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WO2006038098A2 - Gas supply system and gas supply method - Google Patents

Gas supply system and gas supply method Download PDF

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Publication number
WO2006038098A2
WO2006038098A2 PCT/IB2005/002964 IB2005002964W WO2006038098A2 WO 2006038098 A2 WO2006038098 A2 WO 2006038098A2 IB 2005002964 W IB2005002964 W IB 2005002964W WO 2006038098 A2 WO2006038098 A2 WO 2006038098A2
Authority
WO
WIPO (PCT)
Prior art keywords
gas
tank
gas supply
flow rate
unit
Prior art date
Application number
PCT/IB2005/002964
Other languages
French (fr)
Other versions
WO2006038098A3 (en
Inventor
Koji Katano
Original Assignee
Toyota Jidosha Kabushiki Kaisha
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Toyota Jidosha Kabushiki Kaisha filed Critical Toyota Jidosha Kabushiki Kaisha
Publication of WO2006038098A2 publication Critical patent/WO2006038098A2/en
Publication of WO2006038098A3 publication Critical patent/WO2006038098A3/en

Links

Classifications

    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00Fuel cells; Manufacture thereof
    • H01M8/04Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04082Arrangements for control of reactant parameters, e.g. pressure or concentration
    • H01M8/04089Arrangements for control of reactant parameters, e.g. pressure or concentration of gaseous reactants
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00Fuel cells; Manufacture thereof
    • H01M8/04Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04082Arrangements for control of reactant parameters, e.g. pressure or concentration
    • H01M8/04201Reactant storage and supply, e.g. means for feeding, pipes
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00Fuel cells; Manufacture thereof
    • H01M8/04Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04298Processes for controlling fuel cells or fuel cell systems
    • H01M8/04313Processes for controlling fuel cells or fuel cell systems characterised by the detection or assessment of variables; characterised by the detection or assessment of failure or abnormal function
    • H01M8/0438Pressure; Ambient pressure; Flow
    • H01M8/04388Pressure; Ambient pressure; Flow of anode reactants at the inlet or inside the fuel cell
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00Fuel cells; Manufacture thereof
    • H01M8/04Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04298Processes for controlling fuel cells or fuel cell systems
    • H01M8/04313Processes for controlling fuel cells or fuel cell systems characterised by the detection or assessment of variables; characterised by the detection or assessment of failure or abnormal function
    • H01M8/04664Failure or abnormal function
    • H01M8/04686Failure or abnormal function of auxiliary devices, e.g. batteries, capacitors
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17CVESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2270/00Applications
    • F17C2270/07Applications for household use
    • F17C2270/0763Fuel cells
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00Fuel cells; Manufacture thereof
    • H01M8/10Fuel cells with solid electrolytes
    • H01M2008/1095Fuel cells with polymeric electrolytes
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00Fuel cells; Manufacture thereof
    • H01M8/04Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04082Arrangements for control of reactant parameters, e.g. pressure or concentration
    • H01M8/04201Reactant storage and supply, e.g. means for feeding, pipes
    • H01M8/04216Reactant storage and supply, e.g. means for feeding, pipes characterised by the choice for a specific material, e.g. carbon, hydride, absorbent
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00Fuel cells; Manufacture thereof
    • H01M8/04Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04298Processes for controlling fuel cells or fuel cell systems
    • H01M8/04313Processes for controlling fuel cells or fuel cell systems characterised by the detection or assessment of variables; characterised by the detection or assessment of failure or abnormal function
    • H01M8/0438Pressure; Ambient pressure; Flow
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00Fuel cells; Manufacture thereof
    • H01M8/04Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04298Processes for controlling fuel cells or fuel cell systems
    • H01M8/04313Processes for controlling fuel cells or fuel cell systems characterised by the detection or assessment of variables; characterised by the detection or assessment of failure or abnormal function
    • H01M8/04664Failure or abnormal function
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30Hydrogen technology
    • Y02E60/32Hydrogen storage
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30Hydrogen technology
    • Y02E60/50Fuel cells

Definitions

  • the invention relates to a technology for detecting an amount of gas supplied to a unit that demands gas supply.
  • Japanese Patent Application Laid-Open Publication No. JP-A-IO- 284098 discloses the system that detects leakage of the fuel gas on the basis of the difference between an amount of supplied fuel gas which has been detected by the flow meter and an amount of consumed fuel gas which has been calculated based on the current value of the fuel cell.
  • Related art of the invention are disclosed in Japanese Patent Application Laid-Open Publication No. JP-A-2002-352824, Japanese Patent Application Laid-Open Publication No . JP-A- 10-281011, Japanese Patent Application Laid-Open Publication No.JP-A-2004-55339 and Japanese Patent Application Laid-Open Publication No.JP-A-2001-295996.
  • the gas supply system is provided with m (an integer equal to or greater than 2) units of gas tanks, a gas passage that admits a gas from the m units of gas tanks so as to be supplied to a unit that demands a gas supply, and a control unit that controls the gas supply from the m units of gas tanks to the gas passage.
  • the gas passage includes a passage portion through which the gas flows to the unit that demands the gas supply from n (n ⁇ m) units as a first group selected from the m units of the gas tanks, and the gas does not flow to the unit that demands the gas supply from the rest of the gas tanks as a second group.
  • the gas supply system further includes a flow rate detection unit capable of detecting a flow rate of the gas in the passage portion.
  • the gas flowing toward the unit that demands gas supply does not draw heat from the gas tank as the second group.
  • the above-structured gas supply system makes it possible to reduce the degree at which the flow rate detection unit is cooled by the gas supplied to the unit that demands gas supply. This may reduce the chance of the operation failure in the flow rate detection unit upon detection of the flow rate of the gas supplied to the unit that demands gas supply.
  • the gas supply to the unit that demands gas supply from the other tank is interrupted.
  • the above structure may prevent the gas from being supplied to the unit that demands gas supply from the gas tank as the first group when the gas tank as the second group supplies the gas to the unit that demands gas supply. Accordingly in the aforementioned case, heat of the flow rate detection unit is not drawn by the gas supplied from the gas tank to the unit that demands gas supply.
  • the flow rate detection unit detects the flow rate of the gas
  • the gas supply from the gas tank as the first group is allowed while interrupting the gas supply from the gas tank as the second group.
  • the flow rate detection unit upon detection of the flow rate of the gas supplied to the unit that demands gas supply, such gas flows through the aforementioned passage portion. This makes it possible to accurately detect the flow rate of the gas supplied to the unit that demands gas supply.
  • the detected flow rate is higher than a predetermined reference value, it is preferable to make a determination that there is a leakage of the gas.
  • the above-described system makes it possible to accurately detect the leakage of gas using the flow rate detection unit with less chance of the operation failure.
  • the gas is supplied from the gas tank as the second group in preference to the gas tank as the first group under a predetermined condition.
  • the above- described structure makes it possible to maintain the gas in the gas tank as the first group so as to be used for detecting the flow rate for the subsequent flow rate detection.
  • the gas supply system is provided with a residual gas amount detection unit that detects an amount of a residual gas within each of the gas tanks. It is preferable to control the gas supply from the respective gas tanks such that the gas tank as the first group becomes a last gas tank capable of supplying the gas to the unit that demands gas supply after the gas in the rest of the gas tanks is used up. It is further preferable to control the gas supply such that a total of the residual amount of the gas in the gas tank as the first group is equal to or smaller than a first predetermined value when the gas in all the gas tanks as the second group is used up.
  • the flow rate of gas to be supplied to such unit may be detected to the end in case of necessity. It is preferable to set the first predetermined value such that no operation failure occurs in the flow rate detection unit which has been cooled in the gas even though the gas is continuously supplied to the unit from the state where the total amount of the residual gas in all the gas tanks as the first group is the first predetermined value until the gas in all the gas tanks as the first group is used up.
  • the flow rate of the gas is not detected by the flow rate detection unit, it is preferable to supply (a) the gas preferentially from the gas tank as the first group to the unit that demands gas supply when a total amount of the residual gas in the n units of the gas tanks as the first group is larger than the first predetermined value, and (b) the gas preferentially from the gas tank as the second group to the unit that demands gas supply when the total amount of the residual gas in the n units of the gas tanks as the first group is smaller than the first predetermined value.
  • the gas stored in the gas tank as the second group is preferentially used. This makes it possible to control gas supply such that the gas stored in the gas tank as the first group is supplied to the unit that demands gas supply when the gas supply from the gas tank as the second group is used up, and accordingly is no longer supplied to the unit.
  • the total amount of the residual gas in the n units of the gas tanks as the first group is equal to or smaller than a second predetermined value, it is preferable to supply the gas from the gas tank as the second group to the gas tank as the first group via the gas passage.
  • the amount of gas remained in the gas tank as the first group is reduced to the unexpectedly low level, which prevents the flow rate detection unit from detecting the flow rate in spite of various types of control with respect to the gas supply.
  • the above-described structure makes it possible to supply gas to the gas tank as the first group from that as the second group. This makes it possible to avoid such trouble, allowing detection of the flow rate of gas to be supplied to the unit to the end.
  • the number n is set to 1. This makes it possible to reduce the amount of heat drawn from the flow rate detection unit by the gas supplied from the gas tank as the first group to the unit that demands gas supply during operation of the gas supply system.
  • the gas supply system includes a single unit of gas tank, a plurality of gas passages which admit a gas from the single unit of gas tank so as to be supplied to a unit that demands gas supply and a control unit that controls a gas supply to the plurality of gas passages of the gas tank, the gas supply system characterized by further comprising a flow rate detection unit that is capable of detecting the flow rate of the gas in a part of the plurality of the gas passages.
  • the unit that demands gas supply is a fuel cell
  • the amount of gas consumed by the fuel cell is substantially small. Accordingly, this makes it possible to detect the leakage of gas by substantially a small amount.
  • Fig. 1 is a view that shows a structure of a gas supply system according to a first embodiment of the invention
  • Fig. 2 is a flowchart that represents a control routine for supplying hydrogen gas
  • Fig. 3 is a flowchart that represents a sub-routine for selecting the tank from which the hydrogen gas is supplied to the fuel cell;
  • Fig. 4 is a flowchart that represents a sub-routine for detecting the flow rate of the hydrogen gas
  • Fig. 5 is a view that shows another structure of the gas supply system according to a second embodiment of the invention
  • Fig. 6 is a view that shows another structure of the gas supply system according to a third embodiment of the invention.
  • Fig. 7 is a view that shows another structure of the gas supply system according to a fourth embodiment of the invention.
  • Fig. 8 is a view that shows another structure of the gas supply system according to a modified example of the invention.
  • A. OUTLINE OF EMBODIMENT In a gas supply system 1 for supplying hydrogen gas to a fuel cell from a plurality of high pressure hydrogen tanks 11, 21, 31, 41 as shown in Fig. 1, a hydrogen gas leakage is detected.
  • a hydrogen gas supply pipe 50 connected to the fuel cell 2 is connected to those four tanks from the one closest to the fuel cell 2, that is, 11, to the one that is the most distant from the fuel cell 2, that is, 41 so as to be selectively operated independently.
  • Each of those tanks 11 to 41 stores the hydrogen gas at a maximum pressure of 35 MPa from which the gas at the pressure reduced to
  • the hydrogen gas leakage is detected by detecting the flow rate of the hydrogen gas within the hydrogen gas supply pipe 50 while the fuel cell 2 is not operated for power generation.
  • the hydrogen gas that permeates, in other words, cross leaks, from the hydrogen electrode to the oxygen electrode of the fuel cell 2 by the amount, for example, 10 to 20 cc/min. will only be consumed. Accordingly the amount of the hydrogen gas that exceeds the aforementioned consumption amount may be considered as having the leakage.
  • a flow rate sensor 74 for detecting the flow rate of the hydrogen gas is arranged in the hydrogen gas supply pipe 50 at a position between the tank 41 that is the most distant from the fuel cell and the tank 31 that is the second most distant from the fuel cell.
  • the hydrogen gas is supplied to the fuel cell 2 only from the tank 41 such that the flow rate of the hydrogen gas within the hydrogen gas supply pipe 50 is detected.
  • the flow rate sensor 74 is exposed to the low temperature hydrogen gas only when the tank 41 is used. This makes it possible to prevent the flow rate sensor 74 from being constantly exposed to the low temperature hydrogen gas during operation of the fuel cell 2. Accordingly the operation failure in the flow rate sensor 74 caused by the low temperature gas may be prevented.
  • Fig. 1 is a view that shows the general structure of a gas supply system according to the first embodiment of the invention.
  • the gas supply system 1 of the first embodiment is structured to supply hydrogen gas as the fuel gas to the fuel cell 2, and provided with four high pressure hydrogen tanks 11, 21, 31, 41. Each of those high pressure hydrogen tanks 11 to 41 stores the hydrogen gas under pressure of 35 MPa at maximum.
  • the respective high pressure hydrogen tanks 11 to 41 are connected to the hydrogen gas supply pipe 50 through which the hydrogen gas is supplied to the fuel cell 2.
  • the tank 41 will be referred to as a "detection tank" having the hydrogen gas discharged therefrom subjected to the flow rate detection.
  • Those high pressure hydrogen tanks 11, 21, 31, 41 are provided with inner pressure sensors 12, 22, 32, 42 for detecting the inner pressure of the respective tanks, and cutoff valves 13, 23, 33, 43 for cutting off the gas supply, respectively.
  • the inner pressure sensors 12, 22, 32, 42 are employed as sensors for detecting the amount of the hydrogen gas stored in the respective high pressure hydrogen tanks 1 1 , 21, 31, 41, respectively.
  • the hydrogen gas As the hydrogen gas is supplied to the outside from the respective high pressure hydrogen tanks 11, 21, 31, 41, the pressure within each of those tanks is reduced. Accordingly the temperature of each hydrogen gas within the respective tanks 11 to 41 will be decreased to, for example, minus several tens degrees.
  • the hydrogen gas supply pipe 50 and the flow rate sensor 74 through which the hydrogen gas flows from those tanks may be cooled in contact with the low temperature hydrogen gas.
  • Each of those high pressure hydrogen tanks 11, 21, 31, 41 is connected to the hydrogen gas supply pipe 50 so as to be branched therefrom in the order as shown in Fig. 1.
  • the high pressure hydrogen tank 11 is connected to the hydrogen gas supply pipe 50 at the position that is the closest to the fuel cell 2
  • the high pressure hydrogen tank 41 is connected to the hydrogen gas supply pipe 50 at the position that is the most distant from the fuel cell 2 in view of the path length of the hydrogen gas flow.
  • the hydrogen gas supply pipe 50 therefore, includes a pipe section 51 that allows the hydrogen gas supplied from the high pressure hydrogen tanks 11, 21, 31, 41 to flow toward the fuel cell 2, a pipe section 52 that allows the hydrogen gas supplied from the high pressure hydrogen tanks 21, 31, 41 to flow toward the fuel cell 2, a pipe section 53 that allows the hydrogen gas supplied from the high pressure hydrogen tanks 31, 41 to flow toward the fuel cell 2, and a pipe section 54 that allows the hydrogen gas supplied only from the high pressure hydrogen tank 41 to flow to the fuel cell 2.
  • the gas that flows from a certain tank toward a unit that demands gas supply does not include “the gas discharged from the tank to flow in the direction away from the unit that demands gas supply on the flow passage before it reaches the unit".
  • the gas discharged from the tank in the case where any one of the tanks 11 to 31 is supplying the hydrogen gas to the fuel cell 2, and the gas discharged from the tank flows away from the fuel cell 2 to reach the pipe section 54, this state is not considered that the "gas flowing from the tank toward the unit (fuel cell 2)" passes through the pipe section 54 in view of the term used in the specification.
  • the pipe section 51 through which the hydrogen gas supplied from the high pressure hydrogen tanks 11, 21, 31, 41 flows toward the fuel cell 2 is provided with a regulator 60.
  • the pressure of the hydrogen gas within the hydrogen gas supply pipe 50 is reduced to 0.8 MPa by the regulator 60 so as to be supplied to the fuel cell 2.
  • the pipe section 54 through which the hydrogen gas supplied only from the high pressure hydrogen tank 41 flows is provided with a flow rate sensor capable of detecting the flow rate of the hydrogen gas passing through the pipe section 54.
  • the gas supply system 1 is provided with an ECU 100 that receives detection values of pressures of the respective tanks from the inner pressure sensors 12, 22, 32, 42, and detection values of the flow rate of the hydrogen gas from the flow rate sensor 74, respectively.
  • the ECU 100 controls switching operations of the cutoff valves 13, 23, 33, 43 so as to control the operation of the fuel cell 2.
  • Fig. 2 is a flowchart that shows how the hydrogen gas is supplied.
  • step Sl 10 it is determined whether the pressure P4 within the detection tank 41 is higher than a predetermined reference value Pthl . If the pressure P4 within the detection tank 41 is higher than the reference value Pthl, that is, Yes is obtained in step Sl 10, the process proceeds to step S 120.
  • step S 120 it is determined whether the power generation level E4 produced using the hydrogen gas which has been continuously supplied from the detection tank 41 to the fuel cell 2 is lower than a predetermined reference value Ethl .
  • the hydrogen gas is supplied to the fuel cell 2 from the tank other than the detection tank 41, that is, any one of those tanks 11, 21, or 31, the value of the level E4 becomes 0. If the continuous power generation level E4 using the hydrogen gas supplied from the detection tank 41 is lower than the predetermined reference value Ethl, the process proceeds to step S130. Meanwhile, if the continuous power generation level E4 is equal to or higher than the predetermined reference value Ethl, the process proceeds to step S 140.
  • step S 120 By executing step S 120 where the continuous supply of the hydrogen gas from the detection tank 41 is restricted, the flow rate sensor 74 provided in the pipe section 54, which has been exposed to the low temperature hydrogen gas may be prevented from being excessively cooled having its heat drawn by the hydrogen gas, and accordingly from causing the operation failure upon detection of the flow rate.
  • the tank for supplying the hydrogen gas is switched to the one other than the detection tank 41 so as to prevent the hydrogen gas from flowing through the pipe section 54, the heat of the flow rate sensor 74 is no longer drawn by the low temperature hydrogen gas.
  • the flow rate sensor 74 having its temperature once reduced by the hydrogen gas may draw heat from its periphery. Then the temperature of the flow rate sensor 74 is increased to become approximately the same level as that of the periphery if the flow of the hydrogen gas through the pipe section 54 is interrupted for a predetermined period.
  • step S 130 the hydrogen gas is supplied from the detection tank 41 to the fuel cell 2. If the pressure P4 of the detection tank 41 is higher than the reference value Pthl (see step Sl 10), continuous use of the detection tank 41 for the long period of time is avoided (see S 120). Then the detection tank 41 is selected as the one for supplying the hydrogen gas in preference to the other tanks (see S 130).
  • the gas supply system 1 may be operated such that the pressure P4 of the detection tank 41 becomes close to the reference value Pthl upon start-up of the gas supply system 1.
  • the reference value Pthl is set to the value of pressure such that no operation failure occurs in the flow rate sensor 74 owing to excessive cooling even if the hydrogen gas is continuously supplied from the state of the inner pressure of the detection tank 41 at Pthl to the state of the pressure at which the gas cannot be supplied outside.
  • the phrase "the tank A is selected or used in preference to the tank B" represents that the tank A is used (see step S 130) after the determination is made (see step S 120) that the tank A is usable, and the tank B is used when the tank A is not usable. When the determination is made that both tanks A and B are not usable, the tank B is not used.
  • step S 130 The supply of the hydrogen gas from the detection tank 41 to the fuel cell 2 is continuously performed in step S 130 until the power generation amount in the fuel cell 2 reaches a fixed value E4u.
  • the fixed value of the power generation amount Eu4 is smaller than the power generation value Ethl as the reference level in step S 120.
  • the continuous supply of the hydrogen gas from the detection tank 41 is restricted on the basis of the continuous power generation amount so as to prevent the operation failure in the flow rate sensor 74 owing to cooling by the hydrogen gas as in step S 120. Thereafter, the process proceeds to step S 140.
  • step S 140 the tank for supplying the hydrogen gas to the fuel cell 2 is selected.
  • Fig. 3 is a flowchart showing how the tank for supplying the hydrogen gas to the fuel cell 2 is selected.
  • step S210 it is determined whether the hydrogen gas is left in any of the tanks 11 to 31 so as to be supplied to the fuel cell 2. More specifically, if the inner pressure in any one of the tanks 11 to 31 is higher than the reference value Ps, it is determined that there is the hydrogen gas left in such tank. That is, if Yes is obtained in step S210, the process proceeds to step S220.
  • step S220 the tank having the hydrogen gas at the highest inner pressure is selected as the tank for supplying the hydrogen gas to the fuel cell 2.
  • step S230 the detection tank 41 is selected as the one for supplying the hydrogen gas to the fuel cell 2.
  • step S220 the tank for supplying the hydrogen gas to the fuel cell 2 is selected from those tanks 11 to 31.
  • step S 230 the detection tank 41 is selected. If the pressure P4 within the detection tank 41 is reduced to the reference value Pthl, that is, No is obtained in step Sl 10 of the flowchart shown in Fig. 2, any one of the tanks 11 to 31 is selected as the tank for supplying the hydrogen gas in preference to the detection tank 41.
  • the aforementioned process makes it possible to control the supply of the hydrogen gas such that the hydrogen gas at the pressure slightly lower than the pressure Pthl is left in the detection tank 41.
  • the hydrogen gas may be supplied from the detection tank 41 to the fuel cell 2.
  • the flow rate sensor 74 is provided in the pipe section 54 that allows the hydrogen gas supplied from only the high pressure hydrogen tank 41 to flow therethrough. Accordingly the flow rate of the hydrogen gas supplied to the fuel cell 2 can be detected only when the hydrogen gas is supplied from the detection tank 41 to the fuel cell 2.
  • the gas supply system 1 is operated such that the hydrogen gas is left in the detection tank 41 when the hydrogen gas in the tanks 11 to 31 is used up as described above. This makes it possible to detect the flow rate of the hydrogen gas supplied to the fuel cell 2 until the hydrogen gas in all the tanks 11 to 41 is used up in case of necessity.
  • the reference value Pthl is set as the gas pressure such that no operation failure occurs in the flow rate sensor 74 even if it has been excessively cooled as being exposed to the hydrogen gas continuously supplied from the detection tank 41 to the fuel cell 2 until the hydrogen gas is no longer supplied. Even if the hydrogen gas is continuously supplied from the detection tank 41 after the hydrogen gas stored in the tanks 11 to 31 is used up, the flow rate sensor 74 never has the operation failure owing to excessive cooling.
  • the phrase "use up the hydrogen gas stored in the tank” represents that the residual amount of the hydrogen gas in the gas tank becomes the level at which the gas cannot be supplied to the unit that demands gas supply. The detection of the flow rate of the hydrogen gas will be described later.
  • step S 150 of the flowchart shown in Fig. 2 the supply of the hydrogen gas that has been continuously performed from the tank to the fuel cell 2 is stopped, and the supply of the hydrogen gas from the tank selected in step S 140 is started.
  • the tank for supplying the hydrogen gas to the fuel cell 2 is the one selected from the tanks 11 to 41.
  • step S 160 it is determined whether the condition for finishing the operation of the fuel cell 2 has been established.
  • the aforementioned condition is established when it is determined that the operation switch (not shown) of the fuel cell 2 has been switched to OFF, or the hydrogen gas which can be supplied to the fuel cell 2 is not left in all the tanks 11 to 41. If the condition for finishing the operation of the fuel cell 2 is established, the ECU 100 ends the operation of the gas supply system 1.
  • step S 170 it is determined whether the signal indicating the request for detecting the flow rate of the hydrogen gas supplied to the fuel cell 2 has been received by the ECU 100.
  • the signal indicating the request for detecting the flow rate of the hydrogen gas is transmitted at a predetermined time interval when the power generation is not performed by the fuel cell 2. If it is determined that the ECU 100 receives the signal indicating the request for detecting the flow rate of the hydrogen gas, the process proceeds to step S 180 where the flow rate of the hydrogen gas is detected.
  • Fig. 4 is a flowchart that shows how the flow rate of the hydrogen gas is detected.
  • step S310 it is determined whether the pressure P4 of the detection tank 41 is higher than a predetermined reference value Pth2 by the ECU 100.
  • the reference value Pth2 is set as the pressure such that the detection tank 41 is allowed to continuously supply the hydrogen gas for the period sufficient to detect the flow rate of the hydrogen gas at a fixed accuracy.
  • the reference value Pht2 is lower than the reference value Pthl (see step S 110 in Fig. 2), which is higher than the reference pressure Ps at which the gas is allowed to be supplied outside. If the pressure P4 of the detection tank 41 is higher than the reference value Pth2, that is, Yes is obtained in step S310, the process proceeds to step S320.
  • step S320 the supply of the hydrogen gas to the fuel cell 2, which has been performed is stopped, and the supply of the hydrogen gas from the detection tank 41 is started.
  • the hydrogen gas is continuously supplied therefrom.
  • the signal indicating the request for detecting the flow rate of the hydrogen gas is issued while the fuel cell 2 is not operated for power generation.
  • the amount of the hydrogen gas supplied from the detection tank 41 in steps subsequent to step S320 is smaller than the amount of the hydrogen gas supplied while the fuel cell 2 is operated for power generation. That is, such amount is substantially small corresponding to the amount of the hydrogen gas that permeates (cross leaks) from the hydrogen electrode to the oxygen electrode of the fuel cell 2.
  • the aforementioned value can be preliminarily estimated. More specifically, the amount of consumed hydrogen gas owing to cross leak is in the range from approximately 10 to 20 cc/min.
  • step S330 the ECU 100 receives the signal sent from the flow rate sensor 74, and detects the flow rate V of the hydrogen gas supplied from the detection tank 41 to the fuel cell 2 via the pipe section 54.
  • step S340 the ECU 100 determines whether the detected flow rate V of the hydrogen gas is greater than a predetermined reference value Vt.
  • the reference value Vt is set on the basis of the appropriate cross leak amount in the fuel cell 2. If the detected flow rate V of the hydrogen gas is equal to or lower than the reference value Vt, that is, No is obtained in step S340, the process returns to step S 140 of the flowchart shown in Fig. 2. Meanwhile if Yes is obtained in step S340, the process proceeds to step S350 where the ECU 100 allows the warning with respect to the hydrogen gas leakage to be displayed on a monitor screen (not shown). The process then returns to step S 140.
  • step S 340 detection of the flow rate of the hydrogen gas supplied to the fuel cell 2 (see step S 340), and determination with respect to the hydrogen gas leakage (see step S350) are performed while the fuel cell 2 is not operated for power generation.
  • the flow rate sensor of the type capable of accurately detecting the flow rate in the range from several tens to 100 cc/min. may be employed as the flow rate sensor 74 so as to detect a small amount of the leaked hydrogen gas.
  • step S310 if the pressure P4 of the detection tank 41 is lower than the reference value Pth2, that is, No is obtained, the process proceeds to step S360.
  • step S36O it is determined whether the pressure Pp of the tank that has been supplying the hydrogen gas at that time is higher than a predetermined reference value Pth3 that is higher than the reference value Pth2 (see step S310). If the tank that has been supplying the hydrogen gas at that time is the detection tank 41, that is, No is obtained in step 310, the determination result in step S360 also becomes No.
  • step S410 the cutoff valve 43 of the detection tank 41 is opened in parallel with opening of the cutoff valve (13 to 33 in Fig. 1) of the tank that has been supplying the hydrogen gas.
  • the hydrogen gas stored in the tank that has been supplying the hydrogen gas is supplied to the fuel cell 2, and at the same time, supplied to the detection tank ⁇ 41 via the hydrogen gas supply pipe 50.
  • step S410 the cutoff valve 43 of the detection tank 41 is opened until the pressure of the detection tank 41 reaches a reference value Pth4.
  • step S410 the pressure P4 of the detection tank 41 becomes higher than the pressure Pth2.
  • the determination result in step S310 in the subsequent cycle becomes Yes.
  • step S410 brings the inner pressure of the detection tank 41 to a level too low to allow the flow rate sensor 74 to detect the flow rate
  • the hydrogen gas may be supplied from the tank that has been supplying to the detection tank 41.
  • the hydrogen gas is supplied to the fuel cell 2 from the detection tank 41 so as to allow the detection of the flow rate of the hydrogen gas supplied to the fuel cell 2 (see step S330), and detection of the hydrogen leakage (see step S 340).
  • step S360 if the pressure Pp of the tank that has been supplying the hydrogen gas is equal to or lower than the reference value Pth3, the process proceeds to step S370.
  • step S370 it is determined whether there is a tank having the inner pressure higher than the reference value Pth3.
  • step S380 the ECU 100 allows the warning message with respect to inability of detecting the hydrogen gas leakage to be displayed on the monitor screen (not shown) as the amount of the residual hydrogen gas is insufficient. The process then returns to step S 140 of the flowchart shown in Fig. 2.
  • step S390 the tank that stores the hydrogen gas at the highest pressure is selected as the tank for supplying the hydrogen gas to the fuel cell 2. Then in step S400, the supply of the hydrogen gas that has been supplied from the tank to the fuel cell 2 is stopped, and the supply of the hydrogen gas from the tank selected in step S390 is started. By executing the aforementioned process, even if the pressure of the tank that has been supplying the hydrogen gas is not sufficiently high, the other tank is selected so as to supply the hydrogen gas therefrom to the detection tank 41 (see step S410) .
  • step S 170 of the flowchart shown in Fig. 2 if the ECU 100 has not received the signal indicating the request for detecting the flow rate of the hydrogen gas, that is, No is obtained, the process proceeds to step S 190.
  • step S 190 it is determined whether the condition for switching the tank for supplying the hydrogen gas to the fuel cell 2 has been established. The aforementioned condition for switching the tank is determined to be established when the amount of power generated using the hydrogen gas, that is, Es is larger than a predetermined reference value Eth2, or when there is no hydrogen gas sufficient to be supplied to the fuel cell 2 left in the tank that has been supplying the hydrogen gas.
  • step S 160 the process returns to step S 160, and the hydrogen gas is subsequently supplied from the same tank to the fuel cell 2 unless Yes is obtained in steps S 160 and S 170. If it is determined that the condition for switching the tank is established in step S 190, the process returns to step SI lO. Execution of the aforementioned process makes it possible to switch the tank for supplying the hydrogen gas upon each generation of power at a fixed level.
  • the hydrogen gas is supplied to the fuel cell 2 from any one selected from the high pressure hydrogen tanks 11, 21, 31, 41.
  • the flow rate sensor 74 is provided in the pipe section 54 through which the hydrogen gas supplied from the high pressure hydrogen tank 41 is only allowed to flow. Accordingly the flow rate of the hydrogen gas supplied from the high pressure hydrogen tank 41 to the fuel cell 2 may be detected by the flow rate sensor 74.
  • the flow rate sensor 74 draws heat from its periphery. This makes it possible to prevent the flow rate sensor 74 from being excessively cooled. As a result, the operation failure in the flow rate sensor 74 may be prevented.
  • Fig. 5 is a schematic view that represents a structure of a gas supply system Ia according to the second embodiment.
  • the regulator 60 is arranged in the pipe section 51 that allows the hydrogen gas supplied from all the high pressure hydrogen tanks 11 to 41 to flow therethrough.
  • regulators 14, 24, 34, 44 are arranged between the hydrogen gas supply pipe 50 and the respective tanks 11, 21, 31, 41 such that each pressure of the hydrogen gas supplied from the tanks 11 to 41 is reduced to 0.8 MPa.
  • the pressure within the hydrogen gas supply pipe 50 is kept at 0.8 MPa.
  • the pressure of the hydrogen gas within the hydrogen gas supply pipe 50 is kept at 0.8 MPa. Even if the cutoff valve 43 of the detection tank 41 is opened simultaneously with opening of the cutoff valve of the other tank, the hydrogen gas cannot be supplied to the detection tank 41 from the other tank. In the second embodiment, therefore, the process to be executed in steps S310, S360 to S410 of the flowchart shown in Fig. 4 is not performed.
  • the gas supply system according to the second embodiment is structured such that the flow rate sensor 74 is not exposed to the low temperature hydrogen gas, thus reducing possibility of the operation failure in the flow rate sensor 74 upon detection of the flow rate.
  • the pressure of the hydrogen gas within the hydrogen gas supply pipe 50 is decreased by the regulators 14, 24, 34, 44, respectively so as to enhance the strength of the hydrogen gas supply pipe 50 compared with the gas supply system according to the first embodiment as well as to reduce the weight and the cost of the hydrogen gas supply pipe 50.
  • Fig. 6 is a schematic view that represents the structure of a gas supply system Ib according to a third embodiment.
  • a single unit of the flow rate sensor is arranged in the hydrogen gas supply pipe 50.
  • three units of the flow rate sensors are arranged in the hydrogen gas supply pipe 50. That is, a flow rate sensor 82 is arranged in the pipe section 502 through which the hydrogen gas from the tank 21 to the fuel cell 2 flows and the hydrogen gas from the other tank to the fuel cell 2 does not flow so as to detect the flow rate of the hydrogen gas passing through the pipe section 502.
  • flow rate sensors 83, 84 are arranged in the pipe sections 503, 504 through which the hydrogen gas from the tanks 31, 41 to the fuel cell 2 flows and the hydrogen gas from the other tanks to the fuel cell 2 does not flow so as to detect the flow rate of the hydrogen gas passing through the pipe sections 503, 504, respectively.
  • the high pressure hydrogen tanks 21, 31, 41 function as the detection tanks in the third embodiment.
  • the tank is selected from the high pressure hydrogen tanks 11 to 41 one by one.
  • Each of the flow rate sensors 82 to 84 is not in contact with the low temperature hydrogen gas when the hydrogen gas is supplied to the fuel cell 2 from the tank other than the tank corresponding thereto.
  • each of the flow rate sensors 82 to 84 is not constantly exposed to the low temperature hydrogen gas, resulting in the reduced possibility in the operation failure of the flow rate sensor upon detection of the flow rate.
  • the gas supply system Ib according to the third embodiment is provided with a plurality of flow rate sensors 82 to 84. This makes it possible to cause any one of the high pressure hydrogen tanks 21, 31, 41 corresponding to the respective flow rate sensors by which each amount of the hydrogen gas discharged therefrom is detectable to function as the last tank for supplying the hydrogen gas to the fuel cell 2. That is, the gas supply system according to the third embodiment has a higher degree of freedom with respect to control of the hydrogen gas supply compared with the gas supply systems 1 and Ia according to the first and the second embodiments, respectively.
  • the flow rate sensor is not arranged in the pipe section 501 through which the hydrogen gas from the tank 11 to the fuel cell 2 flows, and the hydrogen gas from the other tank to the fuel cell 2 does not flow.
  • a flow rate sensor 81 may be arranged in the pipe section 501 such that the value of the flow rate of the hydrogen gas detected by the flow rate sensor 81 is input to the ECU 100.
  • Fig. 7 is a schematic view that represents the structure of a gas supply system Ic according to a fourth embodiment.
  • the hydrogen gas supply pipe 50 according to the first to the third embodiments has the pipe section 51 through which the hydrogen gas flows from the respective tanks to the fuel cell 2.
  • the hydrogen gas supply pipe 50 is joined with the single pipe section 51 before it reaches the fuel cell 2 at the end.
  • a hydrogen gas supply pipe 50c is capable of independently supplying the hydrogen gas to the fuel cell 2 via two pipe sections 56, 58 each connected to the fuel cell 2.
  • the hydrogen gas supply pipe 50c of the gas supply system Ic includes the pipe section 56 through which the hydrogen gas flows from the high pressure hydrogen tanks 11, 21 to the fuel cell 2, the pipe section 57 through which the hydrogen gas flows from only the high pressure hydrogen tank 21 to the fuel cell 2, and the pipe section 58 through which the hydrogen gas flows from the high pressure hydrogen tanks 31, 41 to the fuel cell 2, and the pipe section 59 through which the hydrogen gas flows from only the high pressure hydrogen tank 41 to the fuel cell 2.
  • a flow rate sensor 93 is arranged in the pipe section 58 so as to detect the flow rate of the hydrogen gas passing through the pipe section 58. The value of the flow rate of the hydrogen gas detected by the flow rate sensor 93 is input to the ECU 100. That is, in the fourth embodiment, the high pressure hydrogen tanks 31 and 41 function as the detection tanks.
  • the pipe sections 56 and 58 are provided with corresponding regulators 61 and 62, respectively.
  • Each structure of the regulators 61 and 62 is the same as that of the regulator 60 of the first embodiment.
  • the structure of the flow rate sensor 93 is the same as that of the flow rate sensor 74 of the first embodiment.
  • Other features with respect to the structure of the gas supply system Ic according to the fourth embodiment are the same as those of the gas supply system 1 according to the first embodiment.
  • a single tank is selected from the high pressure hydrogen tanks 11 to 41 one by one.
  • the flow rate sensor 93 is not exposed to the low temperature hydrogen gas so long as the hydrogen gas is supplied from the high pressure hydrogen tanks 11 and 21. Accordingly the possibility of the operation failure in the flow rate sensor 93 upon detection of the flow rate of the hydrogen gas may be restricted to a substantially low level.
  • the flow rate sensor for detecting the flow rate of the hydrogen gas flowing through the hydrogen gas supply pipe 50 is arranged in the pipe section 54 through which the hydrogen gas flows from only the high pressure hydrogen tank 41.
  • the flow rate sensors 72 and 73 may be arranged in the pipe section through which the hydrogen gas supplied from two or more tanks flow.
  • the flow rate sensor may be arranged in the position through which the hydrogen gas flows from part of a plurality of tanks to the unit that demands gas supply, and the hydrogen gas does not flow from the rest of the tank to the unit.
  • the portion where the flow rate sensor is arranged may be located upstream of the position through which the hydrogen gas supplied from all the tanks flows such that the hydrogen gas supplied only from the part of the tanks flows to the unit that demands gas supply.
  • the aforementioned structure makes it possible to supply the hydrogen gas from the tank 11 to the unit that demands gas supply without allowing the hydrogen gas to flow through the pipe section where the flow rate sensor is arranged.
  • the excessive cooling of the flow rate sensor may be prevented.
  • the number of the gas tanks as the first group for supplying the hydrogen gas through the pipe section where the flow rate sensor is arranged is preferably equal to or smaller than a half of the total number of tanks for supplying gas to the unit that demands gas supply, and more preferably, such number is set to 1.
  • the tank is switched one by one.
  • a plurality of tanks may be simultaneously used as those for supplying the hydrogen gas to the unit that demands gas supply.
  • the flow rate of the hydrogen gas which is supplied only from the gas tank as the first group for supplying the gas through the pipe section where the flow rate sensor is arranged.
  • This makes it possible to supply the hydrogen gas from the gas tank as the first type through the pipe section where the flow rate sensor is arranged. Accordingly accurate detection of the flow rate of the gas may be made. As a result, the determination with respect to the leakage of the gas flow may be made.
  • the hydrogen gas may be supplied from a plurality of gas tanks as the first group.
  • the flow rate sensor draws heat from its periphery during the set period so as to increase its temperature. Accordingly, the operation failure in the flow rate sensor caused by the excessive cooling may be prevented.
  • the period for which the hydrogen gas can be continuously supplied from the respective tanks is restricted on the basis of the power generation amount (see steps S 120 and S 190 in the flowchart of Fig. 2).
  • the period for which the hydrogen gas can be continuously supplied from the respective tanks may be restricted on the basis of other reference value. For example, in the case where the rate of decrease in the inner pressure of the tank that has been supplying the hydrogen gas reaches a predetermined reference value, the supply of the gas from the tank may be stopped. In the case where the flow rate of the gas supplied from the tank can be detected, the supply of the gas from the tank can be detected when the gas at a fixed volume is supplied.
  • the supply of gas from the tank may be stopped. It is especially preferable to make a predetermined restriction with respect to the continuous supply of gas from the gas tank of the first group through the pipe section where the flow rate sensor is arranged. In the above-described structure, the excessive cooling of the flow rate sensor may be prevented.
  • each of the tanks stores hydrogen gas.
  • the gas supplied by the gas supply system is not limited to the hydrogen gas, but the gas may be oxygen, propane and the other type of gas. It is especially efficient for the structure such that the high pressure gas has been stored in the tank, and as the gas is supplied, the temperature of the gas supplied as the decrease in the pressure within the tank is reduced.
  • a plurality of tanks are used.
  • Fig. 8 shows, a single unit of tank may be used. That is, a plurality of gas passages are provided in the tank, and a gas flow rate detection unit may be provided in a part of the gas passages. It is, thus, possible to form the gas supply system by providing the gas flow rate detection unit arranged in the gas passage.

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Abstract

A gas supply system (1) for supplying a hydrogen gas to a fuel cell (2) from a plurality of hydrogen tanks (11, 21, 31, 41) is structured to detect a leakage of the hydrogen gas. Each one of the respective tanks is selectively used. A flow rate of the hydrogen gas within a hydrogen gas supply pipe (50) is compared with a reference value so as to detect the leakage of the hydrogen gas. A flow rate sensor (74) is arranged in the hydrogen gas supply pipe at a position between the tank (41) that is the most distant from the fuel cell and the tank (31) that is the second most distant from the fuel cell. The hydrogen gas is supplied only from the tank (41) to the fuel cell so as to detect (74) the flow rate of the hydrogen gas.

Description

GAS SUPPLY SYSTEM AND GAS SUPPLY METHOD
FIELD OF THE INVENTION
[0001] The invention relates to a technology for detecting an amount of gas supplied to a unit that demands gas supply.
BACKGROUND OF THE INVENTION
[0002] A fuel cell system that generates power upon fuel gas supply has been well known. Japanese Patent Application Laid-Open Publication No. JP-A-IO- 284098 discloses the system that detects leakage of the fuel gas on the basis of the difference between an amount of supplied fuel gas which has been detected by the flow meter and an amount of consumed fuel gas which has been calculated based on the current value of the fuel cell. Related art of the invention are disclosed in Japanese Patent Application Laid-Open Publication No. JP-A-2002-352824, Japanese Patent Application Laid-Open Publication No . JP-A- 10-281011, Japanese Patent Application Laid-Open Publication No.JP-A-2004-55339 and Japanese Patent Application Laid-Open Publication No.JP-A-2001-295996.
[0003] In the case where the fuel gas is stored in a high pressure tank so as to be supplied to the fuel cell therefrom, the more the amount of the fuel gas is supplied to the outside, the lower the inner pressure of the tank becomes. Accordingly this may decrease the temperature of the fuel gas within the tank. In the art disclosed in Japanese Patent Application Laid-Open Publication No. JP-A- 10-284098, the fuel flow meter is constantly exposed to the fuel gas supplied to the fuel cell. As the fuel gas at the low temperature draws heat from the fuel flow meter, there is a possibility to cause the operation failure in the fuel flow meter. In the art of the publication, reducing the chance of the operation failure in the flow sensor caused by the low temperature fuel gas has never been considered. There exists a problem in the detection of the flow rate of gas, for example, fuel gas supplied to the unit that demands gas supply, for example, the fuel cell.
SUMMARY OF THE INVENTION [0004] It is an object of the invention to provide the technology for reducing the chance of the operation failure in the flow rate detection unit upon detection of the flow rate of the gas supplied to the unit that demands gas supply.
[0005] In order to achieve the aforementioned object, a predetermined process is executed in the gas supply system in accordance with the invention. The gas supply system is provided with m (an integer equal to or greater than 2) units of gas tanks, a gas passage that admits a gas from the m units of gas tanks so as to be supplied to a unit that demands a gas supply, and a control unit that controls the gas supply from the m units of gas tanks to the gas passage. The gas passage includes a passage portion through which the gas flows to the unit that demands the gas supply from n (n < m) units as a first group selected from the m units of the gas tanks, and the gas does not flow to the unit that demands the gas supply from the rest of the gas tanks as a second group. The gas supply system further includes a flow rate detection unit capable of detecting a flow rate of the gas in the passage portion.
[0006] In the above described embodiment, the gas flowing toward the unit that demands gas supply does not draw heat from the gas tank as the second group.
Compared with the case where the flow rate detection unit is constantly exposed to the gas supplied to the unit that demands gas supply, the above-structured gas supply system makes it possible to reduce the degree at which the flow rate detection unit is cooled by the gas supplied to the unit that demands gas supply. This may reduce the chance of the operation failure in the flow rate detection unit upon detection of the flow rate of the gas supplied to the unit that demands gas supply.
[0007] When the gas is supplied to the unit that demands the gas supply from one of the m units of the gas tanks, preferably the gas supply to the unit that demands gas supply from the other tank is interrupted. The above structure may prevent the gas from being supplied to the unit that demands gas supply from the gas tank as the first group when the gas tank as the second group supplies the gas to the unit that demands gas supply. Accordingly in the aforementioned case, heat of the flow rate detection unit is not drawn by the gas supplied from the gas tank to the unit that demands gas supply.
[0008] When the flow rate detection unit detects the flow rate of the gas, preferably the gas supply from the gas tank as the first group is allowed while interrupting the gas supply from the gas tank as the second group. In the above- described system, upon detection of the flow rate of the gas supplied to the unit that demands gas supply, such gas flows through the aforementioned passage portion. This makes it possible to accurately detect the flow rate of the gas supplied to the unit that demands gas supply.
[0009] When the detected flow rate is higher than a predetermined reference value, it is preferable to make a determination that there is a leakage of the gas. The above-described system makes it possible to accurately detect the leakage of gas using the flow rate detection unit with less chance of the operation failure.
[0010] When the flow rate detection unit is not operated for detecting the flow rate, preferably the gas is supplied from the gas tank as the second group in preference to the gas tank as the first group under a predetermined condition. The above- described structure makes it possible to maintain the gas in the gas tank as the first group so as to be used for detecting the flow rate for the subsequent flow rate detection.
[0011] When the gas is supplied from the gas tank as the first group continuously for a predetermined period, it is preferable to stop the gas supply from the gas tank as the first group, and to start the gas supply from the gas tank as the second group. The above-described system makes it possible to reduce the chance of the operation failure that occurs in the flow rate detection unit which has been excessively cooled by the gas continuously supplied from the gas tank as the first group to the unit that demands gas supply.
[0012] Preferably the gas supply system is provided with a residual gas amount detection unit that detects an amount of a residual gas within each of the gas tanks. It is preferable to control the gas supply from the respective gas tanks such that the gas tank as the first group becomes a last gas tank capable of supplying the gas to the unit that demands gas supply after the gas in the rest of the gas tanks is used up. It is further preferable to control the gas supply such that a total of the residual amount of the gas in the gas tank as the first group is equal to or smaller than a first predetermined value when the gas in all the gas tanks as the second group is used up. In the above-described system, as one of the gas tanks as the first group becomes the last gas tank capable of supplying gas to the unit that demands gas supply, the flow rate of gas to be supplied to such unit may be detected to the end in case of necessity. It is preferable to set the first predetermined value such that no operation failure occurs in the flow rate detection unit which has been cooled in the gas even though the gas is continuously supplied to the unit from the state where the total amount of the residual gas in all the gas tanks as the first group is the first predetermined value until the gas in all the gas tanks as the first group is used up.
[0013] When the flow rate of the gas is not detected by the flow rate detection unit, it is preferable to supply (a) the gas preferentially from the gas tank as the first group to the unit that demands gas supply when a total amount of the residual gas in the n units of the gas tanks as the first group is larger than the first predetermined value, and (b) the gas preferentially from the gas tank as the second group to the unit that demands gas supply when the total amount of the residual gas in the n units of the gas tanks as the first group is smaller than the first predetermined value. In the above- described structure, when the total amount of the gas stored in the gas tank as the first group becomes smaller than the first predetermined value, the gas stored in the gas tank as the second group is preferentially used. This makes it possible to control gas supply such that the gas stored in the gas tank as the first group is supplied to the unit that demands gas supply when the gas supply from the gas tank as the second group is used up, and accordingly is no longer supplied to the unit.
[0014] When the total amount of the residual gas in the n units of the gas tanks as the first group is equal to or smaller than a second predetermined value, it is preferable to supply the gas from the gas tank as the second group to the gas tank as the first group via the gas passage. There may be the case where the amount of gas remained in the gas tank as the first group is reduced to the unexpectedly low level, which prevents the flow rate detection unit from detecting the flow rate in spite of various types of control with respect to the gas supply. However, the above-described structure makes it possible to supply gas to the gas tank as the first group from that as the second group. This makes it possible to avoid such trouble, allowing detection of the flow rate of gas to be supplied to the unit to the end.
[0015] Preferably the number n is set to 1. This makes it possible to reduce the amount of heat drawn from the flow rate detection unit by the gas supplied from the gas tank as the first group to the unit that demands gas supply during operation of the gas supply system.
[0016] In order to achieve the aforementioned object, a predetermined process is also executed in another gas supply system in accordance with the invention. The gas supply system includes a single unit of gas tank, a plurality of gas passages which admit a gas from the single unit of gas tank so as to be supplied to a unit that demands gas supply and a control unit that controls a gas supply to the plurality of gas passages of the gas tank, the gas supply system characterized by further comprising a flow rate detection unit that is capable of detecting the flow rate of the gas in a part of the plurality of the gas passages.
[0017] It is preferable to perform the procedures of (a) supplying a gas from the gas tank as the first group to the unit that demands gas supply while interrupting the gas supply to the unit from the gas tank as the second group using the gas supply system according to claim 1, (b) detecting an amount of the gas supplied to the unit that demands gas supply in step (a) using a flow rate detection unit, and (c) making a determination with respect to a leakage of the gas when the detected amount of the gas is larger than a predetermined reference value. This makes it possible to accurately detect the leakage of gas using the flow rate detection unit with less chance of the operation failure upon the gas supply
[0018] If the unit that demands gas supply is a fuel cell, it is preferable to detect the flow rate of the gas when the fuel cell is not operated for power generation. In the case where the fuel cell is not operated for power generation, the amount of gas consumed by the fuel cell is substantially small. Accordingly, this makes it possible to detect the leakage of gas by substantially a small amount.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The foregoing and further objects, features and advantages of the invention will be 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 view that shows a structure of a gas supply system according to a first embodiment of the invention; Fig. 2 is a flowchart that represents a control routine for supplying hydrogen gas;
Fig. 3 is a flowchart that represents a sub-routine for selecting the tank from which the hydrogen gas is supplied to the fuel cell;
Fig. 4 is a flowchart that represents a sub-routine for detecting the flow rate of the hydrogen gas;
Fig. 5 is a view that shows another structure of the gas supply system according to a second embodiment of the invention; Fig. 6 is a view that shows another structure of the gas supply system according to a third embodiment of the invention;
Fig. 7 is a view that shows another structure of the gas supply system according to a fourth embodiment of the invention; and Fig. 8 is a view that shows another structure of the gas supply system according to a modified example of the invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS [0020] Embodiments of the invention will be described in the following order. A OUTLINE OF EMBODIMENT
B FIRST EMBODIMENT
Bl General System Structure
B2 System Operation
C SECOND EMBODIMENT D THIRD EMBODIMENT
E FOURTH EMBODIMENT
F MODIFIED EXAMPLES [0021]
A. OUTLINE OF EMBODIMENT In a gas supply system 1 for supplying hydrogen gas to a fuel cell from a plurality of high pressure hydrogen tanks 11, 21, 31, 41 as shown in Fig. 1, a hydrogen gas leakage is detected. A hydrogen gas supply pipe 50 connected to the fuel cell 2 is connected to those four tanks from the one closest to the fuel cell 2, that is, 11, to the one that is the most distant from the fuel cell 2, that is, 41 so as to be selectively operated independently. Each of those tanks 11 to 41 stores the hydrogen gas at a maximum pressure of 35 MPa from which the gas at the pressure reduced to
0.8 MPa is supplied to the fuel cell 2. As the hydrogen gas is supplied, the inner pressure of the tank is reduced. The temperature of the hydrogen gas within the tank, thus, is lowered to minus several tens degrees.
[0022] The hydrogen gas leakage is detected by detecting the flow rate of the hydrogen gas within the hydrogen gas supply pipe 50 while the fuel cell 2 is not operated for power generation. In the case where the fuel cell 2 is not operated for power generation, the hydrogen gas that permeates, in other words, cross leaks, from the hydrogen electrode to the oxygen electrode of the fuel cell 2 by the amount, for example, 10 to 20 cc/min. will only be consumed. Accordingly the amount of the hydrogen gas that exceeds the aforementioned consumption amount may be considered as having the leakage. A flow rate sensor 74 for detecting the flow rate of the hydrogen gas is arranged in the hydrogen gas supply pipe 50 at a position between the tank 41 that is the most distant from the fuel cell and the tank 31 that is the second most distant from the fuel cell. While the fuel cell stops generating power, the hydrogen gas is supplied to the fuel cell 2 only from the tank 41 such that the flow rate of the hydrogen gas within the hydrogen gas supply pipe 50 is detected. In this case, the flow rate sensor 74 is exposed to the low temperature hydrogen gas only when the tank 41 is used. This makes it possible to prevent the flow rate sensor 74 from being constantly exposed to the low temperature hydrogen gas during operation of the fuel cell 2. Accordingly the operation failure in the flow rate sensor 74 caused by the low temperature gas may be prevented.
[0023]
B. FIRST EMBODIMENT Bl. General Structure of System
Fig. 1 is a view that shows the general structure of a gas supply system according to the first embodiment of the invention. The gas supply system 1 of the first embodiment is structured to supply hydrogen gas as the fuel gas to the fuel cell 2, and provided with four high pressure hydrogen tanks 11, 21, 31, 41. Each of those high pressure hydrogen tanks 11 to 41 stores the hydrogen gas under pressure of 35 MPa at maximum. The respective high pressure hydrogen tanks 11 to 41 are connected to the hydrogen gas supply pipe 50 through which the hydrogen gas is supplied to the fuel cell 2. The tank 41 will be referred to as a "detection tank" having the hydrogen gas discharged therefrom subjected to the flow rate detection. [0024] Those high pressure hydrogen tanks 11, 21, 31, 41 are provided with inner pressure sensors 12, 22, 32, 42 for detecting the inner pressure of the respective tanks, and cutoff valves 13, 23, 33, 43 for cutting off the gas supply, respectively. The inner pressure sensors 12, 22, 32, 42 are employed as sensors for detecting the amount of the hydrogen gas stored in the respective high pressure hydrogen tanks 1 1 , 21, 31, 41, respectively.
[0025] As the hydrogen gas is supplied to the outside from the respective high pressure hydrogen tanks 11, 21, 31, 41, the pressure within each of those tanks is reduced. Accordingly the temperature of each hydrogen gas within the respective tanks 11 to 41 will be decreased to, for example, minus several tens degrees. The hydrogen gas supply pipe 50 and the flow rate sensor 74 through which the hydrogen gas flows from those tanks may be cooled in contact with the low temperature hydrogen gas.
[0026] Each of those high pressure hydrogen tanks 11, 21, 31, 41 is connected to the hydrogen gas supply pipe 50 so as to be branched therefrom in the order as shown in Fig. 1. The high pressure hydrogen tank 11 is connected to the hydrogen gas supply pipe 50 at the position that is the closest to the fuel cell 2, and the high pressure hydrogen tank 41 is connected to the hydrogen gas supply pipe 50 at the position that is the most distant from the fuel cell 2 in view of the path length of the hydrogen gas flow. The hydrogen gas supply pipe 50, therefore, includes a pipe section 51 that allows the hydrogen gas supplied from the high pressure hydrogen tanks 11, 21, 31, 41 to flow toward the fuel cell 2, a pipe section 52 that allows the hydrogen gas supplied from the high pressure hydrogen tanks 21, 31, 41 to flow toward the fuel cell 2, a pipe section 53 that allows the hydrogen gas supplied from the high pressure hydrogen tanks 31, 41 to flow toward the fuel cell 2, and a pipe section 54 that allows the hydrogen gas supplied only from the high pressure hydrogen tank 41 to flow to the fuel cell 2.
[0027] In the specification, "the gas that flows from a certain tank toward a unit that demands gas supply" does not include "the gas discharged from the tank to flow in the direction away from the unit that demands gas supply on the flow passage before it reaches the unit". In the first embodiment, in the case where any one of the tanks 11 to 31 is supplying the hydrogen gas to the fuel cell 2, and the gas discharged from the tank flows away from the fuel cell 2 to reach the pipe section 54, this state is not considered that the "gas flowing from the tank toward the unit (fuel cell 2)" passes through the pipe section 54 in view of the term used in the specification.
[0028] The pipe section 51 through which the hydrogen gas supplied from the high pressure hydrogen tanks 11, 21, 31, 41 flows toward the fuel cell 2 is provided with a regulator 60. The pressure of the hydrogen gas within the hydrogen gas supply pipe 50 is reduced to 0.8 MPa by the regulator 60 so as to be supplied to the fuel cell 2. Meanwhile, the pipe section 54 through which the hydrogen gas supplied only from the high pressure hydrogen tank 41 flows is provided with a flow rate sensor capable of detecting the flow rate of the hydrogen gas passing through the pipe section 54. [0029] The gas supply system 1 is provided with an ECU 100 that receives detection values of pressures of the respective tanks from the inner pressure sensors 12, 22, 32, 42, and detection values of the flow rate of the hydrogen gas from the flow rate sensor 74, respectively. The ECU 100 controls switching operations of the cutoff valves 13, 23, 33, 43 so as to control the operation of the fuel cell 2. [0030]
B2. System Operation
Fig. 2 is a flowchart that shows how the hydrogen gas is supplied. In step Sl 10, it is determined whether the pressure P4 within the detection tank 41 is higher than a predetermined reference value Pthl . If the pressure P4 within the detection tank 41 is higher than the reference value Pthl, that is, Yes is obtained in step Sl 10, the process proceeds to step S 120.
[0031] In step S 120, it is determined whether the power generation level E4 produced using the hydrogen gas which has been continuously supplied from the detection tank 41 to the fuel cell 2 is lower than a predetermined reference value Ethl . In the case where the hydrogen gas is supplied to the fuel cell 2 from the tank other than the detection tank 41, that is, any one of those tanks 11, 21, or 31, the value of the level E4 becomes 0. If the continuous power generation level E4 using the hydrogen gas supplied from the detection tank 41 is lower than the predetermined reference value Ethl, the process proceeds to step S130. Meanwhile, if the continuous power generation level E4 is equal to or higher than the predetermined reference value Ethl, the process proceeds to step S 140.
[0032] By executing step S 120 where the continuous supply of the hydrogen gas from the detection tank 41 is restricted, the flow rate sensor 74 provided in the pipe section 54, which has been exposed to the low temperature hydrogen gas may be prevented from being excessively cooled having its heat drawn by the hydrogen gas, and accordingly from causing the operation failure upon detection of the flow rate. When the tank for supplying the hydrogen gas is switched to the one other than the detection tank 41 so as to prevent the hydrogen gas from flowing through the pipe section 54, the heat of the flow rate sensor 74 is no longer drawn by the low temperature hydrogen gas. The flow rate sensor 74 having its temperature once reduced by the hydrogen gas may draw heat from its periphery. Then the temperature of the flow rate sensor 74 is increased to become approximately the same level as that of the periphery if the flow of the hydrogen gas through the pipe section 54 is interrupted for a predetermined period.
[0033] The larger the amount of the hydrogen gas is continuously discharged outside from the detection tank 41, the lower the inner pressure of the detection tank 41 becomes. The temperature of the hydrogen gas within the tank 41 is also reduced. The larger the amount of the hydrogen gas is supplied from the detection tank 41 so as to flow through the pipe section 54, the more heat of the flow rate sensor 74 provided in the pipe section 54 is drawn. Meanwhile the amount of the hydrogen gas supplied from the tank may be calculated on the basis of the generation amount of heat of the fuel cell 2. Accordingly making a determination whether or not the detection tank 41 has been used on the basis of the continuous power generation of the fuel cell 2 makes it possible to prevent the operation failure in the flow rate sensor 74 owing to excessive cooling. [0034] In step S 130, the hydrogen gas is supplied from the detection tank 41 to the fuel cell 2. If the pressure P4 of the detection tank 41 is higher than the reference value Pthl (see step Sl 10), continuous use of the detection tank 41 for the long period of time is avoided (see S 120). Then the detection tank 41 is selected as the one for supplying the hydrogen gas in preference to the other tanks (see S 130). The gas supply system 1 may be operated such that the pressure P4 of the detection tank 41 becomes close to the reference value Pthl upon start-up of the gas supply system 1. The reference value Pthl is set to the value of pressure such that no operation failure occurs in the flow rate sensor 74 owing to excessive cooling even if the hydrogen gas is continuously supplied from the state of the inner pressure of the detection tank 41 at Pthl to the state of the pressure at which the gas cannot be supplied outside. [0035] In the specification, the phrase "the tank A is selected or used in preference to the tank B" represents that the tank A is used (see step S 130) after the determination is made (see step S 120) that the tank A is usable, and the tank B is used when the tank A is not usable. When the determination is made that both tanks A and B are not usable, the tank B is not used.
[0036] The supply of the hydrogen gas from the detection tank 41 to the fuel cell 2 is continuously performed in step S 130 until the power generation amount in the fuel cell 2 reaches a fixed value E4u. The fixed value of the power generation amount Eu4 is smaller than the power generation value Ethl as the reference level in step S 120. The continuous supply of the hydrogen gas from the detection tank 41 is restricted on the basis of the continuous power generation amount so as to prevent the operation failure in the flow rate sensor 74 owing to cooling by the hydrogen gas as in step S 120. Thereafter, the process proceeds to step S 140.
[0037] In step S 140, the tank for supplying the hydrogen gas to the fuel cell 2 is selected.
[0038] Fig. 3 is a flowchart showing how the tank for supplying the hydrogen gas to the fuel cell 2 is selected. In step S210, it is determined whether the hydrogen gas is left in any of the tanks 11 to 31 so as to be supplied to the fuel cell 2. More specifically, if the inner pressure in any one of the tanks 11 to 31 is higher than the reference value Ps, it is determined that there is the hydrogen gas left in such tank. That is, if Yes is obtained in step S210, the process proceeds to step S220.
[0039] In step S220, the tank having the hydrogen gas at the highest inner pressure is selected as the tank for supplying the hydrogen gas to the fuel cell 2.
[0040] Meanwhile, if it is determined that there is no hydrogen gas left in any one of those tanks 11 to 31 so as to be supplied to the fuel cell 2, that is, No is obtained in step S210, the process proceeds to step S230. In step S230, the detection tank 41 is selected as the one for supplying the hydrogen gas to the fuel cell 2. [0041] In the control routine shown in the flowchart of Fig. 3, it is determined whether there is the hydrogen gas left in any one of the tanks 11 to 31 in step S210, that is, it is determined whether any one of those tanks 11 to 31 is usable. If it is determined that any one of those tanks is usable, the process proceeds to step S220 where the tank for supplying the hydrogen gas to the fuel cell 2 is selected from those tanks 11 to 31. Meanwhile if there is no hydrogen gas left in any one of those tanks 11 to 31, that is, they are not usable, the process proceeds to step S 230 where the detection tank 41 is selected. If the pressure P4 within the detection tank 41 is reduced to the reference value Pthl, that is, No is obtained in step Sl 10 of the flowchart shown in Fig. 2, any one of the tanks 11 to 31 is selected as the tank for supplying the hydrogen gas in preference to the detection tank 41.
[0042] When the hydrogen gas in the tanks 11 to 31 is used up, the aforementioned process makes it possible to control the supply of the hydrogen gas such that the hydrogen gas at the pressure slightly lower than the pressure Pthl is left in the detection tank 41. After the hydrogen gas in the tanks 11 to 31 is used up, the hydrogen gas may be supplied from the detection tank 41 to the fuel cell 2.
[0043] The flow rate sensor 74 is provided in the pipe section 54 that allows the hydrogen gas supplied from only the high pressure hydrogen tank 41 to flow therethrough. Accordingly the flow rate of the hydrogen gas supplied to the fuel cell 2 can be detected only when the hydrogen gas is supplied from the detection tank 41 to the fuel cell 2. The gas supply system 1 is operated such that the hydrogen gas is left in the detection tank 41 when the hydrogen gas in the tanks 11 to 31 is used up as described above. This makes it possible to detect the flow rate of the hydrogen gas supplied to the fuel cell 2 until the hydrogen gas in all the tanks 11 to 41 is used up in case of necessity.
[0044] The reference value Pthl is set as the gas pressure such that no operation failure occurs in the flow rate sensor 74 even if it has been excessively cooled as being exposed to the hydrogen gas continuously supplied from the detection tank 41 to the fuel cell 2 until the hydrogen gas is no longer supplied. Even if the hydrogen gas is continuously supplied from the detection tank 41 after the hydrogen gas stored in the tanks 11 to 31 is used up, the flow rate sensor 74 never has the operation failure owing to excessive cooling. In the specification, the phrase "use up the hydrogen gas stored in the tank" represents that the residual amount of the hydrogen gas in the gas tank becomes the level at which the gas cannot be supplied to the unit that demands gas supply. The detection of the flow rate of the hydrogen gas will be described later. [0045] In step S 150 of the flowchart shown in Fig. 2, the supply of the hydrogen gas that has been continuously performed from the tank to the fuel cell 2 is stopped, and the supply of the hydrogen gas from the tank selected in step S 140 is started. In the first embodiment, the tank for supplying the hydrogen gas to the fuel cell 2 is the one selected from the tanks 11 to 41.
[0046] In step S 160, it is determined whether the condition for finishing the operation of the fuel cell 2 has been established. The aforementioned condition is established when it is determined that the operation switch (not shown) of the fuel cell 2 has been switched to OFF, or the hydrogen gas which can be supplied to the fuel cell 2 is not left in all the tanks 11 to 41. If the condition for finishing the operation of the fuel cell 2 is established, the ECU 100 ends the operation of the gas supply system 1.
[0047] In step S 170, it is determined whether the signal indicating the request for detecting the flow rate of the hydrogen gas supplied to the fuel cell 2 has been received by the ECU 100. The signal indicating the request for detecting the flow rate of the hydrogen gas is transmitted at a predetermined time interval when the power generation is not performed by the fuel cell 2. If it is determined that the ECU 100 receives the signal indicating the request for detecting the flow rate of the hydrogen gas, the process proceeds to step S 180 where the flow rate of the hydrogen gas is detected.
[0048] Fig. 4 is a flowchart that shows how the flow rate of the hydrogen gas is detected. In step S310, it is determined whether the pressure P4 of the detection tank 41 is higher than a predetermined reference value Pth2 by the ECU 100. The reference value Pth2 is set as the pressure such that the detection tank 41 is allowed to continuously supply the hydrogen gas for the period sufficient to detect the flow rate of the hydrogen gas at a fixed accuracy. The reference value Pht2 is lower than the reference value Pthl (see step S 110 in Fig. 2), which is higher than the reference pressure Ps at which the gas is allowed to be supplied outside. If the pressure P4 of the detection tank 41 is higher than the reference value Pth2, that is, Yes is obtained in step S310, the process proceeds to step S320. [0049] In step S320, the supply of the hydrogen gas to the fuel cell 2, which has been performed is stopped, and the supply of the hydrogen gas from the detection tank 41 is started. In the case where the hydrogen gas has been supplied from the detection tank 41, the hydrogen gas is continuously supplied therefrom. The signal indicating the request for detecting the flow rate of the hydrogen gas is issued while the fuel cell 2 is not operated for power generation. Accordingly the amount of the hydrogen gas supplied from the detection tank 41 in steps subsequent to step S320 is smaller than the amount of the hydrogen gas supplied while the fuel cell 2 is operated for power generation. That is, such amount is substantially small corresponding to the amount of the hydrogen gas that permeates (cross leaks) from the hydrogen electrode to the oxygen electrode of the fuel cell 2. The aforementioned value can be preliminarily estimated. More specifically, the amount of consumed hydrogen gas owing to cross leak is in the range from approximately 10 to 20 cc/min.
[0050] In step S330, the ECU 100 receives the signal sent from the flow rate sensor 74, and detects the flow rate V of the hydrogen gas supplied from the detection tank 41 to the fuel cell 2 via the pipe section 54.
[0051] In step S340, the ECU 100 determines whether the detected flow rate V of the hydrogen gas is greater than a predetermined reference value Vt. The reference value Vt is set on the basis of the appropriate cross leak amount in the fuel cell 2. If the detected flow rate V of the hydrogen gas is equal to or lower than the reference value Vt, that is, No is obtained in step S340, the process returns to step S 140 of the flowchart shown in Fig. 2. Meanwhile if Yes is obtained in step S340, the process proceeds to step S350 where the ECU 100 allows the warning with respect to the hydrogen gas leakage to be displayed on a monitor screen (not shown). The process then returns to step S 140.
[0052] In the first embodiment, detection of the flow rate of the hydrogen gas supplied to the fuel cell 2 (see step S 340), and determination with respect to the hydrogen gas leakage (see step S350) are performed while the fuel cell 2 is not operated for power generation. This makes it possible to set the reference value Vt for the determination to the smaller value compared with execution of the aforementioned steps while the fuel cell 2 is operated for power generation. The flow rate sensor of the type capable of accurately detecting the flow rate in the range from several tens to 100 cc/min. may be employed as the flow rate sensor 74 so as to detect a small amount of the leaked hydrogen gas.
[0053] Meanwhile in step S310, if the pressure P4 of the detection tank 41 is lower than the reference value Pth2, that is, No is obtained, the process proceeds to step S360. In step S36O, it is determined whether the pressure Pp of the tank that has been supplying the hydrogen gas at that time is higher than a predetermined reference value Pth3 that is higher than the reference value Pth2 (see step S310). If the tank that has been supplying the hydrogen gas at that time is the detection tank 41, that is, No is obtained in step 310, the determination result in step S360 also becomes No.
[0054] If it is determined that the pressure Pp of the tank that has been supplying the hydrogen gas is higher than the predetermined reference value Pth3, the process proceeds to step S410. In step S410, the cutoff valve 43 of the detection tank 41 is opened in parallel with opening of the cutoff valve (13 to 33 in Fig. 1) of the tank that has been supplying the hydrogen gas. As a result, the hydrogen gas stored in the tank that has been supplying the hydrogen gas is supplied to the fuel cell 2, and at the same time, supplied to the detection tank\41 via the hydrogen gas supply pipe 50. In step S410, the cutoff valve 43 of the detection tank 41 is opened until the pressure of the detection tank 41 reaches a reference value Pth4. The pressure Pth4 is higher than the pressure Pth2, and lower than the pressure Pth3. Thereafter the cutoff valve 43 is closed, and the process returns to step S310. In step S410, the pressure P4 of the detection tank 41 becomes higher than the pressure Pth2. The determination result in step S310 in the subsequent cycle becomes Yes.
[0055] In the case where execution of step S410 brings the inner pressure of the detection tank 41 to a level too low to allow the flow rate sensor 74 to detect the flow rate, the hydrogen gas may be supplied from the tank that has been supplying to the detection tank 41. As a result, the hydrogen gas is supplied to the fuel cell 2 from the detection tank 41 so as to allow the detection of the flow rate of the hydrogen gas supplied to the fuel cell 2 (see step S330), and detection of the hydrogen leakage (see step S 340).
[0056] In step S360, if the pressure Pp of the tank that has been supplying the hydrogen gas is equal to or lower than the reference value Pth3, the process proceeds to step S370. In step S370, it is determined whether there is a tank having the inner pressure higher than the reference value Pth3. [0057] If it is determined that there is no tank having the inner pressure higher than the reference value Pth3, that is, No is obtained in step S370, the process proceeds to step S380. In step S380, the ECU 100 allows the warning message with respect to inability of detecting the hydrogen gas leakage to be displayed on the monitor screen (not shown) as the amount of the residual hydrogen gas is insufficient. The process then returns to step S 140 of the flowchart shown in Fig. 2.
[0058] If it is determined that there is a tank having the inner pressure higher than the reference value Pth3, that is, Yes is obtained in step S370, the process proceeds to step S390. In step S390, the tank that stores the hydrogen gas at the highest pressure is selected as the tank for supplying the hydrogen gas to the fuel cell 2. Then in step S400, the supply of the hydrogen gas that has been supplied from the tank to the fuel cell 2 is stopped, and the supply of the hydrogen gas from the tank selected in step S390 is started. By executing the aforementioned process, even if the pressure of the tank that has been supplying the hydrogen gas is not sufficiently high, the other tank is selected so as to supply the hydrogen gas therefrom to the detection tank 41 (see step S410) .
[0059] In step S 170 of the flowchart shown in Fig. 2, if the ECU 100 has not received the signal indicating the request for detecting the flow rate of the hydrogen gas, that is, No is obtained, the process proceeds to step S 190. In step S 190, it is determined whether the condition for switching the tank for supplying the hydrogen gas to the fuel cell 2 has been established. The aforementioned condition for switching the tank is determined to be established when the amount of power generated using the hydrogen gas, that is, Es is larger than a predetermined reference value Eth2, or when there is no hydrogen gas sufficient to be supplied to the fuel cell 2 left in the tank that has been supplying the hydrogen gas. The determination with respect to the amount of the residual hydrogen gas within the tank is made in consideration with whether or not the inner pressure Pp of the tank is higher than the value Ps. [0060] If it is determined that the condition for switching the tank is not established, the process returns to step S 160, and the hydrogen gas is subsequently supplied from the same tank to the fuel cell 2 unless Yes is obtained in steps S 160 and S 170. If it is determined that the condition for switching the tank is established in step S 190, the process returns to step SI lO. Execution of the aforementioned process makes it possible to switch the tank for supplying the hydrogen gas upon each generation of power at a fixed level.
[0061] In the gas supply system 1 according to the first embodiment, the hydrogen gas is supplied to the fuel cell 2 from any one selected from the high pressure hydrogen tanks 11, 21, 31, 41. The flow rate sensor 74 is provided in the pipe section 54 through which the hydrogen gas supplied from the high pressure hydrogen tank 41 is only allowed to flow. Accordingly the flow rate of the hydrogen gas supplied from the high pressure hydrogen tank 41 to the fuel cell 2 may be detected by the flow rate sensor 74. When the hydrogen gas is not supplied from the high pressure hydrogen tank 41, the low temperature hydrogen gas does not draw heat from the flow rate sensor 74, and on the contrary, the flow rate sensor 74 draws heat from its periphery. This makes it possible to prevent the flow rate sensor 74 from being excessively cooled. As a result, the operation failure in the flow rate sensor 74 may be prevented. [0062]
C. SECOND EMBODIMENT
Fig. 5 is a schematic view that represents a structure of a gas supply system Ia according to the second embodiment. In the gas supply system 1 according to the first embodiment, the regulator 60 is arranged in the pipe section 51 that allows the hydrogen gas supplied from all the high pressure hydrogen tanks 11 to 41 to flow therethrough. Meanwhile in the gas supply system Ia according to the second embodiment, regulators 14, 24, 34, 44 are arranged between the hydrogen gas supply pipe 50 and the respective tanks 11, 21, 31, 41 such that each pressure of the hydrogen gas supplied from the tanks 11 to 41 is reduced to 0.8 MPa. In the gas supply system Ia according to the second embodiment, the pressure within the hydrogen gas supply pipe 50 is kept at 0.8 MPa. Other features with respect to the structure of the gas supply system Ia according to the second embodiment are the same as those of the gas supply system according to the first embodiment. [0063] In the gas supply system Ia according to the second embodiment, the pressure of the hydrogen gas within the hydrogen gas supply pipe 50 is kept at 0.8 MPa. Even if the cutoff valve 43 of the detection tank 41 is opened simultaneously with opening of the cutoff valve of the other tank, the hydrogen gas cannot be supplied to the detection tank 41 from the other tank. In the second embodiment, therefore, the process to be executed in steps S310, S360 to S410 of the flowchart shown in Fig. 4 is not performed. Other features of the process for operating the gas supply system Ia according to the second embodiment are the same as those of the gas supply system 1 according to the first embodiment as has been described referring to Figs. 2 to 4. [0064] The gas supply system according to the second embodiment is structured such that the flow rate sensor 74 is not exposed to the low temperature hydrogen gas, thus reducing possibility of the operation failure in the flow rate sensor 74 upon detection of the flow rate. The pressure of the hydrogen gas within the hydrogen gas supply pipe 50 is decreased by the regulators 14, 24, 34, 44, respectively so as to enhance the strength of the hydrogen gas supply pipe 50 compared with the gas supply system according to the first embodiment as well as to reduce the weight and the cost of the hydrogen gas supply pipe 50. [0065]
D. THIRD EMBODIMENT
Fig. 6 is a schematic view that represents the structure of a gas supply system Ib according to a third embodiment. In the gas supply systems 1 and Ia according to the first and the second embodiments, respectively, a single unit of the flow rate sensor is arranged in the hydrogen gas supply pipe 50. Meanwhile in the third embodiment, three units of the flow rate sensors are arranged in the hydrogen gas supply pipe 50. That is, a flow rate sensor 82 is arranged in the pipe section 502 through which the hydrogen gas from the tank 21 to the fuel cell 2 flows and the hydrogen gas from the other tank to the fuel cell 2 does not flow so as to detect the flow rate of the hydrogen gas passing through the pipe section 502. Likewise flow rate sensors 83, 84 are arranged in the pipe sections 503, 504 through which the hydrogen gas from the tanks 31, 41 to the fuel cell 2 flows and the hydrogen gas from the other tanks to the fuel cell 2 does not flow so as to detect the flow rate of the hydrogen gas passing through the pipe sections 503, 504, respectively. The values indicating the flow rates of the hydrogen gas detected by the flow rate sensors 82 to
84 are input to the ECU 100. In other words, the high pressure hydrogen tanks 21, 31, 41 function as the detection tanks in the third embodiment.
[0066] Other features with respect to the structure of the gas supply system Ib according to the third embodiment are the same as those of the gas supply system 1 according to the first embodiment. Each of the flow rate sensors 82 to 84 may have the same structure as that of the flow rate sensor 74 in the first embodiment.
[0067] In the gas supply system Ib according to the third embodiment, the tank is selected from the high pressure hydrogen tanks 11 to 41 one by one. Each of the flow rate sensors 82 to 84 is not in contact with the low temperature hydrogen gas when the hydrogen gas is supplied to the fuel cell 2 from the tank other than the tank corresponding thereto. In the gas supply system according to the third embodiment, each of the flow rate sensors 82 to 84 is not constantly exposed to the low temperature hydrogen gas, resulting in the reduced possibility in the operation failure of the flow rate sensor upon detection of the flow rate.
[0068] The gas supply system Ib according to the third embodiment is provided with a plurality of flow rate sensors 82 to 84. This makes it possible to cause any one of the high pressure hydrogen tanks 21, 31, 41 corresponding to the respective flow rate sensors by which each amount of the hydrogen gas discharged therefrom is detectable to function as the last tank for supplying the hydrogen gas to the fuel cell 2. That is, the gas supply system according to the third embodiment has a higher degree of freedom with respect to control of the hydrogen gas supply compared with the gas supply systems 1 and Ia according to the first and the second embodiments, respectively.
[0069] In the third embodiment, the flow rate sensor is not arranged in the pipe section 501 through which the hydrogen gas from the tank 11 to the fuel cell 2 flows, and the hydrogen gas from the other tank to the fuel cell 2 does not flow. As shown by the broken line shown in Fig. 6, a flow rate sensor 81 may be arranged in the pipe section 501 such that the value of the flow rate of the hydrogen gas detected by the flow rate sensor 81 is input to the ECU 100.
[0070] E. FOURTH EMBODIMENT
Fig. 7 is a schematic view that represents the structure of a gas supply system Ic according to a fourth embodiment. The hydrogen gas supply pipe 50 according to the first to the third embodiments has the pipe section 51 through which the hydrogen gas flows from the respective tanks to the fuel cell 2. In other words, the hydrogen gas supply pipe 50 is joined with the single pipe section 51 before it reaches the fuel cell 2 at the end. In the fourth embodiment, a hydrogen gas supply pipe 50c is capable of independently supplying the hydrogen gas to the fuel cell 2 via two pipe sections 56, 58 each connected to the fuel cell 2.
[0071] The hydrogen gas supply pipe 50c of the gas supply system Ic according to the fourth embodiment includes the pipe section 56 through which the hydrogen gas flows from the high pressure hydrogen tanks 11, 21 to the fuel cell 2, the pipe section 57 through which the hydrogen gas flows from only the high pressure hydrogen tank 21 to the fuel cell 2, and the pipe section 58 through which the hydrogen gas flows from the high pressure hydrogen tanks 31, 41 to the fuel cell 2, and the pipe section 59 through which the hydrogen gas flows from only the high pressure hydrogen tank 41 to the fuel cell 2. A flow rate sensor 93 is arranged in the pipe section 58 so as to detect the flow rate of the hydrogen gas passing through the pipe section 58. The value of the flow rate of the hydrogen gas detected by the flow rate sensor 93 is input to the ECU 100. That is, in the fourth embodiment, the high pressure hydrogen tanks 31 and 41 function as the detection tanks.
[0072] The pipe sections 56 and 58 are provided with corresponding regulators 61 and 62, respectively. Each structure of the regulators 61 and 62 is the same as that of the regulator 60 of the first embodiment. The structure of the flow rate sensor 93 is the same as that of the flow rate sensor 74 of the first embodiment. Other features with respect to the structure of the gas supply system Ic according to the fourth embodiment are the same as those of the gas supply system 1 according to the first embodiment.
[0073] In the gas supply system Ic according to the fourth embodiment, a single tank is selected from the high pressure hydrogen tanks 11 to 41 one by one. In the aforementioned structure of the fourth embodiment, the flow rate sensor 93 is not exposed to the low temperature hydrogen gas so long as the hydrogen gas is supplied from the high pressure hydrogen tanks 11 and 21. Accordingly the possibility of the operation failure in the flow rate sensor 93 upon detection of the flow rate of the hydrogen gas may be restricted to a substantially low level.
[0074]
F. MODIFIED EXAMPLE The invention is not limited to the embodiments as aforementioned, but may be realized in various forms without departing from the scope of the invention as described in the following examples.
[0075] Fl. Modified Example 1 In the first embodiment, the flow rate sensor for detecting the flow rate of the hydrogen gas flowing through the hydrogen gas supply pipe 50 is arranged in the pipe section 54 through which the hydrogen gas flows from only the high pressure hydrogen tank 41. As shown by the dashed line in Figs. 2 and 5, the flow rate sensors 72 and 73 may be arranged in the pipe section through which the hydrogen gas supplied from two or more tanks flow. The flow rate sensor may be arranged in the position through which the hydrogen gas flows from part of a plurality of tanks to the unit that demands gas supply, and the hydrogen gas does not flow from the rest of the tank to the unit. In other words, the portion where the flow rate sensor is arranged may be located upstream of the position through which the hydrogen gas supplied from all the tanks flows such that the hydrogen gas supplied only from the part of the tanks flows to the unit that demands gas supply.
[0076] The aforementioned structure makes it possible to supply the hydrogen gas from the tank 11 to the unit that demands gas supply without allowing the hydrogen gas to flow through the pipe section where the flow rate sensor is arranged. As the hydrogen gas is supplied to the unit that demands gas supply without allowing the hydrogen gas to flow through the pipe section where the flow rate sensor is arranged, the excessive cooling of the flow rate sensor may be prevented. The number of the gas tanks as the first group for supplying the hydrogen gas through the pipe section where the flow rate sensor is arranged is preferably equal to or smaller than a half of the total number of tanks for supplying gas to the unit that demands gas supply, and more preferably, such number is set to 1.
[007η F2. Modified Example
In the above-described embodiments, the tank is switched one by one. In this example, a plurality of tanks may be simultaneously used as those for supplying the hydrogen gas to the unit that demands gas supply. In the aforementioned structure, upon detection of the flow rate of the gas supplied to the unit that demands gas supply, it is preferable to detect the flow rate of the hydrogen gas which is supplied only from the gas tank as the first group for supplying the gas through the pipe section where the flow rate sensor is arranged. This makes it possible to supply the hydrogen gas from the gas tank as the first type through the pipe section where the flow rate sensor is arranged. Accordingly accurate detection of the flow rate of the gas may be made. As a result, the determination with respect to the leakage of the gas flow may be made. Upon detection of the flow rate of the gas supplied to the unit that demands gas supply, the hydrogen gas may be supplied from a plurality of gas tanks as the first group.
[0078] It is preferable to set the time period for supplying the gas to the unit that demands gas supply only from the gas tank as the second group capable of supplying the gas without allowing the hydrogen gas to flow through the pipe section where the flow rate sensor is arranged while interrupting the supply of the hydrogen gas from the gas tank as the first group. In the above-described structure, the flow rate sensor draws heat from its periphery during the set period so as to increase its temperature. Accordingly, the operation failure in the flow rate sensor caused by the excessive cooling may be prevented.
[0079] F3. Modified Example 3 In the first embodiment, the period for which the hydrogen gas can be continuously supplied from the respective tanks is restricted on the basis of the power generation amount (see steps S 120 and S 190 in the flowchart of Fig. 2). The period for which the hydrogen gas can be continuously supplied from the respective tanks may be restricted on the basis of other reference value. For example, in the case where the rate of decrease in the inner pressure of the tank that has been supplying the hydrogen gas reaches a predetermined reference value, the supply of the gas from the tank may be stopped. In the case where the flow rate of the gas supplied from the tank can be detected, the supply of the gas from the tank can be detected when the gas at a fixed volume is supplied. Furthermore, in the case where the hydrogen gas is continuously supplied for a predetermined period, the supply of gas from the tank may be stopped. It is especially preferable to make a predetermined restriction with respect to the continuous supply of gas from the gas tank of the first group through the pipe section where the flow rate sensor is arranged. In the above-described structure, the excessive cooling of the flow rate sensor may be prevented.
[0080] F4. Modified Example 4
In the aforementioned embodiments, each of the tanks stores hydrogen gas. However, the gas supplied by the gas supply system is not limited to the hydrogen gas, but the gas may be oxygen, propane and the other type of gas. It is especially efficient for the structure such that the high pressure gas has been stored in the tank, and as the gas is supplied, the temperature of the gas supplied as the decrease in the pressure within the tank is reduced.
[0081] F5. Modified Example 5
In the aforementioned embodiments, a plurality of tanks are used. As Fig. 8 shows, a single unit of tank may be used. That is, a plurality of gas passages are provided in the tank, and a gas flow rate detection unit may be provided in a part of the gas passages. It is, thus, possible to form the gas supply system by providing the gas flow rate detection unit arranged in the gas passage.

Claims

CLAIMS:
1. A gas supply system characterized by comprising: m (an integer equal to or greater than 2) units of gas tanks; a gas passage that admits a gas from the m units of gas tanks so as to be supplied to a unit that demands a gas supply; and a control unit that controls the gas supply from the m units of gas tanks to the gas passage, wherein the gas passage includes a passage portion through which the gas flows to the unit that demands the gas supply from n (n < m) units as a first group selected from the m units of the gas tanks, and the gas does not flow to the unit that demands the gas supply from the rest of the gas tanks as a second group, the gas supply system characterized by further comprising a flow rate detection unit capable of detecting a flow rate of the gas in the passage portion.
2. The gas supply system according to claim 1, wherein when the gas is supplied to the unit that demands the gas supply from one of the m units of the gas tanks, the control unit interrupts the gas supply to the unit that demands gas supply from the other gas tank.
3. The gas supply system according to claim 1 or 2, wherein when the flow rate detection unit detects the flow rate of the gas, the control unit allows the gas supply from the gas tank as the first group while interrupting the gas supply from the gas tank as the second group.
4. The gas supply system according to any one of claims 1 to 3, wherein when the flow rate of the gas detected by the flow rate detection unit is higher than a predetermined reference value, the control unit makes a determination that there is a leakage of the gas.
5. The gas supply system according to claim 1, wherein when the flow rate detection unit is not operated for detecting the flow rate, the control unit allows the gas to be supplied from the gas tank as the second group in preference to the gas tank as the first group under a predetermined condition.
6. The gas supply system according to any one of claims 1 to 5, wherein when the gas is supplied from the gas tank as the first group continuously for a predetermined period, the control unit stops the gas supply from the gas tank as the first group, and starts the gas supply from the gas tank as the second group.
7. The gas supply system according to any one of claims 1 to 6, further comprising a residual gas amount detection unit that detects an amount of a residual gas within each of the gas tanks, wherein the control unit controls the gas supply from the respective gas tanks such that the gas tank as the first group becomes a last gas tank capable of supplying the gas to the unit that demands gas supply after the gas in the rest of the gas tanks is used up, and controls the gas supply such that a total of the residual amount of the gas in the n units of the gas tank as the first group is equal to or smaller than a first predetermined value when the gas in all the gas tanks as the second group is used up.
8. The gas supply system according to claim 7, wherein when the flow rate of the gas is not detected by the flow rate detection unit, the control unit:
(a) supplies the gas preferentially from the gas tank as the first group to the unit that demands gas supply when a total amount of the residual gas in the n units of the gas tanks as the first group is larger than the first predetermined value; and
(b) supplies the gas preferentially from the gas tank as the second group to the unit that demands gas supply when the total amount of the residual gas in the n units of the gas tanks as the first group is smaller than the first predetermined value.
9. The gas supply system according to any one of claims 1 to 8, wherein when the total amount of the residual gas in the n units of the gas tanks as the first group is equal to or smaller than a second predetermined value, the gas is supplied from the gas tank as the second group to the gas tank as the first group via the gas passage.
10. The gas supply system according to any one of claims 1 to 9, wherein the n is equal to 1.
11. A gas supply system characterized by comprising: a single unit of gas tank; a plurality of gas passages which admit a gas from the single unit of gas tank so as to be supplied to a unit that demands gas supply; and a control unit that controls a gas supply to the plurality of gas passages of the gas tank, the gas supply system characterized by further comprising a flow rate detection unit that is capable of detecting the flow rate of the gas in a part of the plurality of the gas passages.
12. A method of supplying gas to a unit that demands a gas supply comprising the steps of: (a) supplying a gas from the gas tank as the first group to the unit that demands gas supply while interrupting the gas supply to the unit from the gas tank as the second group using the gas supply system according to claim 1;
(b) detecting an amount of the gas supplied to the unit that demands gas supply in step (a) using a flow rate detection unit of the gas supply system; and (c) making a determination with respect to a leakage of the gas when the detected amount of the gas is larger than a predetermined reference value.
13. The method according to claim 12, wherein the unit that demands the gas supply is a fuel cell, and the step (b) is executed when the fuel cell is not operated for power generation.
PCT/IB2005/002964 2004-10-07 2005-10-06 Gas supply system and gas supply method WO2006038098A2 (en)

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