Power Transmission Losses in V-Belt Drives Part 2: Effects of Small Pulley Radii

Abstract

Run-in AV10 wrapped, raw-edged and cogged V-belts have been used to transmit power between pulleys of equal radii R equal to 51, 36 and 21 mm. Separate measurements of the torque and angular speed losses between the pulleys have shown that these are approximately proportional to 1/R and 1/R2 respectively and are also greater than expected from current theories. The maximum useful belt tension ratio fell from 21 to 5 as R was reduced from 51 to 21 mm. A dimensionless belt deformation parameter (gEI/R4)1/2, arising from a simplified analysis of torque loss, has been found empirically to correlate with both torque loss and the speed loss in excess of that expected from belt extension and radial compliance. Subsidiary tests with thick flat belts on cylindrical pulleys have shown their power losses to be unexpectedly close to those of V-belts of similar cross-sectional area, suggesting that those V-belt losses usually attributed to wedging in the pulley groove are of more general origin. It is speculated that belt carcass warping or shearing distortions must be considered to explain losses on small-radii pulleys.