U.S. patent application number 11/868765 was filed with the patent office on 2008-07-24 for grease composition for use in constant velocity joints.
This patent application is currently assigned to GKN Driveline International GmbH. Invention is credited to Jisheng E., Shinya Kondo, Frank Reher, Akira Taniguchi.
Application Number | 20080176776 11/868765 |
Document ID | / |
Family ID | 37733725 |
Filed Date | 2008-07-24 |
United States Patent
Application |
20080176776 |
Kind Code |
A1 |
E.; Jisheng ; et
al. |
July 24, 2008 |
Grease Composition For Use In Constant Velocity Joints
Abstract
In order to provide for a grease composition which has a good
compatibility with boots made of rubber or thermoplastic elastomer,
and which also gives low wear and low friction, a grease
composition for use in constant velocity joints is suggested,
comprising a) a base oil composition; b) at least one tri-nuclear
molybdenum compound of the formula Mo.sub.3S.sub.kL.sub.nQ.sub.z,
wherein L are independently selected ligands having organo groups
with a sufficient number of carbon atoms to render the compound
soluble or dispersible in the oil, n is from 1 to 4, k varies from
4 though 7, Q is selected from the group of neutral electron
donating compounds such as amines, alcohols, phosphines, and
ethers, and z ranges from 0 to 5 and includes non-stoichiometric
values; c) at least one urea derivative thickener.
Inventors: |
E.; Jisheng; (Hennef,
DE) ; Kondo; Shinya; (Fujisawa, JP) ; Reher;
Frank; (Wenden, DE) ; Taniguchi; Akira;
(Fujisawa, JP) |
Correspondence
Address: |
GIFFORD, KRASS, SPRINKLE,ANDERSON & CITKOWSKI, P.C
PO BOX 7021
TROY
MI
48007-7021
US
|
Assignee: |
GKN Driveline International
GmbH
Lohmar
DE
Kyodo Yushi Co., Ltd.
Tokyo
JP
|
Family ID: |
37733725 |
Appl. No.: |
11/868765 |
Filed: |
October 8, 2007 |
Current U.S.
Class: |
508/376 ;
508/379; 508/552 |
Current CPC
Class: |
C10M 2217/0456 20130101;
C10N 2030/76 20200501; C10M 2207/106 20130101; C10M 2215/1026
20130101; C10M 169/06 20130101; C10M 2227/09 20130101; C10N 2010/12
20130101; C10N 2010/04 20130101; C10N 2030/06 20130101; C10N
2040/046 20200501; C10M 2219/068 20130101; C10M 2223/045 20130101;
C10N 2050/10 20130101 |
Class at
Publication: |
508/376 ;
508/379; 508/552 |
International
Class: |
C10M 137/02 20060101
C10M137/02 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 7, 2006 |
EP |
PCT/EP06/09718 |
Claims
1. A grease composition for use in constant velocity joints
comprising: a) a base oil composition; b) at least one tri-nuclear
molybdenum compound of the formula Mo.sub.3S.sub.kL.sub.nQ.sub.z,
wherein L are independently selected ligands having organo groups
with a sufficient number of carbon atoms to render the compound
soluble or dispersible in the oil, n is from 1 to 4, k varies from
4 though 7, Q is selected from the group of neutral electron
donating compounds such as amines, alcohols, phosphines, and
ethers, and z ranges from 0 to 5 and includes non-stoichiometric
values; c) at least one urea derivative thickener.
2. A grease composition according to claim 1, characterised in that
the urea derivative thickener is selected from the group comprising
di-urea and/or polyurea compounds and mixtures of said compounds
with calcium-based thickeners.
3. A grease composition according to claim 1, further comprising at
least one zinc dithiophosphates, molybdenum dithiocarbamate and/or
molybdenum dithiophosphates.
4. A grease composition according to claim 3, characterised in that
the amount of zinc dithiophosphates, molybdenum dithiophosphates
and/or molybdenum dithiocarbamates is in a range of between 0.1% by
weight to 5% by weight, referred to the total amount of the grease
composition.
5. A grease composition according to claim 4, characterised in that
the weight percent added, referred to the total amount of the
grease composition, of each of zinc dithiophosphates, molybdenum
dithiophosphates and/or molybdenum dithiocarbamates is essentially
identical.
6. A grease composition according to claim 1, further comprising an
agent having at least one anti-oxidation agent, corrosion
inhibitor, anti-wear-agent wax, friction modifier and/or extreme
pressure agent (EP agent).
7. A grease composition according to claim 1, comprising 50% by
weight to 98.9% by weight of the base oil composition, 0.1% by
weight to 5% by weight of at least one tri-nuclear molybdenum
compound, 1% by weight to 25% by weight of at least one urea
derivative thickener, in each case referred to the total amount of
the grease composition.
8. A grease composition according to claim 1, comprising 70% by
weight to 92% by weight of the base oil composition, 0.3% by weight
to 2% by weight of the least one tri-nuclear molybdenum compound,
4.5% by weight to 20% by weight of the least one urea derivative
thickener, 1.5% by weight to 3.5% by weight of at least one
molybdenum dithiocarbamate, 0.5% by weight to 3% by weight of the
least one zinc dithiophosphate, and 0.5% by weight to 2% by weight
of at least one wax.
9. A grease composition according to claim 3, characterised in that
the weight percent added, referred to the total amount of the
grease composition, of tri-nuclear molybdenum compounds is
essentially identical with the weight percent of each one of zinc
dithiophosphates, molybdenum dithiophosphates and/or molybdenum
dithiocarbamates added.
10. A grease composition according to claim 3, characterised in
that the weight percent added, referred to the total amount of the
grease composition, of tri-nuclear molybdenum compounds is four to
ten times lower than the weight percent of the total amount of zinc
dithiophosphates, molybdenum dithiophosphate and/or molybdenum
dithiocarbamate added.
11. A grease composition according to claim 1, characterised in
that the sliding friction coefficient is at most 0.08.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority of International Patent
Application No. PCT/EP2006/009718, filed Oct. 7, 2006, and which is
incorporated in its entirety by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to a lubricating grease which
is intended primarily for use in constant velocity universal
joints, especially ball joints or tripod joints, which are used in
the drivelines of motor vehicles.
BACKGROUND OF THE INVENTION
[0003] The motions of components within constant velocity joints
(CVJ) are complex with a combination of rolling, sliding and
spinning. When the joints are under torque, the components are
loaded together which can not only cause wear on the contact
surfaces of the components, but also rolling contact fatigue and
significant frictional forces between the surfaces. The wear can
result in failure of the joints and the frictional forces can give
rise to noise, vibration and harshness (NVH) in the driveline. NVH
is normally "measured" by determining the axial forces generated in
plunging type CVJ. Ideally the greases used in constant velocity
joints need not only to reduce wear, but also have to have a low
coefficient of friction to reduce the frictional forces and to
reduce or prevent NVH.
[0004] Constant velocity joints also have sealing boots of
elastomeric material which are usually of bellows shape, one end
being connected to the outer part of the CVJ and the other end to
the interconnecting or output shaft of the CVJ. The boot retains
the grease in the joint and keeps out dirt and water.
[0005] Not only must the grease reduce wear and friction and
prevent the premature initiation of rolling contact fatigue in a
CVJ, it must also be compatible with the elastomeric material of
which the boot is made. Otherwise there is a degradation of the
boot material which causes premature failure of the boot, allowing
the escape of the grease and ultimately failure of the CVJ. The two
main types of material used for CVJ boots are polychloroprene
rubber (CR) and thermoplastic elastomer (TPE), especially
ether-ester block co-polymer thermoplastic elastomer (TPC-ET).
[0006] Typical CVJ greases have base oils which are blends of
naphthenic (saturated rings) and paraffinic (straight and branched
saturated chains) mineral oils. Synthetic oils may also be added.
It is known that said base oils have a large influence on the
deterioration (swelling or shrinking) of both boots made of CR and
TPC-ET. Both mineral and synthetic base oils extract the
plasticisers and other oil soluble protective agents from the boot
materials, Paraffinic mineral oils and poly-.alpha.-olefin (PAO)
synthetic base oils diffuse very little into especially boots made
of rubber material causing shrinkage, but on the other hand
naphthenic mineral oils and synthetic esters diffuse into boot
materials and act as plasticisers and can cause swelling. The
exchange of plasticiser or plasticiser compositions for the
naphthenic mineral oil can significantly reduce the boot
performance, especially at low temperatures, and may cause the boot
to fail by cold cracking, ultimately resulting in failure of the
CVJ. If significant swelling or softening occurs, the maximum high
speed capability of the boot is reduced due to the poor stability
at speed and/or excessive radial expansion.
[0007] In order to solve the aforesaid problems, U.S. Pat. No.
6,656,890 B1 suggests a special base oil combination comprising 10
to 35% by weight of one or more poly-.alpha.-olefins, 3 to 15% by
weight of one or more synthetic organic esters, 20 to 30% by weight
of one or more naphthenic oils, the remainder of the combination
being one or more paraffinic oils, and, further, a lithium soap
thickener, and a sulphur-free friction modifier, that may be a
organo-molybdenum complex, and molybdenum dithiophosphate, and a
zinc dialkyldithiophosphate and further additives such as corrosion
inhibitors, anti-oxidants, extreme pressure additives, and
tackiness agents. However, the friction coefficient and the wear of
grease compositions according to U.S. Pat. No. 6,656,890 B1 as
measured in SRV (abbreviation for the German words Schwingungen,
Reibung, Verschlei.beta.) tests needs to be improved.
SUMMARY OF THE INVENTION
[0008] Thus, it is the object of the present invention to provide
for a grease composition, primarily for use in constant velocity
joints, which has a good compatibility with boots made of rubber or
thermoplastic elastomer, and which also gives low wear and low
friction in use in CVJ.
[0009] Said object of the present invention is solved by a grease
composition for use in constant velocity joints comprising
[0010] a) a base oil composition; and
[0011] b) at least one tri-nuclear molybdenum compound, preferable
0.25% by weight to 5% by weight, more preferable 0.3% by weight to
3% by weight, referred to the total amount of the grease
composition, of the formula
Mo.sub.3S.sub.kL.sub.nQ.sub.Z, (I)
wherein L are independently selected ligands having organo groups
with a sufficient number of carbon atoms to render the compound
soluble or dispersible in the oil, n is from 1 to 4, k varies from
4 though 7, Q is selected from the group of neutral electron
donating compounds such as amines, alcohols, phosphines, and
ethers, and z ranges from 0 to 5 and includes non-stoichiometric
values;
[0012] c) at least one urea derivative thickener;
[0013] The number of carbon atoms present in the tri-nuclear
molybdenum compound among all the ligands, organo groups is at
least 21 carbon atoms, preferably at least 25, more preferably at
least 30, and most preferably at least 35. Tri-nuclear molybdenum
compounds usable in the present invention are disclosed in U.S.
Pat. No. 6,172,013 B1, the disclosure of which is incorporated in
the present invention insofar by reference. The presence of at
least 0.25% by weight of the tri-nuclear molybdenum compound
according to claim 1 is preferred and significantly lowers the
friction coefficient as well as the wear when used in CVJ.
[0014] As a base oil composition according to the present
invention, a base oil composition as disclosed in U.S. Pat. No.
6,656,890 B1, the disclosure of which is incorporated insofar
herein by reference, may preferably be used. However, any further
kind of base oil composition, especially a blend of mineral oils, a
blend of synthetic oils or a blend of a mixture of mineral and
synthetic oils may be used. The base oil composition should
preferably have a kinematic viscosity of between about 32 and about
250 mm.sup.2/s at 40.degree. C. and between about 5 and about 25
mm.sup.2/s at 100.degree. C. The mineral oils preferably are
selected from the group comprising at least one naphthenic oil
and/or at least one paraffinic oil. The synthetic oils usable in
the present invention are selected from a group comprising at least
one poly-.alpha.-olefin (PAO) and/or at least one synthetic organic
ester. The organic synthetic ester is preferably a di-carboxylic
acid derivative having subgroups based on aliphatic alcohols.
Preferably, the aliphatic alcohols have primary, straight or
branched carbon chains with 2 to 20 carbon atoms. Preferably, the
organic synthetic ester is selected from a group comprising sebacic
acid-bis(2-ethylhexylester) ("dioctyl sebacate" (DOS)), adipic
acid-bis-(2-ethylhexylester) ("dioctyl adipate" (DOA)), and/or
azelaic acid-bis(2-ethylhexylester) ("dioctyl azelate" (DOZ)).
[0015] If poly-.alpha.-olefin is present in the base oil
composition, preferably poly-.alpha.-olefins are selected having a
viscosity in a range from about 2 to about 40 centistokes at
100.degree. C. The naphthenic oils selected for the base oil
compositions have preferably a viscosity in a range between about
20 to about 150 mm.sup.2/s at 40.degree. C., whereas if paraffinic
oils were present in the base oil composition, preferably the
paraffinic oils have a viscosity in a range between about 25 to
about 170 mm.sup.2/s at 40.degree. C.
[0016] According to the present invention, the grease composition
comprises at least one urea derivative thickener. The urea
derivative thickener used in accordance with the present invention
may also be a urea complex thickener, that is defined as a mixture
of at least one urea derivative thickener with at least one other
thickener not being a urea derivative thickener. Especially
preferred urea complex thickeners in accordance with the present
invention are mixtures of at least one urea derivative thickener
with at least one calcium and/or lithium-based thickener and/or
complex thickener.
[0017] As a urea-derivative type thickener in the present
invention, especially a urea thickener manufactured by the company
Kyodo Yushi Co., Ltd., Tokyo, Japan, is used as defined in U.S.
Pat. No. 5,589,444. The urea-derivative thickener is preferably a
reaction product of at least one organic aliphatic amine with at
least one organic phenyl isocyanate. However, the urea-derivative
thickener is not restricted to specific ones and may be, for
instance, also a diurea compound and/or a polyurea compound.
[0018] Examples of diurea compounds include those obtained from a
reaction of a monoamine with a diisocyanate compound. Examples of
useful diisocyanates include phenylendiisocyanate,
dephenyldiisocyanate, phenyldiisocyanate,
dephenylmethandiisocyanate, octadecanediisocyanate,
decanediisocyanate, and hexanediisocyanate. Examples of useful
monoamines include octylamine, dodecylamine, hexadecylamine,
octadecylamine, oliylamine, aniline, t-toluidine, and
cyclohexylamine. Especially preferred diurea compounds are
compounds obtained by reaction of
(4,4'-methylenediphenyldisocyanate) (MDI) with octadecylamine.
[0019] Examples of useful polyurea compounds include those obtained
from a reaction of a diamine with a diisocyanate compound. Examples
of useful diisocyanate include those used for the formation of the
diurea compounds as mentioned above, whereas examples of useful
diamines include ethylendiamine, propanediamine, butanediamine,
hexanediamine, octanediamine, phenylenediamine, tolylenediamine,
and xylenediamine. Most preferred examples of urea type derivative
thickeners include those obtained through a reaction of arylamine
such as aniline or p-toluidine, cyclohexylamine or a mixture
thereof with a diisocyanate. The aryl group in the diurea compound
has preferably 6 or 7 carbon atoms.
[0020] In a preferred embodiment of the present invention the urea
derivative thickener is selected from the group comprising urea
complex thickeners. Urea complex thickeners are defined as a
mixture of at least one urea derivative thickener with any further
kind of thickener, especially calcium-based thickeners. Especially
preferred as a urea complex thickener in accordance with the
present invention is a mixture of a urea derivative thickener as
defined above with at least one calcium complex thickener and/or
calcium thickener (calcium-based thickeners).
[0021] In the sense of the present invention, a calcium thickener
(soap) is a reaction product of at least one fatty acid with
calcium hydroxide. Preferably, the thickener may be a simple
calcium soap formed from 12-hydroxy stearic acid or from other
similar fatty acids or mixtures thereof or methylesters of such
acids. Alternatively, a calcium complex thickener (soap) may be
used formed for example from a mixture of long-chained fatty acids
together with a mixture of short and/or medium chained carboxylic
acids. However, mixtures of all of the aforesaid thickeners may
also be used.
[0022] The urea derivative thickener may be present in the grease
composition claimed in an amount of about 1% by weight to about 25%
by weight, referred to the total amount of the grease composition,
most preferred in an amount of about 3% by weight to about 11% by
weight, referred to the total amount of the grease composition.
[0023] In a further embodiment of the present invention, the grease
composition claimed further comprising at least one zinc
dithiophosphate, molybdenum dithiocarbamate and/or molybdenum
dithiophosphate as an additive package. Preferably, the amount of
zinc dithiophosphates, molybdenum dithiophosphates and/or
molybdenum dithiocarbamates is in a range of between about 0.1% by
weight to about 7% by weight, preferably to about 5% by weight,
more preferably about 0.3% by weight to about 2% by weight, in each
case referred to the total amount of the grease composition. Most
preferably, the weight percent added, referred to the total amount
of the grease composition, of each of zinc dithiophosphates,
molybdenum dithiophosphates and/or molybdenum dithiocarbamates is
essentially identical. In such an embodiment of the present
invention, preferably the amount of the zinc dithiophosphates,
molybdenum dithiophosphates and/or molybdenum dithiocarbamates is
about 0.4% by weight, 0.5% by weight, 0.6% by weight, and/or 0.7%
by weight, in each case referred to the total amount of the grease
composition.
[0024] In a preferred embodiment of the present invention, the
further molybdenum containing compound is selected from the group
comprising molybdenum dithiocarbamates and/or molybdenum
dithiophosphates. The at least one molybdenum dithiophosphate
(MoDTP) and/or molybdenum dithiocarbamate (MoDTC) is preferably
present in the grease composition according to the present
invention in an amount in a range between about 0.3% by weight,
more preferred about 0.5% by weight, most preferred about 1.5% by
weight, to about 3.5% by weight, most preferred about 3% by weight,
in each case referred to the total amount of the grease
composition. However, also any further molybdenum containing
compound may be present in the grease composition according to the
present invention as component c), of which organic molybdenum
compounds are preferred. The grease composition according to the
present invention may contain one or more MoDTC and/or MoDTP, and
especially mixtures thereof. The MoDTP according to the present
invention is of the following general formula:
##STR00001##
wherein X or Y represents S or O and each of R.sup.1 to R.sup.4
inclusive may be the same or different and each represents a
primary (straight chain) or secondary (branched chain) alkyl group
having between 6 and 30 carbon atoms.
[0025] The MoDTC according to the present invention is of the
following general formula:
[(R.sup.5)(R.sup.6)N--CS--S].sub.2--Mo.sub.2O.sub.mS.sub.n
(III)
wherein R.sup.5 and R.sup.6 each independently represents an alkyl
group having 1 to 24, preferably 3 to 18 carbon atoms; m ranges
from 0 to 3 and n ranges from 4 to 1, provided that m+n=4.
[0026] The grease composition comprises in the additive package at
least one zinc compound additive, more preferably a zinc compound
additive in an amount of about 0.1% by weight to about 3.5% by
weight, preferably to about 2.5% by weight, more preferably to
about 0.5% by weight to about 2.0% by weight, referred to the total
amount of the grease composition. Most preferred the zinc compound
additive is selected from the group comprising at least one of zinc
dithiophosphates (ZnDTP) and/or zinc dithiocarbamates (ZnDTC), and
ZnDTPs are most preferred. The zinc dithiophosphate is preferably
selected from the group of zinc dialkyldithiophosphate of the
following general formula:
(R.sup.7O)(R.sup.8O)SP--S--Zn--S--PS(OR.sup.9)(OR.sup.10) (IV)
wherein each of R.sup.7 to R.sup.10 inclusive may be the same or
different and each represents a primary or secondary alkyl group of
which primary alkyl groups are most preferred having 1 to 24,
preferably 3 to 20, most preferably 3 to 5 carbon atoms. In
particular, excellent effects can be expected if the substituents
R.sup.7, R.sup.8, R.sup.9 and R.sup.10 represent a combination of
primary and secondary alkyl groups, each having 3 to 8 carbon
atoms.
[0027] The zinc dithiocarbamate may be preferably selected from
zinc dialkyldithiocarbamate of the following general formula:
##STR00002##
wherein R, R.sup.11, R.sup.12, R.sup.13, and R.sup.14 may be same
or different and each represents an alkyl group having 1 to 24
carbon atoms or an aryl group having 6 to 30 carbon atoms.
[0028] By adding at least one zinc compound additive to the grease
composition according to the invention, the friction coefficient as
well as the wear in CVJ are diminished further significantly.
[0029] According to a further embodiment of the present invention,
the grease composition may further comprise an agent comprising at
least one anti-oxidation agent, corrosion inhibitor, anti-wear
agent, wax, friction modifier, and/or extreme pressure agent (EP
agent), that may also be part of the additive package. The additive
package, thus, may not only comprise zinc dithiophosphates,
molybdenum dithiocarbonates and/or molybdenum dithiophosphates, but
also the aforesaid agents.
[0030] The EP agent is preferably a metal-free polysulfide or a
mixture thereof, e.g. sulphurised fatty acid methyl ester agents,
with preferably a viscosity of about 25 mm.sup.2/s at 40.degree.
C., being present preferably in an amount between about 0.1 to
about 3% by weight, preferably 0.3 to about 2% by weight, referred
to the total amount of the grease composition. The total inactive
sulphur amount of the EP agent at room temperature preferably
ranges from about 8 to about 50% by weight, preferably to about 45%
by weight. The active sulphur amount as measured in accordance with
ASTM D1662 may be about up to 11% by weight, preferably up to about
8% by weight at 100.degree. C., and preferably up to about 20% by
weight at 140.degree. C., the weight percent being referred to the
amount of the EP agent itself. Such EP agents exhibit excellent
effects with respect to the prevention of scuffing of contacting
CVJ internal components. If the sulphur content exceeds the upper
limit defined above, it may promote the initiation of rolling
contact fatigue and wear of the contacting metal components and may
lead to degradation of the CVJ boot material.
[0031] As an anti-oxidation agent, the grease composition of the
present invention may comprise an amine, preferably an aromatic
amine, more preferably phenyl-.alpha.-naphthylamine or
di-phenylamine or derivatives thereof. The anti-oxidation agent is
used to prevent deterioration of the grease composition associated
with oxidation. The grease composition according to the present
invention may range between about 0.1 to about 2% by weight,
referred to the total amount to the grease composition, of an
anti-oxidant agent in order to inhibit the oxidation degradation of
the base oil composition, as well as to lengthen the life of the
grease composition, thus prolonging the life of the CVJ.
[0032] Typically, the last operation before the assembly of CVJ is
a wash to remove machining debris, and it is therefore necessary
for the grease to absorb any traces of remaining water and to
prevent the water from causing corrosion and adversely effecting
the performance of the CVJ, thus a corrosion inhibitor is required.
As a corrosion inhibitor, the grease composition according to the
present invention may comprise at least one metal or dimetal salt
selected from the group consisting of metal salts of oxidised
waxes, metal salts of petroleum sulphonates, especially prepared by
sulphonating aromatic hydrocarbon components present in fractions
of lubricating oils, and/or metal salts of alkyl aromatic
sulphonates, such as dinonylnaphthalene sulphonic acids,
alkylbenzene sulphonic acids, or overbased alkylbenzene sulphonic
acids. Examples of the metal salts include sodium salts, potassium
salts, calcium salts, magnesium salts, zinc salts, quaternary
ammonium salts, the calcium salts being most preferred. Calcium
salts of oxidised waxes also ensure an excellent effect. Especially
preferred is disodium sebacate as corrosion inhibitor.
[0033] Anti-wear agents according to the present invention prevent
a metal-to-metal contact by adding film-forming compounds to
protect the surface either by physical absorption or chemical
reaction. ZnDTP-compounds may also be used as anti-wear agents. As
anti-corrosion agents according to the present invention preferably
calcium sulphonate salts are used, preferably an amount between
about 0.5 to about 3% by weight, referred to the total amount of
the grease composition.
[0034] As a wax compound, the grease composition of the present
invention may comprise any kind of waxes, preferably oiliness
waxes, known in the state of the art to be used in grease
composition or mixtures thereof, of which montan waxes, especially
ester montan waxes being a reaction product of at least one acid
montan wax with an ester, and polyolefin waxes including micronized
montan and/or polyolefin waxes, or mixtures thereof are most
preferred. Montan waxes in the sense of the present invention
preferably comprise esters of C.sub.22-C.sub.34-fatty acids and
probably wax alcohols having 24 to 28 carbon atoms. Esters may be
present in the montan wax in accordance with the present invention
in an amount in a range of about 35% by weight to about 70% by
weight. Further, free fatty acids as well as free wax alcohols as
well as montan resins may be present. Useful montan waxes are
offered for example by the company Clariant GmbH, 86005 Augsburg,
Germany, especially montan waxes offered and sold under the trade
name "Licowax". Usable polefin waxes in the sense of the present
invention are especially polypropylene and/or polyethylene waxes or
mixtures thereof, also including modified polyolefin waxes,
obtained especially by copolymerization of ethylene with useful
comonomers like vinyl esters or acrylic acid. The wax has
preferably a viscosity of at least about 50 mPas at 100.degree. C.,
more preferred of at least about 100 mPas at 100.degree. C., and
most preferred of at least about 200 mPas at 100.degree. C.,
measured in accordance with DIN 53 018. The wax used in the grease
composition may be supplied as a powder or flakes, and is added to
the grease composition with a long period of stirring, preferably
at elevated temperatures, especially at temperatures about
80.degree. C. to about 100.degree. C.
[0035] Traditional friction modifiers used in the present invention
such as fatty acid amides and fatty amine phosphates have been used
in greases and other lubricants for many years (see, e.g., the
modifiers disclosed in Klamann, Dieter--"Lubricants", Verlag Chemie
GmbH 1983, 1st edition, chapter 9.6). Their role is to give the
lubricant stable but not necessarily low friction over a wide range
of operating conditions.
[0036] In a preferred embodiment of the present invention, the
grease composition claimed comprises about 50% by weight to about
98.9% by weight of the base oil composition, about 0.1% by weight
to about 5% by weight of at least one tri-nuclear molybdenum
compound, about 1% by weight to about 25% by weight of at least one
urea derivative thickener. Most preferred, the grease composition
according to the present invention comprises about 55% by weight to
about 98.1% by weight, preferably to about 97.8% by weight, more
preferred to about to 92.8% by weight, most preferred to about
92.5% by weight of the base oil composition, about 0.1% by weight
to about 5% by weight, preferably about 0.3% by weight to about 2%
by weight, of the tri-nuclear molybdenum compound, about 1% by
weight to about 25% by weight of the urea derivative thickener,
about 0.5% by weight to about 15% by weight of at least one calcium
complex thickener, about 0.1% by weight to about 5% by weight of at
least one ZnDTPs, about 0.1% by weight to about 5% by weight of at
least one MoDTPs, and about 0.1% by weight to about 5% by weight of
at least one MoDTCs. A urea derivative thickener may be present in
a range between about 5 to about 20% by weight. Most preferred is a
grease composition comprising about 70% by weight, preferably about
80% by weight, to about 92% by weight, preferably to about 92.4% by
weight, more preferred to about 92.7% by weight, of the base oil
composition, about 0.3% by weight to about 2% by weight, preferably
to about 1.2% by weight of the least one tri-nuclear molybdenum
compound, about 4.5% by weight to about 20% by weight, preferably
to about 11% by weight, of the least one urea derivative thickener,
about 1.5% by weight to about 3.5% by weight of at least one
molybdenum dithiocarbamate, about 0.5% by weight to about 3% by
weight of the least one zinc dithiophosphate, and about 0.5% by
weight to about 2% by weight of at least one wax. Further, 0.3% by
weight to about 2% by weight of an EP additive are preferably
added.
[0037] Preferably the grease composition in accordance with the
present invention is characterized in that the weight percent
added, referred to the total amount of a grease composition, of
tri-nuclear molybdenum compounds is essentially identical with the
weight per cent of each one of zinc dithiophosphate, molybdenum
dithiophosphate and/or molybdenum dithiocarbamate added. The
compounds mentioned before may also be composed of different zinc
dithiophosphates, molybdenum dithiophosphates and/or molybdenum
dithiocarbamates, and, thus, they may present a mixture of
different zinc dithiophosphates, molybdenum dithiophosphates and/or
molybdenum dithiocarbamates. For clarification purposes it is noted
that the essential identity of the weight percent of the
tri-nuclear molybdenum compound or mixtures of such compounds added
refers to each one of the compounds added, and not to mixtures of
the different compounds mentioned. In a further referred embodiment
of the present invention, the grease composition is characterized
in that the weight percent added, referred to the total amount of
the grease composition, of tri-nuclear molybdenum compound or
mixtures of different tri-nuclear molybdenum compounds is 4 to 10
times lower than the weight percent of all of zinc dithiophosphate,
molybdenum dithiophosphate and/or molybdenum dithiocarbamate added.
If, for example, in the grease composition 2 weight %
dithiophosphate(s) and 1 weight % molybdenum dithiocarbamate(s) are
present as well as 0.5 weight % of a tri-nuclear molybdenum
compound, thus, the weight percent of the tri-nuclear molybdenum
compound added is 6 times lower than the weight percent of zinc
dithiophosphate(s) and molybdenum dithiocarbamate(s) added. It has
to be noted that also the zinc dithiophosphate, molybdenum
dithiophosphate and/or molybdenum dithiocarbamate may be present as
mixtures of said compounds having different structural
formulas.
[0038] Further, the grease composition according to the present
invention has a sliding friction coefficient of not more than 0.08,
as measured with a SRV test.
BRIEF DESCRIPTION OF THE DRAWINGS
[0039] FIG. 1A illustrates the friction coefficient as a function
of grease sample;
[0040] FIG. 1B illustrates the welding load as a function of grease
sample;
[0041] FIG. 2A illustrates the friction coefficient as a function
of grease sample;
[0042] FIG. 2B illustrates the welding load as a function of grease
sample;
[0043] FIG. 3A illustrates the friction coefficient as a function
of grease sample;
[0044] FIG. 3B illustrates the welding load as a function of grease
samples;
[0045] FIG. 4 illustrates the friction coefficient as a function of
grease sample; and
[0046] FIG. 5 illustrates the wear as a function of grease
sample.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0047] In order to determine the effect of the lowering of the
friction coefficient as well as the wear by the grease composition
according to the invention, SRV tests are carried out using an
Optimol Instruments SRV tester. Flat disc lower specimen made of
the 100Cr6 standard bearing steel from Optimol Instruments
Pruftechnik GmbH, Westendstrasse 125, Munich, properly cleaned
using a solvent are prepared and contacted with the grease
composition to be examined. The SRV test is an industry standard
test and is especially relevant for the testing of greases for CVJ.
The test consists of an upper ball specimen with a diameter of 10
mm made from 100Cr6 bearing steel reciprocating under load on the
flat disc lower specimen indicated above. In tests for mimicking
tripod joints a frequency of 7 Hz (for examples D1 and D2 only) and
40 Hz, respectively, with an applied load of 200 N were applied for
60 minutes (including running-in) or 3 hours (for examples D1 and
D2 only) at 80.degree. C., or 40.degree. C. (examples D1 and D2).
The stroke was 0.5 mm (for examples D2 and D2 only), 1.5 mm and 3.0
mm, respectively. The friction coefficients obtained were recorded
on computer. For each grease, the reported value is an average of
four data (two data for examples D1 and D2) at the end of tests in
four runs or two runs, respectively (two runs at 1.5 mm stroke and
two runs with 3.0 mm stroke with the exception of examples D1 and
D2 with two runs with 0.5 mm stroke). Wear is measured using a
profilometer and a digital planimeter. By using the profilometer, a
profile of the cross section in the middle of the worn surfaces can
be obtained. The area (S) of this cross section can be measured by
using the digital planimeter. The wear quantity is assessed by
V=Sl, where V is the volume of the wear and l is the stroke. The
wear rate (W.sub.r) is obtained from W.sub.r=V/L [.mu.m.sup.3/m],
where L is the total sliding distance in the tests. For the
running-in, it is started with an applied load of 50 N for 1 minute
under the above-specified conditions. Afterwards, the applied load
is increased for 30 seconds by 50 N up to 200 N.
[0048] Further, the welding load exerted on CVJs with a different
grease composition is measured in accordance with a bear 4 ball EP
test according to standard IP-239 (Energy Institute, London,
UK).
[0049] The following substances are used in the examined grease
compositions:
Base Oil Composition (Oil Blend)
[0050] The base oil compositions used have a kinematic viscosity of
between about 32 and about 250 mm.sup.2/s at 40.degree. C. and
between about 5 and about 25 mm.sup.2/s at 100.degree. C. Two base
oil blends are used in this invention. The base oil blend A is a
mixture of one or more naphthenic oils in a range between about 10
to about 60% by weight, one or more paraffinic oils in a range
between about 30 to about 80% by weight and one or more
poly-alpha-olefins (PAO) in a range between about 5 to about 40% by
weight, referred to the total amount of the oil mixture. Oil blend
A does not contain an organic synthetic ester, whereas oil blend B
contains DOS in a range between about 2 to about 10% by weight
referred to a total amount of the oil mixture.
[0051] The naphthenic oils are selected with a range of viscosity
between about 20 to about 180 mm.sup.2/s at 40.degree. C.,
paraffinic oils between about 25 to about 400 mm.sup.2/s at
40.degree. C., and PAO between about 6 and about 40 mm.sup.2/s at
100.degree. C.
Tri-Molecular Molybdenum Compound (TNMoS)
[0052] The tri-molecular molybdenum compound used in the grease
compositions according to the present invention is a
sulphur-containing tri-nuclear molybdenum compound obtainable under
the trade name C9455B by Infineum International Ltd., UK. Its
structure is defined in U.S. Pat. No. 6,172,013 B1.
Further Molybdenum Compounds
[0053] A molybdenum dithiophosphate (MoDTP) sold under the
commercial name Sakuralube 300 (S-300) by Asahi Denka Co. Ltd.,
Japan, with the chemical formula 2-Ethylhexyl molybdenum
dithiophosphate, diluted with mineral oil, is used. Further, a
molybdenum dithiocarbamate (MoDTC) sold under the trade name
Sakuralube 600 (S-600) in the solid state, produced by Asahi Denka
Co. Limited, Japan, is used.
Zinc Compound Additive
[0054] As zinc compound additives, ZnDTP, sold by Infineum
International Ltd., Oxfordshire, UK, under the trade name C9425, is
used, being a zinc dialkyldithiophosphate with primary and/or
secondary alkyl groups, especially having 3 to 8 C-atoms,
preferably having 4 to 5 C-atoms, diluted with mineral oil.
Thickener
[0055] The urea thickener ("Thickener" in the examples)
manufactured by the company Kyodo Yushi Co., Ltd., Tokyo, Japan, is
used as defined in U.S. Pat. No. 5,589,444 (hereinafter referred to
as Thickener), and is a reaction product of (4,4'-Methylenediphenyl
diisocyanate) with octadecylamine.
[0056] Further, a calcium complex thickener (Calcium complex
thickener) being a reaction product of calcium hydroxide with two
carboxylic acids, one with a short carbon chain length of 2 to 5
carbon atoms and one with a long carbon chain length of 16 to 20
carbon atoms, in which the short to long chain ratio is between 1:2
and 1:5 is used. Examples having mixtures containing a urea
thickener as well as a calcium complex thickener, thus, comprising
a urea complex thickener in accordance with the definition in the
present invention.
Wax
[0057] As wax compound, an oiliness montan wax sold by Clariant
GmbH, Augsburg, Germany, under the trademark "Licowax OP" being an
ester montan wax, partially saponified, with a drop point about
100.degree. C. (DIN 51 801/1 or ASTM D 127) and a viscosity of
about 300 mPa*s at 120.degree. C. (DIN 53 018) is used ("Montan
wax" in the examples).
Corrosion Inhibitor
[0058] As a corrosion inhibitor, disodium sebacate is used.
Anti-Oxidation Agent
[0059] As an anti-oxidation agent (Anti-Oxidant), a diphenylamine
with butyl- and/or octyl groups is used, supplied by Ciba
Speciality Chemicals, Switzerland, under the trade name "L57"
(Irganox L57).
EP Additive
[0060] As an EP-agent, a sulphurized organic compound (Di-t-butyl
Polysulfide) sold under the trade name C9002 by Infineum
International Ltd., Oxfordshire, UK, with an inactive sulphur
amount of about 45% ("EP additive" in the examples)) at room
temperature (20.degree. C. or 25.degree. C.) and an active sulphur
amount at 100.degree. C. of about 5% by weight, and at 140.degree.
C. of about 15% by weight, the weight percent referred to the
amount of the EP agent itself, is used.
[0061] First, the advantages of the grease composition according to
the present invention were examined by measuring the friction
coefficient and the welding load. Six different grease compositions
were produced, as listed in Table 1:
TABLE-US-00001 TABLE 1 Grease Composition Example Example Example
Example Example Example [wt %] A1 A2 A3 A4 A5 A6 TNMoS 0.5 0.5 0.5
0.5 0.5 0.5 ZnDTP 0.5 0.5 0.5 -- 0.5 0.5 MoDTP 0.5 0.5 -- 0.5 --
0.5 MoDTC 0.5 0.5 -- 0.5 0.5 -- Calcium complex 3.0 -- 3.0 3.0 3.0
3.0 thickener oil blend 87 90 88 85 85 85 Thickener 8 8 8 8 8 8
[0062] The results from the SRV-measurements of the friction
coefficient as well as the welding load measurements of examples A1
to A6 may be derived from FIG. 1. Example A2 does not contain any
calcium complex thickener and/or calcium thickener, and, thus, does
not comprise a urea complex thickener, whereas the other examples
comprise an urea complex thickener. Further, the amounts of the
additive package as well as the composition of the same are amended
in examples A1 to A6. The friction coefficient of example A1 is
below 0.06, and is the lowest friction coefficient measured in said
test series. The friction coefficient of example A2 is above 0.08,
and is the highest friction coefficient measured. Further, also the
friction coefficients of examples A4 and A5 are slightly higher
than the friction coefficients of examples A1, A3 and A6. One may
derive from the friction coefficient measurements that the addition
of an additive package containing at least one ZnDTP, at least one
MoDTP, and at least MoDTC gives the lowest values for the friction
coefficient. Further, the addition of at least one ZnDTP as well as
at least one MoDTP, preferably in combination with each other (see
example A6), is preferred.
[0063] From the measurements of the welding load in FIG. 1b) one
may derive that the welding load of example A1 as well as example
A5 is higher than the welding load measured for the other examples.
Thus, the grease composition according to example A1 shows the best
values not only for the friction coefficient, but also with respect
to the welding load, and, thus, exhibits a good extreme pressure
performance.
[0064] In a further series of tests, the amount of the TNMoS as
well as the additive package composition is amended. Three grease
compositions were prepared in accordance with Table 2.
TABLE-US-00002 TABLE 2 Grease Composition Example Example Example
[wt %] B1 = A1 B2 B3 TNMoS 0.5 1.0 0.1 ZnDTP 0.5 1.0 0.1 MoDTP 0.5
1.0 0.1 MoDTC 0.5 1.0 0.1 Calcium complex 3.0 3.0 3.0 thickener oil
blend 87 85 88.6 Thickener 8 8 8
[0065] In all of the examples B1 to B3, the amount of the thickener
remains unamended, whereas the amount of the TNMoS compound as well
as the components of the additive package were amended to 0.1% by
weight, 0.5% by weight and 1.0% by weight, respectively, in each
case referred to the total amount of the grease composition. The
results from the SRV measurements with respect to the friction
coefficient as well as the welding load may be derived from FIG.
2.
[0066] Example B1 (=A1) shows the lowest friction coefficient and
highest welding load, and, thus, exhibits a very good extreme
pressure performance when compared to examples B2 and B3. Further,
the lowering of the amount of the TNMoS compound as well as the
components of the additive package at values around 0.1% by weight
clearly results in an increase of the friction coefficient and a
decrease in the welding load. Thus, at least about 0.25% by weight
of the TNMoS compound as well as at lest one of ZnDTPs, MoDTPs and
MoDTCs should preferably be present in the grease composition.
[0067] In a third test series, the effect of the addition of a
calcium complex thickener added to four grease compositions C1 to
C4 in accordance with Table 3 is studied.
TABLE-US-00003 TABLE 3 Grease Composition Example Example Example
Example [wt %] C1 = A1 C2 = A2 C3 C4 TNMoS 0.5 0.5 0.5 0.5 ZnDTP
0.5 0.5 0.5 0.5 MoDTP 0.5 0.5 0.5 0.5 MoDTC 0.5 0.5 0.5 0.5 Calcium
complex 3.0 1.5 15 thickener oil blend 87 90 88.5 75 Thickener 8 8
8 8
[0068] Example C2 is identical to example A2. One may derive from
the SRV measurements of the friction coefficient as well as the
measurement of the welding load (see FIG. 3) that the addition of
3% by weight calcium complex thickener resulted in the lowest
friction coefficient values and a welding load above 3000 N. The
welding load is especially increased by adding 15% by weight
calcium complex thickener in accordance with example C4, however,
also the friction coefficient is increased to values about 0.08.
This third test series indicates that the amount of calcium complex
thickener used in the grease composition may be in a range of about
0.5% by weight to about 20% by weight, preferably to about 15% by
weight, thus forming a urea complex thickener with the
Thickener.
[0069] Further preferred grease compositions are grease
compositions as listed in Table 4.
TABLE-US-00004 TABLE 4 Grease Composition Example Example [wt %] D1
D2 TNMoS 0.5 0.5 ZnDTP 1.0 2.0 MoDTC 2.5 2.5 Montan Wax 1.0 1.0
Corrosion inhibitor 0.2 0.2 Anti-oxidant 0.5 0.5 EP additive 0.5
Oil blend 88.3 86.8 Thickener 6 6
[0070] As may be derived from FIG. 4, the friction coefficient of
example D2 is below 0.05, and even lower than the friction
coefficient of example C1. Further, the wear of example D2 is not
detectable. Thus, the adding of an EP additive as well as the
increase in ZnDTP amount lead to a grease composition with highly
preferred properties, when comprising D1 and D2.
[0071] In summary, the grease composition according to the present
invention has an advantageous significant influence on the friction
coefficient and wear, leading to a good extreme pressure
performance as well as a good NVH performance in CVJs.
* * * * *