THE MESHING OF TIMING BELT TEETH IN PULLEY GROOVES

The work described here has been carried out to obtain a better unders tanding of the tooth root cracking failure mode of timing belts. Previ ous work has demonstrated the close dependence of this on the tooth de flections of fully meshed teeth, generated by torque transmission, but has not considered the additional distortions generated in the partia lly meshed conditions at entry to and exit from a pulley groove. Appro ximate compatibility and constitutive equations are combined with a ri gorous consideration of tooth equilibrium in partial meshing to show h ow bending moments are generated at both exit from a driven pulley and entry to a driving pulley. Experimentally determined belt lives corre late very well with a combined measure of fully meshed tooth strain an d strain due to bending at entry or exit. The analysis also shows that this strain measure reduces with increasing belt tooth stiffness, con firming the importance of a high tooth stiffness for a long belt life. Tooth force variations through the partial meshing cycle have also be en predicted and compared with measurements obtained from a special st rain gauge instrumented pulley. A greater pulley rotation than is pred icted is required for a belt tooth to seat in a pulley groove. There i s room for improvement in the modelling.