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

Abstract

A magnetic eddy current braking device (1) for a vehicle wheel, comprising a first element (3) and a second element (2) having a principal surface (2.1) opposite a principal surface (3.1) of the first element, the first element being made of an electrically conductive material and the second element being provided with magnets (7) to produce a magnetic flux between the principal surfaces of said elements capable of generating eddy currents in the first element. The first element comprises a core made of a first metal to transmit a braking torque and at least partially coated with an outer layer made of a second metal to form the principal face of the first element. Vehicle wheel, landing gear, and aircraft comprising such a device, and a method for manufacturing the first element of such a device. FIGURE IN ABRIDGED: Fig. 2

Description

Title of the invention: Eddy current magnetic braking device, braked vehicle wheel and aircraft landing gear, aircraft equipped with such a wheel

[0001] The present invention relates to the field of braking vehicle wheels such as aircraft wheels.

[0002] BACKGROUND OF THE INVENTION

[0003] An aircraft wheel generally comprises 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).

[0004] Eddy current magnetic braking devices are known, used for braking vehicle wheels and more particularly aircraft wheels. Document FR-A-3122405 describes such a device comprising a rotor connected in rotation to the wheel, two stators which surround the rotor and which are connected in rotation 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 distant from the rotor.

[0005] In an eddy current magnetic braking device, the production of eddy currents in the rotor and the resulting braking torque are all the greater the higher the relative rotational speed of the rotor with respect to the stators.

[0006] However, the circulation of eddy currents in the rotor causes very significant heating of the rotor and this heating of the rotor can, if excessive, lead to a reduction in the performance of the braking device or even harm its integrity.

[0007] It has therefore been considered to use thick rotors to increase the thermal drainage capacity of the rotors. However, this has two major drawbacks.

[0008] Having a thick rotor increases the weight of the rotor, which is detrimental for use in a motor vehicle since the energy consumption of the engine depends directly on the mass to be moved.

[0009] Furthermore, it is advantageous, on the contrary, to limit the thickness of the rotor in such a way that the eddy currents generated from the two main faces of the rotor mix in its middle part because this provides a greater braking torque.

[0010] SUBJECT OF THE INVENTION

[0011] The invention aims in particular to propose a braking device which at least partially overcomes the aforementioned drawbacks. Summary of the invention

[0012] To this end, according to the invention, there is provided an eddy current magnetic braking device for a vehicle wheel, comprising a first element and a second element which has a main surface opposite a main surface of the first element and which is mounted so that said main surfaces pivot relative to each other about an axis of rotation, the first element being made of electrically conductive material and the second element being provided with magnets to produce between the main surfaces of said elements a magnetic flux capable of generating the eddy currents in the first element.

[0013] The first element comprises a core which is made of a first metal in a first thickness to transmit a braking torque and at least partly coated with an external layer made of a second metal in a second thickness to form the main face of the first element.

[0014] Thus, the invention makes it possible to take advantage of the properties of the two metals to optimize the weight and the creation of an effective braking torque. For example, it is possible to use copper, which is a very good thermal and electrical conductor, but is relatively heavy, and aluminum, which is a good electrical conductor and is relatively light. One can thus benefit from the better thermal conductivity of copper (aluminum has a thermal conductivity substantially equal to 60% of that of copper) and the low density of aluminum (approximately 30% of that of copper), not to mention that aluminum is also less expensive than copper. Furthermore, the penetration of eddy currents in these two metals is not the same (skin depth).The curve of the braking force produced by the eddy currents flowing in copper and the curve of the braking force produced by the eddy currents flowing in aluminum as a function of speed tend to intersect at a speed of 800 revolutions per minute, the braking force provided with copper being greater than the braking force provided with aluminum below this speed and lower above. The use of two different metals having braking force curves as a function of speed intersecting within the operating speed range of the magnetic brake makes it possible to maximize the braking force over the entire operating speed range. In addition, the braking device can have a smaller footprint for the same braking performance.

[0015] Advantageously, the external layer was produced by cold spraying the second metal onto the first metal.

[0016] Cold spraying promotes the creation, between the two metals, of a sensitive interface ably continuous and homogeneous which limits electromagnetic losses and thermal conduction resistance between the two metals. In addition, this process can be used with metals sensitive to high temperatures and limits the risk of oxidation of the metals which would alter their electrical conductivity.

[0017] According to optional characteristics, used individually or in whole or in part in combination: - the core has an external periphery and an internal periphery connected to each other by an annular part, the first thickness varying in a direction perpendicular to the axis of rotation, from the internal periphery towards the external periphery, and the second thickness varying in a complementary manner to the first thickness; - the first thickness decreases from the inner periphery of the core towards the outer periphery of the core or the first thickness increases from the inner periphery of the core towards the outer periphery of the core; - the outer layer is divided into a plurality of strips, the strips being in the form of angular sectors each aligned with a radial direction of the first element or in the form of concentric rings; - the second thickness is determined as a function of a relative displacement speed of the first element and the second element to be at most equal to approximately twice a penetration depth of the eddy currents in the second metal at said speed; - the first element is framed by two second elements and comprise two external layers each forming the main surface of the first element opposite the main surface of one of the second elements, and the first element is pierced with transverse holes having a wall covered with the second metal to connect the two external layers; - the first metal and the second metal are chosen from the following metals: copper, aluminum, beryllium, molybdenum, etc.

[0018] The invention also relates to a braked wheel equipped with such a device, as well as a landing gear and an aircraft equipped with such a wheel; and a method of manufacturing a stator or rotor of such an eddy current magnetic braking device.

[0019] Other characteristics and advantages of the invention will emerge from reading the following description of particular and non-limiting embodiments of the invention. Brief description of the drawings

[0020] Reference will be made to the accompanying drawings, among which:

[0021] [Fig.l] [Fig.l] is a partial schematic front view of an aircraft equipped of landing gear according to the invention;

[0022] [Fig.2] [Fig.2] is a partial schematic view of a wheel according to the invention, in half axial section;

[0023] [Fig.3] [Fig.3] is a schematic perspective view of a rotor of a device of braking of this wheel, according to a first embodiment of the invention;

[0024] [Fig.4] [Fig.4] is a schematic side view of this rotor;

[0025] [Fig.5] [Fig.5] is a schematic cross-sectional view of this rotor;

[0026] [Fig.6] [Fig.6] is a schematic side view of a rotor according to a variant of the first embodiment;

[0027] [Fig.7] [Fig.7] is a schematic cross-sectional view of this rotor;

[0028] [Fig.8] [Fig.8] is a schematic side view of a rotor according to a second mode of realization of the invention;

[0029] [Fig.9] [Fig.9] is a schematic cross-sectional view of this rotor;

[0030] [Fig. 10] [Fig. 10] is a schematic side view of a rotor according to a third embodiment of the invention;

[0031] [Fig. 11] [Fig. 11] is a schematic cross-sectional view of this rotor;

[0032] [Fig. 12] [Fig. 12] is a schematic side view of a rotor according to a fourth mode of carrying out the invention;

[0033] [Fig. 13] [Fig. 13] is a schematic cross-sectional view of this rotor;

[0034] [Fig. 14] [Fig. 14] is a schematic side view of a rotor according to a fifth mode of carrying out the invention;

[0035] [Fig. 15] [Fig. 15] is a schematic cross-sectional view of this rotor. DETAILED DESCRIPTION OF THE INVENTION

[0036] With reference to the figures, 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 about an axis of rotation 107. 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.

[0037] The wheels 103 are equipped with a magnetic braking device generally designated 1, which extends here into the annular space defined by the rim 105 and the hub 104.

[0038] The magnetic braking device 1 comprises fixed elements, or stators 2, and a mobile element, or rotor 3.

[0039] More precisely here, the stators 2 and the rotor 3 are in the general form of discs, coaxial with the wheel 103, therefore having collinear central axes and merged with the axis of rotation 107. 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.

[0040] The stators 2 are linked in rotation 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 linked in rotation 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.

[0041] 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 roller type, is preferably provided 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.

[0042] 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 for example made of magnetic or non-magnetic steel. Each stator 2 may also comprise a plurality of electromagnets fixed on the support alternating with the permanent magnets 7. The electromagnets comprise a coil connected to a current source.

[0043] The rotor 3 conventionally comprises an annular part having an internal periphery surrounding the torsion tube 4 and an external periphery comprising notches engaged on internal ribs of the rim 105. As we will see in more detail later, the rotor 3 is made of electrically conductive material.

[0044] 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 will be noted that below a certain rotational speed of the rotor 3, the braking torque is negligible regardless of the position of the stators 2. It will then possibly be necessary to consider an additional brake.

[0045] After this general description of the magnetic braking device 1, we will examine in more detail the structure of the rotor 3.

[0046] With reference to figures 3 to 15 and according to the invention, the rotor 3 comprises a core which is made of a first metal in a first thickness to transmit a braking torque and which is at least partly coated by two external layers made of a second metal in a second thickness to each form one of the main faces 3.1 of the rotor 3.

[0047] According to the invention, the rotor 3 is manufactured by a method comprising the steps of: - manufacturing the core, for example by casting, stamping, additive manufacturing, and / or machining... of the first metal; - cold spray the second metal onto two surfaces, here opposite, of the core to form the external layers; - sinter the external layers.

[0048] Cold spraying is carried out using, for example, a pressure of 50 bars at a nozzle temperature of 800°C.

[0049] Sintering is carried out for example using the SPS method (from the English spark plasma sintering), or by CIC (hot isostatic compaction) or HP (from the English hot pressing). It is also possible to carry out machining later, for example if sizing proves necessary.

[0050] In the described embodiments, the first metal is aluminum or an aluminum-based alloy and the second metal is copper or a copper-based alloy.

[0051] With reference to Figures 3 to 5, in the rotor 3 according to the first embodiment, each external layer 32 extends continuously over the annular part of the core 31, covering the internal periphery of the core 31 and leaving the external periphery of the core 31 uncovered.

[0052] It is recalled that the torque produced by an eddy current brake (for a fixed air gap between the rotor and the stator and a fixed magnetic field intensity) varies in depending on the material used for the rotor and the speed at which it rotates relative to the magnetic field (and therefore the stator). The eddy currents generated in a specific material vary depending on the speed, which directly affects the depth of penetration of the eddy currents, and therefore the final braking torque available at any given time.

[0053] The first thickness and the second thickness are determined as a function of the skin depth of the eddy currents in the first metal and in the second metal. The second thickness is determined as a function of a relative displacement speed of the first element and the second element to be at most equal to approximately twice a penetration depth at said speed. The speed considered here is the highest speed.

[0054] Furthermore, it is advantageous for the rotor 3 to have a thickness such that a skin effect (otherwise called a film 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 with respect 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 the 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.

[0055] For example, for a maximum speed of 1300 revolutions per minute and a rotor having a total thickness of 32 mm, a thickness of 8 mm is proposed for each external layer 32 and a thickness of 16 mm for the core 31.

[0056] In the variant of figures 6 and 7, the rotor 3 is pierced with transverse holes 34 (i.e. with an axis parallel to the axis of rotation 107) having a wall covered with the second metal (by cold spraying and / or sintering) to connect the two external layers 32 to each other.

[0057] These holes make it possible to improve electrical conduction, to strengthen the mechanical connection between the two metals and to improve thermal conduction. The positioning and shape of the holes may be determined by those skilled in the art according to these constraints.

[0058] With reference to Figures 8 and 9, in the rotor 3 according to the second embodiment, each external layer 32A is divided into a plurality of bands in the form of angular sectors extending over the annular part of the core 31A, covering the internal periphery of the core 31A and leaving the external periphery of the core 31A uncovered while each being aligned with a radial direction of the rotor.

[0059] Referring to Figures 10 and 11, in the rotor 3 according to the third embodiment, each outer layer 32B is divided into a plurality of shaped strips concentric rings extending over the annular portion of the core 31B, leaving the outer periphery of the core 31B uncovered, one of the rings covering the inner periphery of the core 31B.

[0060] These two strip arrangements make it possible to limit the stresses generated by the existence of differential thermal expansions between the two metals. In addition, these strips can be shaped for the production and distribution of eddy currents.

[0061] In the fourth and fifth embodiments of Figures 12 to 15, the first thickness varies in a direction perpendicular to the axis of rotation, from the inner periphery to the outer periphery of the core, and the second thickness varies in a manner complementary to the first thickness. In these two embodiments, the first thickness is constant at the outer periphery.

[0062] In the fourth embodiment of Figures 12 and 13, the first thickness of the core 31C increases from the inner periphery to the outer periphery. The core 31C therefore has annular main faces which diverge towards each other from the inner periphery to the limit of the annular part and the outer periphery. The outer periphery is here formed by a crown extending in projection relative to said main faces of the core 31C to each of which it is connected by a radial shoulder. The crown of the outer periphery is dimensioned to ensure the transfer of the torque to the rim and, to a lesser extent taking into account the shape of the annular part, to ensure the dissipation, by contact with the ambient air, of part of the heat produced during braking.

[0063] Conversely, the second thickness of each external layer 32C decreases from the internal periphery of the core 31C towards the external periphery thereof.

[0064] In the fifth embodiment of Figures 14 and 15, the first thickness of the core 31D decreases from the inner periphery to the outer periphery. The core 31D therefore has annular main faces which converge towards each other from the inner periphery to the limit of the annular part and the outer periphery. The outer periphery is here formed by a crown extending in projection relative to said main faces of the core 31D to each of which it is connected by a radial shoulder. The crown of the outer periphery is dimensioned to ensure the transfer of the torque to the rim and, to a lesser extent taking into account the shape of the annular part, to ensure the dissipation, by contact with the ambient air, of part of the heat produced during braking.

[0065] Conversely, the second thickness of each external layer 32D increases from the internal periphery of the core 31D towards the external periphery thereof.

[0066] These thickness variations along a radial direction are interesting because the relative speed of the rotor 3 with respect to the stator 2 decreases locally as a function from the distance to the axis of rotation.

[0067] Thus, it is advantageous to have a greater thickness of copper towards the internal periphery of the core from the point of view of the production of braking torque or the dissipation of heat produced during braking.

[0068] 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.

[0069] In particular, the device may have a structure different from that described.

[0070] The first metal and the second metal may be different from those indicated and be chosen in particular from the following metals: copper, aluminum, beryllium, molybdenum... or any other metal suitable for use in an eddy current brake. The metals used can also be magnetic. The number of metals used may be different from that mentioned.

[0071] The crown of the outer periphery of the core may be connected to the annular part of the core by a curved, frustoconical annular surface or a radial shoulder.

[0072] The outer periphery and / or the inner periphery of the core may have a constant thickness or a variable thickness.

[0073] The magnets may be carried by the rotor instead of the stator, with two rotors surrounding a stator. The magnets may be permanent magnets or electromagnets or a combination of both.

[0074] The shape, arrangement and dimensions of the magnets may be different from those described or shown. For example, the magnets may have different dimensions and / or be arranged in a HALBACH pattern.

[0075] The number of rotors and / or the number of stators may be different from those mentioned.

[0076] Although the rotor and the stator have been described in the form of parallel discs facing each other, the stator and the rotor can 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 can for example comprise an outer drum and the rotor an inner drum such that the inner drum has an outer surface facing an inner surface of the outer drum. The magnets are carried by the inner surface of the outer drum (or vice versa).

[0077] 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 discs, 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 motor. electric to press the stack of discs. The electromechanical actuator is thus intended to produce a controlled braking force on the stack of discs. A method of controlling the braking devices is for example known from document FR-A-2953196.

[0078] 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.

[0079] It is possible to use, for the mechanical actuation of the magnetic braking device, 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.

[0080] Other methods of actuation of the magnetic brake are conceivable: for example solely by means of coils generating a magnetic field cancelling that of the permanent magnets, rotors and stators being axially fixed.

[0081] The invention can be used on any type of vehicle, for example aerial, land or amphibious vehicles, or any industrial or transport mobile equipment requiring braking.

Claims

Claims

1. Eddy current magnetic braking device (1) for a vehicle wheel, comprising a first element (3) and a second element (2) which has a main surface (2.1) facing a main surface (3.1) of the first element and which is mounted so that said main surfaces pivot relative to each other about an axis of rotation, the first element being made of electrically conductive material and the second element being provided with magnets (7) to produce between the main surfaces of said elements a magnetic flux capable of generating the eddy currents in the first element, characterized in that the first element comprises a core (31) which is made of a first metal in a first thickness to transmit a braking torque and at least partly coated with an external layer (32) made of a second metal in a second thickness to form the main face of the first element.

2. Device according to claim 1, in which the outer layer (32) has been produced by cold spraying the second metal onto the first metal.

3. A device according to claim 1 or 2, wherein the core (31) has an outer periphery and an inner periphery connected to each other by an annular portion, the first thickness varying in a direction perpendicular to the axis of rotation, from the inner periphery to the outer periphery, and the second thickness varying in a complementary manner to the first thickness.

4. Device according to claim 3, in which the first thickness decreases from the inner periphery of the core (31) towards the outer periphery of the core (31).

5. Device according to claim 3, in which the first thickness increases from the inner periphery of the core (31) towards the outer periphery of the core (31).

6. A device according to claim 1, wherein the outer layer (32A; 32B) is divided into a plurality of strips.

7. Device according to claim 6, in which the strips are in the form of angular sectors each aligned on a radial direction of the first element (3).

8. A device according to claim 6, wherein the bands are in the form of concentric rings.

9. A device according to any preceding claim, wherein the second thickness is determined as a function of a relative displacement speed of the first element (3) and the second element (2) to be at most equal to approximately twice a penetration depth of the eddy currents in the second metal at said speed.

10. Device according to any one of the preceding claims, in which the first element (3) is framed by two second elements (2) and comprise two external layers (32) each forming the main surface of the first element opposite the main surface of one of the second elements, and the first element is pierced with transverse holes (34) having a wall covered with the second metal to connect the two external layers.

11. Device according to any one of the preceding claims, in which the first metal and the second metal are chosen from the following metals: copper, aluminum, beryllium, molybdenum, etc.

12. Braked vehicle wheel (103), comprising a rim (105) and a hub (104) connected by a disc (106) defining an annular space receiving a braking device (1) according to any one of the preceding claims.

13. A 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 12, one of the first element (3) and the second element (2) being rotationally connected to the rim (105) of the wheel (103) and the other of the first element and the second element being rotationally connected to the leg via the shaft (102).

14. Aircraft (100) comprising at least one landing gear (101) according to claim 13.

15. A method of manufacturing the first element (3) of an eddy current magnetic braking device (1) according to any one of claims 1 to 11, comprising the steps of: - manufacturing the core (31) in the first metal, - cold spraying the second metal onto a surface of the core to form the main surface of the first element.

16. Method according to claim 15, comprising a step of sintering the outer layer (32) after cold spraying of the second material.

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