The invention relates to a bearing element, and an engine comprising a bearing element. In particular, the invention relates to a bearing element comprising an intermediate layer between a metal substrate and a bearing layer. Bearing elements embodying the present invention are suitable for use in automotive environments, including for supporting rotatable or slidable engine components and for use as, or as part of, other rotatable or sliding engine components. Such sliding engine components may include 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. Bearing elements embodying the present invention are particularly suitable for use as sliding bearings.

In internal combustion engines, the main-bearing assemblies typically each comprise a pair of half bearings retaining a crankshaft that is rotatable about an axis. Each half bearing is a generally semi-cylindrical bearing shell, and typically at least one is a flanged half bearing provided with a semi-annular thrust washer extending outwardly (radially) at each axial end.

The bearing surfaces of bearing shells conventionally have a layered construction, in which a substrate comprising a strong backing material is coated with one or more layers having preferred tribological properties to provide a bearing surface that, in use, faces a cooperating moving part such as a crankshaft journal. Typically, a metallic running or bearing surface is provided on a strong metal substrate. The metallic bearing layer may comprise an aluminium alloy which may further comprise tin, or silicon. Bearing layers comprising an aluminium-tin alloy may exhibit improved seizure resistance and conformability, but may have a reduced fatigue strength due to the inclusion of the soft tin solute. The metallic bearing layer may comprise a bronze or brass alloy, with or without a soft phase. Bearing layers comprising bronze may be more suitable for higher load applications due to their higher load carrying capabilities. However, such bearing layers may exhibit lower seizure resistance and lower conformability. Due to the high cost of copper, bearing layers comprising bronze may also be considerably more expensive than bearing layers comprising aluminium-tin alloys.

In known bearing elements, a layer of bonding foil may be applied between the metal substrate and the bearing layer. The bonding foil, also known as an interlayer or intermediate layer, typically has a thickness of a few tens of micrometres and is used to facilitate efficient bonding of the bearing layer to the metal substrate. Typically the intermediate layer formed by belt casting or strand casting to form a strip which is subsequently roll bonded to the metal substrate. Known intermediate layers may comprise pure aluminium or a high strength aluminium-copper alloy. Known intermediate layers typically have a thickness considerably less than the thickness of a bearing layer.

However, the provision of an intermediate layer comprising pure aluminium or aluminium-copper alloys can be expensive. In addition, while known bearing elements often exhibit high seizure resistance and conformability, many exhibit poor fatigue resistance. Fatigue is the process by which materials fail due to repeated loading and unloading at stresses below the ultimate strength of the material. Bearing elements and other sliding components need to be capable of being used for a high number of cycles without failure due to fatigue. High fatigue resistance is therefore desirable for bearing elements.

Accordingly, there is a need to provide a bearing element which exhibits both high seizure resistance and high fatigue resistance.

In addition, there is a need to provide a bearing element which is less expensive to produce.

According to a first aspect of the invention, there is provided a bearing element comprising; a metal substrate, an intermediate layer provided on the metal substrate, and a bearing layer provided on the intermediate layer, wherein the intermediate layer comprises a first aluminium alloy comprising: between 0.8 weight percent and 1.4 weight percent manganese, and between 0.8 weight percent and 1.3 weight percent magnesium.

The provision of an intermediate layer comprising manganese and magnesium may be less costly than comparable intermediate layers comprising aluminium-copper alloy. Moreover, the inventors found that the provision of an intermediate layer comprising an aluminium alloy with manganese and magnesium in the weight percentages of the present invention may advantageously and surprisingly improve the fatigue resistance of the bearing element while retaining the good seizure resistance provided by the bearing layer.

Without wishing to be bound by theory, it is thought that the improved fatigue resistance of the bearing element is a result of using an intermediate layer having an increased hardness compared to the intermediate layers of the prior art. As set out in more detail below, in bearing elements of the prior art the aluminium metal or aluminium-copper alloy intermediate layers have a hardness, for example when using a Vickers hardness test, which is lower than the hardness of the material of the bearing layer. In contrast, the aluminium- manganese alloy of the present invention has a hardness greater than that of the material of the bearing layer. For example, the aluminium-manganese alloy of the intermediate layer of the present invention may have a hardness which is about 1.1 times the hardness of the material of the bearing layer.

The intermediate layer comprises a first aluminium alloy comprising between 0.8 weight percent and 1.4 weight percent manganese. For example, the first aluminium alloy may comprise between 1.0 weight percent and 1.4 weight percent manganese.

The intermediate layer comprises a first aluminium alloy comprising between 0.8 weight percent and 1.3 weight percent magnesium. For example, the first aluminium alloy may comprise between 0.8 weight percent and 1.3 weight percent magnesium.

The aluminium alloy of the intermediate layer may have a composition corresponding to the international designation A3004 or A3104.

As used herein, with reference to the present invention, relative amounts of components in the materials used in the bearing element are given in weight percentages. This refers to the dry weight percentages of each component. The skilled person would understand that this is the proportion of each component, given by weight, of the final bearing material following any curing or heat treatment steps.

As used herein, with reference to the present invention, the ‘bearing layer’ refers to the layer of the bearing element which is directly adjacent the intermediate layer, on the opposite surface of the intermediate layer to the metal substrate. The bearing layer may be the layer which is directly in contact with a cooperating moving part such as a crankshaft journal. Alternately, the bearing element may further comprise additional layers provided on the bearing layer, such as a polymeric overlay layer described in more detail below.

The metal substrate may comprise any metal. The metal substrate may comprise steel. The metal substrate may have any thickness. For example, the metal substrate may have a thickness of between 0.25 millimetres and 5 millimetres, between 0.5 millimetres and 3 millimetres, or between 1 millimetre and 2 millimetres.

The intermediate layer may be formed by casting a relatively thin strip of the first aluminium alloy using a belt caster or a strand caster. The surface of the thin strip of first aluminium alloy may be roughened using brushing to achieve a surface roughness (Ra) of between 2 micrometres and 6 micrometres. This surface roughening may be done to facilitate bonding of the intermediate layer to the metal substrate. The bearing layer and the intermediate layer may be applied to the metal substrate using roll bonding. The bearing element may undergo a heat treatment process to improve the mechanical properties of the bearing element. As set out in more detail below, the heat treatment may advantageously facilitate improved bonding of the intermediate layer to the bearing layer. The first aluminium alloy may further comprise copper. The first aluminium alloy may further comprise between 0.01 weight percent and 0.6 weight percent copper. For example, the first aluminium alloy may further comprise between 0.05 weight percent and 0.25 weight percent copper, or between 0.10 weight percent and 0.25 weight percent copper. Alternatively, the first aluminium alloy may comprise about 0.6 weight percent copper.

The first aluminium alloy may further comprise silicon. The first aluminium alloy may further comprise between 0.1 weight percent and 1.0 weight percent silicon. For example, the first aluminium alloy may further comprise between 0.3 and 0.7 weight percent silicon. The first aluminium alloy may comprise about 0.6 weight percent, about 0.3 weight percent, about 0.4 weight percent silicon, about 0.6 weight percent, or about 0.7 weight percent silicon.

The first aluminium alloy may further comprise iron. The first aluminium alloy may further comprise between 0.5 weight percent and 1.0 weight percent iron. For example, the first aluminium alloy may further comprise about 0.7 weight percent, or about 0.8 weight percent iron.

The first aluminium alloy may further comprise about 0.6 weight percent silicon, and about 0.8 weight percent iron.

The bearing layer may comprise a second aluminium alloy. The second aluminium alloy may be any aluminium alloy. The second aluminium alloy may further comprise nickel. The second aluminium alloy may further comprise no more than 2.0 weight percent nickel. The second aluminium alloy may comprise between 0.01 weight percent and 2.0 weight percent nickel.

The second aluminium alloy may further comprise vanadium. The second aluminium alloy may further comprise no more than 0.5 weight percent vanadium. The second aluminium alloy may comprise between 0.01 weight percent and 0.5 weight percent vanadium.

The second aluminium alloy may further comprise manganese. The second aluminium alloy may further comprise between 0.01 weight percent and 0.5 weight percent manganese. The second aluminium alloy may comprise between 0.2 weight percent and 0.3 weight percent manganese.

The second aluminium alloy may comprise between 0.01 weight percent and 2.0 weight percent nickel, between 0.01 weight percent and 0.5 weight percent vanadium, and between 0.2 weight percent and 0.3 weight percent manganese.

It has been surprisingly found that the provision of a bearing layer comprising a second aluminium alloy with this composition may improve the bond strength between the intermediate layer and the bearing layer. In particular, the provision of a second aluminium alloy comprising manganese in combination with an intermediate layer comprising a first aluminium alloy also comprising manganese may improve the bond strength between the intermediate layer and the bearing layer due to diffusion of manganese between the intermediate layer and the bearing layer to reduce the manganese concentration gradient between the intermediate layer and the bearing layer. In some embodiments, the bearing element may undergo a heat treatment once the bearing layer has been applied to the intermediate layer. This process may promote diffusion of manganese between intermediate layer and the bearing layer which may in turn improve the bond strength between the intermediate layer and the bearing layer.

The thickness of the intermediate layer may account for any proportion of the total thickness of the intermediate layer and the bearing layer. The thickness of the intermediate layer may account for at least 5 percent of the total thickness of the intermediate layer and the bearing layer. For example, the thickness of the intermediate layer may account for at least 10 percent, at least 15 percent, or at least 20 percent of the total thickness of the intermediate layer and the bearing layer.

As used herein, with reference to the invention the term ‘thickness’ refers to the thickness of a layer, for example the bearing layer or the intermediate layer, of the bearing element at a running surface of the bearing element. In other words, the ‘thickness’ refers to the thickness of a layer at a point where the bearing element contacts a cooperating moving component such as a crankshaft journal. For example, where the bearing element is a cylindrical half shell bearing, the thickness of a layer is the dimension of that layer in the radial direction.

The thickness of the intermediate layer may account for at least 25 percent of the total thickness of the intermediate layer and the bearing layer. For example, the thickness of the intermediate layer may account for at least 30 percent, at least 35 percent, or at least 40 percent of the total thickness of the intermediate layer and the bearing layer.

The thickness of the intermediate layer may account no more than 50 percent of the total thickness of the intermediate layer and the bearing layer. The thickness of the intermediate layer may account about 50 percent of the total thickness of the intermediate layer and the bearing layer

It has surprisingly been found that the provision of an intermediate layer having a greater thickness that those of the prior art may advantageously increase the load carrying capability of the bearing element. This may advantageously improve the fatigue resistance of the bearing element. The thickness of the intermediate layer may be between 20 micrometres and 150 micrometres. For example, the thickness of the intermediate layer may be between 50 and 100 micrometres, or between 60 micrometres and 80 micrometres. The thickness of the intermediate layer may be between 20 micrometres and 50 micrometres.

However, the intermediate layer may have a greater thickness. For example, the intermediate layer may have a thickness of between 50 micrometres and 150 micrometres. Providing an intermediate layer having a greater thickness within this range may advantageously improve the fatigue resistance of the bearing element,

The bearing layer may have any thickness. The thickness of the bearing layer may be between 150 micrometres and 280 micrometres. For example, the thickness of the bearing layer may be between 200 micrometres and 250 micrometres.

The combined thickness of the intermediate layer and the bearing layer may be between 200 micrometres and 300 micrometres. The combined thickness of the intermediate layer and the bearing layer may be between 225 micrometres and 325 micrometres. The combined thickness of the intermediate layer and the bearing layer may be about 250 micrometres.

While bearing elements of the present invention may include an intermediate layer having a higher thickness than intermediate layers of the prior art, it may be advantageous for the overall dimensions of the bearing element to remain generally consistent with bearing elements of the prior art since the dimensions may need to conform to industry standards or be interchangeable with prior art bearing elements. The overall dimensions of the bearing element may remain the same as those of the prior art, despite a thicker intermediate layer, by providing a bearing layer having a lower thickness than is typically found on bearing elements of the prior art.

In some embodiments, the bearing element may be a thrust washer. Where this is the case, the intermediate layer of the present invention may be provided on a first surface of the metal substrate. A sacrificial layer may be provided on a second surface of the metal substrate, where the first surface of the metal substrate opposes the second surface of the metal substrate. The sacrificial layer may be formed from the same material as the intermediate layer. The sacrificial layer may be formed from the first aluminium alloy.

In thrust washers of the prior art, it is common for the intermediate layer and the sacrificial layer to have substantially the same thickness. In the present invention, the intermediate layer may have a higher thickness than the sacrificial layer. The bearing element may further comprise a polymeric overlay layer provided on the bearing layer.

In the aggressive conditions of modern internal-combustion engines, stop-start operation requires a typical engine to undergo a greatly increased number of stop-start operations. Each time an engine restarts, full hydrodynamic lubrication may not be in place and so bearings such as crankshaft bearings need to be able to survive an increased number of non-hydrodynamically-lubricated start-up operations.

The polymeric overlay layer may advantageously improve the wear resistance of the bearing element under such aggressive stop-start conditions. The provision of a polymeric overlay layer may also improve the fatigue resistance of the bearing element since the loads applied to the bearing element may be distributed more evenly due to the intrinsic elasticity of the polymeric overlay layer.

The function of the polymeric overlay layer is also to provide a relatively soft, conformable layer that can accommodate any small misalignments between the harder steel crankshaft journal and the bearing element, and receive and embed dirt particles that may circulate in the oil supply and enter the bearing, so as to prevent damage to or scoring of the journal. In other words, the provision of the polymeric overlay layer may improve the conformability and embedability of the bearing element.

The polymeric overlay layer may comprise a polymer matrix comprising polyamide- imide.

The provision of a polymer matrix of polyamide-imide (PAI) polymer material advantageously provides a robust and effective base for the polymeric overlay layer.

PAI-based bearing materials, with suitable filler materials, have demonstrated superior performance to other polymer materials under the aggressive stop-start conditions characterising modern internal-combustion engines. The use of polyamide-imide polymer material in the bearing material of the present invention may thus advantageously provide a bearing element with good performance, including conformability and embedability.

The polymeric overlay layer may further comprise metallic particulate.

The inventors have further identified that the provision of metallic particulate may increase the conformability, and the thermal conductivity of the bearing material. This may advantageously improve heat distribution throughout the polymer matrix. Moreover, the provision of metallic particulate may improve the fatigue resistance of the bearing material. However, it has been found that the provision of metallic particulate, particularly in high weight percentages, may reduce the wear resistance of the bearing material. The metallic particulate may comprise any metal. For example, the metallic particulate may comprise at least one of aluminium, aluminium alloys, copper, copper alloys, silver, tungsten, tin, and stainless steel. The inventors of the present invention have identified that aluminium particulate provides the greatest improvement in fatigue resistance.

The metallic particulate may be any metallic particulate but preferably comprises metal flakes. The flake-like nature of the particulate generally results in the maximum area of metallic particulate 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 polymer-based overlay layer that are generally parallel to the bearing surface may be provided by spray deposition of the polymer-based overlay layer.

A further advantage of the platelet flake morphology of the metallic particulate is that the flakes are more securely bonded to the polymer-based matrix by virtue of the relatively large surface area of each individual flake, and thus resists metal flakes becoming plucked from the polymer-based matrix during engine operation.

Preferably, the metallic particulate comprises aluminium flakes.

Preferably, the metallic particulate have a D50 size of between about 5 pm and about 30 pm along the maximal dimension. More preferably, a D50 size of between about 10 pm and about 20 pm along the maximal dimension. This has been found to provide a particularly suitable form of metallic particulate addition. D50 is the median diameter of the particle size distribution of the metallic particulate.

The polymeric overlay layer may comprise any amount of metallic particulate. The polymeric overlay layer may comprise between 10 weight percent and 40 weight percent metallic particulate. For example, the polymeric overlay layer may comprise between 15 weight percent and 35 weight percent, or between 20 weight percent and 30 weight percent metallic particulate.

The polymeric overlay layer may further comprise a solid lubricant.

The provision of a solid lubricant may improve the wear resistance of the bearing element.

The solid lubricant may be any solid lubricant. The solid lubricant may comprise at least one of PTFE, melamine cyanurate, tungsten disulphide, molybdenum disulphide, graphite and hexagonal boron nitride.

Melamine cyanurate may be particularly advantageous as a solid lubricant since it may lead to superior fatigue and seizure resistance in the bearing material due to its hydrogen- bonding network and low coefficient of friction, in addition to its high thermal stability and low corrosively.

The polymeric overlay layer may comprise any amount of solid lubricant. The polymeric overlay layer may comprise between 5 weight percent and 15 weight percent solid lubricant. For example, the polymeric overlay layer may comprise between 8 weight percent and 12 weight percent solid lubricant.

The polymeric overlay layer may further comprise a wear suppressant. The wear suppressant may comprise metal oxide particulate, such as a transition metal oxide particulate.

The wear suppressant, such as metal oxide, may advantageously improve the wear resistance of the bearing material. This is particularly true where the wear suppressant has a high hardness.

The wear suppressant may be any metal oxide. Preferably, the metal oxide particulate comprises one or more of cerium oxide, tin oxide, titanium dioxide, and zirconium dioxide. Preferably, the metal oxide may be one or more of CeC>2, SnO, SnC>2, T1O2, ZrC>2, or Fe ₂ C> ₃ .

In a particularly preferred embodiment, the metal oxide comprises cerium oxide or

CeC>2.

The use of cerium oxide, or CeC>2, in the overlay may allow a user to monitor overlay wear by measurement of the cerium accumulating in the oil of an engine. Unlike iron or other metals, cerium oxide is unlikely to be used elsewhere in the engine system. Therefore, cerium in the oil could only originate from wear of the overlay. The presence of cerium oxide in the overlay may therefore advantageously be used to gauge bearing wear without the need for visual checks and an engine rebuild. Cerium oxide has also been found to be particularly effective at increasing the abrasive wear resistance of the bearing element.

The polymeric overlay layer may comprise any amount of wear suppressant. The polymeric overlay layer may comprise no more than about 5 weight percent wear suppressant. For example, the polymeric overlay layer may comprise no more than about 3 weight percent wear suppressant. Where the polymeric overlay layer comprises wear suppressant, the polymeric overlay layer may comprise at least 0.1 weight percent wear suppressant. For example, the polymeric overlay layer may comprise between 0.1 weight percent and 5 weight percent, or between 0.1 and 3 weight percent wear suppressant.

The polymeric overlay layer may further comprise a pigment.

The colour of the pigment may be chosen to provide the polymer-based overlay layer with a colour that is different to the colour of the underlying bearing layer. This may advantageously allow the presence of the polymeric overlay layer to be readily determined simply by looking at the bearing surface and observing the colour.

For example, the pigment may be blue or black to produce a clear visual indication that the polymeric overlay layer is present. The blue pigment may be copper phthalocyanine powder.

The polymeric overlay layer may comprise any amount of pigment. The polymeric overlay layer may comprise no more than about 10 weight percent pigment. For example, the polymeric overlay layer may comprise no more than about 8 weight percent pigment. Where the polymeric overlay layer comprises pigment, the polymeric overlay layer may comprise at least 0.1 weight percent pigment. For example, the polymeric overlay layer may comprise between 0.1 weight percent and 10 weight percent, or between 0.1 and 8 weight percent pigment.

The polymeric overlay layer may comprise: between 20 weight percent and between 30 weight percent aluminium flakes, between 8 weight percent and 12 weight percent solid lubricant, less than 3 weight percent wear suppressant, and less than 8 weight percent pigment.

The polymeric overlay layer may have any thickness. The polymeric overlay layer may have a thickness of between 2 micrometres and 20 micrometres. For example, the polymeric overlay layer may have a thickness of between 5 micrometres and 15 micrometres.

The first aluminium alloy may further comprise: between 0.05 weight percent and 0.25 weight percent copper, about 0.6 weight percent silicon, about 0.8 weight percent iron, about 0.25 weight percent zinc, about 0.1 weight percent titanium, about 0.05 weight percent gallium, and about 0.05 weight percent vanadium, wherein the bearing layer comprises a second aluminium alloy comprising: between weight percent 5.0 and 23 weight percent tin, between 0.01 weight percent and 6.5 weight percent silicon, between 0.7 weight percent and 1.3 weight percent copper, between 0.01 weight percent and 2.0 weight percent nickel, between 0.01 weight percent and 0.5 weight percent vanadium, between 0.2 weight percent and 0.3 weight percent manganese, between 0.01 weight percent and 0.7 weight percent iron, and between 0.01 weight percent and 0.1 weight percent lead.

The remainder of the first aluminium alloy may comprise aluminium other than up to about 0.15 weight percent impurities. The remainder of the second aluminium alloy may comprise aluminium other than up to about 0.5 weight percent impurities.

According to a second embodiment of the present invention, there is further provided an engine comprising a bearing element according to the first aspect of the present invention. It should be appreciated that any feature in one aspect of the invention may be applied to other aspects of the invention, in any appropriate combination. In particular, method aspects may be applied to apparatus aspects, and vice versa. Furthermore, any, some and/or all features in one aspect can be applied to any, some and/or all features in any other aspect, in any appropriate combination.

It should also be appreciated that particular combinations of the various features described and defined in any aspects of the invention can be implemented and/or supplied and/or used independently.

The invention will further be described by way of example only with reference to the accompanying drawing, in which:-

Figure 1 shows a perspective view of a bearing element according to preferred embodiments of the present invention.

Figure 2 shows a cross-sectional view of a bearing element according to preferred embodiments of the present invention.

Figure 1 schematically illustrates a bearing element 100, the bearing element 100 is a semi-cylindrical bearing shell, which is also commonly referred to as a half bearing or a half shell, for a main bearing assembly of an internal combustion engine for retaining a cylindrical journal of a crankshaft.

The bearing shell 100 has a layered construction incorporating a substrate comprising a metal substrate 102, an intermediate layer 104 provided on the metal substrate 102, and a bearing layer 106 disposed on the intermediate layer 104. The metal substrate 102 comprises a high strength steel. The intermediate layer 104 comprises a first aluminium alloy. The first aluminium alloy comprises between 0.8 weight percent and 1.4 weight percent manganese, between 0.8 weight percent and 1.3 weight percent magnesium, between 0.05 weight percent and 0.25 weight percent copper, about 0.6 weight percent silicon, about 0.8 weight percent iron, about 0.25 weight percent zinc, about 0.1 weight percent titanium, about 0.05 weight percent gallium, and about 0.05 weight percent vanadium.

The intermediate layer 104 has a thickness of about 50 micrometres.

The bearing layer 106 comprises a second aluminium alloy. The second aluminium alloy comprises between weight percent 5.0 and 23 weight percent tin, between 0.01 weight percent and 6.5 weight percent silicon, between 0.7 weight percent and 1.3 weight percent copper, between 0.01 weight percent and 2.0 weight percent nickel, between 0.01 weight percent and 0.5 weight percent vanadium, between 0.2 weight percent and 0.3 weight percent manganese, between 0.01 weight percent and 0.7 weight percent iron, and between 0.01 weight percent and 0.1 weight percent lead.

The bearing layer 106 has a thickness of about 200 micrometres.

The bearing layer 106 and the intermediate layer 104 have a combined thickness of about 250 micrometres. The thickness of the intermediate layer accounts for about 20 percent of the total thickness of the intermediate layer and the bearing layer.

The bearing element 100 further comprises a polymeric overlay layer 108. The polymeric overlay layer 108 is not shown in Figure 1 but it is shown in Figure 2. The polymeric overlay layer 108 comprises between 20 weight percent and between 30 weight percent aluminium flakes, between 8 weight percent and 12 weight percent solid lubricant, less than 3 weight percent wear suppressant, and less than 8 weight percent pigment, the balance being polyamide-imide other than impurities.

The polymeric overlay layer 108 has a thickness of about 10 micrometres.

The intermediate layer 104 is formed by casting a relatively thin strip of the first aluminium alloy using a belt caster or a sand caster. The surface of the thin strip of first aluminium alloy is roughened using brushing to achieve a surface roughness (Ra) of between 2 micrometres and 6 micrometres. The bearing layer and the intermediate layer are applied to the metal substrate using roll bonding. The bearing element undergoes a heat treatment process.

The hardness, measured using a Vickers hardness test, of different materials used in the present invention and the prior art was determined. The Vickers hardness test was conducted in accordance with ISO 6507-1 :2018. The Vickers hardness (HV) of the first aluminium alloy of the intermediate layer 104, the steel substrate 102, and the second aluminium alloy of the bearing layer 106 were determined. In addition, the Vickers hardness (HV) of an aluminium metal and an aluminium-copper alloy were determined. As set out above, both aluminium metal and aluminium-copper alloys are used as intermediate layers in bearing elements of the prior art. The absolute Vickers hardness (HV) results, and the relative hardness values of the materials compared to the hardness of the second aluminium alloy of the bearing layer 106 are shown in Table 1.

Table 1

As shown in Table 1, the first aluminium alloy of the present invention has a higher hardness than the second aluminium alloy. This differs from the aluminium metal and aluminium-copper alloys of the intermediate layer of the prior art which both have a lower hardness than the second aluminium alloy of the bearing layer. As set out above, the harder intermediate layer of the present invention is thought to improve the fatigue resistance of the bearing element.

Bearing elements of the present invention were further evaluated using a bearing fatigue rig. Details of the fatigue evaluation, including the fatigue rig setup is set out in GEORGE, James et al. Polymeric Engine Bearings for Hybrid and Start Stop Applications. SAE International. 2012. ISSN: 0148-7191, e-ISSN: 2688-3627.

Bearing elements of the prior art which include an aluminium metal intermediate layer and an aluminium-copper alloy intermediate layer were similarly evaluated. The fatigue test was used to determine the fatigue limits of bearing elements comprising each material. The test involves applying a load in determining steps for a set duration then the inspecting the component visually to quantify whether they have passed or failed. Key parameters for the fatigue test rig are set out in Table 2 below. The results of the three fatigue tests are shown below in Table 3.

Table 2

Table 3

It is clear that the fatigue resistance of the present invention is higher than that of both of the prior art examples. This may advantageously extend the life of a bearing element according to the present invention compared to bearing elements of the prior art.

Although described herein and illustrated in the drawing in relation to a half bearing shell, the present invention may equally apply to other sliding engine components, including semi-annular, annular or circular thrust washers, and bushes, and engines comprising such sliding engine components.