Methoden und Modelle zur Auslegung von Mikrostrukturen
Final Report Abstract
The main objective of this sub-project consisted in the development of simulation techniques for the tribological characterization of deterministic and stochastic surface structures considering friction, wear and oil consumption in the piston ring-cylinder syslem. On the basis of fluid dynamic computations the influence of micro dimple geometry on the load carrying capacity of lubricated contacts was investigated in the first phase. Results clearly show lhat micro dimples support an increased load carrying capacity, while details in the cross section geometry of the dimpels are of only minor influence on hydrodynamic loads. In addition the effects of different dimple configurations were investigated. It was concluded that the exit length is the most relevant geometric feature for an increased hydrodynamic pressure. In the second project phase the concept of flow tensors was used to transfer the results of the first phase to the piston ring-cylinder liner contact. Calculation of the flow tensor's principal values (the flow factors), the friction factors and contact pressures was performed using the program FLOSIM and the results stored in lookup tables as a function of gap height. With these tables, subsequent programs (KORl, PRO) were employed to compute piston ring motion, piston ring friction and oil consumption. Four different liner manufacturing techniques were compared: honing (series process), fine honing, machining and thermal coating. Results show that close to the top dead center (TDC) position, structured (dimpled) liners exhibit lowest friction rates. All other surfaces show very similar friction rates. Surfaces with micro dimples exhibit low oil consumption especially at low engine speeds. Test results from the one cylinder test engine, provided by ITV, were used to validate the simulation. A comparison between test and simulation shows good agreement.
