JP4388461B2 - Strength member for automobile having excellent collision characteristics and structural member for automobile using the same - Google Patents

Description

  The present invention relates to an automobile strength member excellent in both absorbed energy at the time of collision and reaction force at the beginning of the collision, and an automotive structural member using the same.

  In recent years, standards for side impacts of automobiles are becoming stricter, and the concept of vehicle body structure design is also changing. The door of an automobile is equipped with a door guard bar, and the door guard bar has been considered as a collision energy absorbing member. Recently, however, it has become a body structure design that absorbs collision energy at the time of a side collision with the entire door, and the function of the door guard bar as a collision energy transmission member that transmits collision energy to other members around the door guard bar has become important. ing. In order to transmit the collision energy to other members, it is necessary that the reaction force at the initial stage of the collision is high and the door guard bar itself is difficult to deform. Therefore, the door guard bar member preferably has a cross-sectional shape with high absorbed energy and excellent reaction force at the initial stage of collision.

  Currently, round steel pipes are often used as door guard bars, but the bending deformation behavior of round steel pipes is that the load concentrates directly under the load, and the cross section tends to be flattened due to local buckling. Neither reaction force is high.

  A cross-sectional shape in which a part of a round steel pipe is recessed inward as shown in FIG. 2 shown in Patent Document 1 and a lower end is located in the vicinity of the inner wall of the round steel pipe, and a recess having an upper end as an opening is formed. A member for a door guard bar (hereinafter referred to as an irregular cross section A) has been proposed. 2a and b in FIG. 2 come into contact with each other after the collision to reliably support the load caused by the collision, and the shape is stable with respect to the load, so the reduction in the reaction resistance is suppressed and the energy absorption during the collision is increased. Cross-sectional shape. However, this shape has high absorbed energy, but the reaction force at the beginning of the collision is not high.

A strength member for automobiles of a square steel pipe as shown in FIG. 3 is also currently used. If the corner radius R of the corners at both ends of the upper side of the collision is reduced, the impact load is directly applied to the ends of both ends parallel to the collision load input direction, and the cross-section flattening is difficult to occur. Is known to rise. However, this shape has a high reaction force at the initial stage of collision, but buckling is likely to occur. Once buckling occurs, the reaction force suddenly decreases, so the absorbed energy is not high.
Japanese Patent Laid-Open No. 11-278055

  As described above, the door guard bar member preferably has a cross-sectional shape having high absorbed energy and excellent reaction force at the initial stage of a collision, but no door guard bar member having such a cross-sectional shape has been proposed yet. An object of the present invention is to provide an automobile strength member having a high cross-sectional shape with high absorbed energy and excellent reaction force at the beginning of a collision, and an automobile structural member using the same.

  As described above, the door guard bar member preferably has a cross-sectional shape that has high absorbed energy and excellent reaction force at the initial stage of a collision.

  The deformed cross-sectional shape shown in FIG. 2 has a high absorbed energy because the a part and the b part come into contact with each other to reliably support the load caused by the collision, and the shape is stable with respect to the load. It is known. However, since there are few surfaces parallel to the load input direction, it is easy to cause a cross-sectional deformation with respect to the load, and the reaction force at the beginning of the collision is not high.

  When the corner radius R of the square steel pipe shown in FIG. 3 is reduced, the load load surface is prevented from being flattened, and a large amount of load is directly applied to a surface parallel to the collision load input direction. It is known to be higher. However, square steel pipes are easy to buckle, and once buckling occurs, the reaction resistance decreases rapidly, so the absorbed energy is not high.

As a result of the study by the present inventors, by specifying the conditions of L ₁ , L ₂ , L ₃ of the cross-sectional shape in which the a part and the d part are corners as shown in FIG. Found both to be higher. In FIG. 1, if the lengths of L ₁ and L ₂ are too long, the load loading surface is likely to be flattened, so that buckling is likely to occur. If the lengths of L ₁ and L ₂ are too short, a load is applied. The deformation progresses so that the opening is further expanded, and the absorbed energy is reduced. If the length of L ₃ is too long, buckling occurs without contact between the e point and the g point, so the absorbed energy is reduced. If the length of L ₃ is too short, the e point and the g point are The contact is made at the initial stage of the collision, the pushing displacement until buckling is reduced, and the absorbed energy is reduced. Accordingly, L ₁ , L ₂ , and L ₃ have appropriate values, and the automobile strength member having the cross-sectional shape shown in FIG. 1 under the appropriate values has high absorption energy and reaction force at the initial stage of the collision.

  The present invention obtained from these findings is summarized as follows.

[1]. An irregular cross-sectional shape in which the upper side of a square steel pipe having a square cross-section is formed into a concave portion in the pipe by forming an opposing inwardly curved portion and continuously integrating with a straight portion. The length of the side of the square; L (mm), the straight line length connecting the curved portion and the left side of the square; L ₁ (mm), the straight line length connecting the curved portion and the right side of the square; L ₂ (mm), the curved portion the distance between the lowest point and the square lower side middle point; when L ₃ and _{(mm), L 1, L} 2, L 3 is (1) to (3) superior to the reaction force of the collision initial to satisfy equation excellent automobile strength member in collision characteristics, characterized in that the stuff.
0.2L ≦ L ₁ ≦ 0.4L (1)
0.2L ≦ L ₂ ≦ 0.4L (2)
0.1L ≦ L ₃ ≦ 0.5L (3)

  [2]. A structural member for automobiles, characterized in that the deformed cross-section steel pipe for a strength member for automobiles according to [1] is arranged in a direction in which a bending input load is applied to the upper side of the cross section.

  INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide an automobile strength member having a high cross-sectional shape with high absorbed energy and high reaction force at the beginning of a collision, and an automobile structural member using the same. It becomes possible to make the vehicle body structure design that absorbs rush energy by the whole door, and the cost of the whole door can be reduced.

Hereinafter, the present invention will be described in detail.
First, as shown in FIG. 1, a steel pipe having a modified cross-sectional shape in which a concave portion is formed in which a facing inner surface is a curved portion that swells from the inlet side toward the inside of a square steel pipe having a square cross section. The length of the side of the square having the modified cross-sectional shape is L, the length of the straight line connecting the curved portion and the left side of the square is L ₁ , the length of the straight line connecting the curved portion and the right side of the square is L ₂ , when the distance between the lowest point and the square lower side middle point was _{L 3, L 1, L 2} , L 3 _{are, (1) 0.2L ≦ L 1} ≦ 0.4 L, (2) 0.2L ≦ L 2 ≦ 0.4 The first aspect of the invention that satisfies the expression of L, 0.1 L ≦ L ₃ ≦ 0.5 L will be described.
In order to increase the absorbed energy, it is effective to suppress the load load surface from being flattened, to suppress buckling, and to suppress a decrease in reaction force after a collision to a minimum. The shape shown in FIG. 1 is less likely to be flat because there are few lateral surfaces on the load surface, and as a result, it is possible to suppress buckling and increase energy absorption. 1e and g are located close to each other, so the e and g parts come into contact after the collision and the reaction force rises, and the load caused by the collision is surely supported and the shape becomes stable against the load. Therefore, it is possible to suppress a decrease in the reaction force after the collision and increase the absorption of energy after the collision.

In order to efficiently suppress the buckling of the load surface and suppress the buckling and increase the absorbed energy, the lengths of L ₁ and L _{2 in} the cross-sectional shape shown in FIG. 2 times or more and 0.4 times or less is desirable because the flatness of the load surface is small. If it is less than 0.2 times L, the upper opening is deformed so as to open more simultaneously with the load, and a sufficient reaction force cannot be obtained. On the other hand, if it exceeds 0.4 times L, flattening of the load surface becomes prominent and buckling is likely to occur, and the absorbed energy cannot be increased.

The lengths of L ₁ and L _{2 in} the cross-sectional shape shown in FIG. 1 are desirably 0.9 L ₁ ≦ L ₂ ≦ 1.1 L ₁ . If the lengths of L ₁ and L ₂ are greatly different, the deformation is biased toward the shorter length, and sufficient absorbed energy cannot be obtained. Therefore, by making L ₁ and L _{2 the} same length as much as possible, there is no bias in deformation, and it can be a strength member for automobiles that can efficiently absorb energy. However, even if there is a slight difference between the lengths of L ₁ and L ₂ , the effect of the present invention is sufficiently obtained and does not depart from the scope of the present invention.

Efficiently in order to increase the suppression to absorb energy reduction of the reaction force after the collision, 0.5 times 0.1 times the length L of the side position of the square distance L ₃ in Fig. 1 point e The following is desirable because there is little decrease in reaction force after collision. If it is less than 0.1 times L, the point e and the point g come into contact at the beginning of the collision, and the indentation displacement until buckling becomes small, resulting in a decrease in absorbed energy. On the other hand, if it is more than 0.5 times L, buckling occurs without contact between the e point and the g point, and the absorbed energy decreases.

  In order to efficiently increase the reaction force at the initial stage of collision, it is preferable that as much load as possible be directly applied to a surface parallel to the collision load input direction. For this purpose, it is desirable that the corner corner radius R at the boundary with both side surfaces parallel to the collision load input direction is small. When the corner corner radius R is large, the load loading surface becomes flat and the load cannot be efficiently transmitted to a surface parallel to the collision load input direction. In this shape shown in FIG. 1, the a part and the d part are angular, and the smaller the corner radius R, the more the impact load is applied directly to the ends of both side surfaces parallel to the collision load input direction. Can be a high strength member for automobiles. Further, it is more desirable that the angle R at both ends of the lower side of the f part and the h part in FIG.

  In order to increase both the absorbed energy and the reaction force at the beginning of the collision efficiently, it is also effective to increase the strength of the member. However, since molding is difficult when the strength is high, it is desirable to increase the strength by a heat treatment method such as induction hardening after molding into an irregular cross-sectional shape.

  It is desirable that the variation in hardness in the cross section of the member is small. If the cross section has a variation in hardness, it is not preferable because deformation concentrates in the softest part and locally buckles. The smaller the variation in cross-sectional hardness, the more uniform the deformation.

Next, a second invention, that is, a structural member for an automobile in which a deformed cross-section steel pipe according to the first invention is arranged in a direction in which a bending input load is applied to the upper side of the cross section will be described.
When installing the strength member for automobiles according to the first invention in an automobile, it is necessary to provide directionality so as to maximize the collision characteristics. That is, when installed so that the load is applied to the upper side of the cross section, the load is supported by the four vertical surfaces, so that both the absorbed energy and the reaction force at the beginning of the collision are high, and the most effective automotive strength member It becomes.

  In addition, as a method of manufacturing the steel pipe which is the strength member for automobiles of the first invention, there is a method of forming a round steel pipe by roll forming, drawing, extrusion forming or the like. The most cost-effective manufacturing method is a method in which a round ERW steel pipe is deformed by roll forming and then strengthened as a martensite structure by induction hardening.

  As a material for forming the strength member for automobiles of the first invention, steel is most advantageous and general in terms of cost, but aluminum, titanium, magnesium and their respective alloys are acceptable as long as the conditions of the invention are satisfied. It is also possible to use a lightweight material such as a light metal material.

  The strength member for automobiles of the first invention can be installed at various places for the purpose of improving the collision characteristics at the time of collision of automobile doors, bumpers, roofs, pillars, rockers and the like.

In the automotive strength member of the first invention, the absorbed energy and the reaction force at the beginning of the collision are important.
A three-point bending test as shown in FIG. 4, which is an actual deformation mode of the door guard bar, was performed by FEM analysis. The test conditions were a length L in the longitudinal direction of the test body L = 1000 mm, and a half-columnar loader having a radius of 150 mm was pushed in at 5 m / sec. The bending span length L was set to 600 mm, and the relationship between displacement-load and displacement-absorbed energy when pushed in was examined.

  Table 1 shows various strength members for automobiles. Four types of test specimens were prepared, and the present invention product (Fig. 1) whose outer diameter, strength, and weight are almost the same as the round steel pipe (φ35.0 × t2.0) that is conventionally used as a door guard bar. The three-point bending test results of the modified cross-section A type steel pipe (FIG. 2) and the square type steel pipe (FIG. 3) were compared. Here, the results of the deformed cross-section A-type steel pipe and the product of the present invention differ depending on the load application direction, but both were loaded from the top of the cross section having the best collision characteristics.

  The results were as shown in FIGS. The numerical data of the results are shown in Table 1. First, the absorbed energy when the 150 mm indentation is shown in FIG. 6 is low because the square steel pipe is likely to buckle with respect to the round steel pipe. On the other hand, the modified cross-section A-type steel pipe is less likely to buckle and has a high absorbed energy in order to suppress a decrease in the reaction resistance. Since the product of the present invention has a shape in which the reaction force at the initial stage of collision of the modified cross-section A-shaped steel pipe is increased, the absorbed energy is higher than that of the modified cross-section A-shaped steel pipe in the four types of cross-sectional shapes. It was the highest value.

The reaction force at the initial stage of the collision was evaluated by the absorbed energy at 30 mm indentation in FIG. Since the reaction force (load) × displacement is the absorbed energy, the higher the absorbed energy at 30 mm indentation, the higher the average reaction force at 30 mm indentation. From Table 1, the square steel pipe is not flattened at the beginning of the collision, and the reaction force at the initial stage of the collision is high because a large amount of load is applied to the surface parallel to the load direction. Since the outer periphery of the A-type steel pipe is circular and there are few surfaces parallel to the load direction, the reaction force at the initial stage of collision is low. The product of the present invention is capable of sustaining a high load because many loads are applied to the surface parallel to the load direction and buckling is difficult, and the reaction force at the initial stage of collision is higher than that of a square steel pipe, It was the highest value among the four types of cross-sectional shapes.
Further, from FIG. 5, the maximum load of the product of the present invention was the highest value among the four types of cross-sectional shapes.

It is a figure showing the cross-sectional shape of the 1st invention product. It is a figure showing the cross-sectional shape of the irregular cross-section A-type steel pipe. It is a figure showing the cross-sectional shape of a square steel pipe. It is a figure showing the method and dimension of a three-point bending test. It is a figure showing the relationship between the displacement of a 150 mm indentation 3 point | piece bending test, and a load. It is a figure showing the relationship between the displacement of 150 mm indentation 3 point | piece bending test, and absorbed energy. It is a figure showing the relationship of the displacement and load in the initial stage of a collision of a three-point bending test. It is a figure showing the relationship between the displacement in the initial stage of a collision and absorbed energy of a three-point bending test.

Explanation of symbols

L: Length of square side (mm)
L ₁ : Length of straight line connecting the bent part and the left side of the square (mm)
L ₂ : Length of straight line connecting the bent part and the square right side (mm)
L ₃ : Distance between the lowest point of the fold part and the middle point of the lower side of the square (mm)
R: Square corner radius R (mm)

Claims (2)

It is a deformed cross-sectional shape in which a concave portion is formed in the pipe by forming a concave portion in the pipe by forming an opposing inwardly bent portion on the upper side of a square steel pipe having a square cross section, and forming a concave portion in the pipe. Length; L (mm), straight line length connecting the curved part and the left side of the square; L ₁ (mm), straight line length connecting the curved part and the right side of the square; L ₂ (mm), the lowest point of the curved part the distance between the square lower side middle point; when the _{L 3 (mm), L 1} , L 2, L 3 is (1) to (3) it has excellent in reaction force of the collision initial to satisfy equation excellent automobile strength member in collision characteristics characterized by.
0.2L ≦ L ₁ ≦ 0.4L (1)
0.2L ≦ L ₂ ≦ 0.4L (2)
0.1L ≦ L ₃ ≦ 0.5L (3)   A structural member for an automobile comprising the deformed cross-section steel pipe for an automobile strength member according to claim 1 arranged in a direction in which a bending input load is applied to the upper side of the cross section.

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