A constant force bicycle transmission

A prototype design for a human powered automatic transmission intended for use on an ordinary touring bicycle is presented. The transmission is intended to automatically adjust the gearing of the bicycle to maintain an optimum pedal force, regardless of the current riding conditions. Therefore, the transmission eliminates the need for the cyclist to manually adjust the bicycle gearing. The entire transmission is a self-contained unit designed to bolt onto the rear wheel of an otherwise unmodified 27-inch bicycle. The transmission combines a unique adaptation of a commercially popular continuously variable traction drive with a totally mechanical integral feedback controller. The features of the traction drive unique to its application to a bicycle are outlined in detail, along with an analysis of the important traction drive design parameters. The control system is also uniquely adapted to the requirements of bicycling. A detailed classical analysis of the controller is presented to verify its desirable performance characteristics. In addition, a numerical simulation of the transmission is included to accurately predict its performance under typical operating conditions. A knowledge of typical pedal force profiles for normal touring cycling is prerequisite for the design of the constant force bicycle transmission. This data has not been previously published. An instrumentation package was developed especially to determine this data. A description of the system and a summary of the results are presented. These results are reduced to a set of design criteria for the constant force transmission