Fuel cell system, gas tank system and method for operating a gas tank system

Abstract

The invention relates to a method for operating a gas tank system, which method comprises: measuring a pressure in a high-pressure line system in a state in which the high-pressure line system has been separated for a predetermined period from a gas tank by means of a first valve device which is in a closed state, and from a consumer system by means of a flow-control device which is in a closed state; and comparing the measured pressure with a pressure threshold value. When the measured pressure is lower than the pressure threshold value, the following is also carried out: supplying a limited amount of gas to the high-pressure line system from the gas tank by opening the first valve device for a limited amount of time; determining a leakage mass flow in the high-pressure line system after the limited amount of gas has been supplied; comparing the leakage mass flow with a leakage threshold value; and opening the first valve device only when the determined leakage mass flow is lower than a leakage threshold value.

Description

[0001] Description

[0002] title

[0003] Technical area

[0004] The present invention relates to a fuel cell system, in particular for a vehicle, a gas tank system, in particular for a fuel cell system, and a method for operating a gas tank system.

[0005] State of the art

[0006] Fuel cells are increasingly being used as energy converters, including in vehicles, to convert chemical energy stored in a fuel, such as hydrogen, together with oxygen, directly into electrical energy. Fuel cells have an anode, a cathode, and an electrolytic membrane arranged between the anode and cathode. Oxidation of the fuel occurs at the anode, and reduction of the oxygen occurs at the cathode.

[0007] The fuel is typically supplied to the fuel cell via a piping system from a tank in which the gaseous fuel is stored at high pressure. A separating or shut-off valve is usually provided between the tank and a high-pressure section of the piping system. The high-pressure section is typically also connected to a section of the piping connected to the fuel cell via a flow control valve.

[0008] When the fuel cell is shut down, the shutoff valve and flow control valve are typically closed, leaving the high-pressure section as a sealed volume. Fuel leakage from the piping system can occur due to reduced sealing performance of hydraulic components or due to damage. To reduce the associated hazards, it is desirable to reliably detect such leaks and, if a leak occurs, to minimize the amount of fuel released.

[0009] US 7,127,937 B2 discloses a method for detecting a leak in a fuel cell system, wherein, upon shutting down a fuel cell, a first and a second isolation valve are closed to isolate a supply line from a fuel tank through the first isolation valve and from the fuel cell through the second isolation valve. After the valves are closed, the pressure in the supply line is recorded and stored. Before restarting the fuel cell, with the isolation valves closed, the pressure in the supply line is recorded again and compared with the stored value to determine whether a leak exists if a pressure difference exists.

[0010] Disclosure of the invention

[0011] Against this background, the present invention provides a method for operating a gas tank system having the features of claim 1, a gas tank system having the features of claim 6 and a fuel cell system having the features of claim 10.

[0012] According to a first aspect of the invention, a method for operating a gas tank system comprises detecting a pressure in a high-pressure line system in a state in which the high-pressure line system has been separated from a gas tank by a first valve device which is in a closed state and from a consumer system by a flow control device which is in a closed state for a predetermined period of time, and comparing the detected pressure with a pressure threshold value.If the detected pressure is less than the pressure threshold, a limited amount of gas is supplied from the gas tank into the high-pressure line system by temporarily opening the first valve device, determining a leakage mass flow in the high-pressure line system after supplying the limited amount of gas, comparing the leakage mass flow with a leakage threshold, and opening the first valve device only if the determined leakage mass flow is less than a leakage threshold.

[0013] According to a second aspect of the invention, a gas tank system for a consumer system comprises a tank for storing gas, in particular hydrogen, a high-pressure line system, a first valve device which can be switched between an open state in which it connects the tank to the high-pressure line system and a closed state in which it separates the tank from the high-pressure line system, a flow control device which can be switched between an open state and a closed state for connecting the high-pressure line system to a consumer system, a pressure sensor for detecting a pressure in the high-pressure line system and a control device which is connected to the first valve device, to the flow control device and to the pressure sensor in a signal-conducting manner and is configured to cause the gas tank system to carry out a method according to the first aspect of the invention.

[0014] According to a third aspect of the invention, a fuel cell system, in particular for a motor vehicle, comprises a gas tank system according to the second aspect of the invention and a consumer system with a fuel cell arrangement which has a fuel supply connection connected to the second valve device.

[0015] One idea underlying the invention is to perform a leak test in a high-pressure part of a piping system that connects a gas tank to a consumer system, e.g., a fuel cell, after a predetermined, small amount of gas has been introduced from the tank into the high-pressure piping system. To this end, it is first checked whether there is any suspicion of a leak in the high-pressure piping system. This is done by comparing the pressure in the high-pressure piping system with a limit value after a specific system downtime, at a time when both valves or flow control devices have been closed for a specific time, e.g., for more than one minute.If the pressure is below this limit value, a small amount of gas from the tank is supplied to the high-pressure line system by switching the first valve device or tank valve device from a closed to an open state and after a short time back to the closed state, wherein the flow control device preferably remains closed. This leads to a pressure increase in the high-pressure line system. The leakage mass flow is then determined, e.g. based on a pressure and / or temperature profile which is determined after the predetermined amount of gas has been supplied to the high-pressure line system. According to the invention, the first valve device and optionally also the flow control device are only opened when the leakage mass flow is less than a limit value, preferably close to zero.

[0016] An advantage of the invention is that the leakage check can be carried out when the system is at a standstill and, if a leak occurs, the amount of gas escaping into the environment is reduced due to the temporary opening of the first valve device.

[0017] The features and advantages disclosed herein in connection with one aspect of the invention are also disclosed for the respective other aspects. In particular, the control device can initiate all method steps and carry out various steps itself, such as steps for determining values ​​based on measured physical quantities. For example, the control device can have a computing unit, such as a CPU, an ASIC, an FPGA or the like, and a data memory, in particular a non-volatile data memory such as a flash memory, an SD memory or the like, which is readable by the computing unit. The data memory can store software that is executable by the computing unit in order to cause the system to carry out the steps of the method.

[0018] Advantageous embodiments and further developments emerge from the further subclaims and from the description with reference to the figures of the drawing. According to some embodiments, it can be provided that determining the leakage mass flow comprises recording a pressure profile in the high-pressure line system over a predetermined period of time in a state in which the first valve device and the flow control device are in their closed state, determining a pressure gradient from the recorded pressure profile, and determining the leakage mass flow based on the determined pressure gradient. For example, with the aid of the ideal gas equation, the leakage mass flow can be determined based on the pressure gradient. The advantage of using the measured pressure profile to determine the leakage mass flow is that the pressure is measured anyway and additional sensors are not necessarily required.

[0019] According to some embodiments, it may be provided that the method additionally comprises generating a warning signal and / or writing an error message to a data memory if the determined leakage mass flow is greater than or equal to the leakage threshold value.

[0020] According to some embodiments, it can be provided that, in order to supply the limited amount of gas from the gas tank into the high-pressure line system, the first valve device is opened for a predetermined first period of time, e.g., for a period of between 20 milliseconds and 3 seconds. Thus, the supply of the limited amount of gas can be carried out, e.g., purely time-controlled, wherein the predetermined first period can optionally depend on the pressure in the tank, in particular such that the opening period is shorter the higher the pressure in the tank.

[0021] According to further embodiments, it can be provided that, in order to supply the limited amount of gas from the gas tank into the high-pressure line system, the first valve device is opened until a predetermined pressure is reached in the high-pressure line system. Thus, the supply of the limited amount of gas can take place in a closed-loop control system. This offers the advantage that the leakage mass flow is always determined under precisely defined conditions, thereby increasing the accuracy of the leakage mass flow determination.

[0022] According to some embodiments, it can be provided that a predetermined pressure in the high-pressure line system is set by coordinated opening and closing of the first and second valve devices before the first state is established, wherein the pressure threshold is equal to the set predetermined pressure or is smaller than the set pressure by a predetermined difference, e.g. by a difference corresponding to 5 to 25 percent of the set pressure. For example, when shutting down the system, a predetermined pressure in the high-pressure line system can be set either by first closing the first valve device and then further reducing the pressure in the high-pressure line system until the second valve device closes, or by first closing the second valve device and then increasing the pressure in the high-pressure line system until the first valve device closes.The pressure detected in this state is stored, e.g. in the control device, and can be used as a reference value for the pressure threshold.

[0023] According to some embodiments, it can be provided that the first valve device has a switchable solenoid valve that can be switched between the open state and the closed state.

[0024] According to some embodiments, it can be provided that the flow control device has a second valve device, in particular in the form of a switchable solenoid valve that can be switched between the open state and the closed state. The flow control device can generally be designed to vary a flow and thus a mass flow from the high-pressure line system into the consumer system. Analogously, the pressure at which the gas flows from the high-pressure line system into the consumer system can also be varied by the flow control device. Therefore, the flow control device can also be referred to as a pressure regulator. According to some embodiments, it can be provided that the high-pressure line system has a supply connection for connecting a refueling system, wherein the supply connection is closed by a check valve to prevent gas from escaping from the high-pressure line system.

[0025] In the following, the invention is explained with reference to the figures of the drawings. The figures show:

[0026] Fig. 1 is a schematic representation of a hydraulic circuit diagram of a fuel cell system according to an embodiment of the invention; and

[0027] Fig. 2 is a flowchart of a method according to an embodiment of the invention.

[0028] In the figures, the same reference symbols denote identical or functionally identical components, unless otherwise stated.

[0029] Fig. 1 schematically shows a fuel cell system 200 that can be used, for example, in a vehicle. The fuel cell system 200 includes a gas tank system 100 and a consumer system 205.

[0030] As shown only schematically in Fig. 1, the consumer system 205 has a fuel cell arrangement 210. The fuel cell arrangement 210 has at least one fuel cell, but preferably a plurality of fuel cells connected electrically in series, which are designed to convert chemical energy stored in a gaseous fuel, such as hydrogen, together with oxygen, directly into electrical energy. As further shown schematically in Fig. 1, the fuel cell arrangement 210 has a fuel supply connection 211, via which gaseous fuel can be supplied to the fuel cell arrangement 210, in particular to an anode of the at least one fuel cell. The gas tank system 100 is explained below in connection with the fuel cell system 200, but is not limited to this use, but can also be used in combination with other consumer systems, such asGas engines or the like. As shown schematically in Fig. 1, the gas tank system 100 comprises a tank 1, a high-pressure line system 2, a first valve device 3, a flow control device 5, a pressure sensor 4, and a control device 6. Optionally, the gas tank system 100 may further comprise a refueling connection or supply connection 20.

[0031] Tank 1 is designed to store gas, in particular hydrogen. For example, tank 1 can be configured to store gas at a pressure of up to 800 bar.

[0032] The high-pressure line system 2 can, in particular, have a connecting line 21 and optionally a supply line 22, as shown schematically and purely by way of example in Fig. 1. The connecting line 21 connects the tank 1 to the consumer system 205.

[0033] The first valve device 3 can, for example, have a switchable solenoid valve 3 that can be switched between a closed state and an open state. In general, the first valve device 3 can be switched between a closed state and an open state. As shown schematically in Fig. 1, the valve device 3 is arranged between the tank 1 and the high-pressure line system 2, in particular between the tank 1 and the connecting line 21. In the open state, the first valve device 3 connects the tank 1 to the high-pressure line system 2. In the closed state, the first valve device 3 separates the tank 1 and the high-pressure line system 2 from one another.

[0034] The flow control device 5 is designed to vary a gas flow and / or a pressure of the gas flowing through the flow control device. In general, the flow control device 5 can be switched between a closed state and an open state. The second valve device 5 can, for example, have a switchable solenoid valve that can be switched between the open state and the closed state. As shown schematically in Fig. 1, the flow control device 5 is arranged between the consumer system 205 and the high-pressure line system 2, in particular between the consumer system 205 and the connecting line 21. In the open state, the flow control device 5 connects the consumer system 205 to the high-pressure line system 2. In the closed state, the flow control device 5 separates the consumer system 205 and the high-pressure line system 2 from one another.

[0035] The supply line 22 is connected to the supply connection 20, which can be designed, for example, as a plug-in connection for a tank nozzle. As shown in Fig. 1, a check valve 8 can be arranged in the supply line 22, which closes the supply connection 20 against the escape of gas from the high-pressure line system 2.

[0036] When the first valve device 3 and the flow control device 5 are in a closed state, the high-pressure line system 2 thus forms a closed volume from which a leakage mass flow of gas can escape in the event of leaks.

[0037] As shown in Fig. 1, the pressure sensor 4 is connected to the high-pressure line system 2 and is configured to detect a pressure in the high-pressure line system 2.

[0038] The control device 6 is shown only schematically as a block in Fig. 1 and is implemented as an electronic control device 6. As shown by way of example in Fig. 1, the control device 6 can have a computing unit 61, such as a CPU, an ASIC, an FPGA or the like, and a data memory 62, in particular a non-volatile data memory such as a flash memory, an SD memory or the like, which is readable by the computing unit. As shown schematically in Fig. 1, the control device 6 is connected to the first valve device 3 and the flow control device 5 as well as to the pressure sensor 4 in a signal-conducting manner, for example by wire, such as via a bus system. Alternatively, a wireless connection can also be provided, e.g. via WiFi or the like.

[0039] The control device 6 is configured to cause the gas tank system 100 to execute the method M shown in Fig. 2.

[0040] For example, software executable by the computing unit 61 may be stored in the data memory 62 to cause the system 100 to execute the method M.

[0041] In an optional step MO, a predetermined pressure is set in the high-pressure line system 2 by coordinated opening and closing of the first valve device 3 and the flow control device 5. For example, when both valve devices 3, 5 are open in order to supply the consumer system 205 with gaseous fuel from the tank 1, the control device 6 can first switch the first valve device 3 to the closed state and then switch the flow control device 5 to the closed state when a predetermined pressure is reached in the high-pressure line system 2, which pressure can be detected, for example, by the pressure sensor 4. The pressure prevailing in the high-pressure line system 2 after both valve devices 3, 5 are closed can, for example, be stored in the data memory 62.

[0042] In step M1, a pressure in the high-pressure line system 2 is detected by means of the pressure sensor 4. Step M1 is executed after a predetermined period of time has elapsed since the closing of both valve devices 3, 5, during which the valve devices 3, 5 were not opened, e.g., a period of at least one minute. Furthermore, step M1 is executed in a state in which both valve devices 3, 5 are closed, i.e., in a state in which the high-pressure line system 2 forms a closed volume.

[0043] In step M2, the control device compares the pressure detected in step M1 with a pressure threshold. The pressure threshold can, for example, correspond to the pressure set or detected in step M0 after the closing of the valve devices 3, 5. Alternatively, the pressure threshold can also be lower by a difference than the pressure set or detected in step M0 after the closing of the valve devices 3, 5, e.g., by a difference corresponding to 5 to 25 percent of the set pressure.

[0044] If the pressure detected in step M2 is greater than or equal to the pressure threshold, as indicated by the symbol in Fig. 1, the method M can go directly to step M6 and switch the first valve device 3 and optionally also the flow control device 5 to the open state.

[0045] If in step M2 the detected pressure is less than the pressure threshold, as indicated in Fig. 1 by the symbol “+”, this is an indicator of a leak in the high-pressure line system 2 and the method M proceeds to step M4.

[0046] In step M3, the control device 6 switches the first valve device 3 to the open state for a limited time, so that a limited amount of gas is supplied to the high-pressure line system 2 from the gas tank 2, and then back to the closed state. For example, the control device 6 can switch the first valve device 3 to the open state for a predetermined first period of time, e.g., for a period of between 20 milliseconds and 3 seconds, before closing the first valve device 3 again. Alternatively, the control device 3 can switch the first valve device 3 to the open state until a predetermined pressure is reached in the high-pressure line system, which pressure is detected, e.g., by the pressure sensor 4.

[0047] In step M4, after the limited gas quantity has been supplied M3, i.e., with the valve devices 3, 5 closed, a leakage mass flow in the high-pressure line system 2 is determined. For example, for this purpose, a pressure profile in the high-pressure line system 2 can be recorded using the pressure sensor 4 over a predetermined period of time, which can be, for example, between 0.5 seconds and 2 minutes (step M41). The control device 3 can determine a pressure gradient from the recorded pressure profile in step M42 and, in a further step M43, determine the leakage mass flow based on the determined pressure gradient, e.g., with the aid of the ideal gas equation.

[0048] In step M5, the control device 3 compares the leakage mass flow with a leakage threshold, e.g., by comparing the determined pressure gradient with a threshold. If the pressure gradient or the leakage mass flow is smaller than the leakage threshold, as indicated by the "+" symbol in Fig. 2, the method M proceeds to step M6, and the control device 6 switches the first valve device 3 and, optionally, the flow control device 5 to the open state.

[0049] If it is determined in step M5 that the determined leakage mass flow is greater than or equal to the leakage threshold value, as indicated in Fig. 2 by the symbol ", the method M proceeds to step M7. In step M7, the control device 6 can, for example, generate or output a warning signal, e.g., in the form of a visual or acoustic signal. Alternatively or additionally, the computing unit 61 can write an error message to the data memory 62.

[0050] Although the present invention has been explained above using exemplary embodiments, it is not limited thereto but can be modified in a variety of ways. In particular, combinations of the above embodiments are also conceivable.

Claims

Claims 1. A method (M) for operating a gas tank system (100), comprising: detecting (M1) a pressure in a high-pressure line system (2) in a state in which the high-pressure line system (2) has been separated from a gas tank (1) by a first valve device (3) in a closed state and from a consumer system (205) by a flow control device (5) in a closed state for a predetermined period of time; comparing (M2) the detected pressure with a pressure threshold; if the detected pressure is less than the pressure threshold: Supplying (M3) a limited amount of gas into the high-pressure line system (2) from the gas tank (1) by temporarily opening the first valve device (3); determining (M4) a leakage mass flow in the high-pressure line system (2) after supplying (M3) the limited amount of gas; Comparing (M5) the leakage mass flow with a leakage threshold; and Opening (M6) of the first valve device (3) only if the determined leakage mass flow is less than a leakage threshold value.

2. Method (M) according to claim 1, wherein determining (M4) the leakage mass flow comprises: Detecting (M41) a pressure curve in the high-pressure line system (2) over a predetermined period of time in a state in which the first valve device (3) and the flow control device (5) are in their closed state; Determining (M42) a pressure gradient from the recorded pressure curve; and Determine (M43) the leakage mass flow based on the determined pressure gradient. Method (M) according to claim 1 or 2, additionally comprising: generating (M7) a warning signal and / or writing an error message to a data memory (62) if the determined leakage mass flow is greater than or equal to the leakage threshold. Method (M) according to one of the preceding claims, wherein, in order to supply (M3) the limited gas quantity into the high-pressure line system (2) from the gas tank (1), the first valve device (3) is opened for a predetermined first period of time, e.g., over a period of time between 20 milliseconds and 3 seconds, or until a predetermined pressure is reached in the high-pressure line system. Method (M) according to one of the preceding claims, additionally comprising: Setting (MO) a predetermined pressure in the high-pressure line system (2) by coordinated opening and closing of the first and second valve devices (3, 5) before establishing the first state, wherein the pressure threshold is equal to the set predetermined pressure or is smaller than the set pressure by a predetermined difference. A gas tank system (100) for a consumer system (205), comprising: a tank (1) for storing gas, in particular hydrogen; a high-pressure line system (2); a first valve device (3) which is switchable between an open state, in which it connects the tank (1) to the high-pressure line system (2), and a closed state, in which it separates the tank (1) from the high-pressure line system (2); a flow control device (5) which is switchable between an open state and a closed state for connecting the high-pressure line system (2) to a consumer system (205); a pressure sensor (4) for detecting a pressure in the high-pressure line system (2); and a control device (6) which is connected to the first valve device (3), to the flow control device (5), and to the pressure sensor (4) in a signal-conducting manner and is configured to cause the gas tank system (100) to carry out a method (M) according to one of the preceding claims. The gas tank system (100) according to claim 6, wherein the first valve device (3) has a switchable solenoid valve that can be switched between the open state and the closed state. The gas tank system (100) according to claim 6 or 7, wherein the flow control device (5) has a switchable solenoid valve that can be switched between the open state and the closed state.A gas tank system (100) according to any one of claims 6 to 8, wherein the high-pressure line system (2) has a supply connection (20) for connecting a refueling system, wherein the supply connection (20) is closed by a check valve (8) to prevent gas from escaping from the high-pressure line system (2). A fuel cell system (200), in particular for a motor vehicle, comprising: a gas tank system (100) according to any one of claims 6 to 9; a consumer system (205) with a fuel cell arrangement (210) having a fuel supply connection (211) connected to the flow control device (5).

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