Development of ILSAC GF-5 0W-20 Fuel Economy Gasoline Engine Oil

摘要

We report in this paper our newly developed technology applied to ILSAC GF-5 0W-20 engine oil that offers great fuel economy improvement over GF-4 counterpart, which is a key performance requirement of modern engine oil to reduce CO_2 emissions from a vehicle. Our development strategy of the oil consisted of two elements: (1) further friction reduction under mixed and hydrodynamic lubrication conditions considering use of roller rocker arm type valve train system and (2) lowering viscosity at low temperature conditions to improve fuel economy under cold cycles. Use of roller rocker arm type valve train system has been spreading, because of its advantage of reducing mechanical friction. Unlike engine with conventional direct-acting type valve train system, lubrication condition of engine with the roller rocker arm type valve train system has higher contribution of mixed or hydrodynamic lubrication conditions rather than boundary lubrication condition. Therefore, engine oil for new vehicles, equipped with roller rocker arm type valve train system, should have better friction reduction performance under mixed or hydrodynamic lubrication conditions. Fuel economy improvement under cold conditions has been attracting attention, since it is worse than that under warmed-up conditions. Most of authorized fuel economy tests therefore adopt evaluation under cold driving cycle in addition to hot driving cycle to better simulate real-world fuel economy of vehicles. Consequently, engine oil should offer better fuel economy under cold conditions as well. Based on the strategy, we have conducted extensive study and clarified that a specific organic friction modifier greatly reduced friction under mixed lubrication condition, compared to conventional molybdenum-based friction modifier. We also established low viscosity technology to reduce viscometric resistance under hydrodynamic lubrication condition at low temperature, maintaining sufficient viscosity at high temperature condition. We formulated GF-5 0W-20 engine oil based on the principle of the technology through the study and confirmed significant fuel economy improvement at EC cold test cycle. In addition, the oil demonstrated enough fuel economy retention performance after an aging equivalent to mileage of 10,000 km.