Ball toroidal CVT: a feasibility study based on topology, kinematics, statics and lubrication

In this paper a feasibility study of a special kind of toroidal CVT is presented based on different standpoints. The mechanism is briefly described and its kinematic structure is analysed. Its corresponding graph, which turns out to be not planar, is detected by means of a new method for classifying the nonholonomic pairs. The degrees of freedom are so evaluated and the independent circuits are identified. The kinematic analysis leads to a symbolic expression of the global transmission ratio and a simple relation between the two control angles is found to be necessary to theoretically avoid sliding at the contact points. The static force analysis is also carried out in order to ascertain the best method for applying the static pre-load needed to operate the transmission by friction in automotive applications. Finally, the two spherical pairs, which are embodied in the system, are made subject to a feasibility check by analysing the hydrodynamic lubrication conditions and by obtaining through a numerical approach, the oil film thickness and the pressure field over all the spherical domain. Results are provided which show how the two pairs work better if a component of hydrostatic lubrication is adopted.