Fuel cell module, fuel cell system and method for producing a fuel cell module

Abstract

The invention relates to a fuel cell module (10) having a plurality of fuel cells forming a fuel cell stack and having an enclosure (14) which surrounds the fuel cell stack. The enclosure (14) includes a bottom assembly and a lid cap assembly (30), wherein the bottom assembly includes a jacket at least partly form-fitted to the stack architecture providing internal alignment functions and a bottom plate in pressure contact with the fuel cell stack, wherein the lid cap assembly (30) comprises a compression plate (32) in pressure contact with the fuel cell stack. The bottom assembly (20) and the lid cap assembly (30) are provided with a progressive locking system providing a range of compression pressures to the fuel cell module (10). Further aspects of the invention relate to a fuel cell system and to a method for producing a fuel cell module (10).

Claims

1. A fuel cell module having a plurality of fuel cells forming a fuel cell stack, and having an enclosure which surrounds the fuel cell stack, wherein the enclosure includes a bottom assembly and a lid cap assembly, wherein the bottom assembly includes a jacket at least partly form-fitted to the stack architecture providing internal alignment functions and a bottom plate in pressure contact with the fuel cell stack, wherein the lid cap assembly comprises a compression plate in pressure contact with the fuel cell stack, wherein the bottom assembly and the lid cap assembly are provided with a progressive locking system providing a range of compression pressures to the fuel cell module, characterized in that the progressive locking system provides for an upbuilding of restoring forces through the displacement of the bottom assembly in relation to the lid cap assembly when the fuel cell stack grows during use and requires more volume in the stacking direction.

2. The fuel cell module as claimed in claim 1, wherein the progressive locking system provides for several locking steps, wherein at least one locking step provides pre-compression and at least one other locking step provides full compression to the fuel cell stack.

3. The fuel cell module as claimed in claim 1, wherein the lid cap assembly includes a circumferential jacket section for a form-fitted engagement with the jacket and wherein the progressive locking system comprises first locking elements formed at the jacket section.

4. The fuel cell module as claimed in claim 1, wherein the progressive locking system comprises a spring structure, preferably a leaf spring structure, provided at one of the lid cap assembly and the jacket, and wherein the spring structure engages a ratchet bar provided at the other one of the lid cap assembly and the jacket.

5. The fuel cell module as claimed in claim 4, wherein one of the spring structure and the ratchet bar is arranged on a slider providing the ability of adjusting compression pressures to the fuel cell module.

6. The fuel cell module as claimed in claim 4, wherein the ratchet bar includes a number of protrusions having sliding portions, and wherein a displacement of the lid cap assembly with regards to the bottom assembly translates into a sliding movement of at least one leaf spring of the leaf spring structure over a sliding portion.

7. The fuel cell module as claimed in claim 1, wherein the progressive locking system comprises a spring assembly provided at one of the lid cap assembly and the jacket, and wherein the spring assembly engages a first rail provided at the other one of the lid cap assembly and the jacket.

8. The fuel cell module as claimed in claim 1, wherein the jacket has a rectangular cross section with pockets, and wherein the pockets provide a space for housing the progressive locking system.

9. The fuel cell module as claimed in claim 1, wherein the jacket provides for at least three, preferably at least four alignment regions for stack alignment during assembling and wherein at least one, preferably two, three or four of these alignment regions form mounting through holes for the connection of the fuel cell module to an external support structure.

10. The fuel cell module as claimed in claim 1, comprising humidification means, sensors and/or controllers for monitoring the operation of the fuel cell module and/or power conversion devices, integrated into the enclosure.

11. The fuel cell module as claimed in claim 1, wherein the enclosure is box shaped and wherein the lid cap assembly comprises external connection means for supply and evacuation of compressed air, reactants and coolant to the fuel cell module, wherein the external connection means are arranged at the same side of the box shaped enclosure.

12. The fuel cell module as claimed in claim 11, wherein the fuel cell stack is connected to current collector tabs, and wherein the current collector tabs exit the enclosure at the same side as the external connection means.

13. A fuel cell system having at least one, preferably from 2 to 20 fuel cell modules as claimed in claim 1, the fuel cell modules being connected to an integration backplane having a distribution system for the supply and evacuation of compressed air, reactants and coolant to the fuel cell modules, and/or for providing current collection of the fuel cell modules.

14. A method for producing a fuel cell module as claimed in claim 1, the method comprising the following steps: stacking a multitude of MEA units and bipolar plates on a moveable center mounting plate surrounded by the jacket, the movable center mounting plate providing motion so that the jacket provides alignment during the stacking, raising the jacket or lowering the center mounting plate as the height of the stacked MEAs and bipolar plates increases during the assembly process, locking the center mounting plate in position when it meets fixation points with the aligning jacket, the center mounting plate and the jacket thus forming the bottom assembly, and joining the lid cap assembly to the bottom assembly via the progressive locking system to form the enclosure surrounding the fuel cell stack.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a perspective view of a lunchbox enclosure according to an embodiment of the invention.

(2) FIG. 2 is a cross section of a lunchbox enclosure according to an embodiment of the invention.

(3) FIGS. 3 and 4 provide perspective views of a system with integrated backplane and lunchboxes arranged thereon.

(4) FIG. 5 is a perspective view of a fuel cell module according to an embodiment of the invention, with a lid cap assembly in the foreground.

(5) FIG. 6 is a section view of the fuel cell module of FIG. 5.

(6) FIG. 7 is a section view of the lid cap assembly of the fuel cell module of FIG. 5.

(7) FIG. 8 is a section view at the level of the media manifolding region of the lid cap assembly of the fuel cell module of FIG. 5.

(8) FIG. 9 is an exploded view of an assembly comprising the fuel cell stack, the current collection means and the bottom assembly of the fuel cell module of FIG. 5.

(9) FIG. 10 is a perspective view of the bottom assembly of the fuel cell module of FIG. 5.

(10) FIG. 11 is a top view of the bottom assembly of the fuel cell module of FIG. 5.

(11) FIG. 12 is a top view of the bottom plate of the fuel cell module of FIG. 5.

(12) FIG. 13 is a section and perspective view of the bottom assembly of the fuel cell module of FIG. 5.

(13) FIG. 14 is a section and perspective view of a bottom assembly of a fuel cell module according to a second embodiment of the invention.

(14) FIG. 15 is a perspective view of the bottom assembly depicted from below.

(15) FIG. 16 is a section and perspective view of the lid cap assembly with the ratchet bar of the fuel cell module of FIG. 5.

(16) FIG. 17 is a perspective view of the bottom assembly with the leaf spring structure of the fuel cell module of FIG. 5.

(17) FIG. 18 is a perspective exploded view of the bottom assembly with a leaf spring structure and the ratchet bar of the fuel cell module of FIG. 5.

(18) FIG. 19 is a perspective view of the bottom assembly with the leaf spring structure and the ratchet bar of the fuel cell module of FIG. 5.

(19) FIG. 20 is a perspective view of a bottom assembly filled with a fuel cell stack and a spring assembly of a fuel cell module according to a third embodiment of the invention.

(20) FIG. 21 is a schematic view of the first rail of FIG. 20 with straight sections and wedges.

DESCRIPTION OF THE DRAWINGS

(21) Hereinafter, embodiments of the invention are described in greater detail with reference to the drawings. The embodiments are not to be interpreted as limiting the subject matter of the invention. Many modifications and combinations which are not shown in the drawings will be apparent to a person skilled in the art on the basis of his technical knowledge.

(22) In the drawings, same reference signs are used to identify same elements or elements which are similar in their function. Repetitive statements are avoided, if possible.

(23) FIG. 1 depicts a lunchbox enclosure with one set of possible embodiments for external ratcheting, porting and external electrical connections.

(24) FIG. 2 depicts a cross section of a lunchbox enclosure showing one possible embodiment for the internal compression and porting block, alignment features for the stack assembly, and a port configuration for a U-flow arrangement.

(25) One embodiment of the stacking arrangement is shown in FIGS. 3 and 4. FIGS. 3 and 4 show front and back views of lunchbox arrangement and porting as the stacking and plug-in concept for the integrated backplane.

(26) FIG. 5 shows a fuel cell module 10 in perspective view. The displayed front side of the fuel cell module 10 is formed by a lid cap assembly 30, forming, together with a bottom assembly 20 not displayed, the enclosure 14 of the fuel cell module 10.

(27) The fuel cell module 10, purely by way of example, is designed in a cuboid shape to enable space-saving and modular installation in an installation space, for example, a space for mounting a drive unit of a vehicle, such as a motor vehicle, bus, truck and the like.

(28) External connection means 70 are arranged on a single side of the cuboid fuel cell module 10, preferably at the side of a compression plate 32 described in more detail with regards to FIGS. 6-8. The arrangement of the external connection means 70 on the same side of the box shaped, purely exemplary, cuboid enclosure 14, is advantageously made possible by a plug-in connection to an integration backplane, which can, for example, supply and discharge compressed air, reactants and coolant to the fuel cell module(s).

(29) In FIG. 5, the external connection means 70 include an oxidant inlet 74 and an oxidant outlet 76, which are, by way of example, formed here on two opposing sides to allow a U-shaped passage through the fuel cell module 10 or the fuel cell stack 12 therein (not shown).

(30) The external connection means 70, for example, without limiting the invention, further include two coolant ports 78, which are located, for example, at two opposite corners of the front of the lid cap assembly 30 to allow a U-shaped passage of coolant through the fuel cell stack 12.

(31) The external connection means 70 also include a fuel inlet 80, which, by way of example, is located in another corner of the front of the lid cap assembly 30, without limiting the invention. Reference numeral 82 shows an access window to an ejector valve, and reference numeral 84 shows an access window to a purge valve, which, in this exemplary embodiment, are also located at the front side of the lid cap assembly 30. The functions of ejector and purge valves as parts of the anode sub system of the fuel cell system are well known to the person skilled in the art and do not have to be described in more detail here.

(32) Furthermore, current collector tabs 72 pass through respective though holes 71 in the front of the lid cap assembly 30, so that the connection to the integration backplane can simultaneously enable removal of the current.

(33) At the front side of the lid cap assembly 30, two mounting through holes 86 are provided to fix the fuel cell module 10 to the integration backplane. In other embodiments, there may be more than two mounting through holes 86 present, e.g. three or four through holes 86. Instead of a mounting through hole 86, fixation means 68, such as bolts, screws and the like, can of course be there, which provide a mechanical connection to the integration backplane by means of a corresponding counterpart. It should also be understood that further elements may be provided at the fuel cell module 10 as well, especially centering means or alignment means and the like.

(34) FIG. 6 shows a section through the fuel cell module 10 of FIG. 5, depicting the interior of the fuel cell module 10.

(35) The enclosure 14 comprises the lid cap assembly 30 described with reference to FIG. 5 and a bottom assembly 20 nested in the lid cap assembly 30. The lid cap assembly 30 and the bottom assembly 20 are attached to each other by means of a locking system 16 not shown here. The locking system 16 will be described with reference to FIGS. 16 to 20. The lid cap assembly 30 and the bottom assembly 20 enclose a fuel cell stack 12, which is formed in a known manner from a multitude of membrane electrode assemblies (MEAs), bipolar plates and end plates. Details are known to the person skilled in the art. Typically, a bipolar plate connects two adjacent MEAs, with the negative electrical pole of the bipolar plate being located on the hydrogen side of a first MEA, and the positive electrical pole contacting the oxygen side of the other MEA. The arrangement of the bipolar plates and MEAs is repeated up to the end plates, which causes the voltages of the individual cells to add up.

(36) In a preferred embodiment, fuel cell stacks 12 with bipolar plates are provided, as they typically require little space. Their high current density is also particularly advantageous. However, this is not to limit the invention. The fuel cell stack 12 can also include monopolar base units in which the individual cells are electrically connected to each other.

(37) The bottom assembly 20 includes a jacket 22 with, for example, four circumferential side walls and a bottom plate 26, which functions as a first compression plate.

(38) The lid cap assembly 30 includes a jacket section 36 with four circumferential side walls that surround the jacket 22 of the bottom assembly 20. The lid cap assembly 30 also includes a compression plate 32, which forms a media manifolding region as an additional function.

(39) The compression plate 32 and the bottom plate 26 are arranged opposite each other. The bipolar plates and MEAs, or monopolar plates and MEAs, respectively, of the fuel cell stack 12 are arranged essentially parallel to the bottom plate 26 and the compression plate 32.

(40) Movement towards each other of the lid cap assembly 30 and the bottom assembly 20 means a movement towards each other of the compression plate 32 towards the bottom plate 26. Movement towards each other of the compression plate 32 and the bottom plate 26 leads to a compression of the fuel cell stack 12. A spatial expansion of the fuel cell stack 12 leads accordingly in reverse direction to a movement away from each other of the compression plate 32 from the bottom plate 26. The height of the slot section 38 allows the bottom assembly 20 to be moved relative to the lid cap assembly 30. Various pressure conditions can thus be applied to the fuel cell stack 12. By accurately dimensioning and, in some embodiments, sealing the slot section 38, a loss of media over the joining surfaces of the bottom assembly 20 with the lid cap assembly 30 can be avoided.

(41) The compression plate 32 also includes the external connection means 70 described with reference to FIG. 5, showing in a sectional view also one of the current collecting tabs 72, a coolant port 78, part of the oxidant inlet 74, and part of the oxidant outlet 76, as well as the purge valve access window 84 and mounting through hole 86. The compression plate 32 in this exemplary but not limiting embodiment is not fully massive or solid but contains media routing channels 34 for routing the media from external to internal, i.e. to fuel cell stack 12. The media routing channel 34 shown, for example, in FIG. 6 is assigned to the oxidant inlet 74 and the oxidant outlet 76, by way of example, running straight and vertical through the compression plate 32.

(42) FIG. 7 shows a sectional view through the lid cap assembly 30 with further details of the compression plate 32. The compression plate 32 not only conducts the media through from the outside, but also enables media (fluid) beam splitting, widening or fanning, and precise routing, respectively, to the fuel cell stack 12, which is not shown here. This can be seen, merely as an example, at the coolant port 78, whose circular connection area on the outside of the pressure plate 32 is transferred to a widened area, here with a rectangular cross section, by way of example. The corresponding media distribution channel 34 is thus not provided with constant cross section across the height of the pressure plate 32.

(43) FIG. 8 shows a top view from the inside, i.e. from the perspective of the fuel cell stack 12, which is not shown here, towards the compression plate 32. As already described, the lid cap assembly 30 has a rectangular layout. Reference number 13 shows a projected footprint of the fuel cell stack 12, which is encompassed by lid cap assembly 30.

(44) On the inside, compression plate 32 has corresponding openings for the external connection means 70, and in this embodiment, the oxidant outlet 76 and the oxidant inlet 74 still have the same slot-like rectangular cross section as can be seen on the outside of enclosure 14, described with reference to FIG. 5. The coolant ports 78 have a rectangular cross section, which allows better distribution of the cooling fluid to the fuel cell stack 12. Externally, the coolant ports 78 are designed for hose connectors, as shown in FIG. 5. This allows the coolant to be supplying through hoses which are, for example arranged within the integration backplane. In addition, the slot-like openings for the current collector tabs 72 and the mounting through holes 86 for attachment to the integration backplane can also be seen in this view. Fuel inlet 80 and fuel outlet 81 are arranged in two corners of the compression plate 32.

(45) FIG. 9 shows an exploded view of the bottom assembly 20, the fuel cell stack 12 and associated end plates 73, which the current collector tabs 72 are welded to. The MEAs and bipolar plates of the fuel cell stack 12 typically run parallel to the end plates 73. One of the end plates 73 is located in the area of the bottom plate 26 of the bottom assembly 20, and another of the end plates 73 is located in the open top area of the bottom assembly 20, which is enclosed on top by the compression plate 32 of the lid cap assembly 30, as described with reference to FIG. 2. The current collector tabs 72 protrude upwards beyond the combined assembly, and they pass through the compression plate 32. The end plates 73 typically have the same lateral dimensions as the bipolar plates and MEAs. The shape of the bipolar plates and MEAs in stack 12 and the end plates 73 is essentially rectangular, but includes various recesses and through holes. The through holes provide for media routing, which is known to the skilled person. The recesses are designed to fit positively with the corresponding recesses in jacket 22 of the bottom assembly 20. The function of the recesses is explained in more detail below in relation to FIGS. 10 to 20.

(46) FIG. 10 shows a bottom assembly 20 in perspective view. The jacket 22 of the bottom assembly 20 has an essentially rectangular cross section, with two pockets 24 on its long side. The pockets 24 take up the rectangular cross section on the inside. The two pockets 24 in the embodiment shown here are purely exemplary without limiting the invention and are mirror-symmetrical with respect to a central axis through the bottom assembly 20. The pocket 24 runs evenly from the bottom to the top and is offset slightly away from the center. The pocket 24 provides housing for the locking system 16 described with reference to FIGS. 15 to 20, which is not shown here.

(47) FIG. 11 shows a top view of the bottom assembly 20, with reference mark 13 showing the footprint of the fuel cell stack 12. The footprint 13 essentially follows the shape of the footprint of the jacket 22, thus including, in particular, the pockets 24. The bottom assembly 20 provides alignment functions and is essentially form fitted with the fuel cell stack 12. However, the footprint 13 of the fuel cell stack 12 and the shape of the jacket 22 differ in a number of alignment regions 28. In this embodiment there are four alignment regions 28, which, however, is not to be understood as limiting the invention. There may also be less or more, for example, 3, 5 or even more alignment regions 28. Just by way of example, two such alignment regions 28 are located in the corners of the jacket 22, and two more alignment regions 28 in the region of the pockets 24. In alternative embodiments, three or four alignment regions 28 can be located in the corners of the jacket 22, or three or four alignment regions 28 in the regions of the pockets 24. Alignment regions 28 are used for the precise placement of MEAs and bipolar plates to form the fuel cell stack 12. The alignment regions 28 can have a double function as channels for mounting elements to external structures, such as the integration backplane.

(48) FIG. 12 shows a top view of the bottom plate 26. The footprint of the bottom plate 26, as can be seen, corresponds exactly to the footprint of the jacket 22 described with reference to FIG. 11. The alignment regions 28 shown in FIG. 11 are provided with mounting through holes 28 on the bottom plate 26, so that fasteners can be passed through the bottom plate 26 from the outside, across the stack 12 and finally towards the connection area of the lid cap assembly 30. Thus, the fuel cell module 10 can be favorably mounted from the bottom plate 26 by means of four fixation means 68 such as screws to the integration backplane. In the area of the pockets 24, a notch 25 is provided for retention means 27 depicted in FIG. 13.

(49) FIG. 13 shows a cross section of the bottom assembly 20, depicting a section of the jacket 22 and a section of the bottom plate 26. In the embodiment shown in FIG. 13, the bottom plate 26 is welded to the jacket 22 around the circumference. During assembly, the MEAs and bipolar plates are positioned on top of each other, starting from the bottom plate 26.

(50) Current collector tab retention means 27 are provided, the retention means 27 being form-fitted to the notch 25. The retention means 27 provide for alignment to the current collector tab 72 especially during stack assembly.

(51) FIG. 14 shows an embodiment different from the one described with regards to FIG. 13. The embodiment in FIG. 14 includes a movable bottom plate 26, which is positioned in the upper area of the jacket 22 at the beginning of stacking of the MEAs and bipolar plates. The movable bottom plate 26 may also be called a center mounting plate 23 in the context of the present disclosure. As the stack grows by assembling, the center mounting plate 23 is moved towards the bottom of the jacket 22, or the jacket 22 is moved relative to the center mounting plate 23, depending on the embodiment. This makes it possible that every MEA or bipolar plate to be stacked can be handled at the same place by the assembling machine such as a robot.

(52) FIG. 15 shows the situation from below after stacking the entire fuel cell stack 12 in the bottom assembly 20. As can be seen, there may an excess length of the jacket 22 with respect to the bottom plate 26. The excess length may be laser cut and the bottom plate 26 may be welded to the jacket 22 to form the bottom assembly 20.

(53) The technology involving moveable mounting plate 23 enables different stack sizes of the fuel cell modules 10. Once the required stack size of one fuel cell module 10 is reached, the jacket 22 may be laser cut and the next one may readily be assembled. Thus, the production line may be adapted for assembling different stack sizes to fuel cell modules 10 on demand.

(54) FIG. 16 shows a perspective view of the lid cap assembly 30 with four ratchet bars 60 attached to the jacket section 36 of the lid cap assembly 30, three of which are depicted. The ratchet bars 60 form part of a locking system 16 for securing the lid cap assembly 30 to the bottom assembly 20 as will be described in more detail below.

(55) The ratchet bars 60 are arranged at a distance from each other. Each ratchet bar 60 in the embodiment shown comprises a second rail 63 with a number of protrusions 62 attached to it. Two ratchet bars 60 are attached to each side of the jacket section 36 so that the protrusions 62 face each other. The protrusions 62 each comprise a sliding portion 64 and a knob portion 66 arranged at a distal end of the sliding portion 64 with regards to the second bar 63.

(56) FIG. 17 shows the bottom assembly 20 with the jacket 22 and elements of the locking system 16 arranged in the pockets 24. The pockets 24 can be designed as described above, i.e. slightly asymmetrical with respect to the longitudinal axis of the bottom assembly 20 or, alternatively, opposite each other.

(57) In the embodiment shown, the part of the locking system 16 located on the bottom assembly 20 comprises an assembly with a slider 18 and a leaf spring structure 40. The slider 18 is movably arranged in a backdrop guidance 46. The backdrop guidance 46 is attached to the jacket 22 of the bottom assembly 20 by further fixation means 68. The backdrop guidance 46 can be designed as a guide bracket with a C-profile, for example. The technical function of the slider 18 will be described in more detail below.

(58) The leaf spring structure 40 is attached to the slider 18 by means of a series of fixation means 68. In the embodiment shown in FIG. 17, the leaf spring structure 40 comprises a number of leaf springs 44 which can be attached to slider 18, either rigidly or pivotably. This embodiment comprises, for example, six leaf springs 44, each comprising two prongs 42 extending from a fixation portion 43. The prongs 42 are curved towards the bottom plate 26. If the prongs 42 are bent, they absorb elastic energy. During bending or expansion (here: spreading), the prongs builds up a restoring force.

(59) It shall be understood that the elements of the locking system 16 described with regards to FIGS. 16 and 17 can also be provided in mechanical reverse, i.e., leaf spring structure 40 with slider 18 assigned to lid cap assembly 30, and ratchet bars 60 assigned to bottom assembly 20.

(60) FIG. 18 schematically shows the interaction of the ratchet bars 60 with the leaf spring structures 40. It should be understood that in this embodiment the ratchet bars 60 are attached to the lid cap assembly 30, which is not shown in FIG. 18 for the sake of clarity. Assembling the bottom assembly 20 with the lid cap assembly 30, the protrusions 62 of the ratchet bar 60 run parallel to the bottom plate 26.

(61) What can be seen is the leaf spring structure 40 and the ratchet bars 60 are dimensionally matched so that when the prongs 42 and the protrusions 62 are brought together, the prongs 42 come behind the knob portions 66 and rest on the sliding portions 64. For example, there may be as many prongs 42 on the leaf spring structure 40 as there are protrusions 62 on the ratchet bar 60. Alternatively, more or fewer prongs 42 than protrusions 62 may be provided.

(62) In practice, after mounting the fuel cell module 10, i.e., after inserting the fuel cell stack 12 into the enclosure 14, the bottom assembly 20 and the lid cap assembly 30 can be moved against each other to build up a pre-compression stage. FIG. 19 shows a first locking position of the locking system 16, wherein such a pre-compression is applied to the stack. At least some of the prongs 42 have come behind the knob portions 66.

(63) If the slider 18 is pushed towards the bottom plate 26, the prongs 42 slide on the sliding portions 64 of the ratchet bar 60. More compression can be built up against the fuel cell stack 12. Moving the slider 18 allows a whole range of compression pressures to be applied to the fuel cell stack 12.

(64) In some embodiments, the slider 18 may be accessed via though holes in the lid cap assembly which are not depicted in the Figures. The slider 18 may be pushed towards the bottom plate 26 by using a tool. The bottom assembly 20 and the lid cap assembly 30 can then be tightened more tightly together to provide full compression to the fuel cell stack 12. Once in position, the slider 18 may be fixated by fixation means from below. The fixation means may be provided as a cable system which ties the location. Alternatively, fixing screws, bolts or welds may be used.

(65) During use, when the chemical reactions take place, the fuel cell stack 12 is subject to swelling or thermal expansion and requires more volume in the stacking direction. The bottom plate 26 and the compression plate 32 are displaced from each other. The leaf spring structure 40 and the ratchet bars 60 are also displaced from each other. The prongs 42 are bent and build up a restoring force which adds up to the pressure in the fuel cell stack 12. In practice, a dynamic volume change of the fuel cell stack 12 during operation can be cushioned by the elastic energy in the locking system 16.

(66) Specifically, the leaf spring structure 40 may be a constant force spring, allowing the physical environment for the chemical reaction to be constant in the fuel cell stack 12, even if its volume grows.

(67) FIG. 20 shows an alternative embodiment of a locking system 16 with a first rail 52, which is integrally formed with the jacket 22 in the middle of the pocket 24 and a spring assembly 50. In some embodiments, the first rail 52 may be slidably arranged on the jacket 22, in the same manner as described with regards to the slider 18.

(68) To the left and right of the central first rail 52, interconnected cylinder members 54 are shown in FIG. 20, forming a spring assembly 50. The spring members are attached to the lid cap assembly 30, which is not shown in FIG. 20. Displacement of the lid cap assembly 30 in relation to the bottom assembly 20 leads to an increase or decrease of restoring forces, which enable a dynamic pressure adjustment for the fuel cell stack 12.

(69) To this purpose, first rail 52 comprises wedges 53 which are shown in FIG. 21. FIG. 21 shows the first rail 52 having straight sections 55 and wedges 53. Although straight sections 55 are also shown, some embodiments do not require straight sections 55. If the cylinder members 54 are moved over the wedges 53, several locking steps may be facilitated, the locking steps providing pre-compression and full compression to the fuel cell stack 12.

LIST OF REFERENCE SIGNS

(70) 10 fuel cell module 12 fuel cell stack 13 footprint of fuel cell stack 14 enclosure 16 locking system 18 slider 20 bottom assembly 22 jacket 23 center mounting plate 24 pocket 25 notch 26 bottom plate 27 retention means 28 alignment region 30 lid cap assembly 32 compression plate 34 media routing channel 36 jacket section 38 slot section 40 leaf spring structure 42 prong section 43 central portion 44 leaf spring 46 backdrop guidance 50 spring assembly 52 first rail 53 wedge 54 spring member 55 straight section 60 ratchet bar 62 protrusion 63 second rail 64 sliding portion 65 knob portion 66 fixation means 68 external connection means 70 through hole 71 current collector tab 72 end plate 73 oxidant inlet 74 oxidant outlet 76 coolant port 78 fuel inlet 80 fuel outlet 81 ejector valve access window 82 purge valve access window 84 mounting through hole