Method for checking the tightness and diagnosis of a shut-off device in an air system of a fuel cell system

Abstract

The invention relates to a method for checking the tightness and diagnosing at least one shut-off means used in the air system (5) of a fuel cell system comprising an air compressor (10), comprising a bypass valve / throttle valve (15), a pressure control valve / throttle valve (13) and / or a throttle valve (13; 15) with a tight-closing mode (opD), by carrying out a pressure build-up test and / or a pressure reduction test in the air system (5) in mild surge operation of the air compressor (10).

Description

[0001] The present invention relates to a method for checking the tightness and diagnosis of at least one shut-off device of an air system of a fuel cell system, comprising an air compressor.

[0002] In fuel cell systems for mobile or stationary use, oxygen from the ambient air is used as an oxidizing agent and gaseous hydrogen is used as a reducing agent or fuel to react to form water in the fuel cell and thus generate electrical power through electrochemical conversion. State of the art

[0003] According to the generally known prior art, the cathode path of a fuel cell stack is shut off upstream of the inlet and downstream of the outlet by means of tightly closing shut-off means of the type of interest here, primarily valves or throttle valves, in order to isolate the cathode path from the environment when the fuel cell stack is switched off, to deplete oxygen and the like.

[0004] In practice, throttle valves, in particular, are increasingly being used to perform both control functions and shut-off functions with a sealing effect. Such a throttle valve can also be used in the exhaust gas path to regulate the pressure or mass flow, as well as to shut off the cathode path downstream of the fuel cell stack.

[0005] Such throttle valves or valves can be operated in at least the following two modes: a so-called "opR" (non-sealed mode) for control operation, a control interval, or to ensure a mass flow. In this case, no tightness is required, no sealing function is activated, and no sealing pressure is provided. In a so-called "opD" (sealed mode), which is of interest here, a sealing function is ensured by stronger pressure between the sealing partners.

[0006] It is the object of the present invention to provide the possibility of diagnosing and / or leak testing tight-closing valves or throttle valves with different operating modes. Disclosure of the invention

[0007] The object is achieved by a method according to claim 1.

[0008] The invention includes the technical teaching that, in order to check the tightness and diagnose at least one bypass valve / throttle valve, pressure valve / throttle valve and / or a throttle valve with tight-closing mode (opD) used as a shut-off device in an air system comprising an air compressor, a pressure build-up test and / or a pressure reduction test is carried out in a mild surge operation of the air compressor.

[0009] This makes it easy to diagnose or monitor the actuators of the air system over their lifetime. Operating strategies can be adapted for optimal operation. The diagnostic results can be used via cloud / server to optimize fleets and the like. Functionality, control quality, and the implementation of timely maintenance measures can be carried out on the basis of the diagnostics according to the invention, in particular to increase system reliability. The results obtained as a result of the diagnostics can also be used to enable or improve other or additional diagnoses or to enable additional functionalities, for example, the calibration of platinum-free fuel cells using hot-film air mass meters and the like.

[0010] The term "mild-surge operation" refers to an operating mode in the field of thermal turbomachines. Thermal turbomachines are typically used for the air system of a fuel cell system. These have a surge limit that must not be exceeded to protect components. However, it is possible to exceed the surge limit at certain pressures in order to enter "mild-surge operation," which has no harmful disadvantages for the air compressor. This means that the air compressor can also pump into a volume that has no or only small outflows. If the air system of a fuel cell system is implemented using a different technology, for example, through volumetric pumping via a Roots compressor, no surge limit needs to be taken into account, and operation is not mild-surge, but normal operation.

[0011] It should also be noted that the tightness of the shut-off devices of interest here can also be tested and diagnosed by other means. Possible leaks of the shut-off devices can be taken into account when evaluating the tests of interest here. In addition to the method according to the invention, the electrical stack voltage can also be measured and evaluated to check the tightness of the shut-off devices.

[0012] During pressure build-up and pressure reduction tests, temperature effects and settling or settling times must generally be taken into account. Temperatures can be measured using existing temperature sensors or determined using models. Settling or settling times can be selected using gradient methods or trajectory analysis and applications to ensure robust diagnostics.

[0013] Implementing the method according to the invention requires pressure sensors, which are usually already present in the fuel cell system according to the state of the art, so no additional sensors are required. For the leak test, throttle valves are controlled in opD mode. The throttle valve or valve to be tested can be located in the cathode bypass of the fuel cell stack or in the exhaust path of the air system, which in this way shuts off the entire exhaust path to the environment.

[0014] Leak tests according to the invention can be performed during start-up, in a bypass phase, during stop or shutdown, with the cathode path blocked, which provides a suitable operating status for the leak test.

[0015] Further measures improving the invention are described in more detail below together with the description of preferred embodiments of the invention with reference to the figures. Examples of implementation

[0016] It shows: Fig. 1 a schematic representation of a leak test in an air system of a fuel cell system in a first embodiment, Fig. 2 a schematic representation of a leak test in an air system of a fuel cell system in a second embodiment, Fig. 3 a schematic representation of a leak test in an air system of a fuel cell system in a third embodiment, and Fig. 4 a schematic representation of a leak test in an air system of a fuel cell system in a fourth embodiment.

[0017] According to Fig. 1, a fuel cell system (not shown in detail here) comprises a fuel cell stack 1, a cooling path 2, anode path 3 and cathode path 4. The cathode path 4 is part of a known air system 5.

[0018] In this embodiment, a leak test is carried out using a pressure build-up test “UP” in a bypass path 6 and exhaust air path 7, wherein an inlet-side shut-off valve 8 with respect to the fuel cell stack 1 and an outlet-side shut-off valve 9 with respect to the fuel cell stack 1 are closed.

[0019] The air system 5 further comprises an air compressor 10, also arranged on the inlet side with respect to the cathode path 4 of the fuel cell stack 1, which extracts air from the environment 11 via a filter unit 12 to supply it to the cathode path 4. On the outlet side of the cathode path 4, a compressor 10' operates in suction mode, discharging the exhaust air to the environment 14 via a throttle valve 13 integrated in the exhaust air path 7. The bypass path 6 also contains a throttle valve 15.

[0020] Here, the air system 5 is operated in bypass mode, in which the throttle valves 13 and 15 are open or partially open. The pressure is selected so that it is lower than the maximum pressure for mild-surge operation. Subsequently, the throttle valve 15 of the bypass path 6 is closed "1.OFF" with activation for sealed mode (opD). This switches the air system 5 to mild-surge operation. The other throttle valve 13 is closed with a time delay "2.OFF" with activation for sealed mode (opD), so that the entire area downstream of the shut-off valve 9 and downstream of the bypass path 6 is depressurized beforehand. The pressure trajectory at pressure measuring point A is then measured and evaluated as follows: If the pressure builds up significantly, throttle valve 15 of bypass path 6 is leaking. If the measured pressure increases significantly, then throttle valve 13 of exhaust air path 7 is more tightly sealed than throttle valve 15 of bypass path 6. If the pressure increases slightly but not significantly, then throttle valve 13 in exhaust air path 7 is more tightly sealed than throttle valve 15 in bypass path 6.

[0021] According to Fig. 2, the tightness in exhaust air path 7 is checked using a pressure reduction test "DOWN". Here, the shut-off valves 8 and 9 are again closed. The air system is operated in bypass mode with the same pressure setting as in the previously described embodiment. The throttle valve 13 in exhaust air path 7 is closed "1.OFF" with activation for sealed mode (opD). This causes the air system 5 to switch to mild surge operating mode. After a short time, the throttle valve 15 of the bypass path 6 is also closed "2.OFF" with activation for sealed mode (opD). The air system 5 then continues to operate and is regulated so that the pressure corresponds to the pressure measured at point A. If the pressure measured at this pressure measuring point A drops, the pressure is reduced accordingly. This ensures that there is no significant pressure difference or only a small pressure difference across the bypass path 6 throughout the entire test.A significant pressure drop can then be attributed to a leak in the throttle valve 13. The pressure trajectory at point A is measured and evaluated as follows: If there is a significant pressure drop, throttle valve 13 is leaking. If there is no significant pressure drop, throttle valve 13 is approximately tight.

[0022] According to Fig. 3, a leak test is performed in bypass path 6 and exhaust air path 7 using a pressure reduction test "DOWN." Here, too, shut-off valves 8 and 9 are closed. Air system 5 is also in bypass mode with pressure selection as above. Throttle valve 13 is closed "1.OFF" with activation for sealed mode (opD). This causes air system 5 to enter mild surge operation. The other throttle valve 15 of bypass path 6 is also closed after a short time interval "2.OFF" with activation for sealed mode (opD). Subsequently, air compressor 10 is switched off "3.OFF" and the supply air path is relieved to approximately ambient pressure. The pressure trajectory at pressure measuring point A is measured and evaluated as follows: If there is a significant pressure reduction, throttle valve 13 and / or throttle valve 15 are leaking. If there is no significant pressure reduction, both throttle valves 13 and 15 are sealed.

[0023] In the Fig.4 illustrates an exemplary sequence of steps of the method according to the invention for checking the tightness and diagnosing shut-off devices.

[0024] A diagnostic request 100 is followed by a check 200 to determine whether the system requirements for performing a leak test are met. If this is the case, the diagnostics are performed 300 by carrying out process steps 400a, 400b, and / or 400c as described above. Process steps 400a to 400c can be performed independently of one another or in combination. It is not absolutely necessary that all process steps 400a to 400c be performed; the test execution also depends on the result. For example, it is sufficient to perform process steps 400a and 400b to evaluate the two throttle valves 13 and 15. An evaluation function combines the individual diagnostic results, performs the overall evaluation 500, and saves it.The overall evaluation can be used 600 to implement extended functionalities, such as adapting operating strategies, adding to a central spring storage, and the like. A time-based, load profile-based, or event-based trigger 700 initiates the process.

[0025] The diagnostic results and load profiles regarding the frequency of closing operations of the shut-off devices can be stored locally in control unit memories or transferred centrally to a cloud server in order to use them, for example, for modeling digital twins and the like.

Claims

[1] Method for checking the tightness and diagnosis of at least one shut-off device used in the air system (5) of a fuel cell system comprising an air compressor (10), comprising: - Bypass valve / throttle valve (15), - Pressure control valve / throttle valve (13) and / or - a throttle valve (13; 15) with tight-closing mode (opD), by carrying out a pressure build-up test and / or a pressure reduction test in the air system (5) in a mild-surge operation of the air compressor (10).

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