GREASE COMPOSITION FOR USE IN CONSTANT VELOCITY JOINTS COMPRISING AT LEAST TWO DIFFERENT MOLYBDENUM COMPOUNDS

In order to provide for a grease composition reducing or preventing noise, vibration and harshness (NVH) in the driveline, 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 MO3SkLnQZ, 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 further molybdenum containing compound; and d) at least one simple and/or complex soap thickener.

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Description
CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No. PCT/EP2006/009717 filed Oct. 7, 2006 which is hereby incorporated by reference in its entirety.

FIELD

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

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.

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.

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).

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. Usual mineral and synthetic base oils extract the plasticisers and other oil-soluble protective agents from the boot materials. Paraffinic mineral oils and poly-α-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 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.

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-α-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 dialkyldithio-phosphate 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, Verschleiβ) tests need to be improved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1a is a graph of friction coefficient data for grease composition embodiments of the present invention and comparison compositions that lack the combination of a tri-nuclear molybdenum compound containing sulfur and a further molybdenum containing compound;

FIG. 1b is a graph of wear data for grease composition embodiments of the present invention and comparison compositions that lack the combination of a tri-nuclear molybdenum compound containing sulfur and a further molybdenum containing compound;

FIG. 2a is a graph of friction coefficient data for grease composition embodiments of the present invention with varying amounts of a tri-nuclear compound containing sulfur, and with varying amounts of a further molybdneum containing molybdenum compound and/or a zinc dithiophosphate compound;

FIG. 2b is a graph of wear data for grease composition embodiments of the present invention with varying amounts of a tri-nuclear molybdenum compound containing sulfur, and with varying amounts of a further molybdneum containing compound and/or a zinc dithiophosphate compound;

FIG. 3 is a graph of axial force data for grease compositions B1 and B2 of FIGS. 2a and 2b;

FIG. 4a is graph of welding load data for grease composition embodiments of the present invention with varying amounts of an extra pressure agent; and

FIG. 4b is a graph of friction coefficient data for grease composition embodiments of the present invention with varying amounts of an extra pressure agent.

 DETAILED DESCRIPTION

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.

Said object of the present invention is solved by a grease composition for use in constant velocity joints comprising

    • a) a base oil composition;
    • 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


MO3SkLnQz,

      • 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 further molybdenum containing compound, and
    • d) at least one simple and/or complex soap thickener.

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 inventors of the present invention have found that the presence of at least one tri-nuclear molybdenum compound and a further molybdenum containing compound according to claim 1 would significantly lower the friction coefficient as well as the wear when used in CVJ.

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 mm2/s at 40° C. and between about 5 and about 25 mm2/s at 100° 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-α-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)).

If poly-α-olefin is present in the base oil composition, preferably poly-α-olefins are selected having a viscosity in a range from about 2 to about 40 centistokes at 100° C. Naphthenic oils selected for the base oil compositions have preferably a viscosity in a range between about 20 to about 180 mm2/s at 40° 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 400 mm2/s at 40° C.

In an 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 to 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 also mixtures thereof. The MoDTP according to the present invention is of the following general formula:

wherein X or Y represents S or 0 and each of R1 to R4 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.

The MoDTC according to the present invention is of the following general formula:


[(R5)(R6)N—CS—S]2—Mo2OmSn  (III)

wherein R5 and R6 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.

The addition of two molybdenum containing compounds, one of which is a tri-molecular molybdenum compound containing sulphur (TNMoS), whereas the further molybdenum containing compound is preferably at least one of MoDTPs and/or MoDTCs lowers the friction coefficient and the wear of CVJs in use significantly. Especially, the friction coefficient is diminished by at least about 25% compared to grease compositions containing only at least one TNMoS.

The at least one simple and/or complex soap thickener according to the grease composition claimed is preferably selected from the group comprising Lithium soaps and/or Calcium soaps.

In the sense of the present invention, a lithium soap or a calcium soap is a reaction product of at least one fatty acid with lithiumhydroxide or calciumhydroxide. Preferably, the thickener may be a simple lithium or calcium soap formed from stearic acid, 12-hydroxy stearic acid, hydrogenated castor oil or from other similar fatty acids or mixtures thereof or methylesters of such acids. Alternatively, a lithium and/or calcium complex soap may be used formed for example from a mixture of long-chained fatty acids together with a complexing agent, for example a borate of one or more dicarboxylic acids. The use of complex lithium and/or calcium soaps allows the grease composition according to the present invention to operate up to a temperature of about 180° C., whereas with simple lithium and/or calcium soaps, the grease composition will only operate up to a temperature of about 120° C. However, mixtures of all of the aforesaid thickeners may also be used.

In a further embodiment of the present invention, the grease composition further comprises at least one zinc compound additive, more preferably a zinc compound additive in an amount of about 0.1% by weight to about 3% by weight, preferably about 0.3% by weight to about 2% by weight, referred to the total amount of the grease composition. The most preferred the zinc compound additive is selected from the group comprising at least one of zinc dithiophosphates (ZnDTP). The zinc dithiophosphate is preferably selected from the group of zinc dialkyldithiophosphate of the following general formula:


(R7O)(R8I)SP—S—Zn—S—PS(OR9)(OR10)  (IV)

wherein each of R7 to R10 inclusive may be the same or different and each represents a primary or secondary alkyl group having 1 to 24, preferably 3 to 20, most preferably 3 to 5 carbon atoms. In particular, excellent effects can be expected if the substituants R7, R8, R9 and R10 represent a combination of primary and secondary alkyl groups, each having 3 to 8 carbon atoms.

By adding at least one zinc compound additive to the grease composition according to the invention, the wear in CVJ is diminished further significantly.

According to a further embodiment of the present invention, the grease composition further comprises an additive package selected from the group of agents comprising antioxidation agents, corrosion inhibitors, anti-wear agents, friction modifiers, and/or extreme pressure agents (EP agents).

The EP agent is preferably a metal-free, sulphurised fatty acid methyl ester agent with a viscosity of about 25 mm2/s at 40° C. being present preferably in an amount between about 0.1 to about 3% by weight, referred to the total amount of the grease composition. The total sulphur amount of the EP agent preferably ranges from about 8 to about 10% by weight and the active sulphur amount is about 1% by weight. Such EP agents exhibit excellent effects with respect to the prevention of seizure of CVJ. 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.

As an anti-oxidation agent, the grease composition of the present invention may comprise an amine, preferably an aromatic amine, more preferably phenyl-α-naphthylamine or diphenylamine 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, as well as to lengthen the life of the grease composition, thus prolonging the life of the CVJ. 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, it is therefore necessary to add a corrosion inhibitor. As a corrosion inhibitor, the grease composition according to the present invention may comprise at least one metal 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 dinonylnaphtalene sulphonate, alkylbenzene suiphonic acids, or overbased alkylbenzene sulphonic acids, Examples of the metal salts include sodium salts, potassium salts, calcium salts, magnesium salts, zinc salts and quaternary ammonium salts, the calcium salts being most preferred. Calcium salts of oxidised waxes also ensure an excellent effect.

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 anticorrosion 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.

Traditional friction modifiers such as fatty acid amides and fatty amine phosphates have been used in greases and other lubricants for many years (see, e.g., Klamann, Dieter-“Lubricants”, Verlag Chemie GmbH 1983, chapter 9.6 as reference). Their role is to give the lubricant stable but not necessarily low friction over a wide range of operating conditions.

In a further preferred embodiment of the present invention, a grease composition comprises about 55% by weight to about 98% 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 0.3% by weight to about 2% by weight of at least one further molybdenum compound, and about 1% by weight to about 25% by weight of at least one soap thickener, in each case referred to the total amount of the grease composition.

In a further preferred embodiment of the present invention, the amount of the tri-nuclear molybdenum compounds, molybdenum dithiophosphates, molybdenum dithiocarbamates, and/or zinc dithiophosphates present in the composition is in a range of between 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 percentage added, referred to the total amount of the grease composition, of the tri-nuclear molybdenum compounds is essentially identical with the weight percent of molybdenum dithiophosphates, molybdenum dithiocarbamates, or zinc dithiophosphates added, and is preferably about 0.4% by weight, about 0.5% by weight, about 0.6% by weight and/or about 0.7% by weight, in each case referred to the total amount of the grease composition.

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, and is typically below 0.07.

BEST MODE FOR CARRYING OUT THE INVENTION

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 Prüftechnik 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 40 Hz with an applied load of 200 N were applied for 60 minutes (including running-in) at 80° c. The stroke was 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 at the end of tests in four runs (two runs at 1.5 mm stroke and two runs with 3.0 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=SI, where V is the volume of the wear and I is the stroke. The wear rate (Wr) is obtained from Wr=V/L [μm3/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.

Further, the axial forces generated by a plunging tripod joint at various articulation angles is measured in accordance with the following method:

Axial Cyclic Force Generation Test

This test is for measurement of axial cycles force generated by a driveshaft assembly or plunging constant velocity joint under high torque and low speed, similar to the take off shudder conditions in the vehicle. The driveshaft assembly with a plunging joint, is mounted on a test rig capable of applying rotation, torque and articulation to the constant velocity joint. The test rig is equipped with a joint cooling system. A force transducer is fitted to the test rig and used to measure the force along the rotation axis of the joint.

Before the test, a running-in procedure is applied as follows:

    • Grease distribution: ensure consistent lubrication conditions under a torque of +100 Nm and speed of +200 rpm sweeping sinusoidally at angles between 0 to 20 degree 4 cycles per minute for 5 minutes
    • full stabilized axial force values under the conditions:

Torque (Nm) Speed (rpm) Angle (degree) Duration (hour) +300 +200 sweeping sinusoidally at 0.5 +600 +200 angles between 0 to 20 1 −300 −200 degree 4 cycles per minute 0.5 −600 −200 1
    • Warm-up: ensure stablised temperature and lubrication conditions for joint which have already had a full running-in under a torque of +300 Nm and speed of +200 rpm sweeping sinusoidally at angles between 0 to 20 degree 4 cycles per minute for 15 minutes
    • Grease running-in: to run-in greases for joints which have already had a full running-in under the conditions:

Torque (Nm) Speed (rpm) Angle (degree) Duration (hour) +300 +200 sweeping sinusoidally at 0.5 +600 +200 angles between 0 to 20 1 −300 −200 degree 4 cycles per minute 0.5 −600 −200 1 Other conditions: Joint Angle: 2.5, 5, 7.5, 10, 12.5, 15, 17.5 and 20 degree applied torque +/−600 Nm torque with +/−200 rpm speed

The load carrying capacity of a CVJ grease is an important property that defines the resistance of the grease to adhesive wear and scuffing. For greases it is defined as the welding load in Newtons as measured by a 4 ball EP test according to the IP-239 standard published by the Energy Institute, London, UK.

The following substances are used in the examined grease compositions:

Base Oil Composition

The base oil compositions used have a kinematic viscosity of between about 32 and about 250 mm2/s at about 40° C. and between about 5 and about 25 mm2/s at 40° 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 polyalpha-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 8 contains DOS in a range between about 2 to about 10% by weight referred to a total amount of the oil mixture.

The naphthenic oils are selected with a range of viscosity between about 20 to about 180 mm2/s at 40° C., paraffinic oils between about 25 to about 400 mm2/s at 40° C., and PAO between about 6 and about 40 mm2/s at 100° C.

Tri-Molecular Molybdenum Compound (TNMoS)

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 C94558 by Infineum International Ltd., UK. Its structure is defined in U.S. Pat. No. 6,172,013 B4.

Further Molybdenum Containing Compounds for Comparative Examples

A molybdenum dithophosphate (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 (3-600) in the solid state, produced by Asahi Denka Co. Limited, Japan, being in accordance with formula III, is used.

Zinc Compound Additive

As zinc compound additives, ZnDTP, sold by Infineum International Ltd., UK under the trade name Paranox-15, is used, being a zinc dialkyldithiophosphate with primary and secondary allyl groups, preferably diluted with mineral oil.

Thickener

As a lithium soap (Li soap), a reaction product supplied by Brugarolas S.A., Spain, using fatty acid with lithiumhydroxide is used. Further, a calcium complex soap (Calcium complex soap) 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.

Additives

As an anti-oxidant agent (anti-oxidant), a diphenylamine with butyl and/or octyl-groups is used, supplied by Ciba Specialty Chemicals, Switzerland under the trade name L-57 (Irganox L57). As an EP agent (EP agent 1), a sulphurised organic compound (fatty acid methylester) sold under the trade name Anglamol 33 by The Lubrizol Corporation, OH; U.S.A. (EP agent 1), or sold under the trade name DeoAdd MD 10 by DOG Deutsche Oelfabrik Gesellschaft für chemische Erzeugnisse mbH und Co, Hamburg, Germany (“EP additive” in the examples) is used. Another example of an EP agent is a grease with calcium sulphonate thickeners, as produced by Brugarolas S.A., Spain, under the trade name Ca-S Grease (Ca-S grease).

As a corrosion inhibitor, a calcium salt of dinonyl-naphthalensulphonate, distributed for example by King Industries, Norwalk, Conn., U.S.A., under the trade name NaSul 729 (Ca sulphonate) is used.

First, the advantages of the grease composition according to the invention were examined by comparing the friction coefficient and wear of the same with grease compositions containing no TNMoS compound and no further molybdenum containing compound, or grease compositions containing only a TNMoS compound. Seven different grease compositions were produced, as listed in the following table:

TABLE 1 Grease Composition Example Example Example Example Example Example Example [wt %] A1 A2 A3 A4 A5 A6 A7 TNMoS 0.5 1.5 1.0 2.0 2.0 ZnDTP 0.5 1.0 0.5 1.0 1.0 MoDTP 0.5 1.0 1.0 0.5 1.0 MoDTC 0.5 0.5 Anti-oxidant 0.25 0.25 0.25 0.25 0.25 0.25 0.25 oil blend A 81.75 80.75 81.75 80.75 80.75 81.75 82.75 Calcium complex soap 16 16 16 16 16 16 16

The results from the SRV-measurement of the friction coefficient and the wear of examples A1 to A7 may be derived from FIG. 1. Example A7 contains neither a TNMoS compound nor a further molybdenum containing compound, whereas example A3 does not contain any further molybdenum containing compound. In contrast thereto, example A6 contains a further molybdenum containing compound, but no TNMoS compound. Thus, in accordance with the present invention are only examples A1, A2, A4 and A5. One may clearly derive from FIG. 1(a) that the friction coefficient is significantly decreased in the grease compositions according to the present invention when compared to grease compositions not in accordance with the present invention, and that the friction coefficient is below 0.08. Further, the wear (see FIG. 1(b)) of the grease compositions A1, A2, A4, and A5 is either not measurable, or lower than in the grease compositions being not in accordance with the present invention.

In a further series of tests, 8 grease compositions in accordance with the present invention were prepared containing different concentrations either of the TNMoS compound or the further molybdenum containing compounds (MoDTP and MoDTC). The grease compositions are listed in Table 2.

TABLE 2 Grease Composition Example Example Example Example Example Example Example Example [wt %] B1 B2 B3 B4 B5 B6 B7 B8 TNMoS 0.5 1.5 0.1 0.3 1.0 0.5 0.5 0.5 ZnDTP 0.5 0.5 0.5 0.5 1.0 0.5 0.5 MoDTP 0.5 1.0 0.5 0.5 0.5 0.5 1.0 0.5 MoDTC 0.5 0.5 0.5 0.5 0.5 0.5 0.5 1.0 Anti-oxidant 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 oil blend B 91.5 90.5 91.9 91.7 91.0 91.0 91.0 91.0 Li soap 6 6 6 6 6 6 6 6

Examples B1 and B2 are similar to examples A1 and A2. The results from SRV tests with respect to the friction coefficient and wear will be seen from FIG. 2.

As may be taken from the values for the friction coefficient from FIG. 2, the friction coefficient of grease compositions is for all examples B1 to B8 around or below 0.08. Since the concentration of the TNMoS compound is changed from 0.3% by weight to 1.5% by weight, referred to the total amount of the grease composition, it appears that in a range from about 0.25% by weight to about 2% by weight at least one TNMoS compound should be present in the grease composition in accordance with the present invention. The lowest friction coefficients were obtained by adding about 0.5% by weight of at least one TNMoS compound to the grease composition. The addition of MoDTPs and/or MoDTCs being present in a range from about 0.5% by weight to about 1% by weight, referred to the total amount of the grease composition, resulted in no significant change of the friction coefficient.

Further, from FIG. 2 it may be taken that the addition of at least one ZnDTP in an amount of at least about 0.5% by weight to 1% by weight, referred to the total amount of the grease composition, is advantageous, because example B2 without any ZnDTP additive shows a higher friction coefficient when compared to examples B1 and B3 to B8.

With respect to the wear measurements, examples B1 and B3 show no measurable wear, whereas the addition of about 1% by weight of MoDTPs and/or MoDTCs resulted in a higher value for the wear, as may be taken from examples B2, B7 and B8.

The slightly different values for the friction coefficient and the wear of examples A1 and A2 when compared with examples B1 and B2 is due to the use of a different base oil composition and the use of a lithium soap thickener instead of a calcium complex soap thickener as used in examples A1 to A7. It appears that the addition of a calcium complex soap thickener is slightly more preferable than the addition of the lithium soap thickener with respect to the friction coefficient and the wear.

Further, the axial forces of grease compositions in accordance with examples B1 and B2 were measured, and are graphically represented in FIG. 3.

The axial force should be lower than a requirement set by the applicant. One may derive from FIG. 3 that the example B1 gives values for the axial force being below the values for the requirement whereas at angles around 13°, a grease composition in accordance with example B2 would lead to axial forces being higher than the requirement. Thus, grease composition B1 containing in addition the ZnDTP agent is most preferred.

In a third test series, the effect of the addition of other components on grease compositions in accordance with the present invention was examined by preparing grease compositions in accordance with Table 3.

TABLE 3 Grease Composition Example Example Example Example Example Example [wt %] C1 C2 C3 C4 C5 C6 TNMoS 0.5 0.5 0.5 0.5 0.5 0.5 ZnDTP 0.5 0.5 0.5 0.5 0.5 0.5 MoDTP 0.5 0.5 0.5 0.5 0.5 0.5 MoDTC 0.5 0.5 0.5 0.5 0.5 0.5 EP additive 1 0.5 EP additive 2 0.5 anti corrosion 2.0 Calcium 5 complex soap Ca—S grease 3 Anti-oxidant 0.5 0.5 0.5 0.5 0.5 0.5 oil blend B 91.5 91.0 91.0 89.5 86.5 88.5 Li soap 6.0 6.0 6.0 6.0 6.0 6.0

The results from SRV tests with respect to the friction coefficient as well as the measurement of the welding load with respect to examples C1 to C6 are shown in FIG. 4. The grease composition of example C1 is identical to example B1.

One may derive from FIG. 4 that the addition of a higher amount of an EP agent is preferred, as may be taken from the high value for the welding load especially for example C2. However, the friction coefficient is slightly increased by the addition of EP agents. The addition of a calcium complex grease in addition to a lithium soap grease leads to a further lowering of the friction coefficient, as may be see in example C5. However, the welding load is only slightly increased with respect to example C1. Further, the addition of a calcium sulphonate grease (Ca-S grease) increases the value for the welding load and decreases the friction coefficient of the grease composition, as may be taken from example C6. The addition of the corrosion inhibitor does not significantly influence the friction coefficient, however, the value for the welding load is significantly increased, as may be derived when comparing example C1 with example C4.

Thus, the addition of an EP agent in an amount in a range of about 0.1% by weight to about 1.0% by weight, as well as the addition of an anti-corrosion agent in an amount of between about 0.3% by weight to about 3% by weight, and the addition of a calcium sulphonate grease in an amount of between about 0.5% by weight to about 15% by weight, in each case referred to the total amount of the grease composition, is preferred.

In summary, the grease composition according to the present invention has an advantageous significant influence on the friction coefficient and wear as well as on the welding load and the axial forces, leading to lower wear and lower friction in CVJ, and thus are able to reduce or prevent noise, vibration and harshness (NVH) in the driveline.

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 Mo3SkLnQz,
 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 consisting of amines, alcohols, phosphines, and ethers, and z ranges from 0 to 5 and includes non-stoichiometric values.
c) at least one further molybdenum containing compound; and
d) at least one selected from the group consisting of a simple soap thickener and a complex soap thickener.

2. A grease composition according to claim 1, characterised in that the further molybdenum containing compound is at least one selected from the group consisting of molybdenum dithiocarbamates and molybdenum dithiophosphates.

3. A grease composition according to claim 1, comprising as a further molybdenum compound 0.3% by weight to 3% by weight of at least one selected from the group consisting of molybdenum dithiophosphate (MoDTP) and molybdenum dithiocarbamate (MoDTC), in each case referred to the total amount of the grease composition.

4. A grease composition according to claim 1, characterised in that the soap thickener is at least one selected from the group consisting of Lithium soaps and Calcium soaps.

5. A grease composition according to claim 1, further comprising at least one zinc dithiophosphate additive (ZnDTP).

6. A grease composition according to claim 1, further comprising 0.3% by weight to 3% by weight of at least one zinc dithiophosphate additive (ZnDTP), referred to the total amount of the grease composition.

7. A grease composition according to claim 1, further comprising an additive package including at least one selected from the group consisting of anti-oxidation agents, corrosion inhibitors, anti-wear agents, friction modifiers and extreme pressure agents (EP agents).

8. A grease composition according to claim 1, comprising 50% by weight to 98% by weight of the base oil composition, 0.1% by weight to 5% by weight of at least one tri-nuclear molybdenum compound, 0.3% by weight to 2% by weight of at least one further molybdenum compound, and 1% by weight to 25% by weight of at least one soap thickener, in each case referred to the total amount of the grease composition.

9. A grease composition according to claim 1, characterised in that the amount of the tri-nuclear molybdenum compounds present in the composition is in a range of between 0.3% by weight to 3% by weight, in each case referred to the total amount of the grease composition.

10. A grease composition according to claim 1, 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 one selected from the group consisting of molybdenum dithiophosphates, molybdenum dithiocarbamates, or zinc dithiophosphates added.

11. A grease composition according to claim 1, further comprising an addition of at least one selected from the group consisting of Ca-sulphonate grease in an amount from 0.1% by weight to 10% by weight and at least one sulphur containing extreme pressure agent in an amount from 0.1% by weight to 3% by weight in each case referred to the total amount of the grease composition.

12. A grease composition according to claim 1, characterised in that the sliding friction coefficient of said composition is at most 0.8.

Patent History
Publication number: 20090247437
Type: Application
Filed: Apr 7, 2009
Publication Date: Oct 1, 2009
Inventors: Jisheng E. (Hennef), Frank Resher (Siegburg), Leandro Muntada (Rubi), Stefanie Rosenkranz (Wachtberg)
Application Number: 12/419,694