METHOD FOR OPERATING A FUEL CELL SYSTEM, SHUTOFF VALVE AND FUEL CELL STACK

Abstract

The invention relates to a method for operating a fuel cell system, in which method a supply of air to a fuel cell stack (20) is interrupted intermittently, in particular in the event of a standstill of the system, by means of a pressure-controlled shutoff valve (1), which comprises a valve element (4), which valve element can be moved back and forth between two end positions and is preloaded toward a sealing seat (3) by means of the spring force of a closing spring (2). According to the invention, in at least one of the two end positions, the valve element is held in the end position in question additionally by means of the magnetic force of an electromagnet (5) and/or of a permanent magnet (6), the electromagnet (5) and/or the permanent magnet (6) interacting with a magnetic or magnetizable part (7) of the valve element (4). The invention further relates to a shutoff valve (1) suitable for carrying out the method according to the invention and to a fuel cell stack (20) having at least one shutoff valve (1) according to the invention.

Claims

1. A method for operating a fuel cell system, in which a supply of air to a fuel cell stack (20) is interrupted intermittently by a pressure-controlled shut-off valve (1) comprising a valve element (4) which can be moved back and forth between two end positions and is preloaded in a direction of a sealing seat (3) by a spring force of a closing spring (2), characterized in that in at least one of the two end positions, the valve element (4) is additionally held in the respective end position by a magnetic force of an electromagnet (5) and/or of a permanent magnet (6), wherein the electromagnet (5) and/or the permanent magnet (6) co-operate(s) with a magnetic or magnetizable part (7) of the valve element (4).

2. The method as claimed in claim 1, characterized in that by the magnetic force of the electromagnet (5), the valve element (4) is held in an end position in which the shut-off valve (1) is open.

3. The method as claimed in claim 1, characterized in that by the magnetic force of the permanent magnet (6), the valve element (4) is held in an end position in which the shut-off valve (1) is closed.

4. The method as claimed in claim 1, characterized in that the valve element (4) is loaded with ambient pressure in a closing direction.

5. A pressure-controlled shut-off valve (1) for intermittently interrupting the air supply to a fuel cell stack (20) in a fuel cell system, the shut-off valve (1) comprising a valve element (4) which is configured to be moved back and forth between two end positions and is preloaded in a direction of a sealing seat (3) by a spring force of a closing spring (2), wherein the sealing seat (3) defines a first end position and a housing-side stroke stop (8) defines a second end position, characterized in that in at least one of the two end positions, the magnetic force of an electromagnet (5) and/or of a permanent magnet (6) act(s) on a magnetic or magnetizable part (7) of the valve element (4).

6. The shut-off valve (1) as claimed in claim 5, characterized in that the magnetic force of the electromagnet (5) counters the spring force of the closing spring (2), and/or the magnetic force of the permanent magnet (6) acts in a direction of the spring force of the closing spring (2).

7. The shut-off valve (1) as claimed in claim 5, characterized in that the valve element (4) passes through a housing part (9) which forms the stroke stop (8) and/or a guide (10) for the valve element (4).

8. The shut-off valve (1) as claimed in claim 5, characterized in that the valve element (4) has at one end a valve plate (11) which cooperates with the sealing seat (3).

9. The shut-off valve (1) as claimed in claim 5, characterized in that the magnetic or magnetizable part (7) of the valve element (4) together with the electromagnet (5) and/or the permanent magnet (6) is accommodated in a pressure chamber (12) in which ambient pressure prevails.

10. The shut-off valve (1) as claimed in claim 5, characterized in that at an end facing the sealing seat (3), the valve element (4) is surrounded by a sealing membrane (13) which is radially outwardly attached on a housing side, so that the sealing membrane (13) separates a valve chamber (14) from a spring chamber (15) in which the closing spring (2) is received.

11. The shut-off valve (1) as claimed in claim 5, characterized in that the shut-off valve (1) has an inlet channel (16) and an outlet channel (17) which are arranged at an angle to one another.

12. An apparatus comprising a fuel cell stack (20) and at least one shut-off valve (1) as claimed in claim 5.

13. The method as claimed in claim 1, wherein the supply of air to the fuel cell stack (20) is interrupted intermittently during a shutdown of the fuel cell system.

14. The shut-off valve (1) as claimed in claim 5, characterized in that the valve element (4) has at one end a valve plate (11) which cooperates with the sealing seat (3), and at an other end the magnetic or magnetizable part (7) is plate-like.

15. The shut-off valve (1) as claimed in claim 5, characterized in that the shut-off valve (1) has an inlet channel (16) and an outlet channel (17) which are arranged at a right angle to one another.

16. An apparatus comprising a fuel cell stack (20) and at least one shut-off valve (1) as claimed in claim 5, wherein the at least one shut-off valve (1) is attached to the fuel cell stack (20) via an adapter plate (21).

Description

[0025] A preferred embodiment of the invention is explained in more detail below with reference to the appended drawings. These show:

[0026] FIG. 1 a schematic longitudinal section through a shut-off valve according to the invention,

[0027] FIG. 2 a schematic longitudinal section through two shut-off valves according to FIG. 1 attached to a fuel cell stack, and

[0028] FIG. 3 a schematic longitudinal section through two shut-off valves according to FIG. 1 attached to a fuel cell stack, wherein the orientation of one shut-off valve has been changed relative to FIG. 2.

DETAILED DESCRIPTION OF THE DRAWINGS

[0029] The pressure-controlled shut-off valve 1 shown in FIG. 1 comprises a valve element 4 which can be moved back and forth between two end positions, wherein the first end position is defined by a sealing seat 3 and the second end position by a stroke stop 8. The sealing seat 3 is formed by a first housing part 19, wherein the sealing seat 3 delimits an inlet channel 16 or outlet channel 17, depending on whether the shut-off valve 1 has an axial or a radial inflow. Both are possible. If the shut-off valve 1 has an axial inflow, the sealing seat 3 delimits the inlet channel 16, wherein the outlet channel 17 is arranged at an angle, in the present case at a right angle, to the inlet channel 16. If the shut-off valve 1 has a radial inflow, the inlet channel 16 runs radially and the sealing seat 3 delimits the axially running outlet channel 17 (see reference signs in brackets). The axial orientation is defined by a longitudinal axis A of the shut-off valve 1.

[0030] To optimize the shut-off function, the valve element 4 comprises an elastic sealing element 18 which cooperates with the sealing seat 3 and is let into an end-side valve plate 11 of the valve element 4. A closing spring 2 also rests on the valve plate 11, and its spring force axially preloads the valve element 4 against the sealing seat 3. At the other end, the closing spring 2 is supported on a second housing part 9 which also forms the stroke stop 8 for the valve element 4. At the same time, the housing part 9 forms a guide 10 for the valve element 4, which for this purpose is partially received in the housing part 9.

[0031] In the region of the valve plate 11, the valve element 4 is surrounded by a sealing membrane 13. By deviation from the illustrated embodiment, the sealing membrane 13 and the sealing element 18, provided on the end face of the valve plate 11, may also be formed as one piece. For example, the sealing membrane 13 may be attached to the valve plate 11 by means of a vulcanizing process such that it simultaneously forms the end-side sealing element 18.

[0032] In the embodiment illustrated, the sealing membrane 13 separates a valve chamber 14 from a spring chamber 15 in which the closing spring 2 is received. The spring chamber 15 is connected via at least one connecting channel 24, formed in the housing part 9, to a pressure chamber 12 which is delimited by a cover part 22 connected to the housing part 9. A pressure-balancing element 23, which is provided on the cover part 22, ensures that ambient pressure prevails in the pressure chamber 12. Since, in the present case, the valve element 4 is guided into the pressure chamber 12, ambient pressure prevails at one end and the respective system pressure 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 sufficiently large to overcome the spring force of the closing spring 2. A small spring force accordingly has an advantageous effect with respect to rapid opening of the shut-off valve 1.

[0033] In order to be able to reduce the spring force of the closing spring 2, the shut-off valve 1 shown in FIG. 1 comprises an electromagnet 5 and a permanent magnet 6, which each act on a magnetic or magnetizable part 7 of the valve element 4. This part 7 is an anchor plate which is fixedly connected to the valve element 4 at the end opposite the valve plate 11. The anchor plate is thus arranged in the pressure chamber 12 which at the same time receives the electromagnet 5 and permanent magnet 6 at an axial distance from one another. The axial distance ensures that the effect of the permanent magnet 6 on the anchor plate is greatest 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 anchor plate moves away from the permanent magnet 6, so the effect no longer exists or is minimal in the second end position. The magnetic force of the permanent magnet 6 accordingly provides an additional holding force which guarantees a secure closure of the shut-off valve 1. This in turn has the advantage that the spring force of the closing spring 2 can be reduced. In order to create an additional holding force which acts 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 shut-off valve 1 remains securely open irrespective of the prevailing pressure conditions. To close the shut-off valve 1, the power supply to the electromagnet 5 is simply ended, so that the spring force of the closing spring 2 returns the valve element 4 to the sealing seat 3.

[0034] FIGS. 2 and 3 show different mounting variants of the shut-off valve 1 according to the invention on a fuel cell stack 20. Mounting takes place indirectly via an adapter plate 21.

[0035] As illustrated as an example in FIG. 2, a first shut-off valve 1, which serves for air supply to the fuel cell stack 20, may be mounted radially so that it has an axial inflow. A second shut-off valve 1′, which extracts used air from the fuel cell stack 20 and is structured identically to shut-off valve 1 (same reference sign), may be mounted axially and have an axial inflow.

[0036] If the mounting situation is the same in both cases, the arrangement shown in FIG. 3 may be selected. Here, both shut-off valves 1, 1′ are mounted axially, wherein the shut-off valve 1 has a radial inflow and the shut-off valve 1′ has an axial inflow. In the shut-off valve 1, the pressure present at the sealing membrane 13 exerts the opening force.