Investigations of the friction losses of different engine concepts: Part 3: Friction reduction potentials and risk assessment at the sub-assembly level

One of the biggest requirements of today’s engine development process for passenger cars is the need to reduce fuel consumption. A very effective and economic approach is the use of low-viscosity lubricants. In this work, sub-assembly resolved friction reduction potentials and risks are presented for three different engine concepts. By using a developed combined approach, the friction losses of the base engines are separated to the sub-assemblies piston group, crankshaft journal bearings, and valve train over the full operation range of the engines. Unique analyzing of boundary conditions makes it possible for the first time to compare friction reduction potentials and possible risks, not only between diesel and gasoline engines for passenger car applications, but also with particular focus on the power density of the three engines. Firstly, the engines have been specifically chosen regarding their specific power output. Secondly, one identical SAE 5W30 lubricant suitable for all engines is used to neglect influences from different lubricant properties. Thirdly, identical test programs have been conducted at the same thermal boundary conditions at engine media supply temperatures of 70 ∘ C and 90 ∘ C. For the crankshaft journal bearings, high reduction potentials are identified, while risks arising occur at the valve train and the piston group systems