WO2014073083A1 - Impact absorbing member - Google Patents

Abstract

A cylindrical impact absorbing member (1) that absorbs impact energy by plastically deforming in a bellows shape when an axial compression load has been received, and having side walls that comprise a planar surface that does not have beads for inducing bellows-shaped deformation. In this impact absorbing member (1), a cross-sectional shape orthogonal to the axial direction has a substantially cross-shaped closed cross-section having 12 apexes, and an angle (α) is set within the range of 90°<α≤150°, said angle (α) being formed by straight lines that join apexes at both ends of an oblique side of an octagon formed by using straight lines to connect 8 of the 12 apexes, to an apex therebetween.

Description

Shock absorbing member

The present invention relates to an impact absorbing member that absorbs impact energy.

The car is equipped with a member that absorbs energy in the event of a collision. One such member is a crash box. The crash box is generally formed in a cylindrical shape by one or several members, and absorbs impact energy by deforming in an accordion shape in the axial direction when an impact load is applied in the axial direction. The performance required for the crash box includes a stable bellows deformation in the axial direction when an impact load is applied, and high energy absorption efficiency associated with the deformation. Various proposals have been made to improve the performance required for crash boxes.

In a crash box having a square or hexagonal cross-sectional shape, the number of ridge lines extending in the axial direction is small and the length of one side is long, so that the energy absorption efficiency is deteriorated when absorbing the impact. For this reason, Patent Document 1 proposes a crush box whose cross-sectional shape is an octagon. The crash box described in Patent Document 1 includes a stress concentration portion (bead forming portion) serving as a starting point of plastic deformation so that it can be stably deformed into a bellows shape. The stress concentration portions are formed by convex portions formed inside the crash box, and are provided so as to alternate in the axial direction. By providing the stress concentration portion, deformation of the convex portion in the protruding direction is induced, and the crash box is stably deformed into a bellows shape.

FIG. 2 of Patent Document 1 shows a crash box having two stress concentration portions in the axial direction, and FIG. 9 of the same document shows a crash box having seven stress concentration portions in the axial direction. It is shown in the figure. As another example of a crash box, Patent Document 2 discloses a crash box whose cross-sectional shape is a substantially cross-closed cross-sectional shape. The crash box disclosed in Patent Document 2 is formed such that the angle formed by each side in the substantially cross-closed cross-sectional shape is substantially a right angle (90 °).

JP 2006-123887 A JP 2009-83686 A

However, even the crash box described in Patent Document 1 sufficiently satisfies the performance required for the crash box that is stably deformed into a bellows shape and that the energy absorption efficiency associated with the deformation is high. It can not be said.

That is, even if the cross-sectional shape of the crash box is an octagon like the crash box described in Patent Document 1, the cross-sectional shape is a regular octagon in relation to the shape of the end of the front side member where the crash box is installed. In many cases, it becomes a long octagon (an octagon having a long pair of opposing sides). In that case, a long side part remains, and axial force and energy absorption efficiency fall.

Also, according to the crash box described in Patent Document 1, all the stress concentration portions protrude inward in the same cross section, and induce deformation in the same direction in the same cross section. However, deformation in the same direction in the same cross section has a limit in energy absorption efficiency, and sufficient energy absorption cannot always be performed.

Furthermore, as performance required for the crash box, in addition to the large absorbed energy, the peak impact load when the crash box receives an axial compression load may be small. The reason why the peak impact load is required to be small is that when the peak impact load increases, it is necessary to increase the strength of the vehicle side member such as a bumper member that installs the crash box according to the peak impact load. is there. In this regard, in the crash box disclosed in Patent Document 2, the angle formed by each side in the substantially cross-closed cross-sectional shape is set to be substantially a right angle (90 °), so that the peak impact load increases.

The present invention has been made to solve the above problems, and provides an impact absorbing member that is stably deformed into a bellows shape, has high energy absorption efficiency, and does not have an excessive peak impact load. Objective.

The impact absorbing member according to the present invention is a cylindrical impact absorbing member that absorbs impact energy by plastic deformation in a bellows shape when subjected to an axial compression load, and the side wall induces bellows-like deformation. The cross-sectional shape perpendicular to the axial direction is a substantially cross-shaped closed cross section having 12 vertices, and 8 vertices of the 12 vertices are straight lines. An angle α formed by a straight line connecting the vertices at both ends of the hypotenuse and the vertices between them in the octagon formed by being connected is set in a range of 90 ° <α ≦ 150 °.

The impact absorbing member according to the present invention is stably deformed into an accordion shape, the energy absorption efficiency is increased, and the peak impact load is not excessive.

FIG. 1 is a perspective view of an impact absorbing member according to an embodiment of the present invention. FIG. 2 is a cross-sectional view in the direction perpendicular to the axis of the impact absorbing member according to the embodiment of the present invention. FIG. 3 is an explanatory diagram of a cross-sectional shape of an impact absorbing member according to an embodiment of the present invention. FIG. 4 is an explanatory view of a deformation mode of the shock absorbing member according to the embodiment of the present invention. FIG. 5 is an explanatory diagram of the shape used in the experiment for confirming the performance of the shock absorbing member according to the embodiment of the present invention. FIG. 6 is a graph showing the relationship between the angle α formed by the inclined surface and the energy absorption efficiency in the shock absorbing member according to the embodiment of the present invention. FIG. 7 is a graph showing the relationship between the impact load per unit weight and the stroke when the angle α formed by the inclined surface in the impact absorbing member according to one embodiment of the present invention is 90 ° and 135 °. FIG. 8 is a graph in which the vertical axis of the graph shown in FIG. 7 is normalized by the unit peak impact load. FIG. 9 is a graph showing the relationship between the angle α formed by the inclined surface and the energy absorption efficiency in the unit impact load in the impact absorbing member according to the embodiment of the present invention.

An embodiment of the present invention will be described with reference to FIGS.

The impact absorbing member 1 according to the present embodiment is a cylindrical member that absorbs impact energy by plastic deformation in a bellows shape when subjected to an axial compression load. The side wall of the shock absorbing member 1 is a flat surface that does not have a bead for inducing bellows-like deformation. In the shock absorbing member 1, the cross-sectional shape orthogonal to the axial direction is a substantially cross-shaped closed cross section having 12 vertices. The angle α formed by a straight line connecting the vertices at both ends of the hypotenuse in the octagon formed by connecting eight of the twelve vertices with a straight line is 90 ° <α ≦ 150 °. It is set within the range.

<Overall shape of impact absorbing member>
The shock absorbing member 1 is a cylindrical member, and the cross-sectional shape orthogonal to the axial direction is a substantially cross-shaped closed cross section having 12 vertices A to L as shown in FIG. . The cross-sectional shape of the shock absorbing member 1 will be described in detail. Of the twelve vertices in the cross section of the shock absorbing member 1, the eight vertices A, C, D, F, G, I, J, excluding the four vertices B, E, H, K near the center, The shape formed by connecting L with a straight line (in FIG. 3, the straight line is indicated by a dotted line) is an octagon. The angle α formed by the vertices at both ends of the hypotenuses AC, DF, GI, and JL in the octagon, for example, the straight lines AB and CB connecting the vertices A and C and the vertex B between them is within the range of 90 ° <α ≦ 150 °. (135 degrees in this example) is set.

The shock absorbing member 1 according to the present embodiment configured as described above is deformed into a bellows shape when the material moves inward and outward in the axial direction when receiving an axial compression load. When attention is paid to one cross section in the direction perpendicular to the axis, as shown in FIG. 4, the direction of deformation is reversed inside and outside at each ridgeline, and adjacent surfaces are deformed in opposite directions inside and outside. For this reason, the energy absorbed with a deformation | transformation increases and energy absorption efficiency becomes high. Further, since the angle α is within the above range, it is possible to stably deform without providing a bead for inducing a bellows-like deformation, so there is no need to provide a bead and the shock absorbing member. 1 can be easily manufactured. In addition, the direction of the arrow in FIG. 4 has shown the direction which deform | transforms into a convex side.

As described above, in the shock absorbing member 1 according to the present embodiment, the angle α is set in the range of 90 ° <α ≦ 150 °. Hereinafter, the reason for this setting will be described based on experimental data.

FIG. 5 is an explanatory diagram of a cross-sectional shape of the shock absorbing member 1 used in the experiment. The dimensions of each part are as follows. The tensile strength of the used steel plate is 440 MPa. a = 90.9mm, b = 104.3mm, c = 42.6mm, d = 30.6mm, R = 5mm, α = 135 °

The angle α is changed from the basic shape shown in FIG. 5 to 90 °, 105 °, 120 °, 135 °, 150 °, 165 °, and 180 °, and the absorbed energy when the shock absorbing member 1 is crushed by Smm in each case. Asked. The plate thickness of the steel plate as a raw material was adjusted so that the reaction force at the time of crushing would be equal to or less than the specified yield strength. FIG. 6 is a graph showing the experimental results. The horizontal axis and the vertical axis indicate the value of the angle α and the absorbed energy at the time of Smm crushing, respectively.

As shown in FIG. 6, the absorbed energy increases as the angle α decreases. In addition, when the deformation state is confirmed, if the shape is V-shaped (for example, the shape composed of vertices A, B, and C in FIG. 3), the direction of deformation is reversed inside and outside at each ridgeline, and the adjacent surfaces are opposite to each other It was confirmed that it was deformed in the direction. However, the greater the angle α, the more unclear the range of inversion. Therefore, in the present invention, the range of the angle α at which the effect is obtained is set to 150 ° or less. The reason why the lower limit value of the angle α is set to exceed 90 ° is that when the angle α is 90 ° or less, it is difficult to process the member and the peak impact load is increased.

Using the impact absorbing member 1 shown in FIG. 5 described above, the relationship between the impact load per unit weight and the stroke when the angle α was 90 ° and 135 ° was obtained by experiments. FIG. 7 is a graph showing experimental results, where the vertical axis and the horizontal axis indicate the impact load and stroke per unit weight, respectively. FIG. 8 is a graph in which the vertical axis of the graph shown in FIG. 7 is normalized by the peak impact load.

As shown in FIG. 7, the absolute value of the peak impact load is larger when the angle α is 90 ° than when the angle α is 135 °. For this reason, when the angle α is 90 °, it is necessary to set the vehicle-side member strength in accordance with the peak impact load. On the other hand, referring to FIG. 8, the impact load per unit weight relative to the unit peak impact load is larger when the angle α is 135 °, and the energy that can be absorbed is larger. Thus, comparing the case where the angle α is 90 ° and the case where the angle α is 135 °, it can be said that the angle α is preferably more than 90 ° from the viewpoint of suppressing the peak impact load.

Next, in order to obtain the relationship between the value of the angle α and the absorbed energy with respect to the unit peak impact load, the angle α is 90 °, 105 °, 120 °, 135 °, 150 °, 165 ° from the basic shape shown in FIG. The absorbed energy per unit weight at the time of Smm crushing with respect to the unit peak impact load in each case was determined. The results are shown in the graph of FIG. In FIG. 9, the vertical axis and the horizontal axis indicate the absorbed energy per unit weight and the value of the angle α at the time of Smm crushing with respect to the unit peak impact load, respectively. As shown in FIG. 9, it can be seen that the absorbed energy per unit weight at the time of Smm crushing with respect to the unit peak impact load is large when the value of the angle α is in the range of 90 ° <α ≦ 150 °.

Also, as shown in FIG. 9, the absorbed energy per unit weight at the time of Smm collapse with respect to the unit peak impact load increases rapidly when the value of the angle α is between 90 ° and 105 °. For this reason, it is presumed that there is a preferable value of the angle α between 90 ° and 105 °. From this, it can be said that it is more preferable if the value of the angle α is in the range of 95 ° ≦ α ≦ 150 °. From the graph of FIG. 9, when the value of the angle α is 105 °, the absorbed energy per unit weight at the time of Smm collapse against the unit peak impact load is high, so the value of the angle α is 105 ° ≦ α ≦ 150 °. It can be said that it is more preferable if it is within the range.

In the above embodiment, the shock absorbing member 1 is formed by joining two press-formed products. However, the present invention is not limited to this, and one plate material is formed by bending. You can also Moreover, in the said embodiment, although the case where the end part is overlap | superposed and spot-welded is shown as a joining form of two press molded products, this invention is not limited to this, Abutting an end part You may make it weld (laser welding etc.). This is the same even when the shock absorbing member 1 is formed of a single plate. It should be noted that in any case where the shock absorbing member 1 is formed by joining two press-formed products or when one plate material is bent and joined at the end, Is preferable because the weight of the shock absorbing member 1 can be minimized.

The impact absorbing member according to the present invention can be applied to a member that absorbs energy at the time of a collision installed in an automobile or the like.

1 Shock absorbing member

Claims (1)

A cylindrical impact absorbing member that absorbs impact energy by plastic deformation in a bellows shape when subjected to an axial compression load,
The side wall consists of a flat surface without a bead for inducing bellows-like deformation,
The cross-sectional shape orthogonal to the axial direction is a substantially cross-shaped closed cross section having 12 vertices,
The angle α formed by a straight line connecting the vertices at both ends of the hypotenuse in the octagon formed by connecting eight of the twelve vertices with a straight line is 90 ° <α ≦ 150 °. The shock absorbing member is characterized by being set within the range.

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