Abstract:
An objective of the present invention is to allow desirably installing a fuel cell stack in an installation site with a simple and compact configuration. The fuel cell stack comprises an end plate. A pair of mount parts are integrally disposed on the end plate protruding downward on both sides of the lower end part thereof by a depression part being disposed on the lower end part of the end plate. The mount parts are anchored in the installation site for installing the fuel cell stack. Some screws are positioned in the mount parts to anchor to the end plate manifold members which link to a fuel gas supply connector hole and an oxidant gas exhaust connector hole of the fuel cell stack.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a fuel cell stack including a plurality of unit cells stacked together in a horizontal direction. Each of the unit cells is formed by stacking an electrolyte electrode assembly and separators. The electrolyte electrode assembly includes an electrolyte and electrodes provided respectively on both sides of the electrolyte. 
       BACKGROUND ART 
       [0002]    For example, a solid polymer electrolyte fuel cell employs a polymer ion exchange membrane as an electrolyte membrane, and the polymer electrolyte membrane is interposed between an anode and a cathode to form a membrane electrode assembly (MEA). The membrane electrode assembly and a pair of separators sandwiching the membrane electrode assembly make up a unit cell. In the fuel cell of this type, in use, typically, a predetermined number of the unit cells are stacked together, and terminal plates, insulating plates, and end plates are provided at both ends in the stacking direction to form a fuel cell stack, e.g., mounted in a vehicle. 
         [0003]    In some cases, the fuel cell stack of this type adopts so called internal manifold structure where fluid passages are formed in the fuel cell stack for allowing a fuel gas, an oxygen-containing gas, and a coolant to flow in the stacking direction of the unit cells. For this purpose, in the fuel cell stack, manifold members connected to the fluid passages are attached to the end plates. 
         [0004]    In this regard, the fuel cell stack adopts various types of mounting structures for fixing the fuel cell stack to an installation position such as a fuel cell vehicle. For example, in a fuel cell stack disclosed in Japanese Patent No. 4165876, as shown in  FIG. 11 , a stack body  1  formed by stacking a plurality of unit cells is placed in a box-shaped casing  2 . The casing  2  includes end plate  3   a ,  3   b.    
         [0005]    Manifold piping members  4   a ,  4   b  are attached to one of the end plates  3   a  using a plurality of screws (tightening members)  5   a . Further, mount brackets  6  are fixed to lower ends of the end plates  3   a ,  3   b  using screws  5   b , respectively. Each of the mount brackets  6  is fixed to an installation position (e.g., vehicle body of an automobile) using a plurality of screws  5   c.    
       SUMMARY OF INVENTION 
       [0006]    In the fuel cell stack, the mount brackets  6  are fixed to the end plate  3   a ,  3   b , respectively, only using the screws  5   b . Therefore, the mount brackets  6  themselves need to have sufficient rigidity. Thus, the mount brackets  6  may have a considerably large size undesirably. 
         [0007]    Further, since the mount brackets  6  are fixed to the end plates  3   a ,  3   b  using the screws  5   b , significant space is required for providing the screws  5   b . Consequently, in some cases, the end plates  3   a ,  3   b  themselves may have a large size. 
         [0008]    The present invention has been made to solve the problem of this type, and an object of the present invention is to provide a fuel cell stack having simple and compact structure which makes it possible to provide the fuel stack at an installation position suitably. 
         [0009]    The present invention relates to a fuel cell stack including a stack body formed by stacking a plurality of unit cells together in a horizontal direction and end plates provided at both ends of the stack body in a stacking direction. Each of the unit cells is formed by stacking an electrolyte electrode assembly and separators. The electrolyte electrode assembly includes an electrolyte and electrodes provided respectively on both sides of the electrolyte. A fluid passage is formed in the stack body for allowing at least a fuel gas, an oxygen-containing gas, or a coolant to flow through the fluid passage in the stacking direction. 
         [0010]    In the fuel cell stack, a manifold member connected to the fluid passage is fixed to at least one of the end plates using tightening members, and a recess is formed at a lower end of the end plate to provide a pair of mount sections integrally with the lower end. The mount sections protrude downward from both sides of the recess in the lower end. Further, the pair of mount sections are fixed to an installation portion on which the fuel cell stack is installed. 
         [0011]    Further, preferably, in the fuel cell stack, at least part of the tightening members are provided in the pair of mount sections. 
         [0012]    Further, preferably, in the fuel cell stack, a surface of the end plate for attachment of the manifold member includes the mount section and is flat. 
         [0013]    Further, preferably, in the fuel cell stack, a plurality of the recesses are formed at a lower end of the end plate. 
         [0014]    Further, preferably, in the fuel cell stack, in the end plate, a bottom of the mount section is fixed by use of a screw. 
         [0015]    In the present invention, since the pair of mount sections are provided integrally with the lower end of the end plate, and protrude downward from both sides in the lower end of the end plate, the structure of the mount sections is simplified, and the number of components is reduced suitably. Thus, with the simple and compact structure, it becomes possible to install the fuel cell stack at the installation portion suitably. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0016]      FIG. 1  is a perspective view schematically showing a fuel cell stack according to a first embodiment of the present invention; 
           [0017]      FIG. 2  is an exploded perspective view showing main components of a unit cell of the fuel cell stack; 
           [0018]      FIG. 3  is a front view showing the fuel cell stack; 
           [0019]      FIG. 4  is a perspective view schematically showing a fuel cell stack according to a second embodiment of the present invention; 
           [0020]      FIG. 5  is an exploded perspective view showing main components of a unit cell of the fuel cell stack; 
           [0021]      FIG. 6  is a front view of the fuel cell stack as viewed from one of end plates of the fuel cell stack; 
           [0022]      FIG. 7  is a front view of the fuel cell stack as viewed from the other of the end plates of the fuel cell stack; 
           [0023]      FIG. 8  is a perspective view schematically showing a fuel cell stack according to a third embodiment of the present invention; 
           [0024]      FIG. 9  is a front view of the fuel cell stack as viewed from one of end plates of the fuel cell stack; 
           [0025]      FIG. 10  is a front view of the fuel cell stack as viewed from the other of the end plates of the fuel cell stack; and 
           [0026]      FIG. 11  is a perspective view showing a fuel cell stack disclosed in Japanese Patent No. 4165876. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0027]    As shown in  FIG. 1 , a fuel cell stack  10  according to a first embodiment of the present invention includes unit cells  12 , and a plurality of the unit cells  12  are stacked together in an upright posture in a horizontal direction indicated by an arrow A to form a stack body  14 . At both ends of the stack body  14  in the stacking direction, end plates  16   a ,  16   b  are provided. The end plates  16   a ,  16   b  are fixed to both ends of a plurality of coupling bars  18  using screws  20  to apply a tightening load to the stack body  14  in the stacking direction. 
         [0028]    Instead of the coupling bars  18 , tie-rods may be used. Alternatively, the stack body  14  may be placed in a box. Though not shown, terminal plates and insulating plates are provided between the stack body  14  and the end plates  16   a ,  16   b.    
         [0029]    As shown in  FIG. 2 , each of the unit cells  12  includes a membrane electrode assembly  22  and a first metal separator  24  and a second metal separator  26  sandwiching the membrane electrode assembly  22 . 
         [0030]    The first metal separator  24  and the second metal separator  26  are made of, e.g., metal plates such as steel plates, stainless steel plates, aluminum plates, plated steel sheets, or metal plates having anti-corrosive surfaces by surface treatment. The first metal separator  24  and the second metal separator  26  have rectangular planar surfaces, and are formed by corrugating metal thin plates by press forming to have a corrugated shape in cross section and a wavy shape on the surface. Instead of the first metal separator  24  and the second metal separator  26 , for example, carbon separators may be used. 
         [0031]    Each of the first metal separator  24  and the second metal separator  26  has a laterally elongated rectangular shape including long sides orientated in the horizontal direction indicated by an arrow B and short sides oriented in the gravity direction indicated by an arrow C (The first metal separator  24  and the second metal separator  26  are stacked in the horizontal direction.). Alternatively, the short sides of the first metal separator  24  and the second metal separator  26  may be oriented in the horizontal direction and the long sides of the first metal separator  24  and the second metal separator  26  may be oriented in the gravity direction. 
         [0032]    At one end of the unit cell  12  in the long-side direction indicated by the arrow B, an oxygen-containing gas supply passage  28   a  for supplying an oxygen-containing gas and a fuel gas supply passage  30   a  for supplying a fuel gas, e.g., a hydrogen-containing gas, are provided. The oxygen-containing gas supply passage  28   a  and the fuel gas supply passage  30   a  extend through the unit cell  12  in the direction indicated by the arrow A. 
         [0033]    At the other end of the unit cell  12  in the long-side direction, a fuel gas discharge passage  30   b  for discharging the fuel gas and an oxygen-containing gas discharge passage  28   b  for discharging the oxygen-containing gas are provided. The fuel gas discharge passage  30   b  and the oxygen-containing gas discharge passage  28   b  extend through the unit cell  12  in the direction indicated by the arrow A. 
         [0034]    At both ends of the unit cell  12  in the short-side direction indicated by the arrow C, two coolant supply passages  32   a  for supplying a coolant are provided on one side (adjacent to the reactant gas inlet). On the other side (adjacent to the reactant gas outlet) at both ends of the unit cell  12  in the short-side direction, two coolant discharge passages  32   b  for discharging a coolant are provided. The coolant supply passages  32   a  and the coolant discharge passages  32   b  extend through the unit cell  12  in the direction indicated by the arrow A. 
         [0035]    The membrane electrode assembly  22  includes a solid polymer electrolyte membrane  34 , and a cathode  36  and an anode  38  sandwiching the solid polymer electrolyte membrane  34 . The solid polymer electrolyte membrane  34  is formed by impregnating a thin membrane of perfluorosulfonic acid with water, for example. 
         [0036]    Each of the cathode  36  and the anode  38  has a gas diffusion layer (not shown) such as a carbon paper, and an electrode catalyst layer (not shown) of platinum alloy supported on porous carbon particles. The carbon particles are deposited uniformly on the surface of the gas diffusion layer. The electrode catalyst layer of the cathode  36  and the electrode catalyst layer of the anode  38  are formed on both surfaces of the solid polymer electrolyte membrane  34 , respectively. 
         [0037]    The first metal separator  24  has an oxygen-containing gas flow field  40  on its surface  24   a  facing the membrane electrode assembly  22 . The oxygen-containing gas flow field  40  is connected to the oxygen-containing gas supply passage  28   a  and the oxygen-containing gas discharge passage  28   b . The oxygen-containing gas flow field  40  includes a plurality of flow grooves in a wavy pattern extending in the direction indicated by the arrow B. 
         [0038]    The second metal separator  26  has a fuel gas flow field  42  on its surface  26   a  facing the membrane electrode assembly  22 . The fuel gas flow field  42  is connected to the fuel gas supply passage  30   a  and the fuel gas discharge passage  30   b . The fuel gas flow field  42  includes a plurality of flow grooves in a wavy pattern extending in the direction indicated by the arrow B. 
         [0039]    A coolant flow field  44  is formed between a surface  26   b  of the second metal separator  26  and a surface  24   b  of the first metal separator  24 . The coolant flow field  44  is connected to the coolant supply passages  32   a ,  32   a  and the coolant discharge passages  32   b ,  32   b . In the coolant flow field  44 , the coolant flows over the electrode area of the membrane electrode assembly  22 . 
         [0040]    A first seal member  46  is formed integrally with the surfaces  24   a ,  24   b  of the first metal separator  24  around the outer circumferential end of the first metal separator  24 . A second seal member  48  is formed integrally with the surfaces  26   a ,  26   b  of the second metal separator  26  around the outer circumferential end of the second metal separator  26 . Each of the first seal member  46  and the second seal member  48  is made of seal material, cushion material, or packing material such as an EPDM, an NBR, a fluoro rubber, a silicone rubber, a fluorosilicone rubber, a butyl rubber, a natural rubber, a styrene rubber, a chloroprene rubber, an acrylic rubber, etc. 
         [0041]    As shown in  FIGS. 1 and 3 , recesses  50   a ,  50   b  are formed at central portions in lower ends of the end plates  16   a ,  16   b , respectively, so that a pair of mount sections  52   a  and a pair of mount sections  52   b  are formed integrally with the end plates  16   a ,  16   b . The mount sections  52   a ,  52   b  protrude downward from both sides in the lower ends of the end plates  16   a ,  16   b . Each of the recesses  50   a ,  50   b  is a rectangular opening having an area size of a distance L spaced upward from a lower end position of the end plate  16   a ,  16   b  and a distance H in the horizontal direction. As described later, the distance L and the distance H are determined depending on the positions where manifold members are attached. 
         [0042]    A screw hole  54   a ,  54   b  is formed at each of the bottoms of the mount sections  52   a ,  52   b . A plurality of screw holes  54   a  and a plurality of screw holes  54   b  may be formed. Screws  56  are screwed into the screw holes  54   a ,  54   b  to fix the mount sections  52   a ,  52   b  to an installation position, e.g., a vehicle body frame (not shown) of a fuel cell electric vehicle directly or through other members such as a cover member (not shown) or a bracket. The entire surfaces of the end plates  16   a ,  16   b  including the mount sections  52   a ,  52   b  are flat. 
         [0043]    Manifold members  60 ,  62  are attached to the end plate  16   a  at upper and lower positions, at one end in the long-side direction, using a plurality of screws (tightening members)  63 , respectively. The manifold member  60  includes a pipe  60   a  connected to the oxygen-containing gas supply passage  28   a , and the manifold member  62  includes a pipe  62   a  connected to the fuel gas supply passage  30   a . The tightening members are not limited to the screws  63 . Commonly used mechanical clamp mechanisms may be used. 
         [0044]    Manifold members  64 ,  66  are attached to the end plate  16   a  at upper and lower positions, at the other end in the long-side direction, using a plurality of screws  63 , respectively. The manifold member  64  includes a pipe  64   a  connected to the fuel gas discharge passage  30   b , and the manifold member  66  includes a pipe  66   a  connected to the oxygen-containing gas discharge passage  28   b.    
         [0045]    A manifold member  68  is attached to the end plate  16   a  at an upper end in the short-side direction using a plurality of screws  63 , and a manifold member  70  is attached to the end plate  16   a  at a lower end in the short-side direction using a plurality of screws  63 . The manifold member  68  includes a pipe  68   a  connected to the coolant supply passage  32   a  and a pipe  68   b  connected to the coolant discharge passage  32   b . The manifold member  70  includes a pipe  70   a  connected to the coolant supply passage  32   a  and a pipe  70   b  connected to the coolant discharge passage  32   b.    
         [0046]    In the manifold members  62 ,  66 , the lower screws  63  serving as tightening points are disposed within the mount sections  52   a ,  52   b . The lower screws  63  are positioned within an area of the recess  50   a  in the horizontal direction, i.e., within an area of the height L of the recess  50   a  (in the direction indicated by the arrow C). The distance L and the distance H of the recess  50   a  are determined to have maximum values by which, in particular, the manifold members  62 ,  66 , and  70  can be fixed efficiently to the end plate  16   a  by the screws  63 . 
         [0047]    Operation of the fuel cell stack  10  having the above structure will be described below. 
         [0048]    Firstly, as shown in  FIGS. 1 and 3 , an oxygen-containing gas is supplied from the pipe  60   a  to the oxygen-containing gas supply passage  28   a , and a fuel gas such as a hydrogen containing gas is supplied from the pipe  62   a  to the fuel gas supply passage  30   a . Further, a coolant such as pure water, ethylene glycol, oil, or the like is supplied from the pipes  68   a ,  70   a  to the pair of the coolant supply passages  32   a.    
         [0049]    Thus, as shown in  FIG. 2 , the oxygen-containing gas flows from the oxygen-containing gas supply passage  28   a  into the oxygen-containing gas flow field  40  of the first metal separator  24 . The oxygen-containing gas flows along the oxygen-containing gas flow field  40  in the direction indicated by the arrow B, and the oxygen-containing gas is supplied to the cathode  36  of the membrane electrode assembly  22 . 
         [0050]    The fuel gas is supplied from the fuel gas supply passage  30   a  to the fuel gas flow field  42  of the second metal separator  26 . The fuel gas moves along the fuel gas flow field  42  in the direction indicated by the arrow B, and then, the fuel gas is supplied to the anode  38  of the membrane electrode assembly  22 . 
         [0051]    Thus, in the membrane electrode assembly  22 , the oxygen-containing gas supplied to the cathode  36 , and the fuel gas supplied to the anode  38  are consumed in electrochemical reactions at catalyst layers of the cathode  36  and the anode  38  for generating electricity. 
         [0052]    Then, the oxygen-containing gas consumed at the cathode  36  of the membrane electrode assembly  22  flows along the oxygen-containing gas discharge passage  28   b  in the direction indicated by the arrow A, and the oxygen-containing gas is discharged from the pipe  66   a  (see  FIG. 3 ). In the meanwhile, the fuel gas consumed at the anode  38  of the membrane electrode assembly  22  flows along the fuel gas discharge passage  30   b  in the direction indicated by the arrow A, and the fuel gas is discharged from the pipe  64   a  (see  FIG. 3 ). 
         [0053]    Further, as shown in  FIG. 2 , the coolant supplied to the pair of coolant supply passages  32   a  flows into the coolant flow field  44  between the first metal separator  24  and the second metal separator  26 . After the coolant temporarily flows inward in the direction indicated by the arrow C, the coolant moves in the direction indicated by the arrow B to cool the membrane electrode assembly  22 . After the coolant moves outward in the direction indicated by the arrow C, the coolant flows through the pair of coolant discharge passages  32   b , and then is discharged from the pipes  68   b ,  70   b.    
         [0054]    In the first embodiment, as shown in  FIGS. 1 and 3 , the recesses  50   a ,  50   b  are formed at central portions in lower ends of the end plates  16   a ,  16   b , respectively, whereby the pairs of mount sections  52   a ,  52   b  are provided integrally with the end plates  16   a ,  16   b , respectively. The mount sections  52   a ,  52   b  protrude downward from both sides in the lower ends of the end plates  16   a ,  16   b . In the structure, in comparison with the case where members separate from the end plates  16   a ,  16   b  are used as mounting structure, the structure of the mount sections  52   a ,  52   b  is simplified significantly, and the number of components is reduced suitably and economically. 
         [0055]    Further, as shown in  FIG. 3 , the screws (tightening members)  63  for fixing, to the end plate  16   a , the manifold members  62 ,  66  connected to the fuel gas supply passage  30   a  and the oxygen-containing gas discharge passage  28   b  of the fuel cell stack  10  are disposed within the mount section  52   a . Therefore, the size of the end plates  16   a ,  16   b  in the height direction indicated by the arrow C is reduced as much as possible. With the simple and compact structure, it becomes possible to provide the fuel cell stack  10  at the installation position suitably and advantageously. 
         [0056]      FIG. 4  is a perspective view schematically showing a fuel cell stack  80  according to a second embodiment of the present invention. The constituent elements that are identical to those of the fuel cell stack  10  according to the first embodiment are labeled with the same reference numerals, and description thereof will be omitted. 
         [0057]    The fuel cell stack  80  includes a stack body  14  formed by stacking a plurality of unit cells  82  together in an upright posture in a horizontal direction indicated by an arrow A. 
         [0058]    At both ends of the stack body  14  in the stacking direction, end plates  84   a ,  84   b  are provided. The end plates  84   a ,  84   b  are fixed using a plurality of coupling bars  18 . Both end surfaces of the coupling bars  18  abut against the inner plate surfaces of the end plates  84   a ,  84   b . Screws  20  are screwed from the outer plate surfaces of the end plates  84   a ,  84   b  into the end surfaces of the coupling bars  18  in the stacking direction. 
         [0059]    As shown in  FIG. 5 , the unit cell  82  includes a membrane electrode assembly  86  and a first metal separator  88  and a second metal separator  90  sandwiching the membrane electrode assembly  86 . In the unit cell  82 , the flow direction of the oxygen-containing gas in the oxygen-containing gas supply passage  28   a  and the fuel gas in the fuel gas supply passage  30   a  in the stacking direction is opposite to the flow direction of the coolant in the coolant supply passages  32   a  in the stacking direction. Likewise, the flow direction of the oxygen-containing gas in the oxygen-containing gas discharge passage  28   b  and the fuel gas in the fuel gas discharge passage  30   b  in the stacking direction is opposite to the flow direction of the coolant in the coolant discharge passages  32   b  in the stacking direction. 
         [0060]    As shown in  FIGS. 4 and 6 , recesses  92   a ,  92   b  are formed at central portions in lower ends of the end plates  84   a ,  84   b . Recesses  94   a ,  96   a  are formed on both sides of the recess  92   a  at a predetermined distance. Recesses  94   b ,  96   b  are formed on both sides of the recess  92   b  at a predetermined distance. 
         [0061]    A pair of mount sections  98   a ,  100   a  are provided at the lower end of the end plate  84   a , between the recesses  92   a  and  94   a , and between the recesses  92   a  and  96   a . A pair of mount sections  102   a ,  104   a  are provided outside the recesses  94   a  and  96   a . Likewise, mount sections  98   b ,  100   b ,  102   b , and  104   b  are provided on the end plates  84   b  through recesses  92   b ,  94   b , and  96   b.    
         [0062]    Manifold members  106 ,  108  are attached to one end of the end plate  84   a  in the long-side direction, at upper and lower positions using screws  63 . The manifold member  106  includes a pipe  106   a  connected to the oxygen-containing gas supply passage  28   a , and the manifold member  108  includes a pipe  108   a  connected to the fuel gas supply passage  30   a . Manifold members  110 ,  112  are attached to the other end of the end plate  84   a  in the long-side direction, at upper and lower positions using screws  63 . The manifold member  110  includes a pipe  110   a  connected to the fuel gas discharge passage  30   b , and the manifold member  112  includes a pipe  112   a  connected to the oxygen-containing gas discharge passage  28   b.    
         [0063]    As shown in  FIG. 7 , manifold members  114 ,  116  are attached to the end plate  84   b , at an upper end in the short-side direction using screws  63 , and manifold members  118 ,  120  are attached to the end plate  84   b , at a lower end in the short-side direction of the end plate  84   b  using screws  63 . The manifold members  114 ,  118  provided at upper and lower positions have respective pipes  114   a ,  118   a  connected respectively to the coolant supply passages  32   a , and the pipes  114   a ,  118   a  are connected to a single pipe  122 . The manifold members  116 ,  120  provided at upper and lower positions have respective pipes  116   a ,  120   a  connected respectively to the coolant discharge passages  32   b , and the pipes  116   a ,  120   a  are connected to a single pipe  124 . 
         [0064]    In the second embodiment having the above structure, the pair of mount sections  98   a ,  100   a  are formed integrally with the lower end of the end plate  84   a  on both sides of the recess  92   a , and the pair of mount sections  102   a ,  104   a  are formed integrally with the lower end of the end plate  84   a  with the recesses  94   a ,  96   a  interposed therebetween. Further, the mount sections  98   b ,  100   b  are provided integrally with the end plate  84   b  on both sides of the recess  92   b , and the mount sections  102   b ,  104   b  are provided integrally with the end plate  84   b  with the recesses  94   b ,  96   b  interposed therebetween. Thus, the same advantages as in the case of the first embodiment are obtained. For example, in comparison with the case where members separate from the end plates  84   a ,  84   b  are used as mounting structure, the structure of the mount sections is simplified significantly. 
         [0065]      FIG. 8  is a perspective view schematically showing a fuel cell stack  130  according to a third embodiment of the present invention. The constituent elements of the fuel cell stack  130  according to the third embodiment of the present invention that are identical to those of the fuel cell stack  80  according to the second embodiment are labeled with the same reference numerals, and description thereof will be omitted. 
         [0066]    The fuel cell stack  130  includes end plates  132   a ,  132   b  provided at both ends of the stack body  14  in the stacking direction. As shown in  FIG. 9 , the end plate  132   a  has recesses  134   a ,  136   a  on both sides of a lower central portion thereof, and recesses  138   a ,  140   a , which are provided at positions spaced outward from the recesses  134   a ,  136   a  by a predetermined interval, respectively. A mount section  142   a  is formed between the recesses  134   a ,  138   a , and a mount section  144   a  is formed between the recesses  136   a ,  140   a.    
         [0067]    Mount sections  146   a ,  148   a  are formed outside the recesses  138   a ,  140   a . The recesses  134   a ,  136   a  have a depth spaced upward from a lower end position of the end plate  132   a  by a distance L1. 
         [0068]    Likewise, the end plate  132   b  has recesses  134   b ,  136   b ,  138   b , and  140   b  whereby mount sections  142   b ,  144   b ,  146   b , and  148   b  are formed. Manifold members  106 ,  108 ,  110 , and  112  are fixed to the end plate  132   a  using screws  63 . 
         [0069]    As shown in  FIG. 10 , the manifold members  114 ,  116  are fixed to the end plate  132   b  using screws  63 . The recesses  134   b ,  136   b  have a depth spaced upward from a lower end position of the end plate  132   b  by a distance L1. Screws  63  at lower positions for fixing the manifold members  118 ,  120  are disposed within the distance L1. 
         [0070]    The distance L1 and the distance L may be the same, or different depending on the shapes of attachment members or the like. In the third embodiment having the structure as described above, the same advantages as in the cases of the first and second embodiments are obtained.