JP2021085462A - Impact absorbing material and manufacturing method for impact absorbing material - Google Patents

Abstract

To provide an impact absorbing material that improves impact absorption performance and is easy to deform from one end side in comparison to conventional impact absorbing materials.SOLUTION: A shock absorbing material (2) has a cylindrical body part (2c) whose cross-sectional area increases from one end side to the other end side. In a cross section of the body part (2c) perpendicular to an axis from the one end side to the other end side, for an ellipse (12) inscribed in a rectangle (rectangular cross section) (11), the shock absorbing material (2) has a cross-sectional shape connecting points (c1 to c5) set between the edge of the ellipse (12) and the edge of the rectangle (rectangular cross section) (11) along a plurality of virtual line segments (14a to 14e) that extends toward the edge of the rectangle (rectangular cross section) (11) at predetermined phase intervals with the center of the rectangle (rectangular cross section) (11) as a center (11a).SELECTED DRAWING: Figure 3

Description

The present invention relates to a shock absorbing material that absorbs shocks and a method for manufacturing the same, and more particularly to a shock absorbing material suitable for absorbing shocks at the time of a vehicle collision and a method for manufacturing the same.

Conventionally, as a shock absorbing material for absorbing a shock at the time of a collision in a vehicle such as an automobile, a member called a crash box is installed between a side member which is a strength member and a bumper or the like which is an exterior member. The crash box suppresses the transmission of impact to the side members by buckling and deforming before the side members when the exterior members come into contact with other vehicles or structures such as utility poles and guardrails. is there. Regarding the shock absorbing member that can be used for such a crash box, the techniques described in Patent Documents 1 and 2 below are known.

According to Patent Document 1 (Japanese Unexamined Patent Publication No. 2006-1238887), in a crash box, the cross-sectional shape is not a rectangle (quadrangle) but an octagonal cross-section, and the length a of a pair of first sides of the octagon parallel to each other. 0.4 ≦ a / A ≦ for the length b of the pair of second sides orthogonal to the first side, the distance (interval) B between the first sides, and the distance A between the second sides. It is described that 0.8 and 0.2 ≦ b / B ≦ 0.7. In addition, a bead shape that is recessed from the outside to the inside is also formed at a predetermined interval with respect to the longitudinal direction of the crash box.

According to Patent Document 2 (Japanese Unexamined Patent Publication No. 2002-104107), when manufacturing a crash box (20) having a bellows portion (23), first, a pressurized liquid is sealed inside an octagonal tubular pipe (45). In this state, the upper mold (41) and the lower mold (42) are pressed from the outside to preform the outer shape of the bellows portion (23). After the preforming, the pressure of the pressurized liquid is raised to the main forming pressure (Ps2), and the pipe (45) is pressed against the molds (41, 42) in the form of inflating the pipe (45) from the inside. It is described that the crash box (20) is manufactured.

Japanese Unexamined Patent Publication No. 2006-1238887 (Claim 1, Claim 2, "0023"-"0037", FIG. 1, FIG. 2, FIG. 5, FIG. 6) JP-A-2002-104107 ("0019"-"0021", FIG. 4)

(Problems of conventional technology)
The crash box is for suppressing the deformation of the side member (frame of the main body) by deforming in the event of a vehicle collision, but if the collision is mild, it can be repaired by replacing only the exterior and the crash box part. Is preferable because it facilitates. When removing the crash box from the side member, the removal work is easy if the tip side (exterior side) of the crash box is deformed, but the removal work is difficult if the root side (side member side) is deformed. Become. Therefore, when the crash box is deformed, it is preferable that the crash box is deformed from the tip side, and when the crash box is deformed from the root side, the side members may be deformed before the crash box is completely deformed.

In the technique described in Patent Document 1, the four corners of the rectangle correspond to the chamfered shape, and the energy absorption efficiency is improved as compared with the square shape. In reality, it is difficult to predict where the transformation will occur. That is, there is a risk that the crash box will start to deform from the base side.

In the case of a bellows-like shape in which a plurality of steps of unevenness are repeated as in the technique described in Patent Document 2, it is possible that when absorbing an impact, which part of the plurality of unevenness is deformed each time. It is highly likely and it is uncertain whether the crash box will deform from the tip side. In particular, there is no problem if the unevenness of multiple stages is deformed evenly in the axial direction, but in reality it is difficult to deform evenly due to collisions from the diagonal direction, and it is diagonal in the axial direction, that is, with respect to the longitudinal direction of the crash box. There is also a risk that it will bend like it collapses. At this time, the direction of falling may be different between the root side and the tip side, and in that case, there is a problem that the shock absorption performance expected by the crash box cannot be exhibited.

It is a technical subject of the present invention to provide a shock absorbing material that is easily deformed from one end side while improving the shock absorbing performance as compared with the conventional shock absorbing material.

In order to solve the technical problem, the shock absorbing material of the invention according to claim 1 is used.
A shock absorbing material having a tubular main body extending from one end to the other end and having the main body whose cross-sectional area increases from one end side to the other end side.
In the cross section of the main body portion perpendicular to the axis from one end side to the other end side, the center of the rectangle (rectangular cross section) is centered with respect to the rectangle (rectangular cross section) and the rectangle inscribed in the rectangle (rectangular cross section). Is set in a section from the edge of the ellipse to the inside of the edge of the rectangle (rectangular cross section) along a plurality of virtual line segments extending toward the edge of the rectangle (rectangular cross section) at a predetermined angle. It has a cross-sectional shape that connects the dots.
It is characterized by that.

The invention according to claim 2 is the shock absorbing material according to claim 1.
Steps were formed at predetermined intervals from one end to the other.
It is characterized by that.

In order to solve the technical problem, the method for producing a shock absorbing material according to claim 3 is the method for producing a shock absorbing material.
A rectangular (rectangular cross section) and the cross section of the main body perpendicular to the axis extending from one end side to the other end side with respect to a cylindrical main body portion having a rectangular cross section extending from one end to the other end. With respect to an ellipse inscribed in a rectangle (rectangular cross section), along a plurality of virtual line segments extending toward the edge of the rectangle (rectangular cross section) at a predetermined angle centered on the center of the rectangle (rectangular cross section). Impact is performed by compressing and deforming the main body from the outside so that the cross section shape connects the points set in the section inside the rectangular (rectangular cross section) edge from the edge of the ellipse. It is characterized by producing an absorbent material.

The invention according to claim 4 is the method for producing a shock absorbing material according to claim 3.
It has an inner surface shape corresponding to the outer shape of the main body in a state where both ends of a cylindrical body having a rectangular cross section extending from one end to the other end are held and the inside of the hollow cylinder is filled with a liquid. The shock absorbing material is manufactured from the cylinder by pressing the mold against the outer surface of the cylinder.

According to the inventions of claims 1 and 3, it is possible to provide a shock absorbing material that is easily deformed from one end side while improving the shock absorbing performance as compared with the conventional shock absorbing material.
According to the second aspect of the present invention, when stress concentration occurs around the step portion, the step portion on the tip side is likely to be deformed in order.
According to the fourth aspect of the present invention, the outer shape can be formed more accurately than in the case where the liquid is not filled inside.

FIG. 1 is an explanatory view of a bumper portion of a vehicle including a shock absorbing material according to a first embodiment of the present invention. FIG. 2 is an explanatory diagram of the shock absorbing material of FIG. 3A and 3B are explanatory views of the outer shape of the shock absorbing material of the first embodiment, FIG. 3A is an explanatory view of a rectangular cross section, FIG. 3B is an explanatory view of an ellipse inscribed in the rectangular cross section, and FIG. 3C is radial from the center of the rectangular cross section. 3D is an explanatory view of the outer shape of the node, FIG. 3E is an explanatory view of the outer shape connecting the nodes, and FIG. 3F is an explanatory view of the outer shape of the elliptical stage. 4A and 4B are explanatory views of cross-sectional shapes of even-numbered stages, FIG. 4A is a view corresponding to FIG. 3D, FIG. 4B is a view corresponding to FIG. 3F, and FIG. 4C is an explanatory view of an external shape seen from the side. .. FIG. 5 is an explanatory view of a processing method of the crash box of the first embodiment, FIG. 5A is an explanatory view of a state in which both ends of the base material are held, and FIG. FIG. 5C is an explanatory diagram of a state in which the mold is pressed from the state of FIG. 5B, and FIG. 5D is an explanatory diagram of a state in which an unnecessary portion is deleted after processing. FIG. 6 is an explanatory view of a base material when processing the crash box of the first embodiment. FIG. 7 is an explanatory diagram of the experimental results, and is a list of the experimental results of Experimental Example 1-3 and Comparative Example 1-3. FIG. 8 is an explanatory diagram of the experimental results, and is an explanatory diagram of the initial stage of the crushed state of Experimental Example 3 and Comparative Example 3. FIG. 9 is an explanatory diagram of the experimental results, and is an explanatory diagram in a state in which a time has elapsed as compared with the case of FIG. FIG. 10 is an explanatory diagram of the experimental results, and is an explanatory diagram in a state in which a time has elapsed as compared with the case of FIG. FIG. 11 is an explanatory diagram of the experimental results, and is an explanatory diagram in a state where a time has elapsed as compared with the case of FIG. FIG. 12 is an explanatory diagram of the experimental results, and is an explanatory diagram in a state in which a time has elapsed as compared with the case of FIG. 13A and 13B are explanatory views of a modified example, FIG. 13A is a diagram corresponding to FIG. 4A, FIG. 13B is a diagram corresponding to FIG. 4B, and FIG. 13C is a diagram corresponding to FIG. 4C.

Next, an embodiment which is a specific example of the embodiment of the present invention will be described with reference to the drawings, but the present invention is not limited to the following examples.
In addition, in the explanation using the following drawings, the illustrations other than the members necessary for the explanation are omitted as appropriate for the sake of easy understanding.

FIG. 1 is an explanatory view of a bumper portion of a vehicle including a shock absorbing material according to a first embodiment of the present invention.
FIG. 2 is an explanatory diagram of the shock absorbing material of FIG.
In FIGS. 1 and 2, in a vehicle including a crash box as an example of the shock absorbing material of the first embodiment of the present invention, a bumper 1 as an example of an exterior member is arranged at a front end portion. On the inner surface of the bumper 1, the tip portions (one end portions) of the pair of left and right crash boxes 2 are supported via the tip flange portions 2a. The root portion (the other end portion) of the crash box 2 is supported by the side member 3 as an example of the strength member via the root flange portion 2b. The root flange portion 2b is supported by a fastening member such as a bolt (not shown) with respect to the side member 3, and the crash box 2 and the bumper 1 can be attached to and detached from the side member 3 by loosening the bolt or the like. Has been done.

In FIG. 2, the crash box 2 of the first embodiment has a tubular main body portion 2c extending from one end side to the other end side, and a tip flange portion 2a supported by one end portion of the main body portion 2c by welding or the like. The other end of the main body 2c has a root flange 2b supported by welding or the like.
The main body 2c is formed in a polygonal shape whose cross section will be described later. Further, the main body portion 2c is formed in a tubular shape in which the cross-sectional area increases from one end to the other end, that is, a hollow substantially cone shape. Further, the main body portion 2c is formed with step portions 2d at predetermined intervals from one end to the other end. In the first embodiment, the step portions 2d are formed (concave) so that the outer shape of the even-numbered step portions 2d1 is from the outside to the inside in order from one end side of the crash box 2. As a result, in the odd-numbered step portion 2d2, the outer shape is formed (convexly) from the inside to the outside.
In addition, "the cross-sectional area increases from one end to the other end" means that the even-numbered steps and the odd-numbered steps are compared in each step from one end to the other end. In addition, although the cross-sectional area of the other end side is larger than that of the one end side, it is preferable that the cross-sectional area of all the steps from the one end side to the other end side is gradually increased. That is, it is desirable that the cross-sectional area monotonically increases from one end side to the other end side of the crash box 2, but the cross-sectional area is the same or decreases in the section from the convex step portion to the concave step portion. It is also possible, and it is sufficient that the cross-sectional area of the crash box 2 as a whole is larger on the other end side than on the one end side.

(Explanation of the cross-sectional shape of the crash box)
3A and 3B are explanatory views of the outer shape of the shock absorbing material of the first embodiment, FIG. 3A is an explanatory view of a rectangular cross section, FIG. 3B is an explanatory view of an ellipse inscribed in the rectangular cross section, and FIG. 3C is radial from the center of the rectangular cross section. 3D is an explanatory view of the outer shape of the node, FIG. 3E is an explanatory view of the outer shape connecting the nodes, and FIG. 3F is an explanatory view of the outer shape of the elliptical stage.
In FIG. 3, the outer shape of the crash box 2 of the first embodiment is designed as follows. Here, the "cross section" refers to a cross section perpendicular to the axis from one end side to the other end side of the shock absorbing material. In the present invention, a virtual cross section and a virtual rectangular cross section may be simply referred to as a "cross section" or a "rectangular cross section (rectangular)". In addition, a virtual ellipse inscribed in a virtual rectangular cross section may be simply called an "ellipse".

First, in FIG. 3A, an ellipse 12 inscribed in a quadrangular pyramid-shaped pipe having a rectangular cross section 11 before processing is derived as shown in FIG. 3B.
Next, in FIG. 3C, assuming the X-axis direction (width direction) and the Y-axis direction (height direction) with the center 11a of the rectangular cross section 11 as the origin, the region 13 corresponding to the first quadrant of the XY plane is targeted. And. In the region 13 of the first quadrant, the 90-degree angle range between the X-axis and the Y-axis is divided into six equal parts as an example of a predetermined angle interval. The number of equal parts can be changed arbitrarily according to the design, specifications, etc., but if it is too large, it will be difficult to process, and if it is too small, the strength will be insufficient, so it will be divided into 5 equal parts to 8 equal parts. Is preferable.

Then, radial virtual line segments 14a to 14e that divide 90 degrees into six equal parts are derived from the center 11a of the rectangular cross section 11. That is, as an example of a predetermined angle, the virtual line segments 14a to 14e are derived at intervals of 15 degrees. Then, the points where the virtual line segments 14a to 14e intersect with the ellipse 12 are designated as the first nodes a1 to a5. Further, the points where the virtual line segments 14a to 14e intersect with the edges of the rectangular cross section 11 are designated as the second nodes b1 to b5.

In FIG. 3D, the distance between the first node ai (i = 1 to 5) and the second node bi (i = 1 to 5) (= | ai-bi |) along each virtual line segment 14a to 14e. On the other hand, the third node ci (i = 1 to 5) is set at the position of [| ai-bi | / 20] as an example of a predetermined distance from the second node bi side. That is, the third node ci is a point set in the section from the edge of the ellipse 12 to the inner side of the edge of the rectangular cross section 11 in the virtual line segments 14a to 14e. In Example 1, the position of the third node ci is illustrated as a position separated by a length of 1/20 from the second node bi, but the present invention is not limited to this, and the position is not limited to this, depending on the design, specifications, and the like. It can be changed arbitrarily. If the position of the third node ci is too close to the second node bi, the performance of the crash box 2 approaches that of the rectangular cross section 11, and if the position of the third node ci is too close to the first node ai, Since the amount of deformation when processing from the base material of the rectangular cross section 11 becomes large and processing becomes difficult, it is possible to select from the rectangular cross section 11 to the ellipse 12 according to the performance of the crash box, the material of the base material, the processing method, and the like. Is.

In FIG. 3E, the intersection A of the X-axis and the rectangular cross section 11, the third node ci derived in FIG. 3D, and the intersection B of the Y-axis and the rectangular cross section 11 are connected. In FIG. 3F, the above-mentioned third node ci is also derived for the second to fourth quadrants. The polygonal shape 16 connecting the intersections of the third node ci and the X-axis, the Y-axis, and the rectangular cross section 11 derived in this way is the cross-sectional shape of the odd-step portion 2d2 of the crash box 2. External shape).

4A and 4B are explanatory views of cross-sectional shapes of even-numbered stages, FIG. 4A is a view corresponding to FIG. 3D, FIG. 4B is a view corresponding to FIG. 3F, and FIG. 4C is an explanatory view of an external shape seen from the side. ..
In FIG. 4A, the cross-sectional shape of the even-numbered step portion 2d1 moves inward (center 11a side) by a preset step amount δ with respect to the third node ci derived in FIG. 3D. The fourth node di is derived. The step amount δ can be arbitrarily changed according to the design, specifications, etc., but it needs to be δ << | ai-ci |. It is also possible to move the intersections A and B by the amount of step δ.
In FIG. 4B, the polygonal shape 16'that connects the fourth node dis derived in FIG. 4A is taken as the cross-sectional shape (outer shape) of the even-numbered step portion 2d1 of the crash box 2.
Therefore, as shown in FIG. 4C, a crash box 2 is designed in which the even-numbered steps 2d1 are concave and the odd-numbered steps 2d2 are convex.

(Explanation of how to manufacture a crash box)
FIG. 5 is an explanatory view of a processing method of the crash box of the first embodiment, FIG. 5A is an explanatory view of a state in which both ends of the base material are held, and FIG. 5B is a state in which the base material is filled with a liquid from the state of FIG. 5A. FIG. 5C is an explanatory diagram of a state in which the mold is pressed from the state of FIG. 5B, and FIG. 5D is an explanatory diagram of a state in which an unnecessary portion is deleted after processing.
FIG. 6 is an explanatory view of a base material when processing the crash box of the first embodiment.
In order to facilitate understanding of the manufacturing method, detailed shapes such as lines and stepped portions 2d1 and 2d2 associated with the cross-sectional shape are simplified and described in FIGS. 5 and 6.

In FIGS. 5 and 6, in the method of manufacturing the crash box 2 of the first embodiment, a pipe 21 having a rectangular cross section 11 as an example of a tubular body is used as a base material. In FIG. 6, in the pipe 21 of the first embodiment, the width L1b on the other end side is larger than the width L1a on the one end side. Further, the height L2a on one end side and the height L2b on the other end side are set to be the same. As an example, L1a = 120.99 mm, L1b = 144.77 mm, L2a = L2b = 62.2 mm, and the axial length of the pipe 21 = 576.35 mm, but the length is not limited to this and can be changed as appropriate. Is.

In FIG. 5A, both ends of the pipe 21 are held by the holders 22. The holder 22 has an injection portion 22a that enters the inside of the pipe 21, and a holding portion 22b that holds the pipe 21 from the outside so as to sandwich the pipe 21 with the injection portion 22a. The injection portion 22a is formed corresponding to the cross-sectional shape of the pipe 21, and the holding portion 22b holds the pipe 21 while pressing it from the outside so that the inside of the pipe 21 is sealed.
In FIG. 5B, the pressurized liquid 23 is injected into the sealed pipe 21 through the injection path 22c formed in the injection portion 22a. At this time, it is desirable that the pressure of the pressurized liquid 23 is such that the pipe 21 bulges.

In FIG. 5C, a pair of upper and lower molds 24a and 24b are pressed from the outside against the pipe 21 into which the pressurized liquid 23 is injected. The molds 24a and 24b have an inner surface shape corresponding to the outer shape of the crash box 2 described above in FIG. Therefore, by pressing the outer surface of the pipe 21 with the molds 24a and 24b, the pipe 21 is compressed and deformed and processed into the outer shape of the crash box 2.

In FIG. 5D, the processed pipe 21 has a crash box 2 by allowing the pressurized liquid 23 to flow out, removing the molds 24a and 24b, removing the holder 22, and then cutting unnecessary portions 26 at both ends. The main body portion 2c of the above is obtained.

(Action of Example 1)
In the crash box 2 of the first embodiment having the above configuration, the cross-sectional shape is formed into a polygonal shape between the rectangular cross-section 11 and the ellipse 12.
A simulation experiment was conducted to confirm the effect of the present invention.
The simulation experiment was performed by computer simulation assuming a frontal collision by applying the shape and dimensions of the current crash box used in a 3-ton truck. The material was a steel material having a Young's modulus of 210 [GPa], a Poisson's ratio of 0.3, a yield stress of 270 [MPa], and a density of 7890 [kg / m ³ ]. When the base of the crash box 2 is restrained and a rigid body 3t from the tip is made to collide at an initial velocity of 15000 [mm / s] (corresponding to 56 [km / h]), and the crash box 2 progresses to the bottom. The collision crushing characteristics were evaluated using the amount of absorbed energy of. The side length of the quadrilateral element in the finite element method was 6 mm.
Here, an experiment was conducted by applying a configuration in which the cross-sectional area increases from one end side to the other end side.

In Comparative Example 1, an experiment was conducted in the case where the cross-sectional shape was a rectangular cross-section 11 and the plate thickness was 3.5 mm.
In Experimental Example 1, an experiment was conducted in the case where the cross-sectional shape was elliptical 12 and the plate thickness was 3.5 mm.
In Experimental Example 2, an experiment was conducted in the case where the cross-sectional shape was elliptical 12 and the plate thickness was 3 mm.
In Experimental Example 3, an experiment was conducted in the case where the cross-sectional shape of Example 1 was formed and the plate thickness was 3 mm.
Comparative Example 2 was a diamond-shaped cross-sectional shape that directly connects the intersection A and the intersection B, and an experiment was conducted in the case where the plate thickness was 3 mm.
In Comparative Example 3, an experiment was conducted on an inverted spiral origami structure (Japanese Unexamined Patent Publication No. 2018-187637) having a plate thickness of 3 mm.
The experimental results are shown in FIGS. 7 to 12.

FIG. 7 is an explanatory diagram of the experimental results, and is a list of the experimental results of Experimental Example 1-3 and Comparative Example 1-3.
In FIG. 7, in Comparative Example 1, it can be seen that the peak load is high, that is, the load until the deformation starts is high, and it is difficult to start the deformation. If the peak load is too low, it will be deformed even with a slight impact, which is not preferable. However, if the peak load is too high, the side member 3 will be loaded before the crash box 2 starts to deform (absorb the impact). It is not preferable because it may be deformed or distorted.
On the other hand, in Experimental Example 1, as compared with Comparative Example 1, the peak load is reduced, the weight is reduced, and the amount of energy absorbed is increased. The circumference is 80% of the circumference of the rectangular cross section 11, and the processing may be difficult depending on the material of the base material. By making the plate thickness thinner than that of Experimental Example 1 as in Experimental Example 2, it was possible to further reduce the peak load and reduce the weight, and to make the amount of energy absorption equivalent to that of Comparative Example 1. ..

In Experimental Example 3, the plate thickness is thinner than that of Comparative Example 1, the materials used are reduced, the weight of the crash box is reduced, the peak load is reduced, and the amount of energy absorbed is the same as that of Comparative Example 1. In particular, when converted to the amount of energy absorbed per weight, better results than in Comparative Example 1 are obtained. It is obvious that if the plate thickness is the same as that of Comparative Example 1, the amount of energy absorbed is better than that of Comparative Example 1. Therefore, in Experimental Example 3, the shock absorption performance is improved as compared with Comparative Example 1 which is a conventional configuration.
As shown in Comparative Example 2, the diamond-shaped cross-sectional shape can realize further weight reduction and reduction of the peak load as compared with Comparative Example 1, but the peripheral length is 60.5% of the rectangular cross-section 11. It is very difficult to create by processing.
In Comparative Example 3, compared to Comparative Example 1, good results were obtained in terms of weight reduction, reduction of peak load, and energy absorption amount, but there was a problem that the crushing mode was not crushed in order from the tip side (one end side).

FIG. 8 is an explanatory diagram of the experimental results, and is an explanatory diagram of the initial stage of the crushed state of Experimental Example 3 and Comparative Example 3.
FIG. 9 is an explanatory diagram of the experimental results, and is an explanatory diagram in a state in which a time has elapsed as compared with the case of FIG.
FIG. 10 is an explanatory diagram of the experimental results, and is an explanatory diagram in a state in which a time has elapsed as compared with the case of FIG.
FIG. 11 is an explanatory diagram of the experimental results, and is an explanatory diagram in a state where a time has elapsed as compared with the case of FIG.
FIG. 12 is an explanatory diagram of the experimental results, and is an explanatory diagram in a state in which a time has elapsed as compared with the case of FIG.

As shown in FIGS. 8 to 12, in Experimental Example 3, the crushing is performed in order from the tip side at the time of crushing. On the other hand, in Comparative Example 3, stress concentration occurs in the vicinity of the tip portion and the root portion at the initial stage of crushing, and deformation starts. In particular, therefore, when the crushing does not start from the tip portion and the impact is light and the crushing does not reach the state of FIG. 12, if the crushing of the root portion is advanced as in the states of FIGS. 10 and 11, the crash box It may be difficult to remove 2 from the side member 3. On the other hand, in Experimental Example 3, as shown in FIGS. 8 to 12, it is deformed from the tip side, and it is suppressed that the removal work becomes difficult.

Further, in the rectangular cross section shown in Comparative Example 1, even when an external force is applied from an oblique direction of about 5 degrees instead of an external force from the front (directly in front), the rectangular cross section may be deformed so as to bend in the axial direction. If the crash box 2 is bent in the middle of the axial direction, the energy absorption amount at the time of crushing from the front described above will not be reached. On the other hand, in the first embodiment, the virtual line segments 14a to 14e are set at intervals of 15 °, and the shape is closer to a circle (oval shape) than the rectangular (quadrangular) cross section. Therefore, it is less likely to bend than a rectangular cross section. Therefore, the performance such as the amount of energy absorption tends to be close to that when crushed from the front.

In the first embodiment, the virtual line segments 14a to 14e are set at intervals of 15 °, but when the number of virtual line segments 14a to 14e is increased = the angle interval becomes smaller, the cross section approaches a circle or an ellipse. When the cross section approaches a circle or an ellipse, the strength improves, but there is a problem that it is difficult to predict and control where in the axial direction the crush will occur. On the other hand, in the embodiment, since the step portion 2d is formed, stress concentration is generated at the position of the step portion 2d (2d1, 2d2) and it is easy to crush, and crushing is performed from any part in the axial direction. It is easier to predict and control.

Further, in the first embodiment, when manufacturing from the pipe 21, the molds 24a and 24b are pressed with the pressurized liquid 23 sealed inside. When the pressurized liquid 23 is not provided, the convex portions (concave portions in the crash box 2) in the molds 24a and 24b are likely to be formed with high accuracy. On the other hand, the concave portions (convex portions in the crash box 2) in the molds 24a and 24b are difficult to be formed with high accuracy, and the corner portions may be rounded (not sharp and dull). On the other hand, in the first embodiment, the pressure liquid 23 is pressed from the inside, and the outer shape of the crash box 2 can be formed more accurately than in the case where the pressure liquid 23 is not used. ..

(Change example)
Although the examples of the present invention have been described in detail above, the present invention is not limited to the above-mentioned examples, and various modifications are made within the scope of the gist of the present invention described in the claims. It is possible.
For example, the specific numerical values and material names exemplified in the examples can be appropriately changed according to changes in design and specifications.

Further, in the embodiment, it is preferable to use it as a shock absorbing material for a crash box 2 such as a truck, but the present invention is not limited to this. It can also be applied to any part that needs to absorb impact in the event of an accident, such as play equipment such as railroads, aircraft, ships, and roller coasters.
Further, in the examples, a processing method of pressing with the molds 24a and 24b from the outside in a state of being pressurized with a pressurized liquid from the inside has been illustrated, but the processing method is not limited to this. Depending on the ease of processing the material to be used, it can be manufactured by any conventionally known manufacturing method such as extrusion molding.

Further, the case where the crash box 2 is created by molding and processing the pipe 21 having a rectangular cross section has been illustrated, but the present invention is not limited to this. It is also possible to mold from a pipe 21 having a circular cross section. In addition, for example, in the cross section shown in FIG. 3, the polygonal cylinder is divided into two parts (a polygonal cylinder divided into upper and lower halves), and each part divided into two parts is molded from the plate material, and then the two parts after molding. It is also possible to weld the parts into a tubular shape. It is also possible to divide the cross section into three or more.

13A and 13B are explanatory views of a modified example, FIG. 13A is a diagram corresponding to FIG. 4A, FIG. 13B is a diagram corresponding to FIG. 4B, and FIG. 13C is a diagram corresponding to FIG. 4C.
In the above embodiment, it is desirable to provide the step portion 2d, but it is also possible to provide a configuration in which the step portion 2d is not provided. Further, the case where the even-numbered step portion 2d1 is concave and the odd-numbered step portion 2d2 is convex is illustrated, but the present invention is not limited to this. It is also possible that the even-numbered steps are convex and the odd-numbered steps are concave. Specifically, as shown in FIG. 13, when deriving the fourth node di, the step amount δ is not the inside but the outside (the side away from the center 11a) with respect to the third node ci and the like. It can be derived by setting it as a moved point. In this case, it is necessary to set δ << | bi-ci |.

2 ... Shock absorber,
2c ... Main body,
2d ... Duan tribe,
11 ... Rectangular cross section,
12 ... ellipse,
14a-14e ... Virtual line segment,
21 ... Cylinder,
24a, 24b ... type,
c1 to c5 ... points.

Claims (4)

A shock absorbing material having a tubular main body extending from one end to the other end and having the main body whose cross-sectional area increases from one end side to the other end side.
In the cross section of the main body portion perpendicular to the axis from one end side to the other end side, the edge of the rectangle is provided with a predetermined angle centered on the center of the rectangle with respect to the rectangle and the ellipse inscribed in the rectangle. It has a cross-sectional shape connecting points set in a section inside the rectangular edge from the edge of the ellipse along a plurality of virtual line segments extending toward.
A shock absorber characterized by that. Steps were formed at predetermined intervals from one end to the other.
The shock absorbing material according to claim 1. The rectangular body is inscribed in the rectangular shape in the cross section of the main body perpendicular to the axis extending from one end side to the other end side with respect to the cylindrical main body portion having a rectangular cross section extending from one end to the other end. Set in a section from the edge of the ellipse to the inside of the edge of the rectangle along a plurality of virtual line segments extending toward the edge of the rectangle at a predetermined angle about the center of the rectangle with respect to the ellipse. A method for producing a shock absorbing material, which comprises performing a process of compressing and deforming the main body from the outside so as to form a cross-sectional shape connecting the formed points. It has an inner surface shape corresponding to the outer shape of the main body in a state where both ends of a cylindrical body having a rectangular cross section extending from one end to the other end are held and the inside of the hollow cylinder is filled with a liquid. The method for manufacturing a shock absorber according to claim 3, wherein the mold is pressed against the outer surface of the cylinder to manufacture the shock absorber from the cylinder.

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