EP3529341A1 - Lubricant composition - Google Patents

Abstract

The present application relates to a lubricant composition comprising: - at least one base oil; - at least one polyalkylene glycol (PAG) comprising at least 50% by weight of butylene oxide units and having a kinematic viscosity, measured at 100°C according to standard ASTM D445 (2015), which is greater than or equal to 50 mm2/s, a kinematic viscosity, measured at 40°C according to standard ASTM D445 (2015), which is greater than or equal to 1000 mm2/s and a Viscosity Index, measured according to standard ASTM D2270 (2012), which is greater than or equal to 180. The present application also relates to the use of such a composition for transmission or gear lubrication.

Description

 Lubricating composition

The present application relates to the field of lubricating compositions, more particularly the field of engine lubricating compositions, in particular motor vehicle engine, for transmission and for gearing. More particularly, the present application relates to the field of lubricating compositions for transmission and gearing. Lubricating compositions for transmission (for example gearboxes or gearboxes) or for gearing, in particular for industrial gearing, must satisfy numerous requirements, in particular related to driving comfort (perfect gearshift, quiet operation, trouble-free operation, high reliability ), to the service life of the assembly (reduction of wear during cold passage, no deposits and high thermal stability, safety of lubrication at high temperatures, stable viscosity situation and absence of shear loss, long service life) and consideration of environmental aspects (lower fuel consumption, reduced lubricant consumption, low noise, easy evacuation). These include requirements for lubricating compositions for manual gearboxes and axle gears. Concerning the requirements imposed on the automatic gearbox oils (ATF oils for automatic transmission fluids), they are very specific and relate in particular to a great constancy of the coefficient of friction during all the length of stay for an optimal gearshift, an excellent stability to the aging for long emptying intervals, good viscosity-temperature performance to ensure perfect operation with a hot engine and a cold engine and sufficient sealing compatibility with different elastomers used in the transmission seals so that they do not swell not, do not shrink and do not become fragile. Moreover, in the automotive field, the search for the reduction of C0 ₂ emissions makes it necessary to develop products that make it possible to reduce friction in gearboxes and in bridge differentials. This reduction of friction in the gearboxes and in the bridge differentials must be obtained for different operating conditions. These friction reductions must concern the internal friction of the lubricant but also the friction of the elements constituting the gearboxes or bridge differentials, in particular the metal elements. (Poly) alkylmethacrylate (PAMA) are conventionally used for their very good viscosity index but have a low shear stability, however. In addition, PAMA is expensive.

 Polyalphaolefins (PAO) are also used because they have good shear stability, but their viscosity index contribution is low.

 There is therefore an interest in providing a solution to have a good viscosity and good shear stability.

An object of the present invention is therefore to provide a lubricant composition, especially for transmission and gear, having a compromise between viscosity index and shear stability.

 Another object of the present invention is also to provide such a composition which has a stability of the viscosity as a function of temperature, that is to say a good viscosity index.

 Yet another object of the present invention is to provide such a composition for a fuel saving Eco.

 Still other objects will appear on reading the description of the invention which follows. These objectives are fulfilled by the present application which relates to a lubricant composition comprising:

 at least one base oil;

at least one polyalkylene glycol (PAG), comprising at least 50% by weight of butylene oxide units and propylene oxide units, having a kinematic viscosity, measured at 100 ° C. according to the ASTM D445 (2015) standard, greater or equal to 50 mm ² / s, a kinematic viscosity, measured at 40 ° C according to ASTM D445 (2015), greater than or equal to 500 mm ² / s, more particularly greater than or equal to 1 000 mm ² / s, and a Viscosity Index, measured according to ASTM D2270 (2012), greater than or equal to 160, preferably greater than or equal to 180, even more preferably greater than or equal to 200.

Preferably, the present invention relates to a lubricant composition comprising:

 at least one base oil;

at least one polyalkylene glycol (PAG), comprising at least 50% by weight of butylene oxide units, and preferably comprising only butylene, having a kinematic viscosity, measured at 100 ° C according to ASTM D445 (2015), greater than or equal to 50 mm ² / s, a kinematic viscosity, measured at 40 ° C according to ASTM D445 (2015), superior or 1000 mm ² / s, and a Viscosity Index, measured according to ASTM D2270 (2012), greater than or equal to 180.

It should be understood in the context of the present invention that the base oil and the PAG are two distinct compounds.

 Preferably, the PAG of the invention comprises at least 80% by weight of butylene oxide units and propylene oxide units. Even more preferably, the PAG of the invention is a PAG whose alkylene units are only butylene oxide units.

 The PAG of the invention is therefore described as a PAG whose alkylene oxide units are chosen from butylene oxide and propylene oxide units with at least 50% by weight, preferably at least 80% by weight, and even more preferred 100% by weight of butylene oxide units.

 According to a preferred embodiment, the PAG of the invention comprises 100% by weight of butylene oxide units.

 Particularly advantageously, the PAG of the invention is soluble in the base oil, and advantageously whatever the temperature.

 Preferably, the PAG is obtained by polymerization or copolymerization of butylene oxides. In particular, the PAG of the invention may be prepared according to the known methods described especially in US20120108482 and in particular by reaction of one or more alcohols comprising from 2 to 12 carbon atoms, in particular polyol, preferably diol, with butylene oxide and propylene oxide. The alcohols are especially diols and preferably 1,2-propanediol. The butylene oxide may be selected from 1,2-butylene oxide or 2,3-butylene oxide, preferably 1,2-butylene oxide. In the case where the PAG comprises only butylene oxide units, the method described in US20120108482 is adapted to the single implementation of butylene oxide.

 According to one embodiment, the PAG is obtained by reaction of one or more polyols comprising from 2 to 12 carbon atoms, preferably diol, with butylene oxides.

Preferably, the PAG of the invention comprises from 25 to 300 moles of butylene oxide units, preferably from 50 to 200 moles. Preferably, the PAG of the invention comprises a ratio O / C (oxygen atom / carbon atom) by weight of between 0.29 and 0.38, preferably between 0.29 and 0.35.

 Preferably, the PAG of the invention has a molar mass of between 5,000 and 200,000 g / mol.

Preferably, the PAG of the invention has a kinematic viscosity, measured at 100 ° C. according to ASTM D445 (2015), of between 50 and 500 mm ² / s, a kinematic viscosity, measured at 40 ° C. according to the standard ASTM D445 (2015), between 500 and 4000 mm ² / s and a Viscosity Index, measured according to ASTM D2270 (2012), between 160 and 300.

Preferably, the PAG of the invention, in particular comprising 100% by weight of butylene oxide units, has a kinematic viscosity, measured at 40 ° C. according to ASTM D445 (2015), of between 1000 and 4500 mm ^2. / s, preferably between 1000 and 4250 mm ² / s, and preferably between 1100 and 4250 mm ² / s.

Preferably, the PAG of the invention, in particular comprising 100% by weight of butylene oxide units, has a Viscosity Index, measured according to ASTM D2270 (2012), of between 180 and 300, preferably between 200 and 300. According to a particularly preferred embodiment, the PAG has a kinematic viscosity measured at 100 ° C. according to ASTM D445 (2015) of between 50 and 500 mm ² / s, a kinematic viscosity measured at 40 ° C. according to ASTM D445 ( 2015) between 1000 and 4500 mm ² / s and a viscosity index measured according to ASTM D2270 (2012) between 180 and 300.

Preferably, the lubricating composition of the invention comprises at most 30% by weight of PAG, preferably from 2% to 30% by weight of PAG, more preferably from 2% to 15% relative to the total weight of the PAG. lubricating composition. Preferably, the lubricating composition of the invention comprises at most 30% by weight of PAG, preferably from 6% to 30% by weight of PAG, more preferably from 9% to 16% relative to the total weight of the PAG. lubricating composition.

The lubricant composition used according to the invention comprises at least one base oil. In general, the lubricant composition used according to the invention can include any type of mineral lubricating base oil, synthetic or natural, animal or vegetable, known to those skilled in the art.

 The base oils used in the lubricant compositions according to the invention may be oils of mineral or synthetic origins belonging to groups I to V according to the classes defined in the API classification (or their equivalents according to the ATIEL classification) (Table A) or their mixtures.

 Table A

The mineral base oils according to the invention include all types of base oils obtained by atmospheric and vacuum distillation of crude oil, followed by refining operations such as solvent extraction, desalphating, solvent dewaxing, hydrotreatment, hydrocracking , hydroisomerization and hydrofinition.

 Mixtures of synthetic and mineral oils can also be used.

 There is generally no limitation as to the use of different lubricating bases for producing the lubricating compositions used according to the invention, except that they must have properties, in particular viscosity, oxidation resistance, adapted for use for engines or for vehicle transmissions.

The base oils of the lubricant compositions used according to the invention can also be chosen from synthetic oils, such as certain carboxylic acid esters and alcohols, and from polyalphaolefins (PAOs). The polyalphaolefins used as base oils are, for example, obtained from monomers comprising from 4 to 32 carbon atoms, for example from octene or of decene, and whose viscosity at 100 ° C is between 1, 5 and 15 mm ² .s ^"1 according to the ASTM D445 (2015) standard Their average molecular mass is generally between 250 and 3000 according to the ASTM standard D5296.

 Preferably, the base oils of the present invention are chosen from the above base oils whose aromatic content is between 0 and 45%, preferably between 0 and 30%. The aromatic content of the oils is measured according to UV Burdett method.

 Advantageously, the lubricant composition used according to the invention comprises at least 50% by weight of base oils relative to the total mass of the composition.

 More advantageously, the lubricant composition used according to the invention comprises at least 60% by weight, or even at least 70% by weight, of base oils relative to the total mass of the composition.

 More particularly advantageously, the lubricant composition used according to the invention comprises from 60 to 99.5% by weight of base oils, preferably from 70 to 99.5% by weight of base oils, relative to the total mass of the composition, preferably from 70 to 98%.

 Many additives can be used for this lubricant composition used according to the invention.

 The preferred additives for the lubricant composition used according to the invention are chosen from friction modifiers, detergents, anti-wear additives, extreme pressure additives, viscosity index improvers, dispersants, antioxidants, pour point improvers, defoamers, thickeners and mixtures thereof.

Preferably, the lubricant composition used according to the invention comprises at least one antiwear additive, at least one extreme pressure additive or their mixtures. Anti-wear additives and extreme pressure additives protect friction surfaces by forming a protective film adsorbed on these surfaces. There is a wide variety of anti-wear additives. In a preferred manner for the lubricating composition according to the invention, the anti-wear additives are chosen from phosphosulfur 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 ² ) (OR ³ )) ₂ , in which R ² and R ³ , which may be identical or different, independently represent an alkyl group, preferably an alkyl group containing from 1 to 18 carbon atoms Amine phosphates are also anti-wear additives that can be used in the composition lubricant according to the invention. However, the phosphorus provided by these additives can act as a poison of the catalytic systems of automobiles because these additives are ash generators. These effects can be minimized by partially substituting amine phosphates with non-phosphorus additives, such as, for example, polysulfides, especially sulfur-containing olefins. Advantageously, the 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 mass. total lubricating composition, anti-wear additives and extreme pressure additives.

 Advantageously, the lubricant composition according to the invention may comprise at least one friction-modifying additive. The friction modifying additive may be chosen from a compound providing metal elements and an ash-free compound. Among the compounds providing metal elements, mention may be made of transition metal complexes such as Mo, Sb, Sn, Fe, Cu and Zn, the ligands of which may be hydrocarbon compounds comprising oxygen, nitrogen, sulfur or phosphorus. 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; fatty amines or fatty acid glycerol esters. According to the invention, the fatty compounds comprise at least one hydrocarbon group comprising from 10 to 24 carbon atoms. Advantageously, the lubricant composition according to the invention may comprise from 0.01 to 2% by weight or from 0.01 to 5% by weight, preferably from 0.1 to 1.5% by weight or 0.1 at 2% by weight relative to the total mass of the lubricant composition, friction modifier additive.

Advantageously, the lubricant composition according to the invention may comprise at least one antioxidant additive. The antioxidant additive generally serves to retard 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. Antioxidant additives act in particular as radical inhibitors or destroyers of hydroperoxides. Among the antioxidant additives commonly used, mention may be made of antioxidant additives of phenolic type, antioxidant additives of amine type, antioxidant phosphosulfur 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 with at least one C ₁ -C ₁₂ alkyl group, Ν , Ν'-dialkyl-aryl diamines and mixtures thereof. Preferably, according to the invention, 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 with at least one alkyl group containing ₁₀ carbon atoms, preferably an alkyl group containing CrC ₆ , 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. Examples of amine compounds are the aromatic amines, for example the aromatic amines of formula NR ⁴ R ⁵ R ⁶ in which R ⁴ represents an optionally substituted aliphatic or aromatic group, R ⁵ represents an optionally substituted aromatic group R ⁶ represents a hydrogen atom, an alkyl group, an aryl group or a group of formula R ⁷ S (0) _z R ⁸ wherein R ⁷ represents an alkylene group or alkenylene group, R ⁸ represents an alkyl group, alkenyl group or an aryl group and z represents 0, 1 or 2. Sulfurized alkyl phenols or their alkali and alkaline earth metal salts may also be used as antioxidant additives. Another class of antioxidant additives is copper compounds, for example copper thio- or dithio-phosphates, copper and carboxylic acid salts, dithiocarbamates, sulphonates, phenates, copper acetylacetonates. Copper salts I and II, succinic acid or anhydride salts can also be used. 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, the lubricating composition according to the invention comprises from 0.5 to 2% by weight relative to the total weight of the composition, of at least one antioxidant additive.

The lubricant composition according to the invention may also comprise at least one detergent additive. The detergent additives generally make it possible to reduce the formation of deposits on the surface of the metal parts by dissolving the secondary oxidation and combustion products. The detergent additives that can be used in the lubricant composition according to the invention are generally known to those skilled in the art. The detergent additives can 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 the alkali metal or alkaline earth metal salts of carboxylic acids, the sulphonates, the salicylates, the naphthenates and the phenate salts. The alkali 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 an oil insoluble metal salt, for example a carbonate, a hydroxide, an oxalate, an acetate, a glutamate, preferably a carbonate . Advantageously, the lubricant composition according to the invention may comprise from 0.5 to 4% by weight of detergent additive relative to the total mass of the lubricant composition.

 Also advantageously, the lubricant composition according to the invention may also comprise at least one pour point depressant additive. By slowing the formation of paraffin crystals, pour point depressant additives generally improve the cold behavior of the lubricant composition according to the invention. As examples of pour point depressant additives, mention may be made of alkyl polymethacrylates, polyacrylates, polyarylamides, polyalkylphenols, polyalkylnaphthalenes and alkylated polystyrenes.

 Advantageously, the lubricant composition according to the invention may also comprise at least one dispersing agent. The dispersing agent may be chosen from Mannich bases, succinimides and their derivatives. Also advantageously, the lubricating composition according to the invention may comprise from 0.2 to 10% by weight of dispersing agent relative to the total mass of the lubricating composition.

 The lubricating composition of the present invention may also comprise at least one viscosity index improving additive. Examples of additives improving the viscosity number include polymeric esters, homopolymers or copolymers, hydrogenated or non-hydrogenated, styrene, butadiene and isoprene, polyacrylates, polymethacrylates (PMA) or alternatively olefin copolymers, in particular ethylene / propylene copolymers.

The lubricating composition according to the invention can be in various forms. The lubricant composition according to the invention may in particular be an anhydrous composition. Preferably, this lubricating composition is not an emulsion. Preferably, the base oil of the composition according to the invention is chosen from group II oils and group III oils as defined above. Preferably, the base oil of the composition according to the invention comprises at least one polyalphaolefin (PAO) as described above, in particular an alkene oligomer whose final viscosity is between 2 and 500 cSt.

Preferably, the base oil of the composition according to the invention is chosen from group II oils and group III oils as defined above and at least one polyalphaolefin (PAO) as described above.

Advantageously, the lubricant composition according to the invention has excellent shear stability. The shear stability can in particular be determined from the kinematic viscosities before and after a shearing process according to the KRL 20h test according to the CEC-L-45-A-99 (2014) standard. Advantageously, the shear loss is less than 5%.

Advantageously, the lubricant composition according to the invention has low traction coefficients. The traction coefficient is determined by machine MTM (Mini Traction Machine) sold by PCS instrument. The operating conditions observed are a temperature of 40 ° C under a load of 75N and a disk speed of 1 m / s for a SRR (slip / rolling ratio or sliding-rolling ratio in English) of 20%.

 Advantageously, the lubricant composition according to the invention has a temperature-stable viscosity.

Advantageously, the lubricant composition according to the invention allows a gain in fuel Eco. Advantageously, the lubricant composition according to the invention retains satisfactory anti-wear properties.

 Advantageously, the lubricant composition according to the invention allows a performance gain on the cold properties.

The lubricating composition of the invention is particularly useful for the lubrication of the transmission components of motor vehicles, especially transmission for light or heavy vehicles, for example gearboxes, bridges, preferred manual gearbox and heavy truck bridges; or for gears, especially industrial gears. Thus, the present invention relates to the use of a lubricant composition according to the invention for the lubrication of the transmission members of motor vehicles, in particular transmission for light or heavy vehicles, for example gearboxes, bridges, preferably gearboxes. manual and heavy truck bridges; or for gears, especially industrial gears. Preferably, in the context of lubricants for transmission members of any type of grade 70W and 75W are suitable. The present invention also relates to a method of lubricating at least one mechanical part of a transmission member of motor vehicles, especially transmission for light or heavy vehicle, for example gearboxes, bridges, preferably manual gearbox and bridges. heavyweight ; or gearing, in particular industrial gearing, said method comprising at least one step in which said mechanical part is brought into contact with at least one lubricating composition according to the invention.

The lubricant composition according to the present invention can also be used for engine lubrication, especially motor vehicle engine and preferably for grades SAE OW-8, 0W-12 and 0W-16.

The invention also relates to the use of the lubricant composition according to the invention for reducing the traction coefficient of a vehicle engine oil. The invention also relates to the use of the lubricant composition according to the invention for reducing the fuel consumption of a vehicle equipped with a bridge or a gearbox lubricated with this composition.

The invention also relates to the use of the lubricant composition according to the invention for reducing the fuel consumption of a vehicle equipped with a transmission lubricated with this composition.

The invention also relates to the use of the lubricant composition according to the invention for reducing the traction coefficient of a transmission oil, in particular a gearbox oil or a deck oil. The present application also relates to the use of at least one PAG as defined above in a lubricant composition, in particular for transmission members of motor vehicles or gears, in particular industrial gears, for increasing the viscosity index of the composition. lubricant while providing a stability of the lubricating composition in shear.

The present application will now be described using non-limiting examples.

Examples

Description of the PAGs according to the invention set in the examples:

 Table 1

Lubricating compositions according to the invention:

The lubricating compositions were formulated with PAG of the invention so as to have a kinematic viscosity at 100 ° C of about 7.5 mm ² / s, these compositions are described in Table 2 below.

 CL1 (mass%) CL2 (mass%) CL3 (mass%)

Base oil

 (mix of a

 base oil of

 group III with a

 viscosity

 Kinematic at 40 ° C

71, 97 76.91 77.27 equal to 12 mm ² / s and

 a base oil

 Group III with

 a viscosity

 Kinematic at 40 ° C

equal to 19 mm ² / s)

 PAG1 - 14.54 -

PAG2 - - 14.18

Additives 8.55 8.55 8.55

 Viscosity at 100 ° C

 7.57 7.56 7.59

(mm ² / s) according to the

 Table 2

Comparative lubricating compositions:

The following comparative compositions were formulated to have a kinematic viscosity at 100 ° C of about 7.5 mm ² / sec, these compositions are described in Table 3 below. The base oil and additives are identical to those of compositions CL2 and CL3.

 Table 3 Evaluation of performances of compositions

 The performances of the lubricating compositions CL2, CL3, CC1 and CC2 were determined according to the following methods:

 Cold properties by Brookfield measurement at -40 ° C according to ASTM D2983 (2015),

- Wear according to IS014635-3 (2005), The shear stability determined by the loss of viscosity of the lubricating composition after a shearing process KRL 20h according to the standard CEC-L-45-A-99 (2014),

 The thermo-oxidative stability measured by DKA according to CEC standard L-48-A-00 (2014),

 Viscosity index according to ISO 2909 (2014).

 Table 4

 It appears that the viscosity temperature dependence (VI) is improved with respect to the reference CC2 for PAGs of sufficient viscosity.

 These results also show that the compositions according to the invention have a good brookfield viscosity, improved with respect to the CC1 reference.

 The shear stability is excellent. It can be seen that the solution of the invention, although more viscous, shears less than Viscobase 11-522® during this test, despite the fact that the PAGs tested are more viscous than the Viscobase 1 1 -522®.

Evaluation of the traction coefficients under different conditions

 In order to evaluate the Fuel Economy potential of our solution, lubricant compositions with different viscosity index improvers were made and are described in Table 5 below. These compositions were made in order to have a similar kinematic viscosity at 100 ° C.

The base oil and the additives are identical to those of the above compositions. CC3 CL4 CL5

Basic oils 76.95 78.37 83.5

 Additives 7.25 7.25 7.25

 Polymer Viscoplex 14.5

 0-130®

 PAG 1 14.38

 PAG 3 9.25

 Table 5

The traction coefficient (TOC) was measured using the PCS instrument MTM tribometer. The measurement conditions were 75N load and the disk speed was 1 m / s at an evaluated temperature (40 ° C) and a SRR of 20%. The results are shown in Table 6 below.

 Table 6

Thus, the lubricant compositions according to the invention CL4 and CL5 make it possible to lower the traction coefficient, the reproducibility of the test being of the order of 3%.

This reduction in the coefficient of traction is particularly interesting in that it leads to an increase in the fuel oil gain Eco. Evaluation of the fuel savings Eco

 The composition CL6 and the comparative composition CC4 below were used for this evaluation.

The friction modifier is a conventional organomolybdenum compound commercially available from the company Adeka under the trade name "Sakuralube®".

 The conventional additive package 1 comprises dispersant, detergents and anti-wear.

The test procedure is as follows:

Characterization of the compositions according to the invention and comparative in terms of fuel economy ("Fuel-Eco")

The test is carried out using a Honda L13-B engine, whose power is 81 kW at 5,500 rpm, driven by an electric generator to impose a rotation speed of between 650 and 5,000 revolutions / min while a torque sensor can measure the friction torque generated by the movement of the parts in the engine. The friction torque induced by the test lubricant is compared for each regime and each temperature at the torque induced by the reference lubricating composition (SAE 0W8), here CC4.

The conditions of this test are as follows.

The tests are carried out according to the following sequence:

 - rinsing the engine with a rinsing oil comprising detergent additives, followed by rinsing with a reference lubricant composition;

 measuring the friction torque at the four different temperatures indicated below on the engine using the reference lubricant composition;

- rinsing the engine with a rinsing oil comprising detergent additives, followed by rinsing with a lubricant composition to be evaluated;

 measuring the friction torque at four different temperatures on the engine implementing the lubricant composition to be evaluated;

 - rinsing the engine with a rinsing oil comprising detergent additives, followed by rinsing with the reference lubricant composition; and

 measuring the friction torque at the four different temperatures indicated below on the engine using the reference lubricant composition.

The speed ranges, the variation of the speed as well as the temperature were chosen to cover, in the most representative way possible, the points of the NEDC certified cycle.

 The instructions implemented are:

- Water temperature at the engine outlet: 35 ^° C / 50 ° C / 80 ^o C / 90 ° C ± 0.5 ° C,

- Temperature Ramp oil: 35 ^° C / 50 ° C / 80 ^o C / 90 ° C ± 0.5 ° C.

The friction gain is evaluated for each lubricant composition (CL) as a function of engine temperature and speed and in comparison with the friction of the reference lubricant composition. The results of the "Fuel Eco" test are summarized in the following table, and indicate the percentage averages of the friction gains for each composition at a given temperature over a speed range of 650 rpm to 5,000 rpm. with respect to the "Fuel Eco" results obtained with the reference composition CC4: Average friction gains in

 percentage at a temperature T of CL6

 the lubricating composition

 T = 35 ° C 0.29%

 T = 50 ° C 0.92%

 T = 80 ° C 1, 33%

 T = 90 ° C 1, 71%

These results demonstrate that the friction gains for the CL6 composition according to the invention are much greater than the friction gains obtained with the reference composition CC4.

It is understood that the greater the friction gains, the greater the fuel economy or Fuel Eco is important. This therefore implies that the compositions according to the invention make it possible to increase the Fuel Eco in contrast to the compositions comprising no PAG according to the invention.

Claims

CLAIMS 1 .- Lubricating composition comprising:  at least one base oil; at least one polyalkylene glycol (PAG) comprising at least 50% by weight of butylene oxide units and having a kinematic viscosity measured at 100 ° C. according to ASTM D445 (2015) greater than or equal to 50 mm ² / s, kinematic viscosity measured at 40 ° C according to ASTM D445 (2015) greater than or equal to 1000 mm ² / s and a viscosity index measured according to ASTM D2270 (2012) greater than or equal to 180. 2. - lubricating composition according to claim 1, wherein the PAG comprises from 25 to 300 moles of butylene oxide units, preferably from 50 to 200. 3. - lubricating composition according to any one of claims 1 or 2, wherein the PAG comprises a ratio O / C (oxygen atom / carbon atom) by weight / mol between 0.29 and 0.38 preferably between 0.29 and 0.35. 4. A lubricating composition according to any one of claims 1 to 3, wherein the PAG comprises at least 80% by weight of butylene oxide units. 5. - Lubricating composition according to any one of claims 1 to 4, wherein the alkylene oxide units of PAG are only butylene oxide units. 6. - lubricating composition according to any one of claims 1 to 5, wherein the PAG has a kinematic viscosity measured at 100 ° C according to ASTM D445 (2015) between 50 and 500 mm ² / s, a kinematic viscosity measured at 40 ° C according to ASTM D445 (2015) of between 1000 and 4500 mm ² / s and a viscosity index measured according to ASTM D2270 (2012) of between 180 and 300. 7. - lubricating composition according to any one of claims 1 to 6 comprising at most 30% by weight of PAG, preferably from 6% to 30%, more preferably from 9% to 16%. 8. A lubricating composition according to any one of claims 1 to 7, wherein the PAG is obtained by reaction of one or more polyols comprising 2 to 12 carbon atoms, preferably diol, with butylene oxides. 9. A lubricating composition according to any one of claims 1 to 8, wherein the base oil is selected from Group II oils and Group III oils. 10. - Use of a lubricant composition according to any one of claims 1 to 9 for the lubrication of motor vehicle transmission members, including transmission for light or heavy vehicles, for example gearboxes, bridges, preferably manual gearbox and heavy truck bridges; or for industrial gears. 1 1. - Use of a lubricant composition according to any one of claims 1 to 9, for the lubrication of motor, especially motor vehicle engine and preferably for SAE grades OW-8, OW-12 and OW-16. 12. A method for lubricating at least one mechanical part of a transmission member of motor vehicles or industrial gears, said method comprising at least one step in which said mechanical part is brought into contact with at least one lubricating composition. according to any one of claims 1 to 9.