EP1213340B1 - Urea containing functional fluid for automotive vehicles - Google Patents

Abstract

A functional fluid for automobiles comprises a reducing agent.

Description

The subject matter of this patent is defined in the wording of the independent claim 1. Dependent claims 2 to 5 relate to optative features of the invention.

The invention relates to functional fluids for motor vehicles and more particularly to functional fluids allowing a lasting lubrication of the engines.

Each motor vehicle currently contains a variety of fluids that perform various functions such as engine and / or gear lubricating oils, hydraulic oils such as power steering oils, brake fluid or damper fluid, and coolant. .

All these fluids have a thermal and oxidative instability in use. This instability leads to a modification of their physical and chemical properties. Fluids no longer perform their role satisfactorily, which can be the cause of serious mechanical malfunctions of the vehicle. These fluids must then be removed and disposed of, which poses financial and environmental problems.

Among these functional fluids, the most problematic is probably the engine lubricant. The frequent emptying of these degraded motor oils, currently mostly based on mineral or synthetic oils, with little or no biodegradability and toxicity, are at the origin of a significant pollution related to the storage and non control of these oils.

It was then proposed to use nontoxic and rapidly biodegradable base fluids such as polyalkylene glycols (later PAG in the text), obtained especially from ethylene oxide and propylene oxide ( DE-P-196 47 554 C1 and FR 2792 326 ). GB-A-348 642 relates to improvements in lubricating fluids and for hydraulic applications.

However, it turns out that the phenomenon of thermal and oxidative degradation of lubricants comprising PAG as base fluids is particularly important.

Indeed, it has been observed, using PAGs as base fluids in engine lubricants the formation of deposits and / or fouling around parts such as scraper rings and / or piston bosses.

Current internal combustion engines produce nitrogen oxides NO _x . These nitrogen oxides that form during combustion can dissolve in the existing PAG lubricant film on the jacket. Indeed, the PAG contains by nature or attracts a certain amount of water, which can increase during the operation of the engine. Thus, nitrogenous acids, formed by dissolution of the nitrogen oxides, oxidize the ethylene glycol and propylene glycol PAG to form oxalic acid, and then, at a later stage, dicarboxylic acids such as maleic or malonic acid.

Oxalic acid is a crystalline acid that deposits on parts of the engine whose temperature is below its decomposition temperature (of the order of 189 ° C) and fouls them.

The presence of maleic, malonic and oxalic acid also stimulates an esterification reaction with the polyalkylene glycols (diols). The polyalkylene glycol chains contain terminal hydroxyl groups which are capable of reacting by esterification with a dicarboxylic acid to form water and polyesters. The formation of polyesters is manifested by a volatile loss of the base lubricating oil and an increase in the total acid number and the viscosity of the lubricating fluid thus degrading the qualities of the latter.

Until now, in order to limit as much as possible the oxidation in the functional fluids, antioxidants such as phenols and amines have been used as additives (see US 4,701,273 and DE 28 06 133 ). However, these products are not always satisfactory from the point of view of their efficiency and from the point of view of their ecotoxicity or their biodegradability.

There is therefore a need to further limit or more effectively these oxidation phenomena in functional fluids, in particular increased with the use of PAG as oil basic, to ensure thermal and oxidative stability to these fluids.

There is also a need to provide a motor vehicle functional fluid that allows for durable lubrication of the engine.

In addition, it appears more and more essential to provide a functional fluid of a motor vehicle that also overcomes the problems related to the ecotoxicity and recycling of functional fluids and in particular engine lubricants.

The Applicant has now surprisingly found that it is possible to overcome the problems of thermal and oxidative stability in functional fluids by introducing a reducing agent therein. When the fluid is a motor lubricant, the addition of this reducing additive ensures a long-term lubrication of the engine.

The use of reducing agents present directly in the functional fluid has been found to be particularly effective in ensuring the thermal and oxidative stability of lubricating fluids comprising as base fluids polyalkylene glycols.

By agent or reducing additive is meant a compound capable of reducing the nitrogen oxides emitted during combustion, the nitric and nitrous acids present in the engine under the normal operating conditions of the latter.

Furthermore, the use of such reducing agents has the additional advantage, when lubricating fluid containing them arrives in the combustion chamber, to reduce at the source the nitrogen oxides emitted by combustion or by the valve guides, in order to reduce the concentration of these harmful oxides in the exhaust gas.

The invention relates to the use of a reducing agent for reducing, limiting and / or eliminating oxidation in the functional fluids of motor vehicles.

According to an advantageous embodiment of the invention, the functional fluid comprises, as base fluid, at least one polyalkylene glycol and / or a polyalkylene glycol ether such as those described in the patent applications. EP 0570 121 and EP 0 355 977 . More particularly, the functional fluid may be a motor lubricant.

According to a preferred embodiment of the invention, it is preferred to use urea as reducing agent.

Indeed, it has been found that the use of urea as reducing agent gave excellent results, in particular on the reduction of the oxidation of lubricating fluids comprising polyalkylene glycols as base fluids.

Another advantage of urea is its solubility in PAGs.

In addition, the use of urea in polyalkylene glycol fluids contributes, because of its biodegradability and low toxicity (LD ₅₀ of about 8,500 mg / kg, administered orally to rats), the efforts in terms of ecotoxicity that led to the use of polyalkylene glycols as base fluids.

Although generally applicable to all types of functional fluids for motor vehicles, the invention will be more particularly described in the context of a motor lubricating fluid and more particularly of a motor lubricating fluid using base of the polyalkylene glycols.

The polyalkylene glycols used as base fluid for the manufacture of functional fluids and more particularly motor lubricants, are generally random copolymers containing from 30 to 90% by weight of ethylene oxide unit and from 70 to 10% by weight of ethylene oxide. Propylene oxide-derived unit weight having a weight average molecular weight between 300 and 1200.

According to the present invention, the lubricating fluid is supplemented with a reducing agent capable of reducing the nitrogen oxides emitted during combustion, and nitrous acid and nitric acid dissolved in the lubricating fluid under normal operating conditions of the engine.

The reducing action of the additive thus makes it possible to overcome the oxidation reaction by the nitric and nitrous acids of the PAGs which leads to the formation of crystalline oxalic acid responsible for the fouling or deposits observed on the "cold" parts "whose temperature does not exceed that of decomposition of oxalic acid.

The use of this reducing agent also makes it possible to overcome the esterification reaction initiated by the dicarboxylic acids on the hydroxyl end groups of the polyalkylene glycol chains. This esterification reaction was responsible for thickening of the lubricating fluid.

It is more particularly preferred to use urea as an antioxidant especially because of a selective reducing action.

In addition, the use of urea as a reducing agent has the additional advantages that urea is a natural, biodegradable and low toxicity substance (urea is classified in Germany as a low pollutant ie in pollution class 1 ( Wassergefährdungsklasse 1 )) and is not corrosive to aluminum alloys or gray cast irons.

Indeed, the lubricant may comprise, in addition to the base fluid, a mixture of very varied additives. However, urea, mixed with the lubricant, reacts preferably with nitrogen oxides, nitrous acid and nitric acid by converting them into water, carbon dioxide and nitrogen. In other words, urea reacts selectively with the compounds responsible for the oxidative degradation of the lubricating fluid and thus acts as a consumer of free radicals.

Urea is generally used in concentrations of less than or equal to 10% by weight relative to the total weight of the lubricant. More particularly, urea is present in the lubricating fluid in lower concentrations of between 0.01 and 5% by weight relative to the total weight of the lubricant, even more particularly between 0.5 and 2% by weight relative to the total weight of the lubricant.

It has been found that the use of urea, even in small amounts, in lubricants of the present invention based on polyalkylene glycols, ensures a thermal and oxidative stability of the lubricant over a distance traveled by the motor vehicle which is approximately equivalent to triple of that traveled by not using a reducing agent in the lubricating fluid.

The functional fluid according to the invention, when it is a lubricant, allows a long-term lubrication of the engine, because even a small amount of urea considerably slows the phenomena of fouling and increase of the viscosity of the lubricating fluid.

In general, the functional fluid produced by adding reducing agents to base fluids such as polyalkylene glycols can be, for example, motor oil, gear oil, automatic transmission oil, power steering oil. , a hydraulic fluid for dampers, a brake fluid or a coolant.

Other additives may be added to the final functional fluid depending on the nature of the functional fluid. These are usual additives, preferably biodegradable and of low toxicity.

Claims (5)

1. Use of a reducing agent for limiting or eliminating oxidation by nitrogen oxides, nitric acid and nitrous acid in a functional fluid of a motor vehicle comprising, as base fluid, at least one polyalkylene glycol and/or one polyalkylene glycol ether.
2. Use according to Claim 1, characterized in that the base fluid is a copolymer of ethylene oxide (EO) and of propylene oxide (PO) with an EO/PO weight ratio between 30/70 and 90/10 and having a weight-average molecular weight between 300 and 1200.
3. Use according to one of the preceding claims, characterized in that the reducing agent is urea.
4. Use according to Claim 3, characterized in that the amount of urea is between 0.01 and 5% by weight relative to the total weight of functional fluid, and preferably between 0.5 and 2% by weight relative to the total weight of functional fluid.
5. Use according to one of the preceding claims, characterized in that the functional fluid is an engine lubricant.