Fuel cell stack

A fuel cell stack is provided that comprises a laminate obtained from unit cells of rectangular plates, end plates disposed at both end surfaces of the laminate, and a pair of reinforcing plates disposed on a first and third outer peripheral surfaces, wherein the respective end plates and reinforcing plates are connected. Each reinforcing plate has a base plate covering that covers the first or third outer peripheral surface of the laminate, and a pair of holding portions that cover the second and fourth outer peripheral surfaces of the laminate partly. Each holding portion supports the laminate as a spring element, and the spring elements are attached in the direction of displacement of the laminate. As a result, the resonant frequency of the laminate is increased and vibration resistance is improved without increasing the parts count.

TECHNICAL FIELD

The present invention relates to a fuel cell stack used as a power source for driving a vehicle, for example, and more specifically relates to a fuel cell stack comprising a laminate formed by stacking a plurality of unit cells configured by a membrane electrode assembly and a separator.

BACKGROUND

A conventional fuel cell stack having a laminate or stack of unit cells is described in Japanese Laid-Open Patent Application Publication No. 2003-203670, for example. The fuel cell stack described in Japanese Laid-Open Patent Application Publication No. 2003-203670 has a laminate sandwiched with end plates, and both end plates are connected by a tension plate to maintain a pressurized state of the laminate. Further, the fuel stack has a first layer of low friction characteristics and insulating property and a second layer of buffer characteristics interposed between the laminate and the tension plate to absorb vibration and shock from the outside.

According to the fuel cell stack of the prior art described above, since the buffer material (second layer) is a spring element, increasing in resonant frequency (natural frequency) of the laminate leads to improved performance of vibration resistance. However, in a structure in which a cushioning material and the like are interposed between the tension plate and the laminate, there is a problem of increase in the number of components or parts count. Thus, it has been an issue or challenge to solve such a problem.

BRIEF SUMMARY

The present invention has been made by focusing on the problems of the prior art described above, and has the object to provide a fuel cell stack that may improve the resonant frequency (natural frequency) for improving performance of vibration resistance without causing the number of components.

The fuel cell stack according to the present invention is provided with a laminate comprised of a plurality of stacked unit cells of a plate-like rectangle, a pair of end plates disposed on both end surfaces of the laminate in the stacking direction of cells, and a pair of reinforcing plates disposed on the first and third outer peripheral surfaces, the four surfaces defined to be outer peripheral surfaces which are parallel to a cell stacking direction of the laminate in a circumferential direction, wherein both end plates and each reinforcing plate are connected respectively.

In addition, in the fuel cell stack, each reinforcing plate is provided with a base portion covering the first or third outer peripheral surface of the stack and a pair of holding portions extending perpendicularly from the base portion to cover part of the second and fourth outer peripheral surfaces. Each holding portion is configured to form a structure to hold the stack or laminate as a spring element, whereby the problem of the conventional structure is solved.

Further, in the above configuration, the holding portion of the reinforcing plate and the laminate can be in contact or spaced apart from each other with an extremely small gap so as to be brought in contact upon vibration input. However, it is more preferable to hold in the contact state.

According to the fuel cell stack of the present invention, the resonant frequency of the laminate can be increased without increasing the number of parts. Thus, it is possible to improve the vibration resistance performance.

DETAILED DESCRIPTION

FIGS. 1 to 4are diagrams illustrating an embodiment of the fuel cell stack according to the present invention.

The fuel cell stack FS shown inFIG. 1AandFIG. 2is provided with a laminate or stack1formed by stacking a plurality of unit cells FC of rectangular plate shape, a pair of current collectors disposed on both end surfaces as viewed in the direction of stacking cells (i.e. X direction in the figure), end plates2,2disposed external of respective current collector, a pair of reinforcing plates3,3, and a pair of fastening plates4,4. The materials for the end plate2, reinforcing plate3, and fastening plate4are not particularly limited, but are more desirable to be made of metals.

The unit cell FC is configured in the well-known structure in which a MEA (Membrane-Electrode-Assembly) is sandwiched by a pair of separators, and, as shown inFIG. 2, of a rectangular plate shape and stacked in a horizontal direction with its long sides disposed vertically. Note that the unit cell FC is basically made of rectangular, plate shape, but may well be of a similar shape to which the reinforcing plate3is mountable when structuring the laminate1.

Both end plates2are formed in a rectangle shape having a vertical and horizontal dimensions substantially equal to those of cell unit FC, whereby a manifold M and the like is formed for supplying anode gas (hydrogen), cathode gas (air), and cooling fluid. Both collectors5corresponds to a central portion (power generating unit) of unit cell FC, and is provided with a connector portion5A passing through the end plates2.

Each reinforcing plate3is disposed on a first or third outer peripheral surface respectively when the four surfaces parallel to the cell stacking direction of the laminate are named or defined as the first to four outer peripheral surfaces in the circumferential direction. InFIG. 1A, the right side of laminate1corresponds to the first outer peripheral surface, upper side to the second outer peripheral surface, left side not shown in the figure to the third outer peripheral surface, and the lower side not shown either to the fourth outer peripheral surface, respectively. In other words, in the laminate1shown in the example, unit cells FC of rectangular shape are disposed in the horizontal direction, and since this state is easily subjected to being deformed in a direction along short side of unit cell FC, reinforcing plates3,3are provided on the short sides, i.e., on the first and third outer peripheral surfaces.

Each reinforcing plate3is provided with a base portion3A covering the first or third outer peripheral surfaces of laminate1entirely and a pair of holding portions3B,3B extending perpendicularly from base portion3A to cover the second and fourth outer peripheral surfaces partly in the longitudinal direction (i.e., cell stacking direction). The reinforcing plate3is formed in a grooved shape by both holding portions3B,3B in cross-section.

Further, each reinforcing plate3is mounted or attached onto the laminate1resiliently with both holding portions3B,3B spread slightly. Therefore, each reinforcing plate3is in contact with the laminate so as to cramp the laminate under a predetermined load. Specifically, the holding portion3B of reinforcing plate3constitutes a structure for supporting the laminate1as a spring element.

In addition, both ends of the base portion3A of each reinforcing plate3are bent to form an attachment portion3C and the attachment portion3C is connected to the outer surface (the surface opposite from the laminate) by a plurality of bolts B. Moreover, each reinforcing plate3is formed with a cut-out portion or notch3D to serve as the non-interference portion to avoid contact with the outer peripheral surface of end plate2. Thus, holding portion3B is avoided to contact the end plate2by its tip and the resilient assembly structure by the holding portion3B is configured to be applied on the area (shaded area) of laminate1only inFIG. 3.

Each fastening plate4is disposed so as to cover the second and fourth outer peripheral surfaces of laminate1respectively. Each fastening plate4is sized to cover between holding portions3B,3B of the reinforcing plates3on respective outer periphery of laminate1, and is provided at both ends with an attachment portion4A, which is connected to outer surface (surface opposite from the laminate) of end plates2by a plurality of bolts B.

The fuel cell stack FS constructed above is configured to sandwich the laminate1and current collector5by a pair of end plates2,2in the stacking direction by a predetermined pressure, and both the end plates2,2, each reinforcing plate3,3, and fastening plate4,4so as to hold a pressurized state of laminate1. In addition, the fuel cell stack FS is formed by functional components, i.e., end plate2,2, each reinforcing plate3,3, and fastening plate4,4to form a casing integrated structure.

In the fuel cell stack FS described above, since holding portion3B of each reinforcing plate3is resiliently assembled, it is configured in such a way that a spring element is mounted in the vibration direction of laminate1(vertical direction inFIG. 1A). In other words, as shown inFIG. 4, the system may be regarded to the equivalent structure in which laminate1with mass M is supported at a plurality of locations. Specifically, in the present embodiment, the spring element is structured to be continuous in the cell stacking direction by holding portion3B to support the laminate across the entirety of the cell stacking direction.

In this way, the fuel cell stack FS above described is allowed to increase the resonant frequency (natural frequency) by suppressing displacement of laminate1without increasing the number of parts by a simply structured reinforcing plate3with a basic portion3A and holding portion3B. Moreover a separate member such as buffer material to be interposed between the laminate1and reinforcing plate3is not necessary at all, and thus the resonance frequency may be increased without causing the volume for accommodating the laminate in the structure supported on the side of the two end plates2,2.

Since each manifold M of end plate2of the fuel cell stack FS is connected with a connecting pipe to supply or discharge reactant gas or cooling fluid, when structured by supporting on the side of both the end plates22, the vibrations at the pipe connection portion is advantageously suppressed.

In the fuel cell stack FS, as the increase of resonance frequency of laminate1, vibration suppressing performance will be improved, and in addition to avoidance of damage of components due to vibration and a decrease in power generation, man-hours and costs related to manufacturing may be reduced.

In addition, the fuel cell stack FS may be installed on a vehicle as a power source for driving the vehicle. In this case, it is desirable to be set the natural frequency (resonance frequency) of laminate1at least 60 Hz. Thus, resonance of the laminate1by an external force such as the vehicle-specific vibration can be sufficiently suppressed.

In addition, although, in the above embodiment, a case has been described in which holding portion3B of reinforcing plate3and laminate1are brought into contact, the holding portion3B and laminate1may well be held as well in an adjacent state to each other with an extremely small gap to be brought into contact upon vibration input. In this case, at the same time of, laminate1and holding portion3B contact each other, the vibration of laminate1may be suppressed by way of the holding portion3B as a spring element.

FIG. 5is a diagram illustrating another embodiment of the fuel cell stack according to the present invention. It should be noted that in each of the following embodiments, portions with the same configuration as the previous embodiment, a detailed description thereof will be omitted by attaching the same reference numerals.

The previous embodiment is a configuration in which the holding portion3B of the reinforcing plate3is in contact with laminate1. By comparison, in the present embodiment, the fastening is sized to cover the entirety of the second and fourth outer peripheral surfaces and both end portions of fastening plate4are interposed between the holding portion3B of each reinforcing plate3and the laminate. Therefore, the holding portion3B of reinforcing plate3is configured to provide a spring element imparting a spring action against the laminate1.

Here, in addition to forming a notch3D at the holding portion3B of reinforcing plate3for avoiding the contact with the outer peripheral surface of end plate2as non-interference portion, at both sides of attachment portion4A of each fastening plate4, a similar notch or cut-out4B (seeFIG. 1A) is formed. Thus, the fastening plate3and holding portion3B are prevented from contacting by their tip with end plate2, and the spring element due to holding portion3B acts on the laminate1only.

Even in the fuel cell stack FS above, a similar operation and effect of the previous embodiment is available. In particular, by superposing or overlapping the holding portion3B of reinforcing plate3and fastening plate4, a casing integrated structure may be achieved by end plate2, reinforcing plate3, and fastening plate4, so that a separate, dedicated casing may be eliminated and contribution to further decrease in the number of parts or parts count and reduction of production costs may be made.

FIGS. 6A and 6Bare diagrams illustrating yet another embodiment of the fuel cell stack according to the present invention. The fuel cell stack FS shown is provided at reinforcing plate3with a protruding portion3E from holding portion3B toward the laminate1. The protruding portion3E is formed in a rib along the cell stacking direction and, as shown in FIG.6A, is provided with trapezoidal cross-section in surface contact with laminate1as shown inFIG. 6A, or is provided with a triangular cross section in surface contact with laminated1. These protruding portions (ribs) may be formed by press working.

In the fuel cell stack FS described above, the holding portion3B contacts laminate1reliably by way of protruding portion3E so that the load point of the spring element on the side of laminate1is set, in addition to achieving the same operation and effect as the previous embodiment. More specifically, fuel cell stack FS may set the spring constant k of the spring element arbitrarily by selecting a length L from base portion3A to protruding portion3E, or area of contact with laminate1in accordance with various dimensions, materials, and the like of reinforcing plate3.

In addition, as shown in the embodiment ofFIG. 5, in the overlapped configuration between the holding portion3B of reinforcing plate3and fastening plate4, at the portion of fastening plate4overlapping with the holding portion3B, the fastening plate4may be provided with a protrusion toward the holding portion3B. Even with this configuration, the same operation and effect as the previous embodiment may be achieved. In addition, the protrusion portion is not limited in shape, but other than the continuous rib, a rib which protrudes partially with appropriate shape, for example, is also applicable.

FIGS. 7A and 7Bare diagrams illustrating yet another embodiment of the fuel cell stack according to the present invention. The fuel cell stack FS shown inFIG. 7Ais structured with holding portion3of reinforcing plate3overlaid with fastening plate4, and the holding portion3B is provided with protruding portion3E while fastening plate4is provided with an outwardly projecting portion4C. In this fuel cell stack FS, the protruding portion3E of reinforcing plate3and protruding portion4C of fastening plate4are in contact to each other in a cross section perpendicular to the cell stacking direction of reinforcing plate3.

In this embodiment, reinforcing plate3has a protruding portion3E shaped in triangular cross section and has a length L1between fulcrum to load point. In addition, fastening plate4has a protruding portion4C with a rib of trapezoidal cross section and is formed as a beam supported at both ends of the length L2. Specifically, in this embodiment, the rib (protruding portion4C) of fastening plate4is configured to form a beam structure with setting at the contact point of rib (protruding portion3E) of reinforcing plate3as a load point so that this beam structure forms a spring element to support the laminate1.

The fuel cell stack FS described above, in addition to obtaining the similar operation and effect with the previous embodiment, is capable of increasing the degree of freedom in setting the spring constant of the spring element (holding portion3B, protruding portion4C) by selection of length L1, L2due to contact of the configuration in which the protruding portion3E of holding portion3B of reinforcing plate3with protruding portion4C of fastening plate4. Further, since the stress generated in the reinforcing plate3or fastening plate4(such as stress generated at the fixing end of holding portion3B) may be reduced, ease of assembly of respective parts to laminate1or durability of respective parts may be improved.

In addition, the fuel cell stack FS shown inFIG. 7Bhas a configuration in which the holding plate3B of reinforcing plate3and fastening plate4are overlapped, and the fastening plate4has an outwardly oriented protruding portion4C while the protruding portion4C has further an outwardly protruding portion4E. In this fuel cell stack FS, holding portion3B of reinforcing plate3and the protruding portion4E of fastening plate4are in contact to each other in a cross section of reinforcing plate3perpendicular to a stacking direction of cells.

By the protrusion4E of the fuel cell stack FS described above, the holding portion3B contacts fastening plate4reliably, and the load point of the spring element (holding portion3B) on the laminate1is set. In other words, the fuel cell stack FS may set the spring constant k of the spring element (holding portion3B) freely by selecting the length L1between the basic portion3A and protruding portion4E in accordance with various dimensions and materials of reinforcing plate3required for suppression of vibration of laminate1.

In addition, the protruding portion4C of fastening plate4in the fuel cell stack FS described above has a beam structure in which the position of contact between protruding portion4E formed thereon and holding portion3B represents a load point, and protruding portion4C constitutes a spring element supporting laminate1. In other words, by selecting the length L2of protruding portion4C, the spring constant k of the spring element (protruding portion4C) may be set freely, and by the two spring elements (holding portion3B, protruding portion4C), the degree of freedom in setting the spring constant may even be increased.

FIGS. 8A and 8Bare diagrams illustrating yet another embodiment of the fuel cell stack according to the present invention. The fuel cell stack FS shown, has a configuration in which the reinforcing plate3is attached to the laminate1in the state in which the holding portion3B is bent.

The fuel cell stack FS shown inFIG. 8Ais configured in such a way that holding portion3B of reinforcing plate3directly contacts laminate1, and a protruding portion3E comprised of rib of trapezoidal cross section is formed at holding portion3B along the stacking direction of cells. This fuel cell stack FS represents a load point on one side of protruding portion3E on the holding portion3B as shown in figure by arrow F to thereby generate a pressing load toward lamination1.

The fuel cell stack FS shown inFIG. 8Bis configured in such a way that the holding portion3B of reinforcing plate3is superposed or overlapped with fastening plate4, and the holding portion3B has a protruding portion3E of rib formed of a triangular cross section, while the fastening plate4has a protruding portion4C of rib formed of trapezoidal cross-section. In addition, the protruding portions3E,4C are in contact to each other. This fuel cell stack FS is especially at the protruding portion4C of fastening plate4generate pressing or thrust load toward the laminate1by serving both sides of protruding portion4C as load points as shown in figure by arrow F, F.

The fuel cell stack FS described above can assure contact of holding portion3B with laminate1on even more reliable basis in addition to attaining the similar effect as the previous embodiment.

FIG. 9is a diagram illustrating yet another embodiment of the fuel cell stack according to the present invention. The fuel cell stack FS shown is configured in such a way that the holding portion of reinforcing plate3is superposed or overlapped on the fastening plate4, and at the portion of overlapping, the short side dimension of end plate2is set smaller than the short side dimension of the unit cell FC hatched in the figure.

Here, the fuel cell stack FS according to the present invention may be configured as a more preferred embodiment, to provide a non-interference portion on at least either holding portion3B of reinforcing plate3or outer periphery of end plate2. Further, the fuel cell stack FS according to the present invention is configured, as a more preferable embodiment, to provide a non-interference portion at least either on the superposed or overlaid portion of fastening plate with holding portion or periphery surface of end plate so as to avoid mutual contact between both parts.

That is, as described in the embodiment according toFIGS. 1 to 4, in the configuration in which holding portion3B of reinforcing plate3is in contact with the laminate1, holding portion3B is provided with a notch3D as a non-interference portion. Further, as explained regarding the embodiments based onFIG. 1andFIG. 5, in a configuration in which holding portion3B of reinforcing plate3and fastening plate are superposed or overlaid, both the holding portion3B and fastening plate4have notches3D,4B respectively as non-interference portions. In these embodiments, by providing notches3D,4B, outer peripheral surface is avoided being contacted by holding portion3B or fastening plate4around their tip.

Similar to these embodiments, the fuel cell stack FS shown inFIG. 9is provided with a step portion2A as non-interference portion at the outer periphery of end plate2whereby the short side dimension thereof is smaller than the short side dimension of unit cell FC. Thus, the outer peripheral surface of end plate2is avoided being contacted by holding portion3B or fastening plate4around their tip whereby to apply the spring element to the laminate reliably.

In addition, in order for either holding portion3B or fastening plate4to contact laminate1reliably, on the contrary to the case ofFIG. 9, the short side dimension of at least both ends of the unit cell FC may be sized greater than the short side dimension of end plate2. However, in this type of fuel cell stack, when considering several hundreds of unit cells being employed, compared to providing redundant projections on the side of unit cell, provision of non-interference portion on the sides of end plate2, reinforcing plate3and fastening plate4is more advantageous in terms of structural reasons and manufacturing costs.

FIG. 10is a diagram illustrating yet another embodiment of the fuel cell stack according to the present invention. The fuel cell stack FS shown is configured to bond the holding portion3B of reinforcing plate3and fastening plate4at the superposed or overlaid location (sign W) of both components. This joining may be performed by using welding.

The fuel cell stack FS described above is capable of avoiding reliably the deviation of relative positions between reinforcing plate3and fastening plate4whereby prevent generation of vibration noise or separation of surface processed film previously, in addition to achieving the similar effect as the previous embodiment.

FIGS. 11A, 11B and 12A, 12Bare diagrams illustrating yet another embodiment of the fuel cell stack11according to the present invention. The fuel cell stack FS according to the present invention may be configured, as a more preferred embodiment, in such a way that the reinforcing plate3is provided with a holding portion3B at least on the abdomen or antinode locations in the stacking direction of cells, and a plurality of holding portions3B are provided in the stacking direction of cells.

In other words, in the fuel cell stack FS of this type, when the laminate1is vibrated in a state of being supported by both end plates2,2, the displacement of the abdomen or antinode part along the laminate1is the largest. Thus, by providing the holding portion3with respect to the part or anti-note at which the displacement is largest, a minimum configuration necessary to suppress the vibration of the laminate1is provided and the primary mode resonance of the laminate1may be suppressed at its antinode. Thus, the reinforcing plate3in the fuel cell stack FS may be configured to have a holding portion3B at the central portion and may select a variety of forms.

In the fuel cell stack FS shown inFIG. 11A, the reinforcing plate3is provided with a holding portion3B only at an anti-node or abdomen location, and this holding portion3B is provided with protruding portion3E toward the laminate1. In the fuel cell stack FS shown inFIG. 11B, the reinforcing plate3is provided with holding portion3B across the entire length along the stacking direction of cells while the holding portion3B is provided with a protruding portion3E toward laminate1only at the central position of cell stacking direction.

In the fuel cell stack FS shown inFIG. 12A, the reinforcing plate3is provided with holding portions3B at the abdomen or anti-node position as well as both ends along the stacking direction, and each holding portion3B is provided with protruding portion3E toward laminate1. In the fuel cell stack FS shown inFIG. 12B, the reinforcing plate3is provided with the holding position3B across the entire length of laminate1in the stacking direction, and the holding portion3B is provided with protruding portions3E toward laminate1at three locations, i.e., at the central position as well as both ends of the cell stacking direction.

Thus, in the fuel cell stack FS, depending on the place desired to reduce the amplitude of the laminate1, the position, number, shape, etc. of the holding portion and protruding portion3E of reinforcing plate3may be freely selectable to thereby reduce vibrations of laminate1effectively.

The fuel cell stack according to the present invention, when laminate1is configured to contact holding portion3B, as in a more preferable embodiment, the reinforcing plate3may be subjected to an insulating coating at least on the side of laminate. Further, when the holding portion3B is configured to be superposed overlapped with fastening plate4, as in a more preferable embodiment, the fastening plate4may be subjected to an insulating coating at least on the side of laminate.

Thus, in the fuel cell stack FS described above, without inserting the insulating member either between the reinforcing plate3and laminate1or between fastening plate4and laminate1, the insulation inside and outside may be ensured and thus contribution to further decrease in part counts and costs and man-hours of manufacture is achieved.

FIG. 13is a diagram illustrating yet another embodiment of the fuel cell stack according to the present invention. Compared to those shown inFIG. 1A, the fuel cell stack FS illustrated has a configuration in that the reinforcing plate3does not have an attachment portion (3C) in a bent state. In this case, the reinforcing plate3is connected at both ends of base portion3A to the outer peripheral surface of both end plates2by bolt B.

FIGS. 14A and 14B,FIG. 15andFIG. 16are diagrams illustrating yet another embodiment of the present invention the fuel cell stack. In the fuel cell stack FS illustrated, each fastening plate4is provided with a ventilation space8communicative with the outside formed between the second or fourth outer peripheral surface and the fastening plate. In addition, the fuel cell stack FS of this embodiment does not include a specific ventilation, but the ventilation space8is communicated to outside through a gap between notches3D,4B of reinforcing plate3and fastening plate4and end plate2.

As shown inFIG. 16, the ventilation space is sized to have a larger distance than the sum of one half of the displacement of laminate1(upper displacement amount A1in the vertical vibrations) due to vibration and one half of the displacement of fastening plate4(downward displacement amount A2in the vertical vibrations).

The fuel cell stack FS described above is formed with a ventilation space8between laminate1and fastening plate4. Thus hydrogen gas or steam leaked slightly from laminate1may be quickly discharged, and the occurrence of condensation inside and the accumulation of hydrogen gas may be prevented. In this manner, fuel cell stack FS is provided, as shown inFIG. 14B, with a ventilation function area denoted by mixed lines in the figure by the ventilation space8as well as anti-vibration or vibration resistance function area within a sandwiched or cramped area by the holding portion hatched in the figure.

That is, by employing the fastening plate4and the reinforcing plate3as described above, the fuel cell stack FS can achieve both to ensure improved vibration resistance and an internal ventilation function.

In addition, since the above-described fuel cell stack FS has a ventilation space8having a larger distance than the sum of one half of displacement amount of laminate1due to vibration and one half of displacement amount of fastening plate4, even when laminate1and fastening plate4vibrate, a minimum of space or distance S may be maintained so that noise due to contact and damage to components may be avoided.

FIGS. 17A and 17Bare diagrams illustrating yet another embodiment of the fuel cell stack according to the present invention. The fuel cell stack FS shown is configured to provide a plurality of vent openings for opening the ventilation space8to outside at predetermined intervals at the base portion of the attachment portion4A of fastening plate4. Further, fastening plate4is provided with a protruding portion4C shaped in rib protruding to the side of holding portion3B at the location of superposition between holding portion35of reinforcing plate3to open the end of protruding portion4C to build a ventilation opening.

The fuel cell stack FS described above may increase the internal ventilation function even more by a plurality of vent openings6in addition to the similar operation and effect as the previous embodiment.

FIGS. 18A and 18Bare diagrams illustrating yet another embodiment of the fuel cell stack according to the present invention. The fuel cell stack FS shown is provided at fastening plate4with outwardly protruding ribs4D along the direction of cell stacking. In this embodiment, at three positions, i.e., at the central and both sides of fastening plate4, ribs4D are formed parallel to each other. These ribs4D may be formed by press working, for example.

In addition, the fuel cell stack FS in this embodiment has both ends of each of ribs4D opened to form a vent opening6, and, as in the embodiment inFIG. 17A, both ends of protruding portion4C of fastening plate4are formed by vent openings6.

In the fuel cell stack FS, it is possible to obtain the operation and effect similar to the previous embodiment. Further, it is possible to enhance the ventilation function even more by a plurality of vent openings6. Additionally, the rigidity of fastening plate4may be increased due to the plurality of ribs4D. Thus, the fuel cell stack FS may have a small amplitude of fastening plate4(displacement amount due to vibration) together with a small distance to laminate1, i.e., the space of ventilation space8so as to contribute to compactness of the overall device.

As shown inFIGS. 14A and 14B and 19A and 19B, the fuel cell stack according to the present invention has a power generating unit G in the center and three manifolds M at both sides of the power generating unit respectively for supplying/discharging reactant gas and cooling fluid. Further, the fuel cell stack FS is structured, as shown inFIG. 19B, in such a way that the protruding portions3E,4C apply clamping force to laminate1at the frame portion F which forms the periphery of the manifold M and the power generating unit G.

More specifically, the protruding portions3E,4C of reinforcing plate3and fastening plate4are formed, similar to the embodiment shown inFIG. 7A, by a protruding portion3E in V-shaped cross section and a protruding portion4C of flat, trapezoidal cross section. Moreover, especially the protruding portion4C of fastening plate4has a width extending from the vicinity of long side of unit cell FC to the frame portion F partitioning power generating unit G and manifold M. Thus, the clamping force for laminate1by protruding portions are imparted, as shown by dashed lines inFIG. 19B, in the direction of the short side of unit cell FC at the both sides of manifold M along the long side of unit cell FC.

The fuel cell stack FS described above is capable of avoiding the pressing load to be applied at the portion of low rigidity of unit cell FC, i.e., at the power generating unit G and manifold portion M and give the clamping force due to reinforcing plate3and protruding portions3E,4C to laminate1effectively.

In addition, since reaction gas is constantly circulating in manifold M, by imparting clamping force by avoiding the location of the manifold M, damage to the manifold M and leak of reactant gas are avoidable. Furthermore, in the power generating unit G, water is generated and a large amount of moisture vapor is transferred, as shown inFIG. 19Bby crossed lines, by placing ventilation space8adjacent to power generating unit G, the occurrence of condensation may be effectively prevented.

FIGS. 20A and 20Bare diagrams illustrating yet another embodiment of the fuel cell stack according to the present invention. The fuel cell stack FS according to the present invention may be stored, as mentioned above, on a vehicle as vehicle driving power source. In this case, as a more preferable embodiment, as shown inFIG. 20A, the vent opening6to the outside from ventilation space8opens in the longitudinal direction of the vehicle. In the illustrated example, the direction of stacking cells lies in the vehicle longitudinal direction and, at both sides of fastening plate4, three vent openings6are disposed at preset intervals respectively.

As shown inFIG. 20B, outside air which is introduced associated with the traveling of the vehicle flows into a forward vent6naturally, circulates internally, and then flows out from the rearward vent6. Thus, the ventilation during vehicle travel is greatly increased to achieve a further improvement in ventilation function.

In addition, the fuel cell stack FS according to the present invention, when installed on the vehicle as a power source for driving the vehicle, it is possible to structure, as a more preferred embodiment, in such a way that the vent opening6opens to the rear of the vehicle. In such fuel cell stack FS, in addition to securing good ventilation, water or foreign matter such as dust may be prevented from entering the vehicle interior during travel.

The fuel cell stack according to the present invention may be configured to apply insulating coating on the surface of reinforcing plate3at least on the side of laminate1. Further, it is also possible to apply the insulating coating on the surface of fastening plate4on the side of laminate1. Thus, without inserting insulating member between the reinforcing plate3and laminate1, or between fastening plate4and the laminate1, the fuel cell stack FS above is ensured for insulation inside and outside, contributing to further reduction of the number of components as well as to a further reduction of man-hours and cost of manufacture.

The fuel cell stack according to the present invention is not limited in configuration to those in respective embodiments described above, but configuration, the number, material and the like may be subject to change suitably without departing from the scope of the essence of the present invention.

For example, in the above embodiment, reinforcing plates are disposed on the short sides, i.e., on the first and third outer peripheral surfaces of the laminate. However, instead of on the first and third periphery surfaces, the reinforcing plates may be disposed on the long sides of the laminate, i.e. on the second and fourth outer peripheral surfaces.