided around the outside edge of the gasket for support, to reduce the cantilever effect. Th support corrugation on the outside edge greatly reduces the bending moment due to the corrugation being inside the bolt circle. This problem is further exacerbated during the pressure part of the engine 5 cycle, i.e.

combustion.

The gasket shown in Figs. 7 to 9 has six bo7t holes 25 equally spaced on a pitch circle around a central cylinder aperture and placed in respective logs or fingers 27. Conventional gaskets of this shape have ample and uniform clamping pressure but were found to suffer from leakage due to distortion and inaccurate machining of the cylinder head and block, These problems are overcome by the use of a gasket construction in accordance with the present invention, In applications other than automotive applications, cover plates (e.g. cylinder heads, inspection and maintenance covers for pumps, etc.) can be very thin, and clamping bolts may be widely spaced. As a result, the cover plates may flex to an. extreme extent, leading to substantial variations in the spacing under the cover plate.To accommodate this, it may be found advantageous to provide corrugations of which the heights vary over the area of the gasket, to match the amount of distortion of dflctinn of the cover between the clamping bolts.

Hitherto, multi-layer gaskets have been made by welding or eyeletting the individual plates composing the gasket. With such constructions it has been extremely difficult to avoid leakage between the plates. The use of an adhesive for bonding gasket plates as described herein can completely overcome this problem and revolutionize the performance of multi-layer gaskets, including multi-layer gaskets of otherwise conventional form, for example gaskets of the types described in my Rritish patents numbers 1583322, 2063386, 804880, 2103308, 2097870, 2097871, 2097872, and US patent 4335890.

Claims (1)

1. h gasket which comprises at least two metal sheets each provided with at least one aperture and at least one sheet being corrugated around a said aperture, the sheets being bonded toyether by an interuening layer of adhesive.

2. R gasket which comprises a first metal sheet and a second metal sheet disposed parallel and back to back, each said metal sheet being provided with at least one cylinder aperture and at least one further aperture, each said sheet being corrugated around at least one said further aperture, the corrugations on the respective sheets being mirror images of one another, which corrugation, in cross-section, consists of an arcuate central region of relatively large radius of curvature, joined to the remainder of the gasket by way of shoulder regions of substantially smaller radius of curvature, and a shim provided between the said sheets around the said cylinder aperture and apertures, the said sheets being seciire to form the gasket by an intervening layer of an adhesive.

3. X gasket which comprises a pair of metal sheets each prouided with at least one aperture and with a corrugation extending around the aperture, the corrugations on the two sheets being mirror images of one another.

4. n metal gasket which comprises a pair of metal sheets each having at least one cylinder aperture and at least one further aperture, at least one sheet being corrugated around the further aperture or apertures, and a shim being provided between the sheets, around the cylinder aperture or apertures.

5. fi gasket as claimed in Claim 2 or 4 in which the shim is corrugated.

6. n gasket as claimed in any of claims 3 to 5 in which the sheets composing the gasket are secured by at least one intervening adhesive layer.

6. The gasket claimed in any of claims, 1, 2, 5 and 6, in which the said adhesive extends in a continuous sheet across the corrugation or corrugations.

8. n gasket as claimed in any preceding claim in which the corrugation, in cross section, is of relatively large radius of curvature, joined to the remainder of the gasket by way of shoulder regions of substantially smaller radius of curvature 9. n gasket as claimed in any preceding claim having at least one shim or thickening in an edge region.

10. A metal gasket which has at least one aperture and a corrugation around a said aperture, which corrugation, in cross-section, consists of an arcuate central region of relatively large radius of curvature, joined to the remainder of the gasket by way of shoulder regions of sijbstantially smaller radius of curvature.

11. n gasket as claimed in any preceding claim further including at least one intermediate pLate between outer corrugated metal sheets.

12. A gasket as claimed in any precediny claim, hauing an elastomer coating at least on the peak or peaks of the corrugation or corrugations.

13. fi method of making a gasket, comprising prouiding at least two metal sheets prouided with at least one aperture and corrugated around at least one said aperture, providing a layer of adhesive between said sheets, and placing said sheets together whereby said adhesive bonds said sheets to form said gasket.

14. The method claimed in claim 13 in which the adhesive is provided in the form of a sheet which extends across the corrugation or corrugations.

1S. The method claimed in claim 14 in which the adhesive is provided in the form of an adhesive layer on a backing sheet, the backed adhesive layer is applied to one of the metal sheets composing the gasket, the backing sheet is removed, and thereafter a further sheet composing the gasket is applied to the thus exposed adhesive .

16. n method of making a metal gasket, substantially as herein described with reference to Figs. 1 to 6 or Figs.

7 to 9 of the accompanying drawings.

17. fi gasket substantially as herein described with reference to Figs. 1 to 6 or Figs. 7 to 9 of the accompanying drawings.