JPH07241642A - Structural member and motorcycle using the same - Google Patents

Abstract

PURPOSE:To provide a structural member which can be formed with extruding or drawing, whose sectional shape's size is changed over the longitudinal direction and which is a tapered closed sectional structure with light weight and a few part number and welding point. CONSTITUTION:A shape steel 2 having a T-type sectional shape is formed with extruding or drawing, in widths W1, W2 of wing parts 3 extending to both sides from a leg part 4 of the T-type section, the side ends of the wing parts 3 are cut so that its width is continuously changed in the longitudinal direction of the shape steel 2, on one side, both wing parts 3 are bent toward a free end part 4a of the leg part 4 respectively, top ends 5 of both wing parts 3 are engaged to the free end part 4a of the above leg part 4, welded and a closed sectional structure having plural small closed sections is composed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structural member having high rigidity and a motorcycle using the structural member, and more particularly to a structural member adopting a reinforcing structure with a closed cross section and a motorcycle using the structural member.

[0002]

2. Description of the Related Art For example, a body frame or a swing arm of a motorcycle is required to have a structural member having high rigidity and light weight. As a structural member, a pipe material having a closed cross-section structure is often used because it satisfies the above-mentioned conditions.

The structural member is generally formed by extruding or drawing a pipe material when the cross-sectional shape may be the same in the longitudinal direction.
On the other hand, when it is desired to change the size of the cross-sectional shape of the structural member in the longitudinal direction of the structural member, that is, a so-called tapered structural member in which the size of the cross-sectional shape at one end is different from the size of the cross-sectional shape at the other end is required. In this case, since the above-mentioned extrusion or drawing method cannot be used, for example, plate materials that have been bent or pressed are joined to each other by welding or the like to form a tapered structural member having a closed cross-section structure (bending process). For the tapered swing arm, refer to JP-A-5-246373).

[0004]

In the case of a motorcycle body frame, a portion where stress is concentrated, for example, a connection portion with a head pipe requires higher rigidity than other portions of the body frame. Further, in the case of a swing arm, stress concentrates on the base portion of the swing arm and the connecting portion of the shock absorber, so that this portion requires higher rigidity than other portions. In order to obtain high rigidity, it is necessary to increase the cross-sectional shape of that portion or increase the wall thickness.

However, when a pipe material extruded or drawn into the body frame or swing arm is used, the pipe material has the same cross-sectional shape in the longitudinal direction, so that the stress is concentrated on the portion. It is necessary to increase the size of the cross-sectional shape of the entire pipe material or increase the wall thickness in accordance with the rigidity required for the above, resulting in an unnecessary increase in weight.

Therefore, in recent years, it has become common to use a tapered structural member in which only the cross-sectional shape of a portion requiring high rigidity is increased and the cross-sectional shape of other portions is decreased. There is.

However, as described above, since the taper-shaped structural member cannot be extruded or drawn out, for example, the pressed plate materials are joined to each other by welding or the like to form a taper-shaped centering structure. However, since the member of such a mid-matching structure has low torsional strength, it is necessary to add a reinforcing plate etc. to the part where stress is concentrated, and the number of parts is increased. Welding points will also increase.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a structural member which can be molded by extrusion or drawing, has high mechanical strength, is lightweight, and has high rigidity.

Another object of the present invention is to provide a structural member having a tapered closed cross-section structure and a motorcycle using the structural member, which can be molded by extrusion or drawing, and the size of the cross-sectional shape is changed in the longitudinal direction. The purpose is to provide.

Still another object of the present invention is to provide a motorcycle having a body frame and a swing arm which are lightweight and have a small number of parts and welding points while sufficiently maintaining a large rigidity in a portion where stress is concentrated. .

[0011]

In order to solve the above-mentioned problems, a structural member according to the present invention is formed by extruding or drawing a shape steel having a T-shaped cross-sectional shape as described in claim 1. In addition, the wing portions extending from the leg portion having the T-shaped cross section to both sides are bent toward the free end portions of the leg portions, and the tips of the wing portions are engaged with the free end portions of the leg portions. It is a structure in which a closed cross-section structure having a plurality of small closed cross-sections is formed by joining and welding.

Further, in order to solve the above-mentioned problems, as described in claim 2, there is provided a section steel having a sectional shape in which a flange on one side of an I-shaped section is extended to both sides to form a wing portion. While extruding or drawing, the both wing portions are bent toward the flange portion on the other side of the I-shaped section, and the tips of the wing portions are engaged with the flange portion on the other side and welded. And a closed cross section structure having a plurality of small closed cross sections.

Further, in order to solve the above-mentioned problems,
As described in claim 3, a steel mold having a cross-sectional shape in which wings are extended on both sides of the small closed cross section is formed by extrusion or drawing, and both wings are formed on one side of the small closed cross section. A closed cross-section structure having a plurality of small closed cross-sections is formed by bending it in a direction and engaging the ends of the both blades with one side surface of the small closed cross-section to weld them.

Further, in order to solve the above-mentioned problems, as described in claim 4, the small closed cross section is one of a triangle, a square, a rectangle, a circle, an ellipse, and a semi-elliptical. It is a thing.

In order to solve the above-mentioned problems,
As described in claim 5, the blade side end is cut so that the width of the blade portion of the shape steel continuously changes in the longitudinal direction of the shape steel.

Further, in order to solve the above-mentioned problems, as described in claim 6, a vehicle body frame is constituted by using the structural member according to any one of claims 1 to 5.

Further, in order to solve the above-mentioned problems,
As described in claim 7, a swing arm is configured by using the structural member according to any one of claims 1 to 5.

[0018]

In the present invention having the above-mentioned structure, a steel mold having a T-shaped cross-sectional shape is formed by extrusion or drawing, and the width of the blades extending from the leg of the T-shaped cross section to both sides is While cutting the wing portion side end so as to continuously change in the longitudinal direction of the shape steel, both the wing portions are bent toward the free end direction of the leg portion, and the tips of the both wing portions are Since it has a closed cross-section structure with multiple small closed cross-sections that is welded and welded to the free ends of the legs, it can be molded by extrusion or drawing and has high mechanical strength, high rigidity, and light weight. It is possible to provide a structural member having a tapered closed cross-section structure with a small number of points and welding points and a motorcycle using the structural member.

Further, a steel mold having a cross-sectional shape in which a flange on one side of an I-shaped cross section is extended to both sides to form a wing portion is formed by extrusion or drawing, and the width of the wing portion is set to the above. While cutting the blade side end so as to continuously change in the longitudinal direction of the shape steel, both blade portions are bent toward the flange portion on the other side of the I-shaped cross section, and the tips of the blade portions are Since it has a closed cross-section structure with multiple small closed cross-sections that is engaged and welded to the flange on the other side, it can be molded by extrusion or drawing, has high mechanical strength, high rigidity, and is lightweight and has a large number of parts. It is possible to provide a structural member having a tapered closed cross-section structure with few welding points and a motorcycle using the structural member, and the welding of the structural member is strengthened.

Further, extruding or drawing a shape steel having a cross-sectional shape in which wings are extended on both sides of a small closed cross-section consisting of any one of a triangle, a square, a rectangle, a circle, an ellipse and a semi-elliptical shape. While cutting the wing portion side end so that the width of the wing portion continuously changes in the longitudinal direction of the shaped steel, both wing portions are directed toward one side surface direction of the small closed cross-section portion. Since the closed cross-section structure having a plurality of small closed cross-sections is formed by welding the ends of the both blades to one side surface of the small closed cross-section part by welding, it can be formed by extrusion or drawing. It is possible to provide a structural member having a tapered closed cross-section structure and a motorcycle using the structural member, which has high dynamic strength, high rigidity, light weight, and a small number of parts and welding points. Structure Also of the strength increase.

Furthermore, since the vehicle body frame and the swing arm are constructed by using the structural member according to any one of claims 1 to 5, the structure can be formed by extrusion or drawing, and a large rigidity is sufficiently maintained in a portion where stress is concentrated. At the same time, it is possible to provide a body frame and a swing arm for a motorcycle, which is lightweight and has a tapered closed cross-section structure with a small number of parts and welding points.

[0022]

Embodiments of the present invention will be described below with reference to the drawings.

1 (a), 1 (b) and 1 (c) are views showing a first embodiment of a structural member to which the present invention is applied.

As shown in FIG. 1A, this structural member 1
Is made of T-shaped section steel 2. The T-shaped cross-sectional shape includes, for example, a wing portion 3 extending left and right, and a leg portion 4 which is integrally formed vertically from, for example, the vicinity of the center of the wing portion 3.
The shaped steel 2 is formed by extrusion or drawing.

As shown in FIG. 1 (b), the blade portion 3 of the shaped steel 2 has a width W1 and W2 in the longitudinal direction continuously changing from one end to the other end, that is, a tapered shape. To be disconnected.

Shaped steel 2 in which blade 3 is cut in a taper shape
Is formed by bending the left and right wings 3 toward the free ends 4a of the legs 4 by, for example, roll forming.
The tips 5 of both wings are engaged in the longitudinal direction of the free ends 4a of the legs 4 (see FIG. 1 (c)).

Then, the tips 5 and the legs 4 of these both wings are formed.
By integrally welding with the free end portion 4a of the above, the tapered structural member 1 having a closed cross-section structure having a plurality of small closed cross-sections is formed.

Since the structural member 1 described above is formed as a tapered structural member 1 in which only the size of the cross-sectional shape of the portion where the stress is concentrated is large, the structural member 1 is formed according to the rigidity required in the portion where the stress is concentrated. Since it is not necessary to increase the size of the entire cross-sectional shape or increase the wall thickness, the weight can be reduced.

Further, since the extruded or drawn model steel 2 is bent, the number of parts and the number of welded parts can be reduced unlike the structural member having the middle fitting structure, such as press working.

Further, since the sectional shape of the shape steel 2 is a T-shaped section, the formed structural member 1 has a closed cross-sectional structure in the shape of "Sun", and is sufficiently twisted without additional members such as a reinforcing plate. Can maintain strength.

By the way, in the above-mentioned embodiment, T
An example is shown in which the mold steel 2 having the mold cross-sectional shape is formed on the structural member 1 having a "Sun" -shaped (rectangular) closed cross-section structure.
As shown in (a) to (h), the cross-sectional shape of the structural member 1 may be a triangle, a trapezoid, a polygon, a circle, an ellipse, or the like, and various cross-sectional shapes are conceivable according to the purpose and application. .

FIGS. 3A, 3B and 3C are views showing a second embodiment of the structural member to which the present invention is applied. The same members as those in the first embodiment are designated by the same reference numerals.

As shown in FIG. 3A, this structural member 1
Is made of a steel mold 2 having an I-shaped cross section.

The I-shaped cross section has, for example, a main plate portion 6 and flange portions 7a, 7 formed on both sides thereof.
and a flange portion 7a formed on one side of the main plate portion 6 and extended to both sides to form the wing portion 3. The shaped steel 2 is formed by extrusion or drawing.

As shown in FIG. 3 (b), the blade portion 3 of the shaped steel 2 has a width W1, W2 in the longitudinal direction continuously changing from one end to the other end, that is, a tapered shape. To be disconnected.

Shaped steel 2 in which blade 3 is cut into a taper shape
Is formed by bending the left and right wings 3 toward the flange 7b on the other side of the main plate 6 by roll forming or the like, and the tips 5 of both wings are attached to the flange on the other side of the main plate 6. Engage in the longitudinal direction of the portion 7b (see FIG. 3 (c)).

Then, by integrally welding the tips 5 of the both blades and the flange portion 7b on the other side of the main plate portion 6, a tapered structural member having a closed cross-section structure having a plurality of small closed cross-sections. 1 is formed.

Since the above-described structural member 1 is formed in the tapered structural member 1 in which only the size of the sectional shape of the stress concentrated portion is large as in the first embodiment, the rigidity required for the stress concentrated portion is increased. In addition, since it is not necessary to increase the size of the sectional shape of the entire structural member 1 or increase the wall thickness, the weight can be reduced.

Further, since the extruded or drawn shape steel 2 is bent, the number of parts and welding points can be reduced unlike the structural member having the middle fitting structure such as press working.

Furthermore, since the sectional shape of the shape steel 2 is the I-shaped section in which the wing portion 3 is formed, the formed structural member 1 has a closed cross-section structure of a "Sun" shape, and there is no additional member such as a reinforcing plate. However, while sufficient torsional strength can be maintained, the flange portion 7b on the other side of the main plate portion 6 becomes a welding margin, so that a sufficient welding area can be secured even if the plate steel 2 is thin.

Furthermore, in the above-mentioned embodiment,
An example in which the shape steel 2 having an I-shaped cross-sectional shape is formed in the structural member 1 having a "Sun" -shaped (rectangular) closed cross-section structure is shown. As shown, the cross-sectional shape of the structural member 1 may be a triangle, a trapezoid, a polygon, a circle, an ellipse, or the like, and various cross-sectional shapes can be considered according to the purpose and application.

FIGS. 4A, 4B and 4C are views showing a third embodiment of the structural member to which the present invention is applied. The same members as those in the first embodiment are designated by the same reference numerals.

As shown in FIG. 4A, this structural member 1
Consists of a steel mold 2 having a cross-sectional shape in which wings 3 are provided on both sides of a small closed cross-section 8.

As for this cross-sectional shape, the wing portion 3 is formed by extending the bottom sides 8a of the rectangular small closed cross-section portion 8 on both sides, for example. The shaped steel 2 is formed by extrusion or drawing.

As shown in FIG. 4 (b), the blade portion 3 of the shaped steel 2 has a width W1 and W2 in the longitudinal direction continuously changing from one end to the other end, that is, a tapered shape. To be disconnected.

The blade 2 has a shape steel 2 cut into a taper shape,
For example, the left and right wings 3 are bent toward the upper side 8b, which is one side surface of the rectangular small closed cross section 8 by roll forming or the like, and the tips 5 of both wings are placed on the upper side 8b of the small closed cross section 8. In the longitudinal direction (see FIG. 4 (c)).

Then, by integrally welding the tips 5 of both the blades and the upper side 8b of the small closed cross section 8, the tapered structural member 1 having a closed cross section having a plurality of small closed cross sections is formed. To be done.

Since the structural member 1 described above is formed in the tapered structural member 1 in which only the size of the cross-sectional shape of the stress concentrated portion is large as in the first and second embodiments, it is necessary for the stress concentrated portion. Since it is not necessary to increase the size of the cross-sectional shape of the entire structural member 1 or increase the wall thickness according to the appropriate rigidity, the weight can be reduced.

Further, since the extruded or drawn model steel 2 is bent, the number of parts and the number of welded parts can be reduced unlike the structural member having the middle fitting structure such as press working.

Further, since the wing portions 3 are extended on both sides of the small closed cross-section portion 8 of the shape steel 2, the structural member 1 thus formed has a closed cross-section structure in the shape of an "eye", such as a reinforcing plate. While sufficient torsional strength can be maintained without any additional member, the upper edge 8b of the small closed cross-section portion 8 serves as a welding margin, so that a sufficient welding area can be secured even if the steel plate 2 is thin.

By the way, in the above-mentioned embodiment, an example in which the mold steel 2 having the rectangular small closed cross-section portion 8 is formed in the structural member 1 is shown, but as shown in FIGS. 5 (a) to 5 (e), The shape of the small closed cross section may be a triangle, a square, a circle, an ellipse, a semi-elliptical shape, etc. Further, as shown in FIG. Various cross-sectional shapes are conceivable according to the purpose and application, such as forming the portion 8a to increase rigidity.

Furthermore, in this embodiment, an example in which the formed structural member 1 has a rectangular cross-sectional shape is shown, but as in the first and second embodiments, as shown in FIGS. 2 (a) to 2 (h). In addition, the sectional shape of the structural member 1 may be a triangle, a trapezoid, a polygon, a circle, an ellipse, or the like.

FIGS. 6A and 6B and FIG. 7A.
And (b) are diagrams showing the fourth and fifth embodiments of the structural member to which the present invention is applied, respectively.
The second embodiment and the third embodiment, and the fifth embodiment is a combination of the first embodiment and the third embodiment, respectively, and when it is desired to increase the rigidity partially or entirely. It shows an example of a suitable cross-sectional shape.

FIGS. 8A and 8B are views showing a sixth embodiment of the structural member to which the present invention is applied. The same members as those in the first embodiment are designated by the same reference numerals.

In the above-mentioned first to fifth embodiments, the blade portion 3 of the shape steel 2 is tapered so that its longitudinal widths W1 and W2 continuously change from one end to the other end. In the sixth embodiment, as shown in FIG. 8A, the blade portion 3 of the mold steel 2 is cut into a shape in which a plurality of tapered shapes 9 are combined. By rolling this shaped steel 2 for example, a plurality of tapered members 1 as shown in FIG.
It is possible to form the structural member 1 in which 0s are combined.

The sectional shape of the shape steel 2 may be any of the above-mentioned first to fifth embodiments.

FIG. 10 is a left side view of a motorcycle using the structural member 1 according to the present invention.

In FIG. 10, the motorcycle 11 has a vehicle body frame 12, and an engine 13 is mounted on the lower front portion of the vehicle body frame 12. A fuel tank 14 is provided above the engine 13 and a fuel tank 14 is provided behind the fuel tank 14. The driving seats 15 are installed respectively.

A head pipe 16 is provided in front of the body frame 12, and a steering mechanism 17 is provided on the head pipe 16. The steering mechanism 17 is pivotally attached to the head pipe 16 so as to be rotatable left and right, and a front wheel 19 is steered by a handle bar 18 so as to be rotatable left and right.

On the other hand, a swing arm 21 is pivotally attached to a pivot shaft 20 which is installed in the lower center of the body frame 12 so as to swing around the pivot shaft 20, and a rear wheel 22 is rotated at a rear end of the swing arm 21. Freely supported.
A rear shock absorber 23 and a plurality of links 24 are provided on the base end side of the swing arm 21, and one ends of these links 24 are pivotally attached to a link attachment portion 25 formed in the upper part of the swing arm 21 near the center front. To be done.

The body frame 12 is of, for example, a twin tube type, and is composed of a pair of left and right main frames 12a and a seat rail 12b, and a pivot portion 12c is provided at the lower rear portion of the main frame 12a.

FIG. 10 is a partial sectional side view of the body frame 12 and the swing arm 21.

As shown in FIG. 10, the main frame 12
a shows an example in which the third embodiment of the structural member of the present invention is applied, and the main frame 12a has a "eye" -shaped closed cross-section structure. It is composed of a tapered structural member 1 which is larger than the size.

In the motorcycle 11, since stress concentrates around the head pipe 16 provided with the steering mechanism 17, the end 26 having the larger cross-sectional shape of the main frame 12a is connected to the head pipe 16. on the other hand,
The other end 27 of the main frame 12a is connected to the head pipe 16
Main frame 12
The cross-sectional shape of a is reduced.

Further, as shown in FIG. 10, the swing arm 21 shows an example in which the second and sixth embodiments of the structural member of the present invention are applied, and has a "Sun" -shaped closed cross section structure, In addition, a plurality of structural members 1, in this embodiment, two tapered members 10 are combined to form the structural member 1.

In the motorcycle 11, since stress concentrates on the link mounting portion 25 formed near the center front of the swing arm 21, the cross-sectional shape of the vicinity 28 of the link mounting portion 25 is increased, and the cross-sections of both end portions 29 are increased. The shape is made smaller than the cross-sectional shape near the link mounting portion 25.

By constructing the main frame 12a and the swing arm 21 as described above, the size of the sectional shape of the entire structural member 1 can be increased or the wall thickness can be increased according to the rigidity required in the portion where stress is concentrated. Since it is not necessary to do so, the weight can be reduced.

Further, since the extruded or drawn model steel 2 is bent, the number of parts and the number of welded parts can be reduced unlike the structural member having the middle fitting structure such as press working. In the case of the present embodiment, only one welding location is required in the axial direction of the structural member 1. Therefore, by configuring the welding location to face the inside of the vehicle body, the appearance of the vehicle body frame 12 and the swing arm 21 is improved.

Further, the main frame 12a and the swing arm 21 made of the structural member 1 of the present invention are "day".
Since it has a closed cross-sectional structure in the shape of a letter and an "eye", sufficient torsional strength can be maintained without additional members such as a reinforcing plate.

In the above-mentioned embodiment, the structural member 1 according to the present invention is applied to the motorcycle 11, but the tapered structural member 1 including the structural member for construction is used.
It can be applied to any structure using the above structural member.

[0071]

As described above, according to the structural member of the present invention, a steel mold having a T-shaped cross-sectional shape is formed by extrusion or drawing and is extended from the leg portion of the T-shaped cross section to both sides. While cutting the width of the existing wing part so that the wing part side end is continuously changed in the longitudinal direction of the shape steel, both the wing parts are bent toward the free end part of the leg part, respectively. , Because the closed end structure having a plurality of small closed cross-sections is formed by welding the ends of both wings to the free ends of the legs, it can be formed by extrusion or drawing, and has high mechanical strength. It is possible to provide a structural member having a tapered closed cross-section structure, which has high rigidity, is lightweight and has a small number of parts and welding points, and a motorcycle using the structural member.

A shaped steel having a cross-sectional shape in which a flange portion on one side of an I-shaped cross section is extended to both sides to form a wing portion,
While forming by extrusion or drawing, the blade side end is cut so that the width of the blade portion continuously changes in the longitudinal direction of the shaped steel, while the blade portions are respectively I
A closed cross-section structure having a plurality of small closed cross sections is formed by bending toward the flange part on the other side of the mold cross section, and engaging the ends of the two wing parts with the flange part on the other side and welding them together. It is possible to provide a structural member having a tapered closed cross-section structure that can be molded by extrusion or drawing, has high mechanical strength, high rigidity, is lightweight, and has a small number of parts and welding points, and a motorcycle using the structural member. At the same time, the welding of the structural members becomes strong.

Further, extruding or drawing a shape steel having a cross-sectional shape in which wings are extended on both sides of a small closed cross-section that is empty, which is one of triangle, square, rectangle, circle, ellipse and semi-elliptical. While cutting the wing portion side end so that the width of the wing portion continuously changes in the longitudinal direction of the shaped steel, both wing portions are directed toward one side surface direction of the small closed cross-section portion. Since the closed cross-section structure having a plurality of small closed cross-sections is formed by welding the ends of the both blades to one side surface of the small closed cross-section part by welding, it can be formed by extrusion or drawing. It is possible to provide a structural member having a tapered closed cross-section structure and a motorcycle using the structural member, which has high dynamic strength, high rigidity, light weight, and a small number of parts and welding points. Structural member Strength increases.

Furthermore, since the vehicle body frame and the swing arm are formed by using the structural member according to any one of claims 1 to 5, it can be molded by extrusion or drawing, and a large rigidity is sufficiently maintained in a portion where stress is concentrated. At the same time, it is possible to provide a body frame and a swing arm for a motorcycle, which is lightweight and has a tapered closed cross-section structure with a small number of parts and welding points.

[Brief description of drawings]

1A, 1B and 1C are views showing a first embodiment of a structural member according to the present invention.

2A to 2H are views showing another cross-sectional shape of the first embodiment.

3 (a), (b) and (c) are views showing a second embodiment of the structural member according to the present invention.

4 (a), (b) and (c) are diagrams showing a third embodiment of the structural member according to the present invention.

5A to 5F are views showing another closed cross-sectional shape of the third embodiment.

6A and 6B are views showing a fourth embodiment of the structural member according to the present invention.

7A and 7B are views showing a fifth embodiment of the structural member according to the present invention.

8A and 8B are views showing a sixth embodiment of the structural member according to the present invention.

FIG. 9 is a left side view of a motorcycle using the structural member according to the present invention.

FIG. 10 is a partial sectional side view of a body frame and a swing arm.

[Explanation of symbols]

 1 Structural Member 2 Type Steel 3 Wing Part 4 Leg with T-shaped Cross Section 4a Free End of Leg 5 Tip of Both Wings 6 Main Plate Part with I-shaped Cross Section 7a, 7b Flange Part of Main Plate 8 Small Closed Section Part 8a Bottom of small closed cross section 8b Top of small closed cross section 11 Motorcycle 12 Body frame 12a Main frame 16 Head pipe 21 Swing arm 25 Swing arm link attachment W1, W2 Longitudinal width of wings

Claims (7)

[Claims] 1. A shape steel having a T-shaped cross-section is formed by extrusion or drawing, and wings extending from the leg of the T-shaped cross section to both sides are respectively directed toward the free end of the leg. A structural member having a closed cross-section structure having a plurality of small closed cross-sections by bending and bending the ends of the wings and engaging the ends of the wings with the free ends of the legs. 2. A steel mold having a cross-sectional shape in which a flange on one side of an I-shaped cross section is extended to both sides to form a wing portion is formed by extrusion or drawing, and both of the wing portions are respectively I-shaped cross section. A closed cross-section structure having a plurality of small closed cross-sections is formed by bending toward the flange portion on the other side, and engaging the tips of the two wing portions with the flange portion on the other side and welding. Structural member to be. 3. A steel mold having a cross-sectional shape in which blades are extended on both sides of a small closed cross section, is formed by extrusion or drawing, and both blades are directed toward one side surface of the small closed cross section. A structural member comprising a closed cross-section structure having a plurality of small closed cross sections, which is bent and the tips of the both blades are engaged with and welded to one side surface of the small closed cross section. 4. The structural member according to claim 3, wherein the small closed cross section is one of a triangle, a square, a rectangle, a circle, an ellipse, and a semi-elliptical shape. 5. The structural member according to claim 1, wherein the blade side end is cut so that the width of the blade of the shape steel continuously changes in the longitudinal direction of the shape steel. 6. A motorcycle comprising a vehicle body frame formed by using the structural member according to claim 1. 7. A motorcycle comprising a swing arm using the structural member according to any one of claims 1 to 5.