Fuel cell system for a powertrain of a vehicle

Abstract

The invention relates to a fuel cell system (3) for a drive train (2) of a vehicle (1), comprising - a plurality of fuel cells (5) combined to form a fuel cell stack (4); - an anode supply (6) with an anode supply line (7) for supplying the fuel cell stack (4) with hydrogen gas and an anode exhaust gas line (8) for discharging anode exhaust gas; - a cathode supply (9) with a cathode supply line (10) for supplying the fuel cell stack (4) with oxygen-containing air and a cathode exhaust gas line (11) for discharging cathode exhaust gas; - a hydrogen burner (12) designed to reduce excess hydrogen gas; and - a heat exchanger (13) designed to transfer heat from the hydrogen burner (12). Furthermore, the invention relates to a drive train (2) for a vehicle (1) and to a vehicle (1) having such a drive train (2).

Description

[0001] The invention relates to a fuel cell system for a vehicle. Furthermore, the invention relates to a drive train for a vehicle, comprising an electric drive motor, an electrical energy storage device, and such a fuel cell system. Furthermore, the invention relates to a vehicle, in particular a motor vehicle, comprising such a drive train.

[0002] Fuel cell systems with liquid water management are known. The liquid management can include a passive hydrogen recirculation unit or an active hydrogen recirculation unit. Hydrogen recirculation units serve to control and optimize the hydrogen flow within the fuel cell.

[0003] A passive hydrogen recirculation unit utilizes natural physical properties, such as temperature or pressure differences within the fuel cell, to promote hydrogen flow. Such a unit does not require an external power source, such as a pump or fan. For example, it can create natural convection through temperature differences between the inlet and outlet of the fuel cell, which improves hydrogen flow. Passive recirculation units are often simpler and more cost-effective than active systems. The passive hydrogen recirculation unit can only achieve gas flow through a fuel cell stack if, on the one hand, there is gas consumption within the fuel cell stack, also called the "stack," and / or if the recirculation circuit is deactivated and the hydrogen can flow directly into the exhaust gas.

[0004] In contrast, an active hydrogen recirculation unit uses an external energy source, such as an electric pump or fan, to control the hydrogen flow within the fuel cell. These units require an additional energy source and complex control mechanisms to precisely regulate the hydrogen flow. Active recirculation units often offer greater flexibility and control over the hydrogen flow compared to passive systems and can be more efficient under various operating conditions. Thus, an active hydrogen recirculation unit can also enable gas flow through the stack within the recirculation loop. In combination with a water separator, an active recirculation unit can also remove liquid water from the stack.

[0005] The flammability of hydrogen as a combustible gas is an important consideration in the design of a fuel cell system. Currently, it is not possible to completely seal fuel cell systems against leaks. Some amounts of hydrogen leakage in the fuel cell system are unavoidable. These leaks can occur at various points in the system and pose a risk of fire and / or explosion.

[0006] The object of the present invention is to provide a fuel cell system with an improved temperature control system, particularly for a start-up phase and / or a shutdown process, which is also more resistant to hydrogen leaks. This object is achieved by the subject matter of patent claim 1. Preferred embodiments are set forth in the dependent claims.

[0007] A fuel cell system according to the invention for a drive train of a vehicle comprises, according to a first aspect of the invention, a plurality of fuel cells combined to form a fuel cell stack, an anode supply with an anode supply line for supplying the fuel cell stack with hydrogen gas and an anode exhaust line for discharging anode exhaust gas, a cathode supply with a cathode supply line for supplying the fuel cell stack with oxygen-containing air and a cathode exhaust line for discharging cathode exhaust gas, a hydrogen burner which is designed to reduce excess hydrogen gas, and a heat exchanger which is designed to transfer heat from the hydrogen burner.

[0008] With such a fuel cell system, the primary goal is to reduce the amount or content of hydrogen in the cathode exhaust. In other words, an increased amount of hydrogen in the cathode exhaust is avoided. The hydrogen burner, especially when replacing an electric heater, has the advantage of not placing a load on the electrical system and of reducing the release of hydrogen into the environment, which in turn reduces the risk of explosion. The only remaining byproduct is liquid water.

[0009] A fuel cell generates electrical energy from a chemical reaction of hydrogen with oxygen, with water remaining as a by-product. The hydrogen gas is provided by a hydrogen supply device, in particular a hydrogen tank or reservoir, and fed to the hydrogen electrodes (i.e., to the negative electrodes) of the fuel cell stack via the anode supply, whose anode supply line is designed as a hydrogen supply line. The hydrogen supply line is thus configured to feed the hydrogen gas as the anode operating medium into the anode chambers of the fuel cell. The anode exhaust line or anode exhaust path discharges the anode exhaust gas, comprising excess hydrogen gas, from the anode chambers.

[0010] The cathode supply line of the cathode supply is provided for supplying oxygen-containing air to the oxygen electrodes (i.e., the positive electrodes) of the fuel cell assembly. The cathode supply line is therefore an air line for supplying oxygen-containing air as the cathode operating medium into the cathode chambers of the fuel cell. The cathode exhaust line or cathode exhaust path discharges the cathode exhaust, including excess air, from the cathode chambers. The cathode exhaust line and the anode exhaust line can be combined to form a common exhaust line.

[0011] By means of the hydrogen burner, hydrogen and oxygen are catalytically converted to water without the need for combustion with an open flame. For this purpose, the system preferably comprises an air supply line for supplying oxygen-containing air to the hydrogen burner. The hydrogen burner enables a safe and efficient conversion of hydrogen with oxygen, with heat being generated as a by-product. Alternatively, it is possible to burn hydrogen in a flame in a combustion chamber of the hydrogen burner, with corresponding heat being generated here too. With the help of the hydrogen burner, the heat required to achieve the required operating temperature of one or more components of the fuel cell device can be generated within a short time and transferred to the corresponding component, e.g. the fuel cell or the fuel cell stack. In this way, the start-up time and / orThe duration of the start-up phase of the fuel cell system can be significantly shortened. In particular, preheating can occur even before the fuel cell or fuel cell stack starts up. The hydrogen burner therefore functions as a temperature control unit, designed to control the temperature, particularly for heating, of the fuel cell system during the start-up phase. The burner's function is advantageous at low outside temperatures.

[0012] The hydrogen burner generates a hydrogen concentration gradient between the anode side and the cathode side of the respective fuel cell, particularly during commissioning of the fuel cell system, i.e. in a “startup” phase or when the fuel cell system is switched off, the afterflow of which carries away liquid water.

[0013] The hydrogen burner can be used to break down excess hydrogen gas, which may be present, for example, during the aforementioned start-up processes or a start-up phase or during shutdown processes of the fuel cell system, or which may result from leaks. In other words, if there is more hydrogen in the system than is currently needed, the excess hydrogen gas can be passed through the hydrogen burner and burned afterwards. In particular, a hydrogen concentration gradient can be adjusted between the anode side and the cathode side of the respective fuel cell. Accordingly, "breaking down excess hydrogen gas" is understood to mean the combustion of hydrogen, which generates heat and leaves water as a by-product. The heat is absorbed as generated energy by the heat exchanger and passed on to a medium, which can be used to heat the fuel cell system.The hydrogen burner can therefore be used advantageously in certain operating situations, for example, during a cold start of a vehicle. Further advantages include a lower risk of damage to the fuel cells, lower hydrogen consumption during commissioning, faster commissioning, and a reduction in the flammable gas mixture, especially in the exhaust gas.

[0014] Preferably, the system further comprises at least one hydrogen sensor for detecting a hydrogen concentration within a gas mixture conveyed in the exhaust gas discharge line, in particular in the cathode exhaust gas line. If a predetermined limit value is exceeded, the burner can be activated, and if the predetermined limit value is undershot, the burner can be deactivated.

[0015] Preferably, the hydrogen burner is fluidically connected to the interior of a housing accommodating the fuel cell stack, to a purge valve, to an overpressure valve of the fuel cell system, to the anode supply line and / or the anode exhaust line.

[0016] The purge valve is used to control the flow of gases or liquids into or out of the system. It can be controlled automatically or manually, depending on the operating conditions and the design of the fuel cell system. During a purge process, the purge valve can be opened to remove excess gases or contaminants from the fuel cell system. It can then be closed again when the purge process is complete. During the purge process, nitrogen can be used as an inert gas to purge the fuel cell system of unwanted gases or contaminants. Furthermore, nitrogen helps minimize the risk of explosive mixtures or uncontrolled reactions. The purge valve can be controlled either by the fuel cell system itself or by external control units, depending on the system's requirements and level of automation.When the purge valve is open, the hydrogen burner can be activated to allow excess hydrogen gas to react or burn off.

[0017] The fuel cell system's pressure relief valve is designed to protect the fuel cell system from overload or dangerous pressure buildup by venting excess hydrogen gas from the system when the pressure exceeds a predefined limit. When the pressure relief valve is open, the hydrogen burner can be activated to allow excess hydrogen gas to react or burn off.

[0018] Residual hydrogen gas present in the anode exhaust line can be post-combusted in the hydrogen burner, particularly to reduce the concentration in the anode exhaust line and / or to make the generated energy available for further use. In certain operating situations, particularly during start-up phases, it may also be necessary to combust hydrogen gas from the anode supply line.

[0019] In one embodiment, the cathode supply line is fluidly connected to the cathode exhaust line via a bypass. This makes it possible, in particular, to reduce the hydrogen concentration in the exhaust gas discharge line.

[0020] Preferably, the anode supply has a recirculation path that fluidically connects the anode exhaust line to the anode supply line. Recirculation of the anode operating medium, i.e., the hydrogen gas, is designed to return and utilize the anode operating medium of the fuel cell, which is usually used in excess of stoichiometric amounts. A compressor can also be provided on or in the fuel recirculation line or in the recirculation path.

[0021] The fuel cell system according to the invention can be used, for example, as a vehicle drive with a direct hydrogen system or with upstream reforming, or as a so-called auxiliary power unit (APU). Thus, the fuel cell system according to the invention can be advantageously used in a vehicle drive train.

[0022] In this sense, a drive train for a vehicle according to a second aspect of the invention comprises an electric drive motor, an electrical energy storage device, and a fuel cell system according to the first aspect of the invention. The fuel cell system is designed to recharge the electrical energy storage device. Furthermore, a cooling system is provided which regulates the temperature of the fuel cell system. The cooling system can also be provided for temperature control, in particular cooling, of the drive motor, the energy storage device, and / or power electronics. Alternatively, separate cooling systems can be provided. The drive train can further comprise a hydrogen supply device, in particular designed as a hydrogen tank or hydrogen storage device, which is fluidically connected to the anode supply.

[0023] According to a third aspect of the invention, a vehicle, in particular a motor vehicle, comprises at least one drive train according to the second aspect of the invention. The vehicle typically has multiple axles, wherein one, several, or all axles may have a respective drive train to rotationally drive at least one wheel of the respective axle.

[0024] Further measures improving the invention are described in more detail below together with the description of a preferred embodiment of the invention with reference to the figures. Fig. 1 a highly simplified representation of a vehicle according to the invention with a drive train according to the invention, comprising a fuel cell system according to the invention according to a preferred embodiment, and Fig. 2 a highly simplified representation of the fuel cell system according to the invention according to Fig. 1.

[0025] Fig. 1 shows a vehicle 1, in particular a motor vehicle, comprising two axles 21, 22. A drive train 2 is arranged on the first axle 21, which here is a rear axle of the vehicle 1, and is designed to rotationally drive a wheel 23 of the first axle 21. In the present case, the vehicle 1 is a purely electrically driven vehicle. If an internal combustion engine is used in addition to driving at least one wheel 23, the vehicle 1 can also be a hybrid vehicle.

[0026] The drive train 2 comprises an electrical energy storage unit 20, an electric drive motor 19, a transmission 24, and a differential 25. The energy storage unit 20 provides electrical energy for the drive motor 19, which generates mechanical drive power, which is converted by the transmission 24 and transmitted to the differential 25. The differential 25 distributes the power between two output shafts 26, 27, which are at least indirectly connected to an associated wheel 23. Furthermore, a hydrogen tank 28, an air supply 29, and a fuel cell system 3 are provided. The hydrogen tank 28 provides hydrogen gas, which is supplied to a plurality of fuel cells 5 of a fuel cell stack 4 of the fuel cell system 3 via an anode supply 6.The air supply 29 is, for example, a pump or the like, which supplies oxygen-containing air to the fuel cells 5 of the fuel cell stack 4 via a cathode supply 9. The fuel cells 5 generate electrical energy from a chemical reaction of hydrogen with oxygen, leaving water as a byproduct. The fuel cell system 3 is provided for charging, in particular recharging, the energy storage device 20 and / or for directly supplying power to the drive motor 19.

[0027] After Fig. 2, the fuel cell system 3 is shown in more detail. The fuel cell system 3 serves to convert the energy generated by the electrochemical reaction of hydrogen as fuel and oxygen as emulsifying agent into electrical power. The fuel cell system 3 is constructed from a plurality of fuel cells 5 that form the fuel cell stack 4. Each fuel cell 5 is constructed from a pair of electrodes, an anode and a cathode, as well as a membrane arranged between the electrodes. The fuel cell system 3 is used to supply power to an electrical device, here the energy storage device 20 according to Fig. 1. Hydrogen gas and oxygen-containing air are supplied to the fuel cell system 3, and they induce electrochemical reactions at the electrodes, producing water as a byproduct.

[0028] The fuel cells 5, arranged in a housing 14 and combined to form the fuel cell stack 4, are fluidically connected to the anode supply 6, which supplies hydrogen gas via an anode supply line 7 into the anode compartments (not shown here) of the respective fuel cell 5. An anode exhaust line 8 removes anode exhaust gas from the anode compartments. Furthermore, the fuel cells 5 are fluidically connected to the cathode supply 9, which supplies oxygen-containing air via a cathode supply line 10 into the cathode compartments (not shown here) of the respective fuel cell 5. A cathode exhaust line 11 removes cathode exhaust gas from the cathode compartments.

[0029] A hydrogen burner 12 with a heat exchanger 13 is provided, wherein the hydrogen burner 12 is effectively arranged on the cathode exhaust line 11, i.e., can be fed with the gas mixture from the cathode exhaust line 11 in certain operating situations to reduce or react with excess hydrogen gas and generate heat as a byproduct. For this purpose, the hydrogen burner 12 is connected to an air supply line 17 for supplying oxygen-containing air to the hydrogen burner 12.

[0030] The heat exchanger 13 is designed to transfer the heat of the hydrogen burner 12, which is generated by the chemical reaction of hydrogen and air, to a medium, for example, a coolant. Accordingly, the fuel cell system 3 further comprises a cooling system (not shown here) designed to control the temperature, in particular to heat, of the fuel cell stack 4 and / or other parts of the fuel cell system 3 using the heat generated in the hydrogen burner 12. This allows for faster heating of the entire system to a desired operating temperature, particularly during cold starts or at low outside temperatures.

[0031] The hydrogen burner 12 is fluidically connected via a first line 31 to the interior of a housing 14 accommodating the fuel cell stack 4, via a second line 32 to a purge valve 15, and via a third line 33 to an overpressure valve 16 of the fuel cell system 3. The hydrogen burner 12 can also be fluidically connected to the anode supply line 7 and / or the anode exhaust line 8, although this is not shown here. The hydrogen burner 12 can thus absorb hydrogen from leaks and recombust it.

[0032] The anode supply 6 has a recirculation path 18 which fluidically connects the anode exhaust gas line 8 to the anode supply line 7 in order to feed unused hydrogen gas conducted in the anode exhaust gas line 8 back to the anode supply line 7.

[0033] The cathode supply line 10 is fluidically connected to the cathode exhaust line 11 via a bypass 30 in order to reduce a hydrogen concentration within the cathode exhaust line 11 by supplying oxygen-containing air in certain operating situations.

[0034] During a start-up phase of the fuel cell system 3, the recirculation path 18 is deactivated, allowing hydrogen gas to flow through the fuel cell stack 4, even via a passive recirculation unit. The heat generated in the hydrogen burner 12 is fed into the cooling circuit of the fuel cell system 3 and accelerates the heating of the fuel cell stack 4, particularly at temperatures below 0 °C.

[0035] At certain operating points, for example during the start-up phase or during shutdown of the fuel cell system 3, the hydrogen burner 12 is supplied with hydrogen gas from the hydrogen circuit. The oxygen required for the chemical reaction can be supplied either from the aforementioned air supply line 17 or from a housing ventilation system. Hydrogen leaks from the fuel cell stack 4 can be diluted using air from the housing ventilation system. The hydrogen burner 12 can burn off a potentially flammable gas mixture in a controlled manner, producing liquid water as a by-product and reducing the risk of explosion. Other areas potentially at risk from hydrogen leaks, such as the cathode exhaust line 11 and / or the pressure relief valve 16, can be specifically supplied to the hydrogen burner 12. List of reference symbols 1 vehicle 2 Drivetrain 3 Fuel cell system 4 fuel cell stacks 5 Fuel cell 6 Anode supply 7 Anode supply line 8 Anode exhaust line 9 Cathode supply 10 Cathode supply line 11 Cathode exhaust line 12 hydrogen burners 13 heat exchangers 14 housings 15 Purge valve 16 Pressure relief valve 17 Air supply line 18 Recirculation path 19 Drive engine 20 energy storage units 21 first axis 22 second axis 23 wheels 24 gearboxes 25 Differential 26 first output shaft 27 second output shaft 28 hydrogen tank 29 Air supply 30 Bypass 31 first line 32 second line 33 third line

Claims

[1] Fuel cell system (3) for a drive train (2) of a vehicle (1), comprising - a plurality of fuel cells (5) combined to form a fuel cell stack (4); - an anode supply (6) with an anode supply line (7) for supplying the fuel cell stack (4) with hydrogen gas and an anode exhaust gas line (8) for discharging anode exhaust gas; - a cathode supply (9) with a cathode supply line (10) for supplying the fuel cell stack (4) with oxygen-containing air and a cathode exhaust gas line (11) for discharging cathode exhaust gas; - a hydrogen burner (12) designed to reduce excess hydrogen gas; and - a heat exchanger (13) designed to transfer heat from the hydrogen burner (12). [2] Fuel cell system (3) according to claim 1, characterized bythat the hydrogen burner (12) is fluidically connected to the interior of a housing (14) accommodating the fuel cell stack (4). [3] Fuel cell system (3) according to claim 1 or claim 2, characterized by that the hydrogen burner (12) is fluidly connected to a purge valve (15). [4] Fuel cell system (3) according to one of the preceding claims, characterized by that the hydrogen burner (12) is fluidly connected to an overpressure valve (16) of the fuel cell system (3). [5] Fuel cell system (3) according to one of the preceding claims, characterized by that the hydrogen burner (12) is fluidly connected to the anode supply line (7) and / or the anode exhaust gas line (8). [6] Fuel cell system (3) according to one of the preceding claims, characterized by that the cathode supply line (10) is fluidly connected to the cathode exhaust line (11) via a bypass (30). [7] Fuel cell system (3) according to one of the preceding claims, characterized by an air supply line (17) for supplying oxygen-containing air into the hydrogen burner (12). [8] Fuel cell system (3) according to one of the preceding claims, characterized by that the anode supply (6) has a recirculation path (18) which fluidically connects the anode exhaust gas line (8) to the anode supply line (7). [9] Drive train (2) for a vehicle (1), comprising an electric drive machine (19), an electrical energy store (20) and a fuel cell system (3) according to one of the preceding claims. [10] Vehicle (1) comprising at least one drive train (2) according to claim 9.

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