Method for determining the sealing tightness of a fuel cell stack

Abstract

A method for determining a sealing tightness of a fuel cell stack includes providing of fuel into a cathode space, sealed off gas-tight against further components of a cathode subsystem, formed at least partly by the fuel cell stack, and detecting of a value which is indicative of a pressure change in the cathode space, where a cathode test pressure in the cathode space is higher than a pressure outside the fuel cell stack.

Claims

1. A method for determining a sealing tightness of a fuel cell stack, comprising the acts of: providing of fuel into a cathode space, sealed off gas-tight against further components of a cathode subsystem, formed at least partly by the fuel cell stack, wherein an anode subsystem is connected across at least one fuel line to the cathode space such that the fuel flows from an anode space into the cathode space via the at least one fuel line and such that a pressure equalization occurs between the anode space and the cathode space across the at least one fuel line; and detecting of a value which is indicative of a pressure change in the cathode space, wherein a cathode test pressure in the cathode space is higher than a pressure outside the fuel cell stack.

2. The method according to claim 1, wherein, at least at a beginning of the detecting, a pressure in the anode space corresponds substantially to a pressure in the cathode space.

3. The method according to claim 1 further comprising the acts of closing anode-side stack shutoff valves after the pressure equalization occurs and detecting a value which is indicative of a pressure change in the anode space, wherein an anode test pressure in the anode space is higher than the pressure outside the fuel cell stack.

4. The method according to claim 1 further comprising the acts of closing an anode purge valve and cathode-side stack shutoff valves, subjecting the anode space to a greater pressure than the cathode space, and detecting a value which is indicative of a pressure change in the anode space.

5. The method according to claim 1, wherein at least as much fuel is provided in the cathode space such that an entire oxidizing agent present in the cathode space is converted.

6. The method according to claim 1, wherein cathode-side stack shutoff valves of the cathode subsystem are closed at least during the detecting and/or during the providing.

7. The method according to claim 1, wherein the fuel cell stack is used in a motor vehicle and wherein the sealing tightness is checked during a phase when the motor vehicle is not in use.

8. The method according to claim 1, wherein the fuel cell stack is used in a motor vehicle and wherein the sealing tightness is checked before a predicted use of the motor vehicle.

9. The method according to claim 1, wherein the fuel cell stack is used in a motor vehicle and wherein the sealing tightness is checked 10 minutes or 20 minutes or 30 minutes or 1 hour before a predicted use of the motor vehicle.

10. The method according to claim 1, wherein the detecting is done by making a nominal vs. an actual comparison: between the cathode test pressure and a pressure actually detected in the cathode space after a definite time has elapsed; and/or between an anode test pressure and a pressure actually detected in the anode space after the definite time has elapsed.

11. A method for starting a fuel cell system, comprising the acts of: determining the sealing tightness according to claim 1, wherein the fuel cell system is only started if the pressure change is less than a pressure change limit value.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic view of a fuel cell system;

(2) FIG. 2 is a schematic view of another fuel cell system; and

(3) FIG. 3 is a schematic representation of a flow chart of a method disclosed here for determining the tightness of a fuel cell stack.

DETAILED DESCRIPTION OF THE DRAWINGS

(4) FIG. 1 shows a fuel cell system which is designed to carry out the method disclosed here. Not shown in FIGS. 1 and 2 is the controller to carry out the method disclosed here. It is in particular a controller which can be designed to carry out the method disclosed here even during a phase of non-use of the motor vehicle.

(5) The fuel cell stack 300 is divided here schematically into two parts, one part forming the anode space A and a second part forming the cathode space K. The fuel cell stack 300 is shown here greatly simplified. In actuality, the fuel cell stack 300 generally encompasses several hundred individual cells, each of which has a cathode and an anode, which are separated by an ion-permeable separator.

(6) The cathode subsystem comprises:

(7) an oxidizing agent feed 410, which draws in and compresses the oxidizing agent (here, air);

(8) downstream from the oxidizing agent feed 410, an intercooler 420, which cools the compressed oxidizing agent;

(9) a bypass 460, which branches off upstream from the fuel cell stack 300 and emerges into the exhaust gas line downstream from the fuel cell stack;

(10) a first cathode-side stack shutoff valve 430 or cathode shutoff valve, which is arranged upstream from the fuel cell stack 300; and

(11) a second cathode-side stack shutoff valve 440, which is arranged downstream from the fuel cell stack 300.

(12) The cathode-side stack shutoff valves 430, 440 are arranged directly adjacent to the fuel cell stack 300. An anode purge line 239, which begins here at an anode purge valve or purge valve 238, emerges between the first stack shutoff valve 430 and the fuel cell stack 300.

(13) The anode purge valve 238 here is formed at or adjacent to the water separator 232. The anode purge valve 238 may also be called the anode-side stack shutoff valve 238 downstream from the fuel cell stack 300.

(14) The anode subsystem here further comprises, among other things:

(15) at least one fuel source (represented here by “H2”);

(16) at least one anode-side (first) stack shutoff valve 211, which is arranged upstream from the fuel cell stack 300 and is designed to interrupt the fluidic connection between the fuel source and the rest of the anode subsystem;

(17) at least one ejector 234, which is designed to introduce the recirculated gas into the anode feed line; and

(18) at least one fuel recirculation feed, which is arranged in the recirculation line and delivers the gas being recirculated.

(19) Likewise, the anode-side stack shutoff valve 211 can be provided immediately adjacent to the anode inlet of the fuel cell stack 300, especially in a design with no recirculation.

(20) FIG. 2 shows a layout similar to FIG. 1. The difference is a fuel feed line 239, shown in FIG. 2, which emerges into the cathode space K downstream from the fuel cell stack 300.

(21) What is common to both figures is the fact that the cathode-side stack shutoff valves 430, 440 together with a partial region of the fuel cell 300 form a cathode space K, which is separated gas-tight against the remaining components of the cathode subsystem. Likewise, the anode-side stack shutoff valves 211, 238 here form an anode space A together with a partial region of the fuel cell 300, which can be sealed off against other regions of the anode subsystem and/or the cathode subsystem. According to the embodiment shown here, the fluidic connection between the anode space A and the cathode space K can be interrupted by the anode purge valve 238.

(22) FIG. 3 shows schematically a configuration of the method disclosed here for the determining of the tightness of the fuel cell stack. The method starts with step S100. In step S200, a pressure regulation of the anode is activated. The pressure regulation of the anode regulates the pressure in the anode space A. In step S300, the cathode-side stack shutoff valves 430, 440 are closed. In step S400, the anode purge valve 238 is opened. Thus, the pressure equalization occurs between the anode space A and the cathode space K, whereupon the pressure regulation of the anode influences the pressure both in the anode space A and in the cathode space K on account of the fluidic connection via the fuel line 239. In step S500, a check is made to see whether the pressure in the cathode space K p.sub.Ko is equal to the pressure p.sub.A in the anode space A. Preferably a pressure sensor is arranged for this purpose in the cathode space K and in the anode space A, and sends a signal representing the pressure in the corresponding space to a controller of the fuel cell system or the motor vehicle. If these pressures are not substantially identical, in step S600 a check is made to see whether a certain time-out or dead time t.sub.t for this pressure equalization has already elapsed. If this dead time has elapsed, it can be determined in step 610 that no system start is allowed. Alternatively or additionally, in step S610 a corresponding warning may be put out to the user or to a third party, such as a service control center. If the dead time has not yet elapsed, step S500 is repeated. If a pressure equilibrium has substantially been established between the cathode space K and the anode space A, the pressure regulation of the anode is deactivated in step S700. For this, the anode purge valve 211 may be closed, for example. In step S800, a pressure change in the cathode space K and possibly also in the anode space A is detected. The detecting of the pressure change may be done for example via a pressure sensor in the cathode space K or in the anode space A. Especially preferably, two pressure sensors are used, one pressure sensor detecting the pressure change in the cathode space K and the other pressure sensor detecting the pressure change in the anode space A. It may be provided for this that the anode purge valve 238 is closed during the detecting of the pressure change. The detecting of the pressure change may occur by performing a nominal vs. actual comparison between a test pressure, especially the cathode test pressure or the anode test pressure, and the pressures actually detected (respectively there) after a definite time has elapsed. Alternatively, this nominal vs. actual comparison may also be done continuously over a definite period of time. In step S900, a check is made to see whether the detected pressure difference Δp.sub.K is less than or equal to a still permissible limiting pressure difference. If so, then in step S1000 the system start of the fuel cell system is allowed. If no, then in step S1100 the system start is not allowed. Alternatively or additionally, a warning may be put out to a user or a third party.

(23) The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.