JP2005186776A - Vehicle body structural member - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a vehicle body structural member having a reduced weight and assuring a high bending strength against axial compression. <P>SOLUTION: The vehicle body structural member applies to a member to undergo a bending deformation by axial compression having two surfaces to be deformed flexurally, whose two ends parallel to the longitudinal direction of the member are provided with overhangs convex outward and parallel with the longitudinal direction of the member, and the section shape is set so as to meet the inequalities, 0<h≤Bc/3 and 0<w≤Bb/3 (where h is the height of the overhangs; w is the width, Bc is the width of the compressed surface; and Bb is the width of the bending surface). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a vehicle body structural member for ensuring the collision strength of a vehicle body.

  In recent years, from the viewpoint of occupant protection, there has been a social demand for improving automobile crash safety. From this point, a vehicle body structural member that improves the collision safety of an automobile is important. A structural member constituting an automobile is required to have predetermined rigidity, strength, and energy absorption capability according to each function. In order to achieve the demand, various shape devices have been made.

  A typical example is a bead that is a local concave or convex protrusion. [Patent Document 1] Japanese Patent Laid-Open No. 4-126677 has a bead extending in the front-rear direction of the vehicle body on the side surface of the front side member. By gradually increasing the bead toward the rear, The front side member is compressed and deformed in order from the front to the rear, the bending deformation of the member is suppressed, stable compression deformation is achieved, and the amount of energy absorption is improved.

  [Patent Document 2] Japanese Patent Application Laid-Open No. Hei 8-183473 is caused between spot welding of a flat plate by setting an appropriate bead on the flat plate when a member comprising a channel material having a flange and the flat plate is subjected to axial compression deformation Buckling is prevented and the amount of energy absorption is increased.

  [Patent Document 3] Japanese Patent Application Laid-Open No. 2003-139180 is provided such that an outwardly extending portion is provided on the compression surface flange surface so that the compression-deformed flange surface comes into contact with each other and prevents bending deformation of each other. They are designed to interfere with each other and increase the amount of energy absorption.

As described above, various contrivances have been made with respect to the bead that is a local concave or convex projecting portion, but each is intended to improve the amount of energy absorption. Further, the deformation modes of interest are [Patent Document 1] Japanese Patent Laid-Open No. 4-126677 and [Patent Document 2] Japanese Patent Laid-Open No. 8-183473 are axial compression bending deformation, and [Patent Document 3] Japanese Patent Laid-Open No. 2003-139180 , Bending deformation.
Japanese Patent Laid-Open No. 4-126777 JP-A-8-183473 JP 2003-139180 A

  From the viewpoint of collision safety, the members that make up an automobile can be broadly divided into members that break down to absorb energy, and members that don't break down to transmit force behind and protect passengers. . Generally, what is required for a member to be broken is an energy absorption amount, and what is required for a member that is not broken is strength. In general, many members that do not break are subjected to axial compression bending deformation as represented by the front side member / kick portion, the A-pillar, and the rocker. Accordingly, there is a need for a vehicle body structural member that is lighter and has higher strength when subjected to axial compression bending deformation. An object of the present invention is to provide a vehicle body structural member that is lighter and has high axial compression bending strength.

In order to improve the axial compression bending strength of the vehicle body structural member, the present inventors have conducted various studies on the collapse phenomenon of the member when the vehicle body structural member having a closed cross section undergoes axial compression bending deformation. As a result, it was found that the axial compression bending strength of the member can be improved by suppressing the cross-sectional deformation. This invention is made | formed based on the knowledge. That is,
1) In a member that undergoes axial compression bending deformation, the two surfaces that are subjected to bending deformation have projecting projecting portions on the two end portions parallel to the longitudinal direction of the member and on the outer side parallel to the longitudinal direction of the member. A vehicle structural member characterized by
2) Further, set the cross-sectional shape so that the height of the protruding portion protruding outward is h, the width is w, the width of the compression surface is Bc, the width of the bending surface is Bb, and the following formula is satisfied. It is a member for vehicle body structure characterized by these.
0 <h ≦ Bc / 3 and 0 <w ≦ Bb / 3

  According to the present invention, it is possible to increase the collision strength of the vehicle body without increasing the weight. Therefore, it greatly contributes to the improvement of collision safety and weight reduction of automobiles.

  Hereinafter, the present invention will be described in detail. When a vehicle body structural member having a closed cross section having a mouth shape is subjected to axial compression bending deformation, a compressive load indicated by an arrow in the drawing is applied to the bending surface M1 of the cross section as shown in FIG. As a result, as shown by the dotted line, the cross section is deformed. As a result of intensive studies, it was found that the axial compression bending strength of the member can be improved if this cross-sectional deformation is suppressed. Considering that the deformation of the bending surface M1 is replaced with the compression deformation of the long pillar shown in FIG. The amount of deflection (δ) decreases. Therefore, if the width (Bb) of the bending surface is reduced, the degree of cross-sectional deformation is reduced. However, if the width (Bb) of the bending surface is reduced, the section modulus (Z) on the compression side with respect to the bending around the X axis considered here is reduced, and the axial compression bending strength is reduced. The reason for this is clear from the equation (3) described later.

  Furthermore, as a result of earnest study, as shown in FIG. 1, the two protruding portions protruding outwardly parallel to the longitudinal direction of the member are formed at two ends parallel to the longitudinal direction of the member of the two surfaces subjected to bending deformation. As a result, it was thought that the straight line length (Bb-2w) of the bending surface can be reduced without reducing the width (Bb) of the bending surface.

Therefore, the results of various experiments are shown in FIG. Thus, it can be seen that the maximum load (Fmax) of the present invention having the overhanging portion is increased by about 10 to 20% as compared with the mouth shape having no overhanging portion. The meaning of the horizontal axis is as follows. According to the concept of material mechanics, the maximum compressive stress (σ) of a member that undergoes axial compressive bending deformation is generally expressed by equation (1).
σ = F / A + M / Z = F / A + (F · L) / Z (1)
Here, F is an axial compression load applied to the member, A is a cross-sectional area of the member, M is a bending moment applied to the member, L is a moment arm, and Z is a section modulus on the compression side.

Generally, when the maximum compressive stress (σ) generated in the member becomes equal to the yield stress (σy), the axial compressive load becomes the maximum value (Fmax). Therefore, in the equation (1), σ = σy, F = Fmax And solving for Fmax yields equation (2).
Fmax = [(A · Z · σy) / (Z−A · L)] (2)
= [(A · σy) / (1-A · L / Z)] (3)
The horizontal axis in FIG. 4 is obtained by dividing the right side of equation (2) by 1000 in order to match the unit with the experimental value. In the case of a member having a mouth shape as a comparative example, the maximum load (F actual max) obtained in the experiment is about 80% of [(A · Z · σy) / (Z−A · L)]. The expression (2) derived according to the concept of material mechanics does not consider the influence of cross-sectional deformation. On the other hand, F actual max is affected by cross-sectional deformation. As a result, the F actual max was about 80% of [(A · Z · σy) / (ZA−L)]. On the other hand, in the member having the overhanging portion, the cross-sectional deformation is suppressed by the mechanism described above, and the F actual max is about 90 to 100% of [(A · Z · σy) / (Z−A · L)]. .

  An example of the effect of suppressing cross-sectional deformation by setting the overhang portion is shown in FIGS. FIG. 7 shows the progress of the cross-sectional deformation of the member having the cross-sectional shape of FIG. In order to evaluate the degree of cross-sectional deformation, the cross-sectional height change rate shown in FIG. 6 was measured. As shown in FIG. 7, it can be seen that the presence of the overhang portion is less likely to deform in cross section than the mouth shape.

  Next, the reason for limitation will be described. The position set by the overhang is the two ends parallel to the longitudinal direction of the member of the bending surface. By setting this position, the section modulus (Z) for bending around the X axis is the largest. It is to become. The reason why the protruding portion is convex outward is that the section modulus (Z) with respect to bending around the Y axis is the largest compared to the concave portion. The reason why 0 <h and 0 <w is that, based on the above technical idea, it is considered that the effect is recognized if the overhanging portion exists. In practice, it is preferable that 0.03 × Bc ≦ h and 0.03 × Bb ≦ w. The reason why h ≦ Bc / 3 is set is that when h> Bc / 3, the decrease in the section modulus (Z) with respect to bending around the Y-axis becomes significant. The reason why w ≦ Bb / 3 is set is that when w> Bb / 3, the effect of suppressing the cross-sectional deformation of the overhanging portion decreases. FIG. 10 is a perspective view of the example of the present invention.

  As described above, the preferred overhang portion setting form for the member having the mouth cross-sectional shape has been described, but various design changes can be made in the present invention. For example, the protruding portion may be set in a flanged shape as shown in FIG. 8 or a trapezoidal shape as shown in FIG. Further, the overhang portion may be set only on a part of the member that undergoes axial compression bending. Furthermore, the shape of the protruding portion may be an arc shape or a trapezoidal shape.

  A steel pipe having a diameter of 63.5 mm and a plate thickness of 1.8 mm was processed into an evaluation part shown in FIG. The cross-sectional shape is shown in FIG. The right end of the evaluation component shown in FIG. 11 was fixed, and the displacement was given to the left end in the right direction at a displacement speed of 100 mm / min. Then, the maximum load (Fmax) that the evaluation part can withstand was determined. The obtained result is shown in FIG. By setting the overhang, the maximum load (Fmax) increased from 11.3 kN to 13.2 kN, an increase rate of 17%.

It is explanatory drawing of a cross section. It is explanatory drawing of a cross-sectional deformation | transformation. It is explanatory drawing of the compression deformation of a long pillar. It is a test result which shows the effect of an overhang | projection part. It is explanatory drawing of the cross-sectional shape which performed the progress comparison of cross-sectional deformation. It is explanatory drawing of a cross-section height change rate. It is a test result of the progress comparison of a cross-sectional deformation. It is the figure which showed the example of application of this invention to the shape with a flange. It is the figure which showed the example of application of this invention to trapezoid shape. It is a perspective view of the present invention. It is explanatory drawing of the test method in an Example. It is explanatory drawing of the cross-sectional shape of the evaluation components in an Example. It is the figure which showed the test result of the Example.

Claims (2)

  In a member that undergoes axial compression bending deformation, the two surfaces that are subjected to bending deformation have protruding ends on two outer sides parallel to the longitudinal direction of the member at two ends parallel to the longitudinal direction of the member. A vehicle body structural member. The vehicle body structural member according to claim 1, wherein the height of the protruding portion protruding outward is h, the width is w, the width of the compression surface is Bc, and the width of the bending surface is Bb so that the following equation is satisfied. The vehicle body structure member is characterized in that its cross-sectional shape is set.
0 <h ≦ Bc / 3 and 0 <w ≦ Bb / 3

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