Patent Description:
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 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 (see <CIT>).

Another technique in this field is disclosed in <CIT>. <CIT> discloses a center pillar including a first reinforcement panel which is arranged between an outer panel and an inner panel, comprising a bottom wall portion, both-side vertical wall portions extending in a vehicle width direction from the bottom wall portion, and both-side flange portions, and having a cross section formed in substantially a hat shape. A second reinforcement panel comprising a bottom wall portion and both-side vertical wall portions and having a cross section formed in substantially a U shape is arranged inside the first reinforcement panel. The second reinforcement panel is joined to the first reinforcement panel such that only the bottom wall portion and one of the both-side vertical wall portions, respectively. <CIT> discloses a reinforcement patch disposed at a vehicle inner side of a rail outer. The reinforcement patch includes an upper reinforcing portion and a lower reinforcing portion. At a boundary region between the upper reinforcing portion and the lower reinforcing portion, a reinforcement front-and-rear ridgeline is formed along an outer ridgeline. Spaced apart beads are formed at the reinforcement front-and-rear ridgeline. <CIT> discloses a vehicle frame structure including: an elongated inner panel that is disposed at a vehicle cabin inner side of a vehicle body section, an elongated outer panel that is disposed at the vehicle cabin outer side of the inner panel, and that, together with the inner panel, configures a frame by being joined to the inner panel; an elongated reinforcement member that is disposed at the vehicle cabin outer side of the outer panel, and that reinforces the outer panel by being joined to plural locations of the outer panel along the length direction; and a first excess length portion that is formed at the reinforcement member between adjacent joining portions between the reinforcement member and the outer panel, and that has excess length in a direction linking the joining portions.

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 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.

The present invention in one aspect provides 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. The top wall and the lateral walls form a U-shaped cross section. The lateral wall 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.

In one embodiment, the 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 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> shows a general structure of a center pillar <NUM> for an automobile or other vehicle, and <FIG> shows a cross section of the center pillar <NUM> of <FIG> taken along line II-II. The center pillar <NUM> shown in <FIG> is that of the left side of the vehicle in the traveling direction. As described in the background art 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 <NUM>, commonly called a B pillar, and a rear pillar (not shown), commonly called a C pillar from the front of the automobile. The strength of the center pillar <NUM>, 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>, the center pillar <NUM> includes a reinforcement, which may be called a hinge reinforcement <NUM>, 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> and <FIG>, the center pillar <NUM> includes a long outer panel <NUM> that forms the vehicle outer side of the center pillar <NUM> and an inner panel <NUM> that forms the vehicle inner side of the center pillar <NUM>. The center pillar <NUM> further includes a hinge reinforcement <NUM> arranged inside the outer panel <NUM>.

The outer panel <NUM> has a hat-shaped cross section, open toward the inside of the vehicle, and includes a top wall 12A, lateral walls 12B, and flanges 12C. The top wall 12A is situated on the vehicle outer side (lower side as seen in <FIG>). From opposite edges of the top wall 12A extend the left and right lateral walls 12B, extending toward the inside of the vehicle (upward as seen in <FIG>), forming ridge lines. The left and right lateral walls 12B are inclined such that the distance between them increases toward inside of the vehicle (upward as seen in <FIG>). A flange 12C extends continuously from the edge of each of the lateral walls 12B on the vehicle inner side (upper side in <FIG>). The flanges 12C extend in opposite directions. The flanges 12C extend parallel to the top wall 12A.

When it is needed to distinguish between the symmetrically arranged lateral walls 12B and flanges 12C, those on the vehicle rear side (the right side in <FIG>) will be denoted by their reference symbols followed by an "r," and those on the vehicle front side (left side in <FIG>) by their reference symbols followed by an "f.

As shown in <FIG>, the inner panel <NUM> is generally flat and includes flanges 14C extending outward from its edges on the vehicle forward and rearward side (the left and right sides as seen in <FIG>). The flanges 14C of the inner panel <NUM> are held against the flanges 12C of the outer panel <NUM> in the vehicle width direction and joined thereto by spot welding to form a closed cross section. The filled circles in <FIG> and the crosses in <FIG> 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>, the elongated center pillar <NUM> extends vertically on the vehicle. The center pillar <NUM> 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 <NUM> is inclined such that its upper end is rearward of the vehicle relative to its lower end.

As shown in <FIG> and <FIG>, the elongated center pillar <NUM> has a closed cross-section and thus defines an interior space. As shown in <FIG>, the center pillar <NUM> is joined to the roof side rail <NUM> via a generally T-shaped attachment portion <NUM> at the upper end of the outer panel <NUM>. The center pillar <NUM> is also joined to the side sill <NUM> via another generally T-shaped attachment portion <NUM> at the lower end of the outer panel <NUM>.

The outer panel <NUM> may be made of a sheet of steel having a tensile strength of, for example, <NUM> MPa or more. In one embodiment, a high-tensile steel sheet of <NUM> MPa can be used. The outer panel <NUM> may be formed by room temperature or cold pressing, or hot stamping. The inner panel <NUM> may be made of a sheet of steel having a tensile strength equal to or lower than that of the outer panel <NUM>. In a particular embodiment, it may be made of a steel sheet of <NUM> MPa. The inner panel <NUM> is formed by cold pressing.

The hinge reinforcement <NUM> disposed in the interior space of the center pillar <NUM> will now be described. As best shown in <FIG>, the hinge reinforcement <NUM> is disposed along the inner surface of the outer panel <NUM> of the center pillar <NUM>. The hinge reinforcement <NUM> includes a top wall 20A and lateral walls 20B.

To be arranged along the inner surface of the outer panel <NUM> of the center pillar <NUM> as described above, the hinge reinforcement <NUM> has a generally U-shaped cross section. The top wall 20A of the hinge reinforcement <NUM> is positioned along the inner side of the top wall 12A of the outer panel <NUM>. The two lateral walls 20B are positioned along the inner sides of the lateral walls 12B of the outer panel <NUM>. The two lateral walls 20B extend continuously from the opposite edges of the top wall 20A toward the inside of the vehicle (upward as seen in <FIG>), forming ridge lines L1. The lateral walls 20B, like the lateral walls 12B of the outer panel <NUM>, are inclined such that the distance between them widens toward the inside of the vehicle (upward in <FIG>).

The above described U-shaped cross section of the hinge reinforcement <NUM> comprises a central top wall 20A and two lateral walls 20B extending from the opposite edges of the top wall 20A, thereby forming the ridge lines.

As with the outer panel <NUM>, when the symmetrically arranged left and right lateral walls 20B of the hinge reinforcement <NUM> need to be distinguished from each other, the one on the vehicle rearward side (the right side in <FIG>) will be denoted by its reference symbol followed by an "r," and the one on the vehicle front side (the left side in <FIG>) by its reference symbol followed by an "f.

<FIG> show the entire hinge reinforcement <NUM>. <FIG> shows the top wall 20A of the hinge reinforcement <NUM> as viewed from the inside of the vehicle. <FIG> shows the lateral wall 20Br on the vehicle rearward side when the hinge reinforcement <NUM> of <FIG> is viewed from the direction of arrow IV <FIG> shows a lateral wall 20Bf on the vehicle forward side when the hinge reinforcement <NUM> of <FIG> is viewed from the direction of arrow V As shown in these figures, the hinge reinforcement <NUM> is elongated. As shown in <FIG> and <FIG>, the hinge reinforcement <NUM> is gently curved toward the outside of the vehicle. That is, the hinge reinforcement <NUM> has a curved section in part of its length. In the hinge reinforcement <NUM> shown in <FIG> and <FIG> for example, region VI is the curved section.

The hinge reinforcement <NUM> 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 <NUM> MPa or more. In a particular embodiment, a high tensile strength steel sheet of <NUM> MPa can be used. The thickness of the steel sheet to be pressed may be, for example, about <NUM>-<NUM>. A single high-tensile steel sheet is press formed by normal temperature pressing, cold pressing or hot stamping. The white arrow P in <FIG> and <FIG> indicates the pressing direction. When the high-tensile steel sheet is press formed as described above, the lateral walls 20B, which are to be subjected to bending, tend to have excess material, resulting in wrinkles. In particular, wrinkles are likely to occur in the lateral wall 20B within the curved section of the hinge reinforcement <NUM>.

Although not shown in <FIG>, but as shown in <FIG>, the top wall 20A of the hinge reinforcement <NUM> is joined by spot welding to the inner surface of the top wall 12A of the outer panel <NUM>. For this purpose, the top wall 20A of the hinge reinforcement <NUM> includes welding projections <NUM>. Each welding projection <NUM> is raised toward outside of the vehicle by a height (e.g. <NUM>) to form a raised welding surface <NUM>. The welding projections <NUM> are scattered vertically.

The outer surface of the welding projection <NUM>, i.e. the raised welding surface <NUM>, is planar, as shown in <FIG>, in order to secure the strength of the spot welding joint with the top wall 12A of the outer panel <NUM>. While not clearly seen in <FIG>, in one embodiment, the shape of each welding projection <NUM> may be semicircular or circular. However, in other embodiments, it may take various other shapes, such as a rectangle, triangle, ellipsis, or hexagon.

The center pillar <NUM> and the hinge reinforcement <NUM> may also be welded between the lateral walls 12B of the outer panel <NUM> and the lateral walls 20B of the hinge reinforcement <NUM> at the spots indicated by crosses in <FIG>. Accordingly, the lateral walls 20Br, 20Bf of the hinge reinforcement <NUM> shown in <FIG> and <FIG> each include a plurality of welding projections <NUM>. These plurality of welding projections <NUM> provide for raised welding surfaces <NUM>. Each welding projection <NUM> is raised toward the lateral walls 12B of the outer panel <NUM> and are scattered along the vertical. The raised welding surfaces <NUM> of the hinge reinforcement <NUM> are spot welded to the inner surface of the lateral wall 12B of the outer panel <NUM>.

<FIG> is an enlarged view of the lateral wall 20Br within region VI shown in <FIG>. This region VI is a curved section of the hinge reinforcement <NUM>. The opposite lateral wall 20Bf within region VI shown in <FIG> may have a similar configuration to that shown in <FIG>. As shown in <FIG>, the welding projections <NUM> and anti-wrinkle beads <NUM> are alternately arranged along the lateral wall 20B within the curved section of the hinge reinforcement <NUM>. More specifically, the welding projections <NUM> are arranged at intervals over the entire length, and, within the curved section, an anti-wrinkle bead <NUM> is arranged between two welding projections <NUM>.

The welding projections <NUM> provide a site for welding the hinge reinforcement <NUM> to the outer panel <NUM>, as described above, and at the same time, prevent or suppress wrinkles from forming in the lateral wall 20B when press forming the hinge reinforcement <NUM>. In contrast, the anti-wrinkle beads <NUM> are expected chiefly to prevent or suppress the wrinkles from occurring during the press forming. Therefore, the anti-wrinkle beads <NUM> are arranged within the curved sections, where wrinkles are more likely to occur during the press forming.

<FIG> and <FIG> schematically show the welding projections <NUM> in the lateral wall 20B of the hinge reinforcement <NUM>. In particular, <FIG> is a view of the lateral wall 20B from the edge, with the thickness being omitted and the height being exaggerated. The welding projections <NUM> are raised outward from a base surface <NUM> of the lateral wall 20B by a height T1. In a particular embodiment, this height T1 may be <NUM>. As shown in <FIG> and <FIG>, the welding projection <NUM> extends from the ridge line L1, which is formed between the lateral wall 20B and the top wall 20A, to the edge of the lateral wall 20B that faces inside of the vehicle, over the entire width of the lateral wall 20B.

Each welding projection <NUM> has a trapezoidal front shape, with a width W1 at the edge on the ridge line L1 being narrower than a width W2 at the edge toward the vehicle inner side. The welding projection <NUM> includes an inclined surface <NUM> adjacent the ridge line L1 and a raised welding surface <NUM> adjacent the edge <NUM>. The boundary <NUM> between the inclined surface <NUM> and the raised welding surface <NUM> is shown as a line.

The inclined surface <NUM> of the welding projection <NUM> adjacent to the ridge line L1 rises to the welding surface <NUM>. That is, the height of the inclined surface <NUM>, the height from the base surface <NUM>, is zero at the ridge L1 and gradually increases toward the boundary <NUM> with the raised welding surface <NUM>. This helps prevent cracks from occurring because of shrinkage during press forming.

The raised welding surface <NUM> is formed flat, as shown in <FIG> and <FIG>, in order to secure the strength of the spot welding joint with the lateral wall 12B of the outer panel <NUM>. Specifically, the raised welding surface <NUM> has a sideways trapezoidal front shape, and is flat between the boundary <NUM> with the inclined surface <NUM> and the edge <NUM> of the lateral wall 20B on the vehicle inner side. The width of the raised welding surface <NUM> at the boundary <NUM> is narrower than the width of the raised welding surface <NUM> at the edge <NUM> on the vehicle inner side.

The anti-wrinkle beads <NUM> of the hinge reinforcement <NUM> will now be described. As shown in <FIG>, the anti-wrinkle bead <NUM> is situated between two adjacent welding projections <NUM> of the hinge reinforcement <NUM> as described above. The locations of the anti-wrinkle beads <NUM> are within the curved section of the lateral wall 20B. The structure of the anti-wrinkle beads <NUM> can be generally described as a downsized version of the welding projections <NUM> described above.

The anti-wrinkle beads <NUM> have an arched shape, as shown in <FIG>. The anti-wrinkle beads <NUM> project from the base surface <NUM> of the lateral wall 20B in the same direction as the welding projection <NUM>. That is, the anti-wrinkle beads <NUM> are raised toward the inner surface of the lateral wall 12B of the center pillar <NUM>. The height T2 of the anti-wrinkle beads <NUM>, measured from the base surface <NUM>, is smaller than the height T1 of the welding projections <NUM>. In one embodiment, the height of the anti-wrinkle beads <NUM> can be about half the height of the welding projections <NUM>, for example, T1 = <NUM> and T2 = <NUM>.

Since the height T2 of the anti-wrinkle beads <NUM> are smaller than the height T1 of the welding projections <NUM>, the tops of the anti-wrinkle beads <NUM> may not come into contact with the inner surface of the lateral wall 12B of the outer panel <NUM>. This prevents noise, e.g. that which would otherwise have been generated if the anti-wrinkle beads <NUM> of the hinge reinforcement <NUM> contact the inner surface of the lateral wall 12B of the outer panel <NUM> during traveling of the vehicle.

As shown in <FIG>, the anti-wrinkle beads <NUM> extend in the direction of the width of the lateral wall 20B (vertically as seen in <FIG>) from the open side edge <NUM> of the lateral wall 20B of the hinge reinforcement <NUM> toward the ridge line L1, but has a length shorter than the width of the lateral wall 20B. That is, the length does not reach the ridge line L1. The anti-wrinkle beads <NUM> have an arched shape, in which the height from the base surface <NUM> decreases and the width narrows toward the ridge line L1. This shape corresponds to the fact that the compression of the lateral wall 20B in the press forming is larger on the vehicle inner side (lower side as seen in <FIG>) 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 <NUM> have a length smaller than the width of the lateral wall 20B, the space between the adjacent welding projections <NUM> can be arranged closer to each other. As a result, the number of the welding projections <NUM> can be increased, if necessary.

As shown in <FIG>, in one embodiment, both the welding projection <NUM> and the anti-wrinkle bead <NUM> of the hinge reinforcement <NUM> may be arched or trapezoidal, with the slanted sides <NUM>, <NUM> continuing to the base surface <NUM> of the lateral walls 20B. In this case, the slanted sides <NUM>, <NUM> and the base surface <NUM> are connected to the lateral wall 20B through radiused portions 25R, 30R (rounded transition).

The anti-wrinkle bead <NUM> and the welding projection <NUM> are arranged at intervals such that the radiused portion 30R of the anti-wrinkle bead <NUM> and the radiused portion 25R of the welding projection <NUM> do not overlap each other. In one embodiment, as shown in <FIG>, the radiused portion 30R of the anti-wrinkle bead <NUM> and the radiused portion 25R of the welding projection <NUM> can be continuous without any interval. This may be a suitable configuration when it is required to arrange adjacent welding projections <NUM> closer to each other as described above. In another embodiment, as shown in <FIG>, the radiused portion 30R of the anti-wrinkle bead <NUM> and the radiused portion 25R of the welding projection <NUM> may be separated by a portion of the base surface <NUM>.

The above-described configuration of the non-overlapping radiused portions 30R, 25R of the anti-wrinkle bead <NUM> and the welding projection <NUM> effectively prevents or suppresses the formation of wrinkles while securing the required strength against collision. For this purpose, it is not preferable that the radiused portion 30R of the anti-wrinkle bead <NUM> and the radiused portion 25R of the welding projection <NUM> overlap each other in such a way that they are not connected through any portion of the base surface <NUM> of the lateral wall 20B.

The advantages of the embodiments described above will be listed below. The welding projection <NUM> and the anti-wrinkle bead <NUM> in the lateral wall 20B of the hinge reinforcement <NUM> of the above embodiment prevent or suppress the formation of wrinkles in the lateral wall 20B 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 <FIG> and <FIG>, a plurality of welding projections <NUM> are formed in the lateral wall 20B of the hinge reinforcement <NUM> at appropriate intervals and over the entire length. Firstly, the welding projections <NUM> provide the raised welding surfaces <NUM>, as described above, for welding the hinge reinforcement <NUM> to the inner surface of the lateral wall 12B of the outer panel <NUM>.

Furthermore, when the high-strength hinge reinforcement <NUM> is press formed, the welding projections <NUM> collapse in the longitudinal direction of the hinge reinforcement <NUM> (the left-right direction in the views of <FIG>) to absorb the longitudinal excess of material in the base surface <NUM> of the lateral wall 20B. This prevents or suppresses the excess material from forming wrinkles during the press forming process.

As described above, the welding projection <NUM> prevents or suppresses formation of wrinkles, but the curved section of the hinge reinforcement <NUM> is a region where excess material is more likely to occur. Therefore, as described above, anti-wrinkle beads <NUM> are included within the curved section in order to prevent or suppress formation of wrinkles due to the excess material. The anti-wrinkle beads <NUM> are located between the welding projections <NUM> in the lateral wall 20B within the curved section. As a result, the welding projections <NUM> and the anti-wrinkle beads <NUM> together absorb the excess material occurring in the curved section, thereby preventing or suppressing the occurrence of wrinkles. The anti-wrinkle bead <NUM> also collapses in the longitudinal direction of the hinge reinforcement <NUM> to absorb the excess material.

It may be noted that during the press forming of the hinge reinforcement <NUM>, the lateral wall 20B 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, the more toward the inner side of the curvature, the more excess material need to be absorbed. The above-described shape of the anti-wrinkle bead <NUM> corresponds to this tendency during compression and effectively prevents wrinkles. For example, as shown in <FIG>, the anti-wrinkle bead <NUM> in the curved section has a width that gradually decreases from the edge of the lateral wall 20B toward the ridge line.

A computer-aided engineering (CAE) analysis was performed on the hinge reinforcement <NUM> having the welding projections <NUM> and the anti-wrinkle beads <NUM> in the lateral walls 20B described above. It has been found from the results that a hinge reinforcement <NUM> thus configured relieves the compressive strain and spring back after the press forming process. The hinge reinforcement used for comparison had only the welding projections <NUM> in the lateral walls 20B; no anti-wrinkle beads <NUM> were included. The height of the raised welding surfaces <NUM> of the welding projections <NUM> was T1 = <NUM>. 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 <NUM>. However, the maximum longitudinal compressive strain for the hinge reinforcement <NUM> with the anti-wrinkle beads <NUM> was <NUM>, exhibiting an improvement of <NUM>%. The amount of springback of the lateral wall 20B when press forming a hinge reinforcement according to the conventional configuration was <NUM>. However, it was <NUM> for the present example, which shows an <NUM>% improvement.

The number of the anti-wrinkle beads <NUM> between two welding projections <NUM> in the lateral wall 20B 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 20B where the anti-wrinkle beads <NUM> are provided.

The anti-wrinkle beads <NUM> are effective when included in the curved section of the hinge reinforcement <NUM>. In another embodiment, they may also be included in any non-curved section, if necessary.

The anti-wrinkle beads <NUM> are not limited to the 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 <NUM>, 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 <NUM> and the reinforcement is a hinge reinforcement <NUM> that reinforces the center pillar <NUM>. 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, and each welding projection is 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 that prevents or suppresses the formation of wrinkles during the press forming, and the bead is 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, thereby reliably preventing or suppressing formation of wrinkles in the curved section. 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 height of the welding projection from the base surface. 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.

Claim 1:
A reinforcement (<NUM>) for a vehicle structural member, wherein the reinforcement (<NUM>) is disposed in an interior space of the vehicle structural member having a closed cross section and is joined by welding to the vehicle structural member, the reinforcement (<NUM>) comprising
a curved section (VI) formed in at least a part of a length of the reinforcement (<NUM>);
a top wall (20A) having opposite edges; and
a pair of lateral walls (20B) extending from the edges of the top wall (20A) forming ridge lines, wherein
the top wall (20A) and the lateral walls (20B) form a U-shaped cross section,
the lateral wall includes:
a base surface (<NUM>);
a plurality of welding projections (<NUM>) at intervals along the length, each welding projection (<NUM>) having a raised surface for welding, wherein each welding projection (<NUM>) is raised from the base surface (<NUM>) of the lateral wall (20B) toward the vehicle structural member; and
a bead (<NUM>) between the welding projections (<NUM>) within the curved section (VI)
the bead (<NUM>) is configured to prevent or suppress a wrinkle from forming during press forming, and
the bead (<NUM>) is raised from the base surface (<NUM>) of the lateral wall (20B) toward the vehicle structural member.