Measurements of Forces Between a Synchronous Belt and a Pulley
Abstract In modern belt profiles, power is transmitted by both normal forces and friction forces. To control the load distribution between a belt and a pulley, avoiding power circulation and local tooth load peaks, it is necessary to take into account both types of forces. An analytical model for the load distribution has previously been presented by the authors. This work also introduces the effective pitch difference, EPD, which is the actual pitch difference between a pulley and a loaded belt. To examine these matters and verify the model, a series of 270 experiments was carried out in a two-pulley test rig. Parameters investigated are: torque, tension, belt speed, pitch difference and running time. All of the measurements were conducted under quasi-static conditions. The equipment used included a specially designed measurement pulley that can measure four different engagement forces. Experiments show that belt speed within automotive application range has no effect on load distribution, apart from engagement and disengagement peaks. Tooth flank normal forces and land area friction forces often work against each other. Belts with dissimilar pitch difference give rise to great differences in load distributions. Even a short running time causes a redistribution of the friction forces, although their sum remains constant. The results show that it is possible to tailor the load distribution by adjusting the EPD. This offers an opportunity to avoid power circulation and unnecessary high contact forces. Changing the EPD for the correct load distribution at each interaction is easily achieved by individual adjustment of the pulley radius.