WO2019202150A1

WO2019202150A1 - Lubricant composition for industrial engines with increased fe potential

Info

Publication number: WO2019202150A1
Application number: PCT/EP2019/060237
Authority: WO
Inventors: Stéphane GAVAND; Sophie OPPILLIART; Bernard Lamy
Original assignee: Total Marketing Services
Priority date: 2018-04-20
Filing date: 2019-04-19
Publication date: 2019-10-24
Also published as: CN112154199A; CN112154199B; CA3097251A1; FR3080383A1; US20210171854A1; FR3080383B1; EP3781656A1

Abstract

The present invention relates to the field of multifunctional lubricants that can be used in the various parts of motor vehicles, notably in the engine, the transmission or the hydraulic circuit. The invention relates to the use of at least one viscosity index improver polymer chosen from hydrogenated diene/vinyl aromatic copolymers in a lubricant composition for reducing the viscosity of said lubricant composition in the course of the use of said lubricant composition during the lubrication of the various parts of an industrial vehicle, notably an industrial vehicle with a diesel engine, such as the engine, the gearbox and the hydraulic circuit, said lubricant composition undergoing at least one thermal shearing during the use thereof.

Description

LUBRICATING COMPOSITION FOR INDUSTRIAL ENGINES

A POTENTIAL FE AMPLIFIED

The present invention relates to the field of multifunctional lubricants used in the various bodies of self-propelled vehicles, in particular in the engine of a vehicle, the transmission or the hydraulic circuit. More specifically, the invention relates to the field of lubricants for industrial vehicles, such as public works machinery, typically equipped with industrial diesel engines. The present invention aims in particular to provide the use of specific viscosity index improvers polymers for the development of lubricating compositions demonstrating a "potential FE" ("Fuel Economy" in English terminology) amplified during time or CIFE ("Continuously Increasing Fuel Economy" in English terminology), as explained below. This terminology covers lubricants whose FE potential is increasing over time, which is reflected not only in the fact that the viscosity of the lubricant does not increase significantly as it is used in the industrial diesel engine but it is lower than the viscosity of the same lubricants before use.

Lubricating compositions, also called "lubricants", are commonly used in engines for the main purpose of reducing the friction forces between the various moving metal parts in the engines, the transmission and the hydraulic circuit. They are also effective to prevent premature wear or damage to these parts, especially their surface.

To do this, a lubricant composition is conventionally composed of a base oil to which are generally associated several additives dedicated to boosting the lubricating performance of the base oil, such as viscosity index improving polymers and modifying additives. friction.

In the field of industrial engines, a single lubricating composition is used directly in several types of application, in particular in the various components of self-propelled vehicles such as engines, transmission devices (gearboxes and transfer gearboxes), hydraulic circuits and other secondary organs without modification; in other words, the composition of this fluid is directly adapted for the different types of uses in question. Thus, a multifunctional lubricant composition must immediately meet particular viscosity constraints related to the fact that the operations of the different organs generate particular viscosities of said lubricant composition over time of reuse. In other words, these constraints make it necessary to aim for compromises in terms of viscosity and corollary in the choice of polymers impacting the viscosity index.

In addition, industrial diesel engines are often subjected to severe or even drastic uses.

The fact of having a single lubricating composition or multifunctional composition for lubricating various components of a vehicle, compared to the use of several mono-functional oils, has advantages in particular in terms of ease of maintenance and storage, maintenance of the vehicle or fleet of vehicles, packaging and logistics. This is particularly true for large fleets of public works vehicles, which are often used on isolated sites and subjected to bad weather conditions and lacking adequate storage facilities.

Finally, if need be to meet these intrinsic constraints due to the architecture of industrial engines and to the single use for the various organs constituting it, as well as to a potentially prolonged use of these engines, is added the need to find lubricant compositions whose viscosity decreases over use.

Lubricating compositions, known as "Fuel-Eco" (FE) (for "fuel economy" in English terminology), are known that use polymers with a high index of viscosity (IV or "VI" in English terminology) and little Shearable, especially developed for the lubrication of industrial equipment, for example used in Public Works or Mines and Quarries. These compositions make it possible to obtain a gain in fuel consumption.

Thus, in use, the lubricants of the prior art typically see their viscosity increase, which has a negative impact on the FE character of the lubricants.

In the case of these FE-type lubricants, the viscosity of the lubricating composition is reduced thus making it possible to make FE. Nevertheless, this FE property is not amplified over time. Effectively the viscosity of the fluid decreases because of shearing of the polymer but this is compensated in service by the appearance of soot, oxidation products, which increase the overall viscosity of the lubricant.

GB 1575449 discloses a copolymer of conjugated diene and aromatic vinyl which can be used as a viscosity index improver, in particular because it improves the oxidation stability of lubricating compositions.

WO2013 / 066915 discloses a lubricating oil composition comprising a lubricating viscosity base oil, a low shear stability index viscosity modifier, and a high shear stability index viscosity modifier.

These documents of the state of the art are not aimed at improving the potential of FE over time, when using the lubricating composition, especially under stress, such as shear stresses that are traditionally found when using a lubricating composition in an industrial vehicle, in particular an industrial vehicle with a diesel engine.

In other words, there is a need for viscosity index improving polymers for the preparation of multifunctional lubricating compositions whose viscosity decreases as and when the use of an industrial vehicle, especially an industrial vehicle with diesel engine, and whose viscosity is lower after use to these same lubricant compositions before use, and in particular for all three applications that are the engine, the transmission and the hydraulic circuit.

It follows that the decrease in viscosity that can be observed during use of the lubricating compositions corresponding to these properties is increasing over time.

Such lubricating compositions, the preparation of which is intended in the context of the present invention, may thus be described as lubricating compositions having continuously increasing FE properties or CIFE ("Continuously Increasing Fuel Economy" in English terminology).

In the context of the present invention, said FE properties are also referred to as FE potential or fuel economy potential.

Thus, the invention aims at the use of at least one viscosity index improving polymer chosen from hydrogenated aromatic diene and vinyl vinyl copolymers in a lubricant composition to improve the fuel economy potential of the a lubricant composition as it is used during the lubrication of the various components of an industrial vehicle, in particular an industrial vehicle with a diesel engine, such as the engine, the gearbox and the hydraulic circuit.

The aim of the invention is precisely to propose the use of at least one viscosity index improving polymer chosen from hydrogenated aromatic diene and vinyl vinyl copolymers with a view to preparing a lubricating composition intended to lubricate the various components of a vehicle. industrial, including an industrial vehicle diesel engine, such as the engine, the gearbox and the hydraulic circuit, characterized in that the measured viscosity of said lubricant composition decreases as and when its use to lubricate said vehicle .

The invention also aims to propose the use of at least one viscosity index improving polymer chosen from hydrogenated aromatic diene and vinyl vinyl copolymers in a lubricating composition for reducing the viscosity of said lubricant composition as and when the use of said lubricating composition during the lubrication of the various components of an industrial vehicle, in particular of an industrial vehicle with a diesel engine, such as the engine, the gearbox and the hydraulic circuit, the said lubricant composition being subjected to less thermal shear during its use.

The lubricating composition thus obtained can be used to lubricate the various components of an industrial vehicle and in particular the engine of an industrial vehicle, in particular an industrial vehicle with a diesel engine, such as the machines used in public works or in mining and quarrying. Careers. Said lubricant composition therefore has a viscosity profile adapted to the conditions of use required in each target member, namely the engine, the gearbox and the hydraulic circuit. An industrial vehicle within the meaning of the present invention is to be distinguished from a motor vehicle. Typically, the conditions of use impose mechanical stresses, such as mechanical shear as well as thermal shears in the long term. In the context of the present invention, thermal shear is understood to mean thermal stresses or thermal shear stresses. This thermal shear typically occurs on exposure to at least 70 ° C, in particular at least 90 ° C, more particularly at least 100 ° C, even more particularly from 70 to 300 ° C, for example from 90 to 250 ° C. ° C, or for example from 100 to 200 ° C.

The inventors have discovered that the polymer defined in the present invention in a lubricating composition makes it possible to reduce the viscosity of said lubricating composition during its use, even when the lubricating composition undergoes at least thermal shear during its use, and more particularly thermal shear and mechanical shear.

According to a particular embodiment of the invention, the lubrication in the use condition comprising at least the thermal shear lasts at least 24 hours, for example at least 30 hours, or even at least 40 hours, 80 hours or 120 hours.

According to another embodiment of the invention, the polymer is used in order to reduce the viscosity of the lubricant composition at the end of the dynamic road cycle, in particular over a period of at least 80 hours, in particular at least 180 hours, and even more particularly at least 250 hours, such as for example that described for step 2 of the motor test of Example 3 of the experimental part.

Unexpectedly, the inventors have discovered that the lubricant composition according to the invention obtained, after prolonged use in an industrial vehicle, has a viscosity lower than that of a fresh lubricating composition, and this in usual conditions of use. Such conditions of customary use are for example understood as being conducive to shear stresses, and more particularly without the provision of external oxygen, that is to say other than the oxygen of the ambient air. Typically, the intended use in the present invention is to distinguish from a use to improve the oxidation stability.

In other words, the present invention aims at providing the use of at least one viscosity index improving polymer chosen from hydrogenated aromatic diene and vinyl vinyl copolymers in a lubricating composition for reducing the viscosity of said lubricant composition as and when as the lubricating composition is used during the lubrication of the various components of an industrial vehicle, in particular an industrial vehicle with a diesel engine, such as the engine, the gearbox and the hydraulic circuit, the said lubricant composition undergoing at least thermal shear during its use, without external oxygen supply. The examples below thus demonstrate that the composition according to the invention, as obtained after use, object of the present invention, allows to maintain the grade according SAEJ300 classification after prolonged use in a vehicle industrial diesel engine.

To model and prove this property, the inventors have in particular demonstrated that the compositions obtained with the use of the viscosity improving copolymers according to the present invention.

(i) have a kinematic viscosity after being placed in an oven at 150 ° C. for 504 hours less than that of the composition before being oven dried, and

(ii) have a kinematic viscosity after cycle Bosch-90 cycles lower than that of the composition before this test,

(iii) allow for CIFE after an endurance test performed on an industrial engine, including an industrial diesel engine.

The inventors have also demonstrated the decrease in the viscosity of said lubricant composition during these two tests (i) and (ii) in particular as illustrated in Example 3.

The inventors have also demonstrated that the reduction of the viscosity of said lubricant composition during test (iii), especially as illustrated in Example 4, makes it possible to make CIFE.

Also, as also emerges from the examples below and in particular from Example 2, the hydrogenated aromatic diene and vinyl aromatic copolymers are the only viscosity index improving polymers having this characteristic of progressively decreasing the viscosity of said composition. lubricant during use in an industrial vehicle diesel engine and thus obtain lubricating compositions to make the CIFE.

The present invention also relates to the use of a composition comprising at least one base oil and at least one viscosity index improving polymer chosen from hydrogenated aromatic diene and vinyl vinyl copolymers for lubricating the various components of a vehicle. industrial, and in particular of an industrial vehicle with a diesel engine, such as the engine, the gearbox and the hydraulic circuit, in particular the engine of an industrial vehicle, in particular of an industrial motor vehicle characterized in that the measured viscosity of said lubricating composition decreases as it is used to lubricate said vehicle.

According to one embodiment of the invention, the polymer is used in order to reduce the viscosity of the lubricating composition by at least 4%, preferably by at least 8%, more preferably by at least 10%, preferably at least 12% after conditioning the lubricating composition at 150 ° C for 504 hours.

According to one embodiment of the invention, the polymer is used in order to reduce the viscosity of the lubricating composition by at least 5%, preferably by at least 10%, more preferably by at least 12%, preferentially at least 15% at the end of the dynamic road cycle, such as for example that described for step 2 of the motor test of Example 3 of the experimental part.

The invention also relates to a method of lubricating the various components of an industrial vehicle, and in particular of an industrial vehicle with a diesel engine, such as the engine, the gearbox and the hydraulic circuit, in particular the engine of a industrial vehicle, in particular a diesel industrial vehicle, comprising contacting said members with a lubricating composition comprising at least one base oil and at least one viscosity index improving polymer chosen from diene and carbon copolymers. hydrogenated aromatic vinyl, characterized in that the measured viscosity of said lubricating composition decreases as and when lubrication of said members, said lubricating composition undergoing at least one thermal shear during lubrication, more particularly undergoing at least one thermal shear and at least one mechanical shear, in particular without of oxygen outside.

As indicated above, according to another embodiment of the invention, the lubrication during the process comprising at least the thermal shear lasts at least 24 hours, for example at least 30 hours, or even at least 40 hours, 80 hours or 120 hours.

As indicated above, according to another embodiment of the invention, the polymer makes it possible to reduce the viscosity of the lubricant composition at the end of the dynamic road cycle, especially over a period of at least 80 hours, in particular from 'at least 180 hours, and even more particularly at least 250 hours, such as for example that described for step 2 of the motor test of Example 3 of the experimental part.

FIG. 1 illustrates the behavior of the viscosity of compositions compliant and not in accordance with the invention at 100 ° C. after 90-cycle Bosch tests (example 2).

Figures 2 and 3 illustrate the CIFE behavior of the compositions according to the invention during the endurance test performed on diesel industrial engine and refer to Example 3 (viscosity measurement curves).

In the context of the invention, the lubricating compositions in question are of classification grade SAEJ300, defined by the formula (X) W (Y), in which X represents 5, 10 or 15 and Y represents 30 or 40.

This SAEJ300 classification defines the viscosity grades of new engine oils, in particular by measuring their kinematic viscosities at 100 ° C.

The grade qualifies a selection of lubricant compositions specifically intended for an industrial vehicle application and which satisfy, in particular, quantified specificities with respect to various parameters such as the multifunctionality with respect to the various members, the cold viscosity at start-up. , cold pumpability, low shear kinematic viscosity and high shear rate dynamic viscosity.

Engine oil is grade 30 according to SAE J 300 if its kinematic viscosity at 100 ° C is between 9.3 and 12.5 cSt.

A motor oil is grade 40 according to SAE J 300 if its kinematic viscosity at 100 ° C is between 12.5 and 16.3 cSt.

The ACEA standards define in detail a certain number of additional specifications for engine oils, and in particular require the maintenance of a certain level of viscosity for the oils in operation subjected to shear in the engine.

Thus, according to the ACEA E7 or E9 sequence, the kinematic viscosity of the 30 and 40 grade motor oils, measured at 100 ° C., after the Bosch-90 cycle test, must be greater than 9.3 and 12.5 cSt, respectively. These lubricating compositions in accordance with the present invention have a kinematic viscosity at 100 ° C of greater than 9.3 cSt, preferably in the range of 9.3 to 12.5 cSt after the Bosch-90 cycle test according to the CEC standard. L-14-A-93 for an oil starting from grade 30.

These lubricant compositions according to the present invention have a kinematic viscosity at 100 ° C of greater than 13.0 cSt, preferably in the range of 13.0 to 15.0 cSt after the Bosch-90 cycle test according to the CEC-standard. L-14-A-93 for an oil from grade 40.

Other characteristics, variants and advantages of the lubricant compositions in accordance with the invention will emerge more clearly on reading the description and the examples which follow, given by way of illustration and not limitation of the invention.

In the rest of the text, the expressions "between ... and ...", "going ... to ..." and "varying from ... to ..." are equivalent and mean to signify that are included unless otherwise stated.

In the context of the present invention, the CEC-L-14-A-93 (or ASTM D6278) standard defines tests representative of the shear conditions in the engine, referred to as the Bosch-90 cycle test.

Without further mention in the rest of the text, the terms Bosch-90 cycles refer to this standard.

To characterize the lubricant composition according to the present invention, the Applicant has defined the shear conditions representative of the engine.

LUBRICATING COMPOSITION CONFORMING TO THE INVENTION

Viscosity Index Improving Polymer Selected Among Hydrogenated Diene and Vinyl Aromatic Copolymers

In the context of the present invention, the diene may be a conjugated diene comprising from 4 to 20 carbon atoms, preferably from 2 to 12 carbon atoms. In particular, the diene may be a conjugated diene comprising from 2 to 20 carbon atoms, preferably from 4 to 12 carbon atoms.

Preferably, the diene may be chosen from butadiene, isoprene, piperylene, 4-methylpenta-1,3-diene, 2-phenyl-1,3-butadiene, 3,4-dimethyl-1, 3-hexadiene and 4,5-diethyl-1,3-octadiene.

Advantageously, the diene may be an isoprene or a butadiene.

In the context of the present invention, the aromatic vinyl may comprise from 8 to 16 carbon atoms.

Preferably, the aromatic vinyl may be selected from styrene, alkoxy styrene, vinyl naphthalene and alkyl vinyl naphthalene. Typically, the alkoxy and alkyl groups comprise from 1 to 6 carbon atoms.

Advantageously, the aromatic vinyl is styrene.

Advantageously, the polymer according to the invention may be chosen from a copolymer of isoprene and hydrogenated styrene (PISH), a copolymer of isoprene, butadiene and hydrogenated styrene, a copolymer of butadiene and hydrogenated styrene (SBH) and one of their mixtures.

According to a preferred embodiment, the polymer according to the invention may be chosen from a copolymer of isoprene and hydrogenated styrene (PISH), a copolymer of butadiene and hydrogenated styrene (SBH) and a mixture thereof.

According to this preferred embodiment, the copolymer used in the present invention is not a copolymer of isoprene, butadiene and styrene. Still according to this preferred embodiment, the copolymer used in the present invention is not a terpolymer.

For example, the copolymers of isoprene and hydrogenated styrene and the copolymers of hydrogenated isoprene, butadiene and styrene in the meaning of the invention are described in patent application EP 2 363 454 and the structures and definitions of these polymers. as described in EP 2 363 454 are incorporated in the description of the present application.

In the context of the present invention, the hydrogenated styrene-diene copolymer can be a block copolymer or a starred copolymer. In the context of the present invention, the polymers according to the present invention may have a number average molecular weight of about 10,000 to 700,000, preferably about 30,000 to 500,000. The term "number average molecular weight" As used herein, refers to the number average weight measured by gel permeation chromatography ("GPC") with a polymer standard after hydrogenation.

According to a preferred embodiment, the PISH and SBH copolymers do not comprise monomer additional to the monomers respectively of isoprene and hydrogenated styrene and of butadiene and hydrogenated styrene.

According to a particular embodiment, the polymer is a copolymer of isoprene and hydrogenated styrene (PISH).

For example, among the PISH copolymers suitable for the present invention, mention may be made of the copolymers having the following formula (I) or (II):

with R 1, R 2, R 3 and R 4: isoprene / styrene / isoprene (hydrogenated) copolymers, 1, m, n and o are independently of each other whole numbers greater than or equal to zero such that the number average molar mass the copolymer ranges from 10,000 to 700,000. These copolymers of formula (II) are called star type (English star copolymers), obtained by reaction of block copolymers isoprene / styrene / isoprene with divinylbenzene followed by hydrogenation, according to techniques known to those skilled in the art.

In the context of the invention, mention may in particular be made, as copolymer of isoprene and hydrogenated styrene (PISH) or of isoprene, butadiene and hydrogenated styrene copolymer, those sold under the name SV154 linear, SV300 with a star ( pure or diluted in SV301 form), star SV260 (pure or diluted in SV 261 form) by Infinfeum and Lz 7306 by Lubrizol.

According to a particular embodiment, the polymer is a copolymer of butadiene and hydrogenated styrene (SBH).

For example, the SBH copolymers suitable for the present invention include copolymers having the following formula (G) or (IG):

with R1 ', R2', R3 'and R4': butadiene / styrene / butadiene (hydrogenated) copolymers, 1, m, n and o are, independently of one another, integers greater than or equal to zero such that the mass The molar number average of the copolymer ranges from 10,000 to 700,000. These copolymers of formula (IG) are called star type (English star copolymers), obtained by reaction of butadiene / styrene / butadiene block copolymers with divinylbenzene followed by hydrogenation.

Examples of the SBH copolymer that may be mentioned are those sold under the name Lz 7408 (pure or diluted in the Lz 7418A form) by the company Lubrizol or Hitec 6005 by the company Afton Chemicals.

Thus, according to one particular embodiment of the invention, the isoprene-hydrogenated styrene copolymer (PISH) and the hydrogenated styrene-butadiene copolymer (SBH) is of the star type.

In particular, the content of viscosity index improving polymer (s) in the lubricating composition according to the invention is from 0.1% to 10% by weight, relative to the total weight of the lubricating composition, preferably from 0.1% to 8%, more preferably 0.1% to 5%, still more preferably 0.1% to 2%. This amount refers to the amount of active polymer material. Indeed, the polymer used in the context of the present invention may be in the form of a dispersion in a mineral or synthetic or pure oil.

In particular also, a composition used according to the invention may comprise from 1 to 25% by weight, preferably from 2 to 20% by weight, more preferably from 4 to 20% by weight of polymer (s) improving the index viscosity diluted in a base oil, relative to the total weight of the composition.

It is up to those skilled in the art to adapt the copolymer content as defined above to be used in a lubricant composition.

Thus, according to one particular embodiment, the present invention also relates to the use of a composition comprising at least one base oil and a viscosity index improving polymer chosen from a copolymer of isoprene and hydrogenated styrene (PISH ) and a copolymer of butadiene and hydrogenated styrene (SBH), for lubricating the various components of an industrial vehicle, and in particular of a vehicle industrial diesel engine, such as the engine, the gearbox and the hydraulic circuit, in particular the engine of an industrial vehicle, especially a diesel industrial vehicle, characterized in that the measured viscosity of said lubricating composition decreases as and when it is used to lubricate said vehicle, said lubricant composition undergoing at least thermal shear during its use, more particularly undergoing at least one thermal shear and at least one mechanical shear, in particular without oxygen supply outside.

The copolymers defined above may be mixed with one or more base oils, in particular as defined below, to form a ready-to-use lubricant composition. Alternatively, they may be added alone, or in admixture with one or more other additives, as defined below, as additives to be added to a base oil mixture to improve the properties of the lubricating composition. .

According to one embodiment of the invention, the use according to the present invention is characterized in that the lubricating composition comprises a base oil of groups I to V, more particularly II or III, and optionally a package of additives. and optionally a pour point improver.

Base oil

The base oils used in the formulation of lubricants according to the present invention are oils, of mineral origin, synthetic or natural, used alone or as a mixture, belonging to groups I to V according to the API classification (Table A), or their equivalents according to the ATIEL classification, or mixtures thereof, one of the characteristics of which is to be insensitive to shear, that is to say that their viscosity is not modified under shear.

Table A

Mineral base oils include all types of bases obtained by atmospheric and vacuum distillation of crude oil, followed by refining operations such as solvent extraction, desalphating, solvent dewaxing, hydrotreating, hydrocracking, hydroisomerization and hydrofining.

The synthetic base oils may be esters of carboxylic acids and alcohols or polyalphaolefins or polyalkylenes glycols. The polyalphaoleils used as base oils are, for example, obtained from monomers comprising from 4 to 32 carbon atoms, for example from decene, octene or dodecene, and whose viscosity at 100 ° C. is between 1.5 and 15 mm ² . s ¹ according to ASTM D445. Their average molecular weight is generally between 250 and 3000 according to ASTM D5296.

The polyalkylene glycols are obtained by polymerization or copolymerization of alkylene oxides comprising from 2 to 8 carbon atoms, in particular from 2 to 4 carbon atoms.

Mixtures of synthetic and mineral oils can also be used.

There is generally no limitation on the use of different lubricating bases to make the lubricating compositions according to the invention, except that they must have properties, in particular viscosity, viscosity index, sulfur content. , resistance to oxidation, adapted to use for the various components of an industrial vehicle, such as the engine, the gearbox and the hydraulic circuit, in particular for industrial vehicle engines. Of course, they must also not affect the properties provided by the oil or with which they are combined.

According to a particular embodiment, the lubricant composition according to the present invention, the use of which is the subject of the present invention, implements a Group II base oil.

They represent in the lubricant composition according to the invention at least 50% by weight, based on the total weight of the composition, in particular at least 60% by weight, and more particularly between 60 and 90% by weight.

additives

The composition according to the present invention may further comprise additives, or "package of additives" according to the terminology conventionally used in the context of multifunctional lubricating compositions.

The additive packages used in the lubricant formulations in accordance with the invention are conventional and also known to those skilled in the art and meet performance levels defined inter alia by the ACEA (Association of European Automobile Manufacturers) and or API (American Petroleum Institute).

A lubricating composition according to the invention may thus comprise one or more additives chosen from friction modifying additives, antiwear additives, extreme pressure additives, detergent additives, antioxidant additives, viscosity index improvers (VI ) different from hydrogenated aromatic diene and vinyl aromatic copolymers, pour point depressant (PPD) additives, dispersants, defoamers, thickeners, and mixtures thereof.

As for the friction modifying additives, they may be chosen from compounds providing metal elements and compounds free of ash.

Among the compounds providing metal elements, mention may be made of transition metal complexes such as Mo, Sb. Sn, Fe, Cu, Zn whose ligands can be hydrocarbon compounds comprising oxygen, nitrogen, sulfur or phosphorus atoms.

The ashless friction modifier additives are generally of organic origin and may be selected from monoesters of fatty acids and polyols, alkoxylated amines, alkoxylated fatty amines, fatty epoxides, borate fatty epoxides, amines oily fatty acid esters or glycerol esters. According to the invention, the fatty compounds comprise at least one hydrocarbon group comprising from 10 to 24 carbon atoms.

According to an advantageous variant, a lubricant composition according to the invention comprises at least one friction-modifying additive, in particular based on molybdenum.

In particular, the molybdenum-based compounds may be chosen from molybdenum dithiocarbamates (Mo-DTC), molybdenum dithiophosphates (Mo-DTP), and mixtures thereof.

According to a particular embodiment, a lubricant composition according to the invention comprises at least one Mo-DTC compound and at least one Mo-DTP compound. A lubricating composition may in particular comprise a molybdenum content of between 1000 and 2500 ppm.

Advantageously, such a composition allows for additional fuel savings.

Advantageously, a lubricant composition according to the invention may comprise from 0.01 to 5% by weight, preferably from 0.01 to 5% by weight, more particularly from 0.1 to 2% by weight, or even more particularly from 0.1 to 1.5% by weight, based on the total weight of the lubricant composition, of friction modifying additives, advantageously including at least one molybdenum-based friction modifying additive.

With regard to the anti-wear additives and the extreme pressure additives, they are more particularly dedicated to protecting the friction surfaces by forming a protective film adsorbed on these surfaces. There is a wide variety of anti-wear additives.

The lubricant compositions according to the invention are particularly suitable for anti-wear additives chosen from polysulfide additives and olefin additives. sulfur or phospho-sulfur-containing additives such as metal alkylthiophosphates, in particular zinc alkylthiophosphates, and more specifically zinc dialkyldithiophosphates or ZnDTPs. The preferred compounds have the formula Zn ((SP (S) (OR) (OR ')) 2, in which R and R', which may be identical or different, independently represent an alkyl group, preferably containing from 1 to 18 carbon atoms.

Advantageously, a lubricant composition according to the invention may comprise from 0.01 to 6% by weight, preferably from 0.05 to 4% by weight, more preferably from 0.1 to 2% by weight, relative to the weight total composition, anti-wear additives and extreme pressure additives.

As regards the antioxidant additives, they are essentially dedicated to delaying the degradation of the lubricating composition in service. This degradation can notably result in the formation of deposits, the presence of sludge or an increase in the viscosity of the lubricant composition. They act in particular as radical inhibitors or destroyers of hydroperoxides. Among the antioxidant additives commonly used, mention may be made of phenolic type antioxidants, amine antioxidant additives and phosphosulfur antioxidant additives. Some of these antioxidant additives, for example phosphosulfur antioxidant additives, can be ash generators. Phenolic antioxidant additives may be ash-free or may be in the form of neutral or basic metal salts. The antioxidant additives may especially be chosen from sterically hindered phenols, sterically hindered phenol esters and sterically hindered phenols comprising a thioether bridge, diphenylamines, diphenylamines substituted by at least one C 1 -C 12 alkyl group, and N, N'-dialkyl-aryl diamines and mixtures thereof

Preferably, the sterically hindered phenols are chosen from compounds comprising a phenol group in which at least one vicinal carbon of the carbon bearing the alcohol function is substituted by at least one C 1 -C 10 alkyl group, preferably a C 1 -C 4 alkyl group. , preferably a C ₄ alkyl group, preferably by the ter-butyl group.

Amino compounds are another class of antioxidant additives that can be used, optionally in combination with phenolic antioxidant additives. of the examples of amine compounds are aromatic amines, for example aromatic amines of formula NR ⁵ R ⁶ R ⁷ in which R ⁵ represents an optionally substituted aliphatic or aromatic group, R ⁶ represents an optionally substituted aromatic group, R ⁷ represents a hydrogen atom, an alkyl group, an aryl group or a group of formula R ⁸ S (O) _z R ⁹ in which R ⁸ represents an alkylene group or an alkenylene group, R ⁹ represents an alkyl group, a group alkenyl or an aryl group and z represents 0, 1 or 2.

Sulfurized alkyl phenols or their alkali and alkaline earth metal salts can also be used as antioxidant additives.

The lubricant composition according to the invention may contain all types of antioxidant additives known to those skilled in the art. Advantageously, the lubricating composition comprises at least one ash-free antioxidant additive.

Also advantageously, a lubricating composition according to the invention may comprise from 0.1 to 2% by weight, relative to the total weight of the composition, of at least one antioxidant additive.

With regard to so-called detergent additives, they generally make it possible to reduce the formation of deposits on the surface of the metal parts by dissolving the secondary products of oxidation and combustion.

The detergent additives that can be used in a lubricant composition according to the invention are generally known to those skilled in the art. The detergent additives may be anionic compounds comprising a long lipophilic hydrocarbon chain and a hydrophilic head. The associated cation may be a metal cation of an alkali metal or alkaline earth metal.

The detergent additives are preferably chosen from alkali metal or alkaline-earth metal salts of carboxylic acids, sulphonates, salicylates, naphthenates, as well as salts of phenates. The alkaline and alkaline-earth metals are preferably calcium, magnesium, sodium or barium. These metal salts generally comprise the metal in stoichiometric amount or in excess, therefore in an amount greater than the stoichiometric amount. It is then overbased detergent additives; the excess metal bringing the overbased character to the detergent additive is then generally in the form of a metal salt insoluble in the base oil, for example a carbonate, a hydroxide, an oxalate, an acetate, a glutamate, preferably a carbonate.

A lubricating composition according to the invention may comprise from 0.5 to 8%, preferably from 0.5 to 4% by weight, relative to the total weight of the lubricant composition, of detergent additive.

Advantageously, a lubricating composition according to the invention may comprise less than 4% by weight of detergent additive (s), in particular less than 2% by weight, in particular less than 1% by weight, or even be free of detergent additive.

As regards pour point depressant additives (also called "PPD" agents for "Pour Point Depressant" in English), they make it possible, by slowing down the formation of paraffin crystals, to improve the cold behavior of the lubricant composition. according to the invention.

As examples of pour point reducing agents, there may be mentioned alkyl polymethacrylates, polyacrylates, polyarylamides, polyalkylphenols, polyalkylnaphthalenes and alkylated polystyrenes.

As for the dispersing agents, they ensure the suspension and evacuation of the insoluble solid contaminants constituted by the secondary oxidation products that form when the lubricant composition is in use. They can be chosen from Mannich bases, succinimides and their derivatives.

In particular, a lubricant composition according to the invention may comprise from 0.2 to 10% by weight of dispersing agent (s), relative to the total weight of the composition.

Additional viscosity index (VI) improvers, other than the hydrogenated aromatic diene and vinyl aromatic copolymers, may also be present in a lubricant composition according to the present invention. These improvers of the viscosity index (VI) may be present in a composition according to the present invention in contents which do not disturb the desired effect in the context of the present invention, namely the CIFE effect. These additional viscosity index (VI) improvers, particularly the additional viscosity index improving polymers, make it possible to guarantee a good resistance to cold and a minimum viscosity at high temperature. Examples of viscosity index improver polymers include polymeric esters, homopolymers or copolymers of olefin, such as ethylene or propylene, polyacrylates and polymethacrylates (PMA).

In particular, a lubricating composition according to the invention may comprise from 1 to 15% by weight of additive (s) improving the viscosity index, relative to the total weight of the lubricating composition.

The anti-foam additives may be chosen from polar polymers such as polymethylsiloxanes or polyacrylates.

In particular, a lubricant composition according to the invention may comprise from 0.01 to 3% by weight of anti-foam additive (s), relative to the total weight of the lubricant composition.

Packages of additives ready to be incorporated in a lubricating composition comprise between 20% and 30% by weight of a diluent consisting of base oil. The weight percentage of additive package relative to the weight of the lubricant composition according to the invention is at least 5%, the diluent being included in this percentage.

According to one embodiment, the lubricant composition according to the invention comprises from 10 to 25% by weight, relative to the weight of the composition, of a package of additives, in particular from 10 to 20% by weight, and more particularly from 13 to 18% by weight.

CHARACTERIZATION OF THE LUBRICATING COMPOSITION IN ACCORDANCE WITH THE INVENTION

Preferably, a composition according to the present invention has a kinematic viscosity at 100 ° C of between 9.3 and 16.3 cSt measured by ASTM D445 (SAE grade 30 and 40).

According to a particular embodiment, the grade according to the SAEJ300 classification of a lubricant composition according to the invention is chosen from 5W30, 10W30, 10W40, 15W40. According to a particular embodiment, a composition according to the present invention has a viscosity index VI of between 140 and 165.

In the context of the present invention, the viscosity number is measured according to the ASTM D2270-93 standard, as is the case in Example 1 below.

According to one particular embodiment of the invention, the use which is the subject of the invention is further characterized in that the measured kinematic viscosity of said lubricating composition decreases by at least 0.5 mm ² / s, preferably at least 0.6 mm ² / s, and even more preferably at least 0.8 mm ² / s, and for example at least 1 mm%, when said lubricating composition is implemented in the test described below, with respect to the initial kinematic viscosity before implementation of said lubricant composition in said test:

150 g of lubricating composition is placed in a ventilated oven heated at 150 ° C. for 504 hours. At the end of this test, a sample of the lubricating composition is taken and the kinematic viscosity at 100 ° C. according to ASTM D445-97 (mm ² / s) of this composition is measured.

Examples of this reduction in the kinematic viscosity observed for the compositions according to the present invention after thermal stability test are given in Example 2.

USE OF COPOLYMERS FOR PREPARING A

LUBRICANT COMPOSITION

The lubricant compositions according to the invention find a particularly advantageous application as lubricants for the various components of an industrial vehicle, such as engines, transmission systems (gearbox and transfer), hydraulic circuits and other secondary organs, and especially the engine of an industrial vehicle, in particular diesel engine.

They not only allow, thanks to their viscosity properties, to lubricate these different organs, but also to lengthen the emptying intervals and to save fuel. PROCESS FOR PREPARING A LUBRICATING COMPOSITION

A lubricant composition according to the invention may be prepared according to conventional methods known to those skilled in the art.

The invention will now be described by means of the following examples given of course by way of illustration and not limitation of the invention.

EXAMPLES

Example 1 Preparation of Lubricating Compositions

Table 1 below shows the details of the lubricant compositions according to the invention (CL) and comparative compositions (CC) for which the contents are expressed as a percentage by weight, as well as their physicochemical characteristics.

The lubricating compositions are obtained by simply mixing at room temperature, the following components:

Base oil 1 is a Group I base oil (kinematic viscosity at 100 ° C. measured according to ASTM D445 = 5.30 mm ² / s) commercially available for example from the company TOTAL under the trade name " 150 NS »

⁽²⁾ Base oil 2 is a Group II base oil (kinematic viscosity at 100 ° C. measured according to ASTM D445 = 4.10 mm ² / s) commercially available for example from Chevron under the trade name "100R".

Base oil 3 is a Group II base oil (kinematic viscosity at 100 ° C. measured according to ASTM standard D445 = 6.4 mm ² / s) commercially available for example from Chevron under the trade name "220R" ._

⁽³⁾ A conventional additive package comprising at least a dispersant, detergents, anti-wear, antioxidants, friction modifiers

⁽⁴⁾ A pour point depressant additive which is a conventional polymer of polymethacrylate commercially available from Evonik under the trade name "Viscoplex®",

^(5> Polymer 1 (outside the invention) is a polyisobutylene polymer commercially available from Ineos under the trade name "Indopole® H300", ⁽⁶⁾ Polymer 2 is a hydrogenated styrene-butadiene polymer commercially available from Lubrizol under the trade name "Lz® 7418",

⁽¹⁾ Polymer 3 is a hydrogenated styrene-butadiene polymer commercially available from Afton under the trademark "Hitec® 6005",

⁽⁾ Polymer 4 is a stellar hydrogenated isoprene-styrene polymer commercially available from Infneum under the trade name "SV® 301",

^<9) Polymer 5 is a stellar hydrogenated isoprene-styrene polymer commercially available from the company Infneum under the trade name "SV® 261",

0 ° ⁾ Polymer 6 is a linear hydrogenated isoprene-styrene polymer commercially available from the company Infneum under the trade name "SV® 154", b Polymer 7 is a hydrogenated isoprene-styrene polymer commercially available from Lubrizol under the name trade name "Lz® 7306",

^{(I 2)} Polymer 8 is a polymethacrylate polymer commercially available from Evonik under the trade name "Viscoplex® 6-950",

³⁾ Polymer 9 is a polymethacrylate polymer commercially available from Evonik under the trade name "Viscoplex® 6-850".

⁴⁾ Polymer 10 is a polymethacrylate polymer commercially available from Sanyo Chemical under the trade name "AClub® VI 0-70".

Table 1 Example 2 Compared Viscosity Behaviors Illustrating the Decrease in Viscosity As It Is Used

The present examples were carried out in order to demonstrate the selection made among the viscosity index improver polymers, making it possible to prepare lubricating compositions having CIFE properties as referred to within the scope of the present invention.

The tests implemented are as follows:

Thermal stability at 150 ° C

The kinematic viscosities of the comparative compositions and the compositions according to the invention as described in Table 1 having previously undergone the thermal stability test as described above, were measured and collated in Table 2 below.

Table 2 It emerges from these results that the compositions according to the invention exhibit a kinematic viscosity at 100 ° C., measured according to the ASTM D445-97 standard, after the thermal stability test, which decreases over time with respect to their kinematic viscosities measured before the test. stability.

It also results from these results that the comparative compositions exhibit a kinematic viscosity at 100 ° C. measured according to the ASTM D445-97 standard after the thermal stability tests, which increases over time with respect to their kinematic viscosities measured before the stability tests. .

These results illustrate the evolution of the decrease of the viscosity of the compositions according to the invention as a function of time and consequently the behavior as required according to the present invention, namely the decrease of the viscosity as a function of time of the compositions according to the invention. to the invention, during thermal shear, unlike comparative compositions for which there is an increase in viscosity during thermal shear.

These results also make it possible to demonstrate the impact of polymer chemistry on the viscosity profile of lubricating compositions during thermal shearing.

In fact, the polymers according to the invention make it possible to obtain compositions whose viscosity decreases during thermal shearing, unlike the polymers outside the invention which, when they are included in a lubricating composition, do not make it possible to reduce the viscosity of that in the case of thermal shear, on the contrary, the viscosity of the latter increases.

Mechanical Stability

Measured viscosity at 100 ° C of sheared oil after Bosch tests 90 cycles ("KYl00 ° C Bosch 90 cycles")

The compositions described in Example 1 were subjected to mechanical shear (Bosch 90 cycle injector test).

Figure 1 illustrates the phenomenon of decreasing the viscosity of the compositions as a function of the number of Bosch cycles.

This figure also illustrates the behavior as required according to the present invention, including following mechanical shearing. In general conclusion of Example 2, following the thermal and mechanical shears, it is observed that only the lubricant compositions according to the invention have viscosity values lower than that of the same composition before shearing.

Consequently, the kinematic viscosities of the compositions according to the invention after thermal and mechanical stability tests do not increase with time, but on the contrary decrease. This demonstrates that the compositions according to the invention respond to the properties of CIFE. In fact, the higher the viscosity of a composition, the more the various lubricated parts of the engine consume energy and therefore fuel.

Example 3: Motor tests

Motor tests were carried out on the lubricant compositions as described in Example 1.

Principle of the test

The engine tests are carried out on a Volvo Dl engine l € 5 (440hp), the thermal management of the lubricant is voluntarily set at 1 l8 ° C temperature in oil bowl, to be representative of hot operating conditions and thus promote the shearing of lubricating compositions by thermal effect.

Each lubricating composition test is characterized as follows:

- Step 1: new oil, measure fuel consumption on the WHSC (World Harmonized Stationary Cycle) standardized cycle.

Step 2: Aging of the lubricant composition on an endurance cycle, which consists in reproducing on the engine test bench a dynamic road cycle representative of a field use, which has been recorded under real conditions by an OEM heavy weights. The test has a duration of 300 hours. The dynamism of the test road cycle is favorable to shearing by mechanical effect of the lubricating compositions tested. Fuel consumption is monitored dynamically throughout the endurance test for guidance. Samples of intermediate oils are made during the study for perform various measurements (kinematic viscosity at 100 ° C. in particular, represented in FIGS. 2 and 3).

Step 3: after the endurance test, the lubricant composition present in the test engine is remeasured according to the WHSC standardized cycle in order to characterize the fuel consumption after the endurance test. The fuel consumption results for each of the 13 measurement points (speed / load) are compared with the results from step 1, in order to evaluate the CIFE performance of the lubricating composition tested.

It is therefore the result from step 3 that will characterize the CIFE potential of the lubricant composition tested with respect to a reference lubricant tested under the same conditions (steps 1,2,3). Fuel consumption gains are established over the entire engine field.

Results

The CL2 composition was evaluated before and after the endurance test on the WHSC cycle. FIG. 2 represents the curve for measuring the viscosity at 100 ° C. of this composition CL2 during the engine test. A gain of 0.87% in fuel consumption was measured on the sheared oil that performed the endurance test against the oil before endurance test. This gain is significant compared to the discrimination threshold between two products of the method (0.34%).

A comparative lubricating composition CC5 was then evaluated according to the same criteria.

Said comparative lubricating composition is detailed in Table 3 below:

The contents are expressed as a percentage by mass

Table 3

The meanings of the components defined by indices are those given in Example 1.

An overconsumption of 0.25% of fuel was measured on the sheared oil having carried out the endurance test with respect to the oil before endurance test. Figure 3 shows the viscosity measurement curve at 100 ° C of this comparative composition during the engine test.

This example shows very clearly the difference in behavior in terms of viscosity and more particularly the satisfaction of the CIFE characteristic required in the context of the invention, for the lubricant compositions according to the invention, namely comprising at least one polymer improving the viscosity. Viscosity index selected from hydrogenated aromatic diene and vinyl vinyl copolymers, compared to lubricating compositions comprising other viscosity index improvers. Example 4 Comparative Viscosity Behaviors Illustrating the Decrease in Viscosity as Used in the Gearbox and in the Hydraulic System

The present examples have been carried out in order to demonstrate the selection made among the viscosity index improving polymers, making it possible to prepare lubricating compositions having CIFE properties when they are used in the gearbox and in the hydraulic circuit. .

It is known that the temperatures operated in the gearbox and in the hydraulic circuit are lower than those in the engine and generally do not exceed 110.degree. It is also known that the emptying interval is longer on the gearbox and on the hydraulic circuits compared to that of the engine. Therefore, this thermal stability test carried out at a lower temperature and over a period corresponding to the emptying interval makes it possible to demonstrate the viscosity behavior of the compositions according to the invention in gearboxes and hydraulic circuits.

The tests implemented are as follows:

Thermal stability at 80 ° C

150 g of lubricating composition is placed in a ventilated oven heated at 80 ° C. for 1008 hours. At the end of this test, a sample of the lubricating composition is taken and the kinematic viscosity at 100 ° C. according to ASTM D445-97 (mm ² / s) of this composition is measured.

Thermal stability at 100 ° C

150 g of lubricating composition is placed in a ventilated oven heated at 100 ° C. for 1008 hours. At the end of this test, a sample of the lubricating composition is taken and the kinematic viscosity at 100 ° C. according to ASTM D445-97 (mm ² / s) of this composition is measured.

The kinematic viscosities of the comparative compositions and the compositions according to the invention as described in Table 1 having previously undergone the thermal stability test as described above, were measured and summarized in Table 4 below.

Table 4

It emerges from these results that the compositions according to the invention exhibit a kinematic viscosity at 100 ° C., measured according to the ASTM D445-97 standard, after the thermal stability test, which decreases over time with respect to their kinematic viscosities measured before the test. stability.

These results also show that the comparative composition has a kinematic viscosity at 100 ° C. measured according to the ASTM D445-97 standard after the thermal stability tests, which remains constant over time with respect to its kinematic viscosity measured before the tests. stability.

These results illustrate the evolution of the decrease of the viscosity of the compositions according to the invention as a function of time and consequently the behavior as required according to the present invention, namely the decrease of the viscosity as a function of time of the compositions according to the invention. to the invention, during a thermal shear, unlike the comparative composition for which there is observed the maintenance of the viscosity during thermal shearing.

In fact, the polymers according to the invention make it possible to obtain compositions whose viscosity decreases during thermal shearing, unlike the polymers outside the invention which, when they are included in a lubricating composition, do not make it possible to reduce the viscosity of this one during a thermal shear.

In conclusion, following thermal shears, it is observed that only the lubricant compositions in accordance with the invention have viscosity values that are lower than those of the same composition before shearing. Therefore, this demonstrates that the compositions according to the invention respond to the properties of CIFE when the composition is implemented in the gearbox and in the hydraulic circuit. Indeed, the higher the viscosity of a composition increases, the more the lubricated parts of the gearbox and the hydraulic circuit, are energy-consuming, and therefore fuel.

Example 5

The compositions according to the invention CL1 and CL2 were subjected to a KRL shear test of 3 hours and 20 hours according to the CEC-L-45-A-99 standard. This test is representative of the shear conditions of the gearboxes when it is carried out over a period of 20 hours and the conditions of the hydraulic circuit when it is conducted over 3 hours. The viscosities before the test and after the test were measured at 100 ° C. and 40 ° C. (ASTM standard D445-97), and are summarized in Table 5 below, where the viscosities are given in mm ² / s.

Table 5

These results show that the compositions according to the invention exhibit a kinematic viscosity at 100 ° C. measured according to ASTM D445-97 after the KRL shear test, which decreases over time with respect to their kinematic viscosities measured before the test. shearing.

These results illustrate the evolution of the decrease of the viscosity of the compositions according to the invention as a function of time and consequently the behavior as required according to the present invention, namely the decrease of the viscosity as a function of time of the compositions according to the invention. to the invention, during shearing such as that suffered by a lubricant composition in a gearbox and a hydraulic circuit, in particular an industrial vehicle, in particular an industrial vehicle with a diesel engine.

Claims

1. Use of at least one viscosity index improving polymer selected from hydrogenated aromatic diene and vinyl vinyl copolymers in a lubricating composition for decreasing the viscosity of said lubricating composition as the lubricating composition is used during the lubrication of the various components of an industrial vehicle, in particular of an industrial vehicle with a diesel engine, such as the engine, the gearbox and the hydraulic circuit, the said lubricant composition undergoing at least one thermal shear during its use .

2. Use according to the preceding claim, characterized in that the diene is chosen from a conjugated diene comprising from 4 to 20 carbon atoms, preferably from 2 to 12 carbon atoms.

3. Use according to claim 1, characterized in that the aromatic vinyl comprises from 8 to 16 carbon atoms.

4. Use according to any one of the preceding claims, characterized in that the copolymer is a block copolymer or a star copolymer.

5. Use according to any one of the preceding claims, characterized in that the copolymer is chosen from a copolymer of isoprene and hydrogenated styrene (PISH), a copolymer of isoprene, butadiene and hydrogenated styrene, a copolymer of butadiene and hydrogenated styrene (SBH) and one of their mixtures

6. Use according to any one of the preceding claims, characterized in that the active material content (s) improving the viscosity index in the lubricant composition according to the invention is from 0.1% to 10% by weight, relative to the total weight of the lubricating composition, preferably from 0.1% to 8%, more preferably from 0.1% to 5%, more preferably from 0.1% to 2%.

7. Use according to any one of the preceding claims, characterized in that the lubricating composition further comprises one or more additives selected from friction modifying additives, anti-wear additives, extreme pressure additives, detergent additives, antioxidant additives, viscosity index (VI) improvers other than hydrogenated aromatic diene and vinyl aromatic copolymers, pour point depressant (PPD) additives, dispersing agents, anti foam agents, thickeners and their mixtures.

8. Use according to any one of the preceding claims, characterized in that the lubricating composition has a kinematic viscosity at 100 ° C between 9.3 and 16.3 cSt measured by ASTM D445.

9. Use according to any one of the preceding claims for improving the fuel economy potential of the lubricant composition as it is used during the lubrication of the various components of an industrial vehicle, in particular a vehicle. industrial diesel engine, such as engine, gearbox and hydraulic system.

10. Use according to any one of the preceding claims, wherein the lubricating composition undergoes during its use further mechanical shearing.

Use according to any one of the preceding claims, wherein the polymer is a copolymer of isoprene and hydrogenated styrene (PISH).

The use according to claim 11, wherein the hydrogenated styrene-isoprene copolymer (PISH) has the following formula (I) or (II):

with R1, R2, R3 and R4: hydrogenated isoprene / styrene / isoprene copolymers,

1, m, n and o are, independently of one another, integers greater than or equal to zero such that the number-average molar mass of the copolymer ranges from 10,000 to 700,000.

13. Use according to any one of claims 1 to 10, wherein the polymer is a copolymer of butadiene and hydrogenated styrene (SBH).

The use according to claim 13, wherein the butadiene and hydrogenated styrene copolymer (SBH) has the following formula (G) or (IG):

with R1 ', R2', R3 'and R4': hydrogenated butadiene / styrene / butadiene copolymers,

15. A method of lubricating the various components of an industrial vehicle, including an industrial vehicle diesel engine, such as the engine, the gearbox and the hydraulic circuit, in particular the engine of an industrial vehicle, in particular an industrial vehicle with a diesel engine, comprising contacting said members with a lubricating composition comprising at least one base oil and at least one viscosity index improving polymer chosen from hydrogenated aromatic diene and vinyl aromatic copolymers, characterized in that the measured viscosity of said lubricating composition decreases as lubrication of said members occurs, said lubricant composition undergoing at least one thermal shear during lubrication, more particularly undergoing at least one thermal shear and at least one mechanical shear, in particular without external oxygen supply.