Daimler AG and

Ford Global Technologies, LLC

Fuel Cell System

The invention relates to a fuel cell system having at least one fuel cell, which comprises an anode compartment and a cathode compartment and comprises an anode branch connected to the anode compartment for supplying fuel and removing anode waste gas and a cathode branch connected to the cathode compartment for supplying oxidizing agent and removing cathode waste gas.

When such fuel cell systems are in operation, liquid may arise in the form of liquid water. In particular at low ambient temperatures, for example close to or below the 0 ⁰ C boundary, this may lead to operating problems for the fuel cell system. Components of the fuel cell system may freeze, whereby in particular restarting of a fuel cell system after it has been stopped may be problematic.

It is the object of the present invention to provide a fuel cell system which makes it possible reliably and inexpensively to detect the occurrence of liquid in the system.

The object is achieved with a fuel cell system which has the features as claimed in Claim 1.

A fuel cell system according to the invention comprises at least one fuel cell, which comprises an anode compartment and a cathode compartment. The fuel cell system additionally comprises an anode branch, which is connected to the anode compartment and with which fuel may be supplied to the anode compartment and anode waste gas may be removed from the anode compartment. In addition, the fuel cell system comprises a cathode branch, which is connected to the cathode compartment of the fuel cell and which is designed to supply oxidizing agent to the cathode compartment and to remove

cathode waste gas from the cathode compartment. The fuel cell system comprises at least one sensor device for detecting liquid in at least one of the branches. The sensor device comprises at least one light source and at least one detector, which is designed to detect light emitted by the light source and reflected by a part, which takes up liquid, of a branch. The quantity of light reflected by the part is dependent on the liquid taken up by the part. Such a configuration of the fuel cell system makes possible reliable yet inexpensive detection of liquid.

Preferably, the sensor device is arranged outside a line, conveying the oxidizing agent or the fuel or a waste gas, of a branch. The sensor system is thus arranged to have virtually no contact with liquid which may be produced in a branch. In this way, wear may be kept low. Not least, this also allows simple accessibility for assembly purposes, for example, or adjustments or calibration.

In particular, the anode compartment of the fuel cell is associated with the anode branch and the cathode compartment of the fuel cell is associated with the cathode branch. The sensor device may preferably be designed to detect liquid, in particular liquid water, in a line of a branch and/or at least in one of the compartments of the fuel cell.

Preferably, the part of a branch optionally taking up the liquid comprises a light- transmitting element. In particular, provision is made for the part itself to form the light- transmitting element. The light-transmitting element may in particular take the form of a transparent element. In particular, acrylic polymer or PMMA (polymethyl methacrylate) may be used in this regard as the material. Such a configuration may particularly preferably support the functionality of the sensor device.

Preferably, the part of the branch is arranged in a line or associated therewith and the light-transmitting element is constructed in the wall of the line. In particular, the light- transmitting element thus forms a wall area. Such a configuration allows the functional principle of the sensor device based on reflection to be achieved simply and cheaply via the outside and the deposition or taking up of liquid on the inside of the line to be detected.

Preferably, the operating state of the fuel cell system may be modified depending on the quantity of liquid detected by the sensor device in at least one branch. Thus, information

about the occurrence of liquid, in particular water, may accordingly allow optimum adjustment of operation of the fuel cell system. In this regard, it is for example possible to provide for operation to be changed over where necessary from a consumption-optimized mode to an operating mode in which minimization of the liquid water arising has priority. In precisely this context, the production of undesirably high quantities of liquid in the fuel cell system may then be avoided. The production of liquid in the fuel cell system may thereby be minimized precisely when low ambient temperatures of close to the 0°C boundary or below prevail, so at least reducing the probability of system components freezing.

Preferably, the light source of the sensor device takes the form of a light-emitting diode. The detector of the sensor device is preferably a photodiode.

In particular, the light source and the detector of the sensor device are arranged on one side, at a distance from the outside of a line of a branch. This allows a configuration minimized as regards structural space, which is particularly suitable with regard to achieving the functional principle.

In particular, the fuel cell system takes the form of a mobile system and is provided for use in a vehicle.

The at least one fuel cell of the system takes the form in particular of a PEM fuel cell. Preferably, the fuel cell system comprises a plurality of fuel cells, which form a fuel cell stack.

An exemplary embodiment of the invention is explained in greater detail below with reference to schematic drawings, in which:

Fig. 1 is a schematic representation of components of a fuel cell system according to the invention; and

Fig. 2 is a schematic representation of a detail according to Fig. 1.

In the figures, elements which are the same or have the same function are provided with the same reference symbols.

Fig. 1 shows a fuel cell system 1 , wherein in this regard only the components needed to understand the invention are illustrated. The fuel cell system 1 takes the form of a mobile fuel cell system and is arranged in a vehicle.

The fuel cell system 1 comprises at least one fuel cell 2, in particular a fuel cell stack with a plurality of fuel cells 2. The fuel cell 2 comprises an anode compartment 3 and a cathode compartment 4, which are separated from one another by a membrane electrode assembly (MEA) 5. Furthermore, the fuel cell system 1 comprises an anode branch 6. The anode branch 6 comprises a feed line 7, via which fuel may be supplied to the anode compartment 3. Hydrogen or a hydrogen-containing gas may be used as the fuel. The anode branch 6 further comprises a discharge line 8, which is provided for the removal of anode waste gas. Furthermore, the anode branch 6 comprises a recirculation line 9, which branches off from the discharge line 8 and leads into the feed line 7.

The fuel cell system 1 additionally comprises a cathode branch 10, which comprises a feed line 11 , via which oxidizing agent may be supplied to the cathode compartment 4. The oxidizing agent may be oxygen or an oxygen-containing gas, e.g. air. The cathode branch 10 further comprises a discharge line 12, which is designed for the removal of cathode waste gas. The cathode branch 10 may also comprise a recirculation line 13, which branches off from the discharge line 12 and leads into the feed line 11.

Provision may also be made for the fuel cell system 1 to comprise just one of the two recirculation lines 9 or 13 or indeed neither of these two lines 9 or 13.

Moreover, the fuel cell system 1 comprises a sensor device 14 for detecting liquid water in the fuel cell system 1. In particular, the sensor device 14 is designed to detect liquid water which may arise in the process gas during operation of the fuel cell system 1.

Provision may be made for the fuel cell system 1 also to comprise a plurality of sensor devices 14, which are arranged at various positions for example in the anode branch 6 and/or in the cathode branch 13. The arrangement of the sensor device 14 in the area of the discharge line 8 of the anode branch 6 as shown in Fig. 1 is merely one possible example.

Fig. 2 shows an enlarged schematic representation for further explanation of the mode of operation of the sensor device 14. The sensor device 14 is arranged outside the line 8. The discharge line 8 is defined by a wall 15 forming for example a hollow cylinder, a part designed as a light-transmitting element 16 being arranged, in particular incorporated, in the wall 15. In the exemplary embodiment, the light-transmitting element 16 is made of acrylic polymer and is thus of transparent design.

The sensor device 14 comprises a printed circuit board or circuit carrier 18 on which at least one light source 19 in the form of a light-emitting diode is arranged. Furthermore, a detector 20 in the form of a photodiode is mounted on this board 18. The light source 19 and the detector 20 are both arranged on one side of the wall 15.

The sensor device 14 is designed to detect liquid, which is illustrated by way of example by the droplets 17.

The light source 19 emits light 21 in the direction of the outside of the element 16. A corresponding quantity of light is reflected depending on the quantity of droplets 17 on the inside of the element 16. The reflected light 22 may be detected by the detector 20. The light 21 is introduced into the element 16 and the reflected light 22 is measured preferably constantly by the detector 20. The more liquid droplets 17 which are deposited or taken up on the inside of the element 16, the less is the reflection.

Mention may be made of the fact that the liquid 17 is not only taken up by the inside of the element 16, but may also be taken up by the inside of the entire wall 15 of the discharge line 8 or other lines and components of the system 1.

Depending on the detected quantity of reflected light 22, a conclusion may then be drawn about the quantity of liquid water. The operating state of the fuel cell system 1 may then be modified as a function thereof. Provision is made in this context, in particular, for operation of the fuel cell system 1 to be correspondingly adjustable as a function of the information about the occurrence of process water. Production of relatively large amounts of liquid water may thereby be prevented precisely at very low ambient temperatures, so additionally preventing or at least reducing the freezing of system components.

List of reference numerals

1 Fuel cell system

2 Fuel cell

3 Anode compartment

4 Cathode compartment

5 Membrane electrode assembly (MEA)

6 Anode branch

7 Feed line

8 Discharge line

9, 13 Recirculation lines

10 Cathode branch

11 Feed line

12 Discharge line

14 Sensor device

15 Wall

16 Light-transmitting element

17 Liquid

18 Printed circuit board

19 Light-emitting diode

20 Photodiode

21 Emitted light

22 Reflected light