Member to be fastened and fastened structure using said member to be fastened

Abstract

A member (2) to be fastened comprises: a metal base material (21) that has a through-hole (211); and a conductive ring (22) that is fitted into the through-hole (211) of the metal base material (21) and has an insertion hole (221) into which a fastening member is inserted. The Vickers hardness of the conductive ring (22) is greater than the Vickers hardness of the metal base material (21), and an inner surface (212) of the through-hole (211) of the metal base material (21) is in contact with and electrically connected to an outer peripheral surface (223) of the conductive ring (22). A fastened structure (1) comprises the member (2) to be fastened, another member (3) to be fastened that is different from the member (2) to be fastened, and the fastening member that securely fastens the member (2) to be fastened together with the other member (3) to be fastened.

Description

Fastened member and fastening structure using said fastened member

[0001] The present invention relates to fastened members and a fastening structure using the fastened members.

[0002] With the recent spread of electric vehicles (Battery Electric Vehicles), battery packs are becoming larger in size in order to extend the driving range of electric vehicles. However, as larger battery packs also increase in weight, there is a demand for battery packs to be as small and light as possible. Therefore, in order to reduce the size and weight of the wiring material that electrically connects the cells inside the battery pack, the wiring material is being replaced from electric wires to bus bars.

[0003] To install busbars in large battery packs, long busbars are required. However, there are limitations to the shaping of long busbars by press work, so it is necessary to bend and shape the long busbars by forming. However, even when installing such long busbars, the ends of the busbars must be fastened. Therefore, it may be necessary to plate the ends of the busbars to reduce the connection resistance of the fastening portions of the busbars.

[0004] Patent Document 1 discloses a module battery including multiple battery cells each provided with a positive electrode terminal and a negative electrode terminal, and a copper bus bar electrically connected to the positive electrode terminal and the negative electrode terminal. The copper bus bar is provided with a tin-plated layer. This suppresses the formation of an oxide film on the bus bar itself and prevents electrolytic corrosion caused by direct contact between the aluminum positive electrode terminal and the copper bus bar.

[0005] JP 2018-055892 A

[0006] However, plating a long busbar requires a plating layer that is only required for the fastening portion, resulting in unnecessary costs. Additionally, plating a long busbar requires masking and other processes, which complicates the manufacturing process and further increases costs.

[0007] The present invention has been made in view of the problems inherent in the prior art, and an object of the present invention is to provide fastened members and a fastening structure using the fastened members that can simplify the manufacturing process and reduce manufacturing costs.

[0008] The fastened member according to a first aspect of the present invention comprises a metal base material having a through hole, and a conductive ring having an insertion hole that is fitted into the through hole of the metal base material and into which a fastening member is inserted, the Vickers hardness of the conductive ring being greater than the Vickers hardness of the metal base material, and the inner surface of the through hole of the metal base material and the outer peripheral surface of the conductive ring being in contact with each other and electrically conductive.

[0009] A fastening structure according to a second aspect of the present invention comprises the above-mentioned fastened member, another fastened member different from the fastened member, and a fastening member that fastens and fixes the fastened member and the other fastened member to each other.

[0010] According to the present invention, it is possible to provide fastened members and a fastening structure using the fastened members, which can simplify the manufacturing process and reduce manufacturing costs.

[0011] FIG. 1A is a side view showing an example of a fastening structure. FIG. 1B is a plan view showing an example of the fastening structure. FIG. 2 is a schematic diagram for explaining fluctuations in axial force, repulsive force between a bolt head and a fastened member, and repulsive force between a fastened member and another fastened member when a fastening structure is repeatedly subjected to high-temperature and low-temperature conditions. FIG. 3A is a cross-sectional view showing an example of a conventional fastening structure. FIG. 3B is a cross-sectional view showing an example of a fastening structure of the present embodiment. FIG. 4A is a plan view and a cross-sectional view showing a state in which a metal base material and a conductive ring are separated in a fastened member according to the present embodiment. FIG. 4B is a plan view and a cross-sectional view showing a state in which a conductive ring is fitted into a metal base material in a fastened member according to the present embodiment. FIG. 5 is a schematic cross-sectional view for explaining an example of a method for manufacturing a fastened member according to the present embodiment. FIG. 6 is a schematic cross-sectional view for explaining an example of a method for manufacturing a fastened member according to the present embodiment. FIG. 7 is a schematic cross-sectional view for explaining an example of a method for manufacturing a fastened member according to the present embodiment. FIG. 8 is a schematic plan view for explaining an example of a method for manufacturing a fastened member according to the present embodiment. FIG. 9 is a schematic cross-sectional view for explaining an example of a method for manufacturing a fastened member according to the present embodiment. FIG. 10 is a schematic cross-sectional view illustrating an example of a manufacturing method for fastened members according to this embodiment. FIG. 11 is a schematic cross-sectional view illustrating an example of a manufacturing method for fastened members according to this embodiment. FIG. 12 is a schematic cross-sectional view illustrating an example of a manufacturing method for fastened members according to this embodiment. FIG. 13 is a schematic cross-sectional view and a schematic plan view illustrating an example of a manufacturing method for fastened members according to this embodiment. FIG. 14 is a schematic cross-sectional view and a schematic plan view illustrating an example of a manufacturing method for fastened members according to this embodiment. FIG. 15 is a schematic plan view illustrating an example of a manufacturing method for fastened members according to this embodiment. FIG. 16 is a photograph showing a fastening structure according to Reference Example 1. FIG. 17 is a diagram schematically illustrating the structures of test samples (fastened members) of Examples 1-1 and 1-2. FIG. 18 is a schematic view illustrating a method for measuring the electrical resistance of the test sample in Example 1. FIG. 19A is a schematic plan view illustrating the fastening structures and the method for measuring the electrical resistance in Examples 1-1 and 1-2. FIG. 19B is a schematic side view showing the fastening structure in Example 1.FIG. 20 is a graph showing the relationship between the tightening torque of a bolt and a nut and the electrical resistance of the fastened portion of the fastening structure in Example 1. FIG. 21 is a diagram schematically showing the structures of test samples (fastened members) in Examples 2-1 and 2-2. FIG. 22 is a schematic diagram for explaining a method for measuring the electrical resistance of a test sample in Example 2. FIG. 23A is a schematic plan view for explaining the fastening structures and the method for measuring the electrical resistance in Examples 2-1 and 2-2. FIG. 23B is a schematic side view showing the fastening structure in Example 2. FIG. 24 is a graph showing the relationship between the tightening torque of a bolt and a nut and the electrical resistance of the fastened portion of the fastening structure in Example 2. FIG. 25A is a schematic plan view for explaining the fastening structure and the method for measuring the electrical resistance in Reference Example 2. FIG. 25B is a schematic side view showing the fastening structure in Reference Example 2. FIG. 26 is a graph showing the relationship between the tightening torque of a bolt and a nut and the electrical resistance of the fastened portion of the fastening structure in Reference Example 2.

[0012] Hereinafter, the fastened members and the fastening structure using the fastened members according to the present embodiment will be described in detail with reference to the drawings. Note that the dimensional proportions in the drawings are exaggerated for the convenience of explanation and may differ from the actual proportions.

[0013] 1A and 1B, the fastening structure 1, 1a includes fastened members 2, 2a, other fastened members 3, 3a different from the fastened members 2, 2a, and fastening members that fasten the fastened members 2, 2a to the other fastened members 3, 3a. The fastened members 2, 2a and the other fastened members 3, 3a are fastened together by inserting threaded portions of bolts 4 as fastening members into holes provided in the fastened members 2, 2a and the other fastened members 3, 3a and then screwing nuts 5 onto the threaded portions.

[0014] In the fastening structure 1, 1a, the fastened members 2, 2a, the other fastened members 3, 3a, and the fastening members are generally made of metal materials, which have the property of expanding with increasing temperature and contracting with decreasing temperature. If the metal materials of the fastening members and the fastened members are different from each other, a difference in thermal expansion occurs between the metal materials.

[0015] When a fastening structure in which the fastening member and the fastened member are made of different materials are repeatedly used in high-temperature and low-temperature environments, the axial force of the fastening member fluctuates significantly due to the difference in thermal expansion of the materials. Repeated fluctuations in the axial force of the fastening member cause stress relaxation in the fastened member, resulting in a decrease in the axial force, the repulsive force between the bolt head and the fastened member, and the repulsive force between the fastened member and other fastened members. That is, as shown in Figure 2 , in the initial stage before the cycle between high-temperature and low-temperature environments, the axial force A1, the repulsive force B1 between the head of the bolt 4 and the fastened member 2a, and the repulsive force C1 between the fastened member 2a and other fastened members 3a are maintained at a high level. In contrast, when the cycle between high-temperature and low-temperature environments is repeatedly used, stress relaxation occurs in the fastened member 2a, for example. Therefore, in order to balance the forces in the fastening structure, the axial force A2, the repulsive force B2 between the head of the bolt 4 and the fastened member 2a, and the repulsive force C2 between the fastened member 2a and other fastened members 3a are all relaxed. As a result, the axial force (fastening force) of the bolt 4 to the fastened member 2a and the other fastened member 3a decreases. Note that stress relaxation occurs not only between the head of the bolt 4 and the fastened member 2a, but also between the nut 5 and the other fastened member 3a.

[0016] As described above, in conventional fastening structures, the fastening force of the fastening member can deform the fastened member 2a, causing loosening between the fastening member and the fastened member 2a and other fastened members 3a, potentially reducing the conductivity between the fastened member 2a and other fastened members. Furthermore, when aluminum or an aluminum alloy is used as the metal material for the fastened member 2a, an insulating oxide film is present on the surface of the aluminum or aluminum alloy. This can increase the contact resistance between the fastened member 2a and other fastened members 3a, potentially reducing the conductivity between the fastened member 2a and other fastened members 3a. Therefore, to reduce the connection resistance between the fastened member 2a and other fastened members 3a, the fastened member 2a is sometimes plated. However, plating the fastened member 2a results in unnecessary costs because a plating layer, which is only required for the fastening portion between the fastened member 2a and other fastened members 3a, is applied to the entire surface. Furthermore, plating the fastened member 2a requires additional steps such as masking, complicating the manufacturing process and further increasing costs.

[0017] As described above, in conventional fastening structures, the entire surface of the fastened members 2a is plated to reduce connection resistance. However, to improve this treatment, methods such as welding a high-strength member to the end of the fastened members 2a to connect them have also been used. However, welding a high-strength member to the end of the fastened members 2a requires a welding process, which complicates the manufacturing process and increases costs.

[0018] Here, as a result of the inventor's investigations, it was found that the main point of conduction between the fastened member and the other fastened member is the interface between the fastened member and the other fastened member present between the fastening members. That is, as shown in FIG. 3A , when viewing a cross section along the stacking direction of the fastened member 2a and the other fastened member 3a, the contact surface between the fastened member 2a and the other fastened member 3a present between the bearing surface 411 of the head 41 of the bolt 4 and the bearing surface 511 of the nut 5 is the conductive surface E1. Conversely, other contact surfaces other than the contact surface between the fastened member 2a and the other fastened member 3a present between the bolt 4 and the nut 5 have low conductivity. That is, among the contact surfaces between the fastened member 2a and the other fastened member 3a, the main conductive surface E1 is directly below the bearing surface 411 of the bolt 4. Therefore, by increasing the conductivity at the conductive surface E1 between the fastened member 2a and the other fastened member 3a, it is possible to further improve the conductivity between the fastened member 2a and the other fastened member 3a.

[0019] The fastened members and fastening structure of this embodiment have been created taking into consideration the above issues and study results, and have a structure that can increase conductivity between the fastened members while reducing manufacturing costs.

[0020] 3B, 4A, and 4B, the fastened member 2 of this embodiment includes a metal base material 21 having a through hole 211, and a conductive ring 22 fitted into the through hole 211 of the metal base material 21. The inner surface 212 of the through hole 211 of the metal base material 21 and the outer peripheral surface 223 of the conductive ring 22 are in contact with each other and are electrically connected.

[0021] The shape of the metal base material 21 constituting the fastened members 2 is not particularly limited, but may be, for example, a flat plate. The metal base material 21 may be a long flat plate. The metal base material 21 may also be partially bent by forming.

[0022] A through hole 211 is formed in the metal base material 21 in the thickness direction, penetrating from the front surface 214 to the back surface 215. The shape of the through hole 211 may be cylindrical as shown in Fig. 4A. However, the shape of the through hole 211 is not particularly limited as long as the conductive ring 22 can be fitted therein, and it may be a prism, a truncated cone, or a truncated pyramid.

[0023] 3B and 4A, the conductive ring 22 has an insertion hole 221 into which the threaded portion 42 of the bolt 4, which is a fastening member, is inserted. As shown in Fig. 4A, the external shape of the conductive ring 22 can be cylindrical to match the shape of the through hole 211 of the metal base material 21. However, the external shape of the conductive ring 22 is not particularly limited as long as it can be fitted into the through hole 211, and may be a rectangular parallelepiped, a cube, a truncated cone, or a truncated pyramid.

[0024] The insertion hole 221 is formed in the center of the conductive ring 22 and penetrates along the thickness direction from the front surface 224 to the back surface 225. The shape of the insertion hole 221 can be cylindrical so that the threaded portion 42 of the bolt 4 can be inserted therein.

[0025] 4B , the conductive ring 22 is fitted inside the through hole 211 of the metal base material 21. In this case, the surface 214 of the metal base material 21 and the surface 224 of the conductive ring 22 can be flush with each other. Similarly, the back surface 215 of the metal base material 21 and the back surface 225 of the conductive ring 22 can be flush with each other.

[0026] When the conductive ring 22 is fitted into the through hole 211 of the metal base material 21, the inner surface 212 of the through hole 211 of the metal base material 21 and the outer peripheral surface 223 of the conductive ring 22 are in contact with each other. The inner surface 212 of the through hole 211 of the metal base material 21 and the outer peripheral surface 223 of the conductive ring 22 are electrically connected to each other. Here, the inner surface 212 of the through hole 211 of the metal base material 21 and the outer peripheral surface 223 of the conductive ring 22 are preferably in direct contact without a metal oxide coating therebetween. That is, it is preferable that the metal of the metal base material 21 and the metal of the conductive ring 22 are in direct contact with each other between the inner surface 212 of the through hole 211 of the metal base material 21 and the outer peripheral surface 223 of the conductive ring 22, and it is more preferable that the metal of the metal base material 21 and the metal of the conductive ring 22 are in direct contact and adhere to each other. This state allows the conductivity between the metal base material 21 and the conductive ring 22 to be maintained at a high level.

[0027] The metal base material 21 is made of a conductive metal. The metal base material 21 is preferably a member whose main component is a metal selected from the group consisting of pure aluminum, an aluminum alloy, pure copper, or a copper alloy, and more preferably a member made of a metal selected from the group consisting of pure aluminum, an aluminum alloy, pure copper, or a copper alloy. Note that, since there is no need to plate the metal base material 21, the surface of the metal base material 21 does not have a plated layer.

[0028] The conductive ring 22 is made of a conductive metal. However, it is preferable that the Vickers hardness of the conductive ring 22 is greater than the Vickers hardness of the metal base material. In this case, when the conductive ring 22 is fitted into the through hole 211 of the metal base material 21, the outer peripheral surface 223 of the conductive ring 22 can destroy the metal oxide coating present on the inner surface 212 of the through hole 211 of the metal base material 21. This makes it possible to bring the inner surface 212 of the through hole 211 of the metal base material 21 and the outer peripheral surface 223 of the conductive ring 22 into direct contact without the metal oxide coating interposed therebetween. Note that, in this specification, the Vickers hardness can be measured in accordance with Japanese Industrial Standards JIS Z2244-1:2024 (Vickers Hardness Test - Part 1: Test Method).

[0029] The conductive ring 22 is preferably a member whose main component is a metal selected from the group consisting of an aluminum alloy, pure copper, or a copper alloy, and more preferably a member made of a metal selected from the group consisting of an aluminum alloy, pure copper, or a copper alloy.

[0030] Therefore, the metal base material 21 may be made of pure aluminum or an aluminum alloy, and the conductive ring 22 may be made of pure copper or a copper alloy. However, as long as the Vickers hardness of the conductive ring 22 is greater than that of the metal base material, the metal base material 21 may be made of pure aluminum, and the conductive ring 22 may be made of an aluminum alloy. Alternatively, the metal base material 21 may be made of pure copper, and the conductive ring 22 may be made of a copper alloy.

[0031] The metals constituting the metal base material 21 and the conductive ring 22 are not limited to aluminum, aluminum alloys, copper, and copper alloys. Gold, silver, iron, and alloys of these metals can also be used as the metals constituting the metal base material 21 and the conductive ring 22.

[0032] In the fastened components 2, it is not necessary to provide a plating layer on the surface of the metal base material 21. Furthermore, the surface of the conductive ring 22 may or may not have a plating layer. However, it is preferable to provide a plating layer on the surface of the conductive ring 22. For example, if the metal base material 21 is made of pure aluminum or an aluminum alloy and the conductive ring 22 is made of pure copper or a copper alloy, the difference in standard electrode potential between aluminum and copper may act as a local cell, causing the aluminum to dissolve, which is known as galvanic corrosion. Therefore, by providing a plating layer on the conductive ring 22 to reduce the difference in standard electrode potential between aluminum and copper, the progression of galvanic corrosion can be slowed.

[0033] Since the conductive ring 22 is an annular part, a plating layer can be easily formed by a conventional plating process.

[0034] As described above, in order to fit the conductive ring 22 into the metal base material 21 while destroying the oxide film thereon, the plating layer formed on the surface of the conductive ring 22 is preferably harder than the metal base material 21. Specifically, the Vickers hardness of the conductive ring 22 on which the plating layer is formed is preferably greater than the Vickers hardness of the metal base material 21. Furthermore, the plating layer preferably has low contact resistance so that electrical continuity can be ensured between the conductive ring 22 and the other fastened member 3 when the fastening member 2 is connected to the other fastened member 3. Such a plating layer is preferably selected from the group consisting of nickel plating, nickel-phosphorus plating, silver plating, silver alloy plating, silver-antimony plating, silver-germanium plating, and tin plating.

[0035] The Vickers hardness of the plating layer formed on the surface of the conductive ring 22 is preferably greater than that of pure aluminum. There is no particular upper limit to the Vickers hardness of the plating layer, but it can be, for example, the hardness of a nickel-phosphorus plating layer. Note that the hardness of a nickel-phosphorus plating layer is approximately 700 HV in the case of a nickel plating layer containing 3 wt% phosphorus.

[0036] The yield stress of the conductive ring 22 is preferably equal to or greater than the yield stress of the metal base material 21. Furthermore, the yield stress of the conductive ring 22 is more preferably equal to or greater than the yield stress of the metal base material 21 and 134 MPa or greater. As described above, the fastened members 2 and other fastened members 3 are fastened together with a fastening member. Therefore, by making the yield stress (proof strength) of the conductive ring 22 greater than that of the metal base material 21, the conductive ring 22 has a higher yield stress than the metal base material 21. Therefore, when fastened with a fastening member, buckling of the conductive ring 22 and loosening between the fastening member and the fastened members 2 are suppressed. As a result, a conductive surface is secured between the fastened members 2 and other fastened members 3, thereby improving conductivity between them. Furthermore, if the yield stress of the conductive ring 22 is 134 MPa or greater, even when the fastening member (bolt) is fastened with the maximum axial force, the yield stress of the conductive ring 22 exceeds the compressive force due to the axial force, thereby suppressing buckling. The yield stress of the conductive ring 22 can be measured using the material that constitutes the conductive ring 22 in accordance with JIS Z2241:2022 (Method of tensile testing of metallic materials).

[0037] The conductive ring 22 preferably has a Vickers hardness of 30 to 700 HV. This allows the outer peripheral surface 223 of the conductive ring 22 to destroy the metal oxide coating present on the inner surface 212 of the through hole 211 of the metal base material 21 when the conductive ring 22 is fitted into the through hole 211 of the metal base material 21. Therefore, the inner surface 212 of the through hole 211 of the metal base material 21 and the outer peripheral surface 223 of the conductive ring 22 can be brought into direct contact without the intervention of the metal oxide coating, thereby improving the conductivity between the metal base material 21 and the conductive ring 22.

[0038] In the fastened members 2 of this embodiment, the fastening portion of the metal base material 21 is replaced with a conductive ring 22. Therefore, if necessary, a plating layer can be provided only on the conductive ring 22, which simplifies the manufacturing process and reduces manufacturing costs compared to providing a plating layer on the metal base material 21. Furthermore, by using a high-strength material for the conductive ring 22, deformation of the conductive ring 22 due to fastening can be suppressed, and conductivity between the fastened members 2 and the other fastened members 3 can be increased.

[0039] Furthermore, by using a highly conductive material for the conductive ring 22, the conductivity between the fastened member 2 and the other fastened member 3 can be increased. That is, as shown in FIG. 3B , when a cross section along the stacking direction of the fastened member 2 and the other fastened member 3 is viewed, the contact surface between the fastened member 2 and the other fastened member 3, which exists between the bearing surface 411 of the head 41 of the bolt 4 and the bearing surface 511 of the nut 5, becomes the conductive surface E2. That is, of the contact surfaces between the fastened member 2 and the other fastened member 3, the main conductive surface E2 is located directly below the bearing surface 411 of the bolt 4. Furthermore, by using the conductive ring 22 in the fastened member 2, the conductivity at the conductive surface E2 can be increased, thereby further improving the conductivity between the fastened member 2 and the other fastened member 3.

[0040] The fastened members 2 of this embodiment can be manufactured as follows. As shown in Fig. 5 , the fastened members 2 can be obtained by fitting a conductive ring 22 into a through hole 211 in a metal base material 21. At this time, as shown in the left diagram of Fig. 5 , the through hole 211 in the metal base material 21 is machined into a cylindrical or prismatic shape. Furthermore, if the through hole 211 is cylindrical, the conductive ring 22 is machined into a cylindrical shape, and if the through hole 211 is prismatic, the conductive ring 22 is machined into a rectangular tube. At this time, the conductive ring 22 is machined so that the outer diameter of the conductive ring 22 is slightly larger than the inner diameter of the through hole 211.

[0041] Then, as shown in the right diagram of Fig. 5 , the conductive ring 22 is press-fitted into the through hole 211 of the metal base material 21. It is preferable to use a press machine when press-fitting the conductive ring 22. By press-fitting the conductive ring 22 into the through hole 211 in this manner, it is possible to destroy the metal oxide coating present on the inner surface 212 of the through hole 211 of the metal base material 21. Therefore, it is possible to bring the inner surface 212 of the metal base material 21 and the outer peripheral surface 223 of the conductive ring 22 into direct contact without the metal oxide coating interposed therebetween.

[0042] The fastened member 2 can also be manufactured by the method shown in Fig. 6. As shown in the left diagram of Fig. 6, the through hole 211 of the metal base material 21 is machined into a frustum shape, and the inner surface of the through hole 211 is tapered. Furthermore, if the through hole 211 is frustum-shaped, the conductive ring 22 is machined into a cylindrical shape, and if it is frustum-shaped, the conductive ring 22 is machined into a rectangular tube shape.

[0043] Then, as shown in the right diagram of Fig. 6 , the conductive ring 22 is press-fitted into the through hole 211 of the metal base material 21. By press-fitting the conductive ring 22 into the through hole 211 having a tapered surface in this manner, the metal oxide film present on the inner surface 212 of the through hole 211 of the metal base material 21 can also be destroyed. Therefore, the inner surface 212 of the metal base material 21 and the outer peripheral surface 223 of the conductive ring 22 can be brought into direct contact without the intervention of the metal oxide film. Furthermore, because the through hole 211 is tapered, the oxide film can be destroyed while facilitating the press-fitting of the conductive ring 22.

[0044] In this way, by the method of FIG. 6, the conductive ring 22 is fitted into the through hole 211 of the metal base material 21, and the fastened member 2 can be obtained in which the through hole 211 is tapered along the thickness direction.

[0045] The fastened members 2 can also be manufactured by the method shown in FIG. 7 . As shown in the left diagram of FIG. 7 , a flange 226 is integrally formed from the surface 224 of the conductive ring 22 radially outward. Then, as shown in the right diagram of FIG. 7 , the conductive ring 22 is press-fit into the through hole 211 of the metal base material 21. This allows the inner surface 212 of the metal base material 21 to be in direct contact with the outer peripheral surface 223 of the conductive ring 22, while also allowing the surface 214 of the metal base material 21 to be in direct contact with the flange 226. As a result, the contact area between the metal base material 21 and the conductive ring 22 is increased, thereby further improving the conductivity between the metal base material 21 and the conductive ring 22. Furthermore, the fastened members 2 shown in FIG. 7 can have the flange 226 side as a contact surface with another fastened member 3, and the side opposite the flange 226 as a contact surface with the bearing surface 411 of the head 41 of the bolt 4. As shown in the right diagram of Figure 7, the surface of the flange portion 226 is flat, so the flatness of the conductive surface E1 formed between the fastened member 2 and the other fastened member 3 can be improved.

[0046] In this way, by the method of Figure 7, the conductive ring 22 is inserted into the through hole 211 of the metal base material 21, and a fastened member 2 can be obtained in which a flange portion 226 is integrally formed radially outward from the surface 224 of the conductive ring 22.

[0047] The fastened member 2 can also be manufactured by the method shown in Fig. 8. As shown in the left diagram of Fig. 8, a protrusion 2231 is integrally formed radially outward from the outer circumferential surface 223 of the conductive ring 22. In addition, a recess 2121 into which the protrusion 2231 is fitted is formed on the inner surface 212 of the through hole 211 of the metal base material 21.

[0048] Then, the conductive ring 22 is press-fitted into the through-hole 211 of the metal base material 21. This allows the inner surface 212 of the metal base material 21 to be in direct contact with the outer peripheral surface 223 of the conductive ring 22, while also allowing the recess 2121 of the metal base material 21 to be in direct contact with the protrusion 2231 of the conductive ring 22. As a result, the contact area between the metal base material 21 and the conductive ring 22 increases, thereby further improving the conductivity between the metal base material 21 and the conductive ring 22.

[0049] Similarly, as shown in the right diagram of FIG. 8 , protrusions 2122 are integrally formed from the inner surface 212 of the through hole 211 of the metal base material 21 toward the radially inward direction. In addition, recesses 2232 into which the protrusions 2122 are fitted are formed on the outer peripheral surface 223 of the conductive ring 22. Then, the conductive ring 22 is press-fitted into the through hole 211 of the metal base material 21. This allows the inner surface 212 of the metal base material 21 to be in direct contact with the outer peripheral surface 223 of the conductive ring 22, while also allowing the protrusions 2122 of the metal base material 21 to be in direct contact with the recesses 2232 of the conductive ring 22. As a result, the contact area between the metal base material 21 and the conductive ring 22 is increased, thereby further improving the conductivity between the metal base material 21 and the conductive ring 22.

[0050] In this way, by the method of Figure 8, a fastened member 2 can be obtained in which the outer surface 223 of the conductive ring 22 has protrusions 2231 or recesses 2232 that come into contact with the inner surface 212 of the through hole 211 of the metal base material 21.

[0051] The fastened member 2 can also be manufactured by the method shown in Fig. 9. As shown in the left diagram of Fig. 9, a step 216 that reduces the diameter of the through hole 211 is integrally formed on the inner surface 212 of the through hole 211 in the metal base material 21. The step 216 is formed from the back surface 215 of the metal base material 21 to approximately the middle of the through hole 211 in the thickness direction. The diameter of the through hole 2111 located inside the step 216 is approximately the same as the diameter of the insertion hole 221 of the conductive ring 22. The thickness of the conductive ring 22 is also approximately the same as the depth of the through hole 211.

[0052] Then, the conductive ring 22 is press-fitted into the through-hole 211 of the metal base material 21. This allows the inner surface 212 of the metal base material 21 to be in direct contact with the outer peripheral surface 223 of the conductive ring 22, while also allowing the opposing surfaces of the conductive ring 22 and the stepped portion 216 to be in direct contact with each other. As a result, the contact area between the metal base material 21 and the conductive ring 22 increases, further improving the conductivity between the metal base material 21 and the conductive ring 22.

[0053] In this way, by the method of Figure 9, it is possible to obtain a fastened member 2 in which a step portion 216 formed by reducing the diameter of the through hole 211 is integrally formed on the inner surface 212 of the through hole 211 of the metal base material 21.

[0054] 10 , a step portion 216 may be provided in the metal base material 21, and a protrusion 2251 may be formed on the back surface 225 of the conductive ring 22 so as to protrude toward the step portion 216. In this way, when the conductive ring 22 is press-fitted into the through-hole 211 of the metal base material 21 and the opposing surfaces of the conductive ring 22 and the step portion 216 are brought into contact with each other, the protrusion 2251 penetrates into the step portion 216. Therefore, the oxide film present on the surface of the step portion 216 can be destroyed, and the contact area between the metal base material 21 and the conductive ring 22 can be further increased. As a result, the conductivity between the metal base material 21 and the conductive ring 22 can be further improved.

[0055] The fastened member 2 can also be manufactured by the method shown in Fig. 11. As shown in the left diagram of Fig. 11, the entire outer peripheral surface 223 of the conductive ring 22 is threaded to form a thread 2233. Similarly, the entire inner surface 212 of the through hole 211 of the metal base material 21 is threaded to form a thread 2123.

[0056] 11, the conductive ring 22 is screwed into the through hole 211 of the metal base material 21. This destroys the metal oxide film present on the inner surface 212 of the through hole 211 of the metal base material 21, and allows the inner surface 212 of the metal base material 21 and the outer peripheral surface 223 of the conductive ring 22 to come into direct contact without the metal oxide film in between.

[0057] In this way, by the method of FIG. 11, a fastened member 2 can be obtained in which the outer peripheral surface 223 of the conductive ring 22 has threads 2123 that come into contact with the inner surface 212 of the through hole 211 of the metal base material 21.

[0058] The fastened member 2 can also be manufactured by the method shown in Fig. 12. As shown in the left diagram of Fig. 12, the entire outer peripheral surface 223 of the conductive ring 22 is threaded to form a thread 2233. However, the entire inner surface 212 of the through hole 211 of the metal base material 21 is not threaded.

[0059] 12 , the conductive ring 22 is screwed into the through hole 211 of the metal base material 21. As a result, the conductive ring 22 taps (threads) the inner surface 212 of the metal base material 21, forming a thread 2123 on the inner surface 212. This makes it possible to destroy the metal oxide coating present on the inner surface 212 of the through hole 211 of the metal base material 21, and therefore the inner surface 212 of the metal base material 21 and the outer peripheral surface 223 of the conductive ring 22 can be brought into direct contact without the metal oxide coating therebetween.

[0060] The fastened members 2 can also be manufactured by the method shown in Fig. 13. As shown in the left diagram of Fig. 13, a cylindrical conductive ring 22 is press-fitted into a through hole 211 in a metal base material 21. This destroys the metal oxide coating present on the inner surface 212 of the through hole 211 in the metal base material 21, allowing the inner surface 212 of the metal base material 21 and the outer peripheral surface 223 of the conductive ring 22 to come into direct contact without the metal oxide coating interposed therebetween.

[0061] Here, because the length of the conductive ring 22 is greater than the thickness of the metal base material 21, both ends of the conductive ring 22 protrude from the front surface 214 and the back surface 215 of the metal base material 21. Pressure is applied to the protruding ends of the conductive ring 22, causing plastic deformation radially outward. As a result, as shown in the right diagram of FIG. 13 , the protruding ends of the conductive ring 22 expand radially outward, forming umbrella portions 227 on the front surface 214 and the back surface 215 of the metal base material 21. The outer diameter (umbrella diameter) of the umbrella portion 227 is greater than the diameter of the through hole 211 in the metal base material 21, preventing the conductive ring 22 from slipping out of the through hole 211. In this embodiment, the umbrella portion 227 has a 12-tooth gear shape. To facilitate the formation of the umbrella portion 227, the cylindrical conductive ring 22 may be provided with a groove and / or a slit.

[0062] In this way, by the method of FIG. 13, it is possible to obtain a fastened member 2 in which the conductive ring 22 has an eyelet shape.

[0063] The fastened members 2 can also be manufactured by the method shown in Fig. 14. As shown in the left diagram of Fig. 14, a conductive ring 22 with an umbrella portion 227 formed at its upper end in advance is press-fitted into a through hole 211 in a metal base material 21. This destroys the metal oxide coating present on the inner surface 212 of the through hole 211 in the metal base material 21, allowing the inner surface 212 of the metal base material 21 and the outer peripheral surface 223 of the conductive ring 22 to come into direct contact without the metal oxide coating interposed therebetween.

[0064] At this time, because the length of the conductive ring 22 is greater than the thickness of the metal base material 21, an end of the conductive ring 22 protrudes from the back surface 215 of the metal base material 21. Then, after the protruding end of the conductive ring 22 is spread radially outward, the washer 228 is fitted in. Note that, because the outer diameters of the umbrella portion 227 and the washer 228 are greater than the diameter of the through hole 211 of the metal base material 21, it is possible to prevent the conductive ring 22 from falling out of the through hole 211.

[0065] In this way, by the method of FIG. 14, it is possible to obtain a fastened member 2 in which the conductive ring 22 has an eyelet shape on both sides.

[0066] The fastened member 2 can also be manufactured by the method shown in Fig. 15. First, the through hole 211 in the metal base material 21 is machined into a cylindrical or prismatic shape, similar to the method shown in Fig. 5. The conductive ring 22 is machined into a cylindrical shape if the through hole 211 is cylindrical, or into a rectangular tube if the through hole 211 is prismatic.

[0067] Next, when the metal base material 21 is heated, the metal base material 21 thermally expands, and the diameter of the through hole 211 increases, as shown in the left diagram of Fig. 15 . The inner diameter of the expanded through hole 211 becomes larger than the diameter of the conductive ring 22, so that the conductive ring 22 can be fitted into the through hole 211 of the metal base material 21. When the metal base material 21 is cooled, the metal base material 21 contracts, as shown in the right diagram of Fig. 15 , so that the inner surface 212 of the through hole 211 of the metal base material 21 comes into contact with the outer peripheral surface 223 of the conductive ring 22, and the conductive ring 22 can be fixed in the through hole 211.

[0068] In this way, by the method of FIG. 15, it is possible to obtain a fastened member 2 in which the conductive ring 22 is fitted into the through hole 211 of the metal base material 21.

[0069] The fastened members 2 of this embodiment may be manufactured by a combination of two or more of the methods shown in FIGS. 5 to 15.

[0070] [Fastening Structure] Next, the fastening structure of this embodiment will be described. As shown in Figures 1A and 3B, the fastening structure 1 of this embodiment includes a fastened member 2, another fastened member 3 different from the fastened member 2, and a fastening member that fastens the fastened member 2 and the other fastened member 3 to each other. The fastened member 2 and the other fastened member 3 are fastened together by inserting the threaded portion of a bolt 4 as a fastening member into an insertion hole 221 of the fastened member 2 and a hole in the other fastened member 3, and then screwing a nut 5 onto the threaded portion. The other fastened member 3 can be a bus bar or a terminal.

[0071] A fastening member is a member that can fasten a fastened member 2 and another fastened member 3 by applying an appropriate fastening force (compression force) to them. As shown in Fig. 1A, a bolt 4 and a nut 5 can be used as such a fastening member. However, members other than the bolt 4 and the nut 5 may be used as the fastening member as long as they can apply an appropriate fastening force to the fastened member 2 and the other fastened member 3. Furthermore, by cutting an internal thread into the other fastened member 3, the other fastened member 3 itself may serve as the fastening member.

[0072] 3B , when the fastening structure 1 is viewed in cross section along the stacking direction of the fastened member 2 and the other fastened member 3, the contact surface between the fastened member 2 and the other fastened member 3, which exists between the seat surface 411 of the head 41 of the bolt 4 and the seat surface 511 of the nut 5, becomes the conductive surface E2. The use of the conductive ring 22 in the fastened member 2 can increase the conductivity at the conductive surface E2, thereby making it possible to further improve the conductivity between the fastened member 2 and the other fastened member 3.

[0073] Here, in the fastening structure 1, if the axial force of the fastening members when fastening the fastened members 2 and the other fastened members 3 is 0.1 kN, the electrical resistance of the fastened portion between the fastened members 2 and the other fastened members 3 is preferably 44.7 μΩ or less. Furthermore, if the axial force of the fastening members when fastening the fastened members 2 and the other fastened members 3 is 0.7 kN or more, the electrical resistance of the fastened portion between the fastened members 2 and the other fastened members 3 is more preferably 26.3 μΩ or less. In this case, heat generation in the fastened portion between the fastened members 2 and the other fastened members 3 is suppressed, thereby suppressing stress relaxation and allowing the fastening force of the fastening members to be maintained at a high level.

[0074] As described above, the fastened member 2 of this embodiment includes the metal base material 21 having the through hole 211, and the conductive ring 22 having the insertion hole 221 into which the fastening member is inserted, which is fitted into the through hole 211 of the metal base material 21. The Vickers hardness of the conductive ring 22 is greater than that of the metal base material 21, and the inner surface 212 of the through hole 211 of the metal base material 21 and the outer peripheral surface 223 of the conductive ring 22 are in contact with each other and are electrically conductive.

[0075] The fastened member 2 has the conductive ring 22 fitted into the through hole 211 of the metal base material 21, which simplifies the manufacturing process and reduces manufacturing costs. In addition, by reducing the contact resistance of the conductive ring 22 and using a material for the conductive ring 22 that has high yield strength, i.e., is resistant to crushing and loosening, an inexpensive metal base material 21 can be used.

[0076] The conductive ring 22 can be determined taking into consideration the conductivity between the conductive ring 22 and the metal base material 21, the linear expansion coefficient between the conductive ring 22 and the metal base material 21, and a shape that can withstand fastening by a fastening member. Since the linear expansion coefficients of the conductive ring 22 and the metal base material 21 are similar, it is possible to prevent the conductive ring 22 from coming off the through hole 211 of the metal base material 21 even when the fastened member 2 generates heat.

[0077] In the fastened members 2 of this embodiment, the metal base material 21 and the conductive ring 22 may be made of a metal selected from the group consisting of aluminum, aluminum alloys, copper, and copper alloys. These metals have excellent conductivity and workability, and are therefore suitable for use as materials for the fastened members 2.

[0078] In the fastened members 2 of this embodiment, the conductive ring 22 may have a yield stress equal to or greater than the yield stress of the metal base material 21 and a Vickers hardness of 30 to 700 HV. Having the yield stress of the conductive ring 22 within this range reduces the likelihood of the conductive ring 22 buckling and causing loosening between the fastening member and the fastened member 2 when fastened with a fastening member. As a result, a conductive surface is secured between the fastened member 2 and the other fastened member 3, thereby increasing the conductivity therebetween. Furthermore, having the Vickers hardness of the conductive ring 22 within this range allows the metal oxide coating present on the inner surface 212 of the through hole 211 in the metal base material 21 to be destroyed when the conductive ring 22 is inserted.

[0079] In the fastened members 2 of this embodiment, the surface of the conductive ring 22 may be provided with a metal plating layer having a Vickers hardness greater than that of the metal base material 21. By providing such a metal plating layer, it is possible to destroy the metal oxide film present on the inner surface 212 of the through hole 211 of the metal base material 21 during insertion. Furthermore, by providing the metal plating layer, it is possible to suppress galvanic corrosion.

[0080] In the fastened member 2 of this embodiment, the outer peripheral surface 223 of the conductive ring 22 may have a protrusion or a recess that comes into contact with the inner surface 212 of the through hole 211 in the metal base material 21. By providing the protrusion or the recess on the outer peripheral surface 223 of the conductive ring 22, the contact area between the metal base material 21 and the conductive ring 22 increases, and therefore the conductivity between the metal base material 21 and the conductive ring 22 can be further improved.

[0081] In the fastened member 2 of this embodiment, the outer peripheral surface 223 of the conductive ring 22 may have threads 2233 that come into contact with the inner surface 212 of the through hole 211 in the metal base material 21. By providing the threads 2233 on the outer peripheral surface 223 of the conductive ring 22, the contact area between the metal base material 21 and the conductive ring 22 increases, thereby further improving the conductivity between the metal base material 21 and the conductive ring 22.

[0082] In the fastened members 2 of this embodiment, the conductive ring 22 may have a flange 226 that comes into contact with a surface other than the inner surface 212 of the through hole 211 of the metal base material 21. By providing the flange 226 on the conductive ring 22, the contact area between the metal base material 21 and the conductive ring 22 increases, thereby further improving the conductivity between the metal base material 21 and the conductive ring 22.

[0083] In this embodiment, the fastened members 2 may be bus bars. The fastened members 2 can be suitably used as bus bars because they can increase electrical conductivity and strength against fastening members.

[0084] The fastening structure 1 of this embodiment includes a fastened member 2, another fastened member 3 different from the fastened member 2, and a fastening member that fastens and fixes the fastened member 2 and the other fastened member 3 to each other. As described above, the fastened member 2 uses the conductive ring 22, and therefore the fastening structure 1 reduces manufacturing costs while providing good conductivity between the fastened member 2 and the other fastened member 3.

[0085] Hereinafter, the present embodiment will be described in more detail with reference to examples, comparative examples and reference examples, but the present embodiment is not limited to these examples.

[0086] [Reference Example 1] In Reference Example 1, it is explained, along with experimental data, that the contact surface between the fastened member 2a and another fastened member 3a, which exists between the seat surface 411 of the head 41 of the bolt 4 and the seat surface 511 of the nut 5, becomes a conductive surface.

[0087] (Preparation of test sample) In this example, the following members were first prepared: - Fastened member: Pure aluminum A1050 test piece (bare material), 2 mm thick, 20 mm wide, 40 mm long, with a φ6.4 mm hole - Fastening member: Titanium M6 flange bolt (no surface treatment) - Fastening member: Titanium M6 flange nut (no surface treatment)

[0088] Next, two A1050 test pieces were fastened together with titanium bolts and nuts to obtain a fastening structure, as shown in the upper diagram of Fig. 16. In this example, titanium bolts and nuts were used because using steel bolts and nuts, which are magnetic materials, would cause noise in magnetic field measurements.

[0089] (Test Conditions) Next, under the following conditions, the magnetic field strength distribution in the X direction shown in the lower diagram of Fig. 16 was mapped while current was applied between the fastened member 2a of the above-mentioned fastening structure and another fastened member 3a. Testing machine: Magnetic field microscope FOCUS005 (manufactured by Integral Geometry Science Co., Ltd.) Current application conditions: AC 37mApp, 113Hz Scanning conditions: Observation of the side direction of the fastening structure

[0090] (Evaluation) The relationship between electric current and the magnetic field generated around it can be expressed by Ampere's law, or right-hand rule. Therefore, as shown in the lower diagram of Figure 16, the magnitude of the magnetic field X component represents the magnitude of the electric current Y component.

[0091] When the magnitude of the magnetic field X component in the fastening structure is represented as a contour diagram, it is found that a region where the magnetic field X component is large (a dark colored region) exists only in the region sandwiched between the bearing surface of the bolt 4 and the bearing surface of the nut 5, as shown in the lower diagram of Figure 16. In other words, it is found that there is a region where the current Y component is locally large, and that the current in the region sandwiched between the bearing surface of the bolt 4 and the bearing surface of the nut 5 is particularly large.

[0092] If the entire contact area between the workpiece 2a and the other workpiece 3a functions as a conducting surface, the current Y component will be present throughout the entire contact area between the workpiece 2a and the other workpiece 3a, and the current density will be reduced because the conducting surface will be wider than the cross section of the workpiece. Therefore, the magnetic field X component should be detected uniformly over a wide area of ​​the interface between the workpieces.

[0093] However, as described above, in the fastened members 2a and 3a, a region where the magnetic field X component is large exists only in the region sandwiched between the seating surface of the bolt 4 and the seating surface of the nut 5. Therefore, it can be seen that the region that functions as the conductive surface between the fastened member 2a and the other fastened member 3a in the fastening structure is not the entire contact surface between the fastened members, but only the region sandwiched between the bolt seating surface and the nut seating surface. Therefore, it can be seen that the conductivity of the fastening structure is improved by interposing a conductive ring in the region sandwiched between the bolt seating surface and the nut seating surface.

[0094] Example 1 In Example 1, the electrical conductivity of fastened members whose base metal is made of an aluminum alloy was evaluated.

[0095] (Preparation of Test Samples) Test samples of Examples 1-1 and 1-2 and Comparative Examples 1-1 and 1-2 were prepared as follows.

[0096] Example 1-1 First, a plate material made of aluminum alloy A6101, measuring 7 mm thick, 20 mm wide, and 40 mm long, was prepared. Then, as shown in Fig. 17, a cylindrical through-hole with an inner diameter of 14.95 mm was drilled in the center of the plate material to produce a metal base material. Note that no surface treatment such as plating was performed on the metal base material.

[0097] Next, a cylindrical conductive ring made of pure copper C1020 was prepared. The conductive ring had an insertion hole with an inner diameter of 6.4 mm, an outer diameter of 15.10 mm, and a thickness of 7 mm. In other words, the outer diameter of the conductive ring was slightly larger than the inner diameter of the through hole in the metal base material. The conductive ring was not subjected to surface treatment such as plating.

[0098] Next, a conductive ring was placed on top of the through hole in the metal base material, and the conductive ring was pressed into the through hole in the metal base material by applying pressure from above using a compression testing machine. In this way, the test sample of this example was obtained. The material, shape, and presence or absence of surface treatment of the metal base material, as well as the material, shape, and presence or absence of surface treatment of the conductive ring, are summarized in Table 1.

[0099] The Vickers hardness of the aluminum alloy A6101 plate and the conductive ring made of pure copper C1020 was measured three times each, and the results are shown in Table 1. Table 1 shows that the Vickers hardness of the conductive ring is greater than that of the metal base material.

[0100] Example 1-2 First, the same metal base material as in Example 1-1 was prepared. Next, a cylindrical conductive ring made of pure copper C1020 was prepared in the same manner as in Example 1-1. Furthermore, the conductive ring was nickel-plated to a thickness of 5 μm. Then, in the same manner as in Example 1-1, the conductive ring was press-fitted into the through-hole of the metal base material. In this manner, the test sample of this example was obtained.

[0101] The Vickers hardness of the conductive ring made of pure copper C1020 and plated with nickel was measured three times, and the results are shown in Table 1. From Table 1, it can be seen that the Vickers hardness of the conductive ring is greater than that of the metal base material.

[0102] <Comparative Example 1-1> First, a plate material made of aluminum alloy A6101 and measuring 7 mm thick, 20 mm wide, and 40 mm long was prepared. This metal base material was not subjected to any surface treatment, such as plating. A cylindrical insertion hole with an inner diameter of 6.5 mm was then drilled in the center of the plate material to obtain the test sample of this example. In other words, this test sample of this example was a sample in which only an insertion hole was formed in the metal base material, without including a conductive ring.

[0103] Comparative Example 1-2 First, a plate material made of aluminum alloy A6101, measuring 7 mm thick, 20 mm wide, and 40 mm long, was prepared. This metal base material was not subjected to any surface treatment, such as plating. A cylindrical through-hole with an inner diameter of 14.95 mm was then drilled in the center of the plate material to obtain the test sample of this example. In other words, this test sample was a sample in which only a through-hole was formed in the metal base material, without any conductive ring.

[0104]

[0105] (Evaluation) <Measurement of Electrical Resistance of Test Sample> The electrical resistance of each test sample was measured using a four-terminal method. Specifically, as shown in Fig. 18, a current source clip 611 of a DC current source 61 was connected to a corner at one end in the width direction of each test sample. Furthermore, a voltmeter clip 621 of a voltmeter 62 was connected to a corner at the other end in the width direction of each test sample. Note that a SourceMeter2401 manufactured by Keithley Instruments, Inc. was used as the DC current source 61, and a MultiMeter2002 manufactured by Keithley Instruments, Inc. was used as the voltmeter 62.

[0106] To eliminate the influence of measurement errors due to thermoelectric power, the electrical resistance of each test sample was determined as the slope of the IV line obtained by sweeping the current from -1 A to +1 A. The electrical resistance of the test sample for each example is shown in Table 2.

[0107]

[0108] As shown in Table 2, the test samples of Examples 1-1 and 1-2 have electrical resistance equivalent to that of Comparative Example 2-1, which is a metal base material with an insertion hole. If no current passes through the conductive ring, the test samples of Examples 1-1 and 1-2 should have electrical resistance equivalent to that of Comparative Example 1-2, which does not have a conductive ring fitted. Therefore, this result indicates that the metal base material and the conductive ring are in contact with each other and are electrically conductive.

[0109] Furthermore, when current passes through the conductive ring, contact resistance occurs at the boundary between the metal base material and the conductive ring due to the presence of voids and an oxide film. However, the difference in contact resistance between the test samples of Examples 1-1 and 1-2 and the test sample of Comparative Example 1-1 is less than 1 μΩ. Thus, in the test samples of Examples 1-1 and 1-2, the metal base material is an aluminum alloy, while the conductive ring is made of copper, which has excellent conductivity. Therefore, it is believed that the reduction in electrical resistance due to the conductive ring is greater than the increase in electrical resistance due to the contact resistance at the boundary. Furthermore, because the conductive ring is harder than the metal base material, when the conductive ring is press-fitted into the through hole of the metal base material, it scrapes off the oxide film on the inner surface of the through hole of the metal base material, thereby improving the contact condition at the interface between the metal base material and the conductive ring. Therefore, it can be seen that even when the conductive ring is fitted into the metal base material, the current-carrying function of the fastened members is not impaired.

[0110] <Measurement of Electrical Resistance of Fastening Structure Using Test Sample> Fastening structures were fabricated using the test samples of Example 1-1, Example 1-2, and Comparative Example 1-1, and the electrical resistance of the fastening structures was measured by the four-terminal method.

[0111] First, a test piece was prepared as the mating material (the other fastened member 3), which had a thickness of 2 mm, a width of 20 mm, a length of 40 mm, and a bolt insertion hole with a diameter of 6.4 mm. The test piece was made of pure copper (C1020) and had a matte tin-plated surface (plating thickness of 2 μm). Furthermore, the bolts were steel M6 flange bolts with trivalent chromium treatment on the surface, and the nuts were steel M6 flange nuts with trivalent chromium treatment on the surface.

[0112] Then, the test sample 2 of Example 1-1 and the mating member 3 were fastened together with a bolt 4 and a nut 5 to obtain the fastening structure according to Example 1-1 shown in FIGS. 19A and 19B. At this time, the test sample was provided on the bearing surface side of the bolt, and then the bolt side was fastened. When fastening the bolt and nut, a torque wrench (DIW-15 manufactured by Sugisaki Keiki Co., Ltd.) was used to tighten the bolts with a tightening torque of 5 Nm, 10 Nm, or 15 Nm. Then, three fastening structures were produced, each tightened with a tightening torque of 5 Nm, 10 Nm, and 15 Nm.

[0113] Similarly, the fastening structure according to Example 1-2 was obtained by fastening the test sample 2 of Example 1-2 and the mating material 3 with a bolt 4 and a nut 5. Furthermore, the fastening structure according to Comparative Example 1-1 was obtained by fastening the test sample of Comparative Example 1-1 and the mating material with a bolt and a nut. In this case, three fastening structures were produced each, fastened with a tightening torque of 5 Nm, 10 Nm, and 15 Nm.

[0114] Next, the electrical resistance of each fastening structure was measured using a four-terminal method. Specifically, as shown in Fig. 19A, a current source clip 611 of a DC current source 61 was connected to a corner at one end of each fastening structure in the width direction. Furthermore, a voltmeter clip 621 of a voltmeter 62 was connected to a corner at the other end of each fastening structure in the width direction. Note that a SourceMeter2401 manufactured by Keithley Instruments, Inc. was used as the DC current source 61, and a MultiMeter2002 manufactured by Keithley Instruments, Inc. was used as the voltmeter 62.

[0115] To eliminate the influence of measurement errors due to thermoelectric power, the slope of the IV line obtained by sweeping the current from -1 A to +1 A was taken as the electrical resistance of each fastening structure. The electrical resistance of the fastening structure for each example is shown in Figure 20.

[0116] As shown in FIG. 20, the fastening structures according to Examples 1-1 and 1-2 have lower electrical resistance in the fastened portion at any tightening torque than the fastening structure according to Comparative Example 1-1.

[0117] As explained above, the flow of electricity in the fastened portion of a fastening structure is dominated by the area between the bolt and nut bearing surfaces. The presence of a conductive ring fitted in this area reduces the conductor resistance in this area. Furthermore, when pure aluminum or an aluminum alloy with an insulating oxide film on its surface is used as the metal base material, the conductive ring reduces the contact resistance with the mating material more than the metal base material.

[0118] Furthermore, because the conductive ring has a higher Vickers hardness than the base metal, the conductive ring improves the hardness of the part that comes into contact with the bolt bearing surface. As a result, it is thought that loosening caused by deformation of the part that comes into contact with the bolt bearing surface in the test sample due to the fastening force can be suppressed. Therefore, even when fastened with a large fastening force, the electrical resistance of the fastened part in the fastening structure can be stabilized.

[0119] In contrast, the fastening structure of Comparative Example 1-1 has an insulating oxide coating on the surface of the test sample, which increases the contact resistance between the test sample and the mating material. In particular, when the tightening torque is low, the electrical resistance of the fastened part increases significantly.

[0120] As such, it can be seen that the fastening structures according to Examples 1-1 and 1-2 can reduce the electrical resistance of the fastened portion even at a lower tightening torque than the fastening structure of Comparative Example 1-1. Also, M6 bolts are mainly used at tightening torques of about 5 to 10 Nm. Therefore, the fastening structures according to Examples 1-1 and 1-2 are advantageous in that they can stably reduce the electrical resistance of the fastened portion even at low tightening torques.

[0121] Example 2 In Example 2, the electrical conductivity of fastened members whose base metal was made of pure aluminum was evaluated.

[0122] (Preparation of Test Samples) Test samples of Examples 2-1 and 2-2 and Comparative Example 2-1 were prepared as follows.

[0123] Example 2-1 First, a plate material made of pure aluminum A1050, measuring 7 mm thick, 20 mm wide, and 60 mm long, was prepared. Then, as shown in Fig. 21, a cylindrical through-hole with an inner diameter of 14.95 mm was drilled at the longitudinal end of the plate material, thereby producing a metal base material. Note that no surface treatment such as plating was performed on the metal base material.

[0124] Next, a cylindrical conductive ring made of pure copper C1020 was prepared. The conductive ring had an insertion hole with an inner diameter of 6.4 mm, an outer diameter of 15.10 mm, and a thickness of 7 mm. In other words, the outer diameter of the conductive ring was slightly larger than the inner diameter of the through hole in the metal base material. The conductive ring was not subjected to surface treatment such as plating.

[0125] Next, a conductive ring was placed on top of the through hole of the metal base material, and the conductive ring was pressed into the through hole of the metal base material by applying pressure from above using a compression testing machine. In this way, the test sample of this example was obtained. The material, shape, and surface treatment of the metal base material of this example, as well as the material, shape, and surface treatment of the conductive ring, are summarized in Table 3.

[0126] The Vickers hardness of the plate material made of pure aluminum A1050 was measured three times, and the results are shown in Table 3. As shown in Table 3, it can be seen that the Vickers hardness of the conductive ring is greater than the Vickers hardness of the metal base material.

[0127] Example 2-2 First, the same metal base material as in Example 2-1 was prepared. Next, a cylindrical conductive ring made of pure copper C1020 was prepared in the same manner as in Example 2-1. Furthermore, the conductive ring was nickel-plated to a thickness of 5 μm. Then, in the same manner as in Example 2-1, the conductive ring was press-fitted into the through-hole of the metal base material. In this manner, the test sample of this example was obtained.

[0128] Comparative Example 2-1 First, a plate material made of pure aluminum A1050, measuring 7 mm thick, 20 mm wide, and 60 mm long, was prepared. Then, as shown in FIG. 21 , a cylindrical insertion hole with an inner diameter of 6.4 mm was drilled at the longitudinal end of the plate material. Furthermore, the surface of the plate material was subjected to a matte tin plating (plating thickness: 2 μm). In this manner, the test sample of this example was obtained. The test sample of this example was subjected to a tin plating process, which is a common method for reducing the contact resistance of aluminum surfaces.

[0129]

[0130] (Evaluation) <Measurement of Electrical Resistance of Test Samples> The electrical resistance of each test sample was measured using a four-terminal method. Specifically, as shown in Fig. 21, a current terminal clip 631 of a current terminal 63 of a resistance meter was connected to a corner at one end in the width direction of each test sample. Furthermore, a voltage terminal clip 641 of a voltage terminal 64 of the resistance meter was connected to a corner at the other end in the width direction of each test sample. The resistance meter used was an RM3545A manufactured by Hioki E.E. Corporation.

[0131] Then, to eliminate the influence of measurement errors due to thermoelectromotive force, measurements were carried out while reversing the polarity of the current terminals. The measurement current was set to DC 1A. The electrical resistance of each test sample was calculated using the following formula. The electrical resistance of the test sample for each example is shown in Table 4. R = (Vp - Vn) / 2I Vp: voltage drop before reversing the polarity of the current terminals Vn: voltage drop after reversing the polarity of the current terminals (becomes a negative value) I: measured current R: measured electrical resistance

[0132]

[0133] As shown in Table 4, the test samples of Examples 2-1 and 2-2 have electrical resistance equivalent to that of Comparative Example 2-1, which is a metal base material having an insertion hole. This result indicates that the metal base material and the conductive ring are in contact with each other and are electrically conductive.

[0134] Furthermore, compared with Examples 1-1 and 1-2, it can be seen that even if the metal base material becomes soft pure aluminum, the current-carrying function of the fastened components can be maintained in a good state by fitting the conductive ring in. Furthermore, it can be seen that even if the difference in hardness between the conductive ring and the metal base material becomes large, good fastened components can be produced by the manufacturing method of this embodiment.

[0135] <Measurement of Electrical Resistance of Fastening Structure Using Test Sample> Fastening structures were fabricated using the test samples of Example 2-1, Example 2-2, and Comparative Example 2-1, and the electrical resistance of the fastening structures was measured by the four-terminal method.

[0136] First, a test piece was prepared as the mating material (the other fastened member 3), measuring 4 mm in thickness, 20 mm in width, and 60 mm in length, with a bolt insertion hole having a diameter of 6.4 mm. The test piece was made of pure copper (C1020) and had a matte tin-plated surface (2 μm thick). Furthermore, the bolts were steel M6 flange bolts with trivalent chromium treatment on the surface, and the nuts were steel M6 flange nuts with trivalent chromium treatment on the surface.

[0137] Then, the test sample 2 of Example 2-1 and the mating member 3 were fastened together with a bolt 4 and a nut 5 to obtain the fastening structure according to Example 2-1 shown in FIGS. 23A and 23B. At this time, the test sample was provided on the bearing surface side of the bolt, and then the bolt side was fastened. When fastening the bolt and nut, a torque wrench (DIW-15 manufactured by Sugisaki Keiki Co., Ltd.) was used to tighten the bolt and nut with a tightening torque of 5 Nm, 10 Nm, or 15 Nm. Then, three fastening structures were produced, each tightened with a tightening torque of 5 Nm, 10 Nm, and 15 Nm.

[0138] Similarly, the fastening structure according to Example 2-2 was obtained by fastening the test sample 2 of Example 2-2 and the mating material 3 with a bolt 4 and a nut 5. Furthermore, the fastening structure according to Comparative Example 2-1 was obtained by fastening the test sample of Comparative Example 2-1 and the mating material with a bolt and a nut. In this case, three fastening structures were produced each, fastened with a tightening torque of 5 Nm, 10 Nm, and 15 Nm.

[0139] Next, the electrical resistance of each fastening structure was measured using a four-terminal method. Specifically, as shown in Fig. 23A, a current terminal clip 631 of a current terminal 63 of a resistance meter was connected to a corner at one end of each fastening structure in the width direction. Furthermore, a voltage terminal clip 641 of a voltage terminal 64 of the resistance meter was connected to the other end of each fastening structure in the width direction. The resistance meter used was an RM3545A manufactured by Hioki E.E. Corporation.

[0140] Then, to eliminate the influence of measurement errors due to thermoelectromotive force, measurements were carried out while reversing the polarity of the current terminal. The measurement current was set to DC 1A. The electrical resistance of each test sample was calculated using the following formula. The electrical resistance of the fastening structure of each example is shown in Figure 24. R = (Vp - Vn) / 2I Vp: voltage drop before reversing the polarity of the current terminal Vn: voltage drop after reversing the polarity of the current terminal (becomes a negative value) I: measured current R: measured electrical resistance

[0141] 24, it can be seen that the fastening structures of Examples 2-1 and 2-2 have electrical resistance at the fastened portion that is as low as that of the fastening structure of Comparative Example 2-1 at any tightening torque. It can also be seen that the fastening structures of Examples 2-1 and 2-2 have low dependency on tightening torque, and are stable in a low electrical resistance state even at low tightening torques.

[0142] The fastening structure of Comparative Example 2-1 was subjected to tin plating, a common method for reducing the contact resistance of aluminum surfaces. However, because bus bars, which are fastened components for electric vehicles, are long, plating the bus bars would require a lot of work to handle, complicating the manufacturing process and increasing costs.

[0143] However, by fitting a conductive ring into the metal base material, as in the fastening structures of Examples 2-1 and 2-2, it is possible to reduce the electrical resistance to the same level as the conventional fastening structure of Comparative Example 2-1. Furthermore, by fitting a conductive ring into the metal base material, it is possible to stably achieve low electrical resistance, even though the metal base material is not plated.

[0144] Reference Example 2 In Reference Example 2, the conductivity of a fastening structure using fastened members made of aluminum was evaluated.

[0145] (Preparation of Test Samples) Test samples of Reference Examples 2-1 and 2-2 were prepared as follows.

[0146] <Reference Example 2-1> First, a plate material made of aluminum and measuring 2 mm thick, 20 mm wide, and 40 mm long was prepared. This metal base material was not subjected to any surface treatment, such as plating. A cylindrical insertion hole with an inner diameter of 6.5 mm was then drilled in the center of the plate material to obtain a test sample for this example. This test sample was a sample that did not include a conductive ring and was made of a metal base material made of aluminum with only an insertion hole formed therein.

[0147] <Reference Example 2-2> First, a plate material made of tin-plated aluminum, 2 mm thick, 20 mm wide, and 40 mm long, was prepared. Then, a cylindrical insertion hole with an inner diameter of 6.5 mm was drilled in the center of the plate material, to obtain a test sample of this example. The test sample of this example was a sample that did not include a conductive ring and was made of a metal base material made of tin-plated aluminum with only an insertion hole formed therein.

[0148] (Evaluation) Fastening structures were fabricated using the test samples of Reference Examples 2-1 and 2-2, and the electrical resistance of the fastening structures was measured by the four-terminal method.

[0149] First, a test piece was prepared as the mating material (the other fastened member 3), measuring 2 mm in thickness, 20 mm in width, and 40 mm in length, with a bolt insertion hole having a diameter of 6.4 mm. The test piece was made of pure copper (C1020) with a tin-plated surface. Furthermore, the bolts were steel M6 flange bolts with trivalent chromium treatment on the surface, and the nuts were steel M6 flange nuts with trivalent chromium treatment on the surface.

[0150] Then, the test sample 2a of Reference Example 2-1 and the mating member 3 were fastened with a bolt 4 and a nut 5 to obtain the fastening structure according to Reference Example 2-1 shown in FIGS. 25A and 25B. At this time, the test sample was provided on the bearing surface side of the bolt, and the bolt side was further fastened. When fastening the bolt and nut, a torque wrench (DIW-15 manufactured by Sugisaki Keiki Co., Ltd., DB50N manufactured by Tohnichi Manufacturing Co., Ltd.) was used to tighten the bolt and nut with a tightening torque of 6 Nm, 18 Nm, or 30 Nm. Then, three fastening structures were produced, each tightened with a tightening torque of 6 Nm, 18 Nm, and 30 Nm.

[0151] Similarly, a fastening structure according to Reference Example 2-2 was obtained by fastening the test sample 2a of Reference Example 2-2 and the mating member 3 with a bolt 4 and a nut 5. When fastening the bolt and nut, a torque wrench was used to tighten them with a tightening torque of 3 Nm, 9 Nm, or 15 Nm. Three fastening structures were produced, each tightened with a tightening torque of 3 Nm, 9 Nm, and 15 Nm.

[0152] Next, the electrical resistance of each fastening structure was measured using a four-terminal method. Specifically, as shown in Fig. 25A, a current source clip 611 of a DC current source 61 was connected to a corner at one end of each fastening structure in the width direction. Furthermore, a voltmeter clip 621 of a voltmeter 62 was connected to the other end of each fastening structure in the width direction. Note that a SourceMeter2401 manufactured by Keithley Instruments, Inc. was used as the DC current source 61, and a MultiMeter2002 manufactured by Keithley Instruments, Inc. was used as the voltmeter 62.

[0153] Then, to eliminate the influence of measurement errors due to thermoelectric power, the slope of the IV line obtained by sweeping the current from -1 A to +1 A was taken as the electrical resistance of each fastening structure. The electrical resistance of the fastening structure for each example is shown in Figure 26.

[0154] 26, it can be seen that the fastening structure of Reference Example 2-2, which was tin-plated, had lower electrical resistance than the fastening structure of Reference Example 2-1, which was not tin-plated. It can also be seen that the fastening structure of Reference Example 2-1, which was not tin-plated, did not have a lower electrical resistance and also had a large variation in electrical resistance.

[0155] Typically, an insulating oxide film exists on the surface of pure aluminum and aluminum alloys. Therefore, when aluminum and its alloys are used as fastened components, the presence of this oxide film increases the electrical resistance of the fastened portion of the fastening structure. Even if the tightening torque when fastening a bolt and nut is increased to break down the oxide film on the contact surface of the fastened components with the tightening force, the electrical resistance does not decrease and the electrical resistance varies significantly due to the following two reasons: (1) The efficiency with which the tightening torque is converted into tightening force varies greatly depending on the frictional characteristics of the contact surfaces between the fastening component and the fastened component; and (2) Because the tightening force acts perpendicular to the contact surface of the fastened components, the destruction of the oxide film due to the crushing of the surface irregularities of the fastened components is dominant. Therefore, once the irregularities are crushed to a certain extent, the film destruction effect decreases.

[0156] For this reason, when aluminum and its alloys are used as fastened components, plating is applied to remove coatings from the fastened components and improve the surface friction characteristics. For example, tin plating the fastened components can stabilize the electrical resistance of the fastened parts. However, plating aluminum or its alloys complicates the manufacturing process and increases costs.

[0157] However, by fitting a conductive ring into the metal base material, as in the fastened members of this embodiment, it is possible to stably achieve low electrical resistance even though the metal base material is not plated.

[0158] The entire contents of Japanese Patent Application No. 2024-124678 (filing date: July 31, 2024) are incorporated herein by reference.

[0159] Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims.

[0160] REFERENCE SIGNS LIST 1 Fastening structure 2 Fastened member 3 Other fastened member 4 Bolt (fastening member) 5 Nut (fastening member) 21 Metal base material 22 Conductive ring 211 Through hole in metal base material 212 Inner surface of through hole in metal base material 221 Insertion hole in conductive ring 223 Outer surface of conductive ring 2231 Protrusion on outer surface of conductive ring 2232 Recess on outer surface of conductive ring 2233 Thread on outer surface of conductive ring

Claims

1. A fastened member comprising: a metal base material having a through hole; and a conductive ring having an insertion hole that is fitted into the through hole of the metal base material and into which a fastening member is inserted, wherein the Vickers hardness of the conductive ring is greater than the Vickers hardness of the metal base material, and the inner surface of the through hole of the metal base material and the outer peripheral surface of the conductive ring are in contact with each other and are electrically conductive.

2. The fastened members according to claim 1, wherein the metal base material and the conductive ring are made of a metal selected from the group consisting of aluminum, aluminum alloys, copper, and copper alloys.

3. The fastened members according to claim 1 or 2, wherein the conductive ring has a yield stress equal to or greater than the yield stress of the metal base material and a Vickers hardness of 30 to 700 HV.

4. A fastened member according to any one of claims 1 to 3, wherein the surface of the conductive ring is provided with a metal plating layer having a Vickers hardness greater than that of the metal base material.

5. A fastened member according to any one of claims 1 to 4, wherein the outer surface of the conductive ring has a protrusion or recess that comes into contact with the inner surface of the through hole in the metal base material.

6. A fastened member according to any one of claims 1 to 4, wherein the outer surface of the conductive ring has a thread that contacts the inner surface of the through hole in the metal base material.

7. A fastened member according to any one of claims 1 to 6, wherein the conductive ring has a flange portion that contacts a surface other than the inner surface of the through hole of the metal base material.

8. A fastened member according to any one of claims 1 to 7, wherein the fastened member is a bus bar.

9. A fastening structure comprising: a fastened member according to any one of claims 1 to 8; another fastened member different from the fastened member; and a fastening member that fastens and fixes the fastened member and the other fastened member to each other.

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