GB2108217A - Flat gasket - Google Patents

Abstract

A flat gasket 22 has one or more openings around which extends a sealed cavity 26 defined by a metal wall. The cavity 26 is filled with either a fluid or a plastically deformable material 32. As shown, the cavity wall is formed by a folded over part of the gasket material. In an alternative embodiment the wall may be a separate metal strip having a U-shaped cross section which engages and is secured to the upper and lower surfaces of the gasket. The metal sheet comprising the gasket body may be provided with a coating of laquer or plastic material or each side of the gasket body may be provided with conventional "soft boards" of for asbestos fibres impregnated with a binder. <IMAGE>

Description

SPECIFICATION Flat gasket This invention relates to a flat gasket having a gasket board comprising at least one opening, and an annular channel provided in the vicinity of the edge of the opening and having a metal channel wall, and a filling which is pliable under compression of the channel; the invention relates more particularly to a cylinder head gasket of this kind.

Primarily because of the modern lightweight construction of lifting piston engines, it is becoming more and more difficult to provide a reliable and durable seal between engine parts, particularly the cylinder head and the engine bed. On the one hand, the lightweight construction means that, for example, a cylinder head gasket can no longer be clamped with a relatively high pressure per unit of sealing surface over a large expanse of sealing surface and, on the other hand, the thermal and dynamic deformation to which a cylinder head gasket is exposed during operation is increasing more and more. The modern engine designs thus results in considerable spatical differences in the pressure per unit of sealing surface, particularly in the region of the combustion chamber.

Therefore, flat gaskets of the kind described hereinbefore have already been provided, wherein the gasket board, formed by a conventional sheet of asbestos, for example, is fitted adjacent the edge of each opening, with a sheet metal ring of U-shaped cross-section in such a way that an annular channel is formed between said ring and the edge the gasket board, in which a rubber ring of circular or oval cross-section is placed (see for example DE-OS 26 04 253 and US-PS 3 595 589). This known cylinder head gasket behaves in the same way as another flat gasket (DE-AS 1 974 988), wherein the rubber ring is replaced by a helical spring ring.

When used in cases where the pressure per unit of sealing surface is spatially not even substantially constant, all the known flat gaskets of the kind described herein before have the disadvantage that the gasket element formed by the above-mentioned channel can provide no or only very little compensation for varying pressures along the circumference of the edge of the opening, with the result that these known flat gaskets cannot be guaranteed to provide a reliable, durable seal, particularly in the region of a cylinder head gasket adjacent to the combustion chamber, especially in lifting piston engines, which are increasingly extremely light-weight in construction. A further disadvantage ofthe known flat gaskets is the fact that, when deformed by the clamping forces, they have only a limited resilience with correspondingly small eleastic forces.

The aim of the invention is therefore to provide a flat gasket of the kind described hereinbefore, more particularly a cylinder head gasket, which will form a durable and reliable seal even if sealing surface pressures occur which vary considerably along the circumference of the edge of the opening of the flat gasket, as in the case particularly in the combustion chamber region of cylinder head gaskets in modern lifting piston engines.

According to the invention there is provided a flat gasket having at least one opening therein around which is provided a sealed cavity defined by a metal wall, the cavity being at least partially filled by a material which is either fluid or plastically deformable at least before the gasket is used.

The plastically deformable material for the filling is not necessarily a plastic material in the narrower sense but may for example be a powder. A filling of this kind is capable of adapting to surfaces to be sealed off relative to each other even where the sealing surface pressures vary considerably across the surfaces, since, when the flat gasket in accordance to the invention is installed, elements of volume of the filling can be displaced within the sealed cavity and in this way differing pressures along the edge of a gasket opening can be balanced out. Since the cavity has metal walls and is completely sealed, the volume of the cavity remains at least substantially constant, even under deformation caused by compressive stress.As a result, not only are the peak values of the sealing surface pressure broken down, but in areas of the components to be sealed off from one another which are more prone to deformation as a result of their construction, higher sealing surface pressures are built up than is the case with a conventional flat gasket.

Whereas powder used as the filling material, for example, is largely compressible, substantially incompressible liquid or plastic materials are preferred for the filling of the cavity. In this case, the desired compressibility may be achieved by including a suitable gas content in the filling.

The above remarks shows that practically any desired deformation characteristics can be obtained in the vicinity of the edge of the opening with a flat gasket according to the invention.

For machines which function at operating temperatures above ambient temperature, more particularly for internal combustion engines, it is preferable to use, as the liquid or plastic material for the filling, a material which changes into an elastomeric material at the operating temperature of the flat gasket.

When a flat gasket of this kind is used, the condition of the gasket is fixed the first time the engine is run, in that the first heating causes the material of the filling to vulcanise or polymerise or solidify by some other type of reaction; at the same time, the deformation characteristics of the gasket in the region of the edge of the opening change from being originally predominantly plastic deformation characteristics to predominantly elastic characteristics. Thus, a flat gasket of this kind is otimally suited both to assembly and also to providing a durable seal in operation.

By suitably selecting the material used for the filling and the nature and quantity of any fillers used, etc, it is possible to obtain the desired long-term characteristics of the flat gasket according to the invention (setting properties, behaviour under the effect of tempera- ture and the like). The metal cavity wall also has a favourable effect, since it proides a measure of protection from the effects of peak temperatures occuring for short periods, as bursts of heat of this kind are conducted away through the metal without being able to have their full effect an the filling of the cavity.

Finally, the deformation characteristics of the gasket element formed by the cavity may be influenced by the choice of a suitable quality and thickness of sheet metal.

Most simply, the cavity is formed by a piece of sheet metal bent back on itself and sealed by an inherently closed annular weld seam or soldered seam. To prevent undesirable buckling of the sheet metal during the welding or soldering, it is advisable to use a method of manufacture wherein the welding or soldering is begun simultaneously at a plurality of points arranged at uniform spacings from one another along the cavity and the cavity is progressively closed off completely, starting from these points, in the same direction.

The invention also provides an opportunity of getting away from the so-called soft boards which have hitherto generally been used for gasket boards; these known soft boards are usually sheets of asbestos fibres impregnated with a binder. In fact, according to the invention, a flat gasket may be constructed so that the gasket board is in the form of a single-or multi-layer metal sheet and this sheet is provided with cavities as sealing elements according to the invention at every point where a special linear seal is required. Thus, in the case of a cylinder head gasket, all the openings in the gasket board in the vicinity of the edge of the opening would be provided with a cavity according to the invention, whilst these cavities could be formed by the sheet metal of the gasket board.

Certain preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, wherein: Figure 1 shows a cylinder head gasket, viewed from above; Figures 2 to 5 show sections on the line 2-2 in Fig. 1 illustrating various embodiments of cylinder head gasket, in accordance with the invention; and Figure 6 is a perspective view of an area of a cylinder head gasket comprising an opening illustrating a method of production in accordance with invention.

The cylinder head gasket 10 shown in Fig.

ihai a gasket board 1 2 with combustion chamber passages 14, cooling water passages 1 6, oil passages 18 and screw holes 20. As can be seen from Fig. 2, in this embodiment the gasket board 1 2 consists of a metal sheet 22, optionally coated with a lacquer or with a layer of plastics, and this metal sheet 22 has been bent back on itself in the region of the edge of the appropriate opening, to form an annular channel 24 with a cavity 26 which is completely closed off, as illustrated with refer- ence to the left-hand opening 14 for the combustion chamber. An annular edge strip 28 is thus formed which abuts on the actual gasket board 1 2 and may be joined thereto to form a hermetic seal by electric roll welding, for example.A welding roll shown by dotted lines in Fig. 2 has the reference numeral 30.

As shown in Fig. 2, the cavity 26 is completely filled with a filling 32. This filling may be a filled fluorine elastomer or a filled silicone elastomer which is introduced into the cavity 26 in the unvulcanised state and is of a material nature such that, after being n- stalled, it vulcanises the first time the engine is operated, as a result of being heated to the Operating temperature of the engine, and thus changes over from being in a predominantly plastic state to being in a predominantly elas turmeric state.

Instead of being welded, however, the cavity 26 could also be sealed off by soldering or adhesive bonding.

Figure 3 shows an alternative embodiment which is approximately symmetrical in con struction relative to the plane of the metal sheet 22' which forms the gasket board 1 2.

As the embodiments shown in Figs. 2 and 3 correspond to each other in every other respect, the same reference numerals have been used as in Fig. 2, but with the addition of an apostrophe.

Whereas the gasket board 1 2 in the em embodiments illustrated in Figs 2 and 3 is constructed as a simple sheet metal plate, the embodiment according to Fig. 4 has a more conventional construction. In other words, a support sheet 22" is provided here in the usual way which, like the metal sheet 22' in the embodiment according to Fig. 3, forms a channel 24", but is coated on both sides with the conventional soft boards 50". However, .-jn the embodiment according to Fig. 4, the cavity 2G'' is only largely, but not completely, filled with a material 32" which is liquid or plastic in the assembled position of the gasket, and futhermore the cavity 26" also contains a gas 33" which ensures that the channel 24" has a measure of compressibil ity.

Figure 5 shows an embodiment similar to those in Figs 2 and 3. Again, only an optionally thinly coated metal sheet 22a is provided, the edge of which is fitted, in the region of an opening such as a combustion chamber opening, with a sheet metal strip 24b of approximately U-shaped section, which forms an annular cavity 24a filled with a filling 32a Its arms engage over the metal sheet 22a and are connected to the sheet by weld seams 30a. This results in functional advantages and, in addition, a lower quality material may be used for the metal sheet 22a, if desired, so that the high quality material i.e. the metal strip 24b, is restricted to the region of the combustion chamber opening, Figure 6 is intended to show the preferred method of production of the cavity 26 in the embodiment Fig. 2. The sealing of the cavity 26 by welding or soldering is, in fact, begun at a plurality of points I, II and Ill arranged at uniform spacings from one another, the welding or soldering tools being advanced in the direction of the arrows. The weld.seam is indicated by dotted lines and designated 52.

Appropriately, the sheet metal used is standard commercially available sheet steel, preferably 0.1 to 0.4 mm thick, or high-alloyed steels.

Claims (11)

1. A flat gasket having at least one opening therein around which is provided a sealed cavity defined by a metal wall, the cavity being at least partially filled by a material which is either fluid or plastically deformable at least before the gasket is used.

2. A gasket as claimed in claim 1, wherein the fluid or plastically deformable material is substantially incompressible.

3. A flat gasket as claimed in claim 2, wherein the cavity filling additionally includes a quantity of gas which provides a given compressibility to the channel.

4. A flat gasket as claimed in any of claims 1 to 3 for apparatus which operates at above ambient temperature, wherein the nature of the fluid or plastically deformable material is such that in use it changes into an elastomeric material at the temperature of operation of the flat gasket.

5. A flat gasket as claimed in any of claims 1 to 4, wherein the cavity filling material is a heat carrying oil, a synthetic material, or an unvulcanised fluorine or silicone elastomer.

6. A flat gasket as claimed in any of claims 1 to 5, wherein the cavity is defined by a piece of sheet metal bent back on itself and is sealed off by a closed annular weld seam or soldered seam.

7. A flat gasket as claimed in any of the preceding claims, wherein the cavity is defined by a single-or multi-layer support sheet of the flat gasket.

8. A fiat gasket as claimed in any of claims 1 to 5, wherein the cavity is defined by an approximately U-shaped sheet metal strip, the arms of which engage over a sheet metal plate of the flat gasket and are connected thereto by annular weld seams or soldered seams.

9. A flat gasket as claimed in any of the preceding claims wherein the gasket is constructed as a single-or multi-layer sheet metal plate.

10. A process for the production of a flat gasket as claimed in any of claims 6 to 8 wherein the welding or soldering is begun simultaneously at several points arranged at uniform intervals from one another around the channel, and the cavity is progressively closed off, by advancing the welding or soldering from these points in the same direction.

11. A flat gasket substantially as herein described with reference to any of the accompanying drawings.