EP1213340A1 - Urea containing functional fluid for automotive vehicles - Google Patents

Abstract

The invention relates to a new functional fluid for motor vehicles comprising, in addition to the usual additives, a reducing agent capable of reducing the nitrogen oxides emitted during combustion, nitric acid and nitrous acid, and capable of protecting PAGs. against oxidation by these acids. This reducing agent is preferably urea.

Description

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

Each motor vehicle currently contains a variety fluids with different functions such as oils engine and / or gear lubricants, hydraulic oils such as power steering oils, brake fluid or shock absorber fluid and coolant.

All of these fluids exhibit thermal instability and oxidative in use. This instability leads to a modification of their physical and chemical properties. Fluids do not fill plus their role satisfactorily, which can be the cause of serious mechanical malfunctions of the vehicle. These fluids must then be removed and landfilled, which poses financial and environmental issues.

Among these functional fluids, the most problematic is without doubt the engine lubricant. Frequent emptying of these degraded engine, currently mainly based on oils mineral or synthetic, little or not biodegradable and toxic, are at the origin of significant pollution linked to storage and control of the recycling of these oils.

It was then proposed to use non-toxic base fluids and rapidly biodegradable like polyalkylene glycols (later PAG in the text), obtained notably from of ethylene oxide and propylene oxide (DE-P-196 47 554 C1 and FR 2792 326).

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

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

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

Oxalic acid is a crystalline acid which is deposited on parts of the engine whose temperature is lower than its temperature decomposition (around 189 ° C) and fouls them.

The presence of maleic, malonic and oxalic acid stimulates moreover an esterification reaction with polyalkylene glycols (Diols). Polyalkylene glycol chains contain groups terminal hydroxyls which are liable to react by esterification with a dicarboxylic acid to form water and polyesters. The polyester formation is manifested by volatile loss of oil base lubricant and an increase in the total acid number and the viscosity of the lubricating fluid thus degrading the qualities of this latest.

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

There is therefore a need to limit more or more effectively these oxidation phenomena in fluids functional, especially increased with the use of PAG as oil base, in order to guarantee thermal and oxidative stability to these fluids.

There is also a need to provide a functional fluid of a motor vehicle which allows lasting lubrication of the engine.

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

The plaintiff has now discovered in a way surprising that it was possible to overcome the problems associated with the thermal and oxidative stability in functional fluids in introducing into them a reducing agent. When the fluid is a engine lubricant, the addition of this reducing additive allows ensure long-term lubrication of the engine.

The use of reducing agents present directly in the functional fluid has proven particularly effective in ensuring thermal and oxidative stability of lubricating fluids including as base fluids of polyalkylene glycols.

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

Furthermore, the use of such reducing agents presents the additional advantage, when lubricating fluid containing them reaches the combustion chamber, reducing at the source the nitrogen oxides emitted by combustion or by valve guides, so as to decrease the concentration of these harmful oxides in the exhaust gas.

The present invention therefore relates to a new type of functional fluids for motor vehicles characterized in that it includes a reducing additive.

The invention also relates to the use of an agent reducing agent to reduce, limit and / or eliminate oxidation in motor vehicle functional fluids.

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

According to a preferred implementation of the invention, one prefers to use urea as a reducing agent.

Indeed, it has been found that the use of urea as an agent reducer gave excellent results in particular on the reduction 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-based fluids contributes, due to its biodegradability and low toxicity (LD ₅₀ of approximately 8,500 mg / kg, oral administration to rats), to the efforts in terms of ecotoxicity which led to the use of polyalkylene glycols as base fluids.

Although generally applicable to any type of functional fluids for motor vehicles, the invention will be more particularly described in the context of an engine lubricating fluid and more particularly of an engine lubricating fluid using as the base fluid for polyalkylene glycols.

Polyalkylene glycols used as base fluid for the manufacture of functional fluids and more particularly of engine lubricants, are generally random copolymers containing from 30 to 90% by weight of unit derived from ethylene oxide and from 70 to 10% by weight of unit derived from propylene oxide, having a weight average molecular weight of between 300 and 1,200.

According to the present invention, the lubricating fluid is added a reducing agent capable of reducing the nitrogen oxides emitted during combustion, and the 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 nitric and nitrous acids of PAG which leads to the formation of crystalline oxalic acid responsible for fouling or deposits observed on "cold" parts, including temperature does not exceed that of decomposition of oxalic acid.

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

It is more particularly preferred to use urea as an agent antioxidant in particular due to a selective reducing action.

In addition, the use of urea as a reducing agent has the additional advantages that urea is a natural, biodegradable substance of low toxicity (urea is classified in Germany as a compound with low polluting power, it i.e. in pollution class 1 ( Wassergefährdungsklasse 1 )) and is not corrosive to aluminum alloys or gray cast iron.

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

Urea is generally used in concentrations less than or equal to 10% by weight relative to the total weight of the lubricant. More particularly, urea is present in the fluid lubricant in lower concentrations between 0.01 and 5% by weight compared 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 turns out that the use of urea, even in small quantities, in lubricants of the present invention based on polyalkylene glycols, guarantees thermal and oxidative stability of lubricant over a distance traveled by the motor vehicle which approximately three times the distance traveled without using an agent reducer in the lubricating fluid.

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

Generally speaking, the functional fluid produced by addition of reducing agents to basic fluids such as polyalkylene glycols can be for example, a motor oil, a gear oil, automatic transmission oil, oil for power steering, a hydraulic fluid for shock absorbers, a brake fluid or coolant.

Other additives can be added to the functional fluid final according to the nature of the functional fluid. These are common additives preferably biodegradable and of low toxicity.

Claims (11)

Functional fluid for motor vehicles, characterized in that it comprises a reducing additive. Functional fluid for motor vehicles according to claim 1, characterized in that it comprises, as base fluid, at least one polyalkylene glycol and / or a polyalkylene glycol ether. Functional fluid for motor vehicles according to claim 2, characterized in that the basic fluid is a copolymer of ethylene oxide (OE) and propylene oxide (OP) with an OE / OP weight ratio of between 30 / 70 and 90/10 and having a weight average molecular weight between 300 and 1200. Functional fluid for motor vehicles according to any one of Claims 1 to 3, characterized in that it is an engine lubricating fluid. Functional fluid for motor vehicles according to any one of Claims 1 to 4, characterized in that the reducing additive is urea. Functional fluid for motor vehicles according to claim 5, characterized in that the amount of urea is less than or equal to 10% by weight relative to the total weight of functional fluid. Functional fluid for motor vehicles according to claim 6, 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. Use of a reducing agent to reduce, limit or suppress oxidation by nitrogen oxides, nitric acid and acid nitrous in a functional fluid of a motor vehicle. Use according to claim 8, characterized in that the functional fluid comprises polyalkylene glycols as the base fluid. Use according to claim 8 or 9, characterized in that the functional fluid is an engine lubricant. Use according to claim 8 or 10, characterized in that the reducing agent is urea.