Abstract: 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, 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. In the method used to form the crank arm body according to the present invention, a sand mold core is positioned into a casting mold so that a melt space is formed around the sand mold core, molten metal is poured into the casting mold, and the molten metal is solidified to form a crank billet. Sand is preferably 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 sand mold and then removing sand through the pedal attachment hole.
Abstract: A bicycle crank arm assembly for a bicycle is designed for mounting a sprocket thereto. The crank arm has a centrally located hub portion, a crank portion extending radially outwardly from the hub portion and at least three fastening fingers extending radially outwardly from the hub portion. The fastening fingers are designed to have substantially the same stiffness at their free ends. This can be accomplished in a variety of ways such as change the cross-section of the fastening fingers adjacent the crank portion or changing the shape of the sprocket mounting portions of the fastening fingers. Also, in certain embodiments, the fastening fingers adjacent the crank portion are constructed such that their rear surfaces lie in the same plane as the rear surface of the crank portion adjacent thereto, or in a lower plane.
Abstract: A curved, tetrahelix bicycle crank arm composed of a helical array of tetrahedra. This design will transmit the propelling force away from the top dead center point providing more efficient use of the propelling energy. With this Tetrahelical design a hollow core is possible that will reduce weight and permit lubrication if needed without reducing strength. This design is also applicable to the connecting rod of internal or external combustion engine.
Abstract: A bicycle crank assembly utilizing a hollow crank arm is disclosed. The crank arm is welded to a hub for mounting to an axle and reinforced using a doubler provided at a point of maximum stress to minimize the likelihood of breakage at the maximum stress point. The resulting bicycle crank assembly exhibits reduced weight without a substantial reduction of torsional or bending strength.