AN OPTIMUM NONCIRCULAR CHAINWHEEL DESIGN FOR A BICYCLE DRIVE SYSTEM

A new and systematic approach for the analysis and simulation of a non -circular chainwheel in a bicycle drive system is presented. The propo sed leg-bicycle model is based on a five-bar linkage and explicit expr essions for the kinematics and kinetics are derived. The generated sha pe of the chainwheel is smoothed to an ellipse, for practical reasons. The performance of this elliptical chainwheel is assessed by comparin g the joint moments, leg angular accelerations, crank angular relociti es. crank angular accelerations and output forces with those of a conv entional circular chainwheel. The results suggest combining the ellipt ical and circular chainwheels into a single unit, in order to accommod ate a wide range of pedalling speeds. At low speeds, the elliptical ch ainwheel is engaged, but as the speed increases, a switch over to the circular chainwheel is recommended.