WO2010020653A2

WO2010020653A2 - Lubricating composition

Info

Publication number: WO2010020653A2
Application number: PCT/EP2009/060706
Authority: WO
Inventors: David Colbourne; David John Wedlock
Original assignee: Shell Internationale Research Maatschappij BV
Current assignee: Shell Internationale Research Maatschappij BV
Priority date: 2008-08-19
Filing date: 2009-08-19
Publication date: 2010-02-25
Anticipated expiration: 2011-02-19
Also published as: JP2012500315A; WO2010020653A3

Abstract

The present invention provides a lubricating composition comprising a base oil and one or more additives, wherein the composition has: - a dynamic viscosity at -30°C (according to ASTM D 5293) of below 6600 cP; - a kinematic viscosity at 100°C (according to ASTM D 445) of at least 9.3 cSt; - a high temperature, high shear viscosity ("HTHS"; according to ASTM D 4683) of at least 2.9 cP; - a Noack volatility (according to ASTM D 5800) of below 14 wt.%; wherein the base oil has a kinematic viscosity at 100°C (according to ASTM D 445) of at least 4.8 cSt.

Description

LUBRICATING COMPOSITION

The present invention relates to a lubricating composition comprising a base oil and one or more additives for particular use in the crankcase of an engine, in particular a heavy duty diesel engine. In practice various lubricating compositions for crankcase engines are known.

A disadvantage of known crankcase engine oils is that, especially when they are based on conventional mineral Group III base oils, they have undesirable fuel economy oil performance values.

A further problem of known crankcase engine oils is that they may have undesirable properties for one or more of wear performance and Noack volatility.

Also in blending known engine oils, it has been found difficult to meet the so-called SAE J300 Specifications (as revised in May 2004) whilst using mineral Group III base oils. SAE stands for Society of Automotive Engineers. It is an object of the present invention to minimize one or more of the above problems. It is another object of the present invention to provide alternative lubricating compositions for use in the crankcase of an engine, which compositions meet the SAE J300 Specifications.

It is a further object to provide alternative 5W-30 and 5W-40 crankcase engine oils according to the above SAE J300 Specifications.

One or more of the above or other objects can be obtained by the present invention by providing a lubricating composition comprising a base oil and one or more additives, wherein the composition has: a dynamic viscosity at -30⁰C (according to ASTM D 5293} of below 6600 cP; a kinematic viscosity at 100⁰C (according to ASTM D 445) of at least 9.3 cSt; a high temperature, high shear viscosity ("HTHS"; according to ASTM D 4683) of at least 2.9 cP; a Noack volatility (according to ASTM D 5800) of below 14 wt.%; wherein the base oil has a kinematic viscosity at 100⁰C (according to ASTM D 445) of at least 4.8 cSt

It has surprisingly been found that the lubricating compositions according to the present invention exhibit improved fuel economy properties whilst maintaining desirable wear performance and Noack volatility properties.

Another advantage of the present invention is that the above desirable properties can be achieved for a top- tier heavy duty diesel engine lubricant as well. A characteristic of such top-tier heavy duty diesel engine lubricants is that they require a relatively high treat of a performance additive package. Such a performance additive package thickens the overall finished- lubricant, which consequently means that a lower viscosity contribution is left for the base oil to meet the same viscosity requirements. A consequence of using a lower viscosity base oil is that volatility control according to industry specifications may be lost. However, it has been surprisingly found according to the present invention that this volatility control is not lost in case a Fischer-Tropsch derived base oil is used; something which has not been achieved whilst using only mineral derived base oils having the same kinetic viscometric properties at 100⁰C.

There are no particular limitations regarding the base oil used in lubricating composition according to the present invention, and various conventional mineral oils, synthetic oils as well as naturally derived esters such as vegetable oils may be conveniently used, provided that the base oil has a kinematic viscosity at 100⁰C {according to ASTM D 445) of at least 4.8 cSt and provided that the requirements in respect of the lubricant composition according to the present invention are met .

The base oil used in the present invention may conveniently comprise mixtures of one or more mineral oils and/or one or more synthetic oils; thus, according to the present invention, the term "base oil" may refer to a mixture containing more than one base oil. 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.

Suitable base oils for use in the lubricating oil composition of the present invention are Group III mineral base oils, Group IV poly-alpha olefins (PAOs) , Group III Fischer-Tropsch derived base oils and mixtures- thereof.

By "Group III" and "Group IV" base oils in the present invention are meant lubricating oil base oils according to the definitions of American Petroleum Institute (API) for category III and IV. These API categories are defined in API Publication 1509, 15th Edition, Appendix E, April 2002.

Fischer-Tropsch derived base oils are known in the art. By the term ^Fischer-Tropsch derived" is meant that a base oil is, or is derived from, a synthesis product of a Fischer-Tropsch process. A Fischer-Tropsch derived base oil may also be referred to as a GTL (Gas-To-Liquids) base oil. Suitable Fischer-Tropsch derived base oils that may be conveniently used as the base oil in the lubricating composition of the present invention are those as for example disclosed in EP 0 776 959, EP 0 668 342, WO 97/21788, WO 00/15736, WO 00/14188, WO 00/14187, WO 00/14183, WO 00/14179, WO 00/08115, WO 99/41332, EP 1 029 029, WO 01/18156 and WO 01/57166. Synthetic oils include hydrocarbon oils such as olefin oligomers (including polyalphaolefin base oils; PAOs}, dibasic acid esters, polyol esters, polyalkylene glycols (PAGs) , alkyl naphthalenes and dewaxed waxy isomerates. Synthetic hydrocarbon base oils sold by the Shell Group under the designation "Shell XHVI" (trade mark) may be conveniently used.

Poly-alpha olefin base oils (PAOs) and their manufacture are well known in the art. Preferred poly- alpha olefin base oils that may be used in the lubricating compositions of the present invention may be derived from linear C₂ to C₃₂, preferably C₆ to Ci₆, alpha olefins. Particularly preferred feedstocks for said poly-alpha olefins are 1-octene, l-decene_f 1-dodecene and 1- tetradecene. Preferably, the base oil as used in the lubricating composition according to the present invention comprises a base oil selected from the group consisting of a poly- alpha olefin base oil and a Fischer-Tropsch derived base oil or a combination thereof. There is a strong preference for using a Fischer-

Tropsch derived base oil over a PAO base oil, in view of the high cost of manufacture of the PAOs. Thus, preferably, the base oil contains more than 50 wt.%, preferably more than 60 wt.%, more preferably more than 70 wt. %, even more preferably more than 80 wt.%. most preferably more than 90 wt.% Fischer-Tropsch derived base oil. In an especially preferred embodiment not more than 5 wt.%, preferably not more than 2 wt.%, of the base oil is not a Fischer-Tropsch derived base oil. It is even more preferred that 100 wt% of the base oil is based on one or more Fischer-Tropsch derived base oils.

Please note in this respect that WO 02/064711 and WO 2004/081157, as well as D.J. Wedlock et al., "Gas-to- Liquids Base Oils to assist in meeting OEM requirements 2010 and beyond", presented at the 2^nά Asia-Pacific base oil Conference, Beijing, China, 23-25 October 2007, disclose the use of Fischer-Tropsch derived base oils in engine oils. However, none of these publications disclose or suggest in actual examples a lubricating composition meeting the specific requirements of the lubricating composition according to the present invention wherein the base oil has a kinematic viscosity at 100⁰C {according to ASTM D 445) of at least 4.8 cSt . The total amount of base oil incorporated in the lubricating composition of the present invention is preferably present in an amount in the range of from 60 to 99 wt.%, more preferably in an amount in the range of from 65 to 90 wt •% and most preferably in an amount in the range of from 70 to 85 wt.%, with respect to the total weight of the lubricating composition.

According to the present invention the base oil has a kinematic viscosity at 100⁰C of at least 4.8 cSt (according to ASTM D445) . In the event the base oil contains a blend of two or more base oils, it is preferred that the total contribution of the base oil to this kinematic viscosity is at least 4.8 cSt.

In a preferred embodiment according to the present invention, the base oil has a kinematic viscosity at 100⁰C of at least 5.0 cSt, preferably at least 5.2 cSt. Typically, the base oil has a kinematic viscosity at 100°C below 10.0, preferably below 8.5, more preferably below 7.0 cSt, or even below 5.5.

As mentioned above, the composition according to the present invention meets certain specific requirements for _ g _

the dynamic viscosity at -3O⁰C,. the kinematic viscosity at 100⁰C, the high temperature, high shear viscosity and the Noack volatility.

Typically, the dynamic viscosity at -30⁰C (according to ASTM D 5293) of the composition is between 3000 and

6600 cP, preferably between 4000 and 6450 cP (1 cP is the same as 1 mPa. s) .

Typically, the dynamic viscosity at -35⁰C {according to ASTM D 5293) of the composition is between 4000 and 8000 cP.

Typically, the kinematic viscosity at 100⁰C

(according to ASTM D 445} of the composition is between

9.3 and 26.1 cSt, preferably between 9.3 and 16.3, more preferably between 9.3 and 12.5. Typically, the high temperature, high shear viscosity

("HTHS"; according to ASTM D 4683) of the composition is between 2.9 and 5.0 cP, preferably between 3.0 and 3.7 cP. Typically, the Noack volatility (according to ASTM D

5800) of the composition is between 1 and 14 wt.%, preferably below 13.0 wt.%, more preferably below 11.0 wt.%, even more preferably below 10.5 wt.%, most preferably below 10.0 wt.%.

Also it is preferred that the composition has a mini rotary viscometer (MRV) value at -35⁰C (according to ASTM D 4684) of below 60,000 cP, more preferably below 50,000 cP, even more preferably below 40,000 cP, and typically above 20,000.

The lubricating composition according to the present invention further comprises one or more additives such as anti-oxidants, anti-wear additives, dispersants, detergents, overbased detergents, extreme pressure additives, friction modifiers, viscosity index improvers, pour point depressants, metal passivators, corrosion inhibitors, demulsifiers, anti-foam agents, seal compatibility agents and additive diluent base oils, etc. As the person skilled in the art is familiar with the above and other additives, these are not further discussed here in detail. Specific examples of such additives are described in for example Kirk-Othmer Encyclopedia of Chemical Technology, third edition, volume 14, pages 477-526.

Anti-oxidants that may be conveniently used include phenyl-naphthylamines (such as "IRGANOX L-O 6" available from Ciba Specialty Chemicals) and diphenylamines (such as "IRGANOX L™57" available from Ciba Specialty

Chemicals) as e.g. disclosed in WO 2007/045629 and EP 1 058 720 Bl, phenolic anti-oxidants, etc. The teaching of WO 2007/045629 and EP 1 058 720 Bl is hereby incorporated by reference. Anti-wear additives that may be conveniently used include zinc-containing compounds such as zinc dithiophosphate compounds selected from zinc dialkyl-, diaryl- and/or alkylaryl- dithiophosphates, molybdenum- containing compounds, boron-containing compounds and ashless anti-wear additives such as substituted or unsubstituted thiophosphoric acids, and salts thereof.

Examples of such molybdenum-containing compounds may conveniently include molybdenum dithiocarbamates, trinuclear molybdenum compounds, for example as described in WO 98/26030, sulphides of molybdenum and molybdenum dithiophosphate .

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.

The dispersant used is preferably an ashless dispersant. Suitable examples of ashless dispersants are polybutylene succinimide polyamines and Mannic base type dispersants. o „

The detergent used is preferably an overbased detergent or detergent mixture containing e.g. salicylate, sulphonate and/or phenate-type detergents.

Examples of viscosity index improvers which may conveniently be used in the lubricating composition of the present invention include the styrene-butadiene stellate copolymers, styrene-isoprene stellate copolymers and the polymethacrylate copolymer and ethylene-propylene copolymers. Dispersant-viscosity index improvers may be used in the lubricating composition of the present invention.

Preferably, the composition contains at least 0.1 wt .% of a pour point depressant. As an example, alkylated naphthalene and phenolic polymers, polymethacrylates, maleate/fumarate copolymer esters may be conveniently used as effective pour point depressants. Preferably not more than 0.3 wt . % of the pour point depressant is used.

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 composition of the present invention as corrosion inhibitors.

Compounds such as polysiloxanes, dimethyl polycyclohexane and polyacrylates may be conveniently used in the lubricating composition of the present invention as defoaming agents.

Compounds which may be conveniently used in the lubricating composition of the present invention as seal fix or seal compatibility agents include, for example, commercially available aromatic esters.

The lubricating compositions of the present invention may be conveniently prepared by admixing the one or more additives with the base oil{s) .

The above-mentioned additives are typically present in an amount in the range of from 0.01 to 35.0 wt . % , based on the total weight of the lubricating composition , preferably in an amount in the range of from 0.05 to 25.0 wt. %, more preferably from 1.0 to 20.0 wt.%, based on the total weight of the lubricating composition. Preferably, the composition contains at least 9.0 wt.%, preferably at least 10.0 wt.%, more preferably at least 11.0 wt% of an additive package comprising an anti- wear additive, a metal detergent, an ashless dispersant and an anti-oxidant . According to an especially preferred embodiment of the present invention, the composition meets the requirements of a 5W-30 or 5W-40 formulation (according to the above-mentioned SAE J300 Specifications as revised in May 2004) , preferably those of a 5W-30 formulation. In another aspect, the present invention provides the use of a lubricating composition according to the present invention in the crankcase of an engine, in particular a heavy duty diesel engine, in order to improve fuel economy properties whilst maintaining desirable wear performance and Noack volatility properties, especially in city cycle or rural cycle, especially city cycle, in particular according to the Directive 1999/96/EC of the European Parliament. With "city cycle" is meant the status of the engine before it has reached steady-state thermal equilibrium (as is usually the case when driving in a city}, i.e. as opposed to "highway cycle".

Also the present invention provides a method of improving fuel economy properties whilst maintaining desirable wear performance and Noack volatility properties, which method comprises lubricating the crankcase of an engine, in particular a heavy duty diesel engine, with a lubricating composition according to the present invention.

The present invention is described below with reference to the following Examples, which are not intended to limit the scope of the present invention in any way. Examples

Lubricating Oil Compositions Various engine oils for use in a crankcase engine were formulated.

Table 1 indicates the properties for the base oils used. Table 2 indicates the composition and properties of the fully formulated engine oil formulations that were tested; the amounts of the components are given in wt.%, based on the total weight of the fully formulated formulations .

All tested engine oil formulations contained a combination of a base oil, an additive package and a viscosity modifier, which additive package was the same in all tested compositions.

The additive package was a so-called low SAPS (low sulphated ash, phosphorus and sulphur) formulation suitable for use with diesel particulate filter after- treatment devices.

The additive package contained a combination of additives including anti-oxidants, a zinc-based anti-wear additives, an ashless dispersant, an overbased detergent mixture, a pour point depressant and about 10 ppm of an anti-foaming agent.

A conventional viscosity modifier concentrate was used to adjust the viscosity.

"Base oil 1" was a Fischer-Tropsch derived base oil ("GTL 5") having a kinematic viscosity at 100⁰C (ASTM D445) of approx. 5 cSt (IHm²S^"1) .

"Base oil 2" was a Fischer-Tropsch derived base oil ("GTL 8") having a kinematic viscosity at 100⁰C (ASTM D445) of approx. 8 cSt (Hm²S^"1) .

These GTL 5 and GTL 8 base oils may be conveniently manufactured by the process described in e.g. WO-A- 02/070631, the teaching of which is hereby incorporated by reference.

"Base oil 3" was a commercially available Group III base oil having a kinematic viscosity at 100⁰C (ASTM D445) of approx. 4.34 cSt . Base oil 3 is commercially available from e.g. SK Energy {Ulsan, South Korea) (under the trade designation "Yubase 4") .

"Base oil 4" was a commercially available Group III base oil having a kinematic viscosity at 100⁰C (ASTM D445) of approx. 6.42 cSt. Base oil 4 is commercially available from e.g. SK Energy (under the trade designation "Yubase 6") .

The compositions of Example 1 and Comparative Example

1 were obtained by mixing the base oils with the additive package using conventional lubricant blending procedures. The composition of Example 1 meets the requirements of a 5W-30 formulation, whilst the composition of

Comparative Example 1 meets the requirements of a 10W-30 formulation, both according to SAE J300. This is because the mineral base oil of Comparative Example 1 (having the same base oil viscosity as the Fischer-Tropsch derived base oil of Example 1) did not allow to meet adequately the low temperature performance and Nfoack volatility requirements of 5W-30 at the same time. The kinematic viscosities at 100⁰C (ASTM D 445) for the base oil blends as used in Table 2 was 5.46 cSt for the blend of base oil 1+2 (84.75 + 15.25 wt.%) and 5.45 cSt for the blend of base oil 3+4 (41.5 + 58.5 wt.%) . Table 1

ccording to ASTM D 445

According to ASTM D 2270

According to ASTM D 5950

^According to CEC L-40-A-93 / ASTM D 5800

According to IP 368 (modified)

Table 2

^■•According to ASTM D 5293. NB 1 cP { centi Poise) 1 mPa.s

According to ASTM D 445

According to ASTM D 4683

"According to ASTM D 5800

to ASTM D 4951 Fuel Economy Test

In order to demonstrate the fuel economy properties of the present invention, bench engine test measurements were performed on a MAN D2066 Euro 4, 6 cylinder inline common rail engine {displacement: 10.5 1; power: 324 kW; torque: 2100 Nm) linked to a ZF AS-Tronic transmission and a Daimler HL8 axle, whilst running the engine according to the European Transient Cycle (ETC) standard test. The ETC standard test has been introduced, together with the ESC (European Stationary Cycle) test, for emission certification of heavy-duty diesel engines in Europe starting in the year 2000 (see Directive 1999/96/EC of the European Parliament and of the Council dated 13 December 1999; . The ETC test has been developed by the FIGE Institute (Aachen, Germany) , based on real road cycle measurements of heavy duty vehicles (see FIGE Report 104 05 316, January 1994).

Different driving conditions are represented by three phases of the ETC test cycle, including urban, rural and motorway driving. The duration of the entire test cycle is 1800s (30 minutes) . The duration of each phase is 600s (10 minutes) .

The ETC test comprises the following parts: Phase one represents urban driving ("City Cycle") with a maximum speed of 50 km/hour, frequent starts, stops, and idling;

Phase two is rural driving ("Rural Cycle") starting with a steep acceleration segment. The average speed is about 72 km/hour; - Phase three is motorway driving ("Highway Cycle"} with average speed of about 88 km/hour.

The measured fuel consumptions (in g/kWh) are indicated in Table 3 below. Table 3 also show the CO₂ emissions over the full ETC test cycle, i.e. phases 1-3. Fuel 1 was a Fischer-Tropsch derived diesel, whilst Fuel 2 was a conventional low S (sulphur) mineral derived diesel .

Table 3

In addition to the above industry standard fuel economy test, measurements were performed on a dedicated driveline rig equipped with the same MAN D2066 Euro 4, 6 cylinder inline common rail engine (displacement: 10.5 1; power: 324 kW; torque: 2100 Nm) linked to a ZF AS-Ironic transmission and a Daimler HL8 axle.

City Cycle and Highway Cycle modes of engine operation,, controlled from a computer model, were monitored for fuel consumption. The computer control of the engine (torque and speed in revolutions per minute) was carried out by using City and Highway Cycles that had been determined by interfacing a data logger to the engine management system of a Hamburg bus, which was driven on typical City and Highway cycle applications. The data logger was then downloaded to the computer controlling the driveline rig.

The measured fuel consumptions (in grams) are indicated in Table 4 below; as fuel a conventional low sulphur mineral diesel was used. Table 4

Wear Performance

In order to demonstrate the wear properties of the present invention, wear measurements were performed according to the industry standard 4 -ball wear test of IP- 239-4. The measured wear scars according to IP-239-4 are indicated in Table 5 below.

It was also found that Example 1 according to the present invention exceeded the ACEA E-7 limits for the Cummins ISM heavy duty diesel engine test. The Cummins ISM test of the ACEA E-7 category measures cross-head mass loss (in mg) . Example 1 produced a result of 6.3 mg weight loss against an ACEA E-7 limit of 7.5 mg maximum. Table 5

In respect of the wear performance it is noted that - when properly comparing the fuel economy properties of two lubricants - the lubricant exhibiting improved fuel economy properties (i.e. Example 1) should provide at least equivalent extreme pressure wear protection compared to the reference oil (i.e. Comparative Example 1). This requires that both the viscometrics of the finished lubricants (kinematic viscosity at 100⁰C (ASTM D 445}, and HTHS at 150⁰C (ASTM D 4683}) should be equivalent within SAE J300 specification, but also base oil contribution to the viscosity at 100⁰C (ASTM D 445) should be equivalent. The former (finished lubricant viscosity) is to guarantee wear protection in for example low pressure plain main bearings, the latter (base oil viscosity) is to guarantee wear protection in for example high pressure environments such as non-conformal contacts (e.g. cross heads in heavy duty diesel engines) .

The above means that if the kinematic viscosity at 100⁰C and HTHS of the finished lubricant are controlled, the low temperature viscometrics (the cold crank viscosity} will "float". It is possible to meet all of the above requirements where kinematic viscosity at 100⁰C, HTHS and cold crank viscosity fall in the same SAE multigrade specification or where because of differences in cold crank viscosity - two crankcase lubricants fall within two different SAE multigrade specifications (as is the case for the compositions of Example 1 (5W-30) and Comparative Example 1 (10W-30) } . Discussion

As can be learned from Table 3, the fuel economy values for Example 1 were significantly improved when compared with Comparative Example 1, especially for the urban (or "City") and rural cycle of the ETC fuel consumption test cycle. This is shown in terms of weight (in grams) of fuel consumed (per kilo Watt hour of engine work) and also weight (in grams) of carbon dioxide {CO₂) emitted {per kilo Watt hour of engine work) . The above improved fuel economy values for the present invention were confirmed (see Table 4) in a "real life" test using a dedicated driveline rig equipped with the same MAN D2066 Euro 4, 6 cylinder inline common rail engine . Further, it was found (see Table 5) that the wear performance of the heavy duty diesel lubricant of Example 1 formulated with the Fischer-Iropsch derived base oil was at least as good (at a load of 40 kg) or significantly better (at a load of 60 kg) than the lubricant of Comparative Example 1 formulated with a mineral Group III base oil. Also, desirable Cummins ISM test values were obtained using Example 1 according to the present invention.

The above indicates that the compositions according to the present invention exhibit not only improved fuel efficiency properties, but (as can be learned from Tables 2 and 5) at the same time desirable wear performance and Noack volatility properties, especially when compared with a similar lubricating composition using a Group III mineral oil.

An important advantage of the present invention is that 5W-30 formulations also meeting stringent Noack volatility requirements (less than 10 wt.%) can be obtained without the need of using (relatively expensive) poly-alpha olefin (PAO) base oils. As can be seen from Table 2, the composition of Example 1 shows a surprisingly low Noack volatility when compared to the composition of Comparative Example 1 (using a Group III mineral base oil) . Another important advantage of the present invention is that (as can be learned from Tables 1 and 2) at equal base oil viscosity within the finished lubricating composition the Fischer-Tropsch derived base oil results in a substantially lower cold-crank viscosity (i.e. dynamic viscosities according to ASTM D 5293) than a Group III mineral base oil.

Claims

C L A I M S

1. A lubricating composition comprising a base oil and one or more additives, wherein the composition has: a dynamic viscosity at -30⁰C (according to ASTM D 5293) of below 6600 cP; a kinematic viscosity at 100⁰C (according to ASTM D

445) of at least 9.3 cSt; a high temperature, high shear viscosity ("HTHS"; according to ASTM D 4683) of at least 2.9 cP; a Noack volatility (according to ASTM D 5800) of below 14 wt.%; wherein the base oil has a kinematic viscosity at 100⁰C (according to ASTM D 445) of at least 4.8 cSt.

2. Lubricating composition according to claim 1, wherein the base oil comprises a base oil selected from the group consisting of a Fischer-Tropsch derived base oil and a poly-alpha olefin (PAO) base oil or a combination thereof.

3. Lubricating composition according to claim 1 or 2, wherein the base oil contains more than 50 wt.%, preferably more than 60 wt.%, more preferably more than 70 wt.%, even more preferably more than 80 wt.%, most preferably more than 90 wt.% Fischer-Tropsch derived base oil.

4. Lubricating composition according any one of claims 1 to 3, wherein the base oil has a kinematic viscosity at 100⁰C of at least 5.0 cSt, preferably at least 5.2 cSt.

5. Lubricating composition according any one of claims 1 to 4, wherein the composition has a Noack volatility of below 13.0 wt.%, preferably below 11.0 wt.%, more preferably below 10.5 wt.%, most preferably below 10.0 wt.%.

6. Lubricating composition according to any one of claims 1 to 5, wherein the composition has a mini rotary viscometer (MRV) value at -35⁰C (according to ASTM D 4684) of below 60,000 cP.

7. Lubricating composition according to any one of claims 1 to 6, wherein the composition contains at least 0.1 wt. % of a pour point depressant.

8. Lubricating composition according to any one of claims 1 to 7, wherein the composition contains at least 9.0 wt.%, preferably at least 10.0 wt.%, more preferably at least 11.0 wt% of an additive package comprising an anti-wear additive, a metal detergent, an ashless dispersant and an anti-oxidant .

9. Lubricating composition according to any one of claims 1 to 8, wherein the composition meets the requirements of a 5W-30 or 5W-40 formulation.

10. Use of a lubricating composition according to any one of claims 1 to 9 in the crankcase of an engine, in particular a heavy duty diesel engine, in order to improve fuel economy properties whilst maintaining desirable wear performance and Noack volatility properties. .

11. Use according to claim 10 in city cycle or rural cycle, especially city cycle, in particular according to the ETC test (Directive 1999/96/EC of the European Parliament} .

12. A method of improving fuel economy properties whilst maintaining desirable wear performance and Noack volatility properties, which method comprises lubricating the crankcase of an engine, in particular a heavy duty diesel engine, with a lubricating composition according to any one of Claims 1 to 9.