Reducing CO2 emission of cars and trucks is a major challenge for the industry. One way to decrease emissions of cars and trucks is to improve the fuel economy of vehicles. This has led the oil, additive and automotive industry to evaluate a great variety of options aimed at reducing energy losses. In this context, minimizing the energy lost by friction in automotive transmissions helps to improve fuel efficiency. The operating temperature for transmission lubricants keeps on increasing as a result of higher engine output, increased vehicle loading and improved aerodynamic body styling that reduces airflow around transmission. A higher operating temperature leads to shorter lifetimes of lubricant and can result in damage to the transmission. Therefore, an important parameter in formulating transmission lubricants is the ability to minimize the operating temperature through the selection of proper additives and base stocks. Using two tests developed at VW, the ARKL test and the FZG efficiency test rig evaluated the influence of the base stock type and viscosity and of the VI Improver chemistry and molecular weight on operating temperature and transmission efficiency. For a given oil type, the higher the viscosity at 100 deg C, the higher the end of test temperature (EOTT). For a given kinematic viscosity at 100 deg C, PAO's give a lower EOTT than an ester which, in turns, produced a lower EOTT than a mineral oil. Addition of a VI Improver to PAO 4 and to a mineral oil of grade 150 N results in an increase in EOTT. However, the level of EOTT increase depends on the nature of the base stock used for the blend. EOTT correlates in a first approximation with the VI of the formulation. VI Improved oils that exhibit a high EOTT have also a low kinematic and dynamic viscosity at EOTT. The PIB based oils had a significantly higher EOTT and lower viscosity at EOTT than any of the other test oils. Compared to monograde gear oil SAE 90 having the same KV 100 and formulated with the same DI package the use of multigrade oils lead to increased transmission efficiency. Compared to PIB, the use of PAMA as VII in the multigrades led to doubled efficiency increase in the temperature range of the MVEG test cycle. Torque loss in FZG test correlates well to the VI of the oils tested.
Influence of viscosity index improvers in lubricants on the mechanical efficiency and operating temperature of transmissions
2002
6 Seiten, 10 Bilder, 4 Tabellen, 8 Quellen
Conference paper
English
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