Optimization of the piston assembly friction

Abstract

Increasingly stringent emission standards creates the key challenge for the automotive industry to reduce the CO2 emissions of modern internal combustion engines further and further. Besides the thermodynamic innovations, one of the most effective ways is the improvement of the mechanical efficiency of existing engine components. About 5 - 8 % of the fuels energy get lost by the friction of the piston assembly consisting of piston, piston rings and cylinder liner. Hence, this system causes the largest amount of the mechanical losses in an internal combustion engine. Accordingly a high optimiza- tion potential is imputed to the piston assembly. [1], [2] The piston assembly is the most complex tribological system of the internal combus- tion engine. The continuously changing boundary conditions like pressures, velocities and temperatures cause different friction states. At high velocities and high lubrication hydrodynamic friction occurs. In the area of the dead centers boundary friction ap- pears. Furthermore additional functional parameters like wear, acoustics, oil consump- tion and blow-by must be considered in a friction optimization of the piston assembly. This complex challenge requires a high level of system knowledge, which demands systematic experimental verifications. Therefore, a test carrier based on the floating liner method was developed and operat- ed at the Institute of Internal Combustion Engines of the Technical University of Mu- nich. This research engine enables to measure the friction forces of the piston assem- bly high accurate, crank angle resolved and in a technically relevant field. In a joint research project with Federal-Mogul GmbH specific component tests were performed with the aim to understand and prove the relevant influences of piston assembly de- sign features on the friction force.