Timing belt drive - Definitions. Geometry

A toothed belt drive is often referred to as a synchronous drive. From a global point of view, the presence of active teeth on the belt, which mesh with the teeth on the pulleys, as well as the relative longitudinal rigidity of the belts, ensure an average transmission known as synchronous. However, if we look a little more closely at the angular movement on the receiving pulleys, taking into account the elongation of the stretched belt strands, the deformation of the teeth during meshing and the transmission of forces, then deviations from the theoretical position occur, known as transmission error, and synchronism is not guaranteed. Increasing machine performance (speed, torque) means that dynamic effects linked to external or internal excitations must be considered alongside kinematic and static aspects. In addition, environmental conditions, and in particular noise limits, require dynamic and acoustic studies of toothed belt drives. Finally, toothed belts are flexible links, often perceived as the least resistant elements (fusible elements) of the transmission. Degradation and durability aspects therefore also need to be addressed.

Timing belts are widely used, whether in micromechanics and consumer goods (cameras, printers, lawnmowers, etc.), in transport (engine timing, motorcycles, etc.) or in many industrial sectors with conveyor belts (mechanical engineering, food processing, etc.). This wide variety of applications and dimensions leads to specific features in each case, highlighting certain capabilities of timing belts. However, the nature of the problems encountered remains unchanged.

There are two main categories of timing belts with slightly different technologies:

• belt bearing on the pulley tooth bottom (pulley tooth top) for medium- and high-speed drives with medium power ratings. Belts are single-toothed (arranged on the inside of the belt) and endless (closed belt with defined length at manufacture). These types of belts are mainly considered in this dossier;

• belt span on the pulley at the head of the belt tooth (pulley tooth recess) for low- and medium-speed drives, usually with high power ratings. The length is either defined during manufacture, or made to order (the connection always imposes particular operating conditions). In addition to the meshing teeth, this type of belt can be fitted with handling studs (on the outside of the belt), which can either be manufactured directly or mounted on request.

The approach proposed in this series of dossiers aims, in the current state of knowledge, to :

• define the components of the timing belt drive and define a working context...