WO2006030269A2

WO2006030269A2 - Fuell cell system with pressure regulated fuel supply

Info

Publication number: WO2006030269A2
Application number: PCT/IB2005/002656
Authority: WO
Inventors: Norimasa Ishikawa; Hideaki Mizuno
Original assignee: Toyota Jidosha Kabushiki Kaisha
Priority date: 2004-09-16
Filing date: 2005-09-08
Publication date: 2006-03-23
Also published as: WO2006030269A3; JP2006086006A

Abstract

In a fuel cell system where a hydrogen gas supply passage (21) is provided with a hydrogen pressure regulating valve (6), an operation characteristic which is changed in accordance with a state of the fuel cell system. For example, when the fuel cell system is in the state where foreign substances have been accumulated in the hydrogen gas supply passage (21), and the foreign substances are required to be discharged, a discharge pressure of the hydrogen pressure regulating valve (6) is increased. Meanwhile, when the fuel cell system is in the state where hydrogen gas leaks from the hydrogen gas supply passage (21), the discharge pressure of the hydrogen pressure regulating valve (6) is decreased.

Description

FUEL CELL SYSTEM

FIELD OF THE INVENTION

[0001] The invention relates to a fuel cell system which generates electricity through a reaction of hydrogen and oxygen, and more particularly, to an improvement in a fuel (hydrogen) gas supply system.

BACKGROUND OF THE INVENTION [0002] A fuel cell is structured to allow hydrogen gas as fuel gas and air (oxygen) as oxidizing gas to be electrochemically reacted so as to bring electricity generated in the course of the reaction to the outside. The fuel cell, is structured by laminating a predetermined number of cells each formed of a fuel electrode (anode) to which the hydrogen gas is supplied, an air electrode (cathode) to which air is supplied, and an electrolyte membrane interposed therebetween. For example, in a fuel cell of polymer electrolyte type (PEFC) which is optimum to be mounted for the vehicle, a polymer ion-exchange membrane is employed as the electrolyte membrane. As the ion-exchange membrane has a small thickness of several ten microns, the pressure difference between the hydrogen pressure at the fuel electrode side and the air pressure at the air electrode side, that is, pressure difference between electrodes, is required to be controlled so as not to be excessively large for the purpose of preventing the membrane from being damaged.

[0003] Japanese Patent Publication No. JP 2003-68334 A discloses that a pump is provided in the hydrogen circulation line so as to feed the hydrogen supplied through a pressure regulating valve together with hydrogen off-gas into the fuel cell. In the above-structured system, the pressure regulating valve for the hydrogen gas is driven by the pressure of air applied to the fuel cell by the air compressor such that the pressure difference between the fuel gas pressure and the air pressure is maintained to be in a predetermined range. [0004] In the above-structured system, although the pressure difference between electrodes may be maintained to be in the predetermined range, the range of pressure supplied through the pressure regulating valve for the hydrogen gas is influenced by the magnitude of dynamic range of the discharge pressure of the air compressor. The mechanical pressure regulating valve using diaphragm having one side applied with air pressure is employed for the above-structured system Therefore, the hydrogen gas pressure supplied to the fuel cell cannot be independently controlled.

[0005] It is preferable that the hydrogen gas pressure supplied to the fuel cell be relatively low for the purpose of improving durability of the fuel cell.

However, if such pressure is always held low, foreign substance that resides in the fuel gas supply passage cannot be removed, and accordingly various problems may occur, for example, the power generation state becomes instable, a long time is required for stabilizing the power generation upon start-up of the fuel cell, resumption from the intermittent operation, the voltage of the cell falls owing to flooding, there is a limitation of improving precision for detecting hydrogen leakage, and the like. Meanwhile, if such pressure is always held high, problems may also occur, for example, the durability is deteriorated, amount of discharged hydrogen gas is increased resulting from leakage, and the fuel cell may be damaged in case of fail.

DISCLOSURE OF THE INVENTION [0006] It is an object of the invention to control the fuel gas pressure supplied to the fuel cell in accordance with the state of the fuel cell system. [0007] A fuel cell system according to the invention includes a fuel gas supply passage through which a fuel gas is supplied from a fuel gas source to a fuel cell, and a variable pressure regulator that is provided in the fuel gas supply passage, and adjusts a pressure of the fuel gas supplied from the fuel gas source so that the fuel gas is discharged toward a downstream side. The system is provided with change means that changes an operation characteristic of the variable pressure regulator in accordance with a state of the fuel cell system.

[0008] The above-structured system makes it possible to control the fuel gas pressure in accordance with the state of the fuel cell system. [0009] The operation characteristics of the variable pressure regulator may be changed by the change means based on the output of the state detection means that detects physical quantity with respect to the state of the fuel cell system.

[0010] The operation characteristics of the variable pressure regulator may be changed so as to increase the discharge pressure thereof when the system is in conditions as described below.

A. A case where the foreign substance accumulated in the fuel gas supply passage is discharged based on a state of the accumulated foreign substance.

B. A case where the system is in the state of start-up of the fuel cell or resumption from the intermittent operation. C. A case where the cell voltage is equal to or lower than a predetermined value D. A case where the fuel gas leakage in the fuel cell is detected.

[0011] In the aforementioned structure, the low pressure operation is normally performed for keeping the durability of the fuel cell. Meanwhile, when the foreign substance is accumulated in the fuel gas supply passage, and as a result, the power generation state becomes instable, the operation mode is switched from the low pressure operation to the high pressure operation so as to force the residual foreign substance to be out of the fuel gas supply system. This makes it possible to stabilize the power generation state.

[0012] In the case where a certain length of time is required for stabilizing the power generation state, for example, upon start-up of the fuel cell, and resumption from the intermittent operation, such state may be stabilized as early as possible by increasing the amount of the fuel gas supplied to the fuel cell,

[0013] When the cell voltage becomes equal to or lower than a predetermined value, discharge of generated water out of the cell is facilitated so as to eliminate flooding as one of factors of decrease in the cell voltage.

[0014] The fuel gas pressure in the fuel gas supply passage is temporarily increased upon detection of the fuel gas leakage in the fuel cell system so as to improve the leakage detection accuracy. [0015] When the fuel gas pressure as the detected physical quantity deviates from a target pressure by a predetermined or larger value, the operation characteristics of the variable pressure regulator are changed so as to reduce the discharge pressure thereof.

[0016] When the fuel gas pressure deviates from the target pressure by a predetermined or larger value, the operation area of the fuel cell is limited to a fixed load or lower so as to protect the fuel cell irrespective of abnormality occurred in the variable pressure regulator.

[0017] The variable pressure regulator may be structured to be capable of adjusting the discharge pressure by introducing the pressurized fluid from the outside thereof. The change means may be formed of a pressurized fluid supply passage through which the pressurized fluid introduced from the outside of the variable pressure regulator is supplied thereinto, an exhaust valve that allows the pressurized fluid to be discharged outside of the supply passage at an intermediate position of the pressurized fluid supply passage, and control means that controls an opening degree of the exhaust valve in accordance with the state of the fuel cell system.

[0018] In the above-described structure, the amount of the pressurized fluid that is supplied from the outside of the variable pressure regulator thereto, and discharged at the intermediate position of the pressurized fluid supply passage is increased or decreased. Accordingly, the discharge pressure of the variable pressure regulator can be controlled. This makes it possible to control the discharge pressure with no limitation of the pressure of the pressurized fluid supply source.

[0019] The above-described invention makes it possible to control the fuel gas pressure in accordance with the state of the fuel cell system. Such control may be effective especially when the system is resumed from the instable power generation state, the power generation is required to be stabilized at an earlier stage upon start-up of the fuel cell or resumption from the intermittent operation, the accuracy in the fuel gas leakage detection is required to be improved, quantity of the fuel gas discharged to the outside owing to the fuel gas leakage is required to be reduced, and the fuel cell is required to be protected after the fail occurs.

BRIEF DESCRIPTION OF THE DRAWINGS [0020] The foregoing and further objects, features and advantages of the invention will become apparent from the following description of preferred embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein:

Fig. 1 is a block diagram of a basic structure of a fuel cell system according to an embodiment of the invention;

Fig. 2 is an explanatory view indicating that operation characteristics of a hydrogen pressure regulating valve are changed in accordance with a (small) valve opening rate of an exhaust valve;

Fig. 3 is an explanatory view indicating that operation characteristics of a hydrogen pressure regulating valve are changed in accordance with a (large) valve opening rate of an exhaust valve;

Fig. 4 is a map that represents a relation between operation states of the fuel cell and the target hydrogen supply pressure;

Fig. 5 is a flowchart that represents how to change the operation characteristics of the hydrogen pressure regulating valve;

Fig. 6 is a map based on which the target hydrogen supply pressure upon detection of hydrogen leakage is set;

Fig. 7 is an explanatory view that represents how the determination with respect to fail is made on the basis of the difference between the actual measurement value and the target value of the hydrogen pressure;

Fig. 8 is a block diagram of a basic structure of the fuel cell system to which a check valve is added in the air pressure transmission passage; and

Fig. 9 is an explanatory view indicating that the startability of the fuel cell is improved by the structure shown in Fig. 8.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS [0021] An embodiment of the invention will be described hereinafter referring to the drawings. [0022] Fig. 1 is a block diagram that schematically shows a basic structure of a fuel cell system according to an embodiment of the invention. Referring to Fig. 1, air serving as oxidizing gas is supplied into an air inlet of a fuel cell 1 through an air supply passage 11. The air supply passage 11 is provided with an air compressor 3, an air filter 2 and a humidifier (not shown). Air passing through the air filter 2 is pressurized under an appropriate pressure, and water required for the electrolyte membrane of the cell of the fuel cell is supplied.

[0023] Air off-gas discharged from the fuel cell 1 is discharged to the outside through an exhaust passage 12. The exhaust passage 12 is provided with a pressure regulating valve (not shown) serving as a pressure regulator that adjusts a pressure of supplied air (air pressure) such that the pressure of air supplied to the fuel cell 1 is maintained to a predetermined value. A control unit (control means) 50 formed of a computer system for control operation serves to set the air pressure by adjusting the air compressor 3 and the pressure regulating valve.

[0024] Hydrogen gas serving as fuel gas is supplied to a hydrogen inlet of the fuel cell 1 from a hydrogen supply source (fuel gas source) through a hydrogen gas supply passage (fuel gas supply passage) 21. The hydrogen supply source may be formed as a high-pressure hydrogen tank, a tank containing hydrogen absorbing/desorbing alloy, and a methanol fuel reformer as well as the pressure regulating valve and the pump. The hydrogen gas supply passage 21 is provided with a hydrogen pressure regulating valve (variable pressure regulator) 6 which reduces (performs pressure regulation) the pressure of the hydrogen gas supplied from the hydrogen supply source so as to be discharged to the downstream side at the reduced pressure. [0025] The hydrogen gas (fuel gas) that has not been consumed in the fuel cell 1 is discharged to a hydrogen circulation passage 22 as the hydrogen off-gas. The hydrogen off-gas pressurized by a hydrogen pump 5 provided in the hydrogen circulation passage 22 is returned to the hydrogen gas supply passage 21 downstream of the hydrogen pressure regulating valve 6 so as to be joined with the hydrogen gas and reused in the fuel cell 1. The operation of the hydrogen pump 5 is controlled by the control unit 50.

[0026] The hydrogen pressure regulating valve 6 is a mechanically structured pressure regulating valve using a diaphragm urged by a spring. Pressure is applied to the diaphragm from a pressure source that applies air pressure to the fuel cell 1 through an air pressure transmission passage (pressurized fluid supply passage) 31 branched from the air supply passage 11.

[0027] The diaphragm displaces in accordance with the differential pressure among the applied pressure as described above, the spring pressure, and the supplied hydrogen pressure at the inlet of the fuel cell 1 so as to set the valve opening degree (valve opening rate) of the hydrogen pressure regulating valve 6 in the hydrogen gas supply passage 21. As the discharge pressure of the hydrogen pressure regulating valve 6 fluctuates, the hydrogen supply pressure at the inlet of the fuel cell 1 is adjusted to be in a predetermined pressure range under the pressure applied to the hydrogen pressure regulating valve 6. [0028] The hydrogen pressure regulating valve 6 is structured to be capable of adjusting the discharge pressure by introducing air (pressurized fluid) supplied from the air compressor 3.

[0029] The air pressure transmission passage 31 is provided with an orifice 4 and a buffer tank 8 for preventing pulsation in the order from the upstream side. An exhaust passage 32 is branched from the air pressure transmission passage 31 at a position between the buffer tank 8 and the hydrogen pressure regulating valve 6. The exhaust passage 32 is provided with an exhaust valve (discharge valve) 7 that reduces the air pressure to the hydrogen pressure regulating valve 6. The valve opening rate of the exhaust valve 7 is controlled by the control unit 50 so as to be adjusted from the fully closed position to the fully opened position continuously or in a plurality of steps.

[0030] When the exhaust valve 7 is in the fully closed position (valve opening rate = 0), substantially the whole air pressure from the air compressor 3 is applied to the hydrogen pressure regulating valve 6 as the applied pressure.

Meanwhile when the exhaust valve 7 is in the fully opened position (valve opening rate = 100 %), substantially the whole air supplied from the air compressor 3 is discharged from the exhaust passage 32, and accordingly the air pressure is not applied to the hydrogen pressure regulating valve 6. That is, the air pressure applied to the fuel cell 1 has no relation with (independent from) the hydrogen supply pressure. In the case where the air pressure from the air compressor 3 serves as the pressure source, the valve opening rate of the exhaust valve 7 may be set to an appropriate value so as to obtain a desired applied pressure. The thus obtained pressure is supplied to the diaphragm of the hydrogen pressure regulating valve 6 as the applied pressure.

[0031] In the embodiment as aforementioned, the air pressure transmission passage 31 through which air supplied to the hydrogen pressure regulating valve 6 from the air compressor 3, the exhaust valve 7 through which the supplied air can be discharged to the outside of the transmission passage 31 at the intermediate position thereof, and the control unit 50 that controls the opening degree of the exhaust valve 7 in accordance with a state of the fuel cell 1 can be regarded as the change means of the invention.

[0032] The relation between the operation of the exhaust valve 7 and the air pressure applied to the hydrogen pressure regulating valve 6, which varies with the operation of the exhaust valve 7 will be described referring to Figs. 2 and 3 hereinafter.

[0033] Referring to Fig. 2, when the valve opening rate of the exhaust valve 7 is decreased (pressure increase), air Al from the air compressor 3, which has been distributed into the air pressure transmission passage 31 from the air supply passage 11 flows toward the hydrogen pressure regulating valve 6 by quantity larger than that of discharged air through the exhaust passage 32, and accordingly the pressure applied to the hydrogen pressure regulating valve 6 becomes high. The discharge pressure of the hydrogen pressure regulating valve 6 becomes high, which increases the hydrogen pressure supplied to the inlet of the fuel cell 1 to a high value.

[0034] Referring to Fig. 3, when the valve opening rate of the exhaust valve 7 is increased (pressure decrease), air Al from the air compressor 3, which has been distributed from the air supply passage 11 to the air pressure transmission passage 31 is discharged through the exhaust passage 32 by quantity larger than that of air flowing to the hydrogen pressure regulating valve 6. Accordingly the pressure applied to the hydrogen pressure regulating valve 6 becomes low. The discharge pressure of the hydrogen pressure regulating valve 6, thus, becomes low to reduce the hydrogen pressure supplied to the inlet of the fuel cell 1.

[0035] Air pressure serving as the pressure supply source is reduced by the exhaust valve 7 so as to be supplied to the hydrogen pressure regulating valve 6 as the applied pressure. As shown in the target pressure map of Fig. 4, the hydrogen pressure supplied to the inlet of the fuel cell 1 may be adjusted to a desired value in a predetermined range without correlating the hydrogen pressure supplied to the inlet of the fuel cell 1 with the air pressure, in other words, without being limited by the pressure supplied from the air compressor 3 as the air supply source.

[0036] Supplementarily with respect to Fig. 4, the fuel cell system allows the target hydrogen pressure supplied to the inlet of the fuel cell 1 to be controlled in the range from mechanical operation characteristics X structurally exhibited in the hydrogen pressure regulating valve 6 to operation characteristics Y set by adding the air pressure (see arrow mark) supplied from the air compressor 3 to the operation characteristics X.

[0037] The aforementioned control may be realized by executing a duty control of the exhaust valve 7 so as to bring the air pressure applied to the hydrogen pressure regulating valve 6 to the target hydrogen supply pressure by preliminarily setting each value of the target hydrogen supply pressure at the inlet of the fuel cell 1 in maps (see characteristics upon intrusion of foreign substances and upon fail as shown in Fig. 4) for each case of the normal operation, the operation upon intrusion of foreign substance into the hydrogen gas supply passage 21, and the fail state, for example, hydrogen gas leakage from the fuel cell 1 or the hydrogen passage such as the hydrogen gas supply passage 21 , respectively.

[0038] A control routine executed by the control unit 50 will be described referring to the flowchart of Fig. 5. The control routine is executed by interruption that occurs at a predetermined cycle or occurrence of the specific event under the control program. First in step S l, it is determined whether the foreign substance exists in the hydrogen gas supply passage 21. The determination is made based on an output value of a pressure sensor 10 (state detection means) provided at an appropriate position of the hydrogen gas supply passage 21.

[0039] If it is determined that the foreign substance exists in the hydrogen gas supply passage 21 , that is, YES is obtained in step S l, the process proceeds to step S3 where the target pressure map for the operation upon intrusion of the foreign substance as shown in Fig. 4 is referred so as to set the target hydrogen pressure supplied to the inlet of the fuel cell 1. Meanwhile if it is determined that the foreign substance does not exist, that is, NO is obtained in step S l, the process proceeds to step S lO where the target pressure map for the normal operation is referred so as to set the target supply hydrogen pressure at the inlet of the fuel cell 1. [0040] When the target supply hydrogen pressure at the inlet of the fuel cell 1 is set as described above, the process proceeds to step S5 where a duty control of the exhaust valve 7 is performed for the purpose of controlling the hydrogen pressure regulating valve 6 such that the air pressure applied to the hydrogen pressure regulating valve 6 becomes the target hydrogen supply pressure.

[0041] If the foreign substance exists in the hydrogen gas supply passage 21, the operation characteristics of the hydrogen pressure regulating valve 6 is changed such that the discharge pressure of the hydrogen pressure regulating valve becomes higher than the one in the normal operation as shown in Fig. 4, and the flow of the hydrogen gas in the hydrogen gas supply passage 21 is facilitated. Accordingly the accumulated foreign substances are forced out to be removed from the hydrogen passage. This makes it possible to stabilize the instable power generation state due to the foreign substance as an earlier stage

[0042] In the fuel cell system according to the embodiment, the determination to be described below may be made instead of executing the process in steps S l and S3 in Fig. 5.

[0043] [First fail determination] [0044] The fail determination is made based on the presence/absence of the hydrogen leakage from the hydrogen passage such as the hydrogen gas supply passage 21. In step S3 to be executed when it is determined as being fail (presence of hydrogen leakage), the target pressure map for fail as shown in Fig. 4 is referred. Then the target hydrogen supply pressure at the inlet of the fuel cell 1 is set to the value that is lower than the pressure in the normal operation.

[0045] The operation characteristics of the hydrogen pressure regulating valve 6 may be changed such that the discharge pressure of the hydrogen pressure regulating valve 6 becomes lower than the one in the normal operation. In the case where the hydrogen leakage from the hydrogen passage is detected, the amount of the hydrogen gas released to the outside may be reduced.

[0046] The discharge pressure of the hydrogen pressure regulating valve 6 may be changed to a high value prior to execution of the hydrogen leakage detection in the fuel cell system. For example, the target pressure map for the hydrogen leakage detection as shown in Fig. 6 is referred, and the target hydrogen supply pressure at the inlet of the fuel cell 1 is set to be higher than the pressure in the normal operation within a predetermined range (see dotted line of Fig. 6).

[0047] The operation characteristics of the hydrogen pressure regulating valve 6 are changed such that the discharge pressure thereof becomes higher than the pressure in the normal operation. Accordingly the accuracy in the leakage detection may be improved by temporarily increasing the hydrogen pressure upon detection of the leakage of hydrogen from the hydrogen passage. [0048] [Second fail determination]

[0049] The fail determination is made based on the hydrogen pressure in the hydrogen passage such as the hydrogen gas supply passage 21. More specifically as shown in Fig. 7, if the actual measurement value (indicated by the dotted line in Fig. 7) detected by the pressure sensor 10 provided at an appropriate position of the hydrogen gas supply passage 21 deviates from the target value (indicated by the solid line) by a predetermined or larger value, it is determined to be fail. In step S3 to be executed when it is determined as being fail, the target pressure map for the fail as shown in Fig. 4 is referred, based on which the target hydrogen supply pressure at the inlet of the fuel cell 1 is set to be lower than the pressure in the normal operation.

[0050] In this case, the operation characteristics of the hydrogen pressure regulating valve 6 are changed such that the discharge pressure thereof is reduced to be lower than the pressure in the normal operation. When there may be an abnormality in the hydrogen pressure regulating valve 6, the operation area of the fuel cell 1 is limited to the fixed load or lower so as to protect the fuel cell 1.

[0051] [Cell voltage determination] [0052] It is determined whether the voltage detected by a cell voltage monitor 11 of the fuel cell 1 has been lowered to a predetermined value. In step S3 to be executed when YES is obtained, that is, the voltage has been lowered to reach the predetermined value, the target pressure map similar to the one shown in Fig. 4 is referred. In the same way as in the case of intrusion of the foreign substance, the target hydrogen supply pressure at the inlet of the fuel cell 1 is set to be higher than the pressure in the normal operation.

[0053] In this way, the operation characteristics of the hydrogen pressure regulating valve 6 are changed so as to increase the discharge pressure thereof to be higher than the pressure in the normal operation. Accordingly, the flooding, if any, may be prevented, thus avoiding decrease in the cell voltage.

[0054] [Determination of start-up or resumption from intermittent operation] [0055] It is determined in step S l whether the fuel cell system is currently in such a state as start-up of the fuel cell 1 or as resumption from the intermittent operation. In step S3 to be executed when YES is obtained in step S l, that is, the system is in the state of start-up or resumption from the intermittent operation, the target pressure map similar to the one shown in Fig. 4 is referred. In the same way as in the case of intrusion of the foreign substance, the target supply hydrogen pressure at the inlet of the fuel cell 1 is set to become higher than the pressure in the normal operation.

[0056] The operation characteristics of the hydrogen pressure regulating valve 6 are changed such that the discharge pressure thereof becomes higher than the pressure in the normal operation. Accordingly the startability of the fuel cell 1 upon its start-up or resumption from the intermitting operation may be improved. [0057] In order to further improve the startability, a check valve 41 may be provided at the upstream side of the buffer tank 8 in the air pressure transmission passage 31 as shown in Fig. 8. Fig. 9 is a graph that represents each change in the supply hydrogen pressure at the inlet of the fuel cell 1 and the pressure downstream of the buffer tank 8 in the aforementioned case. [0058] In the above-structured system, even if the pressure of the air compressor 3 is relatively low in such a state as start-up or resumption from the intermittent operation, the pressure within the air pressure transmission passage 31 before the operation of the fuel cell 1 or the intermittent operation is stopped is accumulated in the buffer tank 8 and downstream thereof. [0059] As indicated by a dashed line of the graph shown in Fig. 9, upon start-up or resumption from the intermittent operation of the fuel cell 1 , the pressure initially applied to the hydrogen pressure regulating valve 6 is assured. Compared with the structure having no check valve 41 as indicated by the broken line of Fig. 9, the time taken for the rise in the supply hydrogen pressure at the inlet of the fuel cell 1 may be shorter. Thus, further improvement of the startability is realized.

[0060] In the above-described structure, the air pressure supplied to the fuel cell 1 serves as the pressure source, which is also employed as the pressure for driving the diaphragm of the hydrogen pressure regulating valve 6. The system may be structured such that the supply air pressure serves to increase or decrease the pressure of the pressure transmitting medium (for example, inert gas such as nitrogen gas or liquid) so as to be applied to the diaphragm of the hydrogen pressure regulating valve 6. By transmitting the air pressure to the diaphragm of the hydrogen pressure regulating valve 6 via the inert gas (pressure transmitting medium), the hydrogen pressure regulating valve 6 has an elongated life or improved reliability through restriction of oxidization (deterioration) of the hydrogen pressure regulating valve 6.

[0061] The structure for changing the operation characteristics of the variable pressure regulator is not limited to the one which has been described in the embodiment so long as the fluid that has been pressurized to a predetermined pressure is depressurized halfway, and introduced into the variable pressure regulator. For example, the operation state of the pump may be changed in accordance with the state of the fuel cell system (increasing or decreasing the discharge pressure by controlling the rotational speed). [0062] The operation characteristics may be changed without introducing the pressurized fluid into the variable pressure regulator. For example, the diaphragm may be directly or indirectly moved by an electrically driven actuator instead of introducing the pressurized fluid into an atmosphere chamber of the variable pressure regulator.

Claims

CLAIMS :

1. A fuel cell system which includes a fuel gas supply passage through which a fuel gas is supplied from a fuel gas source to a fuel cell, and a variable pressure regulator that is provided in the fuel gas supply passage, and adjusts a pressure of the fuel gas supplied from the fuel gas source so that the fuel gas is discharged toward a downstream side, comprising change means that changes an operation characteristic of the variable pressure regulator in accordance with a state of the fuel cell system.

2. The fuel cell system according to claim 1, further comprising state detection means that detects a physical quantity with respect to the state of the fuel cell system, wherein the change means changes the operation characteristic of the variable pressure regulator based on the detected physical quantity.

3. The fuel cell system according to claim 2, wherein: the change means determines whether a foreign substance is accumulated in the fuel gas supply passage based on the detected physical quantity; and when the change means determines that the foreign substance is accumulated in the fuel gas supply passage, and the foreign substance is required to be discharged, the change means changes the operation characteristic of the variable pressure regulator so that a discharge pressure of the variable pressure regulator increases.

4. The fuel cell system according to claim 2, wherein: the change means determines whether the fuel cell is in a state upon start-up or resumption from an intermittent operation based on the detected physical quantity; and when the change means determines that the fuel cell is in the state upon start-up or resumption from the intermittent operation, the change means changes the operation characteristic of the variable pressure regulator so that a discharge pressure of the variable pressure regulator increases.

5. The fuel cell system according to claim 2, wherein the state detection means detects a cell voltage as the physical quantity, and when the detected cell voltage is equal to a predetermined volume or lower, the change means changes the operation characteristic of the variable pressure regulator so that a discharge pressure of the variable pressure regulator increases.

6. The fuel cell system according to claim 2, wherein the state detection means detects a fuel gas pressure as the physical quantity; and when the detected fuel gas pressure deviates from a target pressure by a predetermined value or larger, the change means changes the operation characteristic of the variable pressure regulator so that a discharge pressure of the variable pressure regulator decreases.

7. The fuel cell system according to claim 1 or 2, wherein: the state of the fuel cell system is accumulated state of a foreign substance in the fuel gas supply passage; and when the foreign substance is discharged, the change means changes the operation characteristic of the variable pressure regulator so that a discharge pressure of the variable pressure regulator increases.

8. The fuel cell system according to claim 1 or 2, wherein: the fuel cell is in a state upon start-up or resumption from an intermittent operation; and when the fuel cell is in the state upon start-up or resumption from the intermittent operation, the change means changes the operation characteristic of the variable pressure regulator so that a discharge pressure of the variable pressure regulator increases.

9. The fuel cell system according to claim 1 or 2, wherein: when the fuel cell system is in a state where a fuel gas leakage is detected, and the fuel gas leakage is to be detected, the change means changes the operation characteristic of the variable pressure regulator so that a discharge pressure of the variable pressure regulator increases.

10. The fuel cell system according to any one of claims 1 to 9, wherein: the variable pressure regulator is structured to be able to adjust the discharge pressure by introducing a pressurized fluid from outside of the variable pressure regulator; the change means includes a pressurized fluid supply passage through which the pressurized fluid from outside of the variable pressure regulator thereinto, and an exhaust valve that is capable of discharging the pressurized fluid from an intermediate portion of the pressurized fluid supply passage to outside of the pressurized fluid supply passage, and control means that controls an opening degree of the exhaust valve in accordance with the state of the fuel cell system.

11. A fuel cell system comprising: a fuel gas supply passage through which a fuel gas is supplied from a fuel gas source to a fuel cell; a variable pressure regulator that is provided in the fuel gas supply passage, and adjusts a pressure of the fuel gas from the fuel gas source so that the fuel gas is discharged toward a downstream side; and a change device that changes an operation characteristic of the variable pressure regulator in accordance with a state of the fuel cell system.