FR2812915A1 - Hydraulic system useful for the control of motor vehicles, comprises a lubricant having a specific density greater than that of the hydraulic fluid or that is insoluble in the hydraulic fluid. - Google Patents

Abstract

A hydraulic system preferably for a motor vehicle comprises a subsidiary cylinder consisting of a casing with an axially arranged sealed piston and an inlet for hydraulic fluid as well as a master cylinder whereby at least one sealing face between a piston and casing has a lubricant having a specific density greater than that of the hydraulic fluid or that is insoluble in the hydraulic fluid. A hydraulic system preferably for a motor vehicle comprises a subsidiary cylinder consisting of a casing with an axially arranged sealed piston and an inlet for hydraulic fluid as well as a master cylinder consisting of a casing with an axially arranged sealed piston and an outlet for hydraulic fluid with interconnecting pipework between the inlet and outlet as well as a pressure medium for filling the hydraulic system and optionally a hydraulic fluid reservoir whereby at least one sealing face between one of the pistons and the corresponding casing has a lubricant having a specific density greater than that of the hydraulic fluid or that is insoluble in the hydraulic fluid.

Description

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HYDRAULIC SYSTEM The invention relates to a hydraulic system in particular for motor vehicles, comprising a transmitting cylinder consisting of at least one cylinder with a piston which can move axially therein and is sealed against the first cylinder and d '' an outlet for the pressurized fluid as well as a receiving cylinder consisting of at least one cylinder with a piston which can move axially therein and is sealed against the cylinder and an inlet for the pressurized fluid , as well as a pressurized fluid line hydraulically positively connecting the inlet of the pressurized fluid and the outlet of the pressurized fluid as well as a pressurized fluid for filling the hydraulic system.

In particular, such hydraulic systems are used in motor vehicles as devices for operating brakes, as power steering systems and as a device for operating friction clutches, for example on the force flow between an internal combustion engine and a gearbox. and / or an electric motor and a drive line. Generally a linear movement is there, by means of a hydraulic cylinder acting as a transmitter cylinder, transmitted, by the driver or by an actuator controlled automatically according to the running situation of the vehicle, by a pressure transmission, produced in the transmitter cylinder by means of the piston of the transmitter cylinder, in the line filled with pressurized fluid and connecting the transmitter cylinder and the receiver cylinder, to the receiver cylinder which then performs the desired action, for example the operation of the brakes, a process of clutch and / or the like, by a linear movement, induced by pressure, of the piston of the receiving cylinder with respect to the cylinder of the receiving cylinder, mounted fixed. Here the piston can be sealed against the cylinder of the receiving cylinder by means of a seal. Document DE 199 46 593 shows for this purpose an example with a receiving cylinder arranged concentrically around a shaft and having a U-shaped lip seal.

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 To improve the sliding characteristics of the piston in the cylinder, the hydraulic system can be lubricated, that is to say that on a contact surface between the piston and the cylinder or on a seal arranged between them, as a U-shaped lip seal can be provided with a lubricant to reduce the friction between the parts which move axially with respect to each other. Lubricants of this type are generally greases or mixtures containing a proportion of grease which have a non-negligible solubility in the fluid under pressure and which, as a result of the action of the fluid under pressure, detach themselves from the surface of contact and therefore lead in the long run to a degraded friction behavior of the piston or of the U-shaped lips which seal it with respect to the cylinder and the cylinder itself. According to the state of the art, composites are used which contain a so-called background oil based on polyglycol. Components of this type and possibly other components have significant solubility in the brake fluid and therefore tend to pollute it. These materials therefore partially saponify or hydrolyze under the action of water. The components or reaction products of these components can float in the hydraulic system for example into the hydraulic fluid tank and cause undesirable effects such as changes in the viscosity of the hydraulic fluid, obstructions in pipes or the like.

Disadvantageous is in addition in hydraulic systems the presence of water which for example promotes the saponification of lubricants, but in particular lowers the boiling point of the lubricant such as for example the lubricants DOT3, DOT4 / reference 3 and 4 of the US Department of Transport and can, for example, result in hydraulic braking mechanisms, due to the formation of heat on the brake, failures, jeopardizing the safety of the braking system by the formation of vapor bubbles on the hydraulic circuit . Another drawback appears in hydraulic clutch release systems, in particular in clutch release systems.

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 the clutch controlled automatically by means of an actuator. Here, processes such as determining the point of engagement are necessary, an adaptation of the moments to control the moment that can be transmitted by the clutch, with rapid control cycles whose speed and precision depend inter alia on the viscosity of the fluid under pressure. The viscosity is degraded there by the water content as well as - as already mentioned above - possibly by components of the lubricant in solution, in emulsion or in suspension, so that the clutch, in particular the automatic clutch, by example, a clutch controlling the emitting cylinder by means of an electric motor is only insufficiently controlled.

The object of the invention is therefore to propose, in the form of an extension of the state of the art, a hydraulic system which can be produced in a simple and inexpensive manner, has high user comfort and is characterized by low operating forces, especially during the life of the hydraulic system. In addition, the operational safety of the hydraulic system must be guaranteed, in particular during its service life. In particular, purity, i.e. the absence of water and the content of foreign bodies, such as the presence of the lubricant and its components in the pressurized fluid, must be avoided or at least lowered. .

This object is achieved in particular by means of a hydraulic system for motor vehicles comprising a receiving cylinder consisting of at least one cylinder with a piston which can move axially therein and is sealed against it and with an inlet for pressurized fluid as well as a transmitter cylinder consisting of at least one cylinder with a piston which can move axially therein and is sealed against it and with a pressurized fluid outlet, as well as a fluid pipe under pressure hydraulically positively connecting the pressurized fluid inlet with the pressurized fluid outlet, as well as a pressurized fluid for filling the hydraulic system and possibly a pressurized fluid reservoir, in which at least one

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 sealing surface located between one of the pistons and the corresponding cylinder acts a lubricant whose specific density is greater than the specific density of the fluid under pressure. This goal can also be achieved by means of a lubricant which is particularly difficult to dissolve in the pressurized fluid and remains adherent to the sealing surface, even in the presence of large temperature variations, for example in the case of use. in the engine space or in the clutch housing of the transmission line, and this advantageously during the lifetime of the hydraulic system or of the vehicle comprising this hydraulic system. Thanks to the invention, it is therefore planned, on the one hand, to keep the lubricant on the contact surface for as long as possible and, if it is partially detached, inevitably under appropriate conditions, to keep it at least in the chamber. under pressure of the receiving cylinder and / or the transmitting cylinder and to prevent it from floating in volumes located statically higher, for example in a tank of pressurized fluid.

According to the inventive idea, the hydraulic system can be a braking device, a power steering device or a hydraulic clutch device, it being specified that in this application it is in particular the use of the lubricant in a receiving jack arranged on a gearbox input shaft which can be advantageous, since for example, due to the notable temperature variations in the clutch housing, the negligible solubility of the lubricant intervenes in a particularly advantageous way in a permanent immobilization of the lubricant on the contact surface. In addition, thanks to the property that the density of the lubricant is greater than that of the pressurized fluid, parts of the lubricant have components of the lubricant which nevertheless detach themselves are not transported towards the lubricant reservoir and / or the jack transmitter, usually arranged higher in the hydrostatic view points, but remain substantially in the pressurized space of the receiving cylinder. It is understood that applications of the lubricant can also be

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 advantageous for the emitting cylinder.

The lubricant can be applied to the seal and / or to the contact surface by means of devices known per se, such as metering mechanisms, grease presses or by hand. According to the invention, with a value greater than 1.1 g / cm 3, the specific density of the lubricant is greater than the specific density of the pressurized fluid, for example the reference DOT4 of the US Department of Transport. It is understood that when using other pressurized fluids such as DOT3 for example, the specific density of the lubricant is adapted accordingly.

The design of the lubricant in the form of a mixture can be particularly advantageous, since materials having different characteristics form the lubricant, this lubricant can also be formed therein of components which are characterized by good stability, by extremely solubility difficult when hot in the pressurized fluid, but nevertheless having a specific gravity lower than that of the pressurized fluid. The components which have a density greater than that of the pressurized fluid can be added and mixed, which makes it possible to obtain a mixture having very poor solubility and a density greater than that of the pressurized fluid. A component according to the inventive idea may be a siloxane, preferably a polydimethylsiloxane. To characterize a dominant characteristic of polymethylsiloxane with regard to poor solubility and specific density, use may be made of its viscosity which, at 25 ° C., is at least greater than 1000 mm 2 / s, preferably between 10000 mm 2 / s and 100,000 mm2 / s and, preferably in particular, is equal to 30,000 mm 2 / s. Other components can elevate the sliding characteristics, for example, polytetrafluoroethylene powder PTFE, graphite, molybdenum sulfide and the like. The addition of an antioxidant can prevent rapid aging of the lubricant. Agents improving the coefficient of friction, which in particular minimize the adhesion of the parts at the start of the movement, as well as components which can improve the thermal characteristics

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 may also be constituents of the lubricant. Melamine cyanurate appeared here as particularly advantageous. In addition, metal oxides, for example magnesium oxide, calcium oxide, zirconium oxide and / or the like, can be incorporated into the lubricant mixture, in particular as antioxidants, these components advantageously having a small particle size on the surface. range from 1 to 20 pm.

A mixture consisting of - 55 to 90 percent by weight of polydimethylsiloxane having a viscosity at 25 C greater than 1000 mm 2 / s, preferably between 10,000 mm2 / s and 100,000 mm2 / s, appeared to be particularly advantageous and preferably being specific 30,000 mm2 / s, - 5 to 45 percent by weight of polytetrafluoroethylene PTFE powder, - 5 to 45 percent by weight of melamine cyanurate, - up to 5 percent by weight of an antioxidant, - up to 5 percent by weight of magnesium oxide.

These mixtures are known from document US Pat. No. 5,874,388 for use in a dry environment. It has appeared in tests that this mixture can be used in hydraulic systems even under the action of the pressurized fluid, as an extremely stable lubricating mixture, exhibiting good adhesion and negligible solubility. Thanks to the use of a - as described above - polydimethylsiloxane, it is also possible to increase the stability of the lubricating mixture with respect to the water contained in the fluid under pressure, because, because of its viscosity fairly high, this lubricant can be attacked by water and hydrolyzed only less strongly than the greases used so far and possibly their additives. In addition, the supply of polydimethylsiloxane in the lubricant is advantageously possible with regard to the viscosity with improved characteristics compared to a lubricant of traditional use, of density lower than that of the fluid under pressure and of comparatively high solubility in that so that already existing production facilities for the components of the

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 hydraulic system, in particular dosing devices can continue to be used. The properties of the lubricant are also advantageously neutral with respect to the components traditionally used in the hydraulic system, for example with regard to plastics, metals and sealing materials, for example EPDM / ethylene-propylene-diene monomer, so that the materials usually used in these systems with the original lubricant can also be adopted when using the lubricant according to the invention.

To achieve the object of the invention, it has also appeared advantageous to reduce, with or without the use of the lubricant according to the invention, the water content of the pressurized fluid, since the pressurized fluid undergoes, with a increasing water content, quality losses, for example a lowering of the boiling point and the formation of a higher viscosity. According to the inventive ideas, the volume of the hydraulic system containing the pressurized fluid is connected for this purpose with a reservoir, or with a chamber, filled with a desiccant. The agent can be a known, water-absorbing substance, for example sodium sulfate, silica gel, potassium hydroxide, phosphorus pentoxide, zeolite or the like. Zeolite in particular, because of its otherwise neutral chemical behavior, can be particularly advantageous. Water is absorbed there into the pores of the zeolite and removed from the fluid under pressure, the pores being determined according to their water absorption capacity. Pore widths of on average 10 "I to 10" 9 m, preferably 2 x 10 "I to 6 x 10" i m have been shown to be particularly advantageous. The shape of the zeolite can be powdery or preferably have an aggregate form.

According to the invention, the reservoir containing the desiccant may be provided at any location, for example in the emitting cylinder, in the receiving cylinder, in the reservoir of pressurized fluid or in a part of the pipe which is linked to it and can be formed of a separate enclosure, flanged to the corresponding component, or of a cartridge added in a volume of the

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 component provided accordingly. In special application cases, it may be advantageous, in particular with a zeolite in the form of granulate, to introduce the granulate without other conditioning, in a volume filled with the fluid under pressure, as for example in the reservoir of fluid under pressure, in a pressure chamber containing an inactive volume, not traversed by the piston, of the emitting jack and / or the receiving jack. In addition, it may be advantageous to place the agent in the line traversed by the pressurized fluid, between emitting jack and receiving jack. In particular for ease of handling, a cage can be provided in the pressurized fluid reservoir which is filled with an agent such as zeolite, which is traversed by the pressurized fluid and which can easily be replaced in the event of need. In particular application cases, an agent, for example zeolite, prepared to have a small particle size, for example less than 20 μm, and / or an agent having this particle size, can be added directly to the pressurized fluid. may be a component of the lubricant, the percentages of metal oxide possibly being reduced by the percentages of zeolite by weight.

The invention is explained in detail using FIG. 1 which is a schematic representation of a hydraulic system, an example of an embodiment of a clutch release device.

FIG. 1 schematically represents a possible embodiment of a hydraulic system as a clutch declutching device 50 comprising a transmitting cylinder 51 and a receiving cylinder 52. The clutch declutching device 50 hydraulically operates l 'clutch 54 by acting on the emitting cylinder 51 by means of an operating element 61 which may be a pedal, an actuator, for example an electric actuator, or the like. Thereby a pressure is established, by means of a mechanical transmission 60, in the emitting cylinder 51, which, by means of the pipe section 59 and the pressure limiting globe valve 71, existing as an option, and from the pipe section 58, establishes a pressure in the receiving cylinder

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 52. The receiving cylinder 52 can - as in the example shown - be arranged concentrically around the input shaft 57 of the gearbox and bear axially against a casing = not shown in detail - of the gearbox speeds and exert, via a declutching bearing, the necessary declutching force on the clutch 54 or on its declutching elements such as a Belleville washer. Other exemplary embodiments can provide a receiving cylinder 52 which operates a declutching member by means of a declutching mechanism and can be arranged outside the clutch housing, this declutching member acting axially on the mechanism. release by means of a piston housed in the cylinder of the receiving cylinder and hydraulically connected to the sending cylinder. To exert the declutching force, the receiving cylinder is attached, fixed, on the gearbox casing or on another fixed component with respect to this casing. The clutch 54, disposed on the crankshaft 56, being engaged, the input shaft of the gearbox 57 transmits the torque of the internal combustion engine 55 to a gearbox not shown in detail then to the drive wheels of a motor vehicle.

The pressurized fluid reservoir 62 serves to store the pressurized fluid. This reservoir is preferably connected to the emitting cylinder 51 when the latter is in the rest position, that is to say when no pressure is exerted on the receiving cylinder 52. In this position, the fluid under pressure may flow into the emitting cylinder due to the hydrostatic pressure difference. Maneuvering the emitter jack 51 separates the pressurized fluid reservoir 62 from the emitter jack 51 by means of a tap so that this reservoir can be provided substantially without pressure.

On the piston 51b or on the cylinder 5 I ç .. is provided a sealing surface on which seals a seal which is suitably disposed on the piston or suitably on the cylinder.

The lubricant is applied to the sliding surfaces 51a, 52a situated between the piston 51b, 52b and the cylinder 51c, 52c of the emitting and / or receiving cylinder, the piston 51b, 52b or the cylinder 51c, 52c possibly having a lining. U-shaped lip seal - not shown - which ensures mutual sealing of the cylinder and

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 piston, the lubricant forming a lubricating film between them. To explain the structure of a receiving or transmitting cylinder, let us refer to this point of view to the patent applications for references DE 199 50 082.7 or DE 199 40 024.5, the entire contents of which are included in the present request. The application of the lubricant according to the inventive ideas in the emitting actuator 51 may in particular also have the advantage of eliminating or at least reducing the squeaking noises during the operation of the operating device.

A container for a desiccant may be present in the pressurized fluid reservoir 62, in the emitting cylinder 51 and / or in the receiving cylinder 52. In designs of hydraulic systems with a sparkling filter or a pressure limiting valve 71, the agent can also be housed there, an appropriate agent lining may already represent resistance and exercise for example a throttling function. In addition, the agent can for example be provided in the form of a cartridge packed in one of the pipe sections 58, 59 between emitter jack 51 and receiver jack 52 or in the take-up pipe 63 between reservoir of pressurized fluid 62 and transmitter cylinder 51.

Particularly advantageous is the arrangement in the reservoir of the pressurized fluid 62 of the container containing the agent such as the zeolite, for desiccation of the pressurized fluid in declutching systems 50 for friction clutches. Contrary to the considerations of origin it appeared that an effective drying can be done even on the receiving cylinder 52. This can be explained by the relatively high flow rates of fluid under pressure in a clutch release system 50. While in braking systems, there is little flow of pressurized fluid between the main braking cylinder and the receiving cylinders placed under the wheels by relatively long lines, in clutch release systems 50, in relatively short lines 58, 59, as a result of the required clutch stroke of several millimeters, a

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 a fairly large amount of pressurized fluid at each clutch operation and the water which has possibly entered the receiving cylinder 52 is regularly distributed and returned to the pressurized fluid reservoir where it is absorbed by the desiccant. It is understood that to prevent other impurities from entering the hydraulic system, in particular the pressurized fluid reservoir, which can also serve as a reservoir of pressurized fluid for the braking device, in particular of lubricant residues contained in the fluid under pressure in circulation and particularly undesirable in the braking circuits, the lubricant can advantageously be in accordance with the inventive idea. Another advantage of the arrangement of the desiccant in the pressurized fluid tank is the good accessibility for maintenance work and services since it has become apparent that it may be necessary to change the agent several times. desiccation during the lifetime. In addition, the desiccant may for this purpose include a humidity indicator which allows simple monitoring of the consumption of this agent. It is advantageous that in this application, unlike its use in the primary circle, that is to say in the area of the hydraulic system under pressure, for example on the receiving cylinder 52, it is not necessary to put the agent under vacuum, which allows easier packaging and simpler handling. It is particularly advantageous that the agent can be packaged in a porous container, for example a container adapted to the geometrical characteristics of the reservoir of pressurized fluid, or a closed net.

The claims filed with the application are proposed formulations without prejudice to obtaining additional protection. The Applicant reserves the right to claim yet another combination of characteristics which has so far only appeared in the description and / or in the drawings.

References used in the subclaims draw attention to the alternative conception of the subject matter of the main claim due to the features of the subclaim

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 respective; they should not be understood as a waiver of obtaining specific, concrete protection for the combinations of characteristics of the referenced sub-claims.

Since the objects of the sub-claims may, with regard to the technique at the priority date, constitute own and independent inventions, the plaintiff reserves the right to make them the subject of independent claims or divisional applications. They may furthermore also contain their own inventions presenting a construction independent of the subjects of the independent subclaims.

The exemplary embodiments are not to be considered as a limitation of the invention. Rather, in the context of this presentation, many variants and modifications are possible, in particular variants, elements and combinations and / or materials which, for example by combining modifications of certain elements in connection with the characteristics or elements or not process described in the general description and in the embodiments as well as in the claims and contained in the drawing, can be concluded by a person skilled in the art having regard to the solution making it possible to reach the aim and lead, by characteristics which can be combined, to a new object or to new process steps or to new process sequences, also insofar as they relate to production, control and work processes.

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Claims (20)

CLAIMS 1 Hydraulic system, in particular for motor vehicles, comprising a receiving cylinder (52) consisting of at least one cylinder with a piston which can move axially therein and is sealed against it and with a fluid inlet under pressure as well as a transmitter cylinder (51) consisting of at least one cylinder with a piston which can move axially therein and is sealed against it and with an outlet for pressurized fluid, as well as a pressurized fluid hydraulically positively connecting the pressurized fluid inlet with the pressurized fluid outlet, as well as a pressurized fluid for filling the hydraulic system and possibly a pressurized fluid reservoir, characterized in that at least on a sealing surface located between one of the pistons and the corresponding cylinder acts a lubricant whose specific density is greater than the specific density of the fluid under pressure. 2. Hydraulic system, in particular for motor vehicles, comprising a receiving cylinder consisting of at least one cylinder with a piston which can move axially therein and is sealed against it and with an inlet for pressurized fluid as well as '' a transmitting cylinder consisting of at least one cylinder with a piston which can move axially therein and is sealed against it and with a pressurized fluid outlet, as well as a pressurized fluid line hydraulically positively connecting l pressurized fluid inlet with pressurized fluid outlet, as well as pressurized fluid for filling the hydraulic system and possibly a pressurized fluid reservoir, characterized in that at least on a sealing surface located between one of the pistons (51b) and the corresponding cylinder (51c,) acts a lubricant which is essentially insoluble in the fluid under pressure. 3. Hydraulic system in particular according to claim 1 and / or 2 characterized in that on the piston (51b) or on the cylinder <Desc / Clms Page number 14>  (51c) is provided a sealing surface on which seals a seal which is suitably disposed on the piston or suitably on the cylinder. 4. Hydraulic system in particular according to claim 1, 2 and / or 3 characterized in that the seal is a U-shaped lip seal. 5. Hydraulic system in particular according to one of claims 1 to 4, characterized in that the hydraulic system is a hydraulic clutch mechanism (50). 6. Hydraulic system in particular according to one of claims 1 to 5, characterized in that the receiving cylinder (52) is arranged coaxially around a shaft such as the input shaft of the gearbox (57 ) and that the seal is made in the form of a U-shaped lip seal with sealing lips pressing in a sealed manner, radially inward and radially outward, against the cylinder of the receiving cylinder. 7. Hydraulic system in particular according to one of claims 1 to 6, characterized in that the lubricant is applied to the seal. 8. Hydraulic system in particular according to one of claims 1 to 7, characterized in that the lubricant is applied to the friction surface. 9. Hydraulic system in particular according to one of claims 1 to 8, characterized in that the specific density of the lubricant is greater than 1.1 g / cm3. 10. Hydraulic system in particular according to one of claims 1 to 9, characterized in that the lubricant is a grease, preferably a mixture of greases. 11. Hydraulic system in particular according to claim 10, characterized in that the mixture of greases contains at least one siloxane. <Desc / Clms Page number 15>  12. Hydraulic system in particular according to claim 11, characterized in that the mixture of fats contains at least one polydimethylsiloxane. 13. Hydraulic system in particular according to claim 11 and / or 12, characterized in that the siloxane or the polydimethylsiloxane has a viscosity at 25 C greater than 1000 mm2 / s, preferably between 10000 mm 2 / s and 100,000 mm2 / s and being preferably preferably 30000 mm 2 / S. 14. Hydraulic system in particular according to one of claims 1 to 13, characterized in that the lubricant is formed from at least the following components - 55 to 90 percent by weight of polydimethylsiloxane according to claim 13, - 5 to 45 percent by weight of polytetrafluoroethylene PTFE powder, - 5 to 45 percent by weight of melamine cyanurate, - up to 5 percent by weight of an antioxidant, - up to 5 percent by weight of magnesium oxide. 15 Hydraulic system, in particular for motor vehicles, comprising a receiving cylinder made up of at least one cylinder with a piston which can move axially therein and is sealed against it and with an inlet for pressurized fluid as well as a transmitting cylinder consisting of at least one cylinder with a piston which can move axially therein and is sealed against it and with a pressurized fluid outlet, as well as a pressurized fluid pipe (59) hydraulically connecting positively the inlet of pressurized fluid with the outlet of pressurized fluid, as well as a pressurized fluid for filling the hydraulic system and possibly a pressurized fluid reservoir (62), characterized in that in the hydraulic system is provided at least one reservoir which is connected to the pressurized fluid and which is filled with a desiccant. 16 Hydraulic system in particular according to claim 15 characterized in that the agent is a zeolite. <Desc / Clms Page number 16>  17 Hydraulic system in particular according to claim 16 characterized in that the pores in the zeolite have a pore width of, on average, 10-1 to 10-9 m, preferably 2 x 10-1 to 6 x 10 "1 m. 18 Hydraulic system in particular according to one of claims 15 to 17, characterized in that the agent has a powder or aggregate form. 19 Hydraulic system in particular according to one of claims 15 to 18, characterized in that at least one reservoir is integrated in the reservoir of pressurized fluid. 20 Hydraulic system in particular according to one of claims 15 to 18, characterized in that at least one reservoir is integrated in an air bleed pipe or a pressurized fluid pipe between receiver cylinder and transmitter cylinder and / or between transmitter cylinder and pressurized fluid tank.