EP2298855A1

EP2298855A1 - Method for lubricating a compression engine with a lubricant oil comprising polyisobutylene

Info

Publication number: EP2298855A1
Application number: EP09252081A
Authority: EP
Inventors: Thakor Kikabhai; Gordon David Lamb
Original assignee: Castrol Ltd
Current assignee: Castrol Ltd
Priority date: 2009-08-27
Filing date: 2009-08-27
Publication date: 2011-03-23

Abstract

A method of lubricating the crankcase of a compression ignition internal combustion engine which method comprises lubricating the crankcase with a monograde lubricating oil composition comprising a major amount of a base oil of lubricating viscosity in which the base oil comprises at least one polyisobutylene polymer as a basestock component. When at least one polyisobutylene polymer is used as a basestock component in the base oil of a monograde lubricating oil composition, the monograde lubricating oil composition exhibits reduced oil consumption when used to lubricate the crankcase of a compression ignition internal combustion engine, for example as compared to a comparable lubricating oil composition which has basestock components in the base oil other than polyisobutylene polymers.

Description

This invention relates to a method of lubricating the crankcase of a compression ignition internal combustion engine.
Automotive lubricating oil compositions can be classified according to their viscosity by SAE (Society of Automotive Engineers) grades, as defined by the SAE J300 Engine Oil Viscosity Classification. Monograde oils fall within a single SAE viscosity grade, whereas multigrade oils meet the requirements of more than one SAE viscosity grade.
Monograde lubricating oil compositions are typically used to lubricate the crankcases of internal combustion engines, for example spark ignition and compression ignition engines, which may be used for example, in passenger cars. Monograde lubricating oil compositions may be used to lubricate the crankcases of internal combustion compression ignition engines, for example, such as heavy duty compression ignition engines. In particular, monograde lubricating oil compositions may be used to lubricate the crankcases of internal combustion engines in regions where the climate is constant. According to SAE J300, any Newtonian oil may be labelled as a single-grade (monograde) oil. Newtonian fluids are fluids which, at a given temperature, have a viscosity which remains constant with varying shear rate or shear stress. Thus, to be classified as a monograde oil, a lubricating oil composition must not contain any material which would cause the lubricating oil composition to deviate significantly from Newtonian behaviour.
When producing a monograde lubricating oil composition having a high viscosity, conventionally there may be used one or more highly viscous basestocks, in particular bright stock, which does not affect the Newtonian behaviour of the oil. Bright stock is a mineral oil with a high viscosity, which does not significantly affect the Newtonian behaviour of the oil. Bright stock is the by-product of the manufacture of Group I base oils. Due to the increasing requirement for Group II, III and IV base oils, the global manufacture of Group I base oils is in decline.
The use of PIBs (polyisobutylenes), polyalphaolefins, naphthenics and other products has been proposed to fill the gap between demand and supply for bright stock. See for example, Nancy DeMarco "How to Fill Bright Stock Deficit?" Lube Report vol 7 Issue 1, Jan. 3, 2007. According to this article, PIB will be the synthetic of choice to replace bright stock followed by naphthenics, PAOs, PAGs and others. According to this article, PIB will fill 80 percent of the shortfall, heavy naphthenic 8 percent; PAO is expected to fill 6 percent of the need and PAG 5 percent.
It is known to use liquid polyisobutylene in diesel cylinder oils. Thus, for example, WO 99/64543 is said to provide a diesel cylinder oil, useful in marine and heavy, low speed stationary diesels. According to WO 99/64543 in large, slow speed diesel engines of the crosshead type used in marine and heavy stationary applications, the cylinders are lubricated separately from the other engine components and the cylinders are lubricated on a total loss basis. This is different to the lubrication of the crankcase of a compression ignition internal combustion engine because the lubrication of the crankcase of a compression ignition internal combustion engine is not a total loss lubrication method.
Thus, there remains a need for a method for lubricating the crankcase of a compression ignition engine which overcomes or at least mitigates these problems.
Thus, according to a first aspect of the present invention, there is provided a method of lubricating the crankcase of a compression ignition internal combustion engine which method comprises lubricating the crankcase with a monograde lubricating oil composition comprising a major amount of a base oil of lubricating viscosity in which the base oil comprises at least one polyisobutylene polymer as a basestock component.
According to a further aspect of the present invention there is provided a method of operating a compression ignition internal combustion engine which method comprises lubricating the crankcase of the engine with a monograde lubricating oil composition comprising a major amount of a base oil of lubricating viscosity in which the base oil comprises at least one polyisobutylene polymer as a basestock component.
It has been found that when at least one polyisobutylene polymer is used as a basestock component in the base oil of a monograde lubricating oil composition, the monograde lubricating oil composition exhibits reduced oil consumption when used to lubricate the crankcase of a compression ignition internal combustion engine, for example as compared to a comparable lubricating oil composition which has basestock components in the base oil other than polyisobutylene polymers. Thus, the present invention solves the problem identified above by using at least one polyisobutylene polymer as a basestock component in the base oil of a monograde oil composition used to lubricate the crankcase of a compression ignition internal combustion engine.
Polyisobutylene polymers are sometimes referred to herein as polyisobutene polymers, PIB or PIBs.
More than one polyisobutylene polymer may be used as a basestock component in the base oil of the lubricating oil composition.
Each polyisobutylene polymer may independently have a number average molecular weight in the range 500 to 5000, preferably in the range 2000 to 2500, for example about 2100.
Each polyisobutylene polymer is preferably liquid at room temperature. Solid polyisobutylene polymers may be used provided that they are soluble or miscible in the base oil and the lubricating oil composition.
Each polyisobutylene polymer may be partially or fully hydrogenated.
The basestock component which is at least one polyisobutylene polymer may have a viscosity measured at 100°C, in the range 100 mm²/s to 3000 mm²/s, preferably in the range 600 mm²/s to 2700 mm²/s.
Suitable polyisobutylene polymers may be obtained from Ineos; for example, one of their Indopol (trade mark) range of polyisobutylene polymers. A suitable polyisobutylene polymer from Ineos is Indopol H-1200, which is believed to have a number average molecular weight of 2100. Other suitable polyisobutylene polymers are Glissopal^® 1000, 1300 and 2300 which may be obtained from BASF. These have molar masses Mn g/mole of 1000, 1300 and 2300 respectively, molar mass distributions Mw/Mn of 1.6, 2.0 and 1.8 respectively, viscosities of 4650, 15000 and 48000 mm²/s respectively and viscosities at 100 °C of 190, 500 and 1500 mm²/s respectively. Other suitable polyisobutylene polymers may be obtained from Lubrizol and Infineum.
The total amount of polyisobutylene polymers used as basestock components in the base oil of the monograde oil composition is suitably an effective amount to reduce the consumption of the lubricating oil when used to lubricate the crankcase of the compression ignition engine. Suitably, the total amount of polyisobutylene polymers used as basestock components in the base oil of the monograde oil composition may be in the range 1 to 10 % by weight of the lubricating oil composition, preferably in the range 2 to 8 % by weight of the lubricating oil composition.
The lubricating oil composition may be an SAE 20 monograde lubricating oil composition, or an SAE 30 monograde lubricating oil composition, or an SAE 40 monograde lubricating oil composition, or an SAE 50 monograde lubricating oil composition. The monograde of the lubricating oil composition is defined according to the SAE J300 standard Rev. Dec. 1999, issued 1999-12.
For an SAE 20 lubricating oil composition, or for an SAE 30 lubricating oil composition or for an SAE 40 lubricating oil composition or for an SAE 50 lubricating oil composition the total amount of polyisobutylene polymers used as basestock components in the base oil of the monograde oil composition may be in the range 1 to 10 % by weight of the lubricating oil composition, preferably 2 to 8 % by weight of the lubricating oil composition.
In addition to the basestock component which is at least one polyisobutylene polymer, the base oil of the lubricating oil composition may also comprise bright stock and/or heavy neutral basestock. Bright stock and heavy neutral basestock are mineral oils. Generally, the base oils of SAE 30, SAE40 and SAE50 lubricating oil compositions will comprise bright stock and/or heavy neutral basestock, thus the base oils of SAE 30, SAE40 and SAE50 lubricating oil compositions may comprise bright stock and heavy neutral basestock. Alternatively, the base oils of SAE 30, SAE40 and SAE50 lubricating oil compositions may comprise bright stock or heavy neutral basestock. Typically, the base oils of SAE 30 lubricating oil compositions will comprise heavy neutral basestock. Typically, the base oils of SAE40 and SAE50 lubricating oil compositions will comprise bright stock and heavy neutral basestock. The use of at least one polyisobutylene polymer as a base stock component in the base oil of the lubricating oil composition may allow the amount of bright stock and/or heavy neutral basestock which is required to achieve the desired viscosity grade of lubricating oil composition to be reduced compared to that required without the use of at least one polyisobutylene polymer as a basestock component.
In addition to the basestock which is at least one polyisobutylene polymer, the base oil of the lubricating oil composition may also comprise one or more basestock selected from Group I basestocks, Group II basestocks, Group III basestocks, Group IV basestocks, Group V basestocks, basestocks derived from Fischer-Tropsch synthesised, waxy, paraffinic hydrocarbon materials (sometimes also called gas-to-liquid basestocks), naphthenic basestocks and mixtures thereof.

Group I, Group II, Group III, Group IV and Group V basestocks are defined according to API standard 1509, "ENGINE OIL LICENSING AND CERTIFICATION SYSTEM", November 2004 version 15th edition Appendix E, as set out in Table 1 below:

Table I

Group	Saturated hydrocarbon content (Wt %)		Sulphur content (Wt %)		Viscosity Index
I	< 90	and/or	> 0.03	and	≥ 80 and < 120
II	≥ 90	and	≤ 0.03	and	≥ 0 and < 120
III	≥ 90	and	≤ 0.03	and	≥ 120
IV	polyalpha olefins
V	all basestocks not in Groups I, II, III or IV

Group I and Group II basestocks are derived from mineral oil by known refinery process. Group III basestocks may be derived from mineral oil by refinery processes known in the art. Group III basestocks may also be known as synthetic basestocks and include for example, Shell XHVI (trade mark) and Nexbase (trade mark).
Basestocks derived from Fischer-Tropsch synthesised, waxy, paraffinic hydrocarbon materials may be made by any suitable known process for the manufacture of basestock from Fischer Tropsch processes. Processes for the manufacture of basestocks derived from Fischer-Tropsch synthesised, waxy, paraffinic hydrocarbon materials which may be used, are described for example in US4943672 , EP-A-0668342 and EP-A-0776959 , the contents of which are hereby incorporated by reference. Thus, the basestock may be made by the steps of (i) producing Syngas, (ii) Fischer-Tropsch synthesis of hydrocarbons from the Syngas, (iii) hydrocracking of the hydrocarbons to produce naphtha and diesel/kerosene fuel process streams together with a waxy paraffinic residue and (iv) hydroisomerising the waxy residue to produce the basestock.
In addition to at least one polyisobutylene polymer, the base oil may suitably comprise at least one heavy neutral 500N mineral oil and/or at least one heavy neutral 600N mineral oil. These may be Group I or Group II basestocks.
A suitable Group I'base stock is Sepehan 500N basestock. This may be used as a basestock component in the base oil to provide an SAE 40 or an SAE 50 monograde lubricating oil composition.
The at least one polyisobutylene polymer may be provided as a basestock component in the base oil of the monograde lubricating oil composition by mixing one or more polyisobutylene polymers with other basestock components in one or more steps to produce the base oil of the lubricating oil composition.
If more than one polyisobutylene polymer is used, the polyisobutylene polymers may be mixed together in one or more steps to form a basestock which may then be mixed in one or more steps with other basestock components, for example one or more Group I basestock, Group II basestock, Group III basestock, Group IV basestock, Group V basestock, basestock derived from Fischer-Tropsch synthesised, waxy, paraffinic hydrocarbon materials (sometimes also called gas-to-liquid basestock) naphthenic basestock, or mixtures thereof, to produce the base oil of the lubricating oil composition. Alternatively, or additionally, the polyisobutylene polymers may be mixed independently with one or more other basestock components before being combined together in one or more steps to produce the base oil of the lubricating oil composition.

Additives.

The lubricating oil composition comprises a major amount of base oil of lubricating viscosity. By major amount is meant greater than 50 % by weight.
The lubricating oil composition may comprise a minor amount of additives. The additives may be provided or used in the manufacture of the lubricating oil composition as an additive package or as two or more part-packs, which may be mixed or blended with the base oil or basestock components in one or more steps. The additive packages or part-packs may comprise solvent. The additive package or part-packs may be mixed with the base oil or base stock components in one or more steps by methods known in the art.
The lubricating oil composition, additive package or part-packs may comprise one or more of the following additives: dispersants, detergents, metal dihydrocarbyl dithiophosphates, friction modifiers, seal swell agents (sometimes also referred to as elastomer compatibility aids), antioxidants, anti foam agents (also sometimes called foam inhibitors), lubricity agents, rust inhibitors, corrosion inhibitors, demulsifiers, pour point depressants and mixtures of two or more thereof.
Viscosity index improvers and dispersant viscosity index improvers are substantially absent from the lubricating oil composition, the additive package and part-packs.
The amount of additives present in the lubricating oil composition may be such as to provide that the lubricating oil composition meets the API standards CC to CF. These standards are defined according to ASTM D4485.

Dispersants.

The lubricating oil composition may comprise 1 to 10 % by weight of a dispersant additive component which may comprise 40 to 50 % by weight active dispersant additive. Suitable dispersant additives comprise one or more oil soluble polymeric hydrocarbon backbones, each having one or more functional groups which are capable of associating with particles to be dispersed. The functional groups may be amine, alcohol, amide, or ester groups.
Suitable dispersants are for example polyisobutylene succinic anhydride polyamines (also sometimes referred to as PIBSA polyamines or PIBSA PAM). Examples of other suitable dispersants include oil soluble salts, esters, amino-esters, amides, imides and oxazolines of long chain hydrocarbon substituted, mono- and di-carboxylic acids and their anhydrides; thiocarboxylate derivatives of long chain hydrocarbons; long chain aliphatic hydrocarbons having a polyamine attached directly thereto; Mannich condensation products formed by condensing a long chain substituted phenol with formaldehyde and polyalkylene polyamine; Koch reaction products and the like.
The oil soluble polymeric hydrocarbon backbone is typically an olefin polymer, especially a polymer comprising greater than 50 mole % of a C₂ to C₁₈ olefin, typically greater than 50 mole % of a C₂ to C₅ olefin. The oil soluble polymeric hydrocarbon backbone may be a homopolymer or a copolymer of two or more olefins. A preferred class of olefin polymers is polybutylenes and more preferably, polyisobutylenes. Other preferred classes of olefin polymers are ethylene alpha-olefin copolymers, alpha-olefin homopolymer and alpha-olefin copolymers. The oil soluble polymeric hydrocarbon backbone usually has a number average molecular weight (Mn) in the range of 300 to 20,000, preferably 500 to 10,000, more preferably 700 to 5,000. The molecular weight may be determined by gel permeation chromatography.
The oil soluble polymeric hydrocarbon backbone may be functionalised with one or more functional groups incorporated into the backbone or with one or more functional groups pendant from the polymer backbone. Typical functional groups may be polar and may contain one or more hereto atoms, for example phosphorus, oxygen, sulphur, nitrogen, halogen or boron.
Preferred dispersants are polyisobutenyl succinimide dispersants.

Detergents

The lubricating oil composition may comprise one or more detergents. The one or more detergents may be present in the lubricating oil composition in a total active concentration of 0.5 to 3 % by weight of the lubricating oil composition.
Suitable detergents are for example, ashless detergents, metal salt detergents and combinations thereof. Suitable metal salt detergents are for example, neutral and overbased phenates, sulphurised phenates, sulphonates, carboxylates, salicylates and combinations thereof. The metals of the salts may be alkali metals, alkaline earth metals and combinations thereof. Preferably, the metals are calcium, magnesium and combinations thereof. Calcium and magnesium detergent salts may both be present in the lubricating oil composition. Suitable metals detergents are for example, neutral and overbased salts a TBN (total base number as measured by ASTM2896) in the range 20 to 450. Suitable calcium sulfonates may have TBN (total base number) values of 85, 300 and 400. Suitable calcium phenates may have TBN values of 150 and 250. A suitable additive package comprising detergent is LZ17001 which is available from Lubrizol and which according to published sources comprises zinc alkyl dithiophosphate (C3-C14) and alkenyl (C11+) amide.

Metal dihydrocarbyl dithiophosphates.

One or more metal dihydrocarbyl dithiophosphates may optionally also be present in the lubricating oil composition. These compounds may be used as anti-wear and/or antioxidant agents. Suitable metals in these compounds are for example, alkali metals, alkaline earth metals, zinc, aluminium, lead, tin, molybdenum, manganese, nickel and copper, most preferably zinc. Primary and/or secondary hydrocarbyl groups may be present in these compounds. Each hydrocarbyl group may have 1 to 18 carbon atoms. The one or more metal dihydrocarbyl dithiophosphates may be present in the lubricating oil composition in a total amount, expressed as phosphorus, of 0.01 to 0.2 % by weight of the lubricating oil composition.

Friction modifiers,

One or more friction modifiers may optionally also be present in the lubricating oil composition. Suitably, such friction modifiers are for example, mono- and di- amines which may be used as such or in the form of an adduct or reaction product with a boron compound. Other suitable friction modifiers are esters for example, formed by reacting carboxylic acids or anhydrides with alkanols. Suitable friction modifiers are for example, molybdenum dithiocarbamate, oleyl amide and glycerol mono-oleate and di-oleate. The one or more friction modifiers may be present in the lubricating oil composition in a total amount of less than 2 % by weight of the composition.

Anti-wear additives

Typical antiwear additives which may be present in the lubricating oil composition are metal dihydrocarbyl dithiophosphates as disclosed herein.
The one or more detergents present in the lubricating oil composition may exhibit anti-wear properties.
One or more supplemental anti-wear agents may optionally also be present in the lubricating oil composition. Suitable supplemental anti-wear agents are for example, boron compounds. The one or more supplemental anti-wear agents may be present in the lubricating oil composition in a total amount of up to 2 % by weight of the composition.

Seal swell agents.

One or more seal swell agents (sometimes referred to as elastomer compatibility aids) may optionally also be present in the lubricating oil composition. Suitable elastomer compatibility aids are for example, long chain organic acids and the like. The one or more elastomer compatibility aids may be present in the lubricating oil composition in a total amount of up to 5% by weight of the lubricating oil composition, preferably in a total amount of about 1 % by weight of the lubricating oil composition.

Antioxidants

One or more anti-oxidants may optionally also be present in the lubricating oil composition. Suitable anti-oxidants are for example, hindered amines, hindered phenols, alkaline earth metals salts of alkylphenolthioesters having preferably C5 to C12 alkyl side chains, calcium nonylphenol sulphide, calcium dodecylphenol sulphide, oil soluble phenates, oils soluble sulphurised phenates, phosphosulphurised hydrocarbons, sulphurised hydrocarbons (for example, sulphurised olefins), phosphorus esters, metal thiocarbamates, oil soluble copper compounds (for example, as described in US4867890 ), molybdenum-containing compounds, and the like. The metal dihydrocarbyl dithiophosphates as herein disclosed may exhibit antioxidant properties. The one or more anti-oxidants may be present in the lubricating oil composition in a total amount of up to 5 % by weight of the lubricating oil composition.

Anti-foaming agents.

One or more antifoaming agents may optionally also be present in the lubricating oil composition. Suitable antifoaming agents are for example, siloxanes, dimethyl siloxanes, phenyl methyl siloxanes, acrylates and the like. The one or more anti-foaming agents may be present in the lubricating oil composition in a total amount by weight typically of 10 to 50 ppm of the lubricating oil composition.

Rust inhibitors

One or more rust inhibitors may optionally also be present in the lubricating oil composition. Suitable rust inhibitors are for example, non-ionic polyoxyalkylene polyols and esters thereof, polyoxyalkylene phenols and anionic alky sulphonic acids. The one or more rust inhibitors may be present in the lubricating oil composition in a total amount of 0.01 to 0.5% by weight of the lubricating oil composition.

Corrosion inhibitors.

One or more corrosion inhibitors may optionally also be present in the lubricating oil composition. Suitable corrosion inhibitors are for example, non-ionic polyoxyalkylene polyols and esters thereof, polyoxyalkylene phenols, triazoles, anionic alkyl sulphonic acids and the like. The one or more corrosion inhibitors may be present in the lubricating oil composition in a total amount of up to1.5% by weight of the lubricating oil composition.

Demulsifiers.

One or more demulsifiers may optionally also be present in the lubricating oil composition. Suitable demulsifiers are for example, ethoxylated compounds and the like. The one or more demulsifiers may be present in the lubricating oil composition in a total amount by weight of up to 1000 pm of the lubricating oil composition.

Pour point depressants.

One or more pour point depressants may optionally also be present in the lubricating oil composition. Suitable pour point depressants are for example, methacrylates, alkyl methacrylates, vinyl fumarates, styrene esters and the like. The one or more pour point depressants may be present in the lubricating oil composition in a total amount of up to 1 % by weight of the lubricating oil composition.
Suitably, the lubricating oil composition or additive package or part packs comprise, anti-oxidants, ashless dispersants, detergents which might typically comprises sulphonate and/or phenate salts of alkaline earth metals and zinc based antiwear additives.
The concentration of additives in the additive package or part packs are such as to provide the required additive concentrations in the lubricating oil composition when the additive package or part packs are combined with the base oil or base stock components.

Engines/Method of Use

Compression ignition engines are sometimes referred to as diesel engines. The compression ignition internal combustion engine has a crankcase which is lubricated by the lubricating oil composition. Thus, the engine is not lubricated on a total loss basis. The lubrication method is a non-total loss lubrication method. The engine is preferably a heavy duty, compression ignition internal combustion engine. The engine is suitably a transportation engine and may be used in a vehicle, for example in a commercial vehicle. Examples of commercial vehicles are trucks, vans, lorries, coaches, buses and the like.
Suitable heavy duty, compression ignition internal combustion engines include those manufactured for example, by Caterpillar, Cummins, DAF, Daimler, Hino, International, Isuzu, IVECO, MAN, Mitsubishi, Nissan, Scania, Volkswagen and Volvo.
The crankcase of the compression ignition internal combustion engine may be lubricated by circulating the lubricating oil composition through the crankcase by methods known in the art, for example with a lubricating oil pump.
The invention will now be illustrated, by way of example only, with reference to the following examples and experiments.

Four lubricating oil compositions were prepared; two suitable for use in the method according to the present invention (Examples 1 and 2) and not suitable for use in the method according to the present invention (Experiments A and B) by mixing basestocks with various amounts of the additive package LZ17001 which is available from Lubrizol and according to public domain information comprises zinc alkyl dithiophosphate (C3-C14) and alkenyl (C11+) amide. Details of the basestocks and amounts of additive package used are given in Table 2 below.

Table 2

	Experiment A	Experiment B	Expample 1	Expample 2
Red. No.	001B	001D	001A	001C
Target SAE Grade	40	40	50	50
Target API Performance	CC	CF	CC	CF
Components (% by weight)
Basestock - polyisobutylene H-1200	0	0	7.5	7.5
Basestock - brightstock Sepehan 500N	72.1	70.7	89.6	88.2
Basestock - mineral oil ExxonMobil 150 BS	25	25	0	0
Additive package LZ 17001	2.9	4.3	2.9	4.3

Chemical analyses and physical properties of the lubricating oil compositions were determined by standard methods and the results are given in Table 3 below.

Table 3

	Experiment A	Experiment B	Example 1	Example 2
Ref. No.	001B	001D	001A	001C
Target SAE Grade	40	40	50	50
Target API Performance	CC	CF	CC	CF
CCS-15 (cP)	24180	24800	27230	28130
HTHS (cP)	4.33	4.37	5.04	5.17
KV100 (cSt)	15.0	15.4	17.7	18.1
KV40 (cSt)	159.7	164.5	191.9	197.2
VI	93	94	100	100
Nitrogen (wt%)	0.069	0.080	0.073	0.075
Noack (%)	3.4	3.6	3.8	4.2
Sulphated ash (%)	0.58	0.79	0.67	0.87
TBN (mg KOH/g)	5.14	6.94	5.17	6.87
Pour Point (°C)	-6	-6	-3	-3
Ca (ppm)	1431	2068	1440	2099
Mg (ppm)	4	5	4	5
P (ppm)	364	530	360	547
S (ppm)	9488	9743	9359	9753
Zn (ppm)	410	581	410	589
B (ppm)	<5	<5	<5	<5
Si (ppm)	3	1	2	2
Na (ppm)	<10	<10	<10	<10

In the table, SAE refers to Society of Automotive Engineers; CCS means cold cranking simulator; HTHS means high temperature high shear; KV 100 means kinematic viscosity at 100°C; KV40 means kinematic viscosity at 40°C; VI means viscosity index and TBN means total base number).
Elemental analysis of the four lubricating oil compositions gave < 1 ppm for each of the following elements in all four compositions: Al, Ba, Cd, Cu Fe, Mn, Mo, Sn, Ti and Va.
Elemental analysis of the four lubricating oil compositions gave < 2 ppm for each of the following elements in all four compositions: Ni and Pb.

Engine Tests.

The lubricating oil compositions were tested in various engine tests and the results are given in Table 4.
The MWMB engine test was used to screen against API CC performance in place of the now obsolete Caterpillar 1H2 test. This tests the performance of a heavy duty compression ignition internal combustion engine under severe operating conditions. The test evaluates Piston Cleanliness in the MWM KD 12E Diesel Test Engine according to Method B of the CEC L-12-A-76 test method.
The API CF specification requires testing according to the Caterpillar 1M-PC and the Sequence VIII engine tests. The Caterpillar 1M-PC test uses a single cylinder supercharged diesel engine to evaluate ring sticking, ring and cylinder wear and piston deposits. The Sequence VIII engine test uses a gasoline engine and is therefore not lubrication of a diesel engine according to the present invention. This test is intended to evaluate crankcase lubricating oil compositions for their copper and lead corrosion control capabilities. It also evaluates shear stability under high temperature operating conditions.
The engine test results in Table 4 show that the lubricating oil compositions in which polyisobutylene polymer was used as a basestock component in the base oil did not exhibit any harm in the engine tests - the lubricating oil composition of Example 1 passed the MWMB test and the lubricating oil composition of Example 2 passed the 1M-PC and Sequence VIII tests.

For the API CC target lubricating oil composition comprising brightstock as a component in the base oil (Experiment A), the lubricating oil composition exhibited a nominal failing result (based upon the indicative pass/fail limit for piston cleanliness) in the MWMB test, but the corresponding lubricating oil composition (Example 1) in which polyisobutylene polymer was used as a basestock component in the base oil of the lubricating oil composition showed a nominal pass in the same test. This test is unable to differential oil consumption differences.

Table 4

	Experiment A	Experiment B	Example 1	Example 2
Ref. No.	001B	001D	001A	001C
Target SAE Grade	40	40	50	50
Target API Performance	CC	CF	CC	CF
1M-PC Test	Not tested	Pass	Not tested	Pass
Weighted demerits (<240)	N/A	186.6	N/A	120.7
Top Grove Fill	N/A	39	N/A	70
(70% vol max)
Piston Ring sticking (none)	N/A	None	N/A	None
Piston, ring and liner scuffing (none)	N/A	None	N/A	None
Oil Consumption (R&R g/kWhr)	N/A	0.433	N/A	0.335

Sequence VIII	Not tested	Pass	Not tested	Pass
Bearing weight loss (<29.3 mg)	N/A	0.6	N/A	0

MWMB	Fail	Not tested	Pass	Not tested
Piston Cleanliness (>55)	48	N/A	57	N/A
Specific Oil Consumption 0- 50hrs (R&R g/hr)	15.3	N/A	15.4	N/A
Total Oil Consumption (R&R g)	765	N/A	768	N/A

N/A = not applicable, lubricating oil composition not tested in that engine test.

For the API CF target lubricating oil compositions, the lubricating oil composition (Example 2) in which polyisobutylene polymer was used as base stock component in the base oil showed improved performance in the 1M-PC demerits and the Sequence VIII bearing weight loss compared to the corresponding lubricating oil composition without polyisobutylene polymer (Experiment B).
A comparison of the oil consumption measured in the 1M-PC engine test shows that Example 2 in which polyisobutylene polymer was used as a basestock component in the base oil of the lubricating composition had reduced oil consumption (0.335 g/kWhr) compared to Example B (0.433 g/kWhr) in which there was no isobutylene polymer as basestock component and the base oil additionally comprised brightstock as a basestock component.
The results show a method of lubricating the crankcase of a compression ignition internal combustion engine which method comprises lubricating the crankcase with a monograde lubricating oil composition comprising a major amount of a base oil of lubricating viscosity in which the base oil comprises at least one polyisobutylene polymer as a basestock component.
The results show a method of operating a compression ignition internal combustion engine which method comprises lubricating the crankcase of the engine with a monograde lubricating oil composition comprising a major amount of a base oil of lubricating viscosity in which the base oil comprises at least one polyisobutylene polymer as a basestock component.
The results also show that when at least one polyisobutylene polymer is used as a basestock component in the base oil of a monograde lubricating oil composition, the monograde lubricating oil composition exhibits reduced oil consumption when used to lubricate the crankcase of a compression ignition internal combustion engine, for example as compared to a comparable lubricating oil composition which has basestock components in the base oil other than polyisobutylene polymers.

Claims

A method of lubricating the crankcase of a compression ignition internal combustion engine which method comprises lubricating the crankcase with a monograde lubricating oil composition comprising a major amount of a base oil of lubricating viscosity in which the base oil comprises at least one polyisobutylene polymer as a basestock component.
A method as claimed in claim 1 in which the total amount of polyisobutylene polymers used as basestocks component in the base oil of the monograde oil is in the range 1 to 10 % by weight of the lubricating oil composition.
A method as claimed in claim 2 in which the total amount of polyisobutylene polymers used as basestocks component in the base oil of the monograde oil is in the range 2 to 8 % by weight of the lubricating oil composition.
A method as claimed in any one of the preceding claims, in which the monograde lubricating oil composition is an SAE 20, SAE 30, SAE 40 or SAE 50 monograde lubricating oil composition.
A method as claimed in any one of the preceding claims, in which each polyisobutylene polymer independently has a number average molecular weight in the range 500 to 5000.
A method as claimed in any one of the preceding claims in which the base oil of the lubricating oil composition also comprises bright stock and/or heavy neutral basestock.
A method as claimed in any one of the preceding claims in which the base oil of the lubricating oil composition also comprises one or more basestock selected from Group I basestocks, Group II basestocks, Group III basestocks, Group IV basestocks, Group V basestocks, basestocks derived from Fischer-Tropsch synthesised, waxy, paraffinic hydrocarbon materials, naphthenic basestocks and mixtures thereof.
A method as claimed in any one of the preceding claims in which the lubricating oil composition comprises one or more of the following additives: dispersants, detergents, metal dihydrocarbyl dithiophosphates, friction modifiers, seal swell agents, antioxidants, anti foam agents, lubricity agents, rust inhibitors, corrosion inhibitors, demulsifiers, pour point depressants and mixtures of two or more thereof.
A method as claimed in claim 8 in which the amount of additives present in the lubricating oil composition are such as to provide that the lubricating oil composition meets the API standards CC to CF.
A method as claimed in any one of the preceding claims in which the compression ignition engine is a heavy duty compression ignition engine.