EP1299509A2 - Friction modifier additive combination - Google Patents

Abstract

This invention relates to a friction modifier additive combination comprising (a) an oil-soluble fatty amine compound and (b) an oil-soluble fatty amide compound. Automatic transmission fluids comprising the above additives achieved a green shudder of 0 hour and a shudder resistance time of 110 hours or above.

Description

FRICTION MODIFIER ADDITIVE COMBINATION

This invention relates to a combination of additives that provides friction modifier benefits to lubricants and functional fluids, especially to power transmission fluids such as gear oils, automatic transmission fluids and fluids for continually variable transmissions.

Power transmissions for automotive vehicles, for example automatic transmissions, are being continually developed to improve their performance. There is a new generation of automatic transmissions currently being produced which are equipped with an electronically controlled converter clutch (hereafter "ec³"). The design provides a more compact and lighter automatic transmission that enables together with the ec³ a fuel saving of up to 10% and exhibits superior shift comfort.

The new automatic transmission designs place higher demands on the automatic transmission fluid (hereafter "ATF"). All ATFs should possess high oxidation stability, good viscometrics and low temperature properties, as well as good corrosion protection, anti-foaming and air separation properties. In addition, the friction properties, measured by friction coefficients displayed in a graph, are key to providing satisfactory performance. The friction property of the ATF must be balanced such that there is sufficient friction to provide adequate power transmission whilst minimising shudder both on start up of the engine (the so called "green shudder") and over the lifetime of the ATF. Excessive shudder causes driver discomfort and gives rise to an unacceptable noise level.

For the recently developed automatic transmissions equipped with an electronically controlled converter clutch, these friction requirements are even more demanding. Typically, the Original Equipment Manufacturer (hereafter "OEM") specifies a minimum friction coefficient at a plate sliding speed of 5 rpm of 0.123 to provide the necessary power transmission to the axle, together with the requirement that the friction coefficient does not decrease with increasing plate sliding speed, ie the gradient of the curve in the graph of friction coefficient against increasing sliding speed is positive or zero; it must not be negative. The latter requirements is to minimise green shudder to an acceptable time period of no more than 0.2 hours (12 minutes).

Furthermore, it is preferred that the ATF will function without noticeable shudder (once any green shudder has ceased) for at least 150,000 km of automotive transmission operation. The minimum hours according to the Zahnradfarbik Friedrichschafen (hereafter "ZF") ec³ test as defined is in the region of >100 hours.

ATFs used hitherto containing conventional friction modifiers (hereafter "FM"), such as fatty acids, fatty amines and fatty alcohols, do not meet these requirements. For example, ETHOMEEN® T-12, a tallow amine supplied by AKZO Chemicals, when incorporated in an ATF formulation at a treat level of 0.15 % by wt. does not always meet the requirement for friction coefficient vs. sliding speed (0.123 at 5 rpm) and never achieves a durability of > 100 hours.

Prior published EP-A-0 713 908 describes an oil-based power transmission fluid composition, especially ATFs which contains inter alia at least one oil-soluble fπction modifier which may be selected from aliphatic amines, aliphatic fatty acid amides, aliphatic carboxylic acids, aliphatic carboxylic esters, aliphatic carboxylic ester amides, aliphatic phosphonates, aliphatic phosphates, aliphatic thiophosphates and aliphatic thiophosphates etc wherein the aliphatic group contains more than 8 carbon atoms to render the compound suitably oil soluble. The compositions of this invention are said to have the capability of exhibiting a positive slope in the plot of coefficient of friction versus sliding speed in the low speed SAE No. 2 Friction Test when performed with Ford Engineering Material Specification WSP-M2CZAA-A. Also, in clutch friction durability tests performed using the above method involving 20,000 cycles, the following results were achieved: μD in the range of 0.130-0.170; μS values (at 0.25 seconds) in the range of 0.110-0.155; low speed dynamic friction values in the range of 0.130-0.170; Sl/D values in the range of 0.90-1.16; and stop times, in seconds, in the range of 0.70-1.0. It would be evident to those skilled in the art that this SAE-test cannot be read across for European OEMs, and hence it is not suitable for European design because it is a laboratory test rig which did not produce the specific results initially and, therefore, had to be abandoned.

The present invention provides a friction modifier additive combination comprising (a) an oil-soluble fatty amine compound and (b) an oil-soluble fatty amide compound. It has been found that by combining a fatty amine with a fatty amide, the friction properties of a lubricant or functional fluid containing the same are improved. For example, by formulating an ATF using the amine/amide friction modifier combination of the present invention it is possible to achieve a friction coefficient at 5 rpm of at least 0.123 together with a positive or zero gradient in the graph of friction coefficient versus sliding speed. After the end of the green shudder, if any, the ATF can operate for 150 hours or more before the onset of shudder.

The fatty amine compound is suitably a secondary or a tertiary amine compound, preferably a tertiary amine compound wherein of the substituents bonded to the aminic nitrogen atom at least one is an alkyl or an aryl group derived from a fatty acid, and at least one substituent is a polar group such as eg an alkylenehydroxy group of the formula

-R^!OH, or a polyoxyalkylenehydroxy group of the formula -(R¹O)_x-R¹OH wherein R¹ and x are as defined in the structure of formula (I) below:

(R^ ^OH / R-N (I)

\ (R²O)_y-R²OH

wherein:

R is an alkyl group containing from 8 to 24 carbon atoms or any aryl group containing one or more alkyl substituents containing from 8 to 24 carbon atoms; R¹ and R² are each independently an alkylene group containing from 1-8 carbon atoms; and x and y are each independently 0 or an integer from 1 to 5.

The substituent group R is suitably an alkyl group containing from 10 to 18 carbon atoms, preferably from 12 to 14 carbon atoms. The substituent group R is suitably derived from a fatty acid which is usually a naturally occurring substance and therefore may contain a mixture of carbon chain lengths, in which case the average chain length of the substituent group R is more preferably within the carbon atom ranges specified above.

The substituent groups R¹ and R² are each independently an alkylene group as stated above and these groups suitably have 1 to 4 carbon atoms, most preferably 2 carbon atoms such as eg a -CH₂-CH₂- grouping. The groupings -R'O- and -R²O- are 1 9 preferably oxyethylene groups and correspondingly -R OH and -R OH are ethylenehydroxy groups.

The number of oxyalkylene groups represented by x and y are each independently suitably 0, 1 or 2 and are preferably 0.

Specific examples of suitable fatty amine compounds include a coco-bis(2- hydroxyethyl)amine, a polyoxyethylene(5)coco-amine, a tallow-bis(2- hydroxyethyl)amine, a polyoxyethylene(5)tallow amine, a tallow/oleyl-bis(2- hydroxyethyl)amaine and an oleyl-bis- (2-hydroxyethyl)amine. Such compounds are commercially available from eg AKZO Chemicals. Particularly preferred are compounds such as eg the coco-bis(2-hydroxyethyl)amine (ETOMEEN® C/12) which contains a mixture of C₈ to C₁₈ alkyl groups, with C₁₂ groups predominating sold by Akzo Chemicals.

The fatty amide compound is suitably a secondary or a tertiary amide, preferably a tertiary amide in which the alkyl or aryl group is bonded to the carbon atom of the carbonyl group in the amide function, and of the two groups bonded to nitrogen atom of the amide function at least one is an organic polar group such as an alkylenehydroxy group of the formula - R^]OH or a polyoxyalkylenehydroxy group of the formula - (R¹O)_x-R¹OH wherein R¹ and x have the same significance as defined in formula (II) below. The fatty acid amide is preferably a compound of the formula (II)

(R^_x-^OH

/ R-C-N (II)

II \ O (R²O)_y-R²OH

wherein R, R , R , x and y are each independently as defined above for formula (I), both in respect of general and preferred embodiments.

Specific examples of suitable fatty amide compounds include the compound polyoxyethylene(5)oleamide sold under the trade name ETHOMID® 0/15 (ex Akzo Chemicals) which contains a mixture of C₁₂ to C₁₈ alkyl groups predominating in C₁₈ groups; and a fatty acid amide derived from lauric acid sold as COMPERLAN® LD (ex Henkel).

In a preferred embodiment, the friction modifier additive combination according to the present invention comprises a mixture of (a) a bis(hydroxyethyl) fatty amine wherein the fatty group comprises an alkyl group which has 12 to 14 carbon atoms and (b) a bis(hydroxyethyl) fatty amide wherein the fatty group comprises an alkyl group which has 12 to 18 carbon atoms.

In another embodiment, the present invention provides a lubricant or functional fluid formulation comprising a major amount of base oil of lubricating viscosity and a minor amount of a friction modifier additive combination as defined above. The lubricant or functional fluid is suitably useable as a power transmission fluid, preferably as an automatic transmission fluid (ATF). To illustrate the invention, the following description will focus on ATF formulations although it will be understood that the compositions of the present invention are not limited to such fluids but embraces within its scope other lubricant and functional fluids.

ATFs typically have a kinematic viscosity at 100°C (KV₁₀₀) ranging from 2-15 mm²/s, preferably from 4-10 mm²/s, more preferably from 5-8 mm²/s measured according to the standard test procedure of ASTM D-446. The Brookfield viscosity at - 40°C is suitably less than 50,000 mPa s, preferably from 4,000-20,000 mPa s, and more preferably from 5,000-18,000 mPa s measured according to the standard test procedure of ASTM D-2983. The viscosity index is suitably in the range from 100-200, preferably from 150-200 measured according to the standard test procedure of ASTM D-2270.

Generally, the amount of base oil contained in the ATF ranges from 50% by weight to 99.9%, suitably from 60-95% by weight and preferably from 70-90% by wt, based on the total weight of the ATF formulation.

The amount of friction modifier additive combination present in the ATF formulation (ie the total amount of fatty amine and fatty amide) is broadly in the range from 0.05-1.2% by weight. Within this range the specific amount used will depend not only upon the friction properties desired but also, at least to some extent, upon the design of the automatic transmission. Thus the amount of friction modifier additive combination used is suitably in the range from 0.1-1% by weight, preferably from 0.2- 0.8% by weight and more preferably from 0.3-0.6% by weight.

The amount of fatty amine compound in this friction modifier additive combination is suitably in the range from 0.03-1.0% by weight, preferably from 0.05- 0.8% by weight and more preferably from 0.1-0.6% by weight. The fatty amide compound in the additive combination is suitably from 0.05-0.8% by weight, preferably from 0.05-0.5% by weight and more preferably from 0.08-0.3% by weight.

The weight ratio of the fatty amine to fatty amide in the additive combination is suitably in the range from 0.5 : 1 to 10: 1 , preferably from 1 : 1 to 8 : 1 and more preferably

The amounts of the fatty amine and fatty amide in the additive combination are with respect to the active ingredients in such compounds. The compounds specified above are generally liquids at room temperature and within conventional lubricant additive handling and blending temperatures, and are therefore usually supplied and used in neat, 100% active ingredient form. However, if desired, they may be diluted with a solvent, such as eg mineral oil, which is inert under the conditions especially with respect to the performance of the lubricant.

The base oil of the ATF or other lubricant or functional fluid according to the invention may be a mineral oil, a synthetic oil or mixtures thereof. The base oils are suitably selected from refined mineral oils, for example, a solvent refined and/or hydrotreated oils, oils derived from coal tar or shale, vegetable oils, animal oils, hydrocracked oils, hydroisomerised oils, poly-alphaolefins (PAO), esters, alkylbenzenes, polyglycols, alkylene oxide polymers, silicone oils and the like.

Where the base oil comprises a mineral oil, it is suitably a solvent refined and/or hydrotreated oil. Examples of suitable oils of this type include inter alia solvent refined mineral oils in the range of 50N to 150N, preferably 80N to 130N. Such mineral oils are available, for example, from Esso under the trade name Esso Solvent Neutral.

Where the base oil is a severely refined mineral oil such as eg white oil, these may be one of the varieties supplied by Esso under the trade names MARCOL® 52 and 172, PRIMOL® 352, PLASTOL® 135 and 352, and BAYOL® 52. The base oils used may also be a hydrocracked or hydroisomerised oils such as eg a hydroisomerised paraffin.

Where the base oil is a synthetic oil, it is preferably a PAO produced by the oligomerisation of 1-alkenes which suitably contain 6-20 carbon atoms, preferably 8-14 carbon atoms. PAOs produced from 1-decene are particularly preferred. The KN₁₀o of the PAO selected is usually determined by the viscosity desired in the final lubricant formulation and is suitably in the range from 2-8mm²/s, preferably from 4-6mm²/s. Such PAOs are commercially available eg from ExxonMobil.

In a preferred embodiment, the base oil is a mix of mineral oils and synthetic oils, eg a mixture of one or more solvent refined mineral oils with PAOs; or a mixture of solvent refined mineral oil with white oil, a hydrocracked oil or a hydroisomerised oil as stated above. In a particularly preferred embodiment, the base oil is a mixture of solvent refined mineral oil, a PAO and white oil.

The functional fluid formulations of the present invention may also contain other optional additives depending upon the intended use of the functional fluid. Such additives include inter alia viscosity index improvers, pour point depressants, antioxidants, anti-wear agents, extreme pressure additives, dispersants, detergents, corrosion inhibitors, erosion inhibitors, anti-foaming agents, seal swell conditioning agents (seal fix), anti-pitting agents and the like. Such additives are all commercially available, the choice of one or more of these and the amounts of each used depending upon the intended end use of the functional fluid. Thus, eg, a viscosity index improver would typically be included in the functional fluids at a treat level of 2-15% by weight based on active ingredient (ie excluding solvent and carrier fluids, if any), preferably from 2-10% by weight, and the other additives would typically be included in the functional fluids at a treat level of 0.01-5% by weight based on active ingredient.

The optional additives recited above may be added individually to the base oil, or, two or more may be pre-mixed with a carrier fluid such as eg a mineral oil, to form an additive concentrate and can then be blended with the base oil. The friction modifier additive combination according to the invention may also be pre-mixed with or without other additives into an additive concentrate. Of the optional additives recited above:

the dispersants are suitably ashless dispersants such as eg polyalkenyl succinic anhydrides, polyalkenyl succinimides and derivatives thereof wherein the polyalkenyl group is derived from a long chain polyolefin such as eg polyisobutylene;

the extreme pressure additives are suitably phosphorus- or zinc-based;

the antioxidants are suitably aminic and/or phenolic type;

the pitting booster is suitably sulphurised fatty oil eg Sulperm® 307 (ex Ferro Corporation);

the anti-foam agents are suitably silicon based; and

the viscosity index improver is suitably acrylic based such as eg a polymethylmethacrylate.

The friction modifier additive combination and lubricating oil formulations produced therefrom are particularly effective when used in automatic transmission fluids, especially for automatic transmissions equipped with an electronically controlled converter clutch.

The present invention is further illustrated with reference to the following Examples.

The following formulation was tested for its performance as an ATF in which all the amounts in the columns are % by weight: TABLE 1

*Refers to a proprietary ATF additive package, Hitec® 403 but without Ethomeen T/12 (ex Ethyl Corp).

The formulations in Tests 1-4 above passed the Electronically controlled converter clutch (ECCC) tests on the Mannesmann Sachs (MS) German for Geregelte Wandlerkupplung (hereafter "GWK"). The formulations shown above achieved a green shudder of 0 hours and a shudder resistance time of 110 hours or above (as against a specification time of a minimum of 100 hours) thereby meeting the demanding GWK requirements from MS and ZF.

Claims

Claims:

1. A friction modifier additive combination comprising (a) an oil-soluble fatty amine compound and (b) an oil-soluble fatty amide compound wherein the weight ratio of the fatty amine to fatty acid amide in the additive combination is in the range from 0.5:1 to 10:1.

2. A combination according to claim 1 wherein the fatty amine compound (a) is a secondary or a tertiary amine compound.

3. A combination according to Claim 1 or 2 wherein of the substituents bonded to the aminic nitrogen atom in (a), at least one substituent is an alkyl or an aryl group derived from a fatty acid and at least one substituent is a polar group.

4. A combination according to Claim 3 wherein the polar group substituted on the aminic nitrogen atom is a alkylenehydroxy group or a polyoxyalkylene-hydroxy group.

5. A combination according to any one of the preceding Claims wherein the fatty amine is of formula (I):

R-N (I) \

(R²O)_y-R²OH

wherein:

R is an alkyl group containing from 8 to 24 carbon atoms or any aryl group containing one or more alkyl substituents containing from 8 to 24 carbon atoms;

R¹ and R² are each independently an alkylene group containing from 1-8 carbon atoms; and x and y are each independently 0 or an integer from 1 to 5.

6. A combination according to Claim 5 wherein the substituent groups R¹ and R² are each independently an alkylene group and have 1 to 4 carbon atoms.

A combination according to Claims 5 and 6 wherein the number of oxyalkylene groups represented by x and y are each independently suitably 0, 1 or 2 and are preferably 0.

A combination according to Claims 5-7 wherein the fatty amine is selected from the group of coco-bis(2-hydroxyethyl)amine, a polyoxyethylene(5)coco-amine and an oleyl-bis- (2-hydroxyethyl)amine, and mixtures thereof.

9. A friction modifier additive combination according to any one of the preceding Claims wherein said combination comprises a mixture of (a) a bis(hydroxyethyl) fatty amine wherein the fatty group comprises an alkyl group which has 12 to 14 carbon atoms and (b) a bis(hydroxyethyl) fatty amide wherein the fatty group comprises an alkyl group which has 12 to 18 carbon atoms.

10. A lubricant formulation comprising a major amount of base oil of lubricating viscosity and a minor amount of a friction modifier additive combination as defined in any one of the preceding Claims 1-9.

11. A lubricant formulation according to Claim 10 wherein said formulation is a functional fluid useable as a power transmission fluid.

12. A lubricant formulation according to Claim 10 or 11 wherein said formulation is an automatic transmission fluid (ATF).

13. A lubricant formulation according to Claim 12 wherein said formulation is an automatic transmission fluid having a kinematic viscosity at 100°C (KV ₁₀₀) ranging from 2-15 mm² /s measured according to the standard test procedure of ASTM D-446, a Brookfield viscosity at -40°C of less than 50,000 mPa s measured according to the standard test procedure of ASTM D-2983 and a viscosity index in the range from 100-200 measured according to the standard test procedure of ASTM D-2270.

14. A lubricant formulation according to Claims 10-13 wherein the total amount of the fatty amine and fatty acid amide present as the friction modifier additive combination is in the range from 0.05-1.2% by weight.

15. A lubricant formulation according to any one of the preceding Claims 10-14 wherein the base oil comprises a poly-alpha-olefin (PAO) having a KN₁₀o in the range from 2-8mm²/s.

16. A lubricant formulation according to any one of the preceding Claims 10-15 wherein said formulation comprises a mixture of a solvent refined mineral oil, a PAO and white oil.

17. A lubricant formulation according to any one of the preceding Claims 10-16 wherein said formulation comprises a viscosity index improver at a level of 2- 15% by weight based on active ingredient.

18. A lubricant formulation according to Claim 17 wherein the viscosity index improver is a polymethylmethacrylate.