EP0275351A1 - Lubricating hydraulic fluid, especially a brake fluid, process for its manufacture, and its use - Google Patents

Abstract

A lubricant hydraulic fluid, in particular brake fluid, with improved lubricant properties and anti-wear protection, is composed of a commercially available brake fluid with usual additives and of a combination of a least one metallic dialkyldithiocarbonate and at least one metallic dialkyldithiophosphate as lubricant additive. Also disclosed are a process for producing the same and its uses as working fluid for central hydraulic systems, in particular as brake fluid, for servo-steering, central locking, spring hydraulic systems and the levelling and ventilating hydraulic systems of vehicles, in particular motor vehicles.

Description

The invention relates to a new lubricable hydraulic fluid, in particular brake fluid, for motor vehicles based on a commercially available brake fluid with customary additives, processes for its production and its use as a working fluid for central hydraulics, in particular as a brake fluid, for power steering, central locking and fan hydraulics Level control and suspension hydraulics, in motor vehicles and generally as hydraulic fluid in other land, water and aircraft and power machines.

Hydraulic fluids are important structural elements for the operation of the brakes, the steering, the opening and closing of the doors as well as other auxiliary units and the suspension on vehicles, in particular motor vehicles. Of particular importance is the brake fluid, the properties of which are essential for the design of the brake system Meaning.

The invention is explained below on the basis of its use as a brake fluid for motor vehicles, but the same or similar considerations also apply to its use as a different hydraulic fluid, in particular as a working fluid for the central hydraulics, power steering, fan hydraulics, central locking and suspension hydraulics, and generally as Hydraulic fluid in other land, water and aircraft, especially motor vehicles, and engines.

The brake fluid in motor vehicles must meet a wide variety of requirements, the most important of which are the following:
it should have a boiling point that is as high as possible in order to prevent the formation of vapor bubbles at the temperatures occurring in the braking system and thus the failure of the brake,
- their boiling point should remain as constant as possible over the period of use of the liquid in the system, ie it should not be changed or should be changed as little as possible due to atmospheric influences or the prevailing operating conditions (pressure, temperature, if necessary, impurities),
- small amounts of water (in the order of about 2% by volume) must not significantly lower the boiling point of the brake fluid contaminated with it,
the viscosity in the cold should be as low as possible, in the heat as high as possible, ie the viscosity-temperature index should be as favorable as possible, the brake fluid should still be functional down to temperatures of -50 ° C,
- The compressibility should be as low as possible and as little as possible dependent on temperature and pressure,
- It should be as little as possible corrosive to the metal components of the braking system, since their service life is decisively influenced by this,
it should have the best possible lubrication properties in order to protect the parts which move against one another in the brake system, in particular seals and feed pumps, from wear,
- it should have a defined interaction with the elastomer parts of the brake system, which swell only slightly under the influence of the brake fluid (especially in the case of long-term exposure) but should not shrink under any circumstances,
it should have a favorable foaming behavior, ie once a foam has formed should disappear quickly,
it should have a low solubility of gases in order to avoid harmful foaming in the event of local suppression caused by flow processes, but the "undersaturated" fluid should have a certain ability to absorb the residual air remaining in the brake system when the filling is underpressure,
- it should be miscible with property-improving additives (additives, inhibitors),
it should be insensitive to catalytic decomposition or polymerization under the influence of the finest particles of the elements contained in the braking system and in the street dust,
- it should be resistant to oxidation under all temperatures in the braking system,
- it should not attack the vehicle paint excessively with accidental wetting,
- Any spilled liquid should be easily removed from the wetted surface and
- It should be as little toxic as possible to humans and mammals.

In the past few decades, two main groups of substances have emerged as the basis for brake fluids, which meet the above requirements to varying degrees. A liquid that everyone No requirements, in particular those that meet lubricity and wear protection requirements, have so far been found.

The best known, commercially available brake fluids are those based on polyglycol ether and mineral oil.

The brake fluids based on polyglycol ethers and their derivatives, in particular the borate esters, currently have the largest share on the world market.

Polyglycol ethers can be represented by the formula
HO- (CH₂-CH₂-O) _n -H
where n = 5 to 25.

These compounds have ether bonds that are relatively stable and are only slowly hydrolyzed in quite acidic media.

In practice, many variations of the above type of connection are used as components of brake fluids.

To improve the cold resistance of the brake fluids, for example, glycol ethers are also used, which are derived from propylene glycol. Thereby ether is mostly used, which are not composed of a single building block, but represent a certain mixed form. The following empirical formula can be given for these substances:
HO- (CH₂-CH₂-O) _x - (CH · CH₃-CH₂-O) _y -H
where the indices x and y are between 0 and 25, with the sum of x and y generally not exceeding 25. The distribution of the building blocks can be irregular, which is why these compounds are referred to as "statistical copolymers".

Compounds of the above structure are contained in modern brake fluids in an amount of 10 to 20 wt.

If the substances described above are further etherified with simple alcohols (e.g. with methanol, ethanol, propanol or butanol), polyglycol ethers of the following type are formed:
RO- (CH₂-CH₂-O) _x - (CH-CH₃-CH₂-O) _y -H
wherein R is CH₃ or C₂H₅ or i- or n-C₃H₇ or n- or i- or t-C₄H₉. Here x + y = 2 to 4, mainly 3.

The representatives of this class of substances make up the majority of DOT3 brake fluids, depending on the type, their share is between 50 and 80% by weight.

worin R H oder CH₃,
R₁, R₂, R₃ CH₃ oder C₂H₅, C₃H₇, C₄H₉ (alle Isomere),
x, y and z eine Zahl von 2 bis 4, vorzugsweise 3, bedeuten.Brake fluids that contain a third type of polyglycol ether, namely borate esters, have also been on the market for some years. These include in particular the DOT 4 brake fluids. They arise from the fact that the polyglycol ethers described above are subjected to a further modification to form their borate esters. The reactive OH group still present is esterified with boric acid H₃BO₃, so that compounds of the following type are formed:

wherein RH or CH₃,
R₁, R₂, R₃ CH₃ or C₂H₅, C₃H₇, C₄H₉ (all isomers),
x, y and z represent a number from 2 to 4, preferably 3.

This class of compounds is contained in a proportion of approximately 40% by weight in the brake fluids according to DOT 4.

The brake fluids on the market (such as Hydraulan H 407® from BASF, DOT 4 + TSA® from Hoechst, and Brakefluid DOT Plus® from Dow Chemical) consist of a balanced mixture of the three classes of compounds described above. The compounds and mixing ratios are modified to optimize the end product with regard to certain properties.

Small amounts of the usual additives are added to the brake fluids described above, which prevent corrosion, further improve the lubrication, regulate the behavior towards the elastomers of the brake system and improve the oxidation resistance. The proportion of these "inhibitors" is usually 2 to 5% by weight of the brake fluid.

A general disadvantage of these brake fluids based on polyglycol ethers is that their lubricity is limited, i.e. the pressure generators, in particular the feed pumps, cylinders and the like. The hydraulic systems containing them must be lubricated separately, which entails a considerable technical outlay.

H)_n
worin R n-Alkyl mit 1 bis 10 Kohlenstoffatomen bedeutet.Another type of usable brake fluids are those based on mineral oil / synthetic oil. Due to the diverse requirements placed on brake fluids, only highly refined mineral oil fractions from selected crude oils can be considered for this purpose. The boiling cut must be based on the boiling point requirements on the one hand and the viscosity requirements on the other hand, whereby the use of viscosity index improvers (VI) in higher concentrations must be used. This inevitably also increases the shear sensitivity of the hydraulic fluid. In those applications in which the shear sensitivity interferes, components based on synthetic oil can be used which are less sensitive in this regard. These are mostly poly-α-olefins with the structural formula

- (CH₂-

H) _n
wherein R is n-alkyl having 1 to 10 carbon atoms.

Often, oligomers of propene, n-butene-1, n-pentene-1 and n-decene-1 are used either alone or as a mixture with one another or with mineral oil-based components.

The synthetic components mentioned are relatively expensive, so that they are only used if special requirements are placed on the shear stability.

The entire range of additives commonly used in the mineral oil industry is available for property-improving additives, e.g. Antioxidants, wear inhibitors, metal deactivators, detergents, dispersants, antifoams, viscosity index improvers and the like.

The commercial brake fluids usually contain about 5% additives, VI improvers are added up to 15%.

So far, liquids based on mineral oil / synthetic oil for power transmission in hydraulic systems have only been used in hydraulic steering and hydropneumatic suspension. In brake systems, these fluids are only considered in special cases. A central hydraulic system for which mineral oil appears to have been predestined has so far not been able to establish itself. An important reason is that brake fluids based on mineral oil and the sealing materials commonly used in brake systems based on SBR and EPDM are not compatible. Therefore, despite their good properties, brake fluids based on mineral oils or synthetic oils cannot be used on a large scale. This is not least due to the fact that they cannot be used in combination with elastomers based on SBR or EPDM, since they cause them to swell very strongly. To counteract this, it is possible to work with elastomers based on NBR, Neoprene or Viton, but these materials have a considerably smaller permissible temperature range (at a permissible continuous temperature of + 120 ° C, a sufficient cooling function is only possible up to about -30 ° C)), which is a clear disadvantage of a brake fluid based on mineral oil.

In view of the fact that brake fluids have to meet a large number of requirements if they are to prove themselves in practice, it has proven to be more advantageous proved to further develop the currently known and proven fluids based on polyglycol ethers instead of switching to alternative brake fluids.

The object of the invention is therefore to develop a hydraulic fluid, in particular brake fluid, which offers the advantages of the fluids based on polyglycol ether, but is significantly improved with regard to its lubricity and wear protection.

• a) mindestens einem Metalldialkyldithiocarbamat und
• b) mindestens einem Metalldialkyldithiophosphat.

It has now been found that this object can be achieved according to the invention with a hydraulic fluid, in particular brake fluid, based on a commercially available brake fluid with customary additives, which has significantly improved lubricity and wear protection and is characterized in that it is a lubricating additive contains a combination of

• a) at least one metal dialkyldithiocarbamate and
• b) at least one metal dialkyldithiophosphate.

The hydraulic fluid according to the invention, in particular brake fluid, has an unprecedented lubricating capacity and an unprecedented wear protection, so that additional, structurally separate lubrication of the components that come into contact with the hydraulic fluid, in particular brake cylinders, pressure generator pumps, feed pumps and the like, no longer exists is required. The wear protection that can be achieved with the hydraulic fluid according to the invention, in particular brake fluid, is at least 4 to 20 times higher than with the commercially available brake fluids without the additive according to the invention. Your wear situation is in the order of a good to very good gear oil. The hydraulic fluid according to the invention is therefore not only suitable as an excellent brake fluid, but can also be used to operate the power steering, suspension, central locking and as operating fluid for other hydraulic units in motor vehicles, but also in other land, water and aircraft vehicles and engines. In particular, it offers the advantage that, due to its good lubricating effect and its good wear protection, it enables all hydraulic units to be combined into a central hydraulic system, which includes both the brake hydraulics, the steering hydraulics, the suspension hydraulics, the locking hydraulics, the Nievauregulation and fan hydraulics, and similar hydraulic functions and the same required feed pumps and hydraulic cylinders. Particularly preferred configurations of the lubricatable hydraulic fluid according to the invention, in particular brake fluid, are evident from the subclaims mentioned above.

An essential feature of the lubricating hydraulic fluid, in particular brake fluid, claimed here is its content of an lubricating additive which consists of a combination of at least one metal dialkyldithiocarbamate and at least one metal dialkyldithiophosphate. The lubricating additive generally makes up 0.1 to 5% by weight, preferably 0.5 to 2.5% by weight, of the total weight of the lubricating hydraulic fluid, in particular brake fluid.

The weight ratio between components (a) and (b) is generally a: b = 1: 1 to 4: 1, preferably 1: 1 to 7: 3.

Component (a) of the lubricating additive used according to the invention contains the metal dialkyldithiocarbamate and optionally one or more further metal dialkyldithio carbamates generally in a weight ratio of 5: 1 to 1: 1, preferably 2.5: 1 to 1: 1, to each other.

Component (a) of the lubricating additive is one or more dialkyldithiocarbamates of the metals copper (Cu), silver (Ag); Zinc (Zn), cadmium (CD); Boron (B); Titanium (Ti), zirconium (Zr), tin (Sn), lead (Pb); Vanadium (V), tantalum (Ta), antimony (Sb); Chromium (Cr), Molybdenum (Mo), Tungsten (W); Manganese (Mn); Cobalt (Co) and nickel (Ni), the dialkyldithiocarbamates of boron (B), nickel (Ni), cobalt (Co), manganese (Mn), vanadium (V), tungsten (W) and molybdenum (Mo) being particularly preferred are.

worin Me für eines der obengenannten Metalle steht und Alkyl die nachstehend angegebenen Bedeutungen hat. Beispiele für erfindungsgemäß mit besonderem Vorteil ver­wendbare Metalldialkyldithiocarbamate sind folgende: Kupferdialkyldithiocarbamate und Kupferbisdialkyldithio­carbamate; Silberdialkyldithiocarbamate; Zink- und Cadmium­bisdialkyldithiocarbamate; Bortrisdialkyldithiocarbamate; Titan-, Zirkonium-, Zinn- und Bleitetrakisdialkyldithio­carbamate sowie Zinn- und Bleibisdialkyldithiocarbamate; Antimon-, Vanadin- und Tantaltrisdialkyldithiocarbamate, -tetrakis- und -pentakisdialkyldithiocarbamate sowie die Dialkyldithiocarbamate, in denen diese Metalle in gemisch­ten Oxidationsstufen vorliegen; Chrombis-, Chromtris-, Chromtetrakis- und Chromhexakisdialkyldithiocarbamate, Molybdän- und Wolframtetrakis-, -hexakis- und -oxybis- und -oxy­tetrakisdialkyl-dithiocarbamate; Manganbis-, -tris-,-tetrakis- und -hexakisdialkyldithiocarbamate; und Kobalt- und Nickel- bis- und -tris-dialkyldithiocarbamate.The metal dialkyldithiocarbamates used according to the invention can be represented by the general formula

wherein Me is one of the metals mentioned above and alkyl has the meanings given below. Examples of metal dialkyldithiocarbamates which can be used according to the invention with particular advantage are the following: copper dialkyldithiocarbamates and copper bisdialkyldithiocarbamates; Silver dialkyldithiocarbamates; Zinc and cadmium bisdialkyldithiocarbamates; Boron trisdialkyldithiocarbamate; Titanium, zirconium, tin and lead tetrakisdialkyldithiocarbamates as well as tin and lead bisdialkyldithiocarbamates; Antimony, vanadium and tantalum dialkyldithiocarbamates, tetrakis and pentakis dialkyldithiocarbamates and the dialkyldithiocarbamates in which these metals are present in mixed oxidation states; Chromium, Chromium, Chromium tetrakis and chromium hexakis dialkyldithiocarbamates, molybdenum and tungsten tetrakis, hexakis and oxybis and oxytetrakis dialkyl dithiocarbamates; Manganese bis, tris, tetrakis and hexakisdialkyldithiocarbamates; and cobalt and nickel bis and tris dialkyldithiocarbamates.

Particularly preferred among these compounds are the boron trisdialkyldithiocarbamates, the nickeltrisdialkyldithiocarbamates, the molybdenum tetrakis and molybdenum oxytetrakisdialkyldithiocarbamates, the manganese, vanadium and tungsten tetrakisdialkyldithiocarbamates.

Component (b) of the lubricating additive used according to the invention is one or more dialkyldithiophosphates of the metals copper (Cu), silver (Ag); Zinc (Zn), cadmium (Cd); Boron (B); Titanium (Ti), zirconium (Zr), tin (Sn), lead (Pb); Vanadium (V), tantalum (Ta), antimony (Sb); Chromium (Cr), Molybdenum (Mo), Tungsten (W); Manganese (Mn); Cobalt (Co) and nickel (Ni), among which the dialkyldithiophosphates of zinc, nickel, titanium, vanadium, molybdenum, tungsten and manganese are particularly preferred.

worin Me für eines der obengenannten Metalle steht und Alkyl die nachstehend angegebene Bedeutung hat.The metal dialkyldithiophosphates used according to the invention can be represented by the general formula:

where Me is one of the metals mentioned above and alkyl has the meaning given below.

Metal dialkyldithiophosphates which can be used with particular advantage in accordance with the invention are the dialkyldithiophosphates of the same metals in the same oxidation states as those above for the metal dialkyldi thiocarbamates have been listed.

Zinc bisdialkyldithiophosphates, nickel bis and tris dialkyl dithiophosphates, titanium and vanadium tetrakis dialkyl dithiophosphates, molybdenum and tungsten tetrakis dialkyl dithiophosphates and molybdenum and tungsten oxytetrakis dialkyl dithiophosphates are very particularly advantageous.

The alkyl group in the above-mentioned metal dialkyldithiocarbamates and metal dialkyldithiophosphates each contains 4 to 8 carbon atoms, so that the metal salts mentioned are still soluble in the commercially available brake fluid, examples of particularly advantageous alkyl groups include the n-, i- and tert-butyl groups; the n- and i-amyl group; the n- and i-pentyl group; the n- and i-hexyl group; the n- and i-heptyl group; and the 2-ethylhexyl group. The i-butyl group, the n-amyl group and the 2-ethylhexyl group are very particularly preferred.

Particularly preferred representatives of Metalldialkyldithiocarbamate present invention are: Bortrisdiisobutyldithiocarbamat, Bortrisdi-2-ethylhexyldithiocarbamat, Nickeltrisdiisobutyldithiocarbamat, Nickeltrisdiamyldithiocarbamat, Nickeltrisdi-2-ethylhexyldithiocarbamat, Molybdäntetrakisdi-ethylhexyldithiocarbamat 2, Molybdänoxytetrakisdi-2-ethylhexyldithiocarbamat, manganese, vanadium and Wolframtetrakis-2-ethylhexyldithiocarbamat and cobalt bisdiisobutyldithiocarbamate.

Particularly preferred representatives of the metal dialkyldithiophosphates used according to the invention are zinc bisdi-2-ethylhexyldithiophosphate, nickel bis- and trisdi-2-ethylhexyldithiophosphate, manganese, titanium and vanadium tetrakisdi-2-ethylhexyldithiophosphate as well as molybdenum and tungsten tetrakis and molybdate.

The invention further relates to a method for producing the lubricating hydraulic fluid described above, in particular brake fluid, which is characterized in that the commercially available brake fluid, which may contain customary additives, is initially introduced, optionally under pressure, heated to 100 to 120 ° C. and the metal dialkyldithiocarbamate is added with stirring within 5 to 60 minutes, preferably within 10 minutes, then with further stirring at a temperature below 100 ° C., preferably at about 90 ° C., within 2 to 20 minutes, preferably within 5 to 10 minutes, one or more further metal dialkyldithiocarbamates are added and the metal dialkyldithiophosphate is added with further stirring at a temperature of about 90 ° C. within 2 to 20 minutes, preferably within 5 to 10 minutes. The mixture obtained is then allowed to cool and is filled into suitable containers in which it can be stored, preferably in the absence of air.

The preferred metal dialkyldithiocarbamate used is nickel trisdiisobutyldithiocarbamate, nickel trisdi-n-amyldithiocarbamate, nickel trisdi-2-ethylhexyldithiocarbamate, manganese, vanadium, tungsten and / or molybdenum tetrakis-2-ethylhexamate dithiocarbamate.

Bortrisdiisobutyldithiocarbamate and / or Bortrisdi-2-ethylhexyldithiocarbamate are preferably used as further metal dialkyldithiocarbamates.

In the practical implementation of the method according to the invention, it has proven expedient to first add the nickel, manganese, vanadium, tungsten and / or molybdenum salt to the commercially available brake fluid and then the boron salt.

Zinc bisdi-2-ethylhexyldithiophosphate, nickel trisdi-2- is preferably used as the metal dialkyldithiophosphate. ethylhexyldithiophosphate, manganese, titanium tetrakisdi-2-ethylhexyldithiophosphate, vanadine tetrakisdi-2-ethylhexyldithiophosphate, molybdenum tetrakis or molybdenum oxytetrakisdi-2-ethylhexyldithiophosphate, tungsten tetrakis and / or tungsten 2-ethoxophosphate. Molybdenum oxytetrakisdi-2-ethylhexyldithiophosphate and nickel trisdi-2-ethylhexyldithiophosphate are particularly preferred.

Hydraulic H 407 (a commercial product available from BASF) or DOT 4 Plus (a commercial product from Hoechst AG) or Brakefluid DOT 4 Plus (a commercial product from Dow Chemical Europe) are preferably used as the commercially available brake fluid.

The invention also relates to the use of the lubricating hydraulic fluid described above as a working fluid for the central hydraulics, in particular as a brake fluid, for the servo steering, the central locking, the level control, the suspension hydraulics, the fan hydraulics and other hydraulic auxiliary units for land, water and aircraft , especially motor vehicles and engines.

The invention is explained in more detail by the following examples, but without being restricted thereto.

example 1

According to the method according to the invention, a lubricable brake fluid according to the invention (sample A) is produced from the following components:
97.2 g Hydraulan H 407 (commercially available brake fluid from BASF)
1.2 g nickel trisdiisobutyldithiocarbamate (first metal dialkyldithiocarbamate)
1.0 g boron trisdi-2-ethylhexyldithiocarbamate (second metal dialkyldithiocarbamate)
0.6 g molybdenum oxytetrakisdi-2-ethylhexyldithiophosphate (metal dialkyldithiophosphate)

The commercially available brake fluid is introduced and heated to 100 ° C., then 1.2 g of the first metal dialkyldithiocarbamate are added with stirring over the course of 40 minutes at normal pressure and at a temperature of 100 ° C., and the mixture obtained is then allowed to cool to 95 ° C. and 1.0 g of the second metal dialkyldithiocarbamate is added within 10 minutes. With further stirring, the metal dialkyldithiophosphate is added at 10 ° C. in the course of 10 minutes (0.6 g).

After cooling to room temperature, a lubricating brake fluid according to the invention (sample A) is obtained.

In the comparative test described below, the brake fluid according to the invention (sample A) thus produced is examined with the commercially available hydraulic fluid Hydraulan H 407 without the lubricating additive used according to the invention (sample Aʹ) with regard to its lubricating properties, in particular its wear protection properties.

Example 2

To produce a brake fluid sample according to the invention, 98 g of commercially available brake fluid (DOT 4 Plus from Hoechst AG) are heated to 108 ° C. To make this brake fluid lubricable, the following components are added:
1 g nickel trisdi-n-amyldithiocarbamate (first metal dialkyldithiocarbamate)
0.4 g boron trisdi-2-ethylhexyldithiocarbamate (second metal dialkyldithiocarbamate)
0.6 g molybdenum oxytetrakisdi-2-ethylhexyldithiophosphate (metal dialkyldithiophosphate)

1 g of the first metal dialkyldithiocarbamate is added to the commercially available brake fluid heated to 108 ° C. at normal pressure within 10 minutes while stirring at the same temperature, then 0.4 g of the second mixture is added within 5 minutes at a temperature of 95 ° C. with stirring Metalldialkyldithiocarbamats added. Finally, 0.6 g of the metal dialkyldithiophosphate are added over the course of 5 minutes at a temperature of 90 ° C. with stirring. The mixture obtained is allowed to cool, whereby a lubricating brake fluid according to the invention is obtained (sample B).

The brake fluid sample B according to the invention is subjected to the comparative test described below with the commercially available brake fluid DOT 4 Plus without the lubricating additive (sample Bʹ) used according to the invention under the same test conditions.

Comparison test

The lubricating properties, in particular the wear protection properties, of the brake fluid samples A and B according to the invention described above were compared with those of the commercially available brake fluid comparison samples Aʹ and Bʹ, the results evident from the diagrams below being achieved.

A circular disk was used to carry out the tests made of stainless steel with a diameter of 23 mm and a thickness of 10 mm, on the surface of which a drop of the brake fluid to be examined was applied. A ball made of the same stainless steel with a diameter of 10 mm was applied to the place where the drop of brake fluid was located, which exerted pressure on the surface of the metal disc due to its loading. The metal ball was reciprocated at a frequency of 50 Hz over an amplitude of 1 mm for 90 minutes under load on the surface of the metal disc, the load being within the range of 50 to 150 N and the temperature within the range of during the experiment 50 to 150 ° C was varied (SRV (vibrating-friction-wear) device, which is sold by Optimol GmbH worldwide). The wear profile transverse to the direction of oscillation of the ball, which was generated due to the friction between the loaded ball and the surface of the metal disk within the test period, was recorded by means of a suitable recording device, whereby the diagrams given below were obtained, in which the closing height as the difference between the highest was obtained on the ordinate and the lowest point of the surface profile of the metal disk as a function of the scanning distance of the surface of the metal disk is shown on the abscissa.

In the diagrams A and B below, a profile depth on the ordinate of 1 cm corresponds to a real profile depth in the surface of the metal disk of 1 μm, while in diagrams Aʹ and Bʹ the scanning device was damped so that a profile depth of 1 cm in the diagram one corresponds to the real profile depth in the surface of the pane of 2.5 µm.

The diagrams A and Aʹ were identical in the rest Conditions recorded (load on the ball 50 to 122 N, friction frequency 50 Hz, temperature 50 to 150 ° C, friction amplitude 1 mm, test duration 90 min).

The diagrams A and Aʹ show the measurement results when using the brake fluid sample A according to the invention or the commercially available comparison sample Aʹ.

While in the sample A according to the invention the profile depth was at most 1.3 μm, a maximum profile depth of 13.8 μm was obtained in the comparison sample Aʹ, which means that the wear in the comparison sample Aʹ was 10 times higher than in the inventive sample Sample A.

Diagrams B and Bʹ were also recorded under identical test conditions (load on the ball 50 to 112 N, test temperature 50 to 100 ° C, friction frequency 50 Hz, friction amplitude 1 mm, test duration 90 min).

In this case, too, there was a profile depth when using the brake fluid sample B according to the invention of at most 1.1 μm compared to a profile depth when using the commercially available comparison brake fluid sample Bʹ of up to 13.6 μm, which means that the sample B according to the invention is effective with regard to its wear protection The commercial sample Bʹ was superior by a factor of 12.

Although the invention has been explained in more detail above with reference to preferred embodiments, it goes without saying that it is not restricted to them, but that they can be modified and modified in many ways in a manner which is obvious to the person skilled in the art, without thereby reducing the scope of the present invention is left.

Claims (15)

1. Lubricable hydraulic fluid, in particular brake fluid, based on a commercially available brake fluid with customary additives,
characterized in that it contains a combination of a lubricating additive a) at least one metal dialkyldithiocarbamate and b) at least one metal dialkyldithiophosphate. 2. Lubricable hydraulic fluid according to claim 1, characterized in that it contains the lubricating additive in an amount of 0.1 to 5 wt .-%, in particular from 0.5 to 2.5 wt .-%, based on the total weight of the lubricating hydraulic fluid. 3. Lubricable hydraulic fluid according to claim 1 or 2, characterized in that in the lubricating additive components (a) and (b) in the weight ratio a to b of 1: 1 to 4: 1, in particular from 1: 1 to 7: 3, are present. 4. Lubricable hydraulic fluid according to one of claims 1 to 3, characterized in that it is component (a) of the lubricating additive to one or more dialkyldithiocarbamates of the metals copper, silver; Zinc, cadmium; Boron; Titanium, zirconium, tin, lead; Vanadium, tantalum, antimony; Chromium, molybdenum, tungsten; Manganese; Cobalt and nickel, especially boron, nickel, cobalt, manganese, vanadium, tungsten and molybdenum. 5. Lubricable hydraulic fluid according to one of claims 1 to 4, characterized in that it is component (b) of the lubricating additive to a dialkyldithiophosphate of the metals copper, silver; Zinc, cadmium; Boron; Titanium, zirconium, tin, lead; Vanadium, tantalum, antimony; Chromium, molybdenum, tungsten; Manganese; Cobalt and nickel, especially zinc, nickel, molybdenum, tungsten, titanium, vanadium and manganese. 6. Lubricable hydraulic fluid according to one of claims 1 to 5, characterized in that in the components (a) and (b) of the lubricating additive, the alkyl group contains 4 to 8 carbon atoms. 7. Lubricable hydraulic fluid according to claim 6, characterized in that the alkyl group is the isobutyl group, the tert-butyl group, the n- and iso-amyl group, the n- and iso-hexyl group, the n- and iso-heptyl group or the 2-ethylhexyl group, in particular the isobutyl, n-amyl or 2-ethylhexyl group. 8. Lubricable hydraulic fluid according to one of claims 1 to 7, characterized in that it as component (a) of the lubricating additive Bortrisdiisobutyldithiocarbamat and / or Bortrisdi-2-ethylhexyldithiocarbamat in combination with Nickeltrisdiisobutyldithiocarbamat, Nickeltrisdiamyldithiocarbamat, Mangit , Vanadium, tungsten and / or molybdenum tetrakis-2-ethylhexyldithiocarbamate, contains. 9. Lubricable hydraulic fluid according to one of claims 1 to 8, characterized in that it comprises as component (b) the lubricating additive zinc bisdi-2-ethylhexyldithiophosphate, nickel trisdi-2-ethylhexyldithiophosphate, titanium tetrakisdi-2-ethylhexyldithiophosphate, vanadium tetrakisdi-2-ethylhexyldithiophosphate Contains molybdenum tetrakis or molybdenum oxytetrakisdi-2-ethylhexyldithiophosphate, tungsten tetrakis or tungsten oxytetrakisdi-2-ethylhexyldithiophosphate. 10. Lubricable hydraulic fluid according to one of claims 1 to 9, characterized in that the commercially available brake fluid is one based on polyglycol ether. 11. Lubricable hydraulic fluid according to one of claims 1 to 10, characterized in that it contains, as a conventional additive, one or more antioxidants, metal deactivators, detergents, dispersants and antifoams. 12. A process for the preparation of the lubricious hydraulic fluid, in particular brake fluid, according to one of claims 1 to 11, characterized in that the commercial brake fluid which is present and which optionally contains customary additives is heated, if appropriate under pressure, to 100 to 120 ° C and with stirring within 5 to 60 min, preferably 10 min, the metal dialkyldithiocarbamate is added, then with further stirring at a temperature below 100 ° C., preferably at about 90 ° C., within 2 to 20 min, preferably 5 to 10 min, if appropriate one or more further metal dialkyldithiocarbamates are added and the metal dialkyldithiophosphate is added with further stirring at a temperature of about 90 ° C. within 2 to 20 minutes, preferably 5 to 10 minutes. 13. The method according to claim 12, characterized in that as the metal dialkyldithiocarbamate, nickel trisdiisobutyldithiocarbamate, nickel trisdi-n-amyldithiocarbamate, nickel trisdi-2-ethylhexyldithiocarbamate, manganese, vanadium, tungsten and / or molybdenum hexamodiocarbamate, as well as / or molybdenum tetrakisdithiocarbamate -2-ethylhexyl dithiocarbamate is used. 14. The method according to claim 12 or 13, characterized in that as the metal dialkyldithiophosphate zinc bisdi-2-ethylhexyldithiophosphate, nickel trisdi-2-ethylhexyldithiophosphate, titanium tetrakisdi-2-ethylhexyldithiophosphate, vanadine tetrakishexylethyldithiophosphatetaphdiethyldithiophosphetthi-tetrahydithiophosphate-oxy-dithiophosphate-thiophosphate-2, and / or tungsten oxytetrakisdi-2-ethylhexyl dithiophosphate is used. 15. Use of the lubricatable hydraulic fluid according to one of claims 1 to 11 as a working fluid for the central hydraulics, in particular as a brake fluid, for the power steering, the central locking, the suspension hydraulics, the level control and fan hydraulics, in motor vehicles.