Thermal and Electrical Compatibility of Lubricants in Electrified Transmissions
Authors: Tuero, A.G., Rivera, N., RodrÃguez, E., Viesca, J.L. and Battez, A.H.
Journal: Lecture Notes in Mechanical Engineering
Pages: 57-67
eISSN: 2195-4364
ISSN: 2195-4356
DOI: 10.1007/978-981-99-9264-5_5
Abstract:When the electric motor (EM) of a hybrid electric vehicle (HEV) is located inside the transmission housing, the cooling performance and the electrical compatibility of the automatic transmission fluids (ATFs) play a more relevant role. These two features depend on both physicochemical and thermal properties of the lubricant, but these properties change with the aging or oxidation of the ATF. This work studies the influence of external factors like temperature, time, and air exposition on the oxidation of three commercial ATFs and how this oxidation affects properties such as density, viscosity, thermal conductivity, heat capacity, ionicity, and some cooling-related figures-of-merit (FOMs) of the fluids, and thus, their cooling performance and electrical compatibility. The results showed that the molecular structure of the ATFs has more influence on thermal conductivity and heat capacity than on density, and hardly affects the FOMs of the fresh lubricants. Those ATFs formulated with API Group III base oils resulted in better cooling properties than the ATF with base oils from API Group I. The electrical compatibility of the tested lubricants was good for the three ATFs after the thermo-oxidative process, and it was less affected in the ATF with a higher content of additives. The electrical conductivity measurements showed to be a better method to check the degradation of the ATFs at the initial stages than FT-IR.
Source: Scopus