Fuel cell system and method for controlling water discharge for the system

Abstract

A fuel cell system (1) comprising: a fuel cell (2); a water discharge channel (25) through which water content discharged from said fuel cell (2) flows; and a water discharge valve (31) that discharges the water content in said water discharge channel (25) out of the system, the fuel cell system (1) further comprising: water discharge control means for controlling said water discharge valve (31) so as to prevent discharge of water from said water discharge valve (31) from a time when starting of the system is requested until a time when the temperature of the system reaches a predetermined temperature, in a case where starting of the system is requested under conditions where an outside air temperature is below a predetermined threshold.

Description

Technical FieldThe present invention relates to a fuel cell system and a method for controlling water discharge for the system.Prior ArtHeretofore, a fuel cell system including a fuel cell that receives supply of a reactive gas (a fuel gas and an oxidizing gas) to generate a current has been proposed and put into practice. In the fuel cell of such a fuel cell system and a circulation channel for the fuel off gas, impurity gas such as nitrogen or carbon monoxide generated during power generation and water content accumulate over time. In order to discharge such a gas and such a content of water from the system, a technology (a purification technology) is proposed in which the circulation channel (or a discharge channel connected to this circulation channel) is provided with a gas discharge valve and a water discharge valve, and these gas and water discharge valves are controlled in their opening and closing, whereby the accumulated gas and the accumulated content of water are discharged after a predetermined period of time, respectively.At present, a technology is also proposed in which a purge valve for performing gas / water discharge is controlled in terms of opening and closing at low temperatures, thereby improving the starting performance of the fuel cell system at low temperatures. For example, JP 2004-178 901A proposes a technology in which an ignition switch is turned on at low temperatures and then the cleaning valve is opened once to perform the cleaning operation. Subsequently, the cleaning operation in a process of temperature increase is prohibited until the fuel cell is warmed up, thereby suppressing a temperature drop of the fuel cell due to the supply of a new hydrogen gas. A fuel cell system in which, after the fuel cell system has stopped, the probability is determined that the water located in the system is freezing and, if appropriate, appropriate countermeasures, such as, for example, the activation of a heating device for heating up a water tank, are initiated in order to counteract the freezing, is the subject matter of US 2005 / 0 255 351 A1. Finally, JP 2006-134 771 A discloses that when the water in a discharge system is frozen during the stop of the fuel cell system, an opening timing for the discharge valve is adjusted accordingly until dewing of the frozen water occurs so that the thawed water can be discharged.Disclosure of the InventionHowever, in a case where the technology described in JP 2004-178 901 A is used, an ignition switch is turned on and then cleaning is performed once, so that a content of water flows into a cleaning valve whose temperature is lowered at low temperatures, and the content of water that has flowed into this valve may freeze. In a case where the content of water flown into the cleaning valve freezes in this manner, it is considered that the cleaning valve closes and it becomes difficult to perform the subsequent cleaning operation.The present invention has been developed in view of such a situation, and an object thereof is to prevent freezing of a water discharge valve at low temperatures in a fuel cell system equipped with the water discharge valve.To achieve the object, a fuel cell system according to the present invention includes: a fuel cell; a water discharge passage through which a content of water discharged from this fuel cell flows; and a water discharge valve that discharges the content of water into this water discharge passage from the system, the fuel cell system further including: water discharge control means for controlling the water discharge valve so as to prevent the discharge of the water from the water discharge valve from a time point when the start of the system is requested to a time point when the temperature of the system reaches a predetermined temperature in a case where the start of the system is requested under conditions where an outside air temperature is below a predetermined threshold.Further, a water discharge control method according to the present invention is a water discharge control method of a fuel cell system including a fuel cell, a water discharge passage through which a content of water discharged from this fuel cell flows, and a water discharge valve that discharges the content of water into this water discharge passage from the system, the water discharge control method comprising: a first step of judging whether or not start-up of the system has been requested; a second step of judging whether or not an outside air temperature is below a set threshold; and a third step of preventing water discharge from the water discharge valve from a time when the start of the system is requested to a time when the temperature of the system reaches a set temperature, in a case where it is judged in the first step that the start of the system is requested and it is judged in the second step that the outside air temperature is below a set threshold value.In a case where such an arrangement and method are used, the content of water in the discharge passage can be prevented from flowing into the water discharge valve from the time when the startup of the system is requested under conditions (e.g., low temperatures below the freezing point) where the outside air temperature is below the set threshold until the temperature of the system reaches the set temperature. Therefore, even at low temperatures, freezing of the water discharge valve (and closing of the water discharge valve due to freezing) can be prevented. Here, the "request for starting the system" denotes information (e.g., the ON signal of an ignition switch) for starting the fuel cell system with a state of operation stop. Further, the "temperature of the system" denotes the average temperature of the entire fuel cell system or the temperature (e.g., the temperature in the water discharge passage) of a certain arrangement in the fuel cell system.In the fuel cell system, the water discharge control means may be used that controls the water discharge valve to allow discharge of water from the water discharge valve in a case where the amount of heat of water received in the water discharge valve exceeds a predetermined amount of heat. Further, as the "set amount of heat", a zero-degree-to-be-broken amount of heat (the amount of heat required for the water discharge valve and the water discharge passage to exceed zero degrees Celsius under conditions where the outside air temperature is zero degrees Celsius or less) may be used.In a case where such an arrangement is used, the amount of heat of the absorbed water exceeds the set amount of heat even when the water is absorbed in the water discharge valve, and the discharge of water from the water discharge valve can then be permitted. Therefore, it is possible to solve the problem that water in the water discharge valve or the water discharge passage freezes and that the discharge of water is stopped (for example, in a case where a gas / water discharge valve is used for simultaneously performing the discharge of gas and water, any substance that does not contribute to power generation, for example, nitrogen is not discharged from the water discharge passage or the like).Further, the gas / water discharge valve that performs both the discharge of water and the discharge of gas can be used as the water discharge valve in the fuel cell system. In such a case, the system may be provided with fuel supply control means for adjusting the amount of a fuel gas to be supplied to and / or circulated through the fuel cell to an amount larger than a predetermined amount while preventing discharge of water from the gas / water discharge valve by the water discharge control means.While preventing the discharge of gas or water from the gas / water discharge valve, the amount of the fuel gas to be supplied to and / or circulated through the fuel cell in a case where such an arrangement is used may be set to the amount larger than the set amount (e.g., the amount of the fuel gas to be supplied and / or circulated during ordinary starting when the discharge of gas or water is not prevented). Therefore, lowering of the concentration of a fuel to be supplied to the fuel cell due to the prevention of the gas and water discharge can be prevented.The fuel cell system may further include a supply passage that supplies the fuel gas supplied from a fuel supply source to the fuel cell, and a variable gas supply device that adjusts a gas state on the upstream side of the supply passage to supply the gas to a downstream side. In such a case, the fuel supply control means may be used to control the variable gas supply device so that the amount of the fuel gas to be supplied to the fuel cell is set to the amount larger than the predetermined amount to be supplied while preventing the discharge of water from the water discharge valve by the water discharge control means.While preventing the discharge of gas or water from the gas / water discharge valve, in a case where such an arrangement is used, the variable gas supply means may be controlled so that the amount of the fuel gas to be supplied to the fuel cell is set to the amount larger than the set supply amount (e.g., the amount to be supplied during the usual starting when the discharge of gas or water is not prevented). It is to be noted that the "gas state" is a gas state represented by a flow rate, a pressure, a temperature, a molecular concentration, or the like, and particularly includes at least one of the flow rate of the gas and the gas pressure. As a variable gas supply device, for example, an injection valve may be used.Further, the fuel cell system may further include a supply channel that supplies the fuel gas supplied from a fuel supply source to the fuel cell, a circulation channel that corresponds to the water discharge channel and circulates a fuel off gas discharged from the fuel cell through the supply channel, and a circulation pump that forcibly circulates the gas in the circulation channel through the supply channel. In such a case, fuel supply control means for setting the amount of the fuel gas to be circulated by the fuel cell to an amount larger than a predetermined amount to be circulated while preventing the discharge of water from the gas / water discharge valve by the water discharge control means may be used.According to such an arrangement, while preventing the discharge of gas or water from the gas / water discharge valve, the circulation pump may be controlled so that the amount of the fuel gas to be circulated by the fuel cell is set to the amount larger than the set amount to be circulated (e.g., the amount to be circulated during the usual starting when the discharge of gas or water is not prevented).According to the present invention, in the fuel cell system equipped with the water discharge valve, it is possible to prevent freezing of the water discharge valve or the water discharge passage at low temperatures below the freezing point or the like.Brief Description of the FiguresFIG. 1 is an arrangement diagram of a fuel cell system according to an embodiment of the present invention; FIG. 2 is a control block diagram showing the arrangement of control of a control portion in the fuel cell system shown in FIG. 1 ; FIG. 3 is a flowchart showing a method of controlling cleaning (a method of controlling water discharge according to the embodiment of the present invention) during startup of the fuel cell system shown in FIG. 1 ; and FIG. 4 is an arrangement diagram showing a modification of the fuel cell system shown in FIG. 1.BEST MODE FOR CARRYING OUT THE INVENTIONReferring to the figures, a fuel cell system 1 in an embodiment according to the present invention will be described below. In the present embodiment, an example in which the present invention is applied to a vehicle-mounted power generation system of a vehicle having a fuel cell will be described.First, the arrangement of the fuel cell system 1 according to the embodiment of the present invention will be described with reference to FIG. 1. As shown in FIG. 1, the fuel cell system 1 according to the present embodiment includes a fuel cell 2 that receives supply of a reactive gas (an oxidizing gas and a fuel gas) to generate power; an oxidizing gas piping 3 that supplies air as an oxidizing gas to the fuel cell 2; a fuel gas piping 4 that supplies hydrogen gas as a fuel gas to the fuel cell 2; a coolant piping 5 that supplies a coolant to the fuel cell 2 to cool the fuel cell 2; a power supply system 6 that supplies power to the system or discharges power from the system; and a control section 7 that generally controls the entire system.The fuel cell 2 has a stack structure that is constructed of, for example, a solid polymer electrolyte type and in which many unit cells are laminated. On one surface of an electrolyte made of an ion exchange film, the unit cell of the fuel cell 2 has an air electrode, on the other surface a fuel electrode, and further a pair of separators to hold the air electrode and the fuel electrode on opposite sides. The fuel gas is supplied to the fuel gas passage of one separator, and the oxidizing gas is supplied to the oxidizing gas passage of the other separator. These gases are supplied, whereby the fuel cell 2 generates power. A current sensor 2 athat detects a current during power generation is attached to the fuel cell 2.The oxidizing gas piping 3 includes an air supply passage 11 through which the oxidizing gas to be supplied to the fuel cell 2 flows, and a gas discharge passage 12 through which an oxidizing gas exhaust gas discharged from the fuel cell 2 flows. The air supply passage 11 is equipped with a compressor 14 that receives the oxidizing gas via a filter 13, and a humidifier 15 that wets the oxidizing gas supplied under pressure by the compressor 14. The oxidizing gas exhaust gas flowing through the gas discharge passage 12 passes through a ram pressure adjusting valve 16, is used for exchanging the water content in the humidifier 15, and is finally discharged as exhaust gas into the atmosphere outside the system. To take in the oxidizing gas from the atmosphere, the compressor 14 is controlled by a motor (not shown).The piping system 4 for the fuel gas includes a hydrogen supply source 21; a hydrogen supply passage 22 through which the hydrogen gas to be supplied from the hydrogen supply source 21 to the fuel cell 2 flows; a circulation passage 23 for returning a hydrogen off-gas discharged from the fuel cell 2 to a joint A 1 of the hydrogen supply passage 22; a hydrogen pump 24 supplying the hydrogen off-gas under pressure in the circulation passage 23 to the hydrogen supply passage 22; and a branched gas / water discharge passage 25 connected to the circulation passage 23.The hydrogen supply source 21 corresponds to a fuel supply source according to the present invention, is composed of, for example, a high-pressure container, a hydrogen occlusion alloy, or the like, and may be configured to receive hydrogen gas at, for example, 35 MPa or 70 MPa. When a shut-off valve 26 described later is opened, the hydrogen gas from the hydrogen supply source 21 flows into the hydrogen supply passage 22, and by means of a regulator 27 and an injection valve 28 described later, the pressure of the hydrogen gas is finally reduced to, for example, about 200 kPa, and the gas is supplied to the fuel cell 2. It is to be noted that the hydrogen supply source 21 may be constructed of a reformer which forms a hydrogen-rich reformed gas from a hydrocarbon-based fuel and a high-pressure gas container which brings the reformed gas formed by this reformer into a high-pressure state to increase the pressure. Alternatively, a container containing the hydrogen occlusion alloy may be used as the source 21 for fuel supply.The hydrogen supply passage 22 is equipped with the shut-off valve 26 that closes or permits supply of the hydrogen gas from the hydrogen supply source 21, the regulator 27 that adjusts the pressure of the hydrogen gas, and the injection valve 28. On the downstream side of the injection valve 28 and on the upstream side of the joint A 1 of the hydrogen supply passage 22 and the circulation passage 23, a pressure sensor 29 that detects the pressure of the hydrogen gas in the hydrogen supply passage 22 is provided. Further, on the upstream side of the injection valve 28, a pressure sensor and a temperature sensor (not shown) that detect the pressure and temperature of the hydrogen gas in the hydrogen supply passage 22 are provided.The regulator 27 is a device that sets the upstream pressure (the primary pressure) of the regulator to a preset secondary pressure. In the present embodiment, a mechanical pressure reducing valve that reduces the primary pressure is employed as the regulator 27. As the arrangement of the mechanical pressure reducing valve, a known arrangement may be used which comprises a casing provided with a back pressure chamber and a pressure compensation chamber formed via a diaphragm, and in which the primary pressure is reduced to a predetermined pressure due to the back pressure of the back pressure chamber to form the secondary pressure in the pressure compensation chamber. As shown in FIG. 1, in the present embodiment, two regulators 27 are disposed on the upstream side of the injection valve 28, whereby the upstream pressure of the injection valve 28 can be effectively reduced. Therefore, the degree of freedom in design of the mechanical structure (a valve body, a housing, a passage, a controller, and the like) of the injection valve 28 can be increased. Further, the upstream pressure of the injection valve 28 can be reduced, so that the valve body of the injection valve 28 can be prevented from easily moving due to the increase of a pressure difference between the upstream pressure of the injection valve 28 and the downstream pressure thereof. Therefore, the range of variable pressure setting of the downstream pressure of the injector 28 can be widened, and decrease in responsiveness of the injector 28 can be prevented. The regulator 27 adjusts the gas state (gas pressure) on the upstream side of the hydrogen supply passage 22 to supply the gas to a downstream side, and corresponds to a variable gas supply device according to the present invention.The injection valve 28 is an electromagnetic driving type opening / closing valve in which the valve body is directly driven by an electromagnetic driving force and is disposed away from a valve seat in a predetermined driving stroke, whereby a flow speed of the gas or a gas pressure can be adjusted. The injection valve 28 includes the valve seat having an injection hole that injects a gaseous fuel such as hydrogen gas, and also includes a nozzle body that supplies and guides the gaseous fuel to the injection hole and the valve body movably received and held in an axial direction (a flow direction of the gas) with respect to this nozzle body for opening and closing the injection hole. In the present embodiment, the valve body of the injection valve 28 is driven by a magnet which is an electromagnetic driving device, and an in-pulse excitation current supplied to this magnet may be turned on or off to switch the opening area of the injection hole in two or more stages. The duration and timing of injection of the gas by the injection valve 28 are controlled based on a control signal output from the control section 7, whereby the flow rate and pressure of the hydrogen gas are accurately controlled. In the injection valve 28, the valve (the valve body and the valve seat) is directly driven by the electromagnetic driving force to open or close, and the driving stroke of the valve can be controlled in a high-responsiveness range so that the injection valve exhibits high responsiveness.In the injection valve 28, in order to supply the gas to the downstream side of the injection valve at a required flow rate, at least one of the opening area (degree of opening) and the opening duration of the valve body provided in the gas passage of the injection valve 28 is changed, thereby adjusting the flow rate (or the molecular concentration of hydrogen) of the gas to be supplied to the downstream side (a side of the fuel cell 2). Note that the valve body of the injection valve 28 is opened or closed to adjust the flow rate of the gas, and the pressure of the gas to be supplied to the downstream side of the injection valve 28 is reduced as compared with the gas pressure at the upstream side of the injection valve 28, so that the injection valve 28 can be regarded as a pressure control valve (a pressure reducing valve, a regulator). In the present embodiment, the injection valve may be further considered as a variable pressure control valve that can change the amount to be adjusted (the amount to be decreased) of the upstream gas pressure of the injection valve 28 so that the pressure coincides with a required pressure in a predetermined pressure range on the basis of a gas demand. The injection valve 28 sets a gas state (a flow rate of the gas, a molecular concentration of the hydrogen, or a gas pressure) on the upstream side of the hydrogen supply passage 22 to supply the gas to the downstream side, and corresponds to the variable gas supply device according to the present invention.Note that, in the present embodiment, as shown in FIG. 1, the injection valve 28 is disposed on the upstream side of the joint A 1 of the hydrogen supply passage 22 and the circulation passage 23. Moreover, as shown by the broken lines in FIG. 1, in a case where a plurality of hydrogen supply sources 21 are used as fuel supply sources, the injection valve 28 is disposed on the downstream side of a piece (a hydrogen gas joint A 2) in which the hydrogen gases supplied from the hydrogen supply sources 21 are joined.The circulation passage 23 is connected to the gas / water discharge passage 25 via a gas / liquid separator 30 and a gas / water discharge valve 31. The gas / liquid separator 30 collects the water contained in the hydrogen off-gas. The gas / water discharge valve 31 operates according to a command from the control section 7 to discharge (purify) the water content collected by the gas / liquid separator 30 and hydrogen off-gas (the combustion off-gas) including impurities from the system in the circulation channel 23. The gas / water discharge valve 31 is opened, thereby reducing the concentration of the impurities in the hydrogen off-gas in the circulation channel 23, and increasing a concentration of the hydrogen in the hydrogen off-gas to be circulated and supplied. The gas / liquid separator 30 is provided with a water temperature sensor (not shown) which detects the temperature of the water content received therein, and the gas / water discharge passage 25 is provided with a temperature sensor 32 which detects the temperature in the passage. The temperature information acquired by the water temperature sensor and the temperature sensor 32 is used in the control of the purification during starting, as described later. The circulation channel 23 and the gas / water discharge channel 25 correspond to an embodiment of a water discharge channel according to the present invention.The hydrogen off-gas discharged through the gas / water discharge valve 31 and the gas / water discharge passage 25 is diluted by a diluter (not shown) to be combined with the oxidizing gas off-gas in the gas discharge passage 12. The hydrogen pump 24 is driven by a motor (not shown) to circulate and supply the hydrogen gas in a circulation system to the fuel cell 2, and functions as an embodiment of a circulation pump in the present invention. The circulation system of the hydrogen gas is composed of the channel on the downstream side of the joint A 1 of the hydrogen supply channel 22, a fuel gas channel formed in the separators and the fuel cell 2, and the circulation channel 23.The piping system 5 for the coolant includes a coolant passage 41 connected to a coolant passage in the fuel cell 2, a cooling pump 42 provided in the coolant passage 41, and a radiator 43 cooling the coolant discharged from the fuel cell 2. The cooling pump 42 is driven by a motor (not shown) to circulate the coolant in the coolant passage 41 and supply it to the fuel cell 2.The power system 6 includes a high voltage DC / DC converter 61, a battery 62, a drive inverter 63, a traction motor 64, any type of auxiliary inverter (not shown), and the like. The high voltage DC / DC converter 61 is a DC-DC converter, and has a function of adjusting input of a DC voltage from the battery 62 to output the voltage to the drive inverter 63 side, and a function of adjusting input of the DC voltage from the fuel cell 2 or the traction motor 64 to output the voltage to the battery 62. The charge / discharge of the battery 62 is realized by these functions of the high voltage DC / DC converter 61. Further, the output voltage of the fuel cell 2 is controlled by the high voltage DC / DC converter 61.The battery 62 is configured by laminating battery cells, has a fixed high voltage as a terminal voltage, and can be controlled by a battery computer (not shown) to charge an excess current or to assistly supply a current. The drive inverter 63 converts a direct current into a three-phase alternating current to supply the current to the travel motor 64. The travel motor 64 is, for example, a three-phase AC motor, and constitutes the main power supply of a vehicle to which the fuel cell system 1 is mounted. The assist inverter is a motor drive control portion that controls the drive of each motor and converts the direct current to the three-phase alternating current to supply power to each motor. The assist inverter is, for example, the PWM converter of a pulse width modulator system, and converts the output of the DC voltage from the fuel cell 2 or the battery 62 into the three-phase AC voltage according to a control instruction from the control section 7 to control a torque generated in each motor.The control section 7 detects the amount of operation of an acceleration executing member (an accelerator pedal or the like) provided in the vehicle, and receives control information such as a required acceleration value (e.g., the amount of power generation required by a load device such as the traction motor 64) to control the operations of the various units in the system. Note that the load device is an ordinary power-consumption device including, besides the travel motor 64, an auxiliary device required for the operation of the fuel cell 2 (e.g., the motors of the compressor 14, the hydrogen pump 24, the cooling pump 42, and the like), an operation part connected to the running of the vehicle for use in any type of device (a change wheel, a wheel control portion, a steering device, a suspension structure, or the like), the air conditioning device (an air conditioner) of a passenger compartment, lighting, audio equipment, or the like.The control section 7 is constituted by a computer system (not shown). Such a computer system includes a CPU, a ROM, a RAM, an HDD, an input / output interface, a display, and the like, and the CPU reads any control program stored in the ROM to execute a desired calculation, thereby executing various operations and controls such as the control of the cleaning described later.Specifically, as shown in FIG. 2, the control section 7 calculates the flow rate (hereinafter, referred to as "hydrogen consumption") of the hydrogen gas consumed by the fuel cell 2 on the basis of the current value detected by the current sensor 2 aduring power generation of the fuel cell 2 (a function for calculating the fuel consumption: B 1). In the present embodiment, the hydrogen consumption is calculated using a specific calculation formula indicating a relationship between the current value during power generation and the hydrogen consumption, and updated for each calculation cycle of the control section 7.Further, the control section 7 calculates a target value for the pressure of the hydrogen gas to be supplied to the fuel cell 2 in the downstream position of the injection valve 28 based on the current value during power generation of the fuel cell 2 (a function for calculating the target value for the pressure: B 2), and the section calculates a target amount of purification (the target amount of the discharged hydrogen off gas from the gas / water discharge valve 31) (a function for calculating the target amount of purification: B 3). In the present embodiment, the target value for the pressure and the target amount of purification are calculated using a specific map indicating a relationship between the current value during power generation and the target value for the pressure and the target amount of purification for each calculation cycle of the control section 7.The control section 7 further calculates a deviation between the calculated target value for the pressure and the pressure value (the detected pressure value) of the downstream position of the injection valve 28 detected by the pressure sensor 29 (a function of calculating the pressure deviation: B 4). Then, the control section 7 calculates a flow rate of the hydrogen gas to be added to the hydrogen consumption (a flow rate for correcting the feedback) to decrease the calculated deviation (a function for calculating the flow rate for correcting the feedback: B5). In the present embodiment, the flow velocity for correcting the feedback is calculated using the target control of a repetitive type PI control or the like. The control section 7 also adds the hydrogen consumption and the flow rate for feedback correction to calculate the flow rate of injection of the injection valve 28 (a function for calculating the flow rate of injection: B 6). Then, the control section 7 calculates the injection period of the injection valve 28 based on the calculated flow rate of injection and a drive stroke, and outputs a control signal for executing this injection period, thereby controlling the period and timing of injection of the gas from the injection valve 28 to adjust the flow rate and pressure of the hydrogen gas to be supplied to the fuel cell 2.Besides, the control section 7 performs the control of the injection valve 28 (controls the duration and timing of injection of the gas from the injection valve 28 so that the detected pressure value at the downstream position of the injection valve 28 follows a predetermined target value for the pressure), and the section also performs the control of opening / closing the gas / water discharge valve 31, thereby discharging the water content and the hydrogen off gas in the circulation passage 23 from the system via the gas / water discharge valve 31. In this case, the control section 7 calculates the total discharged amount (the amount of purification) of the hydrogen off gas from the gas / water discharge valve 31 based on the change of a state of the gas supply from the injection valve 28 (a function for calculating the amount of purification: B7), to judge whether or not the calculated amount of purification is a predetermined target amount of purification or more (a function for judging the deviation of the amount of purification: B8). Then, the control portion 7 opens the gas / water discharge valve 31 in a case where a calculated amount Q of purification is a target amount Q 0 of purification or more (function for controlling purification. B9).Here, the function B 7 for calculating the amount of cleaning of the control portion 7 will be described in detail. In a case where the gas / water discharge valve 31 is opened to discharge the hydrogen off gas from the circulation passage 23 in a state where the detected pressure value of the pressure sensor 29 at the downstream position of the injection valve 28 follows the target value for the pressure due to the feedback control of the injection valve 28, the detected pressure value temporarily decreases. The control section 7 calculates such a pressure drop due to discharge (purging) of the hydrogen off-gas, and calculates the discharged amount corresponding to the pressure drop (the flow rate corresponding to the pressure change) of the hydrogen off-gas based on this calculated pressure drop (a function for calculating the flow rate corresponding to the pressure change: B7a). In the present embodiment, a flow rate Q 1 corresponding to the pressure change is calculated using a specific calculation formula indicating a relationship between the pressure drop due to the purging and the discharged amount of the hydrogen off-gas corresponding to this pressure drop. Further, the control section 7 calculates the feedback correction flow rate (a gas supply correction flow rate) to compensate for the pressure drop due to the discharge (purging) of the hydrogen off gas (a corrected flow rate calculation function: B5), to calculate the integrated value Q 2 for this feedback correction flow rate with the lapse of time from a time when purging is started (a corrected flow rate integration function: B7b). Then, the control section 7 adds the flow rate Q 1 corresponding to the pressure change and the integrated value Q 2 for the flow rate for correcting the feedback with the lapse of time from a time when the purging starts, to calculate the total discharged amount (the amount Q of purging) of the hydrogen off gas from the gas / water discharge valve 31 (the function for calculating the amount of purging: B7).Further, the function B 9 for controlling the cleaning of the control portion 7 will be described in detail. The control section 7 detects the ON signal (a request for starting the system) of the ignition switch of the vehicle with the fuel cell, and detects an outside air temperature by means of an outside air temperature sensor (not shown). Then, the control section 7 controls the gas / water discharge valve so as to prevent water from being discharged from the gas / water discharge valve 31 from a time when the ON signal is detected to a time when the temperature of the system reaches a predetermined temperature in a case where the ON signal of the ignition switch is detected under conditions where the outside air temperature is below a predetermined threshold (e.g., zero degrees Celsius). That is, the control section 7 in the present invention serves as a means for controlling the discharge. Here, the "temperature of the system" denotes the average temperature of the entire system or the temperature of a specific arrangement in the system. In the present embodiment, the discharge of water from the gas / water discharge valve 31 is prevented until the temperature detected by the temperature sensor 32 (the temperature in the gas / water discharge passage 25) reaches the predetermined temperature. In a case where discharge of water is permitted, the "predetermined temperature" may be set as a standard appropriately according to the scale or the configuration of the entire system, the outside air temperature, or the like.Further, the control section 7 controls the gas / water discharge valve 31 so as to allow water to be discharged from the gas / water discharge valve 31 (even when the temperature in the gas / water discharge passage 25 is below the predetermined temperature) in a case where the amount of heat of the water received in the gas / liquid separator 30 (the water received in the gas / water discharge valve 31) exceeds a predetermined amount of heat. In the present embodiment, the amount of heat of absorbed water is calculated based on the temperature of absorbed water detected by a water temperature sensor and the amount of absorbed water estimated from the current value during power generation of the fuel cell 2. In a case where the discharge of water is permitted, the "predetermined amount of heat" may be set as a standard appropriately according to the scale or the configuration of the entire system, the sectional area or the channel length of the gas / water discharge channel 25, or the like. In the present embodiment, a heat amount to be broken through at zero degrees Celsius (the heat amount required for the gas / water discharge valve 31 and the gas / water discharge passage 25 to exceed zero degrees Celsius under conditions where the outside air temperature is at zero degrees Celsius) calculated on the basis of the temperature in the gas / water discharge passage 25 detected by the temperature sensor 32 and the heat capacity of the gas / water discharge passage 25 is used as "predetermined heat amount".Further, while preventing water from being discharged from the gas / water discharge valve 31, the control section 7 controls the injection valve 28 so that the amount of hydrogen gas to be supplied to the fuel cell 2 is set to an amount larger than a predetermined amount to be supplied, and the section controls the hydrogen pump 24 so that the amount of hydrogen gas to be circulated by the fuel cell 2 is larger than a predetermined amount to be circulated. That is, the control section 7 in the present invention also serves as a means for controlling the supply of fuel. In the present embodiment, as the "set supply (to be circulated) amount", the supply (to be circulated) amount during the usual starting when the discharge of gas or water is not prevented is used.Next, a method of controlling purification (a method of controlling discharge of water) during startup of the fuel cell system 1 according to the present embodiment will be described with reference to the flowchart of FIG. 3.During the usual operation of the fuel cell system 1, the hydrogen gas is supplied from the hydrogen container 30 to the fuel electrode of the fuel cell 10 via the hydrogen supply passage 31, and the humidified and adjusted air is supplied to the oxidizing electrode of the fuel cell 10 via the air supply passage 21 to generate a current. In this case, the current (required current) to be discharged from the fuel cell 10 is calculated by the controller 4, and the amounts of hydrogen gas and air corresponding to the amount of current generated by the fuel cell are supplied to the fuel cell 10. In the present embodiment, during starting of the system, before such an ordinary operation is performed, the control of the cleaning is performed. It is to be noted that the gas / water discharge valve 31 is closed before starting the fuel cell system 1.First, the control section 7 of the fuel cell system 1 judges whether or not the ON signal of the ignition switch (the request for starting the system) is in a state of the operation stop (a step for judging the request for starting: S1). Subsequently, in a case where the ON signal of the ignition switch is detected, the control section 7 detects the temperature of the outside air using an outside air temperature sensor to judge whether or not the outside air temperature is below a predetermined threshold (e.g., zero degrees Celsius) (an outside air temperature judgment step: S 2).Subsequently, in a case where it is judged in the outside air temperature judgment step S 2 that the outside air temperature is at a set threshold value or more, the control section 7 switches to a step of opening the gas / water discharge valve 31 (a later-described cleaning valve opening step S 6). On the other hand, in a case where it is judged in the outside air temperature judgment step S 2 that the outside air temperature is below the predetermined threshold value, the control section 7 maintains the closed state of the gas / water discharge valve 31 and controls the injection valve 28 and the hydrogen pump 24 so that the amount of the hydrogen gas to be supplied to and circulated through the fuel cell 2 is set to an amount larger than a predetermined amount (a cleaning valve closed maintenance step: S 3).After the cleaning valve closed maintaining step S 3, the control portion 7 judges whether or not the temperature in the gas / water discharge passage 25 detected by the temperature sensor 32 reaches a predetermined temperature (a system temperature judging step: S 4). In a case where an affirmative judgment is obtained, the step shifts to a step of opening the gas / water discharge valve 31 (the cleaning valve opening step S 6 described later). In a case where a negative judgment is obtained in the system temperature judgment step S 4, on the other hand, the control section 7 judges whether or not the amount of heat of the water received in the gas / water discharge valve 31 (the water received in the gas / liquid separator 30) exceeds a predetermined amount of heat (the received water amount judgment step: S 5).If a negative judgment is obtained in the absorbed water heat amount judgment step S 5, then the control section 7 repeatedly executes the step of switching to the cleaning valve closed maintenance step S 3. When an affirmative judgment is obtained, the control section opens, on the other hand, the gas / water discharge valve 31 (the cleaning valve opening step: S 6). By the above-described sequence of steps, the cleaning of the fuel cell system 1 during the startup is realized.Note that the step S 1 for judging the request for starting and the step S 2 for judging the outside air temperature in the present embodiment correspond to the first and second steps in the present invention, and the step S 3 for maintaining the cleaning valve closed and the step S 4 for judging the temperature of the system in the present embodiment correspond to the third step in the present invention.In the fuel cell system 1 of the above-described embodiment, it is possible to prevent the water contained in the circulation passage 23 from flowing into the gas / water discharge valve 31 from a time when the ON operation of the ignition switch (the request for starting the system) is performed at low temperatures at which the outside air temperature is below the set threshold until a time when the temperature of the system reaches the set temperature. Therefore, freezing of the gas / water discharge valve 31 (and closing of the gas / water discharge valve 31 due to freezing) can be prevented even at low temperatures.Further, in the fuel cell system 1 of the above-described embodiment, when the amount of heat of the water received in the gas-liquid separator 30 exceeds the set amount of heat, the discharge of the water from the gas / water discharge valve 31 can be permitted. A solution to the problem that the water in the gas / water discharge valve 31 freezes while stopping the discharge of water, and that any substance that does not contribute to power generation, for example, nitrogen, is not discharged in a similar manner but is accumulated instead is therefore possible.Further, while preventing the discharge of gas / water from the gas / water discharge valve 31, the amounts of the hydrogen gas to be supplied to and circulated through the fuel cell 2 in the fuel cell system 1 of the above embodiment can be set to the amount larger than the set amount (the amount to be supplied during the usual starting and the amount to be circulated when the discharge of gas / water is not inhibited). Therefore, it can be prevented that the concentration of hydrogen to be supplied to the fuel cell 2 decreases due to the prevention of gas discharge simultaneous with the discharge of water.Note that, in the above embodiment, the example in which the pipe system 4 for the hydrogen gas of the fuel cell system 1 is provided with the circulation passage 23 has been described, but as shown in FIG. 4, for example, a discharge passage 33 is connected to a fuel cell 2, and the circulation passage 23 may be omitted. Even when such an arrangement (dead end system) is used, the ON operation of the ignition switch is performed at low temperatures, and the control section 7 maintains the closed state of the gas / water discharge valve 31, whereby functions and effects similar to those of the above embodiment can be obtained. The discharge passage 33 in such an arrangement corresponds to an embodiment of a water discharge passage in the present invention.Further, in the above embodiment, the example in which the circulation passage 23 is provided with the hydrogen pump 24 has been described, but an ejector may be used instead of the hydrogen pump 24. In the above embodiment, the example in which the gas / water discharge valve 31 for performing discharge of both gas and water is provided in the circulation channel 23 has been further described. However, a water discharge valve that discharges the water content collected by the gas / liquid separator 30 from the system is provided separately from a gas discharge valve for discharging the gas in the circulation channel 23 from the system, and the control section 7 may control the water discharge valve and the gas discharge valve separately from each other. Even in a case where such an arrangement is used, when the ON operation of the ignition switch is performed at low temperatures, the control portion 7 maintains the closed state of the water discharge valve, whereby functions and effects similar to those of the above embodiment can be obtained.Further, in the above embodiment, the example in which the injection valve 28 is prevented from being controlled so as to increase the amount of hydrogen gas to be supplied to the fuel cell 2 during discharge of water from the gas / water discharge valve 31 has been described. However, in place of the injection valve 28 (or simultaneously with the injection valve 28), the regulator 27 may be controlled to increase the amount of hydrogen gas to be supplied to the fuel cell 2.In the above embodiment, the example in which both the injection valve 28 and the hydrogen pump 24 are prevented during discharge of water from the gas / water discharge valve 31 has been described so as to increase both the amount of the hydrogen gas to be supplied to the fuel cell 2 and that of the hydrogen gas to be circulated through the fuel cell 2. However, either only the injection valve 28 or only the hydrogen pump 24 may be controlled to increase either the amount of hydrogen gas to be supplied to the fuel cell 2 or the amount of hydrogen gas to be circulated through the fuel cell 2.Industrial applicabilityAs described in the embodiment, a fuel cell system according to the present invention may be mounted on a vehicle having a fuel cell, and the system may be mounted on any type of mobile object (a robot, a ship, an airplane, or the like) other than a vehicle having a fuel cell. Furthermore, the fuel cell system according to the present invention can be applied to a stationary power generation system for use as a power generation device for a structure (a housing, a building, or the like).

Claims

A fuel cell system (1) comprising: a fuel cell (2); a water discharge passage (25) through which a water content discharged from this fuel cell (2) flows; and a water discharge valve (31) that discharges the water content in this water discharge passage (25) from the system, wherein the fuel cell system (1) further comprises: water discharge control means for controlling the water discharge valve (31) so as to prevent the discharge of the water from the water discharge valve (31) from a time when the system start-up is requested to a time when the system temperature reaches a predetermined temperature in a case where the system start-up is requested under conditions where an outside air temperature is below a predetermined threshold.The fuel cell system (1) according to claim 1, wherein the water discharge control means controls the water discharge valve (31) so as to allow water to be discharged from the water discharge valve (31) in a case where the amount of heat of the water received in the water discharge valve (31) exceeds a predetermined amount of heat.The fuel cell system (1) according to claim 2, wherein the set amount of heat is an amount of heat required for the water discharge valve (31) and the water discharge passage (25) to exceed zero degrees Celsius under conditions where the outside air temperature is zero degrees Celsius or less.The fuel cell system (1) according to any one of claims 1 to 3, wherein the water discharge valve (31) is a gas / water discharge valve (31) that performs both the discharge of water and the discharge of air, the fuel cell system (1) further comprising: fuel supply control means for adjusting the amount of a fuel gas to be supplied to and / or circulated through the fuel cell (2) to an amount greater than a predetermined amount while preventing the discharge of water from the gas / water discharge valve (31) by the water discharge control means.The fuel cell system (1) according to claim 4, further comprising: a supply channel (22) that supplies the fuel gas supplied from a fuel supply source to the fuel cell (2); and a variable gas supply device that sets a gas state on the upstream side of the supply channel (22) to supply the gas to a downstream side, wherein the fuel supply control means controls the variable gas supply device so as to set the amount of the fuel gas to be supplied to the fuel cell (2) to an amount larger than the set amount to be supplied while preventing the discharge of water from the gas / water discharge valve (31) by the water discharge control means.The fuel cell system (1) according to claim 4, further comprising: a supply channel (22) that supplies the fuel gas supplied from a fuel supply source to the fuel cell (2); a circulation channel (23) that corresponds to the water discharge channel (25) and circulates a fuel off gas discharged from the fuel cell (2) through the supply channel (22); and a circulation pump that circulates the gas in the circulation channel (23) forcibly through the supply channel (22), wherein the fuel supply control means controls the circulation pump so that the amount of the fuel gas to be circulated by the fuel cell (2) is set to an amount larger than a set circulation amount while preventing the discharge of water from the gas / water discharge valve (31) by the water discharge control means.A method of controlling water discharge of a fuel cell system (1) including a fuel cell (2), a water discharge passage (25) through which a water content discharged from said fuel cell (2) flows, and a water discharge valve (31) that discharges the water content in said water discharge passage (25) from said system, the method of controlling water discharge comprising: a first step of judging whether or not starting of said system has been requested; a second step of judging whether or not an outside air temperature is below a set threshold value; and a third step of preventing water discharge from the water discharge valve (31) from a time when the start is requested to a time when the temperature of the system reaches a predetermined temperature, in a case where it is judged in the first step that the start of the system is requested and it is judged in the second step that the outside air temperature is below the predetermined threshold value.

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