LUBRICANT COMPOSITION IN PARTICULAR FOR LIMITING FRICTION

Abstract

The present application relates to a lubricant composition comprising: at least one base oil; from 0.05 to 1.5% by weight of an organomolybdenum compound; and from 0.005 to 1% by weight of TiO.sub.2 particles.

Claims

1. Lubricant composition comprising: at least one base oil; from 0.05 to 1.5% by weight of an organomolybdenum compound; and from 0.005 to 1% by weight of TiO.sub.2 particles.

2. Composition according to claim 1, wherein the particles have an average size of between 10 nm and 1 m.

3. Composition according to claim 1, comprising from 0.08 to 1% by weight of organomolybdenum compound relative to the total weight of said composition.

4. Composition according to claim 1, comprising from 0.01 to 0.8% by weight of titanium particles relative to the total weight of said composition.

5. Composition according to claim 1, in which the organomolybdenum compound is chosen from organic complexes of molybdenum comprising at least one molybdenum (Mo) chemical element and at least one ligand chosen from carboxylate and ester, amide, dithiophosphate or dithiocarbamate ligands.

6. Composition according to claim 1, wherein the organomolybdenum compound is chosen from organic complexes of molybdenum with amide ligands obtained by reaction: (i) a mono, di or tri glyceride fatty substance, or fatty acid, (ii) an amine source of formula (A): ##STR00008## in which: X.sup.1 represents an oxygen atom or a nitrogen atom, X.sup.2 represents an oxygen atom or a nitrogen atom, n or m represents 1 when X.sup.1 or X.sup.2 respectively represents an oxygen atom, n or m represents 2 when X1 or X2 respectively represents a nitrogen atom, (iii) and a molybdenum source selected from molybdenum trioxide or molybdates, preferably ammonium molybdate.

7. Composition according to claim 1, wherein the organomolybdenum compound comprises at least one organic complex of molybdenum of formula (III) or (IV), alone or as a mixture: ##STR00009## in which: X.sup.1 represents an oxygen atom or a nitrogen atom; X.sup.2 represents an oxygen atom or a nitrogen atom; n represents 1 when X.sup.1 represents an oxygen atom and m represents 1 when X.sup.2 represents an oxygen atom; n represents 2 when X.sup.1 represents a nitrogen atom and m represents 2 when X.sup.2 represents a nitrogen atom; R.sub.1 represents a linear or branched, saturated or unsaturated alkyl group comprising from 4 to 36 carbon atoms, preferably from 4 to 20 carbon atoms, advantageously from 6 to 18 carbon atoms; ##STR00010## in which: X.sup.1 represents an oxygen atom or a nitrogen atom; X.sup.2 represents an oxygen atom or a nitrogen atom; n represents 1 when X.sup.1 represents an oxygen atom and m represents 1 when X.sup.2 represents an oxygen atom; n represents 2 when X.sup.1 represents a nitrogen atom and m represents 2 when X.sup.2 represents a nitrogen atom; R.sub.1 represents a linear or branched, saturated or unsaturated alkyl group comprising from 4 to 36 carbon atoms, preferably from 4 to 20 carbon atoms, advantageously from 6 to 18 carbon atoms; R.sub.2 represents a linear or branched, saturated or unsaturated alkyl group comprising from 4 to 36 carbon atoms, preferably from 4 to 20 carbon atoms, advantageously from 6 to 18 carbon atoms.

8. Composition according to claim 1, wherein the organomolybdenum compound is selected from organic complexes of molybdenum with dithiophosphate ligands or organic complexes of molybdenum with dithiocarbamate ligands.

9. Composition according to claim 1, wherein the organomolybdenum compound is a molybdenum dithiocarbamate compound (MoDTC).

10-12. (canceled)

13. Method for lubricating mechanical parts, in particular in an engine, in particular an internal combustion engine, comprising at least one step of contacting at least one part with a lubricant composition according to claim 1.

14. Method for reducing friction in an engine, preferably internal combustion engine, for example vehicle engine, comprising at least one step of contacting at least one part of the engine with a lubricant composition according to claim 1.

15. Method for reducing wear in an engine, preferably internal combustion engine for example vehicle engine, comprising at least one step of contacting at least one part of the engine with a lubricant composition according to claim 1.

Description

[0157] The present invention will now be described by way of non-limiting examples.

[0158] FIG. 1 represents the X-ray photoelectron spectrum (the spectrum gives the binding energies (eV)) produced on the lubricant films (from compositions according to the invention) obtained at the end of tribological tests on steel/steel parts.

EXAMPLE 1

Lubricant Compositions

[0159] The compositions of Table 1 (CL: lubricant composition according to the invention, CC: comparative composition) were prepared by mixing the TiO.sub.2 particles and the organomolybdenum compound in a base oil at 60 C. to obtain a good dispersion of the particles in the composition.

TABLE-US-00002 TABLE 1 Lubricant compositions according to the invention and comparatives Lubricant composition according to CL1 (% CL2 (% CL3 (% CL4 (% CC1 (% CC2 (% CC3 (% the invention in weight) in weight) in weight) in weight) in weight) in weight) in weight) Anatase TiO.sub.2 0.5 0.1 0.5 0.5 particles Rutile TiO.sub.2 0.5 0.5 particles MoDTC 0.5 0.5 0.1 0.5 0.5 Group III 99 99 99.8 98 99.5 99.5 99.5 base oil ZDDP 1

EXAMPLE 2

Results of Tribological Tests

[0160] 2.1 Tests on Alternative Tribometer Ball-Plane

[0161] Measurements of the coefficient of friction and the wear of the balls in micrometers in diameter of the ball impression (Table 2) were carried out on an alternating ball-plane tribometer. These tests were performed by changing for each test the mechanical parts of a flat surface. The parts used are as follows: [0162] the balls have a diameter of 5 mm and are mechanical parts made of reference steel AISI52100 having a surface roughness (Ra) of 50 nm; [0163] the plane is a flat mechanical part chosen from: [0164] PM1: a reference steel AISI52100; or [0165] PM2: made of APS steel plasma treated steel.

[0166] where

[0167] PM1 has a surface roughness (Ra) of 50 nm.

[0168] PM2 has a surface roughness (Ra) of between 170 and 200 nm.

[0169] The conditions of the alternative tribometer ball-plane test are: [0170] Temperature: 100 C. [0171] Frequency: 5 Hz [0172] Maximum contact pressure: 700 MPa [0173] Trace length: 5 mm [0174] Duration: 1h [0175] Volume of lubricant composition: 2-3 mL

[0176] The coefficients of friction and the wear of the balls in m in diameter of the impression of the ball indicated in Table 2 were measured following the contact of a smooth surface ball (Ra=50 nm) with respectively a flat part PM1 smooth surface (Ra=50 nm) or a flat part PM2 rough surface (Ra=170-200 nm), said parts also being in contact with a composition according to the invention or a comparative composition.

TABLE-US-00003 TABLE 2 Coefficients of friction and wear of the ball measured on an alternating ball-plane tribometer during the contacts between the ball and the parts PM1 and PM respectively, the parts also being in contact with a composition according to the invention or a comparative composition Coefficient of friction/ wear of the Base oil balls in mg alone CL1 CL3 CC1 CC3 Ball/PM1 0.16/370 0.039/184 nd 0.12/444 0.05/215 Ball/PM2 0.12/300 0.036/275 0.031/230 0.13/290 0.05/275 Nd: not determined

[0177] These results demonstrate that: [0178] The coefficient of friction between ball/PM1 is decreased when the lubricant composition comprises an organomolybdenum compound and titanium, whatever the content of organomolybdenum compound and titanium. This coefficient of friction being measured between two pieces of smooth surface, makes it possible to determine the formation of MoS.sub.2 from the organomolybdenum compound. Nevertheless, in the case of the PM1 parts having smooth surfaces, the friction contacts are decreased relative to the friction contacts between a smooth surface piece and a rough surface piece such as PM2. [0179] The wear of the balls is lower when there is a combination between a composition according to the invention (CL1 or CL3) and the base oil in comparison with the base oil alone or with the comparative compositions (CC1, CC3 or CC4), for both types of surfaces (smooth or rough). [0180] When the concentration of organomolybdenum compound is decreased (composition CL3), there is a more significant decrease in the coefficient of friction and the wear of the balls both with respect to the oil alone and compared to the comparative compositions. [0181] The coefficient of friction between ball/PM2 (rough surface) is decreased when the lubricant composition comprises an organomolybdenum compound and titanium, regardless of the content of organomolybdenum compound and titanium. [0182] That there is a synergy between the molybdenum and the titanium particles within the lubricant composition that significantly reduces the coefficient of friction and therefore to limit friction between the parts.

EXAMPLE 3

X-Ray Spectra

[0183] X-ray photoelectron spectroscopies were performed on the lubricant films (from compositions CL1 and CC3) obtained at the end of the tribological ball/PM1 tests.

[0184] FIG. 1 shows the top spectrum of composition CC3 and bottom spectrum of composition CL1. This figure shows that in the absence of TiO.sub.2 particles (CC3) decomposition of MoDTC is not complete and gives rise to the formation of MoS.sub.2 and MoOxSy Mo oxysulfide in large quantities. On the contrary the presence of TiO.sub.2 allows a better decomposition of the MoDTC and the formation of pure MoS.sub.2.