DESCRIPTION
CONTINUOUSLY VARIABLE TRANSMISSION OIL COMPOSITION
TECHNICAL FIELD
[0001]
The present invention relates to a continuously variable transmission oil
composition. In particular, the invention relates to a lubricating oil composition that
achieves excellent frictional properties between a metal belt and a pulley or between a
metal chain and a pulley in a continuously variable transmission comprising such metal
parts.
BACKGROUND ART
[0002]
Since a metal-belt type or metal-chain type continuously variable transmission
allows selective utilization of high combustion efficiency ranges of an engine, it has
been attracting attention as a transmission of excellent fuel saving capability. In
particular, an increasing number of car models are equipped with a metal-belt
continuously variable transmission in recent years. The metal-belt or metal-chain
continuously variable transmission is so configured that the torque is transmitted via the
friction between the metal belt or chain and the metal pulley, and the speed is changed
by varying the pulley radius ratio. Therefore, lubricating oil used for the metal-belt or
metal-chain continuously variable transmission is required to provide a high
metal-to-metal friction coefficient in order to improve the torque capacity.
[0003]
A method of adding zinc dialkyldithiophosphate has been proposed for
increasing the metal-to-metal friction coefficient (see Non-patent Document 1).
However, zinc dialkyldithiophosphate gets worn out through use, causing the problem
of decreased metal-to-metal friction coefficient. Moreover, some of the belt-type
continuously variable transmissions nowadays are combined with a wet clutch, which is
problematic because in such a situation the deterioration products of the zinc
dialkyldithiophosphate tend to clog the clutch plate and thus impair its function.
[0004]
Therefore, a variety of continuously variable transmission fluids that do not
contain zinc dialkyldithiophosphate have been proposed, such as a continuously
variable transmission oil comprising calcium salicylate, a phosphorus antiwear agent, a
friction modifier and a dispersion-type viscosity index improver (Patent Document 1), a
continuously variable transmission fluid comprising an ashless polyisobutenyl
succinimide dispersant, an organic phosphite, a calcium overbased phenate detergent, a
friction modifier containing a succinimide and an ethoxylated amine, and a primary
amide of a long-chain carboxylic acid (Patent Document 2), a continuously variable
transmission oil comprising a specific mineral lubricating oil base oil, a phosphorous
compound and a boron-modified succinimide as ashless dispersant (Patent Document 3),
a continuously variable transmission oil comprising a specific phosphorus compound
and a boron-modified succinimide as ashless dispersant (Patent Document 4), and a
continuously variable transmission oil comprising a boron-containing succinimide
ashless dispersant (Patent Document 5).
[0005]
However, the above transmission oils do not provide a satisfactory friction
coefficient for transmitting the high output of high-power engines, and further
improvements have thus been desired.
Meanwhile, a use of a lubricant or a functional oil comprising a combination of
a specific hydrocarbon-soluble aryl phosphate and a specific hydrocarbon-soluble aryl
polyphosphate as antiwear agent has been proposed (Patent Document 6). However,
Patent Document 6 does not disclose that the aryl polyphosphate may be used as an
additive for the continuously variable transmission oil or that it may increase the
metal-to-metal friction coefficient.
PRIOR ART DOCUMENTS
PATENT DOCUMENTS
[0006]
Patent Document 1: JP-A-2000-355695
Patent Document 2: JP-A-2000-336386
Patent Document 3: JP-A-2000-109875
Patent Document 4: JP-A-2000-109872
Patent Document 5: JP-A-2000-109867
Patent Document 6: Japanese Patent No. 3199844
NON-PATENT DOCUMENT
[0007]
Non-patent Document 1: Mabuchi et al, "Effect of CVTF additive, ZnDTP, on
improvement of transferred torque of belt CVT (First Report)", Japanese Society of
Tribologists, proceedings of the Tribology Conference (Tokyo 1998-5), p. 511.
SUMMARY OF THE INVENTION
PROBLEMS TO BE SOLVED BY THE INVENTION
[0008]
The present invention solves the above-mentioned problems, and thus an object
of the invention is to provide a continuously variable transmission oil composition that
significantly improves the friction coefficient between a metal belt or chain and a pulley,
maintains the high friction coefficient over a long period of time, and does not cause
clogging of a clutch plate.
MEANS FOR SOLVING THE PROBLEMS
[0009]
The present invention, as a means for solving the above problems, is as follows.
(1) A continuously variable transmission oil composition comprising a
lubricating oil base oil, and at least one phosphorus compound shown by the following
general formula (1) in such an amount that the phosphorus in the phosphorus compound
accounts for 0.005 to 0.15 mass% of the total mass of the composition,
[0010]

[0011]
wherein
each of R1, R2, R3 and R4 independently represents a hydrocarbyl group having 1 to 30
carbon atoms, or a hydrogen atom, with at least one of R1, R2, R3 and R4 representing a
hydrocarbyl group;
R5 represents a hydrocarbylene group having 1 to 30 carbon atoms;
X1 and X2 each represent an oxygen atom or a sulfur atom; and
n is an integer from 1 to 10.
[0012]
(2) The composition according to (1), further comprising at least one sulfur
compound that contains within each molecule one or more chemical bonds selected
from S-S bond, S-P bond, S=P bond, S-C bond and S=C bond, and no metal element, in
such an amount that the sulfur in the sulfur compound accounts for 0.005 to 0.15 mass%
of the total mass of the composition.
(3) The composition according to (1) or (2), wherein the sulfur compound is at
least one compound selected from polysulfide compound, thiophosphate ester
compound and thiophosphite ester compound.
(4) The composition according to any one of (1) to (3), further comprising a
succinimide dispersant in an amount of 0.5 to 10.0 mass% relative to the total mass of
the composition.
(5) The composition according to any one of (1) to (4), further comprising an
alkaline earth metal detergent in an amount of 0.05 to 1.0 mass% relative to the total
mass of the composition.
EFFECTS OF THE INVENTION
[0013]
Since the continuously variable transmission oil composition according to the
invention contains the specific phosphorus compound, and preferably further contains
the specific sulfur compound, the succinimide dispersant, and/or the alkaline-earth
metal detergent, it provides particularly advantageous effects including significantly
improved friction coefficient between the metal belt or chain and the pulley, prolonged
maintenance of the high friction coefficient, and avoidance of clogging of the clutch
plate.
MODES FOR CARRYING OUT THE INVENTION
[0014]
Lubricating oil base oil
A mineral base oil and/or a synthetic base oil, which is a commonly used
lubricating oil base oil, may be used as the lubricating oil base oil in the present
invention.
The mineral base oil used in the invention may be, for example, a paraffinic, a
naphthenic, or other type of lubricating oil base oil obtained by subjecting a lube oil
fraction (which is obtained by distilling crude oil under atmospheric pressure and
reduced pressure) to an appropriate combination of purification means such as solvent
deasphalting, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing,
hydrorefining, sulfuric acid treatment and clay treatment, or may be a lubricating oil
base oil obtained by subjecting the wax obtained in solvent dewaxing to isomerization
and further dewaxing. Generally, the kinematic viscosity at 100°C of the mineral base
oil is preferably 2 to 7 mm2/s, and more preferably 3 to 5 mm2/s. The viscosity index
of the mineral base oil is preferably 80 or higher, while the viscosity index of 100 or
higher is especially preferred.
[0015]
The synthetic base oil suitably used in the invention may be, for example, a
poly-a-olefin (such as 1-octene oligomer, 1-decene oligomer, ethylene-propylene
oligomer, and the like) or a hydrogenated product thereof, an isobutene oligomer or a
hydrogenated product thereof, an isoparaffin, an alkylbenzene, an alkylnaphthalene, a
diester, a polyol ester, a polyoxyalkylene glycol, a dialkyl diphenyl ether, a polyphenyl
ether, or the like.
[0016]
A viscosity index improver may be added to the lubricating oil base oil.
Specific examples of the viscosity index improver that may be used in the invention
include non-dispersion-type viscosity index improvers such as (co)polymer of one or
more monomers selected from various methacrylate esters and hydrogenated products
thereof, dispersion-type viscosity index improvers such as (co)polymers of various
methacrylate esters of nitrogen compounds, non-dispersion-type or dispersion-type
ethylene-a-olefin copolymers and hydrogenated products thereof, polyisobutylene and
hydrogenated products thereof, hydrogenated styrene-diene copolymers, styrene-maleic
anhydride copolymer, polyalkylstyrene, and the like, all of which are viscosity index
improvers commonly used in lubricating oils.
One or more viscosity index improvers selected from the above may be added in
appropriate amounts to impart the desired effect. The viscosity index improver is
preferably added in an amount of 1 to 20 mass% relative to the total mass of the
composition. It is preferable that the lubricating oil base oil including the viscosity
index improver has a kinematic viscosity at 100°C of 4 to 10 mm2/s, more preferably 5
to 9 mm /s, and has a viscosity index of 120 or higher, more preferably 140 or higher.
[0017]
Generally, it is preferable that the lubricating oil base oil is used in an amount of
98 mass% at most, more preferably in an amount of 98 to 62 mass%, relative to the total
mass of the composition (i.e. the continuously variable transmission oil composition).
The kinematic viscosity of the lubricating oil base oil may be appropriately selected
within the above ranges depending on the type of the continuously variable
transmission.
[0018]
Phosphorus compound
The continuously variable transmission oil composition according to the
invention comprises at least one phosphorus compound shown by the following general
formula (1).
[0019]

[0020]
In the general formula (1), each of the functional groups Ri, R.2, R3 and R4
independently represents a hydrocarbyl group or a hydrogen atom. However, Ri, R2,
R3 and R4 cannot all represent hydrogen atoms, i.e. at least one of them is a hydrocarbyl
group. Examples of the hydrocarbyl group include alkyl groups, cycloalkyl groups,
aryl groups, alkylaryl groups and the like. The number of carbon atoms of the
hydrocarbyl group is 1 to 30, preferably 1 to 20, and more preferably 3 to 9. R1, R2, R3
and R4 may have identical or different structures from one another. R5 represents a
hydrocarbylene group. Examples of the hydrocarbylene group include alkylene groups,
cycloalkylene groups, arylene groups, alkylarylene groups and the like. The number
of carbon atoms of the hydrocarbylene group is 1 to 30, preferably 1 to 20, and more
preferably 3 to 9. X1 and X2 each represent an oxygen atom or a sulfur atom, n is an
integer from 1 to 10, preferably from 1 to 5, and more preferably from 1 to 3. In the
case where n is plural, R4 (or R5 or X2) in one unit may have an identical or different
structure from R4 (or R5 or X2, respectively) in another unit. An especially preferable
compound of the formula (1) is tetraphenyl (m-phenylene) bisphosphate in which X1 and X2 each represent an oxygen atom, Ri, R2, R3 and R4 each represent a phenyl group,
R5 represents a phenylene group, and n is 1.
[0021]
The phosphorus compounds shown by the general formula (1) have been
disclosed in Japanese Patent No. 3199844, and can be synthesized according to the
disclosures therein. The phosphorus compounds are also widely known as flame
retardants for synthetic resins (see JP-A-2003-192919, for example), some of which are
commercially available. The phosphorus compound used in the present invention may
be suitably chosen from these commercially available ones.
The continuously variable transmission oil composition according to the
invention should contain at least one phosphorus compound shown by the general
formula (1), and it may further contain other phosphorus compounds, such as a
phosphate ester, a phosphite ester, an alkyl acid phosphate or an alkyl acid phosphite
each containing one phosphorus atom in the molecule, amine salts thereof, a
thiophosphate ester that further contains a sulfur atom in the molecule, and the like, all
of which are used as antiwear additives in common lubricating oils.
[0022]
The phosphorus compound shown by the general formula (1) is added in the
composition in such an amount that the mass of the phosphorus element in the
phosphorus compound accounts for 0.005 to 0.15 mass%, preferably 0.005 to 0.10
mass%, of the total mass of the composition. The total phosphorus content in the
composition is preferably 0.01 to 0.15 mass% relative to the total mass of the
composition, more preferably 0.01 to 0.10 mass%. If the amount of the phosphorus is
less than 0.005 mass%, the metal-to-metal friction coefficient may not be sufficiently
improved and sufficient antiwear performance may not be obtained. If the amount of
the phosphorus exceeds 0.15 mass%, the material compatibility may be compromised.
[0023]
Sulfur compound
The continuously variable transmission oil composition according to the
invention preferably contains at least one sulfur compound. The sulfur compound has
at least one S-S bond, S-P bond, S=P bond, S-C bond or S=C bond within an individual
molecule (i.e. intra-molecularly), and is devoid of a metal element. Specific examples
of the sulfur compound include dibenzyl disulfide which is a polysulfide compound
(R-Sn-R) having an S-S bond and S-C bonds in one molecule, and trilauryl
trithiophosphate which is a thiophosphate ester compound ((R-X)3-P=X, wherein X
represents an oxygen atom or a sulfur atom and at least one of the four Xs represents a
sulfur atom) having S-P bonds in one molecule. Further examples of the sulfur
compound include sulfide compounds (R-S-R), sulfoxide compounds (R-S(=0)-R),
sulfone compounds (R-S(=0)2-R), polysulfone compounds (R-[S(=0)2]n-R), thiazole
compounds, thiadiazole compounds, thiol compounds (R-SH), thioketone compounds
(R-C(=S)-R), thiophosphite compounds ((R-X)3-P, wherein X represents an oxygen
atom or a sulfur atom and at least one of the three Xs represents a sulfur atom), and the
like. Among these sulfur compounds, polysulfide compounds, thiophosphate
compounds and the thiophosphite compounds are particularly preferable. R in the
sulfur compounds above represents a hydrocarbon group, which may be an alkyl group,
aryl group, alkylaryl group, or the like. The number of carbon atoms of the
hydrocarbon group is preferably 1 to 30, and more preferably 1 to 20.
The sulfur compound may be selected from commercially available products
that are added to various lubricating oils such as gear oil, metalworking fluid, hydraulic
oil, automatic transmission fluid and the like, as an extreme pressure agent or for other
purposes. These sulfur compounds may be used either individually or in combination.
[0024]
The sulfur compound is preferably added to the composition in such an amount
that the sulfur in the sulfur compound accounts for 0.001 to 0.15 mass% of the total
mass of the composition, and more preferably 0.005 to 0.10 mass%. If the amount of
the sulfur is less than 0.001 mass%, the metal-to-metal friction coefficient may not be
sufficiently improved. On the other hand, if the amount of the sulfur exceeds 0.15
mass%, the oxidation stability and the wear resistance capability of the composition
may be compromised. The total sulfur content of the composition is preferably 0.005
to 0.20 mass%, more preferably 0.01 to 0.15 mass%.
[0025]
Succinimide dispersant
The succinimide dispersant which can preferably be used in the continuously
variable transmission oil composition according to the invention contains a succinimide
compound as a main component. Examples of the succinimide compound include
so-called mono-type succinimides shown by the following general formula (2) in which
a succinic anhydride is added to one end of a polyamine during imidation, and so-called
bis-type succinimides shown by the following general formula (3) in which a succinic
anhydride is added to each of the two ends of a polyamine, as well as variations of these
succinimides that contain boron.
[0026]
[0028]
In the formulas (2) and (3) above, R6, R7 and R.8 independently represent an
alkyl group or an alkenyl group, a is an integer from 1 to 10, preferably from 2 to 5, and
b is an integer from 1 to 10, preferably from 2 to 5.
[0029]
In the present invention any dispersant selected from these succinimide
compounds may be used. The dispersant may be selected from the commercially
available products that are used as ashless dispersant in various lubricating oils, such as
gear oil, metalworking oil, hydraulic oil, automatic transmission oil and the like.
These dispersants may be used either individually or in combination.
The succinimide dispersant is preferably used in an amount of 0.5 to 10.0
mass% relative to the total mass of the composition, and more preferably 2.0 to 8.0
mass%.
[0030]
Alkaline-earth metal detergent
An alkaline-earth metal detergent which may be preferably used in the
continuously variable transmission oil composition according to the invention can
reduce the sliding speed dependency of the friction coefficient between the belt or chain
and the pulley of a continuously variable transmission when the lubricating oil has
started deteriorating, and can improve the metal-to-metal frictional properties. The
alkaline-earth metal detergent used in the invention may comprise a sulfonate, phenate
or salicylate that contains an alkaline-earth metal, such as magnesium, calcium and
barium. So-called overbased metal detergent having a high base number (BN) may
also be used. In the present invention, one or more alkaline-earth metal detergents
selected from these compounds, or other compounds used as metal detergent in
common lubricating oils, may be used.
[0031]
The metal detergent is preferably added in an amount of 0.05 to 1.0 mass%
relative to the total mass of the composition, and more preferably 0.1 to 0.5 mass%.
This makes it possible to increase the friction coefficient and to significantly improve
the performance of the continuously variable transmission. If the metal detergent
content is within the above ranges, a high metal-to-metal friction coefficient can be
maintained even after the lubricating oil composition has been used for a long period of
time, and moreover, the oxidation stability of the lubricating oil is also maintained.
[0032]
Zinc dialkyldithiophosphate
The continuously variable transmission oil composition according to the
invention does not substantially contain a zinc dialkyldithiophosphate. The expression
"does not substantially contain" herein means that the continuously variable
transmission oil composition does not contain a zinc dialkyldithiophosphate at all, or
even if does, the amount of the zinc dialkyldithiophosphate is less than the amount that
would damage the function of the clutch plate due to clogging when the lubricating oil
has started deteriorating, or more specifically, the amount of the zinc
dialkyldithiophosphate is such that the zinc element in the said compound accounts for
no more than 0.001 mass% of the total mass of the composition. It is more preferable
that the continuously variable transmission oil composition does not contain a zinc
dialkyldithiophosphate at all.
[0033]
Other additives
The continuously variable transmission oil composition according to the
invention may further comprise other additives not mentioned above, such as
antioxidant, pour-point depressant, friction modifier, and the like.
A phenol compound, an amine compound or the like that is commonly used as
antioxidant for lubricating oil may be used in the present invention suitably. Specific
examples of suitable antioxidants include alkylphenols such as
2,6-di-tert-butyl-4-methylphenol, bisphenols such as
methylene-4,4-bisphenol(2,6-di-tert-butyl-4-methylphenol), naphthylamines such as
phenyl-a-naphmylamine, dialkyldiphenylamines, esters of a
(3,5-di-tert-butyl-4-hydroxyphenyl) fatty acid (e.g. propionic acid, etc.) and
monohydric or polyhydric alcohols (e.g. methanol, octadecanol, 1,6-hexanediol,
neopentyl glycol, thiodiethylene glycol, triethylene glycol, pentaerythritol, etc.), and the
like. One or more compounds appropriately selected from these antioxidants may be
added to the composition, and the added amount is preferably 0.1 to 2 mass% relative to
the total mass of the composition.
[0034]
Any compound commonly used as friction modifier for lubricating oil may be
used as the friction modifier in the present invention. Specific examples of the friction
modifier include amine compounds, fatty acid amides, fatty acid metal salts, and the
like having at least one alkyl group or alkenyl group having 6 to 30 carbon atoms
(particularly at least one linear alkyl group or linear alkenyl group having 6 to 30 carbon
atoms) in the molecule. One or more compounds appropriately selected from these
friction modifiers may be added to the composition in a desired amount, but it is
generally preferable that the amount is within the range of 0.1 to 2 mass% relative to the
total mass of the composition.
EXAMPLES
[0035]
The invention is further described in detail below by way of examples and
comparative examples. However, the invention is not limited to the following
examples.
Preparation of continuously variable transmission oil composition
Continuously variable transmission oil compositions of Examples 1 to 19 and
Comparative Examples 1 to 14 were prepared respectively by mixing the following
lubricating oil base oil and additives in the mixing ratios shown in the upper portion of
Tables 1 to 3 (the added amounts are expressed as mass% in relation to the total mass of
the composition).
[0036]
Lubricating oil base oil
O-l: Hydrorefined base oil (kinematic viscosity at 100°C: 4.3 mm2/s, viscosity index:
124)
0-2: Diisodecyl adipate (kinematic viscosity at 100°C: 3.6 mm2/s, viscosity index: 146)
[0037]
Additive
(1) Phosphorus compound shown by the above-mentioned general formula (1)
P-l: Tetraphenyl (m-phenylene) bisphosphate
(in formula (1), X1=X2=O, R1=R2=:R.3=R4=phenyl group, R5=phenylene group, and n=l;
phosphorus content in the compound itself: 10.9 mass%)
[0038]
(2) Phosphorus compound other than (1) above
P-2: Tricresyl phosphate
P-3: 2-Ethylhexyl acid phosphate oleylarnine salt
[0039]
(3) Sulfur compound
S-l: Dibenzyl disulfide
S-2: Trilauryl trithiophosphate
S-3: Triphenyl phosphorothionate
S-4: Emyl-3-[|^is(l-memylemoxy)phosphinothioyl]thio]propionate
[0040]
(3) Succinimide dispersant
1-1: Non-boron-containing succinimide (mono-type)
1-2: Non-boron-containing succinimide (bis-type)
1-3: Boron-containing succinimide (bis-type; boron content (the amount of boron
element): 0.5 mass%)
[0041]
(4) Alkaline-earth metal detergent
C-l: Overbased calcium sulfonate (TBN: 300)
C-2: Neutral calcium sulfonate (TBN: 20)
[0042]
(5) Other additives
In all Examples and Comparative Examples, a same package of additives,
consisting of those selected from antioxidants, corrosion inhibitors, pour-point
depressants, viscosity index improvers and friction modifiers, was added in a same
amount (4.9 mass% relative to the total mass of the composition).
[0043]
Evaluation
The friction coefficient and the wear track width of the test block obtained with
the continuously variable transmission oil compositions of Examples and Comparative
Examples were measured under the following test conditions by using a block-on-ring
tester (LFW-1) in accordance with ASTM D2174. The friction coefficient was
measured after 60 minutes from the start of the test (i.e. immediately before the end of
the test), and the wear track width of the block was measured after the end of the test.
[0044]
Test conditions
Ring: Falex S-10 Test Ring (SAE4620 steel)
Block: Falex H-60 Test Block (SAE01 steel)
Temperature: 80°C
Load: 445 N
Sliding speed: 0.33 m/s
Test time: 60 min
[0045]
The measurement results are shown in Tables 1 to 3. The larger friction
coefficient in the test means higher transfer efficiency of the continuously variable
transmission, and hence the superiority of the corresponding continuously variable
transmission oil.
[0049]
As is clear from these results, the compositions of Comparative Examples 1 to
14 that did not contain the phosphorus compound of the general formula (1) had a
friction coefficient (u60), which was measured after 60 minutes from the start of the test,
of 0.117 to 0.138. On the other hand, the continuously variable transmission oil
compositions of Examples 1 to 19 that contained the phosphorus compound shown by
the general formula (1) had a friction coefficient (µ60) of 0.139 to 0.164, which was
clearly higher than that of Comparative Examples. As shown in Examples 3,5,13,
and 15 to 19, it was found that the phosphorus compound expressed by the general
formula (1) was capable of increasing the friction coefficient even when it was
combined with another phosphorus compound not expressed by the general formula (1).
Meanwhile, the extent of wear was not changed by addition of the phosphorus
compound, indicating that the compositions consistently provided satisfactory wear
resistance. Moreover, the continuously variable transmission oil compositions of
Examples 1 to 19 did not contain any of those additives that would tend to cause
clogging of a clutch plate upon deterioration of the lubricating oil, such as zinc
dialkyldithiophosphate, and therefore such problems as clogging of a clutch plate may
be avoided even when the composition is used for a long period of time.
With the compositions of Examples 14 to 19 which comprised the sulfur
compound in addition to the phosphorus compound of the general formula (1), the
friction coefficient at 60 minutes (u60) exceeded 0.16, which was remarkably high.
INDUSTRIAL APPLICABILITY
[0050]
Since the continuously variable transmission oil composition according to the
present invention exhibits a high friction coefficient and does not contain those
additives which would cause clogging of a clutch plate, it is expected that the
continuously variable transmission oil composition may be effectively used as
lubricating oil composition for metal-belt or metal-chain continuously variable
transmissions which are attracting attention for the excellent energy efficiency they
could provide in automobiles, to enable trouble-free and energy-efficient performance
for a long period of time.
CLAIMS
1. A continuously variable transmission oil composition comprising a lubricating
oil base oil, and at least one phosphorus compound shown by the following general
formula (1) in such an amount that the phosphorus in the phosphorus compound
accounts for 0.005 to 0.15 mass% of the total mass of the composition,

wherein
each of R1, R2, R3 and R4 independently represents a hydrocarbyl group having 1 to 30
carbon atoms, or a hydrogen atom, with at least one of R1, R2, R3 and R4 representing a
hydrocarbyl group,
R5 represents a hydrocarbylene group having 1 to 30 carbon atoms,
X1 and X2 each represent an oxygen atom or a sulfur atom, and
n is an integer from 1 to 10.
2. The composition according to claim 1, further comprising at least one sulfur
compound that contains one or more chemical bonds selected from S-S bond, S-P bond,
S=P bond, S-C bond and S=C bond within each molecule, and is devoid of a metal
element, in such an amount that the sulfur in the sulfur compound accounts for 0.005 to
0.15 mass% of the total mass of the composition.
3. The composition according to claim 1 or 2, wherein the sulfur compound is at
least one compound selected from polysulfide compound, thiophosphate ester
compound and thiophosphite ester compound.
4. The composition according to any one of claims 1 to 3, further comprising a
succinimide dispersant in an amount of 0.5 to 10.0 mass% relative to the total mass of
the composition.
5. The composition according to any one of claims 1 to 4, further comprising an
alkaline-earth metal detergent in an amount of 0.05 to 1.0 mass% relative to the total
mass of the composition.

Provided is a continuously variable transmission oil composition that can markedly increase the coefficient of friction
between a metal belt or a chain and a pulley, that can maintain the high coefficient of friction over a long period of time, and
that causes no clogging of the clutch plate. The continuously variable transmission oil composition includes 0.005-0.15 mass%, as
phosphorous compound-derived phosphorus content with respect to the total amount of the composition, of at least one type of
phosphorous compound represented by general formula (1) in a lubricating oil base. (1) In general formula (1), R1, R2, R3 and R4
each represents a hydrocarbyl with carbon number 1-30 or a hydrogen atom, R5 represents a hydrocarbylene group with carbon
number 1-30, X1 and X2 represent an oxygen atom or a sulfur atom, and n represents an integer 1-10.