Abstract
Some power is not transferred from the driving pulley to the driven pulley of CVT using pushing metal V-belts. The belt must slip in the tangential direction in the pulley groove to transmit the power between two pulleys (elastic slip). Consequently some power is lost in the CVT. However, the elastic slip rate is extremely low, and the power loss by the elastic slip must be too small to explain the true loss. The objectives of the present study are to show the power loss mechanisms of the metal V-belt CVT and to find a way for increasing the power transmitting efficiency. It has been found that the belt significantly penetrates into pulley groove for CVT using dry hybrid V-belts. Even for metal ones having much higher transverse stiffness, belt penetration must exist. Then, belt penetration was measured for CVT using pushing metal V-belts. Displacement sensors were arranged along the contact arc. It was confirmed that the metal V-belt also penetrated deeply into the pulley groove due to tilting of the movable pulley flange. Consequently, the belt moved in the radial direction all over the contact arc of the pulley. Such movement of the belt in the radial direction was accompanied by additional slips of the belt itself and its components in both radial and tangential directions in the CVT, resulting in significant energy dissipation. The power loss significantly decreased when a solid pulley was used, reducing the belt penetration into the pulley groove. Therefore, it was revealed that when the clearance between the pulley boss and the shaft was smaller, the friction loss also decreased. The effect of belt speed on the power loss was also examined from 1000 to 5000 rpm of the driving pulley under no load condition while the speed ratio was changed from 0.5 to 2.0. The experimental results revealed that the power loss parabolically increased with respect to pulley rotational speed. The increase of power loss with respect to belt speed is due to the centrifugal force of the belt in conjunction with a large amount of slip of the belt due to belt penetration into pulley groove. An engineering model was proposed for estimating each power loss of CVT components based on the fact that the belt penetrates into the pulley groove. The model can reasonably estimate the total power loss of the pushing metal V-belt CVT.
Keywords: CVT, Metal pushing V-belt, Power loss, Belt penetration, Boss clearance