What Are the Functions of a Camshaft?

by B.T. Alo
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A camshaft is a device to convert circular or rotational motion into reciprocating or oscillatory motion. Such devices have been used since as early as the Hellenistic era in the Third century BC in the form of toys that automatically performed repeated functions, and later in automated music boxes for striking a hammer in a pre-programmed way to play a tune. One of the most widely used applications of camshafts in the world today is the opening and closing of fuel valves in virtually all piston-driven internal combustion engines.

Mechanics of a Camshaft

The device features a shaft with discs fitted around it along its length called cams. Each cam is eccentric--it isn't a uniform circular disc, but rather has a bulge. This enables the bulge to press on to an object called a follower once during every complete rotation of the shaft about its axis.

Valve Timing

In internal combustion engines, the timing of the opening and closing of the fuel injection and gas exhaust valves is extremely important, and must be synchronized with the corresponding motion of the piston to facilitate proper engine strokes. This is achieved by using the camshaft for opening and closing the valves at pre-set timings. The camshaft is connected to the crankshaft directly via gears or indirectly with a belt or chain and thus, rotates as the crankshaft rotates. The cams are positioned against the corresponding valves of each cylinder in a manner that enables the right valve to be open only during the right engine stroke, keeping it closed throughout the rest of the strokes. Slight discrepancies in this critical valve timing result in inefficient engine performance. Major timing differences could lead to engine failure.

Camshaft Operation

The camshaft is designed to rotate twice with every rotation of the crankshaft and for each rotation of the camshaft, four valve events occur. Cams on the camshaft open the intake valves during the intake stroke, which are then closed at the beginning of the compression stroke. When the compressed fuel has been ignited, the crankshaft has completed one rotation. Other cams come into play to open the exhaust valves once the piston has moved down considerably, but not all the way. These valves remain open as the piston returns upwards for the exhaust stroke, letting all the burned gases escape before they begin to close. The cams for the intake valves start to open them again to begin the next intake stroke.

Performance Tuning

The timings of the camshaft play an important role in performance tuning of vehicles. Both the timing and the dimensions of the cams are altered to deliver not just the precise valve opening timing, but also the correct extent to which the valve is opened for optimal performance. A properly timed and tuned camshaft could mean the split-second difference between first place and second place in a race in otherwise identical vehicles.

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