Development of Continuously Variable Power Transmission for Electric Vehicle with Solar Assisted Battery

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Electric vehicles have a potential to be used in the urban-city logistics where no-emission of exhaust-gas is favorable and short range of cruising-range can be accepted. Technological issues for the power-train of the electric vehicle are how to provide smooth and quick acceleration within a limited electric energy-source and to recover the mechanical energy to electric energy at deceleration or down-hill. This project is to examine the possibility of the continuously variable power transmission, CVT, as an mechanical transmission for the electric vehicle by making a traction-drive prototype of 2.2kW power-capacity with speed-ratio range of 0.4 to 2.5. The innovative technology is to develop a speed-ratio control servomechanism consisting of a set of nut and screw and small-size rolling-elements working at a maximum Hertzian pressure of 2.5GPa. The test result is that it transmits 40N.m torques at 3000rpm with an efficiency of 85%, and the nut and screw servomechanism changes the speed-ratio quickly with a first-order time-constant of 0.2s. The CVT is applied to the electric vehicle with a dead mass of 250kg including 60kg lead-acid battery. The power train is consisted of a serially-wounded motor with 36V-80A rated-power of which output shaft is connected directly with the CVT input-shaft. The output torque of the CVT is transmitted to the wheel axle through the differential gear box with reduction-ratio of 12.5. The acceleration of the electric vehicle with CVT is improved by 10% compared to the constant-gear box.