Dispersants automatic transmission fluids

Dispersant VI improvers are used to a certain extent in engine oils but are more often used in automatic transmission fluids and multipurpose tractor fluids. Incorporating dispersancy into a polymer requires carefully engineered addition of a strongly polar functional group to the base polymer backbone. The most commonly employed functional groups are amines, alcohols or amides. Their mode of incorporation depends largely on the base polymer, and specific details will be described later. 

Together with engine oils, the other major industrial uses of dispersants are in automatic transmission fluids, gear oils and fuels. In general, the concepts developed in this chapter are also applicable to these applications. 

Automatic transmission fluids, ATFs Frictional behaviour is a key performance characteristic of an ATF. During operational lifetime, thermal and oxidation byproducts can form in the lubricant. These have the potential to fill the porous holes found in the surface of the transmission, causing the clutch plates to slip. A dispersant is necessary to keep these by-products suspended in the oil, and typical treat rates vary between 1 and 6%. Additionally, the dispersant can positively affect friction if chosen correctly. A number of reasons for this have been proposed, including... 

Typical manual transmission fluids additive packs contain 6-10 components, many being the same components used for modern automatic transmission fluids. The key differences are the treat levels of components, e.g. dispersants and friction modifiers, and the type and level of antiwear components. A typical manual gearbox standard operating temperature of 90 C is not as thermally challenging as that of a modern automatic transmission in excess of 120°C. This is usually reflected in the superior oxidative stability exhibited by modern automatic transmission fluids compared with manual transmission fluids. Table 10.3 shows the generic composition of a manual transmission fluid, with the component(s) that differ from an automatic transmission fluid highlighted. 

Chem. Descrip. Hydroxyethyl alkyl imidazoline Uses Adhesion promoter in solv.-based paints and varnishes dispersant wetting agent foaming agent corrosion inhibitor in min. oils and soivs., aq. systems friction modifier in automatic transmission fluids Properties Gardner 15 max. clear Iiq. sol. in ethanol, xylene, trichloroethylene, wh. spirit, paraffin oil, and dilute sulfuric, hydrochloric, phosphoric and acetic acids disp. in water m.w. 360 dens. 930 kg/m vise. 300 mPa-s- pour pt. 3 C clear pt. 28 C flash pt. > 100 C pH 10-11 (1% aq.) surf. tens. 28 mN/m (0.1%) Draves wetting 250 s (0.1%) Ross-Miies foam 180 mm (initial, 0.05%, 50 C) cationic 90% act. 

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