WO2015024898A2

WO2015024898A2 - Sliding engine component

Info

Publication number: WO2015024898A2
Application number: PCT/EP2014/067554
Authority: WO
Inventors: Jon Forder
Original assignee: Mahle Engine Systems Uk Limited; Mahle International Gmbh
Priority date: 2013-08-19
Filing date: 2014-08-18
Publication date: 2015-02-26
Also published as: DE212014000172U1; GB201314815D0; WO2015024898A3; CN205917333U

Abstract

A sliding engine component having a plastic polymer-based layer on surface of a metallic substrate, the polymer-based layer comprising: a plastic polymer-based matrix; and a pigment of a different colour to the surface of the substrate onto which the polymer-based layer is provided.

Description

SLIDING ENGINE COMPONENT

FIELD OF INVENTION The present invention relates to sliding engine components having a plastic polymer-based bearing "overlay" layer, and in particular to sliding engine components for sliding bearing assemblies such as bearing lining shells, bushes, bearing surfaces of crankshafts, bearing surfaces of camshafts, bearing surfaces of connecting rods, thrust washers, bearing surfaces of a bearing block, bearing surfaces of a bearing cap, and piston assembly components such as piston rings, piston skirts, and cylinder walls and cylinder liners.

BACKGROUND

In internal combustion engines, the bearing assemblies typically each comprise a pair of half bearings retaining a crankshaft that is rotatable about an axis. Each half bearing is a hollow generally semi-cylindrical bearing shell, and typically at least one is a flange half bearing, in which the bearing shell is provided with a generally semi-annular thrust washer extending outwardly (radially) at each axial end. In other bearing assemblies it is also known to use an annular or circular thrust washer.

The bearing surfaces of sliding bearings generally have a layered construction, in which a strong backing material is coated with one or more layers having preferred tribological properties, which provide the bearing surface that faces the cooperating moving part, in use. In known half bearings and thrust washers: the strong backing material may be steel, having a thickness of about 1 mm or more; the bearings surface is coated with a layer (the "overlay layer") of 6 to 25 μηη of a plastic polymer-based composite layer; and optionally at least one intervening layer (a "lining layer") may be provided between the backing and the overlay layer, such as an aluminium-based material (e.g. aluminium-tin alloy) or a copper-based material (e.g. copper-tin bronze), adhered to the backing, and the thickness of the optional lining layer is generally in the range from about 0.1 to 0.5 mm (e.g. 300 μηη of aluminium-tin alloy).

It is known in the field to use composite plastic polymer-based overlay layers on a steel backing, in which the overlay comprises a matrix of a colourless, white or pale grey polymer material, having distributed throughout the matrix mechanical performance enhancing additives, such as metal powder to improve wear resistance, silane compounds to improve adhesion to the underlying substrate, and dry lubricant particulate to enhance lubrication in the event of contact between the bearing surface and the cooperating moving part. The metal powder may be a silvery-coloured metal powder (e.g. aluminium), copper-coloured metal powder (e.g. copper). Alternatively to the metal powder, or additionally, the wear resistance may be improved by the addition of other hard-wearing particulate (e.g. iron oxide).

For example, WO2010066396 describes a plastic polymer-based composite material for use as an overlay layer on a steel backing, in which the overlay comprises a matrix of a polyamide/imide plastic polymer material, having distributed throughout the matrix: from 5 to less than 15 %vol of a metal powder; from 1 to 15 %vol of a fluoropolymer particulate, the balance being the polyamide/imide resin apart from incidental impurities (e.g. a layer of 12 μηη thickness that comprises 12.5 %vol Al, 5.7 %vol PTFE particulate, 4.8 %vol silane, <0.1 %vol other components, and balance (approximately 77 %vol) polyamide/imide).

Such plastic polymer-based overlay layers may be deposited by various different methods, including spraying, pad printing (an indirect offset printing process, e.g. in which a silicone pad transfers a patterned layer of the plastic polymer composite material onto the sliding bearing substrate), screen printing, or by a transfer rolling process. Prior to deposition, the plastic polymer is in solution in a solvent, and the solid particulate is suspended in the solution. The composite overlay layer may be built up as a succession of sub-layers, in which repeated depositions of thin coatings are interspersed with flash-off phases to remove the solvent. After the deposition has been completed, the deposited polymer is thermally cured by prolonged heating to set the polymer by inducing cross-linking, e.g. at 140 to 240°C for a duration that may range from a few minutes to a few hours (e.g. 10 minutes to 2 hours).

A composite polymer-based layer of silver-, white- or grey-coloured or colourless mechanical performance enhancing additives (e.g. silver-coloured aluminium powder, colourless 3- aminopropyltriethoxysilane, and white polytetrafluoroethylene [PTFE] dry lubricant particulate) distributed through the cured polymer matrix typically results in a silver-coloured composite overlay layer that is the same or similar in appearance to the steel backing or an optional aluminium-based lining layer.

SUMMARY OF THE DISCLOSURE According to a first aspect, there is provided a sliding engine component having a plastic polymer-based layer on surface of a metallic substrate, the polymer-based layer comprising: a plastic polymer-based matrix; and a pigment of a different colour to the surface of the substrate onto which the polymer-based layer is provided.

According to a second aspect, there is provided a sliding engine component having a plastic polymer-based layer on a metallic substrate, the polymer-based layer comprising: a plastic polymer-based matrix; and a pigment of a different colour to that which the polymer-based layer would have in the absence of the pigment.

According to a third aspect, there is provided an engine comprising a sliding engine component according to the first or second aspect.

The substrate may comprise a silver-coloured steel backing, and the plastic polymer-based layer may be provided directly onto the backing, and the pigment may have a colour other than silver, white, or grey.

The substrate may comprise a backing and a silver-coloured aluminium-based lining layer between the plastic polymer-based layer and the backing, and the pigment may have a colour other than silver, white, or grey.

The substrate may comprise a backing and a copper-based lining layer between the plastic polymer-based layer and the backing, and the pigment may have a colour other than copper, red or brown.

The polymer-based layer may be silver-coloured in the absence of pigment, and the pigment may have a colour other than silver, white, or grey.

The polymer-based layer may be copper, red or brown in colour in the absence of the pigment, and the pigment may have a colour other than copper, red or brown.

The polymer-based layer may comprise a mechanical performance enhancing additive distributed throughout the polymer-based matrix. The mechanical performance enhancing additive may comprise a mechanical performance enhancing particulate. The pigment may be blue.

The pigment may have a colour index of 15.1 to 15.3.

The pigment may comprise copper phthalocyanine.

The pigment may be black. The proportion of pigment may be 5 to 20 %vol.

The concentration of pigment may be greatest at the surface of the plastic polymer-based layer remote from the substrate. The sliding engine component may comprise a further plastic polymer-based layer that does not comprise a pigment, which is provided between the substrate and the plastic polymer- based layer that does comprises the pigment.

The pigment may comprise a pigmented particulate distributed throughout the polymer- based matrix.

The pigment may comprise a pigmented solute that is dissolved in the polymer-based matrix. The sliding engine component may be a sliding bearing assembly component selected from the group consisting of bearing lining shells, bushes, bearing surfaces of crankshafts, bearing surfaces of camshafts, bearing surfaces of connecting rods, thrust washers, bearing surfaces of a bearing block, and bearing surfaces of a bearing cap. BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are further described hereinafter with reference to the accompanying drawings, in which:

• Figure 1A shows a bearing shell;

· Figure 1 B shows a cross-sectional view through the bearing shell of Figure 1 A; and • Figures 2 and 3 show cross-sectional views through alternative bearing shells according to the present invention.

DETAILED DESCRIPTION

In the described embodiments, like features have been identified with like numerals, albeit in some cases having one or more of: increments of integer multiples of 100. For example, in different figures, 104, 204 and 304 have been used to indicate an overlay layer.

Figure 1A schematically illustrates a sliding bearing 100 (e.g. a sliding engine component) in the form of a hollow semi-cylindrical bearing lining shell (commonly referred to as a "half bearing"). The half bearing 100 has a substrate 102 comprising a strong steel backing 102A and an optional bearing lining layer 102B (e.g. an aluminium-tin alloy layer) on the concave inner surface of the backing. A plastic polymer-based "overlay" layer 104 is provided on the substrate 102. The overlay layer 104 is configured to provide a running surface over the lifetime of the sliding bearing 100. The overlay layer 104 is the innermost layer of the half bearing, which is configured to face a cooperating moving part in a bearing assembly (e.g. the overlay layer receives a journaled shaft in an assembled bearing, which mutually cooperate, with an intervening film of lubricating oil).

The plastic polymer-based overlay layer 104 is a composite layer of a plastic polymer-based matrix with particulate distributed throughout the matrix. The plastic polymer material is selected from the group consisting of: polyamide/imide resin, acrylate resin, epoxy resin, polyurethane, fluoropolymer, polyetheretherketone, formaldehyde resin, and phenolic resin.

The plastic polymer-based overlay layer 104 comprises an addition of 5 to 20 %vol, and preferably 10 to 15 %vol, of pigment (i.e. a pigmented particulate and/or a pigmented solute) that contrasts in colour with the inner surface of the substrate onto which the polymer-based layer is deposited and/or contrasts in colour with the colour that the polymer-based layer would have in the absence of the pigment. Less than 5 %vol of the pigment may produce a colour change that is difficult to distinguish, relative to an unpigmented overlay layer. The addition of over 20 %vol of pigment in the overlay may compromise the structural integrity of the polymer matrix. The composite overlay layer is deposited as a mixture of a plastic polymer-based matrix material and suspended material, and may further comprise solvent, which may facilitate forming the mixture. Suitable solvents may be non-polar (e.g. xylene, toluene), polar aprotic (e.g. acetone, n-ethyl-2-pyrrolidone {NEP}, n-methyl-2-pyrrolidone {NMP}, gamma- butyrolactone, dipropylene glycol dimethyl ether) or polar protic (e.g. water, alcohol, glycol). The solvent can be employed in various proportions in order to achieve a particular desired viscosity of mixture for coating onto the substrate.

The plastic polymer mixture may also contain an addition of a silane material. Silane materials have been found to promote stability of the polyamide/imide matrix and have also been found to promote adhesion of the polyamide/imide resin material to the substrate. A suitable silane material may be gamma-aminopropyltriethoxysilane (e.g. 3- aminopropyltriethoxysilane), and an addition in the range of 3 to 6 %vol may be made to the mixture. A suitable alternative silane material may comprise bis-(gamma- trimethoxysilpropyl)amine.

The plastic polymer-based layer may further comprise from 1 to 15 %vol of a dry lubricant particulate, and a preferred range of 2 to 8 %vol. A dry lubricant particulate may be included in the plastic polymer-based layer for its beneficial effect on material frictional properties and its self-lubricating effect. The dry lubricant particulate may be fluoropolymer, Mo₂S, or graphene. The fluoropolymer particulate addition may preferably be constituted by polytetrafluoroethylene (PTFE), as this is the most effective of the fluoropolymers in terms of reducing the friction coefficient and improving the self-lubricating properties of the plastic polymer-based layer. However, other suitable fluoropolymers, such as fluorinated ethylene-propylene (FEP), may be used if desired.

Below 1 %vol of the dry lubricant particulate, the improvement in wear resistance and tribological properties is not significant. Above 15 %vol of the dry lubricant particulate, the structural integrity of the plastic polymer-based layer may be compromised. Too high a content of dry lubricant particulate reduces the matrix hardness and strength by an unacceptable degree. Particle size of the dry lubricant particulate desirably lies in the range from 1 to 5 μηη, and a size range of 2 to 4 μηη is preferred. The plastic polymer-based layer further comprises from 1 %vol to less than 15 %vol of a metal powder. Advantageously, the metal powder (particularly in the form of metallic flakes) enhances the thermal conductivity of the plastic polymer-based layer. The metal powder may further enhance the wear resistance of the plastic polymer-based layer. Below 1 %vol of the metal powder, the improvement in wear resistance and tribological properties are not significant. Above 15 %vol of the metal powder, the structural integrity of the plastic polymer-based layer may be compromised. In a preferred embodiment of the plastic polymer-based layer of the present invention, the metal powder content may lie in the range from 2 to 25 %vol, and more preferably from 5 to 15 %vol.

The metal powder may be chosen from: aluminium, aluminium alloys, copper, copper alloys, silver, tungsten, stainless steel. We have found that pure aluminium powder on its own gives the best results. Aluminium powder having particles in the form of flake-like platelets of about 5 to 25 μηη in size, and preferably 10 to 20 μηη in size (along the maximal dimension), provides a particularly suitable form of metal powder addition. The flake-like nature of the powder generally results in the maximum area of metal powder being exposed to a co-operating shaft journal by virtue of the plane of the flakes orientating generally parallel to the bearing surface. The provision of flakes within the plastic polymer-based layer that are generally parallel to the bearing surface may be provided by spray deposition of the plastic polymer-based layer.

A further advantage of the platelet flake morphology of the aluminium powder is that the particles are more securely bonded to the matrix by virtue of the relatively large surface area of each individual particle, and thus resists aluminium particles becoming plucked from the matrix during engine operation.

Without wishing to be bound by any particular theory, it is believed that the alumina film formed on the surface of the aluminium flakes may provide enhanced wear resistance. It is believed that the alumina in the plastic polymer-based layer of the sliding engine component provides a very fine abrasive, which tends to polish the machining asperities on the surface of the cooperating member (e.g. shaft journal surface), rendering the shaft journal surface less abrasive to the plastic polymer-based layer, thus reducing the wear rate of the layer. In the illustrated embodiment, the pigment is chosen to clearly visually contrast with the appearance that the polymer-based layer 104 would have in the absence of the pigment (i.e. to contrast with the appearance of the composite of the matrix and the mechanical performance enhancing additives), and to clearly visually contrast with the appearance of the surface of the substrate 102 onto which the polymer-based layer is deposited. In the case that the polymer-based layer would have a silver-colour in the absence of the pigment (e.g. having aluminium flakes and PTFE particulate), the pigment has a colour other than silver, white, or grey, in order to produce a clear contrast in visual appearance. In the case that the mechanical performance enhancing additives comprise copper or copper-alloy flakes to enhance wear resistance, the polymer-based layer would have a copper/red/brown-colour in the absence of the pigment, and the pigment has a colour other than copper/red/brown. For example, the pigment may be blue or black to produce a clear visual contrast in either case. The blue pigment may be copper phthalocyanine powder.

In particular, the plastic polymer-based overlay layer may comprise a matrix of a polyamide/imide-based polymer, having distributed throughout the matrix: from 10 to 15 %vol pigment; from 1 to less than 15 %vol of a metal particulate (e.g. metal powder and/or metal flakes); from 1 to 15 %vol of a fluoropolymer, the balance being the polyamide/imide resin apart from incidental impurities; and 3 to 6 %vol of silane compound. Further, the plastic polymer-based layer may comprise 12.5 %vol Al, 5.7 %vol PTFE particulate, 4.8 %vol silane, <0.1 %vol other components, and balance polyamide/imide, apart from incidental impurities. The plastic polymer-based layer may comprise at least 60 %vol of plastic polymer-based matrix material (proportions are specified with respect to content of the overlay layer after the polymer has been cured).

Figure 1A shows the half bearing 100 after the overlay layer 104 has been deposited and the polymer has been cured. Figure 1 B shows a cross-sectional view of the structure of the half bearing 100 of Figure 1A.

In the illustrated embodiment, the half bearing 100 has an aluminium-tin based alloy lining layer 102B, and the pigment in the polymer-based overlay layer 104 is a blue pigment, e.g. copper phthalocyanine powder.

The polymer may be cured at about 140 to 240°C. The thermal curing may be provided by baking in an oven or irradiating the half bearing with infrared radiation. Alternatively, the plastic polymer-based material may be cured by a non-thermal process, for example being cured by exposure to ultraviolet light. Although in Figures 1A and 1 B, the plastic polymer-based overlay layer 104 has been shown as a single layer comprising pigment that is homogeneously distributed throughout the layer, other arrangements are also possible. Figure 2 illustrates an alternative, in which the density of pigment is greater remote from the substrate (e.g. backing 202A) than proximate the substrate, e.g. having a density gradient of pigment that increases away from the backing.

By providing more of the pigment remote from the substrate (i.e. proximate the free surface of the half bearing), the visual appearance of the pigment may be more pronounced and/or less pigment may be required. This is of particular benefit where the plastic polymer-based overlay comprises a significant proportion of performance-enhancing particulate, such as aluminium flakes, which may obscure the deeper regions of the overlay. Such a concentration gradient may be provided by varying the concentration of pigment as the layer is deposited by spraying. Or, if deposited as a series of sub-layers, e.g. by screen printing, the successive sub-layers may be deposited with an increasing concentration of pigment, or with pigment only in the final sub-layers.

Figure 3 illustrates a further alternative in which pigment is provided in a plastic polymer- based overlay layer 304, but is not provided in a further plastic polymer-based layer 306 between that overlay layer and the substrate 302A and 302B.

In the bearing of Figure 3, the uppermost layer 304 may be a thin running-in layer that is worn away relatively rapidly in use (i.e. a sacrificial layer), and which serves as a nonstructural visual identifier prior to use.

Although illustrated in Figure 1A in relation to a half bearing shell, the present invention equally applies to other sliding engine components, including semi-annular, annular or circular thrust washers, and bushes. The mechanical performance enhancing additives (e.g. dry lubricant particulate, silane and metal powder) dispersed within the polymer-based matrix provide significant enhancements to the mechanical performance of the sliding engine component, such as wear resistance and adhesion promotion. In contrast, the additional pigment substantially only provides an optical effect by changing the visual appearance of the polymer-based layer, and does not affect the performance of the polymer-based layer, and in particular does not change the performance of any mechanical performance enhancing additives. In particular, in the case of increased wear resistance, the combined effects of the dry lubricant and metal powder provide a synergistic effect. The additional pigment does not substantially compromise the synergistic effect of the dry lubricant and metal powder.

Where the polymer-based layer would otherwise match or be similar to the colour of the backing (e.g. an otherwise silver-coloured layer on a steel backing or a steel backing with an aluminium lining layer) the addition of a pigment that visually contrasts the colour that the layer would otherwise have enables enhanced reliability during manufacturing, by facilitating a visual distinction between sliding engine components that have and have not been coated with a composite polymer-based overlay layer, and to distinguish between different coatings. This facilitates distinguishing between sliding engine components of different colours in an automated quality control process. In particular, the colour that the layer would otherwise have may be primarily determined by the colour of the mechanical performance enhancing particulate, and the pigment visually contrasts with the colour of the mechanical performance enhancing particulate.

Additionally, in the case that the polymer-based layer would not otherwise match or be similar to the colour of the substrate, the addition of the pigment that visually contrasts with the appearance that the polymer-based layer would have without the pigment can enable different overlay layers with the same or similar mechanical performance enhancing additives to be distinguished (e.g. use of the pigment can enable manual or automatic identification of different curing regimes). The addition of a pigment enables the sliding engine components to be distinguished from those of a different provenance, so enhancing traceability.

Yet further, the addition of the present pigment may avoid the requirement to apply identifying features to the surface of the component by a stamping process or through an additional printing or etching process, which would require additional manufacturing steps and may interfere with the operation of the component. For example, in the case of a bearing shell, an identification mark stamped into the outer surface risks bruising the inner surface, which is configured to cooperate with a rotating journal with very small tolerances. Similarly, printing or etching an identification mark onto the outside of a bearing shell may affect the way in which the bearing shell sits within its housing, in use, thereby affecting performance. The figures provided herein are schematic and not to scale.

Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of them mean "including but not limited to", and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

Claims

1 . A sliding engine component having a plastic polymer-based layer on surface of a metallic substrate, the polymer-based layer comprising:

a plastic polymer-based matrix; and

a pigment of a different colour to the surface of the substrate onto which the polymer- based layer is provided.

2. A sliding engine component according to claim 1 , wherein the substrate comprises a silver-coloured steel backing, the plastic polymer-based layer is provided directly onto the backing, and the pigment has a colour other than silver, white, or grey.

3. A sliding engine component according to claim 1 , wherein the substrate comprises a backing and a silver-coloured aluminium-based lining layer between the plastic polymer- based layer and the backing, and the pigment has a colour other than silver, white, or grey.

4. A sliding engine component according to claim 1 , wherein the substrate comprises a backing and a copper-based lining layer between the plastic polymer-based layer and the backing, and the pigment has a colour other than copper, red or brown.

5. A sliding engine component having a plastic polymer-based layer on a metallic substrate, the polymer-based layer comprising:

a plastic polymer-based matrix; and

a pigment of a different colour to that which the polymer-based layer would have in the absence of the pigment.

6. A sliding engine component according to claim 5, wherein the polymer-based layer would be silver-coloured in the absence of pigment, and the pigment has a colour other than silver, white, or grey.

7. A sliding engine component according to claim 5, wherein the polymer-based layer would be copper, red or brown in colour in the absence of the pigment, and the pigment has a colour other than copper, red or brown.

8. A sliding engine component according to any preceding claim, the polymer-based layer comprising a mechanical performance enhancing additive distributed throughout the polymer-based matrix.

9. A sliding engine component according to claim 8, wherein the mechanical performance enhancing additive comprises a mechanical performance enhancing particulate.

10. A sliding engine component according to any preceding claim, wherein the pigment is blue.

1 1 . A sliding engine component according to claim 10, wherein the pigment has a colour index of 15.1 to 15.3.

12. A sliding engine component according to claims 10 or 1 1 , wherein the pigment comprises copper phthalocyanine.

13. A sliding engine component according to any one of claims 1 to 9, wherein the pigment is black.

14. A sliding engine component according to any preceding claim, wherein the proportion of pigment is 5 to 20 %vol.

15. A sliding engine component according to any preceding claim, wherein the concentration of pigment is greatest at the surface of the plastic polymer-based layer remote from the substrate.

16. A sliding engine component according to any preceding claim, comprising a further plastic polymer-based layer that does not comprise a pigment, which is provided between the substrate and the plastic polymer-based layer that does comprises the pigment.

17. A sliding engine component according to any preceding claim, wherein the pigment comprises a pigmented particulate distributed throughout the polymer-based matrix.

18. A sliding engine component according to any preceding claim, wherein the pigment comprises a pigmented solute that is dissolved in the polymer-based matrix.

19. A sliding engine component according to any preceding claim, wherein the sliding engine component is a sliding bearing assembly component selected from the group consisting of bearing lining shells, bushes, bearing surfaces of crankshafts, bearing surfaces of camshafts, bearing surfaces of connecting rods, thrust washers, bearing surfaces of a bearing block, and bearing surfaces of a bearing cap.

20. An engine comprising a sliding engine component according to any preceding claim.

21 . A sliding engine component substantially as hereinbefore described with reference to the accompanying description and/or any one of the Figures.

22. An engine comprising a sliding engine component substantially as hereinbefore described with reference to the accompanying description and/or any one of the Figures.