Method of lubricating a driveline device
The invention provides a method of lubricating a mechanical device by supplying a lubricating composition containing an oil of lubricating viscosity and a compound having 2 to 20 hydroxy-carboxylic acid residues. The invention further relates to the use of the compound in a driveline device to provide at least one of antiwear performance, friction modification (particularly for enhancing fuel economy).
1. A method of lubricating a driveline device comprising supplying to the driveline device a lubricating composition comprising:
(a) an oil of lubricating viscosity and
(b) 0.01 wt % to 3 wt % of a compound having 2 to 20 repeat units of a residue of a hydroxy-carboxylic acid, wherein the compound is obtained/obtainable by a reacting a hydroxy-carboxylic acid with a hydrogen bonding donor capable of forming an ester or amide group with a carboxylic acid group of the hydroxy-carboxylic acid,
wherein the hydrogen bonding donor is selected from at least one member of the group consisting of an alcohol, a primary mono-amine and a secondary mono-amine,
wherein the hydroxy-carboxylic acid is a hydroxy-substituted carboxylic acid having 2 to 10 carbon atoms,
wherein, when the hydrogen bonding donor is a mono-ol, the mole ratio of mono-ol to the hydroxy-carboxylic acid ranges from 1:1.1 to 1:10, and
wherein the driveline device is an axle, a gearbox or a manual transmission.
2. The method of claim 1 , wherein the compound has 2 to 5 hydroxy-carboxylic acid residues.
3. The method of claim 1 , wherein the hydroxy-carboxylic acid is a hydroxy-substituted carboxylic acid having 2 to 3 carbon atoms.
4. The method of claim 1 , wherein the hydroxy-carboxylic acid is non-aromatic.
5. The method of claim 1 , wherein the hydroxy-carboxylic acid is aromatic.
6. The method of claim 1 , wherein the hydroxy-carboxylic acid has 1 to 6 hydroxyl groups.
7. The method of claim 1 , wherein the hydroxy-carboxylic acid contains two hydroxyl groups and two or three carboxylic acid moieties.
8. The method of claim 1 , wherein the hydroxy-carboxylic acid has two hydroxyl groups.
9. The method of claim 1 , wherein the hydroxy-carboxylic acid is selected from the group consisting of a glycolic acid, a malic acid, a salicylic acid, a mandelic acid, or a lactic acid, a tartaric acid, a citric acid, and mixtures thereof, and derivatives thereof.
10. The method of claim 1 , wherein the hydroxy-carboxylic acid is glycolic acid.
11. The method of claim 1 , wherein the hydroxy-carboxylic acid is tartaric acid.
12. The method of claim 1 , wherein the compound having 2 to 20 repeat units of a residue of a hydroxy-carboxylic acid is present 0.05 wt % to 0.8 wt % of the lubricating composition.
13. The method of claim 1 , wherein the lubricating composition further comprises at least one organo-sulphide selected from the group consisting of a polysulphide, a thiadiazole compound, or mixtures thereof.
14. The method of claim 13 , wherein the organo-sulphide is present in a range of 0.25 wt % to 6 wt %; of the lubricating composition.
15. The method of claim 1 , wherein the lubricating composition has a sulphur-content of 0.5 wt % to 3 wt % of the lubricating composition.
16. The method of claim 1 , wherein the manual transmission does contain a synchronizer system.
17. The method of claim 1 , wherein the manual transmission does not contain a synchronizer system.
18. The method of claim 1 , wherein the hydrogen bonding donor is a mono-alcohol.
19. The method of claim 18 , wherein the mole ratio of mono-ol to the hydroxy-carboxylic acid ranges from 1:1.1 to 1:5.
20. The method of claim 19 , wherein the mole ratio of mono-ol to the hydroxy-carboxylic acid ranges from 1:1.2 to 1:2.5.