JP2010146978A - Fuel cell system - Google Patents

Abstract

A fuel cell system capable of detecting a gas leak in a predetermined region in a fuel supply path by reducing the pressure in a predetermined region in a fuel supply path while preventing a discharge valve from freezing in a low temperature environment.
SOLUTION: A fuel cell 10, a fuel supply path 31 for supplying fuel gas from a fuel gas supply source 30 to the fuel cell 10 via a plurality of on-off valves 33, 34A, 34B, and 35; A discharge passage 32 for discharging the fuel off-gas through the discharge valve 37, and a detecting means for reducing the pressure in the region 5 divided by the plurality of on-off valves and detecting a gas leak based on the pressure change after the pressure reduction. The provided fuel cell system 1 is configured. The control device 4 determines the possibility of freezing of the discharge valve 37 when detecting a gas leak. If it is determined that there is a possibility of freezing, the control device 4 reduces the pressure in the region 5 without opening the discharge valve 37. To do.
[Selection] Figure 1

Description

  The present invention relates to a fuel cell system. More specifically, the present invention relates to an improvement in gas leak detection in a fuel cell system mounted on a moving body such as a vehicle.

  In recent years, a fuel cell system including a fuel cell that generates power by receiving supply of reaction gas (fuel gas and oxidizing gas) has been proposed and put into practical use. Such a fuel cell system is provided with a fuel supply path for flowing fuel gas supplied from a fuel supply source such as a hydrogen tank to the fuel cell.

In such a fuel cell system, for example, hydrogen is used as a fuel gas. Therefore, it is necessary to sufficiently consider safety in handling. Therefore, conventionally, in order to detect gas leakage, a plurality of on-off valves are provided in the fuel supply passage, and the fuel gas (hydrogen) is reduced to a predetermined pressure in a piping region between the on-off valves and the on-off valves, The fuel gas leakage is determined from the subsequent pressure change (for example, Patent Document 1). In this case, the decompression of the fuel gas is performed by consuming the fuel gas by the power generation of the fuel cell or by releasing the fuel off-gas by the discharge valve.
JP 2007-121210 A

  However, the gas leak detection by the conventional decompression method may not function sufficiently in a low temperature environment. In particular, when the system is started, fuel gas cannot be consumed by the power generation of the fuel cell. On the other hand, if the exhaust valve discharges the fuel off-gas and tries to reduce the pressure, Due to the opening operation of the valve and its discharge pressure, the cooling water scatters and condenses on the discharge valve and freezes instantaneously when the discharge valve is open or closed, thereby enabling the fuel cell system to start up itself. There is also a possibility of disappearing.

  Therefore, the present invention has been made in view of the above-described problems of the prior art. In a low temperature environment, the pressure in a predetermined region in the fuel supply path is reduced while preventing the discharge valve from freezing, and gas leakage in the region is prevented. An object of the present invention is to provide a fuel cell system capable of performing detection.

  In the present invention, the following means are adopted in order to solve the above-mentioned problems. That is, a fuel cell, a fuel supply path for supplying fuel gas from a fuel gas supply source to the fuel cell via a plurality of on-off valves, and a discharge for discharging fuel off-gas from the fuel cell via a discharge valve A fuel cell system comprising: a passage; and a detection means for reducing a pressure in a region divided by the plurality of on-off valves and detecting a gas leak based on a pressure change after the pressure reduction, the detection means comprising: A fuel cell system that determines the possibility of freezing of the discharge valve at the time of gas leak detection and reduces the pressure in the region without opening the discharge valve when it is determined that there is a possibility of freezing. Constitute.

  According to this configuration, when there is a possibility that the discharge valve is frozen in a low-temperature environment, pressure reduction in the region using the discharge valve is not performed. At the time of detection, it is possible to prevent the discharge valve from freezing due to the discharge pressure of the fuel off gas. In addition, if the discharge valve has already been frozen when the gas leak is detected, it is possible to prevent the discharge valve from being forcibly opened. As a result, it is possible to prevent the malfunction of the discharge valve caused by the gas leak detection and the subsequent operation of the fuel cell system (for example, startup) cannot be performed.

  In this specification, “freezing possibility” means both the possibility that the discharge valve is frozen when the gas leak is detected and the possibility that the discharge valve is frozen when the gas leak is detected. The determination of the possibility of freezing is performed based on, for example, the temperature environment of the fuel cell system, the time when the fuel cell system is placed in the temperature environment, the likelihood of the discharge pressure from the discharge valve, and the like.

  In the above configuration, the on-off valve on the downstream side of the region is an injector, and when the detection unit determines that the discharge valve may be frozen, the pressure adjustment target value on the low pressure side of the injector , The injector may be opened or maintained in the open state.

  According to this configuration, by increasing the pressure adjustment target on the low pressure side of the injector, it is not necessary to actually lower the fuel gas pressure downstream of the injector, that is, without opening the discharge valve and discharging the fuel off-gas. The injector is opened (or the open state is maintained). Thereby, the fuel gas pressure in the region upstream of the injector can be reduced without using the discharge valve. Moreover, the accuracy and responsiveness to the setting of the pressure regulation target are improved by using the injector.

  In the present specification, between the fuel supply source and the fuel cell, the fuel supply source side is “upstream”, the fuel cell side is “downstream”, the upstream of the injector is “the high pressure side of the injector”, and the downstream is “ "Low pressure side of the injector". The injector is typically an electromagnetically driven on-off valve capable of adjusting the gas state by driving the valve body directly with a predetermined driving cycle with an electromagnetic driving force and separating it from the valve seat. Configured as

  Further, in the above configuration, when the detection unit determines that the discharge valve is not frozen, the fuel off-gas is discharged through the discharge valve to reduce the pressure of the fuel gas on the low pressure side of the injector. Thus, the injector may be opened or maintained in the open state.

  According to this configuration, after determining the possibility of freezing of the discharge valve in advance, the discharge valve is opened only when there is no possibility of freezing, and the injector is opened (or the open state is maintained). ). Thereby, the fuel gas pressure in the region upstream of the injector can be reduced without fear of freezing of the discharge valve.

  In the above configuration, the gas leak detection may be performed when the system is started.

  At the time of starting the system, the possibility of freezing the discharge valve in a low-temperature environment is high, and on the other hand, the fuel gas cannot be consumed in the fuel cell, so the utility of using the above configuration is particularly high.

  In the present specification, “when the system is started” indicates when the operation of the fuel cell system that has been stopped for a certain period of time or more is started.

  According to the present invention, it is possible to provide a fuel cell system capable of detecting a gas leak in an area by reducing the pressure in a predetermined area in the fuel supply path while preventing the discharge valve from freezing in a low temperature environment. it can.

  Hereinafter, a fuel cell system according to an embodiment of the present invention will be described with reference to the drawings.

(Overall configuration of fuel cell system)
First, the overall configuration of a fuel cell system 1 mounted on a fuel cell vehicle according to an embodiment of the present invention will be described with reference to FIG. As shown in FIG. 1, the fuel cell system 1 includes a fuel cell 10 that generates power by receiving supply of reaction gas (oxidation gas and fuel gas), and supplies air as an oxidation gas to the fuel cell 10. An oxidizing gas piping system 2, a hydrogen gas piping system 3 for supplying hydrogen gas as a fuel gas to the fuel cell 10, a control device 4 for integrated control of the entire system, and the like.

  The fuel cell 10 has a stack structure in which a required number of unit cells that generate power upon receiving a reaction gas are stacked. The electric power generated by the fuel cell 10 is supplied to a PCU (Power Control Unit) 11. The PCU 11 includes an inverter, a DC-DC converter, and the like that are disposed between the fuel cell 10 and the traction motor 12. Further, the fuel cell 10 is provided with a current sensor 13 for detecting a current during power generation.

  The oxidizing gas piping system 2 includes an air supply path 21 for supplying the oxidizing gas (air) humidified by the humidifier 20 to the fuel cell 10, and an air discharging path for guiding the oxidizing off-gas discharged from the fuel cell 10 to the humidifier 20. 22 and an air discharge path 23 for guiding the oxidant off-gas from the humidifier 20 to the outside. The air supply path 21 is provided with a compressor 24 that takes in the oxidizing gas in the atmosphere and pumps it to the humidifier 20.

  The hydrogen gas piping system 3 includes a hydrogen tank 30 as a fuel supply source storing high-pressure hydrogen gas, a hydrogen supply path 31 as a fuel supply path for supplying the hydrogen gas in the hydrogen tank 30 to the fuel cell 10, A discharge path 32 for discharging the hydrogen off-gas discharged from the fuel cell 10 and a circulation path 38 for returning the hydrogen off-gas to the hydrogen supply path 31 are provided.

  The hydrogen tank 30 is a tank filled with hydrogen gas compressed to a high pressure. For example, the internal pressure is set to 35 MPa to 70 MPa. The hydrogen tank 30 may be a plurality of hydrogen tanks connected by a hydrogen supply path A2 as indicated by a dotted line in FIG. Further, in place of the hydrogen tank 30, a reformer that generates a hydrogen-rich reformed gas from a hydrocarbon-based fuel, a high-pressure gas tank that stores the reformed gas generated in the reformer in a high-pressure state, and Can also be employed as a fuel supply source. A tank having a hydrogen storage alloy may be employed as a fuel supply source.

  A main stop valve 33 that supplies or stops the supply of hydrogen gas from the hydrogen tank 30 to the hydrogen supply path 31 from the upstream side toward the downstream side, and a high pressure that detects the supply pressure of hydrogen gas from the hydrogen tank 30. The pressure sensor 41, a primary pressure reducing valve 34A for reducing and adjusting the supply pressure of hydrogen gas to the fuel cell 10, an intermediate pressure sensor 42 for detecting the hydrogen gas pressure downstream of the primary pressure reducing valve 34A, and further reducing the hydrogen gas. The secondary pressure reducing valve 34B, the low pressure sensor 43 for detecting the hydrogen gas pressure downstream of the secondary pressure reducing valve 34B, the injector 35 for further depressurizing the hydrogen gas and supplying it to the fuel cell 10 inlet, and the hydrogen gas fuel cell 10 inlet An inlet pressure sensor 44 that detects pressure is provided.

  In the present embodiment, mechanical pressure reducing valves are employed as the primary pressure reducing valve 34A and the secondary pressure reducing valve 34B. Such a mechanical pressure reducing valve has, for example, a housing in which a back pressure chamber and a pressure adjusting chamber are formed with a diaphragm therebetween, and the primary pressure is set to a predetermined pressure in the pressure adjusting chamber by the back pressure in the back pressure chamber. It is possible to adopt a known configuration in which the pressure is reduced to a secondary pressure. In the present embodiment, by arranging two pressure reducing valves upstream of the injector 35, the upstream pressure of the injector 35 is effectively reduced.

  The injector 35 is an electromagnetically driven on-off valve capable of adjusting the gas flow rate and gas pressure by driving the valve body directly with a predetermined driving cycle with an electromagnetic driving force and separating it from the valve seat. In this embodiment, the valve body of the injector 35 is driven by a solenoid that is an electromagnetic drive device, and the opening area of the injection hole is made two or more stages by turning on and off the pulsed excitation current supplied to the solenoid. It can be switched. Thereby, the pressure of hydrogen gas can be controlled with high accuracy. The injector 35 directly opens and closes the valve body with an electromagnetic driving force, and has a high responsiveness because its driving cycle can be controlled to a highly responsive region. In the present embodiment, as shown in FIG. 1, the injector 35 is disposed on the upstream side from the junction A <b> 1 between the hydrogen supply path 31 and the circulation path 38.

  In the hydrogen supply path 31 described above, the range surrounded by the broken line in FIG. 1, that is, the range from the main stop valve 33 to the injector 35 is the gas leak detectable region 5.

  A circulation path 38 is connected to the discharge path 32 via a gas-liquid separator 36 and an exhaust / drain valve (exhaust valve) 37. The gas-liquid separator 36 collects moisture from the hydrogen off gas. The exhaust / drain valve 37 operates according to a command from the control device 4 to discharge (purge) the moisture collected by the gas-liquid separator 36 and the hydrogen off-gas (fuel off-gas) containing impurities to the outside. . The circulation path 38 is provided with a hydrogen pump 39 that pressurizes the hydrogen off-gas in the circulation path 38 and sends it to the hydrogen supply path 31 side. Note that the hydrogen off-gas discharged through the exhaust / drain valve 37 is diluted by the diluter 40 and merges with the oxidizing off-gas in the air discharge path 23.

  The control device 4 detects an operation amount of an acceleration operation member (accelerator or the like) provided in the vehicle, receives control information such as an acceleration request value (for example, a required power generation amount from a load device such as the traction motor 12), Control the operation of various devices in the system. In addition to the traction motor 12, the load device is an auxiliary device (for example, a compressor 24, a hydrogen pump 39, a cooling pump motor, or the like) necessary for operating the fuel cell 10, and various types of vehicles involved in traveling of the vehicle. It is a collective term for power consumption devices including actuators used in devices (transmissions, wheel control devices, steering devices, suspension devices, etc.), occupant space air conditioners (air conditioners), lighting, audio, and the like.

  The control device 4 is configured by a computer system (not shown). Such a computer system includes a CPU, ROM, RAM, HDD, input / output interface, display, and the like, and various control operations are realized by the CPU reading and executing various control programs recorded in the ROM. It is like that.

  In the present embodiment, the control device 4 also functions as a detection unit that performs hydrogen gas leak detection (gas leak detection) when the system is started. The control device 4 controls the opening and closing of the on / off valves of the main stop valve 33, the primary pressure reducing valve 34A, the secondary pressure reducing valve 34B, the injector 35, and the exhaust / drain valve 37 at the time of starting the system to detect gas leakage. Hydrogen gas leakage in the possible region 5 can be detected. This will be specifically described below.

(Hydrogen gas leak detection process at system startup)
The detection of leakage of hydrogen gas at the time of system startup by the control device 4 will be described with reference to FIG. Here, FIG. 2 is a flowchart showing a hydrogen gas leak detection process at the time of system startup according to the present embodiment.

  When the control device 4 determines that the fuel cell system 1 has been activated (for example, upon receiving a signal indicating that the ignition key has been turned on), the main stop valve 33, the primary pressure reducing valve 34A, the secondary pressure reducing valve 34B, and the injector 35 Is opened, hydrogen is supplied from the hydrogen tank 30 to the hydrogen supply path 31, and a hydrogen gas leak detection process is started (start).

  Next, the control device 4 determines whether or not hydrogen gas leak detection was performed at the time of the previous system stop (step S1).

  If hydrogen gas leak detection was performed at the time of the previous stop (step S1: NO), it is not necessary to perform hydrogen gas leak detection again at the time of system startup, so normal startup processing is performed (step S5). ).

  On the other hand, when hydrogen gas leak detection is not performed at the previous stop (step S1: YES), it is necessary to detect hydrogen gas leak at the start timing, and the control device 4 first performs exhaust drainage for that purpose. It is determined whether or not the valve 37 is likely to be frozen (step S2). Specifically, the current temperature of the discharge path 32, the temperature of the discharge path 32 at the previous system stop, the elapsed time from the previous system stop to the current start, the pressure of the hydrogen off-gas in the discharge path 32, etc. 1 and / or a temperature sensor or the like provided in the fuel cell vehicle, and based on the calculated value, the possibility of freezing of the exhaust / drain valve 37 (possibility of freezing or opening of the exhaust / drain valve 37) The possibility that the water contained in the hydrogen off-gas will freeze instantaneously is determined by the discharge pressure due to (1). Typically, when the fuel cell vehicle has been left in a low temperature environment below freezing for a long time, it is determined that the exhaust drain valve 37 may be frozen. When the vehicle is placed or when almost no time has passed since the previous system stop, it is determined that the exhaust drain valve 37 is not likely to freeze.

  If it is determined that the exhaust / drain valve 37 may be frozen (step S2: YES), the control device 4 detects hydrogen gas leakage without using the exhaust / drain valve (step S3).

  Specifically, the control device 4 closes the main stop valve 33 and stops the supply of hydrogen gas from the hydrogen tank 30 to the fuel supply path 31. Then, the control device 4 continues the valve opening of the injector 35 to reduce the gas leak detectable region 5 until the pressure detection capability of each of the pressure sensors 41 to 43 becomes, for example, near the limit value, and causes the fuel cell 10 to Hydrogen gas is supplied. At this time, instead of opening the exhaust / drain valve 37 to reduce the pressure on the low pressure side of the injector 35 and continuing the valve opening of the injector 35, the control device 4 does not adjust the pressure regulation target pressure on the downstream side of the injector 35. By raising, the valve opening of the injector 35 is continued. When the pressure is reduced to the pressure close to the limit value, the control device 4 closes the injector 35 and stops the supply of hydrogen gas to the fuel cell 10. That is, the main stop valve 33 to the injector 35 are sealed. Thereafter, the control device 4 monitors fluctuations in detection values by the pressure sensors 41 to 43. If the pressure rises above a predetermined pressure during monitoring, it is determined that the gas stop of the main stop valve 33 of the hydrogen tank 30 is defective. Further, when the pressure drops to a predetermined pressure or higher, it is determined that hydrogen gas leaks from the gas leak detectable region 5 to the outside. The control device 4 immediately notifies the user of these determination results. When the hydrogen gas leak detection is completed, the control device 4 performs a normal startup process (step S5).

  If it is determined that the exhaust / drain valve 37 is not frozen (step S2: NO), the control device 4 uses the exhaust / drain valve to detect hydrogen gas leakage (step S4).

  The difference between Step S4 and Step S3 is the pressure reducing method for the gas leak detectable region 5. Specifically, in step S4, the control device 4 opens the exhaust / drain valve 37 to reduce the pressure on the low pressure side of the injector 35 in order to decompress the gas leak detectable region 5, thereby reducing the injector 35. Is continuously opened, and the gas leak detectable region 5 is decompressed. Other operations in step S4 are the same as those in step S3, and a description thereof will be omitted.

  As described above, in the present embodiment, when the exhaust / drain valve 37 is likely to be frozen at the time of starting the system, the gas leak detectable region 5 using the exhaust / drain valve 37 is not decompressed and may be frozen. Only when there is not, decompression of the gas leak detectable region 5 using the exhaust / drain valve 37 is performed. As a result, when hydrogen gas leakage is detected when the system is started in a low-temperature environment, moisture contained in the hydrogen off-gas instantaneously condenses due to the discharge pressure of the hydrogen off-gas, and the exhaust drain valve 37 freezes. When the exhaust / drain valve 37 is already frozen, it is possible to prevent the exhaust / drain valve 37 from being forcibly opened.

  The above-described embodiment is an example of a preferred embodiment of the present invention. However, the present invention is not limited to this, and can be implemented in various modes without departing from the scope of the invention. For example, in the above embodiment, the fuel cell system according to the present invention is mounted on the fuel cell vehicle. However, the fuel cell according to the present invention is applied to various mobile bodies (robots, ships, aircrafts, etc.) other than the fuel cell vehicle. A system can also be installed. Further, the fuel cell system according to the present invention may be applied to a stationary power generation system used as a power generation facility for a building (house, building, etc.).

The block diagram which shows the whole structure of the fuel cell system 1 mounted in a fuel cell vehicle. The flowchart which shows the leak detection process of the hydrogen gas at the time of system starting.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Fuel cell system, 10 ... Fuel cell, 11 ... PCU, 12 ... Traction motor, 13 ... Current sensor, 2 ... Oxidation gas piping system, 20 ... Humidifier, 21 ... Air supply , 22 ... Air discharge passage, 23 ... Air discharge passage, 24 ... Compressor, 3 ... Hydrogen gas piping system (fuel supply passage), 30 ... Hydrogen tank (fuel supply source), 31 ... Hydrogen supply 32, discharge passage, 33 ... main stop valve, 34A ... primary pressure reducing valve, 34B ... secondary pressure reducing valve, 35 ... injector, 36 ... gas-liquid separator, 37 ... exhaust drain valve ( Discharge valve), 38 ... circulation path, 39 ... hydrogen pump, 4 ... control device, 40 ... diluent, 41 ... high pressure sensor, 42 ... medium pressure sensor, 43 ... low pressure sensor, 44 …… Inlet pressure sensor

Claims (4)

A fuel cell;
A fuel supply path for supplying fuel gas from a fuel gas supply source to the fuel cell via a plurality of on-off valves;
A discharge path for discharging the fuel off-gas from the fuel cell via a discharge valve;
A fuel cell system comprising: a detecting unit that reduces a pressure in a region divided by the plurality of on-off valves and detects a gas leak based on a pressure change after the pressure reduction;
The detection means determines the possibility of freezing of the discharge valve at the time of gas leak detection, and when it is determined that there is a possibility of freezing, the pressure in the region is reduced without opening the discharge valve. Fuel cell system. The on-off valve on the downstream side of the region is an injector,
The detection means, when determining that there is a possibility of freezing of the discharge valve, increases the pressure adjustment target value on the low pressure side of the injector, thereby opening the injector or maintaining the valve open state. 2. The fuel cell system according to 1.   When the detection means determines that the discharge valve is not likely to freeze, the fuel off-gas is discharged through the discharge valve to reduce the pressure of the fuel gas on the low pressure side of the injector, thereby The fuel cell system according to claim 2, wherein the valve is opened or maintained in the open state.   The fuel cell system according to claim 1, wherein the gas leak detection is performed when the system is started.

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