Designing a high-efficiency hydrostatic bicycle transmission

Abstract

Hydrostatic bicycle drives use a working fluid instead of the common roller-chain to transmit power to the drive wheel. These transmissions are typically considered too inefficient for human power applications. An experiment consisting of a very simple hydrostatic drive was designed and built in an attempt to measure the efficiency of these devices at approximate cycling speeds. A theoretical model was also developed to help predict losses using a wider range of operational parameters. Due to shortcomings of the experiment design, the measured efficiencies were on the order of 60% - considerably lower than those theoretically possible. Although the experimental results are of limited value, this study highlights the importance of minimizing side-loading on hydraulic cylinder piston-rods during low-speed, low-pressure operation. The research is used to suggest several design features which may aid in continued attempts to develop a highly efficient hydrostatic transmission.