Camshaft

For OHC and DOHC engines, the camshaft operates the valve directly or via a short rocker arm.

[14] Accurate control of the position and speed of the camshaft is critically important in allowing the engine to operate correctly.

Alternative drive systems used in the past include a vertical shaft with bevel gears at each end (e.g. pre-World War I Peugeot and Mercedes Grand Prix Cars and the Kawasaki W800 motorcycle) or a triple eccentric with connecting rods (e.g. the Leyland Eight car).

The camshaft's duration determines how long the intake/exhaust valve is open for, therefore it is a key factor in the amount of power that an engine produces.

A lay person can readily spot a long duration camshaft by observing the broad surface of the lobe where the cam pushes the valve open for a large number of degrees of crankshaft rotation.

[21] This could be a result of a very steep rise of the lobe,[18] where the cam follower separates from the cam lobe (due to the valvetrain inertia being greater than the closing force of the valve spring), leaving the valve open for longer than intended.

[20][21] The timing (phase angle) of the camshaft relative to the crankshaft can be adjusted to shift an engine's power band to a different RPM range.

This avoids the above compromise required when choosing a fixed cam timing for use at both high and low RPM.

[20] In general, the optimal LSA for a given engine is related to the ratio of the cylinder volume to intake valve area.

As the camshaft rotates, its lobes push against the valves, allowing the intake of air and fuel and the expulsion of exhaust gases.

This synchronized process is crucial for optimizing engine performance, fuel efficiency, and emissions control.

[24] The most common methods of valve actuation involve camshafts and valve springs, however alternate systems have occasionally been used on internal combustion engines: Before the advent of solid state electronics, camshaft controllers were used to control the speed of electric motors.

By this means, resistors or tap changers were switched in or out of the circuit to vary the speed of the main motor.