Cell stack

Abstract

Cell stack (1) comprising several cell units (4) stacked between a first stack end (2) of the cell stack (1) and a second stack end (3) of the cell stack (1) and at least one tension element (5) with which a tensioning force can be transmitted between the first stack end (2) and the second stack end (3) for tensioning the cell units (4), wherein the at least one tension element (5) comprises a first subsection (6) extending from the first stack end (2) and towards the second stack end (3) and a second subsection (7) extending from the second stack end (3) and towards the first stack end (2), wherein the at least one tension element (5) comprises at least one compressionally loaded spring element (13,14) has for generating the clamping force and wherein the first subsection (6) of the at least one tension element (5) and the second subsection (7) of the at least one tension element (5) overlap each other in an overlap area (20) between the two stack ends (2, 3), characterized in that the at least one tension element (5) comprises a shortening element (19) for shortening the tension element (5), wherein the shortening element (19) comprises a first connecting element (17) connected to the first subsection (6) and a second connecting element (18) connected to the second subsection (7), wherein the shortening element (19) is tiltable between a first tilting orientation in which the first connecting element faces the first stack end (2) and the second connecting element (18) faces the second stack end (3), and a second tilting orientation,in which the first connecting element (17) faces the second stack end (3) and the second connecting element (18) faces the first stack end (2), wherein the at least one spring element (13, 14) connects the first subsection (6) with the second subsection (7) and wherein the at least one spring element (13, 14) is subjected to compression to generate the clamping force, provided that the shortening element (19) is in the second tilting orientation.

Description

[0001] The invention relates to a cell stack comprising several cell units stacked between a first stack end and a second stack end. This cell stack includes at least one clamping element for clamping the cell units between the stack ends. The clamping element comprises a first section extending from the first stack end towards the second stack end and a second section extending from the second stack end towards the first stack end. The clamping element further comprises at least one elastic element, tensioned by a preload force, connecting the first section to the second section.

[0002] Cell stacks of this type comprise several cell units, typically flat, stacked on top of each other between two stack ends. These cell units include, for example, cells from electrochemical systems or cells from humidifiers for electrochemical systems. The cell stack or cell units can be part of a humidifier for an electrochemical system or an electrochemical system itself, such as an electrochemical energy storage device, a redox flow battery, an electrochemical compressor, or part of a fuel cell system.

[0003] In the operation of such cell stacks, it is necessary, for example to generate the required sealing and / or contact forces between the cell units, to press the cell units of the cell stack against each other. For this purpose, tension forces are transferred between the stack ends by means of one or more tension elements, so that the cell units are pressed together.

[0004] Due to changes in the internal pressure of the cell units, contraction of the cell units or other components of the cell stack, as well as settling of the cell units or other components of the cell stack after tensioning or commissioning, the overall height of the cell stack, i.e., the distance between the stack ends, can change over time. To compensate for this and to keep the tensioning forces, as well as any contact and sealing forces between the cell units, within permissible limits, spring assemblies or bending beams can be installed between the cell units and at the stack ends. However, this leads to a more complex cell stack structure and increases the required installation space. Furthermore, the assembly and tensioning of such spring assemblies and bending beams generally require additional or complex process steps and are therefore relatively time-consuming.

[0005] DE 10 2010 012 930 A1 describes a battery with individual battery cells that are clamped between two plates using clamping devices to form a stack. The clamping devices are designed as tie rods and include an elastic spring element in the stacking direction. The spring and an element of the clamping device establish the preload. One of the plates is fixed to the battery housing, and the other plate is mounted so that it can move relative to the housing.

[0006] US 2006 / 0093890 A1 relates to fuel cell stack compression systems and fuel cell stacks and fuel cell systems containing them. The compression systems include banded, framed, and / or segmented compression systems. In some embodiments, the compression systems include at least one compression band extending around the end plates and fuel cells, for example, in a closed ring. In some embodiments, the banded compression systems include a force-directing structure, compression inserts, and / or band positioning mechanisms. In some embodiments, the compression systems include a frame in which the end plates and cells of the stack are positioned and into which at least one end plate may be integrated. The frame includes a compression mechanism, which may be an adjustable compression mechanism and / or which includes one or more lifting elements and / or a compression plate.In some embodiments, the compression systems include toothed or striped segments that connect the end plates together and compress the plates with ratchet locking arrangements.

[0007] US 3,860,998 A relates to a strap and buckle assembly for holding and / or binding objects together. The strap is wrapped around the objects, and the buckle is used like a ratchet to tighten the strap and secure it in its tightened position. In one embodiment, increasing the tension on the strap serves to improve the clamping of the buckle parts around the strap to prevent accidental release between the buckle and the strap. A second embodiment also provides a positive locking of the buckle to the strap, regardless of increased tension applied to the strap.

[0008] Further clamping devices for cell stacks can be found in documents US 2002 / 0132150 A1 and DE 971 191 B.

[0009] It is therefore the object of the present invention to create a cell stack of the type described above which can be assembled and clamped as easily and quickly as possible.

[0010] To solve this problem, a first cell stack according to claim 1 is proposed. Specific embodiments and further developments of the cell stack as well as of the proposed manufacturing process are described in the dependent claims.

[0011] The cell stack therefore comprises several cell units stacked between a first stack end and a second stack end, for example of the type mentioned above. Furthermore, the cell stack has at least one tension element with which a tensioning force can be transmitted between the first and second stack ends to clamp the cell units, for example to create the aforementioned sealing and / or contact forces between the cell units.

[0012] The cell stack comprises one or more such pull elements. If, in the following, reference is made only to one of these at least one pull element, the respective description can always be applied to the other pull elements if the cell stack has multiple pull elements, so that several or all pull elements of the cell stack can have the described characteristics without this being explicitly mentioned.

[0013] The tension element, which typically connects the first stack end to the second stack end, comprises a first subsection extending from the first stack end towards the second stack end, and a second subsection extending from the second stack end towards the first stack end. These subsections can be ribbon-shaped or strip-shaped and can be sections of a tension band of the tension element.

[0014] The tensile element of the first cell stack further comprises at least one compression spring element that connects the first subsection to the second subsection and generates the tension force. The compression spring element exerts a force on the first subsection directed towards the second stack end and, likewise, exerts a force on the second subsection directed towards the first stack end. The two forces are equal in magnitude and opposite in direction. For example, a first end of a spring element can be connected to a first connecting element of the first subsection. A second end of the spring element, opposite the first end, can similarly be connected to the second subsection by means of a second connecting element.These connecting elements allow the aforementioned forces of the spring element to be transferred to the first and second sections of the tension element. These connections between the ends of the spring element and the first and second sections can be fixed or movable along the sections. For possible configurations of these connections between the first and second sections and the connecting elements, please refer to the description of the shortening element of the second cell stack described below. This shortening element contains corresponding connections to the first and second sections, which can also be configured to connect a spring element to the sections.

[0015] It should be emphasized that even though the tensile element exerts a clamping force on the cell stack, the spring element itself is pre-tensioned with a compression force. Therefore, an increase in the compression of the cell stack is accompanied by an elongation of the spring element; a decrease in the compression of the cell stack corresponds to a compression of the spring element.

[0016] The tension element further comprises a shortening element, into which at least one first connecting element, connected to the first subsection, and a second connecting element, connected to the second subsection, are integrated. The shortening element is tiltable between a first tilting orientation, in which the first connecting element faces the first stack end and the second connecting element faces the second stack end, and a second tilting orientation, in which the first connecting element faces the second stack end and the second connecting element faces the first stack end. By tilting the shortening element from the first tilting orientation to the second tilting orientation, the tension element can thus be shortened. The dimensions of the shortening element are relative to the overall length of the tension element and to the height or...The circumference of the cell stack is chosen such that, if the shortening element is in the second tilting orientation, the tensioning element transmits the specified clamping force. If the shortening element is in the first tilting orientation, the specified clamping force is not transmitted, and typically no clamping force or only a much lower one is generated.

[0017] A compression-resistant spring element can be integrated into the shortening element. This spring element is subjected to compression in the second tilting orientation, thereby generating the tensioning force. For example, the first end of the spring element can be connected to the first connecting element and, via the first connecting element, to the first section. Similarly, the second end of the spring element, opposite the first end, can be connected to the second connecting element and, via the second connecting element, to the second section. These connecting elements allow the tensioning forces to be transferred to the first and second sections of the tensioning element.

[0018] The connections made to the first and second sections by means of the connecting elements can be fixed or movable along the sections. In the case of a fixed connection, this connection typically exists between the first (or second) connecting element and a first (or second) end piece or end of the first (or second) section. In the case of a movable connection, for example, a sloping, sliding, and / or rolling connection, this connection typically exists between the first (or second) connecting element and a transition area of ​​the tension element adjacent to and merging with the first (or second) section. In this case, the first section and / or the second section rests against and / or borders the respective connecting element, as described in more detail below.For example, the connecting elements can be designed as deflection elements, in particular as rollers, roller brackets, deflection pulleys, sliding brackets, or also as anchors, clamps, screw or rivet connections, snap connections or similar. The connections mentioned can therefore be, for example, positive locking (anchored, looped, riveted, screwed, snapped, etc.) and / or friction locking (clamped, screwed, etc.).

[0019] Provided the shortening element of the tension element of the second cell stack is in the second tilting orientation, the first and second sections of the tension element overlap in an overlap area between the two stack ends. Within this overlap area, the first section extends from the first stack end towards the second stack end. Similarly, within the overlap area, the second section extends from the second stack end towards the first stack end. In this overlap area, the first and second sections essentially pass each other.

[0020] If this overlap of the tension element's sections does not exist, as is the case in the unassembled and / or untensioned state, the tension element can have such a large overall length that it can be easily slid over the stacked cell units, which may have been pre-tensioned using a press, or connected to the two ends of the cell stack without needing to be tensioned itself. Only in a final step is the described overlap of the tension element's sections created, for example, by tilting the spring element accordingly in the case of the first cell stack. Due to the resulting effective shortening of the tension element, the tensioning force is simultaneously generated, and the cell units are pressed against each other.

[0021] Another advantage gained from the overlapping sections of the tension element is that it allows for a spring-like movement of the element in a simple way and without requiring much installation space. This is useful, for example, in the event of a change in the height of the cell stack, such as due to thermal expansion of the cell units or a change in the internal pressure of the cell units. For instance, increasing the overlap area effectively shortens the tension element, or decreasing the overlap area effectively lengthens it. This spring-like movement also allows the clamping force to be easily maintained within a nearly constant range, ensuring that the cell units are always pressed together with sufficient force, but not excessive force, and preventing damage to other components, such as the tension element itself.If the overlap area decreases, the spring element is compressed. Conversely, the spring element expands when the overlap area increases.

[0022] As already emphasized above, the tension element of the cell stack can also have a shortening element for shortening this tension element. The spring element of the tension element is subjected to compression and generates the aforementioned tension force, provided the shortening element is in the second tilting orientation. The at least one spring element can be part of the shortening element, i.e., integrated into it. Accordingly, the first connecting element of the shortening element is preferably connected to the first end of the at least one spring element, and the second connecting element of the shortening element is connected to the second end of the at least one spring element.

[0023] In a particularly compact embodiment, the at least one spring element is arranged in the overlap area of ​​the tension element. For example, the at least one spring element can be arranged between the first section of the tension element and the second section of the tension element.

[0024] In one embodiment, the tension element comprises an intermediate section extending between two connecting elements within the overlap region of the tension element, connecting the first subsection to the second subsection. Here, the first subsection transitions into the aforementioned intermediate section of the tension element in a first transition region, and the intermediate section finally transitions into the second subsection in a second transition region. Thus, the intermediate section overlaps with both the first and second subsections in the overlap region. Typically, the first subsection, the intermediate section, and the second subsection, together with the transition regions, form a Z-shaped or S-shaped arrangement, with the necessary deflection occurring in the transition regions.In the spring-like motion described above, the intermediate section between the connecting elements shortens when the overlap area decreases and lengthens when the overlap area increases. For example, the first and second subsections, the intermediate section, and the transition areas can together form a continuous, coherent structure connecting the two ends of the stack, such as a tension band. In this case, the first and second connecting elements are typically movable along this structure, for example, sliding or unrolling. When the cell stack is under tension, the first and second connecting elements typically cause the aforementioned deflection of the structure within the transition areas by the connecting elements, which in this case act as deflection elements. An increase orReducing the overlap area typically corresponds to a movement of the first and second connecting elements along the structure, a shift in the locations of the aforementioned deflections or transition areas along the structure, and possibly a simultaneous compression or extension or decompression of the spring element. The described deflection requires, in particular, sufficient flexibility (bending ability) of the aforementioned sections of the tension element.

[0025] In the aforementioned spring movement caused by the enlargement or reduction of the overlap area, there is preferably practically no change in length of the aforementioned sections of the tension element, i.e., the first subsection, the second subsection, and, if applicable, the aforementioned intermediate section and the first and second transition areas, but only a change in length (compression or decompression or elongation) of the spring element.

[0026] If steel is used as the material for the tension element, its tensile strength is between 900 and 1500 N / mm². In an average stack, for example, 20 to 30 kN is distributed across 8 springs. The spring force of each individual spring is therefore between approximately 2.5 kN and 3.75 kN. For a different number of springs, the spring force must be adjusted accordingly.

[0027] Preferably, the first and / or second section of the tension element is configured entirely or at least partially as a tension band. For example, the tension band can be a metal band, a steel band, a stainless steel band, or a plastic band, in particular a fiber-reinforced, especially a glass fiber-reinforced or carbon fiber-reinforced plastic band. It is also possible that the first and second sections differ in their configuration, for example, in their material or structure. Furthermore, it is possible that the first and / or second section has differently configured subsections along its length between the two stack ends, which differ, for example, in their material or structure.

[0028] The aforementioned at least one spring element of the tension element can be one or more compression springs, such as one or more coil springs, one or more leaf springs, or one or more flexible legs or bodies.

[0029] In one embodiment, the shortening element has at least two spring elements which, together with the first and second connecting elements of the shortening element, form an annular arrangement and thus define or enclose a central opening in the shortening element. The intermediate section of the tension element described above can then pass through this central opening in the shortening element. In the first tilting orientation, the shortening element is typically freely movable along the tension element, which is typically not or only slightly tensioned. In the second tilting orientation, the tension element undergoes the described deflection, leading to the overlap of the first section with the second section, which in turn effectively shortens the tension element and tensions the cell stack.

[0030] In a specific embodiment, the spring elements are designed as compression springs, for example, as coil springs. The compression springs or coil springs can each be guided by a guide pin, in particular centrally. The at least one guide pin is movably connected to the first and / or the second connecting element to allow spring movement between the first and the second connecting element.

[0031] The tension element typically includes a fixing element for securing and / or stabilizing the mutual overlap of the first and second sections of the tension element. For example, the fixing element can be designed to fix, hold, and / or stabilize the shortening element in the second tilting orientation. The fixing element can be, for example, a clamp, sleeve, locking element, metal plate, bending tab, screw, pin, or hook, or at least incorporate one or more of these elements. In the case of a sleeve, for example, it can stabilize the first and second sections in the overlap area and, if necessary, also enclose and thus stabilize the shortening element.

[0032] The fixing element can also be formed from, or have a hook-shaped portion of the pull cord from the first or second section. This portion can, for example, function as a hook, a clip, or a locking lug.

[0033] To adjust the tension or spring force of the spring element, the spring element and / or the shortening element can have a suitably designed retaining and / or adjusting element, for example in the form of a screw or a clamp. For example, after creating the aforementioned overlap, the spring element can be brought into an extreme initial preload by means of the retaining and / or adjusting element and then brought into a desired spring range for the desired tension, for example by turning the aforementioned screw or by removing or loosening the aforementioned clamp.

[0034] In one embodiment, the fixing element is arranged on an end plate of the cell stack. Typically, the overlap area of ​​the first and second subsections of the tension element then borders directly on this end plate.

[0035] The at least one tension element can encircle a first end plate of the cell stack located at the first stack end or a second end plate of the cell stack located at the second stack end. It is also possible for the tension element to encircle both of these end plates. The at least one tension element can comprise an annularly closed tension band, which in particular includes the first subsection and the second subsection. Furthermore, the annularly closed tension band can include the intermediate section and the transition area described above. The annularly closed tension element or tension band can have two ends connected to each other by welding, soldering, gluing, riveting, hooking, clinching, or crimping.

[0036] Instead of the described circumferential routing of the end plates, it is also possible that the first section of the tension element is attached to the first end plate and that the second section of the tension element is attached to the second end plate, for example by hooking it in, such as by means of a hooking lug on the first and / or second end plate.

[0037] As already described at the beginning, the cell stack or cell units can, for example, be part of a humidifier for an electrochemical system or an electrochemical system, such as an electrochemical energy storage device, a redox flow battery, an electrochemical compressor, or part of a fuel cell system.

[0038] In addition to the description of the structural and functional characteristics of the proposed cell stacks and the resulting advantages in assembling and clamping such cell stacks, a method for assembling and clamping a cell stack of the type proposed here will be explicitly described below. In this method, after pre-tensioning the cell stack, for example using a press, the (at least one) tension element, which may be designed as a closed ring, is arranged such that a first section of the tension element extends from the first end of the stack towards the second end, and a second section extends from the second end of the stack towards the first end.In a subsequent step, the described overlap of these two sections is created in an overlap area between the two stack ends, thereby shortening the tension element and simultaneously creating the tension (or increased pre-tension) of the cell stack. This can be achieved, for example, by having the tension element encompass the described shortening element and tilting it from the first tilting orientation to the second tilting orientation. This tilting can advantageously be automated using a suitably configured tilting device of a manufacturing machine.

[0039] The overlap can then be fixed and / or held in place using the described fixing element. Furthermore, the press, if used, can be opened and the cell stack removed. Finally, the tension generated by the spring element can be readjusted or adjusted, for example, from an increased pre-tension to a desired target value, as described above, using the holding and / or adjusting element.

[0040] The invention is described below with reference to in Fig. Examples 1 to 15 are described schematically. Fig. 1 a front view of a cell stack of the type proposed here, in which a tiltable shortening element is located in a second of two tilting orientations, Fig. 2 a side view of the in Fig. 1 cell stack shown, Fig. 3 a front view of the in Fig. 1 cell stack shown, in which the shortening element is in a first of two tilting orientations, Fig. 4 a front view of another cell stack of the type proposed here, in which an alternative tiltable shortening element is located in a second of two tilting orientations, Fig. 5 a front view of the in Fig. 4 cell stack shown, in which the shortening element is in a first of two tilting orientations, Fig. 6-8 partial front views of further cell stacks of the type proposed here, in each of which a tiltable shortening element is located in a second of two tilting orientations, Fig. 9 a partial view of a special embodiment of a tensile element of a cell stack of the type proposed here, in which a shortening element is located in a first of two tilting orientations, Fig. 10 a partial view of another special embodiment of a tensile element of a cell stack of the type proposed here, in which a shortening element is located in a second of two tilting orientations, Fig. 11 to 14 different special embodiments of shortening elements of tensile elements of cell stacks of the type proposed here; and Fig. 15 in four schematic representations the difference between a spring under tension and a spring under compression in the first and second tilting orientations.

[0041] Recurring reference symbols denote identical or functionally equivalent features.

[0042] A in Fig. 1 and Fig. The cell stack 1 of the proposed type, shown schematically in a front view and a side view, comprises several cell units 4, such as fuel cells, stacked between a first stack end 2 of the cell stack 1 and a second stack end 3 of the cell stack 1. The cell stack 1 is thus part of a fuel cell system. However, the cell units 4 could just as easily be other electrochemical cells or cells from humidifiers for electrochemical systems. The cell stack or the cell units could therefore also be part of a humidifier for an electrochemical system or part of another electrochemical system, such as an electrochemical energy storage device, a redox flow battery, an electrochemical compressor, or part of a fuel cell system.

[0043] The cell stack 1 also has two pull elements 5 of the same design type (in Fig. (Only one is visible) with which a tensioning force is transmitted between the first stack end 2 and the second stack end 3 to clamp the cell units 4, in order to create the sealing and / or contact forces between the cell units 4 required for the operation of the cell stack 1. It would also be possible for the cell stack 1 to have only one or more than two tensioning elements.

[0044] Both pull elements 5 of the cell stack are identical in construction. The following description therefore applies equally to both pull elements 5. Fig. For clarity, the left of the two tension elements, shown without a reference symbol, is represented by element 2. Tension element 5 connects the two stack ends 2 and 3 and comprises a first subsection 6 extending from the first stack end 2 towards the second stack end 3, and a second subsection 7 extending from the second stack end 3 towards the first stack end 2. These subsections are linear and are designed as subsections of a tension band 8 of tension element 5.

[0045] The tensile band 8 is a metal band, for example a steel band, preferably a stainless steel band. However, it could also be a plastic band, in particular a fiber-reinforced, especially a glass fiber-reinforced or carbon fiber-reinforced plastic band. It is important that the tensile band is as resistant to elongation as possible. It surrounds a first end plate 9 of the cell stack arranged at the first stack end 2 and a second end plate 10 of the cell stack 1 arranged at the second stack end 3. The tensile band 8 is furthermore designed in a ring shape, with two ends 11, 12 of the tensile band 8 being joined together by welding. The ends 11, 12 could also be joined by soldering, gluing, riveting, hooking, clinching, or crimping.

[0046] The tensile element 5 of the cell stack has two compression spring elements 13, 14, but it could also have only one or more than two spring elements. The spring elements 13, 14 connect the first subsection 6 to the second subsection 7 and serve to generate the tension force. Each of these compression spring elements 13, 14 exerts a force on the first subsection 6 directed towards the second stack end 3 and likewise exerts a force on the second subsection directed towards the first stack end 2. The two forces are equal in magnitude and opposite in direction. For example, a first end 15 of a spring element 13, 14 can be connected to the first subsection 6 by means of a first connecting element 17.A second end 16 of the spring element opposite the first end 15 of a spring element 13, 14 can accordingly be connected to the second subsection 7 by means of a second connecting element 18, as shown in . Fig. Figure 1 clearly shows that the tension forces generated by the spring elements 13, 14 can be transmitted by means of these connecting elements. In this embodiment, these connections between the ends 15, 16 of the spring elements 13, 14 and the first and second sections 6, 7 are designed to be movable along the sections 7, 6 of the tension element 5 and the connecting elements 17, 18, as described in more detail below.

[0047] The spring elements 13, 14 and the connecting elements 17, 18 of the tension element 5 are parts of a shortening element 19 of the tension element 5. As can be seen by comparing the Fig. 1 with Fig. As can be seen in section 3, the shortening element 19 is located between a in Fig. 3 first tilting orientation shown, in which the first connecting element 17 and the first end 15 of the spring element 13, 14 are facing the first stack end 2 and the second connecting element 18 and the second end 16 of the spring element 13, 14 are facing the second stack end 3, and one in Fig. 1 and Fig. The second tilting orientation shown in Figure 2, in which the first connecting element 17 and the first end 15 of the spring element 13, 14 face the second stack end 3, and the second connecting element 18 and the second end 16 of the spring element 13, 14 face the first stack end 2, is tiltable. By tilting the shortening element 19 from the first tilting orientation to the second tilting orientation, the tension element 5 can thus be shortened. The dimensions of the shortening element 19 are chosen such that, as long as the shortening element 19 is in the second tilting orientation, the tension element 5 transmits the ideal clamping force. If the shortening element is in the first tilting orientation, the aforementioned clamping force is not transmitted, and typically no clamping force or only a much lower clamping force is generated.The spring elements 13, 14 are subjected to pressure in the second tilting orientation and generate the clamping force here, but not in the first tilting orientation.

[0048] As in Fig. As can be seen in Figure 1, the first section 6 and the second section 7 of the tension element 5 overlap each other in an overlap area 20 between the two stack ends 2, 3, provided that the shortening element of the tension element of the second cell stack is in the second tilting orientation. An increase in the height of the cell stack, for example due to thermal expansion of the cell units or an increase in the internal pressure of the cell units, leads to a reduction in the overlap area 20 and an effective lengthening of the sections 6, 7 of the tension element 5. Conversely, a reduction in the height of the cell stack leads to an increase in the overlap area 20 and an effective shortening of the tension element 5. The reduction or increase in the overlap area 20 is accompanied by a compression or relaxation of the spring. This keeps the tension force within a permissible range.As the overlap area decreases, the spring elements 13, 14 arranged in the overlap area 20 between the first and second sub-areas 6, 7 are compressed. Conversely, the spring elements 13, 14 expand when the overlap area increases. As a consequence, the tensile force of the tension element 5 remains essentially constant.

[0049] Provided that this overlap of the subsections 6, 7 of the tension element 5 does not exist because the shortening element is located approximately in the first tilting orientation, as in Fig. As shown in Figure 3, the tension element 5 has such a large overall length that it practically does not cause any tension in the cell stack 1.

[0050] In the Fig. In the example shown in Figures 1 to 3, the tension element 5 comprises an intermediate section 21 of the tension band 8, which runs within the overlap area 20 of the tension element 5 and connects the first subsection 6 with the second subsection 7. Here, the first subsection 6 transitions into the aforementioned intermediate section 21 in a first transition area of ​​the tension band 8, and the intermediate section 21 finally transitions into the second subsection 7 in a second transition area 23 of the tension band. Thus, the intermediate section 21 overlaps with both the first subsection 6 and the second subsection 7 in the overlap area 20. As shown in Figure 1, the tension element 5 comprises an intermediate section 21 of the tension band 8, which connects the first subsection 6 with the second subsection 7. Fig. As can be seen in Figure 1, the first subsection 6, the intermediate section 21 and the second subsection 7 together with the transition areas 22, 23 form a Z-shaped or S-shaped arrangement.

[0051] In the spring movement described above, the intermediate section 21 shortens when the overlap area 20 decreases, and lengthens when the overlap area 20 increases. For this purpose, the first and second connecting elements 17, 18 are movably connected to the tension band 8, for example, by being slidable or rollable. In the tensioned state of the cell stack 1, as in Fig. As shown in Figure 1, the first and second connecting elements 17, 18 cause a deflection of the tension band 8 within the transition areas 22, 23. An increase or decrease in the overlap area 20 therefore corresponds to a movement of the first and second connecting elements 17, 18 along the tension band 8, a displacement of the locations of the aforementioned deflections or the transition areas 22, 23 along the tension band 8, and a simultaneous compression or stretching of the spring elements 13, 14. For this purpose, the tension band is designed to be as bendable and flexible as possible, yet still resistant to stretching. In this example, the connecting elements 17, 18 are thus designed as deflection pulleys that bear against the transition areas 22, 23 and define the first and second sections 6, 7, but could also be designed, for example, as rollers, roller brackets, or sliding brackets.

[0052] The in Fig. 4 and Fig. The further embodiment of a cell stack 1 of the type proposed here, shown in Figure 5, differs from the one in Figure 5. Fig. The difference in the example shown is determined solely by the design of the tension elements 5, in particular by the design of the tension band 8 and the connecting elements 17, 18 of the shortening element 19. In this example, the connecting elements 17, 18 are fixed, i.e., non-slidably, connected to the ends 24, 25 of the first and second subsections 6, 7, respectively. The tension band is therefore not designed as a closed ring. The first and second subsections 6, 7 are thus not connected to each other by an intermediate section 21 of the tension band 8, but only via the tiltable shortening element 19. In this example, the connecting elements 17, 18 are anchor elements that are firmly anchored in end loops of the ends 24, 25 of the first and second subsections 6, 7. Alternatively, the connecting elements 17, 18 could, for example, be clamps, screw or rivet connections, or snap-fit ​​connections.The drawbar 8 extends as part of the connecting element 17 to the connecting element 18.

[0053] In Fig. In position 4, the shortening element 19 is in the second tilting position, thus the tension is established. Fig. 5 the shortening element 19 is in the first tilting orientation, so that there is no tension.

[0054] The in Fig. The specific embodiments of cell stacks of the type proposed here, shown in Figures 6 to 8, differ from that in Figure 6. Fig. 4 and Fig. The example shown in section 5 differs essentially only in the design of the pull elements 5, which are shown in the examples of the Fig. 6 to 8 connect and clamp the end plates 9, 10 of the cell stack together, but do not encircle them. For example, the tension bands 8 of the tension elements 5 can be connected to the end plates 9, 10 at their ends by means of locking lugs (not shown).

[0055] Furthermore, in the Fig. 6 to 8 fixing elements 26 of the tension elements 5 shown, which are in the Fig. Figures 1 to 5 are not shown for the sake of clarity. The fixing elements 26 serve to fix and stabilize the mutual overlap of the first subsection 6 and the second subsection 7 of the respective tension element 5 and are designed to hold the respective shortening element 19 in the second tilting orientation, as shown in the Fig. Figures 6 to 8 are shown, to fix and hold.

[0056] The fixing element can, for example, have a hook or locking lug(s) attached to the first end plate 9. In this embodiment, a sufficient length of the hook(s) is essential to accommodate the maximum length increase of the cell stack 1. The fixing element can, for example, have a hook or locking lug as shown in Fig. 7 shown, at the first end plate 9 or, as in Fig. Figure 8 shows a screw attached to the first and / or second subsection 6, 7. Such a screw can also serve as a retaining and / or adjusting element 27. This allows, for example, the connection point of the spring element 13, 14 and / or the tension of the spring element 13, 14 to be adjusted or readjusted.

[0057] In Fig. Figures 9 to 14 are different embodiments of shortening elements 19 for cell stacks according to the invention, such as for example for the in Fig. Examples 1 to 8 are shown. This is how it can be done in Fig. Shortening element 19 shown in 1 to 3, for example, corresponds to one of the in Fig. Shortening elements 19 shown in 9 and 11 to 14 can be executed. Furthermore, each of the elements shown in Fig. 4 to 8 shortening elements shown 19, for example, each corresponding to one of those in Fig. The shortening elements shown in 9 and 11 to 14 must be executed in 19.

[0058] The in Fig. The shortening elements shown in Figures 9 and 11 to 14 correspond to each other in that each of them has two spring elements 13, 14 which, together with the first and second connecting elements 17, 18 of the shortening element 19, form an annular arrangement and define or enclose a central passage opening 28 of the shortening element 19. As in the embodiment of the Fig. 1 to 3 the intermediate section 21 of the tension element 5 can then pass through this central passage opening 28 of the shortening element 19.

[0059] In the Fig. In the example shown in Figure 9, the shortening element 19 comprises several fixing elements 26, namely bending tabs arranged on the spring elements 13, 14 as well as a hook-shaped portion of the tension band 8 in the first section 6, which has the function of a hook, a clip or a locking lug for fixing the shortening element 19 in the second tilting orientation.

[0060] In the Fig. The shortening elements 19 shown in figures 9 to 14 are spring elements 13, 14 designed as compression springs, in Fig. 9, Fig. 13 and Fig. 14 as flexible legs, in Fig. 10 as a leaf spring and in Fig. 11 and Fig. 12 as coil springs. The coil springs are also each guided centrally by a guide pin 29, the guide pins 29 being movably connected to the first and second connecting elements 17, 18. In Fig. 12 The shortening element 19 additionally has a holding or adjusting element 27 in the form of a threaded sleeve, with which the length of the respective section of the guide pins 29, which regulates the compression of the spiral springs, can be adjusted.

[0061] The connecting elements 17, 18 are in Fig. 9 as pulleys and in Fig. 11 to 13 designed as sliding bars. As in Fig. As shown in Figure 10, the first subsection 6 and the second subsection 7 can have differently designed subsections along their paths between the two stack ends 2, 3. For example, the end 24 of the first subsection 6 is designed as a fiber-reinforced plastic strip, and the end 25 of the second subsection is designed as a metal bracket that laterally surrounds the spring element 13, provided that the shortening element 19 is in the second tilting position.

[0062] The embodiments shown in the figures can be assembled and pressed using the method proposed here. To pre-tension the cell stack using a press, the tension elements 5 are first arranged such that the first section 6 of the tension element 5 extends from the first stack end 2 and towards the second stack end 3, and that the second section 7 of the tension element 5 extends from the second stack end 3 and towards the first stack end 2. In the case of a ring-shaped closed tension band 8, as shown in Fig. 1 to 3 shown, or of a ring-shaped closed tension element 5, as in Fig. 4 and Fig. As shown in Figure 5, the pulling element 5 can, for example, be looped over the end plates 9 and 10. In the Fig. In the examples shown in 6 to 8, the two subsections 6, 7 can be attached to the end plates 9 and 10, for example by hooking or screwing them on.

[0063] In a subsequent step, the described overlap of the two sections 6 and 7 in the overlap area 20 between the two stack ends is created by tilting the shortening element 19 from the first tilting orientation to the second tilting orientation, for example, using a suitably configured tilting device of a production machine. The overlap is then fixed by means of the fixing element 26, the press is opened, and the cell stack 1 is removed from the press. If necessary, the tension generated by the spring elements 13, 14 can then be readjusted or recalibrated using the holding and / or adjusting element 27, for example, from the increased pre-tension to a desired target tension value.

[0064] Fig.Figure 15 shows, in four schematic representations, the difference between a spring (A, B) under tension, i.e., a spring arrangement of a conventional cell stack, and a spring (C, D) under compression in the second tilting orientation. Both springs are shown in a situation where there is a high (A, C) and a low (B, D) stress in the stack according to the invention. The spring under tension (A, B) shortens to the same extent between the situation with higher stress (A) and the situation with lower stress (B) as the spring under compression (C, D) lengthens between the situation with higher stress (C) and the situation with lower stress (D). The figure demonstrates that with the spring arrangement according to the invention, with the spring compressed under compression in the second tilting orientation, the same lengthening or compression of the spring as such results in a more efficient compression or compression.Extending the compression system of the cell stack enables a compression system with a spring under tensile stress, in accordance with the state of the art. Reference symbol list 1 cell stack 2 first stack end 3 second stack end 4 cell units 5 tension element 6 first subsection 7 second subsection 8 drawstring 9 first end plate 10 second end plate 11 End of the pull cord 12 End of the pull cord 13 Spring element 14 spring element 15 first end of the spring element 16 second end of the spring element 17 first connecting element 18 second connecting element 19 Shortening element 20 Overlap area 21 Intermediate section 22 first transition zone 23 second transition area 24 End of the first section 25 End of the second subsection 26 fixing element 27 Holding and / or adjusting element 28 Passage opening 29 Guide pen

Claims

[1] Cell stack (1) comprising several cell units (4) stacked between a first stack end (2) of the cell stack (1) and a second stack end (3) of the cell stack (1) and at least one tension element (5) with which a tensioning force can be transmitted between the first stack end (2) and the second stack end (3) for tensioning the cell units (4), wherein the at least one tension element (5) comprises a first subsection (6) extending from the first stack end (2) and towards the second stack end (3) and a second subsection (7) extending from the second stack end (3) and towards the first stack end (2), wherein the at least one tension element (5) comprises at least one compressionally loaded spring element (13,14) has for generating the tension force and wherein the first subsection (6) of the at least one tension element (5) and the second subsection (7) of the at least one tension element (5) overlap each other in an overlap area (20) between the two stack ends (2, 3), , characterized by, that the at least one tension element (5) comprises a shortening element (19) for shortening the tension element (5), wherein the shortening element (19) comprises a first connecting element (17) connected to the first subsection (6) and a second connecting element (18) connected to the second subsection (7), wherein the shortening element (19) is tiltable between a first tilting orientation in which the first connecting element faces the first stack end (2) and the second connecting element (18) faces the second stack end (3), and a second tilting orientation in which the first connecting element (17) faces the second stack end (3) and the second connecting element (18) faces the first stack end (2), wherein the at least one spring element (13, 14) connects the first subsection (6) to the second subsection (7) and wherein the at least one spring element (13, 14) is subjected to compression to generate the clamping force,provided that the shortening element (19) is in the second tilting orientation. [2] Cell stack (1) according to claim 1, characterized by , that the at least one spring element (13, 14) is arranged in the overlap area (20) of the at least one tension element (5). [3] Cell stack (1) according to claim 2, characterized by , that the at least one spring element (13, 14) is arranged between the first subsection (6) of the tension element (5) and the second subsection (7) of the tension element (5). [4] Stack of cells (1) according to any of the preceding claims, characterized by , that the at least one tension element (5) includes an intermediate section running in the overlap area (20) of the tension element (5) which connects the first subsection (6) with the second subsection (7). [5] Cell stack (1) according to claim 4, characterized by, that the first subsection (6), the intermediate section (21) and the second subsection (7) together form a Z-shaped or S-shaped arrangement. [6] Stack of cells (1) according to any of the preceding claims, characterized by , that the first subsection (6) and / or the second subsection (7) of the at least one tension element (5) is designed completely or partially as a tension band (8). [7] Cell stack (1) according to claim 6, characterized by , that the drawbar (6) is a metal band, a steel band, a stainless steel band or a plastic band, in particular a fiber-reinforced, especially glass fiber-reinforced or carbon fiber-reinforced plastic band. [8] Stack of cells (1) according to any of the preceding claims, characterized by , that the at least one spring element (13, 14) comprises at least one compression spring, in particular at least one coil spring, at least one leaf spring or at least one flexible leg. [9] Stack of cells (1) according to any of the preceding claims, characterized by , that the at least one spring element (13, 14) of the at least one tension element (5) is a part of the shortening element (19) of the at least one tension element (5), wherein the first connecting element (17) of the shortening element (19) is connected to a first end (15) of the at least one spring element (13, 14) and the second connecting element (18) of the shortening element (19) is connected to a second end (16) of the at least one spring element (13, 14). [10] Stack of cells (1) according to any of the preceding claims, characterized by, that the first connecting element (17) of the shortening element (19) is fixedly or movably connected to an end (24) of the first subsection of the at least one tension element (5) and that the second connecting element of the shortening element (19) is fixedly or movably connected to an end (25) of the second subsection of the at least one tension element (5). [11] Stack of cells (1) according to any of the preceding claims, characterized by , that the shortening element (19) has at least two spring elements (13, 14) which together with the first and second connecting element (17, 18) of the shortening element (19) form a ring-shaped arrangement. [12] Cell stack (1) according to claim 11, characterized by , that the intermediate area of ​​the tension element (5) passes through a central passage opening (28) of the shortening element (19). [13] Stack of cells (1) according to any of the preceding claims, characterized by, that the spring elements (13, 14) are designed as compression springs, wherein the compression springs are each guided by a guide pin (29), wherein the guide pins (29) are movably connected to the first and / or the second connecting element (17, 18) for a spring movement between the first and the second connecting element (17, 18). [14] Stack of cells (1) according to any of the preceding claims, characterized by , that the first connecting element (17) and / or the second connecting element (18) of the shortening element (19) are designed as a deflection element, wherein the first subsection (6) and / or the second subsection (7) of the at least one tension element (5) abuts or borders the respective deflection element. [15] Stack of cells (1) according to any of the preceding claims, characterized by , that the at least one tension element (5) has a fixing element (26) for fixing the shortening element (19) in the second tilting orientation. [16] Cell stack (1) according to claim 15, characterized by , that the fixing element (26) comprises a clamp, a sleeve, a locking element, a metal sheet, a bending tab, a screw, a pin or a hook. [17] Cell stack (1) according to one of claims 15 or 16, provided that it is related back to claim 6, characterized by , that the fixing element (26) has a hook-shaped portion of the tension band (8) of the first or second section (6, 7). [18] Cell stack (1) according to any one of claims 15 to 17, characterized by , that the fixing element (26) is arranged on a first or second end plate (9, 10) of the cell stack (1) arranged at the first stack end (2) or second stack end (3). [19] Cell stack (1) according to any one of the preceding claims, characterized by, that the at least one pulling element (5) revolves around a first end plate (9) of the cell stack (1) arranged at the first stack end (2) or a second end plate (10) of the cell stack (1) arranged at the second stack end. [20] Cell stack (1) according to any of the preceding claims except claim 19, characterized by , that the at least one pulling element (5) revolves around the first end plate (9) of the cell stack (1) arranged at the first stack end and the second end plate (10) of the cell stack (1) arranged at the second stack end. [21] Cell stack (1) according to claim 20, characterized by , that the at least one tension element (5) is ring-shaped or comprises a ring-shaped closed tension band (8) which includes the first subsection (6) and the second subsection (7). [22] Cell stack (1) according to claim 21, characterized by, that the at least one ring-shaped closed tension element (5) has two ends connected to each other by welding, soldering, gluing, riveting, hooking, clinching or crimping. [23] Cell stack (1) according to any of the preceding claims, characterized by that the cell units are part of an electrochemical system or a humidifier, an electrochemical compressor, or a fuel cell system.

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