Grease composition for constant velocity joints

Abstract

The disclosure relates to an improved grease composition for use in constant velocity joints, especially ball joints and/or tripod joints used in the drivelines of motor vehicles, with the grease composition comprising at least one base oil, at least one simple or complex soap thickener, at least one zinc sulphonate, at least one molybdenum dithiocarbamate in the solid state, and at least one molybdenum dithiophosphate.

Claims

1. A grease composition for use in constant velocity joints comprising a) at least one base oil; b) at least one simple or complex soap thickener; c) at least one zinc sulphonate; d) at least one molybdenum dithiocarbamate in the solid state; and e) at least one molybdenum dithiophosphate; wherein the ratio between the percent-by-weight (wt-%) amount of the at least one zinc sulphonate and both the amount of the at least one molybdenum dithiocarbamate and the amount of the at least one molybdenum dithiophosphate is in a range between approximately 0.2:1 to approximately 2.5:1; wherein the total amount of the at least one zinc sulphonate is comprised in an amount between approximately 0.3 wt-% and approximately 3.0 wt-% of the total amount of the grease composition; wherein the total amount of the at least one zinc sulphonate, of the at least one molybdenum dithiocarbamate, as well as of the at least one molybdenum dithiophosphate, is at most 10 wt-% of the total amount of the grease composition; wherein the at least one molybdenum dithiophosphate acts as a metal surface activator of the at least one zinc sulphonate; and wherein the zinc sulphonate comprises sulphur in an amount between approximately 33 wt-% and approximately 50 wt-%, the wt-% referring to the total amount of the zinc sulphonate.

2. A grease composition in accordance with claim 1, wherein the at least one zinc sulphonate is comprised in an amount between approximately 0.7 wt-% and approximately 2.6 wt-% of the total amount of the grease composition.

3. A grease composition in accordance with claim 1, wherein the at least one molybdenum dithiocarbamate is comprised in an amount between approximately 1 wt-% and approximately 3 wt-% of the total amount of the grease composition.

4. A grease composition in accordance with claim 1, wherein the at least one molybdenum dithiophosphate is comprised in an amount between approximately 0.3 wt-% and approximately 2.5 wt-% of the total amount of the grease composition.

5. A grease composition in accordance with claim 1, wherein the zinc sulphonate comprises zinc in an amount between approximately 1.9 wt-% and approximately 3.8 wt-%, the wt-% referring to the total amount of the zinc sulphonate.

6. A grease composition in accordance with claim 1, wherein the zinc sulphonate is selected from a group comprising a zinc salt of dinonylnaphthalene sulphonic acid, petroleum sulphonate acid, and/or dodezyl benzene sulphonic acid.

7. A grease composition in accordance with claim 1, wherein the thickener is selected from a group comprising at least one lithium soap and/or at least one lithium complex soap.

8. A grease composition in accordance with claim 1, wherein the at least one base oil comprises poly--olefins, naphthenic oils, paraffinic oils, and/or synthetic organic esters.

9. A grease composition in accordance with claim 1, further comprising at least one anti-oxidation agent.

10. A grease composition in accordance with claim 1, further comprising approximately 65 wt-% to approximately 90 wt-% of at least one base oil, approximately 4 wt-% to approximately 20 wt-% of at least one simple or complex lithium soap thickener, approximately 0.8 wt-% to approximately 2.3 wt-% of at least one zinc sulphonate, approximately 1.2 wt-% to approximately 2.6 wt-% of at least one solid molybdenum dithiocarbamate, and approximately 0.4 wt-% to approximately 2.2 wt-% of at least one molybdenum dithiophosphate.

11. A grease composition in accordance with claim 1, wherein the grease composition consists of at least one base oil, at least one simple or complex soap thickener, at least one zinc sulphonate, at least one solid molybdenum dithiocarbamate, and at least one molybdenum dithiophosphate.

12. A grease composition in accordance with claim 1, wherein the grease composition consists of approximately 70 wt-% to approximately 90 wt-% of a base oil composition comprising naphthenic and parathenic oils, approximately 4 wt-% to approximately 15 wt-% of at least one simple or complex lithium soap thickener, approximately 0.8 wt-% to approximately 2.3 wt-% of at least one zinc sulphonate, approximately 1.2 wt-% to approximately 2.6 wt-% of at least one solid molybdenum dithiocarbamate, and approximately 0.4 wt-% to approximately 2.2 wt-% of at least one molybdenum dithiophosphate, in each case the wt-% values referring to the total amount of the grease composition.

13. A constant velocity joint comprising a grease composition comprising a) at least one base oil; b) at least one simple or complex soap thickener; c) at least one zinc sulphonate; d) at least one molybdenum dithiocarbamate in the solid state; and e) at least one molybdenum dithiophosphate; wherein the ratio between the percent-by-weight (wt-%) amount of the at least one zinc sulphonate and both the amount of the at least one molybdenum dithiocarbamate and the amount of the at least one molybdenum dithiophosphate is in a range between approximately 0.2:1 to approximately 2.5:1; wherein the total amount of the at least one zinc sulphonate is comprised in an amount between approximately 0.3 wt-% and approximately 3.0 wt-% of the total amount of the grease composition; wherein the total amount of the at least one zinc sulphonate, of the at least one molybdenum dithiocarbamate, as well as of the at least one molybdenum dithiophosphate, being at most 10 wt-% of the total amount of the grease composition; wherein the at least one molybdenum dithiophosphate acts as a metal surface activator of the at least one zinc sulphonate; and wherein the zinc sulphonate comprises sulphur in an amount between approximately 33 wt-% and approximately 50 wt-%, the wt-% referring to the total amount of the zinc sulphonate.

14. A grease composition in accordance with claim 1, wherein the at least one base oil is comprised in an amount between approximately 84 wt-% and approximately 92 wt-% of the total amount of the grease composition; the at least one simple or complex soap thickener is comprised in an amount between approximately 5.2 wt-% and approximately 7.8 wt-% of the total amount of the grease composition; the at least one zinc sulphonate is comprised in an amount between approximately 0.5 wt-% and approximately 3.0 wt-% of the total amount of the grease composition; the at least one molybdenum dithiocarbamate is comprised in an amount between approximately 1.34 wt-% and approximately 1.72 wt-% of the total amount of the grease composition; and the at least one molybdenum dithiophosphate is comprised in an amount between approximately 0.5 wt-% and approximately 1.0 wt-% of the total amount of the grease composition.

Description

SUMMARY OF THE DRAWINGS

(1) The Figures show:

(2) FIGS. 1a and 1b: Experimental results for friction and wear, respectively, as presented in Table 1, are shown for the common greases A1 to A5;

(3) FIGS. 2a and 2b: Experimental results, as presented in Table 5, for friction and wear are shown, of an inventive example C4 and common grease composition A2 and comparative composition B1;

(4) FIGS. 3a and 3b: Experimental results, as presented in Table 6, for friction and the wear are shown, respectively, of example inventive compositions C4 and C5 with different amounts of molybdenum dithiophosphate (MoDTP); and

(5) FIGS. 4a and 4b: Experimental results, as presented in Table 7, for friction and the wear are shown, respectively, of example inventive compositions C1 to C4 with different amounts of zinc sulfonate (ZSN).

DETAILED DESCRIPTION

EXAMPLES

(6) 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 disclosure, 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 Prftechnik 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 CV joint. The test includes 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 (Hertz) with an applied load of 500 N (newtons) were applied for 60 minutes (including running-in) at 80 C. The stroke was 1.5 mm (millimeters). The friction coefficients obtained were recorded on a computer. For each grease, the reported value is an average of two data at the end of tests in two runs (two runs at 1.5 mm stroke). The running-in measurement of the friction coefficient 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 500 N. 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 (W.sub.r) is obtained from W.sub.r=V/L [m/m], where L is the total sliding distance in the tests.

(7) Further, the load carrying capacity (LCC) is measured in order to evaluate the extreme pressure performance of the grease composition in accordance with the present disclosure. It is determined in stepload tests with a frequency of 40 Hz with an applied load of 50 N for 15 minutes at the start at 80 C. The stroke was 1.5 mm. After the start test of 15 minutes, the load was increased step by step by 50 N for 15 minutes up to failure (the SRV test stops automatically once friction is higher than 0.3 for 30 seconds). The LCC is then determined as the maximum load without a failure during a time period of 15 minutes. The higher the values for the LCC, the better is the performance of the grease composition. The experimentally determined LCC values given in the Tables below are mean values of two separately determined values.

(8) Further, tests regarding the properties of a thermoplastic elastomer boot, i.e. a TPE-boot, carried out with inventive grease composition C6 and with three commercial greases, i.e. commercial grease composition 1 for ball CV joints and commercial grease compositions 2 and 3 for tripod CV joints (see Table 9), were carried out with respect to the change of hardness (shore D) and the percentage change of tensile, elongation, and volume before and after a heat ageing of the boot material immersed in the grease at 125 C. for 336 hours. Said values are measured in accordance with ISO 868 (shore D), ISO 37 (tensile change and elongation change), and ISO 2781 (volume change).

(9) The base oil composition as used for compositions A1 to A5, B1, B2 as well as C1 to C6, has a kinematic viscosity of about 165 mm.sup.2/s at 40 C. and about 16 mm.sup.2/s at 100 C. The base oil blend may be a mixture of one or more paraffinic oils in a range between about 10 to about 60% by weight, preferably about 20 to 40% by weight, one or more naphthenic oils in a range between about 30 to about 80% by weight, preferably about 55 to about 80% by weight, and, if necessary, one or more poly--olefins (PAO) in a range between about 5 to about 40% by weight, referred to the total amount of the oil mixture. The oil blend may further contain DOS in a range between about 2 to about 10% by weight, referred to a total amount of the oil mixture. The concrete oil blend used in the examples is made of 73% by weight of naphthenic oil SR130, produced by AB Nyns Petroleum, Stockholm, Sweden, 25% by weight of paraffinc oil NS600, obtained from Total, and 2% by weight of DOS.

(10) The naphthenic oils are selected with a range of viscosity between about 20 to about 180 mm.sup.2/s at 40 C., paraffinic oils between about 25 to about 400 mm.sup.2/s at 40 C., and PAO between about 6 and about 40 mm.sup.2/s at 100 C.

(11) Commercial grease composition 1 is produced by BP Europa S.A, Germany. Commercial grease compositions 2 and 3 have been prepared according to U.S. Pat. No. 5,672,571 and GB 5,672,571.

(12) As zinc sulfonate (ZSN) Vanlube IR-ZSN (Vanderbilt Chemicals, LLC, Norwalk, Conn., USA) was used.

(13) As zinc dithiophosphate (ZDPT), RC3038 from Rhein Chemie was used.

(14) As MoDTP, Molyvan L from Vanderbilt was used. As MoDTC (solid), Molyvan A from Vanderbilt was used. As S/P-free organo Molybdenum compound, Molyvan 855 from Vanderbilt was used.

(15) As an anti-oxidant, Irganox L57 from BASF was used.

(16) As Li soap thickener, Lithiumstearate obtained by reaction of 12-hydroxystearic acid with Lithiumhydroxide (LiOH) was used.

(17) Common CV joint grease compositions without molybdenum compounds are designated as A1 to A5:

(18) TABLE-US-00001 TABLE 1 [wt %] A1 A2 A3 A4 A5 Li soap 6 6 6 6 6 Oils 93.7 90.7 88.7 85.7 92.7 Anti-oxidant 0.3 0.3 0.3 0.3 0.3 ZSN 3 5 8 ZDTP 1

(19) Comparative grease compositions comprising only MoDTC are designated as B1 and B2:

(20) TABLE-US-00002 TABLE 2 [wt %] B1 B2 Li soap 6 6 Oils 89.2 88.7 Anti-oxidant 0.3 0.3 ZSN 3 3 MoDTC .1.5 .1.5 (solid) MoDTP S-/P-free 0.5 organo Mo

(21) Inventive grease composition comprising ZSN, MoDTC (solid) and MoDTP are designated as C1 to C6:

(22) TABLE-US-00003 TABLE 3 [wt %] C1 C2 C3 C4 C5 C6 Li soap 6 6 6 6 6 6 Oils 91.2 90.7 89.7 88.7 88.2 89.2 Anti-oxidant 0.3 0.3 0.3 0.3 0.3 0.3 ZSN 0.5 1 2 3 3 2 MoDTC (solid) .1.5 .1.5 .1.5 .1.5 .1.5 2 MoDTP 0.5 0.5 0.5 0.5 1 0.5

(23) Experimental values for friction at 6 min and 55 min and wear as well as LCC values are presented in Tables 4 to 8 and in FIGS. 1a, 1b, 2a, 2b, 3a, 3b, 4a and 4b.

(24) Experimental results regarding the compatibility of the inventive composition with boot materials as compared to commercially available greases is presented in Table 9.

(25) TABLE-US-00004 TABLE 4 A1 A2 A3 A4 A5 ZSN 3 5 8 ZDTP 1 Friction 0.14 0.13 0.12 0.13 0.12 at 6 min Friction 0.15 0.14 0.12 0.12 0.11 at 55 min Wear 4680 8047 11021 10719 538 (m.sup.3/m)

(26) TABLE-US-00005 TABLE 5 A2 B1 C4 ZSN 3 3 3 MoDTC .1.5 .1.5 (solid) MoDTP 0.5 Friction at 0.13 0.122 0.102 6 min Friction at 0.14 0.067 0.059 55 min Wear 8047 518 238 (m.sup.3/m) LCC (N) n.d. 800 850

(27) TABLE-US-00006 TABLE 6 C4 C5 ZSN 3 3 MoDTC .1.5 .1.5 (solid) MoDTP 0.5 1 Friction at 0.102 0.081 6 min Friction at 0.059 0.057 55 min Wear 238 375 (m.sup.3/m) LCC (N) 850 975

(28) TABLE-US-00007 TABLE 7 C1 C2 C3 C4 ZSN 0.5 1 2 3 MoDTC .1.5 .1.5 .1.5 .1.5 (solid) MoDTP 0.5 0.5 0.5 0.5 Friction at 0.128 0.08 0.068 0.102 6 min Friction at 0.08 0.098 0.061 0.059 55 min Wear 469 679 543 238 (m.sup.3/m) LCC (N) 825 800 975 850

(29) TABLE-US-00008 TABLE 8 C4 B2 ZSN 3 3 MoDTC .1.5 .1.5 (solid) MoDTP 0.5 S-/P-free 0.5 organo Mo Friction at 6 min 0.102 0.128 Friction at 0.059 0.128 55 min Wear 238 10123 (m.sup.3/m) LCC (N) 850 375

(30) TABLE-US-00009 TABLE 9 Commercial Commercial Commercial Property C6 grease 3 grease 1 grease 2 Hardness 5 0 10 8 change (Shore D) Tensile 25.5 47.3 48 35.0 change (%) Elongation +3.6 21.1 15.0 16 change (%) Volume +16.3 +14.5 20 17 change (%)

(31) In Table 4 and FIGS. 1a and 1b, experimental results are presented for the common greases A1 to A5 which do not contain any molybdenum compounds at different or no amounts of zinc sulfonate (ZSN). Friction at 6 minutes and at 55 minutes decreases slightly upon increasing the amount of zinc sulfonate (ZSN) in the composition from 0 wt-% to 5 wt-%. Further increasing the amount of zinc sulfonate (ZSN) by 3 wt-% does not change the friction values at 55 minutes whereas the friction at 6 minutes increases very slightly. According to FIG. 1b, the wear increases by increasing amounts of zinc sulfonate (ZSN). A saturation value of the wear is achieved at about 5 wt-% zinc sulfonate (ZSN). Friction values of a composition comprising ZDTP are similar to the corresponding values for a composition of zinc sulfonate (ZSN).

(32) ZDTP is a common anti wear additive. The disadvantage of using ZDTP is that it is not compatible with sealing materials, especially sealing boots. Composition A5 contains ZDTP instead of ZSN. According to the experimental results presented in Table 4, compositions with ZSN (A1 to A5) have significantly higher values for wear as compared to compositions with ZDTP. The results show that, although ZSN is more compatible with seal materials than ZDTP, in grease compositions without any molybdenum compounds ZSN cannot suitably replace ZDTP due to the poor anti-wear properties of ZSN, when used in compositions without molybdenum.

(33) Table 5 and FIGS. 2a and 2b show the experimental results of composition C4 in comparison with common grease composition A1 and comparative grease composition B1 with ZSN being present in essentially the same amounts in the three compositions, i.e. 3 wt-%. The inventive composition C4 yields reduced wear and the friction values, notably a lower friction at 6 minutes. Hence, in a composition comprising zinc sulfonate (ZSN), at least one molybdenum dithiocarbamate (MoDTC) and at least one molybdenum dithiophosphate (MoDTP) results in low friction values even at an early stage of the running-in process of the CV joint, thereby preventing damages of CV joint which result from the bad performance of compositions known from the state of the art at an early stage of the running-in process. The compositions according to the disclosure, i.e. with dithiocarbamate (MoDTC) and at least one molybdenum dithiophosphate (MoDTP), provide advantageous anti-wear and anti friction values at suitable LCC values.

(34) In Table 6 and FIGS. 3a and 3b, the friction and wear are shown for inventive compositions C4 and C5 with two different molybdenum dithiophosphate (MoDTP) amounts, i.e. at 0.5 wt-% and 1 wt-% molybdenum dithiophosphate (MoDTP). By increasing the amount of molybdenum dithiophosphate (MoDTP) from 0.5 wt-% to 1 wt-%, the wear increases. On the other hand, the friction at 6 minutes decreases upon increasing the molybdenum dithiophosphate (MoDTP) amount from 0.5 wt-% to 1 wt-%. All in all, these results show that the composition according to the disclosure provides advantageous overall properties even upon variation of the amount of MoDTP. This is further corroborated by the friction values at 55 minutes, which do not change significantly upon increasing the amount of molybdenum dithiophosphate (MoDTP).

(35) In Table 7 and the corresponding FIGS. 4a and 4b, the influence of different amounts of zinc sulfonate (ZSN) in the inventive compositions C1 to C4 comprising 1.5.5 wt-% molybdenum dithiocarbamate (MoDTC) and 0.5 wt-% molybdenum dithiophosphate (MoDTP) is presented. The zinc sulfonate (ZSN) amount is varied within a range from 0.5 wt-% to 3 wt-%. Friction values at 55 minutes show a maximum at 1 wt-% ZSN. On the other hand, friction values at 6 minutes show a minimum at a zinc sulfonate (ZSN) amount of about 1 to 2 wt-%. With respect to the wear, there is a maximum at a zinc sulfonate (ZSN) amount of 1 wt-%. Wear values decrease upon increasing the amount of zinc sulfonate (ZSN) from 1 wt-% to 3 wt-%. Generally speaking, upon changing the amount of ZSN, wear, friction at 6 min and friction at 55 minutes effectively change in different directions. All in all, the composition according to the disclosure provides advantageous overall properties even when the amount of ZSN is varied.

(36) Table 8 demonstrates the advantageous effect of composition C4 relative to comparative composition B2, which comprises instead of MoDTP 0.5 wt-% sulphur- and phosphorus-free organic molybdenum compounds (S/P-free organo Mo). Replacing molybdenum dithiophosphate (MoDTP) by such compounds increases the wear dramatically while the friction values also increase.

(37) In conclusion, these results show that it is in particular the use of molybdenum dithiophosphate (MoDTP) in combination with molybdenum dithiocarbamate (MoDTC) in the presence of zinc sulfonate (ZSN) which results in the advantageous values for friction and wear. These Mo-compounds cannot be replaced by simple organic molybdenum compounds.

(38) The experimental results clearly show that the addition of MoDTP to compositions containing ZSN and MoDTC results in significantly better performances with respect to wear and friction. In particular, such compositions provide an advantageous performance with respect to wear and anti-friction properties even at an early stage of the running-in process. LCC values of the examples are above 800 N to 1000 N being values in suitable ranges.

(39) Table 9 shows the compatibility of grease composition C6 with a CV joint boot (Pibiflex B5050 MWR) in comparison with commercial greases 1 to 3. Composition C6 provides less changes in hardness, lower tensile, elongation and volume change than commercial grease 1 and commercial grease 2. With respect to commercial grease 3, the inventive composition provides similar values with respect to a change of hardness and volume, but improved values regarding tensile change and elongation change.