LUBRICANT COMPOSITION COMPRISING TRACTION COEFFICIENT ADDITIVE

Abstract

A lubricant composition suitable for use in an electric vehicle comprising a traction coefficient additive is provided herewith. The lubricant composition provides utility as an electric vehicle gear oil, and in particular electric vehicle transmission fluids. The lubricant composition provides improved coefficient of traction properties when in use as compared to equivalent lubricant compositions devoid of the traction coefficient additive.

Claims

1. A lubricant composition, suitable for use in an electric vehicle, comprising a base stock and at least 2 wt % of a traction coefficient additive compound, based on the total weight of the lubricant composition, of the Formula (I):
R.sup.1[(AO).sub.nR.sup.2].sub.m (I) wherein: R.sup.1 is the residue of a group having at least 2 active hydrogen atoms; m is at least 2; AO is an alkylene oxide residue; each n is independently from 0 to 100; and each R.sup.2 is independently H or R.sup.3, where each R.sup.3 is independently a residue of a polyhydroxyalkyl or polyhydroxyalkenyl carboxylic acid, a residue of a hydroxyalkyl or hydroxyalkenyl carboxylic acid and/or a residue of an oligomer of the hydroxyalkyl or hydroxyalkenyl carboxylic acid; and on average at least 0.5 of R.sup.2 groups are R.sup.3.

2. A lubricant composition in accordance with claim 1, wherein R.sup.1 of the traction coefficient additive compound of the Formula (I) is the residue of a C.sub.3 to C.sub.30 substituted hydrocarbyl compound.

3. A lubricant composition in accordance with claim 2, wherein R.sup.1 of the traction coefficient additive compound of the Formula (I) is the residue of, or a residue derived from, a sugar, preferably a monosaccharide.

4. A lubricant composition in accordance with claim 3, wherein R.sup.1 of the traction coefficient additive compound of the Formula (I) is the residue of, or a residue derived from glucose, fructose, or sorbitol.

5. A lubricant composition in accordance with claim 4, wherein m of the traction coefficient additive compound of the Formula (I) is at least 3.

6. A lubricant composition in accordance with claim 5, wherein m of the traction coefficient additive compound of the Formula (I) is in the range from 4 to 10.

7. A lubricant composition in accordance with claim 6, wherein the alkylene oxide groups AO of the traction coefficient additive compound of the Formula (I) are of the formula:
(C.sub.rH.sub.2rO) where r is 2, 3 or 4.

8. A lubricant composition in accordance with claim 7, wherein n of the traction coefficient additive compound of the Formula (I) is in the range from 1 to 50.

9. (canceled)

10. A lubricant composition in accordance with claim 8, wherein each R.sup.3 of the traction coefficient additive compound of the Formula (I) is a residue of a polyhydroxylalkyl or polyhydroxyalkenyl carboxylic acid of formula HOXCOOH where X is a divalent saturated or unsaturated, preferably saturated, aliphatic radical containing at least 8 carbon atoms and no more than 20 carbon atoms.

11. A lubricant composition in accordance with claim 10, wherein each R.sup.3 of the traction coefficient additive compound of the Formula (I) is (poly) 12-hydroxystearic acid.

12. (canceled)

13. (canceled)

14. A lubricant composition in accordance with claim 1, comprising up to 20 wt % of the traction coefficient additive, based on the total weight of the lubricant composition.

15.-18. (canceled)

19. A lubricant composition in accordance claim 1, wherein the lubricant composition is a gearbox oil, comprising 2 wt % to 10 wt % of the traction coefficient additive, based on the total weight of the gearbox oil.

20. A method of reducing traction coefficient in a gearbox of an electric vehicle which comprises using a lubricant composition of claim 1 in the gearbox.

21. (canceled)

22. (canceled)

Description

EXAMPLES

[0089] The invention will now be illustrated by the following non-limiting examples, wherein the following materials and test procedures are used:

Test Materials

[0090] PAO 4Spectra Syn 4-an API Group IV synthetic poly alpha olefin base stock made by the reaction of linear alpha olefins available from ExxonMobil.

[0091] YUBASE 4an API Group III VHVI base stock, available from SK Lubricants.

[0092] Priolube 3970an API Group V synthetic ester base stock, available from Croda Inc.

[0093] EHC-45API GRII base stock, available from ExxonMobil.

[0094] Perfad 3050a commercially available polymeric friction modifier, available from Croda Inc.

Test Procedures

Mini-Traction Machine (MTM)

[0095] The MTM was supplied by PCS Instruments of London, UK. The MTM provide a method for measuring the coefficient of traction and friction of a given test sample using a ball-on-disc configuration whilst varying several properties such as speed, load and temperature. The MTM is a computer-controlled precision traction measurement system whose test specimens and configuration have been designed such that realistic pressures, temperatures and speeds can be attained without requiring large loads, motors or structures. Details of the test parameters employed in the data provided herein follow.

[0096] The disc was AISI 52100 hardened bearing steel with a mirror finish (Ra<0.01 mm) and the ball was AISI 52100 hardened bearing steel. The contact pressure was 0.43 GPa at rolling speed of 0.2 m/s, and 1 GPa at rolling speed of 0.1 m/s. Approximately 50 ml of the test sample was then added. The ball was loaded against the face of the disc and the ball and disc were driven independently to create a mixed rolling/sliding contact with a slide-roll ratio (SRR) of 30%. The frictional force between the ball and disc was measured by a force transducer. Additional sensors measured the applied load and test sample temperature.

[0097] The coefficient of traction of a lubricant control composition (i.e. a base stock with no traction reducing additive present) test sample was determined at 40 C. and 60 C. utilizing the MTM with a inch ball on a smooth disc (as defied above). The MTM tests were then repeated using test samples comprising the lubricant control composition with the addition of 2.5, 5, 7.5, or 10 wt % of the traction reducing additive being evaluated (either Sample 1 or Sample 2 as described below). Further tests were carried out utilizing test samples comprising the addition of a commercial lubricant additives. The test samples are more fully descried below.

Example 1 Preparation of Coefficient of Traction Additive (Sample 1)

[0098] Traction Additive Sample 1 was prepared in accordance with the following method: 12-hydroxystearic acid (68.7 wt %), PEG-12 sorbitol (31.3 wt %) and tin oxalate catalyst

[0099] (Tegokat 160 ex Goldschmidt) were charged to a glass reactor and heated to 190 C. under nitrogen. The reaction was continued for 12-24 hours then cooled to below 100 C. and the product discharged. This provided a product (Sample 1) with a generalized composition as shown:

R.sup.1[(AO).sub.nR.sup.2].sub.m

wherein: [0100] R.sup.1 is the residue of a sorbitol discharged. [0101] m is 6; [0102] AO is an ethylene oxide residue; [0103] n average is 2; [0104] each R.sup.2 is independently H or R.sup.3, where each R.sup.3 is poly (12-hydroxystearic acid) [0105] on average 0.58 of R.sup.2 groups are R.sup.3.

Example 2 Preparation of Coefficient of Traction Additive (Sample 2)

[0106] Traction Additive Sample 2 was prepared in accordance with the following method: 12-hydroxystearic acid (68.7 wt %), PEG-50 sorbitol (31.3 wt %) and tin oxalate catalyst (Tegokat 160 ex Goldschmidt) were charged to a glass reactor and heated to 190 C. under nitrogen. The reaction was continued for 12-24 hours then cooled to below 100 C. and the product discharged. This provided a product (Sample 2) with a generalized composition as shown:

R.sup.1[(AO).sub.nR.sup.2].sub.m

wherein: [0107] R.sup.1 is the residue of a sorbitol [0108] m is 6; [0109] AO is an ethylene oxide residue; [0110] n average is 9; [0111] each R.sup.2 is independently H or R.sup.3, where each R.sup.3 is poly (12-hydroxystearic acid) [0112] on average 0.58 of R.sup.2 groups are R.sup.3.

Example 3. MTM Test Data

[0113] The MTM data presented in the Tables 1,2, 3, 4 and 5 below, show that both Sample 1 and Sample 2 (as described above) are effective at reducing the traction coefficient of the conventional lubricant base stocks; a reduction of the coefficient of traction as compared to the control sample of base stock alone is observed after introduction of the additive. MTM test data is provided for a selection of lubricant base stocks (i.e. control samples), selected to show the utility of the present additive technology across a range of API base stocks. The selection of base stocks for testing includes the following base stocks: Group III (YUBASE 4), and blends of conventional Group II, Group V (PAO 4) and ester (Priolube 3970).

[0114] The effectiveness of Sample 1 and Sample 2 as an additive for improving traction coefficient of a base stock is also compared to the effect on coefficient of traction of the base stock with inclusion of PAO 100. PAO 100 is a very commonly utilized thickener for traditional automotive gear oil formulations; it is known that the inclusion of PAO 100 increases the viscosity of a base stock, and the increase in viscosity can have a positive effect on coeffect of traction as a more viscous base stock is able to maintain a film at the test boundary.

[0115] From the data provided in the Tables below it can be seen that use of Samples 1 and 2 resulted in 2 to 10 times larger (in percent value) reduction of the traction coefficient of the base stock, especially for 2.5 wt % to 7.5 wt % treat rate range. For Samples 1 and 2 there appears to be an optimal treat rate between 5 wt % and 7.5 wt % inclusion based on the total weight of the composition, with further increase in concentration providing no benefit or even a detrimental increase in traction coefficient; this coefficient of traction improvement is distinct from the viscosity increase effect achieved by PAO 100 inclusion.

TABLE-US-00002 TABLE 1 MTM Traction coefficient data for a base stock comprising 80% PAO 4 and 20% Priolube 3970. Additive treat rate (wt %) 0 2.5 5 7.5 10 40 C. 0.1M/S sliding speed Sample 1 0.042 0.0403 0.0348 0.0375 0.0358 Sample 2 0.042 0.0392 0.0373 0.0374 0.0379 PAO 100 0.042 0.0428 0.0399 0.0406 0.0388 Traction coefficient, percent reduction compared to base stock Sample 1 4 17 11 15 Sample 2 7 11 11 10 PAO 100 2 5 3 8 40 C. 0.2M/S sliding speed Sample 1 0.0249 0.0243 0.0225 0.0218 0.0227 Sample 2 0.0249 0.0234 0.0216 0.0222 0.0221 PAO 100 0.0249 0.0242 0.024 0.0242 0.0241 Traction coefficient, percent reduction compared to base stock Sample 1 2 10 12 9 Sample 2 6 13 11 11 PAO 100 3 4 3 3 60 C. 0.1M/S sliding speed Sample 1 0.0465 0.0421 0.0366 0.0397 0.0345 Sample 2 0.0465 0.0382 0.0357 0.0368 0.0458 PAO 100 0.0465 0.052 0.0443 0.0398 0.0404 Traction coefficient, percent reduction compared to base stock Sample 1 9 21 15 26 Sample 2 18 23 21 2 PAO 100 12 5 14 13 60 C. 0.2M/S sliding speed Sample 1 0.0258 0.0229 0.0193 0.0196 0.0206 Sample 2 0.0258 0.0248 0.0205 0.0252 0.0259 PAO 100 0.0258 0.0301 0.0235 0.0225 0.0216 Traction coefficient, percent reduction compared to base stock Sample 1 11 25 24 20 Sample 2 4 21 2 0 PAO 100 17 9 13 16

TABLE-US-00003 TABLE 2 MTM Traction coefficient data for a base stock comprising 80% YUBASE 4 and 20% Priolube 3970. Additive treat rate (wt %) 0 2.5 5 7.5 10 40 C. 0.1M/S sliding speed Sample 1 0.0526 0.0451 0.0438 0.0426 0.0426 Sample 2 0.0526 0.0448 0.0419 0.0416 0.0415 PAO 100 0.0526 0.0489 0.0487 0.0463 0.0466 Traction coefficient, percent reduction compared to base stock Sample 1 14 17 19 19 Sample 2 15 20 21 21 PAO 100 7 7 12 11 40 C. 0.2M/S sliding speed Sample 1 0.0332 0.0292 0.0275 0.0262 0.0262 Sample 2 0.0332 0.0285 0.0266 0.0264 0.0261 PAO 100 0.0332 0.0308 0.0301 0.0295 0.0291 Traction coefficient, percent reduction compared to base stock Sample 1 12 17 21 21 Sample 2 14 20 20 21 PAO 100 7 9 11 12 60 C. 0.1M/S sliding speed Sample 1 0.0622 0.0445 0.0409 0.0378 0.0438 Sample 2 0.0622 0.0389 0.0359 0.0361 0.0354 PAO 100 0.0622 0.0508 0.0546 0.045 0.0438 Traction coefficient, percent reduction compared to base stock Sample 1 28 34 39 30 Sample 2 37 42 42 43 PAO 100 18 12 28 30 60 C. 0.2M/S sliding speed Sample 1 0.0443 0.0272 0.0231 0.0207 0.0258 Sample 2 0.0443 0.0235 0.0208 0.0208 0.0202 PAO 100 0.0443 0.0309 0.0327 0.0275 0.0244 Traction coefficient, percent reduction compared to base stock Sample 1 39 48 53 42 Sample 2 47 53 53 54 PAO 100 30 26 38 45

TABLE-US-00004 TABLE 3 MTM Traction coefficient data for a base stock of YUBASE 4. Additive treat rate (wt %) 0 2.5 5 7.5 10 40 C. 0.1M/S sliding speed Sample 1 0.0509 0.0496 0.0461 0.0452 0.0489 Sample 2 0.0509 0.0473 0.0452 0.0457 0.0471 PAO 100 0.0509 0.0539 0.0518 0.0504 0.0489 Traction coefficient, percent reduction compared to base stock Sample 1 3 9 11 4 Sample 2 7 11 10 7 PAO 100 6 2 1 4 40 C. 0.2M/S sliding speed Sample 1 0.0348 0.0334 0.0315 0.031 0.0311 Sample 2 0.0348 0.0325 0.0313 0.0315 0.0302 PAO 100 0.0348 0.0359 0.0352 0.0342 0.0334 Traction coefficient, percent reduction compared to base stock Sample 1 4 9 11 11 Sample 2 7 10 9 13 PAO 100 3 1 2 4 60 C. 0.1M/S sliding speed Sample 1 0.0454 0.0446 0.0384 0.0394 0.0449 Sample 2 0.0454 0.0426 0.0383 0.0415 0.0408 PAO 100 0.0454 0.0528 0.0505 0.0493 0.0451 Traction coefficient, percent reduction compared to base stock Sample 1 2 15 13 1 Sample 2 6 16 9 10 PAO 100 16 11 9 1 60 C. 0.2M/S sliding speed Sample 1 0.0298 0.0293 0.0242 0.0242 0.0266 Sample 2 0.0298 0.0279 0.0239 0.0263 0.0259 PAO 100 0.0298 0.0333 0.0309 0.0304 0.0272 Traction coefficient, percent reduction compared to base stock Sample 1 2 19 19 11 Sample 2 6 20 12 13 PAO 100 12 4 2 9

TABLE-US-00005 TABLE 4 MTM Traction coefficient data for a base stock of EHC 45. Additive treat rate (wt %) 0 2.5 5 7.5 10 40 C. 0.1M/S sliding speed Sample 1 0.0587 0.0542 0.0537 0.0513 0.0507 Sample 2 0.0587 0.0527 0.0513 0.0534 0.0522 PAO 100 0.0587 0.0585 0.0567 0.0575 0.056 Traction coefficient, percent reduction compared to base stock Sample 1 8 9 13 14 Sample 2 10 13 9 11 PAO 100 0 3 2 5 40 C. 0.2M/S sliding speed Sample 1 0.0432 0.0404 0.0395 0.038 0.0372 Sample 2 0.0432 0.0399 0.0388 0.0389 0.037 PAO 100 0.0432 0.0426 0.0419 0.0421 0.0412 Traction coefficient, percent reduction compared to base stock Sample 1 6 9 12 14 Sample 2 8 10 10 14 PAO 100 1 3 3 5 60 C. 0.1M/S sliding speed Sample 1 0.0545 0.0461 0.0469 0.0439 0.043 Sample 2 0.0545 0.0435 0.0432 0.0464 0.0529 PAO 100 0.0545 0.054 0.0533 0.0553 0.051 Traction coefficient, percent reduction compared to base stock Sample 1 15 14 19 21 Sample 2 20 21 15 3 PAO 100 1 2 1 6 60 C. 0.2M/S sliding speed Sample 1 0.0365 0.0309 0.031 0.0287 0.0279 Sample 2 0.0365 0.0301 0.0295 0.0313 0.0389 PAO 100 0.0365 0.0359 0.0348 0.0353 0.0338 Traction coefficient, percent reduction compared to base stock Sample 1 15 15 21 24 Sample 2 18 19 14 7 PAO 100 2 5 3 7

[0116] Referring now to Table 5, below, the traction data for Perfad 3050, a commercially available polymeric friction modifier, clearly shows that it is not effective in reducing coefficient of traction at 40 C. In less severe, more hydrodynamic lubrication type test conditions contact the inclusion of Perfad 3050 leads to undesirable increased traction coefficients. For more severe test conditions at 60 C., and slower speed, Perfad 3050 does show some traction reduction effect akin to that of PAO 100, but this is inferior to the reduction in traction coefficient improvement observed for samples according to the present invention.

TABLE-US-00006 TABLE 5 MTM Traction coefficient data for a base stock comprising 80% PAO4 and 20% Priolube 3970. Additive treat rate (wt %) 0 2.5 5 7.5 10 40 C. 0.1M/S sliding speed Perfad 3050 0.042 0.0419 0.0418 0.0442 0.0419 Sample 1 0.042 0.0403 0.0348 0.0375 0.0358 PAO 100 0.042 0.0428 0.0399 0.0406 0.0388 Traction coefficient, percent reduction compared to base stock Perfad 3050 0 0 5 0 Sample 1 4 17 11 15 PAO 100 2 5 3 8 40 C. 0.2M/S sliding speed Perfad 3050 0.0249 0.0254 0.0253 0.0268 0.026 Sample 1 0.0249 0.0243 0.0225 0.0218 0.0227 PAO 100 0.0249 0.0242 0.024 0.0242 0.0241 Traction coefficient, percent reduction compared to base stock Perfad 3050 2 2 8 4 Sample 1 2 10 12 9 PAO 100 3 4 3 3 60 C. 0.1M/S sliding speed Perfad 3050 0.0465 0.0391 0.0414 0.0404 0.0382 Sample 1 0.0465 0.0421 0.0366 0.0397 0.0345 PAO 100 0.0465 0.052 0.0443 0.0398 0.0404 Traction coefficient, percent reduction compared to base stock Perfad 3050 16 11 13 18 Sample 1 9 21 15 26 PAO 100 12 5 14 13 60 C. 0.2M/S sliding speed Perfad 3050 0.0258 0.0221 0.0226 0.0238 0.0214 Sample 1 0.0258 0.0229 0.0193 0.0196 0.0206 PAO 100 0.0258 0.0301 0.0235 0.0225 0.0216 Traction coefficient, percent reduction compared to base stock Perfad 3050 14 12 8 17 Sample1 11 25 24 20 PAO 100 17 9 13 16