Fuel cell separator and power generation cell

A passage bead seal of a fuel cell joint separator includes a straight portion and curved portions. An oxygen-containing gas bridge section connecting the inside and the outside of a portion surrounded by a passage bead seal includes inner tunnels and outer tunnels coupled to an inner side wall and an outer side wall of a straight portion, and protruding in a separator thickness direction. The tunnel height is determined to be smaller than the bead seal height by not less than a predetermined value in a manner that a line pressure applied by a compression load to a front end surface of the straight portion becomes the same as a line pressure applied by the compression load to a front end surface of the curved portion.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2019-212148 filed on Nov. 25, 2019, 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 separator and a power generation cell including a passage bead seal surrounding a fluid passage.

Description of the Related Art

For example, a solid polymer electrolyte fuel cell includes a membrane electrode assembly (MEA) including an anode provided on one surface of an electrolyte membrane, and a cathode provided on the other surface of the electrolyte membrane. The electrolyte membrane is a solid polymer electrolyte membrane. The membrane electrode assembly is sandwiched between separators (bipolar plates) to form a power generation cells, and a plurality of power generation cells are stacked together to form a stack body. End plates are stacked on both ends of the stack body in the stacking direction to form a fuel cell stack. The end plates hold the plurality of power generation cells, etc. that are stacked together, and apply a compression load (stacking load) to the stack boy in a stacking direction.

In some cases, metal separators are used in this type of the fuel cell stack. In such cases, seal members are provided to prevent leakage of fluid such as reactant gasses (an oxygen-containing gas and a fuel gas) and a coolant. Elastic rubber seals, such as fluorine and silicone rubbers are used as the seal members, and the cost of the separator is pushed up due to the use of the seal members. In this regard, for example, as disclosed in the specification of U.S. Pat. No. 7,718,293, structure where a protruding bead seal is formed in the separator instead of the elastic rubber seal has been adopted.

SUMMARY OF THE INVENTION

In a stack body, in order to supply and discharge an oxygen-containing gas, a fuel gas, and a coolant (also collectively referred to as fluid) to/from each of power generation cells, fluid passages penetrate through metal separators in a stacking direction, outside the power generation area of the power generation cells. The fluid passages are sealed by passage bead seals surrounding the fluid passages. In this manner, leakage of the fluid is prevented.

Specifically, the stack body includes a contact section which contacts a front end surface of the passage bead seal in a protruding direction in which the passage bead seal protrudes. A front end surface of the passage bead seal contacts the contact section of the stack body, and the passage bead seal is elastically deformed by the above compression load. Thus, a line pressure having a predetermined strength (the average value of the surface pressure in a direction in the passage bead seal extends) is applied to the front end surface. In this manner, the desired seal performance of the passage bead seal is achieved. As a result, the inside and the outside of the portion surrounded by the passage bead seal is sealed.

As a passage of the fluid between the power generation area of the power generation cell and the fluid passages, the separator is provided with tunnels forming connection channels connecting the inside and the outside of the portion surrounded by the passage bead seal. The rigidity of the coupling portion coupled to the tunnel of the passage bead seal is high in comparison with the portion which is not coupled to the tunnels, and the coupling portion is not deformed easily. Therefore, the line pressure applied to the front end surface of the passage bed seal tends to be large locally at the coupling portion. Therefore, the line pressure added to the front end surface of the passage bead seal may vary, and if there is any portion of the front end surface to which a line pressure having a predetermined strength is not applied, it becomes difficult to achieve the desired seal performance by the passage bead seal.

An object of the present invention is to provide a fuel cell separator and a power generation cell which make it possible to achieve the desired seal performance of the passage bead seal.

According to an aspect of the present invention, a fuel cell separator is provided. The fuel cell separator includes a fluid flow field as a passage of fluid including an oxygen-containing gas, a fuel gas, or a coolant in a separator surface direction, a fluid passage connected to the fluid flow field and penetrating the fuel cell separator in a separator thickness direction, and a passage bead seal formed around the fluid passage, and protruding in the separator thickness direction, wherein the fuel cell separator is stacked on a membrane electrode assembly, and a compression load is applied to the fuel cell separator in the stacking direction, the fuel cell separator further includes a bridge section configured to connect inside and outside of a portion surrounded by the passage bead seal, as viewed in the separator thickness direction, the passage bead seal includes a straight portion where the bridge section is disposed, and curved portions provided on both sides of the straight portion in a peripheral direction of the passage bead seal, the bridge section includes a tunnel coupled to a side wall of the straight portion, and protruding in the separator thickness direction, and a protruding height of the tunnel by which the tunnel protrudes from a reference surface is determined to be smaller than a protruding height of the passage bead seal by which the passage bead seal protrudes from the reference surface, by not less than a predetermined value, in a manner that a line pressure applied by the compression load to a front end surface of the straight portion in a protruding direction becomes same as a line pressure applied by the compression load to a front end surface of the curved portion in a protruding direction.

According to another aspect of the present invention, a power generation cell including the fuel cell separator and the membrane electrode assembly is provided.

In the fuel cell separator, the protruding height of the tunnel by which the tunnel protrudes from the reference surface is determined to be smaller than the protruding height of the passage bead seal by which the passage bead seal protrudes from the reference surface, by not less than a predetermined value in a manner that the line pressure applied by the compression load to the front end surface of the straight portion in the protruding direction becomes the same as the line pressure applied by the compression load to the front end surface of the curved portion in the protruding direction. The line pressure herein means an average value of the line pressure applied to the front end surface, per unit length in the direction in which the passage bead seal extends. Further, in the case where the line pressure applied to the front end surface of the straight portion is within the range between 80% and 120% of the line pressure applied to the front end surface of the curved portion, it is considered that the line pressure applied to the front end surface of the straight portion and the line pressure applied to the front end surface of the curved portion are the “same”. Further, the “predetermined value” herein can be determined, e.g., based on the material, the shape, and the size of the fuel cell joint separator, and the shapes, the sizes, and the layout of the passage bead seals, the tunnels, and the fluid passages, and can be calculated in advance by simulations, etc.

In the passage bead seal, though the straight portion is coupled to the tunnel, it is possible to avoid the line pressure applied to the front end surface of the straight portion to becomes locally higher than the line pressure applied to the portion of the front end surface which is not coupled to the tunnel such as the curved portion. In the structure, it is possible to apply the line pressure to the front end surface of the passage bead seal uniformly.

Further, in this case, since increase in the rigidity in the straight portion of the passage bead seal is suppressed, it becomes possible to suitably deform the straight portion elastically in correspondence with the compression load, and suppress occurrence of bucking of the straight portion. In this manner, it is possible to suitably maintain the state where the line pressure having the predetermined strength is applied to the front end surface of the passage bead seal.

In view of the above, in the present invention, it is possible to suitably achieve the desired seal performance by the passage bead seal.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A preferred embodiment of a fuel cell separator and a power generation cell according to the present invention will be described with reference to accompanying drawings. In the drawings mentioned below, the constituent elements which have the same or similar functions and which offer the same or similar advantages are labeled with the same reference numerals, and description of such constituent elements may not be repeated.

As shown inFIGS. 2 and 3, a fuel cell joint separator10(fuel cell separator) according to the embodiment of the present invention forms a power generation cell12(unit fuel cell). As shown inFIGS. 1 and 2, a fuel cell stack14(fuel cell) includes a stack body16formed by stacking a plurality of the power generation cells12together in a horizontal direction (indicated by an arrow A) or in the gravity direction (indicated by an arrow C). For example, the fuel cell stack14is mounted in a fuel cell vehicle such as a fuel cell electric automobile, etc.

As shown inFIGS. 1 and 2, at one end of the stack body16in the stacking direction (end in the direction indicated by an arrow A1), a terminal plate18ais provided (FIG. 2). An insulator20ais provided outside the terminal plate18a, and an end plate22ais provided outside the insulator20a. At the other end of the stack body16in the stacking direction (end in the direction indicated by the arrow A2), a terminal plate18b(FIG. 2) is provided. An insulator20bis provided outside the terminal plate18b, and an end plate22bis provided outside the insulator20b.

As shown inFIG. 1, each of the end plates22a,22bhas a rectangular shape elongated in a lateral direction (or elongated in a longitudinal direction). Coupling bars24are disposed between the sides of the end plates22a,22b. The coupling bars24extend in the stacking direction (indicated by the arrow A). Both ends of the coupling bars24are fixed to inner surfaces of the end plates22a,22busing bolts26. Therefore, a compression load having a predetermined strength is (hereinafter simply also referred to as the “compression load”) is applied to the plurality of power generation cells12held between the end plates22a,22b. It should be noted that the fuel cell stack14may include a casing including the end plates22a,22b, and the stack body16may be placed in the casing.

As shown inFIGS. 2 and 3, in the embodiment of present invention, each of the power generation cells12includes a resin frame equipped MEA28, and a first separator30and a second separator32sandwiching the resin frame equipped MEA28. The outer peripheral portions of the first separator30and the second separator32are joined together by welding, brazing, crimping, etc. to form a fuel cell joint separator10. The fuel cell joint separator10(the first separator30and the second separator32) is formed by press forming of a metal thin plate to have a corrugated shape in cross section.

For example, the metal plate is a steel plate, a stainless steel plate, an aluminum plate, a plated steel plate, or a metal plate having an anti-corrosive surface by surface treatment.

The resin frame equipped MEA28includes a membrane electrode assembly (MEA)34, and a resin frame member36provided around the outer periphery of the membrane electrode assembly34. As shown inFIG. 2, the membrane electrode assembly34includes an electrolyte membrane38, an anode40provided on one surface (surface on the side indicated by the arrow A2) of the electrolyte membrane38, and a cathode42provided on the other side (surface on the side indicated by the arrow A1) of the electrolyte membrane38.

For example, the electrolyte membrane38is a solid polymer ion exchange membrane (cation ion exchange membrane). For example, the sold polymer electrolyte membrane is a thin membrane of perfluorosulfonic acid containing water. The electrolyte membrane38is interposed between the anode40and the cathode42. A fluorine based electrolyte may be used as the electrolyte membrane38. Alternatively, an HC (hydrocarbon) based electrolyte may be used as the electrolyte membrane38. In the embodiment of the present invention, as shown inFIG. 2, the surface size (outer size) of the electrolyte membrane38is smaller than the surface sizes (outer sizes) of the anode40and the cathode42. However, the present invention is not limited specially in this respect.

As shown inFIG. 2, the cathode42includes a cathode catalyst layer42ajoined to the surface of the electrolyte membrane38on the side indicated by the arrow A1, and a cathode gas diffusion layer42bstacked on the cathode catalyst layer42a. The anode40includes an anode catalyst layer40ajoined to a surface of the electrolyte membrane38on the side indicated by the arrow A2, and an anode gas diffusion layer40bstacked on the anode catalyst layer40a.

For example, the cathode catalyst layer42ais formed by porous carbon particles deposited uniformly on the surface of the cathode gas diffusion layer42btogether with an ion conductive polymer binder and platinum alloy supported on the surfaces of the porous carbon particles. The anode catalyst layer40ais formed by porous carbon particles deposited uniformly on the surface of the anode gas diffusion layer40btogether with an ion conductive polymer binder and platinum alloy supported on the surfaces of the porous carbon particles. Each of the cathode gas diffusion layer42band the anode gas diffusion layer40bcomprises an electrically conductive sheet such as a carbon paper or a carbon cloth.

An electrically conductive porous layer (not shown) may be provided at least at one of a position between the cathode catalyst layer42aand the cathode gas diffusion layer42b, and a position between the anode catalyst layer40aand the anode gas diffusion layer40b.

The resin frame member36has a frame shape. For example, an inner marginal portion of the resin frame member36is held between an outer marginal portion of the cathode gas diffusion layer42band an outer marginal portion of the anode gas diffusion layer40b. The inner peripheral end surface of the resin frame member36may be positioned close to, in contact with, or overlapped with the outer peripheral end surface of the electrolyte membrane38.

Examples of materials of the resin frame member36include PPS (polyphenylene sulfide), PPA (polyphthalamide), PEN (polyethylene naphthalate), PES (polyethersulfone), LCP (liquid crystal polymer), PVDF (polyvinylidene fluoride), a silicone resin, a fluororesin, m-PPE (modified polyphenylene ether) resin, PET (polyethylene terephthalate), PBT (polybutylene terephthalate), or modified polyolefin. Instead of using the resin frame member36, it may be possible to adopt structure where the electrolyte membrane38protrudes outward. Alternatively, frame shaped films may be provided on both sides of the electrolyte membrane38which protrude outward.

As shown inFIG. 3, in a marginal portions of the power generation cell12at one end in the long side direction of the first separator30, the second separator32, and the resin frame member36in the long side direction (on the side indicated by the arrow B1), one oxygen-containing gas supply passage44a, two coolant supply passages46a, and two fuel gas discharge passages48bare provided. In a marginal portions of the power generation cell12at the other end in the long side direction of the first separator30, the second separator32, and the resin frame member36(on the side indicated by the arrow B2), one fuel gas supply passage48a, two coolant discharge passages46b, and two oxygen-containing gas discharge passages44bare provided.

For example, a fuel gas such as the hydrogen-containing gas is discharged from the fuel gas discharge passage48b. For example, an oxygen-containing gas is supplied to the oxygen-containing gas supply passage44a. For example, at least any one of pure water, ethylene glycol, and oil is supplied as a coolant to the coolant supply passages46a. A fuel gas is supplied to the fuel gas supply passage48a. The coolant is discharged from the coolant discharge passages46b. The oxygen-containing gas is discharged from the oxygen-containing gas discharge passages44b.

The oxygen-containing gas supply passage44a, the coolant supply passages46a, the fuel gas discharge passages48b, the fuel gas supply passage48a, the coolant discharge passages46b, oxygen-containing gas discharge passages44b(hereinafter referred to as the “fluid passages44a,44b,46a,46b,48a,48b,” collectively) penetrate through the structure of the fuel cell stack14excluding the terminal plates18a,18b(FIG. 2).

It should be noted that the fuel gas supply passage48aand the fuel gas discharge passages48bare also referred to as the “fuel gas passages48a,48b”, collectively. The oxygen-containing gas supply passage44aand the oxygen-containing gas discharge passages44bare also referred to as the “oxygen-containing gas passages44a,44b”), collectively. Further, the coolant supply passages46aand the coolant discharge passages46bare also referred to as the “coolant passages46a,46b”, collectively.

These fluid passages44a,44b,46a,46b,48a,48bare arranged in the upper/lower direction (in the direction indicated by arrows C1, C2). Specifically, in a marginal portion at one end side (side indicated by the arrow B1) in the long side direction of the power generation cells12, the two coolant supply passages46aare arranged remotely from each other in the upper/lower direction, between the two fuel gas discharge passages48barranged remotely from each other in the upper/lower direction. The oxygen-containing gas supply passage44ais provided between these coolant supply passages46a.

In the marginal portion at the other end side (side indicated by the arrow B2) of the power generation cell12in the long side direction, the two coolant discharge passages46bare arranged remotely from each other in the upper/lower direction, between the two oxygen-containing gas discharge passages44barranged remotely from each other in the upper/lower direction. The fuel gas supply passage48ais disposed between these coolant discharge passages46b.

The fluid passages44a,44b,46a,46b,48a,48bare not limited to the above layout. The layout of the fluid passages44a,44b,46a,46b,48a,48bcan be determined as necessary depending on the required specification. Unlike the embodiment of the present invention, the pair of coolant supply passages46amay be provided on both sides of the fuel gas supply passage48ain the upper/lower direction (in the direction indicated by the arrows C1, C2), and the pair of coolant discharge passages46bmay be provided on both sides of the oxygen-containing gas supply passage44ain the upper/lower direction. Further, in the embodiment of the present invention, the number of the fuel gas discharge passages48bis two, the number of the oxygen-containing gas discharge passages44bis two, the number of the coolant supply passages46ais two, and the number of the coolant discharge passages46bis two. Alternatively, one fuel gas discharge passage48b, one oxygen-containing gas discharge passage44b, one coolant supply passage46a, and one coolant discharge passage46bmay be provided.

In the embodiment of the present invention, for example, as shown inFIGS. 4 to 7, the shape of the fluid passages44a,44b,46a,46b,48a,48bin the stacking direction (indicated by the arrow A) is a hexagonal shape. The opposing two sides of the hexagonal shape are oriented in the upper/lower direction (indicated by the arrow C). However, the shape of the fluid passages44a,44b,46a,46b,48a,48bin the stacking direction (indicated by the arrow A) is not limited specially to the hexagonal shape, and may be a polygonal shape other than the hexagonal shape, or a polygonal shape having rounded corners.

As shown inFIG. 3, the first separator30and the second separator32have MEA side surfaces30a,32afacing the resin frame equipped MEA28, and coolant side surfaces30b,32bon the back of the MEA side surfaces30a,32a. As shown inFIG. 4, an oxygen-containing gas flow field52is provided on the MEA side surface30aof the first separator30as a passage of the oxygen-containing gas in the separator surface direction (directions indicated by the arrows B and C). The oxygen-containing gas flow field52is connected to (in fluid communication with) the one oxygen-containing gas supply passage44aand the two oxygen-containing gas discharge passages44b. A plurality of ridges52aare provided on the MEA side surface30aof the first separator30. The ridges52aextend straight in the direction indicated by the arrow B. Straight flow grooves52bare formed between the ridges52a. At least part of the oxygen-containing gas flow field52is provided inside the flow grooves52b. It should be noted that the oxygen-containing gas flow field52may not be provided inside the plurality of straight flow grooves52b, and may be provided inside a plurality of wavy flow grooves (not shown).

As shown inFIG. 4, in the MEA side surface30aof the first separator30, an inlet buffer54is provided between the oxygen-containing gas supply passage44aand the oxygen-containing gas flow field52. The inlet buffer54includes a plurality of boss arrays54aeach formed by a plurality of bosses protruding toward the resin frame equipped MEA28(on the side indicated by the arrow A2) and arranged in the direction indicated by the arrow C. Further, an outlet buffer56is provided in the MEA side surface30aof the first separator30, between the oxygen-containing gas discharge passages44band the oxygen-containing gas flow field52. The outlet buffer56includes a plurality of boss arrays56aeach formed by a plurality of bosses protruding toward the resin frame equipped MEA28and arranged in the direction indicated by the arrow C.

It should be noted that, as shown inFIG. 3, on the coolant side surface30bof the first separator30, boss arrays54beach formed by a plurality of bosses arranged in the direction indicated by the arrow C are provided between the adjacent boss arrays54aof the inlet buffer54, and boss arrays56beach formed a plurality of bosses arranged in the direction indicated by the arrow C are provided between the adjacent boss arrays56aof the outlet buffer56. Each of the boss arrays54b,56bprotrudes toward a coolant flow field60(in the direction indicated by the arrow A1) described later to form a buffer on the coolant side.

As shown inFIG. 5, a fuel gas flow field58is provided on the MEA side surface32aof the second separator32, as a passage of the fuel gas in the separator surface direction (directions indicated by the arrows B and C). The fuel gas flow field58is connected to one fuel gas supply passage48aand the two fuel gas discharge passages48b. The plurality of ridges58aextending straight in the direction indicated by the arrow B are provided on the MEA side surface32aof the second separator32, and straight flow grooves58bare formed between the ridges58a. At least part of the fuel gas flow field58is formed inside these flow grooves58b. The fuel gas flow field58may be provided inside a plurality of wavy flow grooves (not shown), instead of the plurality of straight flow grooves58b.

An inlet buffer54is provided on the MEA side surface32aof the second separator32, between the fuel gas supply passage48aand the fuel gas flow field58. The inlet buffer54includes a plurality of boss arrays54aeach formed by a plurality of bosses protruding toward the resin frame equipped MEA28, and arranged in the direction indicated by the arrow C. Further, an outlet buffer56is provided on the MEA side surface32aof the second separator32, between the fuel gas discharge passage48band the fuel gas flow field58. The outlet buffer56includes a plurality of boss arrays56aeach formed by a plurality of bosses protruding toward the resin frame equipped MEA28, and arranged in the direction indicated by the arrow C.

It should be noted that, as shown inFIG. 6, on the coolant side surface32bof the second separator32, boss arrays54beach formed by a plurality of bosses arranged in the direction indicated by the arrow C are provided between the adjacent boss arrays54aof the inlet buffer54, and boss array56beach formed a plurality of bosses arranged in the direction indicated by the arrow C are provided between the adjacent boss arrays56aof the outlet buffer56. Each of the boss arrays54b,56bprotrudes toward the coolant flow field60(in the direction indicated by the arrow A2) to form a buffer on the coolant side.

The coolant flow field60is provided between the coolant side surface30bof the first separator30and the coolant side surface32bof the second separator32that are joined together. The coolant flows through the coolant flow field60in the separator surface directions (directions indicated by the arrows B and C). The coolant flow field60is connected to (in fluid communication with) the two coolant supply passages46aand the two coolant discharge passages46b. When the MEA side surface30aof the first separator30where the oxygen-containing gas flow field52is formed and the MEA side surface32aof the second separator32where the fuel gas flow field58is formed are overlapped with other, the coolant flow field60is formed between the back surface of the MEA side surface30aand the back surface of the MEA side surface32a.

Hereinafter, the oxygen-containing gas flow field52, the fuel gas flow field58, and the coolant flow field60are referred to as the “fluid flow fields52,58,60”. Portions around the fluid passages44a,44b,46a,46b,48a,48bin the first separator30and the second separator32are joined together by welding, brazing, etc.

As shown inFIG. 4, an outer bead seal70a, an inner bead seal72a, and passage bead seals74a(metal bead seals) are formed by press forming of the first separator30in a manner that the outer bead seal70a, the inner bead seal72a, and the passage bead seals74aare expanded in the separator thickness direction toward the resin frame equipped MEA28(FIG. 3). It should be that the outer bead seal70a, the inner bead seal72a, and the passage bead seals74aare also referred to as the first seal line, collectively.

As shown inFIG. 5, an outer bead seal70b, an inner bead seal72b, and passage bead seals74b(metal bead seals) are formed by press forming of the second separator32in a manner that the outer bead seal70b, the inner bead seal72b, and the passage bead seals74bare expanded in the separator thickness direction toward the resin frame equipped MEA28(FIG. 3). It should be that outer bead seal70b, the inner bead seal72b, and the passage bead seals74bare also referred to as the second seal line, collectively.

As shown inFIG. 2, resin material68is fixed to each of a front end surface62of the first seal line and a front end surface64of the second seal line by printing, coating, etc. In the drawings other thanFIG. 2, the resin material68is not illustrated. The front end surface62of the first seal line is brought into contact with the front end surface64of the second seal line of the second separator32of the other joint separator through the resin material68and the resin frame member36. For example, polyester fiber, etc. is used as the resin material68. The resin material68may be fixed to the resin frame member36, instead of the first seal line and the second seal line. Further, the fuel cell joint separator10may not include the resin material68.

As shown inFIG. 4, the outer bead seal70ais formed around the outer marginal portion of the first separator30. The inner bead seal72ais formed around all of the oxygen-containing gas flow field52, the inlet buffer54, the outlet buffer56, the oxygen-containing gas passages44a,44b, and the fuel gas passages48a,48b. The plurality of passage bead seals74aare formed around the fluid passages44a,44b,46a,46b,48a,48b, respectively.

Hereinafter, as shown inFIG. 4, the passage bead seals74aformed around the oxygen-containing gas passages44a,44bare also referred to as an “oxygen-containing gas passage bead seals76a”, the passage bead seals74aformed around the fuel gas passages48a,48bare also referred to as a “fuel gas passage bead seals78a”, and the passage bead seals74aformed around the coolant passages46a,46bare also referred to as a “coolant passage bead seals80a”.

As shown inFIG. 5, the outer bead seal70bis formed around the outer marginal portion of the second separator32. The inner bead seal72bis formed around all of the fuel gas flow field58, the inlet buffer54, the outlet buffer56, the oxygen-containing gas passages44a,44b, and the fuel gas passages48a,48b. The plurality of passage bead seals74bare formed around the fluid passages44a,44b,46a,46b,48a,48b, respectively.

As shown inFIG. 5, the passage bead seals74bformed around the oxygen-containing gas passages44a,44bare also referred to as an “oxygen-containing gas passage bead seals76b”, the passage bead seals74bformed around the fuel gas passages48a,48bare also referred to as a “fuel gas passage bead seals78b”, and the passage bead seals74bformed around the coolant passages46a,46bare also referred to as a “coolant passage bead seals80b”.

As shown inFIGS. 4 to 6, as viewed in the separator thickness direction (stacking direction indicated by the arrow A), the outer bead seals70a,70bhave a rectangular annular shape extending along the long sides and the short sides of the rectangular fuel cell joint separator10. Further, as viewed in the separator thickness direction, the passage bead seals74a,74bhave a hexagonal annular shape having rounded corners, in correspondence with the shapes of the fluid passages. Each of the passage bead seals74a,74bincludes a straight portion75a, e.g., extending straight in the short side direction (in the direction indicated by the arrow C), on the central side of the fuel cell joint separator10(hereinafter the side adjacent to the flow fields52,58,60will also be simply referred as the flow field side), and curved portions75bprovided on both sides of the straight portion75ain the peripheral direction of the passage bead seals74a,74b. It should be noted that the straight portion75aneed not always extend straight. The straight portion75amay be curved at a radius of curvature which is larger than that of the curved portion75b.

As shown inFIGS. 8 to 10, the passage bead seal74aof the first separator30includes an inner side wall75c(side wall) and an outer side wall75d(side wall) which rise upright from a base plate part82of the first separator30, and a top portion75econnecting the inner side wall75cand the outer side wall75d. The passage bead seal74bof the second separator32includes an inner side wall75c(side wall) and an outer side wall75d(side wall) which rise upright from the base plate part82of the second separator32, and a top portion75econnecting the inner side wall75cand the outer side wall75d.

The inner side wall75cand the outer side wall75dare inclined in directions in which the inner side wall75cand the outer side wall75dget closer to each other, toward the top portion75e. Therefore, each of the passage bead seals74a,74bhas a trapezoidal shape in cross section in the separator thickness direction. It should be noted that the inner side wall75cand the outer side wall75dof the passage bead seals74a,74bmay be in parallel to the separator thickness direction, and the passage bead seals74a,74bmay have a square shape or a rectangular shape in cross section in the separator thickness direction. Further, as in the case of the passage bead seals74a,74b, the cross sectional shape of the outer bead seals70a,70band the inner bead seals72a,72bin the separator thickness direction may have a trapezoidal shape, a square shape or a rectangular shape in the separator thickness direction.

As shown inFIGS. 4 and 7, as viewed in the separator thickness direction, the inner bead seal72aof the first separator30includes a facing portion86awhich extends in the direction indicated by the arrow C, e.g., straight on the flow field side of the straight portion75aof the coolant passage bead seal80a. As shown inFIG. 10, the facing portion86aof the inner bead seals72aincludes a first side wall87aand a second side wall87bwhich rise from the base plate part82of the first separator30toward the side indicated by the arrow A2, and a top portion87cconnecting the first side wall87aand the second side wall87b. The first side wall87afaces the outer side wall75dof the straight portion75aof the coolant passage bead seal80aat a distance. The second side wall87bis provided on the flow field side of the first side wall87a.

As shown inFIG. 5, as viewed in the separator thickness direction, the inner bead seal72bof the second separator32includes a facing portion86b, e.g., extending straight in the direction indicated by the arrow C, on the flow field side of the straight portion75aof the coolant passage bead seal80b. As shown inFIG. 10, the facing portion86bof the inner bead seal72bincludes a first side wall87aand a second side wall87bwhich rise from the base plate part82of the second separator32toward the side indicted by the arrow A1, and a top portion87cconnecting the first side wall87aand the second side wall87b. The first side wall87afaces the outer side wall75dof the straight portion75aof the coolant passage bead seal80bat a distance. The second side wall87bis provided on the flow field side of the first side wall87a.

It should be noted thatFIGS. 8 to 10show the first separator30and the second separator32in cross section in the state where the first separator30and the second separator32are assembled together into the fuel cell stack14(in the state where compression load is applied to the first seal line and the second seal line). In the state before the first separator30and the second separator32are assembled together into the fuel cell stack14(in the state where no compression load is applied), the shape of the top portion75eof the passage bead seals74a,74bmay have a curved shape expanding in the protruding direction. In the state where fuel cell stack14is assembled, the shape of the top portions75eof the passage bead seals74a,74bhas a flat shape as shown inFIGS. 8 to 10.

As shown inFIG. 4, as viewed in separator thickness direction (indicated by the arrow A), an oxygen-containing gas bridge section90is provided on the MEA side surface30aof the first separator30. The oxygen-containing gas bridge section90connects the inside and the outside of the portion surrounded by the oxygen-containing gas passage bead seal76a. The oxygen-containing gas bridge section90is provided in the straight portion75aof each of the oxygen-containing gas passage bead seal76ain a manner to connect the oxygen-containing gas passages44a,44band the oxygen-containing gas flow field52.

As shown inFIG. 5, a fuel gas bridge section92is provided on the MEA side surface32aof the second separator32. The fuel gas bridge section92connects the inside and outside of the portion surrounded by the fuel gas passage bead seal78b, as viewed in the separator thickness direction. The fuel gas bridge section92is disposed in the straight portion75aof the fuel gas passage bead seal78bin a manner to connect each of the fuel gas passages48a,48band the fuel gas flow field58.

As viewed in the separator thickness direction, a coolant bridge section94is provided on each of coolant side surfaces30b,32bof the first separator30and the second separator32facing each other. The coolant bridge section94connects the inside and outside of the portion surrounded by each of the coolant passage bead seals80a,80b. The coolant bridge section94is disposed on the straight portion75aof each of the coolant passage bead seals80a,80band each of the facing portions86a,86bof the inner bead seals72a,72bin a manner to connect each of the coolant passages46a,46band the coolant flow field60.

As shown inFIGS. 4 to 7, each of the oxygen-containing gas bridge section90and the fuel gas bridge section92has a plurality of inner tunnels100and a plurality of outer tunnels102(tunnels). Further, the coolant bridge section94includes a plurality of inner tunnels100, a plurality of outer tunnels104(tunnels), and a plurality of outermost tunnels106.

As show inFIG. 8, the inner tunnel100of the oxygen-containing gas bridge section90is coupled to the inner side wall75cof the straight portion75aof each of the oxygen-containing gas passage bead seals76a,76b. The outer tunnel102of the oxygen-containing gas bridge section90is coupled to the outer side wall75dof the straight portion75aof each of the oxygen-containing gas passage bead seals76a,76b. As shown inFIG. 9, the inner tunnel100of the fuel gas bridge section92is coupled to the inner side wall75cof the straight portion75aof the fuel gas passage bead seals78a,78b. The outer tunnel102of the fuel gas bridge section92is coupled to the outer side wall75dof each of the straight portions75aof each of the fuel gas passage bead seals78a,78b.

In each of the oxygen-containing gas bridge section90and the fuel gas bridge section92, the plurality of inner tunnels100and the plurality of outer tunnels102extend in opposite directions from the straight portion75ain the separator surface directions (directions indicated by the arrows B and C). As shown inFIG. 7, the plurality of inner tunnels100and the plurality of outer tunnels102are disposed at intervals in the direction indicated by the arrow C. In the embodiment, the plurality of inner tunnels100and the plurality of outer tunnels102are arranged in a zigzag pattern along the straight portion75a. It should be noted that the plurality of inner tunnels100and the plurality of outer tunnels102may be disposed to face each other through the straight portion75a.

As shown inFIGS. 8 and 9, the inner tunnel100of each of the oxygen-containing gas bridge section90(FIG. 8) and the fuel gas bridge section92(FIG. 9) includes a first tunnel100aprovided in the first separator30and a second tunnel100bprovided in the second separator32. The outer tunnel102includes a first tunnel102aprovided in the first separator30and a second tunnel102bprovided in the second separator32.

The first tunnels100a,102aare formed by expanding the first separator30by press forming in a manner that the first tunnels100a,102aprotrude from the base plate part82toward the resin frame equipped MEA28adjacent to the first separator30, in the stack body16(FIG. 2). Further, as viewed in the separator thickness direction, each of the plurality of the first tunnel100a,102aextends in the direction indicated by the arrows B.

The second tunnels100b,102bare formed by expanding the second separator32by press forming in a manner that the second tunnels100b,102bprotrude from the base plate part82toward the resin frame equipped MEA28adjacent to the second separator32, in the stack body16. As viewed in the separator thickness direction of the fuel cell joint separator10, the positions of the second tunnels100b,102bare overlapped with the positions of the first tunnels100a,102a.

The first tunnel100aand the second tunnel100b, of the inner tunnel100have the same width in a direction perpendicular to the direction in which the first tunnel100aand the second tunnel100bextend, and has the same protruding height by which the first tunnel100aand the second tunnel100bprotrude from the base plate part82. The first tunnel102aand the second tunnel102b, of the outer tunnels102have the same width in a direction perpendicular to the direction in which the first tunnel102aand the second tunnel102bextend, and has the same protruding height by which the first tunnel102aand the second tunnel102bprotrude from the base plate part82.

As shown inFIGS. 8 and 9, an inner space110is formed at each position between the first tunnel100aand the second tunnel100bin the fuel cell joint separator10. Further, an inner space112is formed at each position between the first tunnel102aand the second tunnel102bof the fuel cell joint separator10.

With reference toFIGS. 7 and 8, the inner tunnel100and the outer tunnel102of the oxygen-containing gas bridge section90which connect the oxygen-containing discharge passage44band the oxygen-containing gas flow field52(FIG. 4) will be described specifically. One end of each of the first tunnel100aand the second tunnel100bof the inner tunnel100(end on the side indicated by the arrow B1) are coupled to the inner side wall75cof the straight portions75aof the oxygen-containing gas passage bead seals76a,76b, through a through hole75fprovided in the inner side wall75c. Further, the other end of each of the first tunnel100aand the second tunnel100bof the inner tunnel100in the direction in which the first tunnel100aand the second tunnel100bextend (end on the side indicated by the arrow B2) is opened to the oxygen-containing gas discharge passage44b.

One end of each of the first tunnel102aand the second tunnel102bof the outer tunnel102in the direction in which the first tunnel102aand the second tunnel102bextends (end on the side indicated by the arrow B2) is coupled to the outer side wall75dof each of the straight portions75aof the oxygen-containing gas passage bead seals76a,76bthrough a through hole75gprovided in the outer side wall75d. Further, the other end of each of the first tunnel102aand the second tunnel102bof the outer tunnel102in the direction in which the first tunnel102aand the second tunnel102bextend (end on the side indicated by the arrow B1) is provided adjacent to the outlet buffer56(seeFIG. 4).

An opening102cis provided at the other end of the first tunnel102aof the outer tunnel102(end on the side indicated by the arrow B1) in the extending direction thereof. The opening102cconnects the inner space112of the outer tunnel102and the oxygen-containing gas flow field52(seeFIG. 4). Therefore, the oxygen-containing gas flow field52(FIG. 4) and the oxygen-containing gas discharge passage44bare connected together through the inner space112of the outer tunnel102, the inside of the oxygen-containing gas passage bead seals76a,76b, and the inner space110of the inner tunnel100.

The inner tunnel100and the outer tunnel102connecting the oxygen-containing gas supply passage44aand the oxygen-containing gas flow field52shown inFIG. 4have substantially the same structure as the inner tunnel100and the outer tunnel102inFIGS. 7 and 8, except that the directions indicated by the arrow B are opposite. That is, the oxygen-containing gas supply passage44a(FIG. 4) and the oxygen-containing gas flow field52are connected together through the inner space110of the inner tunnel100, the inside of the oxygen-containing gas passage bead seals76a,76b, and the inner space112of the outer tunnel102.

With reference toFIGS. 7 and 9, the inner tunnel100and the outer tunnel102of the fuel gas bridge section92connecting the fuel gas supply passage48aand the fuel gas flow field58will be described specifically. One end of each of the first tunnel100aand the second tunnel100bof the inner tunnel100in the direction in which the first tunnel100aand the second tunnel100bextend (end on the side indicated by the arrow B1) is coupled to the inner side wall75cof each of the straight portions75aof the fuel gas passage bead seals78a,78bthrough the through hole75fprovided in the inner side wall75c. Further, the other end of each of the first tunnel100aand the second tunnel100bof the inner tunnel100(end on the side indicated by the arrow B2) is opened to the fuel gas supply passage48a.

One end of each of the first tunnel102aand the second tunnel102bof the outer tunnel102(end on the side indicated by the arrow B2) is coupled to the outer side wall75dof each of the straight portions75aof the fuel gas passage bead seals78a,78bthrough the through hole75gprovided in the outer side wall75d. Further, the other end of each of the first tunnel102aand the second tunnel102bof the outer tunnel102(end on the side indicated by the arrow B1) is disposed adjacent to the inlet buffer54(FIG. 5).

An opening102dis provided at the other end of each of the first tunnel102aof the outer tunnel102in the direction in which the first tunnel102aextends (end on the side indicated by the arrow B1). The opening102dconnects the inner space112of the outer tunnel102and the fuel gas flow field58(FIG. 5). Therefore, the fuel gas supply passage48aand the fuel gas flow field58(FIG. 5) are connected together through the inner space112of the inner tunnel100, the inside of the fuel gas passage bead seals78a,78b, and the inner space112of the outer tunnel102.

The inner tunnel100and the outer tunnel102connecting the fuel gas discharge passage48band the fuel gas flow field58shown inFIG. 5have the same structure as the inner tunnel100and the outer tunnel102inFIGS. 7 and 9except that the directions indicated by the arrow B are opposite. That is, the fuel gas flow field58(FIG. 5) is connected to the fuel gas discharge passage48bthrough the inner space112of the outer tunnel102, the inside of the fuel gas passage bead seals78a,78b, and the inner space110of the inner tunnel100.

As shown inFIGS. 7 and 10, the inner tunnel100of the coolant bridge section94is coupled to the inner side wall75cof each of the straight portions75aof the coolant passage bead seals80a,80b. One end of the outer tunnel104of the coolant bridge section94is coupled to the outer side wall75dof each of the straight portions75aof the coolant passage bead seals80a,80b, and the other end of the outer tunnel104is coupled to the first side wall87aof each of the facing portions86a,86bof the inner bead seals72a,72b. The outermost tunnel106of the coolant bridge section94is coupled to the second side wall87bof each of the facing portions86a,86bof the inner bead seals72a,72b.

In the coolant bridge section94, the plurality of inner tunnels100and the plurality of outer tunnels104extend from the straight portion75ain the separator surface direction (directions indicated by the arrows B and C), in opposite directions. The plurality of outer tunnels104and the plurality of outermost tunnels106extend from the facing portions86a,86bin the separator surface direction, in opposite directions. The plurality of inner tunnels100, the plurality of outer tunnels104, and the plurality of outermost tunnels106are disposed at intervals in the direction indicated by the arrow C.

As shown inFIGS. 4 and 5, in the embodiment of the present invention, the plurality of inner tunnels100and the plurality of outer tunnels104are disposed in a zigzag pattern along the straight portion75a. Further, the plurality of outer tunnels104and the plurality of outermost tunnels106are disposed in a zigzag pattern along the facing portions86a,86b. It should be noted that the plurality of inner tunnels100and the plurality of outer tunnels104may be provided oppositely through the straight portion75a. Further, the plurality of outer tunnels104and the plurality of outermost tunnels106may be disposed oppositely through each of the facing portions86a,86b.

The inner tunnel100of the coolant bridge section94has the same structure as the inner tunnel100of the oxygen-containing gas bridge section90and the fuel gas bridge section92described above. That is, the inner tunnel100includes a first tunnel100aprovided in the first separator30, and a second tunnel100bprovided in the second separator32, and an inner space110is formed between the first tunnel100aand the second tunnel100b.

The outer tunnel104of the coolant bridge section94includes a first tunnel104aprovided in the first separator30, and a second tunnel104bprovided in the second separator32. The outermost tunnel106includes a first tunnel106aprovided in the first separator30and a second tunnel106bprovided in the second separator32.

The first tunnel104aof the outer tunnel104and the first tunnel106aof the outermost tunnel106are formed by expanding the first separator30by press forming in a manner that the first tunnels104a,106aprotrude from the base plate part82in the separator thickness direction toward the resin frame equipped MEA28adjacent to the first separator30, in the stack body16(FIG. 2). Further, as viewed in the separator thickness direction, for example, each of the plurality of first tunnels104a,106aextends in the direction indicated by the arrow B.

The second tunnel104bof the outer tunnel104and the second tunnel106bof the outermost tunnel106is formed by expanding the second separator32by press forming in a manner that the second tunnels104b,106bprotrude from the base plate part82in the separator thickness direction toward the resin frame equipped MEA28adjacent to the second separator32, in the stack body16(FIG. 2). As viewed in the thickness direction of the joint separator, the positions of the second tunnels104b,106bare overlapped with the positons of the first tunnels104a,106a.

As in the case of the inner tunnel100, also in the outer tunnel104, the first tunnel104aand the second tunnel104bhave the same width in a direction perpendicular to the direction in which the first tunnel104aand the second tunnel104bextend. Further, the first tunnel104aand the second tunnel104bhave the same protruding height by which the first tunnel104aand the second tunnel104bprotrude from the base plate part82. Further, also in the outermost tunnel106, the first tunnel106aand the second tunnel106bhave the same width in a direction perpendicular to the direction in which the first tunnel106aand the second tunnel106bextend, and the first tunnel106aand the second tunnel106bhave the same protruding height by which the first tunnel106aand the second tunnel106bprotrude from the base plate part82. As shown inFIG. 10, inner spaces114,116are formed between the first tunnels104a,106aand the second tunnels104b,106bof the fuel cell joint separator10.

With reference toFIGS. 7 and 10, the inner tunnel100, the outer tunnel104, and the outermost tunnel106of the coolant bridge section94connecting the coolant discharge passage46band the coolant flow field60will be described below specifically. One end of each of the first tunnel100aand the second tunnel100bof the inner tunnel100in the direction in which the first tunnel100aand the second tunnel100bextend (end on the side indicated by the arrow B1) is coupled to the inner side wall75cof each of the straight portions75aof the coolant passage bead seals80a,80bthrough the through hole75fprovided in the inner side wall75c. Further, the other end (end on the side indicated by the arrow B2) of each of the first tunnel100aand the second tunnel100bof the inner tunnel100in the direction in which the first tunnel100aand the second tunnel100bextend is opened to the coolant discharge passage46b.

One end of each of the first tunnel104aand the second tunnel104bof the outer tunnel104in the direction in which the first tunnel104aand the second tunnel104bextend (the other end on the side indicated by the arrow B2) is coupled to the outer side wall75dof each of the straight portions75aof the coolant passage bead seals80a,80bthrough the through hole75gprovided in the outer side wall75d. Further, the other end of each of the first tunnel104aand the second tunnel104bin the direction in which the first tunnel104aand the second tunnel104bextend (end on the side indicated by the arrow B1) is coupled to the first side wall87aof each of the facing portions86a,86bof the inner bead seals72a,72bthrough a through hole87dprovided in the first side wall87a.

One end of each of the first tunnel106aand the second tunnel106bof the outermost tunnel106in the direction in which the first tunnel106aand the second tunnel106bextend (end on the side indicated by the arrow B2) is coupled to the second side wall87bof each of the facing portions86a,86bof the inner bead seals72a,72bthrough a through hole87eprovided in the second side wall87b. The other end of each of the first tunnel106aand the second tunnel106bin the direction in which the first tunnel106aand the second tunnel106bextend (end on the side indicated by the arrow B1) is disposed adjacent to the buffer section on the coolant side (boss arrays56binFIGS. 3 and 6).

In the structure, the coolant flow field60and the coolant discharge passage46bare connected together through the position between the coolant side surface30bof the first separator30and the coolant side surface32bof the second separator32, the inner space116of the outermost tunnel106, the inside of the inner bead seals72a,72b, the inner space114of the outer tunnel104, the inside of the coolant passage bead seals80a,80b, and the inner space110of the inner tunnel100.

The inner tunnel100, the outer tunnel104, and the outermost tunnel106connecting the coolant supply passage46aand the coolant flow field60shown inFIG. 6have the same structure as the inner tunnel100, the outer tunnel104, and the outermost tunnel106shown inFIGS. 7 and 10except that the directions indicated by the arrow B are opposite. That is, the coolant supply passage46aand the coolant flow field60are connected together through the inner space110of the inner tunnel100, the inside of the coolant passage bead seals80a,80b, the inner space114of the outer tunnel104, the inside of the inner bead seals72a,72b, the inner space116of the outermost tunnel106, and the position between the coolant side surface30bof the first separator30and the coolant side surface32bof the second separator32.

Hereinafter, as shown inFIGS. 8 to 10, in the case where a surface of the base plate part82adjacent to the resin frame equipped MEA28is referred to as a reference surface82a, the protruding height by which the inner tunnel100and the outer tunnels102and104protrude from the reference surface82awill also be regarded as the “tunnel height H1”. In the embodiment of the present invention, the inner tunnel100and the outer tunnels102,104have the same protruding height. Alternatively, the inner tunnel100and the outer tunnels102,104may have different protruding heights. Further, the protruding height of the passage bead seals74a,74bby which the passage bead seals74a,74bprotrude from the reference surface82awill also be referred to as the “bead seal height H2”.

The average value of the surface pressure in the direction in which the straight portion75aextends, applied to the front end surface (top portion75e) of the straight portion75aof the passage bead seals74a,74bin the direction in which the straight portion75aprotrudes, by the compression load is also referred to as the “straight portion line pressure”. The average value of the surface pressure per unit length in the direction in which the curved portion75bextends, applied to the front end surface (top portion75e) of the curved portion75bin the direction in which the curved portion75bprotrudes, by the compression load is also referred to as the “curved portion line pressure”.

In the fuel cell joint separator10, the tunnel height H1is determined to be lower than the bead seal height H2by not less than a predetermined value, in a manner that the straight portion line pressure becomes equal to the curved portion line pressure. The expression “the straight portion line pressure is the same as the curved portion line pressure” herein means that the straight portion line pressure is within 80% to 120% of the curved portion line pressure. Further, the “predetermined value” herein can be determined, e.g., based on, e.g., the material, the shape, and the size of the fuel cell joint separator10, and the shapes, the sizes, and the layout of the passage bead seals74a,74b, and the fluid passages44a,44b,46a,46b,48a,48b, and can be calculated in advance by simulations, etc. In the embodiment of the present invention, the tunnel height H1is determined to be not more than 50% of the bead seal height H2.

The straight portion75ais coupled to the inner tunnels100and the outer tunnels102,104(hereinafter also collectively referred to as the tunnels). Therefore, the straight portion75acannot be elastically deformed easily, and the line pressure tends to be large in comparison with the other portions of the passage bead seals74a,74bwhich are not coupled to the tunnels. In this regard, in the case where the tunnel height H1becomes small relative to the bead seal height H2, it becomes easy to suppress the increase in the straight portion line pressure. However, in the case where the tunnel height H1becomes small, the pressure loss of the fluid flowing through the tunnels tend to be large. Therefore, it is preferable to reduce the tunnel height H1as long as the flow of the fluid inside the tunnels is not compromised.

As shown inFIG. 2, the terminal plates18a,18bare made of electrically conductive material. For example, the terminal plates18a,18bare made of metal such as copper, aluminum, or stainless steel. Terminal units120(FIG. 1) are provided at substantially the centers of the terminal plates18a,18b. The terminal units120extend outward in the stacking direction. As shown inFIG. 1, the terminal units120are inserted into through holes (not shown) provided in the insulators20a,20band the end plates22a,22b, and protrude outside the end plates22a,22bin the stacking direction.

As shown inFIG. 2the insulators20a,20bare made of insulating material such as polycarbonate (PC), phenol resin, etc. Insulator recesses122a,122bare formed at the centers of the insulators20a,20b. The insulator recesses122a,122bare opened toward the stack body16. A terminal plate18ais accommodated in the insulator recess122a, and a terminal plate18bis accommodated in the insulator recess122b.

Operation of the fuel cell stack14(FIG. 1) having the above structure will be described briefly. As shown inFIG. 1, in the case of performing power generation in the fuel cell stack14, a fuel gas is supplied to the fuel gas supply passage48a, an oxygen-containing gas is supplied to the oxygen-containing gas supply passage44a, and a coolant is supplied to the coolant supply passages46a.

As shown inFIG. 4, the oxygen-containing gas flows from the oxygen-containing gas supply passage44ainto the oxygen-containing gas flow field52through the oxygen-containing gas bridge section90, the oxygen-containing gas moves along the oxygen-containing gas flow field52in the direction indicated by the arrow B, and the oxygen-containing gas is supplied to the cathode42of the membrane electrode assembly34. In the meanwhile, as shown inFIG. 5, the fuel gas flows from the fuel gas supply passage48ainto the fuel gas flow field58through the fuel gas bridge section92, moves along the fuel gas flow field58in the direction indicated by the arrow B, and the fuel gas is supplied to the anode40of the membrane electrode assembly34.

Thus, in each of the membrane electrode assemblies34, the oxygen-containing gas supplied to the cathode42and the fuel gas supplied to the anode40are partially consumed in electrochemical reactions in the cathode catalyst layer42aand the anode catalyst layer40ato perform power generation.

Then, the remaining oxygen-containing gas which has not been consumed in the electrochemical reaction (oxygen-containing exhaust gas) flows from the oxygen-containing gas flow field52into each of the oxygen-containing gas discharge passages44bthrough the oxygen-containing gas bridge section90, and the oxygen-containing gas is discharged along the oxygen-containing gas discharge passages44bof the stack body16in the direction indicated by the arrow A. Likewise, the remaining fuel gas which has not been consumed in the electrochemical reaction (fuel exhaust gas) flows from the fuel gas flow field58into each of the fuel gas discharge passages48bthrough the fuel gas bridge section92, and the fuel gas is discharged along the fuel gas discharge passages48bof the stack body16in the direction indicated by the arrow A.

As shown inFIG. 6, the coolant flows from each of the coolant supply passages46ainto the coolant flow field60through the coolant bridge section94, and the coolant moves along the coolant flow field60in the direction indicated by the arrow B, for performing heat exchange with the membrane electrode assembly34. The coolant after heat exchange flows through the coolant bridge section94into each of the coolant discharge passages46b, and the coolant is discharged along the coolant discharge passages46bof the stack body16.

In the fuel cell joint separator10according to the embodiment of the present invention, as described above, the tunnel height H1is determined to be smaller than the bead seal height H2by not less than the predetermined value in a manner that the straight portion line pressure becomes the same as the curved portion line pressure. In the passage bead seals74a,74bhaving this structure, though the straight portions75aare coupled to the tunnels, it is possible to avoid the situations where the straight portion line pressure at each position does not become locally higher than the curved portion line pressure of the portions which are not coupled to the tunnels such as the curved portions75b. In the structure, it is possible to apply the pressure to each of the front end surfaces of the passage bead seals74a,74buniformly.

Further, in this case, increase in the rigidity of each of the straight portions75aof the passage bead seals74a,74bis suppressed. Therefore, it is possible to suitably and elastically deform the straight portion75ain correspondence with the compression load, and it is possible to suppress buckling of the straight portion75a. As a result, it is possible to suitably maintain the state where the line pressure having the predetermined strength is applied to each of the front end surfaces of the passage bead seals74a,74b.

Therefore, in the fuel cell joint separator10and the power generation cell12including the fuel cell joint separator10, it is possible to suitably achieve the seal performance by the passage bead seals74a,74b.

In this regard, the relationship among the tunnel height H1relative to the bead seal height H2, the load in a compression direction (indicated by the arrow A) applied to the passage bead seal74a(or the passage bead seal74b) of one fuel cell joint separator10, and the line pressure applied to the front end surface of the passage bead seal74awill be described with reference toFIG. 11.

The horizontal axis inFIG. 11represents, as a value of the compression amount corresponding to the load in the compression direction by which the passage bead seal74a(or the passage bead seal74b) is deformed in the stacking direction. Further, the vertical axis inFIG. 11represents the line pressure of the above passage bead seal74a(or the passage bead seal74b).

The graph shown by a solid line X inFIG. 11shows the relationship between the compression amount and the line pressure in each of the curved portions75bof the passage bead seal74a(or the passage bead seal74b). It should be noted that, though not shown in the graph, the line pressure of each of the curved portions75bis slightly larger than the line pressure of the straight portions which are not coupled to the tunnels of the passage bead seals74a,74b.

The graph shown by a broken line Y inFIG. 11shows the relationship between the compression amount and the line pressure in each of the straight portions75aof the passage bead seal74a(or the passage bead seal74b). That is,FIG. 11shows the relationship between the compression amount and the line pressure in the straight portion75ain the case where the tunnel height H1is 50% of the bead seal height (in the case where the tunnel height H1is smaller than the bead seal height H2by not less than the predetermined value).

The graph shown by a one dot chain line Z inFIG. 11shows the relationship between the compression amount in the straight portion75aof the passage bead seal74a(or the passage bead seal74b) and the line pressure according to a comparative example. Specifically,FIG. 11shows the relationship between the compression amount and the line pressure in the straight portion75ain the case where the tunnel height H1is 70% of the bead seal height H2(in the case where the tunnel height H1is not smaller than the bead seal height H2by not less than the predetermined value, i.e., where the tunnel height H1is smaller than the bead seal height H2and the difference therebetween is less than the predetermined value).

As can be seen from the graph ofFIG. 11, in the case where the tunnel height H1is smaller than bead seal height H2by not less than a predetermined value, the line pressure of the straight portion75ais kept within the range between 80% and 120% of the line pressure of the curved portion75b. That is, since it is possible to maintain the state where variation of the line pressure of the passage bead seal74a(or the passage bead seal74b) falls within the range of ±20%, it is possible to obtain excellent sealing characteristics. In the graph ofFIG. 11, the line pressure of the straight portion75ais set to be not more than the line pressure of the curved portion75b.

It should be noted that variation of the line pressure of the passage bead seals74a,74bin the direction in which the passage bead seals74a,74bextend is within ±30%, and more preferably, within ±20%. In this manner, it is possible to effectively eliminate or reduce the situations where the passage bead seals74a,74bhave portions in which the line pressure becomes large to the extent that buckling of the passage bead seals74a,74btends to occur, and portions in which the line pressure becomes small to the extent that the desired seal performance cannot be exerted sufficiently.

On the other hand, in the case where the tunnel height H1is not smaller than the bead seal height H2by not less than the predetermined value, it can be seen that the line pressure of the straight portion75abecomes higher than 120% of the line pressure of the curved portion75b. That is, the line pressure of the passage bead seal74a(or the passage bead seal74b) may vary beyond the range of ±20%.

Further, the cross mark (X) inFIG. 11shows the compression amount at which buckling of the straight portion75aoccurs. It can be seen from this cross mark (X) that in the case where the tunnel height H1is smaller than the bead seal height H2by not less than a predetermined value, in comparison with case where the tunnel height H1is not smaller than the bead seal height H2by not less than a predetermined value, buckling does not occur easily.

Therefore, as can be clearly seen fromFIG. 11, by determining the suitable tunnel height H1relative to the bead seal height H2, it is possible to avoid the situations where the line pressure applied to the front end surface of the straight portion75abecomes locally and significantly higher than the line pressure applied to the front end surface of the curved portion75b, etc. Further, even if the compression amount becomes large, it is possible to suppress buckling of the straight portion75a. In this manner, it is possible to apply the line pressure to the front end surfaces of the passage bead seals74a,74buniformly, and maintain the suitable strength of the line pressure at which the desired seal performance of the passage bead seals74a,74bis exerted. As described above, in the fuel cell joint separator10and the power generation cell12including the fuel cell joint separator10according to the embodiment of the present invention, it is possible to achieve the desired seal performance of the passage bead seals74a,74b.

In the fuel cell joint separator10according to the embodiment of the present invention, the protruding height of the tunnel (tunnel height H1) is determined to be not more than 50% of the protruding height of the passage bead seals74a,74b(bead seal height H2). In this case, it is possible to apply the line pressure to the front end surface of the passage bead seals74a,74buniformly. Also, by suppressing buckling of the straight portion75a, it is possible to suitably maintain the state where the line pressure having the predetermined strength is applied to the front end surfaces of the passage bead seals74a,74b.

In the fuel cell joint separator10according to the embodiment of the present invention, as the tunnel, the bridge section (oxygen-containing gas bridge section90and the fuel gas bridge section92) includes a plurality of inner tunnels100coupled to the inner side wall75cof the straight portion75aof the passage bead seal74a,74b, and a plurality of outer tunnels102coupled to the outer side wall75dof the straight portion75aof the passage bead seal74a,74b, and the plurality of inner tunnels100and the plurality of outer tunnels102are disposed in a zigzag pattern with respect to the passage bead seal74a,74b.

In this case, it is possible to suitably distribute the oxygen-containing gas which flowed from the oxygen-containing gas supply passage44ainto the inner tunnels100and the outer tunnels102toward the oxygen-containing gas flow field52. Further, it is possible to suitably distribute the fuel gas which flowed from the fuel gas supply passage48ainto the inner tunnels100and the outer tunnels102toward the fuel gas flow field58. In this manner, it is possible to improve the power generation characteristics of the fuel cell stack14. Further, since positions of the inner tunnels100and the outer tunnels102are shifted as described above, it is possible to apply the line pressure to the front end surfaces of the passage bead seals74a,74bmore uniformly.

The fuel cell joint separator10according to the embodiment of the present invention further includes the inner bead seal72a,72bprotruding in the separator thickness direction, the inner bead seal72a,72bincluding the facing portion86a,86bfacing the outer side wall75dof the straight portion75aof the passage bead seal74a,74bat a distance, wherein the bridge section (coolant bridge section94) is disposed in the facing portion86a,86b, the facing portion86a,86bincludes the first side wall87apositioned on a side closer to the outer side wall75dof the straight portion75a, and the second side wall87bpositioned opposite to the side closer to the straight portion75a, as the tunnel, the bridge section (coolant bridge section94) includes the plurality of inner tunnels100coupled to the inner side wall75cof the straight portion75aand the plurality of outer tunnels104each having one end coupled to the outer side wall75dof the straight portion75a, and the other end coupled to the first side wall87aof the facing portion86a,86b, and further includes the plurality of outermost tunnels106coupled to the second side wall87bof the facing portion86a,86b.

That is, even in the case where, as viewed in the thickness direction of the fuel cell joint separator10, the coolant flow field60is disposed inside the portions surrounded by the inner bead seals72a,72b, and the coolant passages46a,46bare disposed outside these portion, it is possible to suitably connect the coolant flow field60and the coolant passages46a,46bthrough the coolant bridge section94. At this time, since the tunnel height H1relative to the bead seal height H2is determined as described above, it is possible to apply the pressure to the front end surfaces of the passage bead seals74a,74buniformly, and maintain the state where the suitable line pressure is applied to the front end surfaces of the passage bead seals74a,74b. Moreover, it is possible to achieve the desired seal performance by the passage bead seals74a,74b.

In the fuel cell joint separator10according to the above embodiment, the plurality of inner tunnels100and the plurality of outer tunnels104are disposed in a zigzag pattern with respect to the passage bead seal74a,74b, and the plurality of outer tunnels104and the plurality of outermost tunnels106are disposed in a zigzag pattern with respect to the inner bead seal72a,72b.

In this case, it is possible to suitably distribute the coolant which flowed from the coolant supply passages46ainto the inner tunnels100, the outer tunnels104, and the outermost tunnels106toward the coolant flow field60, it is possible to effectively perform heat exchange between the coolant and the power generation cells12, and moreover, improve the power generation characteristics by the fuel cell stack14. Further, as described above, since the positions the inner tunnels100, the outer tunnels104, and the outermost tunnels106are shifted, it is possible to apply the line pressure to the front end surfaces of the passage bead seals74a,74bmore uniformly.

The present invention is not limited to the above described embodiments. Various modifications may be made without departing from the gist of the present invention.