The invention relates to a fuel cell system, in particular for a motor vehicle, having a fuel cell stack arranged in a housing, and having a measure for ventilating the housing by coupling a ventilation flow to another gas flow. With regard to the prior art, reference is made to DE 10 2008 016 579 A1.
For example, for use in a motor vehicle, it is known for a fuel cell stack to be arranged (to be “integrated”) in a substantially closed housing, wherein, aside from passage openings that are self-evidently required for media-conducting lines, it is also necessary for ventilation openings to be provided in a wall of the housing in order to permit ventilation of the interior of the housing. This is to be understood, in the present case, as being a “substantially closed” housing, wherein the present invention is also intended to encompass possible housing structures in the case of which no substantially closed side walls are provided, but with which a housing is realized which is substantially closed off at least in an upward direction and below the top side of which it is, for example, possible for hydrogen to accumulate. The hydrogen could, via possible leakage points, escape in small quantities from the media-conducting lines connected to the fuel cell stack.
An air flow, referred to in the present case as a ventilation flow, for the ventilation of the housing and discharge of possibly accumulating hydrogen from the housing is commonly introduced from the surroundings into the housing and discharged into the surroundings again. It is desirable for no dedicated (energy-consuming) delivery device to have to be provided for the delivery of the ventilation flow. In DE 10 2008 016 579 A1, it is proposed that the ventilation flow to be discharged from the housing be admixed to the cathode exhaust-gas flow of the fuel cell stack by way of a de Laval nozzle, utilizing the ejector pump effect. The cathode exhaust-gas flow or exhaust-gas flow of the fuel cell stack thus forms the delivery device for the ventilation flow.
The problem addressed by the present invention is to provide a further measure by which a ventilation flow through or out of a housing which contains a fuel cell stack can be discharged in an expedient manner.
The solution to the problem is, for a fuel cell system having a fuel cell stack arranged in a housing and having a measure for ventilating the housing by coupling the ventilation flow to another gas flow, characterized in that the ventilation flow is supplied to an air flow which is conducted through a radiator, in the form of an ambient-air heat exchanger, of the fuel cell system. Here, a radiator of the fuel cell system is to be understood generally to mean an ambient-air heat exchanger which is designed and provided for cooling at least sub-components of the fuel cell system, which may include not only the stack itself but also, for example, the power electronics of the fuel cell system.
A fuel cell system according to the invention has a radiator in the form of an air-cooling fluid heat exchanger, wherein the cooling fluid is conducted in a suitable manner, for example through the fuel cell stack, and the waste heat thereof is dissipated at least partially via the radiator to the ambient air. The radiator exit air flowing through the radiator must in this case be discharged in a suitable manner, such that, for this purpose, an exit-air guide of a certain design is provided. In this case, the so-called ventilation flow is now also conducted away from the fuel cell system by way of the exit-air guide, such that the exit-air guide, in effect, performs a further function. Here, it may also be provided that a pressure gradient or the like, which at least partially contributes to the delivery of the ventilation flow, is generated by way of the ambient-air flow flowing through the radiator.
As used herein, the ventilation flow may be supplied or admixed, upstream of the radiator, to the air flow that is conducted through the radiator, because, upstream of the radiator, a directed flow is encountered which is not disrupted by lamellar structures or the like of the radiator and which, in effect, entrains the ventilation flow in accordance with the ejector pump principle. In this context, a ventilation opening of the housing can be positioned correspondingly, that is to say preferably directly adjacent to the flow path of the radiator inlet-air flow. In the conventional manner, it is then, or in this case, provided that, either for the radiator inlet-air flow or for the radiator exit-air flow, that is to say generally for the ambient-air flow to be conducted through the radiator, a suitable air delivery device in the form of a fan or the like is provided. In the case of a fuel cell system according to the invention installed in a motor vehicle, when the vehicle is moving, the “relative wind” also functions, in effect, as an air delivery device also for the ventilation flow of the housing that contains the fuel cell stack.
Similarly to the known prior art mentioned above, the ventilation flow of the stack housing may, however, also be supplied or admixed to an exhaust-gas flow of the fuel cell stack, for example by way of a Venturi nozzle, wherein, again, the ejector pump effect is utilized for the delivery of the ventilation flow. According to the invention, the exit-air flow of the radiator is then merged with the exhaust-gas flow, comprising the ventilation flow, of the fuel cell stack, such that multiple gas flows are, in accordance with the invention, conducted away from the fuel cell system together or jointly. Here, the exhaust-gas flow of the fuel cell system may be the cathode exhaust-gas flow and/or the anode exhaust-gas flow, which may by all means be merged, preferably downstream of the admixing of the ventilation flow, in a mixer.
In one aspect, a sensor for determining the hydrogen content in a gas flow downstream of the supply of the ventilation flow is provided, that is to say that, by way of a so-called hydrogen sensor of this type, the hydrogen concentration in the gas flow comprising this ventilation flow is measured. This gas flow may be an exhaust-gas flow as mentioned above or may be the radiator inlet-air flow or the radiator exit-air flow or a mixed gas flow comprising one or more of the flows. Thus, with the aid of an electronic monitoring unit, it can be checked whether an inadmissible amount of free hydrogen would pass with the mixed gas flow into the surroundings. It is possible, if appropriate, for suitable measures for this purpose, or for preventing this, to be introduced. If appropriate, with the aid of a sensor of the type and a suitable electronic monitoring unit, it is also possible, on the basis of the hydrogen content (=“sensor signal”) registered by the sensor, for a conclusion to be drawn regarding hydrogen possibly freely situated within the housing. If the gas flow contains exit air, already including hydrogen, of the fuel cell stack, it is specifically the case that the hydrogen concentration present therein is known, at least from a model calculation, to an electronic control unit for the control of the operation of the fuel cell stack, for which reason a hydrogen concentration higher than the known hydrogen concentration is indicative of additional hydrogen from the ventilation flow. It is basically thus possible, by way of a single sensor, to dispense with a (further) dedicated hydrogen sensor within the housing or for the ventilation flow alone.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.
In the figures, identical elements are denoted by the same references designations.