U.S. patent application number 13/103582 was filed with the patent office on 2012-03-15 for lubricating oil composition for transmission.
This patent application is currently assigned to NIPPON OIL CORPORATION. Invention is credited to Masaaki Itou, Toru Matsuoka.
Application Number | 20120065109 13/103582 |
Document ID | / |
Family ID | 36203116 |
Filed Date | 2012-03-15 |
United States Patent
Application |
20120065109 |
Kind Code |
A1 |
Matsuoka; Toru ; et
al. |
March 15, 2012 |
Lubricating oil composition for transmission
Abstract
Lubricating oil compositions for transmissions comprises (A) a
lubricating base oil with a kinematic viscosity at 100.degree. C.
adjusted to 1.5 to 6 mm.sup.2/s, composed of (A1) a lubricating
base oil with a kinematic viscosity at 100.degree. C. of 1.5
mm.sup.2/s or higher and lower than 7 mm.sup.2/s or (A1) the
lubricating oil and (A2) a lubricating base oil with a kinematic
viscosity at 100.degree. C. of 7 to 50 mm.sup.2/s, blended with (B)
a poly(meth)acrylate-based additive, so that the composition has a
kinematic viscosity at 100.degree. C. of 3 to 8 mm.sup.2/s and a
viscosity index of 95 to 200, (A) and (B) fulfill a specific
requirement. The compositions achieve long fatigue life though
having low viscosity.
Inventors: |
Matsuoka; Toru;
(Yokohama-Shi, JP) ; Itou; Masaaki; (Yokohama-shi,
JP) |
Assignee: |
NIPPON OIL CORPORATION
Tokyo
JP
|
Family ID: |
36203116 |
Appl. No.: |
13/103582 |
Filed: |
May 9, 2011 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11737339 |
Apr 19, 2007 |
|
|
|
13103582 |
|
|
|
|
PCT/JP2005/019644 |
Oct 19, 2005 |
|
|
|
11737339 |
|
|
|
|
Current U.S.
Class: |
508/287 ;
508/469 |
Current CPC
Class: |
C10N 2030/02 20130101;
C10M 2219/046 20130101; C10M 2203/1025 20130101; C10N 2020/02
20130101; C10M 2217/028 20130101; C10M 2215/086 20130101; C10N
2020/04 20130101; C10N 2040/045 20200501; C10M 2205/0285 20130101;
C10N 2040/042 20200501; C10N 2030/06 20130101; C10M 145/14
20130101; C10N 2030/08 20130101; C10N 2030/10 20130101; C10M
2215/28 20130101; C10M 2217/022 20130101; C10M 2223/049 20130101;
C10M 2203/1006 20130101; C10N 2040/044 20200501; C10M 2205/028
20130101; C10N 2040/04 20130101; C10M 2209/084 20130101; C10N
2030/76 20200501; C10M 169/04 20130101; C10M 169/041 20130101; C10M
171/02 20130101; C10M 2203/1025 20130101; C10N 2020/02 20130101;
C10M 2203/1006 20130101; C10M 2203/1006 20130101; C10M 2203/1006
20130101; C10M 2203/1006 20130101; C10M 2203/1006 20130101; C10M
2203/1025 20130101; C10N 2020/02 20130101 |
Class at
Publication: |
508/287 ;
508/469 |
International
Class: |
C10M 141/10 20060101
C10M141/10; C10M 145/14 20060101 C10M145/14 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 22, 2004 |
JP |
2004-308828 |
Oct 22, 2004 |
JP |
2004-308829 |
Oct 22, 2004 |
JP |
2004-308830 |
Oct 22, 2004 |
JP |
2004-308831 |
Claims
1. A lubricating oil composition for transmissions, comprising (A)
a lubricating base oil with a kinematic viscosity at 100.degree. C.
adjusted to 1.5 to 6 mm.sup.2/s, composed of (A1) a lubricating
base oil with a kinematic viscosity at 100.degree. C. of 1.5
mm.sup.2/s or higher and lower than 7 mm.sup.2/s wherein Component
(A1) is a lubricating base oil comprising a mixture of one or more
mineral base oils selected from (A1a) a mineral base oil with a
kinematic viscosity at 100.degree. C. of 1.5 mm.sup.2/s or higher
and lower than 3.5 mm.sup.2/s and (A1b) a mineral base oil with a
kinematic viscosity at 100.degree. C. of 3.5 mm.sup.2/s or higher
and lower than 7 mm.sup.2/s, and (A2) a lubricating base oil with a
kinematic viscosity at 100.degree. C. of 7 to 50 mm.sup.2/s,
wherein Component (A2) is a lubricating base oil comprising a
mixture of one or more mineral base oils selected from (A2b) a
lubricating base oil with a kinematic viscosity at 100.degree. C.
of 21.5 mm.sup.2/s or higher and lower than 25 mm.sup.2/s and (A2c)
a lubricating base oil with a kinematic viscosity at 100.degree. C.
of 25 to 50 mm.sup.2/s, blended with (B) a poly(meth)acrylate-based
additive containing a structural unit represented by formula (1)
below, so that the composition has a kinematic viscosity at
100.degree. C. of 3 to 8 mm.sup.2/s and a viscosity index of 95 to
200, the composition fulfilling requirement [I]: [I] Component (A)
is a lubricating base oil having a kinematic viscosity at
100.degree. C. adjusted to 1.5 to 4.5 mm.sup.2/s and Component (B)
is (B1) a poly(meth)acrylate-based additive containing a structural
unit of formula (1) below: ##STR00004## wherein R.sub.1 is hydrogen
or methyl and R.sub.2 is a branched alkyl group having 20 to 30
carbon atoms.
2. The lubricating oil composition according to claim 1, wherein
Component (A1) further comprises (A1c) a poly-.alpha.-olefin base
oil with a kinematic viscosity at 100.degree. C. of 1.5 mm.sup.2/s
or higher and lower than 7 mm.sup.2/s, and/or Component (A2)
further comprises (A2a) a lubricating base oil with a kinematic
viscosity at 100.degree. C. of 7 mm.sup.2/s or higher and lower
than 15 mm.sup.2/s.
3. The lubricating oil composition according to claim 1, wherein
Components (B1) and (B2) are each a poly(meth)acrylate based
additive having a weight-average molecular weight of 10,000 to
60,000.
4. The lubricating oil composition according to claim 1, further
comprising a poly(meth)acrylate containing a structural unit of
formula (1) wherein R.sub.1 is a hydrogen or methyl and R.sub.2 is
methyl.
5. The lubricating oil composition according to claim 1, further
comprising at least one type of additive selected from metallic
detergents, dispersants, friction modifiers, extreme pressure
additives, seal swelling agents, anti-oxidants, and pour point
depressents.
6. The lubricating oil composition according to claim 1, further
comprising, on the basis of the total amount of the composition,
(C) an imide-based friction modifier having 8 to 30 carbon atoms in
an amount of 1 to 5 percent by mass and (D) a sulfer-free
phosphorus-based extreme pressure additive in an amount of 0.015 to
0.05 percent by mass in terms of phosphorus.
7. The lubricating oil composition according to claim 1, further
comprising (B3) a poly(meth)acrylate based additive consisting of a
structural unit represented by formula (1) below and having a
weight-average molecular weight of 50,000 to 300,000 as Component
(B): ##STR00005## wherein R.sub.1 is hydrogen or methyl, R.sub.2 is
a hydrocarbon group having 5 to 20 carbon atoms or a group
represented by --(R).sub.a-E wherein R is an alkylene group having
5 to 20 carbon atoms, E is an amine residue or a heterocyclic
residue, each having 1 or 2 nitrogen atoms and 0 to 2 oxygen atoms,
and a is an integer of 0 or 1.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Continuation of U.S. patent
application Ser. No. 11/737,339, filed Apr. 19, 2007, which is a
Continuation of International Application No. PCT/JP2005/019644,
filed Oct. 19, 2005, which was published in the Japanese language
on Apr. 27, 2006, under International Publication No. 2006/043709,
the disclosures of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] In recent years, from the viewpoint of approaching to
environmental issues such as reduction of carbon dioxide emission,
there has arisen an urgent need that automobiles, construction
machines and agricultural machines consume less energy, i.e., are
reduced in the fuel-consumption thereof. In particular, there is a
growing demand that their units such as engines, transmissions,
final reduction gear units, compressors and hydraulic equipment
contribute to energy saving. Therefore, the lubricating oils used
in these units are demanded to be less in frictional loss by
agitation and frictional resistance than ever before.
[0003] Lowering the viscosity of a lubricating oil may be an
example as a means for improving the fuel economy by a transmission
and a final reduction gear unit. For example, an automobile
automatic transmission or continuously variable transmission has a
torque converter, a wet clutch, a gear bearing mechanism, an oil
pump and a hydraulic control system while a manual transmission or
final reduction gear unit has a gear bearing mechanism. Lowering
the viscosity of the lubricating oil to be used in such
transmissions can reduce the stirring and frictional resistances of
the torque converter, wet clutch, gear bearing mechanism and oil
pump and thus enhance the power transmission efficiency thereof,
resulting in an improvement in the fuel economy performance of the
automobile.
[0004] However, lowering the viscosity of the lubricating oil used
in these transmissions causes the above-described units and
mechanisms thereof to be significantly shortened in fatigue life
and may generate seizure resulting in some malfunctions in the
transmissions. In particular when a low viscosity lubricating oil
is blended with a phosphorus-based extreme pressure additive to
enhance the extreme pressure properties, the fatigue life will be
extremely shortened. Therefore, it is generally difficult to lower
the viscosity of the lubricating oil. It is generally known that
although a sulfur-based extreme pressure additive can improve the
fatigue life of transmissions, the viscosity of the base oil gives
a more effect on the fatigue life than additives under low
lubricating conditions.
[0005] Examples of conventional automobile transmission oils which
can render a transmission capable of maintaining various properties
such as shifting properties for a long time include those obtained
by optimizing and blending synthetic and/or mineral base oils,
antiwear agents, extreme pressure additives, metallic detergents,
ashless dispersants, friction modifiers and viscosity index
improvers (for example, see Patent Documents 1 to 4 below).
However, these compositions are not aimed at improving the fuel
economy performance of an automobile and thus are high in kinematic
viscosity. Any of the publications does not refer to effects on the
fatigue life obtained by lowering the viscosity of the lubricating
oils at all. Therefore, a composition which can solve the foregoing
problems has not been sufficiently studied yet.
[0006] (1) Japanese Patent Laid-Open Publication No. 3-39399
[0007] (2) Japanese Patent Laid-Open Publication No. 7-268375
[0008] (3) Japanese Patent Laid-Open Publication No. 2000-63869
[0009] (4) Japanese Patent Laid-Open Publication No.
2001-262176
BRIEF SUMMARY OF THE INVENTION
[0010] The present invention relates to lubricating oil
compositions for transmissions and more particularly to those
suitable for automatic, manual and continuously variable
transmissions of automobiles, which compositions have a long
fatigue life, though low viscosity, excellent low temperature
viscosity characteristics and oxidation stability, and can be
extended in anti-shudder durability.
DETAILED DESCRIPTION OF THE INVENTION
[0011] The present invention was made in view of the foregoing
situations and intends to provide a lubricating oil for
transmissions which is low in viscosity but capable of providing a
long fatigue life and excellent in low temperature viscosity
characteristics and oxidation stability, and can be extended in
anti-shudder durability, and in particular such a lubricating oil
composition having fuel efficient performance and sufficient
durability for gears and bearings, suitable for the automatic,
manual or continuously variable transmission of an automobile.
[0012] As a result of an extensive study and research conducted for
solving the above-described problems, focusing on lubricating base
oils and polymers, the present invention was achieved on the basis
of the finding that the above problems were able to be solved with
a lubricating oil composition for transmissions which was lowered
in viscosity by selecting a specific base oil and a specific
poly(meth)acrylate-based additive.
[0013] That is, according to the present invention, there is
provided a lubricating oil composition for transmissions,
comprising (A) a lubricating base oil with a kinematic viscosity at
100.degree. C. adjusted to 1.5 to 6 mm.sup.2/s, composed of (A1) a
lubricating base oil with a kinematic viscosity at 100.degree. C.
of 1.5 mm.sup.2/s or higher and lower than 7 mm.sup.2/s or (A1) the
lubricating oil and (A2) a lubricating base oil with a kinematic
viscosity at 100.degree. C. of 7 to 50 mm.sup.2/s, blended with (B)
a poly(meth)acrylate-based additive containing a structural unit
represented by formula (1) below, so that the composition has a
kinematic viscosity at 100.degree. C. of 3 to 8 mm.sup.2/s and a
viscosity index of 95 to 200, the composition fulfilling at least
one requirement selected from the following [I] to [III]:
[0014] [I] Component (A) is a lubricating base oil having a
kinematic viscosity at 100.degree. C. adjusted to 1.5 to 4.5
mm.sup.2/s and Component (B) is (B1) a poly(meth)acrylate-based
additive containing a structural unit of formula (1) wherein R2 is
a straight-chain or branched hydrocarbon group having 16 to 30
carbon atoms;
[0015] [II] Component (A) is a lubricating base oil with a
kinematic viscosity at 100.degree. C. adjusted to 1.5 to 6
mm.sup.2/s, composed of 70 to 97 percent by mass of Component (A1)
and 3 to 30 percent by mass of Component (A2), and Component (B) is
(B2) a poly(meth)acrylate-based additive substantially not
containing a structural unit of formula (1) wherein R2 is a
hydrocarbon group having 20 or more carbon atoms; and
[0016] [III] the kinematic viscosity at 100.degree. C. (Vc) of the
composition is from 4.5 to 8 mm.sup.2/s, and the ratio of the
kinematic viscosity at 100.degree. C. (Vb) of Component (A) to (Vc)
(=VbNc) is 0.70 or greater,
##STR00001##
wherein R.sub.1 is hydrogen or methyl, R2 is a hydrocarbon group
having 1 to 30 carbon atoms or a group represented by --(R).sub.a-E
wherein R is an alkylene group having 1 to 30 carbon atoms, E is an
amine residue or a heterocyclic residue, each having 1 or 2
nitrogen atoms and 0 to 2 oxygen atoms, and a is an integer of 0 or
1.
[0017] The present invention will be described below.
[0018] The lubricating base oil (A) used in the present invention
is a lubricating base oil with a kinematic viscosity at 100.degree.
C. adjusted to 1.5 to 6 mm.sup.2/s, composed of (A1) a lubricating
base oil with a kinematic viscosity at 100.degree. C. of 1.5
mm.sup.2/s or higher and lower than 7 mm.sup.2/s or composed of
(A1) the lubricating base oil and (A2) a lubricating base oil with
a kinematic viscosity at 100.degree. C. of 7 to 50 mm.sup.2/s and
may be a mineral lubricating base oil, a synthetic lubricating base
oil or a mixture thereof.
[0019] Examples of mineral lubricating base oils include paraffinic
or naphthenic oils which can be obtained by subjecting a
lubricating oil fraction produced by atmospheric- or
vacuum-distillation of a crude oil, to any one of or any suitable
combination of refining processes selected from solvent
deasphalting, solvent extraction, hydrocracking, solvent dewaxing,
catalytic dewaxing, hydrorefining, sulfuric acid treatment, and
clay treatment; n-paraffins; and iso-paraffins. These base oils may
be used alone or in combination at an arbitrary ratio.
[0020] Examples of preferred mineral lubricating base oils include
the following base oils: [0021] (1) a distillate oil produced by
atmospheric distillation of a paraffin base crude oil and/or a
mixed base crude oil; [0022] (2) a whole vacuum gas oil (WVGO)
produced by vacuum distillation of the topped crude of a paraffin
base crude oil and/or a mixed base crude oil; [0023] (3) a wax
obtained by a lubricating oil dewaxing process and/or a
Fischer-Tropsch wax produced by a GTL process; [0024] (4) an oil
obtained by mild-hydrocracking (MHC) one or more oils selected from
oils of (1) to (3) above; [0025] (5) a mixed oil of two or more
oils selected from (1) to (4) above; [0026] (6) a deasphalted oil
(DAO) obtained by deasphalting an oil of (1), (2) (3), (4) or (5);
[0027] (7) an oil obtained by mild-hydrocracking (MHC) an oil of
(6); and [0028] (8) a lubricating oil obtained by subjecting a
mixed oil of two or more oils selected from (1) to (7) used as a
feed stock and/or a lubricating oil fraction recovered therefrom to
a normal refining process and further recovering a lubricating oil
fraction from the refined product.
[0029] There is no particular restriction on the normal refining
process used herein. Therefore, there may be used any refining
process conventionally used upon production of a lubricating base
oil. Examples of the normal refining process include (a)
hydro-refining processes such as hydrocracking and hydrofinishing,
(b) solvent refining such as furfural extraction, (c) dewaxing such
as solvent dewaxing and catalytic dewaxing, (d) clay refining with
acidic clay or active clay and (e) chemical (acid or alkali)
refining such as sulfuric acid treatment and sodium hydroxide
treatment. In the present invention, any one or more of these
refining processes may be used in any order.
[0030] The mineral lubricating base oil used in the present
invention is particularly preferably a base oil obtained by further
subjecting a base oil selected from (1) to (8) described above to
the following treatments.
[0031] That is, preferred are a hydrocracked mineral oil and/or
wax-isomerized isoparaffin base oil obtained by hydrocracking or
wax-isomerizing a base oil selected from (1) to (8) described above
as it is or a lubricating fraction recovered therefrom and
subjecting the resulting product as it is or a lubricating fraction
recovered therefrom to dewaxing such as solvent dewaxing or
catalytic dewaxing, followed by solvent refining or followed by
solvent refining and then dewaxing such as solvent dewaxing or
catalytic dewaxing. The hydrocracked mineral oil and/or
wax-isomerized isoparaffin base oil are used in an amount of
preferably 30 percent by mass or more, more preferably 50 percent
by mass or more, and particularly preferably 70 percent by mass or
more, on the basis of the total amount of the base oil.
[0032] Examples of synthetic lubricating base oils include
poly-.alpha.-olefins and hydrogenated compounds thereof; isobutene
oligomers and hydrogenated compounds thereof; isoparaffins;
alkylbenzenes; alkylnaphthalenes; diesters such as ditridecyl
glutarate, di-2-ethylhexyl adipate, diisodecyl adipate, ditridecyl
adipate and di-2-ethylhexyl scebacate; polyol esters such as
trimethylolpropane caprylate, trimethylolpropane pelargonate,
pentaerythritol 2-ethylhexanoate and pentaerythritol pelargonate;
polyoxyalkylene glycols; dialkyldiphenyl ethers; and polyphenyl
ethers.
[0033] Preferred synthetic lubricating base oils are
poly-.alpha.-olefins. Typical examples of poly-.alpha.-olefins
include oligomers or cooligomers of .alpha.-olefins having 2 to 32
and preferably 6 to 16 carbon atoms, such as 1-octene oligomer,
1-decene oligomer, ethylene-propylene cooligomer, and hydrogenated
compounds thereof.
[0034] There is no particular restriction on the method of
producing poly-.alpha.-olefins. For example, poly-.alpha.-olefins
may be produced by polymerizing .alpha.-olefins in the presence of
a polymerization catalyst such as a Friedel-Crafts catalyst
containing aluminum trichloride, boron trifluoride or a complex of
boron trifluoride with water, an alcohol such as ethanol, propanol
and butanol, a carboxylic acid or an ester such as ethyl acetate
and ethyl propionate.
[0035] The lubricating base oil (A) used in the present invention
may be a mixture of two or more types of mineral base oils or two
or more types of synthetic base oils or a mixture of mineral base
oils and synthetic base oils. The mix ratio of two or more base
oils in such mixtures may be arbitrarily selected.
[0036] The lubricating base oil (A) used in the present invention
is a lubricating base oil with a kinematic viscosity at 100.degree.
C. adjusted to 1.5 to 6 mm.sup.2/s, composed of (A1) a lubricating
base oil with a kinematic viscosity at 100.degree. C. of 1.5
mm.sup.2/s or higher and lower than 7 mm.sup.2/s or composed of
(A1) the lubricating base oil and (A2) a lubricating base oil with
a kinematic viscosity at 100.degree. C. of 7 to 50 mm.sup.2/s.
[0037] Component (A1) is preferably one or more types selected from
the following (A1a) to (A1c):
[0038] (A1a) a mineral base oil with a kinematic viscosity at
100.degree. C. of 1.5 mm.sup.2/s or higher and lower than 3.5
mm.sup.2/s and preferably from 1.9 to 3.2 mm.sup.2/s;
[0039] (A1b) a mineral base oil with a kinematic viscosity at
100.degree. C. of 3.5 mm.sup.2/s or higher and lower than 7
mm.sup.2/s and preferably from 3.8 to 4.5 mm.sup.2/s; and
[0040] (A1c) a poly-.alpha.-olefin base oil with a kinematic
viscosity at 100.degree. C. of 1.5 mm.sup.2/s or higher and lower
than 7 mm.sup.2/s and preferably from 3.8 to 4.5 mm.sup.2/s.
[0041] There is no particular restriction on the % C.sub.A of the
lubrication base oils (A1a) to (A1c). However, the % C.sub.A is
preferably 3 or less, more preferably 2 or less, particularly
preferably 1 or less. Component (A) with a % C.sub.A of 3 or less
renders it possible to produce a composition with more excellent
oxidation stability.
[0042] The term "% C.sub.A" denotes a percentage of aromatic carbon
number to total carbon number, determined by a method prescribed in
ASTM D 3238-85.
[0043] There is no particular restriction on the viscosity index of
the lubrication base oils (A1a) to (A1c). However, the viscosity
index is preferably 80 or greater, more preferably 90 or greater,
particularly preferably 110 or greater and usually 200 or less and
preferably 160 or less. The use of a lubricating base oil with a
viscosity index of 80 or greater renders it possible to produce a
composition with excellent viscosity characteristics from low
temperatures to high temperatures. The use of a lubricating base
oil with a too high viscosity index is less effective to fatigue
life.
[0044] There is no particular restriction on the sulfur content of
the lubrication base oils (A1a) to (A1c). However, the sulfur
content is preferably 0.05 percent by mass or less, more preferably
0.02 percent by mass or less, and particularly preferably 0.005
percent by mass or less. Reduction of the sulfur content of
Component (A) renders it possible to obtain a composition with
excellent oxidation stability.
[0045] The lubricating base oils (A1a) to (A1e) may be used alone
or may be arbitrarily mixed. In particular, it is preferable to use
(A1a) and (A1b) and/or (A1c) in combination. When (A1a) and/or
(A1b) and (A1c) are used in combination, the content of (A1c) is
preferably from 1 to 50 percent by mass, more preferably from 3 to
20 percent by mass, and more preferably from 3 to 10 percent by
mass, on the basis of the total amount of the base oil. In
particular, when Component (A1) is used in combination with
Component (A2) described below, blend of 3 to 8 percent by mass of
Component (A1c) renders it possible to produce a lubricating oil
composition which can exhibit excellent fatigue life, low
temperature characteristics and oxidation stability, effectively at
a low cost.
[0046] The lubricating base oil (A) used in the present invention
preferably comprises the above-described (A1) and (A2) a
lubricating base oil with a kinematic viscosity at 100.degree. C.
of 7 to 50 mm.sup.2/s.
[0047] Component (A2) is preferably one or more types selected from
the following (A2a) to (A2c):
[0048] (A2a) a mineral or synthetic, preferably mineral base oil
with a kinematic viscosity at 100.degree. C. of 7 mm.sup.2/s or
higher and lower than 15 mm.sup.2/s and preferably from 8 to 12
mm.sup.2/s;
[0049] (A2b) a mineral or synthetic, preferably mineral base oil
with a kinematic viscosity at 100.degree. C. of 15 mm.sup.2/s or
higher and lower than 25 mm.sup.2/s and preferably from 17 to 23
mm.sup.2/s; and
[0050] (A2c) a mineral or synthetic, preferably mineral base oil
with a kinematic viscosity at 100.degree. C. of 25 to 50 mm.sup.2/s
and preferably from 28 to 40 mm.sup.2/s.
[0051] The % C.sub.A of the lubrication base oils (A2a) to (A2c) is
usually from 0 to 40 and thus is not particularly restricted.
However, the % C.sub.A is preferably 2 or greater, more preferably
5 or greater, particularly preferably 8 or greater and preferably
15 or less, more preferably 10 or less because the resulting
composition can have both fatigue life and oxidation stability.
[0052] There is no particular restriction on the viscosity index of
the lubrication base oils (A2a) to (A2c). However, the viscosity
index is preferably 80 or greater, more preferably 90 or greater,
particularly preferably 95 or greater and usually 200 or less,
preferably 120 or less, more preferably 110 or less, and
particularly preferably 100 or less. The use of a lubricating base
oil with a viscosity index of 80 or greater renders it possible to
produce a composition with excellent viscosity characteristics from
low temperatures to high temperatures. The use of a lubricating
base oil with a too high viscosity index is less effective to
fatigue life.
[0053] There is no particular restriction on the sulfur content of
the lubricating base oils (A2a) to (A2c). However, the sulfur
content is usually from 0 to 2 percent by mass, preferably from
0.05 to 1.5 percent by mass, more preferably 0.3 to 1.2 percent by
mass, more preferably 0.5 to 1 percent by mass, and particularly
preferably 0.7 to 1 percent by mass. The use of Component (A2) with
a relatively high sulfur content can enhance fatigue life while the
use of Component (A2) with a sulfur content of preferably 1 percent
by mass or less renders it possible to obtain a composition with
more excellent oxidation stability.
[0054] When Component (A2) is used in the present invention, it is
preferable to use (A2b) or (A2c) with the objective of improving
fatigue life and particularly preferable to use (A2b) with the
objective of improving both fatigue life and oxidation stability.
The use of (A1C) as Component (A1) renders it possible to obtain a
composition excellent in fatigue life, oxidation stability and low
temperature viscosity.
[0055] There is no particular restriction on the contents of
Components (A1) and (A2) when used in combination. The content of
Component (A1) is preferably from 70 to 97 percent by mass and more
preferably from 85 to 95 percent by mass, on the basis of the total
amount of the lubricating base oil. The content of Component (A2)
is preferably from 3 to 30 percent by mass and more preferably from
5 to 15 percent by mass, on the basis of the total amount of the
lubricating base oil.
[0056] As described above, the lubricating base oil (A) used in the
present invention is a lubricating base oil composed of Component
(A1) or Components (A1) and (A2). The kinematic viscosity at
100.degree. C. of (A) the base oil is from 1.5 to 6 mm.sup.2/s,
preferably from 2.8 to 4.5 mm.sup.2/s, and particularly preferably
from 3.6 to 3.9 mm.sup.2/s. The use of a lubricating base oil with
a kinematic viscosity at 100.degree. C. of 6 mm.sup.2/s or less
renders it possible to obtain a lubricating oil composition with a
small friction resistance at lubricating sites because its fluid
resistance is small and thus with excellent low temperature
viscosity. The use of a lubricating base oil with a kinematic
viscosity at 100.degree. C. of 1.5 mm.sup.2/s or higher renders it
possible to produce a lubricating oil composition which is
sufficient in oil film formation leading to excellent lubricity and
less in evaporation loss of the base oil under elevated temperature
conditions.
[0057] There is no particular restriction on the % C.sub.A of the
lubricating base oil (A). However, the % C.sub.A is preferably 3 or
less, more preferably 2 or less, particularly preferably 1 or less.
The use of Component (A) with a % C.sub.A of 3 or less renders it
possible to produce a composition with more excellent oxidation
stability.
[0058] There is no particular restriction on the sulfur content of
the lubricating base oil (A). However, the sulfur content is
usually from 0 to 0.3 percent by mass, preferably from 0.03 to 0.2
percent by mass, and particularly preferably 0.06 to 0.1 percent by
mass. The use of a lubricating base oil with a sulfur content
within the above ranges, particularly from 0.03 to 0.2 percent by
mass renders it possible to obtain a lubricating oil composition
having both fatigue life and oxidation stability.
[0059] Component (B) is a poly(meth)acrylate-based additive
containing a structural unit represented by formula (1) below and
may be a non-dispersion type poly(meth)acrylate additive having no
polar group or a dispersion type poly(meth)acrylate additive having
a polar group:
##STR00002##
In formula (I), R.sub.1 is hydrogen or methyl, R2 is a hydrocarbon
group having 1 to 30 carbon atoms or a group represented by
--(R).sub.a-E wherein R is an alkylene group having 1 to 30 carbon
atoms, E is an amine residue or a heterocyclic residue, each having
1 or 2 nitrogen atoms and 0 to 2 oxygen atoms, and a is an integer
of 0 or 1.
[0060] Examples of hydrocarbon groups having 1 to 30 carbon atoms
for R2 include straight-chain or branched alkyl groups, such as
such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl,
nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl,
hexadecyl, heptadecyl, octadecyl, nonadecyl, eicosyl, heneicosyl,
docosyl, tricosyl, tetracosyl, pentacosyl, hexacosyl, heptacosyl,
octacosyl, nonacosyl, and triacontyl groups; and straight-chain or
branched alkenyl groups such as propenyl, butenyl, pentenyl,
hexenyl, heptenyl, octenyl, noneyl, decenyl, undecenyl, dodecenyl,
tridecenyl, tetradecenyl, pentadecenyl, hexadecenyl, heptadecenyl,
octadecenyl, nonadecenyl, eicosenyl, heneicosenyl, docosenyl,
tricosenyl, tetracosenyl, pentacosenyl, hexacosenyl, heptacosenyl,
octacosenyl, nonacosenyl, and tiraconetenyl groups, the position of
which the double bonds may vary.
[0061] Examples of alkylene groups having 1 to 30 carbon atoms for
R include methylene, ethylene, propylene, butylene, pentylene,
hexylene, heptylene, octylene, nonylene, decylene, undecylene,
dodecylene, tridecylene, tetradecylene, pentadecylene,
hexadecylene, heptadecylene and octadecylene groups, all of which
may be straight-chain or branched.
[0062] When E is an amine residue, specific examples thereof
include dimethylamino, diethylamino, dipropylamino, dibutylamino,
anilino, toluidino, xylidino, acetylamino, and benzoilamino groups.
When E is a heterocyclic residue, specific examples thereof include
morpholino, pyrrolyl, pyrrolino, pyridyl, methylpyridyl,
pyrolidinyl, piperidinyl, quinonyl, pyrrolidonyl, pyrrolidono,
imidazolino and pyrazino groups.
[0063] Component (B), i.e., the poly(meth)acrylate containing a
structural unit represented by formula (1) may be a
poly(meth)acrylate obtained by polymerizing or copolymerizing one
or more types of monomers represented by formula (1') or may be a
copolymer of one or more types of monomers represented by formula
(1') and monomers other than those represented by formula (1'):
CH.sub.2.dbd.C(R.sub.1)--C(.dbd.O)--OR.sub.2 (1')
wherein R.sub.1 and R.sub.2 are the same as those in formula
(1).
[0064] Specific examples of monomers represented by formula (1')
are the following monomers (Ba) to (Be):
[0065] (Ba) (meth)acrylates having an alkyl group having 1 to 4
carbon atoms, such as methyl(meth)acrylate, ethyl(meth)acrylate, n-
or i-propyl(meth)acrylate, and n-, i- or sec-butyl(meth)acrylate,
preferably methyl(meth)acrylate;
[0066] (Bb) (meth)acrylates having an alkyl or alkenyl group having
5 to 15 carbon atoms, such as pentyl(meth)acrylate,
hexyl(meth)acrylate, heptyl(meth)acrylate, octyl(meth)acrylate,
nonyl(meth)acrylate, decyl(meth)acrylate, undecyl(meth)acrylate,
dodecyl(meth)acrylate, tridecyl(meth)acrylate,
tetradecyl(meth)acrylate, and pentadecyl(meth)acrylate (all of
which may be straight-chain or branched), and
octenyl(meth)acrylate, noneyl(meth)acrylate, decenyl(meth)acrylate,
undecenyl(meth)acrylate, dodecenyl(meth)acrylate,
tridecenyl(meth)acrylate, tetradecenyl(meth)acrylate, and
pentadecenyl(meth)acrylate (all of which may be straight-chain or
branched), preferably (meth)acrylates having an alkyl group having
12 to 15 carbon atoms as the main component;
[0067] (Bc) (meth)acrylates having an alkyl or alkenyl group having
16 to 30 carbon atoms, preferably a straight-chain alkyl group
having 16 to 20 carbon atoms and a straight-chain alkyl group
having 16 or 18 carbon atoms, specifically
n-hexadecyl(meth)acrylate, n-octadecyl(meth)acrylate,
n-eicosyl(meth)acrylate, n-docosyl(meth)acrylate,
n-tetracosyl(meth)acrylate, n-hexacosyl(meth)acrylate, and
n-octacosyl(meth)acrylate, and particularly preferably
n-hexadecyl(meth)acrylate and n-octadecyl(meth)acrylate;
[0068] (Bd) (meth)acrylates having a branched alkyl or alkenyl
group having 16 to 30 carbon atoms, preferably a branched alkyl
group having 20 to 28 carbon atoms and more preferably a branched
alkyl group having 22 to 26 carbon atoms, specifically branched
hexadecyl(meth)acrylate, branched octadecyl(meth)acrylate, branched
eicosyl(meth)acrylate, branched docosyl(meth)acrylate, branched
tetracosyl(meth)acrylate, branched hexacosyl(meth)acrylate, and
branched octacosyl(meth)acrylate, preferably (meth)acrylate having
a branched alkyl group having 16 to 30 carbon atoms, preferably 20
to 28 carbon atoms and more preferably 22 to 26 carbon atoms, as
represented by --C--C(R3)R4 wherein there is no particular
restriction on R3 or R4 as long as the carbon number of R2 is from
16 to 30, but R3 is a straight-chain alkyl group having preferably
6 to 12 and more preferably 10 to 12 carbon atoms, and R4 is a
straight-chain alkyl group having preferably 10 to 16 carbon atoms
and more preferably 14 to 16 carbon atoms, more specifically
(meth)acrylates having a branched alkyl group having 20 to 30
carbon atoms, such as 2-decyl-tetradecyl(meth)acrylate,
2-dodecyl-hexadecyl(meth)acrylate, and
2-decyl-tetradecyloxyethyl(meth)acrylate;
[0069] (Be) polar group-containing monomers such as amide
group-containing monomers, nitro group-containing monomers, primary
to quaternary amino group-containing vinyl monomers,
nitrogen-containing heterocyclic vinyl monomers, hydrochlorides
thereof, sulfates thereof, phosphates thereof, lower alkyl(C.sub.1
to C.sub.8)monocarboxylic acid salts thereof, quaternary ammonium
base-containing vinyl monomers, amphoteric vinyl monomers
containing oxygen or nitrogen, nitrile group-containing monomers,
aliphatic hydrocarbon-based vinyl monomers, alicyclic
hydrocarbon-based vinyl monomers, aromatic hydrocarbon-based vinyl
monomers, vinyl ester, vinyl ether, vinyl ketones, epoxy
group-containing vinyl monomers, halogen atom-containing vinyl
monomers, esters of unsaturated polycarboxylic acids, hydroxyl
group-containing vinyl monomers, polyoxyalkylene chain-containing
vinyl monomers, and ionic group-containing vinyl monomers (anionic
group-, phosphoric acid group-, sulfonic acid group- or sulfuric
acid ester group-containing vinyl monomers), univalent metal salts
thereof, divalent metal salts thereof, amine salts thereof and
ammonium salts thereof, more specifically and preferably
nitrogen-containing monomers such as
4-diphenylamine(meth)acrylamide, 2-diphenylamine(meth)acrylamide,
dimethylaminoethyl(meth)acryl amide,
diethylaminoethyl(meth)acrylamide,
dimethylaminopropyl(meth)acrylamide, dimethylaminomethyl
methacrylate, diethylaminomethyl methacrylate, dimethylaminoethyl
(meth)acrylate, diethylaminoethyl (meth)acrylate, morpholinomethyl
methacrylate, morpholinoethyl methacrylate,
2-vinyl-5-methylpyridine and N-vinylpyrrolidone.
[0070] Component (B) used in the present invention is a
poly(meth)acrylate-based compound obtained by polymerizing or
copolymerizing one or more monomers selected from the
above-described (Ba) to (Be), and more preferable specific examples
of the compound include the following compounds: [0071] (1)
non-dispersion type poly(meth)acrylates, which are copolymers of
(Ba) and (Bb), or hydrogenated compounds thereof; [0072] (2)
non-dispersion type poly(meth)acrylates, which are copolymers of
(Ba), (Bb) and (Bc), or hydrogenated compounds thereof; [0073] (3)
non-dispersion type poly(meth)acrylates, which are copolymers of
(Ba), (Bb), (Bc) and (Bd), or hydrogenated compounds thereof;
[0074] (4) dispersion type poly(meth)acrylates, which are
copolymers of (Ba), (Bb) and (Be), or hydrogenated compounds
thereof; [0075] (5) dispersion type poly(meth)acrylates, which are
copolymers of (Ba), (Bb), (Bc) and (Be), or hydrogenated compounds
thereof; and [0076] (6) dispersion type poly(meth)acrylates, which
are copolymers of (Ba), (Bb), (Bc), (Bd) and (Be), or hydrogenated
compounds thereof. Preferred are non-dispersion type
poly(meth)acrylates (1) to (3) and particularly preferred are
non-dispersion type poly(meth)acrylates (3).
[0077] The content of Component (B), i.e., poly(meth)acrylate-based
additive in the transmission lubricating oil composition of the
present invention is to be such that the kinematic viscosity at
100.degree. C. of the composition is from 3 to 8 mm2/s, preferably
from 4.5 to 6 mm2/s, and the viscosity index of the composition is
from 95 to 200, preferably from 120 to 190, and more preferably
from 150 to 180. The content of Component (B) is usually from 0.1
to 15 percent by mass, preferably from 2 to 12 percent by mass and
particularly preferably from 3 to 8 percent by mass on the basis of
the total mass of the composition. The content of Component (B) may
be a content thereof containing or not containing a diluent as long
as it falls within the above-prescribed ranges. High molecular
weight polymers for lubricating oil are usually used in a state
wherein it is diluted to 10 to 80 percent by mass with a diluent,
in consideration of handling and dissolubility in a lubricating
base oil. Therefore, the above-described content is a preferable
content of Component (B) when it contains a diluent. The content of
Component (B) in excess of the prescribed range of the composition
is not preferable because the resulting composition not only fails
to be improved in an effect of improving fatigue life as balanced
with the content but also is poor in shear stability and hard to
retain the initial extreme pressure properties for a long period of
time.
[0078] The lubricating oil composition of the present invention
comprises Component (A) blended with Component (B) so that the
composition has a kinematic viscosity at 100.degree. c. of 3 to 8
mm2/s and a viscosity index of 95 to 200, the composition
fulfilling at least one requirement selected from the following [1]
to [III]:
[0079] [I] Component (A) is a base oil having a kinematic viscosity
at 100.degree. C. adjusted to 1.5 to 4.5 mm2/s and Component (B) is
(B1) a poly(meth)acrylate containing a structural unit of formula
(1) wherein R2 is a straight-chain or branched hydrocarbon group
having 16 to 30 carbon atoms;
[0080] [II] Component (A) is a lubricating base oil with a
kinematic viscosity at 100.degree. C. adjusted to 1.5 to 6 mm2/s,
composed of 70 to 97 percent by mass of Component (A1) and 3 to 30
percent by mass of Component (A2), and Component (B) is (B2) a
poly(meth)acrylate-based additive substantially not containing a
structural unit of formula (1) wherein R2 is a hydrocarbon group
having 20 or more carbon atoms; and
[0081] [III] the kinematic viscosity at 100.degree. C. (Vc) of the
composition is from 4.5 to 8 mm2/s, and the ratio of the kinematic
viscosity at 100.degree. C. (Vb) of Component (A) to (Vc) (=VbNc)
is 0.70 or greater.
[0082] Requirement [I] is now described below.
[0083] Requirement [I] is to be such that Component (A) is a base
oil having a kinematic viscosity at 100.degree. C. adjusted to 1.5
to 4.5 mm.sup.2/s and Component (B) is (B1) a poly(meth)acrylate
containing a structural unit of formula (1) wherein R.sub.2 is a
straight-chain or branched hydrocarbon group having 16 to 30 carbon
atoms.
[0084] Component (A) is the above-described Component (A1) or
Components (A1) and (A2) and is adjusted in kinematic viscosity at
100.degree. C. to 1.5 to 4.5 mm.sup.2/s, preferably 2.8 to 4.0
mm.sup.2/s, and particularly preferably 3.6 to 3.9 mm.sup.2/s. The
kinematic viscosity at 100.degree. C. of 4.5 mm.sup.2/s or lower
renders it possible to produce a lubricating oil composition which
is small in friction resistance at lubricating sites due to its
small fluid resistance and is excellent in low temperature
viscosity (for example, a Brookfield viscosity at -40.degree. C. of
20000 mPas or lower). The kinematic viscosity at 100.degree. C. of
1.5 mm.sup.2/ or higher renders it possible to produce a
lubricating oil composition which is sufficient in oil film
formation, excellent in lubricity, and less in evaporation loss of
the base oil at elevated temperatures.
[0085] When Component (A) is the combination of Components (A1) and
(A2) in Requirement [I], the blend ratio of Component (A1) is from
70 to 97 percent by mass and preferably from 85 to 95 percent by
mass while the blend ratio of Component (A2) is from 3 to 30
percent by mass and preferably from 5 to 15 percent by mass. The
use of Component (A2) is particularly preferable because the
fatigue life can be more enhanced.
[0086] Component (B) in Requirement [I] is (B1) a
poly(meth)acrylate-based additive containing a structural unit
represented by formula (1) wherein R2 is a straight-chain or
branched hydrocarbon group having 16 to 30 carbon atoms. Specific
examples include poly(meth)acrylate-based additives obtained by
(co)polymerizing a monomer containing the above-described
Components (Bc) and/or (Bd).
[0087] The composition ratio of Components (Bc) and (Bd) of
Component (B) used in Requirement [I] is preferably 5 percent by
mole or more, more preferably 15 percent by mole or more and
particularly preferably 30 percent by mole or more. The composition
ratio is preferably 80 percent by mole or less, and more preferably
60 percent by mole or less, and particularly preferably 50 percent
by mole or less in view of low temperature viscosity
characteristics. More specifically, the composition ratio of the
above-described Components (Bc), (Bd), (Ba), (Bb) and (Be) is
preferably the following ratio on the basis of the total amount of
the monomer constituting the poly(meth)acrylate:
[0088] Component (Bc): preferably 5 to 60 percent by mole, more
preferably 10 to 40 percent by mole, and particularly preferably 20
to 40 percent by mole;
[0089] Component (Bd): preferably 5 to 60 percent by mole, more
preferably 10 to 40 percent by mole, and particularly preferably 10
to 30 percent by mole;
[0090] Component (Ba): preferably 0 to 90 percent by mole, more
preferably 20 to 80 percent by mole, and particularly preferably 30
to 70 percent by mole;
[0091] Component (Bb): preferably 0 to 60 percent by mole, more
preferably 5 to 30 percent by mole, and particularly preferably 10
to 20 percent by mole; and
[0092] Component (Be): preferably 0 to 20 percent by mole, more
preferably 0 to 10 percent by mole, and particularly preferably 1
to 5 percent by mole.
[0093] There is no particular restriction on the weight-average
molecular weight of Component (B) used in Requirement [I], which is
usually from 5000 to 150000. However, the weight-average molecular
weight of Component (B) is preferably from 10000 to 60000, more
preferably from 15000 to 60000, more preferably from 15000 to 30000
and particularly preferably from 15000 to 24000 with the objective
of improving fatigue life.
[0094] The weight-average molecular weight used herein denotes a
weight-average molecular weight in terms of polystyrene determined
with a differential refractive index detector (RI) at a temperature
of 23.degree. C., a flow rate of 1 mL/min, a sample concentration
of 1 percent by mass, using 150-C ALC/GPC manufactured by Waters
having two columns GMHHR-M (7.8 mm Id.times.30 cm) equipped in
series therein and tetrahydrofuran as a solvent.
[0095] Next, Requirement [II] will be described.
[0096] Requirement [II] is to be such that Component (A) is a
lubricating base oil with a kinematic viscosity at 100.degree. C.
adjusted to 1.5 to 6 mm.sup.2/s, composed of 70 to 97 percent by
mass of Component (A1) and 3 to 30 percent by mass of Component
(A2), and Component (B) is (B2) a poly(meth)acrylate-based additive
substantially not containing a structural unit of formula (1)
wherein R2 is a hydrocarbon group having 20 or more carbon
atoms.
[0097] That is, Component (A) is composed of Components (A 1) and
(A2). The blend ratio of Component (A1) is from 70 to 97 percent by
mass and preferably from 85 to 95 percent by mass while the blend
ratio of Component (A2) is from 3 to 30 percent by mass and
preferably from 5 to 15 percent by mass.
[0098] Component (B) is (B2) a poly(meth)acrylate-based additive
substantially not containing a structural unit of formula (1)
wherein R2 is a hydrocarbon group having 20 or more carbon
atoms.
[0099] There is no particular restriction on Component (B) as long
as it contains substantially no structural unit of formula (1)
wherein R2 is a hydrocarbon group having 20 or more carbon atoms.
Specifically, Component (B) is a poly(meth)acrylate composed of a
structural unit of formula (1) wherein R.sub.1 is hydrogen or
methyl, preferably methyl, R.sub.2 is a hydrocarbon group having 1
to 18 carbon atoms or a group represented by --(R).sub.a-E wherein
R is an alkylene group having 1 to 18 carbon atoms, E is an amine
residue or a heterocyclic residue, each having 1 or 2 nitrogen
atoms and 0 to 2 oxygen atoms, and a is an integer of 0 or 1.
[0100] Examples of the poly(meth)acrylate-based additive
substantially not containing a structural unit of formula (1)
wherein R2 is a hydrocarbon group having 20 or more carbon atoms
include poly(meth)acrylates obtained by polymerizing or
copolymerizing one or more types of monomers represented by formula
(2'):
CH.sub.2.dbd.C(R.sub.1)--C(.dbd.O)--OR.sub.2 (2')
wherein R.sub.1 is hydrogen or methyl, preferably methyl, R.sub.2
is a hydrocarbon group having 1 to 18 carbon atoms or a group
represented by --(R).sub.a-E wherein R is an alkylene group having
1 to 18 carbon atoms, E is an amine residue or a heterocyclic
residue, each having 1 or 2 nitrogen atoms and 0 to 2 oxygen atoms,
and a is an integer of 0 or 1.
[0101] Specific examples of the monomers represented by formula
(2') include the above-described Components (Ba), (Bb), (Be) and
the following monomers (Bf):
[0102] Component (Bf): (meth)acrylates having an alkyl group having
16 to 18 carbon atoms.
[0103] Specific examples of Component (Bf) include
hexadecyl(meth)acrylate, heptadecyl(meth)acrylate and
octadecyl(meth)acrylate, all of which may be straight-chain or
branched. Component (Bf) is preferably a (meth)acrylate having a
straight-chain alkyl group having 16 or 18 carbon atoms.
[0104] In Requirement [II], Component (B) is a poly(meth)acrylate
containing no poly(meth)acrylate derived from a (meth)acrylate
monomer having at its side chains a hydrocarbon group having 20 or
more carbon atoms, preferably poly(meth)acrylate containing no
poly(meth)acrylate derived from a (meth)acrylate monomer having at
its side chains a branched hydrocarbon group having 16 or more
carbon atoms, more preferably a poly(meth)acrylate obtained by
polymerizing a (meth)acrylate monomer containing Components (Ba)
and (Bb) as the main components (which may contain slight amount of
Components (Be) and/or 'Bf), and particularly preferably and
effectively a poly(meth)acrylate obtained by polymerizing a
(meth)acrylate monomer consisting of Components (Ba) and (Bb). The
composition ratio of the monomers of Component (B) is the following
ratio on the basis of the total amount of the monomers constituting
the poly(meth)acrylate:
[0105] Component (Ba): preferably 10 to 90 percent by mole, more
preferably 20 to 80 percent by mole, and particularly preferably 30
to 70 percent by mole;
[0106] Component (Bb): preferably 10 to 90 percent by mole, more
preferably 20 to 80 percent by mole, and particularly preferably 30
to 70 percent by mole;
[0107] Component (Bf): preferably 0 to 50 percent by mole, more
preferably 0 to 20 percent by mole, and particularly preferably 0
to 5 percent by mole;
[0108] Component (Be): preferably 0 to 20 percent by mole, more
preferably 0 to 10 percent by mole, and particularly preferably 0
to 5 percent by mole.
[0109] There is no particular restriction on the weight-average
molecular weight of Component (B) used in Requirement [II], which
is usually from 5000 to 150000. However, the weight-average
molecular weight of Component (B) is preferably from 10000 to
60000, more preferably from 15000 to 60000, more preferably from
15000 to 30000 and particularly preferably from 15000 to 24000 with
the objective of improving fatigue life.
[0110] Next, Requirement [III] will be described below.
[0111] Requirement [III] is to be such that the kinematic viscosity
at 100.degree. C. (Vc) of the composition is from 4.5 to 8
mm.sup.2/s, and the ratio of the kinematic viscosity at 100.degree.
C. (Vb) of Component (A) to (Vc) (=Vb/Vc) is 0.70 or greater.
[0112] When the kinematic viscosity of the composition is constant,
the Vb/Vc is preferably 0.75 or greater, more preferably 0.80 or
greater, and particularly preferably 0.90 or greater and 1.0 or
less with the objective of improving fatigue life.
[0113] In Requirement [III], Component (A) is composed of the
above-described Component (A1) or Components (A1) and (A2). There
is no particular restriction on the contents of Components (A1) and
(A2) when used in combination. The content of Component (A1) is
preferably from 70 to 97 percent by mass and more preferably from
85 to 95 percent by mass while the content of Component (A2) is
preferably from 3 to 30 percent by mass and more preferably from 5
to 15 percent by mass, on the basis of the total amount of the
lubricating oil composition.
[0114] As described above, Component (A) of Requirement [III] is a
lubricating base oil composed of Component (A1) or Components (A1)
and (A2). The kinematic viscosity at 100.degree. C. of Component
(A) is preferably from 4.5 to 6 mm.sup.2/s, more preferably from
5.0 to 5.7 mm.sup.2/s, and particularly preferably from 5.2 to 5.5
mm.sup.2/s. The kinematic viscosity at 100.degree. C. of 6
mm.sup.2/s or lower renders it possible to produce a lubricating
oil composition which is small in friction resistance at
lubricating sites due to its small fluid resistance and is
excellent in low temperature viscosity (for example, a Brookfield
viscosity at -40.degree. C. of 150000 mPas or lower) particularly
as a transmission oil or a gear oil. The kinematic viscosity at
100.degree. C. of 4.5 mm.sup.2/or higher renders it possible to
produce a lubricating oil composition which is sufficient in oil
film formation, excellent in fatigue life, and less in evaporation
loss of the base oil at elevated temperatures.
[0115] Component (B) of Requirement [III] is (B3) a
poly(meth)acrylate-based additive having a weight-average molecular
weight of 50000 to 300000 and substantially composed of only a
structural unit of formula (1) wherein R.sub.1 is hydrogen or
methyl, R.sub.2 is a hydrocarbon group having 5 to 20 carbon atoms
or a group represented by --(R).sub.a-E wherein R is an alkylene
group having 5 to 20 carbon atoms, E is an amine residue or a
heterocyclic residue, each having 1 or 2 nitrogen atoms and 0 to 2
oxygen atoms, and a is an integer of 0 or 1.
[0116] Examples of the poly(meth)acrylate substantially composed of
only a structural unit of formula (1) wherein R.sub.1 is hydrogen
or methyl, R.sub.2 is a hydrocarbon group having 5 to 20 carbon
atoms or a group represented by --(R).sub.a-E wherein R is an
alkylene group having 5 to 20 carbon atoms, E is an amine residue
or a heterocyclic residue, each having 1 or 2 nitrogen atoms and 0
to 2 oxygen atoms, and a is an integer of 0 or 1, constituting
Component (B3) include poly(meth)acrylates obtained by polymerizing
or copolymerizing one or more types of monomers represented by
formula (3'):
CH.sub.2.dbd.C(R.sub.1)--C(.dbd.O)--OR.sub.2 (3')
wherein R.sub.1 and R.sub.2 are as described above.
[0117] Specific examples of the monomer include the above-described
Components (Bb) and (Be) and the following monomers (Bg):
[0118] Component (Bg): (meth)acrylates having an alkyl group having
16 to 20 carbon atoms.
[0119] Examples of Component (Bg) include (meth)acrylates having
preferably a straight-chain alkyl group having 16 to 20 carbon
atoms, more preferably a straight-chain alkyl group having 16 or 18
carbon atoms. Specific examples include n-hexadecyl(meth)acrylate,
n-octadecyl(meth)acrylate, and n-eicosyl(meth)acrylate.
[0120] In the present invention, Component (B3) is preferably a
poly(meth)acrylate which is a copolymer of a monomer of one or more
types of monomers selected from (Bb) monomers and one or more types
of monomers selected from (Bg) monomers (if necessary, one or more
types of monomers selected from (Be) monomers may also be
copolymerized) and more preferably which is a copolymer of (Bb) a
(meth)acrylate mixture having a straight-chain alkyl group having
12 to 15 carbon atoms and a monomer mixture composed of (Bg) a
meth(acrylate) having a straight-chain alkyl group having 16 carbon
atoms and a meth(acrylate) having a straight-chain alkyl group
having 18 carbon atoms, as the main components.
[0121] There is no particular restriction on the weight-average
molecular weight of Component (B3). However, the weight-average
molecular weight is preferably from 50000 to 300000, more
preferably from 60000 to 250000, more preferably from 80000 to
230000, and particularly preferably from 200000 to 230000 in view
of excellent low temperature viscosity and fatigue life.
[0122] There is no particular restriction on the ratio of the
weight-average molecular weight (Mw) to the number-average
molecular weight of Component (B3). However, the ratio is
preferably from 1.5 to 4, more preferably from 2 to 3.5, and
particularly preferably from 2.2 to 3.
[0123] The weight-average molecular weight and the number-average
molecular weight used herein denote a weight-average molecular
weight and a number-average molecular weight in terms of
polystyrene determined with a differential refractive index
detector (RI) at a temperature of 23.degree. C., a flow rate of 1
mL/min, a sample concentration of 1 percent by mass, using 150-C
ALC/GPC manufactured by Waters having two columns GMHHR-M (7.8 mm
Id.times.30 cm) equipped in series therein and tetrahydrofuran as a
solvent.
[0124] The content of (B3) a poly(meth)acrylate-based additive used
in Requirement [III] is to be such an amount that the kinematic
viscosity at 100.degree. C. (Vc) of the composition is from 4.5 to
8 mm.sup.2/s, the viscosity index of the composition is from 95 to
200, and the VbNc is 0.70 or greater. More specifically, the
content is usually from 0.1 to 2 percent by mass and preferably
from 0.2 to 1 percent by mass.
[0125] The transmission lubricating oil composition fulfilling
Requirement [III] is excellent in low temperature viscosity and
fatigue life but may further contain a non-dispersion type or
dispersion type poly(meth)acrylate-based additive other than the
above-described Component (B3), as Component (B) as long as the
kinematic viscosity at 100.degree. C. (Vc) of the composition is
from 4.5 to 8 mm.sup.2/s, the viscosity index of the composition is
from 95 to 200, and the VbNc is 0.70 or greater.
[0126] Preferably, the lubricating oil composition contains (B4) a
poly(meth)acrylate containing a structural unit represented by
formula (1) wherein R.sub.1 is hydrogen or methyl, and R.sub.2 is
methyl.
[0127] The poly(meth)acrylate constituting Component (B4) may be a
poly(meth)acrylate obtained by polymerizing a monomer (B4')
represented by formula (4') or a copolymer of a monomer represented
by formula (4') and a monomer other than the monomer represented by
formula (4'):
CH.sub.2.dbd.C(R.sub.1)--C(.dbd.O)--OR.sub.2 (4)
wherein R.sub.1 is hydrogen or methyl, and R.sub.2 is methyl.
[0128] Specific example of the monomer represented by formula (4')
includes methyl(meth)acrylate.
[0129] Examples of the monomer other than the monomer represented
by formula (4') include the following Components (Ba') and the
above-described Components (Bb) to (Be):
[0130] Component (Ba'): (meth)acrylates having an alkyl group
having 2 to 4 carbon atoms.
[0131] Specific examples of Component (Ba') include
ethyl(meth)acrylate, n- or i-propyl(meth)acrylate, and n-, i- or
sec-butyl(meth)acrylate.
[0132] Component (B4) is a poly(meth)acrylate-based compound
obtained by polymerizing monomer (B4') or obtained by
copolymerizing the above-described Components (B4') and (Ba') and
one or more types of monomers selected from the above-described
Components (Bb) to (Be). More preferable specific examples include
the following compounds: [0133] (1) non-dispersion type
poly(meth)acrylates, which are copolymers of (B4') and (Bb), or
hydrogenated compounds thereof; [0134] (2) non-dispersion type
poly(meth)acrylates, which are copolymers of (B4'), (Bb) and (Bc),
or hydrogenated compounds thereof; [0135] (3) non-dispersion type
poly(meth)acrylates, which are copolymers of (B4'), (Bb), (Bc) and
(Bd), or hydrogenated compounds thereof; [0136] (4) dispersion type
poly(meth)acrylates, which are copolymers of (B4'), (Bb) and (Be),
or hydrogenated compounds thereof; [0137] (5) dispersion type
poly(meth)acrylates, which are copolymers of (B4'),(Bb), (Bc) and
(Be), or hydrogenated compounds thereof; and [0138] (6) dispersion
type poly(meth)acrylates, which are copolymers of (B4'), (Bb),
(Bc), (Bd) and (Be), or hydrogenated compounds thereof. Preferred
are non-dispersion type poly(meth)acrylates (1) to (3), more
preferred are non-dispersion type poly(meth)acrylates (2) and (3)
and particularly preferred are non-dispersion type
poly(meth)acrylates (3).
[0139] The composition ratio of the structural unit of formula (1)
wherein R.sub.1 is hydrogen or methyl and R.sub.2 is methyl is
preferably 5 percent by mole or more, more preferably 15 percent by
mole or more, and particularly preferably 30 percent by mole or
more and preferably 80 percent by mole or less, more preferably 60
percent by mole or less, and in view of low temperature viscosity
characteristics particularly preferably 50 percent by mole or less,
on the basis of the total amount of the monomer constituting the
poly(meth)acrylate.
[0140] There is no particular restriction on the weight-average
molecular weight of Component (B4), which is usually from 5000 to
150000. However, the weight-average molecular weight is preferably
from 10000 to 60000, more preferably from 15000 to 60000, more
preferably from 15000 to 30000, and particularly preferably from
15000 to 24000 with the objective of improving fatigue life.
[0141] When the transmission lubricating oil composition fulfilling
Requirement [III] contains (B4) a poly(meth)acrylate-based
additive, the content thereof is to be such an amount that the
kinematic viscosity at 100.degree. C. (Vc) of the composition is
from 4.5 to 8 mm.sup.2/s, the viscosity index of the composition is
from 95 to 200, and the VbNc is 0.70 or greater. More specifically,
the content is usually from 0.1 to 5 percent by mass, preferably
from 0.5 to 2 percent by mass, and particularly preferably from 0.8
to 1.5 percent by mass, on the basis of the total amount of the
composition. Component (B4) blended in the above-described range
renders it possible to produce a composition excellent in fatigue
life and low temperature viscosity characteristics. When the
content of Component (B4) exceeds the above-described range, it is
not preferable because the resulting composition not only fails to
be improved in an effect of improving fatigue life as balanced with
the content but also is poor in shear stability and hard to retain
the initial extreme pressure properties for a long period of
time.
[0142] The transmission lubricating oil composition fulfilling
Requirement [I] may contain, in addition to Component (B1), a
polymer other than Component (B1), for example a non-dispersion
type or dispersion type poly(meth)acrylate-based additive (more
specifically Components (B2), (B3) and (B4)) other than Component
(B1) and one or more types of polymers selected from those other
than the poly(meth)acrylate-based additive as long as the
composition fulfills Requirement [I]. When the composition contains
these components, the content thereof is usually from 0.01 to 10
percent by mass. In particular, the composition contains Component
(B3) in an amount of preferably 0.1 to 2 percent by mass and more
preferably 0.2 to 1 percent by mass.
[0143] The transmission lubricating oil composition fulfilling
Requirement [II] may contain, in addition to Component (B2), a
polymer other than Component (B2), for example a non-dispersion
type or dispersion type poly(meth)acrylate-based additive other
than Component (B2) (more specifically Components (B 1), (B3) and
(B4)) and one or more types of polymers selected from those other
than the poly(meth)acrylate-based additive as long as the
composition fulfills Requirement [II]. When the composition
contains these components, the content thereof is usually from 0.01
to 10 percent by mass. In particular, the composition contains
Component (B3) in an amount of preferably 0.1 to 2 percent by mass
and more preferably 0.2 to 1 percent by mass.
[0144] The transmission lubricating oil composition fulfilling
Requirement [III] may contain, in addition to Component (B3) or
Components (B3) and (B4), a non-dispersion type or dispersion type
poly(meth)acrylate-based additive such as Component (B1) or (B2)
and one or more types of polymers selected from those other than
the poly(meth)acrylate-based additive. When the composition
contains these components, the content thereof is usually from 0.01
to 10 percent by mass. However, the content is preferably to be
such that Requirement [III] is fulfilled.
[0145] Examples of the polymer other than the
poly(meth)acrylate-based additive include non-dispersion type or
dispersion type ethylene-.alpha.-olefin copolymers and hydrogenated
compounds thereof, polyisobutylene and hydrogenated compounds
thereof, styrene-diene hydrogenated copolymers, styrene-maleic
anhydride ester copolymers, and polyalkylstyrenes.
[0146] Preferably, the transmission lubricating oil composition of
the present invention contains (C) an imide-based friction modifier
having a hydrocarbon group having 8 to 30 carbon atoms and (D) a
sulfur-free phosphorus-based extreme pressure additive for the
purpose of further enhancing the performances of the
composition.
[0147] There is no particular restriction on Component (C) which
may be used in the present invention as long as Component (C) has a
hydrocarbon group having 8 to 30 carbon atoms and an imide
structure. For Example, Component (C) is preferably a succinimide
represented by formula (2) or (3) and/or a derivative thereof:
##STR00003##
[0148] In formula (2), R.sub.11 is a straight-chain or branched
hydrocarbon group having 8 to 30 carbon atoms, R.sub.12 is hydrogen
or a hydrocarbon group having 1 to 30 carbon atoms, R.sub.13 is a
hydrocarbon group having 1 to 4 carbon atoms, and m is an integer
of 1 to 7.
[0149] In formula (3), R.sub.14 and R.sub.15 are each independently
a straight-chain or branched hydrocarbon group having 8 to 30
carbon atoms, R.sub.16 and R.sub.17 are each independently a
hydrocarbon group having 1 to 4 carbon atoms, and n is an integer
of 1 to 7.
[0150] R.sub.11 in formula (2) and R.sub.14 and R.sub.15 in formula
(3) are each independently a straight-chain or branched hydrocarbon
group having 8 to 30 carbon atoms, preferably 12 to 25 carbon
atoms. Examples of such a hydrocarbon group include alkyl and
alkenyl groups. Preferred are alkyl groups. Examples of alkyl
groups include octyl, octenyl, nonyl, nonenyl, decyl, decenyl,
dodecyl, dodecenyl, octadecyl, octadecenyl groups as well as
straight-chain or branched alkyl groups having up to 30 carbon
atoms. When the hydrocarbon group has fewer than 8 or more than 30
carbon atoms, it is difficult to obtain sufficient anti-shudder
properties. In the present invention, the hydrocarbon group is more
preferably a branched alkyl group having 8 to 30 carbon atoms and
particularly preferably a branched alkyl group having 10 to 25
carbon atoms. The use of a branched alkyl group having 8 to 30
carbon atoms renders it possible to produce a lubricating oil
composition which is more enhanced in anti-shudder durability,
compared with the use of a straight-chain alkyl group.
[0151] R.sub.13 in formula (2) and R.sub.16 and R.sub.17 in formula
(3) are each independently a hydrocarbon group having 1 to 4 carbon
atoms. Examples of such a hydrocarbon group include alkylene groups
having 1 to 4 carbon atoms. The hydrocarbon group is preferably an
alkylene group having 2 or 3 carbon atoms (ethylene and propylene
groups).
[0152] R.sub.12 in formula (2) is hydrogen or a straight-chain or
branched hydrocarbon group having 1 to 30 carbon atoms. Examples of
the straight-chain or branched hydrocarbon group having 1 to 30
carbon atoms include straight-chain or branched alkyl and alkenyl
groups having 1 to 30 carbon atoms. The hydrocarbon group is a
branched alkyl or alkenyl group having preferably 1 to 30 carbon
atoms, more preferably 8 to 30 carbon atoms, and more preferably 10
to 25 carbon atoms. Particularly preferred are branched alkyl
groups.
[0153] In formulas (2) and (3), n and m are each an integer of 1 to
7. In order to obtain a lubricating oil composition with more
enhanced anti-shudder durability, n and m are each preferably an
integer of 1, 2 or 3 and particularly preferably 1.
[0154] The succinimide compound represented by formula (2) or (3)
may be produced by a conventional method. For example, the compound
may be obtained by reacting an alkyl or alkenyl succinic anhydride
with a polyamine. Specifically, a mono succinimide of formula (2)
wherein R.sub.12 is hydrogen may be obtained by adding slowly
dropwise one mole of succinic anhydride having an straight-chain or
branched alkyl or alkenyl group having 8 to 30 carbon atoms to one
or more moles of a polyamine such as diethylenetriamine,
triethylenetetramine, and tetraethylenepentamine, at a temperature
of 130 to 180.degree. C., preferably 140 to 175.degree. C. under
nitrogen atmosphere and reacting the compounds for one to 10 hours,
preferably 2 to 6 hours, followed by removal of the unreacted
polyamine by distillation. A mono succinimide of formula (2)
wherein R.sub.12 is a hydrocarbon group having 1 to 30 carbon atoms
may be obtained by reacting N-octadecyl-1,3-propane diamine and the
above succinic anhydride by the same method as described above. A
bis succinimide of formula (3) may be obtained by adding dropwise
0.5 mole of a polyamine as mentioned above to one mole of a
succinic anhydride under the same conditions as described above and
reacting these compounds in the same manner as described above,
followed by removal of the produced water.
[0155] Examples of derivatives of the succinimides of formulas (2)
and (3) include compounds obtained by modifying the succinimides
with boric acid, phosphoric acid, carboxylic acids, derivatives
thereof, sulfur compounds, and triazoles. Specific examples of the
derivatives and method for producing the same includes those
specifically described in Japanese Patent Laid-Open Publication No.
2002-105478.
[0156] In the present invention, Component (C) is particularly
preferably a bis type succinimide of formula (3) because a
composition with more enhanced anti-shudder durability can be
obtained, compared with the use of a mono-type succinimide of
formula (2).
[0157] The content of Component (C) in the transmission lubricating
oil composition of the present invention is preferably one percent
by mass or more and more preferably 2 percent by mass or more on
the basis of the total amount of the composition. On the other
hand, the content is preferably 5 percent by mass or less and more
preferably 4 percent by mass or less on the basis of the total
amount of the composition. When the content of Component (C) is
less than one percent by mass, it would be difficult to achieve the
higher target of the present invention regarding anti-shudder
durability (anti-shudder durability; for example 300 hours or
longer). When the content of Component (C) is in excess of 5
percent by mass, the fatigue life would tend to degrade.
[0158] Specific examples of (D) a sulfur-free phosphorus-based
extreme pressure additive include phosphoric acid monoesters,
phosphoric acid diesters, phosphoric acid triesters, phosphorus
acid monoesters, phosphorus acid diesters, and phosphorus acid
triesters, each having an alkyl or aryl group having 3 to 30 carbon
atoms, preferably 4 to 18 carbon atoms, and salts of these esters
and amines, alkanol amines, or metals such as zinc.
[0159] In the present invention, Component (D) is preferably
phosphoric and phosphorus acid esters having an alkyl group having
3 to 30 carbon atoms and particularly preferably phosphorus acid
esters having 3 to 30 carbon atoms.
[0160] The content of Component (D) is preferably from 0.015 to
0.05 percent by mass and more preferably from 0.02 to 0.04 percent
by mass in terms of phosphorus on the basis of the total amount of
the composition. When the phosphorus content of Component (D) is
less than the above range, the resulting composition would tend to
be degraded in anti-shudder durability while the phosphorus content
exceeds the above range, the resulting composition would tend to be
degraded in fatigue life.
[0161] If necessary, the transmission lubricating oil composition
of the present invention may further contain any of one or more
additives selected from those such as viscosity index improvers,
extreme pressure additives other than Component (D), dispersants,
metallic detergents, friction modifiers other than Component (C),
anti-oxidants, corrosion inhibitors, rust inhibitors, demulsifiers,
metal deactivators, pour point depressants, seal swelling agents,
anti-foaming agents and dyes for the purposes of enhancing the
performances of or providing performances necessary for a
transmission lubricating oil.
[0162] Examples of the viscosity index improvers include known
non-dispersion and dispersion types polymethacrylates (excluding
Components (B)), non-dispersion and dispersion types
ethylene-.alpha.-olefin copolymers and hydrogenated compounds
thereof, polyisobutylene and hydrogenated compounds thereof,
styrene-diene hydrogenated copolymers, styrene-maleic anhydride
ester copolymers, and polyalkylstyrenes.
[0163] When the transmission lubricating oil composition of the
present invention contains a viscosity index improver (excluding
Component (B)), there is no particular restriction on the content
thereof as long as the kinematic viscosity at 100.degree. C. and
viscosity index of the composition fall within the range defined by
the present invention. The content is usually from 0.1 to 15
percent by mass and preferably from 0.5 to 5 percent by mass on the
basis of the total amount of the composition.
[0164] Examples of the extreme pressure additives other than
Component (D) include those composed of at least one type of
sulfur-based extreme pressure additive selected from sulfurized
fats and oils, olefin sulfides, dihydrocarbyl polysulfides,
dithiocarbamates, thiadiazoles and benzothiazoles and/or at least
one type of phosphorus-sulfur-based extreme pressure additive
selected from thiophosphorus acid, thiophosphorus acid monoesters,
thiophosphorus acid diesters, thiophosphorus acid triesters,
dithiophosphorus acid, dithiophosphorus acid monoesters,
dithiophosphorus acid diesters, dithiophosphorus acid triesters,
trithiophosphorus acid, trithiophosphorus acid monoesters,
trithiophosphorus acid diesters, trithiophosphorus acid triesters
and salts thereof.
[0165] Examples of the dispersants include ashless dispersants such
as succinimides, benzylamines and polyamines, each having a
hydrocarbon group having 40 to 400 carbon atoms, and/or boron
compound derivatives thereof.
[0166] In the present invention, any one or more types of compounds
selected from the above-exemplified dispersants may be blended in
any amount. However, the content is usually from 0.01 to 15 percent
by mass and preferably from 0.1 to 8 percent by mass on the basis
of the total amount of the composition.
[0167] Examples of the metallic detergents include alkaline earth
metal sulfonates, alkaline earth metal phenates, and alkaline earth
metal salicylates.
[0168] In the present invention, any one or more types of compounds
selected from the above-exemplified metallic detergents may be
blended in any amount. However, the content is usually from 0.01 to
10 percent by mass and preferably from 0.1 to 5 percent by mass on
the basis of the total amount of the composition.
[0169] Examples of the friction modifiers other than Component (C)
include any compounds which are usually used as friction modifiers
for lubricating oils. Component (C) is preferably an amine
compound, a fatty acid ester, a fatty acid amide, or a fatty acid
metal salt, each having in its molecule at least one alkyl or
alkenyl group having 6 to 30 carbon atoms in particular at least
one straight-chain alkyl or alkenyl group having 6 to 30 carbon
atoms.
[0170] In the present invention, any one or more types of compounds
selected from the above-exemplified friction modifiers may be
blended in any amount. However, the content is usually from 0.01 to
5.0 percent by mass and preferably from 0.03 to 3.0 percent by mass
on the basis of the total amount of the composition.
[0171] The anti-oxidants may be any of those generally used in a
lubricating oil, such as phenol- or amine-based compounds.
[0172] Specific examples of the anti-oxidants 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-.alpha.-naphthylamine;
dialkyldiphenylamines; zinc dialkyldithiophosphates such as zinc
di-2-ethylhexyldithiophosphate; and esters of
(3,5-di-tert-butyl-4-hydroxyphenyl)fatty acid (propionic acid) or
(3-methyl-5-tert-butyl-4-hydroxyphenyl)fatty acid (propionic acid)
with a monohydric or polyhydric alcohol such as methanol, octanol,
octadecanol, 1,6-hexanediol, neopentyl glycol, thiodiethylene
glycol, triethylene glycol and pentaerythritol.
[0173] One or more compounds selected from these antioxidants may
be blended in an arbitrary amount, but is usually blended in an
amount of from 0.01 to 5.0 percent by mass, preferably from 0.1 to
3 percent by mass on the basis of the total amount of the
composition.
[0174] Examples of the corrosion inhibitors include benzotriazole-,
tolyltriazole, thiadiazole-, and imidazole-based compounds.
[0175] Examples of the rust inhibitors include petroleum
sulfonates, alkylbenzene sulfonates, dinonylnaphthalene sulfonates,
alkenyl succinic acid esters and polyhydric alcohol esters.
[0176] Examples of the demulsifiers include polyalkylene
glycol-based non-ionic surfactants such as polyoxyethylenealkyl
ethers, polyoxyethylenealkylphenyl ethers and
polyoxyethylenealkylnaphthyl ethers.
[0177] Examples of the metal deactivators include imidazolines,
pyrimidine derivatives, alkylthiadiazoles, mercaptobenzothiazoles,
benzotriazoles and derivatives thereof,
1,3,4-thiadiazolepolysulfide,
1,3,4-thiadiazolyl-2,5-bisdialkyldithiocarbamate,
2-(alkyldithio)benzoimidazole and
.beta.-(o-carboxybenzylthio)propionitrile.
[0178] The pour point depressants may be any of known pour point
depressants selected depending on the type of lubricating base oil
but are preferably polymethacrylates having a weight average
molecular weight of preferably 20000 to 500000, more preferably
50000 to 300000, and particularly preferably 80000 to 200000.
[0179] The anti-foaming agents may be any of compounds generally
used as anti-foaming agents for lubricating oils, including
silicones such as dimethylsilicone and fluorosilicone. One or more
types of compounds arbitrarily selected from such silicones may be
blended in an arbitrary amount.
[0180] The seal swelling agents may be any of compounds generally
used as seal swelling agents for lubricating oils, such as ester-,
sulfur- and aromatic-based swelling agents.
[0181] The dyes may be any of compounds generally used as dyes for
lubricating oil and may be blended in an arbitrary amount but in an
amount of usually from 0.001 to 1.0 percent by mass based on the
total amount of the composition.
[0182] When these additives are contained in the transmission
lubricating oil composition of the present invention, the corrosion
inhibitor, rust inhibitor and demulsifier are each contained in an
amount of from 0.005 to 5 percent by mass, the metal deactivator
and the pour point depressant are each contained in an amount of
from 0.005 to 2 percent by mass, the seal swelling agent is
contained in an amount of 0.01 to 5 percent by mass, and the
anti-foaming agent is contained in an amount of from 0.0005 to 1
percent by mass, on the basis of the total amount of the
composition.
[0183] The transmission lubricating oil composition of the present
invention is provided with excellent fatigue life because it is
constituted as described above. However, in order to further
enhance the fuel efficiency caused by a reduction in stirring
resistance, compared with the conventional lubricating oil
composition for automatic transmissions, continuously variable
transmissions, and manual transmissions, the kinematic viscosity at
100.degree. C. of the composition is adjusted to 8 mm.sup.2/s or
less, preferably 7 mm.sup.2/s or less, more preferably 6.5
mm.sup.2/s or less, and particularly preferably 6 mm.sup.2/s or
less. The kinematic viscosity at 40.degree. C. of the composition
is adjusted to preferably 40 mm.sup.2/s or less, more preferably 35
mm.sup.2/s or less, and particularly preferably 30 mm.sup.2/s or
less. Furthermore, in order to further enhance the extreme pressure
properties required for a lubricating oil composition for
automatic, continuously variable, and manual transmissions, the
kinematic viscosity at 100.degree. C. of the composition is
adjusted to preferably 3 mm.sup.2/s or higher, more preferably 4
mm.sup.2/s or higher, and particularly preferably 5 mm.sup.2/s or
higher while the kinematic viscosity at 40.degree. C. of the
composition is preferably 15 mm.sup.2/s or higher, more preferably
20 mm.sup.2/s or higher, and particularly preferably 25 mm.sup.2/s
or higher.
[0184] The transmission lubricating oil composition of the present
invention is excellent in fatigue life and reduced in stirring
resistance caused by a lubricating base oil by optimizing the base
oil even though containing a poly(meth)acrylate which is poor in
fatigue life. Therefore, when the composition is used for an
automobile transmission, particularly an automatic transmission, a
continuously variable transmission, or a manual transmissions, or
an automobile final reduction gear unit, it is able to contribute
to an improvement in the fuel efficiency of the automobile.
APPLICABILITY IN THE INDUSTRY
[0185] The transmission lubricating oil composition of the present
invention is excellent in anti-shudder durability, low temperature
viscosity characteristics and oxidation stability even though
having a low viscosity and also can provide the gears and bearings
of the automatic, manual and continuously variable transmission of
automobiles with sufficient durability and thus can achieve an
improvement in the fuel efficiency of the automobiles.
BEST MODE FOR CARRYING OUT THE INVENTION
[0186] Hereinafter, the present invention will be described in more
details by way of the following examples and comparative examples,
which should not be construed as limiting the scope of the
invention.
Examples 1 to 20, Comparative Examples 1 to 9, and Reference
Examples 1 to 3
[0187] Transmission lubricating oil compositions according to the
present invention (Examples 1 to 20) were prepared in accordance
with the formulations set forth in Tables 1 to 4. These lubricating
oil compositions were subjected to performance evaluating tests
described below, and the results are also set forth in Tables 1 to
4.
[0188] Transmission lubricating oil compositions for comparison
(Comparative Examples 1 to 9) were also prepared in accordance with
the formulations set forth in Tables 1 to 4. These lubricating oil
compositions were also subjected to performance evaluating tests
described below, and the results are also set forth in Tables 1 to
4.
[0189] (a) Fatigue Life Test
[0190] The fatigue life of each of the compositions was determined
in accordance with IP300/82 "Rolling Contact Fatigue Test For Fluid
in a Modified Four-Ball Machine" wherein a test condition "7.
Procedure B" was changed as follow, using a four-ball
extreme-pressure lubricant testing machine.
[0191] (Test Conditions)
[0192] Number of revolutions: 3000 rpm
[0193] Oil temperature: 120.degree. C.
[0194] Surface pressure: 3.9 GPa
[0195] (Evaluation Criterion)
[0196] Time consumed until pitching generated on the balls was
evaluated as fatigue life, and L50 (average) was calculated from 3
times test results.
[0197] (b) Low Temperature Viscosity Measurement
[0198] The low temperature viscosity at -40.degree. C. of each of
the transmission lubricating oil compositions was measured in a
liquid bath cryostat in accordance with "Testing Methods for
Low-Temperature Viscosity of Gear Oils". In the present invention,
the low temperature viscosity is preferably 20,000 mPas or lower
and in view of excellent fatigue life 10,000 mPas or greater.
[0199] (c) High-Speed Four Ball Test
[0200] A high-speed four ball test was carried out at an oil
temperature of 100.degree. C., a load of 294 N and a revolution
number of 1500 rpm in accordance with ASTM D4172-94 to measure the
wear scar diameter (mm) after the lapse of one hour.
[0201] (d) Anti-Shudder Durability
[0202] A low velocity sliding test was carried out in accordance
with "Automatic transmission fluids-anti-shudder performance test"
specified by JASO M349-98 wherein only the oil temperature during
the test was changed from 120.degree. C. to 140.degree. C. thereby
evaluating the anti-shudder durability of each of the Example and
Comparative Example compositions. The durability of the reference
oil specified by this test method is 72 hours. However, the present
invention aims at obtaining the durability 4 times that of the
reference oil (800 h). When the durability exceeded 600 hours, the
test was discontinued.
[0203] (e) Oxidation Stability
[0204] Each of the compositions was forced to degrade at
165.5.degree. C. in an ISOT test in accordance with JIS K 2514, and
the increase of acid number (mgKOH/g) after the lapse of 72 hours
was measured.
TABLE-US-00001 TABLE 1 Ex- Ex- Ex- Ex- Ex- Ex- Ex- Com- Com- Com-
ample ample ample ample ample ample ample parative parative
parative 1 2 3 4 5 6 7 Example 1 Example 2 Example 3 (A) Base oil
(on the basis of the Mass % 17 58 36 42 50 17 42 17 17 17 total
amount thereof) (A1a) Base oil A .sup.1) (A1b) Base oil B .sup.2)
Mass % 83 20 54 43 40 83 43 83 83 83 (A1c) Base oil C .sup.3) Mass
% 5 5 (A1a) Base oil D .sup.4) Mass % 22 (A1a) Base oil E .sup.5)
Mass % 10 (A1b) Base oil F .sup.6) Mass % 10 10 (A1c) Base oil G
.sup.7) Mass % 10 Kinematic viscosity (100.degree. C.) mm.sup.2/s
3.8 3.8 3.8 3.8 3.8 3.8 3.8 3.8 3.8 3.8 of mixed base oil Additives
(on the basis of the Mass % 5 5 5 5 5 total amount of composition)
(B) PMA-A .sup.8) (B) PMA-B .sup.9) Mass % 1.9 1.9 PMA-C .sup.10)
Mass % 5 PMA-D .sup.11) Mass % 10.5 PMA-E .sup.12) Mass % 0.9
Additive package .sup.13) Mass % 11 11 11 11 11 11 11 11 11 11
Composition properties/test mm.sup.2/s 5.7 5.7 5.7 5.7 5.7 5.7 5.7
5.7 5.7 5.7 results viscosity (100.degree. C.) Viscosity index 161
158 161 160 158 163 163 158 152 164 Low temperature viscosity rnPa
s 16800 18700 15900 16500 16900 16500 16100 16000 18400 16800 (BF
method; -40.degree. C.) Fatigue life (IP300, L50) h 80 80 80 150
120 70 110 50 40 40 .sup.1) Hydrocracked mineral oil (100.degree.
C. kinematic viscosity: 2.6 mm2/s, % CA: 0, sulfur content:
<0.001 mass %, viscosity index: 105) .sup.2) Hydrocracked
mineral oil (100.degree. C. kinematic viscosity: 4.2 mm2/s, % CA:
0, sulfur content: <0.001 mass %, viscosity index: 125) .sup.3)
Poly-.alpha. olefin base oil (100.degree. C. kinematic viscosity:
4.0 mm2/s, % CA: 0, sulfur content: 0 mass %, viscosity index: 124)
.sup.4) Solvent-refined mineral oil (100.degree. C. kinematic
viscosity: 10.84 mm2/s, % CA: 7.4, sulfur content: 0.6 mass %,
viscosity index: 94) .sup.5) Hydrorefined mineral oil (100.degree.
C. kinematic viscosity: 11.2 mm2/s, % CA: 2, sulfur content: 0.04
mass %, viscosity index: 106) .sup.6) Solvent-refined mineral oil
(100.degree. C. kinematic viscosity: 21.9 mm2/s, % CA: 7, sulfur
content: 0.91 mass %, viscosity index: 95) .sup.7) Solvent-refined
mineral oil (100.degree. C. kinematic viscosity: 31.3 mm2/s, % CA:
7.4, sulfur content: 1.11 mass %, viscosity index: 94) .sup.8)
Non-dispersion type polymethacrylate-based additive (Mw: 22,900)
derived from a polymer of a mixture of methyl MA, nC12MA, nC13MA,
nC14MA, nC15MA, nC16MA, nC18MA, and 2-decyl-tetradecyl MA, as main
components (MA indicates methacrylate, Mw indicates weight-average
molecular weight, hereinafter the same) .sup.9) Non-dispersion type
polymethacrylate-based additive (Mw: 50,500) derived from a polymer
of a mixture of methyl MA, nC12MA, nC13MA, nC14MA, nC15MA, nC16MA,
nC18MA, and 2-decyl-tetradecyl MA, as main components .sup.10)
Non-dispersion type polymethacrylate-based additive (containing no
methacrylate having an alkyl group of C16 or more, Mw: 20,500)
derived from a polymer of a mixture of methyl MA, nC12MA, nC13MA,
nC14MA, and nC15MA, as main components .sup.11) Non-dispersion type
polymethacrylate-based additive (containing no methacrylate having
an alkyl group of C16 or more, Mw: 10,000) derived from a polymer
of a mixture of methyl MA, nC12MA, nC13MA, nC14MA, and nC15MA, as
main components .sup.12) Non-dispersion type polymethacrylate-based
additive (containing no methacrylate having an alkyl group of C16
or more, Mw: 100,000) derived from a polymer of a mixture of methyl
MA, nC12MA, nC13MA, nC14MA, and nC15MA, as main components .sup.13)
Containing metallic detergent, dispersant, friction modifier,
extreme pressure additive, seal swelling agent, anti-oxidant, and
pour point depressant
TABLE-US-00002 TABLE 2 Comparative Comparative Comparative Example
8 Example 9 Example 10 Example 4 Example 5 Example 6 (A) Base oil
(on the basis of the total Mass % 42 50 50 17 17 17 amount thereof)
(A1a) Base oil A .sup.1) (A1b) Base oil B .sup.2) Mass % 43 40 40
83 83 83 (A1c) Base oil C .sup.3) Mass % 5 (A1b) Base oil D .sup.4)
Mass % 10 (A1c) Base oil E .sup.5) Mass % 10 10 Base oil properties
mm.sup.2/s 3.8 3.8 3.8 3.8 3.8 3.8 Kinematic viscosity (100.degree.
C.) Additives (on the basis of the total amount composition) (B)
PMA-C .sup.6) Mass % 5 5 (B) PMA-D .sup.7) Mass % 10.5 10.5 (B)
PMA-E .sup.8) Mass % 0.9 0.9 Additive package .sup.9) Mass % 11 11
11 11 11 11 Composition properties/test results mm.sup.2/s 5.7 5.7
5.7 5.7 5.7 5.7 Kinematic viscosity (100.degree. C.) Viscosity
index 158 163 168 158 152 164 Low temperature viscosity mPa s 15800
19200 18500 16000 18400 16800 (BF method; -40.degree. C.) Acid
number increase (ISOT165.5.degree. C., after mgKOH/g 0.48 0.68 0.64
0.54 0.6 0.65 72 hours) Fatigue life (IP300, L50) h 80 60 80 50 40
40 .sup.1) Hydrocracked mineral oil (100.degree. C. kinematic
viscosity: 2.6 mm.sup.2/s, % C.sub.A: 0, sulfur content: <0.001
mass %, viscosity index: 105), .sup.2) Hydrocracked mineral oil
(100.degree. C. kinematic viscosity: 4.2 mm.sup.2/s, % C.sub.A: 0,
sulfur content: <0.001 mass %, viscosity index: 125), .sup.3)
Poly-.alpha. olefin base oil (100.degree. C. kinematic viscosity:
4.0 mm.sup.2/s, % C.sub.A: 0, sulfur content: 0 mass %, viscosity
index: 124), .sup.4) Solvent-refined mineral oil (100.degree. C.
kinematic viscosity: 21.9 mm.sup.2/s, % C.sub.A: 7, sulfur content:
0.91 mass %, viscosity index: 95), .sup.5) Solvent-refined mineral
oil (100.degree. C. kinematic viscosity: 31.3 mm.sup.2/s, %
C.sub.A: 7.4, sulfur content: 1.11 mass %, viscosity index: 94)
.sup.6) Non-dispersion type polymethacrylate-based additive
(containing no methacrylate having an alkyl group of C20 or more,
Mw: 20,500) derived from a polymer of a mixture of methyl MA,
nC12MA, nC13MA, nC14MA, and nC15MA as a main components (MA:
methacrylate), .sup.7) Non-dispersion type polymethacrylate-based
additive (containing no methacrylate having an alkyl group of C20
or more, Mw: 10,000) derived from a polymer of a mixture of methyl
MA, nC12MA, nC13MA, nC14MA, and nC15MA as a main components (MA:
methacrylate), .sup.8) Non-dispersion type polymethacrylate-based
additive (containing no methacrylate having an alkyl group of C20
or more, Mw: 100,000) derived from a polymer of a mixture of methyl
MA, nC12MA, nC13MA, nC14MA, and nC15MA as a main components,
.sup.9) Containing metallic detergent, dispersant, friction
modifier, extreme pressure additive, seal swelling agent,
anti-oxidant, and pour point depressant
TABLE-US-00003 TABLE 3 Comparative Comparative Comparative Example
11 Example 12 Example 13 Example 7 Example 8 Example 9 Base oil (on
the basis of the total amount thereof) Mass % 17 17 (A1a) Base oil
A .sup.1) (A1b) Base oil B .sup.2) Mass % 33 53 60 33 83 83 (A1b)
Base oil C .sup.3) Mass % 67 47 35 67 (A2b) Base oil D .sup.4) Mass
% 5 Base oil properties kinematic viscosity (100.degree. C.): Vb
mm.sup.2/s 5.4 5 5 5.4 3.8 3.8 Additives (on the basis of the total
amount 0.3 0.3 0.3 -- 0.3 0.3 composition) PMA-A .sup.5) PMA-B
.sup.6) Mass % 1 1 PMA-C .sup.7) Mass % 0.9 PMA-D .sup.8) Mass % 5
Additive package .sup.9) Mass % 11 11 11 11 11 11 Composition
properties/test results mm.sup.2/s 5.7 5.7 5.7 5.7 5.7 5.7
Kinematic viscosity (100.degree. C.): Vc Vb/Vc 0.95 0.88 0.88 0.95
0.67 0.67 Viscosity index 123 135 132 123 164 158 Wear properties
(four-ball test) mm 0.39 0.39 0.39 0.40 0.40 0.40 Low temperature
viscosity (BF method; -40.degree. C.) mPa s 39000 30000 53000 n/a
16800 16000 Fatigue life (IP300, L50) h 80 100 110 60 40 50 .sup.1)
Hydrocracked mineral oil (100.degree. C. kinematic viscosity: 2.6
mm.sup.2/s, % C.sub.A: 0, sulfur content: <0.001 mass %,
viscosity index: 105) .sup.2) Hydrocracked mineral oil (100.degree.
C. kinematic viscosity: 4.2 mm.sup.2/s, % C.sub.A: 0, sulfur
content: <0.001 mass %, viscosity index: 125) .sup.3)
Hydrocracked mineral oil (100.degree. C. kinematic viscosity: 6.2
mm.sup.2/s, % C.sub.A: 0, sulfur content: 0.001 mass %, viscosity
index: 132) .sup.4) Solvent-refined mineral oil (100.degree. C.
kinematic viscosity: 21.9 mm.sup.2/s, % C.sub.A: 7, sulfur content:
0.91 mass %, viscosity index: 95) .sup.5) Non-dispersion type
polymethacrylate-based additive (Mw: 217,000, Mw/Mn = 2.85) derived
from a polymer of a mixture of nC12MA, nC13MA, nC14MA, and nC15MA,
nC16MA and nC18MA as a main components (MA: methacrylate) .sup.6)
Non-dispersion type polymethacrylate-based additive (containing no
methacrylate having an alkyl group of C20 or more, Mw: 22,900)
derived from a polymer of a mixture of methyl MA, nC12MA, nC13MA,
nC14MA, nC15MA, nC16MA, nC18MA and 2-decyl-tetradecyl MA as a main
components (MA: methacrylate), .sup.7) Non-dispersion type
polymethacrylate-based additive (Mw: 100,000) derived from a
polymer of a mixture of methyl MA, nC12MA, nC13MA, nC14MA, and
nC15MA as a main components, .sup.8) Non-dispersion type
polymethacrylate-based additive (Mw: 10,000) derived from a polymer
of a mixture of methyl MA, nC12MA, nC13MA, nC14MA, and nC15MA as a
main components .sup.9) Containing metallic detergent, dispersant,
friction modifier, extreme pressure additive, seal swelling agent
and anti-oxidant
TABLE-US-00004 TABLE 4 Refer- Refer- Refer- Ex- Ex- Ex- Ex- Ex- Ex-
Ex- ence ence ence ample ample ample ample ample ample ample Ex-
Ex- Ex- 14 15 16 17 18 19 20 ample 1 ample 2 ample 3 (A) Base oil
(on the basis of Mass % 17 78 42 42 42 50 42 42 42 the total amount
thereof) (A1a) Base oil A .sup.1) (A1b) Base oil B .sup.2) Mass %
83 43 43 43 40 60 43 43 43 (A1c) Base oil C .sup.3) Mass % 5 5 5 5
5 5 (A2a) Base oil C .sup.4) Mass % 35 (A2b) Base oil D .sup.5)
Mass % 22 10 10 10 5 10 10 10 (A2c) Base oil E .sup.6) Mass % 10
Base oil properties mm.sup.2/s 3.8 3.8 3.8 3.8 3.8 3.8 5 3.8 3.8
3.8 Kinematic viscosity (100.degree. C.) Additives (on the basis of
the Mass % 5 5 5 5 1 5 5 5 total amount of composition) (B) VM-A
.sup.7) (B) VM-B .sup.8) Mass % 1.9 (B) VM-C .sup.9) Mass % 5 VM-F
.sup.10) Mass % 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 (C)
Imide-based FM .sup.11) Mass % 3 3 3 3 3 3 3 3 0.5 Polybutenyl
succinimide .sup.12) Mass % 3 (D)Non-sulfur-based phosphorus
(P)Mass % 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 compound
.sup.13) Thiophosphate (P)Mass % 0.03 Metallic detergent .sup.14)
(Ca) 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 Mass %
Additive package .sup.15) Mass % 8 8 8 8 8 8 8 8 8 8 Composition
properties/test mm.sup.2/s 5.7 5.7 5.7 5.7 5.7 5.7 5.7 5.7 5.7 5.7
results viscosity (100.degree. C.) Viscosity index 161 157 160 163
158 160 132 160 160 160 Anti-shudder durability h 600 600 600 600
600 600 600 40 80 100 Low temperature viscosity mPa s 16800 18900
16500 16100 15800 16900 53000 16500 16500 16100 (BF method;
-40.degree. C.) Acid number increase mgKOH/g 0.48 0.59 0.56 0.52
0.54 0.97 0.54 0.57 0.98 0.56 (ISOT165.5.degree. C., after 72
hours) Fatigue life (IP300, L50) h 80 80 150 110 80 120 120 120 120
120 .sup.1) Hydrocracked mineral oil (100.degree. C. kinematic
viscosity: 2.6 mm.sup.2/s, % C.sub.A: 0, sulfur content: <0.001
mass % viscosity index: 105) .sup.2) Hydrocracked mineral oil
(100.degree. C. kinematic viscosity: 4.2 mm.sup.2/s, % C.sub.A: 0,
sulfur content: <0.001 mass % viscosity index: 125) .sup.3)
Poly-.alpha. olefin base oil (100.degree. C. kinematic viscosity:
4.0 mm.sup.2/s, % C.sub.A: 0, sulfur content: 0 mass %, viscosity
index: 124), .sup.4) Hydrocracked mineral oil (100.degree. C.
kinematic viscosity: 6.2 mm.sup.2/s, % C.sub.A: 0, sulfur content:
0.001 mass %, viscosity index: 132) .sup.5) Solvent-refined mineral
oil (100.degree. C. kinematic viscosity: 21.9 mm.sup.2/s, %
C.sub.A: 7, sulfur content: 0.91 mass %, viscosity index: 95)
.sup.6) Solvent-refined mineral oil (100.degree. C. kinematic
viscosity: 31.3 mm.sup.2/s, % C.sub.A: 7.4, sulfur content: 1.11
mass %, viscosity index: 94) .sup.7) Non-dispersion type
polymethacrylate-based additive (Mw: 22,900) derived from a polymer
of a mixture of methyl MA, nC12MA, nC13MA, nC14MA, nC15MA, nC16MA,
nC18MA, and 2-decyl-tetradecyl MA, as main components (MA indicates
methacrylate, Mw indicates weight-average molecular weight,
hereinafter the same) .sup.8) Non-dispersion type
polymethacrylate-based additive (Mw: 50,500) derived from a polymer
of a mixture of methyl MA, nC12MA, nC13MA, nC14MA, nC15MA, nC16MA,
nC18MA, and 2-decyl-tetradecyl MA, as main components .sup.9)
Non-dispersion type polymethacrylate-based additive (Mw: 20,500)
derived from a polymer of a mixture of methyl MA, nC12MA, nC13MA,
nC14MA, and nC15MA, as main components .sup.10) Non-dispersion type
polymethacrylate-based additive (Mw: 217,000) derived from a
polymer of a mixture of nC12MA, nC13MA, nC14MA, nC15MA, nC16MA, and
nC18MA, as main components .sup.11) diethylenetriamine
bis(isooctadecyl)succinimide .sup.12) polybutenyl succinimide
(number-average molecular weight of polybutenyl group: 1000)
.sup.13) alkyl phosphite .sup.14) calcium sulfonate (base number
(perchloric acid method): 300 mgKOH/g) .sup.15) containing
dispersant, friction modifier, seal swelling agent, and
anti-oxidant
[0205] As indicated in Table 1, it is appreciated that the
transmission lubricating oil compositions containing Component (B1)
and fulfilling Requirement [I] according to the present invention
(Examples 1 to 7) are excellent in fatigue life though low in
viscosity. In particular, the compositions containing a
polymethacrylate having a weight-average molecular weight of 15000
to 60000, as Component (B1) are more excellent in fatigue life
(from comparison between Examples 1 and 6, and Examples 4 and 7).
It is also appreciated that the use of Component (A2b) in
combination as Component (A2) results in an improvement in fatigue
life (from comparison Example 4 and Examples 1 to 3 and 5, and
comparison between Example 7 and 6).
[0206] On the other hand, the compositions containing a
polymethacrylate-based additive containing substantially no
methacrylate of 16 or more carbon atoms as a structural unit
instead of Component (B1) and containing no Component (A2)
(Comparative Examples 1 to 3) were all poor in fatigue life (from
comparison with Examples 1 and 6).
[0207] As indicated in Table 2, it is appreciated that the
transmission lubricating oil compositions containing Component
(B2), and Components (A1) and (A2) in combination and fulfilling
Requirement [II] according to the present invention (Examples 8 to
10) are excellent in fatigue life though low in viscosity. In
particular, the compositions with optimized Component (A),
containing a polymethacrylate having a weight average molecular
weight of 15000 to 60000, as Component (B) are more excellent in
fatigue life, low temperature viscosity characteristics and/or an
ability to suppressing the acid number from increasing (from
comparison between Example 8 and Examples 9 and 10).
[0208] On the other hand, the compositions containing Component
(B2) but not Component (A2) as Component (A) (Comparative Examples
4 to 6) were all poor in fatigue life. A composition containing no
Component (A1) can not be expected to improve the fuel efficiency
of the automobile because it is difficult to adjust the kinematic
viscosity at 100.degree. C. to 3 to 8 mm.sup.2/s.
[0209] As indicated in Table 3, it is appreciated that the
compositions containing Component (B3) and fulfilling Requirement
[III] wherein the ratio of the kinematic viscosity at 100.degree.
C. of (A) a lubricating base oil (Vb) to the kinematic viscosity at
100.degree. C. of the transmission lubricating oil composition
(Vc), i.e., VbNc is 0.70 or greater (Examples 11 to 13) were
excellent in fatigue life and extreme pressure properties though
low in viscosity. In particular, it is appreciated that the
composition containing Component (A2b) as Component (A) (Example
13) is further improved in fatigue life while the composition
containing Components (B3) and (B4) in combination but not
Component (A2b) (Example 12) is excellent in both fatigue life and
low temperature viscosity characteristics.
[0210] On the other hand, it is appreciated that the composition
containing no Component (B3) (Comparative Example 7) and the
compositions each having a Vb/Vc of less than 0.70 (Comparative
Examples 8 and 9) are all poor in any of the advantageous effects
achieved by the present invention.
[0211] As indicated in Table 4, it is appreciated that the
compositions containing Components (A) to (D) and in particular a
polymethacrylate-based additive having a weight-average molecular
weight of 15000 to 60000 (Examples 14 to 20) are excellent in
fatigue life, anti-shudder durability, and oxidation stability.
[0212] It will be appreciated by those skilled in the art that
changes could be made to the embodiments described above without
departing from the broad inventive concept thereof. It is
understood, therefore, that this invention is not limited to the
particular embodiments disclosed, but it is intended to cover
modifications within the spirit and scope of the present invention
as defined by the appended claims.
* * * * *