JP2012204011A - Fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To determine the source of hydrogen leaked, in detection of hydrogen leakage of a vehicle including a fuel cell.SOLUTION: If hydrogen is detected by a hydrogen detector 24 during intermittent operation in which a fuel cell is not generating power, it is determined that hydrogen has leaked from a hydrogen tank 20 or a fuel supply tube 28 for feeding hydrogen from the hydrogen tank to a fuel cell stack 12. If hydrogen concentration increases in response to operation of a hydrogen pump 40 after hydrogen is detected during intermittent operation, it may be determined that hydrogen has leaked from a hydrogen exhaust/drainage valve 46.

Description

  The present invention relates to a fuel cell system, and more particularly to detection of hydrogen as a fuel gas.

  A vehicle equipped with a fuel cell and using electric power generated by the fuel cell is known. The generated electric power is supplied to, for example, a motor for driving the vehicle and used to drive the vehicle.

  The fuel cell supplies a fuel gas such as hydrogen to the anode side of the fuel cell stack, supplies an oxidizing gas (for example, air) containing oxygen to the cathode side, and generates electric power by reaction through the electrolyte membrane of the supplied gas. Take out. The spent fuel gas and oxidizing gas after the reaction are discharged to the outside of the fuel cell stack as exhaust gas together with water as a reaction product. An exhaust pipe is provided to guide the exhaust gas to an appropriate location on the vehicle.

  In the gas discharged from the anode side, unreacted hydrogen remains, and is returned to the anode side again in order to use hydrogen effectively. That is, the fuel gas is circulated and repeatedly supplied to the anode side. While the fuel gas is circulating, impurities other than hydrogen are mixed in the fuel gas. Examples of the impurity include nitrogen that has permeated through an electrolyte membrane. When the circulation of the fuel gas is repeated, the impurity concentration increases accordingly, and the power generation efficiency decreases, so the fuel gas is discharged at a certain stage. This spent fuel gas contains hydrogen.

  When hydrogen is used as the fuel gas, it is necessary to detect hydrogen leakage. In particular, it is necessary to detect leakage from a hydrogen tank that stores hydrogen. On the other hand, as described above, the spent fuel gas discharged from the fuel cell stack contains hydrogen. A hydrogen detector is provided to detect both hydrogens. Patent Document 1 below discloses a technique for detecting hydrogen from a hydrogen tank and from a fuel cell stack by using a single hydrogen detector disposed above the hydrogen tank.

JP 2005-116358 A

  When hydrogen is detected by a single hydrogen detector disposed above the hydrogen tank, it cannot be determined whether hydrogen has leaked from the hydrogen tank or hydrogen from the fuel cell stack.

  An object of the present invention is to determine the source of hydrogen detected by a hydrogen detector above a hydrogen tank.

  The fuel cell system according to the present invention determines the source of detected hydrogen based on detection of hydrogen during intermittent operation of the fuel cell system. The intermittent operation refers to a state where power generation of the fuel cell system is stopped even when the vehicle is in operation. In brief, if hydrogen is detected during intermittent operation, it can be determined that the hydrogen has leaked from the hydrogen supply system that supplies hydrogen from the hydrogen tank or the hydrogen tank to the fuel cell stack. During the intermittent operation, the fuel cell system is stopped and the spent fuel gas is not discharged, so that it can be determined that the source of hydrogen is not the spent fuel gas.

  Further, when hydrogen is detected during intermittent operation, a hydrogen pump that circulates hydrogen is operated. At this time, the hydrogen exhaust drain valve for discharging spent fuel from the fuel cell stack is closed. In this state, if the hydrogen concentration detected by the hydrogen detector does not increase, it can be determined that hydrogen has leaked from the hydrogen tank or the hydrogen supply system. On the other hand, if the hydrogen concentration increases, it can be determined that hydrogen has leaked from the hydrogen exhaust drain valve.

  The source of hydrogen detected by a hydrogen detector provided above the hydrogen tank can be determined.

1 is a diagram showing a schematic configuration of a vehicle equipped with a fuel cell according to the present invention. 1 is a block diagram showing a schematic configuration of a fuel cell system according to the present invention. It is a flowchart which concerns on the origin determination of leaking hydrogen. It is another flowchart which concerns on the origin determination of leaking hydrogen.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of a vehicle 10 equipped with a fuel cell system. In the fuel cell vehicle 10, the fuel cell stack 12 is disposed under the vehicle floor. The fuel cell stack is mounted under a floor panel constituting a space where a vehicle occupant is present, that is, a floor of a passenger compartment. A portion in which the floor panel is recessed as viewed from the lower side of the vehicle is provided, and the fuel cell stack 12 can be disposed here. Since the position of the floor panel can be raised under the seat cushion in the front seat of the vehicle as compared with the position where the occupant's feet are placed, the fuel cell stack 12 can be mounted by recessing this portion. Further, a portion between the left and right seats (a so-called center tunnel portion) is also a portion where the floor panel can be depressed, and can also be set as a mounting position.

  The part under the front seat and the tunnel as described above are located on the wheel base, that is, between the front wheel and the rear wheel. By mounting the fuel cell stack 12 in the hole base, damage to the fuel cell stack 12 can be suppressed when a forward collision occurs or a rear collision occurs. Further, the outer shape of the fuel cell stack 12 is larger than that of a power unit including an internal combustion engine, and if it is intended to be housed in the engine compartment, the design of the appearance of the vehicle may be restricted. Arranging the fuel cell stack 12 under the floor increases design freedom.

  In the fuel cell vehicle 10, the exhaust pipe 14 from the fuel cell stack 12 opens into the space under the floor, the wheelbase. This opening is referred to as an exhaust port 16. Further, a muffler 18 for noise reduction is arranged in the middle of the exhaust pipe 14. A hydrogen tank 20 is mounted as a hydrogen source in the lower rear portion of the vehicle. Above the hydrogen tank 20, a collecting plate 22 is disposed for receiving hydrogen leaked from the hydrogen tank 20. The collection plate 22 has a function of sending the collected hydrogen to the hydrogen detector 24. The hydrogen detector 24 is arranged above the hydrogen tank 20, that is, at a position where hydrogen leaked from the hydrogen tank rises and is collected and sent by the collecting plate 22. The collecting plate 22 can be a plate-like member provided with unevenness, and can form a flow path for guiding hydrogen to the hydrogen detector 24 due to the uneven shape. By forming the flow path with the recesses and inclining the ceiling, it is possible to move along the flow path by the buoyancy of hydrogen. Alternatively, the hydrogen collected by the collecting plate 22 may be sent to the hydrogen detector 24 by a tubular member. In this case as well, the tubular member is disposed with an inclination so that hydrogen rises in the tube by buoyancy.

  FIG. 2 is a diagram showing a main configuration of the fuel cell system 26 mounted on the fuel cell vehicle 10. The fuel cell stack 12 is configured by stacking a plurality of unit fuel cells called single cells. A plurality of unit cells stacked are connected in series to form an assembled battery, and a desired terminal voltage is obtained. Each single cell has a structure in which a catalyst layer, a diffusion layer, a porous electrode layer, and a separator are arranged on the cathode side and the anode side on both sides of the electrolyte membrane, respectively.

  Hydrogen from the hydrogen tank 20 is supplied to the fuel cell stack 12 as a fuel gas through the fuel supply pipe 28, while air as an oxidant is supplied by the compressor 30 through the air supply pipe 32. One or more mechanical elements such as a valve for adjusting the pressure are arranged in the fuel supply pipe 28. The fuel supply pipe 28 for sending hydrogen from the hydrogen tank 20 and the valves provided in the fuel supply pipe are collectively referred to as a hydrogen supply system. The air supply pipe 32 is provided with a pressure sensor 34 to monitor the pressure of the supplied air. The air supply pipe 32 is provided with an inlet valve 36 for closing the pipe.

  The fuel gas sent to the fuel cell stack 12 is supplied to the anode side of each single cell, and the air is supplied to the cathode side. The gas discharged from the anode side (anode-side exhaust gas) contains hydrogen that has not been consumed, and a circulation pipe 38 is provided in order to return it to the anode side and circulate it again. The circulation pipe 38 is provided with a hydrogen pump 40 and a check valve 42. The circulation pipe 38 is connected to the fuel supply pipe 28, and the anode side exhaust gas from the circulation pipe 38 is mixed with hydrogen supplied from the hydrogen tank 20 and supplied to the fuel cell stack 12. The check valve 42 is provided to prevent hydrogen from the hydrogen tank 20 from flowing into the circulation pipe 38 when the hydrogen pump 40 is not operating.

  As the anode side exhaust gas continues to circulate, hydrogen is consumed while impurities increase. As the impurity, for example, there is nitrogen that has passed through the electrolyte membrane from the cathode side. When the impurities increase, the power generation efficiency decreases, so the anode side exhaust gas is discharged at a certain stage. For this purpose, a discharge pipe 44 branched from a portion of the circulation pipe 38 between the hydrogen pump 40 and the check valve 42 is provided. The exhaust pipe 44 is provided with a hydrogen exhaust drain valve 46 that closes and opens the exhaust pipe 44. When the hydrogen exhaust drain valve 46 is opened, the anode side exhaust gas is sent to the diluter 48 through the exhaust pipe 44.

  Exhaust gas discharged from the cathode side is discharged from the exhaust port 16 via the exhaust pipe 14. A discharge valve 50 is provided in the exhaust pipe 14. The discharge valve 50 is a valve that can adjust the opening, that is, the exhaust pipe 14 can be throttled and the effective sectional area can be adjusted. For example, a butterfly valve can be adopted. The pressure of the air (oxidizing gas) in the fuel cell stack 12 can be adjusted by adjusting the throttle of the exhaust pipe 14. The discharge valve 50 is closed when the power generation of the fuel cell is stopped. The exhaust pipe 14 is provided with a bypass pipe 52 so as to bypass the muffler 18, and the above-described diluter 48 is disposed here. In the diluter 48, the remaining hydrogen in the fuel gas is diluted with air used as the oxidizing gas and returned to the exhaust pipe 14. Exhaust gas containing air, water (steam) as a reaction product, and hydrogen is exhausted from the exhaust port 16 to the atmosphere through the exhaust pipe 14.

  The control unit 54 controls the power generation and the like of the fuel cell system 26 by controlling the compressor 30, the hydrogen pump 40, and the above-described valves. When hydrogen is detected by the hydrogen detector 24, control based on this is executed. This control related to hydrogen detection will be described in detail later. Further, FIG. 2 shows an operation amount 56 of an accelerator pedal, a usage state 58 of an auxiliary machine, and a storage amount 60 of a secondary battery as parameters relating to control during intermittent operation of the fuel cell described later. These parameters are for determining the power required for the fuel cell. The usage status of the auxiliary equipment includes, for example, the operating status of the air conditioner, lights, usage status of the defroster, and the like.

  Since hydrogen is flammable, it is necessary to detect hydrogen leakage from a hydrogen tank or the like. The collecting plate 22 is formed so as to collect the hydrogen leaked from the hydrogen tank 20 and the hydrogen supply system, and to guide the hydrogen to the hydrogen detector 24. When the hydrogen detector 24 detects hydrogen, the control unit 54 determines that hydrogen is leaking and notifies this. On the other hand, as described above, the exhaust from the fuel cell stack contains hydrogen, and when hydrogen in the exhaust discharged from the exhaust port 16 reaches the hydrogen detector 24, it is determined that hydrogen is leaking. . If the exhaust port 16 is sufficiently separated from the periphery of the hydrogen tank 20, erroneous detection of hydrogen leakage can be avoided, but this may not be possible due to the layout of the vehicle. In order to avoid the false detection described above, the threshold value of the concentration at which hydrogen is detected is set higher, or the threshold value is set only during power generation, that is, when hydrogen from the exhaust gas may be detected. Can be set higher. Even in this way, the source of the detected hydrogen is unknown. In the fuel cell system 26, when the hydrogen detector 24 detects hydrogen, the fuel cell system 26 has a determination unit 62 for determining whether the hydrogen leaked from a hydrogen tank or the like or hydrogen contained in the exhaust gas or the source of the detected hydrogen. I have.

  To determine the source of hydrogen, intermittent operation of the fuel cell is used. In the fuel cell-equipped vehicle 10, in a situation where power generation by the fuel cell is unnecessary, an operation mode that covers the necessary power with the power stored in the secondary battery is adopted. For example, when the vehicle stops due to a signal or the like and the amount of power stored in the secondary battery is sufficient, power generation by the fuel cell is stopped. Thus, although the vehicle is operating, the state where the power generation by the fuel cell is stopped is the intermittent operation. During the intermittent operation, the compressor 30 is stopped, no air is supplied, and the exhaust gas exhaust from the exhaust pipe 14 is also stopped. Further, since it is not necessary to circulate the fuel gas, the hydrogen pump 40 is also stopped and the hydrogen exhaust / drain valve 46 is also closed. Therefore, the anode side exhaust gas is not exhausted from the exhaust port 16 through the exhaust pipe 44 and the exhaust pipe 14 from the circulation pipe 38.

  Thus, since the exhaust gas is not discharged during the intermittent operation, it can be determined that the hydrogen detected at this time is leaked from the hydrogen tank 20 or the hydrogen supply system. The control unit 54 sends to the determination unit 62 information that controls the fuel cell system 26 to intermittent operation and information that the hydrogen detector 24 detects hydrogen. Based on the transmitted information, the determination unit 62 determines that hydrogen leakage from a hydrogen tank or the like has occurred if hydrogen is detected during intermittent operation. The control unit 54 receives this information and notifies the driver or the like of this. If hydrogen is not detected during intermittent operation, the determination of hydrogen leakage is suspended until the next intermittent operation is executed.

  In the case of hydrogen leakage from a hydrogen supply system such as a hydrogen tank, it is necessary to stop the vehicle. On the other hand, when hydrogen contained in the exhaust gas is detected, it may be possible to operate with a reduced power generation amount. Therefore, it is desirable to identify the source of the detected hydrogen, that is, whether it is hydrogen from a hydrogen tank or the like, or hydrogen contained in the exhaust, and take measures according to the source.

  In order to further identify the source of the detected hydrogen, the hydrogen pump 40 may be driven to monitor the transition of the hydrogen concentration. When hydrogen is detected by the hydrogen detector 24, the control unit 54 operates the hydrogen pump 40 with the hydrogen exhaust / drain valve 46 closed. If the hydrogen exhaust drain valve 46 is completely closed, the anode side exhaust gas containing hydrogen will not be discharged from the discharge port 16 through the discharge pipe 44 from the circulation pipe 38. Therefore, the concentration of hydrogen detected by the hydrogen detector 24 does not increase. On the other hand, if the hydrogen concentration increases due to the operation of the hydrogen pump 40, it can be determined that the hydrogen exhaust drain valve 46 is not completely closed, and the hydrogen leaking from here is discharged from the discharge port 16 and detected. The determination unit 62 acquires information on the hydrogen concentration after the start of the hydrogen pump 40 from the hydrogen detector 24 via the control unit 54, and monitors the change in the hydrogen concentration. If the hydrogen concentration does not increase, it is determined that there is a leak from the hydrogen tank or the like, and if it increases, it is determined that the leak is from the hydrogen exhaust drain valve 46.

  FIG. 3 is a diagram showing a control flow relating to determination of the origin of hydrogen. If hydrogen is detected by the hydrogen detector 24 during the intermittent operation (S100), the controller 54 commands the operation of the hydrogen pump 40 (S102). During the intermittent operation, the hydrogen exhaust drain valve 46 is controlled to be in a closed state. If the valve is normal, hydrogen does not leak even if the hydrogen pump 40 is operated.

  The determination unit 62 monitors the hydrogen concentration after the operation of the hydrogen pump (S104), and when the hydrogen concentration increases, it is determined that the leakage is from the hydrogen exhaust / drain valve 46 (S106). When leakage from the hydrogen exhaust / drain valve 46 is determined, the control unit 54 sets the upper limit value of the generated power of the fuel cell lower than normal (S108). Thereby, the circulation amount of the fuel gas, that is, the hydrogen supply amount by the hydrogen pump 40 is limited, and leakage from the hydrogen exhaust drain valve 46 can be suppressed. The limit of the hydrogen supply amount is set to a value that does not reach the concentration determined as hydrogen detection in step S100. In this case, the power performance of the vehicle is reduced, but the vehicle cannot be stopped before traveling.

  In step S104, if the hydrogen concentration does not increase after the operation of the hydrogen pump 40, it is determined that the hydrogen tank 20 has leaked (S110). In this case, control for stopping the vehicle is performed (S112).

  FIG. 4 is a diagram showing another control flow relating to the determination of the origin of hydrogen. When hydrogen is detected by the hydrogen detector 24 during the intermittent operation (S100), the determination unit 62 monitors the hydrogen concentration for a predetermined time and measures the rate of increase of the hydrogen concentration during that time (S120). The time for monitoring the hydrogen concentration may be a predetermined fixed time, or may be a value variably determined according to other conditions.

  When the measurement of the rate of increase in the hydrogen concentration is completed, the control unit 54 commands the operation of the hydrogen pump 40 (S102). During the intermittent operation, the hydrogen exhaust drain valve 46 is controlled to be in a closed state. If the valve is normal, hydrogen does not leak even if the hydrogen pump 40 is operated.

  The determination unit 62 measures the rate of increase in the hydrogen concentration after the operation of the hydrogen pump 40, and compares this with the value measured before the operation of the hydrogen pump 40 (S122). If the rate of increase in the hydrogen concentration increases, it is determined that hydrogen in the circulation pipe 38 has leaked from the hydrogen exhaust drain valve 46 due to the operation of the hydrogen pump 40 and this has been detected (S106). When leakage from the hydrogen exhaust / drain valve 46 is determined, the control unit 54 sets the upper limit value of the generated power of the fuel cell lower than normal (S108). Thereby, the circulation amount of the fuel gas, that is, the hydrogen supply amount by the hydrogen pump 40 is limited, and leakage from the hydrogen exhaust drain valve 46 can be suppressed. The limit of the hydrogen supply amount is set to a value that does not reach the concentration determined as hydrogen detection in step S100. In this case, the power performance of the vehicle is reduced, but it does not reach the point where the traveling is stopped.

  In step S122, after the operation of the hydrogen pump 40, if the rate of increase in hydrogen concentration has not increased, it is determined that hydrogen has leaked from the hydrogen tank and the hydrogen supply system (S110). In this case, control for stopping the vehicle is performed (S112).

  In FIG. 2, the control unit 54 and the determination unit 62 are shown as separate blocks, but actually, the same arithmetic unit executes the processing of the control unit and the determination unit.

  The above is the determination of hydrogen leakage during intermittent operation of the fuel cell. During the power generation of the fuel cell, the current value of hydrogen concentration is compared with past data. If the current hydrogen concentration becomes higher than the hydrogen concentration during the past power generation, the hydrogen leakage is determined.

  Below, the preferable aspect of hydrogen leak detection is described.

(1)
A hydrogen detector for detecting hydrogen installed above the hydrogen tank;
A discriminator for discriminating the origin of detected hydrogen based on detection of hydrogen by a hydrogen detector during intermittent operation of the fuel cell system;
A fuel cell system mounted on a vehicle having
A hydrogen pump for circulating hydrogen;
A hydrogen exhaust drain valve for discharging spent fuel gas after the hydrogen reaction from the fuel cell stack;
A control unit that controls the operation of the hydrogen pump and the hydrogen exhaust drain valve;
Have
The determination unit, when hydrogen is detected by the hydrogen detector during the intermittent operation, measures the rate of increase in hydrogen concentration,
After the measurement of the rate of increase in the hydrogen concentration, the control unit closes the hydrogen exhaust drain valve and operates the hydrogen pump to send hydrogen,
The determination unit further includes a hydrogen supply system that sends hydrogen from the hydrogen tank or the hydrogen tank to the fuel cell stack if the speed of increase in the hydrogen concentration detected by the hydrogen detector does not increase after the operation of the hydrogen pump. Determine that hydrogen is leaking from
Fuel cell system.

(2)
A hydrogen detector for detecting hydrogen installed above the hydrogen tank;
A discriminator for discriminating the origin of detected hydrogen based on detection of hydrogen by a hydrogen detector during intermittent operation of the fuel cell system;
A fuel cell system mounted on a vehicle having
A hydrogen pump for circulating hydrogen;
A hydrogen exhaust drain valve for discharging spent fuel gas after the hydrogen reaction from the fuel cell stack;
A control unit that controls the operation of the hydrogen pump and the hydrogen exhaust drain valve;
Have
The determination unit, when hydrogen is detected by the hydrogen detector during the intermittent operation, measures the rate of increase in hydrogen concentration,
After the measurement of the rate of increase in the hydrogen concentration, the control unit closes the hydrogen exhaust drain valve and operates the hydrogen pump to send hydrogen,
When the hydrogen concentration detected by the hydrogen detector increases after the operation of the hydrogen pump, the determination unit determines that hydrogen is leaking from the hydrogen exhaust drain valve,
Fuel cell system.

  DESCRIPTION OF SYMBOLS 10 Fuel cell mounted vehicle, 12 Fuel cell stack, 20 Hydrogen tank, 24 Hydrogen detector, 26 Fuel cell system, 38 Circulation pipe, 40 Hydrogen pump, 44 Discharge pipe, 46 Hydrogen exhaust drain valve, 54 Control part, 62 Discrimination part .

Claims (4)

A fuel cell system mounted on a vehicle,
A hydrogen detector for detecting hydrogen installed above the hydrogen tank;
A discriminator for discriminating the origin of detected hydrogen based on detection of hydrogen by a hydrogen detector during intermittent operation of the fuel cell system;
A fuel cell system. The fuel cell system according to claim 1,
A hydrogen pump for circulating hydrogen;
A hydrogen exhaust drain valve for discharging spent fuel gas after the hydrogen reaction from the fuel cell stack;
A control unit that controls the operation of the hydrogen pump and the hydrogen exhaust drain valve;
Have
When the hydrogen is detected by the hydrogen detector during the intermittent operation, the control unit closes the hydrogen exhaust drain valve and operates the hydrogen pump to send hydrogen,
If the hydrogen concentration detected by the hydrogen detector does not increase after the hydrogen pump is operated, the determination unit leaks hydrogen from the hydrogen tank or a hydrogen supply system that sends hydrogen from the hydrogen tank to the fuel cell stack. To determine,
Fuel cell system. The fuel cell system according to claim 1,
A hydrogen pump for circulating hydrogen;
A hydrogen exhaust drain valve for discharging spent fuel gas after the hydrogen reaction from the fuel cell stack;
A control unit that controls the operation of the hydrogen pump and the hydrogen exhaust drain valve;
Have
When the hydrogen is detected by the hydrogen detector during the intermittent operation, the control unit closes the hydrogen exhaust drain valve and operates the hydrogen pump to send hydrogen,
The determination unit determines that hydrogen is leaking from the hydrogen exhaust drain valve when the concentration of hydrogen detected by the hydrogen detector increases after the operation of the hydrogen pump.
Fuel cell system.   2. The fuel cell system according to claim 1, wherein the determination unit is configured to supply hydrogen from a hydrogen tank or a hydrogen tank to a fuel cell stack when hydrogen is detected by the hydrogen detector during the intermittent operation. A fuel cell system that determines that hydrogen is leaking from the fuel cell system.

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