When the great Islamic scholar AI-Jazari (1150-1220), published in 1206 his Kitab fi ma'rifat al-hiyal al- handasiyya (Book of Knowledge of Ingenious Mechanical Devices], it included a description of a device that could change rotational motion into reciprocating motion: the camshaft. This invention consists of a shaft that has oval-shaped lobes attached to it, which turn with the shaft itself. Because of their noncircular shape, these "cams" appear to oscillate when the shaft spins on its axis. If a cam is positioned next to a valve, as it is in the example of the internal-combustion engine, then, as the camshaft turns, the longest end of the cam will depress, and hence open, the valve each time the shaft makes a turn. Before that, the camshaft played an important role in many medieval technologies. In windmills and waterwheels, for example, camshafts transformed rotational power into the energy and modes of action needed to mill corn, saw wood, or hammer metal.
In modern times the camshaft is best known as an integral part of the internal-combustion engine. When fuel within each combustion chamber of an engine explodes, the mixture of combusting fuel and air expands and drives a piston that is connected to a crankshaft, thus translating the piston's motion into the energy needed to propel a car, lift a weight, or perform some other form of work. A camshaft—or two camshafts, depending on the engine's design— controls the valves that allow new fuel into each combustion chamber, as well as the valves that release exhaust gases from the previous fuel ignitions.
In an engine the camshaft is connected to the crankshaft by a timing belt that allows precise coordination of the firing of the combustion chambers with the intake of fuel and output of exhaust.
