Seal for a joint or juncture – Seal between fixed parts or static contact against... – Contact seal for other than internal combustion engine – or...
Reexamination Certificate
1999-10-18
2001-05-15
Melius, Terry Lee (Department: 3626)
Seal for a joint or juncture
Seal between fixed parts or static contact against...
Contact seal for other than internal combustion engine, or...
C429S006000, C429S006000
Reexamination Certificate
active
06231053
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to gaskets as sealing devices, and particularly relates to a gasket for fuel cells, such as stacked fuel cells. The gasket supports a sheet, such as an electrolytic membrane, in a narrow region and seals working gasses and fluids, such as oxygen, nitrogen, hydrogen and water.
2. Description of the Related Art
In general, each “cell” of a fuel cell includes a pair of porous bipolar plates or collector separator electrodes and a pair of membrane and electrode assemblies (MEAs). Each MEA is composed of a polymer electrolyte membrane, a catalytic layer, and a reactive electrode layer. The MEA is sandwiched between two bipolar plates. The functional requirements in such a composite configuration or cell are, for example, a constant distance between the two adjacent bipolar plates, a high level of hermetic or low permeation sealing, precluding evaporation of water and drying of the polymer electrolyte membrane, and easy assembly and disassembly. Several adjacent “cells” form a fuel cell “stack”.
Normally, the fuel cell stack is sealed with a curable bonding agent. This seal is effective initially, but it has a serious drawback because deteriorated curable bonding agent seals cannot be easily replaced with new ones.
Solutions for solving this problem are, for example, to provide sealing between fuel cell stacks using gaskets, such as disclosed in Japanese Patent Application Laid-Open Nos. 9-231987, 7-227220 and 7-153480, or using a composite gasket composed of a rubber sheet and a cellular or sponge layer, as disclosed in Japanese Patent Application Laid-Open No. 7-312223. These gaskets add to the overall thickness of the fuel cell stack and do not allow for easy assembly and disassembly.
Another solution includes using a composite gasket composed of a metal frame or sheet and a rubber layer. This has the following disadvantages:
A. Gaseous constituents in the fuel cell and cooling water react with the metal sheet to generate contaminating ions. This causes decreased electrical generating efficiency of the fuel cell.
B. Since the metal frame is relatively thick, in the range of 0.5 to 2 mm, a large fuel cell stack which includes approximately 100 cells is heavy and large.
C. Any distortion of the metal frame such as by warping will make positioning and assembly of the polymer electrolyte membrane difficult. This distortion can occur when a seating stress is applied to ensure sealing and as a result the metal frame will warp. The warped part causes curvature of the metal frame of the gasket, and thus making assembly of the fuel cell more difficult.
D. Since a large area is sealed, the fuel cell assembly requires a large compressive force. However, the compressive force of sealing changes significantly as the compressed height of the seal changes slightly, resulting in unstable sealing characteristics.
When assembling fuel cells, polymer electrolyte membranes are apt to be contaminated with dust or the like due to handling the sheets directly. Dust or the like influences the generating efficiency of the fuel cell. It is also difficult to position the sheet correctly in the predetermined position in the fuel cell because the membrane is thin and soft.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a gasket for fuel cells which solves the above-mentioned problems and has improved fuel cell electrical generating efficiency.
It is another object of the present invention to provide a gasket for fuel cells which is suitable for easy assembly.
It is another object of the present invention to provide a gasket for fuel cells which is compact in the size and the weight.
It is still another object of the present invention to provide a gasket for fuel cells which eliminates the need to handle the polymer electrolyte membranes directly.
A first aspect of the present invention is to provide a gasket for fuel cells comprising a gasket body including a metal frame and a resin sheet and having openings, and a sealing section including a liquid rubber vulcanizate, the sealing section being bonded to the gasket body, and the inner face of each of the openings is covered with the sealing section.
A second aspect of the present invention is a gasket for fuel cells which includes a gasket body comprising a metal frame and a resin sheet and having openings and at least one through-hole, and a sealing section comprising a liquid rubber vulcanizate. The sealing section is bonded to the gasket body, and the sealing section is integrally formed so as to pass through the through-hole in the body and cover the side face of each of the openings and the upper and lower faces of the gasket body in the vicinity of the each of the openings.
A third aspect of the present invention is a gasket for fuel cells which includes a gasket body comprising one of a metal frame and a resin sheet is disposed in the openings, and a sealing section comprising a liquid rubber vulcanizate. The sealing section is bonded to the gasket body and the outer portion of the polymer electrolyte membranes, in the body cover the side face of each of the openings and the upper and lower faces of the gasket body and the polymer electrolyte membranes in the vicinity of the each of the openings.
In the present invention, the inner face of each opening is entirely covered with the sealing section; as a result, the working fluid does not come into direct contact with the gasket body when the gasket is mounted in a fuel cell. Thus, the gasket body does not allow formation of contaminants, e.g., ions, which decrease the electrical generating efficiency of the fuel cell. Accordingly, the fuel cell including the gasket has high generating efficiency.
In the second aspect, the sealing section can be tightly fixed to the gasket body without a bonding agent so as to surround the edge portion including the through-hole and each opening. Since a bonding agent is not used for bonding between the gasket body and the sealing section, a fuel cell using this gasket will not cause a decrease in generating electrical efficiency due to any chemical reactions with the bonding agent. Furthermore, the process of applying a bonding agent is not necessary for adhering the gasket body to the frame. Thus, the manufacturing process of the gasket is simplified.
In the first and second aspects, the gasket body preferably has a thickness in a range of 0.03 to 0.3 mm. The distance between two adjacent bipolar plates can be decreased when this gasket body is mounted between them. Thus, a fuel cell using this gasket will have improved electrical generating efficiency and be thinner and lighter.
In the third aspect, the sealing section can be tightly bonded to the gasket body and the polymer electrolyte. Any contamination of the polymer electrolyte membrane can be effectively prevented because there is no need to handle directly the membrane and precise positioning of the membrane can be accomplished because the membrane is tightly bonded to the rigid gasket. Any change in size of the membrane caused by pressure of the working liquid or fuel gas or temperature during use can be effectively absorbed by the sealing section because the sealing section is made of relatively compliant soft material such as liquid rubber.
REFERENCES:
patent: 4666579 (1987-05-01), Beaver et al.
patent: 5145190 (1992-09-01), Boardman
patent: 5284718 (1994-02-01), Chow et al.
patent: 5928807 (1999-07-01), Elias
patent: 5945192 (1999-08-01), Kato et al.
patent: 58-078372 (1983-05-01), None
patent: 59-068171 (1984-04-01), None
patent: 07153480 (1995-06-01), None
patent: 07226220 (1995-08-01), None
patent: 07263004 (1995-10-01), None
patent: 07312223 (1995-11-01), None
patent: 09231987 (1997-09-01), None
patent: WO 9222096 (1992-10-01), None
Harness & Dickey & Pierce P.L.C.
Melius Terry Lee
NOK Corporation
Schwing Karlena D.
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