Abstract:
A fuel cell system, includes: a fuel cell stack that is formed by stacking fuel cells for causing electrochemical reaction of a fuel gas and an oxidizing gas; a fuel gas supply system that is configured to supply the fuel gas to the fuel cell stack from a supply source of the fuel gas; a fuel gas recirculating system that is configured to resupply to the fuel cell stack the fuel gas discharged from the fuel cell stack; and a piping member is configured to connect a junction between the fuel gas supply system and the fuel gas recirculating system with the supply source, the piping member having a bent portion that is curved such that a supply direction of the fuel gas from the supply source is reverse to a flowing direction of the fuel gas toward the junction.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to Japanese Patent Application No. 2014-232029, filed on Nov. 14, 2014, the contents of all of which are incorporated herein by reference in their entirety. 
       BACKGROUND 
       [0002]    1. Field 
         [0003]    The present invention relates to a fuel cell system. 
         [0004]    2. Related Art 
         [0005]    Conventionally, it is known that a fuel cell causes electrochemical reactions of fuel gas and oxidizing gas. It is also known that, for example, JP2009-298196A discloses a fuel cell system provided with a fuel gas supply system which supplies fuel gas to a fuel cell from a supply source of the fuel gas, and, in addition, in order to improve the fuel consumption of the fuel cell, a fuel gas recirculating system which resupplies to the fuel cell the fuel gas discharged from the fuel cell. 
         [0006]    However, water existing in the fuel gas recirculating system flows into the fuel gas supply system, thereby causing a possible malfunction etc. of the fuel cell due to corrosion and freeze of components of the fuel gas supply system. Particularly, when the fuel cell system is not operating, the fuel gas does not flow into the fuel gas recirculating system and the fuel gas supply system, thereby causing a possible corrosion etc. of the components of the fuel gas supply system. 
         [0007]    Here, a method of preventing water from flowing into the fuel gas supply system by disposing an upstream part of the fuel gas supply system higher than a junction between the fuel gas recirculating system and the fuel gas supply system, can be considered. However, if this method is adopted, a subject arises in which the height of the fuel cell system becomes higher. Particularly, if the fuel cell is mounted under a floor of the vehicle, it is difficult to reserve the mounting space because of height restrictions. 
       SUMMARY 
       [0008]    The present invention is made in order to address at least a part of the subject described above, and can be implemented in terms of the following aspects. 
         [0009]    (1) According to one aspect of the invention, a fuel cell system is provided. The fuel cell system includes: a fuel cell stack that is formed by stacking fuel cells for causing electrochemical reaction of a fuel gas and an oxidizing gas; a fuel gas supply system that is configured to supply the fuel gas to the fuel cell stack from a supply source of the fuel gas; a fuel gas recirculating system that is configured to resupply to the fuel cell stack the fuel gas discharged from the fuel cell stack; and a piping member is configured to connect a junction between the fuel gas supply system and the fuel gas recirculating system with the supply source, the piping member having a bent portion that is curved such that; a supply direction of the fuel gas from the supply source is reverse to a flowing direction of the fuel gas toward the junction. According to this aspect, since the bent portions are provided, water which remains in the fuel gas recirculating system can be prevented from flowing into the fuel gas supply system, and a corrosion of the fuel gas supply system components can be prevented. Since the bent portions are curved so that the supply direction of the fuel gas from the supply source is opposite from the flowing direction of the fuel gas to the junction, the height of the fuel cell system can be prevented from being higher. 
         [0010]    (2) The fuel cell system of the aspect described above may further include a plurality of auxiliary machines used for operation of the fuel cell stack. The plurality of auxiliary machines are disposed between the fuel cell stack and the piping member in stacking directions of the fuel cell. According to this aspect, a space between the piping member and the fuel cell can effectively be utilized. 
         [0011]    (3) In the fuel cell system of the aspect described above, the plurality of auxiliary machines may include a fuel gas pump for recirculating the fuel gas in the fuel gas recirculating system. The fuel gas pump may be disposed at a position where the fuel gas pump overlaps with at least a part of the piping member in the stacking directions of the fuel cell. According to this aspect, when the piping member is collided by other adjacent members in a direction toward the fuel cell stack in the stacking directions of the fuel cell, other adjacent members collide the fuel gas pump before the piping member is completely divided due to the collision. Therefore, the possible dividing of the piping can be reduced. 
         [0012]    (4) In the fuel cell system of the aspect described above, at least a part of the fuel gas pump may be disposed at the most distant position from the fuel cell stack in the stacking direction of the fuel cell, among the plurality of auxiliary machines. According to this aspect, when other adjacent members collide the fuel cell system in the direction toward the fuel cell stack in the stacking directions of the fuel cell, the fuel gas pump collides other adjacent members prior to other auxiliary machines. Therefore, the auxiliary machines other than the fuel gas pump can be protected. 
         [0013]    The present invention can be implemented in various forms, for example, can be implemented in the forms of a method of manufacturing a fuel cell case, a computer program for implementing the manufacturing method, a recording medium that records the computer program, etc. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is an exploded perspective view of a fuel cell system used for one embodiment of the invention; 
           [0015]      FIG. 2  is a schematic view illustrating a state where a plurality of auxiliary machines, a piping member, etc. are connected with a manifold; 
           [0016]      FIG. 3  is a schematic view of the piping member seen from above the vehicle (seen from positive Y-axis direction); 
           [0017]      FIG. 4  is a schematic view of the piping member seen from the right side of the vehicle (seen from positive Z-axis direction); 
           [0018]      FIG. 5  is a schematic view of the piping member seen from the rear side of the vehicle (seen from negative X-axis direction); 
           [0019]      FIG. 6  is a schematic view of the piping member seen from the front side of the vehicle (seen from positive X-axis direction); and 
           [0020]      FIG. 7  is a schematic view illustrating a piping member in Modification 1. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
     A. Embodiment 
       [0021]      FIG. 1  is an exploded perspective view of a fuel cell system  10  used for one embodiment of the invention. The fuel cell system  10  includes a fuel cell stack  100 , a stack covering  110 , a current collector  120 , a manifold  130 , a plurality of auxiliary machines  200 , a piping member  300 , and an auxiliary-machinery covering  400 . 
         [0022]    The fuel cell system  10  is mounted on a vehicle. In this embodiment, the fuel cell system  10  is disposed below a vehicle cabin where a vehicle operator and passengers are accommodated. In  FIG. 1 , positive in X-axis directions indicates forward of the vehicle, positive in Y-axis directions indicates upward of the vehicle, and positive in Z-axis directions indicates rightward of the vehicle. The XYZ coordinate system is also the same in other drawings subsequent to  FIG. 1 . 
         [0023]    The fuel cell stack  100  is formed by stacking fuel cells, each of which causes electrochemical reactions of fuel gas and oxidizing gas. In this embodiment, a stacking direction of the fuel cells is in the vehicle width directions (Z-axis directions). In this embodiment, hydrogen gas is used as the fuel gas, and oxygen gas is used as the oxidizing gas. 
         [0024]    The stack covering  110  is a covering for covering the fuel cell stack  100 . The current collector  120  collects electric power produced in each of the fuel cells. The current collector  120  is disposed rightward of the fuel cell stack  100  (positive side in Z-axis directions). 
         [0025]    The manifold  130  forms flow paths of fuel gas, oxidizing gas, and cooling water which cools the fuel cell stack  100 . The manifold  130  is also provided with a function to secure electrical insulation inside the stack covering  110 , as well as a function to mutually compress the fuel cells. The manifold  130  is disposed further rightward of the current collector  120  (positive in Z-axis directions). A plurality of holes and openings are formed in a right-side surface of the manifold  130  (positive side in Z-axis directions). 
         [0026]    The plurality of auxiliary machines  200  are auxiliary machinery used for operation of the fuel cell stack  100 , and are covered by the auxiliary-machinery covering  400 . The plurality of auxiliary machines  200  include injectors  210 , a distribution piping  220 , a pressure sensor  230 , a pressure relief valve  240 , a fuel gas pump  250 , a gas-liquid separator  260 , a purge valve  270 , and a wire harness  280 . 
         [0027]    The plurality of injectors  210  are connected in parallel with corresponding holes in the manifold  130  at one ends, and are connected with the distribution piping  220  at the other ends. The distribution piping  220  is connected with corresponding holes in the manifold  130  at one end, and is connected with the plurality of injectors  210  at the other end. The pressure sensor  230  and the pressure relief valve  240  are provided near the injectors  210  and are connected with corresponding holes in the manifold  130 . The fuel gas pump  250  is connected with the manifold  130  and forces the fuel gas to recirculate. The wire harness  280  is provided with electric wires which supply electric power to the fuel gas pump  250 . The gas-liquid separator  260  is connected with the manifold  130  and provided with a function to remove water from fuel gas which recirculated through the fuel cell stack  100 . The purge valve  270  is connected with the gas-liquid separator  260  and provided with a function to discharge water removed by the gas-liquid separator  260 . 
         [0028]    The fuel gas flow is described below. The fuel gas supplied from a fuel-gas supply source (not illustrated) is then supplied to the manifold  130  via a regulator and a piping. The fuel gas at high pressure which flows into the manifold  130  is depressurized by passing through the injectors  210  connected in parallel with the manifold  130 , after passing through the distribution piping  220 . A pressure of the fuel gas depressurized by the injector  210  is measured by the pressure sensor  230 . Note that when the depressurizing by the injector  210  is insufficient, the fuel gas is discharged from the pressure relief valve  240 . 
         [0029]    The fuel gas at low pressure discharged from the injector  210  passes through the flow paths formed in the manifold  130 , passes through the piping member  300  connected with the manifold  130 , and is then supplied to the fuel gas pump  250 . The fuel gas supplied to the fuel gas pump  250  passes through the manifold  130 , and is then supplied to the fuel cell stack  100 . The fuel gas which passed through the fuel cell stack  100  is again supplied to the fuel gas pump  250 , after moisture is separated from the fuel gas by passing through the gas-liquid separator  2600  Note that the fuel gas containing moisture and impurities is discharged to an exhaust pipe via the purge valve  270  provided to the gas-liquid separator  260 . 
         [0030]    Note that the term “fuel gas supply system” as used herein refers to a system for supplying fuel gas to the fuel cell stack  100  from the fuel-gas supply source, and the term “fuel gas recirculating system” as used herein refers to a system for resupplying to the fuel cell stack  100  the fuel gas discharged from the fuel cell stack  100 . Components of the fuel gas supply system include the injectors  210 , the distribution piping  220 , the pressure sensor  230 , the pressure relief valve  240 , and the piping member  300 . That is, the piping member  300  is a part of the fuel gas supply system. Components of the fuel gas recirculating system include the fuel gas pump  250 , the gas-liquid separator  260 , and the purge valve  270 . A junction between the fuel gas supply system and the fuel gas recirculating system exists in the fuel gas pump  250 . 
         [0031]      FIG. 2  is a schematic view illustrating a state where the plurality of auxiliary machines  200 , the piping member  300 , etc. are connected with the manifold  130 . 
         [0032]    As can also be seen from  FIG. 2 , the piping member  300  is provided with bent portions  310  ( 310   a ,  310   b ) so that the piping member  300  is curved. The bent portions  310  are formed to have a supply direction of fuel gas from the supply source being substantially opposite to a flowing direction of the fuel gas to the junction directions of an entry and an exit of the fuel gas are oriented substantially opposite). The phrase “supply direction of fuel gas from the supply source is substantially opposite to the flowing direction of the fuel gas to the junction” as used herein refers to a directional difference between the supply direction and the flowing direction being within a range of about 180 degrees to about 270 degrees. 
         [0033]      FIG. 3  illustrates a schematic view of the piping member  300  seen from above the vehicle (seen from positive Y-axis direction). Here, the junction between the fuel gas supply system and the fuel gas recirculating system is indicated as a point P, and the flowing direction of the fuel gas is indicated as a direction D. As can be seen from this drawing, since the piping member  300  is provided with the bent portions  310 , water which remains in the fuel gas recirculating system is prevented from flowing into the fuel gas supply system, thereby a corrosion of the fuel gas supply system components can be reduced. Particularly, this presents a remarkable effect when the fuel cell system is not operating (i.e., the remarkable effect can be achieved when the fuel gas is not flowing. The reason is described below. 
         [0034]    Here, it is assumed that water exists at the point P. When the vehicle to which the fuel cell system  10  is mounted is stopped at a place where the left side of the place is higher than the right side of the place (i.e., a downward sideway slope to the right side), although water which exists at the point P moves up to the bent portion  310   b , but it does not move further toward the upstream in the direction D. Moreover, when the vehicle to which the fuel cell system  10  is mounted is stopped at a horizontal place, or a place where either the front side or the rear side of the place is inclined upwardly, it is hard for the water which exists at the point P to move because the entry point and the exit point of the piping member  300  are substantially at the same height, as described later. Moreover, when the vehicle to which the fuel cell system  10  is mounted is stopped at a place where the right side of the place is higher than the left side of the place (i.e., a downward sideway slope to the left side), water which exists at the point P moves to the upstream in the direction D beyond the bent portion  310   b . As described above, since the bent portions  310  are provided in the piping member  300  so that the supply direction of fuel gas from the supply source is substantially opposite to the flowing direction of the fuel gas to the junction, water can be prevented from moving upstream of the fuel gas supply system from the point P. As a result, a corrosion of the fuel gas supply system due to water which remains in the fuel gas recirculating system can be prevented. In such a case, when ambient temperature drops below the freezing point, and the fuel cell system  10  causes a malfunction, such as malfunction of sensor(s) by frozen water adhering to the sensor(s). However, in this embodiment, the sensor(s) are provided upstream in the fuel gas supply system from the point P, and the bent portions  310  are formed, thereby reducing the adverse effects described above. 
         [0035]    As can be seen from  FIG. 3 , the plurality of auxiliary machines  200  are disposed. between the fuel cell stack  100 , and the piping member  300  including the bent portions  310  in the stacking direction of the fuel cell (Z-axis directions). Thus, a space between the fuel cell stack  100 , and the piping member  300  including the bent portions  310  can effectively be utilized. 
         [0036]      FIG. 4  illustrates a schematic view of the piping member  300  seen from the right side of the vehicle (seen from positive Z-axis direction). As can be seen from this drawing, the piping member  300  curves in a substantially horizontal plane. For this reason, the corrosion of the fuel gas supply system due to water which remains in the fuel gas recirculating system can be reduced without increasing in the height of the fuel cell system  10 . The phrase “substantially horizontal plane” as used herein refers to a plane of which inclination is less than ±15 degrees with respect to the horizontal plane. 
         [0037]      FIG. 5  is a schematic view of the piping member  300  seen from the rear side of the vehicle (seen from positive X-axis direction). As can be seen from  FIG. 5 , the fuel gas pump  250  is provided at a position so as to overlap with at least a part of the piping member  300  in the stacking direction of the fuel cell (Z-axis directions). Note that since the fuel gas pump  250  requires high power, the strength of the fuel gas pump  250  is higher than other auxiliary machines. Thus, when the piping member  300  is collided from the right side of the vehicle (from positive Z-axis direction) by another adjacent member, this another adjacent member collides the fuel gas pump  250  before the piping member  300  is completely divided. Therefore, the possible dividing of the piping member  300  can be reduced. 
         [0038]    Note that, in this embodiment, terminal portions of the fuel gas pump  250  are disposed at most distant locations from the fuel cell stack  100 . The terminal portions are configured to have a higher strength than other components of the fuel gas pump  250 . 
         [0039]    As illustrated in  FIG. 3 , the piping member  300  is comprised of a member  300   a , a member  300   b  and a member  300   e . The member  300   b  is made of elastic material, and the members  300   a  and  300   c  are made of metal. Thus, when the another adjacent member collides the piping member  300  from the right side of the vehicle (from positive Z-axis direction), the possible dividing of the piping member  300  can be reduced by the member  300   b  elastically deforming. 
         [0040]    As can be seen from  FIG. 5 , among the plurality of auxiliary machines, at least the part of the fuel gas pump  250  is located at the most distant position from the fuel cell stack  100  in the stacking directions (Z-axis directions) of the fuel cell. The injector  210 , the distribution piping  220 , the pressure sensor  230 , and the pressure relief valve  240  are disposed between the fuel cell stack  100  and the terminal portions of the fuel gas pump  250 , in the stacking direction (Z-axis directions) of the fuel cell. 
         [0041]      FIG. 6  is a schematic view of the piping member  300  seen from the front side of the vehicle (seen from positive X-axis direction). As can be seen from  FIG. 6 , the gas-liquid separator  260  and the purge valve  270  are disposed between the fuel cell stack  100  and the terminal portions of the fuel gas pump  250 , in the stacking direction of the fuel cell (Z-axis directions). 
         [0042]    Thus, when other adjacent members collides the plurality of auxiliary machines  200  from the right side of the vehicle (from positive Z-axis direction), the fuel gas pump  250  collides other adjacent members before other auxiliary machines collides. Therefore, the auxiliary machines which are weaker in strength than the fuel gas pump  250  can be protected. 
       B. Modification 
     B1. Modification 1 
       [0043]    In this embodiment, a part of the piping member  300  between the bent portion  310   a  and the bent portion  310   b  is straight or linear. However, the present invention does not limit the shape to the straight or linear shape. 
         [0044]      FIG. 7  is a schematic view illustrating a piping member in Modification 1. The piping member may be bent along a line W between the bent portion  310   a  and the bent portion  310   b.  Since the highest part of the piping member is lower than the height of the fuel cell stack  100 , the fuel cell system  10  can be prevented from becoming higher, or any part of the piping member exceeds upwardly the upper contour of the fuel cell stack  100 . 
         [0045]    The present invention is not limited to the embodiment and the modifications described above, and can be implemented in various structures without departing from the scope of the invention. For example, technical features in the embodiment and the modifications corresponding to technical features of each aspect cited in the section of “SUMMARY,” can suitably be substituted and/or combined in order to address some or all of the subjects described above, or in order to obtain some or all of the effects described above. The technical features can suitably be deleted if they are not described as essential matters in this specification.