Structural members

Abstract

To provide a structural member for a vehicle body that can reduce the number of parts in the battery unit and its surrounding structure. [Solution] The structural member (10) comprises a lid (111) and a cross member (12). The cross member (12) extends in the width direction of the lid (111). The cross member (12) includes a top plate (121), vertical walls (122a, 122b), and flanges (123a, 123b). The vertical walls (122a, 122b) are connected to the top plate (121) via ridges (124a, 124b), respectively. The flanges (123a, 123b) are connected to the vertical walls (122a, 122b) on the opposite side of the top plate (121). The flanges (123a, 123b) are joined to the lid (111). The reduction in thickness of the top plate (121) based on the thickness of the flange (123a, 123b) is between 2.0% and 30.0%.

Description

Technical Field

[0001] The present disclosure relates to a structural member for a vehicle body.

Background Art

[0002] For example, in electric vehicles, hybrid vehicles, etc., a battery unit is mounted. The battery unit is generally disposed below the floor panel in the vehicle body. The battery unit includes, for example, a battery module and a battery case (housing case) as described in Patent Document 1. The battery module includes a plurality of battery cells. The battery case houses the battery module. The battery case includes a case body (lower case) and a lid body (upper case).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In recent years, in vehicle bodies such as automobiles, reduction of greenhouse gas (life cycle GHG) emissions throughout the life cycle of the vehicle body has been required. In order to reduce life cycle GHG emissions, it is necessary to promote integration of parts to reduce the number of parts and omit processes during vehicle body manufacturing. It is also preferable to proceed with integration of parts and reduce the number of parts for the battery unit and its peripheral structure.

[0005] An object is to provide a structural member for a vehicle body that can reduce the number of parts in the battery unit and its peripheral structure.

Means for Solving the Problems

[0006] The structural member for a vehicle body according to this disclosure comprises a battery case cover and a cross member. The cross member includes a top plate, two vertical walls, and two flanges. The top plate faces the cover with a gap between them. The vertical walls are connected to the top plate via their edges. The flanges are connected to the vertical walls on the opposite side of the top plate. The flanges are joined to the cover. The cross member extends in the width direction of the cover. The reduction in thickness at the center of the top plate, based on the thickness of the flanges, is 2.0% or more and 30.0% or less. [Effects of the Invention]

[0007] According to the structural member for the vehicle body described herein, the number of parts in the battery unit and its surrounding structure can be reduced. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a perspective view showing the schematic configuration of a structural member according to the embodiment. [Figure 2] Figure 2 is a cross-sectional view taken along line II-II of the structural member shown in Figure 1. [Figure 3A] Figure 3A is a schematic diagram illustrating an example of a manufacturing method for the structural members shown in Figures 1 and 2. [Figure 3B] Figure 3B is a schematic diagram illustrating an example of a manufacturing method for the structural members shown in Figures 1 and 2. [Figure 3C] Figure 3C is a schematic diagram illustrating an example of a manufacturing method for the structural members shown in Figures 1 and 2. [Figure 3D] Figure 3D is a schematic diagram illustrating an example of a manufacturing method for the structural members shown in Figures 1 and 2. [Figure 3E] Figure 3E is a schematic diagram illustrating an example of a manufacturing method for the structural members shown in Figures 1 and 2. [Figure 4] Figure 4 is a partial cross-sectional view of a structural member manufactured by the manufacturing method shown in Figures 3A to 3E. [Figure 5]Figure 5 is a partial cross-sectional view of a structural member manufactured by the manufacturing methods shown in Figures 3A to 3E, and is different from the structural member shown in Figure 4. [Modes for carrying out the invention]

[0009] The structural member for the vehicle body according to this embodiment comprises a lid for a battery case and a cross member. The cross member includes a top plate, two vertical walls, and two flanges. The top plate faces the lid with a gap between them. The vertical walls are each connected to the top plate via their edges. The flanges are connected to the vertical walls on the opposite side of the top plate. The flanges are joined to the lid. The cross member extends in the width direction of the lid. The rate of thickness reduction at the center of the top plate, based on the thickness of the flanges, is 2.0% or more and 30.0% or less (first configuration).

[0010] In the structural member relating to the first configuration, a cross member is joined to the lid for the battery case. Therefore, the lid can also serve as the floor panel of the vehicle body. Thus, the number of parts in the vehicle body can be reduced compared to the case where the lid for the battery case is provided separately from the floor panel.

[0011] Furthermore, in the structural members relating to the first configuration, the battery case cover and the cross member are integrally molded, for example, using hydraulic or blow molding. In this case, the reduction in plate thickness at the center of the top plate of the cross member, based on the plate thickness of the flange, is between 2.0% and 30.0%. By integrally molding the cover, which also serves as the floor panel, and the cross member, the number of parts in the vehicle body can be further reduced.

[0012] Therefore, in the structural members relating to the first configuration, the number of parts in the battery unit and its surrounding structure can be reduced. As a result, the manufacturing process of the vehicle body can be streamlined, and life cycle GHG emissions can be reduced. Furthermore, the vehicle body can be made lighter by reducing the number of parts.

[0013] When forming a cross member by general press forming, almost no reduction in plate thickness occurs in the top plate, while a relatively large reduction in plate thickness occurs in the ridge line portion. On the other hand, in the structural member according to the first configuration, for example, by integrally forming the cross member with the lid body using hydraulic pressure or blow forming, a reduction in plate thickness occurs in the top plate. Specifically, the reduction rate of the plate thickness at the center of the top plate based on the plate thickness of the flange is 2.0% or more and 30.0% or less. Thus, by causing a reduction in plate thickness in the top plate, an increase in the reduction rate of the plate thickness at the boundary between each vertical wall and the ridge line portion is suppressed. Further, by dispersing the reduction in plate thickness up to the top plate, the reduction in plate thickness of the ridge line portion can be suppressed, and the collision resistance performance of the member can be improved.

[0014] In the structural member according to the first configuration, the reduction rate of the plate thickness at the center of the top plate based on the plate thickness of the flange may be 3.5% or more (second configuration).

[0015] In the structural member according to the first or second configuration, each of the flanges may be joined to the lid body by spot welding. When viewed in a cross section perpendicular to the width direction of the lid body, the portion where the dots of at least one spot weld are arranged on the surface of the flange located on the opposite side of the lid body may have a concave shape with respect to the other portions of the surface of the flange (third configuration).

[0016] In the structural member according to the third configuration, when viewed in a cross section perpendicular to the width direction of the lid body, the portion where the above-mentioned dots are arranged on the surface of the lid body located on the opposite side of the flange may have a concave shape with respect to the other portions of the surface of the lid body (fourth configuration).

[0017] In the structural member according to any one of the first to fourth configurations, the cross member may have a Vickers hardness of 300 HV or more (fifth configuration).

[0018] Hereinafter, embodiments of the present disclosure will be described while referring to the drawings. In these drawings, the same or corresponding components are denoted by the same reference numerals, and the same description will not be repeated.

[0019] [Structural member] FIG. 1 is a perspective view showing a schematic configuration of a structural member 10 according to the present embodiment. Referring to FIG. 1, the structural member 10 is used for a vehicle body such as an electric vehicle or a hybrid vehicle. The structural member 10 includes a lid 111 for a battery case 11 and at least one cross member 12.

[0020] The lid 111 forms part of the battery case 11. The lid 111 is attached to the main body 112 of the battery case 11. The case main body 112 can have, for example, a tray shape. The case main body 112 has a downwardly concave shape when the battery case 11 is mounted on the vehicle body. A plurality of battery cells (not shown) are arranged in the case main body 112. The lid 111 is attached to the case main body 112 so as to seal the opening of the case main body 112. The lid 111 may have a flat plate shape or an uneven shape.

[0021] In the present embodiment, the structural member 10 includes a plurality of cross members 12. Each of the cross members 12 is disposed on the lid 111. Each of the cross members 12 is disposed on the upper surface 111a of the lid 111.

[0022] The cross members 12 are arranged in parallel with a space therebetween. Each of the cross members 12 extends substantially in the width direction of the lid 111. The width direction of the lid 111 substantially coincides with the left - right direction (vehicle width direction) of the vehicle body to which the structural member 10 is applied. That is, each of the cross members 12 extends in the vehicle width direction when the structural member 10 is attached to the vehicle body. Each of the cross members 12 may extend in the width direction of the lid 111 such that at least one end in its longitudinal direction protrudes outward from the lid 111. In the example of the present embodiment, both ends in the longitudinal direction of each cross member 12 protrude outward from the lid 111.

[0023] The cover 111 and the cross member 12 are each formed from a metal plate. Preferably, the cover 111 and the cross member 12 are each formed from a steel plate. The material of the cross member 12 may be the same as or different from the material of the cover 111.

[0024] The cover 111 is made of, for example, a plated steel sheet. Preferably, the cover 111 is made of an aluminum-based plated steel sheet. Each of the cross members 12 may be made of a steel sheet without a plating layer (bare material), or it may be made of a plated steel sheet such as an aluminum-based plated steel sheet. Known aluminum-based plated steel sheets can be used. When both the cover 111 and the cross members 12 are made of aluminum-based plated steel sheets, the amount of aluminum-based plating on the cover 111 may be greater than the amount of aluminum-based plating on the cross members 12.

[0025] Figure 2 is a cross-sectional view of structural member 10 shown in Figure 1, taken along line II-II. In Figure 2, a cross-section (transverse plane) of structural member 10 perpendicular to the longitudinal direction of the cross member 12 (the width direction of the cover 111) is shown.

[0026] Referring to Figure 2, each cross member 12 is separate from the other cross members 12. Each cross member 12 has a substantially hat shape in cross view. Each cross member 12 includes a top plate 121, two vertical walls 122a, 122b, and two flanges 123a, 123b. Each cross member 12 further includes ridge sections 124a, 124b, 125a, 125b.

[0027] The top plate 121 faces the cover 111 with a gap between them. When the structural member 10 is attached to the vehicle body, the top plate 121 faces the upper surface 111a of the cover 111 in the vertical direction (vehicle height direction) of the vehicle body. In a cross-sectional view of the structural member 10, the top plate 121 extends substantially in the longitudinal direction (vehicle length direction) of the vehicle body. The top plate 121 may be flat overall, or it may have recesses or protrusions. Ridge portions 124a and 124b are continuously provided on both sides of the top plate 121.

[0028] The vertical walls 122a and 122b are connected to the top plate 121 via ridge sections 124a and 124b, respectively. That is, ridge section 124a is the corner between the top plate 121 and the vertical wall 122a. Ridge section 124b is the corner between the top plate 121 and the vertical wall 122b. The ridge sections 124a and 124b may have an arc shape in a cross-sectional view of the structural member 10. In a cross-sectional view of the structural member 10, the vertical walls 122a and 122b extend from the top plate 121 toward the lid 111. The vertical walls 122a and 122b may be parallel to each other or non-parallel to each other.

[0029] The flanges 123a and 123b are connected to the vertical walls 122a and 122b, respectively, on the opposite side of the top plate 121. In this embodiment, one flange 123a is connected to the vertical wall 122a via a ridge portion 125a. The other flange 123b is connected to the vertical wall 122b via a ridge portion 125b. That is, the ridge portion 125a is the corner portion between the vertical wall 122a and the flange 123a. The ridge portion 125b is the corner portion between the vertical wall 122b and the flange 123b. The ridge portions 125a and 125b can have an arc shape in a cross-sectional view of the structural member 10.

[0030] The flanges 123a and 123b protrude outward from the vertical walls 122a and 122b. The flanges 123a and 123b are joined to the cover 111. The flanges 123a and 123b are joined to the cover 111, for example, by welding. The flanges 123a and 123b may be joined to the cover 111 by spot welding or the like, or by laser welding or the like.

[0031] The flanges 123a and 123b have a width W. The width W is the length of the surface of the flanges 123a and 123b that is in contact with the cover 111 in a cross-sectional view of the structural member 10. The width W is, for example, 20.0 mm or more and 40.0 mm or less. In each cross member 12, the width W of flange 123a may be the same as or different from the width W of flange 123b. The width W of flanges 123a and 123b in each cross member 12 may be the same as or different from the width W of flanges 123a and 123b in other cross members 12.

[0032] Each of the cross members 12 has a height H. The height H is the maximum distance in the thickness direction of the flanges 123a and 123b from the contact surface of the flanges 123a and 123b with respect to the cover 111 to the outer surface of the top plate 121. The height H is, for example, 20.0 mm or more, preferably 40.0 mm or more, and more preferably 60.0 mm or more. The height H may also be 100.0 mm or less. The height H of each cross member 12 is preferably the same as the height H of the other cross members 12, but they may be different.

[0033] [Method for manufacturing structural members] Figures 3A to 3E are schematic diagrams illustrating an example of a manufacturing method for the structural member 10. The manufacturing method for the structural member 10 includes, for example, a preparation step, a heating step, and a molding step.

[0034] (preparation process) As shown in Figures 3A and 3B, the preparation step involves preparing the material 20. The material 20 includes a first blank 21 and at least one second blank 22. In this embodiment, the material 20 includes a plurality of second blanks 22.

[0035] The first blank 21 is a blank corresponding to the lid 111 for the battery case 11 (Figures 1 and 2). The second blank 22 is a blank corresponding to the cross member 12 (Figures 1 and 2). The second blank 22 is superimposed on the first blank 21.

[0036] Each of the second blanks 22 is joined to the first blank 21. More specifically, the outer periphery of each second blank 22 is joined to the first blank 21, for example, by welding. The outer periphery of each second blank 22 may be joined to the first blank 21 by spot welding or by laser welding.

[0037] The first blank 21 or each of the second blanks 22 may have through holes 23. In this embodiment, the first blank 21 has a plurality of through holes 23. The through holes 23 are formed in the first blank 21 at positions corresponding to both ends in the longitudinal direction of each of the second blanks 22. The through holes 23 may be formed in the first blank 21 at positions corresponding to one end in the longitudinal direction of each of the second blanks 22. Instead of the first blank 21, through holes 23 can also be formed in each of the second blanks 22.

[0038] Each second blank 22 is joined to the first blank 21 at least near the through hole 23, in a portion of the cross member 12 where the height H (Figure 2) is relatively small. In order to ensure the amount of material flow in the molding process described later, each second blank 22 does not need to be joined to the first blank 21 in a portion of the cross member 12 where the height H is relatively large. The first blank 21 and the second blank 22 may each be formed from a single metal plate, or they may include multiple metal plates (subblanks). The metal plate is preferably a steel plate. The steel plate is, for example, a plated steel plate such as an aluminum-plated steel plate. The material of the first blank 21 may be the same as or different from the material of the second blank 22.

[0039] (Heating process) In the heating process, the material 20, including the first blank 21 and the second blank 22, is heated using, for example, a heating furnace. If the first blank 21 and the second blank 22 are each formed from one or more steel plates, the first blank 21 and the second blank 22 are heated to the austenite transformation completion temperature (A c3 It is heated to a temperature of 1.5°C or higher.

[0040] (molding process) As shown in Figures 3C to 3E, in the molding process, the heated material 20 is molded into a structural member 10. In the molding process, hot stamping and blow molding or hydraulic molding are used in combination to mold the material 20 into a structural member 10.

[0041] In the molding process, for example, a mold 30 including a first mold 31 and a second mold 32 can be used. The mold 30 is used, for example, by being mounted on a known press device. Figures 3C to 3E show cross-sections (transverse views) of the material 20 and the mold 30 perpendicular to the longitudinal direction of the second blank 22.

[0042] Referring to Figure 3C, in the molding process, first, the first mold 31 and the second mold 32 are separated, and the material 20 is placed between the first mold 31 and the second mold 32. If the first mold 31 is positioned below the second mold 32, the material 20 may be placed on top of the first mold 31. Then, the first mold 31 and the second mold 32 are brought relatively close together, and a portion of the material 20 is held between the first mold 31 and the second mold 32.

[0043] Referring to Figure 3D, when the first mold 31 and the second mold 32 are closed, the area of ​​the material 20 other than the area that will become the main body of the cross member 12 (Figures 1 and 2) is sandwiched between the first mold 31 and the second mold 32. The main body of the cross member 12 is the part of the cross member 12 that has a shape that protrudes from the lid 111 (Figures 1 and 2), and is composed of, for example, the top plate 121, the vertical walls 122a, 122b, and the edge portions 124a, 124b, 125a, 125b (Figures 1 and 2). At the location of the area of ​​the material 20 that will become the main body of the cross member 12 (Figures 1 and 2), the first mold 31 and the second mold 32 form a hollow space.

[0044] Referring to Figure 3E, fluid is then supplied between the first blank 21 and each of the second blanks 22, causing the second blanks 22 to expand within the hollow space. The fluid is supplied between the first blank 21 and each of the second blanks 22, for example, through a through hole 23 (Figure 3B). After each of the second blanks 22 has expanded within the hollow space by the fluid, it is pressed against the molding surface 321 of the second mold 32. This forms each second blank 22 into a cross member 12. The first blank 21 is formed into a lid 111 by the molding surface 311 of the first mold 31. The lid 111 and each of the cross members 12 are cooled and hardened by contact with the first mold 31 and the second mold 32.

[0045] The fluid used in the molding process is not particularly limited. The fluid may be a liquid such as water, or a gas such as nitrogen gas or compressed air. The fluid may be a liquid or gas under high pressure, for example, 10 MPa or higher. The temperature of the fluid may be appropriately determined according to the material of the material 20, and may be, for example, room temperature. If a heating process is performed, i.e., when molding is performed by hot stamping, the fluid may be heated.

[0046] The structural member 10 can be obtained through the process described above. After the molding process, the outer periphery of the structural member 10 may be removed by laser cutting or the like. For example, at least the portion of the structural member 10 in which the through holes 23 (Figure 3B) are provided may be removed after the molding process. In this embodiment, the through holes 23 (Figure 3B) for fluid supply are provided in the first blank 21 at positions corresponding to both ends in the longitudinal direction of the second blank 22. Therefore, a portion of the structural member 10 can be removed at these positions after the molding process.

[0047] Figure 4 is a partial cross-sectional view of the structural member 10 after the molding process, for example, after the removal of the outer periphery, which has resulted in its final shape.

[0048] In this embodiment, each of the cross members 12 is formed by fluid-assisted deep drawing (hydraulic or blow molding). By performing hot hydraulic or blow molding, each cross member 12 has a different thickness distribution than when each cross member 12 is formed by general press molding or the like. Specifically, in each cross member 12, the thickness reduction rate at the center of the top plate 121 is 2.0% or more and 30.0% or less. The thickness reduction rate at the center of the top plate 121 may be 3.5% or more. The center of the top plate 121 is the part of the top plate 121 located at the center in the vehicle length direction when viewed in cross-section of the cross member 12.

[0049] The rate of thickness reduction at the center of the top plate 121 is the rate of thickness reduction based on the thickness of flanges 123a and 123b. Flanges 123a and 123b are parts of the cross member 12 where thickness reduction is less likely to occur during the molding process. In other words, the rate of thickness reduction based on the thickness of flanges 123a and 123b corresponds to the rate of thickness reduction from the raw material 20 before the molding process (Figures 3A and 3B).

[0050] When the thickness of flange 123a is t0 and the thickness of the center of top plate 121 is t1, the percentage reduction in thickness at the center of top plate 121 can be calculated as {(t0-t1) / t0}×100. The thicknesses t0 of flanges 123a and 123b, and the thickness t1 at the center of top plate 121 can be measured by cutting the cross member 12, which has been removed from the vehicle body, perpendicular to its longitudinal direction, and measuring the cross section of this cross member 12 using, for example, a micrometer. The thicknesses t0 and t1 are measured at the part of the cross member 12 with the maximum height H, and at the outermost position in the longitudinal direction (vehicle width direction). The thickness t0 of flanges 123a and 123b is measured at the flat portion of flanges 123a and 123b. Specifically, the plate thickness t0 of flanges 123a and 123b is measured at a position 2 mm away from the free end of flanges 123a and 123b.

[0051] The plate thickness t0 of flanges 123a and 123b is, for example, 1.4 mm or more. A plate thickness t0 of 1.6 mm or more is more preferable. The plate thickness t0 may be 2.3 mm or less.

[0052] The plate thickness t2 of the lid 111 is preferably smaller than the plate thickness t0 of the cross member 12. t0-t2 is, for example, 0.4 mm or more, preferably 0.6 mm or more, and more preferably 0.8 mm or more. The plate thickness t2 of the lid 111 may be 0.4 mm or more. The plate thickness t2 of the lid 111 may be 1.4 mm or less. The plate thickness t2 of the lid 111 can be measured, for example, by a micrometer or the like in a flat area of ​​the lid 111, sufficiently far from the outer edge.

[0053] Each of the cross members 12 can have a Vickers hardness of 300 HV or more. The Vickers hardness of the cross members 12 is preferably 400 HV or more, and more preferably 500 HV or more.

[0054] The Vickers hardness of the cross member 12 can be measured by the Vickers hardness test specified in JIS Z 2244-1:2024. Specifically, after removing the cross member 12 from the vehicle body, a test piece is obtained by cutting the cross member 12 perpendicular to its longitudinal direction using laser cutting or the like. The cross member 12 is cut at the point where its height H is maximum and at the outermost position in the longitudinal direction (vehicle width direction). The test piece is then embedded in resin so that the cross section of the cross member 12 is positioned on the surface, and this cross section is polished. Subsequently, the Vickers hardness of the center of the top plate 121 is measured with a test force of 0.49 N at a position 1 / 4 of the plate thickness from the surface of the cross member 12. The measured Vickers hardness can be taken as the Vickers hardness HV1 of the center of the top plate 121. In addition, the Vickers hardness of the flanges 123a and 123b is measured at a position 1 / 4 of the plate thickness from the surface of the cross member 12. The Vickers hardness may be measured at a predetermined distance (e.g., 2 mm) away from the free ends of the flanges 123a and 123b. The measured Vickers hardness can be taken as the Vickers hardness HV2 of the flanges 123a and 123b. Both Vickers hardness HV1 and HV2 may be 300 HV or greater. However, because the cross member 12 is formed by fluid-assisted deep drawing (hydraulic or blow molding), the Vickers hardness HV1 at the center of the top plate 121 is greater than the Vickers hardness HV2 of the flanges 123a and 123b.

[0055] The lid 111 may have a Vickers hardness of 80 HV or higher. Preferably, the Vickers hardness of the lid 111 is 120 HV or higher, and more preferably 400 HV or higher. The Vickers hardness of the lid 111 can be measured in the same manner as the Vickers hardness of the cross member 12. However, when measuring the Vickers hardness of the lid 111, the test specimen for the Vickers hardness test can be obtained at any position on the lid 111.

[0056] Figure 5 is a partial cross-sectional view of the structural member 10 after the molding process, for example, after the removal of the outer periphery, which has resulted in its final shape. Figure 5 shows an example of a structural member 10 different from that in Figure 4.

[0057] Referring to Figure 5, each of the flanges 123a and 123b of the cross member 12 is joined to the cover 111, for example, by spot welding. In this case, multiple spot welds 13 are formed on the flanges 123a and 123b. One or more of the spot welds 13 may be formed after the structural member 10 has been formed.

[0058] Flange 123a may have a recess 126a on the surface opposite to the cover 111. The recess 126a is the portion of the surface of flange 123a where at least one spot weld 13 is located, viewed in a cross-section perpendicular to the width direction of the cover 111, and has a concave shape relative to the rest of the surface. Similarly, the surface of flange 123b may have a recess 126b on the surface opposite to the cover 111. The recess 126b is the portion of the surface of flange 123b where at least one spot weld 13 is located, viewed in a cross-section, and has a concave shape relative to the rest of the surface. On the surfaces of flanges 123a and 123b, the recesses 126a and 126b may be recessed by 0.1 mm or more relative to the rest of the surface.

[0059] The cover 111 may have recesses 113a and 113b on the surface opposite to the flanges 123a and 123b. The recesses 113a and 113b are positioned on the surface of the cover 111 at locations corresponding to the recesses 126a and 126b of the flanges 123a and 123b, respectively. Recess 113a, when viewed in cross-section, is the portion of the surface of the cover 111 where the spot welds 13 are located, and has a concave shape relative to the rest of the surface. Similarly, recess 113b, when viewed in cross-section, is the portion of the surface of the cover 111 where the spot welds 13 are located, and has a concave shape relative to the rest of the surface. On the surface of the cover 111, the recesses 113a and 113b may be recessed by 0.1 mm or more relative to the rest of the surface.

[0060] The recesses 126a, 126b in the flanges 123a, 123b and the recesses 113a, 113b in the cover 111 are formed during the molding process when the first blank 21 and the second blank 22 are sandwiched between the first mold 31 and the second mold 32 (Figures 3D and 3E). That is, if the first mold 31 and the second mold 32 are provided with convex sealing portions (not shown), the pressure from these sealing portions forms minute recesses 126a, 126b, 113a, 113b in the flanges 123a, 123b and the cover 111 of the cross member 12. During the molding process, high-pressure sliding occurs between the sealing portion of the second mold 32 and the flanges 123a, 123b, causing the bottom surfaces of the recesses 126a, 126b to be smoothed. Similarly, during the molding process, high-pressure sliding occurs between the seal portion of the first mold 31 and the lid 111, causing the bottom surfaces of the recesses 113a and 113b to be smoothed. Therefore, when spot welding the lid 111 to the flange 123a of the cross member 12 after the molding process, the lid 111 and the flange 123a of the cross member 12 can be stably joined by positioning the spot welding points 13 within the recesses 126a and 113a. Furthermore, when spot welding the lid 111 to the flange 123b of the cross member 12 after the molding process, the lid 111 and the flange 123b of the cross member 12 can be stably joined by positioning the spot welding points 13 within the recesses 126b and 113b.

[0061] [effect] In this embodiment, the cross member 12 is joined to the lid 111 for the battery case 11. Therefore, the lid 111 can also serve as the floor panel of the vehicle body. In this case, the number of parts of the vehicle body can be reduced compared to the case where the lid 111 is provided separately from the floor panel. Furthermore, in this embodiment, the lid 111 for the battery case 11 and the cross member 12 are integrally molded using a combination of hydraulic and blow molding. By integrally molding the lid 111, which also serves as the floor panel, and the cross member 12, the number of parts of the vehicle body can be further reduced.

[0062] Therefore, according to the structural member 10 of this embodiment, the number of parts in the battery unit and its surrounding structure can be reduced. As a result, the manufacturing process of the vehicle body can be streamlined, and the life cycle GHG emissions can be reduced. Furthermore, the vehicle body can be made lighter by reducing the number of parts.

[0063] In this embodiment, the lid 111 for the battery case 11 and the cross member 12 are integrally molded using hydraulic or blow molding, resulting in a unique plate thickness distribution in each cross member 12. Specifically, in the cross member 12, the plate thickness reduction rate of the top plate 121, based on the plate thickness t0 of the flanges 123a and 123b, is between 2.0% and 30.0%, indicating that a plate thickness reduction also occurs in the top plate 121. This suppresses the increase in the plate thickness reduction rate at the boundary between the vertical wall 122a and the ridge portion 124a, and at the boundary between the vertical wall 122b and the ridge portion 124b. In other words, the plate thickness reduction is distributed not only to the ridge portions 124a and 124b but also to the top plate 121. As a result, the overall plate thickness reduction in the structural member 10 can be suppressed compared to general press molding. Therefore, the collision resistance performance of the structural member 10 can be improved.

[0064] While embodiments relating to this disclosure have been described above, this disclosure is not limited to the embodiments described above, and various modifications are possible as long as they do not deviate from its spirit. [Examples]

[0065] The present disclosure will be further described below with reference to examples. However, the present disclosure is not limited to the following examples.

[0066] To confirm the effects of this disclosure, a commercially available analysis software (LS-DYNA, manufactured by Livermore Software Technology Corporation) was used to perform an analysis on forming the structural member 10 described in the above embodiment. In this analysis, one of the materials (steel plates) shown in Table 1 was used for the cover 111 and the cross member 12.

[0067] [Table 1]

[0068] The analysis conditions and results are shown in Table 2.

[0069] [Table 2]

[0070] Examples 1 to 9 and Reference Example 1 in Table 2 are in which the lid 111 and cross member 12 are blow-molded as a single unit, as described in the above embodiments. Reference Example 2 and Comparative Example 1 are in which the lid 111 and cross member 12 are molded separately by conventional press molding without the use of fluid. Reference Example 2 assumes hot stamping with deep drawing (draw HS molding), and Comparative Example 1 assumes hot stamping with deep bending (draw bend HS molding).

[0071] In this analysis, a crack was determined to have occurred in the cross member 12 if the maximum thickness reduction rate of the cross member 12, based on the material, was 39.0% or more, and no crack was determined to have occurred in the cross member 12 if the maximum thickness reduction rate was less than 39.0%. The maximum thickness reduction rate is the thickness reduction rate at the boundary between the vertical wall 122a and the edge portion 124a, or at the boundary between the vertical wall 122b and the edge portion 124b.

[0072] As shown in Table 2, in each embodiment utilizing blow molding, it was confirmed that the lid 111 and the cross member 12 could be molded as a single integrated part. As can be seen from the results of Examples 1 to 9 and Reference Example 1, with the shape of this analysis, the lid 111 and the cross member 12 can be blow molded as a single integrated part until the height H of the cross member 12 reaches 100 mm. On the other hand, in Reference Example 2, which assumed draw HS molding, the cross member 12 was molded separately from the lid 111, but cracks occurred in the cross member 12. In Comparative Example 1, which assumed draw bend HS molding, no cracks occurred during the individual molding of the cross member 12.

[0073] For each of Examples 1-9 and Comparative Example 1, the rate of thickness reduction at the center of the top plate 121 was measured at the outermost position in the longitudinal direction (vehicle width direction) of the cross member 12, where the height H is the maximum, based on the thickness of the material. Since there is virtually no thickness reduction at the flanges 123a and 123b of the cross member 12 during molding, the thickness of the material corresponds to the thickness of the flanges 123a and 123b. As shown in Table 2, in Examples 1-9, the rate of thickness reduction at the center of the top plate 121 was 2.0% or more. On the other hand, in Comparative Example 1, the rate of thickness reduction at the center of the top plate 121 was 0.1%. Therefore, it can be seen that when the lid 111 and the cross member 12 are integrally molded using fluid, the thickness of the top plate 121 is reduced during molding compared to when the lid 111 and the cross member 12 are separated and molded individually.

[0074] Comparing Example 3 and Comparative Example 1, both of which have the same height H and material for the cross member 12, the maximum thickness reduction rate of the cross member 12 in Example 3 is smaller than that of Comparative Example 1. This is because in Example 3, the thickness reduction is distributed to the top plate 121, and the thickness reduction at the ridges 124a and 124b is suppressed. Thus, when the lid 111 and the cross member 12 are integrally molded using fluid, the maximum thickness reduction rate of the cross member 12 can be suppressed. [Explanation of Symbols]

[0075] 10: Structural members 11: Battery case 111: Lid 12: Crossmember 121: Top plate 122a,122b: Vertical wall 123a, 123b: Flange 124a, 124b: Ridge line part 13: Spot weld

Claims

1. A structural component for the vehicle body, A cover for the battery case, A cross member extending in the width direction of the lid includes a top plate that is spaced apart from the lid, two vertical walls connected to the top plate via their respective edges, and two flanges connected to the vertical walls on the opposite side of the top plate and joined to the lid, Equipped with, A structural member wherein the rate of reduction in plate thickness at the center of the top plate, based on the plate thickness of the flange, is 2.0% or more and 30.0% or less.

2. A structural member according to claim 1, A structural member in which the reduction rate of plate thickness at the center of the top plate, based on the plate thickness of the flange, is 3.5% or more.

3. A structural member according to claim 1, Each of the flanges is joined to the cover by spot welding. A structural member wherein, when viewed in a cross section perpendicular to the width direction, the portion of the surface of the flange opposite the cover where at least one spot weld point is located has a concave shape relative to the rest of the surface of the flange.

4. A structural member according to claim 3, A structural member wherein, when viewed in a cross section perpendicular to the width direction, the portion of the lid's surface located on the opposite side of the flange where the dot is positioned has a concave shape relative to the rest of the lid's surface.

5. A structural member according to claim 1, The aforementioned cross member is a structural member having a Vickers hardness of 300 HV or more.

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