Underwater vehicle equipped with a hydraulic accumulator

Abstract

Underwater vehicle equipped with a hydraulic accumulator. The underwater vehicle is equipped with a buoyancy adjustment system comprising a hydraulic accumulator (6) including a casing (8) within which is defined a fluidic chamber (10) whose volume varies according to the pressure residing inside the fluidic chamber (10), the fluidic chamber (10) being in fluidic communication with the surrounding water or in fluidic communication with an external reservoir (28) containing a liquid (L), the external reservoir (28) being configured such that the pressure of the liquid (L) contained in the external reservoir (28) varies according to the pressure of the surrounding water. Figure for the abbreviation: Figure 1

Description

Title of the invention: Underwater vehicle equipped with a hydraulic accumulator

[0001] The present invention relates to the field of underwater vehicles, in particular underwater gliders.

[0002] The buoyancy of an underwater craft submerged in water is equal to the mass of the volume of water displaced by the underwater craft. The buoyancy of an underwater craft depends on the density of the water.

[0003] As a first approximation, the density of water is considered to be constant. However, the density of water increases with depth, particularly in marine environments.

[0004] The buoyancy of the underwater vehicle therefore increases with depth and this increase in buoyancy increases the difficulty of the underwater vehicle diving to great depths.

[0005] It is then necessary to compensate for the increase in buoyancy, for example by means of a propulsive force, generated for example by a propeller thruster, and / or by means of a ballast system which allows the buoyancy of the underwater vehicle to be modified.

[0006] The energy consumed to generate propulsion or to operate the ballast system negatively affects the autonomy of the underwater vehicle. This is particularly problematic in the case of an autonomous underwater vehicle such as an underwater glider designed to navigate autonomously for extended periods.

[0007] One of the aims of the invention is to provide an underwater vehicle capable of diving to great depths while limiting energy consumption.

[0008] To this end, the invention proposes an underwater vehicle equipped with a buoyancy adjustment system comprising a hydraulic accumulator including a casing within which is delimited a fluidic chamber whose volume varies according to the pressure residing inside the fluidic chamber, the fluidic chamber being in fluidic communication with the surrounding water or in fluidic communication with an external reservoir containing a liquid, the external reservoir being configured in such a way that the pressure of the liquid contained in the external reservoir varies according to the pressure of the surrounding water.

[0009] The hydraulic accumulator allows the buoyancy of the underwater vehicle to be varied passively according to the pressure of the surrounding water in which the underwater vehicle is immersed, and therefore in particular according to the depth at which the underwater vehicle is located.

[0010] Thus, the hydraulic accumulator makes it possible to compensate for variations in the density of the water in which the underwater vehicle is immersed.

[0011] Depending on other advantageous aspects, the underwater vehicle comprises one or more of the following optional features, taken individually or in all technically possible combinations:

[0012] - the volume occupied by the external reservoir varies depending on the volume of liquid contents in the external reservoir;

[0013] - the external reservoir has a separating wall separating the liquid from the water by surrounding, the separating wall being mobile and / or deformable under the effect of a pressure difference between the pressure of the liquid and the pressure of the surrounding water;

[0014] - the fluidic chamber is delimited by a deformable and / or movable internal wall, the the internal wall being subjected, on one side, to the pressure of the surrounding water or the liquid present in the fluidic chamber and, on the other side, subjected, for example, to the action of a pressurized gas present in a pneumatic chamber delimited by the internal wall and / or to the action of a spring;

[0015] - the hydraulic accumulator is calibrated such that when the volume of the fluidic chamber is minimal, the pressurized gas has a calibration pressure strictly greater than 1 bar and / or the spring has a non-zero preload;

[0016] - the hydraulic accumulator is calibrated so that the volume of the chamber fluidic remains minimal as long as the surrounding water pressure is below a reference pressure, the volume of the fluidic chamber increasing with the surrounding water pressure when the surrounding water pressure is above the reference pressure;

[0017] - the external reservoir comprises an elastically deformable bladder, a membrane elastically deformable and / or a piston subjected on one side to the action of the liquid and on the other side to the action of the surrounding water;

[0018] - the external reservoir and the casing are at least partially nested one inside the other the other;

[0019] - the underwater vehicle includes a ballast system, the ballast system including a ballast tank fluidly connected to the external tank, and an activatable actuator to force the transfer of liquid between the ballast tank and the external tank and / or the fluidic chamber;

[0020] - the external reservoir and the fluidic chamber are fluidically connected in parallel to the actuator;

[0021] - the external reservoir and the fluidic chamber are fluidically connected in series to the actuator;

[0022] - the external reservoir is fluidly located between the actuator and the chamber fluidic;

[0023] - the ballast tank is received in a wet compartment of the sub- engine sailor;

[0024] - the external reservoir and / or the hydraulic accumulator are received in a com wet compartment of the underwater vehicle;

[0025] - the underwater craft is an underwater glider or an underwater profiler.

[0026] The invention and its advantages will become apparent from the following description, given solely by way of non-limiting example, and made with reference to the drawings in which:

[0027] [Fig-1] [Fig.1] is a schematic view of an underwater vehicle equipped with a system buoyancy adjustment including a hydraulic accumulator as an example, illustrating different configurations of the hydraulic accumulator;

[0028] [Fig.2] [Fig.2] is a schematic view of an underwater vehicle equipped with a system buoyancy adjustment including a hydraulic accumulator according to another example, illustrating different configurations of the hydraulic accumulator;

[0029] [Fig.3] [Fig.3] is a graph illustrating the buoyancy of an underwater vehicle devoid of a hydraulic accumulator and the buoyancy of the same craft equipped with a hydraulic accumulator;

[0030] [Fig.4] [Fig.4] is a schematic view of an underwater vehicle equipped with a system buoyancy adjustment including a ballast system and a hydraulic accumulator, according to an example;

[0031] [Fig. 5] [Fig. 5] is a schematic view of an underwater vehicle equipped with a system buoyancy adjustment including a ballast system and a hydraulic accumulator, according to another example;

[0032] [Fig. 6] [Fig. 6] is a schematic view of an underwater vehicle equipped with a system buoyancy adjustment including a ballast system and a hydraulic accumulator, according to yet another example.

[0033] As illustrated in [Fig.1], the underwater craft 2 is configured to be submerged in water, in particular in a lake or in the sea.

[0034] The underwater vehicle 2 is for example equipped with a measuring system (not shown) to carry out measurements in the water, for example temperature measurements, pressure measurements and / or salinity measurements.

[0035] The underwater craft 2 includes a buoyancy adjustment system 4 configured to modify the buoyancy of the underwater craft 2.

[0036] The buoyancy adjustment system 4 is for example configured to modify the buoyancy of the underwater vehicle 2 according to the pressure of the surrounding water in a passive manner, i.e. without using energy to activate an actuator.

[0037] The buoyancy adjustment system 4 comprises a hydraulic accumulator 6 including a casing 8 within which a chamber is delimited fluidic chamber 10 receiving a liquid, the volume of the fluidic chamber 10 varying according to the pressure of the liquid.

[0038] The hydraulic accumulator 6 is configured so that the volume of the fluidic chamber 10 varies jointly with the pressure residing in the fluidic chamber, i.e. such that the volume of the fluidic chamber 10 increases when the pressure residing in the fluidic chamber 10 increases and the volume of the fluidic chamber 10 decreases when the pressure residing in the fluidic chamber decreases.

[0039] The fluidic chamber 10 is for example delimited inside the envelope 8 by an internal wall 12 movable inside the envelope and / or deformable depending on the pressure residing in the fluidic chamber 10.

[0040] The internal wall 12 separates, for example, the fluidic chamber 10 from a closed pneumatic chamber 14 containing a gas G, the volume of the pneumatic chamber 14 varying inversely to the volume of the fluidic chamber 10.

[0041] When the pressure in the fluidic chamber 10 increases, the internal wall 12 moves and / or deforms in such a way that the volume of the fluidic chamber 10 increases, the volume of the pneumatic chamber 14 decreases and the pressure of the gas G increases.

[0042] When the pressure in the fluidic chamber 10 decreases, the internal wall 12 moves and / or deforms in such a way that the volume of the fluidic chamber 10 decreases, the volume of the pneumatic chamber 14 increases, and the pressure of the gas G decreases.

[0043] The gas G contained in the pneumatic chamber 14 allows elastic energy to be stored when the pressure of the liquid increases in the fluidic chamber lO and when liquid enters the fluidic chamber 10, this elastic energy then allows the liquid to be pushed out of the fluidic chamber 10 and the volume of the fluidic chamber 10 to decrease when the pressure of the liquid L decreases.

[0044] The hydraulic accumulator 6 advantageously includes a calibration orifice 16 allowing the pneumatic chamber 14 to be filled with gas G. The calibration orifice 16 allows the quantity of gas G in the pneumatic chamber 14 to be adjusted. The calibration orifice 16 is preferably equipped with a valve.

[0045] The inner wall 12 is for example an elastically deformable bladder, an elastically deformable membrane, or a piston received sliding inside the envelope 8.

[0046] In an embodiment in which the inner wall 12 is a piston received sliding inside the casing 8, the hydraulic accumulator 6 comprises, for example, instead of or in addition to gas G, a spring (not shown) arranged to act on the inner wall 12 in such a way that the spring opposes the displacement of the wall internal 12 in the direction of an increase in the volume of the fluidic chamber 10.

[0047] When the pressure in the fluidic chamber 10 increases, the inner wall 12 moves in such a way that the volume of the fluidic chamber 10 against the spring increases. The spring stores energy.

[0048] When the pressure in the fluidic chamber 10 decreases, the spring moves the internal wall 12 in such a way that the volume of the fluidic chamber 10 decreases.

[0049] The casing 8 is preferably the outer casing of the hydraulic accumulator 6.

[0050] The hydraulic accumulator 6 is, for example, arranged so that the casing 8 is immersed in the surrounding water. In this case, the casing 8 is preferably configured to be non-deformable at the pressures corresponding to the operating depth range of the underwater vehicle 2.

[0051] As illustrated in [Fig. 1], the underwater vehicle 2 has a hull 20 delimiting a watertight compartment 22 into which surrounding water does not penetrate and a wet compartment 24 into which surrounding water penetrates. The casing 8 is located in the wet compartment 24.

[0052] As illustrated in [Fig.1], the fluidic chamber 10 is for example fluidically connected to the outside to allow surrounding water to enter the fluidic chamber 10. The fluidic chamber 10 contains surrounding water.

[0053] The envelope 8 is for example provided with an orifice 26 passing through the envelope 8 opening into the fluidic chamber 10 and to the outside.

[0054] As illustrated in [Fig.1] from left to right, in the event of an increase in the pressure of the surrounding water (e.g. if the immersion depth of the underwater craft 2 increases), the volume of the fluidic chamber 10 increases and surrounding water enters the fluidic chamber 10. As a result, the buoyancy of the underwater craft decreases.

[0055] The surrounding water received in the fluidic chamber 10 pushes the internal wall 12 against the gas G present in the pneumatic chamber 14 and / or the spring acting on the internal wall 12.

[0056] As illustrated in [Fig. 1] from right to left, if the surrounding water pressure decreases (e.g., if the immersion depth of the underwater vehicle 2 decreases), surrounding water present in the hydraulic chamber 10 is expelled. As a result, the buoyancy of the underwater vehicle increases.

[0057] The surrounding water present in the hydraulic chamber 10 is for example pushed outwards by the internal wall 12 subjected to the action of the gas G present in the pneumatic chamber 14 and / or the spring.

[0058] In one embodiment, as illustrated in [Fig.2], the buoyancy adjustment system 4 comprises an external reservoir 28 containing a liquid L, the external reservoir 28 being fluidically connected to the fluidic chamber 10, for example via the orifice 26, in such a way that the liquid L circulates between the fluidic chamber 10 and the external reservoir 28.

[0059] The liquid L present in the reservoir 28 and the fluidic chamber 10 is separated from the surrounding water.

[0060] The liquid L is, for example, a hydraulic oil compatible with the fluidic actuator 36

[0061] The external reservoir 28 is configured in such a way that the liquid L present in the external reservoir 28 is subjected to the pressure of the surrounding water.

[0062] The external reservoir 28 is at least partially immersed in the surrounding water.

[0063] The external reservoir 28 is configured such that the volume occupied by the external reservoir 28 in the surrounding water varies depending on the amount of liquid L present in the external reservoir 28.

[0064] The external reservoir 28 includes, for example, a movable and / or deformable external wall 30 such that the liquid L is subjected to the pressure of the surrounding water through the external wall 30 and / or the volume occupied by the external reservoir 28 in the surrounding water varies according to the quantity of liquid L present in the external reservoir 28.

[0065] In one example, as illustrated in [Fig.2], the outer wall 30 forms a bladder or an elastically deformable membrane, subjected on one side to the action of the liquid and on the other side to the action of the surrounding water.

[0066] In an unrepresented variant, the outer wall 30 forms a piston subjected on one side to the action of the liquid and on the other side to the action of the surrounding water.

[0067] As illustrated in [Fig. 2] from left to right, if the surrounding water pressure increases (e.g., if the immersion depth of the underwater vehicle 2 increases), the pressure of the liquid L in the external tank 28 increases along with the surrounding water pressure. Liquid L moves from the external tank 28 to the fluidic chamber 10 via the orifice 26. The volume occupied in the surrounding water by the external tank 28 decreases. As a result, the buoyancy of the underwater vehicle 2 decreases.

[0068] The liquid L received in the fluidic chamber 10 pushes the internal wall 12 against the gas G present in the pneumatic chamber 14 and / or the spring acting on the internal wall 12.

[0069] As illustrated in [Fig. 2] from right to left, if the surrounding water pressure decreases (e.g., if the immersion depth of the underwater vehicle 2 decreases), the pressure of the liquid L in the external reservoir 28 decreases along with the surrounding water pressure. Liquid L moves from the fluidic chamber 10 to the external reservoir 28 via the orifice 26. The volume occupied The pressure in the surrounding water from the external tank 28 increases. As a result, the buoyancy of the underwater vehicle 2 increases.

[0070] The liquid L present in the fluidic chamber 10 is for example pushed outwards by the internal wall 12 subjected to the action of the gas G present in the pneumatic chamber 14 and / or the spring.

[0071] The transfer of the liquid L between the external reservoir 28 and the hydraulic chamber 10 results solely from the action of the surrounding water, and in particular from the variation in the pressure of the surrounding water.

[0072] The buoyancy adjustment system 4 allows buoyancy to be adjusted passively, i.e. without the use of energy to operate an actuator, in particular in such a way that buoyancy decreases when the pressure of the surrounding water increases and buoyancy increases when the pressure of the surrounding water decreases.

[0073] This makes it possible to compensate for a variation in water density such as can occur between the water surface and great depths, for example depths greater than 500 m, in particular greater than 1,000 m.

[0074] The buoyancy adjustment system 4 is, for example, calibrated so that the variation in buoyancy due to pressure as a function of depth compensates for the variation in buoyancy due to the variation in water density as a function of depth.

[0075] The fluidic chamber 10 of the hydraulic accumulator 6, which receives the surrounding water ([Fig. 1]) or the liquid L ([Fig. 2]), has a minimum volume, corresponding to maximum buoyancy. The volume of the fluidic chamber 10 is minimal when the pressure of the surrounding water is insufficient to cause the surrounding water or the liquid L to enter the fluidic chamber.

[0076] The hydraulic accumulator 6 is, for example, calibrated so that the volume of the fluidic chamber 10 remains minimal up to a reference pressure of the surrounding water. The reference pressure corresponds to a reference depth, which is, for example, a desired immersion depth for the underwater vehicle 2.

[0077] As long as the surrounding water pressure is less than the reference pressure, the volume of surrounding water or liquid L present in the fluidic chamber 10 remains constant and minimal.

[0078] As long as the surrounding water pressure is lower than the reference pressure, the hydraulic accumulator 6 is inactive and does not change the buoyancy of the underwater craft 2.

[0079] In the case of a hydraulic accumulator 6 in which a movable internal wall 12 delimiting the fluidic chamber 10 is subjected to the action of a pressurized gas G and / or a spring, the pressure of the gas G and / or a preload of the spring on the wall internal 12 when the volume of the fluidic chamber 10 is minimal determines the reference pressure.

[0080] Advantageously, the pressure of the gas G when the volume of the fluidic chamber 10 is minimal is strictly greater than 1 bar and / or the preload of the spring is non-zero.

[0081] In particular, in the case of a hydraulic accumulator 6 using a pressurized gas G as illustrated in Figures 1 and 2, the gas G exhibits a pressure (called the "calibration pressure") when the volume of the fluidic chamber 10 is minimal. The volume of the fluidic chamber 10 begins to increase with an inlet of surrounding water or liquid L only when the pressure of the surrounding water or liquid L exceeds the calibration pressure of the gas G.

[0082] The calibration orifice 16 allows the calibration pressure to be adjusted. The calibration pressure is adjusted by changing the amount of gas G present in the pneumatic chamber 14 via the calibration orifice 16.

[0083] Figure 3 is a graph with an x-axis representing depth (expressed in meters) and a y-axis representing weight (expressed in kg). A first curve C1 illustrates the buoyancy (expressed in kg) of an underwater vehicle 2 displacing a volume of water V and without a hydraulic accumulator 6. A second curve C2 illustrates the buoyancy of the same underwater vehicle 2 equipped with a hydraulic accumulator 6 calibrated for a reference depth PR. A third curve C3 illustrates the quantity of surrounding water or liquid L that has entered the fluidic chamber of the hydraulic accumulator 6 (expressed in kg) as a function of depth.

[0084] As long as the underwater vehicle 2 equipped with the hydraulic accumulator 6 is at an immersion depth less than the reference depth PR, surrounding water or liquid L does not enter the hydraulic accumulator 6 and the buoyancy of the underwater vehicle 2 equipped with the hydraulic accumulator 6 (curve C2) is not modified compared to that of the underwater vehicle 2 without a hydraulic accumulator 6 (curve Cl).

[0085] When the underwater vehicle 2 equipped with the hydraulic accumulator exceeds the reference depth PR, surrounding water or liquid L begins to enter the fluidic chamber 10 of the hydraulic accumulator 6. The buoyancy of the underwater vehicle 2 equipped with the hydraulic accumulator 6 is limited while that of the underwater vehicle without a hydraulic accumulator 6 increases linearly with depth.

[0086] The numerical values ​​of [Fig.3] correspond to an underwater vehicle 2 displacing a volume of water of 130 liters and a hydraulic accumulator 6 with pressurized gas having a calibration pressure of 70 bars.

[0087] Up to a reference depth PR of approximately 700 meters (corresponding to the calibration pressure of 70 bars), the buoyancy of the underwater vehicle 2 equipped with the hydraulic accumulator 6 (curve C2) is not or is little affected compared to that of the same underwater vehicle 2 without hydraulic accumulator 6 (curve Cl).

[0088] Beyond 700 meters depth, the buoyancy of the underwater vehicle 2 without a hydraulic accumulator 6 increases, reaching approximately 2 kg at 3500 m depth, whereas that of the underwater vehicle 2 equipped with a hydraulic accumulator 6 is limited, and varies here between - 400 g and + 400 g.

[0089] The hydraulic accumulator 6 facilitates the diving of the underwater vehicle 2 to great depths and makes it possible to increase its autonomy by avoiding the need to plan and / or activate a propulsion system to generate a propulsion force and / or to activate a ballast system.

[0090] As illustrated in [Fig.4], the buoyancy adjustment system 4 optionally includes a ballast system 32 configured to actively modify the buoyancy of the underwater craft 2.

[0091] The ballast system 32 includes a ballast tank 34 fluidically connected to the external tank 28 via a fluidic actuator 36 configured to force the transfer of liquid L between the ballast tank 34 and the external tank 28. The fluidic actuator 36 is, for example, a pump.

[0092] The ballast system 32 is configured in such a way that the transfer of liquid between the ballast tank 34 and the external tank 28 is controlled solely by the activation of the fluidic actuator 36.

[0093] The liquid L contained in the ballast tank 34 is not subjected to the pressure of the surrounding water.

[0094] To do this, the ballast tank 34 is installed inside the hull 20 of the underwater vehicle 2, so as not to be subjected to the pressure of the surrounding water, in particular by being disposed in a watertight compartment 22 of the hull 20.

[0095] As illustrated in [Fig.3], the external reservoir 28 and the fluidic chamber 10 of the pressure accumulator 6 are fluidically connected in parallel to the fluidic actuator 36.

[0096] Alternatively, as illustrated in [Fig.5], the external reservoir 28 and the fluidic chamber 10 of the hydraulic accumulator 6 are fluidically connected in series to the fluidic actuator 36. The external reservoir 28 is, for example, located fluidly between the ballast tank 34 and the pneumatic chamber 14 of the hydraulic accumulator 6.

[0097] Advantageously, as illustrated in [Fig.6], the external reservoir 28 and the hydraulic accumulator 6 are at least partially nested one inside the other. This allows for a compact arrangement of the buoyancy adjustment system, particularly when the hull 20 of the underwater vehicle has a hydrodynamic profile.

[0098] As illustrated in [Fig. 5], the hydraulic accumulator 6 is, for example, at least partially fitted into the external reservoir 28. In particular, the external reservoir 28 at least partially surrounds the hydraulic accumulator 6. The external reservoir 28 defines a space in which the hydraulic accumulator 6 is at least partially received.

[0099] In an unshown variant, the configuration is reversed. The external reservoir 28 is, for example, at least partially nested within the hydraulic accumulator 6. In particular, the hydraulic accumulator 6 at least partially surrounds the external reservoir 28. The hydraulic accumulator 6 defines a space in which the external reservoir 28 is at least partially received.

[0100] In operation, to decrease the immersion depth of the underwater vehicle 2, the fluidic actuator 36 is activated to force the transfer of liquid L from the ballast tank 34 to the external tank 28. This causes an increase in the volume occupied in the surrounding water by the external tank 28 and an increase in the buoyancy of the underwater vehicle.

[0101] To increase the immersion depth of the underwater vehicle 2, the fluidic actuator 36 is activated to force the transfer of liquid L from the external tank 28 to the ballast tank 34. This causes a decrease in the volume occupied in the surrounding water by the external tank 28 and a decrease in the buoyancy of the underwater vehicle.

[0102] The transfer of liquid L between the external tank 28 and the ballast tank 34 allows the buoyancy of the underwater vehicle 2 to be actively modified.

[0103] The fluidic link between the external reservoir 28 and the fluidic chamber 10 of the hydraulic accumulator 6 allows the buoyancy of the underwater vehicle 2 to be modified passively, for example to compensate for a variation in buoyancy due to a variation in water density.

[0104] It is therefore not necessary to use the ballast system 32 to compensate for a variation in buoyancy due to a variation in water density.

[0105] It follows that it is possible to control the buoyancy of the underwater vehicle 2 while limiting energy expenditure. It is therefore possible to design an underwater vehicle 2 with satisfactory energy autonomy.

[0106] The underwater craft 2 is, for example, an underwater glider. An underwater glider is configured to navigate underwater autonomously by alternating ascent and descent phases during which the underwater glider moves forward due to a propulsive force generated by the vertical displacement of the underwater glider, for example, due to the shape of the hull of the underwater craft 2 or the presence of hydrodynamic appendages, such as fins. The vertical displacement of the underwater glider is, for example, generated using the ballast system 32 with low energy consumption.

[0107] The underwater vehicle 2 is, for example, a profiler. A profiler is configured to dive and ascend, without necessarily moving forward, to take measurements as a function of depth, for example in a water column.

[0108] The underwater vehicle 2 is for example equipped with a measurement system to carry out measurements during its movement in the water, by examples measurements of temperature, pressure and / or salinity.

Claims

Demands

1. Underwater craft equipped with a buoyancy adjustment system comprising a hydraulic accumulator (6) including a casing (8) within which is delimited a fluidic chamber (10) the volume of which varies according to the pressure residing within the fluidic chamber (10), the fluidic chamber (10) being in fluidic communication with the surrounding water or in fluidic communication with an external reservoir (28) containing a liquid (L), the external reservoir (28) being configured such that the pressure of the liquid (L) contained in the external reservoir (28) varies according to the pressure of the surrounding water.

2. Underwater craft according to claim 1, wherein the volume occupied by the external tank (28) varies according to the volume of liquid contained in the external tank (28).

3. Underwater device according to claim 1 or 2, in which the external tank (28) has a separating wall (30) separating the liquid (L) from the surrounding water, the separating wall (30) being movable and / or deformable under the effect of a pressure difference between the pressure of the liquid (L) and the pressure of the surrounding water.

4. Underwater device according to claim 3, in which the fluidic chamber (10) is delimited by a deformable and / or movable internal wall (12), the internal wall (12) being subjected, on one side, to the pressure of the surrounding water or of the liquid (L) present in the fluidic chamber (10) and, on the other side, subjected, for example, to the action of a pressurized gas (G) present in a pneumatic chamber (14) delimited by the internal wall (12) and / or to the action of a spring.

5. Underwater device according to claim 4, wherein the hydraulic accumulator (6) is calibrated such that when the volume of the fluidic chamber (10) is minimal, the pressurized gas (G) has a calibration pressure strictly greater than 1 bar and / or the spring has a non-zero preload.

6. A submersible device according to any one of the preceding claims, wherein the hydraulic accumulator (6) is calibrated such that the volume of the fluidic chamber (10) remains minimal as long as the surrounding water pressure is below a reference pressure (PR), the volume of the fluidic chamber (10) increasing with the surrounding water pressure as the surrounding water pressure increases. The ronnante is higher than the reference pressure (PR).

7. Underwater device according to any one of the preceding claims, wherein the external reservoir (28) comprises an elastically deformable bladder, an elastically deformable membrane and / or a piston subjected on one side to the action of the liquid and on the other side to the action of the surrounding water.

8. Underwater vehicle according to any one of the preceding claims, wherein the external tank (28) and the casing (8) are at least partially nested one inside the other.

9. Underwater craft according to any one of the preceding claims, comprising a ballast system (32), the ballast system (32) comprising a ballast tank (34) fluidically connected to the external tank, and an actuator (36) activatable to force the transfer of the liquid (L) between the ballast tank (34) and the external tank and / or the fluidic chamber (10).

10. Underwater vehicle according to claim 9, wherein the external tank (28) and the fluidic chamber (10) are fluidically connected in parallel to the actuator (36).

11. Underwater craft according to claim 9, wherein the external tank (28) and the fluidic chamber (10) are fluidically connected in series to the actuator.

12. Underwater vehicle according to claim 11, wherein the external tank (28) is fluidically located between the actuator (36) and the fluidic chamber (10).

13. Submarine craft according to any one of claims 9 to 11, wherein the ballast tank (32) is received in a wet compartment (24) of the submarine craft.

14. Underwater craft according to any one of the preceding claims, wherein the external tank (28) and / or the hydraulic accumulator (6) are received in a wet compartment (24) of the underwater craft.

15. Underwater craft according to any one of the preceding claims, wherein the underwater craft is an underwater glider or an underwater profiler.

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