Method for checking, in particular plausibility checking, calibrating and / or diagnosing a sensor for sensing an oxygen content

Abstract

The invention relates to a method for checking, in particular plausibility checking, calibrating and / or diagnosing a sensor (x) for sensing an oxygen content of exhaust air (A2) from at least one fuel-cell stack (A) of a fuel-cell system (FCS), wherein the at least one fuel-cell stack (A) is formed with an air system (10), in order for the at least one fuel-cell stack (A) to be supplied with oxygen-containing supply air (A1), and wherein the sensor (x) is located in an exhaust-air path (12) or in an exhaust-air return path (14), the method comprising: - providing a comparison value (xO2*) for an oxygen content characteristic of an operating mode (L) of the air system (10) and / or of an operating mode (M) of the fuel-cell stack (A), - operating the fuel-cell stack (A) in the operating mode (L) of the air system (10) and / or in the operating mode (M) of the fuel-cell stack (A), - sensing a measured value (xO2) by means of the sensor (x), - comparing the measured value (xO2) with the comparison value (xO2*) and - assessing the sensor (x) on the basis of the comparison.

Description

[0001] Description

[0002] title

[0003] Method for checking, in particular plausibility, calibration and / or diagnosis, a sensor for detecting an oxygen content

[0004] The invention relates to a method for checking, in particular verifying plausibility, calibrating, and / or diagnosing, a sensor for detecting an oxygen content of exhaust air from at least one fuel cell stack of a fuel cell system. Furthermore, the invention relates to a corresponding computer program product for carrying out a corresponding method. Furthermore, the invention relates to a corresponding control unit for carrying out a corresponding method. Furthermore, the invention relates to a corresponding fuel cell system with a corresponding control unit.

[0005] State of the art

[0006] In vehicles (fuel cell vehicles or FCVs for short), where the energy for the drive is supplied by one or more fuel cell systems (FCS for short), the oxidizing agent oxygen from the ambient air is generally used to react with hydrogen in the fuel cell to form water or water vapor and thus to supply electrical power through electrochemical conversion.

[0007] The ambient air is compressed by an air system and fed to the fuel cell system. The corresponding air mass flow and pressure level can be variably adjusted. The air is typically compressed by a thermal turbomachine (or compression unit, e.g., comprising a turbocompressor). The exhaust gas or exhaust air from the air system, particularly the exhaust gas from a cathode path of the stack, is oxygen-depleted.

[0008] To control and / or monitor the reaction, lambda sensors are used to detect the oxygen content in the exhaust gas path or exhaust air path of the air system.

[0009] In some air systems, exhaust gas recirculation (EGR for short) is used from an exhaust air path to a supply air path, which recirculates part of the exhaust air back into the supply air path.

[0010] In some systems, operating strategies are known that inertize the cathode region of a fuel cell stack and, if necessary, also the anode path.

[0011] For the aforementioned processes, a lambda probe can be used in the exhaust gas path and / or in an EGR path, which can determine the oxygen content of a gas mixture in order to enable a targeted implementation of an operating strategy and / or diagnosis / plausibility check.

[0012] Disclosure of the invention

[0013] The present invention provides a method for checking, in particular plausibility checking, calibrating, and / or diagnosing, a sensor for detecting an oxygen content of exhaust air from at least one fuel cell stack of a fuel cell system, having the features of the independent method claim. Furthermore, the invention provides a corresponding computer program, a corresponding control unit, and a corresponding fuel cell system, having the features of the independent claims. Features and details described in connection with the various embodiments and / or aspects of the invention naturally also apply in connection with the other embodiments and / or aspects, and vice versa, so that reciprocal reference is or can always be made to the individual embodiments and / or aspects in the disclosure.

[0014] According to the first aspect, the present invention provides: a method for checking, in particular plausibility checking, calibrating and / or diagnosing, a sensor for detecting an oxygen content (the sensor can also be referred to as a lambda probe) of an exhaust air from at least one fuel cell stack of a fuel cell system, wherein the at least one fuel cell stack is designed with an air system to supply the at least one fuel cell stack with an oxygen-containing supply air, and wherein the sensor can be arranged in an exhaust air path (or exhaust gas path) or in an exhaust air recirculation path (or EGR path), comprising:

[0015] Providing a comparison value for an oxygen content which is characteristic of an operating mode of the air system and / or of an operating mode of the fuel cell stack, operating the fuel cell stack in the operating mode of the air system and / or in the operating mode of the fuel cell stack, detecting a measured value using the sensor, comparing the measured value with the comparison value, assessing the sensor depending on the comparison.

[0016] The steps of the method according to the invention can be performed in the specified order or in a modified order. The steps of the method according to the invention can be performed simultaneously, at least partially simultaneously, and / or sequentially.

[0017] The fuel cell system according to the invention can preferably be used for mobile applications, for example, in vehicles, especially fuel-powered vehicles. The fuel cell system according to the invention can serve as the main energy supplier for a vehicle. At the same time, however, it is also conceivable that the fuel cell system according to the invention can be a power supply for a power take-off drive and / or an auxiliary drive of a vehicle, for example, a hybrid vehicle. The fuel cell system according to the invention can also be used for stationary applications, for example, in generators.

[0018] The fuel cell system according to the invention can comprise multiple stacks, each containing multiple stacked fuel cells and the associated functional systems, including media systems (air or cathode system, fuel or anode system, cooling system) and an electrical system. Preferably, the fuel cell system according to the invention can comprise multiple modules in the form of individual stacks with multiple stacked fuel cells.

[0019] The method enables verification, i.e., calibration, plausibility check, and / or diagnosis of a lambda sensor in a cathode exhaust path and / or in an EGR path. This ensures the functionality of the lambda sensor, the measured values ​​derived from it, and the resulting operating strategy.

[0020] The procedure for calibrating / plausibility checking / diagnosing a lambda sensor in a cathode exhaust path and / or in an EGR path, in particular over the lifetime of the sensor, can be implemented using the following measures:

[0021] Comparison with the oxygen content of the environment,

[0022] Calibration with an inert gas with oxygen content close to / equal to zero,

[0023] Comparison with an oxygen-depleted gas (characteristic curve), in particular with the help of: stationary and dynamic tests, additional sensors, preferably location detection, e.g. GPS, single cell voltages CVM, stack voltage, heat flow, or similar modeling.

[0024] The method can advantageously implement mutual plausibility checks for a CVM voltage measurement, a stack voltage measurement, and an oxygen content measurement by the lambda sensor. Several advantages can be achieved using this method:

[0025] Ensuring the functionality of the lambda sensor, advantageously over the lifetime of the sensor, and the measured values ​​derived from it, Robust operating strategy through reliable measured values, lifetime monitoring, drift detection,

[0026] Error message, troubleshooting, workshop, etc.

[0027] Furthermore, it can be provided that the comparison value is provided in the form of an oxygen content of the environment surrounding the fuel cell stack. This allows the sensor's measured value to be compared with existing data on the oxygen content of the ambient air. This data may already be available. However, this data can also be received or queried, e.g., from a weather service, a cloud, a navigation system, a news service, local sensors, etc.

[0028] Advantageously, the geographical location of the fuel cell system can be taken into account when providing the comparison value in the form of the ambient oxygen content. This ensures that the data is valid. Preferably, it can be verified that the vehicle is not in a garage, parking garage, or tunnel.

[0029] In addition, the GPS position can be used to obtain or query data on the oxygen content of the surrounding air precisely for the location of the vehicle, e.g. from a weather service, a cloud, a navigation system, a news service, local sensors, etc.

[0030] Furthermore, the following operating mode can be used to provide the comparison value in the form of an oxygen content of the environment of the fuel cell system:

[0031] L11 the air system is switched off, M11 the fuel cell stack is switched off.

[0032] Such an operating mode can occur, for example, when the vehicle is stationary, during preparation for a start, or immediately upon start. The method can be triggered using a wake-up function. The method can also be carried out as a preparatory measure for a start. The method can also be carried out as a verification measure after the vehicle has been parked. To check the sensor, it can be ensured that the sensor is in contact with the environment for a sufficiently long time. Advantageously, a geographical position of the fuel cell system can be checked in order to obtain or query data on the oxygen content of the air in the vicinity of the stack.

[0033] Furthermore, the following operating mode can be used to provide the comparison value in the form of an ambient oxygen content: L12 air transport via a bypass,

[0034] M12 the fuel cell stack is switched off and / or in standby.

[0035] Such an operating mode can occur, for example, when the air system is switched on, but the air is transported via a bypass. The air system can be in bypass mode. The stack can remain switched off and / or, for example, be in standby mode. Advantageously, a geographical position of the fuel cell system can be checked to obtain or query data on the oxygen content of the air in the vicinity of the stack.

[0036] In addition, the following operating mode can be used to provide the comparison value in the form of an ambient oxygen content: L13 Air transport during operation,

[0037] M13 the fuel cell stack is in OCV operation.

[0038] Such an operating mode can arise, for example, when the air system is in operation and the stack is also in operation, but is briefly (and preferably not too frequently) operated with zero current (i.e., without response) and OCV voltage. A trigger for short-term OCV operation can be a regeneration function or a special diagnostic function. This can also be used to derive a trigger for the current procedure or for checking the lambda sensor. The procedure can generally be triggered periodically, regularly, event-controlled and / or operating mode-dependently. When the vehicle is stationary, the procedure can be triggered according to all three rules: periodically, regularly and / or event-controlled. When the air system is in operation, the presence of a specific operating mode can be used as an event-controlled trigger.

[0039] Furthermore, it can be provided that the comparison value can be provided with an oxygen content of approximately zero. In this case, an inerted gas can be present at the sensor. Using a CVM voltage measurement and / or a total voltage measurement of the stack, an expected oxygen content can be determined and used as a comparison value.

[0040] It is conceivable that, when providing the comparison value with an oxygen content of approximately zero, an inert gas can be supplied to the sensor by at least one fuel cell stack and / or another fuel cell stack of the fuel cell system. In this way, different stacks in the system can be used to generate the inert gas.

[0041] Advantageously, when providing the comparison value with an oxygen content approximately zero, at least one CVM voltage and / or a total voltage of the fuel cell stack can be taken into account in order to be able to determine an expected oxygen content and form a comparison value.

[0042] Furthermore, it is conceivable that an impedance of the fuel cell stack can be taken into account when providing the comparison value, and / or that a heat flow through the fuel cell stack can be taken into account when providing the comparison value, etc. Thus, additional sensor values ​​that can indicate an oxygen content in the exhaust air can be advantageously taken into account when determining a comparison value for the sensor. To provide the comparison value with an oxygen content approximately zero, the following operating mode can be implemented: L20 the air system is operated such that an inert gas can be supplied to the sensor by the at least one fuel cell stack and / or another fuel cell stack of the fuel cell system,

[0043] M20 the at least one fuel cell stack and / or another fuel cell stack of the fuel cell system are / is operated in such a way that an inert gas can be provided to the sensor.

[0044] Furthermore, it can be provided that the comparison value is provided in the form of an oxygen content with an oxygen content of oxygen-depleted exhaust air. Using a CVM voltage measurement and / or a total voltage measurement of the stack, an expected oxygen content can be determined and used as a comparison value.

[0045] When providing the comparison value in the form of an oxygen content with an oxygen content of an oxygen-depleted exhaust air, the oxygen-depleted exhaust air can be provided to the sensor by the at least one fuel cell stack and / or another fuel cell stack of the fuel cell system.

[0046] Advantageously, when providing the comparison value in the form of an oxygen content with an oxygen content of an oxygen-depleted exhaust air, at least one CVM voltage and / or a total voltage of the fuel cell stack and / or a waste heat flow through the stack can be taken into account in order to be able to determine an expected oxygen content and form a comparison value.

[0047] Furthermore, it may be advantageous to consider at least one model of the fuel cell system and / or the air system when providing the comparison value in the form of an oxygen content with an oxygen content of oxygen-depleted exhaust air in order to precisely determine the expected oxygen content and accurately generate a comparison value. The following operating mode can be used to provide the comparison value in the form of an oxygen content with an oxygen content of oxygen-depleted exhaust air:

[0048] L30 the air system is operated in such a way that oxygen-depleted exhaust air can be provided to the sensor by the at least one fuel cell stack and / or another fuel cell stack of the fuel cell system,

[0049] M30 the at least one fuel cell stack and / or another fuel cell stack of the fuel cell system is / are operated in such a way that oxygen-depleted exhaust air can be provided to the sensor.

[0050] Furthermore, it is conceivable that the method can be carried out in a dynamic operating mode. In other words, the method can be carried out in a changing operating mode in the air system and / or in a changing operating mode of the at least one fuel cell stack and / or another fuel cell stack of the fuel cell system. This allows for flexible testing. Advantageously, the dynamic behavior of the sensor (e.g., response times, inertia) can be checked and / or evaluated and, furthermore, preferably taken into account or adapted for operational management.

[0051] Advantageously, the method allows data series to be collected over the sensor's lifetime. This can also be used to determine how the sensor value is drifting and / or whether measures such as repair, replacement, or similar should be initiated.

[0052] According to a further advantage, the method can be carried out for checking, in particular for plausibility, calibration, and / or diagnosis, a CVM measurement and / or a total voltage measurement of the fuel cell stack. In this way, the usefulness of the method can be increased. According to a second aspect, the invention provides a computer program product comprising instructions which, when the computer program product is executed by a computer, such as the computing unit of the control unit, cause the computer to carry out the method, which can proceed as described above. With the aid of the computer program product, the same advantages can be achieved that were described above in connection with the method according to the invention. These advantages are fully incorporated herein by reference.

[0053] A corresponding control unit provides a third aspect of the invention. A computer program in the form of code can be stored in a memory unit of the control unit. When the code is executed by a processing unit of the control unit, the program performs a method that can proceed as described above. The control unit can achieve the same advantages as those described above in connection with the method according to the invention. These advantages are incorporated herein by reference in their entirety.

[0054] A corresponding fuel cell system with a corresponding control unit provides a further fourth aspect of the invention. Using the fuel cell system, the same advantages described above in connection with the method according to the invention can be achieved.

[0055] Preferred embodiments:

[0056] The invention and its further developments, as well as their advantages, are explained in more detail below with reference to the accompanying drawings. They show schematically:

[0057] Fig. 1 is a schematic representation of a cathode path for a stack with lambda sensors at different locations in an exhaust air path and / or in an EGR path., Fig. 2 shows different operating points for calibration / plausibility / diagnosis of a lambda sensor, and

[0058] Fig. 3 different procedure options for calibration / plausibility check / diagnosis of a lambda sensor.

[0059] In the different figures, identical parts of the invention are always provided with the same reference numerals, which is why they are usually only described once.

[0060] Fig. 1 shows a schematic representation of an air system 10 for a fuel cell stack A. The air system 10 comprises an air supply path 11, a cathode path through the stack, an exhaust air path 12, a bypass path 13 and optionally an EGR path 14.

[0061] Depending on the topology of the fuel cell system FCS, one or more sensors x or lambda probes can be provided in the exhaust air path 12 and / or in the EGR path 14, for example at the installation locations x1, x2, x3, x4 shown in Fig. 1.

[0062] In multi-stack systems, several stacks can be A and B. In the example shown in Fig. 1, another fuel cell stack B is present.

[0063] Stack B can supply an oxygen-depleted gas and feed it into various locations in the air system 10 of stack A (three locations are shown as examples in Fig. 1).

[0064] With the aid of Fig. 2 and Fig. 3, the method can be described which was developed for checking, in particular for plausibility, calibration, and / or diagnosis, a sensor x for detecting an oxygen content (the sensor can also be referred to as a lambda probe) of an exhaust air A2 from at least one fuel cell stack A of a fuel cell system FCS. The fuel cell system FCS is shown schematically in Fig. 1. The method comprises the following steps:

[0065] Providing a comparison value xO2* for an oxygen content (cf. the values ​​on the x-axis in Fig. 2 and the left column in Fig. 3) which is characteristic of an operating mode L of the air system 10 and / or an operating mode M of the fuel cell stack A, Operating the fuel cell stack A in the operating mode L of the air system 10 and / or in the operating mode M of the fuel cell stack A (cf. columns L and M in Fig. 3),

[0066] Recording a measured value xO2 using the sensor x (see the y-axis in Fig. 2),

[0067] Comparing the measured value xO2 with the reference value xO2*, evaluating the sensor x depending on the comparison.

[0068] As schematically indicated in Figure 1, the vehicle's location can be determined via a GPS and / or cloud / server connection, and a check can be made to determine whether a comparison of the oxygen content with the ambient air (Env) can be provided. Preferably, the comparison with the ambient air should not take place in a tunnel, underground garage, or parking garage, as the oxygen content may be lower there.

[0069] The procedure can be carried out when the sensor is new, close to a strip end and, in principle, at any time during the sensor's lifetime.

[0070] The procedure can be time-triggered and / or event-triggered and / or repeated depending on the operating mode.

[0071] In this procedure, previous results can be included in the overall assessment (drift, plausibility, long-term behavior).

[0072] Figure 2 shows different operating points for calibrating / validating / diagnosing a lambda sensor in exhaust path 12 and / or EGR path 14. The possible oxygen content range for the method can be between the ambient oxygen content xO2env (max) and the oxygen content of an oxygen-free gas (inert gas) xO2=0 (min). The minimum and maximum values ​​can be reliably compared (see thick crosses in Figure 2), as shown below using Figure 3 and operating modes V (max: V11, V12, V13 and min: V20).

[0073] The values ​​in between can be approximately determined using additional sensors, such as CVM sensors, stack voltage measurements, and possibly other values ​​such as impedance, HFR, heat flow, etc., and / or using calibrated models (see thin crosses in Fig. 2 and operating mode V30 in Fig. 3). In the intermediate range (between the ambient oxygen content xO2env (max) and the oxygen content of an oxygen-free gas (inert gas) xO2=0 (min)), the values ​​can be calibrated with a certain degree of accuracy.

[0074] For the limit values, oxygen content of an oxygen-free gas (inert gas) xO2=0 (min) and oxygen content of the environment xO2env (max), a reverse plausibility check of the CVM measured values ​​or the stack voltage measured values ​​can also be carried out using the lambda probe.

[0075] Furthermore, it can be provided that the comparison value xO2* is provided in the form of an oxygen content xO2env of an environment Env of the fuel cell stack A. Thus, the sensor's measured value can be compared with existing data on the oxygen content of the ambient air. This data can be received or queried, e.g., from a weather service, a cloud, a navigation system, a news service, local sensors, etc.

[0076] As shown in Fig. 3, the following operating mode V11 can be used to provide the comparison value xO2* in the form of an oxygen content xO2env of the environment Env of the fuel cell system FCS:

[0077] L11 the air system 10 is switched off, M11 the fuel cell stack A is switched off.

[0078] Such an operating mode V11 can occur, for example, when the vehicle is stationary, during preparatory operation for a start, or immediately upon start. The method can be triggered using a wake-up function. The method can also be carried out as a preparatory measure for a start. The method can also be carried out as a verification measure after the vehicle has been parked. To check the sensor, it can be ensured that the sensor is in contact with the environment for a sufficiently long time. Advantageously, a geographical position GPS of the fuel cell system FCS can be checked in order to obtain or query data on the oxygen content of the air in the vicinity of the stack.

[0079] As shown in Fig. 3, the following operating mode V12 can be used to provide the comparison value xO2* in the form of an oxygen content xO2env of the environment Env:

[0080] L12 Air transport via a bypass 13,

[0081] M12 the fuel cell stack A is switched off and / or in standby; VinA and VoutA are closed.

[0082] Such a V12 operating mode can occur, for example, when the air system is switched on, but the air is transported via a bypass. The air system can be in bypass mode. The stack can remain switched off and / or be in standby mode, for example.

[0083] Advantageously, a geographical position GPS of the fuel cell system FCS can be checked to obtain or query data on the oxygen content of the air in the vicinity of the stack.

[0084] As shown in Fig. 3, the following operating mode V13 can be used to provide the comparison value xO2* in the form of an oxygen content xO2env of the environment Env: L13 Air transport during operation,

[0085] M13 Fuel cell stack A is in OCV operation; VinA and VoutA are open or partially open.

[0086] Such an operating mode V13 can occur, for example, when the air system is operating and the stack is also operating, but is operated briefly and preferably not too frequently with zero current—i.e., without response and OCV voltage. A trigger for brief OCV operation can be a regeneration function or a special diagnostic function. This can also be used to derive a trigger for the current procedure or for checking the lambda sensor.

[0087] Figure 3 shows that the reference value xO2* can be provided with an oxygen content of approximately zero. An inerted gas can be present at the sensor. Using a CVM voltage measurement and / or a total voltage measurement of the stack, an expected oxygen content can be determined and used as a reference value.

[0088] It is conceivable that, when providing the comparison value xO2* with an oxygen content of approximately zero, an inert gas can be provided to the sensor x by at least one fuel cell stack A and / or another fuel cell stack B of the fuel cell system FCS. In this way, different stacks in the system can be used to generate the inert gas.

[0089] Advantageously, when providing the comparison value xO2* with an oxygen content approximately zero, at least one CVM voltage CVM-U and / or a total voltage U of the fuel cell stack A can be taken into account in order to be able to determine an expected oxygen content and form a comparison value.

[0090] Furthermore, it is conceivable that an impedance of the fuel cell stack A can be taken into account when providing the comparison value xO2*, and / or that a heat flow through the fuel cell stack A can be taken into account when providing the comparison value xO2*, etc. Thus, further sensor values ​​that can indicate an oxygen content in the exhaust air can be taken into account in an advantageous manner when determining a comparison value for the sensor.

[0091] As shown in Fig. 3, the following operating mode V20 can be carried out to provide the comparison value xO2* with an oxygen content of approximately zero: L20 the air system 10 is operated in such a way that an inert gas can be provided to the sensor x by the at least one fuel cell stack A and / or another fuel cell stack B of the fuel cell system FCS,

[0092] M20 the at least one fuel cell stack A and / or another fuel cell stack B of the fuel cell system FCS are / is operated in such a way that an inert gas can be provided to the sensor x.

[0093] As shown in Fig. 3, the comparison value xO2* can be provided in the form of an oxygen content 0 < xO2 < xO2env with an oxygen content of an oxygen-depleted exhaust air A2. Using a CVM voltage measurement and / or a total voltage measurement of the stack, an expected oxygen content can be determined and used as a comparison value.

[0094] When providing the comparison value xO2* in the form of an oxygen content 0 < xO2 < xO2env with an oxygen content of an oxygen-depleted exhaust air A2, the oxygen-depleted exhaust air A2 can be provided to the sensor x by the at least one fuel cell stack A and / or another fuel cell stack B of the fuel cell system FCS.

[0095] Advantageously, when providing the comparison value xO2* in the form of an oxygen content 0 < xO2 < xO2env with an oxygen content of an oxygen-depleted exhaust air A2, at least one CVM voltage and / or a total voltage of the fuel cell stack A and / or a waste heat flow through the stack A can be taken into account in order to be able to determine an expected oxygen content and form a comparison value.

[0096] Furthermore, it may be advantageous if, when providing the comparison value xO2* in the form of an oxygen content 0 < xO2 < xO2env with an oxygen content of an oxygen-depleted exhaust air A2, at least one model of the fuel cell system FCS and / or the air system 10 is taken into account in order to precisely determine an expected oxygen content and accurately generate a comparison value. As shown in Fig. 3, the following operating mode V30 can be implemented to provide the comparison value xO2* in the form of an oxygen content 0 < xO2 < xO2env with an oxygen content of an oxygen-depleted exhaust air A2:

[0097] L30 the air system 10 is operated in such a way that an oxygen-depleted exhaust air A2 can be provided to the sensor x by the at least one fuel cell stack A and / or another fuel cell stack B of the fuel cell system FCS,

[0098] M30 the at least one fuel cell stack A and / or another fuel cell stack B of the fuel cell system FCS are / is operated in such a way that an oxygen-depleted exhaust air A2 can be provided to the sensor x.

[0099] Furthermore, it is conceivable that the method can be carried out in a dynamic operating mode V40. In other words, the method can be carried out in a changing operating mode L40 in the air system 10 and / or in a changing operating mode M40 of the at least one fuel cell stack A and / or another fuel cell stack B of the fuel cell system FCS. This allows for flexible implementation of the check.

[0100] Advantageously, in operating mode V50, data series Dt can be collected over a lifetime of the sensor x using the method.

[0101] The detailed implementation of the process depends on the respective system topology. For example, process V12, with respect to installation position x3, depends on how far the lambda sensor is located from the inlet of the bypass mass flow into the exhaust air path 12.

[0102] The method can advantageously use stationary defined operating states V10 to V30.

[0103] However, operating mode V40 can also be used to check the dynamic behavior of sensor x. Operating mode V50 evaluates the data over the lifetime of sensor x and also compares the changes in the xO2 measured values ​​with the changes in the CVM measured values ​​or stack voltage measured values. Mutual plausibility checks can also be performed over a long period of time.

[0104] A corresponding computer program product, a corresponding control unit (CU), and a corresponding fuel cell system (FCS) with a corresponding control unit (CU) represent further aspects of the invention. The above explanation of the embodiments describes the present invention exclusively within the framework of examples. Of course, individual features of the embodiments can be freely combined with one another, provided they are technically feasible, without departing from the scope of the present invention.

Claims

Claims 1. A method for checking, in particular plausibility checking, calibrating and / or diagnosing, a sensor (x) for detecting an oxygen content of an exhaust air (A2) from at least one fuel cell stack (A) of a fuel cell system (FCS), wherein the at least one fuel cell stack (A) is designed with an air system (10) to supply the at least one fuel cell stack (A) with an oxygen-containing supply air (A1), and wherein the sensor (x) is arranged in an exhaust air path (12) or in an exhaust air return path (14), comprising: Providing a comparison value (xO2*) for an oxygen content which is characteristic of an operating mode (L) of the air system (10) and / or of an operating mode (M) of the fuel cell stack (A), Operating the fuel cell stack (A) in the operating mode (L) of the air system (10) and / or in the operating mode (M) of the fuel cell stack (A), Recording a measured value (xO2) using the sensor (x), comparing the measured value (xO2) with the comparison value (xO2*), evaluating the sensor (x) depending on the comparison.

2. The method according to claim 1, wherein the comparison value (xO2*) is provided in the form of an oxygen content (xO2env) of an environment (Env) of the fuel cell stack (A).

3. The method according to claim 1 or 2, wherein a geographical position (GPS) of the fuel cell system (FCS) is taken into account when providing the comparison value (xO2*) in the form of an oxygen content (xO2env) of an environment (Env).

4. The method according to claim 2 or 3, wherein the following operating mode (V11) is carried out to provide the comparison value (xO2*) in the form of an oxygen content (xO2env) of an environment (Env): L11 the air system (10) is switched off, M11 the fuel cell stack (A) is switched off.

5. Method according to claim 2 or 3, wherein the following operating mode (V12) is carried out to provide the comparison value (xO2*) in the form of an oxygen content (xO2env) of an environment (Env): L12 Air transport via a bypass (13), M12 the fuel cell stack (A) is switched off and / or in standby mode.

6. Method according to claim 2 or 3, wherein the following operating mode (V13) is carried out to provide the comparison value (xO2*) in the form of an oxygen content (xO2env) of an environment (Env): L13 air transport during operation, M13 the fuel cell stack (A) is in OCV operation.

7. Method according to one of the preceding claims, wherein the method is triggered periodically, regularly, event-controlled and / or operating mode-dependent.

8. Method according to one of the preceding claims, wherein the comparison value (xO2*) is provided with an oxygen content approximately zero.

9. The method according to claim 8, wherein, when providing the comparison value (xO2*) with an oxygen content approximately zero, an inert gas is provided to the sensor (x) by the at least one fuel cell stack (A) and / or a further fuel cell stack (B) of the fuel cell system (FCS).

10. The method according to claim 8 or 9, wherein at least one CVM voltage (CVM-U) and / or a total voltage (U) of the fuel cell stack (A) is taken into account when providing the comparison value (xO2*) with an oxygen content of approximately zero, and / or wherein an impedance of the fuel cell stack (A) is taken into account when providing the comparison value (xO2*) with an oxygen content of approximately zero, and / or wherein a heat flow through the fuel cell stack (A) is taken into account when providing the comparison value (xO2*) with an oxygen content of approximately zero.

11. Method according to claims 8 to 10, wherein the following operating mode (V20) is carried out to provide the comparison value (xO2*) with an oxygen content approximately zero: L20 the air system (10) is operated in such a way that an inert gas can be provided to the sensor (x) by the at least one fuel cell stack (A) and / or another fuel cell stack (B) of the fuel cell system (FCS), M20 the at least one fuel cell stack (A) and / or another fuel cell stack (B) of the fuel cell system (FCS) are / is operated in such a way that an inert gas can be provided to the sensor (x).

12. Method according to one of the preceding claims, wherein the comparison value (xO2*) is provided in the form of an oxygen content (0 < xO2 < xO2env) with an oxygen content of an oxygen-depleted exhaust air (A2).

13. The method according to claim 12, wherein when providing the comparison value (xO2*) in the form of an oxygen content (0 < xO2 < xO2env) with an oxygen content of an oxygen-depleted exhaust air (A2), the oxygen-depleted exhaust air (A2) is provided to the sensor (x) by the at least one fuel cell stack (A) and / or a further fuel cell stack (B) of the fuel cell system (FCS).

14. The method according to claim 12 or 13, wherein at least one CVM voltage and / or a total voltage (U) of the fuel cell stack (A) and / or waste heat flow through the fuel cell stack (A) is taken into account when providing the comparison value (xO2*) in the form of an oxygen content (0 < xO2 < xO2env) with an oxygen content of an oxygen-depleted exhaust air (A2), and / or wherein at least one model of the fuel cell system (FCS) and / or the air system (10) is taken into account when providing the comparison value (xO2*) in the form of an oxygen content (0 < xO2 < xO2env) with an oxygen content of an oxygen-depleted exhaust air (A2).

15. Method according to claim 12 to 14, wherein the following operating mode (V30) is carried out to provide the comparison value (xO2*) in the form of an oxygen content (0 < xO2 < xO2env) with an oxygen content of an oxygen-depleted exhaust air (A2): L30 the air system (10) is operated in such a way that an oxygen-depleted exhaust air (A2) is passed through the at least one Fuel cell stack (A) and / or another fuel cell stack (B) of the fuel cell system (FCS) can be provided to the sensor (x), M30 the at least one fuel cell stack (A) and / or a further fuel cell stack (B) of the fuel cell system (FCS) are / is operated in such a way that an oxygen-depleted exhaust air (A2) can be provided to the sensor (x).

16. The method according to any one of the preceding claims, wherein the method is carried out in a dynamic operating mode (V40), and / or wherein the method is carried out in a changing operating mode (L40) in the air system (10) and / or in a changing operating mode (M40) of the at least one fuel cell stack (A) and / or a further fuel cell stack (B) of the fuel cell system (FCS).

17. Method according to one of the preceding claims, wherein the method collects data series (D(t)) over a lifetime of the sensor (x).

18. Method according to one of the preceding claims, wherein the method is carried out for checking, in particular plausibility checking, calibrating and / or diagnosing, a CVM measurement and / or a total voltage measurement of the fuel cell stack (A).

19. A computer program product comprising instructions which, when the computer program product is executed by a computer, cause the computer to carry out a method according to any one of the preceding claims.

20. Control unit (cu), comprising a computing unit and a memory unit in which a code is stored, which at least partial execution by the computing unit carries out a method according to one of the preceding claims.

21. Fuel cell system (FCS), comprising a control unit (cu) according to the preceding claim.

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