LAND FRICTION EFFECTS IN THE MESHING OF TIMING BELTS

It is observed experimentally that local peaks occur in the tangential component of the force on a pulley pitch when a timing belt seats at entry to a driving pulley and unseats at exit from a driven pulley. In this paper it is shown that these peaks are caused by forces acting b etween the belt and pulley lands. It is further shown experimentally, in tests on nominally 9.525 mm pitch belts running on 19-tooth pulleys , that the direction of sliding of a belt land over a pulley land can differ in seating conditions from the direction in fully meshed contac t expected from the pitch difference between the pulley and belt. A th eory to predict the direction of sliding is developed that combines th e constraints of synchronous motion with velocity differentials betwee n the belt cord and land surface that depend on the belt radius. The t heory almost agrees with experiments. It needs measurements of belt co rd extension stiffness, belt land radial compliance and bending stiffn ess and belt land shear compliance. Data on all these quantities have been obtained and are presented: the belt land properties are very ani sotropic.