WO2011161662A1

WO2011161662A1 - Lubricant compositions for motor vehicle transmissions

Info

Publication number: WO2011161662A1
Application number: PCT/IB2011/052801
Authority: WO
Inventors: Emmanuel Matray; Richard Vernay
Original assignee: Total Raffinage Marketing
Priority date: 2010-06-25
Filing date: 2011-06-24
Publication date: 2011-12-29
Also published as: EP2585564B1; PT2585564T; RU2012155783A; EP2585564A1; FR2961823B1; CA2818935A1; MX2012015294A; BR112012032500B1; CN102959061B; CA2818935C; JP2013529699A; KR101843950B1; US20130096041A1; RU2564673C2; MX349410B; BR112012032500A2; CN102959061A; ES2644530T3; JP5739525B2; KR20130096168A

Abstract

The invention relates to a lubricant composition comprising: (a) an organomolybdenum compound, (b) one or more antiwear and extreme pressure additives chosen from thia(di)azoles, (c) one or more phosphorus-containing and/or phosphorus-sulphur-containing antiwear and extreme pressure additives chosen from phosphites, phosphates, phosphonates, thiophosphates or thiophosphites, said lubricant composition having a weight content of molybdenum between 90 and 350 ppm. Use for the lubrication of gearboxes.

Description

Lubricating compositions for automotive transmissions

Technical area :

The present invention relates to lubricating compositions, in particular for automotive transmissions, particularly lubricating compositions for manual gearboxes.

Technological background:

The transmission components of motor vehicles operate under heavy load and high speeds. The oils for these transmissions must therefore be particularly effective in protecting the parts against wear and fatigue, and in particular protecting the gear teeth against the phenomenon of chipping.

Chipping occurs after a long time of aging, preceding visible deterioration. The mechanisms are poorly known, but the phenomenon starts with the initiation of cracks to a certain depth below the surface, these cracks propagate, and when normal cracks on the surface are created, scales break off abruptly.

The prevention of this phenomenon involves a reduction of contact stresses thanks to an appropriate geometry of the parts, and the reduction of friction, avoiding adhesion. Lubricant is involved in this prevention process, mainly by the physicochemical reactivity of its additives.

Sulfur, phosphorus, phospho sulfur or borated anti-wear and extreme pressure additives are generally added to give the transmission oils peel protection properties. The other additives present in the lubricant can also have an impact, positive or negative, on the propagation of cracks inside the parts and thus on the phenomenon of chipping.

In manual gearboxes, the presence of synchronizers induces additional constraints. Indeed, these members comprise a cone and ring device between which the friction must be precisely controlled: the friction must be sufficient for the synchronization of speeds, but it is necessary that the cone and the ring can then disengage, because otherwise there is a lock of the synchronizer.

Moreover, if the level of friction is not adapted to the geometry of the parts, there is wear on the ring cone assembly.

The level of friction can be adjusted by adding friction modifiers in these gearbox oils.

Thus, in manual gearbox oils, anti-wear, extreme pressure and friction modifier additives can coexist, all having an action on the surface of the workpieces and potentially an effect on both the level of friction and on the level of friction. the phenomenon of chipping. The formulation of oil for manual gearbox having both a high protection against chipping, avoiding wear and blocking synchronizers, and allowing easy passage of speeds, is based on a precise choice and dosage of additives friction modifiers, anti wear and extreme pressure.

It is known to formulate lubricating compositions comprising organo-molybdenum-friction modifying compounds with organophosphorus and / or organosulfur and / or organophosphorus-sulfur anti-wear and extreme pressure compounds, in particular for improving the anti-wear properties of these oils.

US 6806241 discloses a lubricating composition comprising a molybdenum complex prepared by reaction of 1 mole of fatty substance which can be a glyceride or a fatty acid, del to 2.5 moles of diethanolamine, and a source of molybdenum in amount sufficient to obtain a complex containing from 0.1 to 12% by weight of molybdenum based on the weight of complex, a thiadiazole compound, and optionally a phosphorodithioate. No specific example of a composition comprising both molybdenum, at a mass content of between 90 and 350 ppm, sulfur and phosphorus is given.

EP 0874040 discloses lubricants for internal combustion engines comprising a molybdenum complex prepared by reaction of 1 mole of fatty substance which may be a glyceride or a fatty acid, from 1 to 2.5 moles of diethanolamine, and a source of molybdenum in an amount sufficient to obtain a complex containing from 0.1 to 12% by weight of molybdenum with respect to the weight of complex, and of an organo-sulfur compound chosen from dimercaptothiadiazoles, bisdithiocarbamates, dithiocarbamates, phosphorodithioates .

No indication is given of a specific combination of the molybdenum complex with one or more of the organo-sulfur compounds mentioned, nor on the amount of Mo contained in the lubricating compositions. The examples show a complex amount of between 0.5 and 1.5% by weight in the lubricant, which corresponds to a Mo content of between 5 and 1800 ppm in the lubricant. Too high or low content in Mo is unsuitable for the formulation of a lubricant for gearbox. Indeed, problems of chipping or blocking synchronizers can result. It is the same for the choice and dosage of sulfur and / or phosphosulfur additives.

WO 2005035700 discloses lubricating compositions comprising an organomolybdenum compound selected from molybdenum dithiophosphates or dithiocarbamates, and an anti-wear compound, which may be a dimercaptothiadiazole. This application does not disclose the combination of a specific molybdenum content with the use of a thiazole as an antiwear and extreme pressure agent.

The use of molybdenum in the form of dithiophosphates or dithiocarbamates, is also likely to generate more wear problems and / or blocking synchronizers, and possibly scaling. However, the compositions of the prior art based on molybdenum, sulfur and / or phosphorus relate to the fields of antioxidants and antiwear, mainly for the formulation of oil for internal combustion engines.

In particular, these compositions of the prior art do not have a specific dosage of Mo element, and a sufficient presence of sulfur and phosphorus allowing them to have both protective properties against flaking, wear and tear. synchronizers and avoiding synchronizer locks satisfactorily. These compositions are therefore not suited to the lubrication of gearboxes of motor vehicles, in particular manual gearboxes.

Of the known manual gearbox oils, borated oils have an excellent compromise between the various properties listed above. These oils can be formulated without sulfur, phosphorus or phosphorus compounds, and until now no technology based on sulfur, phosphorus or phospho sulfur additives has made it possible to achieve the level of performance obtained with borates in terms of protection against chipping and wear of synchronizers.

Despite their excellent extreme pressure performance and numerous advantages, the use of borates is not desirable when there is a risk of contamination of the lubricant with water. In fact, the inorganic borates being partially soluble in water, the amount of water present in the molecule can increase which has the effect of changing the borate structure. In the presence of a large amount of water in the medium, the borate structure being thus modified they can crystallize and form crystal shaped knives of sizes greater than 100 m. In this case, the borates can block the synchronization systems in the gearboxes.

The use of borated oils therefore requires a particular design manual gearbox with watertight system, which has a complexity and cost that it is desirable to avoid.

There is therefore a need for motor vehicle gearbox oils, in particular manual gearboxes, providing both a protection against the spalling phenomenon on the gear teeth, making it possible to limit wear. synchronizers and prevent their blocking, allowing easy passage of speeds, and insensitive to water (which may not contain borates or a reduced rate of borates).

The subject of the present invention is lubricating compositions, comprising molybdenum complexes of ester-amide type, in combination with an extreme sulfur pressure additive and an extreme pressure phosphorus or phospho-sulfur additive, and their use for lubricating gearboxes, in particular particular for motor vehicles. A particularly relevant use concerns the manual transmissions of motor vehicles Brief description of the invention

The present invention relates to lubricating compositions comprising:

(a) an organomolybdenum compound,

(b) one or more antiwear and extreme pressure additives selected from thia (di) azoles,

(c) One or more phosphorus and / or phosphosulfur antiwear and extreme pressure additives selected from phosphites, phosphates, phosphonates, thiophosphates or thiophosphites

Said lubricant composition having a mass content of molybdenum of between 90 and 350 ppm.

Preferably, the lubricant compositions according to the invention have a mass content of molybdenum of between 100 and 200 ppm, preferably between 140 and 180 ppm.

Preferably, the lubricant compositions according to the invention have a phosphorus content by mass of between 500 and 700 ppm, more preferably between 520 and 650 ppm.

According to one embodiment, the lubricant compositions according to the invention comprise at least one thiophosphate, preferably at least one dithiophosphate, preferably at least one amine dithiophosphate, as compound (c).

According to a preferred embodiment, the lubricant compositions according to the invention comprise at least one thiadiazole, preferably at least one dimercaptothiadiazole as compound (b).

The lubricant compositions according to the invention may comprise between 0.35% and 1% by weight of thiazole, preferably between 0.35 and 1% by weight of dimercaptothiadiazole.

According to a preferred embodiment, the lubricant compositions according to the invention comprise, as compound (a), at least one organic molybdenum complex, obtained by reaction:

(i) a mono, di or tri glyceride fatty substance, or fatty acid,

an amine source of formula (I)

Where X1 and X2 are either O or N, and n and m = 1 when X1 or X2 is O, and n and m = 2 when X1 or X2 is N, (iii) and a molybdenum source selected from molybdenum trioxide or molybdates, preferably ammonium molybdate, in an amount sufficient to provide 0.1 to 20.0% molybdenum based on the weight of complex.

Preferably, the compound (ii) is diethanolamine or 2- (2-aminoethyl) aminoethanol

Preferably, the fatty substance (i) is a mono, di or tri glyceride of fatty acids having from 4 to 28 carbon atoms, preferably from 8 to 18 carbon atoms, or a fatty acid having from 4 to 28 carbon atoms. , preferably from 8 to 18 carbon atoms

According to a preferred embodiment, the molybdenum complex (a) consists of at least one of the following compounds, alone or as a mixture:

(III)

Where XI and X2 are either O or N, and

• n = l when XI is O and m = 1 when X2 is O, · n = 2 when XI is N and m = 2 when X2 is N,

Where R1 and R2 are fatty hydrocarbon chains comprising between 3 and 27 carbon atoms, preferably between 7 and 17 carbon atoms. According to a particularly preferred embodiment, the molybdenum complex (a) consists of at least one of the compounds corresponding to the following formula:

Where RI is a fatty hydrocarbon chain comprising between 3 and 27 carbon atoms, preferably between 7 and 27 carbon atoms.

According to another preferred embodiment, the molybdenum complex (a) consists of at least one of the compounds corresponding to the following formula:

The present invention also relates to the use of the compositions described above for the lubrication of gearboxes, in particular motor vehicles.

According to a preferred embodiment, the present invention relates to the use of the compositions described above for the lubrication of manual gearboxes, in particular gearboxes manual for motor vehicles.

Detailed description :

Organomolybdenum compound. The lubricating compositions according to the invention may comprise any oil-soluble organomolybdenum compound, in particular and not limited to molybdenum dithiophosphates and dithiocarbamates, and various organic molybdenum complexes such as carboxylates, esters, molybdenum amides, obtainable by reaction of molybdenum oxide or ammonium molybdates with fatty substances, glycerides or fatty acids, or of fatty acid derivatives (esters, amines, amides, etc.).

Preferably, the lubricant compositions according to the invention comprise sulfur and phosphorus-free molybdenum complexes, with amide ligands, mainly prepared by reaction of a molybdenum source, which may be, for example, molybdenum trioxide, and of an amine derivative and of a fatty acid comprising, for example, from 4 to 28 carbon atoms, preferably from 8 to 18 carbon atoms, such as, for example, the fatty acids contained in vegetable or animal oils.

The synthesis of such compounds is described, for example, in US Pat. No. 4,889,647, EP0546357, US Pat. No. 5,412,130 and EP1770153.

These organic complexes of molybdenum can be obtained by reaction:

(i) a mono, di or tri glyceride fatty substance, or fatty acid,

(ii) an amine source of formula (I):

Where X1 and X2 are either O or N, and n and m = 1 when X1 or X2 is O, and n and m = 2 when X1 or X2 is N,

(iii) and a molybdenum source selected from molybdenum trioxide or molybdates, preferably ammonium molybdate, in an amount sufficient to provide 0.1 to 20.0% molybdenum based on the weight of complex.

They generally comprise between 7 and 8.5% by weight of molybdenum with respect to the weight of complex.

In particular, according to one embodiment, the organomolybdenum compound of the compositions according to the invention consists of at least one of the following compounds, alone or as a mixture:

(III)

Where XI and X2 are either O or N, and

• n = l when XI is O and m = 1 when X2 is O,

• n = 2 when XI is N and m = 2 when X2 is N,

Where R1 and R2 are fatty hydrocarbon chains comprising between 3 and 27 carbon atoms, preferably between 7 and 17 carbon atoms. .

According to one embodiment, the molybdenum complexes of the compositions according to the invention are prepared by reaction:

(i) a mono, di or tri glyceride fatty substance, or fatty acid,

(ii) diethanolamine or 2- (2-aminoethyl) aminoethanol,

In particular, according to one embodiment, the organomolybdenum compound of the compositions according to the invention consists of at least one of the following compounds (IV) or (V), alone or as a mixture:

The content of organomolybdenum compound in the compositions according to the invention is adjusted so that the mass content of molybdenum of said compositions is between 90 and 350 ppm, preferably between 100 and 200 ppm, more preferably between 140 and 180 ppm.

Too low a molybdenum content generates synchro blocking problems, and potentially wear of the cone-ring assembly of the synchronizer.

On the other hand, too much molybdenum content has an adverse effect on flaking.

Thi (di) azoles

Thia (di) azoles are compounds that contain both a sulfur and a nitrogen atom in a five-membered ring. Benzothiazoles are a special type of thia (di) azoles. This thia (di) azole term includes, in addition to the cyclic compounds containing one sulfur atom and one nitrogen atom per 5 atom ring, also the thiadiazoles which contain sulfur and two nitrogen atoms in such a ring.

These compounds may be unsubstituted or substituted by hydrocarbon compounds which increase their solubility in the oil.

According to one embodiment, the thia (di) azoles of the lubricant compositions according to the invention are unsubstituted benzothiazoles, thiazoles, thiadiazoles.

According to a preferred embodiment, the thia (di) azoles of the compositions according to the invention are dimercaptothiadiazoles, for example 2,5 dimercapto 1,3,4-thiadiazole, 3,5 dimercaptol, 2,4 thiadiazole, 3,4 dimercaptol 2,4-thiadiazole, 4,5-dimercapto, 1,2,3thiadiazole, 3-methylmercapto, 5-mercapto, 1,2,4-thiadiazole. All these compounds can be used alone or as a mixture.

Typically, thia (di) azoles represent between 0.35 and 1% by weight of the compositions according to the invention.

Preferably, the compositions according to the invention contain between 0.35 and 1%, preferably between 0.35 and 0.45% by weight of dimercaptothiadiazoles.

Phosphorus compounds or phospho-sulfur compounds:

The phosphorus compounds of the lubricating compositions according to the present invention are anti-wear and extreme pressure additives such as phosphates, phosphites, or phosphonates. These terms refer to both phosphoric, phoporous, phosphonic acids their mono, di and triesters, for example alkyl phosphates, alkyl phosphonates, alkyl phosphonates, and their salts, for example amines

The anti-wear and extreme pressure phospho-sulfur additives used in the present invention are (mono or di) thiophosphates and thiophosphites, these terms including thiophosphoric and thiophosphorous acids, esters of these acids, their salts, dithiophosphites and dithiophosphates.

According to a preferred embodiment, the anti-wear and extreme pressure phospho-sulfur additives of the compositions according to the invention are thiophosphates, corresponding to the formula (VI)

Where X 3 and X 4 are independently of each other S or O, at least one of them being S, R 3 and R 4 are either hydrogen or alkyl groups having 1 to 22 carbon atoms, M is a metal of groups MA, III, VA, VIA, IB, VIB, VIII of the Periodic Table, n being the valency of said metal, or M is an ammonium formed from a primary, secondary or tertiary amine, of formula (R5) (R6) (R7) N, wherein R5, R6, R7 are either hydrogen or an alkyl group having from 1 to 18 carbon atoms, and then n = 1. Particularly preferred compounds are dithiophosphates (X3 and X4 are sulfur), preferably zinc or amine. Amine dithiophosphates are particularly preferred compounds.

Mention may be made, as examples of anti-wear and extreme pressure additives phospho sulfur, the monobutylthiophosphate, monooctylthiophosphate, monolaurylthiophosphate, dibutylthiophosphate, dilaurylthiophosphate, tributylthiophosphate, trioctylthiophosphate, triphenylthiophosphate, trilaurylthiophosphate, monobutylthiophosphite, monooctylthiophosphite, monolaurylthiophosphite, dibutylthiophosphite, dilaurylthiophosphite, tributylthiophosphite , trioctylthiophosphite, triphenylthiophosphite, trilaurylthiophosphite and their salts.

Examples of salts of thiophosphoric acid esters and thiophosphorous acid are those obtained by reaction with a nitrogen compound such as ammonia or an amine or zinc oxide or zinc chloride. Preferably, the amount of these additives is adjusted so that the phosphorus mass content of the oils according to the invention is between 500 and 700 ppm, preferably between 520 and 650 ppm.

Too low a content of anti-wear and extreme pressure element (sulfur and phosphorus) will generate peeling problems.

Moreover, a high content of anti-wear and extreme pressure elements, (as well as friction modifier, including organomolybdenum compound), will have an adverse effect on the passage of speeds: the coefficient of friction cone ring will be too low, which prevents the synchronization of speeds and therefore the shifting.

It is also desirable, for environmental reasons, to limit to the necessary sulfur and phosphorus content in the lubricant compositions.

This, in combination with the molybdenum content of the lubricants according to the invention, provides both better anti-peeling, anti-wear synchro and avoid synchro blockages.

The most effective compromise between these 3 properties therefore depends on a precise dosage of friction-modifying compounds, anti-wear and extreme pressure and thus Mo, S and P element from these compounds.

Bases:

The compositions according to the invention may contain any type of mineral lubricating base, synthetic or natural, animal or vegetable adapted (s) to their use. The base oil (s) used in the compositions according to the present invention may be oils of mineral or synthetic origin of groups I to V according to the classes defined in the API classification (or their equivalents according to the ATIEL classification) as summarized herein. below, alone or mixed.

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

The base oils of the compositions according to the present invention may also be synthetic oils, such as certain esters of carboxylic acids and alcohols, or polyalphaolefins. The polyo-olefins used as base oils, for example, are obtained from monomers having from 4 to 32 carbon atoms (for example octene, decene), and a viscosity at 100 ° C of between 1.5 and 15 Cst. Their weight average molecular weight is typically between 250 and 3000. Mixtures of synthetic and mineral oils may also be employed.

There is no limitation as to the use of such or such lubricating base for producing the compositions according to the invention, except that they must have properties, in particular viscosity, viscosity index, sulfur content. , resistance to oxidation ... adapted for use in a gearbox, in particular for motor vehicles, in particular manual gearbox.

Preferably, the lubricating bases represent at least 50%, preferably at least 60%, or at least 70% by weight of the lubricating compositions according to the invention. Typically, they represent between 75 and 90% by weight of the compositions according to the invention.

Preferably, the lubricant compositions according to the invention comprise Group I and / or III mineral bases, or Group IV synthetic bases according to the API classification. Other additives:

The lubricant compositions according to the invention may also contain any type of additive suitable for their use, for example amino or phenolic antioxidants such as diphenylamines, or phenols substituted on at least one of their ortho positions, with groups alkyl, detergents, for example sulfonates.

Viscosity index improvers (VI improvers) are preferably present at contents of between 5 and 25% by weight, so as to confer viscometric properties suitable for use in gearboxes, in particular gearboxes for automobile gearboxes. , preferentially manual, such as, for example, polymethacrylates (PMA), polyisobutenes (PIB), or fatty acid esters ...

Examples:

Mass compositions and performances in synchro wear, synchroblocking, peeling of the lubricating compositions prepared are presented in Table 1 below.

The scaling tests are carried out under the following conditions:

BCFP Sermees Bank

Gearbox Renault JR5-125, 1 differential torque 14x63 secondary shaft

8200280045 and 8200280134 crown, 3 torque 28x37 primary shafts 8200107846 and idle gears 3 ° 7700114048

2.3 liters of oil, oil temperature 110 ° C

Torque input: 148 mN

Primary speed 3000 rpm

Duration 3 phases of 142 hours

Every 142 hours, primary shaft change, 3 ° idle gear and bearings.

Evaluation of the flaking surface:

Final score after 426h of the pinion / differential ring gear pair,

Dimension after 142h of the 3 pairs 28x37 primary shaft / idler of 3 °

Depending on the result of the quotation of these parts, the oil is declared pass (satisfactory rating) or fail (chipped surface too important).

Synchronizer blocking tests are performed on a ring cone couple under the following conditions (SYNC-40 procedure):

Threaded brass ring 54 mm, eg ref 7700 708 152 or 7700 869 430

Cone of crazy gear box JXX, carbonitrided steel ground stone, for example ref 7700 867 612 or 7700 740 880

Oil: 250 ml oil, oil level in the middle of the pinion and ring machine SAE2 / A adapter SAE / 2 synchro

I = 0.155 m2 / kg N = 300 rpm

F = 60 daN

T = 6s (consecutive period between two consecutive braking)

n = 10 125 shift cycles (21 hours)

The synchro-blocking test is passed if, during the 10,125 gear-change cycles, the number of cycles in which the disengagement between the cone and the ring requires the application of a counter torque greater than 2 mN is not more than 100 cycles. Synchronizer wear tests are performed on a ring cone pair under the following conditions (SYNC-13 procedure, SAE 2-A):

Threaded brass ring 54 mm, eg ref 7700 708 152 or 7700 869 430

Oil: 125 ml of oil, oil level on the lower part of the ring

SAE2 / A machine adapter SAE / 2 synchro

I = 0.155 m2 / kg

N = 600 rpm

F = 60 daN

T = 3.5 s (consecutive period between 2 consecutive braking)

n = 20,000 shift cycles (20 hours)

At the end of these 20,000 cycles; the axial wear of the synchronizer ring / pinion cone torque is measured in mm. It must be at most of the order of 0.30 mm to be acceptable (pass). Wear less than 0.15 mm is an excellent performance. Wear greater than 1 mm is eliminatory (catch-up). Discussion

The oils A and B are oils according to the invention; Oils C and D are borated oils, sensitive to water.

Oils A and B have a level of synchronizing wear performance equivalent to that of borated oils, and pass blocking and peeling tests in the same manner.

Oil E contains the same antiwear and extreme pressure additives as oil A, with phosphorus / phosphate phosphorus compounds as well; This E oil does not contain a molybdenum friction modifier. Synchronous wear is at an unacceptable level (0.84 mm).

The oils F, G, H have the same additive in anti-wear and extreme pressure sulfur and phospho sulfur as the oils according to the invention, but contain various friction modifiers without molybdenum. Synchronizer wear is very important with these oils. The oils I and L have the same additive in sulfur and phospho sulfur antiwear and extreme pressure as the oils according to the invention, and contain an amide ester molybdenum friction modifier.

The mass content in Mo of oil I is 400 ppm, and this oil is flaking. The mass content in Mo of oil L is 80 ppm, and this oil is fail in synchro blocking.

The oil J has the same additive in anti-wear and extreme pressure sulfur and phospho sulfur as the oils according to the invention, but does not contain molybdenum. A fatty acid monoester is present as a friction modifier. This oil is fail in synchro blocking.

The oil K has the same additive in anti-wear and extreme pressure sulfur and phospho sulfur as the oils according to the invention, and does not contain molybdenum. It contains no friction modifier. This oil is fail in synchro blocking.

M and N oils do not contain thiazole as the sulfur compound. M oil is also free of molybdenum. These oils have achieved a particularly catastrophic chipping result. It should be noted that these oils do not contain dimercaptothiadiazole.

Table 1: Mass composition and properties

Mo complex: organomolybdenum complex with amide ligands

Claims

Claims:

A lubricating composition comprising:

(a) an organomolybdenum compound,

(b) one or more anti-wear and extreme pressure additives selected from thia (di) azoles, (c) one or more phosphorus and / or phosphosulfur antiwear and extreme pressure additives selected from phosphites, phosphates, phosphonates, thiophosphates or thiophosphites;

said lubricating composition having a mass content of molybdenum of between 90 and 180 ppm.

2. Lubricating composition according to claim 1 having a mass content of molybdenum of between 100 and 200 ppm, preferably between 140 and 180 ppm.

3. Lubricating composition according to one of claims 1 to 2 having a phosphorus content by mass between 500 and 700 ppm, preferably between 520 and 650 ppm.

4. Lubricating composition according to one of claims 1 to 3 comprising at least one thiophosphate, preferably at least one dithiophosphate, preferably at least one dithiophosphate of amine, as compound (c).

5. Lubricating composition according to one of claims 1 to 4 comprising at least one thiadiazole, preferably at least one dimercaptothiadiazole as compound (b).

6. lubricating composition according to one of claims 1 to 5 comprising between 0.35% and 1% by weight of thiazole, preferably between 0.35 and 1% by weight of dimercaptothiadiazole

7. Lubricating composition according to one of claims 1 to 6 comprising, as compound (a), at least one organic complex of molybdenum, obtained by reaction:

(i) a mono, di or tri glyceride fatty substance, or fatty acid,

an amine source of formula (I)

The lubricating composition of claim 7 wherein the compound (ii) is diethanolamine or 2- (2-aminoethyl) aminoethanol

9. Lubricating composition according to one of claims 7 to 8 wherein the fatty substance (i) is a mono, di or tri glyceride of fatty acids having from 4 to 28 carbon atoms, preferably from 8 to 18 carbon atoms, or a fatty acid comprising from 4 to 28 carbon atoms, preferably from 8 to 18 carbon atoms

10. Lubricating composition according to one of claims 7 to 9 wherein the molybdenum complex (a) consists of at least one of the following compounds, alone or in admixture:

(III)

Where XI and X2 are either O or N, and

• n = l when XI is O and m = 1 when X2 is O,

• n = 2 when XI is N and m = 2 when X2 is N,

Where R1 and R2 are fatty hydrocarbon chains comprising between 3 and 27 carbon atoms, preferably between 7 and 17 carbon atoms.

11. Lubricating composition according to one of claims 7 to 9 wherein the molybdenum complex (a) consists of at least one of the compounds corresponding to the following formula:

12. Lubricating composition according to one of claims 7 to 9 wherein the molybdenum complex (a) consists of at least one of the compounds corresponding to the following formula:

13. Use of a composition according to one of claims 1 to 12 for the lubrication of gearboxes, particularly motor vehicles.

14. Use according to claim 13 wherein the gearbox is a manual gearbox.