WO2024008821A1

WO2024008821A1 - Cryogenic fluid storage unit and corresponding production method

Info

Publication number: WO2024008821A1
Application number: PCT/EP2023/068602
Authority: WO
Inventors: Frederic Greber
Original assignee: Faurecia Systemes D'echappement
Priority date: 2022-07-08
Filing date: 2023-07-05
Publication date: 2024-01-11
Also published as: FR3137738A1

Abstract

This storage unit comprises a suspension (9) that fixes the inner tank (3) to the outer tank (7). The suspension (9) comprises a link (23) comprising: - an outer tube (25) located inside the inner tank (3); - a bottom plate (31) closing the end of the outer tube (29) in a sealed manner; - an inner tube (33) extending along a central axis (C) inside the outer tube (25), the inner tube (33) having an inner proximal end (59) fixed to the outer tank (7), an inner distal end (61) fixed to the bottom plate (31), and a central portion (63) connecting the inner proximal end (59) to the inner distal end (61); the central portion (63) having a wall with a given mean thickness (e); the inner distal end (61) comprising a first distal portion (83) having a wall with a thickness greater than 150% of the given mean thickness (e).

Description

TITLE: Cryogenic fluid storage unit and corresponding manufacturing process

The present invention generally relates to a cryogenic fluid storage unit.

Such a storage unit typically comprises an internal tank internally delimiting a storage volume of the cryogenic fluid, an external tank inside which the internal tank is housed, and a suspension fixing the internal tank to the external tank.

In order to limit heat transfer by convection from the external tank to the internal tank, the space defined between the internal tank and the external tank is maintained under a high vacuum.

Transfers by radiation are limited by arranging a layer of insulating material on the internal reservoir.

Heat transfers by conduction from the external tank to the internal tank mainly pass through the suspension. This suspension, to minimize thermal conduction, must offer the heat a particularly long path, and a particularly reduced passage section.

To do this, one solution is to provide in the suspension:

- an external tube having an external proximal end fixed to the internal reservoir, and an external distal end located inside the storage volume;

- a bottom plate sealingly closing the external distal end;

- an internal tube extending inside the external tube, the internal tube having an internal proximal end fixed to the external reservoir, and an internal distal end fixed to the bottom plate.

The heat, to go from the external tank to the internal tank, must pass through the internal tube. This must therefore be as long as possible, and have a wall thickness as thin as possible.

However, this goes against the other function of the suspension, which is to take up the weight of the internal tank and the accelerations experienced by the internal tank.

In the case of a cryogenic fluid storage unit embedded in a motor vehicle, the accelerations in the event of an impact can be high. In this context, the invention aims to propose a suspension making it possible to minimize the heat flow circulating by conduction from the external reservoir to the internal reservoir, while taking up significant forces applied to the internal reservoir.

To this end, the invention relates to a cryogenic fluid storage unit, the storage unit comprising an internal tank internally delimiting a cryogenic fluid storage volume, an external tank inside which the internal tank is housed, and a suspension fixing the internal tank to the external tank, the suspension comprising a connection comprising:

- an external tube, having an external proximal end fixed to the internal reservoir and an external distal end located inside the storage volume;

- a bottom plate sealingly closing the external distal end;

- an internal tube extending along a central axis inside the external tube, the internal tube having an internal proximal end fixed to the external reservoir, an internal distal end fixed to the bottom plate and a central section connecting the end inner proximal to inner distal end; the internal tube having a total length axially; the central section having axially a central length greater than 50% of the total length; the central section having a wall of given average thickness; the internal distal end comprising a first distal section having a wall with a thickness greater than 150% of the given average thickness.

In such a suspension, the forces in the internal tube are particularly high at the internal distal end.

Therefore, the invention provides that this internal distal end has a greater wall thickness than the central section of the internal tube.

The central section is subject to lower forces. It is thus possible to provide a lower wall thickness for the central section, and to minimize heat transfer in this way.

The inner tube only has significant wall thickness in areas of high stress, particularly at the inner distal end.

This makes it possible to satisfy both the requirement of minimizing heat transfers by conduction from the external reservoir to the internal reservoir, and of resuming the accelerations experienced by the internal reservoir. The cryogenic fluid storage unit may also have one or more of the characteristics below, considered individually or in all technically possible combinations:

The internal distal end comprises a second distal section having a wall with a thickness greater than 250% of the given average thickness, the second distal section being connected to the central section by the first distal section.

The inner tube includes a main sleeve and a first distal sleeve arranged in or around the main sleeve, the main sleeve extending along the entire length of the inner tube, the first distal sleeve extending along the first distal section but not the along the central section.

The inner tube includes a second distal sleeve arranged in or around the first distal sleeve and the main sleeve, the first distal sleeve extending along the second distal section, the second distal sleeve extending along the second distal section, but not along the first distal section nor along the central section.

The main sleeve and the first distal sleeve are pressed against each other without play.

The main sleeve and the first distal sleeve have respective ends facing the bottom plate, superimposed and fixed to each other, the first distal sleeve having an opposite end free with respect to the main sleeve.

The connection comprises a fixing ring fixed to the external reservoir, the internal proximal end of the internal tube being directly fixed to the fixing ring, the internal proximal end comprising a first proximal section having a wall thickness greater than 150% of the given average thickness.

The internal proximal end comprises a second proximal section having a wall with a thickness greater than 250% of the given average thickness, the second proximal section being connected to the central section by the first proximal section.

The inner tube includes a first proximal sleeve arranged in or around the main sleeve, the first proximal sleeve extending along the first proximal section but not along the central section.

The inner tube includes a second proximal sleeve arranged in or around the first proximal sleeve and the main sleeve, the first proximal sleeve extending along the second proximal section, the second sleeve proximal extending along the second proximal section, but not along the first proximal section nor along the central section.

According to a second aspect, the invention relates to a method of manufacturing a cryogenic fluid storage unit having the above characteristics, the method comprising the following steps:

- obtaining the main sleeve and the first distal sleeve, the first distal sleeve having an external section strictly less than an internal section of the main sleeve;

- introduction of the first distal sleeve into the main sleeve;

- mechanical expansion of the first distal sleeve.

Other characteristics and advantages of the invention will emerge from the detailed description given below, for information only and in no way limiting, with reference to the appended figures, among which:

- Figure 1 is an axial section view of the cryogenic fluid storage unit;

- Figure 2 is an enlarged sectional view of the suspension of one end of the internal tank of Figure 1;

- Figure 3 is a schematic representation illustrating a manufacturing step of the cryogenic fluid storage unit of Figures 1 to 2;

- Figure 4 is a schematic representation illustrating the level of stresses in the internal tube of Figure 2; And

- Figure 5 is an enlarged sectional view of the bottom plate for an alternative embodiment of the invention.

The storage unit 1 shown in Figure 1 is intended to store a cryogenic fluid.

By cryogenic fluid we mean a fluid at a very low temperature, which is at least partially in the liquid state inside the storage unit.

This fluid is typically hydrogen. Alternatively, the fluid is helium, nitrogen, a natural gas such as methane ChL, air, or any other suitable fluid.

This storage unit is typically intended to be on board a vehicle having an electric propulsion motor, for example a motor vehicle, a train, a boat or any other vehicle.

The motor vehicle is for example a car, a utility vehicle, a truck, etc. The storage unit 1 is typically intended to power a fuel cell. The fuel cell is configured to generate electricity and power the vehicle's electric propulsion motor.

The cryogenic fluid storage unit 1 comprises an internal tank 3 internally delimiting a cryogenic fluid storage volume 5, an external tank 7 inside which the internal tank 3 is housed, and a suspension 9 fixing the internal tank 3 to the external tank 7.

In the example shown, the internal tank 3 has a horizontal central axis X.

The internal reservoir 3 comprises a shell 11, closed at its two axial ends by bases 13.

The ferrule 1 1 is cylindrical, centered on the X axis.

The external tank 7 also has a horizontal axis.

It includes a ferrule 15, closed at its two ends by bases 17.

Ferrule 15 is cylindrical, centered on the X axis.

The internal tank 3 and the external tank 7 define between them an intermediate space 19, maintained under a high vacuum. This vacuum is typically of the order of ^10'5 millibars, so as to strongly limit heat transfer by convection from the external tank 7 to the internal tank 3.

Thermal insulation 21 is interposed between the internal tank 3 and the external tank 7. The thermal insulation 21 is typically placed on the external surface of the internal tank 3. The thermal insulation 21 comprises for example a plurality of metal sheets superimposed on each other on the others, with interposition of layers of fibers.

The suspension 9 is arranged in such a way that the entire weight of the internal tank 3 is taken up by the external tank via the suspension 9.

The weight of the internal tank 3 is understood here to include the weight of the cryogenic fluid stored in the internal tank.

The accelerations experienced by the internal tank 3 and the cryogenic fluid contained in the internal tank 3 are also transmitted to the external tank 7 via the suspension 9.

When the storage unit 1 is loaded into a vehicle, these accelerations result from changes in direction of the vehicle, braking applied to the vehicle or acceleration of the vehicle, as well as roughness or irregularities in the road, or even shocks. applied to the vehicle. In the example shown, the suspension comprises two connections 23. The connections 23 suspend the two opposite axial ends of the internal reservoir 3 to the external reservoir 7. These connections 23 are identical. Only one of these connections 23 will be described below.

As visible in Figure 2, connection 23 comprises:

- an external tube 25, having an external proximal end 27 fixed to the internal reservoir 3 and an external distal end 29 located inside the storage volume 5;

- a bottom plate 31 sealingly closing the external distal end 29;

- an internal tube 33 extending along a central axis C inside the external tube 25.

The X and C axes are preferably combined. Alternatively, they are not confused.

The connection 23 comprises an internal ring 35 directly fixed to the internal surface of the internal reservoir 3.

The internal ring 35 is fixed to the bottom 13.

The internal ring 35 is annular. The internal ring 35 comprises an annular base 37, delimiting a front face 39.

The front face 39 is annular and extends in a plane perpendicular to the central axis C.

The annular base 37 is extended axially by a cylindrical neck 41, opposite the front face 39.

The annular base 37 and the neck 41 internally delimit a cylindrical passage 43, coaxial with the central axis C.

The annular base 37 and the neck 41 are connected to each other by a fillet 45, in the form of a torus portion. A slice 46 connects the front face 40 to the fillet 45.

The annular base 37 is engaged in an orifice provided in the bottom 13 of the internal reservoir 3.

The internal reservoir 3 is fixed to the edge 46 of the annular base 37.

The external tube 25 is substantially cylindrical, and is coaxial with the central axis C.

The external proximal end 27 of the external tube 25 extends axially the neck 41. It has a thickness substantially identical to that of the neck 41.

The external tube 25 has a wall of substantially constant thickness over its entire axial length.

The bottom plate 31 has a substantially circular bottom 47. It also includes a raised edge 49, extending over the entire perimeter of the bottom 47. The erect edge 49 extends from the bottom 47 axially towards the external tube 25. It is placed axially in the extension of the external distal end 29. It is fixed in a sealed manner, for example by welding, at the end external distal 29.

The erect edge 49 has substantially the same thickness as the external tube 25.

The bottom plate 31 has a large face 51 facing the inside of the external tube 25.

The large face 51 carries a circular rib 53, centered on the central axis C.

In Figure 3, the radially internal surface of the circular rib 53 is connected to the large face 51 by a fillet. Likewise, the radially external surface of the circular rib 53 is connected to the large face 51 by a fillet.

In the variant of Figure 5, the radially internal surface of the circular rib 53 is connected to the large face 51 by a surface 54i having, in radial planes containing the central axis C, sections in the form of an ellipse. Likewise, the radially external surface of the circular rib 53 is connected to the large face 51 by a surface 54e having, in radial planes containing the central axis C, sections in the form of an ellipse. Such a shape improves the mechanical strength of the suspension.

A thermal insulation layer 55 is placed inside the outer tube 25, against the inner surface of the outer tube 25. This thermal insulation layer 55 extends over the entire length of the outer tube 25, crosses the passage 43 and extends beyond the front face 39.

The internal tube 33 is placed inside the thermal insulating layer 55, and is separated from it by a void 57.

The internal tube 33 has an internal proximal end 59 fixed to the external reservoir 7, an internal distal end 61 fixed to the bottom plate 31, and a central section 63 connecting the internal proximal end 59 to the internal distal end 61.

The suspension 9 comprises a fixing ring 65 fixed to the external reservoir 7, the internal proximal end 59 of the internal tube 33 being directly fixed to the fixing ring 65.

In the example shown, the fixing ring 65 is fixed to a cup 67, itself fixed to the internal surface of the external tank 7 (figure 1). The cup 67 is placed axially opposite the bottom 13 of the internal reservoir 3. It has a raised edge 71, rigidly fixed to the ferrule 15 of the external reservoir 7.

In the example shown, the fixing ring 65 is similar to the internal ring 35. It thus comprises an annular base 73, defining a front surface 75. The front surface 75 extends in a plane perpendicular to the central axis C. It has an annular shape.

The annular base 73 is extended axially opposite the front surface 75 by a neck 77. The neck 77 is substantially cylindrical, centered on the axis C. The annular base 73 and the neck 77 internally delimit a substantially cylindrical passage 79 , centered on axis C. The annular base 73 and the neck 77 are connected to each other by a fillet 81, in the form of a torus portion.

A slice 82 connects the front face 75 to the fillet 81.

The annular base 73 is engaged in an orifice provided in the cup 67.

The cup 67 is fixed to the edge 82 of the annular base 73.

The internal tube 33 is substantially rectilinear and cylindrical. It is centered on the central axis C.

The internal tube 33 has a total length L axially.

The central section 63 has a wall of given average thickness e. This given average thickness e corresponds to the average of the thickness of all points on the wall.

The thickness of the wall of the central section 63 varies between e-20% and e+20%, preferably between e-10% and e+10%.

Typically, the wall of the central section 63 has a substantially constant thickness over the entire length of the central section 63.

The central section 63 has axially a central length L' greater than 50% of the total length L, preferably greater than 60% of the total length L, and even preferably greater than 70% of the total length L.

The internal distal end 61 of the internal tube 33 has a thicker wall than that of the central section 63.

It has axially a length less than 25% of the total length L, preferably less than 20% of the total length L, and even preferably less than 15% of the total length L.

The internal distal end 61 comprises a first distal section 83 having a wall with a thickness greater than 150% of the given average thickness e.

Advantageously, the internal distal end 61 further comprises a second distal section 85 having a wall with a thickness greater than 250% of the given average thickness e.

The second distal section 85 is connected to the central section 63 by the first distal section 83.

The second distal section 85 is directly connected to the rib 53. The first distal section 83 has a thickness advantageously between 150% and 250% of the given average thickness e, more preferably between 175% and 225%, and worth for example 200% of the given average thickness e.

The second distal section 85 has a thickness of between 250% and 350% of the given average thickness e, preferably between 275% and 325% of the given average thickness e, and worth for example 300% of the thickness given average e.

The thickness of the wall of the second distal section 85 is typically substantially equal to the thickness of the rib 53.

The first distal section 83 has a length of between 1% and 10% of the total length L, preferably between 1% and 6% of the total length L. The second distal section 85 has a length of between 2% and 20% % of the total length L, preferably between 2.5% and 15% of the total length L, and even more preferably between 2.5% and 10% of the total length L.

According to a particularly advantageous embodiment, the internal tube 33 comprises a main sleeve 87 and a first distal sleeve 89 arranged in or around the main sleeve 87.

In the example shown, the first distal sleeve 89 is arranged in the main sleeve 87.

The internal tube 33 further comprises a second distal sleeve 91 arranged in or around the first distal sleeve 89 and the main sleeve 87.

In the example shown, the second distal sleeve 91 is arranged in the first distal sleeve 89.

The main sleeve 87 extends over the entire length of the internal tube 33.

The first distal sleeve 89 extends along the first distal section 83 but not along the central section 63.

The first distal sleeve 89 also extends along the second distal section 85.

The second distal sleeve 91 extends along the second distal section 85, but not along the first distal section 89 nor along the central section 63.

In other words, the central section 63 consists only of the main sleeve 87. The first distal section 83 has two thicknesses, and is formed from the superposition of the first distal sleeve 89 and the main sleeve 87.

The second distal section 85 has three thicknesses, and is formed from the superposition of the second distal sleeve 91, the first distal sleeve 89 and the main sleeve 87. The main sleeve 87 and the first distal sleeve 89 are pressed against each other, without play.

Likewise, the second distal sleeve 91 and the first distal sleeve 89 are pressed against each other, without play.

The main sleeve 87 and the first distal sleeve 89 have respective axial ends 93, 95 facing the bottom plate 31, superimposed and rigidly fixed to each other.

Likewise, the second distal sleeve 91 has an axial end 97 facing the bottom plate 31, superimposed on the end 95 and fixed thereto.

In other words, the ends 93, 95, 97 stop axially at the same level and are rigidly fixed to each other by any suitable means.

These ends 93, 95, 97 are rigidly fixed to the rib 53 by a weld, the fixing weld constituting for example the means allowing the ends 93, 95, 97 to be fixed to each other.

The first distal sleeve 89 has a free axial end 99 vis-à-vis the main sleeve 87. The free axial end 99 is opposite the axial end 95, that is to say the bottom plate 31.

Likewise, the second distal sleeve 91 has an axial end 101 free with respect to the first distal sleeve 89. This end 101 is opposite the end 97 and the bottom plate 31.

Typically, the main sleeve 87 has a thickness of between 1 and 5 millimeters, preferably between 1 and 3 millimeters, and worth for example 1.5 millimeters.

The distal sleeves 89 and/or 91 advantageously have the same thickness as the main sleeve 87.

The internal proximal end 59 of the internal tube 33 is directly fixed to the fixing ring 65.

More precisely, it is attached to collar 77.

The internal proximal end 59 has a thicker wall than that of the central section 63.

The internal proximal end 59 comprises a first proximal section 103 having a wall thickness greater than 150% of the given average thickness e. Advantageously, it also comprises a second proximal section 105 having a wall thickness greater than 250% of the given average thickness e.

The second proximal section 105 is connected to the central section 63 by the first proximal section 103.

The second proximal section 105 is directly connected to the fixing ring 65. It preferably has a wall thickness substantially equal to the thickness of the neck 77.

The first proximal section 103 has a thickness advantageously between 150% and 250% of the given average thickness e, more preferably between 175% and 225%, and worth for example 200% of the given average thickness e.

The second proximal section 105 has a thickness of between 250% and 350% of the given average thickness e, preferably between 275% and 325% of the given average thickness e, and worth for example 300% of the thickness given average e.

The first proximal section 103 has a length of between 1% and 10% of the total length L, preferably between 1% and 6% of the total length L. The second proximal section 105 has a length of between 2% and 20% % of the total length L, preferably between 2.5% and 15% of the total length L, and even more preferably between 2.5% and 10% of the total length L.

The internal tube 33 advantageously comprises a first proximal sleeve 107 arranged in or around the main sleeve 87.

The first proximal sleeve 107, in the example shown, is arranged in the main sleeve 87.

The first proximal sleeve 107 extends along the first proximal section 103 but not along the central section 63.

The internal tube 33 further comprises a second proximal sleeve 109 arranged in or around the first proximal sleeve 107 and the main sleeve 87.

In the example shown, the second proximal sleeve 109 is arranged in the first proximal sleeve 107.

The first proximal sleeve 107 extends along the second proximal section 105.

The second proximal sleeve 109 extends along the second proximal section 105, but not along the first proximal section 103 nor along the central section 63.

The first proximal section 103 has two thicknesses, and is formed from the superposition of the first proximal sleeve 107 and the main sleeve 87. The second proximal section 105 has three thicknesses, and is formed from the superposition of the main sleeve 87, the first proximal sleeve 107 and the second proximal sleeve 109.

As before, the main sleeve 87 and the first proximal sleeve 103 are pressed against each other, without play.

Likewise, the second proximal sleeve 109 and the first proximal sleeve 107 are pressed against each other without play.

The main sleeve 87 and the first proximal sleeve 107 have respective ends facing the fixing ring 65, referenced 1 11 and 113.

Ends 111 and 113 are superimposed and fixed to each other.

Likewise, the second proximal sleeve 109 has an end 115 facing the fixing ring 65. The end 115 is superimposed on the ends 111 and 113, and is fixed at the ends 111 and 113.

The ends 111, 113 and 115 therefore stop axially at the same level, and together constitute the free edge of the internal tube 33. They are rigidly fixed to the fixing ring 65, for example by welding.

This weld advantageously constitutes the fixing fixing the ends 1 11, 1 13 and 115 to each other.

The first proximal sleeve 107 has an end 117 free with respect to the main sleeve 87. This end 117 is opposite the end 113 and the ring 65.

Likewise, the second proximal sleeve 109 has an end 119 free relative to the first proximal sleeve 107. The end 109 is opposite the end 115 and the fixing ring 65.

A manufacturing process for the storage unit above will now be detailed, in particular with reference to Figure 3.

The method includes a step of obtaining the main sleeve 87 and the first distal sleeve 89.

The first distal sleeve 89 has at this stage an external section strictly smaller than the internal section of the main sleeve 87, as illustrated in Figure 3. For example the external diameter of the first distal sleeve 89 is 1 millimeter less than the internal diameter of the sleeve main 87.

Preferably, the method also includes a step of obtaining the second distal sleeve 91, the latter having an external section strictly less than an internal section of the first distal sleeve 89. For example, the second distal sleeve 91 has a lower external section of 1 millimeter to the internal section of the first distal sleeve 89. The method also includes a step of introducing the first distal sleeve 89 into the main sleeve 87.

The method also advantageously comprises a step of introducing the second distal sleeve 91 into the first distal sleeve 89.

The method also includes a step of mechanical expansion of the first distal sleeve 89.

Typically, during this mechanical expansion step, the second distal sleeve 91 is also mechanically expanded.

The mechanical expansion step has the effect of widening the section of the first distal sleeve 89, and of pressing it against the internal surface of the main sleeve 87.

The second distal sleeve 91, during the same operation, is expanded mechanically, its section being increased such that the second distal sleeve 91 is pressed against the internal surface of the first distal sleeve 89.

This operation is carried out for example using a mandrel moved inside the second distal sleeve 91. This operation is known and will not be described in detail here.

As visible in Figure 2, this operation can lead to a slight deformation of the end of the main sleeve 87.

The first proximal sleeve 107 of the inner tube 33 is mounted in the main sleeve 87 using the same steps as the first distal sleeve 89.

Thus, the method comprises a step of obtaining the first proximal sleeve 107, this sleeve having an external section strictly less than the internal section of the main sleeve 87, a step of introducing the first proximal sleeve 107 into the main sleeve 87, and a step of mechanical expansion of the first proximal sleeve 107.

Likewise, the second proximal sleeve 109 of the internal tube 33 is mounted in the first proximal sleeve 107 as described for the second distal sleeve 91.

In other words, the method comprises a step of obtaining the second proximal sleeve 109, this sleeve having an external section strictly less than the internal section of the first proximal sleeve 107, a step of introducing the second proximal sleeve 109 into the first proximal sleeve 107, and a step of mechanical expansion of the second proximal sleeve 109.

Typically, the first proximal sleeve 107 and the second proximal sleeve 109 are expanded simultaneously. Alternatively, the attachment of the first distal sleeve 89, and possibly the second distal sleeve 91, to the main sleeve 87 is carried out according to a different method, by thermal expansion.

In this case, the method includes a step of obtaining the main sleeve 87 and the first distal sleeve 89, the first distal sleeve 89 having an external section substantially equal to or slightly greater than the internal section of the main sleeve 87.

The method then includes a step of heating the main sleeve 87, making it possible to expand this main sleeve 87.

Simultaneously, the first distal sleeve 89 is cooled, so as to contract this distal sleeve 89.

The cooled first distal sleeve 89 is then introduced into the heated main sleeve 87.

Once the main sleeve 87 and the first distal sleeve 89 have returned to room temperature, the first distal sleeve 87 is rigidly fixed inside the main sleeve 87.

The second distal sleeve 91 is fixed inside the first distal sleeve 87 in the same way.

Preferably, the second distal sleeve 91 is fixed inside the first distal sleeve 89 before introduction of the first distal sleeve 89 into the main sleeve 87. Thus, the first and second distal sleeves 89, 91 are cooled simultaneously and introduced together into the main sleeve 87 thermally expanded.

The first proximal sleeve 107, and optionally the second proximal sleeve 109, are introduced into the main sleeve 87 using the same thermal expansion method.

In any case, the process also includes the following steps:

1 - fixing the external proximal end 27 of the external tube 25 to the ring 35;

2- fixing the external distal end 29 of the external tube 25 to the bottom plate 31;

3- fixing the internal distal end 61 of the internal tube 33 to the bottom plate 31;

4- introduction of insulation 55 between the internal tube 33 and the external tube 25;

5- fixing the fixing ring 65 to the internal proximal end 59 of the internal tube 33. These steps are carried out successively in order, from 1 to 5.

The process thus results in the formation of a bond 23 of the type described above.

The method also includes a step of obtaining the internal 3 and external 7 reservoirs, and a step of suspending the internal reservoir 3 from the external reservoir 7 using two connections 23 obtained as described above. The technical effect obtained due to the design of the internal tube 33 is illustrated in Figure 4.

This figure illustrates the mechanical stress levels in the internal tube 33.

Zones of increasing mechanical stress are materialized on the internal tube and referenced from a to i. The stress ranges, in MPa, corresponding to each zone, are indicated in Figure 4. They vary between 40 and 200 MPa.

The connection between the internal tube 33 and the bottom plate 31 is subject to very high stresses, due to the significant overhang between the internal proximal end 59 of the internal tube 33 and the bottom plate. 31

Likewise, the overhang between the external proximal end 27 of the external tube 25, fixed to the internal reservoir 3, and the bottom plate 31 is very important, such that the stresses at the level of the fixing of the tube external 25 to the bottom plate 31 are elevated.

It appears that, due to the progressive variation in thickness of the wall of the internal tube 33 at the level of the internal distal end 61, the mechanical stresses at this internal distal end 61 are well controlled and are at a satisfactory level .

These constraints are greater in the central section 63, relatively less important at the level of the first distal section 83, and even less significant at the level of the second distal section 85, directly linked to the bottom plate 31.

It appears that the zone undergoing the maximum mechanical stresses is the portion of the central section 63 which adjoins the first distal section 83. In all cases, the stresses remain lower than the admissible limit, which here is 180 MPa.

These results were obtained by calculation, for a connection whose different elements are made of type 316L stainless steel. The mechanical calculations were made with an exterior temperature of 20°C and considering that the storage unit is at 20°C, corresponding to the most severe condition, given that the resistance of type 316L stainless steel decreases with temperature.

The length of the inner tube is 560 millimeters and its diameter is 76 millimeters. The thickness of the different sleeves is 1.5 millimeters. The central section of the internal tube thus has a wall of 1.5 millimeters thickness, the first proximal section and the first distal section a wall thickness of 3 millimeters, the second proximal section and the second distal section a wall thickness of 4.5 millimeters.

The axial length of the first proximal sleeve and the first distal sleeve is 55 millimeters. The axial length of the second proximal sleeve and the second distal sleeve is 40 millimeters. The calculation was carried out for an internal tank whose mass is 167 kg, storing 40 kg of hydrogen.

The heat flux passing by conduction along the internal tube 33 is approximately 1 W/m ² .K. This heat transfer by conduction is particularly low.

The complete heat transfer from the external reservoir to the internal reservoir, taking into account the flows by convection, by conduction and by radiation, is approximately 6.2 W, with approximately 1 W each of the two connections.

The suspension architecture described above is particularly advantageous.

It makes it possible to create a connection whose internal tube is very long, with a particularly thin wall over most of its length.

The heat transfer by conduction in the internal tube is thus particularly low.

Furthermore, due to the presence of extra thickness at the internal distal end, the mechanical loading of the connection with the bottom plate remains controlled.

Due to the extra thickness at the internal proximal end, the mechanical loading of the connection with the external reservoir is also controlled.

Producing the extra thicknesses using sleeves allows for convenient and economical manufacturing of the internal tube.

The fact that the main sleeve and the first distal sleeve are pressed against each other without play allows good mechanical behavior of the internal tube, and in particular a gradual reduction of mechanical stresses along the internal distal end.

The fact that the second distal sleeve is pressed against the first distal sleeve without play also contributes to the gradual reduction of stresses in the internal distal end.

The fact that the first distal sleeve has one end fixed to the corresponding end of the main sleeve and a free opposite end allows slight sliding between the first distal sleeve and the main sleeve. This helps to reduce the level of stress at the internal distal end.

The fact that the second distal sleeve is mounted in the same way, with one end rigidly attached to the corresponding end of the first distal sleeve and the opposite end free, contributes to the same result.

Obtaining the internal tube by fixing the first distal sleeve in the main sleeve by mechanical expansion allows the internal tube to be manufactured quickly and conveniently. Fixing the second distal sleeve in the first distal sleeve by mechanical expansion contributes to the same result.

The storage unit and the manufacturing process can have multiple variations.

The internal tank and the external tank are not necessarily horizontal axes but could be vertical axes.

The internal proximal end is not necessarily of the type described above, that is to say with an extra thickness of material compared to the central section. Depending on the accelerations to be taken up, the mass of the internal reservoir, the method of attachment to the external reservoir, the internal proximal end could also be of the same thickness as the central section.

The extra thickness of material in the first distal section, and possibly in the second distal section, could be obtained by a method different from that described above, consisting of using sleeves fitted into each other.

For example, the first distal section, and possibly the second distal section, could be obtained by pushing back the material of the internal tube, so as to create additional thicknesses at the level of the internal distal end.

It could also be obtained by folding the internal tube on itself at its internal distal end.

The first distal sleeve could be arranged outside the main sleeve. The second distal sleeve could then be arranged outside the first distal sleeve or inside the main sleeve. The same variants can be considered for the first proximal sleeve, and possibly the second proximal sleeve.

The internal distal end could not comprise exactly two sections of increasing thickness, but for example only one, or three, four or more than four sections of increasing thickness.

Likewise, the internal proximal end could not comprise exactly two sections of increasing thickness, but for example only one, or three, four or more than four sections of increasing thickness.

Claims

1. Cryogenic fluid storage unit, the storage unit (1) comprising an internal tank (3) internally delimiting a volume (5) for storing the cryogenic fluid, an external tank (7) inside which is housed the internal tank (3), and a suspension (9) fixing the internal tank (3) to the external tank (7), the suspension (9) comprising a connection (23) comprising:

- an external tube (25), having an external proximal end (27) fixed to the internal reservoir (3) and an external distal end (29) located inside the storage volume (5);

- a bottom plate (31) sealingly closing the external distal end (29);

- an internal tube (33) extending along a central axis (C) inside the external tube (25), the internal tube (33) having an internal proximal end (59) fixed to the external reservoir (7), an internal distal end (61) fixed to the bottom plate (31) and a central section (63) connecting the internal proximal end (59) to the internal distal end (61); the internal tube (33) axially having a total length (L); the central section (63) having axially a central length greater than 50% of the total length (L); the central section (63) having a wall of given average thickness (e); the internal distal end (61) comprising a first distal section (83) having a wall with a thickness greater than 150% of the given average thickness (e).

2. Storage unit according to claim 1, in which the internal distal end (61) comprises a second distal section (85) having a wall with a thickness greater than 250% of the given average thickness (e), the second distal section (85) being connected to the central section (63) by the first distal section (83).

3. Storage unit according to claim 1 or 2, wherein the internal tube (33) comprises a main sleeve (87) and a first distal sleeve (89) arranged in or around the main sleeve (87), the main sleeve ( 87) extending over the entire length of the internal tube (33), the first distal sleeve (89) extending along the first distal section (83) but not along the central section (63).

4. Storage unit according to claim 3 combined with claim 2, in which the internal tube (33) comprises a second distal sleeve (91) arranged in or around the first distal sleeve (89) and the main sleeve (87), the first distal sleeve (89) extending along the second distal section (85), the second sleeve distal section (91) extending along the second distal section (85), but not along the first distal section (83) nor along the central section (63).

5. Storage unit according to claim 3 or 4, in which the main sleeve (87) and the first distal sleeve (89) are pressed against each other without play.

6. Storage unit according to any one of claims 3 to 5, in which the main sleeve (87) and the first distal sleeve (89) have respective ends (93, 95) facing the bottom plate (31) , superimposed and fixed to each other, the first distal sleeve (89) having an opposite end (99) free with respect to the main sleeve (87).

7. Storage unit according to any one of the preceding claims, wherein the connection (23) comprises a fixing ring (65) fixed to the external reservoir (7), the internal proximal end (59) of the internal tube (33 ) being directly fixed to the fixing ring (65), the internal proximal end (59) comprising a first proximal section (103) having a wall with a thickness greater than 150% of the given average thickness (e).

8. Storage unit according to claim 7, in which the internal proximal end (59) comprises a second proximal section (105) having a wall with a thickness greater than 250% of the given average thickness (e), the second proximal section (105) being connected to the central section (63) by the first proximal section (103).

9. Storage unit according to claim 7 or 8, wherein the internal tube (33) comprises a first proximal sleeve (107) arranged in or around the main sleeve (87), the first proximal sleeve (107) extending the along the first proximal section (103) but not along the central section (63).

10. Storage unit according to claim 9 combined with claim 8, wherein the internal tube (33) comprises a second proximal sleeve (109) arranged in or around the first proximal sleeve (107) and the main sleeve (87) , the first proximal sleeve (107) extending along the second proximal section (105), the second proximal sleeve (109) extending along the second proximal section (105), but not along the first proximal section ( 103) nor along the central section (63).

11. Process for manufacturing the storage unit of any one of claims 3 to 6, the process comprising the following steps:

- obtaining the main sleeve (87) and the first distal sleeve (89), the first distal sleeve (89) having an external section strictly less than an internal section of the main sleeve (87); - introduction of the first distal sleeve (89) into the main sleeve (87);

- mechanical expansion of the first distal sleeve (89).