Optimization of the Bearing Oil Supply Concept of a High Power-Density Diesel Engine to Minimize Oil Pump Friction 2020-28-0338

Reducing the mechanical friction of internal combustion engines could play a major role in improving the brake specific fuel consumption (BSFC). Hence, it is important to reduce the friction at every component and sub-system level. In the present work, the oil pump friction of a 1.5 liter 4-cylinder diesel engine is optimized by reducing the oil pump displacement volume by 20%. This could be achieved by adopting an optimized oil supply concept which could reduce the oil leakage through the main bearings and connecting rod bearings.

A 1-dimensional oil flow simulation was carried out to predict the oil flow distribution across the engine for different speeds. The results indicate that the oil leakage through the main bearings and connecting rod bearings contribute to ~25% of the total oil flow requirement of the engine. In a conventional oil supply concept, the big-end bearing of each connecting rod is connected to the adjacent main bearing through an internal oil hole. Though this is a standard and robust oil supply concept, the oil leakage through the bearings is relatively higher that demands a bigger oil pump. Hence, several design options were investigated to reduce the overall oil leakage through the bearings using a 3-dimensional elasto-hydrodynamic (3D EHD) simulation tool. Moreover, the robustness of the bearings was also checked by comparing the minimum oil film thickness, total contact pressure, asperity contact pressure and adiabatic temperature rise.

Based on the results, the oil feed concept was optimized in such a way that the oil supply for two of the big-end bearings is supplied from one main bearing. The main bearing shells were optimized in line with the new oil supply concept to overcome the challenges of operating under the peak cylinder pressure of 180 bar. Overall, with this optimized oil supply concept, the oil pump size could be reduced from a theoretical displacement volume of 24 cc/revolution to 19.5 cc/revolution. Thus, the optimization of the oil supply concept of the engine bearings could help to reduce the oil pump size and corresponding power consumption.