Lubricant Composition Having Improved Emulsion Stability

The present application is a U.S. National Phase Application under 35 U.S.C. § 371 of International Patent Application No. PCT/EP2023/062443 filed May 10, 2023, which claims priority of French Patent Application No. 22 04449 filed May 11, 2022. The entire contents of which are hereby incorporated by reference.

The present invention relates to the lubrication of a vehicle comprising at least one combustion engine. In particular, the present invention relates to the lubrication of the engine of a hybrid vehicle such as a plug-in hybrid vehicle and a hybrid vehicle comprising a range extender.

Hybrid vehicles comprise two engines, an internal combustion engine and an electric motor. In most hybrid vehicles, the combustion engine drives the wheels and is assisted by an electric motor. A battery supplies the electricity needed to run the electric motor; in the case of conventional hybrid vehicles, this battery is recharged during braking and deceleration by a kinetic energy recovery system (KERS) built into the vehicle.

There exist a number of different hybrid vehicle technologies. Among these hybrid technologies the following are particularly worth mentioning:

Other complementary technologies have recently been developed: plug-in hybrid vehicles and hybrid vehicles with a range extender. So-called plug-in hybrid vehicles comprise a combustion engine and an electric motor, wherein the battery can be recharged over the electricity grid; as a result, it is possible for such vehicles to be driven in 100% electric mode over a distance of several tens of kilometers, such as 50 kilometers, for example. In hybrid vehicles with an auxiliary power unit referred to as ‘range extender’, only the electric motor drives the wheels. This electric motor is powered by a battery over a distance of several tens of kilometers. When the battery reaches a certain threshold level of charge (e.g. of the order of 30%), the internal combustion engine starts up and drives a current generator thereby enabling production of the electricity needed to recharge the battery and keep the electric motor running.

Lubricant compositions, and in particular those used for the lubrication of combustion engines, generally include small quantities of water resulting notably from the direct adsorption by the lubricant of water contained in the air or indeed even from the condensation of ambient water vapor. A lubricant composition typically comprises 0 to 10% of water. Although present in the form of trace amounts, the water in lubricant compositions is the cause of problems such as cold starting, corrosion and premature wear of the combustion engine. In order to prevent these phenomena, it is therefore necessary to maintain this water in the form of an emulsion.

However, in the engines of hybrid vehicles, particularly of the plug-in hybrid type or those incorporating a range extender, the combustion engine is used less often, which has the particular consequence of favoring problems relating to demixing of the lubricant composition. As the lubricant composition remains stationary, the emulsion becomes unstable and the water separates from the oil phase, thereby forming a continuous phase.

Similar problems are also observed with conventional vehicles equipped only with a combustion engine (non-hybrid vehicles) and operating occasionally, particularly with petrol engines. As the lubricant composition does not get regularly circulated in the engine, the water present tends to separate from the rest of the lubricant composition and form a continuous phase.

It is therefore necessary to provide a specific lubricant composition that enables effectively lubricating such engine systems, while at the same time preventing demixing problems.

One objective of the present invention is to provide a lubricant composition that enables the effective lubrication of an internal combustion engine, in particular the engine of a plug-in hybrid vehicle or a vehicle comprising a range extender.

Another objective of the present patent application is to provide a lubricant composition having improved emulsion stability. In particular, the objective of the invention is to provide a lubricant composition that makes it possible to maintain the water present in the form of stable emulsions.

These objectives are achieved by the present patent application for a lubricant composition comprising:

The base oils used in the lubricant compositions according to the invention may be oils of mineral or synthetic origin, possibly regenerated, belonging to groups I to V according to the categories defined in the American Petroleum Institute (API) classification (or equivalents thereof according to the ATIEL [Technical Association of the European Lubricants Industry] classification) (Table A) or mixtures thereof.

The mineral base oils according to the invention 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 dewaxing, hydrotreating, hydrocracking, hydroisomerisation and hydrofinishing.

Mixtures of synthetic and mineral oils, possibly regenerated, may also be used.

In general, there is no limitation as to the use of different lubricant base oils in order to produce lubricant compositions according to the invention, other than they must have appropriate properties, particularly in terms of viscosity, viscosity index, sulfur content and resistance to oxidation, which are suitable for use in vehicle engines or transmissions.

The base oils of the lubricant compositions according to the invention may also be selected from synthetic oils, such as certain esters of carboxylic acids and alcohols, and from polyalphaolefins. The polyalphaolefins used as base oils are, for example, obtained from monomers that contain from 4 to 32 carbon atoms, for example from octene or decene, and that have a viscosity at 100° C. of between 1.5 and 15 mm2·s-1 according to the standard ASTM D445. Their average molecular weight is generally between 250 and 3,000 according to the standard ASTM D5296.

The lubricant composition according to the invention may comprise at least 50% by weight of base oils relative to the total weight of the composition. In a more advantageous manner, the lubricant composition according to the invention comprises at least 60% by weight, or indeed at least 70% by weight, of base oils relative to the total weight of the composition. In a particularly more advantageous manner, the lubricant composition according to the invention comprises 75% to 95% by weight of base oils relative to the total weight of the composition.

The lubricant composition according to the invention comprises at least one viscosity index improver for improving the viscosity index of the lubricant composition.

For the purposes of the invention, the term “viscosity index improver” is understood to refer to a chemical compound that serves to ensure that the lubricant composition has good cold flow properties and minimum viscosity at high temperatures.

Examples of viscosity index improver polymers that may be mentioned include polymer esters; hydrogenated or non-hydrogenated homopolymers or copolymers of styrene, butadiene and isoprene; homopolymers or copolymers of olefins such as ethylene or propylene; and polyacrylates and polymethacrylates (PMA).

The lubricant composition according to the invention typically comprises from 0.1% to 13% by weight of viscosity index improver(s), relative to the total weight of the lubricant composition.

Preferably, the lubricant composition according to the invention comprises from 0.5% to 12% by weight of viscosity index improver(s), relative to the total weight of the lubricant composition, more preferentially from 1% to 10% by weight, still more preferentially from 5% to 10% by weight.

The lubricant composition according to the invention comprises at least one organomolybdenum compound.

The term ‘organomolybdenum compound’ according to the invention is understood to refer to any liposoluble (fat-soluble) organomolybdenum compound.

The organomolybdenum compound according to the present invention may be selected from organic molybdenum complexes comprising at least one chemical element molybdenum (Mo), preferably at least two chemical elements molybdenum (Mo), and at least one ligand such as a carboxylate ligand, an ester ligand, an amide ligand, a dithiophosphate ligand, or a dithiocarbamate ligand.

For example, organic complexes of molybdenum with carboxylates, esters and amides can be obtained by reacting molybdenum oxide or ammonium molybdates with fatty substances, glycerides, fatty acids or fatty acid derivatives (esters, amines, amides, etc.).

For the purposes of the invention, the carboxylate ligands, ester ligands and amide ligands are free from sulfur and phosphorus.

In one embodiment, the organomolybdenum compound of the invention is selected from complexes of molybdenum with amide ligands, mainly prepared by reacting a molybdenum source, which may for example be molybdenum trioxide, and an amine derivative, and fatty acids containing for example from 4 to 36 carbon atoms such as for example the fatty acids contained in plant or animal oils.

The synthesis of such compounds is described, for example, in the patents U.S. Pat. No. 4,889,647, EP0546357, U.S. Pat. No. 5,412,130 or EP1770153.

According to one preferred embodiment, the organomolybdenum compound is selected from among dinuclear organomolydbene compounds.

For the purposes of the invention the term ‘dinuclear organomolybdenum compound’ is understood to refer to organomolybdenum compounds in which the nucleus contains two molybdenum atoms. They are also referred to as dimeric organomolybdenum compounds.

In one preferred embodiment of the invention, the organomolybdenum compound is selected from organic complexes of molybdenum with amide ligands obtained by reaction of:

In one embodiment of the invention, the organomolybdenum compound may comprise from 0.1 to 30% by weight, preferably from 0.1 to 20%, more preferentially from 2 to 8.5% by weight of molybdenum relative to the total weight of the organomolybdenum complex.

Preferably, the organomolybdenum compound comprises at least one organic molybdenum complex having the formula (I) or (II), alone or in a mixture:

Advantageously, the organic complex of molybdenum having the formula (I) or (II) is prepared by reaction of:

More advantageously, the organic complex of molybdenum having the formula (I) is constituted of at least one compound having the formula (I-a) or (I-b), alone or in a mixture:

By way of an example of sulfur-free molybdenum complexes according to the invention mention may be made of Molyvan 855@ marketed by the company Vanderbilt.

In one other embodiment of the invention, the organomolybdenum compound is selected from among organic complexes of molybdenum with dithiophosphate ligands or organic complexes of molybdenum with dithiocarbamate ligands.

Within the meaning of the invention, organic complexes of molybdenum with dithiophosphate ligands are also referred to as molybdenum dithiophosphates or Mo-DTP compounds, and organic complexes of molybdenum with dithiocarbamate ligands are also referred to as molybdenum dithiocarbamates or Mo-DTC compounds.

In a more preferred embodiment of the invention, the organomolybdenum compound is selected from molybdenum dithiocarbamates.

Mo-DTC compounds are complexes formed from a molybdenum metal core bound to one or more ligands, the ligand being an alkyl dithiocarbamate group. These compounds are well known to the person skilled in the art.

In one embodiment of the invention, the Mo-DTC compound may comprise from 1 to 40%, preferably from 2 to 30%, more preferentially from 3 to 28%, advantageously from 4 to 15% by weight of molybdenum, relative to the total weight of the Mo-DTC compound.

In one other embodiment of the invention, the Mo-DTC compound may comprise from 1 to 40%, preferably from 2 to 30%, more preferentially from 3 to 28%, advantageously from 4 to 15% by weight of sulfur, relative to the total weight of the Mo-DTC compound.