LUBRICANT COMPOSITION COMPRISING TRACTION COEFFICIENT ADDITIVE

Abstract

The present invention relates to a lubricant composition suitable for use in an electric vehicle. The lubricant composition comprises a traction coefficient additive and wherein the traction coefficient additive is an ester, said ester being the reaction product of at least one saturated branched-chain aliphatic monohydric alcohol having between 12 and 32 carbon atoms and at least one aliphatic carboxylic acid having between 6 and 32 carbon atoms. The lubricant composition as described herein provides an electric vehicle gear oil and imparts desirable coefficient of traction properties when in use.

Claims

1-29. (canceled)

30. A method of lubricating a gear box of an electric vehicle, comprising the step of lubricating the gear box with a gear oil including a base oil and a traction coefficient additive present in the gear oil in an amount effective to reduce a traction coefficient characteristic of the gear oil, wherein the traction coefficient additive comprises an ester, said ester being the reaction product of at least one saturated aliphatic carboxylic acid have 6 to 32 carbon atoms and a saturated, branched-chain, aliphatic monohydric alcohol having 12 to 24 carbon atoms.

31. The method of claim 30, wherein the base oil comprises a mixture of two or more base oils selected from at least two different groups among Group I, Group II, Group III, and Group IV base oils.

32. The method of claim 30, wherein the saturated, branched-chain, aliphatic monohydric alcohol is a Guerbet alcohol.

33. The method of claim 30, wherein the saturated, branched-chain, aliphatic monohydric alcohol is selected from the group consisting of a C12 Guerbet alcohol, a C14 Guerbet alcohol, a C16 Guerbet alcohol, a C18 Guerbet alcohol, a C20 Guerbet alcohol, and a C24 Guerbet alcohol

34. The method of claim 30, wherein the saturated, branched-chain, aliphatic monohydric alcohol comprises a main carbon chain that is branched at the beta carbon position of the main carbon chain.

35. The method of claim 30, wherein the saturated, branched-chain, aliphatic monohydric alcohol is 2-octyldodecanol.

36. The method of claim 30, wherein the saturated, branched-chain, aliphatic monohydric alcohol is 2-butyloctanol.

37. The method of claim 30, wherein the saturated, branched-chain, aliphatic monohydric alcohol is

38. The method of claim 30, wherein the saturated aliphatic carboxylic acid is linear.

39. The method of claim 30, wherein the saturated aliphatic carboxylic acid is branched.

40. The method of claim 30, wherein the ester is a heptanoate ester.

41. The method of claim 30, wherein the ester is a stearate ester.

42. The method of claim 30, wherein the ester is a di-sebacate ester.

43. The method of claim 30, wherein the ester is an isostearate ester.

44. The method of claim 30, wherein the ester is 2-octyldodecyl isooctadecanoate.

45. The method of claim 30, wherein the ester is 2-hexyldecyl heptanoate.

46. The method of claim 30, wherein the ester is 2-butyloctyl octadecenoate.

47. The method of claim 30, wherein the ester is bis(2-butyloctyl) decanedioate.

48. The method of claim 30, wherein the ester is 2-octyldodecyl isooctadecanoate.

49. The method of claim 30, wherein the ester is 2-octyldodecyl heptanoate.

50. The method of claim 30, wherein the gear oil includes 3 wt % to 25 wt % of the traction coefficient additive.

51. The method of claim 30, wherein the gear oil includes up to 50 wt % of the traction coefficient additive.

52. The method of claim 30, wherein the gear oil includes up to 35 wt % of the traction coefficient additive.

53. The method of claim 30, wherein the gear oil includes at least 3 wt % of the traction coefficient additive.

54. An electric vehicle comprising a gear box lubricated with a gear oil including a base oil and a traction coefficient additive present in the gear oil in an amount effective to reduce a traction coefficient characteristic of the gear oil, wherein the traction coefficient additive comprises an ester, said ester being the reaction product of at least one saturated aliphatic carboxylic acid have 6 to 32 carbon atoms and a saturated, branched-chain, aliphatic monohydric alcohol having 12 to 24 carbon atoms.

Description

[0067] The present invention will now be described with reference to the following examples and accompanying Figures in which,

[0068] FIG. 1. shows MTM coefficient of traction data for experimental samples and commercial samples at 40 C.,

[0069] FIG. 2. shows MTM coefficient of traction data for experimental samples and commercial samples at 60 C.,

[0070] FIG. 3. shows MTM coefficient of traction data for experimental samples and commercial samples at 75 C.,

[0071] FIG. 4. shows MTM coefficient of traction data for experimental samples and commercial samples at 100 C.,

[0072] FIG. 5. shows MTM coefficient of traction data for experimental samples and commercial samples at 120 C.

Materials

[0073] The following materials are utilised in the present examples: [0074] A Group III Base Oil-Yubase 4. ex. SK Lubricants [0075] A Group IV Base Oil-SpectraSyn PAO 4 ex. Exxon Mobil. [0076] A commercially available low viscosity traditional automotive friction modifier additivePriolube 3959 ex. Croda.

[0077] The invention will now be further illustrated with reference to the following Examples.

1. Examples

[0078] Samples in accordance with the present invention, are detailed in Table 1, below. The method of producing the sample materials is by a conventional esterification method as known to the skilled person. The alcohol in each of the ester example samples is provided by a Guerbet alcohol, available under the ISOFOL trade name from Sasol.

TABLE-US-00002 TABLE 1 Sample Composition Chemistry Type IP-731-89 Isofol 16 isostearate Monoester IP-731-90 Isofol 16 heptanoate Monoester IP-731-84 Isofol 12 stearate Monoester IP-731-78 Isofol 12 di-sebacate Diester DE11845 Isofol 20 isostearate Monoester DE10766 Isofol 20 heptanoate Monoester

2. Testing

[0079] The following tests were used to evaluate the properties of the example base oils:

[0080] 2.1 Oxidative stability was measured using an Anton Paar RapidOxy machine. 4 grams of sample is placed in a pressure vessel and charged with oxygen at 700 kPa before being heated to 140 C. The time taken for the pressure to drop by 10% is measured as the Oxidative Induction Time (OIT). This provides a relative measure of the resistance of the samples tested to oxidative decomposition, the longer the OIT the more oxidatively stable the sample is.

[0081] 2.2 Kinematic viscosity (KV) was measured at 100 C. and 40 C. using an Anton Paar SVM Viscometer. The viscosity index (VI) of the materials tested is also provided. The higher the VI value the more stable a material is over a range of temperatures. 2.3 Thermal conductivity was measured using a Thermtest THW-L2, which is based upon the hot wire transient method. Ten data points were collected at temperatures of 40 C. and 80 C. to create a reliable average, with 5 minutes between each data point to allow the fluid to settle. The test power was set such that the output power measured was 70-90 mW and gave a temperature rise of 3 C., the test time was set to 1 second.

[0082] 2.4 Pour point testing was performed on an ISL Mini Pour Point 5Gs to determine the minimum temperature at which the substance will still flow which is correlated to ASTM D97 and D2500.

[0083] 2.5 Traction was measured using a mini traction machine (MTM), tests were performed on a PCS MTM 1. All pieces required to set up the MTM, and standard test specimens supplied by PCS (as detailed in Table 2, below), were sonicated 3 times in heptane for 15 minutes using Camsonix C940 ultrasonic bath with heptane drained and then refreshed after each sonication. All pieces were dried using nitrogen before assembly in the MTM. The test profile goes from 0-100% slide to roll ratio (SRR) at 16N, taking 41 data points at a given temperature to create a traction curve. This is repeated at 40 C., 60 C., 75 C., 100 C. and 120 C. to show performance across a wide range of temperatures. The test parameters are detailed in Table 3 below.

[0084] 2.6 NOACK volatility at 250 C. is measured in accordance with standard test method ASTM D5800. Since electric vehicles do not operate at such high temperatures, a modified test, based on ASTM D5800 but at a temperature at 200 C. Is also performed, to provide a NOACK volatility at 200 C. measurement.

[0085] 2.7 Hydrolytic stability as measured over 15 days (RR1006).

[0086] 250 g of oil and 25 g of water are mixed in a conical flask and fitted with a water trap (airlock). This is placed in an oven at 90 C for 15 days with acid value being tested once every several days.

[0087] 2.8 Seal swell test. Seals of differing material are subject to submersion in a sample to be tested for 2 weeks at 100 C.

TABLE-US-00003 TABLE 2 MTM Specimen Parameters. Disc Ball Diameter (mm) 46 inch Roughness <0.01 mRa Steel AISI 52100 AISI 52100 Hardness 720-780 Hv

TABLE-US-00004 TABLE 3 MTM Testing Parameters. Parameter Rubbing step Temperature ( C.) 40, 60, 75, 100, 120 Ball load (N) 16 Rolling speed (mms.sup.1) 2200 SRR % 0-100

3. Test Data

[0088] The sample materials as detailed in Table 1, and the commercially available base oils from Group III and Group IV as detailed above, were subject to the tests outlined in Section 2, above.

TABLE-US-00005 TABLE 4 Example Sample physical properties in comparison to Group III and IV base oils. Thermal Thermal KV Pour conductivity conductivity KV@40 C./ @100 C./ point/ @ @ Material Composition cSt cSt VI C. 40 C. 80 C. Group III Yubase 4 19.3 4.2 122 15 0.131 0.126 Base Oil Group IV SpectraSyn 18.6 4.1 122 75 0.136 0.130 Base Oil PAO 4 731-89 Isofol 16 21.0 4.7 148 57 0.141 0.135 Isostearate 731-90 Isofol 16 6.8 2.2 140 87 0.133 0.126 Heptanoate 731-84 Isofol 12 14.3 3.7 154 0 0.146 0.139 stearate 731-78 Isofol 12 di- 21.9 4.8 146 78 0.143 0.137 sebacate DE11845 Isofol 20 25.3 5.5 157 48 01.45 0.138 isostearate DE10766 Isofol 20 9.6 2.9 158 35 0.139 0.13 heptanoate

[0089] The example Samples of the present invention have physical properties which render them useful as additives for use in lubricant compositions for use in electrical vehicles. In particular, the balance between Kinematic Viscosity (KV) and thermal conductivity is particularly desirable for use in the power train of electrical vehicles. More especially, the sample denoted as DE10766 provides a material particularly suited for use in electrical vehicles, as it has a low kinematic viscosity material of just 2.9 cSt at 100 C., an excellent viscosity index (VI) and very low NOACK for its viscosity (NOACK data is provided in Table 5, below). The pour point of DE10766 is also acceptable for use in electric vehicle lubricant applications.

TABLE-US-00006 TABLE 5 DE10766 NOACK Data NOACK @250 C. % loss 17.5 NOACK @200 C. % loss 2

[0090] Sample DE10766 was further tested to consider its electrical breakdown voltage, which is an important consideration for fluids suitable for use in electrical vehicles. The Electrical breakdown voltage value was lower than expected.

TABLE-US-00007 TABLE 6 DE10766 0 days AV 5 days AV 8 days AV 15 days AV mg KOH/g mg KOH/g mg KOH/g mg KOH/g DE10766 0.06 0.06 0.15 0.38

[0091] The hydrolytic stability of Sample DE10766 is excellent and varied by just 0.38 AV units over 15 days; this is surprising for a mono ester, and it believed that the use of the Guerbet alcohol offers some resistance to hydrolysis, although the reason for this is not yet understood.

[0092] Compatibility with engine seals is another important feature of any additive to be used in an electrical vehicle power train. Sample DE10766 was also tested to access seal swell over a two-week time period. Generally, low viscosity materials are highly polar and will swell elastomers significantly. As a comparative additive, Priolube 3959 (a commercially available lubricant additive diester of with a KV at 100 C. of 2.5 cSt) was also tested. A small amount of seal swell is desirable and so the results for DE10766 are desirable where as Priolube 3959 swells elastomers to a greater, undesirable, extent. A result of 1% swell in FKM means that despite its low viscosity, DE10766 can be used at high treat rates.

TABLE-US-00008 TABLE 7 Seal Swell Data for DE10766 as compared to Priolube 3959 (an alternative ester). HNBR FKM DE10766 7% 1% Priolube 3959 37% 16%

[0093] At 40 C., all of the Samples tested had significantly lower traction than both the Group III and Group IV base oils, this trend continued at 60 C. and 75 C., however at 100 C. the Sample denoted as 731-90 started to exhibit high coefficient of traction at low slide to roll ratios. It is thought that the very low viscosity of the 731-90 sample is the reason for this (KV at 100 C. of 2.2 cSt) and that the sample is unable to sustain a lubricant film under the low slide roll ratio conditions. At 120 C. the Sample denoted as 731-84 also shows an increase in coefficient of traction; the reason for this is unknown as the Sample 731-84 has a viscosity higher than DE10766 which is able to maintain low traction levels even at high temperatures and the expectation would be that the higher viscosity material would perform better. However, in any case, since the operating temperature in an electric vehicle are typically lower than 100 C. all the example Samples prepared herewith are believed to have utility for use in an electric vehicle power train. More especially, DE10766 looks to be an excellent choice for use in reduction of traction in electric vehicles. It is low viscosity, low polarity and has excellent thermal properties, low traction properties and elastomer compatibility. Additionally, the other example Samples tested herein show that the Isofol 12 and Isofol 16 containing Samples give desirably very low traction.