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Concept
Crankshaft
Summary
A crankshaft is a mechanical component used in a piston engine to convert the reciprocating motion into rotational motion. The crankshaft is a rotating shaft containing one or more crankpins, that are driven by the pistons via the connecting rods.
The crankpins are also called rod bearing journals, and they rotate within the "big end" of the connecting rods.
Most modern crankshafts are located in the engine block. They are made from steel or cast iron, using either a forging, casting or machining process.
The crankshaft located within the engine block, held in place via main bearings which allow the crankshaft to rotate within the block. The up-down motion of each piston is transferred to the crankshaft via connecting rods. A flywheel is often attached to one end of the crankshaft, in order to smoothen the power delivery and reduce vibration.
A crankshaft is subjected to enormous stresses, in some cases more than per cylinder. Crankshafts for single-cylinder engines are usually a simpler design than for engines with multiple cylinders.
Main bearing
The crankshaft is able to rotate in the engine block due to the 'main bearings'. Since the crankshaft is subject to large horizontal and torsional forces from each cylinder, these main bearings are located at various points along the crankshaft, rather than just one at each end. The number of main bearings is determined based on the overall load factor and the maximum engine speed. Crankshafts in diesel engines often use a main bearing between every cylinder and at both ends of the crankshaft, due to the high forces of combustion present.
Flexing of the crankshaft was a factor in V8 engines replacing straight-eight engines in the 1950s; the long crankshafts of the latter suffered from an unacceptable amount of flex when engine designers began using higher compression ratios and higher engine speeds (RPM).
The distance between the axis of the crankpins and the axis of the crankshaft determines the stroke length of the engine.
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Internal combustion engine
An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combustion engine, the expansion of the high-temperature and high-pressure gases produced by combustion applies direct force to some component of the engine. The force is typically applied to pistons (piston engine), turbine blades (gas turbine), a rotor (Wankel engine), or a nozzle (jet engine).
Crank (mechanism)
A crank is an arm attached at a right angle to a rotating shaft by which circular motion is imparted to or received from the shaft. When combined with a connecting rod, it can be used to convert circular motion into reciprocating motion, or vice versa. The arm may be a bent portion of the shaft, or a separate arm or disk attached to it. Attached to the end of the crank by a pivot is a rod, usually called a connecting rod (conrod). The term often refers to a human-powered crank which is used to manually turn an axle, as in a bicycle crankset or a brace and bit drill.
Connecting rod
A connecting rod, also called a 'con rod', is the part of a piston engine which connects the piston to the crankshaft. Together with the crank, the connecting rod converts the reciprocating motion of the piston into the rotation of the crankshaft. The connecting rod is required to transmit the compressive and tensile forces from the piston. In its most common form, in an internal combustion engine, it allows pivoting on the piston end and rotation on the shaft end.