Research Papers: Lubricants

Tribochemistry on Clutch Friction Material Lubricated by Automatic Transmission Fluids and the Link to Frictional Performance

[+] Author and Article Information
Anne Neville

School of Mechanical Engineering,
University of Leeds,
Woodhouse Lane,
Leeds LS2 9JT, UK

Richard Vickerman

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

Contributed by the Tribology Division of ASME for publication in the Journal of Tribology. Manuscript received April 13, 2012; final manuscript received August 29, 2012; published online June 27, 2013. Assoc. Editor: George K. Nikas.

J. Tribol 135(4), 041801 (Jun 27, 2013) (11 pages) Paper No: TRIB-12-1055; doi: 10.1115/1.4024375 History: Received April 13, 2012; Revised August 29, 2012

Automatic transmissions (AT) for passenger cars are becoming more popular globally, including some countries that traditionally prefer manual transmissions. Some new friction modifiers for transmission fluid technologies have also emerged due to the downsizing trend of transmissions. In order to study the tribology and tribochemistry effects of some new automatic transmission fluid (ATF) additive formulations, both steel and wet-clutch friction materials were assessed by using surface analysis techniques. A variable speed friction test (VSFT) rig was used to study the antishudder properties in lock-up clutch tests and friction modifying mechanisms of ATFs. A test oil matrix containing basic ATF components was tested. The friction results were analyzed using both the linear-defined multiple parameter spider chart ATF evaluation (LSAE) method (Zhao et al., 2008, “A New Method to Evaluate the Overall Anti-Shudder Property of Automatic Transmission Fluids—Multiple Parameters Spider Chart Evaluation,” Proc. Inst. Mech. Eng., Part J: J. Eng. Tribol., 222(J3), pp. 459–470) and the friction coefficient ratio index method (Zhao et al., 2011, “Understanding Friction Behavior in Automatic Transmission Fluid LVFA Test: A New Positive Curve Parameter to Friction Coefficient Ratio Index Evaluation,” ASME J. Tribol., 133(2), p. 021802) (e.g., μ150 on the low-velocity friction apparatus (LVFA) μ-v curve results to compare the overall tribosystem and the snapshot friction performance during the test). Surface analysis results were obtained by using X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectroscopy (ToF-SIMS), and attenuated total reflectance Fourier transformed infrared spectroscopy (ATR FT-IR), and they are presented in this study to investigate the tribofilm compositions formed by different additive formulations. Some organic functional groups were found at the sample surfaces, such as –OH and O–C–O, and their presence is proposed to have a beneficial influence on the ATF friction performance. This paper discusses the surface analysis results of the test sample pieces, the possible links between specific functional groups and friction performance, and the proposed pathways of additive decompositions by using chemical bond dissociation energy comparisons.

Copyright © 2013 by ASME
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Fig. 2

VSFT test steel annulus and friction material plate configuration

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Fig. 3

Structure of VSFT test

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Fig. 4

(a) VSFT test (point 7 oil) posttest pieces (i) steel annulus test piece (ii) friction material plate and (b) Environmental Scanning Electron Microscope (ESEM) image of friction plate wear track

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Fig. 5

LSAE system format results of (a) base oil and single-additive oils—poor behavior group, (b) dual-additive oils results—intermediate group, (c) three-additive oils and fully formulated oil—good group, and (d) point 7, FF, and point 4 oil results comparison

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Fig. 6

Comparison of the LVFA results of three oil formulations at different durability test time: (a) point 7 oil, (b) fully formulated oil, (c) point 4 oil, and (d) P7, FF, and P4 oil's LVFA results at 120 °C after 16-h durability tests

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Fig. 7

ATR FT-IR spectra of P4, P7, FF oil posttest friction material wear track, and fresh sample surface

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Fig. 8

ATR FT-IR spectra of P7, FF, and P4 oil posttest friction material unworn area

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Fig. 9

Posttest friction material surface wear track XPS results of (a) point 4 oil, (b) point 7 oil, and (c) FF oil

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Fig. 10

Posttest friction material surface unworn area XPS results of (a) point 4 oil, (b) point 7 oil, and (c) FF oil

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Fig. 11

ToF-SIMS negative scan on OH peak comparisons. (a) OH spectra outside and inside wear track comparison, (b) OH chemical image on the fresh friction material sample, (c) OH chemical images of three oils tested sample surfaces—outside the wear track, and (d) OH chemical images of three surfaces—inside the wear track.

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Fig. 12

OH and CH3O ion peak intensity versus friction coefficient plot

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Fig. 13

ToF-SIMS positive scan on C4H9O peak spectra comparison

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Fig. 14

C4H9O chemical images of three sample wear track areas from ToF-SIMS

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Fig. 15

Proposed FM2 adsorption pathway on the friction material surface




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