Rocker outer, door ring structure, and method for manufacturing door ring structure

Abstract

To provide a rocker outer which is hardly broken when an automobile collides.SOLUTION: The rocker outer (30, side 30A, side 30B) includes a top plate (31), a ridge portion (3233), a vertical wall (3435), and a flange (3637). At least one of the longitudinal walls (34,35) includes one or more beads (381). The one or more beads (381) extend in a longitudinal direction of the rocker outer (30, 30A, 30B). In the cross section of the rocker outer (30, 30A, 30B), when a straight line connecting an end portion on the top plate (31) side and an end portion on the flange (3637) side of at least one vertical wall (3435) is defined as a reference line (R1), the one or more beads (381) protrude from the reference line (R1) to an inner side or an outer side of the rocker outer (30, 30A, 30B). The sum of the depths of the one or more beads (381) with respect to the reference line (R1) is 4.0 times or more the thickness of the top plate (31).SELECTED DRAWING: Figure 2A

Description

[Technical Field]

[0001] The present disclosure relates to a rocker outer for an automobile, and also to a door ring structure for an automobile and a manufacturing method thereof. [Background technology]

[0002] An automobile body includes multiple frame members, such as bumper beams, A-pillars (front pillars), B-pillars (center pillars), C-pillars (rear pillars), side members, and rockers (side sills).

[0003] For example, Patent Document 1 discloses a body side structural frame that constitutes a door opening of an automobile body. This body side structural frame includes, for example, an A-pillar portion (A-pillar upper outer), a hinge pillar portion (A-pillar lower outer), a B-pillar portion (B-pillar outer), and a rocker outer. Patent Document 1 describes manufacturing the body side structural frame by press forming a composite blank formed by joining multiple blanks. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2021-528248 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, high-strength materials have been increasingly used for automotive frame members to ensure high crashworthiness. Frame members are formed from steel materials with a tensile strength of, for example, 980 MPa or more. However, as the strength of steel materials increases, their ductility decreases, creating a problem in that the higher the strength of the steel materials forming the frame members, the more likely the frame members are to fracture during a vehicle collision.

[0006] For example, in the body side structural frame of Patent Document 1, a load is applied to the rocker outer from the side of the vehicle body when the vehicle is involved in a side collision. This causes the rocker outer to deform, and tensile strain is concentrated in a portion of the rocker outer. If the rocker outer is made of a high-strength material with low ductility, the rocker outer is likely to fracture at the location where the strain is concentrated. If the rocker outer fractures, the energy absorption performance of the rocker outer will be significantly reduced, making it impossible to utilize the benefits of the high-strength material.

[0007] An object of the present disclosure is to provide a rocker outer that is less likely to break during a vehicle collision. [Means for solving the problem]

[0008] The rocker outer for an automobile according to the present disclosure comprises a top plate, two vertical walls disposed on both sides of the top plate and each connected to the top plate via a ridge portion, and a flange connected to each of the two vertical walls on the side opposite the top plate. The rocker outer is formed from a steel plate having a tensile strength of 980 MPa or more. At least one of the two vertical walls includes one or more first beads. The one or more first beads extend in the longitudinal direction of the rocker outer. In a cross section of the rocker outer, when a straight line connecting the top plate-side end of the at least one vertical wall and the flange-side end is taken as a reference line, the one or more first beads protrude from the reference line to the inside or outside of the rocker outer. The total depth of the one or more first beads relative to the reference line is 4.0 times or more the plate thickness of the top plate. [Effects of the Invention]

[0009] According to the present disclosure, it is possible to make it difficult for the rocker outer to break in the event of a vehicle collision. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a side view of the door ring structure according to the first embodiment. [Figure 2A] 2A is a cross-sectional view taken along line II-II of the rocker outer included in the door ring structure shown in FIG. [Figure 2B] FIG. 2B is a partially enlarged view of the rocker outer shown in FIG. 2A. [Figure 3A] FIG. 3A is a schematic view for explaining the method for manufacturing the door ring structure according to the first embodiment. [Figure 3B] FIG. 3B is a schematic view for explaining the method for manufacturing the door ring structure according to the first embodiment. [Figure 3C] FIG. 3C is a schematic view for explaining the method for manufacturing the door ring structure according to the first embodiment. [Figure 3D] FIG. 3D is a schematic view for explaining the method for manufacturing the door ring structure according to the first embodiment. [Figure 3E] FIG. 3E is a schematic view for explaining the method for manufacturing the door ring structure according to the first embodiment. [Figure 4] FIG. 4 is a cross-sectional view of a rocker outer according to the second embodiment. [Figure 5] FIG. 5 is a cross-sectional view of a rocker outer according to the third embodiment. [Figure 6A] FIG. 6A is a schematic view for explaining a manufacturing method different from the manufacturing method of the door ring structure according to the first embodiment. [Figure 6B] FIG. 6B is a schematic view for explaining a manufacturing method different from the manufacturing method of the door ring structure according to the first embodiment. [Figure 6C] FIG. 6C is a schematic view for explaining a manufacturing method different from the manufacturing method of the door ring structure according to the first embodiment. [Figure 7] FIG. 7 is a cross-sectional view of a rocker outer according to a modified example of the above embodiment. [Figure 8] FIG. 8 is a cross-sectional view of a rocker outer according to another modified example of the above embodiment. [Figure 9] FIG. 9 is a side view of a door ring structure according to a modified example of the above embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] A rocker outer for an automobile according to an embodiment includes a top plate, two vertical walls disposed on both sides of the top plate and each connected to the top plate via a ridge portion, and a flange connected to each of the two vertical walls on the side opposite the top plate. The rocker outer is formed from a steel plate having a tensile strength of 980 MPa or more. At least one of the two vertical walls includes one or more first beads. The one or more first beads extend in the longitudinal direction of the rocker outer. In a cross section of the rocker outer, when a straight line connecting the end of the at least one vertical wall on the top plate side to the end on the flange side is taken as a reference line, the one or more first beads protrude from the reference line to the inside or outside of the rocker outer. The total depth of the one or more first beads relative to the reference line is 4.0 times or more the plate thickness of the top plate (first configuration).

[0012] When the rocker outer is assembled to the vehicle body, the top plate of the rocker outer is positioned outward in the left-right direction of the vehicle body relative to the two vertical walls, with one vertical wall positioned below the other vertical wall. When the vehicle body is hit from the side by, for example, a pole-shaped object, the rocker outer is deformed. This deformation generates tensile stress in a portion of the rocker outer, causing strain to concentrate. Therefore, in the rocker outer according to the first configuration, one or more first beads are formed on at least one vertical wall. Unlike typical beads provided on vehicle frame members for the purpose of improving rigidity, the first beads have a sufficient depth. Specifically, the total depth of the one or more first beads is 4.0 times or more the thickness of the top plate. This ensures the cross-sectional line length of the rocker outer, making it easier to distribute strain at and near the deformed portion when the rocker outer is deformed, for example, due to a side impact with a pole. As a result, even if the rocker outer is formed from a high-strength material with a tensile strength of 980 MPa or more, the rocker outer is less likely to break in the event of a vehicle collision.

[0013] In the rocker outer according to the first configuration, each of the two vertical walls may include one or more first beads (second configuration).

[0014] In the rocker outer according to the second configuration, one or more first beads are formed on each of the two vertical walls. This allows the cross-sectional line length of the rocker outer to be extended, so that when the rocker outer is deformed, for example, due to a side impact with a pole, the strain at the deformed area and its vicinity is more easily dispersed. This makes it even less likely for the rocker outer to break during a vehicle collision.

[0015] In the rocker outer according to the first or second configuration, the top plate can include a second bead. The second bead has a concave shape on the inside of the rocker outer and extends in the longitudinal direction of the rocker outer (third configuration).

[0016] In the rocker outer according to the third configuration, the second bead is provided on the top plate, so the cross-sectional line length can be further extended. This allows for better dispersion of strain at the deformed portion of the rocker outer and its vicinity during a vehicle collision, making it even less likely for the rocker outer to break.

[0017] In the rocker outer according to the third configuration, the second bead may have a depth that is 5.0 times or more the plate thickness of the top plate (fourth configuration).

[0018] In the rocker outer according to the fourth configuration, a relatively deep second bead is provided on the top plate. Specifically, the depth of the second bead is 5.0 times or more the thickness of the top plate. This allows the cross-sectional line length of the rocker outer to be further extended, which further disperses strain in and around the deformed portion of the rocker outer during a vehicle collision. This therefore makes it easier to prevent the rocker outer from breaking.

[0019] In the rocker outer of the third or fourth configuration, in a cross section of the rocker outer with the two vertical walls positioned above and below, the center of the bottom of the second bead may be positioned below the center of the top plate (fifth configuration).

[0020] If the rocker outer rotates downward during a side collision, the amount of penetration of the rocker outer into the underside of the vehicle body increases, which could affect components located under the vehicle body, such as the battery. In contrast, in the fifth configuration, the center of the bottom of the second bead is positioned below the center of the top plate. This increases the rigidity of the underside of the vehicle body of the rocker outer, making it easier to prevent the rocker outer from rotating downward during a side collision.

[0021] A door ring structure for an automobile according to an embodiment includes a rocker outer according to any one of the first to fifth configurations (sixth configuration).

[0022] A manufacturing method according to an embodiment manufactures a door ring structure according to the sixth configuration. The manufacturing method includes a preparation step of preparing a blank having an annular shape in a plan view, a heating step of heating the blank to an austenite transformation completion temperature or higher, and a forming step of using a die to form the heated blank into a door ring structure and quench it. The die includes a punch, a die, and a pad. The portion of the punch used to form the rocker outer includes a punch body and a cushion that faces the pad and is receivable within the punch body. In the forming step, the portion of the blank to be formed into the top plate is sandwiched between the pad and the cushion, and then the blank is pressed by the punch body and the die while sandwiched between the pad and the cushion (seventh configuration).

[0023] A manufacturing method according to another embodiment manufactures the door ring structure according to the sixth configuration. The manufacturing method includes a preparation step of preparing a blank having an annular shape in plan view, a heating step of heating the blank to a temperature equal to or higher than the austenite transformation completion temperature, and a forming step of using a die to form the heated blank into a door ring structure and quench it. The die includes a punch, a die, and a pad. In the forming step, a portion of the blank to be formed into the top plate is clamped between the pad and the punch, and the blank is pressed by the punch and the die to form the vertical wall and flange (eighth configuration).

[0024] To simplify the manufacturing process of a door ring structure, it is conceivable to integrate multiple frame components, including a rocker outer, into a single blank. However, when a relatively large door ring structure is formed from an annular blank, the dimensional accuracy of the door ring structure may not be ensured. In particular, when a door ring structure is manufactured by hot stamping, the dimensional accuracy of the door ring structure may be degraded. More specifically, in hot stamping, an annular blank is heated to an austenite transformation completion temperature or higher, and then the heated blank is formed into a door ring structure using a die and quenched. The door ring structure is contacted with the die and rapidly cooled, transforming its microstructure from austenite to martensite. If the cooling rate of the door ring structure is sufficient, a single-phase martensite structure is obtained. However, if the cooling rate is insufficient, ferrite precipitates in addition to martensite.

[0025] When manufacturing a door ring structure by hot stamping, stress is released during the phase transformation from austenite to martensite, making springback less likely to occur. However, if the cooling rate is insufficient in a portion of the door ring structure, causing ferrite to precipitate, stress may not be sufficiently released in that portion, potentially resulting in springback. Because the door ring structure is large and annular, even slight springback in only a portion can have a significant impact on the dimensional accuracy of the entire door ring structure. For example, if stress remains in the top plate of the rocker outer, springback may occur in the rocker outer, which may result in twisting of the door ring structure.

[0026] In the manufacturing method according to the seventh aspect, when forming an annular blank into a door ring structure, the portion of the blank that will become the top plate of the rocker outer is first clamped between the pad and cushion at the position of the rocker outer. That is, the top plate of the rocker outer is in contact with the pad and cushion from the early stages of forming, ensuring a sufficient cooling rate. As a result, the microstructure of the top plate of the rocker outer is likely to become a martensitic single-phase structure, and stress is likely to be released. This reduces springback of the rocker outer and suppresses twisting of the door ring structure. Therefore, the manufacturing method according to the seventh aspect can improve the dimensional accuracy of the door ring structure.

[0027] In the manufacturing methods according to the seventh and eighth configurations, a door ring structure including a rocker outer is manufactured by hot stamping. Therefore, the rocker outer can be made high-strength (tensile strength: 980 MPa or more), and a relatively deep first bead can be formed on at least one of the vertical walls. For example, even if it is difficult to form a first bead by simple bending, by using hot stamping, it is possible to form a relatively deep first bead on one or both of the vertical walls of the rocker outer while suppressing cracks.

[0028] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In each drawing, the same or equivalent components are designated by the same reference numerals, and the same description will not be repeated.

[0029] First Embodiment [Door ring structure] FIG. 1 is a diagram showing a schematic configuration of a door ring structure 100 according to this embodiment. The door ring structure 100 is used in an automobile. The door ring structure 100 is incorporated into the body of the automobile. FIG. 1 shows the door ring structure 100 as viewed from the side (left) of the automobile when incorporated into the body. Hereinafter, this embodiment will be described by assuming that the front, rear, left, and right sides of the automobile body when the door ring structure 100 is incorporated into the body are the front, rear, left, and right sides of the door ring structure 100 and the frame members included in the door ring structure 100.

[0030] 1, the door ring structure 100 has an annular shape in a side view. The door ring structure 100 is joined from the outside in the left-right direction of the vehicle body to another door ring structure not shown in FIG. 1. In other words, the door ring structure 100 is an outer door ring structure. The door ring structure 100 includes an A-pillar upper outer panel 11, an A-pillar lower outer panel 12, a B-pillar outer panel 20, and a rocker outer panel 30.

[0031] The A-pillar lower outer panel 12 is disposed in front of and below the A-pillar upper outer panel 11 and is joined to the A-pillar upper outer panel 11. The B-pillar outer panel 20 is joined to the rear of the A-pillar upper outer panel 11 and extends downward from the A-pillar upper outer panel 11. The rocker outer panel 30 is joined to the lower ends of the A-pillar lower outer panel 12 and the B-pillar outer panel 20 and extends from the A-pillar lower outer panel 12 toward the B-pillar outer panel 20. In other words, the rocker outer panel 30 has an elongated shape and extends in the front-to-rear direction when incorporated into the body of the automobile.

[0032] The size of the annular door ring structure 100 in a side view is, for example, 1.0 m or more. The size of the door ring structure 100 may be, for example, 4.0 m or less. The size of the door ring structure 100 is the length of a line segment connecting any two points on the outer periphery of the door ring structure 100 that are farthest apart when the door ring structure 100 is placed on a horizontal surface and viewed vertically.

[0033] Fig. 2A is a cross-sectional view taken along line II-II in Fig. 1. Fig. 2A shows a cross section of the rocker outer 30 included in the door ring structure 100.

[0034] Referring to FIG. 2A, the rocker outer 30 is formed of a steel plate having a tensile strength of 980 MPa or more. The rocker outer 30 may have a tensile strength of 1470 MPa or more, and more preferably has a tensile strength of 1760 MPa or more. The tensile strength of the rocker outer 30 can be obtained by taking a test piece from a relatively flat portion of the rocker outer 30 and performing a tensile test on this test piece in accordance with JIS Z 2241:2022. When assembled to the body of an automobile, the rocker outer 30 forms a closed cross section together with the rocker inner 40. An energy absorbing member 50 is disposed within the space formed by the rocker outer 30 and the rocker inner 40. The energy absorbing member 50 is, for example, an extruded aluminum alloy.

[0035] The rocker outer 30 has a generally hat-shaped cross section and includes a top plate 31, ridge portions 32 and 33, vertical walls 34 and 35, and flanges 36 and 37.

[0036] The top plate 31 extends in the longitudinal direction of the rocker outer 30. That is, the top plate 31 extends substantially in the front-to-rear direction of the vehicle body. The vertical walls 34, 35 are arranged on both sides of the top plate 31. The flanges 36, 37 are connected to the vertical walls 34, 35, respectively, on the side opposite the top plate 31. The ridge portions 32, 33, the vertical walls 34, 35, and the flanges 36, 37 extend in the longitudinal direction of the rocker outer 30, similar to the top plate 31.

[0037] The vertical wall 34 is connected to the top plate 31 via a ridge portion 32. The ridge portion 32 forms a corner portion between the top plate 31 and the vertical wall 34. The ridge portion 32 has a curved shape that convexly faces outward from the rocker outer 30 in a cross-sectional view of the rocker outer 30. The flange 36 is continuous with the vertical wall 34 on the opposite side of the ridge portion 32. The flange 36 protrudes from the vertical wall 34 to the outside of the rocker outer 30.

[0038] When the rocker outer 30 is assembled to the body of the automobile, the vertical wall 35 is positioned below the vertical wall 34. The vertical wall 35 is connected to the top plate 31 via a ridge portion 33. The ridge portion 33 forms a corner portion between the top plate 31 and the vertical wall 35. The ridge portion 33 has a curved shape that convexly faces outward from the rocker outer 30 in a cross-sectional view of the rocker outer 30. The flange 37 is continuous with the vertical wall 35 on the opposite side of the ridge portion 33. The flange 37 protrudes from the vertical wall 35 to the outside of the rocker outer 30.

[0039] One of the vertical walls 34 includes one or more beads 381 extending in the longitudinal direction of the rocker outer 30. In this embodiment, two beads 381 are provided adjacent to each other on the vertical wall 34. The two beads 381 are formed in a stepped shape on the vertical wall 34.

[0040] In the example of Fig. 2A, in the cross section of the rocker outer 30, one bead 381 protrudes from the reference line R1 toward the inside of the rocker outer 30. In the cross section of the rocker outer 30, the other bead 381 protrudes from the reference line R1 toward the outside of the rocker outer 30. The reference line R1 is an imaginary straight line connecting an end 341 of the vertical wall 34 on the top plate 31 side and an end 342 of the vertical wall 34 on the flange 36 side. The end 341 is the end of the R of the ridge portion 32 on the outer surface of the rocker outer 30 on the vertical wall 34 side. The end 342 is the end of the R on the outer surface of the rocker outer 30 of the curved portion of the flange 36 that is adjacent to the vertical wall 34.

[0041] In this embodiment, the portion of the vertical wall 34 between one bead 381 and the ridge portion 32 is a flat portion 343. A flat portion 344 is also provided in the portion of the vertical wall 34 between the other bead 381 and the flange 36. The flat portions 343, 344 are portions that are located on the reference line R1 and extend substantially along the reference line R1 in a cross-sectional view of the rocker outer 30.

[0042] Each of the beads 381 on the vertical wall 34 has a depth D1. The depths D1 of these beads 381 may be the same or different from each other. In the vertical wall 34, the total depth D1 of the beads 381 relative to the reference line R1 is 4.0 times or more the thickness t of the top plate 31. The total depth D1 of the beads 381 relative to the reference line R1 may be 15.0 times or less the thickness t of the top plate 31. When multiple beads 381 are provided on the vertical wall 34 as in this embodiment, the total depth D1 of the beads 381 is the sum of the depths D1 of all the beads 381. On the other hand, when only one bead 381 is provided on the vertical wall 34, the depth D1 of this bead 381 itself is the total depth D1. The depth D1 of the bead 381 is the shortest distance from the reference line R1 to a straight line L1 that is parallel to the reference line R1 and tangent to the top of the bead 381 that protrudes inward or outward from the rocker outer 30 in a cross section of the rocker outer 30. The straight line L1 is tangent to the top of the bead 381 on the outer surface of the rocker outer 30. The depth D1 of each bead 381 may be constant over the entire length of the bead 381 that extends in the longitudinal direction of the rocker outer 30, or may be variable. The bead 381 may extend in the longitudinal direction of the rocker outer 30 over the entire vertical wall 34, or may be provided only on a portion of the vertical wall 34. In the rocker outer 30, the length (longitudinal direction) of the region where the total depth D1 of the beads 381 is 4.0 times or more the plate thickness t of the top plate 31 is preferably, for example, 600 mm or more.

[0043] 2B is an enlarged view of the vertical wall 34 and its vicinity in the cross section of the rocker outer 30 of FIG. 2A. Referring to FIG. 2B, in the cross section of the rocker outer 30, it is preferable that each of the beads 381 does not have a portion that extends substantially parallel to the reference line R1. In other words, it is preferable that each bead 381 is configured so that its apex, i.e., the portion that contacts the straight line L1, is not flat. In the cross section of the rocker outer 30, each bead 381 can have, for example, a triangular or curved shape that is convex on the inside or outside of the rocker outer 30.

[0044] When multiple beads 381 are provided on the vertical wall 34 as in this embodiment, the side of the bead 381 closest to the top plate 31 forms an angle θ with the reference line R1 in a cross-sectional view of the rocker outer 30. When a single bead 381 is provided on the vertical wall 34, the side of the bead 381 forms an angle θ with the reference line R1 in a cross-sectional view of the rocker outer 30. The angle θ may be, for example, 120° or greater. The side here refers to the outer surface of the bead 381 that protrudes outward or inward from the rocker outer 30 and is located between the reference line R1 and the straight line L1. The angle θ is preferably 135° or greater, and more preferably 150° or greater. The angle θ may be 170° or less. When more than half of the side of the bead 381 is a straight portion, the angle θ is the angle between the straight portion and the reference line R1. When the side surface of the bead 381 is generally arc-shaped, the angle θ is the angle formed between the reference line R1 and a line tangent to the side surface of the bead 381 at a position midway between the reference line R1 and the straight line L1.

[0045] Returning to FIG. 2A , in this embodiment, one vertical wall 34 is provided with multiple beads 381, but the other vertical wall 35 is not provided with any beads 381. However, the vertical wall 34 may not have any beads 381, and one or more beads 381 may be provided on the vertical wall 35. Alternatively, one or more beads 381 may be provided on each of the vertical walls 34, 35. In the cross section of the rocker outer 30, the vertical walls 34, 35 do not have to be symmetrical with respect to the width center line of the top plate 31. For example, the inclinations of the vertical walls 34, 35 with respect to the top plate 31 may be different, or, if both the vertical walls 34, 35 have at least one bead 381, the position, shape, depth D1, etc. of the bead 381 may be different between the vertical walls 34, 35. Furthermore, the number of beads 381 on the vertical wall 35 may be different from the number of beads 381 on the vertical wall 34. The width center line of the top plate 31 is a straight line that passes through the width center C0 and is perpendicular to the straight line L0, when the width center C0 of the top plate 31 is a point on the straight line L0 that connects the boundary B1 between the top plate 31 and one ridge line portion 32 and the boundary B2 between the top plate 31 and the other ridge line portion 33 in the cross section of the rocker outer 30 and is located midway between the boundaries B1 and B2. The boundaries B1 and B2 are the ends of the R of the ridge lines 32 and 33 on the outer surface of the rocker outer 30 on the top plate 31 side.

[0046] 2A, in this embodiment, the top plate 31 also includes a bead 382 extending in the longitudinal direction of the rocker outer 30. The bead 382 has a concave shape on the inside of the rocker outer 30. In a cross section of the rocker outer 30, the width of the opening of the bead 382 is smaller than the width W of the top plate 31 (the linear distance between the boundaries B1 and B2). Therefore, in the cross section of the rocker outer 30, the top plate 31 includes flat portions 311, 312 on both sides of the bead 382. The flat portions 311, 312 are portions that are arranged on a straight line L0 and extend substantially along the straight line L0 in the cross section of the rocker outer 30. The width W of the top plate 31 may be 30 mm or more and 300 mm or less.

[0047] The bead 382 is preferably disposed on the top plate 31 so as not to interfere with the energy absorbing member 50. In the example of Fig. 2A, the bead 382 is disposed offset downward from the width center C0 of the top plate 31.

[0048] More specifically, in a cross section of the rocker outer 30 when the rocker outer 30 is assembled to the body of the automobile, that is, when the vertical walls 34, 35 are positioned vertically, the center (bottom center) C1 of the bottom of the bead 382 is located below the widthwise center C0 of the top plate 31. The bottom center C1 of the bead 382 is preferably offset downward from the widthwise center C0 of the top plate 31 by 10% or more of the width W of the top plate 31. The bottom center C1 of the bead 382 is the vertical center point of the portion of the line L2 that contacts the bottom of the bead 382. The line L2 is parallel to the line L0 connecting the boundaries B1, B2, and contacts the bottom of the bead 381 on the outer surface of the rocker outer 30. In the cross section of the rocker outer 30, when the line L2 makes point contact with the bottom of the bead 382 on the outer surface of the rocker outer 30, the contact point between the bottom of the bead 382 and the line L2 becomes the bottom center C1 of the bead 382.

[0049] In this embodiment, the bead 382 has a shape that is substantially symmetrical with respect to the bottom center line of the bead 382 (a line that passes through the bottom center C1 and is perpendicular to the line L0) when viewed in a cross section of the rocker outer 30. However, the bead 382 does not necessarily have to have a shape that is symmetrical with respect to the bottom center line of the bead 382.

[0050] The bead 382 can have a depth D2 that is 5.0 times or more the thickness t of the top plate 31. The depth D2 of the bead 382 may be 15.0 times or less the thickness t of the top plate 31. The depth D2 of the bead 382 is the shortest distance between the lines L0 and L2 in the cross section of the rocker outer 30. The thickness t of the top plate 31 is the thickness measured, for example, at the positions of the flat portions 311 and 312. The thickness t is, for example, 0.8 mm or more. The thickness t may be 2.0 mm or less. The depth D2 may be constant over the entire length of the bead 382 extending in the longitudinal direction of the rocker outer 30, or may be non-constant. For example, the depth D2 may be smaller at both longitudinal ends of the bead 382 than at other portions.

[0051] [Method of manufacturing door ring structure] 3A to 3E, a method for manufacturing the door ring structure 100 according to this embodiment includes a step of preparing a blank 60, a step of heating the blank 60, and a step of forming the blank 60.

[0052] (preparation process) As shown in FIG. 3A , in the preparation step, a blank 60 having an annular shape in plan view is prepared. The blank 60 has a shape obtained by unfolding the annular door ring structure 100. In this embodiment, the blank 60 includes a plurality of steel plates 61, 62, 63, and 64. The steel plates 61, 62, 63, and 64 are arranged and joined so as to form an annular shape in plan view of the blank 60. Each of the steel plates 61, 62, 63, and 64 is butt-joined to an adjacent steel plate by, for example, laser welding. Alternatively, each of the steel plates 61, 62, 63, and 64 may be overlap-joined to an adjacent steel plate by, for example, spot welding. The joining method of the steel plates 61, 62, 63, and 64 is not particularly limited.

[0053] In the example of FIG. 3A, a steel plate 61 is disposed in a portion of the blank 60 that will become the A-pillar upper outer panel 11 (FIG. 1). Steel plates 62, 63, and 64 are disposed in portions of the blank 60 that will become the A-pillar lower outer panel 12, the B-pillar outer panel 20, and the rocker outer panel 30 (FIG. 1). The thickness of each of the steel plates 61, 62, 63, and 64 may be the same as or different from that of the other steel plates. The tensile strength of each of the steel plates 61, 62, 63, and 64 in the state of the blank 60 may also be the same as or different from that of the other steel plates. The steel plates 61, 62, 63, and 64 may be plated steel plates having an aluminum-based plating layer or a zinc-based plating layer on their surfaces, or may be bare steel plates without any plating layer.

[0054] (Heating process) The prepared blank 60 is formed into the door ring structure 100 (FIG. 1) by hot stamping (hot pressing). During the hot stamping, the blank 60 is subjected to a heating step. Referring to FIG. 3B, in the heating step, the blank 60 is heated by, for example, a heating furnace 70. The blank 60 is heated to an austenite transformation completion temperature (A c3 The blank 60 is heated to, for example, 900° C. or higher, which causes the microstructures of the steel plates 61, 62, 63, and 64 (FIG. 3A) included in the blank 60 to transform into an austenite phase.

[0055] (molding process) Referring to Fig. 3C, in the forming process, a die 80 is used to form the heated blank 60 into a door ring structure 100 (Fig. 1) that is annular in plan view and then quenched. The blank 60 heated in the heating process is removed from the heating furnace 70 (Fig. 3B) and transported to the die 80. The die 80 is attached to a known press device. The die 80 includes a punch 81, a die 82, and a pad 83.

[0056] First, the specific configuration of the mold 80 used in the molding process will be described. Fig. 3C is a cross-sectional view of a portion of the mold 80 that corresponds to the rocker outer 30 (Figs. 1 and 2A). Fig. 3C shows a cross-section of a portion of the mold 80 that forms the bead 382 of the top plate 31 and the bead 381 of the vertical wall 34 in the rocker outer 30 shown in Figs. 1 and 2A.

[0057] As shown in FIG. 3C , the portion of the punch 81 used to form the rocker outer 30 includes a punch body 811 and a cushion 812 that can be accommodated within the punch body 811. The punch body 811 includes a step 811a on its side for forming the bead 381 ( FIGS. 2A and 2B ) on the vertical wall 34. The punch body 811 also has a recessed accommodation portion 811b on its top surface. The cushion 812 is supported on the bottom surface of the accommodation portion 811b via an elastic member 84. The elastic member 84 is a member that can expand and contract in the pressing direction. For example, a gas spring or the like can be used as the elastic member 84. When the elastic member 84 is in an extended state, the top surface of the cushion 812 protrudes from the top surface of the punch body 811. When the elastic member 84 is in a contracted state, the cushion 812 is accommodated in the accommodation portion 811b of the punch body 811 so that the top surface of the cushion 812 is substantially flush with the top surface of the punch body 811.

[0058] The die 82 is disposed opposite the punch 81 in the pressing direction. Steps 821 are provided on each side of the die 82, corresponding to the step 811a on each side of the punch body 811. The pad 83 is disposed opposite the cushion 812 in the pressing direction. In the example shown in FIG. 3C , the pad 83 is supported by the die 82 via an elastic member 85. The elastic member 85 is a member that can expand and contract in the pressing direction. For example, a gas spring or the like can be used as the elastic member 85.

[0059] A recess 812a for forming a bead 382 (FIG. 2A) on the top plate 31 is formed on the surface of the cushion 812 of the punch 81, which faces the pad 83. A protrusion 831 corresponding to the recess 812a of the cushion 812 is formed on the surface of the pad 83, which faces the cushion 812.

[0060] Next, press-forming of the blank 60 using the die 80 will be described. Continuing to refer to FIG. 3C , before press-forming begins, the elastic member 84 is stretched, and the cushion 812 of the punch 81 protrudes from the punch body 811 toward the pad 83. In addition, the elastic member 85 is stretched, and at least the surface of the pad 83 that faces the cushion 812 is positioned on the punch 81 side with respect to the die 82. The blank 60 heated in the heating step is placed between the punch 81 and the die 82 and pad 83. The blank 60 may be placed on the cushion 812, for example.

[0061] 3D, after the blank 60 is placed between the punch 81 and the die 82 and pad 83, the die 82 and pad 83 are moved relative to the punch 81 in the pressing direction, and the die 82 and pad 83 are brought closer to the punch 81. As a result, the blank 60 is first sandwiched between the pad 83 and the cushion 812 of the punch 81. More specifically, the portion of the blank 60 that will be formed into the top plate 31 (FIG. 2A) of the outer rocker 30 is sandwiched between the pad 83 and the cushion 812, and a bead 382 is formed.

[0062] 3E, the blank 60 is sandwiched between the pad 83 and the cushion 812, and then pressed by the punch body 811 and the die 82. More specifically, after the blank 60 is sandwiched between the pad 83 and the cushion 812, the die 82 and the pad 83 are moved closer to the punch 81 in the pressing direction. This causes the elastic member 84 to contract, causing the cushion 812 to be housed in the housing portion 811b of the punch body 811, and the elastic member 85 to contract, causing the die 82 to move toward the punch 81 relative to the pad 83. The blank 60 is then pressed by the punch body 811 and the die 82, and is formed into a shape that conforms to the forming surfaces of the punch 81, the die 82, and the pad 83. The blank 60 remains sandwiched between the punch 81, the die 82, and the pad 83. The blank 60 is cooled (rapidly cooled) by the mold 80, and its microstructure is transformed into martensite.

[0063] Although not shown in the figures, the skeletal members 11, 12, and 20 of the door ring structure 100 other than the rocker outer 30 are also formed by a mold 80 including a punch 81, a die 82, and a pad 83. However, the punch 81 does not need to be provided with a cushion 812 at the positions where the other skeletal members 11, 12, and 20 are formed. In other words, for the portions of the mold 80 where it is not necessary to form a bead on the top plate, forming can be performed using a punch that is not divided into a punch body and a cushion (a general block-shaped punch).

[0064] [effect] When the rocker outer 30 according to this embodiment is assembled to the vehicle body, it forms a closed cross section together with the rocker inner 40. The rocker outer 30 is assembled to the vehicle body with the vertical wall 35 positioned below the vertical wall 34 and the top plate 31 facing outward in the left-right direction of the vehicle body. When the vehicle body is hit from the side by, for example, a pole-shaped object, a load is applied to the rocker outer 30 from the top plate 31 side. The collision load causes a portion of the rocker outer 30 to be pushed inward and deformed in the vehicle body. As a result of the deformation, a ridge-like portion is formed on the rocker outer 30. Tensile stress is generated in the ridge-like portion, causing strain to concentrate. However, in this embodiment, one or more beads 381 are formed on the vertical wall 34, thereby ensuring the cross-sectional line length of the rocker outer 30. In particular, the total depth D1 of the one or more beads 381 on the vertical wall 34 is 4.0 times or more the plate thickness t of the top plate 31, thereby sufficiently extending the cross-sectional line length of the rocker outer 30. Therefore, when the rocker outer 30 is deformed due to, for example, a side collision with a pole, strain is easily dispersed in the cross-sectional line length direction at the deformed area and its vicinity, reducing strain in the ridge-like portion. As a result, even if the tensile strength of the rocker outer 30 is 980 MPa or more, it is possible to make the rocker outer 30 less likely to break during a vehicle collision.

[0065] When viewed in a cross section of the rocker outer 30, the height direction is defined as a direction perpendicular to a straight line L0 connecting a boundary B1 between the top plate 31 and the ridge portion 32 and a boundary B2 between the top plate 31 and the ridge portion 33, and the height of the vertical wall 34 is defined as the linear distance in the height direction from the flat surface of the flange 36 (outside the rocker outer 30) to the surface of the top plate 31 (outside the rocker outer 30). It is preferable that each bead 381 be located at a height measured from the flange 36 that is 70% or less of the height of the vertical wall 34. This ensures a sufficient distance between the ridge portion 32 and the bead 381. In this case, in the event of a vehicle collision, it becomes difficult for the ridge-like portion formed by deformation of the rocker outer 30 to connect with the bead 381, so the bead 381 is more likely to achieve the effect of ensuring the cross-sectional line length. Similarly, when one or more beads 381 are provided on the vertical wall 35, it is preferable that the bead 381 be located at a height measured from the flange 37 that is 70% or less of the height of the vertical wall 35. The height of the vertical wall 35 is the linear distance in the cross section of the rocker outer 30, in a direction perpendicular to a straight line L0 from the flat surface of the flange 37 (outside of the rocker outer 30) to the surface of the top plate 31 (outside of the rocker outer 30).

[0066] In the rocker outer 30 according to this embodiment, a bead 382 is also provided on the top plate 31. This allows the cross-sectional line length of the rocker outer 30 to be further extended. This makes it possible to further reduce strain at the deformed portion of the rocker outer 30 and in its vicinity in the event of a vehicle collision. In particular, when the depth D2 of the bead 382 is 5.0 times or more the plate thickness t of the top plate 31, the strain reduction effect is large. This makes it even more difficult for the rocker outer 30 to break in the event of a vehicle collision.

[0067] However, if the depth D2 of the bead 382 is excessively large, it becomes difficult to form the bead 382 on the top plate 31, so the depth D2 is preferably not more than 15.0 times the thickness t of the top plate 31. Similarly, for the vertical wall 34, if the depth D1 of the bead 381 is excessively large, it becomes difficult to form, so the total of the depths D1 of one or more beads 381 on the vertical wall 34 is preferably not more than 15.0 times the thickness t of the top plate 31. When one or more beads 381 are provided on the vertical wall 35, from the viewpoint of formability, the total of the depths D1 of the one or more beads 381 on the vertical wall 35 is preferably not more than 15.0 times the thickness t of the top plate 31.

[0068] For example, if a bead 381 that is rectangular in cross section of the rocker outer 30 is provided on the vertical wall 34 and / or the vertical wall 35, the top of the bead 381 extends parallel to the reference line R1, so the difference in cross-sectional line length compared to when the bead 381 is not provided is unlikely to be large. Therefore, it is preferable that each of the beads 381 does not have a portion that extends substantially parallel to the reference line R1 in cross-section of the rocker outer 30. This makes it easier for the cross-sectional line length of the vertical wall 34 and / or the vertical wall 35 to be longer than when the bead 381 is not provided, thereby enhancing the effect of the bead 381 in extending the cross-sectional line length. As a result, when deformation occurs in the rocker outer 30 during a vehicle collision, strain is more easily dispersed in the cross-sectional line length direction, and strain on the ridge-like portions formed due to deformation can be further reduced.

[0069] In this embodiment, the angle θ between the side surface of the bead 381 on the top plate 31 side and the reference line R1 in a cross-sectional view of the rocker outer 30 is, for example, 120° or more, preferably 135° or more, and more preferably 150° or more. By ensuring a relatively large angle θ between the side surface of the bead 381 and the reference line R1 in this way, the bead 381 is more likely to deform in an opening direction during a vehicle collision, and the material of the bead 381 is more likely to be supplied to the ridge line portion 32 or 33. As a result, cracks at the ridge line portions 32, 33 can be made less likely to occur.

[0070] In the rocker outer 30 according to this embodiment, the bead 382 of the top plate 31 is positioned offset from the width center C0 of the top plate 31 toward the vertical wall 35 below. More specifically, in the cross section of the rocker outer 30, the bottom center C1 of the bead 382 is positioned below the width center C0 of the top plate 31. This prevents the bead 382 of the top plate 31 from interfering with the energy absorbing member 50. Also, because the rigidity of the portion of the rocker outer 30 below the vehicle body tends to be high, rotation of the rocker outer 30 toward the bottom of the vehicle body during a side collision can be suppressed, and the amount of intrusion of the rocker outer 30 below the vehicle body can be reduced.

[0071] In this embodiment, when the door ring structure 100 including the A-pillar upper outer 11, the A-pillar lower outer 12, the B-pillar outer 20, and the rocker outer 30 is formed from the annular blank 60, the top plate 31 is clamped at the position of the rocker outer 30 by the pad 83 and the cushion 812 provided on the punch 81. That is, the top plate 31 of the rocker outer 30 contacts the pad 83 and the cushion 812 from the early stage of forming. This ensures a sufficient cooling rate of the top plate 31, making it easier for the microstructure of the top plate 31 to become a martensitic single-phase structure, and stress in the top plate 31 is easily released. This reduces springback of the rocker outer 30 and suppresses twisting of the door ring structure 100 due to springback. This improves the dimensional accuracy of the door ring structure 100.

[0072] In this embodiment, the rocker outer 30 is formed by hot stamping. That is, the rocker outer 30 is a hot-stamped member. Therefore, the rocker outer 30 includes a martensite phase in its microstructure. For example, the martensite fraction may be 80% or more in the cross section of the rocker outer 30. The martensite fraction is preferably 85% or more, and more preferably 90% or more. The martensite fraction can be measured as follows. That is, in the cross section of the rocker outer 30 at any position, 10 or more analysis samples (for example, with a long side of approximately 10 mm) are cut out from positions 20 mm or more away from the tips of the flanges 36, 37 and 10 mm or more away from each other. Then, each sample is polished and etched with LePeller's reagent so that the observation surface is in the thickness direction. Then, an optical microscope is used at 1000x magnification to observe a position 1 / 4 of the way through the thickness direction from the surface of the analysis sample, and an optical micrograph is obtained. The obtained optical microscope photograph is subjected to image analysis using, for example, commercially available image analysis software (Photoshop CS5, manufactured by Adobe), and the martensite area ratio can be determined as the martensite fraction.

[0073] The image analysis method involves obtaining the maximum brightness value Lmax and minimum brightness value Lmin from the image, designating the area with pixels whose brightness ranges from Lmax-0.3 (Lmax-Lmin) to Lmax as a white region, and calculating the percentage of pixels in the white region to the total number of pixels to measure the martensite fraction. This type of image analysis is performed on a total of 10 observation fields for each analysis sample to determine the martensite fraction, and the average value is taken as the martensite fraction of the rocker outer 30.

[0074] Second Embodiment 4 is a cross-sectional view of a rocker outer 30A according to the second embodiment. The rocker outer 30A according to this embodiment has a similar configuration to the rocker outer 30 according to the first embodiment (FIGS. 1 and 2A). However, the rocker outer 30A differs from the rocker outer 30 according to the first embodiment in that the vertical walls 34, 35 each include a bead 381.

[0075] 4, a single bead 381 is provided on each of the vertical walls 34, 35. The bead 381 protrudes from the reference line R1 toward the inside of the rocker outer 30A in the cross section of the rocker outer 30A. However, the bead 381 on the vertical wall 34 and / or the vertical wall 35 may be provided so as to protrude from the reference line R1 toward the outside of the rocker outer 30A.

[0076] In the vertical wall 34, the bead 381 has a depth D1 that is 4.0 times or more the thickness t of the top plate 31. In the vertical wall 34, the depth D1 of the bead 381 may be 15.0 times the thickness t of the top plate 31 or less.

[0077] In the vertical wall 35, as in the vertical wall 34, the bead 381 has a depth D1 that is 4.0 times or more the thickness t of the top plate 31. In the vertical wall 35, the depth D1 of the bead 381 may be 15.0 times or less the thickness t of the top plate 31. Although not shown, in each of the vertical walls 34, 35 of the rocker outer 30A, the angle θ formed between the side surface of the bead 381 and the reference line R1 can be set in the same manner as in the first embodiment.

[0078] The rocker outer 30A according to this embodiment can also achieve the same effects as the rocker outer 30 according to the first embodiment. That is, even with the configuration of this embodiment, it is possible to distribute strain that occurs in the rocker outer 30A when the car crashes into a pole, etc., and to prevent the rocker outer 30A from breaking.

[0079] <Third embodiment> 5 is a cross-sectional view of a rocker outer 30B according to the third embodiment. The rocker outer 30B according to this embodiment has roughly the same basic configuration as the rocker outers 30, 30A according to the other embodiments (FIGS. 2A and 4). However, the rocker outer 30B differs from the other rocker outers 30, 30A in the shape of the bead 381.

[0080] In this embodiment, two beads 381 are provided in a stepped shape on each of the vertical walls 34, 35. In this embodiment, one bead 381 on each of the vertical walls 34, 35 has a convex shape on the outside of the rocker outer 30B, while the other bead 381 has a concave shape on the inside of the rocker outer 30B. However, even in this embodiment, the total depth D1 of the multiple beads 381 on each of the vertical walls 34, 35 is 4.0 times or more the thickness t of the top plate 31. Therefore, even with the configuration of this embodiment, as with the other embodiments, it is possible to distribute strain generated in the rocker outer 30B during a side collision of a vehicle with a pole, etc., and to suppress fracture of the rocker outer 30B. In each of the vertical walls 34, 35, the total depth D1 of the multiple beads 381 may be 15.0 times or less the thickness t of the top plate 31. Furthermore, in each of the vertical walls 34 and 35, the angle θ (not shown) formed between the side surface of the bead 381 closest to the top plate 31 and the reference line R1 can be set in the same manner as in the first embodiment.

[0081] When the door ring structure 100 (FIG. 1) includes the rocker outer 30A according to the second embodiment or the rocker outer 30B according to the third embodiment, the door ring structure 100 can be manufactured by the same manufacturing method as in the first embodiment. For example, when there is a portion in the bead 381 of the vertical wall 34 and / or the vertical wall 35 that forms a negative angle, that is, a portion that forms an angle that inwards relative to the pressing direction, as in the rocker outers 30A and 30B, the bead 381 can also be formed using a cam or the like.

[0082] The door ring structure 100 (FIG. 1) including any one of the rocker outers 30, 30A, and 30B may be manufactured by a manufacturing method different from the manufacturing method described in the first embodiment, as shown in FIGS. 6A to 6C.

[0083] 6A to 6C are schematic diagrams illustrating a method for manufacturing a door ring structure 100 (FIG. 1) including a rocker outer 30 (FIG. 2A) according to the first embodiment. The manufacturing method here includes the same preparation and heating steps as those described in the first embodiment, but the manner of the forming step differs from that of the first embodiment. As shown in FIGS. 6A to 6C, in the forming step, a mold 80A different from the mold 80 (FIG. 3C) of the first embodiment is used, and a heated blank 60 is formed into the door ring structure 100 (FIG. 1) that is annular in plan view and quenched.

[0084] 6A to 6C show a cross section of a portion of mold 80A corresponding to rocker outer 30 (FIGS. 1 and 2A). Mold 80A includes a punch 81A, a die 82, and a pad 83. Mold 80A differs from mold 80 of the first embodiment (FIG. 3C) mainly in the configuration of punch 81A.

[0085] In the die 80 of the first embodiment, the portion of the punch 81 used to form the rocker outer 30 (FIG. 2A) includes a cushion 812 (FIG. 3C) that is receivable within the punch body 811. On the other hand, in the die 80A, the portion of the punch 81A used to form the rocker outer 30 does not include such a cushion. The punch 81A has a forming surface that corresponds to the rocker outer 30. The top surface of the punch 81A is provided with a recess 812a for forming the bead 382 (FIG. 2A). The side surface of the punch 81A is provided with a step 811a for forming the bead 381 (FIGS. 2A and 2B).

[0086] As shown in Fig. 6A, in the forming process, first, blank 60 is placed between punch 81A and die 82 / pad 83. Then, die 82 and pad 83 are moved relative to punch 81A in the pressing direction, and die 82 and pad 83 are brought closer to punch 81A. As a result, blank 60 is first sandwiched between pad 83 and punch 81A. More specifically, as shown in Fig. 6B, the portion of blank 60 that will be formed into top plate 31 (Fig. 2A) of outer rocker 30 is sandwiched between pad 83 and punch 81A, and bead 382 is formed in blank 60.

[0087] Thereafter, as shown in FIG. 6C , the blank 60 is pressed by the punch 81A and the die 82 to form the vertical walls 34, 35 and the flanges 36, 37. One or more beads 381 are formed on the vertical wall 34. More specifically, with the blank 60 sandwiched between the pad 83 and the punch 81A, the punch 81A and the die 82 are moved relatively closer in the pressing direction. This causes the elastic member 85 to contract, and the die 82 moves toward the punch 81A relative to the pad 83. The blank 60 is then pressed by the punch 81A and the die 82, and is formed into a shape that conforms to the forming surface of the punch 81A. The blank 60 remains sandwiched between the punch 81A, the die 82, and the pad 83. The blank 60 is cooled (rapidly cooled) by the die 80A, and its microstructure is transformed into martensite. Although not shown, portions of the door ring structure 100 other than the rocker outer 30 are also formed by the die 80A.

[0088] 6A to 6C illustrate an example of manufacturing a door ring structure 100 (FIG. 1) including the rocker outer 30 according to the first embodiment, but a door ring structure 100 including the rocker outer 30A or 30B according to other embodiments can also be manufactured by the manufacturing method shown in FIGS. 6A to 6C. When manufacturing the door ring structure 100 including the rocker outer 30, 30A, 30B, if there are portions in the bead 381 of the vertical wall 34 and / or the vertical wall 35 that form a negative angle, that is, portions that form an angle that inwardly inclines relative to the pressing direction, the bead 381 can also be formed using a cam or the like. Alternatively, the rocker outers 30, 30A, 30B can be appropriately tilted relative to the pressing direction so that there are no portions in the rocker outers 30, 30A, 30B that form a negative angle.

[0089] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present disclosure.

[0090] The above embodiments can be combined as appropriate. For example, the rocker outer 30 according to the first embodiment can also be applied to the configuration of the vertical wall 35 of the rocker outer 30A according to the second embodiment or the rocker outer 30B according to the third embodiment. Similarly, the rocker outer 30A according to the second embodiment can also be applied to the vertical wall 34 or 35 of the rocker outer 30B according to the third embodiment. That is, only one bead 381 can be formed on one of the vertical walls 34, 35, and multiple beads 381 can be formed on the other of the vertical walls 34, 35. Furthermore, in each of the rocker outers 30A, 30B, the bead 381 does not have to be provided on one of the vertical walls 34, 35.

[0091] In each of the rocker outers 30, 30A, 30B according to the above embodiments, the vertical walls 34, 35 each include one or two beads 381. However, each of the vertical walls 34, 35 may also include three or more beads 381 that protrude from the reference line R1 to the inside or outside of the rocker outer in a cross-sectional view of the rocker outer. Even when the vertical wall 34 and / or the vertical wall 35 includes three or more beads 381, the total depth D1 of the beads 381 in the corresponding vertical wall is 4.0 times or more the plate thickness t of the top plate 31.

[0092] In the rocker outer 30 according to the first embodiment, one bead 382 is provided on the top plate 31. However, as shown in FIG. 7, the top plate 31 may be provided with a plurality of beads 382 arranged in the vertical direction of the vehicle body. Alternatively, as shown in FIG. 8, the top plate 31 may not have any beads 382. Similarly, in the rocker outers 30A and 30B according to the other embodiments, the top plate 31 may include a plurality of beads 382 or may not include a bead 382. When the top plate 31 includes a plurality of beads 382, ​​the depth D2 of each bead 382 may be the same as or different from the depth D2 of the other beads 382. It is preferable that the depth D2 of at least one of the plurality of beads 382 is 5.0 times or more the plate thickness t of the top plate 31.

[0093] In the rocker outers 30, 30A, and 30B according to the above embodiments, the bead 382 of the top plate 31 has a generally triangular shape in cross section. However, the cross-sectional shape of the bead 382 is not particularly limited. Similarly, the shape of the bead 381 provided on the vertical walls 34 and / or 35 is not particularly limited. The beads 381, 382 may each have a polygonal shape, such as a rectangular or trapezoidal shape, in cross section. However, from the viewpoint of further extending the cross-sectional line length of the rocker outers 30, 30A, and 30B, it is preferable that the bead 381 of the vertical walls 34 and / or 35 have a shape, such as a triangular or curved shape, whose apex does not extend substantially parallel to the reference line R1. Similarly, the bead 382 of the top plate 31 may also have a shape, such as a triangular or curved shape, whose bottom does not extend substantially parallel to the straight line L0.

[0094] In the above embodiment, the annular blank 60, which is the material for the door ring structure 100, includes four steel plates 61, 62, 63, and 64. However, the blank 60 may be formed of two or three steel plates forming an annular shape, or may include five or more steel plates. The positions of the joints between the steel plates in the blank 60 and the door ring structure 100 can be changed as appropriate.

[0095] In the above embodiment, the plurality of steel plates forming the annular blank 60 may each be a single layer or a multi-layer. That is, each of these steel plates may be a plate material made of a single steel plate, or may be a plate material made by overlapping a plurality of steel plates.

[0096] In the above embodiment, the rocker outers 30, 30A, 30B are manufactured by hot stamping. In order to ensure sufficient depths D1, D2 of the beads 381, 382, ​​respectively, it is preferable that the rocker outers 30, 30A, 30B be manufactured by hot stamping. However, the rocker outers 30, 30A, 30B may also be manufactured by cold forming. Also, in the above embodiment, the rocker outers 30, 30A, 30B are press-formed integrally with the other frame members 11, 12, 20, but the rocker outers 30, 30A, 30B may also be press-formed separately from the other frame members 11, 12, 20.

[0097] In the above embodiment, the door ring structure 100 includes any one of the rocker outers 30, 30A, and 30B, the A-pillar upper outer 11, the A-pillar lower outer 12, and the B-pillar outer 20. However, the door ring structure 100 may further include other components. For example, as shown in FIG. 9, the door ring structure 100 may further include a C-pillar outer 90. The door ring structure 100 according to the above embodiment has a single ring shape. On the other hand, the door ring structure 100 shown in FIG. 9 has a double ring shape. When the double-ring door ring structure 100 is integrally molded, the blank that serves as the material for the structure also has a double ring shape. [Example]

[0098] The present disclosure will be described in more detail below with reference to examples, although the present disclosure is not limited to the following examples.

[0099] To confirm the effects of the present disclosure, CAE analysis was performed on the rocker outer described in the above embodiment using commercially available software (LS-DYNA R9.3.1, manufactured by Ansys) while changing the bead depth on the vertical wall. The analysis conditions and results are shown in Table 1.

[0100] [Table 1]

[0101] In this analysis, for Comparative Examples 1 to 3 and Examples 1 to 6 shown in Table 1, a vehicle body to which a door ring structure including a rocker outer was assembled was collided with a 254 mm diameter pole at an impact angle of 75° and a speed of 32 km / h in accordance with the pole side impact test standards of the National Highway Traffic Safety Administration (NHTSA), and the equivalent plastic strain at that time was evaluated. More specifically, for each Comparative Example and Example, equivalent plastic strain was obtained at 2 mm intervals along the ridge-like portion created by deformation of the rocker outer during the collision from the boundary with the B-pillar outer to a position 34 mm toward the rocker outer, and the maximum value was evaluated. A steel plate with a tensile strength of 1470 MPa and a thickness of 1.2 mm was used as the material for the rocker outer.

[0102] The rocker outer according to Comparative Example 1 has no beads on either the top plate or the two vertical walls. The rocker outer according to Comparative Example 2 has one bead on the top plate but no beads on the two vertical walls. The rocker outer according to Comparative Example 3 has no bead on the top plate but one convex bead on each vertical wall. However, in Comparative Example 3, the depth of the bead on each vertical wall is less than 4.0 times the plate thickness of the top plate: 1.2 mm. On the other hand, the rocker outer according to Example 1 has no bead on the top plate but one concave bead formed on each vertical wall. The rocker outer according to Example 2 has no bead on the top plate but two beads formed in a stepped (convex / concave) shape on each vertical wall. The rocker outer according to Example 3 has one bead on the top plate and two beads formed in a stepped shape on each vertical wall, similar to Example 2. In the rocker outer according to Example 4, there is no bead on the top plate, and one concave bead is provided on each vertical wall. In the rocker outer according to Example 5, there is no bead on the top plate, and one convex bead is provided on each vertical wall. In the rocker outer according to Example 6, there is no bead on the top plate, and one concave bead is provided only on one vertical wall (the vertical wall on the upper side of the vehicle body). In Examples 1 to 6, the total depth of the beads on each vertical wall is 4.0 times or more the plate thickness of the top plate: 1.2 mm.

[0103] As shown in Table 1, in Comparative Example 3, in which a relatively shallow bead (a bead with a depth less than 4.0 times the thickness of the top plate) was formed on each vertical wall, the maximum value of equivalent plastic strain was larger than in Comparative Examples 1 and 2, in which no bead was formed on each vertical wall. In other words, in Comparative Example 3, although beads were provided on each vertical wall, strain concentration resulted. On the other hand, in Examples 1 to 6, in which beads were formed on each vertical wall so that their total depth was 4.0 times or more the thickness of the top plate, the maximum value of equivalent plastic strain was significantly smaller than in Comparative Examples 1 to 3. In Example 1, in which the total bead depth was 4.2 times the thickness of the top plate, the maximum value of equivalent plastic strain was reduced by more than 20% compared to Comparative Example 1. In Example 4, in which the conditions were the same as Example 1 except for the total bead depth, the maximum value of equivalent plastic strain was reduced by more than 25% compared to Comparative Example 1. The total bead depth of each vertical wall in Example 4 was 6.7 times the thickness of the top plate, which is larger than Example 1. Therefore, it was confirmed that providing one or more beads on the vertical walls so that the total depth is 4.0 times or more the plate thickness alleviates the concentration of strain at the deformed portion of the rocker outer during a side impact with a pole. The greater the total bead depth, the more the concentration of strain is alleviated. The total bead depth on each vertical wall should be 4.0 times or more the plate thickness of the top plate, but is preferably 5.0 times or more the plate thickness of the top plate, and more preferably 6.0 times or more the plate thickness of the top plate.

[0104] In Example 6, beads are provided only on the upper vertical wall of the vehicle body. When Example 6 is compared with Example 2, which has the same total bead depth per vertical wall, the maximum values ​​of equivalent plastic strain are almost the same. Therefore, it was confirmed that the effect of alleviating strain concentration can be obtained even when one or more beads are provided on only one vertical wall. However, considering the effect of deformation of the rocker outer on the ridges on the upper and lower sides of the vehicle body, it is preferable to provide beads on both vertical walls.

[0105] In Example 4, a concave bead is provided on each vertical wall on the inside of the rocker outer. On the other hand, in Example 5, a convex bead is provided on each vertical wall on the inside of the rocker outer. In both Examples 4 and 5, the maximum value of equivalent plastic strain was significantly reduced compared to Comparative Example 1. Therefore, regardless of the unevenness of the beads, it is possible to alleviate the concentration of strain at the deformed portion of the rocker outer. However, since the reduction in the maximum value of equivalent plastic strain compared to Comparative Example 1 was greater in Example 5 than in Example 4, in order to further alleviate the concentration of strain, it is preferable that the vertical walls include beads that protrude outside the rocker outer.

[0106] Comparing Examples 2 and 3, which differ only in the presence or absence of a bead on the top plate, Example 3, in which a bead was formed on the top plate, showed a lower maximum value of equivalent plastic strain. Therefore, in order to further alleviate the concentration of strain, it is preferable to provide a bead on the top plate in addition to the vertical wall. The depth of the bead on the top plate is preferably 5.0 times or more the thickness of the top plate, more preferably 6.0 times or more the thickness of the top plate, and even more preferably 7.5 times or more the thickness of the top plate. [Explanation of symbols]

[0107] 30, 30A, 30B: Rocker outer 31: Top plate 32, 33: Ridge 34,35: Vertical wall 36,37: Flange 381: Bead (1st bead) 382: Bead (second bead) 60: Blank 80, 80A: Mold 81, 81A: Punch 811: Punch body 812: Cushion 82: Die 83: Pad 100: Door ring structure

Claims

1. A rocker outer for an automobile, The top plate and Two vertical walls are arranged on both sides of the top plate and are connected to the top plate via ridge portions, respectively; a flange connected to each of the two vertical walls on the opposite side of the top plate; Equipped with The rocker outer is formed from a steel plate having a tensile strength of 980 MPa or more, At least one of the two vertical walls includes one or more first beads extending in the longitudinal direction of the rocker outer, In a cross section of the rocker outer, when a straight line connecting an end portion of the at least one vertical wall on the top plate side and an end portion on the flange side is set as a reference line, the one or more first beads protrude from the reference line to the inside or outside of the rocker outer, A rocker outer, wherein the total depth of the one or more first beads relative to the reference line is 4.0 times or more the plate thickness of the top plate.

2. The rocker outer according to claim 1, A rocker outer, wherein each of the two vertical walls includes the one or more first beads.

3. The rocker outer according to claim 1, The top plate has a concave shape on the inside of the rocker outer and includes a second bead extending in the longitudinal direction.

4. The rocker outer according to claim 3, The second bead has a depth that is 5.0 times or more the plate thickness.

5. The rocker outer according to claim 3, A rocker outer, wherein in a cross section of the rocker outer with the two vertical walls positioned above and below, the center of the bottom of the second bead is positioned below the center of the top plate.

6. A door ring structure for an automobile, comprising: A door ring structure comprising the rocker outer according to any one of claims 1 to 5.

7. A manufacturing method for manufacturing the door ring structure according to claim 6, comprising: a preparation step of preparing a blank having an annular shape in a plan view; a heating step of heating the blank to an austenite transformation completion temperature or higher; a forming step of forming the heated blank into the door ring structure using a die and quenching the formed blank; Equipped with The mold includes a punch, a die, and a pad, a portion of the punch for forming the rocker outer includes a punch body and a cushion that faces the pad and is arranged so as to be receivable within the punch body; In the forming process, the portion of the blank to be formed into the top plate is clamped between the pad and the cushion, and then the blank is pressed by the punch body and the die while being clamped between the pad and the cushion.

8. A manufacturing method for manufacturing the door ring structure according to claim 6, comprising: a preparation step of preparing a blank having an annular shape in a plan view; a heating step of heating the blank to an austenite transformation completion temperature or higher; a forming step of forming the heated blank into the door ring structure using a die and quenching the formed blank; Equipped with The mold includes a punch, a die, and a pad, In the forming process, the portion of the blank to be formed into the top plate is clamped between the pad and the punch, and the blank is pressed by the punch and the die to form the vertical wall and the flange.

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