Connection structure

Abstract

This connection structure includes a terminal, an attachment object to which the terminal is attached, and a bolt connecting the terminal and the attachment object. The terminal includes: a first surface facing the attachment object in a state of being connected to the attachment object; and a cutout through which the bolt passes. The first surface includes protrusions and recesses formed around the cutout. The protrusions and recesses include a specific protrusion. The material of the terminal is pure aluminum or an aluminum alloy. The Vickers hardness of the terminal is 80 HV or more. The ratio S1 / S2 between a first area S1 and a second area S2 is 0.60 or less, where the first area S1 is 5mm2 or more.

Description

Connection structure

[0001] The present disclosure relates to a connection structure. This application claims priority to Japanese Patent Application No. 2023-188901, filed on November 2, 2023. The entire contents of the Japanese patent application are incorporated herein by reference.

[0002] Patent Documents 1 and 2 disclose an electric wire with a terminal that is connected to an attachment object by a bolt. The terminal has a through hole. A bolt that connects the terminal to the attachment object passes through the through hole. The terminal and the attachment object are fastened together with the bolt and nut, thereby mechanically fixing the terminal to the attachment object and electrically connecting them.

[0003] The terminals provided on the electric wire with terminal are made of, for example, aluminum or an aluminum alloy, which is lightweight and contributes to reducing the weight of the terminal and the electric wire with terminal.

[0004] JP 2022-11128 A JP 2022-22609 A

[0005] The connection structure disclosed herein includes a terminal, an attachment object to which the terminal is attached, and a bolt connecting the terminal to the attachment object. The terminal has a first surface facing the attachment object when connected to the attachment object, and a notch through which the bolt passes. The first surface includes an uneven portion formed around the notch. The uneven portion includes at least one of a plurality of circular protrusions concentric with the center axis of the notch, a plurality of arc-shaped protrusions forming part of the concentric circle, a plurality of pyramidal protrusions formed between recesses formed in a square or chevron pattern, and a plurality of linear protrusions arranged in parallel. The terminal is made of pure aluminum or an aluminum alloy. The terminal has a Vickers hardness of 80 HV or higher. When the first surface and the attachment object are connected by tightening the bolt, the ratio S1 / S2 of the first area S1 to the second area S2 is 0.60 or less. The first area S1 is the area of ​​the region where the first surface comes into contact with the object to be attached at a pressure of 25 MPa or more. The second area S2 is the area of ​​a circular region having an inner diameter equal to the nominal diameter D1 of the bolt and an outer diameter equal to the bearing surface diameter D2 of the bolt. The first area S1 is 5 mm ２ That's all.

[0006] FIG. 1 is a schematic side view showing a connection structure of Embodiment 1. FIG. 2 is a schematic plan view showing a first example of a terminal and an end of an electric wire included in the connection structure of Embodiment 1. FIG. 3 is a schematic plan view showing a second example of a terminal included in the connection structure of Embodiment 1. FIG. 4 is a schematic plan view showing a third example of a terminal included in the connection structure of Embodiment 1. FIG. 5 is a schematic plan view showing a fourth example of a terminal included in the connection structure of Embodiment 1. FIG. 6 is a schematic plan view showing a concave-convex portion of a terminal included in the connection structure of Embodiment 1. FIG. 7 is a cross-sectional view taken along line VII-VII of FIG. 6. FIG. 8 is a plan view showing a concave-convex portion of a terminal included in the connection structure of Embodiment 2. FIG. 9 is a cross-sectional view taken along line IX-IX of FIG. 8. FIG. 10 is a cross-sectional view taken along line X-X of FIG. 8. FIG. 11 is a plan view showing a concave-convex portion of a terminal included in the connection structure of Embodiment 3. FIG. 12 is a cross-sectional view taken along line XII-XII of FIG. 11. FIG. 13 is a plan view showing a concave-convex portion of a terminal included in the connection structure of Embodiment 4. FIG. 14 is a cross-sectional view taken along XIV-XIV in FIG. 13. FIG. 15 is a plan view showing the concave-convex portion of a terminal included in the connection structure of embodiment 5. FIG. 16 is a cross-sectional view taken along XVI-XVI in FIG. 15. FIG. 17 is a plan view showing the concave-convex portion of a terminal included in the connection structure of embodiment 6. FIG. 18 is a cross-sectional view taken along XVIII-XVIII in FIG. 17. FIG. 19 is a plan view showing the concave-convex portion of a terminal included in the connection structure of embodiment 7. FIG. 20 is an enlarged view showing an enlarged region α in FIG. 19. FIG. 21 is a cross-sectional view taken along XXI-XXI in FIG. 19. FIG. 22 is a plan view showing the concave-convex portion of a terminal included in the connection structure of embodiment 8. FIG. 23 is a cross-sectional view taken along XXIII-XXIII in FIG. 22. FIG. 24 is a plan view showing the concave-convex portion of a terminal included in the connection structure of embodiment 9. FIG. 25 is a cross-sectional view taken along XXV-XXV in FIG. 24. Fig. 26 is a plan view showing the concave-convex portion of a terminal provided in the connection structure of embodiment 10. Fig. 27 is an enlarged view showing an enlarged region β of Fig. 26. Fig. 28 is a cross-sectional view taken along line XXVIII-XXVIII of Fig. 26. Fig. 29 is a plan view showing the concave-convex portion of a terminal provided in the connection structure of samples 103 and 104. Fig. 30 is a cross-sectional view taken along line XXX-XXX of Fig. 29. Fig. 31 is a plan view showing the concave-convex portion of a terminal provided in the connection structure of sample 105. Fig. 32 is a cross-sectional view taken along line XXXII-XXXII of Fig. 31. Fig. 33 is a schematic plan view of a terminal used in a fastening test.FIG. 34 is an explanatory diagram for explaining an outline of the fastening test.

[0007] [Problem to be Solved by the Present Disclosure] In a connection structure connecting a terminal and an attachment object, contact resistance at the interface between the terminal and the attachment object may increase over time. For example, when vibration and thermal shock act on the connection structure, the bolt fastening the terminal to the attachment object loosens, or the terminal and attachment object rub against each other at the interface. In particular, when the terminal and attachment object are made of different materials, the difference in thermal expansion coefficients between the terminal and attachment object makes the interface more susceptible to thermal shock. Friction and other factors cause a new aluminum surface to form on the surface of the terminal at the interface. When the new aluminum surface oxidizes, the contact resistance between the terminal and attachment object increases.

[0008] Furthermore, when a gap is formed at the interface due to vibration and thermal shock, the portion of the surface of the attachment object that is not in contact with the terminal oxidizes. When maintenance of the connection structure is performed, the bolts are loosened, and when the maintenance is completed, the terminal and attachment object are retightened with the bolts. When the oxidized portion of the attachment object comes into contact with the terminal during retightening, the contact resistance between the terminal and attachment object increases.

[0009] One object of the present disclosure is to provide a connection structure that can suppress an increase in contact resistance over time at the interface between a terminal and an attachment object, and can also suppress an increase in contact resistance after maintenance. [Effects of the Present Disclosure] The connection structure of the present disclosure can suppress an increase in contact resistance over time at the interface between a terminal and an attachment object, and can also suppress an increase in contact resistance after maintenance.

[0010] <Description of Embodiments of the Present Disclosure> First, embodiments of the present disclosure will be listed and described.

[0011] (1) A connection structure according to one aspect of the present disclosure includes a terminal, an attachment target to which the terminal is attached, and a bolt connecting the terminal and the attachment target. The terminal includes a first surface facing the attachment target when connected to the attachment target, and a notch through which the bolt passes. The first surface includes an uneven portion formed around the notch. The uneven portion includes at least one of a plurality of circular protrusions concentric with the center axis of the notch, a plurality of arc-shaped protrusions forming part of the concentric circle, a plurality of pyramidal protrusions formed between recesses formed in a square or chevron pattern, and a plurality of linear protrusions arranged in parallel. The terminal is made of pure aluminum or an aluminum alloy. The terminal has a Vickers hardness of 80 HV or higher. When the first surface and the attachment target are connected by tightening the bolt, the ratio S1 / S2 of the first area S1 to the second area S2 is 0.60 or less. The first area S1 is the area of ​​the region where the first surface comes into contact with the object to be attached at a pressure of 25 MPa or more. The second area S2 is the area of ​​a circular region having an inner diameter equal to the nominal diameter D1 of the bolt and an outer diameter equal to the bearing surface diameter D2 of the bolt. The first area S1 is 5 mm ２ That's all.

[0012] The protrusions of the concave-convex portion of a terminal having a Vickers hardness of 80 HV or more easily bite into the attachment target when the terminal and the attachment target are connected with a bolt. The protrusions that bite into the attachment target are deformed by the attachment target. The deformation of the protrusions destroys the oxide coating near the protrusions, establishing electrical continuity between the terminal and the attachment target. The protrusions bite into the attachment target and deform, thereby firmly mechanically fixing the terminal and the attachment target. Furthermore, protrusions having a Vickers hardness of 80 HV or more are resistant to deformation by thermal shock and vibration after the terminal and the attachment target are connected. Therefore, the connection strength between the terminal and the attachment target is less likely to be reduced by thermal shock and vibration. That is, the clamping between the terminal and the attachment target is less likely to loosen, and the terminal and the attachment target are less likely to rub against each other at the interface between the terminal and the attachment target. As a result, new aluminum surfaces are less likely to form on the surface of the terminal at the interface due to friction, etc., and the contact resistance between the terminal and the attachment target is less likely to increase.

[0013] The first area S1 is the area of ​​the region where the first surface comes into contact with the attachment object when pressure equals or exceeds a specified value. When the axial force of the bolt is constant, the smaller the ratio of the first area S1 to the second area S2, the greater the pressure acting on the region of the first area S1. However, if the absolute value of the first area S1 is too small, the connection strength between the terminal and the attachment object will not be sufficiently ensured. When the ratio S1 / S2 is 0.60 or less and the first area S1 is 5 mm ２ If the above is the case, the terminal and the attachment object are mechanically connected firmly, and the connection strength is likely to be maintained over a long period of time, and as a result, the contact resistance between the terminal and the attachment object is unlikely to increase over time.

[0014] Before maintenance of the connection structure, the portions of the attachment object where the convex portions had dug are less likely to oxidize. By providing specific convex portions among the multiple concave-convex portions on the first surface, when the terminal and attachment object are re-fastened with the bolt after maintenance, the convex portions are more likely to dug into the portions where they had originally dug before maintenance. Therefore, the contact resistance between the terminal and attachment object after maintenance is less likely to increase.

[0015] (2) In the connection structure of (1) above, the first area S1 may be the area of ​​the specific color-developing region of the pressure-sensitive sheet, which is determined by a clamping test that satisfies the following condition: In the clamping test, a laminate in which the pressure-sensitive sheet is disposed between the first surface and the attachment target is clamped to a size of 138 × (D1) ２ The clamping force is ±50 N. The specific color-forming region is a region that has a color that indicates that the clamping force is 25 MPa or more.

[0016] In the connection structure of (2) above, the ratio S1 / S2 can be determined appropriately with good reproducibility. (3) In the connection structure of (1) or (2) above, the point symmetry parameter of the concave-convex portion may be 1.3 or more.

[0017] In the connection structure of (3) above, when the terminal and the attachment object are re-tightened with the bolt after maintenance, the protrusions tend to bite back into the places where they were originally biting in before maintenance, so the connection structure of (3) above can suppress an increase in contact resistance after maintenance.

[0018] (4) In any one of the connection structures (1) to (3) above, the cross-sectional shape of each of the plurality of protrusions may be triangular.

[0019] In the connection structure of (4) above, the protrusions easily bite into the object to be attached, and therefore the connection structure of (4) above easily reduces the contact resistance between the terminal and the object to be attached.

[0020] (5) In the connection structure of (4) above, the angle of the apex of each of the plurality of protrusions in cross section may be greater than 90° and less than or equal to 140°.

[0021] If the angle is greater than 90° and less than or equal to 140°, the apex of each protrusion can easily bite into the object to be attached. (6) In the connection structure of any one of (1) to (5), the material of the object to be attached may be pure copper or a copper alloy.

[0022] Pure copper or copper alloys are relatively easy to deform. Therefore, the convex portions of the terminal's concave and convex portions can easily bite into the object to be attached, strengthening the connection between the terminal and the object. Pure copper or copper alloys have high electrical conductivity, which reduces the amount of heat generated by the object to be attached.

[0023] (7) In any of the connection structures (1) to (6) above, the material of the attachment object may be oxygen-free copper, tough pitch copper, or JC100 according to the Society of Automotive Engineers of Japan standard.

[0024] The connection structure of (7) above can suppress an increase in contact resistance at the interface between the terminal and the attachment object over a long period of time, and can also suppress an increase in contact resistance after maintenance.

[0025] (8) In any of the connection structures (1) to (7) above, the material of the terminal may be International Registered Alloy Number 6061.

[0026] The connection structure of (8) above can suppress an increase in contact resistance at the interface between the terminal and the attachment object over a long period of time, and can also suppress an increase in contact resistance after maintenance.

[0027] <Details of the Embodiments of the Present Disclosure> Hereinafter, embodiments of the connection structure of the present disclosure will be described with reference to the drawings. The shapes, sizes, and positional relationships shown in each figure are expressed for the purpose of clarifying the description and do not necessarily represent the actual shapes, sizes, and positional relationships. The same symbols in the figures indicate the same objects. Note that the present invention is not limited to the configurations shown in the embodiments, but is defined by the claims, and all modifications within the meaning and scope equivalent to the claims are intended to be included.

[0028] First Embodiment [Connection Structure] A connection structure 1 of the embodiment will be described with reference to Fig. 1 to Fig. 7. As shown in Fig. 1, the connection structure 1 of the embodiment includes a terminal 2, an attachment object 3, and a bolt 4. The terminal 2 and the attachment object 3 are connected by the bolt 4. One of the features of the connection structure 1 of the embodiment is that it satisfies the following requirements (A) to (D).

[0029] (A) As shown in FIG. 6 , the terminal 2 has an uneven portion 25 formed around the notch 2h on the first surface 21. The uneven portion 25 has a specific number of convex portions 25a. For convenience of explanation, FIG. 6 shows a member simulating the terminal 2. Furthermore, the three circles shown on the outer periphery of the notch 2h in FIG. 6 indicate the bottom of the convex portion 25a. This also applies to FIGS. 8 , 11 , 15 , 17 , 19 , 22 , 24 , 26 , and so on, which will be described later. The three circles in FIG. 6 indicate, from the inside, the boundary between the left recess 25b and the left convex portion 25a in FIG. 7 , the boundary between the left and right convex portions 25a, and the boundary between the right convex portion 25a and the right recess 25b.

[0030] (B) The material of the terminal 2 is pure aluminum or an aluminum alloy, and the Vickers hardness of the terminal 2 is 80 HV or more.

[0031] (C) The ratio S1 / S2 of the first area S1 to the second area S2 (described later) is 0.60 or less. (D) The first area S1 is 5 mm ２ That's all.

[0032] [Terminal] The shape of the terminal 2 is not particularly limited as long as it is configured to be connected to the attachment object 3 via the bolt 4. As shown in FIGS. 1 and 2 , the terminal 2 in this example is part of a terminal-attached wire 10. The terminal-attached wire 10 is composed of an electric wire 5 and a terminal 2 that is independent of the electric wire 5. The electric wire 5 includes a conductor 50 and an insulating coating 51 that covers the outer periphery of the conductor 50. The outer diameter of the conductor 50 may be, for example, 0.1 mm to 50 mm, or 0.4 mm to 30 mm. The conductor 50 in this example is a stranded wire formed by twisting together multiple strands. The conductor 50 is made of, for example, pure copper, a copper alloy, pure aluminum, or an aluminum alloy. The thickness of the insulating coating 51 may be, for example, 0.1 mm to 10 mm, or 0.2 mm to 5 mm. The insulating coating 51 is made of, for example, a polyolefin-based resin as a main component. The polyolefin-based resin is, for example, polyethylene or polypropylene. The insulating coating 51 may also be made of a silicone-based resin. The terminal 2 is not limited to the form of this example in which it is connected to the electric wire 5. Unlike this example, the terminal 2 may be, for example, a part of a bus bar, i.e., a connection portion formed on the bus bar. The connection portion is a part of the bus bar formed into a terminal shape. Furthermore, unlike this example, the terminal 2 may be, for example, a part of a single-core wire, i.e., a connection portion formed on the tip of the single-core wire.

[0033] The terminal 2 shown in FIG. 2 is a CB-type terminal. Unlike the example of FIG. 2, the terminal 2 may be a U-type terminal, a Y-type terminal, or an R-type terminal. The terminal 2 has a first surface 21 and a second surface 22. The first surface 21 is a surface that faces the attachment object 3 when the terminal 2 is connected to the attachment object 3. The first surface 21 has a portion that overlaps with the attachment object 3 and a portion that does not overlap with the attachment object 3. The second surface 22 is a surface opposite the first surface 21. The terminal 2 has a notch 2h that opens to the first surface 21 and the second surface 22. A bolt 4 passes through the notch 2h. The notch 2h is a concept that includes not only a notch as is commonly thought of, but also a through hole. The notch 2h includes a through hole and a slit. A through hole is a hole that opens only to the first surface 21 and the second surface 22 as shown in FIG. 2 , and does not open to any surfaces perpendicular to the first surface 21 and the second surface 22, such as the left end surface, top end surface, or bottom end surface of the terminal 2 in FIG. 2 . That is, a through hole is a hole whose cross section along the first surface 21 has a closed cross section. The shape of the through hole is, for example, a circular hole shape as shown in FIG. 2 or an elongated hole shape as shown in FIG. 5 . A slit is a region that opens not only to the first surface 21 and the second surface 22 as shown in FIG. 3 , but also to any one of the surfaces perpendicular to the first surface 21 and the second surface 22, i.e., the left end surface, top end surface, or bottom end surface of the terminal 2 in FIG. 3 . In FIG. 3 , the notch 2h also opens to the left end surface of the terminal 2. That is, a slit is a region whose cross section along the first surface 21 has an open cross section.

[0034] The terminal 2 of this example includes a wire barrel 29 that grips the conductor 50 of the electric wire 5. The terminal 2 may further include an insulation barrel that grips the insulating coating 51 of the electric wire 5. The position of the surface of the terminal 2 to which the electric wire 5 is connected is not particularly limited. In this example, the electric wire 5 is connected to the second surface 22. Unlike this example, the electric wire 5 may be connected to the first surface 21, or to another surface perpendicular to both the first surface 21 and the second surface 22. Instead of using the wire barrel 29, the electric wire 5 may be connected to the terminal 2 by welding or solid-state welding. Such joining methods include, for example, resistance welding, laser welding, ultrasonic welding, and friction stir welding.

[0035] The size of the terminal 2 is determined depending on the application of the terminal 2. For example, the length of the terminal 2, i.e., the length along the extending direction of the electric wire 5, may be 5 mm or more and 200 mm or less, or 10 mm or more and 50 mm or less. For example, the thickness of the terminal 2, i.e., the distance between the first surface 21 and the second surface 22, may be 0.1 mm or more and 7 mm or less, 0.3 mm or more and 4 mm or less, or 0.5 mm or more and 3 mm or less.

[0036] The inner diameter D3 of the notch 2h is, for example, 4 mm or more and 20 mm or less. The shape of the notch 2h shown in FIG. 2 is a circular hole shape. That is, the notch 2h in FIG. 2 is a circular through-hole. The center of the inscribed circle 2c of the circular through-hole is the central axis 2a of the notch 2h, and the diameter of the inscribed circle 2c is the inner diameter D3 of the notch. The shape of the notch 2h shown in FIG. 3 is a U-shaped slit extending to the left end of the terminal 2 in FIG. 3. The terminal 2 shown in FIG. 3 is a horizontal spade-type plate terminal (symbol LD) for automotive electric wire terminals according to JIS D 5403-1989. In this case, the center of the inscribed circle 2c at the bottom of the U is the central axis 2a of the notch 2h, and the diameter of the inscribed circle 2c is the inner diameter D3 of the notch 2h. The shape of the notch 2h shown in FIG. 4 is a shape combining a circular hole and two large and small slits. The terminal 2 shown in FIG. 4 is a spade-shaped plate terminal (symbol LE) for automotive electric wire terminals in accordance with JIS D 5403-1989. The width of the two large and small slits is smaller than the diameter of the circular hole. The large slit extends from the circular hole to the left end of the terminal 2 in FIG. 4. The small slit extends from the circular hole to the right of the terminal 2 in FIG. 4. In this case, the center of the inscribed circle 2c of the circular hole is the central axis 2a of the notch 2h, and the diameter of the inscribed circle 2c is the inner diameter D3 of the notch 2h. The shape of the notch 2h shown in FIG. 5 is an elongated hole. The midpoint between the centers of the two inscribed circles 2d located at both ends of the elongated hole is the central axis 2a of the notch 2h, and the diameter of the inscribed circle 2c of the elongated hole centered on the central axis 2a is the inner diameter D3 of the notch 2h.

[0037] (Uneven portion) As shown in Fig. 6, the terminal 2 has an uneven portion 25 around the notch 2h that strengthens the connection between the terminal 2 and the attachment object 3. The uneven portion 25 is provided at a position on the first surface 21 that overlaps with the attachment object 3. The uneven portion 25 may be provided over the entire overlapping position, or may be provided only in a portion of the overlapping position. In this example, the uneven portion 25 is provided over the entire overlapping position. The uneven portion 25 has a specific plurality of convex portions 25a, which will be described in detail later. The uneven portion 25 can be formed by, for example, cutting or rolling.

[0038] The number of protrusions 25a is not particularly limited and can be selected as appropriate. The spacing between adjacent protrusions 25a is not particularly limited and can be selected as appropriate. The cross-sectional shape of each protrusion 25a is, for example, triangular or trapezoidal. The cross-sectional shape of the protrusion 25a refers to the outline shape of the protrusion 25a in a cross section perpendicular to the longitudinal direction of the protrusion 25a. For example, in the case of a protrusion 25a having a circular planar shape, the cross-sectional shape of the protrusion 25a refers to the outline shape of the protrusion 25a in a cross section taken along a direction away from the central axis 2a of the notch 2h. The corners 25c of each protrusion 25a in the cross section may have a curved surface with an arbitrary radius of curvature R.

[0039] The plurality of protrusions 25 a in this example are formed by a plurality of recesses 25 b provided on the first surface 21. In this case, the protrusions 25 a are formed between adjacent recesses 25 b. Unlike this example, the plurality of protrusions 25 a may be formed so as to protrude from the first surface 21.

[0040] In this example, each of the protrusions 25 a has a circular planar shape when the first surface 21 is viewed from above. A circular shape refers to a perfect circle or an ellipse. In this example, the planar shape of each of the protrusions 25 a is a perfect circle. Each of the protrusions 25 a is concentric with the central axis 2 a of the notch 2 h.

[0041] In this example, there are two convex portions 25a. Of the two convex portions 25a, the convex portion 25a with the smaller diameter is referred to as the first convex portion 25a, and the convex portion 25a with the larger diameter is referred to as the second convex portion 25a. In FIG. 7, the convex portion 25a located on the left side is the first convex portion 25a, and the convex portion 25a located on the right side is the second convex portion 25a. As shown in FIG. 6, the first convex portion 25a and the second convex portion 25a are arranged in order in a direction away from the central axis 2a of the notch 2h. In this example, the inner peripheral contour of the first convex portion 25a does not coincide with the notch 2h but is larger than the notch 2h. Unlike this example, the inner peripheral contour of the first convex portion 25a may coincide with the notch 2h. In this example, the outer peripheral contour of the concave-convex portion 25 is rectangular. In this example, recesses 25b are provided between the opening edge of the notch 2h and the first convex portion 25a, between adjacent first convex portions 25a and second convex portions 25a, and between the second convex portion 25a and the outer peripheral contour of the uneven portion 25.

[0042] As shown in Figure 7, the cross-sectional shape of each protrusion 25a in this example is triangular. The vertex of the triangular protrusion 25a forms a corner 25c. The corner 25c may be rounded. The corner 25c may include a flat portion. For example, the cross-sectional shape of the corner 25c may be trapezoidal. The triangular protrusion 25a is a protrusion in which the bisector of the apex angle in the cross-section of the protrusion 25a is perpendicular to the first surface 21. In other words, the cross-sectional shape of this protrusion 25a is an equilateral triangle or an isosceles triangle with the side along the recess 25b as the base.

[0043] The recess 25b between the opening edge of the notch 2h and the first protrusion 25a, i.e., the recess 25b on the left side in FIG. 7, has a flat bottom surface. The height of this bottom surface is lower than the first surface 21. This bottom surface does not have to be flat, but may be curved. This bottom surface and the first protrusion 25a may be connected by a smooth R-shape. When the connection is a curved or R-shape, stress due to vibration, thermal shock, etc. on the terminal 2 is less likely to concentrate on the bottom surface of the recess 25b or the interface between the bottom surface and the first protrusion 25a, making the terminal 2 less likely to be damaged.

[0044] The recess 25b between the adjacent first and second protrusions 25a and 25a has a V-shaped cross section. The bottom surface of this recess 25b may be curved. If the bottom surface of the recess 25b is curved or flat, stress due to vibration, thermal shock, etc. on the terminal 2 is less likely to concentrate around the bottom surface of the V-shaped recess 25b, making the terminal 2 less likely to be damaged.

[0045] The recess 25b between the second protrusion 25a and the outer peripheral contour of the uneven portion 25, i.e., the recess 25b on the right side in FIG. 7, has a flat bottom. The boundary between the recess 25b on the right side in FIG. 7 and the first surface 21 is the outer peripheral contour of the uneven portion 25. The height of the bottom is lower than the first surface 21. This bottom does not have to be flat, but may be a curved surface. This bottom and the second protrusion 25a may be connected by a smooth R-shape. Furthermore, this bottom and the sidewall connecting the bottom and the first surface 21 may be connected by a smooth R-shape. When the connection is a curved or R-shape, stress due to vibration, thermal shock, etc. on the terminal 2 is less likely to concentrate on the bottom of the recess 25b or the boundary between the bottom and the second protrusion 25a, making the terminal 2 less likely to be damaged.

[0046] The diameter of the first protrusion 25a may be, for example, 4 mm to 13 mm, 8 mm to 12 mm, or 8.5 mm to 11 mm. This diameter is the diameter of a circle passing through the corner 25c, which is the vertex of the protrusion 25a. The distance between two adjacent corners 25c, i.e., the pitch P1, may be, for example, 0.4 mm to 5 mm, or 0.5 mm to 3 mm. In this example, the pitch P1 also represents the width W1 of the opening of the recess 25b between the first protrusion 25a and the second protrusion 25a. The height h1 of the protrusion 25a, i.e., the depth of the recess 25b, which is the length from the bottom of the recess 25b to the corner 25c in a direction perpendicular to the first surface 21, may be, for example, 0.005 mm to 1 mm, or 0.01 mm to 0.5 mm.

[0047] The radius of curvature R of the corner 25c may be, for example, 0.01 mm or more and 1 mm or less, or 0.01 mm or more and 0.05 mm or less. The angle θ1 of the apex in the cross section of the first convex portion 25a and the angle θ1 of the apex in the cross section of the second convex portion 25a may be the same or different. If the two angles θ1 are not the same, there is no need to excessively increase processing precision, which makes it easier to reduce production costs. The angle θ1 of the apex in the cross section of each convex portion 25a may be, for example, 60° or more and 170° or less, 80° or more and 160° or less, or 90° or more and 140° or less. Corners 25c having the above angle θ1 are more likely to bite into the attachment target 3.

[0048] When the terminal 2 and the attachment object 3 are connected, the corners 25c of the protrusions 25a bite into the attachment object 3. At that time, the corners 25c are deformed by the attachment object 3. This deformation destroys the oxide film on the corners 25c, establishing electrical continuity between the terminal 2 and the attachment object 3. By pressing the uneven portion 25 against the attachment object 3 with a specified pressure or more, the terminal 2 and the attachment object 3 are firmly connected for a long period of time.

[0049] (Point Symmetry Parameter) The point symmetry parameter is, for example, 1.3 or greater. The point symmetry parameter is a parameter that indicates the degree to which the planar shape of the uneven portion 25 is point-symmetric with respect to the central axis 2a of the notch 2h. The larger the point symmetry parameter, the more point-symmetric the shape of the uneven portion 25 is with respect to the central axis 2a of the notch 2h. Before maintenance of the connection structure 1, the portion of the attachment object 3 where the protrusion 25a had penetrated is less likely to oxidize. If the point symmetry parameter satisfies the above range, when the terminal 2 and the attachment object 3 are re-tightened with the bolt 4 after maintenance, the protrusion 25a is more likely to re-penetrate into the portion where it had originally penetrated before maintenance. Therefore, the contact resistance between the terminal 2 and the attachment object 3 after maintenance is less likely to increase. The point symmetry parameter may be 1.5 or greater, or 2.0 or greater. The upper limit of the point symmetry parameter is not particularly limited, but is practically 6.28. That is, the point symmetry parameter may be 1.3 or more and 6.28 or less, 1.5 or more and 6.2 or less, or 2.0 or more and 6.0 or less. How to determine the point symmetry parameter will be explained in the test examples described later.

[0050] The terminal 2 is made of pure aluminum or an aluminum alloy. The terminal 2 does not have a conductive layer on its surface. Pure aluminum is an alloy containing 99% or more by mass of aluminum. An aluminum alloy is an alloy containing the largest amount of aluminum. The aluminum content of the aluminum alloy is, for example, 80% or more by mass, where the entire aluminum alloy is taken as 100% by mass. The aluminum alloy is allowed to contain inevitable impurities. The aluminum alloy contains, for example, 0.01% to 1.50% by mass of silicon and 0.01% to 2.00% by mass of magnesium. The silicon and magnesium content percentages are values ​​where the entire aluminum alloy is taken as 100% by mass. This also applies to the content percentages of the following elements. The aluminum alloy may further contain one or more additive elements selected from the group consisting of copper, manganese, iron, chromium, zirconium, and titanium. The copper content percentage is, for example, 0.1% to 1.2% by mass. The manganese content is, for example, 0% by mass or more and 1.5% by mass or less. The iron content is, for example, 0% by mass or more and 0.8% by mass or less. The chromium content is, for example, 0% by mass or more and 0.4% by mass or less. The zirconium content is, for example, 0% by mass or more and 0.8% by mass or less. The titanium content is, for example, 0% by mass or more and 0.2% by mass or less. The total content of titanium and zirconium is, for example, 0% by mass or more and 0.3% by mass or less. The aluminum alloy has, for example, International Registered Alloy Number 6061. When the aluminum alloy contains the above-mentioned additional elements, at least one of copper and manganese may be essential.

[0051] The Vickers hardness of the terminal 2 is 80 HV or higher. Vickers hardness is measured in accordance with JIS Z 2244-1:2020. Aluminum alloys containing silicon and magnesium tend to meet a Vickers hardness of 80 HV or higher. The higher the Vickers hardness, the more easily the corners 25c of the convex portions 25a of the concave-convex portion 25 bite into the attachment object 3 when the terminal 2 and the attachment object 3 are fastened by the bolt 4. Furthermore, the higher the Vickers hardness, the less likely the terminal 2 is to creep deform when the terminal 2 heats up due to electrical conduction. As a result, the axial force of the bolt 4 can be prevented from being released from the attachment object 3. The upper limit of the Vickers hardness of the terminal 2 is, for example, 160 HV. The corners 25c of the terminal 2 having a Vickers hardness of 160 HV or less are moderately deformed by the attachment object 3 when they bite into the attachment object 3. The aluminum oxide coating is easily destroyed at the deformed corners 25c. The Vickers hardness may be in the range of, for example, 80 HV to 160 HV, 85 HV to 150 HV, 90 HV to 140 HV, or 90 HV to 110 HV.

[0052] The electrical conductivity of the terminal 2 is, for example, 40% IACS or more and 63% IACS or less. The electrical conductivity is measured in accordance with JIS H 0505:1975. Aluminum alloys containing silicon and magnesium easily meet the above electrical conductivity. When the terminal 2 has the above electrical conductivity, the amount of heat generated by the terminal 2 is reduced. As a result, thermal damage to the wire 5 connected to the terminal 2 and the attachment object 3 is reduced. The electrical conductivity may be 41% IACS or more and 60% IACS or less, or 42% IACS or more and 58% IACS or less. Alternatively, the electrical conductivity may be 40% IACS or more and 50% IACS or less.

[0053] [Mounting target] The shape of the mounting target 3 is not particularly limited as long as it is configured to be connectable to the terminal 2 by the bolt 4. The mounting target 3 in this example has a terminal shape. As shown in FIG. 1 , the mounting target 3 has a notch 3h through which the bolt 4 passes. The notch 3h is a concept that includes not only a notch as is usually thought of, but also a through hole. Like the notch 2h, the notch 3h includes a through hole and a slit. The notch 3h in this example is a through hole.

[0054] The material of the attachment target 3 is, for example, pure copper or a copper alloy. Pure copper or a copper alloy is relatively easy to deform. Therefore, the corners 25c of the uneven portion 25 of the terminal 2 easily bite into the attachment target 3, thereby strengthening the connection between the terminal 2 and the attachment target 3. Specific materials for the attachment target 3 include oxygen-free copper, tough pitch copper, or JC100 according to the Japan Society of Automotive Engineers standard. The Vickers hardness of the attachment target 3 is, for example, less than twice the Vickers hardness of the terminal 2. In this case, the convex portions of the uneven portion 25 of the terminal 2 easily bite into the attachment target 3, thereby strengthening the connection between the terminal 2 and the attachment target 3. The attachment target 3 does not have a coating layer on its surface. The attachment target 3 and the terminal 2 are in direct contact.

[0055] The hardness ratio obtained by dividing the Vickers hardness of the terminal 2 by the Vickers hardness of the attachment object 3 is, for example, 1 or more and 1.5 or less. If the hardness ratio is 1 or more and 1.5 or less, the contact resistance between the terminal 2 and the attachment object 3 is likely to be reduced. The hardness ratio may be 0.9 or more and 1.4 or less, or 1.0 or more and 1.3 or less.

[0056] [Bolt] The bolt 4 tightens the terminal 2 and the attachment object 3 to connect them. The bolt 4 includes a shank 40 and a head 41. The bolt 4 in this example further includes a flange 42. The flange 42 abuts against the second surface 22 of the terminal 2. A nut 4n is fitted onto the shank 40. The nut 4n abuts against the attachment object 3. The terminal 2 and the attachment object 3 are tightened between the flange 42 of the bolt 4 and the nut 4n. In the case of a bolt 4 that does not include a flange 42, a washer is disposed between the head 41 and the terminal 2. The bolt 4 is made of, for example, steel. The bolt 4 may be made of, for example, SNB7 steel specified in JIS G 4107:2010.

[0057] [First Area S1 / Second Area S2] When the first surface 21 having the concave-convex portion 25 is connected to the attachment object 3 by tightening the bolt 4, the ratio S1 / S2 of the first area S1 to the second area S2 is 0.60 or less. The ratio S1 / S2 is an index indicating that the terminal 2 and the attachment object 3 are connected with a predetermined or higher connection strength. The ratio S1 / S2 may be 0.50 or less, 0.40 or less, 0.35 or less, or 0.30 or less. The lower limit of the ratio S1 / S2 is, for example, 0.10. Therefore, the range of the ratio S1 / S2 is, for example, 0.10 or more and 0.60 or less, 0.10 or more and 0.50 or less, 0.10 or more and 0.40 or less, 0.10 or more and 0.35 or less, or 0.10 or more and 0.30 or less.

[0058] The first area S1 is the area of ​​the region where the first surface 21 comes into contact with the attachment object 3 at a pressure equal to or greater than a specified value. The specified value is, for example, 25 MPa. The first area S1 is determined by a tightening test shown in the test example described later. The first area S1 is 5 mm ２ The first area S1 is 5 mm ２ If the first area S1 is equal to or larger than this, the terminal 2 and the attachment object 3 are mechanically connected firmly, and the strength of the connection is likely to be maintained for a long period of time. The larger the first area S1, the higher the connection strength. For example, the first area S1 is 6 mm ２ or more, or 7 mm ２ The upper limit of the first area S1 is limited by the ratio S1 / S2. In other words, the lower limit of the ratio S1 / S2 is limited by the first area S1.

[0059] The second area S2 is the area of ​​a predetermined circular region. The circular region is a virtual region with the nominal diameter D1 of the bolt 4 as the inner diameter and the bearing surface diameter D2 of the bolt 4 as the outer diameter. In other words, S2 = π(D2 / 2) ２ −π(D1 / 2) ２The bolt 4 is selected so that it can properly fasten the terminal 2 and the attachment object 3 when placed in the notch 2h with an inner diameter D3. The nominal diameter D1 and bearing surface diameter D2 of the bolt 4 can be selected appropriately depending on the location where the terminal 2 is to be applied. The selection criteria are exemplified as follows: The nominal diameter D1 is determined based on the inner diameter D3 of the notch 2h. The nominal diameter D1 corresponds to the diameter of the shank 40 of the bolt 4 corresponding to the inner diameter D3. The bearing surface diameter D2 corresponds to the outer diameter of the range where the axial force of the bolt 4 substantially acts on the second surface 22 of the terminal 2. When fastening using the bolt 4, a bolt 4 having a flange portion 42 below the head portion 41 is used. When fastening using a bolt 4 without a flange portion, a washer is used. The outer diameter of the flange portion 42 appropriate for the nominal diameter D1 can be determined by referring to Appendix JA.3 of JIS B 1189:2014. For a bolt 4 having a flange portion 42, the bearing surface diameter D2 can be determined by multiplying the outer diameter of the flange portion 42 by 0.929. If a washer is disposed between the bolt 4 and the terminal 2, the bearing surface diameter D2 can be determined by multiplying the outer diameter of the washer by 0.929. The nominal diameter D1 may be the same as the inner diameter D3. The bearing surface diameter D2 is larger than the inner diameter D3 and the nominal diameter D1. For example, if the inner diameter D3 is 4 mm or greater but less than 5 mm, the nominal diameter D1 is 4 mm and the bearing surface diameter D2 is 9.8 mm. Note that the nominal diameter D1 and the bearing surface diameter D2 may be changed depending on the application of the terminal 2. A person skilled in the art can select an appropriate nominal diameter D1 and bearing surface diameter D2 depending on the application.

[0060] When the axial force of the bolt 4 is constant, the smaller the ratio of the first area S1 to the second area S2, the greater the pressure acting on the region having the first area S1. ２ If the above conditions are met, the terminal 2 and the attachment object 3 are mechanically connected firmly, and the connection strength is likely to be maintained over a long period of time. As a result, the contact resistance between the terminal 2 and the attachment object 3 is unlikely to increase over time.

[0061] Other Embodiments The connection structures of embodiments 2 to 10, which differ from embodiment 1, will be described with reference to Figs. 8 to 28. For ease of explanation, Figs. 8 to 28 show members that resemble terminals 2. The description of embodiments 2 to 7 will focus on the differences from embodiment 1. Description of configurations that are the same as embodiment 1 may be omitted. The description of embodiments 8 to 10 will focus on the differences from embodiment 7. Description of configurations that are the same as embodiment 7 may be omitted.

[0062] Second Embodiment As shown in FIG. 8, in a connection structure according to a second embodiment, the planar shape of each protrusion 25a may be an ellipse that is concentric with the central axis 2a of the notch 2h.

[0063] The planar shapes of the first and second protrusions 25a are similar. That is, the spacing between the first and second protrusions 25a is uniform around the central axis of the notch 2h. The major axis of each protrusion 25a is along the length of the terminal 2, i.e., the extension direction of the wire 5 shown in FIG. 1. The minor axis of each protrusion 25a is along the width of the terminal 2, i.e., a direction perpendicular to the length direction. As shown in FIG. 9, the length of the recess 25b along the major axis between the notch 2h and the first protrusion 25a is longer than the length of the recess 25b along the minor axis between the notch 2h and the first protrusion 25a, as shown in FIG. 10. The major axis of the first protrusion 25a is, for example, 4.1 mm or more and 15 mm or less. The minor axis of the first protrusion 25a is, for example, 4 mm or more and 14 mm or less.

[0064] Third Embodiment As shown in FIG. 11, in a connection structure according to a third embodiment, the planar shape of each protrusion 25a may be an arc shape that is part of a circle concentric with the central axis 2a of the notch 2h.

[0065] In this example, the uneven portion 25 includes a plurality of first convex portions 25a that are part of a first concentric circle and a plurality of second convex portions 25a that are part of a second concentric circle. In this example, the first concentric circle and the second concentric circle are perfect circles. Unlike this example, the first concentric circle and the second concentric circle may be ellipses. The plurality of first convex portions 25a and the plurality of second convex portions 25a are aligned in order in a direction away from the central axis 2a of the notch 2h. The plurality of first convex portions 25a are aligned at intervals around the central axis of the notch 2h. The plurality of second convex portions 25a are aligned at intervals around the central axis of the notch 2h. A recess 25b is provided between the plurality of first convex portions 25a and the plurality of second convex portions 25a. As shown in FIG. 12, recesses 25b are provided between adjacent first protrusions 25a around the central axis of the notch 2h, and between adjacent second protrusions 25a around the central axis of the notch 2h.

[0066] The number of first protrusions 25a, the number of second protrusions 25a, the length of each first protrusion 25a around the central axis of the notch 2h, and the length of each second protrusion 25a around the central axis of the notch 2h can be appropriately selected depending on the diameter of the first protrusion 25a and the diameter of the second protrusion 25a. The number of first protrusions 25a and the number of second protrusions 25a may be the same or different. The number of first protrusions 25a and the number of second protrusions 25a may be, for example, 4 to 32, 6 to 16, or 8 to 12. In this example, the number of the multiple first protrusions 25a and the number of the multiple second protrusions 25a are eight. The central angle of each first protrusion 25a and the central angle of each second protrusion 25a may be the same or different. The central angle of each first protrusion 25 a and each second protrusion 25 a is, for example, 10° or more and 175° or less. The central angle of each first protrusion 25 a and each second protrusion 25 a may be 20° or more and 135° or less, or 30° or more and 90° or less. The spacing between adjacent first protrusions 25 a around the central axis and the spacing between adjacent second protrusions 25 a around the central axis may be the same or different.

[0067] 13 and 14 , in a connection structure according to a fourth embodiment, the inner peripheral contour of the first protrusion 25 a may coincide with the opening edge of the notch 2 h. In this example, there are three protrusions 25 a. The planar shape of each protrusion 25 a is a perfect circle. Each protrusion 25 a is concentric with the central axis 2 a of the notch 2 h. The three protrusions 25 a are referred to as the first protrusion 25 a, the second protrusion 25 a, and the third protrusion 25 a in order of decreasing diameter. The first protrusion 25 a, the second protrusion 25 a, and the third protrusion 25 a are arranged in order in a direction away from the central axis 2 a of the notch 2 h. The distance between the first protrusion 25 a and the second protrusion 25 a and the distance between the second protrusion 25 a and the third protrusion 25 a may be the same or different.

[0068] 15 and 16 , in a connection structure according to a fifth embodiment, the protrusions 25 a may be linearly arranged in parallel. The concave-convex portion 25 in this example is configured with a plurality of linear V-grooves arranged parallel to each other without any gaps on the first surface 21. The V-grooves form recesses 25 b, and mountain-shaped ridges formed between adjacent recesses 25 b form protrusions 25 a. In this example, the plurality of protrusions 25 a are aligned in a direction along the length of the terminal 2. Unlike this example, the plurality of protrusions 25 a may be aligned in a direction perpendicular to the length of the terminal 2. Recesses 25 b are formed between adjacent protrusions 25 a.

[0069] Sixth Embodiment As shown in FIGS. 17 and 18 , in a connection structure according to a sixth embodiment, the protrusions 25 a may be linearly arranged in parallel, and each protrusion 25 a may have a trapezoidal cross-sectional shape. The concave-convex portion 25 in this example is configured with a plurality of linear V-grooves arranged parallel to each other at intervals on the first surface 21. The V-grooves form recesses 25 b, and trapezoidal ridges formed between adjacent recesses 25 b form protrusions 25 a. In this example, the multiple protrusions 25 a are aligned in a direction along the length of the terminal 2. Unlike this example, the multiple protrusions 25 a may be aligned in a direction perpendicular to the length of the terminal 2. In this example, each protrusion 25 a has an isosceles trapezoidal shape. The joint between the first surface 21 and the inclined surface of each protrusion 25 a forms a corner 25 c. The corner 25 c may be rounded.

[0070] The width W2 of the protrusion 25a is, for example, greater than 0 mm and less than 5 mm. The width W2 may be, for example, 0.01 mm or greater and 2 mm or less. The radius of curvature R of the corner 25c may be, for example, 0.01 mm or greater and 1 mm or less. The radius of curvature R of the corner 25c may be 0.01 mm or greater and 0.8 mm or less. The angle θ1 between the first surface 21 and the inclined surface in the cross section of each protrusion 25a may be, for example, greater than 90° and less than 170°, 135° or greater and 165° or less, or 145° or greater and 160° or less. The individual angles θ1 do not have to be consistent. If the individual angles θ1 are not consistent, there is no need to excessively increase processing precision, which makes it easier to reduce production costs.

[0071] Seventh Embodiment As shown in FIG. 19 , in a connection structure according to a seventh embodiment, each protrusion 25 a may be provided between two rectangular recesses 25 b. As shown in FIG. 20 , the angle θ2 between intersecting recesses 25 b is 90°. Each protrusion 25 a has a pyramidal shape. The pyramidal shape includes pyramids and truncated pyramids. In this example, each protrusion 25 a has a quadrangular pyramid shape with a square base, i.e., a rectangular pyramid. As shown in FIG. 21 , the cross-sectional shape of each protrusion 25 a is triangular. Unlike this example, each protrusion 25 a may have a quadrangular pyramid shape with a rectangular base, i.e., a rectangular pyramid.

[0072] Eighth Embodiment As shown in Fig. 22 , the connection structure of the eighth embodiment may have a first surface 21 that has a circular planar shape between the notch 2h and the uneven portion 25. That is, the terminal 2 has the first surface 21, the uneven portion 25, and the first surface 21 in this order in the direction away from the central axis 2a of the notch 2h. As shown in Fig. 23 , the height of the first surface 21 between the notch 2h and the uneven portion 25 is the same as the height of the first surface 21 located outside the uneven portion 25. The outer diameter of the first surface 21 between the notch 2h and the uneven portion 25 is, for example, 5 mm or more and 9 mm or less.

[0073] 24, the connection structure of the ninth embodiment may have a recess 25b having a circular planar shape between a rectangular recess 25b and a protrusion 25a and a notch 2h provided between the recess 25b. As shown in FIG. 25, the bottom surface of the circular recess 25b is flat. The height of the bottom surface of the circular recess 25b is lower than the first surface 21. The outer diameter of the circular recess 25b is, for example, 5 mm or more and 15 mm or less.

[0074] Tenth Embodiment As shown in Fig. 26, in a connection structure according to the tenth embodiment, each protrusion 25a may be provided between recesses 25b formed in a twill pattern. As shown in Fig. 27, the smaller angle θ3 between the intersecting recesses 25b is 60°, and the larger angle θ4 is 120°. In this example, each protrusion 25a has a quadrangular pyramid shape with a diamond-shaped base. As shown in Fig. 28, the cross-sectional shape of each protrusion 25a is triangular.

[0075] In the test example, members simulating the terminal 2 and the attachment target 3 of the embodiment were prepared, and the ratio S1 / S2 was determined by a fastening test. In addition, a test structure simulating the connection structure 1 of the first embodiment was fabricated, and a thermal shock test was performed using the test structure.

[0076] [Sample No. 1] [Terminal] The terminal 2 of Sample No. 1 is rectangular plate-shaped. The size of the terminal 2 is 14 mm x 40 mm. The thickness of the terminal 2 is 2.0 mm. The terminal 2 has a circular hole-shaped notch 2h concentric with the areal center of the terminal 2. The inner diameter D3 of the notch 2h is 6.2 mm. The material of the terminal 2 is International Registered Alloy Number 6061. The material temper is T6. The Vickers hardness of the terminal 2 is 95 HV. The Vickers hardness was measured in accordance with JIS Z 2244-1:2020. The Vickers hardness was the median of 20 measured values. All Vickers hardness values ​​in the following description were determined in the same manner. The terminal 2 does not have a conductive layer formed by plating or the like. This applies to all terminals 2 in the following description.

[0077] The uneven portion 25 of Sample No. 1 had multiple circular convex portions 25a as described with reference to Figures 6 and 7. The size of the outer peripheral contour of the uneven portion 25 was 14 mm x 19 mm. There were two convex portions 25a. The diameter of the first convex portion 25a was 11.0 mm. The diameter of the second convex portion 25a was 12.0 mm. The diameter was the diameter of a circle passing through the corner 25c, which was the vertex of the convex portion 25a. The pitch P1 was 0.5 mm. The cross-sectional shape of each convex portion 25a was triangular. The angle θ1 of the vertex in the cross section of the convex portion 25a was 120°. The radius of curvature R of the corner 25c was 0.03 mm. The height h1 was 0.14 mm.

[0078] [Mounting Object] The mounting object 3 of Sample No. 1 is a circular plate. The thickness of the mounting object 3 is 1.5 mm. The mounting object 3 does not have a conductive layer formed by plating or the like. The material of the mounting object 3 is C1100 as defined in JIS H 3100:2018. C1100 is tough pitch copper. The material temper was 1 / 4H. The Vickers hardness of the mounting object 3 was 78 HV. The inner diameter of the mounting object 3 is equal to the nominal diameter D1 of the bolt 4 (Figure 1). As shown in Figure 33, the outer diameter D4 of the mounting object 3 is the length of the diagonal of a square circumscribing the circle with the bearing surface diameter D2 indicated by the two-dot chain line, i.e., √2 times the bearing surface diameter D2. The example shown in Figure 33 illustrates the relationship between the inner diameter D3, bearing surface diameter D2, and outer diameter D4 when the square coincides with the outer shape of the concave-convex portion 25. The relationship between the inner diameter D3, the nominal diameter D1, the bearing surface diameter D2, and the outer diameter D4 is shown in Table 1. The values ​​in Table 1 were set based on the selection criteria already described.

[0079]

[0080] [Sample No. 2] Sample No. 2 differed from Sample No. 1 in that the diameter of the first convex portion 25a was 8.0 mm and the diameter of the second convex portion 25a was 9.0 mm.

[0081] [Sample No. 3] Sample No. 3 differs from Sample No. 1 in the following respects.

[0082] (a) The three perfectly circular convex portions 25a described with reference to FIGS. 13 and 14 were provided, and the inner peripheral contour of the first convex portion 25a coincided with the notch 2h.

[0083] (b) The inner diameter D3 of the notch 2h was 7.0 mm. (c) The size of the outer peripheral contour of the concave-convex portion was 14 mm x 15 mm.

[0084] (d) The diameter of the first convex portion 25a was 8.0 mm, the diameter of the second convex portion 25a was 10.0 mm, and the diameter of the third convex portion 25a was 12.0 mm.

[0085] (e) The angle θ1 of the apex of each protrusion 25a in the cross section was 90°. (f) The height h1 was 0.5 mm.

[0086] [Sample No. 4] Sample No. 4 differs from Sample No. 3 in that the angle θ1 of the apex in the cross section of each protrusion 25a was 140° and the height h1 was 0.2 mm.

[0087] [Sample No. 5] Sample No. 5 differs from Sample No. 1 in the following respects.

[0088] (a) It had a plurality of elliptical convex portions 25a as described with reference to Figures 8 to 10. (b) The major axis of the first convex portion 25a was 12.65 mm, and the minor axis was 9.21 mm.

[0089] (c) The major axis of the second protrusion 25a was 13.65 mm, and the minor axis was 10.21 mm.

[0090] [Sample No. 6] Sample No. 6 differs from Sample No. 5 in the following respects.

[0091] (a) The major axis of the first convex portion 25a was 14.30 mm, and the minor axis was 7.08 mm.

[0092] (b) The major axis of the second convex portion 25a was 15.30 mm, and the minor axis thereof was 8.08 mm. [Sample No. 7] Sample No. 7 differs from Sample No. 1 in the following respects.

[0093] (a) It had a plurality of arc-shaped protrusions 25a as described with reference to Figures 11 and 12. (b) The diameter of the first protrusion 25a was 8.0 mm.

[0094] (c) The diameter of the second protrusions 25a was 9.0 mm. (d) The central angle between each of the first protrusions 25a and each of the second protrusions 25a was 33.75°.

[0095] [Sample No. 8] Sample No. 8 differs from Sample No. 7 in that the central angle of each of the first convex portions 25a and each of the second convex portions 25a was 22.5°.

[0096] [Sample No. 9] Sample No. 9 differs from Sample No. 7 in that the central angle of each of the first convex portions 25a and each of the second convex portions 25a was 11.25°.

[0097] [Sample No. 10] Sample No. 10 differs from Sample No. 1 in the following respects.

[0098] (a) The plurality of linear protrusions 25a were provided as described with reference to Figures 15 and 16. (b) The inner diameter D3 of the notch 2h was 7.0 mm.

[0099] (c) The size of the outer circumferential contour of the concave and convex portions was 14 mm x 15 mm. (d) The number of convex portions 25a was 14.

[0100] (e) The pitch P1 was 1.0 mm. (f) The angle θ1 of the apex of the cross section of the protrusion 25a was 90°.

[0101] (g) The height h1 was 0.5 mm. [Sample No. 11] Sample No. 11 differs from Sample No. 10 in that the angle θ1 of the apex of the cross section of the protrusion 25 a was 140° and the height h1 was 0.2 mm.

[0102] [Sample No. 12] Sample No. 12 differs from Sample No. 1 in the following respects.

[0103] (a) It had a plurality of linear protrusions 25a as described with reference to Figures 17 and 18. (b) The inner diameter D3 of the notch 2h was 7.0 mm.

[0104] (c) The size of the outer circumferential contour of the concave and convex portions was 14 mm x 15 mm. (d) The number of convex portions 25a was 11.

[0105] (e) The cross-sectional shape of each of the protrusions 25a was an isosceles trapezoid. (f) The width W2 of each of the protrusions 25a was 1.3 mm.

[0106] (g) The angle θ1 of the apex of the cross section of the protrusion 25a was 160°. (h) The height h1 was 0.15 mm.

[0107] [Sample No. 13] Sample No. 13 differs from Sample No. 1 in the following respects.

[0108] (a) The device had a plurality of pyramidal convex portions 25a provided between the square-shaped concave portions 25b described with reference to FIGS. 19 to 21.

[0109] (b) The inner diameter D3 of the notch 2h was 7.0 mm. (c) The size of the outer peripheral contour of the concave-convex portion was 14 mm x 15 mm.

[0110] (d) The shape of each of the protrusions 25a was a quadrangular pyramid with a square base, i.e., a rectangular pyramid. (e) The pitch P1 was 1.0 mm.

[0111] (f) The angle θ1 of the apex of the cross section of the protrusion 25a was 90°. (g) The height h1 was 0.5 mm.

[0112] [Sample No. 14] Sample No. 14 differs from Sample No. 13 in the following respects.

[0113] (a) The angle θ1 of the apex of the cross section of the protrusion 25a was 140°, (b) the height h1 was 0.2 mm.

[0114] [Sample No. 15] Sample No. 15 differs from Sample No. 13 in the following respects.

[0115] (a) The size of the terminal 2 was 30 mm x 30 mm. (b) The size of the outer circumferential contour of the concave-convex portion was 30 mm x 30 mm.

[0116] (c) The angle θ1 of the apex of the cross section of the protrusion 25a was 140°, (d) The height h1 was 0.2 mm.

[0117] [Sample No. 16] Sample No. 16 differs from Sample No. 15 in the following respects.

[0118] (a) As described with reference to FIGS. 22 and 23, the terminal 2 has the first surface 21 having a circular plane shape between the notch 2h and the uneven portion 25.

[0119] (b) The outer diameter of the annular first surface 21 was 9 mm. [Sample No. 17] Sample No. 17 differs from Sample No. 15 in the following respects.

[0120] (a) As described with reference to Figures 24 and 25, the terminal 2 has a recess 25b formed in a square shape and a protrusion 25a provided between the recess 25b and a notch 2h, and the recess 25b has a circular planar shape between the protrusion 25a and the notch 2h.

[0121] (b) The outer diameter of the annular recess 25b was 9 mm. [Sample No. 18] Sample No. 18 differs from Sample No. 17 in that the outer diameter of the annular recess 25b was 13 mm.

[0122] [Sample No. 19] Sample No. 19 differs from Sample No. 1 in the following respects.

[0123] (a) The device had a plurality of pyramidal convex portions 25a provided between the concave portions 25b formed in a chevron pattern as described with reference to FIGS. 26 to 28.

[0124] (b) The size of the outer circumferential contour of the concave-convex portion 25 was 14 mm x 15 mm. (c) The shape of each convex portion 25a was a quadrangular pyramid with a diamond-shaped base.

[0125] (d) The pitch P1 was 1.0 mm. [Sample No. 101] Sample No. 101 differs from Sample No. 1 in the Vickers hardness of the terminal and in that the first surface of the terminal does not have an uneven portion.

[0126] [Sample No. 102] Sample No. 102 differed from Sample No. 16 in that the outer diameter of the annular first surface 21 was 13 mm.

[0127] [Sample No. 103] Sample No. 103 differs from Sample No. 1 in the following respects.

[0128] (a) As shown in FIGS. 29 and 30, the uneven portion 25 had a plurality of radially extending protrusions 25a.

[0129] (b) The inner diameter D3 of the notch 2h was 7.0 mm. (c) The size of the outer peripheral contour of the uneven portion 25 was 14 mm x 15 mm.

[0130] (d) The number of the protruding portions 25a was 16. (e) The angle θ5 between the adjacent protruding portions 25a was 22.5°.

[0131] (f) The angle θ1 of the apex of the cross section of the protrusion 25a was 90°. (g) The height h1 was 0.5 mm.

[0132] [Sample No. 104] Sample No. 104 differs from Sample No. 103 in the following respects.

[0133] (a) The angle θ1 of the apex of the cross section of the protrusion 25a was 140°, (b) The height h1 was 0.2 mm.

[0134] [Sample No. 105] Sample No. 105 differs from Sample No. 1 in the following respects.

[0135] (a) As shown in Figures 31 and 32, the cross-sectional shape of each protrusion 25a was rectangular. (b) The inner diameter D3 of the notch 2h was 7.0 mm.

[0136] (c) The outer diameter of the concave-convex portion 25 was 12.7 mm. (d) The inner diameter of the first convex portion 25a was 9.3 mm, and the inner diameter of the second convex portion 25a was 11.3 mm.

[0137] (e) The width W1 of each recess 25b was 0.3 mm, and the width W2 of each protrusion 25a was 0.7 mm.

[0138] (f) The angle θ1 of the corner 25c in the cross section of the protrusion 25a was 90°. (g) The height h1 was 0.2 mm.

[0139] [Tightening Test] Figure 34 is a schematic diagram of the tightening test. In the tightening test, in addition to the terminal 2 and the attachment target 3 of each sample, a pressure-sensitive sheet 7 was prepared. As shown by the dashed line in Figure 33, the attachment target 3 was placed on top of the terminal 2 in the tightening test.

[0140] The fastening device 8 shown in Figure 34 comprises an upper punch 81, a lower punch 82, and a positioning pin 83. The upper punch 81 has a cylindrical shape. The material of the upper punch 81 was S50C. The outer diameter of the upper punch 81 is the same as the seat diameter D2, and the inner diameter is the same as the nominal diameter D1. The lower punch 82 has a cylindrical shape. The material of the lower punch 82 was S50C. The outer diameter of the lower punch 82 is the same as the seat diameter D2. The inner diameter of the lower punch 82 is smaller than the nominal diameter D1. In this example, a positioning pin 83 is arranged on the end face of the lower punch 82. The positioning pin 83 may be press-fitted into a hole in the lower punch 82.

[0141] The attachment target 3, pressure-sensitive sheet 7, and terminal 2 were set in this order on the end face of the lower punch 82 of the clamping device 8. As a result, a laminate 9, in which the pressure-sensitive sheet 7 was placed between the terminal 2 and attachment target 3, was placed on the end face of the lower punch 82. A through hole of the same shape and diameter as the notch 2h of the terminal was formed in the pressure-sensitive sheet 7. The pressure-sensitive sheet 7 was placed so that the central axis of the through hole in the pressure-sensitive sheet 7 coincided with the central axis 2a of the notch 2h of the terminal 2. The pressure-sensitive sheet 7 was a "Pre-sheet (Pressure Measurement Film) for Medium Pressure MS PS" manufactured by Fujifilm Corporation. The uneven portion 25 of the terminal 2 faced the pressure-sensitive sheet 7.

[0142] The upper punch 81 was compressed and moved downward by the crosshead of the universal testing machine, and pressure was applied to the laminate 9, simulating a state in which an axial force was applied to the bolt 4. The final value L1 of the applied pressure was 138 × (D1). ２ ±50 N. The applied pressure is measured by a load cell of a universal testing machine and controlled by the displacement of the crosshead. The final value L1 is uniquely determined according to the inner diameter D3 of the notch 2h, although there may be some error. The final value L1 was reached 5 seconds after the start of application of the axial force. Tightening at the final value L1 was maintained for 5 seconds, after which the load was removed. The temperature during measurement was 25°C and the relative humidity was 40%.

[0143] The pressure-sensitive sheet 7 was collected from between the terminal 2 and the attachment target 3, and image analysis was performed to calculate the area of ​​the specific color-producing region of the pressure-sensitive sheet 7. The area of ​​the specific color-producing region was the first area S1.

[0144] The color-developing surface of the pressure-sensitive sheet 7 is scanned. At this time, the color chart attached to the pressure-sensitive sheet 7 is scanned simultaneously with the pressure-sensitive sheet 7. The color chart shows the correspondence between the pressure applied to the pressure-sensitive sheet 7 and the color density of the pressure-sensitive sheet 7. The resolution of the scanner was 300 dpi (dots per inch), 24-bit color.

[0145] The scanned image data was analyzed using Image J. Image J is open-source image analysis software. The software version was 1.53k. The image data was converted into an 8-bit monochrome image. Using the software, a histogram of the brightness of the color-producing area of ​​the pressure-sensitive sheet 7 was created, along with a histogram of the brightness of the color chart. With the pressure-sensitive sheet 7, the higher the contact pressure, the darker the color produced. With monochrome images, the higher the contact pressure, the lower the brightness. From the histogram of the color chart, the brightness corresponding to a contact pressure of 25 MPa or more was determined. Meanwhile, from the histogram of the color-producing area of ​​the pressure-sensitive sheet 7, the number N of pixels showing a contact pressure of 25 MPa or more was determined. In a 300 dpi image, the area per pixel was 0.007168 mm ２ Therefore, the first area S1 is 0.007168×N. Once the first area S1 is obtained, the ratio S1 / S2 can be calculated.

[0146] (Point Symmetry Parameter) The point symmetry parameter was calculated as follows. Using the same image analysis as that used to calculate the first area S1, the distance Li from the central axis 2a of the notch 2h of the terminal 2 to the center of each pixel having a brightness corresponding to a contact pressure of 25 MPa or more was measured. The central axis of the through-hole in the pressure-sensitive sheet 7 was considered to be the central axis 2a of the notch 2h of the terminal 2. The shape of each pixel was square. In a 300 dpi image, the area Sp of one pixel was 0.007168 mm ２ The intersection of the diagonals of a square with an area Sp is taken as the center of the pixel. The histogram interval is taken as ΔL, and the number of pixels Ni that show a contact pressure of 25 MPa or more and are included in the interval Li + ΔL is found. ΔL is taken as 0.2 mm. The point symmetry index Pi is found using the following formula:

[0147] Formula: Pi=Ni×Sp / (Li / ΔL) The maximum value of the point symmetry index Pi is the point symmetry parameter.

[0148] [Thermal Shock Test] For each sample, two test structures were prepared by fastening the terminal 2 and the attachment object 3 with a bolt and nut. The material of the bolt was SNB7 steel, with a Vickers hardness of 360 HV. The material of the nut was SWRCH10R, with a Vickers hardness of 210 HV. Since the inner diameter D3 of the notch 2h of the terminal 2 was 6.2 mm or 7.0 mm, the nominal diameter D1 of the bolt and the nominal diameter D1 of the nut were 6 mm. The inner diameter of the attachment object 3 was 6 mm, and the outer diameter was 18.4 mm. The bolt and nut were fastened to a 138 x 6 ２ The relationship between torque and axial force was measured in advance using an axial force bolt with a strain gauge, and the tightening torque of the test structure was set based on this.

[0149] One test structure was subjected to 1000 cycles of the first thermal shock test. Each cycle included steps A through D. Step A involved holding the atmosphere at 150°C for 30 minutes. Step B involved cooling the atmosphere to -40°C within 5 minutes of completing step A. Step C involved holding the atmosphere at -40°C for 30 minutes after completing step B. Step D involved heating the atmosphere to 150°C within 5 minutes of completing step C.

[0150] After the first thermal shock test, the contact resistance of the test specimens was measured using a four-terminal method. In the four-terminal method, alligator clips for supplying current were attached to the terminal 2 of each sample and the attachment target 3, respectively, or electric wires for supplying current were soldered thereto. Also, alligator clips for measuring voltage were attached to the terminal 2 of each sample and the attachment target 3, respectively, or electric wires for measuring voltage were soldered thereto. A measurement current of 1 A was applied under a clamping voltage of 12 V. The measured voltage was divided by the applied current to calculate the contact resistance. The unit of contact resistance is mΩ (milliohms).

[0151] The remaining test structure that had not been subjected to the first thermal shock test was subjected to a second thermal shock test. The second thermal shock test consisted of five 120-cycle cycles, each cycle being the same as the first thermal shock test. In the second thermal shock test, the terminal and the attachment target were detached by detaching the bolts every 120 cycles, and the contact resistance of the test structure before and after detachment was measured using the four-probe method described above.

[0152] The calculated contact resistance results for each thermal shock test are shown in Table 2. The first contact resistance is the result measured after the first thermal shock test. The second contact resistance is the maximum value of the contact resistances measured in the second thermal shock test. Table 2 also shows the Vickers hardness of the terminal 2 of each sample, the Vickers hardness of the attachment target 3, the hardness ratio obtained by dividing the Vickers hardness of the terminal 2 by the Vickers hardness of the attachment target 3, the reference diagram number of the protrusion, the size of the first area S1, and the ratio S1 / S2.

[0153]

[0154] As shown in Table 2, the first contact resistance and second contact resistance of Sample No. 1 to Sample No. 19 were 0.2 mΩ or less. The first contact resistance and second contact resistance of Sample No. 101 were greater than 0.2 mΩ. While the first contact resistance of Sample No. 102 to Sample No. 105 was 0.2 mΩ or less, the second contact resistance was greater than 0.2 mΩ. This test example demonstrated that by satisfying all of the requirements (A) to (D) described at the beginning of the section on embodiment 1, an increase in contact resistance at the interface between the terminal and the attachment object can be suppressed over a long period of time, and even if the bolt is attached or detached for maintenance of the connection structure, an increase in contact resistance at the interface between the terminal and the attachment object can be suppressed.

[0155] 1 Connection structure, 10 Electric wire with terminal, 2 Terminal, 2h Notch, 2a Central axis, 2c, 2d Inscribed circle, 21 First surface, 22 Second surface, 25 Concave and concave portion, 25a Convex portion, 25b Concave portion, 25c Corner, 29 Wire barrel, 3 Mounting object, 3h Notch, 4 Bolt, 4n Nut, 40 Shaft portion, 41 Head portion, 42 Flange portion, 5 Electric wire, 50 Conductor, 51 Insulating coating, 7 Pressure-sensitive sheet, 8 Fastening device, 81 Upper punch, 82 Lower punch, 83 Positioning pin, 9 Laminate, D2 Bearing surface diameter, D3 Inner diameter, D4 Outer diameter, P1 Pitch, W1, W2 Width, h1 Height, θ1, θ2, θ3, θ4, θ5 Angle, α, β region.

Claims

1. A connection structure comprising a terminal, an attachment object to which the terminal is attached, and a bolt connecting the terminal and the attachment object, wherein the terminal comprises: a first surface facing the attachment object when connected to the attachment object; and a notch through which the bolt passes; the first surface comprises an uneven portion formed around the notch; the uneven portion comprises at least one of a plurality of convex portions formed in a circular shape concentric with the central axis of the notch, a plurality of convex portions formed in an arc shape to be part of the concentric circle, a plurality of convex portions formed in a pyramidal shape between concave portions formed in a square or chevron shape, and a plurality of convex portions formed in a straight line to be arranged in parallel; the material of the terminal is pure aluminum or an aluminum alloy; the Vickers hardness of the terminal is 80HV or more; and the ratio S1 / S2 of a first area S1 to a second area S2 when the first surface and the attachment object are connected by tightening the bolt is 0.60 or less; The first area S1 is an area of ​​a region where the first surface contacts the object to be attached at a pressure of 25 MPa or more, the second area S2 is an area of ​​a circular region having an inner diameter equal to the nominal diameter D1 of the bolt and an outer diameter equal to the bearing surface diameter D2 of the bolt, and the first area S1 is 5 mm ２ That's it, the connection structure.

2. The first area S1 is the area of ​​a specific color-developing region of the pressure-sensitive sheet obtained by a clamping test that satisfies the following condition, and in the clamping test, a laminate in which the pressure-sensitive sheet is disposed between the first surface and the mounting target is subjected to a clamping test of 138×(D1) ２ The connection structure according to claim 1 , wherein the connection structure is fastened with an axial force of ±50 N, and the specific color-producing region is a region having a color indicating that the connection structure is pressed with a pressure of 25 MPa or more.

3. The connection structure according to claim 2, wherein the point symmetry parameter of the concave and convex portions is 1.3 or more.

4. A connection structure according to any one of claims 1 to 3, wherein the cross-sectional shape of each of the plurality of protrusions is triangular.

5. The connection structure according to claim 4, wherein the angle of the apex of each of the multiple protrusions in cross section is greater than 90° and is not greater than 140°.

6. A connection structure according to any one of claims 1 to 5, wherein the material of the object to be attached is pure copper or a copper alloy.

7. A connection structure according to claim 6, wherein the material of the object to be attached is oxygen-free copper, tough pitch copper, or JC100 according to the Japan Automotive Engineering Society standard.

8. A connection structure according to any one of claims 1 to 7, wherein the material of the terminal is International Registered Alloy Number 6061.

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