Method for detecting the valve position of at least one drain valve

Abstract

Method for detecting the valve position of at least one drain valve (11) in an anode circuit of a fuel cell system (1), wherein a pressure profile over time is detected in the anode circuit for a predetermined period of time, after which the detected pressure change is compared with a reference value in order to detect an open position or a closed position of the drain valve (11), characterized in that, if the drain valve (11) is used for draining liquid and subsequently gas, a change in a pressure gradient is used to detect whether the drain valve (11) is still being permeated by liquid or already by gas.

Description

[0001] The invention relates to a method for detecting the valve position of at least one drain valve in an anode circuit of a fuel cell system.

[0002] Fuel cell systems are well-known from the general state of the art. They can, for example, be based on so-called PEM fuel cells and can be used, in particular, to provide electrical power in vehicles. Fuel cell systems often feature an anode circuit. This anode circuit connects the inlet of one anode side of the fuel cell to the outlet of the anode side. Fresh fuel is also supplied to the anode circuit. The fresh fuel enters the anode compartment and is only partially converted there. Product water, residual fuel, and inert gases, especially nitrogen, which diffuse through the membrane into the anode compartment, return to the inlet of the anode compartment via the anode circuit, where they are reintroduced along with fresh fuel.This ensures very good utilization of the available active area of ​​the anode compartment. On the other hand, water and inert gas accumulate in the anode circuit over time. Since the anode circuit typically has a constant volume, this inevitably leads to a decrease in the hydrogen concentration and a deterioration in the fuel cell's performance. It is therefore common practice to drain water and / or gas from the anode circuit via at least one drain valve. This can be done, for example, via two separate valves for liquid and gas, or via a single common valve. For example, DE 11 2009 002 277 T5 discloses a fuel cell system with an anode circuit containing a drain valve.

[0003] The release of liquid and / or gas can be time-dependent or dependent on the hydrogen or nitrogen concentration in the anode circuit. Other triggers for the release, such as simulating a certain amount of water, are also conceivable. For a possible setup, reference is made to WO 2008 / 052578 A1.

[0004] US Patent 2008 / 0308157A1 describes methods and devices for indicating the position of a valve. An example device comprises a first pressure sensor for detecting the inlet pressure of a valve, a second pressure sensor for detecting the outlet pressure of the valve, and a control unit operatively coupled to the first and second pressure sensors to determine a position of the valve corresponding to one of several predetermined operating states of the valve, in particular based on a differential pressure between the inlet and outlet pressures.

[0005] Especially when ending the venting process, i.e., when closing the vent valve, it is crucial to know the valve position accurately and reliably to avoid venting too much hydrogen along with the inert gases. This is important for both efficiency and safety reasons.

[0006] It is known from the general state of the art that valves exist which have position feedback. However, these are expensive and, depending on the principle of the position feedback, not always 100% reliable. Alternatively, it is possible to measure the hydrogen concentration at a point where the gas from the anode circuit is discharged, for example, in the exhaust gas of the fuel cell. However, such an additional hydrogen sensor is also expensive and not 100% reliable in practice.

[0007] The object of the present invention is to provide a method for detecting the valve position of at least one drain valve in an anode circuit of a fuel cell system, which provides a simple and efficient cost-effective way to reliably determine the valve position.

[0008] This problem is solved according to the invention by a method with the features in the characterizing part of claim 1. An alternative solution for a fuel cell system in which the pressure in the anode circuit is regulated to a predetermined value—optionally load-dependent—via a fuel supply through a pressure regulating valve is specified by the features in the characterizing part of claim 6. Advantageous embodiments of the methods are described in the respective dependent claims. Furthermore, claim 9 specifies a particularly preferred use for the methods.

[0009] In the inventive method according to claim 1, it is provided that a pressure profile over time in the anode circuit is recorded for a predetermined period of time, after which the recorded pressure change is compared with a reference value in order to detect an open position or a closed position of the drain valve.

[0010] The idea behind the invention is to measure the pressure, or rather its change over time (i.e., the pressure gradient), in the anode circuit and thereby detect whether the drain valve is open or closed. This allows the position of the drain valve to be determined by means of a simple, highly reliable pressure measurement using reliable and cost-effective sensors. This is therefore safe and easy to implement.

[0011] In the method according to the invention, it is further provided that, when the open position of the drain valve is detected (if it is used for draining liquid and subsequently gas), a change in the pressure gradient is used to determine whether the drain valve is still filled with liquid or already with gas. In such a combined drain / purge valve, as is known, for example, from the prior art mentioned above, when the open position of the drain valve is detected, a further change in the pressure value, and in particular the pressure gradient (i.e., the pressure value over time), can be used to determine whether liquid or gas is still flowing through the drain valve.This is crucial for controlling the amount of gas to be released, because in addition to knowing the open or closed position of the release valve, this point in time also plays a role in being able to influence the amount of gas to be released as precisely as possible.

[0012] According to a particularly favorable and advantageous embodiment of the method according to the invention, the specified time interval is further provided for in the range of a few seconds, preferably less than 5 seconds. Even such a short time interval is sufficient for verification. The verification is thus carried out very quickly and reliably. Ideally, the verification is performed such that the pressure profile is recorded during a constant load, preferably zero load, of the fuel cell. This is particularly preferred since the anode pressure is generally load-dependent.Since fuel cell systems, especially when used in vehicles, typically have a battery or electrical energy storage device, the short measurement time of just a few seconds makes it easy to set a constant load point at the fuel station and supply the required load via the energy storage device for that duration. The measurement therefore does not affect the fuel cell system.

[0013] Furthermore, fuel cell systems often feature pressure regulation in the anode circuit, where the pressure in the anode circuit is regulated to a predetermined value via a fuel supply through a pressure regulating valve. The described method according to the invention cannot be readily implemented in such a configuration. Therefore, according to a particularly advantageous embodiment of the method according to the invention, pressure regulation in the anode circuit is suspended during the period required to detect the pressure profile, and the fuel supply is controlled to a constant value corresponding to the respective load. In the most favorable case, the fuel supply is even completely interrupted for the detection period by closing the valve.By controlling the fuel supply depending on the load during the period for recording the pressure curve, i.e. a brief interruption of the pressure regulation in the anode circuit, the use of the inventive method for detecting the valve position of the drain valve is also possible in such fuel cell systems.

[0014] Alternatively, in a subsidiary method for detecting the valve position of at least one drain valve in an anode circuit of a fuel cell system according to the preamble of claim 6, it is therefore provided that the volume flow rate of fuel required at the respective load is determined through the pressure control valve, and that a quantity corresponding at least indirectly to the flow rate through the pressure control valve is compared with the required volume flow rate of fuel, whereby an open drain valve is concluded if the flow rate through the pressure control valve exceeds the volume flow rate of fuel required at the respective load by more than a predetermined reference value.This alternative method allows the position of the drain valve to be determined just as easily and reliably as with the method described above, based on a quantity that corresponds at least indirectly to the flow rate through the pressure regulating valve, in particular a control signal for the pressure regulating valve. The pressure regulation does not need to be suspended for this purpose.

[0015] In both methods according to the invention, the reference values ​​can be calculated as a function of the respective load point. This is particularly useful for load-dependent reference values. A simulation of the system can be used for this purpose, which, for example, predicts the consumption and / or the pressure accordingly. If the methods according to the invention then detect deviating values ​​using these reference values, it must be assumed that the valve is open.

[0016] In addition or alternatively, it is of course also possible to calculate or measure the reference values ​​beforehand and to save them accordingly and use them for one of the methods according to the invention.

[0017] Both methods according to the invention enable a very simple, reliable, and cost-effective determination of whether the drain valve is open or not. They are therefore particularly suitable for fuel cell systems that are manufactured in large quantities and thus must be implemented in a particularly simple and cost-effective manner. Since they also ensure a very high level of reliability in the detection of the value to be determined, the methods according to the invention can nevertheless be used in fuel cell systems that have high safety requirements, for example, because people are frequently in the vicinity of these fuel cell systems and explosive or flammable mixtures must therefore be avoided in all cases.

[0018] The two aspects of a simple and cost-effective fuel cell system, which is also very safe, described above make the methods according to the invention ideal for use in a fuel cell system used in a vehicle to provide electrical power, in particular electric drive power. Special safety requirements apply here, and due to the high production volumes, very simple and cost-effective fuel cell systems are also particularly advantageous.

[0019] Further advantageous embodiments of the methods according to the invention are described in the remaining dependent claims. Furthermore, advantageous embodiments of the method according to the invention, as well as of a fuel cell system for carrying out the method according to the invention, are described in more detail below with reference to the figures.

[0020] This shows: Fig. 1 a section of a fuel cell system for carrying out the method according to the invention in a first embodiment; and Fig. 2 a section of a fuel cell system for carrying out the method according to the invention in a second embodiment.

[0021] In the presentation of the Fig. Figure 1 shows a section of a fuel cell system 1, suitable for carrying out the method according to the invention. The fuel cell system 1 is to be arranged in a vehicle 2, the basic design of which is indicated. It can provide electrical power there. This power can be used, for example, for auxiliary consumers or, in particular, as electric drive power. The core of the fuel cell system 1 is a fuel cell 3, which can, for example, be designed as a PEM fuel cell stack. The fuel cell 3 has a cathode compartment 4 and an anode compartment 5. Air is supplied to the cathode compartment 4 as an oxygen source in a manner known per se, and exhaust air from the cathode compartment 4 is released back into the environment. This process is known per se and is common practice. It can be implemented using suitable compressors, electric turbochargers, or the like.

[0022] Hydrogen is supplied as fuel to the anode compartment 5 of the fuel cell 3 from a pressurized gas storage tank 6. In the illustration of the Fig. 1. This hydrogen passes from the pressurized gas storage tank 6 into the anode chamber 5 via a metering valve 7. Unused residual hydrogen returns to the anode chamber 5 via a recirculation line 8 and a recirculation pump 9, which can be designed, for example, as a hydrogen blower and / or a gas jet pump, and is mixed with fresh hydrogen before being fed back into the chamber. This setup is also known as an anode circuit. A water separator 10 is arranged in the recirculation line 8. This separator is connected via a drain valve 11 to a section where water and gas from the anode circuit can be discharged. This could be, for example, the supply air to the cathode chamber 4 or the exhaust air from the cathode chamber 4. Other sections into which gas and / or water are discharged are also known and conceivable.Since this is not essential to the present invention, a more detailed description has been omitted. As an alternative to the combined drain valve 11 for water and / or gas, a division into two separate drain valves and lines would of course also be conceivable.

[0023] As already mentioned, the fuel cell 3 provides electrical power. In the embodiment shown here, it is configured in parallel with an electrical energy storage device 12, for example a storage battery, a capacitor bank, or a combination thereof. Downstream of this is a power electronics unit 13, through which the electrical power is fed into a basic on-board electrical system 14.

[0024] It is now the case that, in a manner known per se, inert gases accumulate over time in the anode circuit of the fuel cell system 1, particularly nitrogen, which diffuses through the membranes from the cathode compartment 4 into the anode compartment 5. Water also accumulates, which is typically separated in the water separator 10. To maintain the hydrogen concentration in the anode circuit at a level suitable for the functionality of the fuel cell 3, it is necessary to occasionally vent the inert gases and / or water. The aforementioned vent valve 11 is provided for this purpose. The venting can be triggered periodically, depending on the hydrogen and / or nitrogen concentration, or by comparable and known methods. Knowledge of the switching state of the vent valve 11 is important to ensure that not too much hydrogen is vented along with the inert gases and / or water.Firstly, this is crucial for efficiency reasons, and secondly, depending on the wiring, also for safety reasons, in order to avoid causing critical hydrogen emissions in the vicinity of the fuel cell system 1.

[0025] At the in Fig. In the fuel cell system 1 described above, the pressure measured by a pressure sensor 15, or its change over time in the anode circuit, is to be used to detect whether the drain valve 11 is open or closed. Since the anode pressure measured in the area of ​​the pressure sensor 15 is generally load-dependent, the position of the drain valve 11 should preferably be checked under a constant load of the fuel cell 3. However, the check can be performed within a few seconds, so that a constant load state can be established, at least briefly, during the check of the drain valve 11 position, via the energy storage device 12 in the fuel cell system 1 or the vehicle 2. The load actually required by the vehicle electrical system 14 can then be supplied via the energy storage device 12 for this period.The valve position of the drain valve 11 can thus be checked by measuring the pressure over time in the area of ​​the pressure sensor 15 under constant load. Ideally, this would be performed at a load point where there is no load, i.e., zero load. This is possible, for example, in fuel cell systems 1 with start / stop operation during the stop phase. It is also possible to briefly switch the fuel cell 3 to idle mode, since, as already mentioned, the energy storage device 12 could then supply the electrical power to the vehicle electrical system 14 on its own.

[0026] If, at a steady-state load point, the pressure in the area of ​​pressure sensor 15 is measured for a certain period of time (a few seconds) and the pressure drops faster than the rate expected from the balance of flow through metering valve 7 and consumption in fuel cell 3, it can be assumed that the drain valve 11 is open. Other leakage from the anode circuit can typically be ruled out here, as this generally does not involve such a high flow rate as the open drain valve 11. The pressure profile measured over time, i.e., the pressure gradient, can therefore be compared with a reference value, which is recalculated for each current case depending on the load.Alternatively, the measured pressure gradient can also be compared with reference values ​​calculated in previous measurements or independently of the fuel cell system 1, which are then stored accordingly in a control unit 16. As soon as the control unit 16 detects that the detected pressure change deviates from the calculated or stored reference value, the control unit 16 can recognize an open or closed position of the drain valve 11. This information can then be used, for example, to control the drain valve 11.

[0027] Will the draining process be similar to the one in Fig. In the fuel cell system 1 shown in Figure 1, the flow of hydrogen through a single drain valve 11, located in the area of ​​the water separator 10, can be detected by measuring the pressure gradient when the drain valve is open. This allows the system to determine whether the drain valve 11 is still flowing with liquid or already with gas. Since liquid is typically incompressible, the pressure gradient directly correlates with the flow rate of the liquid through the drain valve 11. Due to the compressibility of gas and the pressurized anode circuit, the pressure drops significantly more sharply the moment only gas passes through the drain valve 11, as the gas expands in addition to flowing out. This point in time can be detected and used to control the drain valve 11 so that only a minimal amount of hydrogen is released.

[0028] The method can be implemented in a fuel cell system 1 by controlling the hydrogen supply to the anode circuit via the metering valve 17. The control is typically load-dependent and, as is typical for such a control system, without feedback of the actually metered value. In this case, the detection of a pressure gradient then allows for characteristic evaluation, which enables conclusions to be drawn about the valve position of the drain valve 11. Now, it is often the case that fuel cell systems 1 are designed with an operating mode that provides for the regulation of the anode circuit, in which the pressure in the anode circuit is controlled via a pressure regulating valve 17, as is the case in Fig. As shown in Figure 2, the hydrogen supply is regulated to a constant value by influencing the hydrogen supply. Such a setup is illustrated in the example of a fuel cell system 1 in the diagram. Fig. 2. The differences here are simply in comparison to... Fig. Figure 1 shows the electrical connection of the fuel cell 3 and the vehicle. The illustration of this connection is omitted here, but of course it should also be present.

[0029] The pressure regulating valve 17 is coupled to the anode or the anode circuit via the pressure sensor 15. A control unit, again designated with reference numeral 16, is intended to regulate the anode circuit to a constant pressure.

[0030] With such a fuel cell system configuration featuring regulated anode circuit pressure, there are two ways to check the position of the drain valve 11. The first option is to suspend pressure regulation in the anode circuit during the check, i.e., during the period in which the pressure profile is measured. At a preferably constant load, a predetermined volume flow of hydrogen is then set via the pressure control valve 17, or, ideally under zero load, the hydrogen supply is completely shut off. In this situation, the measurement can then be carried out as described above. After the measurement period of a few seconds, the pressure regulation in the anode circuit can then be reactivated.

[0031] An alternative method for determining the position of the drain valve 11 involves performing the check during controlled operation. In controlled operation, it is verified whether the resulting control signal, and thus ultimately the flow rate through the pressure control valve 17, corresponds to the expected value for the given load-dependent consumption, as determined by the reactions of the fuel cell 3. This value can, for example, be calculated in real time or derived from the electrical load of the fuel cell 3. If the control signal, corresponding to the flow rate through the pressure control valve 17, is greater than the target signal (derived from the expected fuel consumption) by a predefined reference value, then it can be assumed that the drain valve 11 is open.The reference value by which the deviation must exceed the target signal can in turn be calculated in real time depending on the load, or measured or calculated in advance and stored in the control unit 16.

[0032] The method can be applied to both gas-flowing and liquid-flowing drain valves 11. In both configurations, the method is very simple and efficient. It allows for the safe and reliable monitoring of the valve position of the drain valve 11 without the need for complex valve technology and / or gas sensors.

Claims

[1] Method for detecting the valve position of at least one drain valve (11) in an anode circuit of a fuel cell system (1), wherein a pressure profile over time is detected in the anode circuit for a predetermined period of time, after which the detected pressure change is compared with a reference value in order to detect an open position or a closed position of the drain valve (11), characterized by , that when the open position of the drain valve (11) is detected, if it is used for draining liquid and subsequently gas, a change in a pressure gradient is used to determine whether the drain valve (11) is still being filled with liquid or already with gas. [2] Method according to claim 1, characterized by that the specified time period is in the range of a few seconds, preferably less than 5 seconds. [3] Method according to claim 1 or 2, characterized by, that the pressure profile during a constant load of a fuel cell (3) of the fuel cell system (1), preferably during zero load, is recorded. [4] Method according to claim 3, characterized by , that the load required during the recording of the pressure profile in the fuel cell system (1) is provided via an energy storage device (12). [5] Method according to any one of claims 1 to 4, characterized by , that in the case of pressure regulation in the anode circuit, this is suspended during the period for recording the pressure profile, and a fuel supply is controlled to a constant value corresponding to the respective load. [6] Method for detecting the valve position of at least one drain valve (11) in an anode circuit of a fuel cell system (1), wherein a pressure in the anode circuit is regulated to a predetermined value via a fuel supply through a pressure regulating valve (17), characterized by, that the volume flow rate of fuel required at the respective load is determined by the pressure control valve (17), and that a quantity corresponding at least indirectly to the flow rate through the pressure control valve (17) is compared with the required volume flow rate of fuel, whereby an open drain valve (11) is assumed if the flow rate through the pressure control valve (17) exceeds the volume flow rate of fuel required at the respective load by more than a predetermined reference value. [7] Method according to claim 6, characterized by , that the control signal for the pressure control valve (17) is used as the quantity that corresponds at least indirectly to the flow through the pressure control valve (17). [8] Method according to any one of claims 1 to 7, characterized by , that the reference value is calculated depending on the respective load point. [9] Method according to any one of claims 1 to 8, characterized bythat the reference value has been previously calculated and / or measured and stored.

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