Ab welcher Drehzahl greift die Schubabschaltung? | Posts 16+

@ SeatArosa1.7SDI:

It seems you don't know that the radial pressure exerted by the piston rings primarily depends on the pressure inside the combustion chamber.
The piston rings seal axially against the lower face (away from the piston crown) because they are pressed axially against it by the pressure in the combustion chamber. Furthermore, this creates (intentionally!) a connection between the back of the piston ring and the combustion chamber on the upper side, within the axial piston ring clearance. The gas pressure can thus propagate behind the piston ring, applying pressure to the ring. This is absolutely necessary for the sealing function, as the small amount of mechanical pre-tension alone would never be sufficient to reliably seal the combustion chamber at ignition pressures of around 150 bar.

Regards,
Alex.

Aha, eine interessante Erklärung, die ich zum ersten Mal hörte. DThank you!

That also means that the top piston ring is subjected to a significantly higher radial pressure than the lower rings? (due to the pressure gradient between the individual rings).

Best regards,

That's right! That's why the top ring is also called the compression ring.
The oil scraper ring is now practically only pressed against the surface by mechanical pre-tension.

The shape of the piston ring on the outer surface determines what is known as the "relief factor" of the ring. On the inner surface, the entire ring width is subjected to chamber pressure. Depending on the position of the sealing line on the outer surface, different levels of ring pressure can be designed. For example, if the sealing line is placed in the middle of the ring, then 50% of the area is pressure and force-balanced on both the inner and outer sides. The remaining ring height beyond the sealing edge is subjected to a lower pressure on the outer surface. This results in a force surplus from the inside to the outside, which provides the pressure for the ring.
One can determine the optimal balance between sealing, friction, and wear in a constructive manner.

Regards,
Alex.