The major targets of transmission design are higher efficiency, higher torque capacity and reduced size. Increasingly smaller transmissions with higher torque lead to increasing operating temperatures. This trend is further intensified by the use of noise abatement devices and improved aerodynamic body styling that reduces the airflow around transmissions. The friction in the transmission is responsible for temperature increase and efficiency losses, and thus the reduction of friction is the main measure in order to improve the efficiency and to keep the operating temperature low. The torque transmission losses and, as a consequence, the operating temperature can be reduced by the right choice of base oil and additives. In vehicle application today, most OEMs start the lubricant development in an early phase of the development of a new transmission in order to get the optimum contribution of the lubricant. The OEMs have developed screening tests with good correlation to field performance. Such tests range from a simple bearing test to OEM-specific transmission or axle tests. Two tests developed by VW have been used, that correlate well with a car installed on a chassis-dynamometer and a transmission rig test, in order to identify and quanitfy the influences of fluid viscosity, base stock types, and VI Improver chemistry on efficiency and operating temperature. Finally, examples of improved semi- and fully synthetic formulations with significantly reduced operating temperatures and optimum efficiency are presented.
Influence of viscosity index improvers on transmission efficiency
Einfluß von Viskositätsindexverbesserern auf den Kraftübertragungswirkungsgrad
2004
10 Seiten, 24 Bilder, 4 Tabellen, 17 Quellen
Aufsatz (Konferenz)
Englisch
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