Metal welded structure, battery pack using the same, and method for manufacturing a battery pack.

Abstract

The purpose of the present invention is to enable highly reliable laser welding at a connection between a busbar and a voltage detection terminal in a vehicle battery pack.　In order to achieve this purpose, the present invention has a configuration such as the following. The metal welded structure has a first metal member 16, a second metal member 14 having an overlapping part with the first metal member 16, and a welded part 19 formed in the overlapping part, and is characterized in that: the welded part 19 has a melted part formed by carrying out melting so as to penetrate the second metal member 14 in the thickness direction into the first metal member 16; the welded part viewed from the overlapping direction has a U-shape having a first line part and second line parts 20 that respectively extend from the lengthwise direction sides of the first line part to the corresponding end; and a width D1 between two points that are the ends of the welded part 20 and the bead width W of the welded part 20 have the relationship of D1 / W≥2.

Description

Technical Field

[0001] The present invention relates to a welding structure of a storage battery, and particularly to a structure of a storage battery having a welding part of a wiring terminal and a method for manufacturing the same.

Background Art

[0002] For example, an in-vehicle battery module has a mechanism for detecting voltage information, temperature information, etc. of the mounted battery, and the wiring of the mechanism is often a connection structure via a metal plate (bus bar) connecting the battery body and between the batteries and a wiring terminal.

[0003] Here, since the wiring and the terminal are generally connected by mechanical coupling such as caulking, the material of the terminal is often a terminal material having relatively high hardness characteristics among copper-based materials excellent in electrical conduction, for example, a phosphor bronze material. The terminal made of this phosphor bronze member is connected to the mating member, and the connection method includes mechanical couplings such as caulking and press-fitting, solid-state joints such as resistance welding and ultrasonic bonding, and welding methods such as laser welding, arc welding, and electron beam welding that locally melt the member.

[0004] Here, in the last welding method, in the prior art, single spot welding that forms only one spot or single bead welding that forms only one simple straight line or curve has been the mainstream.

[0005] Patent Document 1 describes a molded member having a ridge line part, and a configuration in which the impact resistance is improved by attaching a reinforcing material to the ridge line part by welding. Patent Document 2 describes a method of laser bonding a first metal plate such as a steel plate and an aluminum plate having a lower melting point than this. Patent Document 3 describes a laser bonding method capable of increasing the peel strength when joining the flange parts of two parts having flange parts.

Prior Art Documents

Patent Documents

[0006] [Patent Document 1] Japanese Patent Publication No. 2014-87848 [Patent Document 2] Patent No. 5457605 [Patent Document 3] Patent No. 6176428 [Overview of the project] [Problems that the invention aims to solve]

[0007] In automotive battery modules, the welded joints are required to have sufficient strength and reliability to withstand external environments such as vibration and ensure electrical conductivity. Furthermore, due to the trend towards miniaturization of products, the shape of the components to be welded is becoming smaller, and there is a tendency to require weld structures that can secure the necessary joining area in the narrow parts of small terminals. As a result, weld shapes such as bead shapes with curved sections, multiple straight lines or linear shapes, annular shapes such as arcs or ellipses, or weld shapes with multiple spots are formed in narrow areas, and the distance between opposing beads, adjacent beads, or adjacent spots is forced to be small.

[0008] On the other hand, terminal materials with relatively high hardness characteristics, such as phosphor bronze, exhibit high-temperature embrittlement, where their ductility decreases at high temperatures. When welding is performed on a component terminal with such physical properties to create a bead shape that secures a welding area in the narrow space described above, the inventors have found that in the welding of the opposing or adjacent beads, the weld metal and its surroundings are exposed to high temperatures due to the thermal influence of the welding of the later-formed second-half bead. The displacement behavior of the material as it shrinks during the cooling process after solidification is fixed and inhibited by the earlier-formed first-half bead weld, causing tensile stress to concentrate in the embrittlement high-temperature region, and making it prone to weld cracking in the second-half bead.

[0009] Therefore, in order to create a welded structure for an automotive battery module that is excellent in terms of conductivity and strength reliability, it is necessary to establish a weld shape that provides a sufficiently large weld area in a minutely narrow space, and that prevents welding cracks caused by the physical properties of the terminal material, which has the aforementioned relatively high hardness characteristics. [Means for solving the problem]

[0010] To solve the above problems in current technology, the present invention provides a lap joint structure in which two members, an upper member and a lower member, are overlapped and energy is applied from one side to melt and penetrate the upper member and weld it to the lower member. In a shape in which the weld bead viewed from above has a curved portion and locally facing bead portions, the weld bead shape is formed in which the bead width W of the facing portion and the distance D between the bead centers are in the relationship D / W≧2, thereby providing a welding method that avoids the concentration of tensile stress that inhibits stress relaxation in the high-temperature range during the latter half of welding of adjacent or facing beads, which was a cause of welding cracks in phosphor bronze members.

[0011] Furthermore, the present invention provides a welding method that avoids the concentration of tensile stress that causes cracking by inhibiting stress relaxation in the high-temperature range during the latter half of welding of adjacent or directly facing beads, which was a cause of welding cracks in phosphor bronze members. This is achieved by overlapping the upper and lower members of two members, at least one of which is made of phosphor bronze, and applying energy from one side to melt and penetrate the upper member and weld it to the lower member. In a shape in which the weld bead has two or more straight or curved bead sections when viewed from above, the weld bead shape is formed in such a way that the adjacent bead width W and the distance D between the bead centers are in the relationship D / W≧2.

[0012] Furthermore, the present invention provides a welding method that avoids the concentration of tensile stress that causes cracking by inhibiting stress relaxation in the high-temperature range during the latter half of welding of adjacent or opposing beads, which was a cause of welding cracks in phosphor bronze members. This is achieved by overlapping the upper and lower members of two members, at least one of which is made of phosphor bronze, and applying energy from one side to melt and penetrate the upper member and weld it to the lower member. In a shape in which the weld bead viewed from above has a contour that is an arc, an ellipse, or a combination of a local arc and a straight section, with locally facing bead sections, and by forming a weld bead shape in which the adjacent bead width W and the distance D between the bead centers are in the relationship D / W≧2.

[0013] Furthermore, the present invention provides a welding method that avoids the concentration of tensile stress that causes cracking by inhibiting stress relaxation in the high-temperature range during the latter half of welding of adjacent or directly facing beads, which was a cause of welding cracks in phosphor bronze members. This is achieved by overlapping the upper and lower members of two members, at least one of which is made of phosphor bronze, and applying energy from one side to melt and penetrate the upper member and weld it to the lower member. The weld bead, as viewed from above, has multiple spot shapes, and the weld bead shape is formed such that the width W of adjacent weld beads and the distance D between the centers of the spots are in the relationship D / W≧2.

[0014] Furthermore, the present invention provides a welding method using laser light, an arc, or an electron beam as the energy source for forming the series of weld beads described above.

[0015] Furthermore, the present invention provides a miniaturized and highly reliable in-vehicle battery pack having a welded portion formed by the series of welding methods described above. [Effects of the Invention]

[0016] By adopting the welding shape of the present invention, it is possible to create a welded structure with excellent strength reliability and no weld cracks while ensuring sufficient weld length in terminal joints made of terminal materials with relatively high hardness characteristics. [Brief explanation of the drawing]

[0017] [Figure 1A] Schematic diagram showing the shape of the lap welding of the voltage detection terminal and the bus bar according to Example 1. [Figure 1B] Cross-sectional view showing the laser welding of Example 1. [Figure 1C] Schematic diagram showing another form of Example 1. [Figure 1D] Schematic diagram showing yet another form of Example 1. [Figure 1E] Graph showing the relationship between the shape of the weld bead and welding cracks. [Figure 1F] Schematic diagram showing yet another form of Example 1. [Figure 1G] Schematic diagram showing yet another form of Example 1. [Figure 1H] Schematic diagram showing yet another form of Example 1. [Figure 2A] Schematic diagram showing the shape of the lap welding of the voltage detection terminal and the bus bar according to Example 2. [Figure 2B] Cross-sectional view showing the laser welding of Example 2. [Figure 3A] Schematic diagram showing the shape of the lap welding of the voltage detection terminal and the bus bar according to Example 3. [Figure 3B] Schematic diagram showing the shape of the lap welding of the voltage detection terminal and the bus bar according to another form of Example 3. <00,00100>Cross-sectional view showing the laser welding of Example 3. [Figure 4A] Schematic diagram showing the shape of the lap welding of the voltage detection terminal and the bus bar according to Example 4. [Figure 4B] Schematic diagram showing the shape of the lap welding of the voltage detection terminal and the bus bar according to another form of Example 4. [Figure 4C] Cross-sectional view showing the laser welding of Example 4. [Figure 5A] Schematic diagram showing the shape of the lap welding of the voltage detection terminal and the bus bar according to Example 5. <000011,0>Schematic diagram showing the shape of the lap welding of the voltage detection terminal and the bus bar according to another form of Example 5. <o000112>A cross-sectional view showing the laser welding in Example 5. [Figure 6A] A schematic diagram showing the shape of the overlapping weld between the voltage detection terminal and the busbar according to Example 6. [Figure 6B] A cross-sectional view showing the laser welding in Example 6. [Figure 7A] A schematic diagram showing the shape of the overlapping weld between the voltage detection terminal and the busbar according to Example 7. [Figure 7B] A cross-sectional view showing the laser welding in Example 7. [Figure 8A] A schematic diagram showing the shape of the overlapping weld between the voltage detection terminal and the busbar according to Example 8. [Figure 8B] A cross-sectional view showing the laser welding in Example 8. [Figure 9A] A schematic diagram showing the shape of the overlapping weld between the voltage detection terminal and the busbar according to Example 9. [Figure 9B] A cross-sectional view showing the laser welding in Example 9. [Figure 10A] A schematic diagram showing the shape of the overlapping weld between the voltage detection terminal and the busbar according to Example 10. [Figure 10B] Figure 10A is a cross-sectional view of the busbar along its longitudinal direction. [Figure 10C] Figure 10A is a side view of the busbar along its short axis. [Figure 10D] A schematic diagram showing the shape of the overlapping weld between the voltage detection terminal and the busbar, in another embodiment of Example 10. [Figure 10E] Figure 10D is a side view of the busbar along its short axis. [Figure 11A] A cross-sectional view of the busbar, viewed from the short side, showing the busbar and voltage detection terminal connected to the laser while the busbar is inverted. [Figure 11B] A cross-sectional view of the busbar, viewed from the long side, showing the busbar and voltage detection terminal connected to the laser while inverted. [Figure 11C] A schematic diagram showing the shape of the overlapping weld between the voltage detection terminal and the busbar according to Example 11. [Figure 11D] A cross-sectional view showing the laser welding in Example 11. [Figure 11E]A side view of the relationship between the single cell, busbar, and voltage detection terminal in Example 11, viewed from the long direction of the single cell. [Figure 12A] A side view of the relationship between the single cell, busbar, and voltage detection terminal in Examples 1 to 10, viewed from the long direction of the single cell. [Figure 12B] A side view of the relationship between the single cell, busbar, and voltage detection terminal in Examples 1 to 10, viewed from the short-length direction of the single cell. [Figure 12C] A schematic diagram showing the basic structure arrangement and welding of a single cell, busbar, and voltage detection terminal in an in-vehicle battery pack according to the present invention. [Figure 12D] A side view of the relationship between the single cell, busbar, and voltage detection terminal in Examples 1 to 10, viewed from the short-length direction of the single cell. [Figure 12E] A side view of the relationship between the single cell, busbar, and voltage detection terminal in Examples 1 to 10, viewed from the long direction of the single cell. [Figure 13] A schematic diagram illustrating the automotive battery pack according to the present invention. [Figure 14] A plan view showing the relationship between the harness assembly containing the voltage detection wire, the voltage detection terminal, and the busbar in the automotive battery pack according to the present invention. [Modes for carrying out the invention]

[0018] The present invention will be described in detail below with reference to examples. [Examples]

[0019] In Example 1, the basic configuration of the battery pack, including the busbar and voltage detection terminal of the present invention, will be described with reference to the drawings. [Battery pack structure] Figure 13 shows a battery pack 1 using the terminal welding structure according to the present invention. The battery pack 1 has a structure in which a plurality of individual cells 2 are fixed by a pair of end plates 4 and a pair of side plates 5. The individual cells 2 are, for example, prismatic secondary batteries such as lithium-ion secondary batteries.

[0020] The rectangular cell 2 has a rectangular parallelepiped shape with a top surface, a bottom surface, a pair of large surface areas, and a pair of small surface areas. The cell 2s are arranged in a row with their large surface areas facing each other, and a holder 3 is interposed between each cell 2, in front of the first cell 2 in the row, and behind the last cell 2 in the row.

[0021] Each cell 2 has a positive electrode 2a and a negative electrode 2b on its upper side, and all are the same size, shape, and structure. Adjacent cell 2s are arranged with their positive electrode 2a and negative electrode 2b facing each other, in other words, with their front and back planes alternately reversed. The positive electrode 2a is made of an aluminum-based metal such as aluminum or an aluminum alloy, and the negative electrode 2b is made of a copper-based metal such as copper or a copper alloy.

[0022] End plates 4 are positioned in front of the holder 3 at the front of the row and behind the holder 3 at the rear of the row. The pair of end plates 4 are made of metal, have a substantially rectangular shape, and have openings 4a at the four corners through which bolts 6 are inserted. A pair of side plates 5 are positioned to the sides of the single cells 2 arranged in a row. Each side plate 5 is a rectangular frame having a span portion provided at an interval vertically and a connecting portion that connects this span portion. Openings 5a are formed at each corner of the frame corresponding to the openings 4a of the end plates 4.

[0023] The battery pack 1 is formed by placing the end plate 4 at the front of the row and the end plate 4 at the rear of the row inside the front and rear connecting portions of each side plate 5, and fastening them by inserting bolts 6 through the openings 5a in the side plate 5 and the openings 4a in the end plate 4. The bolts 6 are either screwed into threaded holes (not shown) formed in the holder 3, or fastened with nuts (not shown) on the back side of the end plate 4. Fastening with rivets may be used instead of bolts 6.

[0024] An insulating cover 7 is positioned on the upper side of each cell 2, surrounding the positive and negative electrodes 2a and 2b of the cell 2 arranged in a row. The positive electrode 2a and negative electrode 2b of adjacent cell 2 are connected by a busbar 10. All cell 2 are connected in series by the busbar 10. A busbar 8 is connected to the positive electrode 2a1 of the cell 2 at the front of the row and the negative electrode 2b1 of the cell 2 at the back of the row. The busbar 10 or busbar 8 and the positive and negative electrodes 2a and 2b are joined by welding, such as laser welding or ultrasonic welding. Alternatively, the connection may be made by screw fastening instead of welding.

[0025] Figure 14 is a plan view showing a harness assembly 100 having a voltage detection wiring group 101, a voltage detection terminal 14 connected to the voltage detection wiring group 101, and busbars 8 and 10 connected to the voltage detection terminal 14. The voltage detection wiring group 101 is connected to the outside via a socket 102. In addition, voltage measurement wiring is arranged within the branch harness 110 and connected to the voltage detection terminal 14. Busbar 8 is an end busbar and is connected only to the outermost single cell, while busbar 10 connects the terminals of two single cells 2. Note that the busbars 8 and 10 shown in Figure 14 are the simplest configuration and do not have the measuring structure shown in the following embodiments. Figure 14 corresponds to Figure 13 and corresponds to a configuration corresponding to 12 single cells 2. Note that in order to avoid complicating the diagram, only the above-mentioned parts are shown in Figure 14. The following explanation will use a voltage detection terminal 14 as an example of the first metal component and busbars 8 and 10 (or their welding target parts 16) as an example of the second metal component. The first metal component may be a busbar connecting the battery terminals, or a busbar connecting the battery to an external terminal. This allows for application in environments with harsh conditions such as high temperatures. The second metal component may be a terminal other than a voltage detection terminal. For example, it can be adapted to a temperature detection terminal. The "metal welded structure" of the present invention refers to a product comprising these first and second metal components.

[0026] In Figure 14, the welding target area of ​​the busbar 10 and the voltage detection terminal 14 overlap, and the busbar 10 and the voltage detection terminal 14 are laser-welded in this area. In Figure 14, each busbar 10 is directly connected to the positive electrode 2a and negative electrode 2b of the single cell 2, so the terminal voltage of the battery pack 1 is directly transmitted to the voltage detection terminal 14. The weld bead 19, which indicates the laser-welded portion, is shown as a U-shape. The reliability of the welding in this laser-welded weld bead 19 is extremely important for the reliability of the entire battery pack. The contents of the present invention will be explained in detail using the following embodiments.

[0027] The welded structure and examples according to the present invention are shown below. (Basic structure of voltage detection terminal and busbar) First, the basic structure of the voltage detection terminal and busbar in the battery pack to which the present invention pertains will be explained using Figure 12. Figure 12A is a schematic diagram of the battery pack, consisting of a single cell 2, the negative electrode side 10b of the busbar, and the voltage detection terminal 14, as seen from the long side of the single cell 2. The single cell 2 is equipped with a positive electrode 2a and a negative electrode 2b, and a busbar 10 is connected to the top of each terminal to conduct current between the terminals of adjacent single cells 2. The voltage detection wire 11 is connected to the voltage detection terminal 14, and the voltage detection terminal 14 is positioned on the surface of the welding target portion 16, which is provided to protrude from the negative electrode side of the busbar 10, and is welded in the structure of the present invention. Incidentally, the orientation of the voltage detection wire 11 in Figure 12A differs from that in Figures 13 and 14, as it faces outward relative to the single cell 2. Figure 12A is simply to illustrate the stacking relationship between the busbar 10 and the voltage detection terminal 14 in the laser junction portion, and is not oriented in the same way as the actual product shown in Figures 13 and 14.

[0028] Figure 12B is a schematic diagram of the battery pack 1, showing the single cell 2, the busbar positive electrode sides 10a and 10b, and the voltage detection terminal 14 as viewed from the short-length side of an adjacent single cell 2. The busbar positive electrode side 10a and busbar negative electrode side 10b are arranged to connect the negative electrode 2b and positive electrode 2a of each adjacent single cell 2 and are connected to their respective terminals. The voltage detection terminal 14 is positioned on the surface of the welding target portion 16 with a terminal that protrudes from the busbar negative electrode side 10b and is welded in the structure of the present invention. In this embodiment of the present invention, the upper side of the busbar negative electrode side 10b when mounted on the battery pack 1 will be called the front side, and the lower side will be called the back side.

[0029] Next, the basic structure during welding between the voltage detection terminal 14, which is the subject of the present invention, and the busbar negative electrode side 10b will be described. Figure 12C shows the arrangement of the components before welding between the voltage detection terminal 14 and the busbar negative electrode side 10b. The voltage detection terminal 14 is positioned on the upper part of the welding target portion 16, which is provided to protrude from the negative electrode side 10b of the busbar. Figures 12D and 12E are side views of the welding process, with Figure 12D showing the view from the short side of the busbar and Figure 12E showing the view from the long side of the busbar.

[0030] As described above, a laser beam is shone onto the surface of the voltage detection terminal 14, which is arranged in that manner, and it is welded as an overlapping joint with the welding target portion 16 of the busbar negative electrode side 10b.

[0031] In this invention, not only laser light but also arcs or electron beams can be used as methods for supplying welding energy. The following embodiment describes a welding method using a laser. (Material of voltage detection terminals and busbars) The voltage detection terminal 14 is made of phosphor bronze. The corresponding surface 15 of the welding target portion 16 protruding from the busbar 10 may be nickel-plated or tungsten-plated, or it may be unplated. On the other hand, in this embodiment, the material of the busbar 10 is a copper material such as oxygen-free copper, phosphorus-deoxidized copper, or tough pitch copper, or phosphor bronze, which is the welding target portion 16 that protrudes from the negative electrode side 10b of the busbar connected to the negative electrode 2b to 2b1 of the cell 2 and connects to the voltage detection terminal 14. The positive electrode side 10a of the busbar connected to the positive electrode 2a to 2a1 of the cell 2 is made of an aluminum-based material. The copper and aluminum parts are formed as an electrically conductive structure by joining, bonding, or fastening. (Examples of lasers used) The laser used in the implementation of this invention has a wavelength ranging from 400 to 1100 nm, in the blue visible light to near-infrared region. The spot diameter of the emitted laser beam is 0.04 to 0.6 mm. (Welded structure) Hereinafter, a characterized welded structure as an embodiment of the present invention will be described with reference to Figure 1. Figure 1A shows the welded structure formed by the present invention, with the weld bead shape on the surface being U-shaped, viewed from the upper side, which is the voltage detection terminal 14 side. The busbar negative electrode side 10b is formed such that the welding target portion 16 with respect to the voltage detection terminal 14 protrudes toward the voltage detection line 11 side, and the voltage detection terminal 14 is welded to the welding target portion 16 overlapping with it. Also, as shown in Figure 1B, in this embodiment, the voltage detection terminal 14 is arranged as the upper member, and the welding target portion 16 of the busbar is arranged as the lower member with its surface 15 facing upwards. This is an overlap joint structure in which a continuous beam-shaped laser beam 17 having the above characteristics is irradiated onto the surface of the voltage detection terminal 14, melting and penetrating the voltage detection terminal 14, and the molten portion 18 reaches a predetermined depth from the surface 15 of the welding target portion 16 of the busbar, welding the two members together. In Figure 1A, as an example, a welding bead 19 is shown in which the second linear section is the opposing section 20. An example is also shown in which the first linear section is the portion located between the opposing sections 20 on both sides. The welding bead 19 has the beads of the opposing sections 20 located on both sides in the longitudinal direction where the linear bead is formed.

[0032] As shown in Figure 1A, in the present invention, the weld bead shape is such that the weld bead 19 has a U-shape with a curved portion and facing bead portions, and the bead shape of the weld surface is formed such that the bead width W of the facing portion 20 and the distance D1 between the bead centers are in the relationship D1 / W≧2. If there is variation in the bead width W of the facing portion 20, the average value can be taken. The same applies to other embodiments. Furthermore, while the distance between the centers of the weld beads was used as the width D1 of the two ends of the weld in this embodiment, it is also conceivable to use the distance between one side of the second linear portion in the longitudinal direction of the first linear portion. Measurement becomes easier when there is little variation in the bead width W. The laser is irradiated in the thickness direction of the member.

[0033] In this case, the welding speed (beam scanning speed) for continuous beam welding is within the range of 50 to 300 mm / s. Furthermore, in order to control the welding atmosphere and ensure the bead shape, it is desirable to use a welding method in which an inert gas or nitrogen, or air or oxygen, as an assist gas or surface-activating gas is blown towards the welding site, but welding without the aforementioned gas blowing is also possible.

[0034] Furthermore, in the present invention, in order to obtain sufficient current-carrying area and strength reliability under the above-mentioned laser device and welding conditions, the weld structure is such that the surface width 21 of the weld bead 19 is 0.4 mm or more, and the welding width 22 at the interface shown in the same figure is 0.1 mm or more, as shown in Figure 1B. When the busbar negative electrode side 10b is made of the above-mentioned copper-based material, the melting depth 23 on the busbar side may be within the range of a penetration shape that is 0.1 mm or more and 80% or less of the busbar plate thickness.

[0035] Here, the weld bead shape in this embodiment has been described as U-shaped. However, this shape is not only a weld bead 19 having a straight bend shape as shown in Figure 1A, but also a bend shape 24 that is a combination of a straight line and an R-curve as shown in Figure 1C, or a shape 25 that is a combination of a curve and a straight line as shown in Figure 1D, and these are all weld structures with the same meaning.

[0036] Figure 1E shows the experimental results of verifying the relationship between the ratio of the bead width W and the distance D1 between the bead centers in the facing portion of the weld under the above welding conditions and bead shape, and the probability of cracking occurring in the weld. From the figure, it can be seen that in adjacent weld beads where the distance is small relative to the bead width, the relaxation of tensile stress generated during cooling may be hindered by the first bead, which is already welded, when the second adjacent bead is formed during welding. If the above tensile stress is concentrated without being relaxed when the second bead is in a high-temperature brittle state, cracking is likely to occur. On the other hand, in weld beads where a distance such that D1 / W is 2 or more is secured, the tensile stress at the time of second bead formation is sufficiently relaxed in the region with distance from the weld bead 19, thus avoiding stress concentration when in a high-temperature brittle state, and thus preventing cracking.

[0037] By shaping the weld bead in this way, it is possible to avoid the concentration of tensile stress that hinders stress relaxation in the high-temperature range during the latter half of welding of adjacent or opposing beads, which was a cause of welding cracks in phosphor bronze members, thereby causing cracks. This makes it possible to create a welded structure with excellent strength and reliability that does not crack.

[0038] Furthermore, in Figure 1A, the orientation of the weld bead is such that the facing portion 20 is oriented in the direction of the terminals of the cell 2. However, in the present invention, depending on the conditions during construction, such as the jig arrangement and the direction of irradiation of the laser beam 17, the facing portion 20 can be oriented inverted, as shown in Figure 1F, or oriented to the left or right of the adjacent direction of the cell 2, as shown in Figures 1G and 1H. The same applies to the bead shapes shown in Figures 1C and 1D. [Examples]

[0039] As a second embodiment of the present invention, a welded structure in which the shape of the weld bead is two L-shaped shapes arranged mirror-symmetrically is shown with reference to Figure 2. As shown in Figure 2A, the shape of the weld bead is two L-shaped shapes arranged mirror-symmetrically. In the shape 25 having opposing bead portions, the bead shape of the weld surface is formed such that the bead width W of the opposing portion 20 and the distance D2 between the bead centers are in the relationship D2 / W≧2. In this embodiment, the weld bead is described as having mirror symmetry, but it does not have to be perfectly mirror symmetry; it can be approximately mirror symmetry, where the overall shape is mirror symmetry. For example, the shape of the center of the bead width can be composed of two L-shapes. In this case, the vertical and horizontal lines of the L-shape, or the region where the vertical and horizontal lines intersect, may have curvature.

[0040] As shown in Figure 2B, the welded structure has a surface width 21 of 0.4 mm or more, and a weld width 22 at the interface shown in the figure of 0.1 mm or more. The laser specifications, welding conditions, working atmosphere, depth of the weld, and bead orientation are the same as those described in Example 1.

[0041] In the two L-shaped beads used in this implementation, the relaxation of tensile stress during welding is more effective. This avoids the concentration of tensile stress that hinders stress relaxation in the high-temperature range during the latter half of welding of adjacent or directly facing beads, which was a cause of welding cracks in phosphor bronze members, and thus makes it possible to create a welded structure with excellent strength and reliability that does not crack. [Examples]

[0042] As the next embodiment of the present invention, a welded structure in which the shape of the weld bead is a parallel arrangement of straight lines or curves is shown with reference to Figure 3. As shown in Figure 3A, in shape 26 where the weld bead is a parallel arrangement of straight lines, the bead shape of the weld surface is formed such that the bead width W of the facing portion 20 and the distance D3a between the centers of the beads are in the relationship D3a / W≧2. In this embodiment, the weld beads are described as being in parallel, but they can also be arranged in a substantially parallel configuration with gaps between them. For example, the linear shape viewed from the center of the bead width may be arranged with gaps between it and other beads. In this case, it is preferable that the gap between the two ends is substantially constant. Furthermore, this linear shape may be straight or arc-shaped.

[0043] Alternatively, as shown in Figure 3B, the weld bead shape is such that, in a shape 27 where the weld beads are arranged in parallel curves, the bead shape of the weld surface is such that the bead width W of the facing portion 20 and the distance D3b between the bead centers are in the relationship D3b / W ≥ 2. In either shape, as shown in Figure 3C, the weld structure has a surface width 21 of the weld bead of 0.4 mm or more, and the weld width 22 at the interface shown in the figure is 0.1 mm or more.

[0044] The laser specifications, welding conditions, working atmosphere, weld depth, and bead orientation are the same as those described in Example 1.

[0045] In the parallel arrangement of straight or curved weld beads in this implementation, the concentration of tensile stress during welding is mitigated by the presence of the above-mentioned morphological characteristics. Therefore, it is possible to avoid the concentration of tensile stress that hinders stress relaxation in the high-temperature range during the latter half of welding of adjacent or directly facing beads, which was a cause of welding cracks in phosphor bronze members, and thus cause cracks, resulting in a welded structure with excellent strength reliability that does not occur. [Examples]

[0046] As the next embodiment of the present invention, a welded structure in which the shape of the weld bead is circular or elliptical is shown with reference to Figure 4. As shown in Figure 4A, in the shape 28 in which the weld bead is circular, the bead shape of the weld surface is formed such that the bead width W and the diameter D4a of the circle between the centers of the beads are in the relationship D4a / W≧2.

[0047] Alternatively, as shown in Figure 4B, in a weld bead shape 29, the bead width W and the diameter D4b between the centers of the shorter side of the ellipse are such that D4b / W ​​≥ 2, forming a weld bead shape on the weld surface. In either shape, as shown in Figure 4C, the weld structure has a surface width 21 of 0.4 mm or more, and a weld width 22 at the interface shown in the figure is 0.1 mm or more.

[0048] The laser specifications, welding conditions, working atmosphere, weld depth, and bead orientation are the same as those described in Example 1.

[0049] In the circular or elliptical weld beads of this implementation, the concentration of tensile stress during welding is mitigated by the presence of the above-mentioned morphological characteristics. Therefore, it is possible to avoid the concentration of tensile stress that hinders stress relaxation in the high-temperature range during the latter half of welding of adjacent or directly facing beads, which was a cause of welding cracks in phosphor bronze members, and thus cause cracks, resulting in a welded structure with excellent strength reliability that does not occur. [Examples]

[0050] As the next embodiment of the present invention, a weld structure in which the shape of the weld bead is rectangular is shown with reference to Figure 5. As shown in Figure 5A, in a rectangular weld bead shape 30, the bead shape of the weld surface is formed such that the bead width W of the directly facing portion and the distance D5a between the centers of the beads are in the relationship D5a / W ≥ 2. Alternatively, a bead shape is formed in which the weld region with the distance D5a shown in the same figure is curved rather than straight.

[0051] Alternatively, as shown in Figure 5B, in a trapezoidal rectangular shape 31 where the opposing portions are not parallel, the weld surface bead shape is formed such that the bead width W of the opposing portions and the distance D5b between the bead centers are in the relationship D5b / W≧2.

[0052] In both shapes, as shown in Figure 5C, the welded structure has a surface width 21 of 0.4 mm or more, and a weld width 22 at the interface shown in the same figure of 0.1 mm or more. The laser specifications, welding conditions, working atmosphere, depth of the weld, and bead orientation are the same as those described in Example 1.

[0053] In the rectangular weld bead of this implementation, the concentration of tensile stress during welding is mitigated by the aforementioned morphological characteristics. Therefore, it is possible to avoid the concentration of tensile stress that hinders stress relaxation in the high-temperature range during the latter half of welding of adjacent or directly facing beads, which was a cause of welding cracks in phosphor bronze members, and thus create a welded structure with excellent strength reliability that does not crack. [Examples]

[0054] As the next embodiment of the present invention, a welded structure in which the weld bead shape is not continuous but spot-shaped is shown with reference to Figure 6. Figure 6A is a view of a welded section 32 consisting of two spot shapes formed by the present invention, as seen from the upper side, which is the voltage detection line side. As shown in the figure, a weld bead shape is formed in which the distance D6 between the W of adjacent weld beads 32 and the center of the spot is D6 / W ≥ 2. The number of spots in the spot welded section is not limited to two, but may be many more as long as the above relationship is satisfied. In this embodiment, the weld bead is described as a point shape representing a weld spot. While the width D6 of the two center points of the weld is measured using the distance between the center points, it is also possible to use the distance between the two ends in the direction connecting the spots. Measurement becomes easier when there is little variation in the size of the weld spots.

[0055] The laser used at this time can be either a pulsed laser or a continuous beam, and the spot diameter of the laser beam is 0.04 to 0.6 mm. In the case of a continuous beam, a spot-shaped welding beam can be formed by minute beam scanning accompanied by beam oscillation. The working atmosphere, such as the assist gas, is the same as in Example 1.

[0056] Furthermore, in order to obtain sufficient current-carrying area and strength reliability, the welded structure has a surface width 21 of the welded part of 0.4 mm or more, and a weld width 22 at the interface shown in the same figure of 0.1 mm or more, as shown in Figure 6B.

[0057] By adopting the weld bead shape having the above-described relationship according to the present invention, even in the case of spot welds, it is possible to avoid the concentration of tensile stress that inhibits stress relaxation in the high-temperature range during the latter half of welding of adjacent or directly facing beads, which was a cause of welding cracks in phosphor bronze members, thereby causing cracks, and to create a weld structure with excellent strength reliability that does not cause cracks. [Examples]

[0058] As the next embodiment of the present invention, a welding structure is shown with reference to Figure 7 when the welding target portion on the negative electrode side of the busbar is not made of the copper-based material shown in Example 1, but is made of the same aluminum material as the positive electrode side of the busbar and is in an integrated shape. Figure 7A is a view from the upper side, which is the voltage detection line side, of the weld bead formed by the present invention on the welding target portion 34 which is provided in a shape protruding from the integrated busbar 33 made of an aluminum-based material, and Figure 7B is a cross-sectional view of the welded portion. When the material of the welding target portion 34 with respect to the voltage detection terminal 14 is aluminum-based, the welded portion becomes more susceptible to cracking due to the embrittlement of the copper-aluminum compound, in addition to the crack susceptibility due to the high-temperature brittleness of the phosphor bronze member.

[0059] In this case, as shown in Figure 7A, similar to Example 1, the weld bead shape is such that the weld bead 35 has a U-shape with a curved portion and facing bead portions, and the bead width W of the facing portion 20 and the distance D7 between the centers of the beads are in the relationship D7 / W≧2, forming a bead shape on the surface of the weld.

[0060] Here, the weld bead shape includes not only the shape of the weld bead 35 but also the shapes described in Examples 1 to 6. In any bead shape, as shown in Figure 7B, the weld structure has a surface width 21 of the weld bead of 0.4 mm or more, and a weld width 22 at the interface shown in the same figure of 0.1 mm or more.

[0061] The specifications for the laser and welding conditions are the same as in Examples 1 to 6. In addition, as shown in the figure, by controlling the penetration on the busbar side so that the melting depth 36 on the busbar side of the welding target part 34 made of aluminum is 0.1 mm or more and the upper limit is 1.5 times the plate thickness T of the voltage detection terminal 14 regardless of the busbar plate thickness, the promotion of cracking by brittle compounds can be reduced.

[0062] In this way, by controlling the shape and penetration of the weld bead as described above, it is possible to prevent the occurrence of welding cracks due to phosphor bronze material factors and reduce crack exacerbation by compounds with aluminum busbars, resulting in a welded structure with excellent strength and reliability. [Examples]

[0063] As the next embodiment of the present invention, an example of a change in the position of the welded portion relative to the busbar is shown with reference to Figure 8. In Figure 8A, the welded portion 37 with respect to the voltage detection terminal of the busbar is provided as a flat portion at the outer end of the busbar's negative electrode side 10b in the direction adjacent to the single cell, and a voltage detection terminal 38 with a shape matching the shape of the flat portion is placed on top of it. The weld bead is U-shaped with a curved portion and has a shape 39 with opposing bead portions, and the bead shape of the welded portion surface is formed such that the bead width W of the opposing portion 20 and the distance D8 between the bead centers are in the relationship D8 / W≧2.

[0064] Here, the weld bead shape includes not only shape 39 but also the shapes for each material described in Examples 1 to 7. In all shapes, as shown in Figure 8B, the weld structure has a surface width 21 of the weld bead of 0.4 mm or more, and a weld width 22 at the interface shown in the same figure of 0.1 mm or more.

[0065] The laser specifications, welding conditions, working atmosphere, weld depth, bead orientation, and spot shape are the same as those described in previous examples 1 to 7. This welding structure creates extra space between the busbar of the battery pack and the terminal of the voltage detection wire bundle, making it possible to create a smaller or higher-density battery pack mounting structure. [Examples]

[0066] As the next embodiment of the present invention, an example of further variation in the position of the welded portion relative to the busbar negative electrode side 10b is shown with reference to Figure 9. This embodiment discloses a second configuration showing a change in the position of the joint portion. Figure 9A shows that, without providing a protruding flat portion on the busbar negative electrode side 10b, a voltage detection terminal 40 of a predetermined shape is placed on top of the outer diameter end of the work portion that connects to the terminals of the single cell 2 on the busbar negative electrode side 10b, and in the weld bead shape of the present invention, which is a U-shape with a curved portion and has a bead portion facing the front, the bead shape of the welded portion surface is formed such that the bead width W of the front portion 20 and the distance D9 between the bead centers are in the relationship D9 / W≧2.

[0067] As shown in Figure 9B, the welded structure has a surface width 21 of 0.4 mm or more, and a weld width 22 at the interface shown in the figure of 0.1 mm or more. Here, the welded bead shape includes not only shape 41 but also the shapes for each material described in Examples 1 to 7.

[0068] The laser specifications, welding conditions, working atmosphere, welding depth, bead orientation, and spot shape are the same as those described in previous examples 1 to 7. This welding structure creates space between the busbars 8 and 10 of the battery pack 1 and the terminals of the voltage detection wire 11, while also allowing the busbar 10 to be made smaller, thus enabling a smaller or higher-density mounting structure for the battery pack 1. [Examples]

[0069] As a further embodiment of the present invention, an example of a further change in the shape of the welded portion to the busbar is shown with reference to Figure 10. Figure 10A is a top view of an arrangement in which the welded portion 42 of the busbar with respect to the voltage detection terminal is provided protruding from the outer diameter end on the adjacent cell side and simultaneously bent upward, while the voltage detection terminal 43 is bent into a U-shape or square shape, and the two are fitted together or temporarily fixed by insertion with the voltage detection terminal 43 on the outside. Figure 10B is a cross-sectional view of the fitted portion between the welded portion 42 of the busbar and the voltage detection terminal 43.

[0070] In the figure, a laser beam 17 is irradiated from diagonally above onto the right surface 44 of the fitting portion, and overlapping welding is performed in the lateral direction. Figure 10C is a view of the fitting portion and welded surface between the welding target portion 42 and the voltage detection terminal 43, as seen from the shorter side near the center of the busbar negative electrode side 10b. The weld bead shape of the present invention is a U-shape with a curved portion, and in the weld bead 45 having opposing bead portions, the bead shape of the weld surface is formed such that the bead width W of the opposing portion and the distance D10a between the bead centers are in the relationship D10a / W≧2.

[0071] Furthermore, as shown in Figure 10D, the welded structure has a surface width 21 of 45mm or more, and a weld width 22 at the interface shown in the figure that is 0.1mm or more. Here, the welded bead shape includes not only 45 but also the shapes for each material described in Examples 1 to 7.

[0072] The laser specifications, welding conditions, working atmosphere, weld depth, bead orientation, and spot shape are the same as those described in previous examples 1 to 7.

[0073] Furthermore, this shape also provides the strength effect of a fitted and fixed joint. As shown in Figure 10E, the weld bead shape is bent and does not have a directly facing section, yet it exhibits excellent strength reliability. Even when the distance D10b between the bead centers, which is the bead shape of the present invention, is used as the bead length, and the bead width W and bead length D10b are in the relationship D10b / W≧2, excellent strength can be obtained when forming a weld bead 46 on the surface of the welded joint. Therefore, it is possible to create a welded structure that is smaller in size and has excellent strength reliability. This weld bead 46 is not limited to being formed on the side of the bent section shown in Figure 10E, but can also be formed on the upper surface of the fit. [Examples]

[0074] As the next embodiment of the present invention, an example of a change in the vertical positional relationship between the busbar negative electrode side 10b and the voltage detection terminal 14 is shown with reference to Figure 11. Figure 11 shows a busbar 10 positioned such that the back surface 47, defined above as the front and back surfaces of the busbar when attached to the battery pack 1, is on the upper side during welding, with the voltage detection terminal 14 positioned above it, and welding performed by irradiating the surface of the voltage detection terminal with laser light 17. Figure 11A is a view from the short side of the busbar, and Figure 11B is a view from the long side of the busbar.

[0075] Figure 11C is a view from above of the side irradiated with the laser. As shown in the figure, the weld bead shape is the shape of the weld bead of the present invention, which is a U-shape with a curved portion and has a shape 48 with opposing bead portions, and the bead shape of the weld surface is formed such that the bead width W of the opposing portion 20 and the distance D11 between the bead centers are in the relationship D11 / W≧2. Also, as shown in Figure 11D, the weld structure has a surface width 21 of 0.4 mm or more and a weld width 22 at the interface shown in the figure is 0.1 mm or more.

[0076] Here, the structure of the welded joint or the weld bead shape refers not only to shape 48 but also to the joint structures and weld shapes for each material described in Examples 1 to 10. The laser specifications, welding conditions, working atmosphere, welding depth, bead orientation, and spot shape are the same as those described in previous examples 1 to 7. Figure 11E shows a structure in which the busbar negative electrode side 10b and voltage detection terminal 14 welded using the above method are mounted as a battery pack 1. The voltage detection terminal 14 is welded to the underside of the busbar negative electrode side 10b and 16 when mounted as a battery pack 1. Note that in Figure 11E, the welding target part 16 of the busbar negative electrode side 10b protrudes to the outside of the cell 2, but this is a diagram for explaining Example 11, and in the actual product, the welding target part 16 and voltage detection terminal 14 face inward of the cell 2, as shown in Figures 13 and 14.

[0077] By adopting the welding structure shown in this embodiment, it is possible to obtain a welding structure with excellent adhesion to the voltage detection terminal and superior welding quality when the back surface of the busbar 10 has a higher degree of flatness. Furthermore, in the assembly state of the parts in actual construction, not only is it possible to obtain a construction method in which the busbar 10 is welded to the voltage detection terminal in a standalone position, but also when the busbar is assembled into a resin busbar case that mounts the bundle of voltage detection wires and the busbar on top of the battery pack, the height of the resin part on the back of the case can be shaped so as not to interfere with the jig, thereby obtaining a construction method that minimizes the thermal impact on the resin part during laser welding. [Explanation of Symbols]

[0078] 1...Battery pack, 2...Single cell, 2a...Positive electrode, 2b...Negative electrode, 3...Holder, 4...End plate, 4a...Opening, 5...Side plate, 5b...Opening, 6...Bolt, 7...Insulating cover, 8...End busbar, 10...Busbar, 11...Voltage detection line, 14...Voltage detection terminal, 15...Busbar surface, 16...Welding target area, 17...Laser, 19, 20...Weld bead, 21...Surface width of weld bead, 22...Width of weld bead on the busbar side, 23...Melting depth, 25-32, 33...Busbar, 3 4...Welding target area, 35...Weld bead, 36...Melting depth, 37...Welding target area, 38...Voltage detection terminal, 39...Weld bead, 40...Voltage detection terminal, 41...Weld bead, 42...Welding target area, 43...U-shaped voltage detection terminal, 44...Surface of U-shaped voltage detection terminal, 45...Weld bead, 46...Weld bead, 47...Back surface of busbar, 48...Weld bead, 49...U-shaped weld bead, 100...Harness assembly, 101...Wiring group, 102...Socket, 110...Branch harness.

Claims

1. A metal welded structure comprising a first metal member, a second metal member having an overlapping portion with the first metal member, and a welded portion formed in the overlapping portion, The welded portion has a molten portion formed by melting through the second metal member in the thickness direction and into the interior of the first metal member. The overlapping portion is formed in a rectangular shape, and the welded portion viewed from the overlapping direction is as follows: A pair of second linear portions extending along the opposing sides of the rectangle, and a first linear portion extending in a direction intersecting the direction in which the pair of second linear portions extend, and connected to the ends of the pair of second linear portions on the same direction, are formed. A metal welded structure characterized in that the width D between the ends of a pair of the second linear portions and the bead width W of the welded portion are in a relationship of D / W ≥ 2.

2. The metal welded structure according to claim 1, characterized in that the welded portion is welded using one of the following: a laser, an arc, or an electron beam.

3. The metal welded structure according to claim 1, characterized in that the molten metal is phosphor bronze or bronze.

4. A first cell having a first terminal and a second cell having a second terminal are arranged in the first direction. A battery pack comprising a busbar connecting the first terminal and the second terminal in the first direction, and a voltage detection terminal on the busbar for measuring voltage, A battery pack characterized in that, when the busbar is a first metal member and the voltage detection terminal is a second metal member, the first metal member and the second metal member are a metal welded structure as described in claim 1.

5. A first cell having a first terminal and a second cell having a second terminal are arranged in the first direction. A method for manufacturing a battery pack having a busbar connecting the first terminal and the second terminal in the first direction, and a voltage detection terminal for measuring the voltage of the busbar, A method for manufacturing a battery pack, characterized in that, when the busbar is a first metal member and the voltage detection terminal is a second metal member, the first metal member and the second metal member are welded together such that they form a metal welded structure as described in claim 1.

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