Influence of oxidation of automatic transmission fluids (ATFs) and sliding distance on friction coefficients of a wet cl
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ISSN 2223-7690 CN 10-1237/TH
RESEARCH ARTICLE
Influence of oxidation of automatic transmission fluids (ATFs) and sliding distance on friction coefficients of a wet clutch in the running-in stage Leonardo Israel FARFAN-CABRERA1,*, Ezequiel Alberto GALLARDO-HERNÁNDEZ2, Manuel VITE-TORRES2, Jesús Gilberto GODÍNEZ-SALCEDO3 1 2
Tecnologico de Monterrey, Escuela de Ingeniería y Ciencias, Ave. Eugenio Garza Sada 2501, Monterrey 64849, México Instituto Politécnico Nacional, SEPI-Escuela Superior de Ingeniería Mecánica y Eléctrica, Unidad Zacatenco, Grupo de Tribología, Col. Lindavista, Ciudad de México 07738, México
3
Instituto Politécnico Nacional, ESIQIE, IPN, Col. Lindavista, Ciudad de México 07738, México
Received: 15 January 2019 / Revised: 06 July 2019 / Accepted: 18 May 2020
© The author(s) 2020. Abstract: In this paper, the influence of oxidation of automatic transmission fluids (ATFs) and sliding distance on the friction coefficients of a wet clutch in approached running-in conditions was investigated. The ATFs were oxidized by a laboratory process approaching oxidation occurred in actual ATFs. Oxidation was evaluated by means of increase in carbonyl compounds and depletion of zinc dialkyldithiophosphates (ZDDPs) additives. Also, the changes in kinematic viscosity and viscosity index were evaluated. Pin-ondisk tests were conducted to replicate the actual sliding contact in a wet clutch. The pin specimens were cut from friction material composite plates and the disks were actual steel separators both from an automotive wet clutch. Friction coefficient, μ, was measured at progressive sliding velocity, ν, to obtain μ–ν curves at 26 and 100 °C. Three μ–ν tests were consecutively run using the same pair of specimens and oil. The cumulative sliding distance for each μ–ν test generated surface flattening using the oils. The friction coefficients of the wet clutch increased due to the ATFs oxidation meanwhile the d /dv values decreased in most cases. It suggests that ATF oxidation can enhance torque capacity of the wet clutch, but it could reduce anti-shudder property. Progressive sliding distance improved the slopes in the μ–ν results using fresh ATFs meanwhile it generated a slope decrease by using aged ATFs. Keywords: wet clutch; friction; oil oxidation; automatic transmission fluid (ATF)
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Introduction
Wet clutches are components widely used for power shifting, lock-up, and continuously slipping to transmit torque in automatic transmissions (ATs) from cars. In a clutch engagement, as load is applied to press the set of plates with relative rotating motion, the automatic transmission fluid (ATF) film at the plates is squeezed, so sliding contact of the opposing surfaces occurs to transmit torque.
Torque transmission across the disk interface is due to viscous shearing of the ATF and asperities contact between the surfaces of the plates. Low tribological performance either from the ATF or plates produces poor torque transmission, which leads to increased fuel consumption, vehicle vibration, excessive wear of
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