NuVinci drive: Modeling and performance analysis

The continuous search for more efficient drives, recently motivated also by environmental issues and innovative electro-mechanical applications, has led to a renovated interest in Continuously Variable Transmissions (CVTs). Several novel geometries of traction drives have been proposed in the recent past, to improve the performance sometimes with a look at miniaturization. A modified version of the well-known Kopp variator has recently been engineered under the name of NuVinci drive. NuVinci was designed for being installed on bicycles but with the promise to be suitable also for a wide range of other applications. In this paper, we present a mathematical model of this device, developed to study its performance, compare different relevant variants and improve the design. The performances are discussed in terms of traction capabilities and efficiency. It is shown how a slight modification of the geometry may lead to an evident change of the performance indicators, in particular the efficiency.