U.S. patent application number 14/375507 was filed with the patent office on 2014-12-25 for lubricating oil composition.
This patent application is currently assigned to JX NIPPON OIL & ENERGY CORPORATION. The applicant listed for this patent is JX NIPPON OIL & ENERGY CORPORATION. Invention is credited to Shigeki Matsui, Akira Yaguchi.
Application Number | 20140378355 14/375507 |
Document ID | / |
Family ID | 49005306 |
Filed Date | 2014-12-25 |
United States Patent
Application |
20140378355 |
Kind Code |
A1 |
Matsui; Shigeki ; et
al. |
December 25, 2014 |
LUBRICATING OIL COMPOSITION
Abstract
The present invention provides a lubricating oil composition
that is a lubricating oil composition with a 150.degree. C. HTHS
viscosity of less than 2.6 mPas and can be reduced sufficiently in
the 40.degree. C. kinematic viscosity, 100.degree. C. kinematic
viscosity and 100.degree. C. HTHS viscosity and suppress the
increase of the friction coefficient in a boundary lubrication
region and has excellent fuel saving properties. The lubricating
oil composition comprises a lubricating base oil with a 100.degree.
C. kinematic viscosity of 1 to 5 mm.sup.2/s; (A) a viscosity index
improver with a weight average molecular weight of 400,000 or less
and a PSSI of 20 or less; (B) an overbasic metallic detergent with
a metal ratio of 3.4 or less; and (C) a friction modifier, and
having a 150.degree. C. HTHS viscosity of lower than 2.6 mPas.
Inventors: |
Matsui; Shigeki; (Tokyo,
JP) ; Yaguchi; Akira; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
JX NIPPON OIL & ENERGY CORPORATION |
Tokyo |
|
JP |
|
|
Assignee: |
JX NIPPON OIL & ENERGY
CORPORATION
Tokyo
JP
|
Family ID: |
49005306 |
Appl. No.: |
14/375507 |
Filed: |
November 9, 2012 |
PCT Filed: |
November 9, 2012 |
PCT NO: |
PCT/JP2012/079079 |
371 Date: |
July 30, 2014 |
Current U.S.
Class: |
508/186 |
Current CPC
Class: |
C10M 101/00 20130101;
C10M 2219/068 20130101; C10M 129/54 20130101; C10N 2040/25
20130101; C10N 2030/43 20200501; C10N 2020/02 20130101; C10N
2010/04 20130101; C10N 2010/12 20130101; C10N 2040/252 20200501;
C10N 2030/68 20200501; C10M 171/00 20130101; C10N 2040/04 20130101;
C10M 135/18 20130101; C10M 141/08 20130101; C10M 2203/003 20130101;
C10M 2209/084 20130101; C10M 145/14 20130101; C10M 2215/28
20130101; C10N 2030/06 20130101; C10M 171/02 20130101; C10M
2223/045 20130101; C10M 2207/262 20130101; C10M 2203/1025 20130101;
C10N 2040/255 20200501; C10M 2207/262 20130101; C10N 2010/04
20130101; C10N 2060/14 20130101; C10M 2207/262 20130101; C10N
2010/04 20130101; C10N 2060/14 20130101 |
Class at
Publication: |
508/186 |
International
Class: |
C10M 141/08 20060101
C10M141/08 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 21, 2012 |
JP |
2012-034995 |
Claims
1. A lubricating oil composition comprising: a lubricating base oil
with a 100.degree. C. kinematic viscosity of 1 to 5 mm.sup.2/s; (A)
a viscosity index improver with a weight average molecular weight
of 400,000 or less and a PSSI of 20 or less; (B) an overbasic
metallic detergent with a metal ratio of 3.4 or less; and (C) a
friction modifier, and having a 150.degree. C. HTHS viscosity of
lower than 2.6 mPas.
2. The lubricating oil composition according to claim 1, wherein
the viscosity index improver is a viscosity index improver with a
ratio of the weight-average molecular weight and PSSI (Mw/PSSI) of
1.times.10.sup.4 or greater.
3. The lubricating oil composition according to claim 1, wherein
the overbasic metallic detergent is an overbasic alkaline earth
metal salicylate produced by overbasing an alkaline earth metal
salicylate with an alkaline earth metal borate.
4. The lubricating oil composition according to claim 1, wherein
the friction modifier is preferably an organic molybdenum friction
modifier.
5. The lubricating oil composition according to claim 2, wherein
the overbasic metallic detergent is an overbasic alkaline earth
metal salicylate produced by overbasing an alkaline earth metal
salicylate with an alkaline earth metal borate.
6. The lubricating oil composition according to claim 2, wherein
the friction modifier is preferably an organic molybdenum friction
modifier.
7. The lubricating oil composition according to claim 3, wherein
the friction modifier is preferably an organic molybdenum friction
modifier.
Description
TECHNICAL FIELD
[0001] The present invention relates to lubricating oil
compositions.
BACKGROUND ART
[0002] Conventionally, lubricating oil has been used in an internal
combustion engine, a transmission or other mechanical devices to
facilitate the smooth operation thereof. In particular, a
lubricating oil (engine oil) for an internal combustion engine is
required to have a high level of performances because the internal
combustion engine has been improved in performance, enhanced in
output and used under severe working conditions. Therefore,
conventional engine oils have been blended with various additives
such as antiwear agents, metallic detergents, ashless dispersants,
and anti-oxidants to meet such requisite performances (for example,
see Patent Literatures 1 to 3 below). Furthermore, recently the
fuel saving performance of the lubricating oil has been required to
be increasingly better and better, and thus applications of a high
viscosity index base oil or various friction modifiers have been
studied (for example, see Patent Literature 4 below).
CITATION LIST
Patent Literature
[0003] Patent Literature 1: Japanese Patent Application Publication
No. 2001-279287 [0004] Patent Literature 2: Japanese Patent
Application Publication No. 2002-129182 [0005] Patent Literature 3:
Japanese Patent Application Laid-Open Publication No. 08-302378
[0006] Patent Literature 4: Japanese Patent Application Laid-Open
Publication No. 06-306384
SUMMARY OF INVENTION
Technical Problem
[0007] However, the conventional lubricating oils cannot be
necessarily deemed sufficient in terms of fuel saving
properties.
[0008] As general fuel saving techniques, it is known to reduce the
kinematic viscosity of lubricating oil and enhance the viscosity
index thereof (multi-grading that is a combination of a low
viscosity base oil and a viscosity index improver) and also to
blend a friction reducing agent. For the viscosity reduction, a
reduction in the viscosity of a lubricating oil or the base oil
thereof degrades the lubricating properties under sever lubricating
conditions (high temperature and high shear conditions), and thus
has been concerned to cause defects such as wear, seizure, or
fatigue breaking. With regard to the blending of a friction
reducing agent, it is known to add an ashless or molybdenum
friction modifier. However, a fuel saving oil has still been
sought, which is further superior to the conventional friction
reducing agent-blended oil.
[0009] In order to prevent these defects caused by reducing the
viscosity of a lubricating oil or the base oil thereof to maintain
the durability of an engine and further to impart fuel saving
properties to the oil, it is advantageously effective to maintain
the 150.degree. C. HTHS viscosity ("HTHS viscosity" is also
referred to as "high temperature high shear viscosity") higher and
maintain the 40.degree. C. kinematic viscosity, 100.degree. C.
kinematic viscosity and 100.degree. C. HTHS viscosity lower.
However, it has been difficult to satisfy all of these requirements
with the conventional lubricating oils.
[0010] However, due to recent development of engine technologies,
it has become possible for a lubricating oil to be reduced in the
150.degree. C. HTHS viscosity but still to retain the durability of
an engine. To further improve the fuel saving properties, an engine
oil having a 150.degree. C. HTHS viscosity of below 2.6 mPas which
is the lower limit 150.degree. C. HTHS viscosity, for example of an
SAE OW-20 engine oil has been developed and applied. However, the
engine oil having a 150.degree. C. HTHS viscosity of below 2.6 mPas
has been confirmed to increase the friction coefficient of a
boundary lubrication region where metal parts in some engines or
components contact each other and thus to adversely affect the fuel
saving properties.
[0011] A technology to reduce the friction coefficient in the
boundary lubrication region more than before is needed so as to
enhance the fuel saving properties of all of the engines to which
an engine oil having a 150.degree. C. HTHS viscosity of below 2.6
mPas is applied.
[0012] The present invention has been made in view of such
situations and has an object to provide a lubricating oil
composition that is an engine oil having a 150.degree. C. HTHS
viscosity of lower than 2.6 mPas, can be reduced sufficiently in
the 40.degree. C. kinematic viscosity, 100.degree. C. kinematic
viscosity and 100.degree. C. HTHS viscosity and suppress the
increase of the friction coefficient in a boundary lubrication
region and has excellent fuel saving properties for an engine
having a tough boundary lubrication region.
Solution to Problem
[0013] In order to achieve the above object, the present invention
provides a lubricating oil composition comprising a lubricating
base oil with a 100.degree. C. kinematic viscosity of 1 to 5
mm.sup.2/s, (A) a viscosity index improver with a weight average
molecular weight of 400,000 or less and a PSSI of 20 or less, (B)
an overbasic metallic detergent with a metal ratio of 3.4 or less
and (C) a friction modifier, and having a 150.degree. C. HTHS
viscosity of lower than 2.6 mPas.
[0014] The above (A) viscosity index improver is preferably a
viscosity index improver with a ratio of the weight-average
molecular weight and PSSI (Mw/PSSI) of 1.times.10.sup.4 or
greater.
[0015] The above (B) overbasic metallic detergent is preferably an
overbasic alkaline earth metal salicylate produced by oberbasing an
alkaline earth metal salicylate with an alkaline earth metal
borate.
[0016] The above (C) friction modifier is preferably an organic
molybdenum friction modifier.
[0017] The term "PSSI" used herein denotes the permanent shear
stability index of a polymer calculated on the basis of the data
measured with ASTM D 6278-02 (Test Method for Shear Stability of
Polymer Containing Fluids Using a European Diesel Injector
Apparatus) in conformity with ASTM D 6022-01 (Standard Practice for
Calculation of Permanent Shear Stability Index).
Advantageous Effect of Invention
[0018] The present invention can provide a lubricating oil
composition that is an engine oil having a 150.degree. C. HTHS
viscosity of lower than 2.6 mPas, can reduce sufficiently the
40.degree. C. kinematic viscosity, 100.degree. C. kinematic
viscosity and 100.degree. C. HTHS viscosity and suppress the
friction coefficient in a boundary lubrication region from
increasing and has excellent fuel saving properties.
[0019] The lubricating oil composition of the present invention is
suitably used in gasoline engines, diesel engines and gas engines
for two- and four-wheeled vehicles, power generators and
cogenerations and further not only those using fuel with a sulfur
content of 50 ppm by mass or less but also various engines of ships
and outboard motors.
DESCRIPTION OF EMBODIMENTS
[0020] Hereinafter, suitable embodiments of the present invention
will be described.
[0021] The lubricating oil composition according Lo the present
invention comprises a lubricating base oil with a 100.degree. C.
kinematic viscosity of 1 to 5 mm.sup.2/s, (A) a viscosity index
improver with a weight average molecular weight of 400,000 or less
and a PSSI of 20 or less, (B) an overbasic metallic detergent with
a metal ratio of 3.4 or less and (C) a friction modifier.
[0022] The lubricating oil composition of the present invention
contains a lubricating base oil having a 100.degree. C. kinematic
viscosity of 1 to 5 mm.sup.2/s (hereinafter referred to as "the
lubricating base oil of the present invention").
[0023] Examples of the lubricating base oil of the present
invention include those having a 100.degree. C. kinematic viscosity
of 1 to 5 mm.sup.2/s selected from: paraffinic mineral base oils
which can be produced by subjecting a lubricating oil fraction
produced by atmospheric- and/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, hydroisomerizing, solvent dewaxing, catalytic
dewaxing, hydrorefining, sulfuric acid treatment, and clay
treatment; n-paraffinic base oils; and iso-paraffinic base
oils.
[0024] Examples of preferred lubricating base oils include base
oils produced using the following base oils (1) to (8) as a
feedstock by refining the feedstock and/or a lubricating oil
fraction recovered therefrom in a given refining process and
recovering a lubricating oil fraction:
[0025] (1) a distillate oil produced by atmospheric distillation of
a paraffin-base crude oil and/or a mixed-base crude oil;
[0026] (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;
[0027] (3) a wax produced by dewaxing of lubricating oil (slack
wax) and/or a synthetic wax produced through a gas to liquid (GTL)
process (Fischer-Tropsch wax, GTL wax);
[0028] (4) a mixed oil of one or more types selected from base oils
(1) to (3) and/or an oil produced by mild-hydrocracking the mixed
oil;
[0029] (5) a mixed oil of two or more types selected from base oils
(1) to (4) above;
[0030] (6) a deasphalted oil (DAO) produced by deasphalting base
oil (1), (2) (3), (4) or (5);
[0031] (7) an oil produced by mild-hydrocracking (MHC) base oil
(6); and
[0032] (8) a mixed oil of two or more types selected from base oils
(1) to (7) above.
[0033] The above-mentioned given refining process is preferably
hydro-refining such as hydrocracking or hydrofinishing, solvent
refining such as furfural extraction, dewaxing such as solvent
dewaxing and catalytic dewaxing, clay refining with acidic clay or
active clay or 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 combination and order.
[0034] The lubricating base oil used in the present invention is
particularly preferably the following base oil (9) or (10) produced
by subjecting a base oil selected from the above-described base
oils (1) to (8) or a lubricating oil fraction recovered therefrom
to a specific treatment:
[0035] (9) a hydrocracked base oil produced by hydrocracking a base
oil selected from base oils (1) to (8) or a lubricating oil
fraction recovered from the base oil, and subjecting the resulting
product or a lubricating oil fraction recovered therefrom by
distillation, to a dewaxing treatment such as solvent or catalytic
dewaxing, optionally followed by distillation; or
[0036] (10) a hydroisomerized base oil produced by hydroisomerizing
a base oil selected from base oils (1) to (8) or a lubricating oil
fraction recovered from the base oil, and subjecting the resulting
product or a lubricating oil fraction recovered therefrom by
distillation, to a dewaxing treatment such as solvent or catalytic
dewaxing, optionally followed by distillation.
[0037] If necessary, a solvent refining process and/or a
hydrofinishing process may be carried out at appropriate timing
upon production of lubricating base oil (9) or (10).
[0038] No particular limitation is imposed on the catalyst used in
the above-described hydrocracking and hydroisomerizing. However,
the catalyst is preferably a hydrocracking catalyst comprising any
one of complex oxides having cracking activity (for example,
silica-alumina, alumina boria, or silica zirconia) or one or more
types of such complex oxides bound with a binder, used as a support
and a metal with hydrogenation capability (for example, one or more
types of metals of Groups VIa and VIII of the periodic table)
supported on the support, or a hydroisomerizing catalyst comprising
a support containing zeolite (for example, ZSM-5, zeolite beta, or
SAPO-11) and a metal with hydrogenation capability, containing at
least one or more types of metals of Group VIII of the periodic
table and supported on the support. The hydrocracking and
hydroisomerizing catalysts may be laminated or mixed so as to be
used in combination.
[0039] No particular limitation is imposed on the conditions under
which the hydrocracking and hydroisomerizing are carried out.
Preferably, the hydrogen partial pressure is from 0.1 to 20 MPa,
the average reaction temperature is from 150 to 450.degree. C., the
LHSV is from 0.1 to 3.0 hr.sup.-1, and the hydrogen/oil ratio is
from 50 to 20000 scf/b.
[0040] The 100.degree. C. kinematic viscosity of the lubricating
base oil of the present invention is necessarily 5 mm.sup.2/s or
lower, preferably 4.5 mm.sup.2/s or lower, more preferably 4
mm.sup.2/s or lower, more preferably 3.8 mm.sup.2/s or lower,
particularly preferably 3.7 mm.sup.2/s or lower, most preferably
3.6 mm.sup.2/s or lower. Whilst, the 100.degree. C. kinematic
viscosity is necessarily 1 mm.sup.2/s or higher, preferably 1.5
mm.sup.2/s or higher, more preferably 2 mm.sup.2/s or higher, more
preferably 2.5 mm.sup.2/s or higher, particularly preferably 3
mm.sup.2/s. The 100.degree. C. kinematic viscosity used herein
refers to the 100.degree. C. kinematic viscosity determined in
accordance with ASTM D-445. If the 100.degree. C. kinematic
viscosity of the lubricating base oil exceeds 5 mm.sup.2/s, the
resulting composition would be degraded in low temperature
viscosity characteristics and may not obtain sufficiently improved
fuel saving properties. If the 100.degree. C. kinematic viscosity
is lower than 1 mm.sup.2/s, the resulting lubricating oil
composition would be poor in lubricity due to its insufficient oil
film formation at lubricating sites and would be large in
evaporation loss of the composition.
[0041] The 40.degree. C. kinematic viscosity of the lubricating
base oil of the present invention is preferably 40 mm.sup.2/s or
lower, more preferably 30 mm.sup.2/s or lower, more preferably 25
mm.sup.2/s or lower, particularly preferably 20 mm.sup.2/s or
lower, most preferably 17 mm.sup.2/s or Lower. Whilst, the
40.degree. C. kinematic viscosity is preferably 6.0 mm.sup.2/s or
higher, more preferably 8.0 mm.sup.2/s or higher, more preferably
10 mm.sup.2/s higher, particularly preferably 12 mm.sup.2/s or
higher, most preferably 14 mm.sup.2/s or higher. If the 40.degree.
C. kinematic viscosity of the lubricating base oil exceeds 40
mm.sup.2/s, the resulting composition would be degraded in low
temperature viscosity characteristics and may not obtain
sufficiently improved fuel saving properties. If the 40.degree. C.
kinematic viscosity is lower than 6.0 mm.sup.2/s, the resulting
lubricating oil composition would be poor in lubricity due to its
insufficient oil film formation at lubricating sites and would be
large in evaporation loss of the composition.
[0042] The viscosity index of the lubricating base oil of the
present invention is preferably 100 or greater, more preferably 105
or greater, more preferably 110 or greater, particularly preferably
115 or greater, most preferably 120 or greater. Whilst, the
viscosity index is 180 or less, more preferably 170 or less, more
preferably 160 or less. A viscosity index of less than 100 would
not only cause the viscosity-temperature characteristics,
thermal/oxidation stability, anti-evaporation properties to degrade
but also cause the friction coefficient to increase and likely
cause the friction coefficient to increase and cause the anti-wear
properties to degrade. A viscosity index of greater than 180 would
tend to degrade the low temperature fluidity.
[0043] The viscosity index referred herein denotes the viscosity
index measured in accordance with JIS K 2283-1993.
[0044] The lubricating base oil used in the lubricating oil
composition of the present invention is preferably a mixture of a
first lubricating base oil component having a 100.degree. C.
kinematic viscosity of 3.5 mm.sup.2/s or higher and a second
Lubricating base oil component having a 100.degree. C. kinematic
viscosity of lower than 3.5 mm.sup.2/s. Mixing of the first
lubricating base oil component and second lubricating base oil
component would provide the resulting lubricating oil composition
with excellent viscosity temperature characteristics and thus
further improve the fuel saving properties thereof.
[0045] The 15.degree. C. density (.rho.15) of the first lubricating
base oil component used in the lubricating oil composition of the
present invention is preferably 0.860 g/cm.sup.3 or lower, more
preferably 0.850 g/cm.sup.3 or lower, more preferably 0.840
g/cm.sup.3 or lower, particularly preferably 0.822 g/cm.sup.3 or
lower.
[0046] The 15.degree. C. density referred in the present invention
denotes the density measured at 15.degree. C. in accordance with
JIS K 2249-1995.
[0047] The pour point of the first lubricating base oil component
used in the lubricating oil composition of the present invention is
preferably -10.degree. C. or lower, more preferably -12.5.degree.
C. or lower, more preferably -15.degree. C. or lower, particularly
preferably -20.degree. C. or lower. If the pour point is higher
than -10.degree. C., the whole lubricating oil containing such a
lubricating base oil would tend to be degraded in low temperature
fluidity. The pour point referred in the present invention is the
pour point measured in accordance with JIS K 2269-1987.
[0048] The 100.degree. C. kinematic viscosity of the first
lubricating base oil component used in the lubricating oil
composition of the present invention is preferably 5 mm.sup.2/s or
lower, more preferably 4.5 mm.sup.z/s or lower, more preferably 4.0
mm.sup.2/s or lower, particularly preferably 3.9 mm.sup.2/s or
lower. Whilst, the 100.degree. C. kinematic viscosity is preferably
3.5 mm.sup.2/s or higher, more preferably 3.6 mm.sup.2/s or higher,
more preferably 3.7 mm.sup.2/s or higher, particularly preferably
3.8 mm.sup.2/s or higher. If the 100.degree. C. kinematic viscosity
exceeds 5 mm.sup.2/s, the resulting composition would be degraded
in low temperature viscosity characteristics and may not obtain
sufficiently improved fuel saving properties. If the 100.degree. C.
kinematic viscosity is lower than 3.5 mm.sup.2/s, the resulting
lubricating oil composition would be poor in lubricity due to its
insufficient oil film formation at lubricating sites and would be
large in evaporation loss of the composition.
[0049] The 40.degree. C. kinematic viscosity of the first
lubricating base oil component used in the lubricating oil
composition of the present invention is preferably 40 mm.sup.2/s or
lower, more preferably 30 mm.sup.2/s or lower, more preferably 25
mm.sup.2/s or lower, particularly preferably 20 mm.sup.2/s or
lower, most preferably 17 mm.sup.2/s or lower. Whilst, the
40.degree. C. kinematic viscosity is preferably 6.0 mm.sup.2/s or
higher, more preferably 8.0 mm.sup.2/s or higher, more preferably
10 mm.sup.2/s or higher, particularly preferably 12 mm.sup.2/s or
higher, most preferably 14 mm.sup.2/s or higher. If the 40.degree.
C. kinematic viscosity exceeds 40 mm.sup.2/s, the resulting
composition would be degraded in low temperature viscosity
characteristics and may not obtain sufficiently improved fuel
saving properties. If the 40.degree. C. kinematic viscosity is
lower than 6.0 mm.sup.2/s, the resulting lubricating oil
composition would be poor in lubricity due to its insufficient oil
film formation at lubricating sites and would be large in
evaporation loss of the composition.
[0050] The viscosity index of the first lubricating base oil
component used in the lubricating oil composition of the present
invention is preferably 100 or greater, more preferably 110 or
greater, more preferably 120 or greater, particularly preferably
130 or greater, most preferably 140 or greater. A viscosity index
of less than 100 would not only cause the viscosity-temperature
characteristics, thermal/oxidation stability, anti-evaporation
properties to degrade but also likely cause the friction
coefficient to increase and cause the anti-wear properties to
degrade.
[0051] The 15.degree. C. density (.rho.15) of the second
lubricating base oil component used in the lubricating oil
composition of the present invention is preferably 0.860 g/cm.sup.3
or lower, more preferably 0.850 g/cm.sup.3 or lower, more
preferably 0.840 g/cm.sup.3 or lower, particularly preferably 0.835
g/cm.sup.3 or lower.
[0052] The pour point of the second lubricating base oil component
used in the lubricating oil composition of the present invention is
preferably -10.degree. C. or lower, more preferably -12.5.degree.
C. or lower, more preferably -15.degree. C. or lower, particularly
preferably -20.degree. C. or lower. If the pour point is higher
than -10.degree. C., the whole lubricating oil containing such a
lubricating base oil would tend to be degraded in low temperature
fluidity. The pour point referred in the present invention is the
pour point measured in accordance with JIS K 2269-1987.
[0053] The 100.degree. C. kinematic viscosity of the second
lubricating base oil component used in the lubricating oil
composition of the present invention is preferably lower than 3.5
mm.sup.2/s, more preferably 3.4 mm.sup.2/s or lower, more
preferably 3.3 mm.sup.2/s or lower. Whilst, the 100.degree. C.
kinematic viscosity is preferably 1 mm.sup.2/s or higher, more
preferably 2 mm.sup.2/s or higher, more preferably 2.5 mm.sup.2/s
or higher, particularly preferably 3.0 mm.sup.2/s or higher. If the
100.degree. C. kinematic viscosity is lower than 1 mm.sup.2/s, the
resulting lubricating oil composition would be poor in lubricity
due to its insufficient oil film formation at lubricating sites and
would be large in evaporation loss of the composition.
[0054] The 40.degree. C. kinematic viscosity of the second
lubricating base oil component used in the lubricating oil
composition of the present invention is preferably 20 mm.sup.2/s or
lower, more preferably 18 mm.sup.2/s or lower, more preferably 16
mm.sup.2/s or lower, particularly preferably 14 mm.sup.2/s or
lower. Whilst, the 40.degree. C. kinematic viscosity is preferably
6.0 mm.sup.2/s or higher, more preferably 8.0 mm.sup.2/s or higher,
more preferably 10 mm.sup.2/s or higher, particularly preferably 12
mm.sup.2/s or higher, most preferably 13 mm.sup.2/s or higher. If
the 40.degree. C. kinematic viscosity exceeds 20 mm.sup.2/s, the
resulting composition would be degraded in low temperature
viscosity characteristics and may not obtain sufficiently improved
fuel saving properties. If the 40.degree. C. viscosity is lower
than 6.0 mm.sup.2/s, the resulting lubricating oil composition
would be poor in lubricity due to its insufficient oil film
formation at lubricating sites and would be large in evaporation
loss of the composition.
[0055] The viscosity index of the second lubricating base oil
component used in the lubricating oil composition of the present
invention is preferably 100 or greater, more preferably 105 or
greater, more preferably 110 or greater. A viscosity index of less
than 100 would not only cause the viscosity-temperature
characteristics, thermal/oxidation stability, anti-evaporation
properties to degrade but also likely cause the friction
coefficient to increase and cause the anti-wear properties to
degrade.
[0056] The sulfur content of the lubricating base oil used in the
present invention depends on the sulfur content of the raw material
thereof. For example, when a raw material containing substantially
no sulfur such as a synthetic wax component produced by
Fischer-Tropsch reaction is used, a lubricating base oil containing
substantially no sulfur can be produced. Alternatively, when a raw
material containing sulfur such as slack wax produced through a
refining process of a lubricating base oil or micro wax produced
through wax refining is used, the sulfur content of the resulting
lubricating base oil is usually 100 mass ppm or more. The sulfur
content of the lubricating base oil used in the present invention
is preferably 100 mass ppm or less, more preferably 50 mass ppm or
less, more preferably 10 mass ppm or less, particularly preferably
5 mass ppm or less with the objective of further improving
thermal/oxidation stability and lowering the sulfur content.
[0057] The nitrogen content of the lubricating base oil used in the
present invention is preferably 7 mass ppm or less, more preferably
5 mass ppm or less, more preferably 3 mass ppm or less. If the
nitrogen content exceeds 7 mass ppm, the resulting composition
would tend to be degraded in thermal/oxidation stability. The
nitrogen content referred in the present invention denotes the
nitrogen content measured in accordance with JIS K 2609-1990.
[0058] The % C.sub.P of the lubricating base oil used in the
present invention is preferably 70 or greater, more preferably from
80 to 99, more preferably from 85 to 95, particularly preferably
from 87 to 94, most preferably from 90 to 94. If the % C.sub.P of
the lubricating base oil is less than 70, the resulting composition
would tend to be degraded in viscosity-temperature characteristics,
thermal/oxidation stability and friction characteristics and when
blended with additives, would tend to degrade the efficacy thereof.
If the % CP of the lubricating base oil exceeds 99, the solubility
of additives would tend to be degraded.
[0059] The % C.sub.A of the lubricating base oil used in the
present invention is preferably 2 or less, more preferably 1 or
less, more preferably 0.8 or less, particularly preferably 0.5 or
less. If the % CA of the lubricating base oil exceeds 2, the
resulting composition would tend to be degraded in
viscosity-temperature characteristics, thermal/oxidation stability
and fuel saving properties.
[0060] The % C.sub.N of the lubricating base oil used in the
present invention is preferably 30 or less, more preferably from 4
to 25, more preferably from 5 to 13, particularly preferably from 5
to 8. If the % C.sub.N of the lubricating base oil exceeds 30, the
resulting composition would tend to be degraded in
viscosity-temperature characteristics, thermal/oxidation stability
and friction characteristics. If the % C.sub.N is less than 4, the
solubility of additives would Lend to degrade.
[0061] The % C.sub.P, % C.sub.N, and % C.sub.A referred in the
present invention denote the percentage of paraffin carbon number
in the total carbon number, the percentage of naphthene carbon
number in the total carbon number, and the percentages of the
aromatic carbon number in the total carbon number, respectively,
determined by a method (n-d-M ring analysis) in accordance with
ASTM D 3238-85. Specifically, the above-described preferred ranges
of the % C.sub.P, % C.sub.N and % C.sub.A are based on the values
determined by the above-described method, and for example, even if
a lubricating base oil does not contain naphthene, the % C.sub.N
may represent the value of exceeding 0.
[0062] The saturate content of the lubricating base oil used in the
present invention is preferably 90 percent by mass or more,
preferably 95 percent by mass or more, more preferably 99 percent
by mass or more on the basis of the total mass of the lubricating
base oil. The ratio of the cyclic saturate content of the saturate
content is preferably 40 percent by mass or less, preferably 35
percent by mass or less, preferably 30 percent by mass or less,
more preferably 25 percent by mass or less, more preferably 21
percent by mass or less. The ratio of the cyclic saturate content
of the saturate content is preferably 5 percent by mass or more,
more preferably 10 percent by mass or more. The saturate content
and ratio of cyclic saturate content therein of a lubricating base
oil satisfying the above-described conditions can provide a
lubricating oil composition that can be enhanced in
viscosity-temperature characteristics and thermal/oxidation
stability and when the lubricating base oil is blended with
additives, can retain the additives in the lubricating base oil
sufficiently stably dissolved, allowing the additives Lo exhibit
their functions in a higher level. Furthermore, according to the
present invention, the lubricating base oil itself can be improved
in friction characteristics and as the result improved in friction
reducing effect and moreover achieve the improvement in energy
saving properties.
[0063] The saturate content referred in the present invention is
measured in accordance with the method described in the aforesaid
ASTM D 2007-93.
[0064] Upon separation of the saturate or analysis of the cyclic
saturate and non-cyclic saturate, similar methods that can provide
similar results can be used. Examples of such methods include the
methods described in ASTM D 2425-93 and ASTM D 2549-91, a method
using high-performance liquid chromatography (HPLC) and methods
obtained by improving these methods.
[0065] The aromatic content of the lubricating base oil of the
present invention is preferably 5 percent by mass or less, more
preferably 4 percent by mass or less, more preferably 3 percent by
mass or less, particularly preferably 2 percent by mass or less and
preferably 0.1 percent by mass or more, more preferably 0.5 percent
by mass or more, more preferably 1 percent by mass or more,
particularly preferably 1.5 percent by mass or more. If the
aromatic content exceeds 5 percent by mass, the resulting
composition would tend to be degraded in viscosity-temperature
characteristics, thermal/oxidation stability and friction
characteristics, and furthermore in anti-volatile properties and
low temperature viscosity characteristics and when blended with
additives, would tend to reduce the efficacy thereof. The
lubricating base oil of the present invention may not contain
aromatics. Adjusting the aromatic content to 0.1 percent by mass or
more can further enhance the solubility of additives.
[0066] The aromatic content referred herein denotes the value
measured in accordance with ASTM D 2007-93. The aromatics includes
alkylbenzenes; alkylnaphthalens; anthracene, phenanthrene, and
alkylated products thereof; compounds wherein four or more benzene
rings are condensated to each other; and compounds having hetero
atoms such as pyridines, quinolines, phenols, and naphthols.
[0067] The lubricating base oil of the present invention may be a
synthetic base oil. Examples of the synthetic base oil include
those having a 100.degree. C. kinematic viscosity of 1 to 5
mm.sup.2/s such as poly-.alpha.-olefins and hydrogenated compounds
thereof; isobutene oligomers and hydrogenated compounds thereof;
isoparaffins; alkylbenzenes; alkylnaphthalenes; diestors such as
ditridecyl glutarate, di-2-ethylhexyl adipate, diisodecyl adipate,
ditridecyl adipate and di-2-ethylhexyl sebacate; polyol esters such
as trimethylolpropane caprylate, trimethylolpropane pelargonate,
pentaerythritol 2-ethylhexanoate and pentaerythritol pelargonate;
polyoxyalkylene glycols; dialkyldiphenyl ethers; and polyphenyl
ethers. 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,
preferably 6 to 16 carbon atoms, such as 1-octene oligomer, decene
oligomer, ethylene-propylene cooligomer, and hydrogenated compounds
thereof.
[0068] No particular limitation is imposed 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, or a complex of boron trifluoride
with water, an alcohol such as ethanol, propanol and butanol, a
carboxylic acid or an ester.
[0069] The above lubricating base oils of the present invention may
be used alone or in combination with one or more type of other base
oil. When the base oil of the present invention is used in
combination with the other base oils, the proportion of the base
oil of the present invention in the mixed base oil is preferably 30
percent by mass or more, more preferably 50 percent by mass or
more, more preferably 70 percent by mass or more.
[0070] No particular limitation is imposed on the other base oils
used in combination with the base oil of the present invention.
Examples of the mineral base oil include solvent-refined mineral
oils, hydrocracked mineral oils, hydrorefined mineral oils, and
solvent-dewaxed base oils, all of which have a 100.degree. C.
kinematic viscosity of higher than 5 mm.sup.2/s and 100 mm.sup.2/s
or lower.
[0071] Examples of the synthetic base oil include the
above-described synthetic base oils which, however, have a
100.degree. C. kinematic viscosity outside the range of 1 to 5
mm.sup.2/s.
[0072] The lubricating oil composition of the present invention
comprises (A) a viscosity index improver with a weight average
molecular weight of 400,000 or less and a PSSI of 20 or less.
Whereby, the lubricating oil composition of the present invention
can be enhanced in fuel saving properties compared with a
composition not containing such a viscosity index improver. The
viscosity index improver may take any format if it satisfies the
conditions where the Mw is 400,000 or less and the PSSI is 20 or
less. Specific examples of the compound include non-dispersant type
or dispersant type ester group-containing viscosity index
improvers, non-dispersant type or dispersant type
poly(meth)acrylate viscosity index improvers, styrene-diene
hydrogenated copolymers, non-dispersant type or dispersant type
ethylene-.alpha.-olefin copolymers or hydrogenated compounds
thereof, polyisobutylene and hydrogenated compounds thereof,
styrene-maleic anhydride ester copolymer, polyalkylstyrenes,
(meth)acrylate-olefin copolymers and mixtures thereof.
[0073] The poly(meth)acrylate viscosity index improver
("poly(meth)acrylate" used herein refers collectively to
polyacrylate compounds and polymethacrylate compounds) that may be
used as a viscosity index improver in the present invention is a
polymer of a polymeric monomer containing a (meth)acrylate monomer
(hereinafter referred to as "Monomer M-1") represented by formula
(1) below.
##STR00001##
[0074] In formula (1) above, R.sup.1 is hydrogen or methyl and
R.sup.2 is a straight-chain or branched hydrocarbon group having 1
to 5000 carbon atoms.
[0075] The poly(meth)acrylate compounds produced by
homopolymerizing a monomer represented by formula (1) or
copolymerizing two or more types of monomers represented by formula
(1) are so-called non-dispersant type poly(meth)acrylates. However,
the poly(meth)acrylate compound used in the present invention may
be so-called dispersant type poly(meth)acrylates produced by
copolymerizing a monomer represented by formula (1) with one or
more monomers selected from the group consisting of monomers
represented by formula (2) below and monomers represented by
formula (3) below (hereinafter referred to as "Monomer M-2" and
Monomer M-3", respectively).
##STR00002##
[0076] In formula (2) above, R.sup.3 is hydrogen or methyl, R.sup.4
is an alkylene group having 1 to 18 carbon atoms, E.sup.1 is an
amine residue or heterocyclic residue having 1 or 2 nitrogen atoms
and 0 to 2 oxygen atoms, and a is an integer of 0 or 1.
##STR00003##
[0077] In formula (3), R.sup.5 is hydrogen or methyl, and E.sup.2
is an amine residue or heterocyclic residue having 1 or 2 nitrogen
atoms and 0 to 2 oxygen atoms.
[0078] Specific examples of the amine residue or heterocyclic
residue represented by E.sup.1 and E.sup.2 include dimethylamino,
diethylamino, dipropylamino, dibutylamino, anilino, toluidino,
xylidino, acetylamino, benzoilamino, morpholino, pyrrolyl,
pyrrolino, pyridyl, methylpyridyl, pyrolidinyl, piperidinyl,
quinonyl, pyrrolidonyl, pyrrolidono, imidazolino and pyrazino
groups.
[0079] Specific preferable examples of Monomer M-2 and Monomer M-3
include dimethylaminomethylmethacrylate,
diethylaminomethylmethacrylate, dimethylaminoethylmethacrylate,
diethylaminoethylmethacrylate, 2-methyl-5-vinylpyridine,
morpholinomethylmethacrylate, morpholinoethylmethacrylate,
N-vinylpyrrolidone, and mixtures thereof.
[0080] No particular limitation is imposed on the copolymerization
molar ratio of Monomer M-1, and Monomers M-2 and M-3 in a
copolymer. However, M-1:M-2 and M-3 is preferably from 99:1 to
80:20, more preferably 98:2 to 85:15, more preferably 95:5 to
90:10.
[0081] The styrene-diene hydrogenated copolymer that may be used as
the viscosity index improver in the present invention is a compound
produced by hydrogenating a copolymer of styrene and diene.
Specific examples of the diene include butadiene and isoprene.
Particularly preferred is a hydrogenated copolymer of styrene and
isoprene.
[0082] The ethylene-.alpha.-olefin copolymer or a hydrogenated
compound thereof that may be used as the viscosity index improver
in the present invention is a copolymer of ethylene and an
.alpha.-olefin or a compound produced by hydrogenating the
copolymer.
[0083] Specific examples of the .alpha.-olefin include propylene,
isobutylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene, and
1-dodecene. The ethylene-.alpha.-olefin copolymer may be a
copolymer consisting of hydrocarbons that is of non-dispersant type
or a copolymer produced by reacting a copolymer with a polar
compound such as a nitrogen-containing compound that is a
dispersant-type ethylene-.alpha.-olefin copolymer.
[0084] The viscosity index improver used in the present invention
has a weight-average molecular weight (MW) of necessarily 400,000
or less, preferably 380,000 or less, more preferably 360,000 or
less. The viscosity index improver has a weight-average molecular
weight of preferably 10,000 or greater, more preferably 50,000 or
greater, more preferably 100,000 or greater, particularly
preferably 200,000 or greater. If the viscosity index improver has
a weight average molecular weight of less than 10,000, it would be
less effective in viscosity index enhancement when it is dissolved
in the lubricating base oil and the resulting composition would not
only be poor in fuel saving properties and low temperature
viscosity characteristics but also be high in production cost. If
the viscosity index improver has a weight-average molecular weight
of greater than 400,000, it would exert the viscosity increasing
effect too much and thus the resulting composition would not only
be poor in fuel saving properties and low temperature viscosity
characteristics but also be degraded in shear stability, solubility
in the lubricating base oil and storage stability.
[0085] The viscosity index improver used in the present invention
has a PSSI (permanent shear stability index) of necessarily 20 or
less, more preferably 17 or less, more preferably 16 or less,
particularly preferably 15 or less. If the PSSI exceeds 20, the
resulting composition would be degraded in shear stability and thus
needed to be enhanced in initial kinematic viscosity, possibly
resulting in degraded fuel saving properties. If the PSSI is less
than 1, the viscosity index improver would be less effective in
viscosity index enhancement when it is dissolved in the lubricating
base oil and thus the resulting composition would not only be poor
fuel saving properties and low temperature viscosity
characteristics but also increased in production cost. The PSSI is,
therefore, preferably 1 or greater.
[0086] The ratio of the weight-average molecular weight and PSSI
(MW/PSSI) of the viscosity index improver used in the present
invention is preferably 1.0.times.10.sup.4 or greater, more
preferably 1.5.times.10.sup.4 or greater, more preferably
2.0.times.10.sup.4 or greater. If the MW/PSSI is less than
1.0.times.10.sup.4, the resulting composition would be degraded in
fuel saving properties and low temperature startability, i.e.,
viscosity temperature characteristics and low temperature viscosity
characteristics.
[0087] The ratio of the weight-average molecular weight (M.sub.W)
and number average molecular weight (M.sub.N) (M.sub.W/M.sub.N) of
the viscosity index improver used in the present invention is
preferably 5.0 or less, more preferably 4.0 or less, more
preferably 3.5 or less, particularly preferably 3.0 or less. The
M.sub.W/M.sub.N is preferably 1.0 or greater, more preferably 2.0
or greater, more preferably 2.5 or greater, particularly preferably
2.6 or greater. If the M.sub.W/M.sub.N exceeds 5.0 or less than
1.0, the viscosity index improver would be degraded in solubility
and viscosity temperature characteristics improving effect and thus
the resulting composition would not maintain sufficient storage
stability or fuel saving properties.
[0088] The content of the viscosity index improver in the
lubricating oil composition of the present invention is preferably
from 0.1 to 50 percent by mass, preferably from 0.5 to 20 percent
by mass, more preferably from 1.0 to 15 percent by mass, more
preferably from 1.5 to 12 percent by mass on the basis of the total
mass of the composition. If the content is less than 0.1 percent by
mass, the resulting composition would be insufficient in low
temperature characteristics. If the content exceeds 50 percent by
mass, the resulting composition would be degraded in shear
stability.
[0089] The lubricating oil composition of the present invention
comprises (B) an overbasic metallic detergent with a metal ratio of
3.4 or less. Whereby, the lubricating oil composition of the
present invention can be enhanced in fuel saving properties
compared with a composition not containing such a metallic
detergent.
[0090] Component (B), i.e., the overbasic metallic detergent with a
metal ratio of 3.4 or less used in the present invention may be an
overbasic compound of an oil-soluble metal salt of a compound
having an OH group and/or a carbonyl group. Alternatively, the
overbasic metallic detergent may be an overbasic metal salt that
may be produced by reacting an overbasic metal salt such as an
alkaline earth metal sulfonate, an alkaline earth metal
carboxylate, an alkaline earth metal salicylate, an alkaline earth
metal phenate or an alkaline earth metal phosphonate, an alkaline
earth metal hydroxide or oxide and boric acid or boric anhydride.
Examples of the alkaline earth metal include magnesium, calcium and
barium. Preferred is calcium. The overbasic metal salt is
preferably an overbasic compound of an oil-soluble metal salt of an
OH group and/or carbonyl group-containing hydrocarbon compound,
more preferably an oil-soluble metal salt of an OH group and/or
carbonyl group-containing hydrocarbon compound overbased with an
alkaline earth metal borate. Alkaline earth metal salicylates are
preferably used while alkaline earth metal salicylates overbased
with an alkaline earth metal borate are more preferably used.
[0091] Component (B), i.e., the overbasic metallic detergent with a
metal ratio of 3.4 or less used in the present invention has a base
number of preferably 50 mgKOH/g or greater, more preferably 100
mgKOH/g or greater, more preferably 120 mgKOH/g or greater,
particularly preferably 140 mgKOH/g or greater, most preferably 150
mgKOH/g or greater. Component (B) has a base number of preferably
300 mgKOH/c or less, more preferably 200 mgKOH/g or less, more
preferably 180 mgKOH/g or less, particularly preferably 170 mgKOH/g
or less. If the base number is less than 50 mgKOH/g, the resulting
composition would be degarded in fuel saving properties as the
viscosity increases and likely be insufficient in friction reducing
effect by addition of the metallic detergent. If the base number
exceeds 300 mgKOH/g, the metallic detergent would likely inhibit
the effect of an anti-wear additive and a friction reducing effect
would be insufficient. The term "base number" used herein denotes
the value measured by JIS K 2501 5.2.3.
[0092] Component (B), i.e., the overbasic metallic detergent with a
metal ratio of 3.4 or less used in the present invention has a
particle diameter of preferably 0.1 .mu.m or smaller, more
preferably 0.05 .mu.m or smaller.
[0093] Any method may be used to produce Component (B), i.e., the
overbasic metallic detergent with a metal ratio of 3.4 or less used
in the present invention. For example, the above-described
oil-soluble metal salt, alkaline earth metal hydroxide or oxide and
boric acid or boric anhydride are reacted in the presence of water,
alcohol such as methanol, ethanol, propanol or butanol and a
dilution solvent such as benzene, toluene or xylene at a
temperature of 20 to 200.degree. C. for 2 to 8 hours, and then
heated to a temperature of 100 to 200.degree. C., followed by
removal of water and if necessary the alcohol and dilution solvent
thereby producing Component (B). These detailed reaction conditions
are arbitrarily selected depending on the amounts of the raw
material and the reaction product. The details of the method are
described in for example Japanese Patent Application Laid-Open
Publication Nos. 60-116688 and 61-204298. The oil-soluble metal
salt overbased with an alkaline earth metal borate produced by the
above-described method has a particle diameter of usually 0.1 .mu.m
or smaller and a total base number of usually 100 mgKOH/g or
greater and thus can be used preferably in the lubricating oil
composition of the present invention.
[0094] Component (B), i.e., the overbasic metallic detergent used
in the present invention has necessarily a metal ratio of 3.4 or
less.
[0095] The metallic detergent is adjusted to have a metal ratio of
preferably 3.2 or less, more preferably 3.0 or less, more
preferably 2.8 or less, particularly preferably 2.6 or less, most
preferably 2.5 or less. If the metal ratio exceeds 3.4, the
resulting composition would be insufficient in friction torque
reduction, i.e., fuel saving properties would be.
[0096] The metallic detergent is adjusted to have a metal ratio of
preferably 1.0 or greater, more preferably 1.1 or greater, more
preferably 1.5 or greater, particularly preferably 1.9 or greater,
most preferably 2.2 or greater. This is because if the metal ratio
is less than 1.0, the resulting internal combustion engine
lubricating oil composition would be high in kinematic viscosity
and low temperature viscosity and thus would cause problems with
lubricity or startability.
[0097] A solely synthesized metallic detergent is preferably used
in order to obtain a higher friction reducing effect.
[0098] The term "metal ratio" used herein is represented by
(valence of metal element in a salicylate detergent).times.(metal
element content (mole %))/(soap group content (mole %)). The metal
element denotes calcium and magnesium. The soap group denotes
sulfonic acid, phenol and salicylic acid groups.
[0099] The alkyl or alkenyl group of Component (B), i.e., the
overbasic metallic detergent with a metal ratio of 3.4 or less used
in the present is an alkyl or alkenyl group having 8 or more,
preferably 10 or more, more preferably 12 or more and 19 or fewer
carbon atoms. If Component (B) has an alkyl or alkenyl group having
fewer than 8 carbon atoms, it would be insufficient in oil
solubility.
[0100] The alkyl or alkenyl group may be straight-chain or branched
but is preferably straight-chain. The alkyl or alkenyl group may be
a primary alkyl or alkenyl group, a secondary alkyl or alkenyl
group or a tertiary alkyl or alkenyl group, but for the secondary
alkyl or alkenyl group or tertiary alkyl or alkenyl group, the
position of the branch is preferably only at the carbon bonding to
an aromatic.
[0101] The content of Component (B), i.e., the overbasic metallic
detergent with a metal ratio of 3.4 or less used in the lubricating
oil composition of the present invention is preferably from 0.01 to
30 percent by mass, more preferably from 0.05 to 5 percent by mass,
on the basis of the total mass of the lubricating oil composition.
If the content is less than 0.01 percent by mass, the fuel saving
effect would last only for a short period of time. If the content
exceeds 30 percent by mass, an advantageous effect as balanced with
the content would not be obtained.
[0102] The content of Component (B), i.e., the overbasic metallic
detergent with a metal ratio of 3.4 or less used in the lubricating
oil composition of the present invention is preferably 0.01 percent
by mass or more, more preferably 0.05 percent by mass or more, more
preferably 0.10 percent by mass or more, particularly preferably
0.15 percent by mass or more and preferably 0.5 percent by mass or
less, more preferably 0.4 percent by mass or less, more preferably
0.3 percent by mass or less, particularly preferably 0.25 percent
by mass or less, most preferably 0.22 percent by mass or less on
the metal basis of the total mass of the lubricating oil
composition. If the content is less than 0.01 percent by mass, the
friction reducing effect achieved by addition of the metal
detergent would be likely insufficient and the resulting
lubricating oil composition would be likely insufficient in fuel
saving properties, thermal/oxidation stability and detergency.
Whilst, the content exceeds 0.5 percent by mass, the friction
reducing effect achieved by addition of the metal detergent would
be likely insufficient and the resulting lubricating oil
composition would be likely insufficient in fuel saving
properties.
[0103] The content of Component (B), i.e., the overbasic metallic
detergent with a metal ratio of 3.4 or less used in the lubricating
oil composition of the present invention is preferably 0.01 percent
by mass or more, more preferably 0.03 percent by mass or more, more
preferably 0.04 percent by mass or more, particularly preferably
0.05 percent by mass or more and preferably 0.20 percent by mass or
less, more preferably 0.10 percent by mass or less, more preferably
0.08 percent by mass or less, particularly preferably 0.07 percent
by mass or less, most preferably 0.06 percent by mass or less on
the boron basis of the total mass of the lubricating oil
composition. If the content is less than 0.01 percent by mass, the
friction reducing effect achieved by addition of the metal
detergent would be likely insufficient and the resulting
lubricating oil composition would be likely insufficient in fuel
saving properties, thermal/oxidation stability and detergency.
Whilst, if the content exceeds 0.2 percent by mass, the friction
reducing effect achieved by addition of the metal detergent would
be likely insufficient and the resulting lubricating oil
composition would be likely insufficient in fuel saving
properties.
[0104] The ratio (MB1)/(MB2) of the content of metal derived from
Component (B) (MB1) and the content of boron derived from Component
(B) (MB2) in the lubricating oil composition of the present
invention is preferably 1 or greater, more preferably 2 or greater,
more preferably 2.5 or greater, particularly preferably 3.0 or
greater, most preferably 3.5 or greater. If the (MB1)/(MB2) is less
than 1, the fuel saving properties would be possibly degraded. The
(MB1)/(MB2) is preferably 20 or less, more preferably 15 or less,
more preferably 10 or less, particularly preferably 5 or less. If
the (MB1)/(MB2) exceeds 20, the fuel saving properties would be
possibly degraded.
[0105] The lubricating oil composition of the present invention
comprises (C) a friction modifier. Whereby, the lubricating oil
composition of the present invention can be enhanced in fuel saving
properties compared with a composition not containing such a
friction modifier. Examples of Component (C), i.e., the friction
modifier include one or more types of friction modifiers selected
from organic molybdenum compounds and ashless friction
modifiers.
[0106] Examples of the organic molybdenum compound include
sulfur-containing organic molybdenum compounds such as molybdenum
dithiophosphate and molybdenum dithiocarbamate; complexes of
molybdenum compounds (for example, molybdenum oxides such as
molybdenum dioxide and molybdenum trioxide, molybdic acids such as
orthomolybdic acid, paramolybdic acid, and sulfurized
(poly)molybdic acid, metal salts of these molybdic acids, molybdic
acid salts such as ammonium salts of these molybdic acids,
molybdenum sulfides such as molybdenum disulfide, molybdenum
trisulfide, molybdenum pentasulfide, and molybdenum polysulfide,
sulfurized molybdenum acid, metal and amine salts of sulfurized
molybdenum acid, and halogenated molybdenum such as molybdenum
chloride) and sulfur-containing organic compounds (for example,
alkyl(thio)xanthate, thiaziazole, mercaptothiadiazole,
thiocarbonate, tetrahydrocarbylthiuramdisulfide,
bis(di(thio)hydrocarbyldithiophosphonate)disulfide, organic
(poly)sulfide, and sulfurized esters) or other organic compounds;
complexes of sulfur-containing molybdenum compounds such as the
above-mentioned molybdenum sulfides and sulfurized molybdenum acid
and alkenyl succinicimide.
[0107] Alternatively, the organic molybdenum compound may be a
sulfur-free molybdenum compound. Examples of such a molybdenum
compound include molybdenum-amine complexes,
molybdenum-succinicimide complexes, molybdenum salts of organic
acids, and molybdenum salts of alcohols, among which preferred are
molybdenum-amine complexes, molybdenum salts of organic acids, and
molybdenum salts of alcohols.
[0108] No particular limitation is imposed on the content of the
organic molybdenum compound if contained in the lubricating oil
composition of the present invention, which is, however, preferably
0.001 percent by mass or more, more preferably 0.005 percent by
mass or more, more preferably 0.01 percent by mass or more,
particularly preferably 0.03 percent by mass or more and preferably
0.2 percent by mass or less, more preferably 0.1 percent by mass or
less, more preferably 0.08 percent by mass or less, particularly
preferably 0.06 percent by mass or less on the molybdenum basis of
the total mass of the lubricating oil composition. If the content
is less than 0.001 percent by mass, the friction reducing effect
achieved by addition of the friction modifier would be likely
insufficient and the resulting lubricating oil composition would be
likely insufficient in fuel saving properties and thermal/oxidation
stability. If the content exceeds 0.2 percent by mass, an
advantageous effect as balanced with the content cannot be
obtained, and the resulting lubricating oil composition would tend
to be degraded in storage stability.
[0109] The ashless friction modifier which may be used in the
present invention may be any compound that is usually used as a
friction modifier for lubricating oils. Examples of such an ashless
friction modifier include compounds having 6 to 50 carbon atoms,
containing one or more types of hetero elements selected from
oxygen, nitrogen and sulfur per molecule. More specific examples
include ashless friction modifiers such as amine compounds, fatty
acid esters, fatty acid amides, fatty acids, aliphatic alcohols,
aliphatic ethers, urea compounds, and hydrazide compounds, each
having at least one alkyl or alkenyl group having 6 to 30 carbon
atoms, in particular straight-chain alkyl, straight-chain alkenyl,
branched alkyl or branched alkenyl group having 6 to 30 carbon
atoms per molecule.
[0110] The content of the ashless friction modifier in the
lubricating oil composition of the present invention is preferably
0.01 percent by mass or more, more preferably 0.1 percent by mass
or more, more preferably 0.3 percent by mass or more and preferably
3 percent by mass or less, more preferably 2 percent by mass or
less, more preferably 1 percent by mass or less. If the content is
less than 0.01 percent by mass, the friction reducing effect
achieved by addition of the friction modifier would tend to be
insufficient. If the content is more than 3 percent by mass, the
ashless friction modifier would tend to inhibit anti-wear additives
from exhibiting their effects or deteriorate the solubility
thereof.
[0111] Component (C), i.e., the friction modifier used in the
present invention is preferably an organic molybdenum friction
modifier, more preferably a sulfur-containing organic molybdenum
compound, more preferably molybdenum dithiocarbamate.
[0112] The lubricating oil composition of the present invention may
be blended with any additives that have been generally used in a
lubricating oil depending on the purposes in order to further
enhance the properties. Examples of such additives include metallic
detergents other than Component (B), ashless dispersants, antiwear
agent (or extreme pressure additive), anti-oxidants, corrosion
inhibitors, rust inhibitors, demulsifiers, metal deactivators, and
anti-foaming agents.
[0113] Examples of the metallic detergents other than Component (B)
include normal salt and/or basic salt such as alkali metal/alkaline
earth metal sulfonates, alkali metal/alkaline earth metal phenates,
and alkali metal/alkaline earth metal salicylates. Examples of the
alkali metal include sodium and potassium. Examples of the alkaline
earth metal include magnesium, calcium and barium. Preferred are
magnesium and calcium. Particularly preferred is calcium.
[0114] The ashless dispersant may be any ashless dispersant that is
usually used for a lubricating oil. Examples of the ashless
dispersant include mono- or bis-succinimides having in their
molecules at least one straight-chain or branched alkyl or alkenyl
group having 40 to 400 carbon atoms, benzylamines having in their
molecules at least one alkyl or alkenyl group having 40 to 400
carbon atoms, polyamines having in their molecules at least one
alkyl or alkenyl group having 40 to 400 carbon atoms, and boron-,
carboxylic acid-, and phosphoric acid-modified products thereof.
Any one or more of these ashless dispersants may be blended.
[0115] The anti-oxidant may be an ashless anti-oxidant such as a
phenol- or amine-based anti-oxidant, or a metallic anti-oxidant
such as a copper- or molybdenum-based anti-oxidant. Specific
examples of the phenol-based anti-oxidant include 4,4'-methylene
bis(2,6-di-tert-butylphenol) and 4,4'-bis(2,6-di-tert-butylphenol).
Specific examples of the amine-based anti-oxidant include
phenyl-.alpha.-naphthylamines, alkylphenyl-.alpha.-naphthylamines
and dialkyldiphenylamines.
[0116] The antiwear agent (or extreme pressure additive) may be any
anti-oxidant or extreme pressure additive that has been used for
lubricating oil. For example, sulfuric-, phosphoric- and
sulfuric-phosphoric extreme pressure additives may be used.
Specific examples include phosphorus acid esters, thiophosphorus
acid esters, dithiophosphorus acid esters, trithiophosphorus acid
esters, phosphoric acid esters, thiophosphoric acid esters,
dithiophosphoric acid esters, trithiophosphoric acid esters, amine
salts, metal salts or derivatives thereof, dithiocarbamates, zinc
dithiocaramates, molybdenum dithiocarbamates, disulfides,
polysulfides, and sulfurized fats and oils. Among these antiwear
agents, preferred are sulfuric extreme pressure additives, and
particularly preferred are sulfurized fats and oils.
[0117] Examples of the corrosion inhibitor include benzotriazole-,
tolyltriazole-, thiadiazole-, and imidazole-types compounds.
[0118] Examples of the rust inhibitor include petroleum sulfonates,
alkylbenzene sulfonates, dinonylnaphthalene sulfonates, alkenyl
succinic acid esters, and polyhydric alcohol esters.
[0119] Examples of the demulsifier include polyalkylene
glycol-based non-ionic surfactants such as polyoxyethylenealkyl
ethers, polyoxyethylenealkylphenyl ethers, and
polyoxyethylenealkylnaphthyl ethers.
[0120] Examples of the metal deactivator 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.
[0121] Examples of the anti-foaming agent include silicone oil with
a 25.degree. C. kinematic viscosity of 1,000 to 100,000 mm.sup.2/s,
alkenylsuccinic acid derivatives, esters of polyhydroxy aliphatic
alcohols and long-chain fatty acids, aromatic amine salts of
methylsalicylate and o-hydroxybenzyl alcohol.
[0122] When these additives are contained in the lubricating oil
composition of the present invention, they are contained in an
amount of 0.01 to 10 percent by mass on the total composition mass
basis.
[0123] The 100.degree. C. kinematic viscosity of the lubricating
oil composition of the present invention is preferably 4 to 12
mm.sup.2/s, more preferably 9.0 mm.sup.2/s or lower, more
preferably 8.0 mm.sup.2/s or lower, more preferably 7.0 mm.sup.2/s
or lower, particularly preferably 6.8 mm.sup.2/s or lower. The
100.degree. C. kinematic viscosity of the lubricating oil
composition of the present invention is preferably 4.5 mm.sup.2/s
or higher, more preferably 5.0 mm.sup.2/s or higher, more
preferably 5.5 mm.sup.2/s or higher, particularly preferably 6.0
mm.sup.2/s or higher. The 100.degree. C. kinematic viscosity
referred herein denotes the viscosity at 100.degree. C. defined by
ASTM D-445.
[0124] If the 100.degree. C. kinematic viscosity is lower than 4
mm.sup.2/s, the resulting lubricating oil composition would lack
lubricity. If the 10.degree. C. kinematic viscosity exceeds 12
mm.sup.2/s, the resulting composition would not obtain the required
low temperature viscosity characteristics and sufficient fuel
saving properties.
[0125] The 40.degree. C. kinematic viscosity of the lubricating oil
composition in the present invention is preferably from 4 to 50
mm.sup.2/s, preferably 40 mm.sup.2/s or lower, more preferably 35
mm.sup.2/s or lower, particularly preferably 30 mm.sup.2/s or
lower, most preferably 27 mm.sup.2/s or lower. The 40.degree. C.
kinematic viscosity of the lubricating oil composition of the
present invention is preferably 15 mm.sup.2/s or higher, more
preferably 18 mm.sup.2/s or higher, more preferably 20 mm.sup.2/s
or higher, particularly preferably 22 mm.sup.2/s or higher. The
40.degree. C. kinematic viscosity referred herein denotes the
viscosity at 40.degree. C. defined by ASTM D-445. If the 40.degree.
C. kinematic viscosity is lower than 4 mm.sup.2/s, the resulting
lubricating oil composition would lack lubricity. If the
100.degree. C. kinematic viscosity exceeds 50 mm.sup.2/s, the
resulting composition would not obtain the required low temperature
viscosity and sufficient fuel saving properties.
[0126] The viscosity index of the lubricating oil composition of
the present invention is preferably within the range of 140 to 400,
more preferably 190 or greater, more preferably 200 or greater,
more preferably 210 or greater, particularly preferably 220 or
greater, most preferably 230 or greater. If the lubricating oil
composition of the present invention has a viscosity index of less
than 140, it would be difficult to improve the fuel saving
properties while maintaining the 150.degree. C. HTHS viscosity and
reduce the low temperature viscosity at -35.degree. C. If the
viscosity index of the lubricating oil composition of the present
invention is greater than 400, the resulting composition would be
degraded in evaporability and cause malfunctions caused by the lack
of solubility of additives and the incompatibility with seal
materials.
[0127] The 100.degree. C. HTHS viscosity of the lubricating oil
composition of the present invention is preferably 5.2 mPas or
lower, more preferably 5.0 mPas or lower, more preferably 4.7 mPas
or lower, particularly preferably 4.5 mPas or lower. Whilst, the
100.degree. C. HTHS viscosity is preferably 3.0 mPas or higher,
more preferably 3.5 mPas or higher, particularly preferably 4.0
mPas or higher, most preferably 4.1 mPas or higher. The 100.degree.
C. HTHS viscosity referred herein denotes the high temperature high
shear viscosity at 100.degree. C. defined in accordance with ASTM
D4683. If the 100.degree. C. HTHS viscosity is lower than 3.0 mPas,
the resulting composition would lack lubricity. If the HTHS
viscosity exceeds 5.2 mPas, the resulting composition would not
obtain the required low temperature viscosity and sufficient fuel
saving properties.
[0128] The 150.degree. C. HTHS viscosity of the lubricating oil
composition of the present invention is lower than 2.6 mPas but is
more preferably 2.5 mPas or lower, more preferably 2.45 mPas or
lower, particularly preferably 2.4 mPas or lower and preferably 2.0
mPas or higher, more preferably 2.1 mPas or higher, more preferably
2.2 mPas or higher, particularly preferably 2.3 mPas or higher. The
150.degree. C. HTHS viscosity referred herein denotes the high
temperature high shear viscosity at 150.degree. C. defined in
accordance with ASTM D4683. If the 150.degree. C. HTHS viscosity is
lower than 2.0 mPas, the resulting composition would lack
lubricity. If the 150.degree. C. HTHS viscosity is 2.6 mPas or
higher, the resulting composition would not obtain sufficient fuel
saving properties.
[0129] The ratio of the 150.degree. C. HTHS viscosity and
100.degree. C. HTHS viscosity (150.degree. C. HTHS
viscosity/100.degree. C. HTHS viscosity) in the lubricating oil
composition of the present invention is preferably 0.50 or greater,
more preferably 0.52 or greater, more preferably 0.54, particularly
preferably 0.55 or greater, most preferably 0.56 or greater. If the
ratio is less than 0.50, the resulting composition would not obtain
the required low temperature viscosity or sufficient fuel saving
properties.
[0130] The lubricating oil composition of the present invention is
a lubricating oil composition that is an engine oil having a
150.degree. C. HTHS viscosity of lower than 2.6 mPas, can reduce
sufficiently the 40.degree. C. kinematic viscosity, 100.degree. C.
kinematic viscosity and 100.degree. C. HTHS viscosity and suppress
the friction coefficient of a boundary lubrication region from
increasing and has excellent fuel saving properties. The
lubricating oil composition of the present invention having such
excellent properties can be suitably used as a fuel saving engine
oil such as a fuel saving gasoline engine oil or a fuel saving
diesel engine oil.
EXAMPLES
[0131] The present invention will be described in more detail below
with reference to the following Examples and Comparative Examples
but are not limited thereto.
Examples 1 to 5, Comparative Examples 1 to 4
[0132] In Examples 1 to 5 and Comparative Examples 1 to 4,
lubricating oil compositions having formulations set forth in Table
2 below were prepared using the following base oils and additives.
Table 1 sets forth the properties of base oils O-1, O-2 and
O-3.
[0133] (Base Oils)
[0134] O-1 (base oil 1): mineral oil produced by
hydrocracking/hydroisomerizing a n-paraffin-containing oil
[0135] O-2 (base oil 2): hydrocracked mineral oil
[0136] O-3 (base oil 3): hydrocracked mineral oil
[0137] (Additive)
[0138] A-1: non-dispersant type ?MA viscosity index improver
(Mw=360,000, PSSI=15, Mw/PSSI=2.4.times.10.sup.4)
[0139] A-2: non-dispersant type PMA viscosity index improver
(Mw=330,000, PSSI=15, Mw/PSSI=2.2.times.10.sup.4)
[0140] a-1: non-dispersant type PMA viscosity index improver
(Mw=380,000, PSSI=27, Mw/PSSI=1.4.times.10.sup.4)
[0141] a-2: dispersant type PMA viscosity index improver
(Mw=400,000, PSSI=45, Mw/PSSI=0.88.times.10.sup.4)
[0142] B-1: overbasic boric acid calcium salicylate A (metal ratio
2.0, base number 139 mgKOH/g, Ca content 4.9 percent by mass, B
content 1.3 percent by mass, Ca/B ratio 3.8, alkyl group chain
length 14 to 18)
[0143] B-2: overbasic boric acid calcium salicylate B (metal ratio
2.5, base number 158 mgKOH/g, Ca content 5.6 percent by mass, B
content 1.7 percent by mass, Ca/B ratio 3.3, alkyl group chain
length 14 to 18)
[0144] b-1: overbasic boric acid calcium salicylate C (metal ratio
3.5, base number 192 mgKOH/g, Ca content 6.8 percent by mass, B
content 2.7 percent by mass, Ca/B ratio 2.5, alkyl group chain
length 14 to 18)
[0145] C-1: MoDTC (alkyl group chain length C8/C13, Mo content 10
percent by mass, sulfur content 11 percent by mass)
[0146] d-1: succinimide dispersant (Mw 13,000, alkyl group chain
length 1900, nitrogen content 0.6 percent by mass)
[0147] e-1: ZnDTP (alkyl group chain length C4/C6, secondary, Zn
content 7.8 percent by mass, P content 7.2 percent by mass, S
content 15.0 percent by mass)
[0148] f-1: other additives (anti-oxidant, antiwear agent, pour
point depressants, anti-foaming agents)
TABLE-US-00001 O-1 O-2 0-3 Base oil 1 Base oil 2 Base oil 3 Density
g/cm.sup.3 0.820 0.835 0.8320 (15.degree. C.) Kinematic mm.sup.2/s
15.8 20.0 13.5 viscosity (40.degree. C.) (100.degree. C.)
mm.sup.2/s 3.85 4.29 3.27 Viscosity index 141 123 112 Pour point
.degree. C. -22.5 -17.5 -22.5 Aniline point .degree. C. 119 116 109
Iodine number 0.06 0.05 5.38 Sulfur content mass ppm <1 <1
<1 Nitrogen content mass ppm <3 <3 <3 n-d-M analysis %
CP 93.3 80.7 72.6 % CN 6.7 19.3 23.4 % CA 0 0 0 Chromatographic
Saturate content 99.6 99.7 99.6 fractionation Aromatic content 0.2
0.2 0.3 mass % Resin content 0.1 0.1 0.1 Recovery rate 99.9 100 100
Paraffin mass % 87.1 53.8 50.7 content based on saturate content
Naphthene mass % 12.9 46.2 49.3 content based on saturate
content
[0149] [Evaluation of Lubricating Oil Compositions]
[0150] The 40.degree. C. and 100.degree. C. kinematic viscosities,
viscosity index, and 100.degree. C. and 150.degree. C. HTHS
viscosities were measured for each of the lubricating oil
compositions of Examples 1 to 5 and Comparative Examples 1 to 4.
The fuel saving properties were evaluated by measuring the friction
torque at a driving valve system. Each physical properties and fuel
saving properties were measured in the following evaluation method.
The results are set forth in Table 2 below.
[0151] (1) kinematic viscosity: ASTM D-445
[0152] (2) viscosity index: JIS K 2283-1993
[0153] (3) HTHS viscosity: ASTM D-4683
[0154] (4) Driving valve system motoring friction test: the
friction torques at an oil temperature of 100.degree. C. and a
revolution number 350 rpm was measured using an apparatus that can
measure the friction torque at a pair of cam and tappet of the
driving valve system in a direct strike-type four-cylinder engine.
The rate of improvement of each composition was calculated based on
the friction torque of Comparative Example 1.
TABLE-US-00002 Comparative Example 1 Example 2 Example 3 Example 4
Example 5 Example 1 Base oil Base oil total mass basis O-1 Base oil
1 mass % 50 50 O-2 Base oil 2 mass % 50 50 100 50 O-3 Base oil 3
mass % 50 50 50 50 50 Base oil viscosity (40.degree. C.) mm.sup.2/s
14.7 14.7 16.2 16.2 19.8 16.2 Base oil viscosity (100.degree. C.)
3.6 3.6 3.7 3.7 4.3 3.7 Base oil viscosity index 124 124 117 117
122 117 Additives Composition total mass basis A-1 Viscosity index
improver 1 mass % 9.9 12.4 10.6 10.2 10.9 A-2 Viscosity index
improver 2 mass % 10.8 a-1 Viscosity index improver 3 mass % a-2
Viscosity index improver 3 mass % B-1 Overbasic metallic detergent
1 mass % 4.06 B-2 Overbasic metallic detergent 2 mass % 3.57 3.57
3.57 3.57 b-1 Overbasic metallic detergent 3 mass % 2.94 C-1 MoDTC
mass % 0.8 0.8 0.8 0.8 0.8 0.8 d-1 Succinimide mass % 5 5 5 5 5 5
e-1 ZnDTP mass % 1.1 1.1 1.1 1.1 1.1 1.1 f-1 Other additives mass %
1.5 1.5 1.5 1.5 1.5 1.5 Evaluation results Kinematic viscosity
40.degree. C. mm.sup.2/s 26.3 24.9 26.9 27.6 30.4 26.3 100.degree.
C. mm.sup.3/s 6.7 6.7 6.7 6.8 6.9 6.6 Viscosity index 231 249 224
219 198 224 HTHS viscosity 100.degree. C. mPa s 4.3 4.2 4.3 4.4 4.7
4.3 150.degree. C. mPa s 2.4 2.4 2.4 2.4 2.4 2.4 HTHS viscosity
(150.degree. C.)/HTHS viscosity (100.degree. C.) 0.56 0.57 0.56
0.55 0.51 0.56 Motoring friction improved rate % 7.9 4.4 4.3 4.3
4.0 0.0 Comparative Comparative Comparative Example 2 Example 3
Example 4 Base oil Base oil total mass basis O-1 Base oil 1 mass %
O-2 Base oil 2 mass % 50 50 50 O-3 Base oil 3 mass % 50 50 50 Base
oil viscosity (40.degree. C.) mm.sup.2/s 16.2 16.2 16.2 Base oil
viscosity (100.degree. C.) 3.7 3.7 3.7 Base oil viscosity index 117
117 117 Additives Composition total mass basis A-1 Viscosity index
improver 1 mass % 10.9 A-2 Viscosity index improver 2 mass % a-1
Viscosity index improver 3 mass % 13.3 a-2 Viscosity index improver
3 mass % 5.1 B-1 Overbasic metallic detergent 1 mass % B-2
Overbasic metallic detergent 2 mass % 3.57 b-1 Overbasic metallic
detergent 3 mass % 2.94 2.94 C-1 MoDTC mass % 0.8 0.8 d-1
Succinimide mass % 5 5 5 e-1 ZnDTP mass % 1.1 1.1 1.1 f-1 Other
additives mass % 1.5 1.5 1.5 Evaluation results Kinematic viscosity
40.degree. C. mm.sup.2/s 28.8 34.6 25.9 100.degree. C. mm.sup.3/s
7.3 8.1 6.6 Viscosity index 235 222 229 HTHS viscosity 100.degree.
C. mPa s 4.3 4.9 4.3 150.degree. C. mPa s 2.4 2.4 2.4 HTHS
viscosity (150.degree. C.)/HTHS viscosity (100.degree. C.) 0.56
0.49 0.56 Motoring friction improved rate % 0.0 -0.2 -14.0
[0155] As set forth in Table 2, the lubricating oil compositions of
Examples 1 to 5 containing all of Components (A) to (C) are higher
in rate of friction improvement in the driving valve system
motoring friction test and more excellent in fuel saving properties
compared with the lubricating oil compositions of Comparative
Examples 1 to 4 having a comparable level of 150.degree. C. HTHS
viscosity and containing no Component (B) or Component (C). It is
appreciated that the lubricating oil compositions of Comparative
Examples 1 to 3 containing Component (B) with a metal ratio of
greater than 3.4 are significantly poorer in rate of friction
improvement in the driving valve system motoring friction test
while the lubricating oil compositions of Comparative Examples 2
and 3 containing a viscosity index improver with a PSSI of greater
than 20 as Component (A) are higher in kinematic viscosities and
significantly poorer in fuel saving properties. The lubricating oil
composition of Comparative Example 4 containing no Component (C) is
significantly poorer in the friction improving rate.
* * * * *