Stroke ratio

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Different stroke ratios with the same cubic capacity
Cylinder (blue), piston (gray) and crankshaft (red)

The stroke ratio is the ratio of the piston stroke to the cylinder diameter in a reciprocating piston engine , especially in a reciprocating piston engine .

A distinction is made between

  • Short stroke : stroke ratio <1 (stroke <cylinder diameter)
  • Square Huber : stroke ratio ≈ 1 (≈ stroke cylinder diameter), also referred to as "square design"
  • Long stroke : stroke ratio> 1 (stroke> cylinder diameter)

Short strokes are favorable for high speeds, since a shorter stroke causes lower linear speed and acceleration forces. They are typical for compact, high-speed reciprocating piston engines, especially gasoline engines .

Large, slow- running engines such as marine diesel engines , on the other hand, are designed as long-stroke engines . Their speed is limited by the cavitation on the directly driven screw. The long stroke results from the permissible mean piston speed . From a stroke ratio of 2 or more , the crank drive is designed with a connecting rod, crosshead guide, piston rod and disc piston instead of a connecting rod and plunger piston .

Typical stroke ratio values ​​are between 0.4 for four-stroke racing engines and up to 5 for marine diesel engines such as the two-stroke MAN B&W  5G45ME diesel engine .

See also


  • DIN 1940 standard "Combustion Engines", various editions since July 1946.