Bush member

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] This embodiment relates to a bush member used for a piston pin.

Background Art

[0002] Conventionally, as a bush member used for a piston pin, for example, a Cu-based sliding member disclosed in Patent Document 1 is known. The sliding member disclosed in Patent Document 1 uses brass having a high Zn content as a bearing alloy layer. Thereby, the sliding member of Patent Document 1 secures corrosion resistance against sulfur components generated as the temperature in the combustion chamber rises. However, as the temperature in the combustion chamber rises, the load applied to the piston pin increases, and further improvement in strength of the bush member is required. Also, unlike a bimetal such as that in Patent Document 1, by forming the bush member as a single layer of a brass bearing alloy layer, strength such as fatigue resistance is ensured. However, a single-layer bush member has a problem in that it is easily affected by creep in an environment where it receives a high load.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Therefore, an object is to provide a bush member having high strength and corrosion resistance while reducing the influence of creep.

Means for Solving the Problems

[0005] To solve the above problems, a bush member according to one embodiment is a bush member used for a piston pin including an Fe-based backing layer and a bearing alloy layer joined to the backing layer. The bearing alloy layer is a Cu-based alloy containing 25 to 45% by mass of Zn, and has a Vickers hardness of 150 to 230 HV. The backing layer has a Vickers hardness of 160 to 240 HV.

[0006] Accordingly, in the bush member according to one embodiment, the bearing alloy layer is joined to the Fe-based backing layer. Therefore, the influence of creep on the bearing alloy layer is reduced by the integral backing layer. Further, the bush member according to one embodiment is made of a Cu-based alloy containing Zn, that is, brass. Therefore, it has high resistance to sulfur components caused by additives contained in lubricating oil, and corrosion caused by this sulfur component is reduced. Furthermore, in the bush member according to one embodiment, the hardnesses of the bearing alloy layer and the backing layer are set. Therefore, while maintaining workability for ensuring high dimensional accuracy and roundness accuracy, the fatigue resistance is improved. Thus, the strength and corrosion resistance can be enhanced while maintaining the creep characteristics.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Mode for Carrying Out the Invention

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

[0009] The backing layer 12 is formed of an Fe-based alloy such as steel. The Vickers hardness of the backing layer 12 is 160 to 240 HV. In this specification, both the upper limit value and the lower limit value indicating a numerical range are included in the range. If the Vickers hardness of the backing layer 12 is less than 160, it becomes difficult to ensure the fatigue resistance required for the bush member 10 of the piston pin. On the other hand, if the Vickers hardness of the backing layer 12 exceeds 240 HV, the workability deteriorates.

[0010] The bearing alloy layer 11 is integrally joined to the backing layer 12 and is formed of a Cu-based alloy containing 25 to 45% by mass of Zn. That is, the bearing alloy layer 11 is formed of brass. The Zn contained in the bearing alloy layer 11 is preferably 35 to 45% by mass in order to ensure higher corrosion resistance. In addition to Zn, the bearing alloy layer 11 may contain additive elements such as Sn and P. In the case of the bush member 10 of the present embodiment, it is more preferable that the bearing alloy layer 11 is an alloy of Zn and Cu excluding inevitable impurities.

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

[0012] The Vickers hardness of the backing layer 12 is preferably 0.9 times or more the Vickers hardness of the bearing alloy layer 11. In the case of this embodiment, it is preferable that the bearing alloy layer 11 and the backing layer 12 have approximate hardnesses, and it is more preferable that the backing layer 12 is slightly harder than the bearing alloy layer 11. Thus, by approximating the hardnesses of the bearing alloy layer 11 and the backing layer 12, it is possible to facilitate processing for ensuring the roundness during processing of the bush member 10. Further, if the hardness of the bearing alloy layer 11 or the backing layer 12 becomes excessive, there is a risk that processes such as press-fitting the bush member 10 into, for example, a connecting rod or cutting after press-fitting become difficult. Therefore, the Vickers hardness of the bearing alloy layer 11 and the backing layer 12 is set with an upper limit of 240 HV.

[0013] Next, a method for manufacturing the bush member 10 having the above configuration will be described. As shown in FIG. 2, the bush member 10 is manufactured by press-bonding a plate member 21 that becomes the bearing alloy layer 11 and a plate member 22 that becomes the backing layer 12. After the plate member 21 and the plate member 22 are overlapped, they are pressed by a roller 23 until the total of their thicknesses becomes 40 to 60%.

[0014] The laminated material 24 joined by pressing is heated to 550 to 680° C. and subjected to diffusion annealing. By this heating, joining by diffusion between the plate member 21 and the plate member 22 in the laminated material 24 is promoted, and the plate member 21 and the plate member 22 are firmly joined. On the other hand, due to the diffusion annealing, the hardness of the plate member 21 that becomes the bearing alloy layer 11 decreases. As described above, if the Vickers hardness of the bearing alloy layer 11 is less than 150 HV, it becomes difficult to ensure the fatigue resistance of the bearing alloy layer 11. Therefore, the heated laminated material 24 is pressed by a roller 25 until the total of its thicknesses becomes 3 to 30%. At this time, the pressing step may be in one stage or two or more stages. In this case, the roller 25 may mainly press the plate member 21 side that becomes the bearing alloy layer 11 of the laminated material 24, or may press from both sides of the laminated material 24. Thereby, the formed bearing alloy layer 11 is hardened to a Vickers hardness of 150 HV or more.

[0015] As described above, the plate member 21 that becomes the bearing alloy layer 11 and the plate member 22 that becomes the backing layer 12 are joined to form a laminated material 24. The laminated material 24 is formed into a cylindrical bush member 10. In the manufacturing method of the bush member 10 according to the present embodiment, the plate member 21 that becomes the bearing alloy layer 11 and the plate member 22 that becomes the backing layer 12 are joined by pressure. Therefore, in the manufacturing process of the bush member 10, a process in which the backing layer 12 becomes a hard and brittle structure, such as rapid cooling, is not included. As a result, in the manufacturing method of the bush member 10 according to the present embodiment, the brittleness of the manufactured bush member 10 can be reduced and the strength can be increased. And, since the backing layer 12 of the bush member 10 manufactured by the manufacturing method of the present embodiment has a Vickers hardness of 240 HV or less, the workability is improved. As a result, the formed bush member 10 can be formed into a cylindrical shape with high dimensional accuracy and shape accuracy. At the same time, the bush member 10 can improve workability such as press-fitting into a connecting rod and cutting and polishing performed after press-fitting.

[0016] Next, an example of the bush member 10 according to the above embodiment will be described. (Verification of Creep Characteristics) As shown in FIG. 3, in Example 1 of the bush member 10, the bearing alloy layer 11 and the backing layer 12 are laminated as described above. On the other hand, Comparative Example 1 for comparison has the same dimensions as Example 1, but the portion corresponding to the backing layer 12 is also formed in one layer with brass that becomes the bearing alloy layer 11. That is, Comparative Example 1 is a so-called solid material entirely formed of brass.

[0017] The bush members 10 of Example 1 and Comparative Example 1 were verified for creep characteristics using the withdrawal load. The withdrawal load is the load required to withdraw the bush member 10 from the mating member after the bush member 10 has been press-fitted into the mating member. The bush members 10 of Example 1 and Comparative Example 1 press-fitted into the mating member were heated to 190°C and cooled to room temperature after the preset heating time had elapsed. After cooling, the withdrawal loads of the bush members 10 of Example 1 and Comparative Example 1 were measured. FIG. 3 shows the change rate of the withdrawal load after heating when the withdrawal load before heating is set to "1.00".

[0018] As is clear from FIG. 3, in Example 1, although the withdrawal load tends to increase as the heating time increases, the change in the withdrawal load is small. On the other hand, in Comparative Example 1, the withdrawal load decreases significantly as the heating time increases. Thus, the bush member 10 of Example 1 shows that the influence of creep is small compared to Comparative Example 1. This is because the bush member 10 of Example 1 is provided with an Fe-based backing layer 12 with little influence of creep on the outer peripheral side of the bearing alloy layer 11. In contrast, it can be seen that Comparative Example 1, which is integrally formed of brass, is greatly affected by creep. Note that in the bush member 10 of the present embodiment, the bearing alloy layer 11 and the backing layer 12 are joined. Therefore, the Zn content in the bearing alloy layer 11 does not affect the creep of the bush member 10. Therefore, the bearing alloy layer 11 of the bush member 10 of the present embodiment can reduce the influence of creep regardless of the Zn content.

[0019] (Verification of corrosion resistance) The corrosion resistance of the bush member 10 was verified using Examples 2 to 4, Comparative Example 2, and Comparative Example 3 as shown in FIG. 4. In Examples 2 to 4, the Zn content in the brass bearing alloy layer 11 is controlled. Also, Comparative Example 2 for comparison has a lower Zn content in the bearing alloy layer 11 compared to Examples 2 to 4. Comparative Example 3 has a bearing alloy layer made of bronze with Sn added instead of Zn.

[0020] For each of the samples of Examples 2 to 4, Comparative Example 2, and Comparative Example 3, the corrosion resistance was verified from the change in the mass of each sample. The change in mass becomes larger as corrosion progresses in each sample. That is, the mass of each sample decreases as corrosion progresses. However, since the progress of corrosion depends on the surface area of each sample, it is difficult to accurately grasp the amount of corrosion in each sample only by measuring the change in mass. Therefore, for each sample, the change in mass per unit surface area was measured as the amount of corrosion.

[0021] Each sample was immersed in a lubricating oil at 190 °C, which is close to the operating conditions of an internal combustion engine, in a sealed container for 70 hours to verify the corrosion resistance. Several commercially available genuine products specified by the manufacturer of the internal combustion engine were used as the lubricating oils. These lubricating oils contain additives containing sulfur components in the molecule, for example, for the purpose of improving performance and maintaining quality. This additive may decompose as the temperature rises due to the severer operating conditions in the internal combustion engine, causing the generation of sulfur components contained in the molecule. These generated sulfur components cause corrosion in the bearing alloy layer 11 of the bush member 10.

[0022] As is apparent from FIG. 4, it can be seen that Examples 2 to 4 in which the Zn content in the bearing alloy layer 11 is 25% or more have higher corrosion resistance than Comparative Example 2 in which the Zn content is 20%. Also, it can be seen that Comparative Example 3 with a bearing alloy layer made of bronze corrodes more easily compared to Examples 2 to 4. From these facts, the bush member 10 of the present embodiment with a Zn content of 25% or more can enhance the corrosion resistance. In particular, as can be seen from the comparison between Examples 2 and 3 and Example 4, the bush member 10 with a Zn content of 35% or more can further enhance the corrosion resistance.

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

[0024] Examples 5 to 9 and Comparative Examples 4 to 6 measured the fatigue resistance based on the test conditions shown in FIG. 6. The fatigue resistance was measured based on the load that causes fatigue while lubricating the sample with lubricating oil under the conditions shown in FIG. 6. The lubricating oil is a commercially available lubricating oil for internal combustion engines exemplified above. The load applied to the sample starts from 100 MPa, and the load is increased by 10 MPa each time the fatigue resistance is confirmed, and is set to 200 MPa. The fatigue resistance is considered to pass if the load that causes fatigue is 170 MPa or more. The workability is evaluated based on whether the bush member 10 formed from the bearing alloy layer 11 and the backing layer 12 can be processed to ensure appropriate dimensional accuracy and roundness. For workability, those with low yield but can ensure appropriate processing are rated as "good: ○", those with high yield and can ensure appropriate processing are rated as "excellent: ◎", and those with difficult appropriate processing are rated as "bad: ×".

[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 backing layer 12 is 160 to 240 HV. Also, in Examples 5 to 8, the hardness of the backing layer 12 is 0.9 times or more the hardness of the bearing alloy layer 11. In contrast, in Example 9, the hardness of the backing layer 12 is less than 0.9 times the hardness of the bearing alloy layer 11. Further, in Comparative Example 4, the hardness of the backing layer 12 exceeds 240 HV. Comparative Examples 5 and 6 are examples where the hardnesses of both the bearing alloy layer 11 and the backing layer 12 are insufficient. The hardnesses of the bearing alloy layer 11 and the backing layer 12 in Examples 5 to 9 and Comparative Examples 4 to 6 are controlled by the amount of change in their thickness when pressing the laminated bearing alloy layer 11 and backing layer 12, as described in the above manufacturing method.

[0026] As is clear from FIG. 5, Examples 5 to 9 all exhibited high workability and sufficient fatigue resistance. In particular, in Examples 5 to 8 where the hardness of the backing layer 12 is 0.9 times or more the hardness of the bearing alloy layer 11, both high workability and sufficient fatigue resistance are achieved. On the other hand, in Example 9 where the hardness of the backing layer 12 is less than 0.9 times the hardness of the bearing alloy layer 11, although sufficient fatigue resistance is exhibited, the yield for ensuring appropriate dimensional accuracy and roundness decreases. This is because the hardness of the backing layer 12 is lower than that of the bearing alloy layer 11, making it difficult to ensure accuracy during forming into the cylindrical shape of the bush member 10.

[0027] Also, in Comparative Example 4, since the hardness of the backing layer 12 is excessive at 248 HV, the workability deteriorates, and it is difficult to ensure high dimensional accuracy and roundness as the bush member 10. Therefore, Comparative Example 4 does not hold as the bush member 10, and the fatigue resistance could not be measured. In Comparative Examples 5 and 6, the hardnesses of both the bearing alloy layer 11 and the backing layer 12 are insufficient. Therefore, although workability is ensured in Comparative Examples 5 and 6, the fatigue resistance is insufficient.

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

Explanation of Reference Numerals

[0029] In the drawings, 10 denotes a bush member, 11 denotes a bearing alloy layer, and 12 denotes a backing layer.

Claims

1. A bush member for a piston pin comprising a Fe-based backing layer and a bearing alloy layer joined to the backing layer, wherein the bearing alloy layer is a Cu-based alloy containing 25 to 45% by mass of Zn, has a Vickers hardness of 150 to 230 HV, the backing layer is has a Vickers hardness of 160 to 240 HV, the bush member.

2. The Vickers hardness of the backing layer is 0.9 times or more the Vickers hardness of the bearing alloy layer, The bush member according to claim 1.

3. The bearing alloy layer is a Cu-based alloy containing 35 to 45% by mass of Zn, The bush member according to claim 1.

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