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-on-disk 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 ΰC. 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 dμ/dυ 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.
Highlights
Wet clutches are components widely used for power shifting, lock-up, and continuously slipping to transmit torque in automatic transmissions (ATs) from cars
Another common effect of thermal ageing in automatic transmission fluids (ATFs) is the depletion of additives, in particular, zinc dialkyldithiophosphates (ZDDPs)
The area created by the absorbance in the peak near to 968 cm‒1 represents the content of this kind of additives in the sample according to that specified in the standard method ASTM D-7412, so a decrease of intensity of this area suggests ZDDPs depletion
Summary
Wet clutches are components widely used for power shifting, lock-up, and continuously slipping to transmit torque in automatic transmissions (ATs) from cars. 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 plates, and audible noise (squeal, chatter, and shudder) [1].
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