The purpose of
this component is to change the reciprocating motion(up and down movement) of the piston into rotary
motion. Crankshafts are usually alloy
steel forgings with their journals and crankpins hardened to resist wear. The crankpins and journals are usually
hollow, to reduce weight, these spaces being interconnected by drillings in the
crank webs to provide passages for lubricating oil.
A shaft is classified according to the number
of ‘throws’ or cranks, for instance a
’six throw’ shaft has six crankpins.
The crankwebs are sometimes extended, the extra metal providing a means
of balancing the assembly or provide provisions for attachment of damping weights. Suitable
drives at each end of the crankshaft transmit the torque to the reduction gear
and the accessory drives and In direct drive engines the crankshaft is connected to the propeller with or without the propeller governor.
The simplest
crankshaft is the single-throw or 360° type. This type is used in a single-row radial
engine. It can be constructed in one or two pieces. Two main bearings (one on each end) are
provided when this type of crankshaft is used.
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The double-throw
or 180° crankshaft is used on double-row or 180° crankshaft is used on double-row radial engines. In the radial-type engine, one throw is
provided for each row of cylinders.
