CVT Rolling Traction Drives— A Review of Research Into Their Design, Functionality, and Modeling

This paper details a review of the current state of published work regarding the modelling of rolling traction drive Continuously Variable Transmissions (CVTs). An overview of CVTs operating by traction through small contact areas is performed, the layouts and kinematics of leading examples are reviewed, including the factors affecting design optimisation. Properties of the traction contacts are considered in detail, with particular attention to elastohydrodynamic lubrication and asperity contact. Factors affecting the traction coefficient are reviewed and fundamental empirical predictions are contrasted with modern modelling computations. Finally measurements of the rheology of traction fluids are considered, leading to definition of ideal properties and the development of proprietary fluids.