Patent Publication Number: US-2006014653-A1

Title: Lubricating oil composition

Description:
FIELD OF THE INVENTION  
      The present invention relates to a lubricating oil composition, in particular to a lubricating oil composition which is suitable for lubricating internal combustion engines.  
     BACKGROUND OF THE INVENTION  
      Total Base Number (TBN) is a measure of how well a lubricating oil composition can neutralise acidic by-products of combustion/oxidation and is defined as the quantity of acid, expressed in terms of the equivalent number of milligrams of potassium hydroxide, that is required to neutralize all basic constituents present in 1 gram of a sample of the lubricating oil composition (test methods include, for example, ISO 3771, ASTM D-2896 and ASTM D-4739).  
      A high TBN is desirable in lubricating oil compositions in order to control corrosive engine wear from the acidic by-products of combustion/oxidation. Detergent additives in a lubricating oil composition are the primary source of alkalinity (TBN) and help to control, for example, top-ring deposits and bore polish.  
      Hence, metal-based detergents are the primary source of TBN in crankcase lubricating oil compositions.  
      In view of the adverse affects that the sulphated ash, sulphur and phosphorus concentrations of lubricating oil compositions may have on vehicle exhaust after-treatment devices, there is a trend towards lubricating oil compositions having reduced sulphated ash, sulphur and/or phosphorus concentrations therein (i.e. so-called low-SAPS lubricating oil compositions).  
      Phosphorus concentrations may be generally reduced by reducing the amount of zinc dithiophosphates which are present as anti-wear additives in lubricating oil compositions.  
      Sulphur levels in lubricating oil compositions may be reduced by employing low sulphur level base oils and reducing the amount of sulphur-containing additives employed therein.  
      Sulphated ash is the total weight percent of residue remaining after a lubricating oil composition has been carbonised, and the residue subsequently treated with sulphuric acid and heated to constant weight. The sulphated ash content in a lubricating oil composition is related to the total metal content therein. Sulphated ash may be conveniently measured according to ASTM D874.  
      The major sources of sulphated ash in a lubricating oil composition are generally any metal detergent additives and zinc dithiophosphate anti-wear additives that are employed therein.  
      Hence, in current low-SAPS lubricating oil compositions, sulphated ash levels, and consequently detergent levels, are low. As a result, the starting TBN (i.e. of fresh un-used lubricating oil compositions) of low-SAPS lubricating oil compositions tends to be lower than in lubricating oil compositions having higher sulphated ash, sulphur and/or phosphorus concentrations therein.  
      Thus, TBN retention (i.e. the ability to maintain an advantageous TBN level throughout the lifetime of a lubricating oil composition) is of increased importance for low-SAPS lubricating oil compositions which have lower starting TBNs.  
      U.S. 2004/0102335 A1 describes lubricating oil compositions containing an additive formulation including at least one sulphonate, saligenin and salixarate detergent. However, it is apparent from the Working Examples in U.S. 2004/0102335 A1 that said lubricating oil compositions employ high TBN detergents therein. In this regard, it is of note that the Working Examples in U.S. 2004/0102335 A1 all employ a high TBN calcium sulphonate detergent therein as a TBN booster. Furthermore, U.S. 2004/0102335 A1 is concerned with the development of lubricating oil compositions with improved wear performance and is not directed to the problem of TBN retention for low-SAPs lubricating oil compositions which have lower starting TBNs.  
      EP-A-1167497 discloses a lubricating oil composition having a sulphur content of 0.01 to 0.3 wt. % and a phosphorus content of 0.01 to 0.1 wt. %, and giving a sulphated ash content in the range of 0.1 to 1 wt. %, which is said to have good high temperature detergency, and which comprises: 
      a) a major amount of a mineral base oil having a sulphur content of at most 0.1 wt. %;     b) an ashless dispersant comprising an alkenyl- or alkyl-succinimide or a derivative thereof in an amount of 0.01 to 0.3 wt. % in terms of a nitrogen atom content;     c) a metal-containing detergent containing an organic acid metal salt which is selected from the group consisting of a non-sulphurised alkali metal or alkaline earth metal salt of an alkylsalicylic acid having a TBN of 10 to 350 mg.KOH/g and a non-sulphurised alkali metal or alkaline earth metal salt of an alkylphenol derivative having a Mannich base structure, in an amount of 0.1 to 1 wt. % in terms of a sulphated ash content;     d) a zinc dialkyldithiophosphate in an amount of 0.01 to 0.1 wt. % in terms of a phosphorus content; and     e) an oxidation inhibitor selected from the group consisting of a phenol compound and an amine compound in an amount of 0.01 to 5 wt. %.    

      EP-A-1167497 is in no way concerned with the problem of achieving good TBN retention, in particular with regard to the VW T4 test (PV 1449).  
      EP-A-1104800 describes a lubricating oil composition for internal combustion engines which comprises 
      a) a major amount of a base oil of lubricating viscosity,     b) a metal-containing detergent in an amount of 0.1 to 1 wt % in terms of its sulfated ash content,     c) a boron-containing alkenyl- or alkylsuccinimide in an amount of 1.0 to 15 wt % in terms of its active ingredient,     d) a zinc dialkyldithiophosphate in an amount of 0.1 to 0.1 wt % in terms of its phosphorus content,     e) an oxidation inhibitor in an amount of 0.1 to 5 wt % in terms of its active ingredient, and     f) an ashless dithiocarbamate in an amount of 0.1 to 5 wt % in terms of its active ingredient.    

      U.S. 2003/0148900 A1 discloses a lubricating oil composition for use in natural gas engines which comprises a minor amount of one or more specific hindered phenols and a major amount of at leats one of Group II, III and IV base oils. U.S. 2003/0148900 A1 indicates that increased amounts of antioxidants may have a detrimental effect on piston deposit control. Accordingly, U.S. 2003/0148900 A1 is directed to a method to increase the oxidation life of lubricating oil base oil without increasing the amount of antioxidant therein. However, U.S. 2003/0148900 A1 is not concerned with the problem of TBN retention for low-SAPS lubricating oil compositions which have lower starting TBNs.  
      WO-A-03/083020 describes a method of operating an internal combustion engine that comprises introducing a nitrogen-containing detergent composition into a combustion chamber during the operation of the engine.  
      Said detergent composition comprises 
      (A) a reaction product of a hydrocarbyl-substituted acylating agent and an amine;     (B) a hydrocarbyol-substituted amine;     (C) a Mannich reaction product of a hydrocarbyl-substituted hydroxy-containing aromatic compound, an aldehyde, and an amine;     (D) a high molecular weight polyetheramine prepared by reacting one unit of a hydroxy-containing hydrocarbyl compound with two or more units of butylene oxide to form apolyether intermediate, and aminating the polyether intermediate by reacting the polyether intermediate with an amine or with acrylonitrile and hydrogenating the reaction product of the polyether intermediate and acrylnitrile; or     (E) a mixture thereof.    

      U.S. Pat. No. 5,595,964 describes a method of lubricating a natural gas-fuelled internal combustion engine, comprising supplying thereto a lubricating oil composition comprising an oil of lubricating viscosity, an antioxidant, an anti-nitration agent and preferably at least about 0.1 wt. % of a borated product of an epoxide, wherein the composition is substantially free of metals and wherein the amount of the antioxidant and the anti-nitration agent are sufficient to reduce the amount of varnish formation in a natural gas-fuelled internal combustion engine. The total amount of antioxidant used in said lubricating oil composition is said to be at least 1.8 wt. %, preferably at least 2 wt. %. The lubricating oil composition of U.S. Pat. No. 5,595,964 is said to contain less than 1% sulphated ash, as determined by ASTM D874. The phosphorus level of the lubricating oil composition of U.S. Pat. No. 5,595,964 is said to preferably be less than 0.03% phosphorus, more preferably less than 0.005% phosphorus. It is of note that U.S. Pat. No. 5,595,964 is concerned with reducing varnish formation in a natural gas-fuelled internal combustion engine by the presence of an anti-nitration agent in addition to antioxidant in a lubricating oil composition.  
      U.S. Pat. No. 5,595,964 neither identifies nor addresses the problem of poor TBN retention in lubricating oil compositions having reduced sulphated ash, sulphur and/or phosphorus concentrations therein, and in particular in low-SAPS lubricating oil compositions which have lower starting TBNs. There is no disclosure in U.S. Pat. No. 5,595,964 to suggest how to achieve good TBN retention in such lubricating oil compositions, particularly in order to pass the VW T4 test (PV 1449).  
     SUMMARY OF THE INVENTION  
      A lubricating oil composition is provided for internal combustion engines having a sulphated ash content of not greater than 0.9 wt. % and a phosphorus content in the range of from 0.04 to 0.1 wt. %, comprising 
      (a) a base oil,     (b) at least one detergent selected from the group consisting of phenate detergents, salicylate detergents and sulphonate detergents, wherein said detergent each, independently, have a TBN (total base number) value in the range of from 30 to 350 mg.KOH/g, as measured by ISO 3771; and     (c) at least 3.5 wt. % of at least one antioxidant selected from the group consisting of aminic antioxidants, phenolic antioxidants, and mixtures thereof based on the total weight of the lubricating oil composition.    

      In another embodiment, a method of lubricating an internal combustion engine using such lubricating oil composition is provided.  
      It is desirable to develop lubricating oil compositions having reduced sulphated ash, sulphur and/or phosphorus concentrations therein which have good TBN retention, and in particular low SAPS lubricating oil compositions which have lower starting TBNs and which have good TBN retention.  
     DETAILED DESCRIPTION OF THE INVENTION  
      It is desirable to develop lubricating oil compositions which have good TBN retention with regard to the VW T4 test (PV 1449), more particularly to develop such lubricating oil compositions having an end of test (VW T4 Test (PV 1449)) TBN value of at least 5.0 mg.KOH/g, as measured by ISO 3771.  
      It has now been found in the present invention, a lubricating oil composition having a low sulphated ash content which is suitable for lubricating internal combustion engines and which exhibits advantageous TBN retention properties.  
      Accordingly, the present invention provides a lubricating oil composition for internal combustion engines which has a sulphated ash content of not greater than 0.9 wt. % and a phosphorus content in the range of from 0.04 to 0.1 wt. %, which composition comprises base oil, 
      (A) one or more detergents selected from phenate detergents, salicylate detergents and sulphonate detergents, wherein said one or more detergents each, independently, have a TBN (total base number) value in the range of from 30 to 350 mg.KOH/g, as measured by ISO 3771; and     (B) at least 3.5 wt. % of one or more antioxidants selected from the group of aminic antioxidants and/or phenolic antioxidants, based on the total weight of the lubricating oil composition.    

      In a preferred embodiment, said one or more antioxidants are present in an amount of at least 3.7 wt. %, more preferably in an amount of at least 3.9 wt. %, and most preferably in an amount of at least 4.0 wt. %, based on the total weight of the lubricating oil composition.  
      The lubricating oil composition of the present invention may comprise one or more aminic antioxidants.  
      Examples of aminic antioxidants which may be conveniently used include alkylated diphenylamines, phenyl-α-naphthylamines, phenyl-β-naphthylamines and alkylated α-naphthylamines.  
      Preferred aminic antioxidants include dialkyldiphenylamines such as p,p′-dioctyl-diphenylamine, p,p′-di-α-methylbenzyl-diphenylamine and N-p-butylphenyl-N-p′-octylphenylamine, monoalkyldiphenylamines such as mono-t-butyldiphenylamine and mono-octyldiphenylamine, bis(dialkylphenyl)amines such as di-(2,4-diethylphenyl)amine and di(2-ethyl-4-nonylphenyl)amine, alkylphenyl-1-naphthylamines such as octylphenyl-1-naphthylamine and n-t-dodecylphenyl-1-naphthylamine, 1-naphthylamine, arylnaphthylamines such as phenyl-1-naphthylamine, phenyl-2-naphthylamine, N-hexylphenyl-2-naphthylamine and N-octylphenyl-2-naphthylamine, phenylenediamines such as N,N′-diisopropyl-p-phenylenediamine and N,N′-diphenyl-p-phenylenediamine, and phenothiazines such as phenothiazine and 3,7-dioctylphenothiazine.  
      Preferred aminic antioxidants include those available under the following trade designations: “Sonoflex OD-3” (ex. Seiko Kagaku Co.), “Irganox L-57” (ex. Ciba Specialty Chemicals Co.) and phenothiazine (ex. Hodogaya Kagaku Co.).  
      The lubricating oil composition of the present invention may comprise one or more phenolic antioxidants.  
      Examples of phenolic antioxidants which may be conveniently used include C7-C9 branched alkyl esters of 3,5-bis(1,1-dimethyl-ethyl)-4-hydroxy-benzenepropanoic acid, 2-t-butylphenol, 2-t-butyl-4-methylphenol, 2-t-butyl-5-methylphenol, 2,4-di-t-butylphenol, 2,4-dimethyl-6-t-butylphenol, 2-t-butyl-4-methoxyphenol, 3-t-butyl-4-methoxyphenol, 2,5-di-t-butylhydroquinone, 2,6-di-t-butyl-4-alkylphenols such as 2,6-di-t-butylphenol, 2,6-di-t-butyl-4-methylphenol and 2,6-di-t-butyl-4-ethylphenol, 2,6-di-t-butyl-4-alkoxyphenols such as 2,6-di-t-butyl-4-methoxyphenol and 2,6-di-t-butyl-4-ethoxyphenol, 3,5-di-t-butyl-4-hydroxybenzylmercaptooctylacetate, alkyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionates such as n-octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, n-butyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate and 2′-ethylhexyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, 2,6-d-t-butyl-α-dimethylamino-p-cresol, 2,2′-methylenebis(4-alkyl-6-t-butylphenol) such as 2,2′-methylenebis(4-methyl-6-t-butylphenol, and 2,2-methylenebis(4-ethyl-6-t-butylphenol), bisphenols such as 4,4′-butylidenebis(3-methyl-6-t-butylphenol, 4,4′-methylenebis(2,6-di-t-butylphenol), 4,4′-bis(2,6-di-t-butylphenol), 2,2-(di-p-hydroxyphenyl)propane, 2,2-bis(3,5-di-t-butyl-4-hydroxyphenyl)propane, 4,4′-cyclohexylidenebis(2,6-t-butylphenol), hexamethyleneglycol-bis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], triethyleneglycolbis[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionate], 2,2′-thio-[diethyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], 3,9-bis{1,1-dimethyl-2-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)-propionyloxy]ethyl}2,4,8,10-tetraoxaspiro[5,5]undecane, 4,4′-thiobis(3-methyl-6-t-butylphenol) and 2,2′-thiobis(4,6-di-t-butylresorcinol), polyphenols such as tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane, 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane, 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene, bis-[3,3′-bis(4′-hydroxy-3′-t-butylphenyl)butyric acid]glycol ester, 2-(3′,5′-di-t-butyl-4-hydroxyphenyl)methyl-4-(2″,4″-di-t-butyl-3″-hydroxyphenyl)methyl-6-t-butylphenol and 2,6-bis(2′-hydroxy-3′-t-butyl-5′-methylbenzyl)-4-methylphenol, and p-t-butylphenol-formaldehyde condensates and p-t-butylphenol-acetaldehyde condensates.  
      Preferred phenolic antioxidants include those available under the following trade designations: “Irganox L-135” (ex. Ciba Specialty Chemicals Co.), “Anteeji DBH” (ex. Kawaguchi Kagaku Co.,), “Yoshinox SS” (ex. Yoshitomi Seiyaku Co.), “Antage W-400” (ex. Kawaguchi Kagaku Co.), “Antage W-500” (ex. Kawaguchi Kagaku Co.), “Antage W-300” (ex. Kawaguchi Kagaku Co.), “Ionox 220AH” (ex. Shell Japan Co.), bisphenol A, produced by the Shell Japan Co., “Irganox L109” (ex. Ciba Speciality Chemicals Co.), “Tominox 917” (ex. Yoshitomi Seiyaku Co.), “Irganox L115” (ex. Ciba Speciality Chemicals Co.), “Sumilizer GA80” (ex. Sumitomo Kagaku), “Antage RC” (ex. Kawaguchi Kagaku Co.), “Irganox L101” (ex. Ciba Speciality Chemicals Co.), “Yoshinox 930” (ex. Yoshitomi Seiyaku Co.), “Ionox 330” (ex. Shell Japan Co.).  
      The lubricating oil composition of the present invention may comprise mixtures of one or more phenolic antioxidants with one or more aminic antioxidants.  
      Detergents that may be used in the lubricating oil of the present invention include one or more detergents selected from salicylate detergents, phenate detergents and sulphonate detergents.  
      Alkali metal and alkaline earth metal salicylate, phenate and sulphonate detergents are preferred in the lubricating oil compositions of the present invention. Calcium and magnesium salicylates, phenates and sulphonates are particularly preferred detergents therein.  
      In one embodiment, the lubricating oil composition of the present invention may comprise (i) one or more salicylate detergents; and/or (ii) a mixture of one or more phenate detergents and one or more sulphonate detergents.  
      However, as metal organic and inorganic base salts which are used as detergents can contribute to the sulphated ash content of a lubricating composition, in a preferred embodiment of the present invention, the amounts of such detergent additives are minimised.  
      In order to maintain a low sulphur level, salicylate detergents are particularly preferred.  
      Thus, in a preferred embodiment, the lubricating oil composition of the present invention may comprise one or more salicylate detergents.  
      In order to maintain the total sulphated ash content of the lubricating oil composition of the present invention at a level of not greater than 0.9 wt. %, preferably at a level of not greater than 0.8 wt. %, more preferably at a level of not greater than 0.75 wt. % and most preferably at a level of not greater than 0.7 wt. %, based on the total weight of the lubricating oil composition, said one or more detergents (A) are preferably used in amounts in the range of 0.05 to 12.5 wt. %, more preferably from 1.0 to 9.0 wt. % and most preferably in the range of from 2.0 to 5.0 wt. %, based on the total weight of the lubricating oil composition.  
      Furthermore, it is preferred that said one or more detergents (A), each, independently, have a TBN (total base number) value in the range of from 30 to 350 mg.KOH/g, more preferably in the range of from 50 to 300 mg.KOH/g, as measured by ISO 3771.  
      That is to say, when there is more than one detergent selected from phenate detergents, salicylate detergents and sulphonate detergents present in the lubricating oil composition of the present invention, then each of such detergents will have a TBN (total base number) value in the range of from 30 to 350 mg.KOH/g, more preferably in the range of from 50 to 300 mg.KOH/g, as measured by ISO 3771.  
      The amount of base oil incorporated in the lubricating oil composition of the present invention is preferably present in an amount in the range of from 60 to 92 wt. %, more preferably in an amount in the range of from 75 to 90 wt. % and most preferably in an amount in the range of from 75 to 88 wt. %, with respect to the total weight of the lubricating oil composition.  
      There are no particular limitations regarding the base oil used in the present invention, and various conventional known mineral oils and synthetic lubricating oils may be conveniently used.  
      Mineral oils include liquid petroleum oils and solvent-treated or acid-treated mineral lubricating oil of the paraffinic, naphthenic, or mixed paraffinic/naphthenic type which may be further refined by hydrofinishing processes and/or dewaxing.  
      Naphthenic base oils have low viscosity index (VI) (generally 40-80) and a low pour point. Such base oils are produced from feedstocks rich in naphthenes and low in wax content and are used mainly for lubricants in which colour and colour stability are important, and VI and oxidation stability are of secondary importance.  
      Paraffinic base oils have higher VI (generally &gt;95) and a high pour point. Said base oils are produced from feedstocks rich in paraffins, and are used for lubricants in which VI and oxidation stability are important.  
      Fischer-Tropsch derived base oils may be conveniently used as the base oil in the lubricating oil composition of the present invention, for example, the Fischer-Tropsch derived base oils disclosed in EP-A-776959, EP-A-668342, WO-A-97/21788, WO-00/15736, WO-00/14188, WO-00/14187, WO-00/14183, WO-00/14179, WO-00/08115, WO-99/41332, EP-1029029, WO-01/18156 and WO-01/57166.  
      Synthetic processes enable molecules to be built from simpler substances or to have their structures modified to give the precise properties required.  
      Synthetic lubricating oils include hydrocarbon oils such as olefin oligomers (PAOs), dibasic acids esters, polyol esters, and dewaxed waxy raffinate. Synthetic hydrocarbon base oils sold by the Royal Dutch/Shell Group of Companies under the designation “XHVI” (trade mark) may be conveniently used.  
      Preferably, the base fluid constituted from mineral oils and/or synthetic base oils which contain more than 80% wt of saturates, preferably more than 90% wt., as measured according to ASTM D2007.  
      It is further preferred that the base oil contains less than 1.0 wt. %, preferably less than 0.1 wt. % of sulphur, calculated as elemental sulphur and measured according to ASTM D2622, ASTM D4294, ASTM D4927 or ASTM D3120.  
      Preferably, the viscosity index of base fluid is more than 80, more preferably more than 120, as measured according to ASTM D2270.  
      Preferably, the lubricating oil has a kinematic viscosity in the range of from 2 to 80 mm 2 /s at 100° C., more preferably of from 3 to 70 mm 2 /s, most preferably of from 4 to 50 mm 2 /s.  
      In a preferred embodiment, the lubricating oil composition may comprise a single zinc dithiophosphate or a combination of two or more zinc dithiophosphates as anti-wear additives, the or each zinc dithiophosphate being selected from zinc dialkyl-, diaryl- or alkylaryl-dithiophosphates.  
      Zinc dithiophosphate is a well known additive in the art and may be conveniently represented by general formula II;  
                 
 
 wherein R 2  to R 5  may be the same or different and are each a primary alkyl group containing from 1 to 20 carbon atoms preferably from 3 to 12 carbon atoms, a secondary alkyl group containing from 3 to 20 carbon atoms, preferably from 3 to 12 carbon atoms, an aryl group or an aryl group substituted with an alkyl group, said alkyl substituent containing from 1 to 20 carbon atoms preferably 3 to 18 carbon atoms. 
 
      Zinc dithiophosphate compounds in which R 2  to R 5  are all different from each other can be used alone or in admixture with zinc dithiophosphate compounds in which R 2  to R 5  are all the same.  
      Preferably, the or each zinc dithiophosphate used in the present invention is a zinc dialkyl dithiophosphate.  
      Examples of suitable zinc dithiophosphates which are commercially available include those available ex. Lubrizol Corporation under the trade designations “Lz 1097” and “Lz 1395”, those available ex. Chevron Oronite under the trade designations “OLOA 267” and “OLOA 269R”, and that available ex. Ethyl under the trade designation “HITEC 7197”; zinc dithiophosphates such as those available ex. Lubrizol Corporation under the trade designations “Lz 677A”, “Lz 1095” and “Lz 1371”, that available ex. Chevron Oronite under the trade designation “OLOA 262” and that available ex. Ethyl under the trade designation “HITEC 7169”; and zinc dithiophosphates such as those available ex. Lubrizol Corporation under the trade designations “Lz 1370” and “Lz 1373” and that available ex. Chevron Oronite under the trade designation “OLOA 260”.  
      The lubricating oil composition according to the present invention may generally comprise in the range of from 0.4 to 1.0 wt. % of zinc dithiophosphate, (if primary or secondary alkyl type), preferably in the range of from 0.4 to 0.9 wt. % and most preferably in the range of from 0.45 to 0.8 wt. %, based on total weight of the lubricating oil composition.  
      The total amount of phosphorus in the lubricating oil composition of the present invention is therefore generally in the range of from 0.04 to 0.1 wt. %, more preferably in the range of from 0.04 to 0.09 wt. % and most preferably in the range of from 0.045 to 0.08 wt. %, based on total weight of the lubricating oil composition.  
      At phosphorus levels of 0.04 wt. % and below, there may be insufficient anti-wear performance. At phosphorus levels of 0.1 wt. % and above, the phosphorus may have a detrimental effect on vehicle exhaust after-treatment devices.  
      The lubricating oil composition of the present invention preferably has a sulphated ash content of not greater than 0.8 wt. %, more preferably not greater than 0.75 wt. % and most preferably not greater than 0.7 wt. %, based on the total weight of the lubricating oil composition.  
      The lubricating oil composition of the present invention preferably has a sulphur content of not greater than 1.2 wt. %, more preferably not greater than 0.8 wt. % and most preferably not greater than 0.2 wt. %, based on the total weight of the lubricating oil composition.  
      Preferred compositions according to the present invention have one or more of the following features: 
      (i) greater than 0.04 wt. % of phosphorus;     (ii) greater than 0.045 wt. % of phosphorus;     (iii) at least 0.04 wt. % of phosphorus;     (iv) less than 0.09 wt. % of phosphorus;     (v) not greater than 0.10 wt. % of phosphorus;     (vi) at most 0.08 wt. % of phosphorus;     (vii) not greater than 0.9 wt. % of sulphated ash;     (viii) not greater than 0.8 wt. % of sulphated ash;     (ix) not greater than 0.7 wt. % of sulphated ash;     (x) not greater than 1.2 wt. % of sulphur;     (xi) not greater than 0.8 wt. % of sulphur; and     (xii) not greater than 0.2 wt. % of sulphur, based on the total weight of the lubricating oil composition.    

      Particularly preferred compositions according to the present invention are:  
      (A): those having features (i) and (iv); those having features (i) and (v); those having features (i) and (vi); those having features (ii) and (iv); those having features (ii) and (v); those having features (ii) and (vi); those having features (iii) and (iv); those having features (iii) and (v); and those having features (iii) and (vi);  
      (B): those having features (i), (iv) and (vii); those having features (i), (iv) and (viii); those having features (i), (iv) and (ix); those having features (i), (v) and (vii); those having features (i), (v) and (viii); those having features (i), (v) and (ix); those having features (i), (vi) and (vii); those having features (i), (vi) and (viii); those having features (i), (vi) and (ix); those having features (ii), (iv) and (vii); those having features (ii), (iv) and (viii); those having features (ii), (iv) and (ix); those having features (ii), (v) and (vii); those having features (ii), (v) and (viii); those having features (ii), (v) and (ix); those having features (ii), (vi) and (vii); those having features (ii), (vi) and (viii); those having features (ii), (vi) and (ix); those having features (iii), (iv) and (vii); those having features (iii), (iv) and (viii); those having features (iii), (iv) and (ix); those having features (iii), (v) and (vii); those having features (iii), (v) and (viii); those having features (iii), (v) and (ix); those having features (iii), (vi) and (vii); those having features (iii), (vi) and (viii); and those having features (iii), (vi) and (ix);  
      (C): those having features (i), (iv) and (x); those having features (i), (iv) and (xi); those having features (i), (iv) and (xii); those having features (i), (v) and (x); those having features (i), (v) and (xi); those having features (i), (v) and (xii); those having features (i), (vi) and (x); those having features (i), (vi) and (xi); those having features (i), (vi) and (xii); those having features (ii), (iv) and (x); those having features (ii), (iv) and (xi); those having features (ii), (iv) and (xii); those having features (ii), (v) and (x); those having features (ii), (v) and (xi); those having features (ii), (v) and (xii); those having features (ii), (vi) and (x); those having features (ii), (vi) and (xi); those having features (ii), (vi) and (xii); those having features (iii), (iv) and (x); those having features (iii), (iv) and (xi); those having features (iii), (iv) and (xii); those having features (iii), (v) and (x); those having features (iii), (v) and (xi); those having features (iii), (v) and (xii); those having features (iii), (vi) and (x); those having features (iii), (vi) and (xi); and those having features (iii), (vi) and (xii); and  
      (D): those having features (i), (iv), (vii) and (x); those having features (i), (iv), (viii) and (x); those having features (i), (iv), (ix) and (x); those having features (i), (v), (vii) and (x); those having features (i), (v), (viii) and (x); those having features (i), (v), (ix) and (x); those having features (i), (vi), (vii) and (x); those having features (i), (vi), (viii) and (x); those having features (i), (vi), (ix) and (x); those having features (ii), (iv), (vii) and (x); those having features (ii), (iv), (viii) and (x); those having features (ii), (iv), (ix) and (x); those having features (ii), (v), (vii) and (x); those having features (ii), (v), (viii) and (x); those having features (ii), (v), (ix) and (x); those having features (ii), (vi), (vii) and (x); those having features (ii), (vi), (viii) and (x); those having features (ii), (vi), (ix) and (x); those having features (iii), (iv), (vii) and (x); those having features (iii), (iv), (viii) and (x); those having features (iii), (iv), (ix) and (x); those having features (iii), (v), (vii) and (x); those having features (iii), (v), (viii) and (x); those having features (iii), (v), (ix) and (x); those having features (iii), (vi), (vii) and (x); those having features (iii), (vi), (viii) and (x); those having features (iii), (vi), (ix) and (x); those having features (i), (iv), (vii) and (xi); those having features (i), (iv), (viii) and (xi); those having features (i), (iv), (ix) and (xi); those having features (i), (v), (vii) and (xi); those having features (i), (v), (viii) and (xi); those having features (i), (v), (ix) and (xi); those having features (i), (vi), (vii) and (xi); those having features (i), (vi), (viii) and (xi); those having features (i), (vi), (ix) and (xi); those having features (ii), (iv), (vii) and (xi); those having features (ii), (iv), (viii) and (xi); those having features (ii), (iv), (ix) and (xi); those having features (ii), (v), (vii) and (xi); those having features (ii), (v), (viii) and (xi); those having features (ii), (v), (ix) and (xi); those having features (ii), (vi), (vii) and (xi); those having features (ii), (vi), (viii) and (xi); those having features (ii), (vi), (ix) and (xi); those having features (iii), (iv), (vii) and (xi); those having features (iii), (iv), (viii) and (xi); those having features (iii), (iv), (ix) and (xi); those having features (iii), (v), (vii) and (xi); those having features (iii), (v), (viii) and (xi); those having features (iii), (v), (ix) and (xi); those having features (iii), (vi), (vii) and (xi); those having features (iii), (vi), (viii) and (xi); those having features (iii), (vi), (ix) and (xi); those having features (i), (iv), (vii) and (xii); those having features (i), (iv), (viii) and (xii); those having features (i), (iv), (ix) and (xii); those having features (i), (v), (vii) and (xii); those having features (i), (v), (viii) and (xii); those having features (i), (v), (ix) and (xii); those having features (i), (vi), (vii) and (xii); those having features (i), (vi), (viii) and (xii); those having features (i), (vi), (ix) and (xii); those having features (ii), (iv), (vii) and (xii); those having features (ii), (iv), (viii) and (xii); those having features (ii), (iv), (ix) and (xii); those having features (ii), (v), (vii) and (xii); those having features (ii), (v), (viii) and (xii); those having features (ii), (v), (ix) and (xii); those having features (ii), (vi), (vii) and (xii); those having features (ii), (vi), (viii) and (xii); those having features (ii), (vi), (ix) and (xii); those having features (iii), (iv), (vii) and (xii); those having features (iii), (iv), (viii) and (xii); those having features (iii), (iv), (ix) and (xii); those having features (iii), (v), (vii) and (xii); those having features (iii), (v), (viii) and (xii); those having features (iii), (v), (ix) and (xii); those having features (iii), (vi), (vii) and (xii); those having features (iii), (vi), (viii) and (xii); and those having features (iii), (vi), (ix) and (xii).  
      The lubricating oil composition of the present invention may further comprise additional additives such as supplementary anti-wear additives, supplementary detergents, dispersants, friction modifiers, viscosity index improvers, pour point depressants, corrosion inhibitors, defoaming agents and seal fix or seal compatibility agents.  
      Supplementary anti-wear additives that may be conveniently used include molybdenum-containing compounds and boron-containing compounds.  
      Examples of such molybdenum-containing compounds may conveniently include molybdenum dithiocarbamates, trinuclear molybdenum compounds, for example as described in WO-A-98/26030, sulphides of molybdenum and molybdenum dithiophosphate.  
      Said molybdenum-containing anti-wear additives may be conveniently added to the lubricating oil composition of the present invention in an amount in the range of from 0.1 to 3.0 wt. %, based on the total weight of lubricating oil composition.  
      Boron-containing compounds that may be conveniently used include borate esters, borated fatty amines, borated epoxides, alkali metal (or mixed alkali metal or alkaline earth metal) borates and borated overbased metal salts.  
      Said boron-containing anti-wear additives may be conveniently added to the lubricating oil composition of the present invention in an amount in the range of from 0.1 to 3.0 wt. %, based on the total weight of lubricating oil composition.  
      The TBN value of fresh unused samples of the lubricating oil composition of the present invention is preferably in the range of from 5.0 to 12.0 mg.KOH/g, more preferably in the range of from 6.0 to 11.0 mg.KOH/g, even more preferably in the range of from 6.0 to 10.0 mg.KOH/g and most preferably in the range of 6.0 to 9.0 mg.KOH/g, as measured by ISO 3771.  
      The lubricating oil compositions of the present invention may additionally contain an ash-free dispersant which is preferably admixed in an amount in the range of from 5 to 15 wt. %, based on the total weight of the lubricating oil composition.  
      Examples of dispersants which may be used include the polyalkenyl succinimides and polyalkenyl succininic acid esters disclosed in Japanese Patent Nos. 1367796, 1667140, 1302811 and 1743435. Preferred dispersants include borated succinimides.  
      Preferred friction modifiers that may be conveniently used include fatty acid amides, more preferably unsaturated fatty acid amides.  
      The total amount of friction modifiers added to the lubricating oil composition of the present invention in conveniently in the range of from 0.05 to 1.2 wt. %, based on the total weight of the lubricating oil composition.  
      Examples of viscosity index improvers which may conveniently used in the lubricating oil composition of the present invention include the styrene-butadiene copolymers, styrene-isoprene stellate copolymers and the polymethacrylate-based and ethylene-propylene copolymers and the like disclosed in Japanese Patent Nos. 954077, 1031507, 1468752, 1764494 and 1751082. Such viscosity index improvers may be conveniently employed in an amount in the range of from 1 to 20 wt. %, based on the total weight of the lubricating oil composition. Similarly, dispersing-type viscosity index improvers comprising copolymerized polar monomer containing nitrogen atoms and oxygen atoms in the molecule may also be used therein.  
      Polymethacrylates such as those as disclosed in Japanese Patent Nos. 1195542 and 1264056 may be conveniently employed in the lubricating oil compositions of the present invention as effective pour point depressants.  
      Furthermore, compounds such as alkenyl succinic acid or ester moieties thereof, benzotriazole-based compounds and thiodiazole-based compounds may be conveniently used in the lubricating oil composition of the present invention as corrosion inhibitors.  
      Compounds such as polysiloxanes, dimethyl polycyclohexane and polyacrylates may be conveniently used in the lubricating oil composition of the present invention as defoaming agents.  
      Compounds which may be conveniently used in the lubricating oil composition of the present invention as seal fix or seal compatibility agents include, for example, commercially available aromatic esters.  
      The lubricating oil compositions of the present invention may be conveniently prepared by admixing the one or more detergents (A), the one or more antioxidants (B) selected from phenolic and/or aminic antioxidants, and, optionally, one or more further additives that are usually present in lubricating oils, for example as herein before described, with a mineral and/or synthetic base oil.  
      Lubricating oil compositions of the present invention display advantageous TBN retention, in particular with regard to the VW T4 test (PV 1449).  
      In a preferred embodiment of the present invention, the end of test (VW T4 Test (PV 1449)) TBN value is at least 5.0 mg.KOH/g, as measured by ISO 3771.  
      In a preferred embodiment of the present invention, the TBN value of a fresh unused sample of the lubricating oil composition of the present invention is in the range of from 5.0 to 12.0 mg.KOH/g and the end of test (VW T4 Test (PV 1449)) TBN value of the same lubricating oil composition is at least 5.0 mg.KOH/g, as measured by ISO 3771.  
      In another preferred embodiment of the present invention, the TBN value of a fresh unused sample of the lubricating oil composition of the present invention is in the range of from 6.0 to 11.0 mg.KOH/g and the end of test (VW T4 Test (PV 1449)) TBN value of the same lubricating oil composition is at least 6.0 mg.KOH/g, as measured by ISO 3771.  
      In yet another preferred embodiment of the present invention, the TBN value of a fresh unused sample of the lubricating oil composition of the present invention is in the range of from 6.0 to 10.0 mg.KOH/g and the end of test (VW T4 Test (PV 1449)) TBN value of the same lubricating oil composition is at least 6.0 mg.KOH/g, as measured by ISO 3771.  
      In the present invention, it is preferred that the change in TBN between the TBN of a fresh unused sample of the lubricating oil composition of the present invention and the end of test (VW T4 Test (PV 1449)) TBN value of the same lubricating oil composition (i.e. wherein ΔTBN is the TBN of fresh oil—End of test TBN) is less than 2.5 mg.KOH/g, more preferably less than 2.0 mg KOH/g and most preferably less than 1.8 mg.KOH/g.  
      In a preferred embodiment of the present invention, the end of test (VW T4 Test (PV 1449)) Vk40 value (i.e. kinematic viscosity at 40° C.) is less than 200 mm 2 /s (cSt).  
      Accordingly, in a preferred embodiment of the present invention, there is provided the use of a lubricating oil composition as hereinbefore described to maintain a TBN level of at least 5.0 mg.KOH/g, as measured by ISO 3771, in an internal combustion engine, in particular with regard to the VW T4 test (PV 1449).  
      In another embodiment of the present invention, there is provided a method of lubricating an internal combustion engine comprising applying a lubricating oil composition as hereinbefore described thereto.  
      The present invention is described below with reference to the following Examples, which are not intended to limit the scope of the invention in any way. 
    
    
     EXAMPLES  
      Formulations  
      Table 1 indicates the formulations that were tested.  
      The formulations in Table 1 comprised conventional detergents, antifoam, dispersants, pour point depressants, viscosity index modifiers and zinc dithiophosphate additives, which were present as additive packages in diluent oil.  
      The phenolic antioxidant used was that available under the trade designation “Irganox L-135” ex. Ciba Specialty Chemicals Co. (C7-C9 branched alkyl esters of 3,5-bis(1,1-dimethyl-ethyl)-4-hydroxy-benzenepropanoic acid).  
      The aminic antioxidant used was that available under the trade designation “Irganox L-57” ex. Ciba Speciality Chemicals Co.  
      The base oils used in said formulations were mixtures of Group III base oils available from “The Royal Dutch/Shell Group of Companies” under the trade designations “XHVI-5.2” and “XHVI-8.2”.  
      All formulations described in Table 1 were SAE 5W30 viscosity grade oils.  
      Table 2 indicates the physical characteristics of the formulations that were tested.  
                                           TABLE 1                       Additive (wt. %)   Ex. 1   Ex. 2   Ex. 3   Ex. 4   Ex. 5   Ex. 6   Comp. Ex. 1                  Anti-foam   30 ppm   30 ppm   30 ppm   30 ppm   30 ppm   30 ppm   30 ppm       Additive package A 1     14.0   —   —   —   —   14.0   14.0       Additive Package B 2     —   10.9   —   —   —   —   —       Additive Package C 3     —   10.1   —   —   —   —   —       Additive Package D 4     —   —   10.7   —   —   —   —       Additive Package E 5     —   —   —   11.5   —   —   —       Phenolic Antioxidant   4.0   4.0   4.0   4.0   4.0   —   —       Aminic Antioxidant   —   —   —   —   4.0   —   —       Viscosity modifier 6     9.60   12.0   12.0   12.0   12.0   9.60   9.60       Pour point depressant   0.3   —   —   —   —   0.3   0.3       Base Oil 7     72.10   73.10   73.90   73.80   72.50   72.10   76.10       TOTAL   100   100   100   100   100   100   100                   1 Commercial additive package available ex. Lubrizol under the trade designation “LZ OS183698”, containing sulphonate and phenate detergents each having TBNs in the range of from 30 to 350 mg.KOH/g, dispersant, zinc dithiophosphate and diluent oil.              2 Conventional additive package containing calcium salicylate detergents having TBNs of 165 mg.KOH/g and 280 mg.KOH/g, dispersant, zinc dithiophosphate and diluent oil.              3 Conventional additive package containing magnesium salicylate detergent having a TBN of 345 mg.KOH/g, dispersant, zinc dithiophosphate and diluent oil.              4 Conventional additive package containing magnesium salicylate detergent having a TBN of 345 mg.KOH/g, dispersant, zinc dithiophosphate and diluent oil.              5 Conventional additive package containing calcium salicylate detergents having TBNs of 64 mg.KOH/g and 165 mg.KOH/g, dispersant, zinc dithiophosphate and diluent oil.              6 Mixture of two different viscosity index modifiers.              7 Group III base oil mixtures of XHVI-5.2 and XHVI-8.2             
 
                                         TABLE 2                                   Total                   Total       Phosphorus   Ca   Mg           Sulphated ash   Total Sulphur   (wt. %)   (wt. %)   (wt. %)       Analytical   (wt. %)   (wt. %)   (ICP-OES)   (ICP-OES)   (ICP-OES)       Measurements   (ASTM D874)   (ASTM D2622)   method)   method)   method)                                                        Ex. 1   0.77   0.188   0.068   0.163   0       Ex. 2   0.85   0.186   0.047   0.207   0       Ex. 3   0.64   0.125   0.050   0   0.118       Ex. 4   0.85   0.131   0.049   0   0.163       Ex. 5   0.63   0.135   0.050   0.150   0       Ex. 6   0.82   0.183   0.072   0.166   0       Comp. Ex. 1   0.76   0.131   0.074   0.167   0                    
 VW T4 Test (PV 1449) 
 
      The experimental methodology used for the Examples above was in accordance with the publicly available test specification for the VW T4 test (PV 1449) and as described in the standard test methods referred to in said test specification.  
     RESULTS AND DISCUSSION  
      The formulations described in Tables 1 and 2 were tested using the afore-mentioned test and the results obtained thereon are included in Table 3.  
                                           TABLE 3                                                   Comp.       Test Results   Ex. 1   Ex. 2   Ex. 3   Ex. 4   Ex. 5   Ex. 6   Ex. 1                                                                Vk40* increase (%)   125.5   73.9   69   74.4   77.2   114.1   98       Vk40 at end of   144.6   121   117.8   121.2   122.8   141.7   135.4       test** (mm 2 /s)       (1) TBN of fresh oil   7.8   8.0   7.6   9.4   5.9   5.28   6.9       (mg.KOH/g)       (ISO 3771)       (2) End of test   6.1   7.3   6.2   8.1   5.1   5.12   3.6       TBN***       (mg.KOH/g)       (ISO 3771)       Δ TBN****   1.7   0.7   1.4   1.3   0.8   0.16   3.3       (mg.KOH/g)       % change in TBN   −21.7   −8.8   18.4   −13.8   −13.6   −3.0   −47.3                 *Kinematic viscosity at 40° C.            **End of Test Limit (VW T4 test (PV 1449)) is &lt;200 (mm 2 /s)            ***End of Test Limit (VW T4 test (PV 1449)) is 5.0 mg.KOH/g.            ****TBN of fresh oil - End of test TBN.             
 
      It can be seen from the above results that the formulation of Example 1 which comprises a phenolic antioxidant, displays increased TBN retention according to the VW T4 test (PV 1449), as compared with the formulation of Comparative Example 1 which fails to meet the required minimum end of test TBN result of 5.0 mg.KOH/g.  
      Furthermore, the formulations of Examples 2 to 5 which also contain large amounts of phenolic antioxidant, also surprisingly pass the VW T4 test (PV 1449) end of test TBN limit of 5.0 mg.KOH/g.  
      It is further evident that the formulation of Example 6 which comprises an aminic antioxidant, also displays increased TBN retention according to the VW T4 test (PV 1449), as compared with the formulation of Comparative Example 1.