Internal combustion engines usually function by the combustion of fuels which in turn generate the power needed to propel vehicles. In the case of a diesel engine, the fuel is a diesel fuel and the combustion thereof generally results in emissions from the exhausts of such vehicles which comprise three main components. These are : soot, particulate matter and nitrogen oxides (the latter will hereafter be abbreviated as NOx for convenience). Of these, soot is generally formed as a result of incomplete combustion of the fuel. Soot adversely affects the performance of lubricants by increasing their viscosity (by accumulation of soot in the lubricant) and by causing wear. Moreover, it is important that the presence of soot does not increase the viscosity of the lubricant to undesirably high levels for it is also important to maintain the viscosity within the normal grades in order to enable quick and clean drainage of the engine during servicing. The formation of soot may be alleviated to a significant extent by operating the diesel engine at relatively higher temperatures. However, the higher temperatures whilst mitigating the formation of soot also result in the formation of increased amounts of NOx. If, however, the engine temperature is lowered, incomplete combustion ensues and whilst this reduces the amount of NOx formed in the emissions, it also substantially increases the amount of soot generated. The soot so formed can manifest itself in two ways. It can either appear as a thick black smoke emitted from the exhaust of the vehicle or can be accumulated in the engine lubricant. As the soot builds up in the lubricant, the latter becomes more and more viscous and upon reaching a critical value can cause gelation of the lubricant and may eventually cause seizure of the engine. Several methods have been tried to alleviate this problem including the use of one or more of dispersants, metal salts and solvents which may be ethers, esters and the like. The dispersants function by forming a coating of the dispersant on the surface of soot particles and thereby minimising the tendency of the soot particles to agglomerate. However, the potency of the dispersants to perform this function, in turn, declines with time and thus, one of the methods of improving the useful life of lubricants, particularly crankcase lubricants, would be to improve the dispersancy retention capability of crankcase lubricants. This may be achieved, eg by minimising the risk of oxidation of the dispersants under the conditions prevalent in the engines during use.

Recently published US-A-5, 837, 657 describes a method for improving the performance of a sooted diesel oil and controlling soot induced viscosity increase by adding to the diesel oil a minor amount of a trinuclear molydenum compound of the structure, M03SkLnQz. The ability of this compound to bind with soot is compared with conventional antioxidants such as eg diphenylamine, hindered phenols and zinc dithiodiphosphates

(ZDDP). The conclusion is that the trinuclear molybdenum compounds are far superior in controlling the soot induced viscosity increase than the other compounds tested.

The object of the present invention is to devise a method of mitigating the problem of soot induced viscosity increase in diesel lubricants by maximising the period for which the soot remains in the lubricant in a well dispersed state thereby controlling the rise in the absolute viscosity of the lubricant within the desired ranges for as long as is possible, ie minimising the increase in soot induced viscosity of the lubricant for longer than has been possible hitherto. At the same time, the object of the present invention is to improve the dispersancy retention capability of such lubricants.

It has now been found, however, that the performance of these trinuclear molybdenum compounds can be further improved by using these in combination with amines and/or phenolic compounds for the purpose of controlling soot induced viscosity increase especially in aged oils.

Accordingly, the present invention comprises diesel engine lubricant composition comprising a base stock, a dispersant and an antioxidant comprising an oil soluble trinuclear organomolybdenum compound of the generic formula : Mo3Sx-(Q) (I) wherein x is from 4 to 10, preferably 7, and Q is a core group, which may be a ligand, and at least one other compound selected from a phenolic and an aminic compound.

The compositions of the present invention are those that comprise a major amount of a lubricating oil as base stock suitable for use in an engine crankcase, particularly a diesel engine crankcase. Thus, natural or synthetic lubricating oils having a kinematic viscosity of 3. 5 to 25 cSt at 100°C comprise a major portion of the lubricating compositions.

The dispersancy retention properties of such lubricant compositions is improved in accord with this invention by including in the crankcase lubricant an added oil soluble organomolybdenum compound and at least one other compound selected from a phenolic and an aminic compound.

The trinuclear molybdenum compounds are of formula (I) Mo3Sx-(Q) (I) wherein x is from 4 to 10, preferably 7, and Q is a core group are relatively new and are claimed and described in our prior published US-A-5, 906, 968. The matter disclosed in this prior US patent on the structure, preparation and properties of the trinuclear molybdenum compounds is incorporated herein by reference. In these compounds the core group (Q) may be a ligand capable of rendering the organomolybdenum compound of formula (I) oil soluble and ensuring that said molybdenum compound is substantially charge neutral. The core group (Q) is generally associated with suitable ligands such as Ly wherein L is the ligand and y is of a sufficient number, type and charge to render the compound of formula (I) oil soluble and to neutralise the charge on the compound of formula (I) as a whole. Thus, more

specifically, the trinuclear molybdenum compound used in the compositions of the present invention may be represented by the formula (II) : M03S. Ly (II) The ligands"L"are suitably dihydrocarbyl dithiocarbamates of the structure (-S2CNR2) wherein the dihydrocarbyl groups, R2 impart oil solubility to the molybdenum compound. In this instance, the term"hydrocarbyl"denotes a substituent having carbon atoms directly attached to the remainder of the ligand and is predominantly hydrocarbyl in character within the context of this invention. Such substituents include the following : (1) hydrocarbon substituents, ie, aliphatic (for example alkyl or alkenyl), alicyclic (for example cycloalkyl or cycloalkenyl), aromatic-, aliphatic-and alicyclic-substituted aromatic nuclei and the like, as well as cyclic substituents wherein the ring is completed through another portion of the ligand (that is, any two indicated substituents may together form an alicyclic group) ; (2) substituted hydrocarbon substituents, ie, those containing nonhydrocarbon groups which, in the context of this invention, do not alter the predominantly hydrocarbyl character of the substituent. Those skilled in the art will be aware of suitable groups (eg halo (especially chloro), amino, alkoxyl, mercapto, alkylmercapto, nitro, nitroso, sulphoxy etc.) ; and (3) hetero substituents, ie, substituents which, while predominantly hydrocarbon in character within the context of this invention, contain atoms other than carbon present in a chain or ring otherwise composed of carbon atoms.

The hydrocarbyl groups are preferably alkyl (e. g, in which the carbon atom attached to the remainder of the ligand"L"is primary, secondary or tertiary), aryl, substituted aryl and/or ether groups.

Importantly, the hydrocarbyl groups of the ligands should be such that they have a sufficient number of carbon atoms to render the compound (I) soluble or dispersible in the oil to which the trinuclear organomolybdenum compound containing the ligand is added.

The total number of carbon atoms present among all of the hydrocarbyl groups of the organomolybdenum compounds'ligands is suitably at least 21, preferably at least 25, more preferably at least 30 and even more preferably at least 35, typically e. g., 21 to 800. For instance, the number of carbon atoms in each hydrocarbyl group will generally range from 1 to 100, preferably from 1 to 40 and more preferably from 3 to 20.

The antioxidant in the compositions of the present invention suitably also include at least one other compound selected from a phenolic compound and an aminic compound.

Among the phenolic compounds, hindered phenols are preferred.

The antioxidant in the compositions of the present invention suitably also include at least one other compound selected from a phenolic compound and an aminic compound. Among the phenolic compounds, hindered phenols are preferred.

Examples of such phenolic compounds include inter alia : 4, 4'-methylene bis (2, 6-di-tert-butylphenol) 4, 4'-bis (2, 6-di-tert-butylphenol) 4, 4'-bis (2-methyl-6-tert-butylphenol) 2, 2'-methylene bis (4-ethyl-6-tert-butylphenol) 2, 2'-methylene bis (4-methyl-6-tert-butylphenol) 4, 4'-butylidene bis (3-methyl-6-tert-butylphenol) 4, 4'-isopropylidene bis (2, 6-di-tert-butylphenol) 2, 2'-methylene bis (4-methyl-6-nonylphenol) 2, 2'-isobutylidene bis (4, 6-dimethyl phenol) 2, 2'-methylene bis (4-methyl-6-cyclohexylphenol) 2, 6-di-tert-butyl-4-methylphenol 2, 6-di-tert-butyl-4-ethylphenol and 2, 4-dimethyl-6-tert-butylphenol Specific hindered phenols which are preferred as the antioxidants may be represented by the generic formulae (III)- (IV) below in which Rl, R2, and R3 are the same or different alkyl groups from 3-9 carbon atoms and x and y are integers from 1 to 4.

(III) (IV) (V)

Suitable aminic compounds for use in the compositions of the present invention are diaryl amines, aryl naphthyl amines and alkyl derivatives of diaryl amines and the aryl naphthyl amines. Preferred aminic antioxidants are represented by the formulae (VII) and (VIII) wherein each of R4and R5is a hydrogen atom or represents the same or different alkyl groups from 1-8 carbon atoms.

(VII) (VIII) Specific examples of the aminic compounds that may be used in the compositions of the present invention include inter alia : Monoalkyldiphenyl amines such as eg monooctyldiphenyl amine and monononyl diphenyl amine ; dialkyldiphenyl amines such as eg 4, 4'-dibutyldiphenyl amine, 4, 4'- dipentyldiphenyl amine, 4, 4'-dihexyldiphenyl amine, 4, 4'-diheptyldiphenyl amine, 4, 4'- dioctyldiphenyl amine and 4, 4'-dinonyldiphenyl amine ; polyalkyldiphenyl amines such as eg tetra-butyldiphenyl amine, tetra-hexyldiphenyl amine, tetra-octyldiphenyl amine and tetra- nonyldiphenyl amine ; the naphthylamines such as eg a-naphthylamine and phenyl-a- naphthylamine ; butylpheny-a-naphthylamine, pentylphenyl-a-naphthylamine, hexylphenyl- a-naphthylamine, heptylphenyl-a-naphthylamine, octylphenyl-a-naphthylamine and

nonylphenyl-a-naphthylamine. Of these, dialkyldiphenyl amine and naphthylamines are preferable.

In general, the antioxidant which comprises the organomolybdenum compound in combination with a phenolic and/or an aminic compound will form a minor component of the total lubricant composition. For example, the organomolybdenum compound typically will comprise about 0. 05 to about 5. 00 wt % of the total composition, preferably from 0. 05 to 2. 0 wt%, and more preferably from 0. 1 to 0. 7 wt%, i. e., the molybdenum metal is suitably present in an amount of from about 25 to 2500 ppm, preferably from about 50 to 1000 ppm, and more preferably from 100 to 700 ppm, and the phenolic and/or aminic compounds about 0. 10 to about 3. 0 wt % of the total composition.

It has also been found that if the weight ratio of organomolybdenum compound to the phenolic and/or aminic compound in the antioxidant is in the range of about 80 : 20 to about 20 : 80, optimum dispersancy retention can be achieved by these combined antioxidants of the present invention.

It is particularly preferred that the antioxidant comprises in addition to the organo molybdenum compound a mixture of the phenols (III) and (IV) above and the diaryl amine (V) in a weight ratio ranging from about 80 : 10 : 10 to about 40 : 20 : 40 respectively, preferably typically 75 : 15 : 15 respectively.

Optionally, the antioxidants may be combined with a carrier liquid in the form of a concentrate. The concentration of the combined antioxidants in the concentrate may vary from 1 to 80% by weight, and will preferably be in the range of 5 to 10% by weight.

The antioxidant combination of the present invention can be used with any of the conventional dispersants used hitherto in the lubricating compositions. Examples of such dispersants include inter alia the polyalkylene succinimides, Mannich condensation products of polylalkylphenol-formaldehyde polyamine and boronated derivatives thereof. However, it is preferable to use ashless dispersants such as the ashless succinimides, especially the polyisobutenyl succinimides of a polyamine such as eg tetraethylenepentamine or its homologues, benzylamine ashless dispersants, and ester ashless dispersants. The dispersants are generally used in the compositions of the present invention in an amount ranging from about 2-10% by weight based on the total weight of the lubricant composition, preferably from about 4-8% by weight.

In general, these lubricating compositions may include additives commonly used in lubricating oils especially crankcase lubricants, such as antiwear agents, detergents, rust inhibitors, viscosity index improvers, extreme-pressure agents, friction modifiers, corrosion inhibitors, emulsifying aids, pour point depressants, anti-foams and the like.

A feature of the lubricant compositions of the present invention is that the presence therein of trinuclear organomolybdenum compounds in combination with a phenolic and/or an aminic compound as antioxidant provides unexpected improvement in oxidation control, viscosity increase control and dispersancy retention over compositions which contain only one of these antioxidants used alone.

The present invention is further illustrated with reference to the following Examples : EXAMPLES General Procedure : A series of Test oils were prepared. These oils were then tested in a bench oxidation test which was conducted at 165°C under a mixed nitrogen/air flow, with 40 ppm iron from added ferric acetylacetonate as catalyst. The flow rates of air and nitrogen were controlled at 500 ml/min and 350ml/min respectively.

The remaining dispersancy of the Test oil after 32 hours in the bench oxidation test was then determined by use of a GM 6. 2L soot-laden basestock dispersancy test in which the soot dispersancy of an used oil was determined by viscosity ratio of the diluted Test oil in the presence and absence of soot ; the lower the ratio, the better the dispersancy. The Test oil was mixed with a soot-laden 600 SN basestock (3. 5-4. 5% by weight soot) from the GM 6. 2L engine at the ratio of 25 : 75 by weight and the kinematic viscosity at 100°C of the Test oil and fresh base oil (soot-free 600SN) mixture at the same ratio (25 : 75) was also measured.

Fresh oil dispersancy was also determined using the same method.

In these tests the following commercial materials have been used : Irganox0 L57 is an octylated/butylated diphenylamine (ex Ciba Geigy) Irganox@ L101 is a high molecular weight phenolic antioxidant (ex Ciba Geigy) Irganox Ll 15 and Irganox L 1035 are high molecular weight phenolic antioxidants with a thioether group (ex Ciba Geigy) Irganox (D L06 is an alkylated phenyl-a-naphthylamine (ex Ciba Geigy) Irganox L135 is a high molecular weight phenolic antioxidant (ex Ciba Geigy) Irganox LI 50 is a mixture of alkylated diphenylamine, a phenolic antioxidant and a phenolic antioxidant with a thioether group (ex Ciba Geigy) Paranox@ 106 is a polyisobutenylsuccinimide dispersant (ex Infenium, Linden, NJ) Molyvan0 822 is a dinuclear molybdenum dithiocarbamate (ex R T Vanderbilt Co) Examples A-E The compositions of the Test oils A-E are shown in Table 1 below : TABLE 1 Test Oils A B C D E 600 SN (% wt) 94. 0 93. 0 93. 0 93. 0 93. 0 Paranox0 106 (% wt) 6. 0 6. 0 6. 0 6. 0 6. 0 Irganox (D L150 1. 0 0. 5 0. 5 Mo3-dithiocarbamate*1. 00. 5 Molyvan# 822 (% wt) - - - - 0.5 *containing 11. 5% by weight of molybdenum The characteristics of the fresh Test oils (A-E) are shown in Table 2 below : TABLE 2

Test Oils A B C D E Fresh Oil KV, oo (cSt) 13. 08 13. 06 13. 28 13. 17 13. 05 KVIoo of Test Oil/Soot-14. 84 14. 91 15. 24 14. 52 14. 86 Laden 600SN (4. 4 wt% soot) Mixture (25/75) (cSt) Calculated Ka, oxo of Test 11. 74 11. 73 11. 79 11. 76 11. 73 oil/Fresh 600SN Mixture (25/75) (cSt*) Relative Viscosity 1. 26 1. 27 1. 29 1. 23 1. 27 (Viscosity Ratio), llr (Fresh oil) * Based on additive rule KV (mix) = f KV (1) + (1-f) KV (2) in which f is the mass fraction of component 1.

The following Table 3 shows the characteristics of the used oils (A-E) after the oxidation test.

TABLE 3 Test Oils A B C D E Used Oil KV100 (cSt) 30. 99 14. 52 13. 77 13. 29 13. 59 KV, of Used Oil/Soot-24. 35 19. 05 18. 55 16. 16 17. 84 Laden 600SN (4. 4 wt% soot) Mixture (25/75) (cSt) Calculated KVI oo of Used 13. 85 11. 96 11. 87 11. 77 11. 82 oil/Fresh 600SN Mixture (25/75) (cSt) Relative Viscosity 1. 76 1. 59 1. 56 1. 37 1. 51 (Viscosity Ratio), il, (Used oil)

From the above results it is clear that the compositions containng the trinuclear molybdenum compound according to the present invention significantly improves the viscosity control and the dispersancy retention capability of the composition.

Eamples F-R Using the same methods and materials as described under the General Procedure above for Examples (A-E), the following further tests were carried out on additional Test oils.

The compositions o the Test oils used in Examples (F-R) are shown in Table 4 below:<BR> TABLE 4 Test Oils F G H I J K L M N O P Q R 600 SN (% wt) 94.0 93.0 93.0 93.0 93.0 93.0 93.0 93.0 93.0 93.0 93.0 93.0 93.0 Paranox# 106 (% wt) 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 Irganox# L115 - 1.0 - - - - - 0.5 - - - 0.5 - Irganox# L135 - - 1.0 - - - - - 0.5 - - - - Irganox# L06 - - - 1.0 - - - - - 0.5 - - 0.5 Irganox# L57 - - - - 1.0 - - - - - 0.5 - - Mo3-dithiocarbamate* - - - - - 1.0 - 0.5 0.5 0.5 0.5 - - Molyvan#822 (% wt) - - - - - - 1.0 - - - - 0.5 0.5 #contaming 11.5% by weight of molybdenum As previously with Examples (A-E), the characteristics of the fresh oil used in F-R are shown in Table 5 below:<BR> TABLE 5 Test Oils F G H I J K L M N O P Q R Fresh Oil KV100 (cSt) 13.04 13.11 12.92 13.03 12.96 13.20 12.98 13.17 13.06 13.11 13.09 13.03 13.02 KV100 of Test Oil/Soot- 14.14 14.30 14.198 14.16 14.81 14.16 14.10 14.02 13.94 14.00 14.16 14.26 Laden 600SN (4.4 wt% soot) Mixture (25/75) (cSt) Calculated KV100 of Test 11.71 11.73 11.68 11.71 11.69 11.75 11.70 11.75 11.72 11.73 11.73 11.71 11.71 oil/Fresh 600SN Mixture (25/75) (cSt*) Relative Vicosity 1.21 1.22 1.21 1.21 1.21 1.26 1.21 1.20 1.20 1.19 1.19 1.21 1.22 (Viscosity Ratio), #r (Fresh oil) * Based on additive rule KV (mix) = fKV(1) + (1-f)KV(2) in which f is the mass fraction of componet 1.

As previously with Examples (A-E), Table 6 below shows the characteristics of the Used oil in Examples F-R:<BR> TABLE 6 Test Oils F G H I J K L M N O P Q R Used Oil KV100 (cSt) 44.03 24.48 48.38 28.34 14.74 13.73 17.44 13.35 13.29 13.34 13.32 17.76 13.79 KV100 of Used Oil/Soot- 25.37 19.76 31.17 25.26 16.77 16.12 17.25 15.38 15.27 14.64 14.84 17.32 15.71 Laden 600SN (4.4 wt% soot) Mixture (25/75) (cSt) Calculated KV100 of Used 17.30 14.33 19.92 15.79 12.00 11.82 12.43 11.75 11.74 11.77 11.75 12.48 11.83 oil/Fresh 600SN Mixture (25/75) (cSt) Relative Viscosity 1.47 1.38 1.56 1.60 1.40 1.36 1.39 1.31 1.30 1.24 1.26 1.39 1.33 (Viscosity Ratio), #r (Used oil)