FIELD OF THE INVENTION

The invention relates to a fuel cell arrangement for a hydrogen/oxygen fuel cell.

BACKGROUND INFORMATION

Chemically stored energy is converted into electrical energy in a fuel cell, wherein one reactant is oxidized and the other reactant is reduced. In a hydrogen/oxygen fuel cell (H2/O2 fuel cell), hydrogen (H2) is oxidized by the release of electrons at an anode, while oxygen (O2) is reduced by the acceptance of electrons at a cathode. As a result of this redox reaction, chemical energy stored in the reactants is converted into electrical energy at the anode or respectively cathode and can be tapped from there and utilized.

One exemplary type of utilization is utilizing the electrical energy to drive motor vehicles, wherein the efficiency during the conversion of the chemically bonded energy into electrical energy is up to 60%.

During the deployment of such H2/O2 fuel cells, the hydrogen is provided in a hydrogen tank at a pressure of approximately 350 bar to 700 bar for the application.

FIG. 4shows an exemplary fuel cell arrangement which is known from the prior art and which can be used for driving motor vehicles.

The fuel cell arrangement10inFIG. 4has a hydrogen tank12which provides hydrogen14for a redox reaction in a H2/O2 fuel cell16. In order to prevent the hydrogen14escaping from the hydrogen tank12in an uncontrolled manner in the event of a defect, a shutoff valve18is arranged immediately after the hydrogen tank12. The hydrogen14is stored at a high pressure of approximately 350 bar to 700 bar in the hydrogen tank12. This hydrogen14, which is supplied at high pressure, has its pressure reduced by means of a pressure reducer20to a lower pressure stage in the range of a medium pressure of approximately 10 bar to 70 bar. Within said pressure stage, the hydrogen14is supplied by means of lines22and a hydrogen metering valve24to an anode26of the H2/O2 fuel cell16. The metered addition of the hydrogen14is effected in a targeted manner by means of the hydrogen metering valve24. The prevailing pressure of the hydrogen14at the anode26is low: in a range of approx. 0.8 bar to 4 bar. A hydrogen mass flow is adjusted in the hydrogen metering valve24with the pressure gradient from the medium pressure to the low pressure. The pressure in the anode26, which forms an enclosed volume, is controlled in that said volume is filled by means of a defined mass flow of hydrogen14. As a result, a defined pressure of the hydrogen14is adjusted in the volume of the region of the anode26.

The hydrogen14reacts in the H2/O2 fuel cell16with oxygen28which is supplied to a cathode30of the H2/O2 fuel cell16. The oxygen28is supplied to the cathode30by means of a separate feeding unit32which ensures that sufficient oxygen28at a defined pressure is available in said region.

On the side of the anode26, the concentration of the hydrogen14lowers over time due to the reaction of the hydrogen14with the oxygen28. In order to ensure that there is always sufficient hydrogen14available here for the operation of the H2/O2 fuel cell16, the hydrogen14is recirculated within the region of the anode26. This can be effected, for example, by a gas blower34or an ejector. The hydrogen14is conducted back from an outlet36of the anode26to an inlet38of the anode26. As a result, a gas exchange is effected within the anode26, wherein unconsumed hydrogen14from the volume in the anode26can be utilized for the reaction with oxygen28.

If there is no longer enough hydrogen14present in the volume of the anode26, the gas is conducted out of the volume by a release valve40. The hydrogen metering valve24adds new metered hydrogen14to the anode26. It is important that a defined pressure is observed on the side of the anode26. This is because a pressure difference between the anode26and the cathode30is required for the reaction of the hydrogen14with the oxygen28. At the same time, care must be taken that a diaphragm42(fuel cell membrane) arranged between the anode26and the cathode30is not damaged when a pressure difference between the anode26and the cathode30is too high.

In order to control said pressure difference, the pressure on the anode side and the cathode side is measured by sensors44. An electronic regulating unit46adjusts the hydrogen metering valve24by means of a control algorithm such that the pressure in the anode26is controlled within a predefined range, and the required pressure difference between the anode26and the cathode30is present for the reaction of the hydrogen14and oxygen28.

Until now, the precise controlling of said pressure in the anode26and the required pressure difference between the anode26and the cathode30have therefore been achieved by a complex control system consisting of sensors44, an electronic regulating unit46and one or more electrohydraulic hydrogen metering valves24.

SUMMARY OF THE INVENTION

The object of the invention is to propose a simplified fuel cell arrangement in this respect.

This object can be achieved with a fuel cell arrangement having the combination of features according to the invention as set forth herein.

A fuel cell arrangement for an H2/O2 fuel cell has an anode, at which H2 is oxidized during operation, and which is connected to an H2 inflow for supplying H2 to the anode, wherein a valve having a valve seat and a valve element is arranged in the H2 inflow, which interact in a closing position, in order to interrupt an inflow of H2 from the H2 inflow to the anode. The fuel cell arrangement further has a cathode, at which O2 is reduced during operation, and which is connected to an O2 inflow for supplying O2 to the cathode. A differential pressure control device is arranged between the H2 inflow and the O2 inflow for controlling a differential pressure between the H2 inflow and the O2 inflow, the differential pressure control device having a fluid connection between the H2 inflow and the O2 inflow in which there is arranged a diaphragm for sealing the fluid connection which can be deflected by a deflection force acting due to a pressure difference between the H2 inflow and the O2 inflow. A pin is coupled to the deflectable diaphragm and the valve element in such a manner that the pin, when the diaphragm is deflected in the direction of the H2 inflow, presses the valve element away from the valve seat in the opening direction.

The fuel cell arrangement described can control the differential pressure between the H2 inflow and the O2 inflow and, consequently, between the anode and cathode with only one component, namely the differential pressure control device, and without additional sensors. The system has a robust and compact construction, and an electrical regulating unit can also be dispensed with since the system can have a purely mechanical construction.

The differential pressure control device, which consequently provides an improved hydrogen metering valve, acts as follows: the pressure in the O2 inflow to the cathode acts on the deflectable diaphragm, such that the position thereof changes depending on a pressure difference between the H2 inflow and the O2 inflow. Due to the change in position of the diaphragm, the pin coupled to the diaphragm presses the valve element, as a result of which the position of the valve element is changed and a cross-section on the valve seat is released i.e. opened. The supply of the hydrogen into the anode from the H2 supply is thereby regulated dependent on or as a function of the resulting open cross-section of the valve.

The mass of hydrogen which is supplied to the anode therefore results from the force equilibrium between a pressure which acts in the H2 inflow and a pressure which acts in the O2 inflow, and the pressure surfaces on the valve element or respectively on the valve seat. Due to this construction, a constant pressure difference can be adjustingly set during the operation of the fuel cell arrangement.

A second deflectable diaphragm for sealing the fluid connection is preferably arranged in the fluid connection at a distance from the abovementioned (first) deflectable diaphragm which can be deflected by the deflection force acting due to the pressure difference between the H2 inflow and the O2 inflow.

Preferably, the first diaphragm seals the fluid connection toward the H2 inflow, while the second diaphragm seals the fluid connection toward the O2 inflow.

In an advantageous configuration, a pressure transmission volume is formed by the arrangement of the first and second diaphragms at a distance from one another in the fluid connection, which pressure transmission volume is filled with a pressure transmission fluid that can transmit the deflection force exerted by the pressure difference between the H2 inflow and the O2 inflow from the second diaphragm to the first diaphragm.

The pressure at an inlet of the cathode, that means in the O2 inflow, acts on the second diaphragm in the cathode region. The greater the pressure in the cathode region, the more the second diaphragm is deformed and acts on the pressure transmission fluid in the pressure transmission volume. The pressure transmission fluid continues to act on the first diaphragm at the H2 inflow, that means in the anode region.

From the other side of the first diaphragm, the pressure acts in the anode region, that means in the H2 inflow, on the first diaphragm, such that the position of the first diaphragm depends on the pressure difference between the inlet of the cathode, that means the O2 inflow, and the pressure in the region of the anode, that means in the H2 inflow.

The first diaphragm and the second diaphragm preferably have different active surfaces (i.e. surface areas) for accepting the deflection force. The dependence of the position of the first diaphragm on the pressure difference between the H2 inflow and the O2 inflow can consequently be constructively adjusted by means of the ratios of the active surfaces (surface areas) of the two diaphragms.

A first active surface of the first diaphragm is advantageously smaller than a second active surface of the second diaphragm. Consequently, it is possible, even in the case of small pressure differences between the H2 inflow and the O2 inflow, to realize a sufficiently large deflection of the first diaphragm and, consequently, a raising of the valve element from the valve seat.

The valve preferably has a compression spring which is arranged in the H2 inflow and exerts a spring force on the valve element, which biases the valve element in a closing direction onto the valve seat. Due to the arrangement of the compression spring, the valve element can be securely held on the valve seat in the closing position. The pressure of the hydrogen acting in the H2 inflow consequently acts in the same direction as the spring force of the compression spring such that the valve element is securely held in the valve seat by the forces both of the flowing hydrogen and of the compression spring.

An actuator for controlling the spring force of the compression spring is preferably provided. By providing such an actuator it is possible to additionally adjust the force equilibrium. As a result, the pressure difference to be controlled between the cathode and the anode can additionally be tweaked.

The actuator is, for example, formed by an actuatable piezo actuator. In an alternative configuration, it is possible to form the actuator by an actuatable electromagnetic actuator. It is however conceivable, in a further possible embodiment, to configure the actuator by a controllable electromotor which has a spindle.

