JP3507804B2 - Bicycle crank - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bicycle crank. More particularly, the present invention relates to a bicycle crank which is manufactured by casting a bicycle crank having a core therein to reduce its weight. 2. Description of the Related Art It is desirable to reduce the weight of a bicycle as much as possible. For this purpose, it is preferable that all bicycle parts be as lightweight as possible. Therefore, regarding bicycle cranks, for example, Japanese Patent Publication No. 2-186
As disclosed in Japanese Patent Publication No. 52-52, there has been known a method in which a tube is molded and manufactured, and the inside of a crank is made hollow to reduce the weight. A method has been proposed in which a cavity is formed inside a solid blank by extrusion forging (JP-A-5-11).
No. 6670). Since the hollow crank is formed by welding or plastically deforming the pipe or the crank material, the degree of freedom in designing the crank shape is small. Furthermore, even if there is a portion that is not necessary for material mechanics, the shape is restricted because molding is not possible. Furthermore, even if there is a request from the design, there is a problem that it is difficult to give a high-grade appearance to the external appearance due to processing restrictions. On the other hand, a manufacturing method for manufacturing a bicycle crank from a light alloy by a casting method is known (for example, Japanese Patent Application Laid-Open No. 58-93554). According to the casting method, the shape is released from the above-mentioned restriction, but it is difficult to hollow the inside with a crank which is a small part, and the mechanical strength is also poor. For this reason, pipes and the like are integrally cast therein (Japanese Utility Model Laid-Open Nos. 48-7948 and 61-131391). It is generally said that cast cranks have low mechanical strength. SUMMARY OF THE INVENTION The present invention has been made in view of the above technical background, and has as its object to achieve the following objects. An object of the present invention is to provide a bicycle crank having a high degree of freedom in design because it is manufactured by casting. Another object of the present invention is to provide a bicycle crank capable of obtaining sufficient strength while being light in weight because the cast crank material is forged. SUMMARY OF THE INVENTION The present invention provides a die forging after casting.
A crank for a bicycle which was granulated, the specific gravity than the metal constituting the crank to the crank inside lightly the
A filling material that withstands a compressive load due to die forging, and a pipe core made of a metal pipe-shaped outer cover that covers the filling material, wherein the filling material packed in the pipe core
Prevents the pipe core from being crushed by pressurizing the die forging.
It is characterized by the fact that The first embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a rear view of the left crank 1 of the present invention. The left crank 1 is made of an aluminum alloy. As shown in FIG. 1, the pedal shaft end 4 side where the pedal is mounted is thinner, and the crankshaft end 2 side where the pedal is mounted on a crankshaft (not shown) is thicker in cross section. It is formed as follows. By changing the thickness of the left crank 1 depending on the position in this manner, the strength is designed so that the stress applied to the left crank is made substantially constant in any cross section by changing the size of the cross-sectional area. Further, a chamfered portion 11 is formed at both rear corners of the left crank 1 (see FIG. 2). The crankshaft end 2 of the left crank 1 has a crankshaft mounting hole 5 for mounting the left crank 1 to the crankshaft.
The left crank 1 is mounted on the crankshaft by inserting a crank into the crankshaft mounting hole 5.
A pedal mounting hole 6 is formed in the pedal shaft end 4 of the left crank 1 on the pedal mounting side. One end of a pedal shaft (not shown) of the pedal is attached to the pedal attachment hole 6. FIG. 2 is a plan view of the left crank 1. FIG. FIG. 3 is a cross-sectional view when the left crank 1 is cut along the line III-III in FIG. A pipe core 7 made of pure aluminum is built in the pedal shaft end portion 4 side around the crank center portion 3 and the crank shaft end portion 2 side. The metal of the pipe core 7 may be the same as the metal constituting the left crank 1, but preferably has a specific gravity as low as possible, has heat resistance, and can withstand forging pressure as described later. FIG. 4 is a front view of the left crank 1. FIG. The sectional structure of the pipe core 7 is shown in FIG. FIG. 5 is a sectional view taken along the line aa, bb, cc, dd in FIG. FIG. 5A is a cross-sectional view taken along the line aa, and FIG.
5B is a cross-sectional view taken along arrow bb, FIG. 5C is a cross-sectional view taken along arrow cc, and FIG. 5D is a cross-sectional view taken along arrow dd. The weight is reduced by the pipe core 7 inside the central part 3 of the crank. Further, the pipe core 7 plays a certain role against mechanical stress such as bending. The cross-sectional structure of the pipe core 7 has a semicircular shape obtained by cutting a circle on the crankshaft end 2 side. The pipe core 7 has an opening 15 on the pedal shaft end 4 side. The opening 15 is formed in the inner cavity 14 of the pipe core 7 as described later.
It is communicated with. The inner cavity 14 is temporarily filled with a filler such as sand. The filler packed in the pipe core 7 prevents the pipe core 7 from being crushed by the pressure of hot forging. The product may be constituted in a state where the filler is filled without being taken out as described later. The pedal shaft end 4 has a flattened rectangular shape. The cross-sectional area of the pipe core 7 continuously decreases, and the height is minimized at both ends. That is, the shape of the pipe core 7 is substantially a so-called bottom shape. The weight is reduced by the pipe core 7 inside the central part 3 of the crank. The crankshaft end 2 is provided with a crankshaft mounting hole 5. A flange 8 is provided on the inner surface of the crankshaft mounting hole 5 so as to protrude toward the inner surface side.
A female serration 9 is provided in connection with the back side of the female. The serration 9 has eight teeth in this example as shown in FIG. If the number of teeth is small, the joint strength of the rotational connection is insufficient, and if the number of teeth is too large, machining is difficult and leads to an increase in cost, and errors are likely to occur in the indexing and positioning operation in the rotational direction during assembly. The portion of the crankshaft mounting hole 5 on the back side from the serration 9 is formed as a centering portion (also referred to as a guide portion) 10 which is a tapered hole. Centering part 10
Is a cylindrical tapered hole shape spreading on the back side, and in this example, the taper angle is formed at 2 to 3 °. Centering part 10
Is a centering portion 1 of a crankshaft (not shown).
The two cores are brought into close contact with each other by being brought into close contact with the zero taper surface, and the two are integrally and strongly connected. [Method 1 for Manufacturing Left Crank 1] The left crank 1 described above is manufactured by the following method. FIG. 6 is a sectional view showing a casting state of the left crank 1. Mold 20
Space 22 into which molten metal is poured between
Is partitioned. The melting space 22 is a space defined so as to substantially correspond to the left crank 1, but is slightly larger in consideration of shrinkage of the molten metal. The pipe core 7 is inserted and arranged in the melting space 22. The pipe core 7 is made by baking foaming volcanic glass. FIG. 7 is an oblique axis projection view showing the appearance and the inside of the pipe core 7. A sand-like filler 32 such as volcanic glass is put into the inner hole 30 of the pipe core 7. Filler 32
May be any as long as it can withstand the heat resistance to the molten metal and the compressive load due to forging described later. After filling the filling material 32, the pipe core 7 is pressurized and both ends are sealed with flat portions 33 and 34 provided. One flat portion 33 is integrally cast and fused with the molten metal to form the crankshaft end 4 of the left crank 1. As shown in FIG. 6, the core 7 is positioned in the melting space 22. In order to accurately position the core 7 in the melting space 22, the core 7 is positioned by a spacer 26 made of styrene foam or the like. The melting space 22 communicates with a pouring port 28 via a runner 27. The molten aluminum alloy is poured from a pouring port 28, passes through a runner 27 and enters the melting space 22. The molten metal applies pressure to the melting space 22 by gravity. This casting method is a so-called gravity mold casting method in which ordinary casting is performed with only the pressure of gravity without applying any special pressure to the molten metal. However, cavities and the like may occur in the internal metal structure only by casting. After this casting, die forging is performed with the pipe core 7 placed in the crank blank 29. The die forging is performed by hot forging while being placed on a semi-closed mold 35 for semi-closed die forging. FIG. 8 is a sectional view showing a state where the crank blank 29 is put in the lower mold 36. The lower mold 36 is placed on the crank blank 29. After the crank blank 29 is heated to a required temperature and placed on the lower mold 36, the upper blank 37 presses the same to perform forging. By this hot forging, the length, thickness, thickness, and surface of the cast crank material 29 are accurately processed, and the material of the crank material 29 is forged and homogenized to enhance the mechanical strength. Since the pipe core 7 formed by the hot forging is forged in a state of being placed in the crank blank 29, the pipe core 7 is not crushed and the core shape is secured. Since the crank blank 29 is in a state where the filler 32 is packed in the pipe core 7, it is necessary to take out this. As shown in FIG. 9, a drill 39 is used to make a drill hole in the pedal mounting hole 6 of the crank blank 29 to open the opening 1.
From 5, the filler material 32 is taken out. Also, an extra flat portion 3
The part 3 is also cut. Thereafter, the shape of the left crank 1 shown in FIGS. 1 to 5 is completed by machining such as cutting, grinding, and polishing. EXAMPLES The following fillers 32 were used. Product name: "Terra Balloon", Calseed Co., Ltd. (No. 8-2, Goi-minamikaigan, Ichihara-shi, Chiba) Components (% by weight): SiO ₂ (77.3), Al ₂ O ₃ (1
2.8), Fe ₂ O ₃ (1.7), CaO (1.0), M
_{gO (0.1), Na 2 O} (3.2), K 2 O (2.
9), TiO ₂ (0.2), residual component (0.9) Particle size (μm): 9.41 (10%), 27.71 (50)
%), 71.32 (90%) Density: Light packing density 0.30, Heavy packing density (0.46), Particle density (1.14) Heat resistance temperature (degree C): 1,100 [Other embodiments] In the above-described embodiment, the filler 32 in the pipe core 7 is taken out after forging. However, as shown in FIG. 10, the filler 32 may be filled in the pipe core 7 without being taken out. In addition, volcanic glass was used as the filler, but the specific gravity was lower than that of the base metal, such as natural pumice, foamed gypsum, etc. Other filler materials may be used as long as they are certain. The crank of the present invention has a core inside the crank, so that the crank was lightweight and rigid. In addition, since the crank is manufactured by casting, the shape can be designed in any manner, and the degree of freedom in design is increased, so that it is easy to give a high-quality appearance to the appearance. Further, since the cast blank is die-forged, sufficient strength can be obtained while reducing the weight. Further, since the core having the filler incorporated therein is disposed therein, the shape of the core does not collapse even in die forging.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a rear view of a left crank 1 according to the present invention. FIG. 2 is a plan view of the left crank 1 of the present invention. FIG. 3 is a cross-sectional view of the left crank 1 as viewed from the side. FIG. 4 is a front view of the left crank 1. FIG. FIG. 5 is a diagram showing aa, bb, and c- in FIG.
It is each arrow sectional drawing in a c, dd cutting line. FIG. 5 (a)
FIG. 5B is a cross-sectional view taken along the arrow line a-a, FIG.
FIG. 5C is a cross-sectional view taken along a line cc, and FIG. 5D is a cross-sectional view taken along a line dd. FIG. 6 is a sectional view showing a casting state of the left crank 1. FIG. 7 is an oblique axis projection view showing a core type. FIG. 8 is a cross-sectional view showing a state in which a crank blank 29 is put in a semi-closed mold 30. FIG. 9 is a diagram showing a method of removing a filler from a pipe core 7 after forging. FIG. 10 is a sectional view showing another embodiment of the crank blank. [Description of Signs] 1 ... Left crank 2 ... Crank shaft end 3 ... Crank center 4 ... Pedal shaft end 5 ... Crank shaft mounting hole 7 ... Pipe core 29, 40 ... Crank material 30 ... Core mold 35 ... Semi-hermetic Mold

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B62M 3/00 B21K 1/08

Claims (1)

(1) A bicycle crank subjected to die forging after casting , wherein the specific gravity of the crank inside the crank is smaller than that of a metal constituting the crank, and the compression load due to the die forging is reduced. It has a pipe core consisting of an endurable filling material and a metal pipe-shaped outer cover that covers the filling material, and the filling material packed in the pipe core is formed by the die forging.
A crank for a bicycle , wherein the pipe core is prevented from being crushed by pressurization .