Lubricating oil composition for automatic transmission

Disclosed is a lubricating oil composition for automatic transmissions, which comprises a base oil and additives of (A) a sulfur-containing antioxidant or an amine-type antioxidant, (B) a phosphate or its amine salt, and (C) a reaction product of a carboxylic acid and an amine. The composition has an excellent ability to prevent the brake lining of the clutch of automatic transmissions from shuddering, and can maintain the shudder-preventing ability for a long period of time.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a lubricating oil composition for 
automatic transmissions, and, more precisely, to that having an excellent 
ability to prevent the brake lining of the clutch of automatic 
transmissions from shuddering, and capable of maintaining the 
shudder-preventing ability for a long period of time. 
2. Description of the Related Art 
Automatic transmissions (AT), especially those equipped with a continuous 
slip mechanism are required to have the ability to prevent shudders that 
may occur in the clutch of AT. Cars using a conventional automatic 
transmission fluid (ATF) greatly shudder. Various attempts have been made 
to prevent cars from shuddering. For example, Japanese Patent Application 
Laid-Open No. 7-305082 discloses a lubricating oil composition for 
automatic transmissions, which comprises a base oil and additives of (1) 
zinc dithiophosphate and/or basic zinc dithiophosphate, (2) at least one 
compound selected from the group consisting of phosphates, acid phosphates 
and phosphites and (3) an organic friction regulator having a specific 
bond and/or a functional group as introduced into the molecule. This 
composition is effective in preventing initial shudders but is defective 
in that, while it is used for a long period of time, zinc dithiophosphate 
therein adheres to the surface of a wet clutch to thereby greatly shorten 
the shudder-preventing life of the composition, resulting in that the 
composition could no more maintain its original properties. Japanese 
Patent Application Laid-Open No. 63-254196 discloses the addition of a 
friction regulator of any of phosphates, fatty acid esters and fatty acid 
amides to ATF, which, however, is not satisfactory for preventing initial 
shudders. 
Given the situation, the present invention is to provide a lubricating oil 
composition for automatic transmissions which has an excellent ability to 
prevent the brake lining of the clutch of automatic transmissions from 
shuddering, and can maintain the shudder-preventing ability for a long 
period of time. 
SUMMARY OF THE INVENTION 
We, the present inventors have assiduously studied and, as a result, have 
found that the object of the present invention can be effectively attained 
by adding a specific antioxidant, a phosphate or its amine salt, and a 
reaction product of a carboxylic acid and an amine to a base oil. On the 
basis of this finding, we have completed the present invention. 
Specifically, the present invention is to provide a lubricating oil 
composition for automatic transmissions, which comprises a base oil and 
additives of (A) a sulfur-containing antioxidant or an amine-type 
antioxidant, (B) a phosphate or its amine salt, and (C) a reaction product 
of a carboxylic acid and an amine. 
DETAILED DESCRIPTION OF THE INVENTION 
Now, the modes of carrying out the invention are described hereinunder. 
The lubricating oil composition for automatic transmissions of the present 
invention comprises a mineral oil and/or a synthetic oil as the base oil. 
The mineral oil and the synthetic oil are not specifically defined, but 
may be any ordinary ones that are generally used as the base oil of 
ordinary transmission fluids. However, preferred are those having a 
dynamic viscosity at 100.degree. C. of from 1 to 20 mm.sup.2 /s, more 
preferably from 2 to 10 mm.sup.2 /s. If the base oil has a too high 
dynamic viscosity, its low-temperature viscosity is unfavorably low; but, 
on the contrary, if its dynamic viscosity is too low, such is also 
unfavorable since the base oil having such a too low dynamic viscosity 
causes the increase of the wear in the slide members such as gear bearings 
and clutches of automatic transmissions. The pour point of the base oil, 
which is the index for its low-temperature fluidity, is not specifically 
defined, but is desirably not higher than -10.degree. C. 
Various types of such mineral oil and synthetic oil are known, and any 
desirable ones may be selectively used in accordance with the object. The 
mineral oil includes, for example, paraffinic mineral oils, naphthenic 
mineral oils and intermediate base mineral oils. As specific examples, 
referred to are light neutral oils, medium-gravity neutral oils, heavy 
neutral oils and bright stocks to be prepared through solvent purification 
or hydrogenating purification. 
On the other hand, the synthetic oil includes, for example, 
poly-.alpha.-olefins, .alpha.-olefin copolymers, polybutenes, 
alkylbenzenes, polyol esters, dibasic acid esters, polyoxyalkylene 
glycols, polyoxyalkylene glycol esters, polyoxyalkylene glycol ethers, and 
silicone oils. 
These base oils can be used singly or as combined. Combinations of mineral 
oils and synthetic oils are also employable. 
Now, the additives (A) to (C) to the base oil are referred to hereinunder. 
Component (A) 
The sulfur-containing antioxidant may be any and every antioxidant 
containing sulfur, for example, including dialkyl thiodipropionates such 
as dilauryl thiodipropionate and distearyl thiodipropionate, 
dialkyldithiocarbamic acid derivatives (excluding metal salts), 
bis(3,5-di-t-butyl-4-hydroxybenzyl)sulfide, mercaptobenzothiazole, 
reaction products of phosphorus pentoxide and olefins, and dicetyl 
sulfide. Of these, preferred are dialkyl thiodipropionates such as 
dilauryl thiodipropionate and distearyl thiodipropionate. 
The amine-type antioxidant includes, for example, monoalkyldiphenylamines 
such as monooctyldiphenylamine and monononyldiphenylamine; 
dialkyldiphenylamines such as 4,4'-dibutyldiphenylamine, 
4,4'-dipentyldiphenylamine, 4,4'-dihexyldiphenylamine, 
4,4'-diheptyldiphenylamine, 4,4'-dioctyldiphenylamine and 
4,4'-dinonyldiphenylamine; polyalkyldiphenylamines such as 
tetrabutyldiphenylamine, tetrahexyldiphenylamine, tetraoctyldiphenylamine 
and tetranonyldiphenylamine; and naphthylamines such as 
.alpha.-naphthylamine, phenyl-.alpha.-naphthylamine, 
butylphenyl-.alpha.-naphthylamine, pentylphenyl-.alpha.-naphthylamine, 
hexylphenyl-.alpha.-naphthylamine, heptylphenyl-.alpha.-naphthylamine, 
octylphenyl-.alpha.-naphthylamine and nonylphenyl-.alpha.-naphthylamine. 
Of these, preferred are dialkyldiphenylamines. 
The sulfur-containing antioxidant and the amine-type antioxidant are added 
to the base oil in an amount of from 0.01 to 5% by weight, preferably from 
0.03 to 3% by weight, relative to the total weight of the composition. 
Component (B) 
Phosphates for use in the present invention include phosphates, acid 
phosphates, phosphites and acid phosphites of general formulae (I) to (V): 
##STR1## 
In these general formulae (I) to (V), R.sup.1 to R.sup.3 each represents an 
alkyl, alkenyl, alkylaryl or arylalkyl group having from 4 to 30 carbon 
atoms; and these R.sup.1 to R.sup.3 may be the same or different. 
The phosphates include triaryl phosphates, trialkyl phosphates, 
trialkylaryl phosphates, triarylalkyl phosphates and trialkenyl 
phosphates. As specific examples of these, referred to are triphenyl 
phosphate, tricresyl phosphate, benzyldiphenyl phosphate, ethyldiphenyl 
phosphate, tributyl phosphate, ethyldibutyl phosphate, cresyldiphenyl 
phosphate, dicresylphenyl phosphate, ethylphenyldiphenyl phosphate, 
diethylphenylphenyl phosphate, propylphenyldiphenyl phosphate, 
dipropylphenylphenyl phosphate, triethylphenyl phosphate, tripropylphenyl 
phosphate, butylphenyldiphenyl phosphate, dibutylphenylphenyl phosphate, 
tributylphenyl phosphate, trihexyl phosphate, tri(2-ethylhexyl) phosphate, 
tridecyl phosphate, trilauryl phosphate, trimyristyl phosphate, 
tripalmityl phosphate, tristearyl phosphate, and trioleyl phosphate. 
The acid phosphates include, for example, 2-ethylhexyl acid phosphate, 
ethyl acid phosphate, butyl acid phosphate, oleyl acid phosphate, 
tetracosyl acid phosphate, isodecyl acid phosphate, lauryl acid phosphate, 
tridecyl acid phosphate, stearyl acid phosphate, and isostearyl acid 
phosphate. 
The phosphites include, for example, triethyl phosphite, tributyl 
phosphite, triphenyl phosphite, tricresyl phosphite, tri(nonylphenyl) 
phosphite, tri(2-ethylhexyl) phosphite, tridecyl phosphite, trilauryl 
phosphite, triisooctyl phosphite, diphenylisodecyl phosphite, tristearyl 
phosphite, and trioleyl phosphite. 
The acid phosphites include, for example, dibutyl hydrogenphosphite, 
dilauryl hydrogenphosphite, dioleyl hydrogenphosphite, distearyl 
hydrogenphosphite, and diphenyl hydrogenphosphite. 
Of the above-mentioned phosphates, preferred are oleyl acid phosphate and 
tricresyl phosphate. 
Amines that form amine salts with such phosphates include, for example, 
mono-substituted amines, di-substituted amines and tri-substituted amines 
of a general formula (VI): 
EQU R.sub.n NH.sub.3-n (VI) 
wherein R represents an alkyl or alkenyl group having from 3 to 30 carbon 
atoms, an aryl or arylalkyl group having from 6 to 30 carbon atoms, or a 
hydroxyalkyl group having from 2 to 30 carbon atoms; n represents 1, 2 or 
3; and when the compound has a plurality of Rs, such plural Rs may be the 
same or different. 
In general formula (VI), the alkyl or alkenyl group with from 3 to 30 
carbon atoms to be represented by R may be linear, branched or cyclic. 
Examples of the mono-substituted amines include butylamine, pentylamine, 
hexylamine, cyclohexylamine, octylamine, laurylamine, stearylamine, 
oleylamine and benzylamine; and those of the di-substituted amines include 
dibutylamine, dipentylamine, dihexylamine, dicyclohexylamine, 
dioctylamine, dilaurylamine, distearylamine, dioleylamine, dibenzylamine, 
stearyl monoethanolamine, decyl monoethanolamine, hexyl monopropanolamine, 
benzyl monoethanolamine, phenyl monoethanolamine, and tolyl 
monopropanolamine. Examples of tri-substituted amines include 
tributylamine, tripentylamine, trihexylamine, tricyclohexylamine, 
trioctylamine, trilaurylamine, tristearylamine, trioleylamine, 
tribenzylamine, dioleyl monoethanolamine, dilauryl monopropanolamine, 
dioctyl monoethanolamine, dihexyl monopropanolamine, dibutyl 
monopropanolamine, oleyl diethanolamine, stearyl dipropanolamine, lauryl 
diethanolamine, octyl dipropanolamine, butyl diethanolamine, benzyl 
diethanolamine, phenyl diethanolamine, tolyl dipropanolamine, xylyl 
diethanolamine, triethanolamine, and tripropanolamine. 
Phosphates or their amine salts are added to the base oil in an amount of 
from 0.03 to 5% by weight, preferably from 0.1 to 4% by weight, relative 
to the total weight of the composition. 
Component (C) 
Carboxylic acids to be reacted with amines include, for example, aliphatic 
carboxylic acids, dicarboxylic acids (dibasic acids), and aromatic 
carboxylic acids. The aliphatic carboxylic acids have from 8 to 30 carbon 
atoms, and may be saturated or unsaturated, and linear or branched. 
Specific examples of the aliphatic carboxylic acids include pelargonic 
acid, lauric acid, tridecanoic acid, myristic acid, palmitic acid, stearic 
acid, isostearic acid, eicosanoic acid, behenic acid, triacontanoic acid, 
caproleic acid, undecylenic acid, oleic acid, linolenic acid, erucic acid, 
and linoleic acid. Specific examples of the dicarboxylic acids include 
octadecylsuccinic acid, octadecenylsuccinic acid, adipic acid, azelaic 
acid, and sebacic acid. One example of the aromatic carboxylic acids is 
salicylic acid. 
On the other hand, the amines to be reacted with carboxylic acids include, 
for example, polyalkylene-polyamines such as diethylenetriamine, 
triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, 
hexaethyleneheptamine, heptaethyleneoctamine, dipropylenetriamine, 
tetrapropylenepentamine, and hexabutyleneheptamine; and alkanolamines such 
as monoethanolamine and diethanolamine. 
Of these, preferred are a combination of isostearic acid and 
tetraethylenepentamine, and a combination of oleic acid and 
diethanolamine. The reaction products of carboxylic acids and amines are 
added to the base oil in an amount of from 0.01 to 5% by weight, 
preferably from 0.03 to 3% by weight, relative to the total weight of the 
composition. 
The composition of the present invention can be obtained by adding the 
above-mentioned components (A) to (C) to a base oil. In order to improve 
its physical properties, in general, the lubricating oil composition of 
the invention may optionally contain a viscosity index improver, an 
ash-free dispersant, a detergent, an extreme-pressure agent, a defoaming 
agent, and a rust inhibitor.

Now, the present invention is described in more detail hereinunder with 
reference to the following examples, which, however, are not intended to 
restrict the scope of the invention. 
Methods for Testing Properties of Samples Produced in Examples and 
Comparative Examples 
(1) Shudder-preventing Ability: 
A ratio of .mu..sub.1 /.mu..sub.50 was obtained, according to the method of 
testing properties of automatic transmission fluids (JASO M349-95), to 
evaluate the shudder-preventing ability of samples. 
.mu..sub.1 : coefficient of friction at a sliding velocity of 1 rpm. 
.mu..sub.50 : coefficient of friction at a sliding velocity of 50 rpm. 
(2) Shudder-preventing Life: 
According to JASO M349-95, samples were subjected to a durability test 
under the condition mentioned below, in which the frictional 
characteristics of each sample were measured every 8 hours. The time 
within which the ratio of .mu..sub.1 /.mu..sub.50 reached 1 or more was 
measured to be the life time of each sample. 
Oil temperature: 120.degree. C. 
Surface pressure: 1.00.+-.0.05 MPa 
Number of revolution: 200 rpm 
(3) Transmission Torque Capacity: 
According to JASO M349-95, samples were subjected to a test for frictional 
characteristics, in which the coefficient of static friction (.mu..sub.s) 
was obtained to evaluate the samples. 
EXAMPLE 1 
As the base oil used herein was a paraffinic mineral oil (having a dynamic 
viscosity at 100.degree. C. of 5 mm.sup.2 /s), to which were added 0.5% by 
weight of dilauryl thiodipropionate as the component (A), 0.5% by weight 
of tricresyl phosphate as the component (B) and 0.5% by weight of 
isostearic acid tetraethylenepentamide as the component (C). In addition, 
further added thereto were 9.5% by weight of polymethacrylate (viscosity 
index improver), 2% by weight of polybutenylsuccinimide (ash-free 
dispersant), 2% by weight of calcium sulfonate (detergent), and 0.5% by 
weight of sulfurized oils and fats (extreme-pressure agent), the additives 
being 14% by weight in total. Thus was prepared a lubricating oil 
composition for automatic transmissions, which was subjected to the 
property tests mentioned above. The data obtained are shown in Table 1 
below. 
EXAMPLES 2 TO 6 AND COMATIVE EXAMPLES 1 TO 8 
Various lubricating oil compositions for automatic transmissions were 
prepared in the same manner as in Example 1 except that the amount of the 
base oil, the components (A) to (C) and their amounts were varied to those 
as in Table 1. These were subjected to the property tests mentioned above. 
The data obtained are shown in Table 1. 
TABLE 1-1 
__________________________________________________________________________ 
Example 1 
Example 2 
Example 3 
__________________________________________________________________________ 
Composition wt. % 
Base Oil 84.5 84.45 
83.45 
Component (A) 
Dilauryl Thiodipropionate 
0.5 1.0 0.05 
Dioctyldiphenyiamine 
-- -- -- 
Component (B) 
Tricresyl Phosphate 
0.5 -- 1.0 
Dioleyl Acid Phosphate 
-- 0.5 -- 
Component (C) 
Isostearic Acid Tetraethylenepentamide 
0.5 0.05 -- 
Oleic Acid Diethanoiamide 
-- -- 1.5 
Other Additives: viscosity index improver, 
14.0 14.0 14.0 
extreme-pressure agent, etc. 
Shudder-preventing Ability 0.85 0.86 0.82 
Shudder-preventing Life (hr) 60 55 53 
Transmission Torque Capacity (as .mu.s) 
0.13 0.14 0.12 
__________________________________________________________________________ 
TABLE 1-2 
__________________________________________________________________________ 
Comparative 
Comparative 
Comparative 
Example 1 
Example 2 
Example 3 
__________________________________________________________________________ 
Composition wt. % 
Base Oil 81.5 82.0 83.5 
Component (A) 
Dilauryl Thiodipropionate 
-- 1.0 1.0 
Dioctyldiphenyiamine 
-- -- -- 
Component (B) 
Tricresyl Phosphate 
3.0 3.0 -- 
Dioleyl Acid Phosphate 
-- -- -- 
Component (C) 
Isostearic Acid Tetraethylenepentamide 
1.5 -- -- 
Oleic Acid Diethanoiamide 
-- -- 1.5 
Other Additives: viscosity index improver, 
14.0 14.0 14.0 
extreme-pressure agent, etc. 
Shudder-preventing Ability 0.98 1.10 0.96 
Shudder-preventing Life (hr) 22 0 20 
Transmission Torque Capacity (as .mu.s) 
0.12 0.14 0.10 
__________________________________________________________________________ 
TABLE 1-3 
__________________________________________________________________________ 
Comparative 
Comparative 
Example 4 
Example 5 
Example 4 
__________________________________________________________________________ 
Composition wt. % 
Base Oil 81.5 78.0 84.5 
Component (A) 
Dilauryl Thiodipropionate 
1.0 -- -- 
Dioctyldiphenyiamine 
-- -- 0.5 
Component (B) 
Tricresyl Phosphate 
-- -- 0.5 
Dioleyl Acid Phosphate 
-- 0.8 -- 
Component (C) 
Isostearic Acid Tetraethylenepentamide 
-- -- 0.5 
Oleic Acid Diethanoiamide 
3.5 -- -- 
Other Additives: viscosity index improver, 
14.0 14.0 14.0 
extreme-pressure agent, etc. 
Shudder-preventing Ability 0.88 0.75 0.84 
Shudder-preventing Life (hr) 29 18 62 
Transmission Torque Capacity (as .mu.s) 
0.07 0.05 0.13 
__________________________________________________________________________ 
TABLE 1-4 
__________________________________________________________________________ 
Comparative 
Example 5 
Example 6 
Example 6 
__________________________________________________________________________ 
Composition wt. % 
Base Oil 84.45 
84.45 
81.5 
Component (A) 
Dilauryl Thiodipropionate 
-- -- -- 
Dioctyldiphenyiamine 
1.0 0.05 -- 
Component (B) 
Tricresyl Phosphate 
-- 1.0 3.0 
Dioleyl Acid Phosphate 
0.5 -- -- 
Component (C) 
Isostearic Acid Tetraethylenepentamide 
0.05 -- 1.5 
Oleic Acid Diethanoiamide 
-- 1.5 -- 
Other Additives: viscosity index improver, 
14.0 14.0 14.0 
extreme-pressure agent, etc. 
Shudder-preventing Ability 0.85 0.83 0.98 
Shudder-preventing Life (hr) 60 50 2 
Transmission Torque Capacity (as .mu.s) 
0.14 0.12 0.12 
__________________________________________________________________________ 
TABLE 1-5 
__________________________________________________________________________ 
Comparative 
Comparative 
Example 7 
Example 8 
__________________________________________________________________________ 
Composition wt. % 
Base Oil 82.0 83.5 
Component (A) 
Dilauryl Thiodipropionate 
-- -- 
Dioctyldiphenyiamine 
1.0 1.0 
Component (B) 
Tricresyl Phosphate 
3.0 -- 
Dioleyl Acid Phosphate 
-- -- 
Component (C) 
Isostearic Acid Tetraethylenepentamide 
-- -- 
Oleic Acid Diethanoiamide 
-- 1.5 
Other Additives: viscosity index improver, 
14.0 14.0 
extreme-pressure agent, etc. 
Shudder-preventing Ability 1.15 0.89 
Shudder-preventing Life (hr) 0 20 
Transmission Torque Capacity (as .mu.s) 
0.15 0.09 
__________________________________________________________________________ 
From Examples and Comparative Examples, known are the following. Of the 
samples of Examples, the ratio, .mu..sub.1 /.mu..sub.50 was from 0.82 to 
0.86, which was smaller than 1. Thus, these samples have good 
shudder-preventing ability. Their shudder-preventing life as measured in 
the predetermined test was from 50 to 62 hours, which was two times or 
longer than that of the samples of Comparative Examples. Their 
transmission torque capacity was larger than 0.1, and the samples of 
Examples are excellent as automatic transmission fluids. 
As opposed to these, the samples of Comparative Examples 1 and 6, though 
comprising the components (B) and (C) in predetermined amounts, had an 
extremely short shudder-preventing life and therefore could not attain the 
object of the invention. The samples of Comparative Examples 2 and 7, as 
not containing the component (C), could not have a satisfactory 
shudder-preventing ability; while those of Comparative Examples 3 and 8 
not containing the component (B) had a short shudder-preventing life. The 
samples of Comparative Examples 4 and 5 comprised large amounts of the 
components (B) and (C) in order to have a prolonged shudder-preventing 
life. Though prolonged in some degree, their shudder-preventing life was 
still 1/2 or smaller than the life of the samples of Examples. In 
addition, as their transmission torque capacity was smaller than 0.1, the 
samples of Comparative Examples 4 and 5 are unfavorable as automatic 
transmission fluids. Even if the components (B) and (C) are merely 
increased in order to prolong the shudder-preventing life, such brings 
about the decrease in the torque capacity and the resulting compositions 
could not be put into practical use as automatic transmission fluids. 
As has been mentioned and demonstrated in detail hereinabove, the 
lubricating oil composition for automatic transmissions of the present 
invention has an excellent shudder-preventing ability while maintaining 
the shudder-preventing ability for a long period of time, and has a high 
transmission torque capacity. 
While the invention has been described in detail and with reference to 
specific embodiments thereof, it will be apparent to one skilled in the 
art that various changes and modifications can be made therein without 
departing from the spirit and scope thereof.