Fuel cell stack
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-05-23
- Publication Date
- 2026-04-01
AI Technical Summary
Conventional fuel cell stacks for mobile applications face issues with transverse forces reducing axial force during clamping, bolt jamming, and settling effects leading to misalignment, which can result in inadequate clamping and increased seizing or cold welding.
A fuel cell stack design where the bolt arrangement features bolts with longitudinal axes angled less than 90° relative to the supporting plate, allowing force introduction without transverse forces, and incorporating a spherical or conical joint for alignment, along with a locking element and rounded end plates to distribute force evenly and prevent edge contact.
This design minimizes transverse forces during clamping, prevents bolt jamming, and maintains optimal alignment, ensuring consistent clamping force and reducing the risk of seizing or cold welding, even with settling effects.
Smart Images
Figure EP2024064274_28112024_PF_FP_ABST
Abstract
Description
[0001] Description
[0002] title
[0003] The invention relates to a fuel cell stack having the features of the preamble of claim 1. The preferred field of application is mobile fuel cell systems or fuel cell vehicles.
[0004] State of the art
[0005] A fuel cell stack, particularly a fuel cell stack for mobile applications, can comprise several hundred fuel cells in a stacked arrangement. The typical structure of a fuel cell stack is explained below using Figure 1.
[0006] Figure 1 shows a fuel cell stack 1 with several fuel cells 2 in a stacked arrangement, arranged between two end plates 3, 4. At least one tensioning band 5 is placed around the fuel cell stack 1, by means of which the fuel cells 2 and the end plates 3, 4 are clamped together. The tensioning band 5 is fixed at each of its two ends by means of a bolt arrangement 6. For this purpose, the bolt arrangement 6 has a bolt 8, which is partially received in a further plate 7, also called an X-plate, and axially supported thereon.
[0007] As shown by way of example in Figure 1, the bolts 8 of the bolt assemblies 6 are each arranged axially offset from the outer clamping band 5. The axial distance Ai between the bolts 8 is smaller than the distance A2 between the clamping band sections arranged on both sides of the fuel cell stack 1. It follows that the force introduction from the bolts 8 to the clamping band 5 for clamping the fuel cells 2 and the end plates 3, 4 is not free of transverse forces. This can result in the transverse force reducing the axial force, so that the axial force may be insufficient. Furthermore, the bolts 8 can become jammed within the X-plate 7. Furthermore, the tendency towards seizure and / or cold welding of the bolts 8 within the X-plate 7 increases. Settling effects that lead to a change in the distance between the X-plate 7 and the next end plate 3 can then no longer be compensated for by the bolts 8.
[0008] The present invention is concerned with the task of further developing a fuel cell stack of the type mentioned at the outset in such a way that the force introduction in the area of a clamping band screw connection is as free from transverse forces as possible.
[0009] To achieve this object, the fuel cell stack having the features of claim 1 is proposed. Advantageous further developments of the invention can be found in the subclaims.
[0010] Disclosure of the invention
[0011] The proposed fuel cell stack comprises a plurality of fuel cells in a stacked arrangement, which are arranged between two end plates and clamped together by means of at least one tensioning strap placed in a U-shape around the fuel cell stack. At least one end of the tensioning strap is fastened by a bolt arrangement to a further plate, which is arranged at a distance a from an end plate, preferably from the lower end plate. According to the invention, the bolt arrangement has a bolt, which is partially received in the further plate and has a longitudinal axis which is set at an angle a < 90° relative to the further plate. This means that the bolt is set at an angle a relative to the further plate.
[0012] Because the bolt is positioned at an angle of a < 90° relative to the other plate, the longitudinal axis of the bolt is not perpendicular to the other plate as usual, but rather diagonally. This angled position compensates for the axial offset between the bolt and the clamping band. This allows the force to be transferred via the bolt into the clamping band without, or at least almost without, shear forces.
[0013] The angle a is measured between the longitudinal axis of the bolt and a plane defined by the additional plate or the main orientation of the additional plate. Regardless of the specific design of the additional plate, the plane runs parallel to the fuel cells as well as to the two end plates or the planes defined by them.
[0014] Preferably, the additional plate has a bolt receptacle with a longitudinal axis that is positioned at an angle ß < 90° relative to the additional plate. The angle ß can be the same as the angle α, so that the bolt is simultaneously aligned when inserted into the bolt receptacle. The bolt's position is then determined by the position of the bolt receptacle. The angle ß and the angle α depend essentially on the axial offset between the bolt receptacle and the clamping band, as well as on the distance α between the additional plate and the end plate.
[0015] Since the distance a between the further plate and the end plate can change due to settling effects, it is advantageous if the bolt receptacle is larger than the bolt itself so that it can realign itself. The angle a is then no longer equal to the angle ß.
[0016] Alternatively or additionally, it is proposed that the further plate has a spherical and / or conical support surface on which the bolt is axially supported via a spherically and / or conically shaped section. The support surface and said bolt section then interact to form a joint that enables self-alignment of the bolt. The joint is preferably designed in the manner of a ball joint so that the bolt can be optimally aligned. The spherical and / or conical support surface of the further plate is preferably formed within the bolt receptacle. The sections of the bolt receptacle adjoining the support surface on both sides are dimensioned such that the bolt has sufficient freedom of movement for self-alignment.
[0017] Advantageously, at least one end of the tensioning strap forms a loop in which a locking element is received, which is connected to the bolt and is preferably screwed. The force is transmitted from the bolt to the tensioning strap via the locking element. The locking element is preferably cylindrical so that no edge presses on the tensioning strap in the area of the loop. For connection, preferably screwing, to the bolt, the locking element can have a transverse bore in which the bolt is received in sections. For screwing, the transverse bore can have an internal thread and the corresponding bolt section can have an external thread. The screw connection between the locking element and the bolt has the advantage that if the tensioning force decreases due to settling effects, the bolt can be tightened further.
[0018] Preferably, the locking element has a longitudinal axis AR, at which the longitudinal axis of the bolt and a longitudinal axis of the tensioning strap, preferably the section of the tensioning strap adjoining the loop, intersect. The intersection simultaneously forms a deflection point through which the force is introduced without transverse forces. This is because the deflection point lies in the extension of the tensioning strap.
[0019] Furthermore, it is proposed that at least one end plate be rounded in the area of the adjacent tensioning band. This means that the surface of at least one end plate intended for the tensioning band is free of edges, so that no edge presses against the tensioning band when the tensioning band is tightened. Preferably, both end plates are rounded in the area of the adjacent tensioning band.
[0020] In a further development of the invention, it is proposed that the end plate, preferably the lower end plate, arranged at a distance a from the further plate be rounded in an edge region over which the clamping band is guided. The rounded edge region expands the edge-free contact surface of the clamping band, so that no edge presses against the clamping band even if the alignment of the bolt is not entirely optimal, for example, due to settling effects.
[0021] Preferably, both ends of the at least one tensioning strap are each attached to the additional plate via a bolt arrangement, so that the tensioning strap can be re-tightened at both ends. The longitudinal axes of the bolts of the two bolt arrangements are each set at an angle a relative to the additional plate. However, the setting is opposite. This means that the alignment of the bolts is mirrored.
[0022] Furthermore, several tensioning straps are preferably placed in a U-shape around the fuel cell stack, preferably at regular intervals. The force applied via the tensioning straps for bracing is thus distributed as evenly as possible.
[0023] Advantageous embodiments of a fuel cell stack according to the invention are explained in more detail below with reference to the attached drawings. These show:
[0024] Fig. 1 is a schematic longitudinal section through a fuel cell stack according to the prior art,
[0025] Fig. 2 shows a schematic longitudinal section through a first fuel cell stack according to the invention in the region of a bolt arrangement for fastening a tensioning strap and
[0026] Fig. 3 shows a schematic longitudinal section through a second fuel cell stack according to the invention in the region of a bolt arrangement for fastening a tensioning strap.
[0027] Detailed description of the drawings
[0028] With regard to Figure 1, which shows the typical structure of a fuel cell stack 1, reference is made to the introduction to the description to avoid repetition. Since the axial distance Ai between the two bolts 8 is smaller than the distance A2 between the clamping band sections arranged on both sides of the fuel cell stack 1, an axial offset occurs between the bolts 8 and the clamping band 5. The force transmission from the bolts 8 to the clamping band 5 is therefore not free of transverse forces.
[0029] In the fuel cell stack 1 of Figure 2, the force introduction is at least approximately free of transverse forces, since the bolts 8 are set at an angle a < 90°.
[0030] This means that the bolt longitudinal axes AB are not perpendicular to the other plate 7, but rather at an angle to it. The angled position compensates for the axial offset between the bolts 8 and the clamping band 5.
[0031] This means that the two bolts 8 are positioned in opposite directions (not shown, as the section in Figure 2 only shows one bolt 8). The bolts 8 are accommodated in bolt receptacles 9 of the further plate 7, the longitudinal axes ABA of which are each positioned at an angle ß relative to the further plate 7, wherein the angle ß essentially corresponds to the angle α. The bolt receptacles 9 have a certain amount of play so that the bolt 8 accommodated therein can realign itself if necessary. This may be necessary, for example, to compensate for settling effects. During settling, the distance a between the further plate 7 and the end plate 3 changes, so that ideally the position of the bolts 8 is adjusted accordingly. This is only possible if the bolt 8 has a certain amount of movement in the bolt receptacle 9. This must be present over the entire length of the bolt receptacle 9.
[0032] The bolt 8 shown in Figure 2 is screwed into a locking element 12 that runs transversely to the bolt 8 and is received in a loop 11 at the end of the tensioning strap 5. Ideally, the longitudinal axis AB of the bolt 8, a longitudinal axis AR of the locking element 12, and a longitudinal axis As of the tensioning strap 5 intersect at a common point. This ensures force introduction without transverse forces. Since this condition can change over time, for example due to settling effects, the end plate 3 has a rounded edge region 13 over which the tensioning strap 5 runs. This prevents a sharp edge from pressing into the tensioning strap 5.
[0033] Figure 3 shows a further embodiment of a fuel cell stack 1 according to the invention. This differs from that of Figure 2 essentially in that the bolt receptacle 9 in the further plate 7 does not have an adjusted longitudinal axis ABA, but instead has a conical support surface 14, via which the bolt 8 is axially supported. The bolt 8 also has a section 10 that is spherically shaped and, together with the conical support surface 14, interacts to form a joint. The joint ensures that the bolt 8 can optimally align itself. The bolt receptacle 9 is again sufficiently large to provide the necessary movement space.
Claims
Claims 1. A fuel cell stack (1) comprising a plurality of fuel cells (2) in a stacked arrangement, which are arranged between two end plates (3, 4) and are clamped together by means of at least one tensioning band (5) placed in a U-shape around the fuel cell stack (1), wherein at least one end of the tensioning band (5) is fastened by means of a bolt arrangement (6) to a further plate (7) which is arranged at a distance (a) from an end plate (3, 4), preferably from the lower end plate (3), characterized in that the bolt arrangement (6) has a bolt (8) which is partially received in the further plate (7) and has a longitudinal axis (AB), wherein the longitudinal axis (AB) is set at an angle (a) < 90° with respect to the further plate (7).
2. Fuel cell stack (1) according to claim 1, characterized in that the further plate (7) has a bolt receptacle (9) with a longitudinal axis (ABA) which is set at an angle (ß) < 90° with respect to the further plate (7).
3. Fuel cell stack (1) according to claim 1 or 2, characterized in that the further plate (7) has a spherically and / or conically designed support surface (14) on which the bolt (8) is axially supported via a spherically and / or conically shaped section (10).
4. Fuel cell stack (1) according to one of the preceding claims, characterized in that at least one end of the tensioning band (5) forms a loop (11) in which a locking element (12) connected to the bolt (8), preferably screwed, is received.
5. Fuel cell stack (1) according to claim 4, characterized in that the locking element (12) has a longitudinal axis (AR) on which the longitudinal axis (AB) of the bolt (8) and a longitudinal axis (As) of the tensioning band (5), preferably of the section of the tensioning band (5) adjoining the loop (11), intersect.
6. Fuel cell stack (1) according to one of the preceding claims, characterized in that at least one end plate (3, 4) is rounded in the region of the adjacent clamping band (5).
7. Fuel cell stack (1) according to one of the preceding claims, characterized in that the end plate (3, 4) arranged at a distance (a) from the further plate (7), preferably the lower end plate (3), is rounded in an edge region (13) over which the tensioning band (5) is guided.
8. Fuel cell stack (1) according to one of the preceding claims, characterized in that both ends of the at least one tensioning band (5) are each fastened to the further plate (7) via a bolt arrangement (6), wherein the longitudinal axes (AB) of the bolts (8) of the two bolt arrangements (6) are each adjusted by the angle (a) relative to the further plate (7), but the adjustment is in the opposite direction.
9. Fuel cell stack (1) according to one of the preceding claims, characterized in that a plurality of tensioning bands (5) are placed in a U-shape around the fuel cell stack (1) at preferably regular intervals.