Tensioning belt with corrugated profile compensation structure

Abstract

The invention relates to a tensioning band (10) for strapping a fuel cell stack (20), wherein the fuel cell stack (20) is configured to undergo a predetermined periodic dimensional change, and wherein the tensioning band comprises two end portions (12a, 12b) and an elastic compensation structure (14a, 14b) which is capable of compensating for a predetermined length change of the tensioning band (10) corresponding to the periodic dimensional change of the object, wherein at least a central portion of the compensation structure (14a, 14b) has a periodic corrugation profile with an amplitude A and a period L in a tensioned configuration of the tensioning band (10). It is proposed that in a first region around the maximum and minimum turning points of the corrugation profile, the curvature of the profile is at least 5% smaller than the curvature of a sinusoidal profile with the same amplitude A and period L at its maximum or minimum turning points.

Description

Technical Field

[0001] The present invention relates to a tensioning belt for a fuel cell stack according to claim 1, a fuel cell stack including the tensioning belt, and a method for assembling such a fuel cell stack. Background Technology

[0002] Fuel cells are used to provide electrical energy through electrochemical reactions. To increase available power, multiple fuel cells can be connected in series to form a fuel cell stack. Each fuel cell includes a membrane electrode assembly (MEA) having an anode, a cathode, and a proton-conducting membrane separating the anode and cathode. This proton-conducting membrane is coated with a catalyst to facilitate the electrochemical reaction. Furthermore, in the fuel cell stack, at least the central fuel cell has bipolar plates on both sides of the membrane to supply reactants and, if necessary, coolant. Additionally, a gas diffusion layer is used to distribute the reactants supplied from the bipolar plates as uniformly as possible across the entire surface of the catalyst-coated membrane. Since the open-circuit voltage of a fuel cell is typically about 1 volt (V), and the maximum permissible voltage in the high-voltage system of a fuel cell stack is, for example, 330 V, a fuel cell stack can be formed with 330 MEAs, 228 bipolar plates, and two end plates.

[0003] Multiple fuel cells assembled in a fuel cell stack are typically compressed together by tensioning elements with forces on the order of tons to achieve sufficient contact pressure on the catalyst coating membrane, thereby reducing ohmic losses and preventing leakage of the inserted seals due to high compression. The internal resistance of the compressed fuel cell depends on the compression force, which has an optimal value that minimizes internal resistance.

[0004] However, it should be noted that forces can be generated during fuel cell stack operation that may increase or decrease the clamping force. Increased clamping force is caused by the thermal expansion of the components used, the pressure used to supply and distribute reactants, and the swelling of the membranes used during hydration.

[0005] The decrease in compressive force may be caused by negative thermal expansion at low temperatures or when the temperature drops, or by the settling behavior of the gas diffusion layer. This settling behavior appears after the fuel cell stack is first put into operation and increases with the time of use, and then intensifies as the fuel cell stack ages.

[0006] Document EP 1 870 952 A2 discloses a fuel cell stack according to the preamble of claim 1, the fuel cell stack having a tension band with an elastic compensation structure having a wavy or serrated profile, wherein the end of the band is attached to the lower end plate of the fuel cell stack or connected to one side of the fuel cell stack. Document DE 103 43 766 A1 discloses another example of a wavy or corrugated compensation structure.

[0007] Furthermore, assembling fuel cell stacks can be challenging because tensioning elements need to be pre-tensioned properly and uniformly, preferably in a cost-effective manner that avoids complex mechanical components. Uniform and controlled pre-tensioning of the tensioning elements ultimately results in efficient, high-quality, and long-life fuel cell stacks. Summary of the Invention

[0008] The problem upon which this invention is based is to provide a tension belt with a structure that can increase the range of elasticity and cycle life, an improved fuel cell stack, and a method for assembling a fuel cell stack.

[0009] According to a first aspect of the invention, this problem is solved by a device having the features of claim 1. Advantageous embodiments of the invention are defined in the dependent claims.

[0010] The inventors have proposed a tensioning band for bundling fuel cell stacks, wherein the fuel cell stacks are configured to undergo predetermined periodic dimensional changes, and the tensioning band includes two ends and an elastic compensation structure capable of compensating for predetermined length changes of the tensioning band corresponding to the periodic dimensional changes of the object, wherein, in the tensioning configuration of the tensioning band, at least the central portion of the compensation structure has a periodic corrugated profile with amplitude A and period L.

[0011] The inventors propose that, in a first region surrounding the maximum and minimum inflection points of the corrugated profile, the curvature of the profile is at least 5% smaller than that of a sinusoidal profile with the same amplitude A and period length L at its maximum or minimum inflection point, or alternatively at least 10% or at least 20% smaller.

[0012] Regions with higher curvature should preferably occupy a considerable portion of the period length L, particularly at least 5% of the period length L, and preferably at least 10% of the period length L.

[0013] The tensioning band according to the present invention is preferably a metal band having a pre-formed corrugated profile and other structures such as clamping structures, joining structures or end rings.

[0014] By using this profile, the local curvature variation of the strip near its maximum and minimum values ​​is smaller than that of known strips with sinusoidal or sawtooth profiles. Given that the material strengthening of spring steel depends on the bending radius or bending curvature, this shape ensures more uniform bending strength, whereas a profile with non-uniform curvature results in non-uniform bending strength, where the weaker portions exhibit inelastic behavior and / or fatigue at lower threshold tensions and / or fewer cycles.

[0015] In the context of this invention, the term "curvature" refers to the reciprocal of the radius of curvature.

[0016] In the context of this invention, the term "periodic" can refer to periodic temperature changes that cause periodic thermal expansion / contraction cycles, or to other cycles, such as the periodic expansion of the tank diameter caused by the periodic filling and emptying of a high-pressure tank.

[0017] Furthermore, in the context of this invention, if all the small segments, except for those connecting the regions, have certain curvature values, then the profile is considered to be "substantially" composed of regions having these curvature values, wherein, when measured along the shape of the strip, the total length of these small segments is preferably less than 10% of the total length of the corrugated portion, more preferably less than 20% of the total length of the corrugated portion.

[0018] The inventors further propose that, in a second region between the adjacent maximum and minimum inflection points of at least one corrugated profile, the curvature is greater than the curvature at the maximum and minimum inflection points of the corrugated profile.

[0019] In a preferred embodiment of the present invention, the corrugated profile can be represented as follows:

[0020]

[0021] Where L is the period length of the periodic corrugated profile, H(x) is the height of the profile above its average height, and 0.05 ≤ a1 / a0 ≤ 1. The profile of the tension belt according to the invention is not a perfect sine wave, but includes non-negligible higher harmonics, particularly the first harmonic a1, which contributes to the overall elasticity of the belt, especially within the tension range encountered in the actual use of fuel cells.

[0022] Furthermore, the end of the compensation structure is formed to include an outermost portion shaped as an arc extending within an angular range of approximately 30°, followed by an adjacent portion with reverse curvature extending within an angular range of approximately 60°. In this document, "approximately" should be understood to indicate a tolerance range of ±10°.

[0023] Furthermore, it is proposed that the tension belt includes two compensation structures, which are arranged in a position that is mirror-symmetrical to each other and have a configuration that is mirror-symmetrical to each other.

[0024] According to another aspect of the invention, the inventors have proposed a fuel cell stack comprising an upper end plate and a lower end plate, a stack having a plurality of bipolar plates sandwiched between the end plates, and at least one tension band, wherein the tension band includes two ends and at least an elastic compensation structure, and wherein the tension band extends around the entire fuel cell stack including the upper end plate and the lower end plate.

[0025] The proposed structure comprises an elastic compensation structure disposed in the side portion of the tensioning band extending along the stacking direction, with its ends positioned at or above the upper end plate and / or below the lower end plate of the fuel cell stack. By closing the tensioning band at the top of the fuel cell stack, the force is evenly distributed across the sides due to symmetrical tension and friction. The same applies when closing it below the lower end plate.

[0026] According to another aspect of the present invention, a fuel cell stack is provided, comprising an upper end plate and a lower end plate, a stack having a plurality of bipolar plates sandwiched between the end plates, and at least one tensioning band, wherein the tensioning band includes two ends and at least an elastic compensation structure.

[0027] The proposed structure is an elastic compensation structure that extends along the stacking direction and whose ends are connected to both the upper and lower end plates.

[0028] Preferably, at least one end includes a clamping structure formed as a hole, which is configured to engage with hooks disposed on the upper end plate and / or lower end plate. Similar to the case of closing tension bands below the top or lower end plate of a fuel cell stack, arranging multiple tension bands and multiple attachment points in a symmetrical manner helps to achieve a uniform, symmetrical force distribution.

[0029] In a preferred embodiment of the fuel cell stack or tension belt according to the invention, the tension belt includes a joining structure or clamping structure for a tensioning mechanism at the top of its side portion.

[0030] When the ends are connected by welding or crimping, cost-effective and reliable assembly can be achieved.

[0031] Alternatively, the ends are connected via a tensioning mechanism.

[0032] Another aspect of the invention relates to a method for assembling a fuel cell stack as described above. The method includes the steps of: clamping a stack having a plurality of bipolar plates between end plates, pulling two ends while applying pressure to the upper end plate of the fuel cell stack, and connecting the ends of tension bands to each other or to the end plates.

[0033] Other features and advantages will become apparent from the following description of the embodiments and accompanying drawings. The features of the invention are disclosed throughout the specification, claims, and drawings by way of specific embodiments and combinations. Those skilled in the art will also consider these features individually and combine them into other combinations or sub-combinations to suit their needs or specific fields of application. Attached Figure Description

[0034] The attached diagram shows the following:

[0035] Figure 1 A tensioning band according to a first embodiment of the present invention is shown;

[0036] Figure 2 A detailed outline diagram of the compensation structure in the tension belt according to the present invention is shown;

[0037] Figure 3 The system shown includes a tension belt and a fuel cell stack;

[0038] Figure 4 An exemplary fuel cell stack with two different embodiments of a leaf spring according to the prior art and a tension belt according to the present invention is shown;

[0039] Figure 5 A fuel cell stack according to the present invention and an assembly method according to the present invention are shown. Detailed Implementation

[0040] Figure 1 A tension band 10 according to a first embodiment of the present invention is shown. The tension band 10 is designed to bind a fuel cell stack 20 as an object with a force equal to or less than the yield force Fwy. Figure 3 In this configuration, the object is configured to undergo predetermined periodic dimensional changes, and the tension band 10 is made of spring steel strip having a Young's modulus E, yield strength Re, and cross-sectional area A. The tension band 10 is pre-formed into a generally rectangular shape corresponding to the shape of the fuel cell stack 20 (see [reference]). Figure 3 The tension belt 10 includes two ends 12a and 12b and two elastic compensation structures 14a and 14b. The ends 12a and 12b are formed as loops for attaching to the closure and tensioning structures. The elastic compensation structures 14a and 14b are configured to be arranged on the vertical sides of the fuel cell stack 20 and are capable of compensating for a predetermined length change ΔL corresponding to periodic dimensional changes in the tension belt 10. The two compensation structures 14a and 14b are arranged in a position mirror-symmetrical to each other with respect to the midpoint P of the belt and have a mirror-symmetrical configuration with respect to that midpoint. The lower portion 14c of the tension belt 10 is flat and is configured to pass under the bottom side of the fuel cell stack 20.

[0041] In the tensioned and untensioned configurations of the tensioned belt 10, at least the central portion of the compensation structures 14a and 14b has a periodic corrugated profile with amplitude A and period L, wherein amplitude A and period L obviously depend on the tension state.

[0042] Furthermore, in the second region between adjacent maximum and minimum inflection points, specifically between each maximum or minimum inflection point and an adjacent inflection point, the curvature changes sign after becoming zero at that adjacent inflection point. The curvature is greater than the curvature of a sine curve profile with the same amplitude A and period L at the corresponding point, and may even be greater than the curvature at the maximum and minimum inflection points of the ripple profile.

[0043] In a preferred embodiment of the present invention, the corrugated profile can be represented as follows:

[0044]

[0045] Where L is the period length of the periodic wavy profile, H(x) is the height of the profile above its average height, and 0.05≤a1 / a0≤1.

[0046] Figure 2 It shows that when a1 / a0 = 0.1 and for n ≥ 2, a n When the value is 0, the profiles of the compensation structures 14a and 14b of the tension band 10 in the tension configuration are shown. In this configuration, the compensation structures 14a and 14b have a corrugated profile with a period L and an amplitude A. This corrugated profile is not sinusoidal but is essentially composed of portions formed as flat arcs with alternating curvature directions. The local curvature of the profile is expressed as the second derivative of the graph describing the profile and is shown together with the local curvature of a sinusoidal profile with the same amplitude and period length.

[0047] According to the invention, in a first region R1 surrounding the maximum and minimum inflection points of the corrugated profile, the curvature of the profile is at least 5% smaller than that of a sinusoidal profile with the same amplitude A and period L at its maximum or minimum inflection point.

[0048] Furthermore, in the second region R2 between the adjacent maximum and minimum inflection points of the wavy profile, the curvature is greater than the curvature at the maximum and minimum inflection points of the wavy profile.

[0049] It should be noted that, in the context of this specification, when comparing curvature, the absolute value of the curvature is being compared, especially the absolute value of the second derivative of the figure describing the contour, specifically the centerline of the tensioned band along its thickness direction when viewed from the side.

[0050] This shape ensures uniform bending strength, while a profile with non-uniform curvature results in non-uniform bending strength, where the weaker portions exhibit inelastic behavior and / or fatigue at lower threshold tension and / or fewer cycles.

[0051] Figure 3 A fuel cell stack 20 according to the present invention is shown. The fuel cell stack 20 has specifications in which its height and width change periodically according to temperature, wherein, by setting the maximum stroke ΔL of the two compensation structures 14a, 14b, the compensation structures 14a, 14b jointly compensate for the total change in the perimeter of the fuel cell stack 20, making the tension belt 10 suitable for its use.

[0052] The fuel cell stack 20 includes an upper end plate 16a and a lower end plate 16b, a stack having a plurality of bipolar plates 18 sandwiched between the end plates 16a and 16b, and in Figure 3 The diagram shows three tensioning bands 10, each including two ends 12a, 12b and two elastic compensation structures 14a, 14b. The tensioning bands 10 extend around the entire fuel cell stack, including the upper end plate 16a and the lower end plate 16b.

[0053] Elastic compensation structures 14a and 14b are disposed in the sides of the tension band 10 extending in the stacking direction, and the ends 12a and 12b are arranged and connected at or above the upper end plate 16a of the fuel cell stack 20, such that the tension band 10 can be closed at the top of the fuel cell stack 20. In an alternative embodiment of the invention, the tension band 10 can be closed below the bottom of the fuel cell stack 20.

[0054] Figure 4 Another example of a fuel cell stack 20 according to the present invention is shown. For illustration, Figure 4 Not only are two different examples of tensioning bands 10a and 10b according to the invention shown, but also a tensioning system 24 according to the prior art is shown, which includes a leaf spring 24a or a disc spring arranged as a compensation structure between the stack of the top plate 24b and the bipolar plate 18.

[0055] A joining structure or clamping structure 22a is provided on the top of each side of the tensioning bands 10a and 10b, the joining structure or clamping structure 22a being formed as a punch for the tensioning mechanism.

[0056] Tensioning belts 10a and 10b are also provided with embossed portions 26, which ensure lateral offset of the lateral vertical portions of tensioning belts 10a and 10b, ensuring sufficient distance between the trough of the compensation structure 14a and the bipolar plate 18, thereby preventing short circuits. The tensioning mechanism... Figure 5 As shown in the image.

[0057] Depending on the specific circumstances, ends 12a and 12b are connected by welding or by pressing and stamping.

[0058] Alternatively, ends 12a and 12b are connected by a tensioning mechanism 28, such as... Figure 3 The image shows one of the tensioning bands.

[0059] Figure 5 A fuel cell stack 20 according to the invention and an assembly method according to the invention are shown. Figure 5In one embodiment, the fuel cell stack 20 includes an upper end plate 16a and a lower end plate 16b, a stack having a plurality of bipolar plates 18 sandwiched between the end plates 16a and 16b, and a plurality of tension bands 10a–10c. Each of the tension bands 10a–10c includes two ends 12a and 12b and an elastic compensation structure 14a extending along the stacking direction.

[0060] exist Figure 5 In one embodiment, each of the ends 12a and 12b is connected to one of the upper end plate 16a and the lower end plate 16b by a form-fit connection. Specifically, in Figure 5 In one embodiment, each of the ends 12a and 12b includes a clamping structure 22c formed as a hole, which is configured to engage with hooks 26 respectively provided on the upper end plate 16a and the lower end plate 16b.

[0061] The tensioning band 10 also includes a engagement structure or clamping structure 22a for the tensioning mechanism 28, which is disposed in the upper end 12a of each tensioning band 10.

[0062] The tensioning mechanism 28 is formed as a lifting column with a hook 28a, which is configured to engage with the clamping structure 22a of the tensioning band 10. For assembly, the tensioning band 10 is connected to the lower end plate 16b via a hook hole. Subsequently, the hook 28a of the tensioning mechanism 28 is engaged with the clamping structure 22a, and the tensioning mechanism 28 is operated to pull the upper end 12a of the band upward with a pre-tension force F1. At the same time, a support force F2 is applied to the upper end plate 16a in the opposite direction to the pre-tension force F1, and the hook 26 of the upper end plate is engaged with the clamping structure 22c (hole) of the tensioning band 10.

[0063] Although Figure 5 Only one tensioning mechanism 28 is shown, but those skilled in the art will understand that multiple tensioning mechanisms can be operated simultaneously to pretension multiple tensioning bands 10, particularly the tensioning bands on opposite sides of the fuel cell stack.

[0064] It should be noted that, although Figure 1 and Figures 3 to 5 The corrugated portion in the tension belt 10 shown according to the invention is an elastic compensation structure 14a, which prevents the belt 10 from twisting, i.e., the width direction of the belt 10 does not change along the longitudinal direction of the belt 10, and the amplitude of the wave is oriented in a direction perpendicular to the width direction. However, in other embodiments of the invention not shown, the belt 10 may twist. For example, the wave in the elastic compensation structure 14a may rotate 90° around the longitudinal direction of the tension belt 10, i.e., the belt 10 twists 90° above and below the compensation structure 14a.

[0065] List of reference numerals

[0066] 10 tension bands

[0067] 10a Outermost part

[0068] 10b Adjacent parts

[0069] Ends of 12a and 12b

[0070] Compensation structures 14a and 14b

[0071] The lower part of the 14c tension belt

[0072] 16a Top Plate

[0073] 16b lower end plate

[0074] 18 bipolar plates

[0075] 20 Fuel Cell Stacks

[0076] 22a, 22b Joint structure or clamping structure

[0077] 26 hooks

[0078] 28 tensioning mechanisms

[0079] 28a hook

[0080] Midpoint of P.

Claims

1. A tensioning band (10) for securing a fuel cell stack (20), wherein, The fuel cell stack (20) is configured to undergo predetermined periodic dimensional changes, and wherein the tension band (10) includes two ends (12a, 12b) and elastic compensation structures (14a, 14b) capable of compensating for predetermined length changes of the tension band (10) corresponding to the periodic dimensional changes of the object. In the tensioning configuration of the tensioning band (10), at least the central portion of the compensation structure (14a, 14b) has a periodic corrugated profile with amplitude A and period L. The feature is that, in a first region surrounding the maximum and minimum inflection points of the corrugated profile, the curvature of the profile is at least 5% smaller than that of a sinusoidal profile with the same amplitude A and period L at its maximum or minimum inflection point.

2. The tensioning band (10) according to claim 1. Its features are, In a second region between at least one adjacent maximum and minimum inflection point of the corrugated profile, the curvature is greater than the curvature at the maximum and minimum inflection points of the corrugated profile.

3. The tensioning band (10) according to claim 1 or 2, characterized in that, The ripple profile can be represented as Where L is the period length of the periodic wavy profile, H(x) is the height of the profile above its average height, and 0.05≤a1 / a0≤1.

4. The tension band (10) according to any one of the preceding claims. Its features are, The ends (12a, 12b) of the compensation structure (14a, 14b) are formed as the outermost portion, which is shaped as an arc extending within an angle range of about 30°, followed by an adjacent portion with reverse curvature extending within an angle range of about 60°.

5. The tension band (10) according to any one of the preceding claims. Its features are, The curvature of the profile is at least 10% smaller than that of a sinusoidal profile with the same amplitude A and period L at its maximum or minimum inflection point.

6. The tension band (10) according to any one of the preceding claims. Its features are, The curvature of the profile is at least 20% smaller than that of a sinusoidal profile with the same amplitude A and period L at its maximum or minimum inflection point.

7. The tension band (10) according to any one of the preceding claims. Its features are, The tension band (10) includes two compensation structures (14a, 14b) arranged in a position that is mirror-symmetrical to each other and have a configuration that is mirror-symmetrical to each other.

8. A fuel stack comprising a tensioning belt (10) according to any one of the preceding claims.

9. A fuel cell stack comprising an upper end plate (16a) and a lower end plate (16b), a stack having a plurality of bipolar plates (18) sandwiched between the end plates (16a, 16b), and at least one tensioning band (10), wherein, The tension band (10) includes two ends (12a, 12b) and at least elastic compensation structures (14a, 14b), wherein the tension band (10) extends around the entire fuel cell stack including the upper end plate (16a) and the lower end plate (16b). The elastic compensation structure (14a, 14b) is disposed in the side of the tension band (10) extending in the stacking direction, and the ends (12a, 12b) are arranged and connected to the upper end plate (16a) or above the lower end plate (16b) of the fuel cell stack (20).

10. A fuel cell stack comprising an upper end plate (16a) and a lower end plate (16b), a stack having a plurality of bipolar plates (18) sandwiched between the end plates (16a, 16b), and at least one tensioning band (10), wherein, The tension band (10) includes two ends (12a, 12b) and at least elastic compensation structures (14a, 14b). The elastic compensation structure (14a, 14b) extends along the stacking direction, and the ends (12a, 12b) are connected to both the upper end plate (16a) and the lower end plate (16b).

11. The fuel cell stack according to claim 10, Its features are, At least one of the ends (12a, 12b) includes a clamping structure (22c) formed as a hole, the clamping structure (22c) being configured to engage with a hook disposed on the upper end plate (16a) and / or the lower end plate (16b).

12. The fuel cell stack according to any one of claims 9 to 11, Its features are, A coupling structure or clamping structure (22a, 22b) for the tensioning mechanism is provided on the top of the side portion.

13. The fuel cell stack according to claim 9, Its features are, The ends (12a, 12b) are connected by welding.

14. The fuel cell stack according to claim 9, Its features are, The ends (12a, 12b) are connected by crimping.

15. The fuel cell stack according to claim 9, Its features are, The ends (12a, 12b) are connected by a tensioning mechanism.

16. The fuel cell stack according to any one of claims 9 to 15, Its features are, The tension band is the tension band according to any one of claims 1 to 7.

17. A method for assembling a fuel cell stack according to any one of claims 9 to 14, the method comprising the following steps: - A stack having multiple bipolar plates (18) is sandwiched between the end plates (16a, 16b). - While applying pressure to the upper end plate (16a) of the fuel cell stack, pull the two ends (12a, 12b), and - Connect the ends (12a, 12b) of the tension band (10) to each other or to the end plates (16a, 16b).

18. The method according to claim 17, characterized in that, The step includes binding the tension band (10) around the entire fuel cell stack, including the upper end plate (16a) and the lower end plate (16b).

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