Machine element or mechanism – Elements – Cranks and pedals
Reexamination Certificate
1997-12-18
2001-05-08
Luong, Vinh T. (Department: 3682)
Machine element or mechanism
Elements
Cranks and pedals
C029S897200
Reexamination Certificate
active
06227070
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is directed to bicycle crank arms and, more particularly, to a bicycle crank arm that includes a shell to define an interior cavity or to hold a filler material.
It is desirable for a bicycle to be as lightweight as possible, so the bicycle parts should be reduced in weight as much as possible. This is true of bicycle cranks as well. A bicycle crank that is made lightweight by being manufactured in the form of a hollow tube is known from Japanese Patent Publication 2-18652, for example. Furthermore, a method for forming an internal cavity in a solid material by extrusion forging has also been proposed in Japanese Laid-Open Patent Application 5-116670. This hollow crank is obtained by the welding or plastic deformation of a pipe or crank billet, but this method affords little freedom in the design of the crank shape. The shape is further restricted because molding is impossible without certain portions that are otherwise unnecessary in terms of material dynamics, among other reasons. Another drawback is that a high quality appearance is difficult to achieve because of limitations in the machining process, despite demand for certain types of designs.
Methods for manufacturing a bicycle crank from a light alloy by casting are also known from Japanese Laid-Open Patent Application 58-93554. The shape restrictions noted above are eliminated with these casting methods, but forming a cavity on the inside is difficult with a crank because of the small size of the part and the hollow interior can degrade the mechanical strength of the product Accordingly, it has been proposed that a pipe or the like be integrally cast in the interior as shown in Japanese Laid-Open Utility Model Applications 48-7948 and 61-131391. Integrally embedding a pipe or other such member with high strength in the crank does indeed preserve the strength of the crank, but a problem remains in terms of making the product lightweight and strong at the same time.
SUMMARY OF THE INVENTION
The present invention is directed to a hollow bicycle crank that can be manufactured by casting while providing substantial design freedom. Such a crank can be lightweight while also being strong. In one embodiment of a bicycle crank according to the present invention, a crank arm for a bicycle includes a crank arm body having a pedal attachment hole on a first end thereof and a spindle attachment hole on a second end thereof The crank arm body defines an elongated interior cavity surrounded by a shell, wherein the interior cavity is open to an exterior of the crank arm body. The opening can be used to access the cavity during and after manufacturing. The shape of the cavity may be varied to produce a lightweight yet strong structure. For example, the interior cavity may have a substantially semicircular cross sectional shape in proximity to the spindle attachment hole and a substantially rectangular shape in proximity to the pedal attachment hole, and a cross sectional diameter of the cavity may decrease from a central portion of the crank arm body to the first and second ends of the crank arm body. The cavity may be filled with a material having a lower specific gravity than the metal forming the crank arm to provide strength while still saving weight.
In one embodiment of a method used to form the crank arm body according to the present invention, a mold core formed by a shell containing a sand-like filler material is positioned into a casting mold so that a melt space is formed around the mold core, molten metal is poured into the casting mold, and the molten metal is solidified to form a crank billet. The filler material may be removed through an opening in the crank billet. This may be accomplished by drilling the crank billet to form the pedal attachment hole in a location that communicates with the filler material and then removing filler material through the pedal attachment hole.
Since the crank of the present invention, and the manufacturing method therefor, have a core on the inside of the crank, the crank is lightweight and yet rigid. Furthermore, since the crank is manufactured by casting, it can be designed in any shape, allowing a greater degree of latitude in design, so it is easier to achieve a high-quality appearance. If the cast blank is also mold-forged, the product is lightweight and also has sufficient strength. Also, since a core containing a filler is positioned on the inside of the crank arm, the shape of the core is not flattened during mold forging.
REFERENCES:
patent: D. 265812 (1982-08-01), Kastan
patent: D. 384603 (1997-10-01), Chen
patent: D. 401539 (1998-11-01), Humphries et al.
patent: 2350468 (1944-06-01), Kraeft
patent: 4292368 (1981-09-01), Mialon
patent: 4295388 (1981-10-01), Mialon et al.
patent: 4425820 (1984-01-01), Swozil
patent: 4465392 (1984-08-01), Lang
patent: 4811626 (1989-03-01), Bezin
patent: 4841801 (1989-06-01), Tice
patent: 5125288 (1992-06-01), Amiet
patent: 5179873 (1993-01-01), Girvin
patent: 5197353 (1993-03-01), Trenerry et al.
patent: 5609070 (1997-03-01), Lin et al.
patent: 5690034 (1997-11-01), Schahl et al.
patent: 5852954 (1998-12-01), Yamanaka
patent: 5904072 (1999-05-01), Yamanaka
patent: 6079294 (2000-06-01), Mizobe
patent: 270388 A1 (1988-06-01), None
patent: 0850826 (1998-07-01), None
patent: 0850825 (1998-07-01), None
patent: 0850827 (1998-07-01), None
patent: 980071 (1951-05-01), None
patent: 981600 (1951-05-01), None
patent: 982352 (1951-06-01), None
patent: 48-7948 (1973-01-01), None
patent: 58-93554 (1983-06-01), None
patent: 60-13761 (1985-09-01), None
patent: 61-131391 (1986-08-01), None
patent: 61-150691 (1986-09-01), None
patent: 2-18652 (1990-04-01), None
patent: 5-116670 (1993-05-01), None
Patent Abstracts of Japan, vol. 7, No. 193, Aug. 24, 1983; for JP 58-093554 A (Arai), published Jun. 3, 1983.
Masahiro Yamanaka
Mizobe Eiji
Deland James A.
Luong Vinh T.
Shimano Inc.
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