Modern Automotive Gear Oils - Classification, Characteristics, Market Analysis, and Some Aspects of Lubrication

Abstract

1.1 Classification of automotive gear oils Modern gear oils can be divided into three main groups (Chwaja, Marko, 2010): manual transmission fluids (MTF) intended for lubrication of automotive manual gear boxes, transaxles, axles, and differentials, automatic transmission fluids (ATF) which lubricate: step-type automatic transmissions (AT), double clutch transmissions (DCT), and continuously variable transmissions (CVT), oils for lubrication of gears in off-road vehicles (e.g. tractors). In European automotive market manual transmission fluids (MTF) are predominant with over 75% of the market compared to only 25% of ATFs. However, in USA and Japan the situation is reversed: ATFs take respectively 92% and 75% of the market, leaving 8% and 25% to MTFs. This chapter concerns solely the first group of oils, i.e. manual transmission fluids (MTF); for simplification, the equivalent name “automotive gear oils” will be used throughout the text. There are two different classifications of automotive gear oils. The first one specifies lubricant service designations or the so-called performance levels of automotive gear oils. It has been provided by the American Petroleum Institute (API) in the API Publication 1560, 7th Edition, published in July, 1995. The API classification divides automotive gear oils into 7 performance levels. Four performance levels are in current use, three are not. The reason for the performance level not to be in current use results from the unavailability of test equipment and does not mean that such products have been withdrawn from the market. The API classification has been described in Tab. 1 (API designations in current use) and Tab. 2 (designations not in current use). Apart from the designations from Tabs. 1 and 2, there is also a class denoted as API GL-5(LS) or GL-5+. Gear oils that meet the requirements of this class contain special friction modifiers (FM) preventing from the stick-slip occurrence under conditions of limited slip (LS). As such, GL-5(LS) oils are intended for lubrication of limited slip differentials. To reduce the number of various gear oils in the market and in turn simplify oil selection, many lubricant manufacturers implement more universal (multi grade) gear oils. In this group gear oils denoted as API GL-4/GL-5 or GL-4+ predominate.