Lubricant composition for preventing or reducing friction in a mechanical system

Abstract

The present application relates to a lubricant composition, in particular for preventing and / or reducing friction in a mechanical system lubricated with the lubricant composition, which comprises: i. at least one base oil; ii. at least one spiro compound having the following formula (I) wherein: M is an atom selected from boron and aluminium; n1 and n2, independently of one another, have a value of 0, 1, 2, 3 or 4, and R represent, independently of one another, a hydrocarbon group comprising from 1 to 50 carbon atoms; iii. at least one molybdenum dithiocarbamate compound; and iv. at least one phosphorus-sulphur additive.

Description

[0001] Description Title: Lubricating composition for preventing or reducing friction in a mechanical system Technical field The present invention relates to the field of lubricating compositions, in particular usable in mechanical systems, such as engines, in particular internal combustion engines, and mechanical transmission components. More particularly, the present invention provides new lubricating compositions which, when used, prevent or reduce friction present in a mechanical system and, optionally, prevent or reduce wear of such a mechanical system. Prior art Lubricating compositions, also called "lubricants", are commonly used in mechanical systems, to reduce friction between parts and thus protect the parts against wear.In addition to wear phenomena, friction can oppose the relative movement of the parts in contact and induce energy losses that are detrimental to optimal operation of the mechanical system. Lubricants are used for multiple applications, for example for metalworking, in particular for metal deformation operations, for gas or steam turbines in the fields of aeronautics, naval, rail transport and electricity production, for propulsion systems of motor vehicles, for example for the lubrication of bearings, gears, an engine, etc.For example, in the field of lubricants for motor vehicle engines or transmissions, the formulation of lubricants represents an important issue insofar as they make it possible to act on fuel consumption, and consequently on carbon dioxide emissions, via their impact on the friction forces generated between the various components of motor vehicles. In addition, engines using so-called decarbonized fuel, in particular hydrogen or ammonia fuel, do not generate carbon dioxide but consume an expensive fuel whose production is particularly energy-intensive. Reducing the consumption of fossil or decarbonized fuels through the use of lubricants that reduce friction between parts is therefore both an environmental and economic issue. Whatever the intended application, the most widespread lubricants are hydrocarbon-based lubricants.These hydrocarbon lubricants are conventionally composed of one or more base oils, to which are generally associated additives dedicated to boosting the lubricating performance of the base oils, such as for example friction modifier additives. Lubricants comprising a combination of friction modifier additives in base oils are notably proposed. For example, the document Bec S. et al., “Synergistic effect of MoDTC and ZDTP on frictional behavior of tribofilms at the nanometer scale”, Tribology Letters, 2004, 4, pp. 797-809, proposes the combination of a molybdenum dithiocarbamate compound (MoDTC) and a zinc dialkyldithiophosphate compound (ZDTP), i.e. two modifier additives, in a base oil in order to improve the tribological properties, in particular friction reduction, compared to a base oil without these additives.Nevertheless, despite the synergistic effect of the combination of these two compounds in a lubricating composition, friction within mechanical systems lubricated by compositions comprising such a combination, in particular in mixed or limit lubrication regimes, remains high, leading in particular to a significant source of inefficiency and excess energy consumption of the system. Thus, there remains a need to be able to develop new lubricating compositions making it possible to improve the tribological properties, in particular in terms of reducing friction, in particular in moderate lubrication regimes or severe lubrication conditions, of existing lubricating compositions, in particular lubricating compositions comprising one or more base oils. The present invention aims precisely to meet this need.Disclosure of the invention According to a first aspect, the present invention relates to a lubricating composition comprising: i. at least one base oil; ii. at least one spiro compound of the following formula (I). in which: M is an atom chosen from boron and aluminum; n1 and n2 are, independently of each other, 0, 1, 2, 3 or 4, and R represent, independently of each other, a hydrocarbon group comprising from 1 to 50 carbon atoms; iii. at least one molybdenum dithiocarbamate compound; and iv. at least one phosphosulfur additive. In the remainder of the text, the term "lubricating composition" or "lubricant" according to the invention will be used to refer to a lubricating composition as defined above. In the remainder of the text, the term "spiro compound" according to the invention will also be used to refer to a spiro compound of formula (I) as defined above. Examples of spiro compounds considered according to the invention are described in more detail in the remainder of the text.The spiro compounds of formula (I) as defined above have already been described for their use as detergent and / or antioxidant additives, in particular for controlling deposit or oxidation in a mechanical system. However, the detergent and / or antioxidant properties of the spiro compounds of formula (I) could in no way suggest an improvement in the tribological properties of a lubricant, when such a spiro compound is used in association with a molybdenum dithiocarbamate compound and a phosphosulfur additive.Surprisingly, as illustrated in the examples which follow, the inventors have discovered that the implementation of the association of a spiro compound of formula (I), a molybdenum dithiocarbamate compound and a phosphosulfur additive, in a lubricating composition, synergistically allows a reduction in friction, in particular in mixed or limit lubrication regimes, in a mechanical system. Thus, the tribological properties of a lubricating composition as defined above are improved. The lubrication conditions in "limit regime" (conditions of high temperature and / or pressure, severe mechanical contacts, high shear, etc.), are known to the person skilled in the art and are defined for example in the Manuel des Techniques de l'ingénieur, Introduction à la tribologie, Partie 2.1, Jean Frêne and Hamid Zaïdi, publication date September 10, 2011.The good tribological properties of the lubricating compositions according to the invention, in particular in mixed or limit lubrication regimes, allow their widespread use. According to a particular embodiment, the lubricating composition according to the invention has properties for protecting parts against wear in a mechanical system. The inventors have thus also discovered that the use of a spiro compound of formula (I), a molybdenum dithiocarbamate compound and a phosphosulfur additive as defined above, in lubricating compositions, also allows an improvement in the wear resistance of a mechanical system. Lubricating compositions according to the invention therefore advantageously combine good friction reduction properties, in particular in moderate lubrication regimes or severe lubrication conditions, and protection of parts against wear in a mechanical system.These tribological properties, particularly in terms of friction reduction and wear resistance, can be evaluated by implementing conditions such as those defined in the test detailed in the section “Evaluation of tribological properties”, carried out on a so-called Anton Paar MCR302 rheometer with a T-PTD-200 tribological assembly (“ball on three planes”), also called a tribometer with a rotating three-plane ball contact, as described in the publication by Yu Min Kiw et al., “Molecular evidence for improved tribological performances of MoDTC induced by methylene-bis(dithiocarbamates) in engine lubricants”, RSC Adv., 2022, 12, pp. 23083–23090.Such conditions more particularly require lubrication to be carried out for contact present between the ball and the three rotating planes, under conditions of temperature greater than or equal to 80°C; pressure greater than or equal to 700 MPa; and rotation speeds greater than or equal to 0.01 m / s. More particularly, the present invention relates to a lubricating composition comprising: i. at least one base oil chosen from group I to V base oils, for example a group IV base oil; ii. at least one spiro compound of formula (I) as defined above, in which M is a boron atom, n1 and n2 are 1, each R represents a C10 to C20, or C10 to C18, or C10 to C16, and for example C16 or C18, alkyl chain; iii. at least one molybdenum dithiocarbamate compound as defined such as those described below; iv. at least one phosphorus-sulfur additive such as those described below; and v.optionally at least one detergent additive distinct from the spiro compound of formula (I), chosen from alkali metal or alkaline earth metal salts of carboxylic acids corresponding to salicylates, carboxylates, or mixtures thereof, the alkali and alkaline earth metals being chosen from calcium, magnesium, sodium and barium. According to another aspect, the present invention relates to the use in a lubricating composition of at least one spiro compound of formula (I), a molybdenum dithiocarbamate compound and a phosphosulfur additive, as defined below, for preventing and / or reducing friction in a mechanical system lubricated by means of said lubricating composition, said system comprising in particular an engine, for example an internal combustion engine, and / or a mechanical transmission member.According to a particular embodiment, the present invention relates to a use as mentioned above, for preventing and / or reducing, in addition, the wear of a mechanical system lubricated by means of a lubricating composition according to the invention. According to another aspect, the present invention relates to the use of a lubricating composition according to the invention, for preventing and / or reducing friction in a mechanical system lubricated by means of said lubricating composition, said system comprising in particular an engine, for example an internal combustion engine, and / or a mechanical transmission member, more particularly an internal combustion engine. According to a particular embodiment, the present invention relates to a use as mentioned above, for preventing and / or reducing, in addition, the wear of a mechanical system lubricated by means of a lubricating composition according to the invention.According to another aspect, the present invention also relates to the use of at least one spiro compound of formula (I) as an additive for improving the tribological properties, in particular in terms of friction reduction and optionally in terms of wear reduction, of a composition comprising at least one base oil, a molybdenum dithiocarbamate compound and a phosphosulfur additive. The invention also relates to a process or method for preventing and / or reducing friction in a mechanical system comprising the lubrication of said mechanical system with a lubricating composition according to the invention as defined above. Such a system comprises, in particular, an engine, for example an internal combustion engine, and / or a mechanical transmission member.Additionally, the invention also relates to a method or process for preventing and / or reducing the wear of a mechanical system comprising the lubrication of said mechanical system with a lubricating composition according to the invention as defined above. Such a system comprises, in particular, an engine, for example an internal combustion engine and / or a mechanical transmission member. Said methods or processes more particularly comprise a step of bringing at least one mechanical part of said mechanical system, for example a mechanical part of an engine, into contact with a lubricating composition according to the invention as defined above. Other characteristics, variants and advantages of a lubricating composition according to the invention will become more apparent upon reading the description and examples which follow, given by way of illustration and not limitation of the invention.The expressions “between … and …”, “ranging from … to …”, “forming from … to …”, and “varying from … to …”, must be understood inclusively, unless otherwise stated. In the description and examples, unless otherwise stated, the percentages are percentages by weight. The percentages are therefore expressed by mass relative to the total mass of the composition. The temperature is expressed in degrees Celsius unless otherwise stated, and the pressure is atmospheric pressure, unless otherwise stated. Detailed description Definitions By alkyl group, we mean a hydrocarbon group, in particular an aliphatic hydrocarbon, linear or branched, comprising from 1 to 24 carbon atoms, in other words C1 to C. 24, for example from 4 to 18 carbon atoms, in other words from C4 to C18. In particular, the alkyl group is selected from the group consisting of methyl, ethyl, propyl, isopropyl, n-butyl, iso-butyl, tert-butyl, n-pentyl, iso-pentyl, neopentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, isotridecyl, tetradecyl, hexadecyl, stearyl, icosyl, docosyl, tetracosyl, triacontyl, 2-ethylhexyl, 2-butyloctyl, 2-butyldecyl, 2-hexyloctyl, 2-hexyldecyl, 2-octyldecyl, 2-hexyldodecyl, 2-octyldodecyl, 2-decyltetradecyl, 2-dodecylhexadecyl, 2-hexadecyloctadecyl, 2-tetradecyloctadecyl, myristyl, palmityl and stearyl. Alkenyl group means a linear or branched hydrocarbon group comprising at least one double bond and comprising from 2 to 24 carbon atoms, in other words C2 to C24.The alkenyl group may be chosen from vinyl, allyl, propenyl, butenyl, isobutenyl, pentenyl, isopentenyl, hexenyl, heptenyl, octenyl, nonenyl, decenyl, undecenyl, dodecenyl, tetradecenyl and oleic. Aryl group means a polycyclic aromatic hydrocarbon group or an aromatic group, substituted or not. The aryl group may comprise from 6 to 24 carbon atoms, in other words C6 to C24. In particular, the aryl group may be selected from the group consisting of phenyl, toluyl, xylyl, cumenyl, mesityl, benzyl, phenethyl, styryl, cinnamyl, benzhydryl, trityl, ethylphenyl, propylphenyl, butylphenyl, pentylphenyl, hexylphenyl, heptylphenyl, octylphenyl, nonylphenyl, decylphenyl, undecylphenyl, dodecylphenyl, phenylphenyl, benzylphenyl, phenyl-styrene, p-cumylphenyl and naphthyl.Cycloalkyl group means a polycyclic or cyclic hydrocarbon, substituted or not by an alkyl group. Cycloalkenyl group means a polycyclic or cyclic hydrocarbon, substituted or not by an alkyl group, and comprising at least one unsaturation. Cycloalkyl groups and cycloalkenyl groups can comprise from 3 to 24 carbon atoms, in other words C3 to C. 24. In particular, the cycloalkyl groups and the cycloalkenyl groups may be chosen, in a non-limiting manner, from the group consisting of cyclopentyl, cyclohexyl, cycloheptyl, methylcyclopentyl, methylcyclohexyl, methylcycloheptyl, cyclopentenyl, cyclohexenyl, cycloheptenyl, methylcyclopentenyl and methylcyclohexenyl. Base oil As mentioned previously, a lubricating composition according to the invention comprises at least one base oil. These base oils may be chosen from base oils conventionally used in the field of lubricating oils for engines, in particular for internal combustion engines, such as mineral, synthetic or natural, animal or vegetable oils. It may be a base oil alone or a mixture of several base oils, for example a mixture of two, three or four base oils.The base oils of the lubricating compositions considered according to the invention may in particular be oils of mineral or synthetic origin belonging to groups I to V according to the classes defined in the API classification (or their equivalents according to the ATIEL classification) and presented in Table 1 below or their mixtures. [Table 1] The mineral base oils include all types of base oils obtained by atmospheric and vacuum distillation of crude oil, followed by refining operations such as solvent extraction, dealphating, solvent dewaxing, hydrotreatment, hydrocracking, hydroisomerization and hydrofinishing. The synthetic base oils may be esters of carboxylic acids and alcohols, polyalphaolefins or polyalkylene glycols (PAG) obtained by polymerization or copolymerization of alkylene oxides comprising from 2 to 8 carbon atoms, in particular from 2 to 4 carbon atoms.Polyalphaolefins used as base oils are, for example, obtained from monomers containing 4 to 32 carbon atoms, for example from decene, octene or dodecene, and whose viscosity at 100°C is between 1.5 and 15 mm².s. -1according to ASTM D445. Their average molecular weight is generally between 250 and 3000 according to ASTM D5296. Mixtures of synthetic and mineral oils, which may be bio-sourced, may also be used. There is generally no limitation on the use of different base oils in the lubricating composition, except that they must have properties, in particular viscosity, viscosity index, sulfur content or oxidation resistance, suitable for use in internal combustion engines, in particular vehicle engines, for example light vehicles, heavy goods vehicles, off-road vehicles, engines used in marine, trains, and aviation. Preferably, a lubricating composition considered according to the invention comprises at least one base oil chosen from group I to V base oils and mixtures thereof, for example a group IV base oil.In particular, such a lubricating composition may comprise at least one mixture of at least two group I to V base oils, for example a mixture of group IV base oil and a group V base oil. The base oils suitable for the invention may have a kinematic viscosity measured at 40°C according to the ASTM D445 (KV40) standard ranging from 10 to 550 mm² / s. They may have a kinematic viscosity measured at 100°C according to the ASTM D445 (KV100) standard ranging from 1 to 35 mm² / s. In a particular embodiment, the base oils suitable for the invention may have a kinematic viscosity measured at 40°C according to the ASTM D445 (KV40) standard ranging from 10 to 150 mm² / s, in particular from 12 to 50 mm² / s, more particularly from 15 to 40 mm² / s.The base oils suitable for the invention may have a kinematic viscosity measured at 100°C according to the ASTM D445 (KV100) standard ranging from 1 to 15 mm² / s, in particular from 2 to 10 mm² / s, more particularly from 3 to 8 mm² / s. Other base oils of a more viscous grade may be used, in particular in combination with more fluid base oils as described above, for example group I base oils of the BBS (distillation residue) type, with a kinematic viscosity measured at 40°C according to the ASTM D445 (KV40) standard of the order of 450 to 550 mm² / s and / or a kinematic viscosity measured at 100°C according to the ASTM D445 (KV100) standard of the order of 30 to 35 mm² / s. These base oils are traditionally used for cylinder lubricants for marine engines.The base oil(s) may be present in a lubricating composition according to the invention in a content of at least 50% by mass relative to the total mass of the lubricating composition, in particular at least 60% by mass relative to the total mass of the lubricating composition, more particularly ranging from 60 to 99% by mass relative to the total mass of the lubricating composition, even more particularly ranging from 70 to 99% by mass relative to the total mass of the lubricating composition and preferably ranging from 80 to 99% by mass relative to the total mass of the lubricating composition.Preferably, the group IV oil or oils represent(s) at least 50% by mass of the total mass of the base oils of the lubricating composition, in particular at least 60% by mass of the total mass of the base oils of the lubricating composition, more particularly between 70 and 100% by mass of the total mass of the base oils of the lubricating composition, for example between 80 and 100% by mass of the total mass of the base oils of the lubricating composition. The lubricating composition may comprise at least one mixture of at least two base oils, for example at least one group IV base oil and at least one group V base oil, in particular in a content ranging from 80 to 95% by mass of group IV base oil(s) relative to the total mass of the lubricating composition, and in a content ranging from 1 to 15% by mass of group V base oil(s) relative to the total mass of the lubricating composition.According to a particular embodiment, the inventors have advantageously shown, as illustrated in Example 6, that the use of a mixture of at least two base oils, in particular a group IV base oil and a group V base oil, in a composition according to the invention also has good tribological properties, in particular in terms of friction reduction and optionally wear reduction. In particular, the results illustrated in Example 6 show that the good tribological properties of a composition according to the invention can be generalized to a mixture of at least two base oils from distinct groups, in particular group IV base oils mixed with another base oil chosen from group V base oils. Spiro compound As indicated previously, a lubricating composition according to the invention comprises at least one spiro compound of formula (I) as defined above.As mentioned previously, the spiro compound considered according to the invention is of the following formula (I) [Chem 2]. in which: M is an atom chosen from boron and aluminum, in particular is a boron atom; n1 and n2 are, independently of one another, 0, 1, 2, 3 or 4; and R represent, independently of one another, a hydrocarbon group comprising from 1 to 50 carbon atoms, in particular from 3 to 30 carbon atoms, in particular from 5 to 25 carbon atoms, more particularly from 10 to 20 carbon atoms or from 10 to 18 carbon atoms, or from 10 to 16 carbon atoms, and for example in C 16 or in C 18. The hydrocarbon groups considered according to the invention may optionally be interrupted by one or more heteroatoms, for example -O-, -NH-, -N= or -S-, in particular -O- or -NH-; and / or optionally substituted by one or more -OH, -NH2 and -SH groups, in particular -OH or -NH2. According to a particular embodiment, the R groups are composed solely of carbon and hydrogen atoms. The hydrocarbon groups may in particular be alkyl, alkenyl, aryl or aralkyl groups.According to a particular embodiment, the substituents R represent, independently of one another, a hydrocarbon group, preferably a linear or branched aliphatic chain, comprising from 3 to 50 carbon atoms, in particular from 3 to 30 carbon atoms, in particular from 5 to 25 carbon atoms and more particularly from 10 to 20 carbon atoms, or else 10 to 18 carbon atoms or else 10 to 16 carbon atoms, and for example 16 or 18 carbon atoms. In particular, the substituents R may represent, independently of one another, a linear or branched aliphatic chain, in particular an alkyl chain, preferably linear, from C1 to C. 50 , especially in C3 to C 30 , especially in C5 to C 25, more particularly in C10 to C20 or in C10 to C18, or in C10 to C16, and for example in C16 or in C18. According to a particular embodiment, n1 and n2 are 0. According to another particular embodiment, n1 and n2 are 1 or 2. When n1 is 2 or n2 is 2, the R groups, carried by the same cycle, may be identical or different. According to a particular embodiment, the spiro compound may be of formula (I) above, in which n1 and n2 are 1; the R substituents may be identical or different, preferably identical. According to a particular embodiment, the spiro compound is of formula (I) above, in which: n1 and n2 are 1; and the R groups, which are identical, represent alkyl groups, preferably linear, in C1 to C 50 , especially in C3 to C 30 , especially in C5 to C 25 and more particularly in C 10 to C 20 , or even in C 10 to C 18, or even in C 10 to C 16 , and for example in C 16 or in C 18 . According to a particular embodiment, the spiro compound is of formula (I) in which M is a boron atom. In other words, according to this particular embodiment, the spiro compound may be a compound called spiroboronate, of the following formula (I'): [Chem 3] in which n1 and n2 and R are as defined previously. According to another particular embodiment, the spiro compound is of formula (I) in which M is an aluminum atom. In other words, according to this particular embodiment, the spiro compound may be a compound called spiroaluminate, of the following formula (I''): [Chem 4] in which n1, n2 and R are as defined above. The invention thus relates, according to another of its aspects, to a spiro compound of formula (I) above, in which: - M is an aluminum atom; - n1 and n2 are, independently of each other, 0, 1 or 2, at least one of n1 and n2 being 1 or 2; preferably n1 and n2 are 1; - the R groups represent, independently of each other, a linear or branched aliphatic chain, in particular an alkyl chain, preferably linear, in C1 to C 50 , especially in C3 to C 30 , especially in C5 to C 25 , more particularly in C 10 to C 20, or C10 to C18, or C10 to C16, and for example C16 or C18. In other words, the invention relates to a spiroaluminate type compound of formula (I'') above, in which: - n1 and n2 are, independently of each other, 0, 1 or 2, at least one of n1 and n2 being 1 or 2; preferably n1 and n2 are 1; and - the R groups represent, independently of each other, a linear or branched aliphatic chain, in particular an alkyl chain, preferably linear, C1 to C 50 , especially in C3 to C 30 , especially in C5 to C 25 , more particularly in C 10 to C 20, or in C10 to C18, or in C10 to C16, and for example in C16 or in C18. According to a particular embodiment, the spiroaluminate type compound according to the invention is of formula (I'') in which: - n1 and n2 are 1; and - the R groups, identical or different, preferably identical, represent alkyl chains, preferably linear, in C1 to C50, in particular in C3 to C30, in particular in C5 to C25, more particularly in C10 to C20, or in C10 to C18, or in C10 to C 16 , and for example in C 16 or in C 18 . The spiro compound used according to the invention can be prepared from at least salicylic acid or a salicylic acid derivative and a boron compound or an aluminum compound. More particularly, it can be obtained by reaction: - of at least one compound chosen from salicylic acid and its derivatives, of the following formula (Ia): in which R is as defined above and n is as defined above for n1 and n2; and - at least one boron or aluminum compound, in particular boric acid or aluminum hydroxide. The preparation of the spiro compound used in the lubricating composition according to the invention does not involve any step, subsequent to the reaction of salicylic acid or one of its derivatives with said boron or aluminum compound, of reaction with an amine compound, as is the case for example in the context of the preparation of the compounds proposed in applications WO2018 / 220007 and WO2018 / 220009. Salicylic acid and its derivatives of formula (Ia) above can be synthesized according to synthesis methods known to those skilled in the art or be commercially available.The boron compound (in other words, boron-based) may be chosen in particular from boric acid (B(OH)3), boronic acids, boric and boronic esters, boron oxide and boric acid complexes. In particular, the boron compound may be chosen from boric acid; boron oxide; boric acid complexes; trialkyl borates, in particular in which the alkyl groups comprise, independently of one another, from 1 to 4 carbon atoms; boronic acids having a C1-C group. 12 alkyl; boric acids substituted by two alkyl groups, in particular C1 to C 12 ; boric acids substituted by two aryl groups, in particular C6 to C12; boric acids substituted by one or two aralkyl groups, in particular C7 to C 12, and derivatives of these compounds obtained by substitution of at least one alkyl group by one or more alkoxy groups. Boric acid complexes are in particular complexes of boron with one or more molecules comprising one or more alcohol functions. According to a particular embodiment, the boron compound is boric acid. The aluminum compound (in other words, aluminum-based) may be chosen, for example, from aluminum hydroxide (Al(OH)3), aluminum oxide, aluminum sulfate (Al2SO4)3. It is up to the person skilled in the art to adjust the reaction conditions between said compound(s) (Ia) and the boron or aluminum compound to obtain the desired spiro compound. In particular, the reaction may be carried out in a solvent medium consisting of one or more apolar solvents and / or protic polar solvents.The solvent medium may consist of one or more solvents chosen from naphtha, protic polar solvents, such as water and alcohols, for example methanol, ethanol, propanol, butanol; and mixtures thereof. According to one embodiment, one or more spiro compounds of formula (I) are used in a content of between 0.1 and 5.0% by mass relative to the total mass of the lubricating composition. In particular, one or more spiro compounds of formula (I) are used in a content of between 0.5 and 4.0% by mass relative to the total mass of the lubricating composition. More particularly, one or more spiro compounds of formula (I) are used in a content of between 1 and 3.0% by mass relative to the total mass of the lubricating composition.Molybdenum dithiocarbamate compound As indicated above, a lubricating composition according to the invention comprises at least one molybdenum dithiocarbamate compound as mentioned above, also called MoDTC. MoDTC compounds are complexes formed from at least one molybdenum metal core bound to one or more ligands, the ligand being an alkyl dithiocarbamate group. These compounds are well known to those skilled in the art. According to a particular embodiment, the molybdenum dithiocarbamate compound is chosen from: - the dimeric molybdenum dithiocarbamates of the following formula (II). in which R1, R2, R3 and R4, which may be identical or different, independently represent a hydrocarbon group chosen from alkyl groups, in particular C4 to C18, alkenyl, aryl, cycloalkyl or cycloalkenyl, and X3, X4, X5 and X6, which may be identical or different, independently represent an oxygen atom or a sulfur atom; - trimeric molybdenum dithiocarbamates of formula Mo3SkLn in which: (i) k represents an integer at least equal to 4, in particular between 4 and 10, more particularly between 4 and 7, (ii) n is an integer ranging from 1 to 4, and (iii) L is an alkyl dithiocarbamate group comprising from 1 to 100 carbon atoms, in particular from 1 to 40 carbon atoms, more particularly from 3 to 20 carbon atoms; and - mixtures thereof.In other words, the MoDTC compound used in the present invention may be chosen from those whose nucleus has two molybdenum atoms (also called dimeric MoDTC) and those whose nucleus has three molybdenum atoms (also called trimeric MoDTC). According to one embodiment, the molybdenum dithiocarbamate compound is chosen from the dimeric molybdenum dithiocarbamates of the following formula (II) [Chem 6]. in which R1, R2, R3 and R4, identical or different, independently represent a hydrocarbon group chosen from alkyl groups, in particular C4 to C18, alkenyl, aryl, cycloalkyl or cycloalkenyl, and X3, X4, X5 and X6, identical or different, independently represent an oxygen atom or a sulfur atom. According to one embodiment, R1, R2, R3 and R4, identical or different, independently represent an alkyl group comprising C1 to C 24 , preferably in C4 to C 18, or an alkenyl group comprising C2 to C24 carbon atoms. According to one embodiment, X3, X4, X5 and X6 may be the same and may represent a sulfur atom. In another embodiment, X3, X4, X5 and X6 may be the same and may be an oxygen atom. In another embodiment, X3 and X4 may represent a sulfur atom and X5 and X6 may represent an oxygen atom. In another embodiment, X3 and X4 may represent an oxygen atom and X5 and X6 may represent a sulfur atom. In another embodiment, the ratio of sulfur atoms to oxygen atoms (S / O) in the MoDTC compound may vary from (1 / 3) to (3 / 1). In another embodiment, the MoDTC compound of formula (II) may be selected from a symmetrical MoDTC compound, an asymmetrical MoDTC compound and a combination thereof.By symmetrical MoDTC compound is meant a MoDTC compound of formula (II) in which the groups R1, R2, R3 and R4 are identical. By asymmetrical MoDTC compound is meant a MoDTC compound of formula (II) in which the groups R1 and R2 are identical, the groups R3 and R4 are identical and the groups R1 and R2 are different from the groups R3 and R4. According to one embodiment, the MoDTC compound is a mixture of at least one symmetrical MoDTC compound and at least one asymmetrical MoDTC compound. According to one embodiment, R1 and R2, which are identical, represent a C5 to C15 alkyl group, preferably a C8 to C13 alkyl group, and R3 and R4, which are identical, represent a C5 to C alkyl group. 15 , preferably in C8 to C 13 , and the groups R1 and R2 are identical to or different from the groups R3 and R4. In another embodiment, R1 and R2, which are identical, represent a C6 to C alkyl group 10and R3 and R4, identical, represent a C alkyl group 10 to C 15 , and the groups R1 and R2 are different from the groups R3 and R4. In another embodiment, R1 and R2, which are identical, represent a C alkyl group 10 to C 15 and R3 and R4, identical, represent a C6 to C alkyl group 10 , and the groups R1 and R2 are different from the groups R3 and R4. In another embodiment, R1, R2, R3 and R4, which are identical, represent a C5 to C15, preferably C8 to C13, alkyl group. According to one embodiment, the MoDTC compound is chosen from the compounds of formula (II) in which: - X3 and X4 represent an oxygen atom, - X5 and X6 represent a sulfur atom, - R1 represents a C8 carbon alkyl group or a C 13, - R2 represents a C8 carbon alkyl group or a C13 alkyl group, - R3 represents a C8 carbon alkyl group or a C 13 , - R4 represents a C8 carbon alkyl group or a C 13 . In particular, the MoDTC compound is chosen from the compounds of formula (IIa) following: [Chem 7] in which the groups R1, R2, R3 and R4 are as defined previously for formula (II). More particularly, the MoDTC compound is a mixture of: - a MoDTC compound of formula (IIa) in which R1, R2, R3 and R4 represent a C8 alkyl group, - a MoDTC compound of formula (IIa) in which R1, R2, R3 and R4 represent a C 13, and / or - a MoDTC compound of formula (IIa) in which R1, R2 represent a C8 alkyl group and R3 and R4 represent a C13 alkyl group. According to one embodiment, the MoDTC compound may be chosen from the MoDTC compounds as defined in document EP2920283. According to one embodiment, the MoDTC compound is molybdenum dialkyl dithiocarbamate. According to an alternative embodiment, the molybdenum dithiocarbamate compound is chosen from trimeric molybdenum dithiocarbamates of formula Mo3S k L nin which: - k represents an integer at least equal to 4, in particular between 4 and 10, more particularly between 4 and 7, - n is an integer ranging from 1 to 4, and - L is an alkyl dithiocarbamate group comprising from 1 to 100 carbon atoms, in particular from 1 to 40 carbon atoms, more particularly from 3 to 20 carbon atoms. Examples of trimeric MoDTC compounds that may be mentioned are the compounds and their preparation processes as described in document WO1998 / 26030. According to one embodiment, one or more of the aforementioned molybdenum dithiocarbamate compounds provide a quantity of molybdenum atoms of between 10 and 2000 ppm by mass relative to the total mass of the lubricating composition. In particular, one or more molybdenum dithiocarbamate compounds provide a quantity of molybdenum atoms of between 100 and 1000 ppm by mass relative to the total mass of the lubricating composition.More particularly, one or more molybdenum dithiocarbamate compounds provide a quantity of molybdenum atoms of between 200 and 800 ppm by mass relative to the total mass of the lubricating composition. Phosphosulfur additive As indicated previously, a lubricating composition according to the invention comprises at least one phosphosulfur additive as mentioned previously. According to one embodiment, the phosphosulfur additive is chosen from dithiophosphates, thiophosphates, and mixtures thereof. According to one embodiment, the phosphosulfur additive is chosen from metal alkyldithiophosphates, particularly metal dialkyldithiophosphates, more particularly zinc dialkyldithiophosphates or DTPZn. For example, zinc dialkyldithiophosphates may be of formula Zn((SP(S)(OR5)(OR6))2, in which R5 and R6, identical or different, independently represent an alkyl chain, in particular C1 to C18.According to a particular embodiment, the zinc dialkyldithiophosphate of formula Zn((SP(S)(OR5)(OR6))2is obtained from the secondary alcohols of formulas R5OH and R6OH, in which R5represents a C4 alkyl group and R6represents a C6 alkyl group. According to another embodiment, the zinc dialkyldithiophosphate of formula Zn((SP(S)(OR5)(OR6))2is obtained from the primary alcohols of formulas R5OH and R6OH, in which R5 represents a C4 alkyl group and R6 represents a C5 alkyl group. According to a particular embodiment, the phosphosulfur additive is chosen from non-metallic dithiophosphates and non-metallic thiophosphates, or mixtures thereof, for example as defined in document US8404624. According to a particular embodiment, the non-metallic dithiophosphates are chosen from compounds derived of 3-dithiophosphorylpropionic acid of the following formula (III) [Chem 8]. in which R7 and R8, identical or different, independently represent a C3 to C18 alkyl group, a (C5-C12)cycloalkyl group, in particular a (C9-C 10 )cycloalkyl, a group (C9-C 10 )bicycloalkylmethyl, a (C9-C10)tricycloalkylmethyl group, a phenyl group or a (C7-C24)alkylphenyl group, or R7 and R8 together form a group: [Chem 9] R9 represents a hydrogen atom or a methyl group. According to a particular embodiment, R7 and R8 independently represent a C3 to C18 alkyl group, more particularly an isopropyl, isobutyl or 2-ethylhexyl group.R7 and R8 may also represent other groups including an n-propyl group, an n-butyl group, a tert-butyl group, an n-pentyl group, an isoamyl group, a neopentyl group, a 2-ethylbutyl group, an n-hexyl group, a 1-methylpentyl group, a 1,3-dimethylbutyl group, an n-heptyl group, an isoheptyl group, an n-octyl group, a 1,4,4-trimethyl-2-pentyl group, a 3,4-dimethyl-1-hexyl group, a 3,5-dimethyl-1-hexyl group, a 4,5-dimethyl-1-hexyl group, a 3-methyl-heptyl group, a 5-methyl-heptyl group, a 1,1,3,3- tetramethylbutyl, a branched octyl group as obtained from an isobutylene dimer, an n-nonyl group, a 1,1,3-trimethylhexyl group, a branched nonyl group as obtained from a tripropylene trimer.More particularly, non-metallic dithiophosphates correspond to compounds derived from 3-dithiophosphorylpropionic acid of formula (III) as defined above, in which R7 and R8 represent a C3 to C alkyl group. 18 , for example a 2-methylpropyl group, and R9 represents a methyl group. For example, a non-metallic dithiophosphate corresponds to a derivative of 3-dithiophosphorylpropionic acid corresponding to 3-bis(2-methylpropoxy)phosphinothioylthio-2-methyl-propanoic acid. According to another particular embodiment, the phosphosulfur additive is chosen from non-metallic thiophosphates, in particular the thiophosphoric acid esters of the following formula (IV) [Chem 10] in which R10, R11 and R12, identical or different, represent hydrocarbon groups comprising from 3 to 20 carbon atoms. In particular, R 10 , R 11 and R 12independently represent a C3 to C3 aliphatic or aromatic group 20 , in particular a phenyl group optionally substituted by a C7 to C alkyl chain 24 linear or branched. According to a particular embodiment, R10, R11 and R12 independently represent a phenyl group or a group (C7-C 20 )alkylphenyl. According to a particular embodiment, R 10 , R 11 and R 12 independently represent a phenyl group or a (C1-C9alkyl)1-3phenyl group. According to a particular embodiment, R 10 , R 11 and R 12 represent a phenyl group; or one of R 10 , R 11 and R 12 represents a phenyl group and two of R 10 , R11 and R12 represent a (C1-C9alkyl)1-3phenyl group; or two of R10, R11 and R12 represent a phenyl group and one of R 10 , R 11 and R 12represents a (C1-C9alkyl) group 1-3 phenyl; or R 10 , R 11 and R 12 represent a (C1-C9alkyl)1-3phenyl group. According to a particular embodiment, R 10 , R 11 and R 12 identical or different, represent a C3 to C20 alkyl group, a (C5-C12)cycloalkyl group, a phenyl group, a (C7-C20)alkylphenyl group, a (C7-C20)alkoxyphenyl, naphthyl and (C7-C9)phenylalkyl group. In particular, a C3 to C20 alkyl group is, for example, an isopropyl group, n-nonyl group, a 1,1,3-trimethylhexyl group, an n-decyl group, an n-undecyl group, an n-dodecyl group, a 1-methylundecyl group, an n-tridecyl group, an n-tetradecyl group, an n-pentadecyl group, an n-hexadecyl group, an n-neptadecyl group or an n-octadecyl group. In particular, a grouping (C5-C 12)cycloalkyl is, for example, a cyclopentyl group or a cyclohexyl group. In particular, a (C5-C12)cycloalkyl-(C1-C4)alkyl group is, for example, a cyclopentylmethyl group, a 2-cyclopentylethyl group, a cyclohexylmethyl group or a 2-cyclohexylethyl group. In particular, a (C7-C20)alkylphenyl group is a phenyl group which is substituted, for example, by one, two or three C1-C4 alkyl groups, or by one, two or three C1-C6 alkyl groups, or one, two or three C1-C 12. In particular, a (C7-C2)alkoxyphenyl group is a phenyl group which is substituted, for example, by one, two or three C1-C4 alkoxy groups, in particular a methoxy or ethoxy group, or by one, two or three C1-C6 alkoxy groups, or by one, two or three C1-C12 alkoxy groups, these groups being analogous to the aforementioned alkyl groups. In particular, a (C7-C9)phenylalkyl group is, for example, a benzyl group, a 1-phenyl-1-ethyl group or a 2-phenyl-1-ethyl group. According to a particular embodiment, the phosphosulfur additive is a mixture of thiophosphoric acid esters of the following formula (IVa) [Chem 11] in which x is between 0 and 2.5, y is equal to 3−(x+z), z is between 0 and 3−(x+y), and x+y+z=3, and Ar represents a phenyl group, a (C7-C18)alkylphenyl group, a (C7-C18)alkoxyphenyl group, a naphthyl group or a (C7-C9)phenylalkyl group mentioned above. The preparation of thiophosphoric acid esters of formula (IVa) is for example described in document EP368803. According to one embodiment, the thiophosphoric acid esters of formula (IVa) are mixtures of triarylthiophosphate, such as mixtures of n-decylphenyl-n-nonylphenyl-phenylthiophosphate, o-tert-butylphenyl-o-isopropylphenyl-phenylthiophosphate, and / or n-hexylphenyl-phenylthiophosphate. According to another embodiment, the phosphosulfur additive is a thiophosphoric acid ester of the triphenylthiophosphate type such as O,O,O-tris(2(or4)-C9-10-isoalkylphenyl)phosphorothioate.According to a particular embodiment, the non-metallic dithiophosphates correspond to ammonium salts of dithiophosphoric acid of formula (V): [Chem 12]. in which R7 and R8 are as defined above, Ra, Rb, Rc and Rd, identical or different, represent a hydrogen atom or a C6 to C hydrocarbon group 20 . According to a particular embodiment, R7 and R8 of formula (V) independently represent a phenyl group or a (C3-C8)alkyl group, and in particular an isopropyl group. According to a particular embodiment, R a , R b , R c and R d, independently represent a hydrogen atom or a (C12-C20)alkyl group. According to another embodiment, the phosphosulfur additive is chosen from compounds derived from 3-dithiophosphorylpropionic acid of formula (III) as described above, thiophosphoric acid esters of formula (IV) as described above, ammonium salts of dithiophosphoric acid of formula (V) as described above, and mixtures thereof. According to one embodiment, one or more phosphosulfur additives provide a quantity of phosphorus atoms of between 50 and 2000 ppm by mass relative to the total mass of the lubricating composition. In particular, one or more phosphosulfur additives provide a quantity of phosphorus atoms of between 100 and 1000 ppm by mass relative to the total mass of the lubricating composition.More particularly, one or more phosphosulfur additives provide a quantity of phosphorus atoms of between 200 and 800 ppm by mass relative to the total mass of the lubricating composition. Other additives According to a particular embodiment, the composition further comprises one or more additional additives, distinct from the aforementioned spiro compound(s) of formula (I), from the aforementioned molybdenum dithiocarbamate(s) and from the aforementioned phosphosulfur additive(s). In particular, such additional additives are chosen from antioxidants, anti-wear additives, dispersants, detergents, anti-corrosion additives, anti-foaming agents, pour point lowering additives, seal swelling additives and viscosity index improvers. It is understood that the said additional additive(s) are compatible with their implementation in a lubricating composition as considered above.The said additive(s) are of course chosen with regard to the intended application for the lubricant. Of course, a person skilled in the art will take care to choose the possible additives and / or their quantity in such a way that the advantageous properties of the lubricating composition according to the invention, in particular the tribological properties, in particular friction reduction and possibly protection against wear, are not impaired by the envisaged addition. A lubricating composition considered according to the invention may comprise at least one antioxidant additive. The antioxidant additives are essentially dedicated to delaying the degradation of the lubricating composition in service. This degradation can in particular result in the formation of deposits, the presence of sludge or an increase in the viscosity of the lubricating composition. They act in particular as radical inhibitors or hydroperoxide destroyers.Commonly used antioxidant additives include phenolic antioxidant additives and amine antioxidant additives. Phenolic antioxidant additives may be ash-free or in the form of neutral or basic metal salts. Antioxidant additives may include sterically hindered phenols, sterically hindered phenol esters, and sterically hindered phenols comprising a thioether bridge, diphenylamines, diphenylamines substituted with at least one C1-C12 alkyl group, N,N'-dialkylaryldiamines, and mixtures thereof. In a particular embodiment, an antioxidant additive is alkylated (butyl / octyl) diphenylamine. Preferably, the sterically hindered phenols are chosen from compounds comprising a phenol group of which at least one vicinal carbon of the carbon carrying the alcohol function is substituted by at least one C1-C alkyl group.10 , preferably a C1-C6 alkyl group, preferably a C4 alkyl group, preferably by the tert-butyl group. Sulphurized alkyl phenols or their alkali and alkaline earth metal salts can also be used as antioxidant additives. Amino compounds are another class of antioxidant additives that can be used, optionally in combination with the phenolic antioxidant additives. Examples of amine compounds are aromatic amines, for example aromatic amines of formula NR ’ R ’’ R ’’’ in which R ’ represents an aliphatic group or an aromatic group, optionally substituted, R ’’ represents an aromatic group, optionally substituted, R ’’’ represents a hydrogen atom, an alkyl group, an aryl group or a group of formula R e S(O) z R f in which R erepresents an alkylene group or an alkenylene group, R frepresents an alkyl group, an alkenyl group or an aryl group and z represents 0, 1 or 2. In particular, an antioxidant amine compound is chosen from alkylated diphenylamines or ADPA. According to one embodiment, a lubricating composition considered according to the invention may comprise from 0.1% to 5% by mass, relative to the total mass of the lubricating composition, of at least one antioxidant additive. In particular, a lubricating composition considered according to the invention may comprise from 0.2% to 3% by mass, relative to the total mass of the lubricating composition, of at least one antioxidant additive.More particularly, a lubricating composition considered according to the invention may comprise from 0.3% to 2% by mass, relative to the total mass of the lubricating composition, of at least one antioxidant additive. A lubricating composition considered according to the invention may also comprise at least one pour point depressant additive (also called “PPD” agents for “Pour Point Depressant” in English). By slowing down the formation of paraffin crystals, pour point depressant additives generally improve the cold behavior of the lubricating composition. Examples of pour point reducing agents include polyalkyl methacrylates, polyacrylates, polyarylamides, polyalkylphenols, polyalkylnaphthalenes and alkylated polystyrenes. A lubricating composition considered according to the invention may also comprise at least one viscosity index (VI) improver.Viscosity index (VI) improvers, in particular viscosity index improving polymers, ensure good cold resistance and minimal viscosity at high temperatures. Examples of viscosity index improving polymers include polymer esters, homopolymers or copolymers, hydrogenated or non-hydrogenated, of styrene, butadiene and isoprene, homopolymers or copolymers of olefin, such as ethylene or propylene, polyacrylates and polymethacrylates (PMA). Advantageously, a lubricating composition according to the invention comprises at least one viscosity index improver chosen from polymethacrylates (PMA) and hydrogenated polyisoprene-styrene (PISH), linear, grafted, comb or star, preferably star.In particular, the viscosity index improving additive(s) may be present in a lubricating composition used according to the invention in a content ranging from 1 to 15% by mass, in particular from 2 to 10% by mass relative to the total mass of the lubricating composition. According to one embodiment, a lubricating composition according to the invention is free of viscosity index improving additive. A lubricating composition considered according to the invention may also comprise at least one dispersing agent. The dispersing agents ensure the maintenance in suspension and the removal of insoluble solid contaminants consisting of the secondary oxidation products which form when the lubricating composition is in service. They may be chosen from Mannich bases, succinimides and their derivatives.In particular, a lubricating composition considered according to the invention may comprise from 0.2 to 10% by mass of dispersing agent(s) relative to the total mass of the lubricating composition. A lubricating composition considered according to the invention may also comprise at least one anti-foam additive. The anti-foam additives may be chosen from polar polymers such as polymethylsiloxanes or polyacrylates. In particular, a lubricating composition considered according to the invention may comprise from 0.01 to 3% by mass of anti-foam additive(s), relative to the total mass of the lubricating composition. According to a particular embodiment, the composition further comprises at least one detergent additive, distinct from the spiro compound of formula (I).These are generally anionic compounds comprising a long lipophilic hydrocarbon chain and a hydrophilic head, the associated cation being able to be a metal cation of an alkali or alkaline-earth metal. They are generally chosen from alkali metal or alkaline-earth metal salts of carboxylic or sulfonic acids, in particular sulfonates, salicylates, naphthenates, phenates, carboxylates and mixtures thereof. The alkali and alkaline-earth metals are preferably calcium, magnesium, sodium or barium. These metal salts generally comprise the metal in a stoichiometric quantity or in excess, therefore in a quantity greater than the stoichiometric quantity.These are then overbased detergent additives; the excess metal providing 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. According to a particular embodiment, a lubricating composition according to the invention comprises at least one metallic detergent additive, distinct from the spiro compounds of formula (I) according to the invention, in particular chosen from salts of alkali metals or alkaline-earth metals, overbased or not, in particular from calcium salts, magnesium salts and their mixtures.According to a particular embodiment, a detergent additive distinct from the spiro compound of formula (I) is chosen from alkali metal or alkaline earth metal salts of carboxylic acids and mixtures thereof, and in particular from alkali metal or alkaline earth metal salts of a hydroxyaromatic carboxylic acid substituted by at least one hydrocarbon group, for example an alkyl group and mixtures thereof. In particular, the alkali metal or alkaline earth metal salts of a hydroxyaromatic carboxylic acid substituted by at least one alkyl are chosen from salicylates, carboxylates, or mixtures thereof. In particular, the alkali and alkaline earth metals are chosen from calcium, magnesium, sodium and barium.The hydroxyaromatic part of the alkali metal or alkaline earth metal salts of a hydroxyaromatic carboxylic acid, substituted by at least one alkyl, is chosen from, for example, monocyclic aromatic hydrocarbons having at least one hydroxyl function. Such aromatic hydrocarbons are, for example, chosen from phenol, catechol, resorcinol, hydroquinone, pyrogallol, cresol, and in particular phenol. In particular, the hydrocarbon group(s) of the carboxylates or salicylates originate from an alpha olefin having from 10 to 80 carbon atoms. The olefin may be linear, linear isomerized, linear branched or partially branched. The olefin may also be a mixture of linear olefins, a mixture of isomerized linear olefins, a mixture of branched olefins, a mixture of partially branched linear olefins, or a mixture of all of the above.In a particular embodiment, the detergent additive distinct from the spiro compound is chosen from salicylate or carboxylic salts, in particular calcium salicylate or carboxylate salts, in particular overbased. Such detergent additives are for example described in application EP 2308953. Surprisingly and advantageously, as illustrated in example 6, the inventors have demonstrated that the use of a spiro compound of formula (I), a molybdenum dithiocarbamate compound, a phosphosulfur additive as defined above and a detergent additive mentioned above in a lubricating composition allows synergistically and additionally a reduction in friction, in particular in moderate lubrication regimes or severe lubrication conditions, in a mechanical system.Thus, the tribological properties of such a lubricating composition according to the invention supplemented with detergent additive as defined above are improved. In addition, the inventors have also discovered that the use of a spiro compound of formula (I), a molybdenum dithiocarbamate compound and a phosphosulfur additive as defined above and a detergent additive mentioned above, in lubricating compositions, also allows a reduction in the wear of a mechanical system. Lubricating compositions according to the invention supplemented with detergent additive therefore advantageously combine good friction reduction properties, in particular in moderate lubrication regimes or severe lubrication conditions, and wear reduction. Application As indicated above, a lubricating composition according to the invention is intended for the lubrication of a mechanical system.A mechanical system comprises, for example, an engine and / or one or more transmission components. The lubricating compositions according to the invention are advantageously used for any type of engine, for mobile or stationary applications, which may be subject, during their operation, to friction phenomena. These are more particularly internal combustion engines of vehicles, such as gasoline engines, Diesel engines, gas-powered engines, engines powered by alternative fuels such as oxygenated biofuels, hydrogen, ammonia, methanol or synthetic fuel. A “Diesel engine” within the meaning of the invention is a combustion engine whose fuel is diesel. Gas-powered engines designate internal combustion engines whose fuel comprises at least one gas, including biogas.They include engines running exclusively on gas, known as gas engines, for example engines running on natural gas (liquefied natural gas (LNG) or compressed natural gas (CNG)) or liquefied petroleum gas (LPG), and hydrogen or ammonia engines, but also engines running on gas and gasoline (gas / gasoline “dual fuel” engines), engines running on gas and diesel (“dual fuel” gas / diesel engines). Engines for mobile applications are more specifically engines used in vehicles, including heavy-duty vehicles, so-called “off-road” mobile machines, light vehicles, electric vehicles or even marine vehicles, trains or aircraft. Engines for stationary applications, or stationary engines, can find applications, for example, in devices for producing electrical energy. This may be, for example, a stationary gas engine.The term "transmission members" means, for example, elements corresponding to the bearings, gears and bearings known to those skilled in the art. The lubricating compositions according to the invention are advantageously used for any type of mechanical vehicle transmissions defined above, in particular synchronized or not. The lubricating compositions according to the invention are advantageously used for any type of industrial gear reducers, in particular such a reducer is intended to modify the speed ratio and / or the torque between the input shaft and the output shaft of a mechanism such as a gear. The invention will now be described by means of the following examples, given as an illustration and not as a limitation of the invention.Examples Evaluation of tribological properties Tribological properties can be evaluated by measuring the coefficients of friction by a test on a tribometer with a rotating three-plane ball contact, for example a so-called Anton Paar MCR302 rheometer with a T-PTD-200 tribological assembly (“ball on three planes”) described in the publication by Yu Min Kiw et al. mentioned above, having the following characteristics: - ball diameter: 12.7 mm, - Ball material: 100C6, - Plane material: AISI5200, - temperature: 80°C, - Normal load: 12 N, and - Rotation speed: increase from 0 to 210 rpm in 850 s – hold at 210 rpm for 400 s – decrease from 210 to 0 rpm in 850 s. Note that the previous conditions correspond to limit regime lubrication conditions. The coefficient of friction is measured throughout the test procedure described above.The measurement of the area under the friction curve over the test time reflects the friction quality of the lubricant composition tested and is called the friction score. The lower the friction score, the higher the friction loss reduction performance of a lubricant composition. During the test protocol, four separate reference lubricant compositions were repeated twice each in order to establish a friction score measurement uncertainty within a 95% confidence interval. The lubricant compositions tested in the examples below were only tested once. Another tribological property is also evaluated in a complementary manner with respect to wear reduction, in particular by measuring the wear volume according to this test under conditions similar to those mentioned above.For each test carried out on a given composition, the wear volume produced during the test is measured on each of the 3 planes by optical interferometry by comparing the profile of the new planes and the worn planes. The wear volumes are expressed in µm. 3and has a negative value since material is removed during the implementation of the test. It is understood that a reduction in wear is associated with a reduction in the value of the wear rate considered in absolute value.Example 1 Preparation of the lubricating compositions Six lubricating compositions were formulated: - a reference lubricant, not in accordance with the invention, denoted CC1, free of spiro compounds of formula (I) as defined previously; - a lubricant not in accordance with the invention, denoted CC2, free of molybdenum dithiocarbamate compounds as defined previously; - a lubricant not in accordance with the invention, denoted CC3, free of phosphosulfur additives as defined previously; - a lubricant, in accordance with the invention, denoted I1, corresponding to the formulation CC1 supplemented by a spiro compound of formula (I), in particular spiroboronate; - a lubricant, in accordance with the invention, denoted I2, corresponding to the formulation I1, free of ADPA antioxidant; and - a lubricant, in accordance with the invention, denoted I3, corresponding to the formulation I1, in which the ADPA antioxidant is replaced by another antioxidant corresponding to a hindered phenol.The components and quantities (expressed as mass percentages) for the three lubricants are shown in the following table. The lubricants are formulated by simple mixing and stirring at 60°C of the different components. [Table 2].

[0002] (1) Molybdenum dialkyl dithiocarbamate. (2) Phosphosulfur additive, DTPZn of formula Zn((SP(S)(OR5)(OR6))2 obtained from secondary alcohols of formula R5OH and R6OH, R5 representing a C4 alkyl group and R6 representing a C6 alkyl group. (3) Spiro compound of formula (I), in which M is a boron atom, R each represents an octadecyl group (C18), n1 and n2 are 1. (4) ADPA or alkylated diphenylamine (butyl / octyl) corresponding to an antioxidant. (5) Phenolic antioxidant. (6)Group IV base oil (KV100 = 3.9 – 4.6; KV40 = 17.0 – 22.0; VI (Viscosity Index) 124). Example 2 Evaluation of the lubricants of Example 1 The tribological performances, particularly in terms of friction reduction and additional wear reduction, of the different lubricants prepared in Example 1 were evaluated according to the Tribological Properties Evaluation protocol described above. The results of the friction scores and wear rates are presented in the table below. [Table 3] Conclusion: These results show that the use of a spiro compound of formula (I), a molybdenum dithiocarbamate compound and a phosphosulfur additive, in lubricating compositions according to the invention, makes it possible to improve the tribological properties, particularly by reducing friction and additionally by reducing wear. In particular, the tribological properties of the lubricating compositions according to the invention I1,I2 and I3 are improved in comparison with those of the comparative compositions CC1, CC2 and CC3 which do not comprise at least one of the compounds chosen from a spiro compound of formula (I), a molybdenum dithiocarbamate compound and a phosphosulfur additive. The standard deviation of each value of the friction scores shows a repeatability of the results and the presence of a significant difference between the value of the results obtained for the comparative compositions CC1, CC2 and CC3 and the value of the results obtained for the compositions according to the invention I1, I2 and I3, since no overlap of the deviation values ​​is present. Furthermore, the good tribological properties of the lubricating composition according to the invention I2 are maintained in the presence or absence of antioxidant,in particular ADPA or a hindered phenol. This also shows that the use of any antioxidant does not contribute in any generalizable manner to the improvement of the tribological properties of a lubricating composition. Example 3 Preparation of lubricating compositions with or without molybdenum dithiocarbamate compound, or with or without phosphosulfur additive Six lubricating compositions were formulated: - a reference lubricant, not in accordance with the invention, noted CC4, corresponding to the formulation CC3 supplemented by a phosphite compound; - a reference lubricant, not in accordance with the invention, noted CC5, corresponding to the formulation CC3 supplemented by a phosphate compound; - a reference lubricant, not in accordance with the invention, noted CC6, corresponding to the formulation CC3 supplemented by an amine phosphate compound; - a reference lubricant, not in accordance with the invention, noted CC7,corresponding to the formulation CC2 supplemented by a molybdenum complex with ligands free of sulfur and phosphorus; - a lubricant, in accordance with the invention, noted I4, corresponding to the formulation I1 in which the phosphosulfur additive DTPZn (C4 / C6) has been replaced by another phosphosulfur additive DTPZn (C4 / C5) at 0.66% by mass relative to the total mass of the lubricant; and - a lubricant, in accordance with the invention, noted I4, corresponding to the formulation I1 in which the metallic phosphosulfur additive DTPZn (C4 / C6) has been replaced by a non-metallic phosphosulfur additive at 0.54% by mass relative to the total mass of the lubricant. [Table 4], (1) Molybdenum dithiocarbamates, as defined in Example 1. (2) Phosphosulfur additive, as defined in Example 1. (3) Molybdenum complex resulting from the reaction between coconut oil glycerides, diethanolamine and molybdenum oxide. (4)Phosphosulfur additive DTPZn of formula Zn((SP(S)(OR5)(OR6))2 obtained from primary alcohols of formula R5OH and R6OH, R5 representing a C4 alkyl group and R6 representing a C5 alkyl group. (5) 3-bis(2-methylpropoxy)phosphinothioylthio-2-methyl-propanoic acid. (6) Dibutyl hydrogen phosphite of general formula P(OH)(OR) c )(GOLD d ), with R c and R d representing a butyl group. (7) Phosphoric acid ester. (8) Ammonium phosphate ester salt, of general formula P(O)(OR) p ) 1-2 (OH) 2-1 (NHRq2), with R p hexyl and R q representing a branched C alkyl group 11 -C 14 . (9) Spiro compound of formula (I), as defined in Example 1. (7) ADPA, as defined in Example 1. (8)Group IV base oil, as defined in Example 1. Example 4 Evaluation of the lubricants of Example 3 The tribological performances, particularly in terms of friction reduction and additional wear reduction, of the different lubricants prepared in Example 3 were evaluated according to the Tribological Properties Evaluation protocol described above. It is noted that the compositions comprise identical amounts of molybdenum and phosphorus, respectively; in other words, the compositions have an isotenor in molybdenum and phosphorus, potentially making it possible to enrich a tribofilm, such as a molybdenum disulfide (MoS2) film, in a similar manner during the tests. Such tests are therefore directly comparable with respect to their performance potential. The results of the friction scores and wear rates are presented in the table below.[Table 5] Conclusion: These results also show that the use of a spiro compound of formula (I), a molybdenum dithiocarbamate compound and a phosphosulfur additive, in lubricating compositions according to the invention, makes it possible to improve the tribological properties, in particular by reducing friction and additionally by reducing wear. In particular, the tribological properties of lubricating compositions I4 and I5 are improved compared to compositions in which the phosphosulfur additive is replaced by a phosphorus additive not comprising sulfur such as a phosphite, phosphate or amine phosphate compound, for example such as a compound of general formula P(OH)(OR. c )(GOLD d ), with R c and R drepresenting a butyl group corresponding to the lubricating composition CC4, a phosphoric acid ester corresponding to the lubricating composition CC5 or an ammonium phosphate ester salt, for example such as a compound of general formula P(O)(OR p ) 1-2 (OH) 2-1 (NHRq2), with R p hexyl and R q representing a branched C alkyl group 11 -C 14corresponding to the lubricating composition CC6. The standard deviation of each value of the friction scores shows a repeatability of the results and the presence of a significant difference between the value of the results obtained for the comparative compositions CC4, CC5 and CC6 and the value of the results obtained for the compositions according to the invention I4 and I5, since no overlap of the deviation values ​​is present. Example 5 Preparation of the lubricating compositions with or without additional additives Five lubricating compositions were formulated: - a lubricant in accordance with the invention, noted I6, corresponding to the formulation I1 comprising a spiro compound of formula (I), in particular spiroboronate, at 1% by mass relative to the total mass of lubricant; - a lubricant in accordance with the invention, noted I7, corresponding to the formulation I6 supplemented by a detergent additive, in particular a salicylate-type salt, at 1% by mass relative to the total mass of lubricant;- a lubricant in accordance with the invention, noted I8, corresponding to formulation I6 supplemented by a detergent additive, in particular a carboxylate type salt, at 1% by mass relative to the total mass of lubricant; - a lubricant in accordance with the invention, noted I9, corresponding to formulation I1 comprising a mixture of a group IV base oil and a group V base oil, more particularly a polyglycol oil, at 10% by mass relative to the total mass of lubricant; and - a lubricant in accordance with the invention, noted I10, corresponding to formulation I1 supplemented by another additional group V base oil, more particularly an ester oil, at 10% by mass relative to the total mass of lubricant. [Table 6]; (1) Molybdenum dithiocarbamates, as defined in Example 1. (2) Phosphosulfur additive, as defined in Example 1. (3) Spiro compound of formula (I), as defined in Example 1. (4)ADPA, as defined in Example 1. (5) Group IV base oil, as defined in Example 1. (6) Calcium-based salicylate detergent (2.3% by mass of calcium; 64 mgKOH / g); (7) Calcium-based overbased carboxylate detergent (6.4% by mass of calcium; 180 mgKOH / g). (8) Polyalkylene glycol (PAG) oil corresponding to a polyglycol base oil and in particular an additional group V base oil. (9)Ester oil corresponding to an additional group V base oil. Example 6 Evaluation of the lubricants of example 5 The tribological performances, particularly in terms of friction reduction and additional wear reduction, of the different lubricants prepared in example 5 were evaluated according to the tribological properties evaluation protocol described above. It is noted that the compositions comprising an identical quantity of molybdenum atom and phosphorus atom for the same reasons as mentioned in example 4 above. The results of the friction scores and wear rates are presented in the table below.[Table 7] Conclusion: These results also show that the use, in addition, of a detergent additive distinct from a spiro compound of formula (I), in lubricating compositions according to the invention, makes it possible to additionally improve the tribological properties, in particular by additionally reducing friction and also by reducing wear. In particular, the tribological properties of the lubricating compositions according to the invention I7 and I8 comprising a detergent additive are superior compared to those of the lubricating composition according to the invention I6.Furthermore, these results show that the use, in addition, of a mixture of base oils, in particular a group IV base oil and a group V base oil, in lubricating compositions according to the invention I9 and I10, allows the maintenance of tribological properties, in terms of reduction of friction and additionally reduction of wear, compared for example to the lubricating composition according to the invention I1. Thus, compositions according to the invention comprising a mixture of at least two base oils have maintained tribological properties, in terms of reduction of friction and additionally reduction of wear.The standard deviation of each value of the friction scores shows a repeatability of the results and the presence of a significant gap between the value of the results obtained for the comparative compositions CC1, CC2 and CC3 and the value of the results obtained for the compositions according to the invention I1, I2 and I3, since no overlap of the deviation values ​​is present.

Claims

Claims 1. Lubricating composition comprising: i. at least one base oil; ii. at least one spiro compound of the following formula (I): wherein: M is an atom selected from boron and aluminum; n1 and n2 are, independently of each other, 0, 1, 2, 3 or 4, and R represent, independently of each other, a hydrocarbon group comprising from 1 to 50 carbon atoms; iii. at least one molybdenum dithiocarbamate compound; and iv. at least one phosphosulfur additive.

2. A lubricating composition according to claim 1, wherein said base oil is selected from group I to V base oils and mixtures thereof, for example a group IV base oil.

3. A lubricating composition according to any one of claims 1 or 2, wherein said spiro compound is of formula (I) in which: - M is a boron atom; and / or - the substituents R represent, independently of one another, a linear or branched aliphatic chain, in particular an alkyl chain, preferably linear, C1 to C 50, in particular in C3 to C30, in particular in C5 to C25, more particularly in C10 to C20 or even in C10 to C18, or even in C10 to C16, and for example in C16 or in C18; and / or - n1 and n2 are equal to 1, the substituents R being identical.

4. Lubricating composition according to any one of the preceding claims, in which said molybdenum dithiocarbamate compound is chosen from: - dimeric molybdenum dithiocarbamates of the following formula (II): in which R1, R2, R3 and R4, identical or different, independently represent a hydrocarbon group chosen from alkyl groups, in particular C4 to C 18 , alkenyl, aryl, cycloalkyl or cycloalkenyl, and X3, X4, X5 and X6, which may be identical or different, independently represent an oxygen atom or a sulfur atom; - trimeric molybdenum dithiocarbamates of formula Mo3S k L nin which: (i) k represents an integer at least equal to 4, in particular between 4 and 10, more particularly between 4 and 7, (ii) n is an integer ranging from 1 to 4, and (iii) L is an alkyl dithiocarbamate group comprising from 1 to 100 carbon atoms, in particular from 1 to 40 carbon atoms, more particularly from 3 to 20 carbon atoms; and - mixtures thereof. 5.Lubricating composition according to any one of the preceding claims, in which said phosphosulfur additive is chosen from dithiophosphates, thiophosphates, and mixtures thereof, in particular: - metal alkyldithiophosphates, more particularly metal dialkyldithiophosphates, even more particularly zinc dialkyldithiophosphates of formula Zn((SP(S)(OR5)(OR6))2, in which R5 and R6, identical or different, independently represent an alkyl chain, in particular C1 to C18; - non-metal dithiophosphates, more particularly compounds derived from 3-dithiophosphorylpropionic acid of the following formula (III). in which R7 and R8, identical or different, independently represent a C3 to C alkyl group 18 , a grouping (C5-C 12 )cycloalkyl, a group (C9-C 10 )bicycloalkylmethyl, a group (C9-C 10)tricycloalkylmethyl, a phenyl group or a (C7-C24)alkylphenyl group, or R7 and R8 together form a group: R9 represents a hydrogen atom or a methyl group; - non-metallic thiophosphates, in particular thiophosphoric acid esters of the following formula (IV): in which R10, R11 and R12, identical or different, represent hydrocarbon groups comprising from 3 to 20 carbon atoms; - the ammonium salts of dithiophosphoric acid of the following formula (V): in which R7 and R8, identical or different, are as defined for formula (III), and in particular independently represent a phenyl group or a (C3-C8)alkyl group, and Ra, Rb, Rc and Rd, identical or different, represent a hydrogen atom or a C6 to C hydrocarbon group 20 , and independently represent an atom of hydrogen or a group (C 12 -C 20)alkyl; and - mixtures thereof.

6. Lubricating composition according to any one of the preceding claims, in which said spiro compound(s) are used in a content of between 0.1 and 5.0% by mass relative to the total mass of the lubricating composition, in particular of between 0.5 and 4.0% by mass relative to the total mass of the lubricating composition, more particularly of between 1 and 3.0% by mass relative to the total mass of the lubricating composition; and / or said molybdenum dithiocarbamate compound(s) provide a quantity of molybdenum atoms of between 10 and 2000 ppm by mass relative to the total mass of the lubricating composition, particularly of between 100 and 1000 ppm by mass relative to the total mass of the lubricating composition,more particularly between 200 and 800 ppm by mass relative to the total mass of the lubricating composition; and / or said phosphosulfur additive(s) provide a quantity of phosphorus atoms of between 50 and 2000 ppm by mass relative to the total mass of the lubricating composition, particularly between 100 and 1000 ppm by mass relative to the total mass of the lubricating composition, more particularly between 200 and 800 ppm by mass relative to the total mass of the lubricating composition.

7. Lubricating composition according to any one of the preceding claims, further comprising at least one detergent additive distinct from the spiro compound of formula (I), in particular chosen from alkali metal or alkaline earth metal salts of a hydroxyaromatic carboxylic acid substituted by at least one hydrocarbon group, for example an alkyl group, and more particularly chosen from salicylates,carboxylates, or mixtures thereof, the alkali and alkaline earth metals being in particular chosen from calcium, magnesium, sodium and barium.

8. Lubricating composition according to any one of the preceding claims, comprising one or more additional additives, distinct from said base oil(s), said spiro compound(s) of formula (I), said molybdenum dithiocarbamate(s) and said phosphosulfur additive(s), chosen from antioxidants, additives, anti-wear agents, dispersants, detergents, anti-corrosion additives, anti-foaming agents, pour point lowering additives, seal swelling additives and viscosity index improvers.

9. Use in a lubricating composition of at least one spiro compound of formula (I), a molybdenum dithiocarbamate compound and a phosphosulfur additive, as defined according to any one of claims 1 to 5, for preventing and / or reducing friction in a mechanical system lubricated by means of said lubricating composition, said system comprising in particular an engine, for example an internal combustion engine, and / or a mechanical transmission member.

10. Use according to the preceding claim, for further preventing and / or reducing wear of said mechanical system lubricated by means of said lubricating composition. 11.Use of the lubricating composition defined according to one of claims 1 to 8, for preventing and / or reducing friction in a mechanical system lubricated by means of said lubricating composition, said system comprising in particular an engine, for example an internal combustion engine, and / or a mechanical transmission member, more particularly an internal combustion engine.

12. Use according to the preceding claim, for preventing and / or reducing, in addition, the wear of said mechanical system lubricated by means of said lubricating composition.

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