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Theoretical Relationships
Radial Pressure Distribution

Radial pressure distribution is an important aspect that determines the sealing function between the piston ring periphery and cylinder wall [7].
Continuing development led from constant unit pressures (Fig. 6) to unit pressures with a variable radial pressure distribution (Fig. 7, Fig. 8) designed to influence piston ring behaviour in the engine. Variable radial pressure distributions in the past could only be created when there was an additional requirement for positive or negative ovality.
The measure of ovality is assumed as the difference between outer diameters measured in the direction ring gap/ring back and at an offset of 90°.

Fig. 6: Radial Pressure Distribution "Constant Characteristic" (round)

Fig. 7: Radial Pressure Distribution "Four-Stroke Characteristic" (positive ovality)

Fig. 8: Radial Pressure Distribution "Two-Stroke Characteristic" (negative ovality)


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