Cryogenic tank for storing a cryogenic fluid.

Description

11 Cryogenic tank for storing a cryogenic fluid. Technical Field

[001] The present invention relates to a cryogenic tank for storing a cryogenic fluid. Fundamentals of the Technique

[002] A cryogenic tank for storing a cryogenic fluid is frequently used in the aerospace field. For example, a rocket equipped with an engine whose fuel is liquid hydrogen is fitted with tanks to store liquid hydrogen and liquid oxygen, which is an oxidizing agent, respectively. As part of measures to combat global warming, hydrogen-powered aircraft that do not emit carbon dioxide have been developed, and each of these hydrogen-powered aircraft also requires a tank to store liquid hydrogen.

[003] The cryogenic tank for aerospace use, as described above, is highly sought after for being lightweight and also for demonstrating the basic function of storing a cryogenic fluid. Therefore, a tank has been proposed that adopts a fiber-reinforced composite material instead of a known metal (for example, see Patent Document 1).

[004] A tank made of a fiber-reinforced composite material includes a structure in which a metal or resin liner is bonded to an inner surface of an outer cover made of a fiber-reinforced composite material. In this structure, the outer cover made of fiber-reinforced composite material functions as a structural element, and the metal or resin liner functions as a liquid-tight element to prevent leaks of the cryogenic fluid stored in the tank. The liner must also be lightweight, and this is highly required due to the use of a resin liner with a specific gravity lower than that of metal. Petition 870250087667, dated 09 / 26 / 2025, page 10 / 27 / 11

[005] However, in a tank with such a structure, the linear expansion coefficient of the fiber-reinforced composite material included in the outer cover is significantly lower than the linear expansion coefficient of the resin included in the lining. Therefore, when the tank enters a cryogenic state when its interior is filled with cryogenic fluid, the outer cover, which contracts relatively less, may limit the shrinkage of the lining with the relatively high linear expansion coefficient. As a result, tensile stress may act on the lining, and the lining may be damaged and separated from the inner surface of the outer cover.

[006] One method considered for solving such a problem includes, instead of bonding an outer covering made of a fiber-reinforced composite material with a resin coating, placing a release element in the form of a film or tape made of resin between the outer covering and the coating, more specifically, on an inner surface of the outer covering or on an outer surface of the coating.

[007] Figure 1 is a schematic explanatory diagram illustrating the structure of a cryogenic tank that adopts the method described above and illustrates an end surface taken along a plane passing through an axial center C'.

[008] A cryogenic tank T' is a hollow body of revolution with an opening O' in each of the end parts of the hollow body of revolution in a direction from the axial center C'. The cryogenic tank T' includes a structure in which an outer cover S' is arranged on an outer side and a lining L' is arranged on an inner side, and a release element R' is arranged between the outer cover S' and the lining L'. Here, the shape of an inner surface of the outer cover S' is substantially the same as the shape of an outer surface of the release element R', and the shape of an inner surface of the Petition 870250087667, dated 09 / 26 / 2025, page 11 / 27 / 11 release element R' is substantially the same as the shape of an external surface of the coating L'. Openings O' are provided for attaching a tank lid, a pipe or something similar.

[009] The outer cover S' is an element that functions as a structural element of the cryogenic tank T' and is made of a fiber-reinforced composite material.

[0010] The L' coating is an element that functions as a liquid-tight element to prevent leaks of the cryogenic fluid stored in the cryogenic tank T', and is made of resin.

[0011] The release element R' is an element bonded to the inner surface of the outer cover S' and to the outer surface of the coating L' to prevent adhesion between the outer cover S' and the coating L', and is made of resin.

[0012] As described above, in tank T' with the structure in which the outer cover S' made of fiber-reinforced composite material, the release element R' made of resin, and the lining L' made of resin are arranged in order from the outside in this way, when tank T' enters a cryogenic state from the inside of tank T' which is filled with cryogenic fluid, the action of the release element R' allows the outer cover S' and the lining L' to shrink by their respective coefficients of linear expansion while the outer cover S' and the lining L' are separated from each other. Therefore, it is unlikely that the lining L' will be damaged and can sufficiently demonstrate the function of a liquid-tight element that prevents leakage of the cryogenic fluid stored in tank T'. Related Technical Document Patent Document

[0013] Patent Document 1: Publication of unexamined Japanese patent application no. 2006-62320 Petition 870250087667, dated 09 / 26 / 2025, page 12 / 27 / 11 Summary of the Invention Problems to be Solved by the Invention

[0014] However, in tank T' with the structure illustrated in Figure 1, when a crack appears in the lining L', the liquid's tightness can be lost immediately and the cryogenic fluid stored inside can leak out. Consequently, the conventional cryogenic tank T' has room for improvement from a reliability standpoint.

[0015] The present invention is made in view of the problem described above, and one objective thereof is to provide a cryogenic tank with improved reliability compared with a cryogenic tank of the related art. Ways to Solve the Problems

[0016] To solve the problem described above, a cryogenic tank of the present invention includes an outer cover made of a fiber-reinforced composite material and multiple inner layers arranged on an inner side of the outer cover. The multiple inner layers include respective coatings made of resins and respective release elements made of resins and arranged on the outer surfaces of the respective coatings. Advantageous Effects of the Invention

[0017] The cryogenic tank of the present invention provides redundancy against the generation of a crack in the lining and has greater reliability than a cryogenic tank of the related art. Brief Description of the Drawings

[0018] Figure 1 is a schematic explanatory diagram illustrating the structure of a cryogenic tank of the related technique.

[0019] Figure 2 is a schematic explanatory diagram illustrating the structure of a cryogenic tank of an embodiment of the present invention. Petition 870250087667, dated 09 / 26 / 2025, page 13 / 27 / 11 Method for Carrying Out the Invention

[0020] Next, one embodiment of the present invention is described in detail with reference to the drawings.

[0021] Figure 2 is a schematic explanatory diagram illustrating the structure of a cryogenic tank T of an embodiment of the present invention and illustrates an end surface taken along a plane passing through an axial center C. Note that the cryogenic tank T is used to store a cryogenic fluid. Examples of cryogenic fluid include liquid hydrogen (temperature: -253°C), liquid nitrogen (temperature: -196°C), liquid oxygen (temperature: -183°C) and LNG (temperature: -162°C).

[0022] A cryogenic tank T structure of the present invention is similar to the cryogenic tank T' structure of the related art described with reference to Figure 1. However, the cryogenic tank T structure of the present invention differs from the cryogenic tank T' structure of the related art because the cryogenic tank T' of the related art includes only one layer, which includes the release element R' and the coating L' on the inner side of the outer cover S', whereas the cryogenic tank T of the present invention includes multiple layers (inner layers), each of which includes a release element R and a coating L on an inner side of an outer cover S.

[0023] As illustrated in Figure 2, the cryogenic tank T of the embodiment of the present invention is a hollow body of revolution with an opening O in each of the end parts of the hollow body of revolution in a direction from the axial center C. The cryogenic tank T includes, in order from outside to inside, the outer cover S and at least two inner layers IL, each of which includes the release element R and the lining L. The openings O are provided for attaching a tank lid, a tube, or something else. Petition 870250087667, dated 09 / 26 / 2025, page 14 / 27 / 11 similar. Note that, although in the illustrated example the openings O provided in the respective end parts have the same diameter, the openings O may have different diameters, or the opening O may be provided only in one end part.

[0024] In the illustrated example, the two inner layers IL, namely a first inner layer IL1 and a second inner layer IL2, are provided in order from inside to outside on the inner side of the outer cover S. Note that the number of inner layers provided on the inner side of the outer cover S is appropriately selectable according to a degree of reliability required for the cryogenic tank T, and three or more inner layers may be provided.

[0025] The first inner layer IL1 includes a first coating L1 and a first release element R1 arranged on an outer side of the first coating L1. In addition, the second inner layer IL2 includes a second coating L2 arranged on an outer side of the first inner layer IL1 (first release element R1) and a second release element R2 arranged on an outer side of the second coating L2.

[0026] The shape of an inner surface of the outer cover S is substantially the same as the shape of an outer surface of the second release element R2. The shape of an inner surface of the second release element R2 is substantially the same as the shape of an outer surface of the second coating L2. The shape of an inner surface of the second coating L2 is substantially the same as the shape of an outer surface of the first release element R1. The shape of an inner surface of the first release element R1 is substantially the same as the shape of an outer surface of the first coating L1.

[0027] The external cover S is an element that functions as a Petition 870250087667, dated 09 / 26 / 2025, page 15 / 27 / 11 structural element of the cryogenic tank T and is made of a fiber-reinforced composite material. Examples of such fiber-reinforced composite material may include fiber-reinforced plastic (FRP), such as carbon fiber reinforced plastic (CFRP), glass fiber reinforced plastic, and aramid fiber reinforced plastic. As a matrix resin for the fiber-reinforced composite material, a matrix resin with a molding temperature lower than the melt start temperatures of the resins (described later) included in the respective first coating L1 and second coating L2 is used.Alternatively, the same resin may be used as one of the resins included in the respective coatings of the first coating L1 and the second coating L2 with a lower melting start temperature (when three or more inner layers are provided, one of the resins included in the coatings of the respective inner layers with the lower melting start temperature). Alternatively, when the first coating L1 and the second coating L2 are made of the same resin, the same resin included in the first coating L1 and the second coating L2 may be used.

[0028] The first lining L1 and the second lining L2 are elements that function as a liquid-tight element to prevent leaks of the cryogenic fluid stored in the cryogenic tank T and are made of a thermoplastic resin. As such, a resin is used that has resistance to corrosion of the cryogenic fluid stored in tank T and liquid tightness within a temperature range from ambient temperature to cryogenic temperature. Examples of such resin include polycarbonate (PC), polyetheretherketone (PEEK), and liquid crystal polymer (LCP).

[0029] The first release element R1 and the second release element R2 are elements bonded to the outer surfaces of the first coating L1 and the second coating L2, respectively, to prevent the Petition 870250087667, dated 09 / 26 / 2025, p. 16 / 27 / 11 adhesion between the second coating L2 and the first coating L1 and between the outer coating S and the second coating L2, respectively, and are made of a thermoplastic resin. As such resin, a resin with a higher melt start temperature than the melt start temperature of the matrix resin is used for the fiber-reinforced composite material included in the outer coating S, as described above, and the melt start temperatures of the resins included in the respective first coating L1 and second coating L2. Examples of such resin include Teflon (registered trademark), polyimide and polyetheretherketone (PEEK) according to a combination with the thermoplastic resins used for the first coating L1 and the second coating L2.

[0030] As described above, the cryogenic tank T of the embodiment of the present invention includes the structure in which the outer cover S, the second inner layer IL2 which includes the second release element R2 and the second lining L2, and the first inner layer IL1 which includes the first release element R1 and the first lining L1 are arranged in order from the outside. Therefore, even if a crack is generated in the first inner lining L1, the second lining L2 can assume the function of a liquid-tight element to prevent leakage of the cryogenic fluid stored in the cryogenic tank T. Therefore, the generation of a crack in the first lining L1 does not immediately lead to the loss of liquid tightness and, consequently, to the leakage of the cryogenic fluid stored inside to the outside.

[0031] Note that the thicknesses of the release elements and the coatings included in the corresponding inner layers are appropriately selectable according to characteristics such as the required strength for the release elements and the coatings and a restriction on the weight of the cryogenic tank T.

[0032] As such, the cryogenic tank T of the present embodiment Petition 870250087667, dated 09 / 26 / 2025, page 17 / 27 / 11 The invention presents redundancy for generating a crack in the lining and, therefore, presents greater reliability than that of the cryogenic tank T' of the related technique described with reference to Figure 1.

[0033] Note that the cryogenic tank T of the embodiment of the present invention can be manufactured, first, by the first lining L1 which is molded, then by the first release element R1, the second lining L2 and the second release element R2 which is arranged sequentially on the outside of the first lining L1 and then by the outer cover S which is arranged on the outside of the second release element R2.

[0034] In this case, the fiber-reinforced composite material included in the outer coating S, which is placed last, is molded at a temperature lower than the melting start temperatures of the resins included in the respective first coating L1 and second coating L2. Therefore, the molding of the fiber-reinforced composite material does not present an adverse effect, such as deformation in the first coating L1 and the second coating L2 that were molded or placed. Furthermore, the melting start temperatures of the resins included in the respective first release element R1 and second release element R2 are higher than the melting start temperatures of the resins included in the respective first coating L1 and second coating L2. Therefore, performing the heat treatment described above allows each of the two release elements to demonstrate a release action.

[0035] When the matrix resin for the fiber-reinforced composite material included in the outer covering S is the same as one of the resins included in the respective coatings of the first coating L1 and the second coating L2 with a lower initial melt temperature (when three or more inner layers are provided, one of the resins included in the coatings of the respective inner layers with the Petition 870250087667, dated 09 / 26 / 2025, page 18 / 27 / 11 (lower initial melting temperature), or when the matrix resin for the fiber-reinforced composite material included in the outer cover S is the same as the resins included in the respective coatings of the first coating L1 and the second coating L2, by the molding temperature of the fiber-reinforced composite material included in the outer cover S finally disposed which is an appropriate temperature equal to or higher than the initial melting temperature of the matrix resin for the fiber-reinforced composite material, the fiber-reinforced composite material is moldable without losing the liquid tightness of the first coating L1 and the second coating L2 that were molded or disposed.In this case as well, the melting start temperatures of the resins included in the respective first release element R1 and second release element R2 are higher than the melting start temperatures of the resins included in the respective first coating L1 and second coating L2. Therefore, performing the heat treatment described above allows each of the two release elements to demonstrate a release action. (Aspects of the Present Invention)

[0036] A cryogenic tank of a first aspect of the present invention includes: an outer cover made of a fiber-reinforced composite material; and multiple inner layers arranged on an inner side of the outer cover, wherein the multiple inner layers include: respective coatings made of resins; and respective release elements made of resins and arranged on outer surfaces of the respective coatings.

[0037] In the cryogenic tank of a second aspect of the present invention, the resins included in the respective linings are resins, each with resistance to cryogenic fluid corrosion and liquid tightness within a temperature range from ambient temperature to cryogenic temperature, and the resins included in the respective elements of Petition 870250087667, dated 09 / 26 / 2025, page 19 / 27 / 11 release are resins, each with a higher melt start temperature than the melt start temperature of a matrix resin for the fiber-reinforced composite material included in the outer covering and the melt start temperatures of the resins included in the respective coatings.

[0038] In the cryogenic tank of a third aspect of the present invention, the matrix resin for the fiber-reinforced composite material included in the outer cover is the same as the resins included in the respective coatings, or the matrix resin for the fiber-reinforced composite material included in the outer cover is the same as a resin that has the lowest initial melting temperature among the resins included in the respective coatings. Explanation of Reference Signs

[0039] Internal layer IL, IL1, IL2 L, L1, L2 Coating Release element R, R1, R2 External cover S Cryogenic tank T Petition 870250087667, dated 09 / 26 / 2025, page 20 / 27

Claims

CLAIMS 1. Cryogenic tank for storing a cryogenic fluid, characterized in that it comprises: an outer cover made of a fiber-reinforced composite material; and multiple inner layers arranged on an inner side of the outer cover, wherein the multiple inner layers include: respective coatings made of resins; and respective release elements made of resins and arranged on the outer surfaces of the respective coatings.

2. Cryogenic tank according to claim 1, characterized in that the resins included in the respective linings are resins, each with resistance to cryogenic fluid corrosion and liquid tightness within a temperature range from ambient temperature to cryogenic temperature, and the resins included in the respective release elements are resins, each with a melt start temperature higher than the melt start temperature of a matrix resin for the fiber-reinforced composite material included in the outer cover and the melt start temperatures of the resins included in the respective linings.

3. Cryogenic tank according to claim 2, characterized in that the matrix resin for the fiber-reinforced composite material included in the outer cover is the same as the resins included in the respective linings, or the matrix resin for the fiber-reinforced composite material included in the outer cover is the same as a resin with the lowest initial melting temperature among the resins included in the respective linings. Petition 870250087667, dated 09 / 26 / 2025, pp. 21 / 27

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