Fuel cell system and method of controlling the same

The fuel cell system performs prevention control for preventing an anode gas detector from erroneously detecting anode gas discharged from an exhaust port as leakage of anode gas from an anode gas flow path, when at least one of (i) a flow rate proportion, found by dividing a measured flow rate of cathode gas by an assumed flow rate of the cathode gas, is smaller than a predetermined flow rate proportion threshold, (ii) a pressure proportion, found by dividing a measured gas pressure by an assumed gas pressure, is larger than a predetermined pressure proportion threshold, and (iii) a voltage proportion, found by dividing a measured voltage of the fuel cell by an assumed voltage of the fuel cell, is smaller than a predetermined voltage proportion threshold, is satisfied. This prevents the anode gas detector from erroneous detection as leakage of anode gas.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese patent application 2018-048666 filed on Mar. 16, 2018, the content of which is hereby incorporated by reference into this application.

BACKGROUND

The present disclosure relates to a fuel cell system and a method of controlling the fuel system.

2. Related Art

As described in Japanese Patent Application Laid-open No. 2008-279955, there is proposed a fuel cell vehicle provided with an anode gas detector that detects leakage of anode gas used for a fuel cell. Moreover, in the fuel cell vehicle described in Japanese Patent Application Laid-open No. 2010-61960, anode exhaust gas containing liquid is discharged to an exhaust pipe from a gas-liquid separator provided in the anode gas circulation system, diluted with cathode gas, and then discharged to the outside of the vehicle after being.

Here, when the fuel cell vehicle travels on a flooded road, if a water surface has reached an exhaust port for discharging gas including anode gas, the gas discharged from the exhaust port may not be normally diffused to the outside of the vehicle. The inventors of the present application found that in such a case, gas including anode gas enters the inside of the vehicle through gaps of the vehicle and reaches an anode gas detector provided in the vehicle, which may cause the anode gas detector to erroneously detect it as leakage of anode gas from an anode gas flow path. Moreover, this is a problem not only in the fuel cell vehicle but in common to the fuel cell system.

SUMMARY

The present disclosure is made to solve the above-described problems, and may be achieved by the following forms.

(1) One form of the present disclosure provides a fuel cell system. The fuel cell system includes a fuel cell that generates power by electrochemical reaction between anode gas and cathode gas, an exhaust pipe that has an exhaust port for discharging exhaust gas including the cathode gas and the anode gas discharged from the fuel cell, a cathode gas supply flow path that supplies the cathode gas to the fuel cell, a compressor that is provided in the cathode gas supply flow path to feed the cathode gas to the fuel cell, an anode gas detector that is provided outside a flow path of the anode gas to detect the anode gas, and a control unit that performs, with a condition satisfied, prevention control for preventing the anode gas detector from detecting the anode gas as leakage of the anode gas. Here, the prevention control unit determines the condition when at least one of:

(i) a flow rate proportion found by dividing a measured flow rate that is a flow rate of cathode gas introduced by the compressor by an assumed flow rate of the cathode gas estimated on a basis of an outside air pressure and a rotation speed of the compressor, is smaller than a predetermined flow rate proportion threshold,

(ii) a pressure proportion found by dividing a measured gas pressure that is a pressure at a cathode gas inlet or a cathode gas outlet of the fuel cell by an assumed gas pressure estimated on the basis of the outside air pressure and the rotation speed of the compressor, is larger than a predetermined pressure proportion threshold, and

(iii) a voltage proportion found by dividing a measured voltage that is an outlet voltage of the fuel cell by an assumed voltage of the fuel cell estimated on the basis of a measured current that is an output current of the fuel cell and the rotation speed of the compressor, is smaller than a predetermined voltage proportion threshold,

is satisfied.

In the fuel cell system of this form, the prevention control is performed in a situation supposing that a water surface has reached the exhaust port, which prevents erroneous detection of anode gas discharged from the exhaust port as leakage of anode gas from the anode gas flow path.

The present disclosure may be achieved by various forms, and may be achieved by the form of a method of controlling a fuel cell system, for example.

DETAILED DESCRIPTION

A. First Embodiment

FIG. 1is a schematic view of a vehicle100with a fuel cell system according to an embodiment of the present disclosure. The description related to directions in the vehicle100(“right”, “left”, “front”, “rear”, “upper”, “lower”) indicates directions from a driver seated in the vehicle100. InFIG. 1, an X-axis positive direction directs the vehicle front side, a Y-axis positive direction directs the gravity upper side, and a Z-axis positive direction directs the vehicle right side. That is, the X-axis direction represents a vehicle front-rear direction, the Y-axis direction represents a gravity direction, and the Z-axis direction represents a vehicle width direction. The XYZ axes are also applied to the diagrams followingFIG. 1. Note that although the fuel cell system is provided in a vehicle in the embodiment, it may be provided in other moving bodies such as a ship, or a house, for example. Note that as anode gas, alcohol or hydrocarbon, for example, may be used instead of hydrogen gas.

The vehicle100includes a fuel cell stack (hereinafter, simply referred to as a “fuel cell”)10, an exhaust pipe38having an exhaust port75, an anode gas tank60, and an anode gas detector70. The fuel cell10is configured by laminated power generation modules including a membrane electrode assembly (MEA) in which both electrodes of an anode and a cathode are joined to both sides of an electrolyte membrane. The fuel cell10generates power by electrochemical reaction between hydrogen gas as anode gas supplied from the anode gas tank60and oxygen in the atmosphere as cathode gas. In the embodiment, the fuel cell10is arranged in the front side (+X axis direction side) of the vehicle100. To be more specific, in the front-rear direction (X-axis direction) of the vehicle100, the fuel cell10is arranged at a position partially overlapping a front wheel FW. Note that the number and arrangement of the fuel cell10may be set arbitrarily. For example, the fuel cell10may be provided under a floor of the vehicle100.

In the embodiment, the anode gas tank60of the vehicle100includes a first anode gas tank62, a second anode gas tank64, and a third anode gas tank66. In the embodiment, the first anode gas tank62is provided between the front wheel FW and a rear wheel RW in the front-rear direction (X-axis direction) of the vehicle100, and is provided along the front-rear direction (X-axis direction) of the vehicle100. The second anode gas tank64is provided at a position overlapping the rear wheel RW in the front-rear direction (X-axis direction) of the vehicle100, and is provided along the width direction (Z-direction) of the vehicle100. The third anode gas tank66is provided at a position where a part thereof overlaps the rear wheel RW and the remaining part thereof is on the rear side than the rear wheel RW, and is provided along the width direction (Z-direction) of the vehicle100. In the embodiment, the second anode gas tank64is provided on the front side (+X-axis direction side) of the vehicle100than the third anode gas tank66. Note that the number and arrangement of the anode gas tank60may be set arbitrarily.

The anode gas detector70is an apparatus that detects leakage of anode gas from an anode gas flow path. In the embodiment, when the anode gas detector70has determined leakage of anode gas, an electronic control unit (ECU)82described later forcedly stops a fuel cell system110. Moreover, in the embodiment, the anode gas detector70is an apparatus capable of also measuring concentration of anode gas. The anode gas detector70includes a first anode gas detector72and a second anode gas detector74. In the embodiment, a hydrogen detector is used as the anode gas detector70.

Generally, hydrogen tends to accumulate on the upper side of closed space. Thus, in the embodiment, the first anode gas detector72is provided on the upper side of the anode gas tank60to detect leakage of anode gas from the anode gas tank60. To be more specific, the first anode gas detector72is provided between the front wheel FW and the rear wheel RW in the front-rear direction (X-axis direction). More concretely, the first anode gas detector72is provided on the rear side than the center of the vehicle100and front side than the rear wheel RW in the front-rear direction (X-axis direction).

In the embodiment, the second anode gas detector74is provided on the upper side of the fuel cell10to detect leakage of anode gas from the fuel cell10. To be more specific, the second anode gas detector74is provided at a position overlapping the fuel cell10in the front-rear direction (X-axis direction). Note that the number and arrangement of the anode gas detectors70and the number and arrangement of the anode gas tank60may be set arbitrarily.

The exhaust pipe38is provided to discharge gas not used by the fuel cell10and water generated in the fuel cell10to the outside of the vehicle. The exhaust port75of the exhaust pipe38projects to the lower side of the vehicle100from a hole provided on an undercover77of the vehicle100. In the embodiment, the exhaust port75is provided between the front wheel FW and the rear wheel RW in the front-rear direction (X-axis direction). Note that the arrangement of the exhaust pipe38and the exhaust port75may be set arbitrarily.

FIG. 2is a schematic view illustrating a configuration of the fuel cell system110provided in the vehicle100. The fuel cell system110includes the fuel cell10, a cathode gas flow path20, an anode gas flow path30, an exhaust pipe38, and a control unit80.

The cathode gas flow path20is a flow path for supplying and discharging cathode gas to and from the fuel cell10. The cathode gas flow path20includes a cathode gas supply flow path22for supplying cathode gas to the fuel cell10, a cathode gas exhaust flow path24for discharging cathode gas from the fuel cell10, and a bypass flow path26connecting the cathode gas supply flow path22and the cathode gas exhaust flow path24.

In the cathode gas supply flow path22, there are provided, in the order from the upstream side, a barometer41, a flowmeter40, a compressor42, a supply valve44, and a pressure measuring unit45. The barometer41is an apparatus that measures an outside air pressure. The flowmeter40is an apparatus that measures a flow rate of cathode gas introduced by the fuel cell system110. The compressor42is an apparatus that compresses introduced cathode gas and feeds it to the fuel cell10. The supply valve44is a valve that controls the presence and absence of inflow of cathode gas to the fuel cell10from the compressor42, and is provided on the downstream side of the cathode gas supply flow path22than a connection portion with the bypass flow path26. The pressure measuring unit45is an apparatus that measures a pressure at a cathode gas inlet of the fuel cell10. In the embodiment, the pressure measuring unit45measures a pressure at a cathode gas inlet of the fuel cell10. However, the embodiment is not limited thereto, and the pressure measuring unit45may be provided in the cathode gas exhaust flow path24to measure a pressure at a cathode gas outlet of the fuel cell10, for example.

On the upstream side of the cathode gas exhaust flow path24than the connection portion with the bypass flow path26, there is provided a pressure regulating valve46that adjusts a pressure of cathode gas on the cathode outlet side of the fuel cell10. In the bypass flow path26, there is provided a bypass valve48that adjusts a flow rate of cathode gas in the bypass flow path26. In the embodiment, the bypass flow path26is a flow path connecting a portion between the compressor42and the supply valve44in the cathode gas supply flow path22and the downstream side than the pressure regulating valve46in the cathode gas exhaust flow path24.

The anode gas flow path30is a flow path for supplying and discharging anode gas to and from the fuel cell10. The anode gas flow path30includes an anode gas supply flow path32for supplying anode gas to the fuel cell10, an anode gas exhaust flow path34for discharging anode gas from the fuel cell10, and an anode gas circulation flow path36connecting the anode gas supply flow path32and the anode gas exhaust flow path34.

The anode gas supply flow path32is connected to the anode gas tank60. In the anode gas supply flow path32, there are provided, in the order from the upstream side, a switching valve52, a regulator54, and an injector56. The switching valve52is a valve that controls the presence and absence of inflow of anode gas to the upstream side of the injector56from the anode gas tank60. The regulator54is a valve that adjusts a pressure of anode gas on the upstream side of the injector56. The injector56is a valve that controls the inflow of anode gas to the fuel cell10. In the embodiment, the injector56is provided on the upstream side of the anode gas supply flow path32than a portion connected to the anode gas circulation flow path36.

The anode gas exhaust flow path34is connected to a gas-liquid separator58. The anode gas exhaust flow path34guides unreacted gas (anode gas, nitrogen gas, etc.) not used for electrochemical reaction in the fuel cell10to the gas-liquid separator58.

The gas-liquid separator58separates gas and liquid discharged from the anode of the fuel cell10. The gas-liquid separator58is connected to the anode gas circulation flow path36and the exhaust pipe38. The gas-liquid separator58guides unreacted anode gas not used for electrochemical reaction in the fuel cell10to the anode gas circulation flow path36, and liquid including water generated in the fuel cell10and nitrogen gas to the exhaust pipe38.

The exhaust pipe38is a pipe for discharging liquid and gas separated by the gas-liquid separator58to the outside of the fuel cell system110. In the exhaust pipe38, there are provided, in the order from the upstream side, an exhaust valve57that discharges gas and drains water and a silencer59that reduces noise during such discharge and drain. The exhaust port75is provided at a terminal end of the exhaust pipe38. There are discharged, from the exhaust port75, water generated in the vehicle100, nitrogen gas contained in anode exhaust gas, and cathode exhaust gas. In addition, a minute amount of anode gas (hydrogen gas) may be included. That is, the exhaust pipe38also discharges exhaust gas including anode gas and cathode gas.

In the embodiment, the cathode gas exhaust flow path24is connected to a portion between the exhaust valve57and the silencer59of the exhaust pipe38. In this manner, the cathode gas flow path20and the compressor42and the valves44,46,48provided in the cathode gas flow path20function as a “cathode gas supply unit” that supplies cathode gas to the exhaust pipe38.

In the anode gas circulation flow path36, a pump50is provided. The pump50feeds out gas including anode gas separated by the gas-liquid separator58to the anode gas supply flow path32. The fuel cell system110lets anode gas circulate and supplies it again to the fuel cell10, thus improving the anode gas utilization efficiency.

The control unit80is configured as a computer including a central processing unit (CPU), a memory, and an interface circuit to which the above-described parts are connected. In accordance with an order from the ECU82, the control unit80outputs signals for controlling activation and stop of the components in the fuel cell system110. The ECU82is a control unit that controls the whole vehicle100including the fuel cell system110. For example, in the vehicle100, the ECU82performs control of the vehicle100in accordance with values of a plurality of driving state parameters such as a stepping amount of an accelerator pedal, a stepping amount of a brake pedal, and a vehicle speed. Note that the ECU82may be included in a part of the functions of the control unit80. The CPU executes control programs stored in the memory to control power generation by the fuel cell system110and achieve inundation determination processing described later.

The DC/DC converter94increases an output voltage of the fuel cell10and supplies it to a PCU95. The generated power of the fuel cell10is supplied to a load such as a drive motor that drives wheels, and the compressor42, the pump50, and the various valves described above, through a power circuit including the PCU95. The PCU95restricts a current of the fuel cell10by the control of the control unit80. Note that between the fuel cell10and the DC/DC converter94, there are provided a current measuring unit91that measures a current of the fuel cell10and a voltage measuring unit92that measures a voltage of the fuel cell10.

FIG. 3is a diagram illustrating a flowchart of inundation determination processing performed by the control unit80. The inundation determination processing is constantly performed in a repeated manner during the operation of the vehicle100.

When the inundation determination processing has started, the control unit80first determines whether or not an exhaust port inundation condition is fulfilled. Here, the “exhaust port inundation condition” is a predetermined condition that is supposed to be satisfied in the state where a water surface has reached the exhaust port75. The exhaust port inundation condition includes the conditions 1, 2, and 3. In the embodiment, the control unit80determines that the exhaust port inundation condition is fulfilled if at least one of the conditions 1, 2, and 3 is satisfied. However, the control unit80may determine that the exhaust port inundation condition is fulfilled if two or more of the above-described conditions are fulfilled.

A flow rate proportion (%) found by dividing a measured flow rate of cathode gas measured by the flowmeter40by an assumed flow rate of cathode gas estimated on the basis of an outside air pressure and a rotation speed of the compressor42, is smaller than a predetermined flow rate proportion threshold.

A pressure proportion found by dividing a measured gas pressure measured by the pressure measuring unit45by an assumed gas pressure estimated on the basis of an outside air pressure and a rotation speed of the compressor42, is larger than a predetermined pressure proportion threshold.

A voltage proportion (%) found by dividing a measured voltage of the fuel cell10measured by the voltage measuring unit92by an assumed voltage of the fuel cell10estimated on the basis of a measured current of the fuel cell10measured by the current measuring unit91and a rotation speed of the compressor42, is smaller than a predetermined voltage proportion threshold.

FIG. 4is a diagram illustrating the relation between a pressure ratio and a flow rate of cathode gas [NL/minute] in relation to the above-described conditions 1 and 2. The pressure ratio is a value found by dividing an outlet pressure of the compressor42by an inlet pressure thereof. The inlet pressure may be considered to be equal to an outside air pressure. Each of a plurality of curved lines inFIG. 4is a line showing the relation between a pressure ratio and a flow rate at the same rotation speed of the compressor42. In the embodiment, a turbo compressor is used as the compressor42. Thus, even if cathode gas is fed to the fuel cell10at the same rotation speed, the flow rate of cathode gas considerably differs depending on a pressure ratio.

It is supposed that FA1is a flow rate of cathode gas in a case where the rotation speed of the compressor42is a rotation speed on a curved line RA and a water surface has not reached the exhaust port75. In such a case, when a water surface has reached the exhaust port75, cathode gas discharged from the exhaust port75is reduced, which increases a pressure in the fuel cell10and increases a pressure ratio illustrated inFIG. 4. As a result, even with the same outside air pressure and rotation speed of the compressor42, the flow rate of cathode gas becomes FA2smaller than FA1.

FIG. 5is a diagram for describing the condition 1. InFIG. 5, the vertical axis represents a flow rate proportion (%) of the condition 1, and the horizontal axis represents time. Generally, cathode gas having reached the exhaust port75is normally discharged from the exhaust port75. Thus, the flow rate of cathode gas measured by the flowmeter40is substantially equal to an assumed flow rate of cathode gas estimated on the basis of a rotation speed of the compressor42, and the flow rate proportion is substantially 100%. However, when a water surface has reached the exhaust port75, the flow rate of cathode gas measured by the flowmeter40is reduced relative to the assumed flow rate of cathode gas estimated on the basis of an outside air pressure and a rotation speed of the compressor42, and a flow rate proportion is also reduced. InFIG. 5, the flow rate proportion starts to be reduced from time t11, and becomes smaller than a predetermined flow rate proportion threshold at time t12. Thus, the condition 1 is fulfilled.

Here, the flow rate proportion threshold of the condition 1 in the embodiment is set to 85%. This flow rate proportion threshold may be defined experimentally. Note that the flow rate proportion threshold of the condition 1 is not limited thereto, and may be 90%, 80% or 75%, for example. Note that in the embodiment, a map showing the relation between a pressure ratio and a flow rate of cathode gas is stored in the control unit80, and the control unit80determines an assumed flow rate using the map. However, the embodiment is not limited thereto, and the control unit80may calculate an assumed flow rate on the basis of a pressure ratio and a rotation speed of the compressor42. Moreover, a rotation torque of the compressor42may be used instead of a rotation speed of the compressor42.

The condition 2 uses the same principle as the above-described condition 1. That is, the condition 2 also uses the principle in which when a water surface has reached the exhaust port75, cathode gas having reached the exhaust port75is not normally discharged from the exhaust port75, thereby increasing a pressure in the fuel cell10. On the basis of this principle, if a value found by dividing a measured gas pressure measured by the pressure measuring unit45by an assumed gas pressure estimated on the basis of an outside air pressure and a rotation speed of the compressor42is larger than a predetermined pressure proportion threshold (e.g., 120%), the condition 2 is fulfilled.

The pressure proportion threshold of the condition 2 is not limited thereto, and may be 115%, 110%, or 105%, for example. Note that in the embodiment, a map showing the relation between a pressure ratio and a flow rate of cathode gas is stored in the control unit80, and the control unit80determines an assumed gas pressure using the map. However, the embodiment is not limited thereto, and the control unit80may calculate an assumed gas pressure on the basis of a pressure ratio and a rotation speed of the compressor42.

FIG. 6is a diagram illustrating the relation between a voltage and a current of the fuel cell10, in relation to the above-described condition 3. The solid line shows a case where a water surface has not reached the exhaust port75, and the broken line shows a case where a water surface has reached the exhaust port75. If a water surface has reached the exhaust port75, a pressure of the outlet of the fuel cell10is increased and cathode gas supplied to the fuel cell10is reduced. Thus, as compared with a case where a water surface has not reached the exhaust port75, a voltage value relative to the same current value tends to be reduced.

It is supposed that VA1is a voltage of the fuel cell10in a case where a water surface has not reached the exhaust port75. In this case, when a water surface has reached the exhaust port75, cathode gas in the fuel cell10is not normally discharged even with the same current value. Thus, the voltage of the fuel cell10becomes VA2smaller than VA1.

FIG. 7is a diagram for describing the condition 3. InFIG. 7, the vertical axis represents a voltage proportion (%), and the horizontal axis represents time. Generally, cathode gas having reached the exhaust port75is normally discharged from the exhaust port75. Thus, the measured voltage of the fuel cell10is substantially equal to an assumed voltage of the fuel cell10estimated on the basis of a measured current of the fuel cell10and a rotation speed of the compressor42, and the voltage proportion is substantially 100%. However, when a water surface has reached the exhaust port75, a measured voltage of the fuel cell10is reduced relative to an assumed voltage of the fuel cell10estimated on the basis of a measured current of the fuel cell10and a rotation speed of the compressor42, and the voltage proportion is also reduced. InFIG. 7, the voltage proportion starts to be reduced from time t21, and becomes smaller than a predetermined voltage proportion threshold at time t22. Thus, the condition 3 is fulfilled.

Here, the voltage proportion threshold in the condition 3 is 85%, for example. The voltage proportion threshold may be defined experimentally. Note that the voltage proportion threshold of the condition 3 is not limited thereto, and may be 90%, 80% or 75%, for example. Note that in the embodiment, a map showing the relation between a voltage and a current of the fuel cell10in accordance with a rotation speed of the compressor42is stored in the control unit80, and the control unit80determines an assumed voltage using the map. However, the embodiment is not limited thereto, and the control unit80may calculate an assumed voltage on the basis of a rotation speed of the compressor42and a measured current of the fuel cell10. Moreover, in the embodiment, the voltage of the fuel cell10is used in the condition 3. However, instead of the voltage of the fuel cell10, there may be used a generated power of the fuel cell10that is a product of a voltage and a current of the fuel cell10. From the viewpoint of accuracy, it may be preferable to use generated power in some instances.

As illustrated inFIG. 3, when the control unit80has determined that the exhaust port inundation condition is not fulfilled (No at Step S110), the flow returns to Step S110. Meanwhile, when the control unit80has determined that the exhaust port inundation condition is fulfilled (Yes at Step S110), the control unit80performs prevention control (Step S130). The “prevention control” is a control for preventing the anode gas detector70from erroneously detecting anode gas discharged from the exhaust port75as leakage of anode gas from the anode gas flow path30.

In the embodiment, the control unit80performs gas amount increase control as prevention control. Here, the “gas amount increase control” is a control for increasing a supply flow rate of cathode gas to the exhaust pipe38, as compared with a case where the prevention control is not performed. In the embodiment, the rotation speed of the compressor42as a cathode gas supply unit is increased to increase a supply amount of cathode gas to the exhaust pipe38. In the embodiment, the prevention control is performed for one minute. However, the embodiment is not limited thereto, and the prevention control may be performed until the exhaust port inundation condition is not fulfilled any more or until a flow rate proportion, a voltage proportion, or a pressure proportion is improved (e.g., until such a proportion becomes 100%), for example. After the prevention control is performed, the flow returns to Step S110. The control unit80repeats the above-described sequence of processing until the operation of the vehicle100is finished.

FIG. 8is a diagram illustrating the state in which a water surface S has reached the exhaust port75. Generally, gas discharged from the exhaust port75is diffused to the atmosphere. Meanwhile, if the water surface S has reached the exhaust port75, the water prevents diffusion of gas discharged from the exhaust port75, which may allow the discharged gas to enter the inside of the vehicle100through a gap between the exhaust port75and the undercover77of the vehicle100and other gaps. As a result, the anode gas detector70provided in the vehicle100may erroneously detect anode gas contained in the discharged gas as leakage of anode gas from the anode gas flow path30. Consequently, the ECU82may request the control unit80to stop the operation of the fuel cell system110.

However, in the embodiment, the prevention control is performed if the above-described exhaust port inundation condition is fulfilled. Thus, it is possible to prevent the anode gas detector70from erroneously detecting leakage of anode gas from the anode gas flow path30. In the embodiment, the gas amount increase control for increasing a supply amount of cathode gas to the exhaust port75is performed as the prevention control. As a result, the amount of anode gas relative to the entire amount of gas discharged from the exhaust port75is diluted relatively, which prevents detection by the anode gas detector70even if the discharged gas enters the inside of the vehicle100. Especially, in the embodiment, the exhaust port75is provided between the first anode gas detector72and the second anode gas detector74in the travelling direction (+X-axis direction) of the vehicle100. Thus, gas having entered the inside of the vehicle100may reach the first anode gas detector72and the second anode gas detector74. However, in the embodiment, the prevention control effectively prevents the anode gas detector70from erroneously detecting leakage of anode gas. Note that the embodiment exerts the same effects not only in a case where a water surface has reached the exhaust port75but also in a case where snow on a road has reached the exhaust port75.

B. Second Embodiment

FIG. 9is a diagram illustrating a flowchart of inundation determination processing according to the second embodiment. The second embodiment is different from the first embodiment in the aspect that Step S120is arranged between Step S110and Step S130, and is same as the first embodiment in the other aspects.

In the second embodiment, when the control unit80has determined that the exhaust port inundation condition is fulfilled (Yes at Step S110), the control unit80determines whether or not the predetermined time tA or longer has elapsed since the exhaust valve57is closed (Step S120). In the embodiment, the time tA is five seconds. However, the embodiment is not limited thereto, and it may be three seconds or ten seconds, for example.

When the control unit80has determined that the predetermined time tA or longer has not elapsed since the exhaust valve57is closed (No at Step S120), the control unit80performs prevention control (Step S130). Meanwhile, when the control unit80has determined that the predetermined time tA or longer has elapsed since the exhaust valve57is closed (Yes at Step S120), the flow returns to Step S110. That is, in the second embodiment, when the control unit80has determined that the predetermined time tA or longer has elapsed since the exhaust valve57is closed, the control unit80does not perform prevention control.

In this manner, in the second embodiment, the prevention control is not performed in a case where the fulfillment of the exhaust port inundation condition is not supposedly due to the opening of the exhaust valve57. That is, the prevention control is not performed in the situation supposing that the leakage of anode gas from the anode gas flow path30and the like actually occurs. Therefore, in the second embodiment, it is possible to securely detect leakage of anode gas from the anode gas flow path30and the like. Note that in the embodiment, Step S120is performed between Step S110and Step S130. However, the embodiment is not limited thereto, and Step S120may be performed before Step S110.

The third embodiment is different from the first embodiment in the method of cathode gas flow rate increase control, and is same as the first embodiment in the other aspects. In the third embodiment, the control unit80performs bypass flow rate increase control as the cathode gas flow rate increase control. Here, the “bypass flow rate increase control” is a control for increasing a flow rate of cathode gas in the bypass flow path26, as compared with a case where the prevention control is not performed.

To be more specific, as the bypass flow rate increase control, the control unit80controls at least one of the compressor42, the supply valve44, the pressure regulating valve46, and the bypass valve48to increase a flow rate of cathode gas in the bypass flow path26, as compared with a case where the exhaust port inundation condition is not fulfilled. In the embodiment, the control unit80opens the bypass valve48while the compressor42is operated to increase a flow rate of cathode gas in the bypass flow path26. However, the embodiment is not limited thereto. For example, the control unit80may control the supply valve44and the bypass valve48and increases an amount of cathode gas passing the bypass flow path26to increase a supply amount of cathode gas to the exhaust port75.

In a case where cathode gas passes the bypass flow path26, a pressure loss is smaller than a case where cathode gas passes the fuel cell10. Thus, in the third embodiment, a flow rate of cathode gas passing the bypass flow path26and reaching the exhaust port75is increased, which makes it possible to reduce a load of the compressor42, prevent drying of the fuel cell10, and improve the fuel efficiency, as compared with a case where a flow rate of cathode gas passing the fuel cell10and reaching the exhaust port75is increased.

FIG. 10is a diagram illustrating a flowchart of inundation determination processing according to the fourth embodiment. The fourth embodiment is different from the first embodiment in the aspect that Step S125is arranged between Step S110and Step S130, and is same as the first embodiment in the other aspects.

In the fourth embodiment, when the control unit80has determined that the exhaust port inundation condition is fulfilled (Yes at Step S110), the control unit80determines whether or not a measured gas pressure measured by the pressure measuring unit45is equal to or larger than a predetermined pressure threshold (Step S125). In the embodiment, the above-described pressure threshold is a pressure at which a flow rate of cathode gas at the cathode gas inlet of the fuel cell10is 1000 NL/minute. However, the embodiment is not limited thereto, and the above-described pressure threshold may be a pressure at which a flow rate of cathode gas at the cathode gas inlet of the fuel cell10is 700 NL/minute or 1500 NL/minute, for example.

When the control unit80has determined that the measured gas pressure is not equal to or larger than the predetermined pressure threshold (No at Step S125), the control unit80performs prevention control (Step S130). Meanwhile, when the control unit80has determined that the measured gas pressure is equal to or larger than the predetermined pressure threshold (Yes at Step S125), it is considered that the anode gas discharged from the exhaust port75is sufficiently diluted by cathode gas discharged from the fuel cell10. Thus, the flow returns to Step S110.

In this manner, in the fourth embodiment, unnecessary prevention control does not need to be performed. Note that in the embodiment, Step S125is performed between Step S110and Step S130. However, the embodiment is not limited thereto, and Step S125may be performed before Step S110.

The fifth embodiment is different from the first embodiment in the aspect that easing control is performed as the prevention control, and is same as the first embodiment in the other aspects. The “easing control” is a control for easing a detection criterion for the anode gas detector70to detect leakage of anode gas within a regulation range. Here, the detection criterion of the embodiment is satisfied when an average concentration of anode gas in a detection period (e.g., two seconds) exceeds an average concentration threshold (e.g., 3%), so that the anode gas detector70detects leakage of anode gas. The regulation range is a range in which an anode gas average concentration in an arbitrary three seconds is smaller than 4%.

FIG. 11is a diagram illustrating the transition of concentration of anode gas in a case where gas discharged from the exhaust port75enters the inside of the vehicle100. InFIG. 11, the horizontal axis represents time, and the vertical axis represents, from the upper side, opening and closing of the exhaust valve57, the concentration of anode gas, and the average concentration of anode gas. As illustrated inFIG. 11, if gas discharged from the exhaust port75has entered the inside of the vehicle100, the concentration of anode gas measured by the anode gas detector70increases when the exhaust valve57is opened and reduces when the exhaust valve57is closed. Moreover, similarly to the increase and decrease of anode gas concentration, the average concentration in a detection period also increases and decreases. The solid line L1illustrated inFIG. 11shows an average concentration L1in a detection period.

In the embodiment, the average concentration threshold is set to a first concentration C1(e.g., 3%) in a case where the exhaust port inundation condition is not fulfilled, and to a second concentration C2(e.g., 4%) in a case where the exhaust port inundation condition is fulfilled. In the embodiment, the detection criterion is eased within a regulation range in such a manner, which makes it possible to prevent the anode gas detector70from erroneously detecting leakage of anode gas even if gas discharged from the exhaust port75has entered the inside of the vehicle100.

The easing control is not limited thereto, and the detection period may be eased. To be more specific, the detection period may be set to a first period P1(e.g., two seconds) in a case where the exhaust port inundation condition is not fulfilled, and to a second period P2(e.g., three seconds) longer than the first period P1in a case where the exhaust port inundation condition is fulfilled. InFIG. 11, the solid line L1shows an average concentration in the first period P1, and the broken line L2shows an average concentration in the second period P2. In such a manner, a peak of the average concentration becomes lower. Thus, even if gas discharged from the exhaust port75has entered the inside of the vehicle100, it is possible to prevent the anode gas detector70from detecting it as leakage of anode gas. Note that easing by the detection period may be used with easing by the average concentration threshold.

The sixth embodiment is different from the first embodiment in the aspect that the prevention control is not performed in a case of predetermined condition, and is same as the first embodiment in the other aspects. To be more specific, in the sixth embodiment, if an increase width of concentration of anode gas detected by the anode gas detector70is equal to or larger than a predetermined allowed range, the control unit80does not perform prevention control.

FIG. 12is a diagram illustrating the transition of concentration of anode gas in a case where leakage of anode gas occurs. The vertical axis represents concentration of anode gas, and the horizontal axis represents time. As illustrated inFIG. 12, when anode gas leaks from the anode gas tank60or the fuel cell10, the anode gas concentration continues to increase.

In the embodiment, if an increase width ΔR of anode gas concentration in a predetermined period ΔT (e.g., ten seconds) is equal to or larger than a predetermined allowed range, the control unit80does not perform prevention control. The allowed range may be set to 3%, for example. In this manner, in the embodiment, the prevention control is not performed in a situation supposing that the leakage of anode gas from the anode gas flow path30and the like actually occurs. Therefore, it is possible to securely detect leakage of anode gas from the anode gas flow path30and the like.

G. Other Embodiments

(1) In the above-described first embodiment, the control unit80performs prevention control when the flow rate proportion (%) is determined to be equal to or smaller than a flow rate proportion threshold. However, the embodiment is not limited thereto. For example, the control unit80may not perform prevention control when the flow rate proportion (%) is determined to be equal to or smaller than a lower limit threshold that is smaller than a flow rate proportion threshold.

FIG. 13is a diagram for describing a lower limit threshold. As illustrated inFIG. 13, if the flow rate proportion becomes equal to or smaller than a lower limit threshold (e.g., 70%) (after time t14), it is assumed that a pressure loss is high not because inundation to the exhaust port75occurs but because the pipe in which cathode gas flows is blocked partially. Therefore, in this manner, unnecessary control does not need to be performed.

(2) In the fuel cell system of the above-described form, the prevention control may include gas amount increase control for increasing a supply flow rate of the cathode gas to the exhaust pipe, as compared with a case where the prevention control is not performed. In the fuel cell system of this form, the prevention control sufficiently dilutes an anode gas amount in gas discharged from the exhaust port. As a result, it is possible to prevent the anode gas detector from erroneously detecting leakage of anode gas.

(3) The fuel cell system of the above-described form includes a cathode gas supply unit that includes the compressor and the cathode gas supply flow path and supplies the cathode gas to the exhaust pipe, the cathode gas supply unit further including a cathode gas exhaust flow path that discharges the cathode gas from the fuel cell and is connected to the exhaust pipe, a bypass flow path that connects the cathode gas supply flow path and the cathode gas exhaust flow path, a supply valve that is provided on the downstream side of the cathode gas supply flow path than a connection portion with the bypass flow path, a pressure regulating valve that is provided on the upstream side of the cathode gas exhaust flow path than a connection portion with the bypass flow path, and a bypass valve that is provided in the bypass flow path, in which the control unit may control the cathode gas supply unit and perform, as the prevention control, bypass flow rate increase control for increasing a flow rate of the cathode gas in the bypass flow path, as compared with a case where the prevention control is not performed. In the fuel cell system of this form, a flow rate of cathode gas passing the bypass flow path and reaching the exhaust port is increased, which makes it possible to reduce a load of the compressor, prevent drying of the fuel cell, and improve the fuel efficiency, as compared with a case where a flow rate of cathode gas passing the fuel cell and reaching the exhaust port is increased.

(4) In the fuel cell system of the above-described form, the control unit may not perform the bypass flow rate increase control if the measured gas pressure is equal to or larger than a predetermined pressure threshold. The fuel cell system of this form improves the fuel efficiency.

(5) The fuel cell system of the above-described form further includes an exhaust valve provided in the exhaust pipe, in which the control unit may not perform the prevention control if elapsed time since the exhaust valve is closed is equal to or longer than predetermined time, even if the given condition is satisfied. In the fuel cell system of this form, unnecessary control does not need to be performed.

(6) In the fuel cell system of the above-described form, the prevention control may include easing control for easing a detection criterion for the anode gas detector to detect leakage of anode gas within a regulation range, as compared with a case where the prevention control is not performed. In the fuel cell system of this form, the easing control is performed in a situation supposing that a water surface has reached an exhaust port, which prevents erroneous detection of anode gas discharged from the exhaust port as leakage of anode gas from an anode gas flow path.

(7) In the fuel cell system of the above-described form, the control unit may not perform the prevention control if an increase width of concentration of the anode gas detected by the anode gas detector is equal to or larger than a predetermined allowed range. In the fuel cell system of the above-described form, the prevention control is not performed in a situation supposing that the leakage of anode gas actually occurs. Therefore, it is possible to securely detect leakage of anode gas.

The present disclosure is not limited to the above-described embodiments, and may be achieved by various configurations without departing from the scope of the disclosure. For example, the technical features in the embodiments corresponding to the technical features of each form in SUMMARY may be appropriately replaced or combined in order to solve a part or all of the above-described problems or achieve a part or all of the above-described effects. Moreover, unless the technical features are explained as necessary in the specification, they may be deleted appropriately.