Krukas: Verskil tussen weergawes

Krukasse kan ook uit 'n staalknuppel gemasjineer word, dikwels 'n staaf hoë gehalte vakuumgesmelte staal. Alhoewel die veselvloei (plaaslike onsuiwerhede van die materiaal se chemiese samestelling wat tydens die gietproses vorm) nie volg die vorm van die krukas (wat ongewens is), is dit gewoonlik nie 'n probleem nie, want 'n hoër gehalte staal, wat gewoonlik moeilik is om te bewerk, kan gebruik word. Hierdie kruk is geneig om baie duur te wees as gevolg van die groot hoeveelheid van die materiaal wat verwyder moet word met draaibanke en freesmasjiene, die hoë materiaalkoste, en die bykomende hittebehandeling vereis. Maar, aangesien daar geen duur gereedskap nodig is nie, kan hierdie produksiemetode vir klein produksielope aangewend word sonder hoë koste.

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As the crankshaft undergoes a great deal of sideways load from each cylinder in a multicylinder engine, it must be supported by several such bearings, not just one at each end; this was also a factor in the rise of [[V8]] engines with their shorter crankshafts, in preference to [[straight-8]] engines. High performance engines will often have more main bearings than their lower performance cousins, for this reason. In addition, to convert the reciprocating motion into rotation, the crankshaft has "crank throws" or "crank pins", additional bearing surfaces whose axis is offset from that of the crank, to which the "big ends" of the [[connecting rod]]s from each cylinder attach. The distance of the axis of the crank throws from the axis of the crankshaft determines the [[piston stroke]] measurement, and thus [[engine displacement]]; a common way to increase the power of an engine is to increase the stroke. This also increases the reciprocating vibration, however, limiting the high [[RPM]] capability of the engine; in compensation, it improves the low speed operation of the engine, as the longer intake stroke through smaller valve(s) results in greater turbulence and mixing of the intake charge. For this reason, even such high speed production engines as current [[Honda]] engines are classified as long-stroke, in that the stroke is larger than the diameter of the [[cylinder bore]]. In production [[V engine|V]] or [[flat engine|flat]] engines, neighboring connecting rods attach side by side to the same crank throw, simplifying crank design.

 

In the [[Wankel engine]], the rotors drive the eccentric shaft, which can be considered the equivalent of the crankshaft in a piston engine.

 

Crankshafts can be [[forge]]d or [[cast]] from either [[mild steel]] or [[high strength steel]], or machined out of a single [[billet]] of forged steel. Mild steel is only used for engines in models or other such applications, where the engine runs but does not supply power. Cast crankshafts are usually found in production engines, with forged and billet crankshafts being more expensive but reliable for higher performance. The rough casting or forging is machined to size and shape, the holes are drilled, the main and connecting rod bearing journals are precision ground and [[case hardening|case hardened]], and the appropriate holes are threaded.

 

The crankshaft is subjected to various forces but it needs to be checked in two positions.

Firstly, failure may occur at the position of maximum bending. In such a condition the failure is due to bending and the pressure in the cylinder is maximal. Secondly, the crank may fail due to twisting, so the crankpin needs to be checked for shear at the position of maximal twisting. The pressure at this position is not the maximal pressure, but a fraction of maximal pressure.

* [[Controlled Combustion Engine]]

 

*[http://www.mustangandfords.com/howto/29178/ Nicely detailed discussion of crankshaft features, from ''Mustang & Fords'' magazine, with many photographs]

*[http://pdmec4.mecc.unipd.it/~cos/DINAMOTO/twin%20motors/twin.html Animated representations of the vibrations characteristic of various two cylinder engine and crankshaft configurations]