Investigations of the Friction Losses of Different Engine Concepts. Part 2: Sub-Assembly Resolved Friction Loss Comparison of Three Engines

Abstract

In this work, friction loss investigations and comparisons of three different four-cylinder engines for passenger car applications are presented, using a recently developed combined approach. By merging extensive experimental with reliable and predictive journal bearing simulation results, a sub-assembly-resolved friction loss analysis of the piston group, crankshaft journal bearings and valve train is conducted for all three engines. The engines have been chosen individually based on their specific power output and crank train geometry. The measurement program covers a wide range of corresponding engine operation points (identical speed, load and thermal boundary conditions). In addition, the investigations are carried out for different engine media supply temperatures ranging from 70 ∘ C to 110 ∘ C for a comprehensive consideration of the friction losses at reduced lubricant viscosity. For reasons of comparability, all investigations conducted in this work have been carried out using the same modern SAE 5W30 lubricant. This is done to exclude influences from different lubricant properties which may have significant effects on the tribological behaviour of the engines’ sub-assemblies. While the diesel engine showed a friction reduction potential over the entire engine operation range when increasing the engine media supply temperatures, the gasoline engines showed a different behaviour. For the gasoline engines, disadvantages arise especially at low engine speeds. By using the developed combined approach, it was possible to assign mixed lubrication regimes at the valve train systems and at the piston groups.