JP2006290139A - Bicycle and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a bicycle and its manufacturing method capable of increasing sufficiently the bonding strength of a joining part of a head pipe and assuring good workability using a small number of part items. <P>SOLUTION: In the joining place of the head pipe 4 with a main pipe 5, a backward extended part 21 extended cylindrically approximately to the back and a forward extended part 23 extended forward so that the diameter of the head pipe 4 in its front becomes larger are integrally formed by the bulge forming process, and with the backward extended part 21 inserted in the main pipe 5 along its forefront inside circumferential surface, the forefront of the main pipe 5 is joined with the head pipe 4 by welding. The forefront of the main pipe 5 is joined with the head pipe 4 only by welding by butting the forefront of the main pipe 5 to the head pipe 4 by externally fitting the forefront of the main pipe 5 to the backward extended part 21, which requires easy locating process, and provides easy working requiring less labor. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a bicycle and a manufacturing method thereof, and more particularly, to a frame structure at a joint portion of a head pipe with a main pipe and a manufacturing method thereof.

  The main pipe is joined to the head pipe that forms part of the bicycle frame, and if more strength is required, a sub pipe (so-called upper pipe) is joined in addition to the main pipe (so-called lower pipe). .

  As this joining structure, as shown in FIG. 9A, the front end surface of the main pipe 52 is directly brought into contact with the rear surface portion of the head pipe 51 and joined by brazing or welding. As shown in FIG. 2, a rear bulge portion (so-called outer lug) 53 that bulges rearward is formed in the head pipe 51, and the front end portion of the main pipe 52 is inserted into the rear bulge portion 53. The rear end surface of the protruding portion 53 and the main pipe 52 are joined by brazing or welding.

  Note that the head pipe 51 and the main pipe 52 each have a perfect circular cross section, and the joining portion has a perfect circular cross section. Further, when a lower pipe as a main pipe and an upper pipe as a sub pipe are provided, they are joined with the same joining structure.

  By the way, BMX type bicycles (motocross bicycles) and MTB type (mountain bike types) bicycles often run on uneven road surfaces or jump with the bicycle and land. An extremely large impact or force acts on the bicycle frame. At the joint between the head pipe 51 and the main pipe 52, when the bicycle is jumped and landed, the weight of the driver acts as a force that pushes down the pedal and saddle downward due to inertia. As a result, the main pipe 52 side A force to push down the head pipe 51 to the joint portion of the head pipe 51 acts, and at the upper portion of the joint portion between the head pipe 51 and the main pipe 52, a force pulling the head pipe 51 toward the main pipe 52 is generated. At the lower part of the joint with 52, a compressive force is generated to press the head pipe 51 by the main pipe 52. When a person who is not used to this type of driving performs a failure jump, a particularly large impact or force may be applied.

  However, in the structure shown in FIG. 9A, the head pipe 51 and the front end surface of the main pipe 52 are simply brought into contact with each other and joined by brazing, welding, or the like. When it acts, there exists a possibility that a junction part may fracture | rupture or may be damaged.

  In the structure shown in FIG. 9B, since the rear bulge 53 is integrally formed with the head pipe 51, the structure has a higher strength than the structure simply joined as shown in FIG. 9A. However, since tensile stress and compressive stress are concentrated on the connection portion 54 between the head pipe 51 and the rear bulge portion 53, there is a possibility that the breakage and damage of the connection portion 54 cannot be reliably prevented.

  In order to cope with such a problem, there is one disclosed in Patent Document 1 for improving the joint strength between pipes. As shown in FIGS. 10A and 10B, when the second pipe 62 corresponding to the main pipe is joined to the first pipe 61 corresponding to the head pipe, the pipe shape is formed at the end of the second pipe 62. The joining core 63 is inserted so that only the cut end face portion is slightly exposed, the slightly exposed cut end face portion of the joining core 63 and the first pipe 61 are brought into contact with and brought into contact with each other, and A pipe joining method is disclosed in which the end of the second pipe 62 and the first pipe 61 are welded together. In FIGS. 10A and 10B, reference numeral 64 denotes a through hole for temporarily fixing the joining core 63 to the end of the second pipe 62.

  According to this joining structure, since the end portions of the first pipe 61 and the second pipe 62 are joined to each other at the same time, the joining core 63 is also provided and joined. There is an advantage that can be increased.

Further, the joining core 63 is inserted into the end portion of the second pipe 62, and in the state where the first pipe 61 and the second pipe 62 are joined, the joining core 63 is not exposed to the outside and the uneven portion is formed. Therefore, there is an advantage that the appearance of the joint portion is good. That is, as shown in FIG. 9B, in the structure in which the front end portion of the main pipe 52 is inserted into the rear bulge portion 53 integrally formed with the head pipe 51, the rear bulge portion 53 is exposed to the outside. At the same time, a step is formed with respect to the main pipe 52 at the rear end portion of the rear bulge portion 53, so that the appearance of the joint portion is not so good. On the other hand, such a problem does not occur in the structure in which the joining core 63 is inserted into the end of the second pipe 62 as described above.
JP 2001-58264 A

  However, when the structure as shown in Patent Document 1 is adopted, in addition to the first pipe 61 corresponding to the head pipe and the second pipe 62 corresponding to the lower pipe, which are joined to each other, another Since the joining core 63 is required as a component, the number of components is large, and a lot of labor and time are required. Therefore, there are problems that workability is poor and manufacturing cost is high.

  The present invention solves the above-described problem, and provides a bicycle that can sufficiently increase the joint strength of the joint portion of the head pipe and at the same time has a small number of parts and good workability, and a method for manufacturing the same. It is intended to do.

  In order to solve the above-described problem, the bicycle of the present invention has a head pipe with a rear bulging portion that bulges substantially rearward in a tubular shape at a connection point with the main pipe, and a large pipe diameter in the forward direction of the head pipe. A front bulge portion that bulges forward so that the front bulge portion is integrally formed by a bulge forming method and the rear bulge portion is inserted along the inner periphery of the front end portion of the main pipe. The part and the head pipe are joined by welding or brazing.

  With the above configuration, the front end of the main pipe and the head pipe are joined by welding or brazing in a state where the rear bulge is inserted along the inner periphery of the front end of the main pipe. The force acting from the main pipe side to the head pipe side when jumping and landing, etc., is the joint between the front end portion of the main pipe and the head pipe, the rear bulge portion inserted into the main pipe, and the main pipe. It is possible to obtain a strength that can be sufficiently endured even when an extremely large force or impact force is applied. In addition, since the rear bulge is integrally formed with the head pipe, the number of parts can be reduced, and when the front end of the main pipe is joined to the head pipe, the front end of the main pipe is It only needs to be abutted and welded to the head pipe while being externally fitted to the bulging portion, and positioning is easy, and workability is good because there is no need to weld the core as in the prior art.

  In addition, since the front bulge portion that bulges forward is integrally formed at the location where the main pipe of the head pipe is joined, the sectional shape of the head pipe in the plan view of the head pipe provided with the front bulge portion is provided. The front and rear diameters are larger than the left and right diameters. As a result, the strength in the front-rear direction at the location where the front bulge of the head pipe is provided increases, and a large impact or force is applied from the main pipe side to the head pipe. Even if it acts, sufficient joint strength can be obtained without the main pipe being deformed or damaged.

  Further, since the head pipe is provided with a front bulge portion and a rear bulge portion, when the head pipe is manufactured using the bulge forming method, the pipe material is not only the rear bulge portion but also the front bulge portion. It can also flow into the exit side satisfactorily and can be manufactured with a uniform thickness. That is, for example, when a head pipe having only a rear bulge portion is manufactured using a bulge method, the front side of the head pipe opposite to the rear bulge portion is thick, Although the thickness is non-uniform and there is a risk of stress concentration when an external force is applied, the head pipe can be manufactured satisfactorily without causing such problems.

  Further, the present invention is characterized in that the rear bulge portion and the front end portion of the main pipe into which the rear bulge portion is inserted are formed in a different shape so that the vertical diameter is larger than the left and right diameters. .

  With this configuration, the strength in the vertical direction at the joint portion of the main pipe with the head pipe is particularly large, and even when a very large impact or force is applied in the vertical direction, the joint portion between the head pipe and the main pipe is broken. It is possible to more reliably prevent damage.

  In addition, even when the main pipe and the sub pipe are joined to the head pipe, similar effects can be obtained at the joint between the head pipe and the main pipe and the joint between the head pipe and the sub pipe. .

  In addition, by opening the rear end surface of the rear bulge and communicating with the inside of the main pipe, when the head pipe and the main pipe are made of titanium and are welded by TIG welding, the head pipe and the main pipe are inserted into the joint portion. An inert gas can be poured in and good welding can be performed without oxidizing the joint.

  As described above, according to the present invention, the head pipe has a rear bulging portion that bulges substantially rearward in a cylindrical shape at a connection position with the main pipe, and a forward pipe diameter of the head pipe is increased. A front bulge portion that bulges forward is integrally formed by a bulge forming method, and the front end portion of the main pipe and the head are inserted with the rear bulge portion being inserted along the inner periphery of the front end portion of the main pipe. When the pipe is welded or brazed and joined, the force acting from the main pipe side to the head pipe side when jumping and landing with the bicycle is applied to the joint between the front end of the main pipe and the head pipe. In addition, it is distributed and received in the rear bulge part inserted in the main pipe and the connection part of the main pipe, and it is possible to obtain sufficient strength to withstand even when extremely large force or impact force is applied. Reliability is improved. In addition, since the rear bulge is integrally formed with the head pipe, the number of parts can be reduced, and positioning at the time of joining is easy, and there is no need to weld the core as in the prior art. Therefore, workability is good. Further, since the rear bulge portion is inserted into the front end portion of the main pipe, the rear bulge portion is not exposed to the outside, and the appearance of the joint portion is good.

  In addition, since the front bulge portion that bulges forward is integrally formed at the location where the main pipe of the head pipe is joined, the sectional shape of the head pipe in the plan view of the head pipe provided with the front bulge portion is provided. The front and rear diameters are larger than the left and right diameters. As a result, the strength in the front-rear direction at the location where the front bulge of the head pipe is provided increases, and a large impact or force is applied from the main pipe side to the head pipe. Even when it acts, a sufficient joint strength is obtained without the main pipe being deformed or damaged, and this also improves the reliability.

  Furthermore, since the head pipe has a front bulge and a rear bulge, when this head pipe is manufactured using the bulge molding method, the pipe material is good not only in the rear but also in the front. It is possible to manufacture by making the thickness uniform and making the thickness uniform, and it is possible to prevent the thickness from fluctuating greatly and producing a weak portion in strength, which also improves the reliability.

Hereinafter, a bicycle according to an embodiment of the present invention and a bicycle frame used in the bicycle will be described with reference to the drawings.
FIG. 1 is an overall side view of a bicycle according to an embodiment of the present invention, and FIG. 2 (a) is a side view of a bicycle frame. As shown in FIGS. 1 and 2A, the bicycle frame 1 used in the bicycle is made of, for example, titanium. The bicycle frame 1 includes an upper portion of a front fork 2 and a steering column 3. Is connected to the head pipe 4, the main pipe 5 called the so-called lower pipe, the sub-pipe 6 called the so-called upper pipe, and the rear end of the sub-pipe 6 and the seat post. 7 is inserted, a back fork 9 extending obliquely downward from the upper portion of the standing pipe 8, and a hanger lug (or round pipe) joined to the lower end portion of the standing pipe 8 and the rear end portion of the main pipe 5. The chain stay 10 extends rearward from 13. Further, the front wheel 11 is rotatably supported by the lower end portion of the front fork 2, and the rear wheel 12 is rotatably supported at the rear end joint portion of the back fork 9 and the chain stay 10. A crankshaft 14 is rotatably supported in a hanger lug (or round pipe) 13 that joins the rear end of the main pipe 5 and the front end of the chain stay 10. Reference numeral 15 denotes a handle, 16 denotes a pedal, and 17 denotes a saddle.

  The front end portions of the sub pipe 6 and the main pipe 5 are joined to the rear surface portion of the head pipe 4. As shown in FIGS. 2A and 2B to FIG. 4, the head pipe 4 swells in a cylindrical shape substantially backward (in detail, obliquely downward toward the rear) at the connection point with the main pipe 5. The sub-rear bulging portion 22 that bulges in a substantially rearward direction (specifically, substantially rearward in the horizontal direction) at the connection location between the rear bulge portion 21 and the sub-pipe 6, and the connection location between the main pipe 5 and the sub-pipe 6 A front bulge portion 23 that bulges forward so that the diameter in the front direction of the head pipe 4 increases in detail (specifically, the forward extension direction of each axis of the main pipe 5 and the sub pipe 6) is a bulge forming method described later. Are integrally formed. And in the state where the rear bulge portion 21 is inserted so as to be along the outer periphery inner periphery of the front end portion of the main pipe 5 (that is, the state where the front end portion of the main pipe 5 is externally fitted to the rear bulge portion 21), The front end portion of the main pipe 5 and the head pipe 4 are welded and joined, and the sub-rear bulging portion 22 is inserted so as to follow the outer periphery of the front end portion of the sub pipe 6 (that is, the front end portion of the sub pipe 6 In a state of being externally fitted to the sub rear bulging portion 22), the front end portion of the sub pipe 6 and the head pipe 4 are welded and joined.

  In particular, as shown in FIGS. 3C, 4A, and 4B, the rear bulge 21 and the front end of the main pipe 5 into which the rear bulge 21 is inserted are vertically The diameter L1 is larger than the left and right diameter L2 and is formed in a deformed shape that is pointed in the vertical direction (more specifically, the upper surface is flat and bulges vertically downward, and the lower end is pointed in a triangular shape) Has been. Further, as shown in FIGS. 3B, 4A, and 4B, the sub rear bulge portion 22 and the front end portion of the sub pipe 6 into which the sub rear bulge portion 22 is inserted have its vertical diameter. L3 is larger than the left and right diameter L4, and is formed in a deformed shape that is pointed in the vertical direction (more specifically, the bottom surface is flat and bulges upward in a vertically long state, and the upper end is pointed in a triangular shape). ing. As shown in FIGS. 3 and 4, the rear end surfaces of the rear bulge portion 21 and the sub rear bulge portion 22 are opened, and the head pipe 4 internal space, the main pipe 5 internal space, and the head pipe 4 The internal space and the internal space of the sub pipe 6 are communicated with each other.

  Further, since the front bulging portion 23 bulging forward is integrally formed at the connecting portion of the main pipe 5 and the sub pipe 6 in the head pipe 4, as shown in FIG. The front and rear diameter L5 of the cross-sectional shape of the head pipe 4 provided with 23 is larger than the left and right diameter L6. In particular, the head pipe 4 is formed in an irregular shape such that the front bulging portion 23 has a sharp tip. . As shown in FIG. 3D, the upper end portion and the lower end portion of the head pipe 4 have a perfectly circular cross section, and the upper portion of the front fork 2 and the steering column 3 can be held in a freely rotatable manner from the outer peripheral side. It is like that.

The rear bulge portion 21, the sub rear bulge portion 22, and the front bulge portion 23 of the head pipe 4 are integrally formed by a bulge forming method (hydroforming) as follows.
As shown in FIGS. 5 and 6, the bulge forming apparatus includes an upper die 31 having a first concave portion 30 having a shape corresponding to the front bulging portion 23 according to the shape of the head pipe 4 as a product, and a rear portion. In a space formed by the lower mold 34 having the second concave portion 32 having a shape corresponding to the bulging portion 21 and the third concave portion 33 having a shape corresponding to the sub-rear bulging portion 22, and the upper die 31 and the lower die 34. And pistons 35 and 36 that can be moved back and forth from the left and right, as shown in FIGS. 5 (c), 6 (a), and 6 (b). A fluid (liquid or fluid) 39 can be introduced into the head pipe material 4 ′ through the introduction paths 37 and 38.

  First, as shown in FIG. 5 (a), a head pipe member 4 'made of a titanium material having a circular cross section has a first recess 30 having a shape corresponding to the shape of the product, that is, the front bulging portion 23. Set between the mold 31 and the lower mold 34 having the second concave portion 32 having a shape corresponding to the rear bulge portion 21 and the third concave portion 33 having a shape corresponding to the sub rear bulge portion 22 (in practice, It is placed on the lower die 34).

Next, as shown in FIG. 5B, the upper die 31 is lowered onto the lower die 34 to press down the head pipe material 4 ′.
Thereafter, as shown in FIG. 5 (c), the left and right pistons 35, 36 are advanced until they come into contact with both ends of the head pipe material 4 ′ to be sealed, and the head pipe is passed through the fluid introduction paths 37, 38. Fluid is injected into the material 4 '. Then, as shown in FIG. 6A, the fluid pressure is increased until the head pipe material 4 ′ is slightly expanded.

  Further, as shown in FIG. 6B, the fluid pressure is further increased, and the left and right pistons 35 and 36 are allowed to enter the space between the upper die 31 and the lower die 34, so that the head pipe material 4 ′ The front bulge portion 23, the rear bulge portion 21, and the sub-rear bulge portion 22 are integrally formed. However, at this time, the rear bulge portion 21 and the sub rear bulge portion 22 remain in a shape in which the end surfaces are closed.

  When the molding is completed, as shown in FIG. 6 (c), after discharging the fluid, the upper die 31 is raised and the pistons 35 and 36 are retracted, and the front bulging portion 23 and the rear bulging portion 21, The head pipe material 4 ′ in which the sub rear bulge portion 22 is integrally formed is taken out. It should be noted that the portions 34a and 34b of the lower mold 34 are configured in advance to be separable as necessary so that the head pipe material 4 'can be easily taken out.

  Thereafter, as described above, the front bulge portion 23, the rear bulge portion 21, and the sub rear bulge portion 22 are integrally formed with the rear bulge portion 21 and the sub rear bulge portion 22. As shown in FIG. 7A, the rear bulging portion 21 and the sub rear bulging portion 22 are opened. In this case, the end surfaces of the rear bulge portion 21 and the sub rear bulge portion 22 may be simply opened by opening holes. Further, if necessary, both ends of the head pipe material 4 ′ are processed so that an upper portion of the front fork 2 and a mounting portion for a small head portion and a crown portion (not shown) that rotatably receive the steering column 3 are provided. Form. Thereby, the head pipe 4 is completed.

  Thereafter, as shown in FIG. 7B, the front end of the main pipe 5 is externally fitted to the rear bulge 21 so that the rear bulge 21 of the head pipe 4 is inserted into the front end of the main pipe 5. The head pipe 4 is butted against the rear surface portion, and the head pipe 4 and the front end portion of the main pipe 5 are welded by TIG welding. Although not shown, when performing this welding operation, the outside of the joint portion between the head pipe 4 and the main pipe 5 is filled with an inert gas such as argon gas, or an inert gas is ejected from the welding torch. Welding and filling the inside of the head pipe 4 and the main pipe 5 with an inert gas from the inside through the opening of the rear bulge portion 21 while preventing the welded portion from being oxidized and nitrided To do.

  Finally, as shown in FIG. 7C, the front end portion of the sub-pipe 6 is sub-rearly swelled by the same welding method so that the sub-rear bulge portion 22 of the head pipe 4 is inserted into the front end portion of the sub-pipe 6. The head pipe 4 and the front end portion of the sub-pipe 6 are welded by TIG welding.

  With the above configuration, the front end portion of the main pipe 5 and the head pipe 4 are welded and joined in a state in which the rear bulge portion 21 is inserted along the inner periphery of the front end portion of the main pipe 5. The force acting from the main pipe 5 side to the head pipe 4 side when jumping and landing, for example, is a welded joint between the front end portion of the main pipe 5 and the head pipe 4 and the rear portion inserted in the main pipe 5. It is received in a distributed manner between the bulging portion 21 and the abutting connection portion between the main pipe 5, and it is possible to obtain sufficient strength to withstand even when an extremely large force or impact force is applied. Moreover, since the back bulging part 21 is inserted in the front-end part of the main pipe 5, the back bulging part 21 is not exposed outside, and the external appearance of a joining location is favorable.

  Further, since the rear bulge portion 21 is integrally formed with the head pipe 4, the number of parts can be reduced, and when the front end portion of the main pipe 5 is joined to the head pipe 4, the main pipe 5 It is only necessary to abut the head pipe 4 while welding the front end portion to the rear bulge portion 21 and weld it. The positioning is easy, and the labor for welding the core is not required as in the prior art. It is good.

  Further, since the front bulging portion 23 that bulges forward is integrally formed at the location where the main pipe 5 is joined in the head pipe 4, the head pipe 4 provided with the front bulging portion 23 is provided. The front-rear diameter of the cross-sectional shape in plan view is larger than the left-right diameter, and as a result, the strength in the front-rear direction at the location where the front bulge portion 23 of the head pipe 4 is provided becomes extremely large. Even when a large impact or force is applied to the pipe 4, it is possible to obtain a sufficient bonding strength without causing the main pipe 5 to be deformed or damaged.

  Further, the head pipe 4 is provided with a front bulging portion 23 bulging forward, a rear bulging portion 21 bulging rearward, and a sub rear bulging portion 22. When manufactured using a construction method, the pipe material flows well not only to the rear bulge portion 21 and the sub rear bulge portion 22 but also to the front bulge portion 23 side, and is manufactured with a uniform thickness. Can do. That is, for example, when a head pipe having only a rear bulge portion is manufactured using a bulge method, the front side of the head pipe opposite to the rear bulge portion is thick, Although the thickness becomes non-uniform and there is a risk of stress concentration when an external force is applied, the head pipe 4 can be manufactured satisfactorily without causing such problems.

  Further, the rear bulge portion 21 and the sub rear bulge portion 22 and the front end portions of the main pipe 5 and the sub pipe 6 in which these portions are inserted are formed so that the vertical diameter thereof is larger than the left and right diameters. Therefore, the strength in the vertical direction at the joint of the main pipe 5 and the sub pipe 6 with the head pipe 4 is greater than the strength in the horizontal direction, and even when a very large impact or force is applied in the vertical direction, It is possible to more reliably prevent the joint portion between the main pipe 5 and the sub pipe 6 from being broken or damaged, and extremely good reliability can be obtained.

  Further, the rear end surface of the rear bulge portion 21 and the sub rear bulge portion 22 are opened and communicated with the inside of the main pipe 4, so that the head pipe 4, the main pipe 5 and the sub pipe 6 are made of titanium and welded by TIG welding. In this case, the inert gas can be poured into the joint between the head pipe 4 and the main pipe 5 and the sub-pipe 6 and can be welded well without oxidizing the joint. Reliability is improved.

  Moreover, as shown in FIG. 8, you may further provide and weld the reinforcement board 25 which receives the front-end lower surface location of the main pipe 5 from the downward direction, According to this, the front-end part of the main pipe 5 may be pressed below. The force and impact which are compressed can be received still more favorably.

  In the above embodiment, the case where the fluid (liquid or fluid) 39 is introduced into the head pipe material 4 ′ through the fluid introduction paths 37 and 38 in the bulge forming method (hydroforming) has been described. The present invention is not limited to this, and a rubber body that can introduce fluid into the inside may be inserted.

  In the above embodiment, a case where a titanium material is used as the bicycle frame 1 is described. In this case, TIG welding as described above is suitable, but other materials (aluminum, iron, iron alloy, aluminum) are used. It is also possible to use an alloy or the like. In the case of iron or an alloy material in which various materials are mixed with iron, it may be joined by brazing instead of welding.

  In the above-described embodiment, the case where the sub pipe 6 is also described. However, the present invention is not limited to this, and it is needless to say that the present invention can be applied to a bicycle having only the main pipe 5.

  The bicycle of the present invention is useful not only for BMX type bicycles and MTB type bicycles but also for various types of bicycles such as general bicycles and folding bicycles.

1 is an overall side view of a bicycle according to an embodiment of the present invention. (A) is a side view of the bicycle frame of the same bicycle, (b) is an enlarged side sectional view of the main part thereof. (A) is a side view of a head pipe of the bicycle frame, (b) is an end view of a sub-rear bulge portion of the head pipe, (c) is an end view of a rear bulge portion of the head pipe, (d) ) Is an end view taken along line dd of FIG. 3A, and FIG. 5E is an end view taken along line ee of FIG. (A) And (b) is a perspective view of a head pipe, respectively. (A)-(c) is sectional drawing which shows simply the manufacturing process of the head pipe of this invention using the bulge forming method, respectively. (A)-(c) is sectional drawing which shows simply the manufacturing process of the head pipe of this invention using the bulge forming method, respectively. (A)-(c) is sectional drawing which shows simply the manufacturing process of the head pipe of this invention, and the joining process of a main pipe and a subpipe, respectively. It is side surface sectional drawing of the head pipe of the bicycle which concerns on other embodiment of this invention. (A) And (b) is side sectional drawing which shows the connection structure of the conventional pipe, respectively. (A) And (b) is a schematic side view which shows the other conventional connection method of a pipe.

Explanation of symbols

1 Bicycle frame 4 Head pipe 4 'Head pipe material 5 Main pipe (lower pipe)
6 Sub-pipe (upper pipe)
21 Rear bulging portion 22 Sub rear bulging portion 23 Front bulging portion 25 Reinforcing plate 30 First concave portion 31 Upper die 32 Second concave portion 33 Third concave portion 34 Lower die 35, 36 Piston

Claims (6)

The head pipe has a rear bulging portion that bulges substantially rearward in a cylindrical shape at a connection point with the main pipe, and a front bulging portion that bulges forward so that the pipe diameter in the forward direction of the head pipe increases. Is integrally formed by the bulge molding method,
A bicycle characterized in that the front end of the main pipe and the head pipe are joined by welding or brazing in a state where the rear bulge is inserted along the inner periphery of the front end of the main pipe.   The bicycle according to claim 1, wherein the rear bulge portion and the front end portion of the main pipe into which the rear bulge portion is inserted are formed in an irregular shape so that the vertical diameter is larger than the left and right diameters. . The head pipe has a rear bulge portion, a sub-rear bulge portion that bulges substantially rearward at the connection location with the sub-pipe, and a head pipe having a forward diameter at the confrontation of the connection location between the main pipe and the sub-pipe. A front bulge portion that bulges forward so as to become larger is integrally formed by a bulge molding method,
In a state where the rear bulge portion is inserted along the inner periphery of the front end portion of the main pipe, the front end portion of the main pipe and the head pipe are joined by welding or brazing,
2. The front end portion of the sub pipe and the head pipe are joined by welding or brazing in a state where the sub rear bulge portion is inserted along the inner periphery of the front end portion of the sub pipe. Or the bicycle according to 2.   The bicycle according to any one of claims 1 to 3, wherein a rear end surface of the rear bulge portion is opened and communicated with the inside of the main pipe.   The bicycle according to any one of claims 1 to 4, wherein the head pipe and the main pipe are made of titanium. A bulge forming step of forming a front bulge portion bulging forward and a rear bulge portion bulging in a cylindrical shape on the titanium head pipe by a bulge forming method so that the pipe diameter increases. ,
After this bulging portion forming step, an opening step for forming an opening at the rear end portion of the rear bulging portion;
A butting process in which the front end of the main pipe is externally fitted to the rear end of the head pipe so that the rear bulge is inserted into the front end of the titanium main pipe;
A bicycle manufacturing method comprising: a welding step of welding a head pipe and a front end portion of a main pipe attached to the head pipe by TIG welding.

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