Patent Publication Number: US-8522834-B2

Title: Gas filling device, gas filling system, gas filling method and moving device

Description:
This is a 371 national phase application of PCT/JP2009/005435 filed 19 Oct. 2009, the contents of which are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to filling a gas from a gas supply device to a gas tank, and more specifically to filling a gas from a gas station to a plurality of gas tanks. 
     BACKGROUND OF THE INVENTION 
     One known technique to fill a gas into a plurality of gas tanks is disclosed in PTL1. This method simultaneously fills a fuel gas, such as hydrogen, from a hydrogen station into a plurality of fuel tanks to store the fuel gas in a fuel cell vehicle. The method detects pressure and temperature in each of the fuel tanks and controls opening/closing of valves respectively connecting the hydrogen station with the respective tanks, based on the detected pressure and temperature in each of the fuel tanks. 
     CITATION LIST 
     Patent Literature 
     
         
         [PTL1] JP2004-84808 A 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     The fuel tanks may have different heat dissipation capacities according to their materials and structures or the surrounding environment of their installation location. The fuel tank of the higher heat dissipation capacity facilitates release of heat from the fuel gas in the tank and thereby reduces the temperature increase in the fuel tank. The fuel tank of the lower heat dissipation, on the other hand, has a high temperature increase rate accompanied with a high pressure increase rate in the tank. 
     In an application of filling hydrogen into a plurality of fuel tanks having different heat dissipation capacities, the prior art method of controlling the start/stop of the fuel gas supply to the respective fuel tanks according to the temperatures and the pressures in the respective fuel tanks may fail to fill the fuel gas efficiently. 
     The present invention is made to address at least part of the problem described above, and an object of the present invention is to efficiently fill a gas into a plurality of tanks having different heat dissipation capacities. 
     Solution to Problem 
     [Aspect 1] 
     
         
         
           
             1. A gas filling device configured to fill a gas into a plurality of tanks provided to store the gas through separate gas filler passages with respective valves, the gas filling device comprising: 
           
         
       
    
     a gas supplier configured to supply the gas to the gas filler passages; and 
     a controller configured to separately open and close each of the valves provided in the respective gas filler passages, so as to control gas flows supplied from the gas supplier, 
     wherein the controller comprises:
         a heat dissipation information acquirer configured to obtain heat dissipation information regarding heat dissipation capacity of each of the plurality of tanks; and   an in-tank information acquirer configured to obtain information regarding at least one of temperature and pressure in each of the plurality of tanks, and       

     wherein the controller causes opening and closing of the valves to sequentially fill the gas into the plurality of tanks one by one, and then to allow communication between the separate gas filler passages after the plurality of tanks are filled with the gas, based on the heat dissipation information obtained by the heat dissipation information acquirer and the information in the tank obtained by the in-tank information acquirer. 
     The gas filling device of this aspect allows communication between the plurality of tanks having different heat dissipation capacities during gas filling. Even when the temperature or the pressure increases in the tank of the lower heat dissipation capacity, this reduces the temperature increase or the pressure increase and ensures efficient gas filling. 
     [Aspect 2] 
     The gas filling device according to aspect 1, wherein 
     after the gas is supplied through the separate gas filler passages to be filled into the plurality of tanks, the heat dissipation information acquirer of the controller calculates and obtains heat dissipation information with respect to each of the plurality of tanks, based on the information obtained by the in-tank information acquirer. 
     The gas filling device of this aspect readily obtains the heat dissipation information showing which of the tanks has the higher heat dissipation capacity. And the controller refers to this heat dissipation information to ensure efficient gas filling. 
     [Aspect 3] 
     The gas filling device according to either one of aspects 1 and 2, wherein 
     the controller is configured to perform a first gas filling process comprising the steps of; 
     (a) filling the gas into a first tank of higher heat dissipation capacity of the plurality of tanks, based on the heat dissipation information; 
     (b) stopping the gas filling into the first tank, and filling the gas into a second tank of lower heat dissipation capacity; and 
     (c) stopping the gas filling into the second tank, and allowing communication between the first tank and the second tank. 
     The gas filling device of this aspect fills the gas first into the first tank of the higher heat dissipation capacity and later into the second tank of the lower heat dissipation capacity. This accelerates heat release from the first tank during the gas filling into the second tank. As the result, this allows the gas filling in a shorter time period, thus ensuring the efficient gas filling. 
     [Aspect 4] 
     The gas filling device according to aspect 3, wherein 
     the first gas filling process performed by the controller further comprises the step of 
     (d) filling the gas into the first tank and the second tank, after the step (c). 
     The gas filling device of this aspect increases the amount of gas filling by the additional step (d), so as to ensure the efficient gas filling. 
     [Aspect 5] 
     The gas filling device according to either one of aspects 3 and 4, wherein 
     the controller stops the gas filling into the first tank when either gas temperature or gas pressure in the first tank reaches a preset value in the step (b). 
     The gas filling device of this aspect enables the gas filling to the limit of the first tank, thus ensuring the efficient gas filling. 
     [Aspect 6] 
     The gas filling device according to any one of aspects 3 to 5, wherein 
     the controller stops the gas filling into the second tank when either gas temperature or gas pressure in the second tank reaches a preset value in the step (c). 
     The gas filling device of this aspect enables the gas filling to the limit of the second tank, thus ensuring the efficient gas filling. 
     [Aspect 7] 
     The gas filling device according to any one of aspects 3 to 6, wherein 
     the controller is further configured to perform a second gas filling process of simultaneously filling the gas into the first tank and the second tank, and 
     the controller selectively performs either the first gas filling process or the second gas filling process, based on the information in the tank prior to gas filling, which is obtained by the in-tank information acquirer. 
     The gas filling device of this aspect enables selection of the more efficient gas filling process, based on the tank condition prior to gas filling, between the first gas filling process of sequentially filling the gas into the first tank and into the second tank and the second gas filling process of simultaneously filling the gas into the first tank and the second tank. 
     [Aspect 8] 
     The gas filling device according to aspect 7, wherein 
     the controller performs the second gas filling process when pressures in the first tank and in the second tank prior to the gas filling are not greater than a preset pressure level which is determined according to temperatures in the first tank and in the second tank. 
     The gas filling device of this aspect enables selection of the more efficient gas filling process. 
     [Aspect 9] 
     A gas filling system configured to supply a gas from a gas filling device to a moving device, 
     the gas filling system comprising the moving device and the gas filling device, 
     the moving device comprising:
         a plurality of tanks configured to store the supplied gas;   separate gas filler passages connected with the plurality of tanks; and   valves provided in the separate gas filler passages, wherein       

     the gas filling device comprises a gas supplier configured to supply the gas to the gas filler passages, 
     at least one of the moving device and the gas filling device comprises a controller configured to separately open and close each of the valves, so as to control a gas flow supplied from the gas supplier to corresponding one of the gas filler passages, wherein 
     the controller comprises:
         a heat dissipation information acquirer configured to obtain heat dissipation information regarding heat dissipation capacity of each of the plurality of tanks; and   an in-tank information acquirer configured to obtain information regarding at least one of temperature and pressure in each of the plurality of tanks, and       

     the controller causes opening and closing of the valves to sequentially fill the gas into the plurality of tanks and, after gas filling into the plurality of tanks, to allow communication between the separate gas filler passages, based on the heat dissipation information obtained by the heat dissipation information acquirer and the information in the tank obtained by the in-tank information acquirer. 
     [Aspect 10] 
     A gas filling method of filling a gas through separate gas filler passages to a plurality of tanks provided to store the gas, 
     the gas filling method comprising: 
     (a) a heat dissipation information acquisition step of obtaining heat dissipation information regarding heat dissipation capacity of each of the plurality of tanks; 
     (b) a step of separately opening and closing each of valves provided in the respective gas filler passages, so as to control a gas flow supplied from the gas supplier; 
     (c) a step of obtaining information regarding at least one of temperature and pressure in each of the plurality of tanks; and 
     (d) a step of opening and closing each of the valves to sequentially fill the gas into the plurality of tanks one by one, and then to allow communication between the separate gas filler passages after the plurality of tanks are filled with the gas, based on the heat dissipation information obtained by the heat dissipation information acquirer and the information in the tank obtained by the in-tank information acquirer. 
     [Aspect 11] 
     A moving device, comprising: 
     a plurality of tanks provided to store a gas supplied; 
     a plurality of sensors, each being configured to measure at least one of gas temperature and gas pressure in each of the plurality of tanks; 
     separate gas filler passages connected with the plurality of tanks; 
     valves provided in the separate gas filler passages; and 
     a controller configured to separately open and close each of the valves, so as to sequentially fill the gas into the plurality of tanks one by one, and then to control a gas flow supplied from the gas supplier after the plurality of tanks are filled with the gas, wherein 
     the controller comprises:
         a heat dissipation information acquirer configured to obtain heat dissipation information regarding heat dissipation capacity of each of the plurality of tanks; and   an in-tank information acquirer configured to obtain information regarding at least one of temperature and pressure in each of the plurality of tanks, and       

     the controller causes opening and closing of the valves to sequentially fill the gas into the plurality of tanks one by one, and then to allow communication between the separate gas filler passages after the plurality of tanks are filled with the gas, based on the heat dissipation information obtained by the heat dissipation information acquirer and the information in the tank obtained by the in-tank information acquirer. 
     The moving device of this aspect allows communication between the plurality of tanks having different heat dissipation capacities during gas filling. Even when the temperature or the pressure increases in the tank of the lower heat dissipation capacity, this reduces the temperature increase or the pressure increase and ensures efficient gas filling. 
     [Aspect 12] 
     The moving device according to aspect 11, wherein 
     the controller is configured to perform a gas filling process comprising the steps of: 
     (a) filling the gas into a first tank of higher heat dissipation capacity of the plurality of tanks, based on the heat dissipation information; 
     (b) stopping the gas filling into the first tank, and filling the gas into a second tank of lower heat dissipation capacity; and 
     (c) stopping the gas filling into the second tank, while allowing communication between the first tank and the second tank. 
     [Aspect 13] 
     The moving device according to aspect 12, wherein 
     the plurality of tanks are at least three tanks and include at least two first tanks, and 
     the controller sequentially selects one of the at least two first tanks to fill the gas into the selected first tank in the step (a) in each cycle of the first filling process, and fills the gas into a remaining non-selected first tank and the second tank in the step (b). 
     The moving device of this aspect fills the gas first into the first tank, thus improving the gas filling efficiency, while switching the plurality of first tanks to be used, thus improving the durability of the first tanks. 
     [Aspect 14] 
     The moving device according to either one of aspects 12 and 13, wherein 
     the second tank is lighter in weight than the first tank. 
     The moving device of this aspect improves the gas filling efficiency, while reducing the weight of the moving device. 
     The above aspects of the invention are not limited to the gas filling device but may be adopted in the other aspects, such as the gas filling system, the gas filing method and the moving device. The invention is not limited to the above aspects, but a multiplicity of variants and modifications may be made to these aspects without departing from the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  illustrates the configuration of a hydrogen filling system. 
         FIG. 2  illustrates a hydrogen filling model to a tank. 
         FIG. 3  shows variations in hydrogen temperature in the tank after hydrogen filling against the fill time. 
         FIG. 4  shows variations in hydrogen temperature to be filled into the tank against the time elapsed since start of filling. 
         FIG. 5  is a flowchart showing a procedure of hydrogen filling process. 
         FIG. 6  shows which of the tanks is filled with hydrogen, in relation to the fill time and the fill hydrogen temperature. 
         FIG. 7  shows variations in hydrogen pressure against the elapsed time with respect to the respective tanks. 
         FIG. 8  shows variations in hydrogen temperature against the elapsed time with respect to the respective tanks. 
         FIG. 9  shows variations in hydrogen pressure in the first vehicle tank  220  against the elapsed time with respect to an embodiment and a comparative example. 
         FIG. 10  shows variations in hydrogen temperature in the first vehicle tank  220  against the elapsed time with respect to the embodiment and the comparative example. 
         FIG. 11  is a flowchart showing a control switching procedure according to the second embodiment. 
         FIG. 12  shows a control switching map according to the second embodiment. 
         FIG. 13  illustrates a system configuration in which the controller  150  of the hydrogen station  10  controls the hydrogen filling. 
         FIG. 14  illustrates a system configuration in which the controller  240  of the vehicle  20  controls the hydrogen filling. 
         FIG. 15  illustrates a system configuration in which a gas filler passage branches off in the hydrogen station. 
     
    
    
     DETAILED DESCRIPTION 
     First Embodiment 
       FIG. 1  illustrates the configuration of a hydrogen filling system. The hydrogen filling system is configured to fill and supply hydrogen from a hydrogen station  10  to a vehicle  20 . The hydrogen station  10  includes a tank  100 , a compressor  110 , a pre-cooler  120 , an electrically-operated valve  130 , a nozzle  140  and a controller  150 . The vehicle  20  includes a receptacle  200 , first and second electrically-operated valves  210  and  215 , first and second vehicle tanks  220  and  225 , first and second sensors  230  and  235 , a controller  240  and a fuel cell  250 . 
     The tank  100  stores hydrogen, which is to be supplied to the vehicle. The compressor  110  increases the hydrogen pressure to be higher than the gas pressures inside the vehicle tanks (described later), in order to fill hydrogen into the vehicle tanks. The compressor  110  is connected with the pre-cooler  120 , which serves to lower the temperature of compressed hydrogen. The lowered temperature may be minus several tens degrees Celsius. The nozzle  140  is connected with the pre-cooler  120 . The electrically-operated valve  130  is located between the pre-cooler  120  and the nozzle  140 . The controller  150  is electrically connected with the compressor  110  and the electrically-operated valve  130  to control their operations. The controller  150  also includes a heat dissipation information acquirer  151  and an in-tank information acquirer  152 . The heat dissipation information acquirer  151  obtains heat dissipation information of the first and second vehicle tanks  220  and  225 . The in-tank information acquirer  152  obtains internal temperature and pressure data of the first and second vehicle tanks  220  and  225  from the first and second sensors  230  and  235 . 
     The receptacle  200  serves as a joint with the nozzle  140  of the hydrogen station  10 . The receptacle  200  is connected with the first and second vehicle tanks  220  and  225 . The first and second vehicle tanks  220  and  225  store hydrogen as a fuel gas and supply hydrogen to the fuel cell  250 . The first vehicle tank  220  has the higher heat dissipation capacity than the second vehicle tank  225 . The heat dissipation capacity herein means the capability of releasing heat from inside of the vehicle tank to outside, and the high heat dissipation capacity indicates that the internal heat of the vehicle tank is readily releasable. This heat dissipation capacity depends on the material and the shape of the vehicle tank and the surrounding environment at the location of the vehicle tank. For example, the vehicle tank made of aluminum is expected to have the higher heat dissipation capacity than the vehicle tank made of resin. Similarly, the vehicle tank with radiation fins on the surface is expected to have the higher heat dissipation capacity than the vehicle tank without such radiation fins. Further, the vehicle tank located in the surrounding environment of good ventilation or in the surrounding environment with lower-temperature equipment than the temperature of the vehicle tank is expected to have the higher heat dissipation capacity than the vehicle tank located in the surrounding environment of poor ventilation or in the surrounding environment with higher-temperature equipment than the temperature of the vehicle tank. 
     The heat dissipation information showing which of the vehicle tanks has the higher heat dissipation capacity may be readily obtained, for example, by filling a gas into the two vehicle tanks to the same temperature level and subsequently monitoring the temperature changes or the pressure changes of the vehicle tanks  220  and  225  per unit time. The higher rate of temperature decrease indicates the higher heat dissipation capacity, and the higher rate of pressure decrease also indicates the higher heat dissipation capacity. In the gas equation PV=nRT, the volume “V” of the vehicle tank, the mole number “n” of the gas in the&#39;vehicle tank, and the gas constant “R” are unchanged during heat dissipation, so that the pressure P of the gas in the vehicle tank is proportional to the temperature T of the gas in the vehicle tank. The higher rate of gas temperature decrease accordingly leads to the higher rate of gas pressure decrease. Which of the vehicle tanks has the higher heat dissipation capacity can thus be determined by comparison between the gas pressure changes in the vehicle tanks  220  and  225 . 
     Also, the heat dissipation information may be obtained, based on the material, the shape and the installation location of the vehicle tank. According to another embodiment, the heat dissipation information may be calculated in advance with respect to each of the vehicle tanks and stored as data of the vehicle tank into an ECU (not shown) or the controller  240  of the vehicle  20 . In this case, the heat dissipation information acquirer  151  may obtain the heat dissipation information from the ECU or the controller  240 . According to another embodiment, such heat dissipation information with respect to each vehicle tank type may be stored in the controller  150  of the hydrogen station  10 . The heat dissipation information acquirer  151  may obtain only data showing vehicle tank type from, for example, the ECU of the vehicle  20  and read the stored heat dissipation information at the time of gas filling. 
     Gas filler passages  201  and  202  connect the receptacle  200  with the first and second vehicle tanks  220  and  225 . The first and second electrically-operated valves  210  and  215  are provided respectively on the gas filler passages  201  and  202 . The first and second sensors  230  and  235  are also connected with the first and second vehicle tanks  220  and  225 . The first and sensor sensors  230  and  235  respectively obtain either one or both of the internal gas temperature and pressure in the first and second vehicle tanks  220  and  225 . The controller  240  is electrically connected with the first and second sensors  230  and  235  to obtain the internal gas temperature and pressure in the first and second vehicle tanks  220  and  225 . The controller  240  is also connected with the first and second electrically-operated valves  210  and  215  to control opening/closing of the first and second electrically-operated valves  210  and  215  and control the hydrogen filling, based on the internal gas temperature and pressure in the first and second vehicle tanks  220  and  225 . The concrete procedure of control will be described later. The controller  240  is also electrically connected with the controller  150  of the hydrogen station  10  and cooperates with the controller  150  to control the hydrogen filling from the hydrogen station  10  into the vehicle  20 . In this case, the controller  240  of the vehicle  20  may receive a signal (control signal) from the controller  150  of the hydrogen station  10  and control opening/closing of the first and second electrically-operated valves  210  and  215 . The electrical connection between the controller  150  and the controller  240  may be achieved, for example, by wired connection, infrared connection or wireless connection. The fuel cell  250  is connected with the first and second vehicle tanks  220  and  225  and receives the hydrogen supply from the first and second vehicle tanks  220  and  225  to generate electric power, which is used as the driving force of the vehicle  20 . 
       FIG. 2  illustrates a hydrogen filling model to a tank. The gas temperature T 2  in the tank after gas filling is expressed by Equation (1) given below (Kazuyasu MATSUO “Compressible Hydrodynamics”, Nov. 10, 1994, Rikogakusha Publishing Co., Ltd): 
     
       
         
           
             
               
                 
                   
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     Wherein P 1 , T 1 , Tin and P 2  respectively represent the initial gas pressure in the tank, the initial gas temperature in the tank, the temperature of externally supplied gas, and the gas pressure in the tank after gas filling; γ represents the specific heat ratio and γ=1.41 for hydrogen. 
     When P 2 &gt;&gt;P 1 , T 2 =γ·Tin according to Equation (1) given above. In an application of this model to the embodiment, Tin denotes the temperature of hydrogen to be filled into the first or second vehicle tank  220  or  225 . In order to prevent the gas temperature T 2  in the first or second vehicle tank  220  or  225  after hydrogen filling from reaching the maximum working temperature of the first or second vehicle tank  220  or  225 , for example, 85° C. (358.15K), Tin should meet the relationship of Tin&lt;−20° C. (253.15K). It is thus preferable to lower the hydrogen temperature to or below −20° C. by the pre-cooler  120 . 
       FIG. 3  shows variations in hydrogen temperature in the tank after hydrogen filling against the fill time. The abscissa of the graph shows the time required for filling hydrogen to a specified pressure level in the first or second vehicle tank  220  or  225  (filling completion time). In general, the longer fill time tends to lower the gas temperature T 2  in the tank after gas filling. For example, with respect to the first vehicle tank  220 , hydrogen filling in a time period tm 1  causes the hydrogen temperature in the first vehicle tank  220  to just reach a specified temperature level (for example, maximum working temperature of 85° C.). The lower rate of hydrogen filling causes the hydrogen temperature in the first vehicle tank  220  to be lower than the specified temperature level. With respect to the second vehicle tank  225 , however, hydrogen filling in a time period tm 2  or a longer time period causes the hydrogen temperature in the second vehicle tank  225  to be lower than the specified temperature level. This difference in time may be attributed to the higher heat dissipation capacity and the resulting easier heat release to the outside air of the first vehicle tank  220  than the second vehicle tank  225 . 
       FIG. 4  shows variations in hydrogen temperature to be filled into the tank against the time elapsed since start of filling. The abscissa of the graph shows the time elapsed since the start of filling. In general, the higher filling rate (shorter filling completion time) causes the piping system including the electrically-operated valve  130  and the nozzle  140  to be cooled more quickly and thereby lowers the fill gas temperature Tin at the higher rate. For example, the higher fill rate gives the lower fill gas temperature Tin at an elapsed time tm 3 . The lower fill rate gives the higher fill gas temperature after gas filling, since hydrogen flowing through the pathway from the pre-cooler  120  to the nozzle  140  is warmed by the ambient temperature. 
       FIG. 5  is a flowchart showing a procedure of hydrogen filling process. The hydrogen filling process is triggered by connecting the receptacle  200  of the vehicle  20  to the nozzle  140  of the hydrogen station  10 . At this moment, the controller  150  of the hydrogen station  10  is electrically connected with the controller  240  of the vehicle  20 . 
     At step S 500 , the controller  150  opens the electrically-operated valve  130  of the hydrogen station  10 , and the controller  240  opens the first electrically-operated valve  210  while keeping the second electrically-operated valve  215  closed. At step S 505 , the hydrogen in the tank  100  is pressurized to be higher than the pressure level of hydrogen in the first vehicle tank  220  by the compressor  110 . The pressure of hydrogen is expected to decrease during subsequent cooling with the pre-cooler  120  (as the pressure is proportional to the temperature under the condition of the fixed volume and the fixed mole number according to the gas equation). Preferably, the controller  150  should thus pressurize the hydrogen by taking into account this subsequent pressure decrease. The hydrogen is then cooled by the pre-cooler  120 , flows through the nozzle  140  and the receptacle  200  and is filled into the first vehicle tank  220 . 
     At step S 510 , the controller  240  obtains hydrogen pressure P 21  and temperature T 21  in the first vehicle tank  220  from the first sensor  230 , for example, at fixed time intervals. In the symbol “Pnm” for the pressure, “P” represents the pressure. The subscript “n” shows differentiation between before and after gas filling; n=1 indicates before gas filling and n=2 indicate after gas filling. The subscript “m” shows differentiation between the vehicle tanks; m=1 indicates the first vehicle tank and m=2 indicates the second vehicle tank. The symbol P 21  accordingly shows the gas pressure in the first vehicle tank  220  after gas filling. In the symbol “Tnm” for the temperature, “T” represents the temperature and the subscripts “n” and “m” have the same meaning as those for the pressure. When either the hydrogen pressure P 21  or the hydrogen temperature T 21  in the first vehicle tank  220  exceeds a preset reference value Px or Tx, the processing flow proceeds to step S 515 . 
     At step S 515 , the controller  240  closes the first electrically-operated valve  210  and opens the second electrically-operated valve  215 . The procedure then fills hydrogen into the second vehicle tank  225  at step S 520 , while stopping the hydrogen filling into the first vehicle tank  220 . 
     At step S 525 , the controller  240  obtains hydrogen pressure P 22  and temperature T 22  in the second vehicle tank  225  from the second sensor  235 , for example, at fixed time intervals. When either the hydrogen pressure P 22  or the hydrogen temperature T 22  in the second vehicle tank  225  exceeds a preset reference value Py or Ty, the processing flow proceeds to step S 530 . The reference values Py and Ty used at step S 525  may be equal to the reference values Px and Tx used at step S 510 . The first and second vehicle tanks  220  and  225  are made of different materials, so that the reference values may be determined according to the properties, such as pressure resistances and upper temperature limits, of the respective vehicle tanks  220  and  225 . 
     At step S 530 , the controller  240  sends an instruction to the controller  150  to close the electrically-operated valve  130  of the hydrogen station  10 . The controller  240  then opens the first and second electrically-operated valves  210  and  215  to allow communication between the first vehicle tank  220  and the second vehicle tank  225 . At subsequent step S 535 , hydrogen moves from the vehicle tank of the higher pressure to the vehicle tank of the lower pressure. When the reference pressure Px at step S 510  is equal to the reference pressure Py at step S 525 , the hydrogen pressure in the first vehicle tank  220  is lower than the hydrogen pressure in the second vehicle tank  225 , due to the earlier stop of the hydrogen filling into the first vehicle tank  220  and the higher heat dissipation capacity of the first vehicle tank  220 . Hydrogen is accordingly moved from the second vehicle tank  225  to the first vehicle tank  220 . 
     At step S 540 , the controller  240  obtains the hydrogen pressures P 21  and P 22  in the first and second vehicle tanks  220  and  225  from the first and second sensors  230  and  235 . When the pressures P 21  and P 22  are equal to each other, these pressures (P 21 =P 22 ) are supposed to be lower than the reference pressure Px at step S 510  or the reference pressure Py at step S 525 . This indicates that further hydrogen filling to the reference pressure Px or to the reference pressure Py is allowable. For further hydrogen filling, the controller  240  shifts the processing to step S 545 . 
     At step S 545 , the controller  240  sends an instruction to the controller  150  to open the electrically-operated valve  130  of the hydrogen station  10 . This valve opening allows further hydrogen filling into the first and second vehicle tanks  220  and  225 . At step S 550 , the controller  240  obtains the hydrogen pressures P 21  and P 22  in the first and second vehicle tanks  220  and  225  from the first and second sensors  230  and  235  and determines whether the hydrogen pressure P 21  or P 22  in the first or second vehicle tank exceeds the reference pressure Px or Py. When the hydrogen pressure P 21  or P 22  exceeds the reference pressure Px or Py, the controller  240  closes the first and second electrically-operated valves  210  and  215 , while sending an instruction to the controller  150  to close the electrically-operated valve  130  of the hydrogen station  10  at step S 555 . 
       FIG. 6  shows which of the tanks is filled with hydrogen, in relation to the fill time and the fill hydrogen temperature.  FIG. 6  corresponds to the graph of  FIG. 4 . The shorter elapsed time since the start of filling causes the relatively high fill hydrogen temperature Tin. The hydrogen should thus be filled first into the first vehicle tank  220  having the higher thermal conductivity and the higher heat dissipation capacity. After the fill hydrogen temperature Tin is lowered, the hydrogen is filled into the second vehicle tank  225 , because of the reason described below. 
     The hydrogen temperature T 2  in the tank after hydrogen filling is given by γ*Tin (Equation (1)) as explained above. As shown in  FIG. 6 , the fill gas temperature Tin decreases over time. 
     (1) Filling hydrogen first into first vehicle tank and then into second vehicle tank: 
     In this case, hydrogen is filled first into the first vehicle tank  220  at the high fill gas temperature Tin (Tin=Ta). The hydrogen temperature in the first vehicle tank  220  after hydrogen filling is accordingly given by T 21   a =γ·Ta. The subscript “x” of the symbol “Tnmx” shows which of the vehicle tanks is filled first with hydrogen; x=a indicates that hydrogen is filled first into the first vehicle tank  220  and x=b indicates that hydrogen is filled first into the second vehicle tank  225 . Hydrogen is then filled into the second vehicle tank  225 . When the fill gas temperature Tin is temperature Tb (Tb&lt;Ta), the hydrogen temperature in the second vehicle tank  225  after hydrogen filling is given by T 22   a =γ·Tb. Temperature T 31   a  of the first vehicle tank  220  after hydrogen filling into the second vehicle tank  225  is lower than γ·Ta. The subscript “3” means immediately after hydrogen filling into the other vehicle tank (second vehicle tank  225  in this case). The temperature of the first vehicle tank  220  is lowered by heat dissipation from the first vehicle tank  220  during hydrogen filling into the second vehicle tank  225 . 
     (2) Filling hydrogen first into second vehicle tank and then into first vehicle tank: 
     In this case, hydrogen is filled first into the second vehicle tank  225  at the high fill gas temperature Tin (Tin=Ta). The hydrogen temperature in the second vehicle tank  225  after hydrogen filling is accordingly given by T 22   b =γ·Ta. Hydrogen is then filled into the first vehicle tank  220 . When the fill gas temperature Tin is temperature Tb (Tb&lt;Ta), the hydrogen temperature in the first vehicle tank  220  after hydrogen filling is given by T 21   b =γ·Tb. Temperature T 32   b  of the second vehicle tank  225  after hydrogen filling into the first vehicle tank  220  is lower than γ·Tb. The subscript “3” means immediately after hydrogen filling into the other vehicle tank (first vehicle tank  220  in this case). 
     The comparison between the temperatures T 31   a  and T 32   b  of the first hydrogen-filled vehicle tanks immediately after hydrogen filling into the other vehicle tank gives the relation of T 31   a &lt;T 32   b . This depends on the heat dissipation from the first gas-filled vehicle tank during gas filling into the other vehicle tank. The first vehicle tank  220  has the higher thermal conductivity and the higher heat dissipation capacity than the second vehicle tank  225 , so that a greater amount of heat is released from the first vehicle tank  220 . This results in lowering the temperature of the first vehicle tank  220 . The comparison between the temperatures of the later hydrogen-filled vehicle tanks  220  and  225 , on the other hand, indicates the equal temperatures (as given by T 22   a =T 21   b =γ·Tb). 
     Since T 21   a =T 22   b =γ·Ta, according to the gas equation, the first hydrogen-filled vehicle tanks  220  and  225  after hydrogen filling have the same mole number of hydrogen, as long as the first and second vehicle tanks have the same inner volume. This mole number is shown as n1 moles. Since T 22   a =T 21   b =γ·Tb, the later hydrogen-filled vehicle tanks have the same mole number of hydrogen after hydrogen filling. This mole number is shown as n2 moles. 
     The gas temperatures in the vehicle tanks after the communication between the first vehicle tank  220  and the second vehicle tank  225  (after step S 540  in  FIG. 5 ) are then compared. According to the law of conservation of heat, hydrogen temperature T 4   a  in the first hydrogen-filled first vehicle tank  220  after hydrogen filling is given as T 4   a =(n1·T 31   a +n2·T 22   a )/(n1+n2), whilst hydrogen temperature T 4   b  in the first hydrogen-filled second vehicle tank  225  after hydrogen filling is given as T 4   b =(n2·T 21   b +n1·T 32   b )/(n1+n2). Since T 22   a =T 21   b  cancels out n2·T 22   a  and n2·T 21   b  each other, Ta−Tb=n1·(T 31   a −T 32   b )/(n1+n2). Since T 31   a &lt;T 32   b  as given above, Ta−Tb&lt;0. Filling hydrogen first into the first vehicle tank  220  and then into the second vehicle tank  225  accordingly lowers the hydrogen temperature in the vehicle tank, compared with filling hydrogen first into the second vehicle tank  225  and then into the first vehicle tank  220 . 
       FIG. 7  shows variations in hydrogen pressure against the elapsed time with respect to the respective tanks.  FIG. 8  shows variations in hydrogen temperature against the elapsed time with respect to the respective tanks. Hydrogen is filled into the first vehicle tank  220  until time tm 6  (step S 505  in  FIG. 5 ) and is filled into the second vehicle tank  225  from the time tm 6  to time tm 7  (step S 520 ). The first vehicle tank  220  and the second vehicle tank  225  communicate with each other from the time tm 7  to time tm 8  (step S 535 ). Hydrogen is filled into both the first vehicle tank  220  and the second vehicle tank  225  from the time tm 8  to time tm 9  (step S 545 ). 
     As hydrogen is filled into the first vehicle tank  220  until the time tm 6 , the hydrogen pressure and temperature in the first vehicle tank  220  respectively increase to the pressure P 21  and to the temperature T 21 . As hydrogen is filled into the second vehicle tank  225  from the time tm 6  to the time tm 7 , the hydrogen pressure and temperature in the second vehicle tank  225  respectively increase to the pressure P 22  and to the temperature T 22 , while the hydrogen pressure and temperature in the first vehicle tank  220  are respectively lowered by heat dissipation to pressure P 31  and to temperature T 31 . 
     As hydrogen moves from the second vehicle tank  225  of the higher pressure level to the first vehicle tank  220  of the lower pressure level from the time tm 7  to the time tm 8 , the hydrogen pressure increases in the first vehicle tank  220  while decreasing in the second vehicle tank  225 . At the time tm 8 , hydrogen pressure P 41  in the first vehicle tank  220  is in equilibrium with hydrogen pressure P 42  in the second vehicle tank  225  (P 41 =P 42 ). Similarly the hydrogen temperature increases in the first vehicle tank  220  while decreasing in the second vehicle tank  225 , and eventually reaches the equilibrium state (T 41 =T 42 ). The temperature gradually reaches the equilibrium state by diffusion and accordingly takes more time to the equilibrium state than the pressure. 
     As hydrogen is filled into both the first vehicle tank  220  and the second vehicle tank  225  from the time tm 8  to the time tm 9 , the hydrogen temperature and pressure in both the first and second vehicle tanks  220  and  225  increase. 
       FIG. 9  shows variations in hydrogen pressure in the first vehicle tank  220  against the elapsed time with respect to an embodiment and a comparative example.  FIG. 10  shows variations in hydrogen temperature in the first vehicle tank  220  against the elapsed time with respect to the embodiment and the comparative example. The comparative example fills hydrogen at a fixed fill rate to reach the same pressure level as that of the embodiment at the time tm 9 . In the embodiment, on the other hand, both the hydrogen pressure and the hydrogen temperature in the first vehicle tank  220  abruptly increase until the time tm 6  and then decrease in the time period between the time tm 6  and the time tm 7  as described above with reference to  FIGS. 7 and 8 . 
     In the time period between the time tm 7  and the time tm 8 , hydrogen moves from the second vehicle tank  225  of the higher pressure and the higher temperature to the first vehicle tank  220  of the lower pressure and the lower temperature. The hydrogen pressure and the hydrogen temperature in the first vehicle tank  220  accordingly increase in the time period between the time tm 7  and the time tm 8 . Hydrogen is filled again into both the first vehicle tank  220  and the second vehicle tank  225  in the time period between the time tm 8  and the time tm 9 , which further increases the hydrogen pressure and the hydrogen temperature in the first vehicle tank  220 . 
     The hydrogen temperature in the first vehicle tank  220  of the embodiment measured at the time tm 9  is lower than the hydrogen temperature in the first vehicle tank  220  of the comparative example. The lower hydrogen temperature in the first vehicle tank  220  of the embodiment at the time tm 9  than the hydrogen temperature in the first vehicle tank  220  of the comparative example results from that the embodiment has the longer time period when the hydrogen temperature in the first vehicle tank  220  is higher than the ambient temperature than the comparative example. This results in the longer heat dissipation time and thereby causes the lower hydrogen temperature in the first vehicle tank  220  of the embodiment than that of the comparative example. 
     According to the gas equation, under the condition of the fixed hydrogen pressure in the first vehicle tank  220  and the fixed volume of the first vehicle tank  220 , the mole number of hydrogen in the first vehicle tank  220  is inversely proportional to the hydrogen temperature in the first vehicle tank  220 . This means that a greater amount of hydrogen is filled into the first vehicle tank  220  of the embodiment than that of the comparative example. In other words, the embodiment has the shorter fill time to fill the same amount of hydrogen than the comparative example. 
     As described above, according to the embodiment, during hydrogen filling, the second tank of the lower heat dissipation capacity has the higher temperature and the higher pressure. Communication between the first tank of the higher heat dissipation capacity and the second tank of the lower heat dissipation capacity reduces such temperature difference and pressure difference to ensure the efficient gas filling. 
     The procedure of this embodiment fills hydrogen first into the first vehicle tank  220  of the higher heat dissipation capacity and then into the second vehicle tank  225  of the lower heat dissipation capacity and subsequently allows communication between the first vehicle tank  220  and the second vehicle tank  225 . This enables the efficient gas filling into the first and the second vehicle tanks  220  and  225 . The communication between the first vehicle tank  220  and the second vehicle tank  225  lowers the temperature of the second vehicle tank  225  and thereby improves the durability of the second vehicle tank. Subsequent hydrogen filling into both the first and the second vehicle tanks further increases the total amount of hydrogen filling. 
     Second Embodiment 
     A second embodiment has the same device structure as that of the first embodiment but adopts a different method of gas filling from that of the first embodiment. The difference from the first embodiment is that the second embodiment allows switching between the gas filling method (a) of filling hydrogen first into the first vehicle tank  220  and then into the second vehicle tank  225  and subsequently allowing communication between the first vehicle tank  220  and the second vehicle tank  225  described in the first embodiment and another gas filling method (b) of simultaneously filling hydrogen into the first and the second vehicle tanks  220  and  225 . The controller  240  makes switching, based on the hydrogen pressure and the hydrogen temperature in the first or second vehicle tank before hydrogen filling. 
       FIG. 11  is a flowchart showing a control switching procedure according to the second embodiment. At step S 1100 , the controller  240  obtains the hydrogen pressures and the hydrogen temperatures in the first and the second vehicle tanks  220  and  225  from the first and the second sensors  230  and  235 . Prior to hydrogen filling, hydrogen temperatures T 11  and T 12  in the first vehicle tank  220  and in the second vehicle tank  225  are substantially equal to the ambient temperature. Hydrogen pressures P 11  and P 12  in the first vehicle tank  220  and in the second vehicle tank  225  are substantially equal to each other. At step S 1110 , the controller  240  determines whether the obtained hydrogen pressure P 11  is greater than a reference value Pz. When the obtained hydrogen pressure P 11  is greater than the reference value Pz, the controller  240  shifts the processing to step S 1120  to simultaneously fill hydrogen into both the first and the second vehicle tanks  220  and  225  (gas filling method (b)). When the obtained hydrogen pressure P 11  is not greater than the reference value Pz, on the other hand, the controller  240  shifts the processing to step S 1130  to fill hydrogen into the first and the second vehicle tanks  220  and  225  according to the method of the first embodiment (gas filling method (a)). 
     The obtained pressure P 11  that is greater than the reference value Pz indicates that a relatively large amount of hydrogen remains in the first and the second vehicle tanks  220  and  225  before hydrogen filling. In this state, hydrogen filling does not satisfy the relation of P 2 &gt;&gt;P 1  (P 1 =P 11 ) in Equation (1) described above in the first embodiment and accordingly does not give the high hydrogen temperature T 21  in the first vehicle tank  220  after hydrogen filling. Hydrogen filling into the second vehicle tank  225  also does not give the high hydrogen temperature T 22  in the second vehicle tank  225  after hydrogen filling. In this case, filling hydrogen simultaneously into the first and the second vehicle tanks  220  and  225  shortens the fill time, compared with filling hydrogen according to the method of the first embodiment. 
     The obtained pressure P 11  that is not greater than the reference value Pz, on the other hand, satisfies the relation of P 2 &gt;&gt;P 1  (P 1 =P 11 ) and gives the high temperatures T 21  and T 22  according to Equation (1) described above in the first embodiment. This causes the greater heat dissipation effect from the first vehicle tank  220 . In this case, filling hydrogen according to the method of the first embodiment shortens the fill time. 
       FIG. 12  shows a control switching map according to the second embodiment. The controller  240  may use such a map to determine whether the hydrogen pressure P 11  is greater than the reference value Pz. 
     Modifications: 
     The system includes one first vehicle tank  220  and one second vehicle tank  225  according to the first embodiment but may include a plurality of first vehicle tanks and/or a plurality of second vehicle tanks. For example, hydrogen is filled first into one of a plurality of first vehicle tanks  220  (first vehicle tank  220   a ) at step S 505  in  FIG. 5  and then into the other first vehicle tank  220   b  and the second vehicle tank  225  at step S 520 . In the next cycle of hydrogen filling after hydrogen consumption, hydrogen is filled first into the first vehicle tank  220   b  at step S 505  in  FIG. 5  and then into the other first vehicle tank  220   a  and the second vehicle tank  225  at step S 520 . Alternately repeating these hydrogen filling cycles improves the durability of the first vehicle tanks. 
     The materials of the first and the second vehicle tanks are not specifically mentioned in the above embodiments. The first vehicle tank may be made of metal material, such as aluminum, while the second vehicle tank  225  may be made of resin material. Using the metal material, such as aluminum, for both the first and the second vehicle tanks  220  and  225  ensures the high heat dissipation capacities but undesirably increases the total weight. Using the resin material for both the first and the second vehicle tanks  220  and  225 , on the other hand, makes weight reduction but undesirably gives the low heat dissipation capacities, which results in the longer gas fill time. Using the metal material, such as aluminum, for the first vehicle tank  220  and the resin material for the second vehicle tank  225  as described in this modification improves the gas filling efficiency, while making weight reduction to some extent. 
     The above embodiment describes the application of the invention to the fuel cell vehicle using hydrogen, but the invention may also be applicable to diversity of other aspects; for example, various moving bodies using gas, such as natural gas vehicle or ship using combustion of natural gas. The invention is not limited to the gas-using application but may also be applicable to fill a gas into a tank for gas transportation. The processing of steps S 545  to S 550  in  FIG. 5  may be omitted. 
     In the system of the embodiment described above, the controller  240  of the vehicle  20  cooperates with the controller  150  of the hydrogen station  10  to control the hydrogen filling. One of the controllers  150  and  240  may be omitted. In this application, the remaining controller  150  or  240  has the heat dissipation information acquirer and the in-tank information acquirer to control the hydrogen filling. 
       FIG. 13  illustrates a system configuration in which the controller  150  of the hydrogen station  10  controls the hydrogen filling. When the controller  150  of the hydrogen station  10  controls the hydrogen filling, the hydrogen station  10  may have a pressure sensor  160  placed in a gas filler passage  101 . The controller  150  may obtain the hydrogen pressures in the first and the second vehicle tanks  220  and  225  from the pressure sensor  160  provided in the gas filler passage  101 , instead of obtaining the pressure data from the sensors  230  and  235  of the vehicle. The controller  150  may control filling hydrogen into the respective vehicle tanks  220  and  225 , based on the obtained hydrogen pressures. 
       FIG. 14  illustrates a system configuration in which the controller  240  of the vehicle  20  controls the hydrogen filling. The controller  240  includes a heat dissipation information acquirer  241  and an in-tank information acquirer  242 . The vehicle  10  may have a communication valve  218  to allow communication between the gas filler passages  201  and  202 . The communication valve  218  may be connected between the first vehicle tank  220  and a first electrically-operated valve  210  on the gas filler passage  201  and between the second vehicle tank  225  and a second electrically-operated valve  215  on the gas filler passage  202 . This arrangement allows the direct communication between the first vehicle tank  220  and the second vehicle tank  225  without the hydrogen station  10  in the closed positions of the first and the second electrically-operated valves  210  and  215 . 
       FIG. 15  illustrates a system configuration in which a gas filler passage branches off in the hydrogen station. According to this modification, a gas filler passage  101  branches off to two gas filler passages  170  and  175  in the hydrogen station, and electrically-operated valves  180  and  185  are provided in the respective gas filler passages  170  and  175 . A nozzle  145  has inside separated into two parts, which are respectively connected with the gas filler passages  170  and  175 . The vehicle  20  has a common receptacle  205  having the parted structure to receive the internally-parted nozzle  145 . As described, the hydrogen station  10  may have two gas filler passages  170  and  175 . 
     The foregoing has described the invention in detail with reference to some embodiments. The embodiments of the invention described above are only illustrative for the purpose of better understanding of the invention, and the invention is not limited to these embodiments in any sense. Various variants and modifications may be made to the embodiments without departing from the spirit and the scope of the invention. The invention includes such variants, modifications and equivalents. 
     DESCRIPTION OF MARK 
     
         
         
           
               10  Hydrogen Station 
               20  Vehicle 
               100  Tank 
               110  Compressor 
               120  Pre-cooler 
               130  electrically-operated valve 
               140 ,  145  Nozzle 
               150  Controller 
               151  Heat Dissipation Information Acquirer 
               152  In-Tank Information Acquirer 
               200 ,  205  Receptacle 
               210  First electrically-operated valve 
               215  Second electrically-operated valve 
               220  First Vehicle Tank 
               225  Second vehicle Tank 
               230  First sensor 
               235  Second sensor 
               240  Controller 
               241  Heat Dissipation Information Acquirer 
               242  In-Tank Information Acquirer 
               250  Fuel cell