JP5316935B2 - Steel pipe for impact energy absorption for automobile and method for manufacturing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a collision energy absorbing steel pipe suitable for use in a portion requiring a collision energy absorption characteristic such as a bumper or a door impact beam of a vehicle, and a method of manufacturing the same.

  A member such as a bumper or a door impact beam of an automobile plays a role of securing a living space for an occupant by absorbing the collision energy by deforming itself when the automobile collides. For this purpose, it goes without saying that the amount of collision energy absorbed during crushing or bending deformation must be large. However, since these members need to be stored in a limited space inside the automobile, the cross-sectional area is required to be as small and lightweight as possible. With the recent trend of miniaturization and weight reduction of automobiles, This demand is getting stronger.

For this purpose, collision energy absorbing members having various structures have been proposed in the past. Among them, as shown in Patent Document 1, a composite tube structure in which one or more inner tubes are housed inside a circular outer tube is disclosed. The outer tube is deformed at the time of a mild collision, and the inner tube is also deformed at the time of a strong impact, which is excellent in that a large collision energy can be absorbed.
JP 2003-137129 A

  However, the collision energy absorbing member having a composite pipe structure disclosed in Patent Document 1 is formed by inserting the inner pipe into the outer pipe and welding it, or press-fitting the inner pipe into the outer pipe. There are many gaps between the tube and the inner tube. For this reason, a part of the tube wall of the outer tube is deformed relatively easily without being constrained by the inner tube, and the amount of collision energy absorbed is small during that time. For this reason, it cannot be said that sufficient impact energy absorption characteristics are exhibited.

  In addition, since the collision energy absorbing member having a composite tube structure disclosed in Patent Document 1 is based on a structure in which one or a plurality of inner tubes are housed inside a circular or rectangular outer tube, the cross-sectional shape is circular or square. Limited. For this reason, the installation space may be limited.

Accordingly, an object of the present invention is to solve the above-described conventional problems, exhibit a sufficient collision energy absorption characteristic, and can also be applied to a mounting space having an irregular cross section, and a novel automobile collision energy absorption steel pipe for manufacturing the same. Is to provide.

The steel pipe for impact energy absorption for automobiles of the present invention made to solve the above-mentioned problem has a composite pipe structure in which a plurality of inner steel pipes are inserted into the outer steel pipe without being press-fitted, and the outer steel pipe is The outer-hard / inner-soft structure that is crimped to the outer peripheral surface of the inner steel pipe by drawing processing corresponding to the cross-sectional shape of the multiple inner steel pipes, causes work hardening in the outer steel pipe, and retains ductility in the inner steel pipe And the sum of the non-contact length with the inner steel pipe of the inner peripheral length of the outer steel pipe is 20% or less of the inner peripheral length. In addition, as described in claim 2, the inner steel pipe can be a steel pipe having a circular cross section or a deformed steel pipe having a non-circular cross section.

Further, the method for manufacturing a steel pipe for impact energy absorption for automobiles according to the present invention includes a plurality of inner steel pipes inserted into the outer steel pipe having a circular cross-section without press-fitting with a gap between the outer steel pipes, subjected to drawing Te in grooved corresponding to the cross-sectional shape of the inner steel tube a plurality of, the outer steel tube to generate work hardening, thereby crimping the outer steel tube to the outer circumferential surface of the inner steel tube leaving the ductility inside the steel pipe It is characterized by. As described in claim 4, as the inner steel pipe, a steel pipe having a circular cross section or a deformed steel pipe having a non-circular cross section can be used.

In the steel pipe for impact energy absorption for automobiles of the present invention, the outer steel pipe is crimped to the outer peripheral surface of the inner steel pipe by drawing, and the sum of the non-contact length with the inner steel pipe of the inner peripheral length of the outer steel pipe is It is 20% or less of the inner circumference. For this reason, most of the outer steel pipe is constrained by the outer peripheral surface of the inner steel pipe, and has a wall thickness like a double pipe. Moreover, since there are a plurality of inner steel pipes, a structure in which a plurality of partition walls having a circular cross section are formed inside the outer steel pipe is different from a simple double pipe. Therefore, it shows excellent collision energy absorption characteristics at the time of collision.

Further, the steel pipe for impact energy absorption of an automobile of the present invention has a plurality of inner steel pipes inserted into the outer steel pipe having a circular cross section, and a hole type corresponding to the cross-sectional shape of the plurality of inner steel pipes or the outer steel pipe is shrunk. Since the outer steel pipe is crimped to the outer peripheral surface of the inner steel pipe by drawing with a die having a hole shape that has a diameter, the outer shape can be set variously by changing the cross-sectional shape and arrangement of the inner steel pipe Can do. For this reason, it is possible to cope with a case where only a mounting space with an irregular cross section can be secured.

Furthermore , the impact energy absorbing steel pipe for automobiles according to the present invention has an outer steel pipe that has improved mechanical strength due to work hardening at the time of drawing and improved impact energy absorption characteristics. I'm leaving. Therefore, it becomes a composite pipe structure of outer-hard / inner-soft structure, and can be moderately deformed when it receives a large collision energy.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
1 and 2 show a first embodiment of the present invention. First, as shown in FIG. 1, a plurality of inner steel pipes 2 are inserted into the outer steel pipe 1. As the outer steel pipe 1 and the inner steel pipe 2, a normal steel pipe for machine structure can be used, but a high strength steel pipe to which a strengthening alloy element is added may be used. In the present invention, since it is not necessary to press-fit a plurality of inner steel pipes 2 into the outer steel pipe 1, the inner steel pipe 2 can be inserted with a space as shown in FIG. The number of the inner steel pipes 2 is four, and in this embodiment, four. Moreover, although the cross-sectional shape of the inner steel pipe 2 may be circular, square or other irregular shapes, it is a normal round steel pipe in this embodiment.

  Next, the outer steel pipe 1 in which a plurality of inner steel pipes 2 are inserted in the state shown in FIG. 1 is drawn using a die. The die is formed with a hole shape corresponding to the cross-sectional shape of the plurality of inner steel pipes 2, and the pipe wall of the outer steel pipe 1 is plastically deformed inward by drawing, and the composite pipe structure having the cross-sectional shape shown in FIG. It becomes. At this time, the deformation amount of the portion along the outer peripheral surface of the inner steel pipe 2 located at the corner of the tube wall of the outer steel pipe 1 is small, but the portion between the inner steel pipes 2 is greatly narrowed inward.

  As a result, most of the tube wall of the outer steel pipe 1 is crimped to the outer peripheral surface of the inner steel pipe 2, but a part thereof is in a non-contact state. And in this invention, it is made for the sum of the non-contact length with the inner side steel pipe 2 among the inner peripheral lengths of the outer side steel pipe 1 to be 20% or less of the inner peripheral length of the outer side steel pipe 1. The non-contact length is determined by the amount of narrowing of the outer steel pipe 1, and the amount of narrowing is determined by the die hole shape, so that the sum of the non-contact lengths is 20% or less of the inner peripheral length of the outer steel pipe 1. This is easy if drawing is performed. In the present invention, the sum of the non-contact lengths is set to 20% or less of the inner peripheral length of the outer steel pipe 1 because when the sum of the non-contact lengths is larger than this, only the outer steel pipe 1 may be deformed, and the collision energy This is because the effect of improving the absorption characteristics may be insufficient. The lower limit of the sum of the non-contact lengths varies depending on the shape and number of the inner steel pipes 2, but cannot be zero, and is actually at least about 1%.

  Along with this drawing process, the outer steel pipe 1 is mechanically hardened by work hardening, and the impact energy absorption characteristics during bending and crushing are improved. On the other hand, the inner steel pipe 2 remains ductile. However, since the outer periphery is strongly fixed by the outer steel pipe 1, the positions of the inner steel pipe 2 are not shifted unless receiving strong collision energy.

  In the first embodiment described above, four inner steel pipes 2 are inserted into the outer steel pipe 1, but in the second embodiment shown in FIGS. 3 and 4, the number is two. Also in this case, the sum of the non-contact length with respect to the inner peripheral length of the outer steel pipe 1 is set to 20% or less. As described above, this value can be determined by the hole type of the die. In addition, the number of the inner steel pipes 2 inserted into the outer steel pipe 1 can be three, or five or six. However, if the number is increased too much, positioning at the time of drawing processing becomes difficult, so 2 to 6 is an appropriate number.

  The inner steel pipe 2 may be a deformed pipe. In the third embodiment shown in FIGS. 5 and 6, the inner steel pipe 2 is a square pipe. In this case, the ratio of the sum of the non-contact length to the inner peripheral length of the outer steel pipe 1 can be further reduced as compared with the case where the inner steel pipe 2 is a round pipe. However, since the square tube is constituted by a flat surface, it is likely to be deformed depending on the direction of impact. For this reason, the arrangement which considered the difference of the collision energy absorption characteristic by a direction is required.

  7 and 8 show a fourth embodiment in which the inner steel pipe 2 has three square tubes. Also in this case, the same effects as those of the other embodiments described above can be obtained.

As described above, the automobile impact energy absorbing steel pipe of the present invention exhibits excellent impact energy absorption characteristics, and can obtain a large impact energy absorption effect with a smaller cross-sectional area than a conventional product. In addition, since the outer shape can be set in various ways, it is possible to cope with a case where only a sufficient mounting space can be secured. For this reason, it has a high utility value as a collision energy absorbing steel pipe suitable for the trend of miniaturization and weight reduction of automobiles.

An impact bending test was performed on three types of steel pipes having substantially the same weight shown in Table 1. As shown in FIG. 9 , the cross section of each steel pipe is as follows: Comparative Example 1 is a φ40 steel pipe, Comparative Example 2 is a composite steel pipe composed of an outer steel pipe of φ40 and four inner steel pipes of φ15.5 (the inner circumference of the outer steel pipe). The total inner non-contact length is 95%). Inventive Example 1 is a composite drawn steel pipe obtained by drawing the composite steel pipe of Comparative Example 2 with a die (the inner non-contact length of the inner peripheral length of the outer steel pipe is 7%). Each steel pipe has a length of 1200 mm.
As shown in FIG. 10 , the impact bending test method places a sample on a support base fixed with a span of 800 mm, collides a semi-cylindrical load element having a collision portion R of 150 mm at 55 km / h, The load was measured with a load cell. A filter was applied to the load cell, and the relationship between the load value excluding the influence of vibration and the displacement was investigated. Further, the absorbed energy from the displacement-load curve to 150 mm displacement was calculated (the area surrounded by the displacement-load curve was calculated).

The results are shown in Table 1 and FIG . From FIG. 11 , the steel pipe of Comparative Example 1 has a large second moment of section, so the load rises at the beginning of the collision is large. However, since the cross section tends to flatten, once the buckling occurs, the load may drop rapidly. I understand. In the composite steel pipe of Comparative Example 2, since four inner steel pipes are inserted, buckling is unlikely to occur, but since there is a large gap between the outer steel pipe and the inner steel pipe, until the outer steel pipe and the inner steel pipe come into contact after the collision. Since only the outer steel pipe handles the load, the way of increasing the load at the beginning of the collision is small. On the other hand, the composite drawn steel pipe of Invention Example 1 has a small gap between the outer steel pipe and the inner steel pipe, and therefore takes up the entire load from the beginning of the collision, so the load rises greatly, and because four inner steel pipes are inserted, it buckles. It is hard to happen. Moreover, since the outer steel pipe is work-hardened when the composite drawn steel pipe of the present invention is drawn, the collision resistance is further increased. For this reason, it is characterized in that a high load can be stably maintained from the initial collision to a displacement of 150 mm. From the above, the 150 mm absorbed energy is 5200 J in Comparative Example 1 and 5400 J in Comparative Example 2 as shown in Table 1, whereas Inventive Example 1 of the present invention shows a high collision energy absorbing ability of 6000 J.

As described above, the composite drawn steel pipe of the present invention showed a high absorbed energy capability with respect to a steel pipe and a composite drawn steel pipe having the same weight. If it is used as in the embodiment, there is a merit in terms of absorbed energy, but if the plate thickness is reduced as necessary, the merit of weight reduction can be obtained instead of the merit of absorbed energy. Further, as can be seen from FIG. 9 , the composite drawn steel pipe of the present invention has a small cross-sectional area, so that it can be mounted in a small mounting space.

In 1st Embodiment, it is sectional drawing which shows the state which inserted the inner side steel pipe inside the outer side steel pipe. In 1st Embodiment, it is sectional drawing which shows the state after a drawing process. In 2nd Embodiment, it is sectional drawing which shows the state which inserted the inner side steel pipe inside the outer side steel pipe. In 2nd Embodiment, it is sectional drawing which shows the state after drawing. In 3rd Embodiment, it is sectional drawing which shows the state which inserted the inner side steel pipe inside the outer side steel pipe. In 3rd Embodiment, it is sectional drawing which shows the state after drawing. In 4th Embodiment, it is sectional drawing which shows the state which inserted the inner side steel pipe inside the outer side steel pipe. In 4th Embodiment, it is sectional drawing which shows the state after drawing. It is a figure which shows the cross section of the steel pipe of an Example. It is a figure which shows the impact bending test method of an Example. It is a figure which shows the impact bending test result of an Example.

Explanation of symbols

1 outer steel pipe 2 inner steel pipe

Claims (4)

Equipped with a composite pipe structure in which multiple inner steel pipes are inserted without being pressed into the outer steel pipe, and the outer steel pipe is crimped to the outer peripheral surface of the inner steel pipe by drawing processing corresponding to the cross-sectional shape of the multiple inner steel pipes. The outer steel pipe is made of work hardening and the inner steel pipe has a ductile outer-hard / soft structure , and the sum of the non-contact length with the inner steel pipe of the inner peripheral length of the outer steel pipe is A steel pipe for absorbing collision energy for automobiles , characterized by being 20% or less of the inner circumference. The steel pipe for collision energy absorption for automobiles according to claim 1, wherein the inner steel pipe is a steel pipe having a circular cross section or a deformed steel pipe having a non-circular cross section. Inside the circular cross section of the outer steel pipe, drawn Te in the caliber of inserting the inner steel pipe a plurality of, corresponding to the cross-sectional shape of the inner steel tube plurality of without press-fit to have a gap between the outer steel pipe A method of manufacturing a steel pipe for absorbing impact energy for automobiles , characterized in that the outer steel pipe is made work hardening and the inner steel pipe remains ductile, and the outer steel pipe is pressure-bonded to the outer peripheral surface of the inner steel pipe. 4. The method for producing a steel pipe for absorbing collision energy for automobiles according to claim 3, wherein the inner steel pipe is a steel pipe having a circular cross section or a deformed steel pipe having a non-circular cross section.

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