WO2013083777A1

WO2013083777A1 - Engine lubricant for hybrid or micro-hybrid motor vehicles

Info

Publication number: WO2013083777A1
Application number: PCT/EP2012/074786
Authority: WO
Inventors: Olivier Lerasle; Jérôme VALADE; Mickael DEBORD; Roger THOLLON
Original assignee: Total Raffinage Marketing
Priority date: 2011-12-09
Filing date: 2012-12-07
Publication date: 2013-06-13
Also published as: ES2764736T3; EP2788462A1; FR2983867B1; JP2015500367A; KR20140110852A; FR2983867A1; EP2788462B1; CN103975047A

Abstract

The present invention relates to the use of a lubricating composition comprising at least one base oil and at least one organomolybdenum compound for reducing wear to the bearings and for lubricating the thermal internal combustion engines of hybrid and/or micro-hybrid motor vehicles.

Description

Engine lubricant for vehicles with hybrid or microhybrid drive

Technical area

The present invention relates to the lubrication of hybrid motor vehicle engines and micro-hybrid powered vehicles, in particular micro-hybrid powered vehicles equipped with the "Stop-and-Start" system.

Technical background

Environmental concerns and the search for savings on fossil fuel resources have led to the development of electric motor vehicles. However, the latter are limited in power, autonomy, and require a very long battery recharging time.

Hybrid drive systems overcome these disadvantages by implementing an electric motor and a conventional thermal internal combustion engine, in series, in parallel or in combination.

In a hybrid vehicle, starting is provided by the electric motor. Up to a speed of the order of 50 km / h, it is the electric motor that ensures the traction of the vehicle. As soon as a higher speed is reached or a strong acceleration is required, the internal combustion engine takes over. When the speed decreases or when the vehicle stops, the internal combustion engine stops and the electric motor takes over. Thus, the internal combustion engine of hybrid vehicles undergoes a significant number of stops and restarts compared to a conventional combustion engine thermal vehicles.

Moreover, some vehicles are equipped with an automatic stop and start device (also called "Stop-and-Start" system in the English terminology, this terminology will be used below). These vehicles are generally considered "micro-hybrid" vehicles. Indeed, these vehicles are equipped with a thermal internal combustion engine and an alternator-starter or a reinforced starter which ensure the stopping and restarting of the internal combustion engine thermal when the vehicle comes to a stop. Thermal internal combustion engines of microhybrid vehicles equipped with the "Stop-and-Start" system, such as the internal combustion engines of hybrid vehicles, undergo a significant number of shutdowns and restarts compared to a thermal internal combustion engine. conventional vehicles. Thus, the thermal internal combustion engine of hybrid vehicles or micro-hybrid vehicles undergoes, during its life, a number of stops and starts much higher than that of a conventional vehicle. This potentially generates, for the internal combustion engines of hybrid and micro-hybrid vehicles, specific wear problems, in particular in the long term. These specific wear problems are particularly visible at the bearings of the cone heads. The wear of the bearings in a combustion engine of hybrid and micro-hybrid vehicles is therefore greater than in a conventional combustion engine.

It is well known to those skilled in the art that the means envisaged in the first place to reduce the wear of the bearings would be to increase the viscosity of the lubricant to improve the maintenance of the oil film on the surface of the bearings.

In addition, anti-wear compositions comprising a friction modifier have been described.

The application WO2011045773 describes the use of a kinematic viscosity motor oil at 100 ° C. according to the ASTM D445 standard of between 16 and 27 cSt, comprising at least one ester of formula (a) for the lubrication of internal combustion engines of vehicles with hybrid engines whose maximum torque, measured between 1000 and 3000 revolutions / minute, is greater than 1000 Nm The ester of formula (a) is an organic friction modifier. The use of this particular organic friction modifier makes it possible to reduce the wear of the conrod bearings of the engine. However the reduction of wear can be further improved.

Furthermore, the documents WO 2010/046620 and US 2011/071062 describe compositions comprising an organomolybdenum compound as a friction modifier. However, these documents do not teach or suggest the use of such compositions to specifically reduce bearing wear in a combustion engine of hybrid and micro-hybrid vehicles. It is also well known to those skilled in the art that the anti-wear solutions applicable to a thermal combustion engine of a conventional vehicle are not systematically transferable into a thermal combustion engine of a hybrid and micro-hybrid vehicle .

There is therefore a need for the development of lubricant compositions that allow reliable operation of the internal combustion engines of hybrid vehicles and micro-hybrids equipped with the Stop-and-Start system, and in particular that can reduce wear, in particular the wear of the bearings, in particular the wear of the conrod bearings, in the internal combustion engines of said vehicles.

Surprisingly, the Applicant has found that the use in thermal internal combustion engines of hybrid and hybrid motor vehicles equipped with the Stop-and-Start system, lubricating compositions comprising some inorganic friction modifiers allowed to reduce considerably wear of the bearings present in said engines, this without increasing the viscosity of the compositions, which makes possible their commissioning in real conditions, which allows to increase the life of the engine, to increase the interval of time between engine parts changes.

brief description

The invention relates to the use of a lubricating composition comprising at least one base oil and at least one organomolybdenum compound for reducing wear of the bearings and for lubricating metal surfaces, polymeric surfaces and / or carbon surfaces. amorphous, thermal internal combustion engines of hybrid and / or microhybrid vehicles.

The invention also relates to a lubricating composition comprising at least one base oil and at least one organomolybdenum compound for reducing wear of the bearings and for lubricating metal surfaces, polymeric surfaces and / or amorphous carbon surfaces, motors thermal internal combustion of vehicles with hybrid and / or microhybrid motorization.

Preferably, the micro-hybrid powered vehicles are equipped with an alternator-starter or a reinforced starter.

Preferably, the use of the lubricant composition makes it possible to reduce the wear of the internal combustion engine, in particular the wear of the bearings of the internal combustion engine, in particular the wear of the connecting rod bearings of the combustion engine. internal heat.

Preferably, the use of the lubricant composition makes it possible to increase the service life of the internal combustion engine, in particular the service life of the bearings of the internal combustion engine, in particular the service life of the connecting rod bearings. internal combustion engine.

Preferably, the use of the lubricating composition makes it possible to increase the time interval between the parts changes of the internal combustion engine, in particular the time interval between the changes of the combustion engine bearings. internal thermal, in particular the time interval between the changes of the connecting rod bearings of the internal combustion engine thermal.

Preferably, the lubricating composition comprises from 0.1 to 10% by weight, relative to the total weight of lubricating composition, of organomolybdenum compound, preferably from 0.5 to 8%, more preferably from 1 to 5%, more preferably more preferably from 2 to 4%.

Preferably, the organomolybdenum compounds are chosen from dithiocarbamates and / or dithiophosphates of molybdenum, taken alone or as a mixture.

According to one embodiment, the organomolybdenum compounds are chosen from molybdenum dithiocarbamates of formula (I):

in which R 1, R ₂ , R ₃ and R ₄ are, independently of each other, linear or branched, saturated or unsaturated alkyl groups, preferably containing from 4 to 18 carbon atoms, preferably from 8 to 13 carbon atoms.

According to another embodiment, the organomolybdenum compounds are chosen from molybdenum dithiophosphates of formula (II):

wherein R _5, R _6, R _7, R _g are independently from each other alkyl groups, linear or branched, saturated or unsaturated, preferably comprising from 4 to 18 carbon atoms, preferably from 8 to 13 .

According to one embodiment, the metal surface is an alloy.

Preferably, the alloy is steel.

Preferably, the alloy comprises as base element tin (Sn), lead (Pb), copper (Cu), aluminum (Al), cadmium (Cd), silver ( Ag) or zinc (Zn).

Preferably, an alloy comprising lead (Pb) and copper (Cu).

Preferably, the polymeric surface comprises polytetrafluoroethylene.

Preferably, the kinematic viscosity at 100 ° C of the lubricating composition, measured according to AST D445, is between 5.6 and 12.5 cSt.

detailed pesçrjptipp The present invention relates to the reduction of bearing wear and the lubrication of internal combustion engines of vehicles with hybrid or microhybrid drive.

Hybrid motorized vehicles are here understood to mean vehicles using two different energy storages capable of moving said vehicles. In particular, hybrid vehicles combine a thermal internal combustion engine and an electric motor, said electric motor participating in the traction of the vehicle. The operating principle of hybrid vehicles is as follows:

during stationary phases (where the vehicle is stationary), both engines are stopped,

at the start, it is the electric motor which ensures the setting in motion of the car, up to higher speeds (25 or 30 km / h),

when higher speeds are reached, the internal combustion engine takes over,

in case of great acceleration, we observe the start of the two engines at a time, which allows to have accelerations equivalent to the engine of the same power, or even higher,

optionally, in the deceleration and braking phase, the kinetic energy is used to recharge the batteries.

Thus, in hybrid vehicles, the thermal internal combustion engine undergoes, during its life, a number of stops and starts much higher than in a conventional vehicle (phenomenon of "Stop-and-Start") .

Here, the term "vehicle with micro-hybrid powertrain" means vehicles comprising a thermal internal combustion engine, but no electric motor such as hybrid vehicles, the "hybrid" character being provided by the presence of the Stop and Start system provided by an alternator. -starter or a reinforced starter which ensure the stopping and restarting of the engine when the vehicle comes to rest and then restarts.

The present invention is more preferably aimed at the lubrication of internal combustion engines of vehicles equipped with hybrid or micro-hybrid systems circulating in an urban environment, where the Stop-and-Start phenomenon and the resulting wear are increased.

The wear generated by these frequent stops and restarts will be visible in the various parts in contact with the lubricant: piston, piston ring, piston pin, piston pin boss, small end, big end, connecting rod bearings, crankpin, journal, shaft line bearing, shaft line bushings or journal bushings or crankshaft bearings, chain axle, oil pump gear, gear, camshaft, camshaft bearing, dispensing plungers, latch roller, hydraulic stop for retrofitting, turbocharger shaft, turbocharger bearing.

In a motor vehicle, there is a fixed part comprising the engine block, the cylinder head, the cylinder head gasket, the liner and various parts ensuring the assembly and sealing of these different parts. There is also a movable part comprising the crankshaft, the connecting rod and its bearings, the piston and its segments.

The role of the connecting rod is to transmit to the crankshaft the forces received by the piston, transforming a reciprocating rectilinear motion into a circular motion in one direction.

A connecting rod has two circular bores, one of small diameter, called small end, and the other of large diameter called big end. Between these two bores, is the body of the connecting rod connecting the small end and the small end.

The small end is engaged around the axis of the piston, the friction between the small end and the axis of the piston is reduced by the interposition between the two moving parts of a circular ring covered or made of anti-metal. friction (bronze, for example), or bearings (usually needle).

The big end, it, encloses the crankpin crankpin. The friction between the crankpin and crankpin assembly is reduced by the existence of an oil film and the interposition between the crankpin and the crankpin, pads. In this case we speak of big-end bearings.

The crankshaft is a rotating part. Its positioning and maintenance are achieved by a number of bearings, called trunnions. So we have a fixed part, the bearing crankshaft, which encloses a moving part, the crankshaft journal. Lubrication between these two parts is imperative and pads are put in place to resist the forces applied to these bearings. In this case we speak of trunnion bushings (or bearings of shaft line or crankshaft bearings).

The role of the bearing in the case of a big end or a trunnion, is to allow a good rotation of the crankshaft. The pads are thin shells in the shape of a half-cylinder. These are parts that are extremely sensitive to lubrication conditions. If there is contact between the bushing and the rotating shaft, crankpin or pin, the energy released systematically leads to significant wear or engine breakage. The generated wear can also play the role of amplifying the phenomenon and the severity of the contact.

In the case of frequent stops and restart, as is the case for vehicles with hybrid or micro-hybrid powertrain, the bearings are subject to frequent rupture and re-ignition of the oil film. So at each stop / restart a contact takes place between the metal interfaces and it is the frequency of occurrence of these contacts that is problematic for the pads.

The bearings are subject to several types of wear in the motors. The different types of wear encountered in the motors are: adhesive wear or metal-metal contact wear, abrasive wear, corrosive wear, fatigue wear, or complex forms of wear ( contact corrosion, cavitation erosion, electrical wear). The pads are subject in particular to adhesive wear, the invention is particularly useful for improving this type of usu re but the invention can nevertheless be applied to the other types of wear mentioned above.

Surfaces that will be susceptible to wear, in particular the surface of the bearings, are metal-like surfaces, or metallic-type surfaces coated with another layer which may be either a polymer or an amorphous carbon layer. . Wear occurs at the interface between said surfaces that come into contact when the oil film becomes insufficient.

The metal type surface may be a surface made of a pure metal such as tin (Sn) or lead (Pb). Most of the time, the metal type surface will be a metal type alloy, based on a metal and at least one other metal element or not. A frequently used alloy is steel, iron alloy (Fe) and carbon (C). The bearings used in the automotive industry, are mostly bearings whose support is made of steel, a support coated or not with another metal alloy.

The other metal alloys constituting the metal surfaces according to the invention are alloys comprising as base element tin (Sn), lead (Pb), copper (Cu) or aluminum (Al). Cadmium (Cd), silver (Ag) or zinc (Zn) may also be basic elements of the metal alloys constituting the metal surfaces according to the invention. To these basic elements will be added other elements chosen from antimony (Sb), arsenic (As), chromium (Cr), indium (In), magnesium (Mg), nickel (Ni), platinum (Pt) or silicon (Si).

Preferred alloys are based on the following combinations Al / Sn, Al / Sn / Cu, Cu / Sn, Cu / Al, Sn / Sb / Cu, Pb / Sb / Sn, Cu / Pb, PB / Sn / Cu, Al / Pb / Si, Pb / Sn, Pb / In, Al / Si, Al / Pb. The preferred combinations are Sn / Cu, Sn / Al, Pb / Cu or Pb / Al combinations.

Copper and lead-based alloys are preferred alloys, and are also known as cupro-lead or white metal alloys.

According to another embodiment, the surfaces affected by wear are polymeric surfaces. Most of the time, the pads will be steel and will include in addition this polymeric surface. The polymers that can be used are either thermoplastics such as polyamides, polyethylenes, fluoropolymers such as tetrafluoroethylenes, in particular polytetrafluoroethylenes (PTFE), or thermosetting agents such as polyimides and phenoplasts.

According to another embodiment, the surfaces concerned by the wear are surfaces of amorphous carbon type. Most of the time, the bearings will be made of steel and will include in addition this amorphous carbon type surface. Amorphous carbon type surfaces are also called DLC, or Diamond Like Carbon or Diamond Like Coati ng, whose carbons are of sp ² and sp ³ hybridizations.

The surfaces affected by wear are not ceramic surfaces. This type of ceramic coating is used very little in the field of vehicles because of their fragility and recyclability constraints applied to modern engines.

The lubricant compositions used in the invention comprise at least one inorganic friction modifier selected from organomolybdenum compounds. These compounds are, as their name indicates, compounds based on molybdenum, carbon and hydrogen, but these compounds also contain sulfur and phosphorus, and also oxygen and nitrogen.

The organomolybdenum compounds according to the invention are, for example, molybdenum dithiophosphates, molybdenum dithiocarbamates, molybdenum dithiophosphinates, molybdenum xanthates, molybdenum thioxanthates, and various organic molybdenum complexes such as molybdenum carboxylates, molybdenum esters, the molybdenum amides, obtainable by reacting molybdenum oxide or ammonium molybdates with fatty substances, glycerides or fatty acids, or fatty acid derivatives (esters, amines, amides ...).

Organomolybdenum compounds which are suitable for the lubricant compositions according to the present invention are for example described in application EP2078745, of the paragraph

In [062].

Preferred organomolybdenum compounds are molybdenum dithiophosphates and / or molybdenum dithiocarbamates.

In particular, molybdenum dithiocarbamates have been found to be very effective in reducing pad wear. These molybdenum dithiocarbamates have the following general formula (I) in which R 1, R ₂ , R 3 or R 4 are independently of each other linear or branched alkyl groups, saturated or unsaturated, comprising from 4 to 18 carbon atoms preferentially from 8 to 13.

The same applies to molybdenum dithiophosphates. These molybdenum dithiophosphates have the following general formula (II) in which R ₅ , R ₆ , R ₇ or R _g are independently of each other linear or branched alkyl groups, saturated or unsaturated, comprising 4 to 18 carbon atoms, preferably 8 to 13.

The lubricating compositions according to the invention may comprise between 0.1 and 10% by weight, relative to the total mass of lubricating composition, of organomolybdenum compound, preferably between 0.5 and 8%, more preferably between 1 and 5% more preferably between 2 and 4%.

Surprisingly, the Applicant has shown that the use of these organomolybdenum compounds, in a motor oil, can significantly reduce the wear of the connecting rod bearings on the engines of hybrid or micro-hybrid vehicles, without changing the consumption. of fuel or reducing fuel consumption.

The organomolybdenum compounds that can be used according to the invention comprise from 1 to 30% by weight of molybdenum, relative to the total weight of organomolybdenum compound, preferably from 2 to 20%, more preferably from 4 to 10%, even more preferably from 8 to 10% by weight. at 5%.

The organomolybdenum compounds which can be used according to the invention comprise from 1 to 30% by weight of sulfur, relative to the total weight of organomolybdenum compound, preferably from 2 to 20%, more preferably from 4 to 10%, even more preferably from 8 to 10% by weight. at 5%.

The organomolybdenum compounds which can be used according to the invention comprise from 1 to 10% by weight of phosphorus, with respect to the total weight of organomolybdenum compound, preferably from 2 to 8%, more preferably from 3 to 6%, even more preferably from 4 to 10% by weight. at 5%.

The lubricating compositions used according to the present invention comprise one or more base oils, generally representing from 50% to 90% by weight, relative to the total mass of the lubricating composition, preferably from 60% to 85%, more preferably from 65 to 80%, even more preferably 70 to 75%.

The base oil (s) used in the lubricant 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 ATI EL classification) as summarized below, alone or as a mixture.

These oils may be oils of vegetable, animal or mineral origin. 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 polyalphaolephines 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 (measured according to ASTM D 445). Their weight average molecular weight is typically between 250 and 3000 (measured according to ASTM D5296).

Mixtures of synthetic and mineral oils may also be employed, for example when formulating multigrade oils to avoid cold start problems.

The lubricating compositions can comprise improving polymers of viscosity index (VI improving), such as, for example, polymeric esters, olefins copolymers (OCP), homopolymers or copolymers of styrene, butadiene or isoprene, polymethacrylates. (LDCs).

The lubricant compositions according to the present invention may contain from 0 to 20%, or from 5 to 15%, or from 7 to 10% by weight, based on the total weight of the lubricating composition, of improving polymers. viscosity index (VI improvers), by examples chosen from polymeric esters, olefins copolymers (OCP), homopolymers or copolymers of styrene, butadiene or isoprene, polymethacrylates (PMA).

Preferably, the lubricant compositions according to the invention preferably have a viscosity index value or VI, measured according to ASTM D2270 greater than 130, preferably greater than 140, preferably greater than 150.

Preferably, the lubricant compositions according to the invention have a kinematic viscosity (KV100) at 100 ° C. according to ASTM D445, of between 3.8 cSt and 26.1 cSt, preferably between 5.6 and 12.5 cSt, which corresponds, according to the SAE J 300 classification, to grades 20 (5.6 to 9.3 cSt) or 30 (9.3 to 12.5 cSt) hot.

Preferably, the lubricant compositions according to the invention are multigrade engine oils grade 0W or 5W cold, and 20 or 30 hot according to classification SAE J 300.

The lubricant compositions for engines used according to the invention may furthermore contain all types of additives suitable for use as engine oil. These additives can be introduced in isolation and / or included in packages of additives used in commercial lubricant formulations, with performance levels as defined by the ACEA (Association of European Automobile Manufacturers) and / or ΓΑΡΙ (American Petroleum Institute). These additive packages (or additive compositions) are concentrates comprising about 30% by weight of dilution base oil.

Thus, the lubricant compositions according to the invention may contain, in particular and without limitation, anti-wear and extreme pressure additives, antioxidants, overbased or non-overbased detergents, pour point improvers, dispersants, antifoams, thickeners ...

The anti-wear and extreme pressure additives protect the friction surfaces by forming a protective film adsorbed on these surfaces. The most commonly used is zinc dithiophosphate or ZnDTP. This category also contains various phosphorus, sulfur, nitrogen, chlorine and boron compounds.

There is a wide variety of antiwear additives, but the most used category in motor oils is that of phosphosulfur additives such as metal alkylthiophosphates, particularly zinc alkylthiophosphates, and more specifically zinc dialkyldithiophosphates or ZnDTPs. The preferred compounds are of formula Zn ((SP (S) (O ₉ ) (ORio)) 2, or R ₉ and R ₁₀ are linear or branched, saturated or unsaturated alkyl groups, preferably containing from 1 to 18 carbon atoms. The ZnDTP is typically present at levels of the order of 0.1 to 2% by weight, based on the total weight of the lubricating composition. Amine phosphates, polysulfides, especially sulfur olefins, are also commonly used antiwear additives.

The anti-wear and extreme-pressure additives are generally present in the compositions for motor lubricants at contents of between 0.5 and 6% by weight, preferably between 0.7 and 2%, preferably between 1 and 1.5%. relative to the total mass of the lubricating composition.

Antioxidants delay the degradation of oils in service, which can result in the formation of deposits, the presence of sludge, or an increase in the viscosity of the oil. They act as free radical inhibitors or destroyers of hydroperoxides. Among the commonly used antioxidants are phenolic and / or amine antioxidants.

Phenolic antioxidants may be ashless, or may be in the form of neutral or basic metal salts. Typically, these are compounds containing a sterically hindered hydroxyl group, for example when two hydroxyl groups are in the ortho or para position of each other, or when the phenol is substituted by an alkyl group comprising at least 6 carbon atoms. .

Amino compounds are another class of antioxidants that can be used alone or possibly in combination with phenolic compounds. Typical examples are aromatic amines, of formula RnRuRuN, where Ru is an aliphatic group, or an optionally substituted aromatic group, R _i2 is an optionally substituted aromatic group, R ₁₃ is hydrogen, or an alkyl or aryl group, or a group of formula R "S (0) _x _¾ Ri wherein R ₁₄ and R ₅ are alkylene, alkenylene, or aralkylene, and x is 0, 1 or 2.

Sulfurized alkyl phenols or their alkali and alkaline earth metal salts are also used as antioxidants.

Another class of antioxidants is that of oil-soluble copper compounds, for example copper thio- or dithiophosphates, copper and carboxylic acid salts, dithiocarbamates, sulphonates, phenates, acetylacetonates of copper. Copper salts I and II, succinic acid or anhydride are used.

These compounds, alone or as a mixture, are typically present in the engine lubricating compositions in amounts of between 0.1 and 5% by weight, preferably between 0.3 and 2%, even more preferably between 0.5 and 1, 5%, based on the total mass of the lubricating composition.

Detergents reduce the formation of deposits on the surface of metal parts by dissolving secondary products of oxidation and combustion, and allow the neutralization of some acid impurities from combustion and found in the oil.

The detergents commonly used in the formulation of lubricating compositions are typically anionic compounds having a long lipophilic hydrocarbon chain and a hydrophilic head. The associated cation is typically a metal cation of an alkali or alkaline earth metal.

The detergents are preferably chosen from alkali metal or alkaline earth metal salts of carboxylic acids, sulphonates, salicylates and naphthenates, as well as the salts of phenates, preferably of calcium, magnesium, sodium or barium.

These metal salts may contain the metal in an approximately stoichiometric amount or in excess (in an amount greater than the stoichiometric amount). In the latter case, we are dealing with so-called overbased detergents.

The excess metal providing the overbased detergent character is in the form of oil-insoluble metal salts, for example carbonate, hydroxide, oxalate, acetate, glutamate, preferably carbonate, preferably calcium, magnesium, sodium or barium.

The lubricant compositions according to the present invention may contain any type of detergent known to those skilled in the art, neutral or overbased. The more or less overbased character of the detergents is characterized by the base number BN (base number or BN in English terminology), measured according to the ASTM D2896 standard, and expressed in mg of KOH per gram. Neutral detergents have a BN between about 0 and 80 mg KOH / g. Overbased detergents, they, BN values typically of the order of 150 mg KOH / g and more, or 250 mg KOH / g or 450 mg KOH / g or more. The BN of the lubricant composition containing detergents is measured by ASTM D2896 and expressed as mg KOH per gram of lubricant.

Preferably, the amounts of detergents included in the motor oils according to the invention are adjusted so that the BN of said oils, measured according to ASTM D2896, is between 5 and less than or equal to 20 mg of KOH per gram of d motor oil, preferably between 8 and 15 mg of KOH per gram of engine oil

Pour point depressant additives improve the cold behavior of oils by slowing the formation of paraffin crystals. They are, for example, alkyl polymethacrylates, polyacrylates, polyarylamides, polyalkylphenols, polyalkylnaphthalenes, alkylpyrystyrene. They are generally present in the oils according to the invention at contents of between 0.1 and 0.5% by weight, relative to the mass of lubricating composition. Dispersants such as succinimides, PIB (polyisobutene) succinimides, annich bases provide suspension maintenance and evacuation of insoluble solid contaminants consisting of secondary oxidation products that are formed when the engine oil is in use. The dispersant level is typically between 0.5 and 10% by weight, preferably between 1 and 5%, relative to the total weight of the lubricant composition.

The invention also relates to a method for reducing bearing wear and for lubricating metal surfaces, polymeric surfaces and / or amorphous carbon surfaces, thermal internal combustion engines of hybrid and / or microhybrid vehicles by means of use of a lubricating composition comprising at least one base oil and at least one organomolybdenum compound. The set of characteristics and preferences presented for the lubricant composition according to the invention also applies to the method according to the invention.

Examples

The aggravation on the wear of the bearings of an engine equipped with a Stop-and-Start system was simulated by a test consisting of a succession of 12000 cycles stop / start for 150 hours:

1) Engine start,

2) 10 seconds operation on idle point,

3) Engine stop,

Resumption of sequence 1 to 3.

The system tested includes a 4-cylinder diesel engine with a maximum torque of 200 Nm from 1750 to 2500 rpm. It is of the Stop-and-Start type and includes an alternator-starter between the clutch and the gearbox of the vehicle. The engine oil is maintained at about 100 ° C in these tests. The wear is followed by a usual technique of radiotracers, consisting of irradiating the surface of the connecting rod bearings whose wear is to be tested, and measuring during the test the increase in radioactivity of the engine oil, that is, the rate of loading of the oil into irradiated metal particles. This speed is directly proportional to the wear speed of the bearings.

The results are based on a comparative analysis of these damage rates (reference oil and oil to be tested) and are validated by a frame with a reference oil in order to integrate positive or negative surface adaptation elements to the speed of damage.

The damage rates of the oils tested are all compared to the rate of damage of the reference oil and quantified as a speed ratio named Usure in Table I below.

The lubricant composition A is a grade 5W30 reference lubricant composition.

The lubricating composition B is an additive lubricant composition with a known antiperspirant ZnDTP, zinc dithiophosphate of formula (III) wherein R _{: 6} is an alkyl group comprising carbon atoms.

The lubricant composition C is an additive lubricant composition with a known anti-wear ZnDTC, a zinc diamyldithiocarbamate.

The lubricating composition D is a lubricating composition according to the prior art, and in particular according to the application WO2011045773, in which the ester-type organic friction modifier which corresponds to the general formula (a) R (OH) _m (COOR '( OH) _p (OOC ") _q ) _n with m equal to 1, p equal to 0, q equal to 0, n equal to 3 and R 'is an ethyl group.

The lubricating composition E is a lubricating composition according to the invention with, as inorganic friction modifier, an organomolybdenum compound of general formula (I) with R _{1 (} R ₂ , _R¾R ₄₎ which are alkyl groups of 13 and / or 18 atoms. of carbon, the amount of molybdenum by weight, relative to the weight of the compound, is 10%, the amount of sulfur by weight, relative to the weight of the compound, is 11%.

The lubricating composition F is a lubricant composition according to the invention with inorganic friction modifier as an organomolybdenum compound of the general formula (II) with R _5, R _s, R _7, R ₈ are alkyl groups of 8 carbon atoms, the amount of molybdenum by weight, relative to the weight of the compound, is 9%, the amount of sulfur by weight, relative to the weight of the compound, is 10.1%, the amount of phosphorus by weight, relative to the mass of the compound, is 3.2%.

The mass compositions and properties of the lubricating compositions tested are summarized in Table I below:

Table I

* excluding base oil dilution of the additive package

The base oil used is a blend of Group III base oils with a viscosity number of 171.

The polymer used is a linear styrene / butadiene polymer of mass M _w equal to

139 700, of mass M "equal to 133,000, polydispersity index equal to 1.1, PSSI (permanent shear stability index or Permanent Shear Stability Index in English terminology) equal to 15, 8% of active ingredient in a Group III base oil.

The antioxidant is an amine antioxidant of alkylarylamine structure.

The PPD (or Depressant Point in English terminology) or

Flow Point is polymethacrylate type.

The additive package used includes conventional anti-wear, anti-oxidant, dispersant and detergent additives.

The lubricant composition A is taken as a reference. Tests with the lubricating composition B showed a high wear rate, corroborated by visual observations (wear of 72%). Likewise for the lubricating composition C (wear of 74). The use of the organic friction modifier in lubricant composition D reduces wear (68% wear), but this can be improved. Thus, the use of inorganic friction modifiers in the lubricant compositions E and F makes it possible to improve this result and to obtain wear levels less than or equal to 50%.

Claims

Claims:

1. Use of a lubricating composition comprising at least one base oil and at least one organomolybdenum compound for reducing wear of the bearings and for lubricating metal surfaces, polymeric surfaces and / or amorphous carbon surfaces, motors thermal internal combustion of vehicles with hybrid and / or microhybrid motorization.

2. Use according to claim 1 wherein the microhybrid motorized vehicles are equipped with an alternator-starter or a reinforced starter.

3. Use according to claim 1 or 2 for reducing the wear of the connecting rod bearings of the internal combustion engine thermal.

4. Use according to any one of claims 1 to 3 to increase the life of the internal combustion engine thermal, in particular the life of the bearings of the internal combustion engine thermal, particularly the life of the bearings of connecting rod of the internal combustion engine.

5. Use according to any one of claims 1 to 4 to increase the time interval between the changes of the bearings of the internal combustion engine thermal, especially the time interval between the changes of the connecting rod bearings of the combustion engine internal heat.

6. Use according to any one of claims 1 to 5 wherein the lubricating composition comprises from 0.1 to 10% by weight, based on the total weight of the lubricating composition, organomolybdenum compound, preferably from 0.5 to 8%, more preferably 1 to 5%, even more preferably 2 to 4%.

7. Use according to any one of claims 1 to 6 wherein the organomolybdenum compounds are selected from dithiocarbamates and / or dithiophosphates molybdenum, alone or in a mixture.

8. Use according to any one of claims 1 to 7 wherein the organomolybdenum compounds are selected from molybdenum dithiocarbamates of formula (I):

9. Use according to any one of claims 1 to 7 wherein the organomolybdenum compounds are selected from molybdenum dithiophosphates of formula (II):

10. Use according to any one of claims 1 to 9 wherein the metal surface is an alloy.

11. Use according to claim 10 wherein the alloy is steel.

12. Use according to claim 10 wherein the alloy comprises as base element of tin (Sn), lead (Pb), copper (Cu), aluminum (Al), cadmium (Cd) , silver (Ag) or zinc (Zn).

13. Use according to claim 12 wherein the alloy comprises lead (Pb) and copper (Cu).

14. Use according to any one of claims 1 to 9 wherein the polymeric surface comprises polytetrafluoroethylene.

15. Use according to any one of claims 1 to 14 wherein the kinematic viscosity at 100 ° C of the lubricating composition, measured according to ASTM D445, is between 5.6 and 12.5 cSt.