In-Situ Measurements of the Piston and Connecting Rod Dynamics Correlated with TEHL-Simulation Techniques 2017-24-0157

High combustion pressure in combination with high pressure gradient, as they e.g. can be evoked by high efficient combustion systems and e.g. by alternative fuels, acts as broadband excitation force which stimulates natural vibrations of piston, connecting rod and crankshaft during engine operation. Starting from the combustion chamber the assembly of piston, connecting rod and crankshaft and the main bearings represent the system of internal vibration transfer. To generate exact input and validation values for simulation models of structural dynamic and elasto-hydrodynamic coupled multi-body systems, experimental investigations are done. These are carried out on a 1.5-l inline four cylinder Euro 6 Diesel engine. The modal behaviour of the system was examined in detail in simulation and test as a basis for the investigations.

In an anechoic test bench airborne and structure-borne noises and combustion pressure are measured to identify the engine´s vibrational behaviour. To understand the behaviour of the connecting rod as the key component in more detail its elongation, using semiconductor strain gauges at the connecting rod shank and a linkage system, is also measured. Furthermore temperature measurements of piston and liner under fired conditions, allow the determination of their warm contours for a better geometrical description. Variation of injection timing and connecting rod stiffness allows the basic adjustment of the simulation model. In a further step the simulation model is calibrated by the results of the measurement of the qualitative oil content in the gap between the liner and the piston. For this purpose a combined gap measurement system consisting of eddy-current and capacitive type sensors was specially developed. To adapt sensor and liner surface these are honed together after sensor installation. Finally the elasto-hydrodynamic simulation model is extended by a new software component to a so called thermo elasto-hydrodynamic coupled multi-body system. This leads, especially on Diesel engines, to an improved robustness of the simulation of NVH behaviour.