U.S. patent application number 12/325935 was filed with the patent office on 2009-03-26 for fuel cell.
This patent application is currently assigned to HONDA MOTOR CO., LTD.. Invention is credited to Takaki NAKAGAWA, Tadashi NISHIYAMA, Daisuke OKONOGI, Hiroyuki TANAKA.
Application Number | 20090081509 12/325935 |
Document ID | / |
Family ID | 32708247 |
Filed Date | 2009-03-26 |
United States Patent
Application |
20090081509 |
Kind Code |
A1 |
TANAKA; Hiroyuki ; et
al. |
March 26, 2009 |
FUEL CELL
Abstract
A first seal member is provided integrally on a surface of a
first metal separator. The first seal member includes a base
portion provided integrally on the first metal separator, a
columnar portion protruding from the base portion, and a curved
edge portion provided on the columnar portion. The curved edge
portion has a predetermined radius of curvature.
Inventors: |
TANAKA; Hiroyuki;
(Utsunomiya-shi, JP) ; NISHIYAMA; Tadashi;
(Sakura-shi, JP) ; OKONOGI; Daisuke; (Shioya-gun,
JP) ; NAKAGAWA; Takaki; (Tochigi-shi, JP) |
Correspondence
Address: |
LAHIVE & COCKFIELD, LLP;FLOOR 30, SUITE 3000
ONE POST OFFICE SQUARE
BOSTON
MA
02109
US
|
Assignee: |
HONDA MOTOR CO., LTD.
Tokyo
JP
|
Family ID: |
32708247 |
Appl. No.: |
12/325935 |
Filed: |
December 1, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10745161 |
Dec 22, 2003 |
7488550 |
|
|
12325935 |
|
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Current U.S.
Class: |
429/434 |
Current CPC
Class: |
H01M 8/0254 20130101;
H01M 8/0276 20130101; H01M 8/0267 20130101; Y02E 60/50 20130101;
H01M 8/0273 20130101; H01M 8/2483 20160201; H01M 8/0206 20130101;
H01M 8/241 20130101 |
Class at
Publication: |
429/26 ;
429/35 |
International
Class: |
H01M 2/08 20060101
H01M002/08 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 25, 2002 |
JP |
2002-375441 |
Claims
1. A fuel cell, comprising: an electrolyte electrode assembly
including a pair of electrodes and an electrolyte interposed
between said electrodes; and metal separators for sandwiching said
electrolyte electrode assembly, wherein a reactant gas supply
passage, and a reactant gas discharge passage extend through said
fuel cell in a stacking direction of said fuel cell; a reactant gas
flow field is connected between said reactant gas supply passage
and said reactant gas discharge passage on at least one of said
metal separators along a surface of said electrode; and a first
seal member or a third seal member provided integrally on one of
said metal separators, around at least one of said electrode, said
reactant gas supply passage, and said reactant gas discharge
passage, said first seal member and said third seal member
including: a base portion provided integrally on said metal
separator; a columnar portion protruding from said base portion;
and a curved edge portion provided on said columnar portion, and
having a predetermined curvature, wherein said third seal member is
provided between a second seal member and said metal separator.
2. A fuel cell according to claim 1, wherein dimensions of said
first seal member and said third seal member satisfy the following
expression: H/W.ltoreq.1.5 where W is a width of said columnar
portion, and H is a height of said first seal member and said third
seal member from said base portion to said curved edge portion.
3. A fuel cell according to claim 1, wherein said columnar portion
protrudes from said base portion with a draft angle.
4. A fuel cell, comprising: an electrolyte electrode assembly
including a pair of electrodes and an electrolyte interposed
between said electrodes; and metal separators for sandwiching said
electrolyte electrode assembly, wherein a coolant supply passage,
and a coolant discharge passage extend through said fuel cell in a
stacking direction of said fuel cell; a coolant flow field is
connected between said coolant supply passage and said coolant
discharge passage on at least one of said metal separators along a
surface of said electrode; and a first seal member or a third seal
member provided integrally on one of said metal separators, around
at least one of said coolant supply passage and said coolant
discharge passage, said first seal member and said third seal
member including: a base portion provided integrally on said metal
separator; a columnar portion protruding from said base portion;
and a curved edge portion provided on said columnar portion, and
having a predetermined curvature, wherein said third seal member is
provided between a second seal member and said metal separator.
5. A fuel cell according to claim 4, wherein dimensions of said
first seal member and said third seal member satisfy the following
expression: H/W.ltoreq.1.5 where W is a width of said columnar
portion, and H is a height of said first seal member and said third
seal member from said base portion to said curved edge portion.
6. A fuel cell according to claim 4, wherein said columnar portion
protrudes from said base portion with a draft angle.
Description
RELATED APPLICATIONS
[0001] This application is a divisional application of U.S.
application Ser. No. 10/745161 filed Dec. 22, 2003 which claims
priority to Japanese Patent Application No. 2002-375441 filed Dec.
25, 2002. The contents of the aforementioned applications are
hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a fuel cell including an
electrolyte electrode assembly, and metal separators for
sandwiching the electrolyte electrode assembly. The electrolyte
electrode assembly includes a pair of electrodes and an electrolyte
interposed between the electrodes. In the fuel cell, fluid flow
fields are formed on surfaces of the separators for supplying
fluids such as a reactant gas and a coolant along surfaces of the
separators. Each of the fluid flow fields is connected between a
fluid supply passage and a fluid discharge passage.
[0004] 2. Description of the Related Art
[0005] For example, a solid polymer electrolyte fuel cell employs a
membrane electrode assembly (MEA) which includes two electrodes
(anode and cathode), and an electrolyte membrane interposed between
the electrodes. The electrolyte membrane is a polymer ion exchange
membrane. The membrane electrode assembly is interposed between
separators. The membrane electrode assembly and the separators make
up a unit of a fuel cell (unit cell) for generating electricity. A
predetermined number of the fuel cells are stacked together to form
a fuel cell stack.
[0006] In the fuel cell, a fuel gas (reactant gas) such as a gas
chiefly containing hydrogen (hydrogen-containing gas) is supplied
to the anode. The catalyst of the anode induces a chemical reaction
of the fuel gas to split the hydrogen molecule into hydrogen ions
(protons) and electrons. The hydrogen ions move toward the cathode
through the electrolyte, and the electrons flow through an external
circuit to the cathode, creating a DC electric current. A gas
chiefly containing oxygen (oxygen-containing gas) or air is
supplied to the cathode. At the cathode, the hydrogen ions from the
anode combine with the electrons and oxygen to produce water.
[0007] In the fuel cell, the fuel gas, the oxygen-containing gas,
and the coolant flow through their dedicated fluid passages which
are hermetically sealed for preventing gas or liquid leakages.
Typically, seal members are interposed between the electrolyte
electrode assembly and the separator for preventing leakages.
Various types of seal members are known, for example, Japanese
Laid-Open Patent Application No. 2001-332276 discloses a seal
member shown in FIG. 9. The seal member includes an elastic base
gasket 1 with a higher hardness of 70 to 90 degree and gaskets 2
with a lower hardness of 30 to 50 degree. The base gasket 1 is made
of a synthetic rubber or a synthetic resin, and the gasket 2 is
made of a synthetic rubber. The gaskets 2 are placed on both
surfaces of the base gasket 1.
[0008] In the seal member of Japanese Laid-Open Patent Application
No. 2001-332276, the gaskets 2 may be displaced undesirably on the
base gasket 1. If the desired sealing function of the gaskets 2 can
not be performed due to the positional displacement, leakage of the
reactant gas (fuel gas and/or oxygen-containing gas) and coolant
may occur.
[0009] In an attempt to address the problem, U.S. Patent
Application Publication No. US2002/0122970A1 discloses a method for
fabricating a seal-integrated separator. According to the
disclosure, a separator body of a fuel cell and seal members on
both surfaces of the separator body are formed integrally into one
piece. In contrast to the technique in which seal members are
separately provided on both surfaces of the separator body, or the
technique in which the separator body is coated with seal members,
in the seal-integrated separator of U.S. Patent Application
Publication No. US2002/0122970A1, the seal members are positioned
with a high degree of accuracy, and the number of steps for
assembling the fuel cells is significantly reduced.
[0010] Typically, the seal members are formed in a lip shape. The
seal members are tapered to have thin end portions. Therefore, even
if the seal members and the separator body are formed into one
piece, the desired sealing performance may not be achieved for the
fuel cell in some automobile applications.
[0011] Specifically, positional displacement may occur at the end
portions of the seal members due to vibrations during the travel of
the vehicle and impacts at the time of sudden acceleration and
sudden braking. The positional displacement reduces the contact
area of the seal members. If the positional displacement occurs, it
is difficult to maintain the desired sealing performance. In the
case of the fuel cell using a metal separator, surfaces of the
metal separator are deformed, distorted or warped easily. However,
the end portions of the seal members can not be deformed in
accordance with the deformation of the metal separator. Thus, the
sealing pressure between the surfaces of the separator and the seal
member is not maintained at a sufficient level for sealing.
[0012] If a plurality of fuel cells are stacked together to form a
fuel cell stack, the positional displacement occurs easily at the
end portions of the seal members. Consequently, the end portions of
the seal members are tilted, the surface pressure applied to the
seal members is reduced, and the contact area between the separator
and the seal members is reduced. It is difficult to maintain the
desired sealing performance.
SUMMARY OF THE INVENTION
[0013] A main object of the present invention is to provide a fuel
cell having a seal member with a simple structure in which the
sealing performance between the seal member and the metal separator
is reliably maintained, and the desired power generation
performance can be achieved.
[0014] According to the present invention, a seal member is
provided integrally on a metal separator, around at least one of an
electrode, a reactant gas supply passage, and a reactant gas
discharge passage. The seal member includes a base portion provided
integrally on the metal separator, a columnar portion protruding
from the base portion, and a curved edge portion provided on the
columnar portion. The curved edge portion has a predetermined
radius of curvature.
[0015] Since the seal member includes the base portion, the
columnar portion, and the curved edge portion in contact with the
sealing area under pressure, the contact area between the seal
member and the sealing area is large in comparison with the
conventional seal member having a lip shape. Even if the metal
separators are deformed due to the gas pressure in the fuel cell,
or even if surfaces of the metal separators are corrugated, warped,
or distorted, the desired sealing performance can be achieved.
[0016] When a plurality of the fuel cells are stacked to form a
fuel cell stack, the toughness of the seal member against the
positional displacement is improved. The curved edge portion of the
seal member is in contact with the sealing area under pressure.
When the sealing area is displaced laterally, the columnar portion
of the seal member is deformed, and thus, the curved edge portion
of the sealing member moves laterally together with the sealing
area. When the fuel cell is mounted in a vehicle, the seal member
is kept tightly in contact with the metal separator under pressure,
and the anti-vibration and the anti-shock performance can be
improved.
[0017] The aspect ratio (H/W) of the seal member is 1.5 or less.
Therefore, when the fuel cells are stacked to form the fuel cell
stack, it is unlikely that the curved edge portion of the seal
member is deformed excessively, or tilted away from the sealing
area. The toughness of the seal member against the positional
displacement is improved.
[0018] The radius of curvature of the curved edge portion is
ranging from 1.0 mm to 3.0 mm. If the radius of curvature is less
than 1.0 mm, the columnar portion of the seal member may not be
deformed in accordance with the movement of the sealing area, i.e.,
may not be deformed to compensate for offset of the sealing area.
If the radius of curvature is greater than 3.0 mm, the curved edge
portion is not compressed, and the desired sealing performance can
not be achieved.
[0019] The above and other objects, features and advantages of the
present invention will become more apparent from the following
description when taken in conjunction with the accompanying
drawings in which preferred embodiments of the present invention
are shown by way of illustrative example.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is an exploded perspective view showing main
components of a fuel cell according to an embodiment of the present
invention;
[0021] FIG. 2 is a cross sectional view showing main components of
a fuel cell stack formed by stacking a plurality of the fuel
cells;
[0022] FIG. 3 is a cross-sectional view showing a seal member of
the fuel cell;
[0023] FIG. 4 is a cross-sectional view showing a part of a
conventional seal member having a lip shape;
[0024] FIG. 5 is a graph showing relationship between pressure
applied to seal surfaces and gas pressure which causes leakage in
each of the conventional structure and the present embodiment;
[0025] FIG. 6 is a graph showing relationship between pressure
applied to seal surfaces and gas pressure which causes leakage when
the seal member was offset in each of the conventional structure
and the present embodiment;
[0026] FIG. 7 is a graph showing relationship between pressure
applied to seal surfaces and gas pressure which causes leakage when
corrugated separators were used in each of the conventional
structure and the present embodiment;
[0027] FIG. 8 is a graph showing relationship between displacement
of cell and shear load applied on fuel cell stack in each of the
conventional structure and the present embodiment; and
[0028] FIG. 9 is a cross sectional view showing a conventional seal
member.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0029] FIG. 1 is an exploded view showing main components of a fuel
cell 10 according to an embodiment of the present invention and
FIG. 2 is a cross sectional view showing main components of a fuel
cell stack 12 formed by stacking a plurality of the fuel cells
10.
[0030] As shown in FIG. 2, the fuel cell stack 12 is formed by
stacking a plurality of the fuel cells 10 in a direction indicated
by an arrow A. End plates 14a, 14b are provided at opposite ends of
the fuel cell stack 12 in the stacking direction. The end plates
14a, 14b are fastened by tie rods (not shown) for tightening the
fuel cells 10 with a predetermined tightening force in the
direction indicated by the arrow A.
[0031] As shown in FIG. 1, the fuel cell 10 includes a membrane
electrode assembly (electrolyte electrode assembly) 16 and first
and second metal separators 18, 20 for sandwiching the membrane
electrode assembly 16. The first and second metal separators 18, 20
are steel plates, stainless steel plates, aluminum plates, plated
steel sheets, or metal plates having anti-corrosive surfaces by
surface treatment. For example, the first and second metal
separators 18, 20 have a thickness of 0.05 mm to 1.0 mm.
[0032] As shown in FIG. 1, at one horizontal end of the fuel cell
10 in a direction indicated by an arrow B, an oxygen-containing gas
supply passage (reactant gas supply passage) 30a for supplying an
oxygen-containing gas, a coolant discharge passage 32b for
discharging a coolant, and a fuel gas discharge passage (reactant
gas discharge passage) 34b for discharging a fuel gas such as a
hydrogen-containing gas are arranged vertically in a direction
indicated by an arrow C. The oxygen-containing gas supply passage
30a, the coolant discharge passage 32b, and the fuel gas discharge
passage 34b extend through the fuel cell 10 in a stacking direction
indicated by an arrow A.
[0033] At the other horizontal end of the fuel cell 10 in the
direction indicated by the arrow B, a fuel gas supply passage
(reactant gas supply passage) 34a for supplying the fuel gas, a
coolant supply passage 32a for supplying the coolant, and an
oxygen-containing gas discharge passage (reactant gas discharge
passage) 30b for discharging the oxygen-containing gas are arranged
vertically in the direction indicated by the arrow C. The fuel gas
supply passage 34a, the coolant supply passage 32a, and the
oxygen-containing gas discharge passage 30b extend through the fuel
cell 10 in the direction indicated by the arrow A.
[0034] The membrane electrode assembly 16 comprises an anode 38, a
cathode 40, and a solid polymer electrolyte membrane 36 interposed
between the anode 38 and the cathode 40. The solid polymer
electrolyte membrane 36 is formed by impregnating a thin membrane
of perfluorosulfonic acid with water, for example.
[0035] Each of the anode 38 and cathode 40 has a gas diffusion
layer such as a carbon paper, and an electrode catalyst layer of
platinum alloy supported on carbon particles. The carbon particles
are deposited uniformly on the surface of the gas diffusion layer.
The electrode catalyst layer of the anode 38 and the electrode
catalyst layer of the cathode 40 are fixed to both surfaces of the
solid polymer electrolyte membrane 36, respectively.
[0036] The first metal separator 18 has an oxygen-containing gas
flow field (reactant gas flow field) 42 on its surface 18a facing
the membrane electrode assembly 16. The oxygen-containing gas flow
field 42 includes a plurality of grooves extending straight in the
direction indicated by the arrow B, for example. The
oxygen-containing gas flow field 42 is connected to the
oxygen-containing gas supply passage 30a at one end, and connected
to the oxygen-containing gas discharge passage 30b at the other
end. As shown in FIGS. 1 and 2, the second metal separator 20 has a
fuel gas flow field (reactant gas flow field) 44 on its surface 20a
facing the membrane electrode assembly 16. The fuel gas flow field
44 includes a plurality of grooves extending in the direction
indicated by the arrow B. The fuel gas flow field 44 is connected
to the fuel gas supply passage 34a at one end, and connected to the
fuel gas discharge passage 34b at the other end.
[0037] A coolant flow field 46 is formed between a surface 18b of
the first metal separator 18 and a surface 20b of the second metal
separator 20. The coolant flow field 46 includes a plurality of
grooves extending straight in the direction indicated by the arrow
B. The coolant flow field 46 is connected to the coolant supply
passage 32a at one end, and connected to the coolant discharge
passage 32b at the other end.
[0038] A first seal member 50 is formed integrally on the surface
18a of the first separator 18, around the cathode 40, i.e., around
the oxygen-containing gas flow field 42, the oxygen-containing gas
supply passage 30a, and the oxygen-containing gas discharge passage
30b. The first seal member 50 is made of seal material, cushion
material or packing material such as EPDM (Ethylene Propylene Diene
Monomer), NBR (Nitrile Rubber), fluoro rubber, silicon rubber,
fluoro silicon rubber, butyl rubber (Isobutene-Isoprene Rubber),
natural rubber, styrene rubber, chloroprene rubber, or acrylic
rubber. The first seal member 50 has a hardness ranging from 30
degrees to 60 degrees.
[0039] The first seal member 50 includes a seal 52a for preventing
leakage of the oxygen-containing gas from the oxygen-containing gas
flow field 42 into the coolant supply passage 32a, a seal 52b for
preventing leakage of the oxygen-containing gas from the
oxygen-containing gas flow field 42 into the coolant discharge
passage 32b. Further, the first seal member 50 includes a seal 54a
for preventing leakage of the oxygen-containing gas from the
oxygen-containing gas flow field 42 into the fuel gas supply
passage 34a, and a seal 54b for preventing leakage of the
oxygen-containing gas into the fuel gas discharge passage 34b.
These seals 52a, 52b, 54a, 54b may be formed integrally into one
piece. Alternatively, these seals 52a, 52b, 54a, 54b may be formed
separately.
[0040] As shown in FIG. 3, the first seal member 50 includes a base
portion 56 formed integrally on the surface 18a of the first
separator 18, and a columnar portion 58 having a columnar cross
section, and a curved edge portion 60 having a curved cross section
with a predetermined radius of curvature. The columnar portion 58
protrudes from the base portion 56, and the curved edge portion 60
is formed on the columnar portion 58. The columnar portion 58
protrudes from the base portion 56 with a small draft angle. The
draft angle is produced at the time of molding.
[0041] The radius of curvature R1 of the curved edge portion 60 is
ranging from 1.0 mm to 3.0 mm. The sealing width of the curved edge
portion 60 is 1.0 mm or greater. When the curved edge portion 60 is
in contact with the solid polymer electrolyte membrane 36 for
pressing the surface 20a of the second separator 20, the width of
the contact area is 1.5 mm or greater. The aspect ratio of the
first seal member 50 is not more than 1.5, i.e., H/W.ltoreq.1.5
(where W is the width of the columnar portion 58, and H is the
height from the base portion 56 to the curved edge portion 60). The
radius of curvature R2 of the base portion 56 is ranging from 0.3
mm to 1.0 mm for preventing stress concentration between the
columnar portion 58 and the base portion 56.
[0042] As shown in FIGS. 1 and 2, a second seal member 62 is formed
integrally on the surface 18b of the first separator 18, around the
coolant flow field 46, the coolant supply passage 32a, and the
coolant discharge passage 32b. The second seal member 62 includes a
seal 64a for preventing leakage of the coolant from the coolant
flow field 46 into the oxygen-containing gas supply passage 30a, a
seal 64b for preventing leakage of the coolant from the coolant
flow field 46 into the oxygen-containing gas discharge passage 30b.
Further, the second seal member 62 includes a seal 66a for
preventing leakage of the coolant from the coolant flow field 46
into the fuel gas supply passage 34a, and a seal 66b for preventing
leakage of the coolant from the coolant flow field 46 into the fuel
gas discharge passage 34b. These seals 64a, 64b, 66a, 66b may be
formed integrally into one piece. Alternatively, these seals 64a,
64b, 66a, 66b may be formed separately. The second seal member 62
has a rectangular cross section.
[0043] A third seal member 68 is formed integrally on the surface
20b of the second separator 20, around the coolant flow field 46,
the coolant supply passage 32a, and the coolant discharge passage
32b. The third seal member 68 includes a seal 70a for preventing
leakage of the coolant from the coolant flow field 46 into the
oxygen-containing gas supply passage 30a, a seal 70b for preventing
leakage of the coolant from the coolant flow field 46 into the
oxygen-containing gas discharge passage 30b. Further, the third
seal member 68 includes a seal 72a for preventing leakage of the
coolant from the coolant flow field 46 into the fuel gas supply
passage 34a, and a seal 72b for preventing leakage of the coolant
from the coolant flow field 46 into the fuel gas discharge passage
34b.
[0044] The third seal member 68 has the same structure with the
first seal member 50. The constituent elements of the third seal
member 68 that are identical to those of the first seal member 50
are labeled with the same reference numeral, and description
thereof is omitted.
[0045] A fourth seal member 74 is formed integrally on the surface
20a of the second separator 20, around the anode 38, i.e., around
the fuel gas flow field 44, the fuel gas supply passage 34a, and
the fuel gas discharge passage 34b.
[0046] The fourth seal member 74 includes a seal 76a for preventing
leakage of the fuel gas from the fuel gas flow field 44 into the
oxygen-containing gas supply passage 30a, a seal 76b for preventing
leakage of the fuel gas from the fuel gas flow field 44 into the
oxygen-containing gas discharge passage 30b. Further, the fourth
seal member 74 includes a seal 78a for preventing leakage of the
fuel gas from the fuel gas flow field 44 into the coolant supply
passage 32a, and a seal 78b for preventing leakage of the fuel gas
into the coolant discharge passage 78b. The fourth seal member 74
has a rectangular cross section as with the second seal member
62.
[0047] Next, operation of the fuel cell 10 will be described.
[0048] In operation, as shown in FIG. 1, a fuel gas such as a
hydrogen-containing gas is supplied to the fuel gas supply passage
34a, an oxygen-containing gas such as air is supplied to the
oxygen-containing gas supply passage 30a, and a coolant such as
pure water, an ethylene glycol or an oil are supplied to the
coolant supply passage 32a.
[0049] The fuel gas flows from the fuel gas supply passage 34a into
the fuel gas flow field 44 of the second metal separator 20. The
fuel gas flows in the direction indicated by the arrow B along the
anode 38 of the membrane electrode assembly 16 to induce a chemical
reaction at the anode 38. The oxygen-containing gas flows from the
oxygen-containing gas supply passage 30a into the oxygen-containing
gas flow field 42 of the first metal separator 18. The
oxygen-containing gas flows in the direction indicated by the arrow
B along the cathode 40 of the membrane electrode assembly 16 to
induce a chemical reaction at the cathode 40.
[0050] In the membrane electrode assembly 16, the fuel gas supplied
to the anode 38, and the oxygen-containing gas supplied to the
cathode 40 are consumed in the electrochemical reactions at
catalyst layers of the anode 38 and the cathode 40 for generating
electricity.
[0051] After the fuel gas is consumed at the anode 38, the fuel gas
flows into the fuel gas discharge passage 34b, and flows in the
direction indicated by the arrow A. Similarly, after the
oxygen-containing gas is consumed at the cathode 40, the
oxygen-containing gas flows into the oxygen-containing gas
discharge passage 30b, and flows in the direction indicated by the
arrow A.
[0052] The coolant supplied to the coolant supply passages 32a
flows into the coolant flow field 46 between the first and second
metal separators 18, 20, and flows in the direction indicated by
the arrow B. After the coolant is used for cooling the membrane
electrode assembly 16, the coolant is discharged into the coolant
discharge passages 32b.
[0053] In the embodiment of the present invention, the first seal
member 50 is formed integrally on the surface 18a of the first
metal separator 18. As shown in FIG. 3, the first seal member 50
includes the base portion 56 formed integrally on the first
separator 18, the columnar portion 58 protruding from the base
portion 56, and the curved edge 60 provided on the columnar portion
58.
[0054] Thus, the area of contact between the first seal member 50
and the sealing area (solid polymer electrolyte membrane 36) is
large in comparison with the conventional seal member having a lip
shape. Thus, even if the first and second metal separators 18, 20
are deformed due to the gas pressure in the fuel cell 10, or
surfaces of the metal separators 18, 20 are corrugated, warped, or
distorted, the desired sealing performance can be maintained.
[0055] Further, when a plurality of the fuel cells 10 are stacked
together to form the fuel cell stack 12, the first seal member 50
has the toughness. The positional displacement of the first seal
member 50 does not occur. When the curved edge portion 60 of the
first seal member 50 is pressed against the sealing area, the
columnar portion 58 of the first seal member 50 is deformed to
compensate for the movement of the sealing area so that the curved
edge 60 moves together with the sealing area.
[0056] Thus, when the fuel cell stack 12 is mounted on a vehicle,
the first seal member 50 is reliably in contact with the sealing
area, absorbing vibrations while the vehicle is traveling, and
shocks at the time of sudden braking and sudden acceleration. The
anti-vibration capability and anti-shock capability of the fuel
cell stack 12 are improved.
[0057] The radius of curvature R1 of the curved edge portion 60 is
ranging from 1.0 mm to 3.0 mm. The modulus of elasticity is low so
that the curved edge portion 60 can be tightly in contact with the
sealing area. If the radius of curvature R1 is less than 1.0 mm,
the columnar portion 58 of the first seal member 50 can not be
deformed to compensate for the offset of sealing area. If the
radius of curvature R1 is greater than 3.0 mm, the curved edge
portion 60 can not be compressed sufficiently, and the desired
sealing performance is not achieved.
[0058] The seal width of the curved edge portion is 1.0 mm or
greater, and the width of contact area between the curved edge
portion 60 and the sealing area when the curved edge portion 60 is
compressed under pressure is 1.5 mm or greater. Thus, the sealing
performance of the first seal member 50 is maintained even if the
first and second metal separators 18, 20 are deformed. The
toughness against the positional displacement when the fuel cells
10 are stacked to form the fuel cell stack 12 is improved. Further,
the anti-vibration capability and anti-shock capability of the fuel
cell stack 12 in the automobile application are improved.
[0059] The aspect ratio (H/W) of the first seal member 50 is 1.5 or
less. Therefore, when the fuel cells 10 are stacked to form the
fuel cell stack 12, the curved edge portion 60 of the first seal
member 50 is not tilted easily. The toughness of the first seal
member 50 against the positional displacement is improved.
[0060] The radius of curvature R2 at the corner between the base
portion 56 and the columnar portion 58 is ranging from 0.3 mm to
1.0 mm. Thus, the stress is not concentrated at the base portion 56
when the first seal member 50 is compressed. The radius of the
curvature R2 at the corner of the base portion 56 is 0.3 mm or
greater. Thus, the stress applied to the base portion 56 is
efficiently distributed for preventing cracks from being formed in
the first seal member 50. The radius of curvature R2 at the corner
of the base portion 56 is 1.0 mm or less. Thus, the first seal
member 50 can be deformed to compensate for the lateral movement of
the sealing surface.
[0061] The third seal member 68 has the same structure with the
first seal member 50, and thus, description of the third seal
member 68 is omitted.
[0062] An experiment was carried out for comparing sealing
performance of a conventional seal member 3 having a lip shape and
sealing performance of the seal member according to the present
embodiment. As shown in FIG. 4, the seal member 3 had a tapered
shape, and the radius of curvature R3 of the curved edge portion 4
of the seal member 3 was ranging from 0.1 mm to 0.3 mm.
[0063] The conventional fuel cell stack was formed by stacking a
pair of fuel cells 10 each including the seal member 3. Further,
the fuel cells 10 including the seal member according to the
present embodiment were stacked to form the fuel cell 12. In the
seal member according to the present embodiment, the radius of
curvature R1 of the curved edge portion 60 was 1.5 mm, and the
aspect ratio H/W of the seal member was 1.2. A helium gas was used
for applying a gas pressure to the anode 38. Relationship between
pressure applied to seal surfaces, and gas pressure which causes
leakage is shown in FIG. 5. The seal members used in the
experiments as described later with reference to FIGS. 6 through 8
were similar to the seal member used in this experiment.
[0064] In the conventional structure, when the first and second
metal separators 18, 20 were deformed due to the difference between
the gas pressure applied to the first metal separator 18 and the
gas pressure applied to the second metal separator 20, the sealing
performance was lowered significantly. In the present embodiment,
the first and third seal members 50, 68 each having the base
portion, the columnar portion, and the curved edge portion are
used. Even if the first and second separators 18, 20 were deformed
due to the difference in the gas pressure, the first and second
seal members 50, 68 were deformed to compensate for the deformation
of the first and seal separators 18, 20. Thus, the sealing
performance of the present embodiment was considerably better than
the sealing performance of the conventional structure.
[0065] In the next experiment, the first seal member 50 was offset
by 0.25 mm on the separator surface, and the seal member 3 was
offset by 0.20 mm on the separator surface. The pressure which
causes leakage was detected in each of the present embodiment and
the conventional structure.
[0066] As shown in FIG. 6, in the conventional structure, the
offset of the seal member 3 caused the significant deterioration in
the sealing performance. In contrast, in the present embodiment,
the offset of the first seal member 50 did not cause any
significant deterioration in the sealing performance. The first
seal member 50 was deformed to reliably compensate for the
offset.
[0067] In the next experiment, corrugated plates with a rise of 0.2
mm and a pitch of 10 mm were used for the first and second metal
separators 18, 20. The pressure which causes leakage was detected
in each of the present embodiment and the conventional structure.
The result of the experiment is shown in FIG. 7. As shown in FIG.
7, in the conventional structure, the corrugated surfaces of the
first and second metal separators 18, 20 caused the significant
deterioration in the sealing performance. In contrast, in the
present embodiment, the corrugated surfaces of the first and second
metal separators 18, 20 did not cause any significant deterioration
in the sealing performance. The seal members of the present
embodiment were deformed to reliably compensate for the corrugated
surfaces.
[0068] In the next experiment, a shear load was applied to the fuel
cell stack 12, on a surface perpendicular to the stacking direction
of the fuel cell stack 12. Likewise, a shear load was applied to
the conventional fuel cell stack, on a surface perpendicular to the
stacking direction of the conventional fuel cell stack. The
positional displacement of the seal members in the direction in
which the shear load was applied, was detected in each of the
present embodiment and the conventional structure.
[0069] The result of the experiment is shown in FIG. 8. As shown in
FIG. 8, the seal members 3 having a lip shape did not have the
toughness against the shear load. The positional displacement of
the seal members 3 was large. In contrast, the first and third seal
members 50, 68 of the present embodiment had the toughness against
the shear load. The first and third seal members 50, 68 were not
displaced significantly.
[0070] In the fuel cell according to the present invention, the
seal member has the base portion, the columnar portion, and the
curved edge portion. Therefore, in contrast to the conventional
seal member having a lip shape, the contact area with the metal
separator is large. Thus, even if the metal separators are
deformed, or surfaces of the metal separators are corrugated,
warped, or distorted, the sealing performance is not
deteriorated.
[0071] When the fuel cells are stacked to form a fuel cell stack,
the toughness of the seal member against the positional
displacement is improved. The curved edge portion of the seal
member is in contact with the metal separator under pressure, the
curved edge portion of the seal member move laterally together with
the metal separator. Thus, when the fuel cell is mounted in a
vehicle, the seal member is kept tightly in contact with the metal
separator under pressure, and the anti-vibration and the anti-shock
performance can be improved.
[0072] While the invention has been particularly shown and
described with reference to preferred embodiments, it will be
understood that variations and modifications can be effected
thereto by those skilled in the art without departing from the
spirit and scope of the invention as defined by the appended
claims.
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