Patent Publication Number: US-RE43219-E

Title: Fuel cell fuel supply system and mobile body

Description:
TECHNICAL FIELD  
     The present invention relates to a fuel supply system for fuel cells and a movable body. Specifically the present invention pertains to a fuel supply system for fuel cells, which functions to supply a fuel for the fuel cells or a source material used to generate the fuel for the fuel cells, as well as to a movable body. 
     BACKGROUND ART  
     A diversity of electric vehicles have been proposed, which utilize electrical energy output from fuel cells for the driving energy. Supply of a fuel, such as hydrogen, to the fuel cells is naturally required for power generation in the fuel cells. The electric vehicle of one known construction has hydrogen mounted thereon as the fuel for the fuel cells. The electric vehicle of another known construction has a source material, such as a hydrocarbon or a hydrocarbon compound, mounted thereon and reforms the source material to generate hydrogen gas and supply the hydrogen gas to the fuel cells. 
     One proposed arrangement to make hydrogen mounted on a vehicle as the fuel for fuel cells uses a storage tank including a hydrogen absorbing alloy on the vehicle and makes hydrogen absorbed by the hydrogen absorbing alloy as the fuel for fuel cells (for example, PATENT LAID-OPEN GAZETTE No. 2000-88196). This structure ensures the safety in storage of hydrogen on the vehicle as the movable body. 
     In the structure of utilizing the hydrogen absorbing alloy for storage of hydrogen on the vehicle, supply of hydrogen to the storage tank including the hydrogen absorbing alloy is required for a continuous drive of the vehicle. Sufficient safety is naturally an important factor in the course of supplying hydrogen under such conditions. The safety of fuel supply to a system with fuel cells has, however, not been discussed fully. 
     A fuel supply system for fuel cells and a movable body of the present invention are provided to solve the problems of the prior art technique and to enhance the safety of supply of a fuel, such as hydrogen, or its source material to any system with fuel cells. 
     DISCLOSURE OF THE INVENTION 
     The present invention is directed to a first fuel supply system for fuel cells, which functions to supply either one of a fuel for the fuel cells and a source material used to generate the fuel for the fuel cells. The first fuel supply system includes: the fuel cells; a storage module that stores either one of the fuel and the source material therein; a supply module that connects with the storage module to supply either one of the fuel and the source material to the storage module; a fuel cells working status specification module that determines whether or not the fuel cells are in a power generation state; and a supply prohibition module that, when the fuel cells working status specification module determines that the fuel cells are in the power generation state, prohibits a start of the supply of either one of the fuel and the source material from the supply module to the storage module. 
     The first fuel supply system for fuel cells according to the present invention has the fuel cells and the storage module, which stores either the fuel for the fuel cells or the source material used to generate the fuel for the fuel cells. The supply module is connected to the storage module, in order to supply the fuel or the source material to the storage module. In this process, it is determined whether or not the fuel cells are in the power generation state. When it is determined that the fuel cells are in the power generation state, the technique prohibits a start of the supply of the fuel or the source material from the supply module to the storage module. 
     The present invention is also directed to a first movable body with fuel cells mounted thereon, where the movable body utilizes electrical energy produced by the fuel cells as a driving energy source for movement. The first movable body includes: a storage module that stores therein either one of a fuel for the fuel cells and a source material used to generate the fuel for the fuel cells; a fuel cells working status specification module that determines whether or not the fuel cells are in a power generation state; and a supply prohibition module that, when the fuel cells working status specification module determines that the fuel cells are in the power generation state, prohibits a start of supply of either one of the fuel and the source material from a predetermined supply device, which is disposed outside the movable body for supplying either one of the fuel and the source material, to the storage module. 
     The first movable body of the present invention has the storage module that stores therein either the fuel for the fuel cells, which produce electrical energy as the driving energy for movement, or the source material used to generate the fuel for the fuel cells. It is determined whether or not the fuel cells are in the power generation state. When it is determined that the fuel cells are in the power generation state, the technique prohibits a start of supply of either the fuel or the source material from a predetermined supply device, which is disposed outside the movable body for supplying the fuel or the source material, to the storage module. 
     The present invention is further directed to a fuel supply control method that controls a process of supplying either one of a fuel for fuel cells and a source material used to generate the fuel for the fuel cells. The fuel supply control method includes the steps of: (a) determining whether or not the fuel cells are in a power generation state; and (b) when it is determined at the step (a) that the fuel cells are in the power generation state, prohibiting a start of the supply of either one of the fuel and the source material to a storage module, which is arranged with the fuel cells and stores either one of the fuel and the source material. 
     In the first fuel supply system for fuel cells, the first movable body, and the fuel supply control method of the present invention, when it is determined that the fuel cells are in the power generation state, the technique prohibits a start of the supply of either the fuel or the source material to the storage module. This arrangement desirably prevents supply of the fuel or the source material during power generation of the fuel cells and thus ensures the safety in power generation of the fuel cells as well as in supply of the fuel or the source material. Namely the fuel supply accompanied with connection of the storage module with the fuel supply device is not carried out simultaneously with power generation of the fuel cells. This ensures sufficient safety. The determination of whether or not the fuel cells are in the power generation state may be, for example, based on the actual power generation of the fuel cells or based on input of an instruction of starting operation of the fuel cells. 
     In accordance with one preferable application of the present invention, the first fuel supply system for fuel cells further includes an input module that receives an instruction of starting operation of the fuel cells and an instruction of stopping the operation of the fuel cells. The fuel cells working status specification module determines that the fuel cells are in the power generation state when the instruction of starting the operation of the fuel cells is given to the input module but no instruction of stopping the operation of the fuel cells is subsequently given to the input module. 
     In accordance with the corresponding application of the present invention, the first movable body includes an input module that receives an instruction of starting operation of the fuel cells and an instruction of stopping the operation of the fuel cells. The fuel cells working status specification module determines that the fuel cells are in the power generation state when the instruction of starting the operation of the fuel cells is given to the input module but no instruction of stopping the operation of the fuel cells is subsequently given to the input module. 
     This arrangement effectively prevents a start of supply of either the fuel or the source material in response to the instruction of starting the operation of the fuel cells, even prior to a sufficient output of electric power from the fuel cells, thus enhancing the safety. 
     In accordance with another preferable application of the present invention, the first fuel supply system for fuel cells further includes a voltage detection module that measures an output voltage of the fuel cells. The supply prohibition module prohibits the start of the supply of either one of the fuel and the source material when the output voltage measured by the voltage detection module is not less than a predetermined level, while the fuel cells working status specification module determines that the fuel cells are not in the power generation state. 
     In accordance with the corresponding application of the present invention, the first movable body further includes a voltage detection module that measures an output voltage of the fuel cells. The supply prohibition module prohibits the start of the supply of either one of the fuel and the source material when the output voltage measured by the voltage detection module is not less than a predetermined level, while the fuel cells working status specification module determines that the fuel cells are not in the power generation state. 
     A start of the supply of the fuel or the source material is prohibited when the output voltage from the fuel cells is not less than the predetermined level, even in the case where it is determined that the fuel cells are not in the power generation state. This arrangement desirably enhances the safety. In the fuel cells, even when the supplies of the fuel gas and the oxidizing gas are stopped in response to input of an instruction of stopping the operation of the fuel cells, the electrochemical reactions proceed until consumption of the existing supplies of the gases in the fuel cells. While it is determined that the fuel cells are not in the power generation state, in response to input of the instruction of stopping the operation of the fuel cells, the arrangement prohibits the start of the supply of either the fuel or the source material during the progress of the electrochemical reactions. This effectively prevents fuel supply while an undesired output voltage is produced. 
     It is preferable that the first movable body further includes: another energy source that is different from the fuel cells and generates driving energy for movement of the movable body; and an actuation prohibition decision module that determines whether or not actuation of another energy source is prohibited. The supply prohibition module prohibits the start of the supply of either one of the fuel and the source material to the storage module when the actuation prohibition decision module determines that actuation of another energy source is not prohibited, in addition to when the fuel cells working status specification module determines that the fuel cells are in the power generation state. 
     The arrangement effectively prevents the start of fuel supply when actuation of another energy source is not prohibited, that is, when there is a possibility that the movable body moves. This effectively enhances the safety in fuel supply. 
     The present invention is directed to a second fuel supply system for fuel cells, which functions to supply either one of a fuel for the fuel cells and a source material used to generate the fuel for the fuel cells. The second fuel supply system includes: the fuel cells; a storage module that stores either one of the fuel and the source material therein; a supply module that connects with the storage module to supply either one of the fuel and the source material to the storage module; a fuel filling status specification module that determines whether or not either one of the fuel and the source material is being supplied from the supply module to the storage module; and a power generation prohibition module that, when the fuel filling status specification module determines that either one of the fuel and the source material is being supplied, prohibits a start of power generation in the fuel cells. 
     The second fuel supply system for fuel cells according to the present invention has the fuel cells and the storage module, which stores either the fuel for the fuel cells or the source material used to generate the fuel for the fuel cells. The supply module is connected to the storage module, in order to supply the fuel or the source material to the storage module. It is determined whether or not the fuel or the source material is being supplied from the supply module to the storage module. When it is determined that the fuel or the source material is being supplied, the technique prohibits a start of power generation in the fuel cells. 
     The present invention is also directed to a second movable body with fuel cells mounted thereon, where the movable body utilizes electrical energy produced by the fuel cells as a driving energy source for movement. The second movable body includes: a storage module that stores therein either one of a fuel for the fuel cells and a source material used to generate the fuel for the fuel cells; a fuel filling status specification module that determines whether or not either one of the fuel and the source material is being supplied from a predetermined supply module, which is disposed outside the movable body for supplying either one of the fuel and the source material, to the storage module; and a power generation prohibition module that, when the fuel filling status specification module determines that either one of the fuel and the source material is being supplied, prohibits a start of power generation in the fuel cells. 
     The second movable body of the present invention has the storage module that stores therein either the fuel for the fuel cells, which produce electrical energy as the driving energy for movement, or the source material used to generate the fuel for the fuel cells. It is determined whether or not the fuel or the source material is being supplied from a predetermined supply module, which is disposed outside the movable body for supplying the fuel or the source material, to the storage module. When it is determined that the fuel or the source material is being supplied, the technique prohibits a start of power generation in the fuel cells. 
     The present invention is further directed to an operation control method that controls operation of fuel cells. The operation control method includes the steps of: (a) determining whether or not either one of a fuel for the fuel cells and a source material used to generate the fuel for the fuel cells is being supplied to a storage module, which is arranged with the fuel cells and stores either one of the fuel and the source material; and (b) when it is determined at the step (a) that either one of the fuel and the source material is being supplied, prohibiting a start of power generation in the fuel cells. 
     In the second fuel supply system for fuel cells, the second movable body, and the operation control method of the present invention, when it is determined that the fuel or the source material is being supplied to the storage module, the technique prohibits a start of power generation in the fuel cells. This arrangement desirably prevents operation of the fuel cells during supply of the fuel or the source material and thus ensures the safety in supply of the fuel or the source material. Namely the fuel supply accompanied with connection of the storage module with the fuel supply device is not carried out simultaneously with power generation of the fuel cells. This ensures sufficient safety. The determination of whether or not the fuel or the source material is being supplied may be, for example, based on the actual supply of the fuel or the source material to the storage module or based on input of a predetermined instruction, which is to be given prior to the start of the supply of the fuel or the source material. 
     In accordance with one preferable application of the present invention, the second movable body further has a movement prohibition module that prohibits movement of the movable body when the fuel filling status specification module determines that either one of the fuel and the source material is being supplied. 
     This arrangement effectively prevents movement of the movable body in the course of supply of either the fuel or the source material, thus enhancing the safety in fuel supply. 
     In the first and the second fuel supply systems for fuel cells according to the present invention, the storage module may store hydrogen as the fuel for the fuel cells and include a hydrogen absorbing alloy for the storage of hydrogen. 
     In the first and the second movable bodies of the present invention, the storage module may store hydrogen as the fuel for the fuel cells and include a hydrogen absorbing alloy for the storage of hydrogen. 
     In the first and the second fuel supply systems for fuel cells according to the present invention, the fuel cells and the storage module may be mounted on a movable body, which utilize electrical energy produced by the fuel cells as driving energy for movement. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates the general construction of an electric vehicle  10 ; 
         FIG. 2  is a sectional view illustrating the structure of a unit cell  38 ; 
         FIG. 3  shows the electric vehicle  10  and an external hydrogen supply device; 
         FIG. 4  shows the structure of a connector receptor  40 ; 
         FIG. 5  shows the construction of a main part of the hydrogen supply device  80 ; 
         FIG. 6  is a flowchart showing a fuel supply-time processing routine; and 
         FIG. 7  is a flowchart showing a fuel cells starting-time processing routine. 
     
    
    
     BEST MODES OF CARRYING OUT THE INVENTION 
     In order to clarify the construction and the functions of the present invention, one mode of carrying out the present invention is described below in the following sequence as a preferred embodiment: 
     1. General Construction of Electric Vehicle 
     2. Structure Related to Supply of Hydrogen 
     3. Control in Process of Hydrogen Supply 
     4. Another Construction of Electric Vehicle 
     (1) General Construction of Electric Vehicle 
     The construction of an electric vehicle is described first as one embodiment of the present invention.  FIG. 1  illustrates the general construction of an electric vehicle  10  in one embodiment of the present invention. The electric vehicle  10  has a fuel tank  20 , a stack of fuel cells  30 , a connector receptor  40 , and a controller  50 , in addition to a predetermined vehicle structure including a motor  70 . The following describes the respective constituents of the electric vehicle  10 . 
     The fuel tank  20  stores externally supplied hydrogen gas, and feeds the hydrogen gas to the stack of fuel cells  30  according to the requirements. The fuel tank  20  includes a solid metal hydride or a hydrogen absorbing alloy, which absorbs hydrogen therein for storage of hydrogen. The hydrogen absorbing alloys have varying weights, varying hydrogen storage capacities, varying quantities of heat produced in the course of hydrogen absorption, varying quantities of heat required for release of hydrogen, and varying pressures required for handling. The hydrogen absorbing alloys that are capable of storing and releasing hydrogen at relatively low temperatures (not higher than 100° C.) and at relatively low pressures (not higher than 10 kg/cm 2 )), for example, titanium alloys and rare earth alloys, are preferably applicable for automobile use. 
     The fuel tank  20  is connected with a hydrogen gas inlet conduit  47 , through which a supply of hydrogen gas is fed into the fuel tank  20 , and a fuel supply conduit  22 , through which a supply of hydrogen gas taken out of the hydrogen absorbing alloy in the fuel tank  20  is fed into the stack of fuel cells  30 . As discussed later, the electric vehicle  10  receives a supply of hydrogen gas fed from a predetermined external hydrogen supply device. The hydrogen gas fed from the hydrogen supply device is led into the fuel tank  20  via the connector receptor  40  and the hydrogen gas inlet conduit  47 , and is absorbed by the hydrogen absorbing alloy to be stored in the fuel tank  20 . The hydrogen gas released from the hydrogen absorbing alloy in the fuel tank  20  is supplied as the fuel gas to the stack of fuel cells  30  via the fuel supply conduit  22 . 
     The fuel supply conduit  22  is provided with a valve  22 A. The valve  22 A is connected with the controller  50 , which regulates the on-off state of the valve  22 A. Regulating the on-off state of the valve  22 A varies the quantity of the fuel gas fed to the stack of fuel cells  30  and thereby controls the quantity of power generation by the stack of fuel cells  30 . 
     A humidifier  66  is disposed in the fuel supply conduit  22  to moisten the fuel gas passing through the fuel supply conduit  22 . Humidification of the fuel gas by the humidifier  66  prevents a polymer electrolyte membrane included in the fuel cells from being dried. The humidifier  66  of the embodiment utilizes a porous membrane to moisten the fuel gas. The porous membrane separates the fuel gas fed from the fuel tank  20  from hot water under a predetermined pressure, so that a preset quantity of water vapor is supplied from the hot water to the fuel gas via the porous membrane. The hot water used for humidification is, for example, cooling water in the stack of fuel cells  30 . The stack of fuel cells  30  of the embodiment are polymer electrolyte fuel cells as described later. In order to keep the driving temperature in a desired temperature range of 80 to 100° C., cooling water is circulated around the fuel cells  30 . The hot water heated in the stack of fuel cells  30  may be utilized to moisten the fuel gas. 
     The hydrogen absorbing alloy included in the fuel tank  20  absorbs hydrogen for storage of hydrogen in the fuel tank  20 . The process of hydrogen absorption is exothermic. The fuel tank  20  is accordingly provided with a heat exchange module  26  as the structure of discharging heat produced in the process of hydrogen storage. The heat exchange module  26  is defined by a cooling water conduit  45 , through which cooling water is circulated. The cooling water conduit  45  has an opening end at the connector receptor  40 . Namely the opening end of the cooling water conduit  45  forms a water flow path joint  42  at the connector receptor  40 . The cooling water conduit  45 , which defines the heat exchange module  26  of the fuel tank  20 , leads to a cooling water conduit  43 . The cooling water conduit  43  forms a water flow path joint  44  at the connector receptor  40 . In the process of hydrogen absorption into the hydrogen absorbing alloy in the fuel tank  20 , the flow of cooling water is led into the heat exchange module  26  via the water flow path joint  42  and carries out heat exchange with the hydrogen absorbing alloy to be warmed up by the heat produced in the process of hydrogen absorption. The warmed-up cooling water is discharged outside via the water flow path joint  44 . Elimination of heat from the fuel tank  20  in this manner accelerates the action of hydrogen absorption and prevents the fuel tank  20  from being warmed up to an undesired level. 
     In the electric vehicle  10 , the cooling water conduits  45  and  43  are branched off at specific positions. The branched flow paths are laid in the stack of fuel cells  30  to define a heat exchange module  39  in the stack of fuel cells  30 . The branched flow paths are connected to each other in the heat exchange module  39 . Changeover valves for changing over the flow path are provided at the specific branch positions of the cooling water conduits  45  and  43  off to the heat exchange module  39 . A changeover valve  42 A is disposed at the branch position of the cooling water conduit  45 , and a changeover valve  44 A is disposed at the branch position of the cooling water conduit  43 . These changeover valves  42 A and  44 A are connected to the controller  50 , which outputs driving signals to change over the flow path. In the course of hydrogen supply from an external hydrogen supply device connected via the connector receptor  40  to the fuel tank  20 , the changeover valves  42 A and  44 A are controlled to close the flow path to the heat exchange module  39  and to circulate the flow of cooling water between the external hydrogen supply device and the heat exchange module  26 . 
     While the electric vehicle  10  runs with hydrogen in the fuel tank  20 , the state of the changeover valves  42 A and  44 A is controlled to make the flow path of the heat exchange module  26  linked with the flow path of the heat exchange module  39 . In this case, the flow of cooling water is circulated between the heat exchange module  26  in the fuel tank  20  and the heat exchange module  39  in the stack of fuel cells  30 . The electric vehicle  10  of the embodiment having the above construction enables hydrogen to be taken out of the hydrogen absorbing alloy by utilizing the heat produced in the stack of fuel cells  30 . In the process of power generation by the stack of fuel cells  30 , the energy not converted into electrical energy is released as thermal energy to produce heat. The flow of cooling water passing through the heat exchange module  39  carries out heat exchange with the stack of fuel cells  30 , so as to be warmed up while keeping the driving temperature of the fuel cells stack  30  in a temperature range of 80 to 100° C. Heat supply is required to take out hydrogen absorbed by the hydrogen absorbing alloy in the fuel tank  20 . In the structure of this embodiment, the cooling water warmed up by the heat exchange module  39  is led into the heat exchange module  26 . This gives the required heat to the fuel tank  20  to allow release of hydrogen from the hydrogen absorbing alloy, while cooling down the flow of cooling water passing through the heat exchange module  26 . Circulation of cooling water between the heat exchange module  39  and the heat exchange module  26  enables the heat produced in the stack of fuel cells  30  to be utilized in the fuel tank  20 . 
     A pump  29  is disposed in the cooling water conduit  45 . The pump  29  is under control of the controller  50  to circulate the flow of cooling water in the cooling water conduit  45  and a flow path connecting therewith. In the structure of the embodiment, the flow of cooling water is circulated in the cooling water conduit  45  to cool the fuel tank  20  down in the process of absorption of hydrogen by the hydrogen absorbing alloy. The cooling-down action of the fuel tank  20  may be implemented by circulation of a fluid other than water or by air cooling. 
     In the electric vehicle  10  of the embodiment, the fuel tank  20  is provided with a heating unit  25 . The heating unit  25  is used to heat the fuel tank  20  up. As discussed above, in the electric vehicle  10 , the heat produced in the stack of fuel cells  30  is utilized for release of hydrogen stored in the hydrogen absorbing alloy included in the fuel tank  20 . The heating unit  25  functions to heat the fuel tank  20  up in the case of transmission of insufficient heat from the stack of fuel cells  30  via the flow of cooling water or in the case of requirement of heat supplement to the fuel tank  20  when the stack of fuel cells  30  has not yet been warmed up sufficiently, for example, at the time of starting the electric vehicle  10 . The heating unit  25  is, for example, a heater and accomplishes heating by utilizing electric power supplied from a secondary battery mounted on the electric vehicle as discussed later. The heating unit  25  is connected to the controller  50 . The controller  50  controls the heating state of the heating unit  25 , which accordingly ensures production of a required quantity of heat for taking out a desired amount of hydrogen. The heating unit  25  may alternatively utilize a combustion reaction to produce heat. In this case, hydrogen taken out of the fuel tank  20  or fuel gas exhaust discharged from the stack of fuel cells  30  as discussed later may be used for the fuel of the combustion. 
     The fuel tank  20  is further provided with a hydrogen remaining quantity monitor  27 , which accumulates a quantity of hydrogen supplied from the fuel tank  20  to the stack of fuel cells  30  and its supply time. The controller  50  computes the remaining quantity of hydrogen in the fuel tank  20  based on results of the accumulation. The quantity of hydrogen supplied from the fuel tank  20  to the stack of fuel cells  30  may be obtained by directly measuring the flow of hydrogen gas passing through the fuel supply conduit  22  or by estimating indirectly from the output of the fuel cells stack  30 . When it is determined that the remaining quantity of hydrogen in the fuel tank  20  is equal to or below a preset level in response to a signal from the hydrogen remaining quantity monitor  27 , the controller  50  outputs a signal to a predetermined alarm unit, which is recognizable by a user of the vehicle. Notifying the user of the less remaining quantity of hydrogen prompts the user to feed a supply of hydrogen. 
     The fuel tank  20  is also provided with a hydrogen fill monitor  28 , which is constructed as a pressure sensor and detects absorption of a sufficient quantity of hydrogen by the hydrogen absorbing alloy included in the fuel tank  20 . At the time of filling hydrogen, that is, in the process of absorption of hydrogen by the hydrogen absorbing alloy, the inside of the fuel tank  20  is pressurized to a preset level by an external supply of hydrogen. The inner pressure of the fuel tank  20  rises when the hydrogen absorbing alloy absorbs a sufficient quantity of hydrogen and the rate of hydrogen absorption is lowered. The pressure sensor disposed in the fuel tank  20  detects an increase in inner pressure, which shows that the hydrogen absorbing alloy has been filled with the sufficient quantity of hydrogen. The hydrogen fill monitor  28  is connected to the controller  50 , which receives a signal representing conclusion of the hydrogen filling action. 
     The fuel cells  30  are polymer electrolyte fuel cells and form a stack structure including a plurality of constitutional units or unit cells  38  laid one upon another. In the stack of fuel cells  30 , the anode receives a supply of fuel gas, whereas the cathode receives a supply of oxidizing gas containing oxygen. An electromotive force is then produced through electrochemical reactions shown below:
 
H 2 →2H + +2e −   (1)
 
(½)O 2 +2H + +2e − →H 2 O  (2)
 
H 2 +(½)O 2 →H 2 O  (3)
 
     Equation (1), Equation (2), and Equation (3) respectively denote a reaction at the anode of the fuel cells, a reaction at the cathode of the fuel cells, and a total reaction in the fuel cells.  FIG. 2  is a sectional view illustrating the structure of the unit cell  38 , which is a constitutional unit of the fuel cells stack  30 . The unit cell  38  includes an electrolyte membrane  31 , an anode  32 , a cathode  33 , and a pair of separators  34  and  35 . 
     The anode  32  and the cathode  33  are gas diffusion electrodes and are arranged across the electrolyte membrane  31  to form a sandwich-like structure. The separators  34  and  35  are arranged across this sandwich-like structure and are combined with the anode  32  and the cathode  33  to form flow paths of the fuel gas and the oxidizing gas. A flow path of fuel gas  34 P is defined by the anode  32  and the separator  34 , whereas a flow path of oxidizing gas  35 P is defined by the cathode  33  and the separator  35 . Each of the separators  34  and  35  actually has ribs on both faces thereof, although the flow path is formed only on its single face in the illustration of  FIG. 2 . Namely one face of each separator  34  or  35  is combined with the anode  32  to form the flow path of fuel gas  34 P, whereas the other face of the separator  34  or  35  is combined with the cathode  33  to form the flow path of oxidizing gas  35 P. The separators  34  and  35  are combined with the adjoining gas diffusion electrodes to define the gas flow paths, while functioning to separate the flow of fuel gas from the flow of oxidizing gas in each pair of adjoining unit cells. 
     The electrolyte membrane  31  is a proton-conductive ion exchange membrane composed of a solid polymer material, for example, a fluororesin, and has favorable electrical conductivity in the wet state. In this embodiment, a Nafion membrane (manufactured by du Pont) is applied for the electrolyte membrane  31 . Platinum or a platinum-containing alloy as a catalyst is applied on the surface of the electrolyte membrane  31 . The method of applying the catalyst adopted in this embodiment prepares carbon powder with platinum or a platinum-containing alloy carried thereon, makes the carbon powder with the catalyst carried thereon dispersed in an appropriate organic solvent, adds a suitable quantity of an electrolyte solution (for example, Nafion solution manufactured by Aldrich Chemical Company Inc.,) to the dispersion to yield a paste, and screen prints the paste on the electrolyte membrane  31 . Another applicable method forms a paste containing the carbon powder with the catalyst carried thereon to a sheet and presses the sheet on the electrolyte membrane  31 . The platinum or another catalyst may be applied on, instead of the electrolyte membrane  31 , the anode  32  and the cathode  33 , which are in contact with the electrolyte membrane  31 . 
     The anode  32  and the cathode  33  are both made of carbon cloth woven of carbon fiber threads. Although the anode  32  and the cathode  33  are made of carbon cloth in this embodiment, the anode  32  and the cathode  33  may be made of carbon paper or carbon felt of carbon fibers. 
     The separators  34  and  35  are made of a gas-impermeable conductive material, for example, gas-impermeable dense carbon obtained by compression of carbon. Each of the separators  34  and  35  has multiple ribs arranged in parallel on both faces thereof, and is combined with the surface of the anode  32  in one unit cell to form the flow path of fuel gas  34 P while being combined with the surface of the cathode  33  in an adjoining unit cell to form the flow path of oxidizing gas  35 P. The multiple ribs formed on both faces of each separator may not be parallel to each other but may have a predetermined angle, such as at right angles. The ribs are not restricted to the parallel grooves but may have any suitable shape to feed a supply of fuel gas or oxidizing gas to the gas diffusion electrode. 
     The unit cell  38  or the basic constituent of the fuel cells stack  30  has the above structure. In the actual assembly of the fuel cells stack  30 , a plurality of (100 in this embodiment) the unit cells  38 , each including the separator  34 , the anode  32 , the electrolyte membrane  31 , the cathode  33 , and the separator  35  in this order, are laid one upon another to form a cell laminate. A pair of collectors made of dense carbon or copper plates are arranged across the cell laminate. This completes the stack structure. In this embodiment, the fuel cells  30  are polymer electrolyte fuel cells. The technique of the present invention is also applicable to other types of fuel cells, for example, phosphoric acid fuel cells, mounted on an electric vehicle. 
     As shown in  FIG. 1 , in the electric vehicle  10 , hydrogen absorbed by the hydrogen absorbing alloy included in the fuel tank  20  is taken out of the hydrogen absorbing alloy and is supplied as the fuel gas to the anode of the fuel cells  30  via the fuel supply conduit  22  to be subjected to the electrochemical reaction in the flow path of fuel gas  34 P. The proton produced by the reaction expressed by Equation (1) on the anode side of the electrolyte membrane  31  is hydrated and shifted to the cathode side. Water is accordingly consumed on the cathode side. As mentioned previously, humidification of the fuel gas supplements the water content insufficient in the electrolyte membrane  31 . The fuel gas exhaust after the electrochemical reaction is discharged from the flow path of fuel gas  34 P to a fuel discharge conduit  24 . The fuel discharge conduit  24  is linked with the fuel supply conduit  22 , and the fuel gas exhaust is again supplied as the fuel gas to the fuel cells  30 . A pump  68  is disposed in the fuel discharge conduit  24  to pressurize the fuel gas exhaust and feed the pressurized fuel gas exhaust to the fuel supply conduit  22 . 
     A supply of the air as the oxidizing gas is fed to the flow path of oxidizing gas  35 P via an oxidizing gas supply conduit  62 . A compressor  60  is disposed in the oxidizing gas supply conduit  62  to pressurize an external supply of the air and feed the pressurized air to the stack of fuel cells  30 . The oxidizing gas exhaust after the electrochemical reaction is discharged outside from the flow path of oxidizing gas  35 P via an oxidizing gas discharge conduit  64 . 
     A voltage sensor  23  is attached to the stack of fuel cells  30  to measure an output voltage of the fuel cells  30  and give information on the observed output voltage to the controller  50  as discussed later. 
     The controller  50  is constructed as a microcomputer-based logic circuit and includes a CPU  52 , a ROM  54 , a RAM  56 , and an input-output port  58 . The CPU  52  carries out predetermined operations according to preset control programs. Control programs and control data required for execution of diverse operations by the CPU  52  are stored in advance in the ROM  54 . Various data required for execution of the diverse operations by the CPU  52  are temporarily written in and read from the RAM  56 . The input-output port  58  receives a signal from the hydrogen supply device and outputs driving signals to the compressor  60  and other relevant units involved in operation of the fuel cells  30  according to results of the operations by the CPU  52 , so as to control the driving state of the respective units of the electric vehicle  10 . 
     The connector receptor  40  is arranged at a predetermined position on the outer surface of the electric vehicle  10  and has a connectable structure to a connector of the predetermined external hydrogen supply device. The connector receptor  40  has a hydrogen flow path joint element  46 , a connection terminal  48 , and water flow path joint elements  42  and  44 . The hydrogen flow path joint element  46  forms an end structure of the hydrogen gas inlet conduit  47 , and the connection terminal  48  forms an end structure of a signal line  49  connecting with the controller  50 . The water flow path joint elements  42  and  44  respectively form end structures of the cooling water conduits  45  and  43 . The connector of the hydrogen supply device is linked with the connector receptor  40 , and the respective joint elements of the connector receptor  40  are connected to mating joint elements of the connector. This ensures circulation of hydrogen gas and cooling water between the hydrogen supply device and the electric vehicle  10 . The linkage of the connector with the connector receptor  40  and connection of the connection terminal  48  with a mating terminal of the hydrogen supply device ensure transmission of information regarding the control executed by the controller  50  between the hydrogen supply device and the electric vehicle  10 . Each of the hydrogen flow path joint element  46  and the water flow path joint elements  42  and  44  is provided with a solenoid valve. These solenoid valves are connected to the controller  50  and are opened and closed in response to driving signals output from the controller  50 . The closed state of these solenoid valves causes the electric vehicle  10  to stop the circulation of hydrogen gas and cooling water between the electric vehicle  10  and the hydrogen supply device. 
     The electric power produced by the electrochemical reactions in the stack of fuel cells  30  is supplied to the motor  70 , which accordingly produces a rotational driving force. The rotational driving force is transmitted to front wheels and/or rear wheels of the electric vehicle  10  via an axle of the vehicle  10  and functions as power for driving the vehicle. The motor  70  is under control of a control unit  72 . The control unit  72  is connected with an accelerator pedal position sensor  72 b, which measures a step-on amount of an accelerator pedal  72 a. The control unit  72  is also connected with the controller  50  to transmit information regarding actuation of the motor  70  to and from the controller  50 . 
     The electric vehicle  10  has a non-illustrated secondary battery, which supplements electric power given to the motor  70  to ensure a higher driving force in the case of increased loading, for example, when the electric vehicle  10  climbs up a slope or runs at high speed. The secondary battery functions as an energy source for supplying electric power required for the respective units of the electric vehicle  10 , when no power generation is carried out by the fuel cells  30  or when electric power is required for actuation of the controller  50  and circulation of the cooling water through the cooling water conduit  45  in the process of supplying hydrogen to the fuel tank  20  of the electric vehicle  10 . 
     (2) Structure Related to Supply of Hydrogen 
     The electric vehicle  10  of the embodiment has the construction discussed above. The following describes the details of the structure involved in the action of filling hydrogen in the fuel tank  20  of the electric vehicle  10 .  FIG. 3  shows the electric vehicle  10  and a hydrogen supply device  80  used to supply hydrogen to the electric vehicle  10 . The connector receptor  40  discussed above is arranged at the predetermined position on the outer surface of the body of the electric vehicle  10 . In the illustration of  FIG. 3 , an area F represents the predetermined position, at which the connector receptor  40  is arranged.  FIG. 4  shows the connector receptor  40  in the area F on the outer surface of the vehicle. The hydrogen supply device  80  used to supply hydrogen to the vehicle has two tubular structures extended outside, that is, a hydrogen supply unit  82  and a cooling water supply unit  84 , which are capable of feeding supplies of hydrogen gas and cooling water to the electric vehicle  10 . The hydrogen supply unit  82  and the cooling water supply unit  84  are illustrated in  FIG. 4 . The hydrogen supply unit  82  of the hydrogen supply device  80  has a first connector  86  on one end thereof. The cooling water supply unit  84  of the hydrogen supply device  80  has a second connector  88  on one end thereof. 
     As illustrated in  FIG. 4 , the connector receptor  40  has a hydrogen inlet  14  and a cooling water inlet  12 . The hydrogen inlet  14  open to the outer surface of the body of the electric vehicle  10  has the hydrogen flow path joint element  46  (not shown in  FIG. 4 ), and is connected to the fuel tank  20  via the hydrogen gas inlet conduit  47  laid inside the electric vehicle  10 . The hydrogen inlet  14  also has the connection terminal  48  (not shown in  FIG. 4 ) connecting with the controller  50 . The cooling water inlet  12  open to the outer surface of the body of the electric vehicle  10  has the water flow path joint elements  42  and  44  (not shown in  FIG. 4 ) connecting with the heat exchange module  26  via the cooling water conduits  43  and  45 . The hydrogen inlet  14  of the connector receptor  40  has a structure to receive the first connector  86  fitted therein for attachment. The cooling water inlet  12  of the connector receptor  40  has a structure to receive the second connector  88  fitted therein for attachment. 
       FIG. 5  shows the construction of a main part of the hydrogen supply device  80 . The first connector  86  has a hydrogen flow path joint element  96  and a connection terminal  98 . When the first connector  86  is fitted in and attached to the hydrogen inlet  14 , the hydrogen flow path joint element  96  is joined with the mating hydrogen flow path joint element  46  of the electric vehicle  10  and the connection terminal  98  is joined with the mating connection terminal  48  of the electric vehicle  10 . The second connector  88  has water flow path joint elements  92  and  94 . When the second connector  88  is fitted in and attached to the cooling water inlet  12 , the water flow path joint element  92  is joined with the mating water flow path joint element  42  of the electric vehicle  10  and the water flow path joint element  94  is joined with the mating water flow path joint element  44  of the electric vehicle  10 . 
     One end of a hydrogen gas inlet conduit  97  laid in the hydrogen supply device  80  is open to the hydrogen flow path joint element  96  of the first connector  86 . The other end of the hydrogen gas inlet conduit  97  is linked with a non-illustrated hydrogen reservoir. The hydrogen supply device  80  of the embodiment has the hydrogen reservoir, which stores therein a sufficient quantity of hydrogen. Hydrogen stored in the hydrogen reservoir is supplied to the electric vehicle via the first connector  86  and the connector receptor  40 . In this embodiment, the hydrogen supply device is a device that stores a sufficient quantity of hydrogen and supplies the hydrogen stored therein to outside. The hydrogen supply device may alternatively be a device that reforms a source material, such as a hydrocarbon or a hydrocarbon compound to produce a hydrogen-containing gas, extracts hydrogen from the produced hydrogen-containing gas, and supplies the extracted hydrogen to outside. 
     Cooling water conduits  95  and  93  laid in the hydrogen supply device  80  are respectively open to the water flow path joint elements  92  and  94  of the second connector  88 . The cooling water conduits  95  and  93  are connected with each other in a heat exchange module  90 . The cooling water conduit  95  is provided with a pump  91  for circulation of the cooling water. The heat exchange module  90  has a radiator structure and cools down the flow of cooling water, which is led by the cooling water conduit and passes through the heat exchange module  80 . The fuel tank  20  is cooled down, as the operation of supplying hydrogen to the fuel tank  20  of the electric vehicle  10  is exothermic. The heat exchange module  90  and the pump  91  in the hydrogen supply device  80  function to decrease the temperature of the cooling water, which has been heated up in the course of cooling down the fuel tank  20 . 
     The hydrogen supply device  80  also has a controller  150 . Like the controller  50  of the electric vehicle  10 , the controller  150  includes a CPU  152 , a ROM  154 , a RAM  156 , and an input output port  158 . The connection terminal  98  of the first connector  86  is linked with the controller  150  via a signal line  99 . When the first connector  86  is attached to the hydrogen inlet  14 , the controller  150  can transmit information to and from the controller  50  of the electric vehicle  10 . The controller  150  also connects with the pump  91  to output a driving signal to the pump  91 . The hydrogen flow path joint element  96  and the water flow path joint elements  92  and  94  are respectively provided with solenoid valves. These solenoid valves are connected to the controller  150  and are opened and closed in response to driving signals output from the controller  150 . The closed state of these solenoid valves causes the hydrogen supply device  80  to stop the circulation of hydrogen gas and cooling water between the electric vehicle  10  and the hydrogen supply device  80 . 
     The connector receptor  40  of the electric vehicle  10  is attached to the outer surface of the vehicle body via a hinge  15  in a freely opening and closing manner. The connector receptor  40  has a fuel lid  18 , which is a cover member for covering over the cooling water inlet  12  and the hydrogen inlet  14 . The fuel lid  18  and the vehicle body with the connector receptor  40  disposed thereon respectively have a claw  19  and a catching element  17  at corresponding positions (see  FIG. 4 ). The claw  19  is caught by the catching element  17  in the case of no fuel supply, so that the fuel lid  18  of the connector receptor  40  is closed. 
     The electric vehicle  10  of the embodiment has an opener lever located in the vicinity of the driver&#39;s sheet. The opener lever is electrically connected with the catching element  17  via a predetermined relay. An operational force applied to the opener lever is transmitted to the catching element  17 , so as to release the engagement of the claw  19  with the catching element  17  and thereby open the fuel lid  18 . The mechanism of transmitting the operational force applied to the opener lever is not restricted to the above electrical arrangement but may be a mechanical arrangement in which the opener lever is mechanically connected with the catching element  17  via a predetermined cable. 
     In the case of supply of hydrogen, the opener lever is operated to release the engagement of the claw  19  with the catching element  17  and open the fuel lid  18 . The second connector  88  and the first connector  86  are respectively attached to the cooling water inlet  12  and the hydrogen inlet  14 . The respective connectors are connected to the electric vehicle  10 , and the controllers  50  and  150  communicating with each other output driving signals to open the solenoid valves of the respective joint elements. The opened state of the solenoid valves enables the supply of hydrogen from the hydrogen supply device  80  into the fuel tank  20  as well as the circulation of cooling water between the hydrogen supply device  80  and the electric vehicle  10 . The controllers  50  and  150  respectively output driving signals to actuate the pumps  29  and  91 , so that the flow of cooling water is circulated between the electric vehicle  10  and the hydrogen supply device  80 . The temperature of cooling water rises, as the flow of cooling water passes through the heat exchange module  26  and cools down the fuel tank  20 , which is heated up in the course of absorption of hydrogen by the hydrogen absorbing alloy. The temperature of cooling water is lowered, as the flow of cooling water passes through the heat exchange module  90  of the hydrogen supply device  80 . In response to input of a signal from the hydrogen fill monitor  28  that detects conclusion of the supply of hydrogen, the controllers  50  and  150  respectively suspend actuation of the pumps  29  and  91  and close the solenoid valves of the joint elements, so as to stop the supply of hydrogen from the hydrogen supply device  80  into the fuel tank  20  as well as the circulation of cooling water between the hydrogen supply device  80  and the electric vehicle  10 . 
     In the structure of this embodiment, the hydrogen supply device  80  has the heat exchange module  90 . In the course of hydrogen supply, the flow of cooling water is circulated between the electric vehicle  10  and the hydrogen supply device  80  in order to cool the fuel tank  20  down. Any of other suitable structures may be applied for the same purpose. In one modified structure, the cooling water used to cool the fuel tank  20  down may be taken out of the electric vehicle and utilized for other applications as hot water having a certain quantity of heat, while the structure of the embodiment makes the cooling water circulated between the electric vehicle  10  and the hydrogen supply device  80  to be repeatedly cooled down in the hydrogen supply device  80 . In this modified structure, a continuous supply of cooling water having sufficiently low temperature is externally fed to the electric vehicle during hydrogen supply. 
     (3) Control in Process of Hydrogen Supply 
     The following describes a series of control carried out in the process of hydrogen supply to the electric vehicle  10 .  FIG. 6  is a flowchart showing a fuel supply-time processing routine executed in the process of supplying hydrogen to the electric vehicle  10 . This routine is carried out by the controller  50  of the electric vehicle  10 , when the user of the vehicle operates the opener lever to open the fuel lid  18 , prior to the action of hydrogen supply to the electric vehicle  10 . 
     When the program enters the routine, the CPU  52  of the controller  50  first determines whether or not a predetermined start switch is ON to give a starting instruction of the fuel cells  30  (step S 200 ). The start switch corresponds to an ignition switch in a conventional vehicle with a gasoline engine mounted thereon, and is provided to allow input of the user&#39;s instructions of starting and stopping the operation of the fuel cells  30 . When it is determined at step S 200  that the start switch is ON, that is, when it is determined that the starting instruction of the fuel cells  30  has been given, the CPU  52  does not open the fuel lid  18  regardless of the user&#39;s operation of the opener lever and cancels input of a signal corresponding to the operation of the opener lever (step S 230 ). The program then immediately exits from this routine. In this case, it is desirable to inform the user of the current situation that opening of the fuel lid  18  is not allowed because of the ON state of the start switch, for example, by a display at a preset position on the electric vehicle, an alarm, or a voice guidance. 
     When it is determined at step S 200  that the start switch is OFF, on the other hand, the CPU  52  subsequently determines whether or not the output voltage of the fuel cells  30  is not higher than 40 V (step S 210 ). As discussed previously, the voltage sensor  23  is attached to the fuel cells  30 . The procedure of step S 210  determines whether or not the output voltage of the fuel cells  30  is not higher than 40V based on a signal input from the voltage sensor  23 . The determination of step S 210  is carried out when it is determined at step S 200  that the start switch is OFF, that is, when it is determined that operation of the fuel cells  30  is suspended. The determination of step S 210  further enhances the safety in hydrogen supply. When the start switch is turned OFF to stop power generation in the fuel cells  30  and cease the gas supplies to the fuel cells  30 , the output voltage of the fuel cells  30  does not immediately decrease from the ordinary state level of several hundred volts to substantially zero, but is gradually lowered until consumption of the remaining gases in the fuel cells  30 . Confirmation that the output voltage of the fuel cells  30  is sufficiently small effectively prevents hydrogen supply under the condition of an undesired output from the fuel cells  30 . The value used for the determination of step S 210  is not restricted to 40 V, but may be any value suitable for confirmation that the output voltage from the fuel cells  30  is sufficiently small. 
     When it is determined at step S 210  that the output voltage of the fuel cells  30  is not higher than 40V, the preset relay is coupled to open the fuel lid  18  (step S 220 ). The program then exits from this routine. 
     When it is determined at step S 210  that the output voltage of the fuel cells  30  is higher than 40V, on the other hand, the fuel cells  30  are discharged to lower the output voltage (step S 240 ). In the electric vehicle  10  of the embodiment, a predetermined discharge resistance (not shown) is connectable with the fuel cells  30 . The procedure of Step S 240  connects the predetermined discharge resistance with the fuel cells  30  for a preset time period and accelerates power generation, which consumes the remaining gases in the fuel cells  30 , so as to lower the output voltage of the fuel cells  30 . 
     After the discharge of the fuel cells  30  at step S 240 , the program returns to step S 210  to determine whether or not the output voltage is sufficiently lowered. The processing of steps S 240  and S 210  is repeated until the output voltage is lowered to or below 40 V. When the output voltage is sufficiently lowered by the discharge of the fuel cells, the program proceeds to step S 220  to open the fuel lid  18  and then exits from this routine. In the above description, the fuel cells are connected with the predetermined discharge resistance and are discharged at step S 240 . An alternative procedure may not use the separate discharge resistance, but may connect the fuel cells with a predetermined device, which is mounted on the electric vehicle  10  and consumes electric power, to discharge the fuel cells. 
     In the fuel supply-time processing routine, when it is determined at step S 200  that the start switch is not ON, the state of inputting the signal from the opener lever is maintained. This signal is cancelled in response to a subsequent closing action of the fuel lid  18 . The catching element  17 , which engages with the claw  19  of the fuel lid  18 , has a specific sensor. When it is detected that the fuel lid  18  is closed and the claw  19  is caught by the catching element  17 , the signal input from the opener lever is cancelled. The opening and closing state of the fuel lid  18  is thus specified by the detection that the signal from the opener lever is input or cancelled. 
     The fuel supply-time processing routine shown in  FIG. 6  is carried out to prevent supply of hydrogen during operation of the fuel cells. There is another series of processing executed to prevent operation of the fuel cells during supply of hydrogen.  FIG. 7  is a flowchart showing a fuel cells starting-time processing routine carried out in the electric vehicle  10 . This routine is executed by the controller  50  of the electric vehicle  10  when the user of the vehicle operates the start switch to start operation of the fuel cells  30 . 
     When the program enters this routine, the CPU  52  of the controller  50  first determines whether or not the fuel lid  18  is open (step S 300 ). When it is determined that the fuel lid  18  is closed, the program starts the fuel cells  30  (step S 310 ) and exits from this routine. The start of the fuel cells here represents a start of sequential processes relating to the start of operation of the fuel cells  30 , which include a process of heating the fuel tank  20  to extract hydrogen from the hydrogen absorbing alloy and starting a supply of the extracted hydrogen as the fuel gas to the fuel cells  30  and a process of actuating the compressor  60  and starting a supply of the compressed air as the oxidizing gas to the fuel cells  30 . 
     When it is determined at step S 300  that the fuel lid  18  is open, on the other hand, the CPU  52  prohibits the start of the fuel cells  30 , lights up an alarm lamp or beeps an alarm sound in order to inform the user of the current situation that the operation of the fuel cells  30  is not allowed because of the opening state of the fuel lid  18 , and cancels the signal input by the operation of the start switch (step S 320 ). The program then exits from this routine. The arrangement of informing the user of the current situation is not restricted to lighting up the alarm lamp or beeping the alarm sound, but may apply any suitable structure. 
     The determination of step S 300  regarding the opening and closing state of the fuel lid  18  is based on input of the signal by the operation of the opener lever. During execution of the fuel supply-time processing routine of  FIG. 6  in response to the operation of the opener lever, it is determined that the fuel lid  18  is open even in the course of discharge of the fuel cells  30  at step S 240  prior to the action of opening the fuel lid  18  at step S 220 . 
     In the electric vehicle  10  and the hydrogen supply device  80  of the embodiment discussed above, the fuel lid  18  is not opened in response to the operation of the opener lever, while the start switch is ON. This arrangement does not allow the hydrogen supply during operation of the fuel cells  30 , thus enhancing the safety in hydrogen supply. Especially when the fuel cells are mounted on a movable body, such as the electric vehicle and are used as the driving energy source for movement, there is a possibility that the electric vehicle moves during operation of the fuel cells. The arrangement of the embodiment prohibits supply of hydrogen during operation of the fuel cells and thereby ensures no movement of the electric vehicle during supply of hydrogen, thus further enhancing the safety in hydrogen supply. 
     The procedure of the above embodiment determines at step S 200  that the start switch for giving an instruction of starting the fuel cells is OFF and prevents movement of the electric vehicle during supply of hydrogen. The electric vehicle  10  of the embodiment may have setting of a specific drive mode where the electric vehicle  10  drives with electric power supplied from the secondary battery even while the fuel cells are stopped. In this modified structure, the process of step S 200  in  FIG. 6  determines whether or not the specific drive mode using the secondary battery as the driving energy source is not selected, in addition to the determination of whether or not the fuel cells are being operated. This modified arrangement effectively prevents movement of the electric vehicle during supply of hydrogen. The determination of step S 200  may be based on another condition, as long as it is determined whether or not the electric vehicle is moving or is movable. 
     In the case where the output voltage of the fuel cells exceeds the predetermined value, the technique of the embodiment does not open the fuel lid  18  in response to the user&#39;s operation of the opener lever for hydrogen supply but prohibits a start of hydrogen supply, even when the start switch is OFF to give an instruction of stopping the operation of the fuel cells. This arrangement effectively prevents supply of hydrogen under the condition that the output voltage of the fuel cells exceeds the predetermined value and thus ensures the safety in hydrogen supply. 
     In the electric vehicle of the embodiment, while the fuel lid  18  is open, the start of the fuel cells is not allowed in response to the ON operation of the start switch. This arrangement effectively prevents the start of the fuel cells during supply of hydrogen and thus ensures the safety in hydrogen supply. The structure of prohibiting not only the start of the fuel cells but any movement of the vehicle including a drive using the secondary battery as the driving energy source in the opening state of the fuel lid  18  further enhances the safety in hydrogen supply. 
     Execution or non-execution of hydrogen supply is determined based on the opening and closing state of the fuel lid  18  at step S 300  in the fuel cells starting-time processing routine of the embodiment described above. The determination regarding the execution of hydrogen supply may be based on another condition. One example is based on the communicable connection or disconnection of the controller  50  of the electric vehicle with or from the controller  150  of the hydrogen supply device  80 . Another example is based on the input or non-input of a preset signal to give an instruction of starting hydrogen supply (that is, an instruction signal from a predetermined switch operated by the user to start the feed of hydrogen from the hydrogen supply device  80  and to start the circulation of cooling water). The determination based on the opening and closing state of the fuel lid  18  as executed in the above embodiment can determine execution or non-execution of hydrogen supply prior to connection of the hydrogen flow path between the hydrogen supply device  80  and the electric vehicle  10 , thus ensuring the enhanced safety. 
     In the structure of the embodiment, once the opener lever is operated to execute the fuel supply-time processing routine, even when the output voltage of the fuel cells exceeds the predetermined value and opening of the fuel lid  18  is not allowed at the time of operating the opener lever, discharge of the fuel cells is repeatedly carried out to lower the output voltage and eventually allow opening of the fuel lid  18 . In a modified structure, when the output voltage of the fuel cells exceeds the predetermined value (40 V in the embodiment) at the time of operating the opener lever, the procedure may exit from the processing routine only after connection of the fuel cells with the discharge resistance and reset of the input signal by the operation of the opener lever, while requiring another operation of the opener lever to open the fuel lid  18 . In this structure, a display at a preset position or an alarm is desirable to inform the user of the current situation that the output voltage of the fuel cells is undesirably high and opening of the fuel lid  18  is thus not allowed. This procedure resets the input signal by the operation of the opener lever simultaneously with the discharge operation. When the start switch is turned ON to execute the fuel cells starting-time processing routine of  FIG. 7  prior to another operation of the opener lever, it is determined at step S 300  that the fuel lid  18  is not open. 
     In the fuel supply-time processing routine of the embodiment described above, when it is determined that the fuel cells are in operation, the procedure does not allow the fuel lid  18  to be opened in response to the operation of the opener lever, so as to prohibit the start of hydrogen supply. One modified procedure does not allow the solenoid valves of the respective joint elements to be opened in the ON state of the start switch (that is, during operation of the fuel cells), so as to prohibit the start of hydrogen supply, even after the fuel lid  18  is opened by the operation of the opener lever and the connector is attached to the connector receptor. 
     In the fuel supply-time processing routine of the embodiment described above, opening of the fuel lid  18  is not allowed even in the OFF state of the start switch, until the output voltage of the fuel cells is lowered to or below the predetermined value. Another arrangement may be applied to prohibit the start of hydrogen supply when the output voltage of the fuel cells exceeds the predetermined value. One applicable procedure opens the fuel lid  18  to enable attachment of the connector in the OFF state of the start switch, in response to the operation of the opener lever. Even after attachment of the connector to the connector receptor and input of a predetermined instruction of starting hydrogen supply, the controllers  50  and  150  are stood by until the output voltage of the fuel cells is lowered to or below the predetermined value. Only after the output voltage of the fuel cells is lowered to or below the predetermined value, opening of the solenoid valves and actuation of the pumps are allowed to start the supply of hydrogen. This arrangement improves the convenience of operation in hydrogen supply. The user who wants to supply hydrogen is not required to wait for conclusion of discharge of the fuel cells and permission to open the fuel lid  18 , when the output voltage of the fuel cells exceeds the predetermined value. Before the sufficient decrease in output voltage of the fuel cells, the user may complete the series of operations relating to start of hydrogen supply, which include connection of the hydrogen supply device  80  with the electric vehicle  10  through attachment of the connector to the connector receptor and input of the predetermined instruction of starting hydrogen supply. In this structure, a display at a preset position or an alarm is required in at least one of the electric vehicle  10  and the hydrogen supply device  80  to inform the user of the stand-by status for a time period between attachment of the connector and an actual start of hydrogen supply (that is, a time period when the output voltage of the fuel cells is lowered to or below the predetermined value). 
     In the fuel cells starting-time processing routine of  FIG. 7 , when it is determined at step S 300  that the fuel lid  18  is open, the procedure prohibits the start of the fuel cells and cancels the operation of the start switch. One modified procedure does not exits from this routine but returns to step S 300  after the processing of step S 320 , which prohibits the start of the fuel cells and lights up the alarm lamp or beeps the alarm sound. The procedure proceeds to step S 310  to start the fuel cells when the fuel lid  18  is closed after conclusion of hydrogen filling. 
     The structures of the electric vehicle  10  and the hydrogen supply device  80  of the above embodiment may be modified in various ways. For example, in the structure of the above embodiment, the hydrogen supply device  80  feeds a supply of hydrogen to the electric vehicle  10 , while making the flow of cooling water circulated between the hydrogen supply device  80  and the electric vehicle  10 . One possible modification may use a separate device for circulation of cooling water from the hydrogen supply device  80 . A cooling unit for cooling the fuel tank  20  down in the course of hydrogen supply (this corresponds to the heat exchange module  90  built in the hydrogen supply device  80  in the above embodiment) may be mounted on the electric vehicle  10 . In the structure of the above embodiment, the first connector  86  and the second connector  88  are attached to the connector receptor  40 , which is opened and closed with the fuel lid  18 , the single cover member, to allow supplies of hydrogen and cooling water to the electric vehicle  10 . In one modified structure, the connector for hydrogen supply and the connector for cooling water supply may be attached to different connector receptors disposed at separate locations. In another modified structure, a single connector is attached to the electric vehicle  10  to connect both the flow paths of hydrogen and cooling water between the electric vehicle  10  and the hydrogen supply device  80 . The solenoid valve attached to the hydrogen flow path joint element  96  to open and close the flow path of supplying hydrogen from the hydrogen supply device  80  to the electric vehicle may be located at a different position, that is, at an arbitrary position in the hydrogen gas inlet conduit  97 . The fuel tank  20  may store hydrogen by any suitable means other than absorption of hydrogen in the hydrogen absorbing alloy. 
     (4) Another Construction of Electric Vehicle 
     The electric vehicle  10  of the embodiment described above has the fuel tank  20  including the hydrogen absorbing alloy, which absorbs hydrogen therein for storage. The technique of the present invention is also applicable to an electric vehicle with a different fuel mounted thereon. The electric vehicle has a fuel tank for storing therein a hydrocarbon or a hydrocarbon compound, instead of hydrogen, as the fuel and is further provided with a system that reforms the fuel (source material) and produces hydrogen. A variety of hydrocarbons and hydrocarbon compounds including gas fuels like natural gas (methane) and liquid fuels like alcohols and gasoline may be used for the source material to produce hydrogen. The system for producing hydrogen from the source material may include a reformer device that utilizes a noble metal catalyst to accelerate a steam reforming reaction and a partial oxidation reaction and obtain a hydrogen rich gas from the source material and a carbon dioxide reduction device that utilizes a carbon monoxide selective oxidation catalyst to reduce the concentration of carbon monoxide included in the hydrogen rich gas. 
     The technique of the present invention is also applicable for such construction to supply the source material to the fuel tank of the electric vehicle. In a similar manner to that of the embodiment discussed above, the technique prohibits a start of operation of the fuel cells during supply of the source material or a start of supply of the source material during operation of the fuel cells, thus enhancing the safety in supply of the source material. 
     The above embodiment regards the application of the invention to the vehicle. The technique of the present invention is applicable to a diversity of movable bodies that utilize the output from the fuel cells for movement, such as ships, boats, aircraft, and other flying objects as well as vehicles. 
     The above embodiment of the present invention and its application are to be considered in all aspects as illustrative and not restrictive. There may be many modifications, changes, and alterations without departing from the scope or spirit of the main characteristics of the present invention. 
     INDUSTRIAL APPLICABILITY 
     The fuel supply system for fuel cells according to the present invention is suitably applied for diverse movable bodies with fuel cells mounted thereon, such as vehicles, to supply a fuel for the fuel cells.