Fuel cell stack
Patent Information
- Application Number
- EP2023741252
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-07-11
- Filing Date
- 2023-07-04
- Publication Date
- 2025-05-21
AI Technical Summary
Fuel cell stacks for aircraft applications face challenges in achieving uniform force transmission and adapting to different operating conditions due to curvature and reduced profile thickness requirements for lightweight construction, which affects contact pressure and mechanical stability.
The use of convexly curved arch profiles as spring elements decoupled from each other, supported by pairs of carriers, allows for independent adaptation of contact pressure across the surface, with varying curvature and thickness to compensate for center-edge differences and provide localized pressure adjustments, ensuring sufficient contact force and mechanical stability.
This design achieves uniform and adjustable contact pressure across the fuel cell stack, enhancing mechanical stability and accommodating various fuel cell designs and operating conditions, even with reduced profile thickness, thereby supporting lightweight construction and efficient energy transmission.
Smart Images
Figure 1.1
Abstract
Description
[0001] FUEL CELL STACK
[0002] DESCRIPTION
[0003] Technical area
[0004] The present invention relates to a fuel cell stack, in particular for a propulsion unit of an aircraft.
[0005] State of the art
[0006] In a fuel cell stack, also known as a fuel cell stack, several fuel cells are arranged one behind the other in a stacking direction. A channel plate with a channel structure for gas distribution or cooling, such as a bipolar plate, can be arranged between each cell. The power or voltage of the stack can be adjusted to the application by varying the number of fuel cells connected in series in this way.
[0007] Description of the invention
[0008] The present invention is based on the technical problem of providing an advantageous fuel cell stack.
[0009] This is achieved according to the invention with the fuel cell stack according to claim 1. This comprises an inner and an outer cover element which hold the fuel cells together with a pressing force. The outer cover element forms a plurality of spring elements perpendicular to the stacking direction which, when tensioned, are pressed against the inner cover element, which then transfers the pressing force to the stacked fuel cells. The spring elements are constructed in such a way that they each form an arched profile which is convexly curved towards the inner cover element. These arched profiles are suspended separately for each spring element and are therefore decoupled from one another. The inner cover element accommodates the arched profiles; for each spring element it forms a respective receptacle which is concavely curved away from the stacked fuel cells and in which the respective arched profile is arranged. By using the convexly curved arched profiles, for example,By achieving comparatively large area moments of inertia, sufficient transmission of the contact force can be ensured, for example, even with a reduced profile thickness. Reducing the profile thickness can be of interest in light of lightweight construction requirements and thus in mobility applications, particularly in the aviation sector. The combination of a convex profile and a concave mount, which lie flat against each other when clamped, can also result in a more even force transmission across the surface. For example, it can specifically counteract a force introduction that might otherwise be reduced in the center due to warping.
[0010] Due to the "separate suspension," the individual arched profiles are decoupled from one another. This means that, for example, the deflection, deformation, or application of pressure to one arched profile does not automatically cause the next adjacent arched profile to deflect or deform. This allows the adjacent spring elements to be specifically adapted to the contact pressure required in their respective surface area without any interaction between the areas. Dividing the system into several spring elements connected in parallel can, for example, help further compensate for a center / edge difference. For example, a stiffer spring element can be provided in the center so that, despite any warping of the cover elements, for example as a result of bracing with tension rods running laterally alongside the stacked cells, a sufficiently large contact pressure can be applied in the center.
[0011] By using multiple spring elements, it is also possible to address different operating conditions or fuel cell designs, for example (e.g. segmentation, see details below). This means that the contact pressure can be made more uniform over the entire surface and, due to the special design of the respective spring element, even within its partial surface, or that a different contact pressure can be set locally, for example in the area of a seal. Preferred embodiments can be found in the dependent claims and the disclosure as a whole, although the presentation of the features does not always distinguish individually between device and method or use aspects; in any case, the disclosure is to be read implicitly with regard to all claim categories. If, for example, a specific fuel cell stack is described, this is simultaneously a disclosure of a drive unit with such a stack orits application in an aircraft or aircraft.
[0012] The fuel cells are arranged one after the other in the “stacking direction,” and perpendicular to this, they each have their planar extent (and their area is determined accordingly). In detail, the respective fuel cell can, for example, have a catalyst-coated membrane layer or “catalyst membrane layer” and a plate, in particular a bipolar plate, which forms a channel structure (flow field) via which the catalyst membrane layer can be supplied with a reaction gas, for example. This channel structure can, for example, be sealed to the outside with a seal and / or, in the case of segmentation, also across the surface, with the seal then also being clamped into the stack. This can result in locally different stiffness across the surface of the stack, which can be at least partially compensated for, for example, by appropriately adapting the spring element arranged in the respective area (the seal or the catalyst membrane layer). For example, ifIf a higher contact pressure is required in one surface area of the stack, a stiffer spring element can be arranged in alignment with it in the stacking direction (increased stiffness through, for example, greater profile thickness and / or stiffened supports or smaller curvature of the arch profile).
[0013] The first and second spring elements, i.e., the at least two spring elements of the outer cover element, each form an arcuate profile. Viewed in a sectional plane parallel to the stacking direction and perpendicular to a curvature axis around which the respective arcuate profile is curved, the profile describes an arcuate line that is convexly curved as seen from the inner cover element and thus the fuel cells. In general, the profile can vary perpendicular to said sectional plane; for example, the arcuate line can assume different lengths. However, an arcuate profile that is translationally symmetrical along the curvature axis is preferred.
[0014] Preferably, the arc profile is exclusively convexly curved, meaning that the sign of the curvature does not change along the arc line. Reference to the "axis of curvature" does not necessarily imply a curvature with a constant radius; the arc line viewed in section can, for example, follow different radii of curvature along its course. The axis of curvature of the arc profile is determined by its maximum curvature, i.e., the point closest to the fuel cells.
[0015] According to a preferred embodiment, each arched profile is suspended from a respective pair of supports, specifically from its own pair of supports due to the desired decoupling. Two adjacent arched profiles therefore do not share a support, for example, which would contradict the desired decoupling. Each of the spring elements has a first and a second support, which together support the respective arched profile of the respective spring element and, for the sake of simplicity, are referred to as its "pair of supports" or "pair of supports."
[0016] In general, in addition to the first and second supports, a further support can be provided for each spring element or arched profile, meaning that the arched profile can be suspended from more than two points when viewed in the aforementioned sectional plane. However, it is preferably suspended exclusively from the first and second supports, meaning that the pair of supports alone supports the arched profile. Viewed in the aforementioned section, the first and second supports converge toward each other away from the inner cover element, thus forming struts of the arched line. They preferably meet at a single suspension point.
[0017] This suspension point is preferably aligned with the associated support profile in the stacking direction, i.e., not laterally offset. In a preferred embodiment, the suspension point is aligned with the maximum of the arc profile, i.e., the maximum and the suspension point lie on a common straight line parallel to the stacking direction (viewed in said section). The maximum of the arc profile, viewed in the section, is the point on the arc profile closest to the stacked fuel cells.
[0018] According to a preferred embodiment, the first and second supports of the respective support pair are mirror-symmetrical to each other when viewed in section. The corresponding mirror axis is preferably parallel to the stacking direction and / or passes through the maximum and the suspension point (see above), preferably both.
[0019] Whenever a "lateral direction" is generally referred to, it is directed sideways, i.e., perpendicular to the stacking direction. In detail, a distinction is then made between a first lateral direction and a second lateral direction, which is perpendicular to it. The first lateral direction is, by definition, perpendicular to the axis of curvature of the arched profile of the first spring element. The "section" mentioned above in connection with the geometry of the profile and / or the beams—specifically, the associated section plane—is parallel to the first lateral direction (and the stacking direction). The second lateral direction is parallel to the axis of curvature and thus perpendicular to the first lateral direction.
[0020] In a preferred embodiment, at least two spring elements are arranged next to one another in the first lateral direction and / or in the second lateral direction. In principle, a matrix of any size can be spanned, naturally also depending on the area of the fuel cell stack (theoretical upper limits of the spring elements arranged next to one another in a respective direction can be, for example, a maximum of 1,000, 500, 100, 50, or 20). In general, the spring elements can also be "twisted" relative to one another; for example, the axis of curvature of the curved profile of the second spring element can be angled to that of the first spring element. However, an arrangement with mutually parallel axes of curvature is preferred, which more preferably applies to all spring elements of the outer cover element.With a view to standardizing and simplifying the geometry, a structure may be preferred in such a way that at least some or all of the spring elements arranged next to one another in the first lateral direction are translationally symmetrical to one another (in the first lateral direction) and / or spring elements arranged next to one another in the second lateral direction are translationally symmetrical to one another (in the second lateral direction), in each case at least in groups.
[0021] According to a preferred embodiment, the first and second spring elements differ in the curvature of their arched profiles and / or the thickness of their arched profiles and / or the stiffness of their respective arched profile suspensions, i.e., in particular, the support pairs. With a greater curvature, i.e., a smaller radius of curvature, and / or a greater profile thickness, a stiffer spring can be achieved, for example, which also applies to the suspension. This not only makes it possible, for example, to even out the contact pressure across the surface, but also to specifically set a higher contact pressure in specific areas. This allows, for example, the contact pressure to be adapted in the area of seals; see the initial comments.
[0022] According to a preferred embodiment, the first and second spring elements occupy different surface areas. For example, projection areas resulting from a vertical projection of the respective arched profile into a plane perpendicular to the stacking direction are therefore different in size. All spring elements can differ in their respective occupied surface areas; however, there can also be spring elements with groups having the same surface areas, with only a difference from group to group. With the (at least partially) different surface areas of the spring elements, the outer cover element can be tailored to the fuel cells (sealing areas and / or segmented areas, see below).
[0023] According to a preferred embodiment, at least one of the spring elements is suspended in the stacking direction in alignment with a cavity formed in the outer cover element. This cavity can be supplied with a fluid, for which purpose, for example, a fluid channel can open into the cavity. The fluid can be a gas or a liquid, and by supplying fluid to the cavity, a certain deformation of the outer cover element and thus an offset of the at least one spring element towards the inner cover element can be achieved. This can be used, for example, for fine adjustment, for example to compensate for production fluctuations. Alternatively or additionally, the supply of fluid and the associated increase in the contact pressure of the at least one spring element can also serve, for example, to adapt to specific operating conditions.
[0024] In a preferred embodiment, the first and second spring elements are each assigned their own cavity in the outer cover element, and these cavities can be independently pressurized with a fluid, thus allowing the respective contact pressure of each spring element to be adjusted independently. Each of the spring elements can be assigned its own cavity; alternatively, however, spring elements in groups can also be assigned to the same cavity, or some of the spring elements can be assigned no cavity at all (e.g., those at the edge).
[0025] As mentioned at the beginning, each fuel cell can have a respective catalyst membrane layer, which, for example, separates hydrogen and oxygen and simultaneously transports the protons from the anode to the cathode. Preferably, at least in the core of the stack, each catalyst membrane layer is enclosed on both sides by a respective bipolar plate; the bipolar plates preferably form a respective channel structure on both sides, thus also for the respective next-to-neighbor fuel cells or catalyst membrane layers. In the stacking direction, between each respective channel structure and the bipolar plate, a gas diffusion layer can additionally be provided, which, for example, distributes the reaction gas to the electrode of the catalyst membrane layer and conducts the current from there (e.g., also water and heat).
[0026] According to a preferred embodiment, at least one of the fuel cells in the stack is segmented, i.e., divided into at least two segments. For this purpose, the catalyst membrane layer and / or the channel structure can be segmented, and if present, the gas diffusion layer, for example, can also be segmented. Irrespective of these details, the fuel cell segments resulting from this subdivision can preferably be sealed to one another, i.e., a seal can be arranged between them in directions perpendicular to the stacking direction. Aligned with this seal in the stacking direction, the cover element can then be equipped with a spring element that is specifically tailored to the tensioning of this seal (or a plurality of seals arranged successively in the stacking direction). Preferably, even if the fuel cell is partially segmented, a continuous bipolar plate can nevertheless be provided, which, for example, creates mechanical stability.
[0027] In a preferred embodiment, the arch profile(s) are provided in such a way that, in the clamped state, they each rest flat in the respective receptacle, but in the unclamped state there is at least some space between the arch profile and the concave receptacle. Viewed in the section perpendicular to the axis of curvature, the unclamped arch profile can, for example, rest in the receptacle in the region of its maximum and there can be a gap on either side of this. Preferably, a gap width taken in the stacking direction increases from the maximum outwards (towards the side). With clamping, the arch profile is increasingly pressed outwards on both sides, starting at the maximum, thus increasing the contact surface between the arch profile and the receptacle (viewed in section, the contact line becomes longer).This is accompanied by an increasing force introduction into the inner cover element, which also increases the contact pressure transmitted to the fuel cells. Preferably, the concave mounts are adapted to the respective arch profile in such a way that, under nominal load, a continuous, flat contact exists between them, preferably across the entire concave mount (i.e., the contact surface completely fills it).
[0028] The invention also relates to a method for producing a fuel cell stack, wherein the curved profiles of the outer cover element are arranged in the concave receptacles of the inner cover element, and the outer cover element is clamped against the inner cover element and thus against the fuel cells. For clamping, any desired form of pressing force can generally be applied to the outer cover element, for example by pressure or spreading from a side facing away from the fuel cells. Preferably, however, the outer cover element is clamped, at least indirectly, against the inner cover element and the fuel cells using one or, in particular, several tension elements, for example, tension rods or straps.
[0029] Preferably, it is pulled in the direction of a further cover element arrangement arranged at the opposite end of the stacked fuel cells. This further cover element arrangement can also be constructed from an inner and an outer cover element; see the above disclosure for possible details. The tie rod or the tie straps preferably extend outside the stacked fuel cells, i.e., laterally offset (but, for example, parallel to the stacking direction). Independently of these bracing details, during bracing, a respective arched profile is successively drawn, preferably in the manner described above, into an increasing engagement with the respective concave receptacle.
[0030] The invention also relates to a propulsion unit for an aircraft or aeroplane, which comprises a fuel cell stack as disclosed herein. Furthermore, it is directed to the use of such a propulsion unit or the fuel cell stack in an aircraft or aeroplane.
[0031] Short description of the drawings
[0032] In the following, the invention is explained in more detail using exemplary embodiments, whereby the individual features within the scope of the independent claims can also be essential to the invention in other combinations and no distinction is made in detail between the different claim categories.
[0033] In detail,
[0034] Figure 1 shows a fuel cell stack in a schematic section with an inner and an outer cover element at the end; Figure 2a shows the inner and outer cover elements according to Figure 1 in a detailed view;
[0035] Figure 2b shows a detailed view of Figure 2a;
[0036] Figure 3 shows a detailed view of a segmented fuel cell.
[0037] Preferred embodiment of the invention
[0038] Figure 1 shows a schematic section of a fuel cell stack 1 with multiple fuel cells 2. The fuel cells 2 are arranged consecutively in a stacking direction 3, with this stack being mechanically held together by tie rods 4. The tie rods 4 transmit a contact force 5 to the stacked fuel cells 2 via a cover element arrangement 6, with an analogous arrangement being provided at the opposite end (not shown here).
[0039] The present cover element arrangement 6 has an inner cover element 11 and an outer cover element 12, which follows the inner cover element 11 in the stacking direction 3. The force is transferred from the tension elements 4 to the outer cover element 12, which holds the stacked fuel cells 2 and the inner cover element 11 arranged therebetween together. Due to the lateral force transfer to the outer cover element 12, warping can occur, also depending on the surface area of the fuel cell stack 1; see the dashed line (exaggerated representation for illustration).
[0040] Figure 2a illustrates the inner cover element 11 and the outer cover element 12 in a detailed view, specifically in a section parallel to the stacking direction 3 and the first lateral direction 21. The outer cover element 12 forms several spring elements 15, with a first, second, and third spring element 15.1, 15.2, and 15.3 being referenced here as examples. Each of the spring elements 15 forms a convexly curved arched profile 16 toward the inner cover element 11 (a first, second, and third arched profile 16.1, 16.2, and 16.3, according to the numbering). These arched profiles 16 are decoupled from one another, namely each suspended via its own suspension 17, or according to the numbering 17.1-17.3, on a section 12.1 of the outer cover element 12 which is distal to the inner cover element 11 and thus in fuel cells, via which the force is transmitted from the tension elements (not shown).Due to the decoupling, the spring elements 15 can each be individually adapted to the contact pressure required in the respective surface area, for example to at least partially compensate for the warping illustrated in Figure 1.
[0041] The spring elements 15 each form an arched profile 16, their numbering corresponding to a first, second, and third arched profile 16.1-16.3. The arched profiles 16 are each suspended via a pair of supports 30, see the detailed illustration in Figure 2b. This illustrates the support pair 30, which comprises a first support 30a and a second support 30b, which each converge away from the arched profile 16 at a suspension point 35. The support pair 30, i.e., the first and second supports 30a, b, are mirror-symmetrical to one another about a straight line 36 parallel to the stacking direction 3. The axis of curvature 37, perpendicular to the plane of the drawing, and the maximum 38 of the arched profile 16 also lie on this straight line 36.
[0042] Figure 2b shows an unstressed state, with the curved profile 16 only in contact with a concave recess 40 formed by the inner cover element 11 in the region of the maximum 38. A gap 45 is present on either side of the maximum 38, the width of which increases outward from the maximum 38. If the outer cover element 12 is clamped against the inner cover element 11 and thus the stacked fuel cells, this gap gradually closes until the curved profile 16 is in full contact. Due to the high area moment of inertia, particularly in the region of the straight line 36, a high contact force can be achieved even with a comparatively small profile thickness t. The area moment of inertia is particularly high in the region of the maximum 38 or maximum bending moment, and decreases towards the sides and thus the force introduction positions.
[0043] Figure 2a illustrates the spring elements 15 arranged side by side in the first lateral direction 21, each with the respective curved profile 16 or 16.1-16.3 and the respective support pair 30 or 30.1-30.3. Perpendicular to the plane of the drawing, i.e., in a second lateral direction 22, the spring elements 15 are constructed with translational symmetry; it is also possible for several spring elements to be arranged one behind the other in this direction. In the outer cover element 12, each spring element 15 is additionally assigned a cavity 50, i.e., a first, second, and third cavity 50.1-50.3 corresponding to the numbering of the spring elements 15.1-15.3. These cavities 50 can be independently pressurized with a fluid, gas, or liquid, so that the corresponding spring element can be pressed more strongly locally by appropriately pressurizing the corresponding cavity; see the introduction to the description for details.
[0044] Figure 3 shows a detailed view of a fuel cell 2. This has a catalyst membrane layer 60, which is enclosed on both sides by a gas diffusion layer 61 and a respective bipolar plate 62. A segmented structure is shown here; the catalyst membrane and gas diffusion layers 60, 61 are thus subdivided into several segments 60.1-60.3, 61.1-61.3. However, such a structure is not mandatory; the cover element arrangement described above can also be used for non-segmented catalyst membrane and gas diffusion layers 60, 61, which, unlike in Figure 3, are not separated by seals 65, but extend continuously. In this case, too, there would then be, for example, the seals 66 which enclose the catalyst membrane and gas diffusion layers 60, 61 and in particular the channel structures 62a, b formed by the bipolar plates 62 to the outside.The segmentation into decoupled spring elements described above may be of interest, for example, with regard to such seals 65, 66, namely enabling a locally adapted contact force, see the introduction to the description in detail.
[0045] LIST OF REFERENCE SYMBOLS
[0046] Fuel cell stack 1
[0047] Fuel cells 2
[0048] Stacking direction 3
[0049] Tie rod 4
[0050] Contact pressure 5
[0051] Cover element arrangement 6
[0052] Inner cover element 11
[0053] Outer cover element 12
[0054] Spring elements 15 first, second and third spring elements 15.1-15.3
[0055] Arch profile 16 first, second and third arch profile 16.1-16.3
[0056] Suspension 17 first, second and third suspension 17.1-17.3 first lateral direction 21 second lateral direction 22
[0057] Pair of supports 30 first, second and third pair of supports 30.1-30.3 first support 30a second support 3 Ob
[0058] Suspension point 35
[0059] Straight 36
[0060] Curvature axis 37
[0061] Maximum 38
[0062] Recording 40 first, second and third recording 40.1-40.3
[0063] Gap 45
[0064] Cavity 50 first, second and third cavities 50.1-50.3
[0065] Catalyst membrane layer 60 several segments 60.1-60.3
[0066] Gas diffusion layer 61 several segments 61.1-61.3
[0067] Bipolar plate 62 channel structures 62a, b
[0068] Seals 65
[0069] Seals 66
[0070] Profile thickness t
Claims
CLAIMS Fuel cell stack (1), with fuel cells (2) arranged one after the other in a stacking direction (3), an inner cover element (11) which follows the fuel cells (2) in the stacking direction (3), and an outer cover element (12) which follows the inner cover element (11) in the stacking direction (3) and holds the inner cover element and the fuel cells (2) together in a clamped state, wherein the outer cover element (12) forms at least a first and a second spring element (15.1, 15.2) perpendicular to the stacking direction (3), wherein each of the spring elements (15.1, 15.2) forms an arched profile (16.1, 16.2) which is convexly curved towards the inner cover element (11), and the respective arched profile (16.1, 16.2) is suspended separately, and wherein the inner cover element (11) has a respective Receptacle (40.1, 40.2) which is concavely curved towards the outer cover element (12) and the respective convexly curved arch profile (16.1, 16.2). Fuel cell stack (1) according to claim 1, wherein the arcuate profiles (16.1, 16.2) are each suspended on a side facing away from the inner cover element (11) from a pair of supports (30.1, 30.2), wherein a separate pair of supports (30.1, 30.2) is provided for each arcuate profile (16.1, 16.2). Fuel cell stack (1) according to claim 2, wherein, viewed in section, the pair of supports (30.1, 30.2) of the respective spring element (15.1, 15.2) converge at a suspension point (35) which, in the stacking direction (3), is aligned with a maximum (38) which the respective arcuate profile (16.1, 16.2) assumes toward the inner cover element (11). The fuel cell stack (1) according to claim 2 or 3, wherein the pair of supports (30.1, 30.2) of the respective spring element (15.1, 15.2), viewed in section, is mirror-symmetrical with respect to a straight line (36) that is parallel to the stacking direction (3). The fuel cell stack (1) according to one of the preceding claims, wherein at least two spring elements (15) are arranged next to one another in a first lateral direction (21) that is perpendicular to the stacking direction (3) and to an axis of curvature (37) of the arcuate profile (16.1) of the first spring element (15.1). The fuel cell stack (1) according to one of the preceding claims, wherein at least two spring elements (15) are arranged next to one another in a second lateral direction (22) that is perpendicular to the stacking direction (3) and parallel to an axis of curvature (37) of the arcuate profile (16.1) of the first spring element (15.1).Fuel cell stack (1) according to one of the preceding claims, in which the first and the second spring element (15.1, 15.2) differ in at least one of a curvature of the arched profiles (16.1, 16.2), a thickness (t) of the arched profiles (16.1, 16.2), and a stiffness of the suspension (17.1, 17.2). Fuel cell stack (1) according to one of the preceding claims, in which the first and the second spring element (15.1, 15.2) occupy different surface areas in directions perpendicular to the stacking direction (3). Fuel cell stack (1) according to one of the preceding claims, in which the pair of supports (30) of at least one of the spring elements (15) in. the stacking direction (3) is suspended in alignment with a cavity (50) formed on or in the outer cover element (12), which cavity can be supplied with a fluid to adjust a contact pressure of the at least one spring element (15). Fuel cell stack (1) according to claim 9, in which the first and the second spring element (15.1, 15.2) are each assigned their own cavity (50.1, 50.2) in the outer cover element (12), and these cavities (50.1, 50.2) can be supplied with a fluid independently of one another. Fuel cell stack (1) according to one of the preceding claims, in which at least one of the fuel cells (2) is segmented, i.e. divided into at least two segments.Fuel cell stack (1) according to one of the preceding claims, in which the respective curved profile (16) and the respective receptacle (40) are provided in such a way that, in an unstressed state, the curved profile (16) only bears with its maximum (38), but in the stressed state bears flatly in the concave receptacle (40) across its curvature. Method for producing a fuel cell stack (1) according to one of the preceding claims, in which the fuel cells (2) and the inner and outer cover elements (11, 12) are assembled, wherein a respective curved profile (16) of the outer cover element (12) is arranged in a respective receptacle (40) of the inner cover element (11). and wherein the outer cover element (12) is clamped against the inner cover element (11) and thus against the fuel cells (2), and in the process, the spring elements (15) are also clamped.
14. A drive unit for an aircraft or aircraft, comprising a fuel cell stack (1) according to one of the preceding claims.
15. Use of a fuel cell stack (1) according to one of claims 1 to 12 or a drive unit according to claim 14 in an aircraft or aircraft.