EP3393903A1

EP3393903A1 - Marine vehicle thruster control method

Info

Publication number: EP3393903A1
Application number: EP16819935.4A
Authority: EP
Inventors: Christophe Borel; Jean-Philippe Brunet; Benoît THECKES; Cyril BOUYER
Original assignee: Thales SA
Current assignee: Thales SA
Priority date: 2015-12-23
Filing date: 2016-12-22
Publication date: 2018-10-31
Anticipated expiration: 2036-12-22
Also published as: AU2016375035B2; SG11201805437VA; US10723426B2; CA3009568C; EP3393903B1; WO2017109148A1; FR3046132A1; FR3046132B1; CA3009568A1; AU2016375035A1; US20190009871A1

Abstract

The invention relates to a method for controlling a thruster of a marine vehicle (1) that is at least partially submerged in a liquid and includes a body (2) and a thruster (3) that includes two propellers (AV, AR). Each propeller includes blades intended to turn about an axis of rotation of said propeller. The method includes a low-speed maneuver control step, during which the thruster is controlled such that each propeller (AV, AR) generates a flow directed toward and reaching the flow generated by the other propeller.

Description

METHOD FOR CONTROLLING A PROPELLER OF A MARINE VEHICLE

The present invention relates to the propulsion and maneuvering of marine vehicles comprising a thruster comprising two propellers.

The invention is particularly applicable to underwater vehicles comprising a vector propeller with two propellers. A propellant is called vector when it can be controlled so as to produce a thrust or rotational propulsion force on 4π steradian. The so-called vector propulsion of an underwater vehicle is opposed to the conventional propulsion in which the orientation of control surfaces causes a change in the lift generated by the flow of fluid surrounding the control surfaces. The force generated by the fluid on the control surfaces makes it possible to orient the vehicle in the desired direction. A well-known limitation of this form of propulsion is the need to generate a significant flow of fluid around the vehicle to cause a change in lift control surfaces allowing a change of attitude of the vehicle, that is to say to allow maneuvering the underwater vehicle. If this flow is too weak then the efficiency of the control surfaces decreases in inverse ratio of the square of the speed of the flow until becoming zero for a flow rate of zero. In other words, it is not possible by conventional propulsion to orient the vehicle in a desired direction without a significant displacement of the vehicle, when the fluid flow is zero. In addition, the control surfaces generate a drag proportional to the square of the speed which opposes the displacement and which therefore consumes energy and all the more so that the control surfaces are solicited. The control method of a vector propulsion presented in this patent allows the vehicle to dispense with conventional rudders, and thus significantly reduce the hydrodynamic drag of the vehicle. Vector propulsion of the two-helix type has many theoretical advantages, including increased mobility, simplification of the architecture (eg by eliminating the control surfaces), increased vehicle endurance (by reducing the hydrodynamic drag). This lack of steering other than the propeller blades facilitates the realization of a hydrodynamic vehicle called "flush", that is to say, no appendix exceeds, which allows him for example to easily hold in a tube and avoids to damage the control surfaces during a docking. The piloting of a propeller with two propellers encounters however many difficulties, especially at low speeds.

An object of the invention is to provide a method for controlling a propeller with two propellers to maneuver the vehicle efficiently and stable at low speed.

To this end, the subject of the invention is a method for controlling a propulsion engine of a marine vehicle at least partially immersed in a liquid comprising a body and the propellant mounted on said body, the propellant comprising two propellers, each propeller comprising blades for rotating about an axis of rotation of said propeller. According to the invention, the method comprises a low-speed maneuvering control step, during which the thruster is piloted so that each helix generates a flow directed towards the flow generated by the other propeller and reaching the flow generated by the propeller. other propeller.

The method according to the invention advantageously has at least one of the following characteristics taken alone or in combination:

each helix generates a non-zero flow and directed in the same direction, along the axis of the helix, over most of the revolution of the blades of the propeller, in the liquid around the axis of rotation of the helix; 'propeller,

at least one helix generates a flow whose direction, along the x axis, varies on the revolution of the blades of the helix in the liquid around the axis of rotation of the helix,

during the low speed maneuvering control step, the flow generated by each helix is directed towards a point of the other helix, called the center of the other helix, located substantially on the axis of rotation of the other propeller,

during the low speed maneuvering control step, the thruster is piloted so that each helix generates a flow directed towards the flow generated by the other helix and reaching the flow generated by the other helix whatever the motion printed on the vehicle by the thruster,

the distance between the helices is between a non-zero threshold distance and three times the diameter of the largest of the two propellers,

the distance between the propellers is greater than or equal to 20% of the diameter of the smaller of the two propellers, the low-speed maneuvering control step is implemented only when the flows generated by the two propellers meet between the two propellers at a distance from the two propellers,

the low speed maneuvering control step is implemented irrespective of the movement of the vehicle provided that the fluxes generated by the two propellers meet between the two propellers at a distance from the two propellers,

the two propellers comprise an upstream helix and a downstream propeller along a reference axis in a predetermined direction, and in which during the low speed maneuvering control step, for the thruster to exert a thrust having a non-zero component along the reference axis and in said direction, the thruster is piloted so that the upstream thrust force resulting from the upstream flow generated by the upstream propeller has an axial component of intensity greater than that of the axial component of the force downstream thrust resulting from the downstream flow generated by the downstream propeller,

during the low speed maneuvering control step, so that the thruster generates a thrust force having a zero radial component along a radial axis situated in a plane perpendicular to a reference axis, the thruster is piloted so that the combined flow resulting from the combination of the fluxes generated by the two propellers, between the two propellers, or with a symmetry of revolution about the reference axis,

during the low speed operation control step, so that the thruster exerts a thrust force having a non-zero radial component along a radial axis situated in a plane perpendicular to the reference axis, the thruster of the thruster is so that the combined flow resulting from the combination of the fluxes generated by the two propellers between the two propellers is not symmetrical of revolution about the reference axis,

during the low-speed maneuvering control step, so that the thruster exerts a thrust force having a non-zero radial component, the thruster is piloted so that at least one propeller generates a flux that is not with symmetry of revolution around the reference axis,

during the low speed maneuvering control step, so that the vehicle rotates about an axis perpendicular to the reference axis, pilot the thruster so that the thrust force generated by the thruster is applied to a point distant from the center of mass of the vehicle,

during the low-speed maneuvering control step, in order for the vehicle to translate along an axis perpendicular to the reference axis, the thruster is piloted so that the thrust force generated by the thruster is applied to the thruster. the center of mass of the vehicle,

- The thruster is a thruster comprising two contrarotative propellers with variable cyclic and collective pitch, a reference axis being an axis of the helices which is an axis connecting centers of the two propellers which are points on the axes of rotation of the respective propellers. ,

the axes of rotation of the two propellers are substantially coincidental and coincident with the reference axis,

during the low-speed maneuvering control step, so that the thruster generates a thrust having a radial component acting in a radial direction forming, around the reference axis, a first angle α with a direction of reference, the cyclic pitch of the helices is adjusted so that the cyclic angle Θ of the helices is given by the following formula or so that the cyclic angle Θ of one of the two helices is given substantially by the following formula, another propeller with a neutral cyclic pitch:

Θ = a- φ where the cyclic phase φ is the angle formed, around the reference axis, between the thrust generated by the helices and the cyclic angle Θ of the helices or of one of the propellers, the cyclic phase φ being predetermined, the cyclic angle of a helix being the angle formed around the reference axis between the direction in which the cyclic pitch angle of the helix is maximum and the reference direction.

The invention also relates to a marine vehicle intended to be at least partially immersed in a liquid comprising a body and a propellant comprising two propellers, each propeller comprising blades intended to rotate about an axis of rotation of said propeller, characterized in that it comprises a control device configured to be able to implement the method according to the invention, the control device comprising a controller which receives an instruction setpoint of the low speed maneuvering control step is configured to compute a low speed configuration so that each helix generates a stream directed to the stream generated by the other helix and reaching the flow generated by the other propeller, the control device further comprising an actuator configured to control the propeller so as to put it in said low speed configuration.

Advantageously, the implementation instruction of the low speed maneuvering control step comprises a thrust command, the thruster calculating a low speed configuration of the thruster such that the thruster generates a thrust in the direction of the thrust instruction.

The invention also relates to the control device and to a propulsion system comprising the control device and the thruster.

The control method makes it possible to drive the underwater vehicle stably and effectively at low speed even when the vehicle speed is negative or zero and when the mass of the vehicle is important. That is to say that this solution allows the vehicle to be maneuvering even in fixed point or in reverse. It allows precise control of the attitude and position of the underwater vehicle in relation to a fixed reference system.

Other features and advantages of the invention will appear on reading the detailed description which follows, given by way of non-limiting example and with reference to the appended drawings in which:

- Figure 1 shows schematically in plan view an underwater vehicle at equilibrium;

FIG. 2 diagrammatically shows a top view of a submarine vehicle moving along the x-axis towards the front,

FIG. 3 schematically represents a top view of a submarine vehicle moving along the x axis towards the rear,

FIG. 4 is a diagrammatic plan view of an underwater vehicle on which the thruster exerts a non-zero radial thrust, FIG. 5 schematically represents, in a radial plane, the direction of thrust exerted by the thruster as a function of the cyclic angle,

- Figure 6 schematically shows a propulsion system according to the invention.

From one figure to another, the same elements are identified by the same references. The invention proposes a method for controlling a thruster of a marine vehicle. The method is particularly applicable to submarine vehicles intended to move completely immersed in a liquid, including water. The invention also applies to surface vehicles intended to move on the surface of a liquid being partially immersed in the liquid. Marine vehicles may be autonomous vehicles with pilots (humans) on board, or unmanned drones on board such as remotely piloted vehicles or ROVs in reference to the English expression "remotely operated vehicle" or marine vehicles such as autonomous underwater vehicles or AUV with reference to the Anglo-Saxon term "Autonomous Underwater Vehicle". Therefore, the control method, that is to say control, according to the invention can be implemented by an operator (pilot) on board or remotely or by an autonomous control device.

Advantageously, the two propellers are mounted on the body of the marine vehicle so as to be arranged or able to be arranged so that each propeller, taken among these two propellers, can generate a flow of water (or more generally liquid) directed towards the flow generated by the other helix, taken from the two helices. These propellers are advantageously arranged so that the flow generated by each propeller, taken from the two propellers, regardless of the speed of the vehicle relative to the liquid along a reference axis, at least as long as this speed is below a threshold of predetermined speed, can reach the flow generated by the other propeller, taken among the two propellers. Advantageously, the streams must be able to reach in a time less than a predetermined reaction time. This Reaction time is the acceptable reaction time for the maneuver. This makes it possible to guarantee the formation of the combined or radial flow.

This method applies to vehicles comprising a vector thruster comprising two counter-rotating propellers known as cyclic pitch and variable collective pitch. A propeller with variable cyclic and collective pitch is a propeller whose blade pitch angle is controllable collectively to adjust the thrust along the axis of rotation of the propeller. The collective pitch is defined by a collective pitch angle of the blades. In other words, all blades have the same collective pitch angle over the entire revolution of the blades around the axis of rotation of the propeller. As a reminder, the pitch angle of the blades of a helix is the angle formed between the rope of the blade and the plane of rotation of the helix according to the chosen reference. The plane of rotation of the helix is a plane of the helix perpendicular to the axis of rotation of the helix. The angle of adjustment is also cyclically adjustable to direct the thrust perpendicular to the axis of rotation of the propeller. The cyclic pitch angle of the blades varies cyclically, ie during a revolution around the axis of rotation of the helix, as a function of the angular positions of the blades around the axis of rotation. rotation of the propeller. The cyclic pitch is defined by a differential cyclic stall angle during a revolution of the blades as well as by a cyclic angle. The differential cyclic stall angle is defined as the difference between the maximum cyclic stall angle and the minimum stall angle of a blade during a revolution. The collective pitch is the average cyclic stall angle. The cyclic angle is the angle formed around the axis of rotation of the helix between the direction in which the blade pitch angle is maximum and a reference direction connected to the body of the vehicle. The pitch angle of the blades for which the propeller rotates about its axis of rotation exerts a zero thrust, according to its axis of rotation, is called a collective neutral pitch. The neutral cyclic pitch is that for which the blades exert a thrust whose component perpendicular to the axis of rotation of the helix is zero. A coordinated piloting of the two propellers makes it possible to control the orientation of the thrust on 4π steradian. Vector propellers are especially known formed of two coaxial counter-rotating propellers, that is to say whose axes of rotation are substantially merged. For example, coaxial propellers whose axes of rotation are substantially parallel to the main axis of movement of the vehicle. The main axis of movement of the vehicle is the axis, linked to the body of the vehicle, according to which the vehicle is mainly intended to move. By axis connected to the body of the vehicle is meant that the orientation and the position of the body of the vehicle in a plane perpendicular to the axis are fixed. This type of thruster has the advantage of being able to be driven so as to have a good energy efficiency at high speed. Thus the two propellers generate a thrust naturally oriented along the main axis of movement of the vehicle. In a conventional but non-limiting manner, the main axis of movement of the vehicle is the roll axis of the vehicle. The yaw and pitch axes are radial axes, that is, perpendicular to the main axis, passing through the main axis. The axes of rotation of the propellers are fixed relative to the vehicle.

The method is also applicable to thrusters of the type comprising two contrarotating propellers or not variable cyclic and collective propellers whose axes of rotation of the helices are distinct and substantially parallel and those having propellers whose axes of rotation are not parallel. Advantageously, for a vehicle intended to move mainly along a main axis, the axes of rotation of the helices form any respective angles different from 90 ° with this axis which is for example the main axis of movement of the vehicle. More advantageously, the axes of rotation of the propellers are substantially parallel to the main axis of movement of the vehicle, which makes it possible to improve the propulsion efficiency during the progression in a straight line along this axis. The rotational speed of the blades of the propeller around its axis of rotation (called rotational speed of the propeller) is independently or collectively adjustable for both propellers.

The method according to the invention also applies to thrusters comprising two orientable propellants with finger-jointed connection also called "gimbal propellers" in English terminology. These thrusters each have a propeller comprising blades whose pitch is not adjustable. Each of the propellers is connected by a finger ball joint connection to the body of the marine vehicle, for example made by means of a Cardan mounting so that the plane of rotation (or the axis of rotation) of each of the propellers can pivot, relative to the body of the vehicle, around two axes perpendicular to each other. In other words, the orientation of the propellers with respect to the body of the vehicle is modifiable. The speed of rotation of each of the helices around its axis of rotation is also adjustable, preferably independently of one another. A single propellant of the "gimbal propeller" type has a more limited yield than propellers with contra-rotating propellers with variable cyclic and collective pitch and have an action limited to a given angular sector of opening less than 360 °.

The propellers may have the same diameter (as in the figures) or a different diameter, the same number of blades or a different number of blades.

In the remainder of the description, a reference axis connected to the body of the vehicle is defined. By axis connected to the body of the vehicle is meant that the orientation and the position of the body of the vehicle in a plane perpendicular to the axis are fixed. An axis oriented perpendicular to the reference axis passing through this axis is called the radial axis and defines a radial direction. Radial component of a vector means the component of the vector along a radial axis perpendicular to the reference axis. Axial component of a vector means the component of the vector along the reference axis. In the present patent application, for a thrust, a radial thrust is defined which is the radial component of the thrust and the axial thrust which is the axial component of the thrust.

The control method according to the invention comprises a propellant control step called, in the following document, low-speed maneuvering control step.

According to the invention, the method comprises a control step, that is to say control, of low speed maneuvering during which the propeller is piloted, that is to say, controlled so that each helix, among the two helices, generates a flow directed to the flow generated by the other helix, among the two helices, and reaching the flow generated by the other helix. This assumes that both propellers generate a stream of water, i.e., rotate relative to the body of the marine vehicle around their respective propeller rotational axes, and have a non-neutral collective stall angle. This makes it possible to generate a combined flow, resulting from the combination of the flows generated by the two propellers, which has a non-zero radial component and which makes it possible to control the vehicle of stably and to obtain a good maneuverability of the vehicle.

Furthermore, in the embodiment of the figures, during the low speed maneuvering control step, each propeller generates a non-zero flow and directed in the same direction, along the axis of rotation of the helix, on the whole the revolution of the blades of the propeller in the liquid around the axis of rotation of the propeller. In other words, the axial component of the flow has the same sign on the entire revolution of blades of the helix in the liquid around the axis of rotation of the helix. This means that the flow lines generated by the helix in each radial angular sector, fixed relative to the body of the vehicle and swept by the helix, are oriented in the same direction, along the axis of rotation of the helix. This makes it possible to generate a combined flow, resulting from the combination of the flows generated by the two propellers, which has a non-zero radial component all around the reference axis when the reference axis passes into the volume where the flows are combined. between the two propellers when the axes of rotation of the propellers are not perpendicular to this reference axis.

The fact that each flow has essentially the same direction over the entire revolution of the blades of the propeller in the liquid around the axis of rotation avoids the creation of vortices between the propellers which would have the effect of destabilizing the vehicle.

As a variant, at least one helix generates a stream directed in one direction, along the axis of rotation of the helix, which varies on the revolution of the blades of the helix in the liquid around the axis of rotation of the helix. propeller.

Advantageously, the propellers are mounted on the body of the marine vehicle so as to be arranged or able to be arranged so that each propeller can generate a flow of water (or more generally liquid) directed towards the other propeller. In the present patent application, it is considered that a helix generates a flow directed towards another helix when the volume swept by the other helix (when it is rotated about the axis of rotation) is at least partially located at the other end. cylinder interior whose axis is the main axis of the flow generated by the propeller and whose diameter is the diameter of the propeller. Advantageously, the main axis of the flow generated by each helix passes into the volume swept by the other helix during a revolution of the blades of the other helix around the axis of rotation of the other helix. The direction of the main axis is defined relative to the body of the vehicle. The volume swept by a helix includes the axis of rotation of the helix. By main axis of the flow generated by a helix is meant the axis passing through a center of the helix and whose direction is the direction of the flow generated by the helix. By center of a helix is meant a predetermined point of the helix located substantially on the axis of rotation of the helix and inside the volume that can sweep the propeller during a revolution of the blades of the propeller. helix around the axis of rotation of the helix. The center of a propeller can advantageously be defined as the center of mass of the blades. Advantageously, the planes of rotation of the propellers must be non-coplanar or must be able to be arranged in a non-coplanar manner. Advantageously, the flow directed by each of the two propellers is directed towards the center of the other propeller taken from the two propellers. This is done to generate a thrust that does not have a radial component. In this case, the direction of the flow generated by a helix being defined by the main axis of the flow, the main axis of the flow generated by each helix passes through said center of the other helix. This avoids oscillations of the vehicle. The oscillations of the vehicle being all the more controlled that the flow generated by a helix is directed near the center of the other helix. In this configuration the trajectory of the vehicle is more stable and easy to control because on a revolution of the blades of the propeller around the axis of rotation of the propeller, all the blades meet the same flow, especially when the flow of the propellers meet near one of the propellers. The pitch angle of the blades of the other propeller is not disturbed by the flow generated by the propeller. If the flow is off-center, all the blades do not meet a homogeneous flow. The pitch angle of the blades is disturbed by the flow generated by the propeller.

Advantageously, the low speed maneuvering control step is implemented regardless of the movement printed by the thruster to the vehicle when the vehicle speed module is below a predetermined threshold that may be zero. A vector propeller can print to a submarine vehicle movements in 6 degrees of freedom. By the same method, the movement of a building surface can be adjusted by its thruster with 2 degrees of freedom in translation and 1 degree of freedom in rotation.

In general, the low speed operation control step can be implemented regardless of the rotational movement around an axis perpendicular to the reference axis and / or whatever the translation movement along the reference axis and / or whatever the translational movement along an axis perpendicular to the reference axis printed at vehicle by the thruster. If this method is implemented when the vehicle speed module is greater than the predetermined threshold then the vehicle will slow by itself simply by the application of the method to return to a speed below the threshold.

This process is illustrated by FIGS. 1 to 4 showing a submarine vehicle comprising a vector propeller of the type with two counter-rotating propellers with variable cyclic and collective pitch. But what is described later is also applicable to surface vessels and other types of thrusters described above.

Figures 1 to 4 show schematically in plan view a submarine vehicle 1 having a body 2 and a vector thruster 3 mounted on the body of the underwater vehicle 1. This thruster 3 is of the vector propellant type comprising two AV propellers, counter-rotating ARs with variable cyclic and collective pitch. These propellers are coaxial. In other words, they are intended to rotate about axes of rotation substantially merged. In these figures, the reference axis x is the axis of the helices, that is to say the axis connecting the center of the two propellers. Furthermore, this axis is the main axis of movement of the vehicle which is here the roll axis of the vehicle. The main axis of movement of the vehicle x is oriented in the preferred direction of movement of the vehicle when the vehicle has a preferred direction of movement. In the present patent application, the front and the back are defined with respect to the reference axis x in the direction of the reference axis. The propellers comprise a front propeller AV and a rear propeller AR, the forward propeller being located in front of the rear propeller. The blades of each propeller AV, AR are mounted on the body 2 of the vehicle 1 to rotate about the axis of rotation of the corresponding propeller AV, AR. The blades of a helix are secured in rotation around the axis of rotation of the helix. For example, each blade is connected by an axis to a hub rotatably mounted on the body 2 of the underwater vehicle 1 about the axis of rotation of the propeller generally defined by a shaft.

The water flow lines between the two propellers are represented by arrows. As a reminder, a flow generated by a propeller represents the speed water through the propeller. The module or flux intensity, expressed in kg. m. s ^"1 is a flow rate of water flow through the surface of the propeller.The thrust forces generated by the respective propellers are also represented by simple arrows.The thrust force generated by the propeller is represented when it is not zero, by a double arrow For clarity, this arrow is shown on the rear of the vehicle but the thrust advantageously applies between the two propellers on a point of the axis of roll .

In the embodiment of the figures, the two propellers AV, AR are installed at the rear of the vehicle, that is to say on the rear half of the body of the vehicle along the reference axis x. Alternatively, these two propellers are installed at the front of the body of the vehicle or one at the front and one at the rear of the body of the vehicle. To be able to turn the vehicle, that is to say move the vehicle by generating a thrust having a radial component (perpendicular to the x-axis) non-zero, the rotational planes of the propellers are not arranged in symmetrical planes from each other with respect to a plane containing the center of mass of the body 2 of the underwater vehicle 1.

In each of the situations shown in the figures, each helix generates a flow directed towards the other helix. In other words, the forward propeller AV generates a flow to the rear propeller AR which itself generates a stream directed to the propeller before AV. Each stream has a non-zero component with the same sign along the axis of rotation of the helix x, over most of the revolution of the blades of the corresponding helix around the axis of rotation of the helix x, and preferably over the entire revolution of the blades of the helix around the axis of rotation of the helix. As a result, the fluxes generated by the two helices come together and deflect each other all around the x axis. In other words, these flows combine to form between the propellers, at a distance from the propellers, a flow called combined or radial flow as visible in the figures. In the embodiment of the figures, the combined flow generally has a non-zero and positive radial component in each radial angular sector of a fixed disk relative to the body 2 and perpendicular to the reference axis even when the vehicle is not moving. The combined flow moves away from the reference axis all around the reference axis. This makes it possible to obtain a balanced thrust force in all radial directions even when the vehicle is not moving along the axis of the propellers. The nonzero radial components of the combined flow make it possible to ensure efficient radial maneuverability of the vehicle at zero speed along the reference axis and also at non-zero speed when the thruster produces a thrust to move the vehicle axially. This maximizes the thrust generated by the thruster. Indeed, the flow of the helices being generated towards each other, the flow generated by each helix can not reach the other helix, it is deflected by the flow generated by the other helix. These flows do not suck each other which maximizes the radial thrust effect. The reference axis is advantageously the axis of the propellers, the radial flow is then substantially centered on the axis of rotation of the propellers.

The generation, by the two propellers of flow oriented towards each other and by reaction of opposing thrusts, stabilizes the vehicle and control the maneuver of the vehicle.

The vehicle driven by means of the method according to the invention is insensitive to external disturbances. As already mentioned, because the flow generated by each helix can not reach the other helix, the two helices do not disturb one another. In other words, the flow generated by one helix does not disturb the angle of incidence of the other propeller for a given wedging angle of the blades. The angle of incidence is defined relative to the flow of liquid that passes through it. Therefore, by creating the radial combined flow, when the cyclic pitch and collective pitch of the propellers are then adjusted to advance, retreat and / or to rotate the vehicle, the vehicle is stabilized at a speed of travel or rotation with respect to the water depending solely on the adjustment of the propellers and if a disturbance is generated which tends to slow down or accelerate the underwater vehicle, this disturbance generates a variation of speed of the water at the level of the propellers which results by a variation of the angle of attack (or incidence) of the blades of the propellers which generates a variation of thrust which opposes the movement of the external disturbance.

In addition, the good maneuverability and stability of the vehicle at low speed and at zero speed do not require the integration of additional maneuvering systems or elements generating a hydrodynamic drag, which is costly in energy, particularly when the vehicle will want to move. It should be noted that the method according to the invention is anti-intuitive because the generation of flows directed towards each other by the propellers is highly energy consuming, especially since these flows have the same sign on the whole revolution of the volume swept by the blades of the propeller around the rotation of the propeller.

The low speed maneuvering control step is advantageously used to maneuver the vehicle around a fixed point.

We will now describe more precisely the situations represented in each of the figures.

In Figure 1, the vehicle is stationary. The flows generated by the two helices are directed toward each other along the x axis. This means that each of these flows is symmetrical of revolution around the x axis. In other words, they are homogeneous over the entire revolution of the blades of the respective helices around the x axis. Moreover, the fluxes generated by the two propellers have the same intensity. The thrust forces before Fav and rear Far respectively resulting from the forward flow (generated by the front propeller to the rear propeller) and the rear flow (generated by the rear propeller to the front propeller) therefore have the same intensity. As a result, the combined flow that is derived from the flow deflection due to the meeting of these two flows is radial, that is to say perpendicular to the x-axis and all around the x-axis. The combined stream has a generally annular shape. The thruster generates a thrust force F whose axial component is zero. The position of the vehicle 1 in translation in the axial direction x with respect to a reference system remains fixed, for example the liquid.

Therefore, so that the vehicle does not move along the x-axis of the propellers, the thruster 3 is piloted so that the thrust forces resulting from the fluxes generated by the two propellers have axial components of the same intensity (or module). . In other words, the thruster is piloted so that the fluxes generated by the two propellers have the same module along the x axis and opposite directions along the x axis. This is done during the generation of the streams towards each other. The thruster does not generate axial thrust. To achieve this, one plays on the cyclic steps and / or the speeds of rotation of the propellers. In FIG. 1, the combined flow being symmetrical of revolution about the x axis, the thruster generates a thrust force F whose radial component is zero. The vehicle can not be rotated about an axis perpendicular to the x-axis in this configuration. To obtain this configuration, the combination of the speed of rotation and the collective pitch angle (also called collective pitch) of each propeller is such that the propeller generates a flow towards the other propeller and resulting in a thrust equal and opposite to that generated by the other helix.

In Figure 2, the flows generated by the two helices are directed towards each other and along the x axis. Each of these flows is symmetrical of revolution around the x axis. On the other hand, the thrust forces before Fav and rear Far resulting respectively from the forward flow (generated by the front propeller AV towards the rear propeller AR) and the rearward flow (generated by the rear propeller AR towards the propeller before AV ) have different modules. As a result, the combined flow is inclined with respect to the x-axis and globally symmetrical about the x-axis. The combined flow has a frustoconical shape in the vicinity of the vehicle. Since the forward flow generated by the forward propeller AV is greater than the rearward flow generated by the rear propeller AR, the modulus of the force of the thrust Fav resulting from the forward flow is greater than that of the thrust force Far resulting from the backflow. The thruster generates a thrust force F whose axial component is positive. The modulus of this thrust is substantially equal to the modulus of the sum of the axial components of the thrust forces generated by the two propellers. The vehicle is driven in a translational motion along the x-axis forward. This translation changes the relative angle of attack of the blades of the front propeller and tends to reduce forward thrust. Quickly the speed of advance equilibrates to a value such that the two thrusts are in equilibrium.

Therefore, in order to move the vehicle along the x axis of the forward propellers AV, the thruster 3 is piloted so that the forward thrust force Fav resulting from the forward flow has an axial component of intensity greater than that of the axial component of the Far thrust force resulting from the rear flow generated by the rear prop AR. In other words, to obtain a displacement of the vehicle in the forward axial direction, the front and rear flows are unbalanced so that the combined flow is directed towards the rear. The module of the axial component of the generated flow by the forward propeller to the rear must be greater than the modulus of the axial component of the flow generated by the forward propeller. To obtain this axial displacement, the rotation / collective pitch combination of each propeller is adjusted so that the propellers produce a different thrust. For example, this is achieved by increasing the collective pitch before and reducing the collective pitch back without changing the rotational speeds compared to the situation of FIG. 1. It is better to play on the collective rather than modify the rotation speeds of the propellers because too great a difference in vorticity of the generated flows can lead to instability and also generates a roll torque.

In FIG. 2, the combined flow being symmetrical of revolution about the x axis, the thruster generates a thrust force F whose radial component is zero. The vehicle does not rotate about an axis perpendicular to the x-axis in this configuration.

The displacement obtained is purely axial.

In Figure 3, the flows generated by the two helices are directed towards each other and along the x axis. This means that each of these flows is symmetrical of revolution around the x axis. On the other hand, the thrust forces before Fav and rear Far resulting respectively from the forward flow (generated by the front propeller AV towards the rear propeller AR) and the rearward flow (generated by the rear propeller AR towards the propeller before AV ) have different modules. As a result, the combined flow is inclined with respect to the x-axis and globally symmetrical about the x-axis. The combined flow has a frustoconical shape in the vicinity of the vehicle. Since the forward flow generated by the front propeller AV is smaller than the rear flow generated by the rear propeller AR, the modulus of the force of the thrust Fav resulting from the forward flow is less than that of the thrust force Far resulting from the backflow. The thruster generates a thrust force F whose axial component is negative. The vehicle is moved in a translational motion along the x-axis backward. The vehicle moves back along the x axis. This translation modifies the angle of attack of the blades of the rear propeller and tends to reduce the rear thrust. Rapidly the speed of recoil equilibrates to a value such that the two thrusts are in equilibrium.

Therefore, to move the vehicle along the x-axis of the propellers to the rear, the thruster 3 is piloted so that the thrust force before Fav resulting from the forward flow generated by the forward propeller AV has an axial component of intensity less than that of the axial component of the rear thrust force Far resulting from the rear flow generated by the rear propeller AR. In other words, to obtain a displacement of the vehicle in the axial direction towards the rear, unbalance the forward and backward flows so that the combined flow is oriented forward. The modulus of the axial component of the flow generated by the forward propeller must be less than the modulus of the axial component of the flow generated by the rear propeller to the rear. To obtain this configuration, the two propellers of FIG. 1 can be rotated at the same rotational speed with neutral cyclic pitches and combinations of rotation speed and collective pitch chosen so that the rear thrust is greater than the forward thrust. As in the case of Figure 2, and for the same reasons we favor the action on the collective steps rather than the action on the speed of rotation of the propellers.

In FIG. 3, the combined flow being at a symmetry of revolution about the x axis, the thruster generates a thrust force F whose radial component is zero. The vehicle does not rotate about an axis perpendicular to the x axis in this configuration. The pure axial displacement of FIG. 3 is obtained, further using neutral cyclic pitches.

In general, in order to move the vehicle along the x axis in a predetermined direction relative to the liquid, the thruster 3 is piloted so that each helix generates a flow directed towards and reaching the flow generated by the other helix and so that the upstream thrust force resulting from the upstream flow has an axial component of intensity greater than that of the axial component of the downstream thrust force resulting from the downstream flow generated by the downstream propeller. "Upstream propeller" means the propeller located forwardly in the direction of movement of the vehicle along the x-axis and the downstream propeller, the propeller situated aft in the direction of travel of the vehicle according to the x axis.

When driving low speed maneuver, the thruster control can be a steering of the propellers. When the thruster is of the type comprising two contrarotative propellers with variable cyclic and collective pitch, to obtain an axial component of the thrust force exerted by the fixed propeller speed propeller, the collective pitch is varied. at least one propeller so as to obtain the desired thrust. For all movements, in the case of counter-rotating propellers with variable cyclic and collective pitch, the speed of rotation of the helices and / or the cyclic pitch of the propellers and / or the collective pitch of the propellers are adjusted so as to obtain the desired thrust. If the thruster is a gimbal propeller, the orientation of at least one propeller is adjusted to obtain the desired thrust. This is valid regardless of the desired thrust. The configuration of the control device can be chosen according to a desired thrust by calibration. A preliminary phase of measurement of the flow or thrust generated by the vehicle according to different thruster settings can then determine the settings according to the desired thrust.

It can be seen in FIGS. 2 and 3 that the vehicle is moving forward or backward following a controlled imbalance of the flows of the two propellers. The method according to the invention makes it possible to always further produce a radial force making it possible to maneuver the vehicle. In other words, the thruster remains maneuvering perpendicular to the reference axis when it produces a thrust to move the vehicle axially. When the front and rear flows are unbalanced along the x-axis, the vehicle moves forward or backward with respect to the liquid, accelerating to a limit speed of advance or recoil, respectively, depending on the thrust resulting from the two thrusters. (ie rotational speeds, collective incidence and cyclical incidence of both propellers). The maximum speed of advance of the vehicle relative to the liquid is the maximum speed that can take the speed limit advance. This speed is reached when the forward flow directed towards the rear is at its maximum of thrust and the backward flow directed towards the front is with minimum of push compatible with the fact that it remains directed towards the propeller before AV. In other words, the rear propeller generates a flow forward and this flow is not then deflected backwards by the forward propeller. .. As there is a maximum speed of advance, there is a maximum speed of recoil reached when the backward flow directed forward is at its maximum thrust and the forward flow directed to the rear is at a minimum. thrust compatible with the fact that it remains directed to the rear propeller AR. In other words, the rear propeller generates a flow backwards and this flow is not then deflected forward by the flow generated by the rear propeller.

In other words, between the maximum speed of recoil and the speed at maximum advance, the two propellers generate flows that meet between the two propellers at a distance from the two propellers. Outside this range, flows are not encountered between the two propellers.

This speed can be obtained by tests for a given vehicle, a given axis linked to the body of the vehicle and a given direction along this axis. It is conditioned by the ability of each propeller to generate a more or less intense flow.

The speed of movement of the vehicle along the x-axis is a speed of movement of the vehicle relative to a predetermined fixed reference, for example the liquid or the terrestrial reference. The speed of movement of the vehicle relative to the liquid is the speed of the vehicle relative to the liquid located in the vicinity of the vehicle outside the flow generated by the thruster. Advantageously, the speed threshold up to which the low speed pilot stage is implemented is predetermined and fixed for a given position of the axis of the propellers with respect to the body of the vehicle and for a given direction of movement. This threshold is chosen less than or equal to the maximum speed of advance or recoil of the vehicle along this axis in this direction. This threshold is advantageously non-zero.

In other words, the low-speed driving step is advantageously implemented only when the following speed condition is verified: the standard of the vehicle speed along the x-axis is less than or equal to a first predetermined threshold speed which is less than or equal to a maximum recoil speed, when the vehicle is moving backward along the x-axis, and the vehicle speed standard along the x-axis is less than or equal to a second threshold speed that is less than or equal to equal to a maximum speed of advance when the vehicle is moving forward along the x-axis. In other words, the low speed operation control step is implemented only when the flows generated by the two propellers meet between the two propellers at a distance from the two propellers. This avoids energy losses at high speed and ensures good maneuverability of the vehicle at low speed. The point-of-intersection condition between the two propellers sets limit speeds for forward and reverse along the x-axis.

Advantageously, the low speed operation control step is implemented as long as the speed condition is verified. Other said, the low speed maneuvering control step is implemented regardless of the movement of the vehicle provided that the flows generated by the two propellers meet between the two propellers at a distance from the two propellers. This ensures a good maneuverability of the vehicle in this speed range.

The method advantageously comprises a verification step to check whether the speed condition is verified and whether, yes, the low speed maneuvering step is implemented. The verification step can be implemented iteratively and the low speed maneuvering step is carried out as long as the speed condition is verified.

In FIG. 4, the flows generated by the two propellers are directed towards each other but are not directed along the x axis. In other words, the main axis of flux generated by each helix is not parallel to the x axis. Indeed, these flows are not symmetrical of revolution around the x axis. The flow generated port is greater than the flux generated starboard for each of the propellers which deviates the main axis of the flow generated by each of these propellers relative to the x axis. On the other hand, the axial components of the thrust forces before Fav and rear Far resulting respectively from the forward flow (generated by the front propeller towards the rear propeller) and the rear flow (generated by the rear propeller towards the front propeller) have the same intensity. As a result, the combined flow is mainly perpendicular to the x-axis, all around the x-axis. The thruster generates a thrust force F whose axial component is zero. The position of the vehicle 1 in translation in the axial direction x with respect to a terrestrial reference is fixed. On the other hand, the combined flux is not symmetrical of revolution around the axis x, because the fluxes generated by the two propellers are not in symmetry of revolution around the two helices. The combined flow generally has the shape of an asymmetrical ring having a lower flow to starboard than port on the example of Figure 4. The thruster generates a thrust force F having a non-zero radial component which allows rotate the vehicle around an axis perpendicular to the x-axis or move the vehicle along an axis perpendicular to the x-axis. On the other hand, the modulus of the force of the radial component of the thrust is not the sum of the radial component pushes of thrusts generated by the two thrusters because a significant part of this thrust comes from an interaction of the flow with the vehicle.

Therefore, to exert a thrust F having a non-zero radial component, the thruster 3 is piloted so that the combined stream is not symmetrical about the x axis. In other words, at least one helix generates a flux that is not symmetrical about the x axis. In other words, the propeller is piloted so that at least one propeller generates a flow whose main direction forms a non-zero angle with the axial direction, this propeller generating a radial thrust.

To rotate the ship about an axis of rotation perpendicular to the axis of the propellers which is the axis of roll of the object and passing through the center of mass of the object, for example the yaw axis or pitch, the thruster must be adjusted so that the thrust force exerted by the thruster is applied away from the center of mass of the vehicle. Preferably, the thrust is applied between the two propellers.

To change from the situation shown in FIG. 1 to the situation shown in FIG. 4, the cyclic pitch of the two helices is modified so that the cyclic pitch of the two helices are equal (same calibration angle / same cyclic angle) for identical propellers rotating at the same speed of rotation. In the example of FIG. 4, the cyclic angle is maximum on the port side for the two propellers. In other words, the thruster 3 is controlled so that the helices generate fluxes that are not symmetrical about the x axis but have the same intensity in respective radial sectors, linked to the body of the vehicle, having the same angular size and forming, around the x-axis, the same angle with the reference direction. This makes it possible to obtain maximum thrust in a given radial direction. The way to get this direction is described in Figure 5 which we explain below. To advance the vehicle in the axial direction as in Figure 2 while exerting a radial force as in Figure 4, we can change the collective pitch of at least one of the propellers compared to the configuration of Figure 4 of to generate a thrust F having a non-zero axial component. To move the vehicle in translation along an axis perpendicular to the reference axis, for example along the axis of yaw or pitch, the thruster must be controlled so as to generate a radial thrust applied to the center of mass of the object . For example, the cyclic pitch of the front propeller is larger than that of the rear propeller and the helix angle is arbitrary. Advantageously, a cyclic differential pitch angle of cyclic angle of opposite sign to the other helix is used. Thus, it is possible to shift the point of application of the force beyond the segment formed by the centers of the two propellers. If the point of application is shifted to coincide with the center of gravity of the vehicle, the method provides a pure lateral displacement.

To obtain a rotation of the vehicle around the x-axis in the situation of FIG. 1, the rotational speeds of the propellers around the axis of rotation are piloted so as to generate a non-zero torque around the axis x.

The low speed maneuvering control step can be implemented when performing at least one of the movements described above, for example when the speed module of the vehicle with respect to a predetermined reference frame (for example terrestrial or the liquid) along the axis of the helices is less than a predetermined threshold. As a variant, the low speed piloting step can be implemented continuously during the execution of all the movements described above when the speed modulus is less than the speed threshold. The low speed driving step according to the invention can be implemented only when the speed of the vehicle is below the predetermined threshold or even when the vehicle has a value greater than this threshold. In the latter case it will lead to a rapid braking of the vehicle which will stabilize at the speed corresponding to the adjustment of the propellers as described in the analysis of Figure 2.

We will now describe, with reference to FIG. 5, a particular step for adjusting the thruster to obtain a radial thrust in a predetermined radial direction dr forming, around the reference axis, a predetermined thrust angle with a direction reference dref, in a reference linked to the body of the vehicle. The thrust generated by the thruster may also include axial thrust. This step is advantageously implemented when the axes of the two helices are coincident with the reference axis.

The thrust angle is different from the cyclic angle of the propellers. The radial thrust generated by the thruster is directed in a radial direction dr forming, around the reference axis, an angle called cyclic phase (with the direction in which the cyclic pitch angles of the helices are maximal.) This cyclic phase φ is symmetrical, independent of the direction of the radial thrust generated by the thruster.

To obtain the desired radial thrust, the cyclic pitch of the helices is adjusted so that their cyclic angles Θ are given by the following formula or the cyclic angle of one of the two helices is given by the following formula, the other helix having a neutral cyclic pitch:

Θ = a- φ

The corrected radial direction of, according to which the cyclic pitch angle of the blades is maximum, forms around the reference axis, an angle Θ with the reference direction dref.

The cyclic phase φ is advantageously determined during a preliminary calibration step. This calibration step comprises a measuring step comprising a first step of measuring forces and torques exerted by the vehicle on a test stand integral with the vehicle for several cyclic steps of one or more propellers and / or a second measurement step of the direction of movement of the vehicle immersed in the liquid in an unobstructed area for several cyclic pitch of one or more propellers by means of gyrometers and accelerometers of the direction of movement of the underwater vehicle as a function of the cyclic pitch of the propellers. The calibration step further comprises a step of calculating the cyclic phase from measurements made during the measuring step.

Advantageously, the distance between the helices, that is to say between the centers of the helices, is between a non-zero threshold value and three times the diameter D of the larger of the two helices. This limited distance between the propellers makes it possible to ensure a convergence of the flows and an interaction between them. The distance between the propellers does not depend on the length of the vehicle. The limited distance between the propellers makes it possible to obtain flows that converge between the propellers regardless of the length of the vehicle. Thus the energy efficiency is high. The thrust generated by the thruster is the sum of the thrusts generated by the two propellers and a force resulting from the interaction between the flows and the body of the vehicle. The interaction between the flows and the body of the vehicle generates, when at least one of the flows is not symmetrical about the x-axis, a pressure field between the two helices that is not homogeneous on the revolution around the x axis. This pressure gradient generates a lateral thrust which is added to the thrusts generated by the thrusters. The short distance between the propellers maximizes this force and the energy efficiency of the process. An advantage brought is an efficiency of the phenomenon of radial thrust (if the propellers are too far away, the fluxes will lose kinetic energy by the point of meeting). The output flow of each helix is disturbed by its environment. The condition of distance between the propellers thus allows an effective control of the location of the meeting point of the two opposite flows (if the propellers are too far apart, the location of the meeting point is too approximate, if the propellers are too close, the two flow will disrupt each other at the blades).

Advantageously, the threshold distance is greater than or equal to 20% of the diameter D of the smaller of the two helices. Below this threshold, the interaction between the two propellers is too disturbed.

The invention also relates to a marine vehicle 2 as described above comprising a propulsion system 63 as shown in FIG. 6. The propulsion system 63 comprises a control or control device 62 configured to be able to implement the process according to the invention as well as the propellant according to the invention. The invention also relates to the propulsion system and the steering device

The control or control device 62 comprises a control member 60 which receives an implementation instruction of the low speed maneuvering control step is configured to calculate a low speed configuration in which the thruster must be placed so that each helix generates a flow directed to the flow generated by the other helix taken from the two helices and reaching the flow generated by the other helix. Advantageously, each helix generates a non-zero flow and directed essentially in the same direction over the entire revolution of the blades of the helix in the liquid around the axis of rotation of the helix, and so that each propeller taken from the two propellers generates a flow

The controller comprises for example an analog computing device such as an operational amplifier mounted in weighted summation, or a programmable logic component or a processor and an associated memory containing a program configured to determine the configuration. The processor and the memory can be grouped together in the same component often called a microcontroller.

The control device 62 further comprises an actuating device or actuator 61 configured to control the thruster so as to put it in said calculated low-speed configuration, when it receives said low-speed configuration in the form of a command which is sent by the control organ.

The actuator may comprise cylinders, for example electric or hydraulic or a motor actuating cables or chains and to move the point on which they apply their force or even in principle rack. The actuator is configured to tilt and / or move the cyclic and collective trays. Advantageously, the implementation instruction of the low speed maneuvering control step comprises a thrust command, the thruster calculating a low speed configuration of the thruster such that the thruster generates a desired thrust, in particular a thrust in the direction of thrust. the thrust instruction.

When the thruster is a thruster of the type with two counter-rotating propellers with variable cyclic and collective pitch, the configuration obtained comprises a collective pitch, a cyclic pitch and possibly a rotational speed of each propeller and the actuator (s) allow to regulate the collective and cyclic steps of the two propellers. The configuration is a configuration of the propellers and the actuator is used to configure the propellers. This is for example a magnetic device or a motorized device for adjusting the cyclic and collective steps. In a nonlimiting manner, this device comprises cyclic and collective trays. In the case of a thruster comprising two thrusters with Gimbal, the configuration includes the orientations of the axes of rotation of the propellers. The actuating device makes it possible to actuate the universal joints so as to modify the orientations of the axes of rotation of the propellers.

The instruction can be generated on board the vehicle (autonomous vehicle) or on the outside of the vehicle (remotely controlled vehicle).

Claims

A method of driving a thruster of a marine vehicle (1) at least partially immersed in a liquid comprising a body (2) and the thruster (3), the thruster comprising two propellers (AV, AR), each propeller comprising blades designed to rotate about an axis of rotation of said propeller, characterized in that the method comprises a step of low-speed maneuvering control, during which the propeller is piloted so that each propeller generates a flow directed towards the flow generated by the other helix and reaching the flow generated by the other helix.

Control method according to the preceding claim, in which each helix (AV, AR) generates a non-zero flow and directed in the same direction, along the axis of rotation of the helix, over most of the revolution of the rotor blades. the helix in the liquid around the axis of rotation of the helix,

Driving method according to claim 1, in which at least one propeller generates a flow whose direction, along the x axis, varies on the revolution of the blades of the propeller in the liquid around the axis of rotation of the propeller. propeller,

Driving method according to any one of the preceding claims, wherein the distance between the helices is between a non-zero threshold distance and three times the diameter of the larger of the two helices.

Driving method according to the preceding claim, wherein the distance between the helices is greater than or equal to 20% of the diameter of the smaller of the two helices.

The driving method as claimed in any one of the preceding claims, wherein the low speed maneuvering control step is implemented only when the flows generated by the two helices meet between the two propellers at a distance from the two propellers.

Control method according to the preceding claim, wherein the low speed operation control step is implemented regardless of the movement of the vehicle provided that the flows generated by the two helices meet between the two propellers at a distance from the two propellers.

A control method according to any one of the preceding claims, wherein the two propellers comprise an upstream propeller and a downstream propeller along a reference axis in a predetermined direction, and in which during the low speed maneuvering control step , so that the thruster (3) exerts a non-zero thrust along the reference axis and in said direction, the thruster (3) is piloted so that the upstream thrust force resulting from the upstream flow generated by the upstream propeller presents an axial component of intensity greater than that of the axial component of the downstream thrust force resulting from the downstream flow generated by the downstream propeller.

Control method according to any one of the preceding claims, in which, during the low speed maneuvering control step, the thruster (3) generates a thrust force having a zero radial component along a radial axis located in a plane perpendicular to a reference axis, the thruster (3) is piloted so that the combined flow resulting from the combination of the flows generated by the two propellers (AV, AR), between the two propellers, is symmetrical with revolution. around the reference axis. 10. Control method according to any one of the preceding claims, wherein, during the low-speed maneuvering control step, for the thruster (3) exerts a thrust having a non-zero radial component along a radial axis. located in a plane perpendicular to a reference axis, the thruster (3) is piloted so that the combined flow resulting from the combination of the flows generated by the two propellers (AV, AR) between the two propellers (AV, AR) is not symmetrical about the reference axis. 1 1. Control method according to the preceding claim, wherein during the low speed maneuvering control step, so that the thruster (3) exerts a thrust having a non-zero radial component, the thruster is piloted so that at least a helix generates a flux that is not symmetrical about the reference axis.

12. A method according to any one of claims 10 to 11, wherein, during the low speed operation control step, so that the vehicle rotates about an axis perpendicular to the reference axis, pilot the thruster so that the thrust force generated by the thruster (3) is applied to a point distant from the center of mass of the vehicle.

13. A method according to any one of claims 10 to 1 1, wherein, during the low speed operation control step, for the vehicle (1) to translate along an axis perpendicular to the reference axis. the thruster (3) is piloted so that the thrust force generated by the thruster (3) is applied to the center of mass of the vehicle.

14. Control method according to any one of the preceding claims, wherein the thruster is a thruster comprising two contrarotative propellers with variable cyclic and collective pitch, a reference axis being an axis connecting centers of the two propellers which are points located on the axes of rotation of the respective propellers.

15. Control method according to the preceding claim, wherein the axes of rotation of the two helices are substantially coincident with the reference axis.

16. Control device for controlling a thruster comprising two propellers, each propeller comprising blades intended to rotate about an axis of rotation of said propeller, the control device being able to implement the method according to any one of claims 1 to 15, characterized in that the control device comprises a control member which, receiving an instruction to implement the low speed operation control step, is configured to calculate a low speed configuration in which must be put the thruster so that each propeller (AV, AR) generates a flow directed to the flow generated by the other propeller and reaching the flow generated by the other propeller, the control device further comprising an actuator configured to control the thruster so as to put it in said low speed configuration. 17. Control device according to the preceding claim, wherein the implementation instruction of the low speed operation control step comprises a thrust command, the thruster calculating a low speed configuration of the thruster such that the thruster generates a thrust in the direction of the thrust instruction.

18. A propulsion system comprising a control device according to any one of claims 16 to 17, comprising a propellant (3) comprising two propellers, each propeller comprising blades for rotating about an axis of rotation of said propeller, characterized in that it comprises a control device capable of controlling said thruster.

19. Propulsion system according to the preceding claim, wherein the distance between the two helices is between a non-zero threshold distance and three times the maximum diameter of the propellers.

20. A marine vehicle intended to be at least partially immersed in a liquid comprising a body (2), and a propulsion system according to any one of claims 18 to 19.