The crankshaft is located within theengine block and held in place viamain bearings which allow the crankshaft to rotate within the block.[3] The up-down motion of each piston is transferred to the crankshaft viaconnecting rods.[4] Aflywheel is often attached to one end of the crankshaft, in order to smoothen the power delivery and reduce vibration.[5]
A crankshaft is subjected to enormous stresses, in some cases more than 8.6 tonnes (19,000 pounds) per cylinder.[6] Crankshafts forsingle-cylinder engines are usually a simpler design than for engines with multiple cylinders.
The crankshaft is able to rotate in theengine block due to the 'mainbearings'. Since the crankshaft is subject to large horizontal andtorsional forces from each cylinder, these main bearings are located at various points along the crankshaft, rather than just one at each end.[7] The number of main bearings is determined based on the overall load factor and the maximum engine speed. Crankshafts indiesel engines often use a main bearing between every cylinder and at both ends of the crankshaft, due to the high forces of combustion present.[8]
Flexing of the crankshaft was a factor inV8 engines replacingstraight-eight engines in the 1950s; the long crankshafts of the latter suffered from an unacceptable amount of flex when engine designers began using highercompression ratios and higher engine speeds (RPM).[9]
The distance between the axis of thecrankpins and the axis of the crankshaft determines thestroke length of the engine.[1]
Most modern car engines are classified as "over square" or short-stroke,[citation needed] wherein the stroke is less than the diameter of thecylinder bore. 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.[10]
When designing an engine, the crankshaft configuration is closely related to the engine'sfiring order.[11][12]
Most production V8 engines (such as theFord Modular engine and theGeneral Motors LS engine) use across-plane crank whereby the crank throws are spaced 90 degrees apart.[13] However, some high-performance V8 engines (such as theFerrari 488)[14][15] instead use aflat-plane crank, 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,[16] so they are better suited to racing car engines.[17]
For some engines it is necessary to providecounterweights for the reciprocating mass of the piston, conrods and crankshaft, in order to improve theengine balance.[18][19] These counterweights are typically cast as part of the crankshaft but, occasionally, are bolt-on pieces.[citation needed]
Flying arm (the boomerang-shaped link between first and secondcrankpins on a crankshaft)
In some engines, the crankshaft contains direct links between adjacentcrankpins, without the usual intermediate main bearing. These links are calledflying arms.[20]: 16, 41 This arrangement is sometimes used inV6 andV8 engines, 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.[21]
In most engines, eachconnecting rod is attached a single crankshaft, which results in the angle of the connecting rod varying as thepiston moves through its stroke. This variation in angle pushes the pistons against the cylinder wall, which causes friction between the piston and cylinder wall.[22] To prevent this, some early engines – such as the 1900–1904Lanchester 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 tobalance shafts, 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 thecrankshaft, secondarypiston motion, and varying loads during engine operation. Understanding these effects is essential for reducing mechanical wear, improving fuel efficiency, and optimizing engine design.[23]
Crankshafts can be created from a steel bar usingroll forging. Today, manufacturers tend to favour the use of forged crankshafts due to their lighter weight, more compact dimensions and better inherent damping.[24] With forged crankshafts,vanadium 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.
Another construction method is tocast the crankshaft from ductile iron.Cast iron crankshafts are today mostly found in cheaper production engines where the loads are lower.
Crankshafts can also bemachined frombillet, often a bar of high qualityvacuum 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.
In 9th centuryAbbasidBaghdad, automatically operated cranks appear in several of the hydraulic devices described by theBanū Mūsā brothers in theBook of Ingenious Devices.[25] 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 theBanū Mūsā would not have allowed a full rotation, but only a small modification was required to convert it to a crankshaft.[26]
In theArtuqid Sultanate, Arab engineerIsmail al-Jazari (1136–1206) described a crank and connecting rod system in a rotating machine for two of his water-raising machines,[27] which include both crank andshaft mechanisms.[28]
Crankshafts were described byLeonardo da Vinci (1452–1519)[27] and a Dutch farmer and windmill owner by the nameCornelis Corneliszoon van Uitgeest in 1592. His wind-poweredsawmill used a crankshaft to convert a windmill's circular motion into a back-and-forward motion powering the saw. Corneliszoon was granted apatent 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'sThe Diverse and Artifactitious Machines of 1588 depicts eighteen examples, a number that rises in theTheatrum Machinarum Novum byGeorg Andreas Böckler to 45 different machines.[31] Cranks were formerly common on some machines in the early 20th century; for example almost allphonographs before the 1930s were powered byclockwork motors wound with cranks. Reciprocating piston engines use cranks to convert the linear piston motion into rotational motion.Internal combustion engines of early 20th centuryautomobiles were usually started with hand cranks, beforeelectric starters came into general use.
^Andersson BS (1991),Company's perspective in vehicle tribology. In: 18th Leeds-Lyon Symposium (eds D Dowson, CM Taylor and MGodet), Lyon, France, 3–6 September 1991, New York: Elsevier, pp. 503–506
^A. F. L. Beeston, M. J. L. Young, J. D. Latham, Robert Bertram Serjeant (1990),The Cambridge History of Arabic Literature,Cambridge University Press, p. 266,ISBN0-521-32763-6{{citation}}: CS1 maint: multiple names: authors list (link)
Hägermann, Dieter; Schneider, Helmuth (1997),Propyläen Technikgeschichte. Landbau und Handwerk, 750 v. Chr. bis 1000 n. Chr. (2nd ed.), Berlin,ISBN3-549-05632-X{{citation}}: CS1 maint: location missing publisher (link)
Hall, Bert S. (1979),The Technological Illustrations of the So-Called "Anonymous of the Hussite Wars". Codex Latinus Monacensis 197, Part 1, Wiesbaden: Dr. Ludwig Reichert Verlag,ISBN3-920153-93-6
Laur-Belart, Rudolf (1988),Führer durch Augusta Raurica (5th ed.), Augst{{citation}}: CS1 maint: location missing publisher (link)
Lucas, Adam Robert (2005), "Industrial Milling in the Ancient and Medieval Worlds. A Survey of the Evidence for an Industrial Revolution in Medieval Europe",Technology and Culture,46 (1):1–30,doi:10.1353/tech.2005.0026,S2CID109564224
Mangartz, Fritz (2006), "Zur Rekonstruktion der wassergetriebenen byzantinischen Steinsägemaschine von Ephesos, Türkei. Vorbericht",Archäologisches Korrespondenzblatt,36 (1):573–590
Mangartz, Fritz (2010),Die byzantinische Steinsäge von Ephesos. Baubefund, Rekonstruktion, Architekturteile, Monographs of the RGZM, vol. 86, Mainz: Römisch-Germanisches Zentralmuseum,ISBN978-3-88467-149-8
Needham, Joseph (1986),Science and Civilisation in China: Volume 4, Physics and Physical Technology: Part 2, Mechanical Engineering, Cambridge University Press,ISBN0-521-05803-1
Nunney, Malcolm J. (2007),Light and Heavy Vehicle Technology (4th ed.), Elsevier Butterworth-Heinemann,ISBN978-0-7506-8037-0
Ritti, Tullia; Grewe, Klaus; Kessener, Paul (2007), "A Relief of a Water-powered Stone Saw Mill on a Sarcophagus at Hierapolis and its Implications",Journal of Roman Archaeology,20:138–163,doi:10.1017/S1047759400005341,S2CID161937987
Schiöler, Thorkild (2009), "Die Kurbelwelle von Augst und die römische Steinsägemühle",Helvetia Archaeologica, vol. 40, no. 159/160, pp. 113–124
Volpert, Hans-Peter (1997), "Eine römische Kurbelmühle aus Aschheim, Lkr. München",Bericht der Bayerischen Bodendenkmalpflege,38:193–199,ISBN3-7749-2903-3
White, Lynn Jr. (1962),Medieval Technology and Social Change, Oxford: At the Clarendon Press
Grewe, Klaus (2009). "Die Reliefdarstellung einer antiken Steinsägemaschine aus Hierapolis in Phrygien und ihre Bedeutung für die Technikgeschichte. Internationale Konferenz 13.−16. Juni 2007 in Istanbul". In Bachmann, Martin (ed.).Bautechnik im antiken und vorantiken Kleinasien(PDF). Byzas (in German). Vol. 9. Istanbul: Ege Yayınları/Zero Prod. Ltd. pp. 429–454.ISBN978-975-807-223-1. Archived fromthe original(PDF) on 2011-05-11.
