Crankshaft section where connecting rods are attached
A
crankpin
or
crank pin
, also known as a
rod bearing journal
,
[1]
is a mechanical device in an
engine
which connects the
crankshaft
to the
connecting rod
for each cylinder. It has a cylindrical surface, to allow the crankpin to rotate relative to the "big end" of the connecting rod.
[2]
[3]
[4]
The most common configuration is for a crankpin to serve one cylinder. However, many V engines have each crankpin shared by each pair of cylinders.
Design
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The crankpin connects to the larger end of the connecting rod for each cylinder. This end of the connecting rod is called the "big end", as opposed to the "small end" or "little end" (which connects to the
wrist/gudgeon pin
in the piston).
The
bearing
which allows the crankpin to rotate around its shaft is called the "rod bearing".
[5]
In automotive engines, the most common type of rod bearing is the
plain bearing
, however
bushings
or
roller bearings
are also used in some engines.
Configurations
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In a
single-cylinder engine
,
straight engine
or
flat engine
, each crankpin normally serves just one cylinder. This results for a relatively simple design which is the cheapest to produce. Some
V-twin engines
use a single cylinder per crankpin.
Most
V engines
have each pair of cylinders sharing a crankpin. This usually requires an offset between the cylinders in each bank, resulting in a simple connecting rod design. If a cylinder offset is not used, then the connecting rods must be articulated or forked at the big end.
Forked connecting rods
are mainly used in V-twin motorcycle engines, but in the past were found on a number of automobile and aero engines, such as the
Rolls-Royce Merlin
aero engine of the WWII era.
Articulated connecting rods
consist of a "master" rod attached to the crank pin, with a "slave" rod connected to the big end of the master rod. This design was used in older or exotic V engines.
Radial engines
use a more complicated version of articulated connecting rods, where a single "master" connecting rod attached to the single crankpin (one for each row in multi-row designs), and smaller bearings for each of the corresponding cylinders machined into the big end of the master rod.
Cylindrical crank pins were fitted onto the
driving wheels
of steam locomotives. They were connected to the
driving rods
that transmitted power from the
cylinder
to the
wheel
. The crank pin was usually made of high-quality
steel
because it had to withstand high forces.
The crank pin of a locomotive corresponds to the
offset
of a
crankshaft
in other
crank drives
. The distance from the centre of the crank pin to the centre of the wheel is also called offset and is exactly half the
stroke
of the
pistons
.
See also
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References
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