Analytical model for the power losses in rubber V-belt continuously variable transmission (CVT)

Abstract In the present work closed form relationships for the power losses in rubber V-belt CVT are obtained, together with expressions for the axial thrust on both the driving and driven pulleys, starting from simple physical hypotheses. Losses have been grouped into three main contributions: frictional sliding losses, longitudinal and lateral material hysteresis and frictional losses due to the engagement/disengagement of the belt at the entrance and exit from the pulleys. In order to keep the model simple and to obtain a closed form solution, circumferential slip is assumed to take place mainly in the driven pulley and the sliding angle is assumed constant along the sliding portion of the contact arc. The model was validated through comparison with experimental results obtained on a dedicated test bench capable of measuring the transmitted torques and the axial thrusts on both pulleys, the pulleys rotating speeds and the total belt tension. The sliding angle γ and the damping coefficient Ψ, which were introduced in the analytical relationships, were determined by a best fit procedure on the basis of the obtained experimental results. After having obtained those parameters, the model appeared to be capable of reproducing with a fairly satisfactory agreement the power losses, as well as the axial loads on the pulleys, which were obtained in different operating conditions; thus it is proposed as a useful tool for the design of this kind of transmission.