Design considerations for improving transmission efficiency of the rubber V-belt CVT

This paper proposes design considerations for increasing transmission efficiency of rubber V-belt continuously variable transmissions (CVT). Herein, power loss is categorized into speed and torque losses. Since speed loss contributes less than 4% of the total power loss in most operating conditions for the CVT used in motorcycles, only torque loss is considered in this study. The mechanisms resulting in torque loss may be attributed to the hysteresis of belt bending, compression and shear as well as friction due to radial motion of the belt. These loss mechanisms are studied on the basis of belt motion characteristics. Design variables are then analysed to identify their relationship with respect to transmission efficiency. These variables include external load, rotating speed and wedge angle of the pulley, speed ratio, pretension, and thickness and tooth profile of the belt. In addition, an experimental study is performed for verification of the proposed analytical approach.