Axial flux magnetic device comprising magnets enclosed in a protective housing

Abstract

A magnetic device comprising a stator (10, 10', 10'') and a rotor (20) arranged to produce an axial magnetic flux between them capable of generating eddy currents that produce a braking or driving torque on the rotor. The stator and rotor components include magnets (11) and a housing (12, 13, 12', 13a', 13b', 13a'', 13b'') in which the magnets are enclosed. The housing includes a main wall (13.1, 13.1', 13.1'') extending radially around an axis of rotation of the rotor to ensure a minimum air gap between the magnets and the stator and rotor components. (Figure from the abbreviation: Fig. 3)

Description

Title of the invention: Axial flux magnetic device comprising magnets enclosed in a protective housing

[0001] The present invention relates to the protection of magnets in an axial flux magnetic device. The invention is particularly applicable to magnetic braking or drive devices.

[0002] BACKGROUND OF THE INVENTION

[0003] An aircraft wheel generally comprises a rim connected by a disc to a hub which is mounted to rotate on an axle carried by a lower end of a landing gear. The aircraft wheel is traditionally equipped with a braking device to slow down and stop the aircraft when it is on the ground.

[0004] Eddy current magnetic braking devices are known, with the eddy current housed in a space extending between the rim and the hub. These magnetic braking devices generally comprise a rotor mounted on the wheel opposite a stator that slides relative to the axle. One end of the rotor and stator is provided with magnets, while the other end of the rotor and stator is made of an electrically conductive material. The sliding motion of the stator is generally controlled by hydraulic or electromechanical actuators arranged to selectively bring the stator closer to the rotor in order to generate a braking torque on the rotor and thus slow the rotation of the wheel.

[0005] The braking torque of such a device depends in particular on the distance or air gap separating the magnets from the rotor or stator made of electrically conductive material, and is greater the smaller the air gap. That being said, it is desirable that the minimum air gap be non-zero in order to avoid any damage to said magnets by friction with said rotor or stator made of electrically conductive material.

[0006] To guarantee a non-zero minimum air gap, the use of a ball bearing or an axial thrust washer was considered, but such a solution is unsuitable due to the potentially high temperatures generated by the magnets during braking. Indeed, the temperature of the magnets can exceed 300 degrees Celsius in the absence of active cooling, which would lead to irreversible damage to such axial thrust bearings.

[0007] Furthermore, magnets are susceptible to damage from adverse operating or environmental conditions (projection of debris, corrosion, centrifugal force, shocks, vibrations...).

[0008] SUBJECT OF THE INVENTION

[0009] The invention therefore aims to provide a magnetic device that at least partially overcomes the aforementioned disadvantages. Summary of the invention

[0010] To this end, the invention proposes a magnetic device comprising a stator and a rotor arranged to produce an axial magnetic flux between them capable of generating eddy currents that produce a braking or driving torque on the rotor. One part of the stator and the rotor comprises magnets and a housing in which the magnets are enclosed, the housing comprising a main wall extending radially around an axis of rotation of the rotor to ensure a minimum air gap between the magnets and the other part of the stator and the rotor.

[0011] The housing provides both structural protection for the magnets and its main wall prevents any contact between the magnets and the other of the stator and rotor.

[0012] Preferably, the main wall is made of carbon-carbon. This material is known to have a low heat transfer coefficient and exhibits a low rate of wear under friction, so that it is possible to produce a main wall with a relatively small thickness and thus guarantee a minimum air gap allowing to maximize the braking or driving torque of the device, while protecting the magnets from the potentially high temperatures observed on the surface of the other of the stator and the rotor.

[0013] In particular, the main wall has a substantially constant thickness.

[0014] In particular, the thickness of the main wall is between 0.5 millimeter and 1.5 millimeters and is preferably equal to 1 millimeter.

[0015] In particular, the magnets are carried by the stator.

[0016] The invention also relates to an aircraft wheel brake, comprising such a magnetic device.

[0017] In particular, the magnetic device further includes an actuator arranged to move the stator and the rotor relative to each other along the axis of rotation of the rotor.

[0018] The invention also relates to an aircraft wheel comprising at least one such brake.

[0019] The invention further relates to an aircraft landing gear comprising at least one such wheel.

[0020] The invention also relates to an aircraft comprising at least one such landing gear. Brief description of the drawings

[0021] The invention will be better understood in the light of the following description, which is purely illustrative and not limiting, and should be read in conjunction with the accompanying drawings, among which:

[0022] [Fig.1] [Fig.1] is a simplified representation of an aircraft comprising braked wheels;

[0023] [Fig.2] [Fig.2] is an axial cross-sectional view of one of the braked wheels of the aircraft illustrated in [Fig.1], showing a stator according to a first embodiment of the invention;

[0024] [Fig.3] [Fig.3] is an exploded, perspective view of the stator illustrated in [Fig.2];

[0025] [Fig.4] [Fig.4] is an axial cross-sectional view of a second embodiment of the stator illustrated in figures 2 and 3;

[0026] [Fig.5A] [Fig.5A] is an axial cross-sectional view of a third embodiment of the stator illustrated in figures 2 and 3;

[0027] [Fig.5B] [Fig.5B] is an exploded, perspective view of the stator illustrated in [Fig.5A]. DETAILED DESCRIPTION OF THE INVENTION

[0028] With reference to [Fig. 1], the invention is described in application to an aircraft A comprising two main landers P, each of which has a leg J ​​having a first end articulated on a structure S of the aircraft A and, at the opposite end, a second end carrying wheels R rotating about an axis X on a tubular shaft or axle E. The main landers P are here of the retractable type, but the invention is applicable to fixed landers, or even to another type of vehicle such as a land vehicle.

[0029] The wheels R are said to be "braked," that is, equipped with a brake designed to selectively slow down and stop the aircraft A when it is on the ground. The following description relates to one of the aircraft's wheels R; the wheels R are identical here but may also be different.

[0030] The wheel R comprises, as illustrated in [Fig. 2], an annular rim 1 connected by a disc 2 to a hub 3 pivotally received on the axle E by means of bearings (not shown). The rim 1 extends opposite the hub 3 and, together with said hub 3, defines an annular space having one end at least partially closed by the disc 2 and, at the opposite end, an open end.

[0031] The brake of the wheel R comprises an axial flux magnetic braking device extending inside the annular space delimited by the wheel R. The braking device comprises a fixed rotating element, or stator 10, and a movable rotating element, or rotor 20. The stator 10 and the rotor 20 are each in the form of a disc and have central axes coinciding with the X axis of rotation of the wheel R.

[0032] The rotor 20, which is annular in shape, has an outer circumference with axial peripheral grooves, each receiving an end segment of a bar (not shown) fixed to the inner surface of the rim 1 to ensure coupling in rotation of the rotor 20 with the rim 1 around the X axis. Screws (not shown) here connect the rotor 20 to the end sections of the bars so that said rotor 20 is fixed relative to the rim 1.

[0033] The rotor 20 also has an inner perimeter delimiting, with the outer perimeter, a main surface S2o of the rotor 20 facing the stator 10. This main surface S2o, of annular shape, extends radially around the axis X and is axially opposite the stator 10.

[0034] The rotor 20 is made of non-ferromagnetic electrically conductive material, for example copper.

[0035] With reference to Figures 2 and 3, the annular stator 10 comprises a housing containing a series of permanent sector-shaped magnets 11. The housing is in two parts, namely a body 12 forming a container and a cover 13 which, together with the body 12, defines an annular volume for receiving the magnets 11.

[0036] Body 12 comprises: • a background 12.1, of annular shape, extending radially around the X axis; • an external skirt 12.2, cylindrical in shape, extending axially around the X-axis from an outer edge of the bottom towards the rotor 20; and • an internal skirt 12.3, cylindrical in shape, extending axially around the X axis from an internal periphery of the bottom towards the rotor 20.

[0037] The outer skirt 12.2 and the inner skirt 12.3 have a substantially identical axial height h J2. The base 12.1, the outer skirt 12.2 and the inner skirt 12.3 of the body 12 define an annular groove extending axially around the X axis and in which the magnets 11 are received.

[0038] The body 12 is made of metal, for example aluminum.

[0039] The cover 13 comprises: • a disc 13.1, of annular shape, extending radially around the axis X and comprising a main surface Si0 which is turned towards the rotor 20 and which extends axially opposite the main surface S20 of the rotor 20, the disc 13.1 forming a main wall of the cover 13; • an external base 13.2, cylindrical in shape, extending axially around the X-axis from an inner periphery of the disk 13.1 towards the body 12; and • an internal base 13.3, cylindrical in shape, extending axially around the X axis from an internal periphery of the disk 13.1 towards the body 12.

[0040] The disc 13.1 forms a protective shield for the magnets 11 and has a thickness e i3, substantially constant, guaranteeing, as will be seen later, a minimum air gap between the magnets 11 and the rotor 20.

[0041] The outer base 13.2 and the inner base 13.3 of the cover 13 have a substantially identical axial height h 13. The height h 13 of the outer and inner bases 13.2, 13.3 of the cover 13 is less than the height h ]2 of the outer and inner skirts 12.2, 12.3 of the body 12.

[0042] The external base 13.2 and the internal base 13.3 of the cover 13 have a free end cooperating respectively with a free end of the external skirt 12.2 and the internal skirt 12.3 of the body 12: the annular volume for receiving the magnets is totally closed.

[0043] The inner skirt 12.3 of the body 12 and the inner base 13.3 of the cover 13 have axial peripheral notches 12.4, 13.4 symmetrically distributed around the X axis. The number, dimensions and angular positions of the notches 12.4 of the body 12 are respectively substantially identical to the number, dimensions and angular positions of the notches 13.4 of the cover 13.

[0044] Each peripheral notch 12.4 of the body 12 receives, with the corresponding peripheral notch 13.4 of the cover 13, a section of a tenon (not shown) which is fixed on the outer surface of a torsion tube T fixed to a collar Ei of the axle E to ensure a rotational coupling of the stator 10 with the torsion tube T around the axis X.

[0045] The cover 13 is held in contact with the body 12 via riders 14 riveted into the peripheral notches 12.4, 13.4 of the inner skirt 12.3 of said body 12 and of the inner base 13.3 of said cover 13 to cooperate with lateral bearing faces of the tenons and ensure the rotational coupling of the stator 10 with the torsion tube T. It is understood that the cover 13 is fixed with respect to the body 12.

[0046] The cover 13 is here made of carbon-carbon. This material is known to have a low heat transfer coefficient and exhibits a low rate of wear under friction.

[0047] The magnets 11 are fixed relative to the housing 12, 13 of the stator 10 and are arranged in a Halbach pattern so as to generate eddy currents in the rotor 20 when the stator 10 and the rotor 20 are separated by a small air gap and when said rotor 20 rotates about the X-axis relative to said stator 10. Each of the magnets 11 comprises: a front face cooperating with the disc 13.1 of the cover 13; a rear face cooperating with the bottom 12.1 of the body 12; • two lateral faces each cooperating with one of the lateral faces of the adjacent magnet 11; • an outer face cooperating with an internal surface of the outer skirt 12.2 of the body 12 and an internal surface of the outer base 13.2 of the cover 13; and • an inner face cooperating with an internal surface of the inner skirt 12.2 of the body 12 and an internal surface of the inner base 13.2 of the cover 13.

[0048] The tenons (not shown) form slides allowing the stator 10 to slide along the X axis on the torsion tube T between a first position called the braking position (not illustrated) and a second position called the free rotation position of the wheel 1 (illustrated in [Fig.2]). In the braking position, the stator 10 is brought closer to the rotor 20 to the point that the main surface Si0 of the stator 10 is substantially in contact (at most under low pressure) with the main surface S2o of the rotor 20: the front face of the magnets 11 and the main surface S2o of the rotor 20 are separated from each other by a first air gap called the "magnetic" gap substantially equal to the thickness e 13 of the disc 13.1 of the cover 13.In the free-rotating position, the stator 10 is separated from the rotor 20 such that the main surface Sio of the stator 10 is far from the main surface S20 of the rotor 20: the front face of the magnets 11 and the main surface S20 of the rotor 20 are separated from each other by a second "magnetic" air gap which is larger than the first air gap. It is understood that in the braking position, the magnets 11 of the stator 10 generate sufficient eddy currents in the rotor 20 to produce a braking torque on said rotor 20 when the wheel R rotates, and that in the free-rotating position, this braking torque is negligible, or even non-existent.

[0049] The sliding of the stator 10 between the braking position and the free rotation position is controlled by hydraulic actuators 31 which are carried by an actuator-carrying ring 30 fixed to one end of the torsion tube 13. The actuators 31 are identical to each other and have centers lying on the same first circle whose center is located on the X-axis of rotation of the wheel R. Each of the actuators 31 comprises a piston 31.1 received in a cylindrical cavity 30.1 of the actuator-carrying ring 30. The cavities 30.1 are distributed equally around the X-axis of rotation of the wheel 1. The pistons 31.1 are movable in translation about an axis parallel to the X-axis of rotation of the wheel 1, between a first extreme position and a second extreme position, to move the stator 10 respectively between the braking position and the free rotation position, one free end of the actuators 31 being fixed to the stator 10. The pistons 31.1 are returned to their second extreme positions via springs 31.2. We understand. that the sliding of the stator 10 along the X axis is controlled by the movements of the first pistons 31.1.

[0050] The operation of the brake on the braked wheel R will now be detailed.

[0051] To cause the braking of aircraft A, a pressurized fluid is introduced simultaneously into each of the chambers 31.1 of the actuators 31 through supply lines connected to a pressurized fluid supply source.

[0052] Initially, the fluid inserted under pressure exerts a pushing force on the pistons 31.1 tending to move said pistons 31.1 from their first extreme positions to their second extreme positions, in other words to move the stator 10 from the free rotation position to the braking position.

[0053] Once the pistons 31.1 have reached their second extreme positions, in other words, once the stator 10 has reached its braking position, the magnets 11 generate eddy currents in the rotor 20, resulting in the application of a braking torque to the rotating wheel R. At the same time, the main surface Si0 of the stator 10 is potentially in contact with the main surface S2o of the rotor 20, which generates frictional forces between said stator 10 and said rotor 20.

[0054] It is understood that the housing 12, 13 in which the magnets 11 of the stator 10 are received allows both to ensure structural protection of said magnets 11 and to guarantee, when the stator 10 is in braking position, a substantially constant air gap between said magnets 11 and the rotor 20.

[0055] It should be noted that by choosing to make the cover 13 of the housing 12, 13 out of carbon-carbon, said cover 13 also makes it possible to protect the network of magnets 11 from the potentially high temperatures which are observed on the main surface S2o of the rotor 20 when the stator 10 is in the braking position and the main surface Sio of the stator 10 rubs (under low pressure) against said main surface S20 of the rotor 20. Indeed, it is known that carbon-carbon is a material with a low heat transfer coefficient.

[0056] Furthermore, it is known that at low temperature and low contact pressure, carbon-carbon exhibits a low coefficient of friction and a low wear rate, so that the cover 13 tends to wear very little or not at all. The thickness of the disc 13.1 of the cover 13, in other words, that of the main wall of the cover 13, can therefore be relatively small and, for example, between 0.5 millimeters and 1.5 millimeters. The thickness of the disc 13.1 is here approximately 1 millimeter. Such a small thickness maximizes the generation of eddy currents and therefore the braking torque applied to the wheel.

[0057] Moreover, it is known that aircraft wheel friction brake discs are made of carbon-carbon. Subjected to significant contact pressures, these friction discs wear down and must be replaced when their thickness is substantially less than a predetermined thickness, which is generally substantially equal to their thickness when new. Once worn, they can then be re-machined to form the cover 13 of the stator 10, which is advantageous from both a commercial and environmental perspective.

[0058] To stop the braking of aircraft A, the pressure of the fluid introduced into each of the cavities 30.1 of the actuators 31 is reduced. Under the action of the springs 31.2, the pistons 31.1 tend to move towards their first extreme positions ([Fig.2]), so that the stator 10 tends to move from the braking position towards the free rotation position.

[0059] Fig. 4 illustrates a stator 10' which is nothing other than a second embodiment of the stator 10. The stator 10' differs from the stator 10 in that the housing receiving the magnets 11 is here in three parts, namely a body 12' delimiting an annular enclosure, and a first cover 13a' and a second cover 13b' delimiting with the body 12 an annular volume for receiving the magnets 11.

[0060] The body 12' comprises an upper cylindrical wall 12a' and a lower cylindrical wall 12b' extending inside the upper cylinder 12a'. The upper cylindrical wall 12a' and the lower cylindrical wall 12b' extend axially around the X axis and each comprise an internal surface cooperating respectively with the upper and lower faces of the magnets 11.

[0061] The body 12' is made of metal, for example aluminum.

[0062] The first cover 13a' and the second cover 13b' extend on either side of the body 12' and comprise an internal surface cooperating respectively with the front and rear faces of the magnets 11. The first cover 13a' and the second cover 13b' are substantially identical to the cover 13 of the stator 10. The first cover 13a' comprises a main surface Si0' which is oriented towards the rotor 20 and which extends axially opposite the main surface S2o of the rotor 20. The main surface S10' of the stator 10' defines a main wall 13.1' of the first cover 13a' to form a protective shield for the magnets 11, ensuring, as with the cover 13 of the stator 10, a minimum air gap between the magnets 11 and the rotor 20. As with the disc 13.1 of the cover 13, the wall thickness main 13.1' of the first cover 13a' is for example between 0.5 millimeter and 1.5 millimeter and is here approximately equal to 1 millimeter. .

[0063] The first cover 13a' and the second cover 13b' are here made of carbon-carbon.

[0064] Figures 5A and 5B illustrate a stator 10” which is simply a third embodiment of the stator 10. The stator 10” differs from the stator 10 in that the housing receiving the magnets 11 is here in two parts made of carbon-carbon, namely a first body 13a” and a second body 13b” which together define an annular volume for receiving the magnets IL

[0065] The first body 13a” and the second body 13b” each form a container and are substantially identical here. The first body 13a” and the second body 13b” comprise: • a 13.1” annular base, extending radially around the X axis; • an external skirt 13.2”, cylindrical in shape, extending axially around the X-axis from an external periphery of the bottom 13.1” towards the magnets 11; and • an internal skirt 13.3”, cylindrical in shape, extending axially around the X axis from an internal periphery of the bottom towards the magnets 11.

[0066] The outer skirts 13.2” and the inner skirts 13.3” have a substantially identical axial height hn”. The bottoms 13.1”, the outer skirts 13.2” and the inner skirts 13.3” of the first and second bodies 13a”, 13b” define an annular enclosure extending axially around the X axis and in which the magnets 11 are received.

[0067] The first body 13a” comprises a main surface Sio” which is turned towards the rotor 20 and which extends axially opposite the main surface S2o of the rotor 20. The main surface Sio” of the stator 10” delimits the bottom 13.1” of the first body 13a”, this bottom 13.1” constituting a main wall of the stator 10” which forms a protective shield for the magnets 11 defining, as for the cover 13 of the stator 10, a minimum air gap between the magnets 11 and the rotor 20. As for the disc 13.1 of the cover 13, the thickness of the bottom 13.1” of the first body 13a” is for example between 0.5 millimeter and 1.5 millimeter and is here substantially equal to 1 millimeter.

[0068] The internal skirts 13.3” of the bodies 13 have axial peripheral notches 13.4” symmetrically distributed around the X axis. The number, dimensions and angular positions of the notches 13.4” of the first body 13a” are respectively substantially identical to the number, dimensions and angular positions of the notches 13.4” of the second body 13b”.

[0069] Each peripheral notch 13.4” of the first body 13a” receives, with the corresponding peripheral notch 13.4” of the second body 13b”, a section of one of the tenons which is fixed on the outer surface of the torsion tube T to ensure a rotational coupling of the stator 10” with the torsion tube T around the X axis.

[0070] The first body 13a” is held in contact with the second body 13b” via rivets 14” inserted into the peripheral notches 13.4” of the internal skirts 13.3” of the first and second bodies 13a”, 13b” to cooperate with lateral bearing faces of the tenons and ensure the rotational coupling of the stator 10” with the torsion tube T. It is understood that the first body 13a” is fixed with respect to the second body 13b”.

[0071] The stator 10” also includes a metal disc 12” received in the housing 10. The disc 12”, of annular shape, extending radially around the X axis and comprising a first main surface cooperating with the bottom 13.1” of the second body 13b” and, opposite, a second main surface cooperating with the rear faces of the magnets 11. The disc 12” forms a counter-iron or “black-iron” allowing, on the one hand, to limit the leakage of the magnetic flux generated by the magnets 11 towards the bottom 13.1” of the second body 13b” and, on the other hand, to increase the intensity of said magnetic flux towards the bottom 13.1” of the first body 13a” and therefore towards the rotor 20. The efficiency of the braking device is thereby improved.

[0072] 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.

[0073] Although the invention is applied here to the stator of an aircraft braked wheel, it can be applied to any other vehicle, and to any other axial flux magnetic device, such as for example an electric motor.

[0074] Although the permanent magnets 11 are here carried by the stator 10 10', 10', they can also be carried by the rotor 20 which then includes a housing such as that of the stator 10, 10', 10" to receive said magnets 11.

[0075] The carbon-carbon elements can also be made of any other suitable material with a low heat transfer coefficient and a low rate of wear under friction, such as carbon-ceramic.

[0076] Although the magnets 11 here are permanent magnets, they can be electromagnetic.

Claims

Demands

1. Magnetic device comprising a stator (10, 10', 10") and a rotor (20) arranged to produce between them an axial magnetic flux capable of generating eddy currents producing a braking or driving torque of the rotor, one of the stator and the rotor comprising magnets (11) and a housing (12, 13, 12', 13a', 13b', 13a", 13b") in which the magnets are enclosed, the housing comprising a main wall (13.1, 13.1', 13.1") extending radially around an axis of rotation of the rotor to ensure a minimum air gap between the magnets and the other of the stator and the rotor.

2. Magnetic device according to claim 1, wherein the main wall (13.1, 13.1', 13.1”) is made of carbon-carbon.

3. Magnetic device according to any one of the preceding claims, wherein the main wall (13.1, 13.1', 13.1”) has a substantially constant thickness (in).

4. Magnetic device according to claim 3, wherein the thickness (in) of the main wall (13.1, 13.1', 13.1”) is between 0.5 millimeter and 1.5 millimeter and is preferably equal to 1 millimeter.

5. Magnetic device according to any one of the preceding claims, wherein the magnets (11) are carried by the stator (10, 10', 10”).

6. Aircraft wheel brake (R), comprising a magnetic device according to any one of the preceding claims.

7. Brake according to claim 6, wherein the magnetic device further comprises an actuator arranged to move the stator (10, 10', 10") and the rotor (20) relative to each other along the axis of rotation of the rotor (20).

8. Aircraft wheel (R) comprising at least one brake according to claim 6 or 7.

9. Aircraft landing gear (P) comprising at least one wheel according to claim 8.

10. Aircraft (A) comprising at least one landing gear (P) according to claim 9.

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