DE102015200935A1 - Fuel cell system, vehicle with such and method for operating the fuel cell system and / or the vehicle - Google Patents

Abstract

The invention relates to a fuel cell system (100) comprising a fuel cell (10) having a cathode output (38) and a cathode exhaust system (32) for discharging a cathode exhaust stream from the fuel cell (10), the cathode exhaust system (32) comprising: a main cathode exhaust path (34) having a main output (35) for discharging the cathode exhaust stream into the environment (36), the main cathode exhaust path (34) being between the cathode output (38) of the fuel cell (10) and the main output (35). extending, - a secondary cathode exhaust path (40) having a secondary output (41) for discharging the cathode exhaust gas into the environment (36), wherein the secondary cathode exhaust path (40) between a branch (42) from the main cathode exhaust path (34 and at least one flow control means (44, 45) for opening and closing the sub-cathode exhaust path (40) and / or the main cathode exhaust path (34) downstream of the branch (42). , Furthermore, the invention relates to a vehicle (200) with such a fuel cell system (100) and to a method (300) for operating the fuel cell system (100) and / or the vehicle (200).

Description

The invention relates to a fuel cell system and a vehicle with such a fuel cell system. Furthermore, the invention relates to a method for operating the fuel cell system and / or the vehicle.

Fuel cells use the chemical transformation of a fuel with oxygen to water to generate electrical energy. For this purpose, fuel cells contain as a core component, the so-called membrane electrode assembly (MEA for membrane electrode assembly), which is a microstructure of an ion-conducting (usually proton-conducting) membrane and in each case on both sides of the membrane arranged electrode (anode and cathode). In addition, gas diffusion layers (GDL) can be arranged on both sides of the membrane-electrode assembly on the sides of the electrodes facing away from the membrane. As a rule, the fuel cell is formed by a multiplicity of stacked MEAs whose electrical powers add up. Between the individual membrane electrode assemblies bipolar plates (also called flow field plates) are usually arranged, which ensure a supply of the individual cells with the operating media, ie the reactants, and usually also serve the cooling. In addition, the bipolar plates provide an electrically conductive contact to the membrane-electrode assemblies.

During operation of the fuel cell, the fuel, in particular hydrogen H ₂ or a hydrogen-containing gas mixture, is supplied to the anode via an anode-side open flow field of the bipolar plate, where an electrochemical oxidation of H ₂ to H ⁺ takes place with emission of electrons. Via the electrolyte or the membrane, which separates the reaction spaces gas-tight from each other and electrically isolated, takes place (water-bound or anhydrous) transport of protons H ⁺ from the anode compartment in the cathode compartment. The electrons provided at the anode are supplied to the cathode via an electrical line. The cathode is supplied via a cathode-side open flow field of the bipolar plate oxygen or an oxygen-containing gas mixture (for example, air), so that a reduction of O ₂ to O ² taking place taking the electrons. At the same time, the oxygen anions in the cathode compartment react with the protons transported via the membrane to form water.

In order to supply a fuel cell stack with its operating media, that is, the reactants and remove excess reactants and product water, this has, on the one hand, an anode supply and, on the other hand, a cathode supply. The anode supply includes an anode supply path for supplying an anode operating gas into the anode chambers of the stack and an anode exhaust gas path for discharging an anode exhaust gas from the anode chambers. Similarly, the cathode supply includes a cathode supply path for supplying a cathode operating gas into the cathode compartments and a cathode exhaust path, which is typically formed as a cathode exhaust system, for discharging a cathode exhaust gas from the cathode compartments of the fuel cell stack.

In the operation of the fuel cell, heat is generated by the fuel cell reaction, which is why the fuel cell stack is integrated into a cooling circuit, which dissipates the waste heat via a coolant. The cooling of the coolant takes place for example by an air cooler, in the case of a vehicle usually a vehicle radiator. Furthermore, the waste heat is partially removed by the fuel cell exhaust gases.

Another problem is the product water generated in the fuel cell reaction, which is largely removed via the cathode exhaust gas. The cathode exhaust gas thus has a very high Wasserdampfanateil at relatively low temperatures. In cold (ambient) conditions, avoid freezing the exhaust system.

The US 6986959 B2 describes operation of a fuel cell system at cold temperatures. The fuel cell system includes an enthalpy recovery device (ERD) in a cathode exhaust line to transfer heat and moisture from a process exhaust stream to a reactant inlet stream. Furthermore, a bypass line is provided, which branches off from the cathode exhaust gas line upstream of the ERD and opens again downstream of the ERD into the cathode exhaust gas line. In the branch of the bypass line, a valve is provided. By means of the bypass, an exhaust gas flow through the ERD is controlled in dependence on predetermined temperature ranges. As examples of temperatures, an ambient temperature, a cathode exit temperature, or an ERD temperature are listed. When the ambient temperature is low enough for the water to freeze, the ERD is bypassed until more favorable temperature conditions prevail.

Moreover, a problem is that only relatively low exhaust back pressures (especially at full load) are allowed.

The invention is based on the object, a fuel cell system, a vehicle with the fuel cell system and a method for operating the fuel cell system and / or the Define vehicle which solves at least one of the problems of the prior art.

This object is achieved by a fuel cell system, a vehicle and a method for operating the fuel cell system and / or the vehicle having the features of the independent claims.

• – einen Haupt-Kathodenabgaspfad mit einem Haupt-Ausgang zum Abführen des Kathodenabgasstroms in die Umgebung, wobei sich der Haupt-Kathodenabgaspfad zwischen dem Kathodenausgang der Brennstoffzelle und dem Haupt-Ausgang erstreckt,
• – einen Neben-Kathodenabgaspfad mit einem Neben-Ausgang zum Abführen des Kathodenabgasstroms in die Umgebung, wobei sich der Neben-Kathodenabgaspfad zwischen einer Abzweigung vom Haupt-Kathodenabgaspfad und dem Neben-Ausgang erstreckt, und
• – wenigstens ein Durchflusssteuermittel zum Öffnen und Schließen des Neben-Kathodenabgaspfads und/oder des Haupt-Kathodenabgaspfads stromab der Abzweigung.

The fuel cell system according to the invention comprises a fuel cell with a cathode output and a cathode exhaust system for discharging a cathode exhaust stream from the fuel cell, the cathode exhaust system comprising:

• A main cathode exhaust path having a main exit for discharging the cathode exhaust stream into the environment, the main cathode exhaust path extending between the cathode exit of the fuel cell and the main exit,
• A sub-cathode exhaust path having a sub-exit for discharging the cathode exhaust stream into the environment, the sub-cathode exhaust path extending between a branch from the main cathode exhaust path and the sub-exit, and
• At least one flow control means for opening and closing the sub-cathode exhaust path and / or the main cathode exhaust path downstream of the branch.

By the invention, for example, in a cold start at temperatures below 0 ° C, at an already frozen main cathode exhaust path downstream of the branch or at a full load of the fuel cell, the flow control means may conduct the cathode exhaust gas partially or completely into the sub-cathode exhaust path. The cathode exhaust stream then exits the secondary cathode exhaust path through the minor exit. For this purpose, the secondary cathode exhaust gas path is at least partially or completely opened by the flow control means, so released.

The fuel cell is in particular a fuel cell stack, which comprises a plurality of individual cells. This adds up the performance of the individual cells. The cathode output designates a cathode-side output from the fuel cell, through which a cathode exhaust gas stream flows out of the fuel cell during operation of the fuel cell.

The main cathode exhaust path extends downstream from the cathode exit in the cathode exhaust system and terminates in the main exit, which is an exit from the cathode exhaust system into the environment (ie ambient air outside the fuel cell system).

The sub-cathode exhaust path extends from the branch downstream in the cathode exhaust system and ends in the sub-output, which is another output (in addition to the main output) from the cathode exhaust system into the environment.

The main cathode exhaust path and the sub-cathode exhaust path are typically cathode exhaust gas lines or cathode exhaust gas channels, which may each have components for influencing the cathode exhaust gas.

In particular, the fuel cell system includes a cathode supply path for supplying a cathode working gas into the fuel cell. Preferably, in the cathode supply path, an air conveyor, in particular a compressor, arranged to allow an air flow of ambient air from the environment of the fuel cell in the fuel cell. The compressor is in particular part of a turbocompressor, by means of which a use of cathode exhaust enthalpy is made possible.

The at least one flow control means preferably comprises an exhaust flap (a cathode exhaust flap), which is arranged in particular in the secondary cathode exhaust gas path. The flow control means may also be referred to as a means for "directing" the cathode exhaust stream. Thus, by opening the flow control means, the sub-cathode exhaust path for the cathode exhaust stream is opened, ie, released, so that it can leave the fuel cell system through the sub-output. The flow control means is preferably arranged to shut off the sub-cathode exhaust gas path in a (normally energized) normal state (the main cathode exhaust gas path being released). Further preferably, the fuel cell system comprises a further flow control means, in particular a further exhaust flap, which is seconded in the main cathode exhaust gas downstream of the branch. Thus, the main cathode exhaust path for the cathode exhaust gas flow can be shut off so that water contained in the cathode exhaust gas path can not freeze in the main cathode exhaust gas path. However, it is also conceivable that the main cathode exhaust path downstream of the branch is already frozen and impermeable to the cathode exhaust stream, so that the further exhaust valve in the main cathode exhaust path is not needed.

Further preferably, the at least one flow control means, a three-way valve, which is arranged within the branch. In other words, the branch can be formed by the three-way valve. Thus, by means of the three-way valve, a flow through the main Cathode exhaust path and the secondary cathode exhaust path can be controlled.

Preferably, it is contemplated that a length of the sub-cathode exhaust path is shorter than a length of the main cathode exhaust path between the branch and the main exit. Thus, the risk of water condensing in the sub-cathode exhaust path and subsequently freezing is less than in the longer main cathode exhaust path remaining downstream of the branch.

It is preferably provided that a length of the secondary cathode exhaust gas path is shorter than 500 mm, preferably shorter than 300 mm, in particular shorter than 200 mm. The shorter the sub-cathode exhaust path, the less the risk of icing in the sub-cathode exhaust path.

It is particularly preferred that the length of the secondary cathode exhaust gas path is at most 30%, in particular at most 20%, preferably at most 15% of a length of the main cathode exhaust gas path between the branch and the main outlet (ie downstream of the branch). The lower the percentage, the greater the benefit from the sub-cathode exhaust path.

It is preferably provided that the fuel cell system has a moisture transmitter and / or a turbine of a turbocompressor in the main cathode exhaust gas path, the branch being arranged downstream of the moisture transmitter and / or downstream of the turbine. This ensures correct functioning of the moisture transmitter and the turbocompressor even when the secondary cathode exhaust gas path is open.

According to a preferred embodiment of the invention it is provided that between the turbine and the secondary output, in particular between the turbine and the branch, a muffler is arranged, which is adapted to filter out noise of the turbo-compressor from the cathode exhaust gas stream. As a result, the muffler is designed to filter out relatively high frequencies of the air conveying means, in particular of a turbocompressor, from the cathode exhaust gas stream.

It is preferably provided that the secondary cathode exhaust gas path leads downwards. This ensures that condensed product water can flow down from the cathode exhaust gas. The spatial orientation of a fuel cell system can be easily determined, for example, by means of preferably provided water separators.

Furthermore, a vehicle is provided with a fuel cell system according to the invention. The fuel cell system is used in particular for providing an electrical energy for driving the vehicle.

The vehicle according to the invention, like the fuel cell, is distinguished by more reliable operation even at temperatures below 0 ° C. or full load.

It is preferably provided that the fuel cell is arranged in a front end of the vehicle. The front vehicle refers to a part of the vehicle which is arranged in front of a passenger compartment of the vehicle in the direction of travel. Further preferably, it is provided that the secondary output is arranged in the front of the vehicle. In particular, the sub-cathode exhaust path is arranged in the front carriage. As a result, a length of the cathode exhaust system between the cathode output of the fuel cell and the secondary output can be kept as low as possible.

The main exit is preferably located in a rear area of the vehicle. This provides the main cathode exhaust path with sufficient length for necessary components to affect the cathode exhaust stream.

Preferably, the secondary output is disposed in an underbody of the vehicle, whereby condensed product water can flow away.

• – wenigstens eines Umgebungsparameters und/oder
• – wenigstens eines Betriebsparameters des Brennstoffzellensystems

erfolgt. According to another aspect of the invention, there is provided a method of operating a fuel cell system and / or vehicle according to the invention, the method comprising a step of directing the cathode exhaust stream into the main cathode exhaust path downstream of the branch and / or the sub-cathode exhaust path by means of the Flow control means, wherein the routing in dependence

• At least one environmental parameter and / or
• - At least one operating parameter of the fuel cell system

he follows.

By means of the method according to the invention, depending on the ambient and / or operating parameters, the cathode exhaust gas stream can be directed (steered) into the main cathode exhaust gas path downstream of the branch and / or into the subordinate cathode exhaust gas path, thus preventing the cathode exhaust system from freezing or at one already frozen main cathode exhaust gas downstream of the branch of this can be bypassed. Furthermore, it can be ensured that an exhaust back pressure in the cathode exhaust system not become unacceptably high. The at least one environmental parameter (that is, a parameter of the environment of the fuel cell system) and / or the at least one operating parameter (ie, a parameter of operation of the fuel cell system) are particularly useful for predicting freezing of the main cathode exhaust path downstream of the branch or an already-frozen main cathode exhaust path Detect downstream of the branch to respond to expected or existing constrictions of the main cathode exhaust gas path can. The conduction of the cathode exhaust stream is accomplished by opening and closing the sub-cathode exhaust path and / or the main cathode exhaust path downstream of the branch by means of the flow control means.

It is preferably provided that the at least one environmental parameter and / or the at least one operating parameter comprises at least one temperature. Thus, depending on the at least one temperature, the cathode exhaust stream is directed into the sub-cathode exhaust path. In particular, the at least one operating parameter includes a temperature of the cathode exhaust stream or a temperature of the main cathode exhaust path. Specifically, the temperature of the main cathode exhaust path is a temperature of the main cathode exhaust path downstream of the branch, thereby enabling a more accurate determination of a risk of freezing. The at least one environmental parameter comprises in particular an ambient temperature. These are temperatures by means of which it is possible to conclude that the cathode waste gas system is being frozen. The temperature may further preferably also be a differential temperature formed of, for example, the temperature of the cathode exhaust gas stream and the temperature of the main cathode exhaust gas path. Thus it can be determined whether a freezing of product water is to be expected.

It is preferably provided that the conduction of the cathode exhaust gas flow is such that the cathode exhaust gas flow is at least partially, in particular completely, conducted into the secondary cathode exhaust gas path when the at least one temperature falls below a predetermined limit value of the temperature. Thus, for example, when falling below a temperature or only when falling below all temperatures of the cathode exhaust gas flow through the secondary cathode exhaust gas path are conducted into the environment. This ensures that the cathode exhaust stream is directed through the sub-cathode exhaust path as soon as there is a risk of freezing by low temperatures.

It is preferably provided that the at least one operating parameter comprises at least one pressure in the fuel cell system. Thus, depending on the at least one pressure in the fuel cell system, the cathode exhaust gas flow is directed into the sub-cathode exhaust gas path. The pressure in the fuel cell system is in particular a pressure in the cathode exhaust gas system, preferably a pressure in the main cathode exhaust gas path. Thereby, an iced main cathode exhaust path or too high pressure at a full load operation of the fuel cell can be detected. The pressure may also be a differential pressure of pressures, for example, upstream and downstream of a component, of the main cathode exhaust path. Thus it can also be determined which component has been received.

Further preferably, it is provided that the conduction of the cathode exhaust gas flow is such that the cathode exhaust gas flow is at least partially, in particular completely, conducted into the sub-cathode exhaust gas path when the at least one pressure exceeds a predetermined limit value of the pressure. This is a simple design to control the flow control means at too high pressures (or differential pressures).

According to a preferred embodiment of the invention, it is provided that the at least one operating parameter comprises a load of the fuel cell. The load represents another operating parameter in order to conclude that the exhaust gas backpressure in the cathode exhaust system is too high.

Preferably, the conduction of the cathode exhaust stream is such that the cathode exhaust stream is at least partially, in particular, completely directed into the sub-cathode exhaust path when the load of the fuel cell exceeds a predetermined threshold value of the load. Thus, for example, it may be provided that at a load which is in particular greater than 90% of a full load, preferably at full load, the flow control means releases the secondary cathode exhaust path. Thus, an exhaust back pressure and thus losses are reduced by the cathode exhaust system.

Further preferred embodiments of the invention will become apparent from the remaining, mentioned in the dependent claims characteristics.

The various embodiments of the invention mentioned in this application are, unless otherwise stated in the individual case, advantageously combinable with each other.

The invention will be explained below in embodiments with reference to the accompanying drawings. Show it:

1 a block diagram of a fuel cell system according to an embodiment of the invention;

2 a vehicle with the fuel cell system according to an embodiment of the invention;

3 a schematic flow of a method for operating the fuel cell system or the vehicle according to an embodiment of the invention; and

4 a flow control means of the fuel cell system according to an embodiment of the invention.

1 shows a total of 100 designated fuel cell system according to a preferred embodiment of the invention.

The fuel cell system 100 comprises as a core component a fuel cell 10 comprising a plurality of stacked individual cells 11 each of which has an anode space 12 and a cathode compartment 13 which comprises of an ion-conductive membrane 14 (a polymer electrolyte membrane) are separated from each other (see detail). Thus, the fuel cell 10 also referred to as a fuel cell stack. The anode and cathode compartment 12 . 13 each comprises a catalytic electrode, the anode or the cathode (not shown), which catalyzes the respective partial reaction of the fuel cell reaction. Between two such membrane-electrode assemblies, a bipolar plate is further arranged in each case (also not shown), which supplies the operating media into the anode and cathode chambers 12 . 13 serves and also the electrical connection between the individual cells 11 manufactures.

To the fuel cell stack 10 to supply with the operating media, the fuel cell system 100 on the one hand, an anode supply 20 and on the other hand, a cathode supply 30 on.

The anode supply 20 includes an anode supply path 21 which feeds an anode operating gas (the fuel), for example hydrogen, into the anode spaces 12 of the fuel cell stack 10 serves. For this purpose, the anode supply path connects 21 a fuel storage 23 with an anode inlet of the fuel cell 10 , The anode supply 20 further includes an anode exhaust path 22 containing an anode exhaust gas from the anode compartments 12 via an anode outlet of the fuel cell stack 10 dissipates. In addition, the anode supply can 20 a fuel recirculation line (not shown), which the anode exhaust path 22 with the anode supply path 21 combines. Recirculation of fuel is common in order to recycle and utilize the fuel, which is mostly used in excess of stoichiometry.

The cathode supply 30 includes a cathode supply path 31 which is the cathode spaces 13 of the fuel cell stack 10 supplying an oxygen-containing cathode operating gas, in particular air. The cathode supply 30 further includes a cathode exhaust system 32 , which is a cathode exhaust gas from the cathode compartments 12 of the fuel cell stack 10 dissipates.

The cathode exhaust system 32 includes a main cathode exhaust path 34 , which has a main exit 35 and over this into the environment 36 empties. Overall, the main cathode exhaust path extends 34 between a cathode output 38 the fuel cell 10 and the main exit 35 ,

Furthermore, the cathode exhaust system includes 32 a sub-cathode exhaust path 40 which has a side exit 41 and over this into the environment 36 empties. The sub-cathode exhaust path 40 branches in a turnoff 42 the cathode exhaust system 32 from the main cathode exhaust path 34 and extends to the side exit 41 ,

In addition, the cathode exhaust system has 32 at least one flow control means for opening and closing the sub-cathode exhaust path 40 and / or the main cathode exhaust path 34 downstream of the junction 42 on. In the example shown, the cathode exhaust system has a flow control means 44 in the sub-cathode exhaust path 40 and a flow control means 45 in the main cathode exhaust path 34 downstream of the junction 42 on. The flow control means 44 . 45 may be exhaust flaps. The flow control means 44 can have a "normal closed position", that is, the exhaust valve is kept closed without active operation, for example by a spring. By means of the flow control means 45 Thus, the cathode exhaust gas stream may be conducted by accumulating the cathode exhaust stream in that part of the cathode exhaust system 32 downstream of the junction 42 take place, in which the cathode exhaust gas flow is not or only partially flow.

An exhaust valve of a flow control means 44 as in the secondary cathode exhaust path 40 can be arranged (an exhaust gas bypass valve), is in 4 shown. The exhaust flap has a housing 46 which forms part of the sub-cathode exhaust path 40 forms. Furthermore, it has a flap element 48 on which to close the housing 46 serves. To operate the flap 48 The exhaust flap further comprises an actuator 49 ,

In 1 It can be seen that a length of the sub-cathode exhaust gas path 40 significantly shorter than a length of the main cathode exhaust path 34 downstream of the junction 42 is. A length of the sub-cathode exhaust path 40 is, for example, only 200 mm while a length of the main cathode exhaust path 34 downstream of the junction 42 2000 mm can be.

For conveying and compressing the cathode operating gas is in the cathode supply path 31 a compressor 50 arranged, which is in particular an electric turbocharger (ETC), by an electric motor 51 is operated. Optionally, as shown here, the compressor 50 through a turbine 52 can be driven, which in the main cathode exhaust path 34 upstream of the junction 42 is arranged. Here are the compressor 50 and the turbine 52 connected by a common wave. Thus, the compressor 50 also as a turbo compressor 53 be designated.

Furthermore, the cathode supply 30 a humidifier 54 which causes humidification of the cathode operating gas. The humidified cathode operating gas and the humid cathode exhaust gas are conducted on both sides via a water-vapor permeable membrane, so that the water vapor from the moist cathode exhaust gas diffuses across the membrane into the dry cathode operating gas and moisten it. The humidifier 54 is on the one hand in the cathode supply path 31 between compressors 50 and the cathode input and, on the other hand, the main cathode exhaust path 34 between the cathode output 38 and the turbine 52 arranged.

Furthermore, the cathode exhaust system 32 a silencer 56 (a pre-silencer 56 ), to filter out high frequencies of the turbo-compressor 53 exhibit. The silencer 56 is upstream of the secondary cathode exhaust path 40 arranged flow control means 44 arranged. In the example shown, the silencer is upstream of the branch 42 arranged so that it causes a sound attenuation of the cathode exhaust gas flow, regardless of which of the outputs 35 . 41 the cathode exhaust stream is the cathode exhaust system 32 leaves.

In addition, the cathode exhaust system 32 another silencer 58 (a rear silencer 58 ) exhibit. The silencer 58 is between the turnoff 42 and the main exit 35 in the main cathode exhaust path 34 arranged.

Various other details of the anode and cathode supply 20 . 30 are in the simplified 1 not shown for reasons of clarity. Thus, a wastegate line may be present, which is the cathode supply line 31 with the cathode exhaust system 32 , in particular with the main cathode exhaust path 34 between the humidifier 54 , and the turbine 52 combines. Further, in the anode exhaust path 22 and / or the cathode exhaust system 32 a water separator may be installed to condense and drain the product water resulting from the fuel cell reaction. In addition, the fuel cell system 100 a cooling system for cooling the fuel cell 10 include. Finally, the anode exhaust gas line 26 in the cathode exhaust system 32 lead, so that the anode exhaust gas and the cathode exhaust gas through the cathode exhaust system 32 be dissipated.

2 shows a vehicle 200 According to a preferred embodiment of the invention, which is a fuel cell system 100 according to a preferred embodiment of the invention (for example, the 1 known fuel cell system 100 ). The vehicle 200 in particular, is an electric vehicle having an electric traction motor (not shown) passing through the fuel cell system 100 is supplied with electrical energy.

The fuel cell 10 whose position is in 2 framed schematically, can be in a front end 202 of the vehicle 200 be arranged, whose extension in 2 symbolically drawn. Also in the front 202 may be the minor output 41 in an area of a subfloor 204 of the vehicle 200 be arranged. The main exit 35 is typically in a tail area 206 in the area of the subfloor 204 arranged. The sub-cathode exhaust path 40 can, as in 1 is indicated, straight down from the main cathode exhaust path 34 branch. By the above-mentioned "normally closed position" of the flow control means 44 in the sub-cathode exhaust path 40 , is the sub-cathode exhaust path 40 usually not with the outside air in the area of the front end 202 connected. Because of the main output 35 in the rear area 206 is arranged, stands the cathode exhaust system 32 enough space for a rear silencer 58 available: At the same time is arranged by the arranged in the front side auxiliary output a short length of the cathode exhaust system 32 between the fuel cell 10 and the side exit 41 allows.

The following is based on the 3 a procedure 300 According to a preferred embodiment of the invention for operating the fuel cell system 100 and the vehicle 200 described.

At a starting point 301 of the procedure 300 , for example, becomes the fuel cell system 100 started. This can be a cold start.

First, a query 302 with respect to a temperature T _AGA (an operating parameter of the fuel cell system 100 ) of the cathode exhaust system 32 , This may be a temperature of the main cathode exhaust path 34 act. If this is less than a predetermined limit T _{AGA_GW} for the temperature T _{AGA of} the cathode _{exhaust system} 32 is, can be expected with a condensation and freezing of product water in the cathode exhaust gas. The limit T _{AGA_GW} is for example 0 ° C. _Falling below the threshold T _{AGA_GW} are in one step 304 the flow control means 44 . 45 controlled so that the cathode exhaust gas flow from the flow control means 44 . 45 in the sub-cathode exhaust path 40 and this via the secondary output 44 leaves. Thus, a passage of the main cathode exhaust path becomes downstream of the branch 42 prevented.

If the limit value T _{AGA_GW has} not been undershot, a query is made 306 checks whether an ambient temperature T _U (an environmental _parameter ) _{falls below} a predetermined limit value T _{U_GW} for the ambient temperature T _U. The ambient temperature T _U is a temperature of the vehicle 200 surrounding outside air. The predetermined limit value T _{U_GW} may be, for example, -10 ° C. If this is the case, in turn can be calculated with an icing, for example, away from a temperature sampling point for measuring the temperature T _AGA the cathode exhaust system. In this case again in step 304 the sub-cathode exhaust path 40 Approved.

Should the step 304 not already done so is in a query 308 Check if a pressure p _AGA in the main cathode exhaust path 34 greater than a limit p _{AGA_GW} for the pressure p _AGA . The limit value p _{AGA_GW} is for example 80 millibars relative (ie above the pressure of the ambient _air ). If this is the case, it can be concluded that downstream of the diversion 41 there is icing. Also in this case, the step becomes 304 performed so that the cathode exhaust gas flow to the cathode exhaust system 32 through the side exit 41 leaves. Characterized in that the cathode exhaust gas stream from the branch 42 straight down, condensed product water is allowed out of the cathode exhaust system 32 abzurinnen.

Even though the limit value p _{AGA has} not been exceeded, the last query takes place 310 _{_GW} checks whether a load α of the fuel cell 10 or the fuel cell system 100 is greater than a threshold α _GW for the load α. The limit value α _GW can be, for example, 90% of a full load. If the limit value α _{GW is} exceeded, this can lead to undesirably high pressures within the fuel cell 10 to lead. Even if the limit value α _GW is exceeded, the step 304 carried out and the cathode exhaust gas via the secondary Cathode exhaust path 40 in the nearby areas 36 dismiss.

If none of the queries are the step 304 has effected, the secondary cathode exhaust path remains 40 according to a step 312 closed. Subsequently, the process can 300 with a repetition of the query 302 to be continued.

By discharging the cathode exhaust stream through the by-exit 40 Overall, a icing of the cathode exhaust system 32 prevented or at least reduced. This is due to the relatively short length of the sub-cathode exhaust path 40 compared with the length of the main cathode exhaust path 34 downstream of the junction 42 further optimized. Through the secondary cathode exhaust path 40 can even at a downstream of the junction 42 already frozen main cathode exhaust path 34 the fuel cell 10 continue to operate. Thanks to the upstream of the junction 42 arranged pre-silencer 56 can cause a noise emission of the compressor 50 be reduced to an acceptable level. In addition, at full load, the fuel cell 10 reduces a cathode side exhaust back pressure.

LIST OF REFERENCE NUMBERS

10

fuel cell

11

single cell

12

anode chamber

13

cathode space

14

membrane

20

anode supply

21

Anode supply path

22

Anode exhaust gas path

23

fuel storage

30

cathode supply

31

Cathode supply path

32

Cathode exhaust system

34

Main cathode exhaust path

35

Principal output

38

cathode output

36

Surroundings

40

Besides cathode exhaust path

41

In addition to output

42

diversion

44

Flow control means

45

another flow control means

46

casing

48

flap element

49

actuator

50

compressor

51

electric motor

52

turbine

53

Turbo compressor

54

humidifier

56

Silencer / front silencer

58

Silencer / rear silencer

100

The fuel cell system

200

vehicle

202

front end

204

underbody

206

rear area

300

method

301

starting point

302

Query regarding a temperature of the cathode exhaust system

304

Release secondary cathode exhaust path

306

Inquiry regarding an ambient temperature

308

Inquiry regarding a pressure of the cathode exhaust system

310

Query regarding a load of the fuel cell

312

Secondary cathode path remains closed

T _U

ambient temperature

T _{U_GW}

 Limit of ambient temperature

T _AGA

Temperature of the cathode exhaust system

T _{AGA_GW}

Limit value of the temperature of the cathode exhaust system

p _AGA

Pressure in the cathode exhaust system

p _{AGA_GW}

 Threshold of the pressure in the cathode exhaust system

α

 load

α _GW

Limit value of the load

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 6986959 B2 [0007]

Claims (10)

Fuel cell system ( 100 ) comprising a fuel cell ( 10 ) with a cathode output ( 38 ) and a cathode exhaust system ( 32 ) for discharging a cathode exhaust gas stream from the fuel cell ( 10 ), wherein the cathode exhaust system ( 32 ) comprises: a main cathode exhaust path ( 34 ) with a main output ( 35 ) for discharging the cathode exhaust gas stream into the environment ( 36 ), wherein the main cathode exhaust gas path ( 34 ) between the cathode output ( 38 ) of the fuel cell ( 10 ) and the main output ( 35 ), - a secondary cathode exhaust path ( 40 ) with a secondary output ( 41 ) for discharging the cathode exhaust gas stream into the environment ( 36 ), wherein the secondary cathode exhaust gas path ( 40 ) between a branch ( 42 ) from the main cathode exhaust path ( 34 ) and the secondary output ( 41 ), and - at least one flow control means ( 44 . 45 ) for opening and closing the sub-cathode exhaust gas path ( 40 ) and / or the main cathode exhaust path ( 34 ) downstream of the branch ( 42 ). Fuel cell system ( 100 ) according to claim 1, characterized in that a length of the secondary cathode exhaust gas path ( 40 ) shorter than a length of the main cathode exhaust gas path ( 34 ) between the branch ( 42 ) and the main output ( 35 ). Fuel cell system ( 100 ) according to one of the preceding claims, characterized in that the fuel cell system ( 100 ) in the main cathode exhaust path ( 34 ) a moisture transmitter ( 54 ) and / or a turbine ( 52 ) of a turbocompressor ( 53 ), wherein the branch ( 42 ) downstream of the moisture transfer ( 54 ) and / or downstream of the turbine ( 52 ) is arranged. Fuel cell system ( 100 ) according to one of the preceding claims, characterized in that the secondary cathode exhaust gas path ( 40 ) leads down. Vehicle ( 200 ), with a fuel cell system ( 100 ) according to any one of the preceding claims. Vehicle ( 200 ) According to claim 5, characterized in that the fuel cell ( 10 ) and the secondary output ( 41 ) in a front end ( 202 ) of the vehicle ( 200 ) are arranged. Procedure ( 300 ) for operating a fuel cell system ( 100 ) according to one of claims 1 to 4 and / or a vehicle ( 200 ) according to one of claims 5 or 6, wherein the method ( 300 ) a step of directing the cathode exhaust gas stream into the main cathode exhaust gas path ( 34 ) downstream of the branch and / or the secondary cathode exhaust path ( 40 ) by means of the flow control means ( 44 ), wherein the routing in dependence - at least one environmental parameter (T _U ) and / or - at least one operating parameter (T _AGA , p _AGA , α) of the fuel cell system ( 100 ) he follows. Procedure ( 300 ) according to claim 7, characterized in that - the at least one environmental parameter (T _U ) and / or the at least one operating parameter (T _AGA , p _AGA , α) comprises at least one temperature (T _U , T _AGA ) and in particular - the conducting the cathode exhaust stream is such that the cathode exhaust stream at least partially, in particular completely, in the secondary cathode exhaust gas path ( 40 ) is passed when the at least one temperature (T _U , T _AGA ) _{falls below} a predetermined limit value (T _{U_GW} , T _{AGA_GW} ) of the temperature (T _U , T _AGA ). Procedure ( 300 ) according to one of claims 7 or 8, characterized in that - the at least one operating parameter (T _AGA , p _AGA , α) at least one pressure (p _AGA ) in the fuel cell system ( 10 ), and in particular - the conduction of the cathode exhaust gas flow is such that the cathode exhaust gas flow at least partially, in particular completely, into the secondary cathode exhaust gas path ( 40 ) when the at least one pressure (p _AGA ) _exceeds a predetermined limit (p _{AGA_GW} ) of the pressure (p _AGA ). Method according to one of claims 7 to 9, characterized in that - the at least one operating parameter (T _AGA , p _AGA , α) a load (α) of the fuel cell ( 10 ), and in particular - the cathode exhaust gas stream is conducted in such a way that the cathode exhaust gas flow is at least partially, in particular completely, into the secondary cathode exhaust gas path ( 40 ) is conducted when the load (α) of the fuel cell ( 10 ) exceeds a predetermined limit (α _GW ) of the load (α).

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