Metal welded structure, battery pack using same, and battery pack production method

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

Metal welded structure, assembled battery using same, and method of manufacturing assembled battery

[0001] The present invention relates to a welding structure for a storage battery, and more particularly to a structure for a storage battery having a welding portion for a wiring terminal and a manufacturing method thereof.

[0002] For example, an on-board battery module has a mechanism for detecting voltage and temperature information of the on-board battery, and the wiring for this mechanism is often a connection structure that connects the battery body and the battery to a metal plate (bus bar) and wiring terminals.

[0003] Here, wiring and terminals are generally connected by mechanical bonding such as crimping, and the terminal material is often a copper-based material with excellent electrical conductivity and relatively high hardness, such as phosphor bronze. Terminals made of this phosphor bronze material are connected to their mating members by a variety of methods, including mechanical bonding such as crimping or press-fitting, solid-state bonding such as resistance welding or ultrasonic bonding, and welding that locally melts members such as laser welding, arc welding, and electron beam welding.

[0004] Regarding the last welding method, in the prior art, the mainstream was single spot welding, which forms only one spot, or single bead welding, which forms only one simple straight or curved line.

[0005] Patent Document 1 describes a molded member having a ridge line portion, in which a reinforcing material is attached to the ridge line portion by welding to improve impact resistance. Patent Document 2 describes a method for laser joining a first metal plate such as a steel plate to an aluminum plate having a lower melting point. Patent Document 3 describes a laser joining method that can increase peel strength when joining the flange portions of two parts having flange portions.

[0006] JP 2014-87848, Patent 5457605, Patent 6176428

[0007] In automotive battery modules, welds must be strong and reliable enough to withstand external environmental conditions such as vibration and ensure electrical continuity, and because the trend toward miniaturization of products requires smaller shapes for the components to be welded, there is a trend toward a welding structure that ensures the necessary joint area in the narrow areas of small terminals.As a result, weld shapes such as bead shapes with curved sections, multiple straight or linear shapes, circular shapes such as arcs or ellipses, or shapes with multiple spots are formed in the narrow areas, and the distance between opposing bead sections, adjacent beads, or adjacent spots must be small.

[0008] On the other hand, terminal materials with relatively high hardness, such as phosphor bronze, exhibit high-temperature embrittlement, which reduces ductility at high temperatures. The inventors discovered that when welding a terminal with such physical properties to form a bead shape that ensures a sufficient weld area in a narrow portion, the weld metal and its surroundings are exposed to high temperatures due to the thermal effects of the welding of the later-formed second-half bead during welding of the facing or adjacent bead. The contraction and displacement behavior of the material during the cooling process from solidification is inhibited by the previously formed first-half bead weld, resulting in the concentration of tensile stress in the embrittled high-temperature region, making the later-formed second-half bead more susceptible to weld cracking.

[0009] Therefore, to achieve a welded structure for an automotive battery module with excellent electrical conductivity and strength reliability, it is necessary to establish a weld shape that provides a weld area large enough to fit into a minute narrow section, and that prevents weld cracks due to the physical properties of the terminal material, which has the above-mentioned relatively high hardness characteristics.

[0010] In order to solve the above problems in the current technology, the present invention provides a welding method that provides a lap joint structure in which 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, and in which the weld bead seen from above has a shape with a bend and locally opposing bead portions, and the bead width W of the opposing portion and the distance D between the bead centers satisfy the relationship D / W≧2, thereby avoiding the concentration of tensile stress that inhibits stress relaxation in the high temperature range during the latter half of construction of adjacent or opposing beads, which was a cause of weld cracks in phosphor bronze members and causes cracks.

[0011] The present invention also provides a welding method for a lap joint structure in which an upper and a lower member of two members, at least one of which is made of phosphor bronze, are overlapped and energy is applied from one side to melt and penetrate the upper member and weld it to the lower member, and in which the weld bead has a shape in which, when viewed from above, the weld bead has a bead portion that is two or more straight or curved lines, and the weld bead shape is formed such that the adjacent bead width W and the distance D between the bead centers satisfy the relationship D / W≧2, thereby avoiding the concentration of tensile stress that inhibits stress relaxation in the high temperature range of adjacent or opposite beads during the latter half of construction, which was a factor in the occurrence of weld cracks in phosphor bronze members and causes cracks.

[0012] The present invention also provides a welding method for a lap joint structure in which an upper and a lower member of two members, at least one of which is made of phosphor bronze, are overlapped and energy is applied from one side to melt and penetrate the upper member and weld it to the lower member, and the weld bead shape, when viewed from above, has a contour that is an arc, an ellipse, or a combination of local arcs and straight lines, and has locally opposing bead portions, and the weld bead shape is formed such that the adjacent bead width W and the distance D between the bead centers satisfy the relationship D / W≧2, thereby avoiding the concentration of tensile stress that inhibits stress relaxation in the high temperature range of adjacent or opposing beads during later construction, which was a factor in the occurrence of weld cracks in phosphor bronze members and causes cracks.

[0013] The present invention also provides a welding method for a lap joint structure in which an upper member and a lower member of two members, at least one of which is made of phosphor bronze, are overlapped and energy is applied from one side to melt and penetrate the upper member and weld it to the lower member, and the weld beads, viewed from above, are in the shape of multiple spots, and the weld bead shape is formed such that the width W of adjacent weld beads and the distance D between the spot centers satisfy the relationship D / W≧2. This prevents the concentration of tensile stress that inhibits stress relaxation in the high temperature range of adjacent or opposite beads during later construction, which was a factor in the occurrence of weld cracks in phosphor bronze members and causes cracks.

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

[0015] The present invention also provides an assembled battery for vehicle use that is small in size and highly reliable, by having welded portions formed by the above-described series of welding methods.

[0016] By using the weld shape of the present invention, it is possible to obtain a weld structure with excellent strength and reliability, free from weld cracks, while ensuring the weld length in a terminal joint made of a terminal material having relatively high hardness characteristics.

[0017] 1 is a schematic diagram showing the shape of lap welding between a voltage detection terminal and a bus bar according to Example 1. FIG. 2 is a cross-sectional view showing laser welding in Example 1. FIG. 3 is a schematic diagram showing another embodiment of Example 1. FIG. 4 is a schematic diagram showing yet another embodiment of Example 1. FIG. 5 is a graph showing the relationship between weld bead shape and weld cracks. FIG. 6 is a schematic diagram showing yet another embodiment of Example 1. FIG. 7 is a schematic diagram showing yet another embodiment of Example 1. FIG. 8 is a schematic diagram showing yet another embodiment of Example 1. FIG. 9 is a schematic diagram showing the shape of lap welding between a voltage detection terminal and a bus bar according to Example 2. FIG. 10 is a cross-sectional view showing laser welding in Example 2. FIG. 11 is a schematic diagram showing the shape of lap welding between a voltage detection terminal and a bus bar according to Example 3. FIG. 12 is a schematic diagram showing the shape of lap welding between a voltage detection terminal and a bus bar according to another embodiment of Example 3. FIG. 13 is a cross-sectional view showing laser welding in Example 3. FIG. 14 is a schematic diagram showing the shape of lap welding between a voltage detection terminal and a bus bar according to Example 4. FIG. 15 is a schematic diagram showing the shape of lap welding between a voltage detection terminal and a bus bar according to another embodiment of Example 4. 10A is a cross-sectional view showing laser welding in Example 4. FIG. 10B is a schematic diagram showing the shape of lap welding between a voltage detection terminal and a bus bar in Example 5. FIG. 10C is a schematic diagram showing the shape of lap welding between a voltage detection terminal and a bus bar in another embodiment of Example 5. FIG. 10D is a cross-sectional view showing laser welding in Example 5. FIG. 10E is a schematic diagram showing the shape of lap welding between a voltage detection terminal and a bus bar in Example 6. FIG. 10F is a cross-sectional view showing laser welding in Example 6. FIG. 10G is a schematic diagram showing the shape of lap welding between a voltage detection terminal and a bus bar in Example 7. FIG. 10H is a cross-sectional view taken along the longitudinal direction of the bus bar of FIG. 10A. 10B is a side view taken along the short length direction of the bus bar of FIG. 10A. FIG. 10C is a schematic diagram showing the shape of lap welding between a voltage detection terminal and a bus bar according to another form of Example 10. FIG. 10D is a side view taken along the short length direction of the bus bar of FIG. 10D. FIG. 10D is a cross-sectional view of the bus bar in an upside-down state, viewed from the short length direction, showing the state in which the bus bar and the voltage detection terminal are laser-connected, viewed from the long ... in an upside-down state. FIG. 11 is a schematic diagram showing the shape of lap welding between a voltage detection terminal and a bus bar according to Example 11. FIG. 11 is a cross-sectional view showing laser welding of Example 11.1 is a side view of the relationship between a cell, a bus bar, and a voltage detection terminal in Example 11, viewed from the long-length direction of the cell. FIG. 2 is a side view of the relationship between a cell, a bus bar, and a voltage detection terminal in Examples 1 to 10, viewed from the long-length direction of the cell. FIG. 3 is a side view of the relationship between a cell, a bus bar, and a voltage detection terminal in Examples 1 to 10, viewed from the short-length direction of the cell. FIG. 4 is a schematic diagram showing the arrangement of a cell, a bus bar, and a voltage detection terminal in a basic structure and welding work in an automotive battery pack according to the present invention. FIG. 5 is a side view of the relationship between a cell, a bus bar, and a voltage detection terminal in Examples 1 to 10, viewed from the short-length direction of the cell. FIG. 6 is a side view of the relationship between a cell, a bus bar, and a voltage detection terminal in Examples 1 to 10, viewed from the long-length direction of the cell. FIG. 7 is a schematic diagram showing an automotive battery pack according to the present invention. FIG. 8 is a plan view showing the relationship between a harness assembly accommodating a voltage detection wire, the voltage detection terminal, and the bus bar in an automotive battery pack according to the present invention.

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

[0019] In Example 1, the basic configuration of a battery pack including a battery pack bus bar and a 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 a terminal welding structure according to the present invention. The battery pack 1 has a structure in which a plurality of unit cells 2 are fixed by a pair of end plates 4 and a pair of side plates 5. The unit cells 2 are, for example, prismatic secondary batteries such as lithium-ion secondary batteries.

[0020] Each rectangular cell 2 has a rectangular parallelepiped shape with an upper surface, a lower surface, a pair of large-area flat surfaces, and a pair of small-area side surfaces. The cells 2 are arranged in a row with the large-area flat surfaces facing each other, and holders 3 are 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] The cells 2 have a positive electrode 2a and a negative electrode 2b on the upper side, and all have the same size, shape, and structure. Adjacent cells 2 are arranged with their positive electrodes 2a and negative electrodes 2b facing each other, in other words, with their front and back surfaces alternately inverted. The positive electrodes 2a are made of an aluminum-based metal such as aluminum or an aluminum alloy, and the negative electrodes 2b are made of a copper-based metal such as copper or a copper alloy.

[0022] End plates 4 are disposed in front of the first holder 3 in the row and behind the last holder 3 in the row. The pair of end plates 4 are made of metal and have a substantially rectangular shape, with openings 4a at their four corners through which bolts 6 are inserted. A pair of side plates 5 are disposed on the sides of the cells 2 arranged in a row. Each side plate 5 is a rectangular frame having span sections spaced apart above and below and connecting sections that connect these span sections. Openings 5a are formed at each corner of the frame to correspond 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 together with bolts 6 inserted through openings 5a in the side plates 5 and openings 4a in the end plates 4. The bolts 6 are threaded into threaded holes (not shown) formed in the holder 3, or are fastened together with nuts (not shown) placed on the backsides of the end plates 4. Fastening with bolts 6 may be replaced by rivets.

[0024] An insulating cover 7 is disposed above each cell 2 so as to surround the positive and negative electrodes 2a, 2b of the cells 2 arranged in a row. The positive electrodes 2a and negative electrodes 2b of adjacent cells 2 are connected by a bus bar 10. All cells 2 are connected in series by the bus bar 10. A bus bar 8 is connected to the positive electrode 2a1 of the first cell 2 in the row and the negative electrode 2b1 of the last cell 2 in the row. The bus bar 10 or bus bar 8 is joined to the positive and negative electrodes 2a, 2b by welding such as laser welding or ultrasonic welding. Instead of welding, a structure in which the connections are made by screw fastening may also be used.

[0025] FIG. 14 is a plan view illustrating 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 bus bars 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. Furthermore, voltage measurement wiring is arranged within a branch harness 110 and connected to the voltage detection terminal 14. The bus bar 8 is an end bus bar and connects only to the outermost cell, while the bus bar 10 connects between the terminals of two cells 2. The bus bars 8 and 10 shown in FIG. 14 have the simplest configuration and do not have a scaled structure as shown in the following examples. FIG. 14 corresponds to FIG. 13 and is configured to accommodate 12 cells 2. Note that components other than those described above are not shown in FIG. 14 to avoid complicating the illustration. In the following, an example of the first metal member will be explained using a voltage detection terminal 14, and an example of the second metal terminal will be explained using bus bars 8 and 10 (or their welding target portions 16). The first metal member may not be a bus bar connecting battery terminals, but may be a bus bar connecting a battery to an external terminal. This can be applied to locations with harsh usage environments such as high temperatures. The second metal member may not be a voltage detection terminal, but may be another terminal. As an example, it can be applied to a temperature detection terminal, etc. The "metal welded structure" of the present invention refers to a product that includes these first metal member and second metal member.

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

[0027] The following describes a welding structure and examples according to the present invention. (Basic Structure of the Voltage Detection Terminal and Bus Bar) First, the basic structure of the voltage detection terminal and bus bar in the battery pack according to the present invention will be described with reference to FIG. 12 . FIG. 12A is a schematic diagram of the battery pack, including the cell 2, the bus bar negative electrode 10b, and the voltage detection terminal 14, as viewed from the side in the longitudinal direction of the cell 2. The cell 2 has a positive electrode 2a and a negative electrode 2b, and a bus bar 10 is connected to the top of each terminal to conduct electricity between the terminals of adjacent 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 with respect to the terminal protruding from the negative side of the bus bar 10, and is welded using the structure of the present invention. The orientation of the voltage detection wire 11 in FIG. 12A is different from that in FIGS. 13 and 14 , and faces outward relative to the cell 2. FIG. 12A is merely for explaining the layered relationship between the busbar 10 and the voltage detection terminal 14 at the laser-bonded portion, and does not have the same orientation as the actual product as shown in FIGS. 13 and 14 .

[0028] 12B is a schematic diagram of the cells 2, bus bar positive electrode sides 10a, 10b, and voltage detection terminal 14, as viewed from the side in the short length direction of adjacent cells 2 in the battery pack 1. The bus bar positive electrode side 10a and the bus bar negative electrode side 10b are arranged to connect the negative electrode 2b and positive electrode 2a of each adjacent cell 2, and are connected to each terminal. The voltage detection terminal 14 is arranged on the surface of a welding target portion 16 with a protruding terminal on the bus bar negative electrode side 10b, and is welded using the structure of the present invention. In this embodiment of the present invention, the surface that will be the upper side of the bus bar negative electrode side 10b when installed in the battery pack 1 will be called the front side, and the surface that will be the lower side will be called the back side.

[0029] Next, the basic structure of the present invention when welding the voltage detection terminal 14 and the bus bar negative electrode side 10b will be described. Fig. 12C shows the arrangement of components before welding the voltage detection terminal 14 and the bus bar negative electrode side 10b. The voltage detection terminal 14 is arranged above a welding target portion 16 with the voltage detection terminal 14, which protrudes from the negative electrode side 10b of the bus bar. Figs. 12D and 12E are side views of the welding process, with Fig. 12D showing a view from the side of the bus bar's short side and Fig. 12E showing a view from the side of the bus bar's long side.

[0030] The surface of the voltage detection terminal 14 arranged as described above is irradiated with laser light and welded to the welding target portion 16 of the bus bar negative electrode side 10b as a lap joint.

[0031] In the present invention, not only laser light but also arc or electron beam welding can be used as a method for applying welding energy. The following example illustrates a laser welding method. (Materials of the Voltage Detection Terminal and Bus Bar) The voltage detection terminal 14 is made of phosphor bronze. The corresponding surface 15 of the welding target portion 16 protruding from the bus bar 10 is Ni-plated or Sn-plated, or may be unplated. Meanwhile, in this example, the bus bar 10 is made of a pure copper-based copper material, such as oxygen-free copper, phosphorus-deoxidized copper, or tough pitch copper, or a phosphorus bronze-based copper material, for example. The bus bar positive electrode side 10a, which connects to the positive electrode 2a or 2a1 of the battery 2, is made of an aluminum-based material. The copper and aluminum portions are joined, bonded, or fastened together to form a conductive structure. (Example of Laser Used) The laser used in the present invention has a wavelength of 400 to 1100 nm, ranging from blue visible light to the near-infrared region. The spot diameter of the irradiated laser light is 0.04 to 0.6 mm. (Welded Structure) A characterized welded structure as an embodiment of the present invention will be described below with reference to FIG. 1. FIG. 1A shows a welded structure formed according to the present invention, in which the weld bead on the surface is U-shaped, as viewed from the top side, i.e., the voltage detection terminal 14 side. The busbar negative electrode side 10b has a weld target portion 16 with the voltage detection terminal 14 formed so that it protrudes toward the voltage detection line 11, and the voltage detection terminal 14 is welded to the weld target portion 16 overlapping the weld target portion 16. Furthermore, as shown in FIG. 1B, in this embodiment, the voltage detection terminal 14 is positioned as the upper member, and the busbar weld target portion 16 is positioned as the lower member, with the surface 15 facing upward. This is a lap joint structure in which a continuous beam of laser light 17 having the above-described characteristics is irradiated onto the surface of the voltage detection terminal 14, melting and penetrating the voltage detection terminal 14 to form a molten zone 18 reaching a predetermined depth from the surface 15 of the welding target portion 16 of the busbar, thereby welding the two components. In Figure 1A, as an example, an example is shown in which the facing portion 20 is the second linear portion in the weld bead 19. Also, an example is shown in which the first linear portion is the portion located between the facing portions 20 on both sides.The weld bead 19 has beads of opposing portions 20 located on both sides of the linear bead in the longitudinal direction.

[0032] As shown in FIG. 1A , in the present invention, the weld bead shape is a U-shaped weld bead 19 with a bend and two opposing bead portions, and the bead width W of the opposing portion 20 and the distance D1 between the bead centers satisfy the relationship D1 / W≧2. If there is variation in the bead width W of the opposing portion 20, the average value can be taken. This also applies to other embodiments. Furthermore, in this embodiment, the distance between the bead centers is used as the width D1 of the two ends of the weld, but it is also possible to use the distance between one side of the second linear portion in the longitudinal direction of the first linear portion. Measurement is 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) in the case of continuous beam welding is within the range of 50 to 300 mm / s. In addition, in order to control the welding atmosphere and ensure the bead shape during welding, it is desirable to use a welding method in which an inert gas or nitrogen as an assist gas, or air or oxygen as a surface activation gas, is blown toward the welding site, but welding without blowing the gas is also possible.

[0034] Furthermore, in the present invention, in order to obtain a sufficient current-carrying area and strength reliability with the above-described laser device and welding conditions, the weld structure has a surface width 21 of the weld bead 19 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 Fig. 1B. When the bus bar negative electrode side 10b is made of the above-described copper-based material, the fusion depth 23 on the bus bar side may be in the range of a penetration shape that is 0.1 mm or more and 80% or less of the bus bar plate thickness.

[0035] Here, the weld bead shape in this example has been described as U-shaped, but this shape does not only refer to weld bead 19 having a linear bent shape as shown in FIG. 1A , but also to bent shape 24 that is a combination of a straight line and an R-curve as shown in FIG. 1C , or shape 25 that is a combination of a curve and a directly opposed straight line portion as shown in FIG. 1D , which are weld structures with the same meaning.

[0036] Figure 1E shows the results of an experimental study of the relationship between the ratio of the bead width W to the distance D1 between the bead centers and the probability of cracking in the weld under the above welding conditions and bead shape. As shown in Figure 1E, when adjacent weld beads are close to each other relative to the bead width, the first bead, which has already been welded, may prevent the relaxation of tensile stresses that occur during cooling when the second adjacent bead is formed. If the tensile stress is concentrated without relaxation when the second bead is in a high-temperature brittle state, cracking is likely to occur. On the other hand, when a weld bead is spaced apart such that D1 / W is at least twice as large, the tensile stress during the formation of the second bead is sufficiently relaxed in the area distant from the weld bead 19, avoiding stress concentration in a high-temperature brittle state and thereby preventing cracking.

[0037] By using this type of weld bead shape, it is possible to avoid the concentration of tensile stress that inhibits stress relaxation in the high temperature range during the latter half of construction of adjacent or opposite beads, which was a cause of weld cracks in phosphor bronze components, and causes cracks, and to create a weld structure that is crack-free and has excellent strength reliability.

[0038] 1A, the weld bead is oriented such that the facing portion 20 faces the direction in which the terminals of the unit cells 2 are located, but in the present invention, depending on the conditions during welding, such as the jig arrangement and the direction of irradiation of the laser light 17, it is also possible to have the facing portion 20 facing upside down as shown in Fig. 1F, or to have the facing portion 20 facing to the left or right side of the adjacent direction of the unit cells 2 as shown in Figs. 1G and 1H. This is also true for the bead shapes shown in Figs. 1C and 1D.

[0039] As a second embodiment of the present invention, a welding structure in which the weld bead has two L-shaped configurations arranged in mirror symmetry is shown in FIG. 2 . As shown in FIG. 2A , the weld bead has two L-shaped configurations arranged in mirror symmetry. In a shape 25 having opposing bead portions, a bead shape is formed on the weld surface such that the bead width W of the opposing portion 20 and the distance D2 between the bead centers satisfy the relationship D2 / W≧2. In this embodiment, the weld bead shape is described as mirror symmetrical, but it can also be approximately mirror symmetrical, meaning that it does not have to be completely mirror symmetrical but is mirror symmetrical overall. For example, the shape at the center of the bead width may be composed of two L-shaped configurations. In this case, the vertical and horizontal lines of the L and the area where the vertical and horizontal lines intersect may have curvature.

[0040] 2B, the weld bead 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. The laser specifications, welding conditions, working atmosphere, weld depth, and bead orientation are the same as those described in Example 1.

[0041] The two L-shaped beads in this embodiment more effectively relieve tensile stress during welding, and prevent the concentration of tensile stress that inhibits stress relaxation in the high temperature range during the latter half of construction of adjacent or opposite beads, which was a cause of weld cracks in phosphor bronze members, and causes cracks, making it possible to create a welded structure with excellent strength reliability and no cracks.

[0042] As a next example of the present invention, a welding structure in which the weld beads are arranged in parallel, straight or curved lines, is shown using FIG. 3 . As shown in FIG. 3A , the weld beads are arranged in parallel, in a shape 26, and the bead width W of the facing portion 20 and the distance D3a between the bead centers satisfy the relationship D3a / W≧2. While the weld beads are described as being parallel in this example, they may also be arranged in a generally parallel fashion with a gap between them. For example, the weld beads may be arranged in a linear shape from one end to the other end of the bead width center with a gap between them. In this case, it is preferable that the gap between the one end and the other end is approximately constant. Furthermore, the linear shape may be either linear or arc-shaped.

[0043] Alternatively, as shown in Fig. 3B, the weld bead shape is formed on the surface of the welded portion in a shape 27 where the weld beads are parallel curves, and the bead width W of the facing portion 20 and the distance D3b between the bead centers satisfy the relationship D3b / W ≥ 2. In either shape, as shown in Fig. 3C, 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.

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

[0045] The parallel arrangement of straight or curved weld beads in this embodiment also reduces the concentration of tensile stress during welding by providing the above-mentioned geometric characteristics. This prevents the concentration of tensile stress that inhibits stress relaxation in the high temperature range during the latter half of welding of adjacent or opposite beads, which was a cause of weld cracks in phosphor bronze members, and causes cracks, making it possible to achieve a weld structure with excellent strength reliability and no cracks.

[0046] As a next example of the present invention, a weld structure in which the weld bead has a circular or elliptical shape will be shown using Fig. 4. As shown in Fig. 4A, in a circular weld bead shape 28, a bead shape is formed on the weld surface such that the bead width W and the diameter D4a of the circle between the bead centers satisfy the relationship D4a / W≧2.

[0047] Alternatively, as shown in Fig. 4B, when the weld bead has an elliptical shape 29, the bead shape on the surface of the weld is formed such that the bead width W and the bead center-to-center diameter D4b on the shorter side of the ellipse satisfy the relationship D4b / W ​​≥ 2. In either shape, as shown in Fig. 4C, 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.

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

[0049] The circular or elliptical weld bead of this embodiment also has the above-mentioned shape characteristics, which alleviates the concentration of tensile stress during welding. Therefore, 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 opposite beads, which was a cause of weld cracks in phosphor bronze members, and causes cracks, and to achieve a weld structure with excellent strength reliability and no cracks.

[0050] As a next example of the present invention, a weld structure in which the weld bead has a rectangular shape is shown using Fig. 5. As shown in Fig. 5A, in a rectangular weld bead shape 30, a bead shape is formed on the weld surface such that the bead width W of the opposite portion and the distance D5a between the bead centers satisfy the relationship D5a / W ≥ 2. Alternatively, a bead shape is formed in which the weld area having the distance D5a shown in the figure is curved rather than straight.

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

[0052] In either shape, 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 Fig. 5C 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] The rectangular weld bead of this embodiment also has the above-mentioned geometric characteristics, which alleviate the concentration of tensile stress during welding. Therefore, 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 opposite beads, which was a cause of weld cracks in phosphor bronze members, and causes cracks, and to achieve a weld structure with excellent strength reliability and no cracks.

[0054] As a next example of the present invention, a welding structure in which the weld bead shape is not continuous but spot-shaped is shown in FIG. 6 . FIG. 6A is a view of a weld 32 formed by the present invention, consisting of two spot shapes, as seen from the top side, i.e., the voltage detection line side. As shown in the figure, a weld bead shape is formed in which the distance D6 between adjacent weld beads 32 W and the spot center satisfies the relationship D6 / W≧2. The number of spot welds is not limited to two and may be greater as long as the above relationship is satisfied. In this example, the weld bead shape is described as a spot shape, and the width D6 between the centers of the two weld points is the distance between the spot centers in this example. However, it is also possible to use the distance between one end of the spot in the direction connecting the spots. Measurement is easier when there is little variation in the size of the weld spots.

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

[0056] In order to obtain a sufficient current-carrying area and strength reliability, the weld structure has a surface width 21 of the welded portion 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 FIG. 6B.

[0057] By creating a weld bead shape that satisfies the above-described relationship according to the present invention, even in the case of a spot-welded structure, 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 opposing beads, which was a cause of weld cracks in phosphor bronze members and causes cracks, and to achieve a welded structure that is crack-free and has excellent strength reliability.

[0058] As a next example of the present invention, Fig. 7 shows a welded structure in which the weld target portion on the negative electrode side of the bus bar is not made of a copper-based material as in Example 1, but is made of the same aluminum material as the positive electrode side of the same bus bar, forming an integral shape. Fig. 7A shows a weld bead formed by the present invention on a weld target portion 34 that protrudes from a one-piece bus bar 33 made of an aluminum-based material, as viewed from above, i.e., the voltage detection line side, and Fig. 7B is a cross-sectional view of the welded portion. When the weld target portion 34 to the voltage detection terminal 14 is made of an aluminum-based material, the welded portion is susceptible to cracking due to the high-temperature brittleness of phosphor bronze, and also to increased cracking due to the embrittlement of the copper-aluminum compound.

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

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

[0061] The laser specifications and welding conditions are also the same as those in Examples 1 to 6. In addition, as shown in the figure, by controlling the penetration on the bus bar side so that the fusion depth 36 on the bus bar side of the welding target portion 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 plate thickness of the bus bar, it is possible to reduce the promotion of cracks due to brittle compounds.

[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 weld cracks caused by the phosphor bronze material and reduce the promotion of cracks due to compounds with the aluminum bus bar, resulting in a welded structure with excellent strength reliability.

[0063] As a next example of the present invention, an example of changing the position of the welded portion relative to the bus bar is shown in Figure 8. In Figure 8A, the portion 37 to be welded to the bus bar voltage detection terminal is provided as a flat portion on the outer end of the bus bar negative electrode side 10b in the direction adjacent to the battery cells, and a voltage detection terminal 38 having a shape that matches the shape of the flat portion is placed on top of it. The weld bead has a U-shape with a bend and facing bead portions 39, and the bead width W of the facing portion 20 and the distance D8 between the bead centers satisfy the relationship D8 / W≧2.

[0064] Here, the weld bead shape applies not only to shape 39 but also to the shapes for each material described in Examples 1 to 7. In any shape, 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, processing atmosphere, welding depth, bead orientation, and spot shape are the same as those described in Examples 1 to 7. This welding structure creates a margin in the area between the bus bar of the battery pack and the wire bundle terminal of the voltage detection wire, making it possible to achieve a more compact or high-density battery pack mounting structure.

[0066] As a next example of the present invention, a further example of a change in the position of the welded portion relative to the busbar negative electrode side 10b is shown using Figure 9. This example discloses a second configuration illustrating a change in the position of the joint. Figure 9A shows a weld bead shape formed on the surface of the welded portion, in which a voltage detection terminal 40 having a predetermined shape is placed near the outer diameter end of the welded portion that connects to the terminal of the cell 2 on the busbar negative electrode side 10b without providing a protruding flat portion on the busbar negative electrode side 10b. This bead shape is a U-shaped weld bead with a bend and facing bead portions 41, which is the shape of the weld bead of the present invention. The bead width W of the facing portion 20 and the distance D9 between the bead centers satisfy the relationship D9 / W≧2.

[0067] 9B, the weld bead 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 weld 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 Examples 1 to 7. This welding structure creates ample space in the area between the bus bars 8 and 10 of the battery pack 1 and the wire bundle terminal of the voltage detection wire 11, while also making it possible to make the bus bar 10 smaller, thereby enabling a more compact or high-density battery pack 1 to be mounted.

[0069] As a next embodiment of the present invention, a further variation in the shape of the welded portion of the busbar is shown using Fig. 10. Fig. 10A is a top view of an arrangement in which the busbar's voltage detection terminal welding target portion 42 projects from the outer diameter end of the busbar on the adjacent cell side and is simultaneously bent upward, while the voltage detection terminal 43 is bent into a U-shape or a square shape, with the two parts temporarily fixed by fitting or inserting together with the voltage detection terminal 43 on the outside. Fig. 10B is a cross-sectional view of the fitting portion between the busbar's voltage detection terminal 43 and the welded portion 42.

[0070] 10C is a view of the fitting portion and the surface of the weld between the welding target portion 42 and the voltage detection terminal 43, as seen from the short side near the center of the busbar negative electrode side 10b. The weld bead shape of the present invention is a U-shaped weld bead with a bend, and in weld bead 45 having opposing bead portions, the bead width W of the opposing portions and the distance D10a between the bead centers satisfy the relationship D10a / W≧2.

[0071] 10D, the weld structure has a surface width 21 of weld bead 45 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 weld bead shape includes not only weld bead 45 but also the shapes of the materials described in Examples 1 to 7.

[0072] The laser specifications, welding conditions, working atmosphere, depth of the weld, bead direction, and spot shape are the same as those described in the first to seventh embodiments.

[0073] Furthermore, this shape also provides the strength effect of interlocking and fixing, so that, as shown in Fig. 10E, excellent strength reliability is achieved even without a bent weld bead shape having a facing portion, and excellent strength is achieved even when weld bead 46 is formed on the surface of the weld where bead width W and bead length D10b satisfy the relationship D10b / W ≥ 2, where D10b is the distance between bead centers, which is the bead shape of the present invention. Therefore, it is possible to achieve a welded structure with a smaller work target and excellent strength reliability. This weld bead 46 is not limited to being formed on the side of the bent portion as shown in Fig. 10E, but can also be formed on the top surface of the interlocking portion.

[0074] As a next embodiment of the present invention, an example of a change in the vertical positional relationship between the bus bar negative electrode side 10b and the voltage detection terminal 14 is shown using Fig. 11. Fig. 11 shows a construction in which the bus bar 10 is positioned so that the back surface 47, defined above as the top and bottom surfaces of the bus bar when attached to the battery pack 1, is on top during welding, the voltage detection terminal 14 is positioned above it, and the surface of the voltage detection terminal is welded by irradiating it with laser light 17. Fig. 11A is a side view of the bus bar from the short side, and Fig. 11B is a side view of the bus bar from the long side.

[0075] 11C is a top view of the laser-irradiated side. As shown in the figure, the weld bead shape is a U-shaped weld bead with a bend and facing bead portions 48, which is the shape of the weld bead of the present invention. The bead shape on the weld surface satisfies the relationship D11 / W≧2 between the bead width W of the facing portion 20 and the distance D11 between the bead centers. Also, as shown in FIG. 11D, 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 figure of 0.1 mm or more.

[0076] Here, the weld joint structure or weld bead shape includes not only shape 48 but also the joint structures and weld shapes for each material described in Examples 1 to 10. The laser specifications, welding conditions, welding atmosphere, weld depth, bead orientation, and spot shape are the same as those described in 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. When mounted as a battery pack 1, the voltage detection terminal 14 is welded to the underside of the busbar negative electrodes 10b and 16. Note that while Figure 11E shows the weld target portion 16 of the busbar negative electrode side 10b protruding outside the cell 2, this is a diagram for explaining Example 11. In an actual product, the weld target portion 16 and voltage detection terminal 14 face inside the cell 2, as shown in Figures 13 and 14.

[0077] The welding structure shown in this embodiment makes it possible to obtain a welding structure with excellent adhesion to the voltage detection terminal and excellent welding quality when the back surface of the bus bar 10 is flatter. Furthermore, as the assembly state of the parts for actual construction, not only can the bus bar 10 be welded to the voltage detection terminal in a standalone position, but also, even when the bus bar is mounted in a resin bus bar case that carries the bus bar and a bundle of voltage detection wires on top of the assembled battery, the height of the resin part on the back of the case can be shaped so as not to interfere with the jig, thereby achieving a construction method that minimizes the thermal impact on the resin part during laser welding.

[0078] 1... battery pack, 2... 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 bus bar, 10... bus bar, 11... voltage detection wire, 14... voltage detection terminal, 15... bus bar surface, 16... welding target area, 17... laser, 19, 20... weld bead, 21... surface width of weld bead, 22... width of weld bead on bus bar side, 23... melting depth, 25-32, 33... bus bar, 3 4...Welding target portion, 35...weld bead, 36...melting depth, 37...weld target portion, 38...voltage detection terminal, 39...weld bead, 40...voltage detection terminal, 41...weld bead, 42...weld target portion, 43...U-shaped voltage detection terminal, 44...surface of U-shaped voltage detection terminal, 45...weld bead, 46...weld bead, 47...back surface of bus bar, 48...weld bead, 49...U-shaped weld bead, 100...harness assembly, 101...wiring group, 102...socket, 110...branch harness.

Claims

1. A welded structure including a first metal member, a second metal member having an overlapping portion with the first metal member, and a weld portion formed in the overlapping portion, the welded portion has a fusion portion formed by penetrating the second metal member in a thickness direction and melting the first metal member to an inside thereof, The welded portion as viewed from the overlapping direction is a U-shape having a first linear portion and second linear portions extending from both ends of the first linear portion in a longitudinal direction, A metal welded structure, wherein a width D1 between two ends of the weld and a bead width W of the weld satisfy the relationship D1 / W≧2.

2. A welded structure including a first metal member, a second metal member having an overlapping portion with the first metal member, and a weld portion formed in the overlapping portion, the welded portion has a fusion portion formed by penetrating the second metal member in a thickness direction and melting the first metal member to an inside thereof, The welded portion viewed from the overlapping direction has two L-shapes arranged in approximately mirror symmetry, A metal welded structure, wherein a width D2 between two ends of the weld most distant from each other and a bead width W of the weld satisfy the relationship D2 / W≧2.

3. A welded structure including a first metal member, a second metal member having an overlapping portion with the first metal member, and a weld portion formed in the overlapping portion, the welded portion has a fusion portion formed by penetrating the second metal member in a thickness direction and melting the first metal member to an inside thereof, When viewed from the overlapping direction, the welded portion has a plurality of straight lines or arc shapes arranged substantially in parallel, A metal welded structure, wherein a width D3 between two closest lines of the weld and a bead width W of the weld satisfy the relationship D3 / W≧2.

4. A welded structure including a first metal member, a second metal member having an overlapping portion with the first metal member, and a weld portion formed in the overlapping portion, the welded portion has a fusion portion formed by penetrating the second metal member in a thickness direction and melting the first metal member to an inside thereof, The welded portion viewed from the overlapping direction has a circular or elliptical shape, A metal welded structure, wherein a minimum diameter D4 of the weld and a bead width W of the weld satisfy the relationship D4 / W≧2.

5. A welded structure including a first metal member, a second metal member having an overlapping portion with the first metal member, and a weld portion formed in the overlapping portion, the welded portion has a fusion portion formed by penetrating the second metal member in a thickness direction and melting the first metal member to an inside thereof, The welded portion has a rectangular shape when viewed from the overlapping direction, A metal welded structure, wherein a width D5 of a short side of the weld and a bead width W of the weld satisfy a relationship of D5 / W≧2.

6. A welded structure including a first metal member, a second metal member having an overlapping portion with the first metal member, and a weld portion formed in the overlapping portion, the welded portion has a fusion portion formed by penetrating the second metal member in a thickness direction and melting the first metal member to an inside thereof, The welded portion viewed from the overlapping direction has two or more point shapes, A metal welded structure, wherein a width D6 between the centers of two points of the weld and a bead width W of the weld satisfy the relationship D6 / W≧2.

7. 7. The metal welded structure according to claim 1, wherein the weld is formed by one of laser, arc, and electron beam welding.

8. 7. The welded metal structure of claim 1, wherein the molten metal is phosphorus bronze or bronze.

9. a first cell having a first terminal and a second cell having a second terminal are arranged in a first direction; a bus bar connecting the first terminal and the second terminal in the first direction, and a voltage detection terminal for measuring a voltage on the bus bar, 7. A battery pack characterized in that, when the bus bar 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 the metal welded structure described in claim 1.

10. a first cell having a first terminal and a second cell having a second terminal are arranged in a first direction; A method for manufacturing a battery pack including a bus bar connecting the first terminal and the second terminal in the first direction and a voltage detection terminal for measuring a voltage of the bus bar, A method for manufacturing a battery pack, characterized in that, when the bus bar 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 so that the first metal member and the second metal member become the metal welded structure described in any one of claims 1 to 6.