A-pillar upper outer, door ring structure, and method for manufacturing door ring structure

Abstract

A-pillar upper outers (10, 10A, 10B, 10C, 10D) comprise a pillar body (11). The pillar body (11) includes a top plate (111), ridge line sections (112, 113), vertical walls (114, 115), and flanges (116, 117). The pillar body (11) extends while curving with one ridge line section (112), one vertical wall (114), and one flange (116) on the outside of the curve, and the other ridge line section (113), the other vertical wall (115), and the other flange (117) on the inside of the curve. A bead (118) is formed on the top plate (111) within a range (R1) of 200 to 500 mm in the longitudinal direction from an end section (11e) of the pillar body (11). The bead (118) has a recessed shape inside the pillar body (11) and extends in the longitudinal direction of the pillar body (11).

Description

A-pillar upper outer, door ring structure, and method for manufacturing door ring structure

[0001] The present disclosure relates to an A-pillar upper outer for an automobile, and also to a door ring structure for an automobile and a method for manufacturing the same.

[0002] An automobile body includes a plurality of 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 forms 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.

[0004] Special Publication No. 2021-528248

[0005] In recent years, high-strength materials have been increasingly used for automotive frame members in order to ensure high crash resistance. Frame members are formed, for example, from steel materials having a tensile strength of 980 MPa or more. However, as the strength of steel materials increases, their ductility decreases, which poses a problem: 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 longitudinal collision load is applied to the A-pillar upper outer when the vehicle is involved in a frontal collision. When the A-pillar upper outer is deformed by this collision load, tensile strain is concentrated in a portion of the A-pillar upper outer. If the A-pillar upper outer is formed from a high-strength material with low ductility, the A-pillar upper outer is likely to fracture at the location where the strain is concentrated. If the A-pillar upper outer fractures, the energy absorption performance of the A-pillar upper 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 an A-pillar upper outer that is less likely to break during a vehicle collision.

[0008] The A-pillar upper outer for an automobile according to the present disclosure includes a steel pillar body. The pillar body has a tensile strength of 980 MPa or more. The pillar body includes a top plate, a first vertical wall, a first flange, a second vertical wall, and a second flange. The first vertical wall is connected to the top plate via a first ridge portion. The first flange is connected to the first vertical wall on an opposite side of the top plate. The second vertical wall is connected to the top plate via a second ridge portion on an opposite side of the first vertical wall. The second flange is connected to the second vertical wall on an opposite side of the top plate. The pillar body extends while curving, with the first ridge portion, first vertical wall, and first flange side on the outside of the curve and the second ridge portion, second vertical wall, and second flange side on the inside of the curve. A bead is formed on the top plate in a range of 200 mm to 500 mm in the longitudinal direction from the end of one of the longitudinal ends of the pillar body that is located forward when the A-pillar upper outer is installed in the vehicle body. The bead has a concave shape on the inside of the pillar body and extends in the longitudinal direction.

[0009] According to the present disclosure, it is possible to make it less likely that the A-pillar upper outer will break in the event of a vehicle collision.

[0010] FIG. 1 is a side view of the door ring structure according to the first embodiment. FIG. 2 is a cross-sectional view taken along line II-II of FIG. 1. FIG. 3A is a schematic view illustrating a manufacturing method of the door ring structure according to the first embodiment. FIG. 3B is a schematic view illustrating a manufacturing method of the door ring structure according to the first embodiment. FIG. 3C is a schematic view illustrating a manufacturing method of the door ring structure according to the first embodiment. FIG. 3D is a schematic view illustrating a manufacturing method of the door ring structure according to the first embodiment. FIG. 3E is a schematic view illustrating a manufacturing method of the door ring structure according to the first embodiment. FIG. 4 is a side view of an A-pillar upper outer according to the second embodiment. FIG. 5 is a cross-sectional view of an A-pillar upper outer according to the third embodiment. FIG. 6 is a cross-sectional view of an A-pillar upper outer according to the fourth embodiment. FIG. 7 is a cross-sectional view of an A-pillar upper outer according to the fifth embodiment. FIG. 8A is a schematic view illustrating a manufacturing method different from the manufacturing method of the door ring structure according to the first embodiment. FIG. 8B is a schematic view illustrating a manufacturing method different from the manufacturing method of the door ring structure according to the first embodiment. Fig. 8C is a schematic diagram for explaining a manufacturing method different from the manufacturing method of the door ring structure according to the first embodiment. Fig. 9 is a side view of a door ring structure according to a modified example of the above embodiment. Fig. 10 is a graph showing the maximum values ​​of equivalent plastic strain for each example and comparative example.

[0011] An A-pillar upper outer for an automobile according to an embodiment includes a steel pillar body. The pillar body has a tensile strength of 980 MPa or more. The pillar body includes a top plate, a first vertical wall, a first flange, a second vertical wall, and a second flange. The first vertical wall is connected to the top plate via a first ridge portion. The first flange is connected to the first vertical wall on an opposite side of the top plate. The second vertical wall is connected to the top plate via a second ridge portion on an opposite side of the first vertical wall. The second flange is connected to the second vertical wall on an opposite side of the top plate. The pillar body extends while curving, with the first ridge portion, first vertical wall, and first flange side on the outside of the curve and the second ridge portion, second vertical wall, and second flange side on the inside of the curve. A bead is formed on the top plate in a range of 200 mm to 500 mm in the longitudinal direction from the end of one of the longitudinal ends of the pillar body that is located forward when the A-pillar upper outer is installed in the vehicle body. The bead has a concave shape on the inside of the pillar body and extends in the longitudinal direction (first configuration).

[0012] A large portion of the A-pillar upper outer typically curves upward in a convex shape in a side view of the vehicle body and extends in the fore-and-aft direction of the vehicle body. In other words, in the A-pillar upper outer, the pillar body extends while curving, with the first ridgeline, first vertical wall, and first flange side on the outer side of the curve and the second ridgeline, second vertical wall, and second flange side on the inner side of the curve. When a vehicle including an A-pillar upper outer experiences a frontal collision, particularly an offset frontal collision, a collision load is applied to the steel pillar body in its longitudinal direction. According to research conducted by the present inventors, during a vehicle collision, bending deformation is likely to occur in the second vertical wall on the inner side of the curve within a range of 200 mm to 500 mm in the longitudinal direction from the front end of the pillar body, and tensile stress is likely to occur in the second ridgeline adjacent to the second vertical wall, resulting in concentrated strain. Therefore, in the A-pillar upper outer according to the first configuration, a bead is formed on the top plate of the pillar body in a range of 200 mm to 500 mm longitudinally from the front end of the pillar body. By including a bead in the A-pillar upper outer in a region where bending deformation is likely to occur, the cross-sectional line length of that region is extended, making it possible to distribute strain in that region. As a result, even if the pillar body is formed from a high-strength material with a tensile strength of 980 MPa or more, the A-pillar upper outer is less likely to break in a vehicle collision.

[0013] In the A-pillar upper outer according to the first configuration, the bead can have a depth that is 3.0 times or more the thickness of the top plate (second configuration).

[0014] In the second configuration, a deep bead is formed on the top plate of the pillar body in a range of 200 mm to 500 mm from the front end of the pillar body, the bead being at least 3.0 times the plate thickness. This allows the cross-sectional line length of the pillar body to be extended in areas prone to deformation in a vehicle collision, making the A-pillar upper outer more resistant to fracture.

[0015] For the A-pillar upper outer relating to the first or second configuration, when the pillar body is viewed in cross section, it is preferable that the center of the bottom of the bead is positioned at a position offset from the center of the top plate in the width direction of the pillar body (third configuration).

[0016] For example, when the position of the center of the bead bottom is changed while the bead depth and the distance between both edges are fixed in the cross section of the pillar body, the cross-sectional line length of the pillar body is more likely to increase when the center of the bead bottom is shifted in the width direction from the center of the top plate, as in the third configuration, than when the center of the bead bottom in the width direction of the pillar body is aligned with the center of the top plate. When the cross-sectional line length of the pillar body is longer, strain is more easily dispersed when deformation occurs in the pillar body. This makes it less likely for the A-pillar upper outer to break.

[0017] For the A-pillar upper outer relating to the third configuration, when the pillar body is viewed in cross section, the center of the bottom of the bead may be positioned on the second ridge portion side relative to the center of the top plate in the width direction of the pillar body (fourth configuration).

[0018] In the fourth configuration, the center of the bottom of the bead is located closer to the second ridgeline than the center of the top plate in the cross section of the pillar body, i.e., on the lower side of the vehicle body. In this case, when the pillar body deforms during a vehicle collision, strain is more easily dispersed, making it even less likely for the A-pillar upper outer to break.

[0019] For an A-pillar upper outer according to any of the first to fourth configurations, when the pillar body is viewed in cross section, it is preferable that the bead has an asymmetric shape with respect to the center line of the bead in the width direction of the pillar body (fifth configuration).

[0020] In the fifth configuration, the bead has an asymmetric shape with respect to the centerline in the width direction in a cross-sectional view of the pillar body. In this case, the cross-sectional line length of the pillar body can be increased compared to when the bead has a symmetric shape with respect to the centerline in the width direction. This makes it easier to disperse strain when deformation occurs in the pillar body, making it less likely for the A-pillar upper outer to break.

[0021] In the A-pillar upper outer according to any of the first to fifth configurations, one or more steps may be formed in the second vertical wall within a range of 200 mm or more and 500 mm or less in the longitudinal direction from the end of the pillar body (sixth configuration).

[0022] According to the sixth configuration, a step is provided in the second vertical wall within a range of 200 mm to 500 mm in the longitudinal direction from the front end of the pillar body. This extends the cross-sectional line length of the pillar body at the portion where deformation is likely to occur, further dispersing strain. This makes it more difficult for the A-pillar upper outer to break in the event of a vehicle collision.

[0023] A door ring structure for an automobile according to an embodiment includes an A-pillar upper outer according to any one of the first to sixth configurations (seventh configuration).

[0024] A manufacturing method according to an embodiment manufactures a door ring structure according to the seventh 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 and quench the heated blank into a door ring structure. The die includes a punch, a die, and a pad. The portion of the punch used to form the pillar body includes a punch body and a cushion. The cushion faces the pad and is disposed so as to be 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 to form a bead in the blank, and then the blank can be pressed by the punch body and the die while sandwiched between the pad and the cushion (eighth configuration).

[0025] A manufacturing method according to another embodiment manufactures the door ring structure according to the seventh 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 forming the heated blank into a door ring structure and quenching it using a die. 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 to form a bead in the blank, and the blank is pressed with the punch and die to form the first vertical wall, the second vertical wall, the first flange, and the second flange (ninth configuration).

[0026] To simplify the manufacturing process of a door ring structure, it is conceivable to integrate multiple frame components, including an A-pillar upper outer, from the blank stage. 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 the 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 the door ring structure using a die and quenched. The door ring structure is contacted with the die and cooled (rapidly cooled), whereby its microstructure transforms 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.

[0027] 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, in the case of an A-pillar upper outer, residual stress in the top plate can cause springback in the pillar body, resulting in twisting of the door ring structure.

[0028] In the manufacturing method according to the eighth configuration, when forming an annular blank into a door ring structure, the portion of the blank that will become the top plate of the pillar body is first sandwiched between the pad and cushion at the position of the A-pillar upper outer. In other words, the top plate of the pillar body is in contact with the pad and cushion from the early stages of forming, ensuring a sufficient cooling rate. This makes it easier for the microstructure of the top plate of the pillar body to become a martensitic single-phase structure, facilitating stress release. This reduces springback in the pillar body and makes it easier to suppress torsion of the door ring structure. Therefore, the manufacturing method according to the eighth configuration can improve the dimensional accuracy of the door ring structure.

[0029] In the manufacturing methods according to the eighth and ninth configurations, a door ring structure including an A-pillar upper outer is manufactured by hot stamping. This allows the A-pillar upper outer to have high strength (tensile strength: 980 MPa or more) and allows a relatively deep bead to be formed in the top plate of the A-pillar upper outer. For example, even if the cross-sectional shape of the bead is not uniform in the longitudinal direction of the A-pillar upper outer and it is difficult to form the bead by simple bending, hot stamping makes it possible to form a relatively deep bead in the top plate of the A-pillar upper outer while suppressing cracking.

[0030] 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.

[0031] <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 in a state where it is incorporated into the body of the automobile. Hereinafter, this embodiment will be described by assuming that the front, rear, left, and right of the automobile in a state where the door ring structure 100 is incorporated into the body are the front, rear, left, and right of the door ring structure 100 and the frame members included in the door ring structure 100.

[0032] 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 10, an A-pillar lower outer panel 20, a B-pillar outer panel 30, and a rocker outer panel 40.

[0033] The A-pillar lower outer 20 is disposed in front of and below the A-pillar upper outer 10 and is joined to the A-pillar upper outer 10. The B-pillar outer 30 is joined to the rear of the A-pillar upper outer 10 and extends downward from the A-pillar upper outer 10. The rocker outer 40 is joined to the lower end portions of the A-pillar lower outer 20 and the B-pillar outer 30 and extends in the fore-and-aft direction.

[0034] 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.

[0035] Continuing to refer to FIG. 1 , the A-pillar upper outer panel 10 includes a pillar body 11. The pillar body 11 has an elongated shape and extends generally in the longitudinal direction when the A-pillar upper outer panel 10 is installed in the body of an automobile. The pillar body 11 is made of steel. The pillar body 11 is formed from one or more steel plates. The pillar body 11 has a tensile strength of 980 MPa or more, preferably 1470 MPa or more, and more preferably 1760 MPa or more. The tensile strength of the pillar body 11 can be obtained by taking a test specimen from a relatively flat portion of the pillar body 11 and performing a tensile test on this test specimen in accordance with JIS Z 2241:2022.

[0036] The pillar body 11 includes a top plate 111 , ridge portions 112 and 113 , vertical walls 114 and 115 , and flanges 116 and 117 .

[0037] The top plate 111 extends in the longitudinal direction of the pillar body 11. The ridge portions 112, 113, the vertical walls 114, 115, and the flanges 116, 117 also extend in the longitudinal direction of the pillar body 11. The vertical wall 114 is connected to the top plate 111 via the ridge portion 112. The flange 116 is connected to the vertical wall 114 on the opposite side of the top plate 111. The vertical wall 115 is connected to the top plate 111 via the ridge portion 113 on the opposite side of the vertical wall 114. The flange 117 is connected to the vertical wall 115 on the opposite side of the top plate 111.

[0038] The pillar main body 11 extends while curving, with one ridge line portion 112, vertical wall 114, and flange 116 side being the outer side of the curve, and the other ridge line portion 113, vertical wall 115, and flange 117 side being the inner side of the curve. In other words, in a side view of the A-pillar upper outer panel 10, the pillar main body 11 extends from the front to the rear and is curved upwardly convexly as a whole.

[0039] The radius of curvature of the pillar body 11 is, for example, 800 mm or more. The radius of curvature of the pillar body 11 may be 10,000 mm or less. The radius of curvature of the pillar body 11 can be obtained by placing measurement points at 40 mm intervals rearward from the front end 11e of the pillar body 11 along the inside of the curve, i.e., the free end of the flange 117 located lower on the vehicle body, and sequentially measuring the radius of curvature of an arc passing through three adjacent measurement points while shifting the measurement points one by one. The radius of curvature of the pillar body 11 typically varies along the longitudinal direction of the pillar body 11. However, the pillar body 11 may have a substantially constant radius of curvature throughout its entire length.

[0040] A bead 118 is formed on the top plate 111 of the pillar main body 11 at least in a range R1. The range R1 is a range of 200 mm to 500 mm in the longitudinal direction of the pillar main body 11 from the end (front end) 11e of the pillar main body 11 that is located forward when the A-pillar upper outer 10 is installed in the vehicle body. More specifically, the range R1 is determined based on the free end of the flange 117 on the inside of the curve (underside of the vehicle body) of the pillar main body 11, and refers to a range of 200 mm to 500 mm rearward from the front end 11e of the pillar main body 11 along the free end of the flange 117. In a side view of the A-pillar upper outer 10, the free end of the flange 117 extends in the fore-and-aft direction while curving upward in a convex shape.

[0041] Figure 2 is a cross-sectional view (cross-sectional view taken along line II-II in Figure 1) of the pillar body 11. The cross-section of the pillar body 11 is a cross-section obtained by cutting the pillar body 11 along a plane that is substantially perpendicular to the extension direction of the free end of the flange 117. Figure 2 shows the A-pillar upper inner 50 in addition to the pillar body 11 of the A-pillar upper outer 10.

[0042] Referring to FIG. 2 , the A-pillar upper outer 10 and the A-pillar upper inner 50 form a closed cross section. The pillar main body 11 of the A-pillar upper outer 10 has a generally hat-like shape in cross section. In the cross section of the pillar main body 11, ridge lines 112 and 113 are disposed adjacent to both sides of the top plate 111 and each have a curved shape that convexly extends outward from the pillar main body 11. The vertical walls 114 and 115 are continuous with the ridge lines 112 and 113, respectively, and extend from the ridge lines 112 and 113 to the opposite side of the top plate 111 in the cross section of the pillar main body 11. The flanges 116 and 117 protrude outward from the vertical walls 114 and 115, respectively. The flanges 116 and 117 are joined to the A-pillar upper inner 50 by, for example, spot welding. That is, the opening between the vertical walls 114 , 115 of the A-pillar upper outer 10 is closed by the A-pillar upper inner 50 .

[0043] The top plate 111 of the pillar main body 11 of the A-pillar upper outer panel 10 includes a bead 118 in a range R1 ( FIG. 1 ). The bead 118 has a concave shape extending from the top plate 111 toward the inside of the pillar main body 11. The bead 118 extends in the longitudinal direction of the pillar main body 11 over at least the entire range R1. In other words, the bead 118 has a length in the longitudinal direction of the pillar main body 11 that is equal to or greater than the range R1. The bead 118 may be provided only within the range R1, or may extend beyond the range R1 in the longitudinal direction of the pillar main body 11.

[0044] In a cross section of the pillar main body 11, when the direction of extension of a straight line L0 connecting a boundary B1 between the top plate 111 and one ridge line portion 112 and a boundary B2 between the top plate 111 and the other ridge line portion 113 is defined as the width direction of the pillar main body 11, the width of the opening of the bead 118 is smaller than the width W of the top plate 111 (the linear distance between the boundaries B1 and B2). Therefore, flat portions 111a are present in the top plate 111 between the bead 118 and the ridge line portion 112 and between the bead 118 and the ridge line portion 113, respectively. In the cross section of the pillar main body 11, the flat portions 111a are portions of the top plate 111 that are disposed on the straight line L0 and extend substantially along the straight line L0. The width W of the top plate 111 may be, for example, 15 mm or more and 300 mm or less.

[0045] The depth D of the bead 118 is preferably 3.0 times or more the thickness t of the top plate 111. At least within the range R1 ( FIG. 1 ), the depth D of the bead 118 is preferably 3.0 times or more the thickness t of the top plate 111, and more preferably 5.0 times or more the thickness t. The depth D of the bead 118 may be 15.0 times or less the thickness t of the top plate 111. The depth D of the bead 118 is the shortest distance from the line L0 connecting the boundaries B1 and B2 to the line L1 that is parallel to the line L0 and tangent to the bottom of the bead 118 in the cross section of the pillar main body 11. The boundaries B1 and B2 are the ends of the R of the ridges 112 and 113 on the outer surface of the pillar main body 11 on the top plate 111 side, respectively. The line L1 tangent to the bottom of the bead 118 on the outer surface of the pillar main body 11. The thickness t of the top plate 111 is, for example, the thickness measured at the position of the flat portion 111a. The thickness t is, for example, 0.8 mm or more. The thickness t may be 2.0 mm or less. The depth D may be constant over the entire length of the bead 118 extending in the longitudinal direction of the pillar body 11, or may be non-constant. For example, when the bead 118 extends in the longitudinal direction of the pillar body 11 beyond the range R1, the depth D of the bead 118 may be smaller outside the range R1 than within the range R1.

[0046] In this embodiment, when the pillar body 11 is viewed in cross section, the position of the center (bottom center) C1 of the bottom of the bead 118 coincides with the position of the center (width center) C0 of the top plate 111 in the width direction. In this embodiment, when the pillar body 11 is viewed in cross section, the position of the center (width center) of the bead 118 itself also substantially coincides with the position of the width center C0 of the top plate 111 in the width direction. The bead 118 is a portion of the top plate 111 that is located inside the pillar body 11 with respect to the line L0, and the width center of the bead 118 is the center position of that portion in the width direction. The width center C0 of the top plate 111 is a point on the line L0 connecting the boundaries B1 and B2 and is located midway between the boundaries B1 and B2. The bottom center C1 of the bead 118 is the widthwise center point of the line L1, the portion that contacts the bottom of the bead 118 on the outer surface of the pillar body 11. In the cross section of the pillar body 11, when the line L1 makes point contact with the bottom of the bead 118 on the outer surface of the pillar body 11, the contact point between the bottom of the bead 118 and the line L1 becomes the bottom center C1 of the bead 118. In this embodiment, when viewed in the cross section of the pillar body 11, the bead 118 has a shape that is substantially symmetrical with respect to the width center line of the top plate 111 (a line that passes through the width center C0 and is perpendicular to the line L0).

[0047] 3A to 3E, a method for manufacturing the door ring structure 100 will be described. The 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.

[0048] (Preparation Process) As shown in FIG. 3A , in the preparation process, a blank 60 having an annular shape in a 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 multiple 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 a plan view of the blank 60. Each of the steel plates 61, 62, 63, and 64 is butt-joined to an adjacent steel plate, for example, by laser welding. Alternatively, each of the steel plates 61, 62, 63, and 64 may be overlap-joined to an adjacent steel plate, for example, by spot welding. The joining method of the steel plates 61, 62, 63, and 64 is not particularly limited.

[0049] 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 10 (Fig. 1). Steel plates 62, 63, and 64 are disposed in portions of the blank 60 that will become the A-pillar lower outer 20, the B-pillar outer 30, and the rocker outer 40 (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 blank 60 state 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 a plating layer.

[0050] (Heating Step) The prepared blank 60 is formed into the door ring structure 100 (FIG. 1) by hot stamping (hot press working). 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 a temperature of, 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.

[0051] (Forming Process) Referring to Fig. 3C, in the forming process, the heated blank 60 is formed into the door ring structure 100 (Fig. 1) that is annular in plan view using a die 80 and is 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.

[0052] First, a 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 pillar main body 11 (Figs. 1 and 2) of the A-pillar upper outer panel 10. Fig. 3C shows a cross-section of the mold 80 at a portion where the bead 118 is formed on the top plate 111 of the pillar main body 11 shown in Figs. 1 and 2.

[0053] As shown in FIG. 3C , the portion of the punch 81 used to form the pillar body 11 includes a punch body 811 and a cushion 812 that is receivable within the punch body 811. The punch body 811 has a recessed accommodating portion 811a on its top surface. The cushion 812 is supported on the bottom surface of the accommodating portion 811a via, for example, an elastic member 84. The elastic member 84 is a member that is expandable and contractible in the pressing direction. A gas spring, for example, 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 accommodating portion 811a 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.

[0054] The die 82 is disposed so as to face the punch 81 in the pressing direction. The pad 83 is disposed so as to face the cushion 812 in the pressing direction. The pad 83 is supported by the die 82 or a slide of the pressing device 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.

[0055] A recess 812a for forming a bead 118 (FIG. 2) is formed on the surface of the cushion 812 of the punch 81, which faces the pad 83. A protrusion 831 is formed on the surface of the pad 83, which faces the cushion 812, in correspondence with the recess 812a of the cushion 812.

[0056] 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 extended, 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 extended, 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.

[0057] 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 111 ( FIGS. 1 and 2 ) of the pillar main body 11 is sandwiched between the pad 83 and the cushion 812, and the bead 118 is formed.

[0058] 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 811a 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 conforming to the forming surfaces of the punch 81, the die 82, and the pad 83. The blank 60 is held 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 to martensite.

[0059] Although not shown, the portions of the door ring structure 100 other than the A-pillar upper outer 10 are also formed by a mold 80 including a punch 81, a die 82, and a pad 83. However, in the portion of the A-pillar upper outer 10 where the bead 118 does not exist on the top plate 111, and in the positions where the other frame members 20, 30, 40 are formed, the punch 81 does not need to be provided with a cushion 812. In other words, for the portions of the mold 80 where it is not necessary to form a bead on the top plate of the frame member, it is also possible to perform forming using a punch that is not divided into a punch body and a cushion (a general block-shaped punch).

[0060] [Effects] When assembled into a vehicle body, the A-pillar upper outer 10 according to this embodiment forms a closed cross section together with the A-pillar upper inner 50. Furthermore, when viewed from the side of the vehicle body, the pillar body 11 of the A-pillar upper outer 10 is curved as a whole. In this type of A-pillar upper outer 10, bending deformation is likely to occur in a range R1 between 200 mm and 500 mm rearward from the front end 11e of the pillar body 11 during a vehicle collision. However, in this embodiment, the bead 118 is formed on the top plate 111 of the pillar body 11 throughout the entire range R1, increasing the cross-sectional line length of the pillar body 11 at least in the range R1. This allows for the dispersion of tensile strain associated with bending deformation in the range R1 where bending deformation of the pillar body 11 is likely to occur during a collision. Therefore, even if the tensile strength of the pillar body 11 is 980 MPa or more, the A-pillar upper outer 10 is less likely to break during a vehicle collision.

[0061] In the A-pillar upper outer panel 10 according to this embodiment, the depth D of the bead 118 is preferably 3.0 times or more the thickness t of the top plate 111 in a range R1 that is 200 mm or more and 500 mm or less rearward from the front end 11e of the pillar main body 11. This allows the cross-sectional line length of the pillar main body 11 to be increased in the range R1 where bending deformation due to a collision is likely to occur. This makes it more difficult for the A-pillar upper outer panel 10 to break in the event of a vehicle collision. If the depth D is too large, it becomes difficult to form the bead 118, so the depth D is preferably 15.0 times or less the thickness t of the top plate 111.

[0062] In this embodiment, when the door ring structure 100 including the A-pillar upper outer 10, the A-pillar lower outer 20, the B-pillar outer 30, and the rocker outer 40 is formed from the annular blank 60, the top plate 111 of the pillar main body 11 is sandwiched between the pad 83 and the cushion 812 provided on the punch 81 at the position of the A-pillar upper outer 10. That is, the top plate 111 of the pillar main body 11 contacts the pad 83 and the cushion 812 from the early stage of forming. This ensures a sufficient cooling rate of the top plate 111, which makes it easier for the microstructure of the top plate 111 to become a martensitic single-phase structure and releases stress in the top plate 111. This reduces springback of the pillar main body 11 and suppresses twisting of the door ring structure 100 due to springback. This improves the dimensional accuracy of the door ring structure 100.

[0063] In this embodiment, the A-pillar upper outer 10 is formed by hot stamping. That is, the A-pillar upper outer 10 is a hot-stamped member. Therefore, the pillar body 11 of the A-pillar upper outer 10 includes a martensite phase in its microstructure. For example, the martensite fraction may be 80% or more in the cross section of the pillar body 11. The martensite fraction is preferably 85% or more, and more preferably 90% or more. The martensite fraction can be measured as follows. That is, at a cross section of an arbitrary position of the pillar body 11, 10 or more analysis samples (e.g., approximately 10 mm on the long side) are cut out from positions 20 mm or more away from the tips of the flanges 116, 117 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 to observe a position 1 / 4 of the way through the thickness direction from the surface of the analysis sample at 1000x magnification, and an optical micrograph is obtained. The obtained optical microscope photograph can be subjected to image analysis using, for example, commercially available image analysis software (Photoshop CS5, manufactured by Adobe) to determine the martensite area ratio, which can be used as the martensite fraction.

[0064] 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 area, and calculating the percentage of the number of pixels in the white area 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 of each analysis sample to determine the martensite fraction, and the average value is taken as the martensite fraction of the pillar body 11 of the A-pillar upper outer 10.

[0065] When manufacturing a high-strength, curved A-pillar upper outer panel 10 by cold forming, it is difficult to form a deep bead 118 in the top plate 111 of the pillar main body 11. In particular, when it is difficult to form the bead 118 by simple bending, specifically when the cross-sectional shape of the bead 118 is not uniform over the entire length of the pillar main body 11, for example, when the depth D of the bead 118 is smaller at both ends in the extension direction of the bead 118, cracks are likely to occur in the bead 118 when cold forming is performed. In contrast, in this embodiment, the A-pillar upper outer panel 10 is formed by hot stamping. This makes it possible to give the pillar main body 11 high strength (tensile strength: 980 MPa or more), and to form a bead 118 with a depth D of, for example, 3.0 times the plate thickness t or more in the top plate 111.

[0066] 4 is a side view of an A-pillar upper outer part 10A according to a second embodiment. The A-pillar upper outer part 10A according to this embodiment differs from the A-pillar upper outer part 10A according to the first embodiment in that it includes a transition portion 12 in addition to the pillar main body 11.

[0067] The transition portion 12 is a portion of the door ring structure 100 ( FIG. 1 ) where the A-pillar upper outer panel 10A transitions to the A-pillar lower outer panel 20. As shown in FIG. 4 , the transition portion 12 is located adjacent to the front end portion 11e of the pillar main body 11. The transition portion 12 includes a top plate 121, ridge portions 122 and 123, vertical walls 124 and 125, and flanges 126 and 127. The top plate 121 is continuous with the top plate 111 of the pillar main body 11. The ridge portion 122, the vertical wall 124, and the flange 126 are continuous with the ridge portion 112, the vertical wall 114, and the flange 116 on the curved outer side of the pillar main body 11, respectively. The ridge line portion 123, the vertical wall 125, and the flange 127 are continuous with the ridge line portion 113, the vertical wall 115, and the flange 117 on the curved inner side of the pillar body 11, respectively.

[0068] In an A-pillar upper outer panel 10A including a transition portion 12 integral with the pillar main body 11, the front end 11e of the pillar main body 11 can be determined as follows: Specifically, on the underside of the A-pillar upper outer panel 10A, measurement points P are placed along the free end of the flange 127 of the transition portion 12 and the free end of the flange 117 of the pillar main body 11 at intervals of 40 mm from the end of the flange 127 of the transition portion 12. The reference measurement point is shifted one by one toward the pillar main body 11, and the radius of curvature of the arc passing through the reference measurement point and its adjacent measurement points is measured in sequence. The position of the reference measurement point at which the radius of curvature changes from 800 mm or less to more than 800 mm is defined as the front end 11e of the pillar main body 11. As can be seen from Figure 4 , the free end of the flange 127 of the transition portion 12 extends generally in the vertical direction at a position away from the pillar main body 11, but bends rearward near the pillar main body 11. That is, the free end of the flange 127 of the transition section 12 has a relatively small radius of curvature near the pillar body 11. Therefore, the radius of curvature switches from 800 mm or less to over 800 mm at the boundary between the transition section 12 and the pillar body 11. This point of change in the radius of curvature corresponds to the front end 11e of the pillar body 11.

[0069] In this embodiment, as in the first embodiment, a bead 118 is formed on the top plate 111 of the pillar body 11 in a range R1 that is 200 mm or more and 500 mm or less in the longitudinal direction from the front end portion 11e of the pillar body 11. Therefore, the A-pillar upper outer panel 10A according to this embodiment can also achieve the same effects as the A-pillar upper outer panel 10 according to the first embodiment.

[0070] 5 is a cross-sectional view of the pillar body 11 of an A-pillar upper outer part 10B according to a third embodiment. In this embodiment, a bead 118 is formed on the top plate 111 of the pillar body 11 at least in a range R1 (FIGS. 1 and 4) that is 200 mm to 500 mm in the longitudinal direction from the front end 11e of the pillar body 11.

[0071] In the A-pillar upper outer panel 10 according to the first embodiment, when the pillar body 11 is viewed in cross section, the position of the bottom center C1 of the bead 118 coincides with the position of the width center C0 of the top panel 111 in the width direction of the pillar body 11 ( FIG. 2 ). In the first embodiment, when the pillar body 11 is viewed in cross section, the bead 118 has a shape that is substantially symmetrical with respect to the center line of the bead 118 in the width direction of the pillar body 11. On the other hand, in the A-pillar upper outer panel 10B according to the present embodiment, when the pillar body 11 is viewed in cross section, the bead 118 has a shape that is asymmetrical with respect to the center line (width center line) of the bead 118 in the width direction of the pillar body 11. The width center line of the bead 118 is a straight line that passes through the width center of the bead 118 in the cross section of the pillar body 11 and is perpendicular to the line L0. In the width direction of the pillar body 11, the bottom center C1 of the bead 118 is located on the curved outer ridge portion 112 side relative to the width center C0 of the top plate 111. The bottom center C1 of the bead 118 is preferably offset in the width direction from the width center C0 of the top plate 111 by 10% or more of the width W of the top plate 111. In the example shown in FIG. 5 , the position of the width center of the bead 118 substantially coincides with the position of the width center C0 of the top plate 111 in the width direction of the pillar body 11. Therefore, when viewed in cross section of the pillar body 11, the bead 118 also has an asymmetric shape with respect to the width center line of the top plate 111 (a line passing through the width center C0 and perpendicular to the line L1). However, the position of the width center of the bead 118 does not necessarily have to coincide with the position of the width center C0 of the top plate 111 in the width direction of the pillar body 11. The depth D and length of the bead 118 can be set in the same manner as in the first embodiment.

[0072] The A-pillar upper outer panel 10B according to this embodiment can achieve the same effects as the A-pillar upper outer panels 10, 10A according to the other embodiments. In particular, in this embodiment, when the pillar body 11 is viewed in cross section, the center C1 of the bottom of the bead 118 is positioned offset from the center C0 of the top plate 111 in the width direction of the pillar body 11. More specifically, when viewed in cross section of the pillar body 11, the bead 118 is provided on the top plate 111 so as to be asymmetric with respect to the width center line. In this case, the cross-sectional line length of the bead 118 is more likely to be extended than when the position of the bottom center C1 of the bead 118 coincides with the position of the width center C0 of the top plate 111. In other words, the cross-sectional line length of the pillar body 11 where the bead 118 is provided is longer. This makes it easier to distribute strain in the pillar body 11 during a vehicle collision, making it less likely for the A-pillar upper outer panel 10B to break.

[0073] 6 is a cross-sectional view of the pillar body 11 of an A-pillar upper outer part 10C according to the fourth embodiment. In this embodiment, too, a bead 118 is formed on the top plate 111 of the pillar body 11 in at least a range R1 (FIGS. 1 and 4) that is 200 mm to 500 mm in the longitudinal direction from the front end 11e of the pillar body 11.

[0074] In this embodiment, as in the third embodiment, when the pillar body 11 is viewed in cross section, the bead 118 has an asymmetric shape with respect to the center line (width center line) of the bead 118 in the width direction of the pillar body 11. When viewed in cross section of the pillar body 11, the bead 118 has an asymmetric shape with respect to the width center line of the top plate 111 (a line passing through the width center C0 and perpendicular to the line L1). However, in the A-pillar upper outer panel 10C according to this embodiment, the bottom center C1 of the bead 118 is located on the curved inner side of the width center C0 of the top plate 111, that is, on the ridge line 113 side on the underside of the vehicle body. The bottom center C1 of the bead 118 is offset in the width direction from the width center C0 of the top plate 111 by, for example, 10% or more of the width W of the top plate 111. The depth D and length of the bead 118 can be set in the same manner as in the first embodiment.

[0075] The A-pillar upper outer panel 10C according to this embodiment can achieve the same effects as the A-pillar upper outer panels 10, 10A, and 10B according to the other embodiments. In particular, in this embodiment, when the pillar body 11 is viewed in cross section, the center C1 of the bottom of the bead 118 is located closer to the ridge line 113 on the underside of the vehicle body than the center C0 of the top plate 111 in the width direction of the pillar body 11. In this case, strain in the pillar body 11 is more easily dispersed in the event of a vehicle collision, further preventing breakage of the A-pillar upper outer panel 10C.

[0076] Fifth Embodiment FIG. 7 is a cross-sectional view of the pillar body 11 of an A-pillar upper outer panel 10D according to a fifth embodiment. In this embodiment, a bead 118 is formed on the top plate 111 of the pillar body 11 at least in a range R1 ( FIGS. 1 and 4 ) that is 200 mm to 500 mm in the longitudinal direction from the front end 11e of the pillar body 11. In this embodiment, one or more steps 115a are further formed on the vertical wall 115 on the curved inner side at least in the range R1. The steps 115a are preferably provided on the vertical wall 115 throughout the entire range R1. The steps 115a may also be provided on the vertical wall 115 beyond the range R1. This allows the cross-sectional line length of the pillar body 11 to be further extended in the range R1. As a result, strain is more easily distributed in the pillar body 11 during a vehicle collision, making the A-pillar upper outer panel 10D less likely to break.

[0077] Although not shown, one or more steps may be provided on the curved inner vertical wall 115 as well as the curved outer vertical wall 114. Furthermore, each of the vertical walls 114, 115 may be provided with one or more beads in addition to or instead of the steps.

[0078] When the door ring structure 100 (FIG. 1) includes any of the A-pillar upper outer panels 10A to 10D according to the second to fifth embodiments, the door ring structure 100 can be manufactured by the same manufacturing method as in the first embodiment. However, the door ring structure 100 may also be manufactured by a manufacturing method different from that in the first embodiment, as shown in FIGS. 8A to 8C.

[0079] A method for manufacturing a door ring structure 100 (FIG. 1) including an A-pillar upper outer 10C (FIG. 6) according to the fourth embodiment will be described with reference to FIGS. 8A to 8C. The manufacturing method shown in FIGS. 8A to 8C includes the same preparation and heating steps as those of the first embodiment, but differs from the first embodiment in the manner of the forming step. In the forming step, a mold 80A different from the mold 80 (FIG. 3C) of the first embodiment is used to form a heated blank 60 into the door ring structure 100 (FIG. 1) that is annular in plan view and then quenched.

[0080] 8A to 8C show a cross section of a portion of the mold 80A that corresponds to the pillar body 11 (FIG. 6) of the A-pillar upper outer panel 10C. The mold 80A includes a punch 81A, a die 82, and a pad 83. The mold 80A differs from the mold 80 of the first embodiment (FIG. 3C) mainly in the configuration of the punch 81A.

[0081] In the mold 80 of the first embodiment, the portion of the punch 81 used to form the pillar body 11 (FIG. 2) includes a cushion 812 (FIG. 3C) that is arranged so as to be receivable within the punch body 811. On the other hand, in the mold 80A, the portion of the punch 81A used to form the pillar body 11 (FIG. 6) does not include such a cushion. The punch 81A has a forming surface corresponding to the pillar body 11. A recess 812a for forming the bead 118 is provided on the top surface of the punch 81A.

[0082] As shown in Fig. 8A , in the forming process, first, the blank 60 is placed between the punch 81A and the die 82 and pad 83. Then, the die 82 and pad 83 are moved relative to the punch 81A in the pressing direction, and the die 82 and pad 83 are brought closer to the punch 81A. As a result, the blank 60 is first sandwiched between the pad 83 and the punch 81A. More specifically, as shown in Fig. 8B , the portion of the blank 60 that will be formed into the top plate 111 (Fig. 6) of the pillar main body 11 is sandwiched between the pad 83 and the punch 81A, and a bead 118 is formed in the blank 60.

[0083] 8C , the blank 60 is pressed by the punch 81A and the die 82 to form the vertical walls 114, 115 and the flanges 116, 117. More specifically, while the blank 60 is sandwiched between the pad 83 and the punch 81A, the punch 81A and the die 82 are moved relatively closer to each other 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, the portions of the door ring structure 100 other than the pillar body 11 of the A-pillar upper outer 10C are also formed by the mold 80A including the punch 81A, the die 82, and the pad 83.

[0084] 8A to 8C have described an example of manufacturing the door ring structure 100 (FIG. 1) including the A-pillar upper outer part 10C according to the fourth embodiment, but the door ring structure 100 including any of the A-pillar upper outer parts 10, 10A, 10B, and 10D according to the other embodiments can also be manufactured by the manufacturing method shown in Figures 8A to 8C. When manufacturing the door ring structure 100 including the A-pillar upper outer part 10, 10A to 10D, the angle of the A-pillar upper outer part 10, 10A to 10D with respect to the pressing direction can be appropriately set so that, for example, the bead 118 of the top plate 111 and the vertical walls 114, 115 do not have portions with negative angle shapes.

[0085] 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.

[0086] The configurations of the A-pillar upper outer panels 10, 10A to 10D according to the first to fifth embodiments can be combined as appropriate. For example, the step 115a of the vertical wall 115 in the A-pillar upper outer panel 10D according to the fifth embodiment may be applied to the A-pillar upper outer panels 10B, 10C according to the third and fourth embodiments. Also, for example, the A-pillar upper outer panels 10B to 10D according to the third to fifth embodiments may include a transition portion 12 in addition to the pillar main body 11, like the A-pillar upper outer panel 10A according to the second embodiment, or may not include the transition portion 12, like the A-pillar upper outer panel 10 according to the first embodiment.

[0087] In the above embodiment, one bead 118 is formed on the top plate 111 of the pillar main body 11 in a range R1 of 200 mm to 500 mm in the longitudinal direction from the front end 11e of the pillar main body 11. However, two or more beads 118 may be formed on the top plate 111 of the pillar main body 11 and aligned in the width direction at least in the range R1. In this case, the depth D of each bead 118 may be the same as or different from the depth D of the other beads 118. Furthermore, the extension length of each bead 118 may be the same as or different from the extension length of the other beads 118.

[0088] In the above embodiment, the bead 118 has a curved shape that is convex toward the inside of the pillar main body 11 (the A-pillar upper inner panel 50 side) in the cross section of the pillar main body 11. However, the cross-sectional shape of the bead 118 is not limited to this. For example, the bead 118 may have a polygonal shape such as a rectangular shape or a trapezoidal shape in the cross section of the pillar main body 11.

[0089] 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, 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.

[0090] 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.

[0091] In the above embodiment, the A-pillar upper outer panels 10, 10A to 10D are manufactured by hot stamping. In order to ensure a sufficient depth D of the bead 118, it is preferable that the A-pillar upper outer panels 10, 10A to 10D be manufactured by hot stamping. However, the A-pillar upper outer panels 10, 10A to 10D may also be manufactured by cold forming. Also, in the above embodiment, the A-pillar upper outer panels 10, 10A to 10D are press-formed integrally with the other frame members 20, 30, 40, but the A-pillar upper outer panels 10, 10A to 10D may also be press-formed separately from the other frame members 20, 30, 40.

[0092] In the above embodiment, the door ring structure 100 includes any one of the A-pillar upper outer panel 10, 10A to 10D, the A-pillar lower outer panel 20, the B-pillar outer panel 30, and the rocker outer panel 40. 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 panel 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.

[0093] 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.

[0094] To confirm the effects of the present disclosure, CAE analysis was performed on the A-pillar upper outer described in the above embodiment using commercially available software (LS-DYNA R9.3.1, manufactured by Ansys) while changing the conditions of the bead depth and the bottom center position. The analysis conditions and results are shown in Table 1 and Figure 10.

[0095]

[0096] In this analysis, for the Comparative Example and Examples 1 to 5 shown in Table 1, the test conformed to the Insurance Institute for Highway Safety (IIHS) Small Overlap (SOL) frontal crash test standard. The right edge of the barrier surface was positioned so that it was offset 25% of the vehicle width from the centerline of the vehicle to the left of the vehicle body. The barrier surface was then collided with a vehicle body to which the A-pillar upper outer was assembled at a speed of 64.4 km / h, and the equivalent plastic strain at that time was evaluated. More specifically, for the Comparative Example and each Example, equivalent plastic strain was obtained at 2 mm intervals along the ridgeline adjacent to the top plate on the underside of the vehicle body in a range of 200 mm to 500 mm in the longitudinal direction from the front end of the pillar body, and the maximum value was evaluated. A steel plate with a tensile strength of 1470 MPa and a thickness of 1.4 mm was used as the material for the A-pillar upper outer.

[0097] In the Comparative Example, no bead was provided on the top plate of the pillar body, whereas in Examples 1 to 5, a bead extending longitudinally was provided on the top plate of the pillar body over the entire range of 200 mm to 500 mm in the longitudinal direction from the front end of the pillar body. As shown in Table 1 and Figure 10, it was confirmed that the maximum value of equivalent plastic strain was reduced in Examples 1 to 5 compared to the Comparative Example. In other words, by providing a bead on the top plate of the pillar body over the range of 200 mm to 500 mm in the longitudinal direction from the front end of the pillar body, it was possible to distribute the tensile strain at the ridgeline on the inside of the curve that occurs as the pillar body deforms during a frontal collision.

[0098] As shown in Table 1 and Figure 10, in Examples 1 to 5, the greater the bead depth, the smaller the maximum value of equivalent plastic strain. Among Examples 1 to 3, in which the bead had a symmetrical shape with respect to the width centerline and the bottom center of the bead coincided with the width center of the top plate, Examples 1 and 3, in which the bead depth was 3.0 times or more the top plate thickness of 1.4 mm, showed a reduction in the maximum value of equivalent plastic strain of 15.0% or more compared to the comparative example. In Example 3, in which the bead depth was 5.0 times or more the top plate thickness, the maximum value of equivalent plastic strain was reduced by nearly 50% compared to the comparative example. Therefore, it can be said that when the bead depth is 3.0 times or more the top plate thickness, the strain dispersion effect is significantly exhibited.

[0099] Comparing Examples 1, 4, and 5, which have the same ratio of bead depth to top plate thickness, the maximum value of equivalent plastic strain was smaller in Examples 4 and 5, in which the bead had an asymmetric shape with respect to the width centerline and the position of the bead bottom center was shifted in the width direction from the position of the width center of the top plate, than in Example 1, in which the position of the bead bottom center coincided with the position of the width center of the top plate. In particular, in Example 4, in which the bead bottom center was located toward the lower side of the vehicle body from the width center of the top plate, the maximum value of equivalent plastic strain was smaller than in Example 5. Therefore, in order to further distribute the strain, it is preferable that the bottom center of the bead is shifted from the width center of the top plate in the width direction of the pillar body, and it is more preferable that the bottom center of the bead is shifted from the width center of the top plate toward the lower side of the vehicle body (inside the curve of the pillar body).

[0100] In this analysis, the amount of intrusion into the cabin during the SOL frontal collision test was also confirmed. The amount of intrusion was measured at the position of the A-pillar lower outer panel (the mounting portion of the front door hinge) joined to the A-pillar upper outer panel. The amounts of intrusion (reductions compared to the amount of intrusion in the comparative example) for Examples 1, 4, and 5 are shown in Table 2.

[0101]

[0102] As shown in Table 2, Examples 1, 4, and 5 had a reduced intrusion amount compared to the comparative example. In Examples 4 and 5, in which the position of the bottom center of the bead in the A-pillar upper outer was shifted in the width direction from the width center of the top plate, the intrusion amount was reduced compared to Example 1, in which the position of the bottom center of the bead coincided with the width center of the top plate. In Example 4, in which the bottom center of the bead was located lower on the vehicle body than the width center of the top plate, the intrusion amount was reduced compared to Example 5. Therefore, from the perspective of reducing the intrusion amount into the cabin, it is preferable that the bottom center of the bead in the A-pillar upper outer is shifted from the width center of the top plate in the width direction of the pillar body, and it is more preferable that the bottom center of the bead is shifted from the width center of the top plate to the lower side of the vehicle body (toward the curved inner side of the pillar body).

[0103] 10, 10A, 10B, 10C, 10D: A-pillar upper outer 11: Pillar body 11e: End 111: Top plate 112: Ridge portion (first ridge portion) 113: Ridge portion (second ridge portion) 114: Vertical wall (first vertical wall) 115: Vertical wall (second vertical wall) 115a: Step 116: Flange (first flange) 117: Flange (second flange) 118: Bead 60: Blank 80, 80A: Mold 81, 81A: Punch 811: Punch body 812: Cushion 82: Die 83: Pad 100: Door ring structure

Claims

1. An A-pillar upper outer for an automobile, comprising: a top plate, a first vertical wall connected to the top plate via a first ridgeline portion, a first flange connected to the first vertical wall on the opposite side of the top plate, a second vertical wall connected to the top plate via a second ridgeline portion on the opposite side of the first vertical wall, and a second flange connected to the second vertical wall on the opposite side of the top plate, the pillar body being made of steel and having a tensile strength of 980 MPa or more; the pillar body extending while curving with the first ridgeline portion, the first vertical wall, and the first flange side being the outer side of the curve, and the second ridgeline portion, the second vertical wall, and the second flange side being the inner side of the curve, An A-pillar upper outer, in which, in a range of 200 mm to 500 mm in the longitudinal direction from the end of the pillar body that is located forward when the A-pillar upper outer is assembled into the body of an automobile, a bead is formed on the top plate, which has a concave shape on the inside of the pillar body and extends in the longitudinal direction.

2. An A-pillar upper outer as described in claim 1, wherein the bead has a depth that is 3.0 times or more the thickness of the top plate.

3. An A-pillar upper outer as described in claim 1, wherein, when the pillar body is viewed in cross section, the center of the bottom of the bead is positioned offset from the center of the top plate in the width direction of the pillar body.

4. An A-pillar upper outer as described in claim 3, wherein, when the pillar body is viewed in cross section, in the width direction, the center of the bottom of the bead is positioned on the second ridge line side relative to the center of the top plate.

5. An A-pillar upper outer as described in claim 1, wherein, when the pillar body is viewed in cross section, the bead has an asymmetric shape with respect to the center line of the bead in the width direction of the pillar body.

6. An A-pillar upper outer as described in claim 1, wherein one or more steps are formed in the second vertical wall in the range of 200 mm or more and 500 mm or less from the end of the pillar body in the longitudinal direction.

7. A door ring structure for an automobile, comprising an A-pillar upper outer according to any one of claims 1 to 6.

8. A method for manufacturing a door ring structure as described in claim 7, 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; and a forming step of forming the heated blank into the door ring structure and quenching it using a metal mold, wherein the metal mold includes a punch, a die, and a pad, and a portion of the punch for forming the pillar body includes a punch body and a cushion that faces the pad and is arranged so as to be housed within the punch body, and in the forming step, a portion of the blank to be formed into the top plate is sandwiched between the pad and the cushion to form the bead in the blank, and then the blank is pressed by the punch body and the die while being sandwiched between the pad and the cushion.

9. A method for manufacturing a door ring structure as described in claim 7, 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; and a forming step of forming the heated blank into the door ring structure and quenching it using a metal mold, wherein the metal mold includes a punch, a die, and a pad; and in the forming step, a portion of the blank to be formed into the top plate is clamped between the pad and the punch to form the bead in the blank, and the blank is pressed by the punch and the die to form the first vertical wall, the second vertical wall, the first flange, and the second flange.

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