JP2013010392A - Energy absorption member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an energy absorption member comprising a circular tube having a large number of embosses formed on the peripheral wall, in which specific geometrical shaped embosses are provided in a specific distribution form on the sidewall to uniformalize the load characteristic in collision and to improve energy absorption efficiency.SOLUTION: Each emboss has the same shape and a nearly rectangular outline. All embosses belong to any of m-lines of emboss lines 4 in a peripheral direction, which are arrayed at a fixed space d along the axial direction of the circular tube, and each emboss line 4 in the peripheral direction is constituted of n-pieces of the embosses arranged at an equiangular space δ along the peripheral direction. At the same time, all embosses belong to 2×n-lines of emboss lines in an axial direction, which are arranged at an equiangular space δ/2 along the peripheral direction of the circular tube 1 and each emboss line in the axial direction is constituted of a plurality of pieces of the embosses arranged at an equal space along the axial direction of the circular tube 1.

Description

  The present invention relates to a cylindrical energy absorbing member used as a bumper stay that absorbs collision energy at the time of automobile collision.

  In recent years, there has been a growing demand for further collision safety in the field of vehicles such as automobiles. For example, taking the safety standards of passenger cars as an example, in the mainstream barrier (wall) collision tests and so on, the entire vehicle body is compressed evenly, whereas the IIHS (Insurance Institute of Highway Safety) )) And the offset barrier test recently proposed by the EC is a test method in which a load is applied to the vehicle by receiving a collision biased (offset) on one side in the width direction of the vehicle. This is because the actual situation of the collision accident was taken into consideration, but in order to cope with this offset barrier test, a high-performance energy absorption mechanism was provided on the bumper stay, which is a rear member that supports the bumper of the collision portion, and the vehicle It is necessary to increase the safety of That is, when the bumper stay is deformed by receiving a compressive force, it is necessary to stably generate a reaction force load and to reduce the weight.

In response to this requirement, bumper stays (Patent Documents 1 to 6) using the axial crushing characteristics of a circular tube or a hollow member having a polygonal cross section have been proposed. Since these bumper stays are arranged so that the perpendicular to the cross section coincides with the traveling direction of the vehicle, an end plate and a flange are provided at the end of the hollow cross section, and the bumper and the vehicle body are connected via the end plate and the flange. It is concluded.
When using a hollow member with a polygonal cross section in a bumper stay that uses axial crushing characteristics, the crushing characteristics are adjusted by devising the cross-sectional shape or by providing a crush bead (emboss) as a starting point of crushing on the side wall. ing. Even when a circular tube is used, as described in Patent Document 2, for example, an emboss serving as a starting point of crushing is provided on the side wall.

Japanese Patent No. 3217060 JP 2004-189063 A JP 2008-308170 A JP 2008-132988 A Japanese Patent No. 4036234 JP 2008-296716 A

When a circular pipe is used as a material for a bumper stay using the axial crushing characteristic, the load fluctuation at the time of axial crushing is larger than that of a polygonal cross section if the shape is close to the raw pipe. For this reason, in order to flatten the load characteristics at the time of collision and improve the energy absorption efficiency, it is not the same as that of the polygonal cross section, and it is necessary to provide embosses with a geometric shape and a distribution form particularly suitable for a circular pipe Though possible, the guidelines for doing so were not clear.
Therefore, in the present invention, in an energy absorbing member composed of a circular tube having a large number of embossed parts on the peripheral wall, embosses having a specific geometric shape are provided on the side wall in a specific distribution form, thereby flattening the load characteristics at the time of collision. And it aims at improving energy absorption efficiency.

The present invention is used as a bumper stay that absorbs collision energy at the time of a car collision, and is an energy absorbing member that is a circular pipe in which a large number of concave embosses that are the starting points of crushing are formed on a peripheral wall. It has the same shape and has a substantially rectangular outline that is long in the circumferential direction of the circular tube, and all the embossments belong to one of m circumferential embossed rows arranged at regular intervals along the axial direction of the circular tube, Each circumferential emboss row is composed of n embosses arranged at equal intervals along the circumferential direction of the circular tube, and all the embosses are arranged at equal intervals along the circumferential direction of the circular tube. It belongs to one of the n axial embossing rows, and each axial embossing row is composed of a plurality of embosses arranged at equal intervals along the axial direction of the circular tube, and is adjacent to the circumferential embossing row. Embossing which is characterized by not belonging to the same axial embossed column. Note that m is an integer of 4 or more, and n is an integer of 2 or more.
The emboss can be formed by electromagnetic forming (see Patent Document 2) or press forming.

In the above energy absorbing member, the outer diameter of the circular tube is g, and for each embossed geometric shape, the emboss depth is h, the height along the axial direction of the emboss is t, and both circumferential ends of one emboss are When the angle formed by the center of the circular tube is θ, the g, h, t, θ are each formed of a circular tube satisfying one of the following formulas, or the g, h, t, θ are similar to this: It is desirable to consist of a circular tube having
(G, h, t, θ) = (55 mm, 1 mm, 6 mm, 15 °)
(G, h, t, θ) = (55 mm, 1 mm, 8 mm, 20 °)

According to the present invention, a large number of concave embosses are formed in a specific geometric shape and a specific distribution form on the peripheral wall of the circular tube, thereby buckling the energy absorbing member using the circular tube at the time of buckling collapse. Energy absorption efficiency can be improved while changing the mode and suppressing load fluctuation at the time of collision. In addition, by improving the energy absorption characteristics of the bumper stay alone, the characteristics of the entire bumper system including this bumper stay are improved, and a high-performance and lightweight bumper system that responds to the recent enhancement of collision safety standards is provided. be able to.
The energy absorbing member according to the present invention is applied to a bumper stay of an automobile such as a passenger car or a truck, but can be applied as a safety member of a moving body such as a train or aerospace.

It is the top view (a) and front view (b) of the circular pipe which concern on this invention. It is sectional drawing of embossing in the surface perpendicular | vertical to the axial direction of the circular pipe which concerns on this invention. It is a figure which shows the planar view shape (a) and front view shape (b) of the internal peripheral surface of a metal mold | die used when electromagnetically forming the circular tube which concerns on this invention. It is the load-displacement curve obtained by performing the shaping | molding analysis which simulated the crushing deformation | transformation further by the FEM analysis for the circular pipe obtained by performing the shaping | molding analysis imitating electromagnetic shaping | molding by FEM analysis. It is the load-displacement curve obtained by performing the shaping | molding analysis which simulated the crushing deformation | transformation further by the FEM analysis for the circular pipe obtained by performing the shaping | molding analysis imitating electromagnetic shaping | molding by FEM analysis. It is the load-displacement curve obtained by performing the shaping | molding analysis which simulated the crushing deformation | transformation further by the FEM analysis for the circular pipe obtained by performing the shaping | molding analysis imitating electromagnetic shaping | molding by FEM analysis. It is the load-displacement curve obtained by performing the shaping | molding analysis which simulated the crushing deformation | transformation further by the FEM analysis for the circular pipe obtained by performing the shaping | molding analysis imitating electromagnetic shaping | molding by FEM analysis. It is the load-displacement curve obtained by performing the shaping | molding analysis which simulated the crushing deformation | transformation further by the FEM analysis for the circular pipe obtained by performing the shaping | molding analysis imitating electromagnetic shaping | molding by FEM analysis. It is the load-displacement curve obtained by performing the shaping | molding analysis which simulated the crushing deformation | transformation further by the FEM analysis for the circular pipe obtained by performing the shaping | molding analysis imitating electromagnetic shaping | molding by FEM analysis. It is a load-displacement curve when the circular pipe actually obtained by electromagnetic forming is crushed and deformed.

Hereinafter, with reference to FIGS. 1-10, the energy absorption member which concerns on this invention is demonstrated more concretely.
The energy absorbing member shown in FIGS. 1 and 2 includes a circular tube 1 having an appropriate length, an outer diameter g, and a wall thickness, and a plurality of concave embosses 3 are formed on a peripheral wall 2 of the circular tube 1. All the embosses 3 have the same shape, and have a substantially rectangular outline composed of a long side 3 a curved along the circumferential direction of the circular tube 1 and a short side 3 b along the axial direction of the circular tube 1. In addition, the geometric shape of the emboss 3 includes an emboss depth h (see FIG. 2), an emboss axial height t (see FIG. 1 (b)), one circumferential end of one emboss and the center O of the circular tube. It is expressed by an angle (circumferential angle) θ (see FIG. 2).

A large number of embosses 3 take the following distribution form on the peripheral wall 2 of the circular tube 1.
All the embosses belong to one of m circumferential emboss rows 4, 4,... Arranged in a constant interval d along the axial direction of the circular tube 1 (m = 6 in this example). Each circumferential emboss row 4 is composed of n (in this example, n = 6) embosses 3 arranged at equiangular intervals δ (in this example, δ = 60 °) along the circumferential direction of the circular tube 1, The n embosses 3 belonging to each circumferential emboss row 4 are all arranged in a line in the circumferential direction of the peripheral wall 2 of the circular tube 1 along a plane perpendicular to the axial direction of the circular tube 1. In addition, the space | interval d of the circumferential direction emboss row | line | columns 4 becomes the folding width | variety of the circular tube 1 at the time of axial direction collapse.

All the embosses belong to any of 2 × n rows of axial emboss rows 5, 5,... Arranged at equiangular intervals (δ / 2) along the circumferential direction of the circular tube 1. Each axial emboss row 5 is composed of a plurality of (three in this example) embosses 3 arranged at equal intervals (2 × d) along the axial direction of the circular tube 1. The embosses to which they belong are arranged in a line in the axial direction of the circular tube 1. The embosses belonging to the adjacent circumferential emboss rows 4 and 4 do not belong to the same axial emboss row. When the embosses belonging to the adjacent axial emboss rows 5 and 5 are viewed, the so-called staggered arrangement is provided in the axial direction.
In the distribution form of the emboss 3, m is an integer of 4 or more, and n is an integer of 2 or more. These values adjust the length and outer diameter of the circular tube, the geometric shape of the emboss, or the deformation behavior at the time of crushing. Therefore, it is set appropriately.

The circular tube 1 shown in FIGS. 1A and 1B can be formed, for example, by electromagnetic forming. The shape of the inner peripheral surface 6a of the mold 6 for electromagnetically forming the circular tube 1 is shown in FIGS. 3 (a) and 3 (b). The mold 6 is composed of a plurality of divided molds having a cylindrical inner peripheral surface 6a having an inner diameter G at the center when combined, and a plurality of protrusions 7 are formed on the inner peripheral surface 6a.
Since the outer peripheral shape of the circular tube 1 is formed by transferring the shape of the inner peripheral surface 6a of the mold 6 by electromagnetic forming, the inner diameter G of the inner peripheral surface 6a is equal to the outer diameter g of the circular tube 1. The geometric shape and distribution form of the protrusions 7 on the inner peripheral surface 6a substantially match the geometric shape and distribution form of the concave emboss 3 of the circular tube 1.

More specifically, the protrusions 7 are all the same shape and have a substantially rectangular outline, the protrusion height H from the inner peripheral surface 6a, the axial height T, the both ends in the circumferential direction of one protrusion and the inner It is represented by an angle (circumferential angle) Θ formed by the center O of the peripheral surface 6a (see FIG. 3A), and H, T, and Θ of the protrusion 7 are substantially equal to h, t, and θ of the emboss 3, respectively. equal.
The many protrusions 7 have the following distribution form on the inner peripheral surface 6 a of the mold 6.
All the protrusions belong to one of M (M = 6 in this example) rows of circumferential protrusions 8 arranged at a constant interval D along the axial direction of the inner peripheral surface 6a. Each circumferential protrusion row 8 is composed of N (N = 6 in this example) protrusions 7 arranged on the inner peripheral surface 6a of the mold 6 at an equal angular interval Δ (Δ = 60 ° in this example). Yes. M, N, D, and Δ are equal to m, n, d, and δ in the circular tube 1, respectively.
Further, all the protrusions belong to any of 2 × N rows of axial protrusion rows 9 arranged on the inner peripheral surface 6a of the mold 6 at equal angular intervals (Δ / 2). Each axial projection row 9 is composed of a plurality (three in this example) of projections 7 arranged at equal intervals (2 × D) along the axial direction of the inner peripheral surface 6a. The protrusions 7 belonging to the adjacent circumferential protrusion rows 8 do not belong to the same axial protrusion row 9.

At the time of electromagnetic forming, an elemental tube having a circular cross section preferably made of an aluminum alloy extruded material is used, and this elemental tube is inserted into the inner peripheral surface of the mold 6, and an electromagnetic forming coil is inserted inside the elemental tube. Energize the coil. The energization expands the raw tube in a very short time and hits the inner peripheral surface 6a of the mold 6 to form the outer peripheral circular tube 1 along the inner peripheral surface 6a. The concave emboss 3 is transferred to the shape corresponding to the shape of the protrusion 7.
In addition, as an aluminum alloy, JIS6000 type | system | group or 7000 type | system | group is suitable.

(FEM analysis)
As a first step of the FEM analysis, a forming analysis simulating electromagnetic forming was performed, and a circular cross-section element tube was formed into an embossed circular tube (a part of the tube without embossing). Next, as a second step, an analysis is performed in which the embossed circular tube (partially a non-embossed circular tube) obtained by the first step analysis is compressed in the axial direction to be crushed and deformed, and a load-displacement curve. Got. The embossed circular tube obtained by FEM analysis corresponds to the circular tube according to the present invention described above.
An aluminum alloy extruded shape (JIS6063-T5) was assumed as a material model of the raw tube, and its 0.2% proof stress was set to 150 MPa, elastic modulus 68.5 GPa, density 2700 Kg / m ³ , and Poisson's ratio 0.3.

  In the first step, the shape of the raw tube was set to an outer diameter of 51 mm, a length of 100 mm, and a wall thickness of 2 mm. In addition, as a mold model used for electromagnetic forming, basically the one shown in FIGS. 3A and 3B was used. The mold model will be described with reference to FIGS. 3A and 3B. As the basic structure of the mold model, the number of circumferential projection rows is 6, and the number of projections included in each circumferential projection row is 6. The length L of the mold is set to 100 mm, the diameter G of the inner peripheral surface is set to 55 mm, the distance D between the circumferential projections is set to 10 mm, and the distance E (from the lower end of the mold to the nearest circumferential projection is 3 (b)) was set to 20 mm. Under this basic structure, the protrusion height H of the protrusion, the axial height T of the protrusion, and the circumferential angle Θ of the protrusion were used as parameters (variables). Table 1 shows combinations of parameters H, T, and Θ used in the analysis.

  In the FEM analysis of the first step, the raw tube is arranged inside the mold model, the vertical displacement of the upper and lower surfaces of the raw tube is constrained, and 3 GPa is placed inside the raw tube to simulate electromagnetic forming. The pressure was applied. As a result of the FEM analysis, the base tube is expanded and deformed into a shape along the inner peripheral surface of the mold model, and the shape and distribution of the protrusions of the mold are transferred to the circular tube as they are, and a large number of concave embosses are obtained. An embossed circular tube (No. 1 is a non-embossed circular tube) was formed. The embossed circular tube has an outer diameter (g) equal to the inner diameter (D) of the inner peripheral surface of the mold model and 55 mm, and the axial distance (d) between the circumferential embossed rows is between the circumferential projection rows of the mold model. The emboss depth (h), the emboss axial height (t), and the emboss circumferential angle (θ) are the parameters of the mold model (H, T, Θ). ). On the other hand, on the inner peripheral side of the embossed circular tube, the vicinity of the embossed contour (see arrow a in FIG. 2) was a smooth curved surface. The above shape of the embossed circular tube obtained by FEM analysis is very close to the shape actually formed by electromagnetic forming.

In the FEM analysis in the second step, the lower end of the embossed circular tube is placed on the rigid wall, and another rigid wall is lowered from above to compress the embossed circular tube at a quasi-static speed. The load-displacement curves obtained as a result of the analysis are shown in FIGS.
Subsequently, based on the load-displacement curves of FIGS. The energy absorption characteristics of 1 to 6 circular tubes were evaluated. The evaluation target is crushing up to 70% of the total length (displacement: 70 mm), and the evaluation index is a load variation coefficient φα representing load variation, φβ representing the ratio of average load to maximum load, φχ representing energy absorption efficiency, and These were combined into φ.
φα, φβ, φχ, and φ are expressed by the following equations.

  No. Table 2 shows the values of the evaluation indices φα, φβ, φχ, φ for 1-6. The larger the values of the evaluation indexes φα, φβ, φχ, φ, the better the energy absorption characteristics.

From FIGS. In all the embossed circular pipes 2 to 6, No. 2 which is an unembossed circular pipe. The load fluctuation is clearly suppressed as compared with No. 1, and all evaluation indices are No.1. It can be seen that it is better than 1.
Of these, No. 3 is No.3. Compared to 1, the evaluation index is greatly improved. No. 4 is No.4. 3 shows the same deformation behavior as that of No. 3. Although the evaluation index is greatly improved compared to 1. Compared to 3, the degree of improvement is slightly smaller. No. No. 2 shows that the degree of improvement of the evaluation index is No. 2. Next to 4. No. Nos. 5 and 6 are No. 2 shows the same deformation behavior as No. 2, but no. Compared to 2, the degree of improvement of the evaluation index is small.
From these results, in order to improve the evaluation index φα, φβ, φχ, φ of the energy absorption characteristics, the emboss geometry (emboss depth (h), emboss axial height (t ), The circumferential angle (θ) of the embossing is preferably adjusted to (1 mm, 6 mm, 15 °) or (1 mm, 8 mm, 20 °).

(Example)
An aluminum alloy extruded material (JIS6063-T5) having an outer diameter of 91 mm and a wall thickness of 3.5 mm was cut to obtain a raw tube having a length of 145 mm. This base tube was actually electromagnetically molded to form an embossed circular tube (No. 7). No. 7 is an outer diameter (g) of 98 mm, an emboss depth (h) of 1.78 mm, an axial height (t) of 10.7 mm, a circumferential angle (θ) of 15 °, and a circumferential embossed row The axial interval (d) is 17.8 mm. 3 (H1T6-15) is similar in outer diameter, geometric shape and distribution of embossing (similarity ratio: about 1.78 times).
In addition, an element tube made of the same aluminum alloy extruded shape was actually electromagnetically formed to form an unembossed circular tube (No. 8) having an outer diameter of 98 mm. No. 8 has an outer diameter (g) of 98 mm.

Subsequently, no. 7 and 8 were subjected to a crushing deformation by applying a quasi-static compressive load in the axial direction to obtain a load-displacement curve. The result is shown in FIG.
As shown in FIG. In No. 8, a load-displacement curve having a large load variation with displacement is obtained. In No. 7, a load-displacement curve in which load fluctuation was suppressed without causing a decrease in absorbed energy was obtained. No. The load-displacement curve of No. 7 was obtained by FEM analysis. 3 and the load-displacement curve. The load-displacement curve of No. 8 was obtained as No. 8 obtained by FEM analysis. 1 and a load-displacement curve. Thus, no. It can be seen that the energy absorption characteristics are greatly improved even with an embossed circular tube having an outer diameter 3 and an embossed geometric shape (h, t, θ) similar to each other.

1 Round pipe (with emboss)
2 A circumferential wall of a circular tube 3 A concave emboss 4 A circumferential emboss row 5 An axial emboss row 6 A mold 6a for electromagnetic forming An inner peripheral surface 7 of a die 8 A projection 8 A circumferential projection row 9 Axial projection row g Diameter h Emboss depth t Emboss axial height θ Emboss circumferential angle d Circumferential emboss row axial spacing δ Axial emboss train circumferential angle spacing

Claims (3)

In an energy absorbing member consisting of a circular tube, which is used as a bumper stay that absorbs collision energy at the time of a car collision and has a plurality of concave embosses formed on the peripheral wall as a starting point of crushing at the time of the collision, each emboss is the same shape and Each of the circumferential embosses has a substantially rectangular outline that is long in the circumferential direction of the circular tube, and all the embossments belong to one of m circumferential embossed rows arranged at regular intervals along the axial direction of the circular tube. The row is composed of n embosses arranged at equal intervals along the circumferential direction of the circular tube, and all the embossments are arranged at 2 × n columns arranged at equal intervals along the circumferential direction of the circular tube. Belonging to any one of the direction embossing rows, and each of the axial embossing rows is composed of a plurality of embosses arranged at equal intervals along the axial direction of the circular tube, and belongs to the adjacent circumferential embossing row. Scan the energy absorbing member characterized by not belonging to the same axial embossed column. The outer diameter of the circular tube is g, the depth of the emboss is h, the height along the axial direction of the emboss is t, and the angle between the circumferential ends of one emboss and the center of the circular tube is θ. The g, h, t, and θ are each formed of a circular tube that satisfies one of the following formulas, or the g, h, t, and θ are formed of a circular tube having a similar shape thereto. The energy absorbing member according to claim 1.
(G, h, t, θ) = (55 mm, 1 mm, 6 mm, 15 °)
(G, h, t, θ) = (55 mm, 1 mm, 8 mm, 20 °) The energy absorbing member according to claim 1 or 2, wherein the emboss is formed by electromagnetic forming or press forming.

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