Cell stack of fuel cell and method of fastening cell stack of fuel cell

A cell stack of a fuel cell comprises a cell stack body including a cell stack structure including plural cells stacked together; an elastic member disposed at an end of the cell stack structure in a direction in which the plural cells are stacked, and a pair of end plates sandwiching the cell stack structure and the elastic member, and a fastener band extending to surround the cell stack body and to cover a pair of end surfaces and a pair of opposing side surfaces of the cell stack body, the fastener band including a first band engagement portion and a second band engagement portion at both end portions thereof, respectively, and the cell stack body is fastened by the fastener band by direct or indirect engagement between the first band engagement portion and the second band engagement portion.

FIELD OF THE INVENTION

The present disclosure relates to a cell stack of a fuel cell and a method of fastening the cell stack of the fuel cell. More particularly, the present disclosure relates to a cell stack of a fuel cell including a cell stack body fastened using a fastener band, and a method of fastening the cell stack of the fuel cell.

DESCRIPTION OF THE RELATED ART

A cell stack of a typical fuel cell is formed by arranging current collectors, insulating plates and end plates in this order at both ends of a cell stack structure including plural cells (unit cells) stacked, and by fastening this stack structure by fastener rods (bolts and nuts) in a direction in which the cells are stacked (see e.g., Japanese Laid-Open Patent Application Publication No. 2007-59187 (patent document 1). In a fastening structure using the fastener rods (bolts and nuts), since the head portions and tip end portions of the bolts and the nuts protrude from the surfaces of the end plates, the size of the fuel cell increases.

Under the circumstances, various techniques for reducing the size of the fuel cell by reducing the size of the fastening structure of the cell stack have been developed. For example, techniques for fastening the cell stack using a thin fastener band are disclosed (see e.g., Japanese Laid-Open Patent Application Publication No. 2000-67902 (patent document 2) and Translated Japanese Application Publication No. 2001-504632 (patent document 3). In the fuel cells disclosed in patent documents 2 and 3 using the fastener band to fasten the cell stack structure, the end plates and others, the fastener band does not protrude substantially from the surfaces of the end plates. Therefore, the size of the fuel cell can be reduced.

However, in the polymer electrolyte fuel cell disclosed in patent document 2, since a connecting portion of the band is fastened by bolts and nuts, the protruding portions of at least the bolts and the nuts are required as the connecting portion, thereby increasing a weight and a volume of the fuel cell. As a surface area of the fuel cell increases, a heat radiation amount of the fuel cell increases. For example, when the fuel cell is used as an electric power supply in a cogeneration system and therefore heat recovery is necessary, performance of the fuel cell degrades. In addition, the number of steps for fastening the bolts and the nuts and the number of components increases, reducing assembling efficiency.

In the fuel cell stack structure disclosed in patent document 3, since an annular band formed by welding both ends of a band-like member, which is made of metal or the like is used, the cell stack structure is subjected to an unnecessary load or an excess load such as high-temperature heat, in the assembly process. When the band is welded after assembling, heat applied to a weld portion is transmitted to a resin material which is low in heat resistance, such as a gasket or a polymer electrolyte membrane of the cell, degrading durability of the fuel cell.

Furthermore, in the above mentioned conventional fastening method, since it is necessary to adjust each of the plural fastener rods or each of the plural bands, the manufacturing steps increases in number, which is undesirable.

SUMMARY OF THE DISCLOSURE

The present disclosure is directed to solving the above described problem, and an object of the present disclosure is to provide a cell stack of a fuel cell which enables a fuel cell to be compact and have a smaller surface area, and which is assembled with fewer components and fewer steps, without degrading performance of the cell stack in its assembled state, and a method of fastening the cell stack of the fuel cell.

To achieve the above described objective, a cell stack of a fuel cell comprises a cell stack body including a cell stack structure including plural cells stacked; an elastic member disposed at an end of the cell stack structure in a direction in which the cells are stacked; and a pair of end plates sandwiching the cell stack structure and the elastic member; and a fastener band extending so as to surround the cell stack body and so as to cover a pair of end surfaces and a pair of opposing side surfaces of the cell stack body, the fastener band including a first band engagement portion and a second band engagement portion; wherein the cell stack body is fastened by the fastener band by direct or indirect engagement between the first band engagement portion and the second band engagement portion.

In such a configuration, the cell stack of the fuel cell can be made compact and its surface area can be reduced. In addition, the cell stack can be assembled with fewer components and fewer steps without degrading performance of the cell stack in its assembled state.

In the cell stack of the fuel cell of the present disclosure, the fastener band may be disposed such that the first band engagement portion and the second band engagement portion are located on the side surface of the cell stack structure.

The cell stack of the fuel cell of the present disclosure may further comprise an engagement pin. The first band engagement portion and the second band engagement portion may have a first insertion hole and a second insertion hole, respectively; and the engagement pin may be inserted into the first insertion hole of the first band engagement portion and the second insertion hole of the second band engagement portion to cause the first band engagement portion and the second band engagement portion to be engaged with each other via the engagement pin.

In the cell stack of the fuel cell of the present disclosure, the first band engagement portion and the second band engagement portion may be provided such that the first insertion hole and the second insertion hole are arranged in a direction perpendicular to the direction in which the cells are stacked.

In the cell stack of the fuel cell of the present disclosure, the first band engagement portion may protrude from one end of the fastener band in one direction of the direction in which the cells are stacked. The second band engagement portion may protrude from the other end of the fastener band in the other direction of the direction in which the cells are stacked, the other direction being opposite to the one direction. The first band engagement portion and the second band engagement portion may be provided such that the first insertion hole of the first band engagement portion and the second insertion hole of the second band engagement portion extend along a side surface of the cells.

In the cell stack of the fuel cell of the present disclosure, the second band engagement portion may be provided such that the second band engagement portion and the first band engagement portion are arranged in a direction perpendicular to the direction in which the cells are stacked and parallel to the pair of side surfaces of the cell stack structure. The first band engagement portion and the second band engagement portion may be provided such that the first and second insertion holes are arranged in the direction which is perpendicular to the direction in which the cells are stacked and is parallel to the pair of side surfaces of the cell stack structure.

In the cell stack of the fuel cell of the present disclosure, the engagement pin may have a peripheral surface having a circular-arc portion. The circular-arc portion of the engagement pin may be engaged with an inner surface of the first band engagement portion which is formed by the first insertion hole and an inner surface of the insertion hole of the second band engagement portion which is formed by the second insertion hole.

In the cell stack of the fuel cell of the present disclosure, each of the first band engagement portion and the second band engagement portion may have, at both end portions of the fastener band, respectively, a long axis extending in the direction in which the cells are stacked and a short axis extending in a direction perpendicular to the long axis, and the long axis has a length which is not smaller than a length which is twice as large as a length of the short axis.

In the cell stack of the fuel cell of the present disclosure, the first band engagement portion and the second band engagement portion may be deformed by a load applied to fasten the cell stack of the fuel cell.

In the cell stack of the fuel cell of the present disclosure, the first band engagement portion and the second band engagement portion may be provided so as not to overlap with each other when viewed from the direction in which the cells are stacked.

In the cell stack of the fuel cell of the present disclosure, the first band engagement portion and the second band engagement portion may be provided so as to overlap with each other when viewed from the direction perpendicular to the direction in which the cells are stacked.

In the cell stack of the fuel cell of the present disclosure, the first fastener band may include a first band member and a second band member. The first band member may have a first band member engagement portion at one end portion thereof and a second band member engagement portion at the other end portion thereof. The second band member may have a third band member engagement portion at one end portion thereof and a fourth band member engagement portion at the other end portion thereof. Alternatively, the first band engagement portion may include the first band member engagement portion and the third band member engagement portion, and the second band engagement portion may include the second band member engagement portion and the fourth band member engagement portion. The first band member engagement portion and the fourth band member engagement portion may be directly or indirectly engaged with each other, and the second band member engagement portion and the third band member engagement portion are directly or indirectly engaged with each other, to cause the cell stack body to be fastened by the fastener band.

In the cell stack of the fuel cell of the present disclosure, the first band member and the second band member may be configured such that the ends thereof are located at centers of the side surfaces of the cell stack body, respectively.

In the cell stack of the fuel cell of the present disclosure, the fastener band may be provided with a hole into which a pipe is inserted to supply or discharge a fluid flowing in the cell stack body.

A method of fastening a cell stack of a fuel cell of the present disclosure comprises: a step (A) for forming a cell stack body including a cell stack structure including plural cells stacked; an elastic member disposed at an end of the cell stack structure in a direction in which the cells are stacked; and a pair of end plates sandwiching the cell stack structure and the elastic member, and disposing a fastener band so as to surround the cell stack body and so as to cover a pair of end surfaces and a pair of opposing side surfaces of the cell stack body, the fastener band having a first band engagement portion and a second band engagement portion; and a step (B) for directly or indirectly engaging the first band engagement portion and the second band engagement portion with each other to fasten the cell stack body by using the fastener band.

In such a configuration, the cell stack of the fuel cell can be assembled with fewer components and fewer steps without degrading performance of the cell stack in its assembled state.

In the method of fastening the cell stack of the fuel cell of the present disclosure, the step (B) may include: a step (B1) for applying a predetermined load which is larger than a fastening load to portions of the fastener band which cover the pair of end surfaces of the cell stack body, using a presser unit, and inserting the engagement pin into a first insertion hole of the first band engagement portion and a second insertion hole of the second band engagement portion; and a step (B2) for releasing the load applied by the presser unit to engage the engagement pin with an inner surface of the first band engagement portion formed by the first insertion hole, and an inner surface of the second band engagement portion formed by the second insertion hole.

In such a configuration, the cell stack of the fuel cell can be assembled with fewer components and fewer steps without degrading performance of the cell stack in its assembled state.

The above and further objects, features and advantages of the disclosure will more fully apparent from the following detailed description with reference to the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of the present disclosure will be described with reference to the drawings. Throughout the drawings, the same or corresponding components and members are designated by the same reference numerals and repetitive description thereof will be omitted. In the embodiments described below, the present disclosure is applied to a polymer electrolyte fuel cell (PEFC) but is widely applicable to other kinds of fuel cells such as, but not limited to, solid oxide fuel cell (SOFC) or phosphoric acid fuel cell (PAFC).

Configuration of a Cell Stack of a Fuel Cell

FIG. 1is a perspective view schematically showing a configuration of a cell stack of a fuel cell according to Embodiment 1 of the present disclosure.FIG. 2is an exploded schematic view of the cell stack of the fuel cell ofFIG. 1. InFIGS. 1 and 2, the upper and lower sides of the cell stack of the fuel cell are expressed as the upper and lower sides in these Figures.

As shown inFIGS. 1 and 2, a cell stack100of a fuel cell includes a cell stack body50having a rectangular parallelepiped configuration, a fastener band80including a first U-shaped band member60and a second U-shaped band member70, and a pair of engagement pins90. The first band member60and the second band member70extend so as to surround the cell stack body50and so as to cover the upper surface (upper end surface) of the cell stack body50, the lower surface (lower end surface) of the cell stack body50, and a pair of opposing side surfaces of the cell stack body50. The first band member60has plural (in this embodiment, three) through-holes69on a top surface thereof covering the upper surface of the cell stack body50. The second band member70has plural (in this embodiment, three) through-holes79on a bottom surface thereof covering the lower surface of the cell stack body50. Pipes201used for supplying to or discharging from the cell stack100(cell stack body50) of the fuel cell, a fluid such as a fuel gas flowing in the cell stack body50, are respectively inserted into the through-holes69and79.

A first tubular band member engagement portion61and a second tubular band member engagement portion62are provided at both ends of the first band member60, respectively. Likewise, a third tubular band member engagement portion71and a fourth tubular band member engagement portion72are provided at both ends of the second band member70, respectively.

One of the pair of the engagement pins90is inserted into the first band member engagement portion61of the first band member60and the fourth band member engagement portion72of the second band member70. In the same manner, the other engagement pin90is inserted into the second band member engagement portion62of the first band member60and the third band member engagement portion71of the second band member70. Thereby, the first band member engagement portion61of the first band member60and the fourth band member engagement portion72of the second band member70are engageable with each other via the engagement pin90, while the second band member engagement portion62of the first band member60and the third band member engagement portion71of the second band member70are engageable with each other via the engagement pin90. In other words, the first band member engagement portion61of the first band member60and the fourth band member engagement portion72of the second band member70are indirectly engageable with each other via the engagement pin90, while the second band member engagement portion62of the first band member60and the third band member engagement portion71of the second band member70are indirectly engageable with each other via the engagement pin90. Thus, when the engagement pins90are inserted, the first band member60and the second band member70are secured together.

The first band member60and the second band member70are made of a material which is excellent in tensile strength and anticorrosion, such as, but not limited to, resin (engineering plastic, elastomer, etc), stainless steel (e.g., SUS304), or chrome molybdenum steel. The engagement pins90are made of a material such as, but not limited to, chrome molybdenum steel, or stainless steel (e.g., SUS304).

With reference toFIGS. 3A and 3B, the structures of the first band member engagement portion61and the second band member engagement portion62of the first band member60and the third band member engagement portion71and the fourth band member engagement portion72of the second band member70will be described in greater detail. Since the first band member engagement portion61and the second band member engagement portion62of the first band member60have the same structure, and the third band member engagement portion71and the fourth band member engagement portion72of the second band member70have the same structure, the first band member engagement portion61of the first band member60and the fourth band member engagement portion72of the second band member70will be described hereinafter.

FIG. 3Ais a cross-sectional view taken along line IIIA-IIIA ofFIG. 1.FIG. 3Bis a schematic view showing a state where the cell stack100of the fuel cell is assembled (fastened). InFIGS. 3A and 3B, to clearly distinguish between the first band member engagement portion61of the first and member60and the fourth band member engagement portion72of the second band member70, the first band member engagement portion61is hatched.

As shown inFIGS. 1 to 3B, an engagement portion forming section63and an engagement portion forming section73are provided at the end of the first band member60and at the end of the second band member70, respectively so as to protrude along the surfaces (in a vertical direction) of the first and second band members60and70. The engagement portion forming sections63and73form the first band member engagement portion61, the second band member engagement portion62, the third band member engagement portion71and the fourth band member engagement portion72. The engagement portion forming sections63and73are each folded back to form a tubular shape. The tip end portion of the engagement portion forming section63and the base end portion of the engagement portion forming section63are welded and fastened to each other by screws64, while the tip end portion of the engagement portion forming section73and the base end portion of the engagement portion forming section73are welded and fastened to each other by screws74.

To be specific, the first band member engagement portion61protrudes from one end of the first band member60in one direction (in this embodiment, downward) in a direction in which cells10are stacked, and the second band member engagement portion62protrudes downward from the other end of the first band member60. In the same manner, the third band member engagement portion71protrudes from one end of the second band member70in the other direction (in this embodiment, upward) in the direction in which cells10are stacked, and the fourth band member engagement portion72protrudes upward from the other end of the second band member70. In other words, the third band member engagement portion71is disposed such that the third band member engagement portion71and the second band member engagement portion62are aligned when viewed from a direction which is perpendicular to the direction in which the cells10are stacked and extend parallel to a pair of side surfaces of the cell stack structure20. Likewise, the fourth band member engagement portion72is disposed such that the fourth band member engagement portion72and the first band member engagement portion61are aligned when viewed from the direction which is perpendicular to the direction in which the cells10are stacked and extend parallel to the pair of side surfaces of the cell stack structure20. As used herein, the phrase “the direction which is perpendicular to the direction in which the cells10are stacked and extend parallel to the pair of side surfaces of the cell stack structure20” means a direction in which a long side of the side surface of the cells10which is covered with the first band member60or the second band member70extends (hereinafter referred to as the direction in which the long side of the side surface of the cells10extends).

The first band member engagement portion61and the second band member engagement portion62having the above structure are provided with insertion holes (tubular inner spaces)65, respectively extending in the direction perpendicular to the direction (in this embodiment, vertical direction) in which the cells10are stacked. In the same manner, the third band member engagement portion71and the fourth band member engagement portion72are provided with insertion holes (tubular inner spaces)75, respectively extending in the direction perpendicular to the direction (in this embodiment, vertical direction) in which the cells10are stacked.

To be specific, the insertion holes65and the insertion holes75extend along the side surface of the cells10(to be precise, the long side of the side surface of the cells10). The insertion hole65of the first band member engagement portion61and the insertion hole75of the fourth band member engagement portion72are arranged in the direction perpendicular to the direction in which the cells10are stacked. In the same manner, the insertion hole65of the second band member engagement portion62and the insertion hole75of the third band member engagement portion71are arranged in the direction perpendicular to the direction in which the cells10are stacked. To be more specific, the insertion hole65of the first band member engagement portion61and the insertion hole75of the fourth band member engagement portion72are arranged in the direction which is perpendicular to the direction in which the cells10are stacked and is parallel to the pair of side surfaces of the cell stack structure20. In the same manner, the insertion hole65of the second band member engagement portion62and the insertion hole75of the third band member engagement portion71are arranged in the direction which is perpendicular to the direction in which the cells10are stacked and is parallel to the pair of side surfaces of the cell stack structure20.

In other words, the insertion hole65of the first band member engagement portion61and the insertion hole75of the fourth band member engagement portion72are arranged so as to overlap or align with each other when viewed from the direction of the long side of the side surface of the cells10. The insertion hole65of the second band member engagement portion62and the insertion hole75of the third band member engagement portion71are arranged so as to overlap or align with each other when viewed from the direction of the long side of the side surface of the cells10. As used herein, the phrase “the insertion hole65and the insertion hole75are arranged in the direction perpendicular to the direction in which the cells10are stacked or arranged in the direction which is perpendicular to the direction in which the cells10are stacked and is parallel to the pair of side surfaces of the cell stack structure20” is meant to include that a part of the insertion hole65overlaps a part of the insertion hole75when viewed from the direction in which the long side of the side surface of the cells10covered with the first band member60or the second band member70extends, as well as that the insertion hole65and the insertion hole75are arranged so as to overlap or align with each other, when viewed from the direction in which the long side of the side surface of the cells10covered with the first band member60or the second band member70extends.

The first band member engagement portion61and the third band member engagement portion71form a first band engagement portion, while the second band member engagement portion62and the fourth band member engagement portion72form a second band engagement portion. The insertion hole65of the first band member engagement portion61and the insertion hole75of the third band member engagement portion71form a first insertion hole, while the insertion hole65of the second band member engagement portion62and the insertion hole75of the fourth band member engagement portion72form a second insertion hole.

In Embodiment 1, the first band member engagement portion61of the first band member60is formed so as to overlap the second band member engagement portion62of the first band member60, when viewed from the direction which is perpendicular to the direction in which the cells10are stacked. In the same manner, the third band member engagement portion71of the second band member70is formed so as to overlap the fourth band member engagement portion72of the second band member70, when viewed from the direction which is perpendicular to the direction in which the cells10are stacked. In other words, the first band member engagement portion61of the first band member60and the second band member engagement portion62of the first band member60are formed symmetrically with respect to the cell stack body50sandwiched therebetween. In the same manner, the third band member engagement portion71of the second band member70and the fourth band member engagement portion72of the second band member70are formed symmetrically with respect to the cell stack body50sandwiched therebetween. In this embodiment, the first member engagement portion61of the first band member60and the fourth band member engagement portion72of the second member70are arranged at substantially the center of the side surface of the cell stack structure20, and the second member engagement portion62of the first band member60and the third band member engagement portion71of the second band member70are arranged at substantially the center of the side surface of the cell stack structure20.

The first band member engagement portion61of the first band member60and the fourth band member engagement portion72of the second band member60are formed not to overlap, when viewed from the direction in which the cells10are stacked, and the second band member engagement portion62of the first band member60and the third band member engagement portion71of the second band member70are formed not to overlap, when viewed from the direction in which the cells10are stacked.

The width of the first band member60and the width of the second band member70are desirably larger than the width for covering power generation sections (cathode and anode electrode sections) of the cells10. This makes it possible to evenly press the power generation sections of the cells10. In addition, the width of the first band member60and the width of the second band member70are desirably equal to or larger than the width of the end plates34as described later. This makes it possible to cover the entire end surfaces of the end plates34and evenly press the same. Thereby, stiffness of the end plate34need not be high and the material may be selected flexibly.

As shown inFIG. 3B, the first band member engagement portion61of the first band member60and the fourth band member engagement portion72of the second band member70are formed such that a length b in a long axis direction (direction in which the cells10are stacked) is not less than twice as large as a length a in a short axis direction (thickness direction of the first band member60and the second band member70), when viewed from the thickness direction of the first band member60and the second band member70. In this structure, the engagement pin90can be easily inserted into the first band member engagement portion61of the first band member60and the fourth band member engagement portion72of the second band member70.

The engagement pin90is inserted into the first band member engagement portion61of the first band member60and the fourth band member engagement portion72of the second band member70such that the inner surface of the first band member engagement portion61and the inner surface of the fourth band member engagement portion72are engaged with the peripheral surface of the engagement pin90. To be specific, the half of the peripheral surface of the engagement pin90is configured to contact each of the inner surface of the first band member engagement portion61and the inner surface of the fourth band member engagement portion71.

In this state, the engagement pin90, the first band member engagement portion61and the fourth band member engagement portion72are applied with a force from all directions and thereby fixed, increasing a force against a vibration or an impact applied from outside. Unlike the conventional method in which the cell stack body50is fastened using the bolts and the nuts, a large protruding portion is unnecessary. This reduces a space in which the cell stack100of the fuel cell is installed or the surface area of the cell stack100. By reducing the surface area of the cell stack100of the fuel cell, the heat radiation amount of the cell stack100can be reduced. Thus, the cell stack100can be used as an electric power supply of a cogeneration system which has a high heat recovery property.

In the cell stack100of the conventional fuel cell, a contact resistance between adjacent cells10and a contact resistance between the separator and the MEA forming the cell10increase due to a large or small fastening load, an uneven fastening load, etc, which may sometimes result in degraded cell performance. In the structure for fastening the band engagement portion with the nuts and the bolts, in the polymer electrolyte fuel cell disclosed in Patent document 2, for example, there is a distance between a surface (band) generating a tension and a fulcrum point (engagement portion). For this reason, there is a chance that the engagement portion is deformed due to the tension of the band. The extent of such deformation depends greatly on a variation in stiffness of the engagement portion, a variation in the tension of the band, etc. As a result, the polymer electrolyte fuel cell disclosed in Patent document 2 is incapable of obtaining a stable fastening load.

In contrast, in the cell stack100of the fuel cell of Embodiment 1, as shown inFIG. 3A, the fulcrum point (engagement pin90) is positioned on the surface generating a tension (surface including the center lines101A and101B and being perpendicular to the stacking direction) so that the deformation of the engagement portion forming sections63and73is suppressed. Since the surface generating a tension and the fulcrum point are located on substantially the same plane, the cell stack100of the fuel cell can substantially suppress variations in the fastening load due to the deformation.

Although the tip end portion and the base end portion of the engagement portion forming section63are welded and fastened to each other using the screws64and the tip end portion and the base end portion of the engagement portion forming section73are welded and fastened to each other using the screws74, they may alternatively be joined to each other only by welding, only by the screws or by the bonding agent, so long as the engagement portion forming section63and the engagement portion forming section73are able to have a stiffness sufficient to withstand a fastening pressure. Although the engagement pin90has a circular cross-section, its shape is not so limited provided that its peripheral surface has a circular-arc portion. For example, the engagement pin90may have a cross-section of an oval shape or an elongate-circle shape.

Next, the components of the cell stack100of the fuel cell of Embodiment 1 will be described with reference toFIG. 2.

The cell stack body50includes a cell stack structure20including plural plate-shaped cells (unit cells)10which are stacked, a pair of current collectors31, a pair of insulating plates32, an elastic member33, and a pair of end plates34sandwiching these members therebetween. The cell stack body50has a fuel gas supply manifold51, a fuel gas exhaust manifold (not shown), an oxidizing gas supply manifold52, an oxidizing gas exhaust manifold (not shown), a cooling medium supply manifold53, and a cooling medium discharge manifold (not shown), which are formed to penetrate through the cell stack body50. Each manifold is provided with a connecting member202for connecting the pipe201to the cell stack body50(cell stack100of the fuel cell).

Each cell10includes a MEA (membrane-electrode-assembly) consisting of a polymer electrolyte membrane, an anode and cathode disposed on both surfaces thereof, gaskets, and a pair of separators. By contact between the separators of adjacent cells10, all of the cells10are electrically connected in series. By stacking the cells10having the above structure in a thickness direction thereof, the cell stack structure20is formed.

The pair of current collectors31are disposed at the both ends of the cell stack structure20in the direction in which the cells10are stacked. Terminal members31aare provided on the side surfaces of the current collectors31. Electric wires (not shown) are connected to the terminal members31a. Thus, an electric power generated in the respective cells10can be output to outside through the terminal members31a. It is sufficient that the current collectors31are made of a material which is gas-impermeable and electrically conductive. The current collectors31may be made of dense carbon or metal such as, for example, copper.

The pair of insulating plates32are disposed outside the current collectors31of the cell stack structure20such that they are respectively in contact with the main surfaces of the current collectors31. In other words, the pair of insulating plates32sandwich and retain a stack of the cell stack structure20and the current collectors31. The insulating plates32may be made of an insulating material such as rubber or plastic.

The plate-shaped elastic member33is disposed under the insulating plate32located at the lower side of the pair of insulating plates32. The elastic member33serves to apply a pressing force in the stacking direction to the stack including the cell stack structure20, the current collectors31, and others. By the elastic force of the elastic member33, a fastening pressure is applied to the fastener band80. In this embodiment, as the elastic member33, a sheet made of rubber such as fluorine-containing rubber or EPDM may be utilized.

The pair of end plates34are disposed at the both ends of the stack including the cell stack structure20, the current collectors31, and others such that they are in contact with the main surface of the insulating plate32or the main surface of the elastic member33. The end plates34serve to apply the fastening force of the fastener band80to the cell stack structure20, the current collectors31, and others with an even surface pressure. The end plates34are formed using a stiff material such as, hard plastic or steel, to prevent deformation due to the fastening structure. As shown inFIGS. 1 and 2, the size of the main surfaces of the end plates34is preferably set slightly larger than the size of the cells10, the main surfaces of the current collectors31, and others. The pair of sides of the main surfaces of the end plates34, which are in contact with the fastener band80, are preferably chamfered so that the chamfered portions have a smaller thickness than the center portions.

Thus, the fastener band80extends between the pair of end plates34to be apart from the side surfaces (i.e., not in contact) of the cell stack structure20and the current collectors31. This makes it possible to prevent a short circuit between the cell stack structure20and the current collectors31which would otherwise occur because of the fastener band80. In addition, this makes it possible to prevent the fastening pressure from the fastener band80being applied unevenly with respect to the main surfaces of the end plates3. As a result, the anode and the cathode forming the MEA of each cell10can contact the polymer electrolyte membrane of the MEA with an even surface pressure.

Next, a fastening method of the cell stack100of the fuel cell of Embodiment 1 will be described with reference toFIGS. 1 to 3.

[Fastening Method of Cell Stack of Fuel Cell]

Initially, the end plate34is placed on the bottom surface of the second band member70having a U-shape, and the elastic member33, the insulating plate32and the current collector31are placed thereon. Then, the plural cells10are stacked on the main surface of the current collector31, forming the cell stack structure20. Then, on the main surface of the cell10of the cell stack structure20, the current collector31, the insulating plate32and the end plate34are placed, and the first band member60having a U-shape is placed so as to cover the main surface of the end plate34. That is, the cell stack body50is formed, and the first band member60and second band member70are placed so as to surround the periphery of the cell stack body50and so as to cover a pair of end surfaces of the cell stack body50(main surfaces of the end plates34) and a pair of opposing side surfaces of the cell stack body50.

Then, using a presser unit (e.g., flat press machine), the first band member60, the cell stack body50, and the second band member70are pressed together so as to have a specified dimension in the stacking direction. Then, the pair of engagement pins90are inserted into the first band member engagement portion61of the first band member60and the fourth band member engagement portion72of the second band member70, and into the second band member engagement portion62of the first band member60and the third band member engagement portion71of the second band member70(seeFIG. 3B). To be specific, using the presser unit, a predetermined load which is larger than the fastening load of the cell stack100of the fuel cell, is applied to the portions of the first band member60and the second band member70, which cover the pair of end surfaces (main surfaces of the end plates34) of the cell stack body50. Then, the engagement pin90is inserted into the insertion hole65of the first band member engagement portion61and into the insertion hole75of the fourth band member engagement portion72, and the engagement pin90is inserted into the insertion hole65of the second band member engagement portion62and into the insertion hole75of the third band member engagement portion71.

Then, releasing the pressing force of the presser unit, the first band member60and the second band member70are pushed in the direction in which the cells10are stacked by the elastic force of the elastic member33to cause the first band member engagement portion61and the fourth band member engagement portion72to be deformed by a tensile force to cause the center line101A to be oriented in the direction (i.e., vertical direction) along the center line of the first band member60and adhere to the engagement pin90, and to cause the second band member engagement portion62and the third band member engagement portion71to be deformed by a tensile force to cause the center line101B to be oriented in the direction (i.e., vertical direction) along the center line of the second band member70and adhere to the engagement pin90. Thus, the cell stack100of the fuel cell is fastened (seeFIG. 3A). To be specific, by releasing the pressing load of the presser unit, the engagement pin90is engaged with the inner surface of the insertion hole65of the first band member engagement portion61and the inner surface of the insertion hole75of the fourth band member engagement portion72, and the engagement pin90is engaged with the inner surface of the insertion hole65of the second band member engagement portion62and the inner surface of the insertion hole75of the third band member engagement portion71, causing the first band member60and the second band member70to be indirectly engaged with each other via the engagement pins90. In this manner, the cell stack body50is fastened by the fastener band80.

Next, the advantage of the cell stack100of the fuel cell according to Embodiment 1 will be described with reference toFIG. 1toFIG. 3B.

[Advantage of Cell Stack of Fuel Cell]

As described above, in the cell stack100of the fuel cell according to Embodiment 1, by inserting the engagement pin90into the first band member engagement portion61of the first band member60and the fourth band member engagement portion72of the second band member70, and by inserting the engagement pin90into the second band member engagement portion62of the first band member60and the third band member engagement portion71of the second band member70, the cell stack100of the fuel cell can be fastened. Thus, assembling of the cell stack100is accomplished with fewer components and fewer steps. Unlike the method using the bolts and the nuts, what is needed is to provide at the side surfaces of the cell stack100of the fuel cell, the first band member engagement portion61and the third band member engagement portion71forming the first band engagement portion and the second band member engagement portion62and the fourth band member engagement portion72forming the second band engagement portion. Therefore, the cell stack100of the fuel cell can be made compact. In addition, the surface area of the cell stack100of the fuel cell can be reduced, and its heat radiation amount can be reduced.

Since the length b of the first band member engagement portion61, the second band member engagement portion62, the third band member engagement portion71and the fourth band member engagement portion72in the long axis direction is set to a length which is not less than twice as large as the length a in the short axis direction, it is possible to ensure a sufficient clearance required to insert the engagement pin90. As a result, the cell stack100of the fuel cell can be easily assembled.

Since the engagement pins90are inserted in the direction perpendicular to the direction in which the fastening load is applied to the cell stack100and the cells10are stacked, it is possible to avoid that the engagement pins90are disengaged due to a vibration or an impact. Furthermore, since the first band member engagement portion61, the second band member engagement portion62, the third band member engagement portion71and the fourth band member engagement portion72are deformed when fastening the cell stack100of the fuel cell, the inner surfaces of these engagement portions adhere to and are fixed to the peripheral surfaces of the engagement pins90. As a result, vibration proof property and impact resistance of the cell stack100of the fuel cell are improved.

Since the first band member engagement portion61, the second band member engagement portion62, the third band member engagement portion71and the fourth band member engagement portion72are located at substantially the centers of the side surfaces of the cell stack structure20(cell stack body50), it is possible to suppress external forces such as a vibration and an impact concentrating in a localized region.

FIG. 4is a table showing the result of simulations conducted to research whether or not a local stress is generated on the end plates34and the like depending on the positions of the first band engagement portion and the second band engagement portion in the cell stack100of the fuel cell.

As shown inFIG. 4, when the first band member engagement portion61, the second band member engagement portion62, the third band member engagement portion71and the fourth band member engagement portion72of the first band member60and the second band member70were positioned at substantially the centers of the pair of side surfaces of the cell stack body50(the first band engagement portion and the second band engagement portion are positioned at substantially the centers of the pair of side surfaces of the cell stack body50), a local stress was not substantially generated on the end plates34and others. When the first band member engagement portion61of the first band member60and the fourth band member engagement portion72of the second band member70were positioned at the upper portion (or lower portion) of one of the side surfaces of the cell stack body50and the second band member engagement portion62of the first band member60and the third band member engagement portion71of the second band member70were positioned at the lower portion (or upper portion) of the other the side surface of the cell stack body50, a local stress was generated on the end plates34or the like but its magnitude was small. When the first band member engagement portion61, the second band member engagement portion62, the third band member engagement portion71and the fourth band member engagement portion72of the first band member60and the second band member70were positioned at the upper portions (or lower portions) of the pair of side surfaces of the cell stack body50, a local stress was generated on the end plates34or the like.

From the above mentioned result, it was discovered that it is possible to suppress external forces, such as a vibration, and an impact, from concentrating in a localized region, by positioning the first band member engagement portion61, the second band member engagement portion62, the third band member engagement portion71and the fourth band member engagement portion72substantially at the centers of the side surfaces of the cell stack structure20(cell stack body50).

FIG. 5is a perspective view schematically showing an exemplary configuration of a cell stack of a fuel cell according to Embodiment 2 of the present disclosure.FIG. 6is an exploded schematic view of the cell stack of the fuel cell ofFIG. 5. InFIGS. 5 and 6, the upper and lower sides of the cell stack of the fuel cell are expressed as the upper and lower sides in these Figures.

As shown inFIGS. 5 and 6, the cell stack100of the fuel cell according to Embodiment 2 of the present disclosure has a structure which is basically identical to that of the cell stack100of the fuel cell according to Embodiment 1, except for the structures of the elastic member33and the first band member engagement portion61, the second band member engagement portion62, the third band member engagement portion71and the fourth band member engagement portion72.

To be specific, in the cell stack100of Embodiment 2, the elastic member33is formed by compressive springs. In addition, the first band member engagement portion61, the second band member engagement portion62, the third band member engagement portion71and the fourth band member engagement portion72have plural (in this embodiment, seven) engagement units66and plural (seven) engagement units76. The engagement units66have a comb shape and the engagement units76have a comb shape. The engagement units66protrude from the ends of the first band member60along the surface thereof (in this embodiment, vertical direction) and the engagement units76protrude from the ends of the second band member70along the surface thereof (in this embodiment, vertical direction). An insertion hole65and an insertion hole75are defined by an inner space of the engagement unit66and an inner space of the engagement unit76, respectively.

The engagement units66provided at the first band member engagement portion61of the first band member60and the engagement units76provided at the fourth band member engagement portion72of the second band member70are provided such that they are not in contact with each other. In the same manner, the engagement units66provided at the second band member engagement portion62of the first band member60and the engagement units76provided at the third band member engagement portion71of the second band member70are provided such that they are not in contact with each other.

The cell stack100of the fuel cell of Embodiment 2 configured as described above is able to achieve the same advantage as that of the cell stack100of the fuel cell of Embodiment 1.

FIG. 7is a perspective view schematically showing an exemplary configuration of a cell stack of a fuel cell according to Embodiment 3 of the present disclosure.FIG. 8is a perspective view schematically showing a configuration of a first band member and a second band member forming the cell stack of the fuel cell ofFIG. 7. InFIG. 7, the upper and lower sides of the cell stack of the fuel cell are expressed as the upper and lower sides in these Figures. InFIG. 8, the upper and lower sides of the first band member and the second band member are expressed as the upper and lower sides in these Figures.

As shown inFIGS. 7 and 8, the cell stack100of the fuel cell according to Embodiment 3 of the present disclosure has a structure which is basically identical to that of the cell stack100of the fuel cell according to Embodiment 1 except that the first band member engagement portion61, the second band member engagement portion62, the third band member engagement portion71and the fourth band member engagement portion72are not formed by the engagement portion forming sections63and73, but by separate members. To be specific, the first band member engagement portion61, the second band member engagement portion62, the third band member engagement portion71and the fourth band member engagement portion72are formed in such a manner that plate members67and plate members77are folded back to form tubular insertion holes65and75and one ends thereof are fastened by welding. The plate members67are bonded to the first band member60using screws64and by welding, and the plate members77are bonded to the second band member70by screws74and by welding. The plate members67and77are desirably made of a material which can withstand a fastening pressure, and may be made of, for example SUS or the like.

The first band member60is cut at the portions of the both ends where the plate members67are not provided and the second band member70is cut at the portions of the both ends where the plate members77are not provided, to prevent contact with the first band member engagement portion61, the second band member engagement portion62, the third band member engagement portion71and the fourth band member engagement portion72, when fastening the cell stack100of the fuel cell.

The cell stack100of the fuel cell of Embodiment 3 configured as described above is able to achieve the same advantage as that of the cell stack100of the fuel cell of Embodiment 1.

FIG. 9is a perspective view schematically showing an exemplary configuration of a cell stack of a fuel cell according to Embodiment 4 of the present disclosure. InFIG. 9, the upper and lower sides of the cell stack of the fuel cell are expressed as the upper and lower sides in the Figure.

As shown inFIG. 9, the cell stack100of the fuel cell according to Embodiment 4 of the present disclosure has a structure which is basically identical to that of the cell stack100of the fuel cell according to Embodiment 1, except that the first band member engagement portion61of the first band member60is formed not to overlap the second band member engagement portion62of the first band member60, when viewed from the direction perpendicular to the direction in which the cells10are stacked and the third band member engagement portion71of the second band member70is formed not to overlap the fourth band member engagement portion72of the second band member70, when viewed from the direction perpendicular to the direction in which the cells10are stacked.

The first band member engagement portion61of the first band member60and the fourth band member engagement portion72of the second band member70, and the second band member engagement portion62of the first band member60and the third band member engagement portion71of the second band member70are desirably located on the side surfaces of the cell stack structure20and not on the side surfaces of the current collectors31, the insulating plates32, the elastic member33, and the end plates34.

The cell stack100of the fuel cell of Embodiment 4 configured as described above is able to achieve the same advantage as that of the cell stack100of the fuel cell of Embodiment 1.

FIG. 10is a perspective view schematically showing an exemplary configuration of a cell stack of a fuel cell according to Embodiment 5 of the present disclosure.FIG. 11is perspective view schematically showing a configuration of a fastener band of the cell stack of the fuel cell ofFIG. 10. InFIG. 10, the upper and lower sides of the cell stack of the fuel cell are expressed as the upper and lower sides in these Figures. InFIG. 11, the upper and lower sides of the first band member and the second band member are expressed as the upper and lower sides in these Figures.

As shown inFIGS. 10 and 11, the cell stack100of the fuel cell according to Embodiment 5 of the present disclosure has a structure which is basically identical to that of the cell stack100of the fuel cell according to Embodiment 1, except that the fastener band80is formed by a single member. Since the fastener band80is formed by a single member, a first band engagement portion68and a second band engagement portion78are provided at the both ends of the fastener band80.

To be specific, the fastener band80is formed such that a band-like member is bent to form a tubular shape so as to surround the cell stack body50, and the portion of the fastener band80which covers the upper surface of the cell stack body50(hereinafter referred to as the upper surface of the fastener band80) is formed to be tilted obliquely upward with respect to a horizontal direction. Since the first band engagement portion68and the second band engagement portion78have the same structure as the first band member engagement portion61of the first band member60, the fourth band member engagement portion72of the second band member70and others, detailed description thereof is omitted.

When fastening the cell stack100of the fuel cell, the fastener band80and the cell stack body50are pressed in such a manner that the upper surface of the fastener band80and the portion of the fastener band80which covers the lower surface of the cell stack body50(lower surface of the fastener band80) are pressed using the presser unit (e.g., flat press machine) until the upper surface of the fastener band80is pressed down to be tilted slightly downward with respect to a horizontal direction. As a result the insertion hole65of the first band engagement portion68and the insertion hole75of the second band engagement portion78overlap each other when viewed from the direction perpendicular to the direction in which the cells10are stacked, and the engagement pin90can be inserted into the insertion hole65and the insertion hole75. After the engagement pin90is inserted into the insertion hole65and the insertion hole75, the pressing force applied by the presser unit is released, so that the fastener band80and the cell stack body50are pushed back up to a position where the upper surface of the fastener band80is horizontal, because of the elastic force of the elastic member33. At this time, the first band engagement portion68and the second band engagement portion78are deformed due to their tensile forces and are allowed to adhere to the engagement pin90. Thus, the cell stack100of the fuel cell is fastened.

The cell stack100of the fuel cell of Embodiment 5 configured as described above is able to achieve the same advantage as that of the cell stack100of the fuel cell of Embodiment 1.

FIG. 12is a perspective view schematically showing an exemplary configuration of a cell stack of a fuel cell according to Embodiment 6 of the present invention. InFIG. 12, the upper and lower sides of the cell stack of the fuel cell are expressed as the upper and lower sides in the Figure.

As shown inFIG. 12, the cell stack100of the fuel cell according to Embodiment 6 of the present disclosure has a structure which is basically identical to that of the cell stack100of the fuel cell according to Embodiment 1, except that the cell stack100of the fuel cell is fastened using plural (four) thinned and elongated fastener bands80.

The cell stack100of the fuel cell of Embodiment 6 configured as described above is able to achieve the same advantage as that of the cell stack100of the fuel cell of Embodiment 1.

FIG. 13is a perspective view schematically showing an exemplary configuration of a cell stack of a fuel cell according to Embodiment 7 of the present disclosure. InFIG. 13, the upper and lower sides of the cell stack of the fuel cell are expressed as the upper and lower sides in the Figure.

As shown inFIG. 13, the cell stack100of the fuel cell according to Embodiment 7 of the present disclosure has a structure which is basically identical to that of the cell stack100of the fuel cell according to Embodiment 5, except that the opening (both ends) of the fastener band80is formed to be located at a corner portion formed between the side surface and the upper surface of the cell stack body50, and the first band engagement portion68and the second band engagement portion78are different in shape.

To be specific, each first band engagement portion68is formed by a columnar member and is provided on the upper surface of the fastener band80such that its tip end portion protrudes from the end of the upper surface of the fastener band80. A through-hole is formed at the tip end portion of each first band engagement portion68so as to extend along the direction in which the cells10are stacked. In this embodiment, each first band engagement portion68is bonded to the upper surface of the fastener band80by welding. Each second band engagement portion78is formed by a tubular member and is bonded to the side surface of the fastener band80.

The peripheral surfaces of the engagement pins90are configured to contact the inner surfaces of the first band engagement portions68and the inner surfaces of the second band engagement portions78by the elastic force in the upper surface of the fastener band80and the elastic force in the side surface of the fastener band80on which the second band engagement portions78are provided, which are applied in the direction to increase the opening of the fastener band80, to be precise, the elastic force in the upper surface of the fastener band80in an upward direction, and the elastic force in the side surface of the fastener band80on which the second band engagement portions78are provided, which is applied in the direction from the side surface on which the second band engagement portions78are not provided toward the side surface on which the second band engagement portions78are provided. Thus, the engagement pins90, the first band engagement portions68and the second band engagement portions78are fixed, and the cell stack100of the fuel cell is fastened.

The cell stack100of the fuel cell of Embodiment 7 configured as described above is able to achieve the same advantage as that of the cell stack100of the fuel cell of Embodiment 1.