Patent Publication Number: US-2017365901-A1

Title: Warm-up apparatus for fuel cell for vehicle

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a warm-up apparatus for a fuel cell for a vehicle in which a fuel cell and a secondary battery are mounted as power sources of a motor for travelling. 
     Description of the Related Art 
     As awareness with respect to environmental issues in recent years increases, fuel cell systems are attracting attention as one kind of system for clean energy generation that does not rely on fossil fuels. For example, a polymer electrolyte fuel cell is used in a fuel cell system that is mounted in a vehicle. The polymer electrolyte fuel cell is built by forming an MEA by bonding a fuel electrode that carries platinum (Pt) as a catalyst and an air electrode on either side of a polymer electrolyte membrane, and stacking a large number of single cells in each of which the MEA is sandwiched by gas diffusion layers and separators. Humidity-regulated fuel gas is supplied to the fuel electrode and humidity-regulated air is supplied to the air electrode, and by this means a power generation reaction proceeds in the catalyst layers of the fuel electrode and the air electrode, and power generation of the fuel cell is started. 
     In some cases, such a fuel cell system is mounted in an electrically driven vehicle and used together with a secondary battery as power sources of a motor serving as a power source for travelling. For example, electric power is supplied from the secondary battery to the motor of the electrically driven vehicle, and the fuel cell system fulfills a function as a range extender that mainly charges the secondary battery, and the output power thereof is also utilized in an auxiliary manner to drive the motor. When the SOC (state of charge) of the secondary battery decreases as a result of supplying power to the motor it is necessary to charge the secondary battery at a charging station or the like, and operation of the fuel cell is stopped while the secondary battery is being charged. When operation of the fuel cell is stopped, the temperature of the fuel cell gradually decreases and if the temperature thereof falls to less than the rated temperature is it necessary to warm up the fuel cell. There is thus the problem that time is required until the fuel cell is restored to the rated temperature and the rated power output after restarting, and the fuel cell cannot respond immediately with respect to providing a required output. 
     As a measure to overcome the above problem, for example, according to technology disclosed in Patent Literature (Japanese Patent Laid-Open No. 2007-213942), an air-conditioning system and a cooling circuit of a fuel cell that are mounted in an electrically driven vehicle are connected through a heat exchanger, and the fuel cell is warmed up by causing the air-conditioning system to function as a heat pump cycle by means of electric power from an external power source. 
     However, according to the technology in the aforementioned Patent Literature, because an electric power supply from an external power source is required, not only is there a problem in terms of the operating cost, but it is also necessary to keep the electrically driven vehicle parked for an additional time after charging of the secondary battery is completed until the warming up of the fuel cell finishes, and there is thus also the problem that the start of travel of the vehicle is delayed. In addition, the heat quantity obtained by the capacity of an air-conditioning system whose original purpose is to perform air conditioning within the cabin of a vehicle is inadequate, and the fuel cell cannot be warmed up quickly, and this is also the cause of a delay in starting travel of the vehicle. Therefore, it is difficult to say that the technology disclosed in the aforementioned Patent Literature is realistic, and originally there has been a demand for a more fundamental solution. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a warm-up apparatus for a fuel cell for a vehicle, that is excellent in terms of operating cost and that can rapidly warm up a fuel cell and enable the early start of vehicle travel. 
     To achieve the aforementioned object, the present invention is a warm-up apparatus for a fuel cell for an electrically driven vehicle in which a fuel cell and a secondary battery are mounted as power sources of a motor for travelling, and which, when charging of the secondary battery is required, stops operation of the fuel cell and charges the secondary battery with electric power from an external power source by means of a battery charger, including: a secondary battery cooling circuit that cools the secondary battery; a fuel cell cooling circuit that cools the fuel cell; a connection passage that connects the secondary battery cooling circuit and the fuel cell cooling circuit through a switching valve; and a warm-up control unit that, during charging of the secondary battery, controls the switching valve so that the secondary battery cooling circuit and the fuel cell cooling circuit communicate through the connection passage. 
     According to the warm-up apparatus for a fuel cell for a vehicle configured as described above, a coolant is heated by a secondary battery in a secondary battery cooling circuit, and the coolant is transferred to a fuel cell cooling circuit through a connection passage to thereby warm up the fuel cell. Because the fuel cell is warmed up by heat that the secondary battery generates while charging, operating costs are not required, and furthermore because the secondary battery that is being charged generates a large amount of heat and warming up of the fuel cell can be performed concurrently with charging of the secondary battery, warming up of the fuel cell can be completed while the secondary battery is being charged. 
     Thus, the warm-up apparatus for a fuel cell for an electrically driven vehicle according to the present invention is excellent in terms of operating cost, and can rapidly warm up a fuel cell and enable the early start of vehicle travel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description given hereinafter and the accompanying drawings which are given by way of illustration only, and thus, are not limitative of the present invention, and wherein: 
         FIG. 1  is an overall configuration diagram illustrating an electrically driven vehicle in which a warm-up apparatus for a fuel cell according to an embodiment of the present invention is mounted; 
         FIG. 2  is a circuit diagram illustrating circuitry for warming up the fuel cell; and 
         FIG. 3  is a flowchart illustrating a warm-up control routine which a vehicle ECU executes. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereunder, one embodiment of a warm-up apparatus for a fuel cell for a vehicle that embodies the present invention is described. 
       FIG. 1  is an overall configuration diagram illustrating an electrically driven vehicle in which the warm-up apparatus for a fuel cell of the present embodiment is mounted. 
     An electrically driven vehicle  1  of the present embodiment is a hybrid fuel cell vehicle that includes a motor  2  as a power source for travelling and also includes a secondary battery  3  and a fuel cell system  4  as power sources of the motor  2 . As is widely known, the secondary battery  3  is an electric battery that is capable of charging and discharging direct current electric power by means of a chemical reaction, and the fuel cell system  4  is a system that generates electric power by an electrochemical reaction using hydrogen gas in a fuel cell  4   a.  Basically, the motor  2  is driven by electric power from the secondary battery  3 , and the fuel cell system  4  mainly fulfills a function as a range extender that charges the secondary battery  3 , and the output power thereof is also utilized in an auxiliary manner to drive the motor  2 . 
     The secondary battery  3  is connected through an inverter  5  to the motor  2 , and the inverter  5  performs a function of converting between direct current and alternating current. That is, during power running control of the motor  2 , direct current electric power from the secondary battery  3  or the fuel cell system  4  is converted to three-phase AC electric power by the inverter  5  to drive the motor  2 , and during regenerative control of the motor  2 , three-phase AC electric power from the motor  2  is converted to direct current electric power by the inverter  5  to charge the secondary battery  3 . 
     The fuel cell system  4  is connected to the secondary battery  3  and the inverter  5 . The polymer electrolyte fuel cell  4   a  provided in the fuel cell system  4  is built by forming an MEA (Membrane Electrode Assembly) by bonding a fuel electrode (anode) that carries platinum (Pt) as a catalyst and an air electrode (cathode) on either side of a polymer electrolyte membrane, and stacking a large number of single cells in each of which the MEA is sandwiched by gas diffusion layers and separators. 
     The operating principles of the fuel cell  4   a  are widely known and therefore will not be described in detail here. In general, however, the fuel cell  4   a  operates as a result of hydrogen gas from a hydrogen tank  7  that is subjected to humidity regulation being supplied to the fuel electrode, and humidity-regulated air being supplied to the air electrode. The hydrogen gas supplied to the fuel electrode is split into hydrogen ions and electrons by catalytic action, and the hydrogen ions then pass through the polymer electrolyte membrane to reach the air electrode, while the electrons reach the air electrode via an unshown external circuit, and by this means a direct-current voltage is generated with the fuel electrode as negative and the air electrode as positive. Further, at the air electrode, air supplied through an air supply line, hydrogen ions that passed through the polymer electrolyte membrane and electrons that arrived via the external circuit react to generate water. 
     A DC-DC converter  8  is connected to an output terminal of the fuel cell  4   a,  and the DC-DC converter  8  is connected to the secondary battery  3  and the inverter  5 . By this means, it is possible to utilize the output power of the fuel cell  4   a  to charge the secondary battery  3  or to drive the motor  2 . 
     Each device (for example, a control valve that controls switching between hydrogen gas and air, or a humidifying apparatus for gas humidification) constituting the fuel cell system  4  for operating the fuel cell  4   a  as described above are connected to an FC-ECU  9  (fuel cell electronic control unit), and the operating state of the fuel cell  4   a  is controlled by the FC-ECU  9 . 
     On the other hand, a motor ECU (motor electronic control unit)  10  is connected to the inverter  5 , and driving control of the motor  2  is executed by the motor ECU  10 . For example, on one hand the motor ECU  10  drivingly controls the inverter  5  to drive the motor  2  by means of output power supplied from the secondary battery  3  or the fuel cell  4   a,  and on the other hand, during regenerative control of the motor  2 , the motor ECU  10  supplies regenerated electric power to the secondary battery  3 . 
     Further, a battery ECU (battery electronic control unit)  11  is connected to the secondary battery  3 . Charge/discharge control of the secondary battery  3  is executed by the battery ECU  11 , and the battery ECU  11  also calculates the SOC (state of charge) of the secondary battery  3  and the like. 
     The aforementioned FC-ECU  9 , motor ECU  10  and battery ECU  11  are connected to a vehicle ECU  13  (vehicle electronic control unit) that corresponds to a superordinate unit, and the respective ECUs  9  to  11  and  13  each include an input/output device, storage devices (ROM, RAM, nonvolatile RAM or the like) and a central processing unit (CPU). The nonvolatile RAM of each storage device stores commands for various kinds of control, described later, that the respective CPUs perform. 
     The vehicle ECU  13  is a control unit for performing overall control of the electrically driven vehicle  1 . Operation control of the fuel cell  4   a,  driving control of the motor  2  and charging control of the secondary battery  3  and the like that are described above are executed by the respective subordinate ECUs  9  to  11  which receive commands from the vehicle ECU  13 . 
     Therefore, sensors such as an accelerator sensor  14  that detects an accelerator opening degree APS, and also the FC-ECU  9 , the motor ECU  10  and the battery ECU  11  are connected to an input side of the vehicle ECU  13 , and detected information such as an accelerator opening degree APS as well as operating information of each of the fuel cell system  4 , the motor  2  and the secondary battery  3 , for example, a temperature Tfc of the fuel cell  4   a,  a temperature Tb of the secondary battery  3  and a temperature Tc of a battery charger  31  that is described later and the like are input to the vehicle ECU  13 . 
     The vehicle ECU  13  calculates a required output that is necessary for travel of the electrically driven vehicle  1  based on the accelerator opening degree APS detected by the accelerator sensor  14  and the like, and outputs a command signal to the motor ECU  10  so as to achieve the required output. Based on the command signal, the motor  2  is driven by the motor ECU  10  and the required torque is achieved. 
     Further, the vehicle ECU  13  calculates the output power of the fuel cell system  4  based on the SOC of the secondary battery  3  and the required output for vehicle travel, and outputs a command signal to the FC-ECU  9  so as to achieve the output power. For example, in a case where the SOC of the secondary battery  3  has decreased and charging is required, or in a case where it is determined that it is impossible for the motor  2  to achieve the required output using only the electric power supply from the secondary battery  3 , the vehicle ECU  13  sets the output power of the fuel cell  4   a  to an increase side. 
     The FC-ECU  9  calculates the hydrogen gas amount to be supplied to the fuel electrode and the air amount to be supplied to the air electrode in order to achieve the output power, and achieves the required output power by adjusting the calculated gas supply amounts. Naturally, in parallel with such control of the supply of hydrogen gas and air, optimum control is also performed in relation to the humidity of the hydrogen gas and air, the cell pressure and the cell temperature and the like. For example, in a case where the output power is controlled to the increase side as described above, the hydrogen gas amount and air amount are adjusted to the increase side and the output power is increased, and the amount of increase in the electric power is utilized for charging the secondary battery  3  or driving the motor  2 . 
     In this connected, as described above in the “Description of the Related Art” section, because operation of the fuel cell  4   a  is stopped when charging the secondary battery  3  at a charging station or the like, it is necessary to warm up the fuel cell  4   a  after restarting the fuel cell  4   a,  and according to the technology of the aforementioned Patent Literature that performs warming up by means of a vehicle-installed air-conditioning system that utilizes an external power source, in addition to a problem in terms of operating cost, there is also the problem that the start of travel of the vehicle is delayed because the amount of heat is inadequate. 
     In consideration of this point, the present inventors focused their attention on the fact that heat which the secondary battery  3  generates while charging can be utilized for warming up the fuel cell  4   a.  That is, by utilizing heat of the secondary battery  3  that would otherwise be wastefully discarded into the atmosphere, operating costs that occur in the case of utilizing an external power source do not arise and the secondary battery  3  also generates a large amount of heat while charging. Furthermore, because warming up of the fuel cell  4   a  can be carried out concurrently with charging of the secondary battery  3 , the electrically driven vehicle  1  can start travelling immediately upon the completion of charging of the secondary battery  3 . 
     The process for warming up the fuel cell  4   a  that utilizes heat which the secondary battery  3  generates during charging based on these findings is described below. However, before describing that process, the circuitry for transferring heat of the secondary battery  3  to the fuel cell  4   a  will be described. 
       FIG. 2  is a circuit diagram illustrating circuitry for performing warming up of the fuel cell  4   a.    
     The circuitry illustrated in  FIG. 2  can be broadly divided into a fuel cell cooling circuit  16  (hereunder, referred to as “FC cooling circuit”) for maintaining the fuel cell  4   a  at the rated temperature, a hot water circuit  17  for heating the inside of the vehicle cabin, a secondary battery cooling circuit  18  (hereunder, referred to as “charging auxiliary machine cooling circuit”) that cools the secondary battery  3 , and an electrical system for charging the secondary battery  3  and supplying electric power to each circuit. 
     First, the FC cooling circuit  16  will be described. In the FC cooling circuit  16 , a radiator  21  is connected through a pair of cooling lines  20   a  and  20   b  to the fuel cell  4   a.  A pump  22  is installed on the cooling line  20   a  as one of the cooling lines  20   a  and  20   b.  As a result, the annular FC cooling circuit  16  that includes the fuel cell  4   a,  the other cooling line  20   b,  the radiator  21  and the one cooling line  20   a  (and pump  22 ) is formed, and water (coolant) that is sealed in the FC cooling circuit  16  circulates by driving of the pump  22 . 
     A switching valve  23  that is installed on the other cooling line  20   b  is connected to the one cooling line  20   a  through a bypass passage  24 , and water circulates through or bypasses the radiator  21  in accordance with switching of the switching valve  23 . The water temperature is adjusted by means of switching control of the switching valve  23  and flow control of the pump  22  and the like to keep the fuel cell  4   a  at a predetermined rated temperature during operation. 
     Next, the hot water circuit  17  that is used for heating the vehicle cabin will be described. In the hot water circuit  17 , a heat exchanger  25  that is disposed inside an unshown vehicle cabin is connected to a hot water heater  27  through a pair of hot water lines  26   a  and  26   b , and a pump  28  is installed on the hot water line  26   a  as one of the pair of hot water lines. As a result, the annular hot water circuit  17  that includes the other hot water line  26   b,  the hot water heater  27  and the one hot water line  26   a  (and pump  28 ) is formed, and water (coolant) that is sealed in the hot water circuit  17  circulates by driving of the pump  28 . 
     A switching valve  29  that is installed on the one hot water line  26   a  is connected to the other hot water line  26   b  through a bypass passage  30 , and water circulates through or bypasses the heat exchanger  25  in accordance with switching of the switching valve  29 . When the hot water heater  27  is turned on and hot water that was heated thereby circulates through the heat exchanger  25 , air that was warmed by passing through fins of the heat exchanger  25  as a result of being blown by an unshown fan is supplied into the vehicle cabin and the vehicle cabin is heated. 
     Next, the charging auxiliary machine cooling circuit  18  (including a back-up cooling circuit  35  that is described below) will be described. In the present embodiment, the secondary battery  3  and the battery charger  31  are cooled by the cooling circuit  18  as a charging auxiliary machine. A heat exchanger  33  is connected through a pair of cooling lines  32   a  and  32   b  to the secondary battery  3 . A pump  34  is installed on the cooling line  32   a  as one of the cooling lines  32   a  and  32   b.  As a result, the annular back-up cooling circuit  35  that includes the secondary battery  3 , the one cooling line  32   a  (and pump  34 ), the heat exchanger  33  and the other cooling line  32   b  is formed, and a dielectric fluid that is sealed in the back-up cooling circuit  35  circulates by driving of the pump  34 . 
     The heat exchanger  33  is connected to a radiator  37  (heat radiator) through the pair of cooling lines  36   a  and  36   b.  A pump  38  is installed on the one cooling line  36   a,  and the battery charger  31  is installed on the other cooling line  36   b.  As a result, the annular charging auxiliary machine cooling circuit  18  that includes the heat exchanger  33 , the one cooling line  36   a  (and pump  38 ), the radiator  37  and the other cooling line  36   b  (and battery charger  31 ) is formed, and water (coolant) that is sealed in the charging auxiliary machine cooling circuit  18  circulates by driving of the pump  38 . A switching valve  39  that is installed on the one cooling line  36   a  is connected to the other cooling line  36   b  through a bypass passage  40 , and water circulates through or bypasses the radiator  37  in accordance with switching of the switching valve  39 . 
     The dielectric fluid in the back-up cooling circuit  35  is heated by heat that the secondary battery  3  generates during charging and is transferred to the heat exchanger  33 . Water that circulates through the charging auxiliary machine cooling circuit  18  is heated by heat exchange with the dielectric fluid at the heat exchanger  33 , and is also heated by heat generated at the battery charger  31 , and thereafter is radiated by the radiator  37 . By repeating the above described process, the secondary battery  3  and the battery charger  31  are cooled and an increase in the temperature of the secondary battery  3  and the battery charger  31  is suppressed. Note that the reason for cooling the secondary battery  3  by means of dielectric fluid in the back-up cooling circuit  35  is to prevent the occurrence of trouble such as electrification if a water leakage occurs. 
     Next, the electrical system will be described. The secondary battery  3  and the battery charger  31  are electrically connected, and a charging socket  31   a  is provided in the battery charger  31 . Charging of the secondary battery  3  is performed at a charging station or the like. By connecting a charging plug  41   a  of an external power source  41  provided at the charging station to the charging socket  31   a,  alternating current electric power from the external power source  41  is converted to direct current electric power by the battery charger  31  and the direct current electric power is used to charge the secondary battery  3 . A low-voltage auxiliary secondary battery  43  that is used for auxiliary machine driving is connected through a DC-DC converter  42  to the secondary battery  3 . 
     Electric power from the secondary battery  3  is converted to a lower voltage by the DC-DC converter  42  and used to charge the auxiliary secondary battery  43  as appropriate. By this means the auxiliary secondary battery  43  is maintained at a predetermined SOC. The auxiliary secondary battery  43  is electrically connected to auxiliary machines such as the pumps  22 ,  28 ,  34  and  38  of the respective circuits  16  to  18  and  35  and the hot water heater  27 , and is configured to supply electric power that is required for the operations of these auxiliary machines. Note that although the auxiliary secondary battery  43  also supplies electric power to other auxiliary machines, a description of those auxiliary machines is omitted as it is not related to the gist of the present invention. 
     In order to utilize the heat of the hot water circuit  17  and the charging auxiliary machine cooling circuit  18 , configured as described above, to warm up the fuel cell  4   a,  the hot water circuit  17  and the charging auxiliary machine cooling circuit  18  are connected to the FC cooling circuit  16  through connection passages  47   a,    47   b ,  50   a  and  50   b  that are described below. 
     A pair of switching valves  45   a  and  45   b  are installed on the one hot water line  26   a  of the hot water circuit  17 . The switching valves  45   a  and  45   b  are connected through connection passages  47   a  and  47   b  to a pair of switching valves  46   a  and  46   b  that are installed on the one cooling line  20   a  of the FC cooling circuit  16 . Similarly, a pair of switching valves  48   a  and  48   b  are installed on the one cooling line  36   a  of the charging auxiliary machine cooling circuit  18 . The switching valves  48   a  and  48   b  are connected through connection passages - 50   a  and  50   b  to a pair of switching valves  49   a  and  49   b  that are installed on the one cooling line  20   a  of the FC cooling circuit  16 . 
     During normal operation, the respective switching valves  45   a,    45   b,    46   a,    46   b,    48   a,    48   b,    49   a  and  49   b  are switched in a direction that allows circulation of water in the cooling lines  20   a  and  36   a  and the hot water line  26   a , and the hot water circuit  17  and the charging auxiliary machine cooling circuit  18  are disconnected from the FC cooling circuit  16  (non-communicating state). By this means, at the respective switching valves  45   a,    45   b,    46   a ,  46   b,    48   a,    48   b,    49   a  and  49   b,  water circulates in the direction of the arrows A in the drawing, and circulation of hot water in the hot water circuit  17  for heating, or circulation of water in the charging auxiliary machine cooling circuit  18  for cooling the secondary battery  3  and the battery charger  31  is performed. Hereunder, the switching state of the respective switching valves  45   a,    45   b ,  46   a,    46   b,    48   a,    48   b,    49   a  and  49   b  at such time is described as the “A side”. 
     Further, when the respective switching valves  45   a ,  45   b,    46   a,    46   b,    48   a,    48   b,    49   a  and  49   b  are switched from the A side to the connection passages  47   a,    47   b,    50   a  and  50   b  side, the hot water circuit  17  and the charging auxiliary machine cooling circuit  18  communicate with the FC cooling circuit  16  through the connection passages  47   a,    47   b,    50   a  and  50   b  to form a single large circuit. 
     For example, when the respective switching valves  45   a  and  45   b  of the hot water circuit  17  and the corresponding switching valves  46   a  and  46   b  of the FC cooling circuit  16  are switched to the connection passages  47   a  and  47   b  side, water circulates in the direction of the arrows B in the drawing. Water that is discharged from the pump  22  of the FC cooling circuit  16  is transferred to the hot water circuit  17  through the switching valve  46   a,  the connection passage  47   a  and the switching valve  45   a,  and after circulating through or bypassing the heat exchanger  25  from the pump  28  and being heated by the hot water heater  27 , the resultant hot water is returned to the FC cooling circuit  16  through the switching valve  45   b,  the connection passage  47   b  and the switching valve  46   b,  and flows through the fuel cell  4   a  to raise the temperature thereof. 
     Note that, at this time the pump  28  of the hot water circuit  17  may be actuated, or may be left in a stopped state as long as the pump  28  does not hinder the flow of the hot water. Further, in the case of actuating the pump  28  of the hot water circuit  17 , the pump  22  of the FC cooling circuit  16  may be stopped. 
     Similarly, when the respective switching valves  48   a  and  48   b  of the charging auxiliary machine cooling circuit  18  and the corresponding switching valves  49   a  and  49   b  of the FC cooling circuit  16  are switched to the connection passages  50   a  and  50   b  side, water circulates in the direction of the arrows B in the drawing. Water that is discharged from the pump  22  of the FC cooling circuit  16  is transferred to the charging auxiliary machine cooling circuit  18  through the switching valve  49   a,  the connection passage  50   a  and the switching valve  48   a,  and circulates through or bypasses the radiator  37  and is heated by the battery charger  31 , and is further heated by the heat exchanger  33 , and thereafter the resultant hot water is returned to the FC cooling circuit  16  through the switching valve  48   b,  the connection passage  50   b  and the switching valve  49   b  from the pump  34 , and flows through the fuel cell  4   a  to raise the temperature thereof. The switching state of the respective switching valves  45   a,    45   b,    46   a,    46   b,    48   a ,  48   b,    49   a  and  49   b  when switched to the side of the connection passages  47   a,    47   b,    50   a  and  50   b  as described above is described as the “B side”. 
     Note that, at this time the pump  38  of the charging auxiliary machine cooling circuit  18  may be actuated, or may be left in a stopped state as long as the pump  38  does not hinder the flow of water. Further, in the case of actuating the pump  38  of the charging auxiliary machine cooling circuit  18 , the pump  22  of the FC cooling circuit  16  may be stopped. 
     Next, processing for warm up the fuel cell  4   a  that is executed by the vehicle ECU  13  utilizing the above described circuitry is described. 
       FIG. 3  is a flowchart illustrating a warm-up control routine that the vehicle ECU  13  executes. This routine is executed at predetermined control intervals during charging of the secondary battery  3 . 
     First, in step S 1 , the vehicle ECU  13  determines whether or not the temperature Tfc of the fuel cell  4   a  is equal to or higher than a higher side of the temperature Tb of the secondary battery  3  and the temperature Tc of the battery charger. If the result of the determination in step S 1  is “Yes” (affirmative), in step S 2  the vehicle ECU  13  maintains the pump  22  of the FC cooling circuit  16  in a stopped state (the pump  22  already stopped when the FC stopped), and also switches all of the switching valves  45   a ,  45   b,    46   a,    46   b,    48   a,    48   b,    49   a  and  49   b  to the A side to disconnect both the hot water circuit  17  and the charging auxiliary machine cooling circuit  18  from the FC cooling circuit  16 . Since when charging starts initially, neither the secondary battery  3  nor the battery charger  31  generate much heat and the water that circulates through the charging auxiliary machine cooling circuit  18  is also at a low temperature, this processing is performed to avoid the occurrence of a situation in which, on the contrary, the temperature of the fuel cell  4   a  is reduced by allowing the charging auxiliary machine cooling circuit  18  to communicate with the FC cooling circuit  16 . 
     Note that, because the FC cooling circuit  16  and the charging auxiliary machine cooling circuit  18  exchange heat using water as a medium, a configuration may also be adopted in which the temperature of water in the FC cooling circuit  16  is used instead of the temperature Tfc of the fuel cell  4   a,  and the temperature of water in the charging auxiliary machine cooling circuit  18  is used instead of the temperatures Tb and Tc of the secondary battery  3  and the battery charger  31 . The temperature of the fuel cell  4   a  of the present invention shall be taken to also include the water temperature in the FC cooling circuit  16 , and the temperature of the secondary battery  3  of the present invention shall be taken to also include the water temperature in the charging auxiliary machine cooling circuit  18 . 
     When the respective temperatures Tb and Tc of the secondary battery  3  and the battery charger  31  gradually rise accompanying charging and the result of the determination in step S 1  becomes “No” (negative), it is determined that the fuel cell  4   a  can be warmed up utilizing heat from the secondary battery  3  and the battery charger  31 , and hence the processing transitions to step S 3  in which the vehicle ECU  13  determines whether or not the temperature Tfc of the fuel cell  4   a  is equal to or higher than a first determination value T 1  that is set in advance. If the result of the determination in step S 3  is “Yes”, the processing transitions to step S 4  in which the vehicle ECU  13  starts operation of the pump  22  of the FC cooling circuit  16  and then switches the respective switching valves  48   a  and  48   b  of the charging auxiliary machine cooling circuit  18  and each of the corresponding switching valves  49   a  and  49   b  of the FC cooling circuit  16  to the B side. By this means, the charging auxiliary machine cooling circuit  18  communicates with the FC cooling circuit  16  through the connection passages  50   a  and  50   b . Simultaneously, the vehicle ECU  13  switches the switching valve  39  so that water in the charging auxiliary machine cooling circuit  18  circulates through the radiator  37 . 
     Because the first determination value T 1  is set to a temperature that is high to a certain extent, for example, 30° C., it is considered that in this case it is not so necessary to warm up the fuel cell  4   a  as quickly as possible. Hence, first the fuel cell  4   a  is warmed up by means of only heat generated at the charging auxiliary machine cooling circuit  18 , and an increase in the temperature of the water is suppressed to a moderate degree by releasing heat at the radiator  37  to thereby protect the secondary battery  3  and the battery charger  31 . 
     When the result of the determination in step S 3  is “No”, the processing transitions to step S 5  in which the vehicle ECU  13  determines whether or not the temperature Tfc of the fuel cell  4   a  is equal to or greater than a second determination value T 2  (&lt;T 1 ) that is set in advance. If the result of the determination in step S 5  is “Yes”, the processing transitions to step S 6 . In step S 6 , the vehicle ECU  13  starts operation of the pump  22  of the FC cooling circuit  16  and then switches the respective switching valves  48   a  and  48   b  of the charging auxiliary machine cooling circuit  18  and each of the corresponding switching valves  49   a  and  49   b  of the FC cooling circuit  16  to the B side, and also switches the switching valve  39  so that the water circulating through the charging auxiliary machine cooling circuit  18  bypasses the radiator  37 . 
     Because the second determination value T 2  is set to a comparatively low temperature, for example, 5° C., it is considered that in this case, to a certain extent it is necessary to warm up the fuel cell  4   a  as rapidly soon as possible. Similarly to the case in step S 4  that is described above, the fuel cell  4   a  is warmed up by means of only heat generated at the charging auxiliary machine cooling circuit  18 , but in this case, warming up of the fuel cell  4   a  is further accelerated because the release of heat from the radiator  37  is stopped. 
     When executing the processing in the above described steps S 1  to  7 , the vehicle ECU  13  functions as a warm-up control unit of the present invention. 
     Further, when the result of the determination in step S 5  is “No”, the processing transitions to step S 7  in which, similarly to step S 6 , the vehicle ECU  13  starts operation of the pump  22  of the FC cooling circuit  16  and then switches the respective switching valves  48   a  and  48   b  of the charging auxiliary machine cooling circuit  18  and each of the corresponding switching valves  49   a  and  49   b  of the FC cooling circuit  16  to the B side, and also switches the switching valve  39  so that the water circulating through the charging auxiliary machine cooling circuit  18  bypasses the radiator  37 . Subsequently, in step S 8 , the vehicle ECU  13  turns on the hot water heater  27  and then switches the respective switching valves  45   a  and  45   b  of the hot water circuit  17  and each of the corresponding switching valves  46   a  and  46   b  of the FC cooling circuit  16  to the B side, and also switches the switching valve  29  so that the water circulating through the hot water circuit  17  bypasses the heat exchanger  25 . 
     By this means, both the hot water circuit  17  and the charging auxiliary machine cooling circuit  18  communicate with the FC cooling circuit  16  through the connection passages  47   a,    47   b,    50   a  and  50   b,  and the release of heat by the heat exchanger  25  and the radiator  37  in both of the circuits  17  and  18  is stopped. In this case, it is necessary to warm up the fuel cell  4   a  as quickly as possible since the temperature Tfc of the fuel cell  4   a  is less than the first determination value T 1 , and because all of the heat generated in both the hot water circuit  17  and the charging auxiliary machine cooling circuit  18  is not released at the heat exchanger  25  and the radiator  37  and therefore is utilized without waste to warm up the fuel cell  4   a,  the fuel cell  4   a  is rapidly warmed up. 
     In a case such as this in which it is possible to warm up the fuel cell  4   a  with heat of the secondary battery  3  and the battery charger  31  at an initial stage after starting charging of the secondary battery  3 , the fuel cell  4   a  is warmed up by the processing in any of step S 4 , step S 6  and steps S 7  and S 8  in accordance with the temperature Tfc of the fuel cell  4   a.  Further, when warming up of the fuel cell  4   a  progresses and the temperature Tfc rises, the processing switches from steps S 7  and S 8  to step S 6 , and furthermore to step S 4 . According to the specifications of the secondary battery  3  and the battery charger  31  of the present embodiment, it is possible to raise the temperature of the fuel cell  4   a  as far as the rated temperature by utilizing heat generated during charging, and an equilibrium state is entered at the rated temperature and an increase in the temperature is suppressed. Hence, warming up of the fuel cell  4   a  is completed during execution of the processing in step S 4  and the temperature of the fuel cell  4   a  at that time point is maintained, and charging of the secondary battery  3  ends in that state. 
     However, the present invention is not limited to the above configuration and, for example, in a case where the fuel cell  4   a  exceeds the rated temperature as a result of being heated with only heat that the secondary battery  3  and the battery charger  31  generate during charging, a configuration may be adopted so as to end warming up of the fuel cell  4   a  at an upper limit temperature that is set in advance. 
     As described in detail above, according to the warm-up apparatus of the fuel cell  4   a  for an electrically driven vehicle of the present embodiment, the fuel cell  4   a  is warmed up by heat that the secondary battery  3  and the battery charger  31  generate during charging, and because heat that would be wastefully discarded into the atmosphere is utilized, no operating cost at all is required to perform warming up. 
     Further, because the secondary battery  3  and the battery charger  31  generate a large amount of heat during charging, fundamentally the fuel cell  4   a  can be adequately warmed up rapidly by only the process in step S 4  or step S 6 . In this respect, the process that utilizes the heat of the hot water circuit  17  in step S 8  is an auxiliary process and need not necessarily be performed. The fuel cell  4   a  can be rapidly warmed up utilizing a large amount of heat that the secondary battery  3  and the battery charger  31  generate in this way, and furthermore the warming up at this time is executed concurrently with charging of the secondary battery  3 . Hence, warming up of the fuel cell  4   a  can be completed during charging of the secondary battery  3 , and consequently the electrically driven vehicle  1  can start to travel immediately upon the completion of charging of the secondary battery  3 . 
     Note that, in particular the secondary battery  3  generates a larger amount of heat than the battery charger  31 , and therefore a configuration may also be adopted so as to warm up the fuel cell  4   a  using only the heat of the secondary battery  3  during charging. In such a case, the battery charger  31  can be bypassed or can be excluded from the charging auxiliary machine cooling circuit  18 . 
     Further, the existing pump  22  that is provided in the FC cooling circuit  16  is utilized to transfer water between the charging auxiliary machine cooling circuit  18  or the hot water circuit  17  and the FC cooling circuit  16  through the connection passages  47   a,    47   b,    50   a  and  50   b . Therefore, water that is heated in the charging auxiliary machine cooling circuit  18  or the hot water circuit  17  can be quickly and reliably guided to the FC cooling circuit  16 , and this is also a factor that contributes to rapid completion of warming up. 
     However, the pump  22  is not necessarily required, and a configuration may also be adopted in which the charging auxiliary machine cooling circuit  18  or the hot water circuit  17  and the FC cooling circuit  16  are caused to communicate through the connection passages  47   a,    47   b ,  50   a  and  50   b  by switching the switching valves  45   a,    45   b,    46   a ,  46   b,    48   a,    48   b,    49   a  and  49   b  to the B side, and then the water is transferred by utilizing natural convection. In particular, in a layout in which the FC cooling circuit  16  is arranged immediately above the charging auxiliary machine cooling circuit  18  or the hot water circuit  17 , since the heated water will be transferred by natural convection to the FC cooling circuit  16  that is above the charging auxiliary machine cooling circuit  18  or the hot water circuit  17 , the fuel cell  4   a  can be adequately warmed up even without a pump. 
     Further, when the respective temperatures Tb and Tc of the secondary battery  3  and the battery charger  31  rise as a result of charging and a time point is reached when either of the temperatures Tb and Tc becomes equal to or higher than the temperature Tfc of the fuel cell  4   a,  at that time point the operation of the pump  22  of the FC cooling circuit  16  is started and, furthermore, the charging auxiliary machine cooling circuit  18  is caused to communicate with the FC cooling circuit  16  through the connection passages  50   a  and  50   b.  Hence, a situation can be avoided in which, when charging initially starts, water having a low temperature is transferred to the FC cooling circuit  16  and lowers the temperature of the fuel cell  4   a , and thus more efficient warming up of the fuel cell  4   a  can be realized. 
     Further, the secondary battery  3  is cooled by dielectric fluid in the back-up cooling circuit  35 , and the dielectric fluid exchanges heat with water in the charging auxiliary machine cooling circuit  18  through the heat exchanger  33 . Accordingly, the occurrence of trouble such as electrification if a water leakage occurs can be prevented, and even in this form of fuel cell system it is possible to realize warming up of the fuel cell  4   a  that utilizes the heat of the secondary battery  3  and the battery charger  31 . 
     Further, when the temperature Tfc of the fuel cell  4   a  is equal to or higher than the first determination value T 1 , water in the charging auxiliary machine cooling circuit  18  is circulated to the radiator  37 , and when the temperature Tfc of the fuel cell  4   a  is less than the first determination value T 1 , the water is caused to bypass the radiator  37 . When water is circulated to the radiator  37 , a rise in the temperature of the secondary battery  3  and the battery charger  31  is suppressed and the secondary battery  3  and the battery charger  31  can be reliably protected, and when the water bypasses the radiator  37 , warming up of the fuel cell  4   a  can be further accelerated, and therefore warm-up control whose contents are the optimal contents according to the temperature of the fuel cell  4   a  at the relevant time point can be executed. 
     While an embodiment of the present invention has been described above, it is to be noted that aspects of the present invention are not limited to the foregoing embodiment. For example, although in the above described embodiment the heat of the hot water circuit  17  is also utilized for warming up the fuel cell  4   a,  and not just heat that the secondary battery  3  and the battery charger  31  generate in the charging auxiliary machine cooling circuit  18 , the heat of the hot water circuit  17  need not be utilized. 
     Further, although in the above described embodiment a configuration is adopted that cools the secondary battery  3  using dielectric fluid, instead of this configuration, a configuration may be adopted so as to directly cool the secondary battery  3  with water in the charging auxiliary machine cooling circuit  18 .