Development of New Continuously Variable Transmission for Electric Bicycles

A new continuously variable transmission for an electric bicycle (EB-CVT) was developed. The EB-CVT has a new mechanism of the traction drive transmitting power through contacts between inner sphere and outer sphere. The EB-CVT permits three propulsion modes: human-power only, motor-power only or motor-power plus human-power and has high power efficiency with large torque capacity despite narrow space to be installed in. The continuously varying speed ratio enables the EB-CVT to increase efficiency and to improve driveability. The inner spherical surface contacts help satisfying large torque capacity. After minute processes of a conceptual design, performance analysis and optimization, a prototype is manufactured and installed in an electric bicycle to run road test. The performances and reliabilities of the EB-CVT are evaluated.