CA2006347A1

CA2006347A1 - Cylinder head gasket

Info

Publication number: CA2006347A1
Application number: CA 2006347
Authority: CA
Inventors: Terence P. Nicholson
Original assignee: Individual
Current assignee: Individual
Priority date: 1988-12-23
Filing date: 1989-12-22
Publication date: 1990-06-23
Also published as: WO1990007663A1; GB2226371A; GB8929067D0

Abstract

ABSTRACT

CYLINDER HEAD GASKET

A metal gasket comprises perforated metal sheets 11, 13, corrugated around at least 1 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.
Figs. 1, 3, 5.

Description

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CYLJNnER HE~n ~SKET
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- This in~e.ntion relates to the opsrdtional qua~ityJperformance of meta~]ic seals and in particu]ar to me.tallic cylinder head gaskets for sealing between the cy]inder heads and cylinder bJocks of internal combustion engines :, '' ` ~
Metal gaskets ha~e 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 - ttie cy]inders, oil passages, water passages etc , and around each of these apertures the metal gasket has a .:
corrugated cross-section, When the gasket is c~amped between the cylinder head and cylinder block, the peaks ~ of the corrugations contact the cylinder head and t.)~ock surfaces under pressure and the corrugations, during tt~js compression, deform and flow into the mating faces --and establish a Inetal to Inet~l seal Numerous forms of corrugation profj~e ha~e been used, for example arcuate, broad in I-lidth and flat topped, and M-shaped (my patent British 1583322) with the corrugation peaks projecting on one face only, , , ` , . , : ,, ,.'. ,' . ,., , ` : . ' .
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~G~47 ` , , 7 : Known metal gaskets have been.'v~ry successful, but in - some circumstances have been found to be unab]e to .
. provide satisfactory sealing With certain layouts of :. the cy~inder and other apertures and of the c1ampjng ~ bolts, there may be insufficient clampinq load to make .~ the corrugations flow into the opposed mating faces of the cylinder head an~ cylinder block to establish a satisfactory seal simu]taneously at a]l of the apertures, It has been found that with certa.in cy~inder 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 ~ !
J fact that there are 2 points of contact of the base of ,- the corrugation means that load in this area is ilmnediately 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 haue adequate distribution of the clamping load sealing problems can still arise because of distortion and poor quality machining of mating components ;
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G34~7 : ~n object of the present inve~tton is to provide a gaske.t which overcomes the prob]ems outlined above : , ~ccording to one aspect of the invention, a gasket - com~rise.s a pair of metal sheets each provided with at : least one. aperture and with a corrugation extendinq around the ape.rture, the corrugations on the two sheets . being ~nirror images of one another . ~ccording to another aspect of the invention, a meta] ~-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 ,: :
~ccording to a further aspect of the inuention, a metal gasket has at least one aperture and a corrugation . around a s~id 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 shou]der regions of substantially ~Inal.ler radius of curvature Preferably these shou]der regions meet the remainder of the gasket sub~t.antially at right angles, and there is a short . :

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, .. 4 pe.rpendicular wall region extend~ng from the surface of ~ the gasket to meet the first radiu~d portion of the .~ corrugat.ion - ~ccording to yet another aspect of the in~ention, a gasket comprise.s at least two me.tal sheets each provided with at least one aperture and at lea~t one sheet being corrugate.d around a said ape.rture, the sheets being : ~onded together by an intervening ]ayer of adt)esive.

, . The gasket Inay further comprise a centre p~ate between the outer metal sheets, ~ikewise bonded by a layer of adhesive, and/or a fire ring around cylinder apertures, which may ]ikewise be bonded by an adhesiue : .
.. Preferably, an elastomer i5 prouided 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 shjm or other thickening in an edge region, This can reduce or eliminate bowing of the cylinder head when clamped owing to canti]ever action of the corrugations at the apertures, leading to the advantage that the clamping pressure is more even~y distributed and in particular an adequate clalnping pressure is app~ied to the corrugations and to the periphery of the cylinder aperture ,, ' , ' ~
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s . , ' In a preferred embodiment of the inuention, the respecti~e aspects of the in~ention set out abo~e are pro~ided in combination in a gasket, ' . ~ ' , ' cylinder head gasket according to a preferred embodiment of the in~ention tllill be described l-lith reference to the accompanying drawings, in which:

,'' Fig. 1 is a plan ~iew of the gasket.

; Fig, 2 i5 a p~an ~iew of a shim used in the gasket of ;; Fig. 1, ', Fig, 3 is a cross-section on the ljne ~-~ 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-sectjon on the line C-C in Fig, 1 showing an edge shim, ---.
'~ Fig, 6 is a cross-section of a corrugation pro~ided around a secondary aperture of the gasket, ~ .

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Fig, 7 is a cross-section of the completed gasket in the region of a secondary aperture, - Fig, 8 is a ~Jiew corresponding to Fig, 7, after compression of the gaske.t between a cylinder head and cylinde.r block, "
Fig, 9 is a plan view of a sing~e cylinder gasket, Fig, 10 is a cross-section on the line 8-8 in Fig, 9, - Fig, 11 is a cross-secti.on 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 automobi~e engine of 998 cc capacity, The dilnensions yi~en herein and marked in Fig, 6, in inches, relate to this particular engine, The gasket has four ouoid apertures 1 corresponding to the cylinders, and a number of secondary apertures corresponding to oil and water passages and bolt holes.
~pertures ~ are for high pressure oil, Bl for oil drainage, ~1, n, F, G for water, ~ and R are bolt holes, .' ' ., , ~ ', ..
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., ,, "' ' ', : It was found i!npossible to sea~ this engine usin~
conventional metal gaskets The non-uniform widely spaced plAcing of the clamping bolts relative to the ~ cylinders and secondary apertures made it impossible to prouide adequate clamping pressure around all of the apertures.
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The present gasket comprises a pair of metal sheets 11, 13 bonded togethe.r, for example by an interuening layer of adhesiue 15.

- Typically, each sheet tlas a thickness of 0.010 inches- - (0.2S nlln). This thickness has been found suitable to prouide good.sealing without leading to unacceptab]e bowing of the cylinder head when clamped on the gasket.
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~round each of the secondary apertures, each sheet is prouided with a single corrugation 17 hauing a flattened . arcuate profile as shown in Figs 6 and 7, projecting . , from the sheet by 0 025 inches (0 635 mm) The - .-respectiue corrugations on the two sheets are mirror images, so that when the plates are placed toqether back to back, the secondary apertures are surrounded by corrugations projecting symmetrically from both upper . . ., , ~ , ., ~ ~ , , . . , .
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~ ;3~7 ': ' 8 and lower surface,s of the gask-et, The corrugations are : formed conventional]y by embossing the individua3 metal - sheets before these are assembled together, ,::
The illustrated corrugation has ~e,en so designed that it : requires minimal ~oad 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-sectiona] profi3e of the corrugation comprises a shallow ar~ of relatively large radius e,g 0,026 , inches internal (0,660mm), joined to the main f]at 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 p3ate at right angles, and preferably there i5 a short perpendicular wall region extending between the main flat body of the plate and the beginning of the , radiused corners, The provision of these har~er corners -' provides ~ocally increased strength so that when the corrugation is compressed a rolling effect occurs, .~

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Be.cause 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 on]y by f,owi.ng into the base of the. corrugation, as can be seen in Fig 8 With a conventional corrugation profile, there is a te.ndency for the base region of the corrugation and adjacent parts of the yasket plate. to spread outwards and~or buckle The ro]ling effect achieved by the illustrated corrugation results in an e.xtremely small residual aperture within the compressed corrugat.ion as shown in Fig, 8, The corrugations, when fu~y compressed, retain energy providing a restoring or sealing force, such that if the clalnping force where released the height of the corrugation would increase by, for example, 0,001 to 0,002 inches (0 025 to 0 051n~n) '-' The adhesive lS is applied in such a way that jt 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 , , ' ," . ~: , ~ ' , ' ' ' . .

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, compressed, It has been found, that the two gasket plates become so firmly bonded together that air is trapped in the gap betwee.n the corrugations and prouides a cushioning effect when the corrugations are compressed This cushioning effect is additiona~ to the restoring force trapped in the compressed corrugations, and is believed to enhance the ability of the gasket to provide adequate sealing at a~l of the apertures provide~ with corrugations even if the clamping lnad is not uniformly distributed.

~round the cylinder apertures 1, the gasket is not provided with corrugations. Instead, the individual metal she.ets.1l, 13 are spaced apart and have between them metal shims 21 corresponding in shape and size to the cylinder apertures ~round the cy~inder apertures, the metal sheets 11, 13 are provided with em~ossed steps 19 to prouide the spacing between the sheets to accommodate the shims. The shims are for examp~e 0.017 inches thick (0.305 mm).
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.:Jn the i]]ustrated 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.

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., The o~erall thickness of the gasket adjacent the cylinder apertures is 0.032 inches (0.813 mm). The thickness o~er the corrugations at the secondary apertures is 0.072 inches (1.83 mm). The gasket is designed to pro~ide a thickness when compressed of approximately 0.028-0.032 inches (0.71 - 0.81 mm). If greater o~erall thickness is required, a compression plate may be pro~ided between the sheets formlng the gaskets. ~ compression plate is a flat metal plate, of the thickness required to pro~ide 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 pro~ided, so that there is a respecti~e shim on each surface of the compression plate between the plate and the associated corrugated gasket sheet.

The adhesi~e typically has an initial thickness of 0.002 inches (0.05mm), decreasing to 0.001 inches (0.05mm) --.
when the gasket is compressed. The adhesiue 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 o~er the gasket, pro~iding some restoring .-force, and permitting the gasket to flex without cracking the adhesi~e.

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l'o pro~Ji~Je enhanced sealing at. the ~orrugations t.he crests of these are ~referab'ly ~rouided wlth coatirlgs of an elast.omer ~3 ~'or e:~ample a suitable silicone elastomer lrhese coatings can t-e a~li)1ied hy screer printing t'or e~ample.

l'he elast-omer coating is so ~laced that wherl the corrugations are compresse-J the elastomer coating not or~'ly co~ers the com~ressed ~eaks of' the corrugatiorls t~ut also has a wedge et'fect on both the inner and outer edges of th0 flattened corruyatiorls. Xrl comt)ressior~ a corrugation is ~Jery rarely it' e-Jer cornpletely flattened:
there is usually a differerlce of O.OO] to O.OO~ i:nches (0 0~5 to 0.05 mm).

Because of the ~reser~ce of the c~linder t~ore shims ~1 an~J the edge shims ~ (it' pro~ided) which limit l:he nip whi.ch car~ t~e a~lied to the gasket there wi11 t-e a ga~
of 0.003 - O.OO~ inches (0 075 to O.l mm) bet~Jeen each ~ace ol the gasket arld the Qp~osing face of the cylirlder hea~ or cylinder bloc~. -.
Where the hard corltact of' the corrugation firlishes a small we~ige o~' elastomer occurs to ~ill l:his gap ~Jhich ta~ers from O.OOl" (O.O~ mm) to 0.004" (O.O~O mm) ir this uery localised area. I'his wedge et'1ect t'lJrther corltrit)utes to successfuJ sealing at all of the ~' corrugations .
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~he gasket descri~ed ensures that a sufficierlt1y hiyh unit loading can be e:~erted arounrJ all o~' the apertures to erlsure sat~sfactory sealing wlth the elastomer -~
pro-Jiding pert'ect sealing arounl~ the secondary a~i-ertures wlthout de~)ri~ing the rims of the cy1inder apert.ures ot' the necessary share ot' the clamping loall -required to erlsure sea1irl9 of the hiyh ~-ressure cylirlder . , "~, . . ,., ', :"' ~-" ' "', ` ."

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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 o~er the shims to seal the cylinder bores. Only a limited clamping load remains a~ailable for compressing the corrugations. The corrugations are designed with a profile which is relati~ely weak and makes the best use of the a~ailable clamping load, but the elastomer layers are highly desirable to ensure complete sealing around all of the secondary apertures pro~ided with corrugations.
'' In the illustrated gasket, the o~erall thickness o~er the corrugations when compressed is typically 0.0~8 - inches (0.71mm) and the thickness o~er the shims is appreciably greater.
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It is important to ensure that, when the cylinder head is clamped o~er the gasket, the head is not subjected to bowing due to forces applied in cantile~er fashion.
. This can impair the euenness of the pressure ; distribution on the gasket, reducing sealing efficiency, . and in particular, bowing can reduce the pressure ouer the cylinder shims.
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: , , The de.scribed thicknesses of gasket plates and shims and corrugation heights ha~e been selected to reduce these disaduantageous effects .
~s a further measure, additional shims may be fitted at the outer edges of the gasket, to incrsase the ouerall thickness in the edge regions and thereby reduce the cantile.uer effect arising when the cylinder head and gasket are clamped These edge shims support the.sides of the cylinder head, in particular the longitudinal ~ sides, and thereby ensure that the centre ~ine of the cylinder head is not deprived of a proper share of the clamping load .
Jn the il]ustrated 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 meta] as the gaskets The cylinder shims 21 may be plain, i e flat, Howe~er, to reduce the effect of ~ariations of the c~amping load, particularly around the cylinder bores, due to manufacturing ~ariations jn the cy~inder head and/or -~
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;34~7 t5 block, these shims may haue a fine corrugation embossed in the.m, as shown in cross~section in Figure 4, In the case of a doub]e shim as i~lustrated 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 Fiqure. 1 These features prouide improved sçaling performance and in particular, reduce or eliminate loss of sealing performance due to bowing of the cylinder head and manufacturinq uariations in the cylinder he.ad and cylinder block, ~ method of making the illustrated gasket wjll no~l be describsd /

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 respectiue smbosse.d gasket sheets are mirror images of one another.

One sheet is placed on a location jig with the psaks of its corrugations projecting downwards ~ layer of ,, ' ,.,"
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i3~7 - , adhesive, preferably a contact adhesive, for example 3M
Scotch No, 467, is applied to the gasket, rhe adhesiue may for example be applied by-dipping, spraying, or roller coating but these processes make it difficult to apply a tota]ly 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' conuenient way of applying the adhesiue is to provide the adhesjve on a paper backing, the backing being cut to a shape corresponding to the gasket, and applying the ~ -backed adhesi~e to the gasket sheet on the jig, The adhesi~e adh~res to the Inetal gasket sheet, and the paper backing can then be removed from the adhesiue, The adhesive extends across the corrugations, The adhesive is cut so that it terminates at the outer edges of the shims, ~dhesiue is not provided between the shims and the gasket sheets, except that a sma]l 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 adhesive provides excellant results and is ~ery simple to use, and is superior to application by roller coating or other methods, ., , ,, .. , , , ., ~
, . , ,. " ~, , , ", , i347 Next, the shims 2t 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 adhesi~e layer, and pressure is applied to the upper gaske.t p~ate so that the upper and lower gasket p~ates, with the inter~ening shims, are securely bonded togethe.r by the adhesiue.

The assembly operation shou~d 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 assemb~y, and if the assembly process is performed manually, the operator should wear cotton or rubber glo~es to pre~ent contamination These measures not only enhance the quality of the gasket and faci~itate the operation of joining the sheets and shims, but also ensure that the surfaces of the peaks of --ttle 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 e~astomer is nOw Corning 96-083 ., .

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It will be understocd that if a compression plate is provided to increase the overall thickness of the gasket, the assembly process wi]] include the furt~ler steps of placing the compression plate ove.r the shims, p]acing 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 . .

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. , . , . , -, . .,: ,' , ' :, , t9 general~y 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 providsd around the outside. edge of the gasket for support, to re.duce the cantilever effect, The support corrugation on the outside edge greatly reduces the bending mome.nt due to the corrugation being inside the bolt circle, This probtem is further exacerbated during the pressure part of the engine's cyc~e, i,.e, combustion, The gasket shown in Figs, 7 to 9 has six bo]t holes 25 equally spaced on a pitch circle around a central cylinder aperture and p]aced 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 cy]inder 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 p]ates (e,g, cylinder heads, inspection and maintenance covers for pumps, etc,) can be. very thin, ;3~

and c~amping bolts may be wide-ly spaced ~s a result, the couer plates may f~ex to an extreme extent, leading to substantial uariations in the. spacing under the cover plate. To accommodate this, it may be found advantageous to prouide corrugations of which the heights uary ouer the area of the gasket, to match the amount of distortion of defle.ction of the couer between the c]amping bolts, Hitherto, mu~ti-layer gaskets haue been made by welding or eyeletting the indiuidual plates composing the gasket With such constructions it has been extreme]y difficult to auoid leakage between the ptates, The use of an adt!esi~e~for bonding gasket p~ates as described herein can completely ouercome this problem and reuolutionize the performance of multi-layer gaskets, inclu~ing multi-layer gaskets of otherwise conuentional form, for example gaskets of the types described in my 8ritish pate.nts numbers 1583322, 2063386, aO4880, 2l03308, 2097870, 2097871, 2097872, and U~ patent ,, ~ .. .. . . .

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Claims

1. A 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 together by an intervening layer of adhesive.

2. A 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 secured to form the gasket by an intervening layer of an adhesive.

3. A gasket which 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 mirror images of one another.

4. A 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. A gasket as claimed in Claim 2 or 4 in which the shim is corrugatedd

6. A 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.

7. 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 A 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. A 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 substantially smaller radius of curvature.

11. A 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 preceding claim, having an elastomer coating at least on the peak or peaks of the corrugation or corrugations.

13. A method of making a gasket, comprising providing at least two metal sheets provided 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.

15. 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.