Side frame of the battery case

Abstract

The present invention relates to a side frame of a battery case that can simultaneously achieve weight reduction and cost reduction while adequately protecting a battery cell from external impact, and can significantly reduce welds to fundamentally solve defects in the welds, and includes a first frame portion formed to have an open cross section, and a second frame portion disposed within the first frame portion to close the open cross section of the first frame portion and coupled to the first frame portion, the first frame portion and the second frame portion being formed of different materials, and each corner portion of the first frame portion and the second frame portion can be bent.

Description

Technical Field

[0001] The present invention relates to a side frame of a battery case made of different materials, which can sufficiently protect a battery cell from external impacts, achieve weight reduction and cost reduction simultaneously compared with a single material, and significantly reduce welding parts to fundamentally solve defects in welding parts.

Background Art

[0002] For example, a battery system used in an electric vehicle uses various load-bearing members to protect internal battery cells.

[0003] A typical example is the side frame of a battery case. The side frame surrounds the battery cell while forming side walls that partition the space in the battery case where the battery cell is mounted, protecting the battery cell from external impacts.

[0004] In addition, the side frame enables a mounting frame necessary for fixing the battery case to the vehicle body to be mounted on the side surface.

[0005] Generally, the side frame and the battery case are mainly manufactured using aluminum or an aluminum alloy. This is because aluminum has the advantages of being lightweight in itself and having a high degree of freedom in forming, for example, a side frame with a complex cross-section can be easily manufactured using an extrusion process.

[0006] However, despite the above advantages, aluminum or an aluminum alloy is much more expensive than steel, and the extrusion process has a very low production yield, resulting in increased costs.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] The object of the present invention is to provide a side frame of a battery case made of different materials so as to sufficiently protect a battery cell from external impacts, simultaneously achieve weight reduction and cost reduction, and significantly reduce the welding parts to fundamentally solve the defects of the welding parts.

Means for Solving the Problems

[0009] A side frame of a battery case according to an embodiment of the present invention includes a first frame portion formed to have an open cross-section, and a second frame portion disposed within the first frame portion to close the open cross-section of the first frame portion and coupled to the first frame portion. The first frame portion and the second frame portion are formed of different materials, and each corner portion of the first frame portion and the second frame portion can be bent.

Effects of the Invention

[0010] According to the present invention, by forming the side frame with different materials, the advantages of the extruded material and the rigid material can be uniformly utilized, not only exhibiting sufficient structural rigidity, but also achieving weight reduction and cost reduction.

[0011] Also, according to the present invention, by forming the corner portion by bending without welding parts, the welding parts in the side frame can be significantly reduced, the defects of the welding parts can be fundamentally solved, and at the same time, the impact resistance can be enhanced.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Mode for Carrying Out the Invention

[0013] Hereinafter, the present invention will be described in detail through exemplary drawings. When assigning reference numerals to the components of each drawing, it should be noted that for the same components, the same numerals are used as much as possible even if they are shown on different drawings.

[0014] FIG. 1 is a perspective view showing a battery case to which a side frame according to an embodiment of the present invention is applied.

[0015] The battery case can include a first case 1 and a second case 2.

[0016] The first case 1 can include a base plate 20 and a side frame 10 surrounding the base plate. The base plate of the first case can act as a floor material for supporting battery cells, and the side frame can constitute the side wall of the first case.

[0017] The base plate 20 and the side frame 10 can be joined together integrally by welding or the like. Thereby, the first case 1 can have a space portion within a side frame that forms a closed cross-section around the base plate.

[0018] For example, at least one side frame 10 is provided to surround the base plate 20. Both ends of the side frame can be selectively or as required, joined by welding or the like after contacting the corresponding ends of the other side frame.

[0019] The second case 2 can include a simple flat plate or a main body 3 having a hollow portion and a flange 4 formed at an end of the main body. When the main body has a hollow portion, the second case can be manufactured by molding a material having appropriate strength into a predetermined shape using a press.

[0020] By joining the first and second cases 1 and 2 such that the main body 3 of the second case 2 covers the space portion of the first case 1, a storage space for storing battery cells can be formed inside.

[0021] The joining of the first and second cases 1 and 2 can be performed by bolting, for example, by fastening bolts (not shown) after the flange 4 formed at the end of the main body 3 and the side frame 10 overlap each other.

[0022] On the other hand, in evaluating the performance of the battery case, the evaluation against side collisions is important. The evaluation against side collisions is performed by applying an impact to the side surface of the side frame having a substantially rectangular cross section of the battery case with a cylinder made of a rigid body and making it withstand a certain level of collision load. If there is no contact between the side frame and the battery cell until a certain level of collision load is reached, it is evaluated that the battery case satisfies the collision performance.

[0023] In the evaluation against lateral collisions, the deformation mode of the side frame can be roughly classified into a buckling mode at the initial stage of the collision and a bending mode at the later stage of the collision.

[0024] The initial stage of the collision is the first collision point within several milliseconds (msec). At this time, concentrated deformation occurs at the contact part of the side frame with the rigid body. In the initial stage of the collision, the horizontal members in the width direction (Y direction) of the cross-sectional structure of the side frame receive concentrated forces, and when buckling occurs in the horizontal members, the buckling point becomes a plastic hinge, and the horizontal members will lose their function as structural members.

[0025] In order to minimize such buckling and plastic hinge phenomena, the thickness of the material constituting the side frame must be increased. For example, aluminum materials can be designed with a greater thickness because they are lighter than steel materials. However, since steel materials can only be made thinner for weight reduction, side frames made of steel materials are very vulnerable to the buckling mode in the initial stage of the collision.

[0026] Therefore, side frames made of steel materials are heavier and have inferior performance compared to side frames made of aluminum materials or aluminum alloy materials.

[0027] When the above-mentioned buckling mode in the initial stage of the collision ends, the cross-sectional structure of the side frame collapses rapidly, and the concentrated deformation changes to bending deformation of the entire side frame. That is, the deformation of the side frame switches to a bending mode in the form of three-point bending. At this time, the role of the vertical members in the height direction (Z direction) of the cross-sectional structure of the side frame becomes much greater than that of the horizontal members.

[0028] In the bending mode, the vertical members are subjected to maximum compression or tension, and thus the strength of the vertical members becomes an important factor. For example, side frames made of high-strength steel materials can increase their bending resistance and are advantageous in withstanding the compressive stress or tensile stress generated in the bending mode.

[0029] Due to such deformation characteristics of the side frame, the thickness of the horizontal members is important in the initial stage of the collision, and the strength of the vertical members becomes an important factor in the later stage of the collision. However, there is no single material that can satisfy all of the above two conditions.

[0030] In addition, a conventional battery case is provided with a mount frame that is coupled to one side of the side frame to fix the battery case to the vehicle body.

[0031] Here, at the initial stage of a collision, the member that first comes into contact with the rigid body is the mount frame. If the side frame is designed to be sufficiently robust, the buckling mode at the initial stage of the collision occurs in the mount frame rather than the side frame.

[0032] Conversely, if the mount frame is stronger than the side frame, the buckling mode occurs in the side frame instead.

[0033] As a result, although mechanical considerations such as the buckling mode at the initial stage of the collision are also required for the mount frame, usually, since the mount frame and the side frame are separately manufactured and joined by welding or the like, the mechanical balance between these mount frame and side frame is not achieved, so the battery case has only structural weaknesses.

[0034] Therefore, in the side frame of the battery case according to the present invention, different materials are applied to the horizontal member and the vertical member, and the mount frame is integrated with the side frame to satisfy the mechanical characteristics required for the side frame and maximize the structural efficiency.

[0035] FIG. 2 is a perspective view showing a side frame according to an embodiment of the present invention, and FIG. 3 is a cross-sectional view taken along line A-A' of FIG. 2.

[0036] A side frame 10 according to an embodiment of the present invention can include a first frame portion 30 and a second frame portion 40.

[0037] The first frame portion 30 can be formed by bending a single plate material having a predetermined width and length a plurality of times so as to have, for example, a horizontally oriented T-shaped cross section. Thereby, the first frame portion can have a hollow portion with an open cross section inside.

[0038] The first frame portion 30 includes a first vertical member 31 having a first height H1, a second vertical member 32 spaced from the first vertical member by a first length L1 and having a second height H2 shorter than the first height, a third vertical member 33 spaced from the second vertical member 32 in the height direction and spaced from the first vertical member by a second length L2 and having a third height H3 shorter than the first height, a first horizontal member 34 connecting one end of the first vertical member and one end of the second vertical member, a second horizontal member 35 connecting the other end of the first vertical member and one end of the third vertical member, a third horizontal member 36 having one end connected to the other end of the second vertical member and extending in the width direction by a third length L3, and a fourth horizontal member 37 having one end connected to the other end of the third vertical member and extending in the width direction by a fourth length L4.

[0039] The first frame portion 30 can be integrally formed by machining a single plate material such as metal.

[0040] For example, after the plate material extends in the width direction (-Y direction) by the third length L3 from one end to form the third horizontal member 36, it is bent once in the first direction (counterclockwise in FIG. 3). Then, after descending by the second height H2 in the height direction (-Z direction) to form the second vertical member 32, it is bent once in the second direction (clockwise in FIG. 3) opposite to the first bending direction. After extending in the width direction (-Y direction) by about the first length L1 to form the first horizontal member 34, it is further bent once in the second direction in the same manner.

[0041] Then, after rising by the first height H1 in the height direction (Z direction) to form the first vertical member 31, it is bent once in the second direction. After extending in the width direction (Y direction) by the second length L2 to form the second horizontal member 35, it is further bent once in the second direction in the same manner. Then, after descending by the third height H3 in the height direction (-Z direction) to form the third vertical member 33, it is bent once in the first direction which is the first bending direction. After that, it extends in the width direction (Y direction) by the fourth length L4 to form the fourth horizontal member 37.

[0042] In this way, after being extended by a predetermined length and then the bending method is repeated to form an open cross-section together with a desired number of horizontal members (34 to 37) and vertical members (31 to 33), the plate material terminates at the other end.

[0043] As a result, the first frame portion 30 can include a wall portion 38 having a first height H1 and a protruding portion 39 extending from the wall portion by a third length L3 or a fourth length L4 on one side in the width direction (Y direction).

[0044] The wall portion 38 can be partitioned into a substantially first vertical member 31, a first horizontal member 34, a second vertical member 32, a second horizontal member 35, and a third vertical member 33. The protruding portion 39 can be formed by a third horizontal member 36 and a corresponding fourth horizontal member 37.

[0045] The wall portion 38 corresponds to an existing side frame, while the protruding portion 39 corresponds to an existing mount frame. Eventually, in the side frame 10 according to an embodiment of the present invention, the mount frame can be integrated into the side frame and formed integrally with the side frame.

[0046] Also, in the first frame portion 30, the third horizontal member 36 and the fourth horizontal member 37 are separated from each other by a difference between the first height H1 and the height (H2 + H3) obtained by adding the second height H2 and the third height H3, and at the same time, an open portion 29 can be provided between the end of the third horizontal member and the end of the fourth horizontal member.

[0047] As a result, the protruding portion 39 of the first frame portion 30 can include the open portion 29, and the protruding portion and the open portion have a height (H1 - (H2 + H3)) corresponding to the difference between the first height H1 and the height (H2 + H3) obtained by adding the second height H2 and the third height H3.

[0048] Here, the plurality of horizontal members (34 to 37) and the plurality of vertical members are not necessarily formed completely horizontally or vertically, and may have an inclination. As a result, the separation distance, the height difference, etc. may vary.

[0049] Alternatively, optionally, the first length L1 and the second length L2 may be the same as each other, or the second height H2 and the third height H3 may be the same as each other, or the third length L3 and the fourth length L4 may be the same as each other.

[0050] The first frame portion 30 formed in this way can constitute the outside of the side frame 10.

[0051] FIG. 5 is a plan view showing the stage of forming the corner portion of the first frame portion.

[0052] The first frame portion 30 can be formed long so as to have a predetermined length with an open cross section by bending, roll forming, press forming, etc.

[0053] Next, the mounting holes 11 necessary for fixing to the vehicle body and the notch portions 12 used for smoothly forming the corner portions 13 are formed by punching or cutting.

[0054] Finally, using an appropriate bending device, the first frame portion 30 is bent to the side where the notch portion 12 spreads so as to have an angle of about 90 degrees to form the corner portion 13.

[0055] Thereby, an integrated single first frame portion 30 or two first frame portions 30 having substantially the same or symmetric "C" shape can be formed.

[0056] One side surface such as the bottom surface of the first cross member 34 of the first frame portion 30 can be coupled to the base plate 20 by joining such as welding. In this way, even if the first frame portion is only coupled to the base plate by joining such as welding, the first frame portion itself can omit the welded portion.

[0057] Optionally or as required, the first frame part 30 itself can be welded at a maximum of two locations. Further, conventionally, the welded part between the frame members was located at a complex corner, but the first frame part of the present invention can be changed so that the welded part is located at a simple straight part, reducing the number of welded parts and facilitating welding.

[0058] Also, by forming the corner part 13 of the first frame part 30 by bending without welding, the number of parts and the number of processes of the first frame part can be significantly reduced.

[0059] The second frame part 40 can be formed as a pipe member with a substantially square cross-section having a predetermined length and having a constant height and a constant width. Thereby, the second frame part can have a hollow part with a closed cross-section inside.

[0060] The second frame part can include a first lateral member 41 and a second lateral member 43 spaced apart from each other in the height direction (Z direction), and a first longitudinal member 42 and a second longitudinal member 44 spaced apart from each other in the width direction (Y direction) and connecting the first lateral member and the second lateral member.

[0061] Here, the thicknesses of the first lateral member 41 and the second lateral member 43 can be formed thicker than the thicknesses of the first longitudinal member 42 and the second longitudinal member 44. For example, the lateral members can have a thickness more than three times that of the longitudinal members.

[0062] However, the relative thicknesses of the lateral members 41, 43 with respect to the longitudinal members 42, 44 are not necessarily limited to the above example.

[0063] At least the lateral members 41, 43 of the second frame part 40 can have a thickness thicker than that of the first frame part 30.

[0064] The height of the second frame part 40 corresponds to the height of the opening part 29 of the first frame part 30, and the width of the second frame part can correspond to the length (L1 + L3) obtained by adding the first length L1 of the first horizontal member 31 and the third length L3 of the third horizontal member 33 of the first frame part. Alternatively, the width of the second frame part can correspond to the length (L2 + L4) obtained by adding the second length L2 of the second horizontal member 32 and the fourth length L4 of the fourth horizontal member 34 of the first frame part.

[0065] The second frame part 40 can be arranged at least in alignment with the protruding part 39 within the first frame part 30, and the open cross-section of the first frame part, that is, the opening part 29 can be closed to form the entire side frame 10 with a closed cross-section.

[0066] The second frame part 40 formed and arranged in this way can constitute the interior of the side frame 10.

[0067] FIG. 5 is a cross-sectional view showing a modified example of the second frame part.

[0068] When the required level for collision is high, the second frame part 40 can further include a reinforcing vertical member 45 between the lateral members 41 and 43 (see (a) in FIG. 5).

[0069] Also, the first lateral member 41 and the second lateral member 43 can have a length in the width direction (Y direction) that extends beyond the distance between the first vertical member 42 and the second vertical member 44 to form an extension part 46 (see (b) in FIG. 5).

[0070] In this case, the extension parts 46 of the lateral members 41 and 43 extending from or further extending beyond the position of the second vertical member 44 can serve as flanges for joining between the first frame part 30 and the second frame part 40, and can also play a role in complementing impact absorption by generating a buckling mode at the extension part at the initial stage of a collision.

[0071] FIG. 6 is a plan view showing the stage of forming the corner part of the second frame part.

[0072] The second frame portion 40 can be formed to be long so as to have a predetermined length with a closed cross section by extrusion or the like.

[0073] Next, using an appropriate bending device, the second frame portion 40 is bent in the same direction at two locations so as to have an angle of approximately 90 degrees to form the corner portion 14.

[0074] Before or after forming the corner portion 14, mounting holes 11 necessary for fixing to the vehicle body or coupling holes necessary for coupling with the first frame portion 30 are formed by drilling.

[0075] As a result, two second frame portions 40 having a substantially "C" shape can be formed identically or symmetrically.

[0076] In this way, welding is not required for the formation of the second frame portion 40, and the second frame portion has the advantage that the welded portion can be omitted.

[0077] Further, by forming the corner portion 14 of the second frame portion 40 by bending without welding, the number of parts and the number of processes of the second frame portion can be significantly reduced.

[0078] In the side frame 10 according to an embodiment of the present invention, the first frame portion 30 and the second frame portion 40 may be formed of different materials from each other.

[0079] For example, the first frame portion 30 can be made of a heavy metal material having a specific gravity of 4 or more, such as steel. The second frame portion 40 can be made of a material having a lower specific gravity than the first frame portion.

[0080] Alternatively, the second frame portion 40 can be made of a material having a higher specific strength than the first frame portion 30.

[0081] More specifically, by adopting ultra-high-strength steel of 1 GPa or higher for the first frame portion 30, an optimal combination for weight reduction of the side frame 10 and further of the battery case can be achieved.

[0082] For example, the first frame portion 30 can be made of a plate material such as 1470 MART (Martensitic) steel or 1180 CP (Complex Phase) steel with a thickness of about 0.5 mm to 1.5 mm produced by the applicant.

[0083] Here, 1470 MART steel is a steel type with a tensile strength of 1,470 MPa or higher and a yield strength of 1,050 MPa or higher, which improves collision safety. 1180 CP steel guarantees a tensile strength of 1180 MPa or higher and a yield strength of 850 MPa or higher, and is a steel type with improved bend formability.

[0084] In addition, the second frame portion 40 can be made of a material that can be formed by extrusion, such as a light metal like aluminum or its alloy, plastic, composite material, etc.

[0085] Thus, since the first frame portion 30 and the second frame portion 40 are formed of different materials, the first frame portion and the second frame portion can be joined to each other by mechanical joining with fixtures such as rivets (e.g., blind rivets), screws (e.g., flow drill screws), etc., and chemical joining with an adhesive 15 such as a structural adhesive.

[0086] When assembling the side frame 10 according to an embodiment of the present invention, first, while relatively moving the separately formed first frame portion 30 and the second frame portion 40 in the width direction (Y direction) with respect to each other, the second frame portion can be fitted into the protruding portion 39 within the first frame portion.

[0087] Next, an adhesive 15 can be interposed between the third horizontal member 36 of the first frame portion 30 and the first lateral member 41 of the second frame portion 40, and between the fourth horizontal member 37 of the first frame portion and the second lateral member 43 of the second frame portion, so that they can be joined to each other.

[0088] Also, an adhesive 15 can be interposed between the first vertical member 31 of the first frame portion 30 and the first vertical member 42 of the second frame portion 40, so that they can be joined to each other.

[0089] Such an adhesive 15 can not only bond the first frame portion 30 and the second frame portion 40, but also, for example, when the first frame portion is formed of a steel material and the second frame portion is formed of an aluminum material, obtain the effect of preventing corrosion caused by direct contact between these different materials.

[0090] Of course, the assembly method is not necessarily limited to the above-described example, and fasteners such as rivets and screws and an adhesive 15 such as a structural adhesive may be combined and used for joining the first frame portion 30 and the second frame portion 40.

[0091] In this way, welding is not required even in the assembly of the first frame portion 30 and the second frame portion 40. In the side frame 10 according to an embodiment of the present invention, there is an advantage that the welded portions can be significantly reduced and the assembly can be facilitated.

[0092] Thereby, in the side frame 10 according to an embodiment of the present invention, the lightweight second frame portion 40 can provide additional horizontal members (i.e., lateral members 41, 43) within the high-strength first frame portion 30 or at least further increase the thickness of the third and fourth horizontal members 36, 37.

[0093] Also, in the side frame 10 according to an embodiment of the present invention, the lightweight second frame portion 40 surrounds the side surfaces of the battery case and the battery cells, and can improve the structural stability.

[0094] The side frame 10 according to an embodiment of the present invention includes a first frame portion 30 and a second frame portion 40 made of different materials. A lightweight material is arranged in a portion that requires a thick horizontal member, and a high-strength material is arranged in a vertical member that requires strength. In addition, a mounting frame is integrated with the side frame, and it has the advantage of realizing a very efficient structure with high performance and low cost.

[0095] Thereby, at the initial stage of a collision, the phenomenon of buckling and plastic hinges can be prevented by the thick horizontal member, and at the later stage of the collision, bending deformation can be dealt with by the high-strength vertical member.

[0096] Also, considering the role of the mounting frame that receives the first impact, the horizontal member is extended to the position of the existing mounting frame, and the outside is surrounded by a high-strength material, so that the mechanical properties can be satisfied even by the side frame alone, and the efficiency of the structure can be maximized.

[0097] The applicant of the present application has performed performance analysis on the side frame according to an embodiment of the present invention through simulation.

[0098] For example, a cylinder made of a rigid body is used to impact the side surface of the side frame, and it is related to the performance of withstanding a certain level of collision load. A comparison is made between a conventional side frame made of a single material and a side frame made of different materials according to an embodiment of the present invention.

[0099] As a result, it was confirmed that the side frame of the present invention exhibits more than twice the performance despite having a similar weight.

[0100] Therefore, when designing to achieve the same level of performance, the side frame made of different materials according to an embodiment of the present invention can significantly reduce the weight compared to the side frame made of a single material. According to the analysis results by simulation, it was confirmed that a weight reduction effect of up to 20% can be obtained.

[0101] According to the present invention as described above, by forming the side frame with different materials, the advantages of the extruded material and the rigid material can be uniformly utilized, not only exhibiting sufficient structural rigidity, but also achieving weight reduction and cost reduction.

[0102] Further, according to the present invention, by forming the corner portion by bending without welding, the welding portion in the side frame can be significantly reduced, the defects of the welding portion can be fundamentally solved, and at the same time, the impact resistance is enhanced.

[0103] The above description merely exemplarily explains the technical idea of the present invention. Those with ordinary knowledge in the technical field to which the present invention pertains can make various modifications and deformations without departing from the essential characteristics of the present invention.

[0104] It is clarified that in this specification and the drawings, the horizontal member of the first frame portion, the lateral member of the second frame portion, the vertical member of the first frame portion, and the longitudinal member of the second frame portion are used merely for the purpose of differentiating terms and do not have other technical meanings.

[0105] Therefore, the embodiments disclosed in this specification and the drawings are for the purpose of explanation rather than for limiting the technical idea of the present invention, and the scope of the technical idea of the present invention is not limited by such embodiments. The protection scope of the present invention should be interpreted by the following claims, and all technical ideas within the equivalent scope should be construed as being included in the scope of the rights of the present invention.

Explanation of Reference Numerals

[0106] 1: First case 2: Second case 3: Main body 4: Flange 10: Side frame 11: Mounting hole 12: Notch portion 13, 14: Corner portion 15: Adhesive 20: Base plate 29: Open part 30: First frame part 31: First vertical member 32: Second vertical member 33: Third vertical member 34: First horizontal member 35: Second horizontal member 36: Third horizontal member 37: Fourth horizontal member 38: Wall part 39: Protrusion 40: Second frame part 41: First horizontal direction member 42: First vertical direction member 43: Second horizontal direction member 44: Second vertical direction member 45: Reinforcing vertical direction member 46: Extension part

Claims

1. A first frame portion formed to have an open cross section, A second frame portion disposed within the first frame portion so as to close the open cross section of the first frame portion and coupled to the first frame portion and including The first frame portion and the second frame portion are formed of different materials, Each corner portion of the first frame portion and the second frame portion is bent. The first frame portion, in its vertical cross section, A first vertical member extending in the height direction and having a first height, A second vertical member spaced apart from the first vertical member by a first length in the width direction and extending in the height direction and having a second height shorter than the first height, A third vertical member spaced apart from the second vertical member in the height direction and spaced apart from the first vertical member by a second length in the width direction and extending in the height direction and having a third height shorter than the first height, A first horizontal member connecting the lower end of the first vertical member and the lower end of the second vertical member, A second horizontal member connecting the upper end of the first vertical member and the upper end of the third vertical member, A third horizontal member having one end connected to the upper end of the second vertical member and extending outward in the width direction by a third length, A fourth horizontal member having one end connected to the lower end of the third vertical member and extending outward in the width direction by a fourth length and including A side frame of a battery case in which an open portion is formed between the other end of the third horizontal member and the other end of the fourth horizontal member.

2. The first frame portion A wall portion having the first height, A protruding portion extending from the wall portion by the third length or the fourth length to one side in the width direction and including The side frame of the battery case according to claim 1, wherein the open portion is formed on one side of the protruding portion.

3. The second frame part is arranged at least at the protruding part within the first frame part and closes the opening part, and is the side frame of the battery case according to Claim 2.

4. The second frame part is coupled by mechanical joining with a fixture or chemical joining with an adhesive within the first frame part, and is the side frame of the battery case according to Claim 3.

5. At the corner part of the first frame part, a notch part for bending is formed, and is the side frame of the battery case according to Claim 1.

6. In the vertical cross-section of the second frame part, a first lateral member and a second lateral member that extend in the width direction while being spaced apart from each other in the height direction, a first longitudinal member and a second longitudinal member that are spaced apart from each other in the width direction and connect the first lateral member and the second lateral member are included, and is the side frame of the battery case according to Claim 1.

7. The thicknesses of the first lateral member and the second lateral member are formed to be thicker than the thicknesses of the first longitudinal member and the second longitudinal member, and is the side frame of the battery case according to Claim 6.

8. The first lateral member and the second lateral member have a thickness thicker than that of the first frame part, and is the side frame of the battery case according to Claim 6.

9. The second frame part further includes a reinforcing longitudinal member between the first lateral member and the second lateral member, and is the side frame of the battery case according to Claim 6.

10. The first lateral member and the second lateral member form an extension part that extends more than the distance between the first longitudinal member and the second longitudinal member, and is the side frame of the battery case according to Claim 6.

11. The second frame part is made of a material with a lower specific gravity than that of the first frame part, and is the side frame of the battery case according to any one of claims 1 to 10.

12. The second frame part is made of a material having a higher specific strength than that of the first frame part, and is the side frame of the battery case according to any one of claims 1 to 10.

13. The first frame part is formed by bending a single plate material. The second frame part is formed by extrusion, and is the side frame of the battery case according to any one of claims 1 to 10.

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