Pulleys and drive belts - Synchronous drive

Synchronous belt drives combine the advantages of simple belt drives (flat, V-belt or ribbed) in terms of low weight, low maintenance, wide linear speed ranges and high transmission ratios with the benefits of chains: no slippage, synchronized speed transmission, low installation tension, etc.

Thanks to the belt's toothing, which penetrates the corresponding toothing on the synchronous pulleys, power is transmitted directly without slipping, as between two gears.

A synchronous transmission consists of a driving toothed pulley, a belt and one or more driven toothed pulleys, and possibly smooth rollers which, by rewinding the belt onto the back, increase the contact arc on the toothed pulleys. As a general rule, this system uses a single belt of a width appropriate to the power to be transmitted.

Most synchronous belts consist of an elastomer or thermoplastic material that forms the belt body (back and teeth), in which the inextensible armature is embedded to transmit the force taken from the drive pulley to the driven pulleys, and a textile layer protecting the teeth. The inextensibility of the armature is necessary to guarantee synchronism between the drive and driven shafts (elimination of angular misalignment). Synchronous belts are generally manufactured endless to a perfectly defined length, corresponding to a precise number of teeth. However, some belts can be supplied by the metre, enabling tailor-made solutions, particularly for linear transport or handling systems; in the case of power transmission, this type of belt is not recommended, as the connection (by welding or gluing) is a point of weakness.

Synchronous belts come in a variety of designs: single-toothed (with the teeth on the inside), double-toothed or with a profiled coating on the back (for conveying materials). These belts are available with pitches (tooth spacing) measured in inches or millimeters, with tooth shapes evolving according to the manufacturer, in order to be able to transmit increasingly higher powers.

Synchronous drives are used almost universally, wherever synchronous, slip-free operation is required. They can be found in fields as diverse as micromechanics, office automation, machine tools and industrial shredders, not to mention the fact that most automobiles today are equipped with synchronous belts for timing (camshaft drive), or even a single synchronous belt that can drive not only timing, but also all the engine's ancillary components.