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Research Papers: Lubricants

Understanding Friction Behavior in Automatic Transmission Fluid LVFA Test: A New Positive Curve Parameter to Friction Coefficient Ratio Index Evaluation

[+] Author and Article Information
Hongyuan Zhao

Institute of Engineering Thermofluids, Surfaces and Interfaces (iETSI), School of Mechanical Engineering, University of Leeds, Woodhouse Lane, Leeds LS2 9JT, UKh.zhao@leeds.ac.uk

Ardian Morina, Anne Neville

Institute of Engineering Thermofluids, Surfaces and Interfaces (iETSI), School of Mechanical Engineering, University of Leeds, Woodhouse Lane, Leeds LS2 9JT, UK

John Durham

 Lubrizol Limited, P.O. Box 88, Belper DE56 1QN, UK

Richard Vickerman

 The Lubrizol Corporation, 29400 Lakeland Boulevard, Wickliffe, OH 44092-2298

J. Tribol 133(2), 021802 (Mar 22, 2011) (9 pages) doi:10.1115/1.4003480 History: Received March 30, 2010; Revised December 22, 2010; Published March 22, 2011; Online March 22, 2011

The frictional characteristics of some basic additive systems used in automatic transmission fluids (ATFs) were assessed using a variable speed friction test machine. The test evaluates the coefficient of friction in unidirectional sliding contact over a range of speeds, loads, and temperatures. Tests were performed on a steel-versus-clutch friction material tribocouple, mainly to establish the link between the lubricant/surface interactions and additive system performance. A new parameter that measures the positive μ-v curve slope speed range was applied, together with friction coefficient ratio index, to show the antishudder property. It is suggested that this is a good complimentary method to the friction coefficient ratio index evaluation. Lubricant formulation is important to the overall friction performance. Both friction modifiers and detergents are shown to be important to the ATF antishudder performance. Oil absorption ability of the post-test friction material surface is proposed to be an important parameter to indicate the antishudder durability in the test. The detergent and antiwear agents are also suggested to be responsible for the decreased oil absorption and pore plugging of the friction material surface.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

VSFT test sample pieces

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Figure 2

VSFT test steel annulus and friction material plate configuration

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Figure 3

VSFT test sequence

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Figure 4

Two antishudder property evaluation methods

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Figure 5

Antishudder property comparison of the oils based on both μ1/μ50 friction coefficient ratios and friction curve analysis methods

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Figure 6

Four oils’ LVFA result comparison at 8 h, 27°C

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Figure 7

Antishudder performances durability results of four oils

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Figure 8

3D-Talysurf results of fresh and post-test sample surfaces

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Figure 9

ESEM images of fresh and post-test sample surfaces

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Figure 10

Oil absorption results of post-test friction material samples

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Figure 11

Post-test sample surface XPS results C 1s peak fittings

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