Marine vehicle thruster control method

Abstract

The invention relates to a method for controlling a thruster of a marine vehicle (1) including a body (2) and a thruster (3) mounted on the body (2) of the vehicle (1). The vehicle (1) is at least partially submerged in a liquid, moves, relative to the liquid, along a movement axis (x) in a movement direction, and rotates about at least one axis of rotation perpendicular to the movement axis (x) at a rotational speed. The thruster (3) includes an upstream propeller and a downstream propeller along the movement axis in the movement direction. The method includes a stabilization step, during which the thruster is controlled such that the main axis of the upstream flow generated by the upstream propeller at a given time t is an estimated main axis on which a position (P) of a center of the downstream propeller, substantially located on the axis of rotation of the downstream propeller, is estimated to be located at a later time t+dt, at which the flow generated by the upstream propeller at the given time t reaches the downstream propeller. The estimated main axis (xe) depends on the rotational speed of the vehicle.

Description

[0001] The present invention relates to the propulsion and maneuvering of marine vehicles comprising a propeller comprising two propellers. More specifically, the invention relates to a marine vehicle comprising a steering device, to the steering device, to a propulsion system comprising the steering device and to a method of steering the marine vehicle.

[0002] US 9,022,738 B1, US 8,919,274 B1 and EP 0,215,629 A2 describe marine vehicles equipped with twin-propeller thrusters.

[0003] The invention applies particularly to underwater vehicles comprising a twin-propeller vector propulsion unit. A propulsion unit is said to be vector when it can be driven so as to produce a thrust or propulsion force that can be steered over 4π steradian. The so-called vector propulsion of an underwater vehicle is opposed to conventional propulsion in which the orientation of the control surfaces causes a modification of 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 steer 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 the lift of the control surfaces allowing a change in attitude of the vehicle, i.e. to allow the underwater vehicle to be maneuvered.If this flow is too weak, then the efficiency of the control surfaces decreases inversely with the square of the flow velocity until it becomes zero for a zero flow velocity. In other words, it is not possible by conventional propulsion to steer the vehicle in a desired direction without significant movement 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 movement and which therefore consumes energy, all the more so as the control surfaces are used. The method of piloting a vector propulsion presented in this patent allows the vehicle to dispense with conventional rudders, and therefore to significantly reduce the hydrodynamic drag of the vehicle. Vector propulsion of the two-propeller type has many theoretical advantages, including increased mobility, simplification of the architecture (egby removing the control surfaces), an increase in the vehicle's endurance (by reducing hydrodynamic drag). This absence of control surfaces other than the propeller blades facilitates the creation of a so-called "flush" hydrodynamic vehicle, i.e. one with no protruding appendages, which allows it, for example, to fit easily into a tube and avoids damaging the control surfaces when docking.

[0004] However, piloting this type of propeller encounters numerous difficulties, particularly when turning.

[0005] An aim of the invention is to propose a method for piloting a marine vehicle comprising a two-propeller vector propulsion system making it possible to control the trajectory of the vehicle, particularly when turning, a piloting device, a marine vehicle comprising the piloting device and a propulsion system comprising the piloting device.

[0006] For this purpose the invention is set out in the attached set of claims.

[0007] Other characteristics 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: there figure 1 schematically represents in top view an underwater vehicle moving along an x ​​axis, the figure 2 schematically represents in top view an underwater vehicle moving backward along an x ​​axis, the figure 3 schematically represents in top view an underwater vehicle at a time t, moving forward along the x axis and comprising a thruster configured to exert a radial thrust on the vehicle so as to make it turn to the left, the upstream propeller generating a flow directed towards the position of the center of the downstream propeller at time t, the figure 4 schematically represents more precisely the flows and propellers of the figure 3 at time t as well as the estimated position of the downstream propeller at time t+dt, the figure 5 schematically represents more precisely the propellers of the figure 3 as well as the estimated position of the downstream propeller at a time t+dt and the flows generated by the two propellers at time t, the upstream propeller generating, at time t, a flow directed towards an estimated position of the center of the downstream propeller at a time t+dt, the figure 6 schematically represents at an instant t+dt, a vehicle whose flows generated by the propellers at the instant t are those of the figure 5 . The flow lines generated by the upstream propeller at time t are represented on the figure 6 , in a frame linked to the vehicle, until this flow reaches the downstream propeller. The lines of the flow generated by the downstream propeller at time t are also represented. the figure 7 illustrates an example of calculating the estimated principal axis, the figure 8 schematically represents, in a radial plane, the direction of the radial thrust exerted by the propeller as a function of the cyclic angle, the figure 9 schematically represents a propulsion system of a vehicle according to the invention.

[0008] From one figure to another, the same elements are identified by the same references.

[0009] The invention proposes a method for piloting, i.e. controlling, a thruster of a marine vehicle. The method applies particularly to underwater vehicles intended to move completely submerged in a liquid, in particular water. The invention also applies to surface vehicles intended to move on the surface of a liquid while being partially submerged in the liquid. The marine vehicles may be autonomous vehicles with (human) pilots on board, or unmanned drones on board such as remotely operated vehicles or ROVs or autonomous marine vehicles such as autonomous underwater vehicles or AUVs. Consequently, the piloting method according to the invention may be implemented by an operator (pilot) on board or remotely or by an autonomous piloting device.

[0010] This method applies to vehicles comprising a vector propulsion system comprising two counter-rotating propellers known as variable cyclic and collective pitch propellers. A variable cyclic and collective pitch propeller is a propeller whose blade pitch angle is collectively controllable, allowing the thrust to be adjusted along the propeller's axis of rotation. The collective pitch is defined by a collective blade pitch angle. In other words, all the blades have the same collective pitch angle throughout the blade revolution around the propeller's axis of rotation. As a reminder, the blade pitch angle of a propeller is the angle formed between the blade chord and the propeller's plane of rotation according to the chosen reference. The propeller's plane of rotation is a plane of the propeller perpendicular to the propeller's axis of rotation. The pitch angle is also cyclically adjustable, allowing the thrust to be directed perpendicular to the propeller's axis of rotation.The cyclic pitch angle of the blades varies cyclically, i.e., during a revolution around the propeller's axis of rotation, depending on the angular positions of the blades around the propeller's axis of rotation. The cyclic pitch is defined by a differential cyclic pitch angle during a revolution of the blades as well as by a cyclic angle. The differential cyclic pitch angle is defined as the difference between the maximum cyclic pitch angle and the minimum cyclic pitch angle of a blade during a revolution. The collective pitch is the average cyclic pitch angle. The cyclic angle is the angle formed, around the propeller's axis of rotation, between the direction in which the blade pitch angle is maximum and a reference direction related to the body of the vehicle. The neutral collective pitch is the blade pitch angle at which the propeller rotating around its axis of rotation exerts zero thrust, along its axis of rotation.The neutral cyclic pitch is that for which the blades exert a thrust whose component perpendicular to the axis of rotation of the propeller is zero. Coordinated control of the two propellers makes it possible to control the thrust orientation on 4π steradian.

[0011] In particular, vector thrusters are known that are formed from two coaxial counter-rotating propellers, i.e., whose axes of rotation are substantially coincident. For example, coaxial propellers are known 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, along which the vehicle is mainly intended to move. By axis linked to the body of the vehicle, we mean that the orientation and 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 piloted so as to have good energy efficiency at high speed. Thus, the two propellers generate 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.

[0012] The method is also applicable to propellers of the type comprising two counter-rotating or non-counter-rotating propellers with variable cyclic and collective pitches whose axes of rotation of the propellers are distinct and substantially parallel and to 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 propellers form any respective angles other than 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 when moving in a straight line along this axis.The rotational speed of the propeller blades around their axis of rotation (called the propeller rotational speed) can be adjusted independently or collectively for both propellers. The propellers may each have a fixed orientation relative to the vehicle body. In other words, their respective axes of rotation are fixed relative to the vehicle's axis.

[0013] The method according to the invention also applies to thrusters comprising two steerable thrusters with a ball-and-finger connection, also called "gimbal propellers" in English terminology. These thrusters each have a propeller comprising blades whose pitch is not adjustable. Alternatively, the cyclic pitch and / or the collective pitch may be variable. Each of the propellers is connected by a ball-and-finger connection to the body of the marine vehicle, produced for example by means of a cardan assembly 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 relative to the body of the vehicle is modifiable. The speed of rotation of each of the propellers around its axis of rotation is also adjustable, preferably independently of one another.A single gimbal propeller has a more limited efficiency than propellers with counter-rotating propellers with variable cyclic and collective pitch and has an action limited to a given angular sector of opening less than 360°.

[0014] Propellers can have the same or different diameters, the same or different number of blades.

[0015] THE figures 1 à 3 schematically represent in top view an underwater vehicle 1 having a body 2 and a vector thruster 3 mounted on the body of the underwater vehicle 1. This vehicle moves along an axis of movement x in the direction of the x axis. The thruster 3 is of the vector thruster type comprising two counter-rotating front and rear propellers with variable cyclic and collective pitches. The propellers are coaxial. In other words, they are intended to rotate around substantially coincident axes of rotation. The axis of the propellers x is the axis of movement of the vehicle. In the non-limiting example of the figures, the x axis is the preferred axis of movement of the vehicle which is here the roll axis of the vehicle. The 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. The propellers comprise a front front propeller and a rear rear propeller.Front and rear as well as left and right are defined relative to the x-axis of movement of vehicle 1 in the direction of the x-axis. The front propeller AV is the upstream propeller when the vehicle is moving forward along the x-axis, the rear propeller is then the downstream propeller. The front propeller AV is the downstream propeller when the vehicle is moving backward along the x-axis, the rear propeller is then the upstream propeller.

[0016] The blades of each front, rear propeller are mounted on the body 2 of the vehicle 1 to rotate around the axis of rotation of the corresponding front, rear propeller. The blades of a propeller are integral in rotation around the axis of rotation of the propeller. For example, each blade is connected by an axis to a hub mounted to rotate on the body 2 of the underwater vehicle 1 around the axis of rotation of the propeller generally defined by a shaft.

[0017] The water flow lines between the two propellers are represented by arrows. As a reminder, a flow generated by a propeller represents the speed of the water through the propeller. The modulus or intensity of the flow, expressed in kg.ms -1< is a flow rate of momentum of the water through the surface of the propeller. The thrust force generated by the propeller is represented by a double arrow in each figure. In these figures, for clarity, the thrust is represented in the central part of the vehicle but it is advantageously applied to a point of the body of the vehicle located between the two propellers and preferably on the roll axis of the vehicle.

[0018] 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 vehicle body along the reference axis x. Alternatively, these two propellers are installed at the front of the vehicle body or one at the front and one at the rear of the vehicle body. In order to be able to turn the vehicle, that is to say to move the vehicle by generating radial thrust, the planes of rotation of the propellers are not arranged in planes symmetrical to each other with respect to a plane containing the center of mass of the body 2 of the underwater vehicle 1.

[0019] The method according to the invention comprises a so-called navigation step. During this step, the thruster is piloted so that each propeller generates a flow. During this step, as seen in the figures 1 And 3, thruster 3 is driven so that the front and rear propellers generate backward flows along the x axis. The flow generated by thruster 3 is the combination of the flows generated by the two front and rear propellers. On the figures 1 And 3 , each of these flows is oriented backwards along the vehicle's axis of movement x. Therefore, the thrust force F generated by reaction by the thruster 3 includes a positive axial component (along the x-axis). In other words, the vehicle moves along the x-axis in the direction defined by the x-axis. In this case, the front propeller AV is the upstream propeller and the rear propeller AR is the downstream propeller.

[0020] On the figure 2 , the thruster is driven so that the propellers generate forward flows along the x axis. The flow generated by the thruster is the combination of the flows generated by the two propellers. This flow is oriented forward. The thrust force Fgenerated by reaction from the thruster is directed rearward and the vehicle moves backward in the direction of the x axis. In this case, the front propeller AV is the downstream propeller and the rear propeller AR is the upstream propeller.

[0021] Therefore, during the navigation step, for the vehicle to move along the x-axis in a predetermined direction, the thruster is controlled so that the propellers continuously generate flows directed downstream in said direction. Downstream is located towards the rear when the vehicle advances in a predetermined direction in a predetermined direction and upstream is located in front of downstream when the vehicle advances in this direction in this direction.

[0022] Alternatively, the vehicle could move along another axis of movement linked to the vehicle which would not be the axis of the propellers. In this case, the thruster would be controlled so that the flows generated by the propellers along the x axis are oriented in the same direction along the axis of movement of the vehicle, this direction would be opposite to the direction of movement of the vehicle along this axis.

[0023] During the navigation stage, each propeller advantageously generates a non-zero flow directed in the same direction along the axis of rotation of the propeller, over the entire revolution of the propeller blades in the liquid around the axis of rotation of the propeller. In other words, the axial component of the flow has the same sign over the entire revolution of the propeller blades in the liquid around the axis of rotation of the propeller. This means that the flow lines generated by the propeller in each radial angular sector, fixed relative to the body of the vehicle and swept by the propeller, are oriented essentially in the same direction along the axis of rotation of the propeller. Each flow has a non-zero component of the same sign along the axis of rotation of the propeller, over most of the revolution of the propeller blades in the liquid around the axis of rotation of the propeller x and preferably over the entire revolution of the propeller blades around the axis of rotation of the propeller.In other words, the thruster is controlled, for example by limiting the differential cyclic angle as a function of the applied collective pitch, so that each propeller generates thrust in the same direction over most of the revolution of the propeller blades around the axis of rotation, and preferably over the entire revolution of the propeller blades around the axis of rotation of the propeller. The fact that each flow has essentially the same direction over the entire revolution of the propeller blades in the liquid around the axis of rotation makes it possible to avoid the creation of vortices between the propellers which would have the effect of destabilizing the vehicle. Alternatively, the direction of the flow along the axis of rotation of at least one propeller does not have the same sign over the entire revolution of the propeller blades in the liquid around the axis of rotation of the propeller.

[0024] On the figures 1 et 2 , the flows generated by the two propellers AV, AR are rotationally symmetrical around the axis of movement x. Consequently, the flow generated by thruster 3, which is the combination of the flows generated by the two propellers, is rotationally symmetrical around the axis x. Consequently, the thruster generates axial thrust but no radial thrust. Axial thrust is the component of the thrust generated by the thruster along the axis of movement x. Radial thrust is the component of the thrust generated by the thruster along an axis perpendicular to the axis of movement x. The vehicle does not rotate around an axis perpendicular to the axis of rotation of the propeller.

[0025] The thruster is configured (in other words, the properties of each propeller and the arrangement between the propellers are chosen) so that the flow generated by each propeller can reach the other propeller or at least the flow generated by the upstream propeller can reach the downstream propeller. This configuration is valid over a predetermined speed range being advantageously the speed range over which the vehicle is intended to navigate relative to the liquid.

[0026] On the figure 3 , representing a vehicle at a time t, the thruster 3 is controlled so as to rotate the vehicle around an axis perpendicular to the axis of movement x. In this figure, the vehicle moves forward along the x axis and rotates around the x axis. For the vehicle to move forward along the x axis, the orientation of the flows generated by the two propellers along the axis of movement x are the same as in the figure 1 . To rotate the vehicle around an axis perpendicular to the axis of movement x during the navigation stage, the thruster 3 is controlled so that the downstream propeller (here the rear propeller AR) generates a flow which is not rotationally symmetrical around the axis of movement x. In other words, the thruster is controlled so that the downstream propeller (here the rear propeller) generates a downstream flow whose main axis T , shown in thin lines relative to the arrows representing the flow lines, forms a non-zero angle with the x axis. On the figure 3 , the flow generated by the upstream propeller (here the front propeller) at a time t is always rotationally symmetrical around the x axis. The total flow generated by thruster 3 is no longer rotationally symmetrical around the x axis. The thrust F generated by the thruster has a non-zero radial component in the plane of the sheet of the figure 3 , the vehicle will then be animated, under the effect of the thrust, by a gyration movement around an axis perpendicular to the plane of the sheet in the direction of the curved arrow representing the rotation of the vehicle. On the example of the figure 3 , if we had to represent the junction point between the axis of rotation of the vehicle perpendicular to the sheet and the plane of the sheet, it would be represented at the top right of the figure 3 outside the vehicle. If the vehicle turns in the direction of the curved arrow representing the rotation of the vehicle, then if the flow generated by the upstream propeller (here the front propeller AV) at time t is directed towards the position of the center of the downstream propeller (here the rear propeller AR) at time t, that is to say if the main axis of the upstream flow generated by the upstream propeller (here the front propeller AV) includes the position of the center of the downstream propeller (here the rear propeller AR) at time t, this flow arrives at the downstream propeller off-center relative to the axis of rotation of the downstream propeller (here the rear propeller AR). By main axis of the flow generated by a propeller, we mean the axis passing through the center of the propeller and whose direction is the direction of the flow generated by the propeller. The direction of the main axis is defined relative to the body of the vehicle.The center of a propeller is understood to mean a predetermined point of the propeller located on or substantially on the axis of rotation of the propeller and within the volume that the propeller can sweep during one revolution of the propeller blades around the axis of rotation of the propeller. This volume includes the axis of rotation of the propeller. This point is called the center of the propeller. It is, for example, a center of mass of the propeller. The center of mass of a propeller can advantageously be defined as the center of mass of the blades.

[0027] On the figure 4 , the positions of the propellers and the flows of the figure 3 at time t. On the figure 4 , we have represented in continuous lines, the positions of the upstream propeller AM which is the front propeller AV of the figure 3 and the downstream propeller AVA, which is the rear propeller AR on the figure 3 , at a time t at which the propellers generate the flows represented on the figures 3 et 4 . Flow lines generated by the two propellers are represented by solid arrows on the figure 4 . The flow generated by the downstream propeller AVA causes vehicle 1 to rotate in the direction of the curved arrow representing rotation around an axis perpendicular to the plane of the sheet. The flow generated by the upstream propeller AM at time t is directed towards the position P occupied by the center of the downstream propeller at time t. The position of the downstream propeller AVA when the flow from the upstream propeller reaches it is shown in dotted lines. The two positions of the downstream propeller are connected by dotted arrows. It can be seen that the flow generated by the upstream propeller AM is not rotationally symmetrical around the position of the axis of rotation of the downstream propeller x' at time t+dt. This has the effect of disturbing the angle of incidence of the blades of the downstream propeller for a given pitch angle. The angle of incidence defines the orientation of the propellers relative to the liquid.When the blade pitch angle is disturbed, the propeller produces a thrust different from the desired thrust, which can be even opposite to the desired thrust. The vehicle's trajectory is then deflected and the vehicle may begin to oscillate.

[0028] As shown in the figure 5 , the navigation step comprises a step of stabilizing the vehicle according to the invention. During this step, when the vehicle 1 moves along a predetermined axis of movement x, for example linked to the body 2 of the vehicle 1, in a predetermined direction (here the direction of the axis x) and rotates around at least one axis perpendicular to the axis x with a rotation speed (which may be zero), the thruster 3 is controlled so that the main axis of the upstream flow generated by the propeller called upstream AM at a given instant t is an estimated main axis xe (or estimated main axis xe) on which is assumed, that is to say estimated, to be located a position P' of the center of the downstream propeller AVA at a later instant t+dt at which the flow generated by the upstream propeller AM reaches the downstream propeller AVA.

[0029] In other words, the upstream propeller is controlled so that the upstream flow generated by the upstream propeller at time t is substantially centered on the center of the downstream propeller at the time at which the flow generated by the upstream propeller reaches the downstream propeller. The main axis of the flow generated by the upstream propeller AM, relative to the body of the vehicle, is defined so that the upstream flow generated by the upstream propeller AM continues to reach the downstream propeller substantially centered on the center of the downstream propeller AVA even when the vehicle is turning. In other words, the main axis of the upstream flow generated by the upstream propeller AM at a given time t is defined to pass substantially through the center of the downstream propeller at time t+dt. Thus, the method according to the invention may comprise a step of determining the estimated main axis. In other words, this step is a step of estimating an axis on which the position P' of the center of the downstream propeller AVA is positioned at time t+dt.The method then comprises a step of controlling the upstream propeller so that the main axis of the upstream flow generated by the propeller called upstream AM at a given time t is the estimated axis.

[0030] The estimated principal axis may depend on one or more of the quantities listed below. In other words, the estimated principal axis may be determined from one or more of these quantities. In other words, the axis along which the center of the downstream propeller is located at time t+dt may be estimated from one or more of these quantities. This is done during a step of determining the estimated axis.

[0031] The estimated main axis and more particularly the direction of the estimated axis relative to the upstream propeller advantageously depends on the rotational speed of the vehicle. The estimated main axis passes through the center of the upstream propeller. In other words, the axis along which the position of the downstream propeller is estimated to be at time t+dt passes through the upstream propeller. The rotational speed of the vehicle is a rotational speed relative to a fixed reference frame, for example the liquid (outside the flow generated by the thruster) or the terrestrial reference frame.

[0032] Advantageously, the estimated main axis depends on a vehicle movement speed relative to a fixed reference frame along the movement axis. The reference frame fixes, for example, the liquid in the vicinity of the vehicle outside the flow generated by the thruster or the terrestrial reference frame.

[0033] Advantageously, the estimated main axis depends on the flow generated by the upstream propeller.

[0034] Advantageously, the estimated main axis is determined from the rotational speed of the vehicle.

[0035] Advantageously, the estimated main axis is determined from a speed of the liquid carried by the flow generated by the upstream propeller, relative to the body of the vehicle. The speed of the liquid carried by the flow relative to the body 2 depends on the flow generated by the upstream propeller and the speed of movement of the vehicle relative to the liquid.

[0036] The estimated principal axis is advantageously determined from the distance between the centers of the two helices.

[0037] The estimated main axis xe is determined from the vehicle rotational speed and the flow generated by the upstream propeller, relative to the vehicle body.

[0038] In other words, the direction of the flow generated by the upstream propeller AM, relative to the body of the vehicle, is advantageously obtained from the rotational speed of the vehicle 1 possibly composed with its linear forward speed (phenomenon linked to a rotating reference frame integral with the vehicle called the Coriolis “force”) and possibly the value of the flow generated by the upstream propeller so that the upstream flow generated by the upstream propeller AM continues to reach the downstream propeller in a manner substantially centered on the center of the downstream propeller AVA even when the vehicle is turning.

[0039] There figure 5 differs from the figure 4 in that the upstream flow generated by the upstream propeller AM is directed towards an estimated position P' of the center at a time t+dt where the flow generated by the upstream propeller AM has propagated to the downstream propeller AVA. In other words, the main axis of the flow generated by the upstream propeller is an estimated main axis comprising the estimated position P'. In this way, the blades of the downstream propeller AVA, receiving the flow generated by the upstream propeller AM, sweep a homogeneous flow over their entire revolution around the axis of rotation of the downstream propeller, which makes it possible to control the trajectory of the vehicle, in particular when turning, with optimal efficiency at medium and high speed and above all without the appearance of thrust oscillations linked to the modulation of the angle of attack of the blades of the downstream propeller by the vorticity of the flow of the upstream propeller not centered on the center of the downstream propeller. Furthermore, this control method makes it possible to maneuver the device solely from the thruster.The use of water jets or control surfaces in addition to the propeller is not required, which is advantageous in terms of energy (low hydrodynamic drag), in terms of mass, in terms of simplicity, in terms of vehicle maneuverability regardless of the vehicle speed, even in reverse, and in terms of maneuver efficiency, even at high speed.

[0040] During the vehicle stabilization stage, the propellers are driven as previously described with reference to figures 1 à 3 to obtain a desired translational movement along the axis of movement x and a desired rotational movement along an axis perpendicular to the axis of rotation. In other words, as the vehicle moves along the axis of movement, the stabilization step is implemented while the thruster is driven so that the upstream and downstream propellers generate flows oriented downstream along the axis of movement of the vehicle x. The combination of the flows generated by the two propellers makes it possible to obtain an axial thrust force towards the upstream in all radial directions (defined with respect to the x axis) and this regardless of the axial speed of the vehicle as long as a flow allowing the upstream and downstream to be distinguished exists.

[0041] The thruster can be controlled so that the flow generated by the downstream propeller is not rotationally symmetrical around the vehicle's axis of movement x so as to generate the axial thrust allowing the vehicle to rotate around a radial axis.

[0042] There figure 6 differs from the figure 3 by the direction of the flow generated by the upstream propeller (here front propeller AV) at time t relative to the body of the vehicle. This flow is directed along the estimated principal axis xe described previously. In other words, the principal axis of this flow is the estimated principal axis. The lines of the upstream flow generated by the upstream propeller (here the front propeller AV) at time t and propagating until time t+dt are represented on the figure 6 . We note that by directing the upstream flow along the estimated main axis xe, that is to say by not directing the upstream flow generated by the upstream propeller (here the front propeller AV) at time t towards the position occupied by the center of the downstream propeller at time t, this flow arrives homogeneously over the entire revolution of the blades of the downstream propeller around the axis of rotation of the downstream propeller at time t+dt.

[0043] The estimated main axis xe, and in particular the direction of the estimated main axis relative to the upstream propeller, is possibly defined from the rotation speed of the vehicle around at least one perpendicular axis and possibly from a liquid speed in the upstream flow generated by the upstream propeller relative to the body 2 of the vehicle 3.

[0044] The rotational speed of the vehicle is advantageously measured by means of at least one sensor. The rotational speed can be obtained from at least one gyrometer on board the vehicle, for example in an inertial unit.

[0045] The speed of the liquid carried by the upstream flow relative to the body 2 of the vehicle 1 may be a three-dimensional speed or, more simply, a speed of the liquid relative to the vehicle along the reference axis. This speed may be measured using at least one sensor. For example, this speed is measured using a sensor, for example a flow sensor, making it possible to measure the modulus of this speed and possibly an orientation of the speed of the liquid. Alternatively, the speed of the liquid is an estimate of the speed of the liquid carried by the flow generated by the upstream propeller relative to the vehicle. The estimated speed is, for example, determined from the rotation speed and cyclic and collective pitch angles of the upstream propeller and possibly of the downstream propeller.It can also be determined from the electrical or mechanical measurement of the engine torque applied by the upstream propeller and / or by the downstream propeller and / or by the thruster on the vehicle. Alternatively, it can be determined from a measurement of the vehicle's speed relative to the liquid along the axis of movement. Determining the speed by estimation is less precise but simpler to carry out and less expensive than direct measurement.

[0046] We will, with reference to the figure 7 , describe an example of calculating the direction of the estimated principal axis xe. This estimated principal axis passes through a center of the upstream propeller. On the figure 7 , the positions P and Q of the centers of the respective downstream and upstream propellers at time t are represented, as well as the position O of the point of intersection between the axis of rotation of the vehicle (perpendicular to the sheet), around which the vehicle rotates at rotation speed ω, and the plane of the sheet. In this figure, the points P, Q and O are aligned. An estimated position P' of the position of the center of the downstream propeller at time t+dt at which the flow generated by the upstream propeller at time t reaches the downstream propeller is also represented. The velocity of the liquid carried by the flow generated by the upstream propeller, relative to the vehicle, is noted Vf.

[0047] With a good approximation, the estimated angle α' formed between the estimated principal axis and the x axis connecting the centers of the two helices at time t+dt is given by the following formula: α ′ = ω ∗ d Vf

[0048] Where d is the distance between the centers of the two helices.

[0049] During the stabilization step, the thruster is therefore controlled so that the flow generated by the upstream propeller is directed in the estimated direction forming an angle substantially equal to the estimated angle α' with the x axis instead of directing this flow along the x axis. In other words, the thruster is controlled so as to correct, at time t, the direction of the main axis of the flow generated by the upstream propeller relative to the direction connecting the centers of the two propellers so that the main axis is directed in the estimated direction.

[0050] When the rotational speed of the vehicle around the axes perpendicular to the propeller axis is zero, the thruster is controlled so that the flow generated by the upstream propeller at time t is directed towards the position of the center of the downstream propeller at time t.

[0051] Advantageously, the estimated main axis is determined from a distance separating the downstream propeller from the axis of rotation of the vehicle around which the vehicle rotates. The distance separating the downstream propeller from the axis of rotation is for example the distance between the center of the downstream propeller and the axis of rotation of the vehicle along an axis perpendicular to the axis of rotation of the vehicle.

[0052] In order to obtain an estimated main axis closer to the actual position of the center of the downstream propeller than the estimated main axis directed in the direction calculated from the data listed above, the estimated main axis (in particular the direction of this axis) also depends on or is determined from an acceleration of the vehicle relative to the water. This improves control of the vehicle's trajectory. This acceleration can be obtained from one or more accelerometers on board the vehicle. The estimated main axis can be determined from the linear acceleration of the vehicle (along the x axis linked to the vehicle) and / or from the radial acceleration (perpendicular to the axis) of the vehicle. These measurements modify the value of the speed Vf and the rotation speed ω respectively.

[0053] In one embodiment of the invention, the stabilization step is implemented when the modulus of the vehicle speed in the axial direction is greater than a predetermined non-zero threshold. Another control method can then be used to control the vehicle when the modulus of the vehicle speed in the axial direction is less than the threshold in order to allow better maneuverability of the vehicle at low speed.

[0054] Advantageously, the control method comprises the following pair of steps: a determination step comprising a step of determining the current rotational speed of the vehicle and possibly a step of determining the current speed of the liquid carried by the upstream flow generated by the upstream propeller, relative to the body of the vehicle, the stabilization step from the determined value(s).

[0055] The stabilization step is further advantageously carried out from the distance separating the centers of the two helices. In other words, the determination step advantageously uses this distance.

[0056] More precisely, the estimated axis is determined from the determined values ​​and possibly from the distance separating the centers of the two helices.

[0057] This pair of steps is advantageously implemented at regular time intervals.

[0058] The time interval is for example between 1s and 5s. It can depend on the linear speed of the vehicle. It can be determined from a desired stability for the vehicle. Alternatively, the stabilization step comprises the pair of steps implemented at least once.

[0059] This embodiment makes it possible to correct the direction of the flow generated by the upstream propeller regularly at predetermined time intervals so as to prevent the vehicle from deviating from the trajectory that one wishes to impose on it. Only rapid maneuvers carried out over a duration shorter than the chosen time interval will not be able to benefit from this correction.

[0060] Advantageously, the stabilization step and / or the pair of steps is implemented when the linear speed of the vehicle along the axis of movement is greater than the predetermined threshold.

[0061] Advantageously, the stabilization step or the pair of steps is not implemented when the rotational speed of the vehicle exceeds a predetermined rotational speed threshold. This threshold is at least equal to the rotational speed threshold at which the flow from the upstream propeller cannot reach the downstream propeller, i.e. the processing time of the flow generated between the upstream propeller and the downstream propeller is greater than the displacement time of the downstream propeller. In other words, the stabilization step is implemented as long as the rotational speed is less than or equal to the threshold.

[0062] Advantageously, as soon as the rotational speed of the vehicle returns to a value lower than or equal to this threshold, the stabilization step is implemented or the pair of steps is re-implemented at predetermined time intervals.

[0063] The step of determining the rotational speed of the vehicle comprises a step of measuring the rotational speed of the vehicle. The step of determining the speed of the liquid carried by the upstream flow generated by the upstream propeller, relative to the body of the vehicle, comprises for example a step of measuring the speed of the liquid in the upstream flow relative to the vehicle or a step of measuring at least one quantity and / or a step of determining this speed from the quantity (or quantities) and / or from the value of at least one current parameter. For example, the speed of the liquid is determined from the cyclic and collective pitches of the blades of the upstream propeller and the current rotational speed of the upstream propeller and possibly the cyclic and collective pitches of the blades of the downstream propeller and the current rotational speed of the downstream propeller. These data are parameters.The determination step is carried out using a measuring device comprising the required sensor(s) and / or using the control unit.

[0064] The stabilization step includes a step of determining the estimated main axis of the flow generated by the upstream propeller from the value(s) determined during the determination step. This step is carried out from the control unit.

[0065] The stabilization step at time t is advantageously carried out from the main axis of the flow generated by the upstream propeller during the implementation of the previous configuration step.

[0066] The stabilization step further comprises a step of determining the configuration of the thruster so that the upstream propeller generates an upstream flow whose main axis is the estimated main axis and a step of adjusting the thruster according to this configuration. This adjustment step is carried out by means of an actuating device or actuator.

[0067] The thruster control step is advantageously a propeller or upstream propeller control step.

[0068] In the case where the thruster is of the type with two counter-rotating propellers with variable cyclic and collective pitches, the vehicle comprises a control device comprising an actuating device comprising at least one actuator for controlling the collective pitch and the cyclic pitch of each of the propellers. This is for example a magnetic device or a motorized device for adjusting the cyclic and collective pitches. In a non-limiting manner, this device comprises cyclic and collective plates. The configuration obtained comprises a collective pitch, a cyclic pitch and possibly a rotation speed of the upstream propeller or the variation of one or more of these parameters to be applied to the propeller between time t and time t+dt.

[0069] For a vehicle moving in translation along a displacement axis which is the axis of the propellers of two coaxial propellers and rotating around a radial axis perpendicular to the axis of the propellers, it is sufficient to modify the main axis of the flow generated by the upstream propeller relative to the axis of the propellers so that the flow always reaches the downstream propeller. To do this, it is sufficient to adjust the cyclic pitch of the upstream propeller.

[0070] In the case of a thruster comprising two gimballed thrusters, the configuration includes the orientation of the axis of the upstream propeller. In other words, the orientation of the upstream propeller is adjusted to obtain the desired configuration.

[0071] We will now describe, with reference to the figure 8 , a particular method for adjusting the thruster, and more precisely the configuration of the downstream propeller, to obtain radial thrust in a desired radial direction dr forming, in a reference frame linked to the body of the vehicle, around the axis of rotation of the downstream propeller, a predetermined thrust angle α with a reference direction dref. The thrust generated by the thruster may also include non-zero axial thrust.

[0072] The thrust angle α is different from the cyclic angle of the downstream propeller. The radial thrust generated by the downstream propeller is directed in a radial direction dr forming, around the reference axis, an angle called cyclic phase φ with the direction dc according to which the cyclic pitch angle of the downstream propeller. This cyclic phase φ is by symmetry, independent of the direction of the radial thrust generated by the thruster.

[0073] In order for the downstream propeller to generate a desired radial thrust acting in the direction dr perpendicular to the axis of rotation of the downstream propeller, the cyclic pitch of the downstream propeller is adjusted using the following formula: θ = α − φ

[0074] The corrected radial direction dc in which the cyclic pitch angle of the blades is maximum forms, around the axis of rotation of the downstream propeller, an angle θ with the reference direction dref. The cyclic pitch of the downstream propeller is non-neutral.

[0075] The cyclical phase φis advantageously determined during a prior calibration step. This calibration step comprises a measurement step comprising a first step of measuring forces and torques exerted by the vehicle on a test bench secured to the vehicle for several cyclic pitches of one or more propellers and / or a second step of measuring the direction of movement of the vehicle immersed in the liquid in a clear area for several cyclic pitches 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 measurement step.

[0076] The invention also relates to a marine vehicle 2 as described previously comprising a propulsion system 63. The propulsion system 63 comprises a control device 62 capable of controlling the thruster 3 and configured to be able to implement the method according to the invention as well as the thruster 3. The invention also relates to the propulsion system and to the control device.

[0077] The control device 62 comprises a control member 60 which, receiving an instruction for implementing the stabilization step, is configured to calculate a stabilization configuration in which the thruster must be placed so that the main axis of the upstream flow is directed along the estimated main axis, possibly from at least one quantity cited previously such as for example required speeds, and an actuating device or actuator 61 configured to control the thruster so as to configure the thruster according to said configuration. The control member 60 can be implemented by means of software and / or hardware technology. The control member 60 comprises for example 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 within a single component often called a microcontroller.

[0078] The actuator may comprise cylinders, for example electric or hydraulic, or a motor actuating cables or chains and making it possible to move the point on which they apply their force, or even in rack principle. The actuator is configured to tilt and / or move the swashplates and collective plates.

[0079] Advantageously, the piloting or control device 62 is configured, when it receives a navigation instruction comprising a thrust or a thrust direction to be applied by the thruster to the marine vehicle to implement the navigation step according to the invention, so that the downstream propeller generates the thrust in the desired direction and so that the two propellers generate flows in the downstream direction. The piloting step comprises a step of adjusting the two propellers.

[0080] Instructions can be generated on board the vehicle (autonomous vehicle) or outside the vehicle (remotely controlled vehicle).

Claims

1. A method for steering a thruster of a marine vehicle (1) comprising a body (2) and a vector thruster (3) mounted on the body (2) of the vehicle (1), the vehicle (1) being at least partially immersed in a liquid and moving with respect to the liquid along an axis of movement (x) in a direction of movement and rotating about at least one axis of rotation perpendicular to the axis of movement (x) with a rotational speed, the vector thruster (3) comprising an upstream propeller (AM) and a downstream propeller (AVA) along the axis of movement in the direction of movement, characterised in that the method comprises a stabilisation step, during which the thruster is steered in bends such that the main axis of the upstream flow generated by the upstream propeller (AM) at a given instant t is an estimated main axis (xe) on which a position (P) of a centre of the downstream propeller (AVA), situated substantially on the axis of rotation of the downstream propeller (AVA), is estimated to be situated at a later instant t+dt at which the flow generated by the upstream propeller (AM) at the given instant t reaches the downstream propeller (AVA).

2. The steering method according to claim 1, wherein the estimated main axis (xe) depends on the rotational speed of the vehicle.

3. The steering method according to any one of the preceding claims, wherein the estimated axis depends on a speed of movement of the vehicle with respect to the liquid along the axis of movement.

4. The steering method according to any one of the preceding claims, wherein the estimated main axis is determined from the rotational speed of the vehicle and from a speed of the liquid carried by the flow generated by the upstream propeller, relative to the body of the vehicle.

5. The steering method according to any one of the preceding claims, wherein the estimated main axis (xe) is determined from the distance separating the centres of the two propellers.

6. The steering method according to any one of the preceding claims, wherein the estimated main axis (xe) is determined from the acceleration of the vehicle (1) along the axis of movement (x).

7. The steering method according to any one of the preceding claims, comprising the following pair of steps implemented at predetermined intervals of time: - a determination step, comprising a step of determining the rotational speed of the vehicle (1), - a stabilisation step, based on the value determined during the determination step.

8. The steering method according to the preceding claim, wherein the determination step comprises a step of determining the current speed of the liquid carried by the upstream flow generated by the upstream propeller with respect to the body of the vehicle.

9. The steering method according to any one of the preceding claims, wherein, during the stabilisation step, the thruster is steered such that each of the two propellers generates a flow that is directed downstream.

10. The steering method according to any one of the preceding claims, wherein the thruster comprises two counter-rotating propellers with variable collective and cyclic pitches.

11. The steering method according to the preceding claim, wherein the axes of rotation of the two propellers are substantially coincident.

12. The steering method according to any one of the preceding claims, wherein, during the stabilisation step, in order for the thruster to exert a radial thrust so as to rotate the vehicle about an axis perpendicular to the axis of movement (x), the thruster (3) is steered such that the downstream propeller (AVA) generates a flow that is not rotationally symmetrical about the axis of movement (x).

13. The steering method according to the preceding claim, wherein, in order for the thruster to generate a thrust having a radial component exerted in a direction dr, forming, about the axis of rotation of the downstream propeller, a first angle α with a reference direction, the thruster is steered such that the downstream propeller (AVA) has a cyclic pitch comprising a cyclic angle θ given by the following formula: θ = α − φ where the cyclic phase φ is the angle formed, about the axis of rotation of the downstream propeller (x), between the thrust generated by the downstream propeller and the cyclic angle of the downstream propeller, the cyclic angle of a propeller being the angle formed about the axis of rotation of the downstream propeller (x) between the direction in which the cyclic blade angle of the propeller is at a maximum and the reference direction.

14. The steering method according to the preceding claim, wherein the cyclic phase is determined in a calibration phase.

15. A steering device allowing a vector thruster (3) comprising an upstream propeller (AM) and a downstream propeller (AVA), which are counter-rotating, with variable pitch, and variable cyclic pitch, to be steered along one axis of movement in a direction of movement, the steering device being able to implement the method according to any one of the preceding claims, the steering device comprising a control unit configured to determine the estimated main axis during the stabilisation step, and an actuation device configured to actuate the upstream propeller (AM) such that the main axis of the upstream flow generated by the upstream propeller (AM) at an instant (t) is the estimated main axis (xe).

16. A propulsion system comprising the steering device according to the preceding claim and a vector thruster (3) comprising an upstream propeller (AM) and a downstream propeller (AVA), which are counter-rotating, with variable pitch, and variable cyclic pitch according to one axis of movement in a direction of movement.

17. A marine vehicle (1) comprising a steering device according to claim 15, a body (2) and a vector thruster (3) mounted on the body (2), the vector thruster (3) comprising an upstream propeller (AM) and a downstream propeller (AVA), which are counter-rotating, with variable pitch, and variable cyclic pitch according to one axis of movement in a direction of movement.

18. The marine vehicle according to the preceding claim, wherein the estimated main axis is determined from the rotational speed of the vehicle and from the speed of the liquid carried by the flow generated by the upstream propeller, with respect to the body (2) of the vehicle (1).

Images