CVT dynamics: Theory and experiments

We present a detailed experimental study of the pushing V-belt CVT dynamics and compare the experimental data with the theoretical predictions of the Carbone, Mangialardi, Mantriota (CMM) model [G. Carbone, L. Mangialardi, G. Mantriota, The influence of pulley deformations on the shifting mechanisms of MVB-CVT, ASME Journal of Mechanical Design 127 (2005) 103–113]. A very good agreement between theory and experiments is found. In particular it is shown that, during creep-mode (slow) shifting, the rate of change of the speed ratio is a linear function of the logarithm of the ratio between the axial clamping forces acting on the two movable pulleys. The shifting speed is also shown to be proportional to the angular velocity of the primary pulley, and to increase as the clamping force on the secondary pulley is increased. Indeed, a growth of the clamping force increases the pulley bending and, therefore, in agreement with the CMM model, increases the shifting speed. The authors also propose a relatively simple differential equation to describe the creep-mode evolution of the variator. Few parameters appear in the formula, which may be calculated either experimentally or theoretically. The results of this study are of utmost importance for the design of advanced CVT control systems and the improvement of the CVT efficiency, cars’ drivability and fuel economy.