Note: Descriptions are shown in the official language in which they were submitted.
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2151582
LUBRICATING OIL COMPOSITION FOR USE IN FINAL DRIVE
Field of the Invention
The present invention relates to a novel lubricating oil
composition for use in a final drive, and more particularly to a
lubricating oil composition for use in a final drive for use in a car
of a front- engine and rear-wheel-drive system or the like, which
composition improves the efficiency of transmission in a differential
gear under various conditions such as the input torque, the input
number of revolutions and the temperature of the oil, as compared with
the conventional ones comprising S-containing and P-cont~ining additives
blended therein.
Prior Art
The final drive of a ca,r has a function (1) of further decreasing a
driving force decreased by a transmission and rectangularly changing
the direction of the force, and a differential function (2) of securing
smooth driving even when a difference in revolution arises between right
and left driving wheels at the time of turning the car around. The
former function is performed by a decelerator, while the latter
function is performed by a differential gear. The decelerator is
constituted of a decelerating pinion and a decelerating gear wheel.
Hypoid gears are generally used as such decelerating pinion and gear
wheel.
On the other hand, the differential gear (differential) is
constituted of two or four differential pinions and two differential
gear wheels engaged therewith, which are built in a differential gear
box. The differential pinions, which are connected to the differential
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gear box by means of a shaft, is capable of orbital revolution together
with the gear box while revolving on its own axis around the shaft.
Consequently, a difference in revolution between the interior and
exterior driving wheels can be mechanistically absorbed even if such a
difference arises when the car is turned around.
The hypoid gears of a gear transmission mechanism as is used in the
foregoing final drive of the car are exposed to severe conditions such
as a high speed of revolution and a heavy load, leading to the necessity
for a gear oil excellent in seizing-proofing and abrasion-proofing
properties. Accordingly, use is generally made of a gear oil comprising
a base oil admixed with a sulfur-cont~in;ng extreme-pressure additive
such as an olefin sulfide or an alkyl sulfide and a phosphorus-
containing extreme-pressure additive such as a phosphoric ester, a
phosphorous ester or an alkylamine salt of a phosphoric ester, wherein
the sulfur-containing extreme-pressure additive improves the above-
mentioned seizing-proofing properties while the phosphorus-containing
extreme-pressure additive improves the above-mentioned abrasion-
proofing properties.
In the case of such a conventional gear oil comprising S-cont~ining
and P-cont~ining additives blended therein to impart thereto extreme-
pressure properties and abrasion-proofing properties, however, the
efficiency of transmission in a differential gear is about 90 to 95%
depending on variable conditions such as the input torque, the input
number of revolutions and the temperature of the oil, and hence is not
necessarily satisfactory. Thus, it has been desired to develop a
lubricating oil composition for use in a final drive which composition
improves the efficiency of transmission in a differential gear under
various conditions such as the input torque, the input number of
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revolutions and the temperature of the oil to thereby decrease the cost
of fuel.
Disclosure of the Invention
Under such circumstances, an object of the present invention is to
provide a lubricating oil composition for use in a final drive for use
- in a car of a front-engine and rear-wheel-drive system or the like,
which composition improves the efficiency of transmission in a
differential gear under various conditions such as the input torque, the
input number of revolutions and the temperature of the oil and hence
decreases the cost of fuel, as compared with the conventional ones
comprising S-cont~ining and P-containing additives blended therein.
Means for Solving the Problems
As a result of intensive investigations with a view to developing a
lubricating oil composition for use in a final drive which composition
has the foregoing favorable properties, the inventors of the present
invention have found out that the above-mentioned object can be
attained by a lubricating oil composition comprising a lubricant base
oil, and a sulfurized oxymolybdenum organophosphorodithioate, a sulfur-
containing extreme-pressure additive and a phosphorus-containing
extreme-pressure additive each in a given amount. The present
invention has been completed based on such a finding.
Specifically, in accordance with the present invention, there is
provided a lubricating oil composition for use in a final drive
characterized by comprising lubricant base oil(s); (A) 1 to 10 wt. %,
based on the total weight of the composition, of sulfurized
oxymolybdenum organophosphorodithioate(s) represented by the general
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formula [1]:
[(RlO)(R'O)(S)P-S-]2-MO2S pO q ...[1]
(wherein R1 and R2, which may be either the same or different from
each other, are an alkyl or alkenyl group having 4 to 18 carbon atoms;
and p and q are each a positive integer, provided that the sum of both
is 4); (B) 3 to 15 wt. %, based on the total weight of the composition,
of at least one sulfur-contAining extreme-pressure additive selected
from among olefin sulfides and alkyl sulfides; and (C) 0.1 to 5 wt. %,
based on the total weight of the composition, of at least one
phosphorus-containing extreme-pressure additive selected from among
phosphoric esters, phosphorous esters, and alkylamine salts of
phosphoric esters.
srief Description of the Drawings
Fig. 1 is a schematic diagram of an apparatus as used in the LFW-1
friction test.
Fig. 2 is graphs showing the relationships between the input torque
and the efficiency of transmission in the cases of respectively using a
lubricating oil according to the present invention and an S-P blend
oil.
Preferable embodiments of the Invention
The present invention will now be described in detail.
Examples of the base oil to be used in the lubricating oil
composition of the present invention, though not particularly
restricted, include common base oils for use in the conventional
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lubricating oils, such as mineral and synthetic oils.
Examples of the mineral oils include 60 neutral oil, 100 neutral
oil, 150 neutral oil, 300 neutral oil, and 500 neutral oil, which are
prepared by refining with a solvent or through hydrogenation; and low-
pour-point base oils improved in fluidity at low temperatures by
removing wax from the above-enumerated base oils. These mineral oils
may be used either alone or in mixture wherein at least two kinds of
mineral oils are mixed together in a suitable proportion.
On the other hand, examples of the synthetic oils include a -
olefin oligomers, diesters, polyol esters, and polyglycol esters.
These base oils may usually be used alone, but may also be used in
mixture with mineral oil(s) as mentioned above. In the latter case,
the mixing weight ratio of a synthetic oil to mineral oil(s) is, for
example, in the range of 80:20 to 20:80.
The viscosity at 10.0 ~C of the base oil to be used in the
composition of the present invention is preferably in the range of 3 to
20 cSt.
The component (A) to be used in the lubricating oil composition of
the present invention is sulfurized molybdenum organop
hosphorodithioate(s) (MoDTP) represented by the general formula [1]:
[(RlO)(R'O)(S)P-S-]2-MO2S pO q ...[1]
In the above-mentioned formula [1], Rl and R', which may be either
the same or different from each other, are an alkyl or alkenyl group
having four to 18 carbon atoms, which group may be linear, branched, or
cyclic; and p and q are each a positive integer, provided that the sum
of both is four. Examples of Rl and R' include butyl, pentyl, hexyl,
cyclohexyl, octyl, 2-ethylhexyl, decyl, lauryl, myristyl, palmityl,
stearyl, butenyl, pentenyl, octenyl and oleyl groups.
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Specific examples of MoDTP represented by the above-mentioned
general formula [1] include sulfurized oxymolybdenum butyl
phosphorodithioate, sulfurized oxymolybdenum pentyl phosphorodithioate,
sulfurized oxymolybdenum hexyl phosphorodithioate, sulfurized
oxymolybdenum octyl phosphorodithioate, sulfurized oxymolybdenum 2-
ethylhexyl phosphorodithioate, sulfurized oxymolybdenum decyl
phosphorodithioate, sulfurized oxymolybdenum lauryl phosphorodithioate,
sulfurized oxymolybdenum stearyl phosphorodithioate, sulfurized
oxymolybdenum butenyl phosphorodithioate, sulfurized oxymolybdenum
pentenyl phosphorodithioate, sulfurized oxymolybdenum 2-ethylhexenyl
phosphoro-dithioate, sulfurized oxymolybdenum oleyl phosphoro-
dithioate, and sulfurized oxymolybdenum cyclohexyl phosphorodithioate.
These MoDTP compounds may be used either alone or in combination of
two or more kinds thereof. The amount of MoDTP to be blended in the
composition is in the range of 1 to 10 wt. %, preferably 1 to 7 wt. %,
based on the total weight of the composition. When the amount is
smaller than 1 wt. %, no effect of improving the efficiency of
transmission in a differential gear under various conditions such as the
input torque, the input number of revolutions and the temperature of
the oil can sufficiently be exhibited. When it exceeds 10 wt. %, the
resulting improvement in the above-mentioned effect is not worth an
increase in the amount, and troubles such as sludge are liable to be
caused.
The component (B) to be used in the lubricating oil composition of
the present invention is at least one sulfur-containing extreme-pressure
additive selected from among olefin sulfides and alkyl sulfides.
Examples of the olefin sulfides include compounds represented by the
general formula [2]:
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R3-Sx-R~ ...................... [2]
In the above-mentioned general formula [2], R3 is an alkenyl group
having 4 to 12 carbon atoms; R~ is an alkyl or alkenyl group having 4
to 12 carbon atoms; R3 and R~ are each linear, branched, or cyclic; and
x is an integer of 1 to 8. A representative example of the olefin
sulfides is isobutylene sulfide (X=l).
On the other hand, examples of the alkyl sulfides include compounds
represented by the general formula [3]:
Rs-sy_R6 ...[3]
In the above-mentioned general formula [3], Rs and R6, which may be
either the same or different from each other, are each an alkyl group
having 4 to 12 carbon atoms, which group may be linear, branched, or
cyclic; and y is an integer of 1 to 8. Representative examples of the
alkyl sulfides include di-t-butyl disulfide and di-t-butyl trisulfide.
In the composition of the present invention, these sulfur-
cont~ining extreme-pressure additives may be used either alone or in
combination of two or more kinds thereof as the component (B), the
amount of which to be blended therein is in the range of 3 to 15 wt. ~,
preferably 5 to 10 wt. %, based on the total weight of the composition.
The sulfur-containing extreme-pressure additive generally forms a
sulfurized skin in a frictional surface, and hence functions in such a
way as to improve the load resistance performance of the base oil(s).
When the above-mentioned amount is smaller than 3 wt. ~, the foregoing
functional effect cannot sufficiently be exhibited to make the
resulting composition unsuitable as a gear oil for use in a car. When
it exceeds 15 wt. %, the resulting improvement in the foregoing effect
is not worth an increase in the amount, while a difficulty is
encountered in dissolving the increased amount of the component (B) in
2151582
the base oil ( s ) .
The component ( C ) to be used in the lubricating oil composition of
the present invention is at least one phosphorus-containing extreme-
pressure additive selected from among phosphoric esters, phosphorous
esters, and alklyamine salts of phosphoric esters.
Examples of the above-mentioned phosphoric esters ( Pa ) and
phosphorous esters ( Pi ) include a variety of phosphorus-containing
compounds represented by the formula: O=P(OR7 )(OR8 )(OR9 ), O=P(OH)(OR' )
(OR8 )~ O=P(OH)2 (OR7 ), P(OR7 )(OR8 )(OR9 ), P(OH)(OR7 )(OR8 ), or P(OH)
2 (OR7 ). In the above-mentioned formulae, R7, R9 and R9, which may be
either the same or different from each othe~, are each a linear,
branched or cyclic alkyl or alkenyl group having four to 30 of carbon
atoms, preferably 20 or less of carbon atoms, an aryl group, or an
alkylaryl group.
Representative examples of these phosphoric and phosphorous esters
include oleyl acid phosphate in the form of a mixture of (Cl8 )H3sO)P(OH)
2 O and (Cl 8 H3 s O)2 -P(OH)O, and dioleyl hydrogen phosphite represented by
the formula: (Cl 8 H3 s O)2 P(OH) .
On the other hand, an alkylamine salt of a phosphoric ester ( Pa-A )
is a reaction product of the phosphoric ester with the alkylamine,
examples of which are the ones represented by the general formula [ 4 ]:
(Rl )m P(O) (OH)3 ~m [NHn (Rl l )3 ~n ]3 ~m .. [4]
In the above-mentioned general formula [ 4 ], Rl is a linear,
branched or cyclic alkyl or alkenyl group having four to 30 of carbon
atoms, preferably 20 or less of carbon atoms, an aryl group, or an
alkylaryl group; Rl l is a linear, branched or cyclic alkyl or alkenyl
group having four to 30 of carbon atoms, preferably 20 or less of
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carbon atoms; m and n are each 1 or 2; a plurality of Rl, if any, may
be either the same or different from each other; and a plurality of Rll,
if any, may be either the same or different from each other.
In the above-mentioned general formula [4], examples of Rl include
butyl, hexyl, cyclohexyl, octyl, 2-ethylhexyl, decyl, lauryl,
myristyl,palmityl, stearyl, oleyl, eicosyl, phenyl and cresyl groups;
and examples of Rll include butyl, hexyl, cyclohexyl, octyl, 2-
ethylhexyl, decyl, lauryl, myristyl, palmityl, stearyl, oleyl and
eicosyl groups.
Representative examples of the alkylamine salt of the phosphoric
ester represented by the above-mentioned general formula [4] include
oleylamine salt of diisooctyl acid phosphate [a reaction product of (i-
C8 Hl 7 0)2 P(OH)O with (Cl~H3s)NH2], and oleylamine salt of 2-ethylhexyl
acid phosphate.
In the composition of the present invention, the above-mentioned
phosphorus-containing extreme-pressure additives may be used either
alone or in combination of two or more kinds thereof. The amount of the
phosphorus-cont~ining extreme-pressure additive(s) to be blended in the
composition is in the range of 0.1 to 5 wt. %, preferably 0.5 to 4 wt.
%, based on the total weight of the composition. When this amount is
smaller than 0.1 wt. %, the resulting composition is never excellent in
frictional properties and abrasion-proofing properties. When it exceeds
5 wt. %, the resulting improvements in such effects are not worth an
increase in the amount, while a difficulty is encountered in dissolving
the increased amount of the additive(s) in the base oil(s).
The phosphorus-containing extreme-pressure additive(s) as the
component (C) is generally great in abrasion-proofing effect, and
moreover functions as an assistant capable of promoting the effect of
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the sulfur-cont~ining extreme-pressure additive. The phosphoric ester
~.. ... .
attains improvements particularly in initial (run-in) frictional
properties and abrasion-proofing properties, whereas the phosphorous
ester functions in such a way as to secure low frictional properties
over a long period of time particularly after the run-in. On the other
hand, the alkylamine salt of the phosphoric ester is excellent
particularly in abrasion-proofing properties for gears.
In so far as the object of the present invention is not spoiled,
the lubricating oil composition of the present invention may
appropriately be admixed with a variety of common additives for use in
the conventional lubricating oils, examples of which additives include a
metal-cleaning agent, an ash-free leaning dispersant, a viscosity index
improver, a pour point depressant, an antioxidizing agent, a rust
inhibitor, a corrosion inhibitor, and an antifoaming agent.
Examples of the metal.cleaning agent include calcium sulfonates,
magnesium sulfonates, barium sulfonates, calcium phenate, and barium
phenate. The amount of the metal-cleaning agent that may be used is
usually in the range of 0.1 to 5 wt. %. Examples of the ash-free
cleaning dispersant include succinimide compounds, succinamide
compounds, benzylamine compounds and boron-containing derivatives
thereof, and ester compounds. The amount of the ash-free cleaning
agent that may be used is usually in the range of 0.5 to 7 wt. %.
Examples of the viscosity index improver include polymethacrylates,
polyisobutylene, ethylene-propylene copolymers, and hydrogenated
styrene-butadiene copolymers. The amount of the viscosity index
improver that may be used is usually in the range of 0.5 to 35 wt. %.
Examples of the antioxidizing agent include amine antioxidizing agents
such as alkylated diphenylamines, phenyl-a -naphthylamine, and
0
2151582
alkylated-a -naphthylamines; and phenolic antioxidizing agents such as
2,6-di-t-butyl-4-methylphenol and 4,4'- methylenebis(2,6-di-t-
butylphenol). The amount of the antioxidizing agent that may be used
is usually in the range of 0.05 to 2 wt. %.
Examples of the rust inhibitor include alkenylsuccinic acids and
partial esters thereof. Examples of the corrosion inhibitor include
benzotriazole and benzimidazole. Examples of the antifoaming agent
include dimethylpolysiloxane and polyacrylates, which may be
appropriately added.
Examples
The following Examples further illustrates the present invention in
more detail, but should not be construed as limiting the scope of the
invention.
The friction coefficient (LFW-1), efficiency of torque transmission
in a real machine, and seizing-proofing properties (API service
classification) of each lubricating oil composition were determined as
follows.
(1) Friction coefficient (LFW-1)
A tester as shown in Fig. 1 was used together with an S-10 test
ring (steel) manufactured by Falex Corporation and an H-60 block
(steel) manufactured by Falex Corporation under conditions involving a
sliding velocity of 1.4 m/sec, a load of 113 kgf and an oil temperature
of 100 C to carry out the LFW-1 friction test. In Fig. 1, numeral 1
refers to the S-10 test ring, numeral 2 to the H-60 block, and numeral
3 to a strain meter. The load was applied onto the H-60 block to
revolve the ring, whereupon a resistance arose, which was detected with
the strain meter to calculate the friction coefficient. The test oil
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was filled to such an extent that the ring was dipped therein by about
half.
(2) Efficiency of torque transmission in real machine (%)
The test was carried out under conditions involving an input torque
of 3 kgf- m, an input number of revolutions of 1,000 rpm and an oil
temperature of 50 C to determine the efficiency (%) of torque
transmission in the real machine.
(3) Seizing-proofing properties (API service classification)
The seizing-proofing properties were determined in accordance with
the CRC L-42 test. The higher the value, the better the seizing-
proofing properties.
Examples 1 to 4 and Comparative Examples 1 to 4
Lubricating oil compositions each containing a base oil (a highly
refiner mineral oil having a viscosity at 100C of 11.0 cSt) and
various kinds of componen~s as listed in Table 1, the amounts of which
are also specified in Table 1, were prepared to determine the friction
coefficients (LFW-1), efficiencies of torque transmission in the real
machine, and seizing-proofing properties of the compositions. The
results are shown in Table 1.
Further, the graphs in Fig. 2 shows the relationships between the
input torque and the efficiency of transmission in the cases of
respectively using a lubricating oil according to the present invention
and an S-P blend oil.
1 2
Table 1
Ccmp. Comp. Comp. Comp.
Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 1 Ex. 2 Ex. 3 Ex. 4
Sulfurized oxymolybdenum 2.5 4.0 5.0 3.5
(hexyl) phosphorodithir~te - - 4.0
Sulfurized oxymolybdenum
Contents (2-ethylhexyl)
of dithio~arbamate - - - - - - - 4.0
additives Isobutylene sulfide 7.0 8.5 7.0 6.5 7.0 6.5 - 7.0 ~3
~_ (wt. %) Oleylamine salt of 2- CJ~
c~ ethylhexyl acid ~ ~h~te 3.0 3.0 3.0 1.5 3.0 2.5 3.0 3.0
Dioleyl phosphite 2.0 2.0 2.5 1.5 2.5 2.5 2.5 2.5 Cx~
Oleyl acid r~n~h~te 0.5 0.5 ~ 0.5 0.5 0.5 0.5 0.5 0.5 2
Polybutenyl succininimide 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5
Friction ccPffi~i~nt
(LFW-l) 0.076 0.073 0.073 0.075: 0.087 0.085 0.078 0.082
~ffi~i~n~y of torque
Eveluation trar ~inn in real
machine (%) 93.8 94.1 94.3 94.0 92.8 92.8 93.8 93.1
Seizing-proofing properties
(API servioe cl~ific~tion) GL-5 GL-5 GL-5 GL-5 GL-5 GL-5 GL-3 GLr4.5
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As is understandable from Table 1, each of the lubricating oil
compositions according to the present invention was low in the friction
coefficient (LFW-1) and improved in the efficiency of torque
transmission in the real machine and the seizing-proofing properties,
as compared with the conventional ones comprising S-containing and P-
contAining additives blended therein.
Effects of the Invention
The lubricating oil composition of the present invention for use in
a final drive, wherein base oiI(s) is blended with a combination of
phosphorus-containing extreme-pressure additive(s) and sulfur-
containing extreme-pressure additive(s) with MoDTP, improves the
efficiency of transmission in a differential gear under various
conditions such as the input torque, the input number of revolutions and
the temperature of the oil and hence decreases the cost of fuel, as
compared with the conventional ones comprising S-containing and p-
containing additives blended therein.
1 4
