Half toroidal continuously variable transmission: Trade-off between dynamics of ratio variation and efficiency

This paper investigates the trade-off between efficiency and dynamics of CVT's. Energy efficiently varying the speed ratio of the CVT while maintaining the dynamic requirements is of primordial importance to fully utilize the advantages of the CVT in a drivetrain. Although the toroidal CVT is thoroughly discussed in literature, few articles describe its behavior during ratio variation. Therefore, in this paper a procedure is proposed to achieve optimal ratio variation in terms of settling time and efficiency with a half toroidal CVT. The key concept on which the procedure is based is the expression of the maximum output torque of the CVT. It turns out that the given method offers the fastest possible speed ratio variation for given constraints without excessive increase in slip and thus limited loss in efficiency. The most important constraint proves to be the clamping force which has a profound impact on the resulting dynamics and efficiency of the CVT. The paper indicates that higher clamping forces increase the dynamics of the CVT at a certain cost of loss in efficiency which implies that there is a trade-off between efficiency and dynamics.