FR3148005A1 - Eddy current magnetic braking device, braked vehicle wheel and aircraft landing gear, aircraft equipped with such a wheel - Google Patents

Abstract

Magnetic braking device for a vehicle wheel, comprising at least one stator element (2) arranged to be connected in rotation to a part of the vehicle supporting the wheel, a rotor element (3) arranged to be connected in rotation to the wheel, magnets for producing between said elements a magnetic flux capable of generating eddy currents in one of the elements when the wheel rotates, and a braking control unit (11) receiving as input a braking command for applying a braking force according to the braking command. The magnets comprise at least one electromagnet (9) and the device comprises at least one anti-lock control unit (16) receiving as input a vehicle speed signal and a wheel rotation speed signal and providing as output a control signal for the electromagnet according to a comparison of speeds from the signals received as input. Aircraft wheel and landing gear comprising such a device. FIGURE OF THE ABSTRACT: Fig. 3

Description

Eddy current magnetic braking device, braked vehicle wheel and aircraft landing gear, aircraft equipped with such a wheel

The present invention relates to the field of braking vehicle wheels such as aircraft wheels.

BACKGROUND OF THE INVENTION

An aircraft wheel typically consists of a rim surrounded by a tire and connected by a web to a hub mounted to rotate on a wheel support shaft (axle or spindle).

Friction braking devices are known comprising a stack of brake disks which is housed in an annular space extending between the rim and the hub and which comprises an alternation of rotor disks linked in rotation with the wheel and stator disks fixed relative to the wheel support shaft. The braking device also comprises hydraulic or electromechanical actuators mounted on an actuator holder and arranged to apply a pressing force on the stack of disks so as to generate a braking torque to brake the rotation of the wheel.

Many vehicles equipped with a friction braking system have a wheel anti-lock (or anti-skid) system associated with the friction braking system. In fact, if the braking torque is too high in relation to the speed of the braked vehicle and the friction coefficient of the wheel tires relative to the ground, the braking system blocks the wheels, which then skid on the ground: such skidding reduces the vehicle's ability to maneuver and causes rapid wear and heating of the tires, which can burst. To prevent the wheel from locking, the anti-lock system compares the rotation speed of the wheels to the speed of the vehicle and controls the actuator to release the pressing force when the gear ratio is greater than a threshold (corresponding approximately to the circumference of the wheel). To obtain effective anti-lock, the release of the pressing force must be obtained in a response time of between 50 and 100 ms, a response time compatible with most friction braking systems.

Eddy current magnetic braking devices are also known, used for braking vehicle wheels and more particularly aircraft wheels. Document FR-A-3122405 describes such a device comprising a rotor rotatably connected to the wheel, two stators which surround the rotor and which are rotatably connected to the wheel support shaft and free in translation relative to said shaft, magnets for producing an axial magnetic flux between the stators and the rotor, and linear actuators for axially moving the stators between a maximum braking position in which the stators are close to the rotor and a free rotation position in which the stators are far from the rotor.

In an eddy current magnetic braking device, the braking torque produced is all the greater as the relative rotation speed of the rotor in relation to the stators is high and the braking torque decreases with the relative rotation speed. For this reason, an anti-lock system for the wheels was not envisaged. However, it appeared that the risk of wheel locking also existed with an eddy current braking device.

It was therefore considered to drive the actuators to move the stators away from the rotor in exactly the same way as in a friction brake anti-lock system. However, it was determined that the actuator travel required to sufficiently reduce the braking torque to prevent wheel lock is five times greater with a magnetic brake than with a friction brake. As a result, conventional magnetic brakes have too long a response time to provide effective anti-lock.

SUBJECT OF THE INVENTION

The invention aims in particular to propose a braking device which at least partially overcomes the aforementioned drawbacks.

For this purpose, the invention provides an eddy current magnetic braking device for a vehicle wheel, comprising at least one stator element arranged to be connected in rotation to a part of the vehicle supporting the wheel, a rotor element arranged to be connected in rotation to the wheel, magnets for producing between said elements a magnetic flux capable of generating eddy currents in one of the elements when the wheel rotates, and a braking control unit receiving as an input a braking command for applying a braking force according to the braking command. The magnets comprise at least one electromagnet and the device comprises at least one anti-lock control unit receiving as an input a vehicle speed signal and a wheel rotation speed signal and providing as an output a control signal for the electromagnet according to a comparison of speeds from the signals received as an input.

The comparison of speeds from the signals received at the input allows at least the anti-lock control unit to detect a wheel lock and to provide an output signal to control the electromagnet to remedy this lock. By controlling the electromagnet, the magnetic flux produced can be very quickly cancelled and therefore the braking torque can be cancelled. It has thus been observed that anti-lock using an electromagnet is several times faster than anti-lock using the modification of the stator/rotor air gap in order to increase or decrease the braking torque in an eddy current braking device. Indeed, when the air gap is increased, the braking torque takes longer to decrease than when the electromagnet current is decreased. The same phenomenon can be observed when the air gap is decreased: the braking torque takes longer to increase than when the electromagnet current is increased. The response time of the anti-lock braking system by changing the electromagnet current is therefore relatively low: changing the electromagnet supply current allows a variation amplitude of the braking torque equivalent to a rapid release of the press force for a friction braking device. In addition, the anti-lock control circuit can have a rapid dynamic response.

Preferably, the anti-lock control unit is arranged to control the electromagnet to cause a reduction in the braking torque when a wheel lock is detected and then an increase in the braking torque when the lock disappears, the anti-lock control unit controlling the electromagnet such that the increase in the braking torque is slower than the decrease in the braking torque.

This limits the risk of the wheel locking quickly when braking force is applied.

The invention also relates to a braked wheel equipped with such a device; a landing gear comprising a leg having one end carrying a shaft on which the hub of such a wheel is mounted, the stator element of the braking device being rotationally linked to the leg via the shaft; and an aircraft equipped with such a landing gear.

Other characteristics and advantages of the invention will emerge from reading the following description of particular and non-limiting embodiments of the invention.

Reference will be made to the attached drawings, including:

there is a partial schematic front view of an aircraft equipped with landing gear according to the invention;

there is a partial schematic view of a wheel according to the invention, in axial half-section;

there is a partial schematic perspective view of the stators and rotor of the braking device of this wheel;

there is a curve relating a slip ratio (equal to 1 minus the ratio between the product of the angular speed of the wheel and the radius of the wheel on the speed of the vehicle) and a coefficient of friction (Mu) for a given state of the landing runway used by the aircraft (here, dry runway);

there illustrates the modification of the supply current of the electromagnets and shows the superposition of the target current and the supply current of the electromagnets;

there superimposes a curve representing the response time of the braking torque after modification of the air gap and a curve representing the response time of the braking torque after modification of the supply current of the electromagnets;

there represents the braking torque obtained by modifying the supply current of the electromagnets as a function of time;

there is a schematic view of the brake control logic circuit according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

With reference to Figures 1 to 3, the braking system according to the invention is carried by an aircraft 100 comprising landing gears 101. Each landing gear 101 comprises a leg having one end provided with two coaxial shafts 102 on each of which a wheel 103 is mounted to pivot. Each wheel 103 comprises, in a manner known per se, a hub 104 mounted to pivot on the shaft 102 and a rim 105 connected to the hub 104 by a web 106. The rim 105 and the hub 104 define between them an annular space having one end closed by the web 106 and one end open towards the outside of the wheel 103. The rim 105 is encircled by a tire not shown.

According to the invention, the wheels 103 are equipped with a magnetic braking device generally designated 1, which extends here in the annular space defined by the rim 105 and the hub 104.

The magnetic braking device 1 comprises fixed elements, or stators 2, and moving elements, or rotors 3.

More precisely here, the stators 2 and the rotor 3 are in the form of discs, coaxial with the wheel 103, thus having collinear central axes. The rotor 3 is arranged between the two stators 2 and has two opposite main faces 3.1 each facing a main face 2.1 of one of the stators 2. The main faces 2.1, 3.1 are parallel to each other.

The stators 2 are rotationally connected to the shaft 102 or to the leg of the landing gear 101, here by means of a ribbed torque tube 4 which is fixed to an external collar of the shaft 102: the stators 2 are engaged on the torque tube 4. The rotor 3 is rotationally connected to the wheel 103, here to the rim 105 of the wheel 103 by means of bars extending in projection towards the inside of the rim 105. Thus, the rotor 3 rotates on itself around its central axis relative to the stators 2 which frame it: during this movement of the rotor 3 in a circumferential direction, the main faces 3.1 remain opposite the main faces 2.1 and parallel to them.

Each of the stators 2 is mounted to slide (without rotation) on the torque tube 4 to be movable in an axial direction of the torque tube 4 between a first position, or maximum braking position, in which the rotor 3 and the stator 2 are close to each other and have their main faces 3.1, 2.1 separated by a first predetermined air gap and a second position, or free rotation position, in which the rotor 3 and the stator 2 are spaced apart from each other and have their main faces 3.1, 2.1 separated by a second predetermined air gap greater than the first predetermined air gap. Each stator 2 is connected by a mechanism symbolized at 5 to at least one electromechanical actuator symbolized at 6, controllable by the pilot of the aircraft in a manner known per se, to actuate the mechanism 5 which moves the stator 2 between the two aforementioned positions. For example: the actuator may be a linear actuator and the mechanism may be a direct connection of the movable element of the actuator to the stator or comprise one or more intermediate levers; the actuator may be rotary and the mechanism a screw/nut system. An axial stop, of the rolling bearing or needle bearing type, is preferably provided, interposed between the rotor 3 and the stators 2 (or between parts connected to them) to ensure that the stators 2 cannot be brought closer to the rotor 3 beyond the first air gap.

Each stator 2 comprises a plurality of permanent magnets 7 having magnetic fields capable of generating eddy currents in the rotor 3 when the stator 2 is in the first position and the rotor 3 pivots opposite the stator 2. The permanent magnets 7, here based on rare earths, are preferably fixed on a support 8 for example made of magnetic steel.

Each stator 2 also comprises a plurality of electromagnets 9 fixed on the support 8 alternately with the permanent magnets 7. The electromagnets 9 comprise a coil connected to a current source and are sized to be able to generate a magnetic field cancelling the magnetic field produced by the permanent magnets 7 or even reversing the magnetic field emitted by the stator 2.

The rotor 3 is made of copper or any other electrically conductive material. The rotor 3 has a thickness such that a skin effect (otherwise called a skin effect or Kelvin effect) is generated from each face 3.1 of the rotor 3 over more than half of the thickness of the rotor 3 at least over a range of possible relative speeds of the rotor 3 relative to the stators 2. The eddy currents generated from the two faces 3.1 will then circulate in the central part of the rotor 3, which will increase the braking torque. This results in a “superposition of skin effects”, the thickness of the rotor 3 being sufficiently small to obtain this effect while satisfying the thermal and mechanical constraints. In one example, this effect gives approximately 60% more performance.

We will now look in more detail at the brake control.

It is understood that to cause braking, the electromechanical actuators 6 are controlled to bring the stators 2 into the first position and that, to interrupt braking, the electromechanical actuators 6 are controlled to bring the stators 2 into the second position, a position in which the permanent magnets 7 do not allow sufficient eddy currents to be generated in the rotor 3 to cause braking of the rotor 3.

It should be noted that below a certain rotation speed of the rotor 3, the braking torque is negligible regardless of the position of the stators 2. It may then be necessary to consider an additional brake.

It is also understood that braking can be interrupted by supplying power to the electromagnets 9 so as to cancel the magnetic field produced by the permanent magnets 7.

The control circuit 10 of the electromechanical actuators 6 and the electromagnets 9 will now be described in relation to the .

• une première entrée reliée à l’instrument de commande de freinage actionnée par le pilote de l’aéronef 100,
• une deuxième entrée reliée à la voie retour de la boucle de freinage,
• une première sortie reliée à une première entrée d’un premier sommateur 12,
• une deuxième sortie reliée à une première entrée d’un deuxième sommateur 13.

The brake control circuit 10 defines a brake control loop and comprises a brake control unit 11 (or BCU) having:

• a first input connected to the braking control instrument actuated by the pilot of the aircraft 100,
• a second input connected to the return path of the braking loop,
• a first output connected to a first input of a first adder 12,
• a second output connected to a first input of a second adder 13.

The first adder 12 has an output connected to an input of an actuator control unit 14 (or ACU) having an output connected to the actuators 6.

The second adder 13 has an output connected to an input of an electromagnet control unit 15 (or CCU) having an output connected to the electromagnets 9.

• une première entrée reliée à un bus de communication de l’aéronef 100 pour recevoir notamment la vitesse de l’aéronef 100 fournie par des capteurs de l’aéronef 100, comme la vitesse par rapport au sol (inertielle, GNSS ou hybride) fournie par l’unité de navigation de l’aéronef 100 ;
• une deuxième entrée reliée à un capteur de vitesse angulaire 17 agencé pour déterminer la vitesse de rotation des roues 103 ;
• une première sortie reliée à une deuxième entrée du premier sommateur 12 ;
• une deuxième sortie reliée à une deuxième entrée du deuxième sommateur 13.

The brake control circuit 10 further comprises an anti-lock control unit 16 having:

• a first input connected to a communication bus of the aircraft 100 to receive in particular the speed of the aircraft 100 provided by sensors of the aircraft 100, such as the speed relative to the ground (inertial, GNSS or hybrid) provided by the navigation unit of the aircraft 100;
• a second input connected to an angular speed sensor 17 arranged to determine the rotation speed of the wheels 103;
• a first output connected to a second input of the first adder 12;
• a second output connected to a second input of the second adder 13.

Units 11, 14, 15 and 16 are electronic units whose structure is known in itself. They may include one or more integrated circuits, microcontrollers, FPGAs or others.

• un signal de commande de freinage actionneurs envoyé sur la première sortie ;
• un signal de commande de freinage électroaimants envoyé sur la deuxième sortie.

The brake control unit 11 comprises, for example, a calculator in the form here of an integrated circuit programmed to process the signals coming from its inputs so as to produce:

• a brake actuator control signal sent to the first output;
• an electromagnet brake control signal sent to the second output.

• un signal de commande d’antiblocage actionneurs envoyé sur la première sortie ;
• un signal de commande d’antiblocage électroaimants envoyé sur la deuxième sortie.

The anti-lock control unit 16 comprises, for example, a calculator in the form here of an integrated circuit programmed to process the signals coming from its inputs so as to produce:

• an anti-lock actuator control signal sent to the first output;
• an anti-lock electromagnet control signal sent to the second output.

The first adder 12 provides an actuator control signal as output (corresponding either to the actuator braking control signal or to the actuator anti-lock control signal as we will see later).

The second adder 13 provides an electromagnet control signal as output (corresponding either to the electromagnet braking control signal or to the electromagnet anti-lock control signal as we will see later).

The actuator control unit 14 comprises, for example, a calculator in the form here of an integrated circuit programmed to process the actuator control signal arriving at its input so as to produce, via a power circuit associated with the control circuit, an actuator power signal to power the actuators 6.

The electromagnet control unit 15 comprises for example a control circuit in the form here of an integrated circuit programmed to process the electromagnet control signal arriving at its input so as to develop, via a power circuit associated with the control circuit, an electromagnet power signal to power the electromagnets 9. As visible in the , the electromagnet power signal supplying the electromagnets 9 can here vary between positive and negative values, as required.

In operation, the anti-lock control unit 16 has in memory the radius of the tires used on the aircraft 100 and can, from said radius, from the angular speed of rotation provided by the tachometer 17 and from the speed of the aircraft 100 provided by the communication bus, calculate a skid rate and compare it to a threshold here set at 0.12 in the case of a dry runway (see ). The threshold here corresponds to the optimal slip rate: as long as the slip rate is less than or equal to this threshold, the tire is in a stable zone and it is considered that braking is carried out without locking the wheel. If the slip rate exceeds the threshold, a skid is detected.

As long as no skidding is detected, the electromagnets 9 and the actuators 6 are controlled by the brake control unit 11 only, without intervention of the anti-lock control unit 16, to deliver a braking torque proportional to the braking command of the driver. The brake control unit 11 sends control signals to the actuator control unit 14 to modify the value of the air gap between the stators 2 and the rotor 3 and/or to the electromagnet control unit 15 to modify the magnetic field produced by the electromagnets 9 according to the braking force required by the driver. The modification of the air gap by the actuators 6 and the modification of the magnetic field of the electromagnets 9 will increase or decrease the braking torque and therefore the speed of the aircraft 100. The modification of the air gap by the actuators 6 affects the magnetic flux transmitted to the rotor 3 by the permanent magnets 7 and by the electromagnets 9 (at constant supply current). The modification of the supply current of the electromagnets 9 affects the magnetic flux transmitted to the rotor 3 by the electromagnets 9 and also the magnetic flux transmitted by the permanent magnets 7 since the electromagnets 9 can cancel the magnetic field transmitted by the permanent magnets 7.

• n’agir que sur les actionneurs 6 tant que la vitesse de variation de l’effort de freinage demandée par le pilote (déterminée par exemple en fonction de l’amplitude de mouvement de l’instrument de commande manipulé par celui-ci) est inférieure à un seuil ; et
• agir conjointement sur les actionneurs 6 et les électroaimants 9 lorsque la vitesse de variation de l’effort de freinage demandée par le pilote (déterminée par exemple en fonction de l’amplitude de mouvement de l’instrument de commande manipulé par celui-ci) est supérieure au seuil.

As an example, the brake control unit 11 can be configured to:

• only act on actuators 6 as long as the speed of variation of the braking force requested by the pilot (determined for example as a function of the amplitude of movement of the control instrument manipulated by the latter) is below a threshold; and
• act jointly on the actuators 6 and the electromagnets 9 when the speed of variation of the braking force requested by the pilot (determined for example as a function of the amplitude of movement of the control instrument manipulated by the latter) is greater than the threshold.

• au début du freinage, on agit sur les actionneurs 6 et les électroaimants 9 par une modification par exemple de même amplitude mais l’augmentation du flux magnétique des électroaimants 9 étant beaucoup plus rapide que celle du flux magnétique des aimants permanents 7, la part des électroaimants 9 dans l’accroissement du couple de freinage est plus importante,
• au fur et à mesure que le freinage se poursuit et que l’entrefer entre le rotor 3 et le stator 2 diminue, l’unité de commande de freinage 11 peut réduire le courant d’alimentation des électroaimants 9 de manière à équilibrer les contributions des aimants permanents 7 et des électroaimants 9 au couple de freinage, voire faire en sorte que la contribution des aimants permanents 7 vienne progressivement se substituer à celle des électroaimants 9.

In the second case, we understand that the production of the braking torque is distributed between the permanent magnets 7 and the electromagnets 9. This distribution can change over time during braking:

• at the start of braking, the actuators 6 and the electromagnets 9 are acted upon by a modification, for example of the same amplitude, but the increase in the magnetic flux of the electromagnets 9 being much faster than that of the magnetic flux of the permanent magnets 7, the share of the electromagnets 9 in the increase in the braking torque is greater,
• as braking continues and the air gap between the rotor 3 and the stator 2 decreases, the braking control unit 11 can reduce the supply current of the electromagnets 9 so as to balance the contributions of the permanent magnets 7 and the electromagnets 9 to the braking torque, or even ensure that the contribution of the permanent magnets 7 gradually replaces that of the electromagnets 9.

The brake control unit 11 can be configured in the same way to release the braking force. Other strategies for controlling the actuators 6 and the electromagnets 9 are of course conceivable for applying the braking force or for releasing it.

As soon as a skid is detected, the anti-lock control unit 16 sends an interrupt to the brake control unit 11. The outputs of the brake control unit 11 are blocked and the anti-lock control unit 16 takes control of the brake loop. The anti-lock control unit 16 then sends control signals to the electromagnet control unit 15 to modify the magnetic field produced by the electromagnets 9, and possibly to the actuator control unit 14 to modify the value of the air gap between the stators 2 and the rotor 3, depending on the difference between the speed of the aircraft calculated from the rotational speed of the wheels and the speed of the aircraft from the communication bus. The actuator control unit 14 will send a voltage to the actuators 6 to modify the value of the air gap. The electromagnet control unit 15 will send a voltage to the electromagnets 9 to modify the current of the electromagnets 9. These actions aim to reduce the braking torque and to release/unlock the wheel 103 in order to stop the skidding.

Once the skidding has stopped and is detected by the anti-lock control unit 16, the torque is progressively increased (using the electromagnets and/or the air gap adjustment) up to a value corresponding substantially to the theoretical optimum slip rate of the tire-ground contact (the anti-lock control unit 16 has in memory a curve such as that of the or a table corresponding thereto for different runway conditions), depending on the actual conditions (dry, wet, icy runways). The information on the actual conditions is for example provided to the aircraft by the airport control tower and is transmitted to the anti-lock control unit 16 by the communication bus.

Since the anti-lock system using the electromagnets 9 is several times faster than the anti-lock system using the actuators 6 to modify the air gap in order to increase or decrease the torque, the modification of the supply current of the electromagnets 9 is favored to achieve the anti-lock function and reduce the braking torque. Indeed, the braking torque must decrease abruptly so that the wheel lock lasts a minimum of time. illustrates the difference between the response times of the anti-lock brake by changing the air gap and the anti-lock brake by changing the current of the electromagnets 9 (it is illustrative because it does not represent the real behavior of the brake and the real changes in the amplitude of the torque for the electromagnets depend on the arrangement of the magnets 7, 9).

If necessary, if a greater torque variation is required, the air gap can also be modified (by the actuators 6) at the same time as the current of the electromagnets 9 is modulated. This combination improves the anti-lock efficiency of the eddy current brake.

As much as the decrease in braking torque should be as rapid as possible, it is also necessary to ensure a gradual increase in braking torque after the rapid decrease in braking torque, as opposed to the sudden decrease in braking torque, as illustrated in . Thus, the anti-lock control unit 16 is arranged to control the electromagnets 9 to generate a reduction in the braking torque in the event of detection of a wheel lock and then an increase in the braking torque when the lock disappears, the anti-lock control unit 16 controlling the electromagnets 9 in such a way that the increase in the braking torque is slower than the decrease in the braking torque. It can be seen on the that the increase in braking torque follows a curve as a function of time having a substantially straight starting section with a substantially vertical slope (around 80°) and a curved terminal section with a slope gradually decreasing to zero at the time of application of the maximum braking force. The curve of the shows that the response of the anti-lock system is very rapid when acting on the electromagnets 9 and in any case faster than if acting on the air gap only.

The electromagnets allow this progressive increase in braking torque while avoiding instability in the anti-lock loop.

To this end, according to a first control mode, the electromagnets are controlled between three states from a first positive intensity value, a second zero intensity value, and a third intensity value inverse to the first value.

A second control mode consists in modifying the time constant of the control of the electromagnets 9 directly in the anti-lock control unit 16 as a function of the required braking torque. Thus, for example, the supply current of the electromagnets is controlled between two extreme values corresponding to +100% and -100% of a maximum current value in steps of 1%. The braking torque is therefore modulated actively.

A third control mode includes the combination of air gap control and control of the current of the electromagnets 9, for example according to one of the first two control modes.

Of course, the invention is not limited to the embodiments described but encompasses any variant falling within the scope of the invention as defined by the claims.

In particular, the device may have a structure different from that described.

The magnets can be carried by the rotor instead of the stator, with two rotors surrounding a stator.

The shape, arrangement and dimensions of the magnets may differ from those described or shown. For example, the magnets may have different dimensions and/or be arranged in a HALBACH pattern.

The number of rotors and/or the number of stators may be different from those mentioned.

Although the rotor and stator have been described in the form of parallel disks facing each other, the stator and rotor may have other shapes. The device described is axial flux but the invention is applicable to radial flux operation or hybrid operation combining axial flux and radial flux. Thus, the stators may for example be arranged in the form of an outer drum and an inner drum between which extends a central drum forming the rotor in such a way that the central drum has an outer surface facing an inner surface of the outer drum and an inner surface facing an outer surface of the inner drum. The magnets are carried by the outer surface of the inner drum and by the inner surface of the outer drum.

The magnetic braking device according to the invention can be associated with a conventional friction braking device which comprises friction members, for example a stack of carbon disks, and a plurality of electromechanical actuators carried by an actuator holder. Each electromechanical actuator comprises an electric motor and a pusher capable of being moved by the electric motor to press the stack of disks. The electromechanical actuator is thus intended to produce a controlled braking force on the stack of disks. A method of controlling the braking devices is for example known from document FR-A-2953196.

Alternatively, the magnets may be directly attached to the rotor discs or stator discs of the friction brake, or the magnets may be covered with a friction lining, so that the braking device provides magnetic braking to slow the wheel when the discs are spaced apart from each other by an adequate air gap and friction braking when the discs are applied against each other. There is therefore no longer any axial stop between the discs in this embodiment.

For the mechanical actuation of the magnetic braking device, it is possible to use an actuator acting on several stators sliding in the same direction to be brought closer to the adjacent rotor, rather than an actuator for each stator. A single actuator can also act on two stators to move them in opposite directions.

The electromagnets 9 are here driven to produce the braking torque with the permanent magnets. It is conceivable that they are only used in the event of a blockage to cancel the magnetic field of the permanent magnets. Preferably, however, the electromagnets are driven to operate with the permanent magnets so as to complete the magnet network, and thus the field, so that it functions optimally. This is particularly the case with a Halbach network where the interaction between adjacent magnets in the magnet network is important.

The device can only include electromagnets.

The logic example illustrated in the is only one possible solution and one can imagine other ways of arranging the logic to incorporate one or the other or both means of anti-skid control for eddy current braking: for example by using both air gap control and electromagnet control, or conversely electromagnet control only.

The control modes can be combined, for example, based on external information such as the state of the runway or atmospheric conditions to determine first external conditions in which coarse control of the electromagnets is sufficient (first control mode), second conditions requiring fine control (second control mode) and third conditions requiring fine control of greater amplitude (third control mode). Any useful parameter (aircraft speed, wheel speed, torque, etc.) can be used to create a servo or feedback loop in the control of the braking system.

Other methods of actuation of the magnetic brake are possible: for example, solely by means of coils generating a magnetic field cancelling that of the permanent magnets, rotors and stators being axially fixed.

Alternatively, the first summer 12 may output an actuator control current resulting from subtracting the actuator anti-lock control signal from the actuator brake control signal. Similarly, the second summer 13 may output an electromagnet control current resulting from subtracting the electromagnet anti-lock control signal from the electromagnet brake control signal.

The support 8 may be made of a non-magnetic material.

The invention can be used on any type of vehicle, for example aerial, land or amphibious vehicles, or for applications other than a vehicle, for example for any industrial or transport mobile equipment requiring braking.

Claims (10)

Eddy current magnetic braking device for a vehicle wheel, comprising at least one stator element (2) arranged to be rotatably connected to a part of the vehicle supporting the wheel, a rotor element (3) arranged to be rotatably connected to the wheel, magnets for producing between said elements a magnetic flux capable of generating eddy currents in one of the elements when the wheel rotates, and a braking control unit (11) receiving as input a braking command for applying a braking force as a function of the braking command, characterized in that the magnets comprise at least one electromagnet (9) and the device comprises at least one anti-lock control unit (16) receiving as input a vehicle speed signal and a wheel rotation speed signal and providing as output a control signal for the electromagnet as a function of a comparison of speeds from the signals received as input. Device according to claim 1, in which the anti-lock control unit (16) is arranged to control the electromagnet (9) to generate a reduction in the braking torque in the event of detection of a wheel lock and then an increase in the braking torque when the lock disappears, the anti-lock control unit (16) controlling the electromagnet (9) in such a way that the increase in the braking torque is slower than the decrease in the braking torque. Device according to claim 2, in which the increase in the braking torque follows a curve as a function of time having a straight starting section having a substantially vertical slope and a curved terminal section having a slope gradually decreasing to zero. A device according to any preceding claim, wherein the comparison is based on calculating a slip rate of the wheel relative to the ground and the anti-lock control unit (16) comes into operation when the calculated slip rate is greater than an optimum slip rate. Device according to any one of the preceding claims, in which the magnets comprise permanent magnets (7) carried by one of the elements and the device comprises at least one actuator (6) for modifying the air gap between the elements, the anti-lock control unit (16) being connected to said actuator to modify the air gap as a function of the comparison of the speeds from the signals received at the input. Device according to claim 5, comprising several electromagnets (9) each interposed between two of the permanent magnets (7). Device according to any one of claims 5 and 6, in which the brake control unit (11) and the anti-lock control unit (16) each have a first output connected to a first adder (12) connected to a control unit (14) of the actuator (6) and a second output connected to a second adder (13) connected to a control unit (15) of the electromagnet (9). Braked vehicle wheel (103), comprising a rim (105) and a hub (104) connected by a web (106) defining an annular space receiving a braking device according to any one of the preceding claims. Landing gear (101) comprising a leg having one end carrying a shaft (102) on which is mounted the hub of a wheel (103) according to claim 8, the stator element (2) of the braking device being rotationally linked to the leg via the shaft (102). Aircraft comprising at least one landing gear according to claim 9.