APPARATUS AND METHOD FOR COMPRESSING A FUEL CELL STACK

Abstract: Compression of a fuel cell stack is realized via an assembly comprising first and second opposing compression members, first and second adjustable connecting members connecting first opposing sides and second opposing sides, respectively, of the compression members and first and second means acting on the connecting members, respectively, to exert a compression force between the first and second compression members.

Description: Apparatus and method for compressing a fuel cell stack Background of the Invention This invention pertains to fuel cells and, in particular, to methods and apparatus for the construction of fuel cell stacks. In the formation of fuel cell stacks comprised of one or more fuel cells, it is extremely important that the stack be placed and held under a preselected or predetermined compression in order for proper stack operation. Thus, if insufficient pressure is applied, performance may deteriorate and, in fact, the individual cells of the stack might be severely damaged if the pressure is reduced to the point where significant leakage of the reactant gases might develop. On the other hand, excessive pressures can result in the entry of deformable cell members and electrolyte into the reactant gas channels, thereby blocking same and hindering stack performance. In addition, cell components might be cracked by excessive pressures. Thus, too great a pressure also will result in decreased performance and in extreme cases severe damage to the stack. To date a number of procedures have been proposed to realize a desired stack compression. In some techniques, the stack is situated in an assembly comprised of at least one pair of compression bars. Each pair of bars is connected by two threaded compression rods each having compression nuts on its ends for situating the respective compression bars. In one practice using this type of assembly, a torque wrench is used to provide a torque to the compression nuts, this torque having been calculated to provide a desired stack compression. This practice, however, often provides inac curate results due to the inherent and wear-induced imperfections in the rod threads. Another technique which has been used is to determine the degree of deflection required in the compression bars in order to bring about a desired compression in the stack and to compress the stack until the calculated deflection is achieved. While this technique has been found to provide suitable results, the procedure of measuring the deflection of the rods is cumbersome and time consuming, thus making the overall technique unattractive from a production standpoint. A further practice which has been proposed for fuel stack compression is to place the entire stack within a pneumatic or hydraulic press. While this practice enables the desired compression to be realized, it also has a number of drawbacks. If the stack is first assembled and then placed in the press, difficulties arise in moving the stack, which could be upwards of 10 feet in height, in terms of the equipment required and of the need to move the stack with as little shifting of the cells as possible so as to prevent tearing and other injury to the delicate cell components. On the other hand, if the cells are stacked on the press itself, an oversized and much higher press would be needed in order to provide sufficient room to accommodate the personnel and equipment required for assembly. Another disadvantage is that in tall stacks, due to the tolerances in the individual cell components, there might be sections of the stack that are higher than others. Since the press plates are flat on top and bottom, when the stack is compressed only these high spots will receive the desired compression. The remaining sections will, therefore, be undercompressed rendering the stack amenable to the same problems discussed hereinabove for undercompression. It is an object of the present invention to provide a practice for fuel cell stack compression which does not suffer from the disadvantages discussed above. It is a further object of the present invention to provide an apparatus and method for fuel cell stack compression which is relatively simple and easily manageable. Summary of the Invention In accordance with the principles of the present invention, the above and other objectives are realized in an assembly comprising first and second spaced compression members defining a region therebetween for receiving a fuel cell stack, first and second adjustable connecting members connecting first opposing sides and second opposing sides, respectively, of the compression members and first and second means acting on the first and second connecting members, respectively, for exerting a compression force between the first and second compression members. In the embodiment of the invention to be disclosed hereinafter, each compression means is detachably connected to the connecting member upon which it acts. More particularly, each compression means comprises a ram assembly having an axially movable actuating rod whose one end is connected to the assembly ram for movement therewith and whose other end is connected by a detachable coupling to the corresponding connecting member. Spacer means between each ram assembly housing and the first plate provides a counterforce to the force resulting from the ram on the corresponding connecting member, whereby compression of the compression members and, therefore, the stack therebetween is realized. In this embodiment a common pressure source and a distribution means for providing equal pressures to the compression means are also provided. Detailed Description of the Drawings The above and other features and aspects of the present invention will become more apparent upon reading the following detailed description in conjunction with the accompanying drawings, in which: FIG.1 illustrates an assembly for compressing a fuel cell stack in accordance with the principles of the present invention; and FIG.2 shows an enlarged view of one ram assembly of the compression assembly of FIG.1. Detailed Description In FIG 1, a fuel cell stack 1 comprised of a number of fuel cell assemblies 2 is to be placed and held under a predetermined compression desired for the stack. This is realized via a compression assembly 3 in accordance with the principles of the present invention. Upper and lower end plates 11 and 12 sandwich the stack 1 and are held between a first pair of opposing compression members or bars 13 and 14 disposed at one location along the plates and a second pair of opposing compression members or bars 15 and 16 disposed at a second location along the plates. The upper compression members 13 and 15, and the lower compression numbers 14 and 16 are seated on the upper and lower plates 11 and 12 via foot pads 17 which are distributed so as distribute the compression force evenly over the plates. Each pair of the compression bars is held together by adjustable connecting assemblies formed by threaded compression rods and compression nuts disposed at opposing ends of the bars. Thus, compression rods 18 and 19 extend through apertures in opposing ends 13a and 14a and 13b and 14b (not visible) of bars 13 and 14, and compression rods 21 and 22 extend through apertures in opposing ends 15a and 16a and l5b and 16b (not visible) of bars 15 and 16. Compression nuts 23 are situated at the threaded ends of the rods 18, 19, 21 and 22 so as to hold the rods and bars together and to aid in realizing and maintaining the desired compression, as will be discussed below. A ram assembly 41 and associated support assembly 24 and spacer 25 are situated at each end of the upper compression bars 13 and 15 and together provide the forces on the respective pairs of compression bars necessary to compress the stack 1. The ram assemblies may be either pneumatic or hydraulic and are activated by a common pressure source 26 and a valve distribution system 27 which ensures equal pressures are applied to each assembly. FIG. 2 shows an enlarged view of a ram assembly 41 and related equipment at one end of the compression bars 15 and 16. The ram assembly housing 42 is supported on an adapter plate 24a of support assembly 24 and houses a ram 43 whose upper end abuts a retainer nut 44. The retainer nut 44 is threaded onto a translatable central rod or shaft 45 which extends downwardly through the ram housing 42 and through the adapter plate 24a into the interior of U-shaped housing 24b of assembly 24. The upper end of compression rod 21 also enters the interior of housing 24b, the rod 21 having passed through spacer 25 and spherical and load washers 29 situated between the spacer and the compression bar 15. A disconnectable coupling 46 connects the upper end of the rod above the nut 23 to the lower end of the shaft 45. In operation, compression nuts 23 are first hand tightened to fix the compression bars and compression rods in place. The pressure source 26 is then activated and it delivers pressure to the distributor valve 27. The valve 27 in turn, couples equal amounts of pressure to the ram assemblies 41. This pressure causes the respective rams of each assembly and the respective shafts 45 connected thereto to be raised to the position shown in FIG. 2. The shafts 45 thereupon, via couplings 46, similarly raise the compression rods 18, 19, 21 and 22 causing an upward force on the lower compression bars 14 and 16. At the same time a downward counterforce is exerted by the housings 42, support assemblies 24, spacers 25 and washers 29 on the upper compression bars 13 and 15. The respective upward and downward forces on the lower and upper compression bars cause, via foot pads 17, a uniform compression force to be exerted between the plates 11 and 12 and, thereby, the stack 1 is uniformly compressed to the desired compression. After the stack 1 has been compressed, the compression nuts 23 at the upper ends of the compression rods 18, 19, 21 and 22 are tightened against the respective spacers and washers to maintain the compression bars and, thus, the stack under compression. The shafts 45 of the ram assemblies 41 are then disconnected from the compression rods via release of the couplings 46 and the ram assemblies, support assemblies and couplings, along with the distributor valve 27 are removed for use on another stack. With the compression assembly of the present invention, as above-mentioned, equal compression forces are exerted on the compression bars and, therefore, equal forces are uniformly distributed by the foot pads to the compression plates. As a result, uniform compression of the stack is realized with a compression assembly which is of relatively simple construction and which is easily disassembled and assembled for further use. In all cases, it is understood that the abovedescribed arrangements are merely illustrative of the many possible specific embodiments which represent applications of the present invention. Numerous and varied other arrangements can readily be devised in accordance with the principles of the present invention without departing from the spirit and scope of the invention.

Claims: What I Claim Is 1. Apparatus for compressing a fuel cell stack comprising: first and second compression members arranged in opposing spaced relationship; first and second adjustable connecting members connecting opposing first ends and opposing second ends, respectively, of said first and second compression members; first and second means acting on said first and second connecting members, respectively, for exerting a compression force between said first and second compression members. 2. Apparatus in accordance with claim 1 wherein: said first and second means are releasably connectable to said first and second connecting members, re spect ively. 3. Apparatus in accordance with claim 2 wherein: said first adjustable connecting member comprises: a first threaded compression rod extending through said first ends of said compression members; and first and second compression nuts threaded onto opposite ends of said first threaded rod; and said second adjustable connecting member comprises: a second threaded compression rod extending through said second ends of said compression members; and third and fourtn compression nuts threaded onto opposite ends of said second threaded rod. 4. Apparatus in accordance with claim 2 wherein: said first means acts at one end of said first connecting member to apply a force in a first preselected direction and acts on the one of said first ends of said compression members closest said one end of said first connecting member to apply a force in a direction opposite said first preselected direction; and said second means acts at one end of said second connecting member to apply a force in a second preselected direction and acts on the one of said second ends of said compression members closest said one end of said second connecting member to apply a force in a direction opposite said second preselected direction. 5. Apparatus in accordance with claim 4 wherein: said first and second preselected directions are the same. 6. Apparatus in accordance with claim 4 wherein: said first means comprises: a first housing; a first ram translatably supported in said first housing; a first shaft connected to said first ram and translatable therewith; a first coupling for releasably connecting an end of said first shaft to said one end of said first connecting member; said first housing being in force transmitting relationship to the one of said first ends of said compression members closest said one end of said first connecting member; and said second compression means comprises: : a second housing; a second ram translatably supported in said second housing; a second shaft connected to said second ram and translatable therewith; a second coupling for releasably connecting an end of said second shaft to said one end of said second connecting member; said second housing being in force transmitting relationship to the one of said second ends of said compression members closest said one end of said second connecting member. 7. Apparatus in accordance with claim 6 wherein: said one end of said first connecting member and said one end of said second connecting member are above said first compression member. 8. Apparatus in accordance with claim 7 wherein: said first means further comprises: a first support assembly mounted on said one of said first ends and supporting said first housing; and said second means further comprises: a second support assembly mounted on said one of said second ends and supporting said second housing. 9. Apparatus in accordance with claim 8 further comprising: a first spacer situated between said first support assembly and said one of said first ends; and a second spacer situated between said second support assembly and said one of said second ends. 10. Apparatus in accordance with claim 9 wherein: said first support assembly has an open interior and has an opening permitting access to said interior; and said connected ends of said first shaft and said first connecting member and said first coupling are situated within said open interior of said first support assembly: said second support assembly has an open interior and has an opening permitting access to said interior; and said connected ends of said second shaft and second connecting member and said second coupling are situated within said interior of said second support assembly. 11. Apparatus in accordance with claim 1 or 8 further comprising: a common source of pressure; and means for connecting said first and second means to said common source of pressure. 12. Apparatus in accordance with claim 11 wherein: said connecting means provides equal pressures to said first and second means. 13. Apparatus in accordance with claim 1 or 8 further comprising: a number of first pads distributed on the surface of said first compression member facing said second compression member; a number of second pads distributed on the surface of said second compression member facing said first compression member. 14. Apparatus in accordance with claim 13 further comprising: first and second plates disposed between said first and second compression members, said first plate abuttinq said first pads of said first compression member and said second plate abuttinq said second pads of said second compression member. 15. Apparatus in accordance with claim 14 wherein: said first pads and said second pads are distributed to provide a uniform compression force across said first and second plates. 16. Apparatus in accordance with claim 1 further comprising: third and fourth compression members arranged in opposing spaced relationship, said third and fourth members being spaced from said first and second members; third and fourth adjustable connecting members connecting opposing first and second ends, respectively, of said third and fourth compression members; third and fourth means acting on said third and fourth connecting members, respectively, for exerting a compression force between said third and fourth compression members. 17. A method of compressing a fuel cell stack comprising: arranging first and second compression members in opposing spaced relationship; connecting opposing first ends and opposing second ends, respectively, of said first and second compression members; and applying forces to said first and second connecting members for exerting a compression force between said first and second compression members. 18. A method of compressing a fuel cell stack in accordance with claim 17 wherein: the application of force to said first connecting member is through a first ram assembly disconnectably attached to one end of said first connecting member; and the application of force to said second connecting member is through a second ram assembly disconnect ably attached to one end of said second connecting member. 19. A method in accordance with claim 18 wherein: a shaft of said first ram assembly connected to the ram of said first ram assembly is releasably connected to said one end of said first connecting member, the ram of said first ram assembly being translatably mounted to the housinq of said first ram assembly which is in force transmitting rela tionship to the one of said first ends of said compression members which is closest said one end of said first connecting member: : and a shaft of said second ram assembly connected to the ram of said second ram assembly is releasably connected to said one end of said second connecting member, the ram of said second ram assembly being translatably mounted in the housinq of said second ram assembly which is in force transmittina relationship to the one of said second ends of said com pression members which is closest said one end of said second connecting member. 20. A method in accordance with claim 18 or 19 further comprising: arranging first and second plates in spaced relation ship with one another and in force transmitting relationship with said first and second compression members so that a uniform compression force is exerted across said first and second plates. 21. A method in accordance with claim 18 wherein: the force applied to said first connecting member is substantially equal to the force applied to said second connecting member.

Inventors: CHI, CHANG VUM
Applicants: ENERGY RESEARCH CORPORATION
Application year: 1982
Main classification: H01M8
IPC codes: H01M8