JPH0691325A - Steel tube for reinforcing material of automobile door - Google Patents

Abstract

(57) [Summary] (Modified) [Object] The present invention is intended for a vehicle door reinforcement material that is less likely to buckle at a bending load point in order to ensure the safety of passengers in the vehicle in a collision accident from the side of the vehicle. Propose steel pipe. [Structure] A steel pipe 3 for an automobile door reinforcing material of the present invention is characterized by having a solid portion 2 at a central portion in a length direction. [Effects] The steel pipe for automobile door reinforcing material of the present invention is less likely to buckle at a bending load application point, so that the bending load does not decrease and the final bending absorbed energy increases. That is,
When compared with an impact bar having the same bending absorbed energy, it can be made lighter than a conventional full-length hollow steel pipe.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reinforcing member (hereinafter referred to as a door impact bar) mounted inside a vehicle door to protect an occupant when a side collision occurs.

[0002]

2. Description of the Related Art In the recent automobile industry, importance is attached to safety against side collision, and almost all doors of passenger cars for domestic as well as for export are equipped with impact bars. On the other hand, from the viewpoint of environmental problems, improvement of fuel efficiency of automobiles is aimed, and weight reduction of vehicles has become a major issue. Therefore, it is desired to reduce the weight of the door impact bar as much as possible. From the viewpoint of reducing the weight of a door impact bar, a pipe material is more advantageous than a conventional plate material as disclosed in Japanese Patent Laid-Open No. 56-50813, for example.
Steel pipes are becoming popular as impact bars. Furthermore, for example, JP-A-01-205032
As disclosed in Japanese Patent Laid-Open Publication No. 2003-242242, it is intended to increase the strength and reduce the thickness of a steel pipe.

Further, in the door impact bar disclosed in Japanese Patent Laid-Open No. 51-42216, the section modulus at the center from both ends is increased stepwise so that it buckles stepwise when a bending load is applied. Therefore, it is possible to make the bar lighter than a bar having a uniform cross section. That is, as shown in FIG. 2, an outer beam 6 is added as a reinforcing material to the center of the door impact bar inner beam 5 in the longitudinal direction, and both ends thereof are welded to the outer plate 4, The fulcrum distance BB when the outer beam 6 is present is shorter than the fulcrum distance AA when the outer beam 6 is not present, and the bending moment is reduced, so that the weight can be reduced.

[0004]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
In the door impact bar disclosed in Japanese Patent No. 2216, whose section modulus is changed, the bending moment is reduced by welding a portion where the section modulus is changed to an outer plate. If the shape is like a steel pipe, it is difficult to weld the area where the section modulus is changed in terms of welding work, and it is difficult to add another reinforcing material to the outside of the steel pipe in terms of space inside the door. Even if you could attach a reinforcement and weld both ends to the outer plate, the outer plate is much thinner than the door impact bar, so when the door impact bar deforms The plate has no influence, and the fulcrum does not become the BB point, but actually remains the AA point. Therefore, the effect as above cannot be expected.

Assuming that the fulcrum is always located at both ends of the door impact bar, in order to make the same stress in any cross section,
If the cross-section coefficient distribution is as shown in FIG. 3, the weight can be reduced most. However, in reality, it finally buckles at the load point, and thereafter, the deformation concentrates only on the buckling portion and the other portions hardly deform. Therefore, it is very important to prevent the load point from buckling.

[0006]

A feature of the present invention is a steel pipe for an automobile door reinforcing material, which has a solid portion at a central portion in the longitudinal direction.

The details of the present invention will be described below. When the door impact bar is a hollow steel pipe, the buckling at the load point at the center of the length direction is due to the flatness of the cross section at that point. As shown in FIG. 1, the door impact bar of the present invention has a center portion in the longitudinal direction of the steel pipe 1 which is made solid by inserting, for example, a steel bar 2 into the central portion in the longitudinal direction. The flatness of the portion can be prevented, that is, buckling can be prevented. Therefore, in the door impact bar of the present invention, the bending load does not decrease during a large bending deformation, and the final bending absorbed energy increases,
When compared with an impact bar having the same bending absorbed energy, it can be made lighter than a conventional full-length hollow steel pipe.

As a solid method, there is a so-called shrink fitting method in which the original steel pipe 1 is heated and the steel bar 2 is pushed into it. Also, the length in the length direction of the solid part is
Although it depends on the wall thickness-outer diameter ratio (t / D) of the steel pipe 1, at least 2D or more is necessary.

[0009]

[Example] At present, a steel bar having an outer diameter of 31.8 mm and a wall thickness of 2.8 mm, which is a general size for a door impact bar, is used, and a solid steel bar having the same material and a length of 65 mm is used inside. It was fitted by shrink fitting. Table 1 shows the mechanical properties of the product (steel pipe 3) (A in Table 1) and the results of the three-point bending test (Fig. 4). The test conditions are shown below. Distance between fulcrums 8: 950 mm Punch 7 radius: 150 mm Punch 7 load speed: 2 mm / sec For comparison, a steel pipe (B) of the same material and the same thickness,
The results for a steel pipe (C) with a wall thickness of 3.6 mm are also shown.

[0010]

[Table 1]

From the above, when comparing the case where the center is solid with the same steel pipe (A) and the case where it is hollow (B) is compared,
It can be seen that the maximum bending load and absorbed energy of the solid steel pipe are extremely high. Further, when the absorbed energies are almost the same, it can be seen that the weight of the solid steel pipe (A) and the hollow steel pipe (C) can be reduced by about 10% in the case of the solid pipe.

[0012]

In the present embodiment, when solidifying, the same material as the original steel pipe was used for the inside, but since the internal material is for preventing the flatness of the original steel pipe, other materials are used. Even if it becomes, the effect is almost the same. Therefore, for example, by using a steel bar which is not high in strength but is excellent in toughness, it is possible to enhance the safety of an occupant inside the vehicle without completely breaking at the center when an impact bending load is applied. Further, it does not have to be a steel bar, and the use of a material having a small specific gravity, such as aluminum, can contribute to further weight reduction.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a door impact bar obtained by the present invention.

FIG. 2 is an explanatory view of a door impact bar described in Japanese Patent Application Laid-Open No. 51-42216.

FIG. 3 is an ideal sectional coefficient distribution diagram when buckling and the like are ignored.

FIG. 4 is an explanatory diagram of a three-point bending test.

[Explanation of symbols]

 1 Steel pipe 2 Solid material (for example, steel bar) 3 Door impact bar 4 Door outer plate 5 Door impact bar inner beam 6 Door impact bar outer beam 7 Punch 8 Support point

Claims (1)

[Claims] 1. A steel pipe for an automobile door reinforcing material, which has a solid portion in a central portion in a longitudinal direction.