Patent Publication Number: US-2022231318-A1

Title: Fuel cell system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2021-008044 filed on Jan. 21, 2021, the contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a fuel cell system. 
     Description of the Related Art 
     The fuel cell system includes a stacked member and a stack case that houses the stacked member. The stacked member includes a cell stack body, a first terminal member, and a second terminal member. The cell stack body is formed by stacking a plurality of power generation cells one another. The first terminal member and the second terminal member are provided respectively at both ends of the cell stack body in the stacking direction of the plurality of power generation cells. 
     The first terminal member is electrically connected to an electrical unit provided at an upper portion of the stack case via the first power lead-out member. The second terminal member is electrically connected to the electrical unit via the second power lead-out member. 
     For example, as disclosed in JP 2019-175719 A, a first through-hole through which a first power lead-out member is inserted and a second through-hole through which a second power lead-out member is inserted are formed in an upper wall portion of a stack case. A distance between the second through-hole and the second terminal member is shorter than a distance between the first through-hole and the second terminal member. 
     SUMMARY OF THE INVENTION 
     The stacked member is formed by stacking the first terminal member, a plurality of power generation cells, and the second terminal member inside the stack case, for example. In this case, a compression load is applied to the stacked member from the second terminal member toward the first terminal member. 
     Then, the position of the second terminal member in the stacking direction with respect to the first terminal member varies depending on the assembly tolerance of the plurality of power generation cells and the dimensional tolerance of each power generation cell. That is, the second power lead-out member and the second through-hole tend to be out of alignment from each other in the stacking direction. Therefore, the second power lead-out member may fail to be inserted into the second through-hole. If the length of each of the first through-hole and the second through-hole in the stacking direction is set to be large in advance, there is a problem in that the rigidity of the upper wall portion decreases. 
     An object of the present invention is to solve the above-described problems. 
     In an aspect of the present invention, a fuel cell system includes a stacked member and a stack case accommodating the stacked member, the stacked member having a cell stack body, a first terminal member and a second terminal member, the cell stack body being formed of a plurality of power generation cells stacked one another, the first terminal member and the second terminal member being disposed respectively at both ends of the cell stack body, further including a first power lead-out member electrically connected to the first terminal member, a second power lead-out member electrically connected to the second terminal member, wherein the stack case includes an upper wall portion with a first through-hole for inserting the first power lead-out member and a second through-hole for inserting the second power lead-out member, and a length of the second through-hole is greater than a length of the first through-hole in a stacking direction of the plurality of power generation cells. 
     According to the present invention, since the length of the second through-hole in the stacking direction is greater than the length of the first through-hole in the stacking direction, misalignment between the second power lead-out member and the second through-hole in the stacking direction can be compensated for by making the second through-hole elongated in the stacking direction. Thus, even when the position of the second terminal member with respect to the first terminal member in the stacking direction varies, the second power lead-out member can be reliably inserted into the second through-hole. In addition, because the length of the first through-hole does not become greater than necessary in the stacking direction, it is possible to suppress a decrease in rigidity of the stack case. 
     The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings, in which a preferred embodiment of the present invention is shown by way of illustrative example. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a longitudinal cross-sectional view of a fuel cell system according to an embodiment of the present invention; 
         FIG. 2  is a lateral cross-sectional view taken along line II-II of  FIG. 1 ; 
         FIG. 3  is a partially omitted cross-sectional view taken along line III-III of  FIG. 1 ; 
         FIG. 4  is an exploded perspective view of the cell stack of  FIG. 1 ; 
         FIG. 5  is a cross-sectional view taken along line V-V of  FIG. 4 ; 
         FIG. 6  is a plan view of the joined separator shown in  FIG. 4  as viewed from the second separator side; 
         FIG. 7  is an explanatory plan view of the case member shown in  FIG. 1  as seen from above; 
         FIG. 8  is an enlarged cross-sectional view illustrating the first power lead-out member and the second power lead-out member shown in  FIG. 1 ; 
         FIG. 9  is an explanatory view of a method of producing the fuel cell system shown in  FIG. 1 ; and 
         FIG. 10  is an explanatory view of a state in which the center of the second power lead-out member and the center of the second through-hole are out of alignment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A fuel cell system  10  shown in  FIG. 1  is to be mounted on, for example, a fuel cell electric vehicle (fuel cell vehicle) (not shown). In  FIGS. 1 to 3 , the fuel cell system  10  includes a fuel cell stack  12 , a fuel cell auxiliary device  14 , and an electrical unit  16 . 
     The fuel cell stack  12  includes a stacked member  18  and a case unit  20  that houses the stacked member  18 . The stacked member  18  includes a cell stack body  22  in which a plurality of power generation cells  21  are stacked. The fuel cell stack  12  is disposed such that the stacking direction (direction of the arrow A) of the plurality of power generation cells  21  extends horizontally. In the following description, the stacking direction of the plurality of power generation cells  21  may be simply referred to as a “stacking direction”. 
     In  FIG. 1 , a first terminal member  24   a  and a first insulating plate  26   a  are disposed outward (in the direction of the arrow A 1 ) in this order at one end (an end in the direction of the arrow A 1 ) in the stacking direction of the cell stack body  22 . A second terminal member  24   b  and a second insulating plate  26   b  are disposed outward (in the direction of the arrow A 2 ) in this order at the other end of the cell stack body  22  (an end in the direction of the arrow A 2 ) in the stacking direction. The stacked member  18  includes the cell stack body  22 , the first terminal member  24   a , the first insulating plate  26   a , the second terminal member  24   b , and the second insulating plate  26   b.    
     Each of the first terminal member  24   a  and the second terminal member  24   b  collects electric power generated by each power generation cell  21 . Each of the first terminal member  24   a  and the second terminal member  24   b  is formed in a plate shape (quadrangular plate shape). Each of the first terminal member  24   a  and the second terminal member  24   b  is made of a conductive metal material such as pure copper, a copper alloy, pure aluminum, or an aluminum alloy. 
     The first terminal member  24   a  is disposed in a first recess  28   a  formed in an inner surface (surface on the arrow A 2  side) of the first insulating plate  26   a . The first terminal member  24   a  is in electrical contact with the power generation cell  21  located at one end in the stacking direction (an end on the arrow A 1  side). The thickness of the first terminal member  24   a  in the stacking direction is greater than the thickness of the power generation cell  21 . 
     The second terminal member  24   b  is disposed in a second recess  28   b  formed in the inner surface (on the arrow A 1  side) of the second insulating plate  26   b . The second terminal member  24   b  is in electrical contact with the power generation cell  21  located at the other end in the stacking direction (on the arrow A 2  side). The thickness of the second terminal member  24   b  in the stacking direction is greater than the thickness of the power generation cell  21 . The shape and size of the first terminal member  24   a  and the second terminal member  24   b  can be set as appropriate. 
     Each of the first insulating plate  26   a  and the second insulating plate  26   b  is formed of, for example, an electrically insulating resin material into a quadrangular shape. 
     As shown in  FIG. 4 , the power generation cell  21  has a horizontally long rectangular shape. The power generation cell  21  includes a resin-framed membrane electrode assembly (hereinafter referred to as a “resin-framed MEA  30 ”), a first separator  32 , and a second separator  34 . The resin-framed MEA  30  is disposed between the first separator  32  and the second separator  34 . 
     Each of the first separator  32  and the second separator  34  is formed by press-forming a thin metal plate into a corrugated cross-sectional shape. The thin metal plate is, for example, a steel plate, a stainless steel plate, an aluminum plate, or a plated steel plate. The thin metal plate may be a stainless steel plate whose surface has been subjected to anti-corrosive surface treatment or an aluminum plate whose surface has been subjected to anti-corrosive surface treatment. The first separator  32  and the second separator  34  are joined to each other by a plurality of joining lines (not shown) to form a joined separator  33 . 
     The resin-framed MEA  30  includes a membrane electrode assembly (hereinafter referred to as “MEA  36 ”) and a resin-frame member  38  (resin-frame portion, resin film) that is joined to and surrounds an outer peripheral portion of the MEA  36 . 
     In  FIG. 5 , the MEA  36  includes an electrolyte membrane  40 , a cathode  42  provided on one surface  40   a  of the electrolyte membrane  40 , and an anode  44  provided on the other surface  40   b  of the electrolyte membrane  40 . The electrolyte membrane  40  is, for example, a solid polymer electrolyte membrane (cation exchange membrane). For example, the sold polymer electrolyte membrane is a thin membrane of perfluorosulfonic acid containing water. The electrolyte membrane  40  is sandwiched between the cathode  42  and the anode  44 . The electrolyte membrane  40  may be a fluorine-based electrolyte membrane or a hydrocarbon (HC)-based electrolyte membrane. 
     As shown in  FIG. 4 , an oxygen-containing gas supply passage  46   a , a coolant supply passage  48   a , and a fuel gas discharge passage  50   b  are provided in each of the power generation cells  21  at one end of a longer side. The one end in the longer side of the power generation cell  21  is an end portion of the power generation cell  21  in the arrow B 1  direction. The oxygen-containing gas supply passage  46   a , the coolant supply passage  48   a , and the fuel gas discharge passage  50   b  are arranged along the shorter side of the power generation cell  21 . The shorter side of the power generation cell  21  extends in the arrow C direction. 
     An oxygen-containing gas which is one of the reaction gases flows through the oxygen-containing gas supply passage  46   a  in the direction indicated by the arrow A 2 . A coolant (for example, pure water, ethylene glycol, oil, or the like) flows through the coolant supply passage  48   a  in the direction of the arrow A 2 . A fuel gas (e.g., a hydrogen-containing gas) which is the other of the reaction gases flows through the fuel gas discharge passage  50   b  in the direction indicated by the arrow A 1 . 
     A fuel gas supply passage  50   a , a coolant discharge passage  48   b , and an oxygen-containing gas discharge passage  46   b  are provided in each of the power generation cells  21  at the other end of in the longer side (the end portion in the arrow B 2  direction). The fuel gas supply passage  50   a , the coolant discharge passage  48   b , and the oxygen-containing gas discharge passage  46   b  are arranged in the direction indicated by the arrow C. 
     The fuel gas flows through the fuel gas supply passage  50   a  in the direction indicated by the arrow A 2 . The coolant flows through the coolant discharge passage  48   b  in the direction indicated by the arrow A 1 . The oxygen-containing gas flows through the oxygen-containing gas discharge passage  46   b  in the direction indicated by the arrow A 1 . 
     The arrangement, shape, and size of the above-described passages (such as the oxygen-containing gas supply passage  46   a ) are not limited to those in the present embodiment, and may be appropriately set according to required specifications. 
     As shown in  FIGS. 2 and 4 , the first separator  32  includes a first separator main body  52  having a metal plate shape. The first separator main body  52  has a surface facing the resin-framed MEA  30  (hereinafter referred to as a “front surface  52   a ”. The front surface  52   a  includes an oxygen-containing gas flow field  54  (reactant gas flow field) extending in the longer side (direction of the arrow B) of the power generation cell  21 . The oxygen-containing gas flow field  54  fluidly communicates with the oxygen-containing gas supply passage  46   a  and the oxygen-containing gas discharge passage  46   b . The oxygen-containing gas serving as the reactant gas is supplied to the cathode  42  from the oxygen-containing gas flow field  54 . 
     A first seal portion  56  for preventing leakage of a fluid, which is the reaction gas (oxygen-containing gas or fuel gas) or the coolant is provided on the front surface  52   a  of the first separator main body  52 . The first seal portion  56  is pressed against one surface  38   a  of the resin frame member  38  (see  FIG. 5 ). The first seal portion  56  extends linearly when viewed from the separator thickness direction (the arrow A direction). However, the first seal portion  56  may extend in a wavy shape when viewed from the separator thickness direction. 
     The first seal portion  56  includes a plurality of first passage seal portions  60  that individually surround the plurality of passages (such as the oxygen-containing gas supply passage  46   a ), and a first flow field seal portion  58  provided on the outer periphery of the first separator main body  52 . 
     As shown in  FIG. 5 , the first seal portion  56  includes a first seal bead portion  62  protruding toward the resin-framed MEA  30  and a first resin material  64  provided on the first seal bead portion  62 . The first seal bead portion  62  is formed integrally with the first separator main body  52  by press forming. The first seal bead portion  62  is elastically deformed by a compressive load in the direction of the arrow A. 
     As shown in  FIGS. 4 and 6 , the second separator  34  includes a second separator main body  66  having a metal plate shape. The second separator main body  66  has a surface facing the resin-framed MEA  30  (hereinafter referred to as a “front surface  66   a ”. The front surface  66   a  includes a fuel gas flow field  68  (reactant gas flow field) extending in the longer side (direction of arrow B) of the power generation cell  21 . The fuel gas flow field  68  fluidly communicates with the fuel gas supply passage  50   a  and the fuel gas discharge passage  50   b . The fuel gas serving as the reactant gas is supplied to the anode  44  from the fuel gas flow field  68 . 
     A second seal portion  70  for preventing leakage of the fluid, which is the reactant gas (oxygen-containing gas or fuel gas) or the coolant is provided on the front surface  66   a  of the second separator main body  66 . The second seal portion  70  is pressed against the other surface  38   b  of the resin frame member  38  (see  FIG. 5 ). The second seal portion  70  extends linearly when viewed in the separator thickness direction (the direction of the arrow A). However, the second seal portion  70  may extend in a wavy shape when viewed from the separator thickness direction. 
     The second seal portion  70  is disposed so as to overlap the first seal portion  56  when viewed from the stacking direction (the arrow A direction) of the plurality of power generation cells  21 . The second seal portion  70  includes a plurality of second passage seal portions  74  that individually surround the plurality of passages (e.g., the oxygen-containing gas supply passage  46   a ), and a second flow field seal portion  72  provided on the outer peripheral portion of the second separator main body  66 . 
     As shown in  FIG. 5 , the second seal portion  70  includes a second seal bead portion  76  protruding toward the resin-framed MEA  30  and a second resin material  78  provided on the second seal bead portion  76 . The second seal bead portion  76  is formed integrally with the second separator main body  66  by press forming. The second seal bead portion  76  is elastically deformed by a compressive load in the direction of arrow A. 
     In  FIG. 4 , a coolant flow field  80  that fluidly communicates with the coolant supply passage  48   a  and the coolant discharge passage  48   b  is formed between the back surface  52   b  of the first separator main body  52  and the back surface  66   b  of the second separator main body  66  that are joined to each other. The coolant flow field  80  is formed by the back surface shape of the first separator main body  52  and the back surface shape of the second separator main body  66  that are stacked together. 
     As shown in  FIGS. 2 to 4 and 6 , each power generation cell  21  is provided with four load receiving portions  82  (a first load receiving portion  82   a , a second load receiving portion  82   b , a third load receiving portion  82   c , and a fourth load receiving portion  82   d ). When an external load in the direction of the arrow B acts on the fuel cell stack  12 , the four load receiving portions  82  receive the external load. 
     Each load receiving portion  82  is joined to an outer edge portion of the power generation cell  21  so as to protrude outward from the power generation cell  21 . A positioning hole  88  is formed in each load receiving portion  82 . A rod (not shown) is inserted into the positioning holes  88  for positioning the power generation cells  21  in the plane direction at the time of producing the fuel cell stack  12  (at the time of stacking the power generation cells  21 ). 
     In  FIGS. 2 and 4 , the first load receiving portion  82   a  is provided on the first separator main body  52  so as to protrude downward (in the direction of the arrow C 1 ) from the lower end portion of the first separator main body  52 . The first load receiving portion  82   a  is located so as to be shifted from the center of the longer side of the first separator main body  52  in the arrow B 2  direction (in the width direction, in the direction indicated by the arrow B). 
     The second load receiving portion  82   b  is provided on the first separator main body  52  so as to protrude upward (in the direction of the arrow C 2 ) from the upper end portion of the first separator main body  52 . The second load receiving portion  82   b  is positioned so as to be shifted from the center of the longer side of the first separator main body  52  in the arrow B 1  direction. 
     In  FIGS. 4 and 6 , the third load receiving portion  82   c  is provided on the second separator main body  66  so as to protrude downward from the lower end portion of the second separator main body  66 . The third load receiving portion  82   c  is located so as to be shifted from the center of the longer side of the second separator main body  66  in the arrow B 2  direction (in the width direction, in the direction indicated by the arrow B). The third load receiving portion  82   c  faces the first load receiving portion  82   a.    
     The fourth load receiving portion  82   d  is provided on the second separator main body  66  so as to protrude upward from the upper end portion of the second separator main body  66 . The fourth load receiving portion  82   d  is located at a position shifted from the center of the longer side of the second separator main body  66  in the arrow B 1  direction. The fourth load receiving portion  82   d  faces the second load receiving portion  82   b.    
     As shown in  FIG. 1 , the case unit  20  has a quadrangular shape when viewed from a direction orthogonal to the arrow A direction, and the longer side thereof extends along the arrow A direction. The case unit  20  includes a stack case  90  forming a stack housing space S 1  for housing the stacked member  18 , and an auxiliary device case  92  forming an auxiliary machine housing space S 2  for housing the fuel-cell auxiliary device  14 . The stack case  90  and the auxiliary device case  92  are adjacent to each other in the direction of the arrow A. In other words, the auxiliary device case  92  is positioned on the arrow A 1  side of the stack case  90 . 
     The stack case  90  includes a quadrangular cylindrical peripheral wall case  94  that covers the outer peripheral surface of the stacked member  18 , a first end plate  96  disposed at one end (an end on the arrow A 1  side) of the peripheral wall case  94 , and a second end plate  98  disposed at the other end (an end on the arrow A 2  side) of the peripheral wall case  94 . That is, the stack housing space S 1  is defined by the peripheral wall case  94 , the first end plate  96 , and the second end plate portion  98 . 
     In  FIGS. 1 to 3 , the peripheral wall case  94  includes a lower wall portion  94   a , a pair of side wall portions  94   b ,  94   c  protruding upward from the lower wall portion  94   a , and an upper wall portion  94   d  connecting protruding ends of the pair of side wall portions  94   b ,  94   c  to each other. In  FIG. 2 , a first support portion  100  protruding upward is provided on an inner surface of the lower wall portion  94   a . The first support portion  100  extends in the direction of arrow A over the entire length of the peripheral wall case  94 . A first groove portion  102  that accommodates the first load receiving portion  82   a  and the third load receiving portion  82   c  is formed in the protruding end of the first support portion  100 . The first groove portion  102  extends along the arrow A direction. 
     The first support portion  100  is provided with two first support surfaces  104 . The two first support surfaces  104  are positioned so as to sandwich the first load receiving portion  82   a  and the third load receiving portion  82   c  in the direction of the arrow B. When an external load in the arrow B direction acts on the fuel cell stack  12 , the first load receiving portion  82   a  and the third load receiving portion  82   c  come into contact with one of the two first support surfaces  104 , thereby suppressing positional deviation of the plurality of power generation cells  21  in the arrow B direction. 
     As shown in  FIG. 2 , the upper wall portion  94   d  includes a first portion  106 , a second portion  108 , and a connecting portion  110 . The first portion  106  covers the second load receiving portion  82   b  and the fourth load receiving portion  82   d  from above. The second portion  108  is located below (in the direction of the arrow C 1 ) the outer surface (upper surface) of the first portion  106 . The connecting portion  110  connects the first portion  106  and the second portion  108  to each other. 
     The second portion  108  is positioned in the arrow B 2  direction with respect to the first portion  106 . Each of the first portion  106 , the second portion  108 , and the connecting portion  110  extends over the entire length of the peripheral wall portion  154  in the arrow A direction (see  FIG. 7 ). The connecting portion  110  extends so as to be inclined downward from the first portion  106  toward the second portion  108 . The connecting portion  110  is located above the center of the power generation cell  21  in the arrow B direction. The interval L 1  between the inner surface of the first portion  106  and the outer surface of the cell stack body  22  (the upper end of the joined separator  33 ) is wider than the interval L 2  between the inner surface of the second portion  108  and the outer surface of the cell stack body  22  (the upper end of the joined separator  33 ). 
     In  FIGS. 2 and 3 , a second support portion  112  protruding downward is provided on an inner surface of the first portion  106 . The second support portion  112  extends in the direction of the arrow A over the entire length of the peripheral wall case  94 . A second groove portion  114  that accommodates the second load receiving portion  82   b  and the fourth load receiving portion  82   d  is formed in the protruding end of the second support portion  112 . The second groove portion  114  extends along the arrow A direction. 
     The second support portion  112  is provided with two second support surfaces  116 . The two second support surfaces  116  are positioned so as to sandwich the second load receiving portion  82   b  and the fourth load receiving portion  82   d  in the direction of the arrow B. When an external load in the arrow B direction acts on the fuel cell stack  12 , the second load receiving portion  82   b  and the fourth load receiving portion  82   d  come into contact with one of the two second support surfaces  116 , thereby suppressing positional deviation of the plurality of power generation cells  21  in the arrow B direction. 
     As shown in  FIGS. 1 and 7 , a first through-hole  118  and a second through-hole  120  are formed in the first portion  106 . The upper wall portion  94   d  includes a first end located at one end (on the arrow A 1  side) in the stacking direction of the power generation cells  21  and a second end located at the other end (on the arrow A 2  side) in the stacking direction of the power generation cells  21 . The first through-hole  118  is located between the center and the first end of the upper wall portion  94   d  in the stacking direction of the power generation cells  21 . In other words, the first through-hole  118  is positioned closer to the first terminal member  24   a  side (the auxiliary device case  92  side, on the arrow A 1  side) than the center of the stacked member  18  in the longitudinal direction (the arrow A direction). The second through-hole  120  is located between the center and the second end of the upper wall portion  94   d  in the stacking direction of the power generation cells  21 . In other words, the second through-hole  120  is located closer to the second terminal member  24   b  (on the arrow A 2  side) than the center of the stacked member  18  in the longitudinal direction. That is, the second through-hole  120  is located closer to the second terminal member  24   b  than the first through-hole  118 . 
     In  FIG. 7 , the first through-hole  118  and the second through-hole  120  are positioned so as to be shifted on the arrow B 1  side from the center of the power generation cell  21  in the direction of the arrow B. The first through-hole  118  is formed in a perfect circular shape. The second through-hole  120  is an elongated hole elongated in the stacking direction (direction of the arrow A). Specifically, the second through-hole  120  is defined by the combination of a quadrangular central hollow portion  122  extending in the stacking direction, and two end hollow portions  124  provided at both ends of the central hollow portion  122  and connected to the central hollow portion  122  in the arrow A direction. Each of the end hollow portions  124  is formed in a substantially semicircular shape. That is, both ends of the second through-hole  120  in the stacking direction (the arrow A direction) are curved or arc-shaped. 
     The length L 3  of the second through-hole  120  in the stacking direction is greater than the length L 4  of the first through-hole  118  (the diameter of the first through-hole  118 ) in the stacking direction. A length L 5  of the second through-hole  120  (the central hollow portion  122 ) in the direction of the arrow B is the same as a length L 6  of the first through-hole  118  (a diameter of the first through-hole  118 ) in the direction of the arrow B. The center P 1  of the first through-hole  118  and the center P 2  of the second through-hole  120  are located on a single straight line La extending along the direction of the arrow A. 
     The shapes of the first through-hole  118  and the second through-hole  120  can be appropriately set. The first through-hole  118  is not limited to a perfect circular shape, and may be an elongated hole elongated along the direction of the arrow A (a shape similar to the second through-hole  120 ). Even in this case, the length L 3  of the second through-hole  120  in the stacking direction is greater than the length L 4  of the first through-hole  118  in the stacking direction. Each of the first through-hole  118  and the second through-hole  120  may have an elliptical shape longer in the stacking direction. The length L 6  of the first through-hole  118  in the direction of the arrow B may be different from a length L 5  of the second through-hole  120  in the direction of the arrow B. The center P 1  of the first through-hole  118  and the center P 2  of the second through-hole  120  may not be located on the single straight line La extending along the direction of the arrow A. 
     As shown in  FIG. 1 , the first end plate  96  is joined to the peripheral wall case  94  by bolts (not shown) so as to close a first opening portion  130  formed at one end of the peripheral wall case  94 . An annular seal member  132  made of an elastic material is interposed between the first end plate  96  and the peripheral wall case  94  along the outer periphery of the first opening portion  130 . 
     The second end plate  98  is joined to the peripheral wall case  94  by bolts  136  so as to close a second opening portion  134  formed at the other end of the peripheral wall case  94 . An annular seal member  138  made of an elastic material is interposed between the second end plate  98  and the peripheral wall case  94  along the outer periphery of the second opening portion  134 . When the second end plate  98  is fastened to the peripheral wall case  94  by the bolts  136 , a compressive load is applied to the cell stack body  22 . A plate-shaped shim  139  is provided between the second end plate  98  and the second insulating plate  26   b . The compressive load is adjusted by the thickness (number of sheets) of the shim  139 , and the position of the second terminal member  24   b  is displaced in the stacking direction. 
     The auxiliary device case  92  is a protective case for protecting the fuel-cell auxiliary device  14  housed in the auxiliary device housing space S 2 . Examples of the fuel cell auxiliary device  14  include a gas-liquid separator, an injector, an ejector, a fuel gas pump, and valves, which are not illustrated. The auxiliary device case  92  is formed by joining a box-shaped first case member  140  and a box-shaped second case member  142  to each other by bolt members  143 . The first case member  140  opens in the direction of the arrow A 1 . The second case member opens in a direction of the arrow A 2 . 
     The first end plate  96  serves as both a wall portion of the stack case  90  and a wall portion of the auxiliary device case  92 . In other words, the first end plate  96  is a partition wall between the stack housing space S 1  and the auxiliary device housing space S 2 . 
     In  FIGS. 1 and 2 , the electrical unit  16  is provided on an outer surface of an upper wall portion  94   d  of the stack case  90 . The electrical unit  16  includes electrical unit bodies  144  and an electrical component case  146  that houses the electrical unit bodies  144 . The electrical unit bodies  144  include a contactor (switch), a control unit, and the like. The control unit controls the voltage of the electric power generated by the fuel cell stack  12 . The electrical unit bodies  144  include a first terminal portion  145   a  in which a first hole  143   a  is formed and a second terminal portion  145   b  in which a second hole  143   b  is formed (see  FIG. 8 ). 
     The electrical component case  146  includes a case main body  148  whose upper side is open, and a cover  150  that closes the upper opening of the case main body  148 . The case main body  148  includes a bottom wall portion  152  and a peripheral wall portion  154  extending upward from an outer peripheral portion of the bottom wall portion  152 . The bottom wall portion  152  includes a first bottom wall portion  156  provided on an outer surface (upper surface) of the first portion  106  of the stack case  90 , a second bottom wall portion  158  provided on an outer surface (upper surface) of the second portion  108  of the stack case  90 , and a wall portion  160  connecting the first bottom wall portion  156  and the second bottom wall portion  158  to each other. 
     As shown in  FIGS. 1 and 8 , a first communication hole  162  communicating with the first through-hole  118  and a second communication hole  164  communicating with the second through-hole  120  are formed in the first bottom wall portion  156 . The first communication hole  162  is formed in the same size and shape as the first through-hole  118 . The center of the first communication hole  162  is located at a position overlapping the center P 1  of the first through-hole  118  or a position close to the center P 1  when viewed from above. The second communication hole  164  is formed in the same size and shape as the second through-hole  120 . The center of the second communication hole  164  is located at a position overlapping the center P 2  of the second through-hole  120  or a position close to the center P 2  when viewed from above. 
     The first communication hole  162  may be formed larger than the first through-hole  118 . Further, the second communication hole  164  may be formed larger than the second through-hole  120 . 
     As shown in  FIG. 8 , the fuel cell stack  12  includes a first power lead-out member  170   a  and a second power lead-out member  170   b  for leading out the power generated by each of the power generation cells  21  to the electrical unit  16 . 
     The first power lead-out member  170   a  electrically connects the first terminal member  24   a  and the first terminal portion  145   a  of the electrical unit body  144  to each other. The first power lead-out member  170   a  includes a first conductor portion  172   a  and a first connection portion  174   a.    
     The first conductor portion  172   a  is a bus bar formed in a band shape. The first conductor portion  172   a  is made of, for example, copper, aluminum, stainless steel, titanium, or a metal containing any of these as a main component. The first conductor portion  172   a  is an L-shaped integrally molded product. The first conductor portion  172   a  includes a first fixing portion  176   a  extending in the vertical direction (the direction of the arrow C) and a first extending portion  178   a  extending in the stacking direction (the direction of the arrow A). 
     One end portion (lower end portion) of the first fixing portion  176   a  is electrically connected to the first terminal member  24   a  by brazing, swaging, welding, screwing, or the like. The other end (upper end) of the first fixing portion  176   a  is located above the first insulating plate  26   a  (cell stack body  22 ). 
     The first extending portion  178   a  extends from the other end portion of the first fixing portion  176   a  in the arrow A 2  direction. The first extending portion  178   a  is located in the space S 3  between the first portion  106  of the upper wall portion  94   d  and the cell stack body  22 . In other words, the first extending portion  178   a  is spaced apart from both the cell stack body  22  and the first portion  106 . 
     In  FIGS. 2 and 3 , the first extending portion  178   a  is adjacent to the second support portion  112  on the arrow B 2  side of the second support portion  112 . The first extending portion  178   a  is separated from the second support portion  112 . 
     In  FIG. 8 , only one first mounting hole  180   a  is formed through the first extending portion  178   a  for mounting the first connecting portion  174   a . The first connection portion  174   a  is fixed to the first mounting hole  180   a  of the first conductor portion  172   a  in an immovable state. The first connection portion  174   a  includes a first connection portion main body  182   a  and a first fastening member  184   a.    
     The first connection portion main body  182   a  is made of, for example, copper, aluminum, stainless steel, titanium, or a metal containing any of these as a main component. The first connection portion main body  182   a  is formed in a cylindrical shape. The first connection portion main body  182   a  has an outer peripheral surface having a substantially circular cross section. The first connection portion main body  182   a  extends in the up-down direction (in the direction indicated by the arrow C) so as to pass through the first through-hole  118  and the first communication hole  162 . One end surface of the first connection portion main body  182   a  is in contact with an upper surface of the first extending portion  178   a . The other end surface of the first connection portion main body  182   a  is in contact with the lower surface of the first terminal portion  145   a.    
     In  FIG. 7 , the outer-diameter D 1  of the first connecting portion main body  182   a  is smaller than the lengths L 4  and L 6  of the first through-hole  118 . That is, a clearance is formed between the first connection portion main body  182   a  and the inner surface forming the first through-hole  118  so as to ensure electrical insulation. 
     As shown in  FIG. 8 , the first fastening member  184   a  fastens the first conductor portion  172   a  and the first terminal portion  145   a  to each other by screws. Specifically, the first fastening member  184   a  includes a first fixing nut  186   a  and a first bolt portion  188   a . The first fixing nut  186   a  is fixed to the first extending portion  178   a . The first bolt portion  188   a  is screwed into the first fixing nut  186   a  to fasten the first terminal portion  145   a  downward. 
     The first fixing nut  186   a  is fixed to the lower surface of the first extending portion  178   a  by welding or the like, for example. The first bolt portion  188   a  includes a first bolt body  190   a  and a first pressing portion  192   a  provided on the first bolt body  190   a . The first bolt body  190   a  extends in the up-down direction so as to be inserted through the first mounting hole  180   a  of the first extending portion  178   a , the inner hole of the first connection portion main body  182   a , and the first hole  143   a  of the first terminal portion  145   a.    
     One end of the first bolt body  190   a  is formed with a male screw portion  196   a  to be screwed into the female screw portion  194   a  of the first fixing nut  186   a . The other end of the first bolt body  190   a  is formed with a male screw portion  200   a  that is screwed into the female screw portion  198   a  formed in the first pressing portion  192   a . The outer diameter of the first pressing portion  192   a  is larger than the diameter (hole diameter) of the first hole  143   a  of the first terminal portion  145   a . That is, the first pressing portion  192   a  abuts on the upper surface of the first terminal portion  145   a.    
     The second power lead-out member  170   b  electrically connects the second terminal member  24   b  and the second terminal portion  145   b  of the electrical unit body  144  to each other. The second power lead-out member  170   b  includes a second conductor portion  172   b  and a second connection portion  174   b.    
     The second conductor portion  172   b  is a bus bar formed in a band shape. The second conductor portion  172   b  is made of the same material as that of the first conductor portion  172   a  described above. The second conductor portion  172   b  is an L-shaped integrally molded product. The second conductor portion  172   b  includes a second fixing portion  176   b  extending in the vertical direction (the direction of the arrow C) and a second extending portion  178   b  extends in the stacking direction (the direction of the arrow A). 
     One end portion (lower end portion) of the second fixing portion  176   b  is electrically connected to the second terminal member  24   b  by brazing, swaging, welding, screwing, or the like. The other end (upper end) of the second fixing portion  176   b  is located above the second insulating plate  26   b  (cell stack body  22 ). 
     The second extending portion  178   b  extends from the other end of the second fixing portion  176   b  in the arrow A 1  direction. The second extending portion  178   b  is located in the space S 3  between the first portion  106  of the upper wall portion  94   d  and the cell stack body  22 . In other words, the second extending portion  178   b  is spaced apart from both the cell stack body  22  and the first portion  106 . 
     In  FIGS. 2 and 3 , the second extending portion  178   b  is adjacent to the second support portion  112  in the arrow B 2  side of the second supporting portion. The second extending portion  178   b  is separated from the second support portion  112 . 
     In  FIG. 8 , only one second mounting hole  180   b  is formed through the second extending portion  178   b  for mounting the second connection portion  174   b . The second connection portion  174   b  is fixed to the second mounting hole  180   b  (mounting portion) of the second conductor portion  172   b  in an immovable state. The second connecting portion  174   b  includes a second connection portion main body  182   b  and a second fastening member  184   b.    
     The second connection portion main body  182   b  is formed of the same material as that of the first connection portion main body  182   a  described above. The second connection portion main body  182   b  is formed in a cylindrical shape. The second connection portion main body  182   b  has an outer peripheral surface having a round shape in cross section. The second connection portion main body  182   b  extends in the up-down direction (in the direction indicated by the arrow C) so as to pass through the second through-hole  120  and the second communication hole  164 . One end surface of the second connection portion main body  182   b  is in contact with an upper surface of the second extending portion  178   b . The other end surface of the second connection portion main body  182   b  is in contact with the lower surface of the second terminal portion  145   b.    
     In  FIG. 7 , the outer diameter D 2  of the second connecting portion main body  182   b  is the same size as the outer diameter D 1  of the first connecting portion main body  182   a , and is smaller than the lengths L 3  and L 5  of the second through-hole  120 . That is, a clearance is formed between the second connection portion main body  182   b  and the inner surface forming the second through-hole  120  so as to ensure electrical insulation. 
     As shown in  FIG. 8 , the second fastening member  184   b  fastens the second conductor portion  172   b  and the second terminal portion  145   b  to each other by screws. Specifically, the second fastening member  184   b  includes a second fixing nut  186   b  and a second bolt portion  188   b . The second fixing nut  186   b  is fixed to the second extending portion  178   b . The second bolt portion  188   b  is screwed into the second fixing nut  186   b  to fasten the second terminal portion  145   b  downward. 
     The second fixing nut  186   b  is fixed to the lower surface of the second extending portion  178   b  by welding or the like, for example. The second bolt portion  188   b  includes a second bolt body  190   b  and a second pressing portion  192   b  provided on the second bolt body  190   b . The second bolt body  190   b  extends in the up-down direction so as to be inserted through the second mounting hole  180   b  of the second extending portion  178   b , the inner hole of the second connection portion main body  182   b , and the second hole  143   b  of the second terminal portion  145   b.    
     One end portion of the second bolt body  190   b  is formed with a male screw portion  196   b  to be screwed into the female screw portion  194   b  of the second fixing nut  186   b . The other end portion of the second bolt body  190   b  is formed with a male screw portion  200   b  that is screwed into a female screw portion  198   b  formed in the second pressing portion  192   b . The outer diameter of the second pressing portion  192   b  is larger than the diameter (hole diameter) of the second hole  143   b  of the second terminal portion  145   b . That is, the second pressing portion  192   b  is in contact with the upper surface of the second terminal portion  145   b.    
     The operation of the fuel cell stack  12  configured as described above will be described below. 
     First, as shown in  FIG. 4 , the oxygen-containing gas is introduced from the oxygen-containing gas supply passage  46   a  into the oxygen-containing gas flow field  54  of the first separator member  32 . The oxygen-containing gas flows in the direction indicated by the arrow B along the oxygen-containing gas flow field  54  and is supplied to the cathode  42  on the MEA  36 . 
     On the other hand, as shown in  FIGS. 4 and 6 , the fuel gas is introduced from the fuel gas supply passage  50   a  into the fuel gas flow field  68  of the second separator  34 . The fuel gas moves in the direction of arrow B along the fuel gas flow field  68  and is supplied to the anode  44  of the MEA  36 . 
     Accordingly, in each MEA  36 , the oxygen-containing gas supplied to the cathode  42  and the fuel gas supplied to the anode  44  are consumed by electrochemical reactions in the first electrode catalyst layer and the second electrode catalyst layer. As a result, power generation is performed. 
     Next, as shown in  FIG. 4 , a remainder of the oxygen-containing gas supplied to and consumed at the cathode  42  is discharged in the direction indicated by the arrow A along the oxygen-containing gas discharge passage  46   b . Similarly, a remainder of the fuel gas supplied to and consumed at the anode  44  is discharged in the direction of the arrow A along the fuel gas discharge passage  50   b.    
     The coolant supplied to the coolant supply passage  48   a  is introduced into the coolant flow field  80  formed between the first separator member  32  and the second separator  34 . After being introduced into the coolant flow field  80 , the coolant flows in the direction of the arrow B. After cooling the MEA  36 , the coolant is discharged from the coolant discharge passage  48   b.    
     Next, a method of producing the fuel cell system  10  according to the present embodiment will be described. 
     As shown in  FIG. 9 , in the method of producing the fuel cell stack  12 , the first end plate  96  (only the first case member  140 ) is fixed to one end of the peripheral wall case  94 . Then, the first case member  140  is set on the support base  300  in a state in which the surface  97  of the first end plate  96  on the side opposite to the peripheral wall case  94  faces vertically downward. 
     Thereafter, the first insulating plate  26   a , the first terminal member  24   a , the plurality of power generation cells  21  (cell stack body  22 ), the second terminal member  24   b , the second insulating plate  26   b , and the shim  139  are stacked in the peripheral wall case  94  in this order to form the stacked member  18 . Then, the second end plate  98  is fastened to the other end of the peripheral wall case  94  by the bolts  136 . At this time, the second end plate portion  98  presses the second insulating plate  26   b  toward the cell stack body  22 . Thus, a compressive load is applied to the cell stack body  22 . 
     Subsequently, the fuel cell auxiliary device  14  is fixed to the first case member  140 , and the second case member  142  is attached to the first case member  140  so as to cover the fuel cell auxiliary device  14 . Thus, the production of the fuel cell stack  12  is completed. Subsequently, the electrical unit  16  is mounted on the upper wall portion  94   d  of the stack case  90  of the fuel cell stack  12 . 
     Specifically, the case main body  148  of the electrical component case  146  is fixed to the upper wall portion  94   d  of the stack case  90 . At this time, the first communication hole  162  is positioned above the first through-hole  118 . The second communication hole  164  is located above the second through-hole  120 . Next, the first conductor portion  172   a  and the first terminal portion  145   a  are connected to each other by the first connection portion  174   a . The second conductor portion  172   b  and the second terminal portion  145   b  are connected to each other by the second connection portion  174   b . Thereafter, the cover  150  is attached to the case main body  148 , thereby completing the production of the fuel cell system  10  of the present embodiment. 
     In this case, the fuel cell stack  12  according to the present embodiment has the following effects. 
     In the fuel cell stack  12  produced as described above, the position of the second terminal member  24   b  in the stacking direction with respect to the first terminal member  24   a  varies depending on the assembly tolerance of the plurality of power generation cells  21  and the dimensional tolerance of each power generation cell  21 . The assembly tolerance of the plurality of power generation cells  21  includes a difference between elastic deformation amounts (elastic deformation amounts of the first seal portion  56  and the second seal portion  70 ) of the power generation cells  21  in the stacking direction. 
     Therefore, as shown in  FIGS. 8 and 10 , the center of the second mounting hole  180   b  of the second conductor portion  172   b  and the center of the second through-hole  120  tend to be misaligned in the stacking direction. That is, the second connection portion main body  182   b  (the second power lead-out member  170   b ) and the center of the second through-hole  120  tend to be misaligned in the stacking direction. In other words, the second connecting portion main body  182   b  tends to be displaced in the arrow A 1  direction or the arrow A 2  direction with respect to the center P 2  of the second through-hole  120 . 
     However, in the present embodiment, the length L 3  of the second through-hole  120  in the stacking direction is greater than the length L 4  of the first through-hole  118  in the stacking direction. Therefore, the positional deviation in the stacking direction between the second power lead-out member  170   b  (second connection portion  174   b ) and the second through-hole  120  can be absorbed by making the second through-hole  120  in an elongated shape. Thus, even when the position of the second terminal member  24   b  with respect to the first terminal member  24   a  varies in the stacking direction, the second power lead-out member  170   b  (second connection portion  174   b ) can be reliably inserted into the second through-hole  120 . Further, since the length L 4  of the first through-hole  118  in the stacking direction does not become greater than necessary, it is possible to suppress rigidity of the stack case  90  from decreasing. 
     The stack case  90  includes a first end portion accommodating the first terminal member  24   a  and a second end portion accommodating the second terminal member  24   b . An auxiliary device case  92  for protecting the fuel cell auxiliary device  14  is provided at the first end portion of the stack case  90 . 
     According to such a configuration, the power generation cells  21  can be stacked with the auxiliary device case  92  using as a base. 
     The second power lead-out member  170   b  includes a second conductor portion  172   b  located inside the stack case  90  and electrically connected to the second terminal member  24   b , and a second connection portion  174   b  electrically connected to the second conductor portion  172   b  and extending in the vertical direction so as to pass through the second through-hole  120 . 
     According to such a configuration, after the stacked member  18  is disposed in the stack case  90 , the second connection portion  174   b  can be connected to the second conductor portion  172   b  from the outside of the stack case  90 . 
     The second connection portion  174   b  has an outer peripheral surface having a round shape in cross section, and both ends of the second through-hole  120  in the stacking direction are curved or arc-shaped when viewed from above. 
     According to such a configuration, contact (ground fault) between the second connection portion  174   b  and the inner surface forming the second through-hole  120  can be effectively suppressed. 
     The second through-hole  120  includes a quadrangular central hollow portion  122  extending in the stacking direction and substantially semicircular end hollow portions  124  provided at both ends of the central hollow portion and connected to the central hollow portion. 
     According to such a configuration, the second through-hole  120  can be elongated in the stacking direction without extending the second through-hole  120  more than necessary in the arrow B direction orthogonal to the stacking direction. 
     Each of the plurality of power generation cells  21  is provided with a load receiving portion  82  protruding upward. The upper wall portion  94   d  includes a first portion  106  located above the load receiving portion  82 , a second portion  108  located below the outer surface of the first portion  106 , and a connecting portion  110  that connects the first portion  106  and the second portion  108  to each other. A first through-hole  118  and a second through-hole  120  are formed in the first portion  106 , and the first power lead-out member  170   a  (first conductor portion  172   a ) and the second power lead-out member  170   b  (second conductor portion  172   b ) are disposed in a space between the first portion  106  and the cell stack body  22 . 
     According to such a configuration, the space above the second portion  108  can be effectively used. 
     The electrical unit  16  to which the first power lead-out member  170   a  and the second power lead-out member  170   b  are electrically connected is disposed on the outer surface of the second portion  108 . 
     According to such a configuration, a total height dimension of the stack case  90  and the electrical unit  16  can be suppressed to be relatively small. This makes it possible to reduce the size of the fuel cell system  10 . 
     The present invention is not limited to the embodiments described above, and various modifications are possible without departing from the essence and gist of the invention. 
     The above embodiments can be summarized as follows. 
     The above-described embodiment discloses the fuel cell system ( 10 ) includes the stacked member ( 18 ) and the stack case ( 90 ) accommodating the stacked member, the stacked member having the cell stack body ( 22 ), the first terminal member ( 24   a ) and the second terminal member ( 24   b ), the cell stack body being formed of the plurality of power generation cells ( 21 ) stacked one another, the first terminal member and the second terminal member being disposed at both ends of the cell stack body, further including the first power lead-out member ( 170   a ) electrically connected to the first terminal member, and the second power lead-out member ( 170   b ) electrically connected to the second terminal member, wherein the stack case includes the upper wall portion ( 94   d ) with the first through-hole ( 118 ) for inserting the first power lead-out member and the second through-hole ( 120 ) for inserting the second power lead-out member, and a length (L 3 ) of the second through-hole is greater than a length (L 4 ) of the first through-hole in a stacking direction of the plurality of power generation cells. 
     In the above-described fuel cell system, the stack case may include the first end portion accommodating the first terminal member and the second end portion accommodating the second terminal member, and the auxiliary device case ( 92 ) for protecting the fuel cell auxiliary device ( 14 ) may be provided at the first end portion of the stack case. 
     In the above-described fuel cell system, the second power lead-out member may include the conductor portion ( 172   b ) located in the stack case and electrically connected to the second terminal member, and the connection portion ( 174   b ) electrically connected to the conductor portion and extending in the vertical direction so as to pass into the second through-hole. 
     In the above-described fuel cell system, the connecting portion may have an outer peripheral surface having a round shape in cross section, and both ends of the second through-hole in the stacking direction may be curved or arc-shaped when viewed from above. 
     In the fuel cell system described above, the second through-hole may include the rectangular central hollow portion ( 122 ) extending in the stacking direction and substantially semicircular end hollow portions ( 124 ) provided at both ends of the central hollow portion and connected to the central hollow portion. 
     The center (P 1 ) of the first through-hole and the center (P 2 ) of the second through-hole may be located on a single straight line (La) extending along the stacking direction. 
     In the fuel-cell system described above, the length (L 6 ) of the first through-hole in the direction orthogonal to the stacking direction may be the same as the length (L 5 ) of the second through-hole in the direction orthogonal to the stacking direction. 
     In the above-described fuel-cell system, each of the plurality of power generation cells may be provided with the load receiving portion ( 82 ) protruding upward, and the upper wall portion may include the first portion ( 106 ) located above the load receiving portion, the second portion ( 108 ) located below the outer surface of the first portion, and the connecting portion ( 110 ) coupling the first portion and the second portion, the first through-hole and the second through-hole may be formed in the first portion, and the first power outlet member and the second power outlet member may be disposed in the space (S 3 ) between the first portion and the cell stack body. 
     In the above-described fuel cell system, the electrical unit ( 16 ) to which the first power lead-out member and the second power lead-out member are electrically connected may be disposed on the outer surface of the second portion. 
     In the above fuel cell system, the first through-hole may be formed in a perfect circular shape.