Bicycle crank assembly
A bicycle sprocket crank assembly is comprised of first and second crank arms joined to a spindle. One of the crank arms and the spindle may be fabricated as a unitary structure, or both cranks arms may be formed as separate structures and joined together. In either case the spindle has at least a first coupling end with an internally tapped axial bore defined therein and the second crank arm forms at least a first socket at its axle end. At least a first wedging sleeve is provided and is disposed about the first coupling end of the spindle. The first wedging sleeve conforms to the shapes of both the first coupling end of the spindle and the hollow cavity in the first socket. Either the coupling end of the spindle or the hollow cavity is axially tapered, and the wedging sleeve is tapered to match. The wedging sleeve is split in an axial direction, so that as the first socket is drawn onto the first coupling end of the spindle, the wedging sleeve is increasingly forced in between the inner radial surface of the hollow cavity of the socket and the outer radial surface of the coupling end of the spindle.
1. A bicycle sprocket crank assembly, comprising:
a. a first crank arm comprising an axially oriented socket at a first end, said first socket having a hollow cavity defined therein;
b. a second crank arm comprising an axially oriented spindle at a first end, wherein and said spindle comprises a coupling end with an internally tapped axial bore defined therein and wherein said coupling end of said spindle is tapered such that said coupling end narrows in a cross-sectional area in an axial direction with increased distance from said second crank arm, wherein said coupling end of said spindle fits into said hollow cavity of said socket, and said coupling end and said hollow cavity are mating elements;
c. a wedging sleeve disposed about said coupling end of said spindle and said wedging sleeve comprises an inner surface that conforms to the shape of said coupling end and an outer surface that conforms to the shape of said hollow cavity, wherein said outer surface of said wedging sleeve is cylindrical in shape and said inner surface of said wedging sleeve is a frustoconical shape, and said hollow cavity of said first socket has a cylindrical, annular inner wall that completely radially surrounds said coupling end and said wedging sleeve, and said wedging sleeve is split longitudinally in an axial direction along the entire length of said wedging sleeve and thereby allowing for radial expansion of said wedging sleeve as said first coupling end of said spindle is advanced into said wedging sleeve and said hollow cavity of said first socket; and
d. a first threaded fastener comprising a shank engageable in said internally tapped axial bore of said coupling end, and a head that immobilizes said spindle and said first crank arm relative to each other to create a torsional connection between the first crank arm and the spindle and simultaneously eliminate axial movement in the wedging sleeve.
2. The bicycle sprocket crank assembly of claim 1 , wherein said wedging sleeve is an internally tapered split bushing.
3. The bicycle sprocket crank assembly of claim 2 , wherein said head of first threaded fastener bears against said wedging sleeve.
4. The bicycle sprocket crank assembly of claim 1 , wherein said second crank arm and said spindle are formed together as a unitary structure.
5. The bicycle sprocket crank assembly of claim 1 further comprising an annular stop spacer disposed about said first coupling end to hold said first and second crank arms at a spaced distance of separation from each other.