Method for diagnosing a fuel cell system; fuel cell system

Abstract

The invention relates to a method for diagnosing a sensor (131) in a fuel cell system (1) having at least one fuel cell stack (100), which has a cathode (110) and an anode (115), wherein air is supplied to the cathode (110) via an air path (111) and exhaust air emerging from the fuel cell stack (100) is discharged via an exhaust gas path (112), and wherein hydrogen is supplied to the anode (120) via an anode system, wherein the anode system has an anode line (120) and a recirculation circuit (150), and wherein the recirculation circuit (150) is connected to a purge line (160) via a purge valve (161) in order to drain anode gas from the anode system. The anode gas emerging from the purge line (160) is indirectly or directly guided into a housing (130) of the fuel cell stack (100) via a diagnosis line (170) in order to check the functionality of the sensor (131), in particular a hydrogen sensor (131). The invention also relates to a fuel cell system (100) having a corresponding diagnosis line (170).

Description

[0001] Description

[0002] Procedure for diagnosing a

[0003] The invention relates to a method for diagnosing a fuel cell system, as well as a fuel cell system having the features of the preamble of the independent claims.

[0004] State of the art

[0005] Fuel cells are electrochemical energy converters. Hydrogen (H2) and oxygen (O2) can be used as reaction gases. These are converted into electrical energy, water (H2O), and heat using a fuel cell. The core of a fuel cell is a membrane-electrode assembly (MEA), which comprises a membrane coated on both sides with a catalytic material to form electrodes. During operation, the fuel cell supplies hydrogen to one electrode, the anode, and oxygen to the other, the cathode.

[0006] To increase electrical power, a large number of fuel cells are connected to form a fuel cell stack. Furthermore, multiple fuel cell stacks or fuel cell systems can be interconnected.

[0007] A certain amount of hydrogen always escapes from a fuel cell stack into the environment. For this reason, the fuel cell stack is enclosed in a housing. The housing serves to guarantee high-voltage safety, in particular contact protection, and to minimize the risk of flammable gas mixtures. The housing is flushed with air to prevent undesirable high concentrations of flammable gases. As an additional safeguard, a sensor is located in the housing that monitors the hydrogen concentration. Depending on the measuring principle, self-diagnosis of the sensor is not possible. In order to avoid regular maintenance, including complex disassembly and reinstallation of the sensor, the present invention addresses the task of providing a method for diagnosing a fuel cell system, in particular the sensor in the housing, as well as a corresponding fuel cell system.

[0008] In this way, the functionality of the sensor in the housing of the fuel cell stack can be checked.

[0009] To achieve the object, the method having the features of claim 1 is proposed, as well as a fuel cell system having the features of claim 4. Advantageous embodiments of the invention can be found in the subclaims.

[0010] Disclosure of the invention

[0011] A method is proposed for diagnosing a sensor in a fuel cell system having at least one fuel cell stack comprising a cathode and an anode, wherein air is supplied to the cathode via an air path and exhaust air exiting the fuel cell stack is discharged via an exhaust gas path, and wherein the anode is supplied with hydrogen via an anode system, wherein the anode system has an anode line and a recirculation circuit, wherein the recirculation circuit is connected to a purge line via a purge valve in order to discharge anode gas from the anode system. According to the invention, it is proposed that the anode gas exiting the purge line be conducted directly or indirectly into a housing of the fuel cell stack via a diagnostic line in order to check the functionality of the sensor, in particular a hydrogen sensor.

[0012] By means of the inventive method for diagnosing a sensor, anode gas can be introduced from the purge line into the housing, thus checking the functionality of the sensor. Anode gas from the recirculation circuit with an increased hydrogen concentration can be fed into the housing of the fuel cell stack via a diagnostic line. The enrichment of anode gas in the housing of the fuel cell stack only takes place for the duration of the diagnosis. For this purpose, part or all of the volume flow of the anode gas is fed into the housing of the fuel cell stack via the purge line and / or a drain line. This ensures that the hydrogen concentration in the housing is above the threshold of

[0013] Measurement sensitivity of the sensor, but below a critical threshold of 2-4%.

[0014] Advantageous embodiments and further developments of the fuel cell system according to the invention are specified in the dependent claims.

[0015] It is advantageous to open a diagnostic valve to direct the anode gas into the housing of the fuel cell stack, as this ensures that only hydrogen-containing anode gas enters the housing when a diagnosis of the sensor is to be carried out.

[0016] If the sensor doesn't respond to the anode gas, there's a sensor fault. An error message is helpful so that the driver or vehicle operator can take appropriate action, such as replacing the sensor.

[0017] It is advantageous if the diagnostic line is connected to the purge line via a branch located in the purge line, as this provides an effective way to direct hydrogen-containing anode gas into the fuel cell housing.

[0018] It is advantageous to connect the diagnostic line to the exhaust path, with the diagnostic line connecting to the exhaust path downstream of the purge line. The exhaust gas dilutes the concentration of the anode gas entering the housing, ensuring that the hydrogen concentration in the housing does not exceed the critical threshold of 2-4%.

[0019] Locating the diagnostic valve in the diagnostic line or at the branch between the purge line and the diagnostic line is advantageous for allowing anode gas to flow into the housing only when needed. A throttle, particularly a controllable throttle, located in the diagnostic line is advantageous because it allows the amount of anode gas flowing into the housing to be reduced, ensuring that the critical hydrogen concentration threshold of 2-4% is not exceeded.

[0020] It is advantageous if the diagnostic cable is connected directly to the housing of the fuel cell stack, as this enables a compact design.

[0021] A further advantage arises when the diagnostic line is connected to a ventilation line which is arranged between the air path and the housing of the fuel cell stack, since no further opening needs to be provided in the housing of the fuel cell stack.

[0022] Preferred embodiments of the invention are explained in more detail below with reference to the accompanying drawings. These show:

[0023] Figure 1 is a schematic representation of a fuel cell system according to a first embodiment,

[0024] Figure 2 is a schematic representation of a fuel cell system according to a second embodiment and

[0025] Figure 3 is a schematic representation of a fuel cell system according to another embodiment.

[0026] Detailed description of the drawings

[0027] Figure 1 shows a schematic topology of a fuel cell system 1 according to the invention according to a first exemplary embodiment. The fuel cell system 1 comprises a fuel cell stack 100 with an anode 115 and a cathode 110. The fuel cell stack 100 is connected to an air path 111 and an exhaust gas path 112.

[0028] The fuel cell stack 100 is arranged in a housing 130 in order to guarantee high-voltage safety, in particular contact protection, on the one hand, and to minimize the risk of ignitable gas mixtures, on the other hand.

[0029] A certain amount of hydrogen always escapes from the fuel cell stack 100 into the environment, which can accumulate in the housing 130. The housing 130 can be flushed with air through a ventilation line 175. To monitor the hydrogen concentration in the housing 130, a sensor 131 is arranged in the housing 130. The sensor 131 is designed as a hydrogen sensor 131 and measures the hydrogen concentration in the air contained in the housing 130.

[0030] The air path 111 serves as an air supply line to supply air from the environment to the cathode 110 of the fuel cell stack 100. The exhaust path 112 serves to discharge used air, water, and exhaust gases, which are also referred to as exhaust air in the context of the invention, from the fuel cell 100 to the environment.

[0031] Components required for the operation of the fuel cell stack 100 are arranged in the air path 111. An air compressor and / or compressor can be arranged in the air path 111, which compresses or draws in the air according to the respective operating conditions of the fuel cell stack 100. Downstream of the air compressor and / or compressor, a heat exchanger can be located, which cools the air in the air path 111 before it flows into the fuel cell stack 110, thus protecting it from thermal damage.

[0032] Additional components such as a filter and / or a humidifier and / or valves may be provided within the air path 111. Oxygen-containing air is supplied to the fuel cell stack 100 via the air path 111.

[0033] Since the arrangement of the components in the air system is not essential to the invention, they are not explicitly shown in the figures.

[0034] Furthermore, the fuel cell system 100 has an anode system connected to the anode 115 of the fuel cell stack 100. The anode system comprises an anode line 120 and a recirculation circuit 150. Fuel is supplied to the anode 115 of the fuel cell stack 100 via the anode line 120. The anode line 120 is connected to a tank 121 for this purpose.

[0035] In order to always supply the fuel cell stack 100 with sufficient fuel, there is a need for a superstoichiometric metering of fuel via the anode line 120. The excess fuel, as well as certain amounts of water and nitrogen, which diffuse through the cell membranes of the fuel cell stack 100 from the side of the cathode 110 to the side of the anode 115, are returned in the recirculation circuit 150 and mixed with the metered fuel from the anode line 120.

[0036] To drive the flow, a jet pump 151 and a recirculation pump 152 are installed in the recirculation circuit 150.

[0037] The recirculation pump 152 is arranged between an anode outlet of the anode 115 of the fuel cell stack 100 and the jet pump 151. However, a different arrangement of components for driving the flow in the recirculation circuit 150 is also possible.

[0038] Since water and nitrogen accumulate within the recirculation circuit 150 over time, the recirculation circuit 150 is connected to a purge line 160 via a purge valve 161. The purge line 160 is connected to the exhaust path 112. The purge valve 162 can be opened as needed to provide a connection to the exhaust path 112 and to divert anode gas from the anode system into the exhaust path 112.

[0039] Additional components, such as pressure control valves, filters, or sensors, may be arranged in the anode line 120 to supply the anode 115 of the fuel cell stack 115 with fuel as needed. Since the arrangement of these components is not essential to the invention, they are not shown in Figure 1.

[0040] The fuel cell system 1 has a diagnostic line 170, which is directly or indirectly connected to the housing 130 of the fuel cell stack 100. Anode gas can be fed from the purge line 160 into the housing 130 of the fuel cell stack 100 through the diagnostic line 170 in order to check the functionality of the sensor 131, which is arranged in the housing 130.

[0041] In the first embodiment shown in Figure 1, the diagnostic line 170 is connected to the purge line 160 and the housing 130. The diagnostic line 170 is connected to the purge line 160 via a branch 171 arranged in the purge line 160. The branch 171 is preferably arranged downstream of the purge valve 161. A diagnostic valve 172 can be arranged in the diagnostic line 170 or at the branch 171 between the purge line 160 and the diagnostic line 170. The diagnostic valve 172 is closed during normal operation and is only opened if a diagnosis of the sensor 131 in the housing 130 is to be performed, so that hydrogen-containing purge gas can flow into the housing 130.

[0042] Figure 2 shows a second embodiment of the fuel cell system 1 according to the invention. Here, the diagnostic line 170 is connected to the exhaust gas path 112 and the housing 130. The diagnostic line 170 is connected to the exhaust gas path 112 downstream of the connection between the purge line 160 and the exhaust gas path 112. In this way, it can be ensured that the exhaust air also contains purge gas and that the exhaust air has a correspondingly high hydrogen concentration. A diagnostic valve 172 can be arranged in the diagnostic line 170 or at the branch 171 between the exhaust gas path 112 and the diagnostic line 170. The diagnostic valve 172 is closed during normal operation and is only opened for the diagnosis of the sensor 131 in the housing 130, so that hydrogen-containing purge gas can flow into the housing 130.

[0043] In an alternative embodiment, the diagnostic line 170 may be connected to the ventilation line 175 and not directly to the housing 130, as shown in Figure 3. Here, the diagnostic line 170 is connected at one end to the ventilation line 175 and at the other end to the purge line 160. The hydrogen-containing purge gas from the purge line 160 can flow into the housing 130 of the fuel cell 100 via the diagnostic line 170 and the ventilation line 175. The ventilation line 175 is arranged between the air path 111 and the housing 130 of the fuel cell stack and typically supplies the housing 130 of the fuel cell with fresh air via the air path 111.

[0044] In order to vary the amount of purge gas flowing into the housing 130 via the diagnostic line 170, a throttle 173, in particular an adjustable throttle, can be arranged in the diagnostic line 170.

[0045] In order to check the functionality of a sensor 131, in particular a hydrogen sensor, in the housing 130, a sample is taken from the purge line

[0046] 160 escaping anode gas is passed directly or indirectly into the housing 130 of the fuel cell stack 100 via the diagnostic line 170.

[0047] For this purpose, a diagnostic valve 172 is opened to release the connection between the purge line 160 and the housing 130 so that the anode gas can flow into the housing 130 of the fuel cell stack 100.

[0048] Optionally, the amount of purge gas flowing into the housing 130 via the diagnostic line 170 can be reduced or varied using the throttle 173.

[0049] The diagnostic valve 171 is opened when a purge process takes place and anode gas flows from the recirculation circuit 150 via the purge line 160 into the exhaust gas path 112. During a purge process, the purge valve

[0050] 161 is opened so that the diagnostic valve 171 and the purge valve 161 can be opened simultaneously or with a slight delay.

[0051] An error message is generated if the sensor 131 does not respond to the anode gas flowing through the diagnostic line 170 into the housing 130. The error message may be in the form of an error message that prompts an operator or driver of the vehicle with the fuel cell system 1 to visit a workshop or have the corresponding sensor 131 replaced.

Claims

Claims 1. Method for diagnosing a sensor (131) in a fuel cell system (1) with at least one fuel cell stack (100) having a cathode (110) and an anode (115), wherein air is supplied to the cathode (110) via an air path (111) and exhaust air emerging from the fuel cell stack (100) is discharged via an exhaust gas path (112) is discharged, and wherein the anode (120) is supplied with hydrogen via an anode system, wherein the anode system has an anode line (120) and a recirculation circuit (150), wherein the recirculation circuit (150) is connected to a purge line (160) via a purge valve (161) in order to discharge anode gas from the anode system, characterized in that the anode gas emerging from the purge line (160) is conducted directly or indirectly into a housing (130) of the fuel cell stack (100) via a diagnostic line (170) in order to check the functionality of the sensor (131), in particular a hydrogen sensor (131).

2. Method according to claim 1, characterized in that a diagnostic valve (172) is opened in order to direct the anode gas into the housing (130) of the fuel cell stack (100).

3. Method according to one of claims 1 or 2, characterized in that an error message is issued if the sensor (131) does not react to the anode gas.

4. Fuel cell system (1) with at least one fuel cell stack (100) having a cathode (110) and an anode (115), wherein air is supplied to the cathode (110) via an air path (111) and exhaust air emerging from the fuel cell stack (100) is supplied via an exhaust gas path (112), and wherein the anode (120) is supplied with hydrogen via an anode system, wherein the anode system comprises an anode line (120) and a recirculation circuit (150), and wherein the recirculation circuit (150) is connected via a purge valve (161) to a purge line (160) in order to discharge anode gas from the anode system, characterized in that a diagnostic line (170) is connected directly or indirectly to the housing (130) of the fuel cell stack (100) and the purge line (160) so that anode gas is conducted into the housing (130) of the fuel cell stack (100).

5. Fuel cell system (1) according to claim 4, characterized in that the diagnostic line (170) is connected to the purge line (160) via a branch point (171) arranged in the purge line (160).

6. Fuel cell system (1) according to claim 4, characterized in that the diagnostic line is connected to the exhaust gas path (112), wherein the diagnostic line (170) has a connection to the exhaust gas path (112) downstream of the purge line (160).

7. Fuel cell system (1) according to claim 5 or 6, characterized in that a diagnostic valve (171) is arranged in the diagnostic line (170) or at the branch point between the purge line (160) and the diagnostic line (170).

8. Fuel cell system (1) according to claim 5 or 6, characterized in that a throttle (173), in particular a controllable throttle (173), is arranged in the diagnostic line (170).

9. Fuel cell system (1) according to one of claims 4 to 8, characterized in that the diagnostic line (170) is connected directly to the housing (130) of the fuel cell stack (100).

10. Fuel cell system (1) according to one of claims 4 to 8, characterized in that the diagnostic line (170) is connected to a ventilation line (175) which is arranged between the air path (111) and the housing (130) of the fuel cell stack (100).

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