A crankshaft is a mechanical component used in a

piston engine A reciprocating engine, more often known as a piston engine, is a heat engine that uses one or more Reciprocating motion, reciprocating pistons to convert high temperature and high pressure into a Circular motion, rotating motion. This article ...

to convert the

reciprocating motion Reciprocating motion, also called reciprocation, is a repetitive up-and-down or back-and-forth linear motion. It is found in a wide range of mechanisms, including reciprocating engines and pumps. The two opposite motions that comprise a single ...

into

rotational motion Rotation or rotational/rotary motion is the circular movement of an object around a central line, known as an ''axis of rotation''. A plane figure can rotate in either a clockwise or counterclockwise sense around a perpendicular axis interse ...

. The crankshaft is a rotating

shaft Shaft may refer to: Rotating machine elements * Shaft (mechanical engineering), a rotating machine element used to transmit power * Line shaft, a power transmission system * Drive shaft, a shaft for transferring torque * Axle, a shaft around whi ...

containing one or more

crankpin A crankpin or crank pin, also known as a rod bearing journal, is a mechanical device in an engine which connects the crankshaft to the connecting rod for each cylinder. It has a cylindrical surface, to allow the crankpin to rotate relative to th ...

s, that are driven by the

piston A piston is a component of reciprocating engines, reciprocating pumps, gas compressors, hydraulic cylinders and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder (engine), cylinder a ...

s via the

connecting rod A connecting rod, also called a 'con rod', is the part of a reciprocating engine, piston engine which connects the piston to the crankshaft. Together with the crank (mechanism), crank, the connecting rod converts the reciprocating motion of the p ...

s. 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 In an internal combustion engine, the engine block is the structure that contains the cylinders and other components. The engine block in an early automotive engine consisted of just the cylinder block, to which a separate crankcase was attach ...

. They are made from

steel Steel is an alloy of iron and carbon that demonstrates improved mechanical properties compared to the pure form of iron. Due to steel's high Young's modulus, elastic modulus, Yield (engineering), yield strength, Fracture, fracture strength a ...

cast iron Cast iron is a class of iron–carbon alloys with a carbon content of more than 2% and silicon content around 1–3%. Its usefulness derives from its relatively low melting temperature. The alloying elements determine the form in which its car ...

, using either a

forging Forging is a manufacturing process involving the shaping of metal using localized compression (physics), compressive forces. The blows are delivered with a hammer (often a power hammer) or a die (manufacturing), die. Forging is often classif ...

casting Casting is a manufacturing process in which a liquid material is usually poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify. The solidified part is also known as a casting, which is ejected or ...

machining Machining is a manufacturing process where a desired shape or part is created using the controlled removal of material, most often metal, from a larger piece of raw material by cutting. Machining is a form of subtractive manufacturing, which util ...

process.

Design

The crankshaft is located within the

and held in place via

main bearing A main bearing is a bearing in a piston engine which holds the crankshaft in place and allows it to rotate within the engine block. The number of main bearings per engine varies between engines, often in accordance with the forces produced b ...

s 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 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 crankshaf ...

. A

flywheel A flywheel is a mechanical device that uses the conservation of angular momentum to store rotational energy, a form of kinetic energy proportional to the product of its moment of inertia and the square of its rotational speed. In particular, a ...

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 engine A single-cylinder engine, sometimes called a thumper, is a piston engine with one cylinder. This engine is often used for motorcycles, motor scooters, motorized bicycles, go-karts, all-terrain vehicles, radio-controlled vehicles, power tools ...

s are usually a simpler design than for engines with multiple cylinders.

Bearings

The crankshaft is able to rotate in the

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 engine The diesel engine, named after the German engineer Rudolf Diesel, is an internal combustion engine in which Combustion, ignition of diesel fuel is caused by the elevated temperature of the air in the cylinder due to Mechanics, mechanical Compr ...

s 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 replacing

straight-eight engine The straight-eight engine or inline-eight engine (often abbreviated as I8) is an eight-cylinder internal combustion engine with all eight cylinders mounted in a straight line along the crankcase. The type has been produced in side-valve, IO ...

s in the 1950s; the long crankshafts suffered from an unacceptable amount of flex when engine designers began using higher

compression ratio The compression ratio is the ratio between the maximum and minimum volume during the compression stage of the power cycle in a piston or Wankel engine. A fundamental specification for such engines, it can be measured in two different ways. Th ...

s and higher engine speeds (RPM).

Piston stroke

The distance between the axis of the

s and the axis of the crankshaft determines the stroke length of the engine. Most modern car engines are classified as "over square" or short-stroke, wherein the stroke is less than the diameter of the

cylinder bore In a piston engine, the bore (or cylinder bore) is the diameter of each cylinder. Engine displacement is calculated based on bore, stroke length and the number of cylinders: displacement = The stroke ratio, determined by dividing the bore b ...

. A common way to increase the low-RPM torque of an engine is to increase the stroke, sometimes known as "stroking" the engine. Historically, the trade-off for a long-stroke engine was a lower rev limit and increased vibration at high RPM, due to the increased piston velocity.

Cross-plane and flat-plane configurations

When designing an engine, the crankshaft configuration is closely related to the engine's

firing order The firing order of an internal combustion engine is the sequence of ignition for the cylinders. In a spark ignition (e.g. gasoline/petrol) engine, the firing order corresponds to the order in which the spark plugs are operated. In a diesel engi ...

. Most production V8 engines (such as the

Ford Modular engine The Ford Modular engine is an overhead camshaft (OHC) V8 and V10 gasoline-powered small block engine family introduced by Ford Motor Company in 1990 for the 1991 model year. The term “modular” applied to the setup of tooling and casting ...

and the

General Motors LS engine The General Motors LS-based small-block engines are a family of V8 and offshoot V6 engines designed and manufactured by the American automotive company General Motors. Introduced in 1997, the family is a continuation of the earlier first- ...

) use a cross-plane crank whereby the crank throws are spaced 90 degrees apart. However, some high-performance V8 engines (such as the

Ferrari 488 The Ferrari 488 (Type F142M) is a Rear mid-engine, rear-wheel drive layout, mid-engine sports car produced by the Italian automobile manufacturer Ferrari. The car replaced the Ferrari 458, 458, being the first mid-engine Ferrari to use a turboch ...

) instead use a

flat-plane crank The flat-plane crank (sometimes flatplane) is a type of crankshaft for use in internal combustion engines that has a 180-degree angle between crank throws. Details Flat-plane cranks are used in V-configuration engines, generally with eight ...

, whereby the throws are spaced 180° apart, which essentially results in two inline-four engines sharing a common crankcase. Flat-plane engines are usually able to operate at higher RPM, however they have higher second-order vibrations, so they are better suited to racing car engines.

Engine balance

For some engines it is necessary to provide

counterweight A counterweight is a weight (object), weight that, by applying an opposite force, provides balance and stability of a machine, mechanical system. The purpose of a counterweight is to make lifting the load faster and more efficient, which saves e ...

s for the reciprocating mass of the piston, conrods and crankshaft, in order to improve the

engine balance Engine balance refers to how the inertial forces produced by moving parts in an internal combustion engine or steam engine are neutralised with counterweights and Balance shaft#Overview, balance shafts, to prevent unpleasant and potentially dam ...

. These counterweights are typically cast as part of the crankshaft but, occasionally, are bolt-on pieces.

Flying arms

In some engines, the crankshaft contains direct links between adjacent

s, without the usual intermediate main bearing. These links are called ''flying arms''. This arrangement is sometimes used in V6 and

V8 engine A V8 engine is an eight- cylinder piston engine in which two banks of four cylinders share a common crankshaft and are arranged in a V configuration. Origins The first known V8 was the Antoinette, designed by Léon Levavasseur, a ...

s, in order to maintain an even firing interval while using different V angles, and to reduce the number of main bearings required. The downside of flying arms is that the rigidity of the crankshaft is reduced, which can cause problems at high RPM or high power outputs.

Counter-rotating crankshafts

In most engines, each

is attached a single crankshaft, which results in the angle of the connecting rod varying as the

moves through its stroke. This variation in angle pushes the pistons against the cylinder wall, which causes friction between the piston and cylinder wall. To prevent this, some early engines – such as the 1900–1904 Lanchester Engine Company flat-twin engines – connected each piston to two crankshafts that are rotating in opposite directions. This arrangement cancels out the lateral forces and reduces the requirement for counterweights. This design is rarely used, however a similar principle applies to

balance shaft Balance shafts are used in piston engines to reduce vibration by cancelling out unbalanced dynamic forces. The counter balance shafts have eccentric weights and rotate in the opposite direction to each other, which generates a net vertical force ...

s, which are occasionally used.

Eccentricity and dynamic displacement of diesel engines

Eccentricity and dynamic displacement are critical factors influencing the performance, efficiency, and durability of diesel engines. These phenomena arise due to the flexibility of the crankshaft, secondary piston motion, and varying loads during engine operation. Understanding these effects is essential for reducing mechanical wear, improving fuel efficiency, and optimizing engine design.

Construction

Forged crankshafts

Crankshafts can be created from a steel bar using roll forging. Today, manufacturers tend to favour the use of forged crankshafts due to their lighter weight, more compact dimensions and better inherent damping. With forged crankshafts,

vanadium Vanadium is a chemical element; it has Symbol (chemistry), symbol V and atomic number 23. It is a hard, silvery-grey, malleable transition metal. The elemental metal is rarely found in nature, but once isolated artificially, the formation of an ...

micro-alloyed steels are mainly used as these steels can be air-cooled after reaching high strengths without additional heat treatment, except for the surface hardening of the bearing surfaces. The low alloy content also makes the material cheaper than high-alloy steels. Carbon steels also require additional heat treatment to reach the desired properties.

Cast crankshafts

Another construction method is to

cast Cast may refer to: Music * Cast (band), an English alternative rock band * Cast (Mexican band), a progressive Mexican rock band * The Cast, a Scottish musical duo: Mairi Campbell and Dave Francis * ''Cast'', a 2012 album by Trespassers William ...

the crankshaft from ductile iron.

Cast iron Cast iron is a class of iron–carbon alloys with a carbon content of more than 2% and silicon content around 1–3%. Its usefulness derives from its relatively low melting temperature. The alloying elements determine the form in which its car ...

crankshafts are today mostly found in cheaper production engines where the loads are lower.

Machined crankshafts

Crankshafts can also be

machined Machining is a manufacturing process where a desired shape or part is created using the controlled removal of material, most often metal, from a larger piece of raw material by cutting. Machining is a form of subtractive manufacturing, which util ...

from

billet In European militaries, a billet is a living-quarters to which a soldier is assigned to sleep. In American usage, it refers to a specific personnel position, assignment, or duty station to which a soldier can be assigned. Historically, a billet w ...

, often a bar of high quality vacuum remelted steel. Though the fiber flow (local inhomogeneities of the material's chemical composition generated during casting) does not follow the shape of the crankshaft (which is undesirable), this is usually not a problem since higher quality steels, which normally are difficult to forge, can be used. Per unit, these crankshafts tend to be expensive due to the large amount of material that must be removed with lathes and milling machines, the high material cost, and the additional heat treatment required. However, since no expensive tooling is needed, this production method allows small production runs without high up-front costs.

History

Crankshaft

In 9th century

Abbasid The Abbasid Caliphate or Abbasid Empire (; ) was the third caliphate to succeed the prophets and messengers in Islam, Islamic prophet Muhammad. It was founded by a dynasty descended from Muhammad's uncle, Abbas ibn Abd al-Muttalib (566–653 C ...

Baghdad Baghdad ( or ; , ) is the capital and List of largest cities of Iraq, largest city of Iraq, located along the Tigris in the central part of the country. With a population exceeding 7 million, it ranks among the List of largest cities in the A ...

, automatically operated cranks appear in several of the hydraulic devices described by the Banū Mūsā brothers in the ''

Book of Ingenious Devices The ''Book of Ingenious Devices'' (, ) is a large illustrated work on mechanical devices, including automata, published in 850 by the three brothers of Persian descent, the Banū Mūsā brothers (Ahmad, Muhammad and Hasan ibn Musa ibn Shakir) ...

''. These automatically operated cranks appear in several devices, two of which contain an action which approximates to that of a crankshaft, five centuries before the earliest known European description of a crankshaft. However, the automatic crank mechanism described by the Banū Mūsā would not have allowed a full rotation, but only a small modification was required to convert it to a crankshaft. In the Artuqid Sultanate, Arab engineer

Ismail al-Jazari Badīʿ az-Zaman Abu l-ʿIzz ibn Ismāʿīl ibn ar-Razāz al-Jazarī (1136–1206, , ) was a Muslim polymath: a scholar, inventor, mechanical engineer, artisan and artist from the Artuqid Dynasty of Jazira in Mesopotamia. He is best known for ...

(1136–1206) described a crank and connecting rod system in a rotating machine for two of his water-raising machines,

Ahmad Y Hassan Ahmad Yousef Al-Hassan () (June 25, 1925 – April 28, 2012) was a Palestinian/Syrian/Canadian historian of Arabic and Islamic science and technology, educated in Jerusalem, Cairo, and London with a PhD in Mechanical engineering from University ...

The Crank-Connecting Rod System in a Continuously Rotating Machine
which include both crank and

mechanisms.

Donald Hill Donald Routledge Hill (6 August 1922 – 30 May 1994)D. A. King, “In Memoriam: Donald Routledge Hill (1922-1994)”, ''Arabic Sciences and Philosophy,'' Volume 5 / Issue 02 / September 1995, pp 297-302 was a British engineer and historian of s ...

(2012)
''The Book of Knowledge of Ingenious Mechanical Devices'', page 273

Springer Science + Business Media Springer Science+Business Media, commonly known as Springer, is a German multinational publishing company of books, e-books and peer-reviewed journals in science, humanities, technical and medical (STM) publishing. Originally founded in 1842 in ...

The Italian physician

Guido da Vigevano Guido da Vigevano or Guido da Vigevano da Pavia (born c. 1280; died c. 1349) was an Italian physician and inventor. He is notable for his sketchbook ''Texaurus regis Francie'', a catalog of military equipment, and his ''Anothomia Philippi Septimi ...

(), planning for a new

Crusade The Crusades were a series of religious wars initiated, supported, and at times directed by the Papacy during the Middle Ages. The most prominent of these were the campaigns to the Holy Land aimed at reclaiming Jerusalem and its surrounding t ...

, made illustrations for a paddle boat and war carriages that were propelled by manually turned compound cranks and gear wheels, identified as an early crankshaft prototype by Lynn Townsend White. Crankshafts were described by

Leonardo da Vinci Leonardo di ser Piero da Vinci (15 April 1452 - 2 May 1519) was an Italian polymath of the High Renaissance who was active as a painter, draughtsman, engineer, scientist, theorist, sculptor, and architect. While his fame initially rested o ...

(1452–1519) and a Dutch farmer and windmill owner by the name

Cornelis Corneliszoon van Uitgeest Cornelis Corneliszoon van Uitgeest or Krelis Lootjes () was a Dutch windmill owner from Uitgeest who invented the wind-powered sawmill, which made the conversion of log timber into planks 30 times faster than before.

in 1592. His wind-powered

sawmill A sawmill (saw mill, saw-mill) or lumber mill is a facility where logging, logs are cut into lumber. Modern sawmills use a motorized saw to cut logs lengthwise to make long pieces, and crosswise to length depending on standard or custom sizes ...

used a crankshaft to convert a windmill's circular motion into a back-and-forward motion powering the saw. Corneliszoon was granted a

patent A patent is a type of intellectual property that gives its owner the legal right to exclude others from making, using, or selling an invention for a limited period of time in exchange for publishing an sufficiency of disclosure, enabling discl ...

for his crankshaft in 1597. From the 16th century onwards, evidence of cranks and connecting rods integrated into machine design becomes abundant in the technological treatises of the period:

Agostino Ramelli Agostino Ramelli (1531–ca. 1610) was an Italian engineer best known for writing and illustrating the book of engineering designs ''Le diverse et artificiose machine del Capitano Agostino Ramelli'', which contains, among others, his desig ...

's ''The Diverse and Artifactitious Machines'' of 1588 depicts eighteen examples, a number that rises in the ''Theatrum Machinarum Novum'' by

Georg Andreas Böckler Georg Andreas Böckler (c. 1617 – 21 February 1687) was a German architect and engineer who wrote ''Architectura Curiosa Nova'' (1664) and ''Theatrum Machinarum Novum'' (1661). Biography Born in Cronheim, he was an architect in the city of ...

to 45 different machines. Cranks were formerly common on some machines in the early 20th century; for example almost all

phonograph A phonograph, later called a gramophone, and since the 1940s a record player, or more recently a turntable, is a device for the mechanical and analogue reproduction of sound. The sound vibration Waveform, waveforms are recorded as correspond ...

s before the 1930s were powered by

clockwork Clockwork refers to the inner workings of either mechanical devices called clocks and watches (where it is also called the movement (clockwork), movement) or other mechanisms that work similarly, using a series of gears driven by a spring or wei ...

motors wound with cranks. Reciprocating piston engines use cranks to convert the linear piston motion into rotational motion.

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 comb ...

s of early 20th century

automobile A car, or an automobile, is a motor vehicle with wheels. Most definitions of cars state that they run primarily on roads, Car seat, seat one to eight people, have four wheels, and mainly transport private transport#Personal transport, peopl ...

s were usually started with hand cranks, before electric starters came into general use.

References

Sources

* * * * * * * * * * * * * * *

External links

*Interactive crank animation https://www.desmos.com/calculator/8l2kvyivqo *D & T Mechanisms – Interactive Tools for Teachers (applets) https://web.archive.org/web/20140714155346/http://www.content.networcs.net/tft/mechanisms.htm * {{Authority control Engine components Engine technology Linkages (mechanical) Piston engines 13th-century inventions