EP4320663A2

EP4320663A2 - Method for checking a fuel cell system for membrane impermeability

Info

Publication number: EP4320663A2
Application number: EP22715582.7A
Authority: EP
Inventors: Jochen Braun
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2021-04-07
Filing date: 2022-03-15
Publication date: 2024-02-14
Also published as: DE102021203444A1; WO2022214280A3; WO2022214280A2

Abstract

The invention relates to a method for checking a fuel cell system (100) for membrane impermeability, the method comprising the following steps: 1) shutting off sub-systems (Q1, Q2, Q3) of the fuel cell system (100) which could be the direct sources of a fuel leakage and/or a fuel mass flow, 2) operating a cathode system (10) for providing an oxygen-containing reactant, 3) operating an anode system (20) for providing a fuel-containing reactant, and 4) monitoring measurement results of the fuel sensor (S).

Description

description

title

Method for checking a fuel cell system

membrane tightness

The invention relates to a method for checking a fuel cell system for membrane tightness according to the independent method claim, a corresponding fuel cell system according to the independent device claim and a vehicle with a corresponding fuel cell system according to the independent device claim.

State of the art

Fuel cell systems are known in principle, also as energy suppliers in vehicles. In fuel cell systems, oxygen from the ambient air is generally used as the oxidizing agent and hydrogen as the reducing agent or fuel, in order to react to form water (or water vapor) in the fuel cell stack of the system and to supply electrical power by electrochemical conversion. The ambient air is usually provided to the fuel cell stack by means of a cathode system with an air compression system. The hydrogen is usually stored in a high-pressure tank (e.g. 700 bar) and fed to the fuel cell stack via lines and valves and recirculated in a loop-like anode system of an anode system. During operation, the anode loop must be purged and drained periodically during operation in order to reduce the increasing nitrogen content (through diffusion across the membrane) and the accumulation of water in the anode. Part of the purge gas is also hydrogen, which is why the purge gas is routed into the air system exhaust duct and there through the air mass flow is diluted to such an extent that no explosive mixture can form.

The fuel cell stack usually includes several fuel cells that are mutually sealed with many seals. However, these seals are subject to temperature changes, pressure changes, etc. and age accordingly. Therefore, the fuel cell stacks are usually not tight in the absolute sense. Another source of fuel leakage is a leaking, e.g. outdated, overly dry and/or damaged diaphragm. On the other hand, the high-pressure tanks for storing the hydrogen or their fittings, actuators, sensors and/or pipelines can leak.

Since hydrogen is very volatile and can form an explosive mixture with air, especially in confined or closed rooms, it is safety-relevant to detect any hydrogen leaks with certainty. Several hydrogen sensors are usually installed to detect hydrogen leakage. These sensors have a significant cost associated with them. In addition, the sensors have to be calibrated at great expense in order to be able to meet high safety requirements.

Disclosure of Invention

According to a first aspect, the invention provides a method for checking a fuel cell system for membrane tightness with the features of the independent method claim, according to a second aspect a corresponding fuel cell system with the features of the independent device claim and according to a third aspect a vehicle with a corresponding fuel cell system with the features of subordinate independent device claim. Further advantages, features and details of the invention result from the dependent claims, the description and the drawings. Features and details that are described in connection with individual aspects of the invention apply, of course, also in connection with the other aspects of the invention and vice versa, so that with regard to the disclosure individual aspects of the invention is always mutually referred to or can be.

According to the first aspect, the present invention provides: a method for checking a fuel cell system for membrane tightness or for checking a membrane of the fuel cell system for tightness. The fuel cell system can be designed for a vehicle. The fuel cell system can have the following elements: at least one fuel cell, at least one fuel cell per fuel cell stack, whereby preferably several fuel cell stacks can be provided, which can optionally be designed with a stack environment ventilation system, a cathode system for providing an oxygen-containing reactant to the at least one fuel cell, wherein the cathode system has a supply air line for providing supply air to the at least one fuel cell and an exhaust air line for discharging exhaust air from the at least one fuel cell, and wherein the cathode system has a bypass line which connects the supply air line and the exhaust air line, in order to conduct the supply air from the supply air line at least partially past the at least one fuel cell and to introduce it into the exhaust air line, and an anode system for providing a fuel-containing reactant, for example hydrogen , to the at least one fuel cell, which can optionally be designed with an anode system-environment ventilation system, the anode system having a purge and/or drain system for flushing the anode system and/or for discharging product water from the anode system, and a , Preferably modular, tank system with at least one tank or with several tanks per module for the fuel-containing reactant, which may be designed with a tank system environment ventilation system.

The fuel sensor within the meaning of the invention is arranged in the exhaust air line of the fuel cell system. Advantageously, the fuel sensor is designed to a fuel leakage and / or a To sense fuel mass flow from all possible fuel sources inside and outside the fuel cell system. According to the invention, the fuel sensor is preferably designed to sense a fuel leak and/or a fuel mass flow from all subsystems of the fuel cell system, which can be direct and/or indirect sources for a fuel leak and/or a fuel mass flow. such as B. the purge and / or drain system, the stack environment ventilation system, anode system environment ventilation system and / or the tank system environment ventilation system. The cathode path itself can be described as an indirect source, which is caused by various effects, such as e.g. B. membrane leakage or so-called "proton pump", fuel.

The method according to the invention has the following steps:

1) shutting off subsystems of the fuel cell system, which in particular can be direct sources of fuel leakage and/or a fuel mass flow,

2) operating the cathode system to provide an oxygen-containing reactant,

3) operating the anode path to provide a fuel containing reactant,

4) Monitoring fuel sensor readings.

The fuel sensor according to the invention can preferably serve as the only fuel sensor in the entire fuel cell system and in the entire vehicle. If secondary ventilation systems for fuel-carrying components are used in the vehicle, e.g. B. ventilation systems of an anode system, a vehicle interior, a trunk system, etc., no separate fuel sensors are required for this purpose. Thus, all direct and/or indirect sources of fuel leaks and/or fuel mass flows can be detected with just one fuel sensor. The fuel sensor can be designed in the form of a hydrogen sensor, for example. The purge and/or drain system can have at least one purge and/or drain line. The at least one purge and/or drain line can form a combined purge and/or drain discharge line. However, the at least one purge and/or drain line can also have two separate drain lines, comprising a purge drain line for a purge process and a drain drain line for a drain process.

The stack environment ventilation system can have at least one stack environment ventilation line. The at least one stack-environment vent line can each have a stack-environment vent line per fuel cell or stack or be designed as a common stack-environment vent line to the gas or the gas mixture, or to ventilate the near or direct environment of the fuel cell or the stack was used to discharge from the stack environment.

The anode system ambient venting system may include at least one anode system ambient venting line. The at least one anode system ambient vent line to vent from the anode system ambient the gas or gas mixture used to vent the vicinity of the components of the anode system.

The tank system environment ventilation system can have at least one tank ventilation line. The at least one tank vent line can each have one tank vent line per tank or per module with multiple tanks or be designed as a common tank vent line to vent the gas or gas mixture used to vent the near or immediate vicinity of the Tank system was used to discharge from the tank system environment.

Furthermore, it can be provided that the at least one purge and/or drain line, the at least one stack-environment vent line and/or the at least one tank vent line, preferably all Ventilation lines, in the exhaust line, in particular immediately before the fuel sensor, open or are fluidly connected there.

The fuel sensor can preferably be arranged downstream in the exhaust air line of the cathode system. The fuel sensor can advantageously be arranged in the exhaust air duct by means of a media combining device. The media combining device can be designed with or without a water storage function. The media combining device can ensure that the exhaust air from the at least one fuel cell, optionally with the other media streams from the fuel cell system, flows through the media combining device and is mixed there, preferably before it is discharged to the environment.

Downstream in the exhaust air line can be approximately at the end of the exhaust air line, with only one silencer being able to be arranged in the exhaust air line after the fuel sensor according to the invention.

The fuel cell system can be used not only for mobile applications, such as in motor vehicles, but also for stationary applications, such as in generator systems.

Sources of fuel include at least: the at least one purge and/or drain line (desired source of fuel mass flow), if applicable the at least one stack environment vent line (unwanted source of fuel leaks, with the at least one stack environment -Vent line can include multiple stack-environment vent lines, regardless of whether the at least one fuel cell or the at least one fuel cell stack is arranged without an additional housing, at least partially or entirely in an additional housing, optionally the at least one tank-environment vent line , wherein the at least one tank-ambient vent line may comprise multiple tank-vent lines, regardless of whether the tank system is arranged without an additional housing, at least in part or entirely in an additional housing, optionally the at least one anode system-ambient vent line, regardless whether the anode system is arranged without an additional housing, at least partly or completely in an additional housing, an indirect source of fuel leakage can also be referred to as the cathode path, which due to fuel transfer through the membrane or other effects fuel may contain, with further ventilation systems and / or sources for possible fuel leaks and fuel mass flows analogous to the ventilation lines mentioned can be fluidically connected to the exhaust air line just before the fuel sensor.

Advantageously, the detection and dilutions for all possible (unintended) fuel leaks and/or all possible (intended) fuel mass flows can be carried out at one point using only one fuel sensor.

Advantageously, the fuel accumulations can be diluted at least by the exhaust air from the cathode system and possibly by the bypass air of the cathode system.

Advantageously, a diagnostic method and/or a monitoring method with pin-pointing, i.e. detection of the source from which the fuel leak and/or the fuel mass flow originates, can also be carried out.

A further advantage is that the exhaust air line can be used to discharge water to the environment or to discharge water to another functional system of the fuel cell system and/or to a container for further use. Furthermore, it can be advantageous that the exhaust air, which may contain fuel, is diluted by means of a secondary air mass flow, e.g. B. a fresh air fan of a vehicle interior and / or a separate ventilation fan can be carried out. In this way, a decoupling of the air compressor operation in the supply air line and/or a redundancy for the air compressor operation can be created.

The idea of the invention is that the fuel sensor can be used to detect an unwanted fuel transfer through (at least) one membrane of the at least one fuel cell or of the at least one fuel cell stack. The invention also speaks of a membrane leak. A fuel transfer through a membrane can be unintentional when hydrogen transfers from anode to cathode without an electric current being able to be generated for the targeted/intended use. Unintentional fuel transfer can occur if the membrane (this means: at least one membrane or a membrane area in the stack) becomes leaky, e.g. if the membrane is too old, too dry or damaged, e.g. B. if the membrane shows tears or holes, and/or if the membrane is too dry. A membrane leak can be reversible (possibly too dry) or irreversible (damaged). To do this, we operate the cathode system and the anode system and ensure that no other sources of fuel leakage and/or fuel mass flow are open, so that no fuel should arrive at the fuel sensor with an intact membrane. If the fuel sensor nevertheless delivers measurable results, it can then be concluded that there is a membrane leak.

The invention can provide for several diagnoses which can be carried out one after the other or in a combination with one another. To carry out the method, comprising individual diagnoses one after the other or in a combination with each other, all possible sources of fuel, such as e.g. B. the purge and / or drain system, the stack environment ventilation system, anode system environment ventilation system and / or the tank system environment ventilation system shut off. If, for example, the fuel leakage through the membrane is significantly / essentially dependent on the pressure difference between the anode and cathode, then there is a high probability of a membrane hole/crack/etc.. This means that there is very likely irreversible damage to the membrane.

If this is not the case, the membrane could possibly be too dry and thus only be reversibly permeable to the fuel. This may require further (different) diagnostics to investigate the cause of the diaphragm leakage.

The invention can provide a preliminary stage or a rough or provisional diagnosis for a possible membrane leak or a trigger for further more in-depth diagnoses in normal operation of the fuel cell system. For this purpose, the cathode system and the anode system can be operated in such a way that the fuel cell or the stack is operated open to the cathode side (shutoff valves are open), and that the bypass line can be used as required (bypass valve is controlled as desired) or if the Bypass line cannot be sealed. At this point, no fuel should be detectable at the fuel sensor since all possible sources of fuel are shut off except possibly the leaking diaphragm. If the fuel sensor still registers measurable concentrations of the fuel, it can be a sign of a leaking membrane. Further more in-depth diagnoses can then be initiated.

A possibly additional diagnosis can provide for the cathode system and the anode system to be operated in such a way that the stack is operated open to the cathode side (shutoff valves are open), the bypass line is closed (bypass valve is closed) and is preferably sealed. A certain current can be drawn from the stack. Since all other paths for the fuel are complete up to the fuel sensor, the sensor should not detect any measurable concentrations of the fuel. When monitoring readings from the fuel sensor, different thresholds may be checked. Furthermore, from diagnosis to diagnosis, different speeds on the compressor and thus different mass flows are run in the system in order to verify the measurement results of the fuel sensor. The mass flow and/or the pressure in the cathode system can also be measured in order to check the measurement results of the fuel sensor for plausibility. Advantageously, the pressure in the cathode system and in the anode system can be measured and a defined pressure difference can be set across the membrane from diagnosis to diagnosis. If the reading of the fuel sensor also changes with the changing pressure difference, this can be a sign that the diaphragm is actually leaking, probably irreversibly damaged.

Another, possibly additional, diagnosis can provide that the cathode system is operated closed to the stack (shutoff valves are closed). After the oxygen on the cathode side has been depleted by the current draw in the blocked state of the stack (so-called bleed-down), current is no longer drawn from the stack. The compression system in the cathode system can continue to be active, so that the stack can be in standby mode, but without drawing power from the stack. This diagnosis can be advantageous, for example, in a start-stop operation, for example when there are breaks at traffic lights or when driving downhill. This puts the stack in an oxygen-poor state. If the (meaning at least one) membrane has a leak, then fuel passes from the anode path through the membrane into the cathode path. When, after a time, the shut-off valves are opened (the bypass valve can thereby be closed), the volume of gas previously trapped between the shut-off valves in the cathode path is discharged and delivered to the fuel sensor. If fuel has indeed passed through the membrane, the fuel sensor can detect a significant increase in fuel concentration in the exhaust air. In this way, a leak in the membrane can be sensed easily and clearly. The pressure difference between the anode system and the cathode system can be varied from diagnosis to diagnosis. If a higher fuel leakage is sensed with increasing pressure difference, irreversible damage to the membrane can be determined with an increased probability. Furthermore, of diagnosis Different speeds are run on the compressor for diagnostics in order to verify the measurement results of the fuel sensor by varying the operating point. The mass flow and/or the pressure in the cathode system can also be measured in order to check the measurement results of the fuel sensor for plausibility.

It can be advantageous in the context of a preliminary diagnosis that in step 2) the cathode system is operated, if necessary without shutting off and/or sealing the bypass line, and that in step 3) the fuel-containing reactant is recirculated, and that in step 4) a possible membrane leaks are detected and/or a more extensive diagnosis of membrane leaks is initiated when a measured value of the fuel sensor exceeds a first threshold value. In this way, it can be determined quickly and without major interventions in the normal operation of the fuel cell system that the membrane is possibly leaking. This preliminary stage can optionally be carried out as a rough or initial diagnosis for a possible membrane leak. This preliminary stage can also be used as a trigger for further, more in-depth diagnoses that may require more computing power and/or more serious interventions in the operation of the fuel cell system.

It is conceivable that this preliminary stage is carried out during normal operation of the fuel cell system, that the steps of the method in this preliminary stage are carried out simultaneously, at least partly simultaneously and/or one after the other, and/or that this preliminary stage is carried out periodically, in particular after a certain time , and/or is carried out regularly, in particular after a certain consumption, for example of the oxygen-containing reactant and/or of the fuel-containing reactant, and/or depending on the load profile.

A more in-depth diagnosis with few interventions in the normal operation of the fuel cell system can provide that in step 2) the bypass line is closed and shut-off valves in the air supply line and in the exhaust air line are opened in order to provide the entire supply air from the air supply line to the at least one fuel cell. In step 3), the fuel-containing reactant can be recirculated. If there is a reading from the fuel sensor exceeds at least a second threshold value, a membrane leak can be determined in step 4) and optionally a more extensive diagnosis of membrane leaks can be initiated.

It is conceivable that the steps of the method according to the invention are carried out simultaneously, at least partly at the same time and/or one after the other, and/or that the method is carried out periodically, in particular after a certain time, and/or regularly, in particular after a certain consumption, e.g of the oxygen-containing reactant and/or the fuel-containing reactant, and/or is carried out depending on the load profile.

A more in-depth diagnosis with relatively clear or easily recognizable results can provide that the bypass line is operated open for a specific time in step 2) and shut-off valves in the air supply line and in the exhaust air line are closed in order to achieve an oxygen-depleted state in the at least one fuel cell generate. In step 3), the fuel-containing reactant can be recirculated for the specific time. After the specified time has elapsed, the shut-off valves in the supply air line and in the exhaust air line can be opened and preferably the bypass line can be closed. If, after opening the shut-off valves, the measurement results of the fuel sensor show an increase, a membrane leak can be determined in step 4) and optionally a further diagnosis can be initiated. The diagnosis can be repeated again/several times with different pressure differences between the anode and the cathode and/or optionally a further diagnosis can be initiated.

It is conceivable that the method is carried out in a standby mode of the fuel cell system and/or that the method is carried out integrated into an operation of the fuel cell system, particularly at moments when no electrical power is required from the fuel cell system.

Furthermore, the method can have at least one more of the following steps: 2a) operation of a compressor in the supply air line with at least one speed,

2b) determining, e.g. by calculating or estimating, a desired mass flow rate of the oxygen-containing reactant which is to arrive at the fuel sensor,

2c) Checking, e.g. by measuring and calculating, the mass flow of the oxygen-containing reactant that is to arrive at the sensor using measured values from a mass flow sensor in the cathode system, e.g. B. in the supply air line,

2d) checking a pressure in the cathode system by a pressure sensor,

2e) Varying from diagnosis to diagnosis of the speed at which the compressor is operating,

3a) checking a pressure in the anode path using a pressure sensor, 3b) setting a specific pressure difference between the anode path and the cathode system from diagnosis to diagnosis, la) setting a defined current and/or a defined current density through the at least one fuel cell, and/or 4b) Confirming membrane leakage if the readings of the fuel sensor change from diagnosis to diagnosis as the pressure difference between the anode path and the cathode system varies accordingly, in particular as a function of the speed of the compressor, the mass flow of the oxygen-containing reactant, the pressure in the cathode system and /or the pressure in the anode path.

If the diaphragm is leaking, then increasing the pressure differential between the anode path and the cathode system from diagnosis to diagnosis will cause the reading at the sensor to increase. A reduction in the pressure difference from diagnosis to diagnosis in turn causes a reduction in the measured value at the sensor. In this way, it can be determined easily and reliably that the fuel detected at the fuel sensor originates from the membrane that is leaking, which is very likely to be irreversible. The speed of the compressor, the mass flow and/or the pressure in the cathode system and the pressure in the anode system can also be used to check the measurement results. According to the second aspect, the invention provides a corresponding fuel cell system which has been checked for membrane leaks using a method, the method being able to proceed as described above, the fuel sensor being arranged in the exhaust air line and being designed to detect a fuel leak and/or a To sense fuel mass flow in all subsystems of the fuel cell system, which may be sources of fuel leakage and/or fuel mass flow. With the aid of the fuel cell system according to the invention, the same advantages can be achieved that were described above in connection with the method according to the invention. Reference is made in full to these advantages here.

According to the third aspect, the invention provides a vehicle with a fuel cell system, which can be configured as described above. With the aid of the vehicle according to the invention, the same advantages can be achieved that were described above in connection with the method according to the invention. Reference is made in full to these advantages here.

Preferred embodiments:

The invention and its developments as well as its advantages are explained in more detail below with reference to drawings. They each show schematically:

1 shows a schematic representation of a fuel cell system according to the invention,

2 shows a schematic representation of a diagnostic method for possible fuel leaks and/or fuel mass flows in different subsystems of a fuel cell system, 3 shows a schematic representation of a method for checking a fuel cell system for membrane tightness within the meaning of the invention,

4 shows a schematic representation of a method for checking a fuel cell system for membrane tightness within the meaning of the invention, and

5 shows a schematic representation of a method for checking a fuel cell system for membrane tightness within the meaning of the invention.

In the different figures, the same parts of the invention are always provided with the same reference symbols, which is why they are usually only described once.

1 shows a fuel cell system 100 according to the invention, which can be used, for example, as a source of electrical energy in a vehicle 1, preferably in an electric vehicle and/or a highly automated or even autonomously driving vehicle.

The fuel cell system 100 has at least one fuel cell 101 or even a stack or stack of a plurality of fuel cells 101 which are combined to form a fuel cell stack which is designed with a stack ambient ventilation system Q2. The fuel cell 101 or the fuel cell stack or stack can have fuel leakage to the outside, since the many fuel cells 101 are designed with many seals that are subject to various aging mechanisms caused by media, mechanical stresses, temperature changes, pressure changes, etc. The fuel cell 101 or the fuel cell stack or stack can be accommodated at least in part in a housing 102 (at least in the upper area), so that the surroundings can be ventilated in a targeted manner. Escaping fuel, in particular hydrogen, can collect in an upper area from which the stack-environment ventilation line L2 of the stack-environment ventilation system Q2 can lead. The Stack Environment- Vent line L2 of the stack-environment ventilation system Q2 is introduced into an exhaust air line 12 of a cathode system 10 in front of the fuel sensor S, in particular in the form of a hydrogen sensor. The exhaust air from the exhaust line 12 of the cathode system 10 can dilute any accumulated fuel.

For ventilation of the fuel cell 101 or the fuel cell stack, the first supplier Al can be the supply air from the supply air line 11 of the cathode system 10 or from another supplier A2, A3, such as e.g. B. fresh air fan IN a vehicle interior and / or a separate ventilation fan BG can be used. The supply air can be introduced, for example, via a connecting line, which can optionally but advantageously contain a throttle VQ2, VQ3 and/or a controllable valve VSQ2, VSQ3, to the housing 102 of the fuel cell 101 or the fuel cell stack, preferably in the lower area . Various suppliers (such as the supply air line 11, a fresh air fan IN of a vehicle interior and/or a separate ventilation fan BG) for the ventilation lines Al, A2, A3 can be used to supply the air mass flow, as described in detail below becomes.

As already mentioned above, the fuel cell system 100 has a cathode system 10 for providing an oxygen-containing reactant to the at least one fuel cell 101 or to the fuel cell stack, with the cathode system 10 having an air supply line 11 for providing air supply to the at least one fuel cell 101 and an exhaust air line 12 for discharging an exhaust air from the at least one fuel cell 101. The system topology according to the invention provides only one fuel sensor S in the fuel cell system 101 and in the entire vehicle 1 . Various sources of direct and/or indirect (unintended) fuel leaks and/or (intended) fuel mass flows are conducted through corresponding subsystems Q1, Q2, Q3, Q4, Q5 of the fuel cell system 100 into the exhaust air line 12 of the cathode system 10.

The cathode system 10 is shown in FIG. 1 as an example. The supply air can z. B. sucked from the environment U and according to the Requirements of the fuel cell 101 are filtered using an air filter AF. Different system topologies mil/without an intake air cooler IC, with/without a turbine in the exhaust air line 12, mil/without a humidifier H, with single or multi-stage compression, with a single-flow or multi-flow compressor V, with single or double-shaft systems, with/ without water injection, etc. are possible.

Furthermore, the fuel cell system 100 has an anode system 20 for providing a fuel-containing reactant to the at least one fuel cell 101 or to the fuel cell stack, the anode system 20 having a purge and/or drain system Q1 for flushing the anode system 20 and/or for discharging one Product water from the anode system 20 has. The purge and/or drain line LI is advantageously introduced into the exhaust air line 12 of the cathode system 10 in front of the fuel sensor S and diluted there. The anode system 20 may also include an anode system ambient ventilation system Q4 to ventilate the surroundings of the anode system 20 components. The anode system-environment ventilation system Q4 can have at least one anode system-environment ventilation line, not shown, in order to extract the gas or gas mixture that was used to ventilate the immediate or immediate vicinity of the components of the anode system 20 from the anode system -dissipate the environment.

The purge process can advantageously take place not only when the cathode system 10 provides sufficient air mass flow/air volume flow, but also when this is not the case. For this purpose, using the fuel cell system 100 in addition to the supply air from the supply air line 11 other suppliers A2, A3, such. B. fresh air fan IN a vehicle interior and / or a separate ventilation fan BG can be used.

Furthermore, the cathode system 10 has a bypass line 13, which fluidically connects the air supply line 11 and the exhaust air line 12 in order to guide the supply air from the air supply line 11 at least partially past the at least one fuel cell 101 and into the exhaust air line 12. In the A bypass valve BV is preferably provided for supply air line 13 in order to control the amount of supply air that is routed past the at least one fuel cell 101 . The bypass valve BV is opened to operate the bypass line 13 open. The bypass valve BV is closed to operate the bypass line 13 closed. The bypass valve BV can preferably have a sealing function.

In addition, the cathode system 10 has a shut-off valve SV1 in the air supply line 11, just before the air supply line 11 enters the at least one fuel cell 101, and a shut-off valve SV2 in the exhaust air line 12, just after the exhaust air line 12 exits the at least one fuel cell 101, on. The shut-off valves SV1, SV2 are opened in order to provide the supply air to the at least one fuel cell 101.

Furthermore, the fuel cell system 100 has a preferably modular tank system 30 with at least one tank T (preferably several tanks T or bottles per module) for the fuel-containing reactant, which is designed with a tank system environment ventilation system Q3. The tank system 30 can be arranged, for example, in the rear area of the vehicle 1 (e.g. in a trunk), but also in an underbody of the vehicle (e.g. below the fuel cell stack or below the passenger compartment). Due to the modular design of the tank system 20, the distance between the tank system 30 and the stack and/or the cathode system 10 is reduced and connections between these systems can be implemented more easily. Advantageously, the individual tanks T can be enclosed in a module, e.g. by several modules in the tank system 30, by means of (each) a tank housing 31, which can form part of the tank system ambient ventilation system Q3. The tank housing 31 can in turn have a tank ventilation line L3.

For ventilation of the tank system 30, the first supplier A1 can be the supply air from the supply air line 11 of the cathode system 10 and/or the fresh air from another supplier A2, A3, such as e.g. B. fresh air fan IN a vehicle interior and / or a separate ventilation fan BG can be used. The supply air for ventilation is provided by the first supplier Al via a ventilation line Al, which branches off from the supply air line 11 of the cathode system 10, e.g. before the humidifier H (ventilation line Al.l), after the humidifier H (ventilation line Al.2 ) or in front of the supply air cooler IC (ventilation line Al.3).

The purge and/or drain system Q1 can have a (combined or double) purge and/or drain line LI. The stack environment ventilation system Q2 can have at least one (or more) stack environment ventilation line(s) L2. The tank system environment ventilation system Q3 can also have at least one (or more) tank ventilation lines) L3. The anode system ambient ventilation system Q4 can also have a ventilation line, not shown. At the end of or downstream in the exhaust air line 12 of the cathode system 10 is a fuel sensor S, for example in the form of a hydrogen sensor. According to the invention, the purge and/or drain line LI, the at least one stack ambient ventilation line L2, the at least one tank ventilation line L3 and/or the anode system ambient ventilation line, if present, open into the exhaust line 12 of the cathode system 10 (preferably all three lines LI, L2, L3) in front of the fuel sensor S1, as shown in FIG.

Within the scope of the invention, only one fuel sensor S can be used for the complete fuel cell system 100 and for the entire vehicle 1 . All lines L1, L2, L3, which can be sources of fuel, in particular hydrogen, can be brought together in the exhaust air line 12 of the cathode system 10. In Figure 1, the purge and/or drain line LI, the stack environment ventilation line L2 are shown as an example, regardless of whether the at least one fuel cell 101 or the at least one fuel cell stack is/are open or at least partially arranged in a housing 102 isl/are, and the tank vent line L3, regardless of whether the tank system 30 is open or at least partially arranged in a housing 31 is shown. In the context of the invention but other sources of possible fuel leaks are also conceivable, which can also be fluidically connected to the exhaust air line 12 of the cathode system 10, preferably in front of the fuel sensor S, like the ventilation lines L1, L2, L3 mentioned.

Thus, all possible direct and/or indirect fuel leaks can be detected at one point in the fuel cell system 100 . Advantageously, the accumulations of fuel can at least be diluted by the exhaust air from the cathode system 10 .

With the aid of the fuel cell system 100 described, a diagnostic method or a checking method with pin-pointing, i.e. detection of the source from which the hydrogen leak or the hydrogen mass flow originates, can also be carried out, as shown in FIG.

By connecting the anode system ambient ventilation system Q4, the tank system ambient ventilation system Q3 and/or the stack ambient ventilation system Q2, if present, to the exhaust air line 12, the fuel that has accumulated in the respective systems can be reliably routed and diluted.

It is advantageous in the described fuel cell system 100 that the purge gas can be diluted by means of a secondary air mass flow A2, A3, e.g. a fresh air fan IN of a vehicle interior and/or a separate ventilation fan BG. In this way, decoupling from the air compressor operation in the supply air line 11 and redundancy can be created.

But also for the ventilation systems Q2, Q3, Q4 of the tank system 30, the stack and/or the anode system 20, which are provided in the system 100, a decoupling from the cathode system 10 and a redundancy can be created for ventilation of the respective systems.

FIG. 2 schematically shows a possible method for diagnosing a fuel leak and/or a fuel mass flow in a Fuel cell system 100, which can be designed as described above.

The diagnostic method can have at least one of the following steps:

D4) Monitoring of measured values of the fuel sensor S during operation (“normal operation”) of the fuel cell system 100.

During the diagnosis in step D4), the measured value or the measured values or the measured signal of the fuel sensor S can be compared with a threshold value or with a plurality of threshold values. The measured value or the measured values or the measured signal of the fuel sensor S can advantageously be evaluated over time in order to be able to detect fuel content increases and leaks at an early stage. If the measured value or the measured values or the measured signal of the fuel sensor is sufficiently low, no or, depending on the threshold value, initially no more precise diagnosis is necessary. However, if the values are above an applicable limit, further diagnoses D1), D2), D3) can be carried out.

A low limit or a first threshold value that is not exceeded in step D4) can be a sign of “everything is OK”. From the low limit upwards, for example, a checking action can be initiated, e.g. B. more frequent reading of the fuel cell sensor S in step D4), observation of the increase in fuel content and/or initiation of further diagnoses D1), D2), D3). A higher limit or a second threshold value can, for example, result in a warning action, e.g. B. Requesting the driver to stop the vehicle 1, requesting the vehicle occupants to leave the vehicle 1, warning other road users, etc.

Above a certain threshold, the following steps can be taken:

Dl) Operating the purge and / or drain system Ql, the stack ventilation system Q2, the tank ventilation system Q3 and the anode system environment ventilation system Q4, if present, inactive (ie deactivated or not in operation, a purge valve PDV is closed ) are, D2) operating the stack ventilation system Q2, with the purge and/or drain system Q1, the anode system ambient ventilation system Q4 and the tank ventilation system Q3 being inactive, and/or

D3) Operating the tank ventilation system Q3, the purge and/or drain system Q1, the anode system ambient ventilation system Q4 and the stack ventilation system Q2 being inactive.

Furthermore, a further step, not shown in FIG. 2, can be carried out, in which the anode system ambient ventilation system Q4 is operated, with the purge and/or drain system Q1, the stack ventilation system Q2 and the tank ventilation system Q3 being inactive are.

Steps D1), D2) and/or D3) can also be carried out periodically. This makes it possible to detect the source from which the fuel leak or the fuel mass flow originates.

For this purpose, the respective paths Q1, Q2, Q3, Q4, Q5 of the possible sources that are present in the system 100 are switched in such a way that only one possible source for a fuel leak or fuel mass flow is briefly detected.

Specific waiting times and/or averaging, recommendations to the user of the vehicle 1 can be set up between steps D1), D2) and D3). Step D4) can be carried out, for example, when vehicle 1 is parked or shortly before vehicle 1 is started, in order, for example, to quickly check whether the ventilation systems Q2, Q3, Q4 are in order and/or to find out whether an additional diagnosis D2) and/or D3) is required, and/or to obtain a reference measurement for steps D2) and/or D3).

It is also conceivable that the measured values in steps D1) to D4) are compared with one another, with one another or in combination with one another in order to check the plausibility of the results of the diagnostic method (e.g. value in D4=value in D2+value in D3? ) In addition, the diagnostic method can include at least one of the following steps:

D5) Monitoring of measured values of the fuel sensor S in an unventilated operation (“all closed”) of the fuel cell system 100, with the purge and/or drain system Q1, the stack ventilation system Q2, the tank ventilation system Q3 and the anode system-environment ventilation system Q4 all, if any, are turned off. The fuel sensor S1 can thus be gauged or calibrated. An open/closed diagnosis of a purge valve PVD can thus also be carried out.

In addition, the diagnostic method may include at least one of the following steps:

D6) Monitoring of measured values of the fuel sensor S in a fully ventilated operation ("all open") of the fuel cell system 100, wherein the purge and / or drain system Ql, the stack environment ventilation system Q2, the tank environment ventilation system Q3 and the Anode system-environment-ventilation system Q4 all, if any, are active. This step D6) can be carried out, for example, when the vehicle 1 is parked or shortly before the vehicle 1 is started, in order, for example, to quickly check whether everything is in order and/or to find out whether an additional diagnosis D1), D2) and/or D3) is required and/or to obtain a reference measurement for steps D1), D2) and/or D3).

In addition, it is conceivable that the measured values in steps D1) to D6) are compared with one another, with one another or also in combination with one another in order to check the results of the diagnostic method for plausibility (e.g. value in D1 <= value in D6?)

FIGS. 3 to 5 each show a possible diagnosis within the meaning of the method according to the invention for checking the fuel cell system 100 for membrane tightness or in other words for checking a membrane of the at least one fuel cell 101 for tightness. The method is carried out using a fuel sensor S, which is the only fuel sensor S for sensing and/or monitoring all fuel Leaks and/or fuel mass flows in the fuel cell system 100 according to FIG. 1 are used. The method can have at least one or a combined diagnosis according to FIGS. 3, 4 and/or 5.

The method for checking the fuel cell system 100 for membrane tightness, comprising at least one or a combined diagnosis according to FIGS. 3, 4 and/or 5, can be carried out, for example, in step D5) of the diagnosis method according to FIG.

However, it is also conceivable that the method for checking the fuel cell system 100 for membrane tightness, comprising at least one or a combined diagnosis according to FIGS. 3, 4 and/or 5, is carried out as a separate method independently of the diagnostic method according to FIG can be.

All diagnoses according to FIGS. 3 to 5 have the following steps:

1) shutting off subsystems Q1, Q2, Q3, Q4 of the fuel cell system 100, which can be direct sources of fuel leakage and/or a fuel mass flow,

2) operating the cathode system 10 to provide an oxygen-containing reactant,

3) operating the anode path 20 to provide a fuel containing reactant,

4) Monitoring measurement results of the fuel sensor S.

The invention provides that the fuel sensor S can be used to detect an unwanted fuel transfer through (at least) one membrane of the at least one fuel cell 101 or the at least one fuel cell stack (membrane leakage). This can happen, for example, if the membrane becomes too old, too dry and/or damaged.

To carry out the method, comprising individual diagnoses one after the other or in a combination with one another, in step 1) all possible sources of fuel, such as e.g. B. the purge and / or drain system Ql, the Stack ambient ventilation system Q2, the tank system ambient ventilation system Q3 and the anode system ambient ventilation system Q4, if equipped, shut down.

FIG. 3 shows a diagnosis which can serve as a preliminary stage or a rough or initial diagnosis for a possible membrane leak or a trigger for further more in-depth diagnoses, for example according to FIGS. 4 or 5. This procedure can be carried out in a normal operation of the fuel cell system 100 . For this purpose, the cathode system 10 and the anode system 20 can be operated in such a way that the fuel cell 101 or the stack is operated open to the cathode side (shutoff valves SV1, SV2 are open), if the bypass line 13 is used (bypass valve BV is controlled as desired) or if the bypass line 13 cannot be sealed (bypass valve BV without sealing function). In this case, no fuel H2 should be detectable at the fuel sensor S, since all possible sources of fuel H2, with the possible exception of the leaky membrane, are shut off. If the fuel sensor still detects measurable concentrations of the fuel H2, it can be a sign of a leaking diaphragm. Further more in-depth diagnoses, for example according to FIGS. 4 and/or 5, can then be initiated.

FIG. 4 shows a diagnosis which can be used as an additional diagnosis as part of the method for checking the fuel cell system 100 for membrane tightness. This diagnosis can provide for the cathode system 10 and the anode system 20 to be operated in such a way that the stack is operated open to the cathode side (shutoff valves SV1, SV2 are open), the bypass line 13 is closed (bypass valve BV is closed) and is preferably sealed. A certain current can be drawn from the stack. Since all other paths for the fuel are complete up to the fuel sensor S, the sensor should not detect any measurable concentrations of the fuel H2. When monitoring measurement results from the fuel sensor S, different threshold values S2 can be checked. Furthermore, different speeds on the compressor V and thus different mass flows in the system can be run from diagnosis to diagnosis in order to compare the measurement results of the Verify fuel sensor S. The mass flow and/or the pressure in the cathode system 10 can also be measured in order to check the measurement results of the fuel sensor S for plausibility. Advantageously, the respective pressure in the cathode system 10 and in the anode system 20 can be measured and a defined pressure difference (dpMem=pAnod-pKath>0) can be set across the membrane from diagnosis to diagnosis. If the reading of the fuel sensor S also changes from diagnosis to diagnosis as the pressure difference changes, this can be a sign that the membrane is actually leaking.

FIG. 5 shows a diagnosis which can be used as an additional diagnosis as part of the method for checking the fuel cell system 100 for membrane tightness. This diagnosis can provide that the cathode system 10 is operated closed to the stack (shutoff valves SV1, SV2 are closed). After a certain time, after the oxygen has been depleted by current drawing in the blocked state of the stack, no current is drawn from the stack (so-called bleed-down). The compressor V in the cathode system 10 can continue to be active, so that the stack can be in standby mode, but no current is drawn from the stack. This diagnosis can be advantageous, for example, in a start-stop operation, for example when there are breaks at traffic lights or when driving downhill. This puts the stack in an oxygen-poor state. If there is a membrane leak, fuel H2 passes from the anode path through the membrane into the cathode path. When the shut-off valves SV1, SV2 are opened after a time (the bypass valve BV can be closed in the process), the gas volume previously enclosed between the shut-off valves SV1, SV2 in the cathode path is discharged and routed to the fuel sensor S. If fuel has actually passed through the membrane, the fuel sensor S can detect a significant increase in fuel concentration in the exhaust air. A leak in the membrane can thus be detected in a simple and easily detectable manner. Furthermore, the pressure difference between the anode system 20 and the cathode system 10 can be varied from diagnosis to diagnosis. Furthermore, different speeds can be run on the compressor V from diagnosis to diagnosis in order to carry out the measurement results of the fuel sensor S Verify operating point variation. The mass flow and/or the pressure in the cathode system 10 can also be measured in order to check the measurement results of the fuel sensor S for plausibility.

When operating the cathode system 10 in step 2), the following (sub) steps can also be provided:

2a) operation of a compressor V in the supply air line 11 with at least one speed,

2b) determining (by sensing and calculating or estimating) a desired mass flow rate of the oxygen-containing reactant to arrive at the fuel sensor S,

2c) Checking (by recording and calculating) the mass flow of the oxygen-containing reactant that is to arrive at the fuel sensor S using measured values from a mass flow sensor in the cathode system 10, e.g. in the supply air line 11,

2d) checking a pressure in the cathode system 10 by a pressure sensor, and/or

2e) Varying from diagnosis to diagnosis the speed at which the compressor V is operated.

When operating the anode system 20 in step 3), the following (sub) steps can also be provided:

3a) checking a pressure in the anode path 20 by a pressure sensor, and/or

3b) Setting from diagnosis to diagnosis of a certain pressure difference between the anode path 20 and the cathode system 10.

Before and/or during the monitoring of measurement results from the fuel sensor S in step 4), the following (sub)steps can also be provided: la) setting a defined current and/or a defined current density through the at least one fuel cell 101, and/or 4b) confirming the membrane leakage, if the measured values of the fuel sensor S change accordingly from diagnosis to diagnosis when the pressure difference between the anode path 20 and the cathode system 10 varies, in particular as a function of the speed of the compressor V, the mass flow of the oxygen-containing reactant, the pressure in the cathode system 10 and/or the pressure in the anode path 20.

If the membrane is leaking, then increasing the pressure differential between the anode path 20 and the cathode system 10 from diagnosis to diagnosis will cause the reading at the sensor to increase. A reduction in the pressure difference from diagnosis to diagnosis in turn causes a reduction in the measured value at fuel sensor S. In this way it can be determined easily and reliably that the fuel H2 detected at fuel sensor S actually comes from the leaky membrane.

For checking the measurement results of the fuel sensor S, the speed of the compressor V, the mass flow and/or the pressure in the cathode system 10 and the pressure in the anode system 20 can also be taken into account.

According to the second aspect, the invention provides a fuel cell system 100 with a fuel sensor S that has been calibrated by a method that can be run as described above.

A vehicle 1 with a corresponding fuel cell system 100 also represents an aspect of the invention.

The above description of the figures describes the present invention exclusively within the framework of examples. It goes without saying that individual features of the embodiments can be freely combined with one another, insofar as this makes technical sense, without departing from the scope of the invention.

Claims

Expectations

1. Method for checking a fuel cell system (100) for membrane tightness, the fuel cell system (100) having:

- at least one fuel cell (101),

- a cathode system (10) for providing an oxygen-containing reactant to the at least one fuel cell (101), the cathode system (10) having a supply air line (11) for providing supply air to the at least one fuel cell (101) and an exhaust air line (12) for discharging an exhaust air from the at least one fuel cell (101), and wherein the cathode system (10) has a bypass line (13) which connects the air supply line (11) and the exhaust air line (12) in order to circulate the air supply from the air supply line (11) to lead at least partially past the at least one fuel cell (101) and to introduce it into the exhaust air line (12),

- and an anode system (20) for providing a fuel-containing reactant to the at least one fuel cell (101), the fuel sensor (S) being arranged in the exhaust air line (12) and being designed to detect a fuel leakage and/or a fuel mass flow in to sense all subsystems (Q1, Q2, Q3, Q4, Q5) of the fuel cell system (100), which may be sources of a fuel leak and/or a fuel mass flow, the method having the following steps:

1) shutting off subsystems (Q1, Q2, Q3, Q4) of the fuel cell system (100), which can be direct sources of fuel leakage and/or fuel mass flow,

2) operating the cathode system (10) to provide an oxygen-containing reactant,

3) operating the anode system (20) to provide a fuel-containing reactant, 4) Monitoring readings from the fuel sensor (S).

2. The method according to claim 1, characterized in that in step 2) the cathode system (10) is operated, if necessary without shutting off and/or sealing the bypass line (13), and in step 3) the fuel-containing reactant is recirculated, and that in step 4) a possible membrane leak is determined and/or a more extensive diagnosis of membrane tightness, e.g. according to claim 4 and/or 6, is initiated if a measured value of the fuel sensor (S) exceeds a first threshold value (S1).

3. The method according to the preceding claim, characterized in that the method is carried out in normal operation of the fuel cell system (100), that the steps of the method are carried out simultaneously, at least partly. Simultaneously and / or sequentially, and / or that the method periodically , in particular after a certain time, and/or regularly, in particular after a certain consumption, for example of the oxygen-containing reactant and/or of the fuel-containing reactant, and/or depending on the load profile.

4. The method according to any one of the preceding claims, characterized in that in step 2) the bypass line (13) is closed and shut-off valves (SV1, SV2) in the air supply line (11) and in the exhaust air line (12) are opened in order to supply air from the supply air line (11) to the at least one fuel cell (101), and that in step 3) the fuel-containing reactant is recirculated, and that in step 4) a membrane leak is detected and/or a more extensive diagnosis of membrane leaks, e.g Claim 6, initiated when a measured value of the fuel sensor (S) exceeds at least a second threshold value (S2).

5. The method according to the preceding claim, characterized in that the steps of the method according to the invention are carried out simultaneously, at least partly at the same time and/or in succession, and/or that the method is carried out periodically, in particular after a certain time, and/or regularly, in particular carried out after a certain consumption, for example of the oxygen-containing reactant and/or of the fuel-containing reactant, and/or depending on the load profile.

6. The method according to any one of the preceding claims, characterized in that for a certain time (tl) in step 2) the bypass line (13) is operated open and shut-off valves (SV1, SV2) in the air supply line (11) and in the exhaust air line ( 12) are closed to produce an oxygen-depleted state in the at least one fuel cell (101), and that for the specific time (tl) in step 3) the fuel-containing reactant is recirculated, after the specific time (tl) the shut-off valves (SV1, SV2) in the supply air line (11) and in the exhaust air line (12) are opened and in particular the bypass line (13) is closed, and that in step 4) a membrane tightness is determined and/or a further diagnosis of membrane tightness, e.g. according to claim 4, initiated when the readings of the fuel sensor (S) show an increase.

7. The method according to the preceding claim, characterized in that the method is carried out in a standby mode of the fuel cell system (100) and/or that the method is carried out in an integrated manner in an operation of the fuel cell system (100), in particular in Moments when no electrical power from the fuel cell system (100) is required.

8. The method according to any one of the preceding claims, characterized in that the method comprises at least one other of the following

steps:

2a) operating a compressor (V) in the supply air line (11) with at least one speed,

2b) determining a target mass flow of the oxygen-containing

reactants to arrive at the fuel sensor (S),

2c) checking the mass flow of the oxygen-containing reactant to arrive at the fuel sensor (S) using readings from a mass flow sensor in the cathode system (10),

2d) checking a pressure in the cathode system (10) by a pressure sensor,

2e) Varying from diagnosis to diagnosis of the speed at which the compressor (V) is operated,

3a) checking a pressure in the anode system (20) by a pressure sensor,

3b) Setting from diagnosis to diagnosis of a specific

Pressure difference between the anode system (20) and the cathode system (10), la) setting a defined current and/or a defined current density through the at least one fuel cell (101), and/or

4b) Confirming the membrane leak if the measured values of the fuel sensor (S) change accordingly from diagnosis to diagnosis when the pressure difference between the anode system (20) and the cathode system (10) varies, in particular as a function of the speed of the compressor (V) , the mass flow of the oxygen-containing reactant, the pressure in the cathode system (10) and/or the pressure in the anode system (20).

9. fuel cell system (100), which was checked by a method according to any one of the preceding claims, wherein the fuel sensor (S) in the exhaust air line (12) is arranged and designed to a fuel leakage and / or a fuel mass flow in all subsystems (Q1, Q2, Q3, Q4, Q5) of the fuel cell system (100), which can be sources of fuel leakage and/or fuel mass flow.

10. Vehicle (1) with a fuel cell system (100) according to the preceding claim.