Description

[0001 ] The invention relates to a sealing system for a compressor of a gas according to the preamble of claim 1 , and to a compressor according to claim 15 comprising same.

[0002] Internal combustion engines can be replaced by alternative drives. In this case, electrical drive concepts play a central role. The fact that they produce no emissions during use can reduce environmental pollution and immission in highly populated areas. Taking into account the costs and emissions associated with the production of a battery as a storage medium for electrical energy, an overall assessment may not prove to be substantially better than that of a drive concept based on an internal combustion engine. Furthermore, a current disadvantage of batteries is that as yet only a few viable solutions are available for environmentally compatible disposal/recycling of defective or exhausted batteries.

[0003] There is therefore a need for further alternative storage and drive technologies. The use of hydrogen as an energy carrier is one of the most promising concepts.

[0004] Hydrogen can be used, for example, as fuel for operating a hydrogen combustion engine (hydrogen engine), which is operated in the manner of a conventional internal combustion engine. Since only a small amount of carbon, which is introduced by lubricants, for example, occurs during this combustion, such hydrogen engines are vastly superior to conventional internal combustion engines with respect to the emissions of carbonaceous pollutants. Nevertheless, non-negligible amounts of nitrogen oxides are emitted. Another disadvantage of such solutions is that the complex structure of internal combustion engines is maintained and, moreover, it is more complex to store the fuel.

[0005] In contrast, developments based on a drive system having a hydrogenoxygen fuel cell and an electric motor which is supplied with energy by the fuel cell are more promising. Of course, fuels other than hydrogen, for example methanol, butane, natural gas, or the like, can also be used.

[0006] In this case, the fuel (hereinafter referred to as gas) has to be stored in a tank with a comparatively high pressure. A tank station for filling the tank must have the technical means for compressing the gas.

[0007] For this purpose, the prior art knows solutions with a pressure intensifier or piston compressor. These solutions have a reciprocating piston surface and a likewise reciprocating sealing surface surrounding it. The latter is, for example, a peripheral surface of a piston or of a piston rod. The sealing surface interacts with seals via which a gas chamber is separated from a pressure build-up side. In the case of the pressure intensifier, the pressure is built up with a hydraulic pressure medium and, in the case of a compressor, for example, via a drive motor, in particular an electric motor. Compressors use unlubricated seals in order to avoid contamination of the gas with lubricant.

[0008] Compared to dry, unlubricated seals, the use of lubricated seals could extend the service life of the sealing system.

[0009] In this case, a gas seal of the sealing system seals the gas chamber at the sealing surface and a liquid or hydraulic seal of the sealing system spaced apart therefrom seals the lubricant chamber at the sealing surface. In the current pressure intensifier solutions, liquid and gas seals are arranged at a spacing that is greater than the stroke. Ambient air and an undefined amount of lubricant are located therebetween. [0010] The problem here is to ensure the process reliability of this sealing system during continuous operation. For example, the repeated reciprocating movement can result in the lubricant between the seals being contaminated with abraded material. Damage to the seals and a departure from the specifications of the lubricant or lubricant film may result. As the tightness of the gas seal decreases, there is then a risk of the lubricant being displaced into the gas chamber. If the gas is contaminated, it can impairthe usage, which is why lubricated gas seals are not used in the compression of hydrogen.

[0011 ] In contrast, the aim of invention is to provide a sealing system for a compressor of a gas, in particular hydrogen, which is lubricated and the lubricant film of which can be formed with high process reliability. Furthermore, the aim is to provide a compressor comprising a lubricated sealing system, the lubricant film of which can be formed with higher process reliability.

[0012] The first aim is achieved by a sealing system having the features of claim 1 , and the other aim is achieved by a compressor having the features of claim 15.

[0013] Advantageous developments of the sealing system are described in claims 2 to 14.

[0014] A sealing system is provided for a compressor which can compress a gas, in particular hydrogen, with a reciprocating stroke. The compressor is, for example, a compressor or a pressure intensifier. The sealing system is in particular a piston rod sealing system of the pressure intensifier or a piston sealing system of an accumulator or piston compressor. The sealing system is lubricated to improve tightness, reduce wear, and thus increase its service life. It has at least two sealing elements spaced apart in the stroke direction, each of which is in contact with a mating surface, in particular the piston rod or piston, which reciprocates with the stroke. In particular, one or more sealing edges of the at least two sealing elements are in contact. On this side of a first of the two sealing elements, hereinafter referred to as gas seal, a gas chamber, in which the gas can be compressed by means of a change in volume, is delimited by the mating surface in sections. Between the two sealing elements, an intermediate chamber is delimited by the mating surface, and beyond a second of the two sealing elements, hereinafter lubricant or grease seal, a pressure medium chamber or lubricant chamber is delimited by said mating surface in sections. A lubricant film, which can be supplied by the lubricant chamber and is present on the first sealing element, can be formed on at least one mating surface section arranged in the intermediate space, in particular by the action of the at least two sealing elements. This ensures the aforementioned lubrication of the sealing elements. According to the invention, the sealing system has at least one means via which a quantity, in particular a thickness, and/or a quality of the lubricant film, in particular a phase composition and/or an age of the lubricant film, can be controlled.

[0015] Due to the control via the at least one means, the lubricant film, which is present on the gas seal, can be formed with higher process reliability in terms of its quantity and/or quality, and the sealing system can be lubricated with high reproducibility. Compared with dry sealing systems, but also with respect to sealing systems with uncontrolled lubricant films, wear can thus be reduced and service life can be increased, which also reduces maintenance costs. The advantage over conventional lubricated sealing systems is that the control of the lubricant film brings more control over the amount of lubricant to be scraped off the gas seal. Thus, the quantity of lubricant moved into the gas chamber during a compression stroke on the mating surface can be specifically minimized to the point that lubricant is only located in the microscopic surface structure of the mating surface. Contamination of the gas can thus be minimized. A further effect is that the more reliable lubrication ensures that the use of ionic liquids can be avoided.

[0016] In one development, the sealing system is adapted in such a way, in particular by an embodiment of the means, a selection, dimensioning and pretensioning of the sealing elements, a roughness of the mating surface and/or of the lubricant used, including the properties thereof, or the like, that, on the gas chamber side, the lubricant is deposited only in the roughnesses of the mating surface there and/or that a projection of the lubricant film beyond the roughness can be scraped off the gas seal during the stroke, in particular the compression stroke (scraper function). In this way, the quantity or thickness of the lubricant film in both stroke directions is always dimensioned such that the gas seal and the mating surface are sufficiently lubricated, and that, in addition, a quantity of lubricant entrained into the gas chamber, and thus also a potential contamination of the gas, is minimal.

[0017] In order to reduce the risk of the entrainment of lubricant vapor into the gas, the lubricant used in the sealing system preferably has low volatility. Examples include synthetic oils or less harmful liquids, for example water.

[0018] In order to better control the lubricant film thickness in the intermediate chamber, the lubricant used in the sealing system preferably has a low viscosity index.

[0019] In one development, the gas seal is, with more than two sealing edges, in contact with the mating surface to improve the scraping function.

[0020] Preferably, the means has at least one control device via which the quantity and/or quality of the lubricant film can be controlled.

[0021 ] In one development, the control device has a control means via which a lubricant pressure can be controlled or regulated to a value slightly below a gas pressure. In this way, a reduced lubricating film thickness can be achieved. This development preferably relates to the sealing system of a piston rod seal.

[0022] A lubricant source is formed either by a pressure medium of the compressor or separately therefrom. In particular in the case of the pressure intensifier as a compressor, the lubricant is preferably a pressure medium other than that used. A lubricant circuit and pressure medium or hydraulic medium circuit are thus also separated. This enables the costs for providing the pressure medium to be reduced.

[0023] In one development, a pressure of the lubricant, in particular in the intermediate chamber and/or lubricant chamber, can be controlled or regulated via the control device, so that pressure equilibrium with the gas chamber is achieved or can be achieved. The pressure of the lubricant may be used to dynamically control the thickness of the lubricant film.

[0024] In one development, the control device is currentless or it is operated without current. This is a great advantage, in particular when compressing highly flammable gases, such as, for example, the hydrogen mentioned at the outset. In this case, the control device can be completely currentless or is currentless at least in a safety-relevant region with respect to the gas chamber.

[0025] In one development, the control device comprises at least one hydraulic means or hydraulic and pneumatic means which enables, in particular, a reliable currentless operation of the control device.

[0026] In a preferred development, the control device has at least one lubricant flow path, which has a controllable flow cross section and which extends from the intermediate chamber towards a lubricant sink or a lubricant reservoir. In particular, the flow cross section can be controlled. It is thus possible to allow the contents of the intermediate chamber, and thus the lubricant film there, to flow off in a controlled manner. As a result, for example with a next decompression stroke, the lubricant film can be discharged in a controlled manner and subsequently renewed, which further increases the process reliability and reproducibility of the lubrication of the gas seal. [0027] In one development, the lubricant film that has flowed off can be provided to a downstream measuring and/or analysis device of the sealing system or of such an external device. Preferably, said device performs an analysis of a composition, an abraded material content, a phase composition and/or an aging of the lubricant or the like. Depending on the result, measures, in particular maintenance measures, lubricant exchange or repairs or the like, can be planned.

[0028] The controllable flow cross section is advantageously limited by an actuatable valve body, in particular that of a switching, directional or check valve.

[0029] In one development, in order to control the lubricant film, the valve body can be actuated as a function of a stroke position, a stroke direction, a stroke speed and/or a pressure in the gas chamber or lubricant chamber. Thus, the lubricant film control can be coupled to the cyclical course of the reciprocating movement of the compressor or its stroke and thus takes place substantially continuously or at least periodically.

[0030] In particular, in order to realize the currentless configuration of the control device, the valve body is designed in one development to be hydraulically or pneumatically or mechanically actuatable.

[0031 ] For hydraulic or pneumatic actuation, the valve body preferably has a control surface, which is effective when the valve body is in a closed position. In one variant, said control surface is fluidically connected to the gas chamber so that the pressure of the gas controls the flow cross section of the lubricant flow path. In the opposite direction, i.e. , in the opening direction of the flow cross section of the lubricant flow path, the valve body is preferably acted upon by the pressure in the intermediate chamber. [0032] In a preferred development, the gas in the gas chamber is a direct or indirect pressure medium source for actuating the valve body. Since said gas is already subject to a cyclical pressure fluctuation, which is coupled to the stroke and the stroke direction, the actuation of the valve body and thus the control of the lubricant film can thus take place in a simple manner.

[0033] For this purpose, in one development, the sealing system has at least one control flow path via which the gas chamber can be or is fluidically connected to the control surface of the at least one valve body, which control surface has in particular a closing effect. The pressure in the gas chamber and thus also the pressure, which is present on the control surface and which has in particular a closing effect, increases with the compressor stroke. If the pressure drops off, for example in the case of decompression, the lubricant path can be controlled by the pressure in the intermediate chamber and the intermediate chamber, including the lubricant film there, can be drained.

[0034] In order to further improve the control of the lubricant film, in one development, the intermediate chamber is divided by at least a third sealing element. This is preferably structurally identical to the second sealing element. Thus, starting from the lubricant chamber towards the gas seal, the lubricant film thickness can be reduced in stages and can thus be better controlled.

[0035] In one development, in order to protect at least one of the sealing elements - at least the one with the potentially greatest pressure difference - said sealing element is pressure-compensated. In particular, this is the gas seal on which, in the case of an uncompensated embodiment, on the one hand the high gas pressure would be present, and, on the other hand, the potentially significantly lower lubricant pressure.

[0036] In one development, at least one of the sealing elements, preferably the previously mentioned sealing element with the greatest pressure difference, is penetrated or bypassed by a bypass flow path. As a result, the last-mentioned pressure equalization can take place. Depending on the requirement, the construction can be selected to be “penetrated” or “bypassed”. The bypass solution is preferred.

[0037] In order to prevent lubricant from flowing in an undesirable direction via the bypass flow path — which in the case of the gas seal, would mean from the intermediate chamber into the gas chamber and the undesirable contamination of the gas and, in the case of the lubricant seal, would mean from the lubricant chamber into the intermediate chamber and the uncontrolled thickening of the lubricant film — at least one of the bypass flow paths comprises, in one development, a means via which it can be controlled in the direction from the gas chamber to the intermediate chamber or from the intermediate chamber to the lubricant chamber and can be blocked or is blocked in the opposite, undesirable flow direction. For this purpose, a check valve device is preferably provided in the bypass flow path.

[0038] To protect against particles entering towards the first or second sealing element, a sealing element designed as a scraper is arranged upstream of at least one of the two sealing elements. The scraper of the gas seal is arranged upstream on the gas chamber side, that of the lubricant seal is arranged upstream on the lubricant chamber side.

[0039] In one development, if at least one scraper is provided and the bypass flow path is configured to “bypass”, said bypass flow path comprises at least one branch, which opens into a cavity between the scraper and the first sealing element or between scrapers. The at least one scraper is thus also pressure- compensated. Embodiments with a scraper penetrated by a bypass flow path are of course also possible.

[0040] In one development, a detection device for detecting lubricant leakage, in particular when in use as a piston rod sealing system, is provided. [0041 ] Particularly good control of the lubricant film is possible when, in one development, the mating surface extends in the direction of gravity and, with respect to gravity, the gas chamber is arranged at the top and the lubricant chamber is arranged at the bottom.

[0042] The control of the lubricant film is also supported by one development in which a peripheral or lateral surface of the intermediate chamber opposite the mating surface tapers conically or in a funnel shape at least in sections. The peripheral or lateral surface preferably tapers in the stroke direction from the first to the second or third sealing element, or in the direction of gravity,

[0043] A connection of the above-mentioned detection device for detecting lubricant leakage preferably opens into the tapered peripheral or lateral surface. The function of the sealing system can thus be reliably monitored.

[0044] In one development, the sealing system has a carrier module, in particular in sleeve or bushing form, in which at least the sealing elements are received and, in the case of a corresponding development, the scraper(s) are accommodated and/or the bypass flow path(s) are formed

[0045] A particular advantage of the proposed sealing system is that, in particular when used in a compressor configured as a supercharge, it is scalable over a very wide range.

[0046] A compressor according to the invention has a volume-variable gas chamber for compressing the gas by means of a piston or a piston rod. Structural forms can include pressure intensifiers or compressors or the like. A lubricated sealing system configured according to at least one aspect of the preceding description is also provided. The mating surface of the sealing system is formed by an outer lateral surface of the piston or the piston rod. [0047] The invention relates to a lubricated sealing system for a compressor having a reciprocating piston or piston rod, which system has at least two sealing elements which are spaced apart in the stroke direction and are in contact with a mating surface which reciprocates in accordance with the stroke. A first of the sealing elements delimits a volume-variable gas chamber and the second delimits a lubricant chamber, in each case in sections. The sealing system also has at least one means by means of which a lubricant film or grease film between the two sealing elements can be influenced or controlled in such a way that the lubrication of the sealing surfaces is ensured and an entrainment of the lubricant or grease into the gas chamber is prevented in such a way that contamination is zero or within a specification limit.

[0048] The invention also relates to a compressor comprising the sealing system.

[0049] An exemplary embodiment of a sealing system according to the invention is explained in more detail below in drawings. The drawings show

Figure 1 a sealing system according to a first exemplary embodiment in a longitudinal section,

Figure 2 a sealing system according to a second exemplary embodiment in a longitudinal section,

Figure 3 a compressor with sealing elements of a sealing system according to a third exemplary embodiment in a longitudinal section, and

Figure 4 the compressor according to Figure 3 with means for controlling a lubricant film of the sealing system.

[0050] A sealing system according to the invention has the task of reliably sealing a volume-variable chamber in which the gas is compressed during the compression of a gas or supercritical steam, referred to hereinafter as gas. By lubricating sealing elements, the friction between the sealing partners is minimized and the service life is also increased, even at maximum stroke speed.

[0051 ] According to Figure 1 , a first exemplary embodiment of a sealing system 1 has a mating surface 2 which can be moved back and forth in accordance with a stroke (double arrow) and two sealing elements 4, 6 arranged at a distance in the stroke direction. A first sealing element 4, together with the mating surface 2, delimits a gas chamber 8, a second sealing element 6 delimits a lubricant chamber 10, in each case in sections. An intermediate chamber 12 is arranged between the sealing elements 4, 6. The lubricant chamber 10 is filled with lubricant or grease, the gas chamber 8 is filled with the gas to be compressed, in particular hydrogen.

[0052] The sealing elements 4, 6 are in each case pressure-compensated with respect to their front and rear sides by means of a bypass flow path 14, 16. A check valve 18 is arranged in each bypass flow path 14, 16 and ensures, in the region of the gas seal 4, that no lubricant passes from the intermediate chamber 12 into the gas chamber 8 while bypassing the gas seal 4. Similarly, the check valve 18 in the region of the lubricant seal 6 prevents lubricant from entering the intermediate chamber 12 from the lubricant chamber 10 while bypassing the lubricant seal 6.

[0053] Lubricant is conveyed from the lubricant chamber 10 under the lubricant seal 6 into the intermediate chamber 12 by a stroke of the mating surface 2 to the left in Figure 1 , which is, for example, a peripheral surface of a piston rod of a pressure intensifier or a piston of a compressor. A lubricant film 20 results on the mating surface 2 in the intermediate chamber 12. In the same stroke, the gas seal 4 scrapes off the lubricant film 20 present thereupon, so that lubricant 20' or grease only remains in the gas chamber 8 in the microscopic depressions of the surface structure of the mating surface 2. [0054] If the mating surface 2 moves in the opposite direction, that is to say to the right in Figure 2, the lubricant present on the mating surface 2 prevents the gas seal 4 from penetrating the surface structure of the mating surface 2. Friction and wear are thus minimal, while the sealing function of the gas seal

4 is maintained.

[0055] The lubricant seal 6 has at least one sealing lip, which is positioned at an obtuse angle to the mating surface 2, so that, during a return stroke of the mating surface 2, the lubricant film is allowed to pass counter to the compression stroke. In this way, a pumping-back effect is enabled and the lubricant film can be renewed cyclically.

[0056] Figure 2 shows a second exemplary embodiment of a sealing system 1 , wherein only the deviations from the first embodiment will be discussed. Consistent components have the same reference signs as in Figure 1. In a departure from the first exemplary embodiment, the sealing system 1 comprises a third sealing element 22, which is structurally identical to the second sealing element 16 and represents a further lubricant seal. Contrary to the first exemplary embodiment, the gas seal 5 is designed with several sealing edges to improve the scraping function. Connected upstream of the gas seal

5 and the lubricant seal 6, which is on the right in Figure 2, is in each case a sealing element configured as a scraper 24 which prevents impurities or abraded material from the respective gas chamber 8 or lubricant chamber 10 from reaching the gas seal 5 or lubricant seal 6. These 5, 6 are better protected, for example, against damage from particles to be introduced. According to Figure 2, the bypass flow path 14 of the gas seal 4 is branched, wherein one branch opens in front of the scraper 24 into the gas chamber 8 and another opens between the scraper 24 and the gas seal 5. Pressure equilibrium of the scraper 24 is thus also provided.

[0057] The redundancy of the lubricant seals 6 results in the thickness of the lubricant film 20 being able to be controlled in a more targeted manner in that the lubricant is first reduced to a comparatively thick lubricant film 20“ via the lubricant seal 6 arranged on the right in Figure 2 and is then reduced via the lubricant seal 6 (or the third sealing element) on the left in Figure 2 to the lubricant film 20, which is present on the gas seal 5.

[0058] Contrary to the first exemplary embodiment, the intermediate chamber 13 is designed to taper radially towards the third sealing element 6 in the direction of the counterstroke. In the case of a vertical arrangement, that is to say when the gas chamber 8 is arranged at the top in the direction of gravity, lubricant can thus collect in the tapered part of the intermediate chamber 13 by gravity. As a result, the lubricant film 20 is already in situ on the gas seal 5 in a comparatively greatly reduced and defined thickness.

[0059] Figure 3 shows an exemplary embodiment of a compressor 26 by means of a section of a longitudinal section guided along a vertical axis 28, wherein the sealing system 1 used here is largely based on the exemplary embodiment according to Figure 2. Accordingly, at least the differences with respect to the two other exemplary embodiments are set out.

[0060] According to Figure 3, the compressor 26 is designed as a pressure intensifier, the piston rod 30 of which is arranged in the direction of gravity. The compression stroke is performed upward in Figure 3. Accordingly, the gas chamber 8 is arranged at the top and the lubricant chamber 10 is arranged at the bottom.

[0061 ] According to Figure 4, a hydraulic control device 32 is provided as a means according to the invention for controlling the lubricant film. Said hydraulic control device comprises two 2/2-way switching valves 42, 42' which can be controlled as a direct function of the pressure in the gas chamber 8.

[0062] Alternatively, actuation can of course take place via an external control pressure medium source. It is also possible for actuation not to be effected directly by the pressure or stroke of the piston rod, but indirectly via a control unit by virtue of the fact that said control unit starts a temporal control profile of the control pressure as a function of the pressure or stroke in order thus to optimize the control of the lubricant film.

[0063] The switching valves 42, 42' can be designed, for example, as a pre- controllable check valve. In this case, a control surface of the valve body is loaded in the closing direction by the pressure of the gas.

[0064] The sealing system 1 has a carrier bushing 34 on which the sealing elements, i.e. , the gas seal 5 and the lubricant seal 6, as well as the further lubricant seal 22, including their scrapers 24, are radially inwardly arranged. Two lubricant flow paths 36, 36' extend from the intermediate chamber 13 to the respective working connection of the valves 42, 42‘. Control flow paths 38, 38' extend from the gas chamber 8 towards the valves 42, 42‘for the stated actuation. The paths 36, 36‘, 38, 38' pass through a housing 40, which comprises the carrier bushing 34 in sections. The lubricant flow paths 36, 36' are closed by the respective valve body 42, 42‘. The pressure in the control flow path 38, 38' , that is to say the pressure in the gas chamber 8 or a pressure dependent thereon, is present on a control surface of the valve body 42, 42' , which control surface has a closing effect. It is supportingly preloaded into this closed position via a spring.

[0065] During a compression stroke of the piston rod 30 into the gas chamber 8, the pressure therein increases as intended. Accordingly, the valve bodies 42, 42’ are actuated closed and the intermediate chamber 13 remains closed, so that the lubricant film located therein is effective without being influenced.

[0066] If the pressure in the gas chamber 8 drops, for example in the case of a decompression stroke or return stroke, the closing force resulting on the valve bodies 42, 42' drops and the lubricant paths 36, 36' are actuated open by them. Lubricant and gas located in the intermediate chamber 13 can then flow out via the valves 42, 42' in the direction of a tank or other reservoirs, for example.

[0067] Despite this drainage, sufficient residual lubricant film remains on the mating surface 2 in the intermediate chamber 13 for the necessary return stroke.

[0068] In the next compression stroke, the lubricant film 20 and 20“ is again built up in the intermediate chamber 13. In this way, the quantity and quality of lubricant film 20, 20' can be renewed cyclically, resulting in the uniform quality and quantity of the lubricant film. In this way, the function of the sealing system 1 is permanently ensured via the means 32 for controlling the lubricant film, and in particular the prevention of contamination of the gas with lubricant is prevented.

[0069] The invention is used in reciprocating linear sealing systems for separating gas and other media, more precisely in systems for compressing hydrogen to be used in fuel cells. This can be, for example, the piston rod sealing system of a pressure intensifier or a piston sealing system of an accumulator or piston compressor.

List of reference signs

1 Sealing system

2 Mating surface

4; 5 First sealing element

6 Second sealing element

8 Gas chamber

10 Lubricant chamber

12; 13 Intermediate chamber

14, 16 Bypass flow path

18 Check valve 20 Lubricant film

20‘ Lubricant

20‘ Lubricant film (precursor)

22 Third sealing element 24 Scraper

26 Compressor

28 Vertical axis

30 Piston rod

32 Control device 34 Carrier bushing

36, 36‘ Lubricant flow path

38, 38‘ Control flow path

40 Housing portion

42, 42‘ Valve body