Method and device for checking the tightness of a fuel cell system

Abstract

A method for checking the tightness of a fuel cell system (2), in particular an anode subsystem (20) provided in a fuel cell system (2) for supplying at least one fuel cell (4) of the fuel cell system (2) with gaseous hydrogen, and which has an anode shut-off valve (28) and a metering valve (30) in a flow direction of the hydrogen, comprises: closing valves (10, 12) of a cathode (6b) of the at least one fuel cell (4); setting an overpressure in the anode subsystem (20) by supplying a test gas from a gas reservoir (22); closing the anode shut-off valve (28) and the metering valve (30); measuring the anode pressure (p An ) and / or the cathode pressure (p Kat ) before and after a predetermined initial waiting period (T W1 ); Determining an anode pressure gradient (δp An ) and / or a cathode pressure gradient (δ pKat); and output an error message if the magnitude of the anode pressure gradient (δp) An ) exceeds a predetermined anode pressure gradient limit and / or if the magnitude of the cathode pressure gradient (δ) pKat ) exceeds a predetermined cathode pressure gradient limit.

Description

[0001] The invention relates to a method and a device for checking the tightness of a fuel cell system, in particular for checking the tightness of an anode subsystem of a fuel cell system. State of the art

[0002] Following a suspected fault and / or a repair to a fuel cell system, especially to an anode subsystem of the fuel cell system, the fuel cell system must be checked for leaks.

[0003] To ensure the safety and proper operation of the fuel cell system, in particular the areas of the fuel cell system, including the anode subsystem, which contain hydrogen during operation, must be reliably checked for leaks to ensure that there are no leaks.

[0004] To check the tightness, the anode subsystem is currently filled with a test gas, such as gaseous nitrogen or a forming gas, and pressurized. Depending on the test gas, the entire anode subsystem is then scanned for leaks using a gas sniffer or a leak detection spray. With this conventional method, it can take a very long time to detect a leak or to fully test the tightness. Suspected areas can be difficult to access, and especially in workshops, there is a risk of overlooking small leaks.

[0005] It is therefore an object of the invention to provide a method and a device that make it possible to simplify the detection of leaks in a fuel cell system and to increase the reliability of checking the system for leaks. Disclosure of the invention:

[0006] The invention comprises a method for checking the tightness of a fuel cell system, in particular an anode subsystem, which is provided in a fuel cell system for supplying at least one fuel cell of the fuel cell system with gaseous hydrogen, and which has an anode shut-off valve and a metering valve in a flow direction of the hydrogen.A method according to the invention comprises: closing a cathode inlet valve and a cathode outlet valve of a cathode of the at least one fuel cell; setting an overpressure in the anode subsystem by supplying a test gas from a gas reservoir; measuring the anode pressure and / or the cathode pressure of the at least one fuel cell; closing the anode shut-off valve and the metering valve; measuring the anode pressure and / or the cathode pressure after a first waiting period; determining an anode pressure gradient and / or a cathode pressure gradient; and issuing an error message indicating a leak in the fuel cell system if the magnitude of the anode pressure gradient exceeds a predetermined anode pressure gradient limit and / or if the magnitude of the cathode pressure gradient exceeds a predetermined cathode pressure gradient limit.

[0007] The invention also includes a device for checking the tightness of an anode subsystem, which is provided in a fuel cell system for supplying at least one fuel cell with hydrogen, and which has an anode shut-off valve and a metering valve in one direction of hydrogen flow. The device is designed and configured to carry out a method according to the invention for checking the tightness of a fuel cell system, as previously described, in order to check the tightness of the anode subsystem.

[0008] A method and a device according to the invention make it possible to detect leaks in a fuel cell system, in particular leaks in an anode submodule of a fuel cell system, conveniently, quickly and with high reliability, without triggering too many false alarms.

[0009] This eliminates the need for lengthy and costly leak detection in the fuel cell system. Workshops can document and prove that they have performed their work on the fuel cell system correctly. Furthermore, automated execution of the procedure can increase reproducibility and reduce the risk of errors in the workshop.

[0010] In one embodiment, the anode pressure gradient limit is in the range between -0.2 mbar / s and -1 mbar / s. The anode pressure gradient limit can, in particular, be -0.5 mbar / s.

[0011] In one embodiment, the cathode pressure gradient limit lies in the range between 0.07 mbar / s and 0.35 mbar / s. The cathode pressure gradient limit can, in particular, be 0.17 mbar / s.

[0012] Such limit values ​​for the anode pressure gradient or the cathode pressure gradient make it possible to reliably detect leaks in the fuel cell system without causing a significant number of false alarms.

[0013] In one embodiment, the method comprises weighting, in particular multiplying, the anode pressure difference before and after closing the anode shut-off valve and the metering valve by the ratio between the volumes of the anode subsystem and the cathode subsystem; determining the difference between the cathode pressure difference and the weighted anode pressure difference; and issuing an error message if the amount of the weighted difference exceeds a predetermined limit for the weighted difference.

[0014] In an alternative embodiment, the method comprises weighting, in particular multiplying, the cathode pressure difference by the ratio between the volumes of the anode subsystem and the cathode subsystem; determining the difference between the cathode pressure difference and the weighted anode pressure difference; determining the difference between the anode pressure difference and the weighted cathode pressure difference; and issuing an error message if the magnitude of the weighted difference exceeds a predetermined limit for the weighted difference.

[0015] By calculating and evaluating such a weighted difference between the anode pressure difference and the cathode pressure difference, wherein either the anode pressure difference or the cathode pressure difference is weighted by the ratio between the volumes of the anode subsystem and the cathode subsystem, the reliability of a leak detection system according to the invention can be further improved and the number of false alarms can be reduced. Furthermore, by calculating and evaluating the weighted difference between the anode pressure difference and the cathode pressure difference, additional information about the fuel cell system can be obtained, which can facilitate the localization of a leak in the fuel cell system.

[0016] The threshold value for the weighted difference can be in the range between 0.02 mbar / s and 0.08 mbar / s, particularly at 0.05 mbar / s. Such a threshold value for the weighted difference has proven to be well suited for reliably detecting and locating leaks in the fuel cell system.

[0017] In one embodiment, the method comprises measuring the pressure in a region of the fuel cell system between the anode shut-off valve and the metering valve while the anode shut-off valve is open; closing the anode shut-off valve and the metering valve of the fuel cell system; waiting for a predetermined second waiting period; measuring the pressure in the region between the anode shut-off valve and the metering valve again after the second waiting period has elapsed; determining a mean pressure gradient for the region between the anode shut-off valve and the metering valve from the measured pressures; and issuing an error message if the magnitude of the mean pressure gradient exceeds a predetermined mean pressure gradient limit.

[0018] These steps can further improve the reliability of a leak detection system according to the invention. In particular, leaks in the area upstream of the metering valve can be detected and located even more reliably.

[0019] The mean pressure gradient limit can be in the range between -0.2 mbar / s and -5 mbar / s, especially at -1 mbar / s.

[0020] In one embodiment, the method comprises closing a tank valve through which a gas reservoir is connected to the fuel cell system, or a gas cylinder serving as a gas reservoir, so that no further gas can flow into the anode subsystem. The method further comprises measuring the pressure downstream of the closed tank valve; opening the anode shut-off valve; waiting for a predetermined third interval; measuring the pressure downstream of the closed tank valve after the predetermined third interval; determining the magnitude of the pressure difference downstream of the tank valve when the anode shut-off valve is open and closed, and comparing it to a predetermined differential limit; and issuing an error message if the magnitude of the pressure difference downstream of the tank valve exceeds the predetermined differential limit.

[0021] In this way, the reliability of a leak detection system according to the invention can be improved even further. In particular, leaks located downstream of the tank valve can be detected and localized even more reliably, and the risk of false alarms can be reduced.

[0022] The difference limit value can be in the range between -5 mbar and -15 mbar, especially at -10 mbar.

[0023] The anode pressure gradient limit, the cathode pressure gradient limit, the weighted difference limit, the mean pressure gradient limit and / or the difference limit can be determined empirically.

[0024] The limit values ​​can be determined, in particular by measurements on existing fuel cell systems or with the help of numerical calculations / computer simulations, in such a way that leaks in the fuel cell system can be reliably detected and located within the fuel cell system without causing too many false alarms.

[0025] An embodiment of the invention is described below with reference to the accompanying figures. Brief description of the characters Fig. Figure 1 shows a schematic view of a fuel cell system whose tightness can be checked using a method according to the invention. Fig. Figure 2 shows a flowchart of an embodiment of a method according to the invention for checking the tightness of a fuel cell system. Character description

[0026] The Fig. Figure 1 shows a schematic view of a fuel cell system 2, the tightness of which can be checked using a method according to the invention.

[0027] The fuel cell system 2 comprises at least one fuel cell 4, in particular a fuel cell stack 4 containing several fuel cells 4.

[0028] At least one fuel cell 4 has an anode 6a and a cathode 6b, which are separated from each other by a membrane 8.

[0029] Oxygen, for example in the form of oxygen-containing air, is supplied to the cathode 6b of the fuel cell 4 via a cathode inlet valve 10. The cathode 6b also has a cathode outlet valve 12 through which, when open, gas can escape from the cathode 6b of the fuel cell 4.

[0030] A cathode pressure sensor 14 is provided at the output of the cathode 6b, which makes it possible to measure the pressure in or at the cathode 6b.

[0031] The fuel cell system 2 also includes an anode subsystem 20, which is designed and configured to supply hydrogen gas to the anode 6a of the at least one fuel cell 4 during operation.

[0032] The anode subsystem 20 comprises a gas reservoir 22, for example a tank or a gas cylinder, which contains hydrogen gas during the regular operation of the fuel cell system 2. For testing the leak tightness of the fuel cell system 2, the gas reservoir 22 can contain a test gas, for example nitrogen or a forming gas.

[0033] Through a tank valve 24, located at the outlet of the gas reservoir 22, and optionally an optional heat exchanger 26, the gas from the gas reservoir 22 is fed to an anode shut-off valve 28. The anode shut-off valve 28 makes it possible to selectively activate / release and deactivate / shut off the supply of gas from the gas reservoir 22.

[0034] Downstream of the anode shut-off valve 28 is a metering valve 30. The metering valve 30 makes it possible to supply the gas from the gas reservoir 22 to the anode 6a of the at least one fuel cell 4 with a predetermined dosage when the anode shut-off valve 28 is open.

[0035] A medium pressure sensor 32 is provided between the anode shut-off valve 28 and the metering valve 30. The medium pressure sensor 32 makes it possible to measure the pressure of the gas between the anode shut-off valve 28 and the metering valve 30.

[0036] Between an output of the metering valve 30 and an input of the anode 6a there is an anode pressure sensor 34, which makes it possible to measure the pressure of the gas that is supplied to the anode 6a of at least one fuel cell 4.

[0037] The anode 6a also has an anode outlet 7 through which gas can flow out of the anode 6a.

[0038] An anode purge valve 16 and an anode drain valve 18 are arranged at the anode outlet 7, which make it possible to purge the anode 6a of the at least one fuel cell 4 by opening the anode purge valve 16 or to drain it by opening the anode drain valve 18.

[0039] A fuel cell system 2 according to an embodiment of the invention thus comprises four areas: A first area 41 between the gas reservoir 22 and the anode shut-off valve 28.

[0040] A second area (medium pressure area) 42 between the anode shut-off valve 28 and the metering valve 30.

[0041] A third area (low-pressure area) 43 between the outlet of the metering valve 30 and the anode rinsing and draining valves 16, 18 including the anode 6a of the at least one fuel cell 4; and a fourth area (cathode area) 44 on the side of the cathode 6a between the membrane 8 of the at least one fuel cell 4 and the two valves 10, 12 at the cathode 6b.

[0042] The first area 41, the second area 42 and the third area 43 are part of the anode subsystem 20.

[0043] Fig. Figure 1 also shows an embodiment of a device 50 according to the invention, which is designed and provided for checking the tightness of the fuel cell system 2.

[0044] Fig. Figure 2 shows a flowchart of an embodiment of a method 100 according to the invention for checking the tightness of a fuel cell system 2, in particular for checking the tightness of the anode subsystem 20 of the fuel cell system 2.

[0045] To test the tightness of fuel cell system 2, a suitable test gas, such as nitrogen gas, can be used. Alternatively, a readily detectable forming gas can be used as a test gas, making it easy to locate any leaks by detecting the forming gas escaping from fuel cell system 2.

[0046] After starting the process 100, in a first step 110 the cathode outlet valve 12 of the cathode 6b of the at least one fuel cell 4 is opened in order to establish a defined pressure level with a cathode reference pressure p in the cathode area 44 of the fuel cell 4. KatRef to adjust. Since the outlet of the cathode outlet valve 12 is normally connected to the environment, opening the valve 12 at the cathode 6b in the cathode area 44 generally results in the ambient air pressure of approximately 1017 mbar being used as the cathode reference pressure p. KatRef set.

[0047] After the cathode reference pressure p KatRef Once the temperature in the cathode 6b has been set, the cathode inlet valve 10 and the cathode outlet valve 12 are closed in step 120. The anode purge valve 16 and the anode drain valve 18 at the anode outlet 7 of the at least one fuel cell 4 are also closed in step 120.

[0048] After closing the valves 10, 12, 16, 18 on the at least one fuel cell 4, in step 130 an overpressure of, for example, approx. 500 mbar relative to the environment, i.e. an absolute anode pressure p, is created at and in the anode 6a in the low-pressure area 43 by appropriately controlling the anode shut-off valve 28 and the metering valve 30. An set to approximately 1500 mbar.

[0049] After a successful pressure build-up in at least one fuel cell 4, the cathode pressure sensor 14 thus shows a cathode pressure p for the cathode area 44. Katfrom approximately 1017 mbar, and the anode pressure sensor 34 at the anode 6a shows an anode pressure p in the low pressure range 43 at the anode 6a. An from approximately 1500 mbar.

[0050] In the first area 41 and in the second area 42 between the gas reservoir 22 and metering valve 30, a so-called intermediate pressure p prevails. M of, for example, approximately 15 bar. The mean effective pressure p M is displayed by the mean pressure sensor 32.

[0051] In the next step 140, the anode shut-off valve 28 and the metering valve 30 are also closed, so that no pressure adjustment can take place in the anode 6a of at least one fuel cell 4.

[0052] After the anode shut-off valve 28 and the metering valve 30 have been closed, we enter a predetermined first waiting time T in step 150. W1 waited.

[0053] The first waiting time T W1For example, it can be between 60 and 300 seconds. The first waiting time T W1 It can be, in particular, 180 seconds.

[0054] After the first waiting period T has expired W1 Various pressure differences or pressure gradients can be calculated, which make it possible to conclude about any leaks in the fuel cell system 2:

[0055] For the cathode area 44 at the cathode 6b, the cathode pressure p is set in step 160. Kat measured and a cathode pressure difference Δp Kat or a cathode pressure gradient δp Kat = Δp Kat / T W1 determined. For the cathode region 44, a pressure increase, i.e. a positive cathode pressure gradient δp, occurs due to a partial pressure equalization between the anode 6a and the cathode 6b of the at least one fuel cell 4 through the membrane 8. Kat , expected.

[0056] The cathode pressure p Kat after the first waiting period T W1For example, it can be 1077 mbar, resulting in a cathode pressure difference Δp with a cathode outlet pressure of 1017 mbar. Kat This results in 60 mbar. During an initial waiting period T W1 This results in a cathode pressure gradient δp of 600 s. Kat from δpKat=(1077 mbar−1017 mbar) / 600 s=60 mbar / 600 s δpKat=0.1 mbar / s.

[0057] In a subsequent step 170, the anode pressure p An measured in the low-pressure area 43 at the anode 6a, and an anode pressure difference Δp An or an anode pressure gradient δp An The pressure gradient δp on the side of the anode 6a of the at least one fuel cell 4 is determined. In the low-pressure region 4, a pressure drop, i.e., a negative anode pressure gradient δp, is caused by the partial pressure equalization between the anode 6a and the cathode 6b through the membrane 8 of the at least one fuel cell 4. An , expected.

[0058] For example, the anode pressure p An after the first waiting period T W1 1320 mbar, so that with an anode outlet pressure of 1500 mbar, the anode pressure difference Δp An resulting in a pressure of 180 mbar. During an initial waiting period T W1 This results in an anode pressure gradient δp of 600 s. An from δpAn=(1500 mbar−1320 mbar) / 600 s=180 mbar / 600 s δpAn=−0.3 mbar / s.

[0059] Optionally, in a next step, a total deviation Δp can be calculated from 180. gesamt The pressure p in at least one fuel cell 4 is calculated. In particular, different volumes V are taken into account. An and V Kat The low-pressure area 43 at the anode 6a and the cathode area 44 at the cathode 6b are taken into account.

[0060] For example, is the volume V Kat the cathode region is 44 times larger than the volume V Anof the low-pressure area 43 at the anode 6a (V Kat = 3 * V An ), the cathode pressure increase Δp Kat with a volume factor K Vol multiplied by three. Then the difference between the pressure increase Δp weighted by the volume factor is calculated. Kat at the cathode 6b and the pressure drop Δp An calculated in the low-pressure area 43 at the anode 6a: Δptotal=|(KVol*ΔpKat)+ΔpKat|.

[0061] The difference is calculated by addition, since the pressure drop Δp An In the low-pressure area 43 at the anode 6a, the value is negative according to the definition chosen here.

[0062] For the example mentioned above, the following results: Δptotal=(3*60 mbar)+(−180 mbar)=180 mbar−180 mbar Δptotal=0 mbar.

[0063] That is, the pressure drop Δp Kat In the low-pressure area 43 at the anode 6a, a corresponding pressure increase ΔpKat The cathode area 44 is completely balanced. From this, it can be concluded that no gas has escaped from fuel cell system 2, and therefore fuel cell system 2 is sealed.

[0064] For the anode pressure drop Δp Ant or the anode pressure gradient δp An on the side of anode 6a, the cathode pressure increase Δp Kat or the cathode pressure gradient δp Kat on the side of the cathode 6b and / or for the total deviation Δp gesamt Separate limit values ​​can be set for the pressure p.

[0065] By comparing the anode pressure drop Δp An or the anode pressure gradient δp An on the side of the anode 6a, the cathode pressure increase Δp Kat or the cathode pressure gradient δp Kat on the side of the cathode 6b and / or the total deviation Δp gesamtIn step 190, a leak in the fuel cell system 2 can be inferred from the pressure p with the corresponding limit values ​​if these limit values ​​are exceeded or not met.

[0066] In a subsequent step 200, the so-called mean pressure p is measured using the mean pressure sensor 32. M in the area between the closed anode shut-off valve 28 and the closed metering valve 30 before and after a second waiting time T W2 measured.

[0067] The second waiting time T W2 can immediately after the first waiting time T W1 be or differ from it.

[0068] The second waiting time T W2 For example, it can be between 60 s and 300 s, in particular 180 s.

[0069] In step 210, the values ​​before and after the second waiting time T are used. W2 measured mean pressures p M (t1), p M (t2) (t2 = t1 + T W2 ) a mean pressure-pressure difference ΔpM = p M (t2) - p M (t1) or a mean pressure-pressure gradient δpM=ΔpM / Tw2; of mean pressure p M calculated and evaluated, e.g.: δpM=(14.4 bar−15 bar) / 600 s=−1 mbar / s.

[0070] The mean pressure-pressure difference Δp calculated in this way is also M and / or the mean pressure-pressure gradient δp calculated in this way M can be compared with predefined limit values. A leak in fuel cell system 2, in particular a leak in the second area 42 of fuel cell system 2, can be inferred if the magnitude of the mean pressure-pressure difference Δp M and / or the magnitude of the mean pressure-pressure gradient δp m exceeds a predetermined limit.

[0071] In a subsequent step 220, the supply of test gas to the fuel cell system 2 from the gas reservoir 22 is deactivated, e.g. by closing the tank valve 24, so that no further test gas can flow from the gas reservoir 22 into the fuel cell system 2.

[0072] In the next step 230, the pressure p3 downstream of the anode shut-off valve 28 is first measured with the medium pressure sensor 32 with the anode shut-off valve 28 closed and the metering valve 30 closed.

[0073] Then the anode shut-off valve 28 is opened and after a third waiting period T W3 The pressure p3 is measured again using the mean pressure sensor 32.

[0074] The third waiting time T W3 can immediately after the first waiting time T W1 and / or immediately after the second waiting time T W2 be or differ from them.

[0075] The third waiting time T W3For example, it can be between 5 s and 300 s, especially 15 s.

[0076] Here too, the pressure difference Δp3 = p(t2) - p(t1) (t2 = t1 + T W3 ) or the pressure gradient δp3=Δp3 / TW3; calculated and compared with predefined limit values.

[0077] For example, before opening the anode shut-off valve 28, a pressure p3(t1) of 14.95 bar can be present, and after opening the anode shut-off valve 28 and after the third waiting time T has elapsed, W3 A pressure p3(t2) of 14.9 bar was measured. During a third waiting period T W3 Over a period of 10 s, this results in a pressure gradient δp3 of -5 mbar / s: δp3=(14.90 bar−14.95 bar) / 10 s=−5 mbar / s.

[0078] The specified limit value for the pressure gradient δp3 can, for example, be -10 mbar / s.

[0079] Using the aforementioned criteria, and in particular using a combination of the aforementioned criteria, leaks in the fuel cell system 2 can be reliably detected and located or ruled out.

[0080] In step 240, one or more messages can be issued regarding the presence of a leak in fuel cell system 2, the suspected area of ​​fuel cell system 2 where the leak is located, and a possible cause of the fault. The messages can be displayed, for example, on a display device 52 of the device 50 for checking the tightness of fuel cell system 2.

[0081] For example, if the cathode pressure p Kat on the side of the cathode 6b does not increase or only increases slightly, and at the same time the calculated total deviation Δp gesamt If the value is greater than the corresponding limit value, this indicates that at least one of the cathode valves 10, 12 is leaking.

[0082] A rapid and / or greater pressure drop Δp An in the low-pressure area 43 on the side of the anode 6a, which is characterized by an excessive increase Δp Kat of the cathode pressure p Ka and with a total deviation Δp gesamt If the connection is in the expected area, it may indicate a defective membrane 8 in the fuel cell 4.

[0083] A successfully completed test run, in which no indication of a leak was found, can also be displayed on the display device 52.

[0084] A successfully completed test run can also be stored in a storage device 54, for example, for logging purposes. The storage device 54 can be located inside or outside the device 50 for checking the tightness of the fuel cell system 2. The storage device 54 can, for example, be located in a virtual cloud.

Claims

[1] Method for checking the tightness of a fuel cell system (2), in particular an anode subsystem (20) which is provided in a fuel cell system (2) for supplying at least one fuel cell (4) of the fuel cell system (2) with gaseous hydrogen, and which has an anode shut-off valve (28) and a metering valve (30) in a flow direction of the hydrogen, wherein the method comprises: Closing a cathode inlet valve (10) and a cathode outlet valve (12) of a cathode (6b) of the at least one fuel cell (4); Setting an overpressure in the anode subsystem (20) by supplying a test gas from a gas reservoir (22); Measuring an anode pressure (p An ) and / or a cathode pressure (p Kat ) at least one fuel cell (4); Closing the anode shut-off valve (28) and the metering valve (30); Measuring the anode pressure (p An) and / or the cathode pressure (p Kat ) after a predetermined initial waiting period (T W1 ); Determining an anode pressure gradient (δp) An ) and / or a cathode pressure gradient (δp Kat ); and Output an error message if the magnitude of the anode pressure gradient (δp) An ) exceeds a predetermined anode pressure gradient limit and / or if the magnitude of the cathode pressure gradient (δp) Kat ) exceeds a predetermined cathode pressure gradient limit. [2] Method according to claim 1, wherein the anode pressure gradient limit is in the range between -0.2 mbar / s and -1 mbar / s, in particular at -0.5 mbar / s. [3] Method according to claim 1 or 2, wherein the cathode pressure gradient limit is in the range between 0.07 mbar / s and 0.35 mbar / s, in particular at 0.17 mbar / s. [4] Method according to any of the preceding claims, wherein the method comprises, an anode pressure difference (Δp An ) with the ratio (K Vol ) to weight between the volumes of the anode subsystem (20) and the cathode subsystem (44); the difference between the cathode pressure difference (Δp Kat ) and the weighted anode pressure difference (K Vol * Δp An ) to determine; and to issue an error message if the amount of the difference exceeds a predefined difference limit; or the cathode pressure difference (Δp Kat ) with the ratio (K vol ) between the volumes of the anode subsystem (20) and the cathode subsystem; the weighted difference between the anode pressure difference (Δp An ) and the weighted cathode pressure difference (K Vol * Δp Kat ) to determine; and to issue an error message if the amount of the weighted difference exceeds a predefined limit for the weighted difference. [5] Method according to claim 4, wherein the limit value for the weighted difference is in the range between 0.02 mbar / s and 0.08 mbar / s, in particular at 0.05 mbar / s. [6] Method according to any of the preceding claims, wherein the method comprises, the pressure (p M ) to measure in an area (42) between the anode shut-off valve (28) and the metering valve (30); to close the anode shut-off valve (28) and the metering valve (30); a predetermined second waiting time (T W2 to wait; the pressure (p M ) the area (42) between the anode shut-off valve (28) and the metering valve (30) after the specified second waiting time (T) has elapsed W2 ) to measure again; from the measured pressures (p M ) a mean pressure gradient (δp M ) to determine for the area (42) between the anode shut-off valve (28) and the metering valve (30); and to issue an error message if the magnitude of the mean pressure gradient (δp) M ) exceeds a predetermined mean pressure gradient limit. [7] Method according to claim 6, wherein the mean pressure gradient limit is in the range between -0.2 mbar / s and -5 mbar / s, in particular at -1 mbar / s. [8] Method according to any of the preceding claims, wherein the method comprises, to close a tank valve (24) so ​​that no gas can flow into the anode subsystem (20); to measure the pressure (p3) in the anode subsystem (20) downstream of the closed tank valve (24); to open the anode shut-off valve (28); a predetermined third waiting time (T W3 to wait; the pressure (p3) in the anode subsystem (20) downstream of the closed tank valve (24) after the specified third waiting time (T) has elapsed W3 ) to eat; to determine the magnitude of the pressure difference (p3) downstream of the tank valve (24) between the open and closed anode shut-off valve (28) and to compare it with a predetermined differential limit value; and to issue an error message if the amount of the pressure difference downstream of the tank valve (24) exceeds the specified differential limit. [9] Method according to claim 8, wherein the difference limit is in the range between -5 mbar and -15 mbar, in particular at -10 mbar. [10] Method according to any of the preceding claims, wherein at least one of the anode pressure gradient limit, the cathode pressure gradient limit, the difference limit, the mean pressure gradient limit and the difference limit has been empirically determined. [11] Device (50) for checking the tightness of a fuel cell system (2), in particular an anode subsystem (20) which is provided in a fuel cell system (2) for supplying at least one fuel cell (4) with hydrogen, and which has an anode shut-off valve (28) and a metering valve (30) in a flow direction of the hydrogen, wherein the device (50) is provided and configured to carry out a method according to one of the preceding claims in order to check the tightness of the anode subsystem (20).

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