[0001] This invention relates to methods of lubricating surfaces, in particular, to methods
of lubricating surfaces in internal combustion engines.
[0002] Developments in automotive vehicle and engine designs has led to use of a more varied
range of materials for manufacture of the engine components. In particular aluminum
alloys are increasingly being used to manufacture engine components.
[0003] In accordance with a first aspect of the present invention there is provided a method
of lubricating an aluminum alloy surface, which comprises supplying to said surface
a lubricating oil composition comprising an oil of lubricating viscosity, preferably
in a major amount, and an oil-soluble trinuclear organo-molybdenum compound.
[0004] It has been found that the trinuclear organo-molybdenum additive will substantially
reduce friction and surface wear on the aluminum containing alloy surfaces to an extent
not observed with dinuclear-organo-molybdenum compounds.
[0005] The aluminum alloy suitably comprises an aluminum-silicon alloy, which may additionally
contain a proportion of copper and/or magnesium. Suitably the aluminum alloy has a
hardness of 100-150 Hv, preferably 110-130 Hv and more preferably of about 120 Hv.
Suitably, the aluminum alloy has a density of 2.0-3.0 gcm
-3, preferably, 2.4-2.8 gcm
-3, and more preferably, about 2.6 gcm
-3.
[0006] Typically the trinuclear organo-molybdenum additive is used so as to provide 25 to
1000 ppm (parts per million, by weight), preferably 200 to 750 ppm, more preferably
400 to 600 ppm, and advatantageously 500 ppm of elemental molybdenum in the lubricating
oil compositions (as determined by ASTM D5185).
[0007] The lubricating oil composition of the first aspect of the invention may further
comprise an oil soluble, zinc dihydrocarbyl dithiophosphate (ZDDP) produced from a
primary alcohol, herein after referred to as primary ZDDP. Suitably, primary ZDDP
comprises at least 50%, preferably at least 75%, more preferably at least 90%, and
advantageously comprises substantially 100% ZDDP produced from primary.
[0008] The lubricating oil composition suitably comprises 0.2 to 1.0 mass %, preferably
0.4 to 0.8 mass %, and more preferably 0.6 ro 0.75 mass % primary ZDDP.
[0009] The method according the first aspect of the invention suitably involves provision
of lubrication between an aluminum alloy surface and a non-aluminum alloy surface,
such as a ferrous surface, for example.
[0010] A second aspect of this invention is an internal combustion engine having one or
more component parts made from an aluminum alloy, and contained in a reservoir in
the engine, a lubricating oil composition for lubricating said parts comprising an
oil of lubricating viscosity, preferably in a major amount, and an oil-soluble, trinuclear
organo-molybdenum compound. The reservoir in the engine may be a crankcase sump in
four-stroke engines, from where it is distributed around the engine for lubrication.
The invention is applicable to two-stroke and four-stroke spark-ignited and compression-ignited
engines.
[0011] A third aspect of the invention relates to the use of a lubricating oil composition
comprising an oil of lubricating viscosity and an oil-soluble, trinuclear organo-molybdenum
compound to lubricate an aluminum alloy surface.
[0012] A fourth aspect of the invention provides the use of an oil-soluble, trinuclear organo-molybdenum
compound in a lubricating oil composition to reduce the friction between surfaces,
one of which comprising an aluminum alloy.
[0013] In accordance with a fifth aspect of the present invention there has been discovered
a method of providing lubrication between two ferrous surfaces, one of the ferrous
surfaces comprising a chromium containing iron alloy conforming to British Standard
BS EN31 and the other ferrous surfaces comprises a cast iron alloy conforming to British
Standard BS EN1452, which method comprises supplying to said surface a lubricating
oil composition comprising an oil of lubricating viscosity, preferably in a major
amount, and an oil-soluble trinuclear organo-molybdenum compound.
[0014] It has been found that the trinuclear organo-molybdenum additive will substantially
reduce friction and surface wear on the ferrous surfaces to an extent not observed
with dinuclear-organo-molybdenum compounds.
[0015] Typically the trinuclear organo-molybdenum additive is used so as to provide 25 to
1000 ppm (parts per million, by weight), preferably 200 to 750 ppm, more preferably
400 to 600 ppm, and advatantageously 500 ppm of elemental molybdenum in the lubricating
oil compositions (as determined by ASTM D5185).
[0016] The lubricating oil composition of the fifth aspect of the invention may further
comprise an oil soluble, zinc dihydrocarbyl dithiophosphate (ZDDP) made from secondary
alcohol, hereinafter referred to as secondary ZDDP. Suitably, the secondary ZDDP comprises
at least 55%, preferably at least 79% and more preferably at least 85%, and may comprise
subatantially 100% ZDDP made from secondary alcohol.
[0017] The lubricating oil composition suitably comprises 0.2 to 1.0 mass %, preferably
0.4 to 0.8 mass %, and more preferably 0.6 to 0.75 mass % secondary ZDDP.
[0018] A sixth aspect of this invention is an internal combustion engine having a component
part made from a chromium containing ferrous alloy conforming with British Standard
BS EN31 adjacent a component part made from an iron alloy conforming with British
Standard BS EN1452, both compmeat parts being contained in a reservoir in the engine,
a lubricating oil composition for lubricating said parts comprising an oil of lubricating
viscosity, preferably in a major amount, and an oil-soluble, trinuclear organo-molybdenum
compound. The reservoir in the engine maybe a crankcase sump in four-stroke engines,
from where it is distributed around the engine for lubrication, The invention is applicable
to two-stroke and four-stroke spark-ignited and compression-ignited engines.
[0019] A seventh aspect of the invention relates to the use of a lubricating oil composition
comprising an oil of lubricating viscosity an oil-soluble, trinuclear organo-molybdenum
compound to provide lubrication between a chromium containing ferrous alloy surface
conforming with British Standard BS EN31 and an iron alloy surface conforming with
British Standard BS EN1452.
[0020] An eighth aspect of the invention provides the use of an oil-soluble, trinuclear
organo-molybdenum compound in a lubricating oil composition to reduce the friction
between a chromium containing ferrous alloy surface conforming with British Standard
BS EN31 and an iron alloy surface conforming with British Standard BS EN1452.
[0021] The methods of any aspect of this invention are especially applicable to the lubrication
of spark-ignited or compression-ignited two-stroke or four-stroke internal combustion
engines which have parts or components made from the specified materials. Examples
of such components include the cam shaft, especially the cam lobes; pistons, especially
the piston skirt; cylinder liners; and valves.
[0022] As examples of suitable oil-soluble, trinuclear organo-molybdenum compounds, there
may be mentioned dithiocarbamates, dithiophosphates, dithiophosphinates, xanthates,
thioxanthates and sulfides of molybdenum and mixtures thereof.
[0023] Additionally, the molybdenum compounds may be acidic molybdenum compounds. These
compounds will react with a basic nitrogen compound as measured by ASTM test D-664
or D-2896 titration procedure and are typically hexavalent. Included are molybdic
acid, ammonium molybdate, sodium molybdate, potassium molybdate, and other alkaline
metal molybdates and other molybdenum salts, e.g., molybdenum trioxide or similar
acidic molybdenum compounds.
[0024] A group of trinuclear organo-molybdenum compounds useful in the lubricating compositions
of this invention are those of the formula Mo
3S
kL
nQ
z and mixtures thereof wherein L represents independently selected ligands having organo
groups with a sufficient number of carbon atoms to render the compound soluble or
dispersible in the oil, n is from 1 to 4, k varies from 4 through 7, Q is selected
from the group of neutral electron donating compounds such as water, amines, alcohols,
phosphines, and ethers, and z ranges from 0 to 5 and includes non-stoichiometric values.
In the instance n is 3, 2 or 1, appropriately charged ionic species is required to
confer electrical neutrality to the trinuclear molybdenum compound. The ionic species
may be of any valence, for example, monovalent or divalent. Further the ionic species
may be negatively charged,
i,e. an anionic species, or may be positively charged,
i.
e. a cationic species or a combination of an anion and a cation. Such terms are known
to a skilled person in the art The ionic species may be present in the compound through
covalent bonding,
i.e. coordinated to one or more molybdenum atoms in the core, or through electrostatic
bonding or interaction as in the case of a counter-ion or through a form of bonding
intermediate between covalent and electrostatic bonding. Examples of anionic species
include disulfide, hydroxide, an alkoxide, an amide and a thiocyanste or derivate
thereof; preferably the anionic species is disulfide ion. Examples of cationic species
include an ammonium ion and a metal ion, such as an alkali metal, alkaline earth metal
or transition metal, ion, preferably an ammonium ion, such as [NR
4]
+ where R is independently H or alkyl group, more preferably R is H, i.e. [NH
4]
+. At least 21 total carbon atoms should be present among all the ligands' organo groups,
such as at least 25, at least 30, or at least 35 carbon atoms.
[0025] The ligands are independently selected from the group of:
and
mid mixtures thereof, wherein X, X
1, X
2, and Y are independently selected from the group of oxygen and sulfur, and wherein
R
1, R
2, and R are independently selected from hydrogen and organo groups that may be the
same or different Preferably, the organo groups are hydrocarbyl groups such as alkyl
(e,g., in which the carbon atom attached to the remainder of the ligand is primary
or secondary), aryl, substituted aryl and ether groups. More preferably, each ligand
has the same hydrocarbyl group.
[0026] The term "hydrocarbyl" denotes a substituent having carbon atoms directly attached
to the remainder of the ligand and is predominantly hydrocarbyl in character within
the context of this invention. Such substituents include the following:
1, Hydrocarbon substituents, that is, aliphatic (for example alkyl or alkenyl), alicyclic
(for example cycloalkyl or cycloalkenyl) substituents, aromatic-, aliphatic- and alicyclic-substituted
aromatic nuclei and the like, as well as cyclic substituents wherein the ring is completed
through another portion of the ligand (that is, any two indicated substituents may
together form an alicyclic group).
2. Substituted hydrocarbon substituents, that is, those containing non-hydrocarbon
groups which, in the context of this invention, do not alter the predominantly hydrocarbyl
character of the substituent. Those skilled in the art will be aware of suitable groups
(e.g., halo, especially chloro and fluoro, amino, alkoxyl, mercapto, alkylmercapto,
nitro, nitroso and sulfoxy).
3. Hetero substituents, that is substituents which, while predominantly hydrocarbon
in character within the context of this invention, contain atoms other than carbon
present in a chain or ring otherwise composed of carbon atoms.
[0027] Importantly, the organo groups of the ligands have a sufficient number of carbon
atoms to render the compound soluble or dispersible in the oil. For example, the number
of carbon atoms in each group will generally range between 1 to 100, preferably from
1 to 30, and more preferably between 4 to 20. Preferred ligands include dialkyldithiophosphate,
alkylxanthate, and dialkyldithiocarbamate, and of these dialkyldithiocarbamate is
more preferred. Organic ligands containing two or more of the above functionalities
are also capable of serving as ligands and binding to one or more of the cores. Those
skilled in the art will realize that formation of the compounds of the present invention
requires selection of ligands having the appropriate charge to balance the core's
charge.
[0028] Compounds having the formula Mo
3S
kL
nQ
z have cationic cores surrounded by anionic ligands and are represented by structures
such as
and
and have net charges of +4. Consequently, in order to solubilize these cores the total
charge among all the ligands must be -4. Four monoanionic ligands are preferred. Without
wishing to be bound by any theory, it is believed that two or more trinuclear cores
may be bound or interconnected by means of one or more ligands and the ligands may
be multidentate. Such structures fall within the scope of this invention. This includes
the case of a multidentate ligand having multiple connections to a single core. It
is believed that oxygen and/or selenium may be substituted for sulfur in the core(s).
[0029] Oil-soluble or oil-dispersible trinuclear molybdenum compounds can be prepared by
reacting in the appropriate liquid(s) and/or solvent(s) a molybdenum source such as
(NH
4)
2Mo
3S
13·n(H
2O), where n varies between 0 and 2 and includes non-stoichiometric values, with a
suitable ligand source such as a tetralkylthiuram disulfide. Other oil-soluble or
oil-dispersible trinuclear molybdenum compounds can be formed during a reaction in
the appropriate solvent(s) of a molybdenum source such as of (NH
4)
2Mo
3S
13·n(H
2O), a ligand source such as tetralkylthiuram disulfide, dialkyldithiocarbamate, or
dialkyldithiophosphate, and a sulfur-abstracting agent such cyanide ions, sulfite
ions, or substituted phosphines. Alternatively, a trinuclear molybdenum-sulfur halide
salt such as [M
1]
2[Mo
3S
7A
6], where M
1 is a counter ion, and A is a halogen such as Cl, Br, or I, may be reacted with a
ligand source such as a dialkyldithiocarbamate or dialkyldithiophosphate in the appropriate
liquid(s) and/or solvent(s) to form an oil-soluble or oil-dispersible trinuclear molybdenum
compound. The appropriate liquid and/or solvent may be, for example, aqueous or organic.
[0030] A compound's oil solubility or dispersibility may be influenced by the number of
carbon atoms in the ligand's organo groups. In the compounds employed in the present
invention, at least 21 total carbon atoms should be present among all the ligand's
organo groups. Preferably, the ligand source chosen has a sufficient number of carbon
atoms in its organo groups to render the compound soluble or dispersible in the lubricating
composition.
[0031] The molybdenum compound is preferably a trinuclear molybdenum dithiocarbamate.
[0032] Natural oils useful as the oil of lubricating viscosity (also known as basestocks)
in this invention include animal oils and vegetable oils (
e.g. castor, lard oil) liquid petroleum oils and hydrorefined, solvent-treated or acid-treated
mineral lubricating oils of the paraffinic, naphthenic and mixed paraffinic-naphthenic
types. Oils of lubricating viscosity derived from coal or shale are also useful base
oils.
[0033] Alkylene oxide polymers and interpolymers and derivatives thereof where the terminal
hydroxyl groups have been modified by esterification or etherification constitute
a class of known synthetic lubricating oils useful as basestocks in this invention.
These are exemplified by polyoxyalkylene polymers prepared by polymerization of ethylene
oxide or propylene oxide, the alkyl and aryl ethers of these polyoxyalkylene polymers
(
e.
g. methyl-poly isopropylene glycol ether having an average molecular weight of 1000,
diphenyl ether of poly-ethylene glycol having a molecular weight of 500-1000, diethyl
ether of polypropylene glycol having a molecular weight of 1000-1500); and mono- and
polycarboxylic esters thereof, for example, the acetic acid esters, mixed C
3-C
8 fatty acid esters and C
13 Oxo acid diester of tetraethylene glycol.
[0034] Another suitable class of synthetic lubricating oils useful in this invention comprises
the esters of dicarboxylic acids (
e.
g. phthalic acid, succinic acid, alkyl succinic acids and alkenyl succinic acids, maleic
acid, azelaic acid, suberic acid. sebasic acid, furnaric acid, adipic acid, linoleic
acid dimer, malonic acid, alkylmalonic acids, alkenyl malonic acids) with a variety
of alcohols (i-butyl alcohol, hexyl alcohol, dodecyl alcohol, 2-ethylhexyl alcohol,
ethylene glycol, diethylene glycol monoether, propylene glycol). Specific examples
of these esters include dibutyl adipate, di(2-ethylhexyl) sebacate, di-n-hexyl fumarate,
dioctyl sebacate, diisooctyl azelate, diisodecyl azelate, dioctyl phthalate, didecyl
phthalate, dicicosyl scbacate, the 2-ethylhexyl diester of linoleic acid dimer, and
the complex ester formed by reacting one mole of sebacic acid with two moles of tetraethylene
glycol and two moles of 2-ethylhexanoic acid.
[0035] Esters useful as synthetic oils also include those made from C
5 to C
12 monocarboxylic acids and polyols and polyol ethers such as neopentyl glycol, trimethylolpropane,
pentaerythritol, dipentaerythritol and tripentaerythritol.
[0036] Silicon-based oils such as the polyalkyl-, polyaryl-, polyalkoxy-, or polyaryloxysiloxane
oils and silicate oils comprise another useful class of synthetic lubricants; they
include tetracthyl silicate, tetraisopropyl silicate, tetra-(2-ethylhexyl) silicate,
tetra-(4-methyl-2-ethylhexyl) silicate, tetra-(p-tertbutylphenyl) silicate, hexa-(4-methyl-2-pentoxy)
disiloxane, poly(methyl) siloxanes and poly(methylphenyl) siloxanes. Other synthetic
lubricating oils include liquid esters of phosphorus-containing acids (
e.
g. tricresyl phosphate, trioctyl phosphate, diethyl ester of decylphosphonic acid)
and polymeric tetrahydrofurans.
[0037] Unrelined, refined and refined oils can be used in the lubricating oil compositions
of the present invention. Unrefined oils are those obtained directly from a natural
or synthetic source without further purification treatment. For example, a shale oil
obtained directly from retorting operations, a petroleum oil obtained directly from
distillation or ester oil obtained directly from an esterification proces and used
without further treatment would be an unrefined oil. Refined oils are similar to the
unrefined oils except they have been further treated in one or more purification steps
to improved one or more properties, Many such purification techniques, such as distillation,
solvent extraction, acid or base extraction, filtration and percolation are known
to those skilled in the art. Rerefined oils are obtained by processes similar to those
used to obtain refined oils applied to refined oils which have been already used in
service. Such rerefined oils are also known as reclaimed, or reprocessed oils and
often are additionally processed by techniques for removal of spent additives and
oil breakdown products.
[0038] Lubricating oil compositions for use in any aspect of the present invention may also
contain any of the conventional additives listed below (including any additional friction
modifiers) which are typically used in a minor amount,
e.
g. such an amount so as to provide their normal attendant functions. Typical amounts
for individual components are also set forth below. All the values listed are stated
as mass percent active ingredient in the total lubricating oil composition.
ADDITIVE |
MASS % (Broad) |
MASS% (preferred) |
Ashless Dispersant |
0.1 - 20 |
1 - 8 |
Metal Detergents |
0.1 - 15 |
0.2 - 9 |
Corrosion Inhibitors |
0 - 5 |
0 - 1.5 |
Metal Dihydrocarbyl Dithiophosphate |
0,1 - 6 |
0.1 - 4 |
Anti-oxidant |
0 - 5 |
0.01 - 3 |
Pour Point Depressant |
0.01 - 5 |
0.01 - 1.5 |
Anti-foaming Agent |
0 - 5 |
0.001 - 0.15 |
Supplemental Anti-wear Agents |
0 - 5 |
0 - 2 |
Additional Friction Modifier |
0 - 5 |
0 - 1.5 |
Viscosity Modifier |
0 - 6 |
0.01 - 4 |
[0039] The individual additives may be incorporated into a basestock in any convenient way.
Thus, each of the components can be added directly to the basestock by dispersing
or dissolving it in the basestock at the desired level of concentration. Such blending
may occur at ambient temperature or at an elevated temperature.
[0040] Preferably, all the additives except for the viscosity modifier and the pour point
depressant are blended into a concentrate (or additive package) that is subsequently
blended into basestock to make a finished lubricating oil composition. Use of such
concentrates is conventional. The concentrate will typically be formulated to contain
the additive(s) in proper amounts to provide the desired concentration in the final
lubricating oil composition when the concentrate is combined with a predetermined
amount of base oil.
[0041] The concentrate is conveniently made in accordance with the method described in U.S.
4,938,880. That patent describes making a pre-mix of ashless dispersant and metal
detergents that is pre-blended at a temperature of at least about 200°C. Thereafter,
the pre-mix is cooled to at least 85°C and the additional components are added.
[0042] The final crankcase lubricating oil composition may employ from 2 to 20 mass % and
preferably 4 to 15 mass % of the concentrate (or additive package), the remainder
being base oil.
[0043] Ashless dispersants maintain in suspension oil-insoluble matter resulting from oxidation
of the oil during wear or combustion. They are particularly advantageous for preventing
precipitation of sludge and formation of varnish, particularly in gasoline engines.
[0044] Ashless dispersants comprise an oil-soluble polymeric hydrocarbon backbone bearing
one or more functional groups that are capable of associating with particles to be
dispersed. Typically, the polymer backbone is by amine, alcohol, amide, or ester polar
moieties, often via a bridging group. The ashless dispersant may be, for example,
selected from oil-soluble salts, esters, amino-esters, amides, imides, and oxazolines
of long chain hydrocarbon substituted mono and dicarboxylic acids or their anhydrides;
thiocarboxylate derivatives of long chain hydrocarbons; long chain aliphatic hydrocarbons
having a polyamine attached directly thereto; and Mannich condensation products formed
by condensing a long chain substituted phenol with formaldehyde and polyalkylene polyamine.
[0045] The oil-soluble polymeric hydrocarbon backbone of these dispersants is typically
derived from an olefin polymer or polyene, especially polymers comprising a major
molar amount (
i.
e. greater than 50 mole %) of a C
2 to C
18 olefin (
e.
g. ethylene, propylene, butylene, isobutylene, pentene, octene-1, styrene), and typically
a C
2 to C
5 olefin. The oil-soluble polymeric hydrocarbon backbone may be a homopolymer (
e.
g. polypropylene or polyisobutylene) or a copolymer of two or more of such olefins
(
e.
g. copolymers of ethylene and an alpha-olefin such as propylene or butylene, or copolymers
of two different alpha-olefins). Other copolymers include those in which a minor molar
amount of the copolymer monomers, for example, I to 10 mole %, is an α,ω-diene, such
as a C
3 to C
22 non-conjugated diolefin (for example, a copolymer of isobutylene and butadiene, or
a copolymer of ethylene, propylene and 1,4-hexadiene or 5-ethylidene-2-norbornene).
Preferred are polyisobutenyl (Mn 400-2500, preferably 950-2200) succinimide dispersants.
[0046] The viscosity modifier (VM) functions to impart high and low temperature operability
to a lubricating oil composition. The VM used may have that sole function, or may
be multifunctional.
[0047] Multifunctional viscosity modifiers that also function as dispersants are also known.
Suitable viscosity modifiers are polyisobutylene, copolymers of ethylene and propylene
and higher alpha-olefins, polymethacrylates, polyalkylmethacrylates, methacrylate
copolymers, copolymers of an unsaturated dicarboxylic acid and a vinyl compound, inter
polymers of styrene and acrylic ester, and partially hydrogenated copolymers of styrene/isoprene,
styrene/butadiene, and isoprene/butadiene, as well as the partially hydrogenated homopolymers
of butadiene and isoprene and isoprene/divinylbenzene.
[0048] Metal-containing or ash-forming detergents may be present and these function both
as detergents to reduce or remove deposits and as acid neutralizers or rust inhibitors,
thereby reducing wear and corrosion and expending engine life. Detergents generally
comprise a polar head with a long hydrophobic tail, the polar head eompdsing a metal
salt of an acid organic compound. The salts may contain a substantially stoichiometric
amount of the metal in which they are usually described as normal or neutral salts,
and would typically have a total base number (TBN), as may be measured by ASTM D-2896
of from 0 to 80. It is possible to include large amounts of a metal base by leading
an excess of a metal compound such as an oxide or hydroxide with an acid gas such
as carbon dioxide. The resulting overbased detergent comprises neutralized detergent
as the outer layer of a metal base (
e.
g. carbonate) micelle. Such overbased detergents may have a TBN of 150 or greater,
and typically from 250 to 450 or more. Detergents that may be used include oil-soluble
neutral and overbased sulfonates, phenates, sulfurized phenates, thiophosphonates,
salicylates, and naphthenates and other oil-soluble carboxylates of a metal, particularly
the alkali,
e.
g. sodium, potassium, lithium and magnesium. Preferred are neutral or overbased calcium
and magnesium phenates and sulfonates, especially calcium.
[0049] Other friction modifiers include oil-soluble amines, amides, imidazolines, amine
oxides, amidoamines, nitriles, alkanolamides, alkoxylated amines and ether amines;
polyol esters; and esters of polycarboxylic acids.
[0050] Dihydrocarbyl dithiophosphate metal salts are frequently used as anti-wear and antioxidant
agents. The metal may be an alkali or alkaline earth metal, or aluminum, lead, tin,
molybdenum, manganese, nickel or copper. They may be prepared in accordance with known
techniques by first forming a dihydrocarbyl dithiophosphoric acid (DDPA), usually
by reaction of one or more alcohol or a phenol with P
2S
5 and then neutralizing the formed DDPA with a zinc compound. For example, a dithiophosphoric
acid may be made by reacting mixtures of primary and secondary alcohols. Alternatively,
multiple dithiophosphoric acids can be prepared where the hydrocarbyl groups on one
are entirely secondary in character and the hydrocarbyl groups on the others are entirely
primary in character. To make the zinc salt, any basic or neutral zinc compound may
be used but oxides, hydroxides and carbonates are most generally employed. Commercial
additives frequently contain an excess of zinc due to use of an excess of the basic
zinc compound in the neutralization reaction.
[0051] ZDDP provides excellent wear protection at a comparatively low cost and also functions
as an antioxidant. However, there is some evidence that phosphorus in lubricant can
shorten the effective life of automotive emission catalysts. Accordingly, the lubricating
oil compositions of the invention preferably contain no more than 0,8 wt %, such as
from 50 ppm to 0.06 wt %, of phosphorus. Independently of the amount of phosphorus,
the lubricating oil composition preferably has no more than 0.5 wt %, preferably from
50 ppm to 0.3 wt %, of sulfur, the amounts of sulfur and of phosphorus being measured
in accordance with ASTM D5185.
[0052] Oxidation inhibitors or antioxidants reduce the tendency of basestocks to deteriorate
in service, which deterioration can be evidenced by the products of oxidation such
as sludge and varnish-like deposits on the metal surfaces and by viscosity growth.
Such oxidation inhibitors include hindered phenols, alkaline earth metal salts of
alkylphenolthioesters having preferably C
5 to C
12 alkyl side chains, calcium nonylphenol sulfide, ashless oil-soluble phenates and
sulfurized phenates, phosphosulfurized or sulfurized hydrocarbons, phosphorous esters,
metal thiocarbamates, oil-soluble copper compound as described in U.S. 4,867,890,
and molybdenum-containing compounds.
[0053] Rust inhibitors selected from the group consisting of nonionic polyoxyalkylene polyols
and esters thereof, polyoxyalkylene phenols, and anionic alkyl sulfonic acids may
be used.
[0054] Copper- and lead-bearing corrosion inhibitors may be used, but are typically not
required in the lubricating oil compositions of the present invention. Typically such
compounds are thiadiazole polysulfides containing from 5 to 50 carbon atoms, their
derivatives and polymers thereof. Derivatives of 1,3,4-thiadiazoles, such as those
described in U.S. Patent Nos. 2,719,125; 2,719,126; and 3,087,932, are typical Other
similar material are described in U.S. Patent Nos, 3,821,236; 3,904,537; 4,097,387;
4,107,059; 4,136,043; 4,188,299; and 4,193,882. Other additives are thio and polythio
snlfenamides of thiadiazoles such as those described in GB-A-1,560,830. Benzotriazoles
derivatives also fall within this class of additive. When these compounds are included
in the lubricating oil compositionS, they are preferably present in an amount not
exceeding 0.2 wt.% active ingredient.
[0055] A small amount of a demulsifying component may be used. A preferred demulsifying
component is described in EP-A-330 522. It is obtained by reacting an alkylene oxide
with an adduct obtained by reacting a bis-epoxide with a polyhydric alcohol. The demulsifier
should be used at a level not exceeding 0.1 mass % active ingredient. A treat rate
of 0.001 to 0.05 mass % active ingredient is convenient.
[0056] Pour point depressants, otherwise known as lube oil improvers, lower the minimum
temperature at which the fluid will flow or can be poured. Such additives are well-known.
Typical of those additives, which improve the low temperature fluidity of the fluid,
are C
8 and C
18 dialkyl fumarate/vinyl acetate copolymers and polyalkylmethacrylates.
[0057] Foam control can be provided by many compounds including an antifoamant of the polysiloxane
type, for example, silicone oil or polydimethyl siloxane.
[0058] In this specification, the term "comprising" (or cognates such as "comprises") means
the presence of stated features, integers, steps or components, but does not preclude
the presence or addition of one or more other features, integers, steps, components
or groups thereof. If the term "comprising" (or cognates) is used herein, the term
"consisting essentially of" (and its cognates) is within its scope and is a preferred
embodiment; consequently the term "consisting of" (and its cognates) is within the
scope of "consisting essentially of" and is a preferred embodiment thereof.
[0059] The terms "oil-soluble" or "oil-dispersible" do not mean that the compounds are soluble,
dissolvable, miscible or capable of being suspended in the oil in all proportions.
They do mean, however, that the compounds are, for instance, soluble or stably dispersible
in the oil to an extent sufficient to exert their intended effect in the environment
in which the composition is employed. Moreover, the additional incorporation of other
additives such as those described above may affect the solubility or dispersibility
of the compounds.
[0060] The term "major amount" means in excess of 50 mass % of the composition.
[0061] The term "minor amount" means less than 50 mass % of the composition.
[0062] The invention is further illustrated by the following examples which are not to be
considered as limitative of its scope. All percentages are by weight active ingredient
content of an additive without regard for carrier or diluent oil.
EXAMPLES
[0063] All of the following experiments were carried out using were obtained using a Cameron
Plint reciprocating pin on plate tribometer, using the following test protocol:
Test duration |
8 hours |
Load (N) |
185 |
Stroke length (mm) |
10 |
Frequency (Hz) |
1 |
Temperature (°C) |
100 |
[0064] The surface materials used are as set out below:
[0065] The coefficients of friction and wear coefficients for the lubrication of various
surface combinations with a each of the following lubricant compositions, were measured:
1. a Group III base oil having a kinematic viscosity at 100°C of 4.2 µm2s-1 (CSt);
2. a composition containing the base oil of composition 1 and 500 ppm of molybdenum
as trinuclear molybdenum dithiocarbamate, having a structural formula as shown below,
3. a composition containing the base oil of composition 1 and 500 ppm of molybdenum
as dinuclear molybdenum dithiocarbamate, having a structural formula as shown below,
4. a composition according to composition 2 additionally comprising a minor amount
of a secondary ZODP additive, and
5. a composition according to composition 2 additionally comprising a minor amount
of a primary ZDDP.
Example 1 BS EN1452 pin on Al-Si alloy plate
[0066] A comparison of friction coefficient for Compositions 1, 2 and 3 is set out in Table
1 and Graph 1. A comparison of wear coefficient for Compositions 1, 2 and 3 is set
out in Graph 2.
[0067] It can be seen from Table 1 and Graph 1 below, that Composition 2, containing the
trinuclear organo-molybdenum compound, exhibits a significantly lower friction coefficient
than Composition 1 or 2. Furthermore, the coefficient of friction for Composition
2 continues to reduce as the test proceeds, unlike Composition 1 or 3, for which the
friction coefficient increases as the test proceeds.
[0068] A comparison of the percentage improvement in friction coefficient of Composition
2 compared to Composition 1 at equivalent points in the test also illustrates the
generally increasing reduction of friction coefficient of Composition 2 compared to
Composition 1. In addition, Table 1 illustrates that Composition 2 performs significantly
more effectively at reducing the coefficient of friction than Composition 3, which
generally performs less well than Composition 1 (as indicated by the negative prefix).
Table 1 (Friction Coefficient)
Time (min) |
Comp.1 |
Comp.2 |
Comp.3 |
Comp.2 % Improvement |
Comp.3 % Improvement |
0 |
0.0895 |
0.0933 |
0.0920 |
-4.25 |
-2.79 |
30 |
0.0933 |
0.1094 |
0.1141 |
-17.26 |
-22.29 |
60 |
0.1077 |
0.1014 |
0.1253 |
5.85 |
-16.34 |
90 |
0.1105 |
0.0988 |
0.1249 |
10.59 |
-13.03 |
120 |
0.1164 |
0.0958 |
0.1203 |
17.70 |
-3.35 |
150 |
0.1222 |
0.0936 |
0.1218 |
29.31 |
0.32 |
180 |
0.1310 |
0.0926 |
0.1351 |
28.77 |
-3.13 |
210 |
0.1300 |
0.0896 |
0.1463 |
31.08 |
-12.54 |
240 |
0.1406 |
0.0892 |
0.1481 |
36.56 |
-5.33 |
270 |
0.1509 |
0.0871 |
0.1535 |
42.28 |
-1.72 |
300 |
0.1406 |
0.0868 |
0.1494 |
38.26 |
-6.26 |
330 |
0.1500 |
0.0842 |
0.1578 |
43.87 |
-5.20 |
360 |
0.1361 |
0.0847 |
0.1606 |
37.77 |
-18.00 |
390 |
0.1293 |
0.0836 |
0.1555 |
35.34 |
-20.26 |
420 |
0.1448 |
0.0833 |
0.1558 |
42.47 |
-20.49 |
450 |
0.1488 |
0.0805 |
0.1606 |
45.90 |
-7.93 |
480 |
0.1595 |
0.0777 |
0.1610 |
51.29 |
-0.94 |
Note: % Improvement is measured relative to Composition 1 |
[0069] From Graph 2 below, it can be seen that the alumina plate suffers significantly lower
wear when lubricated with Composition 2, containing the trinuclear organo-molybdenum
compound, than when lubricated with lubricating Composition 1 or 3.
[0070] A comparison of friction coefficient for Compositions 2, 4 and 5 is set out is Table
2 and Graph 3.
[0071] From Graph 3 it can be seen that Composition 5 exhibits a lower friction coefficient
than Composition 4. Although, addition of ZDDP to the trinuclear organo-molybdenum
containing composition, Composition 2, has a negative impact on the friction reduction
associated with the trinuclear molybdenum campound, the above graph shows that the
primary ZDDP of Composition 5 has a less detrimental effect on the friction coefficient
than secondary ZDDP of Composition 4.
Table 2 (Friction Coefficient)
Time (min) |
Comp. 2 |
Comp. 4 |
Comp.5 |
0 |
0.0933 |
0.1006 |
0.1512 |
30 |
0.1094 |
0.1105 |
0.1218 |
60 |
0.1014 |
0.1279 |
0.1348 |
90 |
0.0988 |
0.1347 |
0.1362 |
120 |
0.0958 |
0.1366 |
0.1325 |
150 |
0.0936 |
0.1422 |
0.1348 |
180 |
0.0926 |
0.1455 |
0.1344 |
210 |
0.0896 |
0.1501 |
0.1395 |
240 |
0.0892 |
0.1524 |
0.1397 |
270 |
0.0871 |
0.1529 |
0.1344 |
300 |
0.0868 |
0.1531 |
0.1392 |
330 |
0.0842 |
0.1520 |
0.1400 |
360 |
0.0847 |
0.1557 |
0.1388 |
390 |
0.0836 |
0.1568 |
0.1389 |
420 |
0.0833 |
0.1604 |
0.1391 |
450 |
0.0805 |
0.1607 |
0.1387 |
480 |
0.0777 |
0.1603 |
0.1396 |
Example 2 BS EN1452 pin on a BS EN31 plate
[0072] A comparison of friction coefficient for Compositions 1, 2 and 3 is set out in Table
3 and Graph 4. A comparison of wear coefficient for Compositions 1, 2 and 3 is set
out in Graph 5.
[0073] From Table 3 and Graph 4 below, it can be seen that composition 2, comprising the
trinuclear organo-molybdenum compound, results in significantly lower friction coefficient
than lubricant Compositions 1 or 3. The percentage improvement figures in Table 3
illustrate that Composition 2 provides an increasingly better friction performance
when compared with either Composition 1 or 3, as the test proceeds. Graph 4 and Table
3 also illustrates that Composition 3, comprising dinuclear molybdenum actually exhibits
coefficients of friction that are higher than Composition 1, with no molybdenum additive.
Table 3 (Friction Coeficient)
Time (min) |
Comp. 1 |
Comp. 2 |
Comp.3 |
Comp. 2 % Improvement |
Comp. 3 % Improvement |
0 |
0.1537 |
0.1303 |
0.1437 |
6.51 |
6.51 |
30 |
0.1228 |
0.0888 |
0.1539 |
27.69 |
-25.33 |
60 |
0.1302 |
0.0909 |
0.1486 |
30.18 |
-14.13 |
90 |
0.1372 |
0.0921 |
0.1626 |
32.87 |
-18.51 |
120 |
0.1463 |
0.0953 |
0.1825 |
34.86 |
-24.74 |
150 |
0.1606 |
0.0980 |
0.1816 |
38.98 |
-13.08 |
180 |
0.1494 |
0.0990 |
0.1943 |
33.73 |
-30.05 |
210 |
0.1574 |
0.0988 |
0.1935 |
37.23 |
-22.94 |
240 |
0.1593 |
0.1012 |
0.1981 |
36.47 |
-24.36 |
270 |
0.1557 |
0.1013 |
0.1832 |
34.94 |
-17.66 |
300 |
0.1640 |
0.0992 |
0.1954 |
39.51 |
-19.15 |
330 |
0.1641 |
0.1010 |
0.1758 |
38.45 |
-7.13 |
360 |
0.1715 |
0.1015 |
0.2115 |
40.82 |
-23.32 |
390 |
0.1664 |
0.1006 |
0.2142 |
39.54 |
-28.73 |
420 |
0.1635 |
0.0995 |
0.2197 |
39.14 |
-34.37 |
450 |
0.1717 |
0.1003 |
0.2184 |
41.58 |
-27.20 |
480 |
0.1752 |
0.1019 |
0.2183 |
41.84 |
-24.60 |
Note: % Improvement is measured relative to Composition 1 |
[0074] From Graph 5 below, it can be seen that the BS EN31 plate exhibits significantly
less wear when lubricated with Composition 2 than with either of lubricating Compositions
1 or 3.
[0075] A comparison of friction coefficient for Compositions 2, 4 and 5 is set out in Table
4 and Graph 6,
[0076] From Table 4 and Graph 6 below, it can be seen that lubricating Composition 4 effects
a greater reduction in friction coefficient than either of lubricating Compositions
2 or 5. Suprisingly, when lubricating a BS EN1452 pin on a BS EN31 plate addition
of secondary ZDDP additive (Composition 4) to a lubricant containing trinuclar molybdenum
improves the coefficient of friction. It is noted that addition of primary ZDDP (Composition
5) to the lubricant in place of secondary ZDDP has a detrimental effect of the coefficient
of friction.
Table 4 (Friction Coeficient)
Time (min) |
Comp. 2 |
Comp. 4 |
Comp. 5 |
0 |
0.1303 |
0.1225 |
0.1207 |
30 |
0.0888 |
0.0991 |
0.1170 |
60 |
0.0909 |
0.1013 |
0.1140 |
90 |
0.0921 |
0.1016 |
0.1177 |
120 |
0.0953 |
0.0988 |
0.1163 |
150 |
0.0980 |
0.0935 |
0.1169 |
180 |
0.0990 |
0.0942 |
0.1189 |
210 |
0.0988 |
0.0737 |
0.1196 |
240 |
0.1012 |
0.0637 |
0.1213 |
270 |
0.1013 |
0.0650 |
0.1204 |
300 |
0.0992 |
0.0650 |
0.1208 |
330 |
0.1010 |
0.0656 |
0.1204 |
360 |
0.1015 |
0.0648 |
0.1206 |
390 |
0.1006 |
0.0682 |
0.1227 |
420 |
0.0995 |
0.0698 |
0.1227 |
450 |
0.1003 |
0.0707 |
0.1245 |
480 |
0.1019 |
0.0710 |
0.1267 |