Improvements on the range and the performance of a light electric vehicle by making use of a continuously variable transmission

Due to the regular torque-speed characteristics of electric motors, most vehicle manufacturers are producing their electric vehicle models with powertrains without transmissions. In this thesis work, the operating characteristics of electric motors were studied to find out how the range and performance of electric vehicles can be extended. Although most electric motors produce constant torque output versus speed in nominal operating regions and since their efficiency depends on their speed and loading conditions, it was intended to operate the motor in its most efficient regions and broaden the vehicle's speed range by making use of a transmission. Based on this motivation, it was concluded that the continuously variable transmission was the most suitable type for this kind of a light vehicle application, instead of manual and automatic gearboxes. An electric go-kart with a continuously variable transmission in its powertrain was built. Using the technical data of the powertrain components, a mathematical powertrain model was developed. Following the calculations, the interconnecting machine parts were designed, manufactured, and assembled onto the vehicle. In each of the road tests at the first section, the transmission ratio was set to different constant values. An optimum transmission ratio providing the highest range and performance results was found. At the second section of road tests, since the transmission unit is programmable in order to provide the desired transmission ratio for the predefined vehicle speeds, shifting schedules were prepared in the light of the experience gained at the first section of road tests. Running the vehicle with the prepared automatic shifting schedules, improvements in both the range and the performance were obtained.