Simulation-based RNT measurements for oil supply optimization at the connecting rod bearing

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In the present study a systematic approach for the evaluation of oil pressure reduction potential has been implemented. Therefore the connecting rod bearing as one of the most loaded parts of the base engine has been subject of the investigations. In a first step, the oil supply from the main gallery to the connecting rod bearing has been simulated using 3D-CFD. In successively decreasing the oil pressure a borderline oil pressure slightly above the cavitation limit was identified. In the next step these results were used as input data for EHD simulations. Here wear indicators were employed in order to verify the critical oil pressure identified by 3D-CFD. With these findings a modified engine was equipped with an activated connecting rod bearing shell and an appropriate RNT measurement system. Measurements were performed at production oil pressure, borderline pressures identified by simulations and a critical pressure below the aforementioned value. The parameters varied were engine speed and load, oil temperature, oil viscosity and oil aeration. The wear rates determined in these experiments justified a significant decrease in oil pressure without noticeable increases in wear rates. As a last step these findings were validated employing a production engine with a modified oil pump and a reduced pressure level. While a durability test confirmed the expected wear behaviour, the fuel consumption effort was identified in a WLTC test.