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A camshaft operating two valves. A camshaft is a shaft that contains a row of pointed cams in order to convert rotational motion to reciprocating motion.Camshafts are used in piston engines (to operate the intake and exhaust valves), [1] [2] mechanically controlled ignition systems and early electric motor speed controllers.
The cam can be seen as a device that converts rotational motion to reciprocating (or sometimes oscillating) motion. [clarification needed] [3] A common example is the camshaft of an automobile, which takes the rotary motion of the engine and converts it into the reciprocating motion necessary to operate the intake and exhaust valves of the cylinders.
In most piston engines, the camshaft(s) are mechanically connected to the crankshaft. The crankshaft drives the camshaft (via a timing belt, timing chain or gears), which in turn actuates the intake and exhaust valves. [1] These valves allow the engine to inhale air (or an air/fuel mixture) and exhale the exhaust gasses. [2]
The cam's shape determines the piston's stroke length, timing, and speed. These factors directly influence the engine's performance characteristics. In a cam engine, the cam is connected to a drive mechanism, usually a shaft. This shaft rotates the cam at a specific speed. The rotation of the cam is synchronized with the engine's combustion cycle.
An overhead camshaft (OHC) engine is a piston engine in which the camshaft is located in the cylinder head above the combustion chamber. [ 1 ] [ 2 ] This contrasts with earlier overhead valve engines (OHV), where the camshaft is located below the combustion chamber in the engine block .
The camshaft is driven by the crankshaft and, in the case of a four-stroke engine, rotates at half the speed of the crankshaft. Motion is transferred from the crankshaft to the camshaft most commonly by a rubber timing belt , a metallic timing chain or a set of gears.
The balance shaft runs off the small gear on the left (the large gear is for the camshaft, causing it to rotate at half the speed of the crankshaft). Balance shafts are often used in inline-four engines , to reduce the second-order vibration (a vertical force oscillating at twice the engine RPM ) that is inherent in the design of a typical ...
The ratio is determined by the ratio of the distances from the rocker arm's pivot point to the point where it touches the valve and the point where it touches the pushrod/camshaft. A rocker ratio greater than one essentially increases the camshaft's lift. Current automotive design favors rocker arm ratios of about 1.5:1 to 1.8:1.
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