Photon Factory Activity Report 2005 #23 Part B (2006)
Applied Science

9A/2005C022

XANES study of tribofilms generated from belt-drive continuously variabletransmission fluid
Yoshimu IWANAMI*1, Hisayuki WADA1, Masaharu NOMURA2
Nippon Oil Corporation, 8, Chidoricho Naka-ku, Yokohama, 231-0815, Japan
2
KEK-PF, Tsukuba, Ibaraki 305-0801, Japan

Experimental
The block-on-ring friction test[3] was employed toprepare tribofilms and measure the friction coefficients of
4 test fluids at the 30-minute duration point (Table1). The
test conditions are described elsewhere [3]. The
concentrations of S, P, and Ca in CVTF-1 are 5000, 600
and 1300ppm; and those in CVTF-2 are 900, 200 and500ppm, respectively. Tribofilms at 30-minute point ofthe friction test were then subjected to XANESmeasurement.
The S K-edge XANES measurements were carried out
at BL-9A. The samples were placed in a flowing helium
environment, and the spectra were collected using afluorescent ion chamber in the fluorescence yield mode.
Table1: Friction coefficients of test fluids
Test fluidFriction coefficient
CVTF-1
0.141
CVTF-1+Friction Modifier(FM)
0.120
CVTF-2
0.138
CVTF-2+Detergent(Det)
0.119
Results and Discussion
The friction coefficients of both CVTF-1 and CVTF-2
decrease when additives such as a friction modifier and adetergent were added (Table1). Sulfur-containing
compounds in CVTFs are thought to react readily withmetal surface and play an important role in the formationof tribofilms. So, in order to clarify whether additives
affect the chemistry of the S species in the tribofilms, the246

Users' ReportS K-edge XANES
spectrawereCVTF-2+Det
examined. In both
CVTF-1 and CVTF-2,CVTF-2
the shape of theCVTF-1+FM
XANESspectrachanged after theCVTF-1
additives were added(Fig.1). This indicatesthat the chemistry of
the S species in thefilms changed after
theadditionof
2460
2480
2500
additives. In order toPhoton energy (eV)estimate the ratio ofFig. 1 S K-edge XANESthe S species in thefilms, the XANES spectra of films were pattern-fittedwith those of sulfur-containing model compounds
expected to be in the tribofilms. As a result of patternfitting, it was found that the ratios of sulfides with the
exception of iron disulfide decrease in the films when theadditives are added to both CVTF-1 and CVTF-2 (Fig. 2).
Thus, additives such as friction modifiers affect the ratioof sulfur compounds in the tribofilms.
This suggests the following: the decrease in the friction
coefficient by adding additives such as friction modifiersand detergents to CVTFs is the result of decrease in theratio of sulfides (except iron disulfide) in the tribofilms.

IF/I0Introduction
Belt-drive continuously variable transmissions (CVTs)
have attracted attention because they give better fuelefficiency than conventional automatic transmissions(ATs). Belt-drive CVT fluids (belt-drive CVTFs) musthave not only the same physical properties as ATs, suchas low temperature fluidity, oxidation stability, but alsohigh friction coefficients between the belt and pulley inthe transmission system to convey forces efficiently[1].
The friction coefficient of a belt-drive CVTF is governedby its composition. The additives in CVTFs react withmetal surfaces to form tribofilms. However, it is very
difficult to predict the properties of the films only byanalysis of the additives in fluids. In order to design highperformance belt-drive CVTFs, it is necessary toinvestigate the nature of the tribofilms that directly
govern friction coefficients.
In this paper, we report relationship between chemistryof the S species in the films and friction coefficient when
extra additives are added to CVTFs[2].

References
1
Ratio of sulfur species

1

SulfateSulfite

0.8

FeS2

0.6
OrganicsulfideZnS

0.4

FeS

0.2
0CVTF-1 CVTF-1 CVTF-2 CVTF-2++FM
Det

Fig. 2 Ratio of sulfur species in tribofilms[1] Y. Mabuchi et. Al., Trib. Trans. 43, 229 (2000).
[2] Y. Iwanami et. al., ‘ITC Kobe 2005’, 319 (2005).
[3] William C. et. al., ’98 TVT Symposium’, 82 (1998).
*yoshimu.iwanami@eneos.co.jp