GB2182729A

GB2182729A - Plain bearing construction

Info

Publication number: GB2182729A
Application number: GB08626689A
Authority: GB
Inventors: Daniel Paro; Carl-Erik Rosgren; Tapani Haikola
Original assignee: Wartsila Oy AB
Current assignee: Wartsila Oy AB
Priority date: 1985-11-08
Filing date: 1986-11-07
Publication date: 1987-05-20
Anticipated expiration: 2006-11-07
Also published as: GB8626689D0; FI854404A0; GB2182729B; DE3637983A1; FI854404A; FI74786B; JPS62113913A; FI74786C

Abstract

A main or big end bearing of an internal combustion engine, for example a large Diesel engine, comprises a supporting member (2) and an overlay (4). The overlay consists of two or more different metals or alloys (A and B) having different properties of hardness and melting point or having different crystal structures, said metals or alloys being arranged alternately one upon the other so that the overlay (4) is formed by at least three distinct material layers. A diffusion barrier layer (3) of nickel may extend on the supporting member (2). Material A may be tin-antimony; material B aluminium-tin. A sliding layer (5) is preferably of lead- or tin-based alloy. <IMAGE>

Description

SPECIFICATION Plain bearing construction This invention relates to a multi-layer plain bearing for an internal combustion engine (for example a large Diesel engine) which comprises a supporting member and an overlay destined to form the bearing surface of the bearing.

Very large mechanical stresses are placed on the main and big end bearings of a large internal combustion engine, especially a large Diesel engine, since very high maximum pressures occur in the cylinders. These main bearings of modern engines are mostly plain bearings having a stratified construction. By this means, attempts are made to utilize the good sliding properties of some bearing metals and simultaneously to avoid their mechanically weak properties by arranging them as relatively thin surface layers. In a so-called threecomponent bearing there is arranged, upon the bearing's supporting shell of steel, a bearing metal intermediate layer that is about 1 mm thick and which has good strength properties and a good capacity for conducting heat, either a lead bronze or a light metal. This intermediate layer is also called the "lining".

On the lining there is provided a thin sliding layer or overlay of white metal, the galvanically applied thickness of which is between 0.02 and 0.06 mm in the heaviest loaded bearings. Between these three material layers, there may in addition be arranged thin diffusion barriers or layers of tie metals. The endurance limit and heat conducting capacity of this kind of bearing is good, but it does not possess wide possibilities to accommodate small installation faults or to accommodate dirt particles into the bearing metal. Moreover, the adaption of the bearing to a journal can easily destroy the thin overlay.

In plain bearings according to known technology, the uppermost sliding layer consists of one layer of an alloy or some artificial material. The galvanically applied overlay has hereby to be very thin especially due to strength reasons. This causes drawbacks of many kinds, among which may be especially mentioned the susceptibility to wear damage.

When the clearance between the journal and the plain bearing is small, there is a very small margin when the bearing gets warm, which may cause seizing of the bearing. Such a situation may occur when disturbances arise in the lubrication of the bearing, for example, so that dirt particles break the oil membrane of the bearing. As the overlay consists of a softer material having a lower melting point than the lining, a bigger thickness of the overlay should thus be favourable when the bearing gets warm, in view of a potential seizing situation. On the other hand, a thicker overlay is not possible to produce according to the known technology, because the capacity of the bearing surface to carry the required pressure is decisively weakened.

The present invention seeks to create a reliable stratified plain bearing for a combustion engine, which possesses a better adaption, accommodation and dirt absorbing capability than before, without significant reduction in the strength properties of the bearing. The invention also seeks to create a plain bearing, which permits the use of thicker overlays than can at present be used in a bearing, especially by adding a material component to the sliding layer which has a low melting point and low hardness.

What constitutes the invention is set out in the following claim 1.

A preferred basic structure for a bearing according to the invention is a three-component plain bearing, in which the overlay of the bearing consists of three or more metal or alloy layers. By using a plurilayer overlay the total thickness of the overlay may be increased without reducing the capability of the bearing to carry surface pressure. At the same time a better adaption and descending capability of the sliding surface is achieved, so that the reliability of the bearing is considerably improved. In a favourable embodiment, two metals or alloys are used for alternate layers which have different hardnesses and melting points, so that these material layers are arranged alternately one upon the other to form the overlay of the bearing.In this arrangement, the harder material layers provide, by means of their high yield point, the desired surface pressure carrying property to the overlay, while on the other hand the softer material layers give desirable thickness to the sliding layer.

The different material layers of the overlay may consist of metals or alloys with equal hardnesses, if the combined effect based on different crystal structures of the different material layers synergistically produces higher strength. All the different material layers of the overlay do not necessarily have to be fully covering, but one or more netlike or latticelike layers can be used in a multilayer overlay.

The sliding layer is desirably produced using a physical gas-phase coating method. Such known methods, which do not per se fall within the scope of the invention include sputtering coating methods and ionized coating methods. The desired structure of the sliding layer can thus be achieved by vaporizing alternately different metals or alloys. In producing the sliding layer there may also be used other coating methods, for example chemical gasphase reaction methods or metal spraying. By means of these methods it is, however, more difficult to achieve the properties of a sliding layer according to the invention. In metal spraying, for example, the thicknesses of the different material layers are often too great and a further drawback can be that this deposition method leaves a spongy surface.

In heavily loaded engines, the total thickness of the overlay may be at least 0.03 mm, or preferably at least 0.05 mm, i.e. the thickness of the sliding layer may in comparison with known methods be at least three times as thick without compromising the strength requirement of the bearing. When applying the structure of this invention to a plain bearing in a small engine, the overlay may have a thickness as small as 0.012 mm. The overlay should comprise at least three different layers, for example so that the overlay consists of two layers of a soft material with one layer of a harder material sandwiched between them.

By means of vaporisation and sputtering it is possible to form extremely thin material layers. Thus it is possible to produce the overlay of a very large number of layers, for example ten to twenty alternating layers of two different materials. Instead of two different overlay materials it may be favourable to use three or more different materials in the overlay. Thus, it is possible to ensure that when the uppermost layer is worn off, it is not the hardest material that then forms the sliding surface.

The invention will now be more fully described, by way of example, with reference to the accompanying drawings, in which Figure 1 shows a partly sectional view of one embodiment of bearing according to the invention; and Figure 2 shows a section on the line ll-ll of Fig. 1.

In Fig. 1 reference 1 indicates a steel support shell of a bearing. Upon this shell, an intermediate layer or lining 2 is arranged consisting of a lead-bronze alloy or the like, white metal or bronze, which has high load strength and a good thermal conductivity. Between the intermediate layer 2 and a bearing overlay 4, a diffusion barrier layer 3 is arranged which consists, for example, of nickel.

The overlay 4, with which the invention is primarily concerned, is of multi-layer construction and consists of two different metals or alloy layers A and B. The material layers A consist of a metal or metals having a good sliding property, a low hardness and a low melting point, for example tin-antimony, whereas the material layers B consist of a metal or metals possessing higher hardness and strength, for example aluminium-tin. By arranging the material layers A and B alternately upon each other, the total thickness of the overlay 4 may be increased, and the amount of the softer material A may be considerably incresed without any undesirable reduction in the strength properties of the bearing.According to the preferred embodiment of bearing shown in the drawings, the soft material layers A are made thicker than the harder layers B, and further the soft material A forms the uppermost sliding surface of the overlay 4.

The thickness of the overlay 4 can be as little as 0.012 mm in the case of a small engine rising to at least 0.03 mm or at least 0.05 mm in the case of heavily loaded large Diesel engines.

The different layers of the overlay 4 are suitably produced by means of a known vapour-phase coating method, according to which the multilayer effect is achieved for example by alternately changing the material forming the source of the vapour used for the coating. By this means it is also possible to change the content of a particular metal in an alloy within any given layer.

A sliding layer 5, which preferably consists of a lead- or tin-based alloy, forms an outermost thin corrosion protection layer. This protection layer also acts as a running-in layer for the bearing. The protection layer is worn away from the sliding surface in a relatively short operating time and is often referred to as "flash".

It is not essential that each layer, A, B wholly covers the underlying layer since at least one layer can be formed as a netlike or lattice-like layer.

The invention is not limited to the described embodiment, since several modifications are feasible within the scope of the following claims. The number of material layers, and the internal thicknesses of the material layers making up the overlay 4 may alter, and within the scope of the invention it is also possible to use more than two or three different metals or alloys to form the plurilayer overlay.

Claims

1. A main or big end plain bearing of an internal combustion engine, which bearing comprises a supporting member and an overlay destined to form the bearing surface, wherein the overlay consists of two or more different metals or alloys having different properties of hardness and melting point or having different crystal structures, which layers are arranged alternately one upon the other so that the overlay is formed by at least three distinct material layers.

2. A plain bearing according to claim 1, in which the overlay is coated with a flash layer destined to wear away early in the life of the bearing and serve as a running-in layer.

3. A plain bearing according to claim 2, in which the flash layer is a lead- or tin-based alloy.

4. A plain bearing according to any one of the preceding claims, in which the material layers of the overlay are produced by means of sputtering, vaporization or some corresponding physical gas-phase coating method.

5. A plain bearing according to any one of the preceding claims, in which one of the material layers of the overlay is not wholly cover ing the underlying layer but is formed as a netlike or lattice-like layer.

6. A plain bearing according to any one of the preceding claims, in which the total thickness of said overlay is at least 0.03 mm.

7. A plain bearing according to claim 6, in which the thickness of said overlay is at least 0.05 mm.

8. A plain bearing according to any one of the preceding claims, in which alternate layers of the overlay are formed from a tin-anitmony alloy and an aluminium-tin alloy.

9. A plain bearing according to any one of the preceding claims, in which the supporting member comprises a shell and an intermediate layer on which the overlay is arranged.

10. A plain bearing for an internal combustion engine substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.