Pulley drive systems use wheels and belts to transfer power from an engine or other locomotive force to an axle where it can do work. Pulley drive systems allow engineers to change the rotating speed and torque based on what the target source requires. Many automobiles use pulley drive systems to power the alternator and air conditioner.
A pulley drive system includes a driver pulley that provides the source of power and one or more driven pulleys, all connected by a belt under tension. The diameter of the pulleys determines a variety of factors. If both pulleys have the same diameter, the output speed equals the input speed, but if the driver pulley is half the diameter of the driven pulley, the output speed will be twice the input speed. Using pulley ratios, an engineer can provide a wide variety of driven speeds and torque to complete work.
Pulley drive systems transfer power using a belt. Most modern belts use synthetic fibers, but older systems used leather belts. Pulley belts may be flat if the pulley uses a drum design, or they may be V-shaped if a pulley uses a grooved design. Some pulley drives have teeth like a chain-drive system, but these usually operate at lower speeds.