Note: Descriptions are shown in the official language in which they were submitted.
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TITLE
LIMITED SLIP FRICTION MODIFIERS FOR DIFFERENTIALS
BACKGROUND OF THE INVENTION
[0001] The invention relates to a lubricating composition
comprising (a) an oil of lubricating viscosity, and (b) an oil soluble
compound. The invention further provides for the use of the
lubricating composition for lubricating a limited slip differential.
[0002] A vehicle differential typically has bevel gear or spur gear
planetary systems which distribute drive torque evenly to the two
driving wheels irrespective of their rotational speed. This makes it
possible for the driven wheels to roll during cornering without slip
between the wheel and road surface in spite of their different
rotational speed. When one wheel is on a low traction surface, the
amount of torque that can be transmitted is limited to the amount
which can be applied before the wheel slips.
[0003] A limited slip differential typically employs a wet multi-
plate clutch, i.e., clutch plates which are in contact with a lubricant,
to supply more torque to the non-slipping wheels during a slipping
situation. During normal turns, for one wheel to spin faster than the
other, the clutch plates must disengage or break away. There can be
NVH (noise, vibration, harshness) associated with this event.
[0004] In order for the slip to be controlled lubricants containing
compounds capable of improving friction performance, dispersants
and sulfur- and/or phosphorus- containing extreme pressure agents
may be used. Examples of lubricants of this type are disclosed in US
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Patents 4,308,154; 4,180,466; 3,825,495; and European Patent
Application 0 399 764 Al.
[0005] A
certain class of compounds capable of improving friction
performance is taught, for example, in US 5,021,176 to Bullen et al.,
issued June 4, 1991. Bullen teaches, among other things, a diamine
as a friction reducing additive, particularly in wet brake systems,
having the structure shown immediately below.
0 0
II II
R-C-NH-CH2CH2-NH-C-R
[0006]
Similarly, WO 2010/096325 to inventors Saccomando et
al., published August 26, 2010, and US 4,446,053 to Skrobul et al.,
issued May 1, 1984 teach amine type compounds for friction
modification.
[0007]
Saccomando teaches a composition for use as a friction
modifier for an automatic transmission, comprising a long chain
hydrocarbyl amine haying one or two additional groups on one or two
different amine nitrogen atoms thereof.
One of the species
represented in the publication is shown in formula XIIa therein,
haying a formula of R1N((CH2)2CONH(CH2)3NHR12.
[0008]
Skrobul teaches friction reducing additives for engine oils
characterized by the following general formulas.
RNHCH2CH2CO2¨Na+ and
RNHCH2CH2CONH2
[0009]
Neither of Saccomando or Skrobul teach the use of the
amine compounds for friction performance in limited slip differentials,
and the compounds do not encompass the compounds as taught
herein.
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[0010] US
2012/0015855 to Saccomando et al., published
January 19, 2012 and US 2012/0122744 to Saccomando et al.,
published May 17, 2012 teach varying classes of amine friction
modifying compounds that do not include the compounds taught
herein.
[0011] US
5,372,735 to Ohtani et al., issued December 13, 1994
teaches an automatic transmission fluid with a friction modifier
content consisting essentially of a hydrocarbyl substituted
diethanolamine and an hydrocarbyl N-
substituted
trimethylenediamine. The compound of the present invention does
not require a synergistic amount of another compound, such as a
diethanolamine, and further, the compounds taught herein are
different than diethanolamine and N-substituted trimethylenediamine
as taught in Ohtani.
[0012] GB
1209548 teaches a motor fuel composition comprising
an amide represented by the general formula
0
R"--N---CH2CH2CHn-N-C-R
R'
where R is a hydrocarbyl having 17 carbon atoms derived from oleic
acid and R' and R" alternately represent hydrogen and a hydrocarbyl
radical having from 14 to 18 carbon atoms. The GB patent does not
teach the use of the formula in a lubricant for limited slip
differentials.
[0013]
Another patent, JP 63060956, teaches a compound useful
as a lubricant for synthetic resin including, among other things, a
bisamidation reaction of a fatty acid with a diamine. The JP'956
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patent does not teach the use of the amine compounds for friction
performance in limited slip differentials.
[0014] US 4,581,039 to Horodysky, issued April 8, 1986 teaches
antifriction carboxylates of the formula:
RI R3
R¨N¨R2¨N¨R4
(R5COOH)x (HOOCR5)y
for engine oils and fuel compositions. In the preferred embodiments
of the formula R3 and R4 are H. The carboxylate formula does not
encompass the compounds disclosed herein and specifically teaches
against the production of amides (col 2, lines 13-19 - "prevention of
amide formation"). In addition, the patent does not teach the use of
the compounds for limited slip differentials.
[0015] W02010/096318, published August 26, 2010, teaches
anti-friction compounds for automatic transmissions of the formula
below. The publication does not teach the use of the compounds for
limited slip differentials.
-C
!.1
R2 )b 0
[0016] A lubricant for limited slip differentials is desired that is
capable of providing a high coefficient of friction and a low tendency
toward noise, vibration and harshness.
SUMMARY OF THE INVENTION
[0017] An object of the present invention is to provide a
lubricating composition and method as disclosed herein that is
capable of providing a high coefficient of friction and a low tendency
toward noise, vibration and harshness (NVH) often manifested as
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chatter (i.e. an abnormal noise typically referred to as a low-
frequency "growl" and "groan," particularly during low-speed
cornering maneuvers). The inventors have unexpectedly discovered
that the lubricant composition and method disclosed herein may also
be suitable for limited slip systems having one or more distinct plate
materials. For example, the plate materials may be steel, paper,
ceramic, carbon fibers and systems employing a mixture of plate
types such as steel on ceramic, carbon fibers in paper or steel on
paper.
[0018] In one embodiment, the invention provides a lubricant
for limited slip differentials comprising an (a) a major amount of an
oil of lubricating viscosity, and (b) at least one oil soluble compound
comprising the condensation product of (1) an N-substituted 1,3-
diaminopropane, wherein the N-substituent is derived from a C8-28
amine, and (2) a C8-28 acid.
[0019] Preferably, the C8-28 amine of (1) is a fatty amine and the
C8-28 acid of (b) is at least one of a fatty acid or fatty acid chloride.
However, the amine and the acid are not particularly limited and can
be any amine and acid suitable for preparing an oil soluble
compound, as described, for the intended purpose in limited slip
systems.
[0020] In an embodiment of the lubricant, the condensation
product can comprise a compound of formula R'NH(CH2)3NHCOR."
Preferably, R' is the N-substituent derived from the C8-28 amine of (1),
and -COR" is derived from the C8-28 acid of (2).
[0021] In a particularly preferred embodiment, R' can be derived
from a C18 fatty amine, such as oleyl amine, and -COR" can be
derived from a C18 fatty acid, such as oleic acid.
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[0022] In a further embodiment, there is provided a method of
providing limited slip performance to a differential comprising the
step of introducing the oil soluble compound described herein, or a
lubricating composition comprising the oil soluble compound
described herein to a limited slip differential, and operating the
limited slip differential.
[0023] In another embodiment there is provided a use of a
lubricant as described above for providing limited slip performance
in a limited slip differential.
DETAILED DESCRIPTION OF THE INVENTION
[0024] Various preferred features and embodiments will be
described below by way of non-limiting illustration.
[0025] As used herein the expression "oil-soluble" or
"hydrocarbon soluble" is meant a material which will dissolve or
disperse on a macroscopic or gross scale in an oil or hydrocarbon, as
the case may be, typically a mineral oil, such that a practical
solution or dispersion can be prepared. In order to prepare a useful
lubricant formulation, the material should not precipitate or settle
out over a course of several days or weeks. Such materials may
exhibit true solubility on a molecular scale or may exist in the form
of agglomerations of varying size or scale, provided however that they
have dissolved or dispersed on a gross scale.
[0026] As used herein, the term "hydrocarbyl group" or
"hydrocarbyl substituent" is used in its ordinary sense, which is
well-known to those skilled in the art. Specifically, it refers to a
group having a carbon atom directly attached to the remainder of the
molecule and having predominantly hydrocarbon character.
Examples of hydrocarbyl groups include:
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(i) hydrocarbon substituents, that is, aliphatic (e.g., alkyl or
alkenyl), alicyclic (e.g., cycloalkyl, cycloalkenyl) substituents, and
aromatic-, aliphatic-, and alicyclic- substituted
aromatic
substituents, as well as cyclic substituents wherein the ring is
completed through another portion of the molecule (e.g., two
substituents together form a ring);
(ii) substituted hydrocarbon substituents, that is, substituents
containing non-hydrocarbon groups which, in the context of this
invention, do not alter the predominantly hydrocarbon nature of the
substituent (e.g., halo (especially chloro and fluoro), hydroxy, alkoxy,
mercapto, alkylmercapto, nitro, nitroso, and sulfoxy);
(iii) hetero substituents, that is, substituents which, while
having a predominantly hydrocarbon character, in the context of this
invention, contain other than carbon in a ring or chain otherwise
composed of carbon atoms, and encompass substituents as pyridyl,
furyl, thienyl and imidazolyl; and
[0027]
(iv) heteroatoms, including sulfur, oxygen, and nitrogen.
In general, no more than two, preferably no more than one, non-
hydrocarbon substituent will be present for every ten carbon atoms
in the hydrocarbyl group; typically, there will be no non-hydrocarbon
substituents in the hydrocarbyl group.
[0028]
One aspect of the present invention is a lubricant for a
limited slip differential comprising an oil-soluble compound. In one
embodiment, the oil soluble compound can be the condensation
product of (a) an N-substituted 1,3-diaminopropane, and (b) an acid.
The N-substituent on the 1,3-diaminopropane can be derived from
an amine.
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[0029]
The N-substituent amine and the acid are not
particularly limited and can be any amine and acid suitable for
preparing the oil soluble compound, as described, for the intended
purpose in limited slip systems.
[0030] In a
preferred embodiment, the N-substituent of the N-
substituted 1,3-diaminopropane of (a) can be derived from a
hydrocarbyl substituted amine, namely an alkylamine. The
alkylamine can comprise a single alkyl substituent or a mixture of
alkyl substituents. Preferably, the amine is a C8-28 amine, or in some
cases, a C9-26 amine, more preferably a C10-24 amine, or a C11-22
amine. The amine can also be from about C16 or C18 to C20.
[0031]
Particularly preferred amines include fatty amines
and/or fatty amine mixtures, such as, for example, soya amine, oleyl
amine, tallow amine, cocoamine, and the like. In a preferred
embodiment the amine is oleyl amine. In
another preferred
embodiment, the amine is tallow amine.
[0032] In
a preferred embodiment, the acid is a C8-28 acid, or in
some cases, a C9-26 acid, more preferably a C10-24 acid, or a C11-22
acid. The acid may also be from about C16 or C18 to C20. In some
embodiments the acid can be, for example, a fatty acid, and in other
embodiments the acid can be a fatty acid chloride.
[0033]
Particularly preferred acids include fatty acids, such as,
for example, myristic acid, palmitic acid, behenic acid, eruicic acid,
oleic acid, stearic acid, linoleic acid, and lauric acid, and the like. In
a preferred embodiment, the acid can be oleyl acid. In another
preferred embodiment, the acid can be linoleic acid.
[0034] In
an embodiment of the oil soluble compound as
described above, the condensation product can comprise a
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compound of formula R'NH(CH2)3NHCOR". Preferably, R' is the N-
substituent derived from the amine of (a), and -COR" is derived from
the acid of (b).
[0035] R' and -COR" can be derived from a derivative of the
same or different precursor. For example, R' and -COR" can be
derived from a derivative of an oleyl precursor, such as oleic acid, or
R' can be derived from a derivative of, for example, an oleyl precursor
and -COR" can be derived from a derivative of, for example, a erucyl
precursor. In a particularly preferred embodiment, R' can be derived
from a C18 fatty amine, such as oleyl amine, and -COR" can be
derived from a C18 fatty acid, such as oleic acid.
[0036] Oil-soluble compounds according to the foregoing
embodiments can be employed in a lubricating composition with oils
of lubricating viscosity to provide friction performance in limited slip
differentials. The oil-soluble compounds can be included, on an oil-
free basis, at a concentration of from about 0.1 to about 8 wt%, or
0.2 to about 7 wt%, and in some embodiments from about 0.25 to
about 5 or about 6 wt%, or even from about 0.25 to about 1, or 2, or
3 or about 4 wt%.
[0037] Oils of Lubricating Viscosity
[0038] The lubricating composition comprises a major amount of
an oil of lubricating viscosity. Such oils include natural and
synthetic oils, oil derived from hydro cracking, hydrogenation, and
hydrofinishing, unrefined, refined, re-refined oils or mixtures thereof.
A more detailed description of unrefined, refined and re-refined oils
is provided in International Publication W02008/147704,
paragraphs [0054] to [0056].
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[0039] Synthetic lubricating oils include hydrocarbon oils and
halo-substituted hydrocarbon oils such as polymerized and
interpolymerized olefins, also known as polyalphaolefins;
polyphenyls; alkylated diphenyl ethers; alkyl- or dialkylbenzenes;
and alkylated diphenyl sulfides; and the derivatives, analogs and
homologues thereof. Also included are alkylene oxide polymers and
interpolymers and derivatives thereof, in which the terminal hydroxyl
groups may have been modified by esterification or etherification.
Also included are esters of dicarboxylic acids with a variety of
alcohols, or esters made from C5 to C12 monocarboxylic acids and
polyols or polyol ethers. Other synthetic oils include silicon-based
oils, liquid esters of phosphorus-containing acids, and polymeric
tetrahydrofurans. The synthetic oils may be produced by Fischer-
Tropsch reactions and typically may comprise hydroisomerized
Fischer-Tropsch hydrocarbons and/or waxes, or hydroisomerized
slack waxes. In one embodiment oils may be prepared by a Fischer-
Tropsch gas-to-liquid synthetic procedure as well as other gas-to-
liquid oils.
[0040] Oils of lubricating viscosity may also be defined as
specified in April 2008 version of "Appendix E - API Base Oil
Interchangeability Guidelines for Passenger Car Motor Oils and
Diesel Engine Oils", section 1.3 Sub-heading 1.3. "Base Stock
Categories." In one embodiment, the oil of lubricating viscosity may
be an API Group I, Group II, Group III, or Group IVoil.
[0041] Polyalphaolefins are categorized as Group IV oils. In one
embodiment, at least 50% by weight of the oil of lubricating viscosity
is a polyalphaolefin (PAO). Typically, the polyalphaolefins are
derived from monomers having from 4 to 30, or from 4 to 20, or from
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6 to 16 carbon atoms. Examples of useful PAOs include those
derived from 1-decene. These PAOs may have a viscosity of 1.5 to
150 mm2/s (cSt) at 100 C.
PAOs are typically hydrogenated
materials.
[0042] The amount
of the oil of lubricating viscosity present is
typically the balance remaining after subtracting from 100 wt% the
sum of the amount of the compound of the invention and the other
performance additives.
[0043]
The lubricating composition may be in the form of a
concentrate and/or a fully formulated lubricant. If the lubricating
composition of the invention (comprising the additives disclosed
herein) is in the form of a concentrate which may be combined with
additional oil to form, in whole or in part, a finished lubricant), the
ratio of these additives to the oil of lubricating viscosity and/or to
diluent oil includes the ranges of 1:99 to 99:1 by weight, or 80:20 to
10:90 by weight.
Other Performance Additives
[0044]
The composition of the invention optionally further
includes at least one other performance additive. The other
performance additives include dispersants, metal deactivators,
detergents, viscosity modifiers, extreme pressure agents (typically
boron- and/or sulfur- and/or phosphorus-containing), antiwear
agents, antioxidants (such as hindered phenols, aminic antioxidants
or molybdenum compounds), corrosion inhibitors, foam inhibitors,
demulsifiers, pour point depressants, seal swelling agents, friction
modifiers and mixtures thereof.
[0045]
The total combined amount of the other performance
additives (excluding the viscosity modifiers) present on an oil free
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basis may include ranges of 0.01 wt% to 25 wt%, or 0.01 wt% to 20
wt%, or 0.1 wt% to 15 wt% or 0.5 wt% to 10 wt%, or 1 to 5 wt% of
the composition. Although one or more of the other performance
additives may be present, it is common for the other performance
additives to be present in different amounts relative to each other.
[0046]
In one embodiment the lubricating composition is free of
molybdenum-containing additives.
Detergent
[0047]
One additional component of the disclosed lubricant can
be an overbased metal containing detergent. Detergents in general
are typically overbased materials, otherwise referred to as overbased
or superbased salts, which are generally homogeneous Newtonian
systems having by a metal content in excess of that which would be
present for neutralization according to the stoichiometry of the metal
and the detergent anion. The amount of excess metal is commonly
expressed in terms of metal ratio, that is, the ratio of the total equiva-
lents of the metal to the equivalents of the acidic organic compound.
Overbased materials are prepared by reacting an acidic material (such
as carbon dioxide) with an acidic organic compound, an inert reaction
medium (e.g., mineral oil), a stoichiometric excess of a metal base,
and a promoter such as a phenol or alcohol. The acidic organic
material will normally have a sufficient number of carbon atoms, to
provide oil-solubility.
[0048]
Overbased detergents may be characterized by Total Base
Number (TBN), the amount of strong acid needed to neutralize all of
the material's basicity, expressed as mg KOH per gram of sample.
Since overbased detergents are commonly provided in a form which
contains diluent oil, for the purpose of this document, TBN is to be
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recalculated to an oil-free basis. Various detergents may have a TBN
of 100 to 1000, or 150 to 800, or, 400 to 700.
[0049]
The metal compounds generally useful in making the
basic metal salts are generally any Group 1 or Group 2 metal
compounds (CAS version of the Periodic Table of the Elements).
Examples include alkali metals such as sodium, potassium, lithium,
copper, magnesium, calcium, barium, zinc, and cadmium. In one
embodiment the metals are sodium, magnesium, or calcium. The
anionic portion of the salt can be hydroxide, oxide, carbonate, borate,
or nitrate. The detergents of particular interest for the present
technology will be calcium detergents, typically prepared using
calcium oxide or calcium hydroxide.
Since the detergents of
particular interest are carbonated detergents, they will be materials
that have been treated with carbon dioxide. Such treatment leads to
more efficient incorporation of basic metal into the composition.
Formation of high TBN detergents involving reaction with carbon
dioxide is disclosed, for instance, in US 7,238,651, Kocsis et al., July
3, 2007, see, for instance, examples 10-13 and the claims. Other
detergents, however, may also optionally be present, which need not
be carbonated or need not be so highly overbased (i.e., of lower TBN).
However, if multiple detergents are present, it is desirable that the
overbased calcium arylsulfonate detergent is present as the
predominant amount by weight of the metal detergents, that is, at
least 50 weight percent or at least 60 or 70 or 80 or 90 weight percent
of the metal-containing detergents, on an oil free basis.
[0050]
The lubricants useful in the present technology can
contain an overbased sulfonate detergent. Suitable sulfonic acids
include sulfonic and thiosulfonic acids, including mono- or poly-
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nuclear aromatic or cycloaliphatic compounds. Certain oil-soluble
sulfonates can be represented by R2-T-(S03-)a or R3-(S03-)b, where a
and b are each at least one; T is a cyclic nucleus such as benzene or
toluene; R2 is an aliphatic group such as alkyl, alkenyl, alkoxy, or
alkoxyalkyl; (R2)-T typically contains a total of at least 15 carbon
atoms; and R3 is an aliphatic hydrocarbyl group typically containing
at least 15 carbon atoms. The groups T, R2, and R3 can also contain
other inorganic or organic substituents; they may also be described as
hydrocarbyl groups. In one embodiment the sulfonate detergent may
be a predominantly linear alkylbenzenesulfonate detergent as
described in paragraphs [0026] to [0037] of US Patent Application
2005-065045. In some embodiments the linear alkyl (or hydrocarbyl)
group may be attached to the benzene ring anywhere along the linear
chain of the alkyl group, but often in the 2, 3, or 4 position of the
linear chain, and in some instances predominantly in the 2 position.
In other embodiments, the alkyl (or hydrocarbyl) group may be
branched, that is, formed from a branched olefin such as propylene or
1-butene or isobutene. Sulfonate detergents having a mixture of
linear and branched alkyl groups may also be used.
[0051] Another type of overbased material that may additionally
be present (that is, in addition to the arylsulfonate detergent) in
certain embodiments of the present invention is an overbased phenate
detergent. Certain commercial grades of calcium sulfonate detergents
contain minor amounts of calcium phenate detergents to aid in their
processing or for other reasons and may contain, for instance, 4%
phenate substrate content and 96% sulfonate substrate content. The
phenols useful in making phenate detergents can be represented by
(R1)a-Ar-(OH)b, where R1 is an aliphatic hydrocarbyl group of 4 to 400
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or 6 to 80 or 6 to 30 or 8 to 25 or 8 to 15 carbon atoms; Ar is an aro-
matic group such as benzene, toluene or naphthalene; a and b are
each at least one, the sum of a and b being up to the number of
displaceable hydrogens on the aromatic nucleus of Ar, such as 1 to 4
or 1 to 2. There is typically an average of at least 7 or 8 aliphatic
carbon atoms provided by the Rl groups for each phenol compound,
and in some instances about 12 carbon atoms. Phenate detergents
are also sometimes provided as sulfur-bridged species or as
methylene-bridged species. Sulfur-bridged species may be prepared
by reacting a hydrocarbyl phenol with sulfur. Methylene-bridged
species may be prepared by reacting a hydrocarbyl phenol with
formaldehyde (or a reactive equivalent such as paraformaldehyde).
Examples include sulfur-bridged dodecylphenol (overbased Ca salt)
and methylene-coupled heptylphenol.
[0052] In another embodiment, an optional, additional overbased
material is an overbased saligenin detergent. Overbased saligenin
detergents are commonly overbased magnesium salts which are based
on saligenin derivatives. A general example of such a saligenin
derivative can be represented by the formula
Om OM
XN>.........:-YN> _
0 0 ____ X
Rlp_ m
- Rlp
where X is -CHO or -CH2OH, Y is -CH2- or -CH2OCH2-, and the -CHO
groups typically comprise at least 10 mole percent of the X and Y
groups; M is hydrogen, ammonium, or a valence of a metal ion (that
is, if M is multivalent, one of the valences is satisfied by the
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illustrated structure and other valences are satisfied by other species
such as anions or by another instance of the same structure), Ri is a
hydrocarbyl group of 1 to 60 carbon atoms, m is 0 to typically 10,
and each p is independently 0, 1, 2, or 3, provided that at least one
aromatic ring contains an 1R' substituent and that the total number of
carbon atoms in all 1R' groups is at least 7. When m is 1 or greater,
one of the X groups can be hydrogen. In one embodiment, M is a
valence (or equivalent) of a Mg ion or a mixture of Mg and hydrogen.
Saligenin detergents are disclosed in greater detail in U.S. Patent
6,310,009, with special reference to their methods of synthesis
(Column 8 and Example 1) and preferred amounts of the various
species of X and Y (Column 6).
[0053] Other optional detergents include salixarate detergents.
Salixarate detergents are overbased materials that can be represented
by a compound comprising at least one unit of formula (I) or formula
(II):
R4
5
HO
R7 R
COOR3 R6
(I) (II)
each end of the compound having a terminal group of formula (III) or
(IV):
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R4
(R2)j
I I
R7
COOR3 R6
(III) (IV)
such groups being linked by divalent bridging groups A, which may be
the same or different. In
formulas (I)-(IV) R3 is hydrogen, a
hydrocarbyl group, or a valence of a metal ion; R2 is hydroxyl or a
hydrocarbyl group, and j is 0, 1, or 2; R6 is hydrogen, a hydrocarbyl
group, or a hetero-substituted hydrocarbyl group; either R4 is
hydroxyl and R5 and R7 are independently either hydrogen, a
hydrocarbyl group, or hetero-substituted hydrocarbyl group, or else
R5 and R7 are both hydroxyl and R4 is hydrogen, a hydrocarbyl group,
or a hetero-substituted hydrocarbyl group; provided that at least one
of R4, R5, R6 and R7 is hydrocarbyl containing at least 8 carbon atoms;
and wherein the molecules on average contain at least one of unit (I)
or (III) and at least one of unit (II) or (IV) and the ratio of the total
number of units (I) and (III) to the total number of units of (II) and (IV)
in the composition is 0.1:1 to 2:1. The divalent bridging group "A,"
which may be the same or different in each occurrence,
includes -CH2- and -CH2OCH2- , either of which may be derived from
formaldehyde or a formaldehyde equivalent (e.g., paraform, formalin).
[0054]
Salixarate derivatives and methods of their preparation
are described in greater detail in U.S. patent number 6,200,936 and
PCT Publication WO 01/56968. It is believed that the salixarate
derivatives have a predominantly linear, rather than macrocyclic,
structure, although both structures are intended to be encompassed
by the term "salixarate." In one embodiment, a salixarate detergent
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may contain a portion of molecules represented (prior to
neutralization) by the structure
I) Uhl Uhl Uhl Uhl I)
HO 1 \ OH
HO T T y
R8 OH
IR8
where the R8 groups are independently hydrocarbyl groups containing
at least 8 carbon atoms.
[0055]
Glyoxylate detergents are also optional overbased
materials. They are based on an anionic group which, in one
embodiment, may have the structure
C(0)0-
= H I
C OH
0 0
- R
wherein each R is independently an alkyl group containing at least 4
or 8 carbon atoms, provided that the total number of carbon atoms in
all such R groups is at least 12 or 16 or 24. Alternatively, each R can
be an olefin polymer substituent. The acidic material upon from
which the overbased glyoxylate detergent is prepared is the
condensation product of a hydroxyaromatic material such as a
hydrocarbyl-substituted phenol with a carboxylic reactant such as
glyoxylic acid or another omega-oxoalkanoic acid. Overbased glyoxylic
detergents and their methods of preparation are disclosed in greater
detail in U.S. Patent 6,310,011 and references cited therein.
[0056] Another optional overbased detergent is an overbased
salicylate, e,g., an alkali metal or alkaline earth metal salt of a
substituted salicylic acid. The salicylic acids may be hydrocarbyl-
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substituted wherein each substituent contains an average of at least 8
carbon atoms per substituent and 1 to 3 substituents per molecule.
The substituents can be polyalkene substituents. In one embodiment,
the hydrocarbyl substituent group contains 7 to 300 carbon atoms
and can be an alkyl group having a molecular weight of 150 to 2000.
Overbased salicylate detergents and their methods of preparation are
disclosed in U.S. Patents 4,719,023 and 3,372,116.
[0057] Other optional overbased detergents can include
overbased detergents having a Mannich base structure, as disclosed
in U.S. Patent 6,569,818.
[0058] In certain embodiments, the hydrocarbyl substituents on
hydroxy-substituted aromatic rings in the above detergents (e.g.,
phenate, saligenin, salixarate, glyoxylate, or salicylate) are free of or
substantially free of C12 aliphatic hydrocarbyl groups (e.g., less than
1%, 0.1%, or 0.01% by weight of the substituents are C12 aliphatic
hydrocarbyl groups). In some embodiments such hydrocarbyl
substituents contain at least 14 or at least 18 carbon atoms.
[0059] The amount of the detergent in the formulations of the
present technology is typically at least 0.1 weight percent, e.g., 0.14 to
4 percent by weight, or 0.2 to 3.5 percent by weight, or 0.5 to 3
percent by weight, or 1 to 2 percent by weight. Alternative amounts
include 0.5 to 4 percent, 0.6 to 3.5 percent, 1.0 to 3 percent, or 1.5 to
2.8 %, e.g. at least 1.0 percent. One or a plurality of overbased
detergents may be present, and if more than one is present, the total
amount of such materials may be within the aforementioned
percentage ranges.
Viscosity Modifiers
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[0060] In one embodiment, the lubricating composition further
includes one or more viscosity modifiers. When present the viscosity
modifier may be present in an amount of 0.5 wt% to 70 wt%, 1 wt%
to 60 wt%, or 5 wt% to 50 wt%, or 10 wt% to 50 wt% of the
lubricating composition.
[0061] Viscosity modifiers include (a) polymethacrylates, (b)
esterified copolymers of (i) a vinyl aromatic monomer and (ii) an
unsaturated carboxylic acid, anhydride, or derivatives thereof, (c)
esterified interpolymers of (i) an alpha-olefin; and (ii) an unsaturated
carboxylic acid, anhydride, or derivatives thereof, or (d) hydrogenated
copolymers of styrene-butadiene, (e) ethylene-propylene copolymers,
(f) polyisobutenes, (g) hydrogenated styrene-isoprene polymers, (h)
hydrogenated isoprene polymers, (i) poly alpha-olefins, or U) mixtures
thereof.
[0062] In one embodiment the viscosity modifier includes (a) a
polymethacrylate, (b) an esterified copolymer of (i) a vinyl aromatic
monomer; and (ii) an unsaturated carboxylic acid, anhydride, or
derivatives thereof, (c) an esterified interpolymer of (i) an alpha-
olefin; and (ii) an unsaturated carboxylic acid, anhydride, or
derivatives thereof, or (d) mixtures thereof.
[0063] Dispersant viscosity modifiers (often referred to as DVMs)
include functionalized polyolefins, for example, ethylene-propylene
copolymers that have been functionalized with the reaction product
of maleic anhydride and an amine, a polymethacrylate functionalized
with an amine, an amine reacted with an esterified interpolymer, or
esterified styrene-maleic anhydride copolymers reacted with an
amine may also be used in the composition of the invention.
Extreme Pressure Agents
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[0064] Extreme pressure agents include compounds containing
boron and/or sulfur and/or phosphorus. The extreme pressure
agent may be present in the lubricating composition at 0.0 wt% to 20
wt%, or 0.05 wt% to 10 wt%, or 0.1 wt% to 8 wt%, or 0.5 wt% to 6
wt% of the lubricating composition.
[0065] In one embodiment the extreme pressure agent is a
sulfur-containing compound. In one embodiment the sulfur-
containing compound may be a sulfurized olefin, a polysulfide, or
mixtures thereof.
[0066] Examples of the sulfurized olefin include a sulfurized
olefin derived from propylene, isobutylene, pentene; an organic
sulfide and/or polysulfide including benzyldisulfide; bis-
(chlorobenzyl) disulfide; dibutyl tetrasulfide; di-tertiary butyl
polysulfide; and sulfurized methyl ester of oleic acid, a sulfurized
alkylphenol, a sulfurized dipentene, a sulfurized terpene, a
sulfurized Diels- Alder adduct, an alkyl sulfenyl N 'N-dialkyl
dithiocarbamates; or mixtures thereof. In one embodiment the
sulfurized olefin includes a sulfurized olefin derived from propylene,
isobutylene, pentene or mixtures thereof.
[0067] In one embodiment, the extreme pressure agent sulfur-
containing compound includes a dimercaptothiadiazole or derivative,
or mixtures thereof. Examples of the dimercaptothiadiazole include
2,5-dimercapto-1,3,4-thiadiazole or a hydrocarbyl-substituted 2,5-
dimercapto-1 ,3,4-thiadiazole, or oligomers thereof. The oligomers of
hydrocarbyl- substituted2,5-dimercapto-1,3,4-thiadiazole typically
form by forming a sulfur-sulfur bond between 2,5-dimercapto-1 ,3,4-
thiadiazole units to form derivatives or oligomers of two or more of
said thiadiazole units. Suitable 2,5-dimercapto-1 ,3,4-thiadiazole
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derived compounds include 2,5-bis(tert-nonyldithio)- 1 ,3 ,4-
thiadiazole or 2-tert-nonyldithio-5-mercapto- 1 ,3 ,4-thiadiazole.
[0068] The number of carbon atoms on the hydrocarbyl
substituents of the hydrocarbyl-substituted 2,5-dimercapto-1,3,4-
thiadiazole typically include 1 to 30, or 2 to 20, or 3 to 16.
[0069] In one embodiment the extreme pressure agent includes
a boron-containing compound. The boron-containing compound
includes a borate ester (which in some embodiments may also be
referred to as a borated epoxide), a borated alcohol, a borated
dispersant or mixtures thereof. In one embodiment the boron-
containing compound may be a borate ester or a borated alcohol.
[0070] The borate ester may be prepared by the reaction of a
boron compound and at least one compound selected from epoxy
compounds, halohydrin compounds, epihalohydrin compounds,
alcohols and mixtures thereof. The alcohols include dihydric
alcohols, trihydric alcohols or higher alcohols, with the proviso for
one embodiment that hydroxyl groups are on adjacent carbon atoms,
i.e., vicinal.
[0071] Boron compounds suitable for preparing the borate ester
include the various forms selected from the group consisting of boric
acid (including metaboric acid, HB02, orthoboric acid, H3B03, and
tetraboric acid, H2B407), boric oxide, boron trioxide and alkyl
borates. The borate ester may also be prepared from boron halides.
[0072] In one embodiment suitable borate ester compounds
include tripropyl borate, tributyl borate, tripentyl borate, trihexyl
borate, triheptyl borate, trioctyl borate, trinonyl borate and tridecyl
borate.
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[0073] In one embodiment the borate ester compounds include
tributyl borate, tri-2-ethylhexyl borate or mixtures thereof.
[0074] In one embodiment, the boron-containing compound is a
borated dispersant, typically derived from an N-substituted long
chain alkenyl succinimide. In one embodiment the borated
dispersant includes a polyisobutylene succinimide. Borated
dispersants are described in more detail in US Patents 3,087,936;
and Patent 3,254,025.
[0075] In one embodiment the borated dispersant may be used
in combination with a sulfur-containing compound or a borate ester.
[0076] In one embodiment the extreme pressure agent is other
than a borated dispersant.
[0077] The number average molecular weight of the hydrocarbon
from which the long chain alkenyl group was derived includes ranges
of 350 to 5000, or 500 to 3000, or 550 to 1500. The long chain
alkenyl group may have a number average molecular weight of 550,
or 750, or 950 to 1000.
[0078] The N-substituted long chain alkenyl succinimides are
borated using a variety of agents including boric acid (for example,
metaboric acid, HB02, orthoboric acid, H3B03, and tetraboric acid,
H2B407), boric oxide, boron trioxide, and alkyl borates. In one
embodiment the borating agent is boric acid which may be used
alone or in combination with other borating agents.
[0079] The borated dispersant may be prepared by blending the
boron compound and the N-substituted long chain alkenyl
succinimides and heating them at a suitable temperature, such as,
80 C to 250 C, or 90 C to 230 C, or 100 C to 210 C, until the
desired reaction has occurred. The molar ratio of the boron
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compounds to the N-substituted long chain alkenyl succinimides
may have ranges including 10:1 to 1:4, or 4:1 to 1:3; or the molar
ratio of the boron compounds to the N-substituted long chain alkenyl
succinimides may be 1:2.
[0080] An inert
liquid may be used in performing the reaction.
The liquid may include toluene, xylene, chlorobenzene,
dimethylformamide or mixtures thereof.
[0081] In
one embodiment the dispersant may be a post treated
dispersant. The dispersant may be post treated with
dimercaptothiadiazole, optionally in the presence of one or more of a
phosphorus compound, a dicarboxylic acid of an aromatic
compound, and a borating agent.
[0082] In
one embodiment the post treated dispersant may be
formed by heating an alkenyl succinimide or succinimide detergent
with a phosphorus ester and water to partially hydrolyze the ester.
The post treated dispersant of this type is disclosed for example in
U.S. Patent 5,164,103.
[0083] In
one embodiment the post treated dispersant may be
produced by preparing a mixture of a dispersant and a
dimercaptothiadiazole and heating the mixture above about 100 C.
The post treated dispersant of this type is disclosed for example in
U.S. Patent 4,136,043.
[0084] In
one embodiment the dispersant may be post treated to
form a product prepared comprising heating together: (i) a dispersant
(typically a succinimide), (ii) 2,5-dimercapto-1 ,3,4-thiadiazole or a
hydrocarbyl- substituted 2, 5- dimercapto-1, 3 ,4- thiadiazole,
or
oligomers thereof, (iii) a borating agent (similar to those described
above); and (iv) optionally a dicarboxylic acid of an aromatic
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compound selected from the group consisting of 1,3 diacids and 1,4
diacids (typically terephthalic acid), or (v) optionally a phosphorus
acid compound (including either phosphoric acid or phosphorous
acid), said heating being sufficient to provide a product of (i), (ii), (iii)
and optionally (iv) or optionally (v), which is soluble in an oil of
lubricating viscosity. The post treated dispersant of this type is
disclosed for example in International Application WO 2006/654726
A.
[0085]
Examples of a suitable dimercaptothiadiazole include
2,5-dimercapto-1,3-4-thiadiazole or a hydrocarbyl-substituted 2,5-
dimercapto-1,3-4-thiadiazole. In several embodiments the number of
carbon atoms on the hydrocarbyl-substituent group includes 1 to 30,
2 to 25, 4 to 20, or 6 to 16. Examples of suitable 2,5-bis(alkyl-
dithio)-1,3,4-thiadiazoles include
2,5-bis (tert-octyldithio)-1,3,4-
thiadiazole 2 ,5-bis (tert-nonyldithio)-1,3,4-thiadiazole, 2, 5-bis (tert-
decyldithio)- 1,3,4-thiadiazole ,
2,5-bis(tert-undecyldithio)-1,3,4-
thiadiazole, 2,5-bis(tert-dodecyldithio)-1,3,4-thiadiazole, 2, 5-bis(tert-
tridecyldithio)-1,3 ,4-thiadiazole, 2,5 -bis(tert-tetradecyldithio)-1,3,4-
thiadiazole, 2,5-bis(tert-pentadecyldithio)-1,3,4-thiadiazole,
2,5-
bis(tert-hexadecyldithio)-1,3,4-thiadiazole, 2,5-
bis(tert-
heptadecyldithio)-1,3,4-thiadiazole, 2,5-bis(tert-octadecyldithio)-1,3,4-
thiadiazole, 2,5-bis(tert-nonadecyldithio)-1,3,4-thiadi-azole or 2,5-
bis(tert-eicosyldithio)-1,3,4-thiadiazole, or oligomers thereof.
[0086]
Friction modifiers include fatty phosphonate esters,
amine salts of phosphoric acid esters, reaction products from fatty
carboxylic acids reacted with guanidine, aminoguanidine, urea or
thiourea, and salts thereof, fatty amines, fatty hydroxyl amines,
borated phospholipids, borates, borate esters, fatty phosphites, fatty
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acid amides, fatty epoxides, borated fatty epoxides, alkoxylated fatty
amines, borated alkoxylated fatty amines, fatty poly ethers, metal
salts of fatty acids, or fatty imidazolines, condensation products of
carboxylic acids and poly alky lene-poly amines, fatty malimides,
fatty tartrimides, and fatty oxazolines.
[0087] In one embodiment the lubricating composition may
contain phosphorus- or sulfur- containing antiwear agents other
than compounds described as an extreme pressure agent of the
amine salt of a phosphoric acid ester described above. Examples of
the antiwear agent may include a non-ionic phosphorus compound
(typically compounds having phosphorus atoms with an oxidation
state of +3 or +5), a metal dialkyldithiophosphate (typically zinc
dialkyldithiophosphates), a metal mono- or di- alkylphosphate
(typically zinc phosphates), or mixtures thereof.
[0088] The non-ionic phosphorus compound includes a
phosphite ester, a phosphate ester, or mixtures thereof. A more
detailed description of the non-ionic phosphorus compound include
column 9, line 48 to column 11, line 8 of US 6,103,673. Phosphorus
containing anti-wear compounds can be included in the lubricant
composition at from about 100 to about 2000 ppm, or from about
500 to about 1800 ppm, or from about 700 to about 1500 or 1600
PPm=
[0089] In one embodiment the lubricating composition of the
invention further includes a dispersant. The dispersant may be a
succinimide dispersant (for example N-substituted long chain alkenyl
succinimides), a Mannich dispersant, an ester-containing dispersant,
a condensation product of a fatty hydrocarbyl monocarboxylic
acylating agent with an amine or ammonia, an alkyl amino phenol
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dispersant, a hydrocarbyl-amine dispersant, a polyether dispersant
or a poly ether amine dispersant.
[0090] In one embodiment the succinimide dispersant includes
a polyisobutylene-substituted succinimide, wherein the
polyisobutylene from which the dispersant is derived may have a
number average molecular weight of 400 to 5000, or 950 to 1600.
[0091] Succinimide dispersants and their methods of
preparation are more fully described in US Patents 3,172,892,
3,219,666, 3,316,177, 3,340,281, 3,351,552, 3,381,022, 3,433,744,
3,444,170, 3,467,668, 3,501,405, 3,542,680, 3,576,743, 3,632,511,
4,234,435, Re 26,433, and 6,165,235, 7,238,650 and EP Patent
Application 0 355 895 A.
[0092] Suitable ester-containing dispersants are typically high
molecular weight esters. These materials are described in more detail
in U.S. Patent 3,381,022.
[0093] In one embodiment the dispersant includes a borated
dispersant.
[0094] Typically the borated dispersant includes a succinimide
dispersant including a polyisobutylene succinimide, wherein the
polyisobutylene from which the dispersant is derived may have a
number average molecular weight of 400 to 5000. Borated
dispersants are described in more detail above within the extreme
pressure agent description.
[0095] Dispersants may be added to the lubricant compositions
described at a range of from about 0.1 to 5 weight%, or from about
0.5 to about 4 weight%, or even from about 1.0 to about 2.5 or 3
weight%.
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[0096] Corrosion inhibitors include amides, imidazolines,
amines, fatty amines, 1-amino-2-propanol, octylamine octanoate,
condensation products of dodecenyl succinic acid or anhydride
and/or a fatty acid such as oleic acid with a polyamine.
[0097] Metal
deactivators include derivatives of benzotriazoles
(typically tolyltriazole), 1,2 ,4-triazole s,
benzimidazoles, 2-
alkyldithiobenzimidazoles, thiadiazoles, or 2-
alkyldithiobenzothiazoles. The metal deactivators may also be
described as corrosion inhibitors.
[0098] Foam inhibitors include copolymers of ethyl acrylate and
2-ethylhexylacrylate and optionally vinyl acetate. Also included are
siloxanes, typically polydimethylsiloxanes
[0099]
Demulsifiers include trialkyl phosphates, and various
polymers and copolymers of ethylene glycol, ethylene oxide,
propylene oxide, or mixtures thereof.
[00100] Pour point depressants include esters of maleic
anhydride-styrene, polymethacrylates,
polyacrylates or
polyacrylamides.
[00101]
Seal swell agents include Exxon Necton-37TM (FN 1380)
and Exxon Mineral Seal Oi1TM (FN 3200).
Industrial Application
[00102] The self-contained lubricant of the limited slip
differential is generally different from the lubricant supplied to a
manual transmission or an automatic transmission fluid.
[00103] An axle gear may have any one of a number of different
types of differentials. A
differential typically has three major
functions. The first function is to transmit engine power to the
wheels. The second function is act as the final gear reduction in the
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vehicle, slowing the rotational speed from the transmission to the
wheels. The third function is to transmit the power to the wheels
while allowing them to rotate at different speeds. A number of
differentials are known and include an open differential, a clutch-type
limited slip differential, a viscous coupling differential, a Torsen
differential and a locking differential. All of these differentials may be
generically referred to as axle gears.
[00104]
Axle gears typically require a lubricant. The lubricant
formulation is dependent on the type of axle gear, and the operating
conditions of the axle gear. For example, an open differential axle
gear is believed to require antiwear and/or extreme pressure
additives. A
limited slip differential further requires a friction
modifier because, in addition to an open differential (known from
many axle fluids), a spring pack and a clutch pack are typically
present. The clutch pack may contain one or more reaction plates
(often made from steel) and one or more friction plates. The friction
plates are known, and may be made from a number of materials
including paper, carbon, graphite, steel and a composite.
[00105]
The lubricating composition suitable for the limited slip
differential may have a sulfur content in the range of 0.3 wt% to 5
wt%, or 0.5 wt% to 5 wt%, or 0.5 wt% to 3 wt% or 0.8 wt% to 2.5
wt%, or 1 wt% to 2 wt%.
[00106] In
one embodiment the lubricating composition suitable
for the limited slip differential may be a fully formulated fluid.
[00107] In one embodiment the lubricating composition suitable
for the limited slip differential may be a top treat concentrate.
[00108]
When the lubricating composition is in the form of a top
treat concentrate, the concentrate may be added at an actives level of
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about 0.1 wt% to 10 wt%, or 0.2 wt% to 7 wt%, 0.25 wt% to 2, 3, 4 or
5%, or even 0.25 to 1 wt%, or 1.0 to 3.0 wt% relative to the amount
of lubricant in a limited slip differential.
[00109] In
an embodiment of the invention, a method of providing
limited slip performance is provided comprising introducing a
lubricating composition as disclosed herein to a differential, and
operating the differential.
[00110]
The lubricant composition and method disclosed herein
may be suitable for limited slip systems having one or more distinct
plate materials. For example the plate materials may be steel, paper,
ceramic, carbon fibers and systems employing a mixture of plate
types such as steel on ceramic, carbon fibers in paper or steel on
paper.
[00111]
The amount of each chemical component described is
presented exclusive of any solvent or diluent oil, which may be
customarily present in the commercial material, that is, on an active
chemical basis, unless otherwise indicated.
However, unless
otherwise indicated, each chemical or composition referred to herein
should be interpreted as being a commercial grade material which
may contain the isomers, by-products, derivatives, and other such
materials which are normally understood to be present in the
commercial grade.
[00112] It
is known that some of the materials described above
may interact in the final formulation, so that the components of the
final formulation may be different from those that are initially added.
For instance, metal ions (of, e.g., a detergent) can migrate to other
acidic or anionic sites of other molecules. The products formed
thereby, including the products formed upon employing the
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composition of the present invention in its intended use, may not be
susceptible of easy description. Nevertheless, all such modifications
and reaction products are included within the scope of the present
invention; the present invention encompasses the composition
prepared by admixing the components described above.
EXAMPLES
[00113] Preparative Example 1 (EX1):
[00114] Aminopropyl oleylamine (682g) is charged to a 2L 4-necked
flask fitted with a thermowell and heated. Oleic acid (621.5g) is added to
the amine over 15 minutes via addition funnel. The reaction mixture is
heated to reflux and distillate is collected. The final product is a white
waxy solid at room temperature.
Axle Lubricants
[00115] Comparative Example 1 (CE1) is a commercially available
axle fluid having the formulation in table 1, and containing no additional
limited slip friction modifier.
Table 1
Component Wt% - active basis
Oil of lubricating viscosity 65.98
Extreme Pressure Agent 5.38
Viscosity Modifier 25.06
Corrosion Inhibitor 0.22
Antiwear 1.66
Dispersant 1.53
Antifoam 0.04
Friction modifier 0.13
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[00116] Inventive Example 1 (IE1) is a commercially available axle
fluid which has been top-treated with 1.8 wt % of preparative example 1.
Table 2
Component Wt% - active basis
CE1 96.0
Further oil of lubricating viscosity 2.2
Preparative Example 1 1.8
[00117] Lubricants for testing are prepared by adding one of the
materials from the preparative examples identified in the tables below to
the indicated base formulation. The lubricants containing EX1 are
evaluated in a Full-Scale Low-Velocity Friction Apparatus (FSLVFA).
The apparatus uses a clutch test specimen as defined by SAE Paper
2010-01-2231. The test is run while varying the speed, temperature
and pressure. The test consists of friction performance evaluations at
the beginning and after a 17-hour durability stage. A break-in phase
runs 10 minutes at 90 C oil temperature, 16 rpm, and 7070 N load.
The phase conditions the clutch system for the pre-durability
performance evaluation. The pre-durability performance evaluation is
achieved by ramping the speed from 0 to 5 rpm in 5 seconds, then back
to zero. Load is set to two levels, 3535 N and 7070 N, which correspond
to the range of axial compressive load imposed by the axle's internal
clutch pack. The above two loads are evaluated at three oil
temperatures: 40 C, 90 C, and 120 C. The sample clutch pack
undergoes a durability phase that involves running the test rig for 17
hours at 120 C oil temperature, 7070 N load, and 16 rpm. The post-
durability evaluation is then run using the same conditions as the pre-
test evaluation. A more detailed description of the test procedure is
provided in SAE Paper 2010-01-2231. The table below shows a post-
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durability rating of NVH (at 5 rpm) and curvature. The data obtained is
as follows:
Post durability Curvature and NVH at 5 rpm at 40 C and 77N
FRICTION NVH (@ 5
FLUID CURVATURE
MATERIAL RPM)
*a CE1 4.3 13.7
*a CE1 3 5.7
*a TEl 3.4 7.4
*b CE1 7.8 21.6
*b CE1 7.7 20
*b CE1 7.6 16.9
*b
TEl 0.6 3.0
c CE1 7.3 36.2
*c TEl 0.6 4.3
*a - MibaTM MC-631
*b - HoerbigerTM HC-100
*c - FCCTM 3312
Footnotes:
Noise, Vibration, Harshness (NVH) at 5 rpm is the standard deviation of
the torque signal based upon a moving average of the torque signal
during the 2 second hold at 5 rpm. A high NVH rating is indicative of
the occurrence of "stick-slip" at the friction surface. Torque spikes when
the plates "stick" and drops when the plates "slip". NVH describes the
amplitude of the torque signal and is independent of the shape of the
torque signal. Good FM candidates should have low NVH at 5 rpm.
Curvature describes the shape of the torque signal which is believed
to be related to the difference between the static and dynamic
friction coefficients. Curvature is the average difference between the
torque when the plates breakaway and come to rest versus the
torque during the 2 second hold at 5rpms. A positive curvature
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means the torque signal is concave down during the sweep (bows
downward). A negative curvature means the torque signal is concave
up (bows upward) during the sweep. Ideally curvature should be
close to zero which would mean the torque signal is flat across all
speeds. Slight negative curvature value is acceptable but high
positive curvature value is less desirable.
[00118] Each of the documents referred to above is incorporated
herein by reference. The mention of any document is not an
admission that such document qualifies as prior art or constitutes
the general knowledge of the skilled person in any jurisdiction.
Except in the Examples, or where otherwise explicitly indicated, all
numerical quantities in this description specifying amounts of
materials, reaction conditions, molecular weights, number of carbon
atoms, and the like, are to be understood as modified by the word
"about." It is to be understood that the upper and lower amount,
range, and ratio limits set forth herein may be independently
combined. Similarly, the ranges and amounts for each element of
the invention can be used together with ranges or amounts for any of
the other elements.
34
