Modern lubricating oil formulations are formulated to exacting specifications often set by original equipment manufacturers. To meet such specifications, various additives are used, together with base oil of lubricating viscosity. Depending on the application, a typical lubricating oil composition may contain dispersants, detergents, anti-oxidants, wear inhibitors, rust inhibitors, corrosion inhibitors, foam inhibitors just to name a few. Different applications will govern the type of additives that will go into a lubricating oil composition.
A functional fluid is a term which encompasses a variety of fluids including but not limited to tractor hydraulic fluids, automatic transmission fluids including continuously variable transmission fluids, manual transmission fluids, hydraulic fluids, power steering fluids, fluids related to power train components and fluids which have the ability to act in various different capacities. It should be noted that within each of these fluids such as, for example, automatic transmission fluids, there are a variety of different types of fluids due to the various transmissions having different designs which have led to the need for fluids of markedly different functional characteristics.
Tractor hydraulic fluids and automatic transmission fluids are examples of functional fluids having very specific friction requirements. Because such fluids work in wet brake and/or wet clutch systems, the fluid must assist in smooth engagement of these brakes and clutches while maintaining desirably high frictional properties for effective brakes and clutches. These fluids require high friction coefficients. For example, tractor hydraulic fluids that involve wet brake systems must have a high friction coefficient to be effective. Further, automatic transmission fluids must have enough friction for the clutch plates to transfer power. However, the friction coefficient of fluids has a tendency to decline due to the temperature effects as the fluid heats up during operation. It is important that the tractor hydraulic fluid or automatic transmission fluid maintain its high friction coefficient at elevated temperatures, otherwise brake systems or automatic transmissions may fail.