Piston stroke (displacement )


Almost all reciprocating engines use cranks (with connecting rods) to transform the back-and-forth motion of the pistons into rotary motion. The cranks are incorporated into a crankshaft. The displacement of the end of the connecting rod is approximately proportional to the cosine of the angle of rotation of the crank, when it is measured from top dead center (TDC). So the reciprocating motion created by a steadily rotating crank and connecting rod is approximately simple harmonic motion.

Related formulas


xThe distance of the end of the connecting rod from the crank axle (m)
r The length of the crank (m)
zCrank angle (degree)
lThe length of the connecting rod (m)