Sintered alloy bearing and method for manufacturing sintered alloy bearing

Abstract

A sintered alloy bearing 5 includes: a bearing body made of a sintered alloy, obtainable by compressing a raw material powder to form a compressed powder body and sintering the compressed powder body; and a lubricant impregnated into the internal pores of the bearing body. The bearing body has a composition having 1.0 to 5.0 wt.% of Cu, 0.4 to 2.0 wt.% of Sn, 0 wt.% or 0.6 to 3.0 wt.% of C as free carbon, with the balance being Fe and unavoidable impurities. The bearing body further has an Fe structure in which a ferrite structure occupies 90% or more in terms of area ratio. The lubricant contains, as a main component, ethylene glycol to which one or more rust prevention components, selected from the group consisting of aliphatic dibasic acids, phosphoric acid, thiazoles and benzoic acid, are added. The lubricant is adjusted to be weakly alkaline.

Description

Sintered alloy bearing and method for manufacturing sintered alloy bearing

[0001] The present invention relates to a sintered alloy bearing and a method for manufacturing a sintered alloy bearing.

[0002] For example, water pumps are used in automobile engines, inverters, batteries, cooling water circulation in fuel cells, water heaters, and hot water circulation in floor heating systems. As a water pump, an electric type is generally used in which an impeller is rotatably supported on a fixed shaft, and the impeller having a permanent magnet fixed thereto can be rotated by a magnetic field generated by a coil (see, for example, Patent Document 1).

[0003] In the above-mentioned electric water pump (hereinafter referred to as electric water pump), a sliding bearing is interposed between the impeller and the fixed shaft, and the sliding bearing rotates integrally with the impeller, thereby enabling rotational support of the impeller. Carbon bearings or resin bearings are used for this bearing (see, for example, Patent Document 2). Alternatively, a sintered alloy bearing containing Cu as a main component has been proposed as a sliding bearing for shaft support of fluid pumps such as motor-driven water pumps, oil pumps, and fuel pumps (see Patent Document 3).

[0004] Japanese Patent No. 4936258, Japanese Patent Application Laid-Open No. 2015-183650, Japanese Patent Application Laid-Open No. 2019-131834

[0005] Among the above-mentioned types of bearings, resin bearings are the most preferable in terms of cost. On the other hand, along with the higher performance of various devices in recent years, the performance required for bearings has also been further improved. Specifically, with the increasing demand for higher efficiency and higher output of water pumps, not only sliding properties but also wear resistance and further improvement of durability are required for bearings. Therefore, it has become difficult to improve the sliding properties and durability to the required level within a limited cost range with resin bearings alone.

[0006] In contrast, sintered alloy bearings offer superior wear resistance compared to resin bearings, allowing them to withstand the increased load on the bearings associated with higher water pump output and ensuring good sliding characteristics over extended periods. Furthermore, sintered alloy bearings have numerous internal pores. By pre-impregnating these pores with lubricating oil, continuous lubrication can be supplied to the sliding surface with the mating material, preventing lubrication failures. Additionally, while corrosion resistance is a concern when using metal bearings underwater, sintered metal bearings with a copper-based alloy structure (primarily composed of copper), as described in Patent Document 3, eliminate this corrosion resistance issue. However, manufacturing bearings with a sintered alloy primarily composed of expensive copper negates the cost savings achieved through powder metallurgy. Therefore, bearings with this configuration are not suitable for mass-produced, versatile products.

[0007] In view of the above circumstances, the technical problem to be solved by the present invention is to provide a sliding bearing that can exhibit excellent sliding properties and corrosion resistance without causing lubrication problems, while keeping production costs as low as possible.

[0008] The aforementioned problems are solved by the sintered alloy bearing according to the present invention. Specifically, this bearing comprises a bearing body made of a sintered alloy obtained by compressing raw material powder to form a compact and sintering this compact, and a lubricant impregnated into the internal pores of the bearing body. The bearing body has a composition of Cu: 1.0 wt% or more and 5.0 wt% or less, Sn: 0.4 wt% or more and 2.0 wt% or less, C as free carbon: 0 wt% or 0.6 wt% or more and 3.0 wt% or less, the remainder being Fe and unavoidable impurities, and has an Fe structure in which the ferrite structure accounts for 90% or more by area ratio. The lubricant is characterized in that it is mainly composed of ethylene glycol with one or more rust-preventive components selected from the group consisting of aliphatic dibasic acids, phosphoric acid, thiazoles, and benzoic acid added, and is adjusted to be weakly alkaline.

[0009] In this specification, "area ratio" refers to the proportion of the area of ​​each tissue to the total area observed.

[0010] The inventors, in applying sintered alloy bearings to sliding bearings used underwater, such as bearings for electric water pumps, reviewed not only the cost but also the composition of the sintered alloy bearing body, manufacturing conditions such as sintering temperature, and lubricant composition. As a result, they found a combination of bearing body and lubricant suitable for the above-mentioned applications while keeping manufacturing costs low enough to enable mass production for general use. Specifically, in the sintered alloy bearing according to the present invention, the bearing body is made of a sintered alloy mainly composed of Fe, with Cu, Sn, and C as free carbon in predetermined proportions, and the ferrite structure is predominantly Fe. The lubricant impregnated into this bearing body is mainly composed of ethylene glycol with predetermined rust-preventive components added, and is adjusted to be weakly alkaline. By configuring the bearing body as described above, the required strength and sliding characteristics can be ensured while keeping material costs as low as possible. In addition, by impregnating the bearing body with a lubricant primarily composed of ethylene glycol with added rust-preventive components and adjusted to be weakly alkaline, it is possible to compensate for the corrosion resistance of the Fe structure, which has corrosive problems, thereby improving the overall corrosion resistance of the bearing while obtaining excellent lubrication properties. Furthermore, since a lubricant primarily composed of ethylene glycol can be used over a much wider temperature range compared to conventional lubricants used in sintered alloy bearings, such as ester-based lubricants, it is possible to broaden the application fields of the bearing according to the present invention.

[0011] Furthermore, in the sintered alloy bearing according to the present invention, the lubricant may be a coolant for automobile engines.

[0012] The lubricant constituting the sintered alloy bearing according to the present invention is mainly composed of ethylene glycol with a predetermined rust-preventive component added, and has a composition equal to or very close to that of automotive engine coolants such as LLC (Long Life Coolant), and is compatible with the bearing body. Therefore, a sintered alloy bearing equipped with the bearing body according to the present invention can exhibit excellent sliding and lubrication characteristics even when the lubricant is the same liquid as automotive engine coolant.

[0013] As described above, the sintered alloy bearing according to the present invention can be mass-produced at low cost while possessing excellent corrosion resistance, durability, and sliding properties. Therefore, it can be suitably provided as a water pump, for example, comprising this sintered alloy bearing, a fixed shaft, and an impeller that is rotatably supported on the fixed shaft together with the sintered alloy bearing, with the sintered alloy bearing interposed between them.

[0014] Based on the above, the present invention makes it possible to provide a sliding bearing that exhibits excellent sliding properties and corrosion resistance without causing lubrication problems, while keeping production costs as low as possible.

[0015] This is a cross-sectional view of the main part of an electric water pump equipped with a sintered alloy bearing according to one embodiment of the present invention. This is a flowchart showing the manufacturing process of the sintered alloy bearing shown in Figure 1.

[0016] One embodiment of the present invention will be described below with reference to the drawings.

[0017] Figure 1 shows a cross-sectional view of an electric water pump 1 according to this embodiment. The water pump 1 comprises a casing 2, a fixed shaft 3 fixed to the casing 2, an impeller 4 rotatably supported by the fixed shaft 3, a sintered alloy bearing 5 disposed between the fixed shaft 3 and the impeller 4 and rotatable together with the impeller 4 as a sliding bearing, a permanent magnet 6 fixed to the impeller 4, and a coil 7.

[0018] When current is passed through the coil 7, the excitation force generated between the coil 7 and the permanent magnet 6 causes the permanent magnet 6 to rotate. This rotation causes the impeller 4, to which the permanent magnet 6 is fixed, to rotate around the fixed shaft 3. This rotation of the impeller 4 draws in the coolant to be pumped (for example, coolant for an automobile engine such as LLC) in a direction D1 along the rotation axis of the impeller 4, and discharges the coolant in a direction D2 perpendicular to the rotation axis. In addition, a sintered alloy bearing 5 provided on the inner circumference of the impeller 4 rotates together with the impeller 4, so that the impeller 4 is rotatably supported on the fixed shaft 3 via the sintered alloy bearing 5.

[0019] The sintered alloy bearing 5 comprises a bearing body made of sintered alloy and a lubricant impregnated into voids (internal voids) formed inside the bearing body through voids opened on the surface of the bearing body. Here, the shape of the bearing body is the same as the shape of the sintered alloy bearing 5, and is formed in a cylindrical shape as shown in Figure 1, for example. In this illustrated example, the bearing body (sintered alloy bearing 5) has a shape in which the radial dimensions are constant on both the inner and outer circumferential surfaces, but of course, it is possible to have other shapes. For example, although not shown in the illustration, it may have a shape in which a large-diameter section with a relatively large outer diameter and a small-diameter section with a relatively small outer diameter are integrally located at one end in the axial direction.

[0020] The bearing body has a sintered alloy structure with Fe as the main component (in other words, with an Fe structure as the main structure). More specifically, the bearing body of the sintered alloy bearing 5 has the following composition: Cu: 1.0 wt% or more and 5.0 wt% or less, Sn: 0.4 wt% or more and 2.0 wt% or less, C as free carbon: 0 wt% or 0.6 wt% or more and 3.0 wt% or less, the remainder being Fe and unavoidable impurities. Furthermore, of the Fe structure that makes up the majority of the bearing body, the ferrite structure accounts for 90% or more by area ratio.

[0021] If the Cu content is less than 1.0 wt%, or the Sn content is less than 0.4 wt%, it will lead to a decrease in the strength of the sintered alloy bearing 5 (bearing body). Also, if the Cu content is more than 5.0 wt%, or the Sn content is more than 2.0 wt%, it will be expensive compared to the required strength. Furthermore, because the ferrite structure exhibits soft and ductile properties, it can minimize its aggressiveness towards the mating component (in this case, for example, the fixed shaft 3).

[0022] If the free carbon (C) content is less than 0.6 wt%, the sliding properties deteriorate, and if the C content is more than 3.0 wt%, the formability of the bearing deteriorates. On the other hand, when used in linear sliding applications, the presence of free carbon in the bearing can cause the free carbon to adhere to the mating component, which can lead to localized fluctuations in the coefficient of friction and potentially cause vibration during sliding.

[0023] Sintered mechanical parts have a density of 6.2 g / cm³. 3The following low-density components, 6.3 / cm 3 ~6.7 g / cm 3 Medium-density component, 6.8 g / cm³ 3 The components can be divided into the high-density parts described above. In this embodiment, the density of the bearing body of the sintered alloy bearing 5 is 5.4 g / cm³ in dry condition. 3 The above and 7.4 g / cm³ 3 It will be set within the following range.

[0024] The density ratio of the bearing body of the sintered alloy bearing 5 is set to, for example, 70% or more and 95% or less, preferably 70% or more and 90% or less, and more preferably 70% or more and 80% or less. Here, the density ratio is the relative value of the density of a porous material such as a sintered alloy, and is the ratio of the density of the porous material to the density of the same material if it had the same composition as the porous material and there were no voids such as holes inside the solid, and is expressed as a percentage (%).

[0025] The surface opening ratio (porosity) of the bearing surface of the sintered alloy bearing 5 (for example, the inner circumferential surface of the bearing body) is set to, for example, 5% or more and 50% or less. Here, the surface opening ratio refers to the ratio of the sum of the areas of each opening (total area) to the area per unit area. Increasing the surface opening ratio of the sintered alloy bearing 5 promotes the supply of lubricant through self-lubrication, preventing lubrication failure in the high rotational speed range and improving lubrication characteristics. On the other hand, decreasing the surface opening ratio prevents the escape of lubricant, enabling the formation of a stable fluid film of lubricant and improving lubrication characteristics in the low rotational speed range. From the above viewpoint, it is preferable to set the surface opening ratio within the above range.

[0026] The lubricant has ethylene glycol as its main component and contains a predetermined rust inhibitor. One or more rust inhibitors can be selected from the group consisting of aliphatic dibasic acids, phosphoric acid, thiazoles, and benzoic acid. A representative example of a selectable rust inhibitor is sebacic acid, an aliphatic dibasic acid.

[0027] Furthermore, the aforementioned rust-preventive component is added to ethylene glycol in an appropriate amount such that it is, for example, 1.0 wt% or more and 5.0 wt% or less of the total lubricant.

[0028] The lubricant with the above configuration is adjusted to be weakly alkaline. The means of adjustment are, in principle, arbitrary, and for example, by adding a basic solution or sodium hydroxide or potassium hydroxide, the lubricant is adjusted to be weakly alkaline, more specifically, so that the pH is greater than 7.0 and less than 8.5, preferably greater than 7.0 and 8.0 or less.

[0029] The lubricant with the above configuration may be, for example, a 0-70% aqueous solution with water as the solvent. That is, the above lubricant may be used after being diluted to a predetermined concentration (it may be impregnated into the bearing body), or it may be used without being diluted with a solvent.

[0030] The lubricant (including in aqueous solution form) of the above configuration is impregnated into the sintered alloy bearing body such that, for example, the impregnation rate is 10 vol% or more and 25 vol% or less. Here, the impregnation rate is the dimensionless percentage value obtained by dividing the volume of the impregnated lubricant by the volume of the sintered alloy bearing 5 (bearing body). If the impregnation rate is less than 10 vol%, the lubricant will be relatively scarce, that is, there will be insufficient lubricant between the bearing body and the mating material (in this case, the fixed shaft 3), which can lead to a decrease in bearing performance and, consequently, a decrease in bearing life. Also, if the impregnation rate is more than 25 vol%, it will be necessary to lower the density (density ratio) of the bearing body in order to increase the number of voids inside the bearing, which can lead to a decrease in the strength of the sintered alloy bearing 5. From the above viewpoint, it is preferable to set the impregnation rate of the lubricant to 10 vol% or more and 25 vol% or less.

[0031] The sintered alloy bearing 5 with the above configuration is manufactured, for example, through a powder compaction process S1, a sintering process S2, and an impregnation process S3. In this case, although not shown in the figures, one or both of the following may be performed after the sintering process S2 and before the impregnation process S3: a dimensional sizing process to adjust the dimensions of the bearing body as a sintered body, and a surface sizing process to adjust the size of the voids opening on the inner circumferential surface of the bearing body, which will become the radial bearing surface. The following describes each process in detail.

[0032] (S1) Powder compaction process First, raw material powders that will be used as the material for the sintered alloy bearing 5, which will be the final product, are prepared and compressed into a predetermined shape by die press molding. First, as the raw material powder, a mixture is prepared in which Fe powder is the main component, and Cu powder, Sn powder, and C powder such as graphite, which will be free carbon, are added to this Fe powder.

[0033] Here, as the Fe powder, reduced Fe powder, atomized Fe powder, etc., can be used. In this embodiment, it is preferable to use reduced Fe powder made from Fe ore. Here, reduced Fe powder is Fe powder produced by reducing Fe ore or mill scale (oxidized Fe) with coke or the like (carbonizing agent), and then heat-treating it in a hydrogen atmosphere, and has voids in the particles. Atomized Fe powder is Fe powder produced by pulverizing and cooling molten steel with high-pressure water, and then heat-treating it in a hydrogen atmosphere, and has no voids in the particles and is of higher purity than reduced Fe powder. Because atomized Fe powder has a spherical powder shape, when compacted, the Fe powder particles do not intertwine well with each other, so the strength of the compact cannot be secured, and its impregnation properties are also inferior. Furthermore, while reduced Fe powder made from mill scale has better moldability than reduced Fe powder made from Fe ore, when a low density setting is required, such as in bearings, it is difficult to obtain sufficient compact strength.

[0034] As an example of a suitable blending ratio (raw material powder composition), a composition can be given in which Cu powder is 1.0 wt% or more and 5.0 wt% or less, Sn powder is 0.4 wt% or more and 2.0 wt% or less, C powder as free carbon is 0 wt% or 0.6 wt% or more and 3.0 wt%, and the remainder is Fe powder and unavoidable impurities. Furthermore, Fe powder with a maximum particle size of 212 μm, Cu powder with a maximum particle size of 106 μm, Sn powder with a maximum particle size of 75 μm, and C powder with a maximum particle size of 75 μm are preferably used. Of course, it is not necessary to completely exclude components other than Cu powder, Sn powder, and C powder, and various molding aids, such as components to improve mold release (metal soap, etc.), may be added in appropriate amounts as needed.

[0035] Then, although not shown in the diagram, the raw material powder is compressed using a molding die which consists of a die, a core pin inserted into the hole of the die, a lower punch positioned between the die and the core pin and configured to move up and down relative to the die, and an upper punch configured to be displaced (moved up and down) relative to both the die and the lower punch. In this case, the raw material powder is filled into the space formed by the inner circumferential surface of the die, the outer circumferential surface of the core pin, and the upper end surface of the lower punch. With the lower punch fixed, the upper punch is lowered, and the filled raw material powder is pressurized in the axial direction. Then, while pressurizing, the upper punch is lowered to a predetermined position, and the raw material powder is compressed to a predetermined axial dimension, thereby forming a compact. In this case, the compact is formed such that the density ratio of the compact is, for example, 70% or more and 80% or less.

[0036] (S2) Sintering process After obtaining a compacted body as described above, a sintered body is obtained by sintering this compacted body at a temperature corresponding to the type of raw material powder (for example, the melting point of the main component metal). In this embodiment, sintering is performed in a predetermined atmosphere and predetermined temperature conditions. The predetermined atmosphere can be a vacuum, a reducing gas, or an inert gas, and can be selected in various ways depending on the metal powder used. In this case, the predetermined temperature conditions are greater than 850°C and less than 900°C (not including 850°C and 900°C, for example, around 860°C to 890°C), and this temperature is maintained for a predetermined time, for example, 5 minutes.

[0037] By subjecting the compacted powder to a sintering treatment at a temperature exceeding 850°C but below 900°C, the resulting sintered bearing body can be constructed without a network-like cementite structure. If the sintering temperature is below 850°C, sintering does not proceed sufficiently, and if the sintering temperature is above 900°C, carbon diffuses into the Fe, increasing the pearlite and cementite structures and resulting in higher hardness. Here, the pearlite structure is a eutectoid structure of ferrite (α-iron) and cementite (Fe3C). The ferrite and cementite are layered.

[0038] (S3) Impregnation process The sintered alloy bearing 5 is completed by impregnating the internal pores of the sintered body (bearing body) obtained as described above with lubricant. The impregnation of the internal pores of the sintered alloy bearing 5 with lubricant is carried out, for example, by immersing the sintered alloy bearing 5 in a lubricant bath filled with lubricant for a certain period of time under a predetermined reduced pressure environment. At this time, in order to ensure that the lubricant impregnation is carried out reliably and in a short time, the impregnation work may be carried out with the lubricant heated.

[0039] As described above, in the sintered alloy bearing 5 according to this embodiment, the bearing body is made of a sintered alloy in which Fe is the main component and Cu, Sn, and C as free carbon are each contained in predetermined proportions, with the ferrite structure making up the majority of the Fe structure. The lubricant impregnated into the bearing body is a lubricant mainly composed of ethylene glycol with a predetermined rust-preventive component added, and adjusted to be weakly alkaline. By configuring the bearing body as described above, the required strength and sliding characteristics can be secured while keeping material costs as low as possible. In addition, by impregnating the bearing body with a lubricant mainly composed of ethylene glycol with a rust-preventive component added and adjusted to be weakly alkaline, it is possible to compensate for the corrosion resistance of the Fe structure, which has corrosive problems, and obtain excellent lubrication characteristics while improving the corrosion resistance of the entire bearing. Furthermore, since a lubricant mainly composed of ethylene glycol can be used over a much wider temperature range compared to conventional lubricants used in sintered alloy bearings, such as ester-based lubricants, it is possible to broaden the application fields of the bearing according to the present invention.

[0040] Although one embodiment of the present invention has been described above, the sintered alloy bearing according to the present invention is not limited to the above-described embodiment and can take any form within the scope of the present invention.

[0041] For example, in the present embodiment, the case where the sintered alloy bearing according to the present invention is applied to an electric water pump for circulating a coolant of an automobile engine is exemplified, but it is of course also possible to apply the present invention to other uses. For example, the present invention can be applied not only to water pumps for circulating cooling water for automobile inverters, batteries, or fuel cells, but also to sliding bearings for water pumps regardless of temperature, such as circulation of hot water in water heaters and floor heating equipment. Furthermore, since the present invention can be used in a wide temperature range, it can be applied to various sliding bearings regardless of industrial fields.

[0042] 1 Water pump 2 Casing 3 Fixed shaft 4 Impeller 5 Sintered alloy bearing 6 Permanent magnet 7 Coil

Claims

1. A sintered alloy bearing comprising a bearing body made of a sintered alloy obtained by compressing raw material powder to form a compact and sintering the compact, and a lubricant impregnated into the internal voids of the bearing body, wherein the bearing body has a composition of Cu: 1.0 wt% or more and 5.0 wt% or less, Sn: 0.4 wt% or more and 2.0 wt% or less, C as free carbon: 0 wt% or 0.6 wt% or more and 3.0 wt% or less, the remainder being Fe and unavoidable impurities, and has an Fe structure in which the ferrite structure accounts for 90% or more by area ratio, and the lubricant is mainly composed of ethylene glycol with the addition of one or more rust-preventive components selected from the group consisting of aliphatic dibasic acids, phosphoric acid, thiazoles, and benzoic acid, and is adjusted to be weakly alkaline.

2. The sintered alloy bearing according to claim 1, wherein the lubricant is a coolant for an automobile engine.

3. A water pump comprising a sintered alloy bearing according to claim 1 or 2, a fixed shaft, and an impeller that is rotatably supported on the fixed shaft together with the sintered alloy bearing with the sintered alloy bearing interposed therebetween.

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