Fuel cell system

Abstract

Fuel cell system (1), comprising: a fuel cell (10); a fuel gas supply channel (35) which is set up to supply a fuel gas to the fuel cell (10); a fuel supply device (35V) which is set up to open and close in order to control the supply of fuel gas to the fuel cell (10) via the fuel gas supply channel (35); a circulation channel (36) which is designed to circulate fuel exhaust gas discharged from the fuel cell (10) to the fuel gas supply channel (35); a circulation pump (38) arranged in the circulation channel (36), which is configured to direct the fuel exhaust gas under pressure to the fuel gas supply channel (35) so that it is circulated there; and a control unit (50) for controlling the operation of the fuel supply device (35V) and / or circulation pump (38), and for determining that freezing water is present downstream of the fuel supply device (35V) when a degree of increase of a pressure determined by a pressure sensor (33P) is equal to or greater than a freezing determination threshold three times in succession, wherein, if it is determined that freezing water is present downstream of the fuel supply device (35V), the control unit (50) relatively increases a ratio of a quantity of fuel gas to be supplied by the circulation pump (38) to a quantity of fuel gas to be supplied by the fuel supply device (35V).

Description

BACKGROUND Technical area

[0001] The present disclosure relates to a fuel cell system.

[0002] Conventional, previously known fuel cell systems comprise fuel cells (a fuel cell stack) that generate electricity via electrochemical reactions of reaction gases between an oxidizing gas such as air and a fuel gas such as hydrogen.

[0003] In such a fuel cell system, water is produced during electricity generation, and if the produced water remains in the fuel cells after the interruption of electricity generation, it can, for example, freeze when the ambient temperature drops and thereby reduce the efficiency of the next electricity generation.

[0004] A fuel gas supply system designed to supply a fuel gas such as hydrogen to the fuel cells comprises, for example, a fuel gas supply (or hydrogen tank) storing a high-pressure fuel gas, a fuel gas supply channel (pipe) designed to supply fuel gas in the fuel gas supply to the fuel cells, a recirculation channel designed to return fuel exhaust gas (or unused fuel gas) discharged from the fuel cells to the fuel gas supply channel, and the like, and the fuel gas supply channel (in particular, a subsection located upstream of a section where the fuel gas supply channel and the recirculation channel merge) is equipped with an injector designed to supply the fuel gas to the fuel cells by adjusting the flow rate and pressure of the fuel gas, and the like.In such a fuel gas supply system of the fuel cell system, water contained in the fuel gas, which is discharged from the fuel cells and then fed to the fuel gas supply channel via the recirculation channel, can freeze in a pipe connecting the injector and the fuel cells (that is, in a section downstream of the injector), for example as a result of a drop in ambient temperature, and thereby cause a blockage (freezing) of the pipe.

[0005] To prevent a reduction in efficiency due to such freezing, a method has been proposed in which a purging or blow-through treatment is carried out by introducing a dry gas to the fuel cells immediately after the interruption of electricity generation in order to pre-carry out water that remains in the fuel cells and that adheres to the pipe and similar elements of the fuel cell system (see, for example, JP 2008 - 218 164 A). State of the art

[0006] However, in the prior art described in JP 2008 - 218 164 A et al., the operation of the fuel cells must be interrupted to carry out the purging treatment, and furthermore, the removal of water (ice) to the outside is difficult to accomplish once it has frozen in a low-temperature environment. Fuel cell systems are known from JP 2008 - 198 440 A and JP 2009 - 170 295 A, comprising: a fuel cell; a fuel gas supply channel configured for supplying fuel gas to the fuel cell; a fuel supply device configured for supplying fuel gas to the fuel cell via the fuel gas supply channel; and a recirculation channel configured for recirculating fuel exhaust gas discharged from the fuel cell to the fuel gas supply channel.a circulating pump arranged in the recirculation channel, configured to direct the fuel exhaust gas under pressure to the fuel gas supply channel so that it is circulated there; and a control unit for controlling the operation of the fuel supply device and / or circulating pump, wherein, if it is suspected that freezing water is present downstream of the fuel supply device, the control unit relatively increases the ratio of a quantity of fuel gas to be supplied by the circulating pump to a quantity of fuel gas to be supplied by the fuel supply device.

[0007] The present disclosure was developed in consideration of the above-mentioned problem and provides a fuel cell system that effectively prevents the clogging of a pipe by freezing water in a fuel gas supply system of the fuel cell system without interrupting the operation of the fuel cells, and is therefore very reliable. SUMMARY

[0008] To solve the aforementioned problem, a fuel cell system with the features of claim 1 is provided according to the present disclosure, comprising: fuel cells, a fuel gas supply channel configured for supplying fuel gas to the fuel cells, a fuel supply device configured for supplying the fuel gas to the fuel cells via the fuel gas supply channel, a recirculation channel configured for recirculating fuel exhaust gas discharged from the fuel cells to the fuel gas supply channel, a recirculation pump arranged in the recirculation channel configured to deliver the fuel exhaust gas under pressure to the fuel gas supply channel so that it is recirculated there, and a control unit for controlling the operation of the fuel supply device and / or the recirculation pump, and for determining that freezing water is present downstream of the fuel supply device.If the degree of increase of a pressure determined by a pressure sensor is equal to or greater than a freezing threshold three times in succession, and if it is determined that freezing water is present downstream of the fuel supply device, the control unit increases the ratio of the amount of fuel gas to be supplied by the circulation pump to the amount of fuel gas to be supplied by the fuel supply device relatively.

[0009] In some embodiments, the pressure sensor is located downstream of the fuel supply device and upstream of a section where the fuel gas supply channel and the recirculation channel merge into the fuel gas supply channel.

[0010] In some embodiments, if it is determined that freezing water is present downstream of the fuel supply device, the control unit increases the amount of fuel gas supplied by the circulating pump, and if it is further determined that there is a blockage due to freezing water downstream of the fuel supply device, the control unit interrupts the operation of the fuel supply device.

[0011] In some embodiments, if it is determined that freezing water is present downstream of the fuel supply device, the control unit increases a setpoint for a coolant temperature of a coolant to be supplied to the fuel cells.

[0012] In some embodiments, the fuel gas supply channel and the recirculation channel are connected via a T-shaped connecting pipe, so that the recirculation channel is perpendicular to the fuel gas supply channel, and the fuel supply device is arranged upstream of a section where the fuel gas supply channel and the recirculation channel merge in the fuel gas supply channel.

[0013] Since the fuel gas supplied by the circulating pump arranged in the circulating channel is usually warmer than the fuel gas supplied by the fuel supply device arranged in the fuel gas supply channel, according to the present disclosure, if it is recognized or suspected that possible freezing of water downstream of the fuel supply device is present, the quantity of fuel gas to be supplied by the circulating pump arranged in the circulating channel is increased relatively compared to the quantity of fuel gas to be supplied by the fuel supply device, so that frozen sections can be effectively warmed, thereby effectively preventing blockage of the pipe by freezing water.

[0014] Furthermore, the fuel gas supply channel and the recirculation channel, which are connected via the T-shaped connecting pipe, can be used to efficiently guide the fuel gas from the recirculation channel (in a larger quantity) to the fuel supply device, which is located upstream of the section where the fuel gas supply channel and the recirculation channel join, thus further effectively preventing the pipe from becoming clogged by freezing water. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a representation of the system design of a fuel cell system according to the present disclosure; Fig. 2 is a cross-sectional view of the main part of a T-shaped connecting pipe, arranged in a section where a Fig. 1. The fuel gas supply channel and the circulation channel shown merge; Fig. 3 is a flowchart that illustrates the control operation of a system in Fig. The control unit shown in section 1 is explained; and Fig. Figure 4 is a time diagram and shows chronologically the pressure of a fuel gas (or a measured value determined by a pressure sensor), a marker (flag) when a connecting pipe is detected freezing (freeze detection marker), the speed of a circulation pump, a setpoint for a coolant temperature, a marker when a connecting pipe is detected becoming blocked (freeze detection marker), and the operating status of the injector. DETAILED DESCRIPTION

[0015] The design of the present disclosure is described in detail below with reference to an exemplary embodiment illustrated in the figures. As an example of the present disclosure, fuel cells or a fuel cell system containing fuel cells, which is to be installed in a fuel cell vehicle, are described, but the scope of the present disclosure is not limited thereto. [System design of a fuel cell system]

[0016] First, the system design of the fuel cell system with fuel cells according to the present disclosure is described with reference to Fig. 1 explained.

[0017] A in Fig. 1 The fuel cell system 1 shown comprises, for example, fuel cells (a fuel cell stack) 10 formed by stacking several fuel cells, each cell being a unit cell, an oxidation gas supply system 20 configured to supply an oxidation gas such as air to the fuel cells 10, a fuel gas supply system 30 configured to supply a fuel gas such as hydrogen to the fuel cells 10, a coolant supply system 40 configured to adjust the temperature of the fuel cells 10 by flowing a coolant such as cooling water, and a control unit (or electronic control unit (ECU)) 50 configured to integrally control the overall system.

[0018] Each of the fuel cells 10, being polymer electrolyte fuel cells, features a membrane electrode assembly (MEA) comprising an electrolyte membrane with ion permeability, an anode-side catalyst layer (anode electrode), and a cathode-side catalyst layer (cathode electrode), with the electrolyte membrane sandwiched between them. The MEA has gas diffusion layers (GDLs) on opposite sides to supply a fuel gas or an oxidizing gas to the MEA and to capture the electricity generated by electrochemical reactions. Such a membrane electrode assembly with GDLs on opposite sides is called a membrane electrode and gas diffusion layer assembly (MEGA), and the MEGA is positioned between two separators. Here, the MEGA constitutes a power generation section of the fuel cell.If no gas diffusion layers are provided, the MEA is the power generation section of the fuel cell.

[0019] The oxidation gas supply system 20 comprises, for example, an oxidation gas supply channel (pipe) 25 for supplying an oxidation gas to the fuel cells 10 (or to their cathode electrodes), an oxidation gas discharge channel (pipe) 29 for removing an oxidant exhaust gas, which is produced after the oxidation gas has been used for an electrochemical reaction in each fuel cell, from the fuel cells 10, and a bypass channel 26 for recirculating the oxidation gas, which is routed through the oxidation gas supply channel 25 to the oxidation gas discharge channel 29, bypassing the fuel cells 10. Each channel of the oxidation gas supply system 20 can, for example, consist of a rubber hose or a metal pipe.

[0020] The oxidation gas supply channel 25 is equipped with an air filter 21, an air compressor (turbo compressor) (hereinafter simply referred to as compressor) 22, an intercooler 23, and the like, arranged in this order starting from the upstream side, and the oxidation gas discharge channel 29 is equipped with a silencer 28 and the like. It should be noted that the oxidation gas supply channel 25 (or its air filter 21) is, for example, equipped with an air pressure sensor and / or a flow meter (not shown).

[0021] The air filter 21 in the oxidation gas supply channel 25 removes dust in the oxidation gas (such as air) drawn in from the atmosphere.

[0022] The compressor 22 compresses the oxidation gas entered via the air filter 21 and supplies the compressed oxidation gas under pressure to the intercooler 23.

[0023] When the oxidation gas supplied and pressurized from the compressor 22 flows through the intercooler 23, the intercooler 23 cools the oxidation gas, for example by heat exchange with a coolant, and directs the cooled oxidation gas to the fuel cells 10 (or their cathode electrodes).

[0024] The oxidation gas supply channel 25 is also equipped with an inlet valve 25V to shut off the flow of oxidation gas between the intercooler 23 and the fuel cells 10. It should be noted that the inlet valve 25V can be a check valve designed to open when the flow of oxidation gas flows from the intercooler 23 towards the fuel cells 10, thus allowing the passage of the oxidation gas, and to close when the flow of oxidation gas flows from the fuel cells 10 towards the intercooler 23, thus blocking the passage of the oxidation gas.

[0025] The bypass channel 26 is connected at one end to the oxidation gas supply channel 25 (or its intercooler 23, or downstream of the intercooler 23) and at the other end to the oxidation gas discharge channel 29. In other words, the bypass channel 26 branches off from the oxidation gas supply channel 25 (or its intercooler 23, or downstream of the intercooler 23) to and is connected to the oxidation gas discharge channel 29. The oxidation gas, which is pressurized by the compressor 22, cooled by the intercooler 23, and then discharged, flows through the bypass channel 26 to the oxidation gas discharge channel 29, bypassing the fuel cells 10. The bypass channel 26 is equipped with a bypass valve 26V to regulate the flow rate of the oxidation gas flowing through the bypass channel 26 by blocking the flow of oxidation gas to the oxidation gas discharge channel 29.

[0026] In the oxidation gas discharge channel 29, the silencer 28 separates the oxidizing agent exhaust gas flowing through the oxidation gas discharge channel 29 into, for example, the gas phase and the liquid phase, which are to be discharged to the outside.

[0027] The oxidation gas discharge channel 29 is equipped with a pressure regulating valve 29V for controlling the back pressure of the oxidation gas supplied to the fuel cells 10. The aforementioned bypass channel 26 is connected to the downstream side of the pressure regulating valve 29V.

[0028] The fuel gas supply system 30 comprises, for example, a fuel gas supply 31 such as a hydrogen tank that stores a high-pressure fuel gas such as hydrogen, a fuel gas supply channel (pipe) 35 for supplying the fuel gas fed from the fuel gas supply 31 to the fuel cells 10 (or to their anode electrodes), a recirculation channel 36 for returning fuel exhaust gas (unused fuel gas) discharged from the fuel cells 10 to the fuel gas supply channel 35, and a fuel gas discharge channel (pipe) 39 that branches off from the recirculation channel 36 to discharge the fuel exhaust gas in the recirculation channel 36 to the outside (to the air). Each channel of the fuel gas supply system 30 can, for example, consist of a rubber hose or a metal pipe.

[0029] The fuel gas supply channel 35 is equipped with a shut-off valve 35V, which is configured to block the fuel gas flowing to the fuel cells 10 by opening and closing the fuel gas supply channel 35, a regulator 34, which is configured to regulate (reduce) the pressure of the fuel gas flowing through the fuel gas supply channel 35, and an injector (or fuel supply device) 33, which is configured to supply the fuel gas to the fuel cells 10 in a pressure-controlled manner, wherein the shut-off valve 35V, the regulator 34 and the injector 33 are positioned in the fuel gas supply channel 35 in this order, starting from the upstream side. When the shut-off valve 35V is open, a high-pressure fuel gas, stored in the fuel gas supply 31, flows out to the fuel gas supply channel 35 and is directed to the fuel cells 10 (or their anode electrodes), its pressure being regulated (reduced) by the regulator 34 and the injector 33.

[0030] Furthermore, a pressure sensor (or a primary-side pressure sensor) 34P and a temperature sensor 34T, configured to detect the pressure and temperature of the fuel gas respectively, are provided in sections of the fuel gas supply channel 35 located upstream of the injector 33 (in particular between the regulator 34 and the injector 33). Additionally, a pressure sensor (or a secondary-side pressure sensor) 33P, configured to detect the pressure of the fuel gas (the pressure at the outlet of the injector 33), and a relief valve 35R, configured to open when the pressure in the fuel gas supply channel 35 reaches a predetermined operating pressure, are provided in sections downstream of the injector 33 and upstream of the section (or connecting section) where the fuel gas supply channel 35 and the recirculation channel 36 merge.

[0031] The circulation channel 36 is equipped with a gas-liquid separator 37, a circulation pump (also referred to as a hydrogen pump) 38 and the like, which are arranged in this order starting from the upstream side (the side of the fuel cells 10).

[0032] The gas-liquid separator 37 separates the fuel gas (such as hydrogen), which contains the generated water, flowing through the circulation channel 36 into gas and liquid and stores them. A fuel gas discharge channel 39 is provided to branch off from the gas-liquid separator 37.

[0033] The circulation pump 38 is designed to direct the fuel exhaust gas, separated into gas and liquid by the gas-liquid separator 37, to the fuel gas supply channel 35 (or to the downstream side of its injector 33) and to circulate it there.

[0034] The fuel gas discharge channel 39 is equipped with a drain valve 39V, which is designed to open and close the fuel gas discharge channel 39 in order to discharge the water produced, separated from the fuel gas by the gas-liquid separator 37, as well as a portion of the fuel exhaust gas discharged from the fuel cells 10.

[0035] The fuel exhaust gas discharged through the opening and closing adjustment of the drain valve 39V of the fuel gas discharge channel 39 is mixed with the oxidizer exhaust gas flowing through the oxidizer gas discharge channel 29 and then released to the outside air via the silencer 28.

[0036] In the fuel cell system 1 with the above-mentioned configuration, electricity is generated by electrochemical reactions between an oxidation gas such as air, which is supplied to the fuel cells 10 (or their cathode electrodes) via the oxidation gas supply system 20, and a fuel gas such as hydrogen, which is supplied to the fuel cells 10 (or their anode electrodes) via the fuel gas supply system 30.

[0037] The coolant supply system 40 includes, for example, a coolant channel (pipe) 45 which connects an inlet and an outlet of a cooling channel arranged in the fuel cells 10 in order to circulate a coolant therein.

[0038] The coolant channel 45 is equipped with a radiator 41, which is configured to cool the coolant discharged from the fuel cells 10, a coolant pump 42, which is configured to draw the coolant in the coolant channel 45 from the outlet side and deliver it to the inlet side, and a coolant temperature sensor 45T, which is configured to detect the coolant temperature in the coolant channel 45.

[0039] The control unit 50 is configured to control the operation of various devices in the system when control information is received from the various devices arranged in a vehicle. For example, the control unit 50 is configured to detect the amount of actuation of an acceleration control device (such as an accelerator pedal) arranged in the vehicle and to calculate the electricity to be drawn from the fuel cells 10 (or the electrical power requirement), so that a fuel gas and an oxidizer gas are supplied to the fuel cells 10 via the fuel gas supply system 30 and oxidizer gas supply system 20, respectively, in quantities corresponding to the amount of electrical power to be generated.

[0040] The control unit 50 comprises a computer system (not shown) that includes a CPU, ROM, RAM, a hard disk drive (HDD), an input / output interface, a display, and so on. Within the computer system, various control operations are implemented by reading and executing different control programs stored in the ROM via the CPU.

[0041] In the present embodiment, as in Fig. As shown in Figure 2, the fuel gas supply channel 35 and the recirculation channel 36 are connected to each other via a T-shaped connecting pipe 35J. In particular, the T-shaped connecting pipe 35J is arranged in the section (or connecting section) where the fuel gas supply channel 35 and the recirculation channel 36 join, such that the recirculation channel 36 is perpendicular to the fuel gas supply channel 35.One end of the T-shaped connecting pipe 35J on the upstream side in the fuel gas supply channel 35 (or an end section on the upstream side of the section where the fuel gas supply channel 35 and the recirculation channel 36 merge) is coupled to the injector 33, one end of the T-shaped connecting pipe 35J on the downstream side in the fuel gas supply channel 35 (or an end section on the downstream side of the section where the fuel gas supply channel 35 and the recirculation channel 36 merge) is coupled to the fuel cells 10, and one end of the T-shaped connecting pipe 35J on the side of the recirculation channel 36 is coupled to the recirculation pump 38. That is, in the present example, the fuel cells 10 and the injector 33, which are provided separately (as separate parts), are coupled together via the T-shaped connecting pipe 35J.In the present example, the injector 33 is also coupled at a right angle to the fuel gas supply channel 35 in the T-shaped connecting pipe 35J at the end of the T-shaped connecting pipe 35J on the upstream side in the fuel gas supply channel 35. That is, in the present example, the fuel gas from the injector 33 and the fuel gas (or the fuel exhaust gas) from the recirculation channel 36 (or the recirculation pump 38 arranged there) are guided to the fuel gas supply channel 35 in the T-shaped connecting pipe 35J at offset positions and from directions perpendicular to the fuel gas supply channel 35.

[0042] Due to the above-mentioned design, a jet (or vapor) of the fuel gas (or fuel exhaust gas) from the recirculation channel 36 impacts the wall surface in the T-shaped connecting pipe 35J, and a portion of the fuel gas flows on the upstream side (on the side of the injector 33) in the fuel gas supply channel 35 to the end of the T-shaped connecting pipe 35J (see the arrows in Fig. 2) Since the fuel gas supplied from injector 33 is a cold gas with a temperature below zero degrees Celsius, the vapor of the fuel gas flowing upstream is cooled and then freezes on the inner wall of the fuel gas supply channel 35 on the side of injector 33. The frozen fuel gas can accumulate during the operation of the fuel cells 10, which can lead to a blockage due to freezing.

[0043] To prevent freezing or blockage of the aforementioned T-shaped connecting pipe 35J (i.e., the pipe connecting the injector 33 in the fuel gas supply system 30 and the fuel cells 10), the control unit 50 in the present embodiment is configured to control the operation of the injector 33, which is arranged in the fuel gas supply channel 35, the circulation pump 38, which is arranged in the circulation channel 35, the radiator 41, which is arranged in the coolant channel 45, and the like, by means of sensing values ​​(of the fuel gas pressure) determined by the pressure sensor (or secondary-side pressure sensor) 33P arranged downstream of the injector 33. [Control of the fuel cell system by the control unit]

[0044] With reference to the flowchart of Fig. 3 and the time diagram of Fig.4 The above-mentioned control (control to prevent freezing or freezing) of the fuel cell system 1 by the control unit 50 is described below.

[0045] The control unit 50 first determines whether the ambient temperature is below zero degrees Celsius (S11).

[0046] If it is determined that the ambient temperature is below zero degrees Celsius (S11: Yes), the control unit 50 determines whether the pressure increase gradient (the degree of pressure increase during a predetermined pressure increase determination period), calculated from the pressure sensor 33P located downstream of the injector 33, is equal to or greater than a predetermined freezing determination threshold (S12). If it is determined that the pressure increase gradient is equal to or greater than the freezing determination threshold (S12: Yes), the control unit 50 also determines whether the pressure increase gradient is equal to or greater than the freezing determination threshold three times consecutively (S13). In this way, the control unit 50 estimates the freezing state while avoiding misdetermination.

[0047] If it is determined that the gradient of the pressure increase is equal to or greater than the freezing determination threshold three times in a row (S13: Yes), a freezing detection marker is set for the connecting pipe (S14).

[0048] Based on the information that the marker has been set in S14, the control unit 50 increases the speed of the circulation pump 38 to increase the flow rate (or gas quantity) (S15) and also controls the radiator 41 and so on to increase the setpoint for the coolant temperature of the coolant flowing through the fuel cells 10 (S16). In this way, the control unit 50 increases the heat content of the fuel gas (or fuel exhaust) in the circulation channel 36 and thus prevents the aforementioned T-shaped connecting pipe 35J from freezing.

[0049] It should be noted that the flow rate (or quantity) of the fuel gas to be supplied by the circulation pump 38 (in relation to the flow rate (or quantity) of the fuel gas to be supplied by the injector 33) is increased here by increasing the speed of the circulation pump 38, but that, for example, the ratio of the quantity of fuel gas to be supplied by the circulation pump 38 to the quantity of fuel gas to be supplied by the injector 33 can be increased by regulating the flow rate (or quantity) of the fuel gas on the side of the injector 33.

[0050] The control unit 50 then determines whether the pressure increase gradient is equal to or greater than a predetermined threshold for determining a freeze-thaw blockage (S17). If it is determined that the pressure increase gradient is equal to or greater than the threshold for determining a freeze-thaw blockage (S17: Yes), the control unit 50 also determines whether the pressure increase gradient is equal to or greater than the threshold for determining a freeze-thaw blockage three times in a row (S18).

[0051] If the gradient of the pressure increase is found to be equal to or greater than the threshold for determining a freeze-induced blockage three times in a row (S18: Yes), a freeze detection marker is set for the connecting pipe (S19).

[0052] Based on the information that the marker in S19 has been set, the control unit 50 interrupts the operation of the injector 33 (S20) in a fail-safe manner. This prevents a reduction in the amount of heat caused by the fuel gas supplied from the injector 33 and thus avoids freezing of the aforementioned T-shaped connecting pipe 35J.

[0053] It should be noted that if it is determined that the ambient temperature is not below zero degrees Celsius (S11: No), or if it is determined that the gradient of the pressure increase is not equal to or greater than the freezing determination threshold (S12: No), the freezing detection marker for the connecting pipe is set OFF (S21) and normal control is carried out (S22).

[0054] During operation at temperatures below zero degrees Celsius, the control unit 50 detects the gradient of the pressure increase, as determined by the pressure sensor 33P located downstream of the injector 33, and if it is suspected that freezing water is present downstream of the injector 33, the control unit 50 increases the flow rate of the fuel gas in the circulation pump 38 or the setpoint for the coolant temperature, which increases the heat quantity of the fuel gas (or fuel exhaust gas) in the circulation channel 36, thus preventing the T-shaped connecting pipe 35J from freezing.If the control unit 50 also determines that it is not possible to regulate the pressure increase gradient, it interrupts the operation of the injector 33 before the relief pressure is reached, thereby interrupting the supply of a cold gas in order to suppress the reduction in the amount of heat caused by the supplied fuel gas from the injector 33 and thus prevent the T-shaped connecting pipe 35J from freezing.

[0055] Since, as described above, the fuel gas supplied by the circulation pump 38 arranged in the circulation channel 36 is usually warmer than the fuel gas supplied by the injector (or fuel supply device) 33 arranged in the fuel gas supply channel 35, in the fuel cell system 1 of the present embodiment, when it is detected or suspected that water may be freezing downstream of the injector 33, the amount of fuel gas to be supplied by the circulation pump 38 arranged in the circulation channel 36 is increased relative to the amount of fuel gas to be supplied by the injector 33 (that is, the amount of fuel gas to be supplied by the circulation pump 38 in relation to the amount of fuel gas to be supplied by the injector 33), so that frozen sections can be effectively heated, thereby effectively preventing blockage of the pipe by freezing water.

[0056] Furthermore, the fuel gas supply channel 35 and the recirculation channel 36, which are connected via the T-shaped connecting pipe 35J, can be used to efficiently (in a larger quantity) direct the fuel gas from the recirculation channel 36 to the injector 33, which is located upstream of the section where the fuel gas supply channel 35 and the recirculation channel 36 join, thus further effectively preventing blockage of the pipe by freezing water.

[0057] It should be noted that in the aforementioned embodiment, an injector 33 has been described as an example of the fuel supply device, which is configured to supply a fuel gas to the fuel cells 10, but that an ejector can also be used as the fuel supply device, which is configured to discharge and supply the fuel gas supplied by the fuel gas supply 31 to the fuel cells 10.

[0058] In the aforementioned embodiment, the presumption of the presence of freezing water or a blockage due to freezing water in a section located downstream of the injector 33 is based on the degree of pressure increase determined by the pressure sensor 33P located downstream of the injector 33. However, it is understood that the presence of freezing water or a blockage due to freezing water in a section located downstream of the injector 33 can also be inferred, for example, from the temperature of a line located downstream of the injector 33 (such as the T-shaped connecting pipe 35J), the ambient temperature, and so on. DESCRIPTION OF REFERENCE MARKS 1 Fuel cell system 10 fuel cells (fuel cell stack) 20 Oxidation gas supply system 30 Fuel gas supply system 33 Injector (fuel supply device) 33P pressure sensor (secondary side pressure sensor) 35 Fuel gas supply channel (pipe) 35J T-shaped connecting pipe 35R Relief valve 36 Circulation channel 37 Gas-liquid separators 38 Circulation pump 40 Coolant supply system 41 Radiator 42 Coolant pump 45 Coolant channel 50 control unit

Claims

[1] Fuel cell system (1), comprising: a fuel cell (10); a fuel gas supply channel (35) which is set up to supply a fuel gas to the fuel cell (10); a fuel supply device (35V) which is set up to open and close in order to control the supply of fuel gas to the fuel cell (10) via the fuel gas supply channel (35); a circulation channel (36) which is designed to circulate fuel exhaust gas discharged from the fuel cell (10) to the fuel gas supply channel (35); a circulation pump (38) arranged in the circulation channel (36), which is configured to direct the fuel exhaust gas under pressure to the fuel gas supply channel (35) so that it is circulated there; and a control unit (50) for controlling the operation of the fuel supply device (35V) and / or circulation pump (38), and for determining that freezing water is present downstream of the fuel supply device (35V) when a degree of increase of a pressure determined by a pressure sensor (33P) is equal to or greater than a freezing determination threshold three times in succession, wherein, if it is determined that freezing water is present downstream of the fuel supply device (35V), the control unit (50) relatively increases a ratio of a quantity of fuel gas to be supplied by the circulation pump (38) to a quantity of fuel gas to be supplied by the fuel supply device (35V). [2] Fuel cell system (1) according to claim 1, wherein the pressure sensor (33P) is arranged downstream of the fuel supply device (35V) and upstream of a section where the fuel gas supply channel (35) and the recirculation channel (36) merge in the fuel gas supply channel (35). [3] Fuel cell system (1) according to claim 1 or 2, wherein, if it is determined that freezing water is present downstream of the fuel supply device (35V), the control unit (50) increases the amount of fuel gas supplied by the circulation pump (38), and if it is further determined that there is a blockage due to freezing water downstream of the fuel supply device (56V), the control unit (50) interrupts the operation of the fuel supply device (35V). [4] Fuel cell system (1) according to any one of claims 1 to 3, wherein, when it is determined that freezing water is present downstream of the fuel supply device (35V), the control unit (50) increases a setpoint for a cooling temperature of a coolant to be supplied to the fuel cell (10). [5] Fuel cell system (1) according to one of claims 1 to 4, wherein the fuel gas supply channel (35) and the recirculation channel (36) are connected via a T-shaped connecting pipe (35J) such that the recirculation channel (36) is perpendicular to the fuel gas supply channel (35), and the fuel supply device (35V) is arranged upstream of a section where the fuel gas supply channel (35) and the recirculation channel (36) merge in the fuel gas supply channel (35). [6] Fuel cell system (1) according to claim 1 further comprising an injector (33), wherein the pressure sensor (33P) is arranged downstream of the injector (33).

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