Abstract
This research presents a systematic method for improving transmission efficiency of the rubber V-belt Continuously Variable Transmission (CVT). Power loss in the CVT system is relevant not only to the rubber V-belt but also to the speed-ratio-change mechanisms, which includes the axial force induced by centrifugal rollers, compression spring, torque cam, belt radius, tension force, etc. Therefore, a thorough understanding of power-loss mechanisms associated with effective mathematical models must be developed in order to find out the major factors responsible for the low efficiency of the rubber V-belt CVT. Power loss is categorized into speed and torque losses. The mechanisms causing power loss may attribute to the hysteresis of belt bending, compression and shear, and friction due to slip and radial motion of the belt. These loss mechanisms are studied on the basis of motion characteristics of the rubber V-belt. Semi-empirical formulae for estimating the system efficiency are obtained by considering the experimental and simulation results, and can be used as a tool for developing the new models of the CVT systems. Parameters for loss mechanisms are then analyzed to identify their contributions to the system efficiency. These parameters include external load, speed-ratio, rotating speed and wedge angle of the pulley, pre-tension, and thickness and tooth profile of the belt. In addition, a series of experimental studies were performed for the verification of these proposed analytical approaches. Finally, an improved design of the CVT system by adding a two-stage planetary gear train into the system in association with a well-tuned speed-ratio-change mechanism of the CVT is proposed. It was proved that more than 15% efficiency could be gained.