Field of Technology
[0001] The present invention relates to a lubricating oil composition or, more particularly,
relates to a lubricating oil composition which can be used satisfactorily for the
lubrication of parts having a wet-type clutch or wet-type brake such as automatic
transmissions, tractors and the like.
Background Technology
[0002] Lubricating oils used for the lubrication of the parts having a wet-type clutch or
wet-type brake such as automatic transmissions, tractors and the like are required
have properties including good friction characteristic, oxidation stability, corrosion
resistance and rustpreventiveness as well as a large torque for power transmission.
The friction characteristic here implied is a ratio of the coefficient of static friction
and the coefficient of dynamic friction and it is required that this ratio is small
and little influenced by the changes in the temperature or in the lapse of time.
[0003] In the prior art, there is known such a lubricating oil having a large coefficient
of static friction and a good torque for power transmission. This lubricating oil,
however, has defects that the friction characteristic thereof is not satisfactory
so that a shift of the automatic transmission and the like causes a large shock.
[0004] In particular, the trend is more and more outstanding in recent years that automatic
transmissions and the like are designed in a decreased size along with the prevalence
of compact cars and so-called FF cars (front engine front wheel driven cars). This
trend of automatic transmissions toward compact size promotes the adverse influence
that the shift shock is felt sensitively by the driver. Accordingly, it is a technical
problem to further improve the friction characteristics in order to improve the comfortableness
of driving by decreasing the shift shock.
[0005] A proposal has been made accordingly of a lubricating oil by use of a friction modifier
with an object of improving the friction characteristics. There is a problem, however,
that the lubricating oil containing a friction modifier still has only insufficient
friction characteristics along with variation of the friction characteristics by the
change in the oil temperature and that the friction characteristics are subject to
decrease by the degradation (changes in the lapse of time) of the oil after a long-term
service.
[0006] For example, GB-A-2097813 discloses a lubricating oil composition comprising 0.2
% wt. of a glycerol mono-oleate which can be an ester made from high molecular weight
dicarboxylic acids. Another proposal has been made in US-A-4209411 according to which
the use of metholol polyester derivatives of C12/C22 hydrocarbon succinic anhydride
of acid as additives for lubricants leads to reduction of friction, however, the obtained
results are still to be improved.
[0007] Therefore, lubricating oils having good friction characteristics with small changes
by oil temperature and in the lapse of time and having a large transmission torque
have hitherto not been obtained.
[0008] The object of the present invention is to dissolve the above described problems in
the prior art by a specific combination of compounds contained in a base oil and to
provide a lubricating oil composition with a small shock and a large transmission
torque and capable of being satisfactorily used for lubrication of automatic transmissions
and the like.
Disclosure of the Invention
[0009] Namely, the present invention relates to a lubricating oil composition characterized
in that a base oil contains (A) from 0.05 to 5% by weight of an ester of alkenyl substituted
succinic acid and/or an ester of alkyl substituted succinic acid and (B) from 0.005
to 5% by weight of a fatty acid ester of a polyhydric alcohol wherein the base oil
contains 0,5% by weight or less of sulfur.
[0010] The lubricating oil composition of the present invention has a good friction characteristic
or, namely, a small (coefficient of static friction)/(coefficient of dynamic friction)
ratio and gives a small shift shock. In addition, the change in the friction characteristics
depending on the oil temperature is small, and also the changes in the lapse of time
are small so that it is fully adaptable to the trend of transmissions and the like
toward compact size.
Brief Description of the Drawing
[0011] Figure 1 and Figure 3 are each a graph showing the change in time of µ₀/µ₁₂₀₀ at
each time up to 2000 cycles in Example and Comparative Example and Figure 2 is a graph
showing the temperature change thereof.
Best Mode Embodiment to Practice the Invention
[0012] The base oil used in the present invention is the principal ingredient of the lubricating
oil composition and various kinds of mineral oils and/or synthetic oils can be used
among those used in conventional lubricating oils.
[0013] The base oil should preferably have a viscosity of 1.5 to 30 x 10⁻⁶ m²·s⁻¹ (centistokes)
at 100°C and, in particular, those of 2 to 20 x 10⁻⁶ m²·s⁻¹ (centistokes) are preferred
when used as an oil for automatic transmissions and an oil for wet-type brakes in
agricultural tractors.
[0014] To show particular examples of the base oil, the mineral oils include 60 neutral
oil, 100 neutral oil, 150 neutral oil, 300 neutral oil and 500 neutral oil by the
solvent refining or hydrogenation refining.
[0015] On the other hand, the synthetic oils include polyolefins, polyglycol esters, esters
of dibasic acids, polyol esters, phosphoric acid esters, silicone oils, alkyl benzenes
and alkyl diphenyls as well as condensed ring and/or non-condensed ring saturated
hydrocarbons and those mainly composed thereof can be used as the base oil.
[0016] When a mineral oil is used as the base oil in the present invention, incidentally,
various ones can be used provided that the kinematic viscosity at 100°C is from 1.5
to 30 x 10⁻⁶ m²·s⁻¹ (centistokes) or, preferably, from 2 to 20 x 10⁻⁶ m²·s⁻¹ (centistokes)
and those to be used contain 0.5% by weight or less or, preferably, 0.1% by weight
or less or, particularly preferably, 100 ppm or less of sulfur.
[0017] An excess amount of the sulfur over 0.5% by weight is not preferable here due to
the decrease in the oxidation stability.
[0018] Mineral oils having a low pour point can also be used. It should have a pour point
of, preferably, -15°C or below or, more preferably, -25°C or below or, particularly
preferably, -35°C or below. This is because the friction characteristics can be further
improved along with mitigation of the limitation relative to the temperatrue range
for use.
[0019] Incidentally, the preferable conditions for the mineral oil are that the content
of aromatic hydrocarbons (% C
A) is 20 or smaller or, more preferably, 10 or smaller, that the total acid value is
0.1 mg KOH/g or smaller or, preferably, 0.05 mg KOH/g or smaller.
[0020] Mineral oil having the properties as described above can be obtained by refining
a distillate (boiling point under atmospheric pressure, about 250-450°C) as obtained
by distillation of paraffin base crude oil, intermediate base crude oil or naphthene
base crude oil, by the usual method, or by applying deep dewaxing treatment to thus
obtained oil.
[0021] The distillate means an oil obtained either by atmospheric distillation of crude
oil or by vacuum distillation of residual oil resulting from atmospheric distillation
of crude oil. A method of refining is not critical, and any of the methods (1) to
(5) as described below can be employed.
(1) The distillate is subjected to hydrogenation treatment, or alternatively, after
hydrogenation treatment, the distillate is subjected to alkali distillation or sulfuric
acid washing (treating).
(2) The distillate is subjected to solvent refining treatment, or alternatively, after
solvent refining treatment, the distillate is subjected to hydrogenation treatment,alkali
distillation or sulfuric acid washing (treating).
(3) The distillate is subjected to hydrogenation treatment followed by second hydrogenation
treatment.
(4) The distillate is subjected to hydrogenation treatment, then to second hydrogenation
treatment, and further to third hydrogenation treatment.
(5) The distillate is subjected to hydrogenation treatment followed by second hydrogenation
treatment, and further to alkali distillation or sulfuric acid washing (treating).
[0022] One of the methods will hereinafter be explained.
[0023] A crude starting material for lubricating oil is produced from paraffin base crude
oil or intermediate base crude oil by the usual method and then is subjected to severe
hydrogenation treatment. In this treatment, undesirable components, such as aromatics,
for the lubricating oil fraction are removed or converted into useful components.
Almost all of sulfur and nitrogen components are removed at the same time.
[0024] Such fractional distillation as to obtain the necessary viscosity is carried out
by vacuum distillation. Then, the known solvent dewaxing treatment is carried out
so as to dewax to the pour point that the usual paraffin base oil has, that is, about
-15 to -10°C.
[0025] After the dewaxing treatment, if necessary, hydrogenation is carried out to hydrogenate
the major portion of aromatic components into saturated components, thereby increasing
thermal and chemical stability of the base oil. When the thus obtained mineral oil
is insufficient because the pour point is still high, deep dewaxing treatment can
be applied subsequently. For this treatment, there are employed a solvent dewaxing
method which is carried out under severe conditions, and a catalytic hydrogenation
dewaxing method in which a zeolite catalyst is used and paraffin (mainly n-paraffin)
adsorbed on fine pores of the catalyst is selectively decomposed under hydrogen atmosphere
to remove components to be converted into wax components.
[0026] Conditions for hydrogenation treatment vary with the properties, of the feed oil.
Usually, the reaction temperature is 200 to 480°C and preferably 250 to 480°C, the
hydrogen pressure is 4,9 x 10⁵ to 2,94 x 10⁷ Pa (5 to 300 kg/cm²) and preferably 2,94
x 10⁶ to 2,45 x 10⁷ Pa (30 to 250 kg/cm²), and the amount of hydrogen introduced (per
kiloliter of the fed distillate) is 30 to 3,000 Nm³ and preferably 100 to 2,000 Nm³.
In this hydrogenation treatment, there are used catalysts which are prepared by depositing
catalyst components such as Groups VI, VIII group metals, preferably cobalt, nickel,
molybdenum and tungsten on carriers such as alumina, silica, silica alumina, zeolite,
active carbon and bauxite using the known method. It is preferred that the catalyst
be previously subjected to preliminary sulfurization.
[0027] As described above, after hydrogenation treatment, the distillate is subjected to
various treatments. When second hydrogenation treatment or further third hydrogenation
treatment is applied, the treatment may be carried out under conditions falling within
the ranges as described above. Conditions at the first, second and third stage hydrogenation
treatments may be the same or different. Usually the second hydrogenation treatment
is carried out under more severe conditions than the first stage hydrogenation treatment,
and the third stage hydrogenation treatment, under more severe conditions than the
second stage hydrogenation treatment.
[0028] Alkali distillation is carried out as a step where small amounts of acidic substances
are removed to improve the stability of distillate. In this alkali distillation, alkalis
such as NaOH and KOH are added and vacuum distillation is conducted.
[0029] Sulfuric acid washing (treating) is generally carried out as a finishing step of
oil products, in which aromatic hydrocarbons, especially polycyclic aromatic hydrocarbons,
olefins and sulfur compounds are removed to improve the characteristics of distillate.
In the present invention, 0.5 to 5% by weight of concentrated sulfuric acid is added
to the distillate, the treatment is carried out at a temperature ranging between room
temperature and 60°C, and thereafter neutralization using NaOH is applied.
[0030] The aforementioned methods (1) to (5) to be employed in treatment of distillate comprise
combinations of the operations as described above. Of these methods, the methods (1),
(3) and (4) are particularly suitable.
[0031] The distilled oil obtained by the treatment described above has properties including
a kinematic viscosity of 1.5 to 30 x 10⁻⁶ m²·s⁻¹ (centistokes) (100°C), content of
sulfur of 0.5% by weight or less and pour point of -15°C or below. Also, the content
of the aromatic hydrocarbons (% C
A) is 20% or smaller and the total acid value is 0.1 mg KOH/g or smaller.
[0032] The use of such a mineral oil can provide a lubricating oil composition having a
smaller (coefficient of static friction)/(coefficient of dynamic friction) ratio.
[0033] And, preferable synthetic oils include polyolefins and condensed ring and non-condensed
ring saturated hydrocarbons.
[0034] Among various ones named as such a saturated hydrocarbon, saturated hydrocarbons
having a cyclohexyl group and/or a decalyl group and having 10 to 40 carbon atoms
are preferred. The saturated hydrocarbons having a cyclohexyl gorup and/or a decalyl
group here are exemplified particularly by 2-methyl-2,4-dicyclohexyl pentane, cyclohexyl
methyl decalin, 1-(methyl decalyl)-1-cyclohexyl ethane, 2,4-dicyclohexyl pentane and
isododecyl cyclohexane.
[0035] The base oil can be admixed according to need with a viscosity index improver and
corrosion inhibitor.
[0036] In the present invention, an ester of alkenyl substituted succinic acid and/or an
ester of alkyl substituted succinic acid are used as the component (A). The ester
of alkenyl substituted succinic acid or ester of alkyl substituted succinic acid can
be used particularly efficiently when it is represented by the general formula [I]
given below.
In the above given formula [I], R¹ is an alkenyl group or an alkyl group having
6 to 30 carbon atoms or, preferably, 12 to 24 carbon atoms.
[0037] And, R² and R³ in the above given formula [I] are each a hydrogen, an alkyl group
having 1 to 20 carbon atoms, a hydroxyalkyl group having 1 to 20 carbon atoms or a
group represented by the general formula
(in the formula, R⁴ is an alkylene group having 1 to 4 carbon atoms, R⁵ is an alkyl
group having 1 to 20 carbon atoms or a hydroxy-substituted group thereof, n is an
integer of 0 to 6 and x is 1 or 2).
[0038] R² and R³ here can be the same ones or different from each other excepting the case
where R² and R³ are both hydrogens.
[0039] Particular exmaples of the ester of alkenyl substituted succinic acid and ester of
alkyl substituted succinic acid include monomethyl ester of octadecenyl succinic acid,
dimethyl ester of octadecenyl succinic acid, monoethyl ester of octadecenyl succinic
acid, diethyl ester of octadecenyl succinic acid, monooctyl ester of octadecenyl succinic
acid, dioctyl ester of octadecenyl succinic acid, monononyl ester of octadecenyl succinic
acid, dinonyl ester of octadecenyl succinic acid, monolauryl ester of octadecenyl
succinic acid, dilauryl ester of octadecenyl succinic acid, monolauryl ester of dodecyl
succinic acid, dilauryl ester of dodecyl succinic acid, monomethyl ester of hexadecyl
succinic acid, dimethyl ester of hexadecyl succinic acid, monoethyl ester of hexadecyl
succinic acid, diethyl ester of hexadecyl succinic acid, monomethyl ester of octadecyl
succinic acid, dimethyl ester of octadecyl succinic acid, monoethyl ester of octadecyl
succinic acid, diethyl ester of octadecyl succinic acid, monooctyl ester of octadecyl
succinic acid, dioctyl ester of octadecyl succinic acid, monolauryl ester of octadecyl
succinic acid, monolauryl ester of octadecyl succinic acid, dilauryl ester of octadecyl
succinic acid, a reaction product of an alkenyl succinic acid of a propylene oligomer
having 18 carbon atoms on an average and a propylene glycol, a reaction product of
a polybutenyl succinic acid of a polybutene having an average molecular weight of
400 and a propylene glycol, octyl mercaptan ethylene oxide ester of octadecenyl succinic
acid, octyl mercaptan propylene oxide ester of octadecenyl succinic acid, nonyl mercaptan
ethylene oxide ester of octadecenyl succinic acid, nonyl mercaptan propylene oxide
ester of octadecenyl succinic acid, lauryl mercaptan ethylene oxide ester of octadecenyl
succinic acid, lauryl mercaptan propylene oxide ester of octadecenyl succinic acid,
5-hydroxy-3-thiapentyl ester of octadecenyl succinic acid and 6-hydroxy-3,4-dithiahexyl
ester of octadecenyl succinic acid.
[0040] In the present invention, either one of the ester of alkenyl substituted succinic
acid and the ester of alkyl substituted succinic acid or a mixture thereof is added
as the component (A) while the amount of addition thereof depends on the properties
of the desired lubricating oil composition and cannot be definitely selected. It is,
however, from 0.05 to 5.0% by weight or preferably from 0.1 to 3.0% by weight. No
sufficient effect can be obtained with an amount of addition smaller than 0.05% by
weight while an undesirably adverse decrease is caused in the oxidation stability
with an excess over 5.0% by weight.
[0041] In the next place, a fatty acid ester of a polyhydric alcohol, is used as the component
(B) in the present invention. The polyhydric alcohol here implied includes glycerin,
trimethylol propane, pentaerithritol and sorbitol of which glycerin is particularly
preferable. And, the fatty acid includes those having 8 to 30 carbon atoms which may
be either saturated or unsaturated. Particular examples of the fatty acid include
pelargonic acid, lauric acid, palmitic acid, stearic acid, behenic acid, undecylenic
acid, oleic acid, linoleic acid and linolenic acid. Exemplary of the more preferable
esters are partial esters of polyhydric alcohols such as oleic acid monoglyceride,
oleic acid diglyceride, stearic acid monoglyceride and stearic acid diglyceride.
[0042] The amount of addition of the above mentioned component (B) is from 0.005 to 5% by
weight or, preferably, from 0.01 to 3% by weight. No sufficient improvement can be
obtained in the friction characteristics with an amount of addiiton smaller than 0.005%
by weight. On the other hand, the oxidation stability is undesirably affected adversely
by the addition in excess of 5% by weight.
[0043] The lubricating oil composition of the present invention can be obtained basically
by admixing the above described components (A) and (B) with the base oil but it is
optional to add an acid amide or a boron derivative thereof with an object to improve
the friction characteristics and simultaneously to enhance the physical properties
as a lubricating oil. The acid amide is a reaction product of a carboxylic acid having
12 to 30 carbon atoms and an amine compound and the particular examples thereof include
the reaction products of isostearic acid or oleic acid with diethylene triamine, triethylene
tetramine, tetraethylene pentamine and hexaethylene pentamine. And, examples of the
boron-containing derivatives of an acid amide include the reaction products of an
acid amide and a boron compound (boric acid, salts of boric acid and esters of boric
acid). Particular examples include those obtained by the reaction of boric acid with
the above mentioned acid amide, e.g., the reaction product of isostearic acid and
tetraethylene pentamine. The amount of addition is 0.01 to 10% by weight or, preferably,
0.05 to 3% by weight. No sufficient improving effect of the friction characteristics
and cleaning and dispersing effect can be obtained with an amount of addition smaller
than 0.01% by weight while, on the other hand, addition in excess of 10% by weight
is undesirable due to the decrease in the coefficient of static friction resulting
in a decreased transmission torque.
[0044] To the lubricating oil composition of the present invention, if desired, an antioxidant,
a detergent-dispersant and a viscosity index improver can be added. As the antioxidant,
those commonly used such as phenol base compounds, amine base compounds and zinc dithiophosphate
can be used. Representative examples are 2,6-di-tert-butyl-4-methyl-phenol; 2,6-di-tert-butyl-4-ethyl-phenol;
4,4'-methylenebis(2,6-di-tert-butyl-phenol); phenyl-α-naphthylamine, dialkyldiphenylamine,
zinc di-2-ethylhexyldithiophosphate, zinc diamyldithiocarbamate, and pinene pentasulfide.
[0045] The amount of addition is 0.01 to 3% by weight or, preferably,0.05 to 2% by weight.
No effect can be obtained with an amount smaller than 0.01% by weight while no remarkable
improvement can be achieved even with an amount in excess of 3% by weight.
[0046] Detergent-dispersants which can be used include an ashless base dispersant and a
metal-based detergent. For example, alkenylsuccinic acid imide, sulphonates and phenates
are preferred. Representative examples of such preferred compounds are polybutenylsuccinic
acid imide, calcium sulphonate, barium sulphonate, calcium phenate, barium phenate
and calcium salicylate.
[0047] The amount of addition is 0.1 to 10% by weight or, preferably, 0.5 to 5% by weight.
The dispersibility is insufficient with an amount smaller than 0.1% by weight while
an amount in excess of 10% by weight is undesirable due to the decrease in the friction
characteristics.
[0048] Though not particularly limitative, polymethacrylates and copolymers of olefin can
be used as the viscosity index improver. Particularly preferable are the polymethacrylates
having a molecular weight not exceeding 100,000 or, preferably, not exceeding 50,000
having excellent shearing stability and capable of preventing any viscosity changes
over a long period of time. The amount of addition is 0.5 to 15% by weight or, preferably,
2 to 10% by weight. No improvement can be achieved in the viscosity-temperature characteristics
with an amount smaller than 0.5% by weight while an amount in excess of 15% by weight
is undesirable due to the decrease in the wearing resistance and the like as a result
of the use of a low-viscosity base oil.
[0049] Besides, the lubricating oil composition of the present invention can be admixed
according to need with a corrosion inhibitor, rubber swelling agent and defoaming
agent.
[0050] In the following, the present invention is described in more detail by way of examples.
Examples 1 and 2 and Comparative Examples 1 and 2
[0051] As a base oil, a mineral oil I having a kinematic viscosity of 5 x 10⁻⁶ m²·s⁻¹ (centistokes)
at 100°C and containing 200 ppm of sulfur was admixed with 4.0% by weight of a polymethacrylate
(molecular weight 42,000), 4.0% by weight of polybutenyl succinic acid imade (molecular
weight of the polybutenyl group 1000) and 0.5% by weight of an acid amide to give
a base oil which was admixed with a compound in an amount indicated in Table 1 to
give a lubricating oil composition.
[0052] The thus obtained lubricating oil composition was subjected to testing according
to the following methods.
SAE No. 2 friction test
[0053] The friction characteristics were evaluated under the experimental conditions described
below by using a SAE No. 2 testing machine manufactured by Greening Co. (U.S.).
[Experimental conditions]
[0054]
- Discs:
- Japanese-made paper-based discs for automatic transmisison (2 sheets)
- Plates:
- Japanese-made steel plates for automatic transmission (4 plates)
- Revolution of motor:
- 3000 rpm
- Thrusting pressure on piston:
- 3 kg/cm²
- Oil temperature:
- 50°C, 80°C, 100°C and 120°C
The coefficient of dynamic friction at the revolution of 1200 rpm µ₁₂₀₀ and the
coefficient of static friction at a moment of coming into stoppage µ₀ were determined
under the above described experimental conditions and µ₀/µ₁₂₀₀ was calculated. The
change in time and the change by temperature of this µ₀/µ₁₂₀₀ were respectively determined
to evaluate the friction characteristics.
[0055] Namely, the change in time of µ₀/µ₁₂₀₀ was determined up to 2000 cycles at an oil
temperature of 100°C. Figure 1 illustrates the change in time of µ₀/µ₁₂₀₀ at the respective
moments up to 2000 cycles (100, 200, 300, 400, 500, 1000, 1500 and 2000 cycles). Further,
the values of µ₀/µ₁₂₀₀ at 200 cycles and at 2000 cycles are shown in Table 1 as the
results of the
durability test.
[0056] In the next place, the oil temperature was varied stepwise at 50, 80, 100 and 120°C
after a break-in up to 200 cycles at an oil temperature of 100°C and the u₀/µ₁₂₀₀
was determined at each temperature. The results are shown in Figure 2. Further, the
values of µ₀/µ₁₂₀₀ at 50°C and 120°C are shown in Table 1 as the results of the
temperature dependecy test.
Comparative Example 3
[0057] A commercial product was subjected to the evaluation of the friction characteristics
in the same manner as in Example 1. The results are shown in Table 1, Figure 1 and
Figure 2.
Examples 3 and 4 and Comparative Example 4
[0058] The lubricating oil compositions indicated in Table 1 were obtained in the same manner
as in Examples 1 and 2 and Comparative Examples 1 and 2 excepting the use of a mineral
oil II having following properties as the base oil and testing was undertaken. Figure
3 shows the changes in time of the µ₀/µ₁₂₀₀ at the respective moments up to 2000 cycles.
Further, Table 1 shows the results of the durability test and the temperature dependency
test.
Properties of the mineral oil II |
Kinematic viscosity (100°C) |
5.0 x 10⁻⁶ m²·s⁻¹ (centistokes) |
Sulfur content (ppm) |
1 |
Pour point |
-45°C |
% CA |
0.1 > |
Examples 5 to 10 and Comparative Example 5
[0059] Testing was undertaken for the lubricating oil compositions indicated in Table 1
in the same manner as in Examples 1 and 2 and Comparative Examples 1 and 2. Table
1 shows the results of the durability test and the temperature dependency test. Incidentally,
the base oil was admixed, in the same manner as in Examples 1 and 2 and Comparative
Examples 1 and 2 (in the same manner as in the other Examples and Comparative Examples)
with 4.0% by weight of a polymethacrylate (molecular weight 42,000), 4.0% by weight
of a polybutenyl succinic acid imide (molecular weight of the polybutenyl group 1000)
and 0.5% by weight of an acid amide.
[0060] It is understood from Table 1 and Figures 1 to Figure 3 that the lubricating oil
composition of the present invention has excellent friction characteristics. In particular,
it is undertood from the results of the temperature dependency test that the changes
in the friction characteristics depending on the oil temperature are extremely small.
Industrial Utilizability
[0061] Accordingly, the lubricating oil composition of the present invention is very effective
as a lubricating oil for automatic transmissions, lubricating oil for the parts having
a wet-type clutch or wet-type brake in tractors.
[0062] Besides, the composition having such characteristics in combination is also effective
as a lubricating oil in shock absorbers, power steerings, hydraulic suspensions and
as a combined-use oil for a plurality of these objects.