Automotive transmission fluid compositions for improved energy efficiency

Abstract

Automotive transmission fluid compositions are provided having improved power transmission properties through the presence therein of certain defined additives, which increase the fuel efficiency of the vehicle during operation. The invention further provides a process for the manufacture of such transmission fluid compositions, a method of improving the energy efficiency of a transmission, and an additive concentrate for a transmission fluid.

Claims

1. An automotive transmission fluid composition consisting essentially of: (i) a lubricating oil, or blend of lubricating oils; (ii) a viscosity modifier additive or blend of viscosity modifier additives; (iii) a polyalphaolefin compound or compounds consisting of linear C.sub.6 to C.sub.18 alphaolefin monomer units; and (iv) one or more detergent/inhibitor additives, wherein the polyalphaolefin compound(s) (iii) is made by the metallocene-catalysed polymerisation of an alphaolefin feedstock, wherein the alphaolefin feedstock consists of one or more linear C.sub.6 to C.sub.18 alphaolefins, and wherein the total amount of the polyalphaolefin compound(s) (iii) in the transmission fluid composition does not exceed 4 percent by weight of the composition; and wherein at least one viscosity modifier additive (ii) contains a polymer or blend of polymers selected from one or more of the following groups: (ii)(a) random or block poly-alkylacrylates or poly-alkylmethacrylates, or copolymers thereof; (ii)(b) star polymers comprising a polyvalent core of polyalkylacrylate or polyalkylmethacrylate from which a plurality or arms depend, the arms being polymer chains containing alkylacrylate or alkylmethacrylate monomer units; or (ii)(c) comb polymers prepared by the copolymerisation of one or more alkylacrylate or alkylmethacrylate monomers with one or more olefin or polyolefin monomers.

2. The transmission fluid composition of claim 1, wherein the total amount of the polyalphaolefin compound or compounds (iii) in the composition is in the range of 2 to 3 percent by weight of the composition.

3. The transmission fluid composition of claim 1, wherein the viscosity modifier additive is, or the blend of viscosity modifiers comprises, one or more polymers selected from the groups (ii)(b) and/or (ii)(c).

4. The transmission fluid composition of claim 2, wherein the viscosity modifier additive is, or the blend of viscosity modifiers comprises, one or more polymers selected from the groups (ii)(b) and/or (ii)(c).

5. The transmission fluid composition of claim 3, wherein the viscosity modifier additive is, or the blend of viscosity modifiers comprises, one or more polymers from the group (ii)(c).

6. The transmission fluid composition of claim 4, wherein the viscosity modifier additive is, or the blend of viscosity modifiers comprises, one or more polymers from the group (ii)(c).

7. The transmission fluid of claim 1, wherein one or more detergent/inhibitor additives (iv) comprises one or more alkaline earth metal detergent compounds, wherein at least one alkaline earth metal detergent compound is an alkaline earth metal salicylate or sulphonate compound.

8. The transmission fluid of claim 7, wherein one or more detergent/inhibitor additives (iv) comprises a neutral or overbased calcium salicylate compound.

9. The transmission fluid composition of claim 7, wherein each alkaline earth metal detergent compound present in the transmission fluid composition is a neutral or overbased calcium salicylate compound, and wherein the total amount of the calcium salicylate compound(s) present is such as to provide the transmission fluid composition with a calcium content of between 50 and 250 parts per million by weight, per weight of the transmission fluid composition.

10. The transmission fluid composition of claim 1, wherein at least one detergent/inhibitor additive (iv) also comprises one or more dispersant, oxidation inhibitor and/or friction modifier compounds.

11. A process for the manufacture of an automotive transmission fluid composition, the composition consisting essentially of: (i) a lubricating oil, or blend of lubricating oils; (ii) a viscosity modifier additive or blend of viscosity modifier additives containing a polymer or blend of polymers selected from one or more of the following groups: (ii)(a) random or block poly-alkylacrylates or poly-alkylmethacrylates, or copolymers thereof; (ii)(b) star polymers comprising a polyvalent core of polyalkylacrylate or polyalkylmethacrylate from which a plurality or arms depend, the arms being polymer chains containing alkylacrylate or alkylmethacrylate monomer units; or (ii)(c) comb polymers prepared by the copolymerisation of one or more alkylacrylate or alkylmethacrylate monomers with one or more olefin or polyolefin monomers; (iii) a polyalphaolefin compound or compounds consisting of linear C.sub.6 to C.sub.18 alphaolefin monomer units, each made by the metallocene-catalysed polymerisation of an alphaolefin feedstock wherein the alphaolefin feedstock consists of one or more linear C.sub.6 to C.sub.18 alphaolefins; and (iv) one or more detergent/inhibitor additives; the process comprising the following steps: a) obtaining (by manufacture or otherwise) a lubricating oil or blend of lubricating oils containing no polyalphaolefin compound(s) made by the metallocene-catalysed polymerisation of an alphaolefin feedstock; and b) mixing with this lubricating oil or blend of lubricating oils the following: (b)(1) the viscosity modifier additive or blend of viscosity modifier additives (ii), (b)(2) the polyalphaolefin compound(s) (iii) in a total amount not exceeding 4 percent by weight of the transmission fluid composition, and (b)(3) one or more detergent/inhibitor additives (iv); to provide the transmission fluid composition.

12. The process of claim 11, wherein the total amount of the polyalphaolefin compound or compounds (iii) mixed with the lubricating oil or blend of lubricating oils is in the range of 2 to 3 percent by weight of the transmission fluid composition.

13. The process of claim 11, wherein the viscosity modifier additive is, or the blend of viscosity modifiers comprises, one or more polymers selected from the groups (ii)(b) and/or (ii)(c).

14. The process of claim 12, wherein the viscosity modifier additive is, or the blend of viscosity modifiers comprises, one or more polymers selected from the groups (ii)(b) and/or (ii)(c).

15. The process of claim 13, wherein the viscosity modifier additive is, or the blend of viscosity modifiers comprises, one or more polymers from the group (ii)(c).

16. The process of claim 14, wherein the viscosity modifier additive is, or the blend of viscosity modifiers comprises, one or more polymers from the group (ii)(c).

17. The process of claim 11, wherein one or more detergent/inhibitor additives (iv) comprises one or more alkaline earth metal detergent compounds, wherein at least one alkaline earth metal detergent compound is an alkaline earth metal salicylate or sulphonate compound.

18. The process of claim 12, wherein one or more detergent/inhibitor additives (iv) comprises one or more alkaline earth metal detergent compounds, wherein at least one alkaline earth metal detergent compound is an alkaline earth metal salicylate or sulphonate compound.

19. The process of claim 17, wherein one or more detergent additives (iv) comprises a neutral or overbased calcium salicylate compound.

20. The process of claim 18, wherein one or more detergent additives (iv) comprises a neutral or overbased calcium salicylate compound.

21. The process of claim 19 wherein each alkaline earth metal detergent compound mixed with the transmission fluid composition is a neutral or overbased calcium salicylate compound, and wherein the total amount of calcium salicylate compound(s) mixed with the lubricating oil or blend of lubricating is such as to provide the transmission fluid composition with a calcium content of between 50 and 250 parts per million by weight, per weight of the transmission fluid composition.

22. The process of claim 20 wherein each alkaline earth metal detergent compound mixed with the transmission fluid composition is a neutral or overbased calcium salicylate compound, and wherein the total amount of calcium salicylate compound(s) mixed with the lubricating oil or blend of lubricating is such as to provide the transmission fluid composition with a calcium content of between 50 and 250 parts per million by weight, per weight of the transmission fluid composition.

23. The process of claim 11, wherein the additions in step b) improve the efficiency of power transmission provided by the composition when in use as an automotive transmission fluid, as demonstrated by an increase in the fuel efficiency of the vehicle during operation.

24. The process of claim 12, wherein the additions in step b) improve the efficiency of power transmission provided by the composition when in use as an automotive transmission fluid, as demonstrated by an increase in the fuel efficiency of the vehicle during operation.

25. The process of claim 11, wherein the polyalphaolefin compound(s) (iii) are mixed with one or more of the detergent additives (iv) to form a single additive concentrate prior to addition to the lubricating oil or blend of oils.

26. The process of claim 12, wherein the polyalphaolefin compound(s) (iii) are mixed with one or more of the detergent additives (iv) to form a single additive concentrate prior to addition to the lubricating oil or blend of oils.

27. A method of improving the energy efficiency of an automotive transmission, comprising the use therein of the automotive transmission fluid composition defined in claim 1.

28. The method of claim 27, wherein the improvement in energy efficiency is an increase in fuel economy of the vehicle during operation.

29. A method of improving the energy efficiency of an automotive transmission, comprising the use therein of the automotive transmission fluid composition obtained by the process of claim 11.

30. The method of claim 29, wherein the improvement in energy efficiency is an increase in fuel economy of the vehicle during operation.

31. An additive concentrate for an automotive transmission fluid, the concentrate consisting essentially of (i) a suitable carrier liquid, (ii) a viscosity modifier or blend of viscosity modifiers, and (iii) a polyalphaolefin compound or mixture of polyalphaolefin compounds consisting of linear C.sub.6 to C.sub.18 alphaolefin monomer units made by the metallocene-catalysed polymerisation of an alphaolefin feedstock wherein the alphaolefin feedstock consists of one or more linear C.sub.6 to C.sub.18 alphaolefins, and (iv) one or more detergent/inhibitor additives; wherein at least one viscosity modifier additive (ii) contains a polymer or blend of polymers selected from one or more of the following groups: (ii)(a) random or block poly-alkylacrylates or poly-alkylmethacrylates, or copolymers thereof; (ii)(b) star polymers comprising a polyvalent core of polyalkylacrylate or polyalkylmethacrylate from which a plurality or arms depend, the arms being polymer chains containing alkylacrylate or alkylmethacrylate monomer units; or (ii)(c) comb polymers prepared by the copolymerisation of one or more alkylacrylate or alkylmethacrylate monomers with one or more olefin or polyolefin monomers, wherein the total amount of polyalphaolefin compound(s) (iii) present in the concentrate is such that, after addition of the concentrate at its specified treat rate to the transmission fluid, said compounds (iii) constitute no more than 4 percent by weight of the resulting transmission fluid composition.

32. The additive concentrate of claim 31, wherein the total amount of the polyalphaolefin compound or compounds (iii) present in the concentrate is such that, after addition of the concentrate at its specified treat rate to the transmission fluid, said compounds (iii) constitute no more than 2 to 3 percent by weight of the composition.

33. The additive concentrate of claim 31, wherein at least one detergent additive (iv) present in the concentrate comprises one or more alkaline earth metal detergent compounds, wherein at least one alkaline earth metal detergent compound is an alkaline earth metal salicylate or sulphonate compound.

Description

EXAMPLES

(1) The following examples are given as specific illustrations of the claimed invention. It should be understood, however, that the invention is not limited to the specific details set forth in the examples. All parts and percentages are by weight per weight of the resulting transmission fluid composition, unless otherwise specified.

Worked Example 1Benefit of Additive Treat Levels of the Polyalphaolefin (iii)

(2) The essentiality of the defined metallocene-derived polyalphaolefin in the invention is demonstrated by back-to-back tests conducted on transmission fluids with and without this material present.

(3) Four automotive transmission fluids were prepared according to the process aspect of the invention, by blending together the components shown in Table 1. In each case the components (i), (ii), (iv) were the same, and the fluids differ chemically only in the presence or absence of the polyalphaolefin (iii).

(4) TABLE-US-00002 TABLE 1 Component (% Compo- Compo- by weight, per Compo- sition Compo- sition weight of finished sition 1C sition 2C composition) 1 (comparative) 2 (comparative) Base lubricating oil 83.7 86.3 83.3 85.1 Viscosity modifier 3.0 3.0 2.0 4.2 Pour point 0.3 0.2 0.2 0.2 depressant mPolyalphaolefin 2.5 4.0 Detergent additive: Overbased calcium 0.08 0.08 0.08 0.08 salicylate Overbased calcium sulphonate Other components 10.42 10.42 10.42 10.42 KV 40 C. 19.84 17.73 19.23 18.69 KV 100 C. 4.77 4.37 4.63 4.69

(5) In these compositions, the base lubricating oil, viscosity modifier, pour point depressant and detergent additive were the same in each case, and the blends differed only in the relative proportions of these constituents and, in the case of Compositions 1C and 2C, in the absence of the mPAO.

(6) The mPolyalphaolefin was SpectraSyn Elite 150, an item of commerce from Exxonmobil Chemical Company. The detergent additive contained overbased calcium salicylate and additionally contained other components being dispersant, anti-wear, and other minor active components typical of a detergent additive package, combined with a small amount of base oil and diluent. These other components of the detergent additive were the same in each case. The viscosity modifier was VISCOPLEX 12-199, available as an item of commerce from Evonik Rohmax USA, Inc. and falling within the class (ii)(c) described earlier in relation to suitable viscosity modifiers. The pour point depressant was a typical commercially available material and the same in each case.

(7) The performance of these compositions was tested in the following two experiments.

(8) A bench-test experiment called the FE-8 test measures the torque required to rotate a radial thrust roller bearing assembly lubricated by the transmission fluid in question. The efficiency of the formulations was tested by measuring torque to rotate the cylindrical roller bearings at various conditions using an FE-8 radial thrust roller bearing tester. The bearings used are 15 roller FAG/INA 81212 bearings. The bearings were installed in the test rig and then pre-loaded to 60 kN. The bearings are run-in for 20 hours at 500 rpm at 100 C. prior to taking any measurement.

(9) For each test fluid, the test head is heated until the bearing temperature reaches 40 C. While maintaining this temperature, bearings are rotated at 10 rpm for 10 mins then at 100 rpm and 500 rpm for 5 mins each. The reported torque at each condition is calculated by averaging the torque reading during the last 1 minute of the condition. Temperature is then increased to 80 C. and then finally to 120 C. and torque is measured with the same procedure at the three speeds. After this, the rig is cooled down to room temperature and the whole process is repeated. Final test results are the average of two repeats at each temperature and speed.

(10) The FE-8 test thus compares the energy requirements needed to achieve defined bearing rotation with different fluids. Achieving the defined rotations with lower applied torque indicates greater energy efficiency within the mechanical system.

(11) A vehicle test experiment was conducted according to the standard US Federal Test Procedure 75 (FTP 75). A commercially-available SUV with six speed automatic transmission was repeatedly run on a vehicle dynamometer according to the operating cycle specified in FTP 75, and in each case the improvement in fuel economy observed for the transmission fluid employed in the test is reported (as % improvement) over a reference fluid.

(12) The FTP 75 provides a direct measure of fuel economy observed in vehicle operation. A positive percentage indicates greater fuel efficiency compared to reference.

(13) In an FE-8 test, fluid compositions 1, 1C and 2C were compared for energy efficiency. The results are shown in Table 2 below. As can be seen, composition 1 consistently required lower applied torque to achieve rotations of 100 and 500 rpm in the FE-8 test, indicating improved energy efficiency for composition 1 (with polyalphaolefin (iii) at 2.5%) as compared to compositions 1C (and 2C) (no polyalphaolefin (iii)). In this screener test, the presence of polyalphaolefin (iii) shows an overall benefit for energy efficiency.

(14) TABLE-US-00003 TABLE 2 FE-8 Torque, Composition Composition Composition NM 1 1C 2C 40 C., 100 rpm 26.3 27.0 27.1 40 C., 500 rpm 21.2 21.7 21.9 80 C., 100 rpm 30.2 31.2 30.9 80 C., 500 rpm 23.3 24.4 24.1 120 C., 100 rpm 30.1 30.6 30.9 120 C., 500 rpm 23.1 23.9 24.2

(15) In particular, the compared samples were blended to have similar kinematic viscosity behaviour, thus eliminating the possibility of viscosity differences accounting for the differences in measured torque. Comparing the results for compositions 1C and 2C further demonstrates that the small residual differences in the KV values of these samples do not account for the differences in torque seen between composition 1 and composition 1C, which must therefore be attributable to the effect of polyalphaolefin (iii). For example, composition 2C had a KV 100 of 4.69, almost identical to that of composition 1 (4.77), yet at 120 C. the torque results for composition 2C are even higher than those for composition 1C, indicating that the better results obtained for composition 1 cannot be explained by reference to viscosity behaviour per se.

(16) In FTP 75 vehicle tests, composition 1 (polyalphaolefin (iii) at 2.5%) was compared to the test reference fluid (contains no polyalphaolefin (iii)) and to composition 2 ((polyalphaolefin (iii) at the higher treat rate of 4%). The percentage improvement in fuel economy over the whole test was 0.86% for composition 1, compared to only 0.42% for composition 2. Thus the fuel efficiency benefit of polyalphaolefin (iii) in the composition showed an optimum at the treat rate of 2.5%, and at a higher treat rate of 4% the fuel efficiency benefit had dropped off considerably, confirming the benefit seen is one attributable to additive-level proportions of polyalphaolefin (iii).

Worked Example 2Benefit of the Specific Viscosity Modifiers (ii)

(17) The fuel efficiency effect of the defined viscosity modifiers (ii) in the invention is demonstrated by further comparative tests.

(18) Two further automotive transmission fluids were prepared according to the process aspect of the invention, by blending together the components shown in Table 3. These fluids were tested alongside composition 1 from Table 1 in the FTP 75 vehicle test to compare the effect of changing viscosity modifier chemistry on fuel efficiency in the formulations of the invention.

(19) The vehicle test experiment was again conducted according to the standard US Federal Test Procedure 75 (FTP 75), using the same commercially-available SUV with six speed automatic transmission on a vehicle dynamometer. In each case the improvement in fuel economy observed for the transmission fluid employed in the test is again reported (as % improvement) over reference fluid.

(20) TABLE-US-00004 TABLE 3 Component (% by weight, per Composition Composition weight of finished composition) 3 4 Base lubricating oil 83.0 84.7 Viscosity modifier 1 Pour point depressant Viscosity modifier 2 4.0 Viscosity modifier 3 2.8 mPolyalphaolefin 2.5 2.0 Detergent additive: Overbased calcium salicylate 0.08 0.08 Other components 10.42 10.42 KV 40 C. 20.74 20.47 KV 100 C. 4.72 4.76

(21) Viscosity modifier 2 was VISCOPLEX12-075, available as an item of commerce from Evonik Rohmax Additives GmbH and being a solution of polyalkyl methacrylate in diluent oil, ie a viscosity modifier of class (ii) (a) as described herein. Viscosity modifier 3 was LUBRIZOL 87725, also available as an item of commerce from Lubrizol Corporation and being a viscosity modifier of class (ii)(b) as defined herein.

(22) Composition 1 (from Example 1 above, containing Viscosity modifier 1) showed a fuel economy improvement over the total FTP 75 test of 0.86%. Composition 3 (Viscosity modifier 2VISCOPLEX 12-075) showed a lesser improvement of 0.37%, whilst Composition 4 (Lubrizol 87725) showed an intermediate fuel economy result of 0.54%.

(23) In each case, the level of viscosity modifier in the composition was chosen having regard to maintaining the viscosity behavior of the transmission fluid as consistent as practically possible between compositions, so as to exclude conventional bulk viscosity effects from the equation and demonstrate the particular advantages of specific viscosity modifiers in the present invention.

Worked Example 3Comparison with Existing Base-Stock Approach in the Art

(24) The ability of the present invention to achieve fuel efficiency improvements through additive-level quantities of the specific polyalphaolefin (iii), detergent/inhibitor additive (iv) and viscosity modifier (ii) was compared to the prior art PAO basestock approach described in US-A-2010/0035778 referred to above.

(25) US-A-2010/0035778 (to GM Global Technology Operations Inc.) exemplifies a composition comprising 9.4% (by weight, per total weight of fluid) of a first polyalphaolefin (PAO 2 cSt) and 68.0% of a second polyalphaolefin (PAO 6 cSt), together with proprietary additives comprising the additive package Hitec 3491 plus viscosity index improver and ester to a total of 22.6% by weight of the composition. The reference claims a fuel economy benefit for such compositions.

(26) The performance of Composition 1 of the present invention was compared to a commercially-obtained GM automatic transmission fluid (GM ATF 212-B), having a reported PAO composition the same as that of the example from US-A-2010/0035778, and likewise a total additive content of 22.6% (Hitec 3941A). This composition was therefore considered illustrative of the invention exemplified in US-A-2010/0035778.

(27) The performance of Composition 1 in the FTP 75 test has been noted as 0.86% fuel economy improvement over the whole test. In contrast, the GM ATF 212-B sample gave a result in the same test of 0.12% improvement in fuel economy over the reference fluid. Thus, Composition 1 showed substantially better fuel economy than the invention described in US-A-2010/0035778.

(28) US-A-2010/0035778 teaches a solution for fuel economy that requires the blend of two PAOs of differing viscosities as the basestock for the transmission fluid. As shown by the above results, a greater improvement in fuel economy is surprisingly obtained from the composition of the present invention.