Editing Crankshaft (section)

== Design ==
[[File:Cad crank.jpg|thumb|Crankshaft, [[piston#Internal combustion engines|piston]]s and [[connecting rod]]s for a typical [[internal combustion engine]]]]
[[Image:Marine Crankshafts 8b03602r.jpg|right|thumb|Marine engine crankshafts from 1942]]

The crankshaft is located within the [[engine block]] and held in place via [[main bearing]]s which allow the crankshaft to rotate within the block.<ref>{{cite web |title=Crankshaft: Parts, Function, Types, Diagram & More |url=https://www.theengineerspost.com/crankshaft-parts-and-function/ |website=The Engineers Post |access-date=1 September 2022 |language=en-us |date=27 May 2021}}</ref> The up-down motion of each piston is transferred to the crankshaft via [[connecting rods]].<ref>{{cite book |last1=McCune |first1=R. C. |last2=Weber |first2=G. A. |chapter=Automotive Engine materials |title=Encyclopedia of Materials: Science and Technology |date=1 January 2001 |pages=426–434 |chapter-url=https://www.sciencedirect.com/science/article/pii/B0080431526000863 |access-date=1 September 2022 |publisher=Elsevier |doi=10.1016/B0-08-043152-6/00086-3 |bibcode=2001emst.book..426M |isbn=9780080431529 |language=en}}</ref> A [[flywheel]] is often attached to one end of the crankshaft, in order to smoothen the power delivery and reduce vibration.<ref>{{cite web |title=How Does A Flywheel Work? Explained In Simple Words |url=https://carfromjapan.com/article/industry-knowledge/how-does-a-flywheel-work/ |website=Car From Japan |access-date=1 September 2022 |date=13 June 2018}}</ref>

A crankshaft is subjected to enormous stresses, in some cases more than {{convert|19000|lb|tonne|1|abbr=off|order=flip}} per cylinder.<ref>{{cite web |title=How to Build Racing Engines: Crankshafts Guide |url=https://www.musclecardiy.com/performance/how-to-build-racing-engines-crankshafts-guide/ |website=www.musclecardiy.com |accessdate=27 October 2019 |date=5 April 2015}}</ref> Crankshafts for [[single-cylinder engine]]s are usually a simpler design than for engines with multiple cylinders.

===Bearings===
{{main|Main bearing}}
The crankshaft is able to rotate in the [[engine block]] due to the 'main [[Bearing (mechanical)|bearings]]'. Since the crankshaft is subject to large horizontal and [[Torsion (mechanics)|torsional forces]] from each cylinder, these main bearings are located at various points along the crankshaft, rather than just one at each end.<ref>{{cite web |title=Flat-Plane Cranks, Part 2 — Calculating Crankshaft Secondary Forces |url=https://www.enginelabs.com/tech-stories/flat-plane-cranks-part-2-calculating-crankshaft-secondary-forces/ |website=EngineLabs |access-date=28 August 2022 |date=20 January 2022}}</ref> The number of main bearings is determined based on the overall load factor and the maximum engine speed. Crankshafts in [[Diesel engine|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.<ref>{{cite book |last1=Bosch |first1=Robert |title=Automotive Handbook |date=2004 |publisher=Robert Bosch |isbn=978-0-8376-1243-0 |page=465 |url=https://books.google.com/books?id=_t1oPwAACAAJ |access-date=28 August 2022 |language=en}}</ref>

Flexing of the crankshaft was a factor in [[V8 engine]]s replacing [[straight-eight engine]]s in the 1950s; the long crankshafts of the latter suffered from an unacceptable amount of flex when engine designers began using higher [[compression ratio]]s and higher engine speeds (RPM).<ref>{{cite web |title=A Brief History Of The Straight-Eight Engine – Carole Nash |url=https://www.carolenash.com/news/classic-car-news/detail/a-brief-history-of-the-straight-eight-engine |website=Carole Nash UK |access-date=28 August 2022 |language=en}}</ref>

===Piston stroke===
The distance between the axis of the [[Crankpin|crankpins]] and the axis of the crankshaft determines the [[Stroke (engine)#Stroke length|stroke length]] of the engine.<ref name="Howacarworks.com"/>

Most modern car engines are classified as "over square" or short-stroke,{{citation needed|date=August 2022}} wherein the stroke is less than the diameter of the [[cylinder 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.<ref>{{cite web |title=All you need to know about stroker engines and kits |url=https://www.torquecars.com/tuning/stroker-engines.php |website=TorqueCars |access-date=28 August 2022 |date=22 December 2020}}</ref>

=== Cross-plane and flat-plane configurations ===
When designing an engine, the crankshaft configuration is closely related to the engine's [[firing order]].<ref>{{cite web |title=What's the best firing order? |url=https://www.enginelabs.com/engine-tech/engine/firing-order-swaps-whats-best-for-your-engine/ |website=EngineLabs |access-date=30 August 2022 |date=25 April 2017}}</ref><ref>{{cite web |title=Crankshaft Design Evolution |url=http://enginehistory.org/members/articles/CrankDesignEvol.shtml |website=enginehistory.org |access-date=30 August 2022}}</ref>

Most production V8 engines (such as the [[Ford Modular engine]] and the [[LS based GM small-block engine|General Motors LS engine]]) use a [[crossplane|cross-plane crank]] whereby the crank throws are spaced 90 degrees apart.<ref>{{cite web |title=Flat Plane Crankshafts vs. Crossplane Crankshafts |url=https://www.onallcylinders.com/2015/01/15/cross-plane-vs-flat-plane-crankshafts/ |website=OnAllCylinders |access-date=30 August 2022 |language=en |date=15 January 2015}}</ref> However, some high-performance V8 engines (such as the [[Ferrari 488]])<ref>{{cite web |title=Ferrari 488 Spider debuts in Frankfurt, is faster than Lamborghini's new drop-top in every way |url=https://www.autoweek.com/news/auto-shows/a1876761/ferrari-488-spider-drops-its-top-frankfurt-motor-show/ |website=Autoweek |access-date=30 August 2022 |date=15 September 2015}}</ref><ref>{{cite web |title=2016 Ferrari 488 Spider: Losing the Roof Doesn't Compromise the Magic |url=https://www.roadandtrack.com/new-cars/first-drives/reviews/a27051/the-ferrari-488-spider-is-not-compromised-is-really-great/ |website=Road & Track |access-date=30 August 2022 |date=15 October 2015}}</ref> instead use a [[flat-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,<ref>{{cite web |title=Difference Between Cross-Plane and Flat-Plane Cranks |url=https://www.motortrend.com/how-to/difference-between-cross-plane-and-flat-plane-cranks/ |website=MotorTrend |access-date=30 August 2022 |language=en |date=15 June 2022}}</ref> so they are better suited to racing car engines.<ref>{{cite web |title=How The Flat-Plane Crank Turns Muscle Cars Into Exotics |url=https://carbuzz.com/news/carbuzz-explains-how-the-flat-plane-crank-turns-muscle-cars-into-exotics |website=CarBuzz |access-date=30 August 2022 |language=en-us |date=8 April 2016}}</ref>

===Engine balance===
For some engines it is necessary to provide [[counterweight]]s for the reciprocating mass of the piston, conrods and crankshaft, in order to improve the [[engine balance]].<ref>{{cite web |title=Crankshaft Balance Factors |url=http://ohiocrank.com/crankshaft-balance-factors/ |website=Ohio Crankshaft |access-date=31 August 2022}}</ref><ref>{{cite web |title=Finding Balance (Part 1): The Basics of Crankshaft Balancing |url=https://www.onallcylinders.com/2016/03/17/the-basics-of-crankshaft-balancing/ |website=OnAllCylinders |access-date=31 August 2022 |language=en |date=17 March 2016}}</ref> These counterweights are typically cast as part of the crankshaft but, occasionally, are bolt-on pieces.{{citation needed|date=August 2022}}

===Flying arms===
[[File:Crankshaft jap grayscale.jpg|thumb|right|Flying arm (the boomerang-shaped link between first and second [[crankpin]]s on a crankshaft) ]]
In some engines, the crankshaft contains direct links between adjacent [[Crankpin|crankpins]], without the usual intermediate main bearing. These links are called ''flying arms''.<ref name="Nunney">{{cite book |title=Light and Heavy Vehicle Technology|first=Malcolm J.|last=Nunney|year=2007|edition=4th|isbn=978-0-7506-8037-0|publisher=Elsevier Butterworth-Heinemann}}</ref>{{refpage |pages=16, 41}} This arrangement is sometimes used in [[V6 engine|V6]] and [[V8 engine]]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.<ref>{{cite web |title=Crankshaft guide – Flat vs Cross plane & lightened crankshafts |url=https://www.torquecars.com/tuning/crankshafts.php |website=TorqueCars |access-date=31 August 2022 |date=30 June 2015}}</ref>
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=== Counter-rotating crankshafts ===
In most engines, each [[connecting rod]] is attached a single crankshaft, which results in the angle of the connecting rod varying as the [[piston]] moves through its stroke. This variation in angle pushes the pistons against the cylinder wall, which causes friction between the piston and cylinder wall.<ref>{{citation|title=Company's perspective in vehicle tribology. In: 18th Leeds-Lyon Symposium (eds D Dowson, CM Taylor and MGodet), Lyon, France, 3–6 September 1991|author=Andersson BS|publisher= New York: Elsevier|year=1991|pages=503–506}}</ref> To prevent this, some early engines – such as the 1900–1904 [[Lanchester Motor Company|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]]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 equations|piston motion]], and varying loads during engine operation. Understanding these effects is essential for reducing mechanical wear, improving fuel efficiency, and optimizing engine design. <ref>{{Cite journal |last1=Elmoselhy |first1=Salah A. M. |last2=Faris |first2=Waleed F. |last3=Rakha |first3=Hesham A. |date=January 2022 |title=Validated Analytical Modeling of Eccentricity and Dynamic Displacement in Diesel Engines with Flexible Crankshaft |journal=Energies |language=en |volume=15 |issue=16 |pages=6083 |doi=10.3390/en15166083 |doi-access=free |issn=1996-1073|hdl=10919/111637 |hdl-access=free }}</ref>