Patent Publication Number: US-2021178445-A1

Title: Reinforcement for a vehicle structural member

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a U.S. National Phase entry of, and claims priority to, PCT Application No. PCT/JP2019/025867, filed Jun. 28, 2019, which claims priority to Japanese Patent Application No. 2018-125840, filed Jul. 2, 2018, both of which are incorporated herein by reference in their entireties for all purposes. 
    
    
     BACKGROUND 
     The present disclosure relates to a reinforcement for a vehicle structural member. 
     A vehicle, such as an automobile, typically includes pillars on its sides, serving as structural members. Such pillars include a front pillar, commonly referred to as an A-pillar, a center pillar, commonly referred to as a B-pillar, and a rear pillar, commonly referred to as a C-pillar. These pillars are arranged from the front to the rear of the automobile. Among these pillars, the center pillar is required to have a structural strength sufficient enough to resist a side collision with an automobile. The center pillar is therefore provided with a reinforcement, which may be called a hinge reinforcement, to reinforce its strength. 
     The center pillar is elongated and has a closed cross section, the closed cross section comprising an outer panel having a hat-shaped cross section and a flat inner panel. A hinge reinforcement is arranged within the closed cross section and is joined to the outer panel by welding, or other means, to reinforce the center pillar. 
     Since the hinge reinforcement is placed inside the closed cross section of the center pillar, it is elongated and has a U-shaped cross section, in accordance with the inner surfaces of the outer panel of the hat-shaped cross section. The configuration of the U-shaped cross section comprises a central top wall and lateral walls extending from the opposite edges of the top wall, bent to form ridge lines. 
     The center pillar and the hinge reinforcement each have a curved section in part of their lengths, and are oriented in the vehicle such that they are convex toward outside of the vehicle. The hinge reinforcement is formed by pressing. A single steel sheet is bent, by pressing, into a U-shaped cross section (e.g., see JP 2010-115674 A). 
     Another technique in this field is disclosed in Japanese Patent Application Laid-Open No. 10-218017. 
     SUMMARY 
     The material used for the hinge reinforcement tends to have a higher strength, due to the recent demand for improved performance against side impact. Wrinkles, once formed during a press forming when a high-strength material is used, are difficult to be smoothed and flattened during the same sequence of the forming processes. In other words, when the material strength is not high, any wrinkles formed during a forming process can be smoothed and flattened at the final forming stage in the same process sequence. However, in the case of a high-strength material, once wrinkles occur, it is difficult to smooth the wrinkles in the subsequent press forming process in the same process sequence because of the high strength of the material. Furthermore, it is troublesome and difficult to remove wrinkles by other means after press forming. 
     In particular, wrinkles formed during press forming are likely to occur in the lateral wall within the curved section of the U-shaped hinge reinforcement. Since the hinge reinforcement is to be welded to the center pillar at the lateral walls, it is necessary to accurately form the lateral wall without any wrinkles. It should be noted that the wrinkles considered a problem herein are out-of-plane undulation in the steel sheet. 
     As described above, even when a reinforcement having a U-shaped cross section is press formed using a high-strength material, it is desired to prevent or suppress the occurrence of wrinkles in the curved section of the lateral wall of the reinforcement. 
     One aspect of the present disclosure provides for a reinforcement for a vehicle structural member, wherein the reinforcement is disposed in the interior space of the vehicle structural member having a closed cross section and is joined by welding to the vehicle structural member. The reinforcement comprises a curved section formed in at least a part of its length, a top wall having opposite edges, and a pair of lateral walls extending from the edges of the top wall so as to form ridge lines therebetween. The top wall and the lateral walls form a U-shaped cross section. At least one of the lateral walls includes a base surface, and a plurality of welding projections positioned at intervals along its length. Each welding projection has a raised surface for the welding. Each welding projection is raised from the base surface of the lateral wall toward the vehicle structural member. This lateral wall further includes a bead between the welding projections positioned within the curved section. The bead is configured to prevent or suppress wrinkles from forming during a press forming process. The bead is raised from the base surface of the lateral wall toward the vehicle structural member. 
     In some embodiments, a height of the bead, measured from the base surface, is smaller than a height of the welding projections, measured from the base surface. 
     In some embodiments, the bead and the welding projections are arranged at such intervals that a rounded transition from the bead to the base surface does not overlap a rounded transition from the welding projection to the base surface. 
     In some embodiments, the bead extends from an open side edge of the lateral wall toward the ridge line. The bead has a length smaller than a width of the lateral wall. 
     In some embodiments, the welding projections arranged within the curved section of the lateral wall have a height from the base surface, the height being zero at the ridge line and increasing toward the raised surface. 
     In some embodiments, wrinkles are prevented or suppressed from occurring in the lateral wall in the curved section of the reinforcement even when the reinforcement with a U-shaped cross section is press formed from a high-strength material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an overall view of an example of a center pillar arranged on a side of an automobile or other vehicle. 
         FIG. 2  is a cross-sectional view of the center pillar of  FIG. 1 , taken along line II-II. 
         FIG. 3  is a front view of a top wall of a hinge reinforcement, as seen from the inside of the vehicle. 
         FIG. 4  is a side view of a lateral wall on the vehicle rearward side when the hinge reinforcement of  FIG. 3  is viewed from the direction of arrow IV. 
         FIG. 5  is a side view of the lateral wall on the vehicle forward side when the hinge reinforcement of  FIG. 3  is viewed from the direction of arrow V. 
         FIG. 6  is an enlarged perspective view of region VI of the hinge reinforcement of  FIG. 4 . 
         FIG. 7  is an enlarged perspective view of a welding projection in the hinge reinforcement of  FIG. 6 . 
         FIG. 8  is a view of a connection between the welding projections of the lateral wall of the hinge reinforcement and an anti-wrinkle bead as viewed from an edge, in which the thickness is omitted and the height is exaggerated. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present invention will be described below with reference to the drawings. In one embodiment, the described vehicle structural member is a center pillar, which is one of the pillars of a side of an automobile or other vehicle. Also in this embodiment, the described reinforcement is a hinge reinforcement that reinforces the center pillar. The directions indicated in some drawings are with reference to an automobile or other vehicle in the normal position: arrow FR indicates the forward direction, arrow UP the upward direction, and arrow IN the inward direction of the vehicle. In the following description, directional terms are based on these directions. 
       FIG. 1  shows a general structure of a center pillar  10  for an automobile or other vehicle, and  FIG. 2  shows a cross section of the center pillar  10  of  FIG. 1  taken along line II-II. The center pillar  10  shown in  FIG. 1  is that of the left side of the vehicle in the traveling direction. As described in the background section above, the sides of a vehicle have pillars serving as vehicle structural members. The pillars include a front pillar (not shown), commonly called an A pillar, a center pillar  10 , commonly called a B pillar, and a rear pillar (not shown), commonly called a C pillar. These pillars may be arranged in this order, starting from the front of the automobile. The strength of the center pillar  10 , among these pillars, is considered more important because of the need for countermeasures against a side collision with an automobile. Therefore, as shown in  FIG. 2 , the center pillar  10  includes a reinforcement, which may be called a hinge reinforcement  20 , to reinforce its strength. In one embodiment, a high-strength steel sheet may be used, as will be described later, to satisfy the recent demand for even higher strength. 
     As shown in  FIG. 1  and  FIG. 2 , the center pillar  10  includes a long outer panel  12  that forms the vehicle outer side of the center pillar  10  and an inner panel  14  that forms the vehicle inner side of the center pillar  10 . The center pillar  10  further includes a hinge reinforcement  20  arranged inside the outer panel  12 . 
     The outer panel  12  has a hat-shaped cross section, open toward the inside of the vehicle, and includes a top wall  12 A, lateral walls  12 B, and flanges  12 C. The top wall  12 A is situated on the vehicle outer side (lower side as seen in  FIG. 2 ). From opposite edges of the top wall  12 A extend the left and right lateral walls  12 B, extending toward the inside of the vehicle (upward as seen in  FIG. 2 ). These lateral walls  12 B form ridge lines. The left and right lateral walls  12 B are inclined such that the distance between them increases toward inside of the vehicle (upward as seen in  FIG. 2 ). A flange  12 C extends continuously from the edge of each of the lateral walls  12 B on the vehicle inner side (upper side in  FIG. 2 ). The flanges  12 C extend in opposite directions. The flanges  12 C extend parallel to the top wall  12 A. 
     When it is needed to distinguish between the symmetrically arranged lateral walls  12 B and flanges  12 C in this disclosure, those on the vehicle rear side (the right side in  FIG. 2 ) will be denoted by their reference symbols followed by an “r,” and those on the vehicle front side (left side in  FIG. 2 ) by their reference symbols followed by an “f.” 
     As shown in  FIG. 2 , the inner panel  14  is generally flat and includes flanges  14 C extending outward from its edges on the vehicle forward and rearward side (the left and right sides as seen in  FIG. 2 ). The flanges  14 C of the inner panel  14  are held against the flanges  12 C of the outer panel  12  in the vehicle width direction and joined thereto, for instance by spot welding, to form a closed cross section therebetween. The filled circles in  FIG. 1  and the crosses in  FIG. 2  indicate welding spots. The welding method is not limited to spot welding, but may instead be other welding methods, such as laser welding. 
     As shown in  FIG. 1 , the elongated center pillar  10  extends vertically on the vehicle. The center pillar  10  is gently curved, such that it is convex toward the outside of the vehicle at a height slightly below the middle of its length. The center pillar  10  is inclined such that its upper end is rearward relative to its lower end, in the vehicle traveling direction. 
     As shown in  FIGS. 1 and 2 , the elongated center pillar  10  has a closed cross-section and, thus, defines an interior space. As shown in  FIG. 1 , the center pillar  10  is joined to the roof side rail  18  via a generally T-shaped attachment portion  16  at the upper end of the outer panel  12 . The center pillar  10  is also joined to the side sill  19  via another generally T-shaped attachment portion  17  at the lower end of the outer panel  12 . 
     The outer panel  12  may be made of a sheet of steel having a tensile strength of, for example, 1180 MPa or more. In one embodiment, a high-tensile steel sheet having a tensile strength of 1470 MPa can be used. The outer panel  12  may be formed by room temperature or cold pressing, or hot stamping. The inner panel  14  may be made of a sheet of steel having a tensile strength equal to or lower than that of the outer panel  12 . In a particular embodiment, it may be made of a steel sheet having a tensile strength of 590 MPa. The inner panel  14  is formed by cold pressing. 
     The hinge reinforcement  20  disposed in the interior space of the center pillar  10  will now be described. As best shown in  FIG. 2 , the hinge reinforcement  20  is disposed along the inner surface of the outer panel  12  of the center pillar  10 . The hinge reinforcement  20  includes a top wall  20 A and lateral walls  20 B. 
     To be arranged along the inner surface of the outer panel  12  of the center pillar  10  as described above, the hinge reinforcement  20  has a generally U-shaped cross section. The top wall  20 A of the hinge reinforcement  20  is positioned along the inner side of the top wall  12 A of the outer panel  12 . The two lateral walls  20 B are positioned along the inner sides of the lateral walls  12 B of the outer panel  12 . The two lateral walls  20 B extend continuously from the opposite edges of the top wall  20 A toward the inside of the vehicle (upward as seen in  FIG. 2 ), forming ridge lines L 1 . The lateral walls  20 B of the hinge reinforcement  20 , like the lateral walls  12 B of the outer panel  12 , are inclined such that the distance between them widens toward the inside of the vehicle (upward in  FIG. 2 ). 
     The above described U-shaped cross section of the hinge reinforcement  20  comprises a central top wall  20 A and two lateral walls  20 B extending from the opposite edges of the top wall  20 A, thereby forming the ridge lines L 1 . 
     As with the outer panel  12 , when the symmetrically arranged left and right lateral walls  20 B of the hinge reinforcement  20  need to be distinguished from each other in this disclosure, the one on the vehicle rearward side (the right side in  FIG. 2 ) will be denoted by its reference symbol followed by an “r,” and the one on the vehicle front side (the left side in  FIG. 2 ) by its reference symbol followed by an “f.” 
       FIGS. 3 to 5  show the entire hinge reinforcement  20  of this embodiment.  FIG. 3  shows the top wall  20 A of the hinge reinforcement  20  as viewed from the inside of the vehicle.  FIG. 4  shows the lateral wall  20 Br on the vehicle rearward side when the hinge reinforcement  20  of  FIG. 3  is viewed from the direction of the arrow IV shown in  FIG. 3 .  FIG. 5  shows a lateral wall  20 Bf on the vehicle forward side when the hinge reinforcement  20  of  FIG. 3  is viewed from the direction of the arrow V shown in  FIG. 3 . As shown in these figures, the hinge reinforcement  20  is elongated. As shown in  FIGS. 4 and 5 , the hinge reinforcement  20  is gently curved toward the outside of the vehicle. That is, the hinge reinforcement  20  has a curved section in part of its length. In the hinge reinforcement  20  shown in  FIGS. 4 and 5 , for example, the indicated region VI is the curved section. 
     The hinge reinforcement  20  is formed by pressing. To improve the performance against side impact collisions, a high-tensile steel sheet may be used as the material for press forming. The tensile strength is typically 980 MPa or more. In a particular embodiment, a high tensile strength steel sheet of 1180 MPa can be used. The thickness of the steel sheet to be pressed may be, for example, about 1-2 mm. A single high-tensile steel sheet is press formed by normal temperature pressing, cold pressing, or hot stamping. The white arrow P in  FIGS. 4 and 5  indicates the pressing direction of the press forming process. When the high-tensile steel sheet is press formed as described above, the lateral walls  20 B, which are to be subjected to bending, tend to have excess material. This excess material could potentially result in wrinkles. In particular, wrinkles are likely to occur in the lateral wall  20 B within the curved section of the hinge reinforcement  20 . 
     Although not shown in  FIGS. 3 to 5 , but as shown in  FIG. 2 , the top wall  20 A of the hinge reinforcement  20  is joined by spot welding to the inner surface of the top wall  12 A of the outer panel  12 . For this attachment purpose, the top wall  20 A of the hinge reinforcement  20  includes welding projections  22 . Each welding projection  22  is raised toward outside of the vehicle by a height (e.g. 2 mm) to form a raised welding surface  23 . The welding projections  22  are scattered vertically. 
     The outer surface of the welding projection  22 , i.e. the raised welding surface  23 , is planar, as shown in  FIG. 2 , in order to secure the strength of the spot welding joint with the top wall  12 A of the outer panel  12 . While not clearly seen in  FIG. 2 , in one embodiment, the shape of each welding projection  22  may be semicircular or circular. However, in other embodiments, it may take various other shapes, such as a rectangle, triangle, ellipsis, or hexagon. 
     The outer panel  12  and the hinge reinforcement  20  may also be welded between the lateral walls  12 B of the outer panel  12  and the lateral walls  20 B of the hinge reinforcement  20 , for instance at the spots indicated by crosses in  FIG. 2 . Accordingly, the lateral walls  20 Br,  20 Bf of the hinge reinforcement  20  shown in  FIGS. 4 and 5  each include a plurality of welding projections  25 . These plurality of welding projections  25  provide for raised welding surfaces  26 . Each welding projection  25  is raised toward the lateral walls  12 B of the outer panel  12  and are scattered along the vertical. The raised welding surfaces  26  of the hinge reinforcement  20  are spot welded to the inner surface of the lateral wall  12 B of the outer panel  12 . 
       FIG. 6  is an enlarged view of the lateral wall  20 Br within region VI shown in  FIG. 4 . This region VI is a curved section of the hinge reinforcement  20 . The opposite lateral wall  20 Bf within region VI shown in  FIG. 5  may have a similar configuration to that shown in  FIG. 4 . As shown in  FIG. 6 , the welding projections  25  and anti-wrinkle beads  30  are alternately arranged along the lateral wall  20 B within the curved section of the hinge reinforcement  20 . More specifically, the welding projections  25  are arranged at intervals over the entire length, and, within the curved section, an anti-wrinkle bead  30  is arranged between two welding projections  25 . 
     The welding projections  25  provide a site for welding the hinge reinforcement  20  to the outer panel  12 , as described above. The welding projections  25  have the additional benefit of preventing or suppressing wrinkles from forming in the lateral wall  20 B when press forming the hinge reinforcement  20 . In contrast, the anti-wrinkle beads  30  are designed chiefly to prevent or suppress the wrinkles from occurring during the press forming. Therefore, the anti-wrinkle beads  30  are arranged within the curved sections, where wrinkles are more likely to occur during the press forming. 
       FIGS. 7 and 8  schematically show the welding projections  25  in the lateral wall  20 B of the hinge reinforcement  20 . In particular,  FIG. 8  is a view of the lateral wall  20 B from the edge, with the thickness being omitted and the height being exaggerated. The welding projections  25  are raised outward from a base surface  32  of the lateral wall  20 B by a height T 1 . In a particular embodiment, this height T 1  may be 4 mm. As shown in  FIGS. 2 and 7 , the welding projection  25  extends from the ridge line L 1 , which is formed between the lateral wall  20 B and the top wall  20 A, to the edge of the lateral wall  20 B that faces inside of the vehicle. The welding projections  25  may be formed over the entire width of the lateral wall  20 B. 
     Each welding projection  25  has a trapezoidal front shape, with a width W 1  at the edge on the ridge line L 1  being narrower than a width W 2  at the edge toward the vehicle inner side. The welding projection  25  includes an inclined surface  29  adjacent the ridge line L 1  and a raised welding surface  26  adjacent the edge  28 . The boundary  27  between the inclined surface  29  and the raised welding surface  26  is shown as a line. 
     The inclined surface  29  of the welding projection  25  is adjacent to the ridge line L 1  and rises to the welding surface  26 . That is, the height of the inclined surface  29 , the height from the base surface  32 , is zero at the ridge L 1  and gradually increases toward the boundary  27  with the raised welding surface  26 . This helps prevent cracks from occurring because of shrinkage during press forming. 
     The raised welding surface  26  is formed flat, as shown in  FIGS. 2 and 7 , in order to secure the strength of the spot welding joint with the lateral wall  12 B of the outer panel  12 . Specifically, the raised welding surface  26  has a sideways trapezoidal front shape, and is flat between the boundary  27  with the inclined surface  29  and the edge  28  of the lateral wall  20 B on the vehicle inner side. The width of the raised welding surface  26  at the boundary  27  is narrower than the width of the raised welding surface  26  at the edge  28  on the vehicle inner side. 
     An embodiment of the anti-wrinkle beads  30  of the hinge reinforcement  20  will now be described. As shown in  FIG. 6 , the anti-wrinkle bead  30  is situated between two adjacent welding projections  25  of the hinge reinforcement  20 , as described above. The locations of the anti-wrinkle beads  30  are within the curved section of the lateral wall  20 B. The structure of the anti-wrinkle beads  30  can be generally described as a downsized version of the welding projections  25  described above. 
     The anti-wrinkle beads  30  of this embodiment have an arched shape, as shown in  FIG. 8 . The anti-wrinkle beads  30  project from the base surface  32  of the lateral wall  20 B in the same direction as the welding projection  25 . That is, the anti-wrinkle beads  30  are raised toward the inner surface of the lateral wall  12 B of the center pillar  10 . The height T 2  of the anti-wrinkle beads  30 , measured from the base surface  32 , is smaller than the height T 1  of the welding projections  25 . In one embodiment, the height of the anti-wrinkle beads  30  can be about half the height of the welding projections  25 , for example, the height T 1  of the welding projections  25  can be 4 mm and the height T 2  of the anti-wrinkle beads  30  can be 2 mm. 
     Since the height T 2  of the anti-wrinkle beads  30  are smaller than the height T 1  of the welding projections  25 , the tops of the anti-wrinkle beads  30  may not come into contact with the inner surface of the lateral wall  12 B of the outer panel  12 . This prevents noise, e.g. that which would otherwise have been generated if the anti-wrinkle beads  30  of the hinge reinforcement  20  contact the inner surface of the lateral wall  12 B of the outer panel  12  during traveling of the vehicle. 
     As shown in  FIG. 6 , the anti-wrinkle beads  30  extend, along their lengths, in the direction of the width of the lateral wall  20 B (vertically as seen in  FIG. 6 ), from the open side edge  28  of the lateral wall  20 B of the hinge reinforcement  20  toward the ridge line L 1 . The length of the anti-wrinkle beads  30  are shorter than the width of the lateral wall  20 B. That is, the anti-wrinkle beads  30 , in the length direction, does not reach the ridge line L 1 . The anti-wrinkle beads  30  have an arched shape, in which the height from the base surface  32  decreases and the width narrows toward the ridge line L 1 . This shape corresponds to the fact that the compression of the lateral wall  20 B in the press forming is larger on the vehicle inner side (lower side as seen in  FIG. 6 ) than on the vehicle outer side (upper side). Since wrinkles may be formed during press forming due to excess material due to compression, the shape is designed to accommodate such excess material. 
     When, as described above, the anti-wrinkle beads  30  have a length smaller than the width of the lateral wall  20 B, the space between the adjacent welding projections  25  can be arranged closer to each other. As a result, the number of the welding projections  25  can be increased, if necessary. 
     As shown in  FIG. 8 , in one embodiment, both the welding projection  25  and the anti-wrinkle bead  30  of the hinge reinforcement  20  may be arched or trapezoidal, with the slanted sides  25 K,  30 K continuing to the base surface  32  of the lateral walls  20 B. In this case, the slanted sides  25 K,  30 K and the base surface  32  are connected to the lateral wall  20 B through radiused portions  25 R,  30 R (rounded transition). 
     The anti-wrinkle bead  30  and the welding projection  25  are arranged at intervals such that the radiused portion  30 R of the anti-wrinkle bead  30  and the radiused portion  25 R of the welding projection  25  do not overlap each other. In one embodiment, as shown in  FIG. 8 , the radiused portion  30 R of the anti-wrinkle bead  30  and the radiused portion  25 R of the welding projection  25  can be continuous, without any interval formed therebetween. This may be a suitable configuration when it is required to arrange adjacent welding projections  25  closer to each, other than as described above. In another embodiment, as shown in  FIG. 6 , the radiused portion  30 R of the anti-wrinkle bead  30  and the radiused portion  25 R of the welding projection  25  may be separated by a portion of the base surface  32 . 
     The above-described configuration of the non-overlapping radiused portions  30 R,  25 R of the anti-wrinkle bead  30  and the welding projection  25  effectively prevents or suppresses the formation of wrinkles, while securing the required strength against collision. For this purpose, it is preferable that the radiused portion  30 R of the anti-wrinkle bead  30  and the radiused portion  25 R of the welding projection  25  do not overlap each other. For instance, it is preferable that the radiused portions  30 R,  25 R are positioned in such a way that they are connected to each other through a portion of the base surface  32  of the lateral wall  20 B. 
     Some of the advantages of the embodiments described above will be listed below. The welding projection  25  and the anti-wrinkle bead  30  in the lateral wall  20 B of the hinge reinforcement  20  of the above embodiment prevent or suppress the formation of wrinkles in the lateral wall  20 B during press forming. Particularly when a high-strength steel sheet is used in the press forming, wrinkles can be effectively prevented or suppressed. 
     As shown in  FIGS. 4 and 5 , a plurality of welding projections  25  are formed in the lateral wall  20 B of the hinge reinforcement  20  at appropriate intervals and over the entire length. Firstly, the welding projections  25  provide the raised welding surfaces  26 , as described above, for welding the hinge reinforcement  20  to the inner surface of the lateral wall  12 B of the outer panel  12 . 
     Furthermore, when the high-strength hinge reinforcement  20  is press formed, the welding projections  25  collapse in the longitudinal direction of the hinge reinforcement  20  (the left-right direction in the views of  FIGS. 6 to 8 ) to absorb the longitudinal excess of material in the base surface  32  of the lateral wall  20 B. This prevents or suppresses the excess material from forming wrinkles during the press forming process. 
     As described above, the welding projections  25  prevent or suppresses formation of wrinkles. However, they may be incapable of fully preventing or suppressing the formation of wrinkles in the curved section of the hinge reinforcement  20 , which is a region where excess material is more likely to occur. Therefore, as described above, anti-wrinkle beads  30  are included within the curved section in order to prevent or suppress formation of wrinkles due to the excess material. The anti-wrinkle beads  30  are located between the welding projections  25  in the lateral wall  20 B within the curved section. As a result, the welding projections  25  and the anti-wrinkle beads  30  together absorb the excess material occurring in the curved section, thereby preventing or suppressing the occurrence of wrinkles. The anti-wrinkle beads  30  are also able to collapse in the longitudinal direction of the hinge reinforcement  20  to absorb the excess material. 
     It may be noted that during the press forming of the hinge reinforcement  20 , the lateral wall  20 B in the curved section is stretched along its outer side of curvature and compressed along its inner side of curvature. Since during press forming excess material is caused by the compression, wrinkles are more likely to occur on the inner side of curvature. Therefore, as the press forming moves more toward the inner side of the curvature, the more excess material that needs to be absorbed. The above-described shape of the anti-wrinkle bead  30  corresponds to this tendency during compression and effectively prevents wrinkles. For example, as shown in  FIG. 6 , the anti-wrinkle bead  30  in the curved section has a width that gradually decreases from the edge of the lateral wall  20 B toward the ridge line L 1 . 
     A computer-aided engineering (CAE) analysis was performed on the hinge reinforcement  20  having the welding projections  25  and the anti-wrinkle beads  30  in the lateral walls  20 B described above. It has been found from the results that a hinge reinforcement  20  thus configured relieves the compressive strain and spring back after the press forming process. The hinge reinforcement used for comparison in the CAE analysis had only the welding projections  25  in the lateral walls  20 B; no anti-wrinkle beads  30  were included. The height of the raised welding surfaces  26  of the welding projections  25  of both samples were set to a height T 1  of 4 mm. According to an analysis of the results, the maximum longitudinal compressive strain in the lateral walls of the hinge reinforcement with no anti-wrinkle beads was 0.14. However, the maximum longitudinal compressive strain for the hinge reinforcement  20  with the anti-wrinkle beads  30  was 0.12, exhibiting an improvement of 14%. The amount of springback of the lateral wall when press forming a hinge reinforcement according to the conventional configuration was 5.16 mm. However, it was 4.57 mm for the present example, which shows an 11% improvement. 
     The number of the anti-wrinkle beads  30  between two welding projections  25  in the lateral wall  20 B as described above is not limited to one. In other embodiments, the number may be two or more. The number may be determined according to the curvature of the curved section of the lateral wall  20 B. 
     The anti-wrinkle beads  30  are effective when included in the curved section of the hinge reinforcement  20 . In another embodiment, they may also be included in any non-curved section, if necessary. 
     The anti-wrinkle beads  30  are not limited to the above described arched or trapezoidal shapes having the apex as shown in the drawings. In another embodiment, their shapes may be of an inverted V, or any other shape into which the base surface can be compressed to prevent wrinkles. 
     In the above embodiment, a high-strength material is used as the material for the hinge reinforcement  20 , in view of its performance against side collisions. However, in another embodiment, this feature can be applied to a reinforcement that requires wrinkle prevention during press forming, regardless of the strength of the material. 
     In the above embodiment, the vehicle structural member is a center pillar  10  and the reinforcement is a hinge reinforcement  20  that reinforces the center pillar  10 . However, in another embodiment, they may be another kind of pillar and reinforcement. In yet another embodiment, they may be a vehicle structural member other than a pillar and reinforcement. 
     In the embodiments described above, the lateral wall includes a plurality of welding projections at intervals along its length, each having raised surfaces for welding. Each welding projection was described as being raised from the base surface of the lateral wall toward the vehicle structural member. As a result, the welding projection absorbs the excess material in the base surface of the lateral wall during the press forming, thereby preventing or suppressing the formation of wrinkles in the lateral wall. 
     In the above embodiments, the lateral wall includes a bead between the welding projections within the curved section, thereby further preventing or suppressing the formation of wrinkles during press forming. The bead was described above as being raised from the base surface of the lateral wall toward the vehicle structural member. The curved section is a region where wrinkles could easily occur during press forming. Both the above-mentioned welding projections and the anti-wrinkle beads absorb the excess material in the curved section, where wrinkles are more likely to occur. Accordingly, the reliably preventing or suppressing formation of wrinkles in the curved section is increased. This allows for forming of the lateral wall of the reinforcement with greater accuracy. 
     In the above embodiments, the height of the bead, measured from the base surface, is lower than the corresponding height of the welding projection. This arrangement prevents the anti-wrinkle bead from contacting the vehicle structural member, thereby preventing generation of noise due to the contact. 
     In the above embodiments, the bead and the welding projections are arranged at such intervals that the rounded transition from the bead to the base surface does not overlap the rounded transition from the welding projection to the base surface. This configuration effectively prevents or suppresses formation of wrinkles while ensuring the required strength during collisions. 
     In the above embodiments, the bead extends from the open side edge of the lateral wall toward the ridge line. However, the bead has a length smaller than the width of the lateral wall. This configuration allows for a narrowing of the intervals of adjacent welding projections. 
     Further, in the above embodiments, the welding projection in the curved section of the lateral wall has a height measured from the base surface. The height at the ridge line is zero and increases toward the raised welding surface. This configuration prevents cracks due to shrinkage during press forming. 
     While described with reference to specific embodiments, the present disclosure is not limited to these embodiments, and those skilled in the art can make various substitutions, improvements, and/or modifications without departing from the objective of the present invention.