Study on the Influence of Low-Viscosity Engine Oil on Engine Friction and Vehicle Worldwide Harmonized Light Vehicles Test Cycle Fuel Economy 2020-01-5062

To study the mechanism of the effect of low-viscosity oils on engine friction loss reduction so as to improve the vehicle fuel economy of the Worldwide harmonized Light vehicles Test Cycle (WLTC) by upgrading the Society of Automotive Engineers (SAE) viscosity grade of the factory fill oil from 5W30 to 0W20, eight 0W20 oil samples were blended with different doses of base oil, viscosity modifier (VM), and friction modifier (FM).

Theoretical analysis by AVL-EXCITE simulation of the key friction pairs combined with practical engine friction torque test and vehicle WLTC fuel consumption tests were carried out. The results showed that 0W20 oils can effectively reduce the engine friction torque by 5.64 Nm and the friction loss by 11.95% with the throttle fully opened; while with the throttle closed, the friction torque decreased by 3.53 Nm and the friction loss by 11.26%, resulting to the improvement of the vehicle WLTC fuel economy by 2.08%. Without deteriorating the durability of the engine, the application of 0W20 engine oil can help to achieve carbon dioxide (CO₂) emission reduction and the Corporate Average Fuel Consumption (CAFC) score accumulation.

Low viscosity plays a leading role in the WLTC low-speed and medium-speed segments, while VMs and FMs contribute more in the high-speed and extra high-speed segments, indicating that the oil viscosity is not the only key factor to reduce engine friction. The coordination of the whole oil formulation, low viscosity combined with different additives, is the key to reduce friction loss and achieve fuel economy.