Abstract
Smoother speed change, high speed-ratio range at the rated speed and load,a simpler mechanism with low cost and less maintenance, etc., have been theultimate goals for transmission design engineers. The belt-driven CVT can nearlyfulfill these requirements. However, the characteristics of less efficiency andlower load-carrying capacity have hampered the applications. This research presents an analytical and experimental investigation on the dynamic behaviors of the CVT under steady-state conditions. It includes the analyses of the speed-ratio-changing mechanisms, the force and stress distributions over the contact region, the vibration of the free span, the power-loss mechanisms and efficiency ofthe entire system, etc. The low efficiency of the V-belt CVT may attribute to the following reasons:slip, radial sliding, vibration, and hysteresis due to bending, shear, andcompression of the V-belt. These may result from the characteristics of the V-belt itself and the interaction between the belt and sheaves. By introducing thebending rigidity of the belt into equilibrium equations, a contact analysis isperformed to determine the force and stress distributions, and the radius of curvature of the belt. This formulation provides a basis for the estimation of power loss by computing the hysteresis and friction losses between the belt andsheaves. The free span of the belt is considered as an axially moving elastic material.The equation of motion, governing the dynamic behaviors of the free span of thebelt in the transverse direction, is derived by employing a mixed variationprinciple. The geometrical boundary and initial conditions are determined from the aforementioned contact analysis of a practical CVT system. A parametricstudy, such as the variation of the belt tension, transporting velocity, on natural frequencies of the belt is then performed by using assumed-modes method. An analysis of parametric instability is performed by the periodic variations of the belt shape and tension. These results may be further utilized in the design of belt-driven CVT systems. A quantitative analysis of the power-loss mechanisms, on the basis of the contact behaviors between the belt and sheaves, is accomplished. The efficiency of a motorcycle CVT under various operating conditions is evaluated by considering the bending hysteresis loss, shear hysteresis loss, shear deflection andfriction loss of radial displacement. These results are further verified by experiments. A methodology for the design of the entire rubber V-belt CVT system can be constructed on the basis of this research, that is applicable for the CVT under various operating conditions.