Method for operating a fuel cell system, shut-off valve and fuel cell stack

Abstract

The invention relates to a method for operating a fuel cell system, in which method, intermittently, especially in a shutdown state of the system, the air supply to a fuel cell stack (20) is interrupted by means of a pressure-controlled shut-off valve (1), the shut-off valve comprising a valve element (4) which can move back and forth between two end positions and is pre-tensioned in the direction of a sealing seat (3) by the spring force of a closing spring (2). According to the invention, in at least one of the two end positions, the valve element (4) is additionally held in the respective end position by the magnetic force of an electromagnet (5) and / or a permanent magnet (6), wherein the electromagnet (5) and / or the permanent magnet (6) cooperate with a magnetic or magnetizable part (7) of the valve element (4). The invention also relates to a shut-off valve (1) suitable for carrying out the method according to the invention and to a fuel cell stack (20) having at least one shut-off valve (1) according to the invention.

Description

Field of the Invention

[0001] The present invention relates to a method for operating a fuel cell system. In the method, intermittently, in particular in the standby state (Stillstand) of the system, the air supply to the fuel cell stack of the fuel cell system is interrupted by means of a pressure-controlled shut-off valve. The invention also relates to a pressure-controlled shut-off valve suitable for carrying out the method and a fuel cell stack having a shut-off valve according to the invention. Background Art

[0002] In a fuel cell system, a valve is required to interrupt the connection between the fuel cell stack and the air supply in the standby state. Thereby, it should be prevented that air or oxygen further reaches the cathode side of the membrane arranged between the cathode and the anode. Because this oxygen diffuses from the cathode side to the anode side through the membrane and thus causes a harmful "Air-to-Air Start" to the fuel cell system during re-commissioning of the system.

[0003] The interruption of the air supply can be caused, for example, by a valve configured as a simple check valve. Such valves are only controlled by the applied pressure or the prevailing flow conditions. That is, they are passive. Thus, the actuator for actively controlling the valve opening can be dispensed with, which is accompanied by space and cost advantages. However, it has proven difficult to design the spring force of the spring acting in the closing direction, which on the one hand must be large enough to keep the check valve reliably closed and on the other hand should not be too large so as not to delay the opening of the valve during re-commissioning of the system. Because after the interruption of the air supply, 100% air flow should be reached again as quickly as possible to avoid temporary local differences in the fuel cell, which can lead to degradation of the system.

[0004] The present invention addresses this task. To solve this task, a method having the features of claim 1, a shut-off valve having the features of claim 5, and a fuel cell stack having the features of claim 12 are proposed. Advantageous developments of the invention are known from the corresponding dependent claims. Summary of the Invention

[0005] In the proposed method for operating a fuel cell system, the air supply to the fuel cell stack is intermittently interrupted, especially in the shutdown state of the system, by means of a pressure-controlled shut-off valve, which includes a valve element that can move back and forth between two end positions and is pre-tensioned in the direction of a sealing seat by the spring force of a closing spring. According to the invention, in at least one of the two end positions, the valve element is additionally held in the respective end position by the magnetic force of an electromagnet and / or a permanent magnet, where the electromagnet and / or the permanent magnet cooperate with a magnetic or magnetizable part of the valve element.

[0006] In the proposed method, a shut-off valve is used that is controlled by the applied pressure and thus behaves like a passive valve. However, different from traditional passive valves, additional magnetic forces can be generated by means of an electromagnet and / or a permanent magnet, which cause a holding force when the valve element of the shut-off valve is in one of the two end positions. Thus, the spring force and at least one magnetic force act on the valve element, where preferably the action of the magnetic force on the valve element is only temporary, especially limited by the following time: during which the valve element is in one end position.

[0007] The magnetic force generated by means of an electromagnet and / or a permanent magnet can act in the closing direction, such that it assists the closing spring. In this case, the closing spring can be designed smaller, such that the shut-off valve opens faster when the pressure rises.

[0008] The magnetic force generated by means of an electromagnet and / or a permanent magnet can act in the opening direction, such that the shut-off valve is reliably held open against the spring force of the closing spring. This is especially advantageous if, for example, the volume flow rate through the shut-off valve is significantly smaller at partial load, such that there is a risk of the closing spring inadvertently closing the valve.

[0009] Preferably, in the proposed method, both an electromagnet and a permanent magnet are used. Preferably, a first magnetic force is generated by means of the electromagnet, and a second magnetic force opposite to the first magnetic force is generated by means of the permanent magnet. In this way, an additional holding force can be applied to the valve element in the two end positions of the valve element.

[0010] Advantageously, the valve element is held in the end position by the magnetic force of the electromagnet in which the shut-off valve is open. Thus, the electromagnet is energized when the shut-off valve is open. To effect the closing of the valve, the energization of the electromagnet is ended, such that the closing spring can reset the valve element into the sealing seat.

[0011] If the valve is ensured to be held open without energizing the electromagnet through the existing pressure conditions, the electromagnet can be deactivated or remain deactivated, so that the energy required for energization is saved.

[0012] Preferably, the valve element is held in an end position by the magnetic force of a permanent magnet, in which end position the shut-off valve is closed. The permanent magnet thus assists the closing spring, so that the closing spring can be designed smaller. Preferably, in the closed state, the action of the permanent magnet on the valve element is high, and this action decreases when the shut-off valve is opened, because the valve element moves away from the permanent magnet. Thus, the action of the permanent magnet can be basically limited to the closing duration of the shut-off valve.

[0013] In an expansion scheme of the present invention, it is proposed that the valve element is loaded by the ambient pressure in the closing direction. Thus, the shut-off valve opens against the spring force of the closing spring and against the ambient pressure. Since the total system pressure is usually higher than the ambient pressure, this pressure difference acts in an opening manner. In some cases, the electromagnet for generating an additional holding force on the opened valve element can thus be omitted.

[0014] Furthermore, a pressure-controlled shut-off valve is proposed, which is used to intermittently interrupt the air supply to a fuel cell stack in a fuel cell system. The shut-off valve includes a valve element that can move back and forth between two end positions and is pre-tensioned in the direction of a sealing seat by the spring force of a closing spring, wherein the sealing seat defines the first end position and a housing-side stroke stop defines the second end position. According to the present invention, in at least one of the two end positions, the magnetic force of an electromagnet and / or a permanent magnet acts on a magnetic or magnetizable part of the valve element.

[0015] The proposed pressure-controlled shut-off valve is particularly suitable for implementing the method according to the present invention described previously, so that basically the same advantages as those achieved by the method according to the present invention described previously can be realized by means of the proposed shut-off valve. In particular, a pressure-controlled valve can be provided, which closes tightly and remains closed if an additional holding force acts on the valve element by magnetic force. When the magnetic force acts in the closing direction, the spring force of the closing spring can be reduced, so that the shut-off valve can be opened faster at the same time. When the magnetic force acts in the opening direction, the shut-off valve itself can be reliably held open by the valve in the case of a small volume flow rate.

[0016] According to a preferred embodiment of the present invention, the magnetic force of the electromagnet acts against the spring force of the closing spring. Therefore, the opened shut-off valve can be reliably held open by means of the magnetic force of the electromagnet. To close the shut-off valve, simply end the energization of the electromagnet, so that the closing spring resets the valve element into the sealing seat.

[0017] Alternatively or additionally, it is proposed that the magnetic force of the permanent magnet acts in the direction of the spring force of the closing spring. The permanent magnet thus assists the closing spring, which can accordingly be designed smaller.

[0018] Advantageously, the shut-off valve includes not only an electromagnet but also a permanent magnet, such that additional magnetic forces act on the valve element in the two end positions of the valve element in order to hold the valve element in the respective end position. If the holding open of the valve is ensured by the existing pressure conditions, the energization of the electromagnet can be dispensed with. In this way, energization energy can be saved.

[0019] Furthermore, it is proposed that the valve element is guided through a housing part which forms a travel stop and / or a guide for the valve element. The housing part can also be used to support the closing spring, where it can be, for example, a helical compression spring which partially surrounds the valve element. At the other end, the closing spring can be supported on a radially protruding part of the valve element.

[0020] Preferably, the valve element has a valve plate at one end which cooperates with a sealing seat and a magnetic or magnetizable part at the other end, which magnetic or magnetizable part is preferably also designed in a plate-like manner. The magnetic or magnetizable part can in particular be an armature plate which is fixedly connected to the valve element. The multi-piece embodiment of the valve element has the advantage of simplifying the assembly of the shut-off valve.

[0021] Furthermore, the magnetic or magnetizable part of the valve element is preferably accommodated together with the electromagnet and / or the permanent magnet in a pressure chamber in which the ambient pressure prevails. Thus, the ambient pressure acts on the valve element at one end and the system pressure acts on the valve element at the other end. Since the system pressure is usually higher than the ambient pressure, an additional opening force can be caused by the pressure difference.

[0022] Advantageously, the valve element is surrounded at its end facing the sealing seat by a sealing membrane which is fixed on the outside in the radial direction on the housing side, such that the sealing membrane separates the valve chamber from the spring chamber in which the closing spring is accommodated. The spring chamber is preferably attached to the pressure chamber in which the ambient pressure prevails via at least one connecting channel, such that the ambient pressure also prevails in the spring chamber. This ensures that, in the case where the system pressure in the valve chamber is higher than the ambient pressure, the force acting on the valve element in the opening direction is retained.

[0023] In a preferred configuration, the shut-off valve has an inlet channel and an outlet channel which are arranged at an angle to one another, preferably at a right angle. Thus, the shut-off valve can be installed on the fuel cell stack of a fuel cell system in different positions or orientations. Thus, the volume flow into or out of the fuel cell stack can be interrupted by means of the shut-off valve.

[0024] To solve the task mentioned at the beginning, a fuel cell stack is also proposed which includes at least one shut-off valve according to the invention, wherein preferably at least one shut-off valve is fixed to the fuel cell stack indirectly via an adapter plate. At least one shut-off valve can be installed axially or radially. If more than one shut-off valve is provided, these shut-off valves can be oriented identically such that all shut-off valves are flowed through axially or radially. Furthermore, the orientations of at least two shut-off valves can be different from each other such that at least one shut-off valve is flowed through axially and at least one further shut-off valve is flowed through radially. Description of the Drawings

[0025] The preferred embodiments of the invention are explained in more detail below with reference to the attached drawings. These drawings show:

[0026] Figure 1 A schematic longitudinal section of a shut-off valve according to the invention,

[0027] Figure 2 Two shut-off valves installed on a fuel cell stack according to Figure 1 and a schematic longitudinal section thereof, and

[0028] Figure 3 Two shut-off valves installed on a fuel cell stack according to Figure 1 wherein the orientation of one shut-off valve has changed compared to Figure 2 the other. Detailed Description of the Invention

[0029] Figure 1 The pressure-controlled shut-off valve 1 presented in

[0030] For optimizing the shut-off function, the valve element 4 has an elastic sealing element 18 which acts together with the sealing seat 3 and is embedded in the valve plate 11 on the end side of the valve element 4. A closing spring 2 is also supported on the valve plate 11, and the valve element 4 is axially pre-tensioned against the sealing seat 3 by the spring force of this closing spring. At the other end, the closing spring 2 is supported on the second housing part 9 which is also configured as a travel stop 8 for the valve element 4. At the same time, the housing part 9 is configured as a guide 10 for the valve element 4, and the valve element is received in the housing part 9 for this section.

[0031] The valve element 4 is surrounded by a sealing membrane 13 in the region of the valve plate 11. Different from the presented embodiment, the sealing membrane 13 and the sealing element 18 embedded in the valve plate 11 on the end face side can also be configured in one piece. For example, the sealing membrane 13 can be attached to the valve plate 11 by means of a vulcanization method such that it simultaneously forms the sealing element 18 on the end face side.

[0032] In the presented embodiment, the sealing membrane 13 separates the valve chamber 14 from the spring chamber 15 in which the closing spring 2 is received. The spring chamber 15 is connected to the pressure chamber 12 by at least one connecting channel 24 configured in the housing part 9, and this pressure chamber is bounded by a cover part 22 connected to the housing part 9. By means of a pressure equalizing element 23 embedded in the cover part 22, it is ensured that the ambient pressure prevails in the pressure chamber 12. Since the current valve element 4 is guided into the pressure chamber 12, the ambient pressure is applied at one end and the corresponding system pressure is applied at the other end. In order to open the shut-off valve 1, the pressure difference between the ambient pressure and the system pressure must be large enough to overcome the spring force of the closing spring 2. Accordingly, a small spring force has a favorable effect on the rapid opening of the shut-off valve 1.

[0033] In order to be able to reduce the spring force of the closing spring 2, Figure 1The shut-off valve 1 shown in FIG. 1 includes an electromagnet 5 and a permanent magnet 6, each acting on a magnetic or magnetizable portion 7 of the valve element 4. This portion 7 is an armature plate, which is fixedly connected to the valve element 4 at the end opposite the valve plate 11. The armature plate is therefore arranged in a pressure chamber 12, which accommodates both the electromagnet 5 and the permanent magnet 6, specifically at an axial distance from each other. This axial distance ensures that the effect of the permanent magnet 6 on the armature plate is maximum when the valve element 4 is in the first end position, i.e., when the shut-off valve 1 is closed. As the opening stroke increases, the armature plate moves away from the permanent magnet 6, so that in the second end position this effect disappears or is minimized. The magnetic force of the permanent magnet 6 thus generates an additional holding force, which ensures secure closing of the shut-off valve 1. This, in turn, has the advantage of reducing the spring force of the closing spring 2. To generate the additional holding force acting on the valve element 4 in the second end position, the electromagnet 5 is energized. In the second end position, the magnetic force of the electromagnet 5 ensures that the shutoff valve 1 remains securely open, regardless of the prevailing pressure conditions. To close the shutoff valve 1, the energization of the electromagnet 5 is simply terminated, so that the spring force of the closing spring 2 returns the valve element 4 to the sealing seat 3.

[0034] exist Figure 2 and Figure 3 1 shows different mounting variants of the shutoff valve 1 according to the invention on a fuel cell stack 20 . The mounting is achieved indirectly via an adapter plate 21 .

[0035] As an example in Figure 2 As shown in FIG, a first shut-off valve 1 for the air supply to the fuel cell stack 20 can be mounted radially so that an axial flow passes through it. A second shut-off valve 1 ′ can be mounted axially and an axial flow passes through it, which removes the consumed air from the fuel cell stack 20 and is constructed identically to the shut-off valve 18 (same reference numerals).

[0036] If the installation situation should be the same in both cases, it is possible to choose Figure 3 Here, the two shut-off valves 1 , 1 ′ are each mounted axially, with flow passing radially through the shut-off valve 1 and axially through the shut-off valve 1 ′. In the shut-off valve 1 , the pressure exerted on the sealing membrane 13 causes the opening force.

Claims

1. A pressure-controlled shut-off valve (1) for intermittently interrupting the air supply to a fuel cell stack (20) in a fuel cell system, said shut-off valve comprising a valve element (4) which is capable of moving back and forth between two end positions and is pre-tensioned in the direction of a sealing seat (3) by the spring force of a closing spring (2), wherein, The sealing seat (3) defines a first end position and the travel stop (8) of the housing part (9) defines a second end position, characterized in that, in the two end positions, the magnetic forces of the electromagnet (5) and the permanent magnet (6) respectively act on the magnetic or magnetizable part (7) of the valve element (4), the valve element (4) has a valve plate (11) at one end which acts together with the sealing seat (3) and has the magnetic or magnetizable part (7) at the other end, the closing spring (2) is supported on the valve plate (11) and the housing part (9) between the valve plate (11) and the magnetic or magnetizable part (7), and the permanent magnet (6) is arranged between the valve plate (11) and the magnetic or magnetizable part (7), and the electromagnet (5) and the permanent magnet (6) are respectively arranged on both sides of the magnetic or magnetizable part (7), the magnetic force of the electromagnet (5) resists the spring force of the closing spring (2), and the magnetic force of the permanent magnet (6) acts in the direction of the spring force of the closing spring (2).

2. The shut-off valve (1) according to claim 1, It is characterized in that wherein the valve element (4) is guided through the housing part (9), and the housing part forms the travel stop (8) and / or the guide (10) for the valve element (4).

3. The shut-off valve (1) according to claim 1 or 2, It is characterized in that wherein the magnetic or magnetizable part is configured in a plate shape.

4. The shut-off valve (1) according to claim 1 or 2, It is characterized in that wherein the magnetic or magnetizable part (7) of the valve element (4) and the electromagnet (5) and / or the permanent magnet (6) are jointly accommodated in a pressure chamber (12) in which ambient pressure exists.

5. The shut-off valve (1) according to claim 1 or 2, It is characterized in that wherein the valve element (4) is surrounded by a sealing membrane (13) at its end facing the sealing seat (3), and the sealing membrane is fixed on the housing side radially on the outside, such that the sealing membrane (13) separates the valve chamber (14) from the spring chamber (15) in which the closing spring (2) is accommodated.

6. The shut-off valve (1) according to claim 1 or 2, It is characterized in that wherein the shut-off valve (1) has an inlet passage (16) and an outlet passage (17), and the inlet passage and the outlet passage are arranged at an angle to each other.

7. The shut-off valve (1) according to claim 6, Characterized in that, wherein the inlet passage and the outlet passage are arranged at a right angle to each other.

8. A fuel cell stack (20) having at least one shut-off valve (1) according to any one of claims 1 to 7.

9. The fuel cell stack (20) according to claim 8, characterized in that, At least one shut-off valve (1) is fixed to the fuel cell stack (20) indirectly via an adapter plate (21).

10. A method for operating a fuel cell system by means of a shut-off valve (1) according to any one of claims 1 to 7, in which the air supply to a fuel cell stack (20) is intermittently interrupted by means of a pressure-controlled shut-off valve (1), the shut-off valve comprising a valve element (4) which can move back and forth between two end positions and is pre-tensioned in the direction of a sealing seat (3) by the spring force of a closing spring (2). It is characterized in that In the two end positions, the valve element (4) is additionally held in the respective end position by the magnetic force of an electromagnet (5) and a permanent magnet (6), wherein the electromagnet (5) and the permanent magnet (6) act together with a magnetic or magnetizable part (7) of the valve element (4).

11. The method according to claim 10. It is characterized in that During a shutdown state of the system, the air supply to the fuel cell stack (20) is interrupted by means of a pressure-controlled shut-off valve (1).

12. The method according to claim 10. It is characterized in that The valve element (4) is held in an end position by the magnetic force of the electromagnet (5) in which the shut-off valve (1) is opened.

13. The method according to any one of claims 10 to 12. It is characterized in that The valve element (4) is held in an end position by the magnetic force of the permanent magnet (6) in which the shut-off valve (1) is closed.

14. The method according to any one of claims 10 to 12. Characterized in that, The valve element (4) is loaded by ambient pressure in the closing direction.

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