Removable load cell for fuel cell stack

Abstract

The present invention relates to a design and method for desirably allowing the addition and / or removal of load sensors (10) in a fuel cell stack (1) without significantly changing the load acting on the tandem stack of the fuel cells when doing so. The associated fuel cell stack (1) has a simple structure, comprising a compression assembly (18) located in an opening in an end plate (3, 4), wherein the assembly comprises a spring cover (11) with an inner shoulder (11a), a spring assembly (13) and a load sensor button (12) that is slidable in the stacking direction. The load sensor (10) can then be added together with a suitable load sensor cover (15) or removed in the same manner without significantly changing the load.

Description

Technical Field

[0001] The present invention relates to designs and methods for allowing load sensors to be added to a fuel cell stack and / or removed without significantly changing the load acting on the fuel cells in the stack. It is particularly applicable to solid polymer electrolyte fuel cell stacks. Background Art

[0002] Fuel cells such as solid polymer electrolyte membrane fuel cells electrochemically convert fuel and oxidant reactants such as hydrogen and oxygen or air to generate electricity. Solid polymer electrolyte fuel cells generally use a solid polymer membrane electrolyte that conducts protons between a cathode and an anode. Electrodes generally include a suitable catalyst to facilitate the electrochemical reaction that occurs at each electrode. The structure comprising a solid polymer membrane electrolyte sandwiched between the two electrodes is referred to as a membrane electrode assembly (MEA). In a common embodiment, MEA includes a catalyst coated membrane (CCM) and a gas diffusion layer (GDL) applied to each side of the CCM. In CCM, a suitable catalyst component has been applied and adhered to either side of the membrane electrolyte. GDL is provided for distributing fluid reactants to electrodes and removing fluid byproducts from electrodes in an improved manner.

[0003] In addition, in a typical fuel cell, a flow field plate including many flow channels for reactants is arranged on either side of the MEA to distribute fuel and oxide to respective electrodes and remove reaction byproducts from the fuel cell. In a battery operated with hydrogen and air reactants, water is the main byproduct. Because the output voltage of a single cell is 1 volt, multiple cells are usually stacked in series for commercial use to provide a higher output voltage for practical purposes. Fuel cell stacks can also be connected in the form of interconnected series and / or parallel stacks in rows to be used in automotive applications, etc.

[0004] For several reasons, the components in such a fuel cell stack are generally required to be under some significant mechanical compression. These reasons include: eliminating gaps and reducing contact resistance between components, reliably obtaining multiple seals that separate different fluids throughout the stack, or even just keeping all components in place when the stack is in operation, transported or subjected to vibration, etc. A certain compliance is required because some components have compression set properties (i.e., permanent deformation under long-term loading). In addition, too strong a compression may cause damage and / or displacement of some components, which adversely affects performance and sealing. Therefore, it is important to provide the correct amount of compliance compression or load and it is therefore desirable to be able to measure it correctly. This applies not only when the stack is assembled, but also for maintenance, diagnosis, refurbishment and / or other purposes, which may be later, for example after the stack has been in use for a period of time.

[0005] The hardware required to provide the desired compression or load within the fuel cell stack can be quite simple. In a stack comprising a plurality of flat fuel cells, compliant compression is generally provided using two rigid end plates, a pressure plate, and a compliant compression assembly therebetween. The two rigid end plates are disposed at opposite ends of the stack and are connected together at a fixed spacing in a certain manner (such as by tie rods or straps). Within the stack, a compression assembly is used to press the pressure plate against the adjacent end of the tandem stack of fuel cells and away from the adjacent end plate, thereby compressing the pressure plate. A typical compression assembly involves a simple spring assembly, such as an appropriate number of stacked coil springs, which can provide the required load and compliance.

[0006] Many options for fuel cell stack design and compression assemblies have been proposed in the prior art. Many of them allow for adjustment of compression or loading on the inside of the cell. For example, US20180145366 relates to a fuel cell device having a clamping device and a pre-tightening unit with an adjusting member for providing adjustable compression for the stack. For another example, WO2004 / 062017 discloses a compression system comprising a press plate and a compression assembly, the compression assembly comprising a compression pack for maintaining a compressive load acting on the stack as the stack creeps within its life span and compensating for thermal expansion of the stack under varying operating conditions. Each compression assembly is at least partially arranged outside the container. For another example, DE102017220595 discloses an arrangement using an externally threaded cover that allows simple assembly, in which the fuel cell stack is pre-tightened by a tensioner and a spring member to compensate for the aging shortening of the fuel cell stack and to keep the fuel cell stack sufficiently pre-tightened.

[0007] It is usually important to carefully control the amount of load applied to the cells in the stack. If the load is too small, the purpose of eliminating gaps, reducing contact resistance, obtaining sealing, etc. cannot be achieved. On the other hand, if the load is too large, damage to the components therein may occur, including deformation, shortening, etc. It is therefore important to set the load during stack assembly and maintain an acceptable load during the life of the stack. It is common that load sensors have been used to measure the load during assembly and are usually added to the assembled stack to monitor the load during the working life of the stack. But load sensors may be relatively expensive devices and may also add undesirable weight and volume to the finished stack. Many options for fuel cell stack arrangements and methods of use have therefore also been proposed in the prior art to allow the use of load sensors. These options include allowing load sensors to be used only during assembly or permanently maintaining the arrangement of load sensors. In addition, although some options may allow the addition or removal of load sensors after assembly, it involves partial disassembly and unloading of the stack. In such an option, when the compression acting on the stack is substantially released, potential permanent adverse consequences may result, including possible leakage of seals, displacement of components, etc.

[0008] As an example of the foregoing, the stack in US20190140302 includes a surface pressure sensor and an adjustment unit for adjusting the surface pressure applied to the unit cell in the stacking direction. As other examples, US8343683, JP2003-173805 and JP5574746 use load sensors in their structures. It is worth noting that the latter uses a load sensor as a moisture detection unit. In addition, JP2006-108058 discloses a method and an arrangement, in which a load sensor is used for assembly purposes in an assembly fixture, but is not permanently added to the fuel cell stack. In addition, options such as those described in US8802325 can include a load sensor in the stack structure, which appears to be removable after assembly, but doing so will require removal of equipment such as a tie rod, so that the internal load applied will be substantially eliminated when doing so. In another approach, US7901828 discloses an arrangement that uses an external adjustable screw to apply a compressive load, the purpose of which is to allow the compressive load to be accurately measured without using any load sensor, thereby not requiring expensive devices such as load sensors at all.

[0009] Notwithstanding the foregoing, if the accuracy provided by load sensor measurements is desired or required at various times during the life of a fuel cell stack, it would be desirable to be able to removably add load sensors in a simple manner, while doing so without significantly changing the load acting on the stack. The present invention satisfies these needs and provides other related advantages. Summary of the invention

[0010] The present invention includes designs and methods that desirably allow load sensors to be added and / or removed from a fuel cell stack at any time without significantly changing the compressive load on the fuel cell tandem stack in doing so. Thus, for example, load sensors may be added or removed to accurately measure and set the load during assembly or after assembly and subsequent operation for diagnostic, maintenance / tuning, refurbishment, or other purposes.

[0011] The present invention is suitable for use in a typical fuel cell stack, which includes a unit cell block, which includes a plurality of substantially flat fuel cells stacked in series. Such a unit cell block has a first and a second end provided with a first and a second end plate, the first and the second end plates being opposite to the first and the second ends of the unit cell block, respectively. In such a fuel cell stack, these first and second end plates are connected to each other at a fixed spacing. This is achieved by making the first end plate serve as a compression surface for the first end of the unit cell block and arranging a pressure plate between the second end of the unit cell block and the second end plate of the fuel cell stack, wherein the pressure plate serves as a compression surface for the second end of the unit cell block. The compression load is provided by a compression assembly, which presses the pressure plate away from the second end plate, thereby applying a load to the second end of the unit cell block through the pressure plate. In particular, the present invention is suitable for use in a typical solid polymer electrolyte fuel cell stack.

[0012] In the present invention, the second end plate in the fuel cell stack includes an opening for a compression assembly, and the compression assembly is located in the opening in the second end plate. The compression assembly itself includes a spring cover, a load sensor button and a spring assembly. The spring cover is attached to the opening in the second end plate and the spring cover includes an inner boss. The load sensor button is used to engage with the load sensor, wherein the load sensor button is located between the spring cover and the pressure plate and is slidable in the stacking direction therebetween. In addition, the inner boss of the spring cover serves as a stop for the load sensor button. The spring assembly is located between the pressure plate and the load sensor button and engages with them at opposite ends of the spring assembly. With this structure, the first load is applied to the second end of the unit cell block through the spring cover, the load sensor button, the spring assembly and the pressure plate.

[0013] In an exemplary practical embodiment of the present invention, the opening in the second end plate and the peripheral surface of the spring cover are coordinated with threads, so that the spring cover threads are engaged with the opening threads and the spring cover can be fixed to the opening. In addition, the spring cover is thus adjustable in the stacking direction of the fuel cell stack by screwing the spring cover into or out of the second end plate.

[0014] The spring assembly suitable for use in the present invention comprises a stack of coil springs. However, other alternatives utilizing different mechanical, pneumatic or other approaches known to the skilled person may be employed.

[0015] Other embodiments of the present invention may include a set screw in the shoulder of the spring cover that can engage the load sensor button and separate it from the shoulder of the spring cover. In addition, the load sensor button may include a central opening for engaging and locating the load sensor. A retaining O-ring or a set of O-rings may also be used to prevent the slidable load sensor button from shaking.

[0016] In some fuel cell stacks, such as those with a relatively large aspect ratio, it may be advantageous or even necessary to include more than one compression assembly to produce uniform compression of the cell block. Such an embodiment would then include more than one opening in the second end plate and more than one corresponding compression assembly.

[0017] The foregoing describes the structure of the fuel cell stack of the present invention, which can removably add a load sensor without significantly interfering with the compressive load on the cell stack. However, it describes the structure of the fuel cell stack in a state in which it is not provided with a load sensor or the load sensor has not yet been added thereto. With the load sensor added according to the present invention, the fuel cell stack also includes a load sensor cover attached to the second end plate or the spring cover and a load sensor that is engaged at one end to the load sensor button and at the other end to the load sensor cover so that the load sensor button is separated from the inner boss of the spring cover. In this way, the second load can be applied to the second end of the unit cell block through the load sensor cover, the load sensor, the load sensor button, the spring assembly and the pressure plate.

[0018] With the present invention, the load within the fuel cell stack can be maintained approximately or substantially constant, regardless of whether a load sensor is added to the fuel cell stack. That is, in static conditions, the load when no load sensor is added (i.e., the first load) can be maintained approximately or substantially equal to the load when the load sensor is added (i.e., the second load). When substantially equal, the ratio of the second load to the first load is then 1:1. However, in some cases, it may even be advantageous for the first and second loads to be slightly different, such as where the ratio of the second load to the first load is between 1.2:1 and 1:1.2. For example, to avoid an undesirable increase in load to facilitate the addition or removal of a load sensor, it may instead be preferred to slightly reduce the load within the fuel cell stack, but this is temporary (before the addition or removal of the load sensor), then remove or add the load sensor, and finally increase the load and restore it to its initial state. In these temporary conditions, the reduced load may be slightly less than the first and / or second load, such as where the ratio of the reduced load to the first or second load may be temporarily as high as about 1:1.2.

[0019] With the above fuel cell stack structure, a load sensor can then be easily added to measure the load applied to the unit cell block with little change to the applied load. This can be achieved simply by adding the load sensor to the fuel cell stack to engage the load sensor button and then attaching the load sensor cover to the second end plate or spring cover so that the load sensor cover contacts the load sensor and the load sensor button is separated from the inner shoulder of the spring cover. In this way, the second load is applied to the second end of the unit cell block through the load sensor cover, load sensor, load sensor button, spring assembly and pressure plate.

[0020] In an embodiment in which the opening in the second end plate and the circumferential surface of the spring cover are threaded and engaged with each other in a coordinated manner so that the spring cover can be adjusted in the stacking direction of the fuel cell stack by screwing the spring cover into or out of the second end plate, the method of adding a load sensor may include the following steps: before the step of attaching the load sensor cover, unscrewing the spring cover from the second end plate to reduce the load applied to the cell block to a reduced load, wherein the ratio of the reduced load to the first load is in the range of 1:1 to 1:1.2, and attaching the load sensor cover so that the load sensor button is separated from the inner boss of the spring cover and the second load applied to the second end of the cell block is approximately equal to the first load.

[0021] In an alternative embodiment in which the fuel cell stack includes a push screw in an inner boss of the spring cover (which engages to the load sensor button and separates it from the boss of the spring cover), a method for adding the load sensor may include the following steps: after attaching the load sensor cover, unscrewing the push screw from the inner boss of the spring cover to transfer the load applied to the cell block to the added load sensor via the push screw so that a second load applied to the second end of the cell block is approximately equal to the first load.

[0022] Typically, the added load sensor can be removed from the fuel cell stack of the present invention simply by removing the load sensor cover from the second end plate or the spring cover and removing the load sensor from the fuel cell stack, with little change in the load applied to the cell block. In the above embodiment where the opening in the second end plate and the peripheral surface of the spring cover are both threaded and mutually engaged with each other so that the spring cover can be adjusted in the stacking direction of the cell block by screwing the spring cover into or out of the second end plate, the step of removing the load sensor cover may cause the load sensor button to slide until it stops on the inner boss of the spring cover and reduce the load applied to the cell block to a reduced load, wherein the ratio of the reduced load to the second load is in the range of 1:1 to 1:1.2. The removal method can then additionally include: screwing the spring cover into the second end plate to increase the load applied to the cell block to a first load, wherein the first load is approximately equal to the second load. In the above-mentioned alternative embodiment in which the fuel cell stack includes a push screw in the inner boss of the spring cover, the removal method includes: screwing the push screw into the inner boss of the spring cover to transfer the load applied to the unit cell block to the push screw through the added load sensor, wherein the first load is approximately equal to the second load. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] These and other aspects of the invention will be apparent upon reference to the drawings and the following detailed description.

[0024] Figure 1 An isometric view of an exemplary fuel cell stack of the present invention is shown having three load sensors incorporated into the stack.

[0025] Figure 2 Show Figure 1 2. A view of a fuel cell stack of the present invention, wherein the component with the middle load sensor has been removed, and the component with the rightmost load sensor and the associated load sensor have been removed.

[0026] Figure 3 Shown with added Figure 1 A cross-sectional view of a compression assembly of a load sensor in a fuel cell stack of the present invention. DETAILED DESCRIPTION

[0027] In this specification, words like "a", "an" and "comprising" should be interpreted in an open-ended sense and be considered to mean at least one but not limited to only one.

[0028] In a quantitative sense, the term "about" is to be interpreted herein as within a range of ±10%.

[0029] The phrase "consisting essentially of should be construed to include not only those specific items mentioned but also other items that do not substantially affect the basic characteristics or properties of the constituent elements or steps.

[0030] The phrase "cell block" refers to a plurality of substantially flat individual fuel cells stacked in series within a fuel cell stack.

[0031] The phrase "stacking direction" is used in relation to a fuel cell stack comprising a unit cell block consisting of fuel cells stacked in series in a substantially flat manner. The "stacking direction" is the direction of the cells along this stack, ie perpendicular to the plane of the fuel cells.

[0032] The design and method provided by the present invention conveniently allows load sensors to be added to and / or removed from a fuel cell stack 1 without even significantly changing the load acting on the unit cell block of the fuel cell. It is particularly suitable for use with solid polymer electrolyte fuel cell stacks. Such stacks can be used as power sources in many applications such as automotive and other traction applications. Figure 1 An isometric view of an exemplary solid polymer electrolyte fuel cell stack 1 according to the invention is shown, wherein three load sensors (not visible in this figure) are integrated into the stack.

[0033] The fuel cell stack 1 includes a unit cell block 2, which includes a plurality of substantially flat solid polymer electrolyte cells stacked in series. The unit cell block 2 has two ends, namely a first end 2a and a second end 2b. A first end plate 3 and a second end plate 4 are opposite to the first end 2a and the second end 2b, respectively. The first and second end plates 3, 4 are connected together at a fixed interval, and as shown in FIG. Figure 1As shown, the connection is achieved using a plurality of straps 5 that are wrapped around the circumference of the stack 1. The straps 5 secure the end plates 3 and 4 together, which in turn serve to support and maintain the cells within the cell block 2 and the end plates 3, 4 aligned within the stack. As also shown, the straps 5 can be loosened (by loosening the screws that secure the straps 5 to the end plates 3) to allow adjustment of the separation distance between the end plates 3, 4 as desired. Figure 1 Three load cell covers 15 are seen, which are attached to the second end plate 4. However, in Figure 1 The pressure plate 16 and the associated components of the compression assembly 18 are not visible.

[0034] then, Figure 2 Show Figure 1 , but after the part with the middle load sensor 10 has been removed and also after the part with the rightmost load sensor and the associated rightmost load sensor have been removed. Figure 2 In the figure, a cylindrical spring cover 11 is seen in connection with the compression assembly for the middle and rightmost load cell 10. The spring cover 11 is attached to an opening in the second end plate 4. Here, this is achieved by threading the circumference of the spring cover 11 (not visible) in coordination with a thread provided in the opening of the second end plate 4. The spring cover 11 can then be screwed into or out of the second end plate 4 as desired and is thus adjustable in the stacking direction (marked by the arrow z).

[0035] Also available in Figure 2 The top side of the load sensor buttons 12 can be seen in the figure, which are located between the spring cover 11 and the pressure plate 16 (at Figure 2 The load sensor button 12 is prevented from jumping out of the stack 1 by an inner shoulder 11a (not visible) provided on the spring cover 11.

[0036] Also available in Figure 2 The central opening 12a in the rightmost load sensor button 12 is seen for positioning and engaging the load sensor to be added. The load sensor 10 is positioned and engaged to the Figure 2 The middle spring cover 11. Figure 2 Not visible is the spring assembly 13 which also forms part of the compression assembly used in the present invention.

[0037] Figure 3 Show Figure 11 is a cross-sectional view of the complete compression assembly 18 in the fuel cell stack 1 of FIG. 1 , with the added load cell 10 and load cell cover 15. Here the pressure plate 16 can be seen, which serves as a compression surface for abutting against the second end 2b of the unit cell block 2. The spring assembly 13, which includes a stack of coil springs, can also be seen. Here, the spring assembly 13 is positioned around a support 16a, which is formed in and is a part of the pressure plate 16. The spring assembly engages with the pressure plate 16 and presses it against the second end 2b of the unit cell block 2 and toward the first end plate 3.

[0038] The simple arrangement and function of the compression assembly 18 is Figure 3 It is clearly visible in Figure 3 , the load applied to the pressure plate 16 is derived from the compression of the coil spring of the spring assembly 13. The spring assembly 13 directly contacts the load sensor button 12, which in turn directly contacts the load sensor 10, which in turn directly contacts the load sensor cover 15. The load sensor cover 15 is attached to the spring cover 11, which in turn is attached to the second end plate 4. In this configuration, the load sensor button 12 is slightly spaced from the inner shoulder 11a of the spring cover 11. Thus, here, substantially all of the load applied to the pressure plate 16 is transmitted through the load sensor 10, and thus the load sensor 10 can be used to provide very accurate applied load measurements.

[0039] On the other hand, with the load cell 10 and the load cell cover 15 removed, Figure 3 It is clearly seen in the figure that the load sensor button 12 will be pressed by the spring assembly 13 so as to contact the inner shoulder 11a. In this case, with the removal of the load sensor, substantially all the load applied to the pressure plate 16 is transmitted to the spring cover 11 again.

[0040] Thus, in a typical application of the present invention, during the assembly of the fuel cell stack, the stack may be assembled in a conventional manner so that the cell block 2 can be compressed. The pressure plate 16, together with the spring assembly 13 and the load sensor button 12 placed on the pillar 16a, may be appropriately positioned at the second end 2b of the cell block 2. The second end plate 4 is prepared for use by partially screwing into the spring cover 11, and then the assembly is appropriately positioned above the pressure plate 16. The assembly is then pressed against each other and the tie 5 is attached to fix the two end plates 3, 4 together according to the desired set spacing. Since the spring cover 11 is only partially screwed into the second end plate 4, the load acting on the cell block may be sufficient to keep the components positioned and aligned, but not yet high enough to be used as the expected nominal working load. At this time, if the load sensor 10 is not installed, this load below the nominal is all directly transmitted from the load sensor button 12 to the shoulder of the spring cover 11, or if the load sensor 10 is installed, these loads are all transmitted from the load sensor button 12 to the load sensor cover 15. Next, in order to set the desired nominal load and thereby complete the assembly, the load sensor 10 and load sensor cover 15 are installed if they have not already been installed. The dimensions of these components are set so that when the load sensor cover 15 is fully engaged to the spring cover 11, the load sensor button 12 is slightly displaced (denoted as displacement "d") away from the inner boss 11a. Now, the load is all transmitted via the load sensor 10 without the aid of the spring cover 11. The spring cover 11 can now be screwed further into the second end plate 4 while continuously and accurately monitoring the applied load until the desired nominal assembly load is obtained, thereby completing the assembly of the fuel cell stack 1.

[0041] To subsequently remove the load sensor 10 for commercial use, the load sensor cover 15 and load sensor 10 need only be removed without disturbing the associated setting of the spring cover 11 within the second end plate 4. In doing so, however, the load sensor button 12 will slide slightly in the z direction (i.e., displacement d) until it stops on the inner shoulder 11a and causes a slightly reduced load to be applied to the cell block 2. If maintaining an exact nominal load is important and / or desired, this is easily done by screwing the spring cover 11 into the second end plate 4 to an appropriate degree to compensate for the displacement d.

[0042] Subsequently, if it is desired to temporarily accurately measure the applied load for maintenance, adjustment, diagnosis, etc., the previous process need only be reversed (i.e., the spring cover 11 is withdrawn by the same amount, and the load sensor 10 and load sensor cover 15 are added). In this way, substantially the same load can be maintained, whether or not the load sensor is added. Only a small load reduction is caused during the transition between these states. In addition, as will be readily apparent to those skilled in the art, the addition and removal process can be simplified to simply tolerate the small load changes associated with changing the position of the load sensor button 12 within the displacement d range.

[0043] The above embodiments and related methods for adding and removing load sensors illustrate the present invention. Those skilled in the art will recognize that there are many variations that can be made within the scope of the present invention. For example, although a coil spring is a common preferred mechanism for use as a spring assembly, other options based on mechanical, pneumatic or hydraulic principles are also contemplated. The following variants can also be considered, in which the load sensor cover is attached to the second end plate 4 opposite to the spring cover, and appropriate changes are made to the method accordingly. In addition, for example, an embodiment in which a top screw is provided in the shoulder of the spring cover can be considered to engage with the load sensor button and separate it from the shoulder of the spring cover. Such a top screw can then be adjusted instead of the spring cover.

[0044] The following examples are illustrative of certain aspects of the present invention, but should not be construed in any limiting sense.

[0045] The "10-unit short stack" (i.e., a fuel cell stack 1 having a unit cell block consisting of 10 solid polymer fuel cells stacked in series) is based on the following Figure 1-3 The short stack is assembled and compressed to the intended target load with the load cell added. The load cell is then removed, causing the compressive load on the cell block to drop to about 20% below the target load. To compensate for the lost load, the spring cap is rotated a full turn (depending on the design) to increase the compressive load back to the intended target load.

Claims

1. A fuel cell stack (1), comprising: A unit cell block (2) comprising a plurality of substantially flat fuel cells stacked in series, wherein the unit cell block (2) has a first end and a second end (2a, 2b); A first end plate and a second end plate (3, 4) respectively opposite to the first end and the second end (2a, 2b) of the unit battery block (2), wherein: - the first end plate and the second end plate (3, 4) are connected together at a fixed distance; and - the first end plate (3) serves as a compression surface for the first end (2a) of the unit battery block (2); a pressure plate (16) between the second end (2b) of the unit battery block (2) and the second end plate (4), wherein the pressure plate (16) serves as a compression surface for the second end (2b) of the unit battery block (2); and a compression assembly (18) that presses the pressure plate (16) away from the second end plate (4), thereby applying a load to the second end (2b) of the unit battery block (2) through the pressure plate (16); Its characteristics are: The second end plate (4) includes an opening for the compression assembly (18); The compression assembly (18) is located in an opening in the second end plate (4) and comprises: - a spring cover (11) attached to the opening in the second end plate (4), wherein the spring cover (11) comprises an inner shoulder (11a); - a load sensor button (12) for engaging with the load sensor (10), wherein the load sensor button (12) is located between the spring cover (11) and the pressure plate (16) and can slide therebetween in the stacking direction z, and wherein an inner shoulder (11a) of the spring cover (11) serves as a stop for the load sensor button (12); and - a spring assembly (13) located between the pressure plate (16) and the load sensor button (12) and joined to the pressure plate and the load sensor button at opposite ends of the spring assembly (13); Wherein, a first load is applied to the second end (2b) of the unit battery block (2) through the spring cover (11), the load sensor button (12), the spring assembly (13) and the pressure plate (16).

2. The fuel cell stack (1) according to claim 1, wherein: The opening in the second end plate (4) and the circumference of the spring cover (11) are both threaded in coordination with each other, wherein the thread of the spring cover (11) engages with the thread of the opening, thereby fixing the spring cover (11) to the opening.

3. The fuel cell stack (1) according to claim 2, wherein: The spring cover (11) can be adjusted in the stacking direction of the fuel cell stack (1) by screwing the spring cover (11) into or out of the second end plate (4).

4. The fuel cell stack (1) according to claim 1 or 2, wherein: The spring assembly (13) includes a stack of coil springs.

5. The fuel cell stack (1) according to claim 1 or 2 comprises a top screw in the inner boss (11a) of the spring cover (11), which is engaged with the load sensor button (12) and separates it from the inner boss (11a) of the spring cover (11).

6. The fuel cell stack (1) according to claim 1 or 2, wherein: The load sensor button (12) includes a central opening (12a) for engaging and positioning with the load sensor (10).

7. A fuel cell stack (1) according to claim 1 or 2, comprising more than one opening in the second end plate (4) and more than one corresponding compression assembly (18).

8. The fuel cell stack (1) according to claim 1 or 2, further comprising: a load cell cover (15) attached to the second end plate (4) or the spring cover (11); and a load sensor (10) engaged with the load sensor button (12) at one end and engaged with the load sensor cover (15) at the other end so that the load sensor button (12) and the inner shoulder (11a) of the spring cover (11) are spaced from each other; The second load is applied to the second end (2b) of the unit battery block (2) through the load sensor cover (15), the load sensor (10), the load sensor button (12), the spring assembly (13) and the pressure plate (16).

9. The fuel cell stack (1) according to claim 8, wherein: A ratio of the second load to the first load is in a range of 1.2:1 to 1:1.

2.

10. The fuel cell stack (1) according to claim 1 or 2, wherein: The fuel cell is a solid polymer electrolyte fuel cell.

11. A method of adding a load sensor (10) to a fuel cell stack (1) to measure the load applied to the unit cell block (2) in a manner that the applied load varies slightly, comprising: Obtaining a fuel cell stack (1) according to any one of claims 1 to 7 or claim 10; adding a load sensor (10) to the fuel cell stack (1) to engage the load sensor button (12); and Attaching a load sensor cover (15) to the second end plate (4) or the spring cover (11) such that the load sensor cover (15) contacts the load sensor (10) and the load sensor button (12) is spaced apart from an inner shoulder (11a) of the spring cover (11); The second load is applied to the second end (2b) of the unit battery block (2) through the load sensor cover (15), the load sensor (10), the load sensor button (12), the spring assembly (13) and the pressure plate (16).

12. The method according to claim 11, wherein: The opening in the second end plate (4) and the circumferential surface of the spring cover (11) are both threaded and mutually engaged in a coordinated manner, so that the spring cover (11) can be adjusted in the stacking direction of the fuel cell stack (1) by screwing the spring cover (11) into or out of the second end plate (4). The method comprises: Prior to the step of attaching the load sensor cover (15), the spring cover (11) is screwed out from the second end plate (4) to reduce the load applied to the unit cell block (2) to a reduced load, wherein the ratio of the reduced load to the first load is in the range of 1:1 to 1:1.2; and The load sensor cover (15) is attached so that the load sensor button (12) is separated from the inner shoulder (11a) of the spring cover (11) and the second end (2b) of the unit battery block (2) is applied with a second load equal to the first load.

13. The method according to claim 11 or 12, wherein: The fuel cell stack (1) includes a push screw in an inner shoulder (11a) of the spring cover (11), the push screw engaging the load sensor button (12) and separating it from the shoulder of the spring cover (11), the method comprising: After the load sensor cover (15) is attached, the top screw is screwed out from the inner boss (11a) of the spring cover (11) to transfer the load applied to the unit battery block (2) to the added load sensor (10) through the top screw, so that the second load applied to the second end (2b) of the unit battery block (2) is equal to the first load.

14. A method for removing a load sensor (10) from a fuel cell stack (1) in such a way that a load applied to a unit cell block (2) varies little, comprising: Obtaining a fuel cell stack (1) according to claim 8 or 9; removing the load cell cover (15) from the second end plate (4) or the spring cover (11); and The load sensor (10) is removed from the fuel cell stack (1).

15. The method according to claim 14, wherein: The opening in the second end plate (4) and the circumferential surface of the spring cover (11) are both threaded and mutually engaged in coordination with each other, so that the spring cover (11) can be adjusted in the stacking direction of the fuel cell stack (1) by screwing the spring cover (11) into or out of the second end plate (4), and wherein the step of removing the load sensor cover (15) causes the load sensor button (12) to slide until it stops at the inner boss (11a) of the spring cover (11) and reduces the load applied to the unit cell block (2) to a reduced load, wherein the ratio of the reduced load to the second load is in the range of 1:1 to 1:1.2; the method comprises: The spring cover (11) is screwed into the second end plate (4) to increase the load applied to the unit battery block (2) to the first load, wherein the first load is equal to the second load.

16. The method according to claim 14 or 15, wherein: The fuel cell stack (1) includes a top screw in a boss of the spring cover (11). The method includes: screwing the top screw into the inner boss (11a) of the spring cover (11) to transfer the load applied to the unit cell block (2) to the top screw through the added load sensor (10), wherein the first load is equal to the second load.

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