JP7633128B2 - Battery case and method for manufacturing the battery case - Google Patents

Description

The present invention relates to a battery case and a method for manufacturing a battery case.

In recent years, the development of electrically powered vehicles (including electric vehicles, hybrid vehicles, etc.) has progressed. The battery systems installed in such vehicles generally have a structure in which a large number of batteries (cells, battery cells) are housed in a battery case formed by a specified frame, etc.

The battery case that houses the battery needs to be strong enough to protect the battery from impacts such as collisions. In addition, from the perspective of improving fuel efficiency to combat global environmental issues such as exhaust gas, there is also a demand for lightweight battery cases.

For example, as shown in FIG. 31, a typical battery case 100 has a rectangular frame portion 101 composed of four frame members 102, a plate-shaped floor portion 103 disposed on the underside of the frame portion 101, and a number of cross members 104 whose both ends are joined to the frame portion 101 to increase strength. For the frame members 102 and cross members 104, aluminum extrusions are often used because they are lightweight and highly rigid.

Patent Document 1 describes an automobile body frame in which a side frame made of aluminum material and having a closed cross-sectional structure and a cross member made of aluminum material and having a closed cross-sectional structure are fastened together via a fastening member to prevent a decrease in the joining strength of the frame members. Specifically, the fastening member is made of aluminum material and is a π-shaped extruded profile having a flat base and a pair of support parts extending perpendicularly to the base. The base is fastened to the side of the side frame with a bolt, the pair of support parts clamp the end of the cross member, and the cross member and the support parts are welded together at a welded part.

JP 2007-269123 A

In this way, if the frame members 102 and cross members 104 that make up the frame-shaped portion 101 are all made of aluminum, it is possible to reduce weight, but the cost is higher than if materials such as steel or iron were used. On the other hand, if the frame members 102 and cross members 104 are all made of steel, the cost can be reduced, but the weight increases.

The present invention was made in consideration of the above-mentioned problems, and its purpose is to provide a lightweight, low-cost battery case and a method for manufacturing the battery case.

The above object of the present invention is achieved by the following configuration [1] relating to a battery case.
[1]
A rectangular frame portion,
At least one cross member extending toward a pair of parallel wall surfaces of the frame portion so as to divide the inside of the frame portion;
Equipped with
The frame-shaped portion is made of aluminum or an aluminum alloy,
The cross member is made of steel;
A battery case in which a steel plate is joined to the wall surface of the frame-shaped portion by welding,
The steel plate has a first hole facing the wall surface,
The steel plate and the wall surface are joined by welding at the first hole,
the first hole is filled with an aluminum or aluminum alloy weld metal;
A battery case characterized in that the steel plate and one longitudinal end of the cross member are joined by welding.

The above object of the present invention can be achieved by the following configuration [2] relating to a manufacturing method of a battery case.
[2]
A rectangular frame portion,
At least one cross member extending toward a pair of parallel wall surfaces of the frame portion so as to divide the inside of the frame portion;
Equipped with
The frame-shaped portion is made of aluminum or an aluminum alloy,
The cross member is made of steel;
A manufacturing method of a battery case in which a steel plate is joined to the wall surface of the frame-shaped portion by welding,
The steel plate has a first hole facing the wall surface,
The first hole is filled with a weld metal of aluminum or an aluminum alloy to join the steel plate and the wall surface;
A method for manufacturing a battery case, characterized in that the steel plate and one longitudinal end of the cross member are joined by welding.

The present invention provides a lightweight, low-cost battery case and a method for manufacturing the battery case.

FIG. 1 is a perspective view of a battery case according to a first embodiment. 2(a) to (e) are diagrams for explaining a manufacturing method of the battery case. FIG. 3 is a diagram for explaining a method of welding the steel plate and the first frame member. FIG. 4 is a cross-sectional view of a joint between a steel plate and a first frame member. FIG. 5 is a cross-sectional view of the joint between the cross member and the floor section. 6(a) to (d) are views for explaining a manufacturing method of a battery case according to a first modified example of the first embodiment. 7(a) to (e) are views for explaining a manufacturing method of a battery case according to the second embodiment. 8(a) to (e) are views for explaining a manufacturing method of a battery case according to a first modified example of the second embodiment. 9(a) to (e) are views for explaining a manufacturing method of a battery case according to a second modified example of the second embodiment. 10(a) to (g) are views for explaining a manufacturing method of a battery case according to a third modified example of the second embodiment. 11(a) to (g) are views for explaining a manufacturing method of a battery case according to a fourth modified example of the second embodiment. 12(a) to (e) are views for explaining a manufacturing method of a battery case according to a fifth modified example of the second embodiment. 13(a) to (e) are views for explaining a manufacturing method of a battery case according to the third embodiment. FIG. 14 is a cross-sectional view taken along line XIV-XIV of FIG. 15(a) to (d) are views for explaining a manufacturing method of a battery case according to a first modified example of the third embodiment. 16(a) to (e) are views for explaining a manufacturing method of a battery case according to a second modified example of the third embodiment. FIG. 17 is a cross-sectional view taken along line XVII-XVII of FIG. 18(a) to (e) are diagrams showing modified examples of the steel plate. 19(a) to (d) are views for explaining a manufacturing method of a battery case according to a third modified example of the third embodiment. 20(a) to (e) are views for explaining a manufacturing method of a battery case according to a fourth modified example of the third embodiment. 21(a) to (d) are views for explaining a manufacturing method of a battery case according to a fifth modified example of the third embodiment. 22(a) to (e) are views for explaining a manufacturing method of a battery case according to the fourth embodiment. FIG. 23 is a cross-sectional view taken along line XXIII-XXIII of FIG. 24(a) to (e) are views for explaining a manufacturing method of a battery case according to a first modified example of the fourth embodiment. 25(a) to (e) are views for explaining a manufacturing method of a battery case according to a second modified example of the fourth embodiment. 26(a) to (e) are views for explaining a manufacturing method of a battery case according to a fifth embodiment. 27(a) to (e) are views for explaining a manufacturing method of a battery case according to a modified example of the fifth embodiment. FIG. 28 is a cross-sectional view taken along line XXVIII-XXVIII of FIG. FIG. 29A is a perspective view showing an example of a method for manufacturing a steel plate. FIG. 29B is a perspective view showing an example of a method for manufacturing a steel plate. FIG. 30A is a perspective view showing an example of a steel plate. FIG. 30B is a perspective view showing an example of a steel plate. FIG. 30C is a perspective view showing an example of a steel plate. FIG. 30D is a perspective view showing an example of a steel plate. FIG. 30E is a perspective view showing an example of a steel plate. FIG. 30F is a perspective view showing an example of a steel plate. FIG. 30G is a perspective view showing an example of a steel plate. FIG. 31 is a perspective view of a conventional battery case.

Each embodiment of the battery case and the method for manufacturing the battery case according to the present invention will be described in detail below with reference to the drawings.

First Embodiment
Fig. 1 is a perspective view of a battery case 10 according to the first embodiment. As shown in Fig. 1, the battery case 10 of the present embodiment includes a rectangular frame portion 11 formed of a plurality of first and second frame members 12, 13, at least one cross member 20 (two in this embodiment) disposed inside the frame portion 11, and a floor portion 40 connected to the frame portion 11 so as to form the bottom surface of the battery case 10.

The first and second frame members 12, 13 constituting the frame portion 11 and the floor portion 40 are all made of aluminum or an aluminum alloy (hereinafter also referred to as aluminum material). The cross member 20 is made of steel. In this way, by making the frame portion 11 and the floor portion 40 of the components of the battery case 10 out of aluminum material and the cross member 20 out of steel, it is possible to achieve both weight reduction and cost reduction.

The frame portion 11 is formed in a rectangular shape in a plan view by a pair of first frame members 12 arranged parallel to each other and a pair of second frame members 13 whose both ends are joined to both ends of the pair of first frame members 12.

2(a) to (e) are diagrams for explaining a manufacturing method of the battery case 10. Specifically, as shown in FIG. 2(b), with the end face of the second frame member 13 butted against the side face 12a of the end of the first frame member 12, the corner formed by the edge of the end face of the second frame member 13 and the side face 12a of the first frame member 12 is line-welded by arc welding, thereby joining the first frame member 12 and the second frame member 13. Therefore, a pair of parallel wall surfaces of the frame-shaped portion 11 is formed by a pair of side faces 12a of a pair of opposing first frame members 12.

The first frame member 12 and the second frame member 13 are welded together by a MIG welding device 50 (hereinafter also referred to as "aluminum MIG welding device") that uses aluminum or an aluminum alloy as a consumable electrode (welding wire). Therefore, the first frame member 12 and the second frame member 13 are joined together by a weld metal WA (hereinafter also referred to as "aluminum weld metal") of aluminum or an aluminum alloy.

In this embodiment, the first frame member 12 and the second frame member 13 are disposed on a floor-like portion 40 made of a plate material. As shown in FIG. 2(b), the corners formed by the lower surfaces of the first frame member 12 and the second frame member 13 and the upper surface of the floor-like portion 40 are also line-welded by the aluminum MIG welding device 50. Therefore, aluminum weld metal WA is formed at these welded locations as well.

Flanges (not shown) extending along the floor portion 40 may be formed on the undersides of the first frame member 12 and the second frame member 13, and the flanges of the first and second frame members 12, 13 and the floor portion 40 may be line-welded by an aluminum MIG welding device 50.

Each cross member 20 is a member for improving the strength of the battery case 10, and extends toward a pair of parallel wall surfaces (the opposing side surfaces 12a of the pair of first frame members 12) of the frame portion 11 so as to partition the interior of the frame portion 11, which is divided by the four first and second frame members 12 and 13.

As shown in FIG. 2(d), the longitudinal length of the cross member 20 (left-right direction in the figure) is slightly shorter than the longitudinal length of the second frame member 13, and steel plates 30 are arranged between both longitudinal ends of the cross member 20 and the side surfaces 12a of the pair of first frame members 12.

The steel plate 30 is a plate-like member made of steel that extends along the side surface 12a of the first frame member 12 and is joined to the side surface 12a by welding. A plurality of first holes 31 are formed in the steel plate 30 at positions that avoid the location where the cross member 20 is joined. In this embodiment, the plurality of first holes 31 are formed on both sides in the width direction (upper right and lower left direction in the figure) perpendicular to the thickness direction (left and right direction in the figure) and height direction (up and down direction in the figure) of the steel plate 30, with six first holes 31 formed on each side. Then, as described later, the cross member 20 is joined between the first holes 31 formed on both sides in the width direction of the steel plate 30, i.e., to the middle part in the width direction of the steel plate 30. The first holes 31 are through holes that penetrate the steel plate 30 in the thickness direction and face the side surface 12a of the first frame member 12. The first holes 31 are holes for joining the steel plate 30 to the side surface 12a by welding.

Since the steel plate 30 is made of steel, while the first frame member 12 is made of aluminum, when attempting to join the two dissimilar materials by normal arc welding, an intermetallic compound formed at the joining interface between the steel and aluminum becomes a problem. Intermetallic compounds (such as _Al3Fe and _Al5Fe2 ) between Fe (steel) and Al ( _aluminum ) are brittle, and so there is a possibility that cracks will occur in the welded portion.

In addition, because the battery case 10 is large in size, it is physically difficult to insert the C-clamps required for many dissimilar metal joining methods, and a dissimilar metal joining method that does not use C-clamps is required.

In addition, because the battery case is extremely sensitive to water infiltration, joining methods that require the provision of through holes in the frame portion 11 or floor portion 40 for the insertion of bolts, screws, or rivets cannot be used.

3 is a diagram for explaining a method of welding a steel plate 30 and a first frame member 12. In this embodiment, as shown in FIG. 3, a steel plate 30 having a first hole 31 is placed on the side surface 12a of the first frame member 12, and spot welding is performed by an aluminum MIG welding device 50 to obtain penetration through the first hole 31 of the steel plate 30. Hereinafter, a method of spot welding a steel member and an aluminum member through a through hole provided in the steel member using an aluminum MIG welding device 50 is called "dissimilar material MIG spot welding". Note that a known inert gas such as argon or helium is used as the shielding gas G. Since welding is performed with a low current that does not melt the steel plate 30 and penetration is obtained between the aluminum weld metal WA and the first frame member 12, the above-mentioned problems due to intermetallic compounds do not occur. In addition, unlike the conventional dissimilar metal joining method, a C-type clamp is not required, and there is no need to provide a through hole in the first frame member 12, and water intrusion into the battery case 10 can be prevented.

Figure 4 is a cross-sectional view of the joint between the steel plate 30 and the first frame member 12. As shown in Figure 4, after welding the steel plate 30 and the first frame member 12, the first hole 31 is filled with aluminum weld metal WA. The aluminum weld metal WA has a rivet shape with an axial portion WA1 that extends in the thickness direction of the steel plate 30 and reaches the first frame member 12, a head portion WA2 that bulges outward from the tip end of the axial portion WA1 that protrudes outside the steel plate 30, and a flange portion WA3 that bulges outward from the base end of the axial portion WA1 that protrudes inside the first frame member 12. The head portion WA1 and the flange portion WA3 sandwich and fix the steel plate 30 and the first frame member 12.

In this way, the steel plate 30 and the side surface 12a of the first frame member 12 are joined by dissimilar material MIG spot welding at the multiple first holes 31. Note that the number and arrangement of the first holes 31 are not particularly limited.

2(c)-(d), the cross member 20 has an inverted U-shaped cross section with an opening at the lower end in the height direction (up-down direction in the figure), and also has openings at both ends in the longitudinal direction (left-right direction in the figure). A pair of flanges 21, 21 extending along the floor portion 40 are provided at the lower end in the height direction of the cross member 20. The pair of flanges 21, 21 extend in the width direction (upper right-lower left direction in the figure) perpendicular to the height direction and longitudinal direction over the entire longitudinal length of the cross member 20. Thus, the cross member 20 has an upper surface 26, a pair of side surfaces 24 extending downward from both ends in the width direction of the upper surface 26, and flanges 21 extending vertically from the lower end of each side surface 24.

The flange portion 21 has a plurality of third holes 22 that penetrate the flange portion 21 in the vertical direction and face the floor portion 40. In this embodiment, the third holes 22 are arranged at equal intervals in the longitudinal direction of the cross member 20, but the number and arrangement of the third holes 22 are not particularly limited.

Since the cross member 20 is made of steel and the floor portion 40 is made of aluminum, dissimilar material MIG spot welding is performed using an aluminum MIG welding device 50, similar to the welding of the steel plate 30 and the first frame member 12 described above. FIG. 5 is a cross-sectional view of the joint between the cross member 20 and the floor portion 40. As shown in FIG. 5, after welding the flange portion 21 and the floor portion 40, the third hole 22 is filled with aluminum weld metal WA. The aluminum weld metal WA has a rivet shape having a shaft portion WA1 that extends in the thickness direction of the flange portion 21 and reaches the floor portion 40, a head portion WA2 that bulges outward from the tip portion of the shaft portion WA1 that protrudes outside the flange portion 21, and a flange portion WA3 that bulges outward from the base portion of the shaft portion WA1 that protrudes outside the floor portion 40. The flange portion 21 and the floor portion 40 are sandwiched and fixed by the head portion WA1 and the flange portion WA3.

In this way, the cross member 20 and the floor portion 40 are joined by dissimilar material MIG spot welding at the multiple third holes 22.

Both longitudinal ends of the cross member 20 and the steel plate 30 joined to the side surfaces 12a of the pair of first frame members 12 are joined by welding. Specifically, as shown in FIG. 2(e), one longitudinal end of the cross member 20 is butted against the steel plate 30, and the corner formed by the edge of the longitudinal end of the cross member 20 and the steel plate 30 is line-welded by arc welding. The other longitudinal end of the cross member 20 is similarly joined to the steel plate 30 by welding.

The cross member 20 and the steel plate 30 are welded by a MAG welding device 60 (hereinafter also referred to as a "steel MAG welding device") using steel as a consumable electrode (welding wire). Therefore, the cross member 20 and the steel plate 30 are joined by the steel weld metal WS (hereinafter also referred to as the "steel weld metal").

Each compartment of the battery case 10, which is separated by the frame portion 11 and multiple cross members 20, houses a battery (not shown).

In this embodiment, the first and second frame members 12, 13 are made of hollow extrusions of aluminum material with a thickness of about 2 to 5 mm. The aluminum alloys used are JIS or AA 5000, 6000, 7000, etc., which have excellent strength and can be made thinner. The hollow extrusions of aluminum alloys are manufactured by a normal material manufacturing process that includes a suitable combination of casting such as DC casting or continuous casting, homogenization heat treatment, hot extrusion, solution treatment and quenching, and, if necessary, tempering treatment such as artificial aging. By manufacturing the first and second frame members 12, 13 by extrusion molding of aluminum material, it is possible to reduce the weight.

The cross member 20 can be manufactured by bending a plate of ordinary carbon steel or high-strength steel into an Ω shape, or by crushing a circular steel tube into a mouth shape. For example, a rib plate can be welded into the inside of a Π-shaped cross section, or it can be bent into an S or B shape and welded to form a "日" shape. Steel plates can also be surface-treated with various plating methods such as zinc plating or electrochemical painting for corrosion prevention purposes.

Next, we will explain the manufacturing method for the battery case of this embodiment.

In the manufacturing method of the battery case of this embodiment, first, as shown in Figs. 2(a)-(b), the aluminum MIG welding device 50 welds the steel plate 30 to the side surface 12a of the first frame member 12 through the first hole 31. Next, the aluminum MIG welding device 50, which is a common welding device, welds the first and second frame members 12, 13 together to form the frame-shaped portion 11. Furthermore, the aluminum MIG welding device 50, which is a common welding device, welds the frame-shaped portion 11 to the floor-shaped portion 40. Note that the order of welding the steel plate 30 to the side surface 12a of the first frame member 12, welding the first frame member 12 to the second frame member 13, and welding the frame-shaped portion 11 to the floor-shaped portion 40 by the aluminum MIG welding device 50 is not particularly limited.

Next, as shown in Figures 2(c) to (d), the cross member 20 is positioned against the steel plate 30 on the floor portion 40, and the flange portion 21 of the cross member 20 is welded to the floor portion 40 by an aluminum MIG welding device 50.

Furthermore, as shown in FIG. 2(e), the longitudinal ends of the cross member 20 are welded to the steel plate 30 using a steel MAG welding device 60.

Through these steps, the battery case 10 is manufactured. The order of the welding steps may be changed as appropriate, but the welding steps performed using the aluminum MIG welding device 50, which is a common welding device, may be performed consecutively to reduce the work time.

As described above, according to the battery case 10 of this embodiment, the frame portion 11 is made of aluminum or aluminum alloy, the cross member 20 is made of steel, the steel plate 30 is joined by welding to the side surface 12a (wall surface of the frame portion 11) of the first frame member 12, and the steel plate 30 is joined by welding to one end of the cross member 20 in the longitudinal direction. Therefore, among the components of the battery case 10, the frame portion 11 is made of aluminum material, while the cross member 20 is made of steel, so that it is possible to achieve both weight reduction and cost reduction. In addition, since the steel plate 30 is joined by welding to the wall surface of the frame portion 11, and then the cross member 20 is joined to the steel plate 30 by welding, the cross member 20 can be firmly fixed to the frame portion 11 via the steel plate 30.

The steel plate 30 is formed with a first hole 31 facing the side surface 12a of the first frame member 12, and the steel plate 30 and the side surface 12a are joined by welding at the first hole 31. Therefore, the steel plate 30, which is made of steel, and the first frame member 12, which is made of aluminum, can be reliably joined by welding via the first hole 31. Furthermore, unlike conventional dissimilar metal joining methods, no C-clamps are required, and there is no need to provide through holes in the frame portion 11, which also prevents water from entering the battery case 10.

In addition, since the first hole 31 is filled with aluminum weld metal WA, the steel plate 30, which is made of steel, and the first frame member 12, which is made of aluminum material, can be reliably joined by welding through the first hole 31.

The battery case 10 further has a floor portion 40 that is connected to the frame portion 11 and forms a floor surface. The floor portion 40 is made of aluminum or an aluminum alloy, and the cross member 20 and the floor portion 40 are joined by welding. Therefore, of the components of the battery case 10, the frame portion 11 and the floor portion 40 are made of aluminum material, while the cross member 20 is made of steel, making it possible to achieve both weight reduction and cost reduction. Furthermore, the cross member 20 and the floor portion 40 are firmly joined by welding.

The cross member 20 has a flange portion 21 that extends along the floor portion 40, and a third hole 22 that faces the floor portion 40 is formed in the flange portion 21, and the flange portion 21 and the floor portion 40 are joined by welding at the third hole 22. Therefore, the cross member 20, which is made of steel, and the floor portion 40, which is made of aluminum, can be reliably joined by welding through the third hole 22. Unlike conventional dissimilar metal joining methods, there is no need for a C-clamp, and there is no need to provide a through hole in the floor portion 40, and water intrusion into the battery case 10 can be prevented.

In addition, since the third hole 22 is filled with aluminum weld metal WA, the cross member 20, which is made of steel, and the floor portion 40, which is made of aluminum material, can be reliably joined by welding through the third hole 22.

(First Modification of the First Embodiment)
6(a) to (d) are diagrams for explaining a manufacturing method of the battery case 10 according to a first modified example of the first embodiment. In the manufacturing method of the battery case 10 according to the first embodiment shown in FIGS. 2(a) to (e), the steel plate 30 is joined to the side surface 12a of the first frame member 12 by welding, and then the cross member 20 is joined to the steel plate 30 by welding. However, as in the first modified example shown in FIGS. 6(a) to (d), the cross member 20 and the steel plate 30 may be joined to be integrated in advance by welding, and then the steel plate 30 may be joined to the side surface 12a of the first frame member 12 by welding. Hereinafter, the manufacturing method of the battery case 10 according to the first modified example will be specifically described.

As shown in FIG. 6(a), the frame portion 11 is formed by welding the first and second frame members 12, 13 together using an aluminum MIG welding device 50. Furthermore, the frame portion 11 is welded to the floor portion 40 using the aluminum MIG welding device 50, which is a common welding device.

Next, as shown in FIG. 6(b), the longitudinal end of the cross member 20 is welded to the steel plate 30 by a steel MAG welding device 60. This causes the cross member 20 and the steel plate 30 to become integrated.

The order of the welding process shown in FIG. 6(a) and the welding process shown in FIG. 6(b) is not particularly limited.

Next, as shown in Figures 6(c) to (d), the steel plate 30 joined and integrated with the cross member 20 is butted against the side surface 12a of the first frame member 12 on the floor portion 40 and positioned thereon, and the flange portion 21 of the cross member 20 is welded to the floor portion 40 by an aluminum MIG welding device 50. The common aluminum MIG welding device 50 also welds the steel plate 30 to the side surface 12a of the first frame member 12 through the first hole 31.

The battery case 10 is manufactured through these steps. Note that the order of each welding step may be changed as appropriate.

Second Embodiment
7(a) to (e) are diagrams for explaining a manufacturing method of a battery case 10 according to the second embodiment. As shown in Fig. 7(a), a first rib 14 and a second rib 15 are provided on the upper and lower parts in the height direction of the side surface 12a of the first frame member 12. The first rib 14 and the second rib 15 are formed on the side surface 12a of the first frame member 12 so as to extend in the longitudinal direction of the first frame member 12 (from the upper right to the lower left in the figure).

The first rib 14 has a first base 14a that extends vertically from the side surface 12a toward the cross member 20, and a first protruding portion 14b that protrudes downward from the tip of the first base 14a. A first groove portion 16 with an inverted U-shaped cross section is defined between the side surface 12a, the first base 14a, and the first protruding portion 14b.

The second rib 15 has a second base 15a that extends vertically from the side surface 12a toward the cross member 20, and a second protruding portion 15b that protrudes upward from the tip of the second base 15a. A second groove portion 17 with a U-shaped cross section is defined between the side surface 12a, the second base 15a, and the second protruding portion 15b.

In the height direction, the first protrusion 14b and the second protrusion 15b face each other with a gap S therebetween, and the steel plate 30 and the cross member 20 can be joined together through the gap S.

In this embodiment, as shown in FIG. 7(a), the steel plate 30 is inserted into the first groove portion 16 and the second groove portion 17 in the longitudinal direction of the first frame member 12 (upper right to lower left in the figure). When the steel plate 30 is inserted into the first groove portion 16 and the second groove portion 17, the multiple first holes 31 of the steel plate 30 are exposed to the inside of the frame-shaped portion 11 through the gap S. Then, as shown in FIG. 7(b), the aluminum MIG welding device 50 welds the steel plate 30 to the side surface 12a of the first frame member 12 through the first holes 31.

The first rib 14 and the second rib 15 are formed on the side surface 12a excluding the ends in the longitudinal direction of the first frame member 12 (upper right, lower left in the figure). As a result, steps 12b, 12c are formed between the side surface 12a and the first rib 14 and the second rib 15. Such steps 12b, 12c may be formed by providing the first rib 14 and the second rib 15 over the entire length of the side surface 12a, and then cutting out the ends of the first rib 14 and the second rib 15.

Then, as shown in FIG. 7(b), with the end face of the second frame member 13 butting against the side face 12a and steps 12b, 12c of the first frame member 12, the corner formed by the edge of the end face of the second frame member 13 and the side face 12a of the first frame member 12 is line-welded by an aluminum MIG welding device 50, thereby joining the first frame member 12 and the second frame member 13.

The corners formed by the second rib 15 of the first frame member 12 and the underside of the second frame member 13 and the upper surface of the floor portion 40 are also line welded by the aluminum MIG welding device 50.

As shown in FIG. 7(c), a convex portion 23 is formed at the longitudinal end of the cross member 20, protruding toward the steel plate 30 in the gap S (see FIG. 7(a)) between the first protruding portion 14b of the first rib 14 and the second protruding portion 15b of the second rib 15. Then, as shown in FIGS. 7(c) to (d), with the cross member 20 placed on the floor portion 40, the convex portion 23 is butted against the steel plate 30 so as to fill the gap S. Here, it is preferable to set the height dimension of the convex portion 23 of the cross member 20 larger than the gap S, and to fit and fix the convex portion 23 to the first and second protruding portions 14b, 15b of the first and second ribs 14, 15. This improves the fixing force between the cross member 20 and the first frame member 12.

Then, as shown in FIG. 7(d), the cross member 20 and the floor portion 40 are joined by dissimilar material MIG spot welding at the multiple third holes 22 using an aluminum MIG welding device 50.

Furthermore, as shown in FIG. 7(e), the corner formed by the edge of the protrusion 23 of the cross member 20 and the steel plate 30 is line welded by a steel MAG welding device 60.

The battery case 10 is manufactured through these steps. Note that the order of each welding step may be changed as appropriate.

According to the battery case 10 of this embodiment, the steel plate 30 is inserted and positioned in the first groove portion 16 and the second groove portion 17. Therefore, it is possible to prevent the steel plate 30 welded to the side surface 12a of the first frame member 12 from peeling off.

In addition, a convex portion 23 that protrudes toward the steel plate 30 is formed between the first protruding portion 14b and the second protruding portion 15b at one longitudinal end of the cross member 20, and the convex portion 23 and the steel plate 30 are joined by welding. Therefore, even if the first rib 14 and the second rib 15 are provided, the cross member 20 and the steel plate 30 can be joined by welding via the convex portion 23.

(First Modification of the Second Embodiment)
8(a) to 8(e) are diagrams for explaining a manufacturing method of the battery case 10 according to a first modified example of the second embodiment. In the manufacturing method of the battery case 10 according to the second embodiment shown in Figs. 7(a) to 7(e), the steel plate 30 is joined to the side surface 12a of the first frame member 12 by welding, and then the cross member 20 is joined to the steel plate 30 by welding. However, as in the first modified example shown in Figs. 7(a) to 7(e), the cross member 20 and the steel plate 30 may be joined to be integrated in advance by welding, and then the steel plate 30 may be joined to the side surface 12a of the first frame member 12 by welding. Hereinafter, the manufacturing method of the battery case 10 according to the first modified example will be specifically described.

As shown in FIG. 8(a), the protruding portion 23 of the cross member 20 is welded to the steel plate 30 by a steel MAG welding device 60. This integrates the cross member 20 and the steel plate 30. Then, as shown in FIG. 8(b), the steel plate 30 joined and integrated with the cross member 20 is inserted into the first groove portion 16 and the second groove portion 17.

8(c)-(d), with the end face of the second frame member 13 butted against the side face 12a and steps 12b, 12c of the first frame member 12, the corner formed by the edge of the end face of the second frame member 13 and the side face 12a of the first frame member 12 is line-welded by an aluminum MIG welding device 50. In addition, the corner formed by the second rib 15 of the first frame member 12 and the lower face of the second frame member 13 and the upper face of the floor-like portion 40 is also line-welded by the aluminum MIG welding device 50.

Next, as shown in FIG. 8(e), the flange portion 21 of the cross member 20 is welded to the floor portion 40 through the third hole 22 by an aluminum MIG welding device 50. The steel plate 30 is also welded to the side surface 12a of the first frame member 12 through the first hole 31 by a common aluminum MIG welding device 50.

The battery case 10 is manufactured through these steps. Note that the order of each welding step may be changed as appropriate.

(Second Modification of Second Embodiment)
9(a) to 9(e) are diagrams for explaining a manufacturing method of the battery case 10 according to the second modified example of the second embodiment. In the battery case 10 according to the second modified example shown in FIG. 7(a) to 7(e), a convex portion 23 protruding toward the steel plate 30 was formed at the longitudinal end of the cross member 20 between the first protruding portion 14b of the first rib 14 and the second protruding portion 15b of the second rib 15. In this modified example, the convex portion 23 is not formed on the cross member 20, and a protrusion 32 protruding toward the cross member 20 is formed on the steel plate 30 between the first protruding portion 14b of the first rib 14 and the second protruding portion 15b of the second rib 15. Hereinafter, the manufacturing method of the battery case 10 according to the second modified example will be specifically described.

As shown in FIG. 9(a), the protrusions 32 are formed between the first holes 31 (six on each side of the width of the steel plate 30), i.e., in the middle of the width of the steel plate 30. The height of the protrusions 32 is approximately equal to or slightly smaller than the dimension of the gap S between the first protrusion 14b and the second protrusion 15b. The steel plate 30 is inserted into the first groove 16 and the second groove 17 in the longitudinal direction of the first frame member 12 (upper right to lower left in the figure).

When the steel plate 30 is inserted into the first groove portion 16 and the second groove portion 17, the first holes 31 of the steel plate 30 are exposed to the inside of the frame portion 11 through the gap S. In addition, the contact surface of the protrusion portion 32 of the steel plate 30 that contacts the cross member 20 is flush with the contact surfaces of the first protrusion portion 14b and the second protrusion portion 15b that contact the cross member 20.

Then, as shown in FIG. 9(b), the aluminum MIG welding device 50 dissimilarly MIG spot welds the steel plate 30 to the side surface 12a of the first frame member 12 through the first hole 31.

In addition, with the end face of the second frame member 13 butted against the side face 12a and steps 12b, 12c of the first frame member 12, the corner formed by the edge of the end face of the second frame member 13 and the side face 12a of the first frame member 12 is line welded by the aluminum MIG welding device 50.

The corners formed by the second rib 15 of the first frame member 12 and the underside of the second frame member 13 and the upper surface of the floor portion 40 are also line welded by the aluminum MIG welding device 50.

Next, as shown in Figures 9(c)-(d), with the cross member 20 placed on the floor portion 40, both end faces of the cross member 20 are butted against the abutment surfaces of the protrusions 32 of the steel plate 30 and the abutment surfaces of the first protrusion 14b and the second protrusion 15b. Then, the cross member 20 and the floor portion 40 are joined by dissimilar material MIG spot welding at the multiple third holes 22 using an aluminum MIG welding device 50.

Furthermore, as shown in FIG. 9(e), the corner formed by the longitudinal end of the cross member 20 and the protrusion 32 of the steel plate 30 is line welded by a steel MAG welding device 60.

The battery case 10 is manufactured through these steps. Note that the order of each welding step may be changed as appropriate.

According to the battery case 10 of this embodiment, a protrusion 32 that protrudes toward the cross member 20 is formed on the steel plate 30 between the first protrusion 14b and the second protrusion 15b, and the protrusion 32 is joined to the longitudinal direction and one end of the cross member 20 by welding. Therefore, even if the first rib 14 and the second rib 15 are provided, the cross member 20 and the steel plate 30 can be joined by welding via the protrusion 32.

In this modified example, as in the first modified example (see Figures 8(a) to (e)), the cross member 20 and the steel plate 30 may be joined together by welding in advance, and then the steel plate 30 may be inserted into the first and second groove portions 16, 17 and joined to the side surface 12a of the first frame member 12 by welding.

(Third Modification of the Second Embodiment)
10(a) to (g) are diagrams for explaining a manufacturing method of a battery case 10 according to a third modified example of the second embodiment. The manufacturing method of this modified example differs from the second embodiment (see FIGS. 7(a) to (e)) in that the steel plate 30 is fixed to the first groove portion 16 and the second groove portion 17 by the first protruding portion 14b and the second protruding portion 15b that have been plastically deformed toward the steel plate 30, as shown in FIGS.

In this modified example, as shown in FIG. 10(a), first, the steel plate 30 is inserted into the first groove 16 and the second groove 17. FIGS. 10(b)-(c) show cross-sectional views of the first frame member 12 and the steel plate 30 before and after the first protrusion 14b and the second protrusion 15b are plastically deformed. As shown in FIG. 10(b), the thickness of the steel plate 30 is set slightly shorter than the width of the first groove 16 and the second groove (the width between the side surface 12a and the first protrusion 14b and the second protrusion 15b), ensuring smooth insertion of the steel plate 30. Therefore, a gap H is generated between the steel plate 30 and the side surface 12a or the first protrusion 14b and the second protrusion 15b.

To eliminate the gap H, as shown in FIG. 10(c), a plastic deformation device such as a hammer 70 is used to plastically deform the first protruding portion 14b and the second protruding portion 15b toward the steel plate 30, thereby bringing the first protruding portion 14b and the second protruding portion 15b into contact with the steel plate 30. As a result, the steel plate 30 is sandwiched between the side surface 12a of the first frame member 12 and the first protruding portion 14b and the second protruding portion 15b, and is fixed to the first groove portion 16 and the second groove portion 17.

The subsequent steps shown in Figures 10(d) to (g) are similar to those described with reference to Figures 7(b) to (e), and therefore will not be described here.

As described above, according to the battery case 10 of this embodiment, the steel plate 30 is fixed to the first groove portion 16 and the second groove portion 17 by the first protrusion portion 14b and the second protrusion portion 15b, which are plastically deformed toward the steel plate 30, so that the steel plate 30 can be prevented from moving in the first groove portion 16 and the second groove portion 17 and the steel plate 30 can be securely fixed to the first frame member 12.
As in a first modified example (see FIGS. 8(a) to 8(e)), the cross member 20 and the steel plate 30 may be joined by welding to be integrated in advance, and then the steel plate 30 may be joined by welding to the side surface 12a of the first frame member 12. Also, as in a second modified example (see FIGS. 9(a) to 9(e)), the cross member 20 may not be formed with the convex portion 23, and the steel plate 30 may be formed with a protrusion 32 that protrudes toward the cross member 20 between the first protruding portion 14b of the first rib 14 and the second protruding portion 15b of the second rib 15.

(Fourth Modification of the Second Embodiment)
11(a) to (g) are views for explaining a manufacturing method of a battery case 10 according to a sixth modified example of the second embodiment. The manufacturing method of this modified example differs from the second embodiment (see FIGS. 7(a) to (e)) in that second holes 18 facing the steel plate 30 are formed in the first protruding portion 14b and the second protruding portion 15b, and the steel plate 30 is fixed to the first groove portion 16 and the second groove portion 17 by fastening members fastened toward the steel plate 30 through the second holes 18.

As shown in FIG. 11(a), the first protruding portion 14b and the second protruding portion 15b each have eight second holes 18, two of which are spaced apart in the longitudinal direction of the first frame member 12 (upper right, lower left, and upper right in the figure). The number and positions of the second holes 18 are not particularly limited, but the second holes 18 are formed in positions that do not overlap with the cross member 20 when the cross member 20 is joined to the steel plate 30 (see FIG. 11(g)). In the illustrated example, the second holes 18 are positioned to be aligned in the vertical direction with the first holes 31 of the steel plate 30. The second holes 18 are also screw holes with female threads for screwing in the bolts 71.

In this modified example, as shown in FIG. 11(a), first, the steel plate 30 is inserted into the first groove 16 and the second groove 17. FIGS. 11(b)-(c) show cross-sectional views of the first frame member 12 and the steel plate 30 before and after the bolt 71 as a fastening member is fastened to the steel plate 30 through the second hole 18. As shown in FIG. 11(b), the thickness of the steel plate 30 is set slightly shorter than the width of the first groove 16 and the second groove (the width between the side surface 12a and the first protruding portion 14b and the second protruding portion 15b), ensuring smooth insertion of the steel plate 30. Therefore, a gap H is generated between the steel plate 30 and the side surface 12a or the first protruding portion 14b and the second protruding portion 15b.

To ensure that the steel plate 30 is positioned even if the gap H occurs, as shown in FIG. 11(c), the bolt 71 is inserted into the second hole 18 and tightened toward the steel plate 30. As a result, the steel plate 30 is sandwiched between the side surface 12a of the first frame member 12 and the bolt 71, and is fixed to the first groove portion 16 and the second groove portion 17.

The subsequent steps shown in Figures 11(d) to (g) are similar to those described with reference to Figures 7(b) to (e), and therefore will not be described here.

As described above, according to the battery case 10 of this embodiment, the second holes 18 facing the steel plate 30 are formed in the first protrusion 14b and the second protrusion 15b, and the steel plate 30 is fixed to the first groove portion 16 and the second groove portion 17 by fastening members fastened toward the steel plate 30 through the second holes 18. This prevents the steel plate 30 from moving in the first groove portion 16 and the second groove portion 17, and allows the steel plate 30 to be securely fixed to the first frame member 12.
As in a first modified example (see FIGS. 8(a) to 8(e)), the cross member 20 and the steel plate 30 may be joined by welding to be integrated in advance, and then the steel plate 30 may be joined by welding to the side surface 12a of the first frame member 12. Also, as in a second modified example (see FIGS. 9(a) to 9(e)), the cross member 20 may not be formed with the convex portion 23, and the steel plate 30 may be formed with a protrusion 32 that protrudes toward the cross member 20 between the first protruding portion 14b of the first rib 14 and the second protruding portion 15b of the second rib 15.

(Fifth Modification of the Second Embodiment)
12(a) to 12(e) are views for explaining a manufacturing method of the battery case 10 according to a ninth modified example of the second embodiment. The manufacturing method of this modified example differs from the second embodiment (see FIGS. 7(a) to 7(e)) in that second holes 18 facing the steel plate 30 are formed in the first protruding portion 14b and the second protruding portion 15b, and the first protruding portion 14b and the second protruding portion 15b are joined to the steel plate 30 by welding at the second holes 18, thereby fixing the steel plate 30 to the first groove portion 16 and the second groove portion 17.

As shown in FIG. 12(a), the first protruding portion 14b and the second protruding portion 15b each have eight second holes 18, two of which are spaced apart in the longitudinal direction of the first frame member 12 (upper right, lower left, and upper right directions in the figure). The number and positions of the second holes 18 are not particularly limited, but the second holes 18 are formed in positions that do not overlap with the cross member 20 when the cross member 20 is joined to the steel plate 30 (see FIG. 12(e)). In the illustrated example, the second holes 18 are positioned to be aligned vertically with the first holes 31 of the steel plate 30.

In this modified example, as shown in FIG. 12(a), first, the steel plate 30 is inserted into the first groove portion 16 and the second groove portion 17. Then, as shown in FIG. 12(b), the steel plate 30 is welded to the side surface 12a of the first frame member 12 through the first hole 31 by the aluminum MIG welding device 50.

With the end face of the second frame member 13 butted against the side face 12a and steps 12b, 12c of the first frame member 12, the corner formed by the edge of the end face of the second frame member 13 and the side face 12a of the first frame member 12 is line-welded by an aluminum MIG welding device 50, thereby joining the first frame member 12 and the second frame member 13.

The corners formed by the second rib 15 of the first frame member 12 and the underside of the second frame member 13 and the upper surface of the floor portion 40 are also line welded by the aluminum MIG welding device 50.

Next, as shown in Figures 12(c)-(d), with the cross member 20 placed on the floor portion 40, the protrusion 23 is butted against the steel plate 30 so as to fill the gap S between the first protrusion 14b and the second protrusion 15b. Then, the flange portion 21 of the cross member 20 and the floor portion 40 are joined by dissimilar material MIG spot welding at the multiple third holes 22 using an aluminum MIG welding device 50.

Then, as shown in FIG. 12(e), the corner formed by the edge of the protrusion 23 of the cross member 20 and the steel plate 30 is line welded by the steel MAG welding device 60.

Furthermore, the first protruding portion 14b and the second protruding portion 15b of the first frame member 12 are joined to the steel plate 30 by welding at the second hole 18. However, since the first frame member 12 is made of aluminum material and the steel plate 30 is made of steel, it is not preferable to apply normal arc welding. Therefore, in this modified example, arc spot welding for joining dissimilar materials, which will be described below, is applied.

First, the joining auxiliary member 80 is inserted into the second hole 18 provided in the first protruding portion 14b and the second protruding portion 15b. The joining auxiliary member 80 has a stepped outer shape with a hollow shaft-shaped insertion portion 81 inserted into the second hole 18 and a flange-shaped non-insertion portion 83 arranged on the surface of the cross member 20 side of the first protruding portion 14b and the second protruding portion 15b. In addition, a hollow portion 85 is formed in the joining auxiliary member 80, penetrating the insertion portion 81 and the non-insertion portion 83. The outer shape of the non-insertion portion 83 is not limited to a circular shape as shown in FIG. 12(e) and can be any shape. The shape of the hollow portion 85 is also not limited to a circular shape and can be any shape. The material of the steel joining auxiliary member 80 is not particularly limited as long as it is pure iron or an iron alloy, and examples thereof include mild steel, carbon steel, and stainless steel.

Furthermore, the hollow portion 85 of the auxiliary joining member 80 is filled with a weld metal of an iron alloy or Ni alloy, which is a filler material (welding material) melted by a dissimilar material arc spot welding device 90. As a result, a molten portion is formed in the hollow portion 85 by the weld metal, the molten steel plate 30, and a part of the auxiliary joining member 80. As a result, the first protruding portion 14b and the second protruding portion 15b are joined to the steel plate 30.

In the illustrated example, the second holes 18 are formed in advance in the first protruding portion 14b and the second protruding portion 15b, and then the joining auxiliary member 80 is inserted into the second holes 18. However, the step of providing the second holes 18 in the first protruding portion 14b and the second protruding portion 15b and the step of inserting the joining auxiliary member 80 into the second holes 18 may be performed simultaneously by using the joining auxiliary member 80 itself as a punch to bring the upper base to which the joining auxiliary member 80 is fixed close to the lower base on which the first protruding portion 14b and the second protruding portion 15b are arranged and performing a punching process.

According to this modified example of the battery case 10, second holes 18 facing the steel plate 30 are formed in the first protrusion 14b and the second protrusion 15b, and the first protrusion 14b and the second protrusion 15b are joined to the steel plate 30 by welding at the second holes 18, thereby fixing the steel plate 30 to the first groove portion 16 and the second groove portion 17. This prevents the steel plate 30 from moving in the first groove portion 16 and the second groove portion 17, and allows the steel plate 30 to be securely fixed to the first frame member 12.
As in a first modified example (see FIGS. 8(a) to 8(e)), the cross member 20 and the steel plate 30 may be joined by welding to be integrated in advance, and then the steel plate 30 may be joined by welding to the side surface 12a of the first frame member 12. Also, as in a second modified example (see FIGS. 9(a) to 9(e)), the cross member 20 may not be formed with the convex portion 23, and the steel plate 30 may be formed with a protrusion 32 that protrudes toward the cross member 20 between the first protruding portion 14b of the first rib 14 and the second protruding portion 15b of the second rib 15.

Third Embodiment
In the above-mentioned battery case 1, a steel plate 30 is joined by welding to the side surface 12a (wall surface of the frame-shaped portion 11) of the first frame member 12, and the steel plate 30 is joined by welding to one end of the cross member 20 in the longitudinal direction. However, the battery case 1 is a structure of a relatively large size for an automobile part, and the dimensional accuracy of the aluminum extrusion molding from which the first frame member 12 is made is not necessarily high, so that the accuracy error that inevitably occurs may result in a large displacement. For this reason, a gap may be generated between the steel plate 30 joined to the side surface 12a of the first frame member 12 and the cross member 20, which may make welding impossible with a simple butt joint structure of each member.

Therefore, in this embodiment, we will describe a lightweight, highly rigid battery case 1 that can be flexibly joined to accommodate gaps that may occur at the joint between the steel plate 30 joined to the side surface 12a of the first frame member 12 and the cross member 20, and a manufacturing method for the battery case 1.

Figures 13(a) to (e) are diagrams for explaining a manufacturing method of a battery case 10 according to a third embodiment. In this embodiment, the length of the cross member 20 is designed to be shorter than the length between a pair of first protrusions 14b or a pair of second protrusions 15b that face each other in the longitudinal direction of the cross member 20, and a gap A is formed between the first protrusions 14b and the second protrusions 15b and the longitudinal end of the cross member 20. A bracket portion 33 formed on a steel plate 30 is disposed in this gap A. The bracket portion 33 is joined to one longitudinal end of the cross member 20, and the joining position with the cross member 20 is adjustable. That is, the cross member 20 and the first frame member 12 are connected via the bracket portion 33 of the steel plate 30.

The bracket portion 33 of the steel plate 30 is formed between the first holes 31 (six on each side of the width of the steel plate 30), i.e., in the middle of the width of the steel plate 30. The bracket portion 33 is flat and extends perpendicular to the side surface 12a of the first frame member 12. The height of the bracket portion 33 is approximately equal to or slightly smaller than the dimension of the gap S between the first protrusion 14b and the second protrusion 15b. As shown in Figures 13(a) and (b), when the steel plate 30 is inserted into the first groove portion 16 and the second groove portion 17, the bracket portion 33 protrudes toward the cross member 20 side beyond the first protrusion 14b and the second protrusion 15b.

As described above, the cross member 20 has an inverted U-shaped cross section with an opening at the lower end, and also has openings at both ends in the longitudinal direction (left-right direction in the figure). A pair of flanges 21, 21 extending along the floor-like portion 40 are provided at the lower end of the cross member 20 in the height direction. Thus, the cross member 20 has an upper surface 26, a pair of side surfaces 24 extending downward from both ends in the width direction of the upper surface 26, and flanges 21 extending vertically from the lower end of each side surface 24.

Figure 14 is a cross-sectional view of XIV-XIV in Figure 13(e). As shown in Figures 13(c) to (e) and Figure 14, the bracket portion 33 is inserted into the cross member 20 and is formed so as to be movable forward and backward in the longitudinal direction relative to the cross member 20. That is, the bracket portion 33 has an outer surface 33a that can abut against the inner surface of the cross member 20, and can relatively slide inside the cross member 20. In addition, rectangular openings 25 that are elongated holes perpendicular to the longitudinal direction of the cross member 20 are formed on the end sides of both side surfaces 24 of the cross member 20. Therefore, when the bracket portion 33 is placed inside the cross member 20, the outer surfaces 33a of the bracket portion 33 are exposed through the openings 25.

Then, the outer surface 33a of the bracket portion facing the opening 25 and the edge portion 25a of the opening 25 on the first frame member 12 side are line-welded and joined using a steel MAG welding device 60.

In this way, the side surface 12a of the first frame member 12 is joined to the steel plate 30, and the bracket portion 3 of the steel plate 30 is joined to the cross member 20, thereby connecting the first frame member 12 to the cross member 20. Therefore, even if the gap A between the first protrusion 14b and the second protrusion 15b and the longitudinal end of the cross member 20 changes, the gap A can be filled by joining the cross member 20 to the bracket portion 33 while changing the overlapping length between the cross member 20 and the bracket portion 33, thereby improving the strength of the battery case 10.

Next, we will explain the manufacturing method for the battery case of this embodiment.

First, as shown in FIG. 13(a), the steel plate 30 is inserted into the first groove portion 16 and the second groove portion 17 in the longitudinal direction of the first frame member 12 (upper right to lower left in the figure).

Next, as shown in FIG. 13(b), the side surface 12a of the first frame member 12 and the steel plate 30 are joined through the first hole 31 by dissimilar material MIG spot welding using an aluminum MIG welding device 50. The first frame member 12 and the second frame member 13 are joined by line welding using the aluminum MIG welding device 50. The second rib 15 of the first frame member 12 and the corner formed by the lower surface of the second frame member 13 and the upper surface of the floor portion 40 are also line-welded and joined using the aluminum MIG welding device 50.

Furthermore, as shown in FIG. 13(c), the cross member 20 is inserted toward the bracket portion 33 of the steel plate 30, and the cross member 20 is placed at the desired position on the floor portion 40. Next, as shown in FIG. 13(d), the flange portion 21 of the cross member 20 and the floor portion 40 are joined through the third hole 22 by dissimilar material MIG spot welding using an aluminum MIG welding device 50.

Then, as shown in Figures 13(e) and 14, the outer surface 33a of the bracket portion 33 facing through the opening 25 of the cross member 20 and the edge portion 25a of the opening 25 on the first frame member 12 side are line-welded by a steel MAG welding device 60 to form a steel weld metal WS. In this way, by welding the edge portion 25a of the opening 25 on the first frame member 12 side, the first frame member 12 does not interfere with the welding torch and become an obstacle to the welding work, compared to welding the edge portion of the opening 25 on the opposite side to the first frame member 12, and the welding work is made easier.

As a method of joining the bracket portion 33 and the cross member 20 at the opening 25, a weld bead may be formed to close the opening 25, i.e., to straddle the periphery of the opening 25, and the opening 25 may be filled with steel weld metal WS to join them. This further improves the resistance of the cross member 20 to forces acting in the longitudinal direction.

As described above, with the battery case 10 of this embodiment, even if the dimensions between the side surfaces 12a of a pair of first frame members 12 at the position where the cross member 20 is connected differ due to the dimensional accuracy of the frame members 12, problems such as the inability to join the cross member 20 to the steel plate 30 joined to the side surface 12a of the first frame member 12 can be eliminated. Furthermore, the cross member 20 and the steel plate 30 joined to the side surface 12a of the frame members 12 can be securely joined using the bracket portion 33, thereby improving the strength of the battery case 1.

In addition, according to the battery case 10 of this embodiment, an opening 25 is formed at the end of the cross member 20, which faces the outer surface 33a of the bracket portion 33 arranged inside the cross member 20. The bracket portion 33 and the cross member 20 are joined by welding at the opening 25, so that the bracket portion 33 and the cross member 20 can be welded together without the welding torch interfering with the first frame member 12.

In the battery case 10 of this embodiment, the first frame member 12 has the first and second ribs 14, 15, but the present invention is also applicable to cases where the first frame member 12 does not have the first and second ribs 14, 15. As shown in Figs. 10(b)-(c), the first and second ribs 14, 15 may be plastically deformed toward the steel plate 30, or the first frame member 12 may be fastened or welded through the second holes 18 formed in the first and second ribs 14, 15 as shown in Figs. 11(b)-(c) and 12(b)-(c).

In addition, the shape of the bracket portion 33 can be changed as appropriate.

(First Modification of the Third Embodiment)
15(a) to (d) are diagrams for explaining a manufacturing method of the battery case 10 according to a first modified example of the third embodiment. In this modified example, as shown in FIG. 15(a), the bracket portion 33 of the steel plate 30 is inserted into the inside of the cross member 20 to temporarily assemble the steel plate 30 and the bracket portion 33. In this manner, the steel plate 30 is inserted into the first and second groove portions 16 and 17 in a state in which the bracket portion 33 of the steel plate 30 is assembled to at least one end of the cross member 20. As a result, the cross member 20 to which the bracket portion 33 is assembled is disposed relative to the frame portion 11. At this time, the bracket portion 33 is loosely fitted in the cross member 20, and the bracket portion 33 and the cross member 20 can freely advance and retreat relative to each other.

Next, as shown in FIG. 15(b), the cross member 20 is moved while being guided by the bracket portion 33, and placed in the desired position on the floor portion 40. Then, the outer surface 33a of the bracket portion 33 facing the opening 25 of the cross member 20 is welded and joined to the opening 25 using a steel MAG welding device.

Furthermore, as shown in FIG. 15(c), the first frame member 12 and the second frame member 13 are joined by line welding using an aluminum MIG welding device 50. In addition, the corners formed by the second rib 15 of the first frame member 12 and the lower surface of the second frame member 13 and the upper surface of the floor portion 40 are also joined by line welding using the aluminum MIG welding device 50.

As shown in FIG. 15(d), the flange portion 21 of the cross member 20 and the floor portion 40 are joined through the third hole 22 by dissimilar material MIG spot welding using an aluminum MIG welding device 50. Also, the side surface 12a of the first frame member 12 and the steel plate 30 are joined through the first hole 31 by dissimilar material MIG spot welding using an aluminum MIG welding device 50.

(Second Modification of the Third Embodiment)
16(a) to 16(e) are diagrams for explaining a manufacturing method of a battery case 10 according to a second modified example of the third embodiment. In this modified example, the steel plate 30 has two bracket portions 33 formed between six first holes 31 formed on each side in the width direction of the steel plate 30. The two bracket portions 33 are spaced apart from each other in the width direction of the steel plate, and each has a flat plate shape extending perpendicular to the side surface 12a of the first frame member 12. The two bracket portions 33 each have inner surfaces 33b facing each other in the width direction of the steel plate 30, and the cross member 20 is sandwiched between these facing inner surfaces 33b.

First, as shown in FIG. 16(a), the steel plate 30 is inserted into the first groove 16 and the second groove 17 in the longitudinal direction of the first frame member 12 (upper right to lower left in the figure). Here, the height of each bracket portion 33 is approximately equal to or slightly smaller than the dimension of the gap S between the first protrusion 14b and the second protrusion 15b. Then, when the steel plate 30 is inserted into the first groove 16 and the second groove 17, each bracket portion 33 protrudes toward the cross member 20 side beyond the first protrusion 14b and the second protrusion 15b.

Next, as shown in FIG. 16(b), the side surface 12a of the first frame member 12 and the steel plate 30 are joined through the first hole 31 by dissimilar material MIG spot welding using an aluminum MIG welding device 50. The first frame member 12 and the second frame member 13 are joined by line welding using the aluminum MIG welding device 50. The second rib 15 of the first frame member 12 and the corner formed by the lower surface of the second frame member 13 and the upper surface of the floor portion 40 are also line-welded and joined using the aluminum MIG welding device 50.

Furthermore, as shown in FIG. 16(c), the cross member 20 is inserted between the inner surfaces 33b of the pair of bracket portions 33 of the steel plate 30, and the cross member 20 is positioned at the desired position on the floor portion 40. That is, the bracket portion 33 has an inner surface 33b that can abut against a pair of side surfaces (outer surfaces) 24) of the cross member 20, and the pair of side surfaces (outer surfaces) 24 of the cross member 20 can slide relatively.

Next, as shown in FIG. 16(d), the flange portion 21 of the cross member 20 and the floor portion 40 are joined through the third hole 22 by dissimilar material MIG spot welding using an aluminum MIG welding device 50.

Figure 17 is a cross-sectional view taken along line XVII-XVII of Figure 16(e). As shown in Figures 16(e) and 17, the corner formed by the bracket portion 33 and the side surface 24 (outer surface) of the cross member 20 is line-welded by a steel MAG welding device 60 to form steel weld metal WS. In this way, the steel plate 30 and the cross member 20 are joined via the bracket portion 33.

As described above, with the battery case 10 of this embodiment, even if the dimensions between the side surfaces 12a of a pair of first frame members 12 at the position where the cross member 20 is connected differ due to the dimensional accuracy of the frame members 12, problems such as the inability to join the cross member 20 to the steel plate 30 joined to the side surface 12a of the frame members 12 can be eliminated. Furthermore, the cross member 20 and the steel plate 30 joined to the side surface 12a of the frame members 12 can be securely joined using the bracket portion 33, thereby improving the strength of the battery case 1.

Figures 18(a) to (e) show modified examples of the steel plate 30. As shown in Figures 18(a) to (e), the steel plate 30 may be composed of two steel plate pieces 30a split in the width direction. In this case, each steel plate piece 30a has a plurality of first holes 31 and a bracket portion 33. Then, the cross member 20 is inserted between the bracket portions 33 of the pair of steel plate pieces 30a, and each bracket portion 33 is welded and joined to the side surface 24 of the cross member 20.

(Third Modification of the Third Embodiment)
19(a) to 19(d) are diagrams for explaining a manufacturing method of a battery case 10 according to a third modified example of the third embodiment. In this modified example, as shown in FIG. 19(a), the cross member 20 is inserted between the pair of bracket portions 33 of the steel plate 30 of the second modified example, so that the steel plate 30 and the bracket portions 33 are temporarily assembled, and then the steel plate 30 is inserted into the first and second groove portions 16, 17. At this time, the cross member 20 is loosely fitted between the pair of bracket portions 33, and the cross member 20 and the pair of bracket portions 33 can freely advance and retreat relative to each other.

Next, as shown in FIG. 19(b), the cross member 20 is moved while being guided by the pair of bracket parts 33, and placed in the desired position on the floor part 40. Then, the corners formed by the bracket parts 33 and the side surfaces 24 of the cross member 20 are welded and joined by the steel MAG welding device 60.

Furthermore, as shown in FIG. 19(c), the first frame member 12 and the second frame member 13 are joined by line welding using an aluminum MIG welding device 50. In addition, the corners formed by the second rib 15 of the first frame member 12 and the lower surface of the second frame member 13 and the upper surface of the floor portion 40 are also joined by line welding using the aluminum MIG welding device 50.

As shown in FIG. 19(d), the flange portion 21 of the cross member 20 and the floor portion 40 are joined through the third hole 22 by dissimilar material MIG spot welding using an aluminum MIG welding device 50. Also, the side surface 12a of the first frame member 12 and the steel plate 30 are joined through the first hole 31 by dissimilar material MIG spot welding using an aluminum MIG welding device 50.

In addition, the steel plate 30 consisting of two steel plate pieces 30a shown in Figure 18 can also be applied to this modified example.

(Fourth Modification of the Third Embodiment)
20(a) to 20(e) are views for explaining a manufacturing method of a battery case 10 according to a second modified example of the third embodiment. In this modified example, a steel plate 30 has bracket portions 33 formed between first holes 31, six of which are formed on each side in the width direction of the steel plate 30. The bracket portions 33 are in an inverted U-shape with an opening at the lower end. The bracket portions 33 also have openings at both ends in the longitudinal direction of the cross member 20.

First, as shown in FIG. 20(a), the steel plate 30 is inserted into the first groove 16 and the second groove 17 in the longitudinal direction of the first frame member 12 (upper right to lower left in the figure). Here, the height of the bracket portion 33 is approximately equal to or slightly smaller than the dimension of the gap S between the first protrusion 14b and the second protrusion 15b. Then, when the steel plate 30 is inserted into the first groove 16 and the second groove 17, the bracket portion 33 protrudes toward the cross member 20 side beyond the first protrusion 14b and the second protrusion 15b.

20(b), the side surface 12a of the first frame member 12 and the steel plate 30 are joined through the first hole 31 by dissimilar material MIG spot welding using an aluminum MIG welding device 50. The first frame member 12 and the second frame member 13 are joined by line welding using the aluminum MIG welding device 50. The second rib 15 of the first frame member 12 and the corner formed by the lower surface of the second frame member 13 and the upper surface of the floor portion 40 are also line-welded and joined using the aluminum MIG welding device 50.

Furthermore, as shown in FIG. 20(c), the cross member 20 is inserted between the inner surfaces 33b of the pair of bracket portions 33 of the steel plate 30, and the cross member 20 is positioned at the desired position on the floor portion 40. That is, the bracket portion 33 has an inner surface 33b that can abut against the pair of side surfaces (outer surfaces) 24 and the top surface 26 of the cross member 20, and the pair of side surfaces (outer surfaces) 24 and the top surface 26 of the cross member 20 can slide relative to each other.

Next, as shown in FIG. 20(d), the flange portion 21 of the cross member 20 and the floor portion 40 are joined through the third hole 22 by dissimilar material MIG spot welding using an aluminum MIG welding device 50.

Furthermore, as shown in FIG. 20(e), the corners formed by the bracket portion 33 and the pair of side surfaces 24 of the cross member 20 are line-welded by a steel MAG welding device 60 to form steel weld metal WS. In this way, the steel plate 30 and the cross member 20 are joined via the bracket portion 33.

(Fifth Modification of the Third Embodiment)
21(a) to (d) are diagrams for explaining a manufacturing method of a battery case 10 according to a fifth modified example of the third embodiment. In this modified example, as shown in FIG. 21(a), the cross member 20 is inserted into the bracket portion 33 of the steel plate 30 of the fourth modified example (see FIGS. 20(a) to (e)) to temporarily assemble the steel plate 30 and the bracket portion 33, and then the steel plate 30 is inserted into the first and second groove portions 16, 17. At this time, the cross member 20 is loosely fitted into the bracket portion 33, and the cross member 20 and the bracket portion 33 can freely advance and retreat relative to each other.

Next, as shown in FIG. 21(b), the cross member 20 is moved while being guided by the bracket portion 33, and placed in the desired position on the floor portion 40. Then, the corner formed by the bracket portion 33 and the side surface 24 of the cross member 20 is welded and joined by the steel MAG welding device 60.

21(c), the first frame member 12 and the second frame member 13 are joined by line welding using an aluminum MIG welding device 50. The second rib 15 of the first frame member 12 and the corner formed by the lower surface of the second frame member 13 and the upper surface of the floor portion 40 are also joined by line welding using the aluminum MIG welding device 50.

21(d), the flange portion 21 of the cross member 20 and the floor portion 40 are joined through the third hole 22 by dissimilar material MIG spot welding using an aluminum MIG welding device 50. Also, the side surface 12a of the first frame member 12 and the steel plate 30 are joined through the first hole 31 by dissimilar material MIG spot welding using an aluminum MIG welding device 50.

(Manufacturing methods for various brackets)
Next, a method for manufacturing the steel plate 30 having various shapes and including the bracket portion 33 will be described. Figures 29A to 29B are perspective views showing an example of a method for manufacturing the steel plate 30. For example, the π-shaped steel plate 30 shown in Figures 16(a) to (e) is formed by vertically welding two steel plates 37 that become the bracket portion 33 to one side of one steel plate 36, as shown in Figures 29A and 29B. As a method for manufacturing the steel plate 30, in addition to a method of welding such plates together, cutting from a plate, casting, 3D printing, rolling, and machining such as cutting and drilling can be applied.

The steel plate 30 shown in Figures 13(a) to (e) and Figure 30A may be modified to have similar shapes as shown in Figures 30B to 30G. In other words, modifications to form chamfers at the orthogonal portions between plates or modifications to form hollows may be made as appropriate as long as the object of this application can be achieved.

(Fourth embodiment)
22(a) to (e) are diagrams for explaining a manufacturing method of the battery case 10 according to the fourth embodiment. As in the third embodiment, the present embodiment aims to eliminate a problem such as the inability to join the cross member 20 to the steel plate 30 joined to the side surface 12a of the first frame member 12 even if the dimensions between the side surfaces 12a of the pair of first frame members 12 at the position where the cross member 20 is joined are different. However, while in the third embodiment, the steel plate 30 and the cross member 20 are joined using the bracket portion 33 formed on the steel plate 30, in this embodiment, the steel plate 30 and the cross member 20 are joined using a steel wedge-shaped member 75 arranged between the steel plate 30 and the cross member 20. Hereinafter, a manufacturing method of the battery case 10 according to this embodiment will be described.

As shown in FIG. 22(a), a protrusion 32 is formed in the middle of the width of the steel plate 30. The protrusions 32 are arranged between first holes 31, six of which are formed on each side of the width of the steel plate 30. The height of the protrusions 32 is approximately equal to or slightly smaller than the dimension of the gap S between the first protrusion 14b and the second protrusion 15b. The steel plate 30 is inserted into the first groove 16 and the second groove 17 in the longitudinal direction of the first frame member 12 (upper right to lower left in the figure).

When the steel plate 30 is inserted into the first groove portion 16 and the second groove portion 17, the first holes 31 of the steel plate 30 are exposed to the inside of the frame portion 11 through the gap S. In addition, the contact surface of the protrusion portion 32 of the steel plate 30 that contacts the wedge-shaped member 75 is flush with the contact surfaces of the first protrusion portion 14b and the second protrusion portion 15b that contact the wedge-shaped member 75.

Then, as shown in FIG. 22(b), the aluminum MIG welding device 50 dissimilarly MIG spot welds the steel plate 30 to the side surface 12a of the first frame member 12 through the first hole 31.

In addition, with the end face of the second frame member 13 butted against the side face 12a and steps 12b, 12c of the first frame member 12, the corner formed by the edge of the end face of the second frame member 13 and the side face 12a of the first frame member 12 is line welded by the aluminum MIG welding device 50.

The corners formed by the second rib 15 of the first frame member 12 and the underside of the second frame member 13 and the upper surface of the floor portion 40 are also line welded by the aluminum MIG welding device 50.

As shown in FIG. 22(c), one end surface 27 of the cross member 20 in the longitudinal direction is inclined with respect to the height direction of the steel plate 30. In other words, one end surface 27 of the cross member 20 is an inclined surface that is inclined so that the gap between the end surface 27 and the protrusion 32 of the steel plate 30 becomes smaller from the upper surface 26 toward the floor portion 40 (from above to below).

Then, the cross member 20 is placed on the floor portion 40 so that one end surface 27 of the cross member 20 is separated from the protrusion 32 of the steel plate 30 and the first and second protrusions 14b, 15b via a gap. Next, a steel wedge-shaped member 75 is inserted from above downward between one end surface 27 of the cross member 20 and the abutment surface of the protrusion 32 of the steel plate 30 and the abutment surfaces of the first and second protrusions 14b, 15b.

The wedge-shaped member 75 has a shape corresponding to the member to be fitted. The wedge-shaped member 75 of this embodiment has a first side surface 75a that abuts against one end surface 27 of the cross member 20, and a second side surface 75b that abuts against the abutment surface of the protrusion 32 of the steel plate 30 and the abutment surfaces of the first and second protrusions 14b, 15b. The first side surface 75a is an inclined surface that inclines toward the steel plate 30 from above to below, similar to the one end surface 27 of the cross member 20. The second side surface 75b is flat, similar to the abutment surface of the protrusion 32 of the steel plate 30 and the abutment surfaces of the first and second protrusions 14b, 15b. In this way, the wedge-shaped member 75 has a wedge shape in which the width in the longitudinal direction of the cross member 20 decreases from above to below.

In addition, the wedge-shaped member 75 has a number of through holes 76 that penetrate the wedge-shaped member 75 in the width direction (upper right to lower left in the figure) to reduce weight. In the example shown, three through holes 76 are provided, but the number is not particularly limited and it does not matter if there are no through holes. In other words, the wedge-shaped member 75 has a cross-sectional shape that is solid or has an internal space. With this configuration, if it is solid, the strength can be increased, and if there is an internal space, the weight can be reduced.

In this way, the wedge-shaped member 75 is inserted from above downward between one end surface 27 of the cross member 20 and the protrusion 32 and the first and second protrusions 14b, 15b of the steel plate 30, thereby fixing the cross member 20 between the pair of first frame members 12.

Next, as shown in FIG. 22(d), the cross member 20 and the floor portion 40 are joined by dissimilar material MIG spot welding at the multiple third holes 22 using an aluminum MIG welding device 50.

Figure 23 is a cross-sectional view taken along line XXIII-XXIII of Figure 22(e). As shown in Figures 22(e) and 23, the steel MAG welding device 60 line-welds the corner formed by one end face 27 of the cross member 20 and the first side face 75a of the wedge-shaped member 75, and line-welds the corner formed by the second side face 75b of the wedge-shaped member 75 and the protrusion 32 of the steel plate 30. This firmly connects the steel plate 30 and the cross member 20 via the wedge-shaped member 75.

The battery case 10 is manufactured through these steps. Note that the order of each welding step may be changed as appropriate.

As described above, with the battery case 10 of this embodiment, even if the dimensions between the side surfaces 12a of a pair of first frame members 12 at the position where the cross member 20 is connected differ due to the dimensional accuracy of the frame members 12, problems such as the inability to join the cross member 20 to the steel plate 30 joined to the side surface 12a of the first frame member 12 can be eliminated. Furthermore, the cross member 20 and the steel plate 30 joined to the side surface 12a of the frame members 12 can be securely joined using the wedge-shaped member 75, thereby improving the strength of the battery case 1.

In addition, the wedge-shaped member 75 has a cross-sectional shape that is solid or has an internal space, so if it is solid, it can be strong, and if there is an internal space, it can be lightweight.

(First Modification of the Fourth Embodiment)
24(a) to (e) are diagrams for explaining a manufacturing method of the battery case 10 according to a first modified example of the fourth embodiment. In the fourth embodiment (see FIGS. 22(a) to (e)), the first and second ribs 14, 15 were provided on the first frame member 12, and therefore the protrusions 32 were formed on the steel plate 30. However, in the case where the first and second ribs 14, 15 are not provided on the first frame member 12 as in the present embodiment, it is not necessary to provide the protrusions 32 on the steel plate 30.

In this case, first, as shown in Figures 24(a)-(b), the steel plate 30 is welded to the side surface 12a of the first frame member 12 through the first hole 31 using an aluminum MIG welding device 50.

The corners formed by the edge of the end face of the second frame member 13 and the side face 12a of the first frame member 12 are line-welded by the aluminum MIG welding device 50. The corners formed by the second rib 15 of the first frame member 12 and the lower surface of the second frame member 13 and the upper surface of the floor portion 40 are also line-welded by the aluminum MIG welding device 50.

As shown in FIG. 24(c), the cross member 20 is placed on the floor portion 40 so that one end surface 27 of the cross member 20 and the steel plate 30 are separated by a gap. Next, a steel wedge-shaped member 75 is inserted from above downward between one end surface 27 of the cross member 20 and the steel plate 30. This fixes the cross member 20 between the pair of first frame members 12.

Next, as shown in FIG. 24(d), the cross member 20 and the floor portion 40 are joined by dissimilar material MIG spot welding at the multiple third holes 22 using an aluminum MIG welding device 50.

Then, as shown in FIG. 24(e), the steel MAG welding device 60 line-welds the corner formed by one end surface 27 of the cross member 20 and the first side surface 75a of the wedge-shaped member 75, and line-welds the corner formed by the second side surface 75b of the wedge-shaped member 75 and the steel plate 30. This firmly connects the steel plate 30 and the cross member 20 via the wedge-shaped member 75.

The battery case 10 is manufactured through these steps. Note that the order of each welding step may be changed as appropriate.

(Second Modification of the Fourth Embodiment)
25(a) to (e) are diagrams for explaining a manufacturing method of the battery case 10 according to the second modified example of the fourth embodiment. In the first modified example of the fourth embodiment, a steel wedge-shaped member 75 is inserted from above downward between one end surface 27 of the cross member 20 and the steel plate 30 (FIG. 24(c)). However, as shown in FIG. 25(c), the wedge-shaped member 75 may be inserted between one end surface 27 of the cross member 20 and the steel plate 30 in the width direction of the steel plate 30 (upper right to lower left direction in the figure).

In this modified example, the wedge-shaped member 75 is inserted in the width direction of the steel plate 30, so that the wedge-shaped member 75 does not interfere with the excess aluminum weld metal WA embedded in the first hole 31 of the steel plate 30, and the steel plate 30 is extended in the width direction, thereby extending the distance between the first holes 31 formed on both sides of the steel plate 30 in the width direction.

As shown in FIG. 25(c), one end surface 27 of the cross member 20 in the longitudinal direction is inclined with respect to the width direction of the steel plate 30, i.e., the extension direction of the side surface 12a of the first frame member 12. In other words, one end surface 27 of the cross member 20 is an inclined surface that inclines so that the gap with the steel plate 30 becomes smaller from one side in the width direction to the other side (from the upper right to the lower left in the figure).

Then, the cross member 20 is placed on the floor portion 40 so that one end surface 27 of the cross member 20 and the steel plate 30 are separated by a gap. Next, a wedge-shaped member 75 is inserted between one end surface 27 of the cross member 20 and the steel plate 30 from one side in the width direction of the steel plate 30 to the other side (from the upper right to the lower left in the figure).

The wedge-shaped member 75 has a shape corresponding to the member to be fitted. The wedge-shaped member 75 of this modified example has a first side surface 75a that abuts against one end surface 27 of the cross member 20, and a second side surface 75b that abuts against the steel plate 30. The first side surface 75a is an inclined surface that inclines toward the steel plate 30 as it moves from one side in the width direction of the steel plate 30 to the other side (from the upper right to the lower left in the figure), just like the one end surface 27 of the cross member 20. Also, the second side surface 75b is flat, just like the steel plate 30. In this way, the wedge-shaped member 75 has a wedge shape in which the width in the longitudinal direction of the cross member 20 decreases as it moves from one side in the width direction of the steel plate 30 to the other side (from the upper right to the lower left in the figure).

The wedge-shaped member 75 is then moved from above toward below so as to enter inside the width direction of the aluminum weld metal WA so as not to interfere with the excess aluminum weld metal WA filled in the first holes 31 on both sides of the width direction of the steel plate 30. Next, the wedge-shaped member 75 is inserted between one end face 27 of the cross member 20 and the steel plate 30 in the width direction of the steel plate 30. This fixes the cross member 20 between the pair of first frame members 12.

Next, as shown in FIG. 25(d), the cross member 20 and the floor portion 40 are joined by dissimilar material MIG spot welding at the multiple third holes 22 using an aluminum MIG welding device 50.

Then, as shown in FIG. 25(e), the steel MAG welding device 60 line-welds the corner formed by one end surface 27 of the cross member 20 and the first side surface 75a of the wedge-shaped member 75, and line-welds the corner formed by the second side surface 75b of the wedge-shaped member 75 and the steel plate 30. This firmly connects the steel plate 30 and the cross member 20 via the wedge-shaped member 75.

The battery case 10 is manufactured through these processes. The order of the welding processes may be changed as appropriate. Furthermore, when wedge-shaped members 75 are inserted between both longitudinal end faces of the cross member 20 and the steel plate 30, the insertion directions of the wedge-shaped members 75 may be the same or reversed.

Fifth Embodiment
26(a) to 26(e) are diagrams for explaining a manufacturing method of a battery case 10 according to a fifth embodiment. As in the third and fourth embodiments, this modification aims to eliminate a problem such as an inability to connect the cross member 20 to the side surface 12a of the first frame member 12 even if the dimensions between the side surfaces 12a of the pair of first frame members 12 at the position where the cross member 20 is connected are different.

In this embodiment, steel plates 30 of different thicknesses are prepared in advance, and the steel plate 30 that corresponds to the gap A between the first frame member 12 and the cross member 20 is selected and placed in the gap. The first frame member 12 and the cross member 20 are then connected via the steel plate 30. The manufacturing method for the battery case 10 of this embodiment is described below.

As shown in FIG. 26(a), in this embodiment, a first frame member 12 is used that does not have first and second ribs 14, 15.

First, as shown in FIG. 26(b), the corners formed by the edge of the end face of the second frame member 13 and the side face 12a of the first frame member 12 are line-welded by an aluminum MIG welding device 50. In addition, the corners formed by the lower surfaces of the first frame member 12 and the second frame member 13 and the upper surface of the floor portion 40 are also line-welded by the aluminum MIG welding device 50.

Next, the flange portion 21 and the floor portion 40 of the cross member 20 are joined by dissimilar material MIG spot welding using an aluminum MIG welding device 50 at the multiple third holes 22. Here, the longitudinal length of the cross member 20 is shorter than the longitudinal length of the second frame member 13, and a gap A is formed between both longitudinal ends of the cross member 20 and the side surfaces 12a of the pair of first frame members 12.

As shown in FIG. 26(c), a plurality of steel plates 30 of different thicknesses are prepared in advance. Then, as shown in FIG. 26(d), a steel plate 30 having a thickness corresponding to the gap A between the side surface 12a of the first frame member 12 and the cross member 20 is selected, and the steel plate 30 is placed in the gap A. Then, the steel plate 30 is welded to the side surface 12a of the first frame member 12 through the first hole 31 by the aluminum MIG welding device 50.

Then, as shown in FIG. 26(e), the corner formed by one end of the cross member 20 and the steel plate 30 is line-welded by the steel MAG welding device 60. This connects the first frame member 12 and the cross member 20 via the steel plate 30.

The battery case 10 is manufactured through these steps. Note that the order of each welding step may be changed as appropriate.

As described above, according to the battery case 10 of this embodiment, even if the dimensions between the side surfaces 12a of a pair of first frame members 12 at the position where the cross member 20 is connected differ depending on the dimensional accuracy of the frame members 12, a steel plate 30 having a thickness corresponding to the gap A between the side surfaces 12a of the first frame members 12 and the cross members 20 is selected and positioned, thereby eliminating problems such as the inability to connect the cross member 20 to the side surfaces 12a of the first frame members 12.

(First Modification of Fifth Embodiment)
27(a) to (e) are views for explaining a manufacturing method of the battery case 10 according to a modified example of the fifth embodiment.

As shown in FIG. 27(a), in this embodiment, a first frame member 12 having first and second ribs 14, 15 is used. Then, a steel plate 30 is inserted into the first groove portion 16 and the second groove portion 17.

Next, as shown in FIG. 27(b), the end of the second frame member 13 is butted against the step portion 12b of the first frame member 12. Also, the end of the cross member 20 is butted against the first and second ribs 14, 15.

27(c), the corner formed by the edge of the end face of the second frame member 13 and the side surface 12a of the first frame member 12 is line-welded by the aluminum MIG welding device 50. Also, the corner formed by the second rib 15 of the first frame member 12 and the lower surface of the second frame member 13 and the upper surface of the floor-like portion 40 is line-welded by the aluminum MIG welding device 50. Also, the aluminum MIG welding device 50 welds the steel plate 30 to the side surface 12a of the first frame member 12 through the first hole 31.

Next, the flange portion 21 and the floor portion 40 of the cross member 20 are joined by dissimilar material MIG spot welding using an aluminum MIG welding device 50 at the multiple third holes 22. Here, a gap B is formed between both longitudinal ends of the cross member 20 and the steel plate 30.

As shown in FIG. 27(d), a number of steel plate members 35 of different thicknesses are prepared in advance. Then, as shown in FIG. 27(d), a plate member 35 having a thickness corresponding to the gap B between the cross member 20 and the steel plate 30 is selected, and the plate member 35 is placed in the gap B. Then,

Figure 28 shows a cross-sectional view of XXVIII-XXVIII in Figure 27(e). As shown in Figures 27(e) and 28, the steel MAG welding device 60 line-welds the corner formed by one end of the cross member 20 and the plate-shaped member 35, and line-welds the corner formed by the plate-shaped member 35 and the steel plate 30. This firmly connects the steel plate 30 and the cross member 20 via the plate-shaped member 35.

The battery case 10 is manufactured through these steps. Note that the order of each welding step may be changed as appropriate.

As described above, according to the battery case 10 of this embodiment, even if the dimensions between the side surfaces 12a of a pair of first frame members 12 at the position where the cross member 20 is connected differ depending on the dimensional accuracy of the frame members 12, a plate-like member 35 having a thickness corresponding to the gap B between the steel plate 30 and the cross member 20 is selected and positioned, thereby eliminating problems such as the inability to connect the cross member 20 to the side surface 12a of the first frame member 12.

Although the battery cases according to each embodiment have been described in detail above, the present invention is not limited to the above-mentioned embodiments and modifications, and can be modified, improved, etc. as appropriate. For example, in the fourth or fifth embodiment, the first and second ribs 14, 15 may be plastically deformed toward the steel plate 30 as shown in Figs. 10(b)-(c), and the first frame member 12 may be fastened or welded through the second holes 18 formed in the first and second ribs 14, 15 as shown in Figs. 11(b)-(c) and 12(b)-(c). In addition, the order of the welding process in each embodiment and modification is not limited to the above-mentioned, and may be changed as appropriate.

As described above, this specification discloses the following:

(1) A rectangular frame portion;
At least one cross member extending toward a pair of parallel wall surfaces of the frame portion so as to divide the inside of the frame portion;
Equipped with
The frame-shaped portion is made of aluminum or an aluminum alloy,
The cross member is made of steel;
A battery case in which a steel plate is joined to the wall surface of the frame-shaped portion by welding,
The steel plate has a first hole facing the wall surface,
The steel plate and the wall surface are joined by welding at the first hole,
the first hole is filled with an aluminum or aluminum alloy weld metal;
A battery case characterized in that the steel plate and one longitudinal end of the cross member are joined by welding.
According to this configuration, among the components of the battery case, the frame-shaped portion is made of aluminum material, while the cross member is made of steel, so that it is possible to achieve both weight reduction and cost reduction. In addition, since the steel plate is welded to the wall surface of the frame-shaped portion, and then the cross member is welded to the steel plate, the cross member can be firmly fixed to the frame-shaped portion via the steel plate.
In addition, the steel plate and the aluminum frame portion can be reliably joined by welding through the first hole.

(2) A first rib and a second rib are provided on the upper and lower parts of the wall surface,
The first rib has a first base portion extending from the wall surface toward the cross member and a first protruding portion protruding downward from a tip end of the first base portion,
A first groove is defined between the wall surface, the first base portion, and the first protruding portion,
The second rib has a second base portion extending from the wall surface toward the cross member and a second protruding portion protruding upward from a tip of the second base portion,
A second groove is defined between the wall surface, the second base portion, and the second protruding portion,
The battery case according to any one of (1), wherein the steel plate is arranged in the first groove portion and the second groove portion.
This configuration can prevent the steel plate welded to the wall surface from peeling off.

(3) A protrusion protruding toward the cross member is formed on the steel plate between the first protruding portion and the second protruding portion,
The battery case according to claim 2, wherein the protrusion and the one end of the cross member in the longitudinal direction are joined by welding.
According to this configuration, even if the first rib and the second rib are provided, the cross member and the steel plate can be joined by welding via the protrusion.

(4) A convex portion that protrudes toward the steel plate is formed between the first protruding portion and the second protruding portion at the one end portion in the longitudinal direction of the cross member,
The battery case according to (2), wherein the protrusion and the steel plate are joined by welding.
According to this configuration, even if the first rib and the second rib are provided, the cross member and the steel plate can be joined by welding via the convex portion.

(5) The steel plate is formed with a bracket portion extending toward the cross member,
the bracket portion has an outer surface that can come into contact with an inner surface of the cross member and is relatively slidable inside the cross member;
The cross member has an opening facing the outer surface of the bracket portion disposed therein,
The battery case according to (1) or (2), wherein the bracket portion and the cross member are joined by welding at the opening.
This configuration makes it possible to eliminate problems such as the inability to join the cross member to the steel plate joined to the wall surfaces even if the dimensions between the pair of wall surfaces at the position where the cross member is connected differ depending on the dimensional accuracy of the frame-shaped portion. Furthermore, the cross member and the steel plate joined to the wall surfaces can be reliably joined using the bracket portion, thereby improving the strength of the battery case.

(6) The steel plate is formed with a bracket portion extending toward the cross member,
the bracket portion has an inner surface capable of abutting against an outer surface of the cross member and is capable of sliding relatively on the outer surface of the cross member;
The battery case according to (1) or (2), wherein the bracket portion and the cross member are joined by welding.
This configuration makes it possible to eliminate problems such as the inability to join the cross member to the steel plate joined to the wall surfaces even if the dimensions between the pair of wall surfaces at the position where the cross member is connected differ depending on the dimensional accuracy of the frame-shaped portion. Furthermore, the cross member and the steel plate joined to the wall surfaces can be reliably joined using the bracket portion, thereby improving the strength of the battery case.

(7) One end surface of the cross member in the longitudinal direction is inclined with respect to a height direction of the steel plate or an extension direction of the wall surface,
A steel wedge-shaped member is disposed between the one end surface of the cross member and the steel plate,
The battery case according to any one of (1) to (3), wherein the wedge-shaped member is joined to the cross member and the steel plate by welding, respectively.
This configuration makes it possible to eliminate problems such as the inability to join the cross member to the steel plate joined to the wall surfaces even if the dimensions between the pair of wall surfaces at the position where the cross member is connected differ depending on the dimensional accuracy of the frame-shaped portion. Furthermore, the cross member and the steel plate joined to the wall surfaces can be reliably joined using the wedge-shaped member, thereby improving the strength of the battery case.

(8) The device further includes a floor portion connected to the frame portion and constituting a floor surface,
The floor portion is made of aluminum or an aluminum alloy,
The battery case according to any one of (1) to (7), wherein the cross member and the floor portion are joined by welding.
According to this configuration, the frame and floor of the battery case are made of aluminum, while the cross member is made of steel, making it possible to achieve both weight reduction and cost reduction. Furthermore, the cross member and the floor are firmly joined by welding.

(9) The cross member has a flange portion extending along the floor portion,
The flange portion is formed with a third hole facing the floor portion,
The flange portion and the floor portion are joined by welding at the third hole,
The battery case according to claim 8, wherein the third hole is filled with a weld metal of aluminum or an aluminum alloy.
With this configuration, the cross member, which is made of steel, and the floor portion, which is made of aluminum material, can be reliably joined by welding through the third hole.

(10) A rectangular frame portion;
At least one cross member extending toward a pair of parallel wall surfaces of the frame portion so as to divide the inside of the frame portion;
Equipped with
The frame-shaped portion is made of aluminum or an aluminum alloy,
The cross member is made of steel;
A manufacturing method of a battery case in which a steel plate is joined to the wall surface of the frame-shaped portion by welding,
The steel plate has a first hole facing the wall surface,
The first hole is filled with a weld metal of aluminum or an aluminum alloy to join the steel plate and the wall surface;
A method for manufacturing a battery case, characterized in that the steel plate and one longitudinal end of the cross member are joined by welding.
According to this configuration, among the components of the battery case, the frame-shaped portion is made of aluminum material, while the cross member is made of steel, so that it is possible to achieve both weight reduction and cost reduction. In addition, since the steel plate is joined to the wall surface of the frame-shaped portion by welding, and then the cross member is joined to the steel plate by welding, the cross member can be firmly fixed to the frame-shaped portion via the steel plate.

(11) A first rib and a second rib are provided on the upper and lower parts of the wall surface,
The first rib has a first base portion extending from the wall surface toward the cross member and a first protruding portion protruding downward from a tip end of the first base portion,
A first groove is defined between the wall surface, the first base portion, and the first protruding portion,
The second rib has a second base portion extending from the wall surface toward the cross member and a second protruding portion protruding upward from a tip of the second base portion,
A second groove is defined between the wall surface, the second base portion, and the second protruding portion,
The method for manufacturing a battery case according to (10), wherein the steel plate is arranged in the first groove portion and the second groove portion.
This configuration can prevent the steel plate welded to the wall surface from peeling off.

(12) The method for manufacturing a battery case according to (11), in which the steel plate is fixed to the first groove portion and the second groove portion by plastically deforming the first protruding portion and the second protruding portion toward the steel plate.
According to this configuration, the steel plate can be prevented from moving in the first groove portion and the second groove portion, and the steel plate can be reliably fixed to the frame-shaped portion.

(13) A second hole facing the steel plate is formed in each of the first protruding portion and the second protruding portion,
The method for manufacturing a battery case described in (11), wherein the steel plate is fixed to the first groove portion and the second groove portion by fastening a fastening member toward the steel plate through the second hole.
According to this configuration, the steel plate can be prevented from moving in the first groove portion and the second groove portion, and the steel plate can be reliably fixed to the frame-shaped portion.

(14) A second hole facing the steel plate is formed in each of the first protruding portion and the second protruding portion,
The method for manufacturing a battery case described in (11), in which the first protrusion and the second protrusion are joined to the steel plate by welding at the second hole, thereby fixing the steel plate to the first groove portion and the second groove portion.
According to this configuration, the steel plate can be prevented from moving in the first groove portion and the second groove portion, and the steel plate can be reliably fixed to the frame-shaped portion.

(15) The steel plate is formed with a bracket portion extending toward the cross member,
the bracket portion has an outer surface that can come into contact with an inner surface of the cross member and is relatively slidable inside the cross member;
The cross member has an opening facing the outer surface of the bracket portion disposed therein,
The method for manufacturing a battery case described in any one of (10) to (14), wherein the bracket portion and the cross member are joined by welding at the opening.
This configuration makes it possible to eliminate problems such as the inability to join the cross member to the steel plate joined to the wall surfaces even if the dimensions between the pair of wall surfaces at the position where the cross member is connected differ depending on the dimensional accuracy of the frame-shaped portion. Furthermore, the cross member and the steel plate joined to the wall surfaces can be reliably joined using the bracket portion, thereby improving the strength of the battery case.

(16) The steel plate is formed with a bracket portion extending toward the cross member,
the bracket portion has an inner surface capable of abutting against an outer surface of the cross member and is capable of sliding relatively on the outer surface of the cross member;
The method for manufacturing a battery case described in any one of (10) to (14), wherein the bracket portion and the cross member are joined by welding.
This configuration makes it possible to eliminate problems such as the inability to join the cross member to the steel plate joined to the wall surfaces even if the dimensions between the pair of wall surfaces at the position where the cross member is connected differ depending on the dimensional accuracy of the frame-shaped portion. Furthermore, the cross member and the steel plate joined to the wall surfaces can be reliably joined using the bracket portion, thereby improving the strength of the battery case.

(17) A step of assembling the bracket portion of the steel plate to at least one end portion of the cross member;
a step of placing the cross member to which the bracket portion is attached relative to the frame-shaped portion;
a step of joining the bracket portion to the cross member by welding;
a step of joining the steel plate to the wall surface of the frame-shaped portion by welding;
The method for manufacturing a battery case according to (15) or (16), comprising:
According to this configuration, the cross member can be firmly fixed to the frame-like portion via the steel plate.

(18) The method for manufacturing a battery case according to any one of (10) to (14), further comprising joining the steel plate to the wall surface of the frame-shaped portion by welding, and then joining the steel plate to one end of the cross member in a longitudinal direction by welding.
According to this configuration, the cross member can be firmly fixed to the frame-like portion via the steel plate.

(19) The method for manufacturing a battery case according to any one of (10) to (14), further comprising joining the steel plate to one longitudinal end of the cross member by welding, and then joining the steel plate to the wall surface of the frame-shaped portion by welding.
According to this configuration, the cross member can be firmly fixed to the frame-like portion via the steel plate.

(20) One end surface in the longitudinal direction of the cross member is inclined with respect to a height direction of the steel plate or an extension direction of the wall surface,
A steel wedge-shaped member is disposed between the one end surface of the cross member and the steel plate,
The method for manufacturing a battery case described in any one of (10) to (14), wherein the wedge-shaped member is joined to the cross member and the steel plate by welding, respectively.
This configuration makes it possible to eliminate problems such as the inability to join the cross member to the steel plate joined to the wall surfaces even if the dimensions between the pair of wall surfaces at the position where the cross member is connected differ depending on the dimensional accuracy of the frame-shaped portion. Furthermore, the cross member and the steel plate joined to the wall surfaces can be reliably joined using the wedge-shaped member, thereby improving the strength of the battery case.

(21) The method for manufacturing a battery case according to (10), further comprising selecting the steel plate having a thickness corresponding to a gap between the wall surface of the frame-shaped portion and the cross member, and arranging the steel plate in the gap.
With this configuration, even if the dimensions between a pair of wall surfaces at the position where the cross member is connected differ depending on the dimensional accuracy of the frame-shaped portion, a steel plate having a thickness corresponding to the gap between the wall surfaces and the cross member is selected and positioned, thereby eliminating problems such as the inability to connect the cross member to the wall surface.

(22) The method for manufacturing a battery case described in any one of (11) to (14), further comprising selecting a plate-shaped member having a thickness corresponding to a gap between the cross member and the steel plate, and arranging the plate-shaped member in the gap.
With this configuration, even if the dimensions between a pair of wall surfaces at the position where the cross member is connected differ depending on the dimensional accuracy of the frame-shaped portion, a plate-shaped member having a thickness corresponding to the gap between the steel plate and the cross member is selected and positioned, thereby eliminating problems such as the inability to connect the cross member to a wall surface.

10 Battery case 11 Frame portion 12 First frame member 12a Side surface (wall surface)
12b, 12c Step portion 13 Second frame member 14 First rib 14a First base portion 14b First protruding portion 15 Second rib 15a Second base portion 15b Second protruding portion 16 First groove portion 17 Second groove portion 18 Second hole 20 Cross member 21 Flange portion 22 Third hole 23 Convex portion 24 Side surface (outer surface)
25 Opening 25a Edge 26 Top surface 27 One end surface 30 Steel plate 30a Steel plate piece 31 First hole 32 Projection 33 Bracket portion 33a Outer surface 33b Inner surface 35 Plate-like member 36, 37 Plate 40 Bed-like portion 50 Aluminum MIG welding device 60 Steel MAG welding device 70 Hammer 71 Bolt (fastening member)
75 Wedge-shaped member 75a First side surface 75b Second side surface 76 Through hole 80 Joining auxiliary member 81 Insertion portion 83 Non-insertion portion 85 Hollow portion 90 Dissimilar material arc spot welding device A, B Gap G Shielding gas H Gap S Air gap WA Aluminum weld metal WA1 Shank portion WA2 Head portion WA3 Flange portion WS Steel weld metal

Claims (16)

A rectangular frame portion,
At least one cross member extending toward a pair of parallel wall surfaces of the frame portion so as to divide the inside of the frame portion;
Equipped with
the frame-shaped portion is made of aluminum or an aluminum alloy,
The cross member is made of steel;
A battery case in which a steel plate is joined to the wall surface of the frame-shaped portion by welding,
The steel plate has a first hole facing the wall surface,
The steel plate and the wall surface are joined by welding at the first hole,
the first hole is filled with an aluminum or aluminum alloy weld metal;
A battery case characterized in that the steel plate and one longitudinal end of the cross member are joined by welding. A first rib and a second rib are provided on the upper and lower parts of the wall surface,
The first rib has a first base portion extending from the wall surface toward the cross member and a first protruding portion protruding downward from a tip end of the first base portion,
A first groove is defined between the wall surface, the first base portion, and the first protruding portion,
The second rib has a second base portion extending from the wall surface toward the cross member and a second protruding portion protruding upward from a tip of the second base portion,
A second groove is defined between the wall surface, the second base portion, and the second protruding portion,
The battery case according to claim 1 , wherein the steel plate is disposed in the first groove portion and the second groove portion. A protrusion portion protruding toward the cross member is formed on the steel plate between the first protruding portion and the second protruding portion,
The battery case according to claim 2 , wherein the protrusion and the one end of the cross member in the longitudinal direction are joined by welding. A convex portion protruding toward the steel plate is formed between the first protruding portion and the second protruding portion at one end of the cross member in the longitudinal direction,
The battery case according to claim 2 , wherein the protrusion and the steel plate are joined by welding. The steel plate is formed with a bracket portion extending toward the cross member,
the bracket portion has an outer surface that can come into contact with an inner surface of the cross member and is relatively slidable inside the cross member;
The cross member has an opening facing the outer surface of the bracket portion disposed therein,
The battery case according to claim 1 or 2, wherein the bracket portion and the cross member are joined by welding at the opening portion. The steel plate is formed with a bracket portion extending toward the cross member,
the bracket portion has an inner surface capable of abutting against an outer surface of the cross member and is capable of sliding relatively on the outer surface of the cross member;
The battery case according to claim 1 or 2, wherein the bracket portion and the cross member are joined by welding. One end surface of the cross member in the longitudinal direction is inclined with respect to the height direction of the steel plate or the extension direction of the wall surface,
A steel wedge-shaped member is disposed between the one end surface of the cross member and the steel plate,
The battery case according to any one of claims 1 to 3, wherein the wedge-shaped member is joined to the cross member and the steel plate by welding. The floor portion is connected to the frame portion and forms a floor surface.
The floor portion is made of aluminum or an aluminum alloy,
The cross member and the floor portion are joined by welding ,
The cross member has a flange portion extending along the floor portion,
The flange portion has a third hole facing the floor portion,
The flange portion and the floor portion are joined by welding at the third hole,
The battery case according to any one of claims 1 to 7 , wherein the third hole is filled with a weld metal of aluminum or an aluminum alloy . A rectangular frame portion,
At least one cross member extending toward a pair of parallel wall surfaces of the frame portion so as to divide the inside of the frame portion;
Equipped with
The frame-shaped portion is made of aluminum or an aluminum alloy,
The cross member is made of steel;
A manufacturing method of a battery case in which a steel plate is joined to the wall surface of the frame-shaped portion by welding,
The steel plate has a first hole facing the wall surface,
The first hole is filled with a weld metal of aluminum or an aluminum alloy to join the steel plate and the wall surface;
A method for manufacturing a battery case, characterized in that the steel plate and one longitudinal end of the cross member are joined by welding. A first rib and a second rib are provided on the upper and lower parts of the wall surface,
The first rib has a first base portion extending from the wall surface toward the cross member and a first protruding portion protruding downward from a tip end of the first base portion,
A first groove is defined between the wall surface, the first base portion, and the first protruding portion,
The second rib has a second base portion extending from the wall surface toward the cross member and a second protruding portion protruding upward from a tip of the second base portion,
A second groove is defined between the wall surface, the second base portion, and the second protruding portion,
The method for manufacturing a battery case according to claim 9 , wherein the steel plate is disposed in the first groove portion and the second groove portion. The method for manufacturing a battery case according to claim 10 , wherein the steel plate is fixed to the first groove portion and the second groove portion by plastically deforming the first protruding portion and the second protruding portion toward the steel plate. A second hole facing the steel plate is formed in each of the first protruding portion and the second protruding portion,
The method for manufacturing a battery case according to claim 10 , wherein the steel plate is fixed to the first groove portion and the second groove portion by fastening a fastening member toward the steel plate through the second hole. The steel plate is formed with a bracket portion extending toward the cross member,
the bracket portion has an outer surface that can come into contact with an inner surface of the cross member and is relatively slidable inside the cross member;
The cross member has an opening facing the outer surface of the bracket portion disposed therein,
The method for manufacturing a battery case according to any one of claims 9 to 12 , wherein the bracket portion and the cross member are joined by welding at the opening. The steel plate is formed with a bracket portion extending toward the cross member,
the bracket portion has an inner surface capable of abutting against an outer surface of the cross member and is capable of sliding relatively on the outer surface of the cross member;
The method for manufacturing a battery case according to any one of claims 9 to 12 , wherein the bracket portion and the cross member are joined by welding. a step of assembling the bracket portion of the steel plate to at least one end of the cross member;
a step of placing the cross member to which the bracket portion is attached relative to the frame-shaped portion;
a step of joining the bracket portion to the cross member by welding;
a step of joining the steel plate to the wall surface of the frame-shaped portion by welding;
The method for manufacturing a battery case according to claim 13 or 14 , comprising: The method for manufacturing a battery case according to claim 9 , further comprising the steps of selecting the steel plate having a thickness corresponding to the gap between the wall surface of the frame portion and the cross member, and placing the steel plate in the gap.

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