Field of Invention
[0002] The present invention relates to a lubricating oil composition favorably employable
for lubricating internal combustion engines such as diesel engines and gasoline engines.
In particular, the invention relates to a lubricating oil composition having a low
sulfur content of about 0.5 wt.% or less, particularly about 0.2 wt.% or less, which
reduces friction occurring in the internal combustion engines mounted to land-travelling
automotives using low sulfur hydrocarbon fuel and shows good high temperature detergency.
Background of Invention
[0003] The sulfur contained in fuels such as gasolines or diesel fuels employed for operating
internal combustion engines is oxidized when it bums in the engine to give sulfur
oxide such as sulfuric acid. A portion of the sulfur oxide enter the lubricating oil
employed for lubricating the engine, and the remaining portion is exhausted with other
exhaust gases. The sulfur oxide exhausted with other exhaust gases causes environmental
pollution. Hence, the sulfur content in the fuel has been heretofore under severe
regulation. The regulation on the sulfur content was initially applied to gasolines
(fuels for gasoline engines). However, the regulation on the sulfur content has been
also applied recently to diesel fuels having a higher sulfur content. The sulfur content
in the diesel fuels has been recently regulated to be not higher than 0.0010 wt.%.
[0004] As a result of the decrease of the sulfur content, the lubricating oil is less contaminated
with sulfur oxide such as sulfuric acid which is produced when the fuel bums. This
means that the amount of the overbasic metal-containing detergent in the lubricating
oil can be reduced. The basic metal-containing detergent serves for neutralizing the
sulfur oxide in the lubricating oil.
[0005] When the fuel bums in the engine, not only the fuel, but also a portion of the lubricating
oil bums in the engine. A gas produced by burnt lubricating oil is also exhausted
with other exhaust gas. Therefore, it is desirable to reduce the amount of the sulfur
content of the lubricating oil.
[0006] By the way, the recently employed lubricating oils for internal combustion engines
comprise a base oil (hydrocarbon oil having lubricating viscosity) and a variety of
additives (i.e., lubricating oil additives) such as a basic metal-containing detergent
for neutralizing the emigrated sulfur oxide, an oxidation inhibitor for keeping the
base oil functioning at elevated temperature from deteriorating, a dispersant for
dispersing soots produced by burning of fuels and residues produced by deterioration
of the base oil and metal-containing detergent in the base oil, an extreme pressure
agent for preventing of seizure of the piston and cylinder, a friction-reducing agent
(friction modifier) for reducing friction occurring between the piston and cylinder.
[0007] Therefore, the phosphorus component and metal component contained in the additive
placed in the lubricating oil composition are decomposed when the lubricating oil
composition bums and enter the exhaust gas in the form of phosphorus oxides and metal
oxides. The phosphorus oxides and metal oxides contained in the exhaust gas, are brought
into contact with oxidative catalyst or reductive catalyst placed in the exhaust gas-cleaning
apparatus and inactivate the catalyst.
[0008] For the reasons described above, it has been demanded to reduce the sulfated ash
content, phosphorus content and sulfur content of the lubricating oil composition.
[0009] Patent publication 1 (
JP 2002-53888 A) discloses a lubricating oil composition favorably employable for lubricating internal
combustion engines operated using a fuel having a low sulfur content, particularly,
diesel engines. The disclosed lubricating oil composition comprises a base oil having
a sulfur content of 0.1 wt.% or less (preferably 0.03 wt.% or less) and the following
additives:
- a) an ashless dispersant comprising an alkenyl- or alkyl-succinimide or a derivative
thereof in an amount of 0.01-0.3 wt.% in terms of the nitrogen content;
- b) a metal-containing detergent having a sulfur content of 3 wt.% or less and a TBN
of 10-350 mg•KOH/g in an amount of 0.1-1 wt.% in terms of the sulfated ash content;
- c) a zinc dialkyldithio phosphate in an amount of 0.01-0.12 wt.% in terms of the phosphorus
content;
- d) an oxidation-inhibiting phenolic compound and/or an oxidation-inhibiting amine
compound in an amount of 0.01-5 wt.%,
the lubricating oil composition having a sulfated ash content of 0.1-1 wt.%, a phosphorus
content of 0.01-0.1, a sulfur content of 0.01-0.3 wt.%, a chlorine content of 40 wt.ppm
or less, and an organic acid salt derived from the metal-containing detergent in an
amount of 0.2 to 7 wt.% (preferably 0.5-5 wt.%, more preferably 1.0-3 wt.%),
wherein the above-mentioned contents and amounts are expressed based on the total
amount of the lubricating oil composition.
[0010] Patent Publication 1 further discloses in the working examples that the disclosed
lubricating oil compositions show good high temperature detergency in the internal
combustion engines.
[0011] Patent Publication 1 furthermore discloses that the lubricating oil composition may
contain a molybdenum-containing compound which can serve as a friction modifier, an
oxidation inhibitor as well as an anti-wear agent. The molybdenum-containing compound
can be one of known molybdenum-containing compounds such as sulfoxymolybdenum dithiocarbamate,
sulfoxymolybdenum dithiophosphate and molybdenum complexes of succinimide possibly
containing sulfur.
[0012] Patent Publication 2 (
JP 2004-149802 A) discloses a lubricating oil composition having a low sulfated ash content, a low
phosphorus content and a low sulfur content, preferably employable for lubricating
internal combustion engines (that is, engine oil), which comprises a base oil, an
ethylene carbonate post-treated ashless dispersant, a borated ashless dispersant,
an overbased metal-containing detergent and a phosphorus compound. Patent Publication
2 further discloses that the disclosed lubricating oil composition may contain a molybdenum-succinimide
complex. In the working examples of Patent Publication 2, it is shown by experimental
data that the lubricating oil composition shows good oxidation stability as well as
good anti-wear performance.
[0013] Patent Publication 3 discloses a low sulfated ash, low phosphorus, low sulfur engine
oil (engine oil composition) comprising a low sulfur base oil, a boron-containing
ashless dispersant, a molybdenum-containing friction modifier, a metal-containing
detergent such as sulfonate, phenate or salicylate, and a zinc dithiophosphate. The
molybdenum-containing friction modifier can be molybdenum diorgano-dithiocarbamate,
molybdenum diorgano-dithiophosphate, molybdenum carboxylate, and a trinuclear molybdenum
compound such as Mo
3S
7(dtc)
4 or Mo
3S
4(dtc)
4. In the working examples, it is shown by the experimental data that the lubricating
oil composition employing the above-mentioned trinuclear molybdenum compound has particularly
good high temperature oxidation stability and a good friction reductive performance.
[0014] As is described above, it has been known that the molybdenum-containing compound
is particularly effective as a friction modifier to be incorporated into lubricating
oil compositions.
[0015] As the known molybdenum-containing compounds, molybdenum diorgano dithiocarbamate
and molybdenum diorgano dithiophosphate are most generally employed. However, both
compounds have disadvantage problems, in that the former contains sulfur (S) in its
molecular structure and the latter contains phosphorous (P) in its molecular structure,
and hence both produce poisonous gases such as sulfur oxide gas and phosphorus oxide
gas when the lubricating oil burns in the internal combustion engine, resulting in
inactivation of the catalysts of the exhaust gas-clearing apparatus. As is explained
above, Patent Publication 3 describes that a trinuclear molybdenum compound such as
Mo
3S
7(dtc)
4 or Mo
3S
4(dtc)
4 shows a good friction-modifying function (friction-reducing function). However, these
trinuclear molybdenum compounds contains sulfur atoms in the molecular structure of
its ligand moiety, i.e., dithiocarbamate, dtc, and further contains other sulfur atoms
directly attached to the molybdenum atom, and hence, the trinuclear molybdenum compounds
contains a relatively large amount of sulfur in the compound
per se. Therefore, the trinuclear molybdenum compound is not favorably employed for incorporation
into the lubricating oil composition if reduction of the sulfur content in the oil
composition is intended.
Summary of Invention
[0016] Accordingly, it is the object of the invention to provide a molybdenum-containing
friction-reducing agent having no or a relatively less amount of sulfur and phosphorus
which is favorably employable in place of the conventionally employed friction-reducing
agents containing sulfur and phosphorus in relatively large amounts, such as molybdenum
diorgano-dithiocarbamate, molybdenum diorgano-dithiophosphate, molybdenum carboxylate,
and a trinuclear molybdenum compound such as Mo
3S
7(dtc)
4 or Mo
3S
4(dtc)
4.
[0017] The present inventors have found that the friction-reducing function of the known
molybdenum complex of a basic nitrogen-containing compound such as a molybdenum-succinimide
complex is prominently enhanced if the molybdenum complex is incorporated into lubricating
oil compositions in combination with specifically selected amounts of an alkenyl-
or alkyl-succinimide or its derivative (which is known as an ashless dispersant) and
an alkenyl- or alkyl-succinic acid ester (succinate) or its derivative (which is also
known as an ashless dispersant).
[0018] The present invention has been made on the above-mentioned inventors' new finding.
It has been further found out that the lubricating oil compositions containing the
above-mentioned molybdenum complex of a basic nitrogen-containing compound but not
containing the succinimide or its derivative (and further not containing the succinate
or its derivative) show improved resistance to oxidation at high temperatures but
the oil compositions show little reduction of the friction coefficient.
[0019] Accordingly, the present invention provides a lubricating oil composition for lubricating
internal combustion engines which has a sulfur content of 0.5 wt.% or less and which
comprises a base oil having a lubricating viscosity and at least the following additive
components a) to e):
- a) an ashless dispersant in an amount of 0.5-5.0 wt.% which comprises an alkenyl-
or alkyl-succinimide or a derivative thereof;
- b) an ashless dispersant in an amount of 0.5-5.0 wt.% which comprises an alkenyl-
or alkyl-succinic ester or a derivative thereof;
- c) a molybdenum complex of a basic nitrogen-containing compound in an amount of 50-1,200
wt.ppm in terms of a molybdenum content thereof;
- d) an alkaline earth metal-containing detergent having a TBN in the range of 10 to
400 mg•KOH/g in an amount of 0.05-1.0 wt.% in terms of an alkaline earth metal content
thereof; and
- e) an anti-wear agent in an amount of 0.05-5.0 wt.%.
[0020] The present invention further provides a method for operating internal engines mounted
to land-travelling vehicles using a fuel having a sulfur content of 0.001 wt.% or
less under lubrication with the above-mentioned lubricating oil composition according
to the invention.
[0021] Preferred embodiments of the invention are stated below.
- (1) The lubricating oil composition has the sulfur content in the range of 0.01 to
0.2 wt.%.
- (2) The lubricating oil composition has the sulfur content in the range of 0.05 to
0.12 wt.%.
- (3) The lubricating oil composition is a multi-grade engine oil further comprising
a viscosity index improver, whereby being classified to 0W5, 0W10, 0W15, 0W20, 0W30,
5W20, 5W30, 10W20, or 10W30.
- (4) The lubricating oil composition contains the component a), namely, an alkenyl-
or alkyl-succinimide or a derivative thereof, in an amount of 1.0-4.0 wt.%.
- (5) The lubricating oil composition contains the component b), namely, an alkenyl-
or alkyl-succinic ester or a derivative thereof, is contained in an amount of 1.0-4.0
wt.%.
- (6) The lubricating oil composition wherein a ratio of the component a) to the component
b) is in the range of 1:4 to 4:1.
- (7) The component c), namely, a molybdenum complex of a basic nitrogen-containing
compound, contains a sulfur not larger than 1 wt.%.
- (8) The component c), namely, the molybdenum complex of a basic nitrogen-containing
compound, contains a sulfur in the range of 0.05 to 0.5 wt.%.
- (9) The component c) is a molybdenum complex of a succinimide.
- (10) The component d) comprises an alkaline earth metal salicylate.
- (11) The anti-wear agent is a zinc dialkyldithiophosphate.
- (12) The lubricating oil composition further comprises an oxidation inhibitor.
- (13) The lubricating oil composition is used for lubricating internal combustion engines
operated using a fuel oil having a sulfur content of 0.001 wt.% or less.
[0022] The lubricating oil composition of the invention contains a molybdenum complex of
a basic nitrogen-containing compound (serving as a friction-modifier) in combination
of a mixture of known dispersants, that is, an alkenyl- or alkyl-succinimide or a
derivative thereof and an alkenyl- or alkyl-succinic acid ester (succinate) or a derivative
thereof both in specific amounts. Therefore, the lubricating oil composition can be
prepared to contain sulfur at a low level. Nevertheless, the lubricating oil composition
of the invention shows a prominently good friction-reducing function.
Detailed Description of Invention
[0023] The base oil and additives employable for the preparation of the lubricating oil
composition of the invention are described below in more detail.
Base Oil
[0024] The base oil generally is a mineral oil or a synthetic oil showing a kinematic viscosity
of 2 to 50 mm
2/s at 100°C. There are no specific limitations on the natures and other properties
of the mineral oil and synthetic oil. However, the sulfur content of the base oil
should be 0.1 wt.% or less. The sulfur content preferably is 0.03 wt.% or less, and
more preferably is 0.005 wt.% or less.
[0025] The mineral oil preferably is an oil which is obtained by processing a lubricating
oil distillate of a mineral oil by solvent refining, hydrogenation, or their combination.
Particularly preferred is a highly hydrogenated refined oil (corresponding to a hydrocracked
oil, typically has a viscosity index of 100 to 150, an aromatic component content
of 5 wt.% or less, a nitrogen content of 50 wt.ppm or less, and a sulfur content of
50 wt. ppm or less. Particularly preferred is a high viscosity index base oil for
instance having a viscosity index of 140-160 which is obtained by hydroisomerization
of slack wax or GTL wax (Gas-To-Liquid).
[0026] Examples of the synthetic oils (synthetic lubricating base oils) include poly-α-olefin
such as a polymerized compound of α-olefin having 3 to 12 carbon atoms; a dialkyl
ester of a di-basic acid such as sebacic acid, azelaic acid or adipic acid and an
alcohol having 4 to 18 carbon atoms, typically dioctyl sebacate; a polyol ester which
is an ester of 1,1,1-trimethylolpropane or pentaerythritol and a mono-basic acid having
3 to 18 carbon atoms; and alkylbenzene having an alkyl group of 9 to 40 carbon atoms.
The synthetic oil generally contains essentially no sulfur, shows good stability to
oxidation and good heat resistance, and gives less residual carbon and soot when it
is burned. Therefore, the synthetic oil is preferably employed for the lubricating
oil composition of the invention. Particularly preferred is poly-α-olefin, from the
viewpoint of the object of the invention.
[0027] Each of the mineral oil and synthetic oil can be employed singly. If desired, however,
two or more mineral oils can be employed in combination, and two or more synthetic
oils can be employed in combination. The mineral oil and synthetic oil can be employed
in combination at an optional ratio.
Ashless Dispersant
[0028] The lubricating oil composition of the invention comprises at least two different
ashless dispersants, that is, an alkenyl- or alkyl-succinimide or a derivative thereof
(component a) and an alkenyl- or alkyl-succinic ester or a derivative thereof (component
b), in an amount of 0.5-5.0 wt.%, preferably 1.0-4.0 wt.%, for each (the amount is
based on the total amount of the lubricating oil composition). The component a) and
component b) are preferably contained in a weight ratio of 1:4 to 4:1, more preferably
1:2 to 2:1.
[0029] The component a), namely, the alkenyl- or alkyl-succinimide or a derivative thereof,
may be a known alkenyl- or alkyl-succinimide or a derivative thereof. For example,
the alkenyl- or alkyl-succinimide derived from a polyolefin or its derivative may
be employed. A representative succinimide can be prepared by the reaction between
succinic anhydride substituted with a high molecular weight alkenyl or alkyl and a
polyalkylene polyamine containing average 4 to 10 (preferably 5 to 7) nitrogen atoms
in one molecule. The high molecular weight alkenyl or alkyl is preferably derived
from a polybutene (particularly a high reactivity polybutene having a vinylidene terminal)
having a number average molecular weight of about 900 to 3,000.
[0030] The process for obtaining the polybutenyl-succinic anhydride by the reaction of polybutene
and maleic anhydride is generally performed by the chlorination process using a chloride
compound. The chlorination process is advantageous in its reaction yield. However,
the reaction product obtained by the chlorination process contains a large amount
(for instance, approx. 2,000-3,000 wt.ppm) of chlorine. In contrast, if the thermal
reaction process using no chloride compound is employed, the reaction product contains
only an extremely small chlorine (for instance, 0-30 ppm). Accordingly, it is preferred
that the succinimide be prepared from a polybutenyl succinic anhydride which is produced
by the thermal reaction, whereby the chlorine content of the resulting succinimide
is in the range of 0 to 30 wt.ppm. The succinimide can be reacted with boric acid,
alcohol, aldehyde, ketone, alkylphenol, cyclic carbonate, organic acid or the like,
to give a modified succinimide. Particularly, a borated alkenyl(or alkyl)-succinimide
which is obtained by the reaction with boric acid or a boron compound is advantageous
from the viewpoints of thermal and oxidation stability.
[0031] The component b), namely, the alkenyl- or alkyl-succinic ester or a derivative thereof,
may be a known alkenyl- or alkyl-succinic ester or a derivative thereof. For example,
the alkenyl- or alkyl-succinic ester derived from a polyolefin or its derivative may
be employed. A representative succinic ester can be prepared by the reaction between
succinic anhydride substituted with a high molecular weight alkenyl or alkyl and an
alcohol containing average 1 to 6 hydroxyl groups in one molecule. The high molecular
weight alkenyl or alkyl is preferably derived from a polybutene (particularly a high
reactivity polybutene having a vinylidene terminal) having a number average molecular
weight of about 900 to 3,000.
[0032] The lubricating oil composition of the invention may contain other ashless dispersants
such as an alkenylbenzylamine ashless dispersant in addition to the ashless dispersant
a) (i.e., component a)) and ashless dispersant b) (i.e., component b)).
Molybdenum complex of basic nitrogen-containing compound
[0033] The lubricating oil composition of the invention further comprises a molybdenum complex
of a basic nitrogen-containing compound in an amount of 50-1,200 wt.ppm in terms of
a molybdenum content thereof. This molybdenum complex is already known as a multifunctional
addi-tive. The molybdenum complex of a basic nitrogen-containing compound may contain
a small amount of sulfur.
[0034] The molybdenum complex of basic nitrogen-containing compound functions mainly as
an oxidation inhibitor, an anti-wear agent or a friction modifier in the lubricating
oil composition.
[0035] A preferred molybdenum complex of a basic nitrogen-containing compound is an oxymolybdenum
complex produced by reaction of an acidic molybdenum compound and a basic nitrogen-containing
compound. Examples of the acidic molybdenum compounds include molybdic acid, ammonium
molybdate, and alkali metal salts of molybdate. Examples of the basic nitrogen-containing
compounds include succinimide, carboxylic amide, hydrocarbylamine and a Mannich basic
compound. Examples of the molybdenum complex of basic nitrogen-containing compounds
include a molybdenum complex of succinimide and a molybdenum complex of a secondary
aliphatic amine.
[0036] The molybdenum complex of a basic nitrogen-containing compound can be employed after
reaction with a small amount of sulfur or a sulfur-containing compound. Specifically,
a reaction product obtained by sulfurization of a molybdenum complex of succinimide
at low temperatures. The reaction product preferably contains sulfur in a relatively
small amount such as 10 wt.% or less. The sulfoxymolybdenum complex can be prepared
in the manner described in Examples C to H of United States Patent
6,562,765 B.
[0037] The lubricating oil composition of the invention can further contain other molybdenum-containing
compounds such as sulfoxymolybdenum dithiocarbamate, sulfoxymolybdenum dithiophosphate,
and oxymolybdenum monoglyceride.
Alkaline earth metal-containing Detergent
[0038] The lubricating oil composition of the invention further comprises an alkaline earth
metal-containing detergent having a TBN in the range of 10 to 400 mg•KOH/g in an amount
of 0.05-1.0 wt.% in terms of an alkaline earth metal content thereof. The known alkaline
earth metal-containing detergent having a TBN in the range of 10 to 400 mg•KOH/g is
employable. Preferred is a calcium alkylsalicylate detergent. The calcium alkylsalicylate
detergent preferably contains an organic acid salt in an amount of 0.2-7 wt.%, more
preferably 0.5-5 wt.%, most preferably 1.0-3 wt.%. The calcium alkylsalicylate detergent
preferably comprises an unsulfurized calcium alkylsalicylate detergent having an alkyl
group containing 14-18 carbon atoms. The unsulfurized calcium alkylsalicylate detergent
having an alkyl group containing 14-18 carbon atoms can be employed in combination
with an unsulfurized calcium alkylsalicylate detergent having an alkyl group containing
20-28 carbon atoms. In the specification, the unsulfurized calcium alkylsalicylate
detergent having an alkyl group containing 14-18 carbon atoms means an unsulfurized
calcium alkylsalicylate detergent having an alkyl group in which 90 mole % or more
of the alkyl groups contain 14-18 carbon atoms. The unsulfurized calcium alkylsalicylate
detergent having an alkyl group containing 20-28 carbon atoms has the same meaning,
that is, the unsulfurized calcium alkylsalicylate detergent having an alkyl group
containing 20-28 carbon atoms means an unsulfurized calcium alkylsalicylate detergent
having an alkyl group in which 90 mole % or more of the alkyl groups contain 20-28
carbon atoms.
[0039] The unsulfurized calcium alkylsalicylate preferably is a calcium salt of an alkylsalicylic
acid which can be prepared from an alkylphenol (which is produced by the reaction
of α-olefin having the desired number of carbon atoms and phenol) by the Kolbe-Schmidt
reaction. Generally, the calcium salt of an alkylsalicylic acid can be overbased by
the use of lime and carbon dioxide, to give an overbased calcium salicylate.
[0040] The calcium salt of an alkylsalicylate can be prepared by the steps of neutralizing
phenol to give its calcium salt and subsequent carbonation.
[0041] The calcium alkylsalicylate detergent is preferably incorporated into the lubricating
oil composition under such conditions that the amount of the organic acid salt (contained
in the calcium alkylsalicylate detergent) is in the range of 0.2 to 7 wt.%, preferably
0.5 to 5 wt.%, more preferably 1.0 to 3 wt.%, based on the total amount of the lubricating
oil composition. In more detail, the calcium alkylsalicylate detergent is an oily
dispersion which comprises an organic acid metal salt (generally called a soap component)
and basic inorganic salt micro-particles (e.g., calcium carbonate particles) aggregated
around the organic acid metal salt in an oily medium. Generally, the dispersion contains
the oily medium in an amount of 30 to 50 wt.%. Even if the amount of the calcium alkylsalicylate
detergent is reduced, the high temperature detergency (i.e., power for keeping the
inside space of an engine operated at high temperatures) of the lubricating oil composition
does not substantially lower provided that the amount of the organic acid metal salt
is kept at or above a certain level.
[0042] The alkaline earth metal-containing detergent can be an alkaline earth metal salt
of an organic acid having a carbon-nitrogen bonding or a phenol derivative. This detergent
can have a high TBN regardless of a sulfated ash content, if it is treated with an
amine compound. The amine compound brings a base number originating from the basic
nitrogen atoms. For example, a metal salt of an aminocarboxylic acid can be employed.
Particularly preferred is an unsulfurized alkylphenate (i.e., alkaline earth metal
salt) having a Mannich base structure. This compound can be obtained by Mannich reaction
using an alkylphenol, formaldehyde, and an amine or an amine compound to give an aminomethylated
phenol, and subsequent neutralization of the reaction product by a base such as calcium
hydroxide.
[0043] Alternatively, the alkaline earth metal-containing detergent can be an alkaline earth
metal salt of a sulfonic acid (i.e., sulfonate) obtained from a petroleum sulfonic
acid, an alkylbenzenesulfonic acid, or an alkyltoluenesulfonic acid.
[0044] Alternatively, the alkaline earth metal-containing detergent can be a sulfurized
phenate, namely, an alkaline earth metal salt of a sulfurized alkyl phenol
Anti-wear agent
[0045] The lubricating oil composition of the invention further comprises an anti-wear agent
(component e)) in an amount of 0.05-5.0 wt.%. There are no specific limitation on
the anti-wear agent, and the known sulfur-containing anti-wear agent as well as the
known phosphorus-containing anti-wear agent can be employed. Examples of the sulfur-containing
anti-wear agents include sulfurized olefin, polysulfide compound, sulfurized ester,
sulfurized alcohol, sulfurized amide, sulfurized oil/fat, ashless dithiocarbamate,
metal (other than molybdenum) dithiocarbamate, mercapto thiadiazole, mercapto benzothiadiazole,
and mercapto thiazoline. Examples of the phosphorus-containing anti-wear agents include
phosphoric acid ester, phosphorous acid ester, thiophosphoric acid ester, their amine
salts, and their metal salts such as zinc dialkyldithiophosphate, zinc dialkyldithiophosphate,
and zinc dialkylphosphate.
[0046] The anti-wear agent, i.e., component e), preferably is zinc dialkyldithiophosphate
or zinc dihydrocarbylphosphate. These zinc phosphate anti-wear agents are well known
and easily produced by the known procedures. The zinc phosphate anti-wear agent can
be employed in an amount of 0.01-0.12 wt.%, but preferably in an amount of 0.01-0.06
wt.%, in consideration of the desired low phosphorus content and sulfur content.
[0047] The zinc dialkyldithiophosphate preferably contains an alkyl group having 3-18 carbon
atoms or an alkylaryl group having C
3-18 alkyl group. Most preferred is a zinc dialkyldithiophosphate containing an alkyl
group derived from a secondary alcohol having 3-18 carbon atoms or a zinc dialkyldithiophosphate
containing a mixture of alkyl groups derived from a mixture of a primary alcohol having
3-18 carbon atoms and a secondary alcohol having 3-18 carbon atoms. Both are particularly
effective for reducing wear. A zinc dialkyldithiophosphate derived from a primary
alcohol shows high thermal resistance. These zinc dialkyldithiophosphates can be employed
alone or in combination in the form of a mixture mainly comprising one derived from
the secondary alcohol and/or one derived from the primary alcohol.
Oxidation Inhibitor
[0048] The lubricating oil composition of the invention preferably contains an oxidation
inhibitor in an amount of 0.01-5 wt.%, preferably 0.1-3 wt.%. The oxidation inhibitor
can be the phenolic oxidation inhibitor and the amine oxidation inhibitor. A lubricating
oil composition having a low sulfated ash content, a low phosphorus content and a
low sulfur content is apt to show a relatively low high-temperature detergency, oxidation-inhibiting
performance and anti-wear performance due to decrease of the amounts of the metal-containing
detergent and zinc dithiophosphate. Therefore, the lubricating oil composition of
the invention preferably contains an oxidation inhibitor so as to keep these performances
high.
[0049] Preferred oxidation inhibitors are a diarylamine oxidation inhibitor and a hindered
phenol oxidation inhibitor. These oxidation inhibitors also function for improving
high-temperature detergency. The diarylamine oxidation inhibitor is advantageous in
giving a base number originating from the nitrogen atoms. The hindered phenol oxidation
inhibitor is advantageous in producing no NO
x gas.
[0050] Examples of the hindered phenol oxidation inhibitors include 2,6-di-t-butyl-p-cresol,
4,4'-methylenebis(2,6-di-t-butylphenol), 4,4'-methylenebis(6-t-butyl-o-cresol), 4,4'-isopropylidenebis(2,6-di-t-butylphenol),
4,4'-bis(2,6-di-t-butylphenol), 2,2'-methylenebis(4-methyl-6-t-butylphenol), 4,4'-thiobis(2-methyl-6-t-butylphenol),
2,2-thio-diethylenebis[3-(3,5-di-t-butyl-4-hydoxyphenyl)propionate], octyl 3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate,
octadecyl 3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, and octyl 3-(3,5-t-butyl-4-hydroxy-3-methylphenyl)propionate.
[0051] Examples of the diarylamine oxidation inhibitors include alkyldiphenylamine having
a mixture of alkyl groups of 4 to 9 carbon atoms, p,p'-dioctyldiphenylamine, phenyl-α-naphthylamine,
phenyl-α-naphthylamine, alkylated β-naphthylamine, and alkylated phenyl-α-naphthylamine.
[0052] Each of the hindered phenol oxidation inhibitor and diarylamine oxidation inhibitor
can be employed alone or in combination. If desired, other oil soluble oxidation inhibitors
can be employed in combination with the above-mentioned oxidation inhibitor(s).
Other Additives
[0053] The lubricating oil composition of the invention may further contain an alkali metal
borate hydrate for increasing stability at high temperatures and a base number. A
representative alkali metal borate hydrate can be prepared in the manner described
in United States Patents
3,929,650 and
4,089,790. For example, the alkali metal borate hydrate can be in the form of a dispersion
containing micro-particles of an alkali metal borate hydrate which is produced by
carbonizing a neutral alkali metal or alkaline earth metal sulfonate in the presence
of an alkali metal hydroxide to yield an overbased sulfonate and reacting the overbased
sulfonate with boric acid. In the carbonizing procedure, it is desired to incorporate
an ashless dispersant such as succinimide into the reaction mixture. The alkali metal
preferably is potassium or sodium. The alkali metal borate hydrate can be a dispersion
of KB
3O
5•H
2O particles having a particle size of about 0.3 µm or less which is dispersed in the
presence of a neutral calcium sulfonate and succinimide. From the viewpoint of resistance
to hydrolysis, potassium is preferably replaced with sodium.
[0054] The lubricating oil composition of the invention preferably contains a viscosity
index improver in an amount of 20 wt.% or less, preferably 1 to 20 wt.%. Examples
of the viscosity index improvers are polymers such as polyalkyl methacrylate, ethylene-propylene
copolymer, styrene-butadiene copolymer, and polyisoprene. A dispersant viscosity index
improver and a multi-functional viscosity index improver which are produced by providing
dispersing properties to the above-mentioned polymer are preferably employed. The
viscosity index improvers can be used alone or in combination.
[0055] The lubricating oil composition of the invention may further contain a small amount
of various auxiliary additives. Examples of the auxiliary additives are described
below. benzotriazol compounds and thiadiazol compounds functioning as metal deactivating
agent; nonionic polyoxyalkylene surface active agents such as polyoxyethylenealkylphenyl
ether and copolymers of ethylene oxide and propylene oxide functioning as an anti-rust
agent and an anti-emulsifying agent. In addition, various compounds functioning as
an anti-foaming agent and a pour point depressant can be incorporated.
[0056] The above-mentioned auxiliary additives may be incorporated into the lubricating
oil composition in an amount of 3 wt.% or less, particularly in an amount of 0.001-3
wt.%.
Examples
(1) Preparation of lubricating oil composition (test oil)
[0057] Lubricating oil compositions having a low sulfur content (0.5 wt.% or less) for evaluation
on the oil performance were prepared in the below-described manner using the below-mentioned
base oil and additives. The lubricating oil compositions were formulated to show a
viscosity grade (SAE viscosity grade) of 5W30 by addition of a viscosity index improver.
(2) Base oil and additives
1) Base oil (mixture of the below-mentioned base stock A and base stock B in the weight
ratio of 46:54)
[0058]
Base stock A: Hydrocracked base stock showing a kinematic viscosity of 6.4 mm2/s (at 100°C), a viscosity index of 132, a saturated component content of 92 wt.%
and a sulfur content of less than 0.001 wt.%.
Base stock B: Hydrocracked base stock showing a kinematic viscosity of 4.1 mm2/s (at 100°C), a viscosity index of 127, a saturated component content of 92 wt.%
and a sulfur content of less than 0.001 wt.%.
2) Additives
[0059] Ashless dispersant A: Ethylene carbonate post-treated succinimide dispersant (nitrogen
content: 0.85 wt.%) prepared by the steps of thermally reacting polybutene (number
average molecular weight: about 2,200) and maleic anhydride to give polyisobutenylsuccinic
anhydride, reacting about 2 moles of the polyisobutenylsuccinic anhydride and polyalkylene
polyamine containing 6.5 nitrogen atoms (average) in one molecule to give a bis-type
succinimide, and finally treating the bis-type succinimide with ethylene carbonate
under reaction.
[0060] Ashless dispersant B: Alkenylsuccinic ester (TAN: 5 mg•KOH/g) prepared by the steps
of thermally reacting polybutene (number average molecular weight: about 1,000) and
maleic anhydride to give polyisobutenylsuccinic anhydride, reacting about 1.14 moles
of the polyisobutenylsuccinic anhydride and one mole of pentaerythritol.
[0061] Mo complex of succinimide: A product (Mo content: 4.5 wt.%, N content: 2.1 wt.%,
S content: 0.16 wt.%) obtained by the steps of reacting a mono-type alkenylsuccinimide
derived from polyisobutene having a number average molecular weight of about 1,000
and molybdic acid to give a molybdenum complex and reacting the molybdenum complex
with a small amount of sulfur.
MoDTC: Sulfoxymolybdenum dialkyldithiocarbamate (Mo content: 10 wt.%, S content: 11
wt.%)
Ca-containing detergent A: Calcium monoalkylsalicylate (alkyl containing about 14-18
carbon atoms, overbase degree: 2.0, Ca content: 6.2 wt.%, S content: 0.12 wt.%)
Ca-containing detergent B: Calcium monoalkylsalicylate (alkyl containing about 20-28
carbon atoms, overbase degree: 8.2, Ca content: 11.4 wt.%, S content: 0.17 wt.%)
Ca-containing detergent C: Calcium sulfonate (neutral type, Ca content: 2.4 wt.%,
sulfur content: 2.7 wt.%)
ZnDTP: zinc dialkyldithiophosphate (P content: 7.2 wt.%, S content: 14.4 wt.%, derived
from a mixture of a secondary alcohol having 4 carbon atoms and a secondary alcohol
having 6 carbon atoms)
Oxidation inhibitor: Mixture of dialkyldiphenylamine oxidation inhibitor and hindered
phenol propionate oxidation inhibitor.
Viscosity index improver (VII): Non-dispersant type ethylene-propylene copolymer (Paratone
8057)
(3) Determination of friction coefficient
[0062] The friction coefficient was determined by means of High Frequency Reciprocating
Rig (HFRR) under the below-described conditions:
[0063] Oil temperature: 105°C, Load: 400 g, Friction length: 1,000 µm, Reciprocating frequency:
20 Hz, Test Period: one hour.
(4) Evaluation of inhibition of production of high-temperature deposit
[0064] The power inhibiting production of a high-temperature deposit (Deposit) was evaluated
by means a hot tube tester (HTT) under the below described conditions:
[0065] In a heater block was placed vertically a glass tube (inner diameter: 2 mm). The
test oil and air were supplied into the tube from its bottom at supply rates of 0.31
cc/h and 10 cc/min., respectively. These procedures were performed under keeping the
temperature of the heater element at 280°C for 16 hours. Thereafter, the glass tube
was taken out from the heater block, washed with petroleum ether, and dried. The deposit
attached to the inner surface of the glass tube was observed and marked according
to the merit rating.
[0066] The merit rating was done in the known manner on the basis of 10 points. The higher
point means that the power of inhibiting production of deposit is high.
(5) Compositions of the test oils and results of determination and evaluation
[0067] The test results of the test oils are set forth in Table 1 below.
Table 1
Base oil/ Additives |
Example 1 |
Com. Ex. 1 |
Com. Ex. 2 |
Ashless dispersant A (wt.%) |
3.0 |
5.5 |
3.0 |
Ashless dispersant B (wt.%) |
2.5 |
- |
2.5 |
Succinimide Mocomplex (Mo wt. ppm) |
220 |
220 |
- |
MoDTC (Mo wt.ppm) |
- |
- |
220 |
Ca detergent A (Ca wt.%) |
0.19 |
0.19 |
0.19 |
Ca detergent B (Ca wt.%) |
0.06 |
0.06 |
0.06 |
Ca detergent C (Ca wt.%) |
0.01 |
0.01 |
0.01 |
ZnDTP (P wt.%) |
0.04 |
0.04 |
0.04 |
Oxidation inhibitor (wt.%) |
1.0 |
1.0 |
1.0 |
VII (wt.%) |
5.0 |
5.0 |
5.0 |
Base oil |
remainder |
remainder |
remainder |
S content (wt.%) |
0.11 |
0.11 |
0.13 |
Friction coefficient |
0.05 |
0.12 |
0.05 |
HTT merit point |
7.5 |
7.5 |
5.5 |
Remarks:
[0068] The test results set forth in Table 1 indicate the following:
[0069] The lubricating oil composition of the invention comprising succinimide-Mo complex,
succinimide dispersant (Ashless dispersant A) and succinic ester dispersant (Ashless
dispersant B) in combination (Test oil of Example 1) shows the same high-temperature
deposit production-inhibiting power but markedly low friction coefficient as compared
with the lubricating oil composition (Test oil of Comparison Example 1) comprising
the succinimide-Mo complex and succinimide dispersant (Ashless dispersant A) in combination
but containing no succinic ester dispersant (Ashless dispersant B). Test oil of Comparison
Example 2 prepared by replacing the succinimide-Mo complex with the same amount of
MoDTC (sulfoxy molybdenum dialkyldithiocarbamate) shows the same friction coefficient
but poor power of inhibiting production of high-temperature deposit.
1. A lubricating oil composition for lubricating internal combustion engines which has
a sulfur content of 0.5 wt.% or less and which comprises a base oil having a lubricating
viscosity and at least the following additive components a) to e):
a) an ashless dispersant in an amount of 0.5-5.0 wt.% which comprises an alkenyl-
or alkyl-succinimide or a derivative thereof;
b) an ashless dispersant in an amount of 0.5-5.0 wt.% which comprises an alkenyl-
or alkyl-succinic ester or a derivative thereof;
c) a molybdenum complex of a basic nitrogen-containing compound in an amount of 50-1,200
wt.ppm in terms of a molybdenum content thereof;
d) an alkaline earth metal-containing detergent having a TBN in the range of 10 to
400 mg•KOH/g in an amount of 0.05-1.0 wt.% in terms of an alkaline earth metal content
thereof; and
e) an anti-wear agent in an amount of 0.05-5.0 wt.%.
2. The lubricating oil composition of claim 1, wherein the sulfur content is in the range
of 0.01 to 0.2 wt.%.
3. The lubricating oil composition of claim 1, wherein the sulfur content is in the range
of 0.05 to 0.12 wt.%.
4. The lubricating oil composition of claim 1, which is a multi-grade engine oil further
comprising a viscosity index improver, whereby being classified to OW5, OW10, OW15,
OW20, OW30, SW20, SW30, 10W20, or 10W30.
5. The lubricating oil composition of claim 1, wherein the component a) is contained
in an amount of 1.0-4.0 wt.%.
6. The lubricating oil composition of claim 1, wherein the component b) is contained
in an amount of 1.0-4.0 wt.%.
7. The lubricating oil composition of claim 1, wherein the ratio of the component a)
to the component b) is in the range of 1:4 to 4:1.
8. The lubricating oil composition of claim 1, wherein the component c) contains sulfur
not larger than 1 wt.%.
9. The lubricating oil composition of claim 1, wherein the component c) contains sulfur
in the range of 0.05 to 0.5 wt.%.
10. The lubricating oil composition of claim 1, wherein the component c) is a molybdenum
complex of a succinimide.
11. The lubricating oil composition of claim 1, wherein the component d) comprises an
alkaline earth metal salicylate.
12. The lubricating oil composition of claim 1, wherein the anti-wear agent is a zinc
dialkyldithiophosphate.
13. The lubricating oil composition of claim 1, which further comprises an oxidation inhibitor.
14. The lubricating oil composition of claim 1, which is employed for lubricating internal
combustion engines operated using a fuel oil having a sulfur content of 0.001 wt.%
or less.
15. A method for operating internal engines mounted to land-travelling vehicles using
a fuel having a sulfur content of 0.001 wt.% or less under lubrication with the lubricating
oil composition of claim 1.