Influence of oxidation of automatic transmission fluids (ATFs) and sliding distance on friction coefficients of a wet clutch in the running-in stage

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.

Structural Design and Friction Performance Test of a New Conical Groove Friction Disks in Wet Clutch

“…Similar behavior was observed by Mohee [13] with CFRP-copper and CFRP-aluminum couples [14]. Farfán [15,16] carried out a series of pin-on-disk tests to evaluate the frictional behaviors of different lubricants. The pin-on-disk test was applicable to evaluate the friction behavior of friction disks, but could not evaluate the multi-cone configuration.…”

Friction Coefficient of Wet Clutches as a Function of Service Mileage

“…In practical applications, the precise control of the transmission torque of the wet clutch is based on the test calibration of the friction coefficient in the new clutch. However, the friction coefficient in the wet clutch changes as the service process proceeds [8,9]. This leads to a decrease in the accuracy at which the vehicle's transmission torque can be controlled, affecting the comfort and safety of the vehicle.…”

Cooling Performance of Fresh and Aged Automatic Transmission Fluids for Hybrid Electric Vehicles

“…It is very important to study how the changes over time in the composition and degree of oxidation influence the thermophysical properties of ATFs and the impact of these changes on the heat transfer/cooling performance and efficiency of the ATFs. Numerous studies have investigated the changes in viscosity, friction reduction, thermogravimetry, and electrical conductivity of fresh and aged/used ATFs [16][17][18][19][20], but none of these have studied the cooling performance of these ATFs through properties of figures of merit, except in the case of thermal conductivity. The goal of this work is to study the cooling performance and efficiency of three conventional ATFs, and the influence of their composition and aging on these characteristics.…”