US20220364010A1 - Use of a succinimide compound as an anti-corrosion additive in a lubricant composition for a propulsion system of an electric or hybrid vehicle

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Abstract

Description

Claims

US20220364010A1

Publication number: US20220364010A1
Application number: US17/619,859
Authority: US
Inventors: Shimin Zhang; Hakim EL-BAHI; Julien Guérin
Original assignee: Total Marketing Services SA; TotalEnergies Onetech SAS
Current assignee: TotalEnergies Onetech SAS
Priority date: 2019-06-28
Filing date: 2020-06-25
Publication date: 2022-11-17
Also published as: JP2022538637A; FR3097873B1; CN114096645A; WO2020260458A1; FR3097873A1; MX2021015548A; CN114096645B; EP3990593A1; KR20220032057A

The invention relates to the use of at least one succinimide compound as an anti-corrosion additive in a lubricant composition for a propulsion system of an electric or hybrid vehicle, said lubricant composition comprising one or more amino and/or sulfur anti-wear additives. The invention also relates to the use of a lubricant composition for lubricating a propulsion system of an electric or hybrid vehicle.

The present invention relates to the field of lubricant compositions for a propulsion system of an electric or hybrid vehicle. The invention more particularly relates to the use of succinimide compounds for improving the anticorrosion properties of a lubricant composition incorporating one or more amine-based and/or sulfur-based antiwear additives.

TECHNICAL FIELD

The changes in the international standards for the reduction of CO₂emissions, but also for the reduction of energy consumption, has driven motor vehicle constructors toward proposing alternative solutions to combustion engines.
One of the solutions identified by motor vehicle constructors consists in replacing combustion engines with electric motors. The research aimed at reducing CO₂emissions has thus led to the development of electric vehicles by a certain number of motor vehicle companies.
For the purposes of the present invention, the term “electric vehicle” denotes a vehicle comprising an electric motor as sole means of propulsion, as opposed to a hybrid vehicle which comprises a combustion engine and an electric motor as combined means of propulsion.
For the purposes of the present invention, the term “propulsion system” denotes a system comprising the mechanical parts required for propelling an electric vehicle. The propulsion system thus more particularly encompasses an electric motor or the rotor-stator assembly of the power electronics (dedicated to regulating the speed), a transmission and a battery.
In general, it is necessary to use, in electric or hybrid vehicles, lubricant compositions, also known as “lubricants”, for the main purposes of reducing the friction forces between the various parts of the propulsion system of the vehicle, notably between the metal parts in motion in the motors. These lubricant compositions are also effective for preventing premature wear or even damage of these parts, and in particular of their surface.
To do this, a lubricant composition is conventionally composed of one or more base oils which are generally combined with several additives intended for stimulating the lubricant performance of the base oil, for instance friction-modifying additives, but also for affording additional performance.
In particular, “antiwear” additives are considered in order to reduce the wear of the mechanical parts of the motor, and thus to prevent degradation of the durability of the motor.
A wide variety of antiwear additives exists, among which mention may be made, for example, of dimercaptothiadiazoles, polysulfides, notably sulfur-based olefins, amine phosphates, or else phospho-sulfur additives, for instance metal alkylthiophosphates, in particular zinc alkylthiophosphates and more specifically zinc dialkyldithiophosphates or ZnDTP.
Among these antiwear additives, the ones that are notably favored are amine-based and/or sulfur-based antiwear agents, such as dimercaptothiadiazoles, zinc dithiophosphate or polysulfides.
Unfortunately, these amine-based and/or sulfur-based antiwear additives, such as dimercaptothiadiazoles, have the drawback of being corrosive. The problem of corrosion is particularly critical in electric propulsion systems. In particular, corrosion can lead to a risk of deterioration of the stator and rotor windings, the sensors in the propulsion system, the solenoid valves in the hydraulic system, but also of the rolling bearings between the rotor and stator of an electric motor, which are generally copper-based and thus particularly susceptible to corrosion, or to the seals or varnishes in the propulsion system.
In addition, in order to be able to cool the propulsion systems of electric or hybrid vehicles, it is essential that the lubricant be insulating in order to avoid any failure in the electrical components. In particular, a conductive lubricant can lead to a risk of electrical current leakage in the stator and rotor windings, which thus reduces the efficiency of the propulsion systems, and creates possible overheating of the electrical components, even to the point of damaging the system. In the context of using lubricants for electric or hybrid vehicle powertrain systems, it is thus crucial for the lubricants to have good “electrical” properties in addition to non-corrosive properties.
The present invention is directed, specifically, towards overcoming this drawback.

SUMMARY OF THE INVENTION

More precisely, the present invention relates to the use of at least one succinimide compound, as an anticorrosion additive in a lubricant composition intended for a propulsion system of an electric or hybrid vehicle and comprising one or more amine-based and/or sulfur-based antiwear additives.
Succinimide compounds, for instance polyalkylene succinimides such as polyisobutylene succinimides (PIBSI), have already been proposed as dispersants, for example in lubricants for vehicle motors, as described, for example, in patent application WO 2014/096 328.
To the inventors' knowledge, it has, however, never been proposed to use succinimide compounds as anticorrosion additives in the context of using a lubricant for a propulsion system of an electric or hybrid vehicle, to overcome the corrosion effects brought about by the use of amine-based and/or sulfur-based antiwear additives.
Surprisingly, as illustrated in the example that follows, the inventors have found that such succinimide additives can efficiently reduce the corrosion effects induced by amine-based and/or sulfur-based antiwear additives.
Thus, the addition of at least one succinimide compound can advantageously improve the anticorrosion properties of a lubricant composition comprising one or more amine-based and/or sulfur-based antiwear additives.
For the purposes of the present invention, the term “anticorrosion additive” denotes an additive for preventing or reducing the corrosion of metal parts. An anticorrosion additive used in a composition thus makes it possible to improve the “anticorrosion” properties of said composition.
The use of one or more succinimide compounds according to the invention together with one or more amine-based and/or sulfur-based antiwear additives advantageously affords access to a lubricant composition which simultaneously has good antiwear performance, while at the same time overcoming the corrosion problems mentioned previously. A composition according to the invention thus simultaneously has good antiwear and anticorrosion properties.
The corrosive (or corroding) power of a compound may be evaluated by means of a test involving study of the variation in the electrical resistance value of a copper wire of a preestablished diameter, as a function of the duration of immersion of this wire in a composition comprising said test compound in a noncorrosive medium, for example in one or more base oils. The variation in this electrical resistance value is directly correlated with the variation in the diameter of the test wire. Thus, in the context of the present invention, a compound is termed “noncorrosive” when the loss of diameter of the copper wire studied is less than or equal to 1.3 μm after immersion for 80 hours, in particular less than or equal to 0.8 μm after immersion for 40 hours in the composition comprising said compound.
The dielectric properties of a lubricant are notably represented by the electrical resistivity and the dielectric loss (tan δ) and may be measured according to the standard IEC 60247. The electrical resistivity represents the capacity of a material to oppose the circulation of an electric current. It is expressed in ohm-metres (Ω.m). The resistivity must not be low to prevent electrical conduction.
The electric dissipation factor or the loss angle tangent. The loss angle δ is the complementary angle of the phase shift between the applied voltage and the alternating current. This factor reflects the Joule-effect energy losses. Heating is thus directly linked to the δ value. A transmission oil typically has a tan δ value of the order of unity at ambient temperature. A good insulating lubricant must maintain a low tan δ level.
Advantageously, the succinimide compound used according to the invention is chosen from polyalkylene mono- or bis-succinimides, such as polyisobutene (PIB) mono- or bis-succinimides; borate derivatives thereof; succinic anhydride derivatives thereof such as polyisobutylene succinic anhydrides (PIBSA); compounds obtained by opening such a succinic anhydride ring, such as PIB pentaerythritol ester succinimides; and mixtures thereof.
Preferably, the succinimide compound is chosen from:

- polyalkylene bis-succinimides in which the alkyl chain is optionally linked to the succinimide via a —(C═CH₂)—group, in particular polyisobutylene (PIB) bis-succinimides in which the alkyl chain is optionally linked to the succinimide via a —(C═CH₂)—group, and borate derivatives thereof, the two succinimide groups being linked together by their respective nitrogen atom via an alkylene group or a polyamine group, in particular polyalkyleneamine;
- polyalkylene mono-succinimides in which the alkyl chain is optionally linked to the succinimide via a —(C═CH₂)—group, in particular polyisobutylene (PM) mono-succinimides in which the alkyl chain is optionally linked to the succinimide via a —(C═CH₂)—group, and borate derivatives thereof, substituted on the nitrogen atom with a polyamine group, in particular polyalkyleneamine; and
- mixtures thereof.

The introduction, into a lubricant composition intended for a propulsion system of an electric or hybrid vehicle, of one or more succinimide compounds according to the invention thus advantageously permits the use, in the composition, of amine-based and/or sulfur-based antiwear additives, such as dimercaptothiadiazoles, without, however, entailing an adverse corrosive effect.
The amine-based and/or sulfur-based antiwear additives used in a lubricant composition according to the invention are more particularly detailed in the text hereinbelow, They are preferably chosen from amine-based and sulfur-based antiwear additives. They may preferably be thia(di)azole compounds, in particular dimercaptothiadiazole derivatives.
In addition, a composition that is suitable for use in the invention has the advantage of being easy to formulate. Besides good antiwear and anticorrosion performance, it has good stability, notably with respect to oxidation, and also good properties in terms of electrical insulation.
The present invention also relates to the use, for lubricating a propulsion system of an electric or hybrid vehicle, in particular for lubricating the electric motor and the power electronics of an electric or hybrid vehicle, of a lubricant composition comprising:

- one or more succinimide compounds as defined in the invention, as anticorrosion additives); and
- one or more amine-based and/or sulfur-based antiwear additives as defined in the invention.

A subject of the present invention is also a process for lubricating a. propulsion system of an electric or hybrid vehicle, comprising at least one step of placing at least one mechanical part of said system in contact with a lubricant composition comprising at least one succinimide compound as defined in the invention, as anticorrosion additive and at least one amine-based and/or sulfur-based antiwear additive as defined in the invention.
Advantageously, a lubricant composition according to the invention is used for lubricating the electric motor itself, in particular the rolling bearings located between the rotor and the stator of an electric motor, and/or the transmission, in particular the reducer, in an electric or hybrid vehicle.
Other features, variants and advantages of the use of succinimide compounds as anticorrosion additives according to the invention will emerge more clearly on reading the description and the examples that follow, which are given as nonlimiting illustrations of the invention.
In the continuation of the text, the expressions “between . . . and . . . ”,“ranging from . . . to . . . ” and “varying from . . . to . . .” are equivalent and are intended to mean that the limits are included, unless otherwise mentioned,
Unless otherwise indicated, the expression “including a(n)” should be understood as “comprising at least one”.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically represents a propulsion system of an electric or hybrid vehicle.

DETAILED DESCRIPTION

Anticorrosion Additives of Succinimide Type

As stated previously, the additive used as anticorrosion agent according to the invention, together with one or more amine-based and/or sulfur-based antiwear additives, in a lubricant composition for the powertrain system of an electric or hybrid vehicle, is a succinimide compound.
As mentioned previously, many succinimide compounds have already been proposed for their use as dispersants, for instance polyalkylene mono- or bis-succinimides, such as polyisobutene (PIB) mono- or bis-succinimides; borate derivatives thereof; succinic anhydride derivatives thereof, for instance polyisobutylene succinic anhydrides (PIBSA); compounds obtained by opening such a succinic anhydride ring, for instance polyisobutylene pentaerythritol ester succinimides.
However, as indicated previously, such compounds have never been proposed as anticorrosion additives in a lubricant for the powertrain system of an electric or hybrid vehicle, for the purposes of reducing or even inhibiting the corrosion effects induced by the use of one or more amine-based and/or sulfur-based antiwear additives.
Succinimide compounds are compounds comprising at least one succinimide group, in other words a group of formula (i) below:
or a borate derivative (B—O bond) thereof; or a succinic anhydride derivative of such a succinimide group, or a compound obtained by opening of the succinic anhydride ring.
As already mentioned previously, succinimide compounds may be of diverse nature. They may be mono-succinimide or bis-succinimide compounds.
Preferably, the succinimide compound is chosen from compounds comprising at least one substituted succinimide group, in particular of formula (ii) below:
or a borate derivative (B—O bond) of such a substituted succinimide group of formula (ii); or a succinic anhydride derivative of such a substituted succinimide group of formula (ii), or a compound obtained by opening of the succinic anhydride ring,

- in which R¹represents a hydrocarbon-based group preferably comprising from 8 to 400 carbon atoms.

R¹may be chosen more particularly from linear or branched C₈to C₄₀₀and in particular C₅₀to C₂₀₀alkyl groups, linear or branched C₈to C₄₀₀and in particular C₅₀to C₂₀₀alkenyl groups, C₆to C₁₀aryl groups, aryIalkyl groups and alkylaryl groups.
Preferably, R¹represents a long C₈to C₄₀₀and in particular C₅₀to C₂₀₀alkyl chain, which is preferably branched, or a long C₈to C₄₀₀and in particular C₅₀to C₂₀₀alkenyl chain, which is preferably branched, including only one double bond, of which one of the two carbon atoms is directly linked to the succinimide ring.
Advantageously, R¹represents a polyalkylene group, preferably having a mass-average molecular mass Mw of between 140 and 50 000, in particular between 2000 and 30 000. According to a particular embodiment, R¹represents a polyisobutylene group, preferably with a number-average molecular mass of between 140 and 30 000, in particular between 2000 and 20 000, or even between 2000 and 7000 and notably between 3000 and 5000.
According to another particular embodiment, R¹represents a polyisobutylene group, preferably with a number-average molecular mass of between 140 and 30 000, in particular between 2000 and 20 000, or even between 2000 and 7000 and notably between 3000 and 5000, linked to the succinimide group via a —(C═CH₂)—group and is of formula (A) below:

- in which the symbol * indicates the point of attachment of this group to the succinimide group, and n represents an integer ranging from 6 to 500.

Thus, according to a particular embodiment, the succinimide compound comprises at least one substituted succinimide group of formula (ii), or a borate derivative of said group (ii), or a succinic anhydride derivative of said group (ii), or a compound obtained by opening of the succinic anhydride ring,

- in which R¹represents a hydrocarbon-based group, preferably comprising from 8 to 400 carbon atoms, in particular a polyalkene group optionally linked to the succinimide group via a —(C═CH₂)—group, preferably having a mass-average molecular mass Mw of between 140 and 50 000, in particular between 2000 and 30 000, and more particularly a polyisobutylene group optionally linked to the succinimide group via a —(C═CH₂)—group, preferably with a mass-average molecular mass Mw of between 140 and 30 000, in particular between 2000 and 20 000 or even between 2000 and 7000 and notably between 3000 and 5000.

More particularly, the succinimide compound may be chosen from mono-succinimide compounds comprising a substituted succinimide group of the abovementioned formula (ii) and bis-succinimide compounds comprising two substituted succinimide groups, in particular of the abovementioned formula (ii), said succinimide groups being more particularly connected at their apex bearing a nitrogen atom with a polyamine group,
According to a particular embodiment, the succinimide compound used according to the invention corresponds to formula (I) below:
or a borate derivative thereof,

- in which A represents a linear or branched C₂to C₂₄and preferably C₂to C₆alkylene group;
- R¹is as defined previously, for example a polyisobutylene group optionally linked to the succinimide group via a —(C═CH₂)—group;
- x represents 0 or an integer ranging from 1 to 6; preferably, x is equal to 2, 3 or 4;
- R²and R³are chosen, independently of each other, from a hydrogen atom, a linear or branched alkyl group, notably of C₁to C_25,an alkoxy group, notably of C₁to C_12,an alkenyl group, in particular of C₂to C_12,optionally bearing one or more hydroxyl and/or amine functions,
- or R²and R³form, together with the nitrogen atom which bears them, an optionally substituted succinimide group, preferably a succinimide group substituted with a group R¹as defined above.

According to a first embodiment variant, a succinimide compound used according to the invention may be a mono-succinimide compound of the abovementioned formula (I) in which R²and R³are chosen, independently of each other, from a hydrogen atom, a linear or branched alkyl group, notably of C₁to C_25;an alkoxy group, notably of C₁to C_12,an alkenyl group, in particular of C₂to C_12,optionally bearing one or more hydroxyl and/or amine functions.
Preferably, a succinimide compound used according to the invention is of the abovementioned formula (I) in which R²and R³represent hydrogen atoms.
In other words, a succinimide compound used according to the invention may be of formula (II) below:
or a borate derivative thereof,

- in which: R¹is as defined previously; in particular, R¹represents a polyalkylene group optionally linked to the succinimide group via a —(C═CH₂)—group, in particular polyisobutylene optionally linked to the succinimide group via a —(C═CH₂)—group,
- A is as defined previously, and preferably represents at least one of the following segments: —CH₂—CH₂—, —CH₂—CH₂—CH₂—,—CH₂—CH(CH₃)—; and
- y represents an integer between 1 and 6; in particular, y represents 2, 3 or 4,

According to another embodiment variant, a succinimide compound used according to the invention may be a bis-succinimide compound of the abovementioned formula (I) in which R²and R³form, together with the nitrogen atom which bears them, an optionally substituted succinimide group, preferably a succinimide group substituted with a group R¹as defined above.
Advantageously, a bis-succinimide compound used according to the invention may be of formula (III) below:
or a borate derivative thereof, in which:

- R¹, which may be identical or different, are as defined previously;
- z represents an integer between 0 and 10 and preferably between 2 and 6;
- s represents an integer between 2 and 6 and preferably between 2 and 4.

Preferably, the bis-succinimide compound may be of formula (III) in which R¹represents polyalkylene groups, in particular polyisobutylene groups, preferably with a molecular mass of between 150 and 15 000, in particular between 500 and 2000 and notably between 500 and 1500.
The borate derivatives of the succinimide compounds of the abovementioned formula (I), (II) or (III) may be obtained from the non-borate succinimide compounds by reaction with borates, for example with boric acid, in particular to reach a concentration of from 0.1% to 3% by mass and notably from 1% to 2% by mass of boron in the succinimide compound.
Among the succinic anhydride derivatives that are suitable for use in the invention, mention may be made of polyisoalkylene succinic anhydrides, in particular polyisobutylene succinic anhydrides (known as PIBSA) such as the following compound, with a number-average molecular mass Mn of between 300 and 30 000 and a mass-average molecular mass Mw of between 300 and 30 000:
in which R is a polyisobutylene group.
Among the compounds obtained by opening the succinic anhydride ring, mention may notably be made of polyalkylene pentaerythritol ester succinimides, for instance polyisobutylenes pentaerythritol ester succinimides having the following formulae, with a number-average molecular mass Mn of between 300 and 30 000 and a mass-average molecular mass Mw of between 300 and 30 000:
in which PIB represents a polyisobutylene;
in which PIB represents a polyisobutylene.
In the context of the invention, the following definitions apply:

“alkyl”: a linear or branched, saturated aliphatic group; for example, a Cx to Cz alkyl represents a linear or branched hydrocarbon-based chain of x to z carbon atoms;
“alkylene” represents a divalent alkyl group. For example, a C_x-C_zalkylene group represents a linear or branched divalent hydrocarbon-based chain of x to z carbon atoms;
“alkenyl”: a linear or branched, unsaturated aliphatic group; for example, a Cx to Cz alkenyl group represents a linear or branched unsaturated carbon-based chain of x to z carbon atoms; “alkoxy”: a radical —O-alkyl, in which the alkyl group is as defined previously; “aryl”: a monocyclic or polycyclic aromatic group in particular comprising between 5 and 10 carbon atoms. Examples of aryl groups that may be mentioned include phenyl, tolyl and naphthyl groups.

Advantageously, the additive of succinimide type (mono-succinimide or bis-succinimide) is chosen from polyalkylene succinimides (in other words compounds comprising at least one group of the abovementioned formula (ii) in which R¹is a polyalkylene group optionally linked to the succinimide group via a —(C═CH₂)—group and notably polyisobutylene (PIB) succinimides in which the polyisobutylene part is optionally linked to the succinimide group via a —(C═CH₂)—group, and borate derivatives thereof.
According to a particular embodiment, the additive of succinimide type is chosen from polyalkylene succinimides in which the alkyl chain is optionally linked to the succinimide via a —(C═CH₂)—group, in particular polyisobutylene (PIB) succinimides in which the alkyl chain is optionally linked to the succinimide via a —(C═CH₂)—group, and borate derivatives thereof, substituted on the nitrogen atom with a polyamine group, in particular polyalkyleneamine, for example polyethyleneamine.
Preferably, the additive of succinimide type is chosen from mono-succinimides or bis-succinimides of the abovementioned formula (I), in particular the mono-succinimides of the abovementioned formula (II), the bis-succinimides of the abovementioned formula (III), and mixtures thereof.
According to a particularly preferred embodiment, the additive of succinimide type is chosen from:

- polyalkylene bis-succinimides in which the alkyl chain is optionally linked to the succinimide via a —(C═CH₂)—group, in particular polyisobutylene (PIB) bis-succinimides in which the alkyl chain is optionally linked to the succinimide via a —(C═CH₂)—group, and borate derivatives thereof, the two succinimide groups being linked together by their respective nitrogen atom via an alkylene group or a polyamine group, in particular polyalkyleneamine, or even polyethyleneamine;
- polyalkylene mono-succinimides in which the alkyl chain is optionally linked to the succinimide via a —(C═CH₂)—group, in particular polyisobutylene (PIB) mono-succinimides in which the alkyl chain is optionally linked to the succinimide via a —(C═CH₂)—group, and borate derivatives thereof, substituted on the nitrogen atom with a polyamine group, in particular polyalkyleneamine, or even polyethyleneamine; and
- mixtures thereof.

According to an even more particularly preferred embodiment, the additive of succinimide type is chosen from the following compounds:

- in which n ranges from 6 to 500 and is preferably 90; and R is a linear or branched C₂to C₂₄and preferably C₂to C₆alkylene or a group —R″—(NH-R′)x—in which R′ and R″ represent, independently of each other, a linear or branched C₂to C₂₄and preferably C₂to C₆alkylene and x is an integer ranging from 1 to 6, and preferably x is equal to 2, 3, 4 or 5. It is more precisely a bis-succinimide for which the average molecular mass Mn is between 3000 and 4000, and is preferably 3410; the average molecular mass Mw is between 5000 and 6000, and is preferably 5225; the polydispersity index Ip is between 1.25 and 2, and is preferably 1.5;

- in which n ranges from 10 to 350 and is preferably 65; and R is a linear or branched C₁to C₂₄and preferably C₂to C₆alkyl or a group —(R′—(NH)y—H in which R′ represents a linear or branched C₂to C₂₄and preferably C₂to C₆alkylene and y is an integer ranging from 1 to 6, and preferably x is equal to 2, 3 or 4. It is more precisely a PIB succinimide for which the average molecular mass Mn is between 800 and 18 000, and is preferably 3519; the average molecular mass Mw is between 1000 and 20 000, and is preferably 6220; the polydispersity index Ip is between 1.5 and 2.3, and is preferably 1.6; and
- mixtures thereof.

It is understood that, in the context of the present invention, a succinimide compound under consideration according to the invention may be in the form of a mixture of at least two succinimide compounds, in particular as defined previously.
The succinimide compounds used according to the invention may be commercially available or prepared according to synthetic methods known to those skilled in the art.
For example, succinimide compounds may be synthesized by condensation of an optionally substituted succinic anhydride, for example of a succinic anhydride substituted with a polyisobutylene group, with a poly(alkyleneamine). The succinic anhydride substituted with a polyisobutylene group (PIB) may be obtained beforehand, for example by reaction of maleic anhydride with methylvinylidene polyisobutene.
The invention is not limited to the succinimide compounds specifically described above.
Other succinimide compounds, notably known as dispersants, may be used as anticorrosion additives according to the invention.
The succinimide compound(s), in particular as defined previously, may be used in a lubricant composition according to the invention in a proportion of from 0.01% to 10% by mass, in particular from 0.1% to 10% by mass and more particularly from 0.5% to 8% by mass relative to the total mass of the lubricant composition.
Advantageously, a lubricant composition under consideration according to the invention does not comprise any anticorrosion additives other than the succinimide compounds.
According to a particular embodiment, a lubricant composition used according to the invention is free of anticorrosion additives of triazole type or of the type such as compounds bearing an amine function or a sterically hindered phenol function.

Lubricant Composition

Amine-Based and/or Sulfur-Based Antiwear Additives
As indicated previously, a lubricant composition under consideration according to the invention comprises one or more amine-based and/or sulfur-based antiwear additives.
The term “amine-based and/or sulfur-based antiwear additive” denotes an additive chosen from amine-based antiwear additives, sulfur-based antiwear additives and amine-based and sulfur-based antiwear additives.
The term “antiwear additive” denotes a compound which, when used in a lubricant composition, notably a lubricant composition for a propulsion system of an electric or hybrid vehicle, makes it possible to improve the antiwear properties of the composition.
The amine-based and/or sulfur-based antiwear additive may be chosen, for example, from additives of thia(di)azole type, in particular dimercaptothiadiazole derivatives; polysulfide additives, notably sulfur-based olefins, amine phosphates, phospho-sulfur additives such as alkylthiophosphates, and mixtures thereof.

Thia(di)azole Additives

According to a particularly preferred embodiment, a lubricant composition under consideration according to the invention comprises at least one thia(di)azole antiwear additive.
Thia(di)azole compounds are compounds which contain both a sulfur atom and at least one nitrogen atom in a five-atom ring. Benzothiazoles are a particular type of thia(di)azoles. This term “thia(di)azole” includes, besides cyclic compounds containing one sulfur atom and one nitrogen atom per five-atom ring, also thiadiazoles which contain sulfur and two nitrogen atoms in such a ring.
In particular, the thia(di)azole compounds may be chosen from benzothiazole derivatives, thiazole derivatives and thiadiazole derivatives.
Preferably, the antiwear additive may be a thiadiazole derivative.
Thiadiazoles are heterocyclic compounds comprising two nitrogen atoms, one sulfur atom, two carbon atoms and two double bonds, of general formula C₂N₂SH_2,which may exist in the following forms, respectively: 1,2,3-thiadiazole; 1,2,4-thiadiazole; 1,2,5-thiadiazole; 1,3,4-thiadiazole:
Preferably, the thiadiazole derivative is a dimercaptothiadiazole derivative.
Thus, according to a particularly preferred embodiment, a lubricant composition according to the invention comprises at least one antiwear additive chosen from dimercaptothiazole derivatives.
The term “dimercaptothiadiazole derivative” according to the invention means chemical compounds derived from the following four dimercaptothiadiazole molecules below: 4,5-dimercapto-1,2,3-thiadiazole, 3,5-dimercapto-1,2,4-thiadiazole, 3,4-dimercapto-1,2,5-thiadiazole, 2,5-dimercapto-1,3,4-thiadiazole, taken alone or as a mixture:
The dimercaptothiadiazole derivatives are more particularly molecules or a mixture of molecules based on 4,5-dimercapto-1,2,3-thiadiazole, 3,5-dimercapto-1,2,4-thiadiazole, 3,4-dimercapto-1,2,5-thiadiazole or 2,5-dimercapto-3,4-thiadiazole, as represented above, in which at least one of the substitutions=S, or even both substitutions=S on the thiadiazole ring is replaced with a substituent:

- in which * represents the bond with a carbon atom of the 5-membered ring; n represents an integer equal to 1, 2, 3 or 4; and R₁is chosen from a hydrogen atom, a linear or branched, saturated or unsaturated alkyl group comprising from1 to 24, preferably from 2 to 18, more preferentially from 4 to 16 and even more preferentially from 8 to 12 carbon atoms or an aromatic substituent.

In particular, taking 2,5-dimercapto-1,3,4-thiadiazole as example, the 2,5-dimercapto-1,3,4-thiadiazole derivatives are molecules having the following formulae, taken alone or as a mixture:

- in which the group(s) R₁represent, independently of each other, hydrogen atoms, linear or branched alkyl or alkenyl groups comprising from 1 to 24, preferably from 2 to 18, more preferentially from 4 to 16 and even more preferentially from 8 to 12 carbon atoms or aromatic substituents, n being, independently of each other, integers equal to 1, 2, 3 or 4, n preferably being equal to 1.

Preferably, R₁represent, independently of each other, linear C₁to C_24,preferably C₂to C₁₈, notably C₄to C_16,more particularly C₈to C₁₂and preferably C₁₂alkyl groups.
The dimercaptothiadiazole derivatives used in the present invention may be commercially available, for example from the suppliers Vanderbilt, Rhein Chemie or Afton.

Polysulfide Additives

The amine-based and/or sulfur-based antiwear additive(s) used in a lubricant composition according to the invention may also be chosen from sulfur-based antiwear additives of polysulfide type, in particular sulfur-based olefins.
The sulfur-based olefins used in a lubricant composition according to the invention may notably be dialkyl sulfides represented by the general formula R_a—S_x—R_b, in which R_aand R_bare alkyl groups including from 3 to 15 carbon atoms, preferentially from 1 to 5 carbon atoms, preferentially 3 carbon atoms, and x is an integer between 2 and 6.
Preferably, the polysulfide additive is chosen from dialkyl trisulfides.
Preferably, the antiwear additive present in a composition used according to the invention is chosen from amine-based and sulfur-based antiwear additives, and advantageously from thia(di)azole compounds as described above and more preferentially from dimercaptothiadiazole derivatives.
A lubricant composition under consideration according to the invention may comprise from 0.01% to 10% by mass, in particular from 0.1% to 5% by mass and more particularly from 0.5% to 3% by mass of amine-based and/or sulfur-based antiwear additive(s), preferably of thia(di)azole type and more preferentially chosen from dimercaptothiadiazole derivatives, relative to the total mass of the lubricant composition.
The use of other antiwear additives, notably known for lubricants for propulsion systems, other than amine-based and/or sulfur-based additives, is envisageable, provided that they do not affect the properties imparted by the combination of said succinimide compound(s) and of said amine-based and/or sulfur-based antiwear additive(s) according to the invention.
A lubricant composition under consideration according to the invention may comprise from 0.01% to 5% by mass, in particular from 0.1% to 10% by mass and more particularly from 0.5% to 5% by mass of antiwear additive(s), including one or more amine-based and/or sulfur-based additives, as described previously.
Preferably, a lubricant composition required according to the invention is free of antiwear additives other than said amine-based and/or sulfur-based antiwear additive(s) used according to the invention.
According to a particularly preferred embodiment, a lubricant composition under consideration according to the invention combines:

- one or more succinimide compounds, in particular chosen from polyalkylene mono-succinimides or bis-succinimides and borate derivatives thereof, such as polyisobutene mono-succinimides or bis-succinimides and borate derivatives thereof, in particular chosen from the compounds of the abovementioned formula (I), preferably from the compounds of formulae (II) and (III) as defined above; and
- one or more amine-based and sulfur-based antiwear additives, preferably chosen from dimercaptothiazole derivatives, in particular as defined above.

A composition used according to the invention may comprise, besides one or more additives of succinimide type and one or more amine-based and/or sulfur-based antiwear additives, in particular as defined previously, one or more base oils, and also other additives, conventionally considered in lubricant compositions.
Base Oil
A lubricant composition under consideration according to the invention may thus comprise one or more base oils.
These base oils may be chosen from the base oils conventionally used in the field of lubricant oils, such as mineral, synthetic or natural, animal or plant oils or mixtures thereof.
It may be a mixture of several base oils, for example a mixture of two, three or four base oils.
The base oils of the lubricant compositions under consideration 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 equivalents thereof according to the ATIEL classification) and presented in Table 1 below or mixtures thereof.

TABLE 1

	Content of	Sulfur	Viscosity
	saturates	content	index (VI)

Group I	<90%	>0.03%	80 ≤ VI < 120
Mineral oils
Group II	≥90%	≤0.03%	80 ≤ VI < 120
Hydrocracked oils
Group III	≥90%	≤0.03%	≥120
Hydrocracked or
hydroisomerized oils

	Group IV	Poly-α-olefins (PAO)
	Group V	Esters and other bases not
		included in groups I to IV

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, deasphalting, solvent deparaffinning, hydrotreating, hydrocracking, hydroisomerization and hydrofinishing.
Mixtures of synthetic and mineral oils, which may be biobased, may also be used. There is generally no limit as regards the use of different base oils for preparing the compositions used according to the invention, other than the fact that they must have properties, notably in terms of viscosity, viscosity index or resistance to oxidation, that are suitable for use for the propulsion systems of an electric or hybrid vehicle.
The base oils of the compositions used according to the invention may also be chosen from synthetic oils, such as certain esters of carboxylic acids and of alcohols, poly-α-olefins (PAO) and 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.
The PAOs used as base oils are obtained, for example, from monomers comprising from 4 to 32 carbon atoms, for example from octene or decene. The weight-average molecular mass of the PAO may vary quite broadly. Preferably, the weight-average molecular mass of the PAO is less than 600 Da. The weight-average molecular mass of the PAO may also range from 100 to 600 Da, from 150 to 600 Da or from 200 to 600 Da.
Advantageously, the base oil(s) of the composition used according to the invention are chosen from poly-α-olefins (PAO), polyalkylene glycols (PAG) and esters of carboxylic acids and of alcohols.
According to an alternative embodiment, the base oil(s) of the composition used according to the invention may be chosen from group II or III base oils.
It falls to a person skilled in the art to adjust the content of base oil to be used in a composition that is suitable for use in the invention.
A lubricant composition under consideration according to the invention may comprise at least 50% by mass of base oil(s) relative to its total mass, in particular from 60% to 99% by mass of base oil(s), relative to its total mass.
Additional Additives
A lubricant composition that is suitable for use in the invention may also comprise any type of additive, different from the additives of succinimide type and from the amine-based and/or sulfur-based antiwear additives defined in the context of the present invention, that are suitable for use in a lubricant for a propulsion system of an electric or hybrid vehicle.
It is understood that the nature and amount of additives used are chosen so as not to affect the properties in terms of antiwear and anticorrosion performance imparted by the combination of said succinimide compound(s) and of said amine-based and/or sulfur-based additive(s) used according to the invention.
Such additives, which are known to a person skilled in the art in the field of the lubrication and/or cooling of the propulsion systems of electric or hybrid vehicles, may be chosen from friction modifiers, detergents, extreme-pressure additives, dispersants other than the succinimide compounds according to the invention, antioxidants, pour point depressants, antifoams and mixtures thereof.
Advantageously, a composition that is suitable for use in the invention comprises at least one additional additive chosen from friction modifiers, viscosity index modifiers, detergents, extreme-pressure additives, dispersants, antioxidants, pour point depressants, antifoams and mixtures thereof.
These additives may be introduced individually and/or in the form of a mixture such as those already available for sale for commercial lubricant formulations for vehicle engines, with a performance level as defined by the ACEA (Association des Constructeurs Européens d'Automobiles) and/or the API (American Petroleum Institute), which are well known to those skilled in the art.
A lubricant composition that is suitable for use in the invention may comprise at least one friction-modifying additive. The friction-modifying additive may be chosen from a compound providing metal elements and an ash-free compound. Among the compounds providing metal elements, mention may be made of complexes of transition metals such as Mo, Sb, Sn, Fe, Cu or Zn, the ligands of which may be hydrocarbon-based compounds comprising oxygen, nitrogen, sulfur or phosphorus atoms. The ash-free friction-modifying additives are generally of organic origin and may be chosen from fatty acid monoesters of polyols, alkoxylated amines, alkoxylated fatty amines, fatty epoxides, borate fatty epoxides, fatty amines or fatty acid esters of glycerol. According to the invention, the fatty compounds comprise at least one hydrocarbon-based group comprising from 10 to 24 carbon atoms.
A lubricant composition that is suitable for use according to the invention may comprise from 0.01% to 2% by weight or from 0.01% to 5% by weight, preferentially from 0.1% to 1.5% by weight or from 0.1% to 2% by weight of friction-modifying additive, relative to the total weight of the composition.
A lubricant composition used according to the invention may comprise at least one antioxidant additive.
The antioxidant additive generally makes it possible to retard the degradation of the composition in service. This degradation may notably be reflected by the formation of deposits, the presence of sludges, or by an increase in the viscosity of the composition.
The antioxidant additives notably act as free-radical inhibitors or hydroperoxide destroyers. Among the commonly used antioxidant additives, mention may be made of antioxidant additives of phenolic type, antioxidant additives of amine type and phospho-sulfur-based antioxidant additives. Some of these antioxidant additives, for example the phospho-sulfur-based antioxidant additives, may be ash generators. The phenolic antioxidants additives may be ash-free or may be in the form of neutral or basic metal salts. The antioxidants additives may notably be chosen from sterically hindered phenols, sterically hindered phenol esters and sterically hindered phenols comprising a thioether bridge, diphenylamines, diphenylamines substituted with at least one C₁-C₁₂alkyl group, N,N′-dialkyl-aryl-diamines, and mixtures thereof.
Preferably according to the invention, the sterically hindered phenols are chosen from compounds comprising a phenol group, in which at least one carbon vicinal to the carbon bearing the alcohol function is substituted with at least one C₁-C₁₀alkyl group, preferably a C₁-C₆alkyl group, preferably a C₄alkyl group, preferably with a tert-butyl group.
Amine compounds are another class of antioxidant additives that may be used, optionally in combination with the phenolic antioxidants additives. Examples of amine compounds are aromatic amines, for example the aromatic amines of formula NR⁴R⁵R⁶in which R⁴represents an optionally substituted aliphatic or aromatic group, R⁵represents an optionally substituted aromatic group, R⁶represents a hydrogen. atom, an alkyl group, an aryl group or a group of formula R⁷S(O)₂R⁸in which R⁷represents an alkylene group or an alkenylene group, R⁸represents an alkyl group, an alkenyl group or an aryl group and z represents 0, 1 or 2.
Sulfurized alkylphenols or the alkali metal and alkaline-earth metal salts thereof may also be used as antioxidant additives.
Another class of antioxidant additives is that of copper compounds, for example copper thio- or dithio-phosphates, copper salts of carboxylic acids, and copper dithiocarbamates, sulfonates, phenates and acetylacetonates. Copper I and II salts and succinic acid or anhydride salts may also be used.
A lubricant composition used according to the invention may contain any type of antioxidant additive known to those skilled in the art.
Advantageously, a lubricant composition used according to the invention comprises at least one ash-free antioxidant additive.
A lubricant composition used according to the invention may comprise from 0.5% to 2% by weight of at least one antioxidant additive, relative to the total weight of the composition.
According to a particular embodiment, a lubricant composition used according to the invention is free of antioxidant additives of aromatic amine type or of sterically hindered phenol type.
A lubricant composition that is suitable for use in the invention may also comprise at least one detergent additive.
The detergent additives generally make it possible to reduce the formation of deposits on the surface of metal parts by dissolving the oxidation and combustion byproducts.
The detergent additives that may be used in a lubricant composition used according to the invention are generally known to those skilled in the art. The detergent additives may be anionic compounds comprising a long lipophilic hydrocarbon-based chain and a hydrophilic head. The associated cation may be a metal cation of an alkali metal or an alkaline-earth metal.
The detergent additives are preferentially chosen from alkali metal or alkaline-earth metal salts of carboxylic acids, sulfonates, salicylates and naphthenates, and also phenate salts. The alkali metals and alkaline-earth metals are preferentially calcium, magnesium, sodium or barium.
These metal salts generally comprise the metal in a stoichiometric amount or in excess, thus in an amount greater than the stoichiometric amount. They are then overbased detergent additives; the excess metal giving the overbased nature to the detergent additive is then generally in the form of a metal salt that is insoluble in the oil, for example a carbonate, a hydroxide, an oxalate, an acetate or a glutamate, preferentially a carbonate.
A lubricant composition that is suitable for use in the invention may comprise, for example, from 2% to 4% by weight of detergent additive relative to the total weight of the composition.
Also, a lubricant composition used according to the invention may comprise at least one dispersant, different from the succinimide compounds defined according to the invention.
The dispersant may be chosen from Mannich bases.
A lubricant composition used according to the invention may comprise, for example, from 0.2% to 10% by weight of dispersant(s) different from the succinimide compounds defined according to the invention, relative to the total weight of the composition.
Advantageously, the lubricant composition used according to the invention does not comprise any dispersants different from the succinimide compounds defined according to the invention.
A lubricant composition that is suitable for use in the invention may also comprise at least one antifoam.
The antifoam may be chosen from silicones.
A lubricant composition that is suitable for use in the invention may comprise from 0.01% to 2% by mass or from 0.01% to 5% by mass, preferentially from 0.1% to 1.5% by mass or from 0.1% to 2% by mass of antifoam, relative to the total weight of the composition.
A lubricant composition that is suitable for use in the invention may also comprise at least one pour-point depressant (PPD).
By slowing down the formation of paraffin crystals, the pour-point depressant additives generally improve the cold-temperature behavior of the composition. Examples of pour-point depressant additives that may be mentioned include polyalkyl methacrylates, polyacrylates, polyarylamides, polyaklphenols, polyalkylnaphthalenes and polyalkylstyrenes.
In particular, a lubricant composition used according to the invention may be free of anticorrosion additive of triazole type and of antioxidant additive of aromatic amine type or of sterically hindered phenol type.
In terms of formulation of such a lubricant composition, said succinimide compound(s) may be added to a base oil or mixture of base oils, and the other additional additives, including the amine-based and/or sulfur-based antiwear additive(s), are then added.
Alternatively, said succinimide compound(s) may be added to a pre-existing conventional lubricant formulation, notably comprising one or more base oils, one or more amine-based and/or sulfur-based antiwear additives, and optionally additional additives.
Alternatively, said anticorrosion additive(s) of succinimide type according to the invention may be combined with one or more additional additives, and the additive “pack” thus formed is added to a base oil or mixture of base oils.
Advantageously, a lubricant composition used according to the invention has a kinematic viscosity, measured at 100° C. according to the standard ASTM D445, ranging from 1 to 15 mm²/s, in particular ranging from 3 to 10 mm²/s.
Advantageously, a lubricant composition used according to the invention has a kinematic viscosity, measured at 40° C. according to the standard ASTM D445, ranging from 3 to 80 mm²/s, in particular from 15 to 70 mm²/s.
According to an advantageous embodiment of the present invention, the electrical resistivity values measured at 90° C. for the lubricant compositions used according to the invention are between 5 and 10 000 Mohm.m, more preferably between 6 and 5000 Mohm.m.
According to an advantageous embodiment of the present invention, the dielectric loss values measured at 90° C. for the lubricant compositions used according to the invention are between 0.01 and 30, more preferably between 0.02 and 25 and more preferentially between 0.02 and 10.
Advantageously, a lubricant composition used according to the invention may be of a grade according to the SAEJ300 classification defined by the formula (X)W(Y), in which X represents 0 or 5, and Y represents an integer ranging from 4 to 20, in particular ranging from 4 to 16 or from 4 to 12.
According to a particular embodiment, a lubricant composition used according to the invention comprises, or even consists of:

a base oil or mixture of base oils, preferably chosen from poly-α-olefins (PAO), polyalkylene glycols (PAG) and esters of carboxylic acids and of alcohols;
one or more additives of succinimide type, preferably chosen from poly alkylene mono-succinimides and bis-succinimides, such as polyisobutene mono-succinimides and bis-succinimides and borate derivatives thereof, in particular chosen from the compounds of the abovementioned formula (I), preferably from the compounds of formulae (II) and (III) as defined above;
one or more amine-based and/or sulfur-based antiwear additives, preferably one or more amine-based and sulfur-based antiwear additives, more preferentially chosen from compounds of thia(di)azole type, in particular dimercaptothiazole derivatives as defined above;
optionally one or more additional additives chosen from friction modifiers, viscosity index modifiers, detergents, extreme-pressure additives, dispersants, antioxidants, pour point depressants, antifoams and mixtures thereof.

According to a particular embodiment, a lubricant composition used according to the invention comprises, or even consists of:

from 0.01% to 10% by mass, in particular from 0.1% to 10% by mass and more particularly from 0.5% to 8% by mass of one or more additives of succinimide type, preferably chosen from polyalkylene mono-succinimides and bis-succinimides, such as polyisobutene mono-succinimides and bis-succinimides and borate derivatives thereof, in particular chosen from the compounds of the abovementioned formula (I), preferably from the compounds of formulae (II) and (III) as defined above;
from 0.01% to 10% by mass, in particular from 0.1% to 5% by mass and more particularly from 0.5% to 3% by mass one or more amine-based and/or sulfur-based antiwear additives, preferably one or more amine-based and sulfur-based antiwear additives, more preferentially chosen from compounds of thia(di)azole type, in particular dimercaptothiazole derivatives as defined above;
from 60% to 99.9% by mass of base oil(s), preferably chosen from poly-α-olefins (PAO), polyalkylene glycols (PAG) and esters of carboxylic acids and of alcohols, and mixtures thereof;
optionally from 0.1% to 5% by mass of one or more additives chosen from friction modifiers, viscosity index modifiers, detergents, extreme-pressure additives, dispersants, antioxidants, pour point depressants, anti foams and mixtures thereof;
the contents being expressed relative to the total mass of said lubricant composition.

APPLICATION

As indicated previously, a lubricant composition that is suitable for use in the invention as described previously is used as lubricant for a propulsion system of an electric or hybrid vehicle, and more particularly for the motor and the power electronics.
Thus, the present invention relates to the use of a lubricant composition as defined previously, combining one or more succinimide compounds, in particular as defined previously, and one or more amine-based and/or sulfur-based antiwear additives, preferably dimercaptothiazole derivatives, for lubricating a propulsion system of an electric or hybrid vehicle, in particular for lubricating the electric motor and the power electronics of an electric or hybrid vehicle.
As represented schematically in FIG. 1, the propulsion system of an electric or hybrid vehicle notably comprises the electric motor part (1), an electric battery (2) and a transmission, and in particular a speed reducer (3).
The electric motor typically comprises power electronics (11) connected to a stator (13) and a rotor (14). The stator comprises coils, in particular copper coils, which are powered by an alternating electric current. This makes it possible to generate a rotating magnetic field. For its part, the rotor comprises coils, permanent magnets or other magnetic materials, and is placed in rotation by the rotating magnetic field.
A rolling bearing (12) is generally incorporated between the stator (13) and the rotor (14). A transmission, and in particular a speed reducer (3), makes it possible to reduce the rotation speed at the outlet of the electric motor and to adapt the speed transmitted to the wheels, making it possible simultaneously to control the speed of the vehicle.
The rolling bearing (12) is notably subjected to high mechanical stresses and poses problems of wear by fatigue. It is thus necessary to lubricate the rolling bearing in order to increase its service life. Also, the reducer is subject to high friction stresses and thus needs to be appropriately lubricated in order to prevent it from being damaged too quickly.
Thus, the invention relates in particular to the use of a composition as described previously for lubricating an electric motor of an electric or hybrid vehicle, in particular for lubricating the rolling bearings located between the rotor and the stator of an electric motor.
The invention also relates to the use of a composition as described previously for lubricating the transmission, in particular the reducer, in an electric or hybrid vehicle.
Advantageously, a composition according to the invention may thus be used for lubricating the various parts of a propulsion system of an electric or hybrid vehicle, in particular the rolling bearings located between the rotor and the stator of an electric motor, and/or the transmission, in particular the reducer, in an electric or hybrid vehicle.
Advantageously, as mentioned previously, a lubricant composition according to the invention has excellent antiwear and anticorrosion performance,
According to another of its aspects, the invention also relates to a process for lubricating at least one part of a propulsion system of an electric or hybrid vehicle, in particular the rolling bearings located between the rotor and the stator of an electric motor; and/or the transmission, notably the reducer, comprising at least one step of placing at least said part in contact with a composition as described previously.
The present invention thus proposes a process for simultaneously reducing the wear and corrosion of at least one part of a propulsion system of an electric or hybrid vehicle, in particular the rolling bearings located between the rotor and the stator of an electric motor; and/or the transmission, notably the reducer, said process comprising at least one step of placing at least said part in contact with a composition as described previously.
All of the features and preferences described for the composition used according to the invention and for the uses thereof also apply to this process.
According to a particular embodiment, a composition according to the invention may have, besides lubricating properties, good electrical insulation properties.
According to this embodiment, a composition according to the invention may simultaneously be used for lubricating one or more parts of a propulsion system of an electric or hybrid vehicle, in particular for lubricating the sensors and the solenoid valves of the motor, the rolling bearings, but also the windings located in the rotor and the stator of an electric motor, or else for lubricating the transmission, in particular the gears, the sensors, the solenoid valves or the reducer which are found in an electric or hybrid vehicle, and for electrically insulating at least one part of said propulsion system, notably the battery.
In the context of such an implementation variant, a lubricant composition under consideration according to the invention advantageously has a kinematic viscosity, measured at 100° C. according to the standard ASTM D445, of between 2 and 8 mm²/s, preferably between 3 and 7 mm²/s.
It is understood that the uses described above may be combined, a composition as described previously possibly being used both as lubricant and as electrical insulator, but also as coolant fluid for the motor, the battery and the transmission of an electric or hybrid vehicle.
According to the invention, the particular, advantageous or preferred features of the composition according to the invention make it possible to define uses according to the invention that are also particular, advantageous or preferred.
The invention will now be described by means of the examples that follow, which are, needless to say, given as nonlimiting illustrations of the invention.

Example

Various compositions were evaluated:

a composition C1 comprising an amine-based and sulfur-based antiwear additive of dimercaptothiadiazole type free of additive of succinimide type;
a composition C2 comprising said antiwear additive of dimercaptothiadiazole type and a dispersant additive of succinimide type, in accordance with the invention, more precisely a bis-succinimide having the following formula:

as defined previously,

a composition C3 comprising said antiwear additive of dimercaptothiadiazole type and a dispersant additive of succinimide type, in accordance with the invention, more precisely a high molecular weight PIB succinimide,
a composition C4 comprising said antiwear additive of dimercaptothiadiazole type and a dispersant additive of succinimide type, in accordance with the invention, more precisely a PIB succinimide having the following formula:

as defined previously.
Compositions C1 to C4 comprise, besides the abovementioned compounds, a group V base oil.
The compositions and the amounts (expressed as mass percentages) are indicated in Table 2 below.

TABLE 2

	C1	C2	C3	C4

Base oil	99%	98%	98%	98%
Dimercaptothiadiazole	1%	1%	1%	1%
antiwear agent
Bis-succinimide	—	1%	—	—
PIB-succinimide	—	—	1%	—
PIB-succinimide	—	—	—	1%

EVALUATION OF THE ANTICORROSION PROPERTIES

Evaluation Method

The corrosive (or corroding) power of a composition may be evaluated by means of a test involving study of the variation in the electrical resistance value of a copper wire of a preestablished diameter, as a function of the duration of immersion of this wire in the composition. The variation in this electrical resistance value is directly correlated with the variation in the diameter of the test wire. In the context of the present invention, the diameter of the wire chosen is 70 μm.
In the present case, a copper wire is immersed in a test tube containing 20 mL of a test composition (compositions C2 to C4 being compositions according to the invention and composition C1 being a composition serving as a comparative).
The resistance of the wire is measured using an ohmmeter.
The measuring current is 1 mA.
The temperature of the test composition is brought to 150° C.
The resistance of the copper wire is calculated by this equation (1):
$\begin{matrix} R = ρ \times \frac{L}{S} & [Math 1] \end{matrix}$
in which R is the resistance, ρis the resistivity of copper, L is the length of the wire and S is the cross-sectional area.
In this equation (1), ρ and L are constants. Thus, the resistance R is inversely proportional to the cross-sectional area of the immersed wire.
The diameter of the wire is calculated from the cross-sectional area (equation (2)):
$\begin{matrix} S = \frac{π}{4} \times D^{2} & [Math 2] \end{matrix}$
in which D is the diameter of the wire.
Equation (2) is inserted into equation (1) to obtain the relationship between the resistance and the diameter (equation (3)):
$\begin{matrix} R = ρ \times \frac{L}{\frac{π}{4} \times D^{2}} & [Math 3] \end{matrix}$
Thus, when the wire is corroded by the test compositions, the diameter of the wire decreases, thus bringing about an increase in the resistance value.
By monitoring the resistance, it is possible to monitor the change in the diameter of the wire, which reflects the state of corrosion suffered by the immersed wire.
The loss of diameter of the wire is thus calculated directly from the measured resistance. When the measured resistance is infinite, this is an open circuit. The wire has thus broken, which defines very severe corrosion.

Results

The results are summarized in the following table and are expressed in μm (loss of diameter). The lower the value obtained, the better the anticorrosion properties of the composition evaluated.
A composition is considered to be “noncorrosive” when the loss of diameter of the copper wire studied is less than or equal to 1.3 μm after immersion for 80 hours, in particular less than or equal to 0.8 μm after immersion for 40 hours in the composition comprising said compound.

Loss of diameter	0.28	0.55	0.44	0
(μm) at 20 hours
Loss of diameter	Broken wire	0.74	0.73	0.47
(μm) at 40 hours
Loss of diameter	Broken wire	0.70	1.03	0.82
(μm) at 60 hours
Loss of diameter	Broken wire	0.82	1.28	1.19
(μm) at 80 hours

It emerges from these results that the addition of a succinimide compound according to the invention makes it possible to reduce the corrosion effects induced by the amine-based and sulfur-based antiwear additive.

Compositions

1-10. (canceled)

11. A method or improving the anti-corrosion properties of a lubricant composition for a propulsion system of an electric or hybrid vehicle, comprising:

adding at least one succinimide compound to a lubricant composition for lubricating the propulsion system, the lubricant composition comprising an amine-based anti-wear additive and/or a sulfur-based anti-wear additive.

12. The method of claim 11, wherein the at least one succinimide compound is chosen from polyalkylene mono- or bis-succinimides; borate derivatives of polyalkylene mono- or bis-succinimides; succinic anhydride derivatives of polyalkylene mono- or bis-succinim ides; compounds obtained by opening such a succinic anhydride ring; or a combination thereof.

13. The method of claim 11, wherein the at least one succinimide compound is chosen from: polyisobutene (PIB) mono- or bis-succinim ides; borate derivatives of polyisobutene (PIB) mono- or bis-succinimides; polyisobutylene succinic anhydrides (PIBSA); polyisobutylene pentaerythritol ester succinimides; or a combination thereof.

14. The method of claim 11, wherein the at least one succinimide compound comprises at least one substituted succinimide group of formula (ii) below:

borate derivatives of formula (ii),

succinic anhydride derivatives of formula (ii), or

a compound obtained by opening of the succinic anhydride ring of formula (ii),

wherein R¹represents a hydrocarbon-based group comprising from 8 to 400 carbon atoms.

15. The method of claim 14, wherein R¹represents a polyalkene group optionally linked to the succinimide group via a —(C═CH₂)—group and having a mass-average molecular mass Mw of between 2000 and 30,000.

16. The method of claim 14, wherein R¹represents a polyisobutylene group optionally linked to the succinimide group via a —(C═CH₂)—group and having a mass-average molecular mass Mw of between 2000 and 7000.

17. The method of claim 11, wherein the at least one succinimide compound is a mono-succinimide of formula (II) below:

or a borate derivative thereof,

wherein:

R¹represents a polyalkylene group optionally linked to the succinimide group via a —(C═CH₂)—group;

A represents a linear or branched C₂to C₆alkylene group; and

y represents an integer ranging from 2 to 5.

18. The method of claim 17, wherein:

R¹represents a polyisobutylene group optionally linked to the succinimide group via a —(C═CH₂)—group;

A represents at least one of the following segments: —CH₂—CH₂—, —CH₂—CH₂—CH₂—, —CH₂—CH(CH₃)—; and

y represents 2, 3, or 4.

19. The method of claim 11, wherein the at least one succinimide compound is a bis-succinimide of formula (III) below:

or a borate derivative thereof,

wherein:

R¹represents polyalkylene groups optionally linked to the succinimide group via a —(C═CH₂)—group;

z represents an integer ranging from 1 to 10; and

s represents an integer ranging from 2 to 6.

20. The method of claim 19, wherein:

R¹represents polyisobutylene groups optionally linked to the succinimide group via a —(C═CH₂)—group;

z represents an integer ranging from 2 to 6; and

s represents an integer ranging from 2 to 4.

21. The method of claim 11, wherein the amine-based anti-wear additive and/or the sulfur-based anti-wear additive is chosen from 2,5-dimercapto-1,3,4-thiadiazole derivatives having the following formulae, taken alone or as a mixture:

wherein:

each R₁group is independently selected from a hydrogen atom, a linear or branched alkyl or alkenyl group comprising from 2 to 18 carbon atoms, or an aromatic substituent; and

each n is independently selected from 1, 2, 3, or 4.

22. The method of claim 21, wherein:

each R₁group is independently selected from a hydrogen atom or linear or branched alkyl or alkenyl groups comprising from 8 to 12 carbon atoms or aromatic substituents; and

n is 1.

23. The method of claim 11, wherein:

the at least one succinimide compound is present in an amount ranging from 0.1% to 10% by mass, relative to the total mass of the lubricant composition; and

the amine-based anti-wear additive and/or the sulfur-based anti-wear additive is present in an amount ranging from 0.01% to 10% by mass, relative to the total mass of the lubricant composition.

24. The method of claim 23, wherein:

the at least one succinimide compound is present in an amount ranging from 0.5% to 8% by mass, relative to the total mass of the lubricant composition; and

the amine-based anti-wear additive and/or the sulfur-based anti-wear additive is present in an amount ranging from 0.5% to 3% by mass, relative to the total mass of the lubricant composition.

25. A method of reducing corrosion in a propulsion system of an electric or hybrid vehicle, the method comprising lubricating an electric motor and/or power electronics of the electric or hybrid vehicle with a lubricant composition comprising:

at least one succinimide compound; and

an amine-based anti-wear additive and/or a sulfur-based anti-wear additive.

26. The method of claim 25, wherein:

at least one succinimide compound is chosen from: polyisobutene (PIB) mono- or bis-succinimides; borate derivatives of polyisobutene (PIB) mono- or bis-succinimides; polyisobutylene succinic anhydrides (PIBSA); polyisobutylene pentaerythritol ester succinim ides; or a combination thereof; and

the amine-based anti-wear additive and/or the sulfur-based anti-wear additive is a 2,5-dimercapto-1,3,4-thiadiazole derivative.

27. The method of claim 25, further comprising lubricating rolling bearings located between a rotor and a stator of the electric motor with the lubricant composition.

28. The method of claim 25, further comprising lubricating a transmission of the electric or hybrid vehicle with the lubricant composition.