Gear oil composition

Abstract

The present invention relates to a gear oil composition containing a base stock and at least 0.01 wt % of a friction reducing additive which comprises a glycerol and/or polyglycerol C.sub.12 to C.sub.24 saturated fatty ester. The gear oil composition is suitable for use in gear boxes in automotive, industrial and marine applications.

Claims

1. A gear oil composition comprising a base stock, at least 0.01 wt % of a friction reducing additive which comprises a diglycerol C.sub.12 to C.sub.24 saturated fatty ester, wherein the friction reducing additive has an iodine value of not more than 20 gI/100 g, and an anti-wear agent selected from phosphates, phosphites, carbamates, esters, and molybdenum complexes, wherein the diglycerol C.sub.12 to C.sub.24 saturated fatty ester comprises at least 10 wt % of monoester, and at least 20 wt % of diester, based upon the total weight of fatty esters of diglycerol in the composition, and the diglycerol C.sub.12 to C.sub.24 saturated fatty ester has a cloud point of not more than 25 C.

2. The gear oil composition as claimed in claim 1 comprising a diglycerol C.sub.18 to C.sub.22 saturated fatty ester.

3. The gear oil composition as claimed in claim 1 wherein the friction reducing additive is obtained by reacting diglycerol with a fatty acid and/or ester thereof.

4. The gear oil composition as claimed in claim 3 wherein the fatty acid is isostearic acid and/or isobehenic acid.

5. The gear oil composition as claimed in claim 1 wherein the diglycerol C.sub.12 to C.sub.24 saturated fatty ester comprises at least 20 wt % of monoester and at least 20 wt % of diester, based upon the total weight of fatty esters of diglycerol in the composition.

6. The gear oil composition as claimed in claim 1 wherein the diglycerol C.sub.12 to C.sub.24 saturated fatty ester comprises at least 10 wt % of monoester, and at least 30 wt % of diester, based upon the total weight of fatty esters of diglycerol in the composition.

7. The gear oil composition as claimed in claim 1 wherein the base stock is selected from the group consisting of an API Group I, II, III, IV, V base oil or mixtures thereof.

8. The gear oil composition as claimed in claim 1 wherein the friction reducing additive reduces the coefficient of friction of the composition when measured by a mini-traction machine at a load of 1.0 GPa by at least 20%.

9. A gear box comprising a gear oil composition as defined in claim 1.

10. The gear box as claimed in claim 9 comprising a spur, helical, bevel, hypoid and/or worm gear.

11. A wind turbine comprising the gear box as claimed in claim 9.

12. A method of reducing friction in a gear box which comprises lubricating the gear box with the gear oil composition as defined in claim 1.

13. The method as claimed in claim 12 wherein the coefficient of friction of the gear oil composition when measured by a mini-traction machine at a load of 1.0 GPa is reduced by at least 20%.

14. The gear oil composition as claimed in claim 1 wherein the friction reducing additive consists of a diglycerol C.sub.18 to C.sub.22 saturated fatty ester.

15. The gear oil composition as claimed in claim 1 wherein the anti-wear agent comprises a phosphate.

16. The gear oil composition as claimed in claim 1 further comprising an extreme pressure agent.

17. A gear oil composition comprising a base stock, a gear oil additive pack, an anti-wear agent selected from phosphates, phosphites, carbamates, esters, and molybdenum complexes, and at least 0.01 wt % of a friction reducing additive which comprises a diglycerol C.sub.12 to C.sub.24 saturated fatty ester, wherein the friction reducing additive has an iodine value of not more than 20 gI/100 g, and wherein the diglycerol C.sub.12 to C.sub.24 saturated fatty ester comprises at least 10 wt % of monoester, and at least 20 wt % of diester, based upon the total weight of fatty esters of diglycerol in the composition, and the diglycerol C.sub.12 to C.sub.24 saturated fatty ester has a cloud point of not more than 25 C.

18. The gear oil composition as claimed in claim 1 wherein the anti-wear agent comprises a zinc dialkyldithiophosphate.

Description

EXAMPLES

Example 1

(1) A friction reducing additive was produced by mixing 280.5 g diglycerol and 719.5 g isostearic acid. 3 g tin oxalate catalyst was added and the mixture was heated to 230 C. The temperature was maintained until the acid value of the mixture was below 1.5 mgKOH/g, at which point the transparency of the product was checked visually. If the product was not transparent, the reaction was continued at the same temperature until transparency was achieved. The reaction was then cooled to 80-90 C., and 4 g phosphoric acid (75 wt %) was added in order to neutralise the catalyst. The product was then filtered to remove solid impurities. If required, a deodorisation process was performed by applying live steam to the product at 125-135 C. for about 2 hours. The final product had a saponification value of 146 mgKOH/g, an acid value of 1.4 mgKOH/g, an iodine value of 1.7 gl/100 g, and contained a mixture of 28 wt % mono-, 41 wt % di- and 28 wt % tri-isostearate esters of diglycerol and 3 wt % of unreacted diglycerol.

Example 2

(2) The friction reducing additive (FRA) produced in Example 1 was evaluated using the test procedures described herein and the results were as follows;

(3) (i) MTM

(4) TABLE-US-00004 Coefficient of Friction Test Composition Control (+1 wt % of FRA of Load (GPa) Composition Example 1) 0.66 0.099 0.069 0.95 0.092 0.065 1.13 0.087 0.062 1.26 0.083 0.061 1.37 0.081 0.061 1.47 0.081 0.060 1.55 0.079 0.060 1.63 0.078 0.060

(5) The results show that the addition of 1 wt % of the friction reducing additive of Example 1 reduced the coefficient of friction by about 30% (0.069 compared to 0.099) at a load of 0.66 GPa and by about 23% at a load of 1.63 GPa when compared to the same formulation without the friction reducing additive.

(6) (ii) HFRR

(7) TABLE-US-00005 (a) Coefficient of Friction Test Composition Control (+1 wt % of FRA Time (s) Composition of Example 1) 100 0.137 0.135 600 0.142 0.143 1100 0.148 0.146 1600 0.151 0.130 2100 0.148 0.110 2600 0.149 0.090 3100 0.150 0.082 3600 0.148 0.078

(8) The results show that the addition of 1 wt % of the friction reducing additive of Example 1 reduced the coefficient of friction by about 47% after 3600 seconds when compared to the same formulation without the friction reducing additive.

(9) TABLE-US-00006 (b) Wear Scar (m) Control Composition 254.1 Test Composition (+ 1 wt % of 152.0 FRA of Example 1)

(10) The results show that the addition of 1 wt % of the friction reducing additive of Example 1 reduced the wear scar on the ball specimen by 40%.

(11) (iii) Demulsification Test

(12) TABLE-US-00007 Volume (ml) Test Composition (+1 Control wt % of FRA of Phase Composition Example 1) Oil 12 36 Water 37 31 Emulsion 31 13

(13) The results show that the addition of 1 wt % of the friction reducing additive of Example 1 produced a much less stable emulsion than the control composition containing no friction reducing additive.

(14) The above examples illustrate the improved properties of a gear oil composition according to the present invention.