JP5049153B2 - Energy absorbing member and energy absorbing structure - Google Patents

Description

  The present invention relates to an energy absorbing member such as a bumper stay, a crash box, and a side member provided on the back side of a vehicle bumper reinforcement.

  Bumper reinforcements (also called bumper reinforcements or bumper armatures) as strength reinforcements are provided on the back of bumpers attached to the front end (front) and rear end (rear) of a vehicle body such as an automobile. . A bumper stay, a crash box, and a side member (also referred to as a side frame) are provided on the back side of the bumper reinforcing material for the purpose of alleviating the impact on the occupant during a vehicle collision and supporting the bumper reinforcing material. These members are required to absorb energy by plastic deformation when the impact energy cannot be absorbed by the bumper reinforcing material alone at the time of medium-high speed collision.

In recent years, due to problems in the global environment, it has become necessary to reduce the weight of automobiles, and these energy absorbing members are also required to be reduced in weight. That is, the performance of the energy absorbing member has been evaluated by the amount of energy absorbed relative to the weight of the component.
In addition, these energy absorbing members are required to have a maximum load so as not to deform a part located on the rear side of the collision, and to efficiently absorb energy within the limitation. In other words, it is also required that the load fluctuation during crushing deformation is small and that energy absorption efficiency is excellent.
Conventionally, aluminum alloy products that replace steel are proposed for such energy absorbing members in order to reduce the weight. In particular, the extruded shape of the aluminum alloy with the longitudinal direction of the vehicle body as the extrusion direction can have a cross-sectional structure that is perpendicular to the collision direction in advance, so there is no increase in cost due to welding, no decrease in strength due to thermal effects, It is known that the lightening effect is great.

As such a vertical crushing type energy absorbing member, various cross-sectional shapes have been proposed so far.
First, the structure proposed for the purpose of increasing the energy absorption efficiency is shown. In order to suppress the load fluctuation and improve the energy absorption performance, it is effective to increase the ridge lines constituting the cross section and shorten the width of each side constituting the cross section. This is because the wavelength of buckling that occurs during crushing deformation is shortened and the period of load variation is shortened, thereby suppressing the amplitude of load variation. For this reason, various proposals for shape with a polygonal outer dimension of the cross section have been proposed and put into practical use. For example, a crush box or a side member having a polygonal cross-sectional shape of a pentagonal, hexagonal, octagonal, or more than a general quadrangular cross-section has been proposed and put into practical use (Patent Literature). 1-3).
Furthermore, an example of improving energy absorption performance by making the straight line constituting the cross section non-linear has been reported (see Patent Document 4). In this case, a plane for joining with other components is secured. There is concern about the inability to do so.

  Next, a structure plan for increasing the energy absorption amount itself will be described. In order to increase the amount of energy absorbed, it is necessary to increase the pressure receiving area. Therefore, it is necessary to increase the thickness of the cross section, or to increase the outer dimension of the cross section if the shape constraints can be satisfied. Become. In addition, the increase in thickness leads to an increase in the buckling wavelength at the time of crushing deformation, and there is a problem that the load fluctuation becomes severe. Further, when the cross-section is simply widened and the outer shape is enlarged, there is a problem that the buckling wavelength becomes long and the load fluctuation becomes severe. In order to prevent this, there has been proposed a structure plan that increases the energy absorption rate by increasing the ridgeline and the number of sides by shortening the width of the sides by making the cross section of the frame of the polygonal cross section two. (See Patent Documents 5 to 8).

  In addition, when the shape restrictions are severe and the cross section cannot be enlarged, it is common practice to provide a medium rib inside the cross section to increase the number of sides and increase the amount of energy absorption without increasing the outer dimensions of the cross section. ing. In particular, in the case of the polygonal section described above, it has been proposed to increase the amount of energy absorption by providing an intermediate rib so as to connect the apex and the center of the section (see Patent Documents 9 to 11).

JP 2000-006840 A JP 2002-173048 A Japanese Patent No. 3381477 JP 2006-207725 A JP 2005-162049 A JP 2006-207724 A JP 2006-207726 A JP 2007-17003 A JP 2004-182088 A JP 2004-106612 A JP 2001-124128 A

  Regarding the energy absorbing member provided with the intermediate rib, the cross-sectional shape proposed so far is the one in which the intermediate rib is provided so as to connect the apexes of the polygonal cross section, and each side constituting the cross-sectional outline is formed by the intermediate rib. By supporting firmly, each side is buckled independently, and energy absorption is performed while suppressing load fluctuations during crushing. Such addition of the intermediate rib naturally leads to an increase in the weight of the component, and therefore it can be said that the arrangement of the intermediate rib so that the energy absorption efficiency and the energy absorption amount in the weight ratio can be increased is important.

  In the present invention, in the energy absorbing member provided with the intermediate rib in the cross section in order to satisfy the shape restriction as described above, the load fluctuation at the time of the collision collapse is further increased as compared with the prior art by efficiently arranging the intermediate rib. An object of the present invention is to provide an energy absorbing member which is small and excellent in energy absorption per weight.

  The present invention provides an energy absorbing member made of an aluminum alloy extruded shape that is provided on the back side of a vehicle bumper reinforcing material and whose extrusion direction is substantially parallel to the longitudinal direction of the vehicle. It has a square or convex hexagonal closed cross-sectional shape, and has three medium ribs inside thereof, each medium rib having one end connected to different sides constituting the outer shape, and the other end. Are connected to each other. The convex polygon means a polygon having all inner angles of less than 180 °.

As a desirable embodiment, the outer shape is a hexagon, and one end of each middle rib is connected to a side that does not adjoin each other constituting the outer shape (Claim 2), and one of the middle ribs Are connected to the central part of the side constituting the outer shape (Claim 3), and the other end of each middle rib is the connecting point of the one end and the side constituting the outer shape. Are connected to each other at the center of gravity of a triangle connecting the two (claim 4). This energy absorbing member is suitable for use as any of a stay, a crash box, and a side member of an automobile bumper reinforcement. Further, by combining this energy absorbing member with a bumper reinforcing material made of an aluminum alloy extruded profile, an energy absorbing structure that is further excellent in weight reduction effect can be obtained.
The intermediate rib is preferably integrally formed with an outer shape having a closed cross-sectional shape at the same time when the extruded profile is manufactured, but after the outer profile and the intermediate rib are separately manufactured as an extruded profile, the intermediate rib is You may join inside. In this case, the middle rib can be joined over the entire length in the extrusion direction of the outer shape, or the middle rib shorter than the outer shape can be joined only in a partial length range of the outer shape in the extrusion direction.

According to the present invention, it is possible to obtain an energy absorbing member having an intermediate rib in the cross section, which has little load fluctuation at the time of collision collapse and is excellent in energy absorption per weight.
In addition, by combining with a bumper reinforcing material made of an extruded aluminum material, a bumper system that is lightweight and has excellent energy absorption performance can be configured.

The energy absorbing member according to the present invention is made of an aluminum alloy extruded shape. When a cross section perpendicular to the extrusion direction is viewed, the cross-sectional outer shape forms a convex pentagon or a convex hexagon, and the inside thereof has a closed cross-sectional shape. Each of the middle ribs has one end connected to different sides constituting the outer shape, and the other end connected to each other at one point in the outer shape.
1 and 2 exemplify a cross section of an aluminum alloy extruded profile according to the present invention. FIG. 1 shows an example of a hexagonal cross section, and FIG. 2 shows an example of a pentagonal cross section.

The cross section of FIG. 1A is a regular hexagonal outer shape 1 in which three middle ribs 2 to 4 are formed, and one end of the middle ribs 2 to 4 constitutes the outer shape 1. The sides 1a to 1c that are not adjacent to each other are connected to the center, and the other ends are connected to each other at a triangular center of gravity G that connects the connection points 5 to 7 between the one end and the sides 1a to 1c constituting the outer shape 1. Has been. This cross section is most desirable.
The cross section of FIG. 1B is obtained by forming three medium ribs 2 to 4 in a regular hexagonal outer shape 1, and one end of each of the middle ribs 2 to 4 forms the outer shape 1. It is connected to the center of the sides 1a to 1c which are not adjacent to each other, and the other end is connected to each other at the center C of the line segment connecting the one end of the middle ribs 3 and 4 and the connecting points 6 and 7 of the sides 1b and 1c. Has been.

The cross section of FIG. 1C is obtained by forming three medium ribs 2 to 4 in a regular hexagonal outer shape 1, and one end of each of the middle ribs 2 to 4 forms the outer shape 1. It is connected to a location that is slightly closer to the apex than the centers of the sides 1a to 1c that are not adjacent to each other, and the other end is connected to each other at the center of gravity G of the triangle that connects the one end and the connecting points 5 to 7 of the sides 1a to 1c. Has been.
The cross section of FIG. 1 (d) has an outer shape 1 in which all inner angles are 120 °, one set of opposite sides 1a and 1d have different lengths from the other two sets of opposite sides, and three pieces formed therein. It consists of the middle ribs 2 to 4, and one end of the middle ribs 2 to 4 is connected to the center of the sides 1a to 1c that are not adjacent to each other constituting the outer shape 1, and the other end is the one end and the side. The triangular centers of gravity G connecting the connecting points 5 to 7 of 1a to 1c are connected to each other.

The cross section of FIG. 2A is a regular pentagonal outer shape 11 in which three medium ribs 12 to 14 are formed, and one end of the medium rib 12 is connected to the center of the side 11c. One end of the other middle ribs 13 and 14 is connected to the center of each of the sides 11d and 11e not adjacent to the side 11c, and the other ends of the middle ribs 12 to 14 are connected to the one end and the side 11c to 11c. They are connected to each other at a triangular center of gravity G connecting connecting points 15 to 17 with 11e. The middle ribs 12 to 14 are not connected to the sides 11a and 11b on both sides.
The cross section of FIG. 2 (b) has two sides 11a and 11b that are parallel and have the same length, a side 11c that is perpendicularly connected to one end of the sides 11a and 11b, and a same length that is connected to the other end of the sides 11a and 11b. A pentagonal outer shape 11 constituted by two sides 11d, 11e (the same length as the sides 11a, 11b) and three middle ribs 12-14 formed therein, and the middle ribs 12-14 3 is connected to the center of the side 11c and the sides 11d and 11e that are not adjacent to the side 11c, and the other end connects the one end and the connecting points 15 to 17 of the sides 1c to 1e. They are connected to each other at the center of gravity G of the square.
The cross section of FIG. 2 (c) is only shown in that the length of the side 11c that is parallel to each other and perpendicular to one end of the sides 11a and 11b having the same length is the same as that of the sides 11a and 11b. Different from the cross section of 2 (a).

  In an energy absorbing member with a polygonal cross section that receives a collision load in the extrusion direction, the buckling strength depends on the width / thickness ratio (plate width / plate thickness) of each side constituting the cross section, and the buckling strength increases as the width / thickness ratio increases. Also decreases. Further, it is known that the load variation depends on the buckling wavelength, and these are proportional to the plate width of each side. When the cross-sectional shape is up to a hexagonal shape, the ridgeline portion (vertex of the cross-section) constrains each side constituting the cross-section so that each side buckles independently, and the plate width becomes equal to the distance between the ridgelines. . However, if the number of corners of the polygonal cross section is further increased, the support effect for each side of the ridge line portion is reduced, so that each side becomes difficult to buckle independently, and the seat of the bent plate configured to straddle the ridge line Deformation that should be bent occurs. As a result, the buckling strength decreases, and an increase in load variation due to an increase in the buckling wavelength becomes a problem. For this reason, in this invention, the cross-sectional external shape of the aluminum alloy extrusion shape material was made into the hexagon or less polygon. In addition, a pentagonal cross-section having a larger number of corners and a shorter side width than a general quadrangular cross-section (so-called rice-shaped cross-section) was targeted. In addition, when a hexagonal cross section is compared, a hexagonal cross section having a large number of angles is more preferable.

The present invention assumes an energy absorbing member such as an automobile stay, a crash box, a side member, etc., and these collision loads are not necessarily input from the front, but the load direction is shifted in the lateral direction of the vehicle body. It is necessary to assume. In order to prevent the energy absorbing member from falling and deforming during such a collision, the cross-sectional outer shape is preferably axisymmetric (can be arranged so as to be symmetrical with respect to the vehicle body left-right direction). In the examples of FIGS. 1 and 2 described above, this is all the case. In addition, the width of each side constituting the outer shape is substantially equal (a regular pentagon, a regular hexagon, or a shape close thereto) so that a difference in the buckling strength of each side occurs with certainty depending on whether or not the middle rib is connected. More preferred.
Furthermore, assuming the case of joining with other parts, there are two sides parallel to each other in the vertical direction of the vehicle body on both the left and right sides of the cross-sectional outline so that these parts can be easily joined, and one or both of these sides. It is desirable that the middle ribs are not connected. In such a side, the side width may be made larger than the other side in order to secure an area required for joining other components.

  In the present invention, as seen in Patent Documents 9 to 11, the middle rib is connected to the middle part of the side (between two adjacent vertices), not to the vertex part of the polygonal cross section. As described above, in the present invention, by defining the cross-sectional outer shape as a hexagon or a pentagon, each side of the ridge line portion constituting the cross-sectional outer shape can be obtained without connecting the middle rib to the apex portion. Although it can hold | maintain sufficiently, this edge | side will be hold | maintained by a middle rib and a ridgeline by further connecting a middle rib to the intermediate part of a edge | side. As a result, at the side where the middle rib is connected, the side width during buckling (plate width of the width-thickness ratio) is the distance between the middle rib connecting portion and the ridgeline, and the side width is shorter than the structure without the middle rib. can do. Thereby, the buckling strength increase of the side where the middle ribs are connected and the buckling wavelength can be reduced, that is, the load fluctuation can be reduced.

Since there are three middle ribs in the structure of the present invention, there are at least two sides where the middle ribs are not connected. However, the high buckling strength side connected with the intermediate ribs restrains deformation of the side where the intermediate ribs are not connected, thereby minimizing an increase in the weight of the component and improving the buckling strength as a component. . That is, the amount of energy absorption per part weight is improved as compared with the structure in which the middle ribs are connected to all sides. For the purpose of maximizing the buckling strength of the side to which the middle rib is connected, the middle rib is preferably connected to the center of the side.
Further, the side width at the time of buckling of the side supported by the middle rib and the ridge line (vertex of the cross section) is not uniform, so that the buckling wavelength is different for each side. With this effect, the load amplitude generation timing is dispersed by each side constituting the outer shape, and the effect of reducing the load fluctuation amplitude itself can be obtained.

  As a longitudinal crushing energy absorbing member for automobiles, it is desirable that the crushing parallel to the load direction at the time of crushing does not cause a collapse deformation or a U-shaped Euler buckling during crushing. For this reason, it is desirable to provide three or more middle ribs in order to prevent the horizontal deformation and vertical deformation, and as described above, the minimum number of the three ribs is three from the viewpoint of minimizing the increase in the weight of the parts. To do. The three middle ribs are preferably provided so as to form a Y-shape or a T-shape in a pentagonal or hexagonal outer shape in cross section. In other words, a triangle connecting one end portion of each middle rib and a connecting point of the sides constituting the outer shape includes a connection point between the other end portions of each middle rib. In the examples of FIGS. 1 and 2 described above, this is all the case. In particular, from the viewpoint of securing a balance at the time of crushing, it is desirable that the position where the middle ribs are connected to each other is the triangular center of gravity connecting the connection points of the three middle ribs and the sides constituting the cross-sectional outline. From the same viewpoint, when the outer shape is a hexagon, it is desirable that one end of each middle rib is connected to non-adjacent sides constituting the outer shape, and the outer shape is a pentagon. It is desirable that one end of each middle rib is connected to one side and two sides that are not adjacent to the side.

In the structure according to the present invention, there are at least two sides (sides 1d to 1e in the example shown in FIG. 1, sides 11a and 11b in the example shown in FIG. 2) where the middle ribs are not connected. For this reason, it is possible to secure a necessary bolt space by joining other parts to these sides, and there is an advantage that the structure with the other parts can be easily performed.
In addition, the fact that the number of medium ribs inside the cross section is smaller than the number of sides of the cross section outline reduces the resistance of the die as well as the light weight effect as a part, thus extending the life of the die and increasing the extrusion speed. Thus, it is possible to obtain an effect on productivity improvement.
In addition, it is desirable to integrally mold the inner rib at the same time as the outer shape at the time of extruding the material. However, after manufacturing as a separate part, the rib may be joined only to a necessary portion in the longitudinal direction of the outer shape made of the closed cross-sectional shape material.

  In order to examine the effect of the present invention, the load-displacement curve at the time of longitudinal crushing was analyzed using FEM analysis. As shown in FIG. 3, the analysis conditions are as follows: a flange 19 having a thickness of 4 mm is placed on the upper surface of a specimen 18 having a length of 150 mm, and this is placed vertically on a surface plate 21 and placed in the axial direction via a pressing plate 22. As a test material, a general 6000 series aluminum alloy extruded shape 6063-T5 material having a stress (σ) -strain (εp) relationship (proof stress σy: 154 MPa) shown in FIG. 4 is assumed. The analysis was performed using the part thickness (constant for all sections) as a parameter. General-purpose dynamic explicit software LS-DYNA was used for FEM analysis. The cross-sectional shape (thickness center shape) of the specimen was assumed as shown in FIG. 5 on the precondition that it can be arranged in a 60 × 60 mm square space.

In FIG. 5, Case 1 has a general rice pad shape (quadrangle: with a middle rib), and one end of the middle rib is connected to the center of the side constituting the outer shape, and the other end is connected to each other at the center of gravity of the outer shape. is doing. Case 2 and Case 3 have a regular hexagonal cross-sectional outer shape, and one end of the middle rib is connected to the apex, and the other end of the middle rib is connected to each other at the center of gravity of the outer shape. Case 4 has a regular hexagonal cross-sectional outer shape, and one end of three medium ribs is connected to the center of the side constituting the outer shape, and the other end is connected to the connecting point of the one end and the side constituting the outer shape. They are connected to each other at the center of gravity of the triangle. Cases 1 to 3 correspond to the conventional structure, and Case 4 corresponds to the structure of the present invention.
Table 1 shows the analysis conditions for each cross-sectional structure.

The initial load peak in the vertical crushing deformation can be reduced by measures such as normal embossing. Therefore, it was decided to evaluate the load-displacement relationship in the stroke 20 to 80 mm section after the end of the initial load peak. The energy absorption performance was evaluated using the following two evaluation indexes. A description of this evaluation index is shown in FIG. As shown in FIG. 6, the maximum load is Pmax, the minimum load is Pmin, and the average load is Pave. It is. The cross-sectional area of the test material was A.
(1) Average load Pave. / Cross sectional area A
(2) Average load Pave. / Maximum load Pmax
In addition, it shows that the amount of energy absorption per weight is so large that the value of said (1) is large. Further, the closer the value of (2) is to 1, the closer the load-displacement curve is to a rectangular wave, indicating that the energy absorption efficiency is good.

FIG. 7 shows the load-displacement relationship obtained by analysis for each of the structures of Cases 1 to 4 in FIG. The results of arranging the load-displacement relationship shown in FIG. 7 with the evaluation indexes (1) and (2) are shown in FIGS.
As shown in FIGS. 8 and 9 and Table 1, the structure of the present invention has a larger amount of energy absorption per unit weight (average load Pave./cross-sectional area A is larger) than the conventional structure, and at the same time energy absorption efficiency. It can be said that it is excellent (average load Pave./maximum load Pmax is large).

It is a cross-sectional shape (example of hexagonal cross section) of an aluminum alloy extruded profile according to the present invention. It is a cross-sectional shape (example of a pentagonal cross section) of an aluminum alloy extruded profile according to the present invention. It is a figure explaining FEM analysis conditions. It is a stress ((sigma))-strain ((epsilon) p) curve of the test material used for FEM analysis. It is the cross-sectional shape (thickness center shape) of the test material used for FEM analysis. It is a figure explaining the evaluation parameter | index of energy absorption performance based on the load-displacement curve obtained as a result of FEM analysis. It is a load-displacement curve obtained as a result of FEM analysis. Pave. Obtained from the load-displacement curve obtained as a result of the FEM analysis. FIG. Pave. Obtained from the load-displacement curve obtained as a result of the FEM analysis. / A-Pave. FIG.

Explanation of symbols

1,11 Outlines 1a to 1d and 11a to 11e of closed cross section Sides 2 to 4 and 12 to 14 constituting the outer shape Middle ribs 5 to 7 and 15 to 17 Connection points between the sides constituting the outer shape and the middle rib

Claims (7)

An energy absorbing member made of an aluminum alloy extruded material provided on the back side of a vehicle bumper reinforcing material, the vehicle longitudinal direction and the extrusion direction being substantially parallel, the outer shape of which is a convex pentagon in a cross section perpendicular to the extrusion direction or It has a convex hexagonal closed cross-sectional shape, and has three medium ribs inside the outer shape, and each medium rib has one end connected to different sides constituting the outer shape, and the other end. Are mutually connected, The energy absorption member characterized by the above-mentioned. 2. The energy absorbing member according to claim 1, wherein the outer shape is a hexagon, and one end portion of each middle rib is connected to sides that are not adjacent to each other that form the outer shape. 3. The energy absorbing member according to claim 1, wherein one end portion of each middle rib is connected to a central portion of a side constituting the outer shape. The other end part of each middle rib is mutually connected in the center of gravity of the triangle which connects the said one end part and the connection point of the edge | side which comprises the said external shape. The energy absorbing member described in 1. The aluminum alloy extruded shape member is formed by joining an outer shape made of an extruded shape member and an intermediate rib, and the intermediate rib is joined over the entire length of the outer shape or a partial length range. Item 5. The energy absorbing member according to any one of Items 1 to 4. The energy absorbing member according to claim 1, wherein the energy absorbing member is any one of a stay, a crash box, and a side member of a bumper reinforcing material for an automobile. An energy absorbing structure comprising an aluminum alloy extruded shape bumper reinforcing material and an energy absorbing member according to any one of claims 1 to 5 fixed directly or via a stay to the back surface thereof.

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