Andreas Leson

The oil supply at the interface between the top ring and the cylinder liner (TRCL) plays a major role in an internal combustion engines efficiency. In particular, the interface forms a trade-off between the serving of enough lubricant for sufficient lubrication conditions and emissions through subsequent combustion. This can lead to deficient top ring lubrication conditions. In this study, a new developed reciprocating long-stroke tribometer, enabling the variation of oil supply, is used to investigate such application-like starved lubrication conditions of the TRCL interface. With the simulative investigations, a comparison with the fired engine is possible. The performance of diamond-like carbon coatings is compared to standard nitrided piston rings. It was found that the tetrahedral amorphous carbon (ta-C) coatings exhibit up to 31% reduced friction as well as a lower wear under starved lubrication conditions. Simulative investigations show a good correlation between engine friction and tribometer measurements for selected oil supply conditions.

In this study, both the plasma process of filtered laser-arc evaporation and the resulting properties of tetrahedral amorphous carbon coatings are investigated. The energy distribution of the plasma species and the arc spot dynamics during the arc evaporation are described. Different ta-C coatings are synthesized by varying the bias pulse time and temperature during deposition. An increase in hardness was observed with the increased overlapping of the bias and arc pulse times. External heating resulted in a significant loss of hardness. A strong discrepancy between the in-plane properties and the properties in the film normal direction was detected specifically for a medium temperature of 120 °C during deposition. Investigations using electron microscopy revealed that this strong anisotropy can be explained by the formation of nanocrystalline graphite areas and their orientation toward the film’s normal direction. This novel coating type differs from standard amorphous a-C and ta-C coatings and offers new possibilities for superior mechanical behavior due to its combination of a high hardness and low in-plane Young’s Modulus.

Funktionale Oberflächen sind der Schlüssel zu innovativen Produkten. Schon heute bestimmen sie sowohl im industriellen als auch im Endverbraucherbereich zunehmend Gebrauchseigenschaften, Lebensdauer und Preis der meisten Güter, ganz allgemein also denWert für den Kunden. In der vom BMBF geförderten Untersuchung “Produktionstechnik zur Erzeugung funktionaler Oberflächen” [1] ermittelten drei Fraunhofer‐Institute den aktuellen Stand der Produktionstechnologien im Bereich funktionaler Oberflächen, ihre Zukunftsperspektiven und den Forschungsbedarf. Die wesentlichen Ergebnisse sind in diesem Beitrag zusammengefasst. Den Bericht können Sie unter info@ist.‐ fraunhofer.de anfordern.