Lubricating oil composition

A lubricating oil composition is herein disclosed which comprises (a) a base oil comprising a mineral oil, a synthetic oil or both the oils, (b) a copolymer having repeating units of the formulae (I) and (II) ##STR1## (c) an amine-based antioxidant, and if necessary, (d) a thiadiazole compound. The repeating unit of the formula (I) is derived from a monomer such as dimethylamino methacrylate. The repeating unit of the formula (II) is derived from a monomer such as a methacrylate of a long-chain alcohol. R.sup.1 and A may be the same or different every repeating unit. This lubricating oil composition is minimized in change with the lapse of time in frictional characteristics (shift shock in an automatic transmission or the like) and is excellent in oxidation stability.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a lubricating oil composition. More 
particularly, it relates to a lubricating oil composition which is 
excellent in frictional characteristics and stability against oxidation, 
inhibits its change with the lapse of time, and is effectively utilizable 
as a lubricating oil for various kinds of equipment such as an automatic 
transmission, a continuously variable transmission, a gear of a tractor, a 
wet brake, a wet clutch and a power steering. 
2. Description of Related Art 
A lubricating oil which can be used to lubricate an automatic transmission, 
a continuously variable transmission, a gear of a tractor, a wet brake, a 
wet clutch, a power steering or the like is required to have good 
properties of frictional characteristics, oxidation stability, corrosion 
resistance, rust resistance and the like. Especially important 
requirements are that a ratio of a coefficient of static friction to a 
coefficient of kinematic friction by which the frictional characteristics 
are indicated is small and that a change in this ratio with the lapse of 
time is small. 
Heretofore, as such a lubricating oil, there is known a lubricating oil 
having a high coefficient of static friction and good transmission torque. 
This kind of lubricating oil, however, is disadvantageous in that the 
frictional characteristics are not sufficiently satisfactory and a shift 
shock is large. 
In recent years, with the miniaturization of cars and the abrupt increase 
in FF cars (front engine front wheel driven cars), the tendency of 
miniaturizing the automatic transmission and the like more and more 
increases. Such a miniaturization of the automatic transmission 
inconveniently makes a driver feel the shift shock more sensitively. Thus, 
in order to relieve the shift shock and to thereby make a car more 
comfortable to drive, it has been a technical subject to improve the 
frictional characteristics especially at an initial stage. 
For the purpose of improving the frictional characteristics at the initial 
stage, there have been suggested a lubricating oil containing a friction 
modifier (Japanese Patent Application Laid-open Nos. 173097/1985 and 
180000/1988) and a lubricating oil in which a base oil having a specific 
composition is used (Japanese Patent Application Laid-open No. 
254196/1988). In these lubricating oils, however, the change with the 
lapse time in the frictional characteristics is large, and so they are not 
considered to have a sufficient performance. 
SUMMARY OF THE INVENTION 
The present invention intends to overcome the above-mentioned problems of 
conventional techniques, and an object of the present invention is to 
provide a lubricating oil composition which is excellent in frictional 
characteristics at an initial stage and oxidation stability and which can 
maintain the frictional characteristics for a long period of time. 
Under such circumstances, the present inventors have conducted research. As 
a result, it has been found that the change with the lapse of time in the 
frictional characteristics can be effectively inhibited by blending a 
lubricating oil composition with a specific copolymer belonging to a 
dispersion type polymer and an amine-based antioxidant. The present 
invention has been completed on the basis of such a knowledge. 
That is, the present invention is directed to a lubricating oil composition 
which comprises (a) a base oil comprising at least one selected from the 
group consisting of mineral oils and synthetic oils, (b) a copolymer 
having a repeating unit (I) represented by the formula (I) 
##STR2## 
wherein R.sup.1 is hydrogen or an alkyl group having 1 to 6 carbon atoms; 
A is a group of the following formula (I-1), (I-2), (I-3), (I-4), (I-5) or 
(I-6); n is an integer of 1 to 8; 
##STR3## 
wherein each of R.sup.2 and R.sup.3 is independently hydrogen or an alkyl 
group having 1 to 20 carbon atoms; each of a and b is independently an 
integer of 1 to 3; each of d and e is independently an integer of 1 to 6; 
f is an integer of 1 or 2; g is an integer of 0 to 6; and R.sup.1 and A 
may be the same or different every repeating unit, 
and a repeating unit (II) represented by the formula (II) 
##STR4## 
wherein R.sup.4 is hydrogen or an alkyl group having 1 to 6 carbon atoms; 
R.sup.5 is an alkyl group having 1 to 24 carbon atoms, and R.sup.4 and 
R.sup.5 may be the same or different every repeating unit, (c) an 
amine-based antioxidant and (d) a thiadiazole compound.

DESCRIPTION OF PREFERRED EMBODIMENTS 
As a base oil which is a component (a) of the present invention, there can 
be used a mineral oil, a synthetic oil or a mixture thereof. No particular 
restriction is put on the kind of mineral oil or synthetic oil, but in 
general, the mineral oil or the synthetic oil having a kinematic viscosity 
at 100.degree. C. of 1.5 to 30 cSt is used. 
Examples of the mineral oil include paraffinic mineral oils, intermediate 
mineral oils and naphthenic mineral oils. Furthermore, examples of the 
synthetic oil include alicyclic hydrocarbons, fused alicyclic 
hydrocarbons, bridgehead alicyclic hydrocarbons, polybutene, polyolefins 
(inclusive of poly-.alpha.-olefins), various kinds of esters (polyol 
esters, dibasic acid esters, phosphoric acid esters and the like), 
alkylbenzenes and alkylnaphthalenes. 
The base oil of the present invention can be beforehand blended with 
additives other than the components (b) to (d). 
A copolymer which is a component (b) of the present invention belongs to a 
dispersion type polymer from the viewpoint of a chemical structure, and it 
is used as a viscosity index improver. It is well known that a viscosity 
index improver is blended with a lubricating oil composition, and as this 
viscosity index improver, there are also known dispersion type polymers 
(dimethylaminopropylmethacrylamide base, vinylpyrrolidone base and the 
like) in addition to the above-mentioned component (b) and non-dispersion 
type polymers. However, if the viscosity index improver other than the 
copolymer specified as the component (b) is used, the change with the 
lapse of time in the frictional characteristics of the lubricating oil 
composition cannot be effectively inhibited. 
The copolymer which is the component (b) is a random copolymer, a block 
copolymer, a graft copolymer or a mixture of these copolymers having a 
repeating unit (I) represented by the formula (I) 
##STR5## 
wherein R.sup.1 is hydrogen or an alkyl group having 1 to 6 carbon atoms; 
A is a group of the following formula (I-1), (I-2), (I-3), (I-4), (I-5) or 
(I-6); n is an integer of 1 to 8; 
##STR6## 
wherein each of R.sup.2 and R.sup.3 is independently hydrogen or an alkyl 
group having 1 to 20 carbon atoms; each of a and b is independently an 
integer of 1 to 3; each of d and e is independently an integer of 1 to 6; 
f is an integer of 1 or 2; g is an integer of 0 to 6; and R.sup.1 and A 
may be the same or different every repeating unit, 
and a repeating unit (II) represented by the formula (II) 
##STR7## 
wherein R.sup.4 is hydrogen or an alkyl group having 1 to 6 carbon atoms; 
R.sup.5 is an alkyl group having 1 to 24 carbon atoms, and R.sup.4 and 
R.sup.5 may be the same or different every repeating unit. 
Above all, preferable is a copolymer in which A in the repeating unit (I) 
is the group of (I-1). 
No particular restriction is put on the contents of the respective 
repeating units in this copolymer, but the content of the repeating unit 
(I) is usually in the range of 0.5 to 20 parts by weight, preferably 1 to 
10 parts by weight with respect to 100 parts by weight of the repeating 
unit (II). 
If the content of the repeating unit (I) is less than 0.5 part by weight, 
the change with the lapse of time in the frictional characteristics cannot 
be sufficiently inhibited sometimes, and if it is more than 20 parts by 
weight, the additional inhibition effect on the change with the lapse of 
time cannot be expected any more. 
No particular restriction is put on the molecular weight of the copolymer, 
but it is usually in the range of 5,000 to 500,000, preferably 10,000 to 
150,000 in terms of number-average molecular weight. 
The copolymer can be obtained by copolymerizing a raw material monomer 
represented by the formula (III) 
##STR8## 
wherein R.sup.1, A and n are as defined above, and a raw material monomer 
represented by the formula (IV) 
##STR9## 
wherein R.sup.4 and R.sup.5 are as defined above, in a known manner. Here, 
the raw material monomer of the formula (III) can provide the repeating 
unit (I), and the raw material monomer of the formula (IV) can provide the 
repeating unit (II). 
Examples of the raw material monomer represented by the formula (III) 
include dimethylaminoethyl acrylate, diethylaminoethyl acrylate, 
dimethylaminopropyl acrylate, dibutylaminopropyl acrylate, 
dioctylaminoethyl acrylate, dilaurylaminopropyl acrylate; methacrylates 
corresponding to these acrylates; and mixtures of these compounds. 
Examples of the raw material monomer represented by the formula (IV) 
include esters of acrylic acid or methacrylic acid and alcohols such as 
methyl alcohol, ethyl alcohol, propyl alcohol, butyl alcohol, pentyl 
alcohol, hexyl alcohol, octyl alcohol, 2-ethylhexyl alcohol, decyl 
alcohol, dodecyl alcohol, tridecyl alcohol, tetradecyl alcohol, hexadecyl 
alcohol, octadecyl alcohol, cyclohexyl alcohol and benzyl alcohol; and 
mixtures of these esters. 
The copolymer which is the component (b) may contain a repeating unit other 
than the above-mentioned repeating units (I) and (II), so long as it does 
not impair the object of the present invention. 
For example, in manufacturing the copolymer which is the component (b), 
another vinyl monomer containing nitrogen or the like which can be used 
with the monomer of the formula (III) (N-vinylpyrrolidone, 
N-vinylthiopyrrolidone, a dialkylaminoalkylmethacrylamide, morpholinoethyl 
methacrylate, N-vinylimidazole or the like) can be copolymerized or 
graft-polymerized. Alternatively, a non-vinyl compound containing nitrogen 
or the like (phenothiazine, imidazole, thiazole, benzothiazole, triazole, 
thiazolidine, pyrimidine, pyridine, piperidine, pyrrolidinone, oxazole, 
thiomorpholine or the like) can be grafted. 
In the case that the component (b) contains the repeating unit derived from 
any of these monomers, its content should be usually 100 parts by weight 
or less, preferably 60 parts by weight or less with respect to 100 parts 
by weight of the repeating unit (I). 
On the other hand, examples of the other monomer which can be used with the 
monomer of the formula (IV) include vinyl aromatic compounds (styrene, 
vinyltoluene and the like). In manufacturing the copolymer which is the 
component (b), any of these monomers can be copolymerized or 
graft-polymerized. In the case that the component (b) contains the 
repeating unit derived from any of these monomers, its content should be 
usually 100 parts by weight or less, preferably 50 parts by weight or less 
with respect to 100 parts by weight of the repeating unit (II). 
The amount of the copolymer which is the component (b) is usually in the 
range of 1 to 20% by weight, preferably 2 to 10% by weight based on the 
total weight of the lubricating oil composition. 
In the lubricating oil composition of the present invention not only the 
component (b) but also an amine-based antioxidant which is a component (c) 
is used as an essential component. It is well known that an antioxidant is 
blended with the lubricating oil composition, and various kinds of 
antioxidants are known in addition to the amine-based antioxidant. 
However, in order to effectively inhibit the change with the lapse of time 
in the frictional characteristics of the lubricating oil composition, it 
is necessary to use the amine-based antioxidant. 
No particular restriction is put on the kind of amine-based antioxidant 
which can be used as the component (c), and various kinds of amine-based 
antioxidants can be used. Examples of such an amine-based antioxidant 
include diphenylamine derivatives represented by the formula (V) 
##STR10## 
wherein each of R.sup.6 and R.sup.7 is independently an alkyl group having 
1 to 20 carbon atoms or an alkenyl group having 1 to 20 carbon atoms; and 
each of m and l is independently an integer of 0 to 4; and when m and/or l 
is 2 or more, R.sup.6 s and/or R.sup.7 s may be the same or different. 
Examples of the compounds represented by the formula (V) include 
diphenylamine, dioctyldiphenylamine, dinonyldiphneylamine, 
dioleyldiphenylamine and p-butyl-p'-octyldiphenylamine. 
In addition, phenyl-.alpha.-naphthylamine derivatives represented by the 
following formula (VI) can also be employed as the amine-based 
antioxidant: 
##STR11## 
wherein R.sup.8 is an alkyl group having 1 to 20 carbon atoms or an 
alkenyl group having 1 to 20 carbon atoms; q is an integer of 0 to 5; and 
when q is 2 or more, R.sup.8 s may be the same or different. 
Examples of the compound represented by the formula (VI) include 
phenyl-.alpha.-naphthylamine, octylphenyl-.alpha.-naphthylamine and 
oleylphenyl-.alpha.-naphthylamine. 
The amount of the amine-based antioxidant which is the component (c) is 
usually in the range of 0.05 to 5.0% by weight, preferably 0.1 to 2.0% by 
weight based on the total weight of the lubricating oil composition. If 
the amount of the amine-based antioxidant is less than 0.05% by weight, 
its antioxidant effect is not sufficient and the effect of inhibiting the 
change with the lapse of time in the frictional characteristics which is 
the primary object of the present invention cannot be sufficiently 
obtained sometimes. On the other hand, if the amount of the amine-based 
antioxidant is more than 5.0% by weight, the additional inhibition effect 
on the change with the lapse of time cannot be expected any more. 
The amine-based antioxidants may be used singly or in combination of two or 
more thereof. 
A thiadiazole compound which is a component (d) of the present invention is 
used as a metal deactivator. In the case that the thiadiazole compound is 
blended with the lubricating oil composition of the present invention, the 
change with the lapse of time in the frictional characteristics of the 
lubricating oil composition can be further effectively inhibited. No 
particular restriction is put on the thiadiazole compound which can be 
used as the component (d), and various kinds of thiadiazole compounds can 
be used. Examples of such a thiadiazole compound include 1,3,4-thiadiazole 
compounds, 1,2,4-thiadiazole compounds and mixtures of these thiadiazole 
compounds represented by the formula (VII) or (VIII) 
##STR12## 
wherein each of R.sup.9 and R.sup.10 is independently hydrogen, a 
hydrocarbon group having 1 to 30 carbon atoms, or a group represented by 
the formula (IX), (X) or (XI) 
##STR13## 
wherein each of R.sup.11, R.sup.12, R.sup.13 and R.sup.14 is independently 
hydrogen or a hydrocarbon group having 1 to 30 carbon atoms. 
Typical examples of the compounds having the formulae (VII) and (VIII) 
include 2,5-dimethylcapto-1,3,4-thiadiazole, 
2,5-bis(hexyldithio)-1,3,4-thiadiazole, 
2,5-bis(octyldithio)-1,3,4-thiadiazole, 
2,5-bis(N,N-diethyldithiocarbamyl)-1,3,4-thiadiazole, 
3,5-dimercapto-1,2,4-thiadiazole, 3,5-bis(hexyldithio)-1,2,4-thiadiazole, 
3,5-bis(octyldithio)-1,2,4-thiadiazole and 
3,5-bis(N,N-diethyldithiocarbamyl)-1,2,4-thiadiazole. 
The amount of the thiadiazole compound which is the component (d) is 
usually in the range of 0.01 to 3.0% by weight, preferably 0.02 to 1.0% by 
weight based on the total weight of the lubricating oil composition. If 
the amount of the thiadiazole compound is less than 0.01% by weight, the 
inhibition effect on the change with the lapse of time in the frictional 
characteristics cannot be sufficiently obtained. On the other hand, if the 
amount is more than 3.0% by weight, sludge is likely to occur. 
These thiadiazole compounds may be used singly or in combination of two or 
more thereof. 
The lubricating oil composition of the present invention can be obtained by 
blending the base oil as the component (a) with the specific copolymer as 
the component (b), the amine-based antioxidant as the component (c), and 
if necessary, the thiadiazole compound as the component (d). 
The lubricating oil composition of the present invention can be blended 
with a friction modifier, if necessary. As described above., the friction 
modifier is blended for the purpose of improving the frictional 
characteristics. 
As the friction modifier, there can be usually employed various substances 
such as an oiliness agent, a friction inhibitor and an extreme pressure 
agent. Preferable examples of the friction modifier include phosphoric 
acid esters, phosphorous acid esters, amine salts of the phosphoric acid 
esters, amine salts of the phosphorous acid esters, sorbitan fatty acid 
esters, pentaerythritol fatty acid esters, glycerin fatty acid esters, 
trimethylolpropane fatty acid esters, glycol fatty acid esters, carboxylic 
acids, carboxylic acid amides, carboxylic acid esters, metal salts of the 
carboxylic acids, oils, fats, higher alcohols and sulfur compounds. They 
can be used singly or in combination. 
Preferable examples of the above-mentioned phosphoric acid esters and 
phosphorous acid esters are represented by the formulae (XII) to (XIV) 
##STR14## 
wherein each of R.sup.15 and R.sup.16 is an alkyl group, an aryl group or 
an alkyl-substituted aryl group each having 4 to 30 carbon atoms, and 
R.sup.15 and R.sup.16 may be the same or different. 
Typical examples of the phosphoric acid esters and the phosphorous acid 
esters include butyl acid phosphate, 2-ethylhexyl acid phosphate, lauryl 
acid phosphate, oleyl acid phosphate, stearyl acid phosphate, 
dibutylhydrogen phosphite, dilaurylhydrogen phosphite, dioleylhydrogen 
phosphite, distearylhydrogen phosphite and diphenylhydrogen phosphite. 
Examples of the amine salts of the phosphoric acid esters and the amine 
salts of the phosphorous acid esters include oleylamine salts, coconut 
amine salts and beef tallow amine salts of the phosphoric acid esters and 
the phosphorous acid esters. 
Next, typical examples of the sorbitan fatty acid esters include sorbitan 
monolaurate, sorbitan monocleate, sorbitan monostearate, sorbitan 
sesquioleate, sorbitan dioleate and mixtures thereof. 
Typical examples of the pentaerythritol fatty acid esters include 
monoesters, diesters and triesters of pentaerythritol or dipentaerythritol 
and fatty acids such as capric acid, lauric acid, myristic acid, palmitic 
acid, stearic acid, oleic acid, linolic acid and behenic acid, and 
mixtures thereof. 
Typical examples of the glycerin fatty acid esters include monoglyceride 
oleate, monoglyceride stearate, diglyceride oleate and mixtures thereof. 
Typical examples of the trimethylolpropane fatty acid esters include 
monoesters and diesters of trimethylolpropane and fatty acids such as 
capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, 
oleic acid, linolic acid and behenic acid, and mixtures thereof. 
Typical examples of the glycol fatty acid esters include monoesters of 
propylene glycol, trimethylene glycol, 1,4-butanediol and neopentyl glycol 
and fatty acids such as capric acid, lauric acid, myristic acid, palmitic 
acid, stearic acid, oleic acid, linolic acid and behenic acid, and 
mixtures thereof. 
Examples of the carboxylic acids include aliphatic carboxylic acids, 
divalent carboxylic acids (dibasic acids) and aromatic carboxylic acids. 
The aliphatic carboxylic acids have 8 to 30 carbon atoms and may be 
saturated or unsaturated. Typical examples of the aliphatic carboxylic 
acids include pelargonic acid, lauric acid, tridecanoic acid, myristic 
acid, palmitic acid, stearic acid, eicosanic acid, behenic acid, 
triacontanoic acid, undecylenic acid, oleic acid, linolic acid, linolenic 
acid, erucic acid, and fatty acids of oils and fats (coconut oil fatty 
acid, palm kernel oil and the like). Typical examples of the divalent 
carboxylic acids include octadecylsuccinic acid, octadecenylsuccinic acid, 
polybutenylsuccinic acid, adipic acid, azelaic acid, sebacic acid and 
dodecanoic diacid. Examples of the aromatic carboxylic acid include 
salicylic acid and the like. 
As the carboxylic acid amides, various amides are usable, and examples of 
the carboxylic acid amides include reaction products of the 
above-mentioned carboxylic acids and amine compounds (diethylenetriamine, 
triethylenetetramine, tetraethylenepentamine, hexaethylenepentamine, 
heptaethyleneoctamine, tetrapropylenepentamine and hexabutyleneheptamine, 
and alkanolamines such as monoethanolamine and diethanolamine). 
Examples of the carboxylic acid esters include aliphatic carboxylic acid 
esters and divalent carboxylic acid esters (dibasic acid esters). As these 
aliphatic carboxylic acid esters, there are usually used alkyl esters of 
the above-mentioned aliphatic carboxylic acids (methyl ester, ethyl ester, 
propyl ester, butyl ester, octyl ester, lauryl ester and oleyl ester). 
Examples of the divalent carboxylic acid esters include monoalkyl esters 
of the above-mentioned divalent carboxylic acids and glycol esters of 
propylene glycol and the like. 
Examples of the above-mentioned metal salts of the carboxylic acids include 
zinc laurate, zinc oleate, zinc stearate, zinc salt of coconut oil fatty 
acid, aluminum stearate and magnesium salicylate. 
Examples of the oils and fats include animal oils and fats such as lard, 
beef tallow and fish oils, and vegetable oils and fats such as soybean 
oil, rapeseed oil, rice bran oil, palm oil, palm kernel oil and coconut 
oil. 
Examples of the higher alcohols include octyl alcohol, lauryl alcohol, 
myristyl alcohol, oleyl alcohol and stearyl alcohol. 
Furthermore, examples of the sulfur compounds include sulfide oils and 
fats, and a reaction product of phosphorus sulfide and pinene. 
In the present invention, any of these compounds can be used as the 
friction modifier, but above all, particularly suitable are the phosphoric 
acid esters, the phosphorous acid esters, their amine salts, the 
carboxylic acid amides, the glycerin fatty acid esters, the sorbitan fatty 
acid esters, the metal salts of the carboxylic acids, the divalent 
carboxylic acid esters (the dibasic acid esters) and mixtures of two or 
more thereof. 
The lubricating oil composition of the present invention can be blended 
with an antioxidant other than the amine-based antioxidant which is the 
component (c), a detergent-dispersant and the like. 
Examples of the antioxidant other than the amine-based antioxidant include 
phenolic antioxidants (2,6-di-t-butyl-4-methylphenol and the like), zinc 
di-2-ethylhexyldithiophosphate, zinc diamyldithiocarbamate and pinene 
pentasulfide. In the case that any of these antioxidants is blended, its 
amount is usually 3% or less by weight based on the total weight of the 
lubricating oil composition. 
As the detergent-dispersant, there can be used an ash-free 
detergent-dispersant, a metallic detergent-dispersant, an ash-free 
detergent-dispersant containing boron, or the like. Typical preferable 
examples of the detergent-dispersant include alkenylsuccinic acid imides, 
sulfonates and phenates such as polybutenylsuccinic acid imide, calcium 
sulfonate, barium sulfonate, calcium phenate, barium phenate and calcium 
salicylate. The amount of the detergent-dispersant to be blended is 
usually in the range of 0.1 to 10% by weight, preferably from 0.5 to 5% by 
weight based on the total weight of the lubricating oil composition. 
Moreover, the lubricating oil composition of the present invention can be 
further blended with a pour point depressant, a corrosion inhibitor, a 
rubber swelling agent, a defoaming agent, a colorant and the like. 
As described above, in the lubricating oil composition of the present 
invention, the change with the lapse of time in frictional characteristics 
can be inhibited, so that the frictional characteristics at an initial 
stage can be maintained for a long period of time and the increase in 
shift shock can be prevented. In addition, the lubricating oil composition 
is excellent in oxidation stability, and hence durability is also 
excellent. 
Therefore, the lubricating oil composition of the present invention can be 
sufficiently applied to the miniaturization of a transmission or the like, 
and it is exceptionally effective as a lubricating oil for an automatic 
transmission or a continuously variable transmission, and as a lubricating 
oil for a wet clutch or a wet brake of an agricultural tractor or the 
like. 
Moreover, the lubricating oil composition of the present invention which 
has such characteristics is also effective as a lubricating oil for a 
shock absorber, a power steering, a hydraulic suspension or any of various 
construction machines, and as a lubricating oil for plural purposes of use 
thereof. 
Next, the present invention will be described in more detail with reference 
to examples and comparative examples, but the scope of the present 
invention should not be limited to any of these examples. 
EXAMPLES 1 TO 5 AND COMATIVE EXAMPLES 1 TO 8 
(1) Preparation of Lubricating Oil Composition 
A base oil was prepared comprising 95.0% by weight of a mineral oil having 
a kinematic viscosity at 100.degree. C. of 5.0 cSt, 1.0% by weight of an 
amine salt of oleylhydrogen phosphite (a friction modifier) and 4.0% by 
weight of polybutenylsuccinic acid imide (a detergent-dispersant). 
Afterward, compounds shown in Table 1 were added to the base oil in 
predetermined ratios to obtain lubricating oil compositions. 
(2) Performance Tests 
For the lubricating oil compositions prepared in the above-mentioned 
paragraph (1) just after the preparation and after the step of forced 
degradation, the following performance tests were made. The results are 
shown in Table 1. The forced degradation was carried out at 150.degree. C. 
for 48 hours in accordance with Oxidation Stability Test of Lubricating 
Oil for Internal Combustion Engine (JIS K 2514). 
SAE (Society of Automotive Engineers) No. 2 Friction Test 
Frictional characteristics were evaluated under the following conditions by 
the use of an SAE No. 2 tester manufactured by Greening Association Inc. 
(U.S.A.). 
Test Conditions 
Discs: Two paper discs for an automatic transmission made in Japan 
Plates: Three steel plates for the automatic transmission made in Japan 
Revolving Speed of motor: 3,600 rpm 
Piston Pressure: 38 psi 
Oil temperature: 120.degree. C. 
A coefficient of kinematic friction (.mu..sub.1200) at a revolving speed of 
1,200 rpm under the above-mentioned conditions and a coefficient of static 
friction (.mu..sub.0) at the time of stop were measured, and .mu..sub.0 
/.mu..sub.1200 (.mu..sub.0 /.mu..sub.K) was then calculated. 
Oxidation Stability Test 
An oxidation stability test was made at 170.degree. C. for 96 hours in 
accordance with Oxidation Stability Test of Lubricating Oil for Internal 
Combustion Engine (JIS K 2514) to measure a viscosity ratio at 40.degree. 
C., an increase in a total acid value and an insoluble residue (% by 
weight) by an n-pentan B method. 
TABLE 1 
______________________________________ 
Example 
1 2 3 4 5 
______________________________________ 
Components of the Composition (wt %) 
Base Oil*.sup.1 94.2 94.2 93.9 93.7 94.2 
Viscosity Index Improver 
Dimethylaminopro- 
5 5 5 5 3 
pyl Methacrylate Base*.sup.2 
Dimethylaminopropyl 
-- -- -- -- -- 
Methacrylamide Base*.sup.3 
Vinylpyrrolidone Base*.sup.4 
-- -- -- -- -- 
Non-dispersion -- -- -- -- 2 
Type Polymethacryalte*.sup.5 
Antioxidant 
Dioctyldiphenylamine*.sup.6 
0.5 -- 0.5 0.5 0.5 
Phenyl-.alpha.-naphthylamine*.sup.7 
-- 0.5 -- -- -- 
2,6-di-t-butyl- -- -- -- 0.5 -- 
4-methylphenol*.sup.8 
1,3,4-thiadi- 0.3 0.3 0.6 0.3 0.3 
azole Polysulfide*.sup.9 
Test Results 
SAE No. 2 Test (.mu..sub.0 /.mu..sub.K) 
Fresh Oil 1.02 1.02 1.01 1.03 1.02 
Degradated Oil 1.04 1.03 1.02 1.06 1.04 
Oxidation Stability Test 
Viscosity Ratio 1.06 1.04 1.02 1.05 1.07 
Increase in Total 
0.94 0.82 0.73 0.77 0.75 
Acid Value 
Insoluble Residue 
0.02 0.02 0.03 0.02 0.08 
______________________________________ 
Comparative Example 
1 2 3 4 5 
______________________________________ 
Components of the Composition (wt %) 
Base Oil*.sup.1 94.7 94.2 94.4 94.2 94.2 
Viscosity Index Improver 
Dimethylaminopro- 
5 5 5 -- -- 
pyl Methacrylate Base*.sup.2 
Dimethylaminopropyl 
-- -- -- -- -- 
Methacrylamide Base*.sup.3 
Vinylpyrrolidone Base*.sup.4 
-- -- -- 5 -- 
Non-dispersion -- -- -- -- 5 
Type Polymethacryalte*.sup.5 
Antioxidant 
Dioctyldiphenylamine*.sup.6 
-- -- -- 0.5 0.5 
Phenyl-.alpha.-naphthylamine*.sup.7 
-- -- -- -- -- 
2,6-di-t-butyl- -- 0.5 -- -- -- 
4-methylphenol*.sup.8 
1,3,4-thiadi- 0.3 0.3 0.6 0.3 0.3 
azole Polysulfide*.sup.9 
Test Results 
SAE No. 2 Test (.mu..sub.0 /.mu..sub.K) 
Fresh Oil 1.02 1.03 1.02 1.03 1.02 
Degradated Oil 1.25 1.18 1.20 1.12 1.14 
Oxidation Stability Test 
Viscosity Ratio 1.36 1.19 1.25 1.10 1.12 
Increase in Total 
5.11 2.02 4.12 1.23 1.41 
Acid Value 
Insoluble Residue 
2.50 0.79 2.00 1.05 1.24 
______________________________________ 
Comparative Example 
6 7 8 
______________________________________ 
Components of the Composition (wt %) 
Base Oil*.sup.1 94.7 94.2 94.2 
Viscosity Index Improver 
Dimethylaminopro- 
-- -- -- 
pyl Methacrylate Base*.sup.2 
Dimethylaminopropyl 
5 5 5 
Methacrylamide Base*.sup.3 
Vinylpyrrolidone Base*.sup.4 
-- -- -- 
Non-dispersion -- -- -- 
Type Polymethacryalte*.sup.5 
Antioxidant 
Dioctyldiphenylamine*.sup.6 
-- -- 0.5 
Phenyl-.alpha.-naphthylamine*.sup.7 
-- -- -- 
2,6-di-t-butyl- -- 0.5 -- 
4-methylphenol*.sup.8 
1,3,4-thiadi- 0.3 0.3 0.3 
azole Polysulfide*.sup.9 
Test Results 
SAE No. 2 Test (.mu..sub.0 /.mu..sub.K) 
Fresh Oil 1.02 1.03 1.01 
Degradated Oil 1.27 1.20 1.12 
Oxidation Stability Test 
Viscosity Ratio 1.40 1.22 1.10 
Increase in Total 
5.72 3.13 1.35 
Acid Value 
Insoluble Residue 
3.00 1.01 1.07 
______________________________________ 
*.sup.1 Base oil: This consists of 95.0% by weight of the mineral oil 
having a kinematic viscosity at 100.degree. C. of 5.0 cSt, 1.0% by weight 
of the amine salt of oleylhydrogen phosphite (the friction modifier) and 
4.0% by weight of polybutenylsuccinic acid imide (the 
detergentdispersant). 
*.sup.2 Dimethylaminopropyl methacrylate base: This is a copolymer of 
dimethylaminopropyl methacrylate which is a monomer having the formula 
(III) and a methacrylate of a longchain alcohol having 12 to 18 carbon 
atoms which is a monomer of the formula (IV). This numberaverage molecula 
weight is 30,000. The content of a repeating unit derived from 
dimethylaminopropyl methacrylate is 5% by weight, and the content of a 
repeating unit derived from the methacrylate of the longchain alcohol 
having 12 to 18 carbon atoms is 95% by weight. This is a dispersion type 
polymer which is a component (b) of the present invention. 
*.sup.3 Dimethylaminopropylmethacylamide base: This is a copolymer of 
dimethylaminopropylmethacrylamide and a methacrylate of a longchain 
alcohol having 12 to 18 carbon atoms which is a monomer of the formula 
(IV). This numberaverage molecular weight is 30,000. The content of a 
repeating unit derived from dimethylaminopropylmethacrylamide is 5% by 
weight, and the content of a repeating unit derived from the methacrylate 
of the longchain alcohol having 12 to 18 carbon atoms is 95% by weight. 
This is a dispersion type polymer other than the component (b) of the 
present invention. 
*.sup.4 Vinylpyrrolidone base: This is a copolymer of vinylpyrrolidone an 
a methacrylate of a longchain alcohol having 12 to 18 carbon atoms which 
is a monomer of the fromula (IV). This numberaverage molecular weight is 
30,000. The content of a repeating unit derived from vinylpyrrolidone is 
3% by weight, and the content of a repesting unit derived from the 
methacrylate of the longchain alcohol having 12 to 18 carbon atoms is 97% 
by weight. This is a dispersion type polymer other than the component (b) 
of the present invention. 
*.sup.5 Nondispersion type polymethacrylate: This is a polymer consisting 
only of a methacrylate of a longchain alcohol having 12 to 18 carbon atom 
which is a monomer of the formula (IV). This numberaverage molecular 
weight is 30,000. 
*.sup.6 Dioctyldiphenylamine: This is a aminebased antioxidant which is a 
component (c) of the present invention. 
*.sup.7 Phenylnaphthylamine: This is an aminebased antioxidant which is 
the component (c) of the present invention. 
*.sup.8 2,6di-t-butyl-4-methylphenol: This is an antioxidant other than 
the aminebased antioxidant, and it does not correspond to the component 
(c) of the present invention. 
*.sup.9 1,3,4thiadiazole polysulfide: This is a thiadiazole compound whic 
can be used as a metal deactivator, and it corresponds to the component 
(d) of the present invention.