Tribology of Mechanical Systems: A Guide to Present and Future Technologies
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About 46 % of all lubricants are engine oils. This means that in spite of the decreasing amount of oil per car, the total amount of engine oil will represent a significant portion of the total lubricant consumption. Recently, the stress level on engine oils has increased tremendously and will increase further in the future. This development is a result of some specific requirements that became more and more important. They can be defined as improved fuel efficiency, reduced emissions and minimized customer service. To realize these goals a new additive and base oil technology has to be adopted. They are characterized by advanced mineral oils, synthetic oils and low-ash, and even no-sulfur-and no-phosphorous-containing additive components. Following this approach, significantly longer oil change periods are realistic, and at the end of this development fill-for-life engine oils will characterize these oils as design elements. All these oils are low viscosity oils that cover the increasing importance of an improved fuel economy. Low viscosity means augmented mixed film lubrication regimes with the potential of higher wear and significantly longer oil change periods, which can result in more oxidation products in the oil—both effects have to be overcome by significantly higher base oil qualities and new additive formulations. Most of these issues as well as their interrelation with engine design and technology parameters will be addressed in the following sections of this chapter.