Abstract:
A vehicle mounting structure for a fuel cell includes a fuel cell box which accommodates a fuel cell stack inside. The fuel cell box includes a bottom frame on which the fuel cell stack is mounted, a top frame, the bottom frame and the top frame sandwiching the fuel cell stack, a side frame which forms a framework of the fuel cell box and which is connected to the bottom frame and to the top frame, a bottom holddown member which fixes a bottom portion of the fuel cell stack to the bottom frame, and a top holddown member which fixes a top portion of the fuel cell stack to the top frame. Structural members which are required to carry a fuel cell stack are reduced in weight and miniaturized in size while ensuring the desired installation rigidity when the fuel cell stack is carried.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     Priority is claimed on Japanese Patent Application No. 2004-14276, filed Jan. 22, 2004, the contents of which are incorporated herein by reference.  
         [0003]     The present invention relates to a vehicle mounting structure for a fuel cell.  
         [0004]     2. Description of Related Art  
         [0005]     Conventionally, there is known a fuel cell vehicle which carries a fuel cell stack as a source of motive power, and travels by driving a propulsion motor using electric power generated by the fuel cell stack.  
         [0006]     In such a fuel cell vehicle, endplates of a fuel cell stack are integrally fixed to a body frame which is the chassis of the vehicle (refer for example, to U.S. Published application No. 2003/0012998).  
         [0007]     It is to be noted that in the fuel cell vehicle according to the aforementioned conventional technology, it has been desired to reduce the weight and miniaturize the size of the structural members which are required to carry the fuel cell stack, while ensuring the desired installation rigidity when the fuel cell stack is carried.  
       SUMMARY OF THE INVENTION  
       [0008]     The present invention was conceived in view of the above situation and it is an object thereof to provide a vehicle mounting structure for a fuel cell, whereby it is possible to reduce the weight and miniaturize the size of the structural members which are required to carry a fuel cell stack while ensuring the desired installation rigidity when the fuel cell stack is carried.  
         [0009]     To solve the aforementioned problems and achieve the object, according to the present invention, there is provided a vehicle mounting structure including a fuel cell box (fuel cell box  140  in the embodiment) which accommodates a fuel cell stack, the fuel cell box comprising: a bottom frame (fuel cell support frame  141  in the embodiment) on which the fuel cell stack is mounted; a top frame (top frames  145  in the embodiment), the bottom frame and the top frame sandwiching the fuel cell stack; a side frame (first and second side frames  143  and  144  in the embodiment) which forms a framework of the fuel cell box and which is connected to the bottom frame and to the top frame; a bottom holddown member (bottom holddown members  147  in the embodiment) which fixes a bottom portion of the fuel cell stack (bottom of endplates  11 A in the embodiment) to the bottom frame; and a top holddown member (top holddown members  148  in the embodiment) which fixes a top portion of the fuel cell stack (top of the endplates  11 A in the embodiment) to the top frame.  
         [0010]     According to the vehicle mounting structure of the above construction, for example, compared to a case where the fuel cell stack is fixed on the bottom frame simply by bottom holddown members, the fuel cell stack itself can be made to function as the structural members of the fuel cell box in addition to the bottom frame and the top frame, enabling an increase in the installation rigidity of the fuel cell and the rigidity of the fuel cell box.  
         [0011]     Furthermore, for example, compared to a case where the rigidity of the fuel cell box is increased not by providing the top frame, but by increasing the weight of the bottom frame and the side frame, which form the framework of the fuel cell box, the weight of the fuel cell box can be kept from being excessively increased.  
         [0012]     Preferably, in the vehicle mounting structure as described above, the fuel cell stack comprises a pair of endplates (endplates  11 A in the embodiment) which sandwich a plurality of fuel cells, and the bottom holddown member fixes a bottom portion of the endplates to the bottom frame, and the top holddown member fixes a top portion of the endplates to the top frame.  
         [0013]     According to the vehicle mounting structure of the above construction, the endplates of the fuel cell stack can made to function as the structural members of the fuel cell box in addition to the bottom frame and the top frame, enabling an increase in the installation rigidity of the fuel cells and the rigidity of the fuel cell box.  
         [0014]     Preferably, in the vehicle mounting structure as described above, the pair of endplates sandwich the fuel cell stack from a longitudinal direction of the vehicle.  
         [0015]     According to the vehicle mounting structure of the above construction, the fuel cell stack which is affected by the vehicle&#39;s acceleration force and deceleration force can be firmly fixed in the fuel cell box.  
         [0016]     Preferably, in the vehicle mounting structure as described above, the side frame is connected to a body frame (floor frames  105  and  106  in the embodiment) which forms a vehicle chassis.  
         [0017]     According to the vehicle mounting structure of the above construction, the fuel cell box can be firmly fixed to the body frame. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]      FIG. 1  is a block diagram of a fuel cell system according to an embodiment of the present invention.  
         [0019]      FIG. 2  is an exploded perspective view of main parts of a vehicle mounting structure of the fuel cell system shown in  FIG. 1 .  
         [0020]      FIG. 3  is a perspective view of the main parts of the vehicle mounting structure of the fuel cell system shown in  FIG. 1 .  
         [0021]      FIG. 4  is a plan view of the main parts of the vehicle mounting structure of the fuel cell system shown in  FIG. 1 , seen from top to bottom in the vehicle vertical direction.  
         [0022]      FIG. 5  is an exploded perspective view of a fuel cell box.  
         [0023]      FIG. 6  is a perspective view of a frame body of the fuel cell box shown in  FIG. 5 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]     Hereunder is a description of a vehicle mounting structure for a fuel cell according to an embodiment of the present invention, with reference to the appended drawings.  
         [0025]     A fuel cell system  10  according to the present embodiment comprises for example as shown in  FIG. 1 : a fuel cell  11 , an air supply device  12 , a humidifier  13 , a hydrogen tank  14 , a fuel supply control valve  15 , an ejector  16 , a fuel pump  17 , a dilution box  18 , a purge valve  19 , a current controller  20 , and a central control unit (ECU)  21 . The fuel cell vehicle installed with this fuel cell system  10  comprises the fuel cell system  10 , a propulsion motor  31 , a power control unit (PCU)  32 , and a capacitor  33 .  
         [0026]     The fuel cell  11  comprises a stack of fuel cell units made up of an electrolyte electrode structure holding solid polymer electrolyte membranes formed from a cation exchange membrane or the like, sandwiched between a fuel electrode (anode) formed from an anode catalyst and a gas diffusion layer, and an oxygen electrode (cathode) formed from a cathode catalyst and a gas diffusion layer, which is further sandwiched between a pair of separators. The stack body of the fuel cell units is sandwiched between a pair of endplates on opposite sides in the stacking direction.  
         [0027]     Air which is an oxidizing gas (reactant gas) containing oxygen is supplied from the air supply device (S/C)  12 , and humidified appropriately by the humidifier  13 , then led into the cathode of the fuel cell  11 . The anode is supplied with a fuel gas (reactant gas) comprising hydrogen which is supplied from the high pressure hydrogen tank  14  via the fuel supply control valve  15  and the ejector  16 . The hydrogen ionized by the catalytic reaction on the anode catalyst of the anode, migrates towards the cathode through an appropriately humidified solid polymer electrolyte membrane. Electrons generated in association with this migration are drawn to an external circuit and used as direct current electric energy. At the same time, hydrogen ions, electrons and oxygen react to form water at the cathode.  
         [0028]     The revolution speed of a motor (not shown) which drives the air supply device (S/C)  12  comprising an air compressor or the like, is controlled by an S/C controller  12   a  furnished with for example a pulse width modulation (PWM) inverter, by means of pulse width modulation (PWM), based on a control command of the input from the ECU  21 . The S/C controller  12   a  is connected in parallel with the current controller  20  and the capacitor  33 .  
         [0029]     The humidifier  13  comprises a water permeable membrane such as a hollow fiber membrane, and uses the air discharged from the air discharge port  11   b  in the fuel cell  11  as the humidifying gas for the air supplied from the air supply device (S/C)  12  to the air supply port  11  a as a reactant gas. That is, when the air and the discharged air are made to contact through the water permeable membrane, the moisture contained in the discharged air (especially steam) is supplied as water vapor into the air after it has permeated through the pores of the water permeable membrane.  
         [0030]     Moreover, the discharged air from the humidifier  13  is led into the dilution box  18  to be described later.  
         [0031]     The hydrogen as fuel for the fuel cell  11  is first supplied from the high pressure hydrogen tank  14  to the fuel supply control valve  15 .  
         [0032]     The fuel supply control valve  15  is, for example, an air type proportional pressure control valve, and is set using air pressure supplied from the air supply device (S/C)  12  as a signal pressure, so that the pressure of the hydrogen flowing through the fuel supply control valve  15  at the outlet of the fuel supply control valve  15  is within a predetermined range according to the signal pressure.  
         [0033]     The hydrogen flowing through the fuel supply control valve  15  flows through the ejector  16  and is supplied from the hydrogen supply port  11   c  into the anode of the fuel cell  11 .  
         [0034]     Moreover, a part of the unreacted gas discharged from the hydrogen discharge port  11   d  in the fuel cell  11  is led into the ejector  16  by means of the hydrogen pump  17 . The hydrogen supplied from the hydrogen tank  14  and the discharged gas from the fuel cell  11  are mixed in the ejector  16  and re-supplied into the fuel cell  11 .  
         [0035]     The ejector  16  sucks in the part of the discharged gas from the fuel cell  11  as a secondary flow due to the negative pressure generated in the vicinity of the high speed flow of the hydrogen gas passing through inside, and mixes this discharged gas with the hydrogen supplied from the hydrogen tank  14  to re-supply into the fuel cell  11 , so that the discharged gas from the fuel cell  11  can be circulated.  
         [0036]     Moreover, the discharged gas from the hydrogen discharge port  11   d  in the fuel cell  11  is led into the dilution box  18  through the discharge control valve  17   a  which is controlled on and off by means of the ECU  21 .  
         [0037]     The dilution box  18  mixes the hydrogen of the unreacted discharge gas which is discharged at the same time as when the nitrogen and the like mixed in the water and hydrogen remaining at the anode in the fuel cell  11  are discharged to the outside, with the air discharged from the cathode so as to reduce the hydrogen concentration below a predetermined concentration, and then discharges it to the outside (such as into the atmosphere) through the purge valve  19 .  
         [0038]     The generated current drawn from the fuel cell  11  is input into the current controller  20 . The capacitor  33  comprising for example an electric double layer capacitor or an electrolytic capacitor as an electric accumulator, is connected to the current controller  20 .  
         [0039]     The current controller  20  comprises for example a DC-DC chopper or the like, and controls the current value of the generated current drawn from the fuel cell  11 , based on the current command value from the output of the ECU  21 , that is, the power generation command for the fuel cell  11 .  
         [0040]     Moreover, the fuel cell  11  and the capacitor  33  are connected in parallel via the current controller  20 , with electrical loads such as the power control unit  32  which controls the propulsion motor  31 , and the S/C controller  12   a  which controls a motor (not shown) that drives the air supply device (S/C)  12 .  
         [0041]     Hereunder is a description of a vehicle mounting structure of the fuel cell system  10  comprising the abovementioned construction, with reference to  FIG. 2  to  FIG. 6 .  
         [0042]     For example, as shown in  FIG. 2 , a rear floor  102  which is formed with a step raising rearwards, is joined to the rear edge of a front floor  101  constituting the vehicle floor. A crossmember  104  which forms the chassis of the vehicle, is joined onto the rear side of a stepped portion  103  of the rear floor  102 . Floor frames  105  and  106  which form the chassis of the vehicle are respectively connected onto the undersurface of the front floor  101  towards the outside on the left and right along the vehicle lengthwise direction.  
         [0043]     Inside sills  107  and  108  are respectively connected to the left and right edges of the front floor  101 . An inside sill extension  109  is provided at the rear end of the inside sill  107  and an inside sill extension  110  is provided at the rear end of the inside sill  108 . The inside sills  107  and  108  are members that are joined to outside sills (not shown) to form the chassis of the vehicle.  
         [0044]     A front bracket  111  is joined onto the inner surface of the inside sill extension  109  and a front bracket  112  is joined onto the inner surface of the inside sill extension  110 .  
         [0045]     The front brackets  111  and  112  are joined to: rear frames  113  and  114  being members that are joined on the undersurface of the rear floor  102  to form the chassis of the vehicle, to the undersurface of the crossmember  104 , and to the floor frames  105  and  106 . As a result the front ends of the rear frames  113  and  114  are connected to the inside sills  107  and  108  and the floor frames  105  and  106  via the front brackets  111  and  112 .  
         [0046]     A rear bracket  117  is attached onto the undersurface of the rear end of the rear frame  113  and a rear bracket  118  is attached onto the undersurface of the rear end of the rear frame  114 .  
         [0047]     Here, two crossmembers  104 A and  104 B are joined towards the front and back between the left and right rear frames  113  and  114 . The respective rear ends of the frames  113  and  114 , specifically the rear brackets  117  and  118 , are attached with a bumper beam  121 .  
         [0048]     Moreover, a sub frame  122  is fixed from beneath to respective collar nuts  115 ,  116 ,  119 , and  120  which are provided on the front brackets  111  and  112  and the rear brackets  117  and  118 , using four bolts  123 .  
         [0049]     As shown in  FIG. 2 , the sub frame  122  is a member which is formed into a rectangular frame shape using left and right frame members  124  and  125  and front and rear frame members  126  and  127 , and a crossbeam  128  is provided in the vehicle widthwise direction. Two hydrogen tanks  14 A and  14 B serving as the hydrogen tank  14 , are fixed into spaces divided by this crossbeam  128 , by fastening with respective bands  131  and  132 . Suspension units  133  are attached to the sub frame  122 .  
         [0050]     Moreover, insertion parts  134  and  135  for the bolts  123  which are inserted into the aforementioned collar nuts  115  and  116 , are provided at corners of the front ends of the left and right frame members  124  and  125  and the opposite ends of the front frame member  126 . Insertion parts  136  and  137  for the bolts  123  which are inserted into the aforesaid collar nuts  119  and  120 , are provided at corners of the rear ends of the left and right frame members  124  and  125  and the opposite ends of the rear frame member  127 .  
         [0051]     The bolts  123  are inserted through the respective insertion parts  134 ,  135 ,  136  and  137  of the sub frame  122  constituted in this manner, and then these bolts  123  are inserted into the collar nuts  115 ,  116 ,  119 , and  120  which are attached to the front brackets  111  and  112  and the rear brackets  117  and  118  of the rear frames  113  and  114 , and tightened securely to thereby secure the sub frame  122  to the rear frames  113  and  114 .  
         [0052]     As shown in  FIG. 4  to  FIG. 6 , a fuel cell box  140  which accommodates and secures the fuel cell  11  and auxiliary units of the fuel cell  11  (for example, the humidifier  13 , the ejector  16 , the fuel pump  17 , the dilution box  18 , and the like) inside, is joined to the left and right floor frames  105  and  106  under the front floor  101 .  
         [0053]     The fuel cell box  140  comprises fuel cell support frames  141 , bottom frames  142 , first and second side frames  143  and  144 , and top frames  145  which form the framework.  
         [0054]     For example, as shown in  FIG. 6 , an approximately rectangular frame body  146  is formed by joining pairs of ends of the two bottom frames  142  and the two first side frames  143  that are arranged facing each other. Furthermore, the two fuel cell support frames  141  are connected to the two first side frames  143  at predetermined positions inside of the frame body  146 .  
         [0055]     The stacking direction of the plurality of fuel cell units (not shown) constituting the fuel cell  11  is set in the vehicle lengthwise direction. The stack body of fuel cell units is sandwiched between a pair of endplates  11 A from stacking direction (that is vehicle lengthwise direction) opposite sides.  
         [0056]     As shown in  FIG. 5  and  FIG. 6  for example, in the frame body  146  where the two first side frames  143  are arranged along the vehicle lengthwise direction, two fuel cells  11  are mounted on the fuel cell support frames  141  so as to span between the two fuel cell support frames  141 .  
         [0057]     The two fuel cells  11  are arranged to sandwich the humidifier  13  from the opposite sides in the vehicle widthwise direction for example. The respective fuel cells  11  are fixed onto the fuel cell support frames  141  by for example, securing and fixing bottom holddown members  147  of approximate L-shaped cross-section plates to the bottom of the endplates  11 A and the top surfaces  141 A of the fuel cell support frames  141  by fasteners such as bolts.  
         [0058]     Moreover, projections  143   a  projecting upward in the vehicle vertical direction are formed at the opposite ends of the first side frame  143  extending in the vehicle lengthwise direction.  
         [0059]     The second side frame  144  is formed in a rectangular frame shape for example, and is provided with fitting holes  144   a  for installing the projections  143   a  of the first side frame  143 .  
         [0060]     The first side frame  143  and the second side frame  144  are connected by installing the projections  143   a  of the first side frame  143  into the fitting holes  144   a  of the second side frame  144 , so that the periphery of the two fuel cells  11  and the humidifier  13  that are mounted on the fuel cell support frame  141  are surrounded by the second side frame  144 .  
         [0061]     Bolt installation holes  143   b  which are bored through in the vehicle vertical direction are provided in the first side frame  143 . Through holes  144   b  which lead to the bolt installation holes  143   b  on the first side frame  143  are provided in the second side frame  144 .  
         [0062]     Over a top position in the vehicle vertical direction of the two fuel cells  11  that are mounted on the fuel cell support frames  141 , are arranged two rectangular tubular top frames  145  extending in the vehicle widthwise direction. Two bolt installation holes  145   a  which are bored through in the vehicle lengthwise direction are formed in the respective top frame  145 .  
         [0063]     Moreover, top holddown members  148  projecting over the top end of the fuel cells  11  upward in the vehicle vertical direction are formed at the tops of the end plates  11 A of the fuel cells  11 . Through holes  148   a  which are bored through in the vehicle lengthwise direction and lead toward the bolt installation holes  145   a  of the top frames  145  are formed in these top holddown members  148 .  
         [0064]     Furthermore, through holes  145   b  which are bored through in the vehicle vertical direction and lead toward the through holes  144   b  of the second side frame  144  are provided in opposite ends of the top frames  145  extending in the vehicle widthwise direction.  
         [0065]     Through holes  105   b  and  106   b  which are bored through in the vehicle vertical direction and lead toward the through holes  145   b  of top frames  145  are formed in the respective bottom walls  105   a  and  106   a  of the cross-sectional approximate U-shaped floor frames  105  and  106 .  
         [0066]     Then, for example, the bolts  151  are installed sequentially from the bottom of the first side frame  143 , into the bolt installation holes  143   b  of the first side frame  143 , the through holes  144   b  of the second side frame  144 , the through holes  145   b  of the top frames  145 , and the through holes  105   b  of the floor frame  105  or the through holes  106   b  of the floor frame  106 , and fastened into nuts  152 , so as to secure the first side frame  143 , the second side frame  144 , the top frames  145 , and the floor frame  105  or the floor frame  106 .  
         [0067]     Furthermore, the bolts  153  are installed sequentially along the vehicle lengthwise direction into the bolt installation holes  145   a  of the top frames  145  and the through holes  148   a  of the top holddown member  148  formed on the top of the endplates  11 A, and fastened into nuts  154 , so as to secure the fuel cells  11  to the top frames  145 .  
         [0068]     In the vehicle mounting structure of the fuel cell system  10  having the above construction, the fuel cells  11  are fixed by sandwiching between the fuel cell support frames  141  and the top frames  145  from opposite sides in the vehicle vertical direction. Therefore, for example, compared to a case where the fuel cells  11  are fixed on the fuel cell support frames  141  simply by the bottom holddown members  147 , the endplates  11 A of the fuel cells  11  can be made to function as structural members of the fuel cell box  140  in addition to the fuel cell support frames  141  and the top frames  145 , enabling an increase in the installation rigidity of the fuel cells  11  and the rigidity of the fuel cell box  140 .  
         [0069]     Furthermore, by forming the top frames  145  in a tubular shape, the weight can be kept from being excessively increased. For example, compared to a case where the rigidity of the fuel cell box  140  is increased not by providing the top frames  145 , but by increasing the weight of the fuel cell support frames  141 , the bottom frames  142 , and the first and second side frames  143  and  144 , which form the framework of the fuel cell box  140 , the weight of the fuel cell box  140  can be kept from being excessively increased.  
         [0070]     Moreover, together with the increase in rigidity of the fuel cell box  140 , the characteristic frequency of the fuel cell box  140  can be increased, so that the occurrence of resonance in a relatively low frequency range due to vehicle vibration received from the road surface while the vehicle is travelling can be suppressed.  
         [0071]     With the vehicle mounting structure for a fuel cell of the present invention, the fuel cell itself can be made to function as the structural members of the fuel cell box in addition to the fuel cell support frame and the top frame, enabling an increase in installation rigidity of the fuel cell and the rigidity of the fuel cell box.  
         [0072]     Furthermore, for example, compared to a case where the rigidity of the fuel cell box is increased not by providing the top frame, but by increasing the weight of the fuel cell support frame and the side frame, which form the framework of the fuel cell box, the weight of the fuel cell box can be kept from being excessively increased.  
         [0073]     With the vehicle mounting structure for a fuel cell according to another embodiment of the present invention, the endplates of the fuel cell can be made to function as the structural members of the fuel cell box, enabling an increase in installation rigidity of the fuel cell and the rigidity of the fuel cell box.  
         [0074]     With the vehicle mounting structure for a fuel cell according to another embodiment of the present invention, the fuel cell which is affected by the vehicle&#39;s acceleration force and deceleration force can be firmly fixed in the fuel cell box.  
         [0075]     With the vehicle mounting structure for a fuel cell according to another embodiment of the present invention, the fuel cell box can be firmly fixed to the body frame.  
         [0076]     While preferred embodiments of the invention have been described and illustrated above, it should be understood that these are exemplary of the invention and are not to be considered as limiting. Additions, omissions, substitutions, and other modifications can be made without departing from the spirit or scope of the present invention. Accordingly, the invention is not to be considered as being limited by the foregoing description, and is only limited by the scope of the appended claims.