Fuel cell with end plate with main and auxiliary devices, method for accessing fuel cell shaft - Patents.com

Abstract

The present invention relates to a fuel cell (1) comprising a stack (2) with a plurality of cells and a plurality of fluid flow shafts, two end plates (3) and a plurality of traction members, wherein at least one end plate (3) comprises a main device (5) having at least one access opening (51) aligned with the flow shaft and at least one main traction member (T1) configured to apply a main compression to the main body (50) to urge the main body against the stack (2) in the flow shaft, and an auxiliary device (6) configured to urge the auxiliary body against the stack (2), wherein the auxiliary compression is applied at a distance away from the flow shaft of the stack (2), and the main device (5) is removably attached to the auxiliary device (6).

Description

[Technical field]

[0001] The invention particularly relates to the field of servicing fuel cells that are installed on board aircraft to provide propulsive and non-propulsive energy. [Background technology]

[0002] Fuel cells are used to generate electrical energy from electrochemical reactions between different fluids. Typically, fuel cells are supplied with hydrogen and oxygen, which react in the fuel cell to produce electrical energy. A fuel cell comprises a stack with a number of cells aligned along a stack axis. The stack of cells enables the electrochemical reaction from the fluids.

[0003] Each cell consists of an ion-conducting electrolyte surrounded by two electrodes, which are in turn surrounded by interconnecting plates. As an example, in the case of a proton exchange membrane type fuel cell, known by the abbreviation PEMFC for "Proton Exchange Membrane Fuel Cell", the electrolyte takes the form of a proton-conducting polymer membrane and the electrodes take the form of a porous medium carrying a catalyst such as platinum. The assembly of electrolyte and electrodes is called a membrane electrode assembly, known by the abbreviation MEA. Each MEA is brought into contact on its two opposing sides with reactant gases (e.g. hydrogen and oxygen, which may be present in the air) through interconnecting plates to form a cell.

[0004] In a known manner, an assembly of two interconnected plates, belonging to two adjacent cells, is called a bipolar plate. The bipolar plate is therefore inserted between the cathode of an MEA and the anode of the adjacent MEA. The bipolar plate supplies the fuel (hydrogen) on the one hand to the first MEA on the anode side and the oxidant (oxygen) on the other hand to the second MEA on the cathode side. Generally, each bipolar plate is equipped with an internal cooling circuit in which a heat transfer fluid circulates to provide heat or to extract heat created by exothermic reactions.

[0005] The current generated by the cells is collected by so-called collector conductor plates at both ends of the stack. The power delivered by a fuel cell depends on the number of cells (delivered voltage capacity), the active surface area of ​​the cells (delivered current capacity) and the flow rate of the reactant fluids (the importance of the electrochemical reactions that create the electric current).

[0006] The entire stack of cells is kept compressed between two so-called end plates, connected by tie rods that hold the assembly and ensure the sealing of the stack. This sealing is provided by seals inserted between the bipolar plates and the MEAs of the cells. The end plates are conventionally solid, since they must apply a uniform pressure on the surfaces of the cells and be dimensionally stable under the influence of the internal pressure and temperature fluctuations of the stack.

[0007] The reaction and heat transfer fluids are introduced and discharged at end plates, which distribute them in flow shafts that pass through the stack. These flow shafts come from stacks of openings formed in the cells. As an example, three shafts introduce fluids (two reaction fluids and one heat transfer fluid, if desired) from one side of the stack and move them into the cells, while the other three shafts discharge the fluids from the other side of the stack.

[0008] Referring to FIG. 1, a fuel cell 101 is shown having a stack 102 with a number of cells aligned along a stack axis X. Tie rods 104 connect outer portions of end plates 103 around the periphery to apply a constant compressive force to the stack 102. The end plates 103 are provided with flow lines 130 that lead to a flow shaft of the stack 102.

[0009] During the electrochemical reactions in the fuel cell 101, the reaction fluids become charged with traces of acid that are part of the composition of the MEA. These traces of phosphoric acid are present in the flow shafts corresponding to the outlets of the two fuel fluid circuits, especially in the form of water vapor in the case of high-temperature fuel cells. This acid can crystallize, especially during the start-up / stop steps of the fuel cell, when the temperature is below the normal operating temperature, which can block the flow paths. Such a blockage can cause damage that can lead to hot spots with the risk of perforation of the MEA. In addition to the efficiency loss of the fuel cell, the possibility of fire and leakage risks increases.

[0010] To avoid failure of the fuel cell 101, the flow shaft of the stack 102 must be inspected and cleaned. In practice, the end plate 103 must be removed to access the shaft of the stack 102, to clean the stack and to replace it. Removal of the end plate 103 leads to a pressure loss that irreparably destroys the stack 102 of cells, resulting in total loss of sealing, contamination of the membranes with the heat transfer fluid and misalignment of the cells of the stack 102. In other words, cleaning the stack can lead to serious disadvantages that prevent the recommissioning of the fuel cell 101.

[0011] A straightforward solution would be to inspect the shaft by means of flow lines 130 formed in the end plate 103, but these circulation lines 130 generally have a smaller diameter than the diameter of the shaft, which prevents optimal inspection / cleaning.

[0012] Furthermore, the flow lines 130 formed in the end plates 103 (FIG. 1) may be curved, making it impossible to pass an inspection or cleaning tool, such as an endoscope or a pipette with resin. Summary of the Invention [Problem to be solved by the invention]

[0013] It is an object of the present invention to provide for easy and rapid inspection and cleaning of the flow shaft of a stack without degrading the structure of the stack. [Means for solving the problem]

[0014] The present invention relates to a fuel cell comprising a stack with a number of cells aligned along a stack axis X and a number of fluid flow shafts within the stack, two end plates arranged at the ends of the stack along the stack axis X, and a number of traction members connecting the end plates to each other for compressing the stack.

[0015] The fuel cell has at least one end plate that: a main body with at least one access opening aligned with the flow shaft, and a main device comprising at least one main traction member configured to apply a main compression to the main body to urge the main body against the stack in the flow shaft of the stack; an auxiliary device comprising an auxiliary body and at least one auxiliary traction member configured to apply an auxiliary compression to the auxiliary body to urge the auxiliary body against the stack, the auxiliary compression being applied a distance away from a flow shaft of the stack, and the main device being removably attached to the auxiliary device; It is distinctive in that it has

[0016] According to the invention, the end plates are configured to apply two separate and independent compressions. The main device can be removed in a detachable manner to allow access to the flow shaft. Advantageously, the auxiliary device allows for providing sufficient compression while avoiding destruction of the stack. Advantageously, loss of sealing, alignment or contamination of the stack is avoided. As the auxiliary compression is performed at a distance from the flow shaft, the auxiliary device does not impede access to the flow shaft and allows for convenient cleaning of the flow shaft.

[0017] Preferably, each end plate comprises a primary device and an auxiliary device. The end plates advantageously have identical construction to ensure homogenous compression. Primary traction members are mounted between opposing primary devices. Auxiliary traction members are mounted between opposing auxiliary devices.

[0018] Preferably, the stack comprises a central portion and a peripheral portion around which the flow shaft is formed, and the auxiliary body is configured to apply the auxiliary compression mainly in the central portion of the stack, such that the auxiliary compression is applied at a distance away from the flow shaft.

[0019] According to one aspect of the invention, the auxiliary body comprises a central portion and at least one tab extending protrudingly relative to the central portion, and the auxiliary traction member is attached to the tab. The tab allows traction to be performed outside the stack without crossing the stack. The auxiliary traction member exerts a force on the tab without exerting a force on the main device.

[0020] Preferably, the stack comprises a central portion and a peripheral portion around which the flow shaft is formed, and the main body is configured to apply a primary compression mainly at the peripheral portion of the stack, thus allowing a direct constraint to be exerted on the flow shaft.

[0021] Preferably, the main body comprises a recess configured to cooperate by form-fitting with the secondary body such that the end plate applies a distributed planar force.

[0022] Preferably, the main compression is higher than the auxiliary compression to ensure a high and uniform compression.

[0023] Preferably, the main body is peripheral to apply force to the flow shaft. According to one aspect, the main body partially covers the auxiliary body to apply a supplemental force to the stack in separate portions. According to another aspect, the main body completely covers the auxiliary body.

[0024] According to one aspect of the invention, the auxiliary body comprises a mesh configured to apply an auxiliary compression to the stack, the mesh defining an opening through which the flow shaft is accessible, thus allowing the auxiliary body to exert a compressive force that is distributed across the stack while ensuring accessibility to the flow shaft through the mesh.

[0025] Preferably, the access opening has a cross section smaller than the cross section of the flow shaft, so that the main body can exert a main compressive force over the entire circumference of the flow shaft.

[0026] Preferably the auxiliary traction member is in the form of a spring leaf configured to generate the auxiliary compression. The use of multiple spring leaves allows for the exertion of multiple independent distributed compression forces.

[0027] Preferably, the end plates are configured so as to no longer generate tension in the auxiliary traction member during compression exerted by the primary traction member.The auxiliary traction member is configured to be removable when the primary device is in place.

[0028] According to one aspect of the invention, the auxiliary body comprises at least one groove in which a spring leaf is attached. The spring leaf can be easily installed / removed without tools. The spring leaf can accommodate pressurization of the stack and can be removed as soon as the main device is attached.

[0029] The invention also relates to a method for accessing at least one flow shaft of a stack of fuel cells as presented above, the method comprising: an end plate compressing the stack, the at least one end plate comprising a main device applying a main compression biasing a main body against the stack at the flow shaft of the stack; and an auxiliary device applying an auxiliary compression biasing an auxiliary body against the stack at a distance away from the flow shaft of the stack, the method comprising: Removing the primary device to stop the primary compression so as not to block access to the flow shaft, and the auxiliary device maintaining the auxiliary compression. The method includes the steps of:

[0030] The auxiliary compression is applied around the periphery of the flow shaft, at a distance from the flow shaft, which makes it possible to avoid destroying the stack without blocking access to the flow shaft.

[0031] Preferably, the method includes the step of inspecting the flow shaft after removal of the main device, particularly for cleaning or repair purposes.

[0032] The present invention also includes, prior to the removing step: - attaching an auxiliary traction member to apply an auxiliary compression at a distance from the flow shaft of the stack to urge an auxiliary body of the auxiliary device against the stack; The present invention relates to a method comprising the steps of:

[0033] Preferably, the auxiliary traction member is mounted between two auxiliary devices belonging to opposing end plates.

[0034] Advantageously, the auxiliary traction members are installed only during maintenance operations, which makes it possible to limit the mass and costs of the fuel cell during normal operation. Advantageously, the same auxiliary traction members can be used for different fuel cells.

[0035] The invention will be better understood by reading the following description, given by way of example, and by referring to the following figures, given by way of non-limiting example, in which similar objects are provided with the same reference symbols: [Brief description of the drawings]

[0036] [Figure 1] FIG. 1 is a schematic diagram of a fuel cell according to the prior art. [Diagram 2]1 is a schematic diagram of a fuel cell according to a first embodiment. [Diagram 3] FIG. 13 is a schematic diagram of an enlarged portion of an endplate including a primary device and an auxiliary device. [Figure 4] This is a schematic diagram of [Figure 3] without the main device. [Diagram 5] FIG. 4 is a schematic diagram of FIG. 3 without the auxiliary device. [Figure 6] FIG. 2 is a schematic diagram of a fluid flow shaft formed in the stack. [Figure 7] FIG. 4 is a schematic diagram of a fuel cell according to a second embodiment. [Figure 8] This is a schematic diagram of [Figure 7] without the main device. [Figure 9] This is a schematic diagram of [Figure 7] without the collector plate and stack. [Figure 10] 4 is a schematic view of an end plate according to a second embodiment, seen from below; FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0037] It should be noted that the drawings represent the invention in detail for the purpose of implementing the invention, and of course, where applicable, said drawings can be used to better define the invention.

[0038] The present invention relates to the field of fuel cells of the proton exchange membrane type, known by the abbreviation PEMFC for "Proton-Exchange Membrane Fuel Cell". Preferably, the fuel cells are installed on board aircraft to power their propulsion equipment.

[0039] Referring to Figure 2, there is shown a fuel cell 1 comprising a stack 2 comprising a plurality of cells aligned along a stack axis X. Each cell comprises a plurality of fluid flow openings aligned parallel to the stack axis X to form a plurality of fluid flow stacks 20 within the stack 2 (Figures 4 to 6).

[0040] The stack 2 of cells allows electrochemical reactions from fluids, in particular hydrogen and oxygen. In this example, each cell comprises a Membrane Electrode Assembly, known by the abbreviation MEA. Each MEA is put in contact with reactant gases (for example hydrogen and oxygen that may be present in the air) through interconnecting plates on its two opposite sides to form a cell. In known manner, an assembly of two interconnecting plates, belonging to two adjacent cells, is called a bipolar plate. The bipolar plate is thus inserted between the cathode of an MEA and the anode of the adjacent MEA. The bipolar plate thus supplies, on the one hand, the fuel (hydrogen) to the first MEA and, on the other hand, the oxidant (oxygen) to the second MEA on the cathode side. Generally, each bipolar plate comprises an internal cooling circuit in which a heat transfer fluid circulates to provide heat or to extract heat created by the exothermic reactions. Such stacks 2 formed of alternating MEAs and bipolar plates are known in the prior art and will not be presented in further detail.

[0041] In this example, referring to FIG. 2, the fuel cell 1 further comprises collector plates 4 positioned at either end of the stack 2 to collect the current generated by the cells. In a known manner, the power delivered by the fuel cell 1 depends on the number of cells (delivered voltage capacity) and the flow rate of the reactant fluids (the importance of the electrochemical reactions producing the current).

[0042] Referring to FIG. 2, the fuel cell 1 further includes two end plates 3 arranged on either end of the stack 2 along the stack axis X, and a plurality of traction members connecting the end plates 3 to each other to compress the stack 2.

[0043] According to the invention, and with reference to FIG. 3, at least one end plate 3 comprises: a main device 5 comprising a main body 50 with at least one access opening 51 aligned with the flow shaft 20 ([FIG. 4]) and at least one main traction member T1 configured to apply a main compression to the main body 50 to urge the main body 50 against the stack 2 in the flow shaft 20 of the stack 2; an auxiliary device 6 comprising an auxiliary body 60 and at least one auxiliary traction member T2 configured to apply an auxiliary compression to the auxiliary body 60 to urge the auxiliary body 60 against the stack 2, the auxiliary compression being applied at a distance away from the flow shaft 20 of the stack 2, and the main device 5 being removably attached to the auxiliary device 6; Equipped with.

[0044] According to the invention, the main device 5 can be removed to access the fluid flow shaft 20. Although the main compression is no longer applied to the stack 2, the stack 2 is not destroyed as the auxiliary device 6 always provides the auxiliary compression. Since the auxiliary compression is performed at a distance from the flow shaft 20, the auxiliary device 6 does not impede access to the flow shaft 20, which allows for the actual cleaning of the flow shaft 20 as described below.

[0045] In this first embodiment, referring to FIG. 3, the primary device 5 is configured to partially cover the auxiliary device 6 in the mounting position, although it goes without saying that the auxiliary device 6 can be completely covered. As shown in FIG. 4, the auxiliary device 6 includes a shoulder 64 on which the primary device 5 rests and can exert a force. As will be described below, the compressive force applied by the primary device 5 can supplement or completely replace the compressive force applied by the auxiliary device 6.

[0046] Referring to FIG. 3, the main body 50 comprises three access openings 51 aligned with the flow shaft 20 of the stack 2. The main body 50 is peripheral and comprises inner openings to which the auxiliary devices 6 are attached. Preferably, the main devices 5 comprise inner lines each with an access opening 51 leading to the flow shaft 20, and an outer opening suitable for receiving an external fluid connector. As previously mentioned, the inner lines may be straight or curved and may run through the thickness of the main body 50.

[0047] In this example, the stack 2 comprises a peripheral portion in which a flow shaft 20 is formed and a central portion without a flow shaft 20 , the central portion forming the active zone of the stack 2 .

[0048] The main device 5 further comprises a number of main traction members T1 for applying a main compression to the stack 2 against the flow stack 20 of the stack 2. In particular, the main body 50 applies a force against the periphery of the opening of the flow shaft 20. Preferably, the access opening 51 has a smaller cross section than the flow shaft 20 so that the main body 50 can be in continuous contact with the periphery of the opening of the flow shaft 20. In other words, the main compression is applied in the immediate vicinity of the flow shaft 20, which ensures optimal compression. In this example, more than about 10 main traction members T1 are used to ensure a distributed main compression. The main device 5 comprises a passage opening in which the main traction members T1 are mounted, in particular a tie rod connected to the other end plate 3 as shown in [Figure 2], but it goes without saying that other traction members may also be suitable.

[0049] As shown in Figures 4 and 5, the primary compression is applied to the flow shaft 20 of the stack 2 through a collector plate 4 that is provided with an orifice 40 to allow fluid communication between the access opening 51 and the flow shaft 20 of the stack 2.

[0050] In this first embodiment, with reference to figures 3 and 4, the auxiliary device 6 comprises an auxiliary body 60 configured to apply an auxiliary compression to the stack 2 at a distance from the flow shaft 20, in particular in a central portion of the stack 2 along the stack axis X. In this example, the auxiliary body 60 comprises an auxiliary traction member T2 in the form of a tie rod, attached to a tab 61 extending protruding from the auxiliary body 60 and configured to be connected to another end plate 3. Preferably, the auxiliary traction member T2 is configured to apply an auxiliary compression less than the main traction member T1 and lower than the main compression but sufficient to avoid destroying the stack 2. Advantageously, the auxiliary device 6 allows to apply the auxiliary compression while leaving uncovered access to the flow shaft 20 when the main device 5 is removed in a detachable manner.

[0051] Next, an exemplary embodiment of a method for accessing the flow shaft is presented.

[0052] 2 and 3, in the initial position, the end plates 3 are attached to the stack 2, the auxiliary device 6 applies an auxiliary compression in the center and the main device 5 applies a main compression circumferentially to the stack 2 along the stack axis X. Advantageously, the main device 5 allows a direct compression of each flow shaft 20. The main compression is preferably higher than the auxiliary compression.

[0053] As previously presented, the primary device 5 applies compression to the secondary device 6 via shoulder 64, although it will be appreciated that compression can also be achieved separately.

[0054] According to a first embodiment, the primary device 5 applies additional compression to the auxiliary device 6, such that when the primary device 5 is in place, all traction members T1, T2 are tensioned. According to a second embodiment, the primary device 5 applies a compression that replaces the compression of the auxiliary device 6, such that when the primary device 5 is in place, the auxiliary traction members T2 are not tensioned.

[0055] The method includes a step consisting of deactivating the main traction member T1 to stop the main compression, and a step consisting of removing the main device 5. By removing the main device 5, the main compression is eliminated, but the stack 2 is not destroyed, since the auxiliary device 6 still provides the auxiliary compression. Preferably, as the main device 5 is loosened, the auxiliary traction member T2 is tensioned and subjected to an increasingly larger force. The auxiliary compression is not applied directly to the flow shaft 20, but at a distance from the flow shaft 20. The flow shaft 20 is thus directly accessible to an operator, who can then inspect, clean or repair it. The stack 2 remains sealed, which avoids any risk of contamination or misalignment of the cells of the stack 2.

[0056] In other words, to perform a maintenance operation, the auxiliary device 6 remains in place by its auxiliary traction member T2, and the operator advantageously acts only on the main traction member T1, so that the operator can insert a syringe, an endoscope, or any other device into the flow shaft 20, the inner surface of which is fully and easily accessible.

[0057] The use of end plates 3 with removable main devices 5 makes it possible to carry out risk-free maintenance operations of the fuel cell 1, in particular to remove acid crystallization.

[0058] 7 to 10, according to a second embodiment, the end plate 3 has a different structure. In particular, in this second embodiment, the main device 5 is configured to completely cover the auxiliary device 6 in the mounting position as shown in FIG. 7, although it goes without saying that the main device 5 can also partially cover the auxiliary device 6.

[0059] In this second embodiment, with reference to figures 8 and 9, the auxiliary device 6 comprises an auxiliary body 60 formed from a mesh internally delimiting a wide opening through which the flow shaft 20 is accessible. In this example, the auxiliary body 60 extends to the periphery of the stack 2 to ensure a distributed auxiliary compression, which is advantageous for ensuring sealing of the stack 2. With reference to figure 10, the main body 50 comprises a recess for form-fitting cooperation with the auxiliary body 60.

[0060] To ensure the auxiliary compression, the auxiliary device 6 comprises auxiliary traction members T2 in the form of spring leaves 7 arranged to cooperate with the auxiliary device 6 of the opposing end plate 3, in particular the opposing end plate 3 shown in FIG. 8. In this example, the auxiliary body 60 comprises, in its outer edge, in particular distributed, several grooves 63 in which the spring leaves 7 are attached.

[0061] As shown in figures 9 and 10, each spring leaf 7 has two ends 71 ​​connected to the grooves 63 of the auxiliary device 6 of the end plate 3. Each end 71 preferably has a hook shape so that it can be conveniently connected to the groove 63, especially when the main device 5 is in place. Preferably, each spring leaf 7 is added to limit its mass. The spring leaf 7 allows traction in the groove 63 to provide auxiliary compression by the auxiliary device 6 on the stack 2. Preferably, each spring leaf 7 is symmetrical, allowing for a convenient and quick assembly.

[0062] It goes without saying that the auxiliary body 60 of the auxiliary device 6 can alternatively be provided with a protruding tab together with the auxiliary traction member T2 as presented with respect to the first embodiment.

[0063] As before, the main device 5 can apply an additional compression to the auxiliary device 6, the spring leaf 7 being tensioned when the main device 5 is in place. Preferably, the main device 5 applies a compression which replaces the compression of the auxiliary device 6. As a result, the spring leaf 7 is not tensioned when the main device 5 is in place. The spring leaf 7 can therefore be removed when the main device 5 is in place and only used during maintenance operations. Advantageously, this makes it possible to reduce the mass and the cost of the fuel cell. Preferably, the spring leaf 7 can be used successively with several different fuel cells 1 during maintenance of those fuel cells 1.

[0064] When the primary device 5 is relaxed, the height of the stack 2 may increase because the spring leaves 7 expand to compensate for this increase in height while maintaining sufficient auxiliary compression force.

[0065] The method for accessing the flow shafts 20 can be carried out in a similar manner as in the first embodiment, since the mesh auxiliary body 60 is provided with openings which, on the one hand, allow to realize an auxiliary compression on the stack 2 and, on the other hand, allow easy access to each flow shaft 20 through the mesh. During maintenance operations, the spring leaves 7 provide the auxiliary compression in a distributed manner, ensuring optimal sealing.

[0066] The invention allows maintenance operations (cleaning, repair or otherwise) to be carried out ergonomically, conveniently and quickly.

Claims

1. A fuel cell (1) comprising: a stack (2) having a plurality of cells aligned along a stack axis (X) and a plurality of fluid flow shafts (20) within the stack (2); two end plates (3) arranged at the ends of the stack (2) along the stack axis (X); and a plurality of traction members connecting the end plates (3) to each other for compressing the stack (2), wherein at least one end plate (3) has: a main device (5) comprising a main body (50) with at least one access opening (51) aligned with the flow shaft (20) and at least one main traction member (T1) configured to apply a main compression to the main body (50) to urge the main body (50) against the stack (2) at the flow shaft (20) of the stack (2); an auxiliary device (6) comprising an auxiliary body (60) and at least one auxiliary traction member (T2) configured to apply an auxiliary compression to the auxiliary body (60) to urge the auxiliary body (60) against the stack (2), the auxiliary compression being applied a distance away from a flow shaft (20) of the stack (2), and a main device (5) removably attached to the auxiliary device (6), the main device (5) being configured to be removed when the auxiliary traction member (T2) applies the auxiliary compression to the auxiliary body (60); A fuel cell (1) comprising:

2. 2. The fuel cell (1) of claim 1, wherein the stack (2) has a central portion and a peripheral portion in which the flow shaft (20) is formed, and the auxiliary body (60) is configured to apply auxiliary compression primarily in the central portion of the stack (2).

3. 3. The fuel cell (1) according to claim 2, wherein the auxiliary body (60) has a central portion and at least one tab (61) extending protruding from the central portion, and the auxiliary traction member (T2) is attached to the tab (61).

4. 2. The fuel cell (1) of claim 1, wherein the stack (2) comprises a central portion and a peripheral portion in which the flow shaft (20) is formed, and the main body (50) is configured to apply a main compression primarily at the peripheral portion of the stack (2).

5. A fuel cell (1) according to claim 4, wherein the main body (5) is peripheral.

6. 4. The fuel cell (1) of claim 3, wherein the auxiliary body (60) comprises a mesh configured to apply auxiliary compression to the stack (2), the mesh defining an opening through which the flow shaft (20) is accessible.

7. 2. The fuel cell (1) according to claim 1, wherein the access opening (51) has a cross section that is smaller than the cross section of the flow shaft (20).

8. 2. The fuel cell (1) according to claim 1, wherein the auxiliary traction member (T2) is in the form of a spring leaf (7) configured to generate an auxiliary compression.

9. 9. The fuel cell (1) according to claim 8, wherein the auxiliary body (60) comprises at least one groove (63) in which the spring leaf (7) is mounted.

10. 10. A method for accessing at least one flow shaft (20) of a stack (2) of a fuel cell (1) according to any one of claims 1 to 9, wherein an end plate (3) compresses the stack (2), and the at least one end plate (3) comprises a main device (5) applying a main compression to urge a main body (50) against the stack (2) at the flow shaft (20) of the stack (2), and an auxiliary device (6) applying an auxiliary compression to urge an auxiliary body (60) against the stack (2) at a distance from the flow shaft (20) of the stack (2), the method comprising: Removing the main device (5) to stop the main compression so as not to block access to the flow shaft (20), while the auxiliary device (6) maintains the auxiliary compression. A method comprising the steps of:

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