Bush material

Abstract

To provide a bush member high in strength and corrosion resistance while maintaining a creeping characteristic.SOLUTION: A bush member 10 according to one embodiment comprises an Fe-based backing metal layer 12, and a bearing alloy layer 11 bonded to the backing metal layer 12. The bearing alloy layer 11 is a Cu-based alloy containing 25 to 45 mass% Zn, and has a Vickers hardness of 150 to 230 HV. The backing metal layer 12 has a Vickers hardness of 160 to 240 HV.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present embodiment relates to a bushing member used for a piston pin. [Background technology]

[0002] Conventionally, a Cu-based sliding member has been known as a bushing member for use in a piston pin, as disclosed in Patent Document 1. The sliding member disclosed in Patent Document 1 uses brass with a high Zn content as the bearing alloy layer. This ensures that the sliding member of Patent Document 1 has corrosion resistance against sulfur components that are generated as the temperature in the combustion chamber increases. However, as the temperature of the combustion chamber rises, the load on the piston pin increases, and further improvements in the strength of the bushing are required. Furthermore, unlike the bimetal described in Patent Document 1, the bushing is made of a single layer of brass bearing alloy, ensuring strength such as fatigue resistance. However, single-layer bushings have the problem of being susceptible to creep in environments where they are subjected to high loads. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 10-30137 Summary of the Invention [Problem to be solved by the invention]

[0004] Therefore, an object of the present invention is to provide a bushing member that has high strength and corrosion resistance while reducing the effects of creep. [Means for solving the problem]

[0005] In order to solve the above problems, one embodiment of the present invention provides a bushing member for use in a piston pin, the bushing member comprising an Fe-based backing metal layer and a bearing alloy layer bonded to the backing metal layer, wherein the bearing alloy layer is a Cu-based alloy containing 25 to 45 mass % Zn and has a Vickers hardness of 150 to 230 HV, and the backing metal layer has a Vickers hardness of 160 to 240 HV.

[0006] As a result, in the bushing member according to one embodiment, the bearing alloy layer is bonded to the Fe-based backing metal layer. Therefore, the bearing alloy layer is less susceptible to creep due to the integral backing metal layer. Furthermore, the bushing member according to one embodiment is made of a Cu-based alloy containing Zn, i.e., brass. Therefore, it has high resistance to sulfur components caused by additives contained in lubricating oil, reducing corrosion caused by these sulfur components. Furthermore, in the bushing member according to one embodiment, the hardness of the bearing alloy layer and the backing metal layer is set. Therefore, fatigue resistance is improved while maintaining workability to ensure high dimensional accuracy and roundness accuracy. Therefore, strength and corrosion resistance can be increased while maintaining creep characteristics. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic cross-sectional view showing a bushing member according to an embodiment; [Figure 2] 5 is a schematic diagram illustrating a manufacturing flow of a bushing member according to an embodiment. [Figure 3] 1 is a schematic diagram showing verification results of creep characteristics in examples and comparative examples of a bushing member according to an embodiment; [Figure 4] Schematic diagrams showing verification results of corrosion resistance in examples and comparative examples of the bushing member according to one embodiment. [Figure 5] Schematic diagrams showing verification results of fatigue resistance in examples and comparative examples of bushing members according to an embodiment. [Figure 6] Schematic diagram showing the test conditions for fatigue resistance testing DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, an embodiment of a bushing member used in a piston pin will be described in detail with reference to the drawings. As shown in FIG. 1, bushing member 10 includes bearing alloy layer 11 and backing metal layer 12. Bushing member 10 is used in a piston pin that connects a piston and a connecting rod of an internal combustion engine (not shown). Bushing member 10 is formed in a cylindrical shape, with bearing alloy layer 11 located on the inner periphery and backing metal layer 12 located on the outer periphery. The surface of bearing alloy layer 11, i.e., the inner periphery of bushing member 10, forms sliding surface 13 that slides against a mating member.

[0009] The back metal layer 12 is formed of an Fe-based alloy such as steel. The back metal layer 12 has a Vickers hardness of 160 to 240 HV. In this specification, the upper and lower limits of numerical ranges are both within the range. If the Vickers hardness of the back metal layer 12 is less than 160, it becomes difficult to ensure the fatigue resistance required for the bushing member 10 of the piston pin. On the other hand, if the Vickers hardness of the back metal layer 12 exceeds 240 HV, workability decreases.

[0010] Bearing alloy layer 11 is integrally bonded to backing metal layer 12 and is formed of a Cu-based alloy containing 25 to 45 mass % Zn. In other words, bearing alloy layer 11 is formed of brass. The Zn content of bearing alloy layer 11 is preferably 35 to 45 mass % to ensure higher corrosion resistance. Bearing alloy layer 11 may contain additive elements such as Sn and P in addition to Zn. In the case of bushing member 10 of this embodiment, bearing alloy layer 11 is more preferably an alloy of Zn and Cu excluding unavoidable impurities.

[0011] Bearing alloy layer 11 has a Vickers hardness of 150 to 230 HV. If the Vickers hardness of bearing alloy layer 11 is less than 150 HV, it becomes difficult to ensure the fatigue resistance required for piston pin bushing member 10. On the other hand, if the Vickers hardness of bearing alloy layer 11 exceeds 230 HV, workability decreases and seizure resistance also decreases.

[0012] The Vickers hardness of back metal layer 12 is preferably at least 0.9 times the Vickers hardness of bearing alloy layer 11. In this embodiment, it is preferable that bearing alloy layer 11 and back metal layer 12 have similar hardnesses, and it is more preferable that back metal layer 12 is slightly harder than bearing alloy layer 11. By making the hardness of bearing alloy layer 11 and back metal layer 12 similar, processing that ensures roundness during processing of bushing member 10 can be facilitated. Furthermore, if bearing alloy layer 11 or back metal layer 12 has excessive hardness, it may become difficult to perform processes such as press-fitting bushing member 10 into, for example, a connecting rod or to perform cutting after press-fitting. Therefore, the upper limit of the Vickers hardness of bearing alloy layer 11 and back metal layer 12 is set to 240 HV.

[0013] Next, a method for manufacturing the bushing member 10 having the above configuration will be described. 2, bushing member 10 is manufactured by pressing plate member 21, which will become bearing alloy layer 11, and plate member 22, which will become backing metal layer 12, together. After being stacked, plate members 21 and 22 are pressed together by rollers 23 until the total thickness of the stacked members reaches 40 to 60%.

[0014] The laminate 24 bonded by pressing is heated to 550 to 680°C and subjected to diffusion annealing. This heating promotes diffusion bonding between the plate members 21 and 22 in the laminate 24, resulting in a strong bond between the plate members 21 and 22. Meanwhile, the hardness of the plate member 21 that will become the bearing alloy layer 11 is reduced by the diffusion annealing. As described above, if the Vickers hardness of the bearing alloy layer 11 is less than 150 HV, it is difficult to ensure the fatigue resistance of the bearing alloy layer 11. Therefore, the heated laminate 24 is pressed by the roller 25 until the total thickness of the laminate 24 is reduced to 3 to 30%. The pressing process may be performed in one step or in two or more steps. In this case, the roller 25 may press the plate member 21 side of the laminate 24 that will become the bearing alloy layer 11, or may press both sides of the laminate 24. As a result, the formed bearing alloy layer 11 is hardened to a Vickers hardness of 150 HV or more.

[0015] As a result, the plate member 21 that will become the bearing alloy layer 11 and the plate member 22 that will become the back metal layer 12 are bonded together to form a laminate 24. The laminate 24 is then formed into a cylindrical bushing member 10. In the method for manufacturing the bushing member 10 according to this embodiment, the plate member 21 that will become the bearing alloy layer 11 and the plate member 22 that will become the back metal layer 12 are bonded together by pressure. Therefore, the manufacturing process of the bushing member 10 does not include a process that would cause the back metal layer 12 to have a hard, brittle structure, such as rapid cooling. As a result, the manufacturing method for the bushing member 10 according to this embodiment can reduce the brittleness of the manufactured bushing member 10 and increase its strength. Furthermore, the back metal layer 12 of the bushing member 10 manufactured by this manufacturing method has a Vickers hardness of 240 HV or less, thereby improving its workability. As a result, the bushing member 10 can be formed into a cylindrical shape with high dimensional and shape accuracy. In addition, the bushing member 10 can be easily worked, for example, when it is press-fitted into a connecting rod and when it is cut or polished after being press-fitted.

[0016] Next, examples of the bushing member 10 according to the above embodiment will be described. (Verification of creep properties) As shown in Fig. 3, Example 1 of bushing member 10 has a laminated structure of bearing alloy layer 11 and back metal layer 12 as described above. On the other hand, Comparative Example 1 for comparison has the same dimensions as Example 1, but the portion corresponding to back metal layer 12 is also formed from a single layer of brass, which becomes bearing alloy layer 11. In other words, Comparative Example 1 is a so-called solid material formed entirely from brass.

[0017] The creep characteristics of the bushing members 10 of Example 1 and Comparative Example 1 were verified using a pull-out load. The pull-out load is the load required to pull the bushing member 10 out of a mating member after the bushing member 10 has been press-fitted into the mating member. The bushing members 10 of Example 1 and Comparative Example 1 that had been press-fitted into the mating member were heated to 190°C and, after a preset heating time had elapsed, cooled to room temperature. After cooling, the pull-out loads of the bushing members 10 of Example 1 and Comparative Example 1 were measured. Figure 3 shows the rate of change in the pull-out load after heating, assuming that the pull-out load before heating was "1.00."

[0018] As is clear from FIG. 3 , in Example 1, the pull-out load tends to increase with increasing heating time, but the change in pull-out load is small. On the other hand, in Comparative Example 1, the pull-out load significantly decreases with increasing heating time. As such, the bushing member 10 of Example 1 is less susceptible to creep than Comparative Example 1. This is because the bushing member 10 of Example 1 includes an Fe-based backing layer 12, which is less susceptible to creep, on the outer circumferential side of the bearing alloy layer 11. In contrast, Comparative Example 1, which is integrally formed of brass, is significantly susceptible to creep. Note that in the bushing member 10 of this embodiment, the bearing alloy layer 11 and the backing layer 12 are bonded together. Therefore, the Zn content of the bearing alloy layer 11 does not affect the creep of the bushing member 10. Therefore, the bearing alloy layer 11 of the bushing member 10 of this embodiment can reduce the effect of creep regardless of the Zn content.

[0019] (Verification of corrosion resistance) The corrosion resistance of bushing member 10 was verified using Examples 2 to 4 and Comparative Examples 2 and 3, as shown in Fig. 4. In Examples 2 to 4, the Zn content in bearing alloy layer 11 made of brass was controlled. In Comparative Example 2, which is used for comparison, the Zn content in bearing alloy layer 11 is lower than in Examples 2 to 4. In Comparative Example 3, the bearing alloy layer is made of bronze to which Sn is added instead of Zn.

[0020] The corrosion resistance of each sample of Examples 2 to 4 and Comparative Examples 2 and 3 was verified based on the change in mass of each sample. The change in mass increases as corrosion progresses in each sample. In other words, the mass of each sample decreases as corrosion progresses. However, because the progress of corrosion depends on the surface area of ​​each sample, it is difficult to accurately determine the amount of corrosion in each sample by simply measuring the change in mass. Therefore, the change in mass per surface area of ​​each sample was measured as the amount of corrosion.

[0021] The corrosion resistance of each sample was verified by immersing it in lubricating oil at 190°C in a sealed container for 70 hours, which is similar to the operating conditions of an internal combustion engine. Several types of lubricating oil were used, including commercially available genuine products specified by the internal combustion engine manufacturer. These lubricating oils contain additives containing sulfur components in their molecules, for example, to improve performance and maintain quality. These additives can decompose as the temperature rises due to the harsh operating conditions of an internal combustion engine, causing the generation of sulfur components in their molecules. These generated sulfur components can cause corrosion in the bearing alloy layer 11 of the bushing member 10.

[0022] As is clear from FIG. 4, Examples 2 to 4, in which the Zn content of bearing alloy layer 11 is 25% or more, have higher corrosion resistance than Comparative Example 2, in which the Zn content is 20%. Furthermore, Comparative Example 3, in which the bearing alloy layer is made of bronze, is more susceptible to corrosion than Examples 2 to 4. These findings suggest that bushing member 10 of this embodiment, in which the Zn content is 25% or more, can improve corrosion resistance. In particular, as can be seen from a comparison of Examples 2 and 3 with Example 4, bushing member 10, in which the Zn content is 35% or more, can improve corrosion resistance.

[0023] (Verification of fatigue resistance) The fatigue resistance of bushing member 10 was verified using Examples 5 to 9 and Comparative Examples 4 to 6, as shown in Figure 5. In Examples 5 to 9 and Comparative Examples 4 to 6, the hardness of bearing alloy layer 11 and the hardness of backing metal layer 12 were controlled to verify fatigue resistance. Figure 5 also shows an evaluation of the workability of bushing member 10 in addition to fatigue resistance.

[0024] The fatigue resistance of Examples 5 to 9 and Comparative Examples 4 to 6 was measured under the test conditions shown in FIG. 6. The fatigue resistance was measured based on the load at which fatigue occurred when a load was repeatedly applied to the sample while lubricating it with a lubricant under the conditions shown in FIG. 6. The lubricant was a commercially available lubricant for internal combustion engines, as exemplified above. The load applied to the sample was started at 100 MPa and increased by 10 MPa each time fatigue resistance was confirmed, up to 200 MPa. A sample with a fatigue-inducing load of 170 MPa or higher was deemed acceptable for fatigue resistance. The workability was evaluated based on whether the bushing member 10, formed from the bearing alloy layer 11 and the backing metal layer 12, could be machined to a degree that ensured appropriate dimensional accuracy and roundness. A sample with adequate workability but low yield was rated "good: ○", a sample with adequate workability and high yield was rated "excellent: ◎", and a sample with difficulty in adequate workability was rated "poor: ×".

[0025] As shown in FIG. 5 , in Examples 5 to 9, the hardness of the bearing alloy layer 11 is 150 to 230 HV, and the hardness of the back metal layer 12 is 160 to 240 HV. Furthermore, in Examples 5 to 8, the hardness of the back metal layer 12 is 0.9 times or more that of the bearing alloy layer 11. In contrast, in Example 9, the hardness of the back metal layer 12 is less than 0.9 times that of the bearing alloy layer 11. Furthermore, in Comparative Example 4, the hardness of the back metal layer 12 exceeds 240 HV. Comparative Examples 5 and 6 are both examples in which the hardness of the bearing alloy layer 11 and the back metal layer 12 is insufficient. The hardness of the bearing alloy layer 11 and the back metal layer 12 in Examples 5 to 9 and Comparative Examples 4 to 6 is controlled by the amount of change in thickness when the laminated bearing alloy layer 11 and back metal layer 12 are compressed, as described in the manufacturing method above.

[0026] As is clear from Figure 5, Examples 5 to 9 all exhibited high workability and sufficient fatigue resistance. In particular, Examples 5 to 8, in which the hardness of back metal layer 12 was 0.9 times or more that of bearing alloy layer 11, all achieved both high workability and sufficient fatigue resistance. On the other hand, Example 9, in which the hardness of back metal layer 12 was less than 0.9 times that of bearing alloy layer 11, exhibited sufficient fatigue resistance, but the yield for ensuring appropriate dimensional accuracy and roundness was reduced. This is because the hardness of back metal layer 12 was lower than that of bearing alloy layer 11, making it difficult to ensure accuracy when forming the bushing member 10 into a cylindrical shape.

[0027] In addition, in Comparative Example 4, the hardness of back metal layer 12 was excessively high at 248 HV, which deteriorated workability and made it difficult to ensure high dimensional accuracy of roundness for bushing member 10. Therefore, Comparative Example 4 was not suitable as bushing member 10, and fatigue resistance could not be measured. In both Comparative Examples 5 and 6, the hardness of bearing alloy layer 11 and back metal layer 12 was insufficient. Therefore, although workability was ensured in Comparative Examples 5 and 6, fatigue resistance was insufficient.

[0028] The present invention described above is not limited to the above-described embodiment, and can be applied to various embodiments without departing from the gist of the invention. [Explanation of symbols]

[0029] In the drawing, 10 denotes a bushing member, 11 denotes a bearing alloy layer, and 12 denotes a backing metal layer.

Claims

[Claim 1] an Fe-based backing layer; a bearing alloy layer bonded to the backing metal layer, The bearing alloy layer is a Cu-based alloy that is an alloy of 35 to 45 mass% Zn and Cu excluding unavoidable impurities; Vickers hardness is 182 to 230 HV, The backing metal layer is Vickers hardness is 200 to 240 HV, The Vickers hardness of the backing metal layer is 0.9 times or more the Vickers hardness of the bearing alloy layer. Bush component.

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