Brake fluid and methods for differentiation and identification

Description

[0001] The present invention relates to a brake fluid and methods enabling its differentiation or identification.

[0002] According to US patent 3 580 847 and to French patent 1 040 993 it is known to produce brake fluids having different properties, in particular by incorporating therein various additives, and in particular anti-corrosion additives, lubricant additives and additives for stabilising the basicity or the acidity of the brake fluid. These brake fluids are used by car manufacturers in the braking circuits of various vehicles. Taking into account the large number of brake fluids available on the market and the large number of suppliers, car manufacturers wish to be able rapidly to identify a brake fluid, that is to say in particular the production batch, the type or the supplier of the brake fluid. This identification may be necessary during introduction of the brake fluid into a braking circuit or after a period of use of the brake fluid in a braking circuit, which period may be relatively prolonged.

[0003] A differentiated brake fluid has now been found which may, in particular, be easily identifiable. Its differentiation is simple and is effected by means of a compound added to the brake fluid as differentiating agent. It modifies none of the properties of the brake fluid and in particular its behaviour towards the materials with which it may be brought into contact in a braking circuit. Moreover, identification of the brake fluid is effected rapidly, without having to determine its complete composition, by virtue of a limited number of analyses.

[0004] The present invention firstly relates to a brake fluid characterised in that it contains in the form of a soluble compound from 1 to 100 parts per million of a metal chosen from cobalt, lithium and barium.

[0005] According to the present invention, the differentiated brake fluid must contain a small amount of a soluble compound in the brake fluid of a metal chosen from cobalt, lithium and barium. In fact, these compounds can be used in order to differentiate a brake fluid because, on the one hand, they are not present in the customary composition of a brake fluid and, on the other hand, the metals used are easily detectable in a brake fluid. Moreover, surprisingly, it has been found that the presence of a small amount of one of these compounds in a brake fluid does not modify its properties in any respect.

[0006] According to the invention the soluble compound can be for example a salt or an hydroxyde. However, in order to avoid corrosion problems in the braking circuit the salt is preferably not chosen from chlorides. Suitable soluble compounds include for example cobalt nitrate, barium nitrate and lithium hydroxide, because these are compounds which solubilise very easily in a small amount in a brake fluid.

[0007] In general, it has been found that a brake fluid is sufficiently differentiated from others if it contains from 1 to 100 ppm (parts per million) and preferably from 2 to 10 ppm of metal. For this reason, the brake fluid generally contains from 1 to 500 ppm of the soluble compound.

[0008] The invention also relates to a method for differentiating a brake fluid characterised in that a small, detectable amount of a metal chosen from cobalt, lithium and barium, in the form of a soluble compound is added to the brake fluid. This amount can represent from 1 to 100 ppm of metal in the brake fluid. The metal can be added to a brake fluid originating from a single production, to brake fluids of a single type, that is to say containing one or more common constituents and particularly common additives, or to all of the brake fluids originating from a single supplier.

[0009] The invention also relates to a method enabling identification of a brake fluid, characterised in that the fluid is tested to determine whether it contains a metal chosen from barium, lithium and cobalt. Advantageously, it is possible rapidly to test for the presence of cobalt or barium in a brake fluid by means of atomic absorption. In this case, the test for cobalt may be carried out by means of a measurement carried out at a wavelength of 345 nanometres and the test for barium by means of a measurement carried out at a wavelength of 553.8 nanometres. On the other hand, the test for the presence of lithium is advantageously carried out by means of an emission spectroscopy determination. If the brake fluid identified by the method contains a metal chosen from cobalt, lithium and barium, the metal concentration in the brake fluid can be determined. This determination can be worthwhile because it makes it possible to know whether a brake fluid initially containing a known amount of metal has been mixed, in particular with another brake fluid containing a different amount of the metal or entirely free from this metal.

[0010] The brake fluid used in the present invention can be any brake fluid essentially based on glycol ethers or a mixture of glycol ethers optionally mixed with polyols. Of course, a glycol ether can be used as such or in the form of a boric ester. The brake fluid can also be based on silicone compounds. The brake fluid can contain conventional additives, in particular anti-corrosion additives.

[0011] The present invention is illustrated by the examples which follow.

Example 1

[0012] Barium nitrate is introduced into a brake fluid essentially based on glycol ethers, partly in the form of boric esters, sold by BP Chemicals SNC (France) under the reference B.F. No. 7 DOT4, in an amount such that the fluid contains 10 ppm of barium. Because of this, the brake fluid is differentiated from others and may be identified by determining the presence of barium by means of an atomic absorption measurement carried out at a wavelength of 553.8 nanometres.

Example 2

[0013] Cobalt nitrate hexahydrate is introduced into a brake fluid essentially based on glycol ethers, partly in the form of boric esters, sold by BP Chemicals SNC (France) under the reference B.F. No. 7 DTO4, in an amount such that the fluid contains 50 ppm of cobalt. Because of this, the brake fluid is differentiated from others and may be identified by determining the presence of cobalt by means of an atomic absorption measurement carried out at a wavelength of 345 nanometres.

Example 3

[0014] Lithium hydroxide monohydrate is introduced into a brake fluid essentially based on glycol ethers, partly in the form of boric esters, sold by BP Chemicals SNC (France) under the reference B.F. No. 7 DTO4, in an amount such that the fluid contains 5 ppm of lithium. Because of this, the brake fluid is differentiated from others and may be identified by determining the presence of lithium by using an emission spectroscopy spectrum.

Claims

1. Brake fluid characterised in that it contains, in the form of a soluble compound from 1 to 100 parts per million of a metal chosen from cobalt, lithium, and barium.

2. Brake fluid according to claim 1, characterised in that the soluble compound is a salt or an hydroxide.

3. Brake fluid according to claim 1 or 2, characterised in that it the soluble compound is chosen from cobalt nitrate, barium nitrate or lithium hydroxide.

4. Brake fluid according to any one of claims 1 to 3 characterised in that it can contain from 1 to 500 parts per million of the soluble compound.

5. Brake fluid according to any one of claims 1 to 4 characterised in that the brake fluid is essentially based on glycol ethers or on silicones.

6. Method for differentiating a brake fluid characterised in that a small detectable amount of a metal chosen from cobalt, lithium and barium, in the form of a soluble compound is added to the brake fluid.

7. Method for differentiating a brake fluid according to Claim 6, characterised in the amount of metal represents from 1 to 100 parts per million in the brake fluid.

8. Method for identifying a brake fluid characterised in that the fluid is tested to determine whether it contains cobalt, barium or lithium.

9. Method according to Claim 8, characterised in that atomic absorption is used to test for cobalt or barium

10. Method according to Claim 8, characterised in that emission spectroscopy is used to test for lithium.