LIMITED SLIP FRICTION MODIFIERS FOR DIFFERENTIALS BACKGROUND OF THE INVENTION

[0001] The invention relates to a lubricating composition comprising (a) an oil of lubricating viscosity, and (b) an oil soluble compound. The invention further provides for the use of the lubricating composition for lubricating a limited slip differential.

[0002] A vehicle differential typically has bevel gear or spur gear planetary systems which distribute drive torque evenly to the two driving wheels irrespective of their rotational speed. This makes it possible for the driven wheels to roll during cornering without slip between the wheel and road surface in spite of their different rotational speed. When one wheel is on a low traction surface, the amount of torque that can be transmitted is limited to the amount which can be applied before the wheel slips.

[0003] A limited slip differential typically employs a wet multi- plate clutch, i.e., clutch plates which are in contact with a lubricant, to supply more torque to the non-slipping wheels during a slipping situation. During normal turns, for one wheel to spin faster than the other, the clutch plates must disengage or break away. There can be NVH (noise, vibration, harshness) associated with this event.

[0004] In order for the slip to be controlled lubricants containing compounds capable of improving friction performance, dispersants and sulfur- and/ or phosphorus- containing extreme pressure agents may be used. Examples of lubricants of this type are disclosed in US Patents 4,308, 154; 4, 180,466; 3,825,495; and European Patent Application 0 399 764 Al .

[0005] A certain class of compounds capable of improving friction performance is taught, for example, in US 5,021 , 176 to Bullen et al., issued June 4, 1991. Bullen teaches, among other things, a diamine as a friction reducing additive, particularly in wet brake systems, having the structure shown immediately below.

[0006] Similarly, WO 2010/096325 to inventors Saccomando et al., published August 26, 2010, and US 4,446,053 to Skrobul et al., issued May 1 , 1984 teach amine type compounds for friction modification.

[0007] Saccomando teaches a composition for use as a friction modifier for an automatic transmission, comprising a long chain hydrocarbyl amine having one or two additional groups on one or two different amine nitrogen atoms thereof. One of the species represented in the publication is shown in formula Xlla therein, having a formula of R ^! NMCH^CONHiCH^aNHR ⁴ ^.

[0008] Skrobul teaches friction reducing additives for engine oils characterized by the following general formulas.

RNHCH ₂ CH ₂ C02-Na+ and

RNHCH2CH2CONH2

[0009] Neither of Saccomando or Skrobul teach the use of the amine compounds for friction performance in limited slip differentials, and the compounds do not encompass the compounds as taught herein. [0010] US 2012/0015855 to Saccomando et al., published January 19, 2012 and US 2012/0122744 to Saccomando et al., published May 17, 2012 teach varying classes of amine friction modifying compounds that do not include the compounds taught herein.

[0011] US 5,372,735 to Ohtani et al., issued December 13, 1994 teaches an automatic transmission fluid with a friction modifier content consisting essentially of a hydrocarbyl substituted diethanolamine and an hydrocarbyl N-substituted trimethylenediamine. The compound of the present invention does not require a synergistic amount of another compound, such as a diethanolamine, and further, the compounds taught herein are different than diethanolamine and N-substituted trimethylenediamine as taught in Ohtani.

[0012] GB 1209548 teaches a motor fuel composition comprising an amide represented by the general formula

where R is a hydrocarbyl having 17 carbon atoms derived from oleic acid and R' and R" alternately represent hydrogen and a hydrocarbyl radical having from 14 to 18 carbon atoms. The GB patent does not teach the use of the formula in a lubricant for limited slip differentials.

[0013] Another patent, JP 63060956, teaches a compound useful as a lubricant for synthetic resin including, among other things, a bisamidation reaction of a fatty acid with a diamine. The JP'956 patent does not teach the use of the amine compounds for friction performance in limited slip differentials.

[0014] US 4,581 ,039 to Horodysky, issued April 8, 1986 teaches antifriction carboxylates of the formula:

R ¹ R3

R— N— R ² — -N— R ⁴

(R ⁵ COOH) _J C (HOOCR¾, for engine oils and fuel compositions. In the preferred embodiments of the formula R3 and R ₄ are H. The carboxylate formula does not encompass the compounds disclosed herein and specifically teaches against the production of amides (col 2, lines 13- 19 - "prevention of amide formation"). In addition, the patent does not teach the use of the compounds for limited slip differentials.

[0015] WO2010/096318, published August 26, 2010, teaches anti-friction compounds for automatic transmissions of the formula below. The publication does not teach the use of the compounds for limited slip differentials.

R ¹ — N— ( ³ ~NH~C~R (R ² )b O

[0016] A lubricant for limited slip differentials is desired that is capable of providing a high coefficient of friction and a low tendency toward noise, vibration and harshness.

SUMMARY OF THE INVENTION

[0017] An object of the present invention is to provide a lubricating composition and method as disclosed herein that is capable of providing a high coefficient of friction and a low tendency toward noise, vibration and harshness (NVH) often manifested as chatter (i.e. an abnormal noise typically referred to as a low- frequency "growl" and "groan," particularly during low- speed cornering maneuvers). The inventors have unexpectedly discovered that the lubricant composition and method disclosed herein may also be suitable for limited slip systems having one or more distinct plate materials. For example, the plate materials may be steel, paper, ceramic, carbon fibers and systems employing a mixture of plate types such as steel on ceramic, carbon fibers in paper or steel on paper.

[0018] In one embodiment, the invention provides a lubricant for limited slip differentials comprising an (a) a major amount of an oil of lubricating viscosity, and (b) at least one oil soluble compound comprising the condensation product of ( 1) an N-substituted 1 ,3- diaminopropane, wherein the N-substituent is derived from a Cs-28 amine, and (2) a Cs-28 acid.

[0019] Preferably, the Cs-28 amine of ( 1) is a fatty amine and the Cs-28 acid of (b) is at least one of a fatty acid or fatty acid chloride. However, the amine and the acid are not particularly limited and can be any amine and acid suitable for preparing an oil soluble compound, as described, for the intended purpose in limited slip systems.

[0020] In an embodiment of the lubricant, the condensation product can comprise a compound of formula R'NH(CH2)3NHCOR. " Preferably, R' is the N-substituent derived from the Cs-28 amine of ( 1), and -COR" is derived from the Cs-28 acid of (2).

[0021] In a particularly preferred embodiment, R' can be derived from a C is fatty amine, such as oleyl amine, and -COR" can be derived from a C is fatty acid, such as oleic acid. [0022] In a further embodiment, there is provided a method of providing limited slip performance to a differential comprising the step of introducing the oil soluble compound described herein, or a lubricating composition comprising the oil soluble compound described herein to a limited slip differential, and operating the limited slip differential.

[0023] In another embodiment there is provided a use of a lubricant as described above for providing limited slip performance in a limited slip differential.

DETAILED DESCRIPTION OF THE INVENTION

[0024] Various preferred features and embodiments will be described below by way of non-limiting illustration.

[0025] As used herein the expression "oil-soluble" or "hydrocarbon soluble" is meant a material which will dissolve or disperse on a macroscopic or gross scale in an oil or hydrocarbon, as the case may be, typically a mineral oil, such that a practical solution or dispersion can be prepared. In order to prepare a useful lubricant formulation, the material should not precipitate or settle out over a course of several days or weeks. Such materials may exhibit true solubility on a molecular scale or may exist in the form of agglomerations of varying size or scale, provided however that they have dissolved or dispersed on a gross scale.

[0026] As used herein, the term "hydrocarbyl group" or "hydrocarbyl substituent" is used in its ordinary sense, which is well-known to those skilled in the art. Specifically, it refers to a group having a carbon atom directly attached to the remainder of the molecule and having predominantly hydrocarbon character. Examples of hydrocarbyl groups include: (i) hydrocarbon substituents, that is, aliphatic (e.g. , alkyl or alkenyl), alicyclic (e.g., cycloalkyl, cycloalkenyl) substituents, and aromatic-, aliphatic-, and alicyclic-substituted aromatic substituents, as well as cyclic substituents wherein the ring is completed through another portion of the molecule (e.g., two substituents together form a ring);

(ii) substituted hydrocarbon substituents, that is, substituents containing non-hydrocarbon groups which, in the context of this invention, do not alter the predominantly hydrocarbon nature of the substituent (e.g., halo (especially chloro and fluoro), hydroxy, alkoxy, mercapto, alkylmercapto, nitro, nitroso, and sulfoxy);

(iii) hetero substituents, that is, substituents which, while having a predominantly hydrocarbon character, in the context of this invention, contain other than carbon in a ring or chain otherwise composed of carbon atoms, and encompass substituents as pyridyl, furyl, thienyl and imidazolyl; and

[0027] (iv) heteroatoms, including sulfur, oxygen, and nitrogen. In general, no more than two, preferably no more than one, non- hydrocarbon substituent will be present for every ten carbon atoms in the hydrocarbyl group; typically, there will be no non-hydrocarbon substituents in the hydrocarbyl group.

[0028] One aspect of the present invention is a lubricant for a limited slip differential comprising an oil-soluble compound. In one embodiment, the oil soluble compound can be the condensation product of (a) an N-substituted 1 ,3-diaminopropane, and (b) an acid. The N-substituent on the 1 ,3-diaminopropane can be derived from an amine. [0029] The N-substituent amine and the acid are not particularly limited and can be any amine and acid suitable for preparing the oil soluble compound, as described, for the intended purpose in limited slip systems.

[0030] In a preferred embodiment, the N-substituent of the N- substituted 1 ,3-diaminopropane of (a) can be derived from a hydrocarbyl substituted amine, namely an alkylamine. The alkylamine can comprise a single alkyl substituent or a mixture of alkyl substituents. Preferably, the amine is a Cs-28 amine, or in some cases, a C9-26 amine, more preferably a C 10-24 amine, or a C 1 1-22 amine. The amine can also be from about C i6 or C is to C20.

[0031] Particularly preferred amines include fatty amines and/or fatty amine mixtures, such as, for example, soya amine, oleyl amine, tallow amine, cocoamine, and the like. In a preferred embodiment the amine is oleyl amine. In another preferred embodiment, the amine is tallow amine.

[0032] In a preferred embodiment, the acid is a Cs-28 acid, or in some cases, a C9-26 acid, more preferably a C io-24 acid, or a C i i-22 acid. The acid may also be from about C i6 or C is to C20. In some embodiments the acid can be, for example, a fatty acid, and in other embodiments the acid can be a fatty acid chloride.

[0033] Particularly preferred acids include fatty acids, such as, for example, myristic acid, palmitic acid, behenic acid, eruicic acid, oleic acid, stearic acid, linoleic acid, and lauric acid, and the like. In a preferred embodiment, the acid can be oleyl acid. In another preferred embodiment, the acid can be linoleic acid.

[0034] In an embodiment of the oil soluble compound as described above, the condensation product can comprise a compound of formula R'NH(CH ₂ ) ₃ NHCOR". Preferably, R' is the N- substituent derived from the amine of (a), and -COR" is derived from the acid of (b) .

[0035] R' and -COR" can be derived from a derivative of the same or different precursor. For example, R' and -COR" can be derived from a derivative of an oleyl precursor, such as oleic acid, or R' can be derived from a derivative of, for example, an oleyl precursor and -COR" can be derived from a derivative of, for example, a erucyl precursor. In a particularly preferred embodiment, R' can be derived from a Cis fatty amine, such as oleyl amine, and -COR" can be derived from a Cis fatty acid, such as oleic acid.

[0036] Oil-soluble compounds according to the foregoing embodiments can be employed in a lubricating composition with oils of lubricating viscosity to provide friction performance in limited slip differentials. The oil-soluble compounds can be included, on an oil- free basis, at a concentration of from about 0. 1 to about 8 wt%, or 0.2 to about 7 wt%, and in some embodiments from about 0.25 to about 5 or about 6 wt%, or even from about 0.25 to about 1 , or 2, or 3 or about 4 wt%.

[0037] Oils of Lubricating Viscosity

[0038] The lubricating composition comprises a major amount of an oil of lubricating viscosity. Such oils include natural and synthetic oils, oil derived from hydro cracking, hydrogenation, and hydrofinishing, unrefined, refined, re-refined oils or mixtures thereof. A more detailed description of unrefined, refined and re-refined oils is provided in International Publication WO2008/ 147704, paragraphs [0054] to [0056] . [0039] Synthetic lubricating oils include hydrocarbon oils and halo-substituted hydrocarbon oils such as polymerized and interpolymerized olefins, also known as polyalphaolefins; polyphenyls; alkylated diphenyl ethers; alkyl- or dialkylbenzenes; and alkylated diphenyl sulfides; and the derivatives, analogs and homologues thereof. Also included are alkylene oxide polymers and interpolymers and derivatives thereof, in which the terminal hydroxyl groups may have been modified by esterification or etherification. Also included are esters of dicarboxylic acids with a variety of alcohols, or esters made from Cs to C 12 monocarboxylic acids and polyols or polyol ethers. Other synthetic oils include silicon-based oils, liquid esters of phosphorus-containing acids, and polymeric tetrahydrofurans. The synthetic oils may be produced by Fischer- Tropsch reactions and typically may comprise hydroisomerized Fischer-Tropsch hydrocarbons and/or waxes, or hydroisomerized slack waxes. In one embodiment oils may be prepared by a Fischer- Tropsch gas-to-liquid synthetic procedure as well as other gas-to- liquid oils.

[0040] Oils of lubricating viscosity may also be defined as specified in April 2008 version of "Appendix E - API Base Oil Interchangeability Guidelines for Passenger Car Motor Oils and Diesel Engine Oils", section 1.3 Sub-heading 1.3. "Base Stock Categories. " In one embodiment, the oil of lubricating viscosity may be an API Group I, Group II, Group III, or Group IVoil.

[0041] Polyalphaolefins are categorized as Group IV oils. In one embodiment, at least 50% by weight of the oil of lubricating viscosity is a polyalphaolefin (PAO). Typically, the polyalphaolefins are derived from monomers having from 4 to 30, or from 4 to 20, or from 6 to 16 carbon atoms. Examples of useful PAOs include those derived from 1 -decene. These PAOs may have a viscosity of 1 .5 to 150 mm ² / s (cSt) at 100°C. PAOs are typically hydrogenated materials.

[0042] The amount of the oil of lubricating viscosity present is typically the balance remaining after subtracting from 100 wt% the sum of the amount of the compound of the invention and the other performance additives.

[0043] The lubricating composition may be in the form of a concentrate and/ or a fully formulated lubricant. If the lubricating composition of the invention (comprising the additives disclosed herein) is in the form of a concentrate which may be combined with additional oil to form, in whole or in part, a finished lubricant), the ratio of these additives to the oil of lubricating viscosity and/or to diluent oil includes the ranges of 1 :99 to 99: 1 by weight, or 80:20 to 10:90 by weight.

Other Performance Additives

[0044] The composition of the invention optionally further includes at least one other performance additive. The other performance additives include dispersants, metal deactivators, detergents, viscosity modifiers, extreme pressure agents (typically boron- and/ or sulfur- and/ or phosphorus-containing) , antiwear agents, antioxidants (such as hindered phenols, aminic antioxidants or molybdenum compounds), corrosion inhibitors, foam inhibitors, demulsifiers, pour point depressants, seal swelling agents, friction modifiers and mixtures thereof.

[0045] The total combined amount of the other performance additives (excluding the viscosity modifiers) present on an oil free basis may include ranges of 0.01 wt% to 25 wt%, or 0.01 wt% to 20 wt%, or 0. 1 wt% to 15 wt% or 0.5 wt% to 10 wt%, or 1 to 5 wt% of the composition. Although one or more of the other performance additives may be present, it is common for the other performance additives to be present in different amounts relative to each other.

[0046] In one embodiment the lubricating composition is free of molybdenum-containing additives.

Detergent

[0047] One additional component of the disclosed lubricant can be an overbased metal containing detergent. Detergents in general are typically overbased materials, otherwise referred to as overbased or superbased salts, which are generally homogeneous Newtonian systems having by a metal content in excess of that which would be present for neutralization according to the stoichiometry of the metal and the detergent anion. The amount of excess metal is commonly expressed in terms of metal ratio, that is, the ratio of the total equivalents of the metal to the equivalents of the acidic organic compound. Overbased materials are prepared by reacting an acidic material (such as carbon dioxide) with an acidic organic compound, an inert reaction medium (e.g. , mineral oil), a stoichiometric excess of a metal base, and a promoter such as a phenol or alcohol. The acidic organic material will normally have a sufficient number of carbon atoms, to provide oil- solubility.

[0048] Overbased detergents may be characterized by Total Base Number (TBN), the amount of strong acid needed to neutralize all of the material's basicity, expressed as mg KOH per gram of sample. Since overbased detergents are commonly provided in a form which contains diluent oil, for the purpose of this document, TBN is to be recalculated to an oil-free basis. Various detergents may have a TBN of 100 to 1000, or 150 to 800, or, 400 to 700.

[0049] The metal compounds generally useful in making the basic metal salts are generally any Group 1 or Group 2 metal compounds (CAS version of the Periodic Table of the Elements). Examples include alkali metals such as sodium, potassium, lithium, copper, magnesium, calcium, barium, zinc, and cadmium. In one embodiment the metals are sodium, magnesium, or calcium. The anionic portion of the salt can be hydroxide, oxide, carbonate, borate, or nitrate. The detergents of particular interest for the present technology will be calcium detergents, typically prepared using calcium oxide or calcium hydroxide. Since the detergents of particular interest are carbonated detergents, they will be materials that have been treated with carbon dioxide. Such treatment leads to more efficient incorporation of basic metal into the composition. Formation of high TBN detergents involving reaction with carbon dioxide is disclosed, for instance, in US 7,238,651 , Kocsis et al., July 3, 2007, see, for instance, examples 10- 13 and the claims. Other detergents, however, may also optionally be present, which need not be carbonated or need not be so highly overbased (i.e., of lower TBN). However, if multiple detergents are present, it is desirable that the overbased calcium arylsulfonate detergent is present as the predominant amount by weight of the metal detergents, that is, at least 50 weight percent or at least 60 or 70 or 80 or 90 weight percent of the metal-containing detergents, on an oil free basis.

[0050] The lubricants useful in the present technology can contain an overbased sulfonate detergent. Suitable sulfonic acids include sulfonic and thiosulfonic acids, including mono- or poly- nuclear aromatic or cycloaliphatic compounds. Certain oil-soluble sulfonates can be represented by R ² -T-(SO3 ^" )a or R ³ -(SO3 ^~ )t>, where a and b are each at least one; T is a cyclic nucleus such as benzene or toluene; R ² is an aliphatic group such as alkyl, alkenyl, alkoxy, or alkoxyalkyl; (R ² )-T typically contains a total of at least 15 carbon atoms; and R ³ is an aliphatic hydrocarbyl group typically containing at least 15 carbon atoms. The groups T, R ² , and R ³ can also contain other inorganic or organic substituents; they may also be described as hydrocarbyl groups. In one embodiment the sulfonate detergent may be a predominantly linear alkylbenzenesulfonate detergent as described in paragraphs [0026] to [0037] of US Patent Application 2005-065045. In some embodiments the linear alkyl (or hydrocarbyl) group may be attached to the benzene ring anywhere along the linear chain of the alkyl group, but often in the 2, 3, or 4 position of the linear chain, and in some instances predominantly in the 2 position. In other embodiments, the alkyl (or hydrocarbyl) group may be branched, that is, formed from a branched olefin such as propylene or 1 -butene or isobutene. Sulfonate detergents having a mixture of linear and branched alkyl groups may also be used.

[0051] Another type of overbased material that may additionally be present (that is, in addition to the arylsulfonate detergent) in certain embodiments of the present invention is an overbased phenate detergent. Certain commercial grades of calcium sulfonate detergents contain minor amounts of calcium phenate detergents to aid in their processing or for other reasons and may contain, for instance, 4% phenate substrate content and 96% sulfonate substrate content. The phenols useful in making phenate detergents can be represented by (R ^! Ja-Ar-fOHJb, where R ¹ is an aliphatic hydrocarbyl group of 4 to 400 or 6 to 80 or 6 to 30 or 8 to 25 or 8 to 15 carbon atoms; Ar is an aromatic group such as benzene, toluene or naphthalene; a and b are each at least one, the sum of a and b being up to the number of displaceable hydrogens on the aromatic nucleus of Ar, such as 1 to 4 or 1 to 2. There is typically an average of at least 7 or 8 aliphatic carbon atoms provided by the R ¹ groups for each phenol compound, and in some instances about 12 carbon atoms. Phenate detergents are also sometimes provided as sulfur-bridged species or as methylene-bridged species. Sulfur-bridged species may be prepared by reacting a hydrocarbyl phenol with sulfur. Methylene-bridged species may be prepared by reacting a hydrocarbyl phenol with formaldehyde (or a reactive equivalent such as paraformaldehyde). Examples include sulfur-bridged dodecylphenol (overbased Ca salt) and methylene-coupled heptylphenol.

[0052] In another embodiment, an optional, additional overbased material is an overbased saligenin detergent. Overbased saligenin detergents are commonly overbased magnesium salts which are based on saligenin derivatives. A general example of such a saligenin derivative can be re resented by the formula

where X is -CHO or -CH ₂ OH, Y is -CH ₂ - or -CH ₂ OCH ₂ -, and the -CHO groups typically comprise at least 10 mole percent of the X and Y groups; M is hydrogen, ammonium, or a valence of a metal ion (that is, if M is multivalent, one of the valences is satisfied by the illustrated structure and other valences are satisfied by other species such as anions or by another instance of the same structure), Ri is a hydrocarbyl group of 1 to 60 carbon atoms, m is 0 to typically 10, and each p is independently 0, 1 , 2, or 3, provided that at least one aromatic ring contains an R ¹ substituent and that the total number of carbon atoms in all R ¹ groups is at least 7. When m is 1 or greater, one of the X groups can be hydrogen. In one embodiment, M is a valence (or equivalent) of a Mg ion or a mixture of Mg and hydrogen. Saligenin detergents are disclosed in greater detail in U.S. Patent 6,310,009, with special reference to their methods of synthesis (Column 8 and Example 1) and preferred amounts of the various species of X and Y (Column 6).

[0053] Other optional detergents include salixarate detergents. Salixarate detergents are overbased materials that can be represented by a compound comprising at least one unit of formula (I) or formula (II):

(I) (II) each end of the compound having a terminal group of formula (III)

(IV):

(III) (IV)

such groups being linked by divalent bridging groups A, which may be the same or different. In formulas (I) -(IV) R ³ is hydrogen, a hydrocarbyl group, or a valence of a metal ion; R ² is hydroxyl or a hydrocarbyl group, and j is 0, 1 , or 2; R ⁶ is hydrogen, a hydrocarbyl group, or a hetero-substituted hydrocarbyl group; either R ⁴ is hydroxyl and R ⁵ and R ⁷ are independently either hydrogen, a hydrocarbyl group, or hetero-substituted hydrocarbyl group, or else R ⁵ and R ⁷ are both hydroxyl and R ⁴ is hydrogen, a hydrocarbyl group, or a hetero-substituted hydrocarbyl group; provided that at least one of R ⁴ , R ⁵ , R ⁶ and R ⁷ is hydrocarbyl containing at least 8 carbon atoms; and wherein the molecules on average contain at least one of unit (I) or (III) and at least one of unit (II) or (IV) and the ratio of the total number of units (I) and (III) to the total number of units of (II) and (IV) in the composition is 0. 1 : 1 to 2: 1. The divalent bridging group "A," which may be the same or different in each occurrence, includes -C¾- and -CH2OCH2- , either of which may be derived from formaldehyde or a formaldehyde equivalent (e.g., paraform, formalin).

[0054] Salixarate derivatives and methods of their preparation are described in greater detail in U.S. patent number 6,200,936 and PCT Publication WO 01 /56968. It is believed that the salixarate derivatives have a predominantly linear, rather than macrocyclic, structure, although both structures are intended to be encompassed by the term "salixarate." In one embodiment, a salixarate detergent may contain a portion of molecules represented (prior to neutralization) by the structure

where the R ⁸ groups are independently hydrocarbyl groups containing at least 8 carbon atoms.

[0055] Glyoxylate detergents are also optional overbased materials. They are based on an anionic group which, in one embodiment, may have the structure

wherein each R is independently an alkyl group containing at least 4 or 8 carbon atoms, provided that the total number of carbon atoms in all such R groups is at least 12 or 16 or 24. Alternatively, each R can be an olefin polymer substituent. The acidic material upon from which the overbased glyoxylate detergent is prepared is the condensation product of a hydroxyaromatic material such as a hydrocarbyl- substituted phenol with a carboxylic reactant such as glyoxylic acid or another omega-oxoalkanoic acid. Overbased glyoxylic detergents and their methods of preparation are disclosed in greater detail in U.S. Patent 6,310,01 1 and references cited therein.

[0056] Another optional overbased detergent is an overbased salicylate, e,g., an alkali metal or alkaline earth metal salt of a substituted salicylic acid. The salicylic acids may be hydrocarbyl- substituted wherein each substituent contains an average of at least 8 carbon atoms per substituent and 1 to 3 substituents per molecule. The substituents can be polyalkene substituents. In one embodiment, the hydrocarbyl substituent group contains 7 to 300 carbon atoms and can be an alkyl group having a molecular weight of 150 to 2000. Overbased salicylate detergents and their methods of preparation are disclosed in U.S. Patents 4,719,023 and 3,372, 1 16.

[0057] Other optional overbased detergents can include overbased detergents having a Mannich base structure, as disclosed in U.S. Patent 6,569,818.

[0058] In certain embodiments, the hydrocarbyl substituents on hydroxy-substituted aromatic rings in the above detergents (e.g., phenate, saligenin, salixarate, glyoxylate, or salicylate) are free of or substantially free of C 12 aliphatic hydrocarbyl groups (e.g., less than 1%, 0. 1%, or 0.01% by weight of the substituents are C 12 aliphatic hydrocarbyl groups). In some embodiments such hydrocarbyl substituents contain at least 14 or at least 18 carbon atoms.

[0059] The amount of the detergent in the formulations of the present technology is typically at least 0. 1 weight percent, e.g., 0. 14 to 4 percent by weight, or 0.2 to 3.5 percent by weight, or 0.5 to 3 percent by weight, or 1 to 2 percent by weight. Alternative amounts include 0.5 to 4 percent, 0.6 to 3.5 percent, 1.0 to 3 percent, or 1.5 to 2.8 %, e.g. at least 1.0 percent. One or a plurality of overbased detergents may be present, and if more than one is present, the total amount of such materials may be within the aforementioned percentage ranges.

Viscosity Modifiers [0060] In one embodiment, the lubricating composition further includes one or more viscosity modifiers. When present the viscosity modifier may be present in an amount of 0.5 wt% to 70 wt%, 1 wt% to 60 wt%, or 5 wt% to 50 wt%, or 10 wt% to 50 wt% of the lubricating composition.

[0061] Viscosity modifiers include (a) polymethacrylates, (b) esterified copolymers of (i) a vinyl aromatic monomer and (ii) an unsaturated carboxylic acid, anhydride, or derivatives thereof, (c) esterified interpolymers of (i) an alpha-olefin; and (ii) an unsaturated carboxylic acid, anhydride, or derivatives thereof, or (d) hydrogenated copolymers of styrene-butadiene, (e) ethylene-propylene copolymers, (f) polyisobutenes, (g) hydrogenated styrene-isoprene polymers, (h) hydrogenated isoprene polymers, (i) poly alpha-olefins, or (j) mixtures thereof.

[0062] In one embodiment the viscosity modifier includes (a) a polymethacrylate, (b) an esterified copolymer of (i) a vinyl aromatic monomer; and (ii) an unsaturated carboxylic acid, anhydride, or derivatives thereof, (c) an esterified interpolymer of (i) an alpha- olefin; and (ii) an unsaturated carboxylic acid, anhydride, or derivatives thereof, or (d) mixtures thereof.

[0063] Dispersant viscosity modifiers (often referred to as DVMs) include functionalized polyolefins, for example, ethylene-propylene copolymers that have been functionalized with the reaction product of maleic anhydride and an amine, a polymethacrylate functionalized with an amine, an amine reacted with an esterified interpolymer, or esterified styrene-maleic anhydride copolymers reacted with an amine may also be used in the composition of the invention.

Extreme Pressure Agents [0064] Extreme pressure agents include compounds containing boron and/ or sulfur and/ or phosphorus. The extreme pressure agent may be present in the lubricating composition at 0.0 wt% to 20 wt%, or 0.05 wt% to 10 wt%, or 0. 1 wt% to 8 wt%, or 0.5 wt% to 6 wt% of the lubricating composition.

[0065] In one embodiment the extreme pressure agent is a sulfur-containing compound. In one embodiment the sulfur- containing compound may be a sulfurized olefin, a polysulfide, or mixtures thereof.

[0066] Examples of the sulfurized olefin include a sulfurized olefin derived from propylene, isobutylene, pentene; an organic sulfide and/ or polysulfide including benzyldisulfide; bis- (chlorobenzyl) disulfide; dibutyl tetrasulfide; di-tertiary butyl polysulfide; and sulfurized methyl ester of oleic acid, a sulfurized alkylphenol, a sulfurized dipentene, a sulfurized terpene, a sulfurized Diels- Alder adduct, an alkyl sulfenyl N 'N-dialkyl dithiocarbamates; or mixtures thereof. In one embodiment the sulfurized olefin includes a sulfurized olefin derived from propylene, isobutylene, pentene or mixtures thereof.

[0067] In one embodiment, the extreme pressure agent sulfur- containing compound includes a dimercaptothiadiazole or derivative, or mixtures thereof. Examples of the dimercaptothiadiazole include 2,5-dimercapto- l ,3,4-thiadiazole or a hydrocarbyl- substituted 2,5- dimercapto-1 ,3,4-thiadiazole, or oligomers thereof. The oligomers of hydrocarbyl- substituted 2,5-dimercapto-l,3,4-thiadiazole typically form by forming a sulfur-sulfur bond between 2,5-dimercapto-l ,3,4- thiadiazole units to form derivatives or oligomers of two or more of said thiadiazole units. Suitable 2,5-dimercapto-l ,3,4-thiadiazole derived compounds include 2,5-bis(tert-nonyldithio)- 1 ,3 ,4- thiadiazole or 2-tert-nonyldithio-5-mercapto- 1 ,3 ,4-thiadiazole.

[0068] The number of carbon atoms on the hydrocarbyl substituents of the hydrocarbyl- substituted 2,5-dimercapto-l,3,4- thiadiazole typically include 1 to 30, or 2 to 20, or 3 to 16.

[0069] In one embodiment the extreme pressure agent includes a boron-containing compound. The boron-containing compound includes a borate ester (which in some embodiments may also be referred to as a borated epoxide), a borated alcohol, a borated dispersant or mixtures thereof. In one embodiment the boron- containing compound may be a borate ester or a borated alcohol.

[0070] The borate ester may be prepared by the reaction of a boron compound and at least one compound selected from epoxy compounds, halohydrin compounds, epihalohydrin compounds, alcohols and mixtures thereof. The alcohols include dihydric alcohols, trihydric alcohols or higher alcohols, with the proviso for one embodiment that hydroxyl groups are on adjacent carbon atoms, i.e., vicinal.

[0071] Boron compounds suitable for preparing the borate ester include the various forms selected from the group consisting of boric acid (including metaboric acid, HBO2, orthoboric acid, H3BO3, and tetraboric acid, H2B4O7), boric oxide, boron trioxide and alkyl borates. The borate ester may also be prepared from boron halides.

[0072] In one embodiment suitable borate ester compounds include tripropyl borate, tributyl borate, tripentyl borate, trihexyl borate, triheptyl borate, trioctyl borate, trinonyl borate and tridecyl borate. [0073] In one embodiment the borate ester compounds include tributyl borate, tri-2-ethylhexyl borate or mixtures thereof.

[0074] In one embodiment, the boron-containing compound is a borated dispersant, typically derived from an N-substituted long chain alkenyl succinimide. In one embodiment the borated dispersant includes a polyisobutylene succinimide. Borated dispersants are described in more detail in US Patents 3,087,936; and Patent 3,254,025.

[0075] In one embodiment the borated dispersant may be used in combination with a sulfur-containing compound or a borate ester.

[0076] In one embodiment the extreme pressure agent is other than a borated dispersant.

[0077] The number average molecular weight of the hydrocarbon from which the long chain alkenyl group was derived includes ranges of 350 to 5000, or 500 to 3000, or 550 to 1500. The long chain alkenyl group may have a number average molecular weight of 550, or 750, or 950 to 1000.

[0078] The N-substituted long chain alkenyl succinimides are borated using a variety of agents including boric acid (for example, metaboric acid, HBO2, orthoboric acid, H3BO3, and tetraboric acid, H2B4O7), boric oxide, boron trioxide, and alkyl borates. In one embodiment the borating agent is boric acid which may be used alone or in combination with other borating agents.

[0079] The borated dispersant may be prepared by blending the boron compound and the N-substituted long chain alkenyl succinimides and heating them at a suitable temperature, such as, 80 °C to 250 °C, or 90 °C to 230 °C, or 100 °C to 2 10 °C, until the desired reaction has occurred. The molar ratio of the boron compounds to the N-substituted long chain alkenyl succinimides may have ranges including 10: 1 to 1 :4, or 4: 1 to 1 :3; or the molar ratio of the boron compounds to the N-substituted long chain alkenyl succinimides may be 1 :2.

[0080] An inert liquid may be used in performing the reaction. The liquid may include toluene, xylene, chlorobenzene, dimethylformamide or mixtures thereof.

[0081] In one embodiment the dispersant may be a post treated dispersant. The dispersant may be post treated with dimercaptothiadiazole, optionally in the presence of one or more of a phosphorus compound, a dicarboxylic acid of an aromatic compound, and a borating agent.

[0082] In one embodiment the post treated dispersant may be formed by heating an alkenyl succinimide or succinimide detergent with a phosphorus ester and water to partially hydrolyze the ester. The post treated dispersant of this type is disclosed for example in U.S. Patent 5, 164, 103.

[0083] In one embodiment the post treated dispersant may be produced by preparing a mixture of a dispersant and a dimercaptothiadiazole and heating the mixture above about 100°C. The post treated dispersant of this type is disclosed for example in U.S. Patent 4, 136,043.

[0084] In one embodiment the dispersant may be post treated to form a product prepared comprising heating together: (i) a dispersant (typically a succinimide), (ii) 2,5-dimercapto-l ,3,4-thiadiazole or a hydrocarbyl- substituted 2,5-dimercapto-l, 3, 4-thiadiazole, or oligomers thereof, (iii) a borating agent (similar to those described above); and (iv) optionally a dicarboxylic acid of an aromatic compound selected from the group consisting of 1 ,3 diacids and 1 ,4 diacids (typically terephthalic acid), or (v) optionally a phosphorus acid compound (including either phosphoric acid or phosphorous acid), said heating being sufficient to provide a product of (i), (ii), (iii) and optionally (iv) or optionally (v), which is soluble in an oil of lubricating viscosity. The post treated dispersant of this type is disclosed for example in International Application WO 2006/654726 A.

[0085] Examples of a suitable dimercaptothiadiazole include 2,5-dimercapto-l,3-4-thiadiazole or a hydrocarbyl- substituted 2,5- dimercapto- l ,3-4-thiadiazole. In several embodiments the number of carbon atoms on the hydrocarbyl- substituent group includes 1 to 30, 2 to 25, 4 to 20, or 6 to 16. Examples of suitable 2,5-bis(alkyl- dithio)-l,3,4-thiadiazoles include 2,5-bis(tert-octyldithio)-l,3,4- thiadiazole 2,5-bis(tert-nonyldithio)-l,3,4-thiadiazole, 2,5-bis(tert- decyldithio)- 1 ,3,4-thiadiazole, 2,5-bis(tert-undecyldithio)- 1 ,3,4- thiadiazole, 2,5-bis(tert-dodecyldithio)-l,3,4-thiadiazole, 2,5-bis(tert- tridecyldithio)- l ,3 ,4-thiadiazole, 2,5 -bis(tert-tetradecyldithio)- 1 ,3,4- thiadiazole, 2,5-bis(tert-pentadecyldithio)-l,3,4-thiadiazole, 2,5- bis(tert-hexadecyldithio)- l ,3,4-thiadiazole, 2,5-bis(tert- heptadecyldithio)-l,3,4-thiadiazole, 2,5-bis(tert-octadecyldithio)-l,3,4- thiadiazole, 2,5-bis(tert-nonadecyldithio)-l,3,4-thiadi-azole or 2,5- bis(tert-eicosyldithio)-l,3,4-thiadiazole, or oligomers thereof.

[0086] Friction modifiers include fatty phosphonate esters, amine salts of phosphoric acid esters, reaction products from fatty carboxylic acids reacted with guanidine, aminoguanidine, urea or thiourea, and salts thereof, fatty amines, fatty hydroxyl amines, borated phospholipids, borates, borate esters, fatty phosphites, fatty acid amides, fatty epoxides, borated fatty epoxides, alkoxylated fatty amines, borated alkoxylated fatty amines, fatty poly ethers, metal salts of fatty acids, or fatty imidazolines, condensation products of carboxylic acids and poly alky lene-poly amines, fatty malimides, fatty tartrimides, and fatty oxazolines.

[0087] In one embodiment the lubricating composition may contain phosphorus- or sulfur- containing antiwear agents other than compounds described as an extreme pressure agent of the amine salt of a phosphoric acid ester described above. Examples of the antiwear agent may include a non-ionic phosphorus compound (typically compounds having phosphorus atoms with an oxidation state of +3 or +5), a metal dialkyldithiophosphate (typically zinc dialkyldithiophosphates), a metal mono- or di- alkylphosphate (typically zinc phosphates), or mixtures thereof.

[0088] The non-ionic phosphorus compound includes a phosphite ester, a phosphate ester, or mixtures thereof. A more detailed description of the non-ionic phosphorus compound include column 9, line 48 to column 1 1 , line 8 of US 6, 103,673. Phosphorus containing anti-wear compounds can be included in the lubricant composition at from about 100 to about 2000 ppm, or from about 500 to about 1800 ppm, or from about 700 to about 1500 or 1600 ppm.

[0089] In one embodiment the lubricating composition of the invention further includes a dispersant. The dispersant may be a succinimide dispersant (for example N-substituted long chain alkenyl succinimides), a Mannich dispersant, an ester-containing dispersant, a condensation product of a fatty hydrocarbyl monocarboxylic acylating agent with an amine or ammonia, an alkyl amino phenol dispersant, a hydrocarbyl-amine dispersant, a polyether dispersant or a poly ether amine dispersant.

[0090] In one embodiment the succinimide dispersant includes a polyisobutylene-substituted succinimide, wherein the polyisobutylene from which the dispersant is derived may have a number average molecular weight of 400 to 5000, or 950 to 1600.

[0091] Succinimide dispersants and their methods of preparation are more fully described in US Patents 3, 172,892, 3,219,666, 3,316, 177, 3,340,281 , 3,351 ,552, 3,381 ,022, 3,433,744, 3,444, 170, 3,467,668, 3,501 ,405, 3,542,680, 3,576,743, 3,632,51 1 , 4,234,435, Re 26,433, and 6, 165,235, 7,238,650 and EP Patent Application 0 355 895 A.

[0092] Suitable ester-containing dispersants are typically high molecular weight esters. These materials are described in more detail in U.S. Patent 3,381 ,022.

[0093] In one embodiment the dispersant includes a borated dispersant.

[0094] Typically the borated dispersant includes a succinimide dispersant including a polyisobutylene succinimide, wherein the polyisobutylene from which the dispersant is derived may have a number average molecular weight of 400 to 5000. Borated dispersants are described in more detail above within the extreme pressure agent description.

[0095] Dispersants may be added to the lubricant compositions described at a range of from about 0. 1 to 5 weight%, or from about 0.5 to about 4 weight%, or even from about 1 .0 to about 2.5 or 3 weight%. [0096] Corrosion inhibitors include amides, imidazolines, amines, fatty amines, l-amino-2-propanol, octylamine octanoate, condensation products of dodecenyl succinic acid or anhydride and/ or a fatty acid such as oleic acid with a poly amine.

[0097] Metal deactivators include derivatives of benzotriazoles (typically tolyltriazole), 1 ,2,4-triazoles, benzimidazoles, 2- alkyldithiobenzimidazoles, thiadiazoles, or 2- alkyldithiobenzothiazoles. The metal deactivators may also be described as corrosion inhibitors.

[0098] Foam inhibitors include copolymers of ethyl acrylate and 2-ethylhexylacrylate and optionally vinyl acetate. Also included are siloxanes, typically polydimethylsiloxanes

[0099] Demulsifiers include trialkyl phosphates, and various polymers and copolymers of ethylene glycol, ethylene oxide, propylene oxide, or mixtures thereof.

[00100] Pour point depressants include esters of maleic anhydride -styrene, polymethacrylates, polyacrylates or polyacrylamides.

[00101] Seal swell agents include Exxon Necton-37™ (FN 1380) and Exxon_Mineral Seal Oil™ (FN 3200).

Industrial Application

[00102] The self-contained lubricant of the limited slip differential is generally different from the lubricant supplied to a manual transmission or an automatic transmission fluid.

[00103] An axle gear may have any one of a number of different types of differentials. A differential typically has three major functions. The first function is to transmit engine power to the wheels. The second function is act as the final gear reduction in the vehicle, slowing the rotational speed from the transmission to the wheels. The third function is to transmit the power to the wheels while allowing them to rotate at different speeds. A number of differentials are known and include an open differential, a clutch-type limited slip differential, a viscous coupling differential, a Torsen differential and a locking differential. All of these differentials may be generically referred to as axle gears.

[00104] Axle gears typically require a lubricant. The lubricant formulation is dependent on the type of axle gear, and the operating conditions of the axle gear. For example, an open differential axle gear is believed to require antiwear and/or extreme pressure additives. A limited slip differential further requires a friction modifier because, in addition to an open differential (known from many axle fluids), a spring pack and a clutch pack are typically present. The clutch pack may contain one or more reaction plates (often made from steel) and one or more friction plates. The friction plates are known, and may be made from a number of materials including paper, carbon, graphite, steel and a composite.

[00105] The lubricating composition suitable for the limited slip differential may have a sulfur content in the range of 0.3 wt% to 5 wt%, or 0.5 wt% to 5 wt%, or 0.5 wt% to 3 wt% or 0.8 wt% to 2.5 wt%, or 1 wt% to 2 wt%.

[00106] In one embodiment the lubricating composition suitable for the limited slip differential may be a fully formulated fluid.

[00107] In one embodiment the lubricating composition suitable for the limited slip differential may be a top treat concentrate.

[00108] When the lubricating composition is in the form of a top treat concentrate, the concentrate may be added at an actives level of about 0. 1 wt% to 10 wt%, or 0.2 wt% to 7 wt%, 0.25 wt% to 2, 3, 4 or 5%, or even 0.25 to 1 wt%, or 1.0 to 3.0 wt% relative to the amount of lubricant in a limited slip differential.

[00109] In an embodiment of the invention, a method of providing limited slip performance is provided comprising introducing a lubricating composition as disclosed herein to a differential, and operating the differential.

[00110] The lubricant composition and method disclosed herein may be suitable for limited slip systems having one or more distinct plate materials. For example the plate materials may be steel, paper, ceramic, carbon fibers and systems employing a mixture of plate types such as steel on ceramic, carbon fibers in paper or steel on paper.

[00111] The amount of each chemical component described is presented exclusive of any solvent or diluent oil, which may be customarily present in the commercial material, that is, on an active chemical basis, unless otherwise indicated. However, unless otherwise indicated, each chemical or composition referred to herein should be interpreted as being a commercial grade material which may contain the isomers, by-products, derivatives, and other such materials which are normally understood to be present in the commercial grade.

[00112] It is known that some of the materials described above may interact in the final formulation, so that the components of the final formulation may be different from those that are initially added. For instance, metal ions (of, e.g., a detergent) can migrate to other acidic or anionic sites of other molecules. The products formed thereby, including the products formed upon employing the composition of the present invention in its intended use, may not be susceptible of easy description. Nevertheless, all such modifications and reaction products are included within the scope of the present invention; the present invention encompasses the composition prepared by admixing the components described above.

EXAMPLES

[00113] Preparative Example 1 (EX1 ):

[00114] Aminopropyl oleylamine (682g) is charged to a 2L 4-necked flask fitted with a thermowell and heated. Oleic acid (621.5g) is added to the amine over 15 minutes via addition funnel. The reaction mixture is heated to reflux and distillate is collected. The final product is a white waxy solid at room temperature.

Axle Lubricants

[00115] Comparative Example 1 (CE1) is a commercially available axle fluid having the formulation in table 1 , and containing no additional limited slip friction modifier.

[00116] Inventive Example 1 (IE1) is a commercially available axle fluid which has been top-treated with 1.8 wt % of preparative example 1.

[00117] Lubricants for testing are prepared by adding one of the materials from the preparative examples identified in the tables below to the indicated base formulation. The lubricants containing EX1 are evaluated in a Full-Scale Low- Velocity Friction Apparatus (FSLVFA). The apparatus uses a clutch test specimen as defined by SAE Paper 2010-01-2231. The test is run while varying the speed, temperature and pressure. The test consists of friction performance evaluations at the beginning and after a 17-hour durability stage. A break-in phase runs 10 minutes at 90 °C oil temperature, 16 rpm, and 7070 N load. The phase conditions the clutch system for the pre-durability performance evaluation. The pre-durability performance evaluation is achieved by ramping the speed from 0 to 5 rpm in 5 seconds, then back to zero. Load is set to two levels, 3535 N and 7070 N, which correspond to the range of axial compressive load imposed by the axle's internal clutch pack. The above two loads are evaluated at three oil temperatures: 40 °C, 90 °C, and 120 °C. The sample clutch pack undergoes a durability phase that involves running the test rig for 17 hours at 120 °C oil temperature, 7070 N load, and 16 rpm. The post- durability evaluation is then run using the same conditions as the pretest evaluation. A more detailed description of the test procedure is provided in SAE Paper 2010-01-2231. The table below shows a post- durability rating of NVH (at 5 rpm) and curvature. The data obtained is as follows:

Post durability Curvature and NVH at 5 rpm at 40°C and 77N

*a - Miba™ MC-631

*b - Hoerbiger™ HC- 100

*c - FCC™ 3312

Footnotes:

Noise, Vibration, Harshness (NVH) at 5 rpm is the standard deviation of the torque signal based upon a moving average of the torque signal during the 2 second hold at 5 rpm. A high NVH rating is indicative of the occurrence of "stick-slip" at the friction surface. Torque spikes when the plates "stick" and drops when the plates "slip". NVH describes the amplitude of the torque signal and is independent of the shape of the torque signal. Good FM candidates should have low NVH at 5 rpm.

Curvature describes the shape of the torque signal which is believed to be related to the difference between the static and dynamic friction coefficients. Curvature is the average difference between the torque when the plates breakaway and come to rest versus the torque during the 2 second hold at 5rpms. A positive curvature means the torque signal is concave down during the sweep (bows downward). A negative curvature means the torque signal is concave up (bows upward) during the sweep. Ideally curvature should be close to zero which would mean the torque signal is flat across all speeds. Slight negative curvature value is acceptable but high positive curvature value is less desirable.

[00118] Each of the documents referred to above is incorporated herein by reference. The mention of any document is not an admission that such document qualifies as prior art or constitutes the general knowledge of the skilled person in any jurisdiction. Except in the Examples, or where otherwise explicitly indicated, all numerical quantities in this description specifying amounts of materials, reaction conditions, molecular weights, number of carbon atoms, and the like, are to be understood as modified by the word "about." It is to be understood that the upper and lower amount, range, and ratio limits set forth herein may be independently combined. Similarly, the ranges and amounts for each element of the invention can be used together with ranges or amounts for any of the other elements.