DE10134999A1 - 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

The invention relates to a hydraulic system, in particular for motor vehicles comprising a master cylinder comprising at least one housing an axially displaceable therein and sealed against the first housing Piston and a pressure medium outlet and a slave cylinder at least consisting of a housing with an axially displaceable therein, against the Housing sealed pistons and a pressure medium inlet and a Hydraulically effective connection of the pressure medium inlet and the pressure medium outlet Pressure medium line and a pressure medium for filling the hydraulic System.

Such hydraulic systems are used in particular in motor vehicles Devices for operating brakes, as steering assistance systems and as Device for actuating friction clutches, for example in the power flow between an internal combustion engine and a transmission and / or one Electric machine and a drive train used. It usually does a linear movement via a hydraulic cylinder as master cylinder from Driver or an automatically controlled actuator system depending on the  Driving situation by transmitting the in the master cylinder by means of Master cylinder piston generated pressure in the pressure medium or Line filled with pressure medium connecting pressure and slave cylinders transfer the slave cylinder, which then has the desired effect, for example, the actuation of the brakes, a clutch process and / or the like, by a linear movement of the pressure induced Slave cylinder piston opposite the fixed one Slave cylinder housing. Here, the piston against the Slave cylinder housing to be sealed by means of a seal. DE 199 46 593 shows an example with a concentric around a shaft arranged slave cylinder with a ring seal.

The hydraulic system can improve the sliding properties of the Piston be greased in the housing, that is, on a contact surface between the piston and the housing or one in between The seal, like the lip seal, can be a lubricant to reduce friction be provided between the axially moving parts. such Lubricants are usually greases or mixtures with a lubricating content that have a not insignificant solubility in the pressure medium and by the action of the pressure medium can be released from the contact surface and thus a deteriorated friction behavior of the piston over the service life approximately this sealing rings against the housing and the Ge draw housing. According to the state of the art, composites are in one  set containing a so-called base oil based on polyglycol. Such and optionally other components have a considerable solubility in Brake fluid and tend to contaminate it. So these are Fabrics partially saponified or hydrolyzed under the influence of water. The Components or reaction products of these can be in the hydraulic system For example, float up to the pressure medium reservoir and undesirable Effects such as changes in the viscosity of the pressure medium, blockages in the line gen or similar.

Another disadvantage in hydraulic systems is the presence of water, which, for example, promotes the saponification of the lubricants, but especially the Boiling point of the pressure medium such as DOT3, DOT4 lowers and at for example in hydraulic braking devices when Brake heat safety-related failures of the brake system through formation of Steam bubbles can result in the hydraulic route. Another A disadvantage arises in particular in hydraulic clutch release systems in clutch release systems with automatic control by means of a Actuator. Here, processes such as determining the gripping point, a mo ment tracking to control the transferable by means of the clutch Moments with fast control cycles necessary, their speed and precision depend among other things on the viscosity of the pressure medium. The viscosity will thereby by the water content and - as already mentioned - given if caused by dissolved, emulsified or suspended lubricant components  deteriorated, so that the clutch in particular the automated, at for example, one that controls the master cylinder by means of an electric motor Clutch is controlled insufficiently.

The object of the invention is therefore a hydraulic system in one To propose further training of the state of the art in a simple manner and is inexpensive to manufacture, has a high ease of use and due to low actuation forces, especially over the life of the hydraulic system. Furthermore, the operational safety of the hydraulic system to be guaranteed in particular over the service life. In particular, the purity, that is, the absence of water and the content of Foreign substances such as the presence of lubricant and its Components in the pressure medium are avoided or at least reduced.

The task is accomplished in particular by means of a hydraulic system for power vehicles solved that a slave cylinder at least consisting of one Housing with an axially displaceable therein and sealed against it Piston and a pressure medium inlet and a master cylinder at least consisting of a housing with an axially displaceable therein, against the sealed piston and a pressure medium outlet as well as a Connect the hydraulic fluid inlet to the hydraulic fluid outlet effectively the pressure medium line and a pressure medium for filling the hydrauli rule system and optionally a pressure medium reservoir, wherein  at least on a sealing surface between the piston and the corresponding housing, sealed for example by means of a seal such as a ring seal Lubricant is effective, its specific density higher than the specific one Density of the pressure medium is. Furthermore, the task can be done with a lubricant be solved, which is particularly difficult to dissolve in the lubricant and also with large temperature fluctuations, for example when used in the engine compartment or in a clutch bell of the drive train, stick to the sealing surface remains, advantageously over the life of the hydraulic system or the vehicle with this hydraulic system. Through the The invention is therefore provided on the one hand, the lubricant as long as possible on the Adhere to the contact surface and not under certain conditions avoidable, partial detachment, at least in the Nehmerzy pressure chamber Hold linder and / or master cylinder and float in statically higher volumes to be avoided, for example in a pressure medium reservoir the.

The hydraulic system can brake according to the inventive idea device, power steering device or a hydraulic clutch device be, in this application in particular the use of the lubricant in a slave cylinder arranged around a transmission input shaft is advantageous can be, for example, because of the significant temperature fluctuations in the clutch bell the negligible solubility of the lubricant particularly advantageous in permanent immobilization of the lubricant  the contact surface affects. Furthermore, the property of over the density of the pressure medium, however, detachable amounts of lubricant or lubricant components not in the direction of the usually hydrosta The pressure medium reservoirs and / or the master cylinder are arranged at a higher table ders transported but remain essentially in the pressure room of the Neh merzylinders. It is understood that applications of the lubricant also for the Master cylinders can be beneficial.

The lubricant can be applied by means of devices known per se, such as metering devices, grease guns or by hand to the seal and / or the contact surfaces. With a value greater than 1.1 g / cm ^{3, the} specific density of the lubricant is, according to the invention, greater than the specific density of the pressure medium, for example DOT 4. It is understood that when using other pressure means such as DOT 3, the specific density of the lubricant is corresponding is adjusted.

The formation of the lubricant as a mixture can be particularly advantageous, in that substances with different properties form the lubricant; the lubricant can also be formed from components which are characterized in particular by good resistance and can be characterized by extremely poor solubility in pressure medium, but a specific one Have density less than that of pressure medium. Components which have a higher density than the printing medium can be admixed with these, whereby a mixture with a very poor solubility and higher density can be set as the printing medium. A component according to the inventive concept can be a siloxane, preferably polydimethylsiloxane. To characterize the outstanding properties of the polymethylsiloxane with respect to poor solubility and the specific density, its viscosity can be used, which at 25 ° C at least greater than 1000 mm ² / s, preferably between 10000 mm ² / s and 100000 mm ² / s and in is particularly preferably 30000 mm ² / s. Other components can increase the sliding properties, for example PTFE powder, graphite, molybdenum sulfide and the like. The addition of antioxidants can prevent the lubricant from aging quickly. Coefficients of friction that, for example, minimize sticking of the parts when movement begins and components that improve the thermal properties can also be part of the lubricant. Melamine cyanurate has proven to be particularly advantageous here. Furthermore, metal oxides, for example magnesium oxide, calcium oxide, zirconium oxide and / or the like, can be introduced into the lubricant mixture, in particular as antioxidants, these advantageously having a small particle size in the range from 1 to 20 μm.

A mixture of is particularly advantageous

• 55 to 90 percent by weight of polydimethylsiloxane,
• - 5 to 45 weight percent PTFE powder,
• 5 to 45% by weight of melamine cyanurate,  
• - up to 5% by weight of antioxidants,
• - up to 5 percent by weight magnesium oxide

proved. These mixtures are from US 5 874 388 for use in tro known environment. Experiments have shown that this mixture in hydraulic systems even under the influence of pressure medium as extremely durable and well adhering as well as with a negligible Solubility lubricant mixture equipped can be used. Through the Use of a - as described above - polydimethylsiloxane can wei the resistance of the lubricant mixture to existing in the pressure medium denes water can be increased because this due to the higher viscosity less attacked and hydrolyzed by water than currently fats used and, if appropriate, their additives. Furthermore, the one position of the lubricant with polydimethylsiloxane with regard to the viscosity improved properties on a conventionally used lubricant lower density than printing medium and comparatively high solubility in the sem advantageously possible, so that already existing production facilities for the components of the hydraulic system in particular the metering device directions can still be used. The properties of the glide means are advantageously also compared to the conventionally used Components of the hydraulic system, for example in relation to plastics, Metals and sealing materials, for example EPDM, neutral, so that the usually use this system with the original lubricant  materials even when using the lubricant according to the invention can be taken.

To achieve the object, it has furthermore proven to be advantageous, with or without the use of the lubricant according to the invention, to minimize the water content of the pressure medium, since the pressure medium suffers quality losses as the water content increases, for example a decrease in the boiling point and the formation of a higher viscosity. According to the inventive concept, the volume of the hydraulic system carrying the pressure medium is connected to a reservoir or a chamber which is filled with a dehydrating agent. 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 can be particularly advantageous because of its otherwise chemically neutral behavior. The water is absorbed in the pores of the zeolite and removed from the pressure medium, the pores being coordinated with regard to the absorption of water. Pore sizes of on average 10 ^-10 to 10 ^-9 m, preferably 2 × 10 ^-10 to 6 × 10 ^-10 m have proven to be particularly advantageous. The shape of the zeolite can be in powder form or preferably in the form of granules.

According to the invention, the reservoir with the dehydrating agent can be on everyone Place, for example in the master cylinder, in the slave cylinder, in the pressure medium reserve  voir or in a line part connecting these and can be provided from a separate housing flanged to the corresponding component or from a cartridge that is in a correspondingly provided volume of Component is introduced, be formed. In special applications it can be particularly advantageous with zeolite in granular form, the granulate without further packaging in a volume filled with pressure medium such as, for example se into the pressure medium reservoir, a pressure chamber with one not from the piston introduce the swept blank volume of the master and / or slave cylinder gen. Can also be advantageous, the agent in the flow through line between to place the master cylinder and slave cylinder. Especially because of the A medium filled with agents such as zeolite can be easily handled for printing medium permeable cage can be provided in the pressure medium reservoir, which in the loading can easily be replaced if necessary. In special applications a suitably confined to small particle size, for example less than 20 µm tioned agent, such as zeolite, added directly to the printing medium and / or agent with this particle size can be part of the lubricant tels, where appropriate, the metal oxide proportions by weight percent proportion of the zeolite can be reduced.

The invention is explained in more detail with reference to FIG. 1, which shows a schematic illustration of a hydraulic system using an exemplary embodiment of a clutch release device.

Fig. 1 shows a possible embodiment in a schematic representation of a hydraulic system as a clutch release device 50 with a master cylinder 51 and a slave cylinder 52. The clutch release system 50 actuates the clutch 54 hydraulically by acting on the master cylinder 51 by means of an actuating element 61 , which can be a foot pedal, an actuator, for example an electric actuator, or the like. As a result, pressure is built up in the master cylinder 51 by means of a mechanical transmission 60 , which builds up a pressure in the slave cylinder 52 via the line line 59 , via the optionally available pressure relief valve 71 and the power line 58 . The slave cylinder 52 can - as in the example shown - be arranged concentrically around the transmission input shaft 57 and be axially supported on a transmission housing (not shown in more detail) and apply the necessary release force via a release bearing on the clutch 54 or on its release elements such as a plate spring , Further exemplary embodiments can provide a slave cylinder 52 , which actuates a releaser via a disengagement mechanism and can be arranged outside the clutch bell, said axially acting on the disengagement mechanism by means of a piston, which is accommodated in the slave cylinder housing and is hydraulically connected to the master cylinder. To apply the disengagement force, the slave cylinder is attached to the transmission housing or to another component fixed to the housing. When the clutch 54, which is arranged on the crankshaft 56 , is closed, the transmission input shaft 57 transmits the torque of the internal combustion engine 55 to a transmission (not shown in more detail) and then to the drive wheels of a motor vehicle.

The pressure medium reservoir 62 serves to store the pressure medium. This is preferably connected to the master cylinder 51 when it is in the rest position, that is, when no pressure is exerted on the slave cylinder 52 . In this position, the pressure medium can flow into the master cylinder by means of the hydrostatic differential pressure. When the Geberzy cylinder 51 is actuated, the pressure medium reservoir 62 is separated from the master cylinder 51 via a valve, so that it can be designed to be essentially depressurized.

The lubricant is applied to the sliding surfaces 51 a, 52 a between the piston 51 b, 52 b and the housing 51 c, 52 c of the master and / or slave cylinder, the piston 51 b, 52 b or the housing 51 c , 52 c can have a - not shown - U-ring seal, which seals the housing and piston against each other, the lubricant forming a lubricating film between them. To clarify the structure of a slave or master cylinder, reference is made in this connection to the patent applications with the file number DE 199 50 082.7 or DE 199 40 024.5, which are hereby fully incorporated into the present application. The use of lubricants according to the inventive concept in the Geberzy cylinder 51 can in particular also have the advantage that squeaking noises are eliminated or at least reduced when the actuating device is actuated.

A container for a dewatering agent can be arranged in the pressure medium reservoir 62 , in the master cylinder 51 and / or in the slave cylinder 52 . In versions of the hydraulic system with a prickle filter or pressure relief valve 71 , the agent can also be accommodated in this, the corresponding pack of the agent can already represent a pressure resistance and can, for example, perform a throttle function. Furthermore, the agent may be for example in the form of a packed cartridge in one of the lead portions 58, 59 between master cylinder 51 and slave cylinder 52 or in the tracking line 63 between the pressure medium reservoir 62 and master cylinder 51 are provided.

The arrangement of the reservoir with the agent such as zeolite for dewatering the pressure medium in release systems 50 for friction clutches in the pressure medium reservoir 62 is particularly advantageous. Contrary to original considerations, it has been shown that effective drainage can take place even on the slave cylinder 52 . This can be explained by the comparatively high pressure medium throughputs in a clutch release system 50 . While in brake systems between the master cylinder and slave cylinders on the wheels only a little pressure medium is shifted over comparatively long lines, in clutch release systems 50 in relatively short lines 58 , 59 a larger amount of pressure medium is shifted with each clutch actuation due to the necessary clutch stroke of several millimeters and so on any water entering the slave cylinder 52 is evenly distributed and rinsed to the pressure medium reservoir, where it is absorbed by the agent. It is understood that to prevent the entry of further impurities in the hydraulic system, in particular the pressure medium reservoir, which can also serve as a pressure medium reservoir for the braking device, the lubricant according to the inventive concept be particularly advantageous due to undesirable lubricant residues contained in the circulating pressure medium, particularly in the brake circuit can. Another advantage of the arrangement of the agent in the pressure medium reservoir is the good accessibility for maintenance and service work, since it has been shown that a multiple replacement of the agent over the life span may be necessary. Furthermore, the agent can be provided with a moisture indicator for this purpose, which enables easy monitoring of the exhaustion of the agent. Advantageously, in contrast to use in the primary circuit, that is to say in the pressurized area of the hydraulic system, for example on the slave cylinder 52 , the agent does not need to be evacuated in this application, which enables easier assembly and easier handling. The assembly of the agent in a porous container, for example a container adapted to the geometry of the pressure medium reservoir or a closed network, can be particularly advantageous.

The claims submitted with the application are drafted strikes without prejudice for obtaining further patent protection. The The applicant reserves the right to do so, so far only in the description and / or to claim the combination of features disclosed.

Relationships used in subclaims point to further details formation of the subject of the main claim by the characteristics of each due subclaim; they are not a waiver of attainment an independent, objective protection for the combinations of features to understand the related subclaims.  

Since the subjects of the subclaims with regard to the prior art reserves the right to make its own and independent inventions on the priority day Applicant before becoming the subject of independent claims or part to make statements of compliance. You can also continue to invent independently containing one of the items in the previous sub-section have independent design.

The exemplary embodiments are not to be understood as a limitation of the invention hen. Rather, numerous Ab are within the scope of the present disclosure Changes and modifications possible, especially such variants, el elements and combinations and / or materials, for example by com combination or modification of individuals in connection with those in general NEN description and embodiments as well as the claims NEN and features or elements or ver contained in the drawings Driving steps for the specialist with a view to solving the task are removable and can be combined to create a new contrast state or lead to new process steps or process step sequences, also insofar as they relate to manufacturing, testing and working processes.

Claims (21)

1. Hydraulic system, in particular for motor vehicles, comprising a slave cylinder at least consisting of a housing with an axially displaceable piston sealed therein and a pressure medium inlet, and a master cylinder at least consisting of a housing with an axially displaceable piston sealed against it and a pressure medium outlet as well as a pressure medium line hydraulically connecting the pressure medium inlet with the pressure medium outlet and a pressure medium for filling the hydraulic system and optionally a pressure medium reservoir, characterized in that a lubricant is effective at least on a sealing surface between one of the pistons and the corresponding housing, the specific of which Density is higher than the specific density of the pressure medium. 2. Hydraulic. System especially for motor vehicles comprising a Slave cylinder at least consisting of a housing with one in it axially displaceable and sealed against this piston and one  At least pressure medium inlet and a master cylinder from a housing with an axially displaceable therein, against this sealed piston and a pressure medium outlet as well as a Hydraulically effective connection of the pressure medium inlet with the pressure medium outlet the pressure medium line and a pressure medium for filling the hydraulic system and possibly a pressure medium reservoir, characterized in that at least on a sealing surface between one of the pistons and the corresponding housing a lubricant sam, which is essentially insoluble in the printing medium. 3. Hydraulic system in particular according to claim 1 and / or 2, characterized characterized in that the piston or the housing has a sealing surface is provided, on which a seal seals, corresponding to the piston or is arranged accordingly on the housing. 4. Hydraulic system in particular according to claim 1, 2 and / or 3, because characterized in that the seal is a U-ring seal. 5. Hydraulic system in particular according to one of claims 1 to 4, characterized in that the hydraulic system is a hydraulic Coupling device is.   6. Hydraulic system in particular according to one of claims 1 to 5, characterized in that the slave cylinder coaxially around a shaft is arranged as the transmission input shaft and the seal as a grooved ring Seal with radially inwards and radially outwards on the slave cylinder Housing sealing lips is designed. 7. Hydraulic system in particular according to one of claims 1 to 6, characterized in that the lubricant is applied to the seal becomes. 8. Hydraulic system in particular according to one of claims 1 to 7, characterized in that the lubricant is applied to the sliding surface will. 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 / cm ³ . 10. Hydraulic system in particular according to one of claims 1 to 9, characterized in that the lubricant is a fat, preferably a Fat mixture is.   11. Hydraulic system in particular according to claim 10, characterized records that the fat mixture contains at least one siloxane. 12. Hydraulic system in particular according to claim 11, characterized records that the fat mixture contains at least polydimethylsiloxane. 13. Hydraulic system in particular according to claim 11 and / or 12, characterized in that the siloxane or polydimethylsi loxane has a viscosity at 25 ° C greater than 1000 mm ² / s, preferably between 10000 mm ² / s and 100000 mm ² / s and in a particularly preferred manner has 30,000 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 weight percent PTFE powder,
• 5 to 45% by weight of melamine cyanurate,
• - up to 5% by weight of antioxidants,
• - up to 5 percent by weight magnesium oxide.

15. Hydraulic system, especially for motor vehicles, comprising a Slave cylinder at least consisting of a housing with one in it  axially displaceable and sealed against this piston and one Pressure medium inlet and a master cylinder at least consisting of a housing with an axially displaceable therein, abge against this sealed piston and a pressure medium outlet as well as the pressure Hydraulically connecting the tel inlet with the pressure medium outlet Pressure medium line and a pressure medium for filling the hydrauli system and possibly a pressure medium reservoir, thereby characterized in that in the hydraulic system at least one with the Pressure medium-connected reservoir is provided, which with a dehydrating agent is filled. 16. Hydraulic system in particular according to claim 15, characterized records that the agent is a zeolite. 17. Hydraulic system in particular according to claim 16, characterized in that the pores present in the zeolite have a pore size of on average 10 ^-10 to 10 ^-9 m, preferably 2 × 10 ^-10 to 6 × 10 ^-10 m. 18. Hydraulic system in particular according to one of claims 15 to 17, characterized in that the agent is in powder or granule form has.   19. Hydraulic system in particular according to one of claims 15 to 18, characterized in that at least one reservoir in the pressure medium reservoir is integrated. 20. Hydraulic system in particular according to one of claims 15 to 18, characterized in that the at least one reservoir in a Ent ventilation line or pressure line between slave cylinder and master cylinder linder and / or integrated between the master cylinder and pressure medium reservoir is. 21. Invention characterized by an open in the application documents beard characteristic.