Tank for storing hydrogen for a motor vehicle, method and motor vehicle

Abstract

The invention relates to a tank (10) for storing hydrogen for a motor vehicle, which tank is produced from a steel material forming an at least partially closed cavity (16) for receiving the hydrogen, the inner side of which steel material is provided with a coating (14) forming a hydrogen barrier. The invention is characterised in that the inner coating (14) of the steel material is formed by a metal material applied in a centrifugal casting process and having a face-centred-cubic or hexagonal-close-packed crystal lattice.

Description

[0001] Tank for storing hydrogen for a motor vehicle, method and motor vehicle

[0002] The invention relates to a tank for storing hydrogen for a motor vehicle according to the preamble of patent claim 1. The invention also relates to a method and a motor vehicle.

[0003] From DE 10 2021 116 300 A1 a pressure vessel is known with a wall which forms at least a first side and a second side, comprising a plurality of deflection elements, a plurality of first bands and a plurality of second bands, as well as a plurality of tension struts, wherein the deflection elements are arranged in the first side and in the second side, wherein in the first side the first bands and the second bands each alternately comprise immediately adjacent deflection elements, wherein in the second side the first bands and the second bands each alternately comprise immediately adjacent deflection elements, wherein viewed along a longitudinal direction of at least one deflection element, first bands and second bands alternately comprise, and wherein the tension struts alternately comprise a deflection element of the first side and a deflection element of the second side.

[0004] The object of the invention is to provide a tank for storing hydrogen for a motor vehicle which can store hydrogen for a particularly long time, a method for producing such a tank and a motor vehicle with such a tank.

[0005] This object is achieved according to the invention by a tank for storing hydrogen for a motor vehicle having the features of patent claim 1, by a method for producing such a tank, and by a motor vehicle having the tank. Advantageous embodiments or further developments of the invention are the subject of the dependent patent claims and the description.

[0006] A first aspect of the invention relates to a tank for storing hydrogen for a motor vehicle, in particular one that can be driven electrically by means of a hydrogen-powered fuel cell and / or by means of a hydrogen-burning internal combustion engine. The motor vehicle is designed, for example, as a motor vehicle, in particular as a passenger car.

[0007] The invention is based in particular on the following findings and considerations: The interaction of hydrogen with a material, particularly a metallic one, can lead to a deterioration of the material properties and thus the material behavior, especially the material's resilience. Components can suffer surface blisters, internal cracks, and stress corrosion cracks due to hydrogen-induced corrosion. The various terms for component damage caused by hydrogen, such as hydrogen-induced stress corrosion cracking, hydrogen-induced corrosion, delayed brittle fracture caused by hydrogen in the metal lattice, which can also be referred to as the crystal lattice, and hydride embrittlement, are summarized under the term "hydrogen embrittlement."Hydrogen embrittlement occurs when atomic hydrogen forms on the metal surface and diffuses into the material faster than it can combine at the surface to form non-diffusible molecules consisting of two hydrogen atoms. Part of the hydrogen is incorporated into the metal lattice, resulting in embrittlement of the metal. The smallest spatial unit of a crystal lattice is a so-called unit cell. Depending on the spatial arrangement of the atoms in such a unit cell, the incorporation or diffusion of hydrogen into or through a material can be influenced.Especially when storing hydrogen in metal tanks under high pressures of, for example, 350-700 bar (1 bar = 100,000 Newton per square meter or Pa), hydrogen embrittlement can pose the risk that the tank will fail after a certain storage time, i.e. burst or rupture, and the hydrogen will escape from the tank.

[0008] The design of tanks or pressure vessels with an internal pressure higher than the ambient pressure can be achieved using the so-called tank formula. This formula states that for a cylindrical tank with an axis of rotational symmetry as the longitudinal axis, the stresses in the material in the tangential direction or in the circumferential direction around the longitudinal axis – regardless of the internal diameter and internal pressure – are twice as great as the stresses in the material in the longitudinal or axial direction.

[0009] The tank according to the invention is made of a steel material that forms an at least partially closed cavity for accommodating hydrogen, the interior of which is provided with a coating that forms a hydrogen barrier. The tank is characterized in that the inner coating of the steel material is formed by a metal material with a face-centered cubic or hexagonal close-packed crystal lattice, applied in a centrifugal casting process.

[0010] In other words, the tank should be designed to store hydrogen, for example in gaseous form, liquefied form, in particular liquefied by cold, or in a two-phase form within the tank's cavity, i.e. with a portion of liquid hydrogen and a portion of gaseous hydrogen. The tank has two layers or two shells that at least partially define the cavity. In particular, an outer shell made of steel material is provided, which can also be referred to as a jacket, and an inner shell formed from the coating, which adjoins the steel material directly or indirectly on the inside of the cavity. With regard to the maximum material stresses that occur, the spherical tank shape is the most favorable.The maximum stress in the wall or in the wall material occurs in every section through the center point, i.e. along the largest diameter or the diameter, and corresponds to the axial stress in a cylindrical tank (at the same internal pressure and internal diameter). The tank can thus be designed as a substantially cylindrical tank, which has, for example, hemispherical ends or end pieces, or as a spherical tank. The tank has at least one opening which is at least indirectly designed to accommodate a valve. The tank can be filled with hydrogen through the at least one valve, and the hydrogen stored in the tank can be removed from the at least one valve, for example to feed it to a fuel cell or a hydrogen-burning combustion engine.The coating, which is in direct contact with the hydrogen stored or stored on the inside of the cavity, is designed to prevent, hinder, or slow down the diffusion of hydrogen into the shell, particularly into the steel material. Materials, especially metal materials, with a face-centered cubic or hexagonal close-packed crystal lattice or the structure of their respective unit cells have proven particularly advantageous for this purpose.

[0011] In particular, the shell, i.e., the envelope encompassing both the coating and the cavity, is intended to absorb the main load, i.e., the stresses arising from the internal overpressure in the tank. The inner coating is intended to prevent hydrogen from embrittlement of the shell and thus structurally weakening the load-bearing structure, namely the shell, during storage.

[0012] This has the advantage that the steel material is not weakened or only weakened slowly when hydrogen is stored in the tank, thus enabling a particularly long storage period for hydrogen in the tank.

[0013] The inner coating, which can also be called the internal coating, is applied to the inside of the shell or the steel material using the centrifugal casting process. The shell, in a partially or fully finished state, can serve as a mold in the centrifugal casting process. The shell is set in rotation, preferably about a rotational symmetry axis of the tank, while the coating is introduced in liquid or molten form, i.e. as a melt, into the tank, more precisely into the cavity, for example through the at least one opening for the at least one valve. In particular, the tank rotates about the rotational symmetry axis, i.e. the mold or the shell, while the liquid coating is introduced into the mold.The rotation distributes the still-liquid coating evenly in the circumferential direction, ensuring a uniform coating of the inside of the tank. The coating material can be stainless steel or an austenitic steel, which has a face-centered cubic crystal lattice.

[0014] Partially closed here means that the cavity is delimited by the steel material and has at least one opening through which hydrogen can be introduced into the tank or cavity for storage or is introduced during a tank filling process and / or through which hydrogen can be removed from the tank or is removed during, for example, operation of the motor vehicle. The opening is designed to allow fluid flow.

[0015] The fact that the motor vehicle is electrically driven can be understood in particular to mean that the motor vehicle has at least one electric machine by means of which the motor vehicle can be driven. Electrical power for operating the electric machine can be provided by a fuel cell of the motor vehicle by oxidizing hydrogen in the fuel cell with an oxidizing agent such as oxygen, in particular atmospheric oxygen. Additionally or alternatively, the motor vehicle can have an internal combustion engine or a combustion motor in which hydrogen can be combusted with oxygen, in particular atmospheric oxygen, and by which it can be driven.

[0016] One embodiment provides that the steel material is formed at least in part as a seamless drawn cylinder.

[0017] As described at the beginning, in a substantially cylindrical pressure tank, i.e. one in which the internal pressure is greater than the ambient or external pressure, the maximum stresses in the material occur in the cylindrical part in the circumferential or tangential direction. If this cylindrical part is manufactured using a drawing process, a structurally weakening weld seam is eliminated precisely in the area of ​​maximum stresses, namely along the longitudinal direction of the cylindrical part in the circumferential direction, as in so-called welded pipes. The area or part of the tank that is shaped as a drawn cylinder can also be referred to as the cylindrical part and, in a substantially cylindrical design of the tank, can be a central area, i.e., located in the axial or longitudinal direction between the end pieces of the tank.This has the advantage that the wall thickness of the cylindrical part can be chosen to be particularly small, thus saving weight.

[0018] One embodiment provides that the tank is made of two tank halves formed from the steel material and materially connected.

[0019] In other words, the coat should consist of two separate

[0020] The parts manufactured in the manufacturing process can be assembled or put together. By assembled we mean that, for example, in the case of an essentially cylindrical shell or tank, two tank halves can be brought together or put together in the axial direction and then welded together in the circumferential direction, for example around the longitudinal or rotational axis of symmetry of the finished tank. By welding, for example, the two tank halves are thus materially connected. By welding the two tank halves in the circumferential direction or joining the two tank halves in the axial direction, there is the advantage that the connection point, which can represent a potential structural weakening of the shell, is located in the direction of the minimum stresses, namely the axial stresses.The two tank halves can also each be hemispherical if the tank, when fully assembled or materially connected, forms or is intended to form a spherical tank.

[0021] This has the advantage of simplifying the manufacturing process for the tank, especially the shell, because each tank halves can be manufactured in a separate process, for example, by deep drawing. Welding here refers, for example, to a MIG and / or MAG and / or GMAW welding process (MIG: Metal Inert Gas, MAG: Metal Active Gas, GMAW: Gas Metal Arc Welding), and / or an oxyacetylene welding process, and / or a laser welding process, and / or a friction stir welding process.

[0022] One embodiment provides that the inner coating is formed from a non-ferrous alloy.

[0023] In other words, the coating contains no iron or only a negligible iron content caused by impurities during production. In particular, the iron content of the coating is less than one percent by weight.

[0024] The austenitic steel considered for a coating here, for example, must have a nickel content of over eight percent by weight. This means that the coating would first have to be alloyed or at least mixed before being applied and incorporated into the shell during the centrifugal casting process, which results in increased manufacturing costs compared to the use of a pure substance. Using a non-ferrous alloy as the inner coating can therefore be a particularly advantageous way of reducing the manufacturing costs of the tank. When using a non-ferrous alloy, a material with a lower melting point than the shell, which is made of steel, can be used for the coating. This has the advantage that the shell is not melted during the centrifugal casting process, which would otherwise weaken its structure.

[0025] One embodiment provides that the material with the face-centered cubic (abbreviation: fcc) crystal lattice consists at least partially of copper, aluminum, nickel, lead, platinum, silver and / or gold.

[0026] In other words, the aforementioned metallic automotive elements are used in their pure form. However, alloys of the aforementioned elements, which also have a face-centered cubic crystal lattice, can also be used. With the exception of nickel and especially platinum, these elements have the advantage that their melting temperature is below that of steel (approximately 1425 °C to 1540 °C for steel), and thus, when the coating is applied in the centrifugal casting process, the steel shell is not partially melted. This prevents structural weakening of the shell, which can also be referred to as the steel shell, due to partial melting.

[0027] One embodiment provides that the material with the hexagonal closest packed (abbreviation: hdp) crystal lattice consists at least partially of cobalt, cadmium, zinc and / or alpha-titanium.

[0028] In other words, the aforementioned metallic materials with an HDP crystal lattice should be used as a coating in their pure form or in an alloy, whereby the alloy must also have an HDP lattice. With the exception of a-titanium and cobalt, the HDP materials mentioned have a significantly lower melting point than steel. This offers the advantage that when these elements, i.e. those with a lower melting point than the steel material or steel, are introduced, the steel shell is not melted, thus preventing any structural weakening of the steel shell.

[0029] One embodiment provides that the steel material is a high-strength steel with a yield strength of greater than 550 MPa (MPa: megapascals). In other words, the tank's shell or outer casing is to be made of high-strength steel. High-strength steel here means an iron alloy with a yield strength of greater than 550 MPa. Iron alloy here means a metal alloy that consists predominantly, in particular more than 50%, preferably more than 80%, of the element iron. High-strength steels with a yield strength of greater than 800 MPa, preferably greater than 1000 MPa, are particularly preferably used for the shell. The higher the yield strength, the thinner the load-bearing shell of the tank can be made, thereby achieving weight savings. The advantage of using high-strength steel is therefore a reduction in the weight of the tank compared to low-strength steels.In general, it can be stated that with an increase in the yield strength of high-strength steels, the susceptibility to hydrogen embrittlement also increases.

[0030] A second aspect of the invention relates to a method for producing a tank for storing hydrogen for a motor vehicle, in particular according to the first aspect of the invention. Advantages and advantageous developments or embodiments of the first aspect of the invention are to be regarded as advantages and advantageous developments or embodiments of the second aspect of the invention, and vice versa.

[0031] This process involves coating the interior of a tank made from a steel material that forms a closed cavity for absorbing hydrogen with a hydrogen barrier. The process is characterized by the fact that the inner coating is formed by a metal material with a face-centered cubic or hexagonal close-packed crystal lattice, which is applied to the steel material of the tank using a centrifugal casting process.

[0032] In the centrifugal casting process, the steel material or shell, in an at least partially finished state, serves as a mold or casting mould for the coating. In particular, in the centrifugal casting process, the shell has at least one opening through which the coating can be introduced in the form of a melt, i.e., a molten metal, or is introduced during the centrifugal casting process. Before, during and / or after the introduction of the melt, the mold, i.e., the shell, is rotated about at least one axis. This axis is preferably an axis of the shell, to which the shell has rotational symmetry. As a result of the centrifugal forces occurring due to the rotation, the melt is evenly distributed over the inside of the shell until it solidifies.For a better distribution of the melt on the inside during the centrifugal casting process, the shell can be heated before and / or during and / or after the centrifugal casting process so that the melt cools more slowly compared to a mold that is not preheated or not heated during the centrifugal casting process.

[0033] A third aspect of the invention relates to a motor vehicle having at least one tank according to the first aspect of the invention. Advantages and advantageous developments or embodiments of the first and second aspects of the invention are to be regarded as advantages and advantageous developments or embodiments of the third aspect of the invention, and vice versa.

[0034] Preferably, the motor vehicle, particularly in its fully manufactured state, has the tank for storing hydrogen.

[0035] A further aspect relates to a method for producing a tank for storing hydrogen for a motor vehicle, in particular according to the first aspect of the invention. Advantages and advantageous developments or embodiments of the first, second, and third aspects of the invention are to be regarded as advantages and advantageous developments or embodiments of the further aspect, and vice versa.

[0036] The process involves coating the interior of a tank made from a steel material that forms a closed cavity for absorbing hydrogen with a hydrogen barrier. The process is characterized by the fact that, in a first step, the inner coating is produced from a metal material with a face-centered cubic or hexagonal close-packed crystal lattice using a centrifugal casting process. In a subsequent step, the tank is coated on its interior by shrinking the steel material onto the coating.If the shell is made of steel material as the mold in the centrifugal casting process, it can be problematic when using, for example, a-titanium or cobalt (for materials with an hdp crystal lattice) or platinum or nickel (materials with a fcc crystal lattice) because these materials have a similarly high or higher melting point than steel. As a result, when the respective materials are introduced as a melt into the shell used as the mold, the shell itself can be melted or completely melted, and due to the associated structural weakening it can no longer be used as a tank or as a component of a tank. In such a case, the inner coating is produced in a mold formed separately from the shell, for example using the centrifugal casting process, at least for a cylindrical part of the tank.The shell, or at least a cylindrical part of the shell, can be heated so that the shell expands and can then be pushed over the cooled coating, which can be shaped or ready as a tube or a hollow cylinder, so that the coating is located on the inside of the shell, lies flat, or rests against the inside. As the shell cools, it contracts around the coating. Particularly advantageous in this case, as the shell cools, a prestress can occur in the shell in the circumferential direction or in the tangential direction, which is directed opposite to the tangential stress that arises solely due to a load caused by internal pressure in the shell. This prestress thus increases the load-bearing capacity, for example the permissible maximum internal pressure of the tank, once it has been manufactured.Particularly advantageously, the coating can have a larger diameter in a cylindrical or tubular state than the inner diameter of the cylindrical part of the shell in a cooled state, for example, at room temperature. This allows the prestress to be increased during shrinking.

[0037] Further features of the invention emerge from the claims, the figures, and the description of the figures. The features and combinations of features mentioned above in the description, as well as the features and combinations of features mentioned below in the description of the figures and / or shown alone in the figures, can be used not only in the respective combinations specified, but also in other combinations or on their own. The invention will now be explained in more detail using a preferred embodiment and with reference to the drawings. They show:

[0038] Fig. 1 is a schematic sectional view of a tank in cylindrical

[0039] Version with a jacket and an inner coating;

[0040] Fig. 2 is a schematic sectional view of the tank in spherical

[0041] Version with the jacket and the inner coating;

[0042] Fig. 3 is a schematic external view of the tank in cylindrical design with a shell assembled from three parts;

[0043] Fig. 4 is a schematic external view of the tank in cylindrical design with a shell assembled from two parts; and

[0044] Fig. 5 is a schematic sectional view of the tank in cylindrical design during application of the inner coating by a centrifugal casting process.

[0045] Fig. 1 shows a schematic sectional view of a tank 10 in a cylindrical design with a shell 12 and an inner coating 14. The tank 10 can have a cavity 16 for receiving and / or storing hydrogen. The tank 10 can be designed to receive hydrogen in liquid form and / or in gaseous form. The tank 10 can be designed to store the hydrogen at a pressure or internal pressure in the cavity 16 of 350-700 bar. The cavity 16 can be at least partially delimited or enclosed by a steel material. The steel material can form an outer shell or shell 12 of the tank 10. The cavity 16 can be enclosed by the shell 12 up to at least one opening 26 through which fluid can flow.The at least one opening 26 can be designed so that hydrogen can be introduced into the tank 10, in particular into the cavity 16, for example during a filling process or a refueling process of the motor vehicle, and / or so that hydrogen can be removed via it, for example during operation of the motor vehicle, for example flowing out of the opening, i.e. being removed. As shown in Fig. 1, the tubular element 27 can be formed integrally with the casing 12, in particular with the front part 24, and can have the coating 14. Fig. 1 can show the tank 10 in a cylindrical design in a finished state. In the cylindrical design, the tank 10 can be rotationally symmetrical to the axis of symmetry 18 shown in Fig. 1. In the radial direction 13, the coating 14 can adjoin the casing 12 towards the axis of symmetry 18, i.e. inwards into the cavity 16.An inner side of the shell 12 can mean the side facing the cavity 16. The coating 14 can be arranged on the entire inner side of the shell 12. The tank 10 can have an end part 22. The end part 22 can be designed as a flat plate perpendicular to the axis of symmetry 18 or, as in Fig. 1, have a curvature pointing outwards, i.e. away from the cavity 16, in particular a hemispherical shape. In the axial direction 15, which can run along the axis of symmetry 18, a cylindrical part 20 can be directly adjacent to the end part 22. The cylindrical part 20 can also be formed as a seamlessly drawn cylinder and referred to as such. The cylindrical part 20 is characteristic of the cylindrical design of the tank 10. In the axial direction shown in Fig. 1, a front part 24 can be directly adjacent to the cylindrical part 20.The front part 24 can have a shape or geometry pointing away from the cavity 16, i.e., curved outwards, in particular a hemispherical shape. The front part 24 can have the opening 26. A tubular element 27 can be connected to the front part 24 in the axial direction. The tubular element 27 can be formed integrally with the front part 24. Alternatively, the tubular element 27 can be fastened to the casing 12 via a thread in the casing 12 in the region of the opening 26 or around the opening 26 via an external thread, or can be screwed into the casing 12. A valve 28 can be connected to the tubular element 27 in the axial direction. The valve 28 can be designed to close the tube element 27 in a fluid-tight manner and / or to release the tube element 27 in a fluid-tight manner, so that hydrogen contained in the cavity 16 can flow out of the opening 26 through the fluid-tight tube element 27 and through the valve.The coating 14 can be formed from a material, in particular from a metallic material, which has a face-centered cubic crystal lattice. This can mean that a so-called unit cell of the material of the coating 14 has a face-centered cubic arrangement of the material's atoms. Additionally or alternatively, the coating can be made from a material with a hexagonal close-packed crystal lattice. In this exemplary embodiment, the coating can be made from aluminum, copper, or lead, to name three examples of a material with a face-centered cubic crystal lattice. Alternatively, the coating can be made from zinc or cadmium, these two metals having a hexagonal close-packed crystal lattice. The tubular element 27 can have the coating 14 on an inner side, i.e. on a side facing the axis of symmetry 18.The cylindrical design of the tank 10 here means that the largest part or the largest portion of the volume of the cavity 16 is encompassed by the cylindrical part 20. The steel material can be a high-strength steel with a yield strength of at least 550 MPa.

[0046] Fig. 2 shows a schematic sectional view of the tank 10 in a spherical design. "Spherical" here means that the shell 12 has a spherical or ball-shaped shape except for the recess for an opening 26. In this initial example, the spherical shell 12 can enclose the cavity 16. Fig. 2 can show the tank 10 in a spherical design in a finished state. As shown in Fig. 2, the shell 12 can have a thread in the region of the opening 26 or in the opening 26, into which thread a tubular element 27 can be screwed. Due to its spherical shape or substantially spherical shape, the tank 10 in this exemplary embodiment can have rotational symmetry with respect to an axis of symmetry 18, which can run through the opening and through a center point of the spherical shell 12. The tubular element 27 may have an end along the axis of symmetry 18 which may open into the cavity 16.At an opposite end of the tubular element 27, along the axis of symmetry 18, the tubular element 27 can have a valve 28. The opening 26, the tubular element 27, and the valve 28 can be designed or constructed analogously to the cylindrical design of the tank 10, i.e., essentially, such that hydrogen can be introduced into the tank 10, in particular into the cavity 16, and removed therefrom via the valve 28, the tubular element 27, and the opening 26. The coating 14 can be arranged on an inner side of the casing 12, i.e., a side facing the cavity 16. When the cavity 16 is filled with hydrogen, a higher internal pressure can develop in the cavity than in the surroundings of the tank. This can cause stresses, in particular tensile stresses, to develop in a material of an outer shell of the tank 10, for example. In all exemplary embodiments, it can be provided that the casing 12 can be designed to absorb these stresses.In other words, the shell 12 made of steel material can be designed to be load-bearing, i.e., to absorb the stresses resulting from the internal pressure of the tank 10. The coating 14 can be designed to be non-load-bearing. The thickness of the shell 12 can be calculated by a person skilled in the art using the boiler formula. According to the boiler formula, the stresses, which can also be referred to as cross-sectional stresses, in the cylindrical tank 10, particularly in the cylindrical part 20, are only half as great as the stresses in the circumferential direction, which can also be referred to as tangential stresses. In the spherical tank shown in Fig. 2, the material stresses are the same in every imaginary section. With an identical inner diameter of the cylindrical version and the spherical version, and with the same internal overpressure, the material stresses of the spherical tank 10, shown in Fig.2, those of the axial stresses in a cylindrical design, shown in Fig. 1. The spherical tank 10 thus represents a preferred embodiment of the tank 10, since it represents a particularly favorable ratio of weight, resulting from the smaller required thickness of the shell 12, to the volume of the cavity 16.

[0047] Fig. 3 shows a schematic external view of the tank 10 in a cylindrical design, in which the shell 12 is assembled from three parts. In the exemplary embodiment shown in Fig. 3, the shell 12 can not be manufactured in one piece, but can be composed of an end part 22, a cylindrical part 20 immediately adjacent to it in the axial direction, and a front part 24 immediately adjacent to this. Due to the tensile stresses that occur in the axial direction in the cylindrical design, the described parts can be assembled in the axial direction, as shown in Fig. 3. "Assembled" here can mean that the three parts can be connected by a material fit, for example by welding.This multi-part design of the shell 12 can offer the advantage that the individual parts can be manufactured using different manufacturing processes, which can reduce the overall manufacturing effort for the tank 10. The cylindrical part 20 can be manufactured as a seamless, for example drawn pipe. Seamless drawing of pipes is known from the prior art and offers the advantage that the cylindrical part 20 does not have a seam running in the longitudinal direction or in the axial direction 15, for example a weld seam, which could weaken the structure. In particular, it is along this seam that the particularly high tangential stresses could occur in the finished state of the tank 10 and when the internal pressure in the tank is greater than the ambient pressure. The end part 22 and the front part 24 can, for example, be manufactured using a deep-drawing process. As shown in Fig.As shown in Fig. 3, the three parts can be materially connected by the two weld seams 30. The front part 24 can have the opening 26 and the tubular element 27, as shown in Fig. 3.

[0048] Fig. 4 shows a schematic external view of the tank 10 in a cylindrical design with a shell 12 assembled from two parts. In this exemplary embodiment, the shell 12 can be made from a first tank half 32 and a second tank half 34 directly adjoining it in the axial direction. The second tank half 34 can have the opening 26 and the tubular element 27. In all exemplary embodiments, the tubular element 27 can be designed to receive the valve 28 and hold it fastened, for example via a thread, preferably via an external thread. The two tank halves 32, 34 can be held together by a material connection running in the circumferential direction, in particular a weld seam 30.The two-part design has the advantage that both tank halves can be manufactured in a deep-drawing process, whereby a cylindrical part of each of the two tank halves cannot have a seam in the longitudinal or axial direction 15.

[0049] Fig. 5 shows a schematic sectional view of the cylindrical tank 10 during the application of the inner coating 14 by a centrifugal casting process. The centrifugal casting process allows the shell 12 to be coated on its inside with the coating. The centrifugal casting process is characterized in that a mold, i.e. a casting mold, is rotated about an axis of rotation when molten material, for example molten metal, is introduced. The axis of rotation is preferably an axis of symmetry 18, for example an axis of rotational symmetry. Due to the centrifugal forces occurring as a result of the rotation, the liquid melt can be evenly distributed in the mold and solidify in this form upon cooling, thus retaining this shape. In this exemplary embodiment, the shell 12 can serve as a mold in the centrifugal casting process or be designed as a mold. Fig. 4 shows the shell 12 in its finished form.During the centrifugal casting process, the shell 12, which in the cylindrical embodiment shown here can be rotationally symmetrical about the axis of symmetry 18, can be rotated in a direction of rotation 40. In the direction of rotation 40, the shell 12 can rotate about the axis of symmetry 18. During rotation of the shell 12, a melt feed 36 can be introduced or introduced into the cavity 16 via the opening 26. The melt feed 36 can be designed so that fluid, here in particular liquid metal, i.e. melt, flows through or through it. At the beginning of the centrifugal casting process, for example, the melt feed 36 can be introduced deep into the shell 12, in particular into a region of the shell 12 enclosed or delimited by the end part 22. Melt, i.e. liquid metal, can be introduced into the cavity via the melt feed.During the centrifugal casting process, the melt feed 36 can be slowly withdrawn or guided out of the cavity 16 while constantly conveying melt into the cavity 16, allowing the melt 38 to be evenly distributed over the inside of the shell 12. The speed at which the melt feed 36 can be withdrawn from the cavity 16 during the centrifugal casting process, as well as the mass flow of melt introduced into the cavity 16 during the centrifugal casting process, can be adjusted by a person skilled in the art to produce a coating 14 of uniform thickness throughout. To ensure a complete and / or evenly thick coating of the inside of the shell 12, the centrifugal casting process can include post-processing.For this purpose, the shell can be positioned vertically, for example, and the end portion 22 can be heated locally, for example by induction, whereby melt can be introduced into the cavity through the opening 26. The front portion 24 can be heated locally by induction during post-processing, whereby melt 38 is introduced into this area, i.e., into the front portion or into the volume of the cavity 16 encompassed or delimited by the front portion.

[0050] If the casing 12 is composed of or can be composed of several parts, as shown, for example, in Fig. 3 or Fig. 4, it can be provided that each of the parts is coated in a separate centrifugal casting process in the manner described before assembly. The coated parts can then be joined, for example, welded, to form the fully manufactured casing 12, as shown, for example, in Fig. 3 and / or Fig. 4.

[0051] The following describes an alternative or additional manufacturing process to the process shown in Fig. 5. The coating 14 can be produced in a separate casting or centrifugal casting process, where "separate" here can mean that the mold used is not the tank 10 or parts of the tank 10, in particular the shell 12, 20, 22, 24, 32, 34, but a separately manufactured mold. In a first process step, the inner coating 14 can be manufactured from a metal material with a face-centered cubic or hexagonal close-packed crystal lattice in a centrifugal casting process, and in a subsequent process step, the tank 10 can be provided with the coating 14 on its inside by shrinking the steel material or the shell 12 onto the coating 14.For example, in a first process step, the coating 14 for the cylindrical part 20 can be cast separately, whereby it can be available as a hollow cylinder or tube after the first process step. In a second process step, this coating, present as a tube, can be introduced into the heated or warmed, for example, heated to 200 to 600 degrees Celsius, cylindrical part 20 of the shell 12. It can be particularly advantageous for the coating to have a larger outer diameter, i.e. an outer dimension across an axis of symmetry 18 up to the outer edges of the delimiting wall of the coating 14, than an inner diameter of the cylindrical part 20 of the shell 12. At room temperature of the cylindrical part 20, the coating 14 might therefore not be able to be introduced into it.Due to the heating, the cylindrical part 20 can expand as a result of thermal expansion, so that the coating 14, which can be at or near room temperature, for example, can be introduced into the cylindrical part 20. When the warm or previously heated cylindrical part 20 cools down, it can shrink onto the coating 14. As a result, the shell 12, in this example the cylindrical part 20, can enclose the coating 14 particularly tightly. In addition, due to the larger outer diameter of the coating 14, compressive stresses can occur in the shell 12 or the cylindrical part 20 upon cooling. These compressive stresses counteract the tensile stresses that occur in the finished tank 10 when there is excess pressure.In other words, shrinking the shell onto the coating creates a prestress that increases the maximum load-bearing capacity of the tank 10 or the shell 12, for example, in the form of a maximum permissible internal tank pressure. Analogous to the shrink-fitting example shown here for the cylinder part 20, shell parts or parts 20, 22, 24, 32, 34 can each be shrunk onto a coating 14 produced in the manner described. In a subsequent process step, the respective coated tank parts can be joined together to form a finished tank, for example by welding. It can be particularly advantageous to select a material with the described crystal lattices as the coating, which has a significantly lower melting point than the steel material of the shell 12.As a result, the heat introduced into the respective parts 20, 22, 24, 32, 34 to be joined during welding of the shell 12 can be sufficient for the respective coatings 14 of the parts 20, 22, 24, 32, 34 to at least melt and bond together, so that the tank 10, in the finished or assembled state, has a complete coating 14 on its inside and / or the coating 14 completely covering the inside, in particular without gaps.

[0052] A particularly preferred embodiment is described below.

[0053] This embodiment may arise from the brainstorming process within the GEN4 (GEN: Generation) hydrogen steel tank project. State-of-the-art Type 3 or Type 4 (CFRP) tank systems are typically used for hydrogen storage in the automotive sector. These types of tanks may have at least one outer shell, also referred to as the casing 12, made of CFRP or GRP (CFRP: Carbon Fiber Reinforced Plastic, GRP: Glass Fiber Reinforced Plastic). One project may investigate the use of Type 1 (steel) tanks for high-pressure technology (up to a pressure of 700 bar). A Type 1 tank may be characterized by having a steel casing.

[0054] The following technical problem can arise: The use of metallic Type 1 tanks in the available installation space of a passenger car (PK: passenger vehicle) can only be effective if a suitable base material (e.g. high-strength steel) can be used, for example as the casing 12. The higher the strength of a steel, the greater its tendency towards hydrogen embrittlement. Accordingly, when using high-strength steel, an internal hydrogen barrier layer, which can also be referred to as a coating 14, may have to be introduced into the tank. This barrier layer can ideally consist of a metal with a face-centered cubic lattice structure. Suitable materials for this purpose include aluminum, stainless steel and / or copper. The introduction of this layer or barrier layer can prove to be a major challenge. The following core idea can solve the technical problem described above.The idea for the tank 10 or for the production of the tank 10 can include the application of a hydrogen barrier layer, which can also be referred to as a coating 14, into a hydrogen tank container, which can also be referred to as a tank 10, using a centrifugal casting process. Currently, the process can be used to manufacture larger components. One idea is as follows: to enable existing technology for an internal coating (in the inner tank or on the inside of the tank 10). The already manufactured tank 10 can be used as a mold and the coating 14 can be applied using a centrifugal casting process. Alternatively, a seamless tube or a billet made of composite materials (300M and / or aluminum, and / or copper and / or stainless steel) can be produced by centrifugal casting. The billet or tube can then be formed into the tank 10.Thus, it can be expected that a successful barrier layer can be created and validated. Implementation of the idea may involve the following: producing the coating 14, hollow sections, or seamless pipe, and then validating the tank 10.

[0055] List of reference symbols

[0056] Tank...

[0057] Mantle ... radial direction

[0058] Coating ... axial direction

[0059] cavity...

[0060] axis of symmetry ...

[0061] Cylinder part ...

[0062] End part...

[0063] Front part...

[0064] Opening ...

[0065] Pipe element

[0066] Valve ...

[0067] Weld seam ... first tank half ... second tank half ...

[0068] Melt feed ...

[0069] Melt...

[0070] Rotation direction ...

Claims

Patent claims 1. Tank (10) for storing hydrogen for a motor vehicle, which tank is made of a steel material forming an at least partially closed cavity (16) for receiving the hydrogen, the inside of which is provided with a coating (14) forming a hydrogen barrier, characterized in that the inner coating (14) of the steel material is formed by a metal material applied in a centrifugal casting process with a face-centered cubic or hexagonal close-packed crystal lattice.

2. Tank (10) according to claim 1, characterized in that the steel material is formed at least in regions as a seamless drawn cylinder.

3. Tank (10) according to claim 1 or 2, characterized in that the tank (10) is made of two tank halves (32, 34) formed from the steel material and materially connected.

4. Tank (10) according to one of the preceding claims, characterized in that the inner coating (14) is formed from a non-ferrous alloy.

5. Tank (10) according to one of the preceding claims, characterized in that the material with the face-centered cubic crystal lattice consists at least partially of copper, aluminum, nickel, lead, platinum, silver and / or gold.

6. Tank (10) according to one of the preceding claims, characterized in that the material with the hexagonal close-packed crystal lattice consists at least partially of cobalt, cadmium, zinc and / or alpha-titanium.

7. Tank (10) according to one of the preceding claims, characterized in that the steel material is a high-strength steel with a yield strength of greater than 550 MPa.

8. A method for producing a tank (10) for storing hydrogen for a motor vehicle, in which the tank (10) produced from a steel material forming a closed cavity (16) for receiving the hydrogen is provided on its inner side with a coating (14) forming a hydrogen barrier, characterized in that the inner coating (14) is formed by a metal material with a face-centered cubic or hexagonal close-packed crystal lattice, which is applied to the steel material of the tank (10) in a centrifugal casting process.

9. Motor vehicle with at least one tank (10) according to one of claims 1 to 7.

Images