Crankshaft

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Crankshaft (red), pistons (gray), cylinders (blue) and flywheel (black) Cshaft.gif
Crankshaft (red), pistons (gray), cylinders (blue) and flywheel (black)

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, [1] that are driven by the pistons via the connecting rods. [2]

Contents

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.

Design

Crankshaft, pistons and connecting rods for a typical internal combustion engine Cad crank.jpg
Crankshaft, pistons and connecting rods for a typical internal combustion engine
Marine engine crankshafts from 1942 Marine Crankshafts 8b03602r.jpg
Marine engine crankshafts from 1942

The crankshaft is located within the engine block and held in place via main bearings which allow the crankshaft to rotate within the block. [3] The up-down motion of each piston is transferred to the crankshaft via connecting rods. [4] A flywheel 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 for single-cylinder engines are usually a simpler design than for engines with multiple cylinders.

Bearings

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. [7] 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. [8]

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). [9]

Piston stroke

The distance between the axis of the crankpins and the axis of the crankshaft determines the stroke 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 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. [10]

Cross-plane and flat-plane configurations

When designing an engine, the crankshaft configuration is closely related to the engine's firing order. [11] [12]

Most production V8 engines (such as the Ford Modular engine and the General Motors LS engine) use a cross-plane crank whereby the crank throws are spaced 90 degrees apart. [13] However, some high-performance V8 engines (such as the Ferrari 488) [14] [15] 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, [16] so they are better suited to racing car engines. [17]

Engine balance

For some engines it is necessary to provide counterweights for the reciprocating mass of the piston, conrods and crankshaft, in order to improve the engine balance. [18] [19] These counterweights are typically cast as part of the crankshaft but, occasionally, are bolt-on pieces.[ citation needed ]

Flying arms

Flying arm (the boomerang-shaped link between first and second crankpins on a crankshaft) Crankshaft jap grayscale.jpg
Flying arm (the boomerang-shaped link between first and second crankpins on a crankshaft)

In some engines, the crankshaft contains direct links between adjacent crankpins, without the usual intermediate main bearing. These links are called flying arms. [20] : 16, 41  This arrangement is sometimes used in V6 and V8 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]

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. [22] 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 shafts, which are occasionally used.

Construction

Forged crankshafts

Forged crankshaft IPH Kurbelwelle.jpg
Forged crankshaft

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. [23] 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.

Cast crankshafts

Another construction method is to cast the crankshaft from ductile iron. Cast iron crankshafts are today mostly found in cheaper production engines where the loads are lower.

Machined crankshafts

Crankshafts can also be machined from billet, 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 Baghdad, automatically operated cranks appear in several of the hydraulic devices described by the Banū Mūsā brothers in the Book of Ingenious Devices . [24] 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. [25]

In the Artuqid Sultanate, Arab engineer Ismail al-Jazari (1136–1206) described a crank and connecting rod system in a rotating machine for two of his water-raising machines, [26] which include both crank and shaft mechanisms. [27]

15th century paddle-wheel boat Anonymous of the Hussite Wars. Clm 197, Part 1, Folio 17v Supra.jpg
15th century paddle-wheel boat

The Italian physician Guido da Vigevano (c. 1280 – c. 1349), planning for a new Crusade, made illustrations for a paddle boat and war carriages that were propelled by manually turned compound cranks and gear wheels, [28] identified as an early crankshaft prototype by Lynn Townsend White. [29]

1661 water pump by Georg Andreas Bockler Fotothek df tg 0006690 Mechanik ^ Wasserforderung ^ Pumpe.jpg
1661 water pump by Georg Andreas Böckler

Crankshafts were described by Leonardo da Vinci (1452–1519) [26] and a Dutch farmer and windmill owner by the name Cornelis Corneliszoon van Uitgeest in 1592. His wind-powered sawmill used a crankshaft to convert a windmill's circular motion into a back-and-forward motion powering the saw. Corneliszoon was granted a patent 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's The Diverse and Artifactitious Machines of 1588 depicts eighteen examples, a number that rises in the Theatrum Machinarum Novum by Georg Andreas Böckler to 45 different machines. [30] Cranks were formerly common on some machines in the early 20th century; for example almost all phonographs before the 1930s were powered by clockwork motors wound with cranks. Reciprocating piston engines use cranks to convert the linear piston motion into rotational motion. Internal combustion engines of early 20th century automobiles were usually started with hand cranks, before electric starters came into general use.

See also

Related Research Articles

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In mechanical engineering, a crosshead is a mechanical joint used as part of the slider-crank linkages of long stroke reciprocating engines and reciprocating compressors to eliminate sideways force on the piston. The crosshead also allows the connecting rod to move freely outside the cylinder. Because of the very small bore-to-stroke ratio on such engines, the connecting rod would hit the cylinder walls and block the engine from rotating if the piston were attached directly to the connecting rod as in a trunk engine. Therefore, the longitudinal dimension of the crosshead must be matched to the stroke of the engine.

<span class="mw-page-title-main">Flat-twin engine</span> Piston engine with two cylinders in opposing directions

A flat-twin engine is a two-cylinder internal combustion engine with the cylinders on opposite sides of the crankshaft. The most common type of flat-twin engine is the boxer-twin engine, where both pistons move inwards and outwards at the same time.

<span class="mw-page-title-main">Crank (mechanism)</span> Simple machine transferring motion to or from a rotating shaft at a distance from the centreline

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<span class="mw-page-title-main">Connecting rod</span> Piston engine component which connects the piston to the crankshaft

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.

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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 shafts, to prevent unpleasant and potentially damaging vibration. The strongest inertial forces occur at crankshaft speed and balance is mandatory, while forces at twice crankshaft speed can become significant in some cases.

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<span class="mw-page-title-main">Crankpin</span> Crankshaft section where connecting rods are attached

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References

  1. 1 2 "How the crankshaft works – All the details". How a Car Works. Retrieved 27 August 2022.
  2. ↑ "Definition of CRANKSHAFT". Merriam-Webster Dictionary . 17 October 2024.
  3. ↑ "Crankshaft: Parts, Function, Types, Diagram & More". The Engineers Post. 27 May 2021. Retrieved 1 September 2022.
  4. ↑ McCune, R. C.; Weber, G. A. (1 January 2001). "Automotive Engine materials". Encyclopedia of Materials: Science and Technology. Elsevier. pp. 426–434. Bibcode:2001emst.book..426M. doi:10.1016/B0-08-043152-6/00086-3. ISBN   9780080431529 . Retrieved 1 September 2022.
  5. ↑ "How Does A Flywheel Work? Explained In Simple Words". Car From Japan. 13 June 2018. Retrieved 1 September 2022.
  6. ↑ "How to Build Racing Engines: Crankshafts Guide". www.musclecardiy.com. 5 April 2015. Retrieved 27 October 2019.
  7. ↑ "Flat-Plane Cranks, Part 2 — Calculating Crankshaft Secondary Forces". EngineLabs. 20 January 2022. Retrieved 28 August 2022.
  8. ↑ Bosch, Robert (2004). Automotive Handbook. Robert Bosch. p. 465. ISBN   978-0-8376-1243-0 . Retrieved 28 August 2022.
  9. ↑ "A Brief History Of The Straight-Eight Engine – Carole Nash". Carole Nash UK. Retrieved 28 August 2022.
  10. ↑ "All you need to know about stroker engines and kits". TorqueCars. 22 December 2020. Retrieved 28 August 2022.
  11. ↑ "What's the best firing order?". EngineLabs. 25 April 2017. Retrieved 30 August 2022.
  12. ↑ "Crankshaft Design Evolution". enginehistory.org. Retrieved 30 August 2022.
  13. ↑ "Flat Plane Crankshafts vs. Crossplane Crankshafts". OnAllCylinders. 15 January 2015. Retrieved 30 August 2022.
  14. ↑ "Ferrari 488 Spider debuts in Frankfurt, is faster than Lamborghini's new drop-top in every way". Autoweek. 15 September 2015. Retrieved 30 August 2022.
  15. ↑ "2016 Ferrari 488 Spider: Losing the Roof Doesn't Compromise the Magic". Road & Track. 15 October 2015. Retrieved 30 August 2022.
  16. ↑ "Difference Between Cross-Plane and Flat-Plane Cranks". MotorTrend. 15 June 2022. Retrieved 30 August 2022.
  17. ↑ "How The Flat-Plane Crank Turns Muscle Cars Into Exotics". CarBuzz. 8 April 2016. Retrieved 30 August 2022.
  18. ↑ "Crankshaft Balance Factors". Ohio Crankshaft. Retrieved 31 August 2022.
  19. ↑ "Finding Balance (Part 1): The Basics of Crankshaft Balancing". OnAllCylinders. 17 March 2016. Retrieved 31 August 2022.
  20. ↑ Nunney, Malcolm J. (2007). Light and Heavy Vehicle Technology (4th ed.). Elsevier Butterworth-Heinemann. ISBN   978-0-7506-8037-0.
  21. ↑ "Crankshaft guide – Flat vs Cross plane & lightened crankshafts". TorqueCars. 30 June 2015. Retrieved 31 August 2022.
  22. ↑ 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
  23. ↑ "Cast vs Forged Crankshaft". www.dropforging.net. Retrieved 2024-07-31.
  24. ↑ 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, ISBN   0-521-32763-6 {{citation}}: CS1 maint: multiple names: authors list (link)
  25. ↑ Banū Mūsā; Hill, Donald Routledge (1979), The Book of Ingenious Devices (Kitáb al-Ḥiyal) by the Banú (sons of) Músà bin Shákir, Springer Publishing, pp. 23–4, ISBN   90-277-0833-9
  26. 1 2 Ahmad Y Hassan. The Crank-Connecting Rod System in a Continuously Rotating Machine.
  27. ↑ Donald Hill (2012), The Book of Knowledge of Ingenious Mechanical Devices, page 273, Springer Science + Business Media
  28. ↑ Hall 1979 , p. 80
  29. ↑ Townsend White, Lynn (1978). Medieval Religion and Technology: Collected Essays . University of California Press. p. 335. ISBN   9780520035669.
  30. ↑ White 1962 , p. 172

Sources

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