# Piston speed

The piston speed is the speed (v) with which the piston of a reciprocating engine covers the way from top dead center (TDC) to bottom dead center (BDC) or vice versa.

The piston speed in piston machines is not uniform:

• The linear movement of the piston is coupled to the rotating movement of the crankshaft . Therefore, depending on the connecting rod ratio λ, there is an approximately sinusoidal curve of the piston speed for each stroke. The movement deviates from a pure sine curve, since it is superimposed with further movements with double the frequency. The maximum piston speed is z. B. for λ = 0.25 at a crank angle of about 76 ° and is about 1.6 times the mean piston speed. The mean piston speed assumes a constant speed over the stroke.
Piston speed in internal combustion engines

The average piston speed is normally used for the calculation.

This is calculated in the MKS system of units as follows:

${\ displaystyle v_ {m} = 2 \ cdot n _ {\ mathrm {s}} \ cdot s _ {\ mathrm {m}}}$
${\ displaystyle v_ {m}}$ = Mean piston speed in m / s
${\ displaystyle n _ {\ mathrm {s}}}$ = Engine speed in 1 / s
${\ displaystyle s _ {\ mathrm {m}}}$ = Piston stroke in m

or in common units:

${\ displaystyle v_ {m} = n \ cdot s: 30000}$
${\ displaystyle v_ {m}}$ = Mean piston speed in m / s
${\ displaystyle n}$ = Engine speed in 1 / min
${\ displaystyle s}$ = Piston stroke in mm

The maximum piston speed is essentially limited by the lubricating oil , the material combination of piston and cylinder and the thermal load on the piston (power), which is why the average piston speed only exceeds 20 m / s in racing engines.

In practice, the piston speed in Langhuber engines is similar to that in Kurzhuber engines . There are also hardly any differences between two-stroke and four-stroke engines. Even the small gasoline, methanol, and nitro engines in model airplanes have piston speeds similar to large diesel engines. Standard values ​​for mean piston speeds in mass-produced engines are between 10 and 15 m / s.

## literature

• Wilfried Staudt: Handbook Vehicle Technology Volume 2. 1st edition, Bildungsverlag EINS, Troisdorf, 2005, ISBN 3-427-04522-6 .
• Peter Gerigk, Detlev Bruhn, Dietmar Danner: Automotive engineering. 3rd edition, Westermann Schulbuchverlag GmbH, Braunschweig, 2000, ISBN 3-14-221500-X .
• Jan Drummans: The car and its technology. 1st edition, Motorbuchverlag, Stuttgart, 1992, ISBN 3-613-01288-X .