FUEL CELL SYSTEM

The invention relates to a fuel cell system (100) having at least one fuel cell stack (101), an air path (10), wherein air from the surroundings reach the fuel cell stack (101) via the air path (10), an exhaust gas path (12), a fuel line (20), wherein fuel is transported to the fuel cell stack (101) via the fuel line (20). According to the invention, the air path (10) is connected to a cooling line (30) via a branch (33), wherein the cooling line (30) is connected to a PDU unit (32).

BACKGROUND OF THE INVENTION

The invention relates to a fuel cell system having at least one fuel cell stack, having an air path through which air from the environment reaches the fuel cell stack, having an exhaust gas path, and having a fuel line through which fuel is transported to the fuel cell stack.

Hydrogen-based fuel cells are seen as a mobility concept of the future, since they only emit water as an exhaust gas and enable rapid refueling times. Fuel cells are usually assembled to form a fuel cell stack. The fuel cell stacks need oxygen, in most cases taken from ordinary air from the environment, and fuel, in most cases hydrogen, for the chemical reaction.

In fuel cell systems, the voltage taps at the fuel cell stack are carried out and processed via a power distribution unit (PDU). The tasks of a PDU are typically: voltage protection, current measurement, disconnection of the stack voltage from the system in the event of an accident, connection of the stack voltage to the DC/DC converter, then to the battery.

The elements and components within the PDU are exposed to high heat development owing to electrical losses and resistances. For this reason, the PDU has to be cooled. Known cooling options are a separate fan within the housing of the PDU and/or water cooling.

SUMMARY OF THE INVENTION

The inventive fuel cell system is advantageous in that air for cooling the PDU is extracted from the air path (cathode path). Costs can thus be reduced, since there is no need to install a separate cooler which provides the necessary safety in the environment of the engine compartment and blows clean air into the housing of the PDU.

In contrast to water cooling, the elements of the PDU can be cooled directly, whereas, with water cooling, the components can only be cooled indirectly by airflows which are generated within the housing due to temperature gradients. A heat pipe and a Peltier element, which is used to cool the PDU, produce only a slight cooling effect in comparison to direct air cooling.

Effective cooling of the PDU can be ensured as a result of the inventive fuel cell system. The components of the PDU have electrical losses, which may be converted into heat so that, without effective cooling, the internal temperature of the PDU continues to increase and the components overheat and, in the worst case, fail.

An arrangement of the branch point between a compressor, which compresses the air in the air path, and the fuel cell stack is advantageous since a high pressure difference between the branch point and the environment can thus be produced, so that, when necessary, a sufficiently high air mass flow rate for cooling can flow to the PDU via the cooling line.

A heat exchanger, which is arranged between the compressor and the branch point, is advantageous since the temperature of the air which flows to the PDU can thus be further reduced.

A particular advantage is achieved by a filter, which is arranged in the air path between an input and the branch point, since the air which flows to the PDU is thus already cleaned of dust and small particles. Clean air is an important basic requirement for the electronic components within the PDU.

It is advantageous if an adjustable throttle is arranged in the cooling line since the quantity of air which flows to the PDU can thus be altered in a variable manner. In the case of a high thermal load on the components of the PDU, a high quantity of air can flow to the PDU via the adjustable throttle. In the case of a small thermal load, the adjustable throttle can reduce its cross section so that less air flows to the PDU.

If the air in the cooling line still has too high a temperature to ensure effective cooling, a cooler in the cooling line can further reduce the temperature so that greater cooling efficiency is achieved with the same quantity of air.

In this case, it is advantageous if the cooler is arranged between the adjustable throttle and the PDU since this ensures that only the air which flows to the PDU is cooled.

In the event of a stoppage of the fuel cell system, hydrogen may escape from the fuel cell stack into the air path. To prevent the penetration of hydrogen into the PDU, it is advantageous if a non-return valve is arranged in the cooling line. As a result of the non-return valve, the gas exchange between the fuel cell stack and the PDU upon a stoppage of the fuel cell system is prevented since, in the stopped state, the closing force of the non-return valve cannot be overcome by the air pressure at the branch point. This is very important since ignition sources may be present in the PDU, which could result in the ignition of a mixture of hydrogen and air.

It is advantageous if the PDU has a pressure equalizing element or a non-return valve via which the air can escape into the environment. In this case, the pressure equalizing element can be designed such that it is permeable to gases but prevents the entry of particles and moisture into the PDU.

DETAILED DESCRIPTION

In the figure, a schematic topology of a fuel cell system100according to a first exemplary embodiment is shown with at least one fuel cell stack101. The at least one fuel cell stack101has an air path10, an exhaust gas path12and a fuel line20. The at least one fuel cell stack101can be used for mobile applications with a high power requirement, for example in trucks, or for stationary applications, for example in generators.

The air path10serves as an air supply line in order to supply air from the environment to the fuel cell stack101via an inlet16. Components which are required for the operation of the fuel cell stack101are arranged in the air path10. An air compressor11and/or supercharger11can be arranged in the air path10, which air compressor and/or supercharger compresses or draws in the air according to the respective operating conditions of the fuel cell stack101. A heat exchanger15can be located downstream of the air compressor and/or supercharger11, which heat exchanger cools the air in the air path10to a lower temperature.

Further components, such as humidifiers and/or valves, for example, can be provided within the air path10. The fuel cell stack101is provided with oxygenated air via the air path10.

The air path10is connected to a cooling line30via a branch point33. Air from the air path10can arrive in a PDU32or the housing31of a PDU32via the cooling line30. A PDU32is a power distribution unit32, which carries out a voltage tap at the fuel cell stack101and processes and connects these voltage taps.

The tasks of a power distribution unit (PDU32) are inter alia: voltage protection, current measurement, disconnection of the stack voltage from the system if an accident is detected, connection of the stack voltage to the DC/DC converter and/or to the battery.

The elements in the housing31of the PDU32can be cooled using the air from the air path10, which arrives in the housing13of the PDU32via the cooling line30.

The branch point33is preferably arranged between the compressor11, which compresses the air in the air path10, and the fuel cell stack101. In order to provide the cooling line30with sufficient cold air, the heat exchanger15can be arranged between the compressor11and the branch point33.

At least one filter13, which filters particles and foreign bodies out of the air, can be arranged in the air path10, between the input16and the branch point33. The air which flows to the PDU32is thus already cleaned of unwanted particles and foreign bodies.

So that the air which arrives in the cooling line30from the air path10is controlled according to requirements, an adjustable throttle34can be arranged in the cooling line30.

If the air which flows into the cooling line30from the air path10does not have the desired temperature, a cooler35can be arranged in the cooling line30, which cooler further cools the air in the cooling line30. In one embodiment, the cooler35can be arranged between the adjustable throttle34and the PDU32.

A gas non-return valve37can furthermore be arranged in the cooling line30, which gas non-return valve prevents hydrogen from the fuel cell stack101from diffusing into the cooling line30in the event of a stoppage of the fuel cell system100.

The air which has arrived in the housing31of the PDU32via the cooling line30can be discharged back into the environment via at least one pressure equalizing element38, which is arranged in the housing31of the PDU32. In one embodiment, the pressure equalizing element38is permeable to gases but prevents the entry of particles and moisture into the PDU.

In an alternative embodiment, a further non-return valve38is arranged in the housing31of the PDU32, via which non-return valve the air, which has arrived in the housing31of the PDU32via the cooling line30, can escape into the environment.

The fuel cell system100furthermore has an exhaust gas path12in which water and further constituents of the air can be transported out of the air path10after its passage through the fuel cell stack101and into the environment via an outlet18.

The fuel cell system100can furthermore have a cooling circuit, which is designed to cool the fuel cell stack101. The cooling circuit is not shown in the figure since it is not part of the invention.

The fuel line20has a high pressure tank21and a shut-off valve22. Further components can be arranged in the fuel line20in order to supply fuel to the fuel cell stack101according to requirements. A circulation line can furthermore be provided, which is not shown in the figure since it is not part of the invention.