LUBRICANT COMPOSITION FOR PREVENTING PRE-IGNITION

Abstract

The present invention relates to the use of a lubricant composition comprising (i) at least one boron derivative; and (ii) at least one base oil, for preventing and/or reducing pre-ignition, in particular at low speed, in a vehicle engine, wherein said composition is used during at least one change interval without the addition of a new lubricant composition, the content of boron in the composition being between 150 ppm and 350 ppm by weight.

Claims

1.-15. (canceled)

16. A method for preventing and/or reducing preignition in a vehicle engine, the method comprising contacting the engine with a lubricant composition in the course of at least one oil change interval without adding fresh lubricant composition, the lubricant composition comprising: (i) at least one boron derivative; and (ii) at least one base oil; wherein the lubricant composition comprises boron in an amount ranging from 150 to 350 ppm by weight.

17. The method of claim 16, wherein the boron derivative is chosen from boric acid derivatives, boronic acid derivatives, boronates, borates, borated dispersants, borated detergents, simple orthoborates, borate epoxides, borate esters, or mixtures thereof.

18. The method of claim 16, wherein the content of boron ranges from 150 to 300 ppm by weight.

19. The method of claim 16, wherein the base oil is chosen from the oils of group III, the oils of group IV, or mixtures thereof.

20. The method of claim 16, wherein the lubricant composition further comprises at least one antioxidant additive.

21. The method of claim 20, wherein the at least one antioxidant additive is present in an amount ranging from 0.05% to 2% by weight, relative to the total weight of the lubricant composition.

22. The method of claim 16, wherein the lubricant composition further comprises at least one detergent additive different from the boron derivative, chosen from alkaline-earth metal salts.

23. The method of claim 16, wherein the lubricant composition further comprises at least one viscosity index-enhancing additive chosen from hydrogenated or non-hydrogenated homopolymers or copolymers, styrene, butadiene, or isoprene.

24. The method of claim 23, wherein the composition comprises from 2% to 15% by weight of viscosity index-enhancing additive, relative to the total weight of the composition.

25. A method for preventing and/or reducing preignition in a vehicle engine, the method comprising adding at least one boron derivative to a lubricant composition comprising at least one base oil in an amount to provide a lubricant composition comprising boron in an amount ranging from 150 to 350 ppm by weight, wherein the lubricant composition is used in the course of at least one oil change interval without adding fresh lubricant composition.

26. A method for limiting the degradation of performance in terms of preventing and/or reducing preignition in a vehicle engine of a lubricant composition comprising at least one base oil, after its use in the course of at least one oil change interval without adding fresh lubricant composition, the method comprising adding at least one boron derivative to a lubricant composition comprising at least one base oil in an amount to provide a lubricant composition comprising boron in an amount ranging from 150 to 350 ppm by weight.

27. A method for increasing the ignition temperature, measured by high-pressure differential scanning calorimetry, of a lubricant composition comprising adding at least one boron derivative to said lubricant composition, said composition being used in the course of at least one oil change interval without adding fresh lubricant composition, relative to a spent lubricant composition free of any boron derivative compound, the content of boron in the composition being between 150 ppm and 350 ppm by weight.

28. A process for preventing and/or reducing preignition in a vehicle engine, comprising: a) contacting the engine with a lubricant composition comprising at least one base oil and at least one boron derivative, wherein the lubricant composition comprises boron in an amount ranging from 150 to 350 ppm by weight; and b) running the engine in the course of at least one oil change interval, without adding fresh lubricant composition.

29. The process of claim 28, wherein the boron derivative is chosen from boric acid derivatives, boronic acid derivatives, boronates, borates, borated dispersants, borated detergents, simple orthoborates, borate epoxides, borate esters, or mixtures thereof.

30. A method for preventing and/or reducing preignition in a vehicle engine, comprising at least a step of contacting the engine with a lubricant composition comprising: (i) at least one boron derivative, the content of boron in the composition being between 150 ppm and 350 ppm by weight; and (ii) at least one base oil; wherein the lubricant composition has undergone iron-catalyzed oxidation at a temperature ranging from 150° C. to 170° C. for a time ranging from 120 hours to 150 hours, according to the GFC Lu-43A-11 method.

31. The method of claim 16, wherein the lubricant composition is contacted with the engine over a distance travelled by the vehicle ranging from 10,000 km to 30,000 km, without adding fresh lubricant composition.

32. The method of claim 16, wherein the content of boron ranges from 150 to 260 ppm.

33. The method of claim 20, wherein the antioxidant additive is chosen from diphenylamine, phenols, phenol esters, or mixtures thereof.

34. The method of claim 16, wherein the lubricant composition further comprises at least one detergent additive different from the boron derivative, chosen from calcium salts, magnesium salts, and mixtures thereof.

35. A method for preventing and/or reducing low-speed preignition in a vehicle engine of a motor vehicle, the method comprising contacting the engine with a lubricant composition in the course of at least one oil change interval without adding fresh lubricant composition, the lubricant composition comprising: (i) at least one boron derivative; and (ii) at least one base oil; wherein the lubricant composition comprises boron in an amount ranging from 150 to 350 ppm by weight.

Description

DETAILED DESCRIPTION

[0057] Composition

[0058] Boron Derivative

[0059] As mentioned above, a lubricant composition used according to the present invention comprises (i) at least one boron derivative.

[0060] The boron derivative may notably be chosen from boric acid derivatives, boronic acid derivatives, boronates, borates, borated dispersants, such as boron succinimide derivatives, in particular borated polyisobutene succinimide, borated detergents, such as borate carboxylates, simple orthoborates, borate epoxides, borate esters and mixtures thereof.

[0061] More preferably, the boron derivative may notably be chosen from C.sub.10-C.sub.24 fatty acid esters of borate, borated dispersants, such as boron succinimide derivatives, in particular borated polyisobutene succinimide, and mixtures thereof.

[0062] The boron derivatives that may be used according to the present invention are compounds that are well known to those skilled in the art and may be obtained via any process also known to those skilled in the art.

[0063] Boron derivatives are more particularly known for their use in a lubricant composition in order to preserve a good level of fuel economy in an engine.

[0064] These compounds are also known for their use as a dispersant or detergent in lubricant compositions.

[0065] An example of a commercial boron derivative that may be mentioned is the borated ester Oloa® 17503 from Oronite.

[0066] The content of boron present in a lubricant composition used according to the invention is between 150 ppm and 350 ppm by weight.

[0067] The boron derivative may be present in a lubricant composition used according to the invention in a content ranging from 0.01% to 3% by weight, preferably from 0.05% to 2.5% by weight, more preferentially from 0.1% to 2% by weight, relative to the total weight of the composition, as long as the total content of boron in the lubricant composition is between 150 ppm and 350 ppm by weight.

[0068] According to one embodiment, the lubricant composition used according to the invention comprises from 150 to 300 ppm by weight of boron, preferably from 160 to 260 ppm by weight of boron.

[0069] Base Oil

[0070] As stated previously, a lubricant composition used according to the present invention comprises (ii) at least one base oil.

[0071] The base oil(s) may be oils of mineral, synthetic or natural, animal or plant origin, known to those skilled in the art.

[0072] In particular, the mineral or synthetic oils generally used in the lubricant composition belong to one of the groups I to V according to the classes defined in the API classification (or the equivalents thereof according to the ATIEL classification) as summarized in Table 1 below.

[0073] The API classification is defined in American Petroleum Institute 1509 “Engine Oil Licensing and Certification System” 17th edition, September 2012.

[0074] The ATIEL classification is defined in “The ATIEL Code of Practice”, number 18, November 2012.

TABLE-US-00001 TABLE 1 Content of Sulfur Viscosity saturates content index 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 PAO (poly-alpha-olefins) Group V Esters and other bases not included in groups I to IV

[0075] There is generally no limit as regards the use of different base oils for preparing a lubricant composition used according to the invention, apart from the fact that they must have properties, notably in terms of viscosity, viscosity index, sulfur content or resistance to oxidation, that are suitable for use in engines, in particular vehicle engines.

[0076] The mineral base oils include any type of base 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.

[0077] The synthetic base oils may be chosen from esters, silicones, glycols, polybutene, poly-alpha-olefins (PAO), alkylbenzene or alkylnaphthalene.

[0078] The base oils may also be oils of natural origin, for example esters of alcohols and of carboxylic acids, which may be obtained from natural resources, such as sunflower oil, rapeseed oil, palm oil, soybean oil, etc.

[0079] The base oil may be chosen more particularly from synthetic oils, mineral oils and mixtures thereof.

[0080] According to one embodiment, a lubricant composition used according to the present invention comprises at least one base oil chosen from the oils of group III, the oils of group IV and mixtures thereof.

[0081] Additives

[0082] A composition used according to the present invention may also comprise one or more additives as defined more precisely in the text hereinbelow, different from the boron derivative defined above.

[0083] The additives that may be incorporated into a composition according to the invention may be chosen from antioxidants, detergents different from the boron derivative defined above, viscosity index improvers, friction modifiers, wear-resistance additives, extreme-pressure additives, dispersants different from the boron derivative defined above, pour point improvers, antifoams, and mixtures thereof.

[0084] It is understood that the nature of the additives used are chosen so as not to affect the properties of the lubricant composition, in particular as regards preventing and/or reducing preignition, notably LSPI, in an engine.

[0085] 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.

[0086] According to a particular embodiment, a composition used according to the invention may also comprise at least one antioxidant additive.

[0087] 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 an increase in the viscosity of the composition. The antioxidant additives notably act as free-radical inhibitors or hydroperoxide destroyers.

[0088] 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.

[0089] 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 C.sub.1-C.sub.12 alkyl group, N,N′-dialkyl-aryl-diamines, and mixtures thereof.

[0090] 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 C.sub.1-C.sub.10 alkyl group, preferably a C.sub.1-C.sub.6 alkyl group, preferably a C.sub.4 alkyl group, preferably with a tert-butyl group.

[0091] Amine compounds are another class of antioxidant additives that may be used, optionally in combination with the phenolic antioxidants additives.

[0092] Examples of amine compounds are aromatic amines, for example the aromatic amines of formula NR.sup.4R.sup.5R.sup.6 in which R.sup.4 represents an optionally substituted aliphatic or aromatic group, R.sup.5 represents an optionally substituted aromatic group, R.sup.6 represents a hydrogen atom, an alkyl group, an aryl group or a group of formula R.sup.7S(O).sub.zR.sup.8 in which R.sup.7 represents an alkylene group or an alkenylene group, R.sup.8 represents an alkyl group, an alkenyl group or an aryl group and z represents 0, 1 or 2.

[0093] Sulfurized alkylphenols or the alkali metal or alkaline-earth metal salts thereof may also be used as antioxidant additives.

[0094] 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.

[0095] A composition used according to the invention may contain any type of antioxidant additive known to those skilled in the art.

[0096] Advantageously, a composition used according to the invention comprises at least one antioxidant additive chosen from diphenylamine, phenols, phenol esters and mixtures thereof.

[0097] A composition used according to the invention may comprise from 0.05% to 2% by weight and preferably from 0.5% to 1% by weight of at least one antioxidant additive relative to the total weight of the composition.

[0098] According to another embodiment, a composition used according to the invention may also comprise at least one detergent additive different from the boron derivative required according to the present invention.

[0099] 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.

[0100] The detergent additives that may be used in a 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.

[0101] 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.

[0102] 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.

[0103] A composition used according to the invention may contain any type of detergent additive known to those skilled in the art.

[0104] Advantageously, a composition used according to the invention comprises at least one detergent additive chosen from alkaline-earth metal salts, preferably from calcium salts, magnesium salts, and mixtures thereof.

[0105] In particular, when the detergent is chosen from alkaline-earth metal salts, the detergent additive may be added to the composition so as to supply a content of metal element ranging from 150 ppm to 2000 ppm, preferably from 250 ppm to 1500 ppm.

[0106] According to yet another embodiment, a composition used according to the present invention may also comprise a viscosity index-enhancing additive.

[0107] As examples of viscosity index-enhancing additives, mention may be made of polymeric esters, hydrogenated or non-hydrogenated homopolymers or copolymers, styrene, butadiene and isoprene, polyacrylates, polymethacrylates (PMA) or olefin copolymers, notably ethylene/propylene copolymers.

[0108] Advantageously, a composition used according to the invention comprises at least one viscosity index-enhancing additive chosen from hydrogenated or non-hydrogenated homopolymers or copolymers, styrene, butadiene and isoprene. Preferably, it is a hydrogenated styrene/isoprene copolymer.

[0109] A composition used according to the invention may comprise, for example, from 2% to 15% by weight of viscosity index-enhancing additive relative to the total weight of the composition.

[0110] The wear-resistance additives and the extreme-pressure additives protect the friction surfaces by forming a protective film adsorbed onto these surfaces.

[0111] A wide variety of wear-resistance additives exists. Preferably, for the lubricant composition according to the invention, the wear-resistance additives are chosen from phospho-sulfur-based additives, such as metal alkylthiophosphates, in particular zinc alkylthiophosphates and more specifically zinc dialkyldithiophosphates or ZnDTP. The preferred compounds are of formula ZnOSP(S)(OR.sup.2)(OR.sup.3)).sub.2, in which R.sup.2 and R.sup.3, which may be identical or different, independently represent an alkyl group, preferentially an alkyl group including from 1 to 18 carbon atoms.

[0112] Amine phosphates are also wear-resistance additives that may be employed in a composition according to the invention. However, the phosphorus introduced by these additives may act as a poison for the catalytic systems of motor vehicles since these additives are ash generators. These effects can be minimized by partially replacing the amine phosphates with additives which do not introduce phosphorus, for instance polysulfides, notably sulfur-based olefins.

[0113] A composition used according to the invention may comprise from 0.01% to 6% by weight, preferentially from 0.05% to 4% by weight and more preferentially from 0.1% to 2% of wear-resistance additives and of extreme-pressure additives, by weight relative to the total weight of the composition.

[0114] A composition used according to the invention is preferably free of wear-resistance additives and of extreme-pressure additives. In particular, a composition used according to the invention may be free of phosphate-based additives.

[0115] A composition used according to the invention may comprise at least one friction-modifying additive. The friction-modifying additive may be chosen from a compound providing metal elements and an ash-free compound. Among the compounds providing metal elements, mention may be made of 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, 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.

[0116] A composition used 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.

[0117] Advantageously, a composition used according to the invention is free of friction-modifying additive.

[0118] A composition used according to the invention may also comprise at least one pour-point depressant additive.

[0119] By slowing down the formation of paraffin crystals, the pour-point depressant additives generally improve the cold-temperature behavior of the composition.

[0120] Examples of pour-point depressant additives that may be mentioned include polyalkyl methacrylates, polyacrylates, polyarylamides, polyalkylphenols, polyalkylnaphthalenes and polyalkylstyrenes.

[0121] Also, a composition used according to the invention may comprise at least one dispersant different from the boron derivative required according to the present invention.

[0122] The dispersant may be chosen from Mannich bases, succinimides and derivatives thereof.

[0123] A composition used according to the invention may comprise, for example, from 0.2% to 10% by weight of dispersant different from the boron derivative required according to the present invention, relative to the total weight of the composition.

[0124] Applications

[0125] A lubricant composition according to the invention is more particularly intended to be used in an engine, notably in a vehicle engine, in particular in a gasoline vehicle engine.

[0126] It thus advantageously has properties, notably in terms of viscosity, viscosity index, sulfur content and oxidation resistance, which are suitable for use in engines, in particular vehicle engines.

[0127] Thus, preferably, a lubricant composition has a kinematic viscosity, measured at 100° C. according to the standard ISO 3104, of between 5 and 20 mm.sup.2/s, preferably between 5 and 15 mm.sup.2/s and more particularly between 6 and 13 mm.sup.2/s.

[0128] As indicated previously, a composition as described previously is advantageous in that it can, by means of its use in an engine, prevent and/or reduce the preignition which takes place in said engine over the long term, notably after use for a period corresponding to at least one oil change interval.

[0129] Thus, the invention relates to the use of a composition as defined previously for preventing and/or reducing preignition, in particular low-speed preignition, in a vehicle engine, preferably of a motor vehicle, said composition being used in the course of at least one oil change interval, preferably over a distance travelled by the vehicle of between 10 000 km and 30 000 km, without adding fresh lubricant composition.

[0130] In particular, preignition was observed at low speed in engines (LSPI) and is further exacerbated in direct-injection engines, in particular downsized engines.

[0131] Thus, the present patent application also relates to the use of a lubricant composition comprising:

[0132] (i) at least one boron derivative; and

[0133] (ii) at least one base oil;

[0134] for preventing and/or reducing low-speed preignition (LSPI), in a vehicle engine, preferably of a motor vehicle, said composition being used in the course of at least one oil change interval, preferably over a distance travelled by the vehicle of between 10 000 km and 30 000 km, without adding fresh lubricant composition,

[0135] the content of boron in the composition being between 150 ppm and 350 ppm by weight.

[0136] Particularly surprisingly, the inventors have found that the presence of a boron derivative in an aged lubricant composition makes it possible to significantly reduce the occurrence of preignition in an engine.

[0137] Thus, the present invention also relates to the use of at least one boron derivative, in particular as defined above, in a lubricant composition comprising at least one base oil, the content of boron in the composition being between 150 ppm and 350 ppm by weight, said lubricant composition being used in the course of at least one oil change interval, preferably over a distance travelled by the vehicle of between 10 000 km and 30 000 km, without adding fresh lubricant composition, for preventing and/or reducing preignition, in particular low-speed preignition, in a vehicle engine, preferably of a motor vehicle.

[0138] As demonstrated in the examples below, the selection of a particular additive, namely a boron derivative, made it possible to propose a lubricant composition for preventing and/or reducing the preignition which may occur in the course of its prolonged use in an engine, without adding fresh lubricant composition.

[0139] Thus, still as demonstrated in the examples, a lubricant composition according to the invention has an ignition temperature higher than that obtained for a lubricant composition not comprising any boron derivative or comprising an additional additive different from the boron derivative required according to the invention.

[0140] In other words, the nature of the boron derivative was not clearly deducible from its functions that may have been known previously.

[0141] The composition defined above thus has the advantage of preventing and/or reducing preignition in an engine, by virtue of its prolonged use in an engine.

[0142] Thus, the invention also relates to a process for preventing and/or reducing preignition, in particular low-speed preignition, in a vehicle engine, preferably of a motor vehicle, preferably in the long term, comprising at least the following steps:

[0143] a) placing the engine in contact with a lubricant composition comprising at least one base oil and at least one boron derivative, the content of boron in the composition being between 150 ppm and 350 ppm by weight;

[0144] b) running the engine in the course of at least one oil change interval, preferably over a distance travelled by the vehicle of between 10 000 km and 30 000 km, without adding fresh lubricant composition.

[0145] As stated above, a spent lubricant composition used according to the invention has an ignition temperature higher than that of a spent lubricant composition not in accordance with this definition. The ignition temperature denotes here the temperature of initiation of the exothermic reaction measured by HPDSC (High-Pressure Differential Scanning calorimetry).

[0146] In particular, the temperature increase is at least 2%, preferably at least 4%, more preferentially at least 5%, measured according to the protocol detailed in the examples, relative to the ignition temperature of a lubricant composition comprising a base oil but free of boron derivative.

[0147] Thus, the invention also relates to the use of at least one boron derivative, in particular as defined above, for the purposes of increasing the ignition temperature, measured by high-pressure differential scanning calorimetry, of a lubricant composition, in particular by at least 2%, preferably by at least 4%, said composition being used in the course of at least one oil change interval, preferably over a distance travelled by the vehicle of between 10 000 km and 30 000 km, without adding fresh lubricant composition, relative to a spent lubricant composition free of any boron derivative compound, the content of boron in the composition being between 150 ppm and 350 ppm by weight.

[0148] 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.

[0149] Throughout the description, including the claims, the expression “including a” should be understood as being synonymous with “including at least one”, unless otherwise specified.

[0150] The terms “between . . . and . . . ”, “comprises from . . . to . . . ”, “formed from . . . to . . . ” and “ranging from . . . to . . . ” should be understood as being limits inclusive, unless otherwise mentioned.

[0151] In the description and the examples, unless otherwise indicated, the percentages are weight percentages. The percentages are thus expressed are as weight percentages relative to the total weight of the composition. The temperature is expressed in degrees Celsius unless otherwise indicated, and the pressure is atmospheric pressure, unless otherwise indicated.

[0152] 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.

EXAMPLES

[0153] Methods

[0154] Method for Aging the Lubricant Oils

[0155] The oils used in the examples below underwent simulated aging. This simulation is performed by oxidation of the oil catalyzed with 100 ppm of iron at 170° C. for 144 hours, according to the GFC-Lu-43A-11 method.

[0156] Laboratory Measurement of the Preignition Tendency

[0157] In the examples detailed below, the preignition tendency is determined in terms of temperature of initiation of the exothermic reaction, measured by HPDSC (High-Pressure Differential Scanning calorimetry).

[0158] This measurement is performed using a Mettler-Toledo LG3300 machine according to the protocol detailed below: [0159] 2±0.05 mg of sample to be analyzed are weighed out in a tank; [0160] The open sample and the reference are placed on the surface of the detector; [0161] The cell is closed hermetically and mechanically; [0162] A pressure of between 1 and 20 bar is applied to the cell; [0163] The temperature of the sample is equilibrated at the measurement starting temperature, between 20° C. and 80° C., preferably between 30° C. and 70° C., maintained for 1 to 15 minutes, preferably for 2 to 10 minutes; [0164] At least one temperature ramp is applied to the sample, between the starting temperature and a temperature of between 100° C. and 400° C., preferably between 150° C. and 350° C., more preferentially between 200° C. and 300° C.

[0165] Software, such as the STARe software, makes it possible to visualize the differences in heat exchange between the sample and the reference.

[0166] The temperature of appearance of an exotherm on the curve thus obtained is likened to the phenomenon of preignition, such as LSPI.

[0167] This temperature is correlated to the time. Thus, the higher it is, the more the preignition will be retarded in the combustion chamber in the course of the use of the composition.

[0168] Measurement of the Oxidation

[0169] The oxidation resistance of the lubricant compositions can be evaluated in the course of iron-mediated aging according to the protocol (Method for aging lubricant oils) described above.

[0170] In the course of aging of the lubricant composition, 20 mL samples of composition are taken at 72 hours, 96 hours and 120 hours. A final 125 mL sample is taken at the end of the 144 hours.

[0171] Each sample is characterized by its viscosity fluctuation (RKV100) by comparing the kinematic viscosity value measured at 100° C. according to the method ISO 3104 or ASTM D445 at the time of the sample collection (KV100.sub.i) relative to its initial value before aging (KV100.sub.0). The calculation performed is as follows:

[00001]$\mathrm{RKV}100=\frac{\mathrm{KV}{100}_1-\mathrm{KV}{100}_0}{\mathrm{KV}{100}_0}\times 100\left(\mathrm{as}a\mathrm{relative}\mathrm{percentage}\right)$

[0172] An RKV100 value of close to 0 means that the viscosity of the composition varies little between each withdrawal, which demonstrates low oxidation.

Example 1: Preparation of the Lubricant Compositions

[0173] The lubricant compositions A0 to A3 were prepared.

[0174] Their kinematic viscosity at 100° C. was determined according to the standard ISO 3104 and their properties of predisposition to self-ignition were measured.

[0175] The details of the compositions are presented in Table 2 below, in which the proportions of the various compounds are indicated as mass percentages.

TABLE-US-00002 TABLE 2 Composition A0 A1 A2 A3 Aged Base oil 72.8 72.0 71.2 72.0 mixture Group III/IV Additive package * 16.7 16.7 16.7 16.7 Viscosity index 10.5 10.5 10.5 10.5 enhancer of hydrogenated styrene/isoprene copolymer type Boron Borated ester (Oloa ® 0 0 0 0.8.sup.(3) derivative 17503 from Oronite) according to Borated dispersant 0 0.8.sup.(1) 1.6.sup.(2) 0 the invention Viscosity KV100 (mm.sup.2/s) 11.52 11.66 11.91 11.49 * The additive package is a mixture of different additives that are common in the field of lubricants and commercially available. It comprises wear-resistance additives of zinc dithiophosphate type, detergents based on calcium and magnesium, and dispersants of PIBSI type. In each of the compositions thus prepared, the amount of calcium is 1350 ppm by weight and the amount of magnesium is 300 ppm by weight. .sup.(1)the amount of boron in composition A1 is 160 ppm by weight. .sup.(2)the amount of boron in composition A2 is 260 ppm by weight. .sup.(3)the amount of boron in composition A3 is 180 ppm by weight.

[0176] The compositions are prepared by mixing, at a temperature of the order of 30 to 40° C., of the compounds detailed in Table 2.

[0177] The lubricant compositions thus prepared have kinematic viscosity values at 100° C. that are suitable for their use in engines, in particular vehicle engines.

[0178] The lubricant compositions are subsequently aged according to the protocol (aging method) detailed above.

Example 2: Evaluation of the LSPI Performance of the Lubricant Compositions

[0179] The exothermic reaction initiation temperature (ignition temperature) was measured for the reference oil and the lubricant compositions of Example 1, according to the measurement method (laboratory preignition tendency method) defined above.

[0180] The results are given in Table 3 below.

TABLE-US-00003 TABLE 3 Composition Ignition temperature [° C.] A0 (Reference) 196 A1 (Invention) 208 A2 (Invention) 209.5 A3 (Invention) 209

[0181] Compositions A1 to A3 according to the invention, comprising at least one boron derivative, have higher ignition temperatures than for the same composition not comprising any boron derivative required according to the invention (reference composition A).

[0182] These measurements thus make it possible to demonstrate that the addition of at least one boron derivative to an aged lubricant composition makes it possible to significantly retard preignition, in particular LSPI, in the course of its use in an engine, under conditions simulating aging of the lubricant composition.

[0183] In the examples that follow, the lubricant compositions are prepared and tested in comparison with a reference lubricant composition not comprising any boron derivative.

[0184] For this reference composition, the kinematic viscosity at 100° C. was determined according to the standard ISO 3104. The composition was subsequently aged according to the catalyzed aging protocol described above, whilst carrying out oxidation measurements over the course of aging, in accordance with the protocol detailed above. Finally, the exothermic reaction initiation temperature (ignition temperature) was measured, according to the measurement method (laboratory preignition tendency method) defined above.

[0185] The details of the reference composition (mass percentages) and the results obtained are presented in Table 4 below.

TABLE-US-00004 TABLE 4 Composition Reference Base oil 72.8 Group III/IV Additive package* 15.7 Viscosity index enhancer of hydrogenated 10.5 styrene/isoprene copolymer type Viscosity index enhancer of polymethacrylate type 0.2 Diphenylamine antioxidant (Irganox ® L-57) 0.8 KV100 (mm.sup.2/s) 11.51 Ignition temperature (° C.) 197 RKV100 at 72 h (%) −8.7 RKV100 at 96 h (%) −9.0 RKV100 at 120 h (%) −8.7 RKV100 at 144 h (%) −7.5 HKV100 (%/hour) 0.012 *The additive package is a mixture of different additives that are common in the field of lubricants and commercially available. It comprises wear-resistance additives of zinc dithiophosphate type, detergents based on calcium and magnesium, and dispersants of PIBSI type.

Example 3: Preparation of the Lubricant Compositions

[0186] The lubricant compositions B0 to B2 were prepared.

[0187] Their kinematic viscosity at 100° C. was determined according to the standard ISO 3104.

[0188] The details of the compositions are presented in Table 5 below, in which the proportions of the various compounds are indicated as mass percentages.

TABLE-US-00005 TABLE 5 Composition B0 B1 B2 Base oil 72.0 72.6 70.8 Group III/IV Additive package* 15.7 15.7 15.7 Viscosity index enhancer of 10.5 10.5 10.5 hydrogenated styrene/isoprene copolymer type Phenylamine antioxidant 0.8 0.8 0.8 (Irganox ® L-57) Polymethacrylate 0.2 0.2 0.2 Borated ester (Oloa ® 17503 0.8.sup.(1) 0.2.sup.(2) 2.0.sup.(3) from Oronite) KV100 (mm.sup.2/s) 11.49 11.61 11.72 *The additive package is a mixture of different additives that are common in the field of lubricants and commercially available. It comprises wear-resistance additives of zinc dithiophosphate type, detergents based on calcium and magnesium, and dispersants of PIBSI type. .sup.(1)the amount of boron in composition B0 is 180 ppm by weight. .sup.(2)the amount of boron in composition B1 is 45 ppm by weight. .sup.(3)the amount of boron in composition B2 is 450 ppm by weight.

[0189] The compositions are prepared by mixing, at a temperature of the order of 30 to 40° C., of the compounds detailed in Table 5.

[0190] The lubricant compositions thus prepared have kinematic viscosity values at 100° C. that are suitable for their use in engines, in particular vehicle engines.

[0191] The lubricant compositions are subsequently aged according to the protocol (aging method) detailed above.

Example 4: Evaluation of the Performance of the Lubricant Compositions

[0192] The exothermic reaction initiation temperature (ignition temperature) was measured for the lubricant compositions of Example 1, according to the measurement method (laboratory preignition tendency method) defined above.

[0193] Furthermore, the oxidation of each of the lubricant compositions was also evaluated by measuring the fluctuation of the kinematic viscosity measured at 100° C. (RKV100) throughout the aging of the compositions and in accordance with the protocol (Measurement of the oxidation) described above.

TABLE-US-00006 TABLE 6 Ignition temper- RKV100 RKV100 RKV100 RKV100 ature at 72 h at 96 h at 120 h at 144 h Composition [° C.] (%) (%) (%) (%) B0 209 0.2 1.8 4.5 10.1 (Invention) B1 204 −9.1 −8.7 −7.5 −4.8 (Outside the invention) B2 221 6.2 10.8 18.7 35.5 (Outside the invention)

[0194] Composition B0 according to the invention, comprising at least one boron derivative in a content of between 150 ppm and 350 ppm by weight, has both an ignition temperature that is higher than that measured for the reference composition and very satisfactory oxidation resistance.

[0195] In contrast, composition B1, comprising less than 150 ppm by weight of boron, has a lower ignition temperature which does not allow the desired level of demand to be achieved.

[0196] As regards composition B2, although it has a higher ignition temperature, its oxidation stability is wholly inadequate for use in an engine in the long term.

[0197] These measurements thus make it possible to demonstrate that the addition of at least one boron derivative to an aged lubricant composition, adding between 150 ppm and 350 ppm by weight of boron to the composition, makes it possible to significantly retard preignition, in particular LSPI, in the course of its use in an engine, under conditions simulating aging of the lubricant composition, whilst having good oxidation resistance.