Lubrication systems play a major role not only in the durability of modern IC engines but also in performance and emissions. The design of the lubrication system influences the brake thermal efficiency of the engine. Also, efficient lubrication reduces the engine's CO2 emissions significantly. Thus, it is critical for an IC engine to have a well-designed lubrication system that performs efficiently at all engine operating conditions. The conventional lubrication system has a fixed-displacement oil pump that can cater to a particular speed range. However, a fully variable displacement oil pump can cater to a wide range of speeds, thereby enhancing the engine fuel efficiency as the oil flow rates can be controlled precisely based on the engine speed and load conditions.
This paper primarily discusses the optimization of a lubrication system with a Variable Displacement Oil Pump (VDOP) and a map-controlled Piston Cooling Jet (PCJ) for a passenger car diesel engine. The drive ratio for the variable oil pump has been optimized with minimum pump capacity to reduce power consumption as well as meet the engine flow rate requirements. Performance of the lubrication system was evaluated with two different drive ratios, considering the multiple application variants that have been presented in the paper. Also, the oil pressure limits were mapped across the engine speed range such that the maximum oil pressure was limited within the durability target oil pressure limits to get the maximum fuel economy benefits. The significant reduction in oil pressure played a key role in reducing oil pump power consumption and enhancing overall engine efficiency as well. PCJ consumes approx. 20% of total oil flow across all engine speeds, irrespective of thermal load acting on the piston. By switching off the PCJ based on thermal load, it can reduce the required oil pressure, which can be regulated by VDOP. With the combined efforts of VDOP Optimization in combination with a map-controlled Piston Cooling Jet, a fuel economy improvement of ~1.5% in standard test conditions was demonstrated in comparison to the conventional fixed displacement oil pump.