Due to the global drive for carbon neutrality, passenger vehicle gasoline engines are transitioning to higher levels of electrification, such as hybrid electric vehicles and plug-in hybrid electric vehicles, HEVs and PHEVs. Compared with conventional internal combustion engine (ICE) vehicles, the HEV or PHEV engine whilst in ICE only operation, typically operates for multiple shorter periods, in turn the engine coolant and lubricant temperatures are lower.
Conventional internal combustion engines are often able to yield valuable fuel economy benefits by selecting appropriate engine lubricating oils, typically employing reduced viscosity and suitable additives. There are commercial engine tests available for measurement, often in an engine test cell for precision. Steady state testing is also a simplified option.
Such efforts require care, as the accurate measurement is technically and practically challenging. This level of difficulty is again increased by the further complication of vehicle hybridisation, aspects of which are discussed. However, this paper presents comparison data of similar engine technology in different vehicle types, namely ICE and two different types of HEV, with different engine operation strategies, to show an effect on lubricant differentiation for fuel economy. Possible explanations of the results are discussed.
Based on field observations, an often highly loaded area of the gasoline direct injection (GDI) ICE is the high-pressure (HP) fuel pump with oil lubricated cam and follower. This often presents a challenge for the engine lubricant. A novel test rig is described, which measures GDI HP fuel pump friction accurately. Further comparison data showing the contribution of this to the engine friction is presented over the transient Worldwide Harmonized Light Duty Transient cycle, WLTC, for both ICE and HEV operation in charge sustaining mode; lubricant friction differentiation in this area is shown.
The choice of a relevant drive cycle is important for developing new and existing lubricant products. The range of engine operation strategies controlled by both the vehicle and the driver is much wider for hybrid engines, when compared with standard ICE vehicles. To illustrate aspects of this, some recent on road PHEV data is also presented.