Scientific American - September 2018

15th century

17th century

13th century

3rd century A.D.

2nd century B.C. (Han Dynasty)

CAM

Protrusions known as cams

situated on a rotating shaft

drive the sequence of open-

ing and closing of valves on

engine cylinders to inject

the fuel-air mixture, contain

the blast and then expel the

exhaust. Camshafts were used

in 15th-century forges, where the

power of a waterwheel repeatedly

lifted and then dropped a heavy trip-

hammer (^) ●●●. On a modern car engine, the
D®å›D†ï›DåD ̈Ÿ ́y¹†D®åDïmŸ‡yày ́ïD ́‘ ̈yå
on the shaft to operate the cylinder valves. The
arrangement ofcams functions as a mechanical
program that physically encodes the correct
sequence ofvalve openings. In fact, the cam-
shaft reproduces the movements of the rotating
pegged cylinder of musical automatons, such as
17th-century water organs●●●.
CRANK
The component that translates the up-and-down
motion of the pistons into the rotary motion
needed for transmission to the wheels is the crank.
Early steam engines employed only one large cylin-
der and a single crank arm, but modern internal-
combustion engines bring together the force
ofseveral pistons turning the same crankshaft—
aspindle with several handlelike kinks along its
length. The crank traces its roots back more than
2,000 years to the handles of Han Dynasty win-
nowing machines, whose manual turning motion
àyDïymD ́ÚDàŸD ̈ĀŸ ́mÛï¹åyÈDàDïy‘àDŸ ́
†à¹®›D‡●●●●●●. In the third century A.D. the ŸyàDȹ ̈ŸååDĀ®Ÿ ̈ ̈ĀDåï›yŠàåïï¹ùåyDàD ́§
attached to a connecting rod to produce its req-
uisite cutting motions●●●. In the 13th century
polymath Ismail al-Jazari created a crankshaft
accommodating twin pistons for use as a water
pump●●●. Development of the crank demon-
strates the slow buildup of technical capabilities strates the slow buildup of technical capabilit
required for the development of the internal-
combustion engine in the mid-19th century.
September 2018, ScientificAmerican.com 41
Crankshaft
Camshaft
Cam
Valve
Cylinder Piston
C
D
E
F G