FORCE APPLICATION DEVICE FOR AN ACTIVE MINISTICK AND CONTROL METHOD FOR MECHANICAL SAFETY

Description

TECHNICAL FIELD OF THE INVENTION

[0001] The invention relates to piloting devices used by the pilot in an aircraft cockpit, in particular an active stick comprising integrated force feedback to assist the pilot. STATE OF THE ART

[0002] A piloting device in an aircraft cockpit usually comprises a pilot stick with, in particular, a lever mounted to rotate along a so-called roll axis and a so-called pitch axis, these two axes being orthogonal to each other. The most common devices are of the "broomstick" type.

[0003] Depending on the position of the lever along the two axes, the piloting device transmits movement commands to the aircraft's piloting components.

[0004] On the most recent aircraft models, the aircraft's movement control is electronic and the piloting device integrated into the cockpit may be of the "mini-stick" type. The position of the lever along the two axes of roll and pitch is measured by sensors and translated into movement commands. The lever is not directly mechanically linked to the moving parts of the aircraft and there is no direct mechanical feedback on the lever.

[0005] However, it is desirable for flight safety that the pilot perceives mechanical feedback at the lever level. Cockpit signaling systems may not be sufficient to provoke a sufficiently rapid reaction from the pilot in the face of unforeseen events during flight. The piloting sensations are much better if the pilot's sidestick incorporates force feedback, also called "haptic feedback".

[0006] It has been proposed to equip the mini-stick with passive mechanical systems, such as spring systems, or active electromechanical systems.

[0007] Patent document FR 3 011 815 describes an aircraft flight control device comprising a control lever mounted on a plate and connected to a roll axis motor and a pitch axis motor via transmission shafts. The two motors are controlled according to a force law, so as to generate a resistive force opposing the force exerted on the lever (force feedback) when a force threshold is exceeded by the pilot.

[0008] An electric motor force feedback device is effective in restoring driving sensations and increasing safety.

[0009] However, in the event of an electrical or mechanical failure in one of the said motors, or in the event of a breakdown in the motor control signal processing chain, the force feedback can be suppressed.

[0010] In the aeronautics industry, the availability requirements for pilot systems are high. It is unacceptable for the pilot to suddenly switch to a pilot mode without force feedback in the event of a failure.

[0011] Furthermore, state-of-the-art active force feedback systems often include a large number of components, including roll and pitch motors, but also clutches, torque limiters, gears, etc. These systems can be expensive, bulky, and difficult to integrate into an aircraft cockpit.

[0012] Document EP 2 081 822 B1 describes an aircraft haptic interface comprising electrically controlled piston dampers that supplement electric force feedback motors when necessary, to exert a resistive torque opposing the pivoting of a lever. However, in the architecture proposed in this document, each damper is connected by connecting rods to the lever, to transform a translational movement of the piston into rotary torque. The force feedback motors themselves act on the lever via gears that achieve a speed reduction.

[0013] Mechanical linkages increase the bulk and reduce the lifespan of the haptic interface. The angular travel allowed for the lever is low, which affects the ergonomics of the lever. The architecture proposed in this document is complex because the piston dampers are mounted in parallel with the force feedback motors.

[0014] Additionally, magnetorheological fluid particles inside the piston damper are likely to stratify during periods when the piston is not in use, further reducing the life of the damper.

[0015] Document US 2001 / 0052893 A1 describes a haptic interface for a motor vehicle comprising magnetorheological brakes exerting a variable resistive force opposing the pivoting of a lever by the user. Each brake acts on the lever via a series of gears comprising at least one intermediate shaft. In the variant illustrated in Figures 8a and 8b of this document, the angular travel allowed for the lever is limited and the use of the lever is not very ergonomic. In addition, this document describes a control of the magnetorheological brakes via force sensors. The presence of intermediate gears requires control of the torque exerted by the brakes as a function of a torque measured on the lever.

[0016] Finally, the magnetorheological brakes in this document are intended to provide haptic feedback on their own. These brakes are only used to resist lever movements induced by the driver, and not to generate movement on the lever.

[0017] Furthermore, the introduction of intermediate mechanical components between the brakes and the lever, such as gear trains or connecting rods, implies a reduction in the dynamic performance of the handle, the inertia of which increases.

[0018] FR 3 056 315 A1 discloses a haptic interface comprising a magnetorheological device for this purpose. GENERAL PRESENTATION OF THE INVENTION

[0019] There is therefore a need for a mini-pilot stick incorporating a mechanical emergency channel, to prevent the lever from rotating completely freely in the event of an electrical failure affecting a force feedback motor.

[0020] The desired mini-stick must not be able to switch, in the event of a failure, into a mode where the pilot can freely pivot the lever without feeling a resistive force.

[0021] There is a subsidiary need for a mini-handle of lower mass, size and power consumption.

[0022] Generally speaking, the reliability, mechanical simplicity and ergonomics of existing control stick force feedback devices can be improved. Existing systems do not allow sufficient angular movement of the stick.

[0023] In this respect, the invention relates, according to a first aspect, to a force application device for an aircraft control stick, this device being in accordance with claim 1.

[0024] The rheological brake, associated with the electromagnetic field control device, constitutes a mechanical backup route capable of taking over from the force motor in the event of a failure affecting said motor or its control chain (for example a loss of power or a failure of the computers).

[0025] The resistance of the rheological material (e.g., an electrorheological or magnetorheological fluid) to shear is modifiable depending on the electromagnetic field applied to it. The electromagnetic field control device is electronically controllable to vary stresses within the rheological brake, these stresses opposing the movement induced by the pivoting of the lever.

[0026] In fact, depending on the electromagnetic field applied, the relative rotary movement between the part arranged on the motor shaft and the opposite part can be braked or prevented. A resistive torque is exerted by the brake on the motor shaft and opposes the rotational movement of the mechanical joint via the motor shaft.

[0027] The force application device is free of mechanical transmission components, for example angle transmission elements or elements providing speed reduction, between the rheological brake and the shaft of the force feedback motor. Advantages of this construction are a reduced size of the rheological brake, better transmission of the resistive torque to the lever and better general ergonomics of the mini-stick incorporating this device due to the absence of parasitic torque variations.

[0028] In the case where the force motor is a direct drive motor, or "direct drive" according to current Anglo-Saxon terminology, the rheological brake can also act on the rotation axes of the lever by direct drive.

[0029] An additional advantage is the absence of additional friction-generating parts between the rheological brake and the drive shaft. The service life of the rheological brake is improved and the presence of the force application device has a minimal impact on the angular travel ranges of the lever.

[0030] Furthermore, strong stratification of the rheological material particles during the inactive ranges of the rheological brake is avoided, because the rheological material is directly positioned between the moving parts rotating relative to each other.

[0031] According to a possible variant, it is possible to provide for a locking of the lever via the rheological brake, in the event of a failure affecting the force motor.

[0032] The rheological brake can also be configured to exert force feedback according to a force and / or damping law instead of or in addition to the force motor. The rheological brake then participates in the normal operation of the mini-stick. It is then not necessary to arrange in the mini-stick electric motors sized to exert on their own the maximum resistive forces expected over the range of use of the stick. It is therefore possible to reduce the mass and size of the mini-stick.

[0033] The force application device of the invention may include the following optional and non-limiting characteristics, taken alone or in any of their technically possible combinations: the rheological material is a magnetorheological fluid comprising suspended magnetic particles, or the rheological material is an electrorheological fluid comprising suspended conductive particles, the control device being controlled to apply a variable magnetic or electric field. the rheological material is a magnetic powder dispersed between the two facing parts. the force motor is a torque motor. the force motor is a direct drive motor. the rheological brake is positioned on the motor shaft opposite the mechanical seal relative to the force motor. the rheological brake is positioned on the motor shaft between the mechanical seal and the force motor. the two facing parts of the rheological brake are located opposite each other along the third axis.the force application device comprises a motor shaft rotation speed sensor, the rheological brake being controlled according to a speed control as a function of a rotation speed acquired by said sensor. the two parts facing the rheological brake are a first disc extending radially from the motor shaft and a second disc facing the first disc, the first disc and the second disc being centered on the third axis. the two parts facing the rheological brake are a sphere centered on the motor shaft and at least partially immersed in the rheological material and a spherical base. the control device is controlled to apply an electromagnetic field increasing the resistance of the rheological material to shear, in the event of a failure on a processing line of the force motor. the sliding torque of the rheological material is between 10 Nm and 100 Nm, preferably between 10 Nm and 75 Nmthe force application device further comprises a roll force sensor configured to measure a roll torque exerted on the lever, and / or a pitch force sensor configured to measure a pitch torque exerted on the lever, to enable force control of the control stick. the rheological brake is configured to exert a resistive torque on the mechanical seal, a value of which is limited to 70 Nm, preferably 25 Nm, as a function of an electric current supplied to the control device. the control device is controlled according to a predetermined law to exert an electromagnetic field which is a function of a position and / or a speed of the lever.the force motor is a roll motor, the rotation of the motor shaft being linked to the rotation of the mechanical seal around the roll axis, the rheological brake being adapted to exert a force feedback on the roll axis, the device further comprises a pitch motor comprising a pitch motor shaft extending along a fourth axis, the rotation of the pitch motor shaft being linked to the rotation of the mechanical seal around the pitch axis, and comprises an additional rheological brake adapted to exert a force feedback on the pitch axis.

[0034] According to a second aspect, the invention relates to an active aircraft piloting stick, comprising a force application device as defined above associated with a lever capable of rotating around the roll axis and the pitch axis, the lever being arranged on the mechanical joint.

[0035] The invention also relates to an aircraft comprising such a control stick.

[0036] According to a third aspect, the invention relates to a method for mechanical backup control of a force application device on an aircraft control stick, the method being implemented using a force application device as defined above and comprising the steps of: detecting a failure on a processing chain of a force motor of the force application device, generating an electromagnetic field command below a sliding torque of a rheological material contained in a rheological brake of the force application device, said command being transmitted to a control device of the force application device to block the lever. Optionally and non-limitingly, this method comprises an additional step of activating a force control mode of the handle.

[0037] According to a fourth aspect, the invention relates to a method for controlling the damping law of a force application device on an aircraft control stick, the method being implemented using a force application device as defined above and comprising the steps of: detecting a position and / or a speed of a lever rotating around a roll axis or a pitch axis, the lever being arranged on a mechanical joint of the force application device, generating an electromagnetic field command according to a predetermined law as a function of the detected position and / or speed, said command being transmitted to a control device of the force application device, so that a rheological brake of the force application device exerts a resistive torque opposing a rotational movement of the lever in addition to a force motor of the force application device. GENERAL PRESENTATION OF THE FIGURES

[0038] Characteristics, aims and advantages of the invention will emerge from the following description, which is purely illustrative and non-limiting, accompanied by the appended drawings among which: There Figure 1 schematically represents a control stick architecture according to an embodiment of the invention; The Figure 2 is a perspective view of a lever and mechanical joint of a mini-stick; The Figure 3 schematically represents a force application device for a handle according to a first variant comprising a rheological brake according to a first variant; The Figure 4 is a close-up view of the magnetorheological brake of the Figure 3 ; THE Figures 5a, 5b and 5c are schematic diagrams of the operation of a magnetorheological fluid; The Figure 6 is a curve representative of a resistive torque exerted by a magnetorheological brake as a function of the electric current; The Figure 7is a view of a rheological brake according to a second variant; The Figure 8 is a view of a rheological brake according to a third variant; The Figure 9a is a view of a rheological brake according to a third variant; The Figures 9b and 9c are schematic diagrams of the operation of a magnetic powder in the brake of the Figure 9a ; There Figure 10 schematically represents a force application device for a handle according to a second variant; The Figure 11 illustrates the steps of a method for controlling a force application device of the invention, in mechanical emergency; The Figure 12 illustrates the steps of a method for controlling a force application device of the invention, in damping law. DETAILED DESCRIPTION OF EMBODIMENTS

[0039] Throughout the following, examples of devices for applying force to a lever of an aircraft control stick are described, comprising at least one “rheological brake”, i.e. a brake comprising a volume configured to be filled with a rheological material. “Rheological material” means a solid or liquid material whose shear strength is variable as a function of an electromagnetic field applied to it, according to a predetermined characteristic (or rheogram). For example, the viscosity of the rheological material is variable as a function of the electromagnetic field. “Electromagnetic field” means a field which may be solely electric, or solely magnetic, or may comprise a magnetic component and an electrical component.

[0040] Furthermore, the term "damping law" of a rheological brake is understood to mean the relationship between the rotary position of the lever along an axis of rotation and the resistance force produced by the brake against the movement around said axis. The term "force law" of the force application device taken as a whole (rheological brake(s) possibly supplemented by electric motors) is understood to mean the force, which may be resistive or motor, restored as a function of the position of the lever along the axis.

[0041] Similar elements in the attached figures will be designated by the same alphanumeric references throughout the description below. Overall architecture of the control system

[0042] We have represented in Figure 1 a functional architecture of an aircraft control system along its roll and pitch axes, including a mini-control stick. The mini-control stick is typically located in the cockpit of the aircraft.

[0043] In this figure, the thicker lines between two functional units correspond to mechanical connections. The other arrowed connections are electronic connections through which data can circulate.

[0044] The system comprises a control lever 1 rotatably mounted on a mechanical joint 2 along a roll axis X and a pitch axis Y of the lever, the two axes being orthogonal. Preferably, the lever 1 is mounted on a plate of the mechanical joint 2. The joint is fixed to a frame secured to the floor of the aircraft cockpit.

[0045] Position sensors, preferably a sensor 4a associated with the roll axis and a sensor 4b associated with the pitch axis, communicate electronic signals of the rotary position of the lever 1 respectively along the X and Y axes to a computer 7. The computer 7 controls the force application device to produce a predetermined force law. The computer 7 comprises an electronic interface for receiving said position signals. The sensors 4a and 4b also communicate information on the rotation speed of the lever 1 along these axes. The position / speed information of the lever is translated into control signals for controlling the moving parts of the aircraft by a flight control unit 8, or FCS for "Flight Control System".

[0046] As will be described below, the control unit 8 is also configured to determine, based on the position / speed information of the lever and possibly other information, commands for applying force to the lever 1. The computer 7 determines, based on the commands for applying force, control signals for the force application device associated with the mini-stick.

[0047] In the present example, the force application device comprises an electric motor 3a having a motor shaft of axis A. The motor shaft is linked to the roll axis X of the lever. By “linked to the axis” is meant that a connection mechanism exists between the motor shaft of axis A and the joint 2 which is set in motion when the lever pivots along the axis X.

[0048] Preferably, the electric motor 3a is a torque motor. This is a motor capable of transmitting a significant rotational torque to the motor shaft, even in the event of rotor lock. Typically, the torque motor used is a low rotational speed, high rotational torque motor.

[0049] The use of this type of motor is advantageous because the main objective of this motor is to transmit a variable resistive torque to the lever through the joint, and not to move the lever.

[0050] Preferably, the motor 3a is a direct drive motor. This eliminates the need for a reduction gear train; there is no speed reduction between the motor shaft and the mechanical joint plate. In addition, the motor acts directly on the plate, without an angle transmission.

[0051] In addition, the use of force feedback motors makes it possible to generate movement on the lever. It is thus possible to provide feedback on the lever, in particular to return it to a predetermined anchor point. State-of-the-art haptic interfaces that only include brakes only allow for damping of pivoting movements of the lever, and do not allow for feedback to be implemented.

[0052] Likewise, the device comprises an electric motor 3b associated with a motor shaft of axis B linked to the pitch axis Y of the lever, which is preferably a torque motor and which is advantageously direct-driven.

[0053] The force application device further comprises two magnetorheological brakes, a first brake 5a linked to axis A and a second brake 5b linked to axis B.

[0054] According to the invention, the brakes are positioned directly respectively on the shaft of the motor 3a of axis A and the shaft of the motor 3b of axis B. By "positioned directly", it is meant that the parts performing the braking (for example brake discs, as will be seen below) are arranged directly on the motor shaft. There are no intermediate mechanical members between the parts performing the braking and the motor shaft.

[0055] In particular, the brake 5a is aligned directly with the axis A of the motor shaft. If the roll motor 3a is located vertically under the lever, the brake 5a is preferably integrated vertically on the motor shaft of axis A. There is no angle transmission between the brake 5a and the motor shaft. Preferably, the brake 5b is also integrated vertically on the motor shaft of axis B.

[0056] This reduces the horizontal footprint of the assembly formed by the mechanical seal, the force feedback motors and the rheological brakes.

[0057] Each of the magnetorheological brakes comprises a control device configured to vary a magnetic field, said device being electronically controlled by the control unit 8 via the computer 7, either as a mechanical backup in the event of failure of the motor 3a and / or the motor 3b, or in damping law, for example according to a control method described below.

[0058] Alternatively, the force feedback motors 3a and 3b could be omitted from the piloting system, retaining the brake 5a configured to act on the roll axis and the brake 5b configured to act on the pitch axis.

[0059] Optionally, the control system also includes force sensors 6a and 6b measuring respectively the torque exerted on the lever when pivoting along the X axis and along the Y axis. These are, for example, capacitive or piezoelectric sensors.

[0060] Such sensors are particularly useful if the piloting system includes a force piloting mode, in which the lever is immobilized and the control unit 8 determines control signals for the moving parts of the aircraft as a function of the forces applied to the lever 1.

[0061] It should be noted, however, that it is possible to omit the force sensors 6a and 6b, particularly in the case where the rheological brakes are used solely to simulate a damping law on the lever. Due to the absence of intermediate mechanical components between the rheological brakes and the motor shaft, the rheological brakes are preferably controlled directly by a speed control. Control of the brakes therefore does not necessarily require torque information.

[0062] There Figure 2 represents an exemplary embodiment. The lever 1 is arranged on a mechanical joint 2 fixed to a frame 9 secured to a chassis of the aircraft. The motors 3a and 3b (not visible) are offset from the lever. The brakes 5a and 5b are also offset from the lever. As indicated previously, the motors 3a and 3b and the brakes 5a and 5b are preferably integrated vertically under the mechanical joint.

[0063] The lever 1 is free at one end and fixed to a first plate 11 at the other end. The first plate 11 is rotatable along the X axis and along the Y axis and is connected to a second plate 10 of the joint 2. The X axis is connected to the first plate 11 so that pivoting the first plate 11 about the Y axis causes the X axis to pivot about the Y axis.

[0064] Two transmissions, each comprising a Cardan joint, translate a rotational movement of the lever along the X axis, respectively along the Y axis, into a rotational movement of a shaft (not shown) extending along the A axis, respectively along the B axis.

[0065] The motors 3a and 3b are thus in direct contact with the mechanical joint 2 and can transmit a resistive or motor force in response to the pivoting movements of the lever 1 by the pilot, according to a predetermined force law or damping law. The motors 3a and 3b are preferably “direct drive” motors, which makes it possible to increase the service life of the mini-stick and which makes it possible to limit the parasitic torque variations felt by the user of the stick.

[0066] For more details on the structure of joint 2 and the mechanical connection with motors 3a and 3b, please refer to Figure 1 of document FR 3 011 815 and the related description.

[0067] We have represented in Figure 3 an architecture of the force application device integrated into the mini-stick according to a first embodiment.

[0068] In this example, the brake 5a, respectively 5b, acts on the axis A, respectively B, and is located opposite the mechanical joint 2 with respect to the corresponding motor. An advantage of this configuration is that the magnetorheological brake can be offset with respect to the joint receiving the lever, which makes it possible to reduce the space requirement in the vicinity of the lever and to save space in the cockpit. Magnetorheological brake of the force application device

[0069] A magnetorheological brake 5a will be described throughout the following, the brake 5b being of similar structure and operation to the brake 5a.

[0070] In the example of the Figure 3 , an output shaft of the brake 5a extends directly along the axis A and is coaxial with a shaft of the roll motor 3a.

[0071] The brake 5a comprises at least two parts 52a and 52b facing each other and adapted to be set in motion relative to each other. In the present example, the parts 52a and 52b are adapted to rotate about the axis A. By "facing parts" is meant that at least part of the external surfaces of the two parts are facing each other without being in contact.

[0072] The brake further comprises a volume 53 delimited by the two facing parts, adapted to receive magnetorheological fluid. The volume 53 is airtight so as not to allow the magnetorheological fluid to leak.

[0073] The term "volume delimited by the two facing parts" means that the parts of the surfaces of the two parts which are located opposite each other are, at least partially and preferably totally, in contact with the volume of magnetorheological fluid.

[0074] One operating principle of the brake is to vary the shear resistance of the fluid contained in volume 53, the two parts 52a and 52b shearing the fluid during their relative rotation around axis A. The shear resistance torque exerted by the fluid is variable depending on the magnetic field.

[0075] Preferably, the two parts 52a and 52b are located opposite each other along the extension axis A of the motor shaft. The two parts shear the rheological fluid substantially perpendicular to the axis A of the motor shaft.

[0076] To vary the shear resistance torque, and to control the brake by the computer 7, the brake comprises a control device 54 configured to apply a variable magnetic field within the volume 53.

[0077] Preferably, the rheological brake 5a is speed-controlled, depending on the rotational speed of the motor shaft. The brake is controlled according to the rotational speed of the motor shaft around its axis A, detected by a speed sensor which may be the sensor 6a or another sensor.

[0078] In fact, the brake acts directly on the motor shaft, without any intermediate mechanical components. It is therefore not necessary to control the brake using torque control.

[0079] We give in Figure 4 a view of the magnetorheological brake 5a of the Figure 3 according to a sectional view passing through axis A.

[0080] The brake comprises a cylindrical enclosure 51 centered on the input shaft 55 extending along the axis A. The input shaft 55 corresponds to the drive shaft of the roll motor 3a.

[0081] The output shaft 56 of the brake is preferably coaxial with the input shaft 55. In the present example, the output shaft 56 is fixed to the frame.

[0082] Within the brake, a plurality of brake discs are included between a first sealed wall 580 and a second sealed wall 581. The brake comprises an alternation between a series of discs mounted on a rotor 57 secured to the input shaft 55, and a series of discs mounted secured to the output shaft 56. The brake discs are pierced in their center and preferably centered on the axis A of the shaft 55.

[0083] In particular, the brake comprises a disc 52a secured to the input shaft and a consecutive disc 52b secured to the output shaft. The discs 52a and 52b are here adapted to rotate relative to each other around the axis A, during a rotation of the output shaft relative to the input shaft.

[0084] Preferably, the disc 52a is centered on the input shaft 55 and is therefore centered on the axis A. The disc 52b is preferably also centered on the axis A.

[0085] Between the faces of two consecutive brake discs, a sealed volume is provided suitable for receiving magnetorheological fluid in the liquid state. In particular, a volume 53 of fluid is delimited by the facing faces of the discs 52a and 52b. The sealing of each of the volumes is ensured by seals at the spacers between the discs. The brake comprises an alternation of brake discs and volumes of magnetorheological fluid at different axial positions along the axis A.

[0086] In this example, the volume of fluid between two faces of consecutive discs is in contact with more than 50% of the surface of said faces.

[0087] According to the invention, a control device 54 is arranged near the fluid volumes. Here, the control device is formed of two coils extending parallel to the axis A in the vicinity of the brake discs. The length of each of the coils is slightly greater than the total length over which the brake discs extend.

[0088] According to a variant, the control device 54 may further comprise a permanent magnet.

[0089] A dotted line M of the field generated when a current flows inside a coil 54 is shown.

[0090] The magnetorheological fluid can be admitted inside the brake via filling channels not shown.

[0091] The brake 5a also includes cooling channels 591 in the vicinity of the brake discs. Air can circulate in the enclosure 51 through ventilation ducts 590.

[0092] The behavior of the magnetorheological fluid of volume 53 at rest and in the presence of a magnetic field is shown schematically on the Figures 5a, 5b and 5c . A carrier fluid 531, preferably insulating, contains a suspension of particles 530. Preferably, the particles are between 1 and 10 micrometers in size. Metallic particles, for example iron, may be used as magnetic particles. At rest, the motion of the particles 530 is random as represented by the arrow in the Figure 5a and the particles do not exert shear resistance. Residual shear resistance of the brake discs is exerted by the carrier fluid.

[0093] There Figure 5brepresents the state of the system when a Lorentz force F is exerted on the 530 particles due to the magnetic field M. The 530 particles align in the form of chains of particles parallel to the magnetic field lines, which increases the resistance of the magnetorheological fluid to shear. The resistive torque of the magnetorheological fluid as a whole increases very significantly compared to the resistive torque of the carrier fluid alone.

[0094] Parts 52a and 52b shear the fluid confined in volume 53 as they rotate relative to each other.

[0095] When the shear strength of the magnetorheological fluid increases, as in the state of Figure 5b , the fluid generates a shear stress at the volume 53. The movements of the disc 52a and the disc 52b are thus coupled.

[0096] The resistive torque of all the fluid volumes, considered together, may be sufficient to couple the input shaft 55 and the output shaft 56. If the output shaft is fixed, for example if it is fixed to the frame as in the present example, the motor shaft is braked, or even blocked, in its pivoting along the roll and / or pitch axis.

[0097] On the Figure 5c , the Lorentz force experienced by the 530 particles is increased due to the increase in the magnetic field. A sliding threshold of the magnetorheological fluid has been exceeded; the particle chains are no longer able to align themselves along the field lines, and drift in the direction of the force F, potentially breaking locally.

[0098] The resistive torque exerted on the lever remains substantially constant and a displacement occurs between the input and output of the magnetorheological brake.

[0099] The shear resistance exerted by the magnetorheological fluid thus depends on the magnetic field, which itself depends on the current applied to the terminals of the coils.

[0100] We have represented in Figure 6 the relationship between the current intensity in the coils (on the abscissa) and the resistive torque generated by a magnetorheological brake (on the ordinate) according to an example.

[0101] The brake is designed to provide a resistive torque of 20 Nm in optimal operation at 100% electrical current. For a DC supply voltage of 36 volts, 100% current corresponds to 0.5 milliamps.

[0102] At 0% there is a brake preload with a torque of approximately 1 Nm. The torque then increases with the current intensity in a quasi-linear manner, according to the R curve. A linear approximation of the R curve is represented by the line R'.

[0103] Thus, the magnetorheological brake constitutes a satisfactory solution for exerting a resistant torque in a controlled manner.

[0104] Controlling this brake is simple since it is sufficient to control the current flowing at the terminals of the magnetic field control device to vary the resistive torque, within the limits of the fluid slip threshold. This brake is therefore advantageously integrated into a mini-control stick to provide an additional force feedback path that is largely independent of any existing paths based on the use of electric motors.

[0105] In addition, the magnetorheological fluid has a natural force threshold beyond which the torque exerted on the brake discs is too great for the fluid to perform its shear resistance function. This ensures that the lever is set in motion if the force exerted by the driver exceeds a certain threshold, which limits damage to the mini-stick components. Mechanical stops can be provided in the mini-stick to provide a lever retention function when the fluid force threshold is exceeded.

[0106] There Figure 7 illustrates an alternative example of a magnetorheological brake that can be used instead of the brake visible on the Figure 3 .

[0107] In this example, the rheological brake comprises a sphere 62a through the center of which passes the drive shaft of the roll motor 3a, said shaft extending along the axis A. The brake also comprises a spherical base 62b receiving the sphere 62a. A pivoting movement of the lever 1 along the roll and / or pitch axis causes a rotation of the shaft around the axis A and a rotary movement of the sphere relative to the base.

[0108] A lower part of the sphere 62a, an upper part of the base 62b and sealing joints form the volume 63 of fluid. Coils 64 arranged in the vicinity of the volume 63 serve as a magnetic field control device.

[0109] The coils are arranged so that the magnetic field lines M pass through a large area of ​​the sphere 62a. This allows the shear strength at the sphere 62a to be controlled and, consequently, the force feedback on the lever to be modulated.

[0110] According to one embodiment, a first shaft of a lever roll motor and a second shaft of a lever pitch motor both pass through the sphere 62a.

[0111] If the magnetic field is sufficient, the brake thus exerts force feedback along both the roll axis and the pitch axis. An advantage of this variant is that it uses a brake threshold to brake or block the lever's movements according to its two degrees of pivoting freedom.

[0112] Another alternative example of a magnetorheological brake is illustrated in Figure 8 . In this example, the magnetorheological fluid is subjected to traction and / or compression.

[0113] The brake comprises two discs 72a and 72b centered on the motor shaft of axis A, the disc 72a being movable relative to the disc 72b in translation along the axis A. In this example, the pivoting movement of the lever along the roll axis causes a translational movement of the disc 72a, a mechanical transmission mechanism connecting the shaft to the lever.

[0114] A volume of magnetorheological fluid is confined in a volume 73 between the two discs. A control device, not shown in the figure, is adapted to generate a magnetic field substantially parallel to the axis A.

[0115] When the magnetic field is below the slip threshold, the fluid's resistance to traction and compression along the A axis increases with the magnetic field, itself dependent on the current at the terminals of the control device.

[0116] Examples of magnetorheological brakes of Figures 4 to 9are easily transposed to electrorheological brakes. The rheological material is then an electrorheological fluid comprising conductive particles in suspension. The control device is then configured to apply a variable electric field to a volume of electrorheological fluid in the brake.

[0117] For use in an aircraft control stick, the sliding torque of the rheological material is preferably between 10 Nm and 100 Nm and even more preferably between 10 Nm and 75 Nm. In fact, the sliding torque must be lower than a threshold torque determined by the maximum torque transmissible by a seized roll or pitch motor.

[0118] Preferably, the brake should be able to restore a resistive force between 100 and 150 Newtons, preferably around 120 Newtons, on the lever.

[0119] Another example of a rheological brake is shown on the Figure 9a. This is a powder brake. The rheological material used in this brake is a magnetic powder.

[0120] This brake consists of two brake discs 86 and 87 whose air gap is partially filled with a magnetic powder in a volume 83.

[0121] The discs are centered on the axis A. The volume 83 is comprised between an external radial surface of the rotor 82a and an internal radial surface of the stator 82b. Said two surfaces extend substantially parallel to the axis A and face each other. When the rotor 82a rotates about the axis A relative to the stator 82b, the rotor 82a shears the magnetic powder comprised in the volume 83, in particular at the level of teeth 85 of the rotor.

[0122] The teeth 85 correspond to channels dug into the external radial surface of the rotor 82a.

[0123] When the magnetic powder is not subjected to a magnetic field or is subjected to a negligible magnetic field, the magnetic powder is distributed by gravity in the air gap and generates a weak torque resisting shear, by friction between the powder and the rotor. This state of the system is represented on the Figure 9b .

[0124] Conversely, when a magnetic field is applied to volume 83, the powder contained in volume 83 aligns along the field lines.

[0125] Thus, the powder grains create powder structures extending between the facing surfaces of the rotor 82a and the stator 82b. These structures are visible on the Figure 9c . These structures exert a resistive shear torque exerted by the rotor 82a. The brake discs are thus coupled.

[0126] The variable magnetic field is here exerted by two coils 84 electrically controlled by the computer. The coils 84 are arranged relative to the volume 83 so that the magnetic field lines are substantially perpendicular to the facing surfaces of the rotor 82a and the stator 82b.

[0127] The magnetic powder contained in dispersion in volume 83 constitutes a rheological material. The resistance of the magnetic powder to the shear exerted by the rotor depends on the magnetic field applied to it, this field being electrically controllable. The greater the magnetic field exerted by the coils, the greater the resistive torque exerted by the magnetic powder.

[0128] On the other hand, if a sliding torque is exceeded at the powder brake, the resistive torque exerted by the magnetic powder of volume 83 no longer increases with the magnetic field, and the brake discs are no longer correctly coupled.

[0129] We have represented in Figure 10 an alternative example of the architecture of the force application device integrated into the mini-stick.

[0130] In this example, brake 5a has as output shaft the motor shaft of roll motor 3a, and brake 5b has as output shaft the motor shaft of pitch motor 3b.

[0131] The rheological brakes correspond to any of the preceding examples. Each brake is here positioned close to the mechanical seal 2, between the corresponding motor 3a or 3b and the seal 2.

[0132] In another example, a magnetorheological brake is directly linked to a pivoting movement of the lever. For example, for the roll X axis of the lever, the roll movement may drive a shaft extending along the X axis, a rheological brake being positioned on said shaft, preferably near the mechanical seal 2.

[0133] In a further alternative example, motors 3a and 3b are omitted and damping of the lever's pivoting movements is provided solely by the brakes.

[0134] Exemplary methods of using a mini-control stick with a force application device are now described. The mini-control stick here comprises one or more brakes according to any of the preceding examples. The control system of the Figure 1 can be configured to implement one and / or the other of these two methods. Mechanical emergency control

[0135] In one embodiment, the magnetorheological brake control device is configured to apply a magnetic field increasing the viscosity of the rheological material in the event of a failure on a processing chain of an engine (roll and / or pitch) associated with the brake. The engine processing chain notably comprises the computer 7.

[0136] In this mode, the force application device therefore comprises a roll and / or pitch motor, preferably electric, associated with a brake which can take over from the motor in the event of failure.

[0137] A method of controlling the force application device in mechanical emergency mode is shown in Figure 11 .

[0138] At a step 100, a failure on a processing chain of the motor associated with the brake is detected, for example a mechanical failure of the motor which is no longer able to provide sufficient force feedback on the pivot axis of the lever associated with it, or a failure in the processing or communication of the control signals of the motor or a power supply part of the computer 7.

[0139] In a step 200, a magnetic field command is transmitted by the unit 8 to the rheological brake control device, for example to an electronic interface controlling a coil of the control device.

[0140] The magnetic field control is such that the viscosity of the rheological material is increased, which increases the shear resistance at the brake so that the resistive torque exerted by the brake on the roll and / or pitch axis increases, without exceeding a slip threshold of the rheological material. If the torque exerted by the pilot on the lever exceeds the slip threshold, the resistive torque of the brake no longer increases and the output of the rheological brake is set in motion relative to the input of the brake.

[0141] Preferably, the lever and the brake are dimensioned so that at a step 250, the lever is locked in pivoting along the roll and pitch axes, under the effect of the field control.

[0142] In this case, the piloting system enters a stick force piloting mode at a step 300.

[0143] In this mode, a roll force sensor 6a and a pitch force sensor 6b take over from the position and / or speed sensors on the roll and pitch axes of the lever. The pilot control signals generated by the control unit 8 (the FCU) are a function of force detection signals on the lever. Thus, the pilot controls the movements of the moving parts of the aircraft according to the force he exerts on the lever.

[0144] The force control mode can then be deactivated as soon as the fault in the processing chain of the motor associated with the brake is resolved. Thus, the force sensors 6a and 6b can only be used during periods of failure.

[0145] An advantage of the mechanical backup control method is that the sidestick cannot switch to a mode where the pilot can freely pivot the lever. Control of the lever's roll and pitch axes is secured, with the rheological brake providing an additional path for applying force to the stick. Control in damping law or in force law

[0146] In another mode, the magnetorheological brake control device is configured to exert a magnetic field which is a function of a position and / or a speed of the lever, according to a predetermined law.

[0147] One or more brakes can act alone on the roll and pitch axes, without electric motors, to provide force feedback on the lever according to a damping law.

[0148] A roll motor and / or a pitch motor may be associated with one or more magnetorheological brakes to restore a force on the lever according to a force law. For example, at extreme positions of the lever, the motor may provide a driving torque to return the lever to an equilibrium position.

[0149] A method of controlling the force application device in damping law is represented in Figure 12 .

[0150] The position of the lever is detected at a step 400 and position detection signals are transmitted to the flight control unit.

[0151] In a step 500, a magnetic field command is determined from the position detection signals, according to a predetermined damping law. The damping law is for example pre-recorded in the flight control unit 8.

[0152] The field command is transmitted to the force application device, which generates a resistive force against the pivoting of the lever at a step 550. The resistive force exerted by the rheological brake is a function of the field exerted by the brake control device, according to the rheogram of the rheological material contained in the brake.

[0153] Damping law or force law control is advantageous because rheological brakes complement or replace electric motors in their force feedback function on the lever. It is therefore not necessary to integrate electric motors sized to ensure the entire force feedback. The mass, size and power consumption of the mini-control stick can be reduced.

Claims

1. A force application device for an aircraft pilot stick, the device comprising: - a mechanical joint (2) configured to receive a lever (1) of an aircraft pilot stick, the mechanical joint (2) being rotatably movable about a roll axis (X) and about a pitch axis (Y), - a force motor (3a) comprising a motor shaft extending along a third axis (A), the rotation of the motor shaft about the third axis being linked to the rotation of the mechanical joint (2) about an axis taken among the roll axis or the pitch axis, the force motor being configured to exert a resistive torque on the motor shaft, - a rheological brake (5a) comprising two facing parts (52a, 52b) facing each other, the brake comprising a volume (53) delimited by said two facing parts, the volume being adapted to contain a rheological material, one (52a) of said two parts being arranged on the motor shaft and being rotatably movable about the third axis (A) relative to the other (52b) of said two facing parts, - a control device (54) controlled to apply an electromagnetic field within said volume (53) so as to vary shear strength of the rheological material.

2. The force application device according to claim 1, wherein the rheological material is a magnetorheological fluid comprising suspended magnetic particles, or wherein the rheological material is an electrorheological fluid comprising suspended conductive particles, the control device (54) being controlled to apply a variable magnetic or electric field.

3. The force application device according to anyone of claims 1 or 2, wherein the force motor (3a) is a torque motor.

4. The force application device according to anyone of claims 1 to 3, wherein the force motor (3a) is a direct drive motor.

5. The force application device according to anyone of claims 1 to 4, wherein the rheological brake is positioned on the motor shaft opposite the mechanical joint (2) relative to the force motor (3a).

6. The force application device according to anyone of claims 1 to 4, wherein the rheological brake is positioned on the motor shaft between the mechanical joint (2) and the force motor (3a).

7. The force application device according to anyone of claims 1 to 6, the force application device comprising a motor shaft rotational speed sensor, the rheological brake (5a) being piloted according to a speed servo-control as a function of a rotational speed acquired by said sensor.

8. The force application device according to anyone of claims 1 to 7, wherein the control device (54) is controlled to apply an electromagnetic field increasing the shear strength of the rheological material in the event of fault on a processing chain of the force motor (3a).

9. The force application device according to claim 7, further comprising a roll force sensor (6a) configured to measure a roll torque exerted on the lever (1) and / or a pitch force sensor (6b) configured to measure a pitch torque exerted on the lever (1), to allow a force-piloting of the pilot stick.

10. The force application device according to anyone of claims 1 to 9, wherein the rheological brake (5a) is configured to exert a resistive torque on the mechanical joint, a value of which is limited to 70 Nm, preferably 25 Nm, as a function of an electric current provided to the control device (54).

11. The force application device according to anyone of claims 1 to 10, wherein the control device (54) is controlled according to a predetermined law to exert an electromagnetic field which is a function of a position and / or speed of the lever (1).

12. The force application device according to anyone of claims 1 to 11, wherein the force motor is a roll motor (3a), the rotation of the motor shaft being linked to the rotation of the mechanical joint (2) about the roll axis (X), the rheological brake (5a) being adapted to exert a force feedback on the roll axis (X), the device further comprising a pitch motor (3b) comprising a pitch motor shaft extending along a fourth axis (B), the rotation of the pitch motor shaft being linked to the rotation of the mechanical joint about the pitch axis (Y), the device comprising an additional rheological brake (5b) adapted to exert a force feedback on the pitch axis (Y).

13. An active aircraft pilot stick comprising: - a force application device according to anyone of claims 1 to 12, - a lever (1) able to rotate about the roll axis (X) and the pitch axis (Y), the lever being arranged on the mechanical joint (2).

14. A method for mechanical back-up monitoring of a device for applying a force on an aircraft pilot stick, the method being implemented using a force application device according to anyone of claims 1 to 12 and comprising the steps of: - detecting (100) a fault on a processing chain of a force motor (3a) of the force application device, - generating an electromagnetic field control (200) below a slip torque of a rheological material contained in a rheological brake (5a) of the force application device, said control being transmitted to a device for controlling the force application device to block the lever, - optionally, activating (300) a force pilot mode of the pilot stick.

15. A method for damping control of a device for applying a force on an aircraft pilot stick, the method being implemented using a force application device according to anyone of claims 1 to 12, the method comprising the steps of: - detecting (400) a position and / or speed of a lever (1) in rotation about a roll axis (X) or a pitch axis (Y), the lever (1) being arranged on a mechanical joint (2) of the force application device, - generating an electromagnetic field control (500) according to a predetermined law as a function of the detected position and / or speed, said control being transmitted to a device for controlling the force application device, so that a rheological brake of the force application device exerts a resistive torque opposing a rotational movement of the lever as a complement to a force motor (3a) of the force application device.