DE102015011275A1 - Fuel cell system and vehicle with a fuel cell system - Google Patents

Abstract

The invention relates to a fuel cell system (10), in particular for a vehicle, having a fuel cell stack (12) which comprises an anode (18) and a cathode (28), wherein in an exhaust air strand (52) the cathode (28) has a shut-off device (12). 54) is arranged. The shut-off device (54) can be acted upon by a coolant of a coolant circuit (16) by means of which heat can be dissipated from the fuel cell stack (12) during operation of the fuel cell system (10). Furthermore, the invention relates to a vehicle with such a fuel cell system (10).

Description

The invention relates to a fuel cell system with a fuel cell stack, which comprises an anode and a cathode. In a Abluftstrang the cathode a shut-off device is arranged. Furthermore, the invention relates to a vehicle with a fuel cell system.

The DE 10 2014 215 828 A1 describes a drive control method for a fuel cell system in which in an exhaust air strand of a cathode of a fuel cell stack, an air shut-off valve is arranged. In certain situations, the air shut-off valve may be closed while supplying hydrogen to the cathode side of the fuel cell stack. This prevents the hydrogen from escaping into the atmosphere. The fuel cell system of DE 10 2014 215 828 A1 can be used in a vehicle which has a plug-in functionality, in which therefore the fuel cell system is frequently stopped while driving and then restarted again. The air shut-off valve is closed at a stop of the fuel cell system.

Furthermore, the describes DE 102 14 727 B4 a fuel cell system in which control valves are arranged in a gas passage for discharging fuel from an anode of the fuel cell. A control valve heater for heating the control valves is supplied with heat from an oxidizing gas supplied to a cathode of the fuel cell. In this way, the control valves can thaw.

Fuel cell vehicles and fuel cell systems are very complex and therefore expensive. Furthermore, the currently available on the market fuel cell vehicles, although good, but still not very high performance, which means that fuel cell vehicles on the market currently can not achieve very high prices.

Another challenge with fuel cell systems is achieving a long service life. A known error mechanism or a known trigger for a comparatively rapid degradation are the so-called air-air starts. In this case, air is present when starting the fuel cell system both on the anode side of the fuel cell stack and on the cathode side. A high number of air-air starts correspondingly leads to a high degradation.

The problem of air-to-air starts is exacerbated when driving modes are provided in a vehicle having a fuel cell stack in which the fuel cell system is not used while driving or is not turned on. In such a driving mode is therefore driven purely battery electric. Due to the driving speed then occur high wind speeds in the region of an intake and an outlet of the exhaust air line of the fuel cell system.

These air currents flush the cathode with air or oxygen from the ambient air. As a result, there is a reaction between the hydrogen occluded on the anode and the oxygen supplied by the above-mentioned air currents. This leads to a significant reduction in the so-called "Hydrogen Protection Time" (ie the time until air-to-air conditions prevail in the fuel cell stack).

This ultimately means that in fuel cell systems that are configured in a plug-in or range-extender application (or possibly even operated only with a lengthy start-stop strategy), a significantly reduced "Hydrogen Protection Time" is to be expected , This leads to an increased degradation rate. To prevent this, appropriate measures must be taken.

Are known as measures (such as the California Fuel Cell Partnership, CFCP) valves, which are arranged in the air path in front of the fuel cell stack or fuel cell stack and closed when the fuel cell system is turned off. The disadvantage of this is that fresh air or fresh oxygen can reach the side of the cathode of the fuel cell stack via the exhaust air system or the exhaust air line due to corresponding air flows (which are caused by the wind). This shortens the "Hydrogen Protection Time".

The arrangement of a valve in the exhaust path or exhaust air line is critical because product air is contained in the exhaust air, which can then freeze at cold ambient temperatures, the valve or the valve. In order to prevent this, electrically heatable flaps or shut-off valves are required, which are correspondingly expensive and also require electrical energy (usually at 12 V level). In cold ambient temperatures, the performance of a 12 V battery is also limited. Under these conditions, therefore, no reliable heating of the flap is guaranteed, or the heating leads to an unfavorable load of the 12 V electrical system.

The effect of freezing increases accordingly, if much product water in liquid Form is obtained, as is the case with fuel cell systems of the prior art.

Object of the present invention is therefore to provide a fuel cell system of the type mentioned and a vehicle with such a fuel cell system, in which a functionality of the shut-off device is achieved in a particularly simple manner.

This object is achieved by a fuel cell system having the features of patent claim 1 and by a vehicle having the features of patent claim 8. Advantageous embodiments with expedient developments of the invention are specified in the dependent claims.

In the fuel cell system according to the invention, which is provided in particular for a vehicle, the shut-off device can be acted upon by a coolant of a coolant circuit. By means of the coolant flowing through the coolant circuit, heat can be removed from the fuel cell stack during operation of the fuel cell system. In other words, the shut-off device is thermally coupled to the coolant circuit of the fuel cell stack. The shut-off device can therefore be thawed by means of the heat released by the coolant.

This can be dispensed with a direct electrical heating of the shut-off device. Thus, in particular as a shut-off device, a comparatively favorable butterfly valve can be used, which need not be electrically heated. This is reflected in corresponding cost advantages. By supplying heat to the shut-off device via the coolant, the functionality of the shut-off device can be achieved in a particularly simple manner. In particular, it is possible to prevent oxygen from the ambient air from entering the cathode of the fuel cell stack via the exhaust air line, where it reacts with the hydrogen trapped on the anode side. In this way it is possible, in particular, to achieve a particularly long Hydrogen Protection Time.

Due to the comparatively long Hydrogen Protection Time can be achieved in particular an improved durability and thus longer life of the fuel cell stack and the fuel cell system.

Because the shut-off device, which is also referred to as cathode blocking valve (CBV) or cathode blocking valve, is thermally coupled to the coolant circuit of the fuel cell system in the exhaust path of the fuel cell stack, the shut-off device is also thawed by the heat introduced into the coolant.

This is particularly advantageous when the fuel cell system is used in a plug-in vehicle, in which either the electric energy supplied by the fuel cell system or the electric energy of a traction battery can be used to move the vehicle. Here, the traction battery can be charged by connecting to a charging station. In fact, in such vehicles, it may happen that only the traction battery is used to move the vehicle and the fuel cell system remains switched off. In such situations, the shut-off of the exhaust air strand of the cathode by means of the shut-off device is then particularly useful to prevent the entry of atmospheric oxygen into the cathode of the fuel cell stack.

The same applies to a fuel cell system, which is used in a vehicle to extend the range used, in which the fuel cell system thus acts as a range extender (Range Extender). It can also be provided that the vehicle is basically moved using the electrical energy provided by the battery. To cover other routes, however, electrical energy is provided by means of the fuel cell system, which is used for moving the vehicle.

In fact, in such vehicles, it can happen that is driven at high speeds for a long time without the fuel cell system is turned on. In particular, in these situations, by means of the shut-off device, it is possible to prevent the entry of ambient air into the cathode of the fuel cell stack due to the travel wind.

Preferably, an electrical heating device is arranged in the coolant circuit, by means of which the fuel cell stack can be heated to a predetermined temperature. It can therefore be ensured by means of the electric heater that the fuel cell system or the fuel cell stack is preheated so far that the fuel cell system does not have to complete a freeze start more.

In particular, the fuel cell stack is therefore heated to the predetermined temperature by means of the electrical heating device before the fuel cell system is started up. Preferably, the fuel cell system is only started when the fuel cell stack and the exhaust-side shut-off device on a corresponding Temperature, for example, at a temperature of +5 degrees Celsius.

In the coolant circuit may further be arranged a heat exchanger, by means of which heat can be introduced into a passenger compartment of the vehicle. In this case, provision can be made, in particular, for the coolant supplied to the heat exchanger to be heated by means of the electric heating device. Thus, the electric heater or the electric heater not only ensures that the shut-off device is thawed by means of the coolant. Rather, the passenger compartment or interior is heated.

So not only the startup of the fuel cell system at particularly low temperatures, ie a freeze start or cold start can be avoided. Rather, the electric heater has an additional purpose, namely the thawing or defrosting of the shut-off device in the exhaust air strand of the cathode.

It is also advantageous if a charge air cooler is arranged in the exhaust air strand of the cathode, by means of which waste heat of the charge air can be transferred to the exhaust air. Here, the charge air cooler is preferably arranged upstream of the shut-off device in the exhaust air line. This leads to a particularly rapid heating or thawing of the shut-off device, since the intercooler can deliver a corresponding amount of waste heat to the exhaust air.

In this embodiment, in which the (exhaust-side) shut-off device is arranged downstream or behind the secondary side of the charge air cooler, the exhaust air and the entrained product water are heated. This is due to the fact that the heat of compression that arises on the primary side of the intercooler is transferred to the secondary side. However, if the exhaust air and the entrained product water heated and evaporated, so is the liquid water content is relatively low, which meets the shut-off device. This leads to a reduced formation of ice in the area of the shut-off device at low ambient temperatures or outside temperatures.

In this way, a particularly easy and quick opening of the shut-off after thawing is possible. This is a distinct advantage over prior art fuel cell systems which do not have the ability to heat the exhaust air and the product water entrained therein to contain a low level of liquid water in the exhaust air.

Finally, it has proven to be advantageous if a further shut-off device is arranged in a supply air strand of the cathode. Thus, it is possible to shut off the cathode from both sides and so particularly safe to prevent entry of ambient air into the cathode.

The vehicle according to the invention has a fuel cell system according to the invention. The advantages and preferred embodiments described for the fuel cell system according to the invention also apply to the vehicle according to the invention.

The features and feature combinations mentioned above in the description as well as the features and feature combinations mentioned below in the description of the figures and / or shown alone in the figures can be used not only in the respectively specified combination but also in other combinations or in isolation, without the scope of To leave invention. Thus, embodiments are also included and disclosed by the invention, which are not explicitly shown or explained in the figures, however, emerge and can be produced by separated combinations of features from the embodiments explained.

Further advantages, features and details of the invention will become apparent from the claims, the following description of preferred embodiments and from the drawings. Showing:

1 schematically a particularly simple constructed fuel cell system in which is dispensed with a humidifier for humidifying the supply air, and in which the exhaust gas of a cathode is heated by heat from the air flowing through a charge air supply air, wherein downstream of the charge air cooler in the exhaust air line a shut-off is arranged;

2 the fuel cell system according to 1 wherein additionally a coolant circuit for cooling the fuel cell stack of the fuel cell system is shown; and

3 the fuel cell system according to 2 , Wherein the coolant circuit has a bypass line, by means of which coolant, bypassing the shut-off device can be supplied to at least one further component of the coolant circuit.

In 1 is a fuel cell system 10 shown with a particularly simple structure. It is preferably provided, the fuel cell system 10 operate so that it has essentially the task of supplying energy for a battery electric vehicle and thus to increase the range of the vehicle. In principle this is The fuel cell system 10 Also suitable for a plug-in application. For the fuel cell vehicle, therefore, instead of a (not shown) battery with a large energy content (for example, about 30 kWh), a battery 74 be provided with a smaller energy content (cf. 2 ) typically used in a plug-in hybrid vehicle or plug-in fuel cell vehicle.

Furthermore, the fuel cell system 10 in particular for stationary applications and / or as an emergency power supply system in interaction with the battery 74 suitable.

The design of the fuel cell system 10 is hereby preferred such that the fuel cell system 10 has a low dynamics. For example, it may be provided that it takes about 3 seconds to 5 seconds to complete the performance of a fuel cell stack 12 of the fuel cell system 10 from an idle power (idle) to increase full load. Also values for the dynamics of the fuel cell system 10 Up to 30 seconds are possible, depending on how powerful the battery is 74 is, which is preferably designed as a high voltage battery.

The operating temperature of the fuel cell system 10 is preferably about 50 degrees Celsius to about 60 degrees Celsius. A so-called "HOT operation" at temperatures in the range of 80 degrees Celsius to 90 degrees Celsius (or beyond) is therefore not provided, in particular, to cause no material stress and to avoid a high Befeuchtungsaufwand, which is associated with a large humidifier.

Furthermore, the fuel cell system 10 preferably not started from negative or very low temperatures out. Rather, it is provided by an appropriate management that the fuel cell system 10 only then provides electrical energy to propel the vehicle when the fuel cell stack 12 via an electric heater 14 (see 2 ) or such a heating element has been heated to a predetermined temperature.

The electric heater 14 which is in for cooling the fuel cell stack 12 provided coolant circuit 16 is arranged (see 2 ), preferably simultaneously takes over the heating or additional heating of an interior or passenger compartment of the vehicle. Due to the relatively large capacity of the battery 74 In the present case, it is practically always out of the battery 74 drove off.

Furthermore, this electrical heating of the fuel cell system 10 due to the particularly small and simple structure (and compared to fuel cell systems designed for a high degree of dynamics) and consequently a lower heat capacity, particularly fast and with little expenditure of energy. In cold outside temperatures, a user of the fuel cell vehicle desires to heat the passenger compartment as quickly as possible. This heating takes place here via the electric heater 14 which is in a branch of the coolant circuit 16 of the fuel cell system 10 , At the same time, however, this also makes the fuel cell system 10 heated. Has the fuel cell stack 12 of the fuel cell system 10 reaches the predetermined temperature (of, for example, +5 degrees Celsius), in the present case, the fuel cell system 10 started.

Characterized in that the propulsion of the fuel cell vehicle in this phase of heating exclusively from the battery 74 done, the fuel cell system can 10 be prepared very moderately on the starting process, for example, by a multiple pre-filling an anode 18 of the fuel cell stack 12 , Once the fuel cell system 10 started, can be a power of the heater 14 reduced or the heater 14 turned off. Then that is the fuel cell system 10 with the resulting waste heat the interior or passenger compartment of the vehicle heat. This reduces consumption and increases range.

According to 1 An oxidant such as air flows over an air filter (not shown) and an air mass meter 20 towards a compressor 22 , which has an electric motor 24 is driven. The compressor 22 can be designed as a turbo compressor, scroll compressor, screw compressor or the like. In principle, however, a blower is also considered. The compressed and heated by the compression air is then a charge air cooler 26 fed, where the compressed air before entering the fuel cell stack 12 is cooled. Subsequently, the air without previous (additional) humidification of a cathode 28 of the fuel cell stack 12 fed.

After exiting the fuel cell stack 12 is the exhaust air (ie the exhaust gas of the cathode 28 of the fuel cell stack 12 ) and the entrained product water of a secondary side 30 of the intercooler 26 fed. As a result, the on the primary side of the intercooler 26 present compression heat is absorbed, whereby the exhaust air stream or the product water contained in the exhaust air stream is evaporated. As a result, there is no or only a small discharge of liquid product water in the environment of the fuel cell vehicle.

This media management of the air is particularly advantageous because the heat of compression is not in the coolant circuit 16 of the fuel cell system 10 is entered, but can be dissipated via the exhaust air. This reduces the over one in the coolant circuit 16 arranged radiator 32 waste heat to be removed (cf. 2 ). In principle, a silencer can still be used, but this is not shown here.

Fuel in the form of hydrogen is taken from a tank 34 via a (not shown) pressure reduction unit to a metering valve 36 guided. About the metering valve 36 the amount of hydrogen is metered or a jet pump 38 fed. The fresh hydrogen from the tank 34 In this case, it forms a so-called propulsion jet which, via the corresponding suction effect, extracts hydrogen from an outlet 40 the anode 18 back to an entrance 42 the anode 18 sucks and there provides the hydrogen in accordance with desired stoichiometry.

A purge valve 44 (Flushing valve) at the outlet 40 the anode 18 serves to nitrogen and water, which has accumulated in the anode circuit before or in the intercooler 26 to guide and to mix the exhaust air.

The humidification of the fuel cells in the fuel cell stack 12 does not take place as in known from the prior art fuel cell systems via an additional component in the form of a humidifier. Rather, the humidification takes place practically internally, ie within the fuel cell stack 12 , For this purpose, it is provided that the media air and hydrogen are passed in countercurrent.

Furthermore, it is advantageous that the coolant circuit 16 flowing coolant in the same flow direction as the air through the fuel cell stack 12 respectively. The dry and heated air thus occurs in a comparatively cold end region of the fuel cell stack 12 into the cathode 28 one. The dry air then absorbs over the run length of the product due to the electrochemical reaction product water and transports it to an air outlet 46 , The air outlet 46 is located at the comparatively warm end of the fuel cell stack 12 ,

At this end is also the entrance 42 for the hydrogen. Accordingly, there is a membrane at this end 48 which in the respective fuel cell, the anode 18 from the cathode 28 separates, a high moisture gradient. So it's on the side of the cathode 28 a lot of product water is present and on the side of the anode 18 little. This moisture gradient causes water from the cathode 28 to the anode 18 overpasses. It is so from the dry and heated hydrogen, which at the warm end in the fuel cell stack 12 enters, water absorbed. The water is then mixed with the hydrogen along the anode side of the fuel cell stack 12 to the exit 40 the anode 18 or to the side of an air intake 50 transported.

At the air inlet 50 on the air side or side of the cathode 28 Thus, relatively dry conditions prevail, so that again there is a liquid gradient or gradient, but in the opposite direction. At the air inlet 50 (and in to the air intake 50 adjacent areas of the cathode 28 ) it is on the anode side 18 relatively humid and on the side of the cathode 28 relatively dry. Due to the fact that the hydrogen and the entrained water (at least partially in the form of steam) towards the side of the air inlet 50 is transported, the water passes over the membrane 48 on the air side or side of the cathode 28 above. There, in turn, the water is taken up by the dry and warm air passing through the cathode 28 towards the air outlet 46 flows.

By this transport mechanism practically a humidification circuit is shown, so that can be dispensed with an external humidifier. The excess water gets over the cathode 28 discharged, or via the purge valve 44 removed from the anode circuit.

Both the purge gas (purge gas) and further exhaust gas in the form of the exhaust air from the cathode 28 will then be the intercooler 26 fed. There, the exhaust air is heated and the water contained therein at least partially evaporated. As a result, there is no or only a greatly reduced discharge of liquid water into the environment.

The exhaust air is via an exhaust air line 52 initially the secondary side 30 of the intercooler 26 fed. In the exhaust air line 52 is also a shut-off device 54 arranged, which is preferably designed as a simple butterfly valve. The of the intercooler 26 Waste heat transferred to the exhaust air is thus present for heating the shut-off device 54 used. In addition, the shut-off device 54 However, with the coolant of the coolant circuit 16 be charged, in particular with respect to 2 will be explained.

1 is further removable that in a Zuluftstrang 56 of the fuel cell system 10 another shut-off device 58 is arranged, which upstream of the air inlet 50 is arranged. Also this shut-off device 58 is preferably designed as a butterfly valve and makes it possible an entry of ambient air into the cathode 28 of the fuel cell stack 12 to prevent.

This is particularly advantageous when the fuel cell system 10 Although out of service, but the vehicle is driving, which is the fuel cell system 10 having. Because then prevent the shut-off devices 54 . 58 that over the airstream ambient air into the cathode 28 arrives.

In the presence of the heater 14 which is in the coolant circuit 16 is arranged, for preheating the fuel cell stack 12 before the fuel cell system 10 put into operation or started up. This is at the same time in the exhaust air line 52 arranged shut-off device 54 thawed. The shut-off device 54 namely, with the coolant of the coolant circuit 16 via a supply line 60 which are from the fuel cell stack 12 to the shut-off device 54 leads.

In the coolant circuit 16 is also a heat exchanger 62 arranged, by means of which heat can be introduced into the passenger compartment of the vehicle. Furthermore, a coolant pump provides 64 for conveying the coolant through the coolant circuit 16 , About one in the coolant circuit 16 arranged valve 66 , which can be designed in particular as a thermostatic valve, it can be ensured that the coolant to the radiator 32 is supplied when the fuel cell stack 12 to be cooled. At the radiator 32 it is preferably the main radiator, which is usually arranged in the region of the vehicle front of the fuel cell vehicle. About the valve 66 can be ensured that the coolant bypassing the heater 14 to the fuel cell stack 12 is encouraged.

Furthermore, in the coolant circuit 16 another heat exchanger 68 arranged over which heat from or to a battery cooling circuit 70 can be transferred. In the battery cooling circuit 70 is another coolant pump 72 arranged, which the coolant of the battery cooling circuit 70 towards the heat exchanger 68 promotes. From the heat exchanger 68 off can be the coolant of the battery 74 be supplied.

From the battery 74 from the coolant can optionally be a battery cooler 76 or a chiller 78 be supplied. This is upstream of the battery cooler 76 and the chiller 78 another valve 80 intended. By means of the chiller 78 Heat may be transmitted to a (not shown) refrigerant circuit of the vehicle when at high ambient temperatures, a particularly high cooling demand of the battery 74 given is.

By driving one upstream of the heat exchanger 68 arranged valve 82 Furthermore, it can be ensured that that of the coolant pump 72 subsidized coolant further high-voltage components 84 is supplied, for example, a charger or on-board loader. Downstream of the high-voltage component 84 and the battery 74 is in the battery cooling circuit 70 another valve 86 arranged.

The heat exchanger 68 is in principle usable as a heat pump, since due to the in the battery cooling circuit 70 arranged chillers 78 even at very high outside temperature the battery 74 and the fuel cell stack 12 can be cooled.

This in 3 shown fuel cell system 10 is essentially the same as in 2 shown fuel cell system 10 , Here, however, the exhaust-side shut-off device 54 not in a main branch of the coolant circuit 16 arranged but in a sub-branch 86 , Accordingly, the coolant circuit 16 a bypass line 88 on, by means of which the coolant, bypassing the shut-off device 54 the heat exchanger 68 can be supplied.

LIST OF REFERENCE NUMBERS

10

The fuel cell system

12

fuel cell stack

14

stoker

16

Coolant circuit

18

anode

20

Air flow sensor

22

compressor

24

engine

26

Intercooler

28

cathode

30

secondary side

32

cooler

34

tank

36

metering valve

38

jet pump

40

output

42

entry

44

purge valve

46

air outlet

48

membrane

50

air inlet

52

exhaust train

54

shut-off

56

Zuluftstrang

58

shut-off

60

supply

62

Heat exchanger

64

Coolant pump

66

Valve

68

Heat exchanger

70

Battery cooling circuit

72

Coolant pump

74

battery

76

battery cooler

78

Chiller

80

Valve

82

Valve

84

High-voltage component

86

subbranch

88

bypass line

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

• DE 102014215828 A1 [0002]
• DE 10214727 B4 [0003]

Claims (8)

Fuel cell system, in particular for a vehicle, with a fuel cell stack ( 12 ), which is an anode ( 18 ) and a cathode ( 28 ), wherein in an exhaust air line ( 52 ) the cathode ( 28 ) a shut-off device ( 54 ), characterized in that the shut-off device ( 54 ) with a coolant of a coolant circuit ( 16 ) is acted upon, by means of which in the operation of the fuel cell system ( 10 ) Heat from the fuel cell stack ( 12 ) is dissipatable. Fuel cell system according to claim 1, characterized in that in the coolant circuit ( 16 ) an electric heater ( 14 ) is arranged, by means of which the fuel cell stack ( 12 ), in particular before a startup of the fuel cell system ( 10 ), is heatable to a predetermined temperature. Fuel cell system according to claim 1 or 2, characterized in that in the coolant circuit ( 16 ) a heat exchanger ( 62 ) is arranged, by means of which heat in a passenger compartment of the vehicle can be introduced. Fuel cell system according to one of claims 1 to 3, characterized in that in the exhaust air strand ( 52 ) the cathode ( 28 ) a charge air cooler ( 26 ) is arranged, by means of which waste heat of the charge air is transferable to the exhaust air. Fuel cell system according to one of claims 1 to 4, characterized in that the coolant circuit ( 16 ) a bypass ( 88 ), by means of which coolant, bypassing the shut-off device ( 54 ) at least one further component of the coolant circuit ( 16 ) can be fed. Fuel cell system according to one of claims 1 to 5, characterized in that in a Zuluftstrang ( 56 ) the cathode ( 28 ) a further shut-off device ( 58 ) is arranged. Fuel cell system according to one of claims 1 to 6, characterized in that the shut-off device ( 54 . 58 ) is designed as a butterfly valve. Vehicle with a fuel cell system ( 10 ) according to one of claims 1 to 7.

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