Experimental analysis of v-belt tensile loads

An experimental investigation was conducted to determine the magnitude of v-belt stresses in automotive drive situations. A constant tension belt test apparatus was designed and fabricated using a variable speed cradled D.C. motor for power and two automotive alternators for absorption. Free span stresses on the dynamic torque loaded belt drive were determined from the equations governing a pivoted drive system. Centrifugal stress was determined by a theoretical analysis of belt motion. Bending stresses were obtained from a static test employing strain gages mounted on the top of belts with exposed cord layers. The variation in load stress around the pulleys in a dynamic torque loaded drive was to be determined by taking time synchronized photographs of a marked belt section and measuring strain from enlarged photographic negatives. The time synchronization of high speed close-up photography was accomplished during this study, but the capability of making measurements from photographic data was not perfected. Insight gained from this work led to the advancement of ideas which may allow photographic determination of belt strain in a future study. A magnetic pickoff and timer system also failed to indicate the magnitude of dynamic belt strains. In order to complete the present analysis, the Hornung analytical solution for tensions around torque loaded pulleys was employed in a digital simulation program. A matrix of computer runs was made for the range of drive parameters studied. Finally, power losses in belt drives were experimentally obtained in order to determine the design acceptability of the drive situations tested. Superposition of bending, centrifugal and load tensions led to the conclusion that bending stress is by far the largest stress factor to be considered in automotive v-belt drives. The fact that small changes in load stress cause noticeable changes in belt fatigue life must be attributed to the creep, slip, and heat generation phenomena which accompany torque transmission --Abstract, pages ii-iii