Protective box, cryogenic fluid storage unit and vehicle

Abstract

Protective box, cryogenic fluid storage unit and vehicle The protective box (9) is shaped to internally receive at least one cryogenic fluid storage tank (7) and to protect this storage tank (7) against external attacks such as impacts or fires. It comprises an external casing (11) comprising: - a fixing wall (37) intended to be fixed to the vehicle (1); - a protective wall (39) opposite the fixing wall (37); - lower and upper walls (41, 43); - a front wall (45) and a rear wall (47).The protective box (9) further comprises a reinforcing structure (65) comprising:- at least one longitudinal beam (67) rigidly fixed to the protective wall (39);- a plurality of oblique beams (69), securing the at least one longitudinal beam (67) to the upper wall (43) and to the lower wall (41); - stiffening profiles (71) each fixed to the upper wall (43) or to the lower wall (41), close to points of fixing of the oblique beams (69) to said upper and lower walls (43, 41) Figure for the abstract: 2.

Description

Title of the invention: Protective box, cryogenic fluid storage unit and vehicle

[0001] The invention generally relates to vehicles equipped with cryogenic fluid tanks.

[0002] It is possible to equip a heavy vehicle such as a truck with two cryogenic fluid storage tanks.

[0003] This vehicle comprises a chassis, with two longitudinal side members spaced transversely relative to each other.

[0004] The two storage tanks can be fixed to the two side members, cantilevered transversely relative to these side members, towards the outside of the vehicle.

[0005] The cryogenic fluid is, for example, hydrogen. The hydrogen powers an internal combustion engine or a fuel cell producing electricity for the vehicle's propulsion engine.

[0006] The storage tank must be protected from shocks and the risk of fire.

[0007] In the event of a transverse impact in particular, the integrity of the tank and the retention of the storage tanks on the side members must be guaranteed. The tank and its equipment must not leak following said impact.

[0008] It is possible to provide, for the storage tanks, very thick walls and fixing of the tanks to the side members by means of straps.

[0009] Such an arrangement has the disadvantage that the tanks are of significant mass. This makes attachment to the side members particularly delicate.

[0010] In this context, the invention aims to propose a vehicle which does not have the above defects.

[0011] To this end, the invention relates, according to a first aspect, to a rigid protective box intended to be mounted on board a vehicle, the protective box being shaped to internally receive at least one cryogenic fluid storage tank and to protect this storage tank against external attacks such as impacts or fires, the protective box comprising an external casing comprising:

[0012] - a fixing wall intended to be fixed to the vehicle;

[0013] - a protective wall opposite the fixing wall;

[0014] - lower and upper walls facing respectively towards a surface of vehicle rolling and opposite the rolling surface;

[0015] - a front wall and a rear wall facing longitudinally forward and towards the rear of the vehicle;

[0016] the protective box further comprising a reinforcing structure comprising:

[0017] - at least one longitudinal beam rigidly fixed to the protective wall;

[0018] - a plurality of oblique beams, securing the at least one longitudinal beam to the upper wall and the lower wall;

[0019] - stiffening profiles each fixed to the upper wall or to the wall lower, near the points of attachment of the oblique beams to said upper and lower walls.

[0020] The protective box provides protection for the storage tank against shocks and flames. It is thus possible to reduce the thickness of the walls of the storage tank, and therefore their mass.

[0021] The protective box of the invention makes it possible to absorb an impact against a vehicle weighing between 250 kg and 2.5 tonnes, preferably between 1 and 1.5 tonnes, the vehicle traveling up to 60 km / h, preferably between 40 and 50 km / h.

[0022] The fact that the outer casing has six walls opposite each other makes it particularly suitable for resisting shocks. Such a structure is very rigid. The forces are transmitted from one wall to the other.

[0023] The reinforcement structure makes it possible to transmit, in the event of a transverse impact, the forces from the protective wall to the upper wall and the lower wall very effectively. The forces are transmitted to several zones, distributed over the lower wall and the upper wall, which helps to reduce the level of stress in these walls.

[0024] The stiffening profiles help to limit the deformation of the upper and lower walls. Indeed, the forces transmitted by the oblique beams to the upper and lower walls tend to deform these walls, creating bumps towards the outside of the box. The stiffening profiles help to limit these deformations.

[0025] The protective box may further have one or more of the following characteristics, considered individually or in all technically possible combinations: - one or more of the following walls are lined with a structured stiffening sheet: the protective wall, the lower wall, the upper wall - the fixing wall, the protective wall, the bottom wall, and the front and rear walls are solid; - in which the upper wall has orifices connecting an internal volume of the external envelope with an atmosphere outside the external envelope.

[0026] According to a second aspect, the invention relates to a cryogenic fluid storage unit, comprising a protective box having the above characteristics, and a cryogenic fluid storage tank rigidly fixed inside the outer casing of the protective box, the storage tank being spaced from the protective wall by at least 40 mm.

[0027] The storage unit may further have one or more of the following characteristics, considered individually or in all technically possible combinations:

[0028] - the storage tank comprises an internal tank delimiting a volume of cryogenic fluid storage, and an external tank inside which the internal tank is housed, the protective box comprising internal partitions securing the external casing to the external tank of the storage tank housed in said external casing;

[0029] - the protective box comprises a front cradle passing under one end front of the external tank and securing the external tank to the front wall, and a rear cradle passing under a rear end of the external tank and securing the external tank to the rear wall;

[0030] - the storage tank is transversely relatively closer to the wall of fixing only the protective wall.

[0031] According to a third aspect, the invention relates to a vehicle comprising:

[0032] - a chassis, comprising two longitudinal side members spaced transversely from each other in relation to the other;

[0033] - two cryogenic fluid storage units having the above characteristics opposite the two side members, the external casing of the protective box of each storage unit comprising an upper part fixed to one of the two side members, the protective box being arranged in a cantilever towards the outside of the vehicle relative to said side member in the transverse direction;

[0034] - a spacer structure, securing respective lower parts of the two outer envelopes to each other.

[0035] The vehicle may further have the following characteristics:

[0036] - the spacer structure comprises crossbars connecting one to the other the lower walls of the two external envelopes.

[0037] Other characteristics and advantages of the invention will emerge from the detailed description given below, for information purposes only and in no way limiting, with reference to the appended figures, among which: - [Fig.l] [Fig.l] is a simplified schematic representation, in top view, of a vehicle in accordance with the invention; - [Fig.2] [Fig.2] is an exploded view showing the storage tank of cryogenic fluid and the protective box for this tank; - [Fig.3] [Fig.3] is an elevation view of the tanks and boxes of protection, considered longitudinally from the front side, the front walls of the protection boxes not being shown to reveal the interior of said protection boxes; - [Fig.4] [Fig.4] a perspective view of the mounted protective boxes on the side members of the vehicle of [Fig.l], the front wall, the upper wall, the protective wall and the storage tank of one of the boxes not being shown; - [Fig.5] [Fig.5] is an elevation view of one of the protective boxes, considered longitudinally from the front side of the vehicle, showing the transmission of forces in the event of a side impact, the attachment wall not being shown; and - [Fig.6] [Fig.6] shows the three simulated loading cases digitally to demonstrate the technical advantages offered by the vehicle of the invention.

[0038] The vehicle 1 shown in [Fig.l] comprises:

[0039] - a chassis 3 comprising two longitudinal side members 5 spaced transversely one in relation to the other;

[0040] - two cryogenic fluid storage units 6, opposite the two side members 5.

[0041] Each cryogenic fluid storage unit 6 comprises:

[0042] - a cryogenic fluid storage tank 7;

[0043] - a protective box 9, the protective box 9 comprising an envelope external 11 inside which the storage tank 7 is rigidly fixed.

[0044] The vehicle is a motor vehicle. This vehicle is for example a truck, or a bus, or a van, or a car, or even a construction vehicle such as a mechanical shovel.

[0045] Alternatively, this vehicle is a train, a boat or any other suitable type of vehicle.

[0046] Cryogenic fluid means a fluid at very low temperature, which can be be at least partially in a liquid state inside the storage tank. This fluid is typically hydrogen. Alternatively, the fluid is helium, nitrogen, a natural gas such as methane CH4, air, or any other suitable fluid.

[0047] The cryogenic fluid is typically intended to power a fuel cell or an internal combustion engine. The fuel cell is configured to produce electricity and electrically power the electric propulsion motor of the vehicle.

[0048] In the present description, the longitudinal direction corresponds to the normal direction of movement of the vehicle. The vertical direction is the direction perpendicular to the vehicle's rolling plane. The transverse direction is perpendicular to both the vertical and longitudinal directions. Front and rear are understood relative to the longitudinal direction. Top and bottom, above and below, are understood relative to the vertical direction.

[0049] The chassis 3 is a rigid structure, on which various parts of the vehicle are mounted, for example the axles. The side members 5 of the chassis 3 extend longitudinally, parallel to each other. They are substantially at the same level vertically relative to the rolling plane of the vehicle 1.

[0050] The two storage units 6 are mounted one on one of the side members 5 and the other on the other side member 5.

[0051] Typically, the vehicle 1 comprises only two storage units 6. Alternatively, the vehicle 1 comprises additional storage units, in addition to said two storage units 6. These additional storage units are of the same type and are mounted in the same way as the storage units 6. The vehicle 1 comprises, for example, an even number of additional storage units, each pair comprising a storage unit mounted on one of the side members 5 and another mounted on the other side member 5.

[0052] Each storage tank 7 comprises an internal tank 13 (see [Fig.2]) delimiting a storage volume for the cryogenic fluid, and an external tank 15 inside which the internal tank 13 is housed.

[0053] The storage tank 7 also comprises a suspension (not shown) fixing the internal tank 13 to the external tank 15.

[0054] The internal reservoir 13 has a substantially longitudinal central axis C.

[0055] The external tank 15 comprises a cylindrical shell 17, coaxial with the central axis C. The shell 17 is closed at its two axial ends by front and rear ends 19.

[0056] The internal tank 13 and the external tank 15 delimit between them an intermediate space maintained under a high vacuum.

[0057] Thermal insulation, not shown, is interposed between the internal tank 13 and the external tank 15.

[0058] Each storage tank 7 also comprises different conduits 21 opening into the cryogenic fluid storage volume ([Fig.3]). The conduits 21 connect the storage volume to different auxiliary equipment 23 such as heat exchangers, valves, safety valves, etc.

[0059] Furthermore, the external tank 15 is equipped with an orifice, not shown, provided for creating a vacuum in the space delimited between the internal tank 13 and the external tank 15. This orifice is closed by a cover, not shown.

[0060] The orifice is provided in the rear bottom 19.

[0061] The conduits 21, the auxiliary equipment 23 are gathered at a front end of the storage tank 7, and are protected by a cover 31.

[0062] The cover 31 is placed opposite the front bottom 19, the conduits 21 being housed between the cover 31 and the front bottom 19.

[0063] The external envelope 11 has an upper part fixed to one of the two side members 5.

[0064] The upper part here corresponds to the half of the external envelope 11 located upwards, that is to say facing away from the rolling surface.

[0065] As can be seen in particular in Figures 1, 3 and 4, the fixing box 9 is arranged in a cantilevered manner towards the outside of the vehicle 1 relative to said side member 5 in the transverse direction.

[0066] This means that each protective box 9 is entirely located towards the outside of the side members 5 of the chassis 3 relative to the side member 5 which carries it, and is not located between the two side members 5.

[0067] Furthermore, the vehicle 1 comprises a spacer structure 35, visible in FIGS. 3 and 4, securing respective lower parts of the two external envelopes 11 to each other.

[0068] The lower part of the outer casing here corresponds to the half of the outer casing 11 facing downwards, that is to say towards the rolling surface of the vehicle 1.

[0069] As visible in the figures, the external envelope 11 is preferably parallelepipedal.

[0070] It thus comprises a fixing wall 37 fixed to the corresponding side member 5, a protective wall 39 opposite the fixing wall 37, lower and upper walls 41 and 43 facing respectively towards the rolling surface of the vehicle and away from the rolling surface, a front wall 45 and a rear wall 47 facing longitudinally respectively towards the front and the rear of the vehicle 1.

[0071] The fixing wall 37 and the protective wall 39 extend in respective planes substantially perpendicular to the transverse direction.

[0072] The upper wall 43 and the lower wall 41 extend in respective planes substantially perpendicular to the vertical direction.

[0073] The front and rear walls 45, 47 extend in planes substantially perpendicular to the longitudinal direction.

[0074] The fixing wall 37, the protective wall 39, the lower and upper walls 41, 43 and the front and rear walls 45, 47 are rigidly fixed to each other and together define a box having high rigidity. Each wall is perpendicular to the four walls which adjoin it.

[0075] The spar 5 is a C-shaped metal profile, with a central core 51 of substantially longitudinal and vertical orientation, and two wings 53 arranged above and below the central core 51, perpendicular to them.

[0076] The fixing wall 37 is pressed against the central core 51 and rigidly fixed to it.

[0077] The walls 37, 39, 41, 43, 45, 47 are steel sheets with a very high elastic limit.

[0078] They are made of martensitic or dual phase steel.

[0079] Each protective box 9 comprises a plurality of internal partitions 55 securing the external casing 11 to the external tank 15 of the storage tank 7 housed in said external casing 11.

[0080] These internal partitions 55 are in planes perpendicular to the longitudinal direction. They are distributed along the shell 17.

[0081] Each internal partition 55 has a central orifice in which the ferrule 17 is engaged.

[0082] Each internal partition 55 is welded to the ferrule 17.

[0083] It is also welded by an external edge to the external envelope 11. More precisely, it is welded to the fixing wall 37, to the protective wall 39, to the upper wall 43 and to the lower wall 4L

[0084] These internal partitions 55 make it possible to stiffen the shell 17, which must resist the vacuum created between the internal reservoir 13 and the external reservoir 15. Adding these internal partitions 55 makes it possible to reduce the wall thickness of the external reservoir 15.

[0085] Advantageously, the fixing wall 37, the protective wall 39, the lower wall 41, the front 45 and rear 47 walls are solid, that is to say without openings. This contributes to improving the fire resistance. Indeed, in the event of a fire under the vehicle, the flames will not be able to directly reach the storage tank 7.

[0086] On the other hand, the upper wall 43 preferably has orifices 57 putting an internal volume of the external envelope 11 into communication with an atmosphere outside the external envelope 11.

[0087] These orifices 57 allow the evacuation of air in the event of a fire. Indeed, in the event of a fire under the vehicle, the lower wall 41 is the most exposed to the flames. It will heat the air contained inside the external envelope 11. This hot air will tend to rise and will be able to escape through the orifices 57 in the upper wall 43. It will be replaced by cooler air, thus creating a convective movement contributing to cooling the storage tank 7.

[0088] Furthermore, in the event of a hydrogen leak, the hydrogen may escape through the orifices 57 in the upper wall 43.

[0089] Advantageously, one or more of the following walls are lined with a structured stiffening sheet 59: the protective wall 39, the lower wall 41, the upper wall 43.

[0090] Preferably, these three walls are lined with a structured stiffening sheet 59.

[0091] The structured stiffening sheet 59 has substantially the same size as the wall to which it is fixed. It is rigidly fixed on a large face of the wall, on the inside or outside of the external envelope.

[0092] The sheet metal is structured in the sense that it has reliefs contributing to stiffening said sheet metal.

[0093] These reliefs are typically hollow rectilinear shapes, separated by projecting rectilinear shapes.

[0094] For the lower wall 41 and the upper wall 43, the recessed rectilinear shapes and the projecting rectilinear shapes are transversely oriented. For the protective wall 39, the recessed rectilinear shapes and the projecting rectilinear shapes are vertically oriented.

[0095] Typically, each structured stiffening sheet 59 is folded into parallel notches. Alternatively, each structured stiffening sheet 59 is a corrugated sheet. Alternatively, the structured stiffening sheet 59 is formed with other types of reliefs.

[0096] The wall 39, 41, 43 and the structured stiffening sheet 59 together form a sandwich having good resistance to buckling.

[0097] The protective box 9 also comprises a front cradle 61 passing under a front end of the external tank 15 and securing the external tank 15 to the front wall 45.

[0098] As visible in [Fig.3], the front cradle 61 is an arched sheet metal, for example in the shape of a half-cylinder. It is rigidly fixed to the shell 17 of the external tank 15. It is also rigidly fixed to an inner face of the front wall 45.

[0099] The front cradle 61 has an internal radius substantially equal to the external radius of the ferrule 17, the ferrule 17 resting in the front cradle 61.

[0100] The front cradle 61 closes downwards the space separating the front bottom 19 of the external tank 15 from the front wall 45. It is in this space that the auxiliary equipment 23 of the external tank 15 and the conduits 21 are located.

[0101] The cradle 61 helps to protect these components from heat in the event of a fire under the vehicle.

[0102] The protective box 9 also includes a rear cradle 63 passing under a rear end of the external tank 15 and securing the external tank 15 to the rear wall 47.

[0103] The rear cradle 63 is a cylindrical metal plate. It forms a ring around the rear end of the ferrule 17, and is fixed thereto. It is also rigidly fixed to the rear wall 47. It has an internal radius substantially equal to the external radius of the ferrule 17.

[0104] Alternatively, the rear cradle 63 does not have a closed contour but extends only over a fraction of a circle, for example over a semicircle closing the bottom of the ferrule 17.

[0105] The protective box 9 also comprises a reinforcement structure 65 comprising:

[0106] - at least one longitudinal beam 67 rigidly fixed to the protective wall 39;

[0107] - a plurality of oblique beams 69, securing the at least one beam longitudinal 67 to the upper wall 43 and to the lower wall 4L

[0108] For example, the reinforcement structure 65 comprises two longitudinal beams 67 rigidly fixed to the protective wall 39. These beams are for example directly fixed to an internal face of the protective wall 39, the structured sheet 59 being fixed to an external face of the protective wall 39.

[0109] The or each longitudinal beam 67 is a flat metal profile.

[0110] The oblique beams 69 are for example metal profiles of closed rectangular section.

[0111] Typically, one of the longitudinal beams 67 is fixed in the upper part of the protective wall 39. The other longitudinal beam 67 is fixed in the lower part of the protective wall 39.

[0112] A group of oblique beams 69 has one end rigidly fixed to the upper longitudinal beam 67, and another end fixed to the upper wall 43.

[0113] Another group of oblique beams 69 has one end rigidly fixed to the lower longitudinal beam 67, and another end fixed to the lower wall 4L

[0114] Each oblique beam 69 is arranged in a plane perpendicular to the longitudinal direction. Considered in said plane, it forms an isosceles triangle with the protective wall 39 and with the lower wall 41 or the upper wall 43.

[0115] Advantageously, the structured sheets 59 are fixed to the inner faces of the upper wall 43 and the lower wall 4L. The ends of the oblique beams 69 are placed in rectilinear hollow shapes of the structured sheets 59.

[0116] Furthermore, the reinforcement structure 65 also comprises stiffening profiles 71 each fixed to the upper wall 43 or to the lower wall 41, close to the fixing points of the oblique beams 69 to said upper and lower walls 43, 4L. These stiffening profiles 71 make it possible to stiffen the upper wall 43 or the lower wall 41, close to the fixing points.

[0117] For example, two stiffening profiles 71 are arranged in the hollow rectilinear shapes receiving the ends of the oblique beams 69, on either side of the end of the oblique beam 69.

[0118] The stiffening profiles 71, and the hollow rectilinear shapes, extend transversely. The end of the oblique beam 69 is pinched longitudinally between the two stiffening profiles 71. The two stiffening profiles 71 are parallel and are arranged side by side, with a space between them to receive the end of the oblique beam 69.

[0119] It should be noted that the storage tank 7 is offset in the transverse direction towards the chassis 3 inside the protective box 9.

[0120] In other words, the storage tank 7 is located transversely closer to the fixing wall 37 than to the protective wall 39, to allow the deformation of the protective wall 39 in the event of a lateral impact.

[0121] The storage tank 7 being spaced from the protective wall 39 by at least 40 mm. The storage tank 7 is located at a distance from the protective wall 39 of between 40 and 100 mm, preferably between 60 and 80 mm, and even more preferably approximately 75 mm.

[0122] The storage tank 7 is located at a distance from the fixing wall 37 less than or equal to 10 mm.

[0123] It should also be noted that the storage tank 7 has no direct contact with the lower wall 41 or the structured sheet 59 reinforcing this wall. The storage tank 7 is in thermal contact with the lower wall 41 only via the internal partitions 55. These internal partitions 55 have a small section, such that the heat transfers by conduction from the lower wall 41 to the external tank 15 are extremely reduced.

[0124] Furthermore, a layer of thermal insulation not shown, for example polyurethane, is placed on the internal side of the lower wall 41, further limiting heating of the storage tank 7 in the event of a fire.

[0125] The spacer structure 35 comprises transverse bars 73 connecting the lower walls 41 of the two external envelopes 11 to each other.

[0126] The transverse bars 73 and the lower walls 41 of the two external envelopes 11 extend in the same horizontal plane, that is to say in the same plane parallel to the rolling plane.

[0127] Typically, the spacer structure 35 comprises two transverse bars 73, one placed longitudinally at the level of the front wall 45 and the other placed longitudinally at the level of the rear wall 47.

[0128] The front side crossbar 73 has opposite ends connected by links 75 to the two external envelopes 11. These links 75 are placed at the top at which the fixing wall 37, the front wall 45 and the lower wall 41 join. The connections 75 are pivot connections, allowing rotation of the transverse bar 73 relative to the external casing 11 around a longitudinal axis.

[0129] In the same way, the transverse bar 73 placed at the rear has its two ends linked to the two external envelopes 11 by links 75. These links 75 are placed at the vertices at which the rear wall 47, the fixing wall 37 and the lower wall 41 meet. They are also of the pivot connection type, around longitudinal axes.

[0130] The spacer structure 35 also has, for each transverse bar 73, two arms 77 connecting the transverse bar 73 to the fixing walls 41 of the two external envelopes 11.

[0131] Each arm 77 has one end 79 rigidly fixed to the bar 73 and another end linked to the external envelope 11 by a connection 81.

[0132] The connection 81 is placed on the edge along which the front wall 45 or the rear wall 47 joins the fixing wall 37. The connection 81 is a pivot type connection, around a longitudinal axis. The connection 81, in the vertical direction, is placed towards the center of the fixing wall 37.

[0133] The end 79 of the arm 77 is rigidly fixed near the center of the crossbar 73.

[0134] The arms 77 and the crossbar 73 extend in a plane perpendicular to the longitudinal direction. Each arm 77 forms with the end of the crossbar 73 a triangle of which the fixing wall 37 constitutes one side.

[0135] The vehicle described above provides excellent crash performance.

[0136] The behavior of this vehicle was simulated by calculation for the three cases of loading shown in [Fig.6]. In the first loading case, a load 83 strikes the storage tank 7 laterally, with an approach angle of 27°. The second loading case corresponds to the impact of a load on a corner of the protective box, with an approach angle of 30°, front side or rear side. The third loading case corresponds to an impact of a linear structure 85 such as a post (crash pole), transversely.

[0137] The numerical parameters retained for these three loading cases are summarized in the table below: Loading case Load mass (kg) Impact speed (km / h) Approach angle (°) Impact angle (°) 1 1368 54 27 90 2 1600 35 30 30 3 1600 15 90 90

[0138] The following table shows the result of the calculations. The second and third columns of the table give the results for a storage tank without a protective box, with an external tank having a wall thickness of 4 mm.

[0139] The second column indicates the maximum depression of the external tank, in millimeters, and the third column the maximum stress experienced by the external tank, in MPa.

[0140] The fourth and fifth columns of the table provide the same indications, but for a tank according to the invention, equipped with a protective box, with an external tank having a wall thickness of only 2 mm. Without protective box, wall thickness 4 mm With protective box, wall thickness 2 mm Loading case Deflection m Stress (MP Deflection m Stress (MP ent ax (mm) a) ax (mm) a) 1 217 595 15 100-390 2 81 610 0 0 3 116 628 0 100 (300)

[0141] For loading case 1, this table shows that in the absence of a protective box, the external tank is very deformed. The risk of destruction of the tank is significant. The pressure inside the tank is significantly increased due to the deformation, such that the shut-off valves of the cryogenic fluid conduits are likely to no longer be able to perform their functions. The weld lines are subjected to very high tractions, which can lead to rupture. The suspension of the internal tank from the external tank is also impacted.

[0142] On the contrary, with the protective box, the depression at the level of the external tank is low, and the internal tank is not deformed. The suspensions are affected by the shock, but the risk of destruction of these suspensions is extremely reduced. Only the areas located at the level of the internal partitions 55 undergo high stresses, but of an acceptable level, without risk of rupture of the external tank.

[0143] Loading case 2, for an unprotected tank, is particularly critical when the impact occurs on the cover 31. The depression in the external tank is significantly lower than in the first loading case, but the mechanical stresses are even higher, particularly at the cover. There is a significant risk of leakage due to a possible breakage of the equipment. tank auxiliaries under the effect of the shock. The suspensions of the primary tank are subjected to significant stresses, of the order of 300 MPa.

[0144] On the contrary, for a tank equipped with the protective box of the invention, there is no impact on the external tank or the internal tank. The risk of leakage is negligible.

[0145] Loading case 3, in the absence of a protective box, leads to a significant risk of tearing of the tank along the impact line if this impact occurs at the level of the shell 17. The depression at the level of the external tank is approximately 116 mm. This depression results in a significant increase in internal pressure, which contributes to further increasing the risk of destruction of the tank. The internal suspensions are significantly affected.

[0146] If the impact occurs at the level of the hood 31, the penetration is more reduced, but there is a risk that the auxiliary equipment of the tank is destroyed, leading to a leak of the cryogenic fluid.

[0147] In the case of a tank equipped with a protective box, the sinking of the external tank is zero. The external tank is subjected to a moderate level of mechanical stress, locally up to a value of 300 MPa at the level of the internal partitions 55. The level of mechanical stress in the suspensions remains moderate.

[0148] The following table details the effects on the internal tank, the external tank and the protective box, for the three loading cases described above, only for the vehicle of the invention. It emerges that the behavior of the vehicle is satisfactory for all the loading cases considered. Loading case Dent (mm) Stress (MPa) Tank damage Suspension damage Protective box damage Inner tank Outer tank Inner tank Outer tank 1 0 15 0-50 100 (390 ) Only the outer tank is damaged Low Significant damage distributed over a wide area, deformation of the lower and upper walls 2 0 0 0 0 No damage None Damage to front and rear walls 3 0 0 0 100 (300 ) Sinking points at external tank level Subject to moderate stresses (180 M Pa) Local sinking

[0149] These results are partly explained by a good distribution of the forces in the protective box 9. As illustrated in [Fig.5], in the event of a lateral impact on the protective wall 39, part of the forces is transmitted directly from the protective wall 39 to the lower and upper walls 41, 43 along the protective wall 39 (arrows F1).

[0150] Another part of the forces is transmitted by the longitudinal beams 67 and the oblique beams 69 to the upper wall 43 and to the lower wall 41 (arrows F2).

[0151] The forces taken up by the upper wall 43 are directly transmitted to the side members 5 (arrow F3).

[0152] The forces taken up by the lower wall 41 are transmitted to the spacer structure 35 (arrow F4) and to the protective box located on the opposite side of the vehicle. These forces cause a very limited movement of said opposite protective box.

[0153] The vehicle described above has multiple advantages.

[0154] Because each protective box comprises internal partitions securing the external envelope to the external tank of the storage tank, the external tank can be of reduced thickness. The presence of the internal partitions makes it possible to stiffen the external tank, which must withstand the vacuum created between the external tank and the internal tank. The external tank in fact has a geometry that is particularly unfavorable for resistance to collapse under the effect of a vacuum. It has a length typically close to 2.5 m, and a diameter close to 700 mm.

[0155] Due in particular to the presence of the internal partitions, it is possible to reduce the wall thickness of the external tank from 4 mm to 2 mm. This makes it possible to very significantly reduce the overall weight of the storage tank.

[0156] The fact that the fixing wall, the protective wall, the bottom wall and the front and rear walls are solid, makes it possible to protect the storage tank from flames in the event of a fire under the vehicle.

[0157] The fact that the upper wall has orifices connecting the internal volume of the external envelope with the external atmosphere, allows in the event of fire to vent hot gases outside the outer casing. The holes also allow hydrogen to escape in the event of a leak.

[0158] The fact that one or more walls are lined with a structured stiffening sheet, in particular the protective wall, the lower wall and the upper wall, means that these walls have good buckling resistance. In the event of an impact, in particular a transverse impact, these walls effectively transmit the forces to the side members of the vehicle or to the opposite protective box.

[0159] Because the protective box comprises a front cradle passing under a front end of the external tank and securing the external tank to the front wall, and a rear cradle passing under a rear end of the external tank and securing the external tank to the rear wall, the storage tank is held in position inside the protective box. Furthermore, the front cradle and the rear cradle protect the ends of the storage tank in the event of a fire. The front cradle in particular constitutes a screen in the event of a fire under the vehicle for the auxiliary equipment of the tank, located between the front end of the external tank and the front wall. Indeed, the auxiliary equipment is particularly vulnerable in the event of a fire. The storage tank itself, because it contains a cryogenic fluid, has significant thermal inertia.This is not the case with auxiliary equipment, which heats up quickly if exposed to flames, or if they are poorly protected against flames. The consequences of a ruptured tube or a damaged valve can be particularly serious.

[0160] If the safety valves, due to the heat, become non-functional, the storage tank may explode due to the rise in temperature.

[0161] If the cover closing the vacuum port is exposed to excessive temperature, the seals used to insulate the cover from this vacuum port may melt. Outside air can then enter the space between the internal tank and the external tank, which considerably degrades the thermal insulation of the internal tank. Immediately after this event, the incoming air will liquefy upon contact with the wall of the internal tank. After a certain period of time, the liquid air will evaporate again, the pressure between the internal tank and the external tank increasing until it expels the cover from the vacuum port. This will result in the entry of a significant flow of external air, at high temperature due to the fire under the vehicle. The cryogenic fluid contained in the internal tank will therefore increase in pressure rapidly, causing the safety valves to open.Safety valves, and the pipes on which these valves are mounted, must therefore be sized accordingly, which increases the cost of the storage tank.

[0162] Furthermore, in the event of a transverse impact on one side of the vehicle, part of the forces applied to the protective box located on said side are transmitted by the spacer structure to the protective box located on the other side. The two protective boxes, the spacer structure and the side members together constitute a rigid structure, limiting or preventing damage to the tank. The primary objective of the box is to deform as little as possible and to protect the tank. The spacer structure limits the rotation of the box so that the object causing the impact is always in the direction for which the box resists best and to prevent the object hitting the box, typically a vehicle, from passing under the tank.

[0163] The spacer structure also helps balance the stresses coming from the road. Indeed, with each bump created by the road, the box and its tank will undergo a vertical acceleration and because of its cantilevered mounting, these stresses will be transformed into micro-deformations which can only be rotations. These deformations will lead to fatigue failures. To withstand these stresses in the absence of a spacer structure, it would be necessary to considerably stiffen the attachment and therefore increase the mass of the assembly by adding reinforcements. The spacer structure limits micro-deformations in rotation, while being much lighter than these reinforcements.

[0164] Because the spacer structure comprises transverse bars connecting the lower walls of the two external envelopes to each other, the forces are transmitted between the two protective boxes at particularly rigid zones.

Claims

Claims

1. Rigid protective box (9) intended to be mounted on board a vehicle (1), the protective box (9) being shaped to internally receive at least one storage tank (7) of cryogenic fluid and to protect this storage tank (7) against external attacks such as impacts or fires, the protective box (9) comprising an external casing (11) comprising: - a fixing wall (37) intended to be fixed to the vehicle (1); - a protective wall (39) opposite the fixing wall (37); - lower and upper walls (41, 43) facing respectively towards a rolling surface of the vehicle (1) and away from the rolling surface; - a front wall (45) and a rear wall (47) facing longitudinally towards the front and towards the rear of the vehicle (1);the protective box (9) further comprising a reinforcing structure (65) comprising: - at least one longitudinal beam (67) rigidly fixed to the protective wall (39); - a plurality of oblique beams (69), securing the at least one longitudinal beam (67) to the upper wall (43) and to the lower wall (41); - stiffening profiles (71) each fixed to the upper wall (43) or to the lower wall (41), near points of fixing of the oblique beams (69) to said upper and lower walls (43, 41).;

2. Protective box (9) according to claim 1, in which one or more of the following walls are lined with a structured stiffening sheet (59): the protective wall (39), the lower wall (41), the upper wall (43).

3. A protective box (9) according to claim 1 or 2, wherein the fixing wall (37), the protective wall (39), the bottom wall (41), and the front and rear walls (45, 47) are solid.

4. Protective box (9) according to any one of the preceding claims, in which the upper wall (43) has orifices (57) putting an internal volume of the external envelope (11) into communication with an atmosphere external to the external envelope (11).

5. A cryogenic fluid storage unit (6), comprising a protective box (9) according to any one of the preceding claims, and a cryogenic fluid storage tank (7) rigidly fixed inside the outer casing (11) of the protective box (9), the storage tank (7) being spaced from the protective wall (39) by at least 40 mm.

6. Storage unit (6) according to claim 5, in which the storage tank (7) comprises an internal tank (13) delimiting a cryogenic fluid storage volume, and an external tank (15) inside which the internal tank (13) is housed, the protective box (9) comprising internal partitions (55) securing the external casing (11) to the external tank (15) of the storage tank (7) housed in said external casing (11).

7. Storage unit (6) according to claim 6, wherein the protective box (9) comprises a front cradle (61) passing under a front end of the external tank (15) and securing the external tank (15) to the front wall (45), and a rear cradle (63) passing under a rear end of the external tank (15) and securing the external tank (15) to the rear wall (47).

8. Storage unit (6) according to any one of claims 5 to 7, wherein the storage tank (7) is transversely relatively closer to the fixing wall (37) than to the protective wall (39).

9. Vehicle (1) comprising: - a chassis (3), comprising two longitudinal side members (5) spaced transversely relative to each other; - two cryogenic fluid storage units (6) according to any one of claims 5 to 8, facing the two side members (5), the external casing (11) of the protective box (9) of each storage unit (6) comprising an upper part fixed to one of the two side members (5), the protective box (9) being arranged cantilevered towards the outside of the vehicle (1) relative to said side member (5) in the transverse direction; - a spacer structure (35), securing respective lower parts of the two external casings (11) to each other.

10. A vehicle according to claim 9, wherein the spacer structure (35) comprises transverse bars (73) connecting the lower walls (41) of the two outer casings (11) to each other.

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