[001] This invention relates to a bearing for internal combustion engines provided with a supporting layer based on steel which may have a low or medium carbon content followed by a layer comprising a bronze alloy containing bismuth and a surface layer of polymer matrix applied directly onto the bronze layer so as to increase the durability of the bearing when working under high pressures and poor lubrication conditions.

Description of the state of the art

[002] Many developments have been made with the intention of improving loading capacity and among other properties reducing the friction coefficient of internal combustion engine components, such as, for example, bearings. On the other hand the increased working pressures of internal combustion engines have made it difficult for such attempts to be successful because they bring about early wear in the bearing.

[003] In addition to increased working pressures, low viscosity lubricating oils are being used to reduce friction. This gives rise to a particularly difficult problem for bearings in an internal combustion engine because this is prejudicial to the formation of the oil film at both low and high speeds. At high speeds more heat is generated in the bearing and the bearing oil film thins, causing greater contact between the metal components. At low speeds formation of the oil film may be insufficient to separate the surfaces. In both cases the service life of the bearing is reduced.

[004] Multiple layer bearings have been developed with a view to overcoming the problems mentioned. Layer construction generally comprises a strong base material such as steel coated with a soft metal alloy and at least one surface layer which remains in contact with the lubricating oil film.

[005] It is important to note that it is not just the surface layer which is important. The function of the layers is brought about through the interaction between them, each having a specific role in the performance of the bearing, as well as a function in respect of the adjacent layer. Furthermore bearings are usually provided with more than one layer with a view to prolonging service life.

[006] Typically the first layer offers lower performance both when accommodating small misalignments between the surfaces of the bearing and the surface of the crankshaft, and in its ability to accommodate particles present in the oil film which give rise to scratching or wear of the surfaces.

[007] With such a concern in mind solutions whose development comprises several layers, each of which has a defined function with a view to improving performance, have been proposed.

[008] One of these solutions takes the form of the use of two-metal or three-metal bearings. A two-metal bearing generally comprises an intermediate alloy layer and a friction-resistant layer. Three-metal bearings generally comprise a layer of bronze followed by a diffusion-prevention barrier and a friction-resistant layer. In both cases there is a steel base layer. The main characteristic of these bearings is the advantage of withstanding a high loading capacity. However their disadvantage is that the metal surface layer may have little lubrication and consequently little sensitivity to great variations or discontinuities in the oil film, resulting in potential deterioration of the bearing and compromising long-term performance, prejudicing the functioning of the engine, or even resulting in its failure .

[009] British document GB2465852 describes a bearing comprising a first layer and a polymer surface layer. The polymer surface layer described contains additives which reduce friction, comprising a matrix containing 5% to 15% by volume of metal powder, preferably selected from a group comprising aluminum, copper, silver, tungsten and stainless steel, 1% to 15% by volume of a fluoropolymer, preferably PTFE or FEP, the remainder being a polyamide-imide resin having an average thickness of 9 to 12 microns. In a first configuration the first layer described comprises a bronze alloy containing tin and nickel and in a second configuration it comprises an aluminum alloy containing tin, copper, nickel and silicon, in a thickness of 300 microns .

[0010] It should be noted that the major characteristic of the bearing described lies in the polymer surface layer, which undergoes minimum wear, and has a higher loading capacity. However the bearing disclosed in this British document may have reduced functionality if there is excessive wear of the polymer layer. The first layer has a simpler composition and is therefore a layer having reduced functionality when in contact with the shaft, being effective for possible emergency contact situations, but not in the nature of a main wearing layer. If the polymer surface layer is damaged the first layer will not be sufficiently lubricated for the entire life of the bearing, reducing accommodation to deformation and misalignments, thus reducing the loading capacity of the bearing. If this disadvantage is combined with the increase in demand for internal combustion engines with higher loadings, this bearing will undoubtedly have limited application once the first layer is exposed.

[0011] It is therefore necessary to have a bearing which is capable of ensuring excellent functioning for a loading capacity of between 85 MPa and 120 MPa at a competitive price, that is for the market in which engines work with loadings of less than 150 MPa, as well as offering a bearing having an improved service life so that when the layer responsible for the friction interface is consumed the layer immediately below maintains the minimum friction properties required for performance under working loads to be sufficient to ensure robust functioning of the engine.

Objects of the invention

[0012] It is therefore one object of this invention to provide a bearing which is capable of reconciling the various characteristics responsible for the durability of the bearing, while also achieving an increase in loading capacity.

[0013] It is also an object of the invention to provide a bearing comprising at least a first layer comprising a bronze alloy containing bismuth so that this layer can act as an emergency surface layer with greater robustness when there is excessive wear of the polymer surface layer.

[0014] It is also an object of the invention to provide a bearing comprising at least one polymer surface layer constituted among other elements of a soft metal alloy.

[0015] And finally one object of the invention is to provide a bearing comprising at least one first layer comprising a cast bronze alloy to improve conformability, accommodating the deformations and misalignments which may occur during the bearing's useful life.

Brief description of the invention

[0016] This invention relates to a bearing for internal combustion engines provided with a ferrous base material onto which there is applied a first layer and a surface layer, the surface layer acting as an interface between the lubricating fluid and the first layer, the first layer comprising a bronze alloy containing 1% to 5% by volume of bismuth in its composition, the surface layer comprising a poly-imide- amide matrix provided with a soft metal, a fluoropolymer and a silane-based material, the surface layer being subject to wear and the first layer optionally acting as an interface between the lubricating fluid and the base material.

[0017] The objects of this invention also comprise a process for obtaining a bearing comprising the stages of:

[0018] stage i) plastic shaping of a ferrous base material having a thickness of between 1000 and 5000 microns ;

[0019] stage ii) casting a first layer onto the base material, the first layer comprising a bronze alloy containing 1% to 5% by volume of bismuth and having a thickness of between 100 and 500 microns; and

[0020] stage iii) spraying a surface layer comprising a poly-imide-amide polymer matrix provided with a soft metal, a fluoropolymer and a silane-based material, the surface layer having a thickness of between 5 and 20 microns . [0021] This invention also relates to an internal combustion engine comprising at least one bearing as defined above.

Brief description of the drawings

[0022] This invention will be described more particularly below on the basis of an embodiment illustrated in the drawings. The drawings show:

[0023] Figure 1 - a bearing with a representation of the layers according to this invention;

[0024] Figure 2 - a representation of the layers of the bearing according to this invention;

[0025] Figure 3 - a photograph of the layers of the bearing according to this invention.

Detailed description of the drawings

[0026] Figures 1 to 3 show a view of a bearing 5 according to this invention in transverse cross- section. Preferentially, but not compulsorily, bearing 5 according to this invention comprises a ferrous base material 10 to which there is applied a first layer 1 of a bronze alloy containing bismuth. First layer 1 receives a surface layer 2 comprising a poly-imide- amide polymer matrix containing a soft metal, a fluoropolymer and a silane-based material.

[0027] With reference to the special features of bearing 5 according to this invention it will be noted that base material 10 comprises a ferrous alloy, preferably a low or medium carbon steel, in a thickness of between 1 mm and 5 mm. [0028] With regard to first layer 1, its composition is preferably 3% to 8% tin, 1% to 5% bismuth, 0.5% to 3% nickel, the remainder being copper, in a thickness of 100 to 500 microns.

[0029] More specifically polymer surface layer 2 comprises a poly-imide-amide matrix provided with a soft metal, a fluoropolymer and a silane-based material .

[0030] Preferably surface layer 2 has a concentration of 1 to 14% by volume of soft metal, more preferably 11 to 14%, with an ideal concentration of 12.5%. The soft metal may be selected from alloys of aluminum, copper, copper alloys, silver, tungsten and stainless steel.

[0031] Thus preferably but not compulsorily surface layer 2 has a concentration of between 2 and 8% by volume of fluoropolymer . This fluoropolymer may be selected from polytetrafluoroethylene and fluorinated ethylene-propylene; preferably the fluoropolymer in surface layer 2 is polytetrafluoroethylene (PTFE) in a quantity of 5.7%. It will be noted that the use of this fluoropolymer reduces the friction coefficient of the bearing and improves its lubricating properties.

[0032] The polymer matrix comprising surface layer 2 also contains a silane material. These materials promote stability of the matrix and adhesion of the material to first layer 1 when sprayed. Surface layer 2 preferably has a concentration of 3 to 6% by volume of a silane material or a mixture of silane materials, preferably 4.8%.

[0033] The polymer matrix in surface layer 2 also comprises a quantity of less than 0.1% of other elements, the remainder being poly-imide-amide, which is normally present in a quantity of 77%. [0034] Finally the thickness of surface layer 2 is between 5 and 20 microns, preferably a thickness of 11 microns .

[0035] The combination between first layer 1 and surface layer 2 of bearing 5 achieves loading capacity values of more than 85 MPa, alternatively withstanding loads of 110 MPa, alternatively supporting loads up to a maximum of 130 MPa.

[0036] Bearing 5 preferably operates with loadings from 85 MPa to 110 MPa.

[0037] In cases where there is a local disturbance in bearing 5 deriving from the high loading and high speed, the impact may go beyond polymer surface layer 2. In this respect the construction configuration of bearing 5 according to this invention works so that layer 1 is capable of absorbing some of the impacts involved in performing its function.

[0038] First layer 1 has bismuth in its composition, and the main function of this is to provide solid lubrication for bearing 5 if polymer surface layer 2 suffers excessive wear and exposes first layer 1 comprised of bronze alloy.

[0039] In addition to this the presence of bismuth in the composition of the cast bronze alloy of first layer 1 has the result that during this process the necessary hardness for functioning is achieved and therefore there is greater conformability to deformations and misalignments which may occur over the service life of bearing 5.

[0040] In addition to conformability, the fact that bearing 5 goes through a casting process ensures greater compatibility with the internal combustion engine's crankshaft, on account of its lesser hardness. Thus this invention not only relates to providing a first layer 1 which can act as an optional surface layer, but also a layer which improves the behavior of bearing 5 when it is working because of the better conformability of first layer 1.

[0041] Thus it should be noted that one of the great advantages of this invention comprises application of first layer 1 by casting, which simultaneously raises the ability of this first layer 1 to have improved performance when acting jointly with surface layer 2, and when the latter no longer exists ensures a lubricating function for bearing 5, guaranteeing the double effect of increasing its service life.

[0042] Thus the casting process applied to first layer 1 makes it possible both to use bismuth in the chemical composition of the bronze alloy and to endow first layer 1 with better conformability properties in relation to the hardness achieved during the process.

[0043] Thus bearing 5 according to this invention has two functional layers, as both act to improve the properties of bearing 5.

[0044] These two functional layers 1 and 2 ensure a bearing 5 which has a high loading capacity.

[0045] Although one preferred embodiment has been described it should be understood that the scope of this invention covers other possible variations, being limited only by the content of the appended claims, including possible equivalents.