Piston engine

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Piston machines are fluid energy machines with a working space , the volume of which is intermittently changed by a usually periodically moving displacer ( piston ) . The fluid flow and pressure differences between inlet and outlet are variable in piston machines due to the intermittent mode of operation , which distinguishes them from continuously operating flow machines such as gas turbines , in which the fluid flow and pressure curve remain stationary .

In general, it can be both working machines (from the point of view of hydraulics : "transmitter" ), as well as power machines (motors; in hydraulics: "slave" ), with some piston machines also being able to work reversibly in both directions, such as hydraulic cylinders as well as some hydraulic pumps that work in reverse as a hydraulic motor or a Stirling motor that is driven as a work machine to become a heat pump . There are two different kinematic principles:

  • Reciprocating piston machines in which the displacer is a piston that moves back and forth in a cylinder . In the broadest sense , machines that work with a diaphragm ( diaphragm pump , diaphragm cylinder ) are also piston machines.
  • Rotary piston machines in which specially shaped displacers either only rotate or also revolve on a circular path.

Reciprocating engines

In reciprocating piston engines which is the displacer , a more or less disc-shaped piston (engl. Piston ) extending in a cylinder reciprocates or a cylindrical plunger , which, for example, in a stuffing box is running. There are reciprocating piston machines both as work machines ( pump = transmitter ) and as prime movers ( slave ) that drive a load, such as a hydraulic cylinder . Similar principles apply in pneumatics , but the compressibility of the working gas with compression and expansion must then also be taken into account. A distinction must be made depending on the type of kinematics :

Rotary piston machines

As a rotary piston machine , the Wankel engine is also one of the piston machines

In rotary piston machines rotation (physics) specially shaped displacers rotate so that the crank drive is not required. A distinction must be made here according to the type of kinematics :

Classification of rotary piston machines
designation Abbreviation Rotating inertial
mass forces
Rotary piston machines DKM - - Roots blower
Rotary piston machines KKM + - Rotary engine
Rotary piston- type rotary piston machines DUKM - +
Rotary piston-type rotary piston machines KUKM + + Vane pump

With DUKM and KUKM, the speeds are usually limited if the inertia forces cannot be balanced.

Machine type Working machines Power machines
Hydraulic piston machines
(≈ incompressible media)
Piston pumps Hydraulic motors
Thermal piston machines
(compressible media)
Reciprocating compressors Internal combustion engine,
gas expansion
engine, steam engine, Stirling engine

See also


  • Wolfgang Kalide: Pistons and flow machines. 1st edition, Carl Hanser Verlag, Munich Vienna, 1974, ISBN 3-446-11752-0
  • DIN 1940 standard "Combustion Engines", various editions since July 1946

Web links

Wiktionary: piston machine  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. a b c d H. Tschöke, K. Mollenhauer, " Dubbel - Taschenbuch für den Maschinenbau ", 24th edition 2014, section P1.1 " Definition and classification of piston engines ", Springer-Verlag Berlin Heidelberg, ISBN 978-3- 642-38890-3
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